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  • Articles  (121)
  • Linear programming  (74)
  • biodegradation  (47)
  • 1990-1994  (121)
  • Mathematics  (74)
  • Energy, Environment Protection, Nuclear Power Engineering  (47)
  • 1
    Electronic Resource
    Electronic Resource
    Polynomiality of infeasible-interior-point algorithms for linear programming (1994)
    Springer
    Mathematical programming 67 (1994), S. 109-119 
    Details
    ISSN: 1436-4646
    Keywords: Polynomial-time ; Linear programming ; Primal-dual ; Interior-point algorithm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract Kojima, Megiddo, and Mizuno investigate an infeasible-interior-point algorithm for solving a primal—dual pair of linear programming problems and they demonstrate its global convergence. Their algorithm finds approximate optimal solutions of the pair if both problems have interior points, and they detect infeasibility when the sequence of iterates diverges. Zhang proves polynomial-time convergence of an infeasible-interior-point algorithm under the assumption that both primal and dual problems have feasible points. In this paper, we show that a modification of the Kojima—Megiddo—Mizuno algorithm “solves” the pair of problems in polynomial time without assuming the existence of the LP solution. Furthermore, we develop anO(nL)-iteration complexity result for a variant of the algorithm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01582216
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  • 2
    Electronic Resource
    Electronic Resource
    Random walks, totally unimodular matrices, and a randomised dual simplex algorithm (1994)
    Springer
    Mathematical programming 64 (1994), S. 1-16 
    Details
    ISSN: 1436-4646
    Keywords: Random walks ; Totally unimodular matrices ; Uniform generation ; Linear programming ; Diameter of polytopes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We discuss the application of random walks to generating a random basis of a totally unimodular matrix and to solving a linear program with such a constraint matrix. We also derive polynomial upper bounds on the combinatorial diameter of an associated polyhedron.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01582563
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  • 3
    Electronic Resource
    Electronic Resource
    Dynamic factorization in large-scale optimization (1994)
    Springer
    Mathematical programming 64 (1994), S. 17-51 
    Details
    ISSN: 1436-4646
    Keywords: Factorization ; Linear programming ; Generalized upper bounds ; Pure networks ; Generalized networks
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract Factorization of linear programming (LP) models enables a large portion of the LP tableau to be represented implicitly and generated from the remaining explicit part. Dynamic factorization admits algebraic elements which change in dimension during the course of solution. A unifying mathematical framework for dynamic row factorization is presented with three algorithms which derive from different LP model row structures: generalized upper bound rows, pure network rows, and generalized network rows. Each of these structures is a generalization of its predecessors, and each corresponding algorithm exhibits just enough additional richness to accommodate the structure at hand within the unified framework. Implementation and computational results are presented for a variety of real-world models. These results suggest that each of these algorithms is superior to the traditional, non-factorized approach, with the degree of improvement depending upon the size and quality of the row factorization identified.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01582564
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  • 4
    Electronic Resource
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    Interior-point algorithms for semi-infinite programming (1994)
    Springer
    Mathematical programming 65 (1994), S. 217-245 
    Details
    ISSN: 1436-4646
    Keywords: Linear programming ; Semi-infinite programming ; Interior-point methods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract In order to study the behavior of interior-point methods on very large-scale linear programming problems, we consider the application of such methods to continuous semi-infinite linear programming problems in both primal and dual form. By considering different discretizations of such problems we are led to a certain invariance property for (finite-dimensional) interior-point methods. We find that while many methods are invariant, several, including all those with the currently best complexity bound, are not. We then devise natural extensions of invariant methods to the semi-infinite case. Our motivation comes from our belief that for a method to work well on large-scale linear programming problems, it should be effective on fine discretizations of a semi-infinite problem and it should have a natural extension to the limiting semi-infinite case.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01581697
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  • 5
    Electronic Resource
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    The maximum entropy method on the mean: Applications to linear programming and superresolution (1994)
    Springer
    Mathematical programming 66 (1994), S. 103-122 
    Details
    ISSN: 1436-4646
    Keywords: 42B05 ; 62A99 ; Maximum entropy ; Linear programming ; Inverse problems ; Superresolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract In this paper, we give two different results. We propose new methods to solve classical optimization problems in linear programming. We also obtain precise quantitative results for the superresolution phenomenon, as observed earlier by practical searchers on specific algorithms. The common background of our work is the generalized moment problem, which is known to be connected with linear programming and superresolution. We describe the Maximum Entropy Method on the Mean that provides solution to the problem and leads to computational criteria to decide the existence of solutions or not.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01581139
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  • 6
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    Superlinear convergence of infeasible-interior-point methods for linear programming (1994)
    Springer
    Mathematical programming 66 (1994), S. 361-377 
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    ISSN: 1436-4646
    Keywords: Linear programming ; Infeasible-interior-point methods ; Superlinear convergence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract At present the interior-point methods of choice are primal—dual infeasible-interior-point methods, where the iterates are kept positive, but allowed to be infeasible. In practice, these methods have demonstrated superior computational performance. From a theoretical point of view, however, they have not been as thoroughly studied as their counterparts — feasible-interior-point methods, where the iterates are required to be strictly feasible. Recently, Kojima et al., Zhang, Mizuno and Potra studied the global convergence of algorithms in the primal—dual infeasible-interior-point framework. In this paper, we continue to study this framework, and in particular we study the local convergence properties of algorithms in this framework. We construct parameter selections that lead toQ-superlinear convergence for a merit function andR-superlinear convergence for the iteration sequence, both at rate 1 +τ whereτ can be arbitrarily close to one.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01581155
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  • 7
    Electronic Resource
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    Limiting behavior of weighted central paths in linear programming (1994)
    Springer
    Mathematical programming 65 (1994), S. 347-363 
    Details
    ISSN: 1436-4646
    Keywords: Linear programming ; (Weighted) central paths ; Limiting behavior on central paths ; Local convergence rates of interior point algorithms ; Primary: 90C05 ; Secondary: 90C33
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We study the limiting behavior of the weighted central paths{(x(μ), s(μ))} μ 〉 0 in linear programming at bothμ = 0 andμ = ∞. We establish the existence of a partition (B ∞,N ∞) of the index set { 1, ⋯,n } such thatx i(μ) → ∞ ands j (μ) → ∞ asμ → ∞ fori ∈ B ∞, andj ∈ N ∞, andx N∞ (μ),s B∞ (μ) converge to weighted analytic centers of certain polytopes. For allk ⩾ 1, we show that thekth order derivativesx (k) (μ) ands (k) (μ) converge whenμ → 0 andμ → ∞. Consequently, the derivatives of each order are bounded in the interval (0, ∞). We calculate the limiting derivatives explicitly, and establish the surprising result that all higher order derivatives (k ⩾ 2) converge to zero whenμ → ∞.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01581702
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  • 8
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    Asymptotic analysis of the exponential penalty trajectory in linear programming (1994)
    Springer
    Mathematical programming 67 (1994), S. 169-187 
    Details
    ISSN: 1436-4646
    Keywords: 90C05 ; 90C25 ; 90C31 ; 49M30 ; Linear programming ; Exponential penalty ; Optimal trajectory ; Asymptotic expansion ; Interior point methods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We consider the linear program min{c′x: Ax⩽b} and the associated exponential penalty functionf r(x) = c′x + rΣexp[(A ix − bi)/r]. Forr close to 0, the unconstrained minimizerx(r) off r admits an asymptotic expansion of the formx(r) = x * + rd* + η(r) wherex * is a particular optimal solution of the linear program and the error termη(r) has an exponentially fast decay. Using duality theory we exhibit an associated dual trajectoryλ(r) which converges exponentially fast to a particular dual optimal solution. These results are completed by an asymptotic analysis whenr tends to ∞: the primal trajectory has an asymptotic ray and the dual trajectory converges to an interior dual feasible solution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01582220
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  • 9
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    Novel malonate-type copolymers containing vinyl alcohol blocks as biodegradable segments and their builder performance in detergent formulations (1994)
    Springer
    Journal of polymers and the environment 2 (1994), S. 89-97 
    Details
    ISSN: 1572-8900
    Keywords: Polycarboxylate ; methylene malonate copolymer ; biodegradation ; design ; poly(vinyl alcohol)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Poly[(disodium methylene malonate)-co-(vinyl alcohol)] [P(DSMM-VA)] and poly[(disodium ethoxymethylene malonate)-co-(vinyl alcohol)] [P(DSEMM-VA)] containing a poly(vinyl alcohol) (PVA) block as a biodegradable segment were prepared and their biodegradability and functionality were evaluated and compared with those of the corresponding fumarate and maleate copolymers. It was found that the 1,1-dicarboxylate-type copolymers, P(DSMM-VA) and P(DSEMM-VA), showed better biodegradability than the corresponding 1,2-dicarboxylate-type copolymers, P(DSF-VA) and P(DSM-VA). This improved biodegradability of P(DSMM-VA) and P(DSEMM-VA) is probably attributable to their more expanded polymer chain in aqueous solution, which will be more accessible to the degrading enzymes. The minimum chain length of the PVA-block, which acts as a biodegradable segment in the polymer chain, is estimated to be 2–3 and 3–4 monomer units for P(DSMM-VA) and P(DSEMM-VA), respectively. On the other hand, the minimum PVA block is about 5 and 7 monomer units for the fumarate and maleate copolymers, respectively. It was confirmed that P(DSMM-VA) showed excellent builder performance compared to the corresponding fumarate copolymer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02074777
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  • 10
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    Biodegradability of blends of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with cellulose acetate esters in activated sludge (1994)
    Springer
    Journal of polymers and the environment 2 (1994), S. 49-57 
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    ISSN: 1572-8900
    Keywords: Poly(3-hydroxyalkanoates) ; cellulose acetate esters ; biodegradation ; activated sludge
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Blends of the bacterially produced polyester poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) with cellulose acetate esters (CAE) further substituted with propionyl or butyryl groups (degree of substitution: 2.60 propionyl and 0.36 acetyl or 2.59 butyryl and 0.36 acetyl, respectively) were exposed for 4 months to activated sludge to determine their biodegradability. Samples of such blends made by solution-mixing and solvent-casting had complex morphologies in which both individual components as well as a miscible blend phase were present. Additionally, the two opposite surfaces of solvent-cast films showed both physical and chemical differences. After 2 months, samples of pure PHBV had degraded by more than 98% (15 mg/cm2 of surface area), whereas a pure CAE sample had degraded less than 1% (〈0.2 mg/cm2). Samples containing 25% CAE lost less than 40% of their initial weights (6 mg/cm2) over the total 4-month period. Samples with 50% CAE lost up to 16% weight (2 mg/cm2), whereas those containing 75% CAE lost only slightly more weight than corresponding sterile control samples (1 mg/cm2). NMR results confirm that weight loss from samples containing 25% CAE resulted only from degradation of PHBV and that the surface of samples became enriched in CAE. Solvent-cast film samples containing equal amounts of PHBV and CAE degraded preferentially on the surface which formed at the polymer-air interface. Scanning electron microscopy and attenuated total reflectance infrared spectroscopy revealed this surface to have a rougher texture and a greater PHBV content.
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    URL: http://dx.doi.org/10.1007/BF02073486
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  • 11
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    A quadratically convergent predictor—corrector method for solving linear programs from infeasible starting points (1994)
    Springer
    Mathematical programming 67 (1994), S. 383-406 
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    ISSN: 1436-4646
    Keywords: 90C05 ; Linear programming ; Primal—dual ; Polynomial complexity ; Infeasible ; Interior-point ; Exterior-point
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract A predictor—corrector method for solving linear programs from infeasible starting points is analyzed. The method is quadratically convergent and can be combined with Ye's finite termination scheme under very general assumptions. If the starting points are large enough then the algorithm hasO(nL) iteration complexity. If the ratio between feasibility and optimality at the starting points is small enough then the algorithm has O( $$\sqrt {n L} $$ ) iteration complexity. For feasible starting points the algorithm reduces to the Mizuno—Todd—Ye predictor—corrector method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01582228
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  • 12
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    Constant potential primal—dual algorithms: A framework (1994)
    Springer
    Mathematical programming 66 (1994), S. 145-159 
    Details
    ISSN: 1436-4646
    Keywords: Linear programming ; Interior point methods ; Primal—dual algorithms ; Potential function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We start with a study of the primal—dual affine-scaling algorithms for linear programs. Using ideas from Kojima et al., Mizuno and Nagasawa, and new potential functions we establish a framework for primal—dual algorithms that keep a potential function value fixed. We show that if the potential function used in the algorithm is compatible with a corresponding neighborhood of the central path then the convergence proofs simplify greatly. Our algorithms have the property that all the iterates can be kept in a neighborhood of the central path without using any centering in the search directions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01581142
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  • 13
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    Physiological properties and substrate specificity of a pentachlorophenol-degradingPseudomonas species (1994)
    Springer
    Biodegradation 5 (1994), S. 47-54 
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    ISSN: 1572-9729
    Keywords: biodegradation ; dechlorination ; pentachlorophenol ; Pseudomonas sp.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A bacterial strain capable of utilizing pentachlorophenol (PCP) as sole source of carbon and energy for growth was isolated from enrichment cultures containing 100 mg/l PCP in a mineral salts medium inoculated with contaminated soil from a lumber treatment waste site. The isolate, designated strain SR3, was identified as a species ofPseudomonas by virtue of its physiological and biochemical characteristics. Mineralization of PCP byPseudomonas sp. strain SR3 was demonstrated by loss of detectable PCP from growth medium, stoichiometry of chloride release (5 equivalents of chloride per mole of PCP), and formation of biomass consistent with the concentration of PCP mineralized. PCP-induced cells of strain SR3 showed elevated rates of oxygen consumption in the presence of PCP, and with different chlorinated phenols, with complete degradation of 2,3,5,6-, 2,3,6-, 2,4,6-, 2,4-, and 2,6-chloro-substituted phenols. Concentrations of PCP up to 175 mg/liter supported growth of this organism, but maximal rates of PCP removal were observed at a PCP concentration of 100 mg/liter. Based on its degradative properties,Pseudomonas sp. strain SR3 appears to have utility in bioremediation of soil and water contaminated with PCP.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00695213
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  • 14
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    Molecular analysis of pentachlorophenol degradation (1994)
    Springer
    Biodegradation 5 (1994), S. 277-288 
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    ISSN: 1572-9729
    Keywords: Pentachlorophenol ; biodegradation ; dechlorination ; dehalogenation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A limited number of microorganisms have been described for their ability to partially degrade pentachlorophenol (PCP), or to completely mineralize it. Several years ago we chose one of these microorganisms,Flavobacterium sp. strain ATCC 39723, for use in a detailed molecular analysis of the catabolism of PCP. This strain was chosen because it had previously been studied in great detail for its growth characteristics in relation to degradation of PCP. In this paper we provide an overview of the degradation pathway of PCP to 2,6-dichloro-p-hydroquinone byFlavobacterium. The specific biochemical reactions and the genes encoding the enzymes are reviewed. The successful transformation and site specific mutagenesis ofFlavobacterium, as well as the discovery of two newpcp alleles is also presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00696465
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  • 15
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    Genetics and biochemistry of 1,2-dichloroethane degradation (1994)
    Springer
    Biodegradation 5 (1994), S. 249-257 
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    ISSN: 1572-9729
    Keywords: chlorinated hydrocarbons ; biodegradation ; 1,2-dichloroethane ; alkanes ; Xanthobacter ; dehalogenase ; adaptation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Dichloroethane (1,2-DCE) is a synthetic compound that is not known to be formed naturally. Nevertheless, several pure microbial cultures are able to use it as a sole carbon source for growth. Degradation of 1,2-DCE proceeds via 2-chloroethanol, chloroacetaldehyde and chloroacetate to glycolate. The genes encoding the enzymes responsible for the conversion of 1,2-DCE to glycolic acid have been isolated. The haloalkane dehalogenase and an aldehyde dehydrogenase are plasmid encoded. Two other enzymes, the alcohol dehydrogenase and the haloacid dehalogenase, are chromosomally encoded. Sequence analysis indicates that the haloacid dehalogenase belongs to the L-specific 2-chloroproprionic acid dehalogenases. From the three-dimensional structure and sequence similarities, the haloalkane dehalogenase appears to be a member of the α/β hydrolase fold hydrolytic enzymes, of which several are involved in the degradation of aromatic and aliphatic xenobiotic compounds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00696463
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  • 16
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    Biotransformation of quinoline and methylquinolines in anoxic freshwater sediment (1994)
    Springer
    Biodegradation 5 (1994), S. 113-120 
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    ISSN: 1572-9729
    Keywords: biodegradation ; quinoline ; methylquinolines ; anaerobic biotransformation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Quinoline (Q) and some isomers of methylquinoline (MQ) were transformed to hydroxylated products in freshwater sediment slurries incubated under methanogenic conditions at 25 °C. Methylquinoline transformation was not affected by a methyl group on the C-3 or C-4 carbon atom of the pyridine ring; 2-MQ, however, was not transformed. All isomers of dimethylquinoline (DMQ) tested (2,4-, 2,6-, 2,7-, and 2,8-DMQ) with a methyl group at the number 2 carbon also persisted in sediments after anaerobic incubation for one year at 25 °C. In most experiments, quinoline initially was transformed to 2-hydroxyquinoline (2-OH-Q), which was further metabolized to unidentified products. A second product, 4-CH3-2-OH-Q, was detected in some experiments. This product accumulated and was not further transformed. 6-, 7-, and 8-Methylquinoline (6-, 7-, 8-MQ) were hydroxylated to form the respective 2-OH-MQ products. These hydroxylated products accumulated and were not further transformed. Hydroxylation of Q and 6-, 7- and 8-MQ at the 2-carbon position was confirmed by GC/FTIR and GC/MS analyses. The transformations of Q and MQs were pH dependent with an optimal pH of 7–8. The results of this study suggest that two pathways may exist for the anaerobic transformation of quinoline; one pathway leads to the formation of a hydroxylated intermediate and the other to a methylated and hydroxylated intermediate. In addition, our results suggest that a methyl substituent on the number 2 carbon inhibits the anaerobic transformation of quinoline derivatives.
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    URL: http://dx.doi.org/10.1007/BF00700636
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  • 17
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    Catabolic transposons (1994)
    Springer
    Biodegradation 5 (1994), S. 323-342 
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    ISSN: 1572-9729
    Keywords: mobile DNA ; insertion sequence ; transposon ; catabolic pathways ; biodegradation ; toluene ; chlorobiphenyl ; chlorobenzoate ; oxygenase ; dehalogenase ; plasmid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The structure and function of transposable elements that code for catabolic pathways involved in the biodegradation of organic compounds are reviewed. Seven of these catabolic transposons have structural features that place them in the Class I (composite) or Class II (Tn3-family) bacterial elements. One is a conjugative transposon. Another three have been found to have properties of transposable elements but have not been characterized sufficiently to assign to a known class. Structural features of the toluene (Tn4651/Tn4653) and naphthalene (Tn4655) elements that illustrate the enormous potential for acquisition, deletion and rearrangement of DNA within catabolic transposons are discussed. The recently characterized chlorobenzoate (Tn5271) and chlorobenzene (Tn5280) catabolic transposons encode different aromatic ring dioxygenases, however they both illustrate the constraints that must be overcome when recipients of catabolic transposons assemble and regulate complete metabolic pathways for environmental pollutants. The structures of the chlorobenzoate catabolic transposon Tn5271 and the related haloacetate dehalogenase catabolic element of plasmid pUO1 are compared and a hypothesis for their formation is discussed. The structures and activities of catabolic transposons of unknown class coding for the catabolism of halogenated alkanoic acids (DEH) and chlorobiphenyl (Tn4371) are also reviewed.
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    URL: http://dx.doi.org/10.1007/BF00696468
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  • 18
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    Thek-server dual and loose competitiveness for paging (1994)
    Springer
    Algorithmica 11 (1994), S. 525-541 
    Details
    ISSN: 1432-0541
    Keywords: On-line algorithms ; k-Server problem ; Linear programming ; Approximation algorithms ; Paging ; Caching ; Competitive analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract Weighted caching is a generalization ofpaging in which the cost to evict an item depends on the item. We study both of these problems as restrictions of the well-knownk-server problem, which involves moving servers in a graph in response to requests so as to minimize the distance traveled. We give a deterministic on-line strategy for weighted caching that, on any sequence of requests, given a cache holdingk items, incurs a cost within a factor ofk/(k−h+1) of the minimum cost possible given a cache holdingh items. The strategy generalizes “least recently used,” one of the best paging strategies in practice. The analysis is a primal-dual analysis, the first for an on-line problem, exploiting the linear programming structure of thek-server problem. We introduceloose competitiveness, motivated by Sleator and Tarjan's complaint [ST] that the standard competitive ratios for paging strategies are too high. Ak-server strategy isloosely c(k)-competitive if, for any sequence, foralmost all k, the cost incurred by the strategy withk serverseither is no more thanc(k) times the minimum costor is insignificant. We show that certain paging strategies (including “least recently used,” and “first in first out”) that arek-competitive in the standard model are looselyc(k)-competitive providedc(k)/Ink→∞ and bothk/c(k) andc(k) are nondecreasing. We show that the marking algorithm, a randomized paging strategy that is Θ(Ink)-competitive in the standard model, is looselyc(k)-competitive providedk−2 In Ink→∞ and both 2 Ink−c(k) andc(k) are nondecreasing.
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    URL: http://dx.doi.org/10.1007/BF01189992
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  • 19
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    Polynomial algorithms for linear programming over the algebraic numbers (1994)
    Springer
    Algorithmica 12 (1994), S. 436-457 
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    ISSN: 1432-0541
    Keywords: Linear programming ; Algebraic numbers ; Computational complexity ; Ellipsoid method ; Polynomial-time algorithms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We derive a bound on the computational complexity of linear programs whose coefficients are real algebraic numbers. Key to this result is a notion of problem size that is analogous in function to the binary size of a rational-number problem. We also view the coefficients of a linear program as members of a finite algebraic extension of the rational numbers. The degree of this extension is an upper bound on the degree of any algebraic number that can occur during the course of the algorithm, and in this sense can be viewed as a supplementary measure of problem dimension. Working under an arithmetic model of computation, and making use of a tool for obtaining upper and lower bounds on polynomial functions of algebraic numbers, we derive an algorithm based on the ellipsoid method that runs in time bounded by a polynomial in the dimension, degree, and size of the linear program. Similar results hold under a rational number model of computation, given a suitable binary encoding of the problem input.
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    URL: http://dx.doi.org/10.1007/BF01188714
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  • 20
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    Estimates of Gibbs free energies of formation of chlorinated aliphatic compounds (1994)
    Springer
    Biodegradation 5 (1994), S. 21-28 
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    ISSN: 1572-9729
    Keywords: biodegradation ; chlorinated compounds ; Gibbs free energy of formation ; group contribution method ; xenobiotic
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The Gibbs free energy of formation of chlorinated aliphatic compounds was estimated with Mavrovouniotis' group contribution method. The group contribution of chlorine was estimated from the scarce data available on chlorinated aliphatics in the literature, and found to vary somewhat according to the position of chlorine in the molecule. The resulting estimates of the Gibbs free energy of formation of chlorinated aliphatic compounds indicate that both reductive dechlorination and aerobic mineralization of these compounds can yield sufficient energy to sustain microbial growth.
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    Accelerated biodegradation of atrazine by a microbial consortium is possible in culture and soil (1994)
    Springer
    Biodegradation 5 (1994), S. 29-35 
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    ISSN: 1572-9729
    Keywords: attrazine ; biodegradation ; hydroxyatrazine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A mixed enrichment culture of microorganisms capable of accelerated mineralization of atrazine was isolated from soil treated with successive applications of the herbicide. Liquid cultures of this consortium, in the presence of simple carbon sources, mineralized 96% of the applied atrazine (0.56 mM) within 7 days. Atrazine mineralization in culture is initiated with the formation of the metabolite hydroxyatrazine. In soil treated with atrazine at a concentration of 0.14 mM (concentration is based on total soil mass), and then inoculated with the microbial consortium, the parent compound was completely transformed in 25 days. After 30 days of incubation, 60% of the applied atrazine was accounted for as14CO2. As was found with the liquid cultures, hydroxyatrazine was the major metabolite. After 145 days, soil extractable hydroxyatrazine declined to zero and 86% of the applied atrazine was accounted for as14CO2. No metabolites, other than hydroxyatrazine, were recovered from either the liquid culture or soil inoculated with the consortium. The use of the mixed microbial culture enhanced mineralization more than 20 fold as compared to uninoculated soil.
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    Degradation of oil sludge by landfarming — a case-study at the Ghent harbour (1994)
    Springer
    Biodegradation 5 (1994), S. 37-46 
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    ISSN: 1572-9729
    Keywords: biodegradation ; landfarming ; mutagenicity ; oil ; plant growth ; toxicity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Large-scale landfarming experiments have been performed on a loamy sand soil. An amount of 1,350 m3/ha oil sludge together with nutrients (N,P,K) and a bacterial inoculum were applied at two different times over a five-year period. At both test periods, biodegradation of the hydrocarbons (HC) was best fitted with first order reaction kinetics with degradation rates ranging from about 4 g HC/kg dry soil per year to about 15 g HC/kg dry soil per year. Toxicity tests on the aqueous soil extracts as well as plant growth and worm tests on the landfarm soil showed no striking negative effects of residual hydrocarbons. Migration of oil, nitrate and phosphate to the groundwater was minimal. In view of the diversity of solvents recommended in the literature, twenty extractants were tested for their capacity to remove HC from the loamy sand soil. Chlorinated solvents, such as dichloromethane and chloroform, were the most effective. Yet, in view of its effectiveness and low toxicity, acetone appears a suitable solvent for the extraction of soils and sediments polluted with hydrocarbons. This case-study revealed that oil sludge can effectively be treated by landfarming, if appropriate technical measures are taken and a sufficient time (minimum 15 years) for bioremediation is provided.
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    Enhanced biodegradation of phenanthrene in a biphasic culture system (1994)
    Springer
    Biodegradation 5 (1994), S. 93-103 
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    ISSN: 1572-9729
    Keywords: biodegradation ; PAH ; phenanthrene ; Pseudomonas aeruginosa ; bioavailability ; 2,2,4,4,6,8,8-heptamethylnonane ; surfactants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Degradation of phenanthrene byPseudomonas aeruginosa AK1 was examined in (i) an aqueous mineral salts medium to which phenanthrene particles of varying size (i.e. diameter) were added, and (ii) an aqueous/organic biphasic culture system consisting of mineral salts medium supplemented with 2,2,4,4,6,8,8-heptamethylnonane (HMN) as the phenanthrene-carrying organic phase. In both systems, the rate of phenanthrene biodegradation could be significantly enhanced by manipulations leading to improved phenanthrene mass transfer into the aqueous phase. With crystalline phenanthrene, the rate of biodegradation was found to be directly correlated to the particle surface area, whereas in the biphasic system the rate of biodegradation of the dissolved phenanthrene was mainly governed by the HMN/water interface area. In the latter system, exponential growth with a doubling time t d of 6–8 hours has been achieved under conditions of intensive agitation of the medium indicating that phenanthrene degradation by strain AK1 is limited mainly by physicochemical parameters. Addition of selected surfactants to the culture medium was found to accelerate phenanthrene degradation by strain AK1 only under conditions of low agitation (in the presence of HMN) and after pretreatment of phenanthrene crystals by ultrasonication (in the absence of HMN). Evidence is presented that the stimulating effect of the surfactants was primarily due to improved dispersion of phenanthrene particle agglomerates (in the aqueous mineral salts medium supplemented with phenanthrene crystals) or of the phenanthrene-carrying lipophilic solvent drops (in the aqueous/organic biphasic culture system) whereas the solubilizing activity towards phenanthrene was neglectible. Under conditions of intensive mixing of the culture medium (i.e. if a high particle surface area or HMN/water interface area, respectively, is provided), the addition of surfactants did not enhance phenanthrene biodegradation.
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    Genetic construction of PCB degraders (1994)
    Springer
    Biodegradation 5 (1994), S. 359-377 
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    ISSN: 1572-9729
    Keywords: Aerobic bacteria ; biodegradation ; genetic manipulations ; polychlorinated biphenyls ; recombinant strains
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Genetic construction of recombinant strains with expanded degradative abilities may be useful for bioremedation of recalcitrant compounds, such as polychlorinated biphenyls (PCBs). Some degradative genes have been found either on conjugative plasmids or on transposons, which would facilitate their genetic transfer. The catabolic pathway for the total degradation of PCBs is encoded by two different sets of genes that are not normally found in the same organism. ThebphABCD genes normally reside on the chromosome and encode for the four enzymes involved in the production of benzoate and chlorobenzoates from the respective catabolism of biphenyl and chlorobiphenyls. The genes encoding for chlorobenzoate catabolism have been found on both plasmids and the chromosome, often in association with transposable elements. Ring fission of chlorobiphenyls and chlorobenzoates involves themeta-fission pathway (3-phenylcatechol 2,3-dioxygenase) and theortho-fission pathway (chlorocatechol 1,2-dioxygenase), respectively. As the catecholic intermediates of both pathways are frequently inhibitory to each other, incompatibilities result. Presently, all hybrid strains constructed by in vivo matings metabolize simple chlorobiphenyls through complementary pathways by comprising thebph, benzoate, and chlorocatechol genes of parental strains. No strains have yet been verified which are able to utilize PCBs having at least one chlorine on each ring as growth substrates. The possible incompatibilities of hybrid pathways are evaluated with respect to product toxicity, and the efficiency of both in vivo and in vitro genetic methods for the construction of recombinant strains able to degrade PCBs is discussed.
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    Linear programming formulation of MDPs in countable state space: The multichain case (1994)
    Springer
    Mathematical methods of operations research 40 (1994), S. 91-108 
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    ISSN: 1432-5217
    Keywords: Markov decision processes ; countable state space ; Linear programming ; duality
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract We present an Linear Programming formulation of MDPs with countable state and action spaces and no unichain assumption. This is an extension of the Hordijk and Kallenberg (1979) formulation in finite state and action spaces. We provide sufficient conditions for both existence of optimal solutions to the primal LP program and absence of duality gap. Then, existence of a (possibly randomized) average optimal policy is also guaranteed. Existence of a stationary average optimal deterministic policy is also investigated.
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    Geometry of optimal value functions with applications to redundancy in linear programming (1994)
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    Journal of optimization theory and applications 81 (1994), S. 35-52 
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    ISSN: 1573-2878
    Keywords: Linear programming ; optimal value functions ; redundancy in linear programming ; convex hull problem ; data envelopment analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In 1967, Wets and Witzgall (Ref. 1) made, in passing, a connection between frames of polyhedral cones and redundancy in linear programming. The present work elaborates and formalizes the theoretical details needed to establish this relation. We study the properties of optimal value functions in order to derive the correspondence between problems in redundancy and the frame of a polyhedral cone. The insights obtained lead to schemes to improve the efficiency of procedures to detect redundancy in the areas of linear programming, stochastic programming, and computational geometry.
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    The simplex method as a global optimizer: A c-programming perspective (1994)
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    Journal of global optimization 4 (1994), S. 89-109 
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    ISSN: 1573-2916
    Keywords: Linear programming ; simplex method ; c-programming ; composite functions ; global optimization ; dc problems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In this paper we give a brief account of the important role that the conventional simplex method of linear programming can play in global optimization, focusing on its collaboration with composite concave programming techniques. In particular, we demonstrate how rich and powerful the c-programming format is in cases where its parametric problem is a standard linear programming problem.
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    On solution-containing ellipsoids in linear programming (1994)
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    Journal of optimization theory and applications 80 (1994), S. 161-173 
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    ISSN: 1573-2878
    Keywords: Linear programming ; interior point methods ; containing ellipsoids ; optimal basic and nonbasic variables
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Ellipsoids that contain all optimal dual slack solutions and those that contain all optimal primal solutions and that are independent of the algorithm used are derived. Based upon these ellipsoids, two criteria each for detecting optimal basic and nonbasic variables prior to optimality in interior-point methods are obtained. Using these results, we then derive a sufficient condition for a linear program to be feasible.
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    Rank-one techniques in log-barrier function methods for linear programming (1994)
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    Journal of optimization theory and applications 82 (1994), S. 405-413 
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    ISSN: 1573-2878
    Keywords: Linear programming ; interior-point methods ; Karmarkar's method ; log-barrier function ; rank-one techniques ; computational complexity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract This short paper presents a primal interior-point method for linear programming. The method can be viewed as a modification of the methods developed in Refs. 1–6. In each iteration, it computes an approximately projected Newton direction and needsO(n 2.5) arithmetic operations to make the log-barrier function significantly decrease. It requires $$O(\sqrt {nL} )$$ iterations, so that the total complexity isO(n 3 L).
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    Primal-dual algorithms for linear programming based on the logarithmic barrier method (1994)
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    Journal of optimization theory and applications 83 (1994), S. 1-26 
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    ISSN: 1573-2878
    Keywords: Linear programming ; primal-dual interior point methods ; logarithmic barrier function ; polynomial algorithms
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    Topics: Mathematics
    Notes: Abstract In this paper, we deal with primal-dual interior point methods for solving the linear programming problem. We present a short-step and a long-step path-following primal-dual method and derive polynomial-time bounds for both methods. The iteration bounds are as usual in the existing literature, namely $$O(\sqrt n L)$$ iterations for the short-step variant andO(nL) for the long-step variant. In the analysis of both variants, we use a new proximity measure, which is closely related to the Euclidean norm of the scaled search direction vectors. The analysis of the long-step method depends strongly on the fact that the usual search directions form a descent direction for the so-called primal-dual logarithmic barrier function.
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    Near boundary behavior of primal—dual potential reduction algorithms for linear programming (1993)
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    Mathematical programming 58 (1993), S. 243-255 
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    ISSN: 1436-4646
    Keywords: Linear programming ; interior point algorithm ; primal—dual potential function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract This paper is concerned with selection of theρ-parameter in the primal—dual potential reduction algorithm for linear programming. Chosen from [n + $$\sqrt n $$ , ∞), the level ofρ determines the relative importance placed on the centering vs. the Newton directions. Intuitively, it would seem that as the iterate drifts away from the central path towards the boundary of the positive orthant,ρ must be set close ton + $$\sqrt n $$ . This increases the relative importance of the centering direction and thus helps to ensure polynomial convergence. In this paper, we show that this is unnecessary. We find for any iterate thatρ can be sometimes chosen in a wide range [n + $$\sqrt n $$ , ∞) while still guaranteeing the currently best convergence rate of O( $$\sqrt n $$ L) iterations. This finding is encouraging since in practice large values ofρ have resulted in fast convergence rates. Our finding partially complements the recent result of Zhang, Tapia and Dennis (1990) concerning the local convergence rate of the algorithm.
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    Combining phase I and phase II in a potential reduction algorithm for linear programming (1993)
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    Mathematical programming 59 (1993), S. 133-150 
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    ISSN: 1436-4646
    Keywords: Linear programming ; interior-point methods ; combined phase I—phase II
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract This paper describes an affine potential reduction algorithm for linear programming that simultaneously seeks feasibility and optimality. The algorithm is closely related to a similar method of Anstreicher. The new features are that we use a two-dimensional programming problem to derive better lower bounds than Anstreicher, that our direction-finding subproblem treats phase I and phase II more symmetrically, and that we do not need an initial lower bound. Our method also allows for the generation of a feasible solution (so that phase I is terminated) during the course of the iterations, and we describe two ways to encourage this behavior.
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    A quadratically convergent O( $$\sqrt n $$ L)-iteration algorithm for linear programming (1993)
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    Mathematical programming 59 (1993), S. 151-162 
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    ISSN: 1436-4646
    Keywords: Linear programming ; primal and dual ; superlinear and quadratic convergence ; polynomiality
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract Recently, Ye, Tapia and Zhang (1991) demonstrated that Mizuno—Todd—Ye's predictor—corrector interior-point algorithm for linear programming maintains the O( $$\sqrt n $$ L)-iteration complexity while exhibiting superlinear convergence of the duality gap to zero under the assumption that the iteration sequence converges, and quadratic convergence of the duality gap to zero under the assumption of nondegeneracy. In this paper we establish the quadratic convergence result without any assumption concerning the convergence of the iteration sequence or nondegeneracy. This surprising result, to our knowledge, is the first instance of a demonstration of polynomiality and superlinear (or quadratic) convergence for an interior-point algorithm which does not assume the convergence of the iteration sequence or nondegeneracy.
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    A note on the prize collecting traveling salesman problem (1993)
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    Mathematical programming 59 (1993), S. 413-420 
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    ISSN: 1436-4646
    Keywords: Linear programming ; prize collecting ; rounding fractional solutions ; traveling salesman problem ; worst-case analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We study the version of the prize collecting traveling salesman problem, where the objective is to find a tour that visits a subset of vertices such that the length of the tour plus the sum of penalties associated with vertices not in the tour is as small as possible. We present an approximation algorithm with constant bound. The algorithm is based on Christofides' algorithm for the traveling salesman problem as well as a method to round fractional solutions of a linear programming relaxation to integers, feasible for the original problem.
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    Strict monotonicity and improved complexity in the standard form projective algorithm for linear programming (1993)
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    Mathematical programming 62 (1993), S. 517-535 
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    ISSN: 1436-4646
    Keywords: Linear programming ; Karmarkar's algorithm ; Projective algorithm ; Standard form
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract In a recent paper, Shaw and Goldfarb show that a version of the standard form projective algorithm can achieve $$O\left( {\sqrt {nL} } \right)$$ step complexity, as opposed to the O(nL) step complexity originally demonstrated for the algorithm. The analysis of Shaw and Goldfarb shows that the algorithm, using a constant, fixed steplength, approximately follows the central trajectory. In this paper we show that simple modifications of the projective algorithm obtain the same complexity improvement, while permitting a linesearch of the potential function on each step. An essential component is the addition of a single constraint, motivated by Shaw and Goldfarb's analysis, which makes the standard form algorithm strictly monotone in the true objective.
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    Determination of optimal vertices from feasible solutions in unimodular linear programming (1993)
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    Mathematical programming 59 (1993), S. 23-31 
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    ISSN: 1436-4646
    Keywords: Linear programming ; duality theorem ; unimodular ; totally unimodular ; interior point methods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract In this paper we consider a linear programming problem with the underlying matrix unimodular, and the other data integer. Given arbitrary near optimum feasible solutions to the primal and the dual problems, we obtain conditions under which statements can be made about the value of certain variables in optimal vertices. Such results have applications to the problem of determining the stopping criterion in interior point methods like the primal—dual affine scaling method and the path following methods for linear programming.
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    Increased biodegradation of a low-density polyethylene (LDPE) matrix in starch-filled LDPE materials (1993)
    Springer
    Journal of polymers and the environment 1 (1993), S. 241-245 
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    ISSN: 1572-8900
    Keywords: Degradation ; biodegradation ; starch-filled ; polyethylene ; prooxidant ; autoxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Preheated14C-labeled LDPE-films with 15% corn starch and a proxidant formulation [masterbatch (MB)] incubated in aqueous solutions with fungi at ambient temperature are about three times more susceptible to biodegradation than the corresponding preheated pure LDPE as observed by liquid scintillation counting (LSC). The inbuilt induction time before autoxidation commences can be shortened by initial heating. Preheated LDPE-MB materials biodegrade about five times faster than nonheated ones. After 1 year of biodegradation of nonheated LDPE-MB, sporadic increases in the evolution of14CO2 have been noted, showing that the induction time may be running toward and end.
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    Biodegradable water-soluble polycarboxylic acid design: Biodegradability and builder performance in detergent formulation of partially dicarboxylated polyuronide containing sugar residues in the backbone (1993)
    Springer
    Journal of polymers and the environment 1 (1993), S. 23-29 
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    ISSN: 1572-8900
    Keywords: Partially dicarboxylated polyuronide ; biodegradation ; design ; pectic acid ; alginic acid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Partially dicarboxylated polyuronide having a variable amount of unreacted sugar blocks as an enzymatically cleavable segment was prepared by the controlled oxidation of pectic acid and alginic acid. It was found that partially dicarboxylated polyuronides containing uronide blocks showed better biodegradability than those having no uronide block in the polycarboxylate chain. The rate of biodegradation varies according to the degree of dicarboxylation. It was confirmed that dicarboxy polyuronides containing more than 70% unreacted uronide residues tended to biodegrade quickly. The biodegradability obtained by the BOD test and the enzymatic degradability are well correlated, suggesting that these polymers are first cleaved at the sugar blocks by carbohydrase with subsequent assimilation of the resultant oligomeric fractions. Detergency was dependent on the content of the carboxylate groups in the polymer. The polymers with high carboxylate contents showed better builder performance. The detergency of dicarboxy pectic acid was better than that of dicarboxy alginic acid when compared on the basis of an equal degree of dicarboxylation.
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    A strictly improving linear programming Phase I algorithm (1993)
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    Annals of operations research 46-47 (1993), S. 409-430 
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    ISSN: 1572-9338
    Keywords: Linear programming ; Phase I ; nonlinear programming ; least squares ; quadratic programming ; strict improvement ; degeneracy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract Instead of trying to recognize and avoid degenerate steps in the simplex method (as some variants do), we have developed a new Phase I algorithm that is impervious to degeneracy. The new algorithm solves a non-negative least-squares problem in order to find a Phase I solution. In each iteration, a simple two-variable least-squares subproblem is used to select an incoming column to augment a set of independent columns (called “basic”) to get a strictly better fit to the right-hand side. Although this is analogous in many ways to the simplex method, it can be proved that strict improvement is attained at each iteration, even in the presence of degeneracy. Thus cycling cannot occur, and convergence is guaranteed. This algorithm is closely related to a number of existing algorithms proposed for non-negative least-squares and quadratic programs. When used on the 30 smallest NETLIB linear programming test problems, the computational results for the new Phase I algorithm were almost 3.5 times faster than a particular implementation of the simplex method; on some problems, it was over 10 times faster. Best results were generally seen on the more degenerate problems.
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    Degeneracy in interior point methods for linear programming: a survey (1993)
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    Annals of operations research 46-47 (1993), S. 107-138 
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    ISSN: 1572-9338
    Keywords: Linear programming ; interior point methods ; degeneracy ; polynomial algorithms ; global and local convergence ; basis recovery ; numerical performance ; sensitivity analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract The publication of Karmarkar's paper has resulted in intense research activity into Interior Point Methods (IPMs) for linear programming. Degeneracy is present in most real-life problems and has always been an important issue in linear programming, especially in the Simplex method. Degeneracy is also an important issue in IPMs. However, the difficulties are different in the two methods. In this paper, we survey the various theoretical and practical issues related to degeneracy in IPMs for linear programming. We survey results, which, for the most part, have already appeared in the literature. Roughly speaking, we shall deal with the effect of degeneracy on the following: the convergence of IPMs, the trajectories followed by the algorithms, numerical performance, and finding basic solutions.
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    Studies of lexicography in the generalized network simplex method (1993)
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    Annals of operations research 46-47 (1993), S. 235-248 
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    ISSN: 1572-9338
    Keywords: Linear programming ; generalized networks ; simplex method ; degeneracy ; lexicography ; cycling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract This paper introduces an analytical approach for studying lexicography in generalized network problems. The equations obtained can help us to understand and to extend the existing theory. First, it is verified that all nonzero elements have the same sign in each row vector of a basis inverse for a generalized network (GN) problem with positive multipliers. However, this property does not necessarily hold when there exist negative multipliers. Second, we developed a strategy to select the dropping arc in the GN simplex algorithm when addressing GN problems with positive andnegative multipliers. This strategy is also based on lexicography and requires performing some comparisons. However, the values to be compared are already known since they can be obtained as a by-product of the calculations necessary to compute the basis representation of the entering arc. Consequently, the computational effort per pivot step isO(n) in the worst case. This worst case effort is the same as that required by the strongly convergent rules for selecting the dropping arc in the method of strong convergence.
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    Pivot rules for linear programming: A survey on recent theoretical developments (1993)
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    Annals of operations research 46-47 (1993), S. 203-233 
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    ISSN: 1572-9338
    Keywords: Linear programming ; simplex method ; pivot rules ; cycling ; recursion ; minimal index rule ; parametric programming
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract The purpose of this paper is to discuss the various pivot rules of the simplex method and its variants that have been developed in the last two decades, starting from the appearance of the minimal index rule of Bland. We are mainly concerned with finiteness properties of simplex type pivot rules. Well known classical results concerning the simplex method are not considered in this survey, but the connection between the new pivot methods and the classical ones, if there is any, is discussed. In this paper we discuss three classes of recently developed pivot rules for linear programming. The first and largest class is the class of essentially combinatorial pivot rules including minimal index type rules and recursive rules. These rules only use labeling and signs of the variables. The second class contains those pivot rules which can actually be considered as variants or generalizations or specializations of Lemke's method, and so they are closely related to parametric programming. The last class has the common feature that the rules all have close connections to certain interior point methods. Finally, we mention some open problems for future research.
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    A practical anti-degeneracy row selection technique in network linear programming (1993)
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    Annals of operations research 46-47 (1993), S. 431-442 
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    ISSN: 1572-9338
    Keywords: Linear programming ; degeneracy ; network simplex algorithm ; pivoting ; minimal cost network flow
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract A characteristic feature of the primal network simplex algorithm (NSA) is that it usually makes a large number of degenerate iterations. Though cycling and even stalling can be avoided by recently introduced pivot rules for NSA, the practical efficiency of these rules is not known yet. For the case when the simplex algorithm is used to solve the continuous linear programming (LP) problem there exists a practical anti-cycling procedure that proved to be efficient. It is based on an expanding relaxation of the individual bound on the variables. In this paper we discuss the adaptation of this method to NSA, taking advantage of the special integer nature of network problems. We also give an account of our experience with these ideas as they are experimentally implemented in the MINET network LP solver. Reductions of CPU time have been achieved on a smaller set of specially structured real-life problems.
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    Degradation of poly(β-hydroxyalkanoates) and polyolefin blends in a municipal wastewater treatment facility (1993)
    Springer
    Journal of polymers and the environment 1 (1993), S. 269-274 
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    ISSN: 1572-8900
    Keywords: Poly(β-hydroxyalkanoates) ; biodegradation ; activated sludge ; starch-polyolefin blends
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Six types of plastics and plastic blends, the latter composed at least partially of biodegradable material, were exposed to aerobically treated wastewater (activated sludge) to ascertain their biodegradability. In one study, duplicate samples of 6% starch in polypropylene, 12% starch in linear low-density polyethylene, 30% polycaprolactone in linear low-density polyethylene, and poly(β-hydroxybutyrate-co-hydroxyvalerate) (PHB/V), a microbially produced polyester, were exposed to activated sludge for 5 months, and changes in mass, molecular weight average, and tensile properties were measured. None of the blended material showed any sign of degradation. PHB/V, however, showed a considerable loss of mass and a significant loss of tensile strength. In a second study, PHB/V degraded rapidly, but another type of microbial polymer which forms a thermoplastic elastomer, poly(β-hydroxyoctanoate), did not degrade. These results illustrate the potential for disposal and degradation of PHB/V in municipal wastewater.
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    An active-set strategy in an interior point method for linear programming (1993)
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    Mathematical programming 59 (1993), S. 345-360 
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    ISSN: 1436-4646
    Keywords: Linear programming ; interior point method ; active set strategy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We will present a potential reduction method for linear programming where only the constraints with relatively small dual slacks—termed “active constraints”—will be taken into account to form the ellipsoid constraint at each iteration of the process. The algorithm converges to the optimal feasible solution in O( $$\sqrt n $$ L) iterations with the same polynomial bound as in the full constraints case, wheren is the number of variables andL is the data length. If a small portion of the constraints is active near the optimal solution, the computational cost to find the next direction of movement in one iteration may be considerably reduced by the proposed strategy.
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    A randomized scheme for speeding up algorithms for linear and convex programming problems with high constraints-to-variables ratio (1993)
    Springer
    Mathematical programming 61 (1993), S. 39-52 
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    ISSN: 1436-4646
    Keywords: Linear programming ; quadratic programming ; convex programming ; randomized algorithms ; fixed dimension optimization problems ; complexity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We extend Clarkson's randomized algorithm for linear programming to a general scheme for solving convex optimization problems. The scheme can be used to speed up existing algorithms on problems which have many more constraints than variables. In particular, we give a randomized algorithm for solving convex quadratic and linear programs, which uses that scheme together with a variant of Karmarkar's interior point method. For problems withn constraints,d variables, and input lengthL, ifn = Ω(d 2), the expected total number of major Karmarkar's iterations is O(d 2(logn)L), compared to the best known deterministic bound of O( $$\sqrt n$$ L). We also present several other results which follow from the general scheme.
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    Load balancing in the parallel optimization of block-angular linear programs (1993)
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    Mathematical programming 62 (1993), S. 41-67 
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    ISSN: 1436-4646
    Keywords: Linear programming ; Dantzig—Wolfe decomposition ; large-scale systems ; parallel processing ; hypercube architecture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract Decomposition algorithms for block-angular linear programs give rise to a natural, coarse-grained parallelism that can be exploited by processing the subproblems concurrently within a distributed-memory environment. The parallel efficiency of the distributed approach, however, is critically dependent on the duration of the inherently serial master phase relative to that of the bottleneck subproblem. This paper investigates strategies for improving efficiency in distributed Dantzig—Wolfe decomposition by better balancing the load between the master and subproblem processors. We report computational experience on an Intel iPSC/2 hypercube multiprocessor with test problems having dimensions up to about 30 000 rows, 87 000 columns, and 200 coupling constraints.
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    Solving symmetric indefinite systems in an interior-point method for linear programming (1993)
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    Mathematical programming 62 (1993), S. 15-39 
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    ISSN: 1436-4646
    Keywords: Linear programming ; interior-point methods ; symmetric indefinite systems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We describe an implementation of a primal—dual path following method for linear programming that solves symmetric indefinite “augmented” systems directly by Bunch—Parlett factorization, rather than reducing these systems to the positive definite “normal equations” that are solved by Cholesky factorization in many existing implementations. The augmented system approach is seen to avoid difficulties of numerical instability and inefficiency associated with free variables and with dense columns in the normal equations approach. Solving the indefinite systems does incur an extra overhead, whose median is about 40% in our tests; but the augmented system approach proves to be faster for a minority of cases in which the normal equations have relatively dense Cholesky factors. A detailed analysis shows that the augmented system factorization is reliable over a fairly large range of the parameter settings that control the tradeoff between sparsity and numerical stability.
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    A primal—dual affine-scaling potential-reduction algorithm for linear programming (1993)
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    Mathematical programming 62 (1993), S. 119-131 
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    ISSN: 1436-4646
    Keywords: Linear programming ; interior point algorithm ; complexity ; potential function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We propose a potential-reduction algorithm which always uses the primal—dual affine-scaling direction as a search direction. We choose a step size at each iteration of the algorithm such that the potential function does not increase, so that we can take a longer step size than the minimizing point of the potential function. We show that the algorithm is polynomial-time bounded. We also propose a low-complexity algorithm, in which the centering direction is used whenever an iterate is far from the path of centers.
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    Finding an interior point in the optimal face of linear programs (1993)
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    Mathematical programming 62 (1993), S. 497-515 
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    ISSN: 1436-4646
    Keywords: Linear programming ; primal—dual methods ; optimal face ; strict complementarity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We study the problem of finding a point in the relative interior of the optimal face of a linear program. We prove that in the worst case such a point can be obtained in O(n 3 L) arithmetic operations. This complexity is the same as the complexity for solving a linear program. We also show how to find such a point in practice. We report and discuss computational results obtained for the linear programming problems in the NETLIB test set.
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    Bioavailability of sorbed- and separate-phase chemicals (1993)
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    Biodegradation 4 (1993), S. 141-153 
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    ISSN: 1572-9729
    Keywords: bioavailability ; biodegradation ; sorption ; oil ; soil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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    Effect of hydrogen peroxide on the biodegradation of PCBs in anaerobically dechlorinated river sediments (1993)
    Springer
    Biodegradation 4 (1993), S. 241-248 
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    ISSN: 1572-9729
    Keywords: aerobic ; anaerobic ; biodegradation ; hydrogen peroxide ; polychlorinated biphenyls ; sequential
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The ability to initiate aerobic conditions in dechlorinated anaerobic sediments was tested using hydrogen peroxide as an oxygenation agent. Hydrogen peroxide additions to the sediment induced aerobic polychlorinated biphenyl (PCB) degraders as indicated first, by an increase in bacterial count and second by a decline in PCB concentration from 135 µg/g to 20 µg/g over a 96-day period. Dechlorinated anaerobic sediment seems also to harbor indigenous anaerobic and aerobic microorganisms with high PCB degradation abilities. Those results support the potential ofin situ degradation of PCBs using a sequential anaerobic-aerobic technique.
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    Microbiological aspects of the removal of chlorinated hydrocarbons from air (1993)
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    Biodegradation 4 (1993), S. 261-282 
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    ISSN: 1572-9729
    Keywords: chlorinated hydrocarbons ; biodegradation ; biotransformation ; cometabolism ; gaseous emissions ; waste gas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Chlorinated hydrocarbons are widely used synthetic chemicals that are frequently present in industrial emissions. Bacterial degradation has been demonstrated for several components of this class of compounds. Structural features that affect the degradability include the number of chlorine atoms and the presence of oxygen substituents. Biological removal from waste streams of compounds that serve as a growth substrate can relatively easily be achieved. Substrates with more chlorine substituents can be converted cometabolically by oxidative routes. The microbiological principles that influence the biodegradability of chlorinated hydrocarbons are described. A number of factors that will determine the performance of microorganisms in systems for waste gas treatment is discussed. Pilot plant evaluations, including economics, of a biological trickling filter for the treatment of dichloromethane containing waste gas indicate that at least for this compound biological treatment is cost effective.
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    Degradation of 2-sec-butylphenol: 3-sec-butylcatechol,2-hydroxy-6-oxo-7-methylnona-2,4-dienoic acid, and 2-methylbutyric acid as intermediates (1993)
    Springer
    Biodegradation 4 (1993), S. 81-89 
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    ISSN: 1572-9729
    Keywords: 2-sec-butylphenol ; 3-sec-butylcatechol ; biodegradation ; meta-cleavage product ; monooxygenase ; metapyrocatechase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Pseudomonas sp. strain HBP1 Prp, a mutant of strain HBP1 that was originally isolated on 2-hydroxybiphenyl, was able to grow on 2-sec-butylphenol as the sole carbon and energy source. During growth on 2-sec-butylphenol, 2-methylbutyric acid transiently accumulated in the culture medium. Its concentration reached a maximum after 20 hours and was below detection limit at the end of the growth experiment. The first three enzymes of the degradation pathway — a NADH-dependent monooxygenase, a metapyrocatechase, and ameta-fission product hydrolase — were partially purified. The product of the the monooxygenase reaction was identified as 3-sec-butylcatechol by mass spectrometry. This compound was a substrate for the metapyrocatechase and was converted to 2-hydroxy-6-oxo-7-methylnona-2,4-dienoic acid which was identified by gas chromatography-mass spectrometry of its trimethylsilyl-derivative. The cofactor independentmeta-cleavage product hydrolase used 2-hydroxy-6-oxo-7-methylnona-2,4-dienoic acid as a substrate. All three enzymes showed highest activities for 2-hydroxybiphenyl and its metabolites, respectively, indicating that 2-sec-butylphenol is metabolized via the same pathway as 2-hydroxybiphenyl.
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    On combined phase 1-phase 2 projective methods for linear programming (1993)
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    Algorithmica 9 (1993), S. 64-83 
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    ISSN: 1432-0541
    Keywords: Linear programming ; Interior-point methods ; Projective methods ; Combined phase 1-phase 2
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We compare the projective methods for linear programming due to de Ghellinck and Vial, Anstreicher, Todd, and Fraley. These algorithms have the feature that they approach feasibility and optimality simultaneously, rather than requiring an initial feasible point. We compare the directions used in these methods and the lower-bound updates employed. In many cases the directions coincide and two of the lower-bound updates give the same result. It appears that Todd's direction and Fraley's lower-bound update have slight advantages, and this is borne out in limited computational testing.
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    On partial updating in a potential reduction linear programming algorithm of Kojima, Mizuno, and Yoshise (1993)
    Springer
    Algorithmica 9 (1993), S. 184-197 
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    ISSN: 1432-0541
    Keywords: Linear programming ; Karmarkar's algorithm ; Potential function ; Primal-dual, Modified method ; Rank-one updates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We consider partial updating in Kojima, Mizuno, and Yoshise's primal-dual potential reduction algorithm for linear programming. We use a simple safeguard condition to control the number of updates incurred on combined primal-dual steps. Our analysis allows for unequal steplengths in the primal and dual variables, which appears to be a computationally significant factor for primal-dual methods. The safeguard we use is a primal-dual Goldstein-Armijo condition, modified to deal with the unequal primal and dual steplengths.
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    A microbial biosensor system for dihalomethanes (1993)
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    Biodegradation 4 (1993), S. 101-105 
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    ISSN: 1572-9729
    Keywords: biodegradation ; biosensor ; dechlorination ; dehalogenase ; dichloromethane ; Hyphomicrobium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A biosensor system able to measure dichloromethane (DCM) and other dihalomethanes has been developed. The analysis is based on Hyphomicrobium DM2 cells immobilized in alginate. A combination of transducers consisting of a flow-calorimeter followed by a chloride-sensitive electrode has been used. By this design it was possible to monitor different aspects of the cell metabolism from one and the same pulse of substrate. The detection limit for the biosensor was 0.1 µM dichloromethane. The biosensor system can be used for continuous measurements in a sample stream.
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    Synergistic interaction between two bacterial isolates in the degradation of carbofuran (1993)
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    Biodegradation 4 (1993), S. 115-123 
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    ISSN: 1572-9729
    Keywords: insecticides ; methylcarbamates ; carbofuran ; carbaryl ; bendiocarb ; carbosulfan ; biodegradation ; bacterial degradation ; synergism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The dominant bacteriaPseudomonas sp. andArthrobacter sp. were isolated from the standing water of carbofuran-retreatedAzolla plot.Arthrobacter sp. hydrolysed carbofuran added to the mineral salts medium as a sole source of carbon and nitrogen while no degradation occurred withPseudomonas sp. Interestingly, when the medium containing carbofuran was inoculated with bothArthrobacter sp. andPseudomonas sp., a synergistic increase in its hydrolysis and subsequent release of CO2 from the side chain was noticed. This synergistic interaction was better expressed at 25° C than at 35° C. Likewise, related carbamates, carbaryl, bendiocarb and carbosulfan were more rapidly degraded in the combined presence of both bacterial isolates.
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    Degradation of the insecticide Hydramethylnon byPhanerochaete chrysosporium (1993)
    Springer
    Biodegradation 4 (1993), S. 131-139 
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    ISSN: 1572-9729
    Keywords: Hydramethylnon ; insecticide ; lignin peroxidase ; biodegradation ; Phanerochaete chrysosporium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The decomposition of the amidinohydrazone-type insecticide Hydramethylnon (HMN) by soil fungi has been investigated. A simple spectrophotometric method was developed for the estimation of HMN in soil and fungal culture media. HMN was found to be degraded in soil with a half life of 14 to 25 days. Degradation of HMN by the lignolytic fungus,Phanerochaete chrysosporium yielded two major breakdown products;p-(trifluoromethyl)-cinnamic acid (TFCA) andp-(trifluoromethyl)-benzoic acid (TFBA). TFCA was converted to TFBA which was subsequently metabolised via themeta-fission pathway. Fluoride release from HMN could not be detected.
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    Aerobic, phenol-induced TCE degradation in completely mixed, continuous-culture reactors (1993)
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    Biodegradation 4 (1993), S. 59-69 
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    ISSN: 1572-9729
    Keywords: trichloroethylene (TCE) ; biodegradation ; phenol ; Pseudomonas ; induction ; cometabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract BothPseudomonas putida F1 and a mixed culture were used to study TCE degradation in continuous culture under aerobic, non-methanotrophic conditions. TCE mass balance studies were performed with continuous culture reactors to determine the total percent removed in the reactors, and to quantify the percent removed by air stripping and biodegradation. Adsorption of TCE to biomass was assumed to be negligible. This research demonstrated the feasibility of treating TCE-contaminated water under aerobic, non-methanotrophic conditions with a mixed-culture, continuous-flow system. Initially glucose and acetate were fed as primary substrates. Pnenol, which has been shown to induce TCE-degrading enzymes, was fed at a much lower concentration (20mg/L). Little degradation of TCE was observed when acetate and glucose were the primary substrates. After omitting glucose and acetate from the feed and increasing the phenol concentration to 50mg/L, TCE biotransformation was observed at a significant level (46%). When the phenol concentration in the feed was increased to 420mg/L, 85% of the incoming TCE was estimated to have been biodegraded. Under the same conditions, phenol utilization by the mixed culture was greater than that ofP. putida F1, and TCE degradation by the mixed culture (85%) exceeded that ofP. putida F1 (55%). The estimated percent-of-TCE biodegraded by the mixed culture was consistently greater than 80% when phenol was fed at 420mg/L. Biodegradation of TCE was also observed in mixed-culture, batch experiments.
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    Metabolic diversity of aromatic hydrocarbon-degrading bacteria from a petroleum-contaminated aquifer (1993)
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    Biodegradation 4 (1993), S. 249-259 
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    ISSN: 1572-9729
    Keywords: aromatic hydrocarbons ; biodegradation ; bioremediation ; denitrification ; groundwater ; Pseudomonas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract We characterized bacteria from contaminated aquifers for their ability to utilize aromatic hydrocarbons under hypoxic (oxygen-limiting) conditions (initial dissolved oxygen concentration about 2 mg/l) with nitrate as an alternate electron acceptor. This is relevant to current intense efforts to establish favorable conditions forin situ bioremediation. Using samples of granular activated carbon slurries from an operating groundwater treatment system, we isolated bacteria that are able to use benzene, toluene, ethylbenzene, orp-xylene as their sole source of carbon under aerobic or hypoxic-denitrifying conditions. Direct isolation on solid medium incubated aerobically or hypoxically with the substrate supplied as vapor yielded 103 to 105 bacteria ml−1 of slurry supernatant, with numbers varying little with respect to isolation substrate or conditions. More than sixty bacterial isolates that varied in colony morphology were purified and characterized according to substrate utilization profiles and growth condition (i.e., aerobic vs. hypoxic) specificity. Strains with distinct characteristics were obtained using benzene compared with those isolated on toluene or ethylbenzene. In general, isolates obtained from direct selection on benzene minimal medium grew well under aerobic conditions but poorly under hypoxic conditions, whereas many ethylbenzene isolates grew well under both incubation conditions. We conclude that the conditions of isolation, rather than the substrate used, will influence the apparent characteristic substrate utilization range of the isolates obtained. Also, using an enrichment culture technique, we isolated a strain ofPseudomonas fluorescens, designated CFS215, which exhibited nitrate dependent degradation of aromatic hydrocarbons under hypoxic conditions.
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    Long steps in an O(n 3 L) algorithm for linear programming (1992)
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    Mathematical programming 54 (1992), S. 251-265 
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    ISSN: 1436-4646
    Keywords: Linear programming ; Karmarkar's algorithm ; potential function ; standard form ; modified method ; rank-one updates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We consider partial updating in Ye's affine potential reduction algorithm for linear programming. We show that using a Goldstein—Armijo rule to safeguard a linesearch of the potential function during primal steps is sufficient to control the number of updates. We also generalize the dual step construction to apply with partial updating. The result is the first O(n 3 L) algorithm for linear programming whose steps are not constrained by the need to remain approximately centered. The fact that the algorithm has a rigorous “primal-only” initialization actually reduces the complexity to less than O(m 1.5 n 1.5 L).
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    On Anstreicher's combined phase I—phase II projective algorithm for linear programming (1992)
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    Mathematical programming 55 (1992), S. 1-15 
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    ISSN: 1436-4646
    Keywords: Linear programming ; interior-point method ; projective algorithm ; combining phase I–phase II
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract Anstreicher has proposed a variant of Karmarkar's projective algorithm that handles standard-form linear programming problems nicely. We suggest modifications to his method that we suspect will lead to better search directions and a more useful algorithm. Much of the analysis depends on a two-constraint linear programming problem that is a relaxation of the scaled original problem.
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    Zur Modellierung logischer Aussagen ergänzend zu Linearen Programmen (1992)
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    OR spectrum 14 (1992), S. 149-160 
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    ISSN: 1436-6304
    Keywords: Lineare Programmierung ; logische Aussagen ; Binärvariablen ; Modellgenerator ; Linear programming ; predicates ; binary variables ; model generator
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Description / Table of Contents: Summary We introduce in the field of formulating logical predicates in addition to linear programs. The error prone process of developing linear constraints including binary variables (“auxilliary formulations”) to accomplish this leads us to discuss the possibilities and capabilities of model generation. Based on Williams [12] we develop the formulae apparatus and discuss formulation and design problems for the development of our model generator now being implemented.
    Notes: Zusammenfassung Wir geben eine Einführung in das Gebiet der Formulierung logischer Aussagen ergänzend zu Linearen Programmen. Der dazu notwendige, fehlerträchtige Prozeß der Aufstellung linearer Restriktionen unter der Verwendung von Binärvariablen („Ersatzformulierungen“) führt uns dazu, die Möglichkeiten und Fähigkeiten eines Modellgenerators für diesen Zweck zu diskutieren. Auf der Grundlage von Williams [12] entwickeln wir den Formelapparat und erörtern Formulierungs- und Entwurfsprobleme für die Entwicklung unseres sich jetzt in der Implementationsphase befindlichen Modellgenerators.
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    URL: http://dx.doi.org/10.1007/BF01783518
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    Polynomial algorithms for LP over a subring of the algebraic integers with applications to LP with circulant matrices (1992)
    Springer
    Mathematical programming 57 (1992), S. 121-143 
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    ISSN: 1436-4646
    Keywords: Linear programming ; polynomial-time algorithms ; strongly polynomial-time algorithms ; circulant matrices ; algebraic numbers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We show that a modified variant of the interior point method can solve linear programs (LPs) whose coefficients are real numbers from a subring of the algebraic integers. By defining the encoding size of such numbers to be the bit size of the integers that represent them in the subring, we prove the modified algorithm runs in time polynomial in the encoding size of the input coefficients, the dimension of the problem, and the order of the subring. We then extend the Tardos scheme to our case, obtaining a running time which is independent of the objective and right-hand side data. As a consequence of these results, we are able to show that LPs with real circulant coefficient matrices can be solved in strongly polynomial time. Finally, we show how the algorithm can be applied to LPs whose coefficients belong to the extension of the integers by a fixed set of square roots.
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    MODLER: Modeling by object-driven linear elemental relations (1992)
    Springer
    Annals of operations research 38 (1992), S. 239-280 
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    ISSN: 1572-9338
    Keywords: Linear programming ; large-scale systems ; modeling ; language design
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract This paper describes a system to represent linear programming models and their instances. In addition to a modeling language, MODLER has an extensive query capability which includes a multi-view architecture. Further, randomization options provide rapid prototyping. The MODLER system is part of a workbench for building and managing decision support systems that are based on linear programming.
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    URL: http://dx.doi.org/10.1007/BF02283655
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    A simplex algorithm for piecewise-linear programming III: Computational analysis and applications (1992)
    Springer
    Mathematical programming 53 (1992), S. 213-235 
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    ISSN: 1436-4646
    Keywords: Linear programming ; simplex methods ; piecewise-linear programming ; nondifferentiable optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract The first two parts of this paper have developed a simplex algorithm for minimizing convex separable piecewise-linear functions subject to linear constraints. This concluding part argues that a direct piecewiselinear simplex implementation has inherent advantages over an indirect approach that relies on transformation to a linear program. The advantages are shown to be implicit in relationships between the linear and piecewise-linear algorithms, and to be independent of many details of implementation. Two sets of computational results serve to illustarate these arguments; the piecewise-linear simplex algorithm is observed to run 2–6 times faster than a comparable linear algorithm, not including any additional expense that might be incurred in setting up the equivalent linear program. Further support for the practical value of a good piecewise-linear programming algorithm is provided by a survey of many varied applications.
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    Biodegradation of haloalkanes (1992)
    Springer
    Biodegradation 3 (1992), S. 299-313 
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    ISSN: 1572-9729
    Keywords: biodegradation ; bromoalkanes ; dehalogenase ; environmental pollution ; haloalkanes ; Pseudomonas sp.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Halogenated alkanes constitute a significant group among the organic pollutants of environmental concern. Their industrial and agricultural uses are extensive, but until 1978 they were considered to be non-biodegradable. In recent years, microorganisms were described that could degrade, partially or fully, singly or in consortia, many of the compounds tested. The first step in haloalkane degradation appears to be universal: removal of the halogen atom(s). This is mediated by a group of enzymes, generally known as dehalogenases, acting in most cases either as halidohydrolases or oxygenases. Nevertheless, information is still severely lacking regarding the biochemical pathways involved in these processes, as well as their genetic control. A recently isolated Pseudomonas strain, named ES-2, was shown to possess a very wide degradative spectrum, and to contain at least one hydrolytic dehalogenase. The utilization by this organism of water-insoluble haloalkanes, such as 1-bromooctane, appears to consist of three phases: extracellular emulsification by a constitutively excreted surface active agent, periplasmic dehalogenation by an inducible dehalogenase, and intracellular degradation of the residual carbon skeleton.
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    Metabolic pathway for the biodegradation of octadecylbis(2-hydroxyethyl)amine (1992)
    Springer
    Biodegradation 3 (1992), S. 435-443 
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    ISSN: 1572-9729
    Keywords: octadecylbis(2-hydroxyethyl)amine ; non-ionic surfactant ; biodegradation ; metabolism ; central fission ; diethanolamine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The biodegradation curve of octadecylbis(2-hydroxyethyl)amine determined in a Closed Bottle test suggested an initial oxidation of the alkyl chain and a subsequent degradation of the diethanolamine formed. Using the sludge from the test as inoculum, a bacterium capable of utilizing octadecylbis(2-hydroxyethyl)amine as sole source of carbon and energy was isolated. This bacterium also utilized various other alkylbis(2-hydroxyethyl)amines and octadecylpolyoxyethylene(5)amide. Respirometric studies and the formation of diethanolamine by a washed cell suspension of the pure culture showed that the bacterium only oxidized the alkyl chain. Furthermore, in cell-free extracts a dehydrogenase activity catalysing the oxidation of octadecylbis(2-hydroxyethyl)amine was detected.
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    Finding effective “force targets” for two-dimensional, multifinger frictional grips (1992)
    Springer
    Algorithmica 8 (1992), S. 1-20 
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    ISSN: 1432-0541
    Keywords: Robotics ; Grasp planning ; Robot control ; Computational Geometry ; Linear programming ; Parametric searching ; Davenport-Schinzel sequences
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract In this paper we apply techniques from computational geometry to solve several problems in grasp planning and control in robotics. We consider the problem of calculating “force targets ” for a collection ofn fingers which grasp a two-dimensional object at known positions, at which the normals to the surface are also assumed to be known at least approximately. If the points at which the fingers touch the body do not allow apositive grip to be exerted (i.e., a grip in which the fingers hold the body in equilibrium by exerting friction-free forces in the directions of the corresponding inward-directed normals), it is appropriate to find the smallest coefficient of friction for which it is possible to assign a set of forces to be exerted by the fingers (so-calledfinger-force targets) which hold the object at equilibrium and such that each individual force lies within the corresponding cone of friction. We present an algorithm for this problem which runs in time0(n log2 n log logn). We also present another algorithm for preprocessing the given data so as to allow fast computation of the desired coefficient of friction for the case in which one needs to balance any given “query” external force and torque. Finally, we discuss simpler variants of our techniques which are likely to be more efficient when the problem is solved for a small number of fingers.
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    A geometric view of parametric linear programming (1992)
    Springer
    Algorithmica 8 (1992), S. 161-176 
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    ISSN: 1432-0541
    Keywords: Parametric linear programming ; Sensitivity analysis ; Postoptimality analysis ; Linear programming
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We present a new definition of optimality intervals for the parametric right-hand side linear programming (parametric RHS LP) Problem ϑ(λ) = min{c t x¦Ax =b + λ¯b,x ≥ 0}. We then show that an optimality interval consists either of a breakpoint or the open interval between two consecutive breakpoints of the continuous piecewise linear convex function ϑ(λ). As a consequence, the optimality intervals form a partition of the closed interval {λ; ¦ϑ(λ)¦ 〈 ∞}. Based on these optimality intervals, we also introduce an algorithm for solving the parametric RHS LP problem which requires an LP solver as a subroutine. If a polynomial-time LP solver is used to implement this subroutine, we obtain a substantial improvement on the complexity of those parametric RHS LP instances which exhibit degeneracy. When the number of breakpoints of ϑ(λ) is polynomial in terms of the size of the parametric problem, we show that the latter can be solved in polynomial time.
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    A projection and contraction method for a class of linear complementarity problems and its application in convex quadratic programming (1992)
    Springer
    Applied mathematics & optimization 25 (1992), S. 247-262 
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    ISSN: 1432-0606
    Keywords: Projection ; Féjer-contraction ; Linear complementarity problem ; Linear programming ; Convex quadratic programming
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In this paper we propose a new iterative method for solving a class of linear complementarity problems:u ≥ 0,Mu + q ≥ 0, uT(Mu + q)=0, where M is a givenl ×l positive semidefinite matrix (not necessarily symmetric) andq is a givenl-vector. The method makes two matrix-vector multiplications and a trivial projection onto the nonnegative orthant at each iteration, and the Euclidean distance of the iterates to the solution set monotonously converges to zero. The main advantages of the method presented are its simplicity, robustness, and ability to handle large problems with any start point. It is pointed out that the method may be used to solve general convex quadratic programming problems. Preliminary numerical experiments indicate that this method may be very efficient for large sparse problems.
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    L 1 Sensitivity minimization for plants with commensurate delays (1992)
    Springer
    Mathematics of control, signals, and systems 5 (1992), S. 281-293 
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    ISSN: 1435-568X
    Keywords: L 1 optimal control ; Delay and infinite-dimensional linear systems ; Linear programming
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics , Technology
    Notes: Abstract In this paper we consider the problem ofL 1 sensitivity minimization for linear plants with commensurate input delays. We describe a procedure for computing the minimum performance, and we characterize optimal solutions. The computations involve solving a one-parameter family of finite-dimensional linear programs. Explicit solutions are presented for important special cases.
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    Characterization of an inducible, membrane-bound iminodiacetate dehydrogenase from Chelatobacter heintzii ATCC 29600 (1992)
    Springer
    Biodegradation 3 (1992), S. 423-434 
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    ISSN: 1572-9729
    Keywords: membrane protein ; biodegradation ; iminodiacetate ; iminodiacetate dehydrogenase ; nitrilotriacetate (NTA) ; ubiquinones
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Iminodiacetate (IDA) is a xenobiotic intermediate common to both aerobic and anaerobic metabolism of nitrilotriacetate (NTA). It is formed by either NTA monooxygenase or NTA dehydrogenase. In this paper the detection and characterization of a membrane-bound iminodiacete dehydrogenase (IDA-DH) from Chelatobacter heintzii ATCC 29600 is reported, which oxidizes IDA to glycine and glyoxylate. Out of 15 compounds tested, IDA was the only substrate for the enzyme. Optimum activity of IDA-DH was found at pH 8.5 and 25°C, respectively, and the Km for IDA was found to be 8mM. Activity of the membrane-bound enzyme was inhibited by KCN, antimycine and dibromomethylisopropyl-benzoquinone. When inhibited by KCN IDA-DH was able to reduce the artificial electron acceptor iodonitrotetrazolium (INT). It was possible to extract IDA-DH from the membranes with 2% cholate, to reconstitute the enzyme into soybean phospholipid vesicles and to obtain IDA-DH activity (more than 50% recovery) using ubiquinone Q1 as the intermediate electron carrier and INT as the final electron acceptor. Growth experiments with different substrates revealed that in all NTA-degrading strains tested both NTA monooxygenase and IDA-DH were only expressed when the cells were grown on NTA or IDA. Furthermore, in Cb. heintzii ATCC 29600 growing exponentially on succinate and ammonia, addition of 0.4 g l-1 NTA led to the induction of the two enzymes within an hour and NTA was utilized simultaneously with succinate. The presence of IDA-DH was confirmed in ten different NTA-degrading strains belonging to three different genera.
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    Microbes and microbial enzymes for cyanide degradation (1992)
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    Biodegradation 3 (1992), S. 3-18 
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    ISSN: 1572-9729
    Keywords: hydrogen cyanide ; enzyme mechanisms ; biodegradation ; microbes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Cyanide is an important industrial chemical produced on a grand scale each year. Although extremely toxic to mammalian life, cyanide is a natural product generated by fungi and bacteria, and as a result microbial systems have evolved for the degradation of cyanide to less toxic compounds. The enzymes which utilize cyanide as a substrate can be categorized into the following reaction types: substitution/addition, hydrolysis, oxidation, and reduction. Each of these categories is reviewed with respect to the known biochemistry and feasibility for use in treatment of cyanide containing wastes.
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    A mechanistic perspective on bacterial metabolism of chlorinated methanes (1992)
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    Biodegradation 3 (1992), S. 19-36 
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    ISSN: 1572-9729
    Keywords: chloromethanes ; chlorofluoromethanes ; mechanisms ; bacteria ; dehalogenation ; biodegradation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Chlorinated methanes are important environmental pollutants, which can be metabolized by bacteria. The biotransformation of chlorinated methanes by bacteria has been shown to be due either to gratuitous metabolism (cometabolism) or their use as a source of carbon and energy. The reactions which result in carbon-halogen bond cleavage include substitutive, reductive, oxygenative, and gem-elimination mechanisms. Certain methylotrophic bacteria can use dichloromethane as a source of carbon and energy. Dichloromethane dehalogenase catalyzes the first substitutive reaction in this metabolism. The enzyme shows a 1010-fold rate enhancement over the reaction of the bisulfide anion with dichloromethane in water. Pseudomonas putida G786 synthesizes cytochrome P-450CAM which catalyzes the gratuitous reduction of chlorinated methanes. These studies with purified enzymes are beginning to reveal more detailed mechanistic features of bacterial chlorinated methane metabolism.
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    Biodegradation of short-chain alkyl sulphates by a coryneform species (1992)
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    Biodegradation 3 (1992), S. 83-91 
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    ISSN: 1572-9729
    Keywords: alkylsulphatase ; alkyl sulphate ; biodegradation ; desulphation ; hydrolysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Coryneform B1a isolated from soil grew well on butyl-, pentyl- and hexyl-1-sulphates esters and on the corresponding parent alcohols as sole sources of carbon, with growth rates around 0.14–0.19 h-1. Propyl-1-sulphate and heptyl-1-sulphate supported slower growth, and their C1, C2 and C8 homologues were not utilised at all. Growth of the organism was accompanied by disappearance of butyl-1-sulphate. In the presence of resting cells, butyl-1-sulphate degradation was stoichiometric with the liberation of inorganic sulphate. Butan-1-ol was also detected but in less than stoichiometric amounts. Non-denaturing polyacrylamide gel electrophoresis of extracts of cells grown on butyl-1-sulphate, followed by incubation of gels in butyl-1-sulphate and precipitation of liberated SO4 2- as BaSO4, revealed a single white band of alkylsulphatase activity. Other zymograms produced in the same way but incubated with the C5 and C6 esters, each produced a single band of the same mobility and intensity. With the C3 and C7 homologues, the same band was present but considerably less intense. No alkylsulphatase band was detected for methyl, ethyl or octyl-1-sulphates. Assays of alkylsulphatase activity in crude cell-extracts indicated maximum activity towards butyl-1-sulphate at pH 7.5 and 30° C, with Km=8.4±1.4 mM and V max =0.13±0.01 μmol/min/mg of protein. The results indicated that degradation of short-chain alkyl sulphates in this organism was initiated by enzymic hydrolysis to the corresponding alcohol.
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    The environment, microbes and bioremediation: microbial activities modulated by the environment (1992)
    Springer
    Biodegradation 3 (1992), S. 125-135 
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    ISSN: 1572-9729
    Keywords: natural evolution ; directed evolution ; biodegradation ; environmental pollutants ; environmental signal transduction ; gene expression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Microorganisms in nature are largely responsible for the biodegradation and removal of toxic and non-toxic chemicals. Many organisms are also known to have specific ecological niches for proliferation and colonization. The nature of the environment dictates to a large extent the biodegradability of synthetic compounds by modulating the evolutionary processes in microorganisms for new degradative genes. Similarly, environmental factors often determine the extent of microbial gene expression by activating or repressing specific gene or sets of genes through a sensory signal transduction process. Understanding how the environment modulates microbial activity is critical for successful bioremediative applications.
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    Biodegradation of polycyclic aromatic hydrocarbons (1992)
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    Biodegradation 3 (1992), S. 351-368 
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    ISSN: 1572-9729
    Keywords: biodegradation ; degradation ; detoxification ; dioxygenase ; hydroxylation ; monooxygenase ; polycyclic aromatic hydrocarbons ; ring cleavage
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The intent of this review is to provide an outline of the microbial degradation of polycyclic aromatic hydrocarbons. A catabolically diverse microbial community, consisting of bacteria, fungi and algae, metabolizes aromatic compounds. Molecular oxygen is essential for the initial hydroxylation of polycyclic aromatic hydrocarbons by microorganisms. In contrast to bacteria, filamentous fungi use hydroxylation as a prelude to detoxification rather than to catabolism and assimilation. The biochemical principles underlying the degradation of polycyclic aromatic hydrocarbons are examined in some detail. The pathways of polycyclic aromatic hydrocarbon catabolism are discussed. Studies are presented on the relationship between the chemical structure of the polycyclic aromatic hydrocarbon and the rate of polycyclic aromatic hydrocarbon biodegradation in aquatic and terrestrial ecosystems.
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    Superlinear and quadratic convergence of primal-dual interior-point methods for linear programming revisited (1992)
    Springer
    Journal of optimization theory and applications 73 (1992), S. 229-242 
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    ISSN: 1573-2878
    Keywords: Linear programming ; primal-dual interior-point algorithms ; superlinear convergence ; quadratic convergence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Recently, Zhang, Tapia, and Dennis (Ref. 1) produced a superlinear and quadratic convergence theory for the duality gap sequence in primal-dual interior-point methods for linear programming. In this theory, a basic assumption for superlinear convergence is the convergence of the iteration sequence; and a basic assumption for quadratic convergence is nondegeneracy. Several recent research projects have either used or built on this theory under one or both of the above-mentioned assumptions. In this paper, we remove both assumptions from the Zhang-Tapia-Dennis theory.
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    Sensitivity method for basis inverse representation in multistage stochastic linear programming problems (1992)
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    Journal of optimization theory and applications 74 (1992), S. 221-242 
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    ISSN: 1573-2878
    Keywords: Linear programming ; stochastic programming ; simplex method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract A version of the simplex method for solving stochastic linear control problems is presented. The method uses a compact basis inverse representation that extensively exploits the original problem data and takes advantage of the supersparse structure of the problem. Computational experience indicates that the method is capable of solving large problems.
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    An unconstrained convex programming view of linear programming (1992)
    Springer
    Mathematical methods of operations research 36 (1992), S. 149-161 
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    ISSN: 1432-5217
    Keywords: Linear programming ; Barrier Function ; Entropy Function ; Geometric Programming ; Convex programming
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract The major interest of this paper is to show that, at least in theory, a pair of primal and dual “ɛ-optimal solutions” to a general linear program in Karmarkar's standard form can be obtained by solving an unconstrained convex program. Hence unconstrained convex optimization methods are suggested to be carefully reviewed for this purpose.
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    Interior proximal point algorithm for linear programs (1992)
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    Journal of optimization theory and applications 74 (1992), S. 425-444 
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    ISSN: 1573-2878
    Keywords: Linear programming ; interior point method ; proximal point method ; Newton method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract An interior proximal point algorithm for finding a solution of a linear program is presented. The distinguishing feature of this algorithm is the addition of a quadratic proximal term to the linear objective function. This perturbation has allowed us to obtain solutions with better feasibility. Implementation of this algorithm shows that the algorithms. We also establish global convergence and local linear convergence of the algorithm.
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    Deriving an unconstrained convex program for linear programming (1992)
    Springer
    Journal of optimization theory and applications 75 (1992), S. 603-612 
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    ISSN: 1573-2878
    Keywords: Linear programming ; convex programming ; geometric programming ; duality theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Consider a linear programming problem in Karmarkar's standard form. By perturbing its linear objective function with an entropic barrier function and applying generalized geometric programming theory to it, Fang recently proposed an unconstrained convex programming approach to finding an epsilon-optimal solution. In this paper, we show that Fang's derivation of an unconstrained convex dual program can be greatly simplified by using only one simple geometric inequality. In addition, a system of nonlinear equations, which leads to a pair of primal and dual epsilon-optimal solutions, is proposed for further investigation.
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    Extensions of the potential reduction algorithm for linear programming (1992)
    Springer
    Journal of optimization theory and applications 72 (1992), S. 487-498 
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    ISSN: 1573-2878
    Keywords: Linear programming ; primal and dual problems ; bimatrix games ; potential function ; potential reduction algorithm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In this work, we study several extensions of the potential reduction algorithm that was developed for linear programming. These extensions include choosing different potential functions, generating the analytic center of a polytope, and finding the equilibrium of a zero-sum bimatrix game.
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    Comparative analysis of affine scaling algorithms based on simplifying assumptions (1991)
    Springer
    Mathematical programming 52 (1991), S. 405-414 
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    ISSN: 1436-4646
    Keywords: Linear programming ; primal and dual ; potential reduction algorithm ; affine scaling algorithm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We analyze several affine potential reduction algorithms for linear programming based on simplifying assumptions. We show that, under a strong probabilistic assumption regarding the distribution of the data in an iteration, the decrease in the primal potential function will be $$\Omega (\rho /\sqrt {log(n)} )$$ with high probability, compared to the guaranteedΩ(1). (ρ ⩾2n is a parameter in the potential function andn is the number of variables.) Under the same assumption, we further show that the objective reduction rate of Dikin's affine scaling algorithm is $$(1 - 1/\sqrt {log(n)} )$$ with high probability, compared to no guaranteed convergence rate.
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    URL: http://dx.doi.org/10.1007/BF01582897
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    Global convergence of the affine scaling methods for degenerate linear programming problems (1991)
    Springer
    Mathematical programming 52 (1991), S. 377-404 
    Details
    ISSN: 1436-4646
    Keywords: Linear programming ; interior point methods ; affine scaling methods ; global analysis ; degenerate problems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract In this paper we show the global convergence of the affine scaling methods without assuming any condition on degeneracy. The behavior of the method near degenerate faces is analyzed in detail on the basis of the equivalence between the affine scaling methods for homogeneous LP problems and Karmarkar's method. It is shown that the step-size 1/8, where the displacement vector is normalized with respect to the distance in the scaled space, is sufficient to guarantee the global convergence of the affine scaling methods.
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    URL: http://dx.doi.org/10.1007/BF01582896
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    A combined phase I—phase II scaled potential algorithm for linear programming (1991)
    Springer
    Mathematical programming 52 (1991), S. 429-439 
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    ISSN: 1436-4646
    Keywords: Linear programming ; potential function ; phase I ; phase II ; artificial variable
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We develop an extension of the affinely scaled potential reduction algorithm which simultaneously obtains feasibility and optimality in a standard form linear program, without the addition of any “M” terms. The method, and its lower-bounding procedure, are particularly simple compared with previous interior algorithms not requiring feasibility.
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    URL: http://dx.doi.org/10.1007/BF01582899
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    An O(n 3 L) adaptive path following algorithm for a linear complementarity problem (1991)
    Springer
    Mathematical programming 52 (1991), S. 587-595 
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    ISSN: 1436-4646
    Keywords: Linear programming ; linear complementarity problem ; interior point algorithms ; path following algorithms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract In this paper we propose an O(n 3 L) algorithm which is a modification of the path following algorithm [8] for a linear complementarity problem. The path following algorithm has to take a short step size in each iteration in order to bound the number of overall arithmetic operations by O(n 3 L). In practical computation, we can determine the step size adaptively. Mizuno, Yoshise, and Kikuchi [11] reported that such an adaptive algorithm required about O(L) iterations for some test problems. Here we show that we can use a rank one update technique in the adaptive algorithm so that the number of overall arithmetic operations is theoretically bounded by O(n 3 L).
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    URL: http://dx.doi.org/10.1007/BF01582906
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    Linear programming with spheres and hemispheres of objective vectors (1991)
    Springer
    Mathematical programming 51 (1991), S. 1-16 
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    ISSN: 1436-4646
    Keywords: Linear programming ; parametric ; homeomorphisms ; spheres ; hemispheres
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract Given a linear program with a boundedp-dimensional feasible region let the objective vector range over ans-sphere, that is, ans-dimensional sphere centered at the origin wheres does not exceedp−1. If the feasible region and the sphere are in general position with respect to each other, then the corresponding set of all optimal solutions is a topologicals-sphere. Similar results are developed for unbounded feasible regions and hemispheres of objective vectors.
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    URL: http://dx.doi.org/10.1007/BF01586923
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    An O(n 3 L) potential reduction algorithm for linear programming (1991)
    Springer
    Mathematical programming 50 (1991), S. 239-258 
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    ISSN: 1436-4646
    Keywords: Linear programming ; primal and dual ; interior algorithms ; potential functions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We describe a primal-dual potential function for linear programming: $$\phi (x,s) = \rho \ln (x^T s) - \sum\limits_{j = 1}^n {\ln (x_j s_j )} $$ whereρ⩾ n, x is the primal variable, ands is the dual-slack variable. As a result, we develop an interior point algorithm seeking reductions in the potential function with $$\rho = n + \sqrt n $$ . Neither tracing the central path nor using the projective transformation, the algorithm converges to the optimal solution set in $$O(\sqrt n L)$$ iterations and uses O(n 3 L) total arithmetic operations. We also suggest a practical approach to implementing the algorithm.
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    URL: http://dx.doi.org/10.1007/BF01594937
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    Improving the rate of convergence of interior point methods for linear programming (1991)
    Springer
    Mathematical programming 52 (1991), S. 467-479 
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    ISSN: 1436-4646
    Keywords: Linear programming ; polynomial methods ; interior point methods ; rate of convergence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract This paper proposes a procedure for improving the rate of convergence of interior point methods for linear programming. If (x k ) is the sequence generated by an interior point method, the procedure derives an auxiliary sequence ( $$\bar x^k$$ ). Under the suitable assumptions it is shown that the sequence ( $$\bar x^k$$ ) converges superlinearly faster to the solution than (x k ). Application of the procedure to the projective and afflne scaling algorithms is discussed and some computational illustration is provided.
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    URL: http://dx.doi.org/10.1007/BF01582901
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    Methanogenic degradation kinetics of phenolic compounds in aquifer-derived microcosms (1991)
    Springer
    Biodegradation 2 (1991), S. 211-221 
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    ISSN: 1572-9729
    Keywords: biodegradation ; creosote ; ground water ; methane bacteria ; Monod kinetics ; phenols
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract In this segment of a larger multidisciplinary study of the movement and fate of creosote derived compounds in a sand-and-gravel aquifer, we present evidence that the methanogenic degradation of the major biodegradable phenolic compounds and concomitant microbial growth in batch microcosms derived from contaminated aquifer material can be described using Monod kinetics. Substrate depletion and bacterial growth curves were fitted to the Monod equations using nonlinear regression analysis. The method of Marquardt was used for the determination of parameter values that best fit the experimental data by minimizing the residual sum of squares. The Monod kinetic constants (μ max , K s, Y, and k d) that describe phenol, 2-, 3-, and 4-methylphenol degradation and concomitant microbial growth were determined under conditions that were substantially different from those previously reported for microcosms cultured from sewage sludge. The K s values obtained in this study are approximately two orders of magnitude lower than values obtained for the anaerobic degradation of phenol in digesting sewage sludge, indicating that the aquifer microorganisms have developed enzyme systems that are adapted to low nutrient conditions. The values for k d are much less than μ max, and can be neglected in the microcosms. The extremely low Y values, approximately 3 orders of magnitude lower than for the sewage sludge derived cultures, and the very low numbers of microorganisms in the aquifer derived microcosms suggest that these organisms use some unique strategies to survive in the subsurface environment.
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    URL: http://dx.doi.org/10.1007/BF00114553
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    Aerobic microbial metabolism of some alkylthiophenes found in petroleum (1991)
    Springer
    Biodegradation 2 (1991), S. 223-236 
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    ISSN: 1572-9729
    Keywords: aerobic ; alkylthiophenes ; bacteria ; biodegradation ; isoprenoidal thiophenes ; petroleum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Six alkylthiophenes, 2-hexadecyl-5-methylthiophene (I), 2-methyl-5-tridecylthiophene (II) and 2-butyl-5-tridecylthiophene (III), 2-(3,7-dimethyloctyl)-5-methylthiophene (IV), 2-methyl-5-(3,7,11,15-tetramethyl-hexadecyl)thiophene (V) and 2-ethyl-5-(3,7,11,15-tetramethylhexadecyl)thiophene (VI) were synthesized and used as substrates in biodegradation studies. The products of their aerobic metabolism by pure bacterial cultures were identified. In most cases, the long alkyl chains of these thiophenes were preferentially attacked and in pure cultures of alkane-degrading bacteria, the major metabolites that accumulated in the medium were 5-methyl-2-thiopheneacetic acid from (I), 5-methyl-2-thiophenecarboxylic acid from (II) and occasionally from (V), 5-butyl-2-thiophenecarboxylic acid from (III) and 5-ethyl-2-thiopheneacetic acid from (VI). These transformations are consistent with the metabolism of the alkyl side chains via the beta-oxidation pathway. In contrast, 5-(3,7-dimethyloctyl)-2-thiophenecarboxylic acid was produced from (IV). Because it was available in greatest supply, (I) was studied most thoroughly. It supported growth of the six n-alkanedegrading bacteria tested and (I) was degraded more quickly than pristance but not as quickly as n-hexadecance in mixtures of these three compounds. In the presence of Prudhoe Bay crude oil and a mixed culture of petroleum-degrading bacteria, the acid metabolites from (I), (II) and (III) underwent further biotransformations to products that were not detected by the analytical methods used. The addition of n-hexadecane to the mixed culture of petroleum-degrading bacteria also enhanced the further biotransformations of the metabolites from (I).
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    URL: http://dx.doi.org/10.1007/BF00114554
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    Dynamic response of naphthalene biodegradation in a continuous flow soil slurry reactor (1991)
    Springer
    Biodegradation 2 (1991), S. 81-91 
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    ISSN: 1572-9729
    Keywords: biodegradation ; dynamics ; naphthalene ; dynamic response ; frequency response ; soils ; reactors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Periodic perturbations were used to evaluate the system stability and robustness of naphthalene biodegradation in a continuous flow stirred tank reactor (CSTR) containing a soil slurry. The experimental design involved perturbing the test system using a sinusoidal input either of naphthalene or non-naphthalene organic carbon at different frequencies during steady state operation of the reactors. The response of the test system was determined by using time series off-gas analysis for naphthalene liquid phase concentration and degradation, total viable cell counts, and gene probe analysis of naphthalene degradative genotype, and by batch mineralization assays. Naphthalene biodegradation rates were very high throughout the experimental run (95 to 〉99% removed) resulting in very low or undetectable levels of naphthalene in the off-gas and reactor effluent. Attempts to reduce the rate of naphthalene biotransformation by either reducing the reactor temperature from 20°C to 10°C or the dissolved oxygen level (〉1 mg/L) were unsuccessful. Significant naphthalene biodegradation was observed at 4°C. While variable, the microbial community as measured by population densities was not significantly affected by temperature changes. In terms of naphthalene biotransformation, the system was able to adapt readily to all perturbations in the reactor.
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    URL: http://dx.doi.org/10.1007/BF00114598
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    Search directions for interior linear-programming methods (1991)
    Springer
    Algorithmica 6 (1991), S. 153-181 
    Details
    ISSN: 1432-0541
    Keywords: Karmarkar's algorithm ; Linear programming ; Projective algorithm ; Conical projection ; Interior methods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract Since Karmarkar published his algorithm for linear programming, several different interior directions have been proposed and much effort was spent on the problem transformations needed to apply these new techniques. This paper examines several search directions in a common framework that does not need any problem transformation. These directions prove to be combinations of two problem-dependent vectors, and can all be improved by a bidirectional search procedure. We conclude that there are essentially two polynomial algorithms: Karmarkar's method and the algorithm that follows a central trajectory, and they differ only in a choice of parameters (respectively lower bound and penalty multiplier).
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    URL: http://dx.doi.org/10.1007/BF01759039
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    Retiming synchronous circuitry (1991)
    Springer
    Algorithmica 6 (1991), S. 5-35 
    Details
    ISSN: 1432-0541
    Keywords: Digital circuitry ; Graph theory ; Linear programming ; Network flow ; Optimization ; Pipelining ; Propagation delay ; Retiming ; Synchronous circuitry ; Systolic circuits ; Timing analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract This paper describes a circuit transformation calledretiming in which registers are added at some points in a circuit and removed from others in such a way that the functional behavior of the circuit as a whole is preserved. We show that retiming can be used to transform a given synchronous circuit into a more efficient circuit under a variety of different cost criteria. We model a circuit as a graph in which the vertex setV is a collection of combinational logic elements and the edge setE is the set of interconnections, each of which may pass through zero or more registers. We give anO(¦V∥E¦lg¦V¦) algorithm for determining an equivalent retimed circuit with the smallest possible clock period. We show that the problem of determining an equivalent retimed circuit with minimum state (total number of registers) is polynomial-time solvable. This result yields a polynomial-time optimal solution to the problem of pipelining combinational circuitry with minimum register cost. We also give a chacterization of optimal retiming based on an efficiently solvable mixed-integer linear-programming problem.
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    URL: http://dx.doi.org/10.1007/BF01759032
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    Selection and isolation of bacteria capable of degrading dinoseb (2-sec-buty-4,6-dinitrophenol) (1991)
    Springer
    Biodegradation 2 (1991), S. 1-13 
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    ISSN: 1572-9729
    Keywords: anaerobic ; biodegradation ; dinitrotoluenes ; dinoseb ; nitrophenols ; 2-sec-butyl-4,6-dinitrophenol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Dinoseb (2-sec-butyl-4,6-dinitrophenol) has been a widely used herbicide that persists in some contaminated soils, and has been found in groundwaters, causing health and environmental hazards. Persistence in some soils may stem from a lack of dinoseb-degrading organisms. We established a chemostat environment that was strongly selective for aerobic (liquid phase) and anaerobic (sediment phase) bacteria able to degrade dinoseb. The chemostat yielded five taxonomically diverse aerobic isolates that could transform dinoseb to reduced products under microaerophilic or denitrifying conditions, but these organisms were unable to degrade the entire dinoseb molecule, and the transformed products formed multimeric material. The chemostat also yielded an anaerobic consortium of bacteria that could completely degrade dinoseb to acetate and CO2 when the Eh of the medium was less than-200 mV. The consortium contained at least three morphologically different bacterial species. HPLC analysis indicated that dinoseb was degraded sequentially via several as yet unidentified products. Degradation of these intermediates was inhibited by addition of bromoethane sulfonic acid. GC-MS analysis of metabolites in culture medium suggested that regiospecific attacks occurred non-sequentially on both the nitro groups and the side-chain of dinoseb. The consortium was also able to degrade 4,6-dinitro-o-cresol, 3,5-dinitrobenzoic acid, 2,4-dinitrotoluene, and 2,6-dinitrotoluene via a similar series of intermediate products. The consortium was not able to degrade 2,4-dinitrophenol. To our knowledge, this is the first report of strictly anaerobic biodegradation of an aromatic compound containing a multicarbon, saturated hydrocarbon side chain.
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    URL: http://dx.doi.org/10.1007/BF00122420
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    Bacterial degradation of 3-chloroacrylic acid and the characterization of cis- and trans-specific dehalogenases (1991)
    Springer
    Biodegradation 2 (1991), S. 139-150 
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    ISSN: 1572-9729
    Keywords: biodegradation ; 3-chloroacrylic acid ; dehalogenase ; dehalogenation ; hydratase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A coryneform bacterium that is able to utilize cis- and trans-3-chloroacrylic acid as sole carbon source for growth was isolated from freshwater sediment. The organism was found to produce two inducible dehalogenases, one specific for the cis- and the other for trans-3-chloroacrylic acid. Both dehalogenases were purified to homogeneity from cells induced for dehalogenase synthesis with 3-chlorocrotonic acid. The enzymes produced muconic acid semialdehyde (3-oxopropionic acid) from their respective 3-chloroacrylic acid substrate. No other substrates were found. The cis-3-chloroacrylic acid dehalogenase consisted of two polypeptide chains of a molecular weight 16.2 kDa. Trans-3-chloroacrylic acid dehalogenase was a protein with subunits of 7.4 and 8.7 kDa. The subunit and amino acid compositions and the N-terminal amino acid sequences of the enzymes indicate that they are not closely related.
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    URL: http://dx.doi.org/10.1007/BF00124488
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    Growth and survival of Pseudomonas cepacia DBO1(pRO101) in soil amended with 2,4-dichlorophenoxyacetic acid (1991)
    Springer
    Biodegradation 2 (1991), S. 245-252 
    Details
    ISSN: 1572-9729
    Keywords: 2,4-dichlorophenoxyacetic acid ; bacterial growth ; biodegradation ; Pseudomonas cepacia ; soil ; survival
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The 2,4-dichlorophenoxyacetic acid (2,4-D) degrading pseudomonad, Pseudomonas cepacia DBO1(pRO101), was inoculated at approximately 107 CFU/g into sterile and non-sterile soil amended with 0, 5 or 500 ppm 2,4-D and the survival of the strain was studied for a period of 44 days. In general, the strain survived best in sterile soil. When the sterile soil was amended with 2,4-D, the strain survived at a significantly higher level than in non-amended sterile soil. In non-sterile soil either non-amended or amended with 5 ppm 2,4-D the strain died out, whereas with 500 ppm 2,4-D the strain only declined one order of magnitude through the 44 days. The influence of 0,0.06, 12 and 600 ppm 2,4-D on short-term (48 h) survival of P. cepacia DBO1(pRO101) inoculated to a level of 6×104, 6×106 or 1×108 CFU/g soil was studied in non-sterile soil. Both inoculum level and 2,4-D concentration were found to have a positive influence on numbers of P. cepacia DBO1(pRO101). At 600 ppm 2,4-D growth was significant irrespective of the inoculation level, and at 12 ppm growth was stimulated at the two lowest inocula levels. P. cepacia DBO1(pRO101) was able to survive for 15 months in sterile buffers kept at room temperature. During this starvation, cells shrunk to about one third the volume of exponentially growing cells.
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    URL: http://dx.doi.org/10.1007/BF00114556
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