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  • 1
    Electronic Resource
    Electronic Resource
    Erratum (1988)
    Springer
    Human genetics 〈Berlin〉 80 (1988), S. 315-315 
    Details
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01790109
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  • 2
    Electronic Resource
    Electronic Resource
    Increased amounts of small polydisperse circular DNA (spcDNA) in angiofibroma-derived cell cultures from patients with tuberous sclerosis (TS) (1988)
    Springer
    Human genetics 〈Berlin〉 79 (1988), S. 286-288 
    Details
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Much greater amounts of small polydisperse circular DNA (spcDNA) have been detected, in cell cultures derived from angiofibromas of six patients with tuberous sclerosis (TS) than in those from the skin of these patients or from the skin of 11 healthy donors. This observation could be confirmed by spreading the DNA of appropriate fractions from CsCl density gradients. The findings suggest the existence of a relationship between the chromosomal instability observed in angiofibroma cultures and the mobilization of spcDNA.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00366254
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  • 3
    Electronic Resource
    Electronic Resource
    A stability analysis of the geostatistical approach to aquifer transmissivity identification (1989)
    Springer
    Stochastic environmental research and risk assessment 3 (1989), S. 293-316 
    Details
    ISSN: 1436-3259
    Keywords: Confined aquifer ; Transmissivity identification ; Geostatistics ; Inverse problem ; Ill-posedness ; Ill-conditioning ; Stability analysis ; Regularization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract In recent years, geostatistical concepts have been applied to the inverse problem of transmissivity estimation from piezometric head data. It has been claimed that such methods overcome various difficulties encountered in other approaches. However, the reconstruction of transmissivity from head measurements is ill-posed as it depends on derivatives of the head field. Consequently, any accurate method for its solution is likely to encounter numerically ill-conditioned systems. This paper reviews the geostatistical approach, and uses the stability analyses of linear algebra to show that, as the amount of available data increases and the discretization of the system is refined, both a numerically ill-conditioned parameter estimation problem and ill-conditioned cokriging equations may appear. Therefore, while the geostatistical approach does have conceptual appeal, it does not avoid the fundamental difficulties arising out of the ill-posed nature of transmissivity identification. Instead, the method is likely to be quite sensitive to these difficulties, so care must be taken in its formulation to minimize their effects. A means to stabilize the geostatistical method is suggested and numerical experiments that highlight key points of our analysis are given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01543462
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  • 4
    Electronic Resource
    Electronic Resource
    The influence of humoral factors upon the melanophores of fishes, especially Phoxinus (1931)
    Springer
    Journal of comparative physiology 15 (1931), S. 613-636 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. Certain groups of melanophores on the head ofPhoxinus can be denervated by severing the ophthalmic branch of the Trigeminal nerve. Other definite groups of melanophores on selected areas on the trunk ofPhoxinus can be denervated by severing one or more spinal nerves or cutting loose a bit of the skin from its underlying cutaneous nerves. 2. Those denervated melanophores on the head and those on the ventral portions of the trunk contract either partially or completely when the fish is set upon a white background. 3. Those denervated melanophores on dorsal portions of the trunk contract either partially or remain expanded when the fish is set upon a white background. 4. All denervated melanophores remain maximally expanded when the fish is left upon a black background. 5. Those denervated melanophores which failed to contract when the fish was set upon a white background will do so if one threatens the fish or attempts to capture it. 6. With the circulation intact these denervated · melanophores all contract following electrical stimulation of the medulla or when the fish is set between two stimulating electrodes, as do the innervated melanophores on the rest of the body. Following the cessation of such stimulation all innervated melanophores rapidly expand, while the denervated melanophores remain well contracted. 7. With the circulation stopped by removal of the heart the denervated melanophores no longer contract during electrical stimulation, though the innervated melanophores continue to do so. 8. If the melanophores over a large body area are denervated by severing the sympathetic cord and if the area affected by this operation includes regions previously denervated by other means, the fish being kept meanwhile upon a white background, the melanophores of these smaller previously denervated regions fail to show the immediate and pronounced expansion characteristic of these cells in other parts of the freshly denervated area. 9. In fishes kept upon a white background the trunk melanophores denervated by severing the sympathetic cord usually contract completely if they are located ventrally, while those cells lying dorsally contract as a rule only partially if at all. 10. When the hearts are removed from fishes previously adapted for a week or more to a white background the animals remain pale for at least a half hour after the operation. Eventually however they darken. When the hearts are removed from fishes previously adapted to a black background for a week or more but set upon a white background immediately after the operation these animals show a momentary paling which does not include the denervated areas. This slight-paling is immediately followed by a pronounced darkening of the entire body. 11. Fishes with denervated head areas kept upon a background of alternating white and black spots show a partial contraction of their innervated melanophores as well as a complete expansion of their denervated melanophores. 12. The following general conclusions were drawn from these experiments: a) Upon a white backgroundPhoxinus elaborated some hormone or hormones not definitely identified but suspected to be adrenalin capable of contracting denervated melanophores either partially or completely. This hormone also supplements the action of the nervous system in bringing the innervated melanophores to a complete contraction on a white background. b) No evidence was found of any hormone capable of expanding the melanophores. The question is left open whether such a hormone exists. c). The melanqphores ofPhoxinus vary in the degree to which they are influenced by this contracting hormone, the denervated cells on the head and ventral portions of the trunk being more readily brought to a complete contraction than those on the dorsal portions of the trunk.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00616374
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  • 5
    Electronic Resource
    Electronic Resource
    Cloning and characterization of a Legionella pneumophila-specific gene encoding a member of the LysR family of transcriptional regulators (2000)
    Springer
    Molecular genetics and genomics 264 (2000), S. 204-211 
    Details
    ISSN: 1617-4623
    Keywords: Legionella pneumophila LysR family Transcription factor Flagellum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Flagellin gene regulation in Legionella pneumophila is modulated by various environmental factors. The expression of the virulent phenotype seems to be linked genetically to flagellum expression. To better understand the mechanisms of flagellin gene expression in L. pneumophila (Lp), we screened a pool of plasmids from a L. pneumophila Corby genomic library for the ability to prevent or reduce luciferase activity in the Escherichia coli strain YK410, which harbours a Lp-pflaA-luxAB fusion. We cloned a DNA fragment encoding the N-terminal part of a protein with significant similarity to members of the LysR family of transcriptional regulators (LTTRs). The entire gene, cloned by inverse PCR, was named flaR. It encodes a protein of 302 amino acids, and computer-assisted analysis of the amino acid sequence revealed a helix-turn-helix motif located near the N-terminus of the protein. The FlaR protein exhibits 21–31% identity to various LTTRs. Furthermore, gel retardation experiments indicate that the FlaR protein is able to bind to its own promoter region and, to a lesser extent, to the flaA promoter of L. pneumophila. The flaR promoter region contains putative LysR binding motifs and two putative Fur boxes. Taken together, these results indicate that FlaR is a DNA-binding protein which belongs to the LTTR family. Southern analysis with a L. pneumophila Corby-specific flaR probe revealed homologous genes in various L. pneumophila strains, but not in the 12 non-pneumophila strains tested so far.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004380000310
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  • 6
    Electronic Resource
    Electronic Resource
    Falling ball viscosimetry of giant vesicle membranes: Finite-size effects (1999)
    Springer
    The European physical journal 12 (1999), S. 589-598 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 68.10.Et Interface elasticity, viscosity, and viscoelasticity – 83.85.Pt Flow computation (e.g. finite element)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: We study the general problem of the friction felt by a spherical solid particle which moves parallel to the membrane of a spherical vesicle. Experiments are carried out with SOPC vesicles at room temperature, with different particle and vesicle sizes. Experimental data show considerable finite-size effects whenever the particle is not very small compared to the vesicle. These effects are found consistent with the hydrodynamical theory of the vesicle-particle problem. This agreement allows for a “robust” determination of membrane viscosity, independently of particle and vesicle sizes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100510051042
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  • 7
    Electronic Resource
    Electronic Resource
    Development of coupling-repulsion-phase SCAR markers diagnostic for the sugar beet Rr1 allele conferring resistance to rhizomania (1997)
    Springer
    Molecular breeding 3 (1997), S. 231-238 
    Details
    ISSN: 1572-9788
    Keywords: BNYVV ; BSA ; RAPD ; rhizomania resistance ; SCAR ; sugar beet
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract In sugar beet genotypes with the ‘Holly’ type of resistance to rhizomania, a disease due to infection of the beet necrotic yellow vein virus (BNYVV), the major gene rrl is responsible for resistance. Twelve RAPD markers linked to rrl were selected by BSA and mapped on linkage group IV using a segregating population previously analysed by the same group. Markers F61050 and N9600 were tightly linked, respectively in coupling and repulsion, to the Rrl allele (recombination values of 1.4 cM for both markers). After sequencing the products amplified by F61050 and N9600, new PCR primers were used to generate the two SCAR markers F6 and N9. The simultaneous use of these markers in a PCR reaction allows the correct fingerprinting of rrl rrl, Rrl rrl and Rrl Rrl sugar beet plants in populations segregating for the ‘Holly’ resistance. In a group of sugar beet elite lines containing the ‘Holly’ type of rhizomania resistance, SCAR F6 is always present whereas the SCAR N9 fragment is absent. Thus, in marker-assisted selection with coupling-repulsion-phase markers, SCAR F6 can be used in combination with N9, or together with any other RAPD marker linked in repulsion to the Rrl allele.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009626214058
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  • 8
    Electronic Resource
    Electronic Resource
    Efficient generation of conditional simulations by chebyshev matrix polynomial approximations to the symmetric square root of the covariance matrix (1995)
    Springer
    Mathematical geology 27 (1995), S. 207-228 
    Details
    ISSN: 1573-8868
    Keywords: Gaussian random fields ; geostatistics ; Monte Carlo simulations ; orthogonal polynomials
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract Consider the problem of generating a realization y1 of a Gaussian random field on a dense grid of points Ω1 conditioned on field observations y2 collected on a sparse grid of points Ω2. An approach to this is to generate first an unconditional realization y over the grid Ω=Ω1 ∪ Ω2, and then to produce y1 by conditioning y on the data y2. As standard methods for generating y, such as the turning bands, spectral or Cholesky approaches can have various limitations, it has been proposed by M. W. Davis to generate realizations from a matrix polynomial approximations to the square root of the covariance matrix. In this paper we describe how to generate a direct approximation to the conditional realization y1, on Ω1 using a variant of Davis' approach based on approximation by Chebyshev polynomials. The resulting algorithm is simple to implement, numerically stable, and bounds on the approximation error are readily available. Furthermore we show that the conditional realization y1 can be generated directly with a lower order polynomial than the unconditional realization y, and that further reductions can be achieved by exploiting a nugget effect if one is present. A pseudocode version of the algorithm is provided that can be implemented using the fast Fourier transform if the field is stationary and the grid Ω1 is rectangular. Finally, numerical illustrations are given of the algorithm's performance in generating various 2-D realizations of conditional processes on large sampling grids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02083211
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  • 9
    Electronic Resource
    Electronic Resource
    Estimation of covariance parameters in kriging via restricted maximum likelihood (1991)
    Springer
    Mathematical geology 23 (1991), S. 119-135 
    Details
    ISSN: 1573-8868
    Keywords: Gaussian random field ; covariance estimation ; geostatistics ; eigenvalue decomposition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract In kriging, parametric approaches to covariance (or variogram) estimation require that unknown parameters be inferred from a single realization of the underlying random field. An approach to such an estimation problem is to assume the field to be Gaussian and iteratively minimize a (restricted) negative loglikelihood over the parameter space. In doing so, the associated computational burden can be considerable. Also, it is usually not easy to check whether or not the minimum achieved is global. In this note, we show that in many practical cases, the structure of the covariance (or variogram) function can be exploited so that iterative minimizing algorithms may be advantageously replaced by a procedure that requires the computation of the roots of a simple rational function and the search for the minimum of a function depending on one variable only. As a consequence, our approach allows one to observe in a straightforward fashion the presence of local minima. Furthermore, it is shown that insensitivity of the likelihood function to changes in parameter value can be easily detected. The note concludes with numerical simulations that illustrate some key features of our estimation procedure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02065971
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  • 10
    Electronic Resource
    Electronic Resource
    Computationally efficient generation of gaussian conditional simulations over regular sample grids (1993)
    Springer
    Mathematical geology 25 (1993), S. 439-451 
    Details
    ISSN: 1573-8868
    Keywords: block Toeplitz structure ; Cholesky factorization ; geostatistics ; Monte Carlo simulations ; spatial random field
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract The generation over two-dimensional grids of normally distributed random fields conditioned on available data is often required in reservoir modeling and mining investigations. Such fields can be obtained from application of turning band or spectral methods. However, both methods have limitations. First, they are only asymptotically exact in that the ensemble of realizations has the correlation structure required only if enough harmonics are used in the spectral method, or enough lines are generated in the turning bands approach. Moreover, the spectral method requires fine tuning of process parameters. As for the turning bands method, it is essentially restricted to processes with stationary and radially symmetric correlation functions. Another approach, which has the advantage of being general and exact, is to use a Cholesky factorization of the covariance matrix representing grid points correlation. For fields of large size, however, the Cholesky factorization can be computationally prohibitive. In this paper, we show that if the data are stationary and generated over a grid with regular mesh, the structure of the data covariance matrix can be exploited to significantly reduce the overall computational burden of conditional simulations based on matrix factorization techniques. A feature of this approach is its computational simplicity and suitability to parallel implementation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00894778
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