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  • stability  (60)
  • gene expression
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  • 1
    Digitale Medien
    Digitale Medien
    Springer
    OR spectrum 20 (1998), S. 101-107 
    ISSN: 1436-6304
    Schlagwort(e): Competitive location model ; Nash equilibria ; stability ; reachability ; Wettbewerbsmodelle in der Standorttheorie ; Nash Gleichgewicht ; Stabilität ; Erreichbarkeit
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik , Wirtschaftswissenschaften
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung In der Arbeit werden die Standorte von Duopolisten in einem Baum untersucht. Unter der Annahme festgesetzter Preise werden notwendige und hinreichende Bedingungen für Nash Gleichgewichte für Standorte auf Bäumen hergeleitet. Unter Verwendung dieser Bedingungen wird dann gezeigt, daß — angenommen Nash Gleichgewichte existieren — diese in einem wiederholt angewandten sequentiellen Standortfindungsprozeß, in dem beide Duopolisten als Zielfunktion kurzfristige Gewinnmaximierung haben, auch erreicht werden.
    Notizen: Abstract This paper examines the location of duopolists on a tree. Given parametric prices, we first delineate necessary and sufficient conditions for locational Nash equilibria on trees. Given these conditions, we then show that Nash equilibria, provided they exist, can be reached in a repeated sequential relocation process in which both facilities follow short-term profit maximization objectives.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    OR spectrum 20 (1998), S. 101-107 
    ISSN: 1436-6304
    Schlagwort(e): Key words: Competitive location model ; Nash equilibria ; stability ; reachability ; Schlüsselwörter: Wettbewerbsmodelle in der Standorttheorie ; Nash Gleichgewicht ; Stabilität ; Erreichbarkeit
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik , Wirtschaftswissenschaften
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung. In der Arbeit werden die Standorte von Duopolisten in einem Baum untersucht. Unter der Annahme festgesetzter Preise werden notwendige und hinreichende Bedingungen für Nash Gleichgewichte für Standorte auf Bäumen hergeleitet. Unter Verwendung dieser Bedingungen wird dann gezeigt, daß– angenommen Nash Gleichgewichte existieren – diese in einem wiederholt angewandten sequentiellen Standortfindungsprozeß, in dem beide Duopolisten als Zielfunktion kurzfristige Gewinnmaximierung haben, auch erreicht werden. “Equilibrium is a place in heaven, but how do we get there from here?”
    Notizen: Abstract. This paper examines the location of duopolists on a tree. Given parametric prices, we first delineate necessary and sufficient conditions for locational Nash equilibria on trees. Given these conditions, we then show that Nash equilibria, provided they exist, can be reached in a repeated sequential relocation process in which both facilities follow short-term profit maximization objectives.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Empirical economics 23 (1998), S. 387-400 
    ISSN: 1435-8921
    Schlagwort(e): Key words: Money demand ; cointegration ; stability ; regime shift ; JEL classification: E41 ; C22
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Wirtschaftswissenschaften
    Notizen: Abstract. Using several tests for structural stability in regressions with I(1) variables and for the existence of cointegration in models with regime shifts, the empirical evidence on the existence of a structural break in the Spanish long-run demand for broad money (ALP2) is analysed.  The results indicate that shifts affecting the demand for ALP2 in recent years have substantially altered its long-run properties. As to the cause of this structural break, emphasis is placed on the role played by the increasing openness of the Spanish financial system to international markets as obstacles to free capital movements have progressively disappeared.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Springer
    Stochastic environmental research and risk assessment 12 (1998), S. 191-204 
    ISSN: 1436-3259
    Schlagwort(e): Keywords: groundwater flow ; inverse problems ; stability ; geostatistical interpolation ; kriging.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Energietechnik , Geographie , Geologie und Paläontologie
    Notizen: Abstract The Differential System Method (DSM) permits identification of the physical parameters of finite-difference groundwater flow models in a confined aquifer when piezometric head and source terms are known at each point of the finite-difference lattice for at least two independent flow situations for which the hydraulic gradients are not parallel. Since piezometric head data are usually few and sparse, interpolation of the measured data onto a regular grid can be performed with geostatistical techniques. We apply kriging to the sparse data of a synthetic aquifer to evaluate the stability of the DSM with respect to uncorrelated measurement errors and interpolation errors. The numerical results show that the DSM is stable.
    Materialart: Digitale Medien
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  • 5
    ISSN: 1572-8358
    Schlagwort(e): Epidemiology ; sleeping sickness ; vector controls ; differential equations ; spacialization ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract A compartmental model is described for the spread of Gambian sleeping sickness in a spatially heterogeneous environment in which vector and human populations migrate between two "patches": the village and the plantations. The number of equilibrium points depends on two "summary parameters": gr the proportion removed among human infectives, and R0, the basic reproduction number. The origin is stable for R0 〈1 and unstable for R0 〉1. Control strategies are assessed by studying the mix of vector control between the two patches that bring R0 below 1. The results demonstrate the importance of vector control in the plantations. For example if 20 percent of flies are in the village and the blood meal rate in the village is 10 percent, then a 20 percent added vector mortality in the village must be combined with a 9 percent added mortality in the plantations in order to bring R0 below 1. The results are quite insentive to the blood meal rate in the village. Optimal strategies (that minimize the total number of flies trapped in both patches) are briefly discussed.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    Journal of dynamics and differential equations 10 (1998), S. 151-188 
    ISSN: 1572-9222
    Schlagwort(e): Fourth-order solitary waves ; stability ; instability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract We study ground-state traveling wave solutions of a fourth-order wave equation. We find conditions on the speed of the waves which imply stability and instability of the solitary waves. The analysis depends on the variational characterization of the ground states rather than information about the linearized operator.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    ISSN: 1572-9281
    Schlagwort(e): asymptotic stability ; dichotomic maps ; retarded functional differential equation ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract This paper deals with the study of the stability of nonautonomous retarded functional differential equations using the theory of dichotomic maps. After some preliminaries, we prove the theorems on simple and asymptotic stability. Some examples are given to illustrate the application of the method. Main results about asymptotic stability of the equation $$x'(t) = - b(t)x(t - r)$$ and of itsnonlinear generalization $$x'(t) = b(t)f(x(t - r))$$ are established.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Springer
    Queueing systems 29 (1998), S. 55-73 
    ISSN: 1572-9443
    Schlagwort(e): multi‐server queue ; customer class ; state‐dependent routing ; stability ; Markov chain ; fluid limit
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract We consider a multi‐station queue with a multi‐class input process when any station is available for the service of only some (not all) customer classes. Upon arrival, any customer may choose one of its accessible stations according to some state‐dependent policy. We obtain simple stability criteria for this model in two particular cases when service rates are either station‐ or class‐independent. Then, we study a two‐station queue under general assumptions on service rates. Our proofs are based on the fluid approximation approach.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Springer
    Queueing systems 28 (1998), S. 33-54 
    ISSN: 1572-9443
    Schlagwort(e): queueing networks ; throughput ; closed networks ; efficiency ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract A closed network is said to be “guaranteed efficient” if the throughput converges under all non-idling policies to the capacity of the bottlenecks in the network, as the number of trapped customers increases to infinity. We obtain a necessary condition for guaranteed efficiency of closed re-entrant lines. For balanced two-station systems, this necessary condition is almost sufficient, differing from it only by the strictness of an inequality. This near characterization is obtained by studying a special type of virtual station called “alternating visit virtual station”. These special virtual stations allow us to relate the necessary condition to certain indices arising in heavy traffic studies using a Brownian network approximation, as well as to certain policies proposed as being extremal with respect to the asymptotic loss in the throughput. Using the near characterization of guaranteed efficiency we also answer the often pondered question of whether an open network or its closed counterpart has greater throughput - the answer is that neither can assure a greater guaranteed throughput.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    Springer
    Queueing systems 29 (1998), S. 129-159 
    ISSN: 1572-9443
    Schlagwort(e): rate-based feedback control ; ATM networks ; stability ; optimal algorithms
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Motivated by ABR class of service in ATM networks, we study a continuous time queueing system with a feedback control of the arrival rate of some of the sources. The feedback about the queue length or the total workload is provided at regular intervals (variations on it, especially the traffic management specification TM 4.0, are also considered). The propagation delays can be nonnegligible. For a general class of feedback algorithms, we obtain the stability of the system in the presence of one or more bottleneck nodes in the virtual circuit. Our system is general enough that it can be useful to study feedback control in other network protocols. We also obtain rates of convergence to the stationary distributions and finiteness of moments. For the single botterneck case, we provide algorithms to compute the stationary distributions and the moments of the sojourn times in different sets of states. We also show analytically (by showing continuity of stationary distributions and moments) that for small propagation delays, we can provide feedback algorithms which have higher mean throughput, lower probability of overflow and lower delay jitter than any open loop policy. Finally these results are supplemented by some computational results.
    Materialart: Digitale Medien
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  • 11
    Digitale Medien
    Digitale Medien
    Springer
    Advances in computational mathematics 9 (1998), S. 145-171 
    ISSN: 1572-9044
    Schlagwort(e): periodic pseudodifferential equations ; multiwavelets ; splines with multiple knots ; generalized Galerkin–Petrov schemes ; boundary element methods ; error analysis ; stability ; Strang–Fix condition ; 65J10 ; 65N30 ; 65N35 ; 65R20 ; 47G30 ; 45P05 ; 41A25 ; 41A30 ; 41A15
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract We develop a stability and convergence analysis of Galerkin–Petrov schemes based on a general setting of multiresolution generated by several refinable functions for the numerical solution of pseudodifferential equations on smooth closed curves. Particular realizations of such a multiresolution analysis are trial spaces generated by biorthogonal wavelets or by splines with multiple knots. The main result presents necessary and sufficient conditions for the stability of the numerical method in terms of the principal symbol of the pseudodifferential operator and the Fourier transforms of the generating multiscaling functions as well as of the test functionals. Moreover, optimal convergence rates for the approximate solutions in a range of Sobolev spaces are established.
    Materialart: Digitale Medien
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  • 12
    Digitale Medien
    Digitale Medien
    Springer
    Celestial mechanics and dynamical astronomy 70 (1998), S. 41-58 
    ISSN: 1572-9478
    Schlagwort(e): three-body problem ; libration points ; stability ; normal forms.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract In this paper we consider the problem of motion of an infinitesimal point mass in the gravity field of an uniformly rotating dumb-bell. The aim of our study is to investigate Liapunov stability of Lagrangian libration points of this problem. We analyze the stability of libration points in the whole range of parameters ω, μ of the problem. In particular, we consider all resonance cases when the order of resonance is not greater than five.
    Materialart: Digitale Medien
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  • 13
    Digitale Medien
    Digitale Medien
    Springer
    Monatshefte für Mathematik 126 (1998), S. 117-124 
    ISSN: 1436-5081
    Schlagwort(e): 52A20 ; 52A22 ; star bodies ; spherical integral transformations ; convex bodies ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract LetK be ad-dimensional star body (with respect to the origino). It is known that the (d−1)-dimensional volume of the intersections ofK with the hyperplanes througho does not uniquely determineK. Uniqueness can only be achieved under additional assumptions, such as central symmetry. Here it is pointed out that if one uses, instead of intersections by hyperplanes, intersections by half-planes that containo on the boundary, then, without any additional assumptions, the volume of these intersections determinesK uniquely. This assertion, and more general results of this kind, together with stability estimates, are obtained from uniqueness results and estimates concerning a particular spherical integral transformation.
    Materialart: Digitale Medien
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  • 14
    Digitale Medien
    Digitale Medien
    Springer
    Catalysis letters 53 (1998), S. 97-101 
    ISSN: 1572-879X
    Schlagwort(e): ethene hydroformylation ; heterogeneous catalysts ; cobalt catalysts ; gas‐phase deposition ; dispersion ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The results from ethene hydroformylation at 173°C showed that a Co(acac)3/SiO2 catalyst prepared from Co(acac)3 precursor by gas‐phase deposition was three times as active as a catalyst prepared by impregnation from cobalt nitrate, but oxo‐selectivities were similar. The high propanal selectivities on the Co(acac)3/SiO2 seem to be related to the presence of highly dispersed active sites favouring CO insertion. As dispersion is decreased from 23 to 8% due to increasing metal content (from 5 to 16 wt%), oxo‐selectivity decreased from 39 to 25%. The activity of Co(acac)3/SiO2 remained unchanged during 68 h on stream. The gas‐phase deposition technique described here is a promising method for the preparation of active, selective and stable heterogeneous hydroformylation catalysts.
    Materialart: Digitale Medien
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  • 15
    ISSN: 1572-879X
    Schlagwort(e): nanolithography ; model catalyst ; palladium ; copper ; stability ; spin-coating ; SEM ; AFM ; XPS
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Metal clusters arranged on nanostructured oxidized silicon wafers are presented as new model catalyst systems. A photoresist layer spun on top of a wafer was patterned by laser interference exposure. The grid obtained after removing the exposed parts of the resist is used as an etching mask. Hollows with diameters of 300 nm and depths between 50 and 60 nm were etched into the oxide layer using wet chemical methods. Two methods were applied to deposit metal clusters (Pd or Cu) in a defined way within the hollows. The particles ranged from 10 to 50 nm in height and from 80 to 200 nm in diameter. The model catalyst systems were characterized by atomic force microscopy and X-ray photoelectron spectroscopy. The method presented here allows us to produce 4 inch wafers that are covered completely by nanometer-sized structures in a reasonable period of time.
    Materialart: Digitale Medien
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  • 16
    Digitale Medien
    Digitale Medien
    Springer
    BioMetals 11 (1998), S. 345-358 
    ISSN: 1572-8773
    Schlagwort(e): calcium ; CREB ; gene expression
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract Through the evolution of multicellular organisms, calcium has emerged as the preferred ion for intracel-lular signalling. It now occupies a pivotal role in many cell types and nowhere is it more important than in neurons, where it mediates both the relaying and long-term storage of information. The latter is a process that enables learning and memory to be formed and requires the activation of gene expression by calcium signals. Evidence from a number of diverse organisms shows that transcription mediated by the transcrip-tion factor CREB is critical for learning and memory. Here we review the features of CREB activation by calcium signals in mammalian cells. In contrast to other transcription factors, its regulation is dependent on an elevation of nuclear calcium concentration, potentially placing this spatially distinct pool of calcium as an important mediator of information storage.© Kluwer Academic Publishers
    Materialart: Digitale Medien
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  • 17
    Digitale Medien
    Digitale Medien
    Springer
    Plant molecular biology reporter 16 (1998), S. 323-339 
    ISSN: 1572-9818
    Schlagwort(e): Aux/IAA genes ; gene expression ; gene families ; RT-PCR ; tomato
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract We have developed an improved method for determination of gene expression levels with RT-PCR. The procedure is rapid and does not require extensive optimization or densitometric analysis. Since the detection of individual transcripts is PCR-based, small amounts of tissue samples are sufficient for the analysis of expression patterns in large gene families. Using this method, we were able to rapidly screen nine members of the Aux/IAA family of auxin- responsive genes and identify those genes which vary in message abundance in a tissue- and light-specific manner. While not offering the accuracy of conventional semi-quantitative or competitive RT-PCR, our method allows quick screening of large numbers of genes in a wide range of RNA samples with just a thermal cycler and standard gel analysis equipment.
    Materialart: Digitale Medien
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  • 18
    Digitale Medien
    Digitale Medien
    Springer
    Journal of intelligent and robotic systems 23 (1998), S. 27-43 
    ISSN: 1573-0409
    Schlagwort(e): autonomous control ; actuator delays ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau
    Notizen: Abstract In this paper, we consider the control design problem of vehicle following systems with actuator delays. An upper bound for the time delays is first constructed to guarantee the vehicle stability. Second, sufficient conditions are presented to avoid slinky-effects in the vehicle following. Next, zero steady state achieved by the proposed controller is proven. Finally, simulations are given to examine our claims.
    Materialart: Digitale Medien
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  • 19
    Digitale Medien
    Digitale Medien
    Springer
    Journal of statistical physics 91 (1998), S. 285-305 
    ISSN: 1572-9613
    Schlagwort(e): Chapman–Enskog expansion ; Burnett equation ; Boltzmann equation ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract This paper continues the author's study of procedures for rewriting the well-known Chapman–Enskog expansion used in the kinetic theory of gases. The usual Chapman–Enskog expansion, when used in isothermal fluid motion, will introduce nonlinear instability at super-Burnett order O(ε3) truncation. The procedure given here eliminates the truncation instability and produces the desired dissipation inequality.
    Materialart: Digitale Medien
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  • 20
    Digitale Medien
    Digitale Medien
    Springer
    Journal of intelligent and robotic systems 22 (1998), S. 23-38 
    ISSN: 1573-0409
    Schlagwort(e): robot dynamic model ; stiffness matrix ; constant disturbance ; integrator backstepping ; Liapunov functions ; Barbalat lemma ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau
    Notizen: Abstract A robust regulator for flexible-joint robots is proposed, which yields constant torque disturbance rejection acting on the links. The design uses the integrator backstepping technique [4,5] to cancel nonlinearities and disturbance not in the range space of the control. Stability of the closed loop system is shown using iterative Liapunov functions.
    Materialart: Digitale Medien
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  • 21
    Digitale Medien
    Digitale Medien
    Springer
    Molecular and cellular biochemistry 178 (1998), S. 275-281 
    ISSN: 1573-4919
    Schlagwort(e): regucalcin ; calcium-binding protein ; gene expression ; calmodulin ; spontaneous hypertensive rats ; rat kidney cortex
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract The expression of calcium-binding protein regucalcin mRNA in the kidney cortex of rats ingested with saline was investigated. The alteration in regucalcin mRNA levels was analyzed by Northern blotting using liver regucalcin complementary DNA (0.9 kb of open reading frame). Rats were freely given saline as drinking water for 7 days. Regucalcin mRNA levels in the kidney cortex were suppressed by saline ingestion. When calcium chloride (10 mg Ca/100 g body weight) was intraperitoneally administered to rats ingested with saline for 7 days, the effect of calcium administration to increase regucalcin mRNA levels was weakened by saline ingestion. Such effect was also seen by the administration of 2.5 and 5 mg Ca/100 g. Regucalcin mRNA levels in the kidney cortex of spontaneous hypertensive rats (SHR) were not appreciably increased by the administration of calcium (10 mg/100 g). Meanwhile, calcium content in the kidney cortex was significantly elevated by the administration of calcium (10 mg/100 g) to normal rats. This increase was weakened in saline-ingested rats. Moreover, Ca2+/calmodulin-dependent protein kinase activity in the cytosol of kidney cortex was significantly decreased by saline ingestion. These results suggest the possibility that saline ingestion-induced suppression of regucalcin mRNA expression in the kidney cortex is partly involved in the attenuation of Ca2+ signalling.
    Materialart: Digitale Medien
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  • 22
    Digitale Medien
    Digitale Medien
    Springer
    Molecular and cellular biochemistry 178 (1998), S. 157-162 
    ISSN: 1573-4919
    Schlagwort(e): protein tyrosine phosphatases ; gene expression ; degenerate deoxyoligonucleotides ; RT-PCR ; Swiss 3T3 fibroblasts
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract The aim of this study was to identify protein tyrosine phosphatases (PTPs) expressed in Swiss 3T3 fibroblasts and to examine their expression levels as well as to characterize quantitative aspects of RT-PCR based on degenerate deoxyoligonucleotides. By using an RT-PCR assay based on degenerate deoxyoligonucleotide primers, expression of mRNAs for two cytoplasmic- and six transmembrane-type PTPs in Swiss 3T3 cells was detected. The sequences of two of them are new. Among nine analyzed PTPs expressed to widely varied extends, only three have mRNA levels high enough to be seen on Northern blots with 10 µg of total RNA per lane. The frequencies with which the examined PTPs are represented among the PCR amplification products, correlate stronger with the primer fidelity, defined as the number of mismatches between the primer- and the cDNA target-sequences, rather than with the PTP expression levels. In conclusion, an RT-PCR assay based on degenerate primers can be successfully used to sample the expressed PTPs and to identify new members of this gene family. However, reliable quantification of their mRNA levels can only be achieved using the classical approaches, like Northern, RNase protection assay or non-degenerate quantitative RT-PCR.
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  • 23
    Digitale Medien
    Digitale Medien
    Springer
    Molecular and cellular biochemistry 186 (1998), S. 43-51 
    ISSN: 1573-4919
    Schlagwort(e): myocardial ischemia ; gene expression ; growth factors ; phospholamban ; calsequestrin heat shock proteins ; preconditioning ; stunning
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract Brief periods of coronary occlusion render the affected myocardium more tolarant to the otherwise devastating effects of long coronary occlusion. Besides this phenomena, called ischemic preconditioning, short periods of ischemia cause a regional dysfunction, namely myocardial stunning. The molecular mechanisms of both syndromes are not very well understood. We therefore investigated the expression of genes which may be involved in cardioprotection or repair processes.Using our porcine model of ischemia and reperfusion we were able to show an induction of genes coding for transcription factors (proto-oncogenes), for proteins involved in repair processes (heat shock genes), for proteins implicated in the calcium homeostasis (calcium-handling genes) and for growth factors. We could show that the increased mRNA levels are due to an enhanced transcriptional activity and not to a prolonged half-life of the transcripts. The angiogenic growth factor vascular endothelial growth factor (VEGF) represents an exception. It exhibits - in addition to a HIF-motif (Hypoxia Inducible Factor) in its promoter/enhancer - a protein binding region in its 3′ UTR which when occupied renders the mRNA more stable. However to what extent the expression of the distinct genes contributes to the cardioprotective effect of ischemic preconditioning or myocardial stunning can only be presumed. Increased mRNA stability can be confered via adenosine which is produced during ischemia by ATP-breakdown. The demasking of unknown genes - via differential display reverse transcription polymerase chain reaction (DDRT-PCR) - should provide a more comprehensive view of the mechanisms underlying both processes.
    Materialart: Digitale Medien
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  • 24
    Digitale Medien
    Digitale Medien
    Springer
    Environmental and resource economics 11 (1998), S. 503-520 
    ISSN: 1573-1502
    Schlagwort(e): biodiversity ; dynamics ; resilience ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik , Wirtschaftswissenschaften
    Notizen: Abstract The ecological concept of resilience has begun to inform analysis of change in economy-environment systems. The linkages between resilience and the stability of dynamical systems are discussed, along with its role in understanding of the evolution of such systems. Particular linkages discussed include those between resilience, biodiversity and the sustainability of alternative states. Recent developments in modelling the resilience of joint economy-environment systems suggest the advantages of analysing change in the system as a Markov process, the transition probabilities between states offering a natural measure of the resilience of the system in such states. It is argued that this ‘emergent property’ of the collaboration between ecology and economics has far-reaching implications for the way we think about, model and manage the environmental sustainability of economic development.
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  • 25
    Digitale Medien
    Digitale Medien
    Springer
    Molecular and cellular biochemistry 178 (1998), S. 283-287 
    ISSN: 1573-4919
    Schlagwort(e): regucalcin ; calcium-binding protein ; gene expression ; fetal development ; rat liver
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract The expression of hepatic calcium-binding protein regucalcin mRNA in fetal rats was investigated. The alteration in regucalcin mRNA levels was analyzed by Northern blotting using liver regucalcin cDNA (0.9 kb with complete open reading frame). Hepatic regucalcin mRNA levels were progressively increased with fetal development; the mRNA was clearly expressed at 15 and 21 days of pregnancy but only slightly at the 8 days. Meanwhile, β-actin mRNA levels in the fetal liver were remarkable at 8 and 15 days of pregnancy. The fetal liver regucalcin mRNA levels at 15 days of pregnancy were significantly decreased by overnight-fasting of maternal rats. The oral administration of calcium chloride (50 mg Ca/100 g body weight) to maternal rats at 15 days of pregnancy caused a remarkable elevation (about 2 fold) of regucalcin mRNA levels in the fetal liver; this increase was seen 60 and 180 min after the calcium administration. After birth, regucalcin mRNA was increasingly expressed in the livers of newborn and weanling rats, while hepatic β-actin mRNA expression was not appreciably altered with increasing ages. These findings demonstrate that the expression of hepatic regucalcin mRNA is increased with fetal development, and that the gene expression may be stimulated by the ingestion of dietary calcium.
    Materialart: Digitale Medien
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  • 26
    ISSN: 1573-4919
    Schlagwort(e): extremely low frequency magnetic fields ; gene expression ; neuron derived orphan receptor-1 ; signal transduction ; Chinese hamster ovary K1 cells
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract Enhanced expression of neuron derived orphan receptor (NOR-1) gene was observed by exposure of Chinese hamster ovary K1 (CHO-K1) cells to an extremely low frequency magnetic field (ELFMF) of 50 Hz at 400 mT, but not at 5 mT. The enhanced expression, reaching the maximum at 6 h, was transient and reduced to the control level after exposure to 400 mT ELFMF for 24 h. The NOR-1 expression induced by treatment with forskolin and TPA was further enhanced by the simultaneous treatment with 400 mT ELFMF, in which the maximum response was at 3 h. The NOR-1 expression by these treatments was induced more earlier than that by 400 mT ELFMF alone. When cells were treated with an inhibitor of the protein kinase C (calphostin C or crocetin) and Ca2+ entry blockers (nifedipin and dantrolen) during the 400 mT ELFMF exposure, the enhanced NOR-1 expression was not observed. Exposure of CHO-K1 cells to the high-density 400 mT ELFMF may affect the signal transduction in the cells, resulting in the enhanced NOR-1 gene expression.
    Materialart: Digitale Medien
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  • 27
    Digitale Medien
    Digitale Medien
    Springer
    Molecular and cellular biochemistry 188 (1998), S. 41-48 
    ISSN: 1573-4919
    Schlagwort(e): zinc ; transcription factors ; gene expression ; organogenesis ; Xenopus laevis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract Zinc regulates the gene expression machinery. It affects the structure of chromatin, the template function of its DNA, the activity of numerous transcription factors and of RNA polymerases. Hence, it determines both the types of mRNA transcripts synthesized and the rate of transcription itself. Alterations in one or more of these zinc dependent processes have been proposed to account for the proliferative arrest and teratology induced by zinc deficiency. To examine this proposal, studies of zinc during X. laevis development have been initiated. The kinetics of X. laevis oocyte zinc uptake and storage and of zinc utilization during embryogenesis have been examined first. Vitellogenin carries zinc into the oocyte. Ten % of the total zinc (10 ng/egg) remains within the cytosol while 90% (90 ng/egg) is stored in the yolk platelets associated with lipovitellin. The cytosolic pool is the source of the zinc for all newly formed metalloproteins involved in embryo development. The yolk platelet zinc pool is stored for later use during early metamorphosis. It is now possible to examine zinc transfer to molecules, such as e.g. transcription factors, and the role of the metal in their function in development and organogenesis.
    Materialart: Digitale Medien
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  • 28
    Digitale Medien
    Digitale Medien
    Springer
    Molecular and cellular biochemistry 189 (1998), S. 107-111 
    ISSN: 1573-4919
    Schlagwort(e): gene expression ; electromagnetic fields ; superinduction ; anisomycin ; immediate early gene
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract Rat pheochromocytoma PC12 cells have been treated with nerve growth factor (NGF) at final concentrations of 2, 4, 8, and 16 ng/ml, and then were exposed to 60-Hz, sinusoidal magnetic fields (MF) of 12.5, 25, 50, and 100 μT (rms) for 30 min. Transcript levels for both c-fos and glyceraldehyde-3 -phosphate dehydrogenase were determined by Northern blot analysis using 32P-labeled cDNA probes. No change in c-fos expression was measured at any condition employed. Treatment of PC12 cells with a combination of agents (NGF, forskolin, and tetradecanoylphorbol acetate [TPA]) increased c-fos expression over that detected with NGF alone. MF exposure of cells treated with the three-agent regimen produced two outcomes, either no change or a doubling of c-fos expression. In subsequent experiments, cells were treated with NGF, NGF + forskolin + TPA, or pre-treated with anisomycin and then treated with NGF + forskolin + TPA. It was determined that MF exposure, like superinduction with anisomycin, increased c-fos expression only in cultures which were not yet exhibiting maximal c-fos expression. It is hypothesized that MF exposure, like anisomycin, may alter the activity of key intracellular protein kinases.
    Materialart: Digitale Medien
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  • 29
    ISSN: 1573-4978
    Schlagwort(e): gene expression ; nuclear matrix proteins ; ocular lens epithelial cells ; transcription factors
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Association of transcription factors with the nuclear matrix represents a mechanism by which nuclear architecture may influence transcriptional control of gene expression. This investigation examines nuclear matrix associated proteins (NMP's) isolated from ocular lens epithelial cells by monitoring DNA binding activities using consensus oligonucleotides recognized by the transcription factors YY1, AML-1, AP-1, SP-1 and ATF. The nuclear matrix fractions tested included an immortilized human lens epithelial cell line containing the SV40 large T-antigen, and two mouse lens epithelial cell lines derived from either a normal mouse or a cataract mouse. A rabbit epidermal epithelial cell line and HeLa cells were also included in this study for comparison. The data from these experiments reveal that ubiquitously represented and tissue restricted regulatory proteins are associated with nuclear matrix of lens epithelial cells. The functional significance of the nuclear matrix association of these transcription factors remains to be determined. However, our findings raise the possibility that the transcription factors associated with the nuclear matrix could have specific roles in gene regulation and eye tissue development.
    Materialart: Digitale Medien
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  • 30
    ISSN: 1573-9368
    Schlagwort(e): transgenic mice ; gene expression ; mammary gland ; co-injection ; milk protein
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract In an attempt to enhance the frequency and level of expression of a poor-performing MMTV-driven transgene, we co-integrated this construct with the ovine β-lactoglobulin (BLG) gene in transgenic mice. Seven lines of transgenic mice possessing co-integrated BLG and MMTV-RZ5 transgenes were compared with 12 lines of mice that possessed only the MMTV-RZ5 construct. Co-integration enhanced the frequency of expression in the mammary gland from two out of 12 lines for the MMTV-RZ5 transgene alone, to five out of seven when co-integrated with BLG. Surprisingly, co-integration also resulted in co-expression of the two transgenes in the salivary gland, lung and spleen in addition to the mammary gland. Furthermore, both transgenes were expressed in virgin animals, and throughout pregnancy and lactation, suggesting that the developmental regulation of the locus follows that of the MMTV-promoter. These findings represent a novel locus control property of the ovine BLG gene that confer s commitment of the locus to the mammary gland, but also to a range of heterogeneous tissues possibly defined by the second promoter at the locus
    Materialart: Digitale Medien
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  • 31
    ISSN: 1573-9368
    Schlagwort(e): transgenic rabbits ; gene expression ; mammary gland ; erythropoietin ; WAP
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract An understanding of the expression of transgenes in the mammary gland during gestation and lactation is crucial for the use of transgenic mammals as bioreactors. Here we describe the temporal pattern of expression of the endogenous rabbit WAP gene and human erythropoietin (hEPO) transgenes under the control of rabbit WAP promoter and 3′ flanking sequences. The endogenous rabbit WAP gene was expressed throughout gestation including the day of mating, as well as during lactation in transgenic rabbits bearing a minigene construct. In non-pregnant cycling females, WAP expression was found independent of transgenic status; however, WAP expression was not detected in non-cycling females. The significance of this new finding is not clear at present. hEPO mRNA was detected in mammary gland biopsies from pregnant transgenic rabbits only on day 28 of gestation. During lactation, transcripts were present in mammary gland biopsy samples taken on days 0, 7, 14 and 21. A sharp decline in the levels ...
    Materialart: Digitale Medien
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  • 32
    Digitale Medien
    Digitale Medien
    Springer
    Acta mechanica Sinica 14 (1998), S. 274-282 
    ISSN: 1614-3116
    Schlagwort(e): time delay ; stability ; frozen time approach ; retarded dynamic systems
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract By means of the frozen time approach and the Kronecker product, two criteria of asymptotic stability are derived for the linear, time variant dynamic systems with either short time delays or with weak feedback involving arbitrary time delays, respectively. It is found that the asymptotic stability of these retarded dynamic systems is governed by the maximal and minimal singular values of the coefficient matrices and their time derivatives.
    Materialart: Digitale Medien
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  • 33
    Digitale Medien
    Digitale Medien
    Springer
    Acta mechanica Sinica 14 (1998), S. 226-233 
    ISSN: 1614-3116
    Schlagwort(e): jet ; stability ; dispersion equation ; swirling gas
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Based on the linear analysis of stability, a dispersion equation is deduced which delineates the evolution of a general 3-dimensional disturbance on the free surface of an incompressible viscous liquid jet injected into a gas with swirl. Here, the dimensionless parameterJ e is again introduced, in the meantime, another dimensionless parameterE called as circulation is also introduced to represent the relative swirling intensity. With respect to the spatial growing disturbance mode, the numerical results obtained from solving the dispersion equation reveal the following facts. First, at the same value ofE, in pace with the changing ofJ e , the variation of disturbance and the critical disturbance mode still keep the same characters. Second, the present results are the same as that of S.P. Lin whenJ e 〉1; but in the range ofJ e 〈1, it's no more the case, the swirl decreases the axisymmetric disturbance, yet increases the asymmetric disturbance, furthermore the swirl may make the character of the most unstable disturbance mode changed (axisymmetric or asymmetric); the above action of the swirl becomes much stronger whenJ e ≪1.
    Materialart: Digitale Medien
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  • 34
    ISSN: 1572-9788
    Schlagwort(e): differential display ; gene expression ; hybrid vigor ; molecular marker heterozygosity ; Oryza sativa L.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Using differential display analysis, we assessed the patterns of differential gene expression in hybrids relative to their parents in a diallel cross involving 8 elite rice lines. The analysis revealed several patterns of differential expression including: (1) bands present in one parent and F1 but absent in the other parent, (2) bands observed in both parents but not in the F1, (3) bands occurring in only one parent but not in the F1 or the other parent, and, (4) bands detected only in the F1 but in neither of the parents. Relationships between differential gene expression and heterosis and marker heterozygosity were evaluated using data for RFLPs, SSRs and a number of agronomic characters. The analysis showed that there was very little correlation between patterns of differential expression and the F1 means for all six agronomic traits. Differentially expressed fragments that occurred only in one parent but not in the other parent or in F1 in each of the respective crosses were positively correlated with heterosis and heterozygosity. And conversely, fragments that were detected in F1s but in neither of the respective parents were negatively correlated with heterosis and heterozygosity. The remaining patterns of differential expression were not correlated with heterosis or heterozygosity. The relationships between the patterns of differential expression and heterosis observed in this study were not consistent with expectations based on dominance or overdominance hypotheses.
    Materialart: Digitale Medien
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  • 35
    Digitale Medien
    Digitale Medien
    Springer
    Biology and philosophy 13 (1998), S. 541-554 
    ISSN: 1572-8404
    Schlagwort(e): complex natural system ; stability ; evolvability ; decomposable hierarchy ; genetic network ; Random NK Boolean Network
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Philosophie
    Notizen: Abstract I criticize Herbert Simon's argument for the claim that complex natural systems must constitute decomposable, mereological or functional hierarchies. The argument depends on certain assumptions about the requirements for the successful evolution of complex systems, most importantly, the existence of stable, intermediate stages in evolution. Simon offers an abstract model of any process that succeeds in meeting these requirements. This model necessarily involves construction through a decomposable hierarchy, and thus suggests that any complex, natural, i.e., evolved, system is constituted by a decomposable hierarchy. I argue that Stuart Kauffman's recent models of genetic regulatory networks succeed in specifying processes that could meet Simon's requirements for evolvability without requiring construction through a decomposable hierarchy. Since Kauffman's models are at least as plausible as Simon's model, Simon's argument that complex natural systems must constitute decomposable, mereological or functional hierarchies does not succeed.
    Materialart: Digitale Medien
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  • 36
    ISSN: 1573-0646
    Schlagwort(e): Antagonist G ([Arg6, D-Trp7,9,,MePhe 8 ]-Substance P {6-11}) ; analytical characterization ; parenteral formulation ; stability ; oxidative degradation products
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Medizin
    Notizen: Abstract The aim of this study was to develop a stable parenteral dosage form for the investigational cytotoxic drug [Arg6, D-Trp7,9, MePhe8]-Substance P {6-11} (Substance P Antagonist G; Antagonist G). Antagonist G bulk drug was structurally and analytically characterized. The drug exhibits excellent aqueous solubility, although relatively poor aqueous stability characteristics. Lyophilization was, therefore, selected as the manufacturing process. Differential scanning calorimetry studies were conducted to determine the freeze-drying cycle parameters which resulted in a stable, lyophilized formulation of Antagonist G. The prototype, containing 50 mg Antagonist G per vial, was found to be the optimal formulation in terms of solubility, length of the freeze-drying cycle, stability, and dosage requirements in the planned phase I clinical trials. Quality control of the freeze-dried formulation showed that the manufacturing process does not change the integrity of Antagonist G. Shelf life studies demonstrated that the formulation is stable for at least 3 years, when stored at 2–8°C in a dark environment. Oxidative degradation products of Antagonist G were isolated and structurally characterized by mass spectrometry, nuclear magnetic resonance spectroscopy, and infrared spectroscopy.
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  • 37
    Digitale Medien
    Digitale Medien
    Springer
    Applied mathematics and mechanics 19 (1998), S. 163-168 
    ISSN: 1573-2754
    Schlagwort(e): nonlinear equation ; stability ; Newton's method ; auto-adjustable damping method ; the vector of damping factors
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Mathematik , Physik
    Notizen: Abstract The general approach for solving the nonlinear equations is linearizing the equations and forming various iterative procedures, then executing the numerical simulation. For the strongly nonlinear problems, the solution obtained in the iterative process is always difficult, even divergent due to the numerical instability. It can not fulfill the engineering requirements. Newton's method and its variants can not settle this problem. As a result, the application of numerical simulation for the strongly nonlinear problems is limited. An auto-adjustable damping method has been presented in this paper. This is a further improvement of Newton's method with damping factor. A set of vector of damping factor is introduced. This set of vector can be adjusted continuously during the iterative process in accordance with the judgement and adjustment. An effective convergence coefficient and quichening coefficient are employed to relax the restricted requirements for the initial values and to shorten the iterative process. Then, the numerical stability will be ensured for the solution of complicated strongly nonlinear equations. Using this method, some complicated strongly nonlinear heat transfer problems in airplanes and aeroengines have been numerically simulated successfully. It can be used for the numerical simulation of strongly nonlinear problems in engineering such as nonlinear hydrodynamics and aerodynamics, heat transfer and structural dynamic response etc.
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  • 38
    Digitale Medien
    Digitale Medien
    Springer
    Applied mathematics and mechanics 19 (1998), S. 861-867 
    ISSN: 1573-2754
    Schlagwort(e): rotating fluids ; motion of body ; small disturbances ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Mathematik , Physik
    Notizen: Abstract In this paper, the disturbances to a uniformly rotating ideal fluid with a sphere moving steadily along the axis of rotation are analysed by using linearization theory, the equations of disturbance, pressure and disturbance stream function governing the stability of motion are derived based on the assumption that the flow is rotational symmetric. The equation of disturbance stream function is analysed with the method of normal modes, and the constraints on wave number and wave velocity of the nontrivial neutral disturbances are established and the exact expression of the neutral disturbances are obtained. The conclusion is drawn that three are three kinds of possible forms of neutral disturbances.
    Materialart: Digitale Medien
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  • 39
    Digitale Medien
    Digitale Medien
    Springer
    Studia geophysica et geodaetica 42 (1998), S. 320-327 
    ISSN: 1573-1626
    Schlagwort(e): MHD ; stability ; bifurcations
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Geologie und Paläontologie , Physik
    Notizen: Abstract A series of numerical studies on the behaviour of magnetic fields and motions in a spherical body of an electrically conducting incompressible fluid have been carried out. The magnetic field was assumed to be maintained by a given electromotive force inside the body and to continue as a potential field in outer space. In view of the motion an external forcing was taken into account, and boundary conditions were considered which correspond to a stress-free surface. The stability of several steady states has been studied as well as the evolutions starting from unstable states. In this paper a configuration with a poloidal magnetic field and a differential rotation, both symmetric about the same axis, is considered. This configuration is stable only for sufficiently small Hartmann numbers but evolves, if disturbed, in the case of larger Hartmann numbers toward a non-axisymmetric state. In this case the well-known symmetrization effect of differential rotation in magnetic fields is destroyed.
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  • 40
    Digitale Medien
    Digitale Medien
    Springer
    Applied mathematics and mechanics 19 (1998), S. 457-462 
    ISSN: 1573-2754
    Schlagwort(e): neural networks ; equilibrium ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Mathematik , Physik
    Notizen: Abstract In this paper, some sufficient conditions are obtained for the global asymptotic stability of the equilibrium of neural networks with interneuronal transmission delays of the type $$x'_i (t) = - b_i x_i (t) + \sum\limits_{j = 1}^n {\omega _{\ddot y} f_j (x_j (t - \tau _j )) + p_i (t 〉 0;i = 1,2, \cdots ,n)} $$
    Materialart: Digitale Medien
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  • 41
    Digitale Medien
    Digitale Medien
    Springer
    Discrete event dynamic systems 8 (1998), S. 137-173 
    ISSN: 1573-7594
    Schlagwort(e): hybrid systems ; switched systems ; timed Petri nets ; stability ; supervisory control
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract In this paper, timed Petri nets are used to model and control hybrid systems. Petri nets are used instead of finite automata primarily because of the advantages they offer in dealing with concurrency and complexity issues. A brief overview of existing results on hybrid systems that are based on Petri nets is first presented. A class of timed Petri nets named programmable timed Petri nets (PTPN) is then used to model hybrid systems. Using the PTPN, the stability and supervisory control of hybrid systems are addressed and efficient algorithms are introduced. In particular, we present sufficient conditions for the uniform ultimate boundness of hybrid systems composed of multiple linear time invariant plants which are switched between using a logical rule described by a Petri net. This paper also examines the supervisory control of a hybrid system in which the continuous state is transfered to a region of the state space in a way that respects safety specifications on the plant's discrete and continuous dynamics.
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  • 42
    Digitale Medien
    Digitale Medien
    Springer
    Journal of scientific computing 13 (1998), S. 173-183 
    ISSN: 1573-7691
    Schlagwort(e): Modified conjugate gradient method ; conjugate gradient method ; Krylov space ; convergence rate ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract In this note, we examine a modified conjugate gradient procedure for solving $$A\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{x} = \underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{b}$$ in which the approximation space is based upon the Krylov space ( $$A\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{x} = \underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{b}$$ ) associated with $$\sqrt A$$ and $$\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{b}$$ . We show that, given initial vectors $$\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{b}$$ and $$\sqrt A \underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{b}$$ (possibly computed at some expense), the best fit solution in $$K^k \sqrt A ,\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{b}$$ can be computed using a finite-term recurrence requiring only one multiplication by A per iteration. The initial convergence rate appears, as expected, to be twice as fast as that of the standard conjugate gradient method, but stability problems cause the convergence to be degraded.
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  • 43
    ISSN: 1573-773X
    Schlagwort(e): constrained learning ; factorization ; feedforward networks ; IIR filters ; polynomials ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Adaptive artificial neural network techniques are introduced and applied to the factorization of 2-D second order polynomials. The proposed neural network is trained using a constrained learning algorithm that achieves minimization of the usual mean square error criterion along with simultaneous satisfaction of multiple equality and inequality constraints between the polynomial coefficients. Using this method, we are able to obtain good approximate solutions for non-factorable polynomials. By incorporating stability constraints into the formalism, our method can be successfully used for the realization of stable 2-D second order IIR filters in cascade form.
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  • 44
    ISSN: 1573-8469
    Schlagwort(e): quorum-sensing ; gene expression ; autoinducer ; secondary metabolites
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract N-acyl homoserine lactones (AHLs) function as cell density (quorum) sensing signals and regulate diverse metabolic processes in several gram negative bacteria. We report that strains of Pseudomonas syringae pvs. syringae (Pss), tabaci and tomato as well as P. corrugata and P. savastanoi produce difussible AHLs that activate the lux operons of Vibrio fischeri or the tra::lacZ fusion of Agrobacterium tumefaciens. In Pss strain B3A, AHL production occurs in cell density dependent manner. Nucleotide sequence and genetic complementation data revealed the presence of ahlIPss, a luxI homolog within the Ahl+ DNA of Pss strain B3A. The $$ahlI_{Pss}^ + $$ DNA expresses in AHL-deficient strains of P. fluorescens and E. carotovora subsp. carotovora (Ecc), and restores extracellular enzyme production and pathogenicity in the Ecc strain. The derivatives of Pss strains B3A and 301D carrying chromosomal ahlI::lacZ do not produce AHL, but like their wild type parents, produce extracellular protease and the phytotoxin syringomycin as well as elicit the hypersensitive reaction in tobacco leaves. While these strains also produce a basal level of β-galactosidase activity, the expression of ahlI::lacZ is substantially stimulated in the presence of multiple copies of the $$ahlI_{Pss}^ + $$ DNA or by the addition of cell-free spent cultures containing AHL. The activation of β-galactosidase production occurs with spent cultures of some, but not all Pseudomonas strains which produce AHL as indicated by the Lux and tra::lacZ assays. Pss strains deficient in the global regulatory genes, gacA or lemA, produce very low levels of AHL. Since inactivation of ahlIPss eliminates AHL production and since Ahl+ Pseudomonas strains carry the homolog of ahlIPss, we conclude that ahlIPss specifies a key step in AHL biosynthesis and it has been conserved in many plant pathogenic pseudomonads.
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  • 45
    Digitale Medien
    Digitale Medien
    Springer
    Plant molecular biology 36 (1998), S. 439-449 
    ISSN: 1573-5028
    Schlagwort(e): ethylene ; gene expression ; leaf senescence ; RNase ; tomato ; wounding
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract A main feature of leaf senescence is the hydrolysis of macromolecules by hydrolases of various types, and redistribution of released materials. We have initiated a study for the characterization of RNases involved in nucleic acid catabolism during senescence. Using a PCR-based cloning approach we isolated from tomato two senescence-induced RNase cDNA clones. Each of these cDNAs hybridized to a senescence-induced transcript in northern analysis. One RNase cDNA was identical to the tomato LX RNase while the second corresponded to the LE RNase. Both LX and LE RNase genes had originally been demonstrated to be induced after phosphate starvation of tomato cell culture but nothing was known about their expression or function in plants. We observed that the expression of the LX and LE genes is induced in leaves during an advanced stage of senescence with the LX transcript level being much more induced than that of LE. Low-level expression of the RNase genes was observed in flowers and artificially senescing detached leaves while no expression could be detected in stems, roots, or fruits at different ripening stages. Ethylene activated the LX gene expression in detached young leaves while LE gene expression, which could be transiently induced by wounding, appeared to be activated by abscisic acid. We suggest that the LX RNase has a role in RNA catabolism in the final stage of senescence, and LE may function during wounding as a plant defense protein.
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  • 46
    Digitale Medien
    Digitale Medien
    Springer
    Plant molecular biology 36 (1998), S. 699-707 
    ISSN: 1573-5028
    Schlagwort(e): actin cytoskeleton ; in situ hybridization ; gene expression ; profilin ; RT-PCR ; tomato pollen
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The actin cytoskeleton plays an important role in the growth of pollen tube. The actin-binding protein profilin could play a role in regulating the organization of the actin filaments. Using the RT-PCR technique, we isolated a cDNA clone (designated LePro1) encoding profilin from pollen grains of tomato (Lycopersicon esculentum Mill. cv. Moneymaker). Sequence analysis of the insert shows 87% similarity to tobacco ntPro2, 78% to timothy grass profilin, 77% to Arabidopsis AthPRF4, 77% to maize ZmPro3, and 73% to birch profilin. Both quantitative PCR and RNA gel blot analyses demonstrated that LePro1 is expressed in a tissue- or cell-type specific manner in the tomato plant. In situ hybridization of 2 µm thick anther sections using a non-radioactive labeling method reveals that LePro1 is expressed only in pollen grains, with undetectable transcription in other parts of the anther or other organs. Phylogenetic analysis of amino acid sequences of 18 plant profilins indicates that two distinct profilin gene classes are present in higher plants. One is pollen-specific, another is constitutive. LePro1 belongs to the former class.
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  • 47
    Digitale Medien
    Digitale Medien
    Springer
    Plant molecular biology 36 (1998), S. 733-739 
    ISSN: 1573-5028
    Schlagwort(e): AGAMOUS ; tomato ; ripening ; calyx ; gene expression ; sepals ; in vitro
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract In vitro culture of VFNT Cherry tomato sepals (calyx) at 16–21 °C results in developmental changes that are similar to those that occur in fruit tissue [10]. Sepals become swollen, red, and succulent, produce ethylene, and have increased levels of polygalacturonase RNA. They also produce many flavor volatiles characteristic of ripe tomato fruit and undergo similar changes in sugar content [11]. We examined the expression of the tomato AGAMOUS gene, TAG1, in ripening, in vitro sepal cultures and other tissues from the plant and found that TAG1 RNA accumulates to higher levels than expected from data from other plants. Contrary to reports on the absence of AGAMOUS in sepals, TAG1 RNA levels in green sepals from greenhouse-grown plants is detectable, its concentration increasing with in vitro ripening to levels that were even higher than in red, ripe fruit. Sepals of fruit on transgenic tomato plants that expressed TAG1 ectopically were induced by low temperature to ripen in vivo, producing lycopene and undergoing cell wall softening as is characteristic of pericarpic tissue. We therefore propose that the induction of elevated TAG1 gene expression plays a key role in developmental changes that result in sepal ripening.
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  • 48
    Digitale Medien
    Digitale Medien
    Springer
    Plant molecular biology 37 (1998), S. 735-748 
    ISSN: 1573-5028
    Schlagwort(e): AMP-activated protein kinase ; carbohydrates ; gene expression ; gene family ; HMG-CoA reductase ; intracellular signalling ; isoprenoids ; nitrate reductase ; phosphorylation ; SNF1 ; starch ; sucrose phosphate synthase ; sucrose synthase ; sugar sensing
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 49
    Digitale Medien
    Digitale Medien
    Springer
    Journal of dynamical and control systems 4 (1998), S. 457-519 
    ISSN: 1573-8698
    Schlagwort(e): Boundary control ; nonlinear distributed parameter system ; center manifold theorem ; stability ; local attractors
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In this paper we consider a boundary control problem for a forced Burgers' equation in a Hilbert state space consisting of square integrable functions on a finite interval. Our first main result consists in proving the global in time existence of solutions of the closed loop boundary control system for arbitrary L 2 initial data and quite general forcing terms (disturbances). For the unforced problem, our main interest is in stability of equilibria, while for the forced problem we are interested in steady state behavior of solutions. We note that the uncontrolled (open loop), unforced problem is not asymptotically stable on L 2. However, for positive gains we show that the unforced closed loop system is globally Lyapunov stable and locally exponentially stable. In addition, for nonzero stationary forcing, we show that there is a local absorbing ball and that the corresponding nonlinear semigroup is compact for all t 〉 0. Using this fact, we are able to deduce several consequences regarding the existence and properties of local attractors. Our method of proof is based on a systematic investigation of the smoothing properties of the controlled dynamics. In particular we establish various regularity results for the dynamics of the closed loop system.
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  • 50
    Digitale Medien
    Digitale Medien
    Springer
    Dynamics and control 8 (1998), S. 83-106 
    ISSN: 1573-8450
    Schlagwort(e): fuzzy modeling ; robust control ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Robust control designs for a discrete Takagi and Sugeno (T-S) fuzzy model are proposed. The T-S fuzzy model contains (possibly fast) time-varying uncertainty. First, a switching-type robust control is shown to stabilize the T-S fuzzy model asymptotically. Second, a saturation-type robust control is shown to render the T-S model practically stable. In both designs, only the bound of uncertainty is needed. The effectiveness of proposed designs is analyzed rigorously and illustrated by simulations.
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  • 51
    Digitale Medien
    Digitale Medien
    Springer
    Mathematical notes 63 (1998), S. 396-400 
    ISSN: 1573-8876
    Schlagwort(e): ordinary differential equations ; fast and slow time ; periodic solutions ; existence ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract We consider a system of ordinary first-order differential equations. The right-hand sides of the system are proportional to a small parameter and depend almost periodically on fast time and periodically on slow time. With this system, we associate the system averaged over fast time. We assume that the averaged system has a structurally unstable periodic solution. We prove a theorem on the existence and stability of almost periodic solutions of the original system.
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  • 52
    Digitale Medien
    Digitale Medien
    Springer
    Pharmaceutical research 15 (1998), S. 1702-1707 
    ISSN: 1573-904X
    Schlagwort(e): stability ; isothermal ; nonisothermal ; thymopentin
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Purpose. The degradation kinetics of thymopentin (RKDVY) and its analogs (RKDVW and RPDVY) in aqueous solution was studied by isothermal and nonisothermal methods. Methods. The isothermal decomposition of thymopentin and its analogs was investigated as a function of pH (2−10), temperature (37, 57, and 80°C) and ionic strength (μ = 0.02 to 1). Nonisothermal decomposition studies were performed using a linear temperature programmer. The temperature increasing rate was set to 0.25°C per hour and the temperature interval varied from 40 to 88°C. Results. The decomposition of thymopentin and its analogs followed first order kinetics. The dependence of the rate constant on temperature followed a linear Arrhenius plot. This indicated that the degradation mechanism of thymopentin and its analogs might be the same within the temperature range studied. The energies of activation were found to be in close agreement for the isothermal and nonisothermal studies, suggesting that the nonisothermal studies may save considerable amount of time in the early stages of drug development. The logK-pH profile of thymopentin suggests that maximum stability is achieved in the pH range of 6−8. Conclusions. These results indicate that the nonisothermal methodology provides an attractive alternative to isothermal methods, as it requires a much lower amount of both material and time, to determine the peptide stability and to estimate the shelf-life for peptide pharmaceutical preparations.
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  • 53
    Digitale Medien
    Digitale Medien
    Springer
    Plant molecular biology 37 (1998), S. 1023-1033 
    ISSN: 1573-5028
    Schlagwort(e): gene expression ; psbA gene ; truncated psbA messages ; DNA-binding protein ; D1 protein
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Expression of the psbA genes, which in the cyanobacterium Synechococcus sp. PCC 7942 encode two different forms of the reaction centre D1 protein of photosystem II (D1:1 and D1:2), was studied under different light and temperature conditions. In addition to the mature 1200 nt psbA messages, three shorter mRNA fragments of 220, 320 and 900 nt were also found. All three mRNA fragments could be recognized by using different gene probes from the coding region of the psbAI gene, whereas the corresponding psbAII/III gene probes recognized only the 220 nt mRNA fragment. The 5' 320 nt mRNA fragment from the psbAI gene probably represents a degradation product, since the corresponding 3' 900 nt psbAI mRNA fragment was also detected. By contrast, the 5' 220 nt mRNA fragment of all psbA messages is suggested to be a truncated psbA transcript, since no corresponding 3' fragment was ever found. Inhibition of translation either by a protein synthesis inhibitor or by a shift of cells to lower temperature, increased the number of 1200 nt psbAII/III messages but the number of 5' 220 nt psbAII/III mRNA fragment increased even more dramatically. The first 66 bp after ATG, where the psbAI and psbAII/III genes mostly differ from each other, also appeared important in determining the amount of produced truncated psbA transcripts, as evidenced by the expression of different tac-psbA constructs in the presence of protein synthesis inhibitor. We suggest that both the psbAI and the psbAII/III genes have a latent intragenic termination site and truncated psbA transcripts are produced at high levels under stress conditions when transcription becomes uncoupled from translation.This is to prevent wasting metabolic energy in the production of unused transcripts.
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  • 54
    ISSN: 1573-5028
    Schlagwort(e): gene expression ; Candida albicans ; dihydrofolate reductase ; dominant selectable marker ; Nicotiana tabacum
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract A new binary vector encoding for Candida albicans dihydrofolate reductase (DFR1) has been constructed and used as a dominant selectable marker for plant transformation. Transgenic tobacco plants with an increased resistance to methotrexate (Mtx) were obtained by co-transformation of tobacco leaf discs with Agrobacterium tumefaciens strains carrying two new binary vectors: pTI20 and pTI18. Co-transformants of Nicotiana tabacum were directly selected for and rooted on medium containing both kanamycin (kan) and Mtx. Leaf discs of transgenic plants were assayed for capacity of regeneration at different Mtx concentrations. Analysis of transcripts was performed on total RNA extracted from two Mtx-resistant plants. The transgenic plants increased resistance to Mtx can be explained by the exceptionally low capacity of Mtx to bind C. albicans dihydrofolate reductase, accountable by the presence of two amino acid residues strategically important in Mtx binding.
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  • 55
    ISSN: 1573-5028
    Schlagwort(e): rice ; waxy ; splicing ; gene expression ; intron
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The rice Waxy gene encodes a granule-bound starch synthase (GBSS) necessary for the synthesis of amylose in endosperm tissue. We have previously shown that a CT microsatellite near the transcriptional start site of the GBSS gene can distinguish 7 alleles that accounted for more than 80% of the variation in apparent amylose content in an extended pedigree of 89 US rice cultivars (Oryza sativa L.). Furthermore, all the cultivars with 18% or less amylose were shown to have the sequence AGTTATA at the putative leader intron 5′ splice site, while all cultivars with a higher proportion of amylose had AGGTATA. Here we demonstrate that this single-base mutation reduces the efficiency of GBSS pre-mRNA processing and results in alternate splicing at three cryptic sites. The predominant 5′ splice site in CT18 low-amylose varieties is 93 bp upstream of the splice site used in intermediate and high amylose varieties and is immediately 5′ to the CT microsatellite that we previously demonstrated to be tightly correlated with amylose content. Use of the leader intron 5′ splice site at either -93 or -1 in conjunction with the predominant 3′ splice site results in formation of a small open reading frame 38 bp upstream of the normal ATG and out of frame with it. This open reading frame is not produced when any of the 5′ leader intron splice sites are used in conjunction with an alternate 3′ splice site five bases further downstream which was observed in all rice varieties tested.
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  • 56
    ISSN: 1573-5028
    Schlagwort(e): antisense RNA ; chalcone synthase ; flavonoid ; gene expression ; rooting ; walnut
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Walnut somatic embryos (Juglans nigra × Juglans regia) were transformed with a vector containing a neomycin phosphotransferase II, a β-glucuronidase and an antisense chalcone synthase (chs) gene. This antisense construct included a 400 bp cDNA fragment of a walnut chs gene under the control of the duplicated CaMV-35S promoter. Molecular, biochemical and biological characterizations were performed both on transformed embryos propagated by secondary somatic embryogenesis and on microshoots developed by in vitro culture of embryonic epicotyls from somatic embryos. Thirteen transformed lines with the vector containing the antisense chs gene, one line with only the gus and nptII genes and one untransformed line were maintained in tissue culture. Six of the antisense lines were shown to be flavonoid-deficient. They exhibited a strongly reduced expression of chs genes, very low chalcone synthase activity and no detectable amounts of quercitrin, myricitrin, flavane-3-ols and proanthocyanidins in stems. Rooting tests showed that decreased flavonoid content in stems of antisense chs transformed lines was associated with enhanced adventitious root formation. Free auxin and conjugated auxin contents were determined during the latter phase of the micropropagation, and no variations were detected between control and antisense chs transformed lines. The in vitro plants developed a large basal callus and apical necrosis upon auxinic induction and the transformed lines highly deficient in flavonoids were more sensitive to exogenous application of indolebutyric acid (IBA).
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  • 57
    ISSN: 1573-5028
    Schlagwort(e): ribonucleotide reductase ; gene expression ; cell cycle ; S-phase ; tobacco BY2 cell suspension
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Eukaryotic ribonucleotide reductase (RNR), the enzyme involved in the synthesis of the deoxyribonucleotides, consists of two R1 and R2 subunits whose activities and gene expression are differentially regulated during the cell cycle and are preferentially induced at the G1/S transition. We have isolated three cDNA clones from a tobacco S phase library, two encoding the large R1 subunit, the first cloned in plants, and one encoding the small R2 subunit. From Southern blot hybridization we deduce that RNR2 is encoded by a single-copy gene whereas RNR1 is encoded by a small multigene family. The level of RNR mRNA is cell-cycle regulated showing a maximum in S phase. In mid-S phase, RNR2 transcripts show a higher maximum level than RNR1 transcripts. Analysis of the effects of various cell cycle inhibitors added to freshly subcultured stationary phase cells leads to the conclusion that RNR gene induction at the entry of the cells into the cell cycle takes place in late G1-early S phase. Addition of DNA synthesis-blocking agents to cycling cells synchronized in mid-S phase resulted in an enhancement of RNR transcript level, thus suggesting that RNR gene expression may be linked to the DNA synthesis rate by a feedback-like regulatory mechanism.
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  • 58
    ISSN: 1573-5028
    Schlagwort(e): Nicotiana tabacum ; tobacco BY-2 cells ; gene expression ; jasmonic acid ; methyl jasmonate ; ornithine decarboxylase ; polyamine ; nicotine ; SAM synthase
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract A cDNA of tobacco BY-2 cells corresponding to an mRNA species which was rapidly induced by methyl jasmonate (MeJA) in the presence of cycloheximide (CHX) was found to encode ornithine decarboxylase (ODC). Another cDNA from a MeJA-inducible mRNA encoded S-adenosylmethionine synthase (SAMS). Although these enzymes could be involved in the biosynthesis of polyamines, the level of putrescine, a reaction product of ODC, increased slowly and while the levels of spermidine and spermine did not change following treatment of cells with MeJA. However, N-methylputrescine, which is a precursor of pyrrolidine ring of nicotine, started to increase shortly after MeJA-treatment of cells and the production of nicotine occured thereafter. The levels of mRNA for arginine decarboxylase (ADC), an alternative enzyme for putrescine synthesis, and that for S-adenosylmethionine decarboxylase (SAMDC), required for polyamine synthesis, were not affected by MeJA. In addition to mRNAs for ODC and SAMS, mRNA for putrescine N-methyltransferase (PMT) was also induced by MeJA. Unlike the MeJA-induction of ODC mRNA, MeJA-induction of SAMS and PMT mRNAs were blocked by CHX. The level of ODC mRNA declined after 1 to 4 h following MeJA treatment, while the levels of mRNAs for SAMS and PMT continued to increase. Auxin significantly reduced the MeJA-inducible accumulation of mRNAs for ODC, SAMS and PMT. These results indicate that MeJA sequentially induces expression of a series of genes involved in nicotine biosynthesis by multiple regulatory mechanisms.p〉
    Materialart: Digitale Medien
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  • 59
    ISSN: 1573-5028
    Schlagwort(e): apoplast ; cDNA cloning ; conifer embryogenesis ; gene expression ; germin-like proteins ; Pinus caribaea
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Germin-like proteins (GLPs) ionically bound to the walls of preglobular somatic embryos of Pinus caribaea Morelet are markers of this early developmental stage. In order to reveal the physiological implications of such markers during early embryo development, we isolated a cDNA clone from somatic embryos predicted to encode a protein with sequence similarity to GLPs. PcGER1 has an open reading frame corresponding to a 220 amino acid polypeptide with a putative N-glycosylation site on Asn-69. The presence of a 24 amino acid putative signal peptide supports the hypothesis of an apoplastic location. The N-terminal 20 amino acid sequence of the predicted mature protein is identical to the amino terminal sequence of GP111, one of the extracellular pine GLPs previously identified. Southern blot hybridizations indicate that PcGER1 is probably unique in the pine genome. Transcripts homologous to PcGER1 are abundant in all embryogenic lines, absent from nonembryogenic lines, and present in quiescent zygotic embryos but not in the female gametophyte, the haploid storage tissue of conifers. Their abundance sharply decreases during germination. Isolation of gf-0.8, a genomic fragment identical to PcGER1 cDNA sequence, confirms that no introns disrupt the coding region as it has been already described for wheat gf-2.8 and gf-3.8 genomic clones. Recombinant PcGER1, produced in Escherichia coli, is recognized by antibodies raised against the GP111 N-terminal nonapeptide and the unglycosylated wheat germin monomer. The implications of GLPs in pine embryogenesis are discussed.
    Materialart: Digitale Medien
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  • 60
    ISSN: 1573-5060
    Schlagwort(e): Triticum turgidum ; farmers' varieties ; genetic diversity ; composite ; stability ; durum wheat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract The Ethiopian peasant farms are characterized by highly varied micro-environments differing in characteristics such as topography, soil type, water, temperature and fertility. The bulk of the durum wheat planting material currently in use on these farms is largely represented by traditional farmers' varieties/landraces. These traditional farmers' varieties/landraces generally, are stable but low yielding, and often fail to adequately meet the level of productivity essential for production beyond subsistence level, unless they are enhanced to improve their competitiveness with modern varieties in respect to yield. Improving the productivity of landraces, while maintaining an appreciable level of genetic diversity is crucial to yield stability. This could be achieved by developing composites that are formed by bulking together three or more potentially high yielding spikes (agrotypes) that vary for various morphologic and agronomic characteristics, but due to their similarity in plant height, maturity, glume color and seed color give the composite a uniform field appearance like a modern variety.
    Materialart: Digitale Medien
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  • 61
    ISSN: 1573-5087
    Schlagwort(e): desiccation tolerance ; dehydrin ; gene expression ; glyoxalase ; grass ; Lea ; protease ; Sporobolus stapfianus
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract In order to identify genes involved in expression of desiccation tolerance in the foliage of the grass Sporobolus stapfianus, a cDNA library was constructed from desiccated leaf tissue of S. stapfianus. Differential screening resulted in the isolation of a number of clones which detect transcripts whose abundance alters during drought stress and the associated induction of desiccation tolerance. The characteristics of 6 of these cDNA clones are presented here. Transcripts represented by three of the cDNA clones accumulate during drying and following treatment of leaves with abscisic acid (ABA). A fourth cDNA clone detects a transcript which also accumulates following application of ABA but the transcript level fluctuates during drying. The remaining two cDNA clones are not responsive to ABA but transcript levels are present throughout the drying process. Characterisation of these cDNAs has led to the identification of the encoded proteins. Some have similarity to proteins which are known to be involved in the protection of cellular organelles and detoxification processes and they include dehydrin, LEA group 3 and thiol proteases which have been identified in other systems and shown to be induced by water stress. In addition one clone showed similarity to glyoxalase I, an enzyme involved in the removal of toxic byproducts produced during glycolysis, which has been shown to be induced by salt stress in tomato.
    Materialart: Digitale Medien
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  • 62
    Digitale Medien
    Digitale Medien
    Springer
    Environmental biology of fishes 53 (1998), S. 365-371 
    ISSN: 1573-5133
    Schlagwort(e): Carassius auratus ; Metynnis hypsauchen ; Pterophyllum scalare ; goldfish ; angelfish ; silver dollar ; swimming ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Goldfish, Carassius auratus, silver dollar, Metynnis hypsauchen, and angelfish, Pterophyllum scalare were induced to swim through narrow vertical and horizontal tubes ranging in length from 0 to 20 cm (approximately 0 to 3 times total fish length, FL). The ability to stabilize the body while negotiating these confined spaces was quantified as (1) the minimum width of vertical (wv) and horizontal (wh) tubes traversed, where width is the smaller cross-sectional dimension of the tube, (2) the ratio wv/wh, and (3) transit speed through the tubes. Tube width was expressed as relative width, obtained by dividing tube width by fish length. Minimum relative widths traversed increased from 0.15 to 0.19 in the order silver dollar 〉 angelfish 〉 goldfish for vertical tubes and from 0.17 to 0.18 in the order goldfish=silver dollar 〉 angelfish for horizontal tubes. wv/wh increased from 0.91 to 1.10 in the order silver dollar=angelfish 〉 goldfish. Minimum tube widths generally increased with tube length for vertical tubes. Although significant differences in relative minimum widths among species were found, these were small. In contrast, for horizontal tubes, there was no significant effect of tube length on minimum tube width for any species. Large differences were found in transit speed. Transit speed generally decreased as the tube length increased. The slope of the relationship between transit speed and tube length varied among species generally increasing from − 0.41 to − 1.16 for horizontal tubes in the order goldfish 〉 silver dollar 〉 angelfish and from − 0.42 to − 1.07 in the order silver dollar 〉 goldfish 〉 angelfish for vertical tubes. As a result, goldfish usually took longest to traverse tubes of zero length but the shortest time to traverse the longest tubes. In contrast, angelfish traversed short tubes in the least time and long tubes in the greatest time. Deeper bodied angelfish swam slowly and traversed tubes with difficulty because they required experience during each trial to replace median and paired fin with body and caudal fin swimming. According to our data, goldfish were best able to swim in confined spaces.
    Materialart: Digitale Medien
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  • 63
    ISSN: 1573-5028
    Schlagwort(e): sedoheptulose-1,7-bisphosphatase ; Chlamydomonas reinhardtii ; light regulation ; Calvin cycle ; gene expression
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract We have studied the light-dependent expression of the Chlamydomonas reinhardtii csbp gene encoding sedoheptulose-1,7-bisphosphatase (SBPase), an enzyme of the pentose-phosphate pathway. Expression studies using light/dark-synchronized cultures revealed that csbp mRNA abundance increases significantly during illumination. We have used a 1.4 kb region upstream of the csbp gene in transcriptional fusions to the homologous arylsulfatase-encoding reporter gene (ars). In transformants carrying the chimeric csbp/ars reporter gene, arylsulfatase activity is detected in the absence of sulfate, a condition under which the endogenous ars gene is repressed. Moreover, ars mRNA accumulation is dramatically stimulated by light, indicating that 1.4 kb of the csbp 5′-untranslated region are sufficient to confer light-dependent expression on the ars reporter gene.
    Materialart: Digitale Medien
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  • 64
    ISSN: 1573-5028
    Schlagwort(e): blue/UV-A-light ; gene expression ; glutamine synthetase ; phytochrome ; tomato aurea mutant ; UV-B-light
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The photomorphogenetic aurea mutant of tomato severely deficient in spectrophotometrically active phytochromes was used to study the light-regulation of the single-copy nuclear gene encoding plastidic glutamine synthetase (GS-2; EC 6.1.3.2). The de-etiolation of dark-grown aurea mutant seedling cotyledons showed an obligatory dependency on blue light. A limited red light-responsiveness of etiolated aurea cotyledons is, however, retained as seen by the stimulation of both the GS-2 transcript and protein level in the cotyledons of aurea seedlings during growth in red light. The subunits of the octameric GS-2 enzyme were represented by polypeptides with similar electrophoretic mobilities (polypeptides a) in etiolated wild-type or aurea mutant cotyledons. GS-2 proteins with similar apparent molecular masses were also seen in the cotyledons of red light-grown aurea mutant seedlings. In contrast, GS-2 polypeptides with different apparent molecular masses (polypeptides a and b) were detected in the cotyledons of wild-type seedlings grown in red light. This difference indicates that the (post-translational) modification of tomato GS-2 subunit composition is mediated by the photoreceptor phytochrome. The illumination of etiolated wild-type or aurea cotyledons with UV-A- or UV-B-light light resulted in an increase in both the GS-2 transcript and protein level. Following illumination of etiolated wild-type seedlings with UV-A-light, the relative proportion of the GS-2 polypeptides a and b was similar than upon irradiation with blue light but different than after exposure to UV-B- or red light. This result suggests the involvement of a blue/ UV-A-light-specific photoreceptor in the regulation of tomato GS-2 subunit composition.
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  • 65
    ISSN: 1435-1536
    Schlagwort(e): Key words Heterophase polymerization ; emulsion ; polymer particle ; stability ; styrene conversion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau
    Notizen: Abstract  Heterophase polymerization of styrene in the presence of di-p-tolyl-o-carbalkoxyphenylcarbinol (DTC) soluble in monomer and insoluble in water, as stabilizer, was investigated. The factors affecting polymer particle diameter, their size distribution and stability were investigated. It was suggested that polymer particles are formed from monomer droplets. The polystyrene suspension with narrow particle size distribution synthesized in the presence of DTC, was used for immunochemical research.
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  • 66
    Digitale Medien
    Digitale Medien
    Springer
    Empirical economics 23 (1998), S. 387-400 
    ISSN: 1435-8921
    Schlagwort(e): Money demand ; cointegration ; stability ; regime shift ; E41 ; C22
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Wirtschaftswissenschaften
    Notizen: Abstract Using several tests for structural stability in regressions with I(1) variables and for the existence of cointegration in models with regime shifts, the empirical evidence on the existence of a structural break in the Spanish long-run demand for broad money (ALP2) is analysed. The results indicate that shifts affecting the demand for ALP2 in recent years have substantially altered its long-run properties. As to the cause of this structural break, emphasis is placed on the role played by the increasing openness of the Spanish financial system to international markets as obstacles to free capital movements have progressively disappeared.
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  • 67
    ISSN: 1572-9699
    Schlagwort(e): Quorum sensing ; N-acylhomoserine lactones ; gene expression ; virulence ; secondary metabolites
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Although it has been clear for some time that individual bacterial cells employ intra-cellular signalling systems to sense, integrate and process information from their surroundings, their widespread capacity to perceive information from other bacterial cells is only just beginning to be recognised. Recent work has established that diverse bacteria exploit a cell-cell communication device to regulate the transcription of multiple target genes. This communication device termed ‘quorum sensing’, depends on the production of one or more diffusible signal molecules termed ‘autoinducers’ or ‘pheromones’ which enable a bacterium to monitor its own cell population density. Quorum sensing is thus an example of multicellular behaviour in prokaryotes and regulates diverse physiological processes including bioluminescence, swarming, antibiotic biosynthesis, plasmid conjugal transfer and the production of virulence determinants in animal, fish and plant pathogens. In Gram-negative bacteria, the best understood family of signal molecules are the N-acylhomoserine lactones (AHLs) which vary predominantly in the presence or absence of an acyl chain C3 substituent (oxo- or hydroxy-) and length of the N-acyl side chain. However not all quorum sensing signal molecules are AHLs; in Gram-positive bacteria, they are often post-translationally modified peptides. Irrespective of the chemical ‘language’ employed, interference with either the synthesis or transmission of a quorum sensing signal molecule in pathogenic bacteria offers an exciting new strategy for controlling infection.
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  • 68
    Digitale Medien
    Digitale Medien
    Springer
    International journal of thermophysics 19 (1998), S. 461-470 
    ISSN: 1572-9567
    Schlagwort(e): small-angle neutron scattering ; stability ; vesicles
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Small-angle neutron scattering (SANS) was used to investigate the structure of mixed colloids of egg yolk phosphatidylcholine (EYPC) with the bile salt, cholylglycine (CG), in D2O as a function of pressure (P) and temperature (T). At atmospheric pressure, the system forms an isotropic phase of mixed, single-bilayer vesicles (SLVs). Increasing the external hydrostatic pressure brought about significant changes in particle morphology. At T=25°C, application of a pressure of 3.5 MPa resulted in collapse of the SLVs. A further increase in P, up to 51.8 MPa, resulted in a transition from a phase of ordered (stacked), collapsed vesicles to one of stacked, ribbon-like particles. A similar collapse of the vesicles was observed at a higher temperature (T=37°C) with increasing P, but at this temperature, no ribbon phase was found at the highest pressure explored.
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  • 69
    Digitale Medien
    Digitale Medien
    Springer
    International journal of infrared and millimeter waves 19 (1998), S. 1721-1734 
    ISSN: 1572-9559
    Schlagwort(e): optical phase-locked loop ; stability ; phase jitter ; four-wave mixing ; semiconductor laser amplifier
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract In this paper, the properties of the optical phase-locked loop(PLL) based on the four-wave mixing in the semiconductor laser amplifiers (SLAs) are discussed. The components that achieve the function of detecting the bit phase of the input optical signal are concerned and discussed in detail together as a function module named as the optical bit phase detector referred to the general electronic PLL. Therefore, most of the properties of the optical PLL can be analyzed by applying the general phase-locked theory. Here the stability of the optical PLL is discussed. It's shown that the variance of input signal power in the practical application will cause optical PLL system unstable because of its long loop delay. The influence on the output phase jitter of the optical PLL is also investigated.
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  • 70
    Digitale Medien
    Digitale Medien
    Springer
    Euphytica 102 (1998), S. 151-161 
    ISSN: 1573-5060
    Schlagwort(e): Oryza sativa ; head rice ; seeding date ; rice ; rough rice yield ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract The rice (Oryza sativa L.) crop in Arkansas is seeded from late March through early June each year. Farmers need new rice cultivars that not only produce both high rough rice yields and high head rice across this range of seeding dates but do so consistently. Thus, a seeding date study was conducted during 1994 and 1995 at Stuttgart, Arkansas, to study seeding date effects on rough rice yield and head rice and selection for stability. Fourteen rice cultivars were seeded at five dates ranging from late March through mid-June. Kang's yield-stability statistic was used to select cultivars for both high rough rice yields and high head rice as well as stability for both traits. Plant stands from March seedings of each year were significantly lower than for the later seeding dates. Maturity (days to 50 percent heading) was extended at the early seeding dates. Some rice cultivars, such as ‘LaGrue’, had lower and more variable head rice when seeded early. In the June seeding dates each year, ‘Kaybonnet’ produced rough rice yields that were more consistent with yields when planted at the earlier planting dates. ‘Bengal’, ‘Cypress’, ‘Kaybonnet’, and ‘Newbonnet’ were cultivars selected by Kang's stability statistic, which was targeted to select cultivars with stable, high rough rice yields and stable, high head rice. The validity of using Kang's yield-stability statistic for cultivar selection is also evident empirically by the adaptation and wide use of these four cultivars by southern U.S. rice producers. These results indicate that seeding date studies and stability analyses would be useful tools for rice breeders to identify cultivars that will be readily adapted and grown by rice producers.
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  • 71
    ISSN: 1573-5028
    Schlagwort(e): aspen ; Populus tremuloides ; xylem ; lignin ; caffeoyl-CoA ; caffeate ; O-methyltransferase ; gene expression ; enzyme activity ; recombinant bacterial overexpression
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Seasonal expression of caffeoyl-CoA O-methyltransferase (EC 2.1.1.104) was analyzed in aspen developing secondary xylem in parallel with caffeate O-methyltransferase (EC 2.1.1.68). Enzyme activity and mRNA levels for both enzymes peaked in the middle of the growing season. These results strongly suggest that both forms of O-methyltransferase were actively participating in lignin precursor biosynthesis during the growing season. To determine the role of each enzyme form, xylem extracts from two days in the growing season were assayed with four substrates: caffeoyl-CoA, 5-hydroxyferuloyl-CoA, caffeate acid and 5-hydroxyferulic acid. Recombinant forms of caffeoyl-CoA and caffeate O-methyltransferase were also assayed with these substrates. The recombinant enzymes have different substrate specificity with the caffeoyl-CoA O-methyltransferase being essentially specific for CoA ester substrates with a preference for caffeoyl-CoA, while caffeate O-methyltransferase utilized all four substrates with a preference for the free acid forms. We suggest that caffeoyl-CoA O-methyltransferase is likely to be responsible for biosynthesis of lignin precursors in the guaiacyl pathway and may represent a more primitive enzyme form leftover from very early land plant evolution. Caffeate O-methyltransferase is more likely to be responsible for lignin precursor biosynthesis in the syringyl pathway, especially since it can catalyze methylation of 5-hydroxyferuloyl-CoA quite effectively. This latter enzyme form then may be considered a more recently evolved component of the lignin biosynthetic pathways of the evolutionarily advanced plants such as angiosperms.
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  • 72
    ISSN: 1573-5028
    Schlagwort(e): binding site selection ; gene expression ; homeobox-leucine zipper genes ; protein-DNA interaction
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract We report the isolation and characterization of two Arabidopsis homeobox genes highly related to the Athb-8 gene. The full-length cDNAs encode proteins of 841 and 852 amino acids which we have designated Athb-9 and -14, respectively. Athb-8, -9 and -14 are members of a small family of HD-Zip proteins (HD-ZIP III) characterized by a HD-Zip motif confined to the N-terminus of the polypeptide. The spatial organization of the HD-Zip domain of Athb-8, -9 and -14 is different from that of the Athb-1 (a member of the HD-ZIP I family) and Athb-2 (a member of the HD-ZIP II family) HD-Zip domains. DNA binding analysis performed with random-sequence DNA templates showed that the Athb-9 HD-Zip (HD-Zip-9) domain, but not the Athb-9 HD alone, binds to DNA. The HD-Zip-9 domain recognizes a 11 bp pseudopalindromic sequence (GTAAT(G/C)ATTAC), as determined by selecting high-affinity binding sites from random-sequence DNA. Moreover, gel retardation assays demonstrated that the HD-Zip-9 domain binds to DNA as a dimer. These data support the notion that the HD-ZIP III domain interacts with DNA recognition elements in a fashion similar to the HD-ZIP I and II domains.
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  • 73
    Digitale Medien
    Digitale Medien
    Springer
    Euphytica 100 (1998), S. 15-18 
    ISSN: 1573-5060
    Schlagwort(e): biparental mating ; stability ; Triticum durum
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Three populations of an intervarietal durum wheat cross IWP5308/PDW208, F5, F5BIP1 (population derived after intermating in F2) and F5BIP2 (population derived after intermating in BIPF1), were evaluated under three different agronomic environments for mean performance and stability of genotypes for grain yield, yield components and protein content. Though the biparental progenies indicated a higher mean performance, they did not differ significantly from progenies of the pedigree method for almost all characters. The biparental progenies, however, produced a higher number of stable genotypes for grain yield per plant, grains per ear and protein content. The F5 population had a higher number of stable genotypes for 1000 grain weight and number of tillers per plant. The BIP progenies also had a higher number of genotypes with above average mean performance, and many were significantly higher than the checks WH896 and WH542, compared with F5 progenies. Hence, in spite of high G x E interactions, the use of cycles of biparental mating and selection of top yielding lines on the basis of yield components can enable selection of stable genotypes with high protein content. Number of tillers per plant and 1000 grain weight were the yield component characters which made maximum contribution to phenotypic stability of the genotypes.
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  • 74
    ISSN: 1573-5060
    Schlagwort(e): adaptation ; correlations ; genotype-environment interaction ; landraces ; performance ; stability ; tetraploid wheat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Plant breeding has always been concerned with genotype-environment interaction. Normally high and stable performance are desirable attributes of cultivars. However, this is practically difficult to achieve where environmental variations are high and unpredictable and significant genotype-environment interactions occur. Stability of performance of 13 landraces evaluated at 4 different locations for 3 years in the highlands of Ethiopia was investigated. The testing locations have different climatic and edaphic conditions providing the conditions necessary for the assessment of stability. Stability parameters like b, s2d, s2, r2 and cv which are in common use were employed. Grain yield and 1000-kernel weight were the agronomic traits considered for the stability analysis. There were differences in the ranks of genotypes across the locations. Significant main environmental as well as interaction effects were observed showing the importance of genotype-environment interaction in both traits. Many of the landraces evaluated are rated as stable for these traits within the environmental conditions prevailing in these highland locations. Genotypes with specific adaptation to poor and favourable conditions were also identified. Certain genotypes showed similar manners of adaptation and stability for both of the traits. Grain yield showed low correlations with the stability parameters showing the possibility of attaining high yield and stability. Correlations between the stability parameters were mainly positive and significant for grain yield. Only a few of these correlations were found to be significant for kernel weight. The good adaptability of landraces should be exploited in the improvement of their yield potential.
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  • 75
    Digitale Medien
    Digitale Medien
    Springer
    Plant molecular biology 36 (1998), S. 811-820 
    ISSN: 1573-5028
    Schlagwort(e): gene expression ; nodules ; phosphoribosyl aminoimidazole synthetase ; purine biosynthesis ; N assimilation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract A cDNA (VUpur5) encoding phosphoribosyl aminoimidazole (AIR) synthetase, the fifth enzyme of the de novo purine biosynthesis pathway has been isolated from a cowpea nodule cDNA library. It encodes a 388 amino acid protein with a predicted molecular mass of 40.4 kDa. The deduced amino acid sequence has significant homology with AIR synthetase from other organisms. AIR synthetase is present in both mitochondria and plastids of cowpea nodules [7]. A signal sequence encoded by the VUpur5 cDNA has properties associated with plastid transit sequences but there is no consensus cleavage site as would be expected for a plastid targeted protein. Although the signal sequence does not have the structural features of a mitochondrial targeted protein, it has a mitochondrial cleavage site motif (RX/XS) close to the predicted N-terminus of the mature protein. Southern analysis suggests that AIR synthetase is encoded by a single gene raising questions as to how the product of this gene is targeted to the two organelles. VUpur5 is expressed at much higher levels in nodules compared to other cowpea tissues and the gene is active before nitrogen fixation begins. These results suggest that products of nitrogen fixation do not play a role in the initial induction of gene expression. VUpur5 was expressed in Escherichia coli and the recombinant protein used to raise antibodies. These antibodies recognize two forms of AIR synthetase which differ in molecular size. Both forms are present in mitochondria, although the larger protein is more abundant. Only the smaller protein was detected in plastids.
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  • 76
    Digitale Medien
    Digitale Medien
    Springer
    Plant molecular biology 37 (1998), S. 425-435 
    ISSN: 1573-5028
    Schlagwort(e): gene expression ; protein-DNA interaction ; plant ; stress ; seed development
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The phytohormone abscisic acid is probably present in all higher plants. This hormone is necessary for regulation of several events during seed development and for the response to environmental stresses such as desiccation, salt and cold. An important part of the physiological response to abscisic acid is achieved through gene expression. Here, we summarize the current knowledge of regulation of abscisic acid-induced transcription. The main focus is on a description of the known abscisic acid-responsive cis-elements, their properties and the possible transacting factors binding to the elements. Results have shown that cooperative action of cis-elements and the promoter configuraton is crucial for regulation by abscisic acid. Furthermore, several elements are organ- and species-specific. Recent studies of the chromatin structure of abscisic acid-responsive genes point to the importance of induction of transcription by coactivators or by phosphorylation/dephosphorylation of transcription factors. An interesting example of activation by a cofactor is the cooperative action between abscisic acid-signaling and the regulatory protein Viviparous 1 through the abscisic acid responsive element.
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  • 77
    Digitale Medien
    Digitale Medien
    Springer
    Plant molecular biology 37 (1998), S. 587-596 
    ISSN: 1573-5028
    Schlagwort(e): Arabidopsis thaliana ; gene expression ; leucine-rich repeat ; PCR ; receptor-like kinase
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract We have isolated three receptor-like kinase cDNAs from an Arabidopsis flower cDNA library by PCR using degenerate oligonucleotide primers for conserved domains of protein kinases. Cloning and sequencing of the full-length cDNAs, designated RKF1 to 3 (receptor-like kinase in flowers), showed that the putative extracellular domain of the RKF1 protein contains 13 tandem repeats of leucine-rich sequences and those of RKF2 and RKF3 have no significant homology with other plant sequences. RNA blot analysis revealed that the RKF1 mRNA is highly expressed in stamens while RKF2 and RKF3 mRNAs are present at low levels in all organs examined. In situ localization experiments indicated that the RKF1 mRNA is detectable in early flower primordia and during stamen development. In addition, when fused to a GUS reporter gene, the RKF1 promoter directed high GUS expression in pollen grains. Recombinant RKF1, produced in Escherichia coli, was found to have kinase activity with serine/threonine specificity in vitro.
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  • 78
    ISSN: 1573-5028
    Schlagwort(e): gene expression ; phytohormone ; Lea ; leaf senescence ; senescence-associated gene ; stress
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The expression of several Arabidopsis thaliana senescence-associated genes (SAGs) in attached and/or detached leaves was compared in response to age, dehydration, darkness, abscisic acid, cytokinin, and ethylene treatments. Most of the SAGs responded to most of the treatments in a similar fashion. Detachment in darkness and ethylene were the strongest inducers of both SAGs and visible yellowing. Detachment in light was also a strong inducer of SAGs, but not of visible yellowing. The other treatments varied more in their effects on individual SAGs. Responses were examined in both older and younger leaves, and generally were much stronger in the older ones. Individual SAGs differed from the norms in different ways, however, suggesting that their gene products play a role in overlapping but not identical circumstances. Some SAGs responded quickly to treatments, which may indicate a direct response. Others responded more slowly, which may indicate an indirect response via treatment-induced senescence. Four new SAGs were isolated as part of this work, one of which shows strong similarity to late embryogenesis-abundant (Lea) genes.
    Materialart: Digitale Medien
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  • 79
    ISSN: 1573-5117
    Schlagwort(e): Planarian ; Hox ; gene expression
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Seven Hox cluster-related genes (Dthox-A to -G) have been isolated from the freshwater triclad Dugesia (G.) tigrina, their sequence compared to other Hox genes and their expression in intact and regenerating organisms analyzed by whole mount in situ hybridization. Sequence comparison analyses show high similarities of D. tigrina Hox genes to anterior and medial groups of coelomate Hox genes. Expression analyses show very early, synchronous, and overlapping expression of Dthox -A, -E, -G and -F in anterior, posterior and lateral regenerative tissues. At one hour of regeneration all Dthox genes studied showed a neat, clear expression at the wound boundary. Later, as the blastema grows, the expression area expands to more proximal regions covering the blastema and the distal postblastema regions. Blastemas formed by intercalary regeneration also show a synchronous expression of the same Hox genes though the onset of activation is much delayed. The finding that the same set of Hox genes is synchronously activated in anterior, posterior, intercalary and lateral regeneration is in sharp contrast to its well established role in specifying antero-posterior pattern during embryonic development. The implications of these results as regards ancestral versus co-opted roles of Hox genes in development and regeneration are discussed.
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  • 80
    Digitale Medien
    Digitale Medien
    Springer
    Hydrobiologia 385 (1998), S. 201-211 
    ISSN: 1573-5117
    Schlagwort(e): hypoxia ; anoxic hypolimnion ; volcanic crater lake ; stratification ; productivity ; heat budget ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract This paper quantifies the temporal pattern of thermal stratification and deoxygenation in Lake Nkuruba, a small (3 ha), deep (maximum depth = 38 m) crater lake in western Uganda. Dissolved oxygen penetrated to an average depth of 9 m and a maximum depth of 15 m below which the lake was permanently anoxic over the 2 years of study. Although surface oxygen levels were correlated with both surface water temperature and rainfall, seasonal cycles of dissolved oxygen were not well-defined and may have been obscured by the high frequency of short-term fluctuations and by inter-annual variations caused by shifts in rainfall. Surface water temperature averaged 23.3±0.7 °C (S.D.) and varied directly with air temperature. Both diurnal changes and top-bottom temperature differentials were small averaging 1.7±0.7 °C and 1.6±0.8 °C, respectively. Thermal stability ranged from 101.3 to 499.9 g-cm cm-2 and was positively related to surface water temperature suggesting that this small protected lake responds rapidly to short-term meteorological changes. Because contribution to the annual heat exchange cycle was confined to upper waters, the lake's annual heat budget was low, 1,073.8 cal cm-2 yr-1. However, net primary productivity was relatively high averaging 1.3 g C m-2d-1. The region where Lake Nkuruba is situated experienced a very strong earthquake (6.2 on the Richter scale) on 4 February, 1994. Subsequently, water levels dropped markedly in the lake, falling 3.14 m over a 5-month period.
    Materialart: Digitale Medien
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  • 81
    Digitale Medien
    Digitale Medien
    Springer
    Hydrobiologia 385 (1998), S. 201-211 
    ISSN: 1573-5117
    Schlagwort(e): hypoxia ; anoxic hypolimnion ; volcanic crater lake ; stratification ; productivity ; heat budget ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract This paper quantifies the temporal pattern of thermal stratification and deoxygenation in Lake Nkuruba, a small (3 ha), deep (maximum depth = 38 m) crater lake in western Uganda. Dissolved oxygen penetrated to an average depth of 9 m and a maximum depth of 15 m below which the lake was permanently anoxic over the 2 years of study. Although surface oxygen levels were correlated with both surface water temperature and rainfall, seasonal cycles of dissolved oxygen were not well-defined and may have been obscured by the high frequency of short-term fluctuations and by inter-annual variations caused by shifts in rainfall. Surface water temperature averaged 23.3±0.7 °C (S.D.) and varied directly with air temperature. Both diurnal changes and top-bottom temperature differentials were small averaging 1.7±0.7 °C and 1.6±0.8 °C, respectively. Thermal stability ranged from 101.3 to 499.9 g-cm cm-2 and was positively related to surface water temperature suggesting that this small protected lake responds rapidly to short-term meteorological changes. Because contribution to the annual heat exchange cycle was confined to upper waters, the lake's annual heat budget was low, 1,073.8 cal cm-2 yr-1. However, net primary productivity was relatively high averaging 1.3 g C m-2d-1. The region where Lake Nkuruba is situated experienced a very strong earthquake (6.2 on the Richter scale) on 4 February, 1994. Subsequently, water levels dropped markedly in the lake, falling 3.14 m over a 5-month period.
    Materialart: Digitale Medien
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  • 82
    Digitale Medien
    Digitale Medien
    Springer
    Journal of optimization theory and applications 97 (1998), S. 707-729 
    ISSN: 1573-2878
    Schlagwort(e): Nonlinear integral equations ; optimal control in L p-spaces ; relaxation ; existence ; stability ; nonconcentration ; optimality conditions ; Pontryagin maximum principle
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract Optimal control problems with nonlinear equations usually do not possess optimal solutions, so that their natural (i.e., continuous) extension (relaxation) must be done. The relaxed problem may also serve to derive first-order necessary optimality condition in the form of the Pontryagin maximum principle. This is done here for nonlinear Fredholm integral equations and problems coercive in an L p-space of controls with p〈+∞. Results about a continuous extension of the Uryson operator play a key role.
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  • 83
    Digitale Medien
    Digitale Medien
    Springer
    Applied mathematics and mechanics 19 (1998), S. 135-146 
    ISSN: 1573-2754
    Schlagwort(e): nonholonomic system ; Lagrange's theorem ; manifold ; stability ; Liapunov's direct method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Mathematik , Physik
    Notizen: Abstract The stability problem for the manifold of equilibrium positions of a class of nonholonomic systems is studied in this paper. Based on Liapunov's direct method and the definition of stability. Lagrange's theorem of holonomic systems is extended to a class of nonholonomic conservative systems and dissipative systems, and a new expression is made to the relation between asymptotic stability for the manifold of equilibrium positions of this class of nonholonomic systems and dissipative forces. Two examples are finally given to illustrate the application of the theorems.
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  • 84
    Digitale Medien
    Digitale Medien
    Springer
    Journal of logic, language and information 7 (1998), S. 143-163 
    ISSN: 1572-9583
    Schlagwort(e): Belief revision ; consolidation ; coherence ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Allgemeine und vergleichende Sprach- und Literaturwissenschaft. Indogermanistik. Außereuropäische Sprachen und Literaturen , Informatik
    Notizen: Abstract The notion of epistemic coherence is interpreted as involving not only consistency but also stability. The problem how to consolidate a belief system, i.e., revise it so that it becomes coherent, is studied axiomatically as well as in terms of set-theoretical constructions. Representation theorems are given for subtractive consolidation (where coherence is obtained by deleting beliefs) and additive consolidation (where coherence is obtained by adding beliefs).
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  • 85
    ISSN: 1573-0778
    Schlagwort(e): CHO ; DHFR ; gene expression ; growth factor ; recombinant protein ; serum-free
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Abstract The dihydrofolate reductase-deficient Chinese hamster ovary cell line, DXB11-CHO, commonly used as a host cell for the production of recombinant proteins requires 7.5% serum-supplementation for optimal growth. Regulatory issues surrounding the use of serum in clinical production processes and the direct and indirect costs of using serum in large-scale production and recovery processes have triggered efforts to derive serum-independent host cell lines. We have successfully isolated a serum-free host that we named Veggie- CHO. Veggie-CHO was generated by adapting DXB11-CHO cells to growth in serum-free media in the absence of exogenous growth factors such as Transferrin and Insulin-like growth factor, which we have previously shown to be essential for growth and viability of DXB11- CHO cells. Veggie-CHO cells have been shown to maintain an average doubling time of 22 hr in continuous growth cultures over a period of three months and have retained the dihydrofolate reductase -deficient phenotype of their parental DXB11-CHO cells. These properties and the stability of its serum-free phenotype have allowed the use of Veggie- CHO as host cells for transfection and amplified expression of recombinant proteins. We describe the derivation a serum-free recombinant cell line with an average doubling time of 20 hr and specific productivity of 2.5 Units recombinant Flt-3L protein per 10e6 cells per day.
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  • 86
    Digitale Medien
    Digitale Medien
    Springer
    Pharmaceutical research 15 (1998), S. 77-81 
    ISSN: 1573-904X
    Schlagwort(e): azetirelin ; thyrotropin-releasing hormone analog ; stability ; nasal absorption ; acylcarnitines
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Purpose. The long-term stability and nasal absorption characteristics of a basic nasal formulation of azetirelin, a thyrotropin-releasing hormone analog and its absorption enhancement by incorporation of acylcarnitines in the formulation were investigated. Methods. The long-term stability of basic nasal azetirelin formulations at 25° C was predicted by calculation from the Arrhenius plot of the data on 6 months' storage at 40, 50 and 60° C. Nasal azetirelin absorption characteristics were kinetically examined by intranasal administration to rats, determination of plasma azetirelin level by radioimmunoassay, and fitting the data to a two-compartment model including absorption rate. Results. Basic nasal azetirelin formulations of pH 4.0 and pH 5.1 were predicted to be highly stable. Residual azetirelin after 2 years storage at 25° C was greater than 95%. Nasal absorption characteristics of this formulation in the pH 4.0−6.3 range showed pH-dependency, with pH 4.0 showing the highest absolute bioavailability (Bioav) of 17.1%. This nasal Bioav was 21 times greater than that of oral administration (0.8%). Acylcarnitines with 12 or more carbon atoms in the acyl chain greatly enhanced nasal absorption of azetirelin: Bioavs with lauroylcarnitine chloride (LCC) and palmitoylcarnitine chloride were 96.9% and 72.9%, respectively. This enhancement by LCC plateaued at the low concentration of 0.1%. Conclusions. The basic nasal azetirelin formulation at pH 4.0 is stable and shows adequate absorption, with nasal absorption having greater Bioav than oral absorption. The 12-carbon acylate LCC was the strongest enhancer among acylcarnitines and provided near-total delivery of the administered dose to the blood.
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  • 87
    ISSN: 1573-904X
    Schlagwort(e): IL-1R type I ; microcalorimetry ; protein formulation ; stability ; aggregation ; preservatives ; far-uv circular dichroism
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Purpose. To elucidate the solution conditions that confer stability of aqueous IL-1R using differential scanning calorimetry (DSC). Methods. Optimal pH conditions were determined by monitoring degradation products encountered during accelerated studies (at elevated temperatures) using SDS-PAGE. At the pH optimum, DSC screened for excipients that enhanced thermal stability by shifting the Tm to higher values. Using SEC the relationship between thermal unfolding and stability was investigated by considering if lower Tm's in the presence of preservatives correlated with degradation products at 37°C over time. The degree of aggregation relative to that of a control determined the level of stability achieved. Results. Circular dichroism (CD) measurements confirmed molecular modeling studies showing IL-1R to be about 39% β-sheet. Two major transitions characterized the DSC data with Tm's observed near 47°C and 66°C. Among 21 excipients screened, NaCl exhibited the greatest stabilizing influences based on shifting the low temperature transition to 53°C. The low temperature transition was later found to comprise two transitions, yielding a total of three melting transitions for IL-1R. High Tm's arising from the presence of preservatives correlated with the order of stability (i.e., 0.065% phenol 〉 0.1% m-Cresol 〉 0.9% benzyl alcohol). Conclusions. The three melting transitions are consistent in origin with the cooperative unfolding of three unique immunoglobulin-like domains of IL-1R. Optimal stability was achieved in 20 mM sodium citrate at pH 6 with sufficient NaCl to attain the tonicity of human serum. A correlation between the predicted ranking of stability and the extent of aggregation was demonstrated using DSC.
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  • 88
    ISSN: 1573-904X
    Schlagwort(e): perfluorodecalin ; nonaqueous suspension ; protein ; alpha interferon ; factor IX ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Purpose. To identify a suitable nonaqueous, parenterally acceptable suspending vehicle whereby a therapeutic protein is delivered as a stable flowable powder, making it amenable to delivery from sustained delivery systems maintained at body temperature. Methods. Formulations of plasma derived Factor IX (pdFIX) and recombinant human alpha interferon (rhα-lFN) were formulated as dry powders, suspended in various vehicles (perfluorodecalin, perfluorotributylamine, methoxyflurane, polyethylene glycol 400, soybean oil, tetradecane or octanol) and stored at 37°C. Stability was assessed by size exclusion chromatography, reverse phase chromatography, ion exchange chromatography, and bioassay, and was compared to the stability of dry powder formulations stored at 37°C and −80°C. Results. PdFIX was stable when stored at 37°C as a dry powder, or when the dry powder was suspended in the pharmaceutically acceptable vehicles perfluorodecalin or perfluorotributylamine. Suspensions of the powder in other pharmaceutically/parenterally acceptable vehicles such as soybean oil or PEG 400 resulted in aggregation and loss of bioactivity. A dry powder formulation of rhα-lFN suspended in perfluorodecalin was also stable at 37°C. Conclusions. This study shows the potential utility of perfluorinated hydrocarbons as nonaqueous suspending vehicles for long term in-vivo delivery of therapeutic proteins.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 89
    ISSN: 1573-904X
    Schlagwort(e): gene expression ; hPepTl ; Caco-2 cells ; adenovirus ; drug screening
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Purpose. Our goals are to establish an in vitro screening system and to evaluate a new approach in improving oral absorption of peptides and peptide-like drugs by overexpression of the human intestinal oligo-peptide transporter (hPepTl). This study characterizes the expression of hPepTl in human intestinal Caco-2 cells, rat intestinal epithelial cells (IEC-18), and human cervix epithelial cells (Hela) after adenoviral transduction. Methods. A recombinant replication-deficient adenovirus carrying the hPepTl gene was made and used as a vector for the expression of hPepTl. The increase in the uptake permeability of cephalexin and Gly-Sar was determined. The effects of time, dose, apical pH, and substrate specificity were evaluated. Results. A significant increase in the uptake permeability of Gly-Sar and cephalexin was found in all three cell lines after viral transduction. The increase of Gly-Sar permeability in Hela, IEC-18, and Caco-2 cells was 85-, 46-, and 15-fold respectively. Immunoblotting using an antibody against hPepTl detected high levels of a 85-98-kDa protein in all three infected cell lines. Substrate permeability was dependent on time of infection, inward pH gradients, and multiplicity of infection (MOI). Decreased infectivity and lower hPepTl expression were observed in differentiated Caco-2 cells. The uptake was inhibited by dipeptides and β-lactam antibiotics but not amino acids. Conclusions. Adenoviral infected Hela cells displayed a pronounced level of hPepTl expression with a low background and high specificity to dipeptides. These features make this system a useful tool for screening of potential substrates. The success of overexpression of hPepTl in Caco-2 and IEC-18 cells may lead to a novel approach in improving oral absorption of peptides and peptidomimetic drugs.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 90
    ISSN: 1573-904X
    Schlagwort(e): cytokine ; rHuMGDF ; PEGylation ; diketopiperazine ; stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Purpose. Determine the effect of PEGylation on in-vitro degradation for recombinant human Megakaryocyte Growth and Development Factor (rHuMGDF) in the neutral pH range. Methods. Degradation products were characterized by cation-exchange HPLC, N-terminal sequencing and mass spectrometry. Results. The main route of degradation was through non-enzymatic cyclization of the first two amino acids and subsequent cleavage to form a diketopiperazine and des(Ser, Pro)rHuMGDF. This reaction was prevented by alkylation of the N-terminus by polyethylene glycol (PEG). Conclusions. PEGylation of proteins is commonly performed to achieve increased in-vivo circulation half-lives. For rHuMGDF, an additional advantage of PEGylation was enhancedin-vitro shelf-life stability.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 91
    Digitale Medien
    Digitale Medien
    Springer
    Nonlinear dynamics 17 (1998), S. 1-21 
    ISSN: 1573-269X
    Schlagwort(e): Symbolic computation ; stability ; bifurcation ; nonlinear ; time-periodic
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract A new technique is presented for symbolic computation of local stability boundaries and bifurcation surfaces for nonlinear multidimensional time-periodic dynamical systems as an explicit function of the system parameters. This is made possible by the recent development of a symbolic computational algorithm for approximating the parameter-dependent fundamental solution matrix of linear time-periodic systems. By evaluating this matrix at the end of the principal period, the parameter-dependent Floquet Transition Matrix (FTM), or the linear part of the Poincaré map, is obtained. The subsequent use of well-known criteria for the local stability and bifurcation conditions of equilibria and periodic solutions enables one to obtain the equations for the bifurcation surfaces in the parameter space as polynomials of the system parameters. Further, the method may be used in conjunction with a series expansion to obtain perturbation-like expressions for the bifurcation boundaries. Because this method is not based on expansion in terms of a small parameter, it can be successfully applied to periodic systems whose internal excitation is strong. Also, the proposed method appears to be more efficient in terms of cpu time than the truncated point mapping method. Two illustrative example problems, viz., a parametrically excited simple pendulum and a double inverted pendulum subjected to a periodic follower force, are included.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 92
    Digitale Medien
    Digitale Medien
    Springer
    Journal of elasticity 53 (1998), S. 199-213 
    ISSN: 1573-2681
    Schlagwort(e): thermoelasticity ; stability ; strong ellipticity.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract A notion of material stability is introduced and discussed in the setting of nonlinear thermoelasticity. Necessary and sufficient conditions are established for the stability of a general thermoelastic material. The adiabatic theory and the theory that accounts for heat conduction are considered separately.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 93
    Digitale Medien
    Digitale Medien
    Springer
    Nonlinear dynamics 15 (1998), S. 311-327 
    ISSN: 1573-269X
    Schlagwort(e): Time delay ; stability ; vibration control ; periodic motion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract The paper presents analytical and numerical studies of the primary resonance and the 1/3 subharmonic resonance of a harmonically forced Duffing oscillator under state feedback control with a time delay. By using the method of multiple scales, the first order approximations of the resonances are derived and the effect of time delay on the resonances is analyzed. The concept of an equivalent damping related to the delay feedback is proposed and the appropriate choice of the feedback gains and the time delay is discussed from the viewpoint of vibration control. In order to numerically solve the problem of history dependence prior to the start of excitation, the concepts of the Poincaré section and fixed points are generalized. Then, a modified shooting scheme associated with the path following technique is proposed to locate the periodic motion of the delayed system. The numerical results show the efficacy of the first order approximations of the resonances.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 94
    Digitale Medien
    Digitale Medien
    Springer
    Mechanics of time-dependent materials 2 (1998), S. 335-349 
    ISSN: 1573-2738
    Schlagwort(e): Lyapunov exponents ; numerical methods ; random processes ; reliability ; rods ; stability ; viscoelasticity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The stability and reliability of a nonlinear viscoelastic rod under a stochastic excitation is investigated. The loads are assumed to be in the form of random stationary processes. The solution is obtained with the help of a numerical method, which is based on the method of the statistical simulation of random input processes and on the numerical solution of the system of nonlinear and linearized integro-differential equations. These equations describe a nonperturbed and perturbed motion of the rod. The estimation of the stability is carried out with the help of top Lyapunov exponents.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 95
    Digitale Medien
    Digitale Medien
    Springer
    Nonlinear dynamics 17 (1998), S. 301-324 
    ISSN: 1573-269X
    Schlagwort(e): parametric excitation ; non-linear complex ; stability ; jump phenomena
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract The effects of parametric excitation on a traveling beam, both with and without an external harmonic excitation, have been studied including the non-linear terms. Non-linear, complex normal modes have been used for the response analysis. Detailed numerical results are presented to show the effects of non-linearity on the stability of the parametrically excited system. In the presence of both parametric and external harmonic excitations, the response characteristics are found to be similar to that of a Duffing oscillator. The results are sensitive to the relative strengths of and the phase difference between the two forms of excitations.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 96
    Digitale Medien
    Digitale Medien
    Springer
    Nonlinear dynamics 16 (1998), S. 187-202 
    ISSN: 1573-269X
    Schlagwort(e): Chaos ; stability ; offset ; bearings
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract Extensive numerical simulation studies with a short bearing film model show that a balanced dual offset rotor bearing subjected to a fixed external load can improve bearing performance for load and speed conditions known to produce undesirable half-speed whirl in conventional zero-offset cylindrical systems. For specific values of dimensionless load, offset ratio, and load orientation, parametric changes in speed show that the dual offset bearing can undergo a variety of bifurcations which produce coexisting period 1–4 subharmonic, quasi-periodic, and chaotic attractors, all of which may be driven by lower-order dynamic processes. For a specific set of initial conditions, the transition to chaos via period doubling in the dual offset bearing actually produces lubricant films which are significantly thicker than those found in the corresponding cylindrical system.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 97
    ISSN: 1573-3904
    Schlagwort(e): antibiotics ; biological activity ; N-carboxy anhydride ; penicillin ; stability ; Cα-tetrasubstituted α-amino acid
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Reaction of the N-carboxyanhydride from Cα-methyld-phenylglycine with either 6-aminopenicillanic acid or 7-amino-3-desacetoxy-cephalosporanic acid furnishes the corresponding ampicillin and cephalexin analogues. Neither the biological activity nor the chemical stability of these new semi-synthetic antibiotics are superior to those of their unmethylated counterparts.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 98
    ISSN: 1573-3904
    Schlagwort(e): antibiotics ; biological activity ; N-carboxy anhydride ; penicillin ; stability ; Cα-amino acid
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Reaction of the N-carboxyanhydride from Cα-methyl d-phenylglycine with either 6-aminopenicillanic acid or 7-amino-3-desacetoxy-cephalosporanic acid furnishes the corresponding ampicillin and cephalexin analogues. Neither the biological activity nor the chemical stability of these new semi-synthetic antibiotics are superior to those of their unmethylated counterparts.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 99
    ISSN: 1573-9368
    Schlagwort(e): luciferase ; scaffold attachment regions ; heat shock ; blastocyst ; gene expression
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Transgenesis in domestic species, as a research tool and in biotechnological applications, has been limited by the expense of producing transgenic offspring by standard microinjection techniques. A major factor is the inefficiency of maintaining large numbers of recipient females, when a high percentage of these carry nontransgenic fetuses. There are two approaches to reduce this cost, the fusion of transfected fetal fibroblasts with enucleated oocytes, and the screening of microinjected embryos for transgene integration in blastocysts, prior to transfer. Here, we develop a luminescent screening system to select transgenic bovine embryos. A transgene with scaffold attachment regions flanking the murine HSP70.1 promoter linked to firefly luciferase cDNA, was microinjected into pronuclei of in vitro produced zygotes. At the blastocyst stage, the transgene was induced by heat shock (45 °C, 15 min) and 4–6 h later, luciferase expression was analyzed by photon counting imaging. Screened blastocysts were transferred to recipients and day 50 fetuses or calves were analyzed by PCR and Southern blot for transgene integration. When nonluminescent blastocysts were transferred, transgene integration was never observed. Of 13 fetuses derived from luminescent blastocysts, 3 contained integrated transgenes that were functional in all tissues examined. Image analysis of the signal emitted by positive blastocysts revealed that 9 nontransgenic fetuses were obtained from blastocysts that exhibited a localized luminescent signal. On the other hand, 3 of 4 fetuses derived from blastocysts that emitted light over more than 70% of their surface were transgenic. Thus, by selecting luminescent blastocysts on the basis of both signal intensity and distribution, the number of recipient females required to produce transgenic offspring can be greatly reduced. Using this technique it should also be possible to improve the efficiency of transgenesis by microinjection through studies in which vector design and integration conditions are examined at the blastocyst stage.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 100
    Digitale Medien
    Digitale Medien
    Springer
    Transgenic research 7 (1998), S. 403-411 
    ISSN: 1573-9368
    Schlagwort(e): transgenic organism ; gene expression ; promoter ; plant ; gene regulation ; heterologous system
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The regulation of gene expression represents a specific process which has different structural and functional requirements in different groups of organisms. It is thus assumed that regulatory sequences of eucaryotes cannot be recognized in procaryotes. This assumption is of interest for risk assessments of the environmental impact of deliberate release experiments with genetically modified organisms. In order to analyse the extent of heterologous gene expression caused by the transfer of plant-specific regulatory sequences into bacteria, we constructed fusions between plant-specific regulatory sequences and the coding regions of the luxAB genes for the luciferase of the bioluminescent bacterium Vibrio harveyi, transferred the fusions into different bacterial species and measured the luminescence to quantify the expression of the luciferase genes. The regulatory sequences investigated included (a) the 35S promoter of the Cauliflower mosaic virus, (b) the B33 promoter of a class I patatin gene of potatoes, (c) the promoter of the ST-LS1 gene of potatoes and (d) the promoter of the rolC gene of Agrobacterium rhizogenes. We could show that in addition to the 35S promoter, which has already been described as being recognized in Escherichia coli, the sequences containing the B33 and the ST-LS1 promoters are recognized in bacteria. Luciferase gene expression promoted by the sequence with the ST-LS1 promoter could be observed in E. coli, Yersinia enterocolitica and Agrobacterium tumefaciens. Comparison of the luminescence caused by fusions between luxAB and different promoters on the chromosome and on an endogenous plasmid of Y. enterocolitica demonstrated that the level of the heterologous gene expression caused by the fragment with the ST-LS1 promoter was within the range of gene expression levels caused by endogenous promoters of Y. enterocolitica.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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