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  • 1
    Title: Scholarly journals at the crossroads : a subversive proposal for electronic publishing; an Internet discussion about scientific and scholarly journals and their future
    Contributer: Okerson, Ann S. , O'Donnell, James J.
    Publisher: Washington, :Ass. of Research Libraries,
    Year of publication: 1995
    Pages: 242 S.
    Type of Medium: Book
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 10 (1998), S. 1249-1255 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Here we investigate the effect of a steady pressure disturbance moving at a constant velocity along the interface of a thin viscous film flowing down an inclined plane. Both steady and unsteady solutions are determined for the interface. We find that it is possible for the steady solutions to have surface waves, either preceding the disturbance or behind it, depending on the values of the Bond and capillary numbers. In addition, for fixed Bond number, disturbance amplitude, and constant film heights both far upstream and downstream, there exists a finite range of capillary numbers for which no steady solutions exist. Within this range of capillary numbers, the transient solution develops a shock like profile which adjusts the heights upstream and downstream of the disturbance and grows in width. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 7 (1997), S. 544-549 
    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Model-independent chaos control techniques are inherently well-suited for the control of physiological systems for which quantitative system models are unavailable. The proportional perturbation feedback (PPF) control paradigm, which uses electrical stimulation to perturb directly the controlled system variable (e.g., the interbeat or interspike interval), was developed for excitable physiological systems that do not have an easily accessible system parameter. We develop the stable manifold placement (SMP) technique, a PPF-type technique which is simpler and more robust than the original PPF control algorithm. We use the SMP technique to control a simple geometric model of a chaotic system in the neighborhood of an unstable periodic orbit (UPO). We show that while the SMP technique can control a chaotic system that has UPO dynamics which are characterized by one stable manifold and one unstable manifold, the success of the SMP technique is sensitive to UPO parameter estimation errors. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In support of the spiral wave theory of reentry, simulation studies and animal models have been utilized to show various patterns of spiral wave tip motion such as meandering and drifting. However, the demonstration of these or any other patterns in cardiac tissues have been limited. Whether such patterns of spiral tip motion are commonly observed in fibrillating cardiac tissues is unknown, and whether such patterns form the basis of ventricular tachycardia or fibrillation remain debatable. Using a computerized dynamic activation display, 108 episodes of atrial and ventricular tachycardia and fibrillation in isolated and intact canine cardiac tissues, as well as in vitro swine and myopathic human cardiac tissues, were analyzed for patterns of nonstationary, spiral wave tip motion. Among them, 46 episodes were from normal animal myocardium without pharmacological perturbations, 50 samples were from normal animal myocardium, either treated with drugs or had chemical ablation of the subendocardium, and 12 samples were from diseased human hearts. Among the total episodes, 11 of them had obvious nonstationary spiral tip motion with a life span of 〉2 cycles and with consecutive reentrant paths distinct from each other. Four patterns were observed: (1) meandering with an inward petal flower in 2; (2) meandering with outward petals in 5; (3) irregularly concentric in 3 (core moving about a common center); and (4) drift in 1 (linear core movement). The life span of a single nonstationary spiral wave lasted no more than 7 complete cycles with a mean of 4.6±4.3, and a median of 4.5 cycles in our samples. Conclusion: (1) Patently evident nonstationary spiral waves with long life spans were uncommon in our sample of mostly normal cardiac tissues, thus making a single meandering spiral wave an unlikely major mechanism of fibrillation in normal ventricular myocardium. (2) A tendency toward four patterns of nonstationary spiral tip motion was observed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 6 (1996), S. 219-228 
    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We explore the application of a pseudo-spectral Fourier method to a set of reaction-diffusion equations and compare it with a second-order finite difference method. The prototype cubic autocatalytic reaction-diffusion model as discussed by Gray and Scott [Chem. Eng. Sci. 42, 307 (1987)] with a nonequilibrium constraint is adopted. In a spatial resolution study we find that the phase speeds of one-dimensional finite amplitude waves converge more rapidly for the spectral method than for the finite difference method. Furthermore, in two dimensions the symmetry preserving properties of the spectral method are shown to be superior to those of the finite difference method. In studies of plane/axisymmetric nonlinear waves a symmetry breaking linear instability is shown to occur and is one possible route for the formation of patterns from infinitesimal perturbations to finite amplitude waves in this set of reaction-diffusion equations. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 496-498 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An automated pressure control system is described. The components consist of a reversible, geared, ac motor, a gate valve, a Granville–Phillips Stabil-ion pressure gauge with set-points and an electronics switching unit. The reversible motor is attached to the adjustment shaft of the gate valve and the system is operated in conjunction with a diffusion pump. The orifice of the gate valve is varied so that the chamber pressure is maintained between two selected set-points fixed on the control unit of the Stabil-ion pressure gauge. The system is used to control the operating pressure in a chemical vapor deposition process. It has been found to work satisfactorily for both gas and liquid phase precursor materials. The simplicity of the system together with its low cost allows for its use in a variety of low-pressure processes. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science
    Wound repair and regeneration 4 (1996), S. 0 
    ISSN: 1524-475X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The European Renaissance was a time of enormous change and rapid progress in the arts, sciences, and medicine. A glimpse of wound care in the last phase of the European Renaissance is provided by the analysis of work by Wilhelm Fabry, the “father of German surgery,” as provided in his book De Combustionibus (“Burns”) which details his range of treatments for the burn wound, as well as his approach to the later problems of scarring and contracture. We describe some of the historic events which may have stimulated Fabry's writings, in particular, the influences passed down from the medical school of Padua which thereby advanced the cause of wound care and surgery. Finally, we briefly explore the potential of such an approach to the works of our medical forefathers.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1539-6924
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: A call for risk assessment approaches that better characterize and quantify uncertainty has been made by the scientific and regulatory community. This paper responds to that call by demonstrating a distributional approachthat draws upon human data to derive potency estimates and to identify and quantify important sources of uncertainty. The approach is rooted in the science of decision analysis and employs an influence diagram, a decision tree, probabilistic weights, and a distribution of point estimates of carcinogenic potency. Its results estimate the likelihood of different carcinogenicrisks (potencies) for a chemical under a specific scenario. For this exercise, human data on formaldehyde were employed to demonstrate the approach. Sensitivity analyses were performed to determine the relative impact of specific levels and alternatives on the potency distribution. The resulting potency estimates are compared with the results of an exercise using animal data on formaldehyde. The paper demonstrates that distributional risk assessment is readily adapted to situations in which epidemiologic data serve as the basis for potency estimates. Strengths and weaknesses of the distributional approach are discussed. Areas for further application and research are recommended.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: The estimation of health risks from exposure to a mixture of chemical carcinogens is generally based on the combination of information from several available single compound studies. The current practice of directly summing the upper bound risk estimates of individual carcinogenic components as an upper bound on the total risk of a mixture is known to be generally too conservative. Gaylor and Chen (1996, Risk Analysis) proposed a simple procedure to compute an upper bound on the total risk using only the upper confidence limits and central risk estimates of individual carcinogens. The Gaylor-Chen procedure was derived based on an underlying assumption of the normality for the distributions of individual risk estimates. In this paper we evaluated the Gaylor-Chen approach in terms of the coverage probability. The performance of the Gaylor-Chen approach in terms the coverages of the upper confidence limits on the true risks of individual carcinogens. In general, if the coverage probabilities for the individual carcinogens are all approximately equal to the nominal level, then the Gaylor-Chen approach shouldperform well. However, the Gaylor-Chen approach can be conservative or anti-conservative if some or all individual upper confidence limit estimates are conservative or anti-conservative.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Acidosis is a universal response of tissue to ischemia. In the brain, severe acidosis has been linked to worsening of cerebral infarction. However, milder acidosis can have protective effects. As part of our investigations of the therapeutic window in our neuronal tissue culture model of ischemia, we investigated the effects of acidosis during recovery from brief simulated ischemia. Ischemic conditions were simulated in dissociated cortical cultures by metabolic inhibition with potassium cyanide to block oxidative metabolism and 2-deoxyglucose to block glycolysis. Lowering the extracellular pH (pHe) to 6.2 during metabolic inhibition had no effect on injury, as measured by lactate dehydrogenase release from cultures after 24 h of recovery. Lowering the pHe during the first hour of recovery, in contrast, had profound protective effects. When the duration of metabolic inhibition was lengthened to 30 min, most of the protective effects of the NMDA receptor antagonist MK-801 were lost. However, the protective effects of acidosis were unchanged. This suggested that the protective effects of extracellular acidosis could be due to more than blockade of NMDA receptors. Intracellular acidosis might be responsible. To test this, recovery of intracellular pH (pHi) was slowed by incubation with blockers of Na+/H+ exchangers at normal pHe. The two compounds tested, dimethylamiloride and harmaline, had protective effects when present during recovery from metabolic inhibition. Measurements of pHi confirmed that the blockers slowed recovery from intracellular acidosis; more rapid pHi recovery was correlated with injury. The protective effects of acidosis could be reversed by brief incubation with the protonophore monensin, which rapidly normalized pHi. These results are the first demonstration of the protective effects of blocking Na+/H+ exchange in a model of cerebral ischemia. The protective effects of acidosis appear to arise either from suppressing pH-sensitive mechanisms of injury or from blocking sodium entry due to Na+/H+ exchange.
    Type of Medium: Electronic Resource
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