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At least 289 records · Page 16Linked to original sources
PubMed1993

Pyeloform-aided percutaneous litholapaxy. I. Case study.

To remove multiple calyceal stones percutaneously is not a simple task. During the act of dilating the pierced channel the stones are apt to drift away towards other parts of the renal cavitary system. For avoidance we recommend the use of Pyeloform, a bicomponent synthetic compound in which chemical reaction between the two substances produces a gel-like matter. This permits the stones partly to be embedded, partly to be fixed against the risk of displacement. Described is the effect of Pyeloform in the removal of multiple calyceal stones.

Humans↗
PubMed1980

Hazards of hospital bulk oxygen delivery systems.

Numerous problems can occur with liquid oxygen delivery systems, in part because of the complexities of such systems. These systems must comply with guidelines of the Joint Commission on Accreditation of Hospitals. During the past year, 18 major problems with the liquid oxygen delivery system have occurred at the authors' hospital. Five times, false alarms have resulted from calibration drift in line pressure sensors. Thrice, excessive depletion of the reverse supply has occurred because of pressure imbalance between the main and reserve systems. Twice, excessive depletion of the reserve supply occurred owing to failure of the vacuum seal on the reserve supply vessel. Eight other potentially serious mishaps have also been reported. These problems, which are inherent in liquid oxygen delivery systems, are for the most part preventable.

Accident Prevention↗
PubMed2005

Robustness, evolvability, and neutrality.

Biological systems, from macromolecules to whole organisms, are robust if they continue to function, survive, or reproduce when faced with mutations, environmental change, and internal noise. I focus here on biological systems that are robust to mutations and ask whether such systems are more or less evolvable, in the sense that they can acquire novel properties. The more robust a system is, the more mutations in it are neutral, that is, without phenotypic effect. I argue here that such neutral change--and thus robustness--can be a key to future evolutionary innovation, if one accepts that neutrality is not an essential feature of a mutation. That is, a once neutral mutation may cause phenotypic effects in a changed environment or genetic background. I argue that most, if not all, neutral mutations are of this sort, and that the essentialist notion of neutrality should be abandoned. This perspective reconciles two opposing views on the forces dominating organismal evolution, natural selection and random drift: neutral mutations occur and are especially abundant in robust systems, but they do not remain neutral indefinitely, and eventually become visible to natural selection, where some of them lead to evolutionary innovations.

Animals↗
PubMedDate not supplied

Response of the difference-of-Gaussians model to circular drifting-grating patches.

Forty years ago R.W. Rodieck introduced the Difference-of-Gaussians (DOG) model, and this model has been widely used by the visual neuroscience community to quantitatively account for spatial response properties of cells in the retina and lateral geniculate nucleus following visual stimulation. Circular patches of drifting gratings are now regularly used as visual stimuli when probing the early visual system, but for this stimulus type the mathematical evaluation of the DOG-model response is significantly more complicated than for moving bars, full-field drifting gratings, or circular flashing spots. Here we derive mathematical formulas for the DOG-model response to centered circular patch gratings. The response is found to be given as the difference between two summed series, where each term in the series involves the confluent hypergeometric function. This function is available in commonly used mathematical software, and the results should thus be readily applicable. Example results illustrate how a strong surround suppression in area-summation curves for iso-luminant circular spots may be reversed into a surround enhancement for circular patch gratings. They also show that the spatial-frequency response changes from band-pass to low-pass when going from the full-field grating situation to the situation where the patch covers only the receptive-field center.

Animals↗
PubMed2006

Hadamard transform ion mobility spectrometry.

Traditionally, the spectrum acquired using ion mobility spectrometry (IMS) is an average of multiple experimental cycles. Each cycle is initiated by passing a short burst of ions into a drift tube containing a homogeneous electric field. Prior to starting the subsequent cycle, all ions in the system must arrive at the detector or spectral overlap may occur. To maximize resolution, the ion pulse admitted to the drift tube is small in relation to the total scan time with the unfortunate consequence of an inherently low duty cycle (approximately 1%). Offering an improved SNR through a 50% duty cycle, the Hadamard transform (HT) applied to ion mobility spectrometry represents a fresh alternative to signal-averaged data acquisition. Initial results from measurements of amphetamine and cytochrome c samples indicate a 2-10-fold increase in SNR for the HT-IMS technique with no reduction in resolution.

Journal Article↗
PubMed2006

A dense array stimulator to generate arbitrary spatio-temporal tactile stimuli.

The generation and presentation of tactile stimuli presents a unique challenge. Unlike vision and audition, in which standard equipment such as monitors and audio systems can be used for most experiments, tactile stimuli and/or stimulators often have to be tailor-made for a given study. Here, we present a novel tactile stimulator designed to present arbitrary spatio-temporal stimuli to the skin. The stimulator consists of 400 pins, arrayed over a 1cm(2) area, each under independent computer control. The dense array allows for an unprecedented number of stimuli to be presented within an experimental session (e.g., up to 1200 stimuli per minute) and for stimuli to be generated adaptively. The stimulator can be used in a variety of modes and can deliver indented and scanned patterns as well as stimuli defined by mathematical spatio-temporal functions (e.g., drifting sinusoids). We describe the hardware and software of the system, and discuss previous and prospective applications.

Brain Mapping↗
PubMed2001

Escape time in anomalous diffusive media.

We investigate the escape behavior of systems governed by the one-dimensional nonlinear diffusion equation theta(t)rho=theta(x)[theta(x)Urho]+Dtheta(x)2rho(nu), where the potential of the drift, U(x), presents a double well and D,nu are real parameters. For systems close to the steady state, we obtain an analytical expression of the mean first-passage time, yielding a generalization of Arrhenius law. Analytical predictions are in very good agreement with numerical experiments performed through integration of the associated Ito-Langevin equation. For nu not equal to 1, important anomalies are detected in comparison to the standard Brownian case. These results are compared to those obtained numerically for initial conditions far from the steady state.

Journal Article↗
PubMed1989

Stimulation of the methylcoenzyme M reduction by uridine-5'-diphospho-sugars in cell-free extracts of Methanobacterium thermoautotrophicum (strain delta H).

The hydrogen-dependent reduction of methylcoenzyme M catalyzed by coenzyme-depleted cell-free extracts of Methanobacterium thermoautotrophicum was stimulated by micromolar concentrations of a UDP-disaccharide present in the organism. The compound was isolated and identified as UDP-1-O-alpha-D-2-acetamido-2-deoxyglucopyranose (UDPGlcpNAc) glycosidically linked to 2-acetamido-2-deoxymannopyranosyluronic acid. Maximal stimulation was observed when both the UDP-disaccharide and mercaptoheptanoylthreonine phosphate were present in the reaction mixtures. The UDP derivative isolated was not specific in its action: other UDP-sugars tested in micromolar concentrations stimulated the methylcoenzyme M reduction to the same extent. The activated sugars presumably substitute for ATP, which is usually required in much higher concentrations to activate the methylcoenzyme M reductase system.

Adenosine Triphosphate↗
PubMed2002

Self-induced slow-fast dynamics and swept bifurcation diagrams in weakly desynchronized systems.

In systems close to the state of phase synchronization, the fast timescale of oscillations interacts with the slow timescale of the phase drift. As a result, "fast" dynamics is subjected to a slow modulation, due to which an autonomous system under fixed parameter values can imitate repeated bifurcational transitions. We demonstrate the action of this general mechanism for a set of two coupled autonomous chaotic oscillators and for a chaotic system perturbed by a periodic external force. In both cases, the Poincaré sections of phase portraits resemble bifurcation diagram of a logistic mapping with time-dependent parameter.

Journal Article↗
PubMed1992

Development of buffer systems for pH control and evaluation of pH effects on fiber digestion in vitro.

An in vitro buffering system capable of pH control between pH 5.8 and 6.8 was developed to examine the effect of media pH on disappearance of NDF at various times of fermentation and to assess initially the effect of media pH on kinetics of NDF digestion. The pH conditions selected for evaluation of these buffer systems were 5.8, 6.2, and 6.8. Use of McIlvaine's solution with sodium bicarbonate was not successful because of rapid drifting of pH downward during fermentation. To evaluate the effectiveness of citric or phosphoric acids as components of phosphate-bicarbonate buffer systems, alfalfa silage and a mixture of alfalfa silage and corn grain (1:1 mixture, dry basis) were fermented for 0, 12, 24, 48, and 72 h. The pH of each flask was measured at 0, 4, 12, 24, 48, and 72 h postinoculation, and pH was readjusted with bicarbonate solution when necessary. Drifting of media pH downward was more noticeable when phosphoric acid was used to adjust the buffer pH than with citric acid. Citric acid had no adverse effects on NDF digestion compared with phosphoric acid when used to adjust a phosphate-bicarbonate buffer system. Alfalfa hay, bromegrass hay, and corn silage were incubated for 0, 12, 24, 48, 72, or 96 h at pH 5.8 or 6.8 using the phosphate-bicarbonate buffer system adjusted with citric acid. Estimation of kinetics of NDF digestion indicated that a decrease in media pH from 6.8 to 5.8 resulted in a marked reduction in NDF digestion; the largest apparent difference was extended digestion lag time.

Animal Feed↗
PubMed1994

Shading correction and calibration in bacterial fluorescence measurement by image processing system.

An image processing system with applications in bacterial (immuno-)fluorescence measurement has been developed. To reach quantitative results, correction for non-uniformities in system sensitivity, both as a function of time (calibration for drifts) and as a function of image coordinates (shading correction), is essential. Both problems can be handled simultaneously by acquiring images of a uniformly fluorescent, solid standard as a reference image. To measure bacterial fluorescence, the average fluorescence intensity of isolated areas of interest (the bacteria) is computed, and corrected using the reference images. Two shading correction methods are theoretically and experimentally compared: direct averaging in the corrected image, and (weighted and unweighted) averaging using the raw image and a separate shading image to determine the weights and correct for shading during the averaging. The latter method proved computationally 3.5-6.5 times faster on average and reduced propagation of truncation errors during computation, resulting in 40% less noise, for 8-bits/pixel images.

Bacteria↗
PubMed1989

[Six channels telemetry system for recording masticatory forces of complete denture wearers].

A six channels telemetry system for recording masticatory force of complete denture wearers has been developed. This system is consisted of three blocks, the transmission block, the receiver block and the data storage and correction block. The transmission block is embedded in a lower complete denture. System has six load sensors and a standard resistor to correct sensor data. Data from six load sensors and standard resistor as well as standard zero are multiplexed using a division multiplex communication method. The sampling frequency is 666 Hz. And the signal is transmitted by FM modulation. The carrier wave frequency is 64 MHz. Receive data are decoded using start-stop system. The wave form noise is reduced using a signal averaging technique at an integrator. The data are input into the computer with an A/D converter. In this system, the sensor data is corrected at the computer with the standard resistor data. This method could reduce the influence of battery power changes and thermal drift significantly. For the load of 10 kg or less, the total linearity of the system remained at +/- 4% of the calibrated value. The noise level is 300 g.

Denture, Complete↗
PubMed1997

Performance Bounds for Single Layer Threshold Networks when Tracking a Drifting Adversary.

This paper finds upper bounds for the generalization error of three tracking algorithms when confronted with a worst case adversary. A system identification model is used where both the target and tracking network are single layer threshold networks, with the target weights changing slowly (the drift problem). Previous work considered random unbiased drifting adversaries. This paper focuses on the analysis of a worst case drifting adversary. For a small drift rate of gamma, we find that upper bounds for the optimal conservative tracker, the perceptron tracker, and the least mean square (LMS) tracker are respectively 2gamma/cos(gammapi),2gamman/, and gamma(2n + 2.5) where n is the number of inputs. Simulation results validate the analysis and also show that the bounds are tight when gamma is small for the perceptron and LMS tracker. The effects of additive noise, correlated inputs and non-Gaussian inputs are also discussed. Copyright 1997 Elsevier Science Ltd.

Journal Article↗
PubMed1980

Convergence to genetically uniform state in stepping stone models of population genetics.

We investigate continuous time stepping stone model. Extending the models treated in population genetics, we consider the system described by the following infinite dimensional stochastic differential equation, (see text in formula) which contains the effects of random sampling drift and a kind of stochastic fluctuation in selection. We obtain a necessary and sufficient condition for the system to converge to a genetically uniform state.

Animals↗
PubMed1994

Thermal method for continuous measurement of cerebral perfusion.

A new thermal system using constant heating power for continuous measurement of cerebral perfusion is presented. It is designed and implemented for optimal perfusion sensitivity and dynamic response based on heat-transfer analysis of perfused brain tissue with thermistors on the cortical surface. Two matched thermistors are used, one to serve as a perfusion sensor and the other to compensate for the base-line temperature changes. To improve the signal-to-noise ratio of the measurement system, lock-in amplifiers are used to minimise long-term drift and low-frequency noise. Errors in the measurement caused by electrical and thermal fluctuations are tested and analysed. In vitro tests show that the measurement accuracy of temperature change is better than 10(-3) degrees C, and the temperature resolution is even greater. In vivo evaluation confirms that the system is responsive to cerebral perfusion changes associated with sudden changes in mean arterial blood pressure caused by bolus injection of norepinephrine, blood withdrawal and blood infusion. The dynamic response of the system is sufficient to detect the autoregulatory perfusion changes in response to arterial blood pressure alteration and the oscillations of cerebral blood flow.

Animals↗
PubMed1993

Random amplified polymorphic DNA markers for DNA fingerprinting and genetic variability assessment of minute parasitic wasp species (Hymenoptera: Mymaridae and Trichogrammatidae) used in biological control programs of phytophagous insects.

Biological control of insects that feed on our crops has become more practical in recent years by mass release of egg parasitoid microhymenoptera. Trichogramma species are now commercially reared and spread in commercial fields to control specific insect pests. Microhymenoptera species are, however, very small and morphologically indistinguishable within species, although strains of a given species differ in their efficiency to control specific insect pests. Traditional taxonomy is unable to differentiate microhymenoptera species at the strain level. It is becoming increasingly important to develop a reliable system to monitor genetic variations both within and between strains of commercially important microhymenoptera, to detect genetic drift occurring during several generations of multiplication, to protect patents, and to certify the lots of commercially released microhymenoptera. We have developed a system based on DNA markers to rapidly characterize individuals of five species of microhymenoptera from the genus Anaphes and Trichogramma including a new species of Anaphes not previously described. The main components of our system are a rapid and simple DNA micro-extraction method and fast DNA polymorphism analyses based on random amplified polymorphic DNA markers.

Animals↗
PubMed2006

Incorporating known sources of uncertainty to determine precautionary harvests of saltwater crocodiles.

It has been demonstrated repeatedly that the degree to which regulation operates and the magnitude of environmental variation in an exploited population will together dictate the type of sustainable harvest achievable. Yet typically, harvest models fail to incorporate uncertainty in the underlying dynamics of the target population by assuming a particular (unknown) form of endogenous control. We use a novel approach to estimate the sustainable yield of saltwater crocodile (Crocodylus porosus) populations from major river systems in the Northern Territory, Australia, as an example of a system with high uncertainty. We used multimodel inference to incorporate three levels of uncertainty in yield estimation: (1) uncertainty in the choice of the underlying model(s) used to describe population dynamics, (2) the error associated with the precision and bias of model parameter estimation, and (3) environmental fluctuation (process error). We demonstrate varying strength of evidence for density regulation (1.3-96.7%) for crocodiles among 19 river systems by applying a continuum of five dynamical models (density-independent with and without drift and three alternative density-dependent models) to time series of density estimates. Evidence for density dependence increased with the number of yearly transitions over which each river system was monitored. Deterministic proportional maximum sustainable yield (PMSY) models varied widely among river systems (0.042-0.611), and there was strong evidence for an increasing PMSY as support for density dependence rose. However, there was also a large discrepancy between PMSY values and those produced by the full stochastic simulation projection incorporating all forms of uncertainty, which can be explained by the contribution of process error to estimates of sustainable harvest. We also determined that a fixed-quota harvest strategy (up to 0.2K, where K is the carrying capacity) reduces population size much more rapidly than proportional harvest (the latter strategy requiring temporal monitoring of population size to adjust harvest quotas) and greatly inflates the risk of resource depletion. Using an iconic species recovering from recent extreme overexploitation to examine the potential for renewed sustainable harvest, we have demonstrated that incorporating major forms of uncertainty into a single quantitative framework provides a robust approach to modeling the dynamics of exploited populations.

Alligators and Crocodiles↗