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At least 163 records · Page 9Linked to original sources
PubMed1987

Performance of an in-vivo, continuous blood-gas monitor with disposable probe.

A fluorescence-based fiber optic measurement system has been developed for monitoring pH, pCO2, and pO2 through a 20-gauge radial artery catheter without compromising capabilities for monitoring arterial pressure or for blood withdrawal. The measuring probe consists of three optical fibers to which the sensing chemistries are attached, and a thermocouple that measures temperature. The probe is designed to meet in-vivo biocompatibility requirements for a one-time use of up to 72 h. The components that are in contact with the patient's blood are nontoxic, nonhemolytic, nonthrombogenic, and sterilizable. Blood compatibility is enhanced by including covalently bound heparin. The in-vitro accuracy of the system has been tested against commercial blood-gas measurement instruments; comparison with tonometry and blood gas values gave r greater than or equal to 0.98 for all three sensors. The standard error for all sensors was within the College of American Pathologists' accuracy guidelines for measuring blood gas. Instrumental drift was minimal, indicating that system performance characteristics should not be the limiting factor in obtaining clinically useful information for up to 72 h. The response times of the sensors in animal and in-vitro studies were less than 2 min, suitable for monitoring physiological changes in blood gas values.

Animals↗
PubMed2002

Design and implementation of algorithms for focus automation in digital imaging time-lapse microscopy.

BACKGROUND: Digital time-lapse microscopy using Nomarski-DIC requires that an autofocusing system adapt to changes in cell shape, size, and position while contending with drift, noise, and hysteresis in the microscope and imager. We have designed and implemented an autofocusing system that tracks subjects under dynamic conditions and maintains focus within a threshold of discriminability. METHODS: With the use of proven and novel algorithms for autofocusing in Nomarski, we performed "virtual" experiments on recorded image stacks to simulate drift and sudden displacements and test the search algorithm response. RESULTS: We found that combining a simple [1, -1] contrast function with an adaptive "warmer-colder" focusing algorithm yields a reasonable compromise between focusing precision and noise tolerance. This method was implemented to record growth kinetics of yeast cells in single and multiple fields of view over several hours. CONCLUSIONS: We have implemented a robust digital autofocus that maintains focus on optically complex samples imaged at high resolution. The tolerance of this system of drift and vibration suggests that it is a practical system for time-lapse imaging in many biological applications.

Algorithms↗
PubMed1998

High-Resolution High-Count-Rate X-ray Spectroscopy with State-of-the-Art Silicon Detectors.

For the European X-ray multi-mirror (XMM) satellite mission and the German X-ray satellite ABRIXAS, fully depleted pn-CCDs have been fabricated, enabling high-speed low-noise position-resolving X-ray spectroscopy. The detector was designed and fabricated with a homogeneously sensitive area of 36 cm(2). At 150 K it has a noise of 4 e(-) r.m.s., with a readout time of the total focal plane array of 4 ms. The maximum count rate for single-photon counting was 10(5) counts s(-1) under flat-field conditions. In the integration mode more than 10(9) counts s(-1) can be detected at 6 keV. Its position resolution is of the order of 100 micro m. The quantum efficiency is higher than 90% from carbon K X-rays (277 eV) up to 10 keV. New cylindrical silicon drift detectors have been designed, fabricated and tested. They comprise an integrated on-chip amplifier system with continuous reset, on-chip voltage divider, electron accumulation layer stabilizer, large area, homogeneous radiation entrance window and a drain for surface-generated leakage current. At count rates as high as 2 x 10(6) counts cm(-2) s(-1), they still show excellent spectroscopic behaviour at room-temperature operation in single-photon detection mode. The energy resolution at room temperature is 220 eV at 6 keV X-ray energy and 140 eV at 253 K, being achieved with Peltier coolers. These systems were operated at synchrotron light sources (ESRF, HASYLAB and NLS) as X-ray fluorescence spectrometers in scanning electron microscopes and as ultra low noise photodiodes. The operation of a multi-channel silicon drift detector system is already foreseen at synchrotron light sources for X-ray holography experiments. All systems are fabricated in planar technology having the detector and amplifiers monolithically integrated on high-resistivity silicon.

Journal Article↗
PubMed1986

Microcomputer-based system for registration of oxygen tension in peripheral muscle.

For registration of oxygen tension fields in peripheral muscle a microcomputer based system was designed on the M6800 microprocessor. The system was designed to record the signals from a multiwire oxygen electrode, MDO, which is a multiwire electrode for measuring oxygen on the surface of an organ. The system contained patient safety isolation unit built on optocopplers and the upper frequency limit was 0.64 Hz. Collected data were corrected for drift and temperature changes during the measurement by using pre- and after calibrations and a linear compensation technique. Measure drift of the electrodes were proved to be linear and thus the drift could be compensated for. The system was tested in an experiment on pig. To study the distribution of oxygen statistically mean, standard deviation, skewness and curtosis were calculated. To see changes or differences between histograms a Kolmogorv-Smirnov test was used.

Animals↗
PubMed2003

Bird orientation: compensation for wind drift in migrating raptors is age dependent.

Despite the potentially strong effect of wind on bird orientation, our understanding of how wind drift affects migrating birds is still very limited. Using data from satellite-based radio telemetry, we analysed the effect of changing winds on the variation of the track direction of individual birds. We studied adults and juveniles of two raptor species, osprey Pandion haliaetus and honey buzzard Pernis apivorus, on autumn migration between North Europe and Africa, and demonstrate an important difference between the age categories of both species in the extent of wind drift. For juveniles, side- and following-wind components affected the rates of movement perpendicular to and along the mean direction, respectively, to a similar degree, suggesting full wind drift. By contrast, for adults the rate of crosswind displacement was significantly smaller than the effect of wind on forward movement, showing much reduced wind drift (29%). This indicates that adults have acquired a more sophisticated orientation system, permitting detection of and compensation for wind drift, than juveniles. These drift effects are likely to reduce the ability of juveniles to locate species-specific wintering areas in case of rapid climatic wind change.

Adaptation, Physiological↗
PubMed2002

Gradual reappearance of post-hibernation circadian rhythmicity correlates with numbers of vasopressin-containing neurons in the suprachiasmatic nuclei of European ground squirrels.

European ground squirrels (Spermophilus citellus) in outside enclosures show suppressed circadian rhythmicity in body temperature patterns during the first days of euthermia after hibernation. This may reflect either gradual reappearance of circadian rhythmicity following suppressed functioning of the circadian system during hibernation, or it may reflect transient days during re-entrainment of the circadian system which, during hibernation, has drifted out of phase with the environmental light-dark cycle. Here we report that animals kept under continuous dim light conditions also showed absence of circadian rhythmicity in activity and body temperature in the first 5-15 days after hibernation. After post-hibernation arrhythmicity, spontaneous circadian rhythms re-appeared gradually and increased daily body temperature range. Numbers of arginine-vasopressin immunoreactive neurons in the suprachiasmatic nuclei correlated positively with individual circadian rhythmicity and increased gradually over time after hibernation. Furthermore, circadian rhythmicity was enhanced rather than suppressed after exposure to a light-dark cycle but not after a single 1-h light pulse (1,700 lux). The results support the view that the functioning of the circadian system in the European ground squirrel is suppressed during hibernation at low temperatures and that it requires several days of euthermia to resume its summer function.

Animals↗
PubMed2004

Ecological and life history characteristics predict population genetic divergence of two salmonids in the same landscape.

Ecological and life history characteristics such as population size, dispersal pattern, and mating system mediate the influence of genetic drift and gene flow on population subdivision. Bull trout (Salvelinus confluentus) and mountain whitefish (Prosopium williamsoni) differ markedly in spawning location, population size and mating system. Based on these differences, we predicted that bull trout would have reduced genetic variation within and greater differentiation among populations compared with mountain whitefish. To test this hypothesis, we used microsatellite markers to determine patterns of genetic divergence for each species in the Clark Fork River, Montana, USA. As predicted, bull trout had a much greater proportion of genetic variation partitioned among populations than mountain whitefish. Among all sites, FST was seven times greater for bull trout (FST = 0.304 for bull trout, 0.042 for mountain whitefish. After removing genetically differentiated high mountain lake sites for each species FST, was 10 times greater for bull trout (FST = 0.176 for bull trout; FST = 0.018 for mountain whitefish). The same characteristics that affect dispersal patterns in these species also lead to predictions about the amount and scale of adaptive divergence among populations. We provide a theoretical framework that incorporates variation in ecological and life history factors, neutral divergence, and adaptive divergence to interpret how neutral and adaptive divergence might be correlates of ecological and life history factors.

Animals↗
PubMed1998

The characterization of a commercial MOSFET dosimeter system for use in diagnostic x ray.

A commercial patient dose verification system utilizing non-invasive metal oxide semiconductor field effect transistor (MOSFET) dosimeters originally designed for radiotherapy applications has been evaluated for use at diagnostic energy levels. The system features multiple dosimeters that may be used to monitor entrance or exit skin dose and intracavity doses in phantoms in real time. We have characterized both the standard MOSFET dosimeter designed for radiotherapy dose verification and a newly developed "high sensitivity" MOSFET dosimeter designed for lower dose measurements. The sensitivity, linearity, angular response, post-exposure response, and physical characteristics were evaluated. The average sensitivity (free in air, including backscatter) of the radiotherapy MOSFET dosimeters ranged from 3.55 x 10(4) mV per C kg(-1) (9.2 mV R(-1)) to 4.87 x 10(4) mV per C kg(-1) (12.6 mV R(-1)) depending on the energy of the x-ray field. The sensitivity of the "high sensitivity" MOSFET dosimeters ranged from 1.15 x 10(5) mV per C kg(-1) (29.7 mV R(-1)) to 1.38 x 10(5) mV per C kg(-1) (35.7 mV R(-1)) depending on the energy of the x-ray field. The high sensitivity dosimeters demonstrated excellent linearity at high energies (90 and 120 kVp) and acceptable linearity at lower energies (60 kVp). The angular response was significant for free-in-air exposures, as illustrated by the sensitivity differences between the two sides of the dosimeter, but was excellent for measurements within a tissue equivalent cylinder. The post-exposure drift response is a complicated but reproducible function of time. Real-time monitoring requires little if any corrections for the post-exposure drift response. The MOSFET dosimeter system brings some unique capabilities to diagnostic radiology dosimetry including small size, real-time capabilities, nondestructive measurement, good linearity, and a predictable angular response.

Health Physics↗
PubMed2003

Global culture: a noise-induced transition in finite systems.

We analyze the effect of cultural drift, modeled as noise, in Axelrod's model for the dissemination of culture. The disordered multicultural frozen configurations are found not to be stable. This general result is proven rigorously in d=1, where the dynamics is described in terms of a Lyapunov potential. In d=2, the dynamics is governed by the average relaxation time T of perturbations. Noise at a rate r or =T(-1) sustains disorder. In the thermodynamic limit, the relaxation time diverges and global polarization persists in spite of a dynamics of local convergence.

Journal Article↗
PubMed1979

Primary position vertical nystagmus: 'directional preponderance' of the pusuit system?

The essential disturbance in five patients with vertical nystagmus was an inability to generate smooth pursuit eye movements in the direction of the quick phase of their nystagmus. As the cause of this behavior, the authors suggest an asymmetric impairment of the visual input to the pursuit system. This defect causes a 'directional preponderance' of the pursuit system detectable as a continuous drift off target. The drift is interrupted by refoveating saccades, thus resulting in a vertical nystagmus.

Adult↗
PubMed1995

Microculture tetrazolium assays: a comparison between two new tetrazolium salts, XTT and MTS.

Microculture tetrazolium assays are being widely exploited to investigate the mechanisms of both cell activation and cell damage. They are colorimetric assays which are based upon the bioreduction of a tetrazolium salt to an intensely coloured formazan. We contrast the responses obtainable with two new tetrazolium salts, MTS and XTT, when used on the rat lymphoma cell line (Nb2 cells), which has been activated by human growth hormone. These tetrazolium salts, unlike the more commonly used MTT, form soluble formazans upon bioreduction by the activated cells. This has the advantage that it eliminates the error-prone solubilisation step which is required for the microculture tetrazolium assays which employ MTT. Bioreduction of XTT and MTS usually requires addition of an intermediate electron acceptor, phenazine methosulphate (PMS). We found that the XTT/PMS, but not the MTS/PMS, reagent mixture was unstable. Nucleation and crystal formation in the XTT/PMS reagent mixture, prepared in DPBS, could occur within 1-3 min. This resulted in a decline in XTT-formazan production and manifested itself in the microculture tetrazolium assay as both poor within-assay precision and serious assay drift. Several features of the system suggested that the formation of charge-transfer complexes between XTT and PMS accounted for this instability. No such instability was encountered when MTS and PMS were mixed. We demonstrate that MTS/PMS provides microculture tetrazolium assays for hGH which are free from these serious artefacts and which are uniquely precise. In conclusion we therefore advocate the use of MTS in preference to XTT for the new generation of microculture tetrazolium assays.

Animals↗
PubMed2005

Real-time nonlinear feedback control of pattern formation in (bio)chemical reaction-diffusion processes: a model study.

Theoretical and experimental studies related to manipulation of pattern formation in self-organizing reaction-diffusion processes by appropriate control stimuli become increasingly important both in chemical engineering and cellular biochemistry. In a model study, we demonstrate here exemplarily the application of an efficient nonlinear model predictive control (NMPC) algorithm to real-time optimal feedback control of pattern formation in a bacterial chemotaxis system modeled by nonlinear partial differential equations. The corresponding drift-diffusion model type is representative for many (bio)chemical systems involving nonlinear reaction dynamics and nonlinear diffusion. We show how the computed optimal feedback control strategy exploits the system inherent physical property of wave propagation to achieve desired control aims. We discuss various applications of our approach to optimal control of spatiotemporal dynamics.

Bacteria↗
PubMed2006

Demonstration of a controllable three-dimensional Brownian motor in symmetric potentials.

We demonstrate a Brownian motor, based on cold atoms in optical lattices, where isotropic random fluctuations are rectified in order to induce controlled atomic motion in arbitrary directions. In contrast to earlier demonstrations of ratchet effects, our Brownian motor operates in potentials that are spatially and temporally symmetric, but where spatiotemporal symmetry is broken by a phase shift between the potentials and asymmetric transfer rates between them. The Brownian motor is demonstrated in three dimensions and the noise-induced drift is controllable in our system.

Journal Article↗
PubMed1999

Making bureaucracy work.

What gives bureaucracy such a bad name? Is it bureaucracy in itself, or the ghosts in the system who, in a million minor drifts, contribute to turning efficiency into red-tape? Undesirable side-effects need not be confused with necessary first-level effects. There is nothing wrong with the bureaucratic system as such. Ultimately we could not work without it as it is the only known way of co-ordinating vast numbers of people to treat mass problems. However, like any tool, it is only as good as the people who use it, and its results are largely linked to the very agendas of the users. Understanding what makes bureaucracy work requires a good look at the implicit biases in the bureaucratic model, mostly seeded by its various founders and theoreticians, as well as tackling pragmatic issues of creating and applying rules--and where and when to change them.

Benchmarking↗
PubMed2000

The human circadian pacemaker can see by the dawn's early light.

The authors' previous experiments have shown that dawn simulation at low light intensities can phase advance the circadian rhythm of melatonin in humans. The aim of this study was to compare the effect of repeated dawn signals on the phase position of circadian rhythms in healthy participants kept under controlled light conditions. Nine men participated in two 9-day laboratory sessions under an LD cycle 17.5:6.5 h, < 30:0 lux, receiving 6 consecutive daily dawn (average illuminance 155 lux) or control light (0.1 lux) signals from 0600 to 0730 h (crossover, random-order design). Two modified constant routine protocols before and after the light stimuli measured salivary melatonin (dim light melatonin onset DLMOn and offset DLMOff) and rectal temperature rhythms (midrange crossing time [MRCT]). Compared with initial values, participants significantly phase delayed after 6 days under control light conditions (at least -42 min DLMOn, -54 min DLMOff, -41 min MRCT) in spite of constant bedtimes. This delay was not observed with dawn signals (+10 min DLMOn, +2 min DLMOff, 0 min MRCT). Given that the endogenous circadian period of the human circadian pacemaker is slightly longer than 24 h, the findings suggest that a naturalistic dawn signal is sufficient to forestall this natural delay drift. Zeitgeber transduction and circadian system response are hypothesized to be tuned to the time-rate-of-change of naturalistic twilight signals.

Adult↗
PubMed2006

Control panels of meat juice samples for a Salmonella enzyme-linked immunosorbent assay.

In the Danish pig production system, an indirect enzyme-linked immunosorbent assay (ELISA) for detection of antibodies in meat juice is used for Salmonella surveillance. Quality control (QC) of this ELISA was previously based on repeated testing of control serum samples. The purpose of the study reported here was to collect, characterize, and implement a panel of meat juice pools for supplemental internal QC. Muscle samples for extraction of meat juice were collected from slaughter pigs of 5 herds infected with Salmonella spp. and from 4 herds without Salmonella infection. A QC panel with 39 pools of meat juice, yielding ELISA optical density (OD) values covering the full range of expected OD values, was prepared and tested repeatedly to determine mean and SD OD values. Each pool was tested twice on each microtitration plate, and the results were used to determine limits for validity of future tests. This QC panel was included as an internal QC to be tested every month. Besides the QC panel, 2 panels containing 100 samples of meat juice with OD above the positive cut-off value and 100 samples with OD below that value were prepared for quarterly control of the diagnostic sensitivity (DSe) and the diagnostic specificity (DSp) of the ELISA. The inclusion of these panels in the QC system will provide information about drifts in DSe and DSp of the test. The procedures described here can be applied to other tests where meat juice samples are used for testing.

Animals↗
PubMed1990

Limitations of ZAF correction factors in the determination of calcium/phosphorus ratios: important forensic science considerations relevant to the analysis of bone fragments using scanning electron microscopy and energy-dispersive x-ray microanalysis.

A series of calcium phosphate standards having calcium/phosphorus (Ca/P) molar ratios of 0.50, 1.00, 1.50, and 1.67, respectively, was prepared for bulk specimen analysis using scanning electron microscopy (SEM) and energy-dispersive X-ray microanalysis (EDXA). The standards were mounted on carbon planchettes as either pure crystals or crystals embedded in epoxy resin. Ten different samples of each embedded and non-embedded standard were analyzed in a JEOL 100 CX electron microscope interfaced with a Kevex 8000 EDXA system using a lithium-drifted silicon detector and a multichannel analyzer. The Ca/P ratios were determined by calculating both net peak intensities without matrix corrections and atomic kappa-ratios using the MAGIC V computer program with ZAF correction factors for quantitative analysis. There was such extensive absorption of phosphorus X-rays in standards embedded in an epoxy matrix that the observed Ca/P ratios were statistically compatible with four different standards ranging in theoretical Ca/P ratios from 1.0 to 1.67. Although the non-embedded crystals showed a greater separation in the Ca/P ratios, both methods of preparation produced serious flaws in analysis. Direct application of the discovery of this caveat to the identification of suspected bone fragments for forensic science purposes is discussed.

Bone and Bones↗
PubMed1998

Evolution by nearly-neutral mutations.

Genetic systems are complex and interact at various levels; among amino acids or nucleotide sites, among gene products, and among regulatory regions and proteins. Patterns of synonymous and nonsynonymous substitutions of mammalian genes indicate that nonsynonymous substitutions are nearly neutral, coming from interactions among amino acids. As an interactive system, the NK model of Kauffman was analysed. This model assumes that each amino acid makes a fitness contribution that depends upon the amino acid and upon K other amino acids among the N that make the protein. Through simulations, it was found that there are numerous nearly-neutral mutations in this model, and that evolution is rapid in small populations and slow in large ones. The system moves on the rugged fitness landscape by mutation, random genetic drift and selection. Small populations have more chance to attain novel genetic systems than large ones because of larger effects of random drift, but the chance of extinction becomes greater.

Animals↗