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Results for “systems drift”

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PubMed2004

Multicentre performance evaluation of the E170 module for modular analytics.

The E170 module was evaluated at 13 sites in an international multicentre study. The objective of the study was to assess the analytical performance of 49 analytes, and to collect feedback on the system's reliability and practicability. The typical, within-run coefficients of variation (CVs) for most of the quantitative assays ranged between 1 and 2% while a range of 2-4% was achieved with the infectious disease methods. Total precision CVs were found to be within the manufacturer's expected performance ranges, demonstrating good concordance of the system's measuring channels and a high reproducibility during the 2-4-week trial period. The functional sensitivity of 11 selected assays met the clinical requirements (e.g., thyreotroponin (TSH) 0.008 mU/l, troponin T 0.02 microg/l, total prostate-specific antigen (PSA) 0.03 microg/l). The E170 showed no drift during an 8-hour period and no relevant reagent carryover. Accuracy was confirmed by ring trial experiments and method comparisons vs. Elecsys 2010. The reliability and practicability of the system's hardware and software met with, or even exceeded, the evaluator's requirements. Workflow studies showed that E170 can cover the combined workload of various routine analysers in a variety of laboratory environment. Throughput and sample processing time requirements were achieved while personnel 'hands-on-time' could be reduced.

Calibration↗

PubMed2006

Convective instability induced by two-points nonlocality.

We consider diffusive nonlinear systems with nonlocal two-points coupling, generally induced by misalignment in optical feedback. We expand the stability analysis in F. Papoff and R. Zambrini [Phys. Rev. Lett. 94, 243903 (2005)] to determine convective and absolute thresholds. Nonlocality leads to different effects in comparison to well-known problems with drift, as the existence of opposite phase and group velocities for some modes and an instability region. The theoretical predictions are in agreement with numerical results in a nonlocal system with saturable nonlinearity over wide parameter regions. The knowledge of the stability diagram for any uniform state allows us to interpret the rich dynamics due to the interplay between finite size, noise, and multiple states.

Journal Article↗

PubMed1977

Population genetics in the province of Ferrara. I. Genetic distances and geographic distances.

The ABO and Rh systems of the population in 26 residential units in the province of Ferrara were studied to detect the effect of genetic drift on the differentiation of gene frequencies. Results obtained from principal components analysis and dendrograms were similar. A significant correlation between genetic and geographic distance was found. It was therefore hypothesized that in the area of Ferrara children born to parents originating from different communes were heterozygous at more loci than children born to parents originating from the same commune. It was also thought that it may be possible to use geographic distance between birthplaces of parents as an indicator of hybridity in their children.

ABO Blood-Group System↗

PubMed2005

Photosynthesis in dynamic light: systems biology of unconventional chlorophyll fluorescence transients in Synechocystis sp. PCC 6803.

Photosynthetic organisms live in a dynamic environment where light typically fluctuates around a mean level that is slowly drifting during the solar day. We show that the far-from-equilibrium photosynthesis occurring in a rapidly fluctuating light differs vastly from the stationary-flux photosynthesis attained in a constant or slowly drifting light. Photosynthetic organisms in a static or slowly drifting light can be characterized by a steady-state quantum yield of chlorophyll fluorescence emission F' that is changing linearly with small and slow variations of the incident irradiance I+DeltaI(t): F'(I+DeltaI(t)) approximately Fmean '(dF)/(dI).DeltaI(t). In Synechocystis sp. PCC 6803, the linear approximation holds for an extended interval covering largely the static irradiance range experienced by the cyanobacteria in nature. The photosynthetic dynamism and, consequently, the dynamism of the chlorophyll fluorescence emission change dramatically when exposing the organism to a fluctuating irradiance. Harmonically-modulated irradiance I+DeltaI . sin(2pit/T), T approximately 1-25 s induces perpetual, far-from-equilibrium forced oscillations that are strongly non-linear, exhibiting significant hysteresis with multiple fluorescence levels corresponding to a single instantaneous level of the incident irradiance. We propose that, in nature, the far-from-equilibrium dynamic phenomena represent a significant correction to the steady-state photosynthetic activity that is typically investigated in laboratory. Analysis of the forced oscillations by the tools of systems biology suggests that the dynamism of photosynthesis observed in fluctuating light can be explained by a delayed action of regulatory agents.

Chlorophyll↗

PubMed1997

Long-term in vitro precision of single slice peripheral Quantitative Computed Tomography (pQCT): multicenter comparison.

In a multicenter evaluation the precision and stability of single slice peripheral Quantitative Computed Tomography (pQCT) systems were assessed. Compared to central Europe the peripheral QCT device is also widely used in the Italian health care system. Phantoms were measured frequently on each machine in four pQCT scanners over a two-year period using an identical automated software program. Intrasite and intersite phantom mineral densities, expressed in units of mg/cm3, were analyzed and examined. The short and long term precision were estimated from the consistency of these measurements using the root mean square error and expressed as coefficient of variation in percent (% CV). Short term precision was good (mean intrasite coefficient of variation (CV) 0.21 +/- 0.056 standard deviation (SD)). Intersite measurements of a single phantom revealed differences between machines of the same type of not more than 2.9 mg/cm3. At four sites frequent phantom measurements revealed a mean CV of 0.18% (range 0.12-0.28). No significant changes in the regression slopes (drift of the machine versus time) were observed. We conclude that the in vitro precision and stability of the single slice pQCT systems are sufficiently high and unlikely to negatively affect the in vivo precision.

Absorptiometry, Photon↗

PubMed2003

Patterns of inbreeding depression and architecture of the load in subdivided populations.

Inbreeding depression is a general phenomenon that is due mainly to recessive deleterious mutations, the so-called mutation load. It has been much studied theoretically. However, until very recently, population structure has not been taken into account, even though it can be an important factor in the evolution of populations. Population subdivision modifies the dynamics of deleterious mutations because the outcome of selection depends on processes both within populations (selection and drift) and between populations (migration). Here, we present a general model that permits us to gain insight into patterns of inbreeding depression, heterosis, and the load in subdivided populations. We show that they can be interpreted with reference to single-population theory, using an appropriate local effective population size that integrates the effects of drift, selection, and migration. We term this the "effective population size of selection" (NS(e)). For the infinite island model, for example, it is equal to NS(e) = N1 + m/hs, where N is the local population size, m the migration rate, and h and s the dominance and selection coefficients of deleterious mutation. Our results have implications for the estimation and interpretation of inbreeding depression in subdivided populations, especially regarding conservation issues. We also discuss the possible effects of migration and subdivision on the evolution of mating systems.

Animals↗

PubMed1987

Receptive field size of human motion detection units.

Receptive field sizes of motion detector units in the human visual system were determined using a summation technique. Contrast sensitivity was measured for detecting the direction of motion of a drifting (8 Hz) sinewave grating (0.01-30.0 c/deg) multiplied by a stationary Gaussian envelope, for various widths of the Gaussian envelope. For each test spatial frequency, sensitivity increased linearly with aperture width up to a certain limit, and thereafter at a rate consistent with a model incorporating probability summation over space and between channels. The limit of linear summation designates the limit of the receptive field. Results show that the receptive field size varies with spatial frequency, from 2' arc at high spatial frequencies to as large as 7 deg at low frequencies. The change in field size was progressive. The smallest aperture width (delta W) for directional discrimination was also measured. Results show delta W to vary from 0.03 cycles at low spatial frequencies to 0.30 cycles at high frequencies.

Discrimination, Psychological↗

PubMed2005

Well characteristics influencing arsenic concentrations in ground water.

Naturally occurring arsenic contamination is common in ground water in the upper Midwest. Arsenic is most likely to be present in glacial drift and shallow bedrock wells that lie within the footprint of northwest provenance Late Wisconsinan glacial drift. Elevated arsenic is more common in domestic wells and in monitoring wells than it is in public water system wells. Arsenic contamination is also more prevalent in domestic wells with short screens set in proximity to an upper confining unit, such as glacial till. Public water system wells have distinctly different well-construction practices and well characteristics when compared to domestic and monitoring wells. Construction practices such as exploiting a thick, coarse aquifer and installing a long well screen yield good water quantity for public water system wells. Coincidentally, these construction practices also often yield low arsenic water. Coarse aquifer materials have less surface area for adsorbing arsenic, and thus less arsenic available for potential mobilization. Wells with long screens set at a distance from an upper confining unit are at lower risk of exposure to geochemical conditions conducive to arsenic mobilization via reductive mechanisms such as reductive dissolution of metal hydroxides and reductive desorption of arsenic.

Adsorption↗

PubMed1996

Validation of the Edslab dual lumen oximetry catheter for continuous monitoring of jugular bulb oxygen saturation after severe head injury.

Continuous jugular bulb venous oximetry has been validated previously for periods of up to 12 h after calibration. We assessed a new Edslab venous oximetry catheter in 15 patients with brain injury in the intensive care unit. After insertion into the jugular bulb, the catheter was calibrated using a laboratory co-oximeter. Subsequent comparisons were made at varying intervals (range 20 min to 100 h); 78 paired samples were obtained during periods of stable recordings. Estimation of haemoglobin saturation by the methods correlated well (r2 = 0.97, P < 0.0001). Mean difference (d) was small (0.28% (SD 2.35%)) and limits of agreement (d +/- (SD x 1.96)) were acceptable (-4.88% to 4.32%). There was no appreciable drift and there was negligible bias. This catheter did not suffer from problems of light intensity described with other systems, and it provided acceptable accuracy for clinical use for periods of up to and exceeding 24 h after calibration.

Brain Injuries↗

PubMedDate not supplied

Population structure and Mdh-1 locus variation in Apis mellifera ligustica.

In a wide area of the Piedmont of Italy the apiaries of Apis mellifera ligustica Spin., (the Italian bee) show homogeneous allelic frequency distributions at the Mdh-1 locus, the only one known to be polymorphic in worker bees. This can be explained by considering that an apiary is not a closed genetic system and that among apiaries gene flow is sufficient to overcome the different forces of inbreeding and random genetic drift. Nevertheless there is some evidence for partial subdivision because the pooled samples show a weak Wahlund effect. Moreover, the M allele at the same locus can be used as a diagnostic marker to distinguish A. m. ligustica populations (M absent or at very low frequencies) from A. m. mellifera French populations (monomorphic for M). The two honey-bee varieties, almost entirely separated by the Alps, hybridize with each other in very limited alpine areas. Hybrid populations show intermediate M frequencies.

Animals↗

PubMed2000

Periodic boundary motion in thermal turbulence

A free-floating plate is introduced in a Benard convection cell with an open surface. It partially covers the cell and distorts the local heat flux, inducing a coherent flow that in turn moves the plate. Remarkably, the plate can be driven to a periodic motion even under the action of a turbulent fluid. The period of the oscillation depends on the coverage ratio, and on the Rayleigh number of the convective system. The plate oscillatory behavior observed in this experiment may be related to a geological model, in which continents drift in a quasiperiodic fashion.

Journal Article↗

PubMed2001

Self-organized stable pacemakers near the onset of birhythmicity.

General amplitude equations are derived for reaction-diffusion systems near the soft onset of birhythmicity described by a supercritical pitchfork-Hopf bifurcation. Using these equations and applying singular perturbation theory, we show that stable autonomous pacemakers represent a generic kind of spatiotemporal patterns in such systems. This is verified by numerical simulations, which also show the existence of breathing and swinging pacemaker solutions. The drift of self-organized pacemakers in media with spatial parameter gradients is analytically and numerically investigated.

Journal Article↗

PubMed2004

Dynamic diffusion model for tracing the real-time potential response of polymeric membrane ion-selective electrodes.

A numerical solution for the prediction of the time-dependent potential response of a polymeric-based ion-selective electrode (ISE) is presented. The model addresses short- and middle-term potential drifts that are dependent on changes in concentration gradients in the aqueous sample and organic membrane phase. This work has important implications for the understanding of the real-time response behavior of potentiometric sensors with low detection limits and with nonclassical super-Nernstian response slopes. As a model system, the initial exposure of membranes containing the well-examined silver ionophore O,O' '-bis[2-(methylthio)ethyl]-tert-butylcalix[4]arene was monitored, and the large observed potential drifts were compared to theoretical predictions. The model is based on an approximate solution of the diffusion equation for both aqueous and organic diffusion layers using a numerical scheme (finite difference in time and finite elements in space). The model may be evaluated on the basis of experimentally available parameters and gives time-dependent information previously inaccessible with a simpler steady-state diffusion model. For the cases studied, the model gave a very good correlation with experimental data, albeit with lower than expected diffusion coefficients for the organic phase. This model may address numerous open questions regarding the response time and memory effects of low-detection-limit ion-selective electrodes and for other membrane electrodes where ion fluxes are relevant.

Diffusion↗

PubMed1975

The independence of channels in human vision selective for direction of movement.

1. Human visual selectivity for direction of movement was determined using a subthreshold summation technique. 2. The threshold contrast for detecting a drifting sinusoidal grating was found to be independent of the contrast of an added subthreshold grating which moved in the opposite direction. 3. The detection threshold for a counterphase flickering grating is twice that for a moving grating, suggesting that the visual system analyses a counterphase grating as the sum of two half-contrast gratings which move in opposite directions. 4. Threshold for a counterphase grating may be linearly reduced by the addition of subthreshold background gratings drifting in either direction. Additivity between counterphase grating and moving background is complete. 5. After adaptation to a drifting grating, the behaviour of counterphase detection threshold as a function of the contrast of a moving subthreshold background depends upon the direction of background movement. When the background moves in a direction opposite that of the adaptation stimulus, complete linear additivity results. When the background moves in the same direction as the adapting grating, counterphase threshold is constant for low background contrasts, but drops linearly for higher background contrasts. 6. The results support the hypothesis that directionally selective channels in human vision are independent contrast detectors. Counterphase gratings are detected by one or the other of these direction-specific mechanisms, whichever is momentarily the more sensitive.

Adaptation, Ocular↗

PubMed2003

The concept of drift and its application to multiphase and multibody problems.

The concept of drift is built around understanding how a rigid body moving in a straight line distorts a material sheet in an unbounded perfect fluid. As the body moves from infinity through a material sheet, which is initially perpendicular to the direction of translation of the body, the sheet is permanently distorted. Darwin showed that the 'drift' volume, D(f), formed between the distorted and undistorted sheet is equal to C(m)V, where the added-mass coefficient, C(m), characterizes the shape of the body whose volume is V. Darwin's result is important for two reasons: first, it provides a means of quantifying how dyed fluid is transported from one place to another and dispersed; second, it provides a fundamental Lagrangian coordinate system to study inhomogeneous inviscid problems. The aim of this article is to review Darwin's contribution to fluid mechanics. By drawing on recent experimental measurements of drift and the drift volume, we aim to demonstrate how Darwin's drift concept has developed and to describe its broader significance for multiphase and multibody problems.

Journal Article↗

PubMed2006

Decomposed pairwise regression analysis of genetic and geographic distances reveals a metapopulation structure of stream-dwelling Dolly Varden charr.

Isolation by distance is usually tested by the correlation of genetic and geographic distances separating all pairwise populations' combinations. However, this method can be significantly biased by only a few highly diverged populations and lose the information of individual population. To detect outlier populations and investigate the relative strengths of gene flow and genetic drift for each population, we propose a decomposed pairwise regression analysis. This analysis was applied to the well-described one-dimensional stepping-stone system of stream-dwelling Dolly Varden charr (Salvelinus malma). When genetic and geographic distances were plotted for all pairs of 17 tributary populations, the correlation was significant but weak (r(2) = 0.184). Seven outlier populations were determined based on the systematic bias of the regression residuals, followed by Akaike's information criteria. The best model, 10 populations included, showed a strong pattern of isolation by distance (r(2) = 0.758), suggesting equilibrium between gene flow and genetic drift in these populations. Each outlier population was also analysed by plotting pairwise genetic and geographic distances against the 10 nonoutlier populations, and categorized into one of the three patterns: strong genetic drift, genetic drift with a limited gene flow and a high level of gene flow. These classifications were generally consistent with a priori predictions for each population (physical barrier, population size, anthropogenic impacts). Combined the genetic analysis with field observations, Dolly Varden in this river appeared to form a mainland-island or source-sink metapopulation structure. The generality of the method will merit many types of spatial genetic analyses.

Animals↗

PubMed2005

Faraday-Michelson system for quantum cryptography.

Quantum key distribution provides unconditional security for communication. Unfortunately, current experimental schemes are not suitable for long-distance fiber transmission because of phase drift or Rayleigh backscattering. In this Letter we present a unidirectional intrinsically stable scheme that is based on Michelson-Faraday interferometers, in which ordinary mirrors are replaced with 90 degree Faraday mirrors. With the scheme, a demonstration setup was built and excellent stability of interference fringe visibility was achieved over a fiber length of 175 km. Through a 125 km long commercial communication fiber cable between Beijing and Tianjin, the key exchange was performed with a quantum bit-error rate of less than 6%, which is to our knowledge the longest reported quantum key distribution experiment under field conditions.

Journal Article↗

PubMedDate not supplied

Evaluation of an automated radioimmunoassay for serum cortisol.

The performance characteristics are reported for a serum cortisol assay using the GAMMAFLO Automated Assay System, an automated continuous-flow system for radioimmunoassay (RIA). This automated system utilizes a combination of continuous-flow methodology and column chromatography techniques. The cortisol assay studied had a standard curve range of 10.0 to 500 microgram per L. The intra-assay and inter-assay precision were 5.1 percent and 7.2 percent (RSD), respectively, for a cortisol concentration of 160 microgram per L. The automated serum cortisol results correlated (r = 0.958 and 0.933) with two established manual radioimmunoassay procedures. No drift or carryover was detectable in 200 within-assay consecutive determinations performed at a rate of 42 determinations per hour (five hours continuous operation). The automated system studied appears to offer a viable alternative to cortisol manual RIA techniques in terms of overall precision simplicity of operation, and sample throughput.

Autoanalysis↗