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At least 415 records · Page 23Linked to original sources
PubMed1995

All rabbits immunized with type A influenza virions have a serum haemagglutination-inhibition antibody response biased to a single epitope in antigenic site B.

Nine rabbits were immunized with type A influenza virions and the epitope specificities of the secondary serum haemagglutination-inhibition (HI) antibody response were analysed with a panel of neutralizing monoclonal (MAb) antibody double escape mutants. Each of the latter was made by sequential selection using a MAb directed to an epitope of a discrete antigenic site, site A, site B or site D, of the haemagglutinin (HA). Thus the epitope reactivity of the escape mutants was represented as A+ B- D-, A- B+ D- and A- B- D+. The HI antibody response of all antisera was biased to the site B epitope. In 9/12 antisera, obtained from seven rabbits immunized with whole virions, the site B epitope was predominant, representing 65-82% of the total HI antibody. The restriction of HI antibody was unaffected by strain of rabbit, route of inoculation (intravenous or subcutaneous), use of Freund's adjuvant, and up to four immunizing injections. In 3/7 rabbits immunized with whole virus, there was a HI antibody response to the HC2 (site A) or HC10 (site D) epitope, but not both, of equal magnitude to the site B epitope. The HI antibody response in one of the rabbits (#40) became more biased to the site B epitope between the third and fourth immunizing doses. Two further rabbits were immunized with virions which had been partially digested with bromelain and then purified from free HA. Both of these made equal HI antibody responses to the site B epitope and the site D epitope, possibly because their remaining HA spikes were better exposed. Overall, these data demonstrate an unexpected degree of restriction in the production of biologically relevant antibody, such that some rabbits (e.g. #45) mount an HI antibody response which is essentially epitope-specific. Implications for epitope specificity of HI antibody stimulated by human influenza vaccines, and also for the generation of antigenic drift variants are discussed. The reason for the non-responsiveness of the immune system to the many other HI epitopes of the HA is not known.

Animals↗
PubMed1976

Serum and red cell enzyme variants in an Amerindian tribe: the Sirionos (Eastern Bolivia).

Blood samples from 109 Siriono (Eastern Bolivia) belonging to the Tupi-Guarani group were investigated for enzyme variants in the following systems: glucose-6-phosphate dehydrogenase, phosphogluconate dehydrogenase, adenylate kinase, phospho-glucomutase (locus 1 and 2), acid phosphatases, lactate dehydrogenase, NADH diaphorase, pseudocholinesterase (E1 and E2 locus), and serum alkaline phosphatase. The most relevant observations are: (1) A relative lack of polymorphism, a characteristic feature of the Amerindian populations studied up to now. These data are consistent with the hypothesis of a 'common ancestral background' in Indian populations whatever the degree of sociocultural and linguistic diversity, and the geographical distances. (2) Specific traits due to the frequency of alleles in some systems confer to that tribe a particular position among Amerindians. The effects of genetic drift may be postulated in order to explain the high rate of PGM and 6PGD polymorphism. Furthermore, in that small community, the disappearance of some alleles (pa gene) can plausibly be explained in terms of a balanced influence of mutational and selective pressure.

Acid Phosphatase↗
PubMed1978

Computation of the equivalent airway resistance: a comparison with routine evaluations of plethysmographic measurements.

Equivalent (effective) values of airway resistance were determined for total breaths, inspiration and expiration in spontaneously breathing patients by means of an off-line processing system. An improvement in the alveolar pressure determination was achieved by subtracting thermal pressure drifts of the pressure plethysmograph and by taking into account instantaneous values of the intrathoracic gas volume. Equivalent resistance values were compared with the results of several simulated routine evaluations. It was found that the equivalent resistance is best approximated by the graphical procedure using average pressure points at +/- 0.5 liter/sec flow levels.

Airway Resistance↗
PubMed1984

Report of a newly redesigned Peak Flow Whistle.

A redesigned Peak Flow Whistle is described. It was evaluated and compared to the Wright Peak Flow Meter (WPFM) and the Vitalograph Pulmonary Monitor (VPM) using a laboratory flow system. These devices were evaluated for accuracy at steady flows, resistance characteristics, measurement of drift and dynamic accuracy. All devices tested correlated to a significant degree for accuracy at steady flows. The resistance of the WPFM and VPM increased with higher flows, whereas the Cardboard Peak Flow Whistle (CPFW) decreased. After pulsing the CPFW did not show any drift in calibration. The dynamic accuracy of the CPFW was excellent. Thus the accuracy of the CPFW and its lower cost makes it a practical device for measuring peak flows.

Asthma↗
PubMed1993

HP, GC and PI polymorphisms in sixteen central Indian tribal populations.

HP, GC and PI polymorphisms have been typed on 16 Central Indian tribal populations with a total of 1658 individuals. The distribution of allele frequencies shows a statistically highly significant heterogeneity, which may be caused by several microevolutionary factors, such as genetic drift, social and geographic isolation. Some new variants were observed in both the GC system (GC 2Cmah) and in the PI system (PI Yori). The PI variants are more frequent and are found in most of the 16 populations under study whereas the GC variants are rather infrequent and restricted to only three populations.

Alleles↗
PubMed1996

Correction of mass spectral drift using artificial neural networks.

For pyrolysis mass spectrometry (PyMS) to be used for the routine identification of microorganisms, for quantifying determinands in biological and biotechnological systems, and in the production of useful mass spectral libraries, it is paramount that newly acquired spectra be compared to those previously collected. Neural network and other multivariate calibration models have been used to relate mass spectra to the biological features of interest. As commonly observed, however, mass spectral fingerprints showed a lack of long-term reproducibility, due to instrumental drift in the mass spectrometer; when identical materials were analyzed by PyMS at dates from 4 to 20 months apart, neural network models produced at earlier times could not be used to give accurate estimates of determinand concentrations or bacterial identities. Neural networks, however, can be used to correct for pyrolysis mass spectrometer instrumental drift itself, so that neural network or other multivariate calibration models created using previously collected data can be used to give accurate estimates of determinand concentration or the nature of bacteria (or, indeed, other materials) from newly acquired pyrolysis mass spectra. This approach is not limited solely to pyrolysis mass spectrometry but is generally applicable to any analytical tool which is prone to instrumental drift, such as IR, ESR, NMR and other spectroscopies, and gas and liquid chromatography, as well as other types of mass spectrometry.

Ampicillin↗
PubMed2003

Eu3+ uptake by calcite: preliminary results from coprecipitation experiments and observations with surface-sensitive techniques.

A lack of information in databases for contamination risk assessment about the transport behaviour of the trivalent f-orbital elements in groundwater systems where calcite is at equilibrium motivated this study of Eu(3+) uptake. The free drift technique was used to examine the effects of Eu(3+) concentration, presence of Na(+) or K(+) and temperature, as well as calcite nucleation and precipitation kinetics, on the partitioning of calcite. Changes in surface composition and morphology resulting from exposure of single crystals of Iceland spar to Eu(3+)-bearing solutions were observed with X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). First results confirm that calcite has high affinity for Eu(3+). Rates of nucleation and precipitation strongly affect the extent of uptake but the presence of Na(+) and K(+) has no effect, suggesting formation of solid solution as CaCO(3)-EuOHCO(3). Surface-sensitive techniques prove that Eu(3+) is adsorbed to calcite even when the surface is dissolving and adsorption is not accompanied by precipitation of a separate Eu(3+)-solid phase. Adsorbed Eu modifies calcite's dissolution behaviour, roughening terraces and rounding step edges, and producing surface morphology where some surface sites appear blocked. Results imply that Eu(3+) concentrations in natural calcites are limited by Eu(3+) availability rather than by a lack of ability to fit into calcite's atomic structure. This behaviour can probably be expected for other trivalent rare Earth elements (REE), actinides and fission products whose behaviour is similar to that of Eu(3+). These elements are likely to be incorporated within the calcite bulk in systems where it is precipitating and the demonstrated strong partitioning ensures some uptake even where calcite is at or under saturation.

Calcium Carbonate↗
PubMed2002

Soliton ratchetlike dynamics by ac forces with harmonic mixing.

The possibility of unidirectional motion of a kink (topological soliton) of a dissipative sine-Gordon equation in the presence of ac forces with harmonic mixing (at least biharmonic) and of zero mean, is presented. The dependence of the kink mean velocity on system parameters is investigated numerically and the results are compared with a perturbation analysis based on a point-particle representation of the soliton. We find that first order perturbative calculations lead to incomplete descriptions, due to the important role played by the soliton-phonon interaction in establishing the phenomenon. The role played by the temporal symmetry of the system in establishing soliton dc motions that resemble usual soliton ratchets, is also emphasized. In particular, we show the existence of an asymmetric internal mode on the kink profile that couples to the kink translational mode through the damping in the system. Effective soliton transport is achieved when the internal mode and the external force get phase locked. We find that for kinks driven by biharmonic drivers consisting of the superposition of a fundamental driver with its first odd harmonic, the transport arises only due to this internal mode mechanism, while for biharmonic drivers with even harmonic superposition, also a point-particle contribution to the drift velocity is present. The phenomenon is robust enough to survive the presence of thermal noise in the system and can lead to several interesting physical applications.

Journal Article↗
PubMed1980

Data acquisition and information processing in MDO oxygen electrode measurement of tissue oxygen pressure.

In 1956, CLARK presented the principle for the modern, membrane-covered, oxygen electrode, comprising the anode and the cathode within the same unit. A further development was the MDO (Mehrdraht Dortmund Oberfläche) oxygen electrode presented by LUBBERS & KESSLER during the 1960s. This electrode comprises eight separate measuring points for collecting statistical samples to calculate tissue oxygen pressure fields. In order to perform studies on humans and to enable fast presentation of measurement results, a system was developed including a PDP 11/03 D computer, which fulfils patient safety demands. The computer program included corrections for electrode drift and temperature influences, as well as statistical calculations including mean, standard deviation, skewness and kurtosis. Also included was the two-sample Kolmogorov-Smirnov test for comparison of tissue oxygen distributions. Experience from studies on humans has shown that the measurement system enables us to collect and read important patient data directly at the bedside in the intensive care ward.

Computers↗
PubMed2003

Evaluation of a new fiber-optic pressure recording system for cardiovascular measurements in mice.

We have tested a new fiber-optic pressure recording system, Samba, with a thin fiber [outer diameter (OD) = 0.25 mm] and a pressure sensor (length and OD = 0.42 mm) attached to the end. The accuracy of the system tested in vitro was good, with a coefficient of variation of 2.54% at 100 mmHg. The drift was <0.45 mmHg/h, and the temperature sensitivity was approximately 0.07 mmHg/1 degrees C between 22 and 37 degrees C. The frequency response characteristics were similar to a 1.4-Fr Millar catheter (0-200 Hz). Introduction of the Samba sensor from the right carotid artery into the left ventricle in six mice caused no drop in mean aortic pressure, whereas introduction of a 1.4-Fr Millar catheter (OD = 0.47 mm; n = 6) caused a pressure drop from 91.6 +/- 9.2 to 65.1 +/- 6.2 mmHg; P < 0.05. Thus the Samba sensor system may represent a new alternative to assess hemodynamic variables in the murine cardiovascular system.

Animals↗
PubMed2002

Capercaillie in the Alps: genetic evidence of metapopulation structure and population decline.

In the Alps, the capercaillie is distributed in a metapopulation pattern with local populations on mountain ranges separated by farmland valleys. Habitat deterioration, primarily related to human land use, resulted in population declines and range contractions became obvious. At the edge of a species' range, lower connectivity and less gene flow may render populations more susceptible to decline and extinction than in the core of the range. If this were true for the capercaillie in the Alps, edge populations should be subject to limited gene flow and should show genetic signs of a more severe population decline than core populations. To test this hypothesis, we used microsatellite DNA typing techniques. We assessed genetic variation within and among 18 local capercaillie populations across the Alps in relation to geographical distribution within the metapopulation system. All populations showed high levels of genetic variation in terms of average number of alleles, allelic richness and heterozygosity. Excess heterozygosity suggested a recent population decline, that was more pronounced in edge than core populations. We found high gene flow, but also significant differentiation among populations. Differentiation among edge populations was related to geographical distance, and appeared to be a recent process, most probably caused by reduced gene flow after population decline. In the core group, the high mountains of the central Alps seem to limit dispersal, and genetic drift was the most likely explanation for the observed differentiation among populations. We conclude that maintaining connectivity within the metapopulation system is vital for capercaillie conservation in the Alps.

Animals↗
PubMed1992

[The Spiegelberg device for epidural registration of the ICP].

The Spiegelberg device is based on air-filled balloon system and was designed for epidural ICP monitoring. Zero adjustment is done automatically with the device in situ, thus avoiding zero drift. In 14 patients with mostly severe head injury (Glasgow Coma Scale score of 8 or lower in 10 patients) and 19-84 years old monitoring was carried out during treatment in the intensive care unit. ICP values were checked by repeating functional tests of the monitoring system, by serial cranial CT, and by a study of the clinical outcomes. Four patients died. There were no technical problems or infections. Clinically reliable data were obtained in 10 patients. The ICP shown was correlated with all other parameters; it was lower than would be expected in 1, and higher in 3 patients. With six simultaneous measurements with Gaeltec ICT/b, Camino subdural or an intraventricular catheter system the values were found to correlate only in 1 case. Experimental and clinical data suggest that the Spiegelberg-monitored ICP is somewhat higher than the ICP shown by other epidural systems. Clinical trials will be continued.

Adult↗
PubMed1991

Inefficacy of moving average algorithm as principal quality control procedure on Technicon System H6000.

Bull's algorithm, in its "revisited" formulation, represents one of the main quality control (QC) procedures in several multichannel automatic hematological analyzers. Its efficacy, however, is reduced in the theoretical event that red blood cells (RBC) and hemoglobin (Hgb) undergo a concomitant analytical drift while mean corpuscular volume (MCV) remains unaffected, so that a null effect is registered on the related erythrocytic indices: mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC). This particular phenomenon has been observed on the Technicon System H6000. Routine daily work was kept in control through the use of commercial controls and fresh blood samples: a reproducible positive drift of two directly measured erythrocytic parameters (RBC and Hgb) and of the calculated hematocrit (Hct) was observed proportional to the time of continuous use of the instrument. The usefulness of Bull's QC scheme was greatly reduced: it failed to detect "out of control" situation in 38%, 15%, and 13% of cases in the monitoring of MCV, MCH, and MCHC, respectively, when compared with the traditional 2 SD limits on QC samples.

Algorithms↗
PubMed2006

Multi-institutional clinical experience with the Calypso System in localization and continuous, real-time monitoring of the prostate gland during external radiotherapy.

PURPOSE: To report the clinical experience with an electromagnetic treatment target positioning and continuous monitoring system in patients with localized prostate cancer receiving external beam radiotherapy. METHODS AND MATERIALS: The Calypso System is a target positioning device that continuously monitors the location of three implanted electromagnetic transponders at a rate of 10 Hz. The system was used at five centers to position 41 patients over a full course of therapy. Electromagnetic positioning was compared to setup using skin marks and to stereoscopic X-ray localization of the transponders. Continuous monitoring was performed in 35 patients. RESULTS: The difference between skin mark vs. the Calypso System alignment was found to be >5 mm in vector length in more than 75% of fractions. Comparisons between the Calypso System and X-ray localization showed good agreement. Qualitatively, the continuous motion was unpredictable and varied from persistent drift to transient rapid movements. Displacements > or =3 and > or =5 mm for cumulative durations of at least 30 s were observed during 41% and 15% of sessions. In individual patients, the number of fractions with displacements > or =3 mm ranged from 3% to 87%; whereas the number of fractions with displacements > or =5 mm ranged from 0% to 56%. CONCLUSION: The Calypso System is a clinically efficient and objective localization method for positioning prostate patients undergoing radiotherapy. Initial treatment setup can be performed rapidly, accurately, and objectively before radiation delivery. The extent and frequency of prostate motion during radiotherapy delivery can be easily monitored and used for motion management.

Aged↗
PubMed1986

What is psychophysically perfect image stabilization? Do perfectly stabilized images always disappear?

High-contrast luminance gratings stabilized on the retina with a Purkinje image eyetracker do not disappear completely. This could be due to small errors of stabilization, or the visual system could include mechanisms capable of responding to temporally constant images. We examined the visual system's sensitivity to small movements of gratings. We (1) replicated previous measurements of contrast sensitivity for gratings with controlled retinal-drift velocities, (2) developed a method for calculating sensitivity to small oscillations of gratings using thresholds for flickering stabilized gratings, and (3) examined the calculations empirically. We calculated that movements of only 8 sec of arc peak to peak produce detectable temporal changes. Since existent stabilization systems cannot eliminate movements this small, residual stabilized-grating detectability does not require detectors sensitive to temporally constant images.

Humans↗
PubMed2002

Feasibility study of a fiber-optic system for invasive blood pressure measurements.

A comparative study was conducted to evaluate the feasibility of a fiber-optic sensor in invasive blood pressure measurements. Static and wide-bandwidth stimuli were offered to the fiber-optic, Millar, Baxter, and Sentron devices to measure static transfer function and transient response. Animal experiments focused on offset drift, dynamic accuracy, and electromagnetic sensitivity. Compared to the Millar, Sentron, and Baxter devices, the fiber-optic sensor had a near-identical static transfer function. Gain and offset errors were < 3.4% and < 0.25%, respectively. Hysteresis nonlinearity was < 0.1%. The dynamic accuracy of the fiber-optic system matched that of the Millar and Sentron systems. Time delay was < 1 msec. Maximum rate of change was > 30,000 mm Hg/sec and bandwidth was 0-150 Hz minimum. Offset drift was 0.6 +/- 0.03 mm Hg. Application of diathermy highlighted the fiber-optic sensor's excellent electromagnetic disturbance rejection. The fiber-optic system appears to be a reliable, high-fidelity pressure monitor in demanding clinical environments.

Animals↗
PubMed2003

Survival and extinction in cyclic and neutral three-species systems.

We study the ABC model ( A + B mapsto 2 B, B + C mapsto 2 C, C + A mapsto 2 A), and its counterpart: the three-component neutral drift model ( A + B mapsto 2 A or 2 B, B + C mapsto 2 B or 2 C, C + A mapsto 2 C or 2 A.) In the former case, the mean-field approximation exhibits cyclic behaviour with an amplitude determined by the initial condition. When stochastic phenomena are taken into account the amplitude of oscillations will drift and eventually one and then two of the three species will become extinct. The second model remains stationary for all initial conditions in the mean-field approximation, and drifts when stochastic phenomena are considered. We analyzed the distribution of first extinction times of both models by simulations of the master equation, and from the point of view of the Fokker-Planck equation. Survival probability vs. time plots suggest an exponential decay. For the neutral model the extinction rate is inversely proportional to the system size, while the cyclic model exhibits anomalous behaviour for small system sizes. In the large system size limit the extinction times for both models will be the same. This result is compatible with the smallest eigenvalue obtained from the numerical solution of the Fokker-Planck equation. We also studied the behaviour of the probability distribution. The exponential decay is found to be robust against certain changes, such as the three reactions having different rates.

Journal Article↗
PubMed1995

Gaussian models for degradation processes-Part I: Methods for the analysis of biomarker data.

We present two stochastic models that describe the relationship between biomarker process values at random time points, event times, and a vector of covariates. In both models the biomarker processes are degradation processes that represent the decay of systems over time. In the first model the biomarker process is a Wiener process whose drift is a function of the covariate vector. In the second model the biomarker process is taken to be the difference between a stationary Gaussian process and a time drift whose drift parameter is a function of the covariates. For both models we present statistical methods for estimation of the regression coefficients. The first model is useful for predicting the residual time from study entry to the time a critical boundary is reached while the second model is useful for predicting the latency time from the infection until the time the presence of the infection is detected. We present our methods principally in the context of conducting inference in a population of HIV infected individuals.

Biomarkers↗