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At least 181 records · Page 10Linked to original sources
PubMed2004

A primary field compensation scheme for planar array magnetic induction tomography.

In biomedical magnetic induction tomography (MIT), measurement precision may be improved by incorporating some form of primary field compensation/cancellation scheme. Schemes which have been described previously include gradiometric approaches and the use of 'back-off' coils. In each of these methods, however, the primary field cancellation was achieved only for a single transmitter/receiver combination. For the purpose of imaging, it would be desirable for a fully electronically scanned MIT system to provide a complete set of measurements, all with the primary field cancelled. A single channel suitable for incorporation into an MIT system with planar-array geometry is described. The transmitter is a 6-turn coil of wire 5 cm in diameter. The receiver is a surface mount inductor, of inductance 10 microH, mounted such that, in principle, no net primary field flux threads it. The results of measurements carried out with the single channel system suggest that the signal due to the primary excitation field can be reduced on average by a factor of 298 by the sensor geometry over the operating frequency range 1-10 MHz. The standard deviation and drift of the signal with the system adjusted for maximum primary field cancellation, expressed as a percentage of the signal when the receiver coil was rotated until its axis of sensitivity lay along the primary field, were 0.0009% and 0.009%, respectively. The filter time constant used was 30 ms.

Artifacts↗
PubMed2006

Controlled multiple reversals of a ratchet effect.

A single particle confined in an asymmetric potential demonstrates an anticipated ratchet effect by drifting along the 'easy' ratchet direction when subjected to non-equilibrium fluctuations. This well-known effect can, however, be dramatically changed if the potential captures several interacting particles. Here we demonstrate that the inter-particle interactions in a chain of repelling particles captured by a ratchet potential can, in a controllable way, lead to multiple drift reversals, with the drift sign alternating from positive to negative as the number of particles per ratchet period changes from odd to even. To demonstrate experimentally the validity of this very general prediction, we performed transport measurements on a.c.-driven vortices trapped in a superconductor by an array of nanometre-scale asymmetric traps. We found that the direction of the vortex drift does undergo multiple reversals as the vortex density is increased, in excellent agreement with the model predictions. This drastic change in the drift behaviour between single- and multi-particle systems can shed some light on the different behaviour of ratchets and biomembranes in two drift regimes: diluted (single particles) and concentrated (interacting particles).

Journal Article↗
PubMed2001

Effects of population size and metapopulation dynamics on a mating-system polymorphism.

The evolutionary dynamics of neutral alleles under the Wright-Fisher model are well understood. Similarly, the effect of population turnover on neutral genetic diversity in a metapopulation has attracted recent attention in theoretical studies. Here we present the results of computer simulations of a simple model that considers the effects of finite population size and metapopulation dynamics on a mating-system polymorphism involving selfing and outcrossing morphs. The details of the model are based on empirical data from dimorphic populations of the annual plant Eichhornia paniculata, but the results are also of relevance to species with density-dependent selfing rates in general. In our model, the prior selfing rate is determined by two alleles segregating at a single diploid locus. After prior selfing occurs, some remaining ovules are selfed through competing self-fertilisation in finite populations as a result of random mating among gametes. Fitness differences between the mating-system morphs were determined by inbreeding depression and pollen discounting in a context-dependent manner. Simulation results showed evidence of frequency dependence in the action of pollen discounting and inbreeding depression in finite populations. In particular, as a result of selfing in outcrossers through random mating among gametes, selfers experienced a "fixation bias" through drift, even when the mating-system locus was selectively neutral. In a metapopulation, high colony turnover generally favoured the fixation of the outcrossing morph, because inbreeding depression reduced opportunities for colony establishment by selfers through seed dispersal. Our results thus demonstrate that population size and metapopulation processes can lead to evolutionary dynamics involving pollen and seed dispersal that are not predicted for large populations with stable demography.

Alleles↗
PubMed2000

[Heavy heat shock induces genetic variation in a polygenic system of a quantitative trait in Drosophila].

Results of two experiments dealing with positive and negative selection on the quantitative trait radius incompletus in an isogenic line of Drosophila melanogaster after heavy heat shock (HHS) are presented. Selection was not effective in the control without HHS. In experiment 1, in which offspring of HHS-exposed males lacked transposition induction, selection also was ineffective. By contrast, selection was highly effective in offspring of males that responded to HHS exposure by transposition induction. Thus, HHS, which is not mutagenic, generates genetic variation in a polygenic system of a quantitative trait via transpositions and excisions of mobile genetic elements. In experiment 2, positive and negative selection was conducted in three replicates, which showed concerted dynamics of the selected trait. This means that the trait dynamics is mainly related to the nearly deterministic process of accumulation of active polygenic alleles rather than to genetic drift. The induced variation of polygenic systems promotes rapid selection of "champion" genotypes. This variation is probably associated with "soft" modification of polygene expression by adjacent MGE copies.

Animals↗
PubMed1993

Micellar acid-base potentiometric titrations of weak acidic and/or insoluble drugs.

The effect of various surfactants [the cationics cetyl trimethyl ammonium bromide (CTAB) and cetyl pyridinium chloride (CPC), the anionic sodium dodecyl sulphate (SDS), and the nonionic polysorbate 80 (Tween 80)] on the solubility and ionization constant of some sparingly soluble weak acids of pharmaceutical interest was studied. Benzoic acid (and its 3-methyl-, 3-nitro-, and 4-tert-butyl-derivatives), acetylsalicylic acid, naproxen and iopanoic acid were chosen as model examples. Precise and accurate acid-base titrations in micellar systems were made feasible using a microcomputer-controlled titrator. The response curve, response time and potential drift of the glass electrode in the micellar systems were examined. The cationics CTAB and CPC were found to increase considerably the ionization constant of the weak acids (delta pKa ranged from -0.21 to -3.57), while the anionic SDS showed negligible effect and the nonionic Tween 80 generally decreased the ionization constants. The solubility of the acids in aqueous micellar and acidified micellar solutions was studied spectrophotometrically and it was found increased in all cases. Acetylsalicylic acid, naproxen, benzoic acid and iopanoic acid could be easily determined in raw material and some of them in pharmaceutical preparations by direct titration in CTAB-micellar system instead of using the traditional non-aqueous or back titrimetry. Precisions of 0.3-4.3% RSD and good correlation with the official tedious methods were obtained. The interference study of some excipients showed that a preliminary test should be carried out before the assay of formulations.

Acids↗
PubMed1984

Origin and evolution of heredity-metabolism system.

The role of "theoretical physics" in the elucidation of the origin of life has been advanced by Eigen's hypercycle theory on ancient protein synthesis system and by Dyson's random drift theory on the autocatalytic formation of enzymes, although these approaches from the informational side involve many problems to be resolved. On the other hand, our C4N model calls for a stronger role of physico-chemistry in the understanding of the origin of life. Plant virus and movable genes could be the fossil vestiges of the ancient protein synthetic system, where tRNA identical to mRNA identical to gene. It is pointed out that functional differentiation of proteins closely correlates with the structure of the primitive tRNAs. Possible initial forms of the primitive tRNAs used by the earliest organisms are explicitly shown, in which the above correlation is carefully taken into account. The system of the primitive genes and the primitive enzymes in the proto-cellular membrane, say the marigranule, might simulate the earliest organism.

Base Sequence↗
PubMed2001

Quasi-distributed fiber-optic strain sensor: principle and experiment.

Sensors capable of making distributed measurements allow for monitoring of the entire structure. Optical fiber sensors are especially attractive for this purpose, since they are geometrically versatile and can be readily integrated within various types of structure and material. Development and characteristics of a quasi-distributed intrinsic fiber-optic strain sensor based on white-light interferometry are described. The research presented here describes the development of a new optical fiber sensor system for measurement of structural strains based on double white-light interferometry. Individual segments of single-mode optical fibers forming a common-path interferometer are linked in series, and a scanning white-light interferometer provides for distributed sensing of strain signals from various locations in the structure. The system is configured for automatic compensation of drift due to environmental effects, i.e., temperature and vibration. Strain gauges were employed for comparison and verification of strain signals as measured by the new system. The experimental results demonstrate the linearity of the system and the capability for distributed sensing of strains.

Journal Article↗
PubMed1996

Ground-based detectability of terrestrial and Jovian extrasolar planets: observations of CM Draconis at Lick Observatory.

The detection of terrestrial-sized extrasolar planets from the ground has been thought to be virtually impossible due to atmospheric scintillation limits. However, we show that this is not the case especially selected (but nevertheless main sequence) stars, namely small eclipsing binaries. For the smallest of these systems, CM Draconis, several months to a few years of photometric observations with 1-m-class telescopes will be sufficient to detect the transits of any short-period planets of sizes > or = 1.5 Earth radii (RE), using cross-correlation analysis with moderately good photometry. Somewhat larger telescopes will be needed to extend this detectability to terrestrial planets in larger eclipsing binary systems. (We arbitrarily define "terrestrial planets" herein as those whose disc areas are closer to that of Earth's than Neptune's i.e., less than about 2.78 RE.) As a "spin-off" of such observations, we will also be able to detect the presence of Jovian-mass planets without transits using the timing of the eclipse minima. Eclipse minima will drift in time as the binary system is offset by a sufficiently massive planet (i.e., one Jupiter mass) about the binary/giant-planet barycenter, causing a periodic variation in the light travel time to the observer. We present here an outline of present observations taking place at the University of California Lick Observatory using the Crossley 0.9-m telescope in collaboration with other observatories (in South Korea, Crete, France, Canary Islands, and New York) to detect or constrain the existence of terrestrial planets around main sequence eclipsing binary star systems, starting with CM Draconis. We demonstrate the applicability of photometric data to the general detection of gas giant planets via eclipse minima timings in many other small-mass eclipsing binary systems as well.

Astronomy↗
PubMed2026

Repair and regeneration across the lifespan: an ontogenetic perspective.

The capacity for tissue repair and regeneration undergoes a profound and progressive decline across the human lifespan, representing a fundamental driver of aging and chronic disease. This review establishes a comprehensive ontogenetic framework by mapping the continuous biological transition from the flawless, scarless regenerative plasticity of embryonic development to the irreversible fibrotic scarring and organ failure characteristic of senescence. We synthesize the hierarchical collapse of reparative networks across multiple biological scales. Importantly, this ontogenetic decline should not be interpreted as a purely degenerative trajectory but rather as a dynamic systems-level reprogramming in which evolutionary trade-offs prioritize tumor suppression, immune surveillance, and reproductive fitness over long-term regenerative fidelity. Recognizing this adaptive reallocation of biological resources reframes aging not simply as failure but as a predictable recalibration of repair hierarchies. At the molecular and cellular levels, the accumulation of genomic instability, unresolvable DNA damage, and mitochondrial dysfunction gradually overwhelms intracellular quality-control mechanisms. Concurrently, epigenetic drift and chronic, low-grade systemic inflammation ("inflammaging") dismantle the stem cell niche, driving adult stem cell exhaustion and shifting wound healing away from functional tissue replacement toward maladaptive fibrosis. Furthermore, we examine divergent, organ-specific repair trajectories. By contrasting the severe regenerative restrictions of the adult central nervous system and myocardium with the persistent, yet exhaustible, resilience of the liver, we elucidate the unique intrinsic and microenvironmental barriers that impede structural and functional recovery. Finally, we evaluate the clinical paradigm shift from passive management of age-related degeneration to active restoration of tissue integrity. By integrating systemic geroscience-which addresses the global hallmarks of aging-with targeted bioengineering and in vivo epigenetic modulation, contemporary regenerative medicine seeks to recreate permissive, youthful microenvironments. Ultimately, mastering these ontogenetic principles holds unprecedented potential to reactivate endogenous repair pathways, mitigate multi-organ collapse, and significantly extend human functional healthspan.

DNA repair↗
PubMed2005

[The fate of patients with very severe and chronic mental disorders when there is no psychiatric hospital: a case study].

The Eastern Townships (Estrie) is an area of Québec which has never had a psychiatric hospital and is thus an extreme example of deinstitutionalization. How can people with the most severe mental illnesses be cared for? Does this system have harmful consequences? The authors present a case study with both qualitative and quantitative data to elucidate their questions. They found 36 patients with very severe mental illness (prevalence 12,4/100 000). This region does not send its most severely ill patients outside and generally succeeds in providing them with care and services in a network of small and medium size residential facilities. On the other hand, the authors have also been able to identify a certain drift of patients towards the correctional system ; cases with double or triple diagnosis do not easily have access to care ; through lack of an alternative, patients with potentially chronic violence often are stuck in a hospital in short stay beds (prevalence 1,6/100 000). It thus appears possible to eliminate the use of a psychiatric hospital for patients with very severe mental disorders as long as they are provided with supervised and long term care facilities (need : 10-20 places/100 000).

Adolescent↗
PubMed1999

[Study on measuring method of pulse oxygen saturation in clinical monitor].

In this paper, a measuring system of pulse oxygen saturation is presented, which is based on the Lambert-beer Principle, using the relative intensities at two wavelengths in the red and infrared ranges. In order to meet the special demand of continuous clinical physiological monitoring, two circuits and appropriate algorithms are designed, one circuit, a feedback circuit controlled by micro-controller, automatically regulates the base line of signal, another circuit is a controlled integral circuit which automatically regulates the amplitude of waveforms. As the result, the drift of base line in this system, especially the effects caused by the physiological differences of human bodies, which will deteriorate the system, have been reduced. The system is satisfactory to clinical monitoring.

Algorithms↗
PubMed2001

Responses of chub (Leuciscus cephalus) populations to chemical stress, assessed by genetic markers, DNA damage and cytochrome P4501A induction.

Indicators of effects at the population level (genetic variation using allozymes) and early indicators of pollution (EROD activity and DNA strand break formation) were analysed in chub (Leuciscus cephalus) living in weakly and heavily contaminated stations of the Rhône River watershed. The genetic erosion was mainly detected in a fish population living in a contaminated small river system, through modifications in allelic and genotypic frequencies for PGM-2 locus and could be linked to a genetic bottleneck and to the reduced gene flow from upstream unable to maintain or restore the genetic diversity. In a contaminated large river system, the genetic diversity for PGM-2 and other loci was maintained and was probably the consequence of a high gene flow from upstream, linked to a sustained drift of larvae and juveniles in the system. A convergent increase of the frequency of the 90 allele at PGM-2 was observed in two contaminated stations compared with the reference station, this trend being confirmed on a more extensive geographic scale over the Rhône River basin. A high level of EROD activity was detected in both contaminated sites but only the fish in the large river system showed a significant DNA damage level compared to the reference population. The low DNA damage level and high hepato-somatic ratio characterized the impacted population of the small river system and could be associated to a chronic high-level exposure of fish to pollutants which selected individuals exhibiting a high level of DNA damage repair. In the two contaminated systems, some genotypes at the PGM-2 and EST-2 loci showed a low level of DNA damage and/or a high EROD activity and may be considered as being tolerant to pollutants. A higher tolerance of the most heterozygous fish was also detected in the contaminated large system and confirmed that a high level of heterozygosity may be necessary for survival in such a system.

Alleles↗
PubMed1992

A new system for ambulatory pulmonary artery pressure recording.

OBJECTIVE: To develop a complete system for the measurement, recording, and analysis of ambulatory pulmonary artery pressure. DESIGN: The new system consists of a pulmonary artery catheter, an ambulatory recorder, and a desktop computer. Pulmonary artery pressure is measured by a micromanometer tipped catheter with an in vivo calibration system to allow correction for zero drift. This catheter is plugged into a small battery powered recorder. The recorder has two input channels, one for pressure and one for an event marker. The pressure wave is sampled 32 times/s, processed by an in built computer, compressed, and stored in semi-conductor memory. On completion of a recording, data is transferred from the ambulatory recorder through a serial data link to an Acorn Archimedes desktop computer on which further data processing, statistical analysis, graphics, and printouts can be obtained. RESULTS: The system has been used in 18 patients, with technically successful recording in 14, less than 15 minutes of data loss in three, and 12 hours of data loss in one. CONCLUSIONS: A new system for ambulatory pulmonary artery monitoring has been developed and used clinically with success. It may provide new perspectives on the pathophysiology of disease as it applies to everyday life.

Blood Pressure Monitors↗
PubMed1987

An electronic processor for use with a whole body plethysmograph to determine specific airways conductance.

The panting manoeuvre traces produced by a whole body plethysmograph during the measurement of specific airways conductance (sGaw) are traditionally analysed by hand. Since this technique is tedious and time consuming it is prone to error, as well as suffering from considerable inter-observer variability. We describe a new inexpensive analogue electronic processor which rapidly produces readouts of sGaw and overcomes many of the problems associated with hand analysis. The system takes as its inputs the mouth flow and plethysmograph volume outputs from a pressure-corrected flow-displacement whole body plethysmograph, but it could be adapted for use with other types of plethysmograph. Since the processor is intended mainly for use during serial measurements of sGaw it does not carry out an unnecessary correction for flowmeter resistance. Using an electronic simulator of sGaw signals the output of the processor was found to be linear to better than 2% of full scale and to be insensitive to drift on the volume signal. The system has been comprehensively evaluated using signals from both normal subjects and patients. The processor output was found to agree well with the results of hand analysis, an agreement which was comparable with that obtained from computer based systems. For the normal subjects the equal value line adequately described the relationship between the processor and hand estimates of sGaw. However, for patients the slope of the best fit line was 18% less than unity but the correlation coefficient was high: 0.95. Reproducibility was found to be better than 3%.(ABSTRACT TRUNCATED AT 250 WORDS)

Airway Resistance↗
PubMed1982

Phenotypic instability of Salmonella typhimurium tester strains: an example of a plasmid-enhanced genetic drift?

Strains derived from Salmonella typhimurium LT-2, which are used as tester strains in mutagenicity assays, show significant changes in biochemical phenotypes. The presence of plasmid pKM101 in these strains greatly increases both the frequency of these shifts as well as the spectrum of phenotypes involved. It is suggested that in plasmid-free strains these variations reflect the effects of endogeneously induced mutations which are amplified in the absence of a functional uvrB gene product. In plasmid-containing strains this genetic drift may be promoted further by the pKM101-coded error-prone DNA repair system. The observation of a plasmid-mediated genetic drift lends support to the suggestion that transposons may contribute to the carcinogenic process.

Escherichia coli↗
PubMed1977

Chimeric drift in allophenic mice.

The composition of the immune system of 33 allophenic mice of four different types [C57BL/6 in equilibrium DBA/1, C57BL/6 in equilibrium (CBA X CBA/H-T6), C57BL/6 in equilibrium (A X SJL), DBA/1 in equilibrium (CBA X CBA/H-T6)] was studied. It was found that the parental composition of the peripheral white blood cells changed significantly during a two-month interval in 11/33 or 33% of the mice studied. This phenomenon has been termed chimeric drift. The animals were sacrificed between 9 and 16 months of age, and the parental composition of the peripheral white blood cells, spleen white blood cells, and thymocytes was determined on the day of sacrifice. It was foound that the peripheral white blood cell and spleen white blood cell compositions showed a high degree of correlation. However 8/33 or 24% of the mice studied showed discordance of the spleen and thymocyte cell populations. Seven of the 8 mice which showed spleen-thymocyte discordance, had also shown evidence of chimeric drift earlier in their lives. We suggest that this is evidence that chimeric drift may have an immunological basis.

Animals↗
PubMed1999

MAS NMR, DRIFT, and FT-Raman Characterization of SiO(2)-AlPO(4)-B(2)O(3) Ternary Catalytic Systems.

This work deals with the preparation of SiO(2)-AlPO(4)-B(2)O(3) ternary systems from impregation of a SiO(2)-AlPO(4) solid previously synthesized with B(OH)(3) (0-10% B(OH)(3), by weight). Characterization of the resulting solids has been carried out from adsorption-desorption isotherms of nitrogen, DRIFT, FT-Raman, pyridine adsorption, and (1)H, (11)B, (27)Al, and (31)P MAS NMR. The textural properties are scarcely changed by the impregnation and calcination steps. Moreover, the MAS NMR experiments indicated that the components of the solids do not interact among them. The solids were tested in the dehydration-dehydrogenation of propan-2-ol, widely used to correlate catalytic activity with the surface acid-base properties of the solids. The catalytic results indicate that the effect of boron dopping is an increase in the overall acidity of the solids. Copyright 1999 Academic Press.

Journal Article↗