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Biomedical subjects

D Boyer

Publications and source records attributed to D Boyer.

At least 19 recordsLinked to original sources
PubMed2003

Single metallic nanoparticle imaging for protein detection in cells.

We performed a visualization of membrane proteins labeled with 10-nm gold nanoparticles in cells, using an all-optical method based on photothermal interference contrast. The high sensitivity of the method and the stability of the signals allows 3D imaging of individual nanoparticles without the drawbacks of photobleaching and blinking inherent to fluorescent markers. A simple analytical model is derived to account for the measurements of the signal amplitude and the spatial resolution. The photothermal interference contrast method provides an efficient, reproducible, and promising way to visualize low amounts of proteins in cells by optical means.

Animals↗
PubMed2001

Domain coarsening of stripe patterns close to onset.

We study domain coarsening of two-dimensional stripe patterns by numerically solving the Swift-Hohenberg model of Rayleigh-Bénard convection. Near the bifurcation threshold, the evolution of disordered configurations is dominated by grain-boundary motion through a background of largely immobile curved stripes. A numerical study of the distribution of local stripe curvatures, of the structure factor of the order parameter, and a finite size scaling analysis of the grain-boundary perimeter, suggest that the linear scale of the structure grows as a power law of time t(1/z), with z=3. We interpret theoretically the exponent z=3 from the law of grain-boundary motion.

Journal Article↗
PubMed2001

Grain-boundary motion in layered phases.

We study the motion of a grain boundary that separates two sets of mutually perpendicular rolls in Rayleigh-Bénard convection above onset. The problem is treated either analytically from the corresponding amplitude equations, or numerically by solving the Swift-Hohenberg equation. We find that if the rolls are curved by a slow transversal modulation, a net translation of the boundary follows. We show analytically that although this motion is a nonlinear effect, it occurs in a time scale much shorter than that of the linear relaxation of the curved rolls. The total distance traveled by the boundary scales as epsilon(-1/2), where epsilon is the reduced Rayleigh number. We obtain analytical expressions for the relaxation rate of the modulation and for the time-dependent traveling velocity of the boundary, and especially their dependence on wave number. The results agree well with direct numerical solutions of the Swift-Hohenberg equation. We finally discuss the implications of our results on the coarsening rate of an ensemble of differently oriented domains in which grain-boundary motion through curved rolls is the dominant coarsening mechanism.

Journal Article↗
PubMed2000

Ultrasound scattering and the study of vortex correlations in disordered flows

In an idealized way, some turbulent flows can be pictured by assemblies of many vortices characterized by a set of particle distribution functions. Ultrasound provides a useful, nonintrusive, tool to study the spatial structure of vorticity in flows. This is analogous to the use of elastic neutron scattering to determine liquid structure. We express the dispersion relation, as well as the scattering cross section, of sound waves propagating in a "liquid" of identical vortices as a function of vortex pair correlation functions. In two dimensions, formal analogies with ionic liquids are pointed out.

Journal Article↗
PubMed1999

Use of the Wisconsin Card Sorting Test in the detection of malingering in student simulator and patient samples.

We analyzed the ability of the Wisconsin Card Sorting Test to distinguish between 41 malingering and 31 normal undergraduates, and 17 probable malingering and 16 brain injured patients. A logistic regression consisting of number of categories (CAT) and failure to maintain set (FMS) distinguished malingering and normal undergraduates with 70.7% sensitivity, 87.1% specificity, and 77.8% overall classification, and distinguished patients suspected of malingering from brain injured controls with 82.4% sensitivity, 93. 3% specificity, and 87.5% overall classification.

Adult↗
PubMed1999

Critical behavior of vorticity in two-dimensional turbulence.

We point out some similarities between the statistics of high Reynolds number turbulence and critical phenomena. An analogy is developed for two-dimensional decaying flows, in particular by studying the scaling properties of the two-point vorticity correlation function within a simple phenomenological framework. The inverse of the Reynolds number is the analog of the small parameter that separates the system from criticality. It is possible to introduce a set of three critical exponents; for the correlation length, the autocorrelation function, and the so-called susceptibility, respectively. The exponents corresponding to the well-known enstrophy cascade theory of Kraichnan and Batchelor are, remarkably, the same as the Gaussian approximation exponents for spin models. The limitations of the analogy, in particular the lack of universal scaling functions, are also discussed.

Journal Article↗
PubMed1998

[Comparative study of epidemiology of spondylarthropathies in indigenous population of the Chukot peninsula and Alaska].

UNLABELLED: The paper sums up the many-year cooperative Russian-American studies of the epidemiology of spondylarthropathies in the arctic populations of the Chukot Peninsula and Alaska. AIM: Comparison of the epidemiology of spondylarthropathies in the indigenous population of the Chukot Peninsula and Alaska. MATERIALS AND METHODS: A universal design of investigation with the same diagnostic criteria was used in both countries. A total of 974 indigenous residents of the Chukot Peninsula were examined simultaneously, on the Alaska the sampling was formed as the residents applied for care. RESULTS: In both regions the study revealed 1) a high incidence of HLA-B27, reaching 40% in the Chukot Eskimos; 2) a similarly high incidence of spondylarthropathies varying from 2 to 3.4%; 3) a similar spectrum of diseases, including, primarily, ankylosing spondylarthritis and Reiter's syndrome and undifferentiated spondylarthropathies and (rarely) psoriatic arthritis. Among HLA-B27 positive adults, the incidence of spondylarthropathies in all groups is 4.2% and of ankylosing spondylarthritis 1.5%. CONCLUSION: A high incidence of spondylarthropathies, varying from 2 to 3.4%, was revealed in the Arctic populations of the Chukot Peninsula and Alaska with a high incidence of HLA-B27 antigen. Although the spectrum of detected diseases was similar in the two groups, ankylosing sponditis was more incident on the Chukot Peninsula, whereas on the Alaska reactive arthritis and nondifferentiated spondylarthropathies predominated, which can be explained by difference in the methods of examination.

Adolescent↗
PubMed1994

Blink rate: a possible measure of fatigue.

The literature on blink rate as a measure of fatigue is reviewed. The evidence of increases in blink rate as a function of time on task is compelling. However, variables other than time on task also affect blink rate. These variables range from perceptual demandingness of the task to cognitive variables. Other aspects of blinking, such as flurries of blinks, timing with respect to information-processing demands, and blink closure duration, are reviewed as additional variables sensitive to task demands and fatigue effects.

Blinking↗
PubMed1989

A clinical, histopathologic, and electron microscopic study of Pneumocystis carinii choroiditis.

We studied the clinical and histopathologic features of Pneumocystis carinii choroiditis in three patients with acquired immunodeficiency syndrome. In two cases, a provisional diagnosis of disseminated P. carinii infection was made by ophthalmologic examination. The characteristic fundus changes in this infection consisted of numerous slightly elevated, plaque-like, yellow-white lesions located in the choroid and unassociated with signs of intraocular inflammation. The diagnosis was confirmed by postmortem examination of the eyes and other organs. Histopathologically, the globes showed many choroidal infiltrates that were eosinophilic, acellular, vacuolated, and frothy. Several such infiltrates were noted within the choroidal vessels and choriocapillaries. Gomori's methenamine silver stain demonstrated many cystic and crescentic organisms. Electron microscopy disclosed thick-walled cystic organisms and large numbers of trophozoites.

Acquired Immunodeficiency Syndrome↗
PubMed1989

In vivo evaluation of hydrophobic and fibrillar microporous polyetherurethane urea graft.

Mitrathane hydrophobic and fibrillar microporous prosthesis was implanted as infrarenal arterial substitute in dogs; it was evaluated in terms of patency rates, healing characteristics and biostability. Segments of grafts were implanted in duplicate for a period of implantation of 24 h, 1 wk, 1 month and 6 month. Two control grafts from the Ontario Research Foundation were implanted: one for 1 month, the other for six month. All except the two Mitrathane grafts implanted for 6 month were patent at death. The Mitrathane grafts showed kinking at one and 6 month post-implantation. The ORF graft implanted for 1 month was found crinkled in its mid-section and the external capsule was ruptured in the graft implanted for 6 month, without crinkling. Histological studies showed fibrin deposits on the flow surface and infiltration of blood elements into the wall of the Mitrathane grafts implanted for 24 h and 1 wk. A thin internal capsule was present on the graft flow surface of both types of graft tested 1 month post-implantation; scanning electron microscopy revealed the presence of endothelial-like cells on the luminal surface, particularly in the vicinity of the anastomoses. At 6 month, the Mitrathane grafts were occluded by a thick thrombus originating from the anastomoses, while the ORF graft showed infiltration of collagen through the polyurethane fibrillar structure of the wall with an endothelial-like lining covering the flow surface in the vicinity of both anastomoses.

Animals↗
PubMed1989

In vivo evaluation of four chemically processed biological grafts implanted as infrarenal arterial substitutes in dogs.

Four chemically processed grafts implanted as arterial substitutes in dogs were evaluated as blood conduits in terms of patency rates, healing characteristics and biostability. Omniflow, Biopolymeric, Dardik-Biograft of the second generation and BIMA grafts were implanted as infrarenal aortic substitutes for 4, 24 and 48 h (short-term), 1, 2 and 4 wk (medium-term), 3 and 6 month (long-term), each type of graft being implanted for a complete series. The explanted grafts were evaluated macroscopically and processed for light and scanning electron microscopy. One Omniflow graft was occluded at 6 months and two Dardik-Biografts were thrombosed, one at 24 h and one at 1 month. All explanted grafts in the Biopolymeric series and in the BIMA were patent at the animals' death. Histological studies revealed frequent subintimal fibrosis in the Biopolymeric and Omniflow grafts. A peripheral inflammatory reaction was present in most grafts explanted. Scanning electron microscopy showed an aggravation of flow surface irregularities, after implantation of Omniflow, Biopolymeric and Dardik-Biograft, compared to virgin prostheses. These grafts presented an internal capsulae on the graft flow surface along the anastomoses. The capsulae slightly extended towards the centre of the graft after long-term implantation, (6 month) and corresponded to the pannus. Endothelial-like cells covered this pannus. The BIMA graft performed the most satisfactorily and retained its blood compatibility best, that is, the luminal surface was smooth with only minor thrombotic deposits and a thin pannus along the anastomotic lines.

Animals↗
PubMed1989

An arterial prosthesis from Argentina: the Barone Microvelour arterial graft.

The manufacture of a polyester vascular prosthesis in the southern hemisphere is a new development in the global dissemination of this maturing technology. Hence the recent introduction of the Barone Microvelour arterial graft from Argentina has highlighted the need for a comparative in vitro and in vivo study to compare its structure and performance with that of existing commercial products. Following a series of laboratory tests and implantations as a thoracoabdominal bypass in dogs, the Barone Microvelour has been identified as a strong graft constructed after the style of early weft-knitted designs. It provides an equivalent sequence and rate of healing to that of other polyester knitted grafts.

Animals↗