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At least 739 records · Page 41Linked to original sources
PubMed1995

Adaptation mechanisms in spatial vision--I. Bleaches and backgrounds.

To examine how the mechanisms of bleaching and background adaptation affect spatial pattern vision, contrast detection thresholds were measured in the fovea for sinusoidal (increment-Gabor) targets, during long-term dark adaptation following full bleaches, and against steady adapting backgrounds of various intensities. The dark-adaptation curves were found to be invariant in shape over the range of spatial frequencies tested (1-15 c/deg); in other words, the amplitude sensitivity functions were invariant during dark adaptation. These results support the hypothesis that bleaching adaptation is local and multiplicative. On the other hand, the background-adaptation curves measured for different spatial frequencies were found to converge as background intensity increased; the amplitude sensitivity functions became flatter. These results reject the equivalent-background hypothesis.

Adaptation, Ocular↗
PubMed2000

[Good clinical practice in using antibiotics in the hospital. Current status in 207 public and private hospitals in 1999].

OBJECTIVES: The purpose of this study was to map activities developed in hospitals to monitor antibiotic usage and evaluate implementation of French guidelines for good clinical practice on use of antibiotics in the hospital setting. METHODS: A questionnaire was mailed to the head of the pharmacy of 300 French hospitals. The questionnaire targeted methods developed to monitor antibiotic usage (antibiotic committees, local recommendations, types of prescription and dispensing, surveillance, information and evaluation activities). RESULTS: The response rate was 69% (207 answers). A local committee supervised antibiotic usage in 49% of the hospitals (nosocomial, drug or antibiotic committees). Local recommendations existed in 120 hospitals (59%) and 42% of the hospitals had a validation process before dispensing drug in accordance with the recommendations. Antibiotic prescription was nominal in 65% of the hospitals and specific monitoring was carried out in 42% of them. Antibiotic consumption was monitored in 80% of the hospitals and resistance was monitored in 53%. Twelve percent of the hospitals used an electronic network to share information on prescription and bacteriological results. Regular internal training existed in 20% of the hospitals and evaluation methods (medical audits, impact measures) in 14%. DISCUSSION: Careful monitoring of antibiotics is implemented in most hospitals. Strict application of guidelines, definition and implementation of indicators, and evaluation methods must be improved. Implementation of better hospital monitoring of antibiotics requires: i) a local consensus to limit the antibiotics available and guidelines to adapt to local infections; ii) dissemination of guidelines and training for prescribers; iii) implementation of a dispensing system to check the validity of prescriptions according to local guidelines; iv) implementation of indicators to monitor bacterial resistance and the volume of antibiotics used.

Anti-Bacterial Agents↗
PubMed2003

Integrated environmental impact assessment: a Canadian example.

The Canadian federal process for environmental impact assessment (EIA) integrates health, social, and environmental aspects into either a screening, comprehensive study, or a review by a public panel, depending on the expected severity of potential adverse environmental effects. In this example, a Public Review Panel considered a proposed diamond mining project in Canada's northern territories, where 50% of the population are Aboriginals. The Panel specifically instructed the project proposer to determine how to incorporate traditional knowledge into the gathering of baseline information, preparing impact prediction, and planning mitigation and monitoring. Traditional knowledge is defined as the knowledge, innovations and practices of indigenous and/or local communities developed from experience gained over the centuries and adapted to local culture and environment. The mining company was asked to consider in its EIA: health, demographics, social and cultural patterns; services and infrastructure; local, regional and territorial economy; land and resource use; employment, education and training; government; and other matters. Cooperative efforts between government, industry and the community led to a project that coordinated the concerns of all interested stakeholders and the needs of present and future generations, thereby meeting the goals of sustainable development. The mitigation measures that were implemented take into account: income and social status, social support networks, education, employment and working conditions, physical environments, personal health practices and coping skills, and health services.

American Indian or Alaska Native↗
PubMed2001

Wolbachia bacteria effects after experimental interspecific transfers in terrestrial isopods.

Wolbachia bacteria are intracellular parasites, vertically transmitted from mothers to offspring through the cytoplasm of the eggs. They manipulate the reproduction of their hosts to increase in frequency in host populations. In terrestrial isopods for example, Wolbachia are responsible for the full feminization of putative males, therefore increasing the proportion of females, the sex by which they are transmitted. Vertical transmission, however, is not the only means for Wolbachia propagation. Infectious (i.e., horizontal) transmission between different host species or taxa is required to explain the fact that the phylogeny of Wolbachia does not parallel that of their hosts. The aim of this study was to investigate, by experimental transinfections, whether Wolbachia strains could be successfully transferred to a different, previously uninfected isopod host. While Wolbachia survived in all the studied recipient species, vertical transmission was efficient only in cases where donor and recipient species were closely related. Even in this case, Wolbachia strains did not always keep their ability to entirely feminize their host, a deficiency that can be link to a low bacterial density in the host tissues. In addition, Wolbachia infection was associated with a decrease in host fertility, except when the bacterial strain came from the same host population as the recipient animals. This suggest that Wolbachia could be adapted to local host populations. It therefore seems that isopod Wolbachia are highly adapted to their host and can hardly infect another species of hosts. The successful infection of a given Wolbachia strain into a new isopod host species therefore probably requires a strong selection on bacterial variants.

Animals↗
PubMedDate not supplied

Adapting national and international leg ulcer practice guidelines for local use: the Ontario Leg Ulcer Community Care Protocol.

BACKGROUND: Because of growing resources devoted to individuals requiring community care for leg ulcers, the authority responsible for home care in Ottawa, Ontario, Canada, established and evaluated a demonstration leg ulcer service. In an effort to provide current and evidence-based care, existing leg ulcer clinical practice guidelines were identified and appraised for quality and suitability to the new service. PROCESS: The Practice Guideline Evaluation and Adaptation Cycle guided development of a local protocol for leg ulcer care, which included: (1) systematically searching for practice guidelines, (2) appraising the quality of identified guidelines using a validated guideline appraisal instrument, (3) conducting a content analysis of guideline recommendations, (4) selecting recommendations to include in the local protocol, and (5) obtaining practitioner and external expert feedback on the proposed protocol. Updating the protocol followed a similar process. RESULTS: Of 19 identified leg ulcer practice guidelines, 14 were not evaluated because they did not meet the criteria (ie, treatment-focused guidelines, written in English and developed after 1998). Of the 5 remaining guidelines, 3 were fairly well developed and made similar recommendations. The level of evidence supporting specific recommendations ranged from randomized clinical trial evidence to expert opinion. By comparing the methodologic quality and content of the guidelines, the Task Force reached consensus regarding recommendations appropriate for local application. Two additional guidelines were subsequently identified and incorporated into the local protocol during a scheduled update. CONCLUSIONS: Local adaptation of international and national guidelines is feasible following facilitation of the Practice Guidelines Evaluation and Adaptation Cycle.

Community Health Services↗
PubMed1999

Physiology of perfusion as it relates to the optic nerve head.

Blood flow in the optic nerve has been demonstrated to be autoregulated, and, thus, within certain limits, to be independent of the local perfusion pressure. As in the brain, a close coupling of neuronal activity and optic nerve head blood flow has been demonstrated. A number of regulatory systems and factors participate in the regulation of vascular tone in various organs, including the optic nerve. Metabolic and myogenic mechanisms keep local perfusion constant or adapted to the local metabolic needs. Such mechanisms seem to be involved in the regulation of optic nerve blood flow as well. In contrast, neuronal blood flow regulation is of minor importance in the optic nerve. Many of the regulatory modalities induce a response of vascular smooth muscle cells through stimulation of factors produced by the endothelial cell layer. Indeed, endothelial factors are of utmost importance in the regulation of optic nerve blood flow. The facts that there is a basal formation of nitric oxide, which leads to an active dilation of the ocular vasculature, and that endothelin-1 decreases blood flow to the anterior optic nerve in a dose-dependent manner suggest that alterations in these regulatory mechanisms might be relevant for optic nerve blood flow alterations as they relate to glaucomatous optic neuropathy. It is hoped that a detailed knowledge of blood flow regulation in the optic nerve might initiate new treatment modalities in optic neuropathies that are hemodynamic and vascular in nature.

Animals↗
PubMed2006

Adaptive MAP error concealment for dispersively packetized wavelet-coded images.

In this paper, we present an adaptive maximum a posteriori (MAP) error concealment algorithm for dispersively packetized wavelet-coded images. We model the subbands of a wavelet-coded image as Markov random fields, and use the edge characteristics in a particular subband, and regularity properties of subband/wavelet samples across scales, to adapt the potential functions locally. The resulting adaptive MAP estimation gives PSNR advantages of up to 0.7 dB compared to the competing algorithms. The advantage is most evident near the edges, which helps improve the visual quality of the reconstructed images.

Algorithms↗
PubMed2006

An experimental study on pedestrian classification.

Detecting people in images is key for several important application domains in computer vision. This paper presents an in-depth experimental study on pedestrian classification; multiple feature-classifier combinations are examined with respect to their ROC performance and efficiency. We investigate global versus local and adaptive versus nonadaptive features, as exemplified by PCA coefficients, Haar wavelets, and local receptive fields (LRFs). In terms of classifiers, we consider the popular Support Vector Machines (SVMs), feed-forward neural networks, and k-nearest neighbor classifier. Experiments are performed on a large data set consisting of 4,000 pedestrian and more than 25,000 nonpedestrian (labeled) images captured in outdoor urban environments. Statistically meaningful results are obtained by analyzing performance variances caused by varying training and test sets. Furthermore, we investigate how classification performance and training sample size are correlated. Sample size is adjusted by increasing the number of manually labeled training data or by employing automatic bootstrapping or cascade techniques. Our experiments show that the novel combination of SVMs with LRF features performs best. A boosted cascade of Haar wavelets can, however, reach quite competitive results, at a fraction of computational cost. The data set used in this paper is made public, establishing a benchmark for this important problem.

Algorithms↗
PubMed2003

Adaptive approximation of the boundary surface of a neuron in confocal microscopy volumetric images.

In biomedical visualisation, the isosurface is usually used to represent (approximate) the boundary surface of the structure within biomedical volumetric images. However, in many confocal microscopy volumetric images of neurons, the grey values of the object and/or background are usually uneven. Therefore a fixed isosurface is not suitable for use in approximating the boundary surface of the neuron. A method is proposed to construct the adaptively approximating surface of the boundary surface of the neuron. In this method, the boundary surface of the neuron could be locally and adaptively approximated with different surface patches in different local regions. Consequently, the approximation accuracy has been considerably improved.

Algorithms↗
PubMed1991

Training-induced muscle adaptations: increased performance and oxygen consumption.

An isolated perfused rat hindlimb preparation was used to study the impact of local muscle adaptations induced by endurance exercise training on muscle performance and peak muscle oxygen consumption. Rats were trained for 12-15 wk by a running program (30 m/min up a 15% grade for 1 h/day 5 days/wk) shown previously to increase muscle mitochondrial enzyme activity. Sedentary (n = 11) and trained (n = 11) hindlimbs of similar size were perfused with a similar inflow (12.1 ml/min) at a similar oxygen content (18.1 ml O2/100 ml blood). Tetanic contractions (100 ms at 100 Hz) at 4, 8, 15, 30, 45, and 60/min were elicited in consecutive order. Initial tension was better maintained by muscles of trained animals at all frequencies above 4 tetani/min (P less than 0.05). Oxygen consumption (mumol.min-1.g-1) increased similarly in both groups at the lower contraction frequencies but was greater (P less than 0.05) in the trained [3.52 +/- 0.32 (SE)] than in the sedentary (2.44 +/- 0.31) group at 60 tetani/min. The peak oxygen consumption of the trained group (3.93 +/- 0.27) was 20% greater (P less than 0.05) than that of the sedentary group (3.28 +/- 0.28) when peak values for each animal, irrespective of the contraction condition, are compared. Blood flows to the contracting muscle (approximately 100 ml.min-1.g-1) and, therefore, oxygen deliveries (mumol.min-1.g-1) were not different between sedentary (7.99 +/- 0.56) and trained groups (8.35 +/- 0.61). Thus the 20% higher peak oxygen consumption was achieved by a greater oxygen extraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗
PubMed1993

Partnership for community health development.

A programme of community health development is reported from two villages in Haiti. It involves close cooperation between a district hospital, a local dispensary, and, most importantly, the inhabitants themselves. The programme is simple, financially realistic, adapted to local conditions, and linked to activities designed to meet basic requirements, such as those of food production and water supply.

Communicable Disease Control↗
PubMed2005

Sparse Bayesian learning for efficient visual tracking.

This paper extends the use of statistical learning algorithms for object localization. It has been shown that object recognizers using kernel-SVMs can be elegantly adapted to localization by means of spatial perturbation of the SVM. While this SVM applies to each frame of a video independently of other frames, the benefits of temporal fusion of data are well-known. This is addressed here by using a fully probabilistic Relevance Vector Machine (RVM) to generate observations with Gaussian distributions that can be fused over time. Rather than adapting a recognizer, we build a displacement expert which directly estimates displacement from the target region. An object detector is used in tandem, for object verification, providing the capability for automatic initialization and recovery. This approach is demonstrated in real-time tracking systems where the sparsity of the RVM means that only a fraction of CPU time is required to track at frame rate. An experimental evaluation compares this approach to the state of the art showing it to be a viable method for long-term region tracking.

Algorithms↗
PubMed1996

Local computed tomography via iterative deblurring.

X-ray computed tomography is a major imaging modality. An iterative deblurring method is adapted for local reconstruction in parallel-beam and cone-beam geometries, utilizing only x-rays passing through a region of interest. The feasibility is demonstrated in numerical simulation with noise-free and noisy projection data. The iterative deblurring method has the theoretical advantages of maintaining nonnegativity, converging monotonically and minimizing Csiszàr's I-divergence.

Algorithms↗
PubMed1985

Contrast gain control in the kitten's visual system.

We have studied the effects of contrast adaptation on cortical cells from 4- and 6-wk-old kittens (49 and 47 cells, respectively) using sine-wave grating stimuli. We wished to know if the effects of adaptation to different contrast levels are more extensive than those in adult animals. Our experiments involved adapting cells to different contrasts (3.1, 12.5, and 50%) while concurrently measuring their contrast-response functions at each of these different levels. We found qualitatively that the effects of adaptation in the kitten are similar to those we have previously documented in adult animals (19). Contrast-response functions are laterally shifted along the log-contrast axis, effectively matching the response range of the cells to prevailing contrast levels. The degree to which this occurred varied from cell to cell. The average degree to which cells showed these effects, as assessed both qualitatively and quantitatively, was greater for kittens than for adult cats, and greater for 4-wk-old kittens than for those aged 6 wk. This suggests that susceptibility to adaptation varies as a function of age. Additional studies were undertaken with the intent of localizing these adaptive effects. First, lateral geniculate cells and fibers (n = 23) were studied with our standard protocol, and second, we investigated the degree to which the effects of adaptation of cortical cells transferred interocularly.(ABSTRACT TRUNCATED AT 250 WORDS)

Acclimatization↗
PubMed1989

Thermal changes observed before and after J.-L. Etienne's journey to the North Pole. Is central nervous system temperature preserved in hypothermia?

The thermoregulatory responses of a French doctor, Jean-Louis Etienne, were examined in a standard cold test before and after his journey to the North Pole, to investigate whether general and/or local cold adaptation had occurred. The two tests were carried out in a climatic chamber for 2 h at rest (dry bulb temperature, 1 degree C; relative humidity, 40%; wind speed, 0.8 m.s-1). After his journey, Etienne showed a general hypothermic-hypometabolic adaptation, i.e. a decrease in rectal temperature (Tre) and metabolic heat production (M), and an increased local skin temperature of the extremities. Between the two tests, a change occurred in the relationship between tympanic temperature (Tty) and M. During the post-journey cold test, Tty [as representative of the central nervous system (CNS) temperature] increased while the decrease in Tre was accelerated, probably due to a redistribution of blood volume towards the CNS. Such a mechanism would protect the central core with special reference to the CNS.

Acclimatization↗
PubMed1980

Phase selectivity of spatial frequency channels.

The phase selectivity of spatial frequency channels was measured, using an adaptation technique. Subjects first adapted to a grating of a given spatial frequency; subsequent threshold measurements were made at various spatial frequencies and phase shifts. Changes in the phase relationship between the test and adaptation gratings due to eye movements were circumvented by viewing the grating through an image stabilization apparatus. Local retinal adaptation was minimized by using an adaptation grating whose contrast flickered sinusoidally as a function of time. We were able to demonstrate channel-like frequency tuning for all conditions studied, but the threshold elevations following adaptation were always independent of the phase shift between the test and adaptation gratings. Our results imply that the channels which are selectively tuned to spatial frequency are not selectively tuned to spatial phase.

Adaptation, Ocular↗
PubMed1995

[The Pasteur network].

Inspired by Louis Pasteur, the international network of Pasteur Institutes forms an original body of research institutes whose vitality has grown steadily since Albert Calmette first created the Saigon Institute in 1891. The dynamic development of the 23 Pasteur Institutes currently implanted throughout the world was made possible by three driving forces. First of all, Pasteur's own teaching--"Advance only what you can prove experimentally"--the founding principle of modern research. Secondly, the international missions headed by leading collaborators including Thuillier who worked on cholera in Egypt, Loir who initiated antirabies research in Australia and Russia, Calmette in Saigon, and others in Rio de Janeiro, Dalat, Tunis and Alger. And finally Pasteur's own personal renown. Today the Pasteur Institutes fill a vital need in their respective countries developing and producing vaccines locally, serving often as the only competent medical laboratory in developing countries and helping improve standards of hygiene adapted to local situations. Fundamental research has always been at the heart of Pasteur Institutes, coupled with essential training for technicians and researchers alike. Despite political incertitudes and turmoil, the international network of Pasteur Institutes has held its place as the leader in scientific progress for over a century, setting the place for modern international research. The Cantacuzene Institute in Bucarest and the Pasteur Institute in Saint-Petersburg which joined the network in 1991 and 1993 are the most recent examples of the fundamental principle of exchange and cooperation so important for further development.

Academies and Institutes↗