PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “ensemble”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 739 records · Page 41Linked to original sources
PubMed2006

[Application of boosting-based decision tree ensemble classifiers for discrimination of thermophilic and mesophilic proteins].

In this paper, the Boosting-based decision tree ensemble classifiers were applied to discriminate thermophilic and mesophilic proteins. Three methods, namely, self-consistency test, 5-fold cross-validation and independent testing with other dataset, were used to evaluate the performance and robust of the models. Logitboost, as a novel classifier in Boosting algorithm, performed better than Adaboost. The overall accuracy of the three methods was 100%, 88.4% and 89.5%, respectively. It was demonstrated that LogitBoost performed comparably or even better than that of neural network, a very powerful classifier widely used in biological literatures. The influence of protein size on discrimination was addressed. It is anticipated that the power in predicting many bio-macromolecular attributes will be further strengthened if the Boosting and some other existing algorithms can be effectively complemented with each other.

Algorithms↗
PubMed1991

Limitations to heavy work at 21 degrees C of personnel wearing the U.S. military chemical defense ensemble.

The purpose of this study was to determine the limitations to work of personnel performing heavy work at 21 degrees C (70 degrees F) while wearing the chemical defense ensemble (CDE) worn by all branches of the U.S. military. Male volunteers (N = 17) wearing the CDE performed an arm and leg work task yielding a time-weighted energy consumption rate of 450 W, under environmental conditions of 21 degrees C and 65-70% relative humidity. Each work bout was continued until one of the following limits occurred: volitional fatigue, rectal temperature (Tre) of 39 degrees C, or calculated heat storage (S) of 140 Wh. Subjects then rested until heat stored due to this work was lost, then repeated the work-rest cycles until refusal, or inability to restart work after a rest cycle. Over a total of 36 work cycles, subjects terminated work cycles for S on only two occasions, with the remainder almost equally divided between cumulative fatigue and high Tre. Intersubject variability was high for work and rest times, S, heat loss, and sweat production. U.S. Air Force Regulation (AFR) 355-8, which provides guidance for heat stress in the form of work/rest cycles, underestimated work tolerance under these study conditions.

Adult↗
PubMedDate not supplied

[Spike transmission in statistical neuronal ensembles. IVa. Stating the problem in a diffusion approximation].

An area of tissue in the field CA3 of the Hippocampus has been selected controled by a basket cell. The functioning of the basket cell has been described by a point approximation method forthe transport equation, and that of the ensemble of pyramidal cells by a diffusion approximation one. Furthermore, the area of tissue is broken up into N2 of "cells" wherein a transition is effected from the diffusion equation of the N2 of the point equations involved. If the sizes of "cells" are commeasurable to the diffusional length of the pyramidal cell collaterals each "cells" being relatively independent generator of activity. In the latter case the fundamental interaction type is the mutual negative influence of the "cells" through the basket cell. Should the area be broken up into further, the mutual influence of the "cells" becomes noticeable and cannot be neglected. The behaviour of spatially homogenous diffusion approximation model is equivalent of the point approximation model.

Action Potentials↗
PubMed1989

[Effects of death of a single neuron on the functional organization of the neuronal ensemble in the leech].

The reaction of leech nervous system after elimination of individual mechanosensory neuron by intracellular Pronase injection were studied. In the motor neurons connected with killed cells at 14-90th days after the operation there were the changes of the resting membrane potential and amplitude of postsynaptic potentials developed by the stimulation of mechanosensory neuron. It is suggested that the leech nervous system serves as the dynamic formation depending on changes of neuronal ensemble structure.

Animals↗
PubMedDate not supplied

[Effect of nonspecific thalamic nuclei on individual ensemble-forming loci in the visual cortex].

Electric stimulation of guinea pigs' medial thalamic nuclei (MT) creates in the area 17 of the visual cortex functional groups of excited neurones, located within the same structural columns as ensembles of neurones excited by flashes of diffuse light. Together with analogous effects of the MBRF stimulation, such results indicate a convergence of different non-specific influences on separate columns of the visual cortex. MT exert their initial and mainly activating influences on the lower, efferent layers, while MBRF, according to literary data, activates afferent, middle layers of the cortex. This points to the existence in the visual cortex of separate non-specific regulation of the input on the part of the reticular formation and of the output on the part of MT.

Afferent Pathways↗
PubMed1995

Improving the ensemble average of visual evoked potentials. I. Theory of correction by spectral phase difference methods.

The considered causes of variability of visual evoked potentials (VEPs) are additive noise and time variability. The time variability can be modelled in three different ways: 1. time invariant VEP waveform and delay-time "jitter"; 2. time variant VEP waveform, due to 2a. jitter of individual components or 2b. constant VEP waveform and "wow", i.e. expansion or compression of the time scale. The wow model has not been considered so far in the literature. Correction of jitter and/or wow is based on a frequency domain method: the "spectral phase difference" method (SPD). When jitter is present the SPD method is applied in the frequency domain on the single responses, or on a subensemble of a small number of responses. For the wow a new method is proposed where the time scale is logarithmically compressed prior to the calculation of the spectrum. It is shown that the SPD method can also be applied then to estimate the compression factor yielding the wow. The single responses, or the averaged sub-ensembles, can subsequently be corrected by this factor and finally be averaged. Improvement of the precision and accuracy of estimates of both the peak latencies and the peak amplitudes, as well as a comparison between the results of the jitter and wow models, have been reported in a companion paper.

Computer Simulation↗
PubMed1995

Thermal study of anti-G ensembles aboard F-16 aircraft in hot weather.

Continuing advances in the performance of new fighter aircraft have engendered requirements for more sophisticated protective clothing and life support systems. A major goal is prevention of acceleration-induced loss of consciousness. The USAF's Advanced Technology Enhanced Design G-Ensemble (COMBAT EDGE) increases acceleration tolerance by providing positive pressure to the oxygen mask; the work of pressure breathing is reduced by adding a counter-pressure bladder over the chest. However, the addition of impermeable layers over the chest reduces the area available for evaporation of sweat. This study was designed to determine whether COMBAT EDGE (CE) was demonstrably hotter than standard summer flight clothing (ST) during F-16 sorties in hot weather. Eight male pilots served as volunteer subjects, each flying missions at 1430 and 1745 h on two consecutive days, one day with CE and the other with ST. Data were logged at 1-min intervals for rectal temperature (Tre), skin temperatures at the chest and thigh (Tch and Tth) and air temperatures outside the clothing at the same two sites (Tach and Tath). The weather was stable over the 4 d of data collection with highs of 34-36 degrees C and simultaneous dewpoints of 19-23 degrees C (relative humidity 35-45%). The mean Tach was stable at 28 degrees C in flight, while individual means for Tath ranged from 22 to 25 degrees C. The lower value and greater variability at the thigh reflect its proximity to the air conditioning vent. Despite the differences in air temperature, Tch and Tth remained in the range 34-36 degrees C throughout the flights.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Connection ensemble model of local neural circuits.

A connection ensemble model (CEM) of local neural circuits in central nervous system (CNS) is proposed in this work. Neuronal interactions are investigated at two levels, i.e. the synaptic connection between single neurons and the macro-connections between different neuronal groups. The efficacy of macro-connection is quantitatively determined by the efficacies of constituent synapses, and is asymptotically stable. This model provides a reasonable description for the functional invariance of local neural circuits with structural diversities, which is a widely observed fact in neurobiology. It is expected that the works in CEM model would enrich the current research in neural dynamics.

Animals↗
PubMed1996

Representation of spatial orientation by the intrinsic dynamics of the head-direction cell ensemble: a theory.

The head-direction (HD) cells found in the limbic system in freely mov ing rats represent the instantaneous head direction of the animal in the horizontal plane regardless of the location of the animal. The internal direction represented by these cells uses both self-motion information for inertially based updating and familiar visual landmarks for calibration. Here, a model of the dynamics of the HD cell ensemble is presented. The stability of a localized static activity profile in the network and a dynamic shift mechanism are explained naturally by synaptic weight distribution components with even and odd symmetry, respectively. Under symmetric weights or symmetric reciprocal connections, a stable activity profile close to the known directional tuning curves will emerge. By adding a slight asymmetry to the weights, the activity profile will shift continuously without disturbances to its shape, and the shift speed can be controlled accurately by the strength of the odd-weight component. The generic formulation of the shift mechanism is determined uniquely within the current theoretical framework. The attractor dynamics of the system ensures modality-independence of the internal representation and facilitates the correction for cumulative error by the putative local-view detectors. The model offers a specific one-dimensional example of a computational mechanism in which a truly world-centered representation can be derived from observer-centered sensory inputs by integrating self-motion information.

Animals↗
PubMed1996

Network analysis of positron emission tomography regional cerebral blood flow data: ensemble inhibition during episodic memory retrieval.

Two important objectives in the neuroscience of memory are (1) identification of neural pathways involved in memory processes; and (2) characterization of the pattern of interactions between these pathways. Functional neuroimaging can contribute to both of these goals. Using image subtraction analysis of regional cerebral blood flow data measured with positron emission tomography, we identified brain regions that changed activity during episodic memory retrieval (visual work recognition). Relative to a baseline reading task, decreased activity was observed in bilateral prefrontal, bilateral anterior and posterior temporal, and posterior cingulate cortices. Brain regions showing increased activity were the right prefrontal (different from deactivated regions), left anterior cingulate, and left occipital cortices, and vermis of cerebellum. We then performed a network analysis with structural equation modeling to test the hypothesis that regional decreases came about through active inhibition by regions showing increased activity during retrieval. This analysis demonstrated that the influence of activated regions on deactivated regions was more negative during retrieval than during reading, confirming the inhibition hypothesis. Such confirmation could not have been made from the subtraction analysis alone because decreases can come about, at the very least, through reduction of functional influences as well as by active inhibition. The concepts of ensemble excitation and inhibition, as defined through network analysis, are introduced. We argue that is is critical to examine the combined pattern of excitatory and inhibitory influences to fully appreciate the neural basis of episodic memory.

Analysis of Variance↗
PubMedDate not supplied

[Spike transmission in statistical neuron ensembles. III. Phase transition in a model of hippocampal field CA3].

The model consists of two types of neurons i. e. excitatory pyramidal cells and inhibitory basket ones. (the problem was formulated by Drs. O. S. Vinogradova and A. G. Bragin). The analysis of neuron activity has been carried out on the basis of "point approximation" of spikes transport equations. The graphs were obtained by computer. These graphs of the postsynaptic potentials averaged over ensemble are in good agreement with experimental data. The model observed demonstrates the phase transition over parameter characterizing the conduction of excitation between pyramidal cells. For weak pyramidal cells link there takes place the spontaneous activity regime. For strong link there were observed the epileptoid firing of neurons at 3 divided by 5 hertz and 140 divided by 240 msec phases of inhibition between bursts.

Hippocampus↗
PubMed1996

Heat strain while wearing the current Canadian or a new hot-weather French NBC protective clothing ensemble.

BACKGROUND: A new nuclear, biological and chemical (NBC) protective garment has been designed for use in hot environments. This NBC battle dress uniform (NBC-BDU) is intended to be worn over the skin or, at most, over underwear and an undershirt. It is unclear whether the documented reductions in heat strain associated with wearing this clothing configuration represent simply the removal of the combat clothing layer normally worn underneath a NBC protective overgarment or an improved heat transfer through the new NBC-BDU. HYPOTHESIS: It was hypothesized that the removal of the combat clothing layer would produce a significant reduction in heat strain. As a result, it was also hypothesized that there would be no difference in heat strain between this new NBC-BDU and the current Canadian protective overgarment when the remaining clothing was standardized. METHODS: There were 9 males who alternated 15 min of walking at 1.11 m.s-1 and 15 min of seated rest for a maximum of 4 h in a chamber set at 40 degrees C, 30% relative humidity and a wind speed less than 0.1 m.s-1 while wearing underwear, an undershirt and the current Canadian protective overgarment either with (C + C) or without (C-C) combat clothing underneath and the new NBC-BDU worn over underwear and an undershirt. RESULTS: All indices of heat strain which included tolerance time, sweat rates, sweat evaporation, Tre, Tsk, skin and garment vapor pressures, and heart rate indicated a significant improvement when the combat clothing was removed regardless of which NBC protective garment was worn. The new NBC-BDU was associated with a lower Tre after 2 h of exposure and lower skin and garment vapor pressures compared with the Canadian overgarment. Other indices of heat strain were not different between the NBC-BDU and C-C configurations. CONCLUSIONS: During light intermittent exercise when the rate of heat production is low, the removal of the combat clothing layer as part of the Canadian NBC protective ensemble is recommended to significantly reduce the heat strain.

Adult↗
PubMed1997

The physiological strain induced by a new low burden chemical protective ensemble.

The physiological responses of a group of nine subjects exercising at a metabolic rate of 510 W in a new low burden chemical protective ensemble, the Chemical/Biological Combat Suit (CBCS), have been determined under a warm, humid climatic condition, 30 degrees C and 60% relative humidity. The CBCS was significantly superior to a current NBC overgarment (MK4) in terms of induced physiological strain. Furthermore, there was no statistically significant difference between the normal combat uniform (DPCU) and the CBCS worn as a combat uniform (CS), without hood, mask and gloves, in terms of increase in rectal temperature and increase in heart rate. The major limitation on performance in the fully encapsulated CBCS was imposed by the combination of mask, permeable hood and impermeable gloves. It was concluded that there would be a significant improvement in soldier performance in the CBCS rather than in the current MK4 overgarment and that there would be no detriment to soldier performance when wearing the CS uniform in times of chemical threat.

Adult↗
PubMed1995

Crystallization of a designed peptide from a molten globule ensemble.

Backgound. The design of amino acid sequences that adopt a desired three-dimensional fold has been of keen interest over the past decade. However, the design of proteins that adopt unique conformations is still a considerable problem. Until very recently, all of the designed proteins that have been extensively characterized possess the hallmarks of the molten globular state. Molten globular intermediates have been observed in both equilibrium and kinetic protein folding/stability studies, and understanding the forces that determine compact non-native states is critical for a comprehensive understanding of proteins. This paper describes the solution and early solid state characterization of peptides that form molten globular ensembles. Results. Crystals diffracting to 3.5Å resolution have been grown of a 16-residue peptide (alpha1A) designed to form a tetramer of alpha-helices. In addition, a closely related peptide, alpha1, has previously been shown to yield crystals that diffract to 1.2Å resolution. The solution properties of these two peptides were examined to determine whether their well defined crystalline conformations were retained in solution. On the basis of an examination of their NMR spectra, sedimentation equilibria, thermal unfolding, and ANS binding, it is concluded that the peptides form alpha-helical aggregates with properties similar to those of the molten globule state. Thus, for these peptides, the process of crystallization bears many similarities to models of protein folding. Upon dissolution, the peptides rapidly assume compact molten globular states similar to the molten globule like intermediates that are formed at short times after refolding is initiated. Following a rate-determining nucleation step, the peptides crystallize into a single or a small number of conformations in a process that mimics the formation of native structure in proteins.

Journal Article↗
PubMed2026

Investigating cross-organism prediction of prokaryotic essential proteins using unsupervised language model and ensemble strategy.

Cross-organism prediction of essential proteins is a critical task for drug discovery and microbial engineering, yet the generalizability of existing machine learning models across diverse species remains a significant challenge. In this study, we propose DeepPEP, a large language model-based framework designed to reliably transfer essential protein annotations between distantly related organisms. Utilizing 66 curated prokaryotic datasets, we systematically evaluated DeepPEP's cross-organism performance under various conditions. Initial pairwise predictions revealed a correlation between performance and evolutionary distance; however, further investigation demonstrated that integrating training data from multiple organisms yields superior predictive power. In a benchmark scenario designed to simulate real-world applications, DeepPEP outperformed the state-of-the-art tool Geptop 2.0, showcasing a robust ability to identify species-specific essential proteins. Finally, a case study on novel genomes confirmed the model's practical effectiveness. Our results suggest that DeepPEP is a powerful strategy for prokaryotic essential protein prediction, and the rigorous evaluation framework established in this study provides a new benchmark for the field.

Large Language Models↗