6,187 research outputs found
Robust non-adiabatic molecular dynamics for metals and insulators
We present a new formulation of the correlated electron-ion dynamics (CEID)
scheme, which systematically improves Ehrenfest dynamics by including quantum
fluctuations around the mean-field atomic trajectories. We show that the method
can simulate models of non-adiabatic electronic transitions, and test it
against exact integration of the time-dependent Schroedinger equation. Unlike
previous formulations of CEID, the accuracy of this scheme depends on a single
tunable parameter which sets the level of atomic fluctuations included. The
convergence to the exact dynamics by increasing the tunable parameter is
demonstrated for a model two level system. This algorithm provides a smooth
description of the non-adiabatic electronic transitions which satisfies the
kinematic constraints (energy and momentum conservation) and preserves quantum
coherence. The applicability of this algorithm to more complex atomic systems
is discussed.Comment: 36 pages, 5 figures. Accepted for publication in Journal of Chemical
Physic
Wide band frequency tracker performance and design of an all angle laser Doppler optical homodyne receiver, ground wind and wind tunnel measurements program, volume 2 Final report
Analysis and measurement of characteristics of wide band frequency trackers and design and fabrication of all angle laser Doppler velocimete
Human performance prediction in man-machine systems. Volume 1 - A technical review
Tests and test techniques for human performance prediction in man-machine systems task
New data on Austroalpine Liassic Ammonites from the Adnet Quarries and adjacent areas (Salzburg, Northern Calcareous Alps)
The biostratigraphic studies of ammonites from the Adnet quarries allow to propose a set of 11 horizons or levels for the Upper Austroalpine Late
Hettangian–Sinemurian. The originality of the faunal assemblages [e.g. Adnethiceras adnethicus (HAUER), Gleviceras doris sensu PIA] and the discontinuity
of the biostratigraphical sequence make local comparisons and correlations with NW Europe, the Middle Austroalpine and the Apennines rather
difficult. By contrast, the Pliensbachian fauna from Wetzsteingraben presents a clear faunal homogeneity with the other studied regions of the Upper
Austroalpine. Moreover, they well integrate with the Euroboreal and Tethyan standard biostratigraphical framework
Human performance prediction in man-machine systems. Part 2 - The test catalog
Human performance prediction in man machine systems - test catalog table
Swimming Efficiency of Bacterium Escherichia Coli
We use in vivo measurements of swimming bacteria in an optical trap to
determine fundamental properties of bacterial propulsion. In particular, we
determine the propulsion matrix, which relates the angular velocity of the
flagellum to the torques and forces propelling the bacterium. From the
propulsion matrix dynamical properties such as forces, torques, swimming speed
and power can be obtained from measurements of the angular velocity of the
motor. We find significant heterogeneities among different individuals even
though all bacteria started from a single colony. The propulsive efficiency,
defined as the ratio of the propulsive power output to the rotary power input
provided by the motors, is found to be 0.2%.Comment: 6 page
Neural correlates and neural computations in posterior parietal cortex during perceptual decision-making
A recent line of work has found remarkable success in relating perceptual decision-making and the spiking activity in the macaque lateral intraparietal area (LIP). In this review, we focus on questions about the neural computations in LIP that are not answered by demonstrations of neural correlates of psychological processes. We highlight three areas of limitations in our current understanding of the precise neural computations that might underlie neural correlates of decisions: (1) empirical questions not yet answered by existing data; (2) implementation issues related to how neural circuits could actually implement the mechanisms suggested by both extracellular neurophysiology and psychophysics; and (3) ecological constraints related to the use of well-controlled laboratory tasks and whether they provide an accurate window on sensorimotor computation. These issues motivate the adoption of a more general “encoding-decoding framework” that will be fruitful for more detailed contemplation of how neural computations in LIP relate to the formation of perceptual decisions
Rat Olfactory Bulb Mitral Cells Receive Sparse Glomerular Inputs
Center-surround receptive fields are a fundamental unit of brain organization. It has been proposed that olfactory bulb mitral cells exhibit this functional circuitry, with excitation from one glomerulus and inhibition from a broad field of glomeruli within reach of the lateral dendrites. We investigated this hypothesis using a combination of in vivo intrinsic imaging, single-unit recording, and a large panel of odors. Assuming a broad inhibitory field, a mitral cell would be influenced by >100 contiguous glomeruli and should respond to many odors. Instead, the observed response rate was an order of magnitude lower. A quantitative model indicates that mitral cell responses can be explained by just a handful of glomeruli. These glomeruli are spatially dispersed on the bulb and represent a broad range of odor sensitivities. We conclude that mitral cells do not have center-surround receptive fields. Instead, each mitral cell performs a specific computation combining a small and diverse set of glomerular inputs.Molecular and Cellular Biolog
Rat Olfactory Bulb Mitral Cells Receive Sparse Glomerular Inputs
Center-surround receptive fields are a fundamental unit of brain organization. It has been proposed that olfactory bulb mitral cells exhibit this functional circuitry, with excitation from one glomerulus and inhibition from a broad field of glomeruli within reach of the lateral dendrites. We investigated this hypothesis using a combination of in vivo intrinsic imaging, single-unit recording, and a large panel of odors. Assuming a broad inhibitory field, a mitral cell would be influenced by >100 contiguous glomeruli and should respond to many odors. Instead, the observed response rate was an order of magnitude lower. A quantitative model indicates that mitral cell responses can be explained by just a handful of glomeruli. These glomeruli are spatially dispersed on the bulb and represent a broad range of odor sensitivities. We conclude that mitral cells do not have center-surround receptive fields. Instead, each mitral cell performs a specific computation combining a small and diverse set of glomerular inputs.Molecular and Cellular Biolog
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