2,645 research outputs found
Dynamic Moment Analysis of the Extracellular Electric Field of a Biologically Realistic Spiking Neuron
Based upon the membrane currents generated by an action potential in a
biologically realistic model of a pyramidal, hippocampal cell within rat CA1,
we perform a moment expansion of the extracellular field potential. We
decompose the potential into both inverse and classical moments and show that
this method is a rapid and efficient way to calculate the extracellular field
both near and far from the cell body. The action potential gives rise to a
large quadrupole moment that contributes to the extracellular field up to
distances of almost 1 cm. This method will serve as a starting point in
connecting the microscopic generation of electric fields at the level of
neurons to macroscopic observables such as the local field potential
Bulk Aluminum at High Pressure: A First-Principles Study
The behavior of metals at high pressure is of great importance to the fields
of shock physics, geophysics, astrophysics, and nuclear materials. In order to
further understand the properties of metals at high pressures we studied the
equation of state of aluminum using first-principles techniques up to 2500 GPa,
pressures within reach of the planned L.L.N.L. National Ignition Facility. Our
simulations use density-functional theory and density-functional perturbation
theory in the generalized gradient approximation at 0K. We found core overlaps
to become relevant beyond pressures of 1200 GPa. The equations of state for
three phases (fcc, bcc, and hcp) were calculated predicting the fcc-hcp,
fcc-bcc, and hcp-bcc transitions to occur at 215 GPa, 307 GPa, and 435 GPa
respectively. From the phonon dispersions at increasing pressure, we predict a
softening of the lowest transverse acoustic vibrational mode along the [110]
direction, which corresponds to a Born instability of the fcc phase at 725 GPa.Comment: 4 pages, 5 figures, accepted to Phys. Rev. B as a Brief Report. This
version has update many figures. Moreover we provided updated and more
accurate numbers based on further in-depth analyses of potential
computational error
Managerial practices that promote voice and taking charge among frontline workers
Process-improvement ideas often come from frontline workers who speak up by voicing concerns about problems and by taking charge to resolve them. We hypothesize that organization-wide process-improvement campaigns encourage both forms of speaking up, especially voicing concern. We also hypothesize that the effectiveness of such campaigns depends on the prior responsiveness of line managers. We test our hypotheses in the healthcare setting, in which problems are frequent. We use data on nearly 7,500 reported incidents extracted from an incident-reporting system that is similar to those used by many organizations to encourage employees to communicate about operational problems. We find that process-improvement campaigns prompt employees to speak up and that campaigns increase the frequency of voicing concern to a greater extent than they increase taking charge. We also find that campaigns are particularly effective in eliciting taking charge among employees whose managers have been relatively unresponsive to previous instances of speaking up. Our results therefore indicate that organization-wide campaigns can encourage voicing concerns and taking charge, two important forms of speaking up. These results can enable managers to solicit ideas from frontline workers that lead to performance improvement.
Nonparametric detection using extreme-value theory
Nonparametric extreme value statistics for constant signal detection in additive nois
Charge asymmetry in high-energy photoproduction in the electric field of a heavy atom
The charge asymmetry in the differential cross section of high-energy
photoproduction in the electric field of a heavy atom is obtained.
This asymmetry arises due to the Coulomb corrections to the amplitude of the
process (next-to-leading term with respect to the atomic field). The deviation
of the nuclear electric field from the Coulomb field at small distances is
crucially important for the charge asymmetry. Though the Coulomb corrections to
the total cross section are negligibly small, the charge asymmetry is
measurable for selected final states of and . We further discuss
the feasibility for experimental observation of this effect.Comment: 6 pages, 3 figure
CDMA overlay situations for microcellular mobile communications
Direct sequence code division multiple access communications is a promising approach to cellular mobile communications, which operates in an environment characterized by multipath Rician fading. In this paper, the CDMA network is assumed to share common spectrum with a narrowband microwave user. Because of the presence of the narrowband waveform, an interference suppression filter at each CDMA receiver is employed to reject the narrowband interference. The problem of interference from adjacent cells is also considered. Average power control is assumed to combat the near/far problem, and multipath diversity, in conjunction with simple interleaved channel coding, is considered for improving the performance of the CDMA system.published_or_final_versio
Operational Failures and Problem Solving: An Empirical Study of Incident Reporting
Operational failures occur in all industries with consequences that range from minor inconveniences to major catastrophes. Many organizations have implemented incident reporting systems to highlight actual and potential operational failures in order to encourage problem solving and prevent subsequent failures. Our study is among the first to develop and empirically test theory regarding which reported operational failures are likely to spur problem solving. We hypothesize that problem solving activities are especially likely to follow reported operational failures that provoke financial and legal liability risks. We also hypothesize that management commitment to problem solving, enacted through managers' communication and engagement practices, can encourage frontline workers to conduct problem solving. We test our hypotheses in the health care context, in which the use of incident reporting systems to highlight operational failures is widespread. Using data on nearly 7,500 reported incidents from a single hospital, we find support for our hypotheses. Our findings suggest that frontline workers' participation in problem solving is motivated by some inherent characteristics of the problems as well as by particular management practices.
Adaptive LMS filters for cellular CDMA overlay situations
This paper extends and complements previous research we have performed on the performance of nonadaptive narrowband suppression filters when used in cellular code-division multiple-access (CDMA) overlay situations. An adaptive least mean square (LMS) filter is applied to a cellular CDMA overlay in order to reject narrowband interference. An accurate expression for the steady-state tap-weight covariance matrix is derived for the real LMS algorithm for arbitrary statistics of the overlaid interference. Numerical results illustrate that when the ratio of the narrowband interference bandwidth to the spread spectrum bandwidth is small, the LMS filter is very effective in rejecting the narrowband interference. Furthermore, it is seen that the performance of the LMS filter in a CDMA overlay environment is not significantly worse than the performance of an ideal Wiener filter, assuming the LMS filter has had sufficient time to converge.published_or_final_versio
The Nature of Superfluidity in Ultracold Fermi Gases Near Feshbach Resonances
We study the superfluid state of atomic Fermi gases using a BCS-BEC crossover
theory. Our approach emphasizes non-condensed fermion pairs which strongly
hybridize with their (Feshbach-induced) molecular boson counterparts. These
pairs lead to pseudogap effects above and non-BCS characteristics below.
We discuss how these effects influence the experimental signatures of
superfluidity.Comment: 4 pages, 3 figures, submitted to PRA Rapid Communications;
introduction rewritten, figure replace
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