8,587 research outputs found
Microwave device investigations Semiannual progress report, 1 Oct. 1969 - 1 Apr. 1970
Beam-plasma interactions, cyclotron harmonic instability study, and millimeter and submillimeter wave detection by paramagnetic material
Microwave device investigations Semiannual progress report, 1 Apr. - 1 Oct. 1969
Summaries of progress in beam plasma interactions, paramagnetic and bulk semiconductor materials, and avalanche diode
Microwave device investigations Semiannual progress report, 1 Oct. 1968 - 1 Apr. 1969
Beam plasma amplification, harmonic generation, and coupling scheme
Microwave device investigations Semiannual progress report, 1 Apr. - 1 Oct. 1968
Beam-plasma interactions, cyclotron harmonic instabilities, harmonic generation in beam-plasma system, relativistic electron beam studies, and materials test
Frequency multiplication in high-energy electron beams Semiannual progress report, 1 Oct. 1967 - 31 Mar. 1968
Electron beam-plasma interactions, cyclotron harmonic instabilities, paramagnetic and semiconductor materials, and harmonic current generatio
Detection of vibronic bands of C in a translucent cloud towards HD 169454
We report the detection of eight vibronic bands of C, seven of which have
been hitherto unobserved in astrophysical objects, in the translucent cloud
towards HD~169454. Four of these bands are also found towards two additional
objects: HD~73882 and HD~154368. Very high signal-to-noise ratio (1000
and higher) and high resolving power () UVES-VLT spectra (Paranal,
Chile) allow for detecting novel spectral features of C, even revealing
weak perturbed features in the strongest bands. The work presented here
provides the most complete spectroscopic survey of the so far largest carbon
chain detected in translucent interstellar clouds. High-quality laboratory
spectra of C are measured using cavity ring-down absorption spectroscopy in
a supersonically expanding hydrocarbon plasma, to support the analysis of the
identified bands towards HD~169454. A column density of N(C) = cm is inferred and the excitation of the molecule
exhibits two temperature components; K for the low-
states and K for the high- tail. The rotational
excitation of C is reasonably well explained by models involving a
mechanism including inelastic collisions, formation and destruction of the
molecule, and radiative pumping in the far-infrared. These models yield gas
kinetic temperatures comparable to those found for . The assignment of
spectral features in the UV-blue range 3793-4054 \AA\ may be of relevance for
future studies aiming at unravelling spectra to identify interstellar molecules
associated with the diffuse interstellar bands (DIBs).Comment: 15 pages, 13 figures, submitted to MNRA
Training deep neural density estimators to identify mechanistic models of neural dynamics
Mechanistic modeling in neuroscience aims to explain observed phenomena in terms of underlying causes. However, determining which model parameters agree with complex and stochastic neural data presents a significant challenge. We address this challenge with a machine learning tool which uses deep neural density estimators-- trained using model simulations-- to carry out Bayesian inference and retrieve the full space of parameters compatible with raw data or selected data features. Our method is scalable in parameters and data features, and can rapidly analyze new data after initial training. We demonstrate the power and flexibility of our approach on receptive fields, ion channels, and Hodgkin-Huxley models. We also characterize the space of circuit configurations giving rise to rhythmic activity in the crustacean stomatogastric ganglion, and use these results to derive hypotheses for underlying compensation mechanisms. Our approach will help close the gap between data-driven and theory-driven models of neural dynamics
Applicability of Modified Effective-Range Theory to positron-atom and positron-molecule scattering
We analyze low-energy scattering of positrons on Ar atoms and N2 molecules
using Modified Effective-Range Theory (MERT) developped by O'Malley, Spruch and
Rosenberg [Journal of Math. Phys. 2, 491 (1961)]. We use formulation of MERT
based on exact solutions of Schroedinger equation with polarization potential
rather than low-energy expansions of phase shifts into momentum series. We show
that MERT describes well experimental data, provided that effective-range
expansion is performed both for s- and p-wave scattering, which dominate in the
considered regime of positron energies (0.4 - 2 eV). We estimate the values of
the s-wave scattering lenght and the effective range for e+ - Ar and e+ - N2
collisions.Comment: RevTeX, 4 pages, 2 figure
Small gain versus positive real modeling of real parameter uncertainty
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76326/1/AIAA-20872-692.pd
Renormalization Group calculations with k|| dependent couplings in a ladder
We calculate the phase diagram of a ladder system, with a Hubbard interaction
and an interchain coupling . We use a Renormalization Group method, in
a one loop expansion, introducing an original method to include
dependence of couplings. We also classify the order parameters corresponding to
ladder instabilities. We obtain different results, depending on whether we
include dependence or not. When we do so, we observe a region with
large antiferromagnetic fluctuations, in the vicinity of small ,
followed by a superconducting region with a simultaneous divergence of the Spin
Density Waves channel. We also investigate the effect of a non local backward
interchain scattering : we observe, on one hand, the suppression of singlet
superconductivity and of Spin Density Waves, and, on the other hand, the
increase of Charge Density Waves and, for some values of , of triplet
superconductivity. Our results eventually show that is an influential
variable in the Renormalization Group flow, for this kind of systems.Comment: 20 pages, 19 figures, accepted in Phys. Rev. B 71 v. 2
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