3,322 research outputs found
Overview of multi-input frequency domain modal testing methods with an emphasis on sine testing
An overview of the current state of the art multiple-input, multiple-output modal testing technology is discussed. A very brief review of the current time domain methods is given. A detailed review of frequency and spatial domain methods is presented with an emphasis on sine testing
Non-adiabatic molecular association in thermal gases driven by radio-frequency pulses
The molecular association process in a thermal gas of Rb is
investigated where the effects of the envelope of the radio-frequency field are
taken into account. For experimentally relevant parameters our analysis shows
that with increasing pulse length the corresponding molecular conversion
efficiency exhibits low-frequency interference fringes which are robust under
thermal averaging over a wide range of temperatures. This dynamical
interference phenomenon is attributed to St\"uckelberg phase accumulation
between the low-energy continuum states and the dressed molecular state which
exhibits a shift proportional to the envelope of the radio-frequency pulse
intensity.Comment: 5 pages, 3 figure
Status of Nucleon Resonances with Masses
We discuss different interpretations of peaks observed a few years ago by
Tatischeff et al. in missing mass spectra of the reaction , which
were declared as new exited nucleon states with small masses. A study of the
possible production of such states in the process by analyzing the invariant mass spectrum of
is proposed. It is shown that the data, obtained recently at MAMI-B, can allow
to analyze this process and to get information about an existence of exited
nucleon states with small masses.Comment: 4 pages, 2 figures, LaTeX with ws-p8-50x6-00.cls. Talk presented at
the NSTAR2001 Workshop, Mainz, Germany, March 7-10, 200
Inelastic semiclassical Coulomb scattering
We present a semiclassical S-matrix study of inelastic collinear
electron-hydrogen scattering. A simple way to extract all necessary information
from the deflection function alone without having to compute the stability
matrix is described. This includes the determination of the relevant Maslov
indices. Results of singlet and triplet cross sections for excitation and
ionization are reported. The different levels of approximation -- classical,
semiclassical, and uniform semiclassical -- are compared among each other and
to the full quantum result.Comment: 9 figure
ProfPPIdb: Pairs of physical protein-protein interactions predicted for entire proteomes
Motivation Protein-protein interactions (PPIs) play a key role in many cellular processes. Most annotations of PPIs mix experimental and computational data. The mix optimizes coverage, but obfuscates the annotation origin. Some resources excel at focusing on reliable experimental data. Here, we focused on new pairs of interacting proteins for several model organisms based solely on sequence-based prediction methods. Results We extracted reliable experimental data about which proteins interact (binary) for eight diverse model organisms from public databases, namely from Escherichia coli, Schizosaccharomyces pombe, Plasmodium falciparum, Drosophila melanogaster, Caenorhabditis elegans, Mus musculus, Rattus norvegicus, Arabidopsis thaliana, and for the previously used Homo sapiens and Saccharomyces cerevisiae. Those data were the base to develop a PPI prediction method for each model organism. The method used evolutionary information through a profile-kernel Support Vector Machine (SVM). With the resulting eight models, we predicted all possible protein pairs in each organism and made the top predictions available through a web application. Almost all of the PPIs made available were predicted between proteins that have not been observed in any interaction, in particular for less well-studied organisms. Thus, our work complements existing resources and is particularly helpful for designing experiments because of its uniqueness. Experimental annotations and computational predictions are strongly influenced by the fact that some proteins have many partners and others few. To optimize machine learning, recent methods explicitly ignored such a network-structure and rely either on domain knowledge or sequence-only methods. Our approach is independent of domain-knowledge and leverages evolutionary information. The database interface representing our results is accessible from https://rostlab.org/services/ppipair/. The data can also be downloaded from https://figshare.com/collections/ProfPPI-DB/4141784
Ionization of clusters in intense laser pulses through collective electron dynamics
The motion of electrons and ions in medium-sized rare gas clusters (1000
atoms) exposed to intense laser pulses is studied microscopically by means of
classical molecular dynamics using a hierarchical tree code. Pulse parameters
for optimum ionization are found to be wavelength dependent. This resonant
behavior is traced back to a collective electron oscillation inside the charged
cluster. It is shown that this dynamics can be well described by a driven and
damped harmonic oscillator allowing for a clear discrimination against other
energy absorption mechanisms.Comment: 4 pages (4 figures
Separation and identification of dominant mechanisms in double photoionization
Double photoionization by a single photon is often discussed in terms of two
contributing mechanisms, {\it knock-out} (two-step-one) and {\it shake-off}
with the latter being a pure quantum effect. It is shown that a quasi-classical
description of knock-out and a simple quantum calculation of shake-off provides
a clear separation of the mechanisms and facilitates their calculation
considerably. The relevance of each mechanism at different photon energies is
quantified for helium. Photoionization ratios, integral and singly differential
cross sections obtained by us are in excellent agreement with benchmark
experimental data and recent theoretical results.Comment: 4 pages, 5 figure
Fast coarsening in unstable epitaxy with desorption
Homoepitaxial growth is unstable towards the formation of pyramidal mounds
when interlayer transport is reduced due to activation barriers to hopping at
step edges. Simulations of a lattice model and a continuum equation show that a
small amount of desorption dramatically speeds up the coarsening of the mound
array, leading to coarsening exponents between 1/3 and 1/2. The underlying
mechanism is the faster growth of larger mounds due to their lower evaporation
rate.Comment: 4 pages, 4 PostScript figure
Threshold detachment of negative ions by electron impact
The description of threshold fragmentation under long range repulsive forces
is presented. The dominant energy dependence near threshold is isolated by
decomposing the cross section into a product of a back ground part and a
barrier penetration probability resulting from the repulsive Coulomb
interaction. This tunneling probability contains the dominant energy variation
and it can be calculated analytically based on the same principles as Wannier's
description for threshold ionization under attractive forces. Good agreement is
found with the available experimental cross sections on detachment by electron
impact from , and .Comment: 4 pages, 4 figures (EPS), to appear in Phys.Rev.Lett, Feb. 22nd, 199
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