130,462 research outputs found
Vertical transport through laterally periodically modulated heterostructures
No full textThe ballistic transport in a laterally periodically modulated heterojunction connecting two reservoirs is studied: this can model the presence of an ordered layer of self-organized quantum dots. The problem is solved in the envelope function formalism using a three-dimensional (3D) generalization of the transfer matrix approach that exploits the two-dimensional (2D) lattice periodicity. Illustrative numerical results are presented showing qualitatively different behaviors of the transmission coefficients due to the multichannel nature of the propagation, In particular, deep minima of the transmission occur due to destructive interference between different conducting channels, a situation that cannot be realized in the absence of the lateral modulation. (C) 2001 Elsevier Science Ltd. All rights reserved
Auger-electron angular distributions calculated without the two-step approximation: Calculation of angle-resolved resonant Auger spectra of C_2H_2
No full textAnalytic expressions for the direct, resonant, and interference contributions to the differential cross section of a resonant Auger process, produced by the inner-shell photoionization of a linear molecule either “fixed in space” or belonging to a gas of randomly oriented molecules, have been derived following Dill’s procedures [ Dill et al. Phys. Rev. Lett. 45 1393 (1980)], but going beyond the two-step approximation. Angle-resolved Auger spectra of the C2H2 molecule measured on top of the C 1s→π* resonance [ Kivimäki et al. J. Phys. B 30 4279 (1997)] have been calculated together with asymmetry parameters, analyzing also the different contributions to the electron angular distributions
Effects of atomic interactions on the resonant tunnelling of sodium condensates
No full textWe investigate the influence of atomic interactions on the tunnelling of sodium condensates across a spatially oscillating optical barrier. In the limit of very fast barrier oscillations, in which resonant tunnelling via a metastable state takes place, the interactions affect the position and lineshape of the transmission peak. We anticipate that the possibility of modulating the interactions in a tunnelling condensate can be exploited to achieve nonlinear effects such as optical limiting and bistability
Effects of atomic interactions on the resonant tunnelling of sodium condensates
No full textWe investigate the influence of atomic interactions on the tunnelling of sodium condensates across a spatially oscillating optical barrier. In the limit of very fast barrier oscillations, in which resonant tunnelling via a metastable state takes place, the interactions affect the position and lineshape of the transmission peak. We anticipate that the possibility of modulating the interactions in a tunnelling condensate can be exploited to achieve nonlinear effects such as optical limiting and bistability
Ab-initio calculation of the C1s photoelectron spectrum of C2H2
No full textThe C1s photoelectron spectrum of C2H2, measured
by Kempgens et al. [Phys. Rev. Lett. 79, 3617 (1997)]
and characterized by the presence of a core-level splitting, has
been calculated and interpreted using an ab initio
quantum-mechanical method that allows detailed analysis of
photoionization processes and accurate reproduction of spectral
profiles. The anisotropy of the electron emission, measured in a
hypothetical experiment in which the orientation of the molecules
can be established, has been also predicted and analyzed
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Microgravity vertical gradient measurement in the site of VIRGO interferometric antenna (Pisa plain, Italy)
No full textThe site of the European Gravitational Observatory (EGO) located in the countryside near Pisa (Tuscany, Italy) was investigated by a microgravity vertical gradient (MVG) Survey. The EGO site houses the VIRGO interferometric antenna for gravitational waves detection. The microgravity survey aims to highlight the gravity anomalies of high-frequency related to more superficial geological sources to obtain a detailed model of the lithologic setting of the VIRGO site, this will allow an estimate of the noise induced by seismic waves and by Newtonian interference. This paper presents the results of the gradiometric survey of 2006 in the area of the interferometric antenna. MVG measurements allow its to enhance the high frequency signal strongly associated with the shallow structures. The gradient gravity map shows a main negative pattern that seems related to the trending of the high density layer of gravel revealed in geotechnical drillings executed along the orthogonal arms during the construction of the VIRGO complex. Calibrating the relationship between the vertical gradient and the depth of the gravel interface we have computed a model of gravity gradient for the whole VIRGO site, defining the 3D distribution of the top surface of this layer. The latter shows a NE-SW negative pattern that may represent a palaeobed alluvial of the Serchio from the Bientina River system
Modelling of the hydro-acoustic signal as a Tsunami Precursor
No full textIn the frame of a 2-D compressible tsunami generation model with flat
porous seabed, we show that acoustic waves are generated and travel
outside the source area at sound speed. These waves carry information
as to sea floor motion. The acoustic wave period depends on water
height at the source area and is given by four times the travel time
the sound takes to reach the sea surface from the sea bottom.
The fundamental frequency ranges from 1 to 0.05 Hz, at 400 m and 8000
m water depth, respectively. The sound waves produced by seafloor
motion can propagate far from the source, with a small attenuation in
amplitude. Moreover, the typical wavelengths of the acoustic waves
produced by the water layer oscillation
allows the waves to overcome most of the seafloor reliefs. The
semi-analytical solution of the 2-D compressible water layer model
overlying a porous seabed is presentedSubmitted381.8. Osservazioni di geofisica ambientaleJCR Journalope
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