52,158 research outputs found
Semiclassical Nonlinear Approach for Mesoscopic Circuit
Based on energy conservation considerations we study the nonlinear dynamic behavior of a quantum mesoscopic circuit, which is characterized through parameters of inductance and capacitance. Nonlinearity is given by the initial conditions of magnetic flux and discreteness charge which oscillate in the interval [- , + ], being the magnetic flux normalized by . This LC circuit with quantized electric charge is excited by energy battery that can produce an electrical discreteness charge on the capacitor. The dynamics of the mesoscopic circuit is highly nonlinear. Our results show for the magnetic flux a nearly square wave with an elongated period when compared with the linear case and a train of narrow pulses for the discrete charge
Probing ferroelectricity in highly conducting materials through their elastic response: persistence of ferroelectricity in metallic BaTiO3-d
The question whether ferroelectricity (FE) may coexist with a metallic or
highly conducting state, or rather it must be suppressed by the screening from
the free charges, is the focus of a rapidly increasing number of theoretical
studies and is finally receiving positive experimental responses. The issue is
closely related to the thermoelectric and multiferroic (also magnetic)
applications of FE materials, where the electrical conductivity is required or
spurious. In these circumstances, the traditional methods for probing
ferroelectricity are hampered or made totally ineffective by the free charges,
which screen the polar response to an external electric field. This fact may
explain why more than 40 years passed between the first proposals of FE metals
and the present experimental and theoretical activity. The measurement of the
elastic moduli, Young's modulus in the present case, versus temperature is an
effective method for studying the influence of doping on a FE transition
because the elastic properties are unaffected by electrical conductivity. In
this manner, it is shown that the FE transitions of BaTiO3-d are not suppressed
by electron doping through O vacancies; only the onset temperatures are
depressed, but the magnitudes of the softenings, and hence of the piezoelectric
activity, are initially even increased
A Seismic Channel Model: The San Ramon Fault
Although seismic waves have been studied for many years, their soliton structure has only recently studied. Deformation solitons propagate along earthquake faults and can induce large earthquakes. Rotation solitons are generated in earthquake sources and propagate throughout the Earth. The conclusion to be reached from our paper is that the research on seismic solitons is essential for investigating the propagation of seismic waves and helps understand mechanisms triggering earthquakes. This paper discusses the development of elastodynamics equations similar to Maxwell's equations in a chiral -mode which is applied to a seismic channel, which is dispersive and nonlinear. The chirality is described in terms of the formalism proposed by Born-Fedorov. The nonlinearity is Kerr-type, and dispersion of the medium is taken into account explicitly through the Taylor series expansion. Through numerical calculations these theoretical results allow us analyze the soliton propagation of S-seismic pulses which can induce strong earthquakes. The numerical calculation is applied to the San Ramon Fault localized in Santiago City, Chile which is a seismically active fault that is a main element to be considered in any study on seismic hazard assessment for this city
The M2/M5 BPS Partition Functions from Supergravity
In the framework of the AdS/CFT duality, we calculate the supersymmetric
partition function of the superconformal field theories living in the world
volume of either -branes or -branes. We used the dual
supergravity partition function in a saddle point approximation over
supersymmetric Black Holes. Since our BHs are written in asymptotically global
co-ordinates, the dual SCFTs are in for . The
resulting partition function shows phase transitions, constraints on the phase
space and allowed us to identify unstable BPS Black hole in the phase.
These configurations should correspond to unstable configurations in the dual
theory. We also report an intriguing relation between the most general Witten
Index, computed in the above theories, and our BPS partition functions.Comment: 9 pages, 2 columns, 4 figures, revtex, typos corrected, reference
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Performance of a Low Noise Front-end ASIC for Si/CdTe Detectors in Compton Gamma-ray Telescope
Compton telescopes based on semiconductor technologies are being developed to
explore the gamma-ray universe in an energy band 0.1--20 MeV, which is not well
covered by the present or near-future gamma-ray telescopes. The key feature of
such Compton telescopes is the high energy resolution that is crucial for high
angular resolution and high background rejection capability. The energy
resolution around 1 keV is required to approach physical limit of the angular
resolution due to Doppler broadening. We have developed a low noise front-end
ASIC (Application-Specific Integrated Circuit), VA32TA, to realize this goal
for the readout of Double-sided Silicon Strip Detector (DSSD) and Cadmium
Telluride (CdTe) pixel detector which are essential elements of the
semiconductor Compton telescope. We report on the design and test results of
the VA32TA. We have reached an energy resolution of 1.3 keV (FWHM) for 60 keV
and 122 keV at 0 degree C with a DSSD and 1.7 keV (FWHM) with a CdTe detector.Comment: 6 pages, 7 figures, IEEE style file, to appear in IEEE Trans. Nucl.
Sc
Exact solution for the energy density inside a one-dimensional non-static cavity with an arbitrary initial field state
We study the exact solution for the energy density of a real massless scalar
field in a two-dimensional spacetime, inside a non-static cavity with an
arbitrary initial field state, taking into account the Neumann and Dirichlet
boundary conditions. This work generalizes the exact solution proposed by Cole
and Schieve in the context of the Dirichlet boundary condition and vacuum as
the initial state. We investigate diagonal states, examining the vacuum and
thermal field as particular cases. We also study non-diagonal initial field
states, taking as examples the coherent and Schrodinger cat states.Comment: 10 pages, 8 figure
Gamma Ray Large Area Space Telescope (GLAST) Balloon Flight Data Handling Overview
The GLAST Balloon Flight Engineering Model (BFEM) represents one of 16 towers
that constitute the Large Area Telescope (LAT), a high-energy (>20 MeV)
gamma-ray pair-production telescope being built by an international partnership
of astrophysicists and particle physicists for a satellite launch in 2006. The
prototype tower consists of a Pb/Si pair-conversion tracker (TKR), a CsI
hodoscopic calorimeter (CAL), an anti-coincidence detector (ACD) and an
autonomous data acquisition system (DAQ). The self-triggering capabilities and
performance of the detector elements have been previously characterized using
positron, photon and hadron beams. External target scintillators were placed
above the instrument to act as sources of hadronic showers. This paper provides
a comprehensive description of the BFEM data-reduction process, from receipt of
the flight data from telemetry through event reconstruction and background
rejection cuts. The goals of the ground analysis presented here are to verify
the functioning of the instrument and to validate the reconstruction software
and the background-rejection scheme.Comment: 5 pages, 4 figures, to be published in IEEE Transacations on Nuclear
Science, August 200
Learning Management System Built Using the MERN Stack
Web based applications play a main role in our day-to-day life and therefore, it is important to ensure the quality and reliability of web applications. With the sudden increase in use of web based applications for online and distant learning, it is important to address existing issues in current Learning Management Systems (LMS), so that users can benefit from a better, uninterrupted learning experience. This work mainly contributes to understanding how the MERN stack can be efficiently used in building a reliable and secure LMS that will provide its services free of charge so that students are provided with a free and uninterrupted learning experience. An LMS that is equipped with user handling functionality, managing courses and course materials, and maintaining a library, has been the focus of the study that resulted in producing this paper. The work also includes reasoning as to why the MERN stack was selected for developing the proposed system
Formation of even-numbered hydrogen cluster cations in ultracold helium droplets
Neutral hydrogen clusters are grown in ultracold helium nanodroplets by successive pickup of hydrogen molecules. Even-numbered hydrogen cluster cations are observed upon electron-impact ionization with and without attached helium atoms and in addition to the familiar odd-numbered H(n)(+). The helium matrix affects the fragmentation dynamics that usually lead to the formation of overwhelmingly odd-numbered H(n)(+). The use of high-resolution mass spectrometry allows the unambiguous identification of even-numbered H(n)(+) up to n congruent to 120 by their mass excess that distinguishes them from He(n)(+), mixed He(m)H(n)(+), and background ions. The large range in size of these hydrogen cluster ions is unprecedented, as is the accuracy of their definition. Apart from the previously observed magic number n = 6, pronounced drops in the abundance of even-numbered cluster ions are seen at n = 30 and 114, which suggest icosahedral shell closures at H(6)(+)(H(2))(12) and H(6)(+)(H(2))(54). Possible isomers of H(6)(+) are identified at the quadratic configuration interaction with inclusion of single and double excitations (QCISD)/aug-cc-pVTZ level of theory (C) 2008 American Institute of Physics. [DOI: 10.1063/1.3035833
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