4,400 research outputs found
Magneto-transport in a quantum network: Evidence of a mesoscopic switch
We investigate magneto-transport properties of a shaped three-arm
mesoscopic ring where the upper and lower sub-rings are threaded by
Aharonov-Bohm fluxes and , respectively, within a
non-interacting electron picture. A discrete lattice model is used to describe
the quantum network in which two outer arms are subjected to binary alloy
lattices while the middle arm contains identical atomic sites. It is observed
that the presence of the middle arm provides localized states within the band
of extended regions and lead to the possibility of switching action from a high
conducting state to a low conducting one and vice versa. This behavior is
justified by studying persistent current in the network. Both the total current
and individual currents in three separate branches are computed by using
second-quantized formalism and our idea can be utilized to study magnetic
response in any complicated quantum network. The nature of localized
eigenstates are also investigated from probability amplitudes at different
sites of the quantum device.Comment: 7 pages, 9 figure
Magnetic Response in a Zigzag Carbon Nanotube
Magnetic response of interacting electrons in a zigzag carbon nanotube
threaded by a magnetic flux is investigated within a Hartree-Fock mean field
approach. Following the description of energy spectra for both non-interacting
and interacting cases we analyze the behavior of persistent current in
individual branches of a nanotube. Our present investigation leads to a
possibility of getting a filling-dependent metal-insulator transition in a
zigzag carbon nanotube.Comment: 9 pages, 14 figure
Influence of Demagnetization Effect on Giant Magneto Impedance of soft Ferromagnetic Metal
The large change in electromagnetic impedance in ferromagnetic state of soft
magnetic metals in presence of biasing magnetic field is associated with change
in screening of electromagnetic field. The screening depends on the
permeability of the metal. Apart from dependence on intrinsic properties of
metal the permeability depends on size of the sample. It is observed that the
decrease in MI in amorphous ferromagnetic ribbon of Fe40Ni40B20 alloy is large
for long sample whereas corresponding change is small for short one with same
biasing field. As intrinsic magnetic properties and bias field are same and the
demagnetization factor increases with reduction of length of the sample the
reduction of MI effect is associated with demagnetization field.Comment: 14 pages,4 figure
Detecting Human-Object Contact in Images
Humans constantly contact objects to move and perform tasks. Thus, detecting human-object contact is important for building human-centered artificial intelligence. However, there exists no robust method to detect contact between the body and the scene from an image, and there exists no dataset to learn such a detector. We fill this gap with HOT ("Human-Object conTact"), a new dataset of human-object contacts for images. To build HOT, we use two data sources: (1) We use the PROX dataset of 3D human meshes moving in 3D scenes, and automatically annotate 2D image areas for contact via 3D mesh proximity and projection. (2) We use the V-COCO, HAKE and Watch-n-Patch datasets, and ask trained annotators to draw polygons for the 2D image areas where contact takes place. We also annotate the involved body part of the human body. We use our HOT dataset to train a new contact detector, which takes a single color image as input, and outputs 2D contact heatmaps as well as the body-part labels that are in contact. This is a new and challenging task that extends current foot-ground or hand-object contact detectors to the full generality of the whole body. The detector uses a part-attention branch to guide contact estimation through the context of the surrounding body parts and scene. We evaluate our detector extensively, and quantitative results show that our model outperforms baselines, and that all components contribute to better performance. Results on images from an online repository show reasonable detections and generalizability
Enhancement of Jc by Hf -Doping in the Superconductor MgB2: A Hyperfine Interaction Study
Measurements of the critical current density (Jc) by magnetization and the
upper critical field (Hc2) by magnetoresistance have been performed for
hafnium-doped MgB2. There has been a remarkable enhancement of Jc as compared
to that by ion irradiation without any appreciable decrease in Tc, which is
beneficial from the point of view of applications. The irreversibility line
extracted from Jc shows an upward shift. In addition, there has been an
increase in the upper critical field which indicates that Hf partially
substitutes for Mg. Hyperfine interaction parameters obtained from time
differential perturbed angular correlation (TDPAC) measurements revealed the
formation of HfB and HfB2 phases along with the substitution of Hf. A possible
explanation is given for the role of these species in the enhancement of Jc in
MgB2 superconductor
Effects of rare earth nanoparticles (M = Sm2O3, Ho2O3, Nd2O3) addition on the microstructure and superconducting transition of Bi1.6Pb0.4Sr2Ca2Cu3O10+δ ceramics
The effect of rare earth nanoparticles, M=Sm2O3, Nd2O3 and Ho2O3 added to (Bi1.6Pb0.4Sr2Ca2Cu3O10+δ)1-x(M)x, where x = 0.00 - 0.05, superconductor were studied by X-ray diffraction technique (XRD), resistivity (R), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDX). The volume fraction of high-Tc phase, Bi-2223, decreased from 84% for pure sample to 48, 30 and 23% at x = 0.05 for Sm2O3, Ho2O3 and Nd2O3 additions, respectively. The critical temperature Tc(R=0) that is 102 K for the pure sample decreased to 78, 73 and 69 K at x = 0.05 for samples with Sm2O3, Nd2O3 and Ho2O3 nanoparticles additions, respectively. The additions of rare earth nanoparticles decreased the grain size and increased the random orientation of the grains. The results showed that the phases’ formations, variations of lattice parameters and electrical properties are sensitive to the size of nanoparticles and magnetic properties of its ions
Absorption cross section in warped AdS_3 black hole revisited
We investigate the absorption cross section for minimal-coupled scalars in
the warped AdS_3 black hole. According to our calculation, the cross section
reduces to the horizon area in the low energy limit as usually expected in
contrast to what was previously found. We also calculate the greybody factor
and find that the effective temperatures for the two chiral CFT's are
consistent with that derived from the quasinormal modes. Observing the
conjectured warped AdS/CFT correspondence, we suspect that a specific sector of
the CFT operators with the desired conformal dimension could be responsible for
the peculiar thermal behaviour of the warped AdS_3 black hole.Comment: 16+1 pages, typos corrected, references and footnotes adde
The Casimir Problem of Spherical Dielectrics: Numerical Evaluation for General Permittivities
The Casimir mutual free energy F for a system of two dielectric concentric
nonmagnetic spherical bodies is calculated, at arbitrary temperatures. The
present paper is a continuation of an earlier investigation [Phys. Rev. E {\bf
63}, 051101 (2001)], in which F was evaluated in full only for the case of
ideal metals (refractive index n=infinity). Here, analogous results are
presented for dielectrics, for some chosen values of n. Our basic calculational
method stems from quantum statistical mechanics. The Debye expansions for the
Riccati-Bessel functions when carried out to a high order are found to be very
useful in practice (thereby overflow/underflow problems are easily avoided),
and also to give accurate results even for the lowest values of l down to l=1.
Another virtue of the Debye expansions is that the limiting case of metals
becomes quite amenable to an analytical treatment in spherical geometry. We
first discuss the zero-frequency TE mode problem from a mathematical viewpoint
and then, as a physical input, invoke the actual dispersion relations. The
result of our analysis, based upon the adoption of the Drude dispersion
relation at low frequencies, is that the zero-frequency TE mode does not
contribute for a real metal. Accordingly, F turns out in this case to be only
one half of the conventional value at high temperatures. The applicability of
the Drude model in this context has however been questioned recently, and we do
not aim at a complete discussion of this issue here. Existing experiments are
low-temperature experiments, and are so far not accurate enough to distinguish
between the different predictions. We also calculate explicitly the
contribution from the zero-frequency mode for a dielectric. For a dielectric,
this zero-frequency problem is absent.Comment: 23 pages, LaTeX, 7 ps figures; expanded discussion, especially in
Sec. 5. To appear in Phys. Rev.
Does the enhancement observed in contain two -wave higher charmonia?
Solved is a new puzzle raised by the observation of an enhancement structure
Z(3930) in . If categorizing Z(3930) as
suggested by Belle and BaBar, we must explain why
dominantly decaying into is missing in the
invariant mass spectrum. In this work, we propose that the Z(3930)
enhancement structure may contain two -wave higher charmonia
{} and . We show that this assumption is
supported by our analysis of the invariant mass spectrum and
distribution of . This observation
would not only provide valuable information of two P-wave higher charmonia
and , but also serve as the crucial test of our
novel proposal to the observed enhancement structure Z(3930), especially at the
forthcoming BelleII and the approved SuperB.Comment: 5 pages, 2 tables, 3 figures. More contents and discussions adde
Infrared activity of hydrogen molecules trapped in Si
The rovibrational-translational states of a hydrogen molecule moving in a cage site in Si, when subjected to an electrical field arising from its surroundings, are investigated. The wave functions are expressed in terms of basis functions consisting of the eigenfunctions of the molecule confined to move in the cavity and rovibrational states of the free molecule. The energy levels, intensities of infrared and Raman transitions, effects of uniaxial stress, and a neighboring oxygen defect are found and compared with existing experimental data
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