3,289 research outputs found
Robust MMSE Precoding Strategy for Multiuser MIMO Relay Systems with Switched Relaying and Side Information
In this work, we propose a minimum mean squared error (MMSE) robust base station (BS) precoding strategy based on switched relaying (SR) processing and limited transmission of side information for interference suppression in the downlink of multiuser multiple-input multiple-output (MIMO) relay systems. The BS and the MIMO relay station (RS) are both equipped with a codebook of interleaving matrices. For a given channel state information (CSI) the selection function at the BS chooses the optimum interleaving matrix from the codebook based on two optimization criteria to design the robust precoder. Prior to the payload transmission the BS sends the index corresponding to the selected interleaving matrix to the RS, where the best interleaving matrix is selected to build the optimum relay processing matrix. The entries of the codebook are randomly generated unitary matrices. Simulation results show that the performance of the proposed techniques is significantly better than prior art in the case of imperfect CSI.
Search for supersolidity in 4He in low-frequency sound experiments
We present results of the search for supersolid 4He using low-frequency,
low-level mechanical excitation of a solid sample grown and cooled at fixed
volume. We have observed low frequency non-linear resonances that constitute
anomalous features. These features, which appear below about 0.8 K, are absent
in 3He. The frequency, the amplitude at which the nonlinearity sets in, and the
upper temperature limit of existence of these resonances depend markedly on the
sample history.Comment: Submitted to the Quantum Fluids and Solids Conf. Aug. 2006 Kyot
Constraining Aerosol Vertical Profile in the Boundary Layer Using Hyperspectral Measurements of Oxygen Absorption
This study attempts to infer aerosol vertical structure in the urban boundary layer using passive hyperspectral measurements. A spectral sorting technique is developed to retrieve total aerosol optical depth (AOD) and effective aerosol layer height (ALH) from hyperspectral measurements in the 1.27âÎŒm oxygen absorption band by the mountaintop Fourier Transform Spectrometer at the California Laboratory for Atmospheric Remote Sensing instrument (1,673 m above sea level) overlooking the LA basin. Comparison to AOD measurements from Aerosol Robotic Network and aerosol backscatter profile measurements from a Mini MicroPulse Lidar shows agreement, with coefficients of determination (r^2) of 0.74 for AOD and 0.57 for effective ALH. On average, the AOD retrieval has an error of 24.9% and rootâmeanâsquare error of 0.013, while the effective ALH retrieval has an error of 7.8% and rootâmeanâsquare error of 67.01 m. The proposed method can potentially be applied to existing and future satellite missions with hyperspectral oxygen measurements to constrain aerosol vertical distribution on a global scale
Isospin Effect on the Process of Multifragmentation and Dissipation at Intermediate Energy Heavy Ion Collisions
In the simulation of intermediate energy heavy ion collisions by using the
isospin dependent quantum molecular dynamics, the isospin effect on the process
of multifragmentation and dissipation has been studied. It is found that the
multiplicity of intermediate mass fragments for the neutron-poor
colliding system is always larger than that for the neutron-rich system, while
the quadrupole of single particle momentum distribution for the
neutron-poor colliding system is smaller than that of the neutron-rich system
for all projectile-target combinations studied at the beam energies from about
50MeV/nucleon to 150MeV/nucleon. Since depends strongly on isospin
dependence of in-medium nucleon-nucleon cross section and weakly on symmetry
potential at the above beam energies, it may serve as a good probe to extract
the information on the in-medium nucleon-nucleon cross section. The correlation
between the multiplicity of intermediate mass fragments and the total
numer of charged particles has the behavior similar to , which
can be used as a complementary probe to the in-medium nucleon-nucleon cross
section.Comment: 18 pages, 9 figure
Slender double-tube ultra-high strength concrete-filled tubular columns under ambient temperature and fire
This paper presents the results of an experimental campaign where both the room temperature and the fire resistance of six double-tube concrete filled steel tubular slender columns with different combinations of concrete strength are studied. Firstly, the ultimate axial load of the specimens at room temperatura was experimentally obtained and afterwards the fire resistance of such columns subjected to a 20% of their load bearing capacity was measured. Given the reduced number of experimental results found in the literature on slender concrete filled tubular columns with double steel tubular cross-sections, the
main objective of this paper is to compare the behaviour of such innovative cross-sections under ambient and high temperatures. The influence of filling the inner ring with concrete on the fire performance of these columns is studied in this paper, as well as the variation of thicknesses of the outer and inner steel
tubes. Despite the fact that the tested columns are not covered by the scope of Eurocode 4, the current simple calculation models were applied in this paper in order to assess the validity of the standard to this typology of columns, unsafe results being found.The authors would like to express their sincere gratitude to the Spanish Ministry of Economy and Competitivity through the project BIA2012-33144 and to the European Community for the FEDER funds.Romero, ML.; Espinós Capilla, A.; Portoles Flaj, JM.; Hospitaler Pérez, A.; Ibåñez Usach, C. (2015). Slender double-tube ultra-high strength concrete-filled tubular columns under ambient temperature and fire. Engineering Structures. 99:536-545. https://doi.org/10.1016/j.engstruct.2015.05.026S5365459
Electronic Transport in a Three-dimensional Network of 1-D Bismuth Quantum Wires
The resistance R of a high density network of 6 nm diameter Bi wires in
porous Vycor glass is studied in order to observe its expected semiconductor
behavior. R increases from 300 K down to 0.3 K. Below 4 K, where R varies
approximately as ln(1/T), the order-of-magnitude of the resistance rise, as
well as the behavior of the magnetoresistance are consistent with localization
and electron-electron interaction theories of a one-dimensional disordered
conductor in the presence of strong spin-orbit scattering. We show that this
behaviour and the surface-enhanced carrier density may mask the proposed
semimetal-to-semiconductor transition for quantum Bi wires.Comment: 19 pages total, 4 figures; accepted for publication in Phys. Rev.
Two band gap field-dependent thermal conductivity of
The thermal conductivity of the new superconductor was
studied as a function of the temperature and a magnetic field. No anomaly in
the thermal conductivity is observed around the superconducting
transition in absence or presence of magnetic fields up to 14 Tesla; upon that
field the superconductivity of persisted. The thermal conductivity in
zero-field shows a -linear increase up to 50K. The thermal conductivity is
found to increase with increasing field at high fields. We interpret the
findings as if there are two subsystems of quasiparticles with different
field-dependent characters in a two ( and )-band superconductor reacting
differently with the vortex structure. The unusual enhancement of at low temperature but higher than a () critical field
is interpreted as a result of the overlap of the low energy states outside the
vortex cores in the -band.Comment: 6 pages,3 figure
Constraining Aerosol Vertical Profile in the Boundary Layer Using Hyperspectral Measurements of Oxygen Absorption
This study attempts to infer aerosol vertical structure in the urban boundary layer using passive hyperspectral measurements. A spectral sorting technique is developed to retrieve total aerosol optical depth (AOD) and effective aerosol layer height (ALH) from hyperspectral measurements in the 1.27âÎŒm oxygen absorption band by the mountaintop Fourier Transform Spectrometer at the California Laboratory for Atmospheric Remote Sensing instrument (1,673 m above sea level) overlooking the LA basin. Comparison to AOD measurements from Aerosol Robotic Network and aerosol backscatter profile measurements from a Mini MicroPulse Lidar shows agreement, with coefficients of determination (r^2) of 0.74 for AOD and 0.57 for effective ALH. On average, the AOD retrieval has an error of 24.9% and rootâmeanâsquare error of 0.013, while the effective ALH retrieval has an error of 7.8% and rootâmeanâsquare error of 67.01 m. The proposed method can potentially be applied to existing and future satellite missions with hyperspectral oxygen measurements to constrain aerosol vertical distribution on a global scale
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