22,029 research outputs found
MIMO System Setup and Parameter Estimation
There is a rat race in wireless communication to
achieve higher spectral efficiency. One technique to achieve this
is the use of multiple antenna systems i.e. MIMO systems. In
this paper we describe a wireless 4x4 Multiple Input Multiple
Output (MIMO) testbed in the 2.2 GHz band including results
from live experiments. MIMO systems have several advantages
compared to SISO (Single Input Single Output) systems. The
most important ones are higher reliability and/or higher throughput
per Herz. In this testbed we used the 802.11a OFDM
Wireless LAN standard as a basis for the MIMO system. The
experiments have been conducted at 2.2 GHz carrier using 5
MHz bandwidth. These can be divided into several subjects:
antenna spacing experiments, effects for increasing antennas,
AD accuracy and performance for different antenna topologies.
Moreover, the performance of the Zero Forcing (ZF), Minimum
Mean Square Error (MMSE) and Vertical Bell labs LAyered
Space Time (VBLAST) have been evaluated
Bringing closure to microlensing mass measurement
Interferometers offer multiple methods for studying microlensing events and
determining the properties of the lenses. We investigate the study of
microlensing events with optical interferometers, focusing on narrow-angle
astrometry, visibility, and closure phase. After introducing the basics of
microlensing and interferometry, we derive expressions for the signals in each
of these three channels. For various forecasts of the instrumental performance,
we discuss which method provides the best means of measuring the lens angular
Einstein radius theta_E, a prerequisite for determining the lens mass. If the
upcoming generation of large-aperture, AO-corrected long baseline
interferometers (e.g. VLTI, Keck, OHANA) perform as well as expected, theta_E
may be determined with signal-to-noise greater than 10 for all bright events.
We estimate that roughly a dozen events per year will be sufficiciently bright
and have long enough durations to allow the measurement of the lens mass and
distance from the ground. We also consider the prospects for a VLTI survey of
all bright lensing events using a Fisher matrix analysis, and find that even
without individual masses, interesting constraints may be placed on the bulge
mass function, although large numbers of events would be required.Comment: 23 pages, aastex, submitted to Ap
Decay of scalar variance in isotropic turbulence in a bounded domain
The decay of scalar variance in isotropic turbulence in a bounded domain is
investigated. Extending the study of Touil, Bertoglio and Shao (2002; Journal
of Turbulence, 03, 49) to the case of a passive scalar, the effect of the
finite size of the domain on the lengthscales of turbulent eddies and scalar
structures is studied by truncating the infrared range of the wavenumber
spectra. Analytical arguments based on a simple model for the spectral
distributions show that the decay exponent for the variance of scalar
fluctuations is proportional to the ratio of the Kolmogorov constant to the
Corrsin-Obukhov constant. This result is verified by closure calculations in
which the Corrsin-Obukhov constant is artificially varied. Large-eddy
simulations provide support to the results and give an estimation of the value
of the decay exponent and of the scalar to velocity time scale ratio
Transverse Lepton Polarization in Polarized W Decays
Calculations of transverse polarization of leptons in the decay with polarized 's are presented. Planned accelerators will produce
enough 's for observation of the Standard Model contributions to this
polarization. One loop corrections to the polarization are given; these are too
small to be seen at presently available sources. The exchange of Majorons
will contribute to these polarizations; these may provide limits on the
couplings of these particles to leptons.Comment: 8 pages set in RevTex III and 4 uucompressed figures. This revised
version studies polarization effects due to the exchange of charged Majoron
doublet
The Mount Wilson optical interferometer: The first automated instrument and the prospects for lunar interferometry
Before contemplating an optical interferometer on the Moon one must first review the accomplishments achieved by this technology in scientific applications for astronomy. This will be done by presenting the technical status of optical interferometry as achieved by the Mount Wilson Optical Interferometer. The further developments needed for a future lunar-based interferometer are discussed
Parton distribution functions and nuclear EMC effect in a statistical model
A new and simple statistical approach is performed to calculate the parton
distribution functions (PDFs) of the nucleon in terms of light-front kinematic
variables. Analytic expressions of x-dependent PDFs are obtained in the whole x
region. And thereafter, we treat the temperature T as a parameter of the atomic
number A to explain the nuclear EMC effect in the region . We
give the predictions of PDF ratios, and they are very different from those by
other models, thus experiments aiming at measuring PDF ratios are suggested to
provide a discrimination of different models.Comment: 4 pages, no figure; talk given at the 5th International Conference On
Quarks and Nuclear Physics (QNP09), Sep 2009, Beijing Chin
Bell Inequalities Classifying Bi-separable Three-qubit States
We present a set of Bell inequalities that gives rise to a finer
classification of the entanglement for tripartite systems. These inequalities
distinguish three possible bi-separable entanglements for three-qubit states.
The three Bell operators we employed constitute an external sphere of the
separable cube.Comment: 8 page
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