9,551 research outputs found
A Coplanar Waveguide Fed Hexagonal Shape Ultra Wide Band Antenna with WiMAX and WLAN Band Rejection
In this paper, a coplanar waveguide (CPW) fed hexagonal shape planar antenna has been considered for ultra-wide band (UWB). This antenna is then modified to obtain dual band rejection. The Wireless Local Area Network (WLAN) and Wireless Microwave Access (WiMAX) band rejections are realized by symmetrically incorporating a pair of L-shape slots within the ground plane as well as a couple of I-shape stubs inserted on the bottom side of radiating patch. The proposed antenna has stop bands of 5.05-5.92 GHz and 3.19-3.7 GHz while maintaining the wideband performance from 2.88 - 13.71 GHz with reflection coefficient of ≤ -10 dB. The antenna exhibits satisfactory omni-directional radiation characteristics throughout its operating band. The peak gain varies from 2 dB to 6 dB in the entire UWB frequency regions except at the notch bands. Surface current distributions are used to analyze the effects of the L-slot and I-shape stub. The measured group delay has small variation within the operating band except notch bands and hence the proposed antenna may be suitable for UWB applications
Maxwell's Refrigerator: An Exactly Solvable Model
We describe a simple and solvable model of a device that -- like the
"neat-fingered being" in Maxwell's famous thought experiment -- transfers
energy from a cold system to a hot system by rectifying thermal fluctuations.
In order to accomplish this task, our device requires a memory register to
which it can write information: the increase in the Shannon entropy of the
memory compensates the decrease in the thermodynamic entropy arising from the
flow of heat against a thermal gradient. We construct the nonequilibrium phase
diagram for this device, and find that it can alternatively act as an eraser of
information. We discuss our model in the context of the second law of
thermodynamics.Comment: 9 pages (Main Text + Supplemental Material), 3 figures, to appear in
Physical Review Letter
Evaluating FOMC forecasts
Federal Reserve policymakers began reporting their economic forecasts to Congress in 1979. These forecasts are important because they indicate what the Federal Open Market Committee (FOMC) members think will be the likely consequence of their policies. We evaluate the accuracy of the FOMC forecasts relative to private sector forecasts, the forecasts of the Research Staff at the Board of Governors, and a naĂŻve alternative forecast. The Fed reports both the range (high and low) of the individual policymaker's forecasts and a truncated central tendency. We find no reason to consider the truncated version. We find that the FOMC output forecasts were better than the naĂŻve model and at least as good as those of the private sector and the Fed staff. The FOMC inflation forecasts were more accurate than the private sector forecasts and the naĂŻve model. For the period ending in 1996, however, they were not as accurate as Fed staff inflation forecasts.Federal Open Market Committee ; Forecasting
Anti-chiral edge states in an exciton polariton strip
We present a scheme to obtain anti-chiral edge states in an exciton-polariton
honeycomb lattice with strip geometry, where the modes corresponding to both
edges propagate in the same direction. Under resonant pumping the effect of a
polariton condensate with nonzero velocity in one linear polarization is
predicted to tilt the dispersion of polaritons in the other, which results in
an energy shift between two Dirac cones and the otherwise flat edge states
become tilted. Our simulations show that due to the spatial separation from the
bulk modes the edge modes are robust against disorder.Comment: 6 pages, 5 figure
Half Cycle Pulse Train Induced State Redistribution of Rydberg Atoms
Population transfer between low lying Rydberg states independent of the
initial state is realized using a train of half-cycle pulses with pulse
durations much less than the classical orbit period. We demonstrate
experimentally the transfer of population from initial states around n=50 down
to n<40 as well as up to the continuum. The measured population transfer
matches well to a model of the process for 1D atoms.Comment: V2: discussion extended, version accepted for publication in Physical
Review
Collapse/Flattening of Nucleonic Bags in Ultra-Strong Magnetic Field
It is shown explicitly using MIT bag model that in presence of ultra-strong
magnetic fields, a nucleon either flattens or collapses in the direction
transverse to the external magnetic field in the classical or quantum
mechanical picture respectively. Which gives rise to some kind of mechanical
instability. Alternatively, it is argued that the bag model of confinement may
not be applicable in this strange situation.Comment: 8 pages, REVTEX, 3 figures .eps files (included
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