8,445 research outputs found
Low-energy quenching of positronium by helium
Very low-energy scattering of orthopositronium by helium has been
investigated for simultaneous study of elastic cross section and pick-off
quenching rate using a model exchange potential. The present calculational
scheme, while agrees with the measured cross section of Skalsey et al,
reproduces successfully the parameter ^ 1Z_{\makebox{eff}}, the effective
number of electrons per atom in a singlet state relative to the positron.
Together with the fact that this model potential also leads to an agreement
with measured medium energy cross sections of this system, this study seems to
resolve the long-standing discrepancy at low energies among different
theoretical calculations and experimental measurements.Comment: 4 latex pages, 3 postscript figure
Effective Operator Treatment of the Anharmonic Oscillator
We analyse the one dimensional quartic oscillator using the effective
operator methodology of Lee and Suzuki. We reproduce known results for low
lying energy eigenvalues.Comment: 9 Pages, Extended version with new references. To appear in
Phys.ReV.
Continuous transition of social efficiencies in the stochastic strategy Minority Game
We show that in a variant of the Minority Game problem, the agents can reach
a state of maximum social efficiency, where the fluctuation between the two
choices is minimum, by following a simple stochastic strategy. By imagining a
social scenario where the agents can only guess about the number of excess
people in the majority, we show that as long as the guess value is sufficiently
close to the reality, the system can reach a state of full efficiency or
minimum fluctuation. A continuous transition to less efficient condition is
observed when the guess value becomes worse. Hence, people can optimize their
guess value for excess population to optimize the period of being in the
majority state. We also consider the situation where a finite fraction of
agents always decide completely randomly (random trader) as opposed to the rest
of the population that follow a certain strategy (chartist). For a single
random trader the system becomes fully efficient with majority-minority
crossover occurring every two-days interval on average. For just two random
traders, all the agents have equal gain with arbitrarily small fluctuations.Comment: 8 pages, 6 fig
Structure and superconductivity of two different phases of Re3W
Two superconducting phases of Re(3)W have been found with different physical properties. One phase crystallizes in a noncentrosymmetric cubic (alpha-Mn) structure and has a superconducting transition temperature T(c) of 7.8 K. The other phase has a hexagonal centrosymmetric structure and is superconducting with a T(c) of 9.4 K. Switching between the two phases is possible by annealing the sample or remelting it. The properties of both phases of Re(3)W have been characterized by powder neutron diffraction, magnetization, and resistivity measurements. The temperature dependences of the lower and upper critical fields have been measured for both phases. These are used to determine the penetration depths and the coherence lengths for these systems
Zeta Function Zeros, Powers of Primes, and Quantum Chaos
We present a numerical study of Riemann's formula for the oscillating part of
the density of the primes and their powers. The formula is comprised of an
infinite series of oscillatory terms, one for each zero of the zeta function on
the critical line and was derived by Riemann in his paper on primes assuming
the Riemann hypothesis. We show that high resolution spectral lines can be
generated by the truncated series at all powers of primes and demonstrate
explicitly that the relative line intensities are correct. We then derive a
Gaussian sum rule for Riemann's formula. This is used to analyze the numerical
convergence of the truncated series. The connections to quantum chaos and
semiclassical physics are discussed
S-, P- and D-wave resonances in positronium-sodium and positronium-potassium scattering
Scattering of positronium (Ps) by sodium and potassium atoms has been
investigated employing a three-Ps-state coupled-channel model with Ps(1s,2s,2p)
states using a time-reversal-symmetric regularized electron-exchange model
potential fitted to reproduce accurate theoretical results for PsNa and PsK
binding energies. We find a narrow S-wave singlet resonance at 4.58 eV of width
0.002 eV in the Ps-Na system and at 4.77 eV of width 0.003 eV in the Ps-K
system. Singlet P-wave resonances in both systems are found at 5.07 eV of width
0.3 eV. Singlet D-wave structures are found at 5.3 eV in both systems. We also
report results for elastic and Ps-excitation cross sections for Ps scattering
by Na and K.Comment: 9 pages, 5 figures, Accepted in Journal of Physics
Calibration of Hurricane Imaging Radiometer C-Band Receivers
The laboratory calibration of airborne Hurricane Imaging Radiometer's C-Band multi-frequency receivers is described here. The method used to obtain the values of receiver frontend loss, internal cold load brightness temperature and injected noise diode temperature is presented along with the expected RMS uncertainty in the final calibration
Characteristic of a Digital Correlation Radiometer Back End with Finite Wordlength
The performance characteristic of a digital correlation radiometer signal processing back end (DBE) is analyzed using a simulator. The particular design studied here corresponds to the airborne Hurricane Imaging radiometer which was jointly developed by the NASA Marshall Space Flight Center, University of Michigan, University of Central Florida and NOAA. Laboratory and flight test data is found to be in accord with the simulation results. Overall design seems to be optimum for the typical input signal dynamic range. It was found that the performance of the digital kurtosis could be improved by lowering the DBE input power level. An unusual scaling between digital correlation channels observed in the instrument data is confirmed to be a DBE characteristic
Starobinsky Model in Schroedinger Description
In the Starobinsky inflationary model inflation is driven by quantum
corrections to the vacuum Einstein equation. We reduce the Wheeler-DeWitt
equation corresponding to the Starobinsky model to a Schroedinger form
containing time. The Schroedinger equation is solved with a Gaussian ansatz.
Using the prescription for the normalization constant of the wavefunction given
in our previous work, we show that the Gaussian ansatz demands Hawking type
initial conditions for the wavefunction of the universe. The wormholes induce
randomness in initial states suggesting a basis for time-contained description
of the Wheeler-DeWitt equation.Comment: 19 Pages, LaTeX, no figure, gross typographical mistake
"Swiss-Cheese" Inhomogeneous Cosmology & the Dark Energy Problem
We study an exact swiss-cheese model of the Universe, where inhomogeneous LTB
patches are embedded in a flat FLRW background, in order to see how
observations of distant sources are affected. We find negligible integrated
effect, suppressed by (L/R_{H})^3 (where L is the size of one patch, and R_{H}
is the Hubble radius), both perturbatively and non-perturbatively. We
disentangle this effect from the Doppler term (which is much larger and has
been used recently \cite{BMN} to try to fit the SN curve without dark energy)
by making contact with cosmological perturbation theory.Comment: 35 pages, 6 figure
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