12,243 research outputs found
[Review of] Clifford I. Uyeda, ed. Americans of Japanese Ancestry and the United States Constitution: 1787-1987
In 1987, the Smithsonian Institution, as part of its observance of the bicentennial of the Constitution, held an exhibit that traced the history of Japanese immigrants and their descendants in the United States. This book, which commemorates the exhibit, consists chiefly of black-and-white photographs, brief notes, and a detailed chronology of the Japanese in this country from 1806, when eight shipwrecked sailors arrived in Hawaii, to 1987, when Senator Daniel K. Inouye (Hawaii) presided over the joint House and Senate hearings into the Iran-Contra affair
Minimally Extended Left-Right Symmetric Model for Dark Matter with U(1) Portal
A minimal extension of the left-right symmetric model for neutrino masses
that includes a vector-like singlet fermion dark matter (DM) is presented with
the DM connected to the visible sector via a gauged U(1) portal. We discuss the
symmetry breaking in this model and calculate the mass and mixings of the extra
heavy neutral gauge boson at the TeV scale. The extra gauge boson can decay to
both standard model particles as well to dark matter. We calculate the relic
density of the singlet fermion dark matter and its direct detection cross
section and use these constraints to obtain the allowed parameter range for the
new gauge coupling and the dark matter mass.Comment: 19 pages, 8 figure
Origin of critical-temperature enhancement of an iron-based high-T_c superconductor, LaFeAsO_{1-x}F_{x} : NMR study under high pressure
Nuclear magnetic resonance (NMR) measurements of an iron (Fe)-based
superconductor LaFeAsO_{1-x}F_x (x = 0.08 and 0.14) were performed at ambient
pressure and under pressure. The relaxation rate 1/T_1 for the overdoped
samples (x = 0.14) shows T-linear behavior just above T_c, and pressure
application enhances 1/T_1T similar to the behavior of T_c. This implies that
1/T_1T = constant originates from the Korringa relation, and an increase in the
density of states at the Fermi energy D(E_F) leads to the enhancement of T_c.
In the underdoped samples (x = 0.08), 1/T_1T measured at ambient pressure also
shows T-independent behavior in a wide temperature range above T_c. However, it
shows Curie-Weiss-like T dependence at 3.0 GPa accompanied by a small increase
in T_c, suggesting that predominant antiferromagnetic fluctuation suppresses
development of superconductivity or remarkable enhancement of T_c. The
qualitatively different features between underdoped and overdoped samples are
systematically explained by a band calculation with hole and electron pockets
Simulations of slow positron production using a low energy electron accelerator
Monte Carlo simulations of slow positron production via energetic electron
interaction with a solid target have been performed. The aim of the simulations
was to determine the expected slow positron beam intensity from a low energy,
high current electron accelerator. By simulating (a) the fast positron
production from a tantalum electron-positron converter and (b) the positron
depth deposition profile in a tungsten moderator, the slow positron production
probability per incident electron was estimated. Normalizing the calculated
result to the measured slow positron yield at the present AIST LINAC the
expected slow positron yield as a function of energy was determined. For an
electron beam energy of 5 MeV (10 MeV) and current 240 A (30 A)
production of a slow positron beam of intensity 5 10 s is
predicted. The simulation also calculates the average energy deposited in the
converter per electron, allowing an estimate of the beam heating at a given
electron energy and current. For low energy, high-current operation the maximum
obtainable positron beam intensity will be limited by this beam heating.Comment: 11 pages, 15 figures, submitted to Review of Scientific Instrument
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