65,919 research outputs found
Chiral spin-wave excitations of the spin-5/2 trimers in the langasite compound Ba3NbFe3Si2O14
The inelastic scattering of neutrons from magnetic excitations in the
antiferromagnetic phase of the langasite compound Ba3NbFe3Si2O14 is analyzed
theoretically. In the calculations presented, the strongly coupled spin-5/2 Fe
triangles are accounted for as trimerized units. The weaker interactions
between the trimers are included within the mean-field/random-phase
approximation. The theory is compared with linear spin-wave theory, and a model
is developed which leads to good agreement with the published results from
unpolarized and polarized neutron-scattering experiments.Comment: 10 pages, 9 figure
Design of an atmospheric sounding radiometer for the GOES meteorological satellite system
An advanced version of the visible infrared spin scan radiometer onboard U.S. geostationary operational environmental satellites was developed to add a vertical dimension to the instrument's infrared atmospheric images. Through the addition of twelve selectable narrow band filters and more precise in-flight calibration of the infrared detectors, the VISSR atmospheric sounder (VAS) will provide increased data to help determine the Earth's atmospheric temperature and water vapor distribution. The radiometer design, filter wheel, calibration shutter mechanisms, and their preflight test performance are discussed
A parallel algorithm for the enumeration of benzenoid hydrocarbons
We present an improved parallel algorithm for the enumeration of fixed
benzenoids B_h containing h hexagonal cells. We can thus extend the enumeration
of B_h from the previous best h=35 up to h=50. Analysis of the associated
generating function confirms to a very high degree of certainty that and we estimate that the growth constant and the amplitude .Comment: 14 pages, 6 figure
Confronting Misconceptions and Acknowledging Imperfections: A Response to Khaled Abou El Fadl\u27s Islam and Democracy
Professor Abou El Fadl\u27s Article, Islam and the Challenge of Democracy, demonstrates the need to move forward with knowledge of the nuance and depth of the historic, philosophic, legal, and theological foundations of both political stasis and political change in Muslim countries. The author comments on three aspects of Khaled Abou El Fadl\u27s paper. First, the author will juxtapose the discourse that Professor Abou El Fadl is stimulating with other perspectives in order to delineate the sets of actors in this debate among Muslims. The author will also argue that âIslamic exceptionalism,â so prominent in post-modern critiques, is unhelpful. Second, the author will comment on the centrality of Shariâah to the internal debate, and discuss widespread misconceptions about Shariâah among non-Muslims. Third, the author will comment on the problem of human agency and imperfect institutions. This imperfection becomes a critical issue when sacred texts are codified into secular law
Closed-shell properties of O with {\em ab initio} coupled-cluster theory
We present an \emph{ab initio} calculation of spectroscopic factors for
neutron and proton removal from O using the coupled-cluster method and a
state-of-the-art chiral nucleon-nucleon interaction at
next-to-next-to-next-to-leading order. In order to account for the coupling to
the scattering continuum we use a Berggren single-particle basis that treats
bound, resonant, and continuum states on an equal footing. We report neutron
removal spectroscopic factors for the O states ,
, and , and proton removal spectroscopic factors for the
N states and . Our calculations support the accumulated
experimental evidence that O is a closed-shell nucleus.Comment: 5 pages, 2 figures, 1 tabl
Quenching of spectroscopic factors for proton removal in oxygen isotopes
We present microscopic coupled-cluster calculations of the spectroscopic
factors for proton removal from the closed-shell oxygen isotopes
O with the chiral nucleon-nucleon interaction at
next-to-next-to-next-to-leading order. We include coupling-to-continuum degrees
of freedom by using a Hartree-Fock basis built from a Woods-Saxon
single-particle basis. This basis treats bound and continuum states on an equal
footing. We find a significant quenching of spectroscopic factors in the
neutron-rich oxygen isotopes, pointing to enhanced many-body correlations
induced by strong coupling to the scattering continuum above the neutron
emission thresholds.Comment: 3 figure
The cytochemical localization of ascorbic acid in root tip cells
The intracellular distribution of ascorbic acid was studied in frozen-dried root tips of Allium cepa and Vicia faba by the silver nitrate procedure. The sites of the ascorbic acid as indicated by the deposited silver appear as spherical (0.2 to 0.6 ” in diameter) cytoplasmic particles. The site appears to have small amounts of lipides and to be rich in ribonucleic acid. These particles are concluded to be submicroscopic in size and associated, in the elongating cell, with the cell surface. In the meristematic cells they appear fewer in number and are distributed throughout the cytoplasm
Vanishing of Gravitational Particle Production in the Formation of Cosmic Strings
We consider the gravitationally induced particle production from the quantum
vacuum which is defined by a free, massless and minimally coupled scalar field
during the formation of a gauge cosmic string. Previous discussions of this
topic estimate the power output per unit length along the string to be of the
order of ergs/sec/cm in the s-channel. We find that this production
may be completely suppressed. A similar result is also expected to hold for the
number of produced photons.Comment: 10 pages, Plain LaTex. Minor improvements. To appear in PR
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