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 $B_h \sim A \kappa^h /h$ and we estimate that the growth constant $\kappa = 5.161930154(8)$ and the amplitude $A=0.2808499(1)$.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 “Islamic exceptionalism,” so prominent in post-modern critiques, is unhelpful. Second, the author will comment on the centrality of Shari‘ah to the internal debate, and discuss widespread misconceptions about Shari‘ah 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 24^{24}O with {\em ab initio} coupled-cluster theory

We present an \emph{ab initio} calculation of spectroscopic factors for neutron and proton removal from $^{24}$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 $^{23}$O states $J^{\pi} = 1/2^+$, $5/2^+$, $3/2^-$ and $1/2^-$, and proton removal spectroscopic factors for the $^{23}$N states $1/2^-$ and $3/2^-$. Our calculations support the accumulated experimental evidence that $^{24}$O is a closed-shell nucleus.Comment: 5 pages, 2 figures, 1 tabl

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 $10^{68}$ 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