A 15.3 GHz satellite-to-ground diversity propagation experiment using a terminal separation of 4 kilometers

The performance of a path diversity satellite-to-ground millimeter wave link with two ground terminals separated by 4 km is discussed. At this separation distance the duration of fades below 6 dB was decreased by at least a factor of 10 when using path diversity and the cumulative crosscorrelation between the attenuations observed at the two terminals during rain events was approximately 0.45. Narrow beam radiometers directed along the propagation paths were also utilized to relate the path radiometric temperature to the path attenuation. An analysis of downlink propagation data for generating diversity link performance statistics is included

Anomaly Cancelation in Field Theory and F-theory on a Circle

We study the manifestation of local gauge anomalies of four- and six-dimensional field theories in the lower-dimensional Kaluza-Klein theory obtained after circle compactification. We identify a convenient set of transformations acting on the whole tower of massless and massive states and investigate their action on the low-energy effective theories in the Coulomb branch. The maps employ higher-dimensional large gauge transformations and precisely yield the anomaly cancelation conditions when acting on the one-loop induced Chern-Simons terms in the three- and five-dimensional effective theory. The arising symmetries are argued to play a key role in the study of the M-theory to F-theory limit on Calabi-Yau manifolds. For example, using the fact that all fully resolved F-theory geometries inducing multiple Abelian gauge groups or non-Abelian groups admit a certain set of symmetries, we are able to generally show the cancelation of pure Abelian or pure non-Abelian anomalies in these models.Comment: 48 pages, 2 figures; v2: typos corrected, comments on circle fluxes adde

How Do Quasicrystals Grow?

Using molecular simulations, we show that the aperiodic growth of quasicrystals is controlled by the ability of the growing quasicrystal `nucleus' to incorporate kinetically trapped atoms into the solid phase with minimal rearrangement. In the system under investigation, which forms a dodecagonal quasicrystal, we show that this process occurs through the assimilation of stable icosahedral clusters by the growing quasicrystal. Our results demonstrate how local atomic interactions give rise to the long-range aperiodicity of quasicrystals.Comment: 4 pages, 4 figures. Figures and text have been updated to the final version of the articl

Educator\u27s Implementation of the Connecticut Guidelines for the Identification and Education of Children and Youth with Autism

The Problem As the number of children with autism needing educational support continues to increase, combined with the limited availability of resources, this study aims to examine how educators responsible for teaching children with autism have experienced implementation of the Connecticut Guidelines for the Identification and Education of Children and Youth with Autism (2005), (Guidelines). At this time there have been no studies done in the State of Connecticut to assess the implementation of the components for effective education of children with autism, as set forth in the Connecticut Guidelines. Method The Connecticut Autism Needs Survey, an on-line self-report survey designed for this study, was used to collect cross sectional data reflecting special education teachers practices and attitudes towards the Connecticut Guidelines for Identification and Education of Children and Youth with Autism. The first three research questions assess participants experience with implementation, level of difficulty implementing and level of importance of the Connecticut Guidelines for Identification and Education of Children and Youth with Autism. To further explore implementation, level of difficulty implementing and importance the data was examined specifically for teachers practice with 17 recommended evidence based practices for students with autism. The responses to the questions were analyzed using descriptive statistics. Three additional research questions address the association between the dependent variables reported on in the first three questions and the predictor variables of (a) years of experience, (b) assignment, (c) place, (d) region of the state, (e) number of students on caseload, (f) percentage of students with ASD on caseload, or (g) personal relationship. The dependent variable for each question and the 7 predictor variables were analyzed using logistic regression. Results The findings reveal 89.5% of respondents were either not familiar with the Connecticut Guidelines or found them difficult to implement. Additionally, the findings suggest an association between a special educator’s use of the Connecticut Guidelines and the specificity of their role and tenure. Teachers who are primarily responsible for students with autism were more likely to use the Guidelines than were teachers who were responsible for providing specialized instruction to students with a range of disabilities. The research found that special education teachers in private schools were nine times less likely to rate the Connecticut Guidelines as difficult to implement than teachers in public schools. The findings suggest teachers with more experience were slightly more likely to implement the Connecticut Guidelines. Interestingly, the findings identified teachers who have a personal relationship were twice as likely to use the Guidelines as those who did not. Three of the most critical evidence-based strategies for educating students with autism: pivotal response training, video modeling, and voice output communication aide had the lowest percentage of implementation and were perceived as not important by teachers. Conclusions The results show the Connecticut Guidelines are not used or viewed as important by the majority of special education teachers in Connecticut. The Guidelines were written 10 years ago and much has changed in the field of autism over that time period. It appears it is time to reexamine and make changes to the Connecticut Guidelines

Sympathetic Cooling of Lithium by Laser-cooled Cesium

We present first indications of sympathetic cooling between two neutral, optically trapped atomic species. Lithium and cesium atoms are simultaneously stored in an optical dipole trap formed by the focus of a CO$_2$ laser, and allowed to interact for a given period of time. The temperature of the lithium gas is found to decrease when in thermal contact with cold cesium. The timescale of thermalization yields an estimate for the Li-Cs cross-section.Comment: 4 pages, proceedings of ICOLS 200

On the universal X-ray luminosity function of binary X-ray sources in galaxies

The empirically determined universal power-law shape of X-ray luminosity function of high mass X-ray binaries in galaxies is explained by fundamental mass-luminosity and mass-radius relations for massive stars.Comment: 4 pages, plain LaTeX, no figures. Submitted to Astronomy Letter

Mixture of ultracold lithium and cesium atoms in an optical dipole trap

We present the first simultaneous trapping of two different ultracold atomic species in a conservative trap. Lithium and cesium atoms are stored in an optical dipole trap formed by the focus of a CO$_2$ laser. Techniques for loading both species of atoms are discussed and observations of elastic and inelastic collisions between the two species are presented. A model for sympathetic cooling of two species with strongly different mass in the presence of slow evaporation is developed. From the observed Cs-induced evaporation of Li atoms we estimate a cross section for cold elastic Li-Cs collisions.Comment: 10 pages 9 figures, submitted to Appl. Phys. B; v2: Corrected evaporation formulas and some postscript problem

Coherent optical transfer of Feshbach molecules to a lower vibrational state

Using the technique of stimulated Raman adiabatic passage (STIRAP) we have coherently transferred ultracold 87Rb2 Feshbach molecules into a more deeply bound vibrational quantum level. Our measurements indicate a high transfer efficiency of up to 87%. As the molecules are held in an optical lattice with not more than a single molecule per lattice site, inelastic collisions between the molecules are suppressed and we observe long molecular lifetimes of about 1 s. Using STIRAP we have created quantum superpositions of the two molecular states and tested their coherence interferometrically. These results represent an important step towards Bose-Einstein condensation (BEC) of molecules in the vibrational ground state.Comment: 4 pages, 5 figure

Tuning the scattering length with an optically induced Feshbach resonance

We demonstrate optical tuning of the scattering length in a Bose-Einstein condensate as predicted by Fedichev {\em et al.} [Phys. Rev. Lett. {\bf 77}, 2913 (1996)]. In our experiment atoms in a $^{87}$Rb condensate are exposed to laser light which is tuned close to the transition frequency to an excited molecular state. By controlling the power and detuning of the laser beam we can change the atomic scattering length over a wide range. In view of laser-driven atomic losses we use Bragg spectroscopy as a fast method to measure the scattering length of the atoms.Comment: submitted to PRL, 5 pages, 5 figure