The role of quantum fluctuations in the optomechanical properties of a Bose-Einstein condensate in a ring cavity

We analyze a detailed model of a Bose-Einstein condensate trapped in a ring optical resonator and contrast its classical and quantum properties to those of a Fabry-P{\'e}rot geometry. The inclusion of two counter-propagating light fields and three matter field modes leads to important differences between the two situations. Specifically, we identify an experimentally realizable region where the system's behavior differs strongly from that of a BEC in a Fabry-P\'{e}rot cavity, and also where quantum corrections become significant. The classical dynamics are rich, and near bifurcation points in the mean-field classical system, the quantum fluctuations have a major impact on the system's dynamics.Comment: 11 pages, 11 figures, submitted to PR

The “secret” impact of population statistics on the metrics of diabetes

The accuracy of disease metrics is dependent on the quality of population-based data. Many diseases, including diabetes, are age and sex dependant. Accurate age- and sexspecific population survey data, population estimates and projections are required to assess the scale and trends in the burden of these diseases. No assessment of the quality of population data being used in the UAE diabetes metrics has been published. We provide insight into the availability and quality of published population data, which is currently being used to inform diabetes research and health services planning in the UAE. We show the absence of credible population-based data impedes the accurate assessment of disease prevalence, incidence and trends. This means that many statements about the burden of this disease in relative and absolute terms are not robust. There has been only one study of sufficient reliability of the prevalence of diabetes in the UAE and this was undertaken in 2000. Hence the calculation and reporting of trends is problematic. Population estimates for the UAE are based on out of date data and are extremely variable. Population projections for the UAE and other Middle East countries with large expatriate labour forces are improbable. The clinical and other implications of accurate population-based metrics are wide reaching. If prevalence rates are to be used to guide public policy and infrastructure planning, then we need to use valid data, including population and population-based data. Whilst specific reference is made to diabetes, and the issues affecting the United Arab Emirates and the Gulf Cooperation Council Countries of the Middle East; the impact of inaccurate population–based metrics have application in other regions, and other diseases

New algorithms for optimizing and linking conical intersection points

In this paper we present two new algorithms to study the extended nature of the crossing seam between electronic potential energy surfaces. The first algorithm is designed to optimize conical intersection geometries: both minima and saddle points. In addition, this method will optimize conical intersection geometries using arbitrary geometrical constraints. We demonstrate its potential on different crossing seams of benzene, z-penta-3,5-dleniminium, and 1,3-butadiene. The second algorithm is designed to explicitly compute the intersection-space minimum energy coordinate. Our computations show how an intersection seam and the energy along it can be unambiguously defined. A finite region of the S0/S11,3-butadiene crossing seam has been mapped out, and a new saddle point linked with two lower-lying geometries on the sea

Photometric Monitoring of the Gravitationally Lensed Ultraluminous BAL Quasar APM08279+5255

We report on one year of photometric monitoring of the ultraluminous BAL quasar APM 08279+5255. The temporal sampling reveals that this gravitationally lensed system has brightened by ~0.2 mag in 100 days. Two potential causes present themselves; either the variability is intrinsic to the quasar, or it is the result of microlensing by stars in a foreground system. The data is consistent with both hypotheses and further monitoring is required before either case can be conclusively confirmed. We demonstrate, however, that gravitational microlensing can not play a dominant role in explaining the phenomenal properties exhibited by APM 08279+5255. The identification of intrinsic variability, coupled with the simple gravitational lensing configuration, would suggest that APM 08279+5255 is a potential golden lens from which the cosmological parameters can be derived and is worthy of a monitoring program at high spatial resolution.Comment: 17 pages, with 2 figures. Accepted for publication in P.A.S.

Attosecond electronic and nuclear quantum photodynamics of ozone: time-dependent Dyson orbitals and dipole

A nonadiabatic scheme for the description of the coupled electron and nuclear motions in the ozone molecule was proposed recently. An initial coherent nonstationary state was prepared as a superposition of the ground state and the excited Hartley band. In this situation neither the electrons nor the nuclei are in a stationary state. The multiconfiguration time dependent Hartree method was used to solve the coupled nuclear quantum dynamics in the framework of the adiabatic separation of the time-dependent Schr\"odinger equation. The resulting wave packet shows an oscillation of the electron density between the two chemical bonds. As a first step for probing the electronic motion we computed the time-dependent molecular dipole and the Dyson orbitals. The latter play an important role in the explanation of the photoelectron angular distribution. Calculations of the Dyson orbitals are presented both for the time-independent as well as the time-dependent situations. We limited our description of the electronic motion to the Franck-Condon region only due to the localization of the nuclear wave packets around this point during the first 5-6 fs

Comparison of MEMS switches and PIN diodes for switched dual tuned RF coils

PURPOSE: To evaluate the performance of micro-electromechanical systems (MEMS) switches against PIN diodes for switching a dual-tuned RF coil between19F and1H resonant frequencies for multi-nuclear lung imaging. METHODS: A four-element fixed-phase and amplitude transmit-receive RF coil was constructed to provide homogeneous excitation across the lungs, and to serve as a test system for various switching methods. The MR imaging and RF performance of the coil when switched between the19F and1H frequencies using MEMS switches, PIN diodes and hardwired configurations were compared. RESULTS: The performance of the coil with MEMS or PIN diode switching was comparable in terms of RF measurements, transmit efficiency and image SNR on both19F and1H nuclei. When the coil was not switched to the resonance frequency of the respective nucleus being imaged, reductions in the transmit efficiency were observed of 32% at the19F frequency and 12% at the1H frequency. The coil provides transmit field homogeneity of ±12.9% at the1H frequency and ±14.4% at the19F frequency in phantoms representing the thorax with the air space of the lungs filled with perfluoropropane gas. CONCLUSION: MEMS and PIN diodes were found to provide comparable performance in on-state configuration, while MEMS were more robust in off-state high-powered operation (>1 kW), providing higher isolation and requiring a lower DC switching voltage than is needed for reverse biasing of PIN diodes. In addition, clear benefits of switching between the19F and1H resonances were demonstrated, despite the proximity of their Larmor frequencies

A human CCT5 gene mutation causing distal neuropathy impairs hexadecamer assembly in an archaeal model

Chaperonins mediate protein folding in a cavity formed by multisubunit rings. The human CCT has eight non-identical subunits and the His147Arg mutation in one subunit, CCT5, causes neuropathy. Knowledge is scarce on the impact of this and other mutations upon the chaperone’s structure and functions. To make progress, experimental models must be developed. We used an archaeal mutant homolog and demonstrated that the His147Arg mutant has impaired oligomeric assembly, ATPase activity, and defective protein homeostasis functions. These results establish for the first time that a human chaperonin gene defect can be reproduced and studied at the molecular level with an archaeal homolog. The major advantage of the system, consisting of rings with eight identical subunits, is that it amplifies the effects of a mutation as compared with the human counterpart, in which just one subunit per ring is defective. Therefore, the slight deficit of a non-lethal mutation can be detected and characterized