Many-Body Rate Limit on Photoassociation of a Bose-Einstein Condensate

We briefly report on zero-temperature photoassociation of a Bose-Einstein condensate, focusing on the many-body rate limit for atom-molecule conversion. An upgraded model that explicitly includes spontaneous radiative decay leads to an unanticipated shift in the position of the photoassociation resonance, which affects whether the rate (constant) maximizes or saturates, as well as the limiting value itself. A simple analytical model agrees with numerical experiments, but only for high density. Finally, an explicit comparison with the two-body unitary limit, set by the size of the condensate, finds that the many-body rate limit is generally more strict.Comment: 4 pages, 3 figures, 59 references. v2: discussion added; to appear in PR

Rate limit for photoassociation of a Bose-Einstein condensate

We simulate numerically the photodissociation of molecules into noncondensate atom pairs that accompanies photoassociation of an atomic Bose-Einstein condensate into a molecular condensate. Such rogue photodissociation sets a limit on the achievable rate of photoassociation. Given the atom density \rho and mass m, the limit is approximately 6\hbar\rho^{2/3}/m. At low temperatures this is a more stringent restriction than the unitary limit of scattering theory.Comment: 5 pgs, 18 refs., 3 figs., submitted to Phys. Rev. Let

On the road to Enlighten-ment: establishing an institutional repository service for the University of Glasgow

Purpose – The purpose of this paper is to chart the development and growth of open access and institutional repositories at the University of Glasgow, Scotland from initial work in 2001 to the University's recently launched service, Enlighten. The University of Glasgow is a signatory to the Scottish Open Access Declaration and recently released a statement on Open Access.<p></p> Design/methodology/approach – The study will focus on the key lessons learned through a twin track approach of advocacy and service development during the DAEDALUS Project (2002-2005) and the transition of that work to a University service called Enlighten. This service includes a repository for published and peer-reviewed papers which has now had over 2 million hits and over 270,000 PDF downloads since it was established in February 2004.<p></p> Findings – The paper reveals the lessons learned by the Library and the project team. It also identifies the range of issues which must be addressed in the successful implementation of a repository and its transition to a production service. These include the development of content policies, copyright clearance and the cultural change necessary to populate a repository service. These challenges have and continue to be addressed by the repository team at the University of Glasgow.<p></p> Originality/value – This paper provides details of the lessons learned in the practical experience of setting up an institutional repository and ensuring its transition to a full and supported University service. It will be of particular interest to institutions implementing a repository or running a pilot service.<p></p&gt

Theory of Combined Photoassociation and Feshbach Resonances in a Bose-Einstein Condensate

We model combined photoassociation and Feshbach resonances in a Bose-Einstein condensate, where the shared dissociation continuum allows for quantum interference in losses from the condensate, as well as a dispersive-like shift of resonance. A simple analytical model, based on the limit of weakly bound molecules, agrees well with numerical experiments that explicitly include dissociation to noncondensate modes. For a resonant laser and an off-resonant magnetic field, constructive interference enables saturation of the photoassociation rate at user-friendly intensities, at a value set by the interparticle distance. This rate limit is larger for smaller condensate densities and, near the Feshbach resonance, approaches the rate limit for magnetoassociation alone. Also, we find agreement with the unitary limit--set by the condensate size--only for a limited range of near-resonant magnetic fields. Finally, for a resonant magnetic field and an off-resonant laser, magnetoassociation displays similar quantum interference and a dispersive-like shift. Unlike photoassociation, interference and the fieldshift in resonant magnetoassociation is tunable with both laser intensity and detuning. Also, the dispersive-like shift of the Feshbach resonance depends on the size of the Feshbach molecule, and is a signature of non-universal physics in a strongly interacting system.Comment: 10 pages, 5 figures, 82 reference

In vivo and in vitro models of demyelinating diseases. V. Comparison of the assembly of mouse hepatitis virus, strain JHM, in two murine cell lines.

The developmental sequence of a neurotropic strain (JHM) of mouse hepatitis virus was examined by transmission electron microscopy and immunocytology. The nucleoprotein core of this coronavirus, which contains RNA of positive polarity and is helical in configuration, becomes incorporated into enveloped particles in the same manner as the nucleocapsids of the orthomyxo- and paramyxoviruses. However, JHM virus is assembled intracellularly by budding at surfaces of smooth membranous vacuoles. A comparison of JHM virus replication in L2 and 17Cl-1 cell lines revealed that L2 cells undergo more rapid cytopathology and cease virus production much sooner than 17Cl-l cells. In L2 cells the accumulation of core material appears to continue after the abrupt cessation of virus assembly. This is evident by the massive cytoplasmic accumulation of structure resembling nucleocapsids, which react with hybridoma antibody to the nucleocapsid antigen as demonstrated by the immunoperoxidase procedure. The current findings are consistent with our previously published demonstration, using cells of neural and other deviation, of the fundamental role of the host cell type in regulating the replication and expression of coronaviruses

Sub-Natural-Linewidth Quantum Interference Features Observed in Photoassociation of a Thermal Gas

By driving photoassociation transitions we form electronically excited molecules (Na$_2^*$) from ultra-cold (50-300 $\mu$K) Na atoms. Using a second laser to drive transitions from the excited state to a level in the molecular ground state, we are able to split the photoassociation line and observe features with a width smaller than the natural linewidth of the excited molecular state. The quantum interference which gives rise to this effect is analogous to that which leads to electromagnetically induced transparency in three level atomic $\Lambda$ systems, but here one of the ground states is a pair of free atoms while the other is a bound molecule. The linewidth is limited primarily by the finite temperature of the atoms.Comment: 4 pages, 5 figure

An Analysis of Intrinsic Motivation in a Summer Enrichment Program for Economically Disadvantaged Middle-School Students

Digitized thesi

Patients with Essential thrombocythaemia have an increased prevalence of antiphospholipid antibodies which may be associated with thrombosis

A significant proportion of patients with Essential Thrombocythaemia (ET) have thrombotic complications which have an important impact upon the quality, and duration of their life. We performed a retrospective cross sectional study of the prevalence of antiphospholipid antibodies (APA) in 68 ET patients. Compared to 200 elderly controls (> 50 years) there was a significant increase in anticardiolipin IgM (p < 0.0001) and anti β2 glycoprotein I (anti-β2GPI) IgM (p < 0.0001) antibodies in ET. Thrombosis occurred in 10/20 with APA and 12/48 without, p = 0.04, relative risk 2.0 (95% confidence intervals 1.03-3.86); these patients did not differ in terms of other clinical features. The prevalence of thrombosis in patients with dual APA (6/7) was significant when compared to those with single APA (p = 0.02) and the remaining patients (p < 0.0002). Also anti-β2GPI IgM antibodies either alone, or in combination with another APA, were associated with thrombosis (p = 0.02). These results suggest that the prevalence of APA in ET and their influence upon thrombotic risk merit investigation in a larger study

Encouraging users to improve password security and memorability

Security issues in text-based password authentication are rarely caused by technical issues, but rather by the limitations of human memory, and human perceptions together with their consequential responses. This study introduces a new user-friendly guideline approach to password creation, including persuasive messages that motivate and influence users to select more secure and memorable text passwords without overburdening their memory. From a broad understanding of human factors-caused security problems, we offer a reliable solution by encouraging users to create their own formula to compose passwords. A study has been conducted to evaluate the efficiency of the proposed password guidelines. Its results suggest that the password creation methods and persuasive message provided to users convinced them to create cryptographically strong and memorable passwords. Participants were divided into two groups in the study. The participants in the experimental group who were given several password creation methods along with a persuasive message created more secure and memorable passwords than the participants in the control group who were asked to comply with the usual strict password creation rules. The study also suggests that our password creation methods are much more efficient than strict password policy rules. The security and usability evaluation of the proposed password guideline showed that simple improvements such as adding persuasive text to the usual password guidelines consisting of several password restriction rules make significant changes to the strength and memorability of passwords. The proposed password guidelines are a low-cost solution to the problem of improving the security and usability of text-based passwords