Photoassociation dynamics in a Bose-Einstein condensate

A dynamical many body theory of single color photoassociation in a Bose-Einstein condensate is presented. The theory describes the time evolution of a condensed atomic ensemble under the influence of an arbitrarily varying near resonant laser pulse, which strongly modifies the binary scattering properties. In particular, when considering situations with rapid variations and high light intensities the approach described in this article leads, in a consistent way, beyond standard mean field techniques. This allows to address the question of limits to the photoassociation rate due to many body effects which has caused extensive discussions in the recent past. Both, the possible loss rate of condensate atoms and the amount of stable ground state molecules achievable within a certain time are found to be stronger limited than according to mean field theory. By systematically treating the dynamics of the connected Green's function for pair correlations the resonantly driven population of the excited molecular state as well as scattering into the continuum of non-condensed atomic states are taken into account. A detailed analysis of the low energy stationary scattering properties of two atoms modified by the near resonant photoassociation laser, in particular of the dressed state spectrum of the relative motion prepares for the analysis of the many body dynamics. The consequences of the finite lifetime of the resonantly coupled bound state are discussed in the two body as well as in the many body context. Extending the two body description to scattering in a tight trap reveals the modifications to the near resonant adiabatic dressed levels caused by the decay of the excited molecular state.Comment: 27 pages revtex, 16 figure

Topological Degeneracy and Vortex Manipulation in Kitaev's Honeycomb Model

The classification of loop symmetries in Kitaev's honeycomb lattice model provides a natural framework to study the Abelian topological degeneracy. We derive a perturbative low-energy effective Hamiltonian that is valid to all orders of the expansion and for all possible toroidal configurations. Using this form we demonstrate at what order the system's topological degeneracy is lifted by finite size effects and note that in the thermodynamic limit it is robust to all orders. Further, we demonstrate that the loop symmetries themselves correspond to the creation, propagation, and annihilation of fermions. We note that these fermions, made from pairs of vortices, can be moved with no additional energy cost

Association of sleep quality and internet addiction among the medical students

Background: The side effects of Internet overuse have been emerging progressively causing the emergence of a problem that is defined as internet addiction or problematic internet use. It also disrupts the sleep wake cycle so adversely affecting quality of sleep. This study is a preliminary step toward understanding the effect of internet addiction on sleep quality among medical college students in India.Methods: This was an observational, cross-sectional, single-centred, and self-assessable. Questionnaire based study administrated among 525 consenting medical students. The participants were assessed by proforma containing demographic details, variables related with internet use, questionnaires of IAT (Internet Addiction Test for Internet Use) and PSQI (Pittsburgh Sleep Quality Index for Sleep quality. Statistical data were analysed by Graph Pad InStat version 3.06 using Chi–square test and Mann-Whitney test.Results: There were 9.3% of all participants were considered problematic internet users with frequency of internet addiction 0.9%. Participants with problematic internet use are likely to have poor sleep quality (p<0.0001). 23.8% of all participants had poor sleep quality and 76.2% of the students had good quality of sleep. Participants with poor quality of sleep were having high IAT scores in comparison to participants with good quality of sleep. Severity of poor sleep quality is positively correlated with internet addiction (r2=0.233, p<0.0001).Conclusions: Participants with problematic internet use were more likely to have poor quality of sleep and vice a versa

Exact results for the star lattice chiral spin liquid

We examine the star lattice Kitaev model whose ground state is a a chiral spin liquid. We fermionize the model such that the fermionic vacua are toric code states on an effective Kagome lattice. This implies that the Abelian phase of the system is inherited from the fermionic vacua and that time reversal symmetry is spontaneously broken at the level of the vacuum. In terms of these fermions we derive the Bloch-matrix Hamiltonians for the vortex free sector and its time reversed counterpart and illuminate the relationships between the sectors. The phase diagram for the model is shown to be a sphere in the space of coupling parameters around the triangles of the lattices. The abelian phase lies inside the sphere and the critical boundary between topologically distinct Abelian and non-Abelian phases lies on the surface. Outside the sphere the system is generically gapped except in the planes where the coupling parameters are zero. These cases correspond to bipartite lattice structures and the dispersion relations are similar to that of the original Kitaev honeycomb model. In a further analysis we demonstrate the three-fold non-Abelian groundstate degeneracy on a torus by explicit calculation.Comment: 7 pages, 8 figure

Plasmid profile, antibiotic resistance, and phenotypic virulent strains of S. flexneri

Shigellosis is an acute gastroenteritis caused by Shigella species. The purpose of this study was to determine plasmid profile, antibiotic resistance and phenotypic virulent by Congo red between S. flexneri strains. The isolated bacteria were identified by standard bacterial and biochemical methods. Plasmids were isolated by alkaline lysis method. Antibiotic susceptibility test was performed according to "kirby-Bauer" method. Serological reactions were carried by slide agglutination tests with both polyclonal and monoclonal antiserum kits. Virulent strains were isolated on a TSA plate contained Congo red dye concentration. From 350 isolated Shigella species, 142 (40.57) were S. flexneri. Eleven distinct plasmid profile patterns were identified. Of S. flexneri isolates, 95 were resistant to tetracycline, 85.6 to SXT and 75.3 to ampicillin. All the isolates were sensitive to ciprofloxacin. Our results showed that 39 were serotype II. 45.56 of S. flexneri were Congo red positive. Antibiotic resistant determination in each case may prevent drug resistance increase. Since Congo red binding test is cheap and simple it can be used to determine virulence properties of S. flexneri

Perfect initialization of a quantum computer of neutral atoms in an optical lattice of large lattice constant

We propose a scheme for the initialization of a quantum computer based on neutral atoms trapped in an optical lattice with large lattice constant. Our focus is the development of a compacting scheme to prepare a perfect optical lattice of simple orthorhombic structure with unit occupancy. Compacting is accomplished by sequential application of two types of operations: a flip operator that changes the internal state of the atoms, and a shift operator that moves them along the lattice principal axis. We propose physical mechanisms for realization of these operations and we study the effects of motional heating of the atoms. We carry out an analysis of the complexity of the compacting scheme and show that it scales linearly with the number of lattice sites per row of the lattice, thus showing good scaling behavior with the size of the quantum computer.Comment: 18 page

Exact ground states of a staggered supersymmetric model for lattice fermions

We study a supersymmetric model for strongly interacting lattice fermions in the presence of a staggering parameter. The staggering is introduced as a tunable parameter in the manifestly supersymmetric Hamiltonian. We obtain analytic expressions for the ground states in the limit of small and large staggering for the model on the class of doubly decorated lattices. On this type of lattice there are two ground states, each with a different density. In one limit we find these ground states to be a simple Wigner crystal and a valence bond solid (VBS) state. In the other limit we find two types of quantum liquids. As a special case, we investigate the quantum liquid state on the one dimensional chain in detail. It is characterized by a massless kink that separates two types of order.Comment: 21 pages, 6 figures, v2: largely rewritten version with more emphasis on physical interpretatio

Determination of distribution of icsA gene and IcsA protein bands between Shigella flexneri isolated from 3 hospitals in Tehran

Introduction: Shigella is a facultative intracellular pathogen that uses the host actin cytoskeleton protein for intra- and intercellular spread. The aim of this study was to determine the distribution of icsA gene and IcsA expressed protein bands among Shigella flexneri strains isolated from 3 clinical centers in Tehran. Material and Methods: Two hundred and seventy five isolated Shigella flexneri strains were identified by standard microbiological and biochemical methods. DNA isolation was performed using sodium perchlorate method. Hot start-PCR was done with 2 pairs of primers and the products were separated through agarose gel (0.8) in TAE buffer. DNA fragments were visualized by ethidium bromide staining under UV illumination. Whole membrane preparation was used to examine the protein profiles and identification of probable IcsA (120-kda) protein band by SDS-PAGE. Results: From 100 isolated Shigella flexneri strains, both bands of 1600 bp and 1709 bp were detected in 46 isolates (46). A 120 kDa band which seems to be related to IcsA protein was detected in 46 isolates (46). The protein bands varied between 30 and 150 kDa. Discussion: IcsA is both necessary and sufficient for actin assembly in Shigella flexneri. Since icsA gene and IcsA protein band were not found in all Shigella strains, it seems that not all strains have the same pathogenesis. On the other hand, since the demonstration of icsA gene by PCR in all Shigella strains (46) corresponded to the presence of a 120 kDa protein band by SDS-PAGE (46), it seems that both tests may confirm each other. However, the PCR may be more accurate than SDS-PAGE