A rapidly expanding Bose-Einstein condensate: an expanding universe in the lab

We study the dynamics of a supersonically expanding ring-shaped Bose-Einstein condensate both experimentally and theoretically. The expansion redshifts long-wavelength excitations, as in an expanding universe. After expansion, energy in the radial mode leads to the production of bulk topological excitations -- solitons and vortices -- driving the production of a large number of azimuthal phonons and, at late times, causing stochastic persistent currents. These complex nonlinear dynamics, fueled by the energy stored coherently in one mode, are reminiscent of a type of "preheating" that may have taken place at the end of inflation.Comment: 12 pages, 7 figure

Self-similar collapse and the structure of dark matter halos: A fluid approach

We explore the dynamical restrictions on the structure of dark matter halos through a study of cosmological self-similar gravitational collapse solutions. A fluid approach to the collisionless dynamics of dark matter is developed and the resulting closed set of moment equations are solved numerically including the effect of halo velocity dispersions (both radial and tangential), for a range of spherically averaged initial density profiles. Our results highlight the importance of tangential velocity dispersions to obtain density profiles shallower than $1/r^2$ in the core regions, and for retaining a memory of the initial density profile, in self-similar collapse. For an isotropic core velocity dispersion only a partial memory of the initial density profile is retained. If tangential velocity dispersions in the core are constrained to be less than the radial dispersion, a cuspy core density profile shallower than $1/r$ cannot obtain, in self-similar collapse.Comment: 25 pages, 7 figures, submitted to Ap

Robustly Unstable Eigenmodes of the Magnetoshearing Instability in Accretion Disk

The stability of nonaxisymmetric perturbations in differentially rotating astrophysical accretion disks is analyzed by fully incorporating the properties of shear flows. We verify the presence of discrete unstable eigenmodes with complex and pure imaginary eigenvalues, without any artificial disk edge boundaries, unlike Ogilvie & Pringle(1996)'s claim. By developing the mathematical theory of a non-self-adjoint system, we investigate the nonlocal behavior of eigenmodes in the vicinity of Alfven singularities at omega_D=omega_A, where omega_D is the Doppler-shifted wave frequency and omega_A=k_// v_A is the Alfven frequency. The structure of the spectrum of discrete eigenmodes is discussed and the magnetic field and wavenumber dependence of the growth rate are obtained. Exponentially growing modes are present even in a region where the local dispersion relation theory claims to have stable eigenvalues. The velocity field created by an eigenmode is obtained, which explains the anomalous angular momentum transport in the nonlinear stage of this stability.Comment: 11pages, 11figures, to be published in ApJ. For associated eps files, see http://dino.ph.utexas.edu/~knoguchi

Synchronization Algorithms for Multi-cores and Multiprocessors

A distributed system is a group of processors that do not allocate memory. As an alternative, each processor has its own local memory, and the processors communicate with one another through communication lines such as local-area or wide-area networks. The processors in a distributed system vary in size and function. Such systems may include small handheld or real-time devices, personal computers, workstations, and large mainframe computer systems. Distributed systems, will have their own set of unique challenges, including synchronizing data and creating sense of conflicts. Effective synchronization algorithms performance depends on runtime factors that are rigid to predict. The designers have protocols to employ the synchronization operation and waiting mechanisms to wait for synchronization delays. In this paper an effort is made to investigate synchronization algorithm that vigorously select waiting mechanisms and protocols in response to runtime factors so as to attain enhanced performance. DOI: 10.17762/ijritcc2321-8169.150615

Broad Band Optical Polarimetric Study of IC 1805

We present the BVR broad band polarimetric observations of 51 stars belonging to the young open cluster IC 1805. Along with the photometric data from the literature we have modeled and subtracted the foreground dust contribution from the maximum polarization (P_{max}) and colour excess (E_{B-V}). The mean value of the P_max for intracluster medium and the foreground are found to be 5.008 +/-0.005 % and 4.865 +/-0.022 % respectively. Moreover, the mean value of the wavelength of maximum polarization (lambda_{max}) for intracluster medium is 0.541 +/- 0.003 micro m, which is quite similar as the general interstellar medium (ISM). The resulting intracluster dust component is found to have negligible polarization efficiency as compared to interstellar dust. Some of the observed stars in IC 1805 have shown the indication of intrinsic polarization in their measurements.Comment: 8 pages, 7 figures, Accepted for publication in MNRA

Critically phase-matched Ti:sapphire-laserpumped deep-infrared femtosecond optical parametric oscillator based on CdSiP2

We report a high-repetition-rate femtosecond optical parametric oscillator (OPO) for the deep-infrared (deep-IR) based on type-I critical phase-matching in CdSiP2 (CSP), pumped directly by a Ti:sapphire laser. Using angle-tuning in the CSP crystal, the OPO can be continuously tuned across 7306–8329 nm (1201–1369  cm−1) in the deep-IR. It delivers up to 18 mW of idler average power at 7306 nm and >7  mW beyond 8000 nm at 80.5 MHz repetition rate, with the spectra exhibiting bandwidths of >150  nm across the tuning range. Moreover, the signal is tunable across 1128–1150 nm in the near-infrared, providing up to 35 mW of average power in ∼266  fs pulses at 1150 nm. Both beams exhibit single-peak Gaussian distribution in TEM00 spatial profile. With an equivalent spectral brightness of ∼5.6×1020photons s−1 mm−2 sr−10.1% BW−1, this OPO represents a viable alternative to synchrotron and supercontinuum sources for deep-IR applications in spectroscopy, metrology, and medical diagnostics.Peer ReviewedPostprint (author's final draft

Efficacy of terbutaline in preterm labour - our experience

Background: Preterm birth is one of the important causes of perinatal mortality and morbidity in developed countries after congenital malformations. Postponement of delivery plays essential role in preventing such incidences by allowing fetal lung maturity.Methods: This is a prospective study conducted over a period of 20 months among the patients admitted for preterm labour with gestational period between 27 to 36 weeks. After the patients obeyed all the inclusion criteria, they were administered terbutaline 250 µg subcutaneously every 8th hourly followed by 5 mg tablet orally twice daily till contractions ceased. The patients were analysed for gestational period at which they presented with preterm labour contractions, associated risk factors, response to terbutaline, and gestational period at delivery, perinatal complications, neonatal and maternal outcomes. The data obtained were analysed by descriptive analysis.Results: There were 1,678 deliveries during study period, out of which 207 (12%) presented with preterm labour and 20 (~10%) patients received terbutaline. Idiopathic (50%) and vaginal infections (25%) were common causes of preterm labour among the patients who received terbutaline. The labour was prolonged by 3 - 5 days among 8 patients, 7 - 15 days in 9 patients and 15 - 30 days in 3 patients. Common maternal side effects were nausea and tremors. Neonatal outcome was good in most of the cases except in 5 (25%) neonates who required NICU admission but they all recovered well without any morbidity.Conclusions: Administration of terbutaline prolonged labour without any serious maternal complications and better neonatal outcome as 90% of the neonates were born without any complications. Hence, terbutaline can be used as a safe and effective tocolytic agent among patients presenting with preterm labour

Permissive Controller Synthesis for Probabilistic Systems

We propose novel controller synthesis techniques for probabilistic systems modelled using stochastic two-player games: one player acts as a controller, the second represents its environment, and probability is used to capture uncertainty arising due to, for example, unreliable sensors or faulty system components. Our aim is to generate robust controllers that are resilient to unexpected system changes at runtime, and flexible enough to be adapted if additional constraints need to be imposed. We develop a permissive controller synthesis framework, which generates multi-strategies for the controller, offering a choice of control actions to take at each time step. We formalise the notion of permissivity using penalties, which are incurred each time a possible control action is disallowed by a multi-strategy. Permissive controller synthesis aims to generate a multi-strategy that minimises these penalties, whilst guaranteeing the satisfaction of a specified system property. We establish several key results about the optimality of multi-strategies and the complexity of synthesising them. Then, we develop methods to perform permissive controller synthesis using mixed integer linear programming and illustrate their effectiveness on a selection of case studies