DSpace Collection: Research Papers (TP)
http://hdl.handle.net/2289/144
The Collection's search engineSearch the Channelsearch
http://dspace.rri.res.in:8080/jspui/simple-search
Directed search for gravitational waves from Scorpius X-1 with initial LIGO data
http://hdl.handle.net/2289/6272
Title: Directed search for gravitational waves from Scorpius X-1 with initial LIGO data<br/><br/>Authors: Aasi, J.; Abbott, B.P.; Abbott, R.; Iyer, B.R.; LIGO Scientific Collaboration and Virgo Collaboration; +250 Co authors<br/><br/>Abstract: We present results of a search for continuously emitted gravitational radiation, directed at the brightest low-mass x-ray binary, Scorpius X-1. Our semicoherent analysis covers 10 days of LIGO S5 data ranging from 50–550 Hz, and performs an incoherent sum of coherent F-statistic power distributed amongst frequency-modulated orbital sidebands. All candidates not removed at the veto stage were found to be consistent with noise at a 1% false alarm rate. We present Bayesian 95% confidence upper limits on gravitational-wave strain amplitude using two different prior distributions: a standard one, with no a priori assumptions about the orientation of Scorpius X-1; and an angle-restricted one, using a prior derived from electromagnetic observations. Median strain upper limits of 1.3×10−24 and 8×10−25 are reported at 150 Hz for the standard and angle-restricted searches respectively. This proof-of-principle analysis was limited to a short observation time by unknown effects of accretion on the intrinsic spin frequency of the neutron star, but improves upon previous upper limits by factors of ∼1.4 for the standard, and 2.3 for the angle-restricted search at the sensitive region of the detector.<br/><br/>Description: Open AccessLive cell plasma membranes do not exhibit a miscibility phase transition over a wide range of temperatures
http://hdl.handle.net/2289/6256
Title: Live cell plasma membranes do not exhibit a miscibility phase transition over a wide range of temperatures<br/><br/>Authors: Lee, Hyung; Saha, Suvrajit; Polley, Anirban; Hunag, Hector; Mayor, Satyajit; Rao, Madan; Groves, Jay T.<br/><br/>Abstract: Lipid/cholesterol mixtures derived from cell membranes as well as their synthetic reconstitutions exhibit well-defined miscibility phase transitions and critical phenomena near physiological temperatures. This suggests that lipid/cholesterol-mediated phase separation plays a role in the organization of live cell membranes. However, macroscopic lipid-phase separation is not generally observed in cell membranes, and the degree to which properties of isolated lipid mixtures are preserved in the cell membrane remain unknown. A fundamental property of phase transitions is that the variation of tagged particle diffusion with temperature exhibits an abrupt change as the system passes through the transition, even when the two phases are distributed in a nanometer-scale emulsion. We support this using a variety of Monte Carlo and atomistic simulations on model lipid membrane systems. However, temperature-dependent fluorescence correlation spectroscopy of labeled lipids and membrane-anchored proteins in live cell membranes shows a consistently smooth increase in the diffusion coefficient as a function of temperature. We find no evidence of a discrete miscibility phase transition throughout a wide range of temperatures: 14–37 °C. This contrasts the behavior of giant plasma membrane vesicles (GPMVs) blebbed from the same cells, which do exhibit phase transitions and macroscopic phase separation. Fluorescence lifetime analysis of a DiI probe in both cases reveals a significant environmental difference between the live cell and the GPMV. Taken together, these data suggest the live cell membrane may avoid the miscibility phase transition inherent to its lipid constituents by actively regulating physical parameters, such as tension, in the membrane.<br/><br/>Description: Restricted Access.Advanced LIGO
http://hdl.handle.net/2289/6255
Title: Advanced LIGO<br/><br/>Authors: Aasi, J.; Abbott, B.P.; Abbott, R.; Iyer, B.R.; LIGO Scientific Collaboration and Virgo Collaboration; +250 Co authors<br/><br/>Abstract: The Advanced LIGO gravitational wave detectors are second-generation instruments designed and built for the two LIGO observatories in Hanford, WA and Livingston, LA, USA. The two instruments are identical in design, and are specialized versions of a Michelson interferometer with 4 km long arms. As in Initial LIGO, Fabry–Perot cavities are used in the arms to increase the interaction time with a gravitational wave, and power recycling is used to increase the effective laser power. Signal recycling has been added in Advanced LIGO to improve the frequency response. In the most sensitive frequency region around 100 Hz, the design strain sensitivity is a factor of 10 better than Initial LIGO. In addition, the low frequency end of the sensitivity band is moved from 40 Hz down to 10 Hz. All interferometer components have been replaced with improved technologies to achieve this sensitivity gain. Much better seismic isolation and test mass suspensions are responsible for the gains at lower frequencies. Higher laser power, larger test masses and improved mirror coatings lead to the improved sensitivity at mid and high frequencies. Data collecting runs with these new instruments are planned to begin in mid-2015.<br/><br/>Description: Restricted Access. An open-access version is available at arXiv.org (one of the alternative locations)Characterization of quantum dynamics using quantum error correction
http://hdl.handle.net/2289/6240
Title: Characterization of quantum dynamics using quantum error correction<br/><br/>Authors: Omkar, S.; Srikanth, R.; Banerjee, Subhashish<br/><br/>Abstract: Characterizing noisy quantum processes is important to quantum computation and communication (QCC), since quantum systems are generally open. To date, all methods of characterization of quantum dynamics (CQD), typically implemented by quantum process tomography, are off-line, i.e., QCC and CQD are not concurrent, as they require distinct state preparations. Here we introduce a method, “quantum error correction based characterization of dynamics,” in which the initial state is any element from the code space of a quantum error correcting code that can protect the state from arbitrary errors acting on the subsytem subjected to unknown dynamics. The statistics of stabilizer measurements, with possible unitary preprocessing operations, are used to characterize the noise, while the observed syndrome can be used to correct the noisy state. Our method requires at most 2(4n−1) configurations to characterize arbitrary noise acting on n qubits.<br/><br/>Description: Open Access.