18125734
Contribution of Compact Mass Transferring Systems to the Galactic Gravitational Wave Background
Compact object binaries, mostly double with dwarfs, are believed to be a potential source of confusion-limited noise for the Laser Interferometer Space Antenna (LISA). In a specific frequency range, this noise may rise above the instrumental noise sources and hence hinder detection of other types of signals, e.g. extreme mass ratio inspirals of stellar mass objects into supermassive black holes. In most previous studies only detached populations of compact object binaries have been considered. Here, we investigate the influence of Galactic populations of compact mass transferring binaries on the shape and strength of the LISA signal and compare our results with the signal for detached binaries only. Our population synthesis includes all binary systems containing two compact remnants. It is found that 99.5% of these systems are double white dwarfs, and therefore we consider only binaries consisting of two white dwarfs when calculating the LISA signal. We find that the mass transferring binaries contributing to the confusion limited noise dominate the population of LISA systems by number (60%), due to their long lifetimes (few Gyrs). However, due to the very specific physical properties of mass transferring systems, it is found that their contribution to the noise is negligible at low frequencies and detached systems will set the magnitude of the confusion-limited signal in this range. However, the mass transferring systems begin to dominate the signal at higher frequencies (f>6 mHz). The transition frequency at which the confusion limited regime becomes important is found at 4 mHz. The addition of mass transferring systems tends to slightly increase the transition frequency (from 3.5 to 4 mHz).
118214092
Addressing LISA Science Analysis Challenges
The principal goal of the \emph{LISA Science Analysis Workshop} is to encourage the development and maturation of science analysis technology in preparation for LISA science operations. Exactly because LISA is a pathfinder for a new scientific discipline -- gravitational wave astronomy -- LISA data processing and science analysis methodologies are in their infancy and require considerable maturation if they are to be ready to take advantage of LISA data. Here we offer some thoughts, in anticipation of the LISA Science Analysis Workshop, on analysis research problems that demonstrate the capabilities of different proposed analysis methodologies and, simultaneously, help to push those techniques toward greater maturity. Particular emphasis is placed on formulating questions that can be turned into well-posed problems involving tests run on specific data sets, which can be shared among different groups to enable the comparison of techniques on a well-defined platform.
118800207
Telescope Array Radar (TARA) Observatory for Ultra-High Energy Cosmic Rays
Abstract Construction was completed during summer 2013 on the Telescope Array RAdar (TARA) bi-static radar observatory for Ultra-High Energy Cosmic Rays (UHECR). TARA is co-located with the Telescope Array, the largest “conventional” cosmic ray detector in the Northern Hemisphere, in radio-quiet Western Utah. TARA employs an 8 MW Effective Radiated Power (ERP) VHF transmitter and smart receiver system based on a 250 MS/s data acquisition system in an effort to detect the scatter of sounding radiation by UHECR-induced atmospheric ionization. TARA seeks to demonstrate bi-static radar as a useful new remote sensing technique for UHECRs. In this report, we describe the design and performance of the TARA transmitter and receiver systems.
6702366
Null geodesics in the Alcubierre warp drive spacetime: the view from the bridge
The null geodesic equations in the Alcubierre warp-drive spacetime are numerically integrated to determine the angular deflection and redshift of photons which propagate through the distortion of the 'warp-drive' bubble to reach an observer at the origin of the warp effect. We find that for a starship with an effective warp speed exceeding the speed of light, stars in the forward hemisphere will appear closer to the direction of motion than they would to an observer at rest. This aberration is qualitatively similar to that caused by special relativity. Behind the starship, a conical region forms from within which no signal can reach the starship, an effective 'horizon'. Conversely, there is also a horizon-like structure in a conical region in front of the starship, into which the starship cannot send a signal. These causal structures are somewhat analogous to the Mach cones associated with supersonic fluid flow.
117048003
The Testbed for LISA Analysis Project
The Testbed for LISA Analysis (TLA) Project aims to facilitate the development, validation and comparison of different methods for LISA science data analysis, by the broad LISA Science Community, to meet the special challenges that LISA poses. It includes a well-defined Simulated LISA Data Product (SLDP), which provides a clean interface between the communities that have developed to model and to analyze the LISA science data stream; a web-based clearinghouse (at ) providing SLDP software libraries, relevant software, papers and other documentation, and a repository for SLDP data sets; a set of mailing lists for communication between and among LISA simulators and LISA science analysts; a problem tracking system for SLDP support; and a program of workshops to allow the burgeoning LISA science community to further refine the SLDP definition, define specific LISA science analysis challenges, and report their results. This note describes the TLA Project, the resources it provides immediately, its future plans, and invites the participation of the broader community in the furtherance of its goals.
56410155
LISA data analysis: Source identification and subtraction
The Laser Interferometer Space Antenna will operate as an AM-FM receiver for gravitational waves. For binary systems, the source location, orientation and orbital phase are encoded in the amplitude and frequency modulation. The same modulations spread a monochromatic signal over a range of frequencies, making it difficult to identify individual sources. We present a method for detecting and subtracting individual binary signals from a data stream with many overlapping signals.
98032634
Progress in the Development of an Alternative Approach to Macromolecular Crystallization
We are developing an alternate strategy for the crystallization of macromolecules that does not, like current methods, depend on the optimization of traditional variables such as pH and precipitant concentration, but is based on the hypothesis that many conventional small molecules might establish stabilizing, intermolecular, noncovalent cross-links in crystals, and thereby promote lattice formation. Earlier experiments provided encouraging results that suggested further research was warranted (Larson, S. B.; Day, J. S.; Cudney, R.; McPherson, A. A novel strategy for the crystallization of proteins: X-ray diffraction validation. Acta Crystallogr., D: Biol. Crystallogr. 2007, 63, 310−318. McPherson, A.; Cudney, B. Searching for silver bullets: an alternative strategy for crystallizing macromolecules. J. Struct. Biol. 2006, 156, 387−406). Here we report additional, large-scale crystallization screening experiments that lend further support, though they suggest that additional mechanisms may play a positive ...
38714824
The structure of tomato aspermy virus by X-ray crystallography.
The three-dimensional structure of tomato aspermy virus (TAV) has been solved by X-ray crystallography and refined to an R factor of 0.218 for 3.4-40 A data (effective resolution of 4A). Molecular replacement, using cucumber mosaic virus (Smith et al., 2000), provided phases for the initial maps used for model building. The coat protein of the 280 A diameter virion has the canonical "Swiss roll" beta-barrel topology with a distinctive amino-terminal alpha-helix directed into the interior of the virus where it interacts with encapsidated RNA. The N-terminal helices are joined to the beta-barrels of protein subunits by extended polypeptides of six amino acids, which serve as flexible hinges allowing movement of the helices in response to local RNA distribution. Segments of three nucleotides of partially disordered RNA interact with the capsid, primarily through arginine residues, at interfaces between A and B subunits. Side chains of cys64 and cys106 form the first disulfide observed in a cucumovirus, including a unique cysteine, 106, in a region otherwise conserved. A positive ion, putatively modeled as a Mg(+)ion, lies on the quasi-threefold axis surrounded by three quasi-symmetric glutamate 175 side chains.