118708943
Multi-taper Spectral Analysis in Gravitational Wave Data Analysis
Spectral estimation plays a significant role in gravitational wave data analysis. We provide a brief introduction to multi-taper methods which use multiple orthogonal tapers (or windows) to provide spectral estimators with excellent bias and variance properties. Multi-taper methods are also extremely powerful for the estimation and removal of sharp spectral peaks in the presence of noise such as arise due to power line harmonics or suspension resonances. We present examples of these methods using the GRASP (Gravitational Radiation Analysis and Simulation Package) software package.
118590129
CMB anisotropy due to cosmic strings: Large angular scale
17612131
CBR Anisotropy from Primordial Gravitational Waves in Two-Component Inflationary Cosmology
We examine stochastic temperature fluctuations of the cosmic background radiation (CBR) arising via the Sachs-Wolfe effect from gravitational wave perturbations produced in the early universe. We consider spatially flat, perturbed FRW models that begin with an inflationary phase, followed by a mixed phase containing both radiation and dust. The scale factor during the mixed phase takes the form a(η) = c1η 2 + c2η + c3, where ci are constants. During the mixed phase the universe smoothly transforms from being radiation to dust dominated. We find analytic expressions for the graviton mode function during the mixed phase in terms of spheroidal wave functions. This mode function is used to find an analytic expression for the multipole moments 〈al 〉 of the two-point angular correlation function C(γ) for the CBR anisotropy. The analytic expression for the multipole moments is written in terms of two integrals, which are evaluated numerically. The results are compared to multipoles calculated for models that are completely dust dominated at last-scattering. We find that the multipoles 〈al 〉 of the CBR temperature perturbations for l > 10 are significantly larger for a universe that contains both radiation and dust at last-scattering. We compare our results with recent, similar numerical work and find good agreement. The spheroidal wave functions may have applications to other problems of cosmological interest. PACS numbers: 98.80.Cq, 98.80.C, 98.80.Es Typeset using REVTEX
119876695
Gravitons in de sitter space
What has been shown in this talk is that the graviton propagator in de Sitter space is OK. If one makes a bad choice of gauge (-fixing term) then the propagator is infra-red divergent. However this is not a problem. You can either make a better choice of gauge (of which there are an infinite number), for which the propagator is completely, finite, or else you can go right ahead and use the infra-red divergent one. We demonstrated that it doesn't matter. Gauge-invariance is the over-riding principle, and it ensures that even if the propagator has an infra-red divergence, the physical scattering amplitudes are finite.
32994345
The PALFA Survey: Going to great depths to find radio pulsars
The on-going PALFA survey is searching the Galactic plane (|b| < 5 ◦ , 32 ◦ < l < 77 ◦ and 168 ◦ < l < 214 ◦ ) for radio pulsars at 1.4 GHz using ALFA, the 7-beam receiver installed at the Arecibo Observatory. By the end of August 2012, the PALFA survey has discovered 100 pulsars, including 17 millisecond pulsars (P < 30 ms). Many of these discoveries are among the pulsars with the largest DM/P ratios, proving that the PALFA survey is capable of probing the Galactic plane for millisecond pulsars to a much greater depth than any previous survey. This is due to the survey's high sensitivity, relatively high observing frequency, and its high time and frequency resolution. Recently the rate of discoveries has increased, due to a new more sensitive spectrometer, two updated complementary search pipelines, the development of online collaborative tools, and access to new computing resources. Looking forward, focus has shifted to the application of artificial intelligence systems to identify pulsar-like candidates, and the development of an improved full-resolution pipeline incorporating more sophisticated radio interference rejection. The new pipeline will be used in a complete second analysis of data already taken, and will be applied to future survey observations. An overview of recent developments, and highlights of exciting discoveries will be presented.
28973038
Cosmic string loops and large-scale structure
We investigate the contribution made by small loops from a cosmic string network as seeds for large-scale structure formation. We show that cosmic string loops are highly correlated with the long-string network on large scales and therefore contribute significantly to the power spectrum of density perturbations if the average loop lifetime is comparable to or above one Hubble time. This effect further improves the large-scale bias problem previously identified in earlier studies of cosmic string models. @S0556-2821~99!01614-8# Quantitative predictions for the large-scale structure induced by cosmic strings have taken some time to crystallize as the understanding of cosmic string physics has improved @1#. In particular, the role of small loops produced by the string network has evolved from a potential one-to-one correspondence between loops and cosmological objects @2# through to a completely subsidiary role relative to the wakes swept out by long strings @3#. This dethronement of loops was a result of numerical studies which showed that the average loop size l ¯ 5at was much smaller than the horizon,
29439632
PROGRESS IN EXPERIMENTAL STUDY OF CURRENT FILAMENTATION INSTABILITY
Current Filamentation Instability, CFI, is of central importance for the propagation of relativistic electron beams in plasmas. CFI could play an important role in the generation of magnetic fields and radiation in the afterglow of gamma ray bursts and also in energy transport for the fast-igniter inertial confinement fusion concept. Simulations were conducted with the particle-in-cell code QuickPIC for e beam and plasma parameters at the Brookhaven National Laboratory – Accelerator Test Facility, BNL-ATF. Results show that for a 2cm plasma the instability reaches near saturation. An experimental program was proposed and accepted at the BNL-ATF and an experiment is currently underway. There are three components to the experimental program: 1) imaging of the filaments, beam density, at the exit from the plasma, 2) measurement and imaging of the transverse plasma density gradient and measurement of the magnetic field and 3) identifying the radiation spectrum of the instability. Preliminary results from phase one will be presented along with the progress and diagnostic design for the following phases of the experiment.
117206415
Event‐by‐Event Energy Estimation and Spectral Determination with Milagro
The observed characteristics of a TeV gamma ray shower which triggers Milagro depend on core location, zenith angle, and primary energy. An algorithm to estimate the primary energy on an event‐by‐event basis based upon observed quantities has been devised. This algorithm is applied to signals observed from sources to determine energy spectra in the energy range 1 to 100 TeV. Results for spectral determination are presented for the Crab nebula. For the Crab nebula our results are similar to atmospheric Cherenkov telescope measurements.
122963493
Neutron-Capture Cross Sections of the Stable Lead Isotopes
Neutron-capture yields for several samples of separated lead isotopes were obtained at the Oak Ridge electron linear accelerator, in the neutron energy range above 2.5 keV. These were analyzed for resonance-capture areas and parameters. The data are included in a new evaluation of lead cross-section data.
9139935
ProtoEXIST: advanced prototype CZT coded aperture telescopes for EXIST
ProtoEXIST1 is a pathfinder for the EXIST-HET, a coded aperture hard X-ray telescope with a 4.5 m2 CZT detector plane a 90x70 degree field of view to be flown as the primary instrument on the EXIST mission and is intended to monitor the full sky every 3 h in an effort to locate GRBs and other high energy transients. ProtoEXIST1 consists of a 256 cm2 tiled CZT detector plane containing 4096 pixels composed of an 8x8 array of individual 1.95 cm x 1.95 cm x 0.5 cm CZT detector modules each with a 8 x 8 pixilated anode configured as a coded aperture telescope with a fully coded 10° x 10° field of view employing passive side shielding and an active CsI anti-coincidence rear shield, recently completed its maiden flight out of Ft. Sumner, NM on the 9th of October 2009. During the duration of its 6 hour flight on-board calibration of the detector plane was carried out utilizing a single tagged 198.8 nCi Am-241 source along with the simultaneous measurement of the background spectrum and an observation of Cygnus X-1. Here we recount the events of the flight and report on the detector performance in a near space environment. We also briefly discuss ProtoEXIST2: the next stage of detector development which employs the NuSTAR ASIC enabling finer (32×32) anode pixilation. When completed ProtoEXIST2 will consist of a 256 cm2 tiled array and be flown simultaneously with the ProtoEXIST1 telescope.
68858618
Targeted cancer therapy: The Potential role of Tb-149