26,099 research outputs found
Kinetic Inflation in Stringy and Other Cosmologies
An inflationary epoch driven by the kinetic energy density in a dynamical
Planck mass is studied. In the conformally related Einstein frame it is easiest
to see the demands of successful inflation cannot be satisfied by kinetic
inflation alone. Viewed in the original Jordan-Brans-Dicke frame, the obstacle
is manifest as a kind of graceful exit problem and/or a kind of flatness
problem. These arguments indicate the weakness of only the simplest
formulation. {}From them can be gleaned directions toward successful kinetic
inflation.Comment: 26 pages, LaTeX, CITA-94-2
Evolution of the bursting-layer wave during a Type 1 X-ray burst
In a popular scenario due to Heyl, quasi periodic oscillations (QPOs) which
are seen during type 1 X-ray bursts are produced by giant travelling waves in
neutron-star oceans. Piro and Bildsten have proposed that during the burst
cooling the wave in the bursting layer may convert into a deep crustal
interface wave, which would cut off the visible QPOs. This cut-off would help
explain the magnitude of the QPO frequency drift, which is otherwise
overpredicted by a factor of several in Heyl's scenario. In this paper, we
study the coupling between the bursting layer and the deep ocean. The coupling
turns out to be weak and only a small fraction of the surface-wave energy gets
transferred to that of the crustal-interface wave during the burst. Thus the
crustal-interface wave plays no dynamical role during the burst, and no early
QPO cut-off should occur.Comment: 8 pages, submitted to MNRA
Calibration of the visible and near-infrared channels of the LANDSAT-5 Thematic Mapper using high-altitude aircraft measurements
Visible near-infrared sensors mounted on operational satellites now in use do not have on-board full aperture absolute calibration devices. One means of establishing an in-orbit calibration for a satellite sensor is to make simultaneous measurements of a bright, uniform scene along the satellite view vector from a calibrated instrument on board a high altitude aircraft. In the work reported here, aircraft data were recorded over White Sands, New Mexico at satellite overpass time for the LANDSAT-5 Thematic Mapper (TM). A comparison of the coincident aircraft and orbiting satellite data showed the radiometric gain for TM channel 1 had degraded 4.7 percent by August 28, 1985; gains for TM channels 2 and 3 were within 1 percent of prelaunch values
Hybrid vehicle assessment. Phase 1: Petroleum savings analysis
The results of a comprehensive analysis of near term electric hybrid vehicles are presented, with emphasis on their potential to save significant amounts of petroleum on a national scale in the 1990s. Performance requirements and expected annual usage patterns of these vehicles are first modeled. The projected U.S. fleet composition is estimated, and conceptual hybrid vehicle designs are conceived and analyzed for petroleum use when driven in the expected annual patterns. These petroleum consumption estimates are then compared to similar estimates for projected 1990 conventional vehicles having the same performance and driven in the same patterns. Results are presented in the form of three utility functions and comparisons of sevral conceptual designs are made. The Hybrid Vehicle (HV) design and assessment techniques are discussed and a general method is explained for selecting the optimum energy management strategy for any vehicle mission battery combination. Conclusions and recommendations are presented, and development recommendations are identified
Cosmic microwave background multipole alignments in slab topologies
Several analyses of the microwave sky maps from the Wilkinson Microwave
Anisotropy Probe (WMAP) have drawn attention to alignments amongst the
low-order multipoles. Amongst the various possible explanations, an effect of
cosmic topology has been invoked by several authors. We focus on an alignment
of the first four multipoles (\ell = 2 to 5) found by Land and Magueijo (2005),
and investigate the distribution of their alignment statistic for a set of
simulated cosmic microwave background maps for cosmologies with slab-like
topology. We find that this topology does offer a modest increase in the
probability of the observed value, but that even for the smallest topology
considered the probability of the observed value remains below one percent.Comment: 6 pages RevTex with 6 figures included. Minor changes to match
version accepted as Physical Review D Rapid Communicatio
Spin frequency evolution and pulse profile variations of the recently re-activated radio magnetar XTE J1810-197
After spending almost a decade in a radio-quiet state, the Anomalous X-ray
Pulsar XTE J1810-197 turned back on in early December 2018. We have observed
this radio magnetar at 1.5 GHz with ~daily cadence since the first detection of
radio re-activation on 8 December 2018. In this paper, we report on the current
timing properties of XTE J1810-197 and find that the magnitude of the spin
frequency derivative has increased by a factor of 2.6 over our 48-day data set.
We compare our results with the spin-down evolution reported during its
previous active phase in the radio band. We also present total intensity pulse
profiles at five different observing frequencies between 1.5 and 8.4 GHz,
collected with the Lovell and the Effelsberg telescopes. The profile evolution
in our data set is less erratic than what was reported during the previous
active phase, and can be seen varying smoothly between observations. Profiles
observed immediately after the outburst show the presence of at least five
cycles of a very stable ~50-ms periodicity in the main pulse component that
lasts for at least tens of days. This remarkable structure is seen across the
full range of observing frequencies.Comment: 9 pages, 7 figures, updated with additional analysis of the 50-ms
oscillation, accepted for publication in MNRA
Appropriating the Returns from Industrial Research and Development
macroeconomics, industrial research and development, patent law
Statistical isotropy of the Cosmic Microwave Background
The breakdown of statistical homogeneity and isotropy of cosmic perturbations
is a generic feature of ultra large scale structure of the cosmos, in
particular, of non trivial cosmic topology. The statistical isotropy (SI) of
the Cosmic Microwave Background temperature fluctuations (CMB anisotropy) is
sensitive to this breakdown on the largest scales comparable to, and even
beyond the cosmic horizon. We propose a set of measures,
() which for non-zero values indicate and quantify statistical
isotropy violations in a CMB map. We numerically compute the predicted
spectra for CMB anisotropy in flat torus universe models.
Characteristic signature of different models in the spectrum are
noted.Comment: Presented at PASCOS'03, January 3-8, 2003, in TIFR, Mumbai; to be
published in a special issue of 'Pramana' (4 pages, 1 figure, style files
included
Uniqueness of the solution to inverse scattering problem with scattering data at a fixed direction of the incident wave
Let be real-valued compactly supported sufficiently smooth function.
It is proved that the scattering data , determine uniquely. Here is a fixed
direction of the incident plane wave
- …