25,047 research outputs found
Opportunities With Decay-At-Rest Neutrinos From Decay-In-Flight Neutrino Beams
Neutrino beam facilities, like spallation neutron facilities, produce copious
quantities of neutrinos from the decay at rest of mesons and muons. The
viability of decay-in-flight neutrino beams as sites for decay-at-rest neutrino
studies has been investigated by calculating expected low-energy neutrino
fluxes from the existing Fermilab NuMI beam facility. Decay-at-rest neutrino
production in NuMI is found to be roughly equivalent per megawatt to that of
spallation facilities, and is concentrated in the facility's target hall and
beam stop regions. Interaction rates in 5 and 60 ton liquid argon detectors at
a variety of existing and hypothetical locations along the beamline are found
to be comparable to the largest existing decay-at-rest datasets for some
channels. The physics implications and experimental challenges of such a
measurement are discussed, along with prospects for measurements at targeted
facilities along a future Fermilab long-baseline neutrino beam.Comment: 6 pages, 3 figure
Acceleration-assisted entanglement harvesting and rangefinding
We study entanglement harvested from a quantum field through local
interaction with Unruh-DeWitt detectors undergoing linear acceleration. The
interactions allow entanglement to be swapped locally from the field to the
detectors. We find an enhancement in the entanglement harvesting by two
detectors with anti-parallel acceleration over those with inertial motion. This
enhancement is characterized by the presence of entanglement between two
detectors that would otherwise maintain a separable state in the absence of
relativistic motion (with the same distance of closest approach in both cases).
We also find that entanglement harvesting is degraded for two detectors
undergoing parallel acceleration in the same way as for two static, comoving
detectors in a de Sitter universe. This degradation is known to be different
from that of two inertial detectors in a thermal bath. We comment on the
physical origin of the harvested entanglement and present three methods for
determining distance between two detectors using properties of the harvested
entanglement. Information about the separation is stored nonlocally in the
joint state of the accelerated detectors after the interaction; a single
detector alone contains none. We also find an example of entanglement sudden
death exhibited in parameter space.Comment: 17 pages, 6 figures. Version 2 updated to address referee comments
and minor correction
A manipulator arm for zero-g simulations
A 12-ft counterbalanced Slave Manipulator Arm (SMA) was designed and fabricated to be used for resolving the questions of operational applications, capabilities, and limitations for such remote manned systems as the Payload Deployment and Retrieval Mechanism (PDRM) for the shuttle, the Free-Flying Teleoperator System, the Advanced Space Tug, and Planetary Rovers. As a developmental tool for the shuttle manipulator system (or PDRM), the SMA represents an approximate one-quarter scale working model for simulating and demonstrating payload handling, docking assistance, and satellite servicing. For the Free-Flying Teleoperator System and the Advanced Tug, the SMA provides a near full-scale developmental tool for satellite servicing, docking, and deployment/retrieval procedures, techniques, and support equipment requirements. For the Planetary Rovers, it provides an oversize developmental tool for sample handling and soil mechanics investigations. The design of the SMA was based on concepts developed for a 40-ft NASA technology arm to be used for zero-g shuttle manipulator simulations
Summary of the electromagnetic compatibility evaluation of the proposed satellite power system
The effects of the proposed solar power satellite (SPS) operations on electronic equipment and systems by fundamental, harmonic, and intermodulation component emissions from the orbital station; and the fundamental, harmonic, and structural intermodulation emissions from the rectenna site were evaluated. The coupling and affects interactions affecting a wide spectrum of electronic equipment are considered. The primary EMC tasking areas are each discussed separately
Using ACIS on the Chandra X-ray Observatory as a particle radiation monitor
The Advanced CCD Imaging Spectrometer (ACIS) is one of two focal-plane
instruments on the Chandra X-ray Observatory. During initial radiation-belt
passes, the exposed ACIS suffered significant radiation damage from trapped
soft protons scattering off the x-ray telescope's mirrors. The primary effect
of this damage was to increase the charge-transfer inefficiency (CTI) of the
ACIS 8 front-illuminated CCDs. Subsequently, the Chandra team implemented
procedures to remove the ACIS from the telescope's focus during high-radiation
events: planned protection during radiation-belt transits; autonomous
protection triggered by an on-board radiation monitor; and manual intervention
based upon assessment of space-weather conditions. However, as Chandra's
multilayer insulation ages, elevated temperatures have reduced the
effectiveness of the on-board radiation monitor for autonomous protection. Here
we investigate using the ACIS CCDs themselves as a radiation monitor. We
explore the 10-year database to evaluate the CCDs' response to particle
radiation and to compare this response with other radiation data and
environment models.Comment: 10 pages, 5 figures. To appear in Proc. SPIE vol. 773
Model Independent Primordial Power Spectrum from Maxima, Boomerang, and DASI Data
A model-independent determination of the primordial power spectrum of matter
density fluctuations could uniquely probe physics of the very early universe,
and provide powerful constraints on inflationary models. We parametrize the
primordial power spectrum as an arbitrary function, and deduce its
binned amplitude from the cosmic microwave background radiation anisotropy
(CMB) measurements of Maxima, Boomerang, and DASI. We find that for a flat
universe with (scale-invariant) for scales h/Mpc, the
primordial power spectrum is marginally consistent with a scale-invariant
Harrison-Zeldovich spectrum. However, we deduce a rise in power compared to a
scale-invariant power spectrum for 0.001 h/{Mpc} \la k \la 0.01 h/{Mpc}. Our
results are consistent with large-scale structure data, and seem to suggest
that the current observational data allow for the possibility of unusual
physics in the very early universe.Comment: substantially revised and final version, accepted by Ap
Surface wave focusing and acoustic communications in the surf zone
Author Posting. © Acoustical Society of America, 2004. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 116 (2004): 2067-2080, doi:10.1121/1.1771591.The forward scattering of acoustic signals off of shoaling surface gravity waves in the surf zone results in a time-varying channel impulse response that is characterized by intense, rapidly fluctuating arrivals. In some cases, the acoustic focusing by the curvature of the wave crest results in the formation of caustics at or near a receiver location. This focusing and the resulting caustics present challenges to the reliable operation of phase coherent underwater acoustic communications systems that must implicitly or explicitly track the fluctuations in the impulse response. The propagation physics leading to focusing are studied with both experimental data and a propagation model using surface wave profiles measured during the collection of the experimental data. The deterministic experimental and modeled data show good agreement and demonstrate the stages of the focusing event and the impact of the high intensity arrivals and rapid fluctuations on the ability of an algorithm to accurately estimate the impulse response. The statistical characterization of experimental data shows that the focusing by surface gravity waves results in focused surface reflected arrivals whose intensity often exceeds that of the direct arrival and the focusing and caustic formation adversely impacts the performance of an impulse response estimation algorithm.This work has been supported by ONR Grant Nos. N00014-96-1-0120, N00014-00-1-0303, N00014-99-1-0274, and N00014-00-1-0048
- …