1,246 research outputs found
CMB Constraints on WIMP Annihilation: Energy Absorption During the Recombination Epoch
We compute in detail the rate at which energy injected by dark matter
annihilation heats and ionizes the photon-baryon plasma at z ~ 1000, and
provide accurate fitting functions over the relevant redshift range for a broad
array of annihilation channels and DM masses. The resulting perturbations to
the ionization history can be constrained by measurements of the CMB
temperature and polarization angular power spectra. We show that models which
fit recently measured excesses in 10-1000 GeV electron and positron cosmic rays
are already close to the 95% confidence limits from WMAP. The recently launched
Planck satellite will be capable of ruling out a wide range of DM explanations
for these excesses. In models of dark matter with Sommerfeld-enhanced
annihilation, where sigma v rises with decreasing WIMP velocity until some
saturation point, the WMAP5 constraints imply that the enhancement must be
close to saturation in the neighborhood of the Earth.Comment: 17 pages, 6 figures, v2 extends discussion of constraints on
Sommerfeld-enhanced model
A determination of the Spectra of Galactic components observed by WMAP
WMAP data when combined with ancillary data on free-free, synchrotron and
dust allow an improved understanding of the spectrum of emission from each of
these components. Here we examine the sky variation at intermediate latitudes
using a cross-correlation technique. In particular, we compare the observed
emission in 15 selected sky regions to three ``standard'' templates.
The free-free emission of the diffuse ionised gas is fitted by a well-known
spectrum at K and Ka band, but the derived emissivity corresponds to a mean
electron temperature of ~4000-5000K. This is inconsistent with estimates from
galactic HII regions. The origin of the discrepancy is unclear.
The anomalous emission associated with dust is clearly detected in most of
the 15 fields studied; it correlates well with the Finkbeiner et al. model 8
predictions (FDS8) at 94 GHz, with an effective spectral index between 20 and
60GHz of -2.85. Furthermore, the emissivity varies by a factor of ~2 from cloud
to cloud. A modestly improved fit to the anomalous dust at K-band is provided
by modulating the template by an estimate of the dust colour temperature,
specifically FDS8*T^n. We find a preferred value n~1.6.
The synchrotron emission steepens between GHz frequencies and the WMAP bands.
There are indications of spectral index variations across the sky but the
current data are not precise enough to accurately quantify this from region to
region. Our analysis of the WMAP data indicates strongly that the
dust-correlated emission at the low WMAP frequencies has a spectrum which is
compatible with spinning dust; we find no evidence for a synchrotron component
correlated with dust (abridged).Comment: 18 pages, 6 figures, revised version uses cross-correlation method
rather than T-T method. Paper re-organised and sent back to refere
Early-type galaxies in the SDSS. II. Correlations between observables
A magnitude limited sample of nearly 9000 early-type galaxies, in the
redshift range 0.01 < z < 0.3, was selected from the Sloan Digital Sky Survey
using morphological and spectral criteria. The sample was used to study how
early-type galaxy observables, including luminosity L, effective radius R_o,
surface brightness I_o, color, and velocity dispersion sigma, are correlated
with one another. Measurement biases are understood with mock catalogs which
reproduce all of the observed scaling relations and their dependences on
fitting technique. At any given redshift, the intrinsic distribution of
luminosities, sizes and velocity dispersions in our sample are all
approximately Gaussian. A maximum likelihood analysis shows that sigma ~
L^{0.25\pm 0.012}, R_o ~ L^{0.63\pm 0.025}, and R_o ~ I^{-0.75\pm 0.02} in the
r* band. In addition, the mass-to-light ratio within the effective radius
scales as M_o/L ~ L^{0.14\pm 0.02} or M_o/L ~ M_o^{0.22\pm 0.05}, and galaxies
with larger effective masses have smaller effective densities: Delta_o ~
M_o^{-0.52\pm 0.03}. These relations are approximately the same in the g*, i*
and z* bands. Relative to the population at the median redshift in the sample,
galaxies at lower and higher redshifts have evolved only little, with more
evolution in the bluer bands. The luminosity function is consistent with weak
passive luminosity evolution and a formation time of about 9 Gyrs ago.Comment: 29 pages, 11 figures. Accepted by AJ (scheduled for April 2003). This
paper is part II of a revised version of astro-ph/011034
Stellar SEDs from 0.3-2.5 Microns: Tracing the Stellar Locus and Searching for Color Outliers in SDSS and 2MASS
The Sloan Digital Sky Survey (SDSS) and Two Micron All Sky Survey (2MASS) are
rich resources for studying stellar astrophysics and the structure and
formation history of the Galaxy. As new surveys and instruments adopt similar
filter sets, it is increasingly important to understand the properties of the
ugrizJHKs stellar locus, both to inform studies of `normal' main sequence stars
as well as for robust searches for point sources with unusual colors. Using a
sample of ~600,000 point sources detected by SDSS and 2MASS, we tabulate the
position and width of the ugrizJHKs stellar locus as a function of g-i color,
and provide accurate polynomial fits. We map the Morgan-Keenan spectral type
sequence to the median stellar locus by using synthetic photometry of spectral
standards and by analyzing 3000 SDSS stellar spectra with a custom spectral
typing pipeline. We develop an algorithm to calculate a point source's minimum
separation from the stellar locus in a seven-dimensional color space, and use
it to robustly identify objects with unusual colors, as well as spurious
SDSS/2MASS matches. Analysis of a final catalog of 2117 color outliers
identifies 370 white-dwarf/M dwarf (WDMD) pairs, 93 QSOs, and 90 M giant/carbon
star candidates, and demonstrates that WDMD pairs and QSOs can be distinguished
on the basis of their J-Ks and r-z colors. We also identify a group of objects
with correlated offsets in the u-g vs. g-r and g-r vs. r-i color-color spaces,
but subsequent follow-up is required to reveal the nature of these objects.
Future applications of this algorithm to a matched SDSS-UKIDSS catalog may well
identify additional classes of objects with unusual colors by probing new areas
of color-magnitude space.Comment: 23 pages in emulateapj format, 17 figures, 7 tables. Accepted for
publication in the Astronomical Journal. To access a high-resolution version
of this paper, as well as machine readable tables and an archive of 'The
Hammer' spectral typing suite, see http://www.cfa.harvard.edu/~kcovey v2 --
fixed typos in Table 7 (mainly affecting lines for M8-M10 III stars
Friendly fire and the proportion of friends to foes
Losses of inhibitory control may be partly responsible for some friendly fire incidents. The Sustained Attention to Response Task (SART; Robertson, Manly, Andrade, Baddeley, & Yiend, 1997) may provide an appropriate empirical model for this. The current investigation aimed to provide an ecologically valid application of the SART to a small arms simulation and examine the effect of different proportions of enemy to friendly confederates. Seven university students engaged in a small arms simulation where they cleared a building floor using a near-infrared emitter gun, tasked with firing at confederates representing enemies and withholding fire to confederates representing friends. All participants completed three conditions which were differentiated by the proportion of enemies to friends present. As hypothesized, participants failed to withhold responses more often when the proportion of foes was higher, suggesting that a prepotent motor response routine had developed. This effect appeared to be disproportionately more substantial in the high foe condition relative to the others. Participants also subjectively reported higher levels of on-task focus as foe proportions increased, suggesting that they found this more mentally demanding. Future research could examine closer the nature of the performance reductions associated with high proportions of foes, as it appears that this is more complex than a simple linear relationship
Proximity Effects and Nonequilibrium Superconductivity in Transition-Edge Sensors
We have recently shown that normal-metal/superconductor (N/S) bilayer TESs
(superconducting Transition-Edge Sensors) exhibit weak-link behavior.1 Here we
extend our understanding to include TESs with added noise-mitigating
normal-metal structures (N structures). We find TESs with added Au structures
also exhibit weak-link behavior as evidenced by exponential temperature
dependence of the critical current and Josephson-like oscillations of the
critical current with applied magnetic field. We explain our results in terms
of an effect converse to the longitudinal proximity effect (LoPE)1, the lateral
inverse proximity effect (LaiPE), for which the order parameter in the N/S
bilayer is reduced due to the neighboring N structures. Resistance and critical
current measurements are presented as a function of temperature and magnetic
field taken on square Mo/Au bilayer TESs with lengths ranging from 8 to 130
{\mu}m with and without added N structures. We observe the inverse proximity
effect on the bilayer over in-plane distances many tens of microns and find the
transition shifts to lower temperatures scale approximately as the inverse
square of the in- plane N-structure separation distance, without appreciable
broadening of the transition width. We also present evidence for nonequilbrium
superconductivity and estimate a quasiparticle lifetime of 1.8 \times 10-10 s
for the bilayer. The LoPE model is also used to explain the increased
conductivity at temperatures above the bilayer's steep resistive transition.Comment: 10 pages, 8 figure
PAMELA, DAMA, INTEGRAL and Signatures of Metastable Excited WIMPs
Models of dark matter with ~ GeV scale force mediators provide attractive
explanations of many high energy anomalies, including PAMELA, ATIC, and the
WMAP haze. At the same time, by exploiting the ~ MeV scale excited states that
are automatically present in such theories, these models naturally explain the
DAMA/LIBRA and INTEGRAL signals through the inelastic dark matter (iDM) and
exciting dark matter (XDM) scenarios, respectively. Interestingly, with only
weak kinetic mixing to hypercharge to mediate decays, the lifetime of excited
states with delta < 2 m_e is longer than the age of the universe. The
fractional relic abundance of these excited states depends on the temperature
of kinetic decoupling, but can be appreciable. There could easily be other
mechanisms for rapid decay, but the consequences of such long-lived states are
intriguing. We find that CDMS constrains the fractional relic population of
~100 keV states to be <~ 10^-2, for a 1 TeV WIMP with sigma_n = 10^-40 cm^2.
Upcoming searches at CDMS, as well as xenon, silicon, and argon targets, can
push this limit significantly lower. We also consider the possibility that the
DAMA excitation occurs from a metastable state into the XDM state, which decays
via e+e- emission, which allows lighter states to explain the INTEGRAL signal
due to the small kinetic energies required. Such models yield dramatic signals
from down-scattering, with spectra peaking at high energies, sometimes as high
as ~1 MeV, well outside the usual search windows. Such signals would be visible
at future Ar and Si experiments, and may be visible at Ge and Xe experiments.
We also consider other XDM models involving ~ 500 keV metastable states, and
find they can allow lighter WIMPs to explain INTEGRAL as well.Comment: 22 pages, 7 figure
Design Study of Wafer Seals for Future Hypersonic Vehicles
Future hypersonic vehicles require high temperature, dynamic seals in advanced hypersonic engines and on the vehicle airframe to seal the perimeters of movable panels, flaps, and doors. Current seals do not meet the demanding requirements of these applications, so NASA Glenn Research Center is developing improved designs to overcome these shortfalls. An advanced ceramic wafer seal design has shown promise in meeting these needs. Results from a design of experiments study performed on this seal revealed that several installation variables played a role in determining the amount of leakage past the seals. Lower leakage rates were achieved by using a tighter groove width around the seals, a higher seal preload, a tighter wafer height tolerance, and a looser groove length. During flow testing, a seal activating pressure acting behind the wafers combined with simulated vibrations to seat the seals more effectively against the sealing surface and produce lower leakage rates. A seal geometry study revealed comparable leakage for full-scale wafers with 0.125 and 0.25 in. thicknesses. For applications in which lower part counts are desired, fewer 0.25-in.-thick wafers may be able to be used in place of 0.125-in.-thick wafers while achieving similar performance. Tests performed on wafers with a rounded edge (0.5 in. radius) in contact with the sealing surface resulted in flow rates twice as high as those for wafers with a flat edge. Half-size wafers had leakage rates approximately three times higher than those for full-size wafers
Fluency Assistance Device (FAD): Masker Upgrades
There are around seventy million people internationally who have a stutter, a form of fluency disorder. Some fluency assistance devices are available to the public, but most are highly expensive or unreliable. The Fluency Assistive Device (FAD) team seeks to assist a niche community of these individuals for whom therapy has not worked, and who currently rely on a device known as the Edinburgh Masker. To best reach this community, FAD is partnering with Dave Germeyer, who has invaluable experience repairing these masker devices for his clientele. FAD is redesigning the masker to increase its portability, functionality, and cost-effectiveness by developing an improved analog and new digital version. The Analog Masker v1.3 focuses on updated components and consolidated circuitry to eliminate troublesome wiring of the original. The Digital Masker v1.0 employs a Bluetooth-enabled microcontroller to achieve masker functionality, offering the flexibility of alternative fluency assistance algorithms to assist a broader group of users. An updated prototype of the Analog Masker v1.3 was fabricated and tested for power consumption and overall functional output characteristics versus the original Edinburgh version. The Analog Masker v1.3 has also been fully packaged and enclosed to produce a client testable unit. Bluetooth audio output for the Digital Masker has almost been completed, and two of the alternative algorithms have been coded for the masking output. One of these algorithms, Delayed Altered Feedback (DAF), now produces the expected output in response to an audio test input. Clarity and integrity of the DAF signal output have also been improved. The Masking Altered Feedback (MAF) algorithm that emulates the behavior of the Edinburgh original on the Digital Masker v1.0 is under development.
Funding for this work provided by The Collaboratory for Strategic Partnerships and Applied Research.https://mosaic.messiah.edu/engr2022/1006/thumbnail.jp
The effect of task-relevant and irrelevant anxiety-provoking stimuli on response inhibition
The impact of anxiety-provoking stimuli on the Sustained Attention to Response Task (SART; Robertson, Manly, Andrade, Baddeley, & Yiend, 1997), and response inhibition more generally, is currently unclear. Participants completed four SARTs embedded with picture stimuli of two levels of emotion (negative or neutral) and two levels of task-relevance (predictive or non-predictive of imminent No-Go stimuli). Negative pictures had a small but detectable adverse effect on performance regardless of their task-relevance. Overall, response times and rates of commission errors were more dependent upon the predictive value (relevance) of the pictures than their attention-capturing nature (i.e., negative valence). The findings raise doubt over whether anxiety improves response inhibition, and also lend support to a response strategy perspective of SART performance, as opposed to a mindlessness or mind-wandering explanation
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