321 research outputs found
History dependence of directly observed magnetocaloric effects in (Mn, Fe)As
We use a calorimetric technique operating in sweeping magnetic field to study
the thermomagnetic history- dependence of the magnetocaloric effect (MCE) in
Mn0.985Fe0.015As. We study the magnetization history for which a "colossal" MCE
has been reported when inferred indirectly via a Maxwell relation. We observe
no colossal effect in the direct calorimetric measurement. We further examine
the impact of mixed-phase state on the MCE and show that the first order
contribution scales linearly with the phase fraction. This validates various
phase-fraction based methods developed to remove the colossal peak anomaly from
Maxwell-based estimates.Comment: 4 pages, 2 figure
Absolute Calibration and Characterization of the Multiband Imaging Photometer for Spitzer. II. 70 micron Imaging
The absolute calibration and characterization of the Multiband Imaging
Photometer for Spitzer (MIPS) 70 micron coarse- and fine-scale imaging modes
are presented based on over 2.5 years of observations. Accurate photometry
(especially for faint sources) requires two simple processing steps beyond the
standard data reduction to remove long-term detector transients. Point spread
function (PSF) fitting photometry is found to give more accurate flux densities
than aperture photometry. Based on the PSF fitting photometry, the calibration
factor shows no strong trend with flux density, background, spectral type,
exposure time, or time since anneals. The coarse-scale calibration sample
includes observations of stars with flux densities from 22 mJy to 17 Jy, on
backgrounds from 4 to 26 MJy sr^-1, and with spectral types from B to M. The
coarse-scale calibration is 702 +/- 35 MJy sr^-1 MIPS70^-1 (5% uncertainty) and
is based on measurements of 66 stars. The instrumental units of the MIPS 70
micron coarse- and fine-scale imaging modes are called MIPS70 and MIPS70F,
respectively. The photometric repeatability is calculated to be 4.5% from two
stars measured during every MIPS campaign and includes variations on all time
scales probed. The preliminary fine-scale calibration factor is 2894 +/- 294
MJy sr^-1 MIPS70F^-1 (10% uncertainty) based on 10 stars. The uncertainty in
the coarse- and fine-scale calibration factors are dominated by the 4.5%
photometric repeatability and the small sample size, respectively. The 5-sigma,
500 s sensitivity of the coarse-scale observations is 6-8 mJy. This work shows
that the MIPS 70 micron array produces accurate, well calibrated photometry and
validates the MIPS 70 micron operating strategy, especially the use of frequent
stimulator flashes to track the changing responsivities of the Ge:Ga detectors.Comment: 19 pages, PASP, in pres
Very-high energy gamma-ray astronomy: A 23-year success story in high-energy astroparticle physics
Very-high energy (VHE) gamma quanta contribute only a minuscule fraction -
below one per million - to the flux of cosmic rays. Nevertheless, being neutral
particles they are currently the best "messengers" of processes from the
relativistic/ultra-relativistic Universe because they can be extrapolated back
to their origin. The window of VHE gamma rays was opened only in 1989 by the
Whipple collaboration, reporting the observation of TeV gamma rays from the
Crab nebula. After a slow start, this new field of research is now rapidly
expanding with the discovery of more than 150 VHE gamma-ray emitting sources.
Progress is intimately related with the steady improvement of detectors and
rapidly increasing computing power. We give an overview of the early attempts
before and around 1989 and the progress after the pioneering work of the
Whipple collaboration. The main focus of this article is on the development of
experimental techniques for Earth-bound gamma-ray detectors; consequently, more
emphasis is given to those experiments that made an initial breakthrough rather
than to the successors which often had and have a similar (sometimes even
higher) scientific output as the pioneering experiments. The considered energy
threshold is about 30 GeV. At lower energies, observations can presently only
be performed with balloon or satellite-borne detectors. Irrespective of the
stormy experimental progress, the success story could not have been called a
success story without a broad scientific output. Therefore we conclude this
article with a summary of the scientific rationales and main results achieved
over the last two decades.Comment: 45 pages, 38 figures, review prepared for EPJ-H special issue "Cosmic
rays, gamma rays and neutrinos: A survey of 100 years of research
Synesthesia and Migraine: Case Report
<p>Abstract</p> <p>Background</p> <p>Synesthesia is, as visual migraine aura, a common and fascinating perceptual phenomenon. Here we present a unique case with synesthesias exclusively during visual migraine auras.</p> <p>Case presentation</p> <p>A 40-year-old woman with a cyclic mood disorder had suffered from migraine with visual aura for several years. On several occasions she had experienced "mixing of senses" during the aura phase. Staring at strong bright light she could experience intense taste of lemon with flow from the salivary glands.</p> <p>Conclusion</p> <p>Acquired synesthesia, exclusively coincident with migraine aura, gives support to the idea of an anomalous cortical processing underlying the phenomenon.</p
New debris disk candidates: 24 micron stellar excesses at 100 Myr
Sixty three members of the 100 Myr old open cluster M47 (NGC 2422) have been
detected at 24 micron with Spitzer. The Be star V 378 Pup shows an excess both
in the near-infrared and at 24 micron (K-[24] = 2.4 mag), probably due to
free-free emission from the gaseous envelope. Seven other early-type stars show
smaller excesses, K-[24] = 0.6-0.9. Among late-type stars, two show large
excesses: P922 - a K1V star with K-[24] = 1.08 pm 0.11 and P1121 - an F9V star
with K-[24] = 3.72 pm 0.02. P1121 is the first known main-sequence star showing
an excess comparable to that of beta Pic, which may indicate the presence of an
exceptionally massive debris disk. It is possible that a major planetesimal
collision has occurred in this system, consistent with the few hundred Myr time
scales estimated for the clearing of the Solar System.Comment: 14 pages, 3 figures, accepted to the special Spitzer issue of the
ApJ
Reduction Algorithms for the Multiband Imaging Photometer for Spitzer
We describe the data reduction algorithms for the Multiband Imaging
Photometer for Spitzer (MIPS) instrument. These algorithms were based on
extensive preflight testing and modeling of the Si:As (24 micron) and Ge:Ga (70
and 160 micron) arrays in MIPS and have been refined based on initial flight
data. The behaviors we describe are typical of state-of-the-art infrared focal
planes operated in the low backgrounds of space. The Ge arrays are bulk
photoconductors and therefore show a variety of artifacts that must be removed
to calibrate the data. The Si array, while better behaved than the Ge arrays,
does show a handful of artifacts that also must be removed to calibrate the
data. The data reduction to remove these effects is divided into three parts.
The first part converts the non-destructively read data ramps into slopes while
removing artifacts with time constants of the order of the exposure time. The
second part calibrates the slope measurements while removing artifacts with
time constants longer than the exposure time. The third part uses the
redundancy inherit in the MIPS observing modes to improve the artifact removal
iteratively. For each of these steps, we illustrate the relevant laboratory
experiments or theoretical arguments along with the mathematical approaches
taken to calibrate the data. Finally, we describe how these preflight
algorithms have performed on actual flight data.Comment: 21 pages, 16 figures, PASP accepted (May 2005 issue), version of
paper with full resolution images is available at
http://dirty.as.arizona.edu/~kgordon/papers/PS_files/mips_dra.pd
The Regenerative Capacity of the Zebrafish Caudal Fin Is Not Affected by Repeated Amputations
Background: The zebrafish has the capacity to regenerate many tissues and organs. The caudal fin is one of the most convenient tissues to approach experimentally due to its accessibility, simple structure and fast regeneration. In this work we investigate how the regenerative capacity is affected by recurrent fin amputations and by experimental manipulations that block regeneration. Methodology/Principal Findings: We show that consecutive repeated amputations of zebrafish caudal fin do not reduce its regeneration capacity and do not compromise any of the successive regeneration steps: wound healing, blastema formation and regenerative outgrowth. Interfering with Wnt/ß-catenin signalling using heat-shock-mediated overexpression of Dickkopf1 completely blocks fin regeneration. Notably, if these fins were re-amputated at the non-inhibitory temperature, the regenerated caudal fin reached the original length, even after several rounds of consecutive Wnt/ß-catenin signalling inhibition and re-amputation. Conclusions/Significance: We show that the caudal fin has an almost unlimited capacity to regenerate. Even after inhibition of regeneration caused by the loss of Wnt/ß-catenin signalling, a new amputation resets the regeneration capacity within the caudal fin, suggesting that blastema formation does not depend on a pool of stem/progenitor cells that require Wnt/ßcateni
The Evolution of Compact Binary Star Systems
We review the formation and evolution of compact binary stars consisting of
white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Binary NSs and
BHs are thought to be the primary astrophysical sources of gravitational waves
(GWs) within the frequency band of ground-based detectors, while compact
binaries of WDs are important sources of GWs at lower frequencies to be covered
by space interferometers (LISA). Major uncertainties in the current
understanding of properties of NSs and BHs most relevant to the GW studies are
discussed, including the treatment of the natal kicks which compact stellar
remnants acquire during the core collapse of massive stars and the common
envelope phase of binary evolution. We discuss the coalescence rates of binary
NSs and BHs and prospects for their detections, the formation and evolution of
binary WDs and their observational manifestations. Special attention is given
to AM CVn-stars -- compact binaries in which the Roche lobe is filled by
another WD or a low-mass partially degenerate helium-star, as these stars are
thought to be the best LISA verification binary GW sources.Comment: 105 pages, 18 figure
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