2,934 research outputs found
Properties of high emittance materials
High emittance coating materials for beryllium, niobium-zirconium compounds, and stainless steel used in spacecraft radiator
Whistleblowing Need not Occur if Internal Voices Are Heard: From Deaf Effect to Hearer Courage; Comment on āCultures of Silence and Cultures of Voice: The Role of Whistleblowing in Healthcare Organisationsā
Whistleblowing by health professionals is an infrequent and extraordinary event and need not occur if internal voices are heard. Mannion and Daviesā editorial on āCultures of Silence and Cultures of Voice: The Role of Whistleblowing in Healthcare Organisationsā asks the question whether whistleblowing ameliorates or exacerbates the ādeaf effectā prevalent in healthcare organisations. This commentary argues that the focus should remain on internal processes and hearer courage
Cryogenic microstripline-on-Kapton microwave interconnects
Simple broadband microwave interconnects are needed for increasing the size
of focal plane heterodyne radiometer arrays. We have measured loss and
cross-talk for arrays of microstrip transmission lines in flex circuit
technology at 297 and 77 K, finding good performance to at least 20 GHz. The
dielectric constant of Kapton substrates changes very little from 297 to 77 K,
and the electrical loss drops. The small cross-sectional area of metal in a
printed circuit structure yields overall thermal conductivities similar to
stainless steel coaxial cable. Operationally, the main performance tradeoffs
are between crosstalk and thermal conductivity. We tested a patterned ground
plane to reduce heat flux.Comment: 3 pages, 3 figures, submitted to The Review of Scientific Instrument
First Season QUIET Observations: Measurements of Cosmic Microwave Background Polarization Power Spectra at 43 GHz in the Multipole Range 25 ā¤ ā ā¤ 475
The Q/U Imaging ExperimenT (QUIET) employs coherent receivers at 43 GHz and 94 GHz, operating on the Chajnantor plateau in the Atacama Desert in Chile, to measure the anisotropy in the polarization of the cosmic microwave background (CMB). QUIET primarily targets the B modes from primordial gravitational waves. The combination of these frequencies gives sensitivity to foreground contributions from diffuse Galactic synchrotron radiation. Between 2008 October and 2010 December, over 10,000 hr of data were collected, first with the 19 element 43 GHz array (3458 hr) and then with the 90 element 94 GHz array. Each array observes the same four fields, selected for low foregrounds, together covering ā1000 deg^2. This paper reports initial results from the 43 GHz receiver, which has an array sensitivity to CMB fluctuations of 69 Ī¼Kās. The data were extensively studied with a large suite of null tests before the power spectra, determined with two independent pipelines, were examined. Analysis choices, including data selection, were modified until the null tests passed. Cross-correlating maps with different telescope pointings is used to eliminate a bias. This paper reports the EE, BB, and EB power spectra in the multipole range ā = 25-475. With the exception of the lowest multipole bin for one of the fields, where a polarized foreground, consistent with Galactic synchrotron radiation, is detected with 3Ļ significance, the E-mode spectrum is consistent with the ĪCDM model, confirming the only previous detection of the first acoustic peak. The B-mode spectrum is consistent with zero, leading to a measurement of the tensor-to-scalar ratio of r = 0.35^(+1.06)_(ā0.87). The combination of a new time-stream "double-demodulation" technique, side-fed Dragonian optics, natural sky rotation, and frequent boresight rotation leads to the lowest level of systematic contamination in the B-mode power so far reported, below the level of r = 0.1
GHRS and ORFEUS-II Observations of the Highly Ionized Interstellar Medium Toward ESO141-055
We present Goddard High Resolution Spectrograph and ORFEUS-II measurements of
Si IV, CIV, N V, and O VI absorption in the interstellar medium of the Galactic
disk and halo toward the nucleus of the Seyfert galaxy ESO141-055. The high
ionization absorption is strong, with line strengths consistent with the
spectral signature expected for hot (log T = 5-6) collisionally ionized gas in
either a ``Galactic fountain'' or an inhomogeneous medium containing a mixture
of conductive interfaces and turbulent mixing layers. The total O VI column
density of log N ~ 15 suggests that the scale height of O VI is large (>3 kpc)
in this direction. Comparison of the high ion column densities with
measurements for other sight lines indicates that the highly ionized gas
distribution is patchy. The amount of O VI perpendicular to the Galactic plane
varies by at least a factor of ~4 among the complete halo sight lines thus far
studied. In addition to the high ion absorption, lines of low ionization
species are also present in the spectra. With the possible exception of Ar I,
which may have a lower than expected abundance resulting from partial
photoionization of gas along the sight line, the absorption strengths are
typical of those expected for the warm, neutral interstellar medium. The sight
line intercepts a cold molecular cloud with log N(H2) ~ 19. The cloud has an
identifiable counterpart in IRAS 100-micron emission maps of this region of the
sky. We detect a Ly-alpha absorber associated with ESO141-055 at z = 0.03492.
This study presents an enticing glimpse into the interstellar and intergalactic
absorption patterns that will be observed at high spectral resolution by the
Far Ultraviolet Spectroscopic Explorer.Comment: 24 pages + 8 figures, uses aaspp4.sty. Accepted for publication in
Ap
Mixed-state quasiparticle transport in high-T_c cuprates: localization by magnetic field
Theory of quasiparticle transport in the mixed state of a d-wave
superconductor is developed under the assumption of disordered vortex array. A
novel universal regime is identified at fields above H*= c*H_{c2}(T/T_c)^2,
characterized by a field-independent longitudinal thermal conductivity. It is
argued that this behavior is responsible for the high-field plateau in the
thermal conductivity experimentally observed in cuprates by Krishana, Ong and
co-workers.Comment: 4 pages REVTeX + 1 PostScript figure. Final version to appear in PRL.
Several changes in response to referee comments. For related work and info
visit http://www.pha.jhu.edu/~fran
The apparent exponential radiation of Phanerozoic land vertebrates reflects spatial sampling biases
There is no consensus about how terrestrial biodiversity was assembled through deep time, and in particular whether it has risen exponentially over the Phanerozoic. Using a
database of 60,859 fossil occurrences, we show that the spatial extent of the worldwide
terrestrial tetrapod fossil record itself expands exponentially through the Phanerozoic.
Changes in spatial sampling explain up to 67% of the change in known fossil species counts
and, because these changes are decoupled from variation in habitable land area that existed
through time, this therefore represents a real and profound sampling bias that cannot be
explained as redundancy. To address this bias, we estimate terrestrial tetrapod diversity for
palaeogeographic regions of approximately equal size. We find that regional-scale diversity
was constrained over timespans of tens to hundreds of millions of years, and similar patterns
are recovered for major subgroups, such as dinosaurs, mammals, and squamates. Although
Cretaceous/Paleogene mass extinction catalysed an abrupt two- to three-fold increase in
regional diversity 66 million years ago, no further increases occurred, and recent levels of
regional diversity do not exceed those of the Paleogene. These results parallel those
recovered in analyses of local community-level richness. Taken together, our findings
strongly contradict past studies that suggested unbounded diversity increases at local and
regional scales over the last 100 million years
Millimeter-wave photoresponse due to excitation of two-dimensional plasmons in InGaAs/InP high-electron-mobility transistors
A polarized photoresponse to mm-wave radiation over the frequency range of 40 to 108 GHz is demonstrated in a grating-gated high electron mobility transistor (HEMT) formed by an InGaAs/InP heterostructure. The photoresponse is observed within the plasmon resonance absorption band of the HEMT, whose gate consists of a 9 mu m period grating that couples incident radiation to plasmons in the 2D electron gas. Gate-bias changes the channel carrier concentration, causing a corresponding change in photoresponse in agreement with theoretical expectations for the shift in the plasmon resonance band. The noise equivalent power is estimated to be 235 pW/Hz(1/2)
Scattering of Phonons by a Vortex in a Superfluid
Recent work gives a transverse force on an isolated moving vortex which is
independent of the normal fluid velocity, but it is widely believed that the
asymmetry of phonon scattering by a vortex leads to a transverse force
dependent on the relative motion of the normal component and the vortex. We
show that a widely accepted derivation of the transverse force is in error, and
that a careful evaluation leads to a much smaller transverse force. We argue
that a different approach is needed to get the correct expression.
\pacs{67.40.Vs,67.57.Fg,47.37.+q,47.32.Cc}Comment: 4 page
Methylmercury neurotoxicity in Amazonian children downstream from gold mining.
In widespread informal gold mining in the Amazon Basin, mercury is used to capture the gold particles as amalgam. Releases of mercury to the environment have resulted in the contamination of freshwater fish with methylmercury. In four comparable Amazonian communities, we examined 351 of 420 eligible children between 7 and 12 years of age. In three TapajĆ³s villages with the highest exposures, more than 80% of 246 children had hair-mercury concentrations above 10 microg/g, a limit above which adverse effects on brain development are likely to occur. Neuropsychological tests of motor function, attention, and visuospatial performance showed decrements associated with the hair-mercury concentrations. Especially on the Santa Ana form board and the Stanford-Binet copying tests, similar associations were also apparent in the 105 children from the village with the lowest exposures, where all but two children had hair-mercury concentrations below 10 microg/g. Although average exposure levels may not have changed during recent years, prenatal exposure levels are unknown, and exact dose relationships cannot be generated from this cross-sectional study. However, the current mercury pollution seems sufficiently severe to cause adverse effects on brain development
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