24,203 research outputs found
Reanalysis of the spectrum of the z=10 galaxy
In a recent paper Pello et al. reported observations of a faint galaxy,
gravitationally lensed by the galaxy cluster Abell 1835. Deep J-band
spectroscopy revealed a weak emission line near 1.34 microns, detected in two
spectra with different central wavelengths. The line was interpreted as
Lyman-alpha at redshift z=10.0. This interpretation is supported by the
broad-band photometric spectral energy distribution, and by the location of the
galaxy close to the lens critical line for this redshift. We have reanalysed
the two spectra, just released from the data archive. Our analysis includes
allowance for wavelength shifts due to transverse drift of the object in the
slit. We do not detect a significant emission line at the reported location, or
nearby, at either grating setting, nor in the combined spectrum. We provide a
possible explanation for the reported detection as due to spurious positive
flux introduced in the sky-subtraction stage as a result of variable hot
pixels. We provide our final reduced 2D frame, and corresponding error array.Comment: 4 pages, 1 figure. To appear in A&A Letters. Added possible
explanation for reported emission line as due to variable hot pixel
Factors Affecting Trade in Mexican Imports of Poultry Meat from the United States
U.S. exports of poultry to Mexico have increased steadily since NAFTA came into force in January 1994. The Mexican poultry industry has become increasingly concerned about these exports, arguing that it cannot compete with U.S. products. The Mexicans argue that U.S. poultry exports to Mexico are duty free under NAFTA (as of January 1, 2003). The Mexican industry also argues that U.S. poultry benefits from low-priced feed resulting from U.S. Government farm programs. We analyzed the impact of tariffs and U.S. feed grain programs on U.S. exports of poultry, and find that other factors appear to be more important in explaining trade. Specifically, Mexican preferences for dark meat provide large price incentives for U.S. exporters, while Mexican Government policies in support of its grain sector penalize poultry producers in Mexico.International Relations/Trade,
Experimental study of equilibrium air total radiation
Experimental study of equilibrium air total radiatio
The cognitive organization of music knowledge: a clinical analysis
Despite much recent interest in the clinical neuroscience of music processing, the cognitive organization of music as a domain of non-verbal knowledge has been little studied. Here we addressed this issue systematically in two expert musicians with clinical diagnoses of semantic dementia and Alzheimer’s disease, in comparison with a control group of healthy expert musicians. In a series of neuropsychological experiments, we investigated associative knowledge of musical compositions (musical objects), musical emotions, musical instruments (musical sources) and music notation (musical symbols). These aspects of music knowledge were assessed in relation to musical perceptual abilities and extra-musical neuropsychological functions. The patient with semantic dementia showed relatively preserved recognition of musical compositions and musical symbols despite severely impaired recognition of musical emotions and musical instruments from sound. In contrast, the patient with Alzheimer’s disease showed impaired recognition of compositions, with somewhat better recognition of composer and musical era, and impaired comprehension of musical symbols, but normal recognition of musical emotions and musical instruments from sound. The findings suggest that music knowledge is fractionated, and superordinate musical knowledge is relatively more robust than knowledge of particular music. We propose that music constitutes a distinct domain of non-verbal knowledge but shares certain cognitive organizational features with other brain knowledge systems. Within the domain of music knowledge, dissociable cognitive mechanisms process knowledge derived from physical sources and the knowledge of abstract musical entities
Hypervelocity heat transfer studies in simulated planetary atmospheres final report
Hypervelocity heat transfer studies in simulated planetary atmosphere
Linear electric field frequency shift (important for next generation electric dipole moment searches) induced in confined gases by a magnetic field gradient
The search for particle electric dipole moments (edm) represents a most
promising way to search for physics beyond the standard model. A number of
groups are planning a new generation of experiments using stored gases of
various kinds. In order to achieve the target sensitivities it will be
necessary to deal with the systematic error resulting from the interaction of
the well-known field with
magnetic field gradients (often referred to as the geometric phase effect
(Commins, ED; Am. J. Phys. \QTR{bf}{59}, 1077 (1991), Pendlebury, JM
\QTR{em}{et al;} Phys. Rev. \QTR{bf}{A70}, 032102 (2004)). This interaction
produces a frequency shift linear in the electric field, mimicking an edm. In
this work we introduce an analytic form for the velocity auto-correlation
function which determines the velocity-position correlation function which in
turn determines the behavior of the frequency shift (Lamoreaux, SK and Golub,
R; Phys. Rev \QTR{bf}{A71}, 032104 (2005)) and show how it depends on the
operating conditions of the experiment. We also discuss some additional issues.Comment: 21 pages, 5 figure
Precision Determination of the Mass Function of Dark Matter Halos
The predicted mass function of dark matter halos is essential in connecting
observed galaxy cluster counts and models of galaxy clustering to the
properties of the primordial density field. We determine the mass function in
the concordance CDM cosmology, as well as its uncertainty, using
sixteen -particle nested-volume dark-matter simulations, spanning a
mass range of over five orders of magnitude. Using the nested volumes and
single-halo tests, we find and correct for a systematic error in the
friends-of-friends halo-finding algorithm. We find a fitting form and full
error covariance for the mass function that successfully describes the
simulations' mass function and is well-behaved outside the simulations'
resolutions. Estimated forecasts of uncertainty in cosmological parameters from
future cluster count surveys have negligible contribution from remaining
statistical uncertainties in the central cosmology multiplicity function. There
exists a potentially non-negligible cosmological dependence (non-universality)
of the halo multiplicity function.Comment: 4 pages, 3 figures, submitted to ApJ
Photoelectrochemical water splitting: silicon photocathodes for hydrogen evolution
The development of low cost, scalable, renewable energy technologies is one of today's most pressing scientific challenges. We report on progress towards the development of a photoelectrochemical water-splitting system that will use sunlight and water as the inputs to produce renewable hydrogen with oxygen as a by-product. This system is based on the design principle of incorporating two separate, photosensitive inorganic semiconductor/liquid junctions to collectively generate the 1.7-1.9 V at open circuit needed to support both the oxidation of H_2O (or OH^-) and the reduction of H^+ (or H_2O). Si microwire arrays are a promising photocathode material because the high aspect-ratio electrode architecture allows for the use of low cost, earth-abundant materials without sacrificing energy-conversion efficiency, due to the orthogonalization of light absorption and charge-carrier collection. Additionally, the high surfacearea design of the rod-based semiconductor array inherently lowers the flux of charge carriers over the rod array surface relative to the projected geometric surface of the photoelectrode, thus lowering the photocurrent density at the solid/liquid junction and thereby relaxing the demands on the activity (and cost) of any electrocatalysts. Arrays of Si microwires grown using the Vapor Liquid Solid (VLS) mechanism have been shown to have desirable electronic light absorption properties. We have demonstrated that these arrays can be coated with earth-abundant metallic catalysts and used for photoelectrochemical production of hydrogen. This development is a step towards the demonstration of a complete artificial photosynthetic system, composed of only inexpensive, earth-abundant materials, that is simultaneously efficient, durable, and scalable
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