4,743 research outputs found
The effect of space flight on bone demineralization
Space flight effects on bone demineralization of Gemini 4, 5, and 7 crews studied by X ray densitometr
Fundamental investigation of losses of skeletal mineral in young adult human males and collaterally in young adult male pigtail monkeys /macacus nemestrima/ through immobilization for varying periods of time, coupled with a study of methods of preven
Skeletal mineral losses in young adult humans and monkeys resulting from immobilizatio
Adrenal suppression in an asthmatic presenting after change from high dose inhaled fluticasone propionate to inhaled budesonide
The effect of bedrest on various parameters of physiological function. part xii- the effect of bedrest on bone mass and calcium balance
Bed rest effect on various parameters of physiological functions - bone mass and calcium balanc
Effect of Primordial Black Holes on the Cosmic Microwave Background and Cosmological Parameter Estimates
We investigate the effect of non-evaporating primordial black holes (PBHs) on
the ionization and thermal history of the universe. X-rays emitted by gas
accretion onto PBHs modify the cosmic recombination history, producing
measurable effects on the spectrum and anisotropies of the Cosmic Microwave
Background (CMB). Using the third-year WMAP data and FIRAS data we improve
existing upper limits on the abundance of PBHs with masses >0.1 Msun by several
orders of magnitude. Fitting WMAP3 data with cosmological models that do not
allow for non-standard recombination histories, as produced by PBHs or other
early energy sources, may lead to an underestimate of the best-fit values of
the amplitude of linear density fluctuations (sigma_8) and the scalar spectral
index (n_s). Cosmological parameter estimates are affected because models with
PBHs allow for larger values of the Thomson scattering optical depth, whose
correlation with other parameters may not be correctly taken into account when
PBHs are ignored. Values of tau_e=0.2, n_s=1 and sigma_8=0.9 are allowed at 95%
CF. This result that may relieve recent tension between WMAP3 data and clusters
data on the value of sigma_8. PBHs may increase the primordial molecular
hydrogen abundance by up to two orders of magnitude, this promoting cooling and
star formation. The suppression of galaxy formation due to X-ray heating is
negligible for models consistent with the CMB data. Thus, the formation rate of
the first galaxies and stars would be enhanced by a population of PBHs.Comment: 17 pages (Apj style), 9 figures, submitted to Ap
Coherent Patterning of Matter Waves with Subwavelength Localization
We propose the Subwavelength Localization via Adiabatic Passage (SLAP)
technique to coherently achieve state-selective patterning of matter waves well
beyond the diffraction limit. The SLAP technique consists in coupling two
partially overlapping and spatially structured laser fields to three internal
levels of the matter wave yielding state-selective localization at those
positions where the adiabatic passage process does not occur. We show that by
means of this technique matter wave localization down to the single nanometer
scale can be achieved. We analyze in detail the potential implementation of the
SLAP technique for nano-lithography with an atomic beam of metastable Ne* and
for coherent patterning of a two-component 87Rb Bose-Einstein condensate.Comment: 6 pages, 5 figure
Conformal Maxwell theory as a singleton field theory on AdS_5, IIB three-branes and duality
We examine the boundary conditions associated with extended supersymmetric
Maxwell theory in 5-dimensional anti-De Sitter space. Excitations on the
boundary are identical to those of ordinary 4-dimensional conformal invariant
super electrodynammics. Extrapolations of these excitations give rise to a
5-dimensional topological gauge theory of the singleton type. The possibility
of a connection of this phenomenon to the world volume theory of 3-branes in
IIB string theory is discussed.Comment: 19 pages, TeX, no figures; v2: misprints corrected, references added,
discussion on Chern-Simons couplings revised. v3: References added, misprints
corrected and a discussion in section 2 revised. v4: Typos corrected and
reference adde
Four Dimensional CFT Models with Rational Correlation Functions
Recently established rationality of correlation functions in a globally
conformal invariant quantum field theory satisfying Wightman axioms is used to
construct a family of soluble models in 4-dimensional Minkowski space-time. We
consider in detail a model of a neutral scalar field of dimension 2. It
depends on a positive real parameter c, an analogue of the Virasoro central
charge, and admits for all (finite) c an infinite number of conserved symmetric
tensor currents. The operator product algebra of is shown to coincide
with a simpler one, generated by a bilocal scalar field of
dimension (1,1). The modes of V together with the unit operator span an
infinite dimensional Lie algebra whose vacuum (i.e. zero energy lowest
weight) representations only depend on the central charge c. Wightman
positivity (i.e. unitarity of the representations of ) is proven to be
equivalent to .Comment: 28 pages, LATEX, amsfonts, latexsym. Proposition 2.3, and Conjecture
in Sec. 6 are revised. Minor errors are correcte
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Tuning the bandgap of Cs2AgBiBr6 through dilute tin alloying.
The promise of lead halide hybrid perovskites for optoelectronic applications makes finding less-toxic alternatives a priority. The double perovskite Cs2AgBiBr6 (1) represents one such alternative, offering long carrier lifetimes and greater stability under ambient conditions. However, the large and indirect 1.95 eV bandgap hinders its potential as a solar absorber. Here we report that alloying crystals of 1 with up to 1 atom% Sn results in a bandgap reduction of up to ca. 0.5 eV while maintaining low toxicity. Crystals can be alloyed with up to 1 atom% Sn and the predominant substitution pathway appears to be a ∼2 : 1 substitution of Sn2+ and Sn4+ for Ag+ and Bi3+, respectively, with Ag+ vacancies providing charge compensation. Spincoated films of 1 accommodate a higher Sn loading, up to 4 atom% Sn, where we see mostly Sn2+ substitution for both Ag+ and Bi3+. Density functional theory (DFT) calculations ascribe the bandgap redshift to the introduction of Sn impurity bands below the conduction band minimum of the host lattice. Using optical absorption spectroscopy, photothermal deflection spectroscopy, X-ray absorption spectroscopy, 119Sn NMR, redox titration, single-crystal and powder X-ray diffraction, multiple elemental analysis and imaging techniques, and DFT calculations, we provide a detailed analysis of the Sn content and oxidation state, dominant substitution sites, and charge-compensating defects in Sn-alloyed Cs2AgBiBr6 (1:Sn) crystals and films. An understanding of heterovalent alloying in halide double perovskites opens the door to a wider breadth of potential alloying agents for manipulating their band structures in a predictable manner
Towards Closing the Window on Strongly Interacting Dark Matter: Far-Reaching Constraints from Earth's Heat Flow
We point out a new and largely model-independent constraint on the dark
matter scattering cross section with nucleons, applying when this quantity is
larger than for typical weakly interacting dark matter candidates. When the
dark matter capture rate in Earth is efficient, the rate of energy deposition
by dark matter self-annihilation products would grossly exceed the measured
heat flow of Earth. This improves the spin-independent cross section
constraints by many orders of magnitude, and closes the window between
astrophysical constraints (at very large cross sections) and underground
detector constraints (at small cross sections). In the applicable mass range,
from about 1 to about 10^{10} GeV, the scattering cross section of dark matter
with nucleons is then bounded from above by the latter constraints, and hence
must be truly weak, as usually assumed.Comment: 12 pages, 2 figures; minor updates to match published versio
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