5,180 research outputs found
PEPSI deep spectra. III. A chemical analysis of the ancient planet-host star Kepler-444
We obtained an LBT/PEPSI spectrum with very high resolution and high
signal-to-noise ratio (S/N) of the K0V host Kepler-444, which is known to host
5 sub-Earth size rocky planets. The spectrum has a resolution of R=250,000, a
continuous wavelength coverage from 4230 to 9120A, and S/N between 150 and
550:1 (blue to red). We performed a detailed chemical analysis to determine the
photospheric abundances of 18 chemical elements, in order to use the abundances
to place constraints on the bulk composition of the five rocky planets. Our
spectral analysis employs the equivalent width method for most of our spectral
lines, but we used spectral synthesis to fit a small number of lines that
require special care. In both cases, we derived our abundances using the MOOG
spectral analysis package and Kurucz model atmospheres. We find no correlation
between elemental abundance and condensation temperature among the refractory
elements. In addition, using our spectroscopic stellar parameters and isochrone
fitting, we find an age of 10+/-1.5 Gyr, which is consistent with the
asteroseismic age of 11+/-1 Gyr. Finally, from the photospheric abundances of
Mg, Si, and Fe, we estimate that the typical Fe-core mass fraction for the
rocky planets in the Kepler-444 system is approximately 24 per cent. If our
estimate of the Fe-core mass fraction is confirmed by more detailed modeling of
the disk chemistry and simulations of planet formation and evolution in the
Kepler-444 system, then this would suggest that rocky planets in more
metal-poor and alpha-enhanced systems may tend to be less dense than their
counterparts of comparable size in more metal-rich systems.Comment: in press, 11 pages, 3 figures, data available from pepsi.aip.d
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
Recent Decisions
Constitutional Law--Grandfather Clause in International Emergency Economic Powers Act Permits the President to Ban Travel to Cuba without Declaring an Emergency Regan v. Wald, 104 S. Ct. 3026 (1984)
Jurisdiction--Bank may not Assert Act of State Doctrine as Defense in Action on Certificate of Deposit Garcia v. Chase Manhattan Bank, N.A., 735 F.2d 645 (2d Cir. 1984).
Jurisdiction--Commercial Activity as Applied to the Foreign Sovereign Immunities Act and the Act of State Doctrine Braka v. Bancomer, S.A., 589 F. Supp. 1465 (S.D.N.Y. 1984
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
Multivalued Fields on the Complex Plane and Conformal Field Theories
In this paper a class of conformal field theories with nonabelian and
discrete group of symmetry is investigated. These theories are realized in
terms of free scalar fields starting from the simple systems and scalar
fields on algebraic curves. The Knizhnik-Zamolodchikov equations for the
conformal blocks can be explicitly solved. Besides of the fact that one obtains
in this way an entire class of theories in which the operators obey a
nonstandard statistics, these systems are interesting in exploring the
connection between statistics and curved space-times, at least in the two
dimensional case.Comment: (revised version), 30 pages + one figure (not included), (requires
harvmac.tex), LMU-TPW 92-1
Linear stability, transient energy growth and the role of viscosity stratification in compressible plane Couette flow
Linear stability and the non-modal transient energy growth in compressible
plane Couette flow are investigated for two prototype mean flows: (a) the {\it
uniform shear} flow with constant viscosity, and (b) the {\it non-uniform
shear} flow with {\it stratified} viscosity. Both mean flows are linearly
unstable for a range of supersonic Mach numbers (). For a given , the
critical Reynolds number () is significantly smaller for the uniform shear
flow than its non-uniform shear counterpart. An analysis of perturbation energy
reveals that the instability is primarily caused by an excess transfer of
energy from mean-flow to perturbations. It is shown that the energy-transfer
from mean-flow occurs close to the moving top-wall for ``mode I'' instability,
whereas it occurs in the bulk of the flow domain for ``mode II''. For the
non-modal analysis, it is shown that the maximum amplification of perturbation
energy, , is significantly larger for the uniform shear case compared
to its non-uniform counterpart. For , the linear stability operator
can be partitioned into , and the
-dependent operator is shown to have a negligibly small
contribution to perturbation energy which is responsible for the validity of
the well-known quadratic-scaling law in uniform shear flow: . A reduced inviscid model has been shown to capture all salient
features of transient energy growth of full viscous problem. For both modal and
non-modal instability, it is shown that the {\it viscosity-stratification} of
the underlying mean flow would lead to a delayed transition in compressible
Couette flow
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
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