132 research outputs found
Feasibility of Exoplanet Coronagraphy with the Hubble Space Telescope
Herein we report on a preliminary study to assess the use of the Hubble Space Telescope (HST) for the direct detection and spectroscopic characterization of exoplanets and debris disks - an application for which HST was not originally designed. Coronagraphic advances may enable the design of a science instrument that could achieve limiting contrasts approx.10deg beyond 275 milli-arcseconds (4 lambda/D at 800 nm) inner working angle, thereby enabling detection and characterization of several known jovian planets and imaging of debris disks. Advantages of using HST are that it already exists in orbit, it's primary mirror is thermally stable and it is the most characterized space telescope yet flown. However there is drift of the HST telescope, likely due to thermal effects crossing the terminator. The drift, however, is well characterized and consists of a larger deterministic components and a smaller stochastic component. It is the effect of this drift versus the sensing and control bandwidth of the instrument that would likely limit HST coronagraphic performance. Herein we discuss the science case, quantifY the limiting factors and assess the feasibility of using HST for exoplanet discovery using a hypothetical new instrument. Keywords: Hubble Space Telescope, coronagraphy, exoplanets, telescope
Space-borne global astrometric surveys: the hunt for extra-solar planets
The proposed global astrometry mission {\it GAIA}, recently recommended
within the context of ESA's Horizon 2000 Plus long-term scientific program,
appears capable of surveying the solar neighborhood within 200 pc for
the astrometric signatures of planets around stars down to the magnitude limit
of =17 mag, which includes late M dwarfs at 100 pc. Realistic end-to-end
simulations of the GAIA global astrometric measurements have yielded first
quantitative estimates of the sensitivity to planetary perturbations and of the
ability to measure their orbital parameters. Single Jupiter-mass planets around
normal solar-type stars appear detectable up to 150 pc (12 mag) with
probabilities 50 per cent for orbital periods between 2.5 and
8 years, and their orbital parameters measured with better than 30 per
cent accuracy to about 100 pc. Jupiter-like objects (same mass and period as
our giant planet) are found with similar probabilities up to 100 pc.These first
experiments indicate that the {\it GAIA} results would constitute an important
addition to those which will come from the other ongoing and planned
planet-search programs. These data combined would provide a formidable testing
ground on which to confront theories of planetary formation and evolution.Comment: 13 pages, 10 figures, uses mn.sty, accepted by MNRA
Electroweak Radiative Corrections To Polarized M{\o}ller Scattering Asymmetries
One loop electroweak radiative corrections to left-right parity violating
M{\o}ller scattering () asymmetries are presented. They
reduce the standard model (tree level) prediction by 40 \% where the
main shift and uncertainty stem from hadronic vacuum polarization loops. A
similar reduction also occurs for the electron-electron atomic parity violating
interaction. That effect can be attributed to an increase of
by in running from to 0. The
sensitivity of the asymmetry to ``new physics'' is also discussed.Comment: 14 pages, Revtex, postscript file including figures is available at
ftp://ttpux2.physik.uni-karlsruhe.de/ttp95-14/ttp95-14.ps or via WWW at
http://ttpux2.physik.uni-karlsruhe.de/cgi-bin/preprints/ (129.13.102.139
Atomic parity nonconservation and neutron radii in cesium isotopes
The interpretation of future precise experiments on atomic parity violation
in terms of parameters of the Standard Model could be hampered by uncertainties
in the atomic and nuclear structure. While the former can be overcome by
measurement in a series of isotopes, the nuclear structure requires knowledge
of the neutron density. We use the nuclear Hartree-Fock method, which includes
deformation effects, to calculate the proton and neutron densities in
{125}Cs-{139}Cs. We argue that the good agreement with the experimental charge
radii, binding energies, and ground state spins signifies that the
phenomenological nuclear force and the method of calculation that we use is
adequate. Based on this agreement, and on calculations involving different
effective interactions, we estimate the uncertainties in the differences of the
neutron radii delta_{N,N'} and conclude that they cause uncertainties in
the ratio of weak charges, the quantities determined in the atomic parity
nonconservation experiments, of less than 10^{-3}. Such an uncertainty is
smaller than the anticipated experimental error.Comment: 24 pages (RevTeX) 4 figures (Postscript/uuencoded compressed) Caltech
Preprint No. MAP-153 (March 1993
Atomic Parity Violation and Precision Electroweak Physics - An Updated Analysis
A new analysis of parity violation in atomic cesium has led to the improved
value of the weak charge, . The implications
of this result for constraining the Peskin-Takeuchi parameters S and T and for
guiding searches for new Z bosons are discussed.Comment: 8 pages, LaTeX, 3 figures, Submitted to Physical Review D. Updated
experimental inputs and references; clarification of notatio
Atomic Parity Nonconservation: Electroweak Parameters and Nuclear Structure
There have been suggestions to measure atomic parity nonconservation (PNC)
along an isotopic chain, by taking ratios of observables in order to cancel
complicated atomic structure effects. Precise atomic PNC measurements could
make a significant contribution to tests of the Standard Model at the level of
one loop radiative corrections. However, the results also depend upon certain
features of nuclear structure, such as the spatial distribution of neutrons in
the nucleus. To examine the sensitivity to nuclear structure, we consider the
case of Pb isotopes using various recent relativistic and non-relativistic
nuclear model calculations. Contributions from nucleon internal weak structure
are included, but found to be fairly negligible. The spread among present
models in predicted sizes of nuclear structure effects may preclude using Pb
isotope ratios to test the Standard Model at better than a one percent level,
unless there are adequate independent tests of the nuclear models by various
alternative strong and electroweak nuclear probes. On the other hand,
sufficiently accurate atomic PNC experiments would provide a unique method to
measure neutron distributions in heavy nuclei.Comment: 44 pages, INT Preprint DOE/ER/40561-050-INT92-00-1
Comparative study of the stability of bimatoprost 0.03% and latanoprost 0.005%: A patient-use study
<p>Abstract</p> <p>Background</p> <p>The stability of ophthalmic preparations in multidose containers is influenced by the preservative as well as the stability of the active ingredient. Unstable drugs may require refrigeration to preserve their active ingredient level and they are more likely to degrade over time, therefore becoming more susceptible to degradation based on patient mishandling. The purpose of this study was to determine the degree of molecular degradation that occurs in bimatoprost and latanoprost in a patient-use setting.</p> <p>Methods</p> <p>This was an open-label, laboratory evaluation of the relative stability of bimatoprost and latanoprost. Patients presently using bimatoprost (n = 31) or latanoprost (n = 34) were identified at 2 clinical sites in Brazil. Patients were instructed to use and store their drops as usual and return all used medication bottles between day 28 and day 34 after opening.</p> <p>Results</p> <p>Bimatoprost demonstrated no degradation, but latanoprost degraded at various levels. The mean age of bimatoprost was 43.0 ± 3.4 days and the mean age of latanoprost was 43.9 ± 2.8 days (P = .072). The mean percentage of labeled concentration was 103.7% in the bimatoprost bottles and 88.1% in the latanoprost bottles (P < 001).</p> <p>Conclusion</p> <p>This study showed that bimatoprost maintained ≥100% concentration throughout the study period while latanoprost did not.</p
Bounds on Vector Leptoquarks
We derive bounds on vector leptoquarks coupling to the first generation,
using data from low energy experiments as well as from high energy
accelerators. Similarly to the case of scalar leptoquarks, we find that the
strongest indirect bounds arise from atomic parity violation and universality
in leptonic pi decays. These bounds are considerably stronger than the first
direct bounds of HERA, restricting vector leptoquarks that couple with
electromagnetic strength to right-handed quarks to lie above 430 GeV or 460
GeV, and leptoquarks that couple with electromagnetic strength to left-handed
quarks to lie above 1.3 TeV, 1.2 TeV and 1.5 TeV for the SU(2)_W singlet,
doublet and triplet respectively.Comment: 14 Pages (LaTeX), including 1 uufiled postscript figure.
WIS-93/119/Dec-P
Bounding Anomalous Gauge-Boson Couplings
In this version we have corrected some minor errors in the tables, corrected
typos, and added a reference. We have also updated our comparison with earlier
workers. Figures are now included as uuencoded compressed tar files.Comment: 32 page
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