118 research outputs found
The colours of the Sun
We compile a sample of Sun-like stars with accurate effective temperatures,
metallicities and colours (from the UV to the near-IR). A crucial improvement
is that the effective temperature scale of the stars has recently been
established as both accurate and precise through direct measurement of angular
diameters obtained with stellar interferometers. We fit the colours as a
function of effective temperature and metallicity, and derive colour estimates
for the Sun in the Johnson/Cousins, Tycho, Stromgren, 2MASS and SDSS
photometric systems. For (B-V)_Sun, we favour the ``red'' colour 0.64 versus
the ``blue'' colour 0.62 of other recent papers, but both values are consistent
within the errors; we ascribe the difference to the selection of Sun-like stars
versus interpolation of wider colour-Teff-metallicity relations.Comment: 5 pages, 2 figures, accepted by MNRA
Unitary k-designs from random number-conserving quantum circuits
Local random circuits scramble efficiently and accordingly have a range of
applications in quantum information and quantum dynamics. With a global
charge however, the scrambling ability is reduced; for example, such random
circuits do not generate the entire group of number-conserving unitaries. We
establish two results using the statistical mechanics of -fold replicated
circuits. First, we show that finite moments cannot distinguish the ensemble
that local random circuits generate from the Haar ensemble on the entire group
of number conserving unitaries. Specifically, the circuits form a -design
with for a system in spatial dimensions with linear
dimension . Second, for , the depth to converge to a
-design scales as . In contrast, without number
conservation . The convergence of the circuit ensemble is
controlled by the low-energy properties of a frustration-free quantum
statistical model which spontaneously breaks symmetries. The
associated Goldstone modes are gapless and lead to the predicted scaling of
. Our variational bounds hold for arbitrary spatial and qudit dimensions;
we conjecture they are tight.Comment: 18 pages, 2 figure
A limit on variations in the fine-structure constant from spectra of nearby Sun-like stars
The fine structure constant, , sets the strength of the
electromagnetic force. The Standard Model of particle physics provides no
explanation for its value, which could potentially vary. The wavelengths of
stellar absorption lines depend on , but are subject to systematic
effects owing to astrophysical processes in stellar atmospheres. We measured
precise line wavelengths using 17 stars, selected to have almost identical
atmospheric properties to those of the Sun (solar twins), which reduces those
systematic effects. We found that varies by 50
parts-per-billion (ppb) within 50 parsecs from Earth. Combining the results
from all 17 stars provides an empirical, local reference for stellar
measurements of with an ensemble precision of 12 ppb.Comment: 33 pages, 6 figures. Published in Science (11 November 2022). This is
the accepted version which includes 20 pages of Supplementary Material
A comprehensive comparison of the Sun to other stars: searching for self-selection effects
If the origin of life and the evolution of observers on a planet is favoured
by atypical properties of a planet's host star, we would expect our Sun to be
atypical with respect to such properties. The Sun has been described by
previous studies as both typical and atypical. In an effort to reduce this
ambiguity and quantify how typical the Sun is, we identify eleven
maximally-independent properties that have plausible correlations with
habitability, and that have been observed by, or can be derived from,
sufficiently large, currently available and representative stellar surveys. By
comparing solar values for the eleven properties, to the resultant stellar
distributions, we make the most comprehensive comparison of the Sun to other
stars. The two most atypical properties of the Sun are its mass and orbit. The
Sun is more massive than 95 -/+ 2% of nearby stars and its orbit around the
Galaxy is less eccentric than 93 +/- 1% of FGK stars within 40 parsecs. Despite
these apparently atypical properties, a chi^2 -analysis of the Sun's values for
eleven properties, taken together, yields a solar chi^2 = 8.39 +/- 0.96. If a
star is chosen at random, the probability that it will have a lower value (be
more typical) than the Sun, with respect to the eleven properties analysed
here, is only 29 +/- 11%. These values quantify, and are consistent with, the
idea that the Sun is a typical star. If we have sampled all reasonable
properties associated with habitability, our result suggests that there are no
special requirements for a star to host a planet with life.Comment: Published in the Astrophysical Journal, 684:691-706, 2008 September
1. This version corrects two small errors the press could not correct before
publication - the errors are addressed in an erratum ApJ will release on Dec
1, 200
Kinematics of the Galactic Halo from Horizontal Branch stars in the Hamburg/ESO Survey
Large samples of Field Horizontal Branch (FHB) stars make excellent tracers
of the Galactic halo; by studying their kinematics, one can infer important
physical properties of our Galaxy. Here we present the results of a
medium-resolution spectroscopic survey of 530 FHB stars selected from the
Hamburg/ESO survey. The stars have a mean distance of ~7 kpc and thus probe the
inner parts of the Milky Way halo. We measure radial velocities from the
spectra in order to test the model of Sommer-Larsen et al., who suggested that
the velocity ellipsoid of the halo changes from radially-dominated orbits to
tangentially-dominated orbits as one proceeds from the inner to the outer halo.
We find that the present data are unable to discriminate between this model and
a more simple isothermal ellipsoid; we suggest that additional observations
towards the Galactic centre might help to differentiate them.Comment: 7 pages, 7 figures. Accepted for publication in MNRA
The Lantern Vol. 69, No. 1, Fall 2001
• Frets • Burn • The Amish-Man • City Children • Coasting West • Futile • Oxymoron • Fleeting Reflection • Pink Geraniums • Moving • Running: Arcola • Expectations • One Time Deal • We Slept • Faraway Field • My Own Giselle • My Father\u27s Will • Meet Me in Montana • Pride is a Lawn Mower • Gloss • 2% Low Fat • Bits of Tuesday • This is not a Pipe • What Ifs • Reconnection • A Bell Called Emily • The Elevatorhttps://digitalcommons.ursinus.edu/lantern/1159/thumbnail.jp
A13K-0336: Airborne Multi-Wavelength High Spectral Resolution Lidar for Process Studies and Assessment of Future Satellite Remote Sensing Concepts
NASA Langley recently developed the world's first airborne multi-wavelength high spectral resolution lidar (HSRL). This lidar employs the HSRL technique at 355 and 532 nm to make independent, unambiguous retrievals of aerosol extinction and backscatter. It also employs the standard backscatter technique at 1064 nm and is polarization-sensitive at all three wavelengths. This instrument, dubbed HSRL-2 (the secondgeneration HSRL developed by NASA Langley), is a prototype for the lidar on NASA's planned Aerosols- Clouds-Ecosystems (ACE) mission. HSRL-2 completed its first science mission in July 2012, the Two-Column Aerosol Project (TCAP) conducted by the Department of Energy (DOE) in Hyannis, MA. TCAP presents an excellent opportunity to assess some of the remote sensing concepts planned for ACE: HSRL-2 was deployed on the Langley King Air aircraft with another ACE-relevant instrument, the NASA GISS Research Scanning Polarimeter (RSP), and flights were closely coordinated with the DOE's Gulfstream-1 aircraft, which deployed a variety of in situ aerosol and trace gas instruments and the new Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR). The DOE also deployed their Atmospheric Radiation Measurement Mobile Facility and their Mobile Aerosol Observing System at a ground site located on the northeastern coast of Cape Cod for this mission. In this presentation we focus on the capabilities, data products, and applications of the new HSRL-2 instrument. Data products include aerosol extinction, backscatter, depolarization, and optical depth; aerosol type identification; mixed layer depth; and rangeresolved aerosol microphysical parameters (e.g., effective radius, index of refraction, single scatter albedo, and concentration). Applications include radiative closure studies, studies of aerosol direct and indirect effects, investigations of aerosol-cloud interactions, assessment of chemical transport models, air quality studies, present (e.g., CALIPSO) and future (e.g., EarthCARE) satellite calibration/validation, and development/assessment of advanced retrieval techniques for future satellite applications (e.g., lidar+polarimeter retrievals of aerosol and cloud properties). We will also discuss the relevance of HSRL-2 measurement capabilities to the ACE remote sensing concept
Evaluating the effectiveness and reliability of the Vibrant Soundbridge and Bonebridge auditory implants in clinical practice: Study design and methods for a multi-centre longitudinal observational study.
BACKGROUND: The Vibrant Soundbridge middle ear implant and the Bonebridge bone conducting hearing device are hearing implants that use radio frequency transmission to send information from the sound processor to the internal transducer. This reduces the risk of skin problems and infection but requires a more involved surgical procedure than competitor skin penetrating devices. It is not known whether more complex surgery will lead to additional complications. There is little information available on the reliability of these systems and adverse medical or surgical events. The primary research question is to determine the reliability and complication rate for the Vibrant Soundbridge and Bonebridge. The secondary research question explores changes in quality of life following implantation of the devices. The tertiary research question looks at effectiveness via changes in auditory performance. METHOD: The study was designed based on a combination of a literature search, two clinician focus groups and expert review.A multi-centre longitudinal observational study was designed. There are three study groups, two will have been implanted prior to the start of the study and one group, the prospective group, will be implanted after initiation of the study. Outcomes are surgical questionnaires, measures of quality of life, user satisfaction and speech perception tests in quiet and in noise. CONCLUSION: This is the first multi-centre study to look at these interventions and includes follow up over time to understand effectiveness, reliability, quality of life and complications
Bodyweight Perceptions among Texas Women: The Effects of Religion, Race/Ethnicity, and Citizenship Status
Despite previous work exploring linkages between religious participation and health, little research has looked at the role of religion in affecting bodyweight perceptions. Using the theoretical model developed by Levin et al. (Sociol Q 36(1):157–173, 1995) on the multidimensionality of religious participation, we develop several hypotheses and test them by using data from the 2004 Survey of Texas Adults. We estimate multinomial logistic regression models to determine the relative risk of women perceiving themselves as overweight. Results indicate that religious attendance lowers risk of women perceiving themselves as very overweight. Citizenship status was an important factor for Latinas, with noncitizens being less likely to see themselves as overweight. We also test interaction effects between religion and race. Religious attendance and prayer have a moderating effect among Latina non-citizens so that among these women, attendance and prayer intensify perceptions of feeling less overweight when compared to their white counterparts. Among African American women, the effect of increased church attendance leads to perceptions of being overweight. Prayer is also a correlate of overweight perceptions but only among African American women. We close with a discussion that highlights key implications from our findings, note study limitations, and several promising avenues for future research
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