7,482 research outputs found
Rotor Spectra, Berry Phases, and Monopole Fields: from Antiferromagnets to QCD
The order parameter of a finite system with a spontaneously broken continuous
global symmetry acts as a quantum mechanical rotor. Both antiferromagnets with
a spontaneously broken spin symmetry and massless QCD with a broken
chiral symmetry have rotor spectra when considered in
a finite volume. When an electron or hole is doped into an antiferromagnet or
when a nucleon is propagating through the QCD vacuum, a Berry phase arises from
a monopole field and the angular momentum of the rotor is quantized in
half-integer units.Comment: 4 page
Precision multi-epoch astrometry with VLT cameras FORS1/2
We investigate the astrometric performance of the FORS1 and FORS2 cameras of
the VLT at long time scales with emphasis on systematic errors which normally
prevent attainning a precision better than 1mas. The study is based on multi-
epoch time series of observations of a single sky region imaged with a time
spacing of 2-6 years at FORS1 and 1-5 months at FORS2. We performed a detailed
analysis of a random error of positions that was shown to be dominated by the
uncertainty of the star photocenter determination. The component of the random
error corresponding to image motion was found to be caused primarily by optical
aberrations and variations of atmospheric PSF size but not by the effect of
atmospheric image motion. Comparison of observed and model annual/monthly epoch
average positions yielded estimates of systematic errors for which temporal
properties and distribution in the CCD plane are given. At frame center, the
systematic component is about 25 mu-as. Systematic errors are shown to be
caused mainly by a combined effect of the image asymmetry and seeing variations
which therefore should be strongly limited to avoid generating random and
systematic errors. For a series of 30 images, we demonstrated presicion of
about 50 mu-as stable on daily, monthly, and annual time scales. Relative
proper motion and trigonometric parallaxes of stars in the center of the test
field were derived with a precision of 20 mu-as/yr and 40 mu-as for 17-19 mag
stars.Comment: 16 pages, 16 figures, 4 tables, accepted in A&A; typos and language
corrections; version sent to the printe
Walking near a Conformal Fixed Point: the 2-d O(3) Model at theta near pi as a Test Case
Slowly walking technicolor models provide a mechanism for electroweak
symmetry breaking whose nonperturbative lattice investigation is rather
challenging. Here we demonstrate walking near a conformal fixed point
considering the 2-d lattice O(3) model at vacuum angle .
The essential features of walking technicolor models are shared by this toy
model and can be accurately investigated by numerical simulations. We show
results for the running coupling and the beta-function and we perform a finite
size scaling analysis of the massgap close to the conformal point.Comment: 5 pages, 4 figure
Extrasolar planets and brown dwarfs around A-F type stars. II. A planet found with ELODIE around the F6V star HD 33564
We present here the detection of a planet orbiting around the F6V star HD
33564. The radial velocity measurements, obtained with the ELODIE echelle
spectrograph at the Haute-Provence Observatory, show a variation with a period
of 388 days. Assuming a primary mass of 1.25 Mo, the best Keplerian fit to the
data leads to a minimum mass of 9.1 MJup for the companion.Comment: 5 pages. Final version, accepted for publication (A&A). Some Spitzer
results on HD33564 (taken this year; not yet published), finally show that
the detection of IR excess around this star (by IRAS) is spuriou
Binary mixtures of condensates in generic confining potentials
We study a binary mixture of Bose-Einstein condensates, confined in a generic
potential, in the Thomas-Fermi approximation. We search for the
zero-temperature ground state of the system, both in the case of fixed numbers
of particles and fixed chemical potentials.Comment: 20 pages, 2 figure
Standardizing Markers to Evaluate and Compare their Performances
Introduction: Markers that purport to distinguish subjects with a condition from those without a condition must be evaluated rigorously for their classification accuracy. A single approach to statistically evaluating and comparing markers is not yet established.
Methods: We suggest a standardization that uses the marker distribution in unaffected subjects as a reference. For an affected subject with marker value Y, the standardized placement value is the proportion of unaffected subjects with marker values that exceed Y.
Results: We apply the standardization to two illustrative datasets. In patients with pancreatic cancer placement values calculated for the CA 19-9 marker are smaller than for the CA-125 marker, indicating that CA19-9 is a better marker. For detecting hearing impairment, the placement values for the test output (the marker) are smaller when the input sound stimulus is of lower intensity. This indicates that the test better distinguishes hearing impaired from unimpaired ears when a lower intensity sound stimulus is used.
Explicit connections are drawn between the distribution of standardized marker values and the receiver operating characteristic (ROC) curve, one established statistical technique for evaluating classifiers.
Discussion: The standardization is an intuitive procedure for evaluating markers. It facilitates direct and meaningful comparisons between markers. It also provides a new view of ROC analysis that may render it more accessible to those as yet unfamiliar with it. The general approach provides a mechanism to statistically address important questions that are typically not addressed in current marker research, such as quantifying and controlling for covariate effects
Arthroscopic transosseous rotator cuff repair: A prospective study on cost savings, surgical time, and outcomes
Objectives: Health expenditures in the United States are outpacing national income, and affordability has become a major policy issue. Over 500,000 rotator cuff repairs (RCR) are performed annually in the United States making RCR a potential source of cost savings. Arthroscopic trans-osseous equivalent (TOE) repair using a double row of anchors has shown superior biomechanical strength compared to other techniques, but at a higher cost. The arthroscopic transosseous (TO) repair is a novel technique allowing arthroscopic rotator cuff repair to be performed without suture anchors. Arthroscopic TO repair may be a means to provide similarly excellent patient outcomes while lowering the cost of care. The primary purpose is to compare the price differential and time of surgery for an arthroscopic rotator cuff repair using anchorless TO repair verses an anchor trans-osseous equivalent (TOE) repair. A secondary purpose of the study was to evaluate outcomes at 6 months postoperatively. Methods: A prospective, case-controlled study evaluating arthroscopic rotator cuff repair using two techniques was performed. The study group consisting of 21 patients undergoing TO repair was compared to a control group consisting of 22 patients undergoing TOE repair. The groups were controlled for size of tear, biceps treatment, acromioplasty, distal clavicle excision, and labral pathology. The primary outcome measures were surgical time as well as total cost of implants and equipment for each surgery, determined by an independent third party, Atlanticare Hospital. Secondary outcomes were changes in the SST, VAS, and SANE scores. Results: Mean total surgical implant/equipment cost per procedure for TOE repair was 1204.97 (SD 330.69; p\u3c0.0001). Mean cut to close time for TOE repair was 85 minutes (95% CI is 77-90) verses 74 (95% CI = 71-98) for TO repair. A log rank test revealed no difference in time (p =0.95). A linear regression model was developed to evaluate the change in SST, VAS, and SANE scores from pre-op to 6 months follow-up. Our study was underpowered but no difference in outcome was observed. Conclusion: Arthroscopic TO rotator cuff repair is a cost savings and time neutral technique compared to TOE repair. A mean of $1100 can be saved in surgical cost per case. In a country that performs over 500,000 RCRs annually, utilizing a TO repair technique can provide substantial cost savings to the healthcare system. © The Author(s) 2015
YARARA V2: reaching sub-m s−1 precision over a decade using PCA on line-by-line radial velocities
Context. The detection of Earth-like planets with the radial velocity (RV) method is extremely challenging today due to the presence of non-Doppler signatures such as stellar activity and instrumental signals that mimic and hide the signals of exoplanets. In a previous paper, we presented the YARARA pipeline, which implements corrections for telluric absorption, stellar activity, and instrumental systematics at the spectral level, and then it extracts line-by-line (LBL) RVs with a significantly better precision than standard pipelines.
Aims. In this paper, we demonstrate that further gains in RV precision can be achieved by performing principal component analysis (PCA) decomposition on the LBL RVs.
Methods. The mean-insensitive nature of PCA means that it is unaffected by true Doppler shifts, and thus can be used to isolate and correct nuisance signals other than planets.
Results. We analysed the data of 20 intensively observed HARPS targets by applying our PCA approach on the LBL RVs obtained by YARARA. The first principal components show similarities across most of the stars and correspond to newly identified instrumental systematics for which we can now correct. For several targets, this results in an unprecedented RV root-mean-square of around 90 cm s−1 over the full lifetime of HARPS. We used the corrected RVs to confirm a previously published 120-day signal around 61 Vir, and to detect a super-Earth candidate (K ~ 60 ± 6 cm s−1, m sin i = 6.6 ± 0.7 M⊕) around the G6V star HD 20794, which spends part of its 600-day orbit within the habitable zone of the host star.
Conclusions. This study highlights the potential of LBL PCA to identify and correct hitherto unknown, long-term instrumental effects and thereby extend the sensitivity of existing and future instruments towards the Earth analogue regime
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