1,989 research outputs found
Large Deviations of the Smallest Eigenvalue of the Wishart-Laguerre Ensemble
We consider the large deviations of the smallest eigenvalue of the
Wishart-Laguerre Ensemble. Using the Coulomb gas picture we obtain rate
functions for the large fluctuations to the left and the right of the hard
edge. Our findings are compared with known exact results for finding
good agreement. We also consider the case of almost square matrices finding new
universal rate functions describing large fluctuations.Comment: 4 pages, 2 figure
Magnetic field tuning of coplanar waveguide resonators
We describe measurements on microwave coplanar resonators designed for
quantum bit experiments. Resonators have been patterned onto sapphire and
silicon substrates, and quality factors in excess of a million have been
observed. The resonant frequency shows a high sensitivity to magnetic field
applied perpendicular to the plane of the film, with a quadratic dependence for
the fundamental, second and third harmonics. Frequency shift of hundreds of
linewidths can be obtained.Comment: Accepted for publication in AP
On the properties of superconducting planar resonators at mK temperatures
Planar superconducting resonators are now being increasingly used at mK
temperatures in a number of novel applications. They are also interesting
devices in their own right since they allow us to probe the properties of both
the superconductor and its environment. We have experimentally investigated
three types of niobium resonators - including a lumped element design -
fabricated on sapphire and SiO_2/Si substrates. They all exhibit a non-trivial
temperature dependence of their centre frequency and quality factor. Our
results shed new light on the interaction between the electromagnetic waves in
the resonator and two-level fluctuators in the substrate.Comment: V2 includes some minor corrections/changes. Submitted to PR
Kepler Transit Depths Contaminated by a Phantom Star
We present ground-based observations from the Discovery Channel Telescope
(DCT) of three transits of Kepler-445c---a supposed super-Earth exoplanet with
properties resembling GJ 1214b---and demonstrate that the transit depth is
approximately 50 percent shallower than the depth previously inferred from
Kepler Spacecraft data. The resulting decrease in planetary radius
significantly alters the interpretation of the exoplanet's bulk composition.
Despite the faintness of the M4 dwarf host star, our ground-based photometry
clearly recovers each transit and achieves repeatable 1-sigma precision of
approximately 0.2 percent (2 millimags). The transit parameters estimated from
the DCT data are discrepant with those inferred from the Kepler data to at
least 17-sigma confidence. This inconsistency is due to a subtle miscalculation
of the stellar crowding metric during the Kepler pre-search data conditioning
(PDC). The crowding metric, or CROWDSAP, is contaminated by a non-existent
"phantom star" originating in the USNO-B1 catalog and inherited by the Kepler
Input Catalog (KIC). Phantom stars in the KIC are likely rare, but they have
the potential to affect statistical studies of Kepler targets that use the PDC
transit depths for a large number of exoplanets where individual follow-up
observation of each is not possible. The miscalculation of Kepler-445c's
transit depth emphasizes the importance of stellar crowding in the Kepler data,
and provides a cautionary tale for the analysis of data from the Transiting
Exoplanet Survey Satellite (TESS), which will have even larger pixels than
Kepler.Comment: 11 pages, 10 figures, 5 tables. Accepted for publication in AJ.
Transit light curves will be available from AJ as Db
Circuit QED with a Flux Qubit Strongly Coupled to a Coplanar Transmission Line Resonator
We propose a scheme for circuit quantum electrodynamics with a
superconducting flux-qubit coupled to a high-Q coplanar resonator. Assuming
realistic circuit parameters we predict that it is possible to reach the strong
coupling regime. Routes to metrological applications, such as single photon
generation and quantum non-demolition measurements are discussed.Comment: 8 pages, 5 figure
Externally Dispersed Interferometry for Precision Radial Velocimetry
Externally Dispersed Interferometry (EDI) is the series combination of a
fixed-delay field-widened Michelson interferometer with a dispersive
spectrograph. This combination boosts the spectrograph performance for both
Doppler velocimetry and high resolution spectroscopy. The interferometer
creates a periodic spectral comb that multiplies against the input spectrum to
create moire fringes, which are recorded in combination with the regular
spectrum. The moire pattern shifts in phase in response to a Doppler shift.
Moire patterns are broader than the underlying spectral features and more
easily survive spectrograph blurring and common distortions. Thus, the EDI
technique allows lower resolution spectrographs having relaxed optical
tolerances (and therefore higher throughput) to return high precision velocity
measurements, which otherwise would be imprecise for the spectrograph alone.Comment: 7 Pages, White paper submitted to the AAAC Exoplanet Task Forc
A physically motivated and empirically calibrated method to measure effective temperature, metallicity, and Ti abundance of M dwarfs
The ability to perform detailed chemical analysis of Sun-like F-, G-, and
K-type stars is a powerful tool with many applications including studying the
chemical evolution of the Galaxy and constraining planet formation theories.
Unfortunately, complications in modeling cooler stellar atmospheres hinders
similar analysis of M-dwarf stars. Empirically-calibrated methods to measure M
dwarf metallicity from moderate-resolution spectra are currently limited to
measuring overall metallicity and rely on astrophysical abundance correlations
in stellar populations. We present a new, empirical calibration of synthetic M
dwarf spectra that can be used to infer effective temperature, Fe abundance,
and Ti abundance. We obtained high-resolution (R~25,000), Y-band (~1 micron)
spectra of 29 M dwarfs with NIRSPEC on Keck II. Using the PHOENIX stellar
atmosphere modeling code (version 15.5), we generated a grid of synthetic
spectra covering a range of temperatures, metallicities, and
alpha-enhancements. From our observed and synthetic spectra, we measured the
equivalent widths of multiple Fe I and Ti I lines and a temperature-sensitive
index based on the FeH bandhead. We used abundances measured from
widely-separated solar-type companions to empirically calibrate transformations
to the observed indices and equivalent widths that force agreement with the
models. Our calibration achieves precisions in Teff, [Fe/H], and [Ti/Fe] of 60
K, 0.1 dex, and 0.05 dex, respectively and is calibrated for 3200 K < Teff <
4100 K, -0.7 < [Fe/H] < +0.3, and -0.05 < [Ti/Fe] < +0.3. This work is a step
toward detailed chemical analysis of M dwarfs at a similar precision achieved
for FGK stars.Comment: accepted for publication in ApJ, all synthetic spectra available at
http://people.bu.edu/mveyette/phoenix
Dramatic robustness of a multiple delay dispersed interferometer to spectrograph errors: how mixing delays reduces or cancels wavelength drift
We describe demonstrations of remarkable robustness to instrumental noises by using a multiple delay externally dispersed interferometer (EDI) on stellar observations at the Hale telescope. Previous observatory EDI demonstrations used a single delay. The EDI (also called “TEDI”) boosted the 2,700 resolution of the native TripleSpec NIR spectrograph (950-2450 nm) by as much as 10x to 27,000, using 7 overlapping delays up to 3 cm. We observed superb rejection of fixed pattern noises due to bad pixels, since the fringing signal responds only to changes in multiple exposures synchronous to the applied delay dithering. Remarkably, we observed a ~20x reduction of reaction in the output spectrum to PSF shifts of the native spectrograph along the dispersion direction, using our standard processing. This allowed high resolution observations under conditions of severe and irregular PSF drift otherwise not possible without the interferometer. Furthermore, we recently discovered an improved method of weighting and mixing data between pairs of delays that can theoretically further reduce the net reaction to PSF drift to zero. We demonstrate a 350x reduction in reaction to a native PSF shift using a simple simulation. This technique could similarly reduce radial velocity noise for future EDI’s that use two delays overlapped in delay space (or a single delay overlapping the native peak). Finally, we show an extremely high dynamic range EDI measurement of our ThAr lamp compared to a literature ThAr spectrum, observing weak features (~0.001x height of nearest strong line) that occur between the major lines. Because of individuality of each reference lamp, accurate knowledge of its spectrum between the (unfortunately) sparse major lines is important for precision radial velocimetry
Cohort profile: Canadian study of prediction of death, dialysis and interim cardiovascular events (CanPREDDICT)
Background: The Canadian Study of Prediction of Death, Dialysis and Interim Cardiovascular Events (CanPREDDICT)
is a large, prospective, pan-Canadian, cohort study designed to improve our understanding of determinants of renal and cardiovascular (CV) disease progression in patients with chronic kidney disease (CKD). The primary objective is to clarify the associations between traditional and newer biomarkers in the prediction of specific renal and CV events, and of death in patients with CKD managed by nephrologists. This information could then be used to better understand biological variation in outcomes, to develop clinical prediction models and to inform enrolment into interventional studies which may lead to novel treatments.
Methods/Designs: Commenced in 2008, 2546 patients have been enrolled with eGFR between 15 and 45 ml/min 1.73m2 from a representative sample in 25 rural, urban, academic and non academic centres across Canada. Patients are to be followed for an initial 3 years at 6 monthly intervals, and subsequently annually. Traditional biomarkers include eGFR, urine albumin creatinine ratio (uACR), hemoglobin (Hgb), phosphate and albumin. Newer biomarkers of interest were selected on the basis of biological relevance to important processes, commercial availability and assay reproducibility. They include asymmetric dimethylarginine (ADMA), N-terminal pro-brain natriuretic peptide (NT-pro-BNP), troponin I, cystatin C, high sensitivity C-reactive protein (hsCRP), interleukin-6 (IL6) and transforming growth factor beta 1 (TGFβ1). Blood and urine samples are collected at baseline, and every 6 monthly, and stored at −80°C. Outcomes of interest include renal replacement therapy, CV events and death, the latter two of which are adjudicated by an independent panel.
Discussion: The baseline distribution of newer biomarkers does not appear to track to markers of kidney function
and therefore may offer some discriminatory value in predicting future outcomes. The granularity of the data
presented at baseline may foster additional questions.
The value of the cohort as a unique resource to understand outcomes of patients under the care of nephrologists
in a single payer healthcare system cannot be overstated. Systematic collection of demographic, laboratory and
event data should lead to new insights.
The mean age of the cohort was 68 years, 90% were Caucasian, 62% were male, and 48% had diabetes. Forty
percent of the cohort had eGFR between 30–45 mL/min/1.73m2, 22% had eGFR values below 20 mL/min/1.73m2; 61% had uACR < 30. Serum albumin, hemoglobin, calcium and 25-hydroxyvitamin D (25(OH)D) levels were progressively lower in the lower eGFR strata, while parathyroid hormone (PTH) levels increased. Cystatin C, ADMA, NT-proBNP, hsCRP, troponin I and IL-6 were significantly higher in the lower GFR strata, whereas 25(OH)D and TGFβ1 values were lower at lower GFR. These distributions of each of the newer biomarkers by eGFR and uACR categories were variable
- …