810 research outputs found
An Analysis of the Shapes of Interstellar Extinction Curves. VI. The Near-IR Extinction Law
We combine new HST/ACS observations and existing data to investigate the
wavelength dependence of NIR extinction. Previous studies suggest a power-law
form, with a "universal" value of the exponent, although some recent
observations indicate that significant sight line-to-sight line variability may
exist. We show that a power-law model provides an excellent fit to most NIR
extinction curves, but that the value of the power, beta, varies significantly
from sight line-to-sight line. Therefore, it seems that a "universal NIR
extinction law" is not possible. Instead, we find that as beta decreases, R(V)
[=A(V)/E(B-V)] tends to increase, suggesting that NIR extinction curves which
have been considered "peculiar" may, in fact, be typical for different R(V)
values. We show that the power law parameters can depend on the wavelength
interval used to derive them, with the beta increasing as longer wavelengths
are included. This result implies that extrapolating power law fits to
determine R(V) is unreliable. To avoid this problem, we adopt a different
functional form for NIR extinction. This new form mimics a power law whose
exponent increases with wavelength, has only 2 free parameters, can fit all of
our curves over a longer wavelength baseline and to higher precision, and
produces R(V) values which are consistent with independent estimates and
commonly used methods for estimating R(V). Furthermore, unlike the power law
model, it gives R(V)'s that are independent of the wavelength interval used to
derive them. It also suggests that the relation R(V) = -1.36 E(K-V)/E(B-V) -
0.79 can estimate R(V) to +/-0.12. Finally, we use model extinction curves to
show that our extinction curves are in accord with theoretical expectations.Comment: To appear in the Astrophysical Journa
Energy distribution and cooling of a single atom in an optical tweezer
We investigate experimentally the energy distribution of a single rubidium
atom trapped in a strongly focused dipole trap under various cooling regimes.
Using two different methods to measure the mean energy of the atom, we show
that the energy distribution of the radiatively cooled atom is close to
thermal. We then demonstrate how to reduce the energy of the single atom, first
by adiabatic cooling, and then by truncating the Boltzmann distribution of the
single atom. This provides a non-deterministic way to prepare atoms at low
microKelvin temperatures, close to the ground state of the trapping potential.Comment: 9 pages, 6 figures, published in PR
Period derivative of the M15 X-ray Binary AC211/X2127+119
We have combined Rossi X-ray Timing Explorer observations of X2127+119, the
low-mass X-ray binary in the globular cluster M15, with archival X-ray
lightcurves to study the stability of the 17.1 hr orbital period. We find that
the data cannot be fit by the Ilovaisky (1993) ephemeris, and requires either a
7sigma change to the period or a period derivative Pdot/P~9x10e-7 per year.
Given its remarkably low L_X/L_opt such a Pdot lends support to models that
require super-Eddington mass transfer in a q~1 binary.Comment: 11 pages, 3 figures, to be published in New Astronom
How Well Do We Know the Orbits of the Outer Planets?
This paper deals with the problem of astrometric determination of the orbital
elements of the outer planets, in particular by assessing the ability of
astrometric observations to detect perturbations of the sort expected from the
Pioneer effect or other small perturbations to gravity. We also show that while
using simplified models of the dynamics can lead to some insights, one must be
careful to not over-simplify the issues involved lest one be misled by the
analysis onto false paths. Specifically, we show that the current ephemeris of
Pluto does not preclude the existence of the Pioneer effect. We show that the
orbit of Pluto is simply not well enough characterized at present to make such
an assertion. A number of misunderstandings related to these topics have now
propagated through the literature and have been used as a basis for drawing
conclusions about the dynamics of the solar system. Thus, the objective of this
paper is to address these issues. Finally, we offer some comments dealing with
the complex topic of model selection and comparison.Comment: Accepted for publication in the Ap
Multi-fractional analysis of molecular diffusion in polymer multilayers by FRAP: a new simulation-based approach
Comprehensive analysis of the multifractional molecular diffusion provides a deeper understanding of the diffusion phenomenon in the fields of material science, molecular and cell biology, advanced biomaterials, etc. Fluorescence recovery after photobleaching (FRAP) is commonly employed to probe the molecular diffusion. Despite FRAP being a very popular method, it is not easy to assess multifractional molecular diffusion due to limited possibilities of approaches for analysis. Here we present a novel simulation-optimization-based approach (S-approach) that significantly broadens possibilities of the analysis. In the S-approach, possible fluorescence recovery scenarios are primarily simulated and afterward compared with a real measurement while optimizing parameters of a model until a sufficient match is achieved. This makes it possible to reveal multifractional molecular diffusion. Fluorescent latex particles of different size and fluorescein isothiocyanate in an aqueous medium were utilized as test systems. Finally, the S-approach has been used to evaluate diffusion of cytochrome c loaded into multilayers made of hyaluronan and polylysine. Software for evaluation of multifractional molecular diffusion by S-approach has been developed aiming to offer maximal versatility and user-friendly way for analysis
Relevant distance between two different instances of the same potential energy in protein folding
In the context of complex systems and, particularly, of protein folding, a
physically meaningful distance is defined which allows to make useful
statistical statements about the way in which energy differences are modified
when two different instances of the same potential-energy function are used.
When the two instances arise from the fact that different algorithms or
different approximations are used, the distance herein defined may be used to
evaluate the relative accuracy of the two methods. When the difference is due
to a change in the free parameters of which the potential depends on, the
distance can be used to quantify, in each region of parameter space, the
robustness of the modeling to such a change and this, in turn, may be used to
assess the significance of a parameters' fit. Both cases are illustrated with a
practical example: the study of the Poisson-based solvation energy in the
Trp-Cage protein (PDB code 1L2Y).Comment: 20 pages, 6 figures, LaTeX file, elsart style. v1: Aknowledgments
modified. v2: y-values of fig. 5 and 6 corrected. v3: Journal-ref added,
aknowledgements modified and fig. 1 and 2 correcte
Clinical Practice Guidelines on the Diagnosis and Management of Polycystic Ovary Syndrome: A Systematic Review and Quality Assessment Study
CONTEXT: Clinical practice guidelines (CPGs) are key instruments to implement the practice of evidence-based medicine. We aimed to evaluate the methodological quality and variations in CPGs recommendations on the diagnosis and management of polycystic ovary syndrome (PCOS). EVIDENCE ACQUISITION: We searched MEDLINE, EMBASE, and CENTRAL until December 2020 for all evidence-based CPGs and consensus statements on PCOS. We extracted data in duplicate to map clinical recommendations across prespecified disease domains and assessed CPGs methodological quality of using the Appraisal of Guidelines, Research & Evaluation II tool. EVIDENCE SYNTHESIS: We included 13 PCOS CPGs published between 2007 and 2018. CPGs recommendations were mostly focused on screening for and managing metabolic disease (12/13, 92%), followed by cardiovascular risk assessment (10/13, 77%). Mental health (8/13, 62%) and diagnosis in adolescents (7/13, 54%) were the least reported domains. Most CPGs had a high quality for scope and purpose description (12/13, 92%) while stakeholder's involvement and applicability of recommendations to clinical practice were appropriate in only 2 CPGs (2/13, 15%). We identified inconsistency in recommendations on PCOS diagnosis in adolescents, optimal lifestyle interventions, hirsutism and acne treatments, interventions to reduce the risk of ovarian hyperstimulation syndrome, the frequency and screening criteria for metabolic and cardiovascular disease, and optimal screening tools for mental health illness in women with PCOS. CONCLUSION: Current CPGs on the diagnosis and management of PCOS vary in their scope and methodological quality, which may hinder evidence translation into clinical practice. We identified disease domains with existing evidence gap to guide future research and guideline updates
A Young Planet Search in Visible and IR Light: DN Tau, V836 Tau, and V827 Tau
In searches for low-mass companions to late-type stars, correlation between
radial velocity variations and line bisector slope changes indicates
contamination by large starspots. Two young stars demonstrate that this test is
not sufficient to rule out starspots as a cause of radial velocity variations.
As part of our survey for substellar companions to T Tauri stars, we identified
the ~2 Myr old planet host candidates DN Tau and V836 Tau. In both cases,
visible light radial velocity modulation appears periodic and is uncorrelated
with line bisector span variations, suggesting close companions of several
M_Jup in these systems. However, high-resolution, infrared spectroscopy shows
that starspots cause the radial velocity variations. We also report unambiguous
results for V827 Tau, identified as a spotted star on the basis of both visible
light and infrared spectroscopy. Our results suggest that infrared follow up
observations are critical for determining the source of radial velocity
modulation in young, spotted stars.Comment: Accepted for publication in the Astrophysical Journal Letter
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