1,316 research outputs found
Remarks on a normal subgroup of GA_n
We show that the subgroup generated by locally finite polynomial
automorphisms of k^n is normal in GA_n. Also, some properties of normal
subgroups of GA_n containing all diagonal automorphisms are given.Comment: 5 page
TESS unveils the phase curve of WASP-33b. Characterization of the planetary atmosphere and the pulsations from the star
We present the detection and characterization of the full-orbit phase curve
and secondary eclipse of the ultra-hot Jupiter WASP-33b at optical wavelengths,
along with the pulsation spectrum of the host star. We analyzed data collected
by the Transiting Exoplanet Survey Satellite (TESS) in sector 18. WASP-33b
belongs to a very short list of highly irradiated exoplanets that were
discovered from the ground and were later visited by TESS. The host star of
WASP-33b is of delta Scuti-type and shows nonradial pulsations in the
millimagnitude regime, with periods comparable to the period of the primary
transit. These completely deform the photometric light curve, which hinders our
interpretations. By carrying out a detailed determination of the pulsation
spectrum of the host star, we find 29 pulsation frequencies with a
signal-to-noise ratio higher than 4. After cleaning the light curve from the
stellar pulsations, we confidently report a secondary eclipse depth of 305.8
+/- 35.5 parts-per-million (ppm), along with an amplitude of the phase curve of
100.4 +/- 13.1 ppm and a corresponding westward offset between the region of
maximum brightness and the substellar point of 28.7 +/- 7.1 degrees, making
WASP-33b one of the few planets with such an offset found so far. Our derived
Bond albedo, A_B = 0.369 +/- 0.050, and heat recirculation efficiency, epsilon
= 0.189 +/- 0.014, confirm again that he behavior of WASP-33b is similar to
that of other hot Jupiters, despite the high irradiation received from its host
star. By connecting the amplitude of the phase curve to the primary transit and
depths of the secondary eclipse, we determine that the day- and nightside
brightness temperatures of WASP-33b are 3014 +/- 60 K and 1605 +/- 45 K,
respectively. From the detection of photometric variations due to gravitational
interactions, we estimate a planet mass of M_P = 2.81 +/- 0.53 M$_J.Comment: 19 pages, 15 figure
Vector Theory of Gravity
We proposed a gravitation theory based on an analogy with electrodynamics on
the basis of a vector field. For the first time, to calculate the basic
gravitational effects in the framework of a vector theory of gravity, we use a
Lagrangian written with gravitational radiation neglected and generalized to
the case of ultra-relativistic speeds. This allows us to accurately calculate
the values of all three major gravity experiments: the values of the perihelion
shift of Mercury, the light deflection angle in the gravity field of the Sun
and the value of radar echo delay. The calculated values coincide with the
observed ones. It is shown that, in this theory, there exists a model of an
expanding Universe.Comment: 9 page
Learning-based Ensemble Average Propagator Estimation
By capturing the anisotropic water diffusion in tissue, diffusion magnetic
resonance imaging (dMRI) provides a unique tool for noninvasively probing the
tissue microstructure and orientation in the human brain. The diffusion profile
can be described by the ensemble average propagator (EAP), which is inferred
from observed diffusion signals. However, accurate EAP estimation using the
number of diffusion gradients that is clinically practical can be challenging.
In this work, we propose a deep learning algorithm for EAP estimation, which is
named learning-based ensemble average propagator estimation (LEAPE). The EAP is
commonly represented by a basis and its associated coefficients, and here we
choose the SHORE basis and design a deep network to estimate the coefficients.
The network comprises two cascaded components. The first component is a
multiple layer perceptron (MLP) that simultaneously predicts the unknown
coefficients. However, typical training loss functions, such as mean squared
errors, may not properly represent the geometry of the possibly non-Euclidean
space of the coefficients, which in particular causes problems for the
extraction of directional information from the EAP. Therefore, to regularize
the training, in the second component we compute an auxiliary output of
approximated fiber orientation (FO) errors with the aid of a second MLP that is
trained separately. We performed experiments using dMRI data that resemble
clinically achievable -space sampling, and observed promising results
compared with the conventional EAP estimation method.Comment: Accepted by MICCAI 201
Broad-band spectrophotometry of the hot Jupiter HAT-P-12b from the near-UV to the near-IR
The detection of trends or gradients in the transmission spectrum of
extrasolar planets is possible with observations at very low spectral
resolution. Transit measurements of sufficient accuracy using selected
broad-band filters allow for an initial characterization of the atmosphere of
the planet. We obtained time series photometry of 20 transit events and
analyzed them homogeneously, along with eight light curves obtained from the
literature. In total, the light curves span a range from 0.35 to 1.25 microns.
During two observing seasons over four months each, we monitored the host star
to constrain the potential influence of starspots on the derived transit
parameters. We rule out the presence of a Rayleigh slope extending over the
entire optical wavelength range, a flat spectrum is favored for HAT-P-12b with
respect to a cloud-free atmosphere model spectrum. A potential cause of such
gray absorption is the presence of a cloud layer at the probed latitudes.
Furthermore, in this work we refine the transit parameters, the ephemeris and
perform a TTV analysis in which we found no indication for an unseen companion.
The host star showed a mild non-periodic variability of up to 1%. However, no
stellar rotation period could be detected to high confidence.Comment: 13 pages, 6 figures, Accepted for publication in A&
Comprehensive maximum likelihood estimation of diffusion compartment models towards reliable mapping of brain microstructure
open4siDiffusion MRI is a key in-vivo non invasive imaging capability that can probe the microstructure of the brain. However,its limited resolution requires complex voxelwise generative models of the diffusion. Diffusion Compartment (DC) models divide the voxel into smaller compartments in which diffusion is homogeneous. We present a comprehensive framework for maximum likelihood estimation (MLE) of such models that jointly features ML estimators of (i) the baseline MR signal,(ii) the noise variance,(iii) compartment proportions,and (iv) diffusion-related parameters. ML estimators are key to providing reliable mapping of brain microstructure as they are asymptotically unbiased and of minimal variance. We compare our algorithm (which efficiently exploits analytical properties of MLE) to alternative implementations and a state-of-theart strategy. Simulation results show that our approach offers the best reduction in computational burden while guaranteeing convergence of numerical estimators to the MLE. In-vivo results also reveal remarkably reliable microstructure mapping in areas as complex as the centrum semiovale. Our ML framework accommodates any DC model and is available freely for multi-tensor models as part of the ANIMA software (https://github.com/Inria-Visages/Anima-Public/wiki).Stamm, Aymeric; Commowick, Olivier; Warfield, Simon K.; Vantini, SimoneStamm, Aymeric; Commowick, Olivier; Warfield, Simon K.; Vantini, Simon
One-loop self-energy correction to the 1s and 2s hyperfine splitting in H-like systems
The one-loop self-energy correction to the hyperfine splitting of the 1s and
2s levels in H-like low-Z atoms is evaluated to all orders in Z\alpha. The
results are compared to perturbative calculations. The residual higher-order
contribution is evaluated. Implications to the specific difference of the
hyperfine structure intervals 8\Delta \nu_2 - \Delta \nu_1 in He^+ are
investigated.Comment: 17 pages, RevTeX, 3 figure
Persistent high burden and mortality associated with advanced HIV disease in rural Tanzania despite uptake of World Health Organization "test and treat" guidelines
BACKGROUND: Information about burden, characteristics, predictors, and outcomes of advanced human immunodeficiency virus disease (AHD) is scarce in rural settings of sub-Saharan Africa. Human immunodeficiency virus (HIV) infections and associated deaths remain high despite specific guidelines issued by the World Health Organization (WHO). METHODS: Burden of AHD and 6-month death/loss to follow-up (LTFU) were described among 2498 antiretroviral therapy (ART)-naive nonpregnant people with HIV (PWH) aged >15 years enrolled in the Kilombero Ulanga Antiretroviral Cohort in rural Tanzania between 2013 and 2019. Baseline characteristics associated with AHD and predictors of death/LTFU among those with AHD were analyzed using multivariate logistic and Cox regression, respectively. RESULTS: Of the PWH, 62.2% had AHD at diagnosis (66.8% before vs 55.7% after national uptake of WHO "test and treat" guidelines in 2016). At baseline, older age, male sex, lower body mass index, elevated aminotransferase aspartate levels, severe anemia, tachycardia, decreased glomerular filtration rate, clinical complaints, impaired functional status, and enrollment into care before 2018 were independently associated with AHD. Among people with AHD, incidence of mortality, and LTFU were 16 and 34 per 100 person-years, respectively. WHO clinical stage 3 or 4, CD4 counts <100 cells/microL, severe anemia, tachypnea, and liver disease were associated with death/LTFU. CONCLUSIONS: More than 50% of PWH enrolled in our cohort after test and treat implementation still had AHD at diagnosis. Increasing HIV testing and uptake and implementation of the WHO-specific guidelines on AHD for prevention, diagnosis, treatment of opportunistic infections, and reducing the risks of LTFU are urgently needed to reduce morbidity and mortality
Proton Zemach radius from measurements of the hyperfine splitting of hydrogen and muonic hydrogen
While measurements of the hyperfine structure of hydrogen-like atoms are
traditionally regarded as test of bound-state QED, we assume that theoretical
QED predictions are accurate and discuss the information about the
electromagnetic structure of protons that could be extracted from the
experimental values of the ground state hyperfine splitting in hydrogen and
muonic hydrogen. Using recent theoretical results on the proton polarizability
effects and the experimental hydrogen hyperfine splitting we obtain for the
Zemach radius of the proton the value 1.040(16) fm. We compare it to the
various theoretical estimates the uncertainty of which is shown to be larger
that 0.016 fm. This point of view gives quite convincing arguments in support
of projects to measure the hyperfine splitting of muonic hydrogen.Comment: Submitted to Phys. Rev.
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