1,504 research outputs found
On the use of machine learning algorithms in the measurement of stellar magnetic fields
Regression methods based in Machine Learning Algorithms (MLA) have become an
important tool for data analysis in many different disciplines.
In this work, we use MLA in an astrophysical context; our goal is to measure
the mean longitudinal magnetic field in stars (H_ eff) from polarized spectra
of high resolution, through the inversion of the so-called multi-line profiles.
Using synthetic data, we tested the performance of our technique considering
different noise levels: In an ideal scenario of noise-free multi-line profiles,
the inversion results are excellent; however, the accuracy of the inversions
diminish considerably when noise is taken into account. In consequence, we
propose a data pre-process in order to reduce the noise impact, which consists
in a denoising profile process combined with an iterative inversion
methodology.
Applying this data pre-process, we have found a considerable improvement of
the inversions results, allowing to estimate the errors associated to the
measurements of stellar magnetic fields at different noise levels.
We have successfully applied our data analysis technique to two different
stars, attaining by first time the measurement of H_eff from multi-line
profiles beyond the condition of line autosimilarity assumed by other
techniques.Comment: Accepted for publication in A&
A search for X-ray pulsations from the galactic center
Data from the SAS-3 satellite were used in a search for X-ray pulsations from the direction of the galactic center. No periodic X-ray behavior was detected in the frequency interval 0.6 Hz to 0.0006 Hz and energy range 2.5 - 35 keV. For periods less than 60 sec, the upper limit to the amplitude of any pulsation in the 2.5 - 10 keV band is approximately .0017 cts/sq cm/s. This corresponds to a pulsed fraction of approximately 1.3 percent of the total GCX flux. Somewhat higher limits apply for longer periods and for energies greater than 10 keV
On 2-group global symmetries and their anomalies
In general quantum field theories (QFTs), ordinary (0-form) global symmetries and 1-form symmetries can combine into 2-group global symmetries. We describe this phenomenon in detail using the language of symmetry defects. We exhibit a simple procedure to determine the (possible) 2-group global symmetry of a given QFT, and provide a classification of the related \u2019t Hooft anomalies (for symmetries not acting on spacetime). We also describe how QFTs can be coupled to extrinsic backgrounds for symmetry groups that differ from the intrinsic symmetry acting faithfully on the theory. Finally, we provide a variety of examples, ranging from TQFTs (gapped systems) to gapless QFTs. Along the way, we stress that the \u201cobstruction to symmetry fractionalization\u201d discussed in some condensed matter literature is really an instance of 2-group global symmetry
Nouvelle découverte d'empreintes laissées par des dinosaures dans la formation des couches rouges (bassin de Cuzco-Sicuani, Sud du Pérou) : conséquences stratigraphiques et tectoniques
La découverte d'empreintes laissées par le dinosaures vers le sommet de la formation des Couches Rouges permet de préciser la stratigraphie du Sud du Pérou. La durée de la sédimentation continentale du bassin de Cuzco-Sicuani n'excéderait pas 20 Ma (santonien - paléocène) et non plus 45 Ma, comme cela était jusqu'à présent admis. Le bassin d'avant-pays de Cuzco-Sicuani est caractérisé par une déformation synsédimentaire essentiellement compressive pendant toute la durée de la sédimentation des "Couches Rouges". En conséquence, une durée équivalente à celle de cette sédimentation peut être retenue pour ces événements tectoniques qui marquent ici le début de la surrection de la chaîne andine. La phase péruvienne, traditionnellement placée vers 85 Ma, représenterait ainsi le début de ces événements tectoniques. (Résumé d'auteur
The discovery of 2.78 hour periodic modulation of the X-ray flux from globular cluster source Bo 158 in M31
We report the discovery of periodic intensity dips in the X-ray source XMMU
J004314.1+410724, in the globular cluster Bo158 in M31. The X-ray flux was
modulated by ~83% at a period of 2.78 hr (10017 s) in an XMM-Newton observation
taken 2002 Jan 6-7. The X-ray intensity dips show no energy dependence. We
detected weaker dips with the same period in observations taken 2000 June 25
(XMM-Newton) and 1991 June 26 (ROSAT/PSPC). The amplitude of the modulation has
been found to be anticorrelated with source X-ray flux: it becomes lower when
the source intensity rises. The energy spectrum of Bo158 was stable from
observation to observation, with a characteristic cutoff at ~4-6 keV. The
photo-electric absorption was consistent with the Galactic foreground value. No
significant spectral changes were seen in the course of the dips. If the 2.78
hr cycle is the binary period of Bo158 the system is highly compact, with a
binary separation of ~10e11 cm. The association of the source with a globular
cluster, together with spectral parameters consistent with Galactic neutron
star sources, suggests that X-rays are emitted by an accreting neutron star.
The properties of Bo 158 are somewhat reminiscent of the Galactic X-ray sources
exhibiting a dip-like modulations. We discuss two possible mechanisms
explaining the energy-independent modulation observed in Bo 158: i) the
obscuration of the central source by highly ionized material that scatters
X-rays out of the line of sight; ii) partial covering of an extended source by
an opaque absorber which occults varying fractions of the source.Comment: 10 pages, 4 figures, ApJ, submitted, uses emulateapj styl
Factors Affecting Pregnancy Rate to Fixed-Time Artificial Insemination in Pen-Raised White-tailed Deer
White-tailed deer farming has experienced significant growth in recent years in the U.S. with the majority of the operations located in Texas. Producers now utilize advanced breeding technologies in deer similar to cattle and other livestock to enhance the genetic merit of their herd. The goal is to produce the best quality bucks to sell as stocker bucks for high priced hunts or breeding. Pen-raised white-tailed does (n=177; 1 to 6 yr; 28.5 to 72.5 kg) from an established breeding program (3-S Whitetails, Bedias, TX) were utilized to evaluate factors affecting pregnancy rate to fixed-time AI (FTAI) across four breeding seasons combined (2013-2016). Does were synchronized using a 14-d controlled internal drug release (CIDR; EAZI-Breed CIDR, Zoetis, Inc., Kalamazoo, MI) device as a progesterone source with an injection (i.m.) of eCG (200 IU) at CIDR removal and inseminated laparoscopically 60 h later. At the time of FTAI, BW, BCS, and disposition score (DISP) were recorded and a blood sample was collected via jugular venipuncture to determine serum cortisol concentration. All does were subsequently placed in a pen with a buck for natural service (NAT) to maximize overall pregnancy rate of the herd. DNA testing of each fawn determined parentage and birth dates based on records from the producer were used to determine method of conception (FTAI or NAT). Serum cortisol concentrations were determined via ELISA. Data were analyzed using the GLM, MIXED, LOGISTIC and CORR procedures of SAS. There were no significant differences (P>0.05) found in BW, age, BCS, DISP, or serum cortisol concentration between does that conceived to FTAI and those that did not. Pregnancy rate to FTAI was 61% and overall pregnancy rate (FTAI and NAT) was 86%. Mean litter size was greater (P<0.02) for FTAI (1.79) than NAT (1.48). Does that did not conceive to FTAI had lower (P<0.05) BW, BCS and were younger (P<0.05) than does that conceived to FTAI. In summary, additional research is needed to determine if any of the physiological factors measured in this study have a significant influence on conception rate to FTAI
Bright X-ray Transients in M31: 2004 July XMM-Newton Observations
We present the results of X-ray observations of four bright transients
sources detected in the July 2004 XMM-Newton observations of the central bulge
of M31. Two X-ray sources, XMMU J004315.5+412440 and XMMU J004144.7+411110,
were discovered for the first time. Two other sources, CXOM31 J004309.9+412332
and CXOM31 J004241.8+411635, were previously detected by Chandra. The
properties of the sources suggest their identification with accreting binary
systems in M31. The X-ray spectra and variability of two sources, XMMU
J004144.7+411110 and CXOM31 J004241.8+411635, are similar to that of the
Galactic black hole transients, making them a good black hole candidates. The
X-ray source XMMU J004315.5+412440 demonstrates a dramatic decline of the X-ray
flux on a time scale of three days, and a remarkable flaring behavior on a
short time scales. The X-ray data on XMMU J004315.5+412440 and CXOM31
J004309.9+412332 suggest that they can be either black hole or neutron star
systems. Combining the results of 2000-2004 XMM observations of M31, we
estimate a total rate of the bright transient outbursts in the central region
of M31 to be 6-12 per year, in agreement with previous studies.Comment: 8 pages, 3 figures, uses emulateapj style. Submitted to Ap
Distinct spatial dependency of carbon distribution between soil pools in grassland SOIL
Grassland soils play a key role in climate change and food security, and carbon (C) and nitrogen
(N) mineralization is central to this. Although there are a number of mathematical models available
to estimate C and N mineralization, they do not encompass the variability of the process and there
is uncertainty in their predictions. The input parameters of the SOMA model (Soil Organic Matter
“A”) have been conceptualized and validated to predict mineralization in arable soils. The objective
of this research was to measure the spatial dependence of the input parameters in order to further ob
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tain spatial predictions of mineralisation in a grassland system. A nested design was applied using
sampling intervals of 30 m, 10 m, 1 m, and 0.12 m as sources of variation. From each sampling point a
soil sample was taken (0-23 cm) and physical sequential fractionation was applied to obtain the free
light fraction (FLF) and intra-aggregate light fraction (IALF). The C and N contents in the fractions
were measured by mass spectrometry, and the results analysed by residual maximum likelihood
(REML) to obtain components of variance at each stage, and then accumulated to plot the approach to
a variogram. Both fractions showed spatial dependence at the finest scales measured, and the general
pattern was different from that in an arable site. The recommended soil sampling interval where
C and N mineralization predictions would be spatially distributed according to the correlation of
input light fractions parameters of SOMA is 0.5m
Probing the Pulsar Wind Nebula of PSR B0355+54
We present XMM-Newton and Chandra X-ray observations of the middle-aged radio
pulsar PSR B0355+54. Our X-ray observations reveal emission not only from the
pulsar itself, but also from a compact diffuse component extending ~50'' in the
opposite direction to the pulsar's proper motion. There is also evidence for
the presence of fainter diffuse emission extending ~5' from the point source.
The compact diffuse feature is well-fitted with a power-law, the index of which
is consistent with the values found for other pulsar wind nebulae. The
morphology of the diffuse component is similar to the ram-pressure confined
pulsar wind nebulae detected for other sources. The X-ray emission from the
pulsar itself is described well by a thermal plus power-law fit, with the
thermal emission most likely originating in a hot polar cap.Comment: 9 pages (uses emulateapj.cls), 8 figures, 2 tables, accepted for
publication in Ap
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