513 research outputs found
Neutrino Spectral Split in the Exact Many Body Formalism
We consider the many-body system of neutrinos interacting with each other
through neutral current weak force. Emerging many-body effects in such a system
could play important roles in some astrophysical sites such as the core
collapse supernovae. In the literature this many-body system is usually treated
within the mean field approximation which is an effective one-body description
based on omitting entangled neutrino states. In this paper, we consider the
original many-body system in an effective two flavor mixing scenario under the
single angle approximation and present a solution without using the mean field
approximation. Our solution is formulated around a special class of many-body
eigenstates which do not undergo any level crossings as the neutrino self
interaction rate decreases while the neutrinos radiate from the supernova. In
particular, an initial state which consists of electron neutrinos and
antineutrinos of an orthogonal flavor can be entirely decomposed in terms of
those eigenstates. Assuming that the conditions are perfectly adiabatic so that
the evolution of these eigenstates follow their variation with the interaction
rate, we show that this initial state develops a spectral split at exactly the
same energy predicted by the mean field formulation.Comment: Published version. 30 pages, 11 figure
De novo Transcriptome Assemblies of Rana (Lithobates) catesbeiana and Xenopus laevis Tadpole Livers for Comparative Genomics without Reference Genomes
In this work we studied the liver transcriptomes of two frog species, the American bullfrog (Rana (Lithobates) catesbeiana) and the African clawed frog (Xenopus laevis). We used high throughput RNA sequencing (RNA-seq) data to assemble and annotate these transcriptomes, and compared how their baseline expression profiles change when tadpoles of the two species are exposed to thyroid hormone. We generated more than 1.5 billion RNA-seq reads in total for the two species under two conditions as treatment/control pairs. We de novo assembled these reads using Trans-ABySS to reconstruct reference transcriptomes, obtaining over 350,000 and 130,000 putative transcripts for R. catesbeiana and X. laevis, respectively. Using available genomics resources for X. laevis, we annotated over 97% of our X. laevis transcriptome contigs, demonstrating the utility and efficacy of our methodology. Leveraging this validated analysis pipeline, we also annotated the assembled R. catesbeiana transcriptome. We used the expression profiles of the annotated genes of the two species to examine the similarities and differences between the tadpole liver transcriptomes. We also compared the gene ontology terms of expressed genes to measure how the animals react to a challenge by thyroid hormone. Our study reports three main conclusions. First, de novo assembly of RNA-seq data is a powerful method for annotating and establishing transcriptomes of non-model organisms. Second, the liver transcriptomes of the two frog species, R. catesbeiana and X. laevis, show many common features, and the distribution of their gene ontology profiles are statistically indistinguishable. Third, although they broadly respond the same way to the presence of thyroid hormone in their environment, their receptor/signal transduction pathways display marked differences
Magnetodielectric coupling and phonon properties of compressively strained EuTiO3 thin films deposited on LSAT
Compressively strained epitaxial (001) EuTiO3 thin films of tetragonal
symmetry have been deposited on (001) (LaAlO3)_0.29-(SrAl_{1/2}Ta_{1/2}O3)_0.71
(LSAT) substrates by reactive molecular-beam epitaxy. Enhancement of the Neel
temperature by 1 K with 0.9% compressive strain was revealed. The polar phonons
ofthe films have been investigated as a function of temperature and magnetic
field by means of infrared reflectance spectroscopy. All three infrared active
phonons show strongly stiffened frequencies compared to bulk EuTiO3 in
accordance with first principles calculations. The phonon frequencies exhibit
gradual softening on cooling leading to an increase in static permittivity. A
new polar phonon with frequency near the TO1 soft mode was detected below 150
K. The new mode coupled with the TO1 mode was assigned as the optical phonon
from the Brillouin zone edge, which is activated in infrared spectra due to an
antiferrodistortive phase transition and due to simultaneous presence of polar
and/or magnetic nanoclusters. In the antiferromagnetic phase we have observed a
remarkable softening of the lowest-frequency polar phonon under an applied
magnetic field, which qualitatively agrees with first principles calculations.
This demonstrates the strong spin-phonon coupling in EuTiO3, which is
responsible for the pronounced dependence of its static permittivity on
magnetic field in the antiferromagnetic phase.Comment: Submitted to Phys. Rev.
Coherent Pair Production by Photons in the 20-170 GeV Energy Range Incident on Crystals and Birefringence
The cross section for coherent pair production by linearly polarised photons
in the 20-170 GeV energy range was measured for photon aligned incidence on
ultra-high quality diamond and germanium crystals. The theoretical description
of coherent bremsstrahlung and coherent pair production phenomena is an area of
active theoretical debate and development. However, under our experimental
conditions, the theory predicted the combined cross section and polarisation
experimental observables very well indeed. In macroscopic terms, our experiment
measured a birefringence effect in pair production in a crystal. This study of
this effect also constituted a measurement of the energy dependent linear
polarisation of photons produced by coherent bremsstrahlung in aligned
crystals. New technologies for manipulating high energy photon beams can be
realised based on an improved understanding of QED phenomena at these energies.
In particular, this experiment demonstrates an efficient new polarimetry
technique. The pair production measurements were done using two independent
methods simultaneously. The more complex method using a magnet spectrometer
showed that the simpler method using a multiplicity detector was also viable.Comment: 10 pages, 13 figures, 1 table, REVTeX4 two column, Version for
publicatio
Linear to Circular Polarisation Conversion using Birefringent Properties of Aligned Crystals for Multi-GeV Photons
We present the first experimental results on the use of a thick aligned Si
crystal acting as a quarter wave plate to induce a degree of circular
polarisation in a high energy linearly polarised photon beam. The linearly
polarised photon beam is produced from coherent bremsstrahlung radiation by 178
GeV unpolarised electrons incident on an aligned Si crystal, acting as a
radiator. The linear polarisation of the photon beam is characterised by
measuring the asymmetry in electron-positron pair production in a Ge crystal,
for different crystal orientations. The Ge crystal therefore acts as an
analyser. The birefringence phenomenon, which converts the linear polarisation
to circular polarisation, is observed by letting the linearly polarised photons
beam pass through a thick Si quarter wave plate crystal, and then measuring the
asymmetry in electron-positron pair production again for a selection of
relative angles between the crystallographic planes of the radiator, analyser
and quarter wave plate. The systematics of the difference between the measured
asymmetries with and without the quarter wave plate are predicted by theory to
reveal an evolution in the Stokes parameters from which the appearance of a
circularly polarised component in the photon beam can be demonstrated. The
measured magnitude of the circularly polarised component was consistent with
the theoretical predictions, and therefore is in indication of the existence of
the birefringence effect.Comment: 12 pages, 12 figures, 1 table, REVTeX4 two column, Version for
publicatio
Assessing the capability of three different altimetry satellite missions to observe the Northern Current by using a high-resolution model
Over the last 3 decades, satellite altimetry has observed sea surface
height variations, providing a regular monitoring of the surface ocean
circulation. Altimetry measurements have an intrinsic signal-to-noise ratio
that limits the spatial scales of the currents that can be captured. However,
the recent progress made on both altimetry sensors and data processing allows
us to observe smaller geophysical signals, offering new perspectives in
coastal areas where these structures are important.
In this methodological study, we assess the ability of three altimeter
missions with three different technologies to capture the Northern Current
(northwestern Mediterranean Sea) and its variability, namely Jason-2 (Ku-band low-resolution-mode altimeter, launched in 2008), SARAL/AltiKa (Ka-band low-resolution-mode altimeter, launched in 2013) and Sentinel-3A (synthetic
aperture radar altimeter, launched in 2016). Therefore, we use a
high-resolution regional model as a reference.
We focus along the French coast of Provence, where we first show that the
model is very close to the observations of high-frequency radars and gliders
in terms of surface current estimates.
In the model, the Northern Current is observed 15â20âkm from the coast on
average, with a mean core velocity of 0.39âmâsâ1. Its signature in terms of sea
level consists of a drop whose mean value at 6.14ââE is 6.9âcm,
extending over 20âkm. These variations show a clear seasonal pattern, but
high-frequency signals are also present most of the time. In comparison, in
1âHz altimetry data, the mean sea level drop associated with the Northern
Current is overestimated by 3.0âcm for Jason-2, but this overestimation is significantly less with
SARAL/AltiKa and Sentinel-3A (0.3 and 1.4âcm respectively). In terms of
corresponding sea level variability, Jason-2 and SARAL altimetry estimates
are larger than the model reference (+1.3 and +1âcm respectively),
whereas Sentinel-3A shows closer values (â0.4âcm). When we derive
geostrophic surface currents from the satellite sea level variations
without any data filtering, in comparison to the model, the standard
deviations of the velocity values are also very different from one mission to the
other (3.7 times too large for Jason-2 but 2.4 and 2.9 times too large for
SARAL and Sentinel-3A respectively). When low-pass filtering altimetry sea
level data with different cutoff wavelengths, the best agreement between the
model and the altimetry distributions of velocity values are obtained with a
60, 30 and 40â50âkm cutoff wavelength for Jason-2, SARAL and
Sentinel-3A data respectively. This study shows that using a high-resolution model as a reference for altimetry data allows us not only to
illustrate how the advances in the performances of altimeters and in the
data processing improve the observation of coastal currents but also to
quantify the corresponding gain.</p
Results on the Coherent Interaction of High Energy Electrons and Photons in Oriented Single Crystals
The CERN-NA-59 experiment examined a wide range of electromagnetic processes
for multi-GeV electrons and photons interacting with oriented single crystals.
The various types of crystals and their orientations were used for producing
photon beams and for converting and measuring their polarisation.
The radiation emitted by 178 GeV unpolarised electrons incident on a 1.5 cm
thick Si crystal oriented in the Coherent Bremsstrahlung (CB) and the
String-of-Strings (SOS) modes was used to obtain multi-GeV linearly polarised
photon beams.
A new crystal polarimetry technique was established for measuring the linear
polarisation of the photon beam. The polarimeter is based on the dependence of
the Coherent Pair Production (CPP) cross section in oriented single crystals on
the direction of the photon polarisation with respect to the crystal plane.
Both a 1 mm thick single crystal of Germanium and a 4 mm thick multi-tile set
of synthetic Diamond crystals were used as analyzers of the linear
polarisation.
A birefringence phenomenon, the conversion of the linear polarisation of the
photon beam into circular polarisation, was observed. This was achieved by
letting the linearly polarised photon beam pass through a 10 cm thick Silicon
single crystal that acted as a "quarter wave plate" (QWP) as suggested by N.
Cabibbo et al.Comment: Presented at International workshop "Relativistic Channeling and
Related Coherent Phenomena", Frascati (Rome) 23-26 March 200
Coherent bremsstrahlung, boherent pair production, birefringence and polarimetry in the 20-170 GeV energy range using aligned crystals
The processes of coherent bremsstrahlung (CB) and coherent pair production
(CPP) based on aligned crystal targets have been studied in the energy range
20-170 GeV. The experimental arrangement allowed for measurements of single
photon properties of these phenomena including their polarization dependences.
This is significant as the theoretical description of CB and CPP is an area of
active theoretical debate and development. With the theoretical approach used
in this paper both the measured cross sections and polarization observables are
predicted very well. This indicates a proper understanding of CB and CPP up to
energies of 170 GeV. Birefringence in CPP on aligned crystals is applied to
determine the polarization parameters in our measurements. New technologies for
high energy photon beam optics including phase plates and polarimeters for
linear and circular polarization are demonstrated in this experiment. Coherent
bremsstrahlung for the strings-on-strings (SOS) orientation yields a larger
enhancement for hard photons than CB for the channeling orientations of the
crystal. Our measurements and our calculations indicate low photon
polarizations for the high energy SOS photons.Comment: 23 pages, 27 figures, 2 tables, REVTeX4 two column
What Is the Important Point Related to Follow-Up Sonographic Evaluation for the Developmental Dysplasia of the Hip?
Developmental dysplasia of the hip (DDH) is an important cause of childhood disability. Subluxation or dislocation can be diagnosed through pediatric physical examination; nevertheless, the ultrasonographic examination is necessary in diagnosing certain borderline cases. It has been evaluated routine sonographic examination of 2,444 hips of 1,222 babies to determine differences in both, developmental dysplasia and types of hips, and evaluated their development on the 3-month follow-up. Evaluating the pathologic alpha angles under 59, there was no statistically significant differences between girls and boys in both right (55.57 +/- 3.73) (56.20 +/- 4.01), (p = 0.480), and left (55.79 +/- 3.96) (57.00 +/- 3.84), (p = 0.160) hips on the 45th day of life. Routine sonographic examinations on the 45th day of life revealed that 51 of (66.2%) 77 type 2a right hips were girls and 26 (33.8%) were boys. The number of the right hips that develop into type 1 was 38 (74.5%) for girls and 26 (100%) for boys on the 90th day of life (p = 0.005). A total of 87 type 2a left hips included 64 girls (73.6%) and 23 boys (26.4%). In the 90th day control, 49 right hip of girls (76.6%) and 21 right hip of boys (91.3%) developed into type 1 (p = 0.126). In the assessment of both left and right hips, girls showed a significantly higher frequency in latency and boys showed significantly higher development in the control sonography. A total of 31 girls (2.5%) and 11 boys (0.9%) accounted for a total of 42 (3.4%) cases who showed bilateral type 2a hips in 1,222 infants. On the 90th day control, 26 girls (83.9%) and all 11 boys (100%) developed into type 1 (p = 0.156). The study emphasizes the importance of the sonographic examination on the 90th day of life. Results of the investigation include the data of sonographic screening of DDH on the 45th day, and also stress the importance of the 90th-day control sonography after a close follow-up with physical examination between 45th and 90th days of life
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