8,992 research outputs found
Inhibited spontaneous emission of quantum dots observed in a 3D photonic band gap
We present time-resolved emission experiments of semiconductor quantum dots
in silicon 3D inverse-woodpile photonic band gap crystals. A systematic study
is made of crystals with a range of pore radii to tune the band gap relative to
the emission frequency. The decay rates averaged over all dipole orientations
are inhibited by a factor of 10 in the photonic band gap and enhanced up to 2?
outside the gap, in agreement with theory. We discuss the effects of spatial
inhomogeneity, nonradiative decay, and transition dipole orientations on the
observed inhibition in the band gap.Comment: 5 figures, update author lis
Severe mesenteric ischemia with multiple organ failure in a patient previously treated with a humanized monoclonal antibody against programmed death receptor-1 (pembrolizumab), a case of pembrolizumab associated catastrophic antiphospholipid syndrome?
Immune checkpoint inhibitors are used in the treatment of different types of tumors including melanoma and non-small cell lung carcinoma. The use of these inhibitors is associated with a broad spectrum of immune-related adverse effects. Here we report a case of a patient admitted to the intensive care unit with multiple organ failure due to catastrophic antiphospholipid syndrome following treatment with pembrolizumab, an immune checkpoint inhibitor, because of metastatic melanoma. The presented patient had multiple organ failure of lung, gastro-intestinal, renal, and the liver. Vascular thrombosis was confirmed by both imaging (pulmonary embolism on computed tomography-thorax) and histopathological examination of the intestines. In combination with the presence of IgA anti-cardiolipin antibodies and initially IgM anti-cardiolipin antibodies, catastrophic antiphospholipid syndrome was suspected. Despite treatment with plasmapheresis and corticosteroids, the patient died due to multiple organ failure. Catastrophic antiphospholipid syndrome is difficult to recognize and has high mortality rates despite supportive treatment. In this case report, discussion is provided regarding the possible immunological mechanism behind catastrophic antiphospholipid syndrome during or after treatment with immune checkpoint inhibitors. It is important to realize that in modern intensive care unit, more patients with immune-related adverse effects of the treatment with immune checkpoint inhibitors will be admitted, because of an increase in the number of patients treated with these checkpoint inhibitors. When these patients are admitted on the intensive care unit, multi-disciplinary consultation is important because of the difficulty of early recognition and optimal treatment of these possible lethal side effects
Childhood BMI in relation to microbiota in infancy and lifetime antibiotic use
Background: Children with high body mass index (BMI) at preschool age are at risk of developing obesity. Early identification of factors that increase the risk of excessive weight gain could help direct preventive actions. The intestinal microbiota and antibiotic use have been identified as potential modulators of early metabolic programming and weight development. To test if the early microbiota composition is associated with later BMI, and if antibiotic use modifies this association, we analysed the faecal microbiota composition at 3 months and the BMI at 5-6 years in two cohorts of healthy children born vaginally at term in the Netherlands (N = 87) and Finland (N = 75). We obtained lifetime antibiotic use records and measured weight and height of all children. Results: The relative abundance of streptococci was positively and the relative abundance of bifidobacteria negatively associated with the BMI outcome. The association was especially strong among children with a history of antibiotic use. Bacteroides relative abundance was associated with BMI only in the children with minimal lifetime antibiotic exposure. Conclusions: The intestinal microbiota of infants are predictive of later BMI and may serve as an early indicator of obesity risk. Bifidobacteria and streptococci, which are indicators of microbiota maturation in infants, are likely candidates for metabolic programming of infants, and their influence on BMI appears to depend on later a\ntibiotic use.Peer reviewe
Comparison of 32-site exact diagonalization results and ARPES spectral functions for the AFM insulator
We explore the success of various versions of the one-band t-J model in
explaining the full spectral functions found in angle-resolved photoemission
spectra for the prototypical, quasi two-dimensional, tetragonal,
antiferromagnetic insulator . After presenting arguments
justifying our extraction of from the experimental data, we rely
on exact-diagonalization results from studies of a square 32-site lattice, the
largest cluster for which such information is presently available, to perform
this comparison. Our work leads us to believe that (i) a one-band model that
includes hopping out to third-nearest neighbours, as well three-site,
spin-dependent hopping, can indeed explain not only the dispersion relation,
but also the quasiparticle lifetimes -- only in the neighbourhood of do we find disagreement; (ii) an energy-dependent broadening
function, , is important in accounting for the
incoherent contributions to the spectral functions.Comment: 8 pages, Revtex
Relationship between quantum decoherence times and solvation dynamics in condensed phase chemical systems
A relationship between the time scales of quantum coherence loss and
short-time solvent response for a solute/bath system is derived for a Gaussian
wave packet approximation for the bath. Decoherence and solvent response times
are shown to be directly proportional to each other, with the proportionality
coefficient given by the ratio of the thermal energy fluctuations to the
fluctuations in the system-bath coupling. The relationship allows the
prediction of decoherence times for condensed phase chemical systems from well
developed experimental methods.Comment: 10 pages, no figures, late
HD 51844: An Am delta Scuti in a binary showing periastron brightening
Pulsating stars in binary systems are ideal laboratories to test stellar
evolution and pulsation theory, since a direct, model-independent determination
of component masses is possible. The high-precision CoRoT photometry allows a
detailed view of the frequency content of pulsating stars, enabling detection
of patterns in their distribution. The object HD 51844 is such a case showing
periastron brightening instead of eclipses. We present a comprehensive study of
the HD 51844 system, where we derive physical parameters of both components,
the pulsation content and frequency patterns. Additionally, we obtain the
orbital elements, including masses, and the chemical composition of the stars.
Time series analysis using standard tools was mployed to extract the pulsation
frequencies. Photospheric abundances of 21 chemical elements were derived by
means of spectrum synthesis. We derived orbital elements both by fitting the
observed radial velocities and the light curves, and we did asteroseismic
modelling as well. We found that HD 51844 is a double lined spectroscopic
binary. The determined abundances are consistent with delta Delphini
classification. We determined the orbital period (33.498 +- 0.002 d), the
eccentricity (0.484 +- 0.020), the mass ratio (0.988 +- 0.02), and the masses
to 2.0 +- 0.2 M_sun for both components. Only one component showed pulsation.
Two p modes (f_22 and f_36) and one g mode (f_orb) may be tidally excited.
Among the 115 frequencies, we detected triplets due to the frequency
modulation, frequency differences connected to the orbital period, and
unexpected resonances (3:2, 3:5, and 3:4), which is a new discovery for a delta
Scuti star.Comment: 15 pages, 11 figures, accepted for publication in A&
Two-hole problem in the t-J model: A canonical transformation approach
The t-J model in the spinless-fermion representation is studied. An effective
Hamiltonian for the quasiparticles is derived using canonical transformation
approach. It is shown that the rather simple form of the transformation
generator allows to take into account effect of hole interaction with the
short-range spin waves and to describe the single-hole groundstate. Obtained
results are very close to ones of the self-consistent Born approximation.
Further accounting for the long-range spin-wave interaction is possible on the
perturbative basis. Both spin-wave exchange and an effective interaction due to
minimization of the number of broken antiferromagnetic bonds are included in
the effective quasiparticle interaction. Two-hole bound state problem is solved
using Bethe-Salpeter equation. The only d-wave bound state is found to exist in
the region of 1< (t/J) <5. Combined effect of the pairing interactions of both
types is important to its formation. Discussion of the possible relation of the
obtained results to the problem of superconductivity in real systems is
presented.Comment: 19 pages, RevTeX, 12 postscript figure
First LOFAR observations at very low frequencies of cluster-scale non-thermal emission: the case of Abell 2256
Abell 2256 is one of the best known examples of a galaxy cluster hosting
large-scale diffuse radio emission that is unrelated to individual galaxies. It
contains both a giant radio halo and a relic, as well as a number of head-tail
sources and smaller diffuse steep-spectrum radio sources. The origin of radio
halos and relics is still being debated, but over the last years it has become
clear that the presence of these radio sources is closely related to galaxy
cluster merger events. Here we present the results from the first LOFAR Low
band antenna (LBA) observations of Abell 2256 between 18 and 67 MHz. To our
knowledge, the image presented in this paper at 63 MHz is the deepest ever
obtained at frequencies below 100 MHz in general. Both the radio halo and the
giant relic are detected in the image at 63 MHz, and the diffuse radio emission
remains visible at frequencies as low as 20 MHz. The observations confirm the
presence of a previously claimed ultra-steep spectrum source to the west of the
cluster center with a spectral index of -2.3 \pm 0.4 between 63 and 153 MHz.
The steep spectrum suggests that this source is an old part of a head-tail
radio source in the cluster. For the radio relic we find an integrated spectral
index of -0.81 \pm 0.03, after removing the flux contribution from the other
sources. This is relatively flat which could indicate that the efficiency of
particle acceleration at the shock substantially changed in the last \sim 0.1
Gyr due to an increase of the shock Mach number. In an alternative scenario,
particles are re-accelerated by some mechanism in the downstream region of the
shock, resulting in the relatively flat integrated radio spectrum. In the radio
halo region we find indications of low-frequency spectral steepening which may
suggest that relativistic particles are accelerated in a rather inhomogeneous
turbulent region.Comment: 13 pages, 13 figures, accepted for publication in A\&A on April 12,
201
Time dependence of the electron and positron components of the cosmic radiation measured by the PAMELA experiment between July 2006 and December 2015
Cosmic-ray electrons and positrons are a unique probe of the propagation of
cosmic rays as well as of the nature and distribution of particle sources in
our Galaxy. Recent measurements of these particles are challenging our basic
understanding of the mechanisms of production, acceleration and propagation of
cosmic rays. Particularly striking are the differences between the low energy
results collected by the space-borne PAMELA and AMS-02 experiments and older
measurements pointing to sign-charge dependence of the solar modulation of
cosmic-ray spectra. The PAMELA experiment has been measuring the time variation
of the positron and electron intensity at Earth from July 2006 to December 2015
covering the period for the minimum of solar cycle 23 (2006-2009) till the
middle of the maximum of solar cycle 24, through the polarity reversal of the
heliospheric magnetic field which took place between 2013 and 2014. The
positron to electron ratio measured in this time period clearly shows a
sign-charge dependence of the solar modulation introduced by particle drifts.
These results provide the first clear and continuous observation of how drift
effects on solar modulation have unfolded with time from solar minimum to solar
maximum and their dependence on the particle rigidity and the cyclic polarity
of the solar magnetic field.Comment: 11 pages, 2 figure
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