12,427 research outputs found
Limits on Non-Linear Electrodynamics
In this paper we set a framework in which experiments whose goal is to test
QED predictions can be used in a more general way to test non-linear
electrodynamics (NLED) which contains low-energy QED as a special case. We
review some of these experiments and we establish limits on the different free
parameters by generalizing QED predictions in the framework of NLED. We finally
discuss the implications of these limits on bound systems and isolated charged
particles for which QED has been widely and successfully tested
Characterization of the Vacuum Birefringence Polarimeter at BMV: Dynamical Cavity Mirror Birefringence
We present the current status and outlook of the optical characterization of
the polarimeter at the Bir\'{e}fringence Magn\'etique du Vide (BMV) experiment.
BMV is a polarimetric search for the QED predicted anisotropy of vacuum in the
presence of external electromagnetic fields. The main challenge faced in this
fundamental test is the measurement of polarization ellipticity on the order of
induced in linearly polarized laser field per pass through a
magnetic field having an amplitude and length
. This challenge is addressed by
understanding the noise sources in precision cavity-enhanced polarimetry. In
this paper we discuss the first investigation of dynamical birefringence in the
signal-enhancing cavity as a result of cavity mirror motion.Comment: To appear in the 2019 CPEM special issue of IEEE Transactions on
Instrumentation and Measuremen
Noise characterization for resonantly-enhanced polarimetric vacuum magnetic-birefringence experiments
In this work we present data characterizing the sensitivity of the
Bir\'{e}fringence Magnetique du Vide (BMV) instrument. BMV is an experiment
attempting to measure vacuum magnetic birefringence (VMB) via the measurement
of an ellipticity induced in a linearly polarized laser field propagating
through a birefringent region of vacuum in the presence of an external magnetic
field. Correlated measurements of laser noise alongside the measurement in the
main detection channel allow us to separate measured sensing noise from the
inherent birefringence noise of the apparatus. To this end we model different
sources of sensing noise for cavity-enhanced polarimetry experiments, such as
BMV. Our goal is to determine the main sources of noise, clarifying the
limiting factors of such an apparatus. We find our noise models are compatible
with the measured sensitivity of BMV. In this context we compare the phase
sensitivity of separate-arm interferometers to that of a polarimetry apparatus
for the discussion of current and future VMB measurements
Vacuum magnetic linear birefringence using pulsed fields: the BMV experiment
We present the current status of the BMV experiment. Our apparatus is based
on an up-to-date resonant optical cavity coupled to a transverse magnetic
field. We detail our data acquisition and analysis procedure which takes into
account the symmetry properties of the raw data with respect to the orientation
of the magnetic field and the sign of the cavity birefringence. The measurement
result of the vacuum magnetic linear birefringence k_\mathrm{CM}8 \times 10^{-21}^{-2}3\sigma$ confidence level
Observation of the Inverse Cotton-Mouton Effect
We report the observation of the Inverse Cotton-Mouton Effect (ICME) i.e. a
magnetization induced in a medium by non resonant linearly polarized light
propagating in the presence of a transverse magnetic field. We present a
detailed study of the ICME in a TGG crystal showing the dependence of the
measured effect on the light intensity, the optical polarization, and on the
external magnetic field. We derive a relation between the Cotton-Mouton and
Inverse Cotton-Mouton effects that is roughly in agreement with existing
experimental data. Our results open the way to applications of the ICME in
optical devices
Ammonia observations in the LBV nebula G79.29+0.46. Discovery of a cold ring and some warm spots
The surroundings of Luminous Blue Variable (LBV) stars are excellent
laboratories to study the effects of their high UV radiation, powerful winds,
and strong ejection events onto the surrounding gas and dust. The LBV
G79.29+0.46 powered two concentric infrared rings which may interact with the
infrared dark cloud (IRDC) G79.3+0.3. The Effelsberg 100m telescope was used to
observe the NH_3 (1,1), (2,2) emission surrounding G79.29+0.46 and the IRDC. In
addition, we observed particular positions in the (3,3) transition toward the
strongest region of the IRDC. We report here the first coherent shell-like
structure of dense NH_3 gas associated with an evolved massive star. The shell,
two or three orders of magnitude more tenuous than the IRDC, is well traced in
both ammonia lines, and surrounds the ionized nebula. The NH_3 emission in the
IRDC is characterized by a low and uniform rotational temperature (T_rot ~ 10
K) and moderately high opacities in the (1,1) line. The rest of the observed
field is spotted by warm or hot zones (T_rot > 30 K) and characterized by
optically thin emission of the (1,1) line. The NH_3 abundances are about
10^{-8} in the IRDC, and 10^{-10}-10^{-9} elsewhere. The warm temperatures and
low abundances of NH_3 in the shell suggest that the gas is being heated and
photo-dissociated by the intense UV field of the LBV star. An outstanding
region is found to the south-west (SW) of the LBV star within the IRDC. The
NH_3 (3,3) emission at the centre of the SW region reveals two velocity
components tracing gas at temperatures > 30K. The northern edge of the SW
region agrees with the border of the ring nebula and a region of continuum
enhancement; here, the opacity of the (1,1) line and the NH_3 abundance do not
decrease as expected in a typical clump of an isolated cold dark cloud. This
strongly suggests some kind of interaction between the ring nebula and the
IRDC.Comment: 15 pages, 13 figures, accepted by A&A. Note the change of title with
respect to previous versio
A clinical review on megalencephaly: A large brain as a possible sign of cerebral impairment.
Megalencephaly and macrocephaly present with a head circumference measurement 2 standard deviations above the age-related mean. However, even if pathologic events resulting in both megalencephaly and macrocephaly may coexist, a distinction between these two entities is appropriate, as they represent clinical expression of different disorders with a different approach in clinical work-up, overall prognosis, and treatment. Megalencephaly defines an increased growth of cerebral structures related to dysfunctional anomalies during the various steps of brain development in the neuronal proliferation and/or migration phases or as a consequence of postnatal abnormal events. The disorders associated with megalencephaly are classically defined into 3 groups: idiopathic or benign, metabolic, and anatomic. In this article, we seek to underline the clinical aspect of megalencephaly, emphasizing the main disorders that manifest with this anomaly in an attempt to properly categorize these disorders within the megalencephaly group
Congenital muscular dystrophy: from muscle to brain.
Congenital muscular dystrophies (CMDs) are a wide group of muscular disorders that manifest with very early onset of muscular weakness, sometime associated to severe brain involvement.The histologic pattern of muscle anomalies is typical of dystrophic lesions but quite variable depending on the different stages and on the severity of the disorder.Recent classification of CMDs have been reported most of which based on the combination of clinical, biochemical, molecular and genetic findings, but genotype/phenotype correlation are in constant progression due to more diffuse utilization of the molecular analysis.In this article, the Authors report on CMDs belonging to the group of dystroglycanopathies and in particular on the most severe forms represented by the Fukuyama CMD, Muscle-Eye-Brain disease and Walker Walburg syndrome.Clinical diagnosis of infantile hypotonia is particularly difficult considering the different etiologic factors causing the lesions, the difficulty in localizing the involved CNS area (central vs. peripheral) and the limited role of the diagnostic procedures at this early age.The diagnostic evaluation is not easy mainly in differentiating the various types of CMDs, and represents a challenge for the neonatologists and pediatricians. Suggestions are reported on the way to reach a correct diagnosis with the appropriate use of the diagnostic means
Inverse Cotton-Mouton effect of the Vacuum and of atomic systems
In this letter we calculate the Inverse Cotton-Mouton Effect (ICME) for the
vacuum following the predictions of Quantum ElectroDynamics. We compare the
value of this effect for the vacuum with the one expected for atomic systems.
We finally show that ICME could be measured for the first time for noble gases
using state-of-the-art laser systems and for the quantum vacuum with
near-future laser facilities like ELI and HiPER, providing in particular a test
of the nonlinear behaviour of quantum vacuum at intensities below the Schwinger
limit of 4.5x10^33 W/m^2.Comment: Submitted to EP
Voros product, noncommutative inspired Reissner-Nordstr{\"o}m black hole and corrected area law
We emphasize the importance of the Voros product in defining a noncommutative
inspired Reissner-Nordstr\"{o}m black hole. The entropy of this black hole is
then computed in the tunneling approach and is shown to obey the area law at
the next to leading order in the noncommutative parameter .
Modifications to entropy/area law is then obtained by going beyond the
semi-classical approximation. The leading correction to the semiclassical
entropy/area law is found to be logarithmic and its coefficient involves the
noncommutative parameter .Comment: 12 pages Late
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