1,176 research outputs found
Fast reconnection in relativistic plasmas: the magnetohydrodynamics tearing instability revisited
Fast reconnection operating in magnetically dominated plasmas is often
invoked in models for magnetar giant flares, for magnetic dissipation in pulsar
winds, or to explain the gamma-ray flares observed in the Crab nebula, hence
its investigation is of paramount importance in high-energy astrophysics. Here
we study, by means of two dimensional numerical simulations, the linear phase
and the subsequent nonlinear evolution of the tearing instability within the
framework of relativistic resistive magnetohydrodynamics, as appropriate in
situations where the Alfven velocity approaches the speed of light. It is found
that the linear phase of the instability closely matches the analysis in
classical MHD, where the growth rate scales with the Lundquist number S as
S^-1/2, with the only exception of an enhanced inertial term due to the thermal
and magnetic energy contributions. In addition, when thin current sheets of
inverse aspect ratio scaling as S^-1/3 are considered, the so-called "ideal"
tearing regime is retrieved, with modes growing independently on S and
extremely fast, on only a few light crossing times of the sheet length. The
overall growth of fluctuations is seen to solely depend on the value of the
background Alfven velocity. In the fully nonlinear stage we observe an inverse
cascade towards the fundamental mode, with Petschek-type supersonic jets
propagating at the external Alfven speed from the X-point, and a fast
reconnection rate at the predicted value R~(ln S)^-1.Comment: 14 pages, 9 figures, accepted for publication (MNRAS
Can Gravity Distinguish Between Dirac and Majorana Neutrinos?
We show that spin-gravity interaction can distinguish between Dirac and
Majorana neutrino wave packets propagating in a Lense-Thirring background.
Using time-independent perturbation theory and gravitational phase to generate
a perturbation Hamiltonian with spin-gravity coupling, we show that the
associated matrix element for the Majorana neutrino differs significantly from
its Dirac counterpart. This difference can be demonstrated through significant
gravitational corrections to the neutrino oscillation length for a two-flavour
system, as shown explicitly for SN1987A.Comment: 4 pages, 2 figures; minor changes of text; typo corrected; accepted
in Physical Review Letter
On the influence of the magnetic field of the GSI experimental storage ring on the time-modulation of the EC-decay rates of the H-like mother ions
We investigate the influence of the magnetic field of the
Experimental storage ring (ESR) at GSI on the periodic time-dependence of the
orbital K-shell electron capture decay ) rates of the H--like heavy ions.
We approximate the magnetic field of the ESR by a uniform magnetic field.
Unlike the assertion by Lambiase et al., arXiv: 0811.2302 [nucl-th], we show
that a motion of the H-like heavy ion in a uniform magnetic field cannot be the
origin of the periodic time-dependence of the EC-decay rates of the H-like
heavy ions.Comment: 3 pages, 1 figur
Nitrate concentration and microbial activities in maize cultivated plots under different weed control management.
Quantum physics in inertial and gravitational fields
Covariant generalizations of well-known wave equations predict the existence
of inertial-gravitational effects for a variety of quantum systems that range
from Bose-Einstein condensates to particles in accelerators. Additional effects
arise in models that incorporate Born reciprocity principle and the notion of a
maximal acceleration. Some specific examples are discussed in detail.Comment: 25 pages,1 figure,to appear in "Relativity in Rotating Frame
Lower Neutrino Mass Bound from SN1987A Data and Quantum Geometry
A lower bound on the light neutrino mass is derived in the framework
of a geometrical interpretation of quantum mechanics. Using this model and the
time of flight delay data for neutrinos coming from SN1987A, we find that the
neutrino masses are bounded from below by eV, in
agreement with the upper bound
eV currently available. When the model is applied to photons with effective
mass, we obtain a lower limit on the electron density in intergalactic space
that is compatible with recent baryon density measurements.Comment: 22 pages, 3 figure
Incentive or Habit Learning in Amphibians?
Toads (Rhinella arenarum) received training with a novel incentive procedure involving access to solutions of different NaCl concentrations. In Experiment 1, instrumental behavior and weight variation data confirmed that such solutions yield incentive values ranging from appetitive (deionized water, DW, leading to weight gain), to neutral (300 mM slightly hypertonic solution, leading to no net weight gain or loss), and aversive (800 mM highly hypertonic solution leading to weight loss). In Experiment 2, a downshift from DW to a 300 mM solution or an upshift from a 300 mM solution to DW led to a gradual adjustment in instrumental behavior. In Experiment 3, extinction was similar after acquisition with access to only DW or with a random mixture of DW and 300 mM. In Experiment 4, a downshift from DW to 225, 212, or 200 mM solutions led again to gradual adjustments. These findings add to a growing body of comparative evidence suggesting that amphibians adjust to incentive shifts on the basis of habit formation and reorganization
The Cosmic-Ray Proton and Helium Spectra measured with the CAPRICE98 balloon experiment
A new measurement of the primary cosmic-ray proton and helium fluxes from 3
to 350 GeV was carried out by the balloon-borne CAPRICE experiment in 1998.
This experimental setup combines different detector techniques and has
excellent particle discrimination capabilities allowing clear particle
identification. Our experiment has the capability to determine accurately
detector selection efficiencies and systematic errors associated with them.
Furthermore, it can check for the first time the energy determined by the
magnet spectrometer by using the Cherenkov angle measured by the RICH detector
well above 20 GeV/n. The analysis of the primary proton and helium components
is described here and the results are compared with other recent measurements
using other magnet spectrometers. The observed energy spectra at the top of the
atmosphere can be represented by (1.27+-0.09)x10^4 E^(-2.75+-0.02) particles
(m^2 GeV sr s)^-1, where E is the kinetic energy, for protons between 20 and
350 GeV and (4.8+-0.8)x10^2 E^(-2.67+-0.06) particles (m^2 GeV nucleon^-1 sr
s)^-1, where E is the kinetic energy per nucleon, for helium nuclei between 15
and 150 GeV nucleon^-1.Comment: To be published on Astroparticle Physics (44 pages, 13 figures, 5
tables
Measurement of forward photon production cross-section in proton-proton collisions at = 13 TeV with the LHCf detector
In this paper, we report the production cross-section of forward photons in
the pseudorapidity regions of and ,
measured by the LHCf experiment with proton--proton collisions at =
13 TeV. The results from the analysis of 0.191 of data
obtained in June 2015 are compared to the predictions of several hadronic
interaction models that are used in air-shower simulations for
ultra-high-energy cosmic rays. Although none of the models agree perfectly with
the data, EPOS-LHC shows the best agreement with the experimental data among
the models.Comment: 21 pages, 4 figure
A Multicentric, Single Arm, Prospective, Stratified Clinical Investigation to Confirm MammoWave’s Ability in Breast Lesions Detection
Novel techniques, such as microwave imaging, have been implemented in different prototypes and are under clinical validation, especially for breast cancer detection, due to their harmless technology and possible clinical advantages over conventional imaging techniques. In the prospective study presented in this work, we aim to investigate through a multicentric European clinical trial (ClinicalTrials.gov Identifier NCT05300464) the effectiveness of the MammoWave microwave imaging device, which uses a Huygens-principle-based radar algorithm for image reconstruction and comprises dedicated image analysis software. A detailed clinical protocol has been prepared outlining all aspects of this study, which will involve adult females having a radiologist study output obtained using conventional exams (mammography and/or ultrasound and/or magnetic resonance imaging) within the previous month. A maximum number of 600 volunteers will be recruited at three centres in Italy and Spain, where they will be asked to sign an informed consent form prior to the MammoWave scan. Conductivity weighted microwave images, representing the homogeneity of the tissues’ dielectric properties, will be created for each breast, using a conductivity = 0.3 S/m. Subsequently, several microwave image parameters (features) will be used to quantify the images’ non-homogenous behaviour. A selection of these features is expected to allow for distinction between breasts with lesions (either benign or malignant) and those without radiological findings. For all the selected features, we will use Welch’s t-test to verify the statistical significance, using the gold standard output of the radiological study review
- …