15,055 research outputs found
Numerical Methods for the 3-dimensional 2-body Problem in the Action-at-a-Distance Electrodynamics
We develop two numerical methods to solve the differential equations with
deviating arguments for the motion of two charges in the action-at-a-distance
electrodynamics. Our first method uses St\"urmer's extrapolation formula and
assumes that a step of integration can be taken as a step of light ladder,
which limits its use to shallow energies. The second method is an improvement
of pre-existing iterative schemes, designed for stronger convergence and can be
used at high-energies.Comment: 17 pages, 11 figure
Medical use of cannabis: italian and european legislation
This review illustrates some brief
considerations of the medical use of cannabis recently
issued in Italy. History and uses of cannabis
throughout centuries and different countries
are illustrated together with a description of botany
and active phytocannabinoids. Then, medical
use of cannabis anti-pain treatment for patients
resistant to conventional therapies is described
in case of chronic neuropathic pain, spasticity,
for anticinetosic and antiemetic effect in nausea
and vomiting caused by chemotherapy, for appetite
stimulating effect in cachexia, anorexia, loss
of appetite in cancer patients or patients with
AIDS and in anorexia nervosa, hypotensive effect
in glaucoma resistant to conventional therapies
and for reduction of involuntary body and facial
movements in Gilles de la Tourette syndrome.
Italian most recent legislation on medical cannabis
is detailed with some law proposals, also
showing the inconsistent legislation within European
Union. Some final considerations of future
studies are also reported
Softening of the equation of state of matter at large densities and temperatures: chiral symmetry restoration vs. quark deconfinement
We discuss two models for describing the behavior of matter at large
densities and intermediate temperatures. In both models a softening of the
equation of state takes place due to the appearance of new degrees of freedom.
The first is a hadronic model in which the softening is due to chiral symmetry
restoration. In the second model the softening is associated with the formation
of clusters of quarks in the mixed phase. We show that both models allow a
significant softening but, in the first case the bulk modulus is mainly
dependent on the density, while in the mixed phase model it also strongly
depends on the temperature. We also show that the bulk modulus is not vanishing
in the mixed phase due to the presence of two conserved charges, the baryon and
the isospin one. Only in a small region of densities and temperatures the
incompressibility becomes extremely small. Finally we compare our results with
recent analysis of heavy ion collisions at intermediate energies.Comment: 4 pages, 4 figures, editorially accepted versio
Localization transition induced by learning in random searches
We solve an adaptive search model where a random walker or L\'evy flight
stochastically resets to previously visited sites on a -dimensional lattice
containing one trapping site. Due to reinforcement, a phase transition occurs
when the resetting rate crosses a threshold above which non-diffusive
stationary states emerge, localized around the inhomogeneity. The threshold
depends on the trapping strength and on the walker's return probability in the
memoryless case. The transition belongs to the same class as the
self-consistent theory of Anderson localization. These results show that
similarly to many living organisms and unlike the well-studied Markovian walks,
non-Markov movement processes can allow agents to learn about their environment
and promise to bring adaptive solutions in search tasks.Comment: 5 pages, 5 figures + 4 pages of Supplemental Information. Accepted in
Physical Review Letter
Information decomposition of multichannel EMG to map functional interactions in the distributed motor system
The central nervous system needs to coordinate multiple muscles during postural control. Functional coordination is established through the neural circuitry that interconnects different muscles. Here we used multivariate information decomposition of multichannel EMG acquired from 14 healthy participants during postural tasks to investigate the neural interactions between muscles. A set of information measures were estimated from an instantaneous linear regression model and a time-lagged VAR model fitted to the EMG envelopes of 36 muscles. We used network analysis to quantify the structure of functional interactions between muscles and compared them across experimental conditions. Conditional mutual information and transfer entropy revealed sparse networks dominated by local connections between muscles. We observed significant changes in muscle networks across postural tasks localized to the muscles involved in performing those tasks. Information decomposition revealed distinct patterns in task-related changes: unimanual and bimanual pointing were associated with reduced transfer to the pectoralis major muscles, but an increase in total information compared to no pointing, while postural instability resulted in increased information, information transfer and information storage in the abductor longus muscles compared to normal stability. These findings show robust patterns of directed interactions between muscles that are task-dependent and can be assessed from surface EMG recorded during static postural tasks. We discuss directed muscle networks in terms of the neural circuitry involved in generating muscle activity and suggest that task-related effects may reflect gain modulations of spinal reflex pathways
Sharp measure contraction property for generalized H-type Carnot groups
We prove that H-type Carnot groups of rank and dimension satisfy the
if and only if and . The latter
integer coincides with the geodesic dimension of the Carnot group. The same
result holds true for the larger class of generalized H-type Carnot groups
introduced in this paper, and for which we compute explicitly the optimal
synthesis. This constitutes the largest class of Carnot groups for which the
curvature exponent coincides with the geodesic dimension. We stress that
generalized H-type Carnot groups have step 2, include all corank 1 groups and,
in general, admit abnormal minimizing curves.
As a corollary, we prove the absolute continuity of the Wasserstein geodesics
for the quadratic cost on all generalized H-type Carnot groups.Comment: 18 pages. This article extends the results of arXiv:1510.05960. v2:
revised and improved version. v3: final version, to appear in Commun.
Contemp. Mat
Patterns of trading profiles at the Nordic Stock Exchange. A correlation-based approach
We investigate the trading behavior of Finnish individual investors trading
the stocks selected to compute the OMXH25 index in 2003 by tracking the
individual daily investment decisions. We verify that the set of investors is a
highly heterogeneous system under many aspects. We introduce a correlation
based method that is able to detect a hierarchical structure of the trading
profiles of heterogeneous individual investors. We verify that the detected
hierarchical structure is highly overlapping with the cluster structure
obtained with the approach of statistically validated networks when an
appropriate threshold of the hierarchical trees is used. We also show that the
combination of the correlation based method and of the statistically validated
method provides a way to expand the information about the clusters of investors
with similar trading profiles in a robust and reliable way.Comment: 25 pages, 8 figure
Magnetic superlattice and finite-energy Dirac points in graphene
We study the band structure of graphene's Dirac-Weyl quasi-particles in a one-dimensional magnetic superlattice formed by a periodic sequence of alternating magnetic barriers. The spectrum and the nature of the states strongly depend on the conserved longitudinal momentum and on the barrier width. At the center of the superlattice Brillouin zone we find new Dirac points at finite energies where the dispersion is highly anisotropic, in contrast to the dispersion close to the neutrality point which remains isotropic. This finding suggests the possibility of collimating Dirac-Weyl quasi-particles by tuning the doping
Ethical and medico-legal remarks on uterus transplantation: may it solve uterine factor infertility?
Uterus transplantation was firstly tested with animal trials sixty-five years ago. Despite several successful attempts in human subjects, the different procedures still lay at the experimental stage, in need of further studies and investigations before they can be considered as standard clinical practices. Uterus transplant cannot be regarded as a life-saving procedure, but rather a method to restore woman ability to procreate, when lost, thus improving her quality of life. Uterus transplant is a complex surgical procedure and presents significant health threats. Medical staff should therefore always obtain informed consent from patients, emphasizing such risks. Before that, women undergoing uterine transplants should be thoroughly informed about the hazards inherent to the procedure and especially about the dangers of immunosuppressant drugs, administered after the surgery which may injure the fetus, eventually formed in the restored organ and even lead to its death, thus nullifying the purpose of the transplant itself. Therefore, the risk-benefit ratio of uterus transplantation needs to be carefully assessed and described
Interaction induced Fermi-surface renormalization in the Hubbard model close to the Mott-Hubbard transition
We investigate the nature of the interaction-driven Mott-Hubbard transition
of the half-filled Hubbard model in one dimension, using a
full-fledged variational Monte Carlo approach including a distance-dependent
Jastrow factor and backflow correlations. We present data for the evolution of
the magnetic properties across the Mott-Hubbard transition and on the
commensurate to incommensurate transition in the insulating state. Analyzing
renormalized excitation spectra, we find that the Fermi surface renormalizes to
perfect nesting right at the Mott-Hubbard transition in the insulating state,
with a first-order reorganization when crossing into the conducting state.Comment: 6 pages and 7 figure
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