5,138 research outputs found
Selective transmission of Dirac electrons and ballistic magnetoresistance of \textit{n-p} junctions in graphene
We show that an electrostatically created n-p junction separating the
electron and hole gas regions in a graphene monolayer transmits only those
quasiparticles that approach it almost perpendicularly to the n-p interface.
Such a selective transmission of carriers by a single n-p junction would
manifest itself in non-local magnetoresistance effect in arrays of such
junctions and determines the unusual Fano factor in the current noise universal
for the n-p junctions in graphene.Comment: 4 pages, 2 fig
Non-Linear Canonical Transformations in Classical and Quantum Mechanics
-Mechanics is a consistent physical theory which describes both classical
and quantum mechanics simultaneously through the representation theory of the
Heisenberg group. In this paper we describe how non-linear canonical
transformations affect -mechanical observables and states. Using this we
show how canonical transformations change a quantum mechanical system. We seek
an operator on the set of -mechanical observables which corresponds to the
classical canonical transformation. In order to do this we derive a set of
integral equations which when solved will give us the coherent state expansion
of this operator. The motivation for these integral equations comes from the
work of Moshinsky and a variety of collaborators. We consider a number of
examples and discuss the use of these equations for non-bijective
transformations.Comment: The paper has been improved in light of a referee's report. The paper
will appear in the Journal of Mathematical Physics. 24 pages, no figure
Path Integral Approach to the Scattering Theory of Quantum Transport
The scattering theory of quantum transport relates transport properties of
disordered mesoscopic conductors to their transfer matrix \bbox{T}. We
introduce a novel approach to the statistics of transport quantities which
expresses the probability distribution of \bbox{T} as a path integral. The
path integal is derived for a model of conductors with broken time reversal
invariance in arbitrary dimensions. It is applied to the
Dorokhov-Mello-Pereyra-Kumar (DMPK) equation which describes
quasi-one-dimensional wires. We use the equivalent channel model whose
probability distribution for the eigenvalues of \bbox{TT}^{\dagger} is
equivalent to the DMPK equation independent of the values of the forward
scattering mean free paths. We find that infinitely strong forward scattering
corresponds to diffusion on the coset space of the transfer matrix group. It is
shown that the saddle point of the path integral corresponds to ballistic
conductors with large conductances. We solve the saddle point equation and
recover random matrix theory from the saddle point approximation to the path
integral.Comment: REVTEX, 9 pages, no figure
Anderson localization of one-dimensional hybrid particles
We solve the Anderson localization problem on a two-leg ladder by the
Fokker-Planck equation approach. The solution is exact in the weak disorder
limit at a fixed inter-chain coupling. The study is motivated by progress in
investigating the hybrid particles such as cavity polaritons. This application
corresponds to parametrically different intra-chain hopping integrals (a "fast"
chain coupled to a "slow" chain). We show that the canonical
Dorokhov-Mello-Pereyra-Kumar (DMPK) equation is insufficient for this problem.
Indeed, the angular variables describing the eigenvectors of the transmission
matrix enter into an extended DMPK equation in a non-trivial way, being
entangled with the two transmission eigenvalues. This extended DMPK equation is
solved analytically and the two Lyapunov exponents are obtained as functions of
the parameters of the disordered ladder. The main result of the paper is that
near the resonance energy, where the dispersion curves of the two decoupled and
disorder-free chains intersect, the localization properties of the ladder are
dominated by those of the slow chain. Away from the resonance they are
dominated by the fast chain: a local excitation on the slow chain may travel a
distance of the order of the localization length of the fast chain.Comment: 31 pages, 13 figure
Global monopole, dark matter and scalar tensor theory
In this article, we discuss the space-time of a global monopole field as a
candidate for galactic dark matter in the context of scalar tensor theory.Comment: 8 pages, Accepted in Mod. Phys. Lett.
Diagonal approximation of the form factor of the unitary group
The form factor of the unitary group U(N) endowed with the Haar measure
characterizes the correlations within the spectrum of a typical unitary matrix.
It can be decomposed into a sum over pairs of ``periodic orbits'', where by
periodic orbit we understand any sequence of matrix indices. From here the
diagonal approximation can be defined in the usual fashion as a sum only over
pairs of identical orbits. We prove that as we take the dimension to
infinity, the diagonal approximation becomes ``exact'', that is converges to
the full form factor.Comment: 9 page
Self-forces in the Spacetime of Multiple Cosmic Strings
We calculate the electromagnetic self-force on a stationary linear
distribution of four-current in the spacetime of multiple cosmic strings. It is
shown that if the current is infinitely thin and stretched along a line which
is parallel to the strings the problem admits an explicit solution.Comment: This paper has been produced in Latex format and has 18 page
A random matrix approach to decoherence
In order to analyze the effect of chaos or order on the rate of decoherence
in a subsystem, we aim to distinguish effects of the two types of dynamics by
choosing initial states as random product states from two factor spaces
representing two subsystems. We introduce a random matrix model that permits to
vary the coupling strength between the subsystems. The case of strong coupling
is analyzed in detail, and we find no significant differences except for very
low-dimensional spaces.Comment: 11 pages, 5 eps-figure
Buprenorphine added on brief cognitive behavioral therapy for treatment of methamphetamine use disorder
Background: Methamphetamine (MA) use remains a major public health concern around the world. Recent findings suggest that buprenorphine may be helpful for cocaine use reduction. Moreover, animal studies described reduced dopamine peak effect following MA use, due to the administration of low dose buprenorphine.
Objectives: This study examined the effectiveness of buprenorphine with brief cognitive behavioral therapy on MA use disorder.
Methods: The study was conducted in an outpatient substance abuse treatment center in Qazvin, Iran. Nineteen MA users received buprenorphine for 24 weeks combined with brief cognitive behavioral therapy in an outpatient substance abuse treatment program, three times per week, as a before and after non - randomization study. Clinical outcomes included treatment retention, MA use, degree of MA dependency and craving, quality of life, cognitive abilities questionnaire, addiction severity and also adverse events. Data was analyzed by performing repeated measures analysis and the Friedman test for nonparametric variables.
Results: Fifteen participants completed the study during six months and frequency of MA use was significantly decreased at 24 weeks (P < 0.001). There were also significant reductions in craving (P < 0.001), degree of MA dependence (P < 0.001), and improvements in quality of life, cognitive ability, and some subscales of addiction severity.
Conclusions: The results of this preliminary clinical study demonstrated that buprenorphine could potentially attenuate MA craving and alternate rewarding effects of MA and had promising effects on cognitive impairment. Furthermore, buprenorphine can be considered as a harm reduction intervention in some communities, in which the people, as a result of cultural beliefs, do not accept a therapy, which only consists of counseling and no medications
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