4,964 research outputs found
Stochastic pumping of heat: Approaching the Carnot efficiency
Random noise can generate a unidirectional heat current across asymmetric
nano objects in the absence (or against) a temperature gradient. We present a
minimal model for a molecular-level stochastic heat pump that may operate
arbitrarily close to the Carnot efficiency. The model consists a fluctuating
molecular unit coupled to two solids characterized by distinct phonon spectral
properties. Heat pumping persists for a broad range of system and bath
parameters. Furthermore, by filtering the reservoirs' phonons the pump
efficiency can approach the Carnot limit
Quantum Hall Effect on the Hyperbolic Plane
In this paper, we study both the continuous model and the discrete model of
the Quantum Hall Effect (QHE) on the hyperbolic plane. The Hall conductivity is
identified as a geometric invariant associated to an imprimitivity algebra of
observables. We define a twisted analogue of the Kasparov map, which enables us
to use the pairing between -theory and cyclic cohomology theory, to identify
this geometric invariant with a topological index, thereby proving the
integrality of the Hall conductivity in this case.Comment: AMS-LaTeX, 28 page
Twisted K-theory and K-theory of bundle gerbes
In this note we introduce the notion of bundle gerbe K-theory and investigate
the relation to twisted K-theory. We provide some examples. Possible
applications of bundle gerbe K-theory to the classification of D-brane charges
in non-trivial backgrounds are discussed.Comment: 29 pages, corrected typos, added references, included new section on
twisted Chern character in non-torsion cas
Cyclic cocycles on twisted convolution algebras
We give a construction of cyclic cocycles on convolution algebras twisted by
gerbes over discrete translation groupoids. For proper \'etale groupoids, Tu
and Xu provide a map between the periodic cyclic cohomology of a gerbe-twisted
convolution algebra and twisted cohomology groups which is similar to a
construction of Mathai and Stevenson. When the groupoid is not proper, we
cannot construct an invariant connection on the gerbe; therefore to study this
algebra, we instead develop simplicial techniques to construct a simplicial
curvature 3-form representing the class of the gerbe. Then by using a JLO
formula we define a morphism from a simplicial complex twisted by this
simplicial curvature 3-form to the mixed bicomplex computing the periodic
cyclic cohomology of the twisted convolution algebras. The results in this
article were originally published in the author's Ph.D. thesis.Comment: 39 page
Corporate governance and quality of forward-looking information: evidence from the Chinese stock market
Fast simulation of a quantum phase transition in an ion-trap realisable unitary map
We demonstrate a method of exploring the quantum critical point of the Ising
universality class using unitary maps that have recently been demonstrated in
ion trap quantum gates. We reverse the idea with which Feynman conceived
quantum computing, and ask whether a realisable simulation corresponds to a
physical system. We proceed to show that a specific simulation (a unitary map)
is physically equivalent to a Hamiltonian that belongs to the same universality
class as the transverse Ising Hamiltonian. We present experimental signatures,
and numerical simulation for these in the six-qubit case.Comment: 12 pages, 6 figure
Malignancy within a tail gut cyst:a case of retrorectal carcinoid tumour
Purpose. Tailgut cysts with malignant transformation are rare entities. We discuss the diagnostic strategy and treatment of a malignancy within a tailgut cyst. Methods. In this study we report on the case of a 61-year-old man with a malignant neuroendocrine tumour arising within a tailgut cyst and an overview of the literature emphasising the histopathological characteristics and differential diagnosis. Results. Our patient presented with lower back pain, rectal pain, and increased urgency of defecation. MRI scan and CT-guided biopsy on histological analysis revealed a diagnosis of carcinoid tumour of the presacral space. The patient subsequently underwent an abdominoperineal excision of the rectum. Conclusions. This case highlights the importance of tailgut cysts as a differential diagnosis of presacral masses. It is a rare congenital lesion developing from remnants of the embryonic postanal gut and is predominantly benign in nature. Approximately half of cases remain asymptomatic; therefore, diagnosis is often delayed. Magnetic resonance imaging is the investigation of choice and an awareness of the possibility of malignant potential is critical to avoiding missed diagnosis and subsequent morbidity. Complete surgical excision allows accurate diagnosis, confirmation of oncological clearance, and prevention of mortality
Screening for sexually transmitted infections at a DeAddictions service in South India
Objectives To estimate the lifetime prevalence of four sexually transmitted infections (STIs) and to identify correlates of these infections among patients seeking care for a substance use disorder at a specialized DeAddictions Unit in southern India. Methods Consecutive inpatients (n = 361; 98% male; M age = 36.7 years) admitted to DeAddictions Unit of the National Institute of Mental Health and Neuro Sciences in Bangalore, India, participated in a structured interview to obtain demographic, psychiatric, sexual behavior, and substance use data; each patient also provided a blood sample for serologic testing for HIV, chlamydia, syphilis, and hepatitis B. Results One-quarter of all patients tested positive for at least one STI. Lifetime seroprevalence rates were 12.9% for syphilis, 10.3% for chlamydia, 3.1% for hepatitis B, and 1.1% for HIV. Analyses did not reveal any consistent pattern of associations between STI status and sociodemographic, psychiatric, and sexual behavioral characteristics. Conclusions All patients should receive a comprehensive sexual assessment during standard care; for those patients who report risky sexual practices, we recommend voluntary counseling and testing for STIs. Although we do not recommend universal testing for STIs at this time, this should be revisited based upon national surveillance data
Exact solution of a 2D interacting fermion model
We study an exactly solvable quantum field theory (QFT) model describing
interacting fermions in 2+1 dimensions. This model is motivated by physical
arguments suggesting that it provides an effective description of spinless
fermions on a square lattice with local hopping and density-density
interactions if, close to half filling, the system develops a partial energy
gap. The necessary regularization of the QFT model is based on this proposed
relation to lattice fermions. We use bosonization methods to diagonalize the
Hamiltonian and to compute all correlation functions. We also discuss how,
after appropriate multiplicative renormalizations, all short- and long distance
cutoffs can be removed. In particular, we prove that the renormalized two-point
functions have algebraic decay with non-trivial exponents depending on the
interaction strengths, which is a hallmark of Luttinger-liquid behavior.Comment: 59 pages, 3 figures, v2: further references added; additional
subsections elaborating mathematical details; additional appendix with
details on the relation to lattice fermion
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