4,979 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
Two-Dimensional Conformal Models of Space-Time and Their Compactification
We study geometry of two-dimensional models of conformal space-time based on
the group of Moebius transformation. The natural geometric invariants, called
cycles, are used to linearise Moebius action. Conformal completion of the
space-time is achieved through an addition of a zero-radius cycle at infinity.
We pay an attention to the natural condition of non-reversibility of time arrow
in order to get a correct compactification in the hyperbolic case.Comment: 8 pages,AMS-LaTeX, 18 PS figures; v2--small corrections; v3--add two
coments on notations and multidimensional generalisation
A Unified Treatment of the Characters of SU(2) and SU(1,1)
The character problems of SU(2) and SU(1,1) are reexamined from the
standpoint of a physicist by employing the Hilbert space method which is shown
to yield a completely unified treatment for SU(2) and the discrete series of
representations of SU(1,1). For both the groups the problem is reduced to the
evaluation of an integral which is invariant under rotation for SU(2) and
Lorentz transformation for SU(1,1). The integrals are accordingly evaluated by
applying a rotation to a unit position vector in SU(2) and a Lorentz
transformation to a unit SO(2,1) vector which is time-like for the elliptic
elements and space-like for the hyperbolic elements in SU(1,1). The details of
the procedure for the principal series of representations of SU(1,1) differ
substantially from those of the discrete series.Comment: 31 pages, RevTeX, typos corrected. To be published in Journal of
Mathematical Physic
A systematic review of ICD complications in randomised controlled trials versus registries: is our 'real-world' data an underestimation?
Implantable cardioverter defibrillator (ICD) implantation carries a significant risk of complications, however published estimates appear inconsistent. We aimed to present a contemporary systematic review using meta-analysis methods of ICD complications in randomised controlled trials (RCTs) and compare it to recent data from the largest international ICD registry, the US National Cardiovascular Data Registry (NCDR). PubMed was searched for any RCTs involving ICD implantation published 1999-2013; 18 were identified for analysis including 6433 patients, mean follow-up 3 months-5.6 years. Exclusion criteria were studies of children, hypertrophic cardiomyopathy, congenital heart disease, resynchronisation therapy and generator changes. Total pooled complication rate from the RCTs (excluding inappropriate shocks) was 9.1%, including displacement 3.1%, pneumothorax 1.1% and haematoma 1.2%. Infection rate was 1.5%.There were no predictors of complications but longer follow-up showed a trend to higher complication rates (p=0.07). In contrast, data from the NCDR ICD, reporting on 356 515 implants (2006-2010) showed a statistically significant threefold lower total major complication rate of 3.08% with lead displacement 1.02%, haematoma 0.86% and pneumothorax 0.44%. The overall ICD complication rate in our meta-analysis is 9.1% over 16 months. The ICD complication reported in the NCDR ICD registry is significantly lower despite a similar population. This may reflect under-reporting of complications in registries. Reporting of ICD complications in RCTs and registries is very variable and there is a need to standardise classification of complications internationally
parafermions from constrained WZNW theories
The conformal field theory based on the coset construction is
treated as the WZNW theory for the affine Lie algebra with the
constrained subalgebra.Using a modification of the generalized
canonical quantization method generators and primary fields of an extended
symmetry algebra are found for arbitrary d.Comment: 14 pages,latex,misprints in formulas 26,40,45 corrected,a reference
adde
Birkhoff strata of the Grassmannian Gr: Algebraic curves
Algebraic varieties and curves arising in Birkhoff strata of the Sato
Grassmannian Gr are studied. It is shown that the big cell
contains the tower of families of the normal rational curves of all odd orders.
Strata , contain hyperelliptic curves of genus
and their coordinate rings. Strata , contain
plane curves for and and
curves in , respectively. Curves in the strata
have zero genus.Comment: 14 pages, no figures, improved some definitions, typos correcte
Does financial integration impact performance of equity anomalies?
We examine prominent market anomalies and evaluate the efficacy of
alternative asset pricing models under different financial integration settings.
A financial integration index is developed for classifying 25 sample markets into high-, medium- and low integration groups. Size is found to be the strongest anomaly in world markets, followed by value and liquidity. Value and profitability effects are larger for low-integrated markets. Highly integrated markets experience short-term momentum while many low-integrated markets exhibit mild reversals. Fama and French five-factor model outperforms capita l asset pricing model (CAPM) and Fama and French three-factor model in explaining returns. International factors augment the role of local factors for more integrated markets. Our study has implications for global investors to design anomaly based investment strategies
GABA Withdrawal Modifies Network Activity in Cultured Hippocampal Neurons
Dissociated hippocampal neurons, grown
in culture for 2 to 3 weeks, tended to fire
bursts of synaptic currents at fairly regular
intervals, representing network activity. A
brief exposure of cultured neurons to GABA
caused a total suppression of the spontaneous
network activity. Following a washout of
GABA, the activity was no longer clustered in
bursts and instead, the cells fired at a high
rate tonic manner. The effect of removing
GABA could be seen as long as 1 to 2 days
after GABA withdrawal and is expressed as
an increase in the number of active cells in a
network, as well as in their firing rates. Such
striking effects of GABA removal may
underlie part of the GABA withdrawal
syndrome seen elsewhere
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