2,454 research outputs found
Kinetic Approach to Fractional Exclusion Statistics
We show that the kinetic approach to statistical mechanics permits an elegant
and efficient treatment of fractional exclusion statistics. By using the
exclusion-inclusion principle recently proposed [Phys. Rev. E49, 5103 (1994)]
as a generalization of the Pauli exclusion principle, which is based on a
proper definition of the transition probability between two states, we derive a
variety of different statistical distributions interpolating between bosons and
fermions. The Haldane exclusion principle and the Haldane-Wu fractional
exclusion statistics are obtained in a natural way as particular cases. The
thermodynamic properties of the statistical systems obeying the generalized
exclusion-inclusion principle are discussed.Comment: 6 pages, REVTE
A remark on interacting anyons in magnetic field
In this remark, we note that the anyons, interacting with each other through
pairwise potential in external magnetic field, exhibit a simple quantum group
symmetry.Comment: IPT-EPFL preprint, typos fixed, minor corrections, references
updated, submitted to Physics Letter A
Charge and Statistics of Quantum Hall Quasi-Particles. A numerical study of mean values and fluctuations
We present Monte Carlo studies of charge expectation values and charge
fluctuations for quasi-particles in the quantum Hall system. We have studied
the Laughlin wave functions for quasi-hole and quasi-electron, and also Jain's
definition of the quasi-electron wave function. The considered systems consist
of from 50 to 200 electrons, and the filling fraction is 1/3. For all
quasi-particles our calculations reproduce well the expected values of charge;
-1/3 times the electron charge for the quasi-hole, and 1/3 for the
quasi-electron. Regarding fluctuations in the charge, our results for the
quasi-hole and Jain quasi-electron are consistent with the expected value zero
in the bulk of the system, but for the Laughlin quasi-electron we find small,
but significant, deviations from zero throughout the whole electron droplet. We
also present Berry phase calculations of charge and statistics parameter for
the Jain quasi-electron, calculations which supplement earlier studies for the
Laughlin quasi-particles. We find that the statistics parameter is more well
behaved for the Jain quasi-electron than it is for the Laughlin quasi-electron.Comment: 39 pages, 27 figure
Hierarchical Wave Functions Revisited
We study the hierarchical wave functions on a sphere and on a torus. We
simplify some wave functions on a sphere or a torus using the analytic
properties of wave functions. The open question, the construction of the wave
function for quasielectron excitations on a torus, is also solved in this
paper.Comment: 28 pages, Late
Microlensing planets in M22: free-floating or bound?
We use detailed numerical simulations and theoretical estimates to show that,
if confirmed, the unusually brief microlensing events observed by Sahu et al.
(2001) in the field of the globular cluster M22 might be explained as a result
of microlensing by a population of clustered MACHOs, a dark cluster or RAMBO,
not associated with the globular cluster. If real, this dark cluster would be
located between M22 and the Galactic bulge and could include at least
substellar members with a typical size of 1-3 pc. Bound planets in wide or/and
eccentric orbits are also able to reproduce the observed microlensing
behaviour, but only if multiplanet systems (including large Kuiper-belt-like
objects) are abundant, although, our calculations argue against the latter
scenario as the ionization rate in M22 is very high. Dynamically ejected or
lone planets are, in principle, incompatible with the observational findings as
they either escape their parent cluster in a relatively short time-scale after
ejection or segregate toward the outskirts of the cluster. We discuss
additional implications of the dark cluster scenario, including the existence
of a population of RAMBOs toward the Galactic bulge.Comment: 6 pages, 1 Postscript figure, LaTeX, uses A&A macros, submitted to
A&A Main Journa
Direct Observation of a Fractional Charge
We performed measurements of Quantum Shot Noise in order to determine the
quasiparticle charge in the Fractional Quantum Hall regime. The noise is
generated by a current flow through a partially transmitting Quantum Point
Contact in a 2DEG. The noise is directly proportional to the charge of the
quasiparticles, thus allowing direct determination of the charge. We measured
Quantum Shot Noise at a filling factor of 1/3 and found that the charge is e/3;
as predicted by Laughlin.Comment: 3 pages, PostScript, 4 figures. Submitted to Natur
Shot noise in coupled dots and the "fractional charges"
We consider the problem of shot noise in resonant tunneling through double
quantum dots in the case of interacting particles. Using a many-body quantum
mechanical description we evaluate the energy dependent transmission
probability, the total average current and the shot noise spectrum. Our results
show that the obtained reduction of the noise spectrum, due to Coulomb
interaction, can be interpret in terms of non--interacting particles with
fractional charge like behavior.Comment: some clarifications added, to appear in Phys. Lett.
Correlated transport of FQHE quasiparticles in a double-antidot system
We have calculated the linear conductance associated with tunneling of
individual quasiparticles of primary quantum Hall liquids with filling factors
through a system of two antidots in series. On-site Coulomb
interaction simulates the Fermi exclusion and makes the quasiparticle dynamics
similar to that of tunneling electrons. The liquid edges serve as the
quasiparticle reservoirs, and also create the dissipation mechanism for
tunneling between the antidots. In the regime of strong dissipation, the
conductance should exhibit resonant peaks of unusual form and a width
proportional to the quasiparticle interaction energy . In the weakly-damped
regime, the shape of the resonant conductance peaks reflects coherent tunnel
coupling of the antidots. The Luttinger-liquid singularity in the rates of
quasiparticle tunneling to/from the liquid edges manifests itself as an
additional weak resonant structure in the conductance curves.Comment: 9 pages including 5 figure
Fly Photoreceptors Demonstrate Energy-Information Trade-Offs in Neural Coding
Trade-offs between energy consumption and neuronal performance must shape the design and evolution of nervous systems, but we lack empirical data showing how neuronal energy costs vary according to performance. Using intracellular recordings from the intact retinas of four flies, Drosophila melanogaster, D. virilis, Calliphora vicina, and Sarcophaga carnaria, we measured the rates at which homologous R1–6 photoreceptors of these species transmit information from the same stimuli and estimated the energy they consumed. In all species, both information rate and energy consumption increase with light intensity. Energy consumption rises from a baseline, the energy required to maintain the dark resting potential. This substantial fixed cost, ∼20% of a photoreceptor's maximum consumption, causes the unit cost of information (ATP molecules hydrolysed per bit) to fall as information rate increases. The highest information rates, achieved at bright daylight levels, differed according to species, from ∼200 bits s(−1) in D. melanogaster to ∼1,000 bits s(−1) in S. carnaria. Comparing species, the fixed cost, the total cost of signalling, and the unit cost (cost per bit) all increase with a photoreceptor's highest information rate to make information more expensive in higher performance cells. This law of diminishing returns promotes the evolution of economical structures by severely penalising overcapacity. Similar relationships could influence the function and design of many neurons because they are subject to similar biophysical constraints on information throughput
Cultivation and genetics of Artemisia annua L. for increased production of the antimalarial artemisinin
Malaria has been treated for over 350 years with quinine and quinine-derived drugs. However, in several areas of the world, some strains of the malarial parasite Plasmodium falciparum have developed resistance against these drugs. Recently, the World Health Organization (WHO) recommended the use of artemisinin-combination treatments (ACT) as the first-line treatment for multidrug-resistant falciparum malaria. The WHO estimates that current supplies of artemisinin are sufficient for only 30 million ACT, and is foreseeing the need for 130-220 million ACT in 2005 (WHO, 2004). Current research on the production of synthetic artemisinin-like compounds by the Roll Back Malaria project, pharmaceutical companies and academia resulted in a promising synthetic artemisinin-like compound (OZ277) which is currently undergoing phase I clinical trials. In about 5 years this drug is expected to be approved and made available to the public, however, meeting current global demands for ACT depends on the immediate availability of affordable artemisinin-derived drugs. This will involve expansion of the area under cultivation of Artemisia annua and improved methods of cultivation and processing of raw material, associated with more efficient methods for extraction and purification of artemisinin from plant material. This review addresses the agricultural, environmental and genetic aspects that may be useful in the successful large-scale cultivation of A. annua and for producing the antimalarial artemisinin in areas where it is urgently needed today. It also includes geographic aspects (latitude and altitude), which will help make decisions about crop establishment in tropical countries, and includes a list of Good Agricultural and Collection Practices for A. annu
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