990 research outputs found
Mass Hierarchy via Mossbauer and Reactor Neutrinos
We show how one could determine the neutrino mass hierarchy with Mossbauer
neutrinos and also revisit the question of whether the hierarchy can be
determined with reactor neutrinos.Comment: contribution to NOW 2008, 3 pages, 4 figures, late
Decoherence of localized spins interacting via RKKY interaction
We theoretically study decoherence of two localized spins interacting via the
RKKY interaction in one-, two-, and three-dimensional electron gas. We derive
the kinetic equation for the reduced density matrix of the localized spins and
show that energy relaxation caused by singlet-triplet transition is suppressed
when the RKKY interaction is ferromagnetic. We also estimate the decoherence
time of the system consisting of two quantum dots embedded in a two dimensional
electron gas.Comment: 4pages, 2figure
Nonequilibrium Kondo Effect in a Quantum Dot Coupled to Ferromagnetic Leads
We study the Kondo effect in the electron transport through a quantum dot
coupled to ferromagnetic leads, using a real-time diagrammatic technique which
provides a systematic description of the nonequilibrium dynamics of a system
with strong local electron correlations. We evaluate the theory in an extension
of the `resonant tunneling approximation', introduced earlier, by introducing
the self-energy of the off-diagonal component of the reduced propagator in spin
space. In this way we develop a charge and spin conserving approximation that
accounts not only for Kondo correlations but also for the spin splitting and
spin accumulation out of equilibrium. We show that the Kondo resonances, split
by the applied bias voltage, may be spin polarized. A left-right asymmetry in
the coupling strength and/or spin polarization of the electrodes significantly
affects both the spin accumulation and the weight of the split Kondo resonances
out of equilibrium. The effects are observable in the nonlinear differential
conductance. We also discuss the influence of decoherence on the Kondo
resonance in the frame of the real-time formulation.Comment: 13 pages, 13 figure
Surface tension in an intrinsic curvature model with fixed one-dimensional boundaries
A triangulated fixed connectivity surface model is investigated by using the
Monte Carlo simulation technique. In order to have the macroscopic surface
tension \tau, the vertices on the one-dimensional boundaries are fixed as the
edges (=circles) of the tubular surface in the simulations. The size of the
tubular surface is chosen such that the projected area becomes the regular
square of area A. An intrinsic curvature energy with a microscopic bending
rigidity b is included in the Hamiltonian. We found that the model undergoes a
first-order transition of surface fluctuations at finite b, where the surface
tension \tau discontinuously changes. The gap of \tau remains constant at the
transition point in a certain range of values A/N^\prime at sufficiently large
N^\prime, which is the total number of vertices excluding the fixed vertices on
the boundaries. The value of \tau remains almost zero in the wrinkled phase at
the transition point while \tau remains negative finite in the smooth phase in
that range of A/N^\prime.Comment: 12 pages, 8 figure
20 Years of Cluster Observations: The Magnetopause,
The terrestrial magnetopause forms the boundary between the solar wind plasma with its embedded interplanetary magnetic field on one side, and the terrestrial magnetosphere, dominated by Earth's dipole field, on the other side. It is therefore a key region for the transfer of mass, momentum, and energy from the solar wind to the magnetosphere. The Cluster mission, comprising a constellation of four spacecraft flying in formation was launched more than 20 years ago to study boundaries in space. During its lifetime, Cluster has provided a wealth of new knowledge about the magnetopause. In this paper, we give an overview of Cluster-based studies of this boundary, and highlight a selection of interesting results.publishedVersio
Phase diagram of depleted Heisenberg model for CaV4O9
We have numerically investigated the 1/5-depleted Heisenberg square lattice
representing CaV4O9 using the Quantum Monte Carlo loop algorithm. We have
determined the phase diagram of the model as a function of the ratio of the two
different couplings: bonds within a plaquette and dimer bonds between
plaquettes. By calculating both the spin gap and the staggered magnetization we
determine the range of stability of the long range ordered (LRO) phase. At
isotropic coupling LRO survives the depletion. But the close vicinity of the
isotropic point to the spin gap phase leads us to the conclusion that already a
small frustrating next nearest neighbor interaction can drive the system into
the quantum disordered phase and thus explain the spin gap behavior of CaV4O9
Implementation of a novel PCR based method for detecting malaria parasites from naturally infected mosquitoes in Papua New Guinea
<p>Abstract</p> <p>Background</p> <p>Detection of <it>Plasmodium species </it>in mosquitoes is important for designing vector control studies. However, most of the PCR-based detection methods show some potential limitations. The objective of this study was to introduce an effective PCR-based method for detecting <it>Plasmodium vivax </it>and <it>Plasmodium falciparum </it>from the field-caught mosquitoes of Papua New Guinea.</p> <p>Methods</p> <p>A method has been developed to concurrently detect mitochondrial cytochrome b (<it>Cyt b</it>) of four human <it>Plasmodium </it>species using PCR (<it>Cytb</it>-PCR). To particularly discriminate <it>P. falciparum </it>from <it>P. vivax</it>, <it>Plasmodium ovale </it>and <it>Plasmodium malariae</it>, a polymerase chain reaction-repeated fragment length polymorphism (PCR-RFLP) has further been developed to use with this method. However, due to limited samples number of <it>P. ovale </it>and <it>P. malariae</it>; this study was mainly confined to <it>P. vivax </it>and <it>P. falciparum</it>. The efficiency of <it>Cytb</it>-PCR was evaluated by comparing it with two 'gold standards' enzyme linked immunosorbent assay specific for circumsporozoite protein (CS-ELISA) using artificially infected mosquitoes; and nested PCR specific for small subunit ribosomal RNA (<it>SSUrRNA</it>) using field caught mosquitoes collected from three areas (Kaboibus, Wingei, and Jawia) of the East Sepic Province of Papua New Guinea.</p> <p>Results</p> <p>A total of 90 mosquitoes were artificially infected with three strains of <it>Plasmodium</it>: <it>P. vivax-</it>210 (<it>n </it>= 30), <it>P. vivax</it>-247 (<it>n </it>= 30) and <it>P. falciparum </it>(<it>n </it>= 30). These infected mosquitoes along with another 32 unfed mosquitoes were first checked for the presence of <it>Plasmodium </it>infection by CS-ELISA, and later the same samples were compared with the <it>Cytb</it>-PCR. CS-ELISA for <it>P. vivax</it>-210, <it>P. vivax</it>-247 and <it>P. falciparum </it>detected positive infection in 30, 19 and 18 mosquitoes respectively; whereas <it>Cytb</it>-PCR detected 27, 16 and 16 infections, respectively. The comparison revealed a close agreement between the two assays (κ = 0.862, 0.842 and 0.894, respectively for Pv-210, Pv-247 and <it>P. falciparum </it>groups). It was found that the eight CS-ELISA-positive mosquitoes detected negative by <it>Cytb</it>-PCR were false-positive results. The lowest detection limit of this <it>Cytb</it>-PCR was 10 sporozoites. A highly concordance result was also found between nested PCR and <it>Cytb</it>-PCR using 107 field caught mosquitoes, and both tests concordantly detected <it>P. falciparum </it>in an <it>Anopheles punctulatus </it>mosquito collected from Kaboibus. Both tests thus suggested an overall sporozoite rate of 0.9% (1/107) in the study areas. Subsequently, PCR-RFLP efficiently discriminated <it>P. falciparum </it>from <it>P. vivax </it>for all of the <it>Cytb</it>-PCR positive samples.</p> <p>Conclusion</p> <p>A single step PCR based method has been introduced here that is highly sensitive, efficient and reliable for identifying <it>P. vivax </it>and <it>P. falciparum </it>from mosquitoes. The reliability of the technique was confirmed by its ability to detect <it>Plasmodium </it>as efficiently as those of CS-ELISA and nested PCR. Application of the assay offers the opportunity to detect vector species of Papua New Guinea and may contribute for designing further vector control programmes.</p
Chiral perturbation theory, finite size effects and the three-dimensional model
We study finite size effects of the d=3 model in terms of the chiral
perturbation theory. We calculate by Monte Carlo simulations physical
quantities which are, to order of , uniquely determined only by two
low energy constants. They are the magnetization and the helicity modulus (or
the Goldstone boson decay constant) in infinite volume. We also pay a special
attention to the region of the validity of the two possible expansions in the
theory.Comment: 34 pages ( 9 PS files are included. harvmac and epsf macros are
needed. ), KYUSHU-HET-17, SAGA-HE-6
Polar Perturbations of Self-gravitating Supermassive Global Monopoles
Spontaneous global symmetry breaking of O(3) scalar field gives rise to
point-like topological defects, global monopoles. By taking into account
self-gravity,the qualitative feature of the global monopole solutions depends
on the vacuum expectation value v of the scalar field. When v < sqrt{1 / 8 pi},
there are global monopole solutions which have a deficit solid angle defined at
infinity. When sqrt{1 / 8 pi} <= v < sqrt{3 / 8 pi}, there are global monopole
solutions with the cosmological horizon, which we call the supermassive global
monopole. When v >= sqrt{3 / 8 pi}, there is no nontrivial solution. It was
shown that all of these solutions are stable against the spherical
perturbations. In addition to the global monopole solutions, the de Sitter
solutions exist for any value of v. They are stable against the spherical
perturbations when v sqrt{3 / 8 pi}.
We study polar perturbations of these solutions and find that all
self-gravitating global monopoles are stable even against polar perturbations,
independently of the existence of the cosmological horizon, while the de Sitter
solutions are always unstable.Comment: 10 pages, 6 figures, corrected some type mistakes (already corrected
in PRD version
Polyhedral vesicles
Polyhedral vesicles with a large bending modulus of the membrane such as the
gel phase lipid membrane were studied using a Brownian dynamics simulation. The
vesicles exhibit various polyhedral morphologies such as tetrahedron and cube
shapes. We clarified two types of line defects on the edges of the polyhedrons:
cracks of both monolayers at the spontaneous curvature of monolayer , and a crack of the inner monolayer at . Around the
latter defect, the inner monolayer curves positively. Our results suggested
that the polyhedral morphology is controlled by .Comment: 4 pages, 5 figure
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