355 research outputs found
Connecting Berry's phase and the pumped charge in a Cooper pair pump
The properties of the tunnelling-charging Hamiltonian of a Cooper pair pump
are well understood in the regime of weak and intermediate Josephson coupling,
i.e. when . It is also known that
Berry's phase is related to the pumped charge induced by the adiabatical
variation of the eigenstates. We show explicitly that pumped charge in Cooper
pair pump can be understood as a partial derivative of Berry's phase with
respect to the phase difference across the array. The phase fluctuations
always present in real experiments can also be taken into account, although
only approximately. Thus the measurement of the pumped current gives reliable,
yet indirect, information on Berry's phase. As closing remarks, we give the
differential relation between Berry's phase and the pumped charge, and state
that the mathematical results are valid for any observable expressible as a
partial derivative of the Hamiltonian.Comment: 5 pages, 5 figures, RevTeX, Presentation has been clarifie
Josephson-phase qubit without tunneling
We show that a complete set of one-bit gates can be realized by coupling the
two logical states of a phase qubit to a third level (at higher energy) using
microwave pulses. Thus, one can achieve coherent control without invoking any
tunneling between the qubit levels. We propose two implementations, using
rf-SQUIDs and d-wave Josephson junctions.Comment: REVTeX4, 4pp., 6 EPS figure files; N.B.: "Alec" is my first, and
"Maassen van den Brink" my family name. v2: gate universality fleshed out,
small fix in d-wave decoherence para, discussion expanded, two Refs. added.
v3: some more Refs., a molecular example, and a few minor fixes; final, to
appear in PRB Rapid
The effect of flows on transverse oscillations of coronal loops
In this paper we study kink oscillations of coronal loops in the presence of flows. Using the thin-tube approximation we derive the general governing equation for kink oscillations of a loop with the density varying along the loop in the presence of flows. This equation remains valid even when the density and flow are time dependent. The derived equation is then used to study the effect of flows on eigenfrequencies of kink oscillations of coronal loops. The implication of the obtained results on coronal seismology is discussed
Weak Localization Effect in Superconductors by Radiation Damage
Large reductions of the superconducting transition temperature and
the accompanying loss of the thermal electrical resistivity (electron-phonon
interaction) due to radiation damage have been observed for several A15
compounds, Chevrel phase and Ternary superconductors, and in
the high fluence regime. We examine these behaviors based on the recent theory
of weak localization effect in superconductors. We find a good fitting to the
experimental data. In particular, weak localization correction to the
phonon-mediated interaction is derived from the density correlation function.
It is shown that weak localization has a strong influence on both the
phonon-mediated interaction and the electron-phonon interaction, which leads to
the universal correlation of and resistance ratio.Comment: 16 pages plus 3 figures, revtex, 76 references, For more information,
Plesse see http://www.fen.bilkent.edu.tr/~yjki
Magnetic fields in supernova remnants and pulsar-wind nebulae
We review the observations of supernova remnants (SNRs) and pulsar-wind
nebulae (PWNe) that give information on the strength and orientation of
magnetic fields. Radio polarimetry gives the degree of order of magnetic
fields, and the orientation of the ordered component. Many young shell
supernova remnants show evidence for synchrotron X-ray emission. The spatial
analysis of this emission suggests that magnetic fields are amplified by one to
two orders of magnitude in strong shocks. Detection of several remnants in TeV
gamma rays implies a lower limit on the magnetic-field strength (or a
measurement, if the emission process is inverse-Compton upscattering of cosmic
microwave background photons). Upper limits to GeV emission similarly provide
lower limits on magnetic-field strengths. In the historical shell remnants,
lower limits on B range from 25 to 1000 microGauss. Two remnants show
variability of synchrotron X-ray emission with a timescale of years. If this
timescale is the electron-acceleration or radiative loss timescale, magnetic
fields of order 1 mG are also implied. In pulsar-wind nebulae, equipartition
arguments and dynamical modeling can be used to infer magnetic-field strengths
anywhere from about 5 microGauss to 1 mG. Polarized fractions are considerably
higher than in SNRs, ranging to 50 or 60% in some cases; magnetic-field
geometries often suggest a toroidal structure around the pulsar, but this is
not universal. Viewing-angle effects undoubtedly play a role. MHD models of
radio emission in shell SNRs show that different orientations of upstream
magnetic field, and different assumptions about electron acceleration, predict
different radio morphology. In the remnant of SN 1006, such comparisons imply a
magnetic-field orientation connecting the bright limbs, with a non-negligible
gradient of its strength across the remnant.Comment: 20 pages, 24 figures; to be published in SpSciRev. Minor wording
change in Abstrac
Constraints on Dark Matter Annihilation in Clusters of Galaxies with the Fermi Large Area Telescope
Nearby clusters and groups of galaxies are potentially bright sources of
high-energy gamma-ray emission resulting from the pair-annihilation of dark
matter particles. However, no significant gamma-ray emission has been detected
so far from clusters in the first 11 months of observations with the Fermi
Large Area Telescope. We interpret this non-detection in terms of constraints
on dark matter particle properties. In particular for leptonic annihilation
final states and particle masses greater than ~200 GeV, gamma-ray emission from
inverse Compton scattering of CMB photons is expected to dominate the dark
matter annihilation signal from clusters, and our gamma-ray limits exclude
large regions of the parameter space that would give a good fit to the recent
anomalous Pamela and Fermi-LAT electron-positron measurements. We also present
constraints on the annihilation of more standard dark matter candidates, such
as the lightest neutralino of supersymmetric models. The constraints are
particularly strong when including the fact that clusters are known to contain
substructure at least on galaxy scales, increasing the expected gamma-ray flux
by a factor of ~5 over a smooth-halo assumption. We also explore the effect of
uncertainties in cluster dark matter density profiles, finding a systematic
uncertainty in the constraints of roughly a factor of two, but similar overall
conclusions. In this work, we focus on deriving limits on dark matter models; a
more general consideration of the Fermi-LAT data on clusters and clusters as
gamma-ray sources is forthcoming.Comment: accepted to JCAP, Corresponding authors: T.E. Jeltema and S. Profumo,
minor revisions to be consistent with accepted versio
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC
Measurements of inclusive jet suppression in heavy ion collisions at the LHC
provide direct sensitivity to the physics of jet quenching. In a sample of
lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated
luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with
a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the
transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the
anti-kt algorithm with values for the distance parameter that determines the
nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of
the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp.
Jet production is found to be suppressed by approximately a factor of two in
the 10% most central collisions relative to peripheral collisions. Rcp varies
smoothly with centrality as characterized by the number of participating
nucleons. The observed suppression is only weakly dependent on jet radius and
transverse momentum. These results provide the first direct measurement of
inclusive jet suppression in heavy ion collisions and complement previous
measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables,
submitted to Physics Letters B. All figures including auxiliary figures are
available at
http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02
Temporal dynamics of the shrub and herbaceous layer of an area of moist grassland in Alto Paraíso de Goiás, Brazil
Este trabalho avaliou a dinâmica estrutural e fl orística de uma comunidade de espécies herbáceo-arbustivas
de uma área de campo limpo úmido em Alto Paraíso de Goiás, o primeiro inventário realizado em 2000 (T0) e o
segundo em 2007 (T1). A diversidade de Shannon entre os períodos foi comparada pelo teste-t de Hutcheson e a
similaridade fl orística, pelo índice de similaridade de Chao-Sørensen. As relações fl orísticas e a cobertura, entre os
períodos e as linhas, foram avaliadas por meio de análises de correspondência retifi cada (DCA). Foram amostradas
98 espécies, 88 no T0 e 67 no T1, sendo 31 exclusivas do T0 e 10 do T1. A diversidade fl orística na comunidade
foi elevada nos dois períodos, porém diferente entre esses (t = 7,12; p < 0,001), devido a variação no número e
cobertura das espécies. A similaridade entre os dois inventários foi alta (Chao-Sørensen ± IC = 0,841 ± 0,074). A
ordenação por DCA indicou relações entre a composição fl orística e a cobertura com o gradiente de umidade e
de matéria orgânica no solo identifi cados em T0. Houve modifi cações nas linhas em zonas sazonais, as quais se
tornaram mais semelhantes às linhas constantemente saturadas por água. Em um intervalo de sete anos o campo
limpo úmido apresentou mudanças na composição fl orística e, principalmente na estrutura devido o aumento da
cobertura de espécies perenes, cespitosas e entouceiradas, que foram favorecidas pela maior umidade no solo em
resposta à elevação da pluviosidade da região. __________________________________________________________________________________________ ABSTRACTTh is study evaluated the fl oristic and structural dynamics of a community of herbaceous-shrub species
in an area of moist grassland in Alto Paraíso de Goiás. Th e fi rst inventory was undertaken in 2000 (T0) and the
second in 2007 (T1). Shannon’s diversity between the periods was compared by Hutchesons´s t-test, and the
fl oristic similarity by the Chao-Sørensen similarity index. Floristic composition and cover, between periods and
lines, were evaluated by detrended correspondence analysis (DCA). We sampled 98 species, 88 at T0 and 67 at T1;
31 were unique to T0 and 10 to T1. Floristic diversity in the community was high in both periods, but diff erent
between them (t = 7.12, p <0.001), due to variation in species number and coverage. Similarity between the two
surveys was high (Chao-Sørensen CI = ± 0.841 ± 0.074). Th e DCA ordination indicated relationships between the
fl oristic composition and cover with a gradient of moisture and organic matter in the soil identifi ed in T0. Th ere
were changes in the lines in the seasonal zones, which became more similar in those constantly saturated with
water. During an interval of seven years the moist grassland showed changes in fl oristic composition and mainly
in structure due to increased cover of the clumped tussock perennial species, which were favored by higher soil
moisture due to high rainfall in the region
- …