249 research outputs found
Breakdown by a magnetic field of the superconducting fluctuations in the normal state: A simple phenomenological explanation
We first summarize our recent observations, through magnetization
measurements in different low-Tc superconductors, of a rather sharp
disappearance of the superconducting fluctuations in the normal state when the
magnetic field approaches Hc2(0), the upper critical field extrapolated to
T=0K. We propose that a crude phenomenological description of the observed
effects may be obtained if the quantum limits associated with the uncertainty
principle are introduced in the Gaussian-Ginzburg-Landau description of the
fluctuation-induced magnetization.Comment: LaTeX, 8 pages, including 2 eps figures. Proceedings of SNS'04,
Sitges, Spai
Neighbor Detection Induces Organ-Specific Transcriptomes, Revealing Patterns Underlying Hypocotyl-Specific Growth.
In response to neighbor proximity, plants increase the growth of specific organs (e.g., hypocotyls) to enhance access to sunlight. Shade enhances the activity of Phytochrome Interacting Factors (PIFs) by releasing these bHLH transcription factors from phytochrome B-mediated inhibition. PIFs promote elongation by inducing auxin production in cotyledons. In order to elucidate spatiotemporal aspects of the neighbor proximity response, we separately analyzed gene expression patterns in the major light-sensing organ (cotyledons) and in rapidly elongating hypocotyls of Arabidopsis thaliana PIFs initiate transcriptional reprogramming in both organs within 15 min, comprising regulated expression of several early auxin response genes. This suggests that hypocotyl growth is elicited by both local and distal auxin signals. We show that cotyledon-derived auxin is both necessary and sufficient to initiate hypocotyl growth, but we also provide evidence for the functional importance of the local PIF-induced response. With time, the transcriptional response diverges increasingly between organs. We identify genes whose differential expression may underlie organ-specific elongation. Finally, we uncover a growth promotion gene expression signature shared between different developmentally regulated growth processes and responses to the environment in different organs
Superconductor-Insulator Transition in a Capacitively Coupled Dissipative Environment
We present results on disordered amorphous films which are expected to
undergo a field-tuned Superconductor-Insulator Transition.The addition of a
parallel ground plane in proximity to the film changes the character of the
transition.Although the screening effects expected from "dirty-boson" theories
are not evident,there is evidence that the ground plane couples a certain type
of dissipation into the system,causing a dissipation-induced phase
transition.The dissipation due to the phase transition couples similarly into
quantum phase transition systems such as superconductor-insulator transitions
and Josephson junction arrays.Comment: 4 pages, 4 figure
Shot Noise at High Temperatures
We consider the possibility of measuring non-equilibrium properties of the
current correlation functions at high temperatures (and small bias). Through
the example of the third cumulant of the current () we demonstrate
that odd order correlation functions represent non-equilibrium physics even at
small external bias and high temperatures. We calculate for a quasi-one-dimensional diffusive constriction. We calculate the
scaling function in two regimes: when the scattering processes are purely
elastic and when the inelastic electron-electron scattering is strong. In both
cases we find that interpolates between two constants. In the low (high)
temperature limit is strongly (weakly) enhanced (suppressed) by the
electron-electron scattering.Comment: 11 pages 4 fig. submitted to Phys. Rev.
Low-Energy Universality in Atomic and Nuclear Physics
An effective field theory developed for systems interacting through
short-range interactions can be applied to systems of cold atoms with a large
scattering length and to nucleons at low energies. It is therefore the ideal
tool to analyze the universal properties associated with the Efimov effect in
three- and four-body systems. In this "progress report", we will discuss recent
results obtained within this framework and report on progress regarding the
inclusion of higher order corrections associated with the finite range of the
underlying interaction.Comment: Commissioned article for Few-Body Systems, 47 pp, 16 fig
Velocity-force characteristics of an interface driven through a periodic potential
We study the creep dynamics of a two-dimensional interface driven through a
periodic potential using dynamical renormalization group methods. We find that
the nature of weak-drive transport depends qualitatively on whether the
temperature is above or below the equilibrium roughening transition
temperature . Above , the velocity-force characteristics is Ohmic,
with linear mobility exhibiting a jump discontinuity across the transition. For
, the transport is highly nonlinear, exhibiting an interesting
crossover in temperature and weak external force . For intermediate drive,
, we find near a power-law velocity-force characteristics
, with , and well-below ,
, with . In the limit
of vanishing drive () the velocity-force characteristics crosses over
to , and is controlled by soliton nucleation.Comment: 18 pages, submitted to Phys. Rev.
A Solvable Regime of Disorder and Interactions in Ballistic Nanostructures, Part I: Consequences for Coulomb Blockade
We provide a framework for analyzing the problem of interacting electrons in
a ballistic quantum dot with chaotic boundary conditions within an energy
(the Thouless energy) of the Fermi energy. Within this window we show that the
interactions can be characterized by Landau Fermi liquid parameters. When ,
the dimensionless conductance of the dot, is large, we find that the disordered
interacting problem can be solved in a saddle-point approximation which becomes
exact as (as in a large-N theory). The infinite theory shows a
transition to a strong-coupling phase characterized by the same order parameter
as in the Pomeranchuk transition in clean systems (a spontaneous
interaction-induced Fermi surface distortion), but smeared and pinned by
disorder. At finite , the two phases and critical point evolve into three
regimes in the plane -- weak- and strong-coupling regimes separated
by crossover lines from a quantum-critical regime controlled by the quantum
critical point. In the strong-coupling and quantum-critical regions, the
quasiparticle acquires a width of the same order as the level spacing
within a few 's of the Fermi energy due to coupling to collective
excitations. In the strong coupling regime if is odd, the dot will (if
isolated) cross over from the orthogonal to unitary ensemble for an
exponentially small external flux, or will (if strongly coupled to leads) break
time-reversal symmetry spontaneously.Comment: 33 pages, 14 figures. Very minor changes. We have clarified that we
are treating charge-channel instabilities in spinful systems, leaving
spin-channel instabilities for future work. No substantive results are
change
Quadrupole collectivity in neutron-rich Cd isotopes
4 pags., 2 figs. -- INPC 2013 â International Nuclear Physics ConferenceThe investigation of the excitation energies of the 21+ âstates in the neutron-rich Cd isotopes shows an irregular behaviour when approaching the neutron shell-closure at N = 82. The energy of the 21+âstate in 128Cd is lower than the one in 126Cd. The transition strength B(E2, 0gs+ â 21+) in the even isotopes 122â128Cd was measured in Coulomb excitation experiments with the high-purity germanium detector array MINIBALL at REXISOLDE (CERN). The values for 122,124Cd coincide with beyond-mean-field calculations with a resultant prolate deformation, whereas 126,128Cd are better described by shell-model calculations.This project is supported by BMBF (No. 06 DA 9036I, No. 05 P12 RDCIA, No. 05 P12 RDCIB and
No. 05 P12 PKFNE), HIC for FAIR, EU through EURONS (No. 506065) and ENSAR (No. 262010)
and the MINIBALL and REX-ISOLDE collaborations
Leaf-inhabiting genera of the Gnomoniaceae, Diaporthales
The Gnomoniaceae are characterised by ascomata that are generally
immersed, solitary, without a stroma, or aggregated with a rudimentary stroma,
in herbaceous plant material especially in leaves, twigs or stems, but also in
bark or wood. The ascomata are black, soft-textured, thin-walled, and
pseudoparenchymatous with one or more central or eccentric necks. The asci
usually have a distinct apical ring. The Gnomoniaceae includes
species having ascospores that are small, mostly less than 25 ÎŒm long,
although some are longer, and range in septation from non-septate to
one-septate, rarely multi-septate. Molecular studies of the
Gnomoniaceae suggest that the traditional classification of genera
based on characteristics of the ascomata such as position of the neck and
ascospores such as septation have resulted in genera that are not
monophyletic. In this paper the concepts of the leaf-inhabiting genera in the
Gnomoniaceae are reevaluated using multiple genes, specifically
nrLSU, translation elongation factor 1-alpha (tef1-α), and RNA
polymerase II second largest subunit (rpb2) for 64 isolates. ITS sequences
were generated for 322 isolates. Six genera of leaf-inhabiting
Gnomoniaceae are defined based on placement of their type species
within the multigene phylogeny. The new monotypic genus
Ambarignomonia is established for an unusual species, A.
petiolorum. A key to 59 species of leaf-inhabiting Gnomoniaceae is
presented and 22 species of Gnomoniaceae are described and
illustrated
Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at sqrt(s) = 7 TeV with the ATLAS experiment
This paper describes an analysis of the angular distribution of W->enu and
W->munu decays, using data from pp collisions at sqrt(s) = 7 TeV recorded with
the ATLAS detector at the LHC in 2010, corresponding to an integrated
luminosity of about 35 pb^-1. Using the decay lepton transverse momentum and
the missing transverse energy, the W decay angular distribution projected onto
the transverse plane is obtained and analysed in terms of helicity fractions
f0, fL and fR over two ranges of W transverse momentum (ptw): 35 < ptw < 50 GeV
and ptw > 50 GeV. Good agreement is found with theoretical predictions. For ptw
> 50 GeV, the values of f0 and fL-fR, averaged over charge and lepton flavour,
are measured to be : f0 = 0.127 +/- 0.030 +/- 0.108 and fL-fR = 0.252 +/- 0.017
+/- 0.030, where the first uncertainties are statistical, and the second
include all systematic effects.Comment: 19 pages plus author list (34 pages total), 9 figures, 11 tables,
revised author list, matches European Journal of Physics C versio
- âŠ