718 research outputs found
Ward identities for disordered metals and superconductors
This article revisits Ward identities for disordered interacting normal
metals and superconductors. It offers a simple derivation based on gauge
invariance and recasts the identities in a new form that allows easy analysis
of the quasiparticle charge conservation (as e.g. in a normal metal) or
non-conservation (as e.g. in a d-wave superconductor).Comment: Discussion of decoherence at T=0 remove
Optical investigation of the charge-density-wave phase transitions in
We have measured the optical reflectivity of the quasi
one-dimensional conductor from the far infrared up to the
ultraviolet between 10 and 300 using light polarized along and normal to
the chain axis. We find a depletion of the optical conductivity with decreasing
temperature for both polarizations in the mid to far-infrared region. This
leads to a redistribution of spectral weight from low to high energies due to
partial gapping of the Fermi surface below the charge-density-wave transitions
at 145 K and 59 K. We deduce the bulk magnitudes of the CDW gaps and discuss
the scattering of ungapped free charge carriers and the role of fluctuations
effects
Inhibition of a yeast LTR retrotransposon by human APOBEC3 cytidine deaminases
The mammalian APOBEC3 family of cytidine deaminases includes several members that possess potent antiretroviral activity. Human APOBEC3F and APOBEC3G are specifically incorporated into human immunodeficiency virus type 1 (HIV-1) progeny virions in the absence of virion infectivity factor (Vif), where they deaminate deoxycytidine to deoxyuridine on the minus strand of nascent reverse transcripts. Editing of the HIV-1 cDNA leads to its degradation or to G to A hypermutation of the integrated provirus [1-8]. Here, we show that APOBEC3 proteins also restrict the activity of a distantly related long terminal repeat (LTR) retrotransposon. When expressed in the yeast Saccharomyces cerevisiae, human APOBEC3C, APOBEC3F, or APOBEC3G or mouse APOBEC3 potently inhibit replication of the Ty1 LTR retrotransposon. APOBEC3G interacts with Ty1 Gag and is packaged into Ty1 virus-like particles (VLPs) by a mechanism that closely resembles the one it uses to enter HIV-1 virions. Expression of APOBEC3G results in a reduced level of Ty1 cDNA integration and G to A editing of integrated Ty1 cDNA. Our findings indicate that APOBEC3G restricts Ty1 and HIV-1 by similar mechanisms and suggest that the APOBEC3 proteins target a substantially broader spectrum of retroelements than previously appreciated
Constraints on early dark energy from CMB lensing and weak lensing tomography
Dark energy can be studied by its influence on the expansion of the Universe
as well as on the growth history of the large-scale structure. In this paper,
we follow the growth of the cosmic density field in early dark energy
cosmologies by combining observations of the primary CMB temperature and
polarisation power spectra at high redshift, of the CMB lensing deflection
field at intermediate redshift and of weak cosmic shear at low redshifts for
constraining the allowed amount of early dark energy. We present these
forecasts using the Fisher-matrix formalism and consider the combination of
Planck-data with the weak lensing survey of Euclid. We find that combining
these data sets gives powerful constraints on early dark energy and is able to
break degeneracies in the parameter set inherent to the various observational
channels. The derived statistical 1-sigma-bound on the early dark energy
density parameter is sigma(Omega_d^e)=0.0022 which suggests that early dark
energy models can be well examined in our approach. In addition, we derive the
dark energy figure of merit for the considered dark energy parameterisation and
comment on the applicability of the growth index to early dark energy
cosmologies.Comment: 25 pages, 14 figures, 3 tables; v2: very minor additions, updated to
match version to be published in JCA
Heterogeneous subsidence and paleogeographic elements in an extensional setting revealed through the correlation of a storm deposit unit (Aptian, E Spain)
Durante el Aptiense, en la Subcuenca de Las Parras (NW Cuenca del Maestrazgo) se depositĂł una unidad siliciclĂĄstica en un contexto tectĂłnico extensional. Esta unidad se ha dividido en cuatro secuencias granocrecientes, de las cuales se analiza en detalle la tercera (S3) ya que presenta un alto potencial de correlaciĂłn lateral. El anĂĄlisis sedimentolĂłgico de la secuencia S3 ha permitido interpretar una evoluciĂłn vertical de shoreface inferior con procesos de tormenta, a shoreface superior; tambiĂŠn ha permitido correlacionar esta secuencia entre dos sectores de la subcuenca que presentan un desarrollo litolĂłgico considerablemente diferente. El techo de la secuencia S3 es una superfi cie erosiva menor con valor cronoestratigrĂĄfi co y se ha utilizado como datum de correlaciĂłn para el anĂĄlisis de la unidad siliciclĂĄstica. Las variaciones laterales de facies de la secuencia S3 permiten interpretar la proximidad de un sistema de descarga siliciclĂĄstico hacia el sureste, y se propone una zona de intersecciĂłn de fallas normales, prĂłxima al sector suroriental de la zona estudiada, como un elemento paleoestructural favorable para la entrada de un sistema de drenaje en la cuenca. En el sector suroriental, por encima del datum de correlaciĂłn, la secuencia S4 presenta un desarrollo muy reducido debido a la ausencia de su parte inferior; esto ha permitido interpretar la presencia de una discontinuidad local intra-S4. Esta discontinuidad local se correlaciona con otra reconocida en el sector noroccidental. Debido a las diferencias de espesor y al grado de desarrollo de la discontinuidad intra-S4 se deduce que la historia de subsidencia de diferentes bloques de la cuenca no es exactamente la misma. Esta discontinuidad intra-S4 podrĂa tener interĂŠs regional ya que separa sedimentos dominantemente siliciclĂĄsticos de sedimentos carbonatados y podrĂa indicar una modifi caciĂłn importante del sistema sedimentario. Para uno de los bloques estudiados, las variaciones espaciales de espesor para cada secuencia podrĂan representar un desarrollo de la subsidencia alternando periodos con subsidencia diferencial atenuada y periodos con subsidencia diferencial acentuada, que pueden estar relacionados con la dinĂĄmica extensional
Aspectos tĂŠcnico-ambientais da produção orgânica na regiĂŁo citrĂcola do Vale do Rio CaĂ, RS.
HĂĄ uma preocupação crescente sobre a necessidade de produção e consumo de alimentos mais saudĂĄveis, sem uso de agrotĂłxicos nem fertilizantes sintĂŠtico-industriais. Neste contexto se insere a prĂĄtica da agricultura orgânica, que, contudo, apresenta resultados ainda pouco avaliados nos meios acadĂŞmicos e cientĂficos. Assim, pretendeu-se nesta pesquisa diagnosticar aspectos tĂŠcnico-ambientais da produção orgânica na regiĂŁo citrĂcola do Vale do Rio CaĂ, no Rio Grande do Sul. Inicialmente, foram selecionadas propriedades de oito agricultores familiares, todas jĂĄ convertidas ao sistema orgânico de produção, sendo aplicadas entrevistas semi-estruturadas. Os produtores mostram-se satisfeitos com o sistema orgânico de produção e revelam bom conhecimento sobre o ambiente, plantas, solos e processos agroecolĂłgicos, adquiridos atravĂŠs da participação em eventos tĂŠcnicos e em reuniĂľes da Cooperativa Ecocitrus. A constante troca de experiĂŞncias entre esses agricultores tem melhorado sua qualificação tĂŠcnica, alĂŠm de melhor conscientizĂĄ-los nos aspectos polĂticos, econĂ´micos e sociais
Confinement and Chiral Symmetry Breaking via Domain-Like Structures in the QCD Vacuum
A qualitative mechanism for the emergence of domain structured background
gluon fields due to singularities in gauge field configurations is considered,
and a model displaying a type of mean field approximation to the QCD partition
function based on this mechanism is formulated. Estimation of the vacuum
parameters (gluon condensate, topological susceptibility, string constant and
quark condensate) indicates that domain-like structures lead to an area law for
the Wilson loop, nonzero topological susceptibility and spontaneous breakdown
of chiral symmetry. Gluon and ghost propagators in the presence of domains are
calculated explicitly and their analytical properties are discussed. The
Fourier transforms of the propagators are entire functions and thus describe
confined dynamical fields.Comment: RevTeX, 48 pages (32 pages + Appendices A-E), new references added
[1,2,4,5] and minor formulae corrected for typographical error
A model for the dependence of polarized structure functions
We present an update of a phenomenological model for the spin dependent
structure functions of the proton and neutron. This model is based
on a broken SU(6) wavefunction parametrized by the unpolarized structure
functions. The two free parameters of the model are choosen to fulfill the
Bjorken and Ellis--Jaffe sum rules. The model respects isospin symmetry and has
zero strange sea polarization. Using new values for from hyperon beta
decay the resulting dependent asymmetries are in perfect agreement
with the existing data. Therefore we do not see any evidence for a ``spin
crisis''. With two choices for the dependence of and
is predicted and shown to be small for both cases.Comment: 18 pages and 11 figures as uudecoded ps file
Topology and chiral symmetry breaking in SU(N) gauge theories
We study the low-lying eigenmodes of the lattice overlap Dirac operator for
SU(N) gauge theories with N=2,3,4 and 5 colours. We define a fermionic
topological charge from the zero-modes of this operator and show that, as N
grows, any disagreement with the topological charge obtained by cooling the
fields, becomes rapidly less likely. By examining the fields where there is a
disagreement, we are able to show that the Dirac operator does not resolve
instantons below a critical size of about rho = 2.5 a, but resolves the larger,
more physical instantons. We investigate the local chirality of the near-zero
modes and how it changes as we go to larger N. We observe that the local
chirality of these modes, which is prominent for SU(2) and SU(3), becomes
rapidly weaker for larger N and is consistent with disappearing entirely in the
limit of N -> infinity. We find that this is not due to the observed
disappearance of small instantons at larger N.Comment: 41 pages, 12 figures, RevTe
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in âs = 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 fbâ1 of protonâproton 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
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