12,550 research outputs found
Intrinsic quark transverse momentum in the nucleon from lattice QCD
A better understanding of transverse momentum (k_T-) dependent quark
distributions in a hadron is needed to interpret several experimentally
observed large angular asymmetries and to clarify the fundamental role of gauge
links in non-abelian gauge theories. Based on manifestly non-local gauge
invariant quark operators we introduce process-independent k_T-distributions
and study their properties in lattice QCD. We find that the longitudinal and
transverse momentum dependence approximately factorizes, in contrast to the
behavior of generalized parton distributions. The resulting quark
k_T-probability densities for the nucleon show characteristic dipole
deformations due to correlations between intrinsic k_T and the quark or nucleon
spin. Our lattice calculations are based on N_f=2+1 mixed action propagators of
the LHP collaboration.Comment: 4 pages, 3 figure
Dynamics of photoinduced Charge Density Wave-metal phase transition in K0.3MoO3
We present first systematic studies of the photoinduced phase transition from
the ground charge density wave (CDW) state to the normal metallic (M) state in
the prototype quasi-1D CDW system K0.3MoO3. Ultrafast non-thermal CDW melting
is achieved at the absorbed energy density that corresponds to the electronic
energy difference between the metallic and CDW states. The results imply that
on the sub-picosecond timescale when melting and subsequent initial recovery of
the electronic order takes place the lattice remains unperturbed.Comment: Phys. Rev. Lett., accepted for publicatio
Scattering Experiments with Microwave Billiards at an Exceptional Point under Broken Time Reversal Invariance
Scattering experiments with microwave cavities were performed and the effects
of broken time-reversal invariance (TRI), induced by means of a magnetized
ferrite placed inside the cavity, on an isolated doublet of nearly degenerate
resonances were investigated. All elements of the effective Hamiltonian of this
two-level system were extracted. As a function of two experimental parameters,
the doublet and also the associated eigenvectors could be tuned to coalesce at
a so-called exceptional point (EP). The behavior of the eigenvalues and
eigenvectors when encircling the EP in parameter space was studied, including
the geometric amplitude that builds up in the case of broken TRI. A
one-dimensional subspace of parameters was found where the differences of the
eigenvalues are either real or purely imaginary. There, the Hamiltonians were
found PT-invariant under the combined operation of parity (P) and time reversal
(T) in a generalized sense. The EP is the point of transition between both
regions. There a spontaneous breaking of PT occurs
Induced Time-Reversal Symmetry Breaking Observed in Microwave Billiards
Using reciprocity, we investigate the breaking of time-reversal (T) symmetry
due to a ferrite embedded in a flat microwave billiard. Transmission spectra of
isolated single resonances are not sensitive to T-violation whereas those of
pairs of nearly degenerate resonances do depend on the direction of time. For
their theoretical description a scattering matrix model from nuclear physics is
used. The T-violating matrix elements of the effective Hamiltonian for the
microwave billiard with the embedded ferrite are determined experimentally as
functions of the magnetization of the ferrite.Comment: 4 pages, 4 figure
Killer on the road?-cells from pancreatic preneoplastic lesions disseminate through pancreatic ducts on their way to cancer
Pancreatic ductal adenocarcinoma (PDAC) is ranked the fourth most common cause of cancer related deaths in western countries with a 5-year survival rate of less than 8 (1). It is estimated to be even the second most common cause by 2030 as there are no successful treatment options (2). Due to the lack of early and specific symptoms as well as non-invasive biomarkers, the majority of patients is diagnosed at an advanced and already metastasized disease stage, where palliative treatment remains the only option (3). Thus, in order to improve the dismal prognosis of PDAC patients, a much better understanding of PDAC evolution is urgently needed allowing earlier detection of the disease and providing novel therapeutic modalities
Fidelity amplitude of the scattering matrix in microwave cavities
The concept of fidelity decay is discussed from the point of view of the
scattering matrix, and the scattering fidelity is introduced as the parametric
cross-correlation of a given S-matrix element, taken in the time domain,
normalized by the corresponding autocorrelation function. We show that for
chaotic systems, this quantity represents the usual fidelity amplitude, if
appropriate ensemble and/or energy averages are taken. We present a microwave
experiment where the scattering fidelity is measured for an ensemble of chaotic
systems. The results are in excellent agreement with random matrix theory for
the standard fidelity amplitude. The only parameter, namely the perturbation
strength could be determined independently from level dynamics of the system,
thus providing a parameter free agreement between theory and experiment
First Experimental Observation of Superscars in a Pseudointegrable Barrier Billiard
With a perturbation body technique intensity distributions of the electric
field strength in a flat microwave billiard with a barrier inside up to mode
numbers as large as about 700 were measured. A method for the reconstruction of
the amplitudes and phases of the electric field strength from those intensity
distributions has been developed. Recently predicted superscars have been
identified experimentally and - using the well known analogy between the
electric field strength and the quantum mechanical wave function in a
two-dimensional microwave billiard - their properties determined.Comment: 4 pages, 5 .eps figure
Methylation landscape in the genome of higher plants of agronomical interest
In eukaryotic cells the methylation of cytosines in DNA is an essential mechanism which is implied in the dynamic organization of the genome structure, in relation to genes expression. Plant genomes contain a significant proportion and variable according to the species, of sequences which are likely to be methylated during the life of the plant. It is known that the establishment and the maintenance of methylation profiles in both genomic areas and specific sequences constitute a crucial mediator in the modulation of genes expression during development. Recent studies have evidenced the implication of epimutations in the adaptation of plants to their environment particularly in response to biotic and abiotic stresses. Recently, the complete mapping of methylation in the genomes of Arabidopsis thaliana and rice provided invaluable information on the distribution of methylation within genes in relation to their expression. The impact of changes in the methylation profiles on the characters of agronomic importance has not been intensively studied yet, whereas this question takes a considerable importance in the context of an increasing food demand and foreseen global climate changes. The METHYLANDSCAPE project proposes to isolate genomic DNA sequences on the basis of their degree of methylation and to connect the variation of their methylation profiles with, on the one hand, the expression of the corresponding genes and, on the other hand, with environmental or developmental processes. Thus, it should be possible to identify genes which expression is differentially controlled by methylation during development and/or in situation of stress, and likely to have an influence on the agronomic value of the plant. The METHYLANDSCAPE partners thus propose to bring signification advances in plant genomics on four original species, by integrating DNA methylation mapping and the relationship between epigenome and transcriptome, up to the generation of methylation-sensitive markers linked with characters of agronomic importance. (Texte intégral
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