The direct evaluation of attosecond chirp from a streaking measurement

We derive an analytical expression, from classical electron trajectories in a laser field, that relates the breadth of a streaked photoelectron spectrum to the group-delay dispersion of an isolated attosecond pulse. Based on this analytical expression, we introduce a simple, efficient and robust procedure to instantly extract the attosecond pulse's chirp from the streaking measurement.Comment: 4 figure

Results for the response function determination of the Compact Neutron Spectrometer

The Compact Neutron Spectrometer (CNS) is a Joint European Torus (JET) Enhancement Project, designed for fusion diagnostics in different plasma scenarios. The CNS is based on a liquid scintillator (BC501A) which allows good discrimination between neutron and gamma radiation. Neutron spectrometry with a BC501A spectrometer requires the use of a reliable, fully characterized detector. The determination of the response matrix was carried out at the Ion Accelerator Facility (PIAF) of the Physikalisch-Technische Bundesanstalt (PTB). This facility provides several monoenergetic beams (2.5, 8, 10, 12 and 14 MeV) and a 'white field'(Emax ~17 MeV), which allows for a full characterization of the spectrometer in the region of interest (from ~1.5 MeV to ~17 MeV. The energy of the incoming neutrons was determined by the time of flight method (TOF), with time resolution in the order of 1 ns. To check the response matrix, the measured pulse height spectra were unfolded with the code MAXED and the resulting energy distributions were compared with those obtained from TOF. The CNS project required modification of the PTB BC501A spectrometer design, to replace an analog data acquisition system (NIM modules) with a digital system developed by the 'Ente per le Nuove tecnologie, l'Energia e l'Ambiente' (ENEA). Results for the new digital system were evaluated using new software developed specifically for this project.Comment: Proceedings of FNDA 201

Experimental phase diagram of moving vortices

In the mixed state of type II superconductors, vortices penetrate the sample and form a correlated system due to the screening of supercurrents around them. Interestingly, we can study this correlated system as a function of density and driving force. The density, for instance, is controlled by the magnetic field, B, whereas a current density j acts as a driving force F=jxB on all vortices. The free motion of vortices is inhibited by the presence of an underlying potential, which tends to pin the vortices. Hence, to minimize the pinning strength we studied a superconducting glass in which the depinning current is 10 to 1000 times smaller than in previous studies, which enables us to map out the complete phase diagram in this new regime. The diagram is obtained as a function of B, driving current and temperature and led a remarkable set of new results, which includes a huge peak effect, an additional reentrant depinning phase and a driving force induced pinning phase.Comment: 4 page

Group classification of (1+1)-Dimensional Schr\"odinger Equations with Potentials and Power Nonlinearities

We perform the complete group classification in the class of nonlinear Schr\"odinger equations of the form $i\psi_t+\psi_{xx}+|\psi|^\gamma\psi+V(t,x)\psi=0$ where $V$ is an arbitrary complex-valued potential depending on $t$ and $x,$ $\gamma$ is a real non-zero constant. We construct all the possible inequivalent potentials for which these equations have non-trivial Lie symmetries using a combination of algebraic and compatibility methods. The proposed approach can be applied to solving group classification problems for a number of important classes of differential equations arising in mathematical physics.Comment: 10 page

Angular position of nodes in the superconducting gap of YBCO

The thermal conductivity of a YBCO single crystal has been studied as a function of the relative orientation of the crystal axes and a magnetic field rotating in the Cu-O planes. Measurements were carried out at several temperatures below T_c and at a fixed field of 30 kOe. A four-fold symmetry characteristic of a superconducting gap with nodes at odd multiples of 45 degrees in k-space was resolved. Experiments were performed to exclude a possible macroscopic origin for such a four-fold symmetry such as sample shape or anisotropic pinning. Our results impose an upper limit of 10% on the weight of the s-wave component of the essentially d-wave superconducting order parameter of YBCO.Comment: 10 pages, 4 figure

Universal Heat Conduction in YBa_2Cu_3O_6.9

The thermal conductivity of YBa_2Cu_3O_6.9 was measured at low temperatures in untwinned single crystals with concentrations of Zn impurities from 0 to 3% of Cu. A linear term kappa_0/T = 0.19 mW/K^2.cm is clearly resolved as T -> 0, and found to be virtually independent of Zn concentration. The existence of this residual normal fluid strongly validates the basic theory of transport in unconventional superconductors. Moreover, the observed universal behavior is in quantitative agreement with calculations for a gap function of d-wave symmetry.Comment: Latex file, 4 pages, 3 EPS figures, to appear in Physical Review Letter

Leading Order Calculation of Shear Viscosity in Hot Quantum Electrodynamics from Diagrammatic Methods

We compute the shear viscosity at leading order in hot Quantum Electrodynamics. Starting from the Kubo relation for shear viscosity, we use diagrammatic methods to write down the appropriate integral equations for bosonic and fermionic effective vertices. We also show how Ward identities can be used to put constraints on these integral equations. One of our main results is an equation relating the kernels of the integral equations with functional derivatives of the full self-energy; it is similar to what is obtained with two-particle-irreducible effective action methods. However, since we use Ward identities as our starting point, gauge invariance is preserved. Using these constraints obtained from Ward identities and also power counting arguments, we select the necessary diagrams that must be resummed at leading order. This includes all non-collinear (corresponding to 2 to 2 scatterings) and collinear (corresponding to 1+N to 2+N collinear scatterings) rungs responsible for the Landau-Pomeranchuk-Migdal effect. We also show the equivalence between our integral equations obtained from quantum field theory and the linearized Boltzmann equations of Arnold, Moore and Yaffe obtained using effective kinetic theory.Comment: 45 pages, 22 figures (note that figures 7 and 14 are downgraded in resolution to keep this submission under 1000kb, zoom to see them correctly

Evaluating elbow osteoarthritis within the prehistoric Tiwanaku state using generalized estimating equations (GEE).

OBJECTIVES:Studies of osteoarthritis (OA) in human skeletal remains can come with scalar problems. If OA measurement is noted as present or absent in one joint, like the elbow, results may not identify specific articular pathology data and the sample size may be insufficient to address research questions. If calculated on a per data point basis (i.e., each articular surface within a joint), results may prove too data heavy to comprehensively understand arthritic changes, or one individual with multiple positive scores may skew results and violate the data independence required for statistical tests. The objective of this article is to show that the statistical methodology Generalized Estimating Equations (GEE) can solve scalar issues in bioarchaeological studies. MATERIALS AND METHODS:Using GEE, a population-averaged statistical model, 1,195 adults from the core and one colony of the prehistoric Tiwanaku state (AD 500-1,100) were evaluated bilaterally for OA on the seven articular surfaces of the elbow joint. RESULTS:GEE linked the articular surfaces within each individual specimen, permitting the largest possible unbiased dataset, and showed significant differences between core and colony Tiwanaku peoples in the overall elbow joint, while also pinpointing specific articular surfaces with OA. Data groupings by sex and age at death also demonstrated significant variation. A pattern of elbow rotation noted for core Tiwanaku people may indicate a specific pattern of movement. DISCUSSION:GEE is effective and should be encouraged in bioarchaeological studies as a way to address scalar issues and to retain all pathology information

Dense Quark Matter Conductivity in Ultra-Intense Magnetic Field

Heavy-ion collisions generate a huge magnetic field of the order of $10^{18} G$ for the duration of about 0.2 fm/c. This time may become an order of magnitude longer if the electrical conductivity of quark matter is large. We calculate the conductivity in the regime of high density and show that contrary to naive expectations it only weakly depends on the MF.Comment: 3 pages, 0 figure