Ionization and charge migration through strong internal fields in clusters exposed to intense X-ray pulses

A general scenario for electronic charge migration in finite samples illuminated by an intense laser pulse is given. Microscopic calculations for neon clusters under strong short pulses as produced by X-ray free-electron laser sources confirm this scenario and point to the prominent role of field ionization by strong internal fields. The latter leads to the fast formation of a core-shell system with an almost static core of screened ions while the outer shell explodes. Substituting the shell ions with a different material such as helium as a sacrificial layer leads to a substantial improvement of the diffraction image for the embedded cluster thus reducing the consequences of radiation damage for coherent diffractive imaging.Comment: 5 pages, 4 figure

Differential Phase Estimation with the SeaMARC II Bathymetric Sidescan Sonar System

A maximum-likelihood estimator is used to extract differential phase measurements from noisy seafloor echoes received at pairs of transducers mounted on either side of the SeaMARC II bathymetricsidescan sonar system. Carrier frequencies for each side are about 1 kHz apart, and echoes from a transmitted pulse 2 ms long are analyzed. For each side, phase difference sequences are derived from the full complex data consisting of base-banded and digitized quadrature components of the received echoes. With less bias and a lower variance, this method is shown to be more efficient than a uniform mean estimator. It also does not exhibit the angular or time ambiguities commonly found in the histogram method used in the SeaMARC II system. A figure for the estimation uncertainty of the phasedifference is presented, and results are obtained for both real and simulated data. Based on this error estimate and an empirical verification derived through coherent ping stacking, a single filter length of 100 ms is chosen for data processing application

On-shell supersymmetry for massive multiplets

The consequences of on-shell supersymmetry are studied for scattering amplitudes with massive particles in four dimensions. Using the massive version of the spinor helicity formalism the supersymmetry transformations relating products of on-shell states are derived directly from the on-shell supersymmetry algebra for any massive representation. Solutions to the resulting Ward identities can be constructed as functions on the on-shell superspaces that are obtained from the coherent state method. In simple cases it is shown that these superspaces allow one to construct explicitly supersymmetric scattering amplitudes. Supersymmetric on-shell recursion relations for tree-level superamplitudes with massive particles are introduced. As examples, simple supersymmetric amplitudes are constructed in SQCD, the Abelian Higgs model, the Coulomb branch of N=4 super Yang-Mills, QCD with an effective Higgs-gluon coupling and for massive vector boson currents.Comment: 49+9 pages, 4 figures, v2: references updated, typos corrected, examples added, v3: final PRD versio

The geometry and thermodynamics of dissipative quantum systems

Dirac's method of classical analogy is employed to incorporate quantum degrees of freedom into modern nonequilibrium thermodynamics. The proposed formulation of dissipative quantum mechanics builds entirely upon the geometric structures implied by commutators and canonical correlations. A lucid formulation of a nonlinear quantum master equation follows from the thermodynamic structure. Complex classical environments with internal structure can be handled readily.Comment: 4 pages, definitely no figure

Forming Early-type Galaxies in Groups Prior to Cluster Assembly

We study a unique proto-cluster of galaxies, the supergroup SG1120-1202. We quantify the degree to which morphological transformation of cluster galaxies occurs prior to cluster assembly in order to explain the observed early-type fractions in galaxy clusters at z=0. SG1120-1202 at z~0.37 is comprised of four gravitationally bound groups that are expected to coalesce into a single cluster by z=0. Using HST ACS observations, we compare the morphological fractions of the supergroup galaxies to those found in a range of environments. We find that the morphological fractions of early-type galaxies (~60 %) and the ratio of S0 to elliptical galaxies (0.5) in SG1120-1202 are very similar to clusters at comparable redshift, consistent with pre-processing in the group environment playing the dominant role in establishing the observed early-type fraction in galaxy clusters.Comment: 5 pages, 2 figures, 2 tables. Accepted for publication in ApJ Letter

The Impact of Accretion Disk Winds on the Optical Spectra of Cataclysmic Variables

Many high-state non-magnetic cataclysmic variables (CVs) exhibit blue-shifted absorption or P-Cygni profiles associated with ultraviolet (UV) resonance lines. These features imply the existence of powerful accretion disk winds in CVs. Here, we use our Monte Carlo ionization and radiative transfer code to investigate whether disk wind models that produce realistic UV line profiles are also likely to generate observationally significant recombination line and continuum emission in the optical waveband. We also test whether outflows may be responsible for the single-peaked emission line profiles often seen in high-state CVs and for the weakness of the Balmer absorption edge (relative to simple models of optically thick accretion disks). We find that a standard disk wind model that is successful in reproducing the UV spectra of CVs also leaves a noticeable imprint on the optical spectrum, particularly for systems viewed at high inclination. The strongest optical wind-formed recombination lines are H$\alpha$ and He II $\lambda4686$. We demonstrate that a higher-density outflow model produces all the expected H and He lines and produces a recombination continuum that can fill in the Balmer jump at high inclinations. This model displays reasonable verisimilitude with the optical spectrum of RW Trianguli. No single-peaked emission is seen, although we observe a narrowing of the double-peaked emission lines from the base of the wind. Finally, we show that even denser models can produce a single-peaked H$\alpha$ line. On the basis of our results, we suggest that winds can modify, and perhaps even dominate, the line and continuum emission from CVs.Comment: 15 pages, 13 figures. Accepted to MNRA

SPECT Imaging of Pulmonary Blood Flow in a Rat

Small animal imaging is experiencing rapid development due to its importance in providing high-throughput phenotypic data for functional genomics studies. We have developed a single photon emission computed tomography (SPECT) system to image the pulmonary perfusion distribution in the rat. A standard gamma camera, equipped with a pinhole collimator, was used to acquire SPECT projection images at 40 sec/view of the rat thorax following injection of Tc99m labeled albumin that accumulated in the rat\u27s lungs. A voxel-driven, ordered-subset expectation maximization reconstruction was implemented. Following SPECT imaging, the rat was imaged using micro-CT with Feldkamp conebeam reconstruction. The two reconstructed image volumes were fused to provide a structure/function image of the rat thorax. Reconstruction accuracy and performance were evaluated using numerical simulations and actual imaging of an experimental phantom consisting of Tc99m filled chambers with known diameters and count rates. Full-width half-maximum diameter measurement errors decreased with increasing chamber diameter, ranging from \u3c 6% down to 0.1%. Errors in the ratio of count rate estimates between tubes were also diameter dependent but still relatively small. This preliminary study suggests that SPECT will be useful for imaging and quantifying the pulmonary blood flow distribution and the distribution of Tc99m labeled ligands in the lungs of small laboratory animals