Thermodynamics of a subensemble of a canonical ensemble

Two approaches to describe the thermodynamics of a subsystem that interacts with a thermal bath are considered. Within the first approach, the mean system energy $E_{S}$ is identified with the expectation value of the system Hamiltonian, which is evaluated with respect to the overall (system+bath) equilibrium distribution. Within the second approach, the system partition function $Z_{S}$ is considered as the fundamental quantity, which is postulated to be the ratio of the overall (system+bath) and the bath partition functions, and the standard thermodynamic relation $E_{S}=-d(\ln Z_{S})/d\beta$ is used to obtain the mean system energy. % ($\beta\equiv 1/(k_{B}T)$, $k_{B}$ is the Boltzmann constant, %and $T$ is the temperature). Employing both classical and quantum mechanical treatments, the advantages and shortcomings of the two approaches are analyzed in detail for various different systems. It is shown that already within classical mechanics both approaches predict significantly different results for thermodynamic quantities provided the system-bath interaction is not bilinear or the system of interest consists of more than a single particle. Based on the results, it is concluded that the first approach is superior

Conversation therapy for agrammatism: exploring the therapeutic process of engagement and learning by a person with aphasia.

A recent systematic review of conversation training for communication partners of people with aphasia has shown that it is effective, and improves participation in conversation for people with chronic aphasia. Other research suggests that people with aphasia are better able to learn communication strategies in an environment which closely mirrors that of expected use, and that cognitive flexibility may be a better predictor of response to therapy than severity of language impairment. This study reports results for a single case, one of a case series evaluation of a programme of conversation training for agrammatism that directly involves a person with aphasia (PWA) as well as their communication partner. It explores how a PWA is able to engage with and learn from the therapy, and whether this leads to qualitative change in post-therapy conversation behaviours

ECDIS Development Laboratory and Navigation Technology Demonstration Center

The U.S. Navy is undergoing a major transition from traditional, paper chart navigation to computer-based electronic charting. The Chief of Naval Operations (CNO) has mandated that all Navy ships will navigate strictly through electronic means by FY07. However, due to some recent groundings, the Navy is now striving to accelerate the full implementation of electronic navigation by FY04. The Naval Oceanographic Office (NAVOCEANO) is making a concerted effort to support this transition with upgrades to state-of-the-art survey ships, instrumentation, and data processing equipment. NAVOCEANO is increasing its capability to rapidly collect and process hydrographic survey data, and to quickly produce new electronic navigational charts in co-production with MMA. In addition to ensuring safe navigation, these new products will include tactical digital overlays for bafflespace awareness. At NAVOCEANO, a new program is under development to expand these capabilities in a joint effort with University of Southern Mississippi\u27s new Hydrographic Sciences Research Program. In September 2001, an ECDIS Development Laboratory and Navigation Technology Demonstration Center will be established. This facility will conduct quality assurance (QA) and test and evaluation @&E) of electronic chart products from NAVOCEANO and other hydrographidoceanographic data providers. This facility will also assist Navy ship personnel in gaining a greater understanding of electronic charting, as well as increased technical proficiency in properly using these systems to safely navigate - particularly in the shallow littoral areas of the world. The ECDIS Development Laboratory is envisioned to become an information clearinghouse and demonstration center on electronic charting technological development. In addition to explaining the range of currently available government data products and services, The Navigation Technology Demonstration Center will showcase the use of electronic charts and its capability when used to avoid groundings and collisions at sea. The Center will The U.S. Navy is undergoing a major transition from traditional, paper chart navigation to computer-based electronic charting. The Chief of Naval Operations (CNO) has mandated that all Navy ships will navigate strictly through electronic means by FY07. However, due to some recent groundings, the Navy is now striving to accelerate the full implementation of electronic navigation by FY04. The Naval Oceanographic Office (NAVOCEANO) is making a concerted effort to support this transition with upgrades to state-of-the-art survey ships, instrumentation, and data processing equipment. NAVOCEANO is increasing its capability to rapidly collect and process hydrographic survey data, and to quickly produce new electronic navigational charts in co-production with MMA. In addition to ensuring safe navigation, these new products will include tactical digital overlays for bafflespace awareness. At NAVOCEANO, a new program is under development to expand these capabilities in a joint effort with University of Southern Mississippi\u27s new Hydrographic Sciences Research Program. In September 2001, an ECDIS Development Laboratory and Navigation Technology Demonstration Center will be established. This facility will conduct quality assurance (QA) and test and evaluation @&E) of electronic chart products from NAVOCEANO and other hydrographidoceanographic data providers. This facility will also assist Navy ship personnel in gaining a greater understanding of electronic charting, as well as increased technical proficiency in properly using these systems to safely navigate - particularly in the shallow littoral areas of the world. The ECDIS Development Laboratory is envisioned to become an information clearinghouse and demonstration center on electronic charting technological development. In addition to explaining the range of currently available government data products and services, The Navigation Technology Demonstration Center will showcase the use of electronic charts and its capability when used to avoid groundings and collisions at sea. The Center will The U.S. Navy is undergoing a major transition from traditional, paper chart navigation to computer-based electronic charting. The Chief of Naval Operations (CNO) has mandated that all Navy ships will navigate strictly through electronic means by FY07. However, due to some recent groundings, the Navy is now striving to accelerate the full implementation of electronic navigation by FY04. The Naval Oceanographic Office (NAVOCEANO) is making a concerted effort to support this transition with upgrades to state-of-the-art survey ships, instrumentation, and data processing equipment. NAVOCEANO is increasing its capability to rapidly collect and process hydrographic survey data, and to quickly produce new electronic navigational charts in co-production with MMA. In addition to ensuring safe navigation, these new products will include tactical digital overlays for bafflespace awareness. At NAVOCEANO, a new program is under development to expand these capabilities in a joint effort with University of Southern Mississippi\u27s new Hydrographic Sciences Research Program. In September 2001, an ECDIS Development Laboratory and Navigation Technology Demonstration Center will be established. This facility will conduct quality assurance (QA) and test and evaluation @&E) of electronic chart products from NAVOCEANO and other hydrographidoceanographic data providers. This facility will also assist Navy ship personnel in gaining a greater understanding of electronic charting, as well as increased technical proficiency in properly using these systems to safely navigate - particularly in the shallow littoral areas of the world. The ECDIS Development Laboratory is envisioned to become an information clearinghouse and demonstration center on electronic charting technological development. In addition to explaining the range of currently available government data products and services, The Navigation Technology Demonstration Center will showcase the use of electronic charts and its capability when used to avoid groundings and collisions at sea. The Center will have commercial-off-the-shelf ECDIS and other electronic chartbased systems. A major focus will be to provide a better appreciation of the limitations electronic chart data produced by both the government and private sector that are derived from century-old hydrographic source data. Another important aspect will be to explain the capability and limitations of using very precise electronic navigation positioning systems (e.g., GPS and Differential GPS) with electronic charting systems. The Navigation Technology Center will also demonstrate the use of tactical digital overlays to provide naval vessels with critical military information that contributes to both safe navigation and increased warfrghting mission capability

Ultrafast Dynamic Metallization of Dielectric Nanofilms by Strong Single-Cycle Optical Fields

We predict a dynamic metallization effect where an ultrafast (single-cycle) optical pulse with a field less or on the order of 1 V/Angstrom causes plasmonic metal-like behavior of a dielectric film with a few-nm thickness. This manifests itself in plasmonic oscillations of polarization and a significant population of the conduction band evolving on a femtosecond time scale. These phenomena are due a combination of both adiabatic (reversible) and diabatic (for practical purposes irreversible) pathways.Comment: 4 pages, 4 figure

Indirect Detection of Little Higgs Dark Matter

Little Higgs models with T parity contain an attractive dark matter candidate, the heavy photon. We compute the cross section of the heavy photon annihilation into Z-photon pairs, which turns out to be substantially higher than the previously computed cross section for the two photon final state. Unfortunately, even with this enhancement, the monochromatic photon flux from galactic heavy photon annihilation is unlikely to be detectable by GLAST or the currently operating atmospheric Cerenkov telescopes. We also compute the flux of high-energy neutrinos from the annihilation of the heavy photons captured by the Sun and the Earth. The maximum flux of upward-going muons due to such neutrinos is about 1 yr^{-1}km^{-2}.Comment: 13 pages, 3 figure

Abell 754: A Non-Head On Collision of Subclusters

We have analyzed spatially resolved spectra of A754 obtained with ASCA. The combination of spectral and imaging capabilities of ASCA has set unprecedented constraints on the hydrodynamical effects of a cluster merger. We find significant gas temperature variations over the cluster face, indicating shock heating of the atmosphere during the merger. The hottest region, >12 keV, is located in the region of the Northwest galaxy clump though the entire region along the cluster axis appears to be hotter than the mean cluster temperature (~9 keV). The cool, ~5 keV gas originally found with the HEAO1-A2 experiment, resides in the exterior of the cluster atmosphere and in plume of gas we identify with a stripped cool atmosphere of the infalling subcluster. We have also attempted to reconstruct an iron abundance map of this merging system. Though poorly constrained, no significant deviations of abundance from the mean value are apparent in the individual regions. A754 is the only cluster so far which shows the significant temperature pattern expected in a subcluster merger, in both the ROSAT (Henry & Briel 1995) and ASCA data, providing the first possibility to compare it with theoretical predictions. The observed temperature and surface brightness maps suggest that the two colliding subunits have missed each other by about 1 Mpc, and are now moving perpendicular to the cluster axis in the image plane (as, e.g., in the simulations by Evrard etal 1996).Comment: Latex, 10 pages, 3 figures incl. color plate, uses aaspp4.sty, flushrt.sty and pstricks.sty. Submitted to ApJ Letter

Compressed sensing performance bounds under Poisson noise

This paper describes performance bounds for compressed sensing (CS) where the underlying sparse or compressible (sparsely approximable) signal is a vector of nonnegative intensities whose measurements are corrupted by Poisson noise. In this setting, standard CS techniques cannot be applied directly for several reasons. First, the usual signal-independent and/or bounded noise models do not apply to Poisson noise, which is non-additive and signal-dependent. Second, the CS matrices typically considered are not feasible in real optical systems because they do not adhere to important constraints, such as nonnegativity and photon flux preservation. Third, the typical $\ell_2$--$\ell_1$ minimization leads to overfitting in the high-intensity regions and oversmoothing in the low-intensity areas. In this paper, we describe how a feasible positivity- and flux-preserving sensing matrix can be constructed, and then analyze the performance of a CS reconstruction approach for Poisson data that minimizes an objective function consisting of a negative Poisson log likelihood term and a penalty term which measures signal sparsity. We show that, as the overall intensity of the underlying signal increases, an upper bound on the reconstruction error decays at an appropriate rate (depending on the compressibility of the signal), but that for a fixed signal intensity, the signal-dependent part of the error bound actually grows with the number of measurements or sensors. This surprising fact is both proved theoretically and justified based on physical intuition.Comment: 12 pages, 3 pdf figures; accepted for publication in IEEE Transactions on Signal Processin

Kinetic energy cascades in quasi-geostrophic convection in a spherical shell

We consider triadic nonlinear interaction in the Navier-Stokes equation for quasi-geostrophic convection in a spherical shell. This approach helps understanding the origin of kinetic energy transport in the system and the particular scheme of mode interaction, as well as the locality of the energy transfer. The peculiarity of convection in the sphere, concerned with excitation of Rossby waves, is considered. The obtained results are compared with our previous study in Cartesian geometry