The discrete fragmentation equations : semigroups, compactness and asynchronous exponential growth

In this paper we present a class of fragmentation semigroups which are compact in a scale of spaces defined in terms of finite higher moments. We use this compactness result to analyse the long time behaviour of such semigroups and, in particular, to prove that they have the asynchronous growth property. We note that, despite compactness, this growth property is not automatic as the fragmentation semigroups are not irreducible

Improvements to the APBS biomolecular solvation software suite

The Adaptive Poisson-Boltzmann Solver (APBS) software was developed to solve the equations of continuum electrostatics for large biomolecular assemblages that has provided impact in the study of a broad range of chemical, biological, and biomedical applications. APBS addresses three key technology challenges for understanding solvation and electrostatics in biomedical applications: accurate and efficient models for biomolecular solvation and electrostatics, robust and scalable software for applying those theories to biomolecular systems, and mechanisms for sharing and analyzing biomolecular electrostatics data in the scientific community. To address new research applications and advancing computational capabilities, we have continually updated APBS and its suite of accompanying software since its release in 2001. In this manuscript, we discuss the models and capabilities that have recently been implemented within the APBS software package including: a Poisson-Boltzmann analytical and a semi-analytical solver, an optimized boundary element solver, a geometry-based geometric flow solvation model, a graph theory based algorithm for determining p$K_a$ values, and an improved web-based visualization tool for viewing electrostatics

Development of nondestructive evaluation methods for structural ceramics

Nondestructive evaluation (NDE) methods using three-dimensional microfocus X-ray computed tomographic imaging (3DXCT) were employed to map axial and radial density variations in hot-gas filters and heat exchanger tubes. 3D XCT analysis was conducted on (a) two 38-mm-OD, 6.5-mm wall, SiC/SiC heat exchanger tubes infiltrated by CVI; (b) eight 10 cm diam. oxide/oxide heat exchanger tubes; and (c) one 26-cm-long Nextel fiber/SiC matrix hot-gas filter. The results show that radial and axial density uniformity as well as porosity, can be assessed by 3D XCT. NDE methods are also under development to assess thermal barrier coatings which are under development as methods to protect gas-turbine first-stage hot section metallic substrates. Further, because both shop and field joining of CFCC materials will be necessary, work is now beginning on development of NDE methods for joining

Selectivity and functional diversity in arbuscular mycorrhizas of co-occurring fungi and plants from a temperate deciduous woodland

1 The arbuscular mycorrhizal (AM) fungi colonizing plants at a woodland site in North Yorkshire (UK) have been characterized from the roots of five plant species (Rubus fruticosus agg. L., Epilobium angustifolium L., Acer pseudoplatanus L., Ajuga reptans L. and Glechoma hederacea L.), and identified using small-subunit rRNA (SSUrRNA) gene amplification and sequencing. 2 Interactions between five plant species from the site and four co-occurring glomalean fungi were investigated in artificial one-to-one AM symbioses. Three of the fungi were isolated from the site; the fourth was a culture genetically similar to a taxon found at the site. Phosphorus uptake and growth responses were compared with non-mycorrhizal controls. 3 Individual fungi colonized each plant with different spatial distribution and intensity. Some did not colonize at all, indicating incompatibility under the conditions used in the experiments. 4 Glomus hoi consistently occupied a large proportion of root systems and outperformed the other fungi, improving P uptake and enhancing the growth of four out of the five plant species. Only G. hoi colonized and increased P uptake in Acer pseudoplatanus, the host plant with which it associates almost exclusively under field conditions. Colonization of all plant species by Scutellospora dipurpurescens was sparse, and beneficial to only one of the host plants (Teucrium scorodonia). Archaeospora trappei and Glomus sp. UY1225 had variable effects on the host plants, conferring a range of P uptake and growth benefits on Lysimachia nummularia and T. scorodonia, increasing P uptake whilst not affecting biomass in Ajuga reptans and Glechoma hederacea, and failing to form mycorrhizas with A. pseudoplatanus. 5 These experimental mycorrhizas show that root colonization, symbiont compatibility and plant performance vary with each fungus-plant combination, even when the plants and fungi naturally co-exist. 6 We provide evidence of physical and functional selectivity in AM. The small number of described AM fungal species (154) has been ascribed to their supposed lack of host specificity, but if the selectivity we have observed is the general rule, then we may predict that many more, probably hard-to-culture glomalean species await discovery, or that members of species as currently perceived may be physiologically or functionally distinct

Theory of nuclear induced spectral diffusion: Spin decoherence of phosphorus donors in Si and GaAs quantum dots

We propose a model for spectral diffusion of localized spins in semiconductors due to the dipolar fluctuations of lattice nuclear spins. Each nuclear spin flip-flop is assumed to be independent, the rate for this process being calculated by a method of moments. Our calculated spin decoherence time $T_{M}=0.64$ ms for donor electron spins in Si:P is a factor of two longer than spin echo decay measurements. For $^{31}$P nuclear spins we show that spectral diffusion is well into the motional narrowing regime. The calculation for GaAs quantum dots gives $T_{M}=10-50$ $\mu$s depending on the quantum dot size. Our theory indicates that nuclear induced spectral diffusion should not be a serious problem in developing spin-based semiconductor quantum computer architectures.Comment: 15 pages, 9 figures. Accepted for publication in Phys. Rev.

Observations of Arp 220 using Herschel-SPIRE: An Unprecedented View of the Molecular Gas in an Extreme Star Formation Environment

We present Herschel SPIRE-FTS observations of Arp~220, a nearby ULIRG. The FTS continuously covers 190 -- 670 microns, providing a good measurement of the continuum and detection of several molecular and atomic species. We detect luminous CO (J = 4-3 to 13-12) and water ladders with comparable total luminosity; very high-J HCN absorption; OH+, H2O+, and HF in absorption; and CI and NII. Modeling of the continuum yields warm dust, with T = 66 K, and an unusually large optical depth of ~5 at 100 microns. Non-LTE modeling of the CO shows two temperature components: cold molecular gas at T ~ 50 K and warm molecular gas at T ~1350 K. The mass of the warm gas is 10% of the cold gas, but dominates the luminosity of the CO ladder. The temperature of the warm gas is in excellent agreement with H2 rotational lines. At 1350 K, H2 dominates the cooling (~20 L_sun/M_sun) in the ISM compared to CO (~0.4 L_sun/M_sun). We found that only a non-ionizing source such as the mechanical energy from supernovae and stellar winds can excite the warm gas and satisfy the energy budget of ~20 L_sun/M_sun. We detect a massive molecular outflow in Arp 220 from the analysis of strong P-Cygni line profiles observed in OH+, H2O+, and H2O. The outflow has a mass > 10^{7} M_sun and is bound to the nuclei with velocity < 250 km/s. The large column densities observed for these molecular ions strongly favor the existence of an X-ray luminous AGN (10^{44} ergs/s) in Arp 220.Comment: Accepted in ApJ on September 1, 201

Strangeness production in proton-proton and proton-nucleus collisions

In these lectures we discuss the investigation of the strange meson production in proton-proton ($pp$) and in proton-nucleus ($pA$) reactions within an effective Lagrangian model. The kaon production proceeds mainly via the excitations of $N^*$(1650), $N^*$(1710), and $N^*$(1720) resonant intermediate nucleonic states, in the collision of two initial state nucleons. Therefore, the strangeness production is expected to provide information about the resonances lying at higher excitation energies. For beam energies very close to the kaon production threshold the hyperon-proton final state interaction effects are quite important. Thus, these studies provide a check on the models of hyperon-nucleon interactions. The in-medium production of kaons show strong sensitivity to the self energies of the intermediate mesons.Comment: 16 pages, 9 figures, Talk presented in the workshop on Hadron Physics, Puri, India, March 7-17,200

'You were quiet - I did all the marching': Research processes involved in hearing the voices of South Asian girls

This article is available open access through the publisher’s website at the link below. Copyright @ 2011 A B Academic Publishers.This article provides insights into the outcomes of reflection following two interview approaches used to explore narratives of the lived, individual experiences of South-Asian girls living in West London. In attempting to illuminate and re-present the cultural experiences as told by these girls, the choice of interview approach became critical in allowing the voices to be effectively heard (Rogers, 2005). This article therefore considers how a semi-structured interview approach offered valuable insights into the girls' experiences but became constraining for both researcher and participant in unveiling the complexity and depth of their lives. These constraints emerged through reflection by both participants and researcher. As a result of reflexivity during the research process, the researcher moved towards the use of research conversations during the second phase of the study. Ultimately the study revealed how the girls felt empowered by the opportunity to narrate their individual experiences and tell of their lives. In narrating their reflections on being part of the research, there was a clear recognition that the process facilitated the articulation of new voices and ‘multi-voicedness’ (Moen, 2006

Role of baryonic resonances in the dilepton emission in nucleon-nucleon collisions

Within an effective Lagrangian model, we present calculations for cross sections of the dilepton production in proton-proton and proton-neutron collisions at laboratory kinetic energies in 1-5 GeV range. Production amplitudes include contributions from the nucleon-nucleon bremsstrahlung as well as from the mechanism of excitation, propagation, and radiative decay of Delta(1232) and N*(1520) intermediate baryonic resonances. It is found that the delta isobar terms dominate the cross sections in the entire considered beam energy range. Our calculations are able to explain the data of the DLS collaboration on the dilepton production in proton-proton collisions for beam energies below 1.3 GeV. However, for incident energies higher than this the inclusion of contributions from other dilepton sources like Dalitz decay of pi0 and eta mesons, and direct decay of rho and omega mesons is necessary to describe the data.Comment: 22 pages, 7 figures, more details of the calculations added, version to appear in Phys. Rev