Quasi-particle spectra, absorption spectra, and excitonic properties of sodium iodide and strontium iodide from many-body perturbation theory

We investigate the basic quantum mechanical processes behind non-proportional response of scintillators to incident radiation responsible for reduced resolution. For this purpose, we conduct a comparative first principles study of quasiparticle spectra on the basis of the $G_0W_0$ approximation as well as absorption spectra and excitonic properties by solving the Bethe-Salpeter equation for two important systems, NaI and SrI$_2$. The former is a standard scintillator material with well-documented non-proportionality while the latter has recently been found to exhibit a very proportional response. We predict band gaps for NaI and SrI$_2$ of 5.5 and 5.2 eV, respectively, in good agreement with experiment. Furthermore, we obtain binding energies for the groundstate excitons of 216 meV for NaI and 195$\pm$25 meV for SrI$_2$. We analyze the degree of exciton anisotropy and spatial extent by means of a coarse-grained electron-hole pair-correlation function. Thereby, it is shown that the excitons in NaI differ strongly from those in SrI$_2$ in terms of structure and symmetry, even if their binding energies are similar. Furthermore, we show that quite unexpectedly the spatial extents of the highly anisotropic low-energy excitons in SrI$_2$ in fact exceed those in NaI by a factor of two to three in terms of the full width at half maxima of the electron-hole pair-correlation function.Comment: 10 pages, 9 figure

LDRD Final Report (08-ERD-037): Important Modes to Drive Protein MD Simulations to the Next Conformational Level

Every action in biology is performed by dynamic proteins that convert between multiple states in order to engage their functions. Often binding to various ligands is essential for the rates of desired transitions to be enhanced. The goal of computational biology is to study these transitions and discover the different states to fully understand the protein's normal and diseased function, design drugs to target/bias specific states, and understand all of the interactions in between. We have developed a new methodology that is capable of calculating the absolute free energy of proteins while taking into account all the interactions with the solvent molecules. The efficiency of the new scheme is an order of magnitude greater than any existing technique. This method is now implemented in the massively parallel popular MD program package NAMD. This now makes it possible to calculate the relative stability of different conformational states of biological macromolecules as well as their binding free energies to various ligands

Coordinating Community Healthcare Needs to Local Services in Paraiso, Dominican Republic Through Strategic Assessment Strategies

Background: The availability of healthcare services is limited in Paraiso, Dominican Republic with the nearest full-service hospital located 34.1 km away. A local, underutilized clinic was unaware of the needs of this disadvantaged community. Method: Researchers adapted a World Health Organization assessment survey with the goals of determining residents’ priority needs and an appraisal of the current clinic capabilities and gaps in services in order to provide the community with relevant healthcare. 106 families were randomly selected in seven separate geographic areas of Paraiso to participate in the self-report assessment. Researchers, along with a community volunteer, conducted interviews utilizing the 63 question instrument. 105 families agreed to participate representing 504 individuals

Ab initio prediction of fast non-equilibrium transport of nascent polarons in SrI2: a key to high-performance scintillation

The excellent light yield proportionality of europium-doped strontium iodide (SrI2:Eu) has resulted in state-of-the-art γ-ray detectors with remarkably high-energy resolution, far exceeding that of most halide compounds. In this class of materials, the formation of self-trapped hole polarons is very common. However, polaron formation is usually expected to limit carrier mobilities and has been associated with poor scintillator light-yield proportionality and resolution. Here using a recently developed first-principles method, we perform an unprecedented study of polaron transport in SrI2, both for equilibrium polarons, as well as nascent polarons immediately following a self-trapping event. We propose a rationale for the unexpected high-energy resolution of SrI2. We identify nine stable hole polaron configurations, which consist of dimerised iodine pairs with polaron-binding energies of up to 0.5 eV. They are connected by a complex potential energy landscape that comprises 66 unique nearest-neighbour migration paths. Ab initio molecular dynamics simulations reveal that a large fraction of polarons is born into configurations that migrate practically barrier free at room temperature. Consequently, carriers created during γ-irradiation can quickly diffuse away reducing the chance for non-linear recombination, the primary culprit for non-proportionality and resolution reduction. We conclude that the flat, albeit complex, landscape for polaron migration in SrI2 is a key for understanding its outstanding performance. This insight provides important guidance not only for the future development of high-performance scintillators but also of other materials, for which large polaron mobilities are crucial such as batteries and solid-state ionic conductors

Creep behaviour and tensile response of adhesively bonded polyethylene joints: Single-Lap and Double-Strap

The static and time-dependent behaviours of adhesively bonded polyethylene Double-Strap (DS) joints were investigated to assess the viability of this joint configuration relative to the Single-Lap (SL) joints. Both experiments and finite element simulations are conducted. First, we individually characterise the tensile and creep behaviour of the adhesive and adherent materials; an epoxy-based adhesive and polyethylene, respectively. This information is used to develop suitable constitutive models that are then implemented in the commercial finite element package ABAQUS by means of user material subroutines, UMATs. The numerical models are used to design the creep tests on the adhesive joints. Afterwards, an extensive experimental campaign is conducted where we characterise the static and creep behaviour of two joint configurations, SL and DS joints, and three selected values of the overlap length. In regard to the static case, results reveal an increase in the failure load with increasing overlap length, of up to 10% for an overlap length of 39 mm. Also, slightly better performance is observed for the SL joint configuration. For the creep experiments, we show that the DS adhesive joint configuration leads to much shorter elongations, relative to the SL joints. These differences diminish with increasing overlap length but remain substantial in all cases. In both joint configurations, the elongation increases with decreasing overlap length. For instance, increasing the overlap length to 39 mm led to a 50% and a 30% reduction in elongation for SL and DS joints, respectively. Moreover, the numerical predictions show a good agreement with the experiments. The stress redistribution is investigated and it is found that the shear stress is highly sensitive to the testing time, with differences being more noticeable for the DS joint system

Thermodynamic ground states of platinum metal nitrides

We have systematically studied the thermodynamic stabilities of various phases of the nitrides of the platinum metal elements using density functional theory. We show that for the nitrides of Rh, Pd, Ir and Pt two new crystal structures, in which the metal ions occupy simple tetragonal lattice sites, have lower formation enthalpies at ambient conditions than any previously proposed structures. The region of stability can extend up to 17 GPa for PtN{sub 2}. Furthermore, we show that according to calculations using the local density approximation, these new compounds are also thermodynamically stable at ambient pressure and thus may be the ground state phases for these materials. We further discuss the fact that the local density and generalized gradient approximations predict different values of the absolute formation enthalpies as well different relative stabilities between simple tetragonal and the pyrite or marcasite structures

Expression of biologically active measles virus hemagglutinin glycoprotein by a recombinant baculovirus

In this study, one of the measles virus membrane proteins, named hemagglutinin (H) which has a key role in tropism, receptor binding, hemagglutinating activity and also induction of protective immunity against viral infection, was expressed by the baculovirus expression system using specific plasmid (pDONR221) to produce entry clone. Measles Virus (AIK-C strain) genome was extracted from infected Vero cells. H gene was amplified by specific primers during RT-PCR reaction and inserted into the specific plasmid (pDONR221) using BP recombination reaction. Recombinant baculovirus harboring H gene was consequently constructed by LR reaction. Insect cells (Sf9) were infected with recombinant baculovirus. In order to increase viral titer, recombinant baculoviruses were passaged four times in Sf9 cells. Synthesis of H protein was verified by SDS-PAGE, western-blot and indirect immunoflourescene using goat polyclonal antibody against Measles Virus. The results showed that H protein was partially glycosylated but it appeared to be active in hemagglutination assay. © 2008 Asian Network for Scientific Information

A suggested prototype for assessing bone health

Background- Osteoporosis is becoming a health concern worldwide. Considering the fact that prevention plays an important role in reducing the burden of this silent disease and in view of the limited resources available, many countries have adopted certain programs to fight osteoporosis through shifting their attention towards at-risk individuals. The Iranian Multicenter Osteoporosis Study (IMOS) is one of these programs. The program aims to assess bone health and the prevalence of vitamin D deficiency in different parts of Iran with various altitudes, latitudes and lifestyle habits in a way that the results could be generalized to the country. Method- The present article presents the protocol used in the third phase of the study. It was designed based on the experiences gathered in the previous phases to overcome the shortcomings particularly subject loss. The questionnaire applied in this study was developed based on a thorough literature review of the risk factors and secondary causes of osteoporosis and was approved by an expert panel. It should be added that while the majority of the existing studies aim to study a certain aspect of osteoporosis, the present protocol provides the information needed for policy makers and researchers to study different osteoporosis-related issues. Conclusion- The authors believe the protocol, to be implemented with small modifications, can help policymakers in different parts of the world, particularly developing countries, gather accurate information on different aspects of bone health at the national level. © 2015, Academy of Medical Sciences of I.R. Iran. All rights reserved