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Sample records for metallic target theory

  1. A generalized target theory and its applications

    PubMed Central

    Zhao, Lei; Mi, Dong; Hu, Bei; Sun, Yeqing

    2015-01-01

    Different radiobiological models have been proposed to estimate the cell-killing effects, which are very important in radiotherapy and radiation risk assessment. However, most applied models have their own scopes of application. In this work, by generalizing the relationship between “hit” and “survival” in traditional target theory with Yager negation operator in Fuzzy mathematics, we propose a generalized target model of radiation-induced cell inactivation that takes into account both cellular repair effects and indirect effects of radiation. The simulation results of the model and the rethinking of “the number of targets in a cell” and “the number of hits per target” suggest that it is only necessary to investigate the generalized single-hit single-target (GSHST) in the present theoretical frame. Analysis shows that the GSHST model can be reduced to the linear quadratic model and multitarget model in the low-dose and high-dose regions, respectively. The fitting results show that the GSHST model agrees well with the usual experimental observations. In addition, the present model can be used to effectively predict cellular repair capacity, radiosensitivity, target size, especially the biologically effective dose for the treatment planning in clinical applications. PMID:26411887

  2. Fuel cells and the theory of metals.

    NASA Technical Reports Server (NTRS)

    Bocciarelli, C. V.

    1972-01-01

    Metal theory is used to study the role of metal catalysts in electrocatalysis, with particular reference to alkaline hydrogen-oxygen fuel cells. Use is made of a simple model, analogous to that used to interpret field emission in vacuum. Theoretical values for all the quantities in the Tafel equation are obtained in terms of bulk properties of the metal catalysts (such as free electron densities and Fermi level). The reasons why some processes are reversible (H-electrodes) and some irreversible (O-electrodes) are identified. Selection rules for desirable properties of catalytic materials are established.

  3. Theory of spin relaxation at metallic interfaces

    NASA Astrophysics Data System (ADS)

    Belashchenko, K. D.; Kovalev, Alexey A.; van Schilfgaarde, Mark

    Spin-flip scattering at metallic interfaces affects transport phenomena in nanostructures, such as magnetoresistance, spin injection, spin pumping, and spin torques. It has been characterized for many material combinations by an empirical parameter δ, which is obtained by matching magnetoresistance data for multilayers to the Valet-Fert model [J. Bass and W. P. Pratt, J. Phys.: Condens. Matter 19, 183201 (2007)]. However, the relation of the parameter δ to the scattering properties of the interface remains unclear. Here we establish this relation using the scattering theory approach and confirm it using a generalization of the magnetoelectronic circuit theory, which includes interfacial spin relaxation. The results of first-principles calculations of spin-flip scattering at the Cu/Pd and Cu/Pt interfaces are found to be in reasonable agreement with experimental data. Supported by NSF Grant DMR-1308751.

  4. Theory of Defect Interactions in Metals.

    NASA Astrophysics Data System (ADS)

    Thetford, Roger

    Available from UMI in association with The British Library. Requires signed TDF. The static relaxation program DEVIL has been updated to use N-body Finnis-Sinclair potentials. Initial calculations of self-interstitial and monovacancy formation energies confirm that the modified program is working correctly. An extra repulsive pair potential (constructed to leave the original fitting unaltered) overcomes some deficiencies in the published Finnis-Sinclair potentials. The modified potentials are used to calculate interstitial energies and relaxations in the b.c.c. transition metals vanadium, niobium, tantalum, molybdenum and tungsten. Further adaptation enables DEVIL to model dislocations running parallel to any lattice vector. Periodic boundary conditions are applied in the direction of the dislocation line, giving an infinite straight dislocation. The energies per unit length of two different dislocations are compared with experiment. A study of migration of point defects in the perfect lattice provides information on the mobility of interstitials and vacancies. The possible reorientation of split dumbbell interstitials in a migration step comes under scrutiny. The total energy needed to form and migrate an interstitial is compared with that required for a vacancy. The interaction between point defects and dislocations is studied in detail. Binding energies for both self-interstitials and monovacancies at edge dislocations are calculated for the five metals mentioned above. Formation energies of the point defects in the neighbourhood of the edge dislocation are calculated for niobium, and the extent of the regions from which the defects are spontaneously absorbed are found. For split dumbbell interstitials, the size and shape of the absorption region depends on the orientation of the dumbbell. Migration of both interstitials and vacancies into the absorption zone is studied; the presence of the dislocation has a particularly dramatic effect on vacancy migration. The

  5. Classical theory for second-harmonic generation from metallic nanoparticles

    SciTech Connect

    Zeng Yong; Liu Jinjie; Moloney, Jerome V.; Hoyer, Walter; Koch, Stephan W.

    2009-06-15

    In this paper, we develop a classical electrodynamic theory to study the optical nonlinearities of metallic nanoparticles. The quasi free electrons inside the metal are approximated as a classical Coulomb-interacting electron gas, and their motion under the excitation of an external electromagnetic field is described by the plasma equations. This theory is further tailored to study second-harmonic generation. Through detailed experiment-theory comparisons, we validate this classical theory as well as the associated numerical algorithm. It is demonstrated that our theory not only provides qualitative agreement with experiments but it also reproduces the overall strength of the experimentally observed second-harmonic signals.

  6. Mitochondrial metals as a potential therapeutic target in neurodegeneration

    PubMed Central

    Grubman, A; White, A R; Liddell, J R

    2014-01-01

    Transition metals are critical for enzyme function and protein folding, but in excess can mediate neurotoxic oxidative processes. As mitochondria are particularly vulnerable to oxidative damage due to radicals generated during ATP production, mitochondrial biometal homeostasis must therefore be tightly controlled to safely harness the redox potential of metal enzyme cofactors. Dysregulation of metal functions is evident in numerous neurological disorders including Alzheimer's disease, stroke, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis and Friedrich's ataxia. This review describes the mitochondrial metal defects in these disorders and highlights novel metal-based therapeutic approaches that target mitochondrial metal homeostasis in neurological disorders. Linked Articles This article is part of a themed issue on Mitochondrial Pharmacology: Energy, Injury & Beyond. To view the other articles in this issue visit http://dx.doi.org/10.1111/bph.2014.171.issue-8 PMID:24206195

  7. XUV spectroscopy of laser plasma from molecular coated metal targets

    NASA Astrophysics Data System (ADS)

    Papanyan, Valeri O.; Nersisyan, Gagik T.; Tittel, Frank K.

    1999-12-01

    Metal targets covered by micrometer layers of metal- phthalocyanines or fullerenes are studied here. An increase in XUV yield due to the optimized absorption of the laser field is reported. Effects of high-temperature plasma rapid expansion (velocity about 106 cm/s) were observed. Moderate power nanosecond and picosecond neodymium lasers are used to produce an incident intensity of 1011 to 1013 W/cm2 on the targets. The plasma electron density was measured by fitting observed spectral profiles to the theoretical profiles. Collisional, Doppler, and Stark broadening mechanisms were considered in the calculations. Our measurement technique permits us to determine the electron density and temperature dependence on distances from the target surface from 1 mm (where Ne approximately equals 1018 cm-3 and Te approximately equals 14 eV are measured for aluminum plasma) up to approximately 5 mm (where Ne targets is greater by a factor of approximately 1.5 than measured from bulk solid metal targets.

  8. XUV spectroscopy of laser plasma from molecular coated metal targets

    NASA Astrophysics Data System (ADS)

    Papanyan, Valeri O.; Nersisyan, Gagik T.; Tittel, Frank K.

    1999-10-01

    Metal targets covered by micrometer layers of metal- phthalocyanines are studied here. An increase in EUV yield due to optimized absorption of the laser field is reported. Effects of high-temperature plasma rapid expansion (velocity about 106 cm/s) were observed. Moderate power nanosecond and picosecond neodymium lasers are used to product an incident intensity of 1011 to 1013 W/cm2 on the targets. The plasma electron density was measured by fitting observed spectral profiles to theoretical profiles. Collisional, Doppler, and Stark broadening mechanisms were considered in the calculations. Our measurement technique makes it possible to determine the electron density and temperature dependence on distances from the target surface from 1 mm (where Ne equals 2.0 (+/- 0.5)1018 cm-3 and Te equals 14 eV are measured for aluminum plasma) up to approximately 5 mm (where Ne targets is greater by a factor of approximately 1.5 than measured from bulk solid metal targets.

  9. Infrared small target detection based on Danger Theory

    NASA Astrophysics Data System (ADS)

    Lan, Jinhui; Yang, Xiao

    2009-11-01

    To solve the problem that traditional method can't detect the small objects whose local SNR is less than 2 in IR images, a Danger Theory-based model to detect infrared small target is presented in this paper. First, on the analog with immunology, the definition is given, in this paper, to such terms as dangerous signal, antigens, APC, antibodies. Besides, matching rule between antigen and antibody is improved. Prior to training the detection model and detecting the targets, the IR images are processed utilizing adaptive smooth filter to decrease the stochastic noise. Then at the training process, deleting rule, generating rule, crossover rule and the mutation rule are established after a large number of experiments in order to realize immediate convergence and obtain good antibodies. The Danger Theory-based model is built after the training process, and this model can detect the target whose local SNR is only 1.5.

  10. A Continuum Theory for Shock Induced Heating of Metalized Explosive

    NASA Astrophysics Data System (ADS)

    Gonthier, Keith; Chakravarthy, Sunada; Rumchik, Chad

    2009-06-01

    A well-developed continuum field theory for Deflagration-to-Detonation Transition (DDT) in granular explosive is generalized to account for the existence of an arbitrary number of condensed phases and a gas product phase. Formulation of the more generic theory is motivated by a desire to model both the low and high pressure impact response of metalized explosive for which the metal and explosive grains may have distinct average densities, velocities, temperatures, and sizes. The theory is consistent with the strong form of the dissipation inequality and allows for flexible partitioning of dissipation between phases. The theory is applied to inert impact of aluminized HMX in the limit of low gas pressure. Emphasis is placed on characterizing the spatial structure of planar deformation waves and its dependence on impact speed and initial metal mass fraction.

  11. On Pressure Wave Simulations in Liquid Metal Neutron Source Targets

    NASA Astrophysics Data System (ADS)

    Fetzer, Jana R.; Class, Andreas

    2014-11-01

    Sound waves generated by fluid flow at low Mach numbers is associated with separated scales and thus with difficulties to construct efficient numerical methods for their approximation. One method is the Multi Pressure Variables (MPV) approach introduced for aero-acoustic applications. The MPV approach is based on a single time scale multiple space scale asymptotic analysis derived for subsonic flow by an asymptotic series expansion in the Mach-number. Distinguished are the flow and acoustic length scales resulting in three pressure contribution, i.e. thermodynamic, acoustic and dynamic pressure which are discretized on numerical meshes of different resolution. We propose to apply MPV to analyse liquid metal cooled spallation targets with a pulsed proton beams. These targets are operating in high power neutron sources for fundamental research. The nearly instantaneous heating of the liquid metal results in volumetric expansion of inertia confined liquid and thus to high pressure waves, which represent a major lifetime limiting thread. Our development accompanies design activities for the META:LIC (MEgawatt TArget: Lead bIsmuth Cooled) target proposed for the European Spallation Source.

  12. Dislocation Theory of the Fatigue of Metals

    NASA Technical Reports Server (NTRS)

    Machlin, E S

    1949-01-01

    A dislocation theory of fatigue failure for annealed solid solutions is presented. On the basis of this theory, an equation giving the dependence of the number of cycles for failure on the stress, the temperature, the material parameters, and the frequency is derived for uniformly stressed specimens. The equation is in quantitative agreement with the data. Inasmuch as one material parameter is indicated to be temperature-dependent and its temperature dependence is unknown, it is impossible to predict the temperature dependence of the number of cycles for failure. A predicted quantitative correlation between fatigue and creep was found to exist, which suggests the practical possibility of obtaining fatigue data for annealed solid solutions and elements from steady-state creep-rate data for these materials. As a result of this investigation, a modification of the equation for the steady-state creep rate previously developed on the basis of the dislocation theory is suggested. Additional data are required to verify completely the dislocation theory of fatigue.

  13. Metal coatings for laser fusion targets by electroplating

    SciTech Connect

    Illige, J.D.; Yu, C.M.; Letts, S.A.

    1980-08-26

    Metal coated laser fusion targets must be dense, uniform spherically symmetric to within a few percent of their diameters and smooth to better than a few tenths of a micron. Electroplating offers some unique advantages including low temperature deposition, a wide choice of elements and substantial industrial plating technology. We have evaluatd electroless and electroplating systems for gold and copper, identified the factors responsible for small grain size, and plated glass microspheres with both metals to achieve smooth surfaces and highly symmetric coatings. We have developed plating cells which sustain the microspheres in continuous random motion during plating. We have established techniques for deposition of the initial conductive adherent layer on the glass microsphere surface. Coatings as thick as 15 ..mu..m have been made. The equipment is simple, relatively inexpensive and may be adopted for high volume production of laser fusion targets.

  14. Analytical theory of extraordinary optical transmission through realistic metallic screens.

    PubMed

    Delgado, V; Marqués, R; Jelinek, L

    2010-03-29

    An analytical theory of extraordinary optical transmission (EOT) through realistic metallic screens perforated by a periodic array of subwavelength holes is presented. The theory is based on our previous work on EOT through perfect conducting screens and on the surface impedance concept. The proposed theory is valid for the complete frequency range where EOT has been reported, including microwaves and optics. A reasonably good agreement with electromagnetic simulations is shown in all this frequency range. We feel that the proposed theory may help to clarify the physics underlying EOT and serve as a first step to more accurate analysis.

  15. Specific capture of uranyl protein targets by metal affinity chromatography.

    PubMed

    Basset, Christian; Dedieu, Alain; Guérin, Philippe; Quéméneur, Eric; Meyer, Daniel; Vidaud, Claude

    2008-03-28

    To improve general understanding of biochemical mechanisms in the field of uranium toxicology, the identification of protein targets needs to be intensified. Immobilized metal affinity chromatography (IMAC) has been widely developed as a powerful tool for capturing metal binding proteins from biological extracts. However uranyl cations (UO2(2+)) have particular physico-chemical characteristics which prevent them from being immobilized on classical metal chelating supports. We report here on the first development of an immobilized uranyl affinity chromatography method, based on the cation-exchange properties of aminophosphonate groups for uranyl binding. The cation distribution coefficient and loading capacity on the support were determined. Then the stability of the uranyl-bonded phase under our chromatographic conditions was optimized to promote affinity mechanisms. The successful enrichment of uranyl binding proteins from human serum was then proven using proteomic and mass spectral analysis. PMID:18308325

  16. Compatibility of materials with liquid metal targets for SNS

    SciTech Connect

    DiStefano, J.R.; Pawel, S.J.; DeVan, J.H.

    1996-06-01

    Several heavy liquid metals are candidates as the target in a spallation neutron source: Hg, Pb, Bi, and Pb-Bi eutectic. Systems with these liquid metals have been used in the past and a data-base on compatibility already exists. Two major compatibility issues have been identified when selecting a container material for these liquid metals: temperature gradient mass transfer and liquid metal embrittlement or LME. Temperature gradient mass transfer refers to dissolution of material from the high temperature portions of a system and its deposition in the lower temperature areas. Solution and deposition rate constants along with temperature, {Delta}T, and velocity are usually the most important parameters. For most candidate materials mass transfer corrosion has been found to be proportionately worse in Bi compared with Hg and Pb. For temperatures to {approx}550{degrees}C, ferritic/martensitic steels have been satisfactory in Pb or Hg systems and the maximum temperature can be extended to {approx}650{degrees}C with additions of inhibitors to the liquid metal, e.g. Mg, Ti, Zr. Above {approx}600{degrees}C, austenitic stainless steels have been reported to be unsatisfactory, largely because of the mass transfer of nickel. Blockage of flow from deposition of material is usually the life-limiting effect of this type of corrosion. However, mass transfer corrosion at lower temperatures has not been studied. At low temperatures (usually < 150{degrees}C), LME has been reported for some liquid metal/container alloy combinations. Liquid metal embrittlement, like hydrogen embrittlement, results in brittle fracture of a normally ductile material.

  17. The vascular system as a target of metal toxicity.

    PubMed

    Prozialeck, Walter C; Edwards, Joshua R; Nebert, Daniel W; Woods, James M; Barchowsky, Aaron; Atchison, William D

    2008-04-01

    Vascular system function involves complex interactions among the vascular endothelium, smooth muscle, the immune system, and the nervous system. The toxic metals cadmium (Cd), arsenic (As), and lead (Pb) can target the vascular system in a variety of ways, ranging from hemorrhagic injury to subtle pathogenic remodeling and metabolic changes. Acute Cd exposure results in hemorrhagic injury to the testis, although some strains of animals are resistant to this effect. A comparison of Cd-sensitive with Cd-resistant mouse strains showed that expression of the Slc39a8 gene, encoding the ZIP8 transporter, in the testis vasculature endothelium is responsible for this difference. Endogenously, ZIP8 is a Mn(2+)/HCO(3)(-)symporter that may also contribute to Cd damage in the kidney. Chronic Cd exposure is associated with various cardiovascular disorders such as hypertension and cardiomyopathy and it is reported to have both carcinogenic and anticarcinogenic activities. At noncytotoxic concentrations of 10-100nM, Cd can inhibit chemotaxis and tube formation of vascular endothelial cells. These angiostatic effects may be mediated through disruption of vascular endothelial cadherin, a Ca(2+)-dependent cell adhesion molecule. With regard to As, ingestion of water containing disease-promoting concentrations of As promotes capillarization of the liver sinusoidal endothelium. Because capillarization is a hallmark precursor for liver fibrosis and contributes to an imbalance of lipid metabolism, this As effect on hepatic endothelial cells may be a pathogenic mechanism underlying As-related vascular diseases. With regard to Pb, perinatal exposure may cause sustained elevations in adult blood pressure, and genetically susceptible animals may show enhanced sensitivity to this effect. Taken together, these data indicate that the vascular system is a critical target of metal toxicity and that actions of metals on the vascular system may play important roles in mediating the

  18. The Vascular System as a Target of Metal Toxicity

    PubMed Central

    Prozialeck, Walter C.; Edwards, Joshua R.; Nebert, Daniel W.; Woods, James M.; Barchowsky, Aaron; Atchison, William D.

    2009-01-01

    Vascular system function involves complex interactions among the vascular endothelium, smooth muscle, the immune system, and the nervous system. The toxic metals cadmium (Cd), arsenic (As), and lead (Pb) can target the vascular system in a variety of ways, ranging from hemorrhagic injury to subtle pathogenic remodeling and metabolic changes. Acute Cd exposure results in hemorrhagic injury to the testis, although some strains of animals are resistant to this effect. A comparison of Cd-sensitive with Cd-resistant mouse strains showed that expression of the Slc39a8 gene, encoding the ZIP8 transporter, in the testis vasculature endothelium is responsible for this difference. Endogenously, ZIP8 is a Mn2+/HCO3−symporter that may also contribute to Cd damage in the kidney. Chronic Cd exposure is associated with various cardiovascular disorders such as hypertension and cardiomyopathy and it is reported to have both carcinogenic and anticarcinogenic activities. At noncytotoxic concentrations of 10–100nM, Cd can inhibit chemotaxis and tube formation of vascular endothelial cells. These angiostatic effects may be mediated through disruption of vascular endothelial cadherin, a Ca2+-dependent cell adhesion molecule. With regard to As, ingestion of water containing disease-promoting concentrations of As promotes capillarization of the liver sinusoidal endothelium. Because capillarization is a hallmark precursor for liver fibrosis and contributes to an imbalance of lipid metabolism, this As effect on hepatic endothelial cells may be a pathogenic mechanism underlying As-related vascular diseases. With regard to Pb, perinatal exposure may cause sustained elevations in adult blood pressure, and genetically susceptible animals may show enhanced sensitivity to this effect. Taken together, these data indicate that the vascular system is a critical target of metal toxicity and that actions of metals on the vascular system may play important roles in mediating the pathophysiologic

  19. Scaling theory of phase-coherent metallic conductors

    NASA Astrophysics Data System (ADS)

    Macêdo, A. M.

    2002-07-01

    We present a scaling theory for describing the smooth crossover from ballistic to diffusive transport in phase-coherent metallic conductors. The theory confirms a recent conjecture by Beenakker [Rev. Mod. Phys. 69, 731 (1997)], and represents a substantial improvement in the two-terminal version of Nazarov's circuit theory [Phys. Rev. Lett. 73, 134 (1994); 73, 1420 (1994)]. In addition, our approach allows for the explicit inclusion of interfaces of arbitrary transparency, which are described using the supersymmetric nonlinear σ model. The problem of two identical barriers separated by a diffusive conductor is solved exactly, and expressions for both the normal and Andreev conductances are presented.

  20. Biological metals and metal-targeting compounds in major neurodegenerative diseases.

    PubMed

    Barnham, Kevin J; Bush, Ashley I

    2014-10-01

    Multiple abnormalities occur in the homeostasis of essential endogenous brain biometals in age-related neurodegenerative disorders, Alzheimer's disease, Parkinson's disease, Huntington's disease and amyotrophic lateral sclerosis. As a result, metals both accumulate in microscopic proteinopathies, and can be deficient in cells or cellular compartments. Therefore, bulk measurement of metal content in brain tissue samples reveal only the "tip of the iceberg", with most of the important changes occurring on a microscopic and biochemical level. Each of the major proteins implicated in these disorders interacts with biological transition metals. Tau and the amyloid protein precursor have important roles in normal neuronal iron homeostasis. Changes in metal distribution, cellular deficiencies, or sequestration in proteinopathies all present abnormalities that can be corrected in animal models by small molecules. These biochemical targets are more complex than the simple excess of metals that are targeted by chelators. In this review we illustrate some of the richness in the science that has developed in the study of metals in neurodegeneration, and explore its novel pharmacology.

  1. Nanostructured target fabrication with metal and semiconductor nanoparticles

    NASA Astrophysics Data System (ADS)

    Barberio, M.; Antici, P.

    2015-10-01

    The development of ultra-intense high-energy (≫1 J) short (<1 ps) laser pulses in the last decade has enabled the acceleration of high-energy short-pulse proton beams. A key parameter for enhancing the acceleration regime is the laser-to-target absorption, which heavily depends on the target structure and material. In this work, we present the realization of a nanostructured target with a sub-laser wavelength nano-layer in the front surface as a possible candidate for improving the absorption. The nanostructured film was realized by a simpler and cheaper method than using conventional lithographic techniques: A colloidal solution of metallic or semiconductor nanoparticles (NPs) was produced by laser ablation and, after a heating and sonication process, was spray-dried on the front surface of an aluminum target. The obtained nanostructured film with a thickness of 1 μm appears, at morphological and chemical analysis, uniformly nanostructured and distributed on the target surface without the presence of oxides or external contaminants. Finally, the size of the NPs can be tuned from tens to hundreds of nanometers simply by varying the growth parameters (i.e., irradiation time, fluence, and laser beam energy).

  2. Cancer targeted metallic nanoparticle: targeting overview, recent advancement and toxicity concern.

    PubMed

    Akhter, Sohail; Ahmad, Zaki; Singh, Anjali; Ahmad, Iqbal; Rahman, Mahfoozur; Anwar, Mohammad; Jain, Gaurav Kumar; Ahmad, Farhan Jalees; Khar, Roop Krishen

    2011-01-01

    The targeted delivery of theranostic agents to the cancer cells is one of the major challenges and an active field of research in the development of cancer chemotherapeutic approaches. Theranostic metallic nanoparticles (TMNPs) have garnered increasing attention in recent years as a novel tool for theranostic application such as imaging, diagnosis, and therapeutic delivery of active agents to tumour specific cells. This paper attempts to unveil the multidimensional theranostic aspects of multifunctional metallic nanoparticles (MNPs)including passive and active targeting (HER2, Folate, Angiogenesis etc.) as well as the RES escaping approach. Special attention is given to the theranostic application of MNPs in oncology. Patents issued by the US office in this nanotechnological arena are also included emphasising the importance of MNPs in current cancer treatment/imaging research scenario. Keeping in mind the blooming research in clinical application directed nanotechnology; toxicity concerns related with MNPs are. also discussed, in element.

  3. Theory of semiconductor and transition metal alloys

    NASA Astrophysics Data System (ADS)

    Zunger, Alex

    1997-03-01

    There is a lot of talk about computer-aided discoveries/design of new materials, but the simple fact is that even limiting oneself to materials made of just two elements, (e.g., Cu-Au or Si-Ge), and to a substitutional system, there can exist as many as 2^N configurations that include compounds, alloys, superlattices, and impurities. Indeed, even for modest number of sites N, this is an astronomical number. Thus, the conventional energy minimization approach (e.g., first-principles pseudopotentials) for selecting the most stable crystal structure for A_qBq is hopeless if one considers the full 2^N space configurations of A, B on a lattice of N points. Molecular-dynamics is of no help, since it does not explore effectively the space of lattice configurations. Thus, contemporary energy minimization approaches use instead the method of ``rounding-up the usual suspects'': selecting the lowest energy from only a small number of well-known candidate configurations. The potential for missing new and important structures is obviously large. This talk gives an outline of the solution. It addresses the questions of (i) finding the lowest energy configuration of substitutional systems, (ii) calculating their composition-temperature phase diagram, and (iii) their finite-temperature thermodynamic properties, using the first-principles local density approximation (LDA). Mapping of the LDA energies of only 10-20 A_qBq compounds onto an Ising-like ``cluster-expansion'' enables use of lattice statistical mechanics techniques that elegantly solve the above problems. This extends the utility of the LDA from simple, perfectly-ordered compounds to truly complex structures, beyond the reach of direct LDA calculations. I will illustrate the method for semiconductor systems and transition-metal intermetallic systems, showing how previously unsuspected structures and materials are predicted, and how one can calculate free energies, short range-order and phase-diagrams of alloys. See

  4. Theory of high-energy electron scattering by composite targets

    SciTech Connect

    Coester, F.

    1988-01-01

    The emphasis of these expository lectures is on the role of relativistic invariance and the unity of the theory for medium and high energies. Sec. 2 introduces the kinematic notation and provides an elementary derivation of the general cross section. The relevant properties of the Poincare group and the transformation properties of current operators and target states are described in Sec 3. In Sec. 4 representations of target states with kinematic light-front symmetry are briefly discussed. The focus is on two applications. An impulse approximation of inclusive electron nucleus scattering at both medium and high energies. A parton model of the proton applied to deep inelastic scattering of polarized electrons by polarized protons. 19 refs.

  5. Quantum theory of the smectic metal state in stripe phases

    PubMed

    Emery; Fradkin; Kivelson; Lubensky

    2000-09-01

    We present a theory of the electron smectic fixed point of the stripe phases of doped layered Mott insulators. We show that in the presence of a spin gap three phases generally arise: (a) a smectic superconductor, (b) an insulating stripe crystal, and (c) a smectic metal. The latter phase is a stable two-dimensional anisotropic non-Fermi liquid. In the absence of a spin gap there is also a more conventional Fermi-liquid-like phase. The smectic superconductor and smectic metal phases (or glassy versions thereof) may have already been seen in Nd-doped La2-xSrxCuO4.

  6. Nonlocal microscopic theory of quantum friction between parallel metallic slabs

    SciTech Connect

    Despoja, Vito

    2011-05-15

    We present a new derivation of the friction force between two metallic slabs moving with constant relative parallel velocity, based on T=0 quantum-field theory formalism. By including a fully nonlocal description of dynamically screened electron fluctuations in the slab, and avoiding the usual matching-condition procedure, we generalize previous expressions for the friction force, to which our results reduce in the local limit. Analyzing the friction force calculated in the two local models and in the nonlocal theory, we show that for physically relevant velocities local theories using the plasmon and Drude models of dielectric response are inappropriate to describe friction, which is due to excitation of low-energy electron-hole pairs, which are properly included in nonlocal theory. We also show that inclusion of dissipation in the nonlocal electronic response has negligible influence on friction.

  7. Investigation of G4 theory for tansition metal thermochemistry.

    SciTech Connect

    Mayhall, N. J.; Raghavachari, K.; Redfern, P. C.; Curtiss, L. A.; Indiana Univ.

    2009-01-01

    An investigation of the performance of Gaussian-4 (G4) methods for the prediction of 3d transition metal thermochemistry is presented. Using the recently developed G3Large basis sets for atoms Sc-Zn, the G4 and G4(MP2) methods with scalar relativistic effects included are evaluated on a test set of 20 enthalpies of formation of transition metal-containing molecules. The G4(MP2) method is found to perform significantly better than the G4 method. The G4 method fails due to the poor convergence of the Moeller-Plesset perturbation theory at fourth-order in one case. The overall error for G4(MP2) of 2.84 kcal/mol is significantly larger than its previously reported performance for molecules containing main-group elements in the G3/05 test set. However, considering the relatively large uncertainties in the experimental enthalpies, the G4(MP2) method performs reasonably well. The performance of other composite methods based on G3 theory [G3(CCSD)//B3LYP and G3(MP2,CCSD)//B3LYP], as well as several density functional methods, are also presented in this paper. The results presented here will assist future development of composite model techniques suitable for use in transition metal-containing systems.

  8. Theory for plasticity of face-centered cubic metals

    PubMed Central

    Jo, Minho; Koo, Yang Mo; Lee, Byeong-Joo; Johansson, Börje; Vitos, Levente; Kwon, Se Kyun

    2014-01-01

    The activation of plastic deformation mechanisms determines the mechanical behavior of crystalline materials. However, the complexity of plastic deformation and the lack of a unified theory of plasticity have seriously limited the exploration of the full capacity of metals. Current efforts to design high-strength structural materials in terms of stacking fault energy have not significantly reduced the laborious trial and error works on basic deformation properties. To remedy this situation, here we put forward a comprehensive and transparent theory for plastic deformation of face-centered cubic metals. This is based on a microscopic analysis that, without ambiguity, reveals the various deformation phenomena and elucidates the physical fundaments of the currently used phenomenological correlations. We identify an easily accessible single parameter derived from the intrinsic energy barriers, which fully specifies the potential diversity of metals. Based entirely on this parameter, a simple deformation mode diagram is shown to delineate a series of convenient design criteria, which clarifies a wide area of material functionality by texture control. PMID:24753563

  9. Process for the fabrication of aluminum metallized pyrolytic graphite sputtering targets

    DOEpatents

    Makowiecki, Daniel M.; Ramsey, Philip B.; Juntz, Robert S.

    1995-01-01

    An improved method for fabricating pyrolytic graphite sputtering targets with superior heat transfer ability, longer life, and maximum energy transmission. Anisotropic pyrolytic graphite is contoured and/or segmented to match the erosion profile of the sputter target and then oriented such that the graphite's high thermal conductivity planes are in maximum contact with a thermally conductive metal backing. The graphite contact surface is metallized, using high rate physical vapor deposition (HRPVD), with an aluminum coating and the thermally conductive metal backing is joined to the metallized graphite target by one of four low-temperature bonding methods; liquid-metal casting, powder metallurgy compaction, eutectic brazing, and laser welding.

  10. Growing Fixed With Age: Lay Theories of Malleability Are Target Age-Specific.

    PubMed

    Neel, Rebecca; Lassetter, Bethany

    2015-11-01

    Beliefs about whether people can change ("lay theories" of malleability) are known to have wide-ranging effects on social motivation, cognition, and judgment. Yet rather than holding an overarching belief that people can or cannot change, perceivers may hold independent beliefs about whether different people are malleable-that is, lay theories may be target-specific. Seven studies demonstrate that lay theories are target-specific with respect to age: Perceivers hold distinct, uncorrelated lay theories of people at different ages, and younger targets are considered to be more malleable than older targets. Both forms of target-specificity are consequential, as target age-specific lay theories predict policy support for learning-based senior services and the rehabilitation of old and young drug users. The implications of target age-specific lay theories for a number of psychological processes, the social psychology of aging, and theoretical frameworks of malleability beliefs are discussed.

  11. The photochemistry of transition metal complexes using density functional theory.

    PubMed

    Garino, Claudio; Salassa, Luca

    2013-07-28

    The use of density functional theory (DFT) and time-dependent DFT (TD-DFT) to study the photochemistry of metal complexes is becoming increasingly important among chemists. Computational methods provide unique information on the electronic nature of excited states and their atomic structure, integrating spectroscopy observations on transient species and excited-state dynamics. In this contribution, we present an overview on photochemically active transition metal complexes investigated by DFT. In particular, we discuss a representative range of systems studied up to now, which include CO- and NO-releasing inorganic and organometallic complexes, haem and haem-like complexes dissociating small diatomic molecules, photoactive anti-cancer Pt and Ru complexes, Ru polypyridyls and diphosphino Pt derivatives.

  12. Effective medium theory for graphene-covered metallic gratings

    NASA Astrophysics Data System (ADS)

    Rahmani, Babak; Bagheri, Amirmasood; Khavasi, Amin; Mehrany, Khashayar

    2016-10-01

    We propose an effective medium theory for a one-dimensional periodic array of rectangular grooves covered by a graphene sheet. Parameters of the effective medium model are given by explicit analytical expressions for both major polarizations TM and TE, and for all incident angles. In extraction of this model, we assumed single mode approximation inside the grooves. The effect of non-specular diffraction orders outside the grating, as well as the plasmonic response of the graphene sheet in the far-infrared spectrum, is addressed by introducing an effective surface conductivity at the interface of the metallic grating and the ambient environment. It is shown that surface plasmons in graphene effectively capture diffracted waves in the metallic grating leading to near total absorption. Results of this work may pave the way for designing wide-band absorbers for terahertz applications.

  13. Quantum Theory of the Smectic Metal State in Stripe Phases

    SciTech Connect

    Emery, V. J.; Fradkin, E.; Kivelson, S. A.; Lubensky, T. C.

    2000-09-04

    We present a theory of the electron smectic fixed point of the stripe phases of doped layered Mott insulators. We show that in the presence of a spin gap three phases generally arise: (a) a smectic superconductor, (b) an insulating stripe crystal, and (c) a smectic metal. The latter phase is a stable two-dimensional anisotropic non-Fermi liquid. In the absence of a spin gap there is also a more conventional Fermi-liquid-like phase. The smectic superconductor and smectic metal phases (or glassy versions thereof) may have already been seen in Nd-doped La{sub 2-x}Sr {sub x}CuO{sub 4} . (c) 2000 The American Physical Society.

  14. Industrial recovered-materials-utilization targets for the metals and metal-products industry

    SciTech Connect

    1980-03-01

    The National Energy Conservation Policy Act of 1978 directs DOE to set targets for increased utilization of energy-saving recovered materials for certain industries. These targets are to be established at levels representing the maximum feasible increase in utilization of recovered materials that can be achieved progressively by January 1, 1987 and is consistent with technical and economic factors. A benefit to be derived from the increased use of recoverable materials is in energy savings, as state in the Act. Therefore, emhasis on different industries in the metals sector has been related to their energy consumption. The ferrous industry (iron and steel, ferrour foundries and ferralloys), as defined here, accounts for approximately 3%, and all others for the remaining 3%. Energy consumed in the lead and zinc segments is less than 1% each. Emphasis is placed on the ferrous scrap users, followed by the aluminum and copper industries. A bibliography with 209 citations is included.

  15. Application of Density Functional Theory to Systems Containing Metal Atoms

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.

    2006-01-01

    The accuracy of density functional theory (DFT) for problems involving metal atoms is considered. The DFT results are compared with experiment as well as results obtained using the coupled cluster approach. The comparisons include geometries, frequencies, and bond energies. The systems considered include MO2, M(OH)+n, MNO+, and MCO+2. The DFT works well for frequencies and geometries, even in case with symmetry breaking; however, some examples have been found where the symmetry breaking is quite severe and the DFT methods do not work well. The calculation of bond energies is more difficult and examples of successes as well as failures of DFT will be given.

  16. A Theory of Eye Movements during Target Acquisition

    ERIC Educational Resources Information Center

    Zelinsky, Gregory J.

    2008-01-01

    The gaze movements accompanying target localization were examined via human observers and a computational model (target acquisition model [TAM]). Search contexts ranged from fully realistic scenes to toys in a crib to Os and Qs, and manipulations included set size, target eccentricity, and target-distractor similarity. Observers and the model…

  17. Density functional theory study of mercury adsorption on metal surfaces

    SciTech Connect

    Steckel, J.A.

    2008-01-01

    Density functional theory _DFT_ calculations are used to characterize the interaction of mercury with copper, nickel, palladium, platinum, silver, and gold surfaces. Mercury binds relatively strongly to all the metal surfaces studied, with binding energies up to _1 eV for Pt and Pd. DFT calculations underestimate the energy of adsorption with respect to available experimental data. Plane-wave DFT results using the local density approximation and the Perdew-Wang 1991 and Perdew-Burke-Ernzerhof parametrizations of the generalized gradient approximation indicate that binding of mercury at hollow sites is preferred over binding at top orbridge sites. The interaction with mercury in order of increasing reactivity over the six metals studied is Ag_Au_Cu_Ni_Pt_Pd. Binding is stronger on the _001_ faces of the metal surfaces, where mercury issituated in fourfold hollow sites as opposed to the threefold hollow sites on _111_ faces. In general, mercury adsorption leads to decreases in the work function; adsorbate-induced work function changes are particularly dramatic on Pt.

  18. Density functional theory study of mercury adsorption on metal surfaces

    SciTech Connect

    Steckel, Janice A.

    2008-03-10

    Density functional theory (DFT) calculations are used to characterize the interaction of mercury with copper, nickel, palladium, platinum, silver, and gold surfaces. Mercury binds relatively strongly to all the metal surfaces studied, with binding energies up to ~1eV for Pt and Pd. DFT calculations underestimate the energy of adsorption with respect to available experimental data. Plane-wave DFT results using the local density approximation and the Perdew-Wang 1991 and Perdew-Burke-Ernzerhof parametrizations of the generalized gradient approximation indicate that binding of mercury at hollow sites is preferred over binding at top or bridge sites. The interaction with mercury in order of increasing reactivity over the six metals studied is Agmetal surfaces, where mercury is situated in fourfold hollow sites as opposed to the threefold hollow sites on (111) faces. Finally, in general, mercury adsorption leads to decreases in the work function; adsorbate-induced work function changes are particularly dramatic on Pt.

  19. Investigation of Coulombic bremsstrahlung spectra of metallic targets for the photon energy region of 1-100keV.

    PubMed

    Singh, Amrit; Dhaliwal, A S

    2016-09-01

    In the present paper, the formation of bremsstrahlung spectra by ordinary bremsstrahlung (OB) and polarization bremsstrahlung (PB) in metallic targets by (35)S beta particles has been investigated in the photon energy region of 1-100keV. From the experimental measurements and the theoretical results obtained from Elwert corrected (non-relativistic) Bethe Heitler (EBH) theory, modified Elwert factor (relativistic) (FmodBH) theories for OB and Avdonina and Pratt (FmodBH+PB) theory for total bremsstrahlung (BS) having the contribution of PB into OB, it has been found that the contribution of PB into BS in a target is limited to a low energy region only and also varies with the atomic number of target material. The FmodBH+PB theory is in agreement with the experimental results in low energy regions of the target, whereas at high energy region FmodBH is found to give better agreement. Further, the present experimental results indicate that the screening effects in the Coulombic bremsstrahlung process cannot be neglected in the high energy region, and the multiple scattering and secondary electron emissions effects in thick target are required to be taken into account in describing the bremsstrahlung process. PMID:27400163

  20. Investigation of Coulombic bremsstrahlung spectra of metallic targets for the photon energy region of 1-100keV.

    PubMed

    Singh, Amrit; Dhaliwal, A S

    2016-09-01

    In the present paper, the formation of bremsstrahlung spectra by ordinary bremsstrahlung (OB) and polarization bremsstrahlung (PB) in metallic targets by (35)S beta particles has been investigated in the photon energy region of 1-100keV. From the experimental measurements and the theoretical results obtained from Elwert corrected (non-relativistic) Bethe Heitler (EBH) theory, modified Elwert factor (relativistic) (FmodBH) theories for OB and Avdonina and Pratt (FmodBH+PB) theory for total bremsstrahlung (BS) having the contribution of PB into OB, it has been found that the contribution of PB into BS in a target is limited to a low energy region only and also varies with the atomic number of target material. The FmodBH+PB theory is in agreement with the experimental results in low energy regions of the target, whereas at high energy region FmodBH is found to give better agreement. Further, the present experimental results indicate that the screening effects in the Coulombic bremsstrahlung process cannot be neglected in the high energy region, and the multiple scattering and secondary electron emissions effects in thick target are required to be taken into account in describing the bremsstrahlung process.

  1. Investigation of metallic and metallic glass hollow spheres for fusion target application

    NASA Technical Reports Server (NTRS)

    Lee, M. C.; Kendall, J. M.; Wang, T. G.; Johnson, W. L.

    1982-01-01

    The first successful formation of submillimeter and millimeter spherical shells of tin and of a gold-lead-antimony alloy by means of the hollow-jet instability technique developed by Kendall is reported. Examination of tin specimens by SEM reveals that surface quality varies from poor to excellent. Whereas the metal is employed only as a convenient and inexpensive material, the gold alloy is important in that it is hard, has a high atomic number, and may be solidified into the amorphous state through the provision of a modest cooling rate. AuPbSb spherules up to 1.5 mm in diameter are produced using LN2 or chilled methanol as a coolant. It is found that these amorphous samples possess a superb surface smoothness compatible with fusion target requirements. It is noted that hollow spheres currently made of this alloy have an average outside diameter of 2000 microns.

  2. A Theory of Eye Movements during Target Acquisition

    PubMed Central

    Zelinsky, Gregory J.

    2008-01-01

    The gaze movements accompanying target localization were examined via human observers and a computational model (Target Acquisition Model, TAM). Search contexts ranged from fully realistic scenes, to toys in a crib, to Os and Qs, and manipulations included set size, target eccentricity, and target-distractor similarity. Observers and the model always previewed the same targets and searched the identical displays. Behavioral and simulated eye movements were analyzed for acquisition accuracy, efficiency, and target guidance. TAM's behavior generally fell within the behavioral mean's 95% confidence interval for all measures in each experiment/condition. This agreement suggests that a fixed-parameter model using spatio-chromatic filters and a simulated retina, when driven by the correct visual routines, can be a good general purpose predictor of human target acquisition behavior. PMID:18954205

  3. Nonlinear hyperbolic theory of thermal waves in metals

    NASA Technical Reports Server (NTRS)

    Wilhelm, H. E.; Choi, S. H.

    1975-01-01

    A closed-form solution for cylindrical thermal waves in metals is given based on the nonlinear hyperbolic system of energy-conservation and heat-flux relaxation equations. It is shown that heat released from a line source propagates radially outward with finite speed in the form of a thermal wave which exhibits a discontinuous wave front. Unique nonlinear thermal-wave solutions exist up to a critical amount of driving energy, i.e., for larger energy releases, the thermal flow becomes multivalued (occurrence of shock waves). By comparison, it is demonstrated that the parabolic thermal-wave theory gives, in general, a misleading picture of the profile and propagation of thermal waves and leads to physical (infinite speed of heat propagation) and mathematical (divergent energy integrals) difficulties. Attention is drawn to the importance of temporal heat-flux relaxation for the physical understanding of fast transient processes such as thermal waves and more general explosions and implosions.

  4. Graphyne on metallic surfaces: A density functional theory study

    NASA Astrophysics Data System (ADS)

    Lazić, P.; Crljen, Ž.

    2015-03-01

    We show how a structural modification of graphene, which gives the carbon allotrope graphyne, can induce an energy gap at the K point of the Brillouin zone. Upon adsorption on metallic surfaces, the same mechanism is responsible for a further modification of energy bands which occurs via the charge transfer mechanism. We perform the calculation based on the density functional theory with the novel nonlocal van der Waals-density functional correlation of the adsorption of graphyne on Cu(111), Ni(111), and Co(0001) surfaces and show the dependence of the band change on the charge transfer in the system. The binding of graphyne appears to be stronger than that of graphene on the same surfaces.

  5. Theory of the spin-1 bosonic liquid metal - Equilibrium properties of liquid metallic deuterium

    NASA Technical Reports Server (NTRS)

    Oliva, J.; Ashcroft, N. W.

    1984-01-01

    The theory of a two-component quantum fluid comprised of spin-1/2 fermions and nonzero spin bosons is examined. This system is of interest because it embodies a possible quantum liquid metallic phase of highly compressed deuterium. Bose condensation is assumed present and the two cases of nuclear-spin-polarized and -unpolarized systems are considered. A significant feature in the unpolarized case is the presence of a nonmagnetic mode with quadratic dispersion owing its existence to nonzero boson spin. The physical character of this mode is examined in detail within a Bogoliubov approach. The specific heat, bulk modulus, spin susceptibility, and thermal expansion are all determined. Striking contrasts in the specific heats and thermal-expansion coefficients of the liquid and corresponding normal solid metallic phase are predicted.

  6. A game theory approach to target tracking in sensor networks.

    PubMed

    Gu, Dongbing

    2011-02-01

    In this paper, we investigate a moving-target tracking problem with sensor networks. Each sensor node has a sensor to observe the target and a processor to estimate the target position. It also has wireless communication capability but with limited range and can only communicate with neighbors. The moving target is assumed to be an intelligent agent, which is "smart" enough to escape from the detection by maximizing the estimation error. This adversary behavior makes the target tracking problem more difficult. We formulate this target estimation problem as a zero-sum game in this paper and use a minimax filter to estimate the target position. The minimax filter is a robust filter that minimizes the estimation error by considering the worst case noise. Furthermore, we develop a distributed version of the minimax filter for multiple sensor nodes. The distributed computation is implemented via modeling the information received from neighbors as measurements in the minimax filter. The simulation results show that the target tracking algorithm proposed in this paper provides a satisfactory result. PMID:20194057

  7. Theory of sum frequency generation from metal surfaces

    NASA Astrophysics Data System (ADS)

    Liebsch, A.

    The time-dependent density functional approach is used to evaluate the optical sum frequency generation from metal surfaces. Attention is focussed on the magnitude and frequency variation of the element χzzz(ω1,ω2). Four types of metal surfaces are considered: simple metals, alkali metal overlayers, noble metals, and charged metal surfaces. Differences and similarities with respect to second harmonic generation from these surfaces are pointed out.

  8. Theory and Simulation of Warm Dense Matter Targets

    SciTech Connect

    Barnard, J J; Armijo, J; More, R M; Friedman, A; Kaganovich, I; Logan, B G; Marinak, M M; Penn, G E; Sefkow, A B; Santhanam, P; Wurtele, J S

    2006-07-13

    We present simulations and analysis of the heating of warm dense matter foils by ion beams with ion energy less than one MeV per nucleon to target temperatures of order one eV. Simulations were carried out using the multi-physics radiation hydrodynamics code HYDRA and comparisons are made with analysis and the code DPC. We simulate possible targets for a proposed experiment at LBNL (the so-called Neutralized Drift Compression Experiment, NDCXII) for studies of warm dense matter. We compare the dynamics of ideally heated targets, under several assumed equation of states, exploring dynamics in the two-phase (fluid-vapor) regime.

  9. Process for the fabrication of aluminum metallized pyrolytic graphite sputtering targets

    DOEpatents

    Makowiecki, D.M.; Ramsey, P.B.; Juntz, R.S.

    1995-07-04

    An improved method is disclosed for fabricating pyrolytic graphite sputtering targets with superior heat transfer ability, longer life, and maximum energy transmission. Anisotropic pyrolytic graphite is contoured and/or segmented to match the erosion profile of the sputter target and then oriented such that the graphite`s high thermal conductivity planes are in maximum contact with a thermally conductive metal backing. The graphite contact surface is metallized, using high rate physical vapor deposition (HRPVD), with an aluminum coating and the thermally conductive metal backing is joined to the metallized graphite target by one of four low-temperature bonding methods; liquid-metal casting, powder metallurgy compaction, eutectic brazing, and laser welding. 11 figs.

  10. The Contributions of Felix Bloch and W. V. Houston to the Electron Theory of Metals

    ERIC Educational Resources Information Center

    Rorschach, H. E., Jr.

    1970-01-01

    Discusses the contributions of Bloch and Houston to the electron theory of metals. Contains (1) a biographical note on W. V. Houston, (2) a review of the development of the electron theory of metals, and (3) a discussion of gravitationally induced electric fields. Bibliography. (LC)

  11. Radiochemical Determination of Polonium in Liquid Metal Spallation Targets

    NASA Astrophysics Data System (ADS)

    Hammer, B.; Schumann, D.; Neuhausen, J.; Wohlmuther, M.; Türler, A.

    2014-05-01

    The MEGAPIE target, consisting of 82 litres of lead-bismuth eutectic (LBE), was irradiated close to the megawatt range (0.8 MW) from August to December 2006 in the SINQ facility at PSI. After a cooling period of 5 years, a post-irradiation examination (PIE) program was started and samples were taken from different positions in the target. In this paper we focus on the measurement of α-emitting 208-210Po in the MEGAPIE target. The experimental results are compared with theoretical predictions obtained by FLUKA and MCNPX calculations.

  12. Sensory perception: an overlooked target of occupational exposure to metals.

    PubMed

    Gobba, Fabriziomaria

    2003-01-01

    The effect of exposure to industrial metals on sensory perception of workers has received only modest interest from the medical community to date. Nevertheless, some experimental and epidemiological data exist showing that industrial metals can affect vision, hearing and olfactory function, and a similar effect is also suggested for touch and taste. In this review the main industrial metals involved are discussed. An important limit in available knowledge is that, to date, the number of chemicals studied is relatively small. Another is that the large majority of the studies have evaluated the effect of a single chemical on a single sense. As an example, we know that mercury can impair hearing, smell, taste, touch and also vision, but we have scant idea if, in the same worker, a relation exists between impairments in different senses, or if impairments are independent. Moreover, workers are frequently exposed to different chemicals; a few available results suggest that a co-exposure may have no effect, or result in both an increase and a decrease of the effect, as observed for hearing loss, but this aspect certainly deserves much more study. As a conclusion, exposure to industrial metals can affect sensory perception, but knowledge of this effect is yet incomplete, and is largely inadequate especially for an estimation of "safe" thresholds of exposure. These data support the desirability of further good quality studies in this field. PMID:18365054

  13. Theory and modeling of light interactions with metallic nanostructures.

    SciTech Connect

    Montgomery, J. M.; Lee, T.-W.; Gray, S. K.; Louisiana State Univ.

    2008-08-13

    Metallic nanostructures such as systems containing metal nanoparticles or nanostructured metal films are intriguing systems of much current interest. Surface plasmons, i.e., special electronic excitations near the metallic surfaces, can then be excited in these systems. Surface plasmons can be intense and localized, and correctly describing their behavior in complex systems can require numerically rigorous modeling techniques. The finite-difference time-domain (FDTD) method is one such technique. This review discusses results obtained mostly with the FDTD method concerning (1) local surface plasmon excitations of metal nanoparticles, (2) surface plasmon polariton propagation on layered structures, and (3) periodic hole arrays in metal films.

  14. Hollow metal target magnetron sputter type radio frequency ion source

    SciTech Connect

    Yamada, N. Kasuya, T.; Wada, M.; Tsubouchi, N.

    2014-02-15

    A 70 mm diameter 70 mm long compact ion source equipped with a hollow sputtering target has been designed and tested. The hollow sputtering target serves as the radio frequency (RF) plasma excitation electrode at 13.56 MHz. A stable beam of Cu{sup +} has been extracted when Ar was used as the discharge support gas. In the extracted beam, Cu{sup +} had occupied more than 85% of the total ion current. Further increase in Cu{sup +} ions in the beam is anticipated by increasing the RF power and Ar pressure.

  15. Simultaneous detection of multiple DNA targets based on encoding metal ions.

    PubMed

    Zheng, Lichun; Li, Xiaoyan; Liu, Panpan; Wu, Guofan; Lu, Xiaoquan; Liu, Xiuhui

    2014-02-15

    We present a novel strategy for simultaneous electrochemical detection of multiple DNA targets based on the use of different encoding metal ions as tags. The principle of this scheme is that metal ions bound to metallothionein (MT) molecules can be released down after hybridization with DNA targets and then be detected by stripping voltammetry. The novel detection probes, ssDNA/MT conjugates, covered with different metal ions were synthesized for the first time, then three encoding metal ions (Zn(2+), Cd(2+), and Pb(2+)) were used to differentiate the signals of three virus DNA due to their well-defined anodic stripping peaks at -1.13 V (Zn), -0.78 V (Cd), and -0.52 V (Pb) at BiFE, respectively. The anodic peak currents increased linearly with the concentrations of DNA targets in the range from 0.1 nM to 10nM with a detection limit of 33 pM. In addition, the one-base mismatched target was effectively discriminated from the complementary target. The described results demonstrated that this method possesses high sensitivity and selectivity for multi-target DNA assay and has great potential in applications for detection of even more targets in biological assays, particularly immunoassays.

  16. Application of immune network theory for target-oriented multi-spectral remote sensing information mining

    NASA Astrophysics Data System (ADS)

    Liu, Qing-jie; Lin, Qi-zhong

    2008-12-01

    To use target information for space transformation in remote sensing data field, artificial immune network theory is introduced to multi-spectral remote sensing information mining, based on the knowledge of target spectrum. First, the target spectrums are fuzzy clustered into several subclasses, to retain different features of target in different subclasses. Then we develop a novel Regional-memory-pattern Artificial Immune Idiotypic Network (RAIN) model based on artificial idiotypic network theory, and train RAIN with subclasses samples. And then, the affinities of the target spectrum and other objects can be calculated according to the immune microscopic dynamics including stimulation and suppression effect. Finally, principal component analysis (PCA) is performed to affinities to explore more weak and hidden information. With its application in Baoguto Area, Xinjiang Uyghur Autonomous Region China, choosing tuffaceous siltstone as target object, the result supports the efficiency of the RAIN-affinity-PCA scheme.

  17. Enhancement of heat removal using concave liquid metal targets for high-power accelerators.

    SciTech Connect

    Konkashbaev, I.; Fischer, P.; Hassanein, A.; Mokhov, N. V.; Mathematics and Computer Science; FNAL

    2007-01-01

    The need is increasing for development of high-power targets and beam dump areas for the production of intense beams of secondary particles. The severe constraints arising from a megawatt beam deposited on targets and absorbers call for nontrivial procedures to dilute the beam. This study describes the development of targets and absorbers and the advantages of using flowing liquid metal in concave channels first proposed by IFMIF to raise the liquid metal boiling point by increasing the pressure in liquid supported by a centrifugal force. Such flow with a back-wall is subject to Taylor-Couette instability. The instability can play a positive role of increasing the heat transfer from the hottest region in the target/absorber to the back-wall cooled by water. Results of theoretical analysis and numerical modeling of both targets and dump areas for the IFMIF, ILC, and RIA facilities are presented.

  18. Targeting divalent metal cations with Re(I) tetrazolato complexes.

    PubMed

    Fiorini, Valentina; Ranieri, Anna Maria; Muzzioli, Sara; Magee, Karen D M; Zacchini, Stefano; Akabar, Nurshadrina; Stefan, Alessandra; Ogden, Mark I; Massi, Massimiliano; Stagni, Stefano

    2015-12-21

    In order to exploit their potential as versatile luminescent sensors, four new Re(I)-tetrazolato complexes with the general formula fac-[Re(CO)3(diim)(L)], where diim is 2,2'-bipyridine (bipy) or 1,10-phenanthroline (phen) and L(-) is either the anion 5-(2'-pyridyl)tetrazolato (2-PTZ(-)) or 5-(2'-quinolyl)tetrazolato (2-QTZ(-)), were prepared and fully characterized. In all cases, the regioselective coordination of the Re(I) center through the N2 atom of the tetrazolato ring was observed. This particular feature ensures the availability of the diiminic (N^N) site that was systematically incorporated into the structure of the 2-PTZ(-) and 2-QTZ(-) ligands for further coordination with metal cations. Such a diimine-type coordination mode was preliminarily tested by using the mononuclear Re(I) complexes as N^N ligands for the preparation of two [(N^N)Cu(POP)] cationic species, where POP is the chelating diphosphine bis[2-(diphenylphosphino)phenyl]ether. The X-ray structures of the resulting Re(I)-Cu(I) dyads revealed that the Re(I) mononuclear complexes effectively behaved as chelating N^N ligands with respect to the [Cu(POP)](+) fragment, the coordination of which also resulted in significant modification of the Re(I)-centered luminescence. With these data in hand, the luminescent sensing abilities of the four new Re(I) tetrazolato complexes were screened with respect to divalent metal ions of toxicological and biological importance such as Zn(II), Cd(II) and Cu(II). The interaction of the Re(I) complexes with Zn(II) and Cd(II) was witnessed by the evident blue shift (Δλmax = 22-36 nm) of the emission maxima, which was also accompanied by a significant elongation of the emission lifetimes. On the contrary, the addition of the cupric ion caused substantial quenching of the radiative processes originating from the Re(I) luminophores. PMID:26554352

  19. Precision Sheet Metal. Progress Record and Theory Outline.

    ERIC Educational Resources Information Center

    Connecticut State Dept. of Education, Hartford. Div. of Vocational-Technical Schools.

    This combination progress record and course outline is designed for use by individuals teaching a course in precision sheet metal. Included among the topics addressed in the course are the following: employment opportunities in metalworking, measurement and layout, orthographic projection, precision sheet metal drafting, simple layout, hand tools,…

  20. Can Multiconfigurational Self-Consistent Field Theory and Density Functional Theory Correctly Predict the Ground State of Metal-Metal-Bonded Complexes?

    PubMed

    Carlson, Rebecca K; Odoh, Samuel O; Tereniak, Stephen J; Lu, Connie C; Gagliardi, Laura

    2015-09-01

    The electronic structure of a diiron (FeFe) complex with strong metal-metal interaction and those of analogous complexes (CoCo, CoMn, CoFe, and FeMn) with much weaker metal-metal bonding are investigated with wave function-based methods and density functional theory. The delocalization and bonding between the metal centers in the diiron complex is only fully captured after inclusion of the complete set of 3d and 4d orbitals in the active space, a situation best suited for restricted active space (RAS) approaches. Truncation of the included set of 4d orbitals results in inappropriate localization of some 3d orbitals, incorrect description of the ground spin state as well as wrong spin state energetics, as compared to experiment. Using density functional theory, some local functionals are able to predict the correct ground spin states, and describe the chemical bonding and structural properties of all the metal-metal complexes considered in this work. In contrast, the introduction of some exact exchange results in increased localization of 3d orbitals and wrong spin state energetics, a situation that is particularly troublesome for the diiron complex.

  1. Modelling of Surfaces. Part 1: Monatomic Metallic Surfaces Using Equivalent Crystal Theory

    NASA Technical Reports Server (NTRS)

    Bozzolo, Guillermo; Ferrante, John; Rodriguez, Agustin M.

    1994-01-01

    We present a detailed description of equivalent crystal theory focusing on its application to the study of surface structure. While the emphasis is in the structure of the algorithm and its computational aspects, we also present a comprehensive discussion on the calculation of surface energies of metallic systems with equivalent crystal theory and other approaches. Our results are compared to experiment and other semiempirical as well as first-principles calculations for a variety of fcc and bcc metals.

  2. Coupled metal partitioning dynamics and toxicodynamics at biointerfaces: a theory beyond the biotic ligand model framework.

    PubMed

    Duval, Jérôme F L

    2016-04-14

    A mechanistic understanding of the processes governing metal toxicity to microorganisms (bacteria, algae) calls for an adequate formulation of metal partitioning at biointerfaces during cell exposure. This includes the account of metal transport dynamics from bulk solution to biomembrane and the kinetics of metal internalisation, both potentially controlling the intracellular and surface metal fractions that originate cell growth inhibition. A theoretical rationale is developed here for such coupled toxicodynamics and interfacial metal partitioning dynamics under non-complexing medium conditions with integration of the defining cell electrostatic properties. The formalism explicitly considers intertwined metal adsorption at the biointerface, intracellular metal excretion, cell growth and metal depletion from bulk solution. The theory is derived under relevant steady-state metal transport conditions on the basis of coupled Nernst-Planck equation and continuous logistic equation modified to include metal-induced cell growth inhibition and cell size changes. Computational examples are discussed to identify limitations of the classical Biotic Ligand Model (BLM) in evaluating metal toxicity over time. In particular, BLM is shown to severely underestimate metal toxicity depending on cell exposure time, metal internalisation kinetics, cell surface electrostatics and initial cell density. Analytical expressions are provided for the interfacial metal concentration profiles in the limit where cell-growth is completely inhibited. A rigorous relationship between time-dependent cell density and metal concentrations at the biosurface and in bulk solution is further provided, which unifies previous equations formulated by Best and Duval under constant cell density and cell size conditions. The theory is sufficiently flexible to adapt to toxicity scenarios with involved cell survival-death processes.

  3. Targeted manipulation of metal-organic frameworks to direct sorption properties.

    PubMed

    Schneemann, Andreas; Henke, Sebastian; Schwedler, Inke; Fischer, Roland A

    2014-04-01

    Metal-organic frameworks are promising materials for manifold applications. This Minireview highlights approaches for the fine-tuning of specific sorption properties (e.g. capacity, selectivity, and breathing behavior) of this interesting class of materials. Central aspects covered are the control over the crystal morphology, the targeted tuning of sorption properties by judicious choice of metal centers and linkers, and the preparation of host-guest systems. We want to introduce the reader to these topics on the basis of the manipulation of a handful of outstanding prototypical metal-organic frameworks.

  4. Plasma Processing of Functional Thin Films by Sputtering Deposition Using Metal-Based Powder Target

    NASA Astrophysics Data System (ADS)

    Kawasaki, Hiroharu; Ohshima, Tamiko; Ihara, Takeshi; Arafune, Kento; Taniyama, Daichi; Yagyu, Yoshihito; Suda, Yoshiaki

    2013-11-01

    Titanium-based functional thin films were prepared by a sputtering deposition method using a metal powder target, and the electron density and temperature of the processing plasma were investigated. The electron density of the plasma, measured by a probe method, when using a powder target was higher than that when using a bulk target. The deposition rate when using a powder target was also higher than that in the case of a bulk target. These results may be due to the net-cathode area of the powder target being larger than that of the bulk target. X-ray photoelectron spectroscopy, X-ray diffraction measurements, and atomic force microscopy images of the films prepared using the Ti powder target indicated nearly the same properties as those of films prepared using a Ti bulk target, and the prepared films are oxide. These results suggest that TiO2 thin films can be prepared using a Ti powder target and that the quality is almost the same as those of films prepared using a Ti bulk target.

  5. Formation of periodic structures upon laser ablation of metal targets in liquids

    SciTech Connect

    Kazakevich, Pavel V; Simakin, Aleksandr V; Shafeev, Georgii A

    2005-09-30

    Experimental data on the formation of ordered microstructures produced upon ablation of metal targets in liquids irradiated by a copper vapour laser or a pulsed Nd:YAG laser are presented. The structures were obtained on brass, bronze, copper, and tungsten substrates immersed in distilled water or ethanol. As a result of multiple-pulse laser ablation by a scanning beam, ordered microcones with pointed vertexes are formed on the target surface. The structures are separated by deep narrow channels. The structure period was experimentally shown to increase linearly with diameter of the laser spot on the target surface. (interaction of laser radiation with matter)

  6. Progress in alkaline peroxide dissolution of low-enriched uranium metal and silicide targets

    SciTech Connect

    Chen, L.; Dong, D.; Buchholz, B.A.; Vandegrift, G.F.; Wu, D.

    1996-12-31

    This paper reports recent progress on two alkaline peroxide dissolution processes: the dissolution of low-enriched uranium metal and silicide (U{sub 3}Si{sub 2}) targets. These processes are being developed to substitute low-enriched for high-enriched uranium in targets used for production of fission-product {sup 99}Mo. Issues that are addressed include (1) dissolution kinetics of silicide targets, (2) {sup 99}Mo lost during aluminum dissolution, (3) modeling of hydrogen peroxide consumption, (4) optimization of the uranium foil dissolution process, and (5) selection of uranium foil barrier materials. Future work associated with these two processes is also briefly discussed.

  7. Peptide-Metal Organic Framework Swimmers that Direct the Motion toward Chemical Targets.

    PubMed

    Ikezoe, Yasuhiro; Fang, Justin; Wasik, Tomasz L; Shi, Menglu; Uemura, Takashi; Kitagawa, Susumu; Matsui, Hiroshi

    2015-06-10

    Highly efficient and robust chemical motors are expected for the application in microbots that can selectively swim toward targets and accomplish their tasks in sensing, labeling, and delivering. However, one of major issues for such development is that current artificial swimmers have difficulty controlling their directional motion toward targets like bacterial chemotaxis. To program synthetic motors with sensing capability for the target-directed motion, we need to develop swimmers whose motions are sensitive to chemical gradients in environments. Here we create a new intelligent biochemical swimmer by integrating metal organic frameworks (MOFs) and peptides that can sense toxic heavy metals in solution and swim toward the targets. With the aid of Pb-binding enzymes, the peptide-MOF motor can directionally swim toward PbSe quantum dots (QD) by sensing pH gradient and eventually complete the motion as the swimmer reaches the highest gradient point at the target position in solution. This type of technology could be evolved to miniaturize chemical robotic systems that sense target chemicals and swim toward target locations. PMID:26010172

  8. Modification of base-side {sup 99}MO production processes for LEU metal-foil targets.

    SciTech Connect

    Vandegrift, G. F.; Leonard, R. A.; Aase, S.; Sedlet, J.; Koma, Y.; Conner, C.; Clark, C. R.; Meyer, M. K.

    1999-09-30

    Argonne National Laboratory is cooperating with the National Atomic Energy Commission of the Argentine Republic (CNEA) to convert their {sup 99}Mo production process, which uses high enriched uranium (HEU), to low-enriched uranium (LEU), The program is multifaceted; however, discussed in this paper are (1) results of laboratory experiments to develop means for substituting LEU metal-foil targets into the current process and (2) preparation of uranium-alloy or uranium-metal/aluminum-dispersion targets. Although {sup 99}Mo production is a multi-step process, the first two steps (target dissolution and primary molybdenum recovery) are by far the most important in the conversion. Commonly, once molybdenum is separated from the bulk of the uranium, the remainder of the process need not be modified. Our results show that up to this point in our study, conversion of the CNEA process to LEU appears viable.

  9. Implicit Personality Theory and Social Judgment: Effects of Familiarity with a Target Person.

    ERIC Educational Resources Information Center

    Vonk, Roos; Heiser, Willem J.

    1991-01-01

    A study involving 11 male and 11 female inhabitants of Leiden (Netherlands) tested the hypothesis that a subject's judgments of the personality of unfamiliar target persons correspond better with the subject's Implicit Personality Theory than do judgments of the personality of familiar persons. The results confirm the hypothesis. (TJH)

  10. Determination of metal ion content of beverages and estimation of target hazard quotients: a comparative study

    PubMed Central

    Hague, Theresa; Petroczi, Andrea; Andrews, Paul LR; Barker, James; Naughton, Declan P

    2008-01-01

    Background Considerable research has been directed towards the roles of metal ions in nutrition with metal ion toxicity attracting particular attention. The aim of this study is to measure the levels of metal ions found in selected beverages (red wine, stout and apple juice) and to determine their potential detrimental effects via calculation of the Target Hazard Quotients (THQ) for 250 mL daily consumption. Results The levels (mean ± SEM) and diversity of metals determined by ICP-MS were highest for red wine samples (30 metals totalling 5620.54 ± 123.86 ppb) followed by apple juice (15 metals totalling 1339.87 ± 10.84 ppb) and stout (14 metals totalling 464.85 ± 46.74 ppb). The combined THQ values were determined based upon levels of V, Cr, Mn, Ni, Cu, Zn and Pb which gave red wine samples the highest value (5100.96 ± 118.93 ppb) followed by apple juice (666.44 ± 7.67 ppb) and stout (328.41 ± 42.36 ppb). The THQ values were as follows: apple juice (male 3.11, female 3.87), stout (male 1.84, female 2.19), red wine (male 126.52, female 157.22) and ultra-filtered red wine (male 110.48, female 137.29). Conclusion This study reports relatively high levels of metal ions in red wine, which give a very high THQ value suggesting potential hazardous exposure over a lifetime for those who consume at least 250 mL daily. In addition to the known hazardous metals (e.g. Pb), many metals (e.g. Rb) have not had their biological effects systematically investigated and hence the impact of sustained ingestion is not known. PMID:18578877

  11. Targeted cleavage of HIV RRE RNA by Rev-coupled transition metal chelates.

    PubMed

    Joyner, Jeff C; Cowan, J A

    2011-06-29

    A series of compounds that target reactive metal chelates to the HIV-1 Rev response element (RRE) mRNA have been synthesized. Dissociation constants and chemical reactivity toward HIV RRE RNA have been determined and evaluated in terms of reduction potential, coordination unsaturation, and overall charge associated with the metal-chelate-Rev complex. Ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), diethylenetriaminepentaacetic acid (DTPA), and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) were linked to a lysine side chain of a Rev-derived peptide by either EDC/NHS or isothiocyanate coupling. The resulting chelate-Rev (EDTA-Rev, DTPA-Rev, NTA-Rev, and DOTA-Rev) conjugates were used to form coordination complexes with Fe(2+), Co(2+), Ni(2+), and Cu(2+) such that the arginine-rich Rev peptide could mediate localization of the metal chelates to the Rev peptide's high-affinity mRNA binding partner, RRE stem loop IIB. Metal complexes of the extended peptides GGH-Rev and KGHK-Rev, which also contain N-terminal peptidic chelators (ATCUN motifs), were studied for comparison. A fluorescence titration assay revealed high-affinity RRE RNA binding by all 22 metal-chelate-Rev species, with K(D) values ranging from ~0.2 to 16 nM, indicating little to no loss of RNA affinity due to the coupling of the metal chelates to the Rev peptide. Dissociation constants for binding at a previously unobserved low-affinity site are also reported. Rates of RNA modification by each metal-chelate-Rev species were determined and varied from ~0.28 to 4.9 nM/min but were optimal for Cu(2+)-NTA-Rev. Metal-chelate reduction potentials were determined and varied from -228 to +1111 mV vs NHE under similar solution conditions, allowing direct comparison of reactivity with redox thermodynamics. Optimal activity was observed when the reduction potential for the metal center was poised between those of the two principal co-reagents for metal-promoted formation of

  12. A van der Waals density functional theory comparison of metal decorated graphene systems for hydrogen adsorption

    NASA Astrophysics Data System (ADS)

    Wong, Janet; Yadav, Shwetank; Tam, Jasmine; Veer Singh, Chandra

    2014-06-01

    Previous Density Functional Theory (DFT) studies on metal decorated graphene generally use local density approximation (LDA) or generalized gradient approximation (GGA) functionals which can cause inaccuracies in hydrogen binding energies as they neglect van der Waals (vdW) interactions and are difficult to compare due to their widely varying simulation parameters. We investigated the hydrogen binding ability of several metals with a consistent set of simulations using the GGA functional and incorporated vdW forces through the vdW-DF2 functional. Metal adatom anchoring on graphene and hydrogen adsorption ability for both single and double sided decoration were studied for eight metals (Al, Li, Na, Ca, Cu, Ni, Pd, and Pt). It was found that the vdW correction can have a significant impact on both metal and hydrogen binding energies. The vdW-DF2 functional led to stronger metal adatom and hydrogen binding for light metals in comparison to GGA results, while heavier transition metals displayed the opposite behaviour but still produced stronger hydrogen binding energies than light metals. Nickel was found to be the best balance between hydrogen binding ability for reversible storage and low weight. The effects on hydrogen binding energy and maximum achievable hydrogen gravimetric density were analyzed for Ni-graphene systems with varying metal coverage. Lower metal coverage was found to improve hydrogen binding but decrease hydrogen gravimetric density. The highest achieved Ni-graphene system gravimetric density was 6.12 wt. %.

  13. To the theory of Ostwald ripening in metallic alloys

    NASA Astrophysics Data System (ADS)

    Ivanskii, B. V.; Vengrenovich, R. D.

    2016-08-01

    The mechanism of growth (dissolution) of nanoparticles controlled simultaneously by the matrix diffusion, diffusion along dislocations, and the rate of the passage of atoms through the interphase boundary (by the rate of formation of interatomic bonds) has been studied in alloys of CuNiAl and AlLi metallic systems at the stage of Ostwald ripening. An expression for the nanoparticle-size distribution function has been obtained, which was calculated based on the dependence of the rate of growth on three fluxes, i.e., diffusion flux j V, dislocation flux j d, and kinetic flux j i . A comparison of the experimental histograms with the theoretically calculated curves indicates their good agreement, which can indicate the opportunity of the realization in practice of the proposed mechanism of growth of nanoparticles in alloys of metallic systems.

  14. Control of Structure in Conventional Friction Stir Welds through a Kinematic Theory of Metal Flow

    NASA Technical Reports Server (NTRS)

    Rubisoff, H.A.; Schneider, J.A.; Nunes, A.C.

    2009-01-01

    In friction stir welding (FSW), a rotating pin is translated along a weld seam so as to stir the sides of the seam together. Metal is prevented from flowing up the pin, which would result in plowing/cutting instead of welding, by a shoulder on the pin. In conventional FSW, the weld metal rests on an "anvil", which supports the heavy "plunge" load on the tool. In this study, both embedded tungsten wires along and copper plating on the faying surfaces were used to trace the flow of AA2219 weld metal around the C-FSW tool. The effect of tool rotational speed, travel speed, plunge load, and pin thread pitch on the resulting weld metal flow was evaluated. Plan, longitudinal, and transverse section x-ray radiographs were examined to trace the metal flow paths. The results are interpreted in terms of a kinematic theory of metal flow in FSW.

  15. Atomistic theory of Ostwald ripening and disintegration of supported metal particles under reaction conditions.

    PubMed

    Ouyang, Runhai; Liu, Jin-Xun; Li, Wei-Xue

    2013-02-01

    Understanding Ostwald ripening and disintegration of supported metal particles under operating conditions has been of central importance in the study of sintering and dispersion of heterogeneous catalysts for long-term industrial implementation. To achieve a quantitative description of these complicated processes, an atomistic and generic theory taking into account the reaction environment, particle size and morphology, and metal-support interaction is developed. It includes (1) energetics of supported metal particles, (2) formation of monomers (both the metal adatoms and metal-reactant complexes) on supports, and (3) corresponding sintering rate equations and total activation energies, in the presence of reactants at arbitrary temperature and pressure. The thermodynamic criteria for the reactant assisted Ostwald ripening and induced disintegration are formulated, and the influence of reactants on sintering kinetics and redispersion are mapped out. Most energetics and kinetics barriers in the theory can be obtained conveniently by first-principles theory calculations. This allows for the rapid exploration of sintering and disintegration of supported metal particles in huge phase space of structures and compositions under various reaction environments. General strategies of suppressing the sintering of the supported metal particles and facilitating the redispersions of the low surface area catalysts are proposed. The theory is applied to TiO(2)(110) supported Rh particles in the presence of carbon monoxide, and reproduces well the broad temperature, pressure, and particle size range over which the sintering and redispersion occurred in such experiments. The result also highlights the importance of the metal-carbonyl complexes as monomers for Ostwald ripening and disintegration of supported metal catalysts in the presence of CO. PMID:23272702

  16. Atomistic theory of Ostwald ripening and disintegration of supported metal particles under reaction conditions.

    PubMed

    Ouyang, Runhai; Liu, Jin-Xun; Li, Wei-Xue

    2013-02-01

    Understanding Ostwald ripening and disintegration of supported metal particles under operating conditions has been of central importance in the study of sintering and dispersion of heterogeneous catalysts for long-term industrial implementation. To achieve a quantitative description of these complicated processes, an atomistic and generic theory taking into account the reaction environment, particle size and morphology, and metal-support interaction is developed. It includes (1) energetics of supported metal particles, (2) formation of monomers (both the metal adatoms and metal-reactant complexes) on supports, and (3) corresponding sintering rate equations and total activation energies, in the presence of reactants at arbitrary temperature and pressure. The thermodynamic criteria for the reactant assisted Ostwald ripening and induced disintegration are formulated, and the influence of reactants on sintering kinetics and redispersion are mapped out. Most energetics and kinetics barriers in the theory can be obtained conveniently by first-principles theory calculations. This allows for the rapid exploration of sintering and disintegration of supported metal particles in huge phase space of structures and compositions under various reaction environments. General strategies of suppressing the sintering of the supported metal particles and facilitating the redispersions of the low surface area catalysts are proposed. The theory is applied to TiO(2)(110) supported Rh particles in the presence of carbon monoxide, and reproduces well the broad temperature, pressure, and particle size range over which the sintering and redispersion occurred in such experiments. The result also highlights the importance of the metal-carbonyl complexes as monomers for Ostwald ripening and disintegration of supported metal catalysts in the presence of CO.

  17. Molecular orbital (SCF-Xα-SW) theory of metal-metal charge transfer processes in minerals

    USGS Publications Warehouse

    Sherman, David M.

    1987-01-01

    Electronic transitions between the Fe-Fe bonding and Fe-Fe antibonding orbitals results in the optically-induced intervalence charge transfer bands observed in the electronic spectra of mixed valence minerals. Such transitions are predicted to be polarized along the metal-metal bond direction, in agreement with experimental observations.

  18. Metal/dendrimer nanocomposites for enhanced optical breakdown: acoustic characterization and initial targeted cell uptake study

    NASA Astrophysics Data System (ADS)

    Tse, Christine; Lesniak, Wojciech; Balogh, Lajos P.; Ye, Jing Yong; O'Donnell, Matthew

    2007-02-01

    Metal/dendrimer nanocomposites (DNCs) uniquely combine the properties of metallic clusters and the biofriendly polymer host in a nanosized hybrid particle. DNCs can biochemically target tissues and locally reduce femtosecond optical breakdown thresholds, making highly precise and selective photodisruption possible. In this study, we have used high-frequency acoustic monitoring of bubble production dynamics to investigate how DNC properties, solution concentration, and optical parameters affect threshold reduction, actual waiting time, and mechanical characteristics of breakdown. Breakdown is defined here as bubble production with an onset of less than 20 seconds after laser exposure. DNC properties varied include metal content (silver, gold) and terminal group (amino-NH II, glycidol-OH, and carboxyl- COOH) which determine pH values. Results indicate that DNC metal content markedly influences solution threshold reduction, while DNC terminal group (and thus net surface charge) and solution concentration influence the details of breakdown at these reduced threshold fluences. {Ag(0)} DNCs reduce breakdown threshold fluence 1-2 orders of magnitude more than {Au(0)} DNCs. Furthermore, concentrated DNC solutions and DNCs carrying a net negative charge (carboxyl terminal groups) increase bubble production up to four times and shorten waiting time for breakdown from seconds to milliseconds. Increasing laser fluence for a given DNC solution concentration also shortens breakdown waiting time. Lastly, utilizing the fluorescence properties of silver nanocomposites, we use confocal microscopy to examine KB cell uptake of folate targeted silver DNCs. Cells incubated with folate targeted silver DNCs exhibit a measurable increase of intracellular fluorescence compared to control cells (no DNC incubation). However, while we observe a threshold reduction in KB cells incubated with 500nM folate-targeted DNC solution, there is no threshold reduction in cells incubated with 50nM folate-targeted

  19. Reactor target from metal chromium for "pure" high-intensive artificial neutrino source

    NASA Astrophysics Data System (ADS)

    Gavrin, V. N.; Kozlova, Yu. P.; Veretenkin, E. P.; Logachev, A. V.; Logacheva, A. I.; Lednev, I. S.; Okunkova, A. A.

    2016-03-01

    The paper presents the first results of development of manufacturing technology of metallic chromium targets from highly enriched isotope 50Cr for irradiation in a high flux nuclear reactor to obtain a compact high intensity neutrino source with low content of radionuclide impurities and minimum losses of enriched isotope. The main technological stages are the hydrolysis of chromyl fluoride, the electrochemical reduction of metallic chromium, the hot isostatic pressing of chromium powder and the electrical discharge machining of chromium bars. The technological stages of hot isostatic pressing of chromium powder and of electrical discharge machining of Cr rods have been tested.

  20. A ROTATING METAL BAND TARGET FOR PION PRODUCTION AT MUON COLLIDERS.

    SciTech Connect

    KING,B.J.; SIMOS,N.; WEGGEL,R.V.; MOKHOV,N.V.

    2002-01-18

    A conceptual design is presented for a high power pion production target for muon colliders that is based on a rotating metal band. Three candidate materials are considered for the target band: inconel alloy 718, titanium alloy 6Al-4V grade 5 and nickel. A pulsed proton beam tangentially intercepts a chord of the target band that is inside a 20 Tesla tapered solenoidal magnetic pion capture channel similar to designs previously considered for muon colliders and neutrino factories. The target band has a radius of 2.5 meters and is continuously rotated at approximately 1 m/s to carry heat away from the production region and through a water cooling tank. The mechanical layout and cooling setup of the target are described, including the procedure for the routine replacement of the target band. A rectangular band cross section is assumed, optionally with I-beam struts to enhance stiffness and minimize mechanical vibrations. Results are presented from realistic MARS Monte Carlo computer simulations of the pion yield and energy deposition in the target and from ANSYS finite element calculations for the corresponding shock heating stresses. The target scenario is found to perform satisfactorily and with conservative safety margins for multi-MW pulsed proton beams.

  1. Catalytic and photocatalytic transformations on metal nanoparticles with targeted geometric and plasmonic properties.

    PubMed

    Linic, Suljo; Christopher, Phillip; Xin, Hongliang; Marimuthu, Andiappan

    2013-08-20

    Heterogeneous catalysis by metals was among the first enabling technologies that extensively relied on nanoscience. The early intersections of catalysis and nanoscience focused on the synthesis of catalytic materials with high surface to volume ratio. These synthesis strategies mainly involved the impregnation of metal salts on high surface area supports. This would usually yield quasi-spherical nanoparticles capped by low-energy surface facets, typically with closely packed metal atoms. These high density areas often function as the catalytically active surface sites. Unfortunately, strategies to control the functioning surface facet (i.e., the geometry of active sites that performs catalytic turnover) are rare and represent a significant challenge in our ability to fine-tune and optimize the reactive surfaces. Through recent developments in colloidal chemistry, chemists have been able to synthesize metallic nanoparticles of both targeted size and desired shape. This has opened new possibilities for the design of heterogeneous catalytic materials, since metal nanoparticles of different shapes are terminated with different surface facets. By controlling the surface facet exposed to reactants, we can start affecting the chemical transformations taking place on the metal particles and changing the outcome of catalytic processes. Controlling the size and shape of metal nanoparticles also allows us to control the optical properties of these materials. For example, noble metals nanoparticles (Au, Ag, Cu) interact with UV-vis light through an excitation of localized surface plasmon resonance (LSPR), which is highly sensitive to the size and shape of the nanostructures. This excitation is accompanied by the creation of short-lived energetic electrons on the surface of the nanostructure. We showed recently that these energetic electrons could drive photocatalytic transformations on these nanostructures. The photocatalytic, electron-driven processes on metal nanoparticles

  2. Metal doped fluorocarbon polymer films prepared by plasma polymerization using an RF planar magnetron target

    NASA Astrophysics Data System (ADS)

    Biederman, H.; Holland, L.

    1983-07-01

    Fluorocarbon films have been prepared by plasma polymerization of CF4 using an RF planar magnetron with an aluminium target. More than one order of magnitude higher deposition rate has been achieved in comparison with an r.f. diode system operated under similar conditions of monomer pressure and flow rate and power input. A glow discharge in a CF4[25%]-argon [75%] mixture was used to incorporate aluminium from a target electrode into the polymer films. The foregoing mixture and another based on CF4 [87%]-argon [13%] were used in the RF discharge with a copper target. Some experiments with a gold target and pure CF4 as the inlet gas were also made. The film structure was examined by SEM and TEM and characteristic micrographs are presented here. The composition of the films was estimated from an AES study. The sheet resistivity of the metal/polymer film complexes was determined.

  3. Ab Initio Theory of Coherent Laser-Induced Magnetization in Metals

    NASA Astrophysics Data System (ADS)

    Berritta, Marco; Mondal, Ritwik; Carva, Karel; Oppeneer, Peter M.

    2016-09-01

    We present the first materials specific ab initio theory of the magnetization induced by circularly polarized laser light in metals. Our calculations are based on nonlinear density matrix theory and include the effect of absorption. We show that the induced magnetization, commonly referred to as inverse Faraday effect, is strongly materials and frequency dependent, and demonstrate the existence of both spin and orbital induced magnetizations which exhibit a surprisingly different behavior. We show that for nonmagnetic metals (such as Cu, Au, Pd, Pt) and antiferromagnetic metals the induced magnetization is antisymmetric in the light's helicity, whereas for ferromagnetic metals (Fe, Co, Ni, FePt) the imparted magnetization is only asymmetric in the helicity. We compute effective optomagnetic fields that correspond to the induced magnetizations and provide guidelines for achieving all-optical helicity-dependent switching.

  4. Phenomenological theory of bulk diffusion in metal oxides

    NASA Astrophysics Data System (ADS)

    Chuvil'deev, V. N.; Smirnova, E. S.

    2016-07-01

    Phenomenological description of bulk diffusion in oxide ceramics has been proposed. Variants of vacancy and vacancy-free diffusion models have been considered. In the vacancy models, ion migration is described as a fluctuation with the formation of a "liquid corridor," along which the diffusion ion transport in a "melt" is performed, or, as a fluctuation with the formation of an "empty corridor," in which the ion motion proceeds without activation. The vacancy-free model considers a fluctuation with the formation of a spherical liquid region whose sizes correspond to the first coordination sphere. It has been shown that both the vacancy models work in cubic metal oxides and the vacancy-free model is effective for describing diffusion in oxides having a noncubic structure. Detailed comparison of the models developed has been performed. It has been shown that the values of the activation energies for diffusion of metal and oxygen ions agree with the published data on bulk diffusion in stoichiometric oxide ceramics.

  5. Steam Reforming on Transition-metal Carbides from Density-functional Theory

    SciTech Connect

    Vojvodic, Aleksandra

    2012-05-11

    A screening study of the steam reforming reaction on clean and oxygen covered early transition-metal carbides surfaces is performed by means of density-functional theory calculations. It is found that carbides provide a wide spectrum of reactivities, from too reactive via suitable to too inert. Several molybdenum-based systems are identified as possible steam reforming catalysts. The findings suggest that carbides provide a playground for reactivity tuning, comparable to the one for pure metals.

  6. Heavy density liquid metal spallation target studies for Indian ADS programme

    NASA Astrophysics Data System (ADS)

    Satyamurthy, P.; Gantayet, L. M.; Ray, A. K.

    2007-02-01

    Department of Atomic Energy, India has taken up the development of ADS in view of many attractive features like inherent safety, capability to transmute large quantities of nuclear waste, better utilization of thorium etc. A roadmap has been finalized for the development of ADS. One of the key components of the ADS is the spallation target. Considering the neutron yield, thermal-hydraulics and radiation damage issues, we are proposing to develop spallation target based on heavy density liquid metals like lead and lead{bismuth{eutectic (LBE). Both window and windowless target configurations are presently being studied. In view of the various advantages we are also studying liquid metal flow circulation based on gas lift mechanism. An R&D programme has been initiated to address various physics and technology issues of ADS target. Under this programme, mercury and LBE experimental facilities are presently being set up. Along with these facilities, computational tools related to spallation physics (FLUKA) and CFD are being developed, and the existing ones are utilized to design the entire target loop as well as sub-systems. In this presentation the details of these activities are presented.

  7. Analysis of metal-matrix composite structures. I - Micromechanics constitutive theory. II - Laminate analyses

    NASA Technical Reports Server (NTRS)

    Arenburg, R. T.; Reddy, J. N.

    1991-01-01

    The micromechanical constitutive theory is used to examine the nonlinear behavior of continuous-fiber-reinforced metal-matrix composite structures. Effective lamina constitutive relations based on the Abouli micromechanics theory are presented. The inelastic matrix behavior is modeled by the unified viscoplasticity theory of Bodner and Partom. The laminate constitutive relations are incorporated into a first-order deformation plate theory. The resulting boundary value problem is solved by utilizing the finite element method. Attention is also given to computational aspects of the numerical solution, including the temporal integration of the inelastic strains and the spatial integration of bending moments. Numerical results the nonlinear response of metal matrix composites subjected to extensional and bending loads are presented.

  8. Theory of the dynamical thermal conductivity of metals

    NASA Astrophysics Data System (ADS)

    Bhalla, Pankaj; Kumar, Pradeep; Das, Nabyendu; Singh, Navinder

    2016-09-01

    The Mori's projection method, known as the memory function method, is an important theoretical formalism to study various transport coefficients. In the present work, we calculate the dynamical thermal conductivity in the case of metals using the memory function formalism. We introduce thermal memory functions for the first time and discuss the behavior of thermal conductivity in both the zero frequency limit and in the case of nonzero frequencies. We compare our results for the zero frequency case with the results obtained by the Bloch-Boltzmann kinetic approach and find that both approaches agree with each other. Motivated by some recent experimental advancements, we obtain several new results for the ac or the dynamical thermal conductivity.

  9. Tomonaga-Luttinger liquid theory for metallic fullurene polymers

    NASA Astrophysics Data System (ADS)

    Yoshioka, Hideo; Shima, Hiroyuki; Noda, Yusuke; Ono, Shota; Ohno, Kaoru

    2016-04-01

    We investigate the low energy behavior of local density of states in metallic C60 polymers theoretically. The multichannel bosonization method is applied to electronic band structures evaluated from first-principles calculation, by which the effects of electronic correlation and nanoscale corrugation in the atomic configuration are fully taken into account. We obtain a closed-form expression for the power-law anomalies in the local density of states, which successfully describes the experimental observation on the C60 polymers in a quantitative manner. An important implication from the closed-form solution is the existence of an experimentally unobserved crossover at nearly a hundred milli-electron volts, beyond which the power-law exponent of the C60 polymers should change significantly.

  10. Robust method for infrared small-target detection based on Boolean map visual theory.

    PubMed

    Qi, Shengxiang; Ming, Delie; Ma, Jie; Sun, Xiao; Tian, Jinwen

    2014-06-20

    In this paper, we present an infrared small target detection method based on Boolean map visual theory. The scheme is inspired by the phenomenon that small targets can often attract human attention due to two characteristics: brightness and Gaussian-like shape in the local context area. Motivated by this observation, we perform the task under a visual attention framework with Boolean map theory, which reveals that an observer's visual awareness corresponds to one Boolean map via a selected feature at any given instant. Formally, the infrared image is separated into two feature channels, including a color channel with the original gray intensity map and an orientation channel with the orientation texture maps produced by a designed second order directional derivative filter. For each feature map, Boolean maps delineating targets are computed from hierarchical segmentations. Small targets are then extracted from the target enhanced map, which is obtained by fusing the weighted Boolean maps of the two channels. In experiments, a set of real infrared images covering typical backgrounds with sky, sea, and ground clutters are tested to verify the effectiveness of our method. The results demonstrate that it outperforms the state-of-the-art methods with good performance.

  11. Properties of helium defects in bcc and fcc metals investigated with density functional theory

    NASA Astrophysics Data System (ADS)

    Zu, X. T.; Yang, L.; Gao, F.; Peng, S. M.; Heinisch, H. L.; Long, X. G.; Kurtz, R. J.

    2009-08-01

    The relative stability of single He defects in bcc and fcc metals is investigated using ab initio calculations based on density functional theory. The results indicate that the tetrahedral position is energetically more favorable for a He interstitial than the octahedral site in bcc metals, but the relative stability of He defects in fcc metals varies, depending on local environments. The He formation energies in bcc Fe and fcc Ni at the tetrahedral and octahedral positions with and without spin polarization are investigated. It is of interest to find that the magnetism of host atoms does not directly affect the relative stabilities of He in interstitial sites in bcc Fe and fcc Ni.

  12. Application of scaled nucleation theory to metallic vapor condensation

    NASA Astrophysics Data System (ADS)

    Martínez, Daniel M.; Ferguson, Frank T.; Heist, Richard H.; Nuth, Joseph A.

    2001-07-01

    In this paper we report that scaled nucleation theory (SNT) can describe moderately well the observed nucleation behavior of a significant number of refractory materials if a more appropriate value of a quantity commonly referred to as the excess surface entropy is used. With the availability of more reliable critical point and liquid property data, we are better able to calculate this quantity and we find that for refractory materials it can be as small as one half to one third the quantity traditionally used in its approximation. As a result of using more accurate values, we find considerably better agreement between SNT and experiment than what was originally determined. We also explain why using surface tension slope information to determine the excess surface entropy can lead to substantial errors in the SNT supersaturation prediction.

  13. Processing of LEU targets for {sup 99}Mo production -- Dissolution of metal foil targets by alkaline hydrogen peroxide

    SciTech Connect

    Dong, D.; Vandegrift, G.F.; Amini, S.; Hersubeno, J.B.; Nasution, H.; Nampira, Y.

    1995-09-01

    In FY 1995, the authors started studies on a new process for dissolution of low-enriched uranium (LEU) targets for {sup 99}Mo production. In this process, an LEU metal foil target is dissolved in a mixture of sodium hydroxide and hydrogen peroxide, then {sup 99}Mo is recovered from the dissolved solution. They focused on the dissolution kinetics to develop a mechanistic model for predicting the products and the rate of uranium dissolution under process conditions. They thoroughly studied the effects of hydrogen peroxide concentration, sodium hydroxide concentration, and temperature on the rate of uranium dissolution. It was found that uranium dissolution can be classified into a low-base (< 0.2M) and a high-base (> 0.2M) process. In the low-base process, both the equilibrium hydrogen peroxide and hydroxide concentrations affect the rate of uranium dissolution; in the high base process, uranium dissolution is a 0.25th order reaction with respect to the equilibrium hydrogen peroxide. The dissolution activation energy was experimentally determined to be 48.8 kJ/mol. Generally, the rate of uranium dissolution increases to a maximum as the hydroxide concentration is increased from 0.01 to about 1.5M, then it decreases as the hydroxide concentration is further increased. The alkalinity of the dissolution solution is an important factor that affects not only the dissolution rate, but also the amount of radioactive waste.

  14. Flat sheet metal girders with very thin metal web. Part I : general theories and assumptions

    NASA Technical Reports Server (NTRS)

    Wagner, Herbert

    1931-01-01

    The object of this report was to develop the structural method of sheet metal girders and should for that reason be considered solely from this standpoint. The ensuing methods were based on the assumption of the infinitely low stiffness in bending of the metal web. This simplifies the basis of calculations to such an extent that many questions of great practical importance can be examined which otherwise cannot be included in any analysis of the bending stiffness of the buckled plate. This report refers to such points as the safety in buckling of uprights to the effect of bending flexibility of spars, to spars not set parallel, etc.

  15. Preparation of mixed metal thin films by a PVD method using several kinds of powder targets

    NASA Astrophysics Data System (ADS)

    Suda, Yoshiaki; Kawasaki, Hiroharu; Ohshima, Tamiko; Yagyu, Yoshihito; Ihara, Takeshi; Yamauchi, Makiko; Plasma process; application Team

    2015-09-01

    Bismuth iron garnet (Bi3Fe5O12) and aluminum doped zinc oxide (AZO) thin films were prepared by a physical vapor deposition method using mixed metal powder targets. The X-ray powder diffraction and X-ray photoelectron spectroscopy results suggest that crystalline thin films can be prepared using powder targets with quality similar to that of the films prepared using bulk targets. Bi3Fe5O12 films prepared using the pulsed laser deposition method were Bi rich, which may be due to the lower melting temperature of Bi (544 K) compared with that of Fe (1811 K). The mean transparency and resistivity of the AZO films prepared by the sputtering method were approximately 79%-84% and 0.5 - 1.4 ohm/cm, respectively.

  16. Demonstration of {sup 99}MO production using LEU metal-foil targets in the cintichem process.

    SciTech Connect

    Vandegrift, G. F.; Conner, C.; Hofman, G. L.; Snelgrove, J. L.; Mutalib, A.; Purwadi, B.; Adang, H. G.; Hotman, L.; Kadarisman, Sukmana, A.; Dicky, T. J.; Sriyono, Suripto, A.; Lutfi, D.; Amin; Basiran, A.; Gogo, A.; Sarwani; Taryo, T.

    1999-09-30

    In March and September 1999, demonstrations of the irradiation, disassembly, and processing of LEU metal foil targets were performed in the Indonesian BATAN PUSPIPTEK Facilities. These demonstrations showed that (1) irradiation and disassembly can be performed so that the uranium foil can be easily removed from the target body, and (2) with only minor changes to the current process, the LEU foil can produce yield and purity of the {sup 99}Mo product at least as great as that obtained with the HEU target. Further, because of these modifications, two hours are cut from the processing time, and the liquid waste volume is reduced. Results of these demonstrations will be presented along with conclusions and plans for future work.

  17. Multilayer Relaxation and Surface Energies of FCC and BCC Metals Using Equivalent Crystal Theory

    NASA Technical Reports Server (NTRS)

    Rodriguez, Agustin M.; Bozzolo, Guillermo; Ferrante, John

    1993-01-01

    The multilayer relaxation of fcc and bcc metal surfaces is calculated using equivalent crystal theory. The results for changes in interplanar spacings of planes close to the surface and the ensuing surface energies are discussed in reference to other theoretical results and compared to available experimental data. The calculation includes high-index surfaces for which no other theoretical results are known.

  18. Sensor reliability evaluation scheme for target classification using belief function theory.

    PubMed

    Zhu, Jing; Luo, Yupin; Zhou, Jianjun

    2013-01-01

    In the target classification based on belief function theory, sensor reliability evaluation has two basic issues: reasonable dissimilarity measure among evidences, and adaptive combination of static and dynamic discounting. One solution to the two issues has been proposed here. Firstly, an improved dissimilarity measure based on dualistic exponential function has been designed. We assess the static reliability from a training set by the local decision of each sensor and the dissimilarity measure among evidences. The dynamic reliability factors are obtained from each test target using the dissimilarity measure between the output information of each sensor and the consensus. Secondly, an adaptive combination method of static and dynamic discounting has been introduced. We adopt Parzen-window to estimate the matching degree of current performance and static performance for the sensor. Through fuzzy theory, the fusion system can realize self-learning and self-adapting with the sensor performance changing. Experiments conducted on real databases demonstrate that our proposed scheme performs better in target classification under different target conditions compared with other methods. PMID:24351632

  19. Sensor Reliability Evaluation Scheme for Target Classification Using Belief Function Theory

    PubMed Central

    Zhu, Jing; Luo, Yupin; Zhou, Jianjun

    2013-01-01

    In the target classification based on belief function theory, sensor reliability evaluation has two basic issues: reasonable dissimilarity measure among evidences, and adaptive combination of static and dynamic discounting. One solution to the two issues has been proposed here. Firstly, an improved dissimilarity measure based on dualistic exponential function has been designed. We assess the static reliability from a training set by the local decision of each sensor and the dissimilarity measure among evidences. The dynamic reliability factors are obtained from each test target using the dissimilarity measure between the output information of each sensor and the consensus. Secondly, an adaptive combination method of static and dynamic discounting has been introduced. We adopt Parzen-window to estimate the matching degree of current performance and static performance for the sensor. Through fuzzy theory, the fusion system can realize self-learning and self-adapting with the sensor performance changing. Experiments conducted on real databases demonstrate that our proposed scheme performs better in target classification under different target conditions compared with other methods. PMID:24351632

  20. Unified Theory of Surface-Plasmonic Enhancement and Extinction of Light Transmission through Metallic Nanoslit Arrays

    PubMed Central

    Yoon, Jae Woong; Lee, Jun Hyung; Song, Seok Ho; Magnusson, Robert

    2014-01-01

    Metallic nanostructures are of immense scientific interest owing to unexpectedly strong interaction with light in deep subwavelength scales. Resonant excitations of surface and cavity plasmonic modes mediate strong light localization in nanoscale objects. Nevertheless, the role of surface plasmon-polaritons (SPP) in light transmission through a simple one-dimensional system with metallic nanoslits has been the subject of longstanding debates. Here, we propose a unified theory that consistently explains the controversial effects of SPPs in metallic nanoslit arrays. We show that the SPPs excited on the entrance and exit interfaces induce near-total internal reflection and abrupt phase change of the slit-guided mode. These fundamental effects quantitatively describe positive and negative effects of SPP excitation in a self-consistent manner. Importantly, the theory shows excellent agreement with rigorous numerical calculations while providing profound physical insight into the properties of nanoplasmonic systems. PMID:25022910

  1. Quantitative treatment of the creep of metals by dislocation and rate-process theories

    NASA Technical Reports Server (NTRS)

    Nowick, A S; Machlin, E S

    1946-01-01

    An equation for the steady-state rate of creep has been derived by applying the theory of dislocations to the creep of pure metals. The form of this equation is in agreement with empirical equations describing creep rates. The theory was also used to predict the dependence of steady-state rate of creep on physical constants of the material and good agreement was obtained with data in the literature for pure annealed metals. The rate of creep was found to decrease with increasing modulus of rigidity. This relation suggest that one of the requirements for a heat-resisting alloy is that its matrix be a metal that has a high modulus of rigidity and therefore a high modulus of elasticity.

  2. A viscoplastic constitutive theory for metal matrix composites at high temperature

    NASA Technical Reports Server (NTRS)

    Robinson, D. N.; Ellis, J. R.; Duffy, S. F.

    1987-01-01

    A viscoplastic theory is presented for representing the high-temperature deformation behavior of metal matrix composites. The point of view taken is a continuum one where the composite is considered a material in its own right, with its own properties that can be determined for the composite as a whole. It is presumed that a single preferential (fiber) direction is identifiable at each material point (continuum element) admitting the idealization of local transverse isotropy. A key ingredient in this work is the specification of an experimental program for the complete determination of the material functions and parameters for characterizing a particular metal matrix composite. The parameters relating to the strength of anisotropy can be determined through tension/torsion tests on longitudinally and circumferentially reinforced thin-walled tubes. Fundamental aspects of the theory are explored through a geometric interpretation of some basic features analogous to those of the classical theory of plasticity.

  3. A viscoplastic constitutive theory for metal matrix composites at high temperature

    NASA Technical Reports Server (NTRS)

    Robinson, David N.; Duffy, Stephen F.; Ellis, John R.

    1988-01-01

    A viscoplastic constitutive theory is presented for representing the high temperature deformation behavior of metal matrix composites. The point of view taken is a continuum one where the composite is considered a material in its own right, with its own properties that can be determined for the composite as a whole. It is assumed that a single preferential (fiber) direction is identifiable at each material point (continuum element) admitting the idealization of local transverse isotropy. A key ingredient is the specification of an experimental program for the complete determination of the material functions and parameters for characterizing a particular metal matrix composite. The parameters relating to the strength of anisotropy can be determined through tension/torsion tests on longitudinally and circumferentially reinforced thin walled tubes. Fundamental aspects of the theory are explored through a geometric interpretation of some basic features analogous to those of the classical theory of plasticity.

  4. A viscoplastic constitutive theory for metal matrix composites at high temperature

    NASA Technical Reports Server (NTRS)

    Robinson, D. N.; Duffy, S. F.; Ellis, J. R.

    1986-01-01

    A viscoplastic constitutive theory is presented for representing the high-temperature deformation behavior of metal matrix composites. The point of view taken is a continuum one where the composite is considered a material in its own right, with its own properties that can be determined for the composite as a whole. It is assumed that a single preferential (fiber) direction is identifiable at each material point (continuum element) admitting the idealization of local transverse isotropy. A key ingredient in this work is the specification of an experimental program for the complete determination of the material functions and parameters for characterizing a particular metal matrix composite. The parameters relating to the strength of anisotropy can be determined through tension/torsion tests on longitudinally and circumferentially reinforced thin-walled tubes. Fundamental aspects of the theory are explored through a geometric interpretation of some basic features analogous to those of the classical theory of plasticity.

  5. First principles theory of metal/oxide and metal/ferroelectric interfaces: Towards an integrated design

    NASA Astrophysics Data System (ADS)

    Nunez, Matias

    The current limits of semiconductor electronics and the challenges for future developments involve the continuous shrinking of the physical dimensions of the devices and the attainment of higher speeds. The drive to produce smaller devices has forced the current research towards the rethinking of electronic phenomena in terms of the individual microscopic component that dominate the quantum effects at the nanoscale. Therefore, it becomes fundamental to be able to obtain a detailed atomistic description of the physical properties of the systems in order to understand fully and manipulate their electronic and response properties. Using calculations from first principles, I will discussthe interplay between structure and functionality at metal-insulator interfaces, where the effects of nanoscale dimensions and scaling are extremely important for the design of efficient and performing electronic devices. Using the paradigmatic example of the junctions between various metals (Ag, Pd, Pt, Ni, Cu, Al) and binary alkaline earth crystalline oxides (BaO, CaO and SrO) and ferroelectric thin films (BaTiO3) I will demonstrate that it is possible to tune the electronic properties of the systems by manipulating the nanoscale structure of the interface. I will start by demonstrating that it is possible to tune the Schottky barrier height between a metal and an insulator such as BaO in a very broad range of values by manipulating the metal at the interface, and elucidate the role of the relative overlap in the density of states of the different components in determining the band alignment. This will allow meto state a modified Schottky-Mott rule for this class of metal-insulator heterojunctions. I have elucidated the nanoscale organization and local polarization in ferroelectric thin films sandwiched between metallic contacts. The profile of the local polarization for different film thicknesses unveils a peculiar spatial pattern of atomic layers with uncompensated dipoles in what

  6. Improving Targeting of Metal-Phenolic Capsules by the Presence of Protein Coronas.

    PubMed

    Ju, Yi; Dai, Qiong; Cui, Jiwei; Dai, Yunlu; Suma, Tomoya; Richardson, Joseph J; Caruso, Frank

    2016-09-01

    Particles adsorb proteins when they enter a physiological environment; this results in a surface coating termed a "protein corona". A protein corona can affect both the properties and functionalities of engineered particles. Here, we prepared hyaluronic acid (HA)-based capsules through the assembly of metal-phenolic networks (MPNs) and engineered their targeting ability in the absence and presence of protein coronas by varying the HA molecular weight. The targeting ability of the capsules was HA molecular weight dependent, and a high HA molecular weight (>50 kDa) was required for efficient targeting. The specific interactions between high molecular weight HA capsules and receptor-expressing cancer cells were negligibly affected by the presence of protein coronas, whereas nonspecific capsule-cell interactions were significantly reduced in the presence of a protein corona derived from human serum. Consequently, the targeting specificity of HA-based MPN capsules was enhanced due to the formation of a protein corona. This study highlights the significant and complex roles of a protein corona in biointeractions and demonstrates how protein coronas can be used to improve the targeting specificity of engineered particles. PMID:27560314

  7. Bifunctional Coupling Agents for Radiolabeling of Biomolecules and Target-Specific Delivery of Metallic Radionuclides

    PubMed Central

    Liu, Shuang

    2008-01-01

    Receptor-based radiopharmaceuticals are of great current interest in early molecular imaging and radiotherapy of cancers, and provide a unique tool for target-specific delivery of radionuclides to the diseased tissues. In general, a target-specific radiopharmaceutical can be divided into four parts: targeting biomolecule (BM), pharmacokinetic modifying (PKM) linker, bifunctional coupling or chelating agent (BFC), and radionuclide. The targeting biomolecule serves as a “carrier” for specific delivery of the radionuclide. PKM linkers are used to modify radiotracer excretion kinetics. BFC is needed for radiolabeling of biomolecules with a metallic radionuclide. Different radiometals have significant difference in their coordination chemistry, and require BFCs with different donor atoms and chelator frameworks. Since the radiometal chelate can have a significant impact on physical and biological properties of the target-specific radiopharmaceutical, its excretion kinetics can be altered by modifying the coordination environment with various chelators or coligand, if needed. This review will focus on the design of BFCs and their coordination chemistry with technetium, copper, gallium, indium, yttrium and lanthanide radiometals. PMID:18538888

  8. Thermophysical properties of simple liquid metals: A brief review of theory

    NASA Technical Reports Server (NTRS)

    Stroud, David

    1993-01-01

    In this paper, we review the current theory of the thermophysical properties of simple liquid metals. The emphasis is on thermodynamic properties, but we also briefly discuss the nonequilibrium properties of liquid metals. We begin by defining a 'simple liquid metal' as one in which the valence electrons interact only weakly with the ionic cores, so that the interaction can be treated by perturbation theory. We then write down the equilibrium Hamiltonian of a liquid metal as a sum of five terms: the bare ion-ion interaction, the electron-electron interaction, the bare electron-ion interaction, and the kinetic energies of electrons and ions. Since the electron-ion interaction can be treated by perturbation, the electronic part contributes in two ways to the Helmholtz free energy: it gives a density-dependent term which is independent of the arrangement of ions, and it acts to screen the ion-ion interaction, giving rise to effective ion-ion pair potentials which are density-dependent, in general. After sketching the form of a typical pair potential, we briefly enumerate some methods for calculating the ionic distribution function and hence the Helmholtz free energy of the liquid: monte Carlo simulations, molecular dynamics simulations, and thermodynamic perturbation theory. The final result is a general expression for the Helmholtz free energy of the liquid metal. It can be used to calculate a wide range of thermodynamic properties of simple metal liquids, which we enumerate. They include not only a range of thermodynamic coefficients of both metals and alloys, but also many aspects of the phase diagram, including freezing curves of pure elements and phase diagrams of liquid alloys (including liquidus and solidus curves). We briefly mention some key discoveries resulting from previous applications of this method, and point out that the same methods work for other materials not normally considered to be liquid metals (such as colloidal suspensions, in which the

  9. Metal-containing plasma-polymerized coatings for laser-fusion targets

    SciTech Connect

    Letts, S.A.; Jordan, C.W.

    1981-09-14

    Addition of metal to plastic layers in some direct drive laser fusion targets is needed to reduce electron induced fuel preheat. A plasma polymerization coating system was constructed to produce a metal seeded polymer by adding an organometallic gas to the usual trans-2-butene and hydrogen feedstocks. Since organometallic gases are highly reactive and toxic, safety is a major concern in the design of a coating system. Our coating apparatus was designed with three levels of containment to assure protection of the operator. The gas handling system has redundant valves and was designed to fail safe. Several sensor controlled interlocks assure safe operating conditions. Waste materials are collected on a specially designed cold trap. Waste disposal is accomplished by heating the traps and purging volatile products through a reactor vessel. The design, operating procedure, and safety interlocks of this novel coating system are described.

  10. Chloroplast targeting of phytochelatin synthase in Arabidopsis: effects on heavy metal tolerance and accumulation.

    PubMed

    Picault, N; Cazalé, A C; Beyly, A; Cuiné, S; Carrier, P; Luu, D T; Forestier, C; Peltier, G

    2006-11-01

    The enzymatically synthesized thiol peptide phytochelatin (PC) plays a central role in heavy metal tolerance and detoxification in plants. In response to heavy metal exposure, the constitutively expressed phytochelatin synthase enzyme (PCS) is activated leading to synthesis of PCs in the cytosol. Recent attempts to increase plant metal accumulation and tolerance reported that PCS over-expression in transgenic plants paradoxically induced cadmium hypersensitivity. In the present paper, we investigate the possibility of synthesizing PCs in plastids by over-expressing a plastid targeted phytochelatin synthase (PCS). Plastids represent a relatively important cellular volume and offer the advantage of containing glutathione, the precursor of PC synthesis. Using a constitutive CaMV 35S promoter and a RbcS transit peptide, we successfully addressed AtPCS1 to chloroplasts, significant PCS activity being measured in this compartment in two independent transgenic lines. A substantial increase in the PC content and a decrease in the glutathione pool were observed in response to cadmium exposure, when compared to wild-type plants. While over-expressing AtPCS1 in the cytosol importantly decreased cadmium tolerance, both cadmium tolerance and accumulation of plants expressing plastidial AtPCS1 were not significantly affected compared to wild-type. Interestingly, targeting AtPCS1 to chloroplasts induced a marked sensitivity to arsenic while plants over-expressing AtPCS1 in the cytoplasm were more tolerant to this metalloid. These results are discussed in relation to heavy metal trafficking pathways in higher plants and to the interest of using plastid expression of PCS for biotechnological applications.

  11. Phishing for suitable targets in the Netherlands: routine activity theory and phishing victimization.

    PubMed

    Leukfeldt, E Rutger

    2014-08-01

    This article investigates phishing victims, especially the increased or decreased risk of victimization, using data from a cybercrime victim survey in the Netherlands (n=10,316). Routine activity theory provides the theoretical perspective. According to routine activity theory, several factors influence the risk of victimization. A multivariate analysis was conducted to assess which factors actually lead to increased risk of victimization. The model included background and financial data of victims, their Internet activities, and the degree to which they were "digitally accessible" to an offender. The analysis showed that personal background and financial characteristics play no role in phishing victimization. Among eight Internet activities, only "targeted browsing" led to increased risk. As for accessibility, using popular operating systems and web browsers does not lead to greater risk, while having up-to-date antivirus software as a technically capable guardian has no effect. The analysis showed no one, clearly defined group has an increased chance of becoming a victim. Target hardening may help, but opportunities for prevention campaigns aimed at a specific target group or dangerous online activities are limited. Therefore, situational crime prevention will have to come from a different angle. Banks could play the role of capable guardian.

  12. Characteristics of flows of energetic atoms reflected from metal targets during ion bombardment

    NASA Astrophysics Data System (ADS)

    Kuzmichev, A.; Perevertaylo, V.; Tsybulsky, L.; Volpian, O.

    2016-07-01

    Particle number and energy reflection coefficients for energetic neutralized gas ions (Ar and O atoms) backscattered from metal targets during ion bombardment have been calculated using TRIM code. The energy distributions of reflected atoms are computed, too, and their dependence on the primary ion energy and the angle of ion incidence is determined. The obtained data confirm the possibility of employing energetic atoms reflection for generation of high energy neutral beams and point out to take this phenomenon into account under analysis of the ion technology for coating deposition.

  13. Photoactivatable metal complexes: from theory to applications in biotechnology and medicine.

    PubMed

    Smith, Nichola A; Sadler, Peter J

    2013-07-28

    This short review highlights some of the exciting new experimental and theoretical developments in the field of photoactivatable metal complexes and their applications in biotechnology and medicine. The examples chosen are based on some of the presentations at the Royal Society Discussion Meeting in June 2012, many of which are featured in more detail in other articles in this issue. This is a young field. Even the photochemistry of well-known systems such as metal-carbonyl complexes is still being elucidated. Striking are the recent developments in theory and computation (e.g. time-dependent density functional theory) and in ultrafast-pulsed radiation techniques which allow photochemical reactions to be followed and their mechanisms to be revealed on picosecond/nanosecond time scales. Not only do some metal complexes (e.g. those of Ru and Ir) possess favourable emission properties which allow functional imaging of cells and tissues (e.g. DNA interactions), but metal complexes can also provide spatially controlled photorelease of bioactive small molecules (e.g. CO and NO)--a novel strategy for site-directed therapy. This extends to cancer therapy, where metal-based precursors offer the prospect of generating excited-state drugs with new mechanisms of action that complement and augment those of current organic photosensitizers.

  14. Cylindrical-Wave Approach for electromagnetic scattering by subsurface metallic targets in a lossy medium

    NASA Astrophysics Data System (ADS)

    Frezza, F.; Pajewski, L.; Ponti, C.; Schettini, G.; Tedeschi, N.

    2013-10-01

    An analytical solution is developed to the two-dimensional scattering problem of a plane-wave propagating in air, impinging on the interface with a dissipative soil, and interacting with a finite set of subsurface metallic targets. The Cylindrical Wave Approach is applied, the electromagnetic field scattered by the targets is expanded into cylindrical waves and use is made of the plane-wave spectrum to take into account the interaction of such waves with the planar interface between air and soil. The theoretical solution is implemented in a Fortran code. The numerical evaluation of the spectral integral relevant to reflected and transmitted cylindrical wave functions in the presence of lossy media is performed by means of Gaussian adaptive quadrature formulas. The method may return the field values in each point of the space, both in the near and far zones; moreover it may be applied for any polarization, and for arbitrary values of the cylinder sizes and positions.

  15. Release from ISOLDE molten metal targets under pulsed proton beam conditions

    NASA Astrophysics Data System (ADS)

    Lettry, J.; Catherall, R.; Cyvoct, G.; Evensen, A. H. M.; Lindroos, M.; Jonsson, O. C.; Kugler, E.; Schindl, K.; Ravn, H.; Wildner, E.; Drumm, P.; Obert, J.; Putaux, J. C.; Sauvage, J.

    1996-04-01

    By moving the ISOLDE mass separators from the 600 MeV Synchrocyclotron (SC) to the 1 GeV Proton-Synchrotron-Booster (PS) the instantaneous energy density of the proton beam went up by 3 orders of magnitude. The developments of the molten metal target units and the optimization of the PS proton beam to cope with the effects of the thermal shocks induced by the proton beam are described. The energy density of the PS proton beam was reduced by spatial defocusing and time staggered extraction of the four PS-accelerators. The release from lanthanum, lead and tin targets is discussed for different settings of the proton beam and compared to the release observed at ISOLDE-SC. The yields of Hg isotopes are presented.

  16. Density functional theory calculations for the oxygen dissociation on nitrogen and transition metal doped graphenes

    NASA Astrophysics Data System (ADS)

    Zheng, Yongping; Xiao, Wei; Cho, Maenghyo; Cho, Kyeongjae

    2013-10-01

    Oxygen adsorption and dissociation on a pristine graphene, nitrogen doped graphene (N-graphene), and transition metal doped graphene (M-graphene) are studied with density functional theory calculations coupled with nudged elastic band (NEB) method. Four 3d transition metals (Fe, Co, Ni, and Cu) are selected as the doping atoms. The O binding energies on the Co-graphene and Ni-graphene have intermediate strength. The O2 dissociation barriers for these two types of doped graphenes are also lower than that on the pristine graphene and N-graphene. The Co and Ni doped graphenes are predicted to be promising ORR catalysts.

  17. A brief perspective on the diverging theories of lymphatic targeting with colloids

    PubMed Central

    Siram, Karthik; Marslin, Gregory; Raghavan, Chellan Vijaya; Balakumar, Krishnamoorthy; Rahman, Habibur; Franklin, Gregory

    2016-01-01

    For targeted delivery of colloids to the lymphatic system, the colloids should efficiently reach and remain in the lymphatics for a considerable period of time. As per the current knowledge, diffusion and phagocytosis are the two mechanisms through which colloids reach the lymphatic system. Several parameters including particle size and charge have been shown to affect the direct uptake of colloids by the lymphatic system. Although many researchers attached ligands on the surface of colloids to promote phagocytosis-mediated lymphatic delivery, another school of thought suggests avoidance of phagocytosis by use of carriers like polyethylene glycol (PEG)ylated colloids to impart stealth attributes and evade phagocytosis. In this perspective, we weigh up the paradoxical theories and approaches available in the literature to draw conclusions on the conditions favorable for achieving efficient lymphatic targeting of colloids. PMID:27366065

  18. Michel Borghini as a Mentor and Father of the Theory of Polarization in Polarized Targets

    NASA Astrophysics Data System (ADS)

    de Boer, Wim

    2016-02-01

    This paper is a contribution to the memorial session for Michel Borghini at the Spin 2014 conference in Bejing, honoring his pivotal role for the development of polarized targets in high energy physics. Borghini proposed for the first time the correct mechanism for dynamic polarization in polarized targets using organic materials doped with free radicals. In these amorphous materials the spin levels are broadened by spin-spin interactions and g-factor anisotropy, which allows a high dynamic polarization of nuclei by cooling of the spin-spin interaction reservoir. In this contribution I summarize the experimental evidence for this mechanism. These pertinent experiments were done at CERN in the years 1971 - 1974, when I was a graduate student under the guidance of Michel Borghini. I finish by shortly describing how Borghini’s spin temperature theory is now applied in cancer therapy.

  19. A brief perspective on the diverging theories of lymphatic targeting with colloids.

    PubMed

    Siram, Karthik; Marslin, Gregory; Raghavan, Chellan Vijaya; Balakumar, Krishnamoorthy; Rahman, Habibur; Franklin, Gregory

    2016-01-01

    For targeted delivery of colloids to the lymphatic system, the colloids should efficiently reach and remain in the lymphatics for a considerable period of time. As per the current knowledge, diffusion and phagocytosis are the two mechanisms through which colloids reach the lymphatic system. Several parameters including particle size and charge have been shown to affect the direct uptake of colloids by the lymphatic system. Although many researchers attached ligands on the surface of colloids to promote phagocytosis-mediated lymphatic delivery, another school of thought suggests avoidance of phagocytosis by use of carriers like polyethylene glycol (PEG)ylated colloids to impart stealth attributes and evade phagocytosis. In this perspective, we weigh up the paradoxical theories and approaches available in the literature to draw conclusions on the conditions favorable for achieving efficient lymphatic targeting of colloids. PMID:27366065

  20. Surveillance theory applied to virus detection: a case for targeted discovery

    USGS Publications Warehouse

    Bogich, Tiffany L.; Anthony, Simon J.; Nichols, James D.

    2013-01-01

    Virus detection and mathematical modeling have gone through rapid developments in the past decade. Both offer new insights into the epidemiology of infectious disease and characterization of future risk; however, modeling has not yet been applied to designing the best surveillance strategies for viral and pathogen discovery. We review recent developments and propose methods to integrate viral and pathogen discovery and mathematical modeling through optimal surveillance theory, arguing for a more targeted approach to novel virus detection guided by the principles of adaptive management and structured decision-making.

  1. Chemical fractionation resulting from the hypervelocity impact process on metallic targets

    NASA Astrophysics Data System (ADS)

    Libourel, Guy; Ganino, Clément; Michel, Patrick; Nakamura, Akiko

    2016-10-01

    In a regime of hypervelocity impact cratering, the internal energy deposited in target + projectile region is large enough to melt and/or vaporize part of the material involved, which expands rapidly away from the impact site. Fast and energetic impact processes have therefore important chemical consequences on the projectile and target rock transformations during major impact events. Several physical and chemical processes occurred indeed in the short duration of the impact, e.g., melting, coating, mixing, condensation, crystallization, redox reactions, quenching, etc., all concurring to alter both projectile and target composition on the irreversible way.In order to document such hypervelocity impact chemical fractionation, we have started a program of impact experiments by shooting doped (27 trace elements) millimeter–sized basalt projectiles on metallic target using a two stages light gas gun. With impact velocity in the range from 0.25 to 7 km.s-1, these experiments are aimed i) to characterize chemically and texturally all the post-mortem materials (e.g., target, crater, impact melt, condensates, and ejectas), in order ii) to make a chemical mass balance budget of the process, and iii) to relate it to the kinetic energy involved in the hypervelocity impacts for scaling law purpose. Irrespective of the incident velocities, our preliminary results show the importance of redox processes, the significant changes in the ejecta composition (e.g., iron enrichment) and the systematic coating of the crater by the impact melt [1]. On the target side, characterizations of the microstructure of the shocked iron alloys to better constrain the shielding processes. We also show how these results have great implications in our understanding on the current surface properties of small bodies, and chiefly in the case of M-type asteroids. [1] Ganino C, Libourel G, Nakamura AM & Michel P (2015) Goldschmidt Abstracts, 2015 990.

  2. Mott Multiferroics and Ferroelectric Metals from Dynamical Mean-Field Theory combined with Density-Functional Theory

    NASA Astrophysics Data System (ADS)

    Capone, Massimo

    2015-03-01

    Multiferroic materials, in which ferroelectricity and long-range magnetic ordering coexist, are natural candidates for applications. In this perspective, the most promising compounds are those in which the two phenomena do not simply coexist, but they influence each other through a magnetoelectric coupling. We present different applications of Density Functional Theory combined with Dynamical Mean-Field Theory in which electron-electron correlation effects are crucial in the stabilization of multiferroic behavior and in the magnetoelectric coupling. Within this wide family we can distinguish different cases. In Sr0.5Ba0.5MnO3 the multiferroic behavior is associated with a Mott insulating state in which the Mn half-filled t2g orbitals are responsible of the magnetic properties and the value of the polarization is strongly affected by the magnetic state. LiOsO3 shares the same electronic configuration with half-filled Os t2g orbitals. Despite this configuration enhances the effect of electron-electron interactions, the material remains metallic and represents a peculiar ferroelectric metal. We propose however how to turn this non-magnetic polar metal into a multiferroic through the design of a superlattice, which increases the degree of correlation, leading to Mott localization of the Os orbitals. In completely different systems, such as organic crystals like (TMTTF)2-X, strong correlations can lead to multiferroicity in organic crystals such as (TMTTF)2-X, where charge ordering promotes a polarization which is favored by an antiferromagnetic ordering. We finally discuss how strong correlations can play a major role away from half-filling when the Hund's coupling is sizable in compounds with a nominal valence of, e.g., two electrons in the three t2g orbitals. Such ``Hund's metals'' are correlated despite being far from Mott localization. This physical regime can be a fertile ground to obtain other ferroelectric metals. This work is supported by ERC/FP7 through the

  3. Fighting Cancer with Transition Metal Complexes: From Naked DNA to Protein and Chromatin Targeting Strategies

    PubMed Central

    Palermo, Giulia; Magistrato, Alessandra; Riedel, Tina; von Erlach, Thibaud; Davey, Curt A.; Dyson, Paul J.

    2015-01-01

    Abstract Many transition metal complexes have unique physicochemical properties that can be efficiently exploited in medicinal chemistry for cancer treatment. Traditionally, double‐stranded DNA has been assumed to be the main binding target; however, recent studies have shown that nucleosomal DNA as well as proteins can act as dominant molecular binding partners. This has raised new questions about the molecular determinants that govern DNA versus protein binding selectivity, and has offered new ways to rationalize their biological activity and possible side effects. To address these questions, molecular simulations at an atomistic level of detail have been used to complement, support, and rationalize experimental data. Herein we review some relevant studies—focused on platinum and ruthenium compounds—to illustrate the power of state‐of‐the‐art molecular simulation techniques and to demonstrate how the interplay between molecular simulations and experiments can make important contributions to elucidating the target preferences of some promising transition metal anticancer agents. This contribution aims at providing relevant information that may help in the rational design of novel drug‐discovery strategies. PMID:26634638

  4. Design of antibody-functionalized carbon nanotubes filled with radioactivable metals towards a targeted anticancer therapy

    NASA Astrophysics Data System (ADS)

    Spinato, Cinzia; Perez Ruiz de Garibay, Aritz; Kierkowicz, Magdalena; Pach, Elzbieta; Martincic, Markus; Klippstein, Rebecca; Bourgognon, Maxime; Wang, Julie Tzu-Wen; Ménard-Moyon, Cécilia; Al-Jamal, Khuloud T.; Ballesteros, Belén; Tobias, Gerard; Bianco, Alberto

    2016-06-01

    In the present work we have devised the synthesis of a novel promising carbon nanotube carrier for the targeted delivery of radioactivity, through a combination of endohedral and exohedral functionalization. Steam-purified single-walled carbon nanotubes (SWCNTs) have been initially filled with radioactive analogues (i.e. metal halides) and sealed by high temperature treatment, affording closed-ended CNTs with the filling material confined in the inner cavity. The external functionalization of these filled CNTs was then achieved by nitrene cycloaddition and followed by the derivatization with a monoclonal antibody (Cetuximab) targeting the epidermal growth factor receptor (EGFR), overexpressed by several cancer cells. The targeting efficiency of the so-obtained conjugate was evaluated by immunostaining with a secondary antibody and by incubation of the CNTs with EGFR positive cells (U87-EGFR+), followed by flow cytometry, confocal microscopy or elemental analyses. We demonstrated that our filled and functionalized CNTs can internalize more efficiently in EGFR positive cancer cells.In the present work we have devised the synthesis of a novel promising carbon nanotube carrier for the targeted delivery of radioactivity, through a combination of endohedral and exohedral functionalization. Steam-purified single-walled carbon nanotubes (SWCNTs) have been initially filled with radioactive analogues (i.e. metal halides) and sealed by high temperature treatment, affording closed-ended CNTs with the filling material confined in the inner cavity. The external functionalization of these filled CNTs was then achieved by nitrene cycloaddition and followed by the derivatization with a monoclonal antibody (Cetuximab) targeting the epidermal growth factor receptor (EGFR), overexpressed by several cancer cells. The targeting efficiency of the so-obtained conjugate was evaluated by immunostaining with a secondary antibody and by incubation of the CNTs with EGFR positive cells (U87

  5. Convection in molten pool created by a concentrated energy flux on a solid metal target

    SciTech Connect

    Dikshit, B.; Zende, G. R.; Bhatia, M. S.; Suri, B. M.

    2009-08-15

    During surface evaporation of metals by use of a concentrated energy flux such as electron beam or lasers, a liquid metal pool having a very high temperature gradient is formed around the hot zone created by the beam. Due to temperature dependence of surface tension, density, and depression of the evaporating surface caused by back pressure of the emitted vapor in this molten pool, a strong convective current sets in the molten pool. A proposition is made that this convection may pass through three different stages during increase in the electron beam power depending upon dominance of the various driving forces. To confirm this, convective heat transfer is quantified in terms of dimensionless Nusselt number and its evolution with power is studied in an experiment using aluminum, copper, and zirconium as targets. These experimentally determined values are also compared to the theoretical values predicted by earlier researchers to test the validity of their assumptions and to know about the type of flow in the melt pool. Thus, conclusion about the physical characteristics of flow in the molten pool of metals could be drawn by considering the roles of surface tension and curvature of the evaporating surface on the evolution of convective heat transfer.

  6. Irving Langmuir Prize Lecture - A predictive theory of transition metal surface catalysis

    NASA Astrophysics Data System (ADS)

    Norskov, Jens

    2015-03-01

    The lecture will outline a theory of heterogeneous catalysis that allows a detailed understanding of elementary chemical processes at transition metal surfaces and singles out the most important parameters determining catalytic activity and selectivity. It will be shown how scaling relations allow the identification of descriptors of catalytic activity and how they can be used to construct activity and selectivity maps. The maps can be used to define catalyst design rules and examples of their use will be given.

  7. Multiconfiguration pair-density functional theory: barrier heights and main group and transition metal energetics.

    PubMed

    Carlson, Rebecca K; Li Manni, Giovanni; Sonnenberger, Andrew L; Truhlar, Donald G; Gagliardi, Laura

    2015-01-13

    Kohn-Sham density functional theory, resting on the representation of the electronic density and kinetic energy by a single Slater determinant, has revolutionized chemistry, but for open-shell systems, the Kohn-Sham Slater determinant has the wrong symmetry properties as compared to an accurate wave function. We have recently proposed a theory, called multiconfiguration pair-density functional theory (MC-PDFT), in which the electronic kinetic energy and classical Coulomb energy are calculated from a multiconfiguration wave function with the correct symmetry properties, and the rest of the energy is calculated from a density functional, called the on-top density functional, that depends on the density and the on-top pair density calculated from this wave function. We also proposed a simple way to approximate the on-top density functional by translation of Kohn-Sham exchange-correlation functionals. The method is much less expensive than other post-SCF methods for calculating the dynamical correlation energy starting with a multiconfiguration self-consistent-field wave function as the reference wave function, and initial tests of the theory were quite encouraging. Here, we provide a broader test of the theory by applying it to bond energies of main-group molecules and transition metal complexes, barrier heights and reaction energies for diverse chemical reactions, proton affinities, and the water dimerization energy. Averaged over 56 data points, the mean unsigned error is 3.2 kcal/mol for MC-PDFT, as compared to 6.9 kcal/mol for Kohn-Sham theory with a comparable density functional. MC-PDFT is more accurate on average than complete active space second-order perturbation theory (CASPT2) for main-group small-molecule bond energies, alkyl bond dissociation energies, transition-metal-ligand bond energies, proton affinities, and the water dimerization energy.

  8. Theory and computation of hot carriers generated by surface plasmon polaritons in noble metals

    NASA Astrophysics Data System (ADS)

    Bernardi, Marco; Mustafa, Jamal; Neaton, Jeffrey B.; Louie, Steven G.

    2015-06-01

    Hot carriers (HC) generated by surface plasmon polaritons (SPPs) in noble metals are promising for application in optoelectronics, plasmonics and renewable energy. However, existing models fail to explain key quantitative details of SPP-to-HC conversion experiments. Here we develop a quantum mechanical framework and apply first-principles calculations to study the energy distribution and scattering processes of HCs generated by SPPs in Au and Ag. We find that the relative positions of the s and d bands of noble metals regulate the energy distribution and mean free path of the HCs, and that the electron-phonon interaction controls HC energy loss and transport. Our results prescribe optimal conditions for HC generation and extraction, and invalidate previously employed free-electron-like models. Our work combines density functional theory, GW and electron-phonon calculations to provide microscopic insight into HC generation and ultrafast dynamics in noble metals.

  9. Theory and computation of hot carriers generated by surface plasmon polaritons in noble metals.

    PubMed

    Bernardi, Marco; Mustafa, Jamal; Neaton, Jeffrey B; Louie, Steven G

    2015-01-01

    Hot carriers (HC) generated by surface plasmon polaritons (SPPs) in noble metals are promising for application in optoelectronics, plasmonics and renewable energy. However, existing models fail to explain key quantitative details of SPP-to-HC conversion experiments. Here we develop a quantum mechanical framework and apply first-principles calculations to study the energy distribution and scattering processes of HCs generated by SPPs in Au and Ag. We find that the relative positions of the s and d bands of noble metals regulate the energy distribution and mean free path of the HCs, and that the electron-phonon interaction controls HC energy loss and transport. Our results prescribe optimal conditions for HC generation and extraction, and invalidate previously employed free-electron-like models. Our work combines density functional theory, GW and electron-phonon calculations to provide microscopic insight into HC generation and ultrafast dynamics in noble metals. PMID:26033445

  10. Theory and computation of hot carriers generated by surface plasmon polaritons in noble metals

    PubMed Central

    Bernardi, Marco; Mustafa, Jamal; Neaton, Jeffrey B.; Louie, Steven G.

    2015-01-01

    Hot carriers (HC) generated by surface plasmon polaritons (SPPs) in noble metals are promising for application in optoelectronics, plasmonics and renewable energy. However, existing models fail to explain key quantitative details of SPP-to-HC conversion experiments. Here we develop a quantum mechanical framework and apply first-principles calculations to study the energy distribution and scattering processes of HCs generated by SPPs in Au and Ag. We find that the relative positions of the s and d bands of noble metals regulate the energy distribution and mean free path of the HCs, and that the electron–phonon interaction controls HC energy loss and transport. Our results prescribe optimal conditions for HC generation and extraction, and invalidate previously employed free-electron-like models. Our work combines density functional theory, GW and electron–phonon calculations to provide microscopic insight into HC generation and ultrafast dynamics in noble metals. PMID:26033445

  11. Coarse-grained density functional theories for metallic alloys: Generalized coherent-potential approximations and charge-excess functional theory

    NASA Astrophysics Data System (ADS)

    Bruno, Ezio; Mammano, Francesco; Fiorino, Antonino; Morabito, Emanuela V.

    2008-04-01

    The class of the generalized coherent-potential approximations (GCPAs) to the density functional theory (DFT) is introduced within the multiple scattering theory formalism with the aim of dealing with ordered or disordered metallic alloys. All GCPA theories are based on a common ansatz for the kinetic part of the Hohenberg-Kohn functional and each theory of the class is specified by an external model concerning the potential reconstruction. Most existing DFT implementations of CPA-based theories belong to the GCPA class. The analysis of the formal properties of the density functional defined by GCPA theories shows that it consists of marginally coupled local contributions. Furthermore, it is shown that the GCPA functional does not depend on the details of the charge density and that it can be exactly rewritten as a function of the appropriate charge multipole moments to be associated with each lattice site. A general procedure based on the integration of the qV laws is described that allows for the explicit construction of the same function. The coarse-grained nature of the GCPA density functional implies a great deal of computational advantages and is connected with the O(N) scalability of GCPA algorithms. Moreover, it is shown that a convenient truncated series expansion of the GCPA functional leads to the charge-excess functional (CEF) theory [E. Bruno , Phys. Rev. Lett. 91, 166401 (2003)], which here is offered in a generalized version that includes multipolar interactions. CEF and the GCPA numerical results are compared with status of art linearized augmented plane wave (LAPW) full-potential density functional calculations for 62 bcc- and fcc-based ordered CuZn alloys, in all the range of concentrations. Two facts clearly emerge from these extensive tests. In the first place, the discrepancies between GCPA and CEF results are always within the numerical accuracy of the calculations, both for the site charges and the total energies. In the second place, the

  12. Photoactivatable metal complexes: from theory to applications in biotechnology and medicine

    PubMed Central

    Smith, Nichola A.; Sadler, Peter J.

    2013-01-01

    This short review highlights some of the exciting new experimental and theoretical developments in the field of photoactivatable metal complexes and their applications in biotechnology and medicine. The examples chosen are based on some of the presentations at the Royal Society Discussion Meeting in June 2012, many of which are featured in more detail in other articles in this issue. This is a young field. Even the photochemistry of well-known systems such as metal–carbonyl complexes is still being elucidated. Striking are the recent developments in theory and computation (e.g. time-dependent density functional theory) and in ultrafast-pulsed radiation techniques which allow photochemical reactions to be followed and their mechanisms to be revealed on picosecond/nanosecond time scales. Not only do some metal complexes (e.g. those of Ru and Ir) possess favourable emission properties which allow functional imaging of cells and tissues (e.g. DNA interactions), but metal complexes can also provide spatially controlled photorelease of bioactive small molecules (e.g. CO and NO)—a novel strategy for site-directed therapy. This extends to cancer therapy, where metal-based precursors offer the prospect of generating excited-state drugs with new mechanisms of action that complement and augment those of current organic photosensitizers. PMID:23776303

  13. Size-Controlled Synthesis of Porphyrinic Metal-Organic Framework and Functionalization for Targeted Photodynamic Therapy.

    PubMed

    Park, Jihye; Jiang, Qin; Feng, Dawei; Mao, Lanqun; Zhou, Hong-Cai

    2016-03-16

    The understanding of nanomaterials for targeted cancer therapy is of great importance as physical parameters of nanomaterials have been shown to be strong determinants that can promote cellular responses. However, there have been rare platforms that can vastly tune the core of nanoparticles at a molecular level despite various nanomaterials employed in such studies. Here we show targeted photodynamic therapy (PDT) with Zr(IV)-based porphyrinic metal-organic framework (MOF) nanoparticles. Through a bottom-up approach, the size of MOF nanoparticles was precisely tuned in a broad range with a designed functional motif, built upon selection of building blocks of the MOF. In particular, molecular properties of the porphyrinic linker are maintained in the MOF nanoparticles regardless of their sizes. Therefore, size-dependent cellular uptake and ensuing PDT allowed for screening of the optimal size of MOF nanoparticles for PDT while MOF nanoparticle formulation of the photosensitizer showed better PDT efficacy than that of its small molecule. Additionally, Zr6 clusters in the MOF enabled an active targeting modality through postsynthetic modification, giving even more enhanced PDT efficacy. Together with our finding of size controllability covering a broad range in the nano regime, we envision that MOFs can be a promising nanoplatform by adopting advanced small molecule systems into the tunable framework with room for postsynthetic modification. PMID:26894555

  14. Application of the Hard and Soft, Acids and Bases (HSAB) theory to toxicant--target interactions.

    PubMed

    Lopachin, Richard M; Gavin, Terrence; Decaprio, Anthony; Barber, David S

    2012-02-20

    Many chemical toxicants and/or their active metabolites are electrophiles that cause cell injury by forming covalent bonds with nucleophilic targets on biological macromolecules. Covalent reactions between nucleophilic and electrophilic reagents are, however, discriminatory since there is a significant degree of selectivity associated with these interactions. Over the course of the past few decades, the theory of Hard and Soft, Acids and Bases (HSAB) has proven to be a useful tool in predicting the outcome of such reactions. This concept utilizes the inherent electronic characteristic of polarizability to define, for example, reacting electrophiles and nucleophiles as either hard or soft. These HSAB definitions have been successfully applied to chemical-induced toxicity in biological systems. Thus, according to this principle, a toxic electrophile reacts preferentially with biological targets of similar hardness or softness. The soft/hard classification of a xenobiotic electrophile has obvious utility in discerning plausible biological targets and molecular mechanisms of toxicity. The purpose of this perspective is to discuss the HSAB theory of electrophiles and nucleophiles within a toxicological framework. In principle, covalent bond formation can be described by using the properties of their outermost or frontier orbitals. Because these orbital energies for most chemicals can be calculated using quantum mechanical models, it is possible to quantify the relative softness (σ) or hardness (η) of electrophiles or nucleophiles and to subsequently convert this information into useful indices of reactivity. This atomic level information can provide insight into the design of corroborative laboratory research and thereby help investigators discern corresponding molecular sites and mechanisms of toxicant action. The use of HSAB parameters has also been instrumental in the development and identification of potential nucleophilic cytoprotectants that can scavenge toxic

  15. APPLICATION OF THE HARD AND SOFT, ACIDS AND BASES (HSAB) THEORY TO TOXICANT-TARGET INTERACTIONS

    PubMed Central

    LoPachin, Richard M.; Gavin, Terrence; DeCaprio, Anthony; Barber, David S.

    2011-01-01

    Many chemical toxicants and/or their active metabolites are electrophiles that cause cell injury by forming covalent bonds with nucleophilic targets on biological macromolecules. Covalent reactions between nucleophilic and electrophilic reagents are however discriminatory, since there is a significant degree of selectivity associated with these interactions. Over the course of the past few decades, the theory of Hard and Soft, Acid and Bases (HSAB) has proven to be a useful tool in predicting the outcome of such reactions. This concept utilizes the inherent electronic characteristic of polarizability to define, for example, reacting electrophiles and nucleophiles as either hard or soft. These HSAB definitions have been successfully applied to chemical-induced toxicity in biological systems. Thus, according to this principle, a toxic electrophile reacts preferentially with biological targets of similar hardness or softness. The soft/hard classification of a xenobiotic electrophile has obvious utility in discerning plausible biological targets and molecular mechanisms of toxicity. The purpose of this Perspective is to discuss the HSAB theory of electrophiles and nucleophiles within a toxicological framework. In principle, covalent bond formation can be described by using the properties of their outermost or frontier orbitals. Because these orbital energies for most chemicals can be calculated using quantum mechanical models, it is possible to quantify the relative softness (σ) or hardness (η) of electrophiles or nucleophiles and to subsequently convert this information into useful indices of reactivity. This atomic level information can provide insight into the design of corroborative laboratory research and thereby help investigators discern corresponding molecular sites and mechanisms of toxicant action. The use of HSAB parameters has also been instrumental in the development and identification of potential nucleophilic cytoprotectants that can scavenge toxic

  16. FFLO strange metal and quantum criticality in two dimensions: Theory and application to organic superconductors

    NASA Astrophysics Data System (ADS)

    Piazza, Francesco; Zwerger, Wilhelm; Strack, Philipp

    2016-02-01

    Increasing the spin imbalance in superconductors can spatially modulate the gap by forming Cooper pairs with finite momentum. For large imbalances compared to the Fermi energy, the inhomogeneous FFLO superconductor ultimately becomes a normal metal. There is mounting experimental evidence for this scenario in two-dimensional (2D) organic superconductors in large in-plane magnetic fields; this is complemented by ongoing efforts to realize this scenario in coupled tubes of atomic Fermi gases with spin imbalance. Yet, a theory for the phase transition from a metal to an FFLO superconductor has not been developed so far and the universality class has remained unknown. Here we propose and analyze a spin imbalance driven quantum critical point between a 2D metal and an FFLO phase in anisotropic electron systems. We derive the effective action for electrons and bosonic FFLO pairs at this quantum phase transition. Using this action, we predict non-Fermi-liquid behavior and the absence of quasiparticles at a discrete set of hot spots on the Fermi surfaces. This results in strange power laws in thermodynamics and response functions, which are testable with existing experimental setups on 2D organic superconductors and may also serve as signatures of the elusive FFLO phase itself. The proposed universality class is distinct from previously known quantum critical metals and, because its critical fluctuations appear already in the pairing channel, a promising candidate for naked metallic quantum criticality over extended temperature ranges.

  17. Theory of quantum metal to superconductor transitions in highly conducting systems

    SciTech Connect

    Spivak, B.

    2010-04-06

    We derive the theory of the quantum (zero temperature) superconductor to metal transition in disordered materials when the resistance of the normal metal near criticality is small compared to the quantum of resistivity. This can occur most readily in situations in which 'Anderson's theorem' does not apply. We explicitly study the transition in superconductor-metal composites, in an swave superconducting film in the presence of a magnetic field, and in a low temperature disordered d-wave superconductor. Near the point of the transition, the distribution of the superconducting order parameter is highly inhomogeneous. To describe this situation we employ a procedure which is similar to that introduced by Mott for description of the temperature dependence of the variable range hopping conduction. As the system approaches the point of the transition from the metal to the superconductor, the conductivity of the system diverges, and the Wiedemann-Franz law is violated. In the case of d-wave (or other exotic) superconductors we predict the existence of (at least) two sequential transitions as a function of increasing disorder: a d-wave to s-wave, and then an s-wave to metal transition.

  18. Adsorptive desulfurization with metal-organic frameworks: A density functional theory investigation

    NASA Astrophysics Data System (ADS)

    Chen, Zhiping; Ling, Lixia; Wang, Baojun; Fan, Huiling; Shangguan, Ju; Mi, Jie

    2016-11-01

    The contribution of each fragment of metal-organic frameworks (MOFs) to the adsorption of sulfur compounds were investigated using density functional theory (DFT). The involved sulfur compounds are dimethyl sulfide (CH3SCH3), ethyl mercaptan (CH3CH2SH) and hydrogen sulfide (H2S). MOFs with different organic ligands (NH2-BDC, BDC and NDC), metal centers structures (M, M-M and M3O) and metal ions (Zn, Cu and Fe) were used to study their effects on sulfur species adsorption. The results revealed that, MOFs with coordinatively unsaturated sites (CUS) have the strongest binding strength with sulfur compounds, MOFs with NH2-BDC substituent group ligand comes second, followed by that with saturated metal center, and the organic ligands without substituent group has the weakest adsorption strength. Moreover, it was also found that, among different metal ions (Fe, Zn and Cu), MOFs with unsaturated Fe has the strongest adsorption strength for sulfur compounds. These results are consistent with our previous experimental observations, and therefore provide insights on the better design of MOFs for desulfurization application.

  19. Time-domain response of a metal detector to a target buried in soil with frequency-dependent magnetic susceptibility

    NASA Astrophysics Data System (ADS)

    Das, Y.

    2006-05-01

    The work reported in this paper is a part of on-going studies to clarify how and to what extent soil electromagnetic properties affect the performance of induction metal detectors widely used in humanitarian demining. This paper studies the specific case of the time-domain response of a small metallic sphere buried in a non-conducting soil half-space with frequency-dependent complex magnetic susceptibility. The sphere is chosen as a simple prototype for the small metal parts in low-metal landmines, while soil with dispersive magnetic susceptibility is a good model for some soils that are known to adversely affect the performance of metal detectors. The included analysis and computations extend previous work which has been done mostly in the frequency domain. Approximate theoretical expressions for weakly magnetic soils are found to fit the experimental data very well, which allowed the estimation of soil model parameters, albeit in an ad hoc manner. Soil signal is found to exceed target signal (due to an aluminum sphere of radius 0.0127 m) in many cases, even for the weakly magnetic Cambodian laterite used in the experiments. How deep a buried target is detected depends on many other factors in addition to the relative strength of soil and target signals. A general statement cannot thus be made regarding detectability of a target in soil based on the presented results. However, computational results complemented with experimental data extend the understanding of the effect that soil has on metal detectors.

  20. Reliable energy level alignment at physisorbed molecule-metal interfaces from density functional theory.

    PubMed

    Egger, David A; Liu, Zhen-Fei; Neaton, Jeffrey B; Kronik, Leeor

    2015-04-01

    A key quantity for molecule-metal interfaces is the energy level alignment of molecular electronic states with the metallic Fermi level. We develop and apply an efficient theoretical method, based on density functional theory (DFT) that can yield quantitatively accurate energy level alignment information for physisorbed metal-molecule interfaces. The method builds on the "DFT+Σ" approach, grounded in many-body perturbation theory, which introduces an approximate electron self-energy that corrects the level alignment obtained from conventional DFT for missing exchange and correlation effects associated with the gas-phase molecule and substrate polarization. Here, we extend the DFT+Σ approach in two important ways: first, we employ optimally tuned range-separated hybrid functionals to compute the gas-phase term, rather than rely on GW or total energy differences as in prior work; second, we use a nonclassical DFT-determined image-charge plane of the metallic surface to compute the substrate polarization term, rather than the classical DFT-derived image plane used previously. We validate this new approach by a detailed comparison with experimental and theoretical reference data for several prototypical molecule-metal interfaces, where excellent agreement with experiment is achieved: benzene on graphite (0001), and 1,4-benzenediamine, Cu-phthalocyanine, and 3,4,9,10-perylene-tetracarboxylic-dianhydride on Au(111). In particular, we show that the method correctly captures level alignment trends across chemical systems and that it retains its accuracy even for molecules for which conventional DFT suffers from severe self-interaction errors. PMID:25741626

  1. s-wave elastic scattering of antihydrogen off atomic alkali-metal targets

    SciTech Connect

    Sinha, Prabal K.; Ghosh, A. S.

    2006-03-15

    We have investigated the s-wave elastic scattering of antihydrogen atoms off atomic alkali-metal targets (Li, Na, K, and Rb) at thermal energies (10{sup -16}-10{sup -4} a.u.) using an atomic orbital expansion technique. The elastic cross sections of these systems at thermal energies are found to be very high compared to H-H and H-He systems. The theoretical models employed in this study are so chosen to consider long-range forces dynamically in the calculation. The mechanism of cooling suggests that Li may be considered to be a good candidate as a buffer gas for enhanced cooling of antihydrogen atoms to ultracold temperature.

  2. Facile graphene transfer directly to target substrates with a reusable metal catalyst

    NASA Astrophysics Data System (ADS)

    Mafra, D. L.; Ming, T.; Kong, J.

    2015-09-01

    High-throughput, roll-to-roll growth and transferring of high-quality, large-area chemical vapor deposited (CVD) graphene directly onto a target substrate with a reusable metal catalyst is an enabling technology for flexible optoelectronics. We explore the direct transfer via hot lamination of CVD graphene onto a flexible substrate, followed by electrochemical delamination (bubble transfer) of the graphene. The transfer method investigated here does not require any intermediate transfer layer and allows the copper to be reused, which will reduce the production cost and avoid the generation of chemical waste. Such integration is one necessary step forward toward the economical and industrial scale production of graphene. Our method bares promise in various applications. As an example, we fabricated flexible solution-gated graphene field-effect-transistors, which exhibited transconductance as high as 200 μS.High-throughput, roll-to-roll growth and transferring of high-quality, large-area chemical vapor deposited (CVD) graphene directly onto a target substrate with a reusable metal catalyst is an enabling technology for flexible optoelectronics. We explore the direct transfer via hot lamination of CVD graphene onto a flexible substrate, followed by electrochemical delamination (bubble transfer) of the graphene. The transfer method investigated here does not require any intermediate transfer layer and allows the copper to be reused, which will reduce the production cost and avoid the generation of chemical waste. Such integration is one necessary step forward toward the economical and industrial scale production of graphene. Our method bares promise in various applications. As an example, we fabricated flexible solution-gated graphene field-effect-transistors, which exhibited transconductance as high as 200 μS. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr03892h

  3. A multifunctional metal-organic framework based tumor targeting drug delivery system for cancer therapy

    NASA Astrophysics Data System (ADS)

    Wang, Xiao-Gang; Dong, Zhi-Yue; Cheng, Hong; Wan, Shuang-Shuang; Chen, Wei-Hai; Zou, Mei-Zhen; Huo, Jia-Wei; Deng, He-Xiang; Zhang, Xian-Zheng

    2015-09-01

    Drug delivery systems (DDSs) with biocompatibility and precise drug delivery are eagerly needed to overcome the paradox in chemotherapy that high drug doses are required to compensate for the poor biodistribution of drugs with frequent dose-related side effects. In this work, we reported a metal-organic framework (MOF) based tumor targeting DDS developed by a one-pot, and organic solvent-free ``green'' post-synthetic surface modification procedure, starting from the nanoscale MOF MIL-101. Owing to the multifunctional surface coating, premature drug release from this DDS was prevented. Due to the pH responsive benzoic imine bond and the redox responsive disulfide bond at the modified surface, this DDS exhibited tumor acid environment enhanced cellular uptake and intracellular reducing environment triggered drug release. In vitro and in vivo results showed that DOX loaded into this DDS exhibited effective cancer cell inhibition with much reduced side effects.Drug delivery systems (DDSs) with biocompatibility and precise drug delivery are eagerly needed to overcome the paradox in chemotherapy that high drug doses are required to compensate for the poor biodistribution of drugs with frequent dose-related side effects. In this work, we reported a metal-organic framework (MOF) based tumor targeting DDS developed by a one-pot, and organic solvent-free ``green'' post-synthetic surface modification procedure, starting from the nanoscale MOF MIL-101. Owing to the multifunctional surface coating, premature drug release from this DDS was prevented. Due to the pH responsive benzoic imine bond and the redox responsive disulfide bond at the modified surface, this DDS exhibited tumor acid environment enhanced cellular uptake and intracellular reducing environment triggered drug release. In vitro and in vivo results showed that DOX loaded into this DDS exhibited effective cancer cell inhibition with much reduced side effects. Electronic supplementary information (ESI) available

  4. Bone as target organ for metals: the case of f-elements.

    PubMed

    Vidaud, Claude; Bourgeois, Damien; Meyer, Daniel

    2012-06-18

    The skeleton is a target organ for most metals. This leads to their bioaccumulation, either as storage of useful oligoelements or as a protection against damage by toxic elements. The different events leading to their accumulation in this organ, under constant remodeling, are not fully understood, nor the full subsequent impact on bone metabolism. This lack of knowledge is particularly true for lanthanides and actinides, whose use has been increasing over recent decades. These metals, known as f-elements, present chemical similarities and differences. After a comparison of the biologically relevant physicochemical properties of lanthanides and actinides, and a brief reminder of the main events of bone metabolism, this review considers the results published over the past decade regarding the interaction between bones and f-elements. Emphasis will be given to the molecular events, which constitute the basis of the most recent toxicological studies in this domain but still need further investigation. Ionic exchanges with the inorganic matrix, interactions with bone proteins, and cellular mechanism disturbances are mainly considered in this review.

  5. CO{sub 2} laser pulse shortening by laser ablation of a metal target

    SciTech Connect

    Donnelly, T.; Mazoyer, M.; Lynch, A.; O'Sullivan, G.; O'Reilly, F.; Dunne, P.; Cummins, T.

    2012-03-15

    A repeatable and flexible technique for pulse shortening of laser pulses has been applied to transversely excited atmospheric (TEA) CO{sub 2} laser pulses. The technique involves focusing the laser output onto a highly reflective metal target so that plasma is formed, which then operates as a shutter due to strong laser absorption and scattering. Precise control of the focused laser intensity allows for timing of the shutter so that different temporal portions of the pulse can be reflected from the target surface before plasma formation occurs. This type of shutter enables one to reduce the pulse duration down to {approx}2 ns and to remove the low power, long duration tails that are present in TEA CO{sub 2} pulses. The transmitted energy is reduced as the pulse duration is decreased but the reflected power is {approx}10 MW for all pulse durations. A simple laser heating model verifies that the pulse shortening depends directly on the plasma formation time, which in turn is dependent on the applied laser intensity. It is envisaged that this plasma shutter will be used as a tool for pulse shaping in the search for laser pulse conditions to optimize conversion efficiency from laser energy to useable extreme ultraviolet (EUV) radiation for EUV source development.

  6. Thermohydraulic behavior of the liquid metal target of a spallation neutron source

    SciTech Connect

    Takeda, Y.

    1996-06-01

    The author presents work done on three main problems. (1) Natural circulation in double coaxial cylindircal container: The thermohydraulic behaviour of the liquid metal target of the spallation neutron source at PSI has been investigated. The configuration is a natural-circulation loop in a concentric double-tube-type container. The results show that the natural-circulation loop concept is valid for the design phase of the target construction, and the current specified design criteria will be fulfilled with the proposed parameter values. (2) Flow around the window: Water experiments were performed for geometry optimisation of the window shape of the SINQ container for avoiding generating recirculation zones at peripheral area and the optimal cooling of the central part of the beam entrance window. Flow visualisation technique was mainly used for various window shapes, gap distance between the window and the guide tube edge. (3) Flow in window cooling channels: Flows in narrow gaps of cooling channels of two different types of windows were studied by flow visualisation techniques. One type is a slightly curved round cooling channel and the other is hemispherical shape, both of which have only 2 mm gap distance and the water inlet is located on one side and flows out from the opposite side. In both cases, the central part of the flow area has lower velocity than peripheral area.

  7. Characterization of methoxy adsorption on some transition metals: A first principles density functional theory study

    NASA Astrophysics Data System (ADS)

    Wang, Gui-Chang; Zhou, Yu-Hua; Nakamura, Junji

    2005-01-01

    Based on the gradient-density functional theory, calculation results of methoxy adsorption on Au(111), Ag(111), Cu(111), Pt(111), Pd(111), Ni(111), Rh(111), and Fe(100) surfaces are presented, and a consistent picture for some key physical properties determining the reactivity of metals appears. These eight metals belong to two groups: either with filled d electrons (group IB) or with unfilled but more than half filled d electrons (group VIII). The calculated adsorption energies are quite in agreement with the experimental data as well as the previous theoretical calculation results. Importantly, using the analysis of B. Hammer and J. K. Nørskov, Nature (London) 376, 232 (1995) and in Chemisorption and Reactivity on Supported Clusters and Thin Films, edited by R. M. Lambert and G. Pacchioni (Kluwer Academic, Dordrecht, 1997), pp. 285-351, the binding energies have selectively been linearly correlated to the d-band center and to the size of the metal d-band orbital overlapping with the adsorbate (coupling matrix element) for these two groups of metals. And by analyzing the nature of the adsorption bonding, the possible reason of this difference is suggested.

  8. A computational theory for the classification of natural biosonar targets based on a spike code.

    PubMed

    Müller, Rolf

    2003-08-01

    A computational theory for the classification of natural biosonar targets is developed based on the properties of an example stimulus ensemble. An extensive set of echoes (84 800) from four different foliages was transcribed into a spike code using a parsimonious model (linear filtering, half-wave rectification, thresholding). The spike code is assumed to consist of time differences (interspike intervals) between threshold crossings. Among the elementary interspike intervals flanked by exceedances of adjacent thresholds, a few intervals triggered by disjoint half-cycles of the carrier oscillation stand out in terms of resolvability, visibility across resolution scales and a simple stochastic structure (uncorrelatedness). They are therefore argued to be a stochastic analogue to edges in vision. A three-dimensional feature vector representing these interspike intervals sustained a reliable target classification performance (0.06% classification error) in a sequential probability ratio test, which models sequential processing of echo trains by biological sonar systems. The dimensions of the representation are the first moments of duration and amplitude location of these interspike intervals as well as their number. All three quantities are readily reconciled with known principles of neural signal representation, since they correspond to the centre of gravity of excitation on a neural map and the total amount of excitation.

  9. Peierls potential of screw dislocations in bcc transition metals: Predictions from density functional theory

    SciTech Connect

    Weinberger, Christopher R.; Tucker, Garritt J.; Foiles, Stephen M.

    2013-02-01

    It is well known that screw dislocation motion dominates the plastic deformation in body-centered-cubic metals at low temperatures. The nature of the nonplanar structure of screw dislocations gives rise to high lattice friction, which results in strong temperature and strain rate dependence of plastic flow. Thus the nature of the Peierls potential, which is responsible for the high lattice resistance, is an important physical property of the material. However, current empirical potentials give a complicated picture of the Peierls potential. Here, we investigate the nature of the Peierls potential using density functional theory in the bcc transition metals. The results show that the shape of the Peierls potential is sinusoidal for every material investigated. Furthermore, we show that the magnitude of the potential scales strongly with the energy per unit length of the screw dislocation in the material.

  10. Polarization Fluctuations in Insulators and Metals: New and Old Theories Merge

    NASA Astrophysics Data System (ADS)

    Resta, Raffaele

    2006-04-01

    The ground-state fluctuation of polarization P is finite in insulators and divergent in metals, owing to the SWM sum rule [I. Souza, T. Wilkens, and R. M. Martin, Phys. Rev. BPRBMDO0163-1829 62, 1666 (2000)10.1103/PhysRevB.62.1666]. This is a virtue of periodic (i.e., transverse) boundary conditions. I show that within any other boundary conditions the P fluctuation is finite even in metals, and a generalized sum rule applies. The boundary-condition dependence is a pure correlation effect, not present at the independent-particle level. In the longitudinal case ∇·P=-ρ, and one equivalently addresses charge fluctuations: the generalized sum rule reduces then to a well-known result of the many-body theory.

  11. Two-component Fermi-liquid theory - Equilibrium properties of liquid metallic hydrogen

    NASA Technical Reports Server (NTRS)

    Oliva, J.; Ashcroft, N. W.

    1981-01-01

    It is reported that the transition of condensed hydrogen from an insulating molecular crystal phase to a metallic liquid phase, at zero temperature and high pressure, appears possible. Liquid metallic hydrogen (LMH), comprising interpenetrating proton and electron fluids, would constitute a two-component Fermi liquid with both a very high component-mass ratio and long-range, species-dependent bare interactions. The low-temperature equilibrium properties of LMH are examined by means of a generalization to the case of two components of the phenomenological Landau Fermi-liquid theory, and the low-temperature specific heat, compressibility, thermal expansion coefficient and spin susceptibility are given. It is found that the specific heat and the thermal expansion coefficient are vastly greater in the liquid than in the corresponding solid, due to the presence of proton quasiparticle excitations in the liquid.

  12. Reliable Energy Level Alignment at Physisorbed Molecule–Metal Interfaces from Density Functional Theory

    PubMed Central

    2015-01-01

    A key quantity for molecule–metal interfaces is the energy level alignment of molecular electronic states with the metallic Fermi level. We develop and apply an efficient theoretical method, based on density functional theory (DFT) that can yield quantitatively accurate energy level alignment information for physisorbed metal–molecule interfaces. The method builds on the “DFT+Σ” approach, grounded in many-body perturbation theory, which introduces an approximate electron self-energy that corrects the level alignment obtained from conventional DFT for missing exchange and correlation effects associated with the gas-phase molecule and substrate polarization. Here, we extend the DFT+Σ approach in two important ways: first, we employ optimally tuned range-separated hybrid functionals to compute the gas-phase term, rather than rely on GW or total energy differences as in prior work; second, we use a nonclassical DFT-determined image-charge plane of the metallic surface to compute the substrate polarization term, rather than the classical DFT-derived image plane used previously. We validate this new approach by a detailed comparison with experimental and theoretical reference data for several prototypical molecule–metal interfaces, where excellent agreement with experiment is achieved: benzene on graphite (0001), and 1,4-benzenediamine, Cu-phthalocyanine, and 3,4,9,10-perylene-tetracarboxylic-dianhydride on Au(111). In particular, we show that the method correctly captures level alignment trends across chemical systems and that it retains its accuracy even for molecules for which conventional DFT suffers from severe self-interaction errors. PMID:25741626

  13. Density functional theory study on Herzberg-Teller contribution in Raman scattering from 4-aminothiophenol-metal complex and metal-4-aminothiophenol-metal junction

    NASA Astrophysics Data System (ADS)

    Liu, Shasha; Zhao, Xiuming; Li, Yuanzuo; Zhao, Xiaohong; Chen, Maodu

    2009-06-01

    Density functional theory (DFT) and time-dependent DFT calculations have been performed to investigate the Raman scattering spectra of metal-molecule complex and metal-molecule-metal junction architectures interconnected with 4-aminothiophenol (PATP) molecule. The simulated profiles of normal Raman scattering (NRS) spectra for the two complexes (Ag2-PATP and PATP-Au2) and the two junctions (Ag2-PATP-Au2 and Au2-PATP-Ag2) are similar to each other, but exhibit obviously different Raman intensities. Due to the lager static polarizabilities of the two junctions, which directly influence the ground state chemical enhancement in NRS spectra, the calculated normal Raman intensities of them are stronger than those of two complexes by the factor of 102. We calculate preresonance Raman scattering (RRS) spectra with incident light at 1064 nm, which is much lower than the S1 electronic transition energy of complexes and junctions. Ag2-PATP-Au2 and Au2-PATP-Ag2 junctions yield higher Raman intensities than those of Ag2-PATP and PATP-Au2 complexes, especially for b2 modes. This effect is mainly attributed to charge transfer (CT) between the metal gap and the PAPT molecule which results in the occurrence of CT resonance enhancement. The calculated pre-RRS spectra strongly depend on the electronic transition state produced by new structures. With excitation at 514.5 nm, the calculated pre-RRS spectra of two complexes and two junctions are stronger than those of with excitation at 1064 nm. A charge difference densities methodology has been used to visually describe chemical enhancement mechanism of RRS spectrum. This methodology aims at visualizing intermolecular CT which provides direct evidence of the Herzberg-Teller mechanism.

  14. A continuum deformation theory for metal-matrix composites at high temperature

    NASA Technical Reports Server (NTRS)

    Robinson, D. N.

    1987-01-01

    A continuum theory is presented for representing the high temperature, time dependent, hereditary deformation behavior of metallic composites that can be idealized as pseudohomogeneous continua with locally definable directional characteristics. Homogenization of textured materials (molecular, granular, fibrous) and applicability of continuum mechanics in structural applications depends on characteristic body dimensions, the severity of gradients (stress, temperature, etc.) in the structure and the relative size of the internal structure (cell size) of the material. The point of view taken here is that the composite is a material in its own right, with its own properties that can be measured and specified for the composite as a whole.

  15. Unified Theory of PT and CP Invariant Topological Metals and Nodal Superconductors.

    PubMed

    Zhao, Y X; Schnyder, Andreas P; Wang, Z D

    2016-04-15

    As PT and CP symmetries are fundamental in physics, we establish a unified topological theory of PT and CP invariant metals and nodal superconductors, based on the mathematically rigorous KO theory. Representative models are constructed for all nontrivial topological cases in dimensions d=1, 2, and 3, with their exotic physical meanings being elucidated in detail. Intriguingly, it is found that the topological charges of Fermi surfaces in the bulk determine an exotic direction-dependent distribution of topological subgap modes on the boundaries. Furthermore, by constructing an exact bulk-boundary correspondence, we show that the topological Fermi points of the PT and CP invariant classes can appear as gapless modes on the boundary of topological insulators with a certain type of anisotropic crystalline symmetry.

  16. k·p theory for two-dimensional transition metal dichalcogenide semiconductors

    NASA Astrophysics Data System (ADS)

    Kormányos, Andor; Burkard, Guido; Gmitra, Martin; Fabian, Jaroslav; Zólyomi, Viktor; Drummond, Neil D.; Fal'ko, Vladimir

    2015-06-01

    We present {k}\\cdot {p} Hamiltonians parametrized by ab initio density functional theory calculations to describe the dispersion of the valence and conduction bands at their extrema (the K, Q, Γ, and M points of the hexagonal Brillouin zone) in atomic crystals of semiconducting monolayer transition metal dichalcogenides (TMDCs). We discuss the parametrization of the essential parts of the {k}\\cdot {p} Hamiltonians for MoS2, MoSe2, MoTe2, WS2, WSe2, and WTe2, including the spin-splitting and spin-polarization of the bands, and we briefly review the vibrational properties of these materials. We then use {k}\\cdot {p} theory to analyse optical transitions in two-dimensional TMDCs over a broad spectral range that covers the Van Hove singularities in the band structure (the M points). We also discuss the visualization of scanning tunnelling microscopy maps.

  17. Theory of the Growth of Epitaxial Graphene on Close-Packed Metals

    NASA Astrophysics Data System (ADS)

    Zangwill, Andrew; Vvedensky, Dimitri

    2011-03-01

    We present a simple rate theory of epitaxial graphene growth on close-packed metals. Motivated by recent low-energy electron microscopy experiments [E. Loginova, N.C.Bartelt, P.J. Feibelman, and K.F. McCarty, New Journal of Physics, 10, 093026 (2008)], our theory supposes that graphene islands grow predominantly by the addition of five-atom clusters, rather than solely by the capture of diffusing carbon atoms. With suitably chosen kinetic parameters, we find quantitative agreement with (i) the measured time-evolution of the adatom density and (ii) the measured temperature-dependence of the adatom density at the onset of nucleation by assuming that the smallest stable precursor to graphene growth is an immobile island composed of six five-atom clusters.

  18. Theory of charge transport in diffusive normal metal/conventional superconductor point contacts

    NASA Astrophysics Data System (ADS)

    Tanaka, Y.; Golubov, A. A.; Kashiwaya, S.

    2003-08-01

    Tunneling conductance in diffusive normal (DN) metal/insulator/s-wave superconductor junctions is calculated for various situations by changing the magnitudes of the resistance and Thouless energy in DN and the transparency of the insulating barrier. The generalized boundary condition introduced by Nazarov [Superlattices and Microstructures 25, 1221 (1999)] is applied, where the ballistic theory by Blonder, Tinkham, and Klapwijk and the diffusive theory by Volkov, Zaitsev, and Klapwijk based on the boundary condition of Kupriyanov and Lukichev are naturally reproduced. It is shown that the proximity effect can enhance (reduce) the tunneling conductance for junctions with a low (high) transparency. A wide variety of dependencies of tunneling conductance on voltage bias is demonstrated including a U-shaped gap like structure, a zero-bias conductance peak, and a zero-bias conductance dip. The temperature dependence of tunneling conductance is also calculated, and the conditions for the reentrance effect are studied.

  19. A simple laminate theory using the orthotropic viscoplasticity theory based on overstress. I - In-plane stress-strain relationships for metal matrix composites

    NASA Technical Reports Server (NTRS)

    Krempl, Erhard; Hong, Bor Zen

    1989-01-01

    A macromechanics analysis is presented for the in-plane, anisotropic time-dependent behavior of metal matrix laminates. The small deformation, orthotropic viscoplasticity theory based on overstress represents lamina behavior in a modified simple laminate theory. Material functions and constants can be identified in principle from experiments with laminae. Orthotropic invariants can be repositories for tension-compression asymmetry and for linear elasticity in one direction while the other directions behave in a viscoplastic manner. Computer programs are generated and tested for either unidirectional or symmetric laminates under in-plane loading. Correlations with the experimental results on metal matrix composites are presented.

  20. Binding Energy of d¹º Transition Metals to Alkenes By Wave Function Theory and Density Functional Theory

    SciTech Connect

    Averkiev, Boris B; Zhao, Yan; Truhlar, Donald G

    2010-06-01

    The structures of Pd(PH₃)₂ and Pt(PH₃)₂ complexes with ethene and conjugated CnHn+2 systems (n=4, 6, 8, and 10) were studied. Their binding energies were calculated using both wave function theory (WFT) and density functional theory (DFT). Previously it was reported that the binding energy of the alkene to the transition metal does not depend strongly on the size of the conjugated CnHn+2 ligand, but that DFT methods systematically underestimate the binding energy more and more significantly as the size of the conjugated system is increased. Our results show that recently developed density functionals predict the binding energy for these systems much more accurately. New benchmark calculations carried out by the coupled cluster method based on Brueckner orbitals with double excitations and a quasiperturbative treatment of connected triple excitations (BCCD(T)) with a very large basis set agree even better with the DFT predictions than do the previous best estimates. The mean unsigned error in absolute and relative binding energies of the alkene ligands to Pd(PH₃)₂ is 2.5 kcal/mol for the ωB97 and M06 density functionals and 2.9 kcal/mol for the M06-L functional. Adding molecular mechanical damped dispersion yields even smaller mean unsigned errors: 1.3 kcal/mol for the M06-D functional, 1.5 kcal/mol for M06- L-D, and 1.8 kcal/mol for B97-D and ωB97X-D. The new functionals also lead to improved accuracy for the analogous Pt complexes. These results show that recently developed density functionals may be very useful for studying catalytic systems involving Pd d¹º centers and alkenes.

  1. Selective pressures for accurate altruism targeting: evidence from digital evolution for difficult-to-test aspects of inclusive fitness theory.

    PubMed

    Clune, Jeff; Goldsby, Heather J; Ofria, Charles; Pennock, Robert T

    2011-03-01

    Inclusive fitness theory predicts that natural selection will favour altruist genes that are more accurate in targeting altruism only to copies of themselves. In this paper, we provide evidence from digital evolution in support of this prediction by competing multiple altruist-targeting mechanisms that vary in their accuracy in determining whether a potential target for altruism carries a copy of the altruist gene. We compete altruism-targeting mechanisms based on (i) kinship (kin targeting), (ii) genetic similarity at a level greater than that expected of kin (similarity targeting), and (iii) perfect knowledge of the presence of an altruist gene (green beard targeting). Natural selection always favoured the most accurate targeting mechanism available. Our investigations also revealed that evolution did not increase the altruism level when all green beard altruists used the same phenotypic marker. The green beard altruism levels stably increased only when mutations that changed the altruism level also changed the marker (e.g. beard colour), such that beard colour reliably indicated the altruism level. For kin- and similarity-targeting mechanisms, we found that evolution was able to stably adjust altruism levels. Our results confirm that natural selection favours altruist genes that are increasingly accurate in targeting altruism to only their copies. Our work also emphasizes that the concept of targeting accuracy must include both the presence of an altruist gene and the level of altruism it produces.

  2. Ground-state properties of rare-earth metals: an evaluation of density-functional theory.

    PubMed

    Söderlind, Per; Turchi, P E A; Landa, A; Lordi, V

    2014-10-15

    The rare-earth metals have important technological applications due to their magnetic properties, but are scarce and expensive. Development of high-performance magnetic materials with less rare-earth content is desired, but theoretical modeling is hampered by complexities of the rare earths electronic structure. The existence of correlated (atomic-like) 4f electrons in the vicinity of the valence band makes any first-principles theory challenging. Here, we apply and evaluate the efficacy of density-functional theory for the series of lanthanides (rare earths), investigating the influence of the electron exchange and correlation functional, spin-orbit interaction, and orbital polarization. As a reference, the results are compared with those of the so-called 'standard model' of the lanthanides in which electrons are constrained to occupy 4f core states with no hybridization with the valence electrons. Some comparisons are also made with models designed for strong electron correlations. Our results suggest that spin-orbit coupling and orbital polarization are important, particularly for the magnitude of the magnetic moments, and that calculated equilibrium volumes, bulk moduli, and magnetic moments show correct trends overall. However, the precision of the calculated properties is not at the level of that found for simpler metals in the Periodic Table of Elements, and the electronic structures do not accurately reproduce x-ray photoemission spectra.

  3. Ground-state properties of rare-earth metals: an evaluation of density-functional theory.

    PubMed

    Söderlind, Per; Turchi, P E A; Landa, A; Lordi, V

    2014-10-15

    The rare-earth metals have important technological applications due to their magnetic properties, but are scarce and expensive. Development of high-performance magnetic materials with less rare-earth content is desired, but theoretical modeling is hampered by complexities of the rare earths electronic structure. The existence of correlated (atomic-like) 4f electrons in the vicinity of the valence band makes any first-principles theory challenging. Here, we apply and evaluate the efficacy of density-functional theory for the series of lanthanides (rare earths), investigating the influence of the electron exchange and correlation functional, spin-orbit interaction, and orbital polarization. As a reference, the results are compared with those of the so-called 'standard model' of the lanthanides in which electrons are constrained to occupy 4f core states with no hybridization with the valence electrons. Some comparisons are also made with models designed for strong electron correlations. Our results suggest that spin-orbit coupling and orbital polarization are important, particularly for the magnitude of the magnetic moments, and that calculated equilibrium volumes, bulk moduli, and magnetic moments show correct trends overall. However, the precision of the calculated properties is not at the level of that found for simpler metals in the Periodic Table of Elements, and the electronic structures do not accurately reproduce x-ray photoemission spectra. PMID:25237839

  4. Nano-fabrication of molecular electronic junctions by targeted modification of metal-molecule bonds

    NASA Astrophysics Data System (ADS)

    Jafri, S. Hassan M.; Löfås, Henrik; Blom, Tobias; Wallner, Andreas; Grigoriev, Anton; Ahuja, Rajeev; Ottosson, Henrik; Leifer, Klaus

    2015-09-01

    Reproducibility, stability and the coupling between electrical and molecular properties are central challenges in the field of molecular electronics. The field not only needs devices that fulfill these criteria but they also need to be up-scalable to application size. In this work, few-molecule based electronics devices with reproducible electrical characteristics are demonstrated. Our previously reported 5 nm gold nanoparticles (AuNP) coated with ω-triphenylmethyl (trityl) protected 1,8-octanedithiol molecules are trapped in between sub-20 nm gap spacing gold nanoelectrodes forming AuNP-molecule network. When the trityl groups are removed, reproducible devices and stable Au-thiol junctions are established on both ends of the alkane segment. The resistance of more than 50 devices is reduced by orders of magnitude as well as a reduction of the spread in the resistance histogram is observed. By density functional theory calculations the orders of magnitude decrease in resistance can be explained and supported by TEM observations thus indicating that the resistance changes and strongly improved resistance spread are related to the establishment of reproducible and stable metal-molecule bonds. The same experimental sequence is carried out using 1,6-hexanedithiol functionalized AuNPs. The average resistances as a function of molecular length, demonstrated herein, are comparable to the one found in single molecule devices.

  5. Nano-fabrication of molecular electronic junctions by targeted modification of metal-molecule bonds.

    PubMed

    Jafri, S Hassan M; Löfås, Henrik; Blom, Tobias; Wallner, Andreas; Grigoriev, Anton; Ahuja, Rajeev; Ottosson, Henrik; Leifer, Klaus

    2015-01-01

    Reproducibility, stability and the coupling between electrical and molecular properties are central challenges in the field of molecular electronics. The field not only needs devices that fulfill these criteria but they also need to be up-scalable to application size. In this work, few-molecule based electronics devices with reproducible electrical characteristics are demonstrated. Our previously reported 5 nm gold nanoparticles (AuNP) coated with ω-triphenylmethyl (trityl) protected 1,8-octanedithiol molecules are trapped in between sub-20 nm gap spacing gold nanoelectrodes forming AuNP-molecule network. When the trityl groups are removed, reproducible devices and stable Au-thiol junctions are established on both ends of the alkane segment. The resistance of more than 50 devices is reduced by orders of magnitude as well as a reduction of the spread in the resistance histogram is observed. By density functional theory calculations the orders of magnitude decrease in resistance can be explained and supported by TEM observations thus indicating that the resistance changes and strongly improved resistance spread are related to the establishment of reproducible and stable metal-molecule bonds. The same experimental sequence is carried out using 1,6-hexanedithiol functionalized AuNPs. The average resistances as a function of molecular length, demonstrated herein, are comparable to the one found in single molecule devices.

  6. Designing mixed metal halide ammines for ammonia storage using density functional theory and genetic algorithms.

    PubMed

    Jensen, Peter Bjerre; Lysgaard, Steen; Quaade, Ulrich J; Vegge, Tejs

    2014-09-28

    Metal halide ammines have great potential as a future, high-density energy carrier in vehicles. So far known materials, e.g. Mg(NH3)6Cl2 and Sr(NH3)8Cl2, are not suitable for automotive, fuel cell applications, because the release of ammonia is a multi-step reaction, requiring too much heat to be supplied, making the total efficiency lower. Here, we apply density functional theory (DFT) calculations to predict new mixed metal halide ammines with improved storage capacities and the ability to release the stored ammonia in one step, at temperatures suitable for system integration with polymer electrolyte membrane fuel cells (PEMFC). We use genetic algorithms (GAs) to search for materials containing up to three different metals (alkaline-earth, 3d and 4d) and two different halides (Cl, Br and I) - almost 27,000 combinations, and have identified novel mixtures, with significantly improved storage capacities. The size of the search space and the chosen fitness function make it possible to verify that the found candidates are the best possible candidates in the search space, proving that the GA implementation is ideal for this kind of computational materials design, requiring calculations on less than two percent of the candidates to identify the global optimum. PMID:25115581

  7. Density functional theory based study of chlorine doped WS2-metal interface

    NASA Astrophysics Data System (ADS)

    Chanana, Anuja; Mahapatra, Santanu

    2016-03-01

    Investigation of a transition metal dichalcogenide (TMD)-metal interface is essential for the effective functioning of monolayer TMD based field effect transistors. In this work, we employ the Density Functional Theory calculations to analyze the modulation of the electronic structure of monolayer WS2 with chlorine doping and the relative changes in the contact properties when interfaced with gold and palladium. We initially examine the atomic and electronic structures of pure and doped monolayer WS2 supercell and explore the formation of midgap states with band splitting near the conduction band edge. Further, we analyze the contact nature of the pure supercell with Au and Pd. We find that while Au is physiosorbed and forms n-type contact, Pd is chemisorped and forms p-type contact with a higher valence electron density. Next, we study the interface formed between the Cl-doped supercell and metals and observe a reduction in the Schottky barrier height (SBH) in comparison to the pure supercell. This reduction found is higher for Pd in comparison to Au, which is further validated by examining the charge transfer occurring at the interface. Our study confirms that Cl doping is an efficient mechanism to reduce the n-SBH for both Au and Pd, which form different types of contact with WS2.

  8. Density-Functional Theory Studies of Correlation Energy Effects at Metallic Surfaces.

    NASA Astrophysics Data System (ADS)

    Mohammed, Abdel-Raouf Eid

    In this thesis we study the effects of correlation in the inhomogeneous electron gas at metallic surfaces. These studies are performed within the context of density-functional theory (DFT). Using accurate representations of the electronic density profile, we have estimated variationally the surface correlation energy of jellium metal. The accuracy of these estimates is founded in the assumption that the exchange -correlation energy functional of the density is approximated accurately by the wave-vector analysis method, and by the fact that the non-local exchange energy contributions are treated exactly. In contrast to the previously accepted conclusion that for surfaces correlation effects are as significant as exchange, our results indicate the ratio of these energies to lie between 34% - 97% over the metallic density range, the smaller ratios corresponding to the higher density metals. In this work we have also examined the local density (LDA) and gradient expansion approximations (GEA) (to O((DEL)('2))) for the correlation energy. We have demonstrated for realistic metal surface densities the cancellation of the errors in the LDA for exchange and correlation, and shown that the density profiles at surfaces would have to be unphysically slowly varying for the correlation energy GEA to converge. We have also studied the effects of correlation at surfaces by screening the exchange, and observe that the surface exchange energy for screened-Coulomb interaction decreases as the screening length is reduced. Thus, the more short-ranged the interaction, the easier it is to split the crystal in two. In addition we have derived the DFT first gradient correction coefficient in the GEA for the screened-Coulomb exchange energy, and shown it to be the same as that obtained within Hartree -Fock theory (HFT) for finite screening. This coefficient reduces to the DFT bare-Coulomb interaction value in the limit of no screening in which limit the HFT coefficient is singular. The GEA

  9. Influence of electronic stopping on sputtering induced by cluster impact on metallic targets

    SciTech Connect

    Sandoval, Luis; Urbassek, Herbert M.

    2009-04-01

    Using molecular-dynamics simulation, we model the sputtering of a Au (111) crystallite induced by the impact of Au{sub 13} projectiles with total energies up to 500 keV. Due to the uncertainty of the electronic stopping of Au moving in particular at small velocities, we performed several simulations, in which the electronic stopping parameters are systematically changed. Our results demonstrate the dominating influence of the cut-off energy E{sub c}, below which the high-velocity electronic stopping of atoms is switched off in the simulation. If E{sub c} is smaller than roughly one half the cohesive energy of the target, sputtering ceases after a few ps; the spike contribution to sputtering (also called phase explosion or gas-flow contribution) is entirely quenched and the sputtering yield is up to an order of magnitude smaller than when electronic stopping is taken into account only at higher atom energies. Our results demonstrate the importance of a careful modeling of electronic stopping in simulations of spike sputtering from metals.

  10. Scattering from extended targets in range-dependent fluctuating ocean-waveguides with clutter from theory and experiments.

    PubMed

    Jagannathan, Srinivasan; Küsel, Elizabeth T; Ratilal, Purnima; Makris, Nicholas C

    2012-08-01

    Bistatic, long-range measurements of acoustic scattered returns from vertically extended, air-filled tubular targets were made during three distinct field experiments in fluctuating continental shelf waveguides. It is shown that Sonar Equation estimates of mean target-scattered intensity lead to large errors, differing by an order of magnitude from both the measurements and waveguide scattering theory. The use of the Ingenito scattering model is also shown to lead to significant errors in estimating mean target-scattered intensity in the field experiments because they were conducted in range-dependent ocean environments with large variations in sound speed structure over the depth of the targets, scenarios that violate basic assumptions of the Ingenito model. Green's theorem based full-field modeling that describes scattering from vertically extended tubular targets in range-dependent ocean waveguides by taking into account nonuniform sound speed structure over the target's depth extent is shown to accurately describe the statistics of the targets' scattered field in all three field experiments. Returns from the man-made targets are also shown to have a very different spectral dependence from the natural target-like clutter of the dominant fish schools observed, suggesting that judicious multi-frequency sensing may often provide a useful means of distinguishing fish from man-made targets.

  11. THE DEPENDENCE OF BROWN DWARF RADII ON ATMOSPHERIC METALLICITY AND CLOUDS: THEORY AND COMPARISON WITH OBSERVATIONS

    SciTech Connect

    Burrows, Adam; Nampaisarn, Thane; Heng, Kevin E-mail: tnampais@astro.princeton.edu

    2011-07-20

    Employing realistic and consistent atmosphere boundary conditions, we have generated evolutionary models for brown dwarfs and very low mass stars (VLMs) for different atmospheric metallicities ([Fe/H]), with and without clouds. We find that the spread in radius at a given mass and age can be as large as {approx}10% to {approx}25%, with higher-metallicity, higher-cloud-thickness atmospheres resulting quite naturally in larger radii. For each 0.1 dex increase in [Fe/H], radii increase by {approx}1% to {approx}2.5%, depending upon the age and mass. We also find that, while for smaller masses and older ages brown dwarf radii decrease with increasing helium fraction (Y, as expected), for more massive brown dwarfs and a wide range of ages they increase with helium fraction. The increase in radius in going from Y = 0.25 to Y = 0.28 can be as large as {approx}0.025 R{sub J} ({approx}2.5%). Furthermore, we find that for VLMs an increase in atmospheric metallicity from 0.0 to 0.5 dex, increases radii by {approx}4%, and from -0.5 to 0.5 dex by {approx}10%. Therefore, we suggest that opacity due to higher metallicity might naturally account for the apparent radius anomalies in some eclipsing VLM systems. Ten to twenty-five percent variations in radius exceed errors stemming from uncertainties in the equation of state alone. This serves to emphasize that transit and eclipse measurements of brown dwarf radii constrain numerous effects collectively, importantly including the atmosphere and condensate cloud models, and not just the equation of state. At all times, one is testing a multi-parameter theory, and not a universal radius-mass relation.

  12. Covalency in Metal-Oxygen Multiple Bonds Evaluated Using Oxygen K-edge Spectroscopy and Electronic Structure Theory

    SciTech Connect

    Minasian, Stefan G.; Keith, Jason M.; Batista, Enrique R.; Boland, Kevin S.; Bradley, Joseph A.; Daly, Scott R.; Kozimor, Stosh A.; Lukens, Wayne W.; Martin, Richard L.; Nordlund, Dennis; Seidler, Gerald T.; Shuh, David K.; Sokaras, Dimosthenis; Tyliszczak, Tolek; Wagner, Gregory L.; Weng, Tsu-Chein; Yang, Ping

    2014-01-01

    Advancing theories of how metal oxygen bonding influences metal oxo properties can expose new avenues for innovation in materials science, catalysis, and biochemistry. Historically, spectroscopic analyses of the transition metal peroxyanions, MO4x-, have formed the basis for new M O bonding theories. Herein, relative changes in M O orbital mixing in MO42- (M = Cr, Mo, W) and MO41- (M = Mn, Tc, Re) are evaluated for the first time by non-resonant inelastic X-ray scattering, X-ray absorption spectroscopy using fluorescence and transmission (via a scanning transmission X-ray microscope), and linear-response density functional theory. The results suggest that moving from Group 6 to Group 7 or down the triads increases M O e () mixing. Meanwhile, t2 mixing ( + ) remains relatively constant within the same Group. These unexpected changes in frontier orbital energy and composition are evaluated in terms of periodic trends in d orbital energy and radial extension.

  13. Evaluation of metal biouptake from the analysis of bulk metal depletion kinetics at various cell concentrations: theory and application.

    PubMed

    Rotureau, Elise; Billard, Patrick; Duval, Jérôme F L

    2015-01-20

    Bioavailability of trace metals is a key parameter for assessment of toxicity on living organisms. Proper evaluation of metal bioavailability requires monitoring the various interfacial processes that control metal partitioning dynamics at the biointerface, which includes metal transport from solution to cell membrane, adsorption at the biosurface, internalization, and possible excretion. In this work, a methodology is proposed to quantitatively describe the dynamics of Cd(II) uptake by Pseudomonas putida. The analysis is based on the kinetic measurement of Cd(II) depletion from bulk solution at various initial cell concentrations using electroanalytical probes. On the basis of a recent formalism on the dynamics of metal uptake by complex biointerphases, the cell concentration-dependent depletion time scales and plateau values reached by metal concentrations at long exposure times (>3 h) are successfully rationalized in terms of limiting metal uptake flux, rate of excretion, and metal affinity to internalization sites. The analysis shows the limits of approximate depletion models valid in the extremes of high and weak metal affinities. The contribution of conductive diffusion transfer of metals from the solution to the cell membrane in governing the rate of Cd(II) uptake is further discussed on the basis of estimated resistances for metal membrane transfer and extracellular mass transport.

  14. Evaluation of metal biouptake from the analysis of bulk metal depletion kinetics at various cell concentrations: theory and application.

    PubMed

    Rotureau, Elise; Billard, Patrick; Duval, Jérôme F L

    2015-01-20

    Bioavailability of trace metals is a key parameter for assessment of toxicity on living organisms. Proper evaluation of metal bioavailability requires monitoring the various interfacial processes that control metal partitioning dynamics at the biointerface, which includes metal transport from solution to cell membrane, adsorption at the biosurface, internalization, and possible excretion. In this work, a methodology is proposed to quantitatively describe the dynamics of Cd(II) uptake by Pseudomonas putida. The analysis is based on the kinetic measurement of Cd(II) depletion from bulk solution at various initial cell concentrations using electroanalytical probes. On the basis of a recent formalism on the dynamics of metal uptake by complex biointerphases, the cell concentration-dependent depletion time scales and plateau values reached by metal concentrations at long exposure times (>3 h) are successfully rationalized in terms of limiting metal uptake flux, rate of excretion, and metal affinity to internalization sites. The analysis shows the limits of approximate depletion models valid in the extremes of high and weak metal affinities. The contribution of conductive diffusion transfer of metals from the solution to the cell membrane in governing the rate of Cd(II) uptake is further discussed on the basis of estimated resistances for metal membrane transfer and extracellular mass transport. PMID:25525993

  15. Exploring Errors in Target Language Learning and Use: Practice Meets Theory

    ERIC Educational Resources Information Center

    Wang, Ping

    2008-01-01

    The paper tries to answer the question--to what extent the English Language Teaching theory informs the ELT practice in a reflective case study. It argues that even if it is challenging considering what is beyond the theory in practical use of theory, yet if teacher educators in the field of ELT have a solid academic foundation, they will have the…

  16. Self-interaction correction in multiple scattering theory: application to transition metal oxides

    SciTech Connect

    Daene, Markus W; Lueders, Martin; Ernst, Arthur; Diemo, Koedderitzsch; Temmerman, Walter M; Szotek, Zdzislawa; Wolfam, Hergert

    2009-01-01

    We apply to transition metal monoxides the self-interaction corrected (SIC) local spin density (LSD) approximation, implemented locally in the multiple scattering theory within the Korringa-Kohn-Rostoker (KKR) band structure method. The calculated electronic structure and in particular magnetic moments and energy gaps are discussed in reference to the earlier SIC results obtained within the LMTO-ASA band structure method, involving transformations between Bloch and Wannier representations to solve the eigenvalue problem and calculate the SIC charge and potential. Since the KKR can be easily extended to treat disordered alloys, by invoking the coherent potential approximation (CPA), in this paper we compare the CPA approach and supercell calculations to study the electronic structure of NiO with cation vacancies.

  17. Exploring the surface reactivity of 3d metal endofullerenes: a density-functional theory study.

    PubMed

    Estrada-Salas, Rubén E; Valladares, Ariel A

    2009-09-24

    Changes in the preferential sites of electrophilic, nucleophilic, and radical attacks on the pristine C60 surface with endohedral doping using 3d transition metal atoms were studied via two useful reactivity indices, namely the Fukui functions and the molecular electrostatic potential. Both of these were calculated at the density functional BPW91 level of theory with the DNP basis set. Our results clearly show changes in the preferential reactivity sites on the fullerene surface when it is doped with Mn, Fe, Co, or Ni atoms, whereas there are no significant changes in the preferential reactivity sites on the C60 surface upon endohedral doping with Cu and Zn atoms. Electron affinities (EA), ionization potentials (IP), and HOMO-LUMO gaps (Eg) were also calculated to complete the study of the endofullerene's surface reactivity. These findings provide insight into endofullerene functionalization, an important issue in their application.

  18. Electronic-Structure Theory of Organic Semiconductors: Charge-Transport Parameters and Metal/Organic Interfaces

    NASA Astrophysics Data System (ADS)

    Coropceanu, Veaceslav; Li, Hong; Winget, Paul; Zhu, Lingyun; Brédas, Jean-Luc

    2013-07-01

    We focus this review on the theoretical description, at the density functional theory level, of two key processes that are common to electronic devices based on organic semiconductors (such as organic light-emitting diodes, field-effect transistors, and solar cells), namely charge transport and charge injection from electrodes. By using representative examples of current interest, our main goal is to introduce some of the reliable theoretical methodologies that can best depict these processes. We first discuss the evaluation of the microscopic parameters that determine charge-carrier transport in organic molecular crystals, i.e., electronic couplings and electron-vibration couplings. We then examine the electronic structure at interfaces between an organic layer and a metal or conducting oxide electrode, with an emphasis on the work-function modifications induced by the organic layer and on the interfacial energy-level alignments.

  19. CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES: The MAEAM Model and Anharmonic Theory for the Bulk Modulus of Al Metal

    NASA Astrophysics Data System (ADS)

    Liao, Shu-Zhi; Wang, Xiao-Li; Zhu, Xiang-Ping; Zhang, Chun; Ouyang, Yi-Fang; Zhang, Bang-Wei

    2009-08-01

    The modified analytic embedded atom method (MAEAM) model and the anharmonic theory are used to study the bulk modulus of f cc Al metal. The result shows that the bulk modulus can be described by a quadratic function of temperature. The result is in good agreement with the experimental data and theoretical results calculated by the first principle calculation etc. This outcome indicates that the temperature dependence of the bulk modulus for f cc Al metal can be academically studied with the MAEAM model combining with the anharmonic theory.

  20. FY2014 FES (Fusion Energy Sciences) Theory & Simulation Performance Target, Final Report

    SciTech Connect

    Fu, Guoyong; Budny, Robert; Gorelenkov, Nikolai; Poli, Francesca; Chen, Yang; McClenaghan, Joseph; Lin, Zhihong; Spong, Don; Bass, Eric; Waltz, Ron

    2014-10-14

    We report here the work done for the FY14 OFES Theory Performance Target as given below: "Understanding alpha particle confinement in ITER, the world's first burning plasma experiment, is a key priority for the fusion program. In FY 2014, determine linear instability trends and thresholds of energetic particle-driven shear Alfven eigenmodes in ITER for a range of parameters and profiles using a set of complementary simulation models (gyrokinetic, hybrid, and gyrofluid). Carry out initial nonlinear simulations to assess the effects of the unstable modes on energetic particle transport". In the past year (FY14), a systematic study of the alpha-driven Alfven modes in ITER has been carried out jointly by researchers from six institutions involving seven codes including the transport simulation code TRANSP (R. Budny and F. Poli, PPPL), three gyrokinetic codes: GEM (Y. Chen, Univ. of Colorado), GTC (J. McClenaghan, Z. Lin, UCI), and GYRO (E. Bass, R. Waltz, UCSD/GA), the hybrid code M3D-K (G.Y. Fu, PPPL), the gyro-fluid code TAEFL (D. Spong, ORNL), and the linear kinetic stability code NOVA-K (N. Gorelenkov, PPPL). A range of ITER parameters and profiles are specified by TRANSP simulation of a hybrid scenario case and a steady-state scenario case. Based on the specified ITER equilibria linear stability calculations are done to determine the stability boundary of alpha-driven high-n TAEs using the five initial value codes (GEM, GTC, GYRO, M3D-K, and TAEFL) and the kinetic stability code (NOVA-K). Both the effects of alpha particles and beam ions have been considered. Finally, the effects of the unstable modes on energetic particle transport have been explored using GEM and M3D-K.

  1. Adsorption structures and energetics of molecules on metal surfaces: Bridging experiment and theory

    NASA Astrophysics Data System (ADS)

    Maurer, Reinhard J.; Ruiz, Victor G.; Camarillo-Cisneros, Javier; Liu, Wei; Ferri, Nicola; Reuter, Karsten; Tkatchenko, Alexandre

    2016-05-01

    Adsorption geometry and stability of organic molecules on surfaces are key parameters that determine the observable properties and functions of hybrid inorganic/organic systems (HIOSs). Despite many recent advances in precise experimental characterization and improvements in first-principles electronic structure methods, reliable databases of structures and energetics for large adsorbed molecules are largely amiss. In this review, we present such a database for a range of molecules adsorbed on metal single-crystal surfaces. The systems we analyze include noble-gas atoms, conjugated aromatic molecules, carbon nanostructures, and heteroaromatic compounds adsorbed on five different metal surfaces. The overall objective is to establish a diverse benchmark dataset that enables an assessment of current and future electronic structure methods, and motivates further experimental studies that provide ever more reliable data. Specifically, the benchmark structures and energetics from experiment are here compared with the recently developed van der Waals (vdW) inclusive density-functional theory (DFT) method, DFT + vdWsurf. In comparison to 23 adsorption heights and 17 adsorption energies from experiment we find a mean average deviation of 0.06 Å and 0.16 eV, respectively. This confirms the DFT + vdWsurf method as an accurate and efficient approach to treat HIOSs. A detailed discussion identifies remaining challenges to be addressed in future development of electronic structure methods, for which the here presented benchmark database may serve as an important reference.

  2. Trends in Formic Acid Decomposition on Model Transition Metal Surfaces: A Density Functional Theory Study

    SciTech Connect

    Herron, Jeffrey A.; Scaranto, Jessica; Ferrin, Peter A.; Li, Sha; Mavrikakis, Manos

    2014-12-05

    We present a first-principles, self-consistent periodic density functional theory (PW91-GGA) study of formic acid (HCOOH) decomposition on model (111) and (100) facets of eight fcc metals (Au, Ag, Cu, Pt, Pd, Ni, Ir, and Rh) and (0001) facets of four hcp (Co, Os, Ru, and Re) metals. The calculated binding energies of key formic acid decomposition intermediates including formate (HCOO), carboxyl (COOH), carbon monoxide (CO), water (H2O), carbon dioxide (CO2), hydroxyl (OH), carbon (C), oxygen (O), and hydrogen (H; H2) are presented. Using these energetics, we develop thermochemical potential energy diagrams for both the carboxyl-mediated and the formate-mediated dehydrogenation mechanisms on each surface. We evaluate the relative stability of COOH, HCOO, and other isomeric intermediates (i.e., CO + OH, CO2 + H, CO + O + H) on these surfaces. These results provide insights into formic acid decomposition selectivity (dehydrogenation versus dehydration), and in conjunction with calculated vibrational frequency modes, the results can assist with the experimental search for the elusive carboxyl (COOH) surface intermediate. Results are compared against experimental reports in the literature.

  3. Atomic collisions in suprafluid helium-nanodroplets: timescales for metal-cluster formation derived from He-density functional theory

    PubMed Central

    Volk, Alexander; Thaler, Philipp

    2015-01-01

    Collision times for the coinage metal atoms Cu, Ag and Au in He-droplets are derived from helium density functional theory and molecular dynamics simulations. The strength of the attractive interaction between the metal atoms turns out to be less important than the mass of the propagating metal atoms. Even for small droplets consisting of a few thousand helium atoms, the collision times are shortest for Cu, followed by Ag and Au, despite the higher binding energy of Au2 compared to Cu2. PMID:25812719

  4. Metals suitable for fluorine gas target bodies: first use of aluminum for the production of [18F]F2.

    PubMed

    Bishop, A; Satyamurthy, N; Bida, G; Phelps, M; Barrio, J R

    1996-04-01

    A comprehensive evaluation of different metals (aluminum, silver, copper, nickel, and gold-plated copper) was undertaken for the fabrication of target bodies with straight and conical bore shapes for the production of [18F]F2 via the 20Ne(d,alpha)18F nuclear reaction. Of these metals, aluminum, silver and copper have never been used for the production of [18F]F2. All these target bodies were easily passivated using a mild beam-induced plasma technique in the presence of 1% F2 in neon or argon. The recovery of 18F activity was higher with electroformed nickel and silver bodies, probably due to favorable thermal conductivities. Aluminum proved to be a useful material for fluorine gas targets. The consistent recovery of 18F activities, ease and low cost of manufacturing and low nuclear activation properties all make aluminum an ideal choice for fluorine gas targetry. To our knowledge, this investigation is the first to highlight the use of aluminum as a target body material for the routine production of [18F]F2. A reasonable mechanism based on the Langmuir-Rideal surface atom recombination is also proposed for the behavior of [18F]F2 recovery from a nickel target body.

  5. The Elastic Behaviour of Sintered Metallic Fibre Networks: A Finite Element Study by Beam Theory

    PubMed Central

    Bosbach, Wolfram A.

    2015-01-01

    Background The finite element method has complimented research in the field of network mechanics in the past years in numerous studies about various materials. Numerical predictions and the planning efficiency of experimental procedures are two of the motivational aspects for these numerical studies. The widespread availability of high performance computing facilities has been the enabler for the simulation of sufficiently large systems. Objectives and Motivation In the present study, finite element models were built for sintered, metallic fibre networks and validated by previously published experimental stiffness measurements. The validated models were the basis for predictions about so far unknown properties. Materials and Methods The finite element models were built by transferring previously published skeletons of fibre networks into finite element models. Beam theory was applied as simplification method. Results and Conclusions The obtained material stiffness isn’t a constant but rather a function of variables such as sample size and boundary conditions. Beam theory offers an efficient finite element method for the simulated fibre networks. The experimental results can be approximated by the simulated systems. Two worthwhile aspects for future work will be the influence of size and shape and the mechanical interaction with matrix materials. PMID:26569603

  6. Report: Central nervous system (CNS) toxicity caused by metal poisoning: Brain as a target organ.

    PubMed

    Gilani, Syeda Rubina; Zaidi, Syed Raza Ali; Batool, Madeeha; Bhatti, Amanat Ali; Durrani, Arjumand Iqbal; Mahmood, Zaid

    2015-07-01

    People relate the neural disorders with either inheritance or psychological violence but there might be some other reasons responsible for the ailment of people that do not have such a background. The present study explains the chronic effect of heavy toxic metals on nervous system. During experimentation, rabbits used as laboratory animals, were given test metals in their diet. Concentration of metals given to them in the diet was less than their tolerable dietary intake. Behavioral changes were observed during experimentation. Periodic increase in the metal concentration was seen in the blood sample of rabbits. They were slaughtered after a period of eight months of slow poisoning. Histological examination of brain tissues was performed. The brain samples were analyzed by Atomic absorption spectroscopy and Inductively Coupled Plasma Mass Spectrometry to find the retention of heavy metals in mammalian brain. Concentration of lead, mercury and cadmium in the blood samples of occupationally exposed people and patients with neurological disorders at the time of neurosurgery was determined by using the same techniques. During circulation, toxic metals passes through the nerve capillaries to settle down in the brain. Heavy metals cross the blood brain barrier and 'may retain themselves in it. Brain tumors and biopsy samples of patients with neurological disorder were also analyzed to relate neurotoxicity and heavy metal poisoning. Results obtained shows that lead, mercury and cadmium retain themselves in the brain for longer period of time and are one of the causes of neurotoxicity.

  7. Methods of studying the composition of the low-energy ion beams and the surface of deuterated-metal targets

    NASA Astrophysics Data System (ADS)

    Kuznetsov, S. I.; Dudkin, G. N.; Nechaev, B. A.; Bystritsky, I. D.

    2016-06-01

    To study the reactions between the light nuclei (dd, pd, d3He, d4He) with ultralow collision energies, there is a need to obtain the high-precision experimental results on the purity of the target surface saturated with the hydrogen isotopes (protium, deuterium) and on the number and composition of the accelerated particles falling on the target. To solve this problem, a method has been developed and tested for operational testing the quality of the vacuum system and the cleaning of the metal target surface saturated with deuterium. The paper also presents the measurement results for the true flow of the accelerated ions and neutrals of hydrogen (deuterium), using a multigrid electrostatic energy analyzer. The values of the ion and neutral components of the accelerated particle flow were received for the Hall ion source. The values of the secondary electron emission coefficients were determined for a number of the metal targets (Cu, Ti, Ta, Zr) in the range of the accelerated ion energies of 3-12 keV.

  8. Measurement of debris and shrapnel plumes from cylindrical metal targets used in high-power laser systems

    NASA Astrophysics Data System (ADS)

    Andrew, J. E.; Wallace, K. A.

    2012-11-01

    All laser targets subjected to heating by focused energetic lasers for the study of high temperature plasmas produce shrapnel, debris or radiation directly or indirectly that impact and coat the optics, instruments and surfaces used in the vacuum chambers employed for such studies. We describe the spatial distributions of the target ejecta arising from various configurations of thin walled metal cylinder targets and their mechanical mounting systems that have been deployed on the Helen and ZBeamlet lasers. We also demonstrate how this data can be used to evaluate threats to optical surfaces and ancillary instruments in high energy, high power laser systems. The methods used for characterizing and quantifying material plumes will also be described.

  9. Refractory metals in molten salts: Theory and simulation of geometry, electronic structure, and electron transport

    NASA Astrophysics Data System (ADS)

    Koslowski, Thorsten

    2000-12-01

    In this work, we present a theoretical and numerical study of the microscopic and electronic structure of solutions of refractory metal halides in alkali halide melts, [NbCl5]x[KCl]1-x and [TaCl5]x[KCl]1-x with 0⩽x⩽0.5. The geometry of the melts is described by ensembles of charged hard spheres, the electronic structure is modeled by a tight-binding Hamiltonian, which is extended by a reaction field to describe the diabatic energy profile of the electronic self-exchange in many-orbital mixed-valence systems. Despite its simplicity, the model leads to the formation of distorted octahedral [NbCl6]- and [TaCl6]- clusters, as evident both from the inspection of the simulation geometries and from the analysis of the partial pair distribution functions. Even in the presence of the strong potential energy fluctuations characteristic of ionic liquids, the octahedral structure is manifest in the density of states in a t2g-eg splitting of the conduction band. The Hamiltonian that describes mixed-valence systems is solved self-consistently. Using an attractive Hubbard parameter of 1.5 eV, we show that the numerical results can be interpreted by Marcus' theory of outer-sphere electron transfer reactions with a reorganization energy of 2.2 eV, an electronic coupling parameter of 0.12 eV, and an activation energy of 0.42 eV. Both anion-d metal cation and intervalence charge transfer excitations contribute to the optical absorption spectrum, the latter leads to a pronounced polaron absorption peak. These findings are compared to recent experimental results.

  10. Proceedings of Soil Decon `93: Technology targeting radionuclides and heavy metals

    SciTech Connect

    Not Available

    1993-09-01

    The principal objective for convening this workshop was to exchange ideas and discuss with scientists and engineers methods for removing radionuclides and/or toxic metals from soils. Over the years there have been numerous symposia, conferences, and workshops directed at soil remediation. However, this may be the first where the scope was narrowed to the removal of radionuclides and toxic metals from soils. The intent was to focus on the separation processes controlling the removal of the radionuclide and/or metal from soil. Its purpose was not intended to be a soil washing/leaching workshop, but rather to identify a variety or combination of processes (chemical, physical, and biological) that can be used in concert with the applicable engineering approaches to decontaminate soils of radionuclides and toxic metals. Abstracts and visual aids used by the speakers of the workshop are presented in this document.

  11. Physics of laser fusion. Vol. I. Theory of the coronal plasma in laser-fusion targets

    SciTech Connect

    Max, C.E.

    1981-12-01

    This monograph deals with the physics of the coronal region in laser fusion targets. The corona consists of hot plasma which has been evaporated from the initially solid target during laser heating. It is in the corona that the laser light is absorbed by the target, and the resulting thermal energy is conducted toward cold high-density regions, where ablation occurs. The topics to be discussed are theoretical mechanisms for laser light absorption and reflection, hot-electron production, and the physics of heat conduction in laser-produced plasmas. An accompanying monograph by H. Ahlstrom (Vol.II) reviews the facilities, diagnostics, and data from recent laser fusion experiments.

  12. Theory of molecule metal nano-particle interaction: Quantum description of plasmonic lasing

    SciTech Connect

    Zhang, Yuan May, Volkhard

    2015-06-14

    The recent quantum description of a few molecules interacting with plasmon excitations of a spherical metal nano-particle (MNP) as presented in the work of Zhang and May [Phys. Rev. B 89, 245441 (2014)] is extended to systems with up to 100 molecules. We demonstrate the possibility of multiple plasmon excitation and describe their conversion into far-field photons. The calculation of the steady-state photon emission spectrum results in an emission line-narrowing with an increasing number of molecules coupled to the MNP. This is considered as an essential criterion for the action of the molecule-MNP system as a nano-laser. To have exact results for systems with up to 20 molecules, we proceed as recently described by Richter et al. [Phys. Rev. B 91, 035306 (2015)] and study a highly symmetric system. It assumes an equatorial and regular position of identical molecules in such a way that their coupling is dominated by that to a single MNP dipole-plasmon excitation. Changing from the exact computation of the system’s complete density matrix to an approximate theory based on the reduced plasmon density matrix, systems with more than 100 molecules can be described. Finally, nonlinear rate equations are proposed which reproduce the mean number of excited plasmons in their dependence of the number of molecules and of the used pump rate. The second order intensity correlation function of emitted photons is related to the respective plasmon correlation function which approaches unity when the system starts lasing.

  13. Density functional theory study of CO2 capture with transition metal oxides and hydroxides

    NASA Astrophysics Data System (ADS)

    Zhang, Bo; Duan, Yuhua; Johnson, Karl

    2012-02-01

    We have used density functional theory (DFT) employing several different exchange-correlation functionals (PW91, PBE, PBEsol, TPSS, and revTPSS) coupled with lattice dynamics calculations to compute the thermodynamics of CO2 absorption/desorption reactions for selected transition metal oxides, (TMO), and hydroxides, TM(OH)2, where TM = Mn, Ni, Zn, and Cd. The van't Hoff plots, which describe the reaction equilibrium as a function of the partial pressures of CO2 and H2O as well as temperature, were computed from DFT total energies, complemented by the free energy contribution of solids and gases from lattice dynamics and statistical mechanics, respectively. We find that the PBEsol functional calculations are generally in better agreement with experimental phase equilibrium data compared with the other functionals we tested. In contrast, the formation enthalpies of the compounds are better computed with the TPSS and revTPSS functionals. The PBEsol functional gives better equilibrium properties due to a partial cancellation of errors in the enthalpies of formation. We have identified all CO2 capture reactions that lie on the Gibbs free energy convex hull as a function of temperature and the partial pressures of CO2 and H2O for all TMO and TM(OH)2 systems studied here.

  14. Theory of intervalley Coulomb interactions in monolayer transition-metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Dery, Hanan

    2016-08-01

    Exciton optical transitions in transition-metal dichalcogenides offer unique opportunities to study rich many-body physics. Recent experiments in monolayer WSe2 and WS2 have shown that, while the low-temperature photoluminescence from neutral excitons and three-body complexes is suppressed in the presence of elevated electron densities or strong photoexcitation, new dominant peaks emerge in the low-energy side of the spectrum. I present a theory that elucidates the nature of these optical transitions showing the role of the intervalley Coulomb interaction. After deriving a compact dynamical form for the Coulomb potential, I calculate the self-energy of electrons due to their interaction with this potential. For electrons in the upper valleys of the spin-split conduction band, the self-energy includes a moderate redshift due to exchange and, most importantly, a correlation-induced virtual state in the band gap. The latter sheds light on the origin of the luminescence in monolayer WSe2 and WS2 in the presence of pronounced many-body interactions.

  15. The electronic properties of noble metal doped silicon nanocrystals using hybrid density functional theory

    NASA Astrophysics Data System (ADS)

    Mayfield, Cedric Leon

    One of the most challenging issues in semiconductor physics is to engineer band structures for a particular device. Contemporary photovoltaic (PV) and photoelectrochemical (PEC) devices rely on defect energy levels and nano-scaling to customize their band structures. As the length scale of a material becomes comparable to the exciton Bohr radius the free particle behavior of charge carriers transition to bound states where energy levels are quantized. In this thesis, hybrid density functional theory has been used to study the electronic properties of silicon nanocrystals (SiNCs) having 75, 150 and 300 silicon atoms. The atomic coordinates were defined by two geometries (diamond and wurtzite) of bulk phase silicon. The global minimum energy structures for both geometries at each size were found for particular variation on magnetic moments, dopant, dopant position, and surface passivation with hydrogen. We report our results on bond lengths, binding energies, formation energies, HOMO-LUMO gaps, and density of states. We also report results on electronic occupations derived from Mulliken population analysis. Our results show that the SiNCs have tunable HOMO-LUMO gaps with respect to size and that the inclusion of noble metals produces inter-gap defect levels. In addition, we have found that hydrogen passivation affected the doping behavior significantly. Contrary to the general expectation, hydrogen passivation contributed to the energy levels near the highest occupied orbital. Overall, our results suggest the SiNCs can be used to construct optimal photovoltaic applications or used individually as photocatalysts.

  16. Electrical conductivity of metals from real-time time-dependent density functional theory

    NASA Astrophysics Data System (ADS)

    Andrade, Xavier; Correa, Alfredo

    In this presentation, I will discuss how to apply real-time electron dynamics to study electronic currents in crystalline systems and, in particular, how to use this method to predict electrical conductivities in different regimes. This approach presents many interesting theoretical challenges associated to the representation of bulk systems as infinitely periodic. For example, in order to induce electronic currents in the system, we use a gauge transformation that allows us to include finite electric fields in the simulation. We have implemented this approach using time-dependent density functional theory (TDDFT). This implementation allows us to induce, measure and visualize the current density as a function of time, in simulations with thousands of electrons (hundreds and even thousands of atoms). We have found that real-time TDDFT can describe how currents naturally decay in metals. From this dissipation process we can directly calculate the frequency-dependent conductivity, including the direct current (DC) conductivity that is not accessible from linear-response approaches like Kubo-Greenwood.

  17. Theory of molecule metal nano-particle interaction: Quantum description of plasmonic lasing.

    PubMed

    Zhang, Yuan; May, Volkhard

    2015-06-14

    The recent quantum description of a few molecules interacting with plasmon excitations of a spherical metal nano-particle (MNP) as presented in the work of Zhang and May [Phys. Rev. B 89, 245441 (2014)] is extended to systems with up to 100 molecules. We demonstrate the possibility of multiple plasmon excitation and describe their conversion into far-field photons. The calculation of the steady-state photon emission spectrum results in an emission line-narrowing with an increasing number of molecules coupled to the MNP. This is considered as an essential criterion for the action of the molecule-MNP system as a nano-laser. To have exact results for systems with up to 20 molecules, we proceed as recently described by Richter et al. [Phys. Rev. B 91, 035306 (2015)] and study a highly symmetric system. It assumes an equatorial and regular position of identical molecules in such a way that their coupling is dominated by that to a single MNP dipole-plasmon excitation. Changing from the exact computation of the system's complete density matrix to an approximate theory based on the reduced plasmon density matrix, systems with more than 100 molecules can be described. Finally, nonlinear rate equations are proposed which reproduce the mean number of excited plasmons in their dependence of the number of molecules and of the used pump rate. The second order intensity correlation function of emitted photons is related to the respective plasmon correlation function which approaches unity when the system starts lasing.

  18. Theory of electron emission stimulated by charged particle reflection from simple metals; glancing incidence

    NASA Astrophysics Data System (ADS)

    Mills, D. L.

    1993-09-01

    Recent experiments by Rau and his colleagues [Phys. Rev. Lett. 64 (1990) 1441; DIET V (Springer, New York, 1992); Ionization of Solids by Heavy Particles (Plenum, New York, 1992)] explore the energy spectrum of electrons emitted from metal surfaces, in response to the reflection of positive ions reflected from the surface, at grazing incidence. We develop a theory of the emission process wherein the Coulomb field of the ion excites particle-hole pairs in the substrate, taken here to be jellium. We obtain a general expression for the energy and angle variation of the emitted electrons, for an ion trajectory which may penetrate into the substrate before reflecting off the planes of substrate nuclei. The result is expressed as an integral over the density-density response functions χ( zz'; Q∥ω) of the substrate. Special limits are explored, with emphasis on glancing incidence. We do not consider Auger processes, in which the ion is neutralized through acquisition of a substrate electron.

  19. Polymer-based metal nano-coated disposable target for matrix-assisted and matrix-free laser desorption/ionization mass spectrometry.

    PubMed

    Bugovsky, Stefan; Winkler, Wolfgang; Balika, Werner; Koranda, Manfred; Allmaier, Günter

    2016-07-15

    The ideal MALDI/LDI mass spectrometry sample target for an axial TOF instrument possesses a variety of properties. Primarily, it should be chemically inert to the sample, i.e. analyte, matrix and solvents, highly planar across the whole target, without any previous chemical contact and provide a uniform surface to facilitate reproducible measurements without artifacts from previous sample or matrix compounds. This can be hard to achieve with a metal target, which has to be extensively cleaned every time after use. Any cleaning step may leave residues behind, may change the surface properties due to the type of cleaning method used or even cause microscopic scratches over time hence altering matrix crystallization behavior. Alternatively, use of disposable targets avoids these problems. As each possesses the same surface they therefore have the potential to replace the conventional full metal targets so commonly employed. Furthermore, low cost single-use targets with high planarity promise an easier compliance with GLP guidelines as they alleviate the problem of low reproducibility due to inconsistent sample/matrix crystallization and changes to the target surface properties. In our tests, polymeric metal nano-coated targets were compared to a stainless steel reference. The polymeric metal nano-coated targets exhibited all the performance characteristics for a MALDI MS sample support, and even surpassed the - in our lab commonly used - reference in some aspects like limit of detection. The target exhibits all necessary features such as electrical conductivity, vacuum, laser and solvent compatibility.

  20. Actinide chelation: biodistribution and in vivo complex stability of the targeted metal ions.

    PubMed

    Kullgren, Birgitta; Jarvis, Erin E; An, Dahlia D; Abergel, Rebecca J

    2013-01-01

    Because of the continuing use of nuclear fuel sources and heightened threats of nuclear weapon use, the amount of produced and released radionuclides is increasing daily, as is the risk of larger human exposure to fission product actinides. A rodent model was used to follow the in vivo distribution of representative actinides, administered as free metal ions or complexed with chelating agents including diethylenetriamine pentaacetic acid (DTPA) and the hydroxypyridinonate ligands 3,4,3-LI(1,2-HOPO) and 5-LIO(Me-3,2-HOPO). Different metabolic pathways for the different metal ions were evidenced, resulting in intricate ligand- and metal-dependent decorporation mechanisms. While the three studied chelators are known for their unrivaled actinide decorporation efficiency, the corresponding metal complexes may undergo in vivo decomposition and release metal ions in various biological pools. This study sets the basis to further explore the metabolism and in vivo coordination properties of internalized actinides for the future development of viable therapeutic chelating agents. PMID:22957518

  1. Actinide chelation: biodistribution and in vivo complex stability of the targeted metal ions.

    PubMed

    Kullgren, Birgitta; Jarvis, Erin E; An, Dahlia D; Abergel, Rebecca J

    2013-01-01

    Because of the continuing use of nuclear fuel sources and heightened threats of nuclear weapon use, the amount of produced and released radionuclides is increasing daily, as is the risk of larger human exposure to fission product actinides. A rodent model was used to follow the in vivo distribution of representative actinides, administered as free metal ions or complexed with chelating agents including diethylenetriamine pentaacetic acid (DTPA) and the hydroxypyridinonate ligands 3,4,3-LI(1,2-HOPO) and 5-LIO(Me-3,2-HOPO). Different metabolic pathways for the different metal ions were evidenced, resulting in intricate ligand- and metal-dependent decorporation mechanisms. While the three studied chelators are known for their unrivaled actinide decorporation efficiency, the corresponding metal complexes may undergo in vivo decomposition and release metal ions in various biological pools. This study sets the basis to further explore the metabolism and in vivo coordination properties of internalized actinides for the future development of viable therapeutic chelating agents.

  2. Metal Nanoparticles as Targeted Carriers Circumventing the Blood-Brain Barrier.

    PubMed

    Sintov, A C; Velasco-Aguirre, C; Gallardo-Toledo, E; Araya, E; Kogan, M J

    2016-01-01

    Metal nanoparticles have been proposed as a carrier and a therapeutic agent in biomedical field because of their unique physiochemical properties. Due to these physicochemical properties, they can be used in different fields of biomedicine. In relation to this, plasmonic nanoparticles can be used for detection and photothermal destruction of tumor cells or toxic protein aggregates, and magnetic iron nanoparticles can be used for imaging and for hyperthermia of tumor cells. In addition, both therapy and imaging can be combined in one nanoparticle system, in a process called theranostics. Metal nanoparticles can be synthesized to modulate their size and shape, and conjugated with different ligands, which allow their application in drug delivery, diagnostics, and treatment of central nervous system diseases. This review is focused on the potential applications of metal nanoparticles and their capability to circumvent the blood-brain barrier (BBB). Although many articles have demonstrated delivery of metal nanoparticles to the brain by crossing the BBB after systemic administration, the percentage of the injected dose that reaches this organ is low in comparison to others, especially the liver and spleen. In connection with this drawback, we elaborate the architecture of the BBB and review possible mechanisms to cross this barrier by engineered nanoparticles. The potential uses of metal nanoparticles for treatment of disorders as well as related neurotoxicological considerations are also discussed. Finally, we bring up for discussion a direct and relatively simpler solution to the problem. We discuss this in detail after having proposed the use of the intranasal administration route as a way to circumvent the BBB. This route has not been extensively studied yet for metal nanoparticles, although it could be used as a research tool for mechanistic understanding and toxicity as well as an added value for medical practice. PMID:27678178

  3. Metal-Ligand Bonds of Second- and Third-Row d-Block Metals Characterized by Density Functional Theory

    NASA Astrophysics Data System (ADS)

    Jensen, Kasper P.

    2009-08-01

    This paper presents systematic data for 200 neutral diatomic molecules ML (M is a second- or third-row d-block metal and L = H, F, Cl, Br, I, C, N, O, S, or Se) computed with the density functionals TPSSh and BP86. With experimental structures and bond enthalpies available for many of these molecules, the computations first document the high accuracy of TPSSh, giving metal-ligand bond lengths with a mean absolute error of ˜0.01 Å for the second row and 0.03 Å for the third row. TPSSh provides metal-ligand bond enthalpies with mean absolute errors of 37 and 44 kJ/mol for the second- and third-row molecules, respectively. Pathological cases (e.g., HgC and HgN) have errors of up to 155 kJ/mol, more than thrice the mean (observed with both functionals). Importantly, the systematic error component is negligible as measured by a coefficient of the linear regression line of 0.99. Equally important, TPSSh provides uniform accuracy across all three rows of the d-block, which is unprecedented and due to the 10% exact exchange, which is close to optimal for the d-block as a whole. This work provides an accurate and systematic prediction of electronic ground-state spins, characteristic metal-ligand bond lengths, and bond enthalpies for many as yet uncharacterized diatomics, of interest to researchers in the field of second- and third-row d-block chemistry. We stress that the success of TPSSh cannot be naively extrapolated to other special situations such as, e.g., metal-metal bonds. The high accuracy of the procedure further implies that the effective core functions used to model relativistic effects are necessary and sufficient for obtaining accurate geometries and bond enthalpies of second- and third-row molecular systems.

  4. Design and fabrication of specific ceramic?metallic fuels and targets

    NASA Astrophysics Data System (ADS)

    Fernández, A.; Konings, R. J. M.; Somers, J.

    2003-06-01

    The fabrication of ceramic-metallic (cermet) composite fuel, containing (Y,An,Zr)O 2- x spheres, by dust free processes has been studied. The influence of several process parameters, such as, ceramic volume fraction, compaction pressure and sintering temperature, on the microstructure of the final composite have been investigated and optimised using cerium as a stand for americium and two metal matrices namely molybdenum and stainless steel. In addition, a cermet fuel with (near) spherical (Y,Pu,Zr)O 2- x particles, dispersed in stainless steel matrix, has been successfully fabricated and characterized.

  5. Physical properties of the 6d-series elements from density functional theory: Close similarity to lighter transition metals

    NASA Astrophysics Data System (ADS)

    Gyanchandani, Jyoti; Sikka, S. K.

    2011-05-01

    We have calculated some of the physical properties of the recently discovered 6d elements by density functional theory. Comparison with those of the 5d metals shows that there is a close analogy for the crystal structures, for parabolic variation of equilibrium atomic volumes and bulk moduli, and an almost linearly increasing behavior of the pressure derivative of the bulk modulus across the 6d series. The Friedel model that is used to explain these trends for homologous series also holds for 6d metals. These elements also seem to be placed correctly in the Periodic Table.

  6. A multi-element screening method to identify metal targets for blood biomonitoring in green sea turtles (Chelonia mydas).

    PubMed

    Villa, C A; Finlayson, S; Limpus, C; Gaus, C

    2015-04-15

    Biomonitoring of blood is commonly used to identify and quantify occupational or environmental exposure to chemical contaminants. Increasingly, this technique has been applied to wildlife contaminant monitoring, including for green turtles, allowing for the non-lethal evaluation of chemical exposure in their nearshore environment. The sources, composition, bioavailability and toxicity of metals in the marine environment are, however, often unknown and influenced by numerous biotic and abiotic factors. These factors can vary considerably across time and space making the selection of the most informative elements for biomonitoring challenging. This study aimed to validate an ICP-MS multi-element screening method for green turtle blood in order to identify and facilitate prioritisation of target metals for subsequent fully quantitative analysis. Multi-element screening provided semiquantitative results for 70 elements, 28 of which were also determined through fully quantitative analysis. Of the 28 comparable elements, 23 of the semiquantitative results had an accuracy between 67% and 112% relative to the fully quantified values. In lieu of any available turtle certified reference materials (CRMs), we evaluated the use of human blood CRMs as a matrix surrogate for quality control, and compared two commonly used sample preparation methods for matrix related effects. The results demonstrate that human blood provides an appropriate matrix for use as a quality control material in the fully quantitative analysis of metals in turtle blood. An example for the application of this screening method is provided by comparing screening results from blood of green turtles foraging in an urban and rural region in Queensland, Australia. Potential targets for future metal biomonitoring in these regions were identified by this approach.

  7. A multi-element screening method to identify metal targets for blood biomonitoring in green sea turtles (Chelonia mydas).

    PubMed

    Villa, C A; Finlayson, S; Limpus, C; Gaus, C

    2015-04-15

    Biomonitoring of blood is commonly used to identify and quantify occupational or environmental exposure to chemical contaminants. Increasingly, this technique has been applied to wildlife contaminant monitoring, including for green turtles, allowing for the non-lethal evaluation of chemical exposure in their nearshore environment. The sources, composition, bioavailability and toxicity of metals in the marine environment are, however, often unknown and influenced by numerous biotic and abiotic factors. These factors can vary considerably across time and space making the selection of the most informative elements for biomonitoring challenging. This study aimed to validate an ICP-MS multi-element screening method for green turtle blood in order to identify and facilitate prioritisation of target metals for subsequent fully quantitative analysis. Multi-element screening provided semiquantitative results for 70 elements, 28 of which were also determined through fully quantitative analysis. Of the 28 comparable elements, 23 of the semiquantitative results had an accuracy between 67% and 112% relative to the fully quantified values. In lieu of any available turtle certified reference materials (CRMs), we evaluated the use of human blood CRMs as a matrix surrogate for quality control, and compared two commonly used sample preparation methods for matrix related effects. The results demonstrate that human blood provides an appropriate matrix for use as a quality control material in the fully quantitative analysis of metals in turtle blood. An example for the application of this screening method is provided by comparing screening results from blood of green turtles foraging in an urban and rural region in Queensland, Australia. Potential targets for future metal biomonitoring in these regions were identified by this approach. PMID:25655987

  8. Theory of catalytic dissociation of hydrogen atoms on a metal surface

    SciTech Connect

    Konstantinov, O. V. Dymnikov, V. D.; Mittsev, M. A.

    2008-08-15

    The model of hydrogen atom ionization near a metal surface is discussed on the basis of a comparison between the metal work function and the atom ionization energy. In the theoretical calculation, it is shown that the hydrogen atom ionization energy decreases when the atom approaches the metal surface. The ionization energy vanishes when the distance between proton and the metal surface is somewhat less than the Bohr radius.

  9. Separation of carrier-free hafnium and lutetium radionuclides produced in 16O activated terbium metal target.

    PubMed

    Lahir, S; Banerjee, K; Nayak, D; Ramaswami, A; Das, N R

    2000-06-01

    Charged particle activation with approximately 88 MeV 16O7+ beam on natural terbium metal foil leads to the production of the short lived carrier-free radioisotopes 170,171Ta and their corresponding daughter products 170,171Hf and 170,171Lu in the target matrix. Liquid-liquid extraction with HDEHP diluted in cyclohexane was carried out for the separation of 170,171Hf and 170,171Lu from the bulk terbium in an aqueous HCl medium.

  10. Inside HOLMES experiment: 163Ho metallic target production for the micro-calorimeter absorber

    NASA Astrophysics Data System (ADS)

    Pizzigoni, G.; Alpert, B.; Balata, M.; Bennett, D.; Biasotti, M.; Boragno, C.; Brofferio, C.; De Gerone, M.; Dressler, R.; Faverazani, M.; Ferri, E.; Folwer, J.; Gatti, F.; Giachero, A.; Heinitz, S.; Hilton, G.; Köster, U.; Lusignoli, M.; Maino, M.; Mates, J.; Nisi, S.; Nizzolo, R.; Nucciotti, A.; Pessina, G.; Puiu, A.; Ragazzi, S.; Reintsema, C.; Ribeiro Gomes, M.; Shmidt, D.; Schumann, D.; Sisti, M.; Swetz, D.; Terranova, F.; Ullom, J.; Day, P. K.

    2016-07-01

    The main goal in the HOLMES experiment is the neutrino mass measurement using an array of 1000 micro-calorimeters with standard metallic absorber. A good isotope for such measurement is the 163Ho, those isotopes embedded in the metallic absorber will be 1011-1013. Since 163Ho is not available in nature, a dedicated process must be set up to produce the amount needed for this neutrino mass experiment. The process with the highest born-up cross-section is the neutron irradiation of Er2O3 enriched in 162Er: 162Er(n,γ)163Er →163Ho+νe, where the decay is an EC with half-life of about 75 min and the (n,γ) is about 20 barns for thermal neutron. After the neutron irradiation in the oxide powder there are several radioactive isotopes which are potentially disturbing because of the background that they cause below 5 keV. The chemical separation of holmium from the irradiation enriched Er2O3 powder is therefore mandatory and will be performed by means of ion exchange chromatography. On the end of those processes the oxide powder enriched in 162Er will have the 163Ho isotope number required. The holmium chemical state influences the end point of the EC spectrum, in order to avoid such effect it is necessary to embed in the absorber only the metallic isotope. Reduction and distillation technique allowed us to obtain a pure metallic holmium, starting from natural oxide holmium. This technique will be applied on the irradiated oxide powder to obtain the metallic 163Ho, ready to be embedded in the micro-calorimeter absorber.

  11. Applying Theory of Mind Concepts When Designing Interventions Targeting Social Cognition among Youth Offenders

    ERIC Educational Resources Information Center

    Noel, Kristine K.; Westby, Carol

    2014-01-01

    This study employed a multiple baseline, across-participants, single-subject design to investigate the feasibility of an individual, narrative-based, social problem-solving intervention on the social problem-solving, narrative, and theory of mind (ToM) abilities of 3 incarcerated adolescent youth offenders identified as having emotional…

  12. Hypoxia inducible factor prolyl hydroxylases as targets for neuroprotection by “antioxidant” metal chelators: from ferroptosis to stroke

    PubMed Central

    Speer, Rachel E.; Karuppagounder, Saravanan S.; Basso, Manuela; Sleiman, Sama; Kumar, Amit; Brand, David; Smirnova, Natalya; Gazaryan, Irina; Khim, Soah J.; Ratan, Rajiv R.

    2015-01-01

    Neurologic conditions including stroke, Alzheimer’s disease, Parkinson’s disease and Huntington’s disease are leading causes of death and long-term disability in the United States, and efforts to develop novel therapeutics for these conditions have historically had poor success in translating from bench to bedside. Hypoxia Inducible Factor-1alpha (HIF-1α) mediates a broad, evolutionarily conserved, endogenous adaptive program to hypoxia, and manipulation of components of the HIF pathway are neuroprotective in a number of human neurological diseases and experimental models. In this review, we discuss molecular components of one aspect of hypoxic adpatation in detail, and provide perspective on which targets within this pathway appear to be ripest for preventing and repairing neurodegeneration. Further, we highlight the role of HIF prolyl hydroxylases as emerging targets for the salutary effects of metal chelators on ferroptosis in vitro as well in animal models of neurological diseases. PMID:23376032

  13. One-pot Synthesis of Metal-Organic Frameworks with Encapsulated Target Molecules and Their Applications for Controlled Drug Delivery.

    PubMed

    Zheng, Haoquan; Zhang, Yuning; Liu, Leifeng; Wan, Wei; Guo, Peng; Nyström, Andreas M; Zou, Xiaodong

    2016-01-27

    Many medical and chemical applications require target molecules to be delivered in a controlled manner at precise locations. Metal-organic frameworks (MOFs) have high porosity, large surface area, and tunable functionality and are promising carriers for such purposes. Current approaches for incorporating target molecules are based on multistep postfunctionalization. Here, we report a novel approach that combines MOF synthesis and molecule encapsulation in a one-pot process. We demonstrate that large drug and dye molecules can be encapsulated in zeolitic imidazolate framework (ZIF) crystals. The molecules are homogeneously distributed within the crystals, and their loadings can be tuned. We show that ZIF-8 crystals loaded with the anticancer drug doxorubicin (DOX) are efficient drug delivery vehicles in cancer therapy using pH-responsive release. Their efficacy on breast cancer cell lines is higher than that of free DOX. Our one-pot process opens new possibilities to construct multifunctional delivery systems for a wide range of applications.

  14. Note: Study of extreme ultraviolet and soft x-ray emission of metal targets produced by laser-plasma-interaction

    SciTech Connect

    Mantouvalou, I.; Bidu, T.; Malzer, W.; Kanngiesser, B.; Jung, R.; Tuemmler, J.; Legall, H.; Stiel, H.; Sandner, W.

    2011-06-15

    Different metal targets were investigated as possible source material for tailored laser-produced plasma-sources. In the wavelength range from 1 to 20 nm, x-ray spectra were collected with a calibrated spectrometer with a resolution of {lambda}/{Delta}{lambda}= 150 at 1 nm up to {lambda}/{Delta}{lambda}= 1100 at 15 nm. Intense line emission features of highly ionized species as well as continuum-like spectra from unresolved transitions are presented. With this knowledge, the optimal target material can be identified for the envisioned application of the source in x-ray spectrometry on the high energy side of the spectra at about 1 keV. This energy is aimed for because 1 keV-radiation is ideally suited for L-shell x-ray spectroscopy with nm-depth resolution.

  15. Theoretical investigation of the thermal hydraulic behaviour of a slab-type liquid metal target

    SciTech Connect

    Dury, T.V.; Smith, B.L.

    1996-06-01

    The thermal hydraulics codes CFDS-FLOW3D and ASTEC have been used to simulate a slabtype design of ESS spallation target. This design is single-skinned, and of tapering form (in the beam direction), with rounded sides in a cross-section through a plane normal to the beam. The coolant fluid used is mercury, under forced circulation, with an inlet temperature of 180{degrees}C. The goal of these computer studies was to understand the behaviour of the coolant flow, and hence to arrive at a design which optimises the heat extraction for a given beam power - in the sense of: (1) minimising the peak local fluid temperature within the target, (2) maintaining an acceptable temperature level and distribution over and through the target outer wall, (3) keeping the overall fluid pressure loss through the complete target to a minimum, (4) staying within the physical limits of overall size required, particularly in the region of primary spallation. Two- and three-dimensional models have been used, with different arrangements and design of internal baffles, and different coolant flow distributions at the target inlet. Nominal total inlet mass flow was 245 kg/s, and a heat deposition profile used which was based on the proton beam energy distribution. This gave a nominal total heat load of 3.23 MW - of which 8.2kW were deposited in the window steel.

  16. A Theory for the RF Surface Field for Various Metals at the Destructive Breakdown Limit

    SciTech Connect

    Wilson, Perry B.

    2006-11-27

    By destructive breakdown we mean a breakdown event that results in surface melting over a macroscopic area in a high E-field region of an accelerator structure. A plasma forms over the molten area, bombarding the surface with an intense ion current ({approx}108 A/cm2), equivalent to a pressure of about a thousand Atmospheres. This pressure in turn causes molten copper to migrate away from the iris tip, resulting in measurable changes in the iris shape. The breakdown process can be roughly divided into four stages: (1) the formation of ''plasma spots'' at field emission sites, each spot leaving a crater-like footprint; (2) crater clustering, and the formation of areas with hundreds of overlapping craters; (3) surface melting in the region of a crater cluster; (4) the process after surface melting that leads to destructive breakdown. The physics underlying each of these stages is developed, and a comparison is made between the theory and experimental evidence whenever possible. The key to preventing breakdown lies in stage (3). A single plasma spot emits a current of several amperes, a portion of which returns to impact the surrounding area with a power density on the order 107 Watt/cm2. This power density is not quite adequate to melt the surrounding surface on a time scale short compared to the rf pulse length. In a crater field, however, the impact areas from multiple plasma spots overlap to provide sufficient power density for surface melting over an area on the order of 0.1 mm2 or more. The key to preventing breakdown is to choose an iris tip material that requires the highest power density (proportional to the square of the rf surface field) for surface melting, taking into account the penetration depth of the impacting electrons. The rf surface field required for surface melting (relative to copper) has been calculated for a large number elementary metals, plus stainless-steel and carbon.

  17. Enantioselectivity of (321) chiral noble metal surfaces: a density functional theory study of lactate adsorption.

    PubMed

    Franke, J-H; Kosov, D S

    2013-12-14

    The adsorption of the chiral molecule lactate on the intrinsically chiral noble metal surfaces Pt(321), Au(321), and Ag(321) is studied by density functional theory calculations. We use the oPBE-vdW functional which includes van der Waals forces on an ab initio level. It is shown that the molecule binds via its carboxyl and the hydroxyl oxygen atoms to the surface. The binding energy is larger on Pt(321) and Ag(321) than on Au(321). An analysis of the contributions to the binding energy of the different molecular functional groups reveals that the deprotonated carboxyl group contributes most to the binding energy, with a much smaller contribution of the hydroxyl group. The Pt(321) surface shows considerable enantioselectivity of 0.06 eV. On Au(321) and Ag(321) it is much smaller if not vanishing. The chiral selectivity of the Pt(321) surface can be explained by two factors. First, it derives from the difference in van der Waals attraction of L- and D-lactate to the surface that we trace to differences in the binding energy of the methyl group. Second, the multi-point binding pattern for lactate on the Pt(321) surface is sterically more sensitive to surface chirality and also leads to large binding energy contributions of the hydroxyl group. We also calculate the charge transfer to the molecule and the work function to gauge changes in electronic structure of the adsorbed molecule. The work function is lowered by 0.8 eV on Pt(321) with much smaller changes on Au(321) and Ag(321). PMID:24329084

  18. Enantioselectivity of (321) chiral noble metal surfaces: A density functional theory study of lactate adsorption

    SciTech Connect

    Franke, J.-H.; Kosov, D. S.

    2013-12-14

    The adsorption of the chiral molecule lactate on the intrinsically chiral noble metal surfaces Pt(321), Au(321), and Ag(321) is studied by density functional theory calculations. We use the oPBE-vdW functional which includes van der Waals forces on an ab initio level. It is shown that the molecule binds via its carboxyl and the hydroxyl oxygen atoms to the surface. The binding energy is larger on Pt(321) and Ag(321) than on Au(321). An analysis of the contributions to the binding energy of the different molecular functional groups reveals that the deprotonated carboxyl group contributes most to the binding energy, with a much smaller contribution of the hydroxyl group. The Pt(321) surface shows considerable enantioselectivity of 0.06 eV. On Au(321) and Ag(321) it is much smaller if not vanishing. The chiral selectivity of the Pt(321) surface can be explained by two factors. First, it derives from the difference in van der Waals attraction of L- and D-lactate to the surface that we trace to differences in the binding energy of the methyl group. Second, the multi-point binding pattern for lactate on the Pt(321) surface is sterically more sensitive to surface chirality and also leads to large binding energy contributions of the hydroxyl group. We also calculate the charge transfer to the molecule and the work function to gauge changes in electronic structure of the adsorbed molecule. The work function is lowered by 0.8 eV on Pt(321) with much smaller changes on Au(321) and Ag(321)

  19. Hyperspectral target detection using graph theory models and manifold geometry via an adaptive implementation of locally linear embedding

    NASA Astrophysics Data System (ADS)

    Ziemann, Amanda K.; Messinger, David W.

    2014-06-01

    Hyperspectral images comprise, by design, high dimensional image data. However, research has shown that for a d-dimensional hyperspectral image, it is typical for the data to inherently occupy an m-dimensional space, with m << d. In the remote sensing community, this has led to a recent increase in the use of non-linear manifold learning, which aims to characterize the embedded lower-dimensional, non-linear manifold upon which the hyperspectral data inherently lie. Classic hyperspectral data models include statistical, linear subspace, and linear mixture models, but these can place restrictive assumptions on the distribution of the data. With graph theory and manifold learning based models, the only assumption is that the data reside on an underlying manifold. In previous publications, we have shown that manifold coordinate approximation using locally linear embedding (LLE) is a viable pre-processing step for target detection with the Adaptive Cosine/Coherence Estimator (ACE) algorithm. Here, we improve upon that methodology using a more rigorous, data-driven implementation of LLE that incorporates the injection of a cloud" of target pixels and the Spectral Angle Mapper (SAM) detector. The LLE algorithm, which holds that the data is locally linear, is typically governed by a user defined parameter k, indicating the number of nearest neighbors to use in the initial graph model. We use an adaptive approach to building the graph that is governed by the data itself and does not rely upon user input. This implementation of LLE can yield greater separation between the target pixels and the background pixels in the manifold space. We present an analysis of target detection performance in the manifold coordinates using scene-derived target spectra and laboratory-measured target spectra across two different data sets.

  20. A Density Functional Theory Analysis of Trends in Glycerol Decomposition on Close-Packed Transition Metal Surfaces

    SciTech Connect

    Liu, Bin; Greeley, Jeffrey P.

    2013-05-07

    We describe an accelerated density functional theory (DFT)-based computational strategy to determine trends in the decomposition of glycerol via elementary dehydrogenation, C–C, and C–O bond scission reactions on close-packed transition metal surfaces. Beginning with periodic DFT calculations on Pt(111), the thermochemistry of glycerol dehydrogenation on Pd(111), Rh(111), Cu(111) and Ni(111) is determined using a parameter-free, bond order-based scaling relationship. By combining the results with Brønsted–Evans–Polanyi (BEP) relationships to estimate elementary reaction barriers, free energy diagrams are developed on the respective metal surfaces, and trends concerning the relative selectivity and activity for C–C and C–O bond scission in glycerol on the various metals are obtained. The results are consistent with available theoretical and experimental literature and demonstrate that scaling relationships are capable of providing powerful insights into the catalytic chemistry of complex biomolecules.

  1. Interaction of carbon monoxide with transition metals: evolutionary insights into drug target discovery.

    PubMed

    Foresti, Roberta; Motterlini, Roberto

    2010-12-01

    The perception that carbon monoxide (CO) is poisonous and life-threatening for mammalian organisms stems from its intrinsic propensity to bind iron in hemoglobin, a reaction that ultimately leads to impaired oxygen delivery to tissues. From evolutionary and chemical perspectives, however, CO is one of the most essential molecules in the formation of biological components and its interaction with transition metals is at the origin of primordial cell signaling. Not surprisingly, mammals have gradually evolved systems to finely control the synthesis and the sensing of this gaseous molecule. Cells are indeed continuously exposed to small quantities of CO produced endogenously during the degradation of heme by constitutive and inducible heme oxygenase enzymes. We have gradually learnt that heme oxygenase-derived carbon monoxide (CO) serves as a ubiquitous signaling mediator which could be exploited for therapeutic purposes. The development of transition metal carbonyls as prototypic carbon monoxide-releasing molecules (CO-RMs) represents a novel stratagem for a safer delivery of CO-based pharmaceuticals in the treatment of various pathological disorders. This review will look back at evolution to analyze and argue that a dynamic interaction of CO with specific intracellular metal centers is the common denominator for the diversified beneficial effects mediated by this gaseous molecule. PMID:20704543

  2. Recent developments in human biomonitoring: non-invasive assessment of target tissue dose and effects of pneumotoxic metals

    PubMed Central

    Mutti, A.; Corradi, M.

    2006-01-01

    Summary Tobacco smoke and polluted environments substantially increase the lung burden of pneumotoxic chemicals, particularly pneumotoxic metallic elements. To achieve a better understanding of the early events between exposure to inhaled toxicants and the onset of adverse effects on the lung, the characterization of dose at the target organ would be extremely useful. Exhaled breath condensate (EBC), obtained by cooling exhaled air under conditions of spontaneous breathing, is a novel technique that could provide a non-invasive assessment of pulmonary pathobiology. Considering that EBC is water practically free of interfering solutes, it represents an ideal biological matrix for elemental characterization. Published data show that several toxic metals and trace elements are detectable in EBC, raising the possibility of using this medium to quantify the lung tissue dose of pneumotoxic substances. This novel approach may represent a significant advance over the analysis of alternative media (blood, serum, urine, hair), which are not as reliable (owing to interfering substances in the complex matrix) and reflect systemic rather than lung (target tissue) levels of both toxic metals and essential trace elements. Data obtained among workers occupationally exposed to either hard metals or chromium (VI) and in smokers with or without chronic obstructive pulmonary disease (COPD) are reviewed to show that – together with biomarkers of exposure – EBC also allows the simultaneous quantification of biomarkers of effect directly sampled from the epithelial lining fluid, thus providing novel insights on both kinetic and dynamic aspects of metal toxicology. Riassunto «Recenti sviluppi nel biomonitoraggio umano: valutazione non invasiva della dose a livello dell’organo bersaglio e degli effetti pneumotossici». L’esposizione cronica a fumo di tabacco ed ad altri inquinati ambientali determina un accumulo polmonare di sostanze pneumotossiche, soprattutto metalli. Allo scopo

  3. Metal concentrations in selected brands of canned fish in Nigeria: estimation of dietary intakes and target hazard quotients.

    PubMed

    Iwegbue, Chukwujindu M A

    2015-03-01

    The concentrations of metals (Cd, Pb, Ni, Cr, Cu, Co, Fe, Mn, and Zn) were determined in selected brands of canned mackerel, sardine, and tuna in Nigeria with a view to providing information on the dietary intakes of metals and lifelong health hazards associated with the consumption of these products. The concentrations of metals were determined by using atomic absorption spectrometry after acid digestion. The mean concentrations of metals in canned mackerel, sardine, and tuna were found as 0.04-0.58, 0.06-0.44, 0.32-0.83 μg/g for Cd; 0.05-2.82, 0.70-2.98, 0.23-2.56 μg/g for Pb, 1.33-11.33, <0.20-17.53, nd-34.2 μg/g for Ni, 0.49-3.79, 0.22-1.89, 0.66-14.39 μg/g for Cr, 0.33-0.92, 0.03-1.51, <0.08-1.31 μg/g for Cu, 0.11-2.17, nd-0.75, 0.14-0.50 μg/g for Co, 6.45-26.90, 6.06-53.54, 3.06-95.78 μg/g for Fe, 2.30-3.84, 0.95-21.78, 1.65-2.33 μg/g for Mn, 1.15-7.19, 3.60-17.88, 1.21-5.35 μg/g for Zn, respectively. The mean concentrations of Cd, Pb, and Fe in some of these brands of canned fish were above their permissible limits while other metals occurred at levels below their permissible limits. The estimated daily intakes of metals from consumption of 20.8 g fish per day by a 60 kg body weight adult were below the provisional tolerable daily intakes for Cd, Pb, Ni, Cr, and Cu and recommended daily intakes for Co, Fe, Mn, and Zn. The estimated target hazard quotients of the examined metals were less than 1 in the majority of the samples indicating no long-term health hazard at the present circumstance. PMID:25655121

  4. Covalency in Metal-Oxygen Multiple Bonds Evaluated Using Oxygen K-edge Spectroscopy and Electronic Structure Theory

    SciTech Connect

    Minasian, Stefan G.; Keith, Jason M.; Batista, Enrique R.; Boland, Kevin S.; Bradley, Joseph A.; Daly, Scott R.; Kozimor, Stosh A.; Lukens, Wayne W.; Martin, Richard L.; Nordlund, Dennis; Seidler, Gerald T.; Shuh, David K.; Sokaras, Dimosthenis; Tyliszczak, Tolek; Wagner, Gregory L.; Weng, Tsu-Chien; Yang, Ping

    2013-01-28

    Advancing theories of how metal-oxygen bonding influences metal oxo properties can expose new avenues for innovation in materials science, catalysis, and biochemistry. Historically, spectroscopic analyses of the transition metal MO4x- anions have formed the basis for new M-O bonding theories. Herein, relative changes in M-O orbital mixing in MO42- (M = Cr, Mo, W) and MO4- (M = Mn, Tc, Re) are evaluated for the first time by nonresonant inelastic X-ray scattering, X-ray absorption spectroscopy using fluorescence and transmission (via a scanning transmission X-ray microscope), and time-dependent density functional theory. The results suggest that moving from Group 6 to Group 7 or down the triads increases M-O e* (pi*) mixing; for example, it more than doubles in ReO4- relative to CrO42-. Mixing in the t(2)* orbitals (sigma* + pi*) remains relatively constant within the same Group, but increases on moving from Group 6 to Group 7. These unexpected changes in orbital energy and composition for formally isoelectronic tetraoxometalates are evaluated in terms of periodic trends in d orbital energy and radial extension.

  5. Perturbation theory of structure in classical liquid mixtures: Application to metallic systems near phase separation. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Henderson, R. L.

    1974-01-01

    The partial structure factors of classical simple liquid mixtures near phase separation are dicussed. The theory is developed for particles interacting through pair potentials, and is thus appropriate both to insulating fluids, and also to metallic systems if these may be described by an effective ion-ion pair interaction. The motivation arose from consideration of metallic liquid mixtures, in which resistive anomalies have been observed near phase separation. A mean field theory correction appropriate to 3 pair potential for the effects of correlated motions in the reference fluid is studied. The work is cast in terms of functions which are closely related to the direct correlation functions of Ornstein and Zernike. The results are qualitatively in accord with physical expectations. Quantitative agreement with experiment seems to turn on the selection of the hard core reference potential in terms of the metallic effective pair potential. It is suggested that the present effective pair potentials are perhaps not properly used to calculate the metallic structure factors at long wavelength.

  6. Nanostructured europium oxide thin films deposited by pulsed laser ablation of a metallic target in a He buffer atmosphere

    SciTech Connect

    Luna, H.; Franceschini, D. F.; Prioli, R.; Guimaraes, R. B.; Sanchez, C. M.; Canal, G. P.; Barbosa, M. D. L.; Galvao, R. M. O.

    2010-09-15

    Nanostrucured europium oxide and hydroxide films were obtained by pulsed Nd:YAG (532 nm) laser ablation of a europium metallic target, in the presence of a 1 mbar helium buffer atmosphere. Both the produced film and the ambient plasma were characterized. The plasma was monitored by an electrostatic probe, for plume expansion in vacuum or in the presence of the buffer atmosphere. The time evolution of the ion saturation current was obtained for several probe to substrate distances. The results show the splitting of the plume into two velocity groups, being the lower velocity profile associated with metal cluster formation within the plume. The films were obtained in the presence of helium atmosphere, for several target-to-substrate distances. They were analyzed by Rutherford backscattering spectrometry, x-ray diffraction, and atomic force microscopy, for as-deposited and 600 deg. C treated-in-air samples. The results show that the as-deposited samples are amorphous and have chemical composition compatible with europium hydroxide. The thermally treated samples show x-ray diffraction peaks of Eu{sub 2}O{sub 3}, with chemical composition showing excess oxygen. Film nanostructuring was shown to be strongly correlated with cluster formation, as shown by velocity splitting in probe current versus time plots.

  7. Measurements of neutron emission induced by muons stopped in metal deuteride targets

    NASA Astrophysics Data System (ADS)

    Chen, M.; Steadman, S. G.; Gaudreau, M. P. J.; Luckhardt, S. C.; Parker, R. R.; Albagli, D.; Cammarata, V.; Schloh, M.; Wrighton, M. S.; Kwok, K.; Thieme, C.; Lowenstein, D. I.; Debbe, R.; Reilly, J. J.

    1990-06-01

    An 80-MeV/c negative muon beam from the Alternating Gradient Synchrotron at Brookhaven National Laboratory was used to investigate the stopping of muons inside Pd, Ti, and Y targets saturated with deuterium. Neutron emission from the targets was measured with an array of3He detectors, and in some runs, the temperature of the target was monitored as a function of time, with and without a flux of muons on the target. The neutron rates were also measured for Pd cathodes in an active electrochemical cell similar in design to those used in so-called “cold fusion” experiments, and the electrolyte solution was analyzed for excess tritium. No evidence was found for muon-catalyzed fusion at rates consistent with those claimed in “cold fusion” experiments. Neutron production from catalyzed fusion due to the presence of deuterium in palladium deuteride, PdD0.7, exposed to muons was determined to be 0.0±0.03 (stat.) ±0.25 (syst.) neutrons per stopped muon.

  8. Melanin as a target for melanoma chemotherapy: pro-oxidant effect of oxygen and metals on melanoma viability.

    PubMed

    Farmer, Patrick J; Gidanian, Shirley; Shahandeh, Babbak; Di Bilio, Angel J; Tohidian, Nilou; Meyskens, Frank L

    2003-06-01

    Melanoma cells have a poor ability to mediate oxidative stress, which may be attributed to constitutive abnormalities in their melanosomes. We hypothesize that disorganization of the melanosomes will allow chemical targeting of the melanin within. Chemical studies show that under oxidative conditions, synthetic melanins demonstrate increased metal affinity and a susceptibility to redox cycling with oxygen to form reactive oxygen species. The electron paramagnetic resonance (EPR)-active 5,5'-dimethyl-pyrollidine N-oxide spin adduct was used to show that binding of divalent Zn or Cu to melanin induces a pro-oxidant response under oxygen, generating superoxide and hydroxyl radicals. A similar pro-oxidant behaviour is seen in melanoma cell lines under external peroxide stress. Melanoma cultures grown under 95% O2/5% CO2 atmospheres show markedly reduced viability as compared with normal melanocytes. Cu- and Zn-dithiocarbamate complexes, which induce passive uptake of the metal ions into cells, show significant antimelanoma activity. The antimelanoma effect of metal- and oxygen-induced stress appears additive rather than synergistic; both treatments are shown to be significantly less toxic to melanocytes.

  9. Cytoplasmic membrane is the target organelle for transition metal mediated damage induced by paraquat in Escherichia coli

    SciTech Connect

    Kohen, R.; Chevion, M.

    1988-04-05

    Bacterial survival indicates that copper or iron is an essential mediator in paraquat toxicity in Escherichia coli. In this study the authors have identified the cytoplasmic membrane as a target organelle in metal-mediated paraquat toxicity and have demonstrated the complete correlation of the membrane damage with the levels of adventitious copper (or iron). The extent of membrane damage was related by use of four parameters: (a) the level of cellular ATP, (b) the level of cellular potassium, (c) the cellular capacity to accumulate and retain radiolabeled leucine, and (d) the cellular integrity as reflected by transmission electron microscopy (TEM). Exposure of bacterial cells to a combination of paraquat and copper caused a marked decline in parameters a, b, and c. This decline was found to occur in parallel with, or even to precede, the sharp loss of survival of E. coli under the same conditions. Likewise, TEM micrographs clearly indicated alternations in cellular structure that possibly reflect sites of detachment of the cytoplasmic membrane from the bacterial capsule. In contradistinction, copper alone or paraquat alone could not bring about similar changes in cellular structure. These findings are in accord with the suggested site-specific metal-mediated Haber-Weiss mechanism for paraquat toxicity and support our notion that specific chelators of transition metals could reduce or prevent the biological deleterious effects of this herbicide.

  10. Targeting high value metals in lithium-ion battery recycling via shredding and size-based separation.

    PubMed

    Wang, Xue; Gaustad, Gabrielle; Babbitt, Callie W

    2016-05-01

    Development of lithium-ion battery recycling systems is a current focus of much research; however, significant research remains to optimize the process. One key area not studied is the utilization of mechanical pre-recycling steps to improve overall yield. This work proposes a pre-recycling process, including mechanical shredding and size-based sorting steps, with the goal of potential future scale-up to the industrial level. This pre-recycling process aims to achieve material segregation with a focus on the metallic portion and provide clear targets for subsequent recycling processes. The results show that contained metallic materials can be segregated into different size fractions at different levels. For example, for lithium cobalt oxide batteries, cobalt content has been improved from 35% by weight in the metallic portion before this pre-recycling process to 82% in the ultrafine (<0.5mm) fraction and to 68% in the fine (0.5-1mm) fraction, and been excluded in the larger pieces (>6mm). However, size fractions across multiple battery chemistries showed significant variability in material concentration. This finding indicates that sorting by cathode before pre-treatment could reduce the uncertainty of input materials and therefore improve the purity of output streams. Thus, battery labeling systems may be an important step towards implementation of any pre-recycling process.

  11. Target organs of the Manila clam Ruditapes philippinarum for studying metal accumulation and biomarkers in pollution monitoring: laboratory and in-situ transplantation experiments.

    PubMed

    Won, Eun-Ji; Kim, Kyung-Tae; Choi, Jin-Young; Kim, Eun-Soo; Ra, Kongtae

    2016-08-01

    To characterize the target organs of the Manila clam Ruditapes philippinarum for use in environmental study, the accumulation of trace metals and three biomarkers was measured in different organs. Exposure with Cu and Pb carried out under laboratory conditions revealed a linear uptake of metals throughout the experimental period in each tissue. In particular, significant increase was observed in gills and mantle. The increase of intracellular reactive oxygen species showed the great potential of gills as a target tissue for both Cu and Pb exposure. The highest activity of glutathione S-transferase and their relative increase in activity were also observed in gills. Metallothionein-like protein levels, however, increased greatly in the digestive gland and mantle during Cu and Pb exposure, respectively, although all tissues, except the foot, showed significant changes after 24 h of metal exposure. In the field study, the highest concentration of metals was recorded in the gills and mantle, accounting for over 50 % of the total accumulated metal in all sites. Additionally, Cu and Pb increased significantly in these two organs, respectively. However, the order of accumulation rate in laboratory exposure was not concomitant with those of the lab-based study, suggesting that different routes of metal uptake and exposure duration induce distinct partitioning of metals and regulating system in R. philippinarum. These series of exposure studies demonstrated that gills, mantle, and digestive gland in R. philippinarum are potential target tissues in environmental monitoring study using metal concentrations and biomarkers. PMID:27450372

  12. Viscosity contribution to the impurity resistivity of metals by means of the current-density functional theory

    NASA Astrophysics Data System (ADS)

    Nazarov, Vladimir U.; Vignale, Giovanni

    2008-03-01

    Within the time-dependent density functional theory formalism we relate the impurity resistivity ρ of a metal to the friction coefficient Q of the metal for the same impurity moving with the infinitesimally small velocity, i.e., ρ=niQ / ne^2 ,1), where ni and ne are the concentrations of the randomly distributed impurities and the valence electrons, respectively. While Eq.(1) occurs trivial within the single-particle theory with the scattering at the statically screened impurities, its general validity within the many-body theory with the dynamical exchange and correlation included presents a progress. We utilize results [1,2] on Q of the electron liquid to put the electron-electron scattering contribution into the terms of the viscosity coefficients [3]. Calculations of the residual resistivity of aluminum as a function of the atomic number of the impurity are performed, improving the agreement with experiment compared to the single- particle theory [4]. [1].V. U. Nazarov, J. M. Pitarke, C. S. Kim, and Y. Takada, Phys. Rev. B 71, 121106(R) (2005). [2].V. U. Nazarov, J. M. Pitarke, Y. Takada, G. Vignale, and Y.-C. Chang, Phys. Rev. B 76, 205103 (2007). [3].G. Vignale, C. A. Ullrich, and S. Conti, Phys. Rev. Lett. 79, 4878 (1997). [4].M. J. Puska and R. M. Nieminen, Phys. Rev. B 27, 6121 (1983).

  13. Design strategies to improve the sensitivity of photoactive metal carbonyl complexes (photoCORMs) to visible light and their potential as CO-donors to biological targets.

    PubMed

    Chakraborty, Indranil; Carrington, Samantha J; Mascharak, Pradip K

    2014-08-19

    The recent surprising discovery of the beneficial effects of carbon monoxide (CO) in mammalian physiology has drawn attention toward site-specific delivery of CO to biological targets. To avoid difficulties in handling of this noxious gas in hospital settings, researchers have focused their attention on metal carbonyl complexes as CO-releasing molecules (CORMs). Because further control of such CO delivery through light-triggering can be achieved with photoactive metal carbonyl complexes (photoCORMs), we and other groups have attempted to isolate such complexes in the past few years. Typical metal carbonyl complexes release CO when exposed to UV light, a fact that often deters their use in biological systems. From the very beginning, our effort therefore was directed toward identifying design principles that could lead to photoCORMs that release CO upon illumination with low-power (5-15 mW/cm(2)) visible and near-IR light. In our work, we have utilized Mn(I), Re(I), and Ru(II) centers (all d(6) ground state configuration) to ensure overall stability of the carbonyl complexes. We also hypothesized that transfer of electron density from the electron-rich metal centers to π* MOs of the ligand frame via strong metal-to-ligand charge transfer (MLCT) transitions in the visible/near-IR region would weaken metal-CO back-bonding and promote rapid CO photorelease. This expectation has been realized in a series of carbonyl complexes derived from a variety of designed ligands and smart choice of ligand/coligand combinations. Several principles have emerged from our systematic approach to the design of principal ligands and the choice of auxiliary ligands (in addition to the number of CO) in synthesizing these photoCORMs. In each case, density functional theory (DFT) and time-dependent DFT (TDDFT) study afforded insight into the dependence of the CO photorelease from a particular photoCORM on the wavelength of light. Results of these theoretical studies indicate that extended

  14. Metal complexes of pyridine-fused macrocyclic polyamines targeting the chemokine receptor CXCR4.

    PubMed

    Hamal, Sunil; D'huys, Thomas; Rowley, William F; Vermeire, Kurt; Aquaro, Stefano; Frost, Brian J; Schols, Dominique; Bell, Thomas W

    2015-11-14

    The chemokine receptor CXCR4 acts as a key cell surface receptor in HIV infections, multiple forms of cancer, and various other pathologies, such as rheumatoid arthritis and asthma. Macrocyclic polyamines and their metal complexes are known to exert anti-HIV activity, many acting as HIV entry inhibitors by specifically binding to CXCR4. Three series of pyridopentaazacylopentadecanes, in which the pyridine ring is fused to zero, one, or two saturated six-membered rings, were synthesized by manganese(ii)-templated Schiff-base cyclization of triethylenetetramine with various dicarbonyl compounds. By evaluating these macrocyclic polyamines and their complexes with Mn(2+), Cu(2+), Fe(3+), and Zn(2+), we have discovered novel CXCR4-binding compounds. The MnCl2 complex of a new pentaazacyclopentadecane with one fused carbocyclic ring (11) was found to have the greatest potency as an antagonist of the chemokine receptor CXCR4 (IC50: 0.014 μM), as evidenced by inhibiting binding of CXCL12 to PBMCs (peripheral blood mononuclear cells). Consequently, this compound inhibits replication of the CXCR4-using (X4) HIV-1 strain NL4-3 in the TZM-bl cell line with an IC50 value of 0.52 μM and low cytotoxicity (CC50: >100 μM). In addition, 18 other compounds were evaluated for their interaction with CXCR4 via their ability to interfere with ligand chemokine binding and HIV entry and infection. Of these, the metal complexes of the two more hydrophobic series with one or two fused carbocyclic rings exhibited the greatest potency. The Zn(2+) complex 21 was among the most potent, showing that redox activity of the metal center is not associated with CXCR4 antagonist activity. PMID:26338723

  15. Effects study on the thermal stresses in a LEU metal foil annular target.

    PubMed

    Govindarajan, Srisharan G; Solbrekken, Gary L

    2015-09-01

    The effects of fission gas pressure, uranium swelling and thermal contact conductance on the thermal-mechanical behavior of an annular target containing a low-enriched uranium foil (LEU) encapsulated in a nickel foil have been presented in this paper. The draw-plug assembly method is simulated to obtain the residual stresses, which are applied to the irradiation model as initial inputs, and the integrated assembly-irradiation process is simulated as an axisymmetric problem using the commercial finite element code Abaqus FEA. Parametric studies were performed on the LEU heat generation rate and the results indicate satisfactory irradiation performance of the annular target. The temperature and stress margins have been provided along with a discussion of the results. PMID:26036440

  16. Target selection and pharma industry productivity: what can we learn from technology S-curve theory?

    PubMed

    Brown, David

    2006-07-01

    The number of new drug approvals per annum has been decreasing regularly over the past decade, and changes made 12 to 15 years ago to the research and development approach of the pharmaceutical industry may have contributed to this fall in productivity. In particular, the rapid switch at that time away from an 'observation-led' approach toward a 'hypothesis-led' approach to target selection may be a key contributing factor to this issue. The strengths and weaknesses of both approaches are analyzed herein, and it is suggested that unsolved weaknesses in both approaches are holding back the productivity of the pharmaceutical/biotechnology industry.

  17. Increasing organizational energy conservation behaviors: Comparing the theory of planned behavior and reasons theory for identifying specific motivational factors to target for change

    NASA Astrophysics Data System (ADS)

    Finlinson, Scott Michael

    Social scientists frequently assess factors thought to underlie behavior for the purpose of designing behavioral change interventions. Researchers commonly identify these factors by examining relationships between specific variables and the focal behaviors being investigated. Variables with the strongest relationships to the focal behavior are then assumed to be the most influential determinants of that behavior, and therefore often become the targets for change in a behavioral change intervention. In the current proposal, multiple methods are used to compare the effectiveness of two theoretical frameworks for identifying influential motivational factors. Assessing the relative influence of all factors and sets of factors for driving behavior should clarify which framework and methodology is the most promising for identifying effective change targets. Results indicated each methodology adequately predicted the three focal behaviors examined. However, the reasons theory approach was superior for predicting factor influence ratings compared to the TpB approach. While common method variance contamination had minimal impact on the results or conclusions derived from the present study's findings, there were substantial differences in conclusions depending on the questionnaire design used to collect the data. Examples of applied uses of the present study are discussed.

  18. Highly conductive indium zinc oxide prepared by reactive magnetron cosputtering technique using indium and zinc metallic targets

    SciTech Connect

    Tsai, T. K.; Chen, H. C.; Lee, J. H.; Huang, Y. Y.; Fang, J. S.

    2010-05-15

    Zn-doped In{sub 2}O{sub 3} film is frequently deposited from an oxide target; but the use of metallic target is increasingly expected as preparing the film with comparable properties. This work aimed to prepare a highly conductive and transparent Zn-doped In{sub 2}O{sub 3} thin film on Corning Eagle{sup 2000} glass substrate by magnetron cosputtering method using indium and zinc targets. Structural characterization was performed using x-ray diffraction and x-ray photoelectron spectroscopy. The film had an amorphous structure when the film was prepared on an unheated substrate, but had an In{sub 2}O{sub 3} polycrystalline structure when the film was deposited on 150 and 300 deg. C substrates. The electrical properties of the film were greatly affected by annealing; the Zn-doped In{sub 2}O{sub 3} film had a low resistivity of 6.1x10{sup -4} {Omega} cm and an average transmittance of 81.7% when the film was deposited without substrate heating and followed a 600 deg. C annealing.

  19. High heat flux sensor for infrared thermography determination of heat transfer coefficient of liquid metal cooled target's wall

    NASA Astrophysics Data System (ADS)

    Patorski, Jacek A.; Gindrat, Malko

    2009-05-01

    The proton beam passing through the wall area of a liquid metal (LM) target container, called entrance window, is causing deposition of maximum high heat flux amount 140 W/cm2.Previous experimental thermo-hydraulics investigations for the MEGAPIE LM-target at the SINQ facility of Heat- Transfer-Coefficient (HTC) using InfraRed-Thermography (IRT) have been presented at Thermosense 2006 and 2007 [1], [2] and references therein. During these investigations the IRT active sensors with applied heat fluxes of the small and low range from 2.5 to 15.2 W/cm2 are used. The heating shell foil of the sensor has been connected to steel dish enclosing LM target container by using electrical insulation ceramic glue. A higher, then achieved 15 W/cm2, heat flux has lead to delaminating of the heater. Because of interest to determinate the HTC-chart under real heat flux conditions and investigate some positive effect of heat flux buoyancy on cooling, the idea for the High Heat Flux (HHF) IRT Sensors, using of the Low Pressure Plasma Spraying - Thin Film (LPPS-TF) technology of the Sulzer Metco Company has been created. The paper presents the idea of multilayer thermal sprayed construction of HHF-IRT-Sensor, few realizations and some results of the first pre-test performed at the PSI LBE Double Pump Loop using the new sensor and the 2DD IRT methodology presented in [1].

  20. R&D-needs and opportunities to broaden the data base on materials and technology for liquid metal spallation targets

    SciTech Connect

    Bauer, G.S.

    1996-06-01

    Liquid metals have so far only been used to a very limited extent as spallation targets, notably at the ISOLDE-facility at CERN (Pb and La) to produce radioactive isotopes. Virtually no systematic studies have been carried out so far. The available data base is by no means sufficient to answer conclusively very important questions such as predicting reliably the service time of medium-to-high power target systems or determining precisely what technological measures are required and appropriate to maintain an optimum coolant quality, to mitigate the effects of pressure waves in short pulse sources and others. During the workshop several areas have been identified, where there exists an urgent need for improved knowledge and reliable data, and opportunities have been presented to acquire such knowledge and to generate such data. Opportunities to do such research and pertinent know-how, although scarce, are spread over institutions in several countries, and efforts to use these opportunities often require substantial resources both in man power and money. The workshop participants therefore unanimously supported the view that a coordinated and internationally concerted effort should be undertaken to make the best possible use of existing opportunities and available resources in order to develop the knowledge and technology necessary for the deployment and safe operation of target systems suitable for pulsed spallation neutron sources in the multi-megawatt range of beam power.

  1. A Theory for the RF Surface Field for Various Metals at the Destructive Breakdown Limit

    SciTech Connect

    Wilson, Perry B.; /SLAC

    2007-03-06

    By destructive breakdown we mean a breakdown event that results in surface melting over a macroscopic area in a high E-field region of an accelerator structure. A plasma forms over the molten area, bombarding the surface with an intense ion current ({approx} 10{sup 8} A/cm{sup 2}), equivalent to a pressure of about a thousand Atmospheres. This pressure in turn causes molten copper to migrate away from the iris tip, resulting in measurable changes in the iris shape. The breakdown process can be roughly divided into four stages: (1) the formation of ''plasma spots'' at field emission sites, each spot leaving a crater-like footprint; (2) crater clustering, and the formation of areas with hundreds of overlapping craters; (3) surface melting in the region of a crater cluster; (4) the process after surface melting that leads to destructive breakdown. The physics underlying each of these stages is developed, and a comparison is made between the theory and experimental evidence whenever possible. The key to preventing breakdown lies in stage (3). A single plasma spot emits a current of several amperes, a portion of which returns to impact the surrounding area with a power density on the order 10{sup 7} Watt/cm{sup 2}. This power density is not quite adequate to melt the surrounding surface on a time scale short compared to the rf pulse length. In a crater field, however, the impact areas from multiple plasma spots overlap to provide sufficient power density for surface melting over an area on the order of 0.1 mm{sup 2} or more. The key to preventing breakdown is to choose an iris tip material that requires the highest power density (proportional to the square of the rf surface field) for surface melting, taking into account the penetration depth of the impacting electrons. The rf surface field required for surface melting (relative to copper) has been calculated for a large number elementary metals, plus stainless-steel and carbon.

  2. A Density Functional Theory Based Protocol to Compute the Redox Potential of Transition Metal Complex with the Correction of Pseudo-Counterion: General Theory and Applications.

    PubMed

    Matsui, Toru; Kitagawa, Yasutaka; Shigeta, Yasuteru; Okumura, Mitsutaka

    2013-07-01

    We propose an accurate scheme to evaluate the redox potential of a wide variety of transition metal complexes by adding a charge-dependent correction term for a counterion around the charged complexes, which is based on Generalized Born theory, to the solvation energy. The mean absolute error (MAE) toward experimental redox potentials of charged complexes is considerably reduced from 0.81 V (maximum error 1.22 V) to 0.22 V (maximum error 0.50 V). We found a remarkable exchange-correlation functional dependence on the results rather than the basis set ones. The combination of Wachters+f (for metal) and 6-31++G(d,p) (for other atoms) with the B3LYP functional gives the least MAE 0.15 V for the test complexes. This scheme is applicable to other solvents, and heavier transition metal complexes such as M1(CO)5(pycn) (M1 = Cr, Mo, W), M2(mnt)2 (M2 = Ni, Pd, Pt), and M3(bpy)3 (M3 = Fe, Ru, Os) with the same quality.

  3. Computational study of the generation of crystal defects in a bcc metal target irradiated by short laser pulses

    NASA Astrophysics Data System (ADS)

    Lin, Zhibin; Johnson, Robert A.; Zhigilei, Leonid V.

    2008-06-01

    The generation of crystal defects in a Cr target irradiated by a short, 200 fs, laser pulse is investigated in computer simulations performed with a computational model that combines the classical molecular dynamics method with a continuum description of the laser excitation of conduction band electrons, electron-phonon coupling, and electron heat conduction. Interatomic interactions are described by the embedded atom method (EAM) potential with a parametrization designed for Cr. The potential is tested by comparing the properties of the EAM Cr material with experimental data and predictions of density functional theory calculations. The simulations are performed at laser fluences close to the threshold for surface melting. Fast temperature variation and strong thermoelastic stresses produced by the laser pulse are causing surface melting and epitaxial resolidification, transient appearance of a high density of stacking faults along the {110} planes, and generation of a large number of point defects (vacancies and self-interstitials). The stacking faults appear as a result of internal shifts in the crystal undergoing a rapid uniaxial expansion in the direction normal to the irradiated surface. The stacking faults are unstable and disappear shortly after the laser-induced tensile stress wave leaves the surface region of the target. Thermally activated generation of vacancy-interstitial pairs during the initial temperature spike and quick escape of highly mobile self-interstitials to the melting front or the free surface of the target, along with the formation of vacancies at the solid-liquid interface during the fast resolidification process, result in a high density of vacancies, on the order of 10-3 per lattice site, created in the surface region of the target. The strong supersaturation of vacancies can be related to the incubation effect in multipulse laser ablation/damage and should play an important role in mixing/alloying of multicomponent or composite

  4. Large-signal model of the bilayer graphene field-effect transistor targeting radio-frequency applications: Theory versus experiment

    SciTech Connect

    Pasadas, Francisco Jiménez, David

    2015-12-28

    Bilayer graphene is a promising material for radio-frequency transistors because its energy gap might result in a better current saturation than the monolayer graphene. Because the great deal of interest in this technology, especially for flexible radio-frequency applications, gaining control of it requires the formulation of appropriate models for the drain current, charge, and capacitance. In this work, we have developed them for a dual-gated bilayer graphene field-effect transistor. A drift-diffusion mechanism for the carrier transport has been considered coupled with an appropriate field-effect model taking into account the electronic properties of the bilayer graphene. Extrinsic resistances have been included considering the formation of a Schottky barrier at the metal-bilayer graphene interface. The proposed model has been benchmarked against experimental prototype transistors, discussing the main figures of merit targeting radio-frequency applications.

  5. Nonlinear absorption of surface plasmons and emission of electrons from metallic targets

    SciTech Connect

    Singh, D. B.; Kumar, Gagan; Tripathi, V. K.

    2007-10-15

    A large-amplitude surface plasma wave (SPW) over a metal-vacuum interface Ohmically heats the electrons and undergoes nonlinear absorption. The attenuation rate increases with the local SPW amplitude. The enhanced electron temperature leads to stronger thermionic emission of electrons. At typical Nd:glass laser intensity I{sub L}=7 GW/cm{sup 2}, if one takes the amplitude of the SPW to be {approx_equal}6 times the amplitude of the laser, one obtains the thermionic electron emission current density J=200 A/cm{sup 2}. However, the emission current density decreases with propagation distance at a much faster rate than the SPW amplitude and electron temperature.

  6. Features of the synthesis of nanocolloid oxides by laser ablation of bulk metal targets in solutions

    NASA Astrophysics Data System (ADS)

    Lapin, Ivan N.; Svetlichnyi, Valery A.

    2015-12-01

    Laser ablation of bulk targets in a fluid -- a promising new method for the synthesis of "pure" nanocolloids. Nanocrystalline materials produced by laser ablation are widely used in biology, medicine, and catalysis. High local temperature during ablation and large surface area of the particles promote chemical reactions and the formation of a complex composition of nanoparticles. In this paper the characteristics of the process of ablation and the obtaining of nanoparticles in a liquid by laser ablation of active materials (Zn, Ce, Ti, Si) were studied. Ways of increasing the productivity of laser ablation were discussed. Characterization of nanocolloids and nanocrystalline powders were performed.

  7. Fundamental correction of Mie's scattering theory for the analysis of the plasmonic resonance of a metal nanosphere

    NASA Astrophysics Data System (ADS)

    Fujii, Masafumi

    2014-03-01

    It is shown that Mie's solution to Maxwell's equations no longer holds for the analysis of resonance of a plasmonic metal nanosphere. The conventional Mie's solution is based on the spherical Bessel and the spherical Hankel functions of an outgoing wave, whereas the permittivity of metals of a negative real part leads to a phase velocity that directs inward to the sphere, which is opposite from the direction of the energy flow as often discussed for negative-index metamaterials. This is a fundamental problem overlooked for a long time; a correction can be found from the viewpoint of a time-reversal problem involving negative permittivity media. The continuity of the field solution at the sphere surface is shown to be corrected by replacing the spherical Hankel function of an outgoing wave with that of an incoming wave, i.e., by adopting the complex conjugate of the conventional solutions. The corrected theory has been verified by the analyses of various metal nanospheres. In addition, the derivation of the scattering cross sections based on the corrected theory has elucidated that the conservation law of energy holds and that, more importantly, the conventional Mie's solution gives the same amplitude of the cross sections when they are obtained for real, not complex, frequency.

  8. Multispectral Detection with Metal-Dielectric Filters: An Investigation in Several Wavelength Bands with Temporal Coupled-Mode Theory

    NASA Astrophysics Data System (ADS)

    Lesmanne, Emeline; Espiau de Lamaestre, Roch; Boutami, Salim; Durantin, Cédric; Dussopt, Laurent; Badano, Giacomo

    2016-09-01

    Multispectral infrared (IR) detection is of great interest to enhance our ability to gather information from a scene. Filtering is a low-cost alternative to the complex multispectral device architectures to which the IR community has devoted much attention. Multilayer dielectric filters are standard in industry, but they require changing the thickness of at least one layer to tune the wavelength. Here, we pursue an approach based on apertures in a metallic layer of fixed thickness, in which the filtered wavelengths are selected by varying the aperture geometry. In particular, we study filters made of at least one sheet of resonating apertures in metal embedded in dielectrics. We will discuss two interesting problems that arise when one attempts to design such filters. First, metallic absorption must be taken into account. Second, the form and size of the pattern is limited by lithography. We will present some design examples and an attempt at explaining the filtering behavior based on the temporal coupled mode theory. That theory models the filter as a resonator interacting with the environment via loss channels. The transmission is solely determined by the loss rates associated with those channels. This model allows us to give a general picture of the filtering performance and compare their characteristics at different wavelength bands.

  9. General atomistic approach for modeling metal-semiconductor interfaces using density functional theory and nonequilibrium Green's function

    NASA Astrophysics Data System (ADS)

    Stradi, Daniele; Martinez, Umberto; Blom, Anders; Brandbyge, Mads; Stokbro, Kurt

    2016-04-01

    Metal-semiconductor contacts are a pillar of modern semiconductor technology. Historically, their microscopic understanding has been hampered by the inability of traditional analytical and numerical methods to fully capture the complex physics governing their operating principles. Here we introduce an atomistic approach based on density functional theory and nonequilibrium Green's function, which includes all the relevant ingredients required to model realistic metal-semiconductor interfaces and allows for a direct comparison between theory and experiments via I -Vbias curve simulations. We apply this method to characterize an Ag/Si interface relevant for photovoltaic applications and study the rectifying-to-Ohmic transition as a function of the semiconductor doping. We also demonstrate that the standard "activation energy" method for the analysis of I -Vbias data might be inaccurate for nonideal interfaces as it neglects electron tunneling, and that finite-size atomistic models have problems in describing these interfaces in the presence of doping due to a poor representation of space-charge effects. Conversely, the present method deals effectively with both issues, thus representing a valid alternative to conventional procedures for the accurate characterization of metal-semiconductor interfaces.

  10. High brightness EUV sources based on laser plasma at using droplet liquid metal target

    NASA Astrophysics Data System (ADS)

    Vinokhodov, A. Yu; Krivokorytov, M. S.; Sidelnikov, Yu V.; Krivtsun, V. M.; Medvedev, V. V.; Koshelev, K. N.

    2016-05-01

    We present the study of a source of extreme ultraviolet (EUV) radiation based on laser plasma generated due to the interaction of radiation from a nanosecond Nd : YAG laser with a liquidmetal droplet target consisting of a low-temperature eutectic indium–tin alloy. The generator of droplets is constructed using a commercial nozzle and operates on the principle of forced capillary jet decomposition. Long-term spatial stability of the centre-of-mass position of the droplet with the root-mean-square deviation of ~0.5 μm is demonstrated. The use of a low-temperature working substance instead of pure tin increases the reliability and lifetime of the droplet generator. For the time- and space-averaged power density of laser radiation on the droplet target 4 × 1011 W cm-2 and the diameter of radiating plasma ~80 μm, the mean efficiency of conversion of laser energy into the energy of EUV radiation at 13.5 +/- 0.135 nm equal to 2.3% (2π sr)-1 is achieved. Using the doublepulse method, we have modelled the repetitively pulsed regime of the source operation and demonstrated the possibility of its stable functioning with the repetition rate up to 8 kHz for the droplet generation repetition rate of more than 32 kHz, which will allow the source brightness to be as large as ~0.96 kW (mm2 sr)-1.

  11. High brightness EUV sources based on laser plasma at using droplet liquid metal target

    NASA Astrophysics Data System (ADS)

    Vinokhodov, A. Yu; Krivokorytov, M. S.; Sidelnikov, Yu V.; Krivtsun, V. M.; Medvedev, V. V.; Koshelev, K. N.

    2016-05-01

    We present the study of a source of extreme ultraviolet (EUV) radiation based on laser plasma generated due to the interaction of radiation from a nanosecond Nd : YAG laser with a liquidmetal droplet target consisting of a low-temperature eutectic indium-tin alloy. The generator of droplets is constructed using a commercial nozzle and operates on the principle of forced capillary jet decomposition. Long-term spatial stability of the centre-of-mass position of the droplet with the root-mean-square deviation of ~0.5 μm is demonstrated. The use of a low-temperature working substance instead of pure tin increases the reliability and lifetime of the droplet generator. For the time- and space-averaged power density of laser radiation on the droplet target 4 × 1011 W cm-2 and the diameter of radiating plasma ~80 μm, the mean efficiency of conversion of laser energy into the energy of EUV radiation at 13.5 +/- 0.135 nm equal to 2.3% (2π sr)-1 is achieved. Using the doublepulse method, we have modelled the repetitively pulsed regime of the source operation and demonstrated the possibility of its stable functioning with the repetition rate up to 8 kHz for the droplet generation repetition rate of more than 32 kHz, which will allow the source brightness to be as large as ~0.96 kW (mm2 sr)-1.

  12. Comments on the possibility of cavitation in liquid metal targets for pulsed spallation neutron sources

    SciTech Connect

    Carpenter J.M.

    1996-06-01

    When short pulses of protons strike the volume of a liquid target, the rapid heating produces a pressurized region which relaxes as the pressure wave propagates outward. Skala and Bauer have modeled the effects of the pressure wave impinging on the container walls of a liquid mercury target under ESS conditions. They find that high pressures and high wall stresses result if the medium is uniform, nearly incompressible liquid. The pressure and the stresses are much reduced if the liquid contains bubbles of helium, due to their high compressibility. However, according to the calculation, the pressure still reaches an atmosphere or so at the surface, which reflects the compressive wave as a rarefaction wave of the same magnitude. Even such modest underpressures can lead to the growth of bubbles (cavitation) at or near the surface, which can collapse violently and erode the container surface. It is necessary to avoid this. Leighton provides a wide ranging discussion of pressure waves in bubbly media, which may provide insights into the nature and control of cavitation phenomena. The paper surveys some of the relevant information from that source.

  13. a Theory of the Metallization of Semiconductor Surfaces by Alkali Atoms.

    NASA Astrophysics Data System (ADS)

    Te, Ronald Lim

    Experimental evidence suggest that alkali metal atoms adsorbed on a semiconductor substrate undergo a transition from insulating to metallic at low coverage. The electrons in the adlayer initially occupy isolated exponentially localized atomic orbitals, and become metallic with increasing coverage. Several investigations have shown that the onset of metallization occurs at less than a quarter of a monolayer. Interpretation of second-harmonic data, where the signal increases sharply at 1/6 monolayer, suggests a metallization transition due to the delocalization of surface electrons. This dissertation provides a theoretical framework for understanding the metallization of alkali overlayers. The adlayer is simulated using a rectangular lattice with more than 80,000 sites that are randomly occupied by atomic-like orbitals up to densities commensurate with the different coverages. A new computational technique called dynamic recursion was developed to handle calculations with large numbers of basis orbitals. Each alkali orbital is taken to have the same on-site energy; however, the orbital interactions involve several nearest neighbors and are an exponentially decreasing function of the orbitals' separation. This model gives a tight-binding Hamiltonian with random off-diagonal disorder. An investigation of states at the Fermi level shows a sharp transition between strongly and weakly localized states as a function of coverage. This numerically observed transition is indicative of an Anderson-type metal-insulator transition where disorder causes states of different degrees of localization to cross the Fermi level. The Hamiltonian studied exhibits a delocalization transition for states at the Fermi level, and is proposed as a model for the metallization of the alkali metal atoms adsorbed on a semiconductor substrate. These results are consistent with other work which show the existence of a mobility edge that separates exponentially localized from power-law localized

  14. Study of the dissociation of a charge-reduced phosphopeptide formed by electron transfer from an alkali metal target.

    PubMed

    Hayakawa, Shigeo; Hashimoto, Mami; Nagao, Hirofumi; Awazu, Kunio; Toyoda, Michisato; Ichihara, Toshio; Shigeri, Yasushi

    2008-01-01

    Doubly protonated phosphopeptide (YGGMHRQET(p)VDC) ions obtained by electrospray ionization were collided with Xe and Cs targets to give singly and doubly charged positive ions via collision-induced dissociation (CID). The resulting ions were analyzed and detected by using an electrostatic analyzer (ESA). Whereas doubly charged fragment ions resulting from collisionally activated dissociation (CAD) were dominant in the CID spectrum with the Xe target, singly charged fragment ions resulting from electron transfer dissociation (ETD) were dominant in the CID spectrum with the Cs target. The most intense peak resulting from ETD was estimated to be associated with the charge-reduced ion with H2 lost from the precursor. Five c-type fragment ions with amino acid residues detached consecutively from the C-terminal were clearly observed without a loss of the phosphate group. These ions must be formed by N--Calpha bond cleavage, in a manner similar to the cases of electron capture dissociation (ECD) and ETD from negative ions. Although the accuracy in m/z of the CID spectra was about +/-1 Th because of the mass analysis using the ESA, it is supposed from the m/z values of the c-type ions that these ions were accompanied by the loss of a hydrogen atom. Four z-type (or y--NH3, or y--H2O) ions analogously detached consecutively from the N-terminal were also observed. The fragmentation processes took place within the time scale of 4.5 micros in the high-energy collision. The present results demonstrated that high-energy ETD with the alkali metal target allowed determination of the position of phosphorylation and the amino acid sequence of post-translational peptides.

  15. Thermal effects in the shear-transformation-zone theory of amorphous plasticity: comparisons to metallic glass data.

    PubMed

    Falk, M L; Langer, J S; Pechenik, L

    2004-07-01

    We extend our earlier shear-transformation-zone theory of amorphous plasticity to include the effects of thermally assisted molecular rearrangements. This version of our theory is a substantial revision and generalization of conventional theories of flow in noncrystalline solids. As in our earlier work, it predicts a dynamic transition between jammed and flowing states at a yield stress. Below that yield stress, it now describes thermally assisted creep. We show that this theory accounts for the experimentally observed strain-rate dependence of the viscosity of metallic glasses, and that it also captures many of the details of the transient stress-strain behavior of those materials during loading. In particular, it explains the apparent onset of superplasticity at sufficiently high stress as a transition between creep at low stresses and plastic flow near the yield stress. We also argue that there are internal inconsistencies in the conventional theories of these deformation processes, and suggest ways in which further experimentation as well as theoretical analysis may lead to better understanding of a broad range of nonequilibrium phenomena. PMID:15324056

  16. Electronic specific heat enhancement in the half-metallic ferromagnet Cro2 explained by Fermi Liquid Theory

    NASA Astrophysics Data System (ADS)

    Chura, Raul; Bedell, Kevin

    2007-03-01

    Available data on the electronic specific heat of the half-metallic ferromagnet (HMF) CrO2, show that the obtained experimental values are systematically greater than the corresponding theoretical ones calculated through various band theory methods. This discrepancy is due to the presence of many-electron correlation effects (spin fluctuations, strong electron-magnon scattering) which are not taken into account in the band theory calculations. A renormalization of the band theory results is therefore needed to account for the observed enhancement in the value of the specific heat. A microscopic many-electron approach has been proposed and explains the referred enhancement in terms of non-quasiparticle effects. It has been argued that Fermi liquid theory is not sufficient to provide the appropriate renormalization able to explain the observed enhancement in the electronic specific heat of HMFs. Contrary to this statement, we have shown that the introduction of a spin-dependent density of states, in the framework of the Fermi liquid theory for spin polarized systems, gives place to a renormalization which, indeed, provides a reasonable account of the observed enhancement in the electronic specific heat of the HMF CrO2.

  17. Targeting Parents for Childhood Weight Management: Development of a Theory-Driven and User-Centered Healthy Eating App

    PubMed Central

    Lahiri, Sudakshina; Brown, Katherine Elizabeth

    2015-01-01

    Background The proliferation of health promotion apps along with mobile phones' array of features supporting health behavior change offers a new and innovative approach to childhood weight management. However, despite the critical role parents play in children’s weight related behaviors, few industry-led apps aimed at childhood weight management target parents. Furthermore, industry-led apps have been shown to lack a basis in behavior change theory and evidence. Equally important remains the issue of how to maximize users’ engagement with mobile health (mHealth) interventions where there is growing consensus that inputs from the commercial app industry and the target population should be an integral part of the development process. Objective The aim of this study is to systematically design and develop a theory and evidence-driven, user-centered healthy eating app targeting parents for childhood weight management, and clearly document this for the research and app development community. Methods The Behavior Change Wheel (BCW) framework, a theoretically-based approach for intervention development, along with a user-centered design (UCD) philosophy and collaboration with the commercial app industry, guided the development process. Current evidence, along with a series of 9 focus groups (total of 46 participants) comprised of family weight management case workers, parents with overweight and healthy weight children aged 5-11 years, and consultation with experts, provided data to inform the app development. Thematic analysis of focus groups helped to extract information related to relevant theoretical, user-centered, and technological components to underpin the design and development of the app. Results Inputs from parents and experts working in the area of childhood weight management helped to identify the main target behavior: to help parents provide appropriate food portion sizes for their children. To achieve this target behavior, the behavioral diagnosis

  18. Production of CeO2 Nanoparticles by Method of Laser Ablation of Bulk Metallic Cerium Targets in Liquid

    NASA Astrophysics Data System (ADS)

    Svetlichnyi, V. A.; Lapin, I. N.

    2016-03-01

    The method of pulsed laser ablation in liquid was used to synthesize dispersions of cerium oxide nanoparticles when subjecting a metallic cerium target in water and alcohol to basic frequency radiation of the nanosecond Nd:YAG laser (1064 nm, 7 ns, 20 Hz). Researchers have studied the effect of laser radiation parameters, duration of impact, and optical scheme of experiment on the ablation process. The average rate of nanoparticle production was 50 mg/h in water and 25 mg/h in alcohol. Researchers have studied the size characteristics and crystalline structure of the nanoparticles produced. The particles have bimodal size distribution with 6 nm and 25 nm maximums. The average crystallite size is 17-19 nm. The crystalline structure of nanoparticles, namely cubic cerium oxide (fluorite structure), space group Fm-3m, is confirmed by the X-ray diffraction data, as well as optical absorption spectra and Raman spectroscopy.

  19. Zinc-sensitive genes as potential new target genes of the metal transcription factor-1 (MTF-1).

    PubMed

    Kindermann, Birgit; Döring, Frank; Budczies, Jan; Daniel, Hannelore

    2005-04-01

    Zinc is an essential trace element that serves as a structural constituent of a large number of transcription factors, which explains its pivotal role in the control of gene expression. Previous studies investigating the effect of zinc deficiency and zinc supplementation on gene expression in the human adenocarcinoma cell line HT-29 led to the identification of a considerable number of genes responding to alterations in cellular zinc status with changes in steady state mRNA levels. For 9 of 20 genes from these previous screenings that were studied in more detail, mRNA steady state levels responded to both high and low media zinc concentrations. As they are primarily zinc-dependent, we assessed whether these genes are controlled by the zinc-finger metal transcription factor MTF-1. To test this hypothesis we generated a doxycyline-inducible Tet-On HT-29 cell line overexpressing MTF-1. Using this conditional expression system, we present evidence that Kruppel-like factor 4 (klf4), hepatitis A virus cellular receptor 1 (hhav), and complement factor B (cfbp) are 3 potential new target genes of MTF-1. To support this, we used in silico analysis to screen for metal-responsive elements (MREs) within promotors of zinc-sensitive genes. We conclude that zinc responsiveness of klf4, hhav, and cfbp in HT-29 cells is mediated at least in part by MTF-1.

  20. Transport properties and metal-insulator transition in oxygen deficient LaNiO3: a density functional theory study

    NASA Astrophysics Data System (ADS)

    Misra, D.; Kundu, T. K.

    2016-09-01

    Density functional theory with appropriate functional has been employed to investigate the metal to insulator transition in oxygen deficient LaNiO3-x (x = 0.0, 0.25, 0.5, 1.0) compounds. While the metallic nature of LaNiO3 is characterized by the low temperature Fermi liquid behavior of resistivity and a finite density of states at the Fermi level, the density of states and the transport properties clearly identify LaNiO2.75 as a semiconductor, and LaNiO2.5 as an insulator, which is followed by another insulator to semiconductor transition with further increase of x to ‘1’ in LaNiO2. This oxygen vacancy controlled metal to insulator transition is explained on the basis of non-adiabatic polaronic transport. From the covalency metric calculation of the chemical bonding and the Bader charge transfer analysis, this metal to insulator transition is attributed to the enhanced covalent part in the chemical bonding and reduced charge transfer from Ni to O atoms in LaNiO3-x compounds.

  1. Magneto-Rayleigh-Taylor Instability: Theory and simulation in planar and cylindrical pulsed power targets

    NASA Astrophysics Data System (ADS)

    Weis, Matthew R.

    Cylindrical liner implosions in the Magnetized Liner Inertial Fusion (MagLIF) concept are susceptible to the magneto-Rayleigh-Taylor instability (MRT). The danger of MRT enters in two phases, (1) during the main implosion, the outer surface of the liner is MRT unstable, and (2) during the short time period when the liner decelerates onto hot fuel, the inner surface becomes unstable. Growth of MRT on the outer surface may also feedthrough, which may seed the inner surface leading to high MRT growth in the second phase. If MRT growth becomes large enough, confinement of the fuel is lost. To characterize MRT we solve the linearized, ideal MHD equations in both planar and cylindrical geometries, including the presence of an axial magnetic field and the effects of sausage and kink modes (present in cylindrical coordinates only). In general, the total instability growth rates in cylindrical geometry are found to be larger than those in planar geometry. MRT and feedthrough is shown to be suppressed by strong magnetic field line bending (tension). However, for the same amount of field line bending, feedthrough is the most stabilized. Application of the planar and the cylindrical model to results from the Z-machine at Sandia National Laboratories is presented. Analytic MRT growth rates for a typical magnetized MagLIF-like implosion show the kink mode to be the fastest growing early and very late in the liner implosion (during deceleration). 1D HYDRA MHD simulations are used to generate realistic, evolving profiles (in density, pressure, and magnetic field) during the implosion from which instantaneous growth rates can be computed exactly, using either the planar or cylindrical analytic formulae developed in this thesis. Sophisticated 2D HYDRA MHD simulations were also performed to compare with the analytic theory and experimental results. In 2D, highly compressed axial magnetic fields can reduce the growth of perturbations at the fuel/liner interface during the implosion

  2. Half-metallic ferromagnetism of RbSe and CsTe compounds: A density functional theory study

    NASA Astrophysics Data System (ADS)

    Xie, Huan-Huan; Ma, Run-Yu; Gao, Qiang; Li, Lei; Deng, Jian-Bo

    2016-09-01

    We investigate the electronic structures and magnetic properties of RbSe and CsTe compounds in CsCl, RS and ZB structures by using density functional theory calculation. It is shown that these two compounds exhibit half-metallic ferromagnetism with an integer magnetic moment of 1.00 μB per formula unit in all the three structures. Total energy calculations indicate the CsCl phase is more stable than the other two phases. We investigate these two compounds with CsCl structure in detail. The ferromagnetism results mainly from the spin-polarization of p states of anion Se (Te) for the two compounds.

  3. THEY MIGHT BE GIANTS: LUMINOSITY CLASS, PLANET OCCURRENCE, AND PLANET-METALLICITY RELATION OF THE COOLEST KEPLER TARGET STARS

    SciTech Connect

    Mann, Andrew W.; Hilton, Eric J.; Gaidos, Eric; Lepine, Sebastien

    2012-07-01

    We estimate the stellar parameters of late K- and early M-type Kepler target stars. We obtain medium-resolution visible spectra of 382 stars with K{sub P} - J > 2 ({approx_equal}K5 and later spectral type). We determine luminosity class by comparing the strength of gravity-sensitive indices (CaH, K I, Ca II, and Na I) to their strength in a sample of stars of known luminosity class. We find that giants constitute 96% {+-} 1% of the bright (K{sub P} < 14) Kepler target stars, and 7% {+-} 3% of dim (K{sub P} > 14) stars, significantly higher than fractions based on the stellar parameters quoted in the Kepler Input Catalog (KIC). The KIC effective temperatures are systematically (110{sup +15}{sub -35} K) higher than temperatures we determine from fitting our spectra to PHOENIX stellar models. Through Monte Carlo simulations of the Kepler exoplanet candidate population, we find a planet occurrence of 0.36 {+-} 0.08 when giant stars are properly removed, somewhat higher than when a KIC log g > 4 criterion is used (0.27 {+-} 0.05). Last, we show that there is no significant difference in g - r color (a probe of metallicity) between late-type Kepler stars with transiting Earth-to-Neptune-size exoplanet candidates and dwarf stars with no detected transits. We show that a previous claimed offset between these two populations is most likely an artifact of including a large number of misidentified giants.

  4. Structure of the I-SceI nuclease complexed with its dsDNA target and three catalytic metal ions.

    PubMed

    Prieto, Jesús; Redondo, Pilar; Merino, Nekane; Villate, Maider; Montoya, Guillermo; Blanco, Francisco J; Molina, Rafael

    2016-06-01

    Homing endonucleases are highly specific DNA-cleaving enzymes that recognize and cleave long stretches of DNA. The engineering of these enzymes provides instruments for genome modification in a wide range of fields, including gene targeting. The homing endonuclease I-SceI from the yeast Saccharomyces cerevisiae has been purified after overexpression in Escherichia coli and its crystal structure has been determined in complex with its target DNA. In order to evaluate the number of ions that are involved in the cleavage process, thus determining the catalytic mechanism, crystallization experiments were performed in the presence of Mn(2+), yielding crystals that were suitable for X-ray diffraction analysis. The crystals belonged to the orthorhombic space group P212121, with unit-cell parameters a = 80.11, b = 80.57, c = 130.87 Å, α = β = γ = 90°. The self-rotation function and the Matthews coefficient suggested the presence of two protein-DNA complexes in the asymmetric unit. The crystals diffracted to a resolution limit of 2.9 Å using synchrotron radiation. From the anomalous data, it was determined that three cations are involved in catalysis and it was confirmed that I-SceI follows a two-metal-ion DNA-strand cleavage mechanism. PMID:27303901

  5. Electronic structure of a metal-insulator interface: Towards a theory of nonreactive adhesion

    NASA Astrophysics Data System (ADS)

    Bordier, G.; Noguera, C.

    1991-09-01

    With the aim of studying metal-insulator adhesion, we have performed an analytical description of the electronic structure of a flat and defectless metal-insulator interface, for both rocksalt and zinc-blende crystallographic structures of the insulator and, respectively, (100) and (110) orientations of the interface. We model the metal by a jellium, and the AB-type insulator by a tight-binding Hamiltonian with one atomic orbital per site. A matching procedure involving a Green's-function method yields the local density of states of the metal-induced gap states (MIGS), which are found to be in good agreement with previous numerical estimations on specific materials. By analytically solving the Poisson equation in a self-consistent way, we are able to determine the position of the Fermi level of the whole system for any value of the insulator ionicity. Our results depend upon the density of electrons in the metal, and upon the penetration length and the density of MIGS at midgap. They do not depend much upon the crystallographic structure and orientation of the interface. The two relevant parameters are the Fermi energy of the metal and a ratio that represents the ionocovalent character of the insulator. This latter quantity can be allowed to vary from zero to infinity, thus describing the whole range of compounds from covalent semiconductors to highly insulating materials. We produce an analytical expression of the Schottky-barrier height and of the index of interface behavior, S, valid in the whole range of ionicity. S is found to fit well the available experimental data. We demonstrate that the capacitor model to estimate S is restricted to strongly ionic insulators, while it was generally used in the opposite limit. We suggest finally that the above electronic parameters also drive the strength of adhesion and wetting in nonreactive metal-insulator systems.

  6. Studies of polarization bremsstrahlung and ordinary bremsstrahlung from 89Sr beta particles in metallic targets in the photon energy region of 1-100 keV

    NASA Astrophysics Data System (ADS)

    Singh, Amrit; Dhaliwal, A. S.

    2015-06-01

    Studies of polarization bremsstrahlung (PB) and ordinary bremsstrahlung (OB) produced by the 89Sr beta emitter in Al, Ti, Sn and Pb targets were undertaken at photon energies of 1-100 keV. The experimental results are compared with the Elwert corrected (non-relativistic) Bethe-Heitler (EBH) theory and the modified Elwert factor (relativistic) Bethe-Heitler (Fmod BH) theory for OB and with the Avdonina and Pratt (Fmod BH + PB) theory for total bremsstrahlung (BS). These results are in agreement with the Fmod BH + PB theory up to 13 keV, 16 keV, 22 keV and 28 keV energies for Al, Ti, Sn and Pb targets, respectively; Fmod BH theory is more accurate at higher energies.

  7. Screening of catalytic oxygen reduction reaction activity of metal-doped graphene by density functional theory

    NASA Astrophysics Data System (ADS)

    Chen, Xin; Chen, Shuangjing; Wang, Jinyu

    2016-08-01

    Graphene doping is a promising direction for developing effective oxygen reduction reaction (ORR) catalysts. In this paper, we computationally investigated the ORR performance of 10 kinds of metal-doped graphene (M-G) catalysts, namely, Al-, Si-, Mn-, Fe-, Co-, Ni-, Pd-, Ag-, Pt-, and Au-G. The results shown that the binding energies of the metal atoms incorporated into the graphene vacancy are higher than their bulk cohesive energies, indicating the formed M-G catalysts are even more stable than the corresponding bulk metal surfaces, and thus avoid the metals dissolution in the reaction environment. We demonstrated that the linear relation among the binding energies of the ORR intermediates that found on metal-based materials does not hold for the M-G catalysts, therefore a single binding energy of intermediate alone is not sufficient to evaluate the ORR activity of an arbitrary catalyst. By analysis of the detailed ORR processes, we predicted that the Au-, Co-, and Ag-G materials can be used as the ORR catalysts.

  8. Signal enhancement in electrospray laser desorption/ionization mass spectrometry by using a black oxide-coated metal target and a relatively low laser fluence.

    PubMed

    Kononikhin, Alexey; Huang, Min-Zong; Popov, Igor; Kostyukevich, Yury; Kukaev, Evgeny; Boldyrev, Alexey; Spasskiy, Alexander; Leypunskiy, Ilya; Shiea, Jentaie; Nikolaev, Eugene

    2013-01-01

    The electrospray Laser desorption/ionization (ELDI) method is actively used for direct sample analysis and ambient mass spectrometry imaging. The optimizing of Laser desorption conditions is essential for this technology. In this work, we propose using a metal target with a black oxide (Fe3O4) coating to increase the signal in ELDI-MS for peptides and small proteins. The experiments were performed on an LTQ-FT mass spectrometer equipped with a home-made ELDI ion source. A cutter blade with black oxide coating was used as a target. A nitrogen laser was used with the following parameters: 337 nm, pulse duration 4ns, repetition rate 10 Hz, fluence to approximately 700 Jm(-2). More than a five times signal increase was observed for a substance P peptide when a coated and a non-coated metal target were compared. No ion signal was observed for proteins if the same fluence and the standard stainless steel target were used. With the assistance of the Fe3O4 coated metal target and a relatively low laser fluence < or =700 Jm(-2)), proteins such as insulin, ubiquitin and myoglobin were successfully ionized. It was demonstrated that the Fe3O4-coated metal target can be used efficiently to assist laser desorption and thus significantly increase the analyte signal in ELDI-MS. A relatively low laser fluence (< or = 700 Jm(-2)) was enough to desorb peptides and proteins (up to 17 kDal with the assistance of the Fe3O4-coated metal target under ambient conditions. PMID:24575623

  9. Heat transfer to a heavy liquid metal in curved geometry: Code validation and CFD simulation for the MEGAPIE lower target

    NASA Astrophysics Data System (ADS)

    Dury, Trevor V.

    2006-06-01

    The ESS and SINQ Heat Emitting Temperature Sensing Surface (HETSS) mercury experiments have been used to validate the Computational Fluid Dynamics (CFD) code CFX-4 employed in designing the lower region of the international liquid metal cooled MEGAPIE target, to be installed at SINQ, PSI, in 2006. Conclusions were drawn on the best turbulence models and degrees of mesh refinement to apply, and a new CFD model of the MEGAPIE geometry was made, based on the CATIA CAD design of the exact geometry constructed. This model contained the fill and drain tubes as well as the bypass feed duct, with the differences in relative vertical length due to thermal expansion being considered between these tubes and the window. Results of the mercury experiments showed that CFD calculations can be trusted to give peak target window temperature under normal operational conditions to within about ±10%. The target nozzle actually constructed varied from the theoretical design model used for CFD due to the need to apply more generous separation distances between the nozzle and the window. In addition, the bypass duct contraction approaching the nozzle exit was less sharp compared with earlier designs. Both of these changes modified the bypass jet penetration and coverage of the heated window zone. Peak external window temperature with a 1.4 mA proton beam and steady-state operation is now predicted to be 375 °C, with internal temperature 354.0 °C (about 32 °C above earlier predictions). Increasing bypass flow from 2.5 to 3.0 kg/s lowers these peak temperatures by about 12 °C. Stress analysis still needs to be made, based on these thermal data.

  10. Study of underwater laser propulsion using different target materials.

    PubMed

    Qiang, Hao; Chen, Jun; Han, Bing; Shen, Zhong-Hua; Lu, Jian; Ni, Xiao-Wu

    2014-07-14

    In order to investigate the influence of target materials, including aluminum (Al), titanium (Ti) and copper (Cu), on underwater laser propulsion, the analytical formula of the target momentum IT is deduced from the enhanced coupling theory of laser propulsion in atmosphere with transparent overlay metal target. The high-speed photography method and numerical simulation are employed to verify the IT model. It is shown that the enhanced coupling theory, which was developed originally for laser propulsion in atmosphere, is also applicable to underwater laser propulsion with metal targets.

  11. Investigation of metal and ceramic-matrix composites moduli: Experiment and theory

    SciTech Connect

    Liaw, P.K.; Miriyala, N.; Yu, N.; Hsu, D.K.; Saini, V.; Jeong, H.

    1996-05-01

    The elastic behavior of metal and ceramic-matrix composites were characterized by ultrasonic techniques. While an immersion ultrasonic technique was used to measure the stiffness moduli of silicon carbide (SiC) particulate reinforced aluminium metal-matrix composites, a dry-coupling method was used to determine the elastic constants of woven Nicalon{trademark} fiber reinforced SiC ceramic-matrix composites. A unified micromechanics model was developed to predict the elastic moduli of these composites from the knowledge of their constituent elastic constants. The model quantitatively predicted the effects of microstructural characteristics, such as the reinforcement content and porosity in the material, on the elastic moduli of the composite systems studied. The predicted moduli were in good agreement with the experimental results for both the particulate reinforced metal-matrix composites and woven fiber reinforced ceramic-matrix composites.

  12. Design of mid-infrared ultra-wideband metallic absorber based on circuit theory

    NASA Astrophysics Data System (ADS)

    Arik, Kamalodin; Abdollahramezani, Sajjad; Farajollahi, Saeed; Khavasi, Amin; Rejaei, Behzad

    2016-12-01

    An ultra-broadband absorber of light is proposed by using periodic array of ultra-thin metallic ribbons on top of a lossless quarter-wavelength dielectric spacer placed on a metallic reflector. We propose a fully analytical circuit model for the structure, and then the absorber is duly designed based on the impedance matching concept. As a result, normalized bandwidth of 99.5% is realized by the proposed absorbing structure in mid-infrared regime. Performing a numerical optimization algorithm, we could also reach to normalized bandwidth of 103%.

  13. Theory of the dissociation dynamics of small molecules on metal surfaces: Finite temperature studies

    SciTech Connect

    Jackson, B.E.

    1992-02-01

    The goal of this study is to gain a better understanding of metal- catalyzed reactions via a detailed examination of the dynamics of molecule-metal interactions. Much effort has focused on treating the molecule as quantum mechanically as possible, and including the effects of finite surface temperature. Recently developed time dependent quantum techniques have been used to compute the dissociative sticking probability of H{sub 2} on various metal surfaces. All molecular degrees of freedom are included either quantum mechanically or classically. The dependence upon translational and internal molecular energy, the angle and site of the surface impact, and the details of the molecule-metal interaction potential were examined. Similar techniques have been used to study the Eley-Rideal mechanism for the recombinative desorption of adsorbed H atoms with gas phase H atoms. Extremely accurate methods for coupling the molecule to the thermal vibrations of the solid have been developed. They are being used in a general study of sticking, as well as to examine the trapping of H{sub 2} and other diatomics in weakly bound molecular precursors to dissociative adsorption.

  14. Resonant Andreev Spectroscopy in normal-Metal/thin-Ferromagnet/Superconductor Device: Theory and Application.

    PubMed

    Romeo, Francesco; Giubileo, Filippo; Citro, Roberta; Di Bartolomeo, Antonio; Attanasio, Carmine; Cirillo, Carla; Polcari, Albino; Romano, Paola

    2015-01-01

    We develop a theoretical model to describe the transport properties of normal-metal/thin-ferromagnet/superconductor device. We perform experimental test of the model using a gold tip on PdNi/Nb bilayer. The resonant proximity effect causes conductance features very sensitive to the local ferromagnetic properties, enabling accurate measurement of polarization and thickness of the ferromagnet by point contact spectroscopy.

  15. Time-Dependent Theory of Laser-Induced Desorption of Small Molecules from Metals, and Related Phenomena

    NASA Astrophysics Data System (ADS)

    Saalfrank, Peter

    1998-03-01

    As an alternative to ``ordinary'', i.e., thermally induced chemistry at the interface of a molecular gas and a solid substrate, surface photochemistry has gained importance in recent years. In this talk, we describe our efforts towards a quantum--dynamical theory of laser--induced elementary processes at adsorbate--covered metal surfaces. First, using time--dependent open--system reduced density matrix theory and nuclear wave packet methods, the indirect (``hot--electron mediated''), ultraviolet/visible--laser induced desorption of small molecules (nitric oxide or ammonia) from metal substrates (platinum or copper) will be addressed. We model both the single-- (DIET, ``desorption induced by electronic transitions'' -- use of continuous wave lasers) and multiple--excitation limits (DIMET, M=``multiple'' -- use of femtosecond lasers). Based on our simulations, the lifetimes of adsorbate electronic states will be estimated, experimental observations will be rationalized, and strategies for the active control of photochemical reactions at surfaces will be proposed. For the example system ammonia/copper, alternatives to the UV/visible--laser induced adsorbate photochemistry will be explored in which the adsorbate remains electronically unexcited. For instance, using laser pulses in the infrared, desorption can also be enforced by ``vibrational ladder climbing''. An analogous, modified strategy can be used to achieve isomerization of adsorbed species. Finally, as the reverse process to desorption, IR laser--induced adsorption will be considered.

  16. Density functional theory screening of gas-treatment strategies for stabilization of high energy-density lithium metal anodes

    NASA Astrophysics Data System (ADS)

    Koch, Stephan L.; Morgan, Benjamin J.; Passerini, Stefano; Teobaldi, Gilberto

    2015-11-01

    To explore the potential of molecular gas treatment of freshly cut lithium foils in non-electrolyte-based passivation of high-energy-density Li anodes, density functional theory (DFT) has been used to study the decomposition of molecular gases on metallic lithium surfaces. By combining DFT geometry optimization and Molecular Dynamics, the effects of atmospheric (N2, O2, CO2) and hazardous (F2, SO2) gas decomposition on Li(bcc) (100), (110), and (111) surfaces on relative surface energies, work functions, and emerging electronic and elastic properties are investigated. The simulations suggest that exposure to different molecular gases can be used to induce and control reconstructions of the metal Li surface and substantial changes (up to over 1 eV) in the work function of the passivated system. Contrary to the other considered gases, which form metallic adlayers, SO2 treatment emerges as the most effective in creating an insulating passivation layer for dosages ≤1 mono-layer. The substantial Li → adsorbate charge transfer and adlayer relaxation produce marked elastic stiffening of the interface, with the smallest change shown by nitrogen-treated adlayers.

  17. Adsorption of a metalorganic complex at a metal surface: A density functional theory study vs. model description

    SciTech Connect

    Kostyrko, T. Ślusarski, T.

    2015-01-21

    A modification of the electronic and magnetic structure of a metalorganic complex by chemisorption at a metallic surface is addressed. The density functional theory (DFT) is applied to investigate a simplified form of a copper-dioxolene complex in a free state and connected to Au(111) surface with alkanethiol linkers. A systematic study of the dependence of the system electronic structure on the linker length is performed. It is found that the electronic structure of the complex is well preserved during the adsorption process. The magnetic moment of the Cu-dioxolene functional group is shown to be strictly correlated with the amount of the charge residing at the complex. On the basis of the DFT results, a model Hamiltonian of the adsorbed metalorganic system is proposed. The model is an extension of the Sandorfy's model of the alkanes and includes explicitly Coulomb interaction between electrons both within the alkane's backbone and the end group. We show that the latter feature is necessary to understand the evolution of the system's properties with the length of the linkers. The advantage of this approach is that it not only reproduces the main results of our DFT analysis but also provides a simple common basis to analyse a wide class of metal complexes bound to metal surfaces with alkanethiol linkers.

  18. Iron-Targeting Antitumor Activity of Gallium Compounds and Novel Insights Into Triapine®-Metal Complexes

    PubMed Central

    Antholine, William E.

    2013-01-01

    Abstract Significance: Despite advances made in the treatment of cancer, a significant number of patients succumb to this disease every year. Hence, there is a great need to develop new anticancer agents. Recent Advances: Emerging data show that malignant cells have a greater requirement for iron than normal cells do and that proteins involved in iron import, export, and storage may be altered in cancer cells. Therefore, strategies to perturb these iron-dependent steps in malignant cells hold promise for the treatment of cancer. Recent studies show that gallium compounds and metal-thiosemicarbazone complexes inhibit tumor cell growth by targeting iron homeostasis, including iron-dependent ribonucleotide reductase. Chemical similarities of gallium(III) with iron(III) enable the former to mimic the latter and interpose itself in critical iron-dependent steps in cellular proliferation. Newer gallium compounds have emerged with additional mechanisms of action. In clinical trials, the first-generation-compound gallium nitrate has exhibited activity against bladder cancer and non-Hodgkin's lymphoma, while the thiosemicarbazone Triapine® has demonstrated activity against other tumors. Critical Issues: Novel gallium compounds with greater cytotoxicity and a broader spectrum of antineoplastic activity than gallium nitrate should continue to be developed. Future Directions: The antineoplastic activity and toxicity of the existing novel gallium compounds and thiosemicarbazone-metal complexes should be tested in animal tumor models and advanced to Phase I and II clinical trials. Future research should identify biologic markers that predict tumor sensitivity to gallium compounds. This will help direct gallium-based therapy to cancer patients who are most likely to benefit from it. Antioxid. Redox Signal. 00, 000–000. PMID:22900955

  19. Three-Dimensional Characterization of Buried Metallic Targets via a Tomographic Algorithm Applied to GPR Synthetic Data

    NASA Astrophysics Data System (ADS)

    Comite, Davide; Galli, Alessandro; Catapano, Ilaria; Soldovieri, Francesco; Pettinelli, Elena

    2013-04-01

    This work is focused on the three-dimensional (3-D) imaging of buried metallic targets achievable by processing GPR (ground penetrating radar) simulation data via a tomographic inversion algorithm. The direct scattering problem has been analysed by means of a recently-developed numerical setup based on an electromagnetic time-domain CAD tool (CST Microwave Studio), which enables us to efficiently explore different GPR scenarios of interest [1]. The investigated 3D domain considers here two media, representing, e.g., an air/soil environment in which variously-shaped metallic (PEC) scatterers can be buried. The GPR system is simulated with Tx/Rx antennas placed in a bistatic configuration at the soil interface. In the implementation, the characteristics of the antennas may suitably be chosen in terms of topology, offset, radiative features, frequency ranges, etc. Arbitrary time-domain waveforms can be used as the input GPR signal (e.g., a Gaussian-like pulse having the frequency spectrum in the microwave range). The gathered signal at the output port includes the backscattered wave from the objects to be reconstructed, and the relevant data may be displayed in canonical radargram forms [1]. The GPR system sweeps along one main rectilinear direction, and the scanning process is here repeated along different close parallel lines to acquire data for a full 3-D analysis. Starting from the processing of the synthetic GPR data, a microwave tomographic approach is used to tackle the imaging, which is based on the Kirchhoff approximation to linearize the inverse scattering problem [2]. The target reconstruction is given in terms of the amplitude of the 'object function' (normalized with respect to its maximum inside the 3-D investigation domain). The data of the scattered field are collected considering a multi-frequency step process inside the fixed range of the signal spectrum, under a multi-bistatic configuration where the Tx and Rx antennas are separated by an offset

  20. Effect of metal in M3(btc)2 and M2(dobdc) MOFs for O2/N2 separations: A combined density functional theory and experimental study

    DOE PAGES

    Parkes, Marie V.; Sava Gallis, Dorina F.; Greathouse, Jeffery A.; Nenoff, Tina M.

    2015-03-02

    Computational screening of metal-organic framework (MOF) materials for selective oxygen adsorption from air could lead to new sorbents for the oxyfuel combustion process feedstock streams. A comprehensive study on the effect of MOF metal chemistry on gas binding energies in two common but structurally disparate metal-organic frameworks has been undertaken. Dispersion-corrected density functional theory methods were used to calculate the oxygen and nitrogen binding energies with each of fourteen metals, respectively, substituted into two MOF series, M2(dobdc) and M3(btc)2. The accuracy of DFT methods was validated by comparing trends in binding energy with experimental gas sorption measurements. A periodic trendmore » in oxygen binding energies was found, with greater oxygen binding energies for early transition-metal-substituted MOFs compared to late transition metal MOFs; this was independent of MOF structural type. The larger binding energies were associated with oxygen binding in a side-on configuration to the metal, with concomitant lengthening of the O-O bond. In contrast, nitrogen binding energies were similar across the transition metal series, regardless of both MOF structural type and metal identity. Altogether, these findings suggest that early transition metal MOFs are best suited to separating oxygen from nitrogen, and that the MOF structural type is less important than the metal identity.« less

  1. Theory of metal atom-water interactions and alkali halide dimers

    NASA Technical Reports Server (NTRS)

    Jordan, K. D.; Kurtz, H. A.

    1982-01-01

    Theoretical studies of the interactions of metal atoms with water and some of its isoelectronic analogs, and of the properties of alkali halides and their aggregates are discussed. Results are presented of ab initio calculations of the heats of reaction of the metal-water adducts and hydroxyhydrides of Li, Be, B, Na, Mg, and Al, and of the bond lengths and angles an; the heats of reaction for the insertion of Al into HF, H2O, NH3, H2S and CH3OH, and Be and Mg into H2O. Calculations of the electron affinities and dipole moments and polarizabilities of selected gas phase alkali halide monomers and dimers are discussed, with particular attention given to results of calculations of the polarizability of LiF taking into account electron correlation effects, and the polarizability of the dimer (LiF)2.

  2. Solid state theory. Quantum spin Hall effect in two-dimensional transition metal dichalcogenides.

    PubMed

    Qian, Xiaofeng; Liu, Junwei; Fu, Liang; Li, Ju

    2014-12-12

    Quantum spin Hall (QSH) effect materials feature edge states that are topologically protected from backscattering. However, the small band gap in materials that have been identified as QSH insulators limits applications. We use first-principles calculations to predict a class of large-gap QSH insulators in two-dimensional transition metal dichalcogenides with 1T' structure, namely, 1T'-MX2 with M = (tungsten or molybdenum) and X = (tellurium, selenium, or sulfur). A structural distortion causes an intrinsic band inversion between chalcogenide-p and metal-d bands. Additionally, spin-orbit coupling opens a gap that is tunable by vertical electric field and strain. We propose a topological field effect transistor made of van der Waals heterostructures of 1T'-MX2 and two-dimensional dielectric layers that can be rapidly switched off by electric field through a topological phase transition instead of carrier depletion.

  3. Modeling of the mass transfer rates of metal ions across supported liquid membranes. 1: Theory

    SciTech Connect

    Elhassadi, A.A.; Do, D.D.

    1999-01-01

    This paper deals with the modeling of the transport and separation of metal ions across supported liquid membranes. The mass transfer resistance at the liquid-membrane interfaces and the interfacial chemical reactions at both the extracting side and the stripping side are taken into account in the model equations. Simple analysis of the time scale of the system shows the influence of various important parameters and their interactions on the overall transport rate. Parametric studies are also dealt with in this paper.

  4. A density functional theory guide to high quality modification of mixed metal oxides used for photocatalytic water splitting

    NASA Astrophysics Data System (ADS)

    Mayfield, Cedric Leon

    Phase stability and charge transport of pristine and transition metal alloyed bismuth titanate (Bi2Ti2O7, a.k.a. BTO), a photocatalytic water splitter, has been studied using the generalized gradient approximated density functional theory (GGA-DFT). The primary goals of this work were to predict the effective conditions for pure phase synthesis of the modified ternary multi-metal oxide and to determine the most suitable modifications for enhancing its photocatalytic properties. To understand the details of phase stability and photoconduction, we have derived the formation enthalpies, defect formation energies, electronic structures, spectral absorptions and polaron activation energies for pristine and transition metal doped bismuth titanate (Bi2Ti2O7, a.k.a. BTO). Implantation of the localized 3d electrons is a primary band engineering technique for extending the spectral absorptions of metal oxides into the visible range. However, localized states typically increase charge trapping that reduces crucial photocurrent for the photocatalytic process. Therefore one objective here is to understand the extent to which localization plays a role in electron transfer and which mode of conduction, band or polaron hopping, is dominantly effected. As predicting the effective conditions for pure phase stability and modeling electron transport of multi metal oxide materials is still in development as a whole, we have benchmarked our methods by reproducing relative quantities of world class metal oxide photocatalyst, rutile TiO2 and monoclinic scheelite BiVO4. In recognition of our methods, our results have been used to enhance H2 production of a facile hydrothermal synthesized Fe-doped BTO. Furthermore, we demonstrate with results for Cr- and Mn-doped BTO how experimental characterization can also be enhanced. For each transition metal ion (M = Cr, Mn, and Fe), pure phase stability has a unique association with the presence or absence of O defects. Band modifications vary with

  5. Stoichiometry determined exchange interactions in amorphous ternary transition metal oxides: Theory and experiment

    SciTech Connect

    Hu, Shu-jun; Yan, Shi-shen Zhang, Yun-peng; Zhao, Ming-wen; Kang, Shi-shou; Mei, Liang-mo

    2014-07-28

    Amorphous transition metal oxides exhibit exotic transport and magnetic properties, while the absence of periodic structure has long been a major obstacle for the understanding of their electronic structure and exchange interaction. In this paper, we have formulated a theoretical approach, which combines the melt-quench approach and the spin dynamic Monte-Carlo simulations, and based on it, we explored amorphous Co{sub 0.5}Zn{sub 0.5}O{sub 1−y} ternary transition metal oxides. Our theoretical results reveal that the microstructure, the magnetic properties, and the exchange interactions of Co{sub 0.5}Zn{sub 0.5}O{sub 1−y} are strongly determined by the oxygen stoichiometry. In the oxygen-deficient sample (y > 0), we have observed the long-range ferromagnetic spin ordering which is associated with the non-stoichiometric cobalt-rich region rather than metallic clusters. On the other hand, the microstructure of stoichiometric sample takes the form of continuous random networks, and no long-range ferromagnetism has been observed in it. Magnetization characterization of experimental synthesized Co{sub 0.61}Zn{sub 0.39}O{sub 1−y} films verifies the relation between the spin ordering and the oxygen stoichiometry. Furthermore, the temperature dependence of electrical transport shows a typical feature of semiconductors, in agreement with our theoretical results.

  6. Paired box gene 2 is associated with estrogen receptor α in ovarian serous tumors: Potential theory basis for targeted therapy

    PubMed Central

    Wang, Min; Ma, Haifen

    2016-01-01

    It has been suggested that Paired box gene (PAX)2 is activated by estradiol via estrogen receptor (ER)α in breast and endometrial cancer. The expression of PAX2 was restricted to ovarian serous tumors and only one case was positive in borderline mucinous tumor in our previous study. In the present study, immunohistochemistry was performed to assess the expression of ERα in 58 cases of ovarian serous tumors, including 30 serous cystadenomas, 16 borderline serous cystadenomas, 12 serous carcinomas and 67 cases of ovarian mucinous tumors, including 29 mucinous cystadenoma, 23 borderline mucinous cystadenoma and 15 mucinous carcinoma, which were the same specimens with detection of PAX2 expression. The results demonstrated that ERα was expressed in 10% (3/30) of serous cystadenomas, 62.5% (10/16) borderline serous cystadenomas and 66.7% (8/12) serous carcinomas. The expression of ERα in borderline serous cystadenomas and serous carcinomas were significantly higher compared with that in serous cystadenomas (P<0.01). ERα was detected in 3.4% (1/29) mucinous cystadenoma, 26.1% (6/23) borderline mucinous cystadenoma and only 6.7% (1/15) mucinous carcinoma. Furthermore, a scatter plot of the expression of PAX2 and ERα revealed a linear correlation between them in ovarian serous tumors (P<0.0001). With few positive results, no correlation was determined in ovarian mucinous tumors. It was demonstrated that PAX2 is associated with ERα in ovarian serous tumors, and this may become a potential theory basis for targeted therapy for ovarian serous tumors. Further research is required to determine how PAX2 and ERα work together, and the role of targeted therapy in ovarian serous tumors. PMID:27446571

  7. Efficient fast electron generation in an interaction of Intense, ultrashort laser with metal nanoparticle coated dielectric target

    NASA Astrophysics Data System (ADS)

    Sarkar, Deep; Tata, Sheroy; Shaikh, Moniruzzaman; Lad, Amit D.; Adak, Amitava; Sarkar, Subhrangsu; Ayyub, Pushan; Kumar, G. Ravindra

    2016-05-01

    Hot electron generation in intense laser-matter interaction studies is a topic of great interest due in significant part to its applications in fast ignitor scheme in Inertial Confinement Fusion (ICF). We measure the hot electron energy spectrum from Ag nanoparticle coated fused silica target (100 μm thick) interacting with an intense (I∼1018W/cm2), short pulse (τ∼ 30× 10-15s) laser and compare the results with those of an uncoated fused silica. Enhancement in hot electron energy and hard x-ray yield is measured as a function of thickness of Ag nano-coating, varied from tens of nm to hundreds of nm. The hot electron temperatures and integrated x-ray yield are observed to be greater for subwavelength film thicknesses for the case of a p-polarized laser. Such results indicate that metal nanoparticle layers have an important role to play in the enhancement of laser-plasma coupling efficiency for short scale-length plasmas created in femtosecond laser interactions.

  8. Analysis of polarization properties of shallow metallic gratings by an extended Rayleigh-Fano theory

    NASA Technical Reports Server (NTRS)

    Koike, Masato; Namioka, Takeshi

    1991-01-01

    Rayleigh-Fano theory has been extended for the purpose of calculating the polarization anomaly of a grating having shallow grooves and finite conductivity. Simple analytic formulas are derived for predicting the position and the appearance of the anomalies. Phenomenological explanations are given to the origin of the anomalies. The validity of our analysis is examined by comparing computed degree of polarization with experimental data obtained in the visible region for Al-, Ag-, and Au-coated blazed gratings.

  9. Solar hydrogen production with semiconductor metal oxides: new directions in experiment and theory.

    PubMed

    Valdés, Álvaro; Brillet, Jeremie; Grätzel, Michael; Gudmundsdóttir, Hildur; Hansen, Heine A; Jónsson, Hannes; Klüpfel, Peter; Kroes, Geert-Jan; Le Formal, Florian; Man, Isabela C; Martins, Rafael S; Nørskov, Jens K; Rossmeisl, Jan; Sivula, Kevin; Vojvodic, Aleksandra; Zäch, Michael

    2012-01-01

    An overview of a collaborative experimental and theoretical effort toward efficient hydrogen production via photoelectrochemical splitting of water into di-hydrogen and di-oxygen is presented here. We present state-of-the-art experimental studies using hematite and TiO(2) functionalized with gold nanoparticles as photoanode materials, and theoretical studies on electro and photo-catalysis of water on a range of metal oxide semiconductor materials, including recently developed implementation of self-interaction corrected energy functionals. PMID:22083224

  10. Theory of magic optical traps for Zeeman-insensitive clock transitions in alkali-metal atoms

    SciTech Connect

    Derevianko, Andrei

    2010-05-15

    Precision measurements and quantum-information processing with cold atoms may benefit from trapping atoms with specially engineered, 'magic' optical fields. At the magic trapping conditions, the relevant atomic properties remain immune to strong perturbations by the trapping fields. Here we develop a theoretical analysis of magic trapping for especially valuable Zeeman-insensitive clock transitions in alkali-metal atoms. The involved mechanism relies on applying a magic bias B field along a circularly polarized trapping laser field. We map out these B fields as a function of trapping laser wavelength for all commonly used alkalis. We also highlight a common error in evaluating Stark shifts of hyperfine manifolds.

  11. Many-Body Theory of Ultrafast Demagnetization and Angular Momentum Transfer in Ferromagnetic Transition Metals.

    PubMed

    Töws, W; Pastor, G M

    2015-11-20

    Exact calculated time evolutions in the framework of a many-electron model of itinerant magnetism provide new insights into the laser-induced ultrafast demagnetization observed in ferromagnetic (FM) transition metal thin films. The interplay between local spin-orbit interactions and interatomic hopping is shown to be at the origin of the observed postexcitation breakdown of FM correlations between highly stable local magnetic moments. The mechanism behind spin- and angular-momentum transfer is revealed from a microscopic perspective by rigorously complying with all fundamental conservation laws. An energy-resolved analysis of the time evolution shows that the efficiency of the demagnetization process reaches almost 100% in the excited states.

  12. Interplay between Theory and Experiment for Ammonia Synthesis Catalyzed by Transition Metal Complexes.

    PubMed

    Tanaka, Hiromasa; Nishibayashi, Yoshiaki; Yoshizawa, Kazunari

    2016-05-17

    Nitrogen fixation is an essential chemical process both biologically and industrially. Since the discovery of the first transition-metal-dinitrogen complex in 1965, a great deal of effort has been devoted to the development of artificial nitrogen fixation systems that work under mild reaction conditions. However, the transformation of chemically inert dinitrogen using homogeneous catalysts is still challenging because of the difficulty in breaking the strong triple bond of dinitrogen, and a very limited number of transition metal complexes have exhibited the catalytic activity for the direct transformation of dinitrogen into ammonia with low turnover numbers. To develop more effective nitrogen fixation systems, it is necessary to retrieve as much information as possible from the limited successful examples. Computational chemistry will provide valuable insights in the understanding of the reaction mechanisms involving unstable intermediates that are hard to isolate or characterize. We have been applying it for clarifying detailed mechanisms of dinitrogen activation and functionalization by transition metal complexes as well as for designing new catalysts for more effective nitrogen fixation. This Account summarizes recent progress in the elucidation of catalytic mechanisms of nitrogen fixation by using mono- and dinuclear molybdenum complexes, as well as cubane-type metal-sulfido clusters from a theoretical point of view. First, we briefly introduce experimental and theoretical contributions to the elucidation of the reaction mechanism of nitrogen fixation catalyzed by a mononuclear Mo-triamidoamine complex. Special attention is paid to our recent studies on Mo-catalyzed nitrogen fixation using dinitrogen-bridged dimolybdenum complexes. A possible catalytic mechanism is proposed based on theoretical and experimental investigations. The catalytic mechanism involves the formation of a monuclear molybdenum-nitride (Mo≡N) intermediate, as well as the regeneration of

  13. Toward a Quantitative Understanding of the Electric Field in Thermal Metal Oxidation and a Self-Consistent Wagner Theory.

    PubMed

    Cheng, Tian-Le; Wen, You-Hai

    2014-07-01

    The electric field in the growing oxide film is important to the kinetics and mechanism of metal oxidation. However, understanding of the essential characteristics of the electric field during oxidation remains insufficient. A special-case analytical model is presented that provides a unified understanding for the electric field from the viewpoints of kinetics and thermodynamics. More general cases are studied by computer simulations that show similar characteristics in the electric field. In particular, simulations indicate that in many situations, the electrostatic potential drop across the bulk oxide is limited to ∼kBT/e, which means that the total electrostatic potential drop across the oxide film, if on the order of 1 V by rough estimation, should have contributions mostly from the electrified interfaces. Finally, regarding the Gibbs-Duhem relation, the commonly used isobaric assumption for the diffusing species is refuted. The results contained herein also provide a self-consistent understanding of Wagner's oxidation theory.

  14. Luminescent properties of metal-organic framework MOF-5: relativistic time-dependent density functional theory investigations.

    PubMed

    Ji, Min; Lan, Xin; Han, Zhenping; Hao, Ce; Qiu, Jieshan

    2012-11-19

    The electronically excited state and luminescence property of metal-organic framework MOF-5 were investigated using relativistic density functional theory (DFT) and time-dependent DFT (TDDFT). The geometry, IR spectra, and UV-vis spectra of MOF-5 in the ground state were calculated using relativistic DFT, leading to good agreement between the experimental and theoretical results. The frontier molecular orbitals and electronic configuration indicated that the luminescence mechanism in MOF-5 follows ligand-to-ligand charge transfer (LLCT), namely, π* → π, rather than emission with the ZnO quantum dot (QD) proposed by Bordiga et al. The geometry and IR spectra of MOF-5 in the electronically excited state have been calculated using the relativistic TDDFT and compared with those for the ground state. The comparison reveals that the Zn4O13 QD is rigid, whereas the ligands BDC(2-) are nonrigid. In addition, the calculated emission band of MOF-5 is in good agreement with the experimental result and is similar to that of the ligand H2BDC. The combined results confirmed that the luminescence mechanism for MOF-5 should be LLCT with little mixing of the ligand-to-metal charge transfer. The reason for the MOF-5 luminescence is explained by the excellent coplanarity between the six-membered ring consisting of zinc, oxygen, carbon, and the benzene ring. PMID:23136957

  15. Nonequilibrium theory of a hot-electron bolometer with normal metal-insulator-superconductor tunnel junction

    SciTech Connect

    Golubev, Dmitri; Kuzmin, Leonid

    2001-06-01

    The operation of the hot-electron bolometer with normal metal-insulator-superconductor (NIS) tunnel junction as a temperature sensor is analyzed theoretically. The responsivity and the noise equivalent power (NEP) of the bolometer are obtained numerically for typical experimental parameters. Relatively simple approximate analytical expressions for these values are derived. The time constant of the device is also found. We demonstrate that the effect of the electron cooling by the NIS junction, which serves as a thermometer, can improve the sensitivity. This effect is also useful in the presence of the finite background power load. We discuss the effect of the correlation of the shot noise and the heat flow noise in the NIS junction. {copyright} 2001 American Institute of Physics.

  16. Theory of edge-state optical absorption in two-dimensional transition metal dichalcogenide flakes

    NASA Astrophysics Data System (ADS)

    Trushin, Maxim; Kelleher, Edmund J. R.; Hasan, Tawfique

    2016-10-01

    We develop an analytical model to describe sub-band-gap optical absorption in two-dimensional semiconducting transition metal dichalcogenide (s-TMD) nanoflakes. The material system represents an array of few-layer molybdenum disulfide crystals, randomly orientated in a polymer matrix. We propose that optical absorption involves direct transitions between electronic edge states and bulk bands, depends strongly on the carrier population, and is saturable with sufficient fluence. For excitation energies above half the band gap, the excess energy is absorbed by the edge-state electrons, elevating their effective temperature. Our analytical expressions for the linear and nonlinear absorption could prove useful tools in the design of practical photonic devices based on s-TMDs.

  17. Theory of light scattering in subwavelength metallic slot antenna array fabricated on subwavelength thin film

    NASA Astrophysics Data System (ADS)

    Choi, S. B.; Park, D. J.

    2015-10-01

    We demonstrate an analytic model that describes the near-field electromagnetic field profile near a subwavelength-sized metallic slot antenna fabricated on a thin dielectric substrate having a subwavelength thickness reaching λ/1000 in the terahertz frequency region. We found two-dimensional light diffraction induced by the two-dimensional nature of the slot antenna, and back-reflected waves interfered with each other in a complicated manner, resulting in a coupling of the Fourierdecomposed field amplitudes between the diffraction orders along the x and the y directions. We applied these findings to our model by modifying a previously developed model [D. J. Park et al., J. Korean Phys. Soc. 65, 1390 (2014)], and we monitor the effect on far-field transmission. This coupling effect was found to contribute to removal of physically-meaningless spikes or divergences in the transmission spectra, especially for relatively thick substrates.

  18. Theory of thermal and charge transport in diffusive normal metal/superconductor junctions

    NASA Astrophysics Data System (ADS)

    Yokoyama, T.; Tanaka, Y.; Golubov, A. A.; Asano, Y.

    2005-12-01

    Thermal and charge transport in diffusive normal metal (DN)/insulator/ s -, d -, and p -wave superconductor junctions are studied based on the Usadel equation with the Nazarov’s generalized boundary condition. We derive a general expression of the thermal conductance in unconventional superconducting junctions. Thermal conductance, electric conductance of junctions and their Lorentz ratio are calculated as a function of resistance in DN, the Thouless energy, magnetic scattering rate in DN and transparency of the insulating barrier. We also discuss transport properties for various orientation angles between the normal to the interface and the crystal axis of superconductors. It is demonstrated that the proximity effect does not influence the thermal conductance while the midgap Andreev resonant states suppress it. Dependencies of the electrical and thermal conductance on temperature are sensitive to pairing symmetries and orientation angles. The results imply a possibility to distinguish one pairing symmetry from another based on the results of experimental observations.

  19. Many-Body Theory of Ultrafast Demagnetization and Angular Momentum Transfer in Ferromagnetic Transition Metals.

    PubMed

    Töws, W; Pastor, G M

    2015-11-20

    Exact calculated time evolutions in the framework of a many-electron model of itinerant magnetism provide new insights into the laser-induced ultrafast demagnetization observed in ferromagnetic (FM) transition metal thin films. The interplay between local spin-orbit interactions and interatomic hopping is shown to be at the origin of the observed postexcitation breakdown of FM correlations between highly stable local magnetic moments. The mechanism behind spin- and angular-momentum transfer is revealed from a microscopic perspective by rigorously complying with all fundamental conservation laws. An energy-resolved analysis of the time evolution shows that the efficiency of the demagnetization process reaches almost 100% in the excited states. PMID:26636871

  20. Observations vs theory: from metallicity correlations of exoplanets and debris discs to HL Tau

    NASA Astrophysics Data System (ADS)

    Nayakshin, Sergei V.

    2015-12-01

    Boley et al (2010) and Nayakshin (2010) proposed Tidal Downsizing (TD), a new hypothesis for forming all types of planets. Gas fragments born by gravitational disc instability at ~ 100 AU migrate inwards rapidly, with some becoming hot Jupiters. Grain sedimentation inside the fragments makes rocky cores. These cores are future Earths and Super Earths, leaved behind when most of the migrating fragments are tidally disrupted.TD can now be tested against data in detail thanks to a numerical population synthesis model (Nayakshin and Fletcher 2015). TD scenario is fundamentally different from Core Accretion (CA), with sub-Saturn planets and debris discs born in gas fragment disruptions, and not vice versa. I therefore find robust observational differences between CA and TD despite uncertainties inherent in any population synthesis. Here I use metallicity correlations of all sorts to test the model. In TD, the only population that correlates with metallicity (Z) of the host strongly is that of moderately massive gas giants interior to a few AU from the host. Super-Earths and debris discs correlate in mass but not in numbers with Z; very massive gas giants, brown dwarfs and directly imaged gas giants are neutral to Z. Fragment self-destruction by core feedback explains simultaneously the core mass function roll-over at ~20 Earth masses, the rapid formation of suspected planets in HL Tau, and the paucity of directly imaged gas giants. Debris discs and gas giants do not correlate in TD, as observed.I argue that TD does a better job in accounting for many of the observed properties of exoplanets and planetary debris than CA. I finish with observational predictions that can distinguish TD from Core Accretion in the near future.

  1. EFFECTS OF LASER RADIATION ON MATTER. LASER PLASMA: Dynamics of formation of the liquid-drop phase of laser erosion jets near the surfaces of metal targets

    NASA Astrophysics Data System (ADS)

    Goncharov, V. K.; Kontsevoi, V. L.; Puzyrev, M. V.

    1995-03-01

    An investigation was made of laser erosion jets formed at 0.1-1.5 mm above the surfaces of Pb, Co, Ni, Sn, and Zn targets. A neodymium laser emitting rectangular pulses of 400 μs duration and of energy up to 400 J was used. The diameters, as well as the number density and volume fraction of the metal particles present in the jet, were measured. An analysis of the results showed that the metal liquid drops broke up near the surface and experienced additional evaporation because of their motion opposite to the laser beam.

  2. Screening for high-spin metal organic frameworks (MOFs): density functional theory study on DUT-8(M1,M2) (with Mi = V,…,Cu).

    PubMed

    Schwalbe, Sebastian; Trepte, Kai; Seifert, Gotthard; Kortus, Jens

    2016-03-21

    We present a first principles study of low-spin (LS)/high-spin (HS) screening for 3d metal centers in the metal organic framework (MOF) DUT-8(Ni). Various density functional theory (DFT) codes have been used to evaluate numerical and DFT related errors. We compare highly accurate all-electron implementations with the widely used plane wave approach. We present electronically and magnetically stable DUT-8(Ni) HS secondary building units (SBUs). In this work we show how to tune the magnetic and electronic properties of the original SBU only by changing the metal centers. PMID:26922864

  3. Energy level alignment and quantum conductance of functionalized metal-molecule junctions: Density functional theory versus GW calculations

    SciTech Connect

    Jin, Chengjun; Markussen, Troels; Thygesen, Kristian S.; Strange, Mikkel; Solomon, Gemma C.

    2013-11-14

    We study the effect of functional groups (CH{sub 3}*4, OCH{sub 3}, CH{sub 3}, Cl, CN, F*4) on the electronic transport properties of 1,4-benzenediamine molecular junctions using the non-equilibrium Green function method. Exchange and correlation effects are included at various levels of theory, namely density functional theory (DFT), energy level-corrected DFT (DFT+Σ), Hartree-Fock and the many-body GW approximation. All methods reproduce the expected trends for the energy of the frontier orbitals according to the electron donating or withdrawing character of the substituent group. However, only the GW method predicts the correct ordering of the conductance amongst the molecules. The absolute GW (DFT) conductance is within a factor of two (three) of the experimental values. Correcting the DFT orbital energies by a simple physically motivated scissors operator, Σ, can bring the DFT conductances close to experiments, but does not improve on the relative ordering. We ascribe this to a too strong pinning of the molecular energy levels to the metal Fermi level by DFT which suppresses the variation in orbital energy with functional group.

  4. Theory, design, and operation of liquid metal fast breeder reactors, including operational health physics

    SciTech Connect

    Adams, S.R.

    1985-10-01

    A comprehensive evaluation was conducted of the radiation protection practices and programs at prototype LMFBRs with long operational experience. Installations evaluated were the Fast Flux Test Facility (FFTF), Richland, Washington; Experimental Breeder Reactor II (EBR-II), Idaho Falls, Idaho; Prototype Fast Reactor (PFR) Dounreay, Scotland; Phenix, Marcoule, France; and Kompakte Natriumgekuhlte Kernreak Toranlange (KNK II), Karlsruhe, Federal Republic of Germany. The evaluation included external and internal exposure control, respiratory protection procedures, radiation surveillance practices, radioactive waste management, and engineering controls for confining radiation contamination. The theory, design, and operating experience at LMFBRs is described. Aspects of LMFBR health physics different from the LWR experience in the United States are identified. Suggestions are made for modifications to the NRC Standard Review Plan based on the differences.

  5. A bioinorganic view of Alzheimer's disease: when misplaced metal ions (re)direct the electrons to the wrong target.

    PubMed

    Faller, Peter; Hureau, Christelle

    2012-12-01

    Metal ions Cu, Zn and Fe, seem to play a pivotal role in Alzheimer's disease and other neurodegenerative diseases. In order to understand this in a broader sense, one has to considerer the peculiarities of metal metabolism in the brain compared to most other tissues, as well as the importance of the redox active metal ions, Fe and Cu, in oxygen metabolism and the connected oxidative stress.

  6. The absence of intraband scattering in a consistent theory of Gilbert damping in pure metallic ferromagnets.

    PubMed

    Edwards, D M

    2016-03-01

    Damping of magnetization dynamics in a ferromagnetic metal, arising from spin-orbit coupling, is usually characterised by the Gilbert parameter α. Recent calculations of this quantity, using a formula due to Kambersky, find that it is infinite for a perfect crystal owing to an intraband scattering term which is of third order in the spin-orbit parameter ξ. This surprising result conflicts with recent work by Costa and Muniz who study damping numerically by direct calculation of the dynamical transverse susceptibility in the presence of spin-orbit coupling. We resolve this inconsistency by following the approach of Costa and Muniz for a slightly simplified model where it is possible to calculate α analytically. We show that to second order in ξ one retrieves the Kambersky result for α, but to higher order one does not obtain any divergent intraband terms. The present work goes beyond that of Costa and Muniz by pointing out the necessity of including the effect of long-range Coulomb interaction in calculating damping for large ξ. A direct derivation of the Kambersky formula is given which shows clearly the restriction of its validity to second order in ξ so that no intraband scattering terms appear. This restriction has an important effect on the damping over a substantial range of impurity content and temperature. The experimental situation is discussed. PMID:26837050

  7. Pressure-induced phase transitions in Pa metal from first-principles theory

    SciTech Connect

    Soederlind, P.; Eriksson, O.

    1997-11-01

    Protactinium metal is shown to undergo a phase transition to the {alpha}-U orthorhombic structure below 1 Mbar pressure. At higher pressures, the bct phase reenters in the phase diagram and at the highest pressures, an ideal hcp structure becomes stable. Hence, Pa undergoes a sequence of transitions; bct{r_arrow}{alpha}-U{r_arrow}bct{r_arrow}hcp, with the first transition taking place at 0.25 Mbar and the subsequent ones above 1 Mbar. The bct{r_arrow}{alpha}-U transition is triggered by the pressure-induced promotion of the spd valence states to 5f states. In this regard, Pa approaches uranium which at ambient conditions has one more 5f electron than Pa at similar conditions. At higher compression of Pa, the 5f band broadens and electrostatic interactions in combination with Born-Mayer repulsion become increasingly important and this drives Pa to gradually more close-packed structures. At ultrahigh pressures, the balance between electrostatic energy, Born-Mayer repulsion, and one-electron band energy stabilizes the hcp (ideal packing) structure. The electrostatic energy and Born-Mayer repulsion rule out open crystal structures under these conditions in Pa and between the close-packed structures, the hcp structure is shown to be stabilized by filling of the 5f band. {copyright} {ital 1997} {ital The American Physical Society}

  8. The absence of intraband scattering in a consistent theory of Gilbert damping in pure metallic ferromagnets

    NASA Astrophysics Data System (ADS)

    Edwards, D. M.

    2016-03-01

    Damping of magnetization dynamics in a ferromagnetic metal, arising from spin-orbit coupling, is usually characterised by the Gilbert parameter α. Recent calculations of this quantity, using a formula due to Kambersky, find that it is infinite for a perfect crystal owing to an intraband scattering term which is of third order in the spin-orbit parameter ξ. This surprising result conflicts with recent work by Costa and Muniz who study damping numerically by direct calculation of the dynamical transverse susceptibility in the presence of spin-orbit coupling. We resolve this inconsistency by following the approach of Costa and Muniz for a slightly simplified model where it is possible to calculate α analytically. We show that to second order in ξ one retrieves the Kambersky result for α, but to higher order one does not obtain any divergent intraband terms. The present work goes beyond that of Costa and Muniz by pointing out the necessity of including the effect of long-range Coulomb interaction in calculating damping for large ξ. A direct derivation of the Kambersky formula is given which shows clearly the restriction of its validity to second order in ξ so that no intraband scattering terms appear. This restriction has an important effect on the damping over a substantial range of impurity content and temperature. The experimental situation is discussed.

  9. Initial observations of cavitation-induced erosion of liquid metal spallation target vessels at the Spallation Neutron Source

    SciTech Connect

    McClintock, David A; Riemer, Bernie; Ferguson, Phillip D; Carroll, Adam J; Dayton, Michael J

    2012-01-01

    During operation of the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory the mechanical properties of the AISI 316L target module are altered by high-energy neutron and proton radiation. The interior surfaces of the target vessel are also damaged by cavitation-induced erosion, which results from repetitive rapid heating of the liquid mercury by high-energy proton beam pulses. Until recently no observations of cavitation-induced erosion were possible for conditions prototypical to the SNS. Post irradiation examination (PIE) of the first and second operational SNS targets was performed to gain insight into the radiation-induced changes in mechanical properties of the 316L target material and the extent of cavitation-induced erosion to the target vessel inner surfaces. Observations of cavitation-induced erosion of the first and second operational SNS target modules are presented here, including images of the target vessel interiors and specimens removed from the target beam-entrance regions.

  10. Predicting density functional theory total energies and enthalpies of formation of metal-nonmetal compounds by linear regression

    NASA Astrophysics Data System (ADS)

    Deml, Ann M.; O'Hayre, Ryan; Wolverton, Chris; Stevanović, Vladan

    2016-02-01

    The availability of quantitatively accurate total energies (Etot) of atoms, molecules, and solids, enabled by the development of density functional theory (DFT), has transformed solid state physics, quantum chemistry, and materials science by allowing direct calculations of measureable quantities, such as enthalpies of formation (Δ Hf ). Still, the ability to compute Etot and Δ Hf values does not, necessarily, provide insights into the physical mechanisms behind their magnitudes or chemical trends. Here, we examine a large set of calculated Etot and Δ Hf values obtained from the DFT+U -based fitted elemental-phase reference energies (FERE) approach [V. Stevanović, S. Lany, X. Zhang, and A. Zunger, Phys. Rev. B 85, 115104 (2012), 10.1103/PhysRevB.85.115104] to probe relationships between the Etot/Δ Hf of metal-nonmetal compounds in their ground-state crystal structures and properties describing the compound compositions and their elemental constituents. From a stepwise linear regression, we develop a linear model for Etot, and consequently Δ Hf , that reproduces calculated FERE values with a mean absolute error of ˜80 meV/atom. The most significant contributions to the model include calculated total energies of the constituent elements in their reference phases (e.g., metallic iron or gas phase O2), atomic ionization energies and electron affinities, Pauling electronegativity differences, and atomic electric polarizabilities. These contributions are discussed in the context of their connection to the underlying physics. We also demonstrate that our Etot/Δ Hf model can be directly extended to predict the Etot and Δ Hf of compounds outside the set used to develop the model.

  11. Monte Carlo simulation of the influence of pressure and target-substrate distance on the sputtering process for metal and semiconductor layers

    NASA Astrophysics Data System (ADS)

    Bouazza, Abdelkader; Settaouti, Abderrahmane

    2016-07-01

    The energy and the number of particles arriving at the substrate during physical vapor deposition (PVD) are in close relation with divers parameters. In this work, we present the influence of the distance between the target and substrate and the gas pressure in the sputtering process of deposited layers of metals (Cu, Al and Ag) and semiconductors (Ge, Te and Si) for substrate diameter of 40 cm and target diameter of 5 cm. The nascent sputter flux, the flux of the atoms and their energy arriving at the substrate have been simulated by Monte Carlo codes. A good agreement between previous works of other groups and our simulations for sputter pressures (0.3-1 Pa) and target-substrate distances (8-20 cm) is obtained.

  12. Monte Carlo simulation of the influence of pressure and target-substrate distance on the sputtering process for metal and semiconductor layers

    NASA Astrophysics Data System (ADS)

    Bouazza, Abdelkader; Settaouti, Abderrahmane

    2016-07-01

    The energy and the number of particles arriving at the substrate during physical vapor deposition (PVD) are in close relation with divers parameters. In this work, we present the influence of the distance between the target and substrate and the gas pressure in the sputtering process of deposited layers of metals (Cu, Al and Ag) and semiconductors (Ge, Te and Si) for substrate diameter of 40 cm and target diameter of 5 cm. The nascent sputter flux, the flux of the atoms and their energy arriving at the substrate have been simulated by Monte Carlo codes. A good agreement between previous works of other groups and our simulations for sputter pressures (0.3-1 Pa) and target-substrate distances (8-20 cm) is obtained.

  13. Noncollinear spin-fluctuation theory of transition-metal magnetism: Role of transverse spin fluctuations in Fe

    NASA Astrophysics Data System (ADS)

    Garibay-Alonso, R.; Dorantes-Dávila, J.; Pastor, G. M.

    2015-05-01

    A local electronic theory of transition-metal magnetism at finite temperatures is presented, which takes into account longitudinal and transverse spin fluctuations on the same footing. The magnetic properties are determined in the framework of a rotational-invariant d -band model Hamiltonian by applying a four-field Hubbard-Stratonovich functional-integral method in the static approximation. The role of transverse spin excitations on the temperature-dependent magnetic properties is investigated by performing alloy averages in the single-site virtual crystal approximation. Bulk Fe is considered as the representative example for the applications. Results are given for the average magnetization M , for the spin-excitation energies, and for the transverse and longitudinal contributions to the local magnetic moments μl at atom l . The importance of noncollinear spin excitations is quantified by comparison with the corresponding collinear calculations. An important reduction of about 33% of the calculated Curie temperature TC is obtained, which now amounts to 1250 K and is thus relatively close to the experimental value. The longitudinal (transverse) components of μl are found to decrease (increase) as a function of temperature until the full rotational symmetry is reached at TC. This reflects the increasing importance of the transverse spin fluctuations. The origin of the temperature dependence of M and μl is analyzed in terms of the local spin-fluctuation energies.

  14. Adsorption and ring-opening of lactide on the chiral metal surface Pt(321)S studied by density functional theory

    NASA Astrophysics Data System (ADS)

    Franke, J.-H.; Kosov, D. S.

    2015-01-01

    We study the adsorption and ring-opening of lactide on the naturally chiral metal surface Pt(321)S. Lactide is a precursor for polylactic acid ring-opening polymerization, and Pt is a well known catalyst surface. We study, here, the energetics of the ring-opening of lactide on a surface that has a high density of kink atoms. These sites are expected to be present on a realistic Pt surface and show enhanced catalytic activity. The use of a naturally chiral surface also enables us to study potential chiral selectivity effects of the reaction at the same time. Using density functional theory with a functional that includes the van der Waals forces in a first-principles manner, we find modest adsorption energies of around 1.4 eV for the pristine molecule and different ring-opened states. The energy barrier to be overcome in the ring-opening reaction is found to be very small at 0.32 eV and 0.30 eV for LL- and its chiral partner DD-lactide, respectively. These energies are much smaller than the activation energy for a dehydrogenation reaction of 0.78 eV. Our results thus indicate that (a) ring-opening reactions of lactide on Pt(321) can be expected already at very low temperatures, and Pt might be a very effective catalyst for this reaction; (b) the ring-opening reaction rate shows noticeable enantioselectivity.

  15. Acoustic emission source location and damage detection in a metallic structure using a graph-theory-based geodesic approach

    NASA Astrophysics Data System (ADS)

    Gangadharan, R.; Prasanna, G.; Bhat, M. R.; Murthy, C. R. L.; Gopalakrishnan, S.

    2009-11-01

    A geodesic-based approach using Lamb waves is proposed to locate the acoustic emission (AE) source and damage in an isotropic metallic structure. In the case of the AE (passive) technique, the elastic waves take the shortest path from the source to the sensor array distributed in the structure. The geodesics are computed on the meshed surface of the structure using graph theory based on Dijkstra's algorithm. By propagating the waves in reverse virtually from these sensors along the geodesic path and by locating the first intersection point of these waves, one can get the AE source location. The same approach is extended for detection of damage in a structure. The wave response matrix of the given sensor configuration for the healthy and the damaged structure is obtained experimentally. The healthy and damage response matrix is compared and their difference gives the information about the reflection of waves from the damage. These waves are backpropagated from the sensors and the above method is used to locate the damage by finding the point where intersection of geodesics occurs. In this work, the geodesic approach is shown to be suitable to obtain a practicable source location solution in a more general set-up on any arbitrary surface containing finite discontinuities. Experiments were conducted on aluminum specimens of simple and complex geometry to validate this new method.

  16. A unified theory of spin-relaxation due to spin-orbit coupling in metals and semiconductors

    PubMed Central

    Boross, Péter; Dóra, Balázs; Kiss, Annamária; Simon, Ferenc

    2013-01-01

    Spintronics is an emerging paradigm with the aim to replace conventional electronics by using electron spins as information carriers. Its utility relies on the magnitude of the spin-relaxation, which is dominated by spin-orbit coupling (SOC). Yet, SOC induced spin-relaxation in metals and semiconductors is discussed for the seemingly orthogonal cases when inversion symmetry is retained or broken by the so-called Elliott-Yafet and D'yakonov-Perel' spin-relaxation mechanisms, respectively. We unify the two theories on general grounds for a generic two-band system containing intra- and inter-band SOC. While the previously known limiting cases are recovered, we also identify parameter domains when a crossover occurs between them, i.e. when an inversion symmetry broken state evolves from a D'yakonov-Perel' to an Elliott-Yafet type of spin-relaxation and conversely for a state with inversional symmetry. This provides an ultimate link between the two mechanisms of spin-relaxation. PMID:24252975

  17. Density-Functional Theory Applied to Rare Earth Metals: Approaches Based on the Random-Phase Approximation

    NASA Astrophysics Data System (ADS)

    Casadei, Marco; Ren, Xinguo; Rinke, Patrick; Scheffler, Matthias; Rubio, Angel

    2013-03-01

    The description of the volume collapse exhibited by some rare earth metals poses a great challenge to density-functional theory (DFT) since local/semilocal functionals (LDA/GGA) fail to produce the associated phase transitions. We approach this problem by treating all electrons at the same quantum mechanical level, using both hybrid functionals (e.g. PBE0 and HSE06) and exact-exchange plus correlation in the random-phase approximation (EX+cRPA). We also assess the performance of recently developed beyond RPA schemes (e.g. rPT2). The calculations are performed for cerium and praseodymium, that display a volume collapse, and neodymium, in which the volume collapse is absent. The isostructural α- γ phase transition in cerium is the most studied. The exact exchange contribution in PBE0 and HSE06 is crucial to produce two distinct solutions that can be associated with the α and γ phases, but quantitative agreement with the extrapolated phase diagram requires EX+cRPA.

  18. Using queuing theory to analyse the government's 4-H completion time target in accident and emergency departments.

    PubMed

    Mayhew, L; Smith, D

    2008-03-01

    This paper uses a queuing model to evaluate completion times in Accident and Emergency (A&E) departments in the light of the Government target of completing and discharging 98% of patients inside 4 h. It illustrates how flows though an A&E can be accurately represented as a queuing process, how outputs can be used to visualise and interpret the 4-h Government target in a simple way and how the model can be used to assess the practical achievability of A&E targets in the future. The paper finds that A&E targets have resulted in significant improvements in completion times and thus deal with a major source of complaint by users of the National Health Service in the U.K. It suggests that whilst some of this improvement is attributable to better management, some is also due to the way some patients in A&E are designated and therefore counted through the system. It finds for example that the current target would not have been possible without some form of patient re-designation or re-labelling taking place. Further it finds that the current target is so demanding that the integrity of reported performance is open to question. Related incentives and demand management issues resulting from the target are also briefly discussed. PMID:18390164

  19. The molecular structure and vibrational spectra of corrolazine metal complexes (CzM) by density functional theory.

    PubMed

    Wang, Hongming; Yang, Chuanlu; Zhang, Zhihong; Wang, Meishan; Han, Keli

    2006-06-01

    The ground-state geometries, electronic structures and vibrational frequencies of metal corrolazine complexes, CzM (M=Mn, Co, Ni and Fe) have been studied using B3LYP/6-311 g(d) method. The molecular geometries are sensitive to the species of the metal, and the bond length of the MN is increase with the metal atom radii. The ground-state electronic structures indicate that there are strong interactions between dx2-y2 of the metal fragments and the corrolazine fragments. The calculations also indicate that the CzNi is the stabilest among the four metal corrolazine complexes. Vibrational frequencies of these metal corrolazine complexes were also calculated and were assigned to the local coordinates of the corrolazine ring, which reveals the some common feature of the molecular vibrations of the metal corrolazine complexes as four-coordination metallocorrolazines.

  20. Benchmark Calculations of Energetic Properties of Groups 4 and 6 Transition Metal Oxide Nanoclusters Including Comparison to Density Functional Theory.

    PubMed

    Fang, Zongtang; Both, Johan; Li, Shenggang; Yue, Shuwen; Aprà, Edoardo; Keçeli, Murat; Wagner, Albert F; Dixon, David A

    2016-08-01

    The heats of formation and the normalized clustering energies (NCEs) for the group 4 and group 6 transition metal oxide (TMO) trimers and tetramers have been calculated by the Feller-Peterson-Dixon (FPD) method. The heats of formation predicted by the FPD method do not differ much from those previously derived from the NCEs at the CCSD(T)/aT level except for the CrO3 nanoclusters. New and improved heats of formation for Cr3O9 and Cr4O12 were obtained using PW91 orbitals instead of Hartree-Fock (HF) orbitals. Diffuse functions are necessary to predict accurate heats of formation. The fluoride affinities (FAs) are calculated with the CCSD(T) method. The relative energies (REs) of different isomers, NCEs, electron affinities (EAs), and FAs of (MO2)n (M = Ti, Zr, Hf, n = 1-4) and (MO3)n (M = Cr, Mo, W, n = 1-3) clusters have been benchmarked with 55 exchange-correlation density functional theory (DFT) functionals including both pure and hybrid types. The absolute errors of the DFT results are mostly less than ±10 kcal/mol for the NCEs and the EAs and less than ±15 kcal/mol for the FAs. Hybrid functionals usually perform better than the pure functionals for the REs and NCEs. The performance of the two types of functionals in predicting EAs and FAs is comparable. The B1B95 and PBE1PBE functionals provide reliable energetic properties for most isomers. Long range corrected pure functionals usually give poor FAs. The standard deviation of the absolute error is always close to the mean errors, and the probability distributions of the DFT errors are often not Gaussian (normal). The breadth of the distribution of errors and the maximum probability are dependent on the energy property and the isomer. PMID:27384926

  1. Benchmark Calculations of Energetic Properties of Groups 4 and 6 Transition Metal Oxide Nanoclusters Including Comparison to Density Functional Theory.

    PubMed

    Fang, Zongtang; Both, Johan; Li, Shenggang; Yue, Shuwen; Aprà, Edoardo; Keçeli, Murat; Wagner, Albert F; Dixon, David A

    2016-08-01

    The heats of formation and the normalized clustering energies (NCEs) for the group 4 and group 6 transition metal oxide (TMO) trimers and tetramers have been calculated by the Feller-Peterson-Dixon (FPD) method. The heats of formation predicted by the FPD method do not differ much from those previously derived from the NCEs at the CCSD(T)/aT level except for the CrO3 nanoclusters. New and improved heats of formation for Cr3O9 and Cr4O12 were obtained using PW91 orbitals instead of Hartree-Fock (HF) orbitals. Diffuse functions are necessary to predict accurate heats of formation. The fluoride affinities (FAs) are calculated with the CCSD(T) method. The relative energies (REs) of different isomers, NCEs, electron affinities (EAs), and FAs of (MO2)n (M = Ti, Zr, Hf, n = 1-4) and (MO3)n (M = Cr, Mo, W, n = 1-3) clusters have been benchmarked with 55 exchange-correlation density functional theory (DFT) functionals including both pure and hybrid types. The absolute errors of the DFT results are mostly less than ±10 kcal/mol for the NCEs and the EAs and less than ±15 kcal/mol for the FAs. Hybrid functionals usually perform better than the pure functionals for the REs and NCEs. The performance of the two types of functionals in predicting EAs and FAs is comparable. The B1B95 and PBE1PBE functionals provide reliable energetic properties for most isomers. Long range corrected pure functionals usually give poor FAs. The standard deviation of the absolute error is always close to the mean errors, and the probability distributions of the DFT errors are often not Gaussian (normal). The breadth of the distribution of errors and the maximum probability are dependent on the energy property and the isomer.

  2. Size dependence of the melting temperature of metallic nanoclusters from the viewpoint of the thermodynamic theory of similarity

    NASA Astrophysics Data System (ADS)

    Samsonov, V. M.; Vasilyev, S. A.; Bembel, A. G.

    2016-08-01

    The generalized Thomson formula T m = T m (∞) (1-δ) R for the melting point of small objects T m has been analyzed from the viewpoint of the thermodynamic theory of similarity, where R is the radius of the particle and T m (∞) is the melting point of the corresponding large crystal. According to this formula, the parameter δ corresponds to the value of the radius of the T m ( R -1) particle obtained by the linear extrapolation of the dependence to the melting point of the particle equal to 0 K. It has been shown that δ = αδ0, where α is the factor of the asphericity of the particle (shape factor). In turn, the redefined characteristic length δ0 is expressed through the interphase tension σ sl at the boundary of the crystal with its own melt, the specific volume of the solid phase v s and the macroscopic value of the heat of fusion λ∞:δ0 = 2σ sl v s /λ∞. If we go from the reduced radius of the particle R/δ to the redefined reduced radius R/ r 1 or R/ d, where r 1 is the radius of the first coordination shell and d ≈ r 1 is the effective atomic diameter, then the simplex δ/ r 1 or δ/ d will play the role of the characteristic criterion of thermodynamic similarity. At a given value of α, this role will be played by the simplex Estimates of the parameters δ0 and δ0/ d have been carried out for ten metals with different lattice types. It has been shown that the values of the characteristic length δ0 are close to 1 nm and that the simplex δ0/ d is close to unity. In turn, the calculated values of the parameter δ agree on the order of magnitude with existing experimental data.

  3. Hydrogen Abundances in Metal Grains from the Hammadah Al Hamra (HaH) 237 Metal-rich Chondrite: A Test of the Nebular-Formation Theory

    NASA Technical Reports Server (NTRS)

    Lauretta, D. S.; Guan, Y.; Leshin, L. A.

    2005-01-01

    The Bencubbin-like (CB) chondrites are metal-rich, primitive meteorites [1,2]. Some of these chondrites (HaH 237, QUE 94411) contain compositionally zoned metal grains with near-chondritic bulk compositions. Thermodynamic modeling of the zoning patterns in these grains suggests that they were formed by condensation in a region of the solar nebula with enhanced dust/gas ratios and a total pressure of 10(exp -4) bars at temperatures between 1400 - 1500 K [3]. If these predictions are correct than the metal grains would have been exposed to abundant H2 gas, which comprises the bulk of nebular systems. Since Fe-based alloys can absorb significant quantities of H, metal grains formed in the solar nebula should contain measurable abundances of H.

  4. Au25 cluster functionalized metal-organic nanostructures for magnetically targeted photodynamic/photothermal therapy triggered by single wavelength 808 nm near-infrared light

    NASA Astrophysics Data System (ADS)

    Yang, Dan; Yang, Guixin; Gai, Shili; He, Fei; An, Guanghui; Dai, Yunlu; Lv, Ruichan; Yang, Piaoping

    2015-11-01

    Near-infrared (NIR) light-induced cancer therapy has gained considerable interest, but pure inorganic anti-cancer platforms usually suffer from degradation issues. Here, we designed metal-organic frameworks (MOFs) of Fe3O4/ZIF-8-Au25 (IZA) nanospheres through a green and economic procedure. The encapsulated Fe3O4 nanocrystals not only produce hyperthemal effects upon NIR light irradiation to effectively kill tumor cells, but also present targeting and MRI imaging capability. More importantly, the attached ultrasmall Au25(SR)18- clusters (about 2.5 nm) produce highly reactive singlet oxygen (1O2) to cause photodynamic effects through direct sensitization under NIR light irradiation. Furthermore, the Au25(SR)18- clusters also give a hand to the hyperthemal effect as photothermal fortifiers. This nanoplatform exhibits high biocompatibility and an enhanced synergistic therapeutic effect superior to any single therapy, as verified by in vitro and in vivo assay. This image-guided therapy based on a metal-organic framework may stimulate interest in developing other kinds of metal-organic materials with multifunctionality for tumor diagnosis and therapy.Near-infrared (NIR) light-induced cancer therapy has gained considerable interest, but pure inorganic anti-cancer platforms usually suffer from degradation issues. Here, we designed metal-organic frameworks (MOFs) of Fe3O4/ZIF-8-Au25 (IZA) nanospheres through a green and economic procedure. The encapsulated Fe3O4 nanocrystals not only produce hyperthemal effects upon NIR light irradiation to effectively kill tumor cells, but also present targeting and MRI imaging capability. More importantly, the attached ultrasmall Au25(SR)18- clusters (about 2.5 nm) produce highly reactive singlet oxygen (1O2) to cause photodynamic effects through direct sensitization under NIR light irradiation. Furthermore, the Au25(SR)18- clusters also give a hand to the hyperthemal effect as photothermal fortifiers. This nanoplatform exhibits high

  5. Study of complexation between two 1,3-alternate calix[4]crown derivatives and alkali metal ions by electrospray ionization mass spectrometry and density functional theory calculations

    NASA Astrophysics Data System (ADS)

    Shamsipur, Mojtaba; Allahyari, Leila; Fasihi, Javad; Taherpour, Avat (Arman); Asfari, Zuhair; Valinejad, Azizollah

    2016-03-01

    Complexation of two 1,3-alternate calix[4]crown ligands with alkali metals (K+, Rb+ and Cs+) has been investigated by electrospray ionization mass spectrometry (ESI-MS) and density functional theory calculations. The binding selectivities of the ligands and the binding constants of their complexes in solution have been determined using the obtained mass spectra. Also the percentage of each formed complex species in the mixture of each ligand and alkali metal has been experimentally evaluated. For both calix[4]crown-5 and calix[4]crown-6 ligands the experimental and theoretical selectivity of their alkali metal complexes found to follow the trend K+ > Rb+ > Cs+. The structures of ligands were optimized by DFT-B3LYP/6-31G method and the structures of complexes were obtained by QM-SCF-MO/PM6 method and discussed in the text.

  6. Simulating Valence-to-Core X-ray Emission Spectroscopy of Transition Metal Complexes with Time-Dependent Density Functional Theory

    SciTech Connect

    Zhang, Yu; Mukamel, Shaul; Khalil, Munira; Govind, Niranjan

    2015-11-09

    Valence-to-core (VtC) X-ray emission spectroscopy (XES) has emerged as a power- ful technique for the structural characterization of complex organometallic compounds in realistic environments. Since the spectrum represents electronic transitions from the ligand molecular orbitals to the core holes of the metal centers, the approach is more chemically sensitive to the metal-ligand bonding character compared with con- ventional X-ray absorption techniques. In this paper we study how linear-response time-dependent density functional theory (LR-TDDFT) can be harnessed to simulate K-edge VtC X-ray emission spectra reliably. LR-TDDFT allows one to go beyond the single-particle picture that has been extensively used to simulate VtC-XES. We con- sider seven low- and high-spin model complexes involving chromium, manganese and iron transition metal centers. Our results are in good agreement with experiment.

  7. Target Practice: Reader Response Theory and Teachers' Interpretations of Students' SAT 10 Scores in Data-Based Professional Development

    ERIC Educational Resources Information Center

    Atkinson, Becky M.

    2012-01-01

    The study reported in this article examines how teachers read and respond to their students' Stanford Achievement Test 10 (SAT 10) scores with the goal of investigating the assumption that data-based teaching practice is more "objective" and less susceptible to divergent teacher interpretation. The study uses reader response theory to frame…

  8. Target Rotations and Assessing the Impact of Model Violations on the Parameters of Unidimensional Item Response Theory Models

    ERIC Educational Resources Information Center

    Reise, Steven; Moore, Tyler; Maydeu-Olivares, Alberto

    2011-01-01

    Reise, Cook, and Moore proposed a "comparison modeling" approach to assess the distortion in item parameter estimates when a unidimensional item response theory (IRT) model is imposed on multidimensional data. Central to their approach is the comparison of item slope parameter estimates from a unidimensional IRT model (a restricted model), with…

  9. How humans search for targets through time: A review of data and theory from the attentional blink

    PubMed Central

    Dux, Paul E.; Marois, Réne

    2009-01-01

    Under conditions of rapid serial visual presentation (RSVP), subjects display a reduced ability to report the second of two targets (Target 2; T2) in a stream of distractors if it appears within 200–500 ms of Target 1 (T1). This effect, known as the attentional blink (AB), has been central in characterizing the limits of humans’ ability to consciously perceive stimuli distributed across time. Here we review theoretical accounts of the AB and examine how they explain key findings in the literature. We conclude that the AB arises from attentional demands of T1 for selection, working memory encoding, episodic registration and response selection, which prevents this high-level central resource from being applied to T2 at short T1–T2 lags. T1 processing also transiently impairs the re-deployment of these attentional resources to subsequent targets, and the inhibition of distractors that appear in close temporal proximity to T2. While these findings are consistent with a multi-factorial account of the AB, they can also be largely explained by assuming that the activation of these multiple processes depend on a common capacity-limited attentional process to select behaviorally relevant events presented amongst temporally distributed distractors. Thus, at its core, the attentional blink may ultimately reveal the temporal limits of the deployment of selective attention. PMID:19933555

  10. Carbon Dots Embedded Magnetic Nanoparticles @Chitosan @Metal Organic Framework as a Nanoprobe for pH Sensitive Targeted Anticancer Drug Delivery.

    PubMed

    Chowdhuri, Angshuman Ray; Singh, Tanya; Ghosh, Sudip Kumar; Sahu, Sumanta Kumar

    2016-07-01

    Recently, nanoscale metal organic frameworks (NMOFs) have been demonstrated as a promising carrier for drug delivery, as they possess many advantages like large surface area, high porosity, and tunable functionality. However, there are no reports about the functionalization of NMOFs, which combines cancer-targeted drug delivery/imaging, magnetic property, high drug loading content, and pH-sensitive drug release into one system. Existing formulations for integrating target molecules into NMOF are based on multistep synthetic processes. However, in this study, we report an approach that combines NMOF (IRMOF-3) synthesis and target molecule (Folic acid) encapsulation on the surface of chitosan modified magnetic nanoparticles in a single step. A noticeable feature of chitosan is control and pH responsive drug release for several days. More importantly, doxorubicin (DOX) was incorporated into magnetic NMOF formulation and showed high drug loading (1.63 g DOX g(-1) magnetic NMOFs). To demonstrate the optical imaging, carbon dots (CDs) are encapsulated into the synthesized magnetic NMOF, thereby endowing fluorescence features to the nanoparticles. These folate targeted magnetic NMOF possess more specific cellular internalization toward folate-overexpressed cancer (HeLa) cells in comparison to normal (L929) cells.

  11. Polarized internal target apparatus

    DOEpatents

    Holt, Roy J.

    1986-01-01

    A polarized internal target apparatus with a polarized gas target of improved polarization and density achieved by mixing target gas atoms with a small amount of alkali metal gas atoms, and passing a high intensity polarized light source into the mixture to cause the alkali metal gas atoms to become polarized which interact in spin exchange collisions with target gas atoms yielding polarized target gas atoms.

  12. Polarized internal target apparatus

    DOEpatents

    Holt, R.J.

    1984-10-10

    A polarized internal target apparatus with a polarized gas target of improved polarization and density (achieved by mixing target gas atoms with a small amount of alkali metal gas atoms, and passing a high intensity polarized light source into the mixture to cause the alkali metal gas atoms to become polarized which interact in spin exchange collisions with target gas atoms yielding polarized target gas atoms) is described.

  13. Optimizing EMI transmitter and receiver configurations to enhance detection and identification of small and deep metallic targets

    NASA Astrophysics Data System (ADS)

    Fernández, Juan Pablo; Barrowes, Benjamin; Bijamov, Alex; O'Neill, Kevin; Shamatava, Irma; Steinhurst, Daniel A.; Shubitidze, Fridon

    2012-06-01

    Current electromagnetic induction (EMI) sensors of the kind used to discriminate buried unexploded orndance (UXO) can detect targets down to a depth limited by the geometric size of the transmitter (Tx) coils, the amplitudes of the transmitting currents, and the noise floor of the receivers (Rx). The last two factors are not independent: for example, one cannot detect a deeply buried target simply by increasing the amplitude of the Tx current, since this also increases the noise and thus does not improve the SNR. The problem could in principle be overcome by increasing the size of the Tx coils and thus their moment. Current multi-transmitter instruments such as the TEMTADS sensor array can be electronically tweaked to provide a big Tx moment: they can be modified to transmit signals from two, three or more Tx coils simultaneously. We investigate the possibility of enhancing the deep-target detection capability of TEMTADS by exploring different combinations of Tx coils. We model different multi-Tx combinations within TEMTADS using a full-3D EMI solver based on the method of auxiliary sources (MAS).We determine the feasibility of honing these combinations for enhanced detection and discrimination of deep targets. We investigate how to improve the spatial resolution and focusing properties of the primary magnetic field by electronically adjusting the currents of the transmitters. We apply our findings to data taken at different UXO live sites.

  14. Au25 cluster functionalized metal-organic nanostructures for magnetically targeted photodynamic/photothermal therapy triggered by single wavelength 808 nm near-infrared light.

    PubMed

    Yang, Dan; Yang, Guixin; Gai, Shili; He, Fei; An, Guanghui; Dai, Yunlu; Lv, Ruichan; Yang, Piaoping

    2015-12-14

    Near-infrared (NIR) light-induced cancer therapy has gained considerable interest, but pure inorganic anti-cancer platforms usually suffer from degradation issues. Here, we designed metal-organic frameworks (MOFs) of Fe3O4/ZIF-8-Au25 (IZA) nanospheres through a green and economic procedure. The encapsulated Fe3O4 nanocrystals not only produce hyperthemal effects upon NIR light irradiation to effectively kill tumor cells, but also present targeting and MRI imaging capability. More importantly, the attached ultrasmall Au25(SR)18(-) clusters (about 2.5 nm) produce highly reactive singlet oxygen ((1)O2) to cause photodynamic effects through direct sensitization under NIR light irradiation. Furthermore, the Au25(SR)18(-) clusters also give a hand to the hyperthemal effect as photothermal fortifiers. This nanoplatform exhibits high biocompatibility and an enhanced synergistic therapeutic effect superior to any single therapy, as verified by in vitro and in vivo assay. This image-guided therapy based on a metal-organic framework may stimulate interest in developing other kinds of metal-organic materials with multifunctionality for tumor diagnosis and therapy. PMID:26540558

  15. Corrosion mechanisms for metal alloy waste forms: experiment and theory Level 4 Milestone M4FT-14LA0804024 Fuel Cycle Research & Development

    SciTech Connect

    Liu, Xiang-Yang; Taylor, Christopher D.; Kim, Eunja; Goff, George Scott; Kolman, David Gary

    2014-07-31

    This document meets Level 4 Milestone: Corrosion mechanisms for metal alloy waste forms - experiment and theory. A multiphysics model is introduces that will provide the framework for the quantitative prediction of corrosion rates of metallic waste forms incorporating the fission product Tc. The model requires a knowledge of the properties of not only the metallic waste form, but also the passive oxide films that will be generated on the waste form, and the chemistry of the metal/oxide and oxide/environment interfaces. in collaboration with experimental work, the focus of this work is on obtaining these properties from fundamental atomistic models. herein we describe the overall multiphysics model, which is based on MacDonald's point-defect model for passivity. We then present the results of detailed electronic-structure calculations for the determination of the compatibility and properties of Tc when incorporated into intermetallic oxide phases. This work is relevant to the formation of multi-component oxides on metal surfaces that will incorporate Tc, and provide a kinetic barrier to corrosion (i.e. the release of Tc to the environment). Atomistic models that build upon the electronic structure calculations are then described using the modified embedded atom method to simulate metallic dissolution, and Buckingham potentials to perform classical molecular dynamics and statics simulations of the technetium (and, later, iron-technetium) oxide phases. Electrochemical methods were then applied to provide some benchmark information of the corrosion and electrochemical properties of Technetium metal. The results indicate that published information on Tc passivity is not complete and that further investigation is warranted.

  16. 99Tc and Re incorporated into metal oxide polyoxometalates: oxidation state stability elucidated by electrochemistry and theory.

    PubMed

    McGregor, Donna; Burton-Pye, Benjamin P; Mbomekalle, Israel M; Aparicio, Pablo A; Romo, Susanna; López, Xavier; Poblet, Josep M; Francesconi, Lynn C

    2012-08-20

    The radioactive element technetium-99 ((99)Tc, half-life = 2.1 × 10(5) years, β(-) of 253 keV), is a major byproduct of (235)U fission in the nuclear fuel cycle. (99)Tc is also found in radioactive waste tanks and in the environment at National Lab sites and fuel reprocessing centers. Separation and storage of the long-lived (99)Tc in an appropriate and stable waste-form is an important issue that needs to be addressed. Considering metal oxide solid-state materials as potential storage matrixes for Tc, we are examining the redox speciation of Tc on the molecular level using polyoxometalates (POMs) as models. In this study we investigate the electrochemistry of Tc complexes of the monovacant Wells-Dawson isomers, α(1)-P(2)W(17)O(61)(10-) (α1) and α(2)-P(2)W(17)O(61)(10-) (α2) to identify features of metal oxide materials that can stabilize the immobile Tc(IV) oxidation state accessed from the synthesized Tc(V)O species and to interrogate other possible oxidation states available to Tc within these materials. The experimental results are consistent with density functional theory (DFT) calculations. Electrochemistry of K(7-n)H(n)[Tc(V)O(α(1)-P(2)W(17)O(61))] (Tc(V)O-α1), K(7-n)H(n)[Tc(V)O(α(2)-P(2)W(17)O(61))] (Tc(V)O-α2) and their rhenium analogues as a function of pH show that the Tc-containing derivatives are always more readily reduced than their Re analogues. Both Tc and Re are reduced more readily in the lacunary α1 site as compared to the α2 site. The DFT calculations elucidate that the highest oxidation state attainable for Re is VII while, under the same electrochemistry conditions, the highest oxidation state for Tc is VI. The M(V)→ M(IV) reduction processes for Tc(V)O-α1 are not pH dependent or only slightly pH dependent suggesting that protonation does not accompany reduction of this species unlike the M(V)O-α2 (M = (99)Tc, Re) and Re(V)O-α1 where M(V/IV) reduction process must occur hand in hand with protonation of the terminal M═O to

  17. Accelerator-based production of the (99m)Tc-(186)Re diagnostic-therapeutic pair using metal disulfide targets (MoS2, WS2, OsS2).

    PubMed

    Gott, Matthew D; Hayes, Connor R; Wycoff, Donald E; Balkin, Ethan R; Smith, Bennett E; Pauzauskie, Peter J; Fassbender, Michael E; Cutler, Cathy S; Ketring, Alan R; Wilbur, D Scott; Jurisson, Silvia S

    2016-08-01

    Novel, natural abundance metal disulfide targets were irradiated for 1h with a 10µA proton beam in a small, medical cyclotron. Osmium disulfide was synthesized by simple distillation and precipitation methods while MoS2 and WS2 were commercially available. The targets dissolved under mild conditions and were analyzed by γ-spectroscopy. Production rates and potential applications are discussed, including target recovery and recycling schemes for OsS2 and WS2.

  18. Accelerator-based production of the (99m)Tc-(186)Re diagnostic-therapeutic pair using metal disulfide targets (MoS2, WS2, OsS2).

    PubMed

    Gott, Matthew D; Hayes, Connor R; Wycoff, Donald E; Balkin, Ethan R; Smith, Bennett E; Pauzauskie, Peter J; Fassbender, Michael E; Cutler, Cathy S; Ketring, Alan R; Wilbur, D Scott; Jurisson, Silvia S

    2016-08-01

    Novel, natural abundance metal disulfide targets were irradiated for 1h with a 10µA proton beam in a small, medical cyclotron. Osmium disulfide was synthesized by simple distillation and precipitation methods while MoS2 and WS2 were commercially available. The targets dissolved under mild conditions and were analyzed by γ-spectroscopy. Production rates and potential applications are discussed, including target recovery and recycling schemes for OsS2 and WS2. PMID:27236832

  19. Effects of Application of Social Marketing Theory and the Health Belief Model in Promoting Cervical Cancer Screening among Targeted Women in Sisaket Province, Thailand.

    PubMed

    Wichachai, Suparp; Songserm, Nopparat; Akakul, Theerawut; Kuasiri, Chanapong

    2016-01-01

    Cervical cancer is a major public health problem in Thailand, being ranked second only to breast cancer. Thai women have been reported to have a low rate of cervical cancer screening (27.7% of the 80% goal of WHO). We therefore aimed to apply the social marketing theory and health belief model in promoting cervical cancer screening in Kanthararom District, Sisaket Province. A total of 92 from 974 targeted women aged 3060 years were randomly divided into two groups. The experimental group underwent application of social marketing theory and a health belief model program promoting cervical cancer screening while the control group received normal services. Two research tools were used: (1) application of social marketing theory and health belief model program and (2) questionnaire used to evaluate perceptions of cervical cancer. Descriptive and inferential statistics including paired sample ttest and independent ttest were used to analyze the data. After the program had been used, the mean score of perception of cervical cancer of experimental group was at a higher level (x=4.09; S.D. =0.30), than in the control group (x=3.82; S.D. =0.20) with statistical significance (p<0.001). This research demonstrated an appropriate communication process in behavioral modification to prevent cervical cancer. It can be recommended that this program featuring social marketing and the health belief model be used to promote cervical cancer screening in targeted women and it can be promoted as a guideline for other health services, especially in health promotion and disease prevention. PMID:27510000

  20. Effects of Application of Social Marketing Theory and the Health Belief Model in Promoting Cervical Cancer Screening among Targeted Women in Sisaket Province, Thailand.

    PubMed

    Wichachai, Suparp; Songserm, Nopparat; Akakul, Theerawut; Kuasiri, Chanapong

    2016-01-01

    Cervical cancer is a major public health problem in Thailand, being ranked second only to breast cancer. Thai women have been reported to have a low rate of cervical cancer screening (27.7% of the 80% goal of WHO). We therefore aimed to apply the social marketing theory and health belief model in promoting cervical cancer screening in Kanthararom District, Sisaket Province. A total of 92 from 974 targeted women aged 3060 years were randomly divided into two groups. The experimental group underwent application of social marketing theory and a health belief model program promoting cervical cancer screening while the control group received normal services. Two research tools were used: (1) application of social marketing theory and health belief model program and (2) questionnaire used to evaluate perceptions of cervical cancer. Descriptive and inferential statistics including paired sample ttest and independent ttest were used to analyze the data. After the program had been used, the mean score of perception of cervical cancer of experimental group was at a higher level (x=4.09; S.D. =0.30), than in the control group (x=3.82; S.D. =0.20) with statistical significance (p<0.001). This research demonstrated an appropriate communication process in behavioral modification to prevent cervical cancer. It can be recommended that this program featuring social marketing and the health belief model be used to promote cervical cancer screening in targeted women and it can be promoted as a guideline for other health services, especially in health promotion and disease prevention.

  1. Influence of alkali metal superoxides on structure, electronic, and optical properties of Be12O12 nanocage: Density functional theory study

    NASA Astrophysics Data System (ADS)

    Raoof Toosi, Ali; Shamlouei, Hamid Reza; Hesari, Asghar Mohammadi

    2016-09-01

    The effect of alkali metal superoxides M3O (M = Li, Na, K) on the electronic and optical properties of a Be12O12 nanocage was studied by density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The energy gaps (Eg) of all configurations were calculated. Generally, the adsorption of alkali metal superoxides on the Be12O12 nanocage causes a decrease of Eg. Electric dipole moment μ, polarizability α, and static first hyperpolarizability β were calculated and it was shown that the adsorption of alkali metal superoxides on Be12O12 increases its polarizability. It was found that the absorption of M3O on Be12O12 nanocluster improves its nonlinear optical properties. The highest first hyperpolarizability (β ≈ 214000 a.u.) is obtained in the K3O-Be12O12 nanocluster. The TD-DFT calculations were performed to investigate the origin of the first hyperpolarizabilities and it was shown that a higher first hyperpolarizability belongs to the structure that has a lower transition energy.

  2. Entropy as a quality descriptor for the dose distribution — theory and practice for the patient target volume

    NASA Astrophysics Data System (ADS)

    Moravek, Zdenek; Bogner, Ludwig

    2008-01-01

    The most common and established way to evaluate the quality of a radiotherapy plan is to use the dose-volume histogram (DVH). The evaluation of the DVH, however, is a subjective procedure. This may not be crucial as long as the two plans are significantly different. In the case of several plans obtained with different planning or optimisation strategies the differences are often subtle and therefore a more objective comparison method is desirable. A commonly used approach is based on evaluation of the conformity index, however we show how it can fail for plans of similar quality. Therefore we propose a new method based on the similarity of DVH to statistical distributions, which can be characterised uniquely by their entropy. The concept is defined separately for target volumes, where it is derived from the Fermi-like distribution, and for organs at risk, where the traditional approach is also considered in its derivation. The artificial illustratory and clinical examples show the properties of the entropy as the quality descriptor and compare it to the conformity index. The examples are focused to the patient target volumes, where the advantage of the concept is more evident.

  3. The Effects of Sensor Performance as Modeled by Signal Detection Theory on the Performance of Reinforcement Learning in a Target Acquisition Task

    NASA Astrophysics Data System (ADS)

    Quirion, Nate

    Unmanned Aerial Systems (UASs) today are fulfilling more roles than ever before. There is a general push to have these systems feature more advanced autonomous capabilities in the near future. To achieve autonomous behavior requires some unique approaches to control and decision making. More advanced versions of these approaches are able to adapt their own behavior and examine their past experiences to increase their future mission performance. To achieve adaptive behavior and decision making capabilities this study used Reinforcement Learning algorithms. In this research the effects of sensor performance, as modeled through Signal Detection Theory (SDT), on the ability of RL algorithms to accomplish a target localization task are examined. Three levels of sensor sensitivity are simulated and compared to the results of the same system using a perfect sensor. To accomplish the target localization task, a hierarchical architecture used two distinct agents. A simulated human operator is assumed to be a perfect decision maker, and is used in the system feedback. An evaluation of the system is performed using multiple metrics, including episodic reward curves and the time taken to locate all targets. Statistical analyses are employed to detect significant differences in the comparison of steady-state behavior of different systems.

  4. Propagation of the shock wave generated from excimer laser heating of aluminum targets in comparison with ideal blast wave theory

    NASA Astrophysics Data System (ADS)

    Jeong, S. H.; Greif, R.; Russo, R. E.

    1998-05-01

    Propagation of the shock wave generated during pulsed laser heating of aluminum targets was measured utilizing a probe beam deflection technique. The transit time of the laser-generated shock wave was compared with that predicted from the Sedov-Taylor solution for an ideal spherical blast wave. It was found that the most important parameters for the laser-generated shock wave to be consistent with the theoretically predicted propagation are the ambient pressure and the laser beam spot size. The prediction for laser energy conversion into the laser-induced vapor flow using the Sedov-Taylor solution overestimated the energy coupling efficiency, indicating a difference between a laser-induced gas-dynamic flow and an ideal blast wave.

  5. The homeostatic set point of the hypothalamus-pituitary-thyroid axis – maximum curvature theory for personalized euthyroid targets

    PubMed Central

    2014-01-01

    Background Despite rendering serum free thyroxine (FT4) and thyrotropin (TSH) within the normal population ranges broadly defined as euthyroidism, many patients being treated for hyperthyroidism and hypothyroidism persistently experience subnormal well-being discordant from their pre-disease healthy euthyroid state. This suggests that intra-individual physiological optimal ranges are narrower than laboratory-quoted normal ranges and implies the existence of a homeostatic set point encoded in the hypothalamic-pituitary-thyroid (HPT) axis that is unique to every individual. Methods We have previously shown that the dose–response characteristic of the hypothalamic-pituitary (HP) unit to circulating thyroid hormone levels follows a negative exponential curve. This led to the discovery that the normal reference intervals of TSH and FT4 fall within the ‘knee’ region of this curve where the maximum curvature of the exponential HP characteristic occurs. Based on this observation, we develop the theoretical framework localizing the position of euthyroid homeostasis over the point of maximum curvature of the HP characteristic. Results The euthyroid set points of patients with primary hypothyroidism and hyperthyroidism can be readily derived from their calculated HP curve parameters using the parsimonious mathematical model above. It can be shown that every individual has a euthyroid set point that is unique and often different from other individuals. Conclusions In this treatise, we provide evidence supporting a set point-based approach in tailoring euthyroid targets. Rendering FT4 and TSH within the laboratory normal ranges can be clinically suboptimal if these hormone levels are distant from the individualized euthyroid homeostatic set point. This mathematical technique permits the euthyroid set point to be realistically computed using an algorithm readily implementable for computer-aided calculations to facilitate precise targeted dosing of patients in this modern

  6. LIQUID TARGET

    DOEpatents

    Martin, M.D.; Salsig, W.W. Jr.

    1959-01-13

    A liquid handling apparatus is presented for a liquid material which is to be irradiated. The apparatus consists essentially of a reservoir for the liquid, a target element, a drain tank and a drain lock chamber. The target is in the form of a looped tube, the upper end of which is adapted to be disposed in a beam of atomic particles. The lower end of the target tube is in communication with the liquid in the reservoir and a means is provided to continuously circulate the liquid material to be irradiated through the target tube. Means to heat the reservoir tank is provided in the event that a metal is to be used as the target material. The apparatus is provided with suitable valves and shielding to provide maximum safety in operation.

  7. Folate-targeted pH-responsive calcium zoledronate nanoscale metal-organic frameworks: Turning a bone antiresorptive agent into an anticancer therapeutic.

    PubMed

    Au, Kin Man; Satterlee, Andrew; Min, Yuanzeng; Tian, Xi; Kim, Young Seok; Caster, Joseph M; Zhang, Longzhen; Zhang, Tian; Huang, Leaf; Wang, Andrew Z

    2016-03-01

    Zoledronate (Zol) is a third-generation bisphosphonate that is widely used as an anti-resorptive agent for the treatment of cancer bone metastasis. While there is preclinical data indicating that bisphosphonates such as Zol have direct cytotoxic effects on cancer cells, such effect has not been firmly established in the clinical setting. This is likely due to the rapid absorption of bisphosphonates by the skeleton after intravenous (i.v.) administration. Herein, we report the reformulation of Zol using nanotechnology and evaluation of this novel nanoscale metal-organic frameworks (nMOFs) formulation of Zol as an anticancer agent. The nMOF formulation is comprised of a calcium zoledronate (CaZol) core and a polyethylene glycol (PEG) surface. To preferentially deliver CaZol nMOFs to tumors as well as facilitate cellular uptake of Zol, we incorporated folate (Fol)-targeted ligands on the nMOFs. The folate receptor (FR) is known to be overexpressed in several tumor types, including head-and-neck, prostate, and non-small cell lung cancers. We demonstrated that these targeted CaZol nMOFs possess excellent chemical and colloidal stability in physiological conditions. The release of encapsulated Zol from the nMOFs occurs in the mid-endosomes during nMOF endocytosis. In vitro toxicity studies demonstrated that Fol-targeted CaZol nMOFs are more efficient than small molecule Zol in inhibiting cell proliferation and inducing apoptosis in FR-overexpressing H460 non-small cell lung and PC3 prostate cancer cells. Our findings were further validated in vivo using mouse xenograft models of H460 and PC3. We demonstrated that Fol-targeted CaZol nMOFs are effective anticancer agents and increase the direct antitumor activity of Zol by 80-85% in vivo through inhibition of tumor neovasculature, and inhibiting cell proliferation and inducing apoptosis.

  8. Structural and tunable characteristics of Ba(Zr x Ti1- x )O3 films prepared by RF-magnetron sputtering using a metal target

    NASA Astrophysics Data System (ADS)

    Kim, Jin-Woong; Shima, Hiromi; Nishida, Ken; Yamamoto, Takashi; Funakubo, Hiroshi

    2014-08-01

    Ba(Zr x Ti1- x )O3 (BZT) thin films with different Zr contents were deposited on (100)MgO and (100)Pt/(100)MgO substrates by RF-magnetron sputtering using metal targets. The BZT thin films epitaxially grew on MgO substrates with only a (001)/(100) orientation and had a single perovskite phase. In all cases, Ba/Ti ratio was stoichiometric and the BZT films possessed a dense microstructure. The grain size decreased with increasing Zr content. At room temperature, a dielectric constant as a function of the DC bais (tunability) of nearly 30% was achieved at 1 MHz; meanwhile, a relatively low dielectric loss was obtained. Moreover, after a post-annealing process, the tunability was increased significantly. These results indicate that we succeeded in depositing high-quality, and potential tunable ferroelectrics.

  9. Meditating metal coenhanced fluorescence and SERS around gold nanoaggregates in nanosphere as bifunctional biosensor for multiple DNA targets.

    PubMed

    Liu, Yong; Wu, Peiyi

    2013-06-26

    Gold nanoparticles (Au NPs) are very attractive candidate nanoparticles in biological assay because of their high chemical stabilities, high homogeneities, good biocompatibilities, and low toxicities. However, molecular beacon assays via encapsulating the combined fluorescence or surface-enhanced Raman scattering (SERS) signals of reporters and Au NPs in nanobarcodes particles usually suffer from fluorescence quenching or weak Raman enhancement when Au NPs are employed (especially with size smaller than 15 nm). Herein, we present a new design of simultaneously realizing metal-enhanced fluorescence and coenhanced surface-enhanced Raman scattering by facilely embedding Ag nanoparticle into the shell of two kinds of Au nanoaggregate (5 and 10 nm), meanwhile, fluorophore is located between the silver core and gold nanoparticle layers and the distance among them is adjusted by SiO2 spacer (Ag@first SiO2 spacer@FiTC+SiO2@second SiO2 spacer@Au nanoaggregate). In this architecture, Ag nanoparticle not only is utilized as an efficient fluorescence enhancer to overcome the common fluorescence quenching around Au nanoaggregates but also behaves like a mirror. Thus, incident light that passes through the SERS-active Au nanoaggregate and the intervening dielectric layer of SiO2 could be reflected multiply from the surface of Ag nanoparticle and coupled with the light at the nanogap between the Au nanoaggregates to further amplify Raman intensity. This results in enhancement factors for fluorescence and SERS ~1.6-fold and more than 300-fold higher than the control samples without silver core under identical experimental conditions, respectively. Moreover, fluorophore and SERS reporters are assembled onto different layers of the concentric hybrid microsphere, resulting in a feasible fabrication protocol when a large number of agents need to be involved into the dual-mode nanobarcodes. A proof-of-concept chip-based DNA sandwich hybridization assay using genetically modified

  10. Classical scattering theory of waves from the view point of an eigenvalue problem and application to target identification

    SciTech Connect

    Bottcher, C.; Strayer, M.R.; Werby, M.F.

    1993-10-01

    The Helmholtz-Poincare Wave Equation (H-PWE) arises in many areas of classical wave scattering theory. In particular it can be found for the cases of acoustical scattering from submerged bounded objects and electromagnetic scattering from objects. The extended boundary integral equations (EBIE) method is derived from considering both the exterior and interior solutions of the H-PWE`s. This coupled set of expressions has the advantage of not only offering a prescription for obtaining a solution for the exterior scattering problem, but it also obviates the problem of irregular values corresponding to fictitious interior eigenvalues. Once the coupled equations are derived, they can by obtained in matrix form be expanding all relevant terms in partial wave expansions, including a biorthogonal expansion of the Green function. However some freedom of choice in the choice of the surface expansion is available since the unknown surface quantities may be expanded in a variety of ways to long as closure is obtained. Out of many possible choices, we develop an optimal method to obtain such expansions which is based on the optimum eigenfunctions related to the surface of the object. In effect, we convert part of the problem (that associated with the Fredholms integral equation of the first kind) an eigenvalue problem of a related Hermition operator. The methodology will be explained in detail and examples will be presented.

  11. Multiconfiguration Pair-Density Functional Theory: A Fully Translated Gradient Approximation and Its Performance for Transition Metal Dimers and the Spectroscopy of Re2Cl8(2-).

    PubMed

    Carlson, Rebecca K; Truhlar, Donald G; Gagliardi, Laura

    2015-09-01

    We extend the on-top density functional of multiconfiguration pair-density functional theory (MC-PDFT) to include the gradient of the on-top density as well as the gradient of the density. We find that the theory is reasonably stable to this extension; furthermore, it provides improved accuracy for molecules containing transition metals. We illustrate the extended on-top density functionals by applying them to Cr2, Cu2, Ag2, Os2, and Re2Cl8(2-) as well as to our previous database of 56 data for bond dissociation energies, barrier heights, reaction energies, proton affinities, and the water dimer. The performance of MC-PDFT is comparable to or better than that of CASPT2. PMID:26575903

  12. The role of repair in the survival of mammalian cells from heavy ion irradiation - Approximation to the ideal case of target theory

    NASA Technical Reports Server (NTRS)

    Lett, J. T.; Cox, A. B.; Story, M. D.

    1989-01-01

    Experiments are discussed in which the cell-cycle dependency of the repair deficiency of the S/S variant of the L5178Y murine leukemic lymphoblast was examined by treatment with the heavy ions, Ne-20, Si-28, Ar-40, Fe-56, and Nb-93. Evidence from those studies provide support for the notion that as the linear energy transfer of the incident radiation increases the ability of the S/S cell to repair radiation damage decreases until it is eliminated around 500 keV/micron. In the region of the latter linear energy transfer value, the behavior of the S/S cell approximates the ideal case of target theory where post-irradiation metabolism does not influence cell survival.

  13. Mathematical models of radiation action on living cells: From the target theory to the modern approaches. A historical and critical review.

    PubMed

    Bodgi, Larry; Canet, Aurélien; Pujo-Menjouet, Laurent; Lesne, Annick; Victor, Jean-Marc; Foray, Nicolas

    2016-04-01

    Cell survival is conventionally defined as the capability of irradiated cells to produce colonies. It is quantified by the clonogenic assays that consist in determining the number of colonies resulting from a known number of irradiated cells. Several mathematical models were proposed to describe the survival curves, notably from the target theory. The Linear-Quadratic (LQ) model, which is to date the most frequently used model in radiobiology and radiotherapy, dominates all the other models by its robustness and simplicity. Its usefulness is particularly important because the ratio of the values of the adjustable parameters, α and β, on which it is based, predicts the occurrence of post-irradiation tissue reactions. However, the biological interpretation of these parameters is still unknown. Throughout this review, we revisit and discuss historically, mathematically and biologically, the different models of the radiation action by providing clues for resolving the enigma of the LQ model.

  14. Theory of bimolecular reactions in a solution with linear traps: Application to the problem of target search on DNA

    NASA Astrophysics Data System (ADS)

    Turkin, Alexander; van Oijen, Antoine M.; Turkin, Anatoliy A.

    2015-11-01

    One-dimensional sliding along DNA as a means to accelerate protein target search is a well-known phenomenon occurring in various biological systems. Using a biomimetic approach, we have recently demonstrated the practical use of DNA-sliding peptides to speed up bimolecular reactions more than an order of magnitude by allowing the reactants to associate not only in the solution by three-dimensional (3D) diffusion, but also on DNA via one-dimensional (1D) diffusion [A. Turkin et al., Chem. Sci. (2015), 10.1039/C5SC03063C]. Here we present a mean-field kinetic model of a bimolecular reaction in a solution with linear extended sinks (e.g., DNA) that can intermittently trap molecules present in a solution. The model consists of chemical rate equations for mean concentrations of reacting species. Our model demonstrates that addition of linear traps to the solution can significantly accelerate reactant association. We show that at optimum concentrations of linear traps the 1D reaction pathway dominates in the kinetics of the bimolecular reaction; i.e., these 1D traps function as an assembly line of the reaction product. Moreover, we show that the association reaction on linear sinks between trapped reactants exhibits a nonclassical third-order behavior. Predictions of the model agree well with our experimental observations. Our model provides a general description of bimolecular reactions that are controlled by a combined 3D+1D mechanism and can be used to quantitatively describe both naturally occurring as well as biomimetic biochemical systems that reduce the dimensionality of search.

  15. Self-consistent many-electron theory of electron work functions and surface potential characteristics for selected metals

    NASA Technical Reports Server (NTRS)

    Smith, J. R.

    1969-01-01

    Electron work functions, surface potentials, and electron number density distributions and electric fields in the surface region of 26 metals were calculated from first principles within the free electron model. Calculation proceeded from an expression of the total energy as a functional of the electron number density, including exchange and correlation energies, as well as a first inhomogeneity term. The self-consistent solution was obtained via a variational procedure. Surface barriers were due principally to many-body effects; dipole barriers were small only for some alkali metals, becoming quite large for the transition metals. Surface energies were inadequately described by this model, which neglects atomistic effects. Reasonable results were obtained for electron work functions and surface potential characteristics, maximum electron densities varying by a factor of over 60.

  16. Cinchonidine adsorption on gold and gold-containing bimetallic platinum metal surfaces: an attenuated total reflection infrared and density functional theory study.

    PubMed

    Behzadi, Bahar; Vargas, Angelo; Ferri, Davide; Ernst, Karl-Heinz; Baiker, Alfons

    2006-08-31

    Adsorption of cinchonidine on monometallic Au and bimetallic Pt-Au and Pd-Au thin model films prepared by physical vapor deposition has been investigated with attenuated total reflection infrared (ATR-IR) spectroscopy. On Au the alkaloid forms an adsorbed layer that shows higher stability against desorption than the corresponding adsorption on Pt. In this adsorption layer the intermolecular interactions dominate over metal-adsorbate interactions as indicated by the absence of the spectroscopic features attributed to strongly flat adsorbed species. This behavior is further supported by Density Functional Theory (DFT) calculations indicating that flat and tilted orientations of the quinoline ring have comparable adsorption energy on Au but lower (7-10 kcal/mol) compared to adsorption on Pt (ca. 40 kcal/mol). As a consequence, the creation of a metal surface with isolated chiral sites is prevented by formation of an adsorbed structure formed by intermolecularly bound cinchonidine molecules on Au. While the binding to Pt is due to the formation of sigma-bonds to surface atoms, such aggregates are bound to Au mainly by van der Waals forces. Given this different nature of bonding of cinchonidine to Au and Pt, addition of Au to Pt and Pd films could be used to probe the changes of fractional coverage of the different adsorbed species of cinchonidine on the platinum metals. It is demonstrated that the lowering of the domain size of the platinum group metal by Au can simulate the effect of particle size on the distribution of the surface conformations of the alkaloid on a metal surface.

  17. Supersymmetric correspondence in spectra on a graph and its line graph: From circuit theory to spoof plasmons on metallic lattices

    NASA Astrophysics Data System (ADS)

    Nakata, Yosuke; Urade, Yoshiro; Nakanishi, Toshihiro; Miyamaru, Fumiaki; Takeda, Mitsuo Wada; Kitano, Masao

    2016-04-01

    We investigate the supersymmetry (SUSY) structures for inductor-capacitor circuit networks on a simple regular graph and its line graph. We show that their eigenspectra must coincide (except, possibly, for the highest eigenfrequency) due to SUSY, which is derived from the topological nature of the circuits. To observe this spectra correspondence in the high-frequency range, we study spoof plasmons on metallic hexagonal and kagomé lattices. The band correspondence between them is predicted by a simulation. Using terahertz time-domain spectroscopy, we demonstrate the band correspondence of fabricated metallic hexagonal and kagomé lattices.

  18. A bifunctional poly(ethylene glycol) silane immobilized on metallic oxide-based nanoparticles for conjugation with cell targeting agents

    SciTech Connect

    Kohler, Nathan J.; Fryxell, Glen E.; Zhang, Miqin

    2004-06-16

    A trifluoroethylester-terminal poly (ethylene glycol) (PEG) silane was synthesized and self-assembled on iron oxide nanoparticles. The nanoparticle system thus prepared has the flexibility to conjugate with cell targeting agents having either carboxylic and amine terminal groups for a number of biomedical applications, including magnetic resonance imaging (MRI) and controlled drug delivery. The trifluoroethylester silane was synthesized by modifying a PEG diacid to form the corresponding bistrifluoroethylester (TFEE), followed by a reaction with 3-aminopropyltriethoxysilane (APS). The APS coupled with PEG chains confers the stability of PEG self-assembled monolayers (SAMs) and increases the PEG packing density on nanoparticles by establishing hydrogen bonding between the carbonyl and amine groups present within the monolayer structure. The success of the synthesis of the PEG TEFE silane was confirmed with 1H NMR and Fourier transform infrared spectroscopy (FTIR). The conjugating flexibility of the PEG TEFE was demonstrated with folic acid having carboxylic acid groups and amine terminal groups respectively and confirmed by FTIR. TEM analysis showed the dispersion of nanoparticles before and after they were coated with PEG and folic acid.

  19. Accurate p-mode measurements of the G0V metal-rich CoRoT target HD 52265

    NASA Astrophysics Data System (ADS)

    Ballot, J.; Gizon, L.; Samadi, R.; Vauclair, G.; Benomar, O.; Bruntt, H.; Mosser, B.; Stahn, T.; Verner, G. A.; Campante, T. L.; García, R. A.; Mathur, S.; Salabert, D.; Gaulme, P.; Régulo, C.; Roxburgh, I. W.; Appourchaux, T.; Baudin, F.; Catala, C.; Chaplin, W. J.; Deheuvels, S.; Michel, E.; Bazot, M.; Creevey, O.; Dolez, N.; Elsworth, Y.; Sato, K. H.; Vauclair, S.; Auvergne, M.; Baglin, A.

    2011-06-01

    Context. The star HD 52265 is a G0V metal-rich exoplanet-host star observed in the seismology field of the CoRoT space telescope from November 2008 to March 2009. The satellite collected 117 days of high-precision photometric data on this star, showing that it presents solar-like oscillations. HD 52265 was also observed in spectroscopy with the Narval spectrograph at the same epoch. Aims: We characterise HD 52265 using both spectroscopic and seismic data. Methods: The fundamental stellar parameters of HD 52265 were derived with the semi-automatic software VWA, and the projected rotational velocity was estimated by fitting synthetic profiles to isolated lines in the observed spectrum. The parameters of the observed p modes were determined with a maximum-likelihood estimation. We performed a global fit of the oscillation spectrum, over about ten radial orders, for degrees l = 0 to 2. We also derived the properties of the granulation, and analysed a signature of the rotation induced by the photospheric magnetic activity. Results: Precise determinations of fundamental parameters have been obtained: Teff = 6100 ± 60 K, log g = 4.35 ± 0.09, [M/H] = 0.19 ± 0.05, as well as vsini=3.6+0.3-1.0kms. We have measured a mean rotation period Prot = 12.3 ± 0.15 days, and find a signature of differential rotation. The frequencies of 31 modes are reported in the range 1500-2550 μHz. The large separation exhibits a clear modulation around the mean value Dnu=98.3 ± 0.1 μHz. Mode widths vary with frequency along an S-shape with a clear local maximum around 1800 μHz. We deduce lifetimes ranging between 0.5 and 3 days for these modes. Finally, we find a maximal bolometric amplitude of about 3.96 ± 0.24 ppm for radial modes. The CoRoT space mission, launched on December 27th 2006, has been developed and is operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA (RSSD and Science Programme), Germany and Spain.

  20. Density functional theory study of oxygen-atom insertion into metal-methyl bonds of iron(II), ruthenium(II), and osmium(II) complexes: study of metal-mediated C-O bond formation.

    PubMed

    Pardue, Daniel B; Mei, Jiajun; Cundari, Thomas R; Gunnoe, T Brent

    2014-03-17

    Metal-mediated C-O bond formation is a key step in hydrocarbon oxygenation catalytic cycles; however, few examples of this reaction have been reported for low-oxidation-state complexes. Oxygen insertion into a metal-carbon bond of Cp*M(CO)(OPy)R (Cp* = η(5)-pentamethylcyclopentadienyl; R = Me, Ph; OPy = pyridine-N-oxide; M = Fe, Ru, Os) was analyzed via density functional theory calculations. Oxygen-atom insertions through a concerted single-step organometallic Baeyer-Villiger pathway and a two-step pathway via a metal-oxo intermediate were studied; calculations predict that the former pathway was lower in energy. The results indicated that functionalization of M-R to M-OR (R = Me, Ph) is plausible using iron(II) complexes. Starting from Cp*Fe(CO)(OPy)Ph, the intermediate Fe-oxo showed oxyl character and, thus, is best considered an Fe(III)O(•-) complex. Oxidation of the π-acid ancillary ligand CO was facile. Substitutions of CO with dimethylamide and NH3 were calculated to lower the activation barrier by ∼1-2 kcal/mol for formation of the Fe(III)O(•-) intermediate, whereas a chloride ligand raised the activation barrier to 26 kcal/mol from 22.9 kcal/mol. PMID:24571202

  1. Chemical trends of barrier heights in metal-semiconductor contacts: on the theory of the slope parameter

    NASA Astrophysics Data System (ADS)

    Mönch, Winfried

    1996-02-01

    The barrier heights in ideal metal-semiconductor contacts are determined by the continuum of the metal-induced gap states (MIGS). In generalizing Pauling's concept, the charge transfer across such interfaces may be modeled by the difference Xm - Xs of the metal and the semiconductor electronegativities. For n-type semiconductors this MIGS-and-electronegativity model describes the chemical trends of the barrier heights as φBn = φcnl + Sx( Xm - Xs). The zero-chargetransfer barrier heights φcnl were calculated for almost all semiconductors. The slope parameters Sx are determined by the density of states of the MIG states, the thickness of the respective interfacial double layer, and the interface dielectric constant ɛi. The densities of states and decay lengths of the metal-induced gap states at their charge neutrality level were computed by others for some of the semiconductors. It is demonstrated that these theoretical data predict the slope parameters Sx to vary proportional to (ɛ ∞ - 1) 2/ɛ i where ɛ∞ is the electronic contribution to the static dielectric constant of the semiconductor. This result confirms a previously found semi-empirical rule.

  2. Van Der Waals-Corrected Density Functional Theory Simulation of Adsorption Processes on Noble-Metal Surfaces: Xe on Ag(111), Au(111), and Cu(111)

    NASA Astrophysics Data System (ADS)

    Silvestrelli, Pier Luigi; Ambrosetti, Alberto

    2016-10-01

    The DFT/vdW-WF2s1 method based on the generation of localized Wannier functions, recently developed to include the van der Waals interactions in the density functional theory and describe adsorption processes on metal surfaces by taking metal-screening effects into account, is applied to the case of the interaction of Xe with noble-metal surfaces, namely Ag(111), Au(111), and Cu(111). The study is also repeated by adopting the DFT/vdW-QHO-WF variant relying on the quantum harmonic oscillator model which describes well many body effects. Comparison of the computed equilibrium binding energies and distances, and the C_3 coefficients characterizing the adatom-surface van der Waals interactions, with available experimental and theoretical reference data shows that the methods perform well and elucidates the importance of properly including screening effects. The results are also compared with those obtained by other vdW-corrected DFT schemes, including PBE-D, vdW-DF, vdW-DF2, rVV10, and by the simpler local density approximation and semi-local (PBE) generalized gradient approximation approaches.

  3. Partition of actinides and fission products between metal and molten salt phases: Theory, measurement, and application to IFR pyroprocess development

    SciTech Connect

    Ackerman, J.P.; Johnson, T.R.

    1993-10-01

    The chemical basis of Integral Fast Reactor fuel reprocessing (pyroprocessing) is partition of fuel, cladding, and fission product elements between molten LiCl-KCl and either a solid metal phase or a liquid cadmium phase. The partition reactions are described herein, and the thermodynamic basis for predicting distributions of actinides and fission products in the pyroprocess is discussed. The critical role of metal-phase activity coefficients, especially those of rare earth and the transuranic elements, is described. Measured separation factors, which are analogous to equilibrium constants but which involve concentrations rather than activities, are presented. The uses of thermodynamic calculations in process development are described, as are computer codes developed for calculating material flows and phase compositions in pyroprocessing.

  4. Reorganization of a topological surface state: Theory for Bi2Te3(111) covered by noble metals

    NASA Astrophysics Data System (ADS)

    Muñoz, Francisco; Flieger, Markus; Henk, Jürgen; Mertig, Ingrid

    2014-09-01

    The electronic structure of Bi2Te3 covered by noble metals is investigated by first-principles calculations. The Dirac surface state of the topological insulator Bi2Te3 hybridizes with the sp states of the noble metal, which gives rise to strong reorganization of the surface electronic structure. Striking features of the modified Dirac surface state are (i) the introduction of new Dirac points within the fundamental band gap of Bi2Te3, (ii) a very weak dispersion, and (iii) a multisheeted Fermi surface which results in an orientation-dependent number of conducting channels in the fundamental band gap of Bi2Te3. Our findings have impact for spin-dependent surface transport.

  5. Theory of plasmon-enhanced high-order harmonic generation in the vicinity of metal nanostructures in noble gases

    SciTech Connect

    Husakou, A.; Im, S.-J.; Herrmann, J.

    2011-04-15

    We present a semiclassical model for plasmon-enhanced high-order harmonic generation (HHG) in the vicinity of metal nanostructures. We show that, besides the field enhancement, both the inhomogeneity of the enhanced local fields and electron absorption by the metal surface play an important role in the HHG process and lead to the generation of even harmonics and a significantly increased cutoff. For the examples of silver-coated nanocones and bowtie antennas, we predict that the required intensity reduces by up to three orders of magnitude due to plasmonic field enhancement. The study of the enhanced high-order harmonic generation is connected with a finite-element simulation of the electric field enhancement due to the excitation of the plasmonic modes.

  6. Theory of charge transport in diffusive normal metal/conventional superconductor point contacts in the presence of magnetic impurity

    NASA Astrophysics Data System (ADS)

    Yokoyama, T.; Tanaka, Y.; Golubov, A. A.; Inoue, J.; Asano, Y.

    2006-01-01

    Charge transport in the diffusive normal metal/insulator/s-wave superconductor junctions is studied in the presence of the magnetic impurity for various situations, where we have used the Usadel equation with Nazarov's generalized boundary condition. It is revealed that the magnetic impurity scattering suppresses the proximity effect. Wide variety of the line shapes of the tunneling conductance is obtained. Only for high transparent junction the normalized conductance around zero voltage can be enhanced by the magnetic impurity scattering.

  7. A Comparison of Density Functional Theory with Ab initio Approaches for Systems Involving First Transition Row Metals

    NASA Technical Reports Server (NTRS)

    Ricca, Alessandra; Bauschlicher, Charles W.; Langhoff, Stephen R. (Technical Monitor)

    1994-01-01

    Density functional theory (DFT) is found to give a better description of the geometries and vibrational frequencies of FeL and FeL(sup +) systems than second order Moller Plesset perturbation theory (MP2). Namely, the DFT correctly predicts the shift in the CO vibrational frequency between free CO and the Sigma(sup -) state of FeCO and yields a good result for the Fe-C distance in the quartet states of FeCH4(+) 4 These are properties where the MP2 results are unsatisfactory. Thus DFT appears to be an excellent approach for optimizing the geometries and computing the zero-point energies of systems containing first transition row atoms. Because the DFT approach is biased in favor of the 3d(exp 7) occupation, whereas the more traditional approaches are biased in favor of the 3d(exp 6) occupation, differences are found in the relative ordering of states. It is shown that if the dissociation is computed to the most appropriate atomic asymptote and corrected to the ground state asymptote using the experimental separations, the DFT results are in good agreement with high levels of theory. The energetics at the DFT level are much superior to the MP2 and in most cases in good agreement with high levels of theory.

  8. Theory of the Dirac half metal and quantum anomalous Hall effect in Mn-intercalated epitaxial graphene

    NASA Astrophysics Data System (ADS)

    Li, Yuanchang; West, Damien; Huang, Huaqing; Li, Jia; Zhang, S. B.; Duan, Wenhui

    2015-11-01

    The prospect of a Dirac half metal, a material which is characterized by a band structure with a gap in one spin channel but a Dirac cone in the other, is of both fundamental interest and a natural candidate for use in spin-polarized current applications. However, while the possibility of such a material has been reported based on model calculations [H. Ishizuka and Y. Motome, Phys. Rev. Lett. 109, 237207 (2012), 10.1103/PhysRevLett.109.237207], it remains unclear what material system might realize such an exotic state. Using first-principles calculations, we show that the experimentally accessible Mn-intercalated epitaxial graphene on SiC(0001) transits to a Dirac half metal when the coverage is >1 /3 monolayer. This transition results from an orbital-selective breaking of quasi-two-dimensional inversion symmetry, leading to symmetry breaking in a single spin channel which is robust against randomness in the distribution of Mn intercalates. Furthermore, the inclusion of spin-orbit interaction naturally drives the system into the quantum anomalous Hall (QAH) state. Our results thus not only demonstrate the practicality of realizing the Dirac half metal beyond a toy model, but also open up an avenue to the realization of the QAH effect.

  9. Fermi surfaces, spin-mixing parameter, and colossal anisotropy of spin relaxation in transition metals from ab initio theory

    NASA Astrophysics Data System (ADS)

    Zimmermann, Bernd; Mavropoulos, Phivos; Long, Nguyen H.; Gerhorst, Christian-Roman; Blügel, Stefan; Mokrousov, Yuriy

    2016-04-01

    The Fermi surfaces and Elliott-Yafet spin-mixing parameter (EYP) of several elemental metals are studied by ab initio calculations. We focus first on the anisotropy of the EYP as a function of the direction of the spin-quantization axis [B. Zimmermann et al., Phys. Rev. Lett. 109, 236603 (2012), 10.1103/PhysRevLett.109.236603]. We analyze in detail the origin of the gigantic anisotropy in 5 d hcp metals as compared to 5 d cubic metals by band structure calculations and discuss the stability of our results against an applied magnetic field. We further present calculations of light (4 d and 3 d ) hcp crystals, where we find a huge increase of the EYP anisotropy, reaching colossal values as large as 6000 % in hcp Ti. We attribute these findings to the reduced strength of spin-orbit coupling, which promotes the anisotropic spin-flip hot loops at the Fermi surface. In order to conduct these investigations, we developed an adapted tetrahedron-based method for the precise calculation of Fermi surfaces of complicated shape and accurate Fermi-surface integrals within the full-potential relativistic Korringa-Kohn-Rostoker Green function method.

  10. Comparative study of the matrix effect in Cl analysis with laser-induced breakdown spectroscopy in a pellet or in a dried solution layer on a metallic target

    NASA Astrophysics Data System (ADS)

    Zheng, Lijuan; Niu, Sheng; Khan, Abdul Qayyum; Yuan, Shuai; Yu, Jin; Zeng, Heping

    2016-04-01

    Chlorine content brought by salt in a composite powder was determined when the sample was prepared in pellet or first dissolved into solution and then dropped on the surface of a pure metallic target. The purpose is to address the matrix effect when the mixture powders of different kinds of mineral salt are used, and to compare the influence of the matrix effect for two kinds of sample preparation. Three types of powder mixture, NaCl + KBr, NaCl + MgSO4, and NaCl + Na2CO3, were then first prepared with well controlled proportion of salt (NaCl) and mineral salt powder. On one hand, pellets were prepared for laser ablation. On the other hand, mixture powder was dissolved in deionized water for analysis with surface-assisted laser-induced breakdown spectroscopy (LIBS) of solution by dropping it on the surface of a pure aluminum target. Calibration curves were established for the pellets and the solutions, respectively. The slopes of these curves provided an assessment of the matrix effect related to the different mineral salt matrix and different forms of the sample preparation. The similar responses from chlorine for the solution samples showed absence of matrix effect for analysis with the surface-assisted solution analysis configuration. This result was further confirmed by the consistence of the measured temperatures and the electron densities of the produced plasmas. In contrast, the slopes of the chlorine calibration curves exhibited significant variation for different pellet samples corresponding to different powder mixtures, which is an indication of matrix effect in the LIBS analysis of the pellet samples.

  11. Modeling of the mass transfer rates of metal ions across supported liquid membranes. 2: Comparison between theory and experiment

    SciTech Connect

    Elhassadi, A.A.; Do, D.D.

    1999-02-01

    The model equations developed in Part 1 were tested using experimental data reported in the literature and produced in this work. It was found that uranium(VI) and thorium(IV) can be selectively separated and concentrated using supported liquid membranes. Depending on the way the liquid membranes are designed, the selectivity toward a specific metal can be predetermined. The effect of the ratio of the effective diffusivity to bulk diffusivity in free solution was found to behave with the same characteristic of systems of preferentially adsorbed solutes.

  12. Density functional theory study of interaction, bonding and affinity of group IIb transition metal cations with nucleic acid bases

    NASA Astrophysics Data System (ADS)

    Bagchi, Sabyasachi; Mandal, Debasish; Ghosh, Deepanwita; Das, Abhijit K.

    2012-05-01

    The structure, bonding, and energetics of the complexes obtained from the interaction between the most stable tautomeric forms of free DNA and RNA bases and Zn2+, Cd2+ and Hg2+ cations have been studied using density functional B3LYP method. The 6-311+G (2df, 2p) basis set along with LANL2DZ pseudopotentials for the cations are used in the calculations. The tautomerization paths of the nucleobases are investigated and transition states between the tautomeric forms of the free bases are located. The relative stability of the complexes and the tautomers of the free nucleobases are discussed referring to MIA and relative energy values. For uracil, thymine and adenine, interaction of the metal cations with the most stable tautomers form the least stable molecular complexes. For cytosine and guanine, the stability of the metalated complexes differs significantly. The enthalpy (ΔH), entropy (TΔS) and free energy (ΔG) of the complexes at 298 K have also been calculated.

  13. Density Functional Theory Study of Hydrogen Adsorption in a Ti-Decorated Mg-Based Metal-Organic Framework-74.

    PubMed

    Suksaengrat, Pitphichaya; Amornkitbamrung, Vittaya; Srepusharawoot, Pornjuk; Ahuja, Rajeev

    2016-03-16

    The Ti-binding energy and hydrogen adsorption energy of a Ti-decorated Mg-based metal-organic framework-74 (Mg-MOF-74) were evaluated by using first-principles calculations. Our results revealed that only three Ti adsorption sites were found to be stable. The adsorption site near the metal oxide unit is the most stable. To investigate the hydrogen-adsorption properties of Ti-functionalized Mg-MOF-74, the hydrogen-binding energy was determined. For the most stable Ti adsorption site, we found that the hydrogen adsorption energy ranged from 0.26 to 0.48 eV H2 (-1) . This is within the desirable range for practical hydrogen-storage applications. Moreover, the hydrogen capacity was determined by using ab initio molecular dynamics simulations. Our results revealed that the hydrogen uptake by Ti-decorated Mg-MOF-74 at temperatures of 77, 150, and 298 K and ambient pressure were 1.81, 1.74, and 1.29 H2  wt %, respectively. PMID:26717417

  14. Generalized Elliott-Yafet theory of electron spin relaxation in metals: origin of the anomalous electron spin lifetime in MgB2.

    PubMed

    Simon, F; Dóra, B; Murányi, F; Jánossy, A; Garaj, S; Forró, L; Bud'ko, S; Petrovic, C; Canfield, P C

    2008-10-24

    The temperature dependence of the electron-spin relaxation time in MgB2 is anomalous as it does not follow the resistivity above 150 K; it has a maximum around 400 K and decreases for higher temperatures. This violates the well established Elliot-Yafet theory of spin relaxation in metals. The anomaly occurs when the quasiparticle scattering rate (in energy units) is comparable to the energy difference between the conduction and a neighboring bands. The anomalous behavior is related to the unique band structure of MgB2 and the large electron-phonon coupling. The saturating spin relaxation is the spin transport analogue of the Ioffe-Regel criterion of electron transport.

  15. Design of spin-forbidden transitions for polypyridyl metal complexes by time-dependent density functional theory including spin-orbit interaction.

    PubMed

    Kanno, Shohei; Imamura, Yutaka; Hada, Masahiko

    2016-05-25

    We explore spin-forbidden transitions for a Ru dye with an N3 skeleton and an Fe dye with a DX1 skeleton by time-dependent density functional theory with spin-orbit interaction. The modified N3-based Ru dye with iodine anions has an absorption edge in the long wavelength region which is not observed in the original N3 dye. The long wavelength absorption edge originates from the spin-orbit interaction with iodine. Although the Fe dye has a small spin-orbit interaction, because of less spin-orbit interaction from the light metal, spin-forbidden transitions also occur for DX1-based Fe dye systems with iodine anions. This result indicates that the introduction of iodine can strengthen the spin-orbit interaction for a dye sensitizer and offers a new approach for designing spin-forbidden transitions.

  16. Spin and orbital magnetism of coinage metal trimers (Cu{sub 3}, Ag{sub 3}, Au{sub 3}): A relativistic density functional theory study

    SciTech Connect

    Afshar, Mahdi; Sargolzaei, Mohsen

    2013-11-15

    We have demonstrated electronic structure and magnetic properties of Cu{sub 3}, Ag{sub 3} and Au{sub 3} trimers using a full potential local orbital method in the framework of relativistic density functional theory. We have also shown that the non-relativistic generalized gradient approximation for the exchange-correlation energy functional gives reliable magnetic properties in coinage metal trimers compared to experiment. In addition we have indicated that the spin-orbit coupling changes the structure and magnetic properties of gold trimer while the structure and magnetic properties of copper and silver trimers are marginally affected. A significant orbital moment of 0.21μ{sub B} was found for most stable geometry of the gold trimer whereas orbital magnetism is almost quenched in the copper and silver trimers.

  17. First-principles theory of field-effect doping in transition-metal dichalcogenides: Structural properties, electronic structure, Hall coefficient, and electrical conductivity

    NASA Astrophysics Data System (ADS)

    Brumme, Thomas; Calandra, Matteo; Mauri, Francesco

    2015-04-01

    We investigate how field-effect doping affects the structural properties, the electronic structure, and the Hall coefficient of few-layers transition-metal dichalcogenides by using density-functional theory. We consider monolayers, bilayers, and trilayers of the H polytype of MoS2, MoSe2, MoTe2, WS2, and WSe2 and provide a full database of electronic structures and Hall coefficients for hole and electron doping. We find that, for both electron and hole doping, the electronic structure depends on the number of layers and cannot be described by a rigid band shift. Furthermore, it is important to relax the structure under the asymmetric electric field. Interestingly, while the width of the conducting channel depends on the doping, the number of occupied bands at each given k point is almost uncorrelated with the thickness of the doping-charge distribution. Finally, we calculate within the constant-relaxation-time approximation the electrical conductivity and the inverse Hall coefficient. We demonstrate that in some cases the charge determined by Hall-effect measurements can deviate from the real charge by up to 50%. For hole-doped MoTe2 the Hall charge has even the wrong polarity at low temperature. We provide the mapping between the doping charge and the Hall coefficient. We present more than 250 band structures for all doping levels of the transition-metal dichalcogenides considered within this work.

  18. Cohesive properties of noble metals by van der Waals-corrected density functional theory: Au, Ag, and Cu as case studies

    NASA Astrophysics Data System (ADS)

    Ambrosetti, Alberto; Silvestrelli, Pier Luigi

    2016-07-01

    The cohesive energy, equilibrium lattice constant, and bulk modulus of Au, Ag, and Cu noble metals are computed by different van der Waals (vdW)-corrected density functional theory (DFT) methods, including vdW-DF, vdW-DF2, vdW-DF-cx, rVV10, and PBE-D. Two specifically designed methods are also developed in order to effectively include dynamical screening effects: the DFT/vdW-WF2p method, based on the generation of maximally localized Wannier functions, and the RPAp scheme (in two variants), based on a single-oscillator model of the localized electron response. Comparison with results obtained without explicit inclusion of van der Waals effects, such as with the local density approximation (LDA), PBE, PBEsol, or the hybrid PBE0 functional, elucidates the importance of a suitable description of screened van der Waals interactions even in the case of strong metal bonding. Many-body effects are also quantitatively evaluated within the RPAp approach.

  19. Two-parameter scaling theory of the longitudinal magnetoconductivity in a Weyl metal phase: Chiral anomaly, weak disorder, and finite temperature

    NASA Astrophysics Data System (ADS)

    Kim, Kyoung-Min; Shin, Dongwoo; Sasaki, M.; Kim, Heon-Jung; Kim, Jeehoon; Kim, Ki-Seok

    2016-08-01

    It is at the heart of modern condensed matter physics to investigate the role of a topological structure in anomalous transport phenomena. In particular, chiral anomaly turns out to be the underlying mechanism for the negative longitudinal magnetoresistivity in a Weyl metal phase. The existence of a dissipationless current channel causes enhancement of electric currents along the direction of a pair of Weyl points or applied magnetic fields (B ). However, temperature (T ) dependence of the negative longitudinal magnetoresistivity has not been understood yet in the presence of disorder scattering since it is not clear at all how to introduce effects of disorder scattering into the topological-in-origin transport coefficient at finite temperatures. The calculation based on the Kubo formula of the current-current correlation function is simply not known for this anomalous transport coefficient. Combining the renormalization group analysis with the Boltzmann transport theory to encode the chiral anomaly, we reveal how disorder scattering renormalizes the distance between a pair of Weyl points and such a renormalization effect modifies the topological-in-origin transport coefficient at finite temperatures. As a result, we find breakdown of B /T scaling, given by B /T1 +η with 0 <η <1 . This breakdown may be regarded to be a fingerprint of the interplay between disorder scattering and topological structure in a Weyl metal phase.

  20. Simulating Ru L3-edge X-ray Absorption Spectroscopy with Time-Dependent Density Functional Theory: Model Complexes and Electron Localization in Mixed-Valence Metal Dimers

    SciTech Connect

    Van Kuiken, Benjamin E.; Valiev, Marat; Daifuku, Stephanie L.; Bannan, Caitlin; Strader, Matthew L.; Cho, Hana; Huse, N.; Schoenlein, R. W.; Govind, Niranjan; Khalil, Munira

    2013-05-01

    Ruthenium L2,3-edge X-ray absorption (XA) spectroscopy probes transitions from core 2p orbitals to the 4d levels of the atom and is a powerful tool for interrogating the local electronic and molecular structure around the metal atom. However, a molecular-level interpretation of the Ru L2,3-edge spectral lineshapes is often complicated by spin–orbit coupling (SOC) and multiplet effects. In this study, we develop spin-free time-dependent density functional theory (TDDFT) as a viable and predictive tool to simulate the Ru L3-edge spectra. We successfully simulate and analyze the ground state Ru L3-edge XA spectra of a series of RuII and RuIII complexes: [Ru(NH3)6]2+/3+, [Ru(CN)6]4-/3-, [RuCl6]4-/3-, and the ground (1A1) and photoexcited (3MLCT) transient states of [Ru(bpy)3]2+ and Ru(dcbpy)2(NCS)2 (termed N3). The TDDFT simulations reproduce all the experimentally observed features in Ru L3-edge XA spectra. The advantage of using TDDFT to assign complicated Ru L3-edge spectra is illustrated by its ability to identify ligand specific charge transfer features in complex molecules. We conclude that the B3LYP functional is the most reliable functional for accurately predicting the location of charge transfer features in these spectra. Experimental and simulated Ru L3-edge XA spectra are presented for the transition metal mixed-valence dimers [(NC)5MII-CN-RuIII(NH3)5]- (where M = Fe or Ru) dissolved in water. We explore the spectral signatures of electron delocalization in Ru L3-edge XA spectroscopy and our simulations reveal that the inclusion of explicit solvent molecules is crucial for reproducing the experimentally determined valencies, highlighting the importance of the role of the solvent in transition metal charge transfer chemistry.

  1. Structures and spectroscopic properties of nonperipherally and peripherally substituted metal-free phthalocyanines: a substitution effect study based on density functional theory calculations.

    PubMed

    Zhong, Aimin; Zhang, Yuexing; Bian, Yongzhong

    2010-11-01

    The molecular structures, molecular orbitals, atomic charges, electronic absorption spectra, and infrared (IR) and Raman spectra of a series of substituted metal-free phthalocyanine compounds with four (1, 3, 5, 7) or eight (2, 4, 6, 8) methoxyl (1, 2, 5, 6) or methylthio groups (3, 4, 7, 8) on the nonperipheral (1-4) or peripheral positions (5-8) of the phthalocyanine ring are studied by density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. The calculated structural parameters and simulated electronic absorption and IR spectra are compared with the X-ray crystallography structures and the experimentally observed electronic absorption and IR spectra of the similar molecules, and good agreement between the calculated and experimental results is found. The substitution of the methoxyl or methylthio groups at the nonperipheral positions of the phthalocyanine ring has obvious effects on the molecular structure and spectroscopic properties of the metal-free phthalocyanine. Nonperipheral substitution has a more significant influence than peripheral substitution. The substitution effect increases with an increase in the number of substituents. The methylthio group shows more significant influence than the methoxyl group, despite the stronger electron-donating property of the methoxyl group than the methylthio group. The octa-methylthio-substituted metal-free phthalocyanine compounds have nonplanar structures whose low-lying occupied molecular orbitals and electronic absorption spectra are significantly changed by the substituents. The present systematical study will be helpful for understanding the relationship between structures and properties in phthalocyanine compounds and designing phthalocyanines with typical properties.

  2. Compressibility and hardness of Co-based bulk metallic glass: A combined experimental and density functional theory study

    SciTech Connect

    Wang Jianfeng; Li Ran; Xu Tao; Li Yan; Liu Zengqian; Huang Lu; Hua Nengbin; Zhang Tao; Xiao Ruijuan; Li Gong; Li Yanchun

    2011-10-10

    An incompressible Co{sub 54}Ta{sub 11}B{sub 35} bulk metallic glass (BMG) was investigated using in situ high-pressure synchrotron diffraction and nanoindendation. The elastic constants were deduced from the experiments based on the isotropic model. The Vickers hardness was measured to be 17.1 GPa. The elastic moduli and hardness are the highest values known in BMGs. The theoretically calculated elastic properties by density-functional study were well consistent with experimental measurements. The analysis of charge density and bonding character indicates the covalent character of Co-B and B-B bonds, underlying the unusually high elastic modulus and hardness in this material.

  3. Towards an ab initio theory for metal L-edge soft X-ray spectroscopy of molecular aggregates

    PubMed Central

    Preuße, Marie; Bokarev, Sergey I.; Aziz, Saadullah G.; Kühn, Oliver

    2016-01-01

    The Frenkel exciton model was adapted to describe X-ray absorption and resonant inelastic scattering spectra of polynuclear transition metal complexes by means of the restricted active space self-consistent field method. The proposed approach allows to substantially decrease the requirements on computational resources if compared to a full supermolecular quantum chemical treatment. This holds true, in particular, in cases where the dipole approximation to the electronic transition charge density can be applied. The computational protocol was applied to the calculation of X-ray spectra of the hemin complex, which forms dimers in aqueous solution. The aggregation effects were found to be comparable to the spectral alterations due to the replacement of the axial ligand by solvent molecules.

  4. Structure and electronic properties of MoVO type mixed-metal oxides - a combined view by experiment and theory.

    PubMed

    Chiu, Cheng-Chau; Vogt, Thomas; Zhao, Lili; Genest, Alexander; Rösch, Notker

    2015-08-21

    In this review we address recent efforts from experimental and theoretical side to study MoVO-type mixed metal oxides (MMOs) and their properties. We illustrate how structures of MMOs have been evaluated using a large variety of experimental techniques, such as electron microscopy, neutron diffraction, and X-ray diffraction. Furthermore, we discuss the current view on structure-catalysis correlations, derived from recent experiments. In a second part, we examine useful tools of theoretical chemistry for exploring MoVO-type systems. We discuss the need for using hybrid DFT methods and we analyze how, in the context of MMOs studies, semi-local DFT approximations can encounter problems due to a notable self-interaction error when describing oxidic species and reactions on them. In addition, we discuss various aspects of the model that are important when attempting to map complex MMO systems. PMID:26126874

  5. Effects of matching conditions in effective-mass theory: Quantum wells, transmission, and metal-induced gap states

    NASA Astrophysics Data System (ADS)

    Harrison, Walter A.

    2011-12-01

    Kroemer and Zhu have shown that the traditional matching of wavefunctions between regions of different effective mass (matching ψ and (1/m*)∂ψ/∂x) is not correct, but that one should match (1/√m*)ψ and (1/√m*)∂ψ/∂x. It has not been clear how serious the error is in using the traditional formula. We apply the two sets of conditions to the calculation of quantum-well states, to the transmission of an interface, and to the formation of metal-induced gap states (MIGS). We find that the predicted effects due to mass difference by the traditional formula are not even qualitatively correct in the first two cases and very much underestimated for the shifts in Schottky-barrier height due to MIGS. The MIGS shifts however always remain very small.

  6. Towards an ab initio theory for metal L-edge soft X-ray spectroscopy of molecular aggregates.

    PubMed

    Preuße, Marie; Bokarev, Sergey I; Aziz, Saadullah G; Kühn, Oliver

    2016-11-01

    The Frenkel exciton model was adapted to describe X-ray absorption and resonant inelastic scattering spectra of polynuclear transition metal complexes by means of the restricted active space self-consistent field method. The proposed approach allows to substantially decrease the requirements on computational resources if compared to a full supermolecular quantum chemical treatment. This holds true, in particular, in cases where the dipole approximation to the electronic transition charge density can be applied. The computational protocol was applied to the calculation of X-ray spectra of the hemin complex, which forms dimers in aqueous solution. The aggregation effects were found to be comparable to the spectral alterations due to the replacement of the axial ligand by solvent molecules. PMID:27679809

  7. Towards an ab initio theory for metal L-edge soft X-ray spectroscopy of molecular aggregates

    PubMed Central

    Preuße, Marie; Bokarev, Sergey I.; Aziz, Saadullah G.; Kühn, Oliver

    2016-01-01

    The Frenkel exciton model was adapted to describe X-ray absorption and resonant inelastic scattering spectra of polynuclear transition metal complexes by means of the restricted active space self-consistent field method. The proposed approach allows to substantially decrease the requirements on computational resources if compared to a full supermolecular quantum chemical treatment. This holds true, in particular, in cases where the dipole approximation to the electronic transition charge density can be applied. The computational protocol was applied to the calculation of X-ray spectra of the hemin complex, which forms dimers in aqueous solution. The aggregation effects were found to be comparable to the spectral alterations due to the replacement of the axial ligand by solvent molecules. PMID:27679809

  8. Bio-inspired transition metal-organic hydride conjugates for catalysis of transfer hydrogenation: experiment and theory.

    PubMed

    McSkimming, Alex; Chan, Bun; Bhadbhade, Mohan M; Ball, Graham E; Colbran, Stephen B

    2015-02-01

    Taking inspiration from yeast alcohol dehydrogenase (yADH), a benzimidazolium (BI(+) ) organic hydride-acceptor domain has been coupled with a 1,10-phenanthroline (phen) metal-binding domain to afford a novel multifunctional ligand (L(BI+) ) with hydride-carrier capacity (L(BI+) +H(-) ⇌L(BI) H). Complexes of the type [Cp*M(L(BI) )Cl][PF6 ]2 (M=Rh, Ir) have been made and fully characterised by cyclic voltammetry, UV/Vis spectroelectrochemistry, and, for the Ir(III) congener, X-ray crystallography. [Cp*Rh(L(BI) )Cl][PF6 ]2 catalyses the transfer hydrogenation of imines by formate ion in very goods yield under conditions where the corresponding [Cp*Ir(L(BI) )Cl][PF6 ] and [Cp*M(phen)Cl][PF6 ] (M=Rh, Ir) complexes are almost inert as catalysts. Possible alternatives for the catalysis pathway are canvassed, and the free energies of intermediates and transition states determined by DFT calculations. The DFT study supports a mechanism involving formate-driven RhH formation (90 kJ mol(-1) free-energy barrier), transfer of hydride between the Rh and BI(+) centres to generate a tethered benzimidazoline (BIH) hydride donor, binding of imine substrate at Rh, back-transfer of hydride from the BIH organic hydride donor to the Rh-activated imine substrate (89 kJ mol(-1) barrier), and exergonic protonation of the metal-bound amide by formic acid with release of amine product to close the catalytic cycle. Parallels with the mechanism of biological hydride transfer in yADH are discussed.

  9. Rapid Electron Transport Phenomenon in the Bis(terpyridine) Metal Complex Wire: Marcus Theory and Electrochemical Impedance Spectroscopy Study.

    PubMed

    Maeda, Hiroaki; Sakamoto, Ryota; Nishihara, Hiroshi

    2015-10-01

    The authors reported previously that bis(terpyiridne)iron(II) complex oligomer wires possess outstanding long-range intrawire electron transport ability. Here, molecular arrays of gold-electrode-bis(terpyridine)iron(II)-ferrocene are constructed by stepwise coordination as simple models of the oligomer wire system. The fast electron transfer between the terminal ferrocene and the gold electrode through the bis(terpyiridne)iron(II) complex unit is studied by potential step chronoamperometry (PSCA) and electrochemical impedance spectroscopy (EIS). Tafel plots derived from PSCA are analyzed based on Marcus theory. The plots reveal greater first-order electron transfer rate constant, weaker electronic coupling between the terminal ferrocene and the gold electrode, and smaller reorganization energy than shown by a conventional ferrocenylalkanethiol self-assembled monolayer. The electron transfer rate constants estimated by EIS agree with the PSCA results.

  10. Four-Component Damped Density Functional Response Theory Study of UV/Vis Absorption Spectra and Phosphorescence Parameters of Group 12 Metal-Substituted Porphyrins.

    PubMed

    Fransson, Thomas; Saue, Trond; Norman, Patrick

    2016-05-10

    The influences of group 12 (Zn, Cd, Hg) metal-substitution on the valence spectra and phosphorescence parameters of porphyrins (P) have been investigated in a relativistic setting. In order to obtain valence spectra, this study reports the first application of the damped linear response function, or complex polarization propagator, in the four-component density functional theory framework [as formulated in Villaume et al. J. Chem. Phys. 2010 , 133 , 064105 ]. It is shown that the steep increase in the density of states as due to the inclusion of spin-orbit coupling yields only minor changes in overall computational costs involved with the solution of the set of linear response equations. Comparing single-frequency to multifrequency spectral calculations, it is noted that the number of iterations in the iterative linear equation solver per frequency grid-point decreases monotonously from 30 to 0.74 as the number of frequency points goes from one to 19. The main heavy-atom effect on the UV/vis-absorption spectra is indirect and attributed to the change of point group symmetry due to metal-substitution, and it is noted that substitutions using heavier atoms yield small red-shifts of the intense Soret-band. Concerning phosphorescence parameters, the adoption of a four-component relativistic setting enables the calculation of such properties at a linear order of response theory, and any higher-order response functions do not need to be considered-a real, conventional, form of linear response theory has been used for the calculation of these parameters. For the substituted porphyrins, electronic coupling between the lowest triplet states is strong and results in theoretical estimates of lifetimes that are sensitive to the wave function and electron density parametrization. With this in mind, we report our best estimates of the phosphorescence lifetimes to be 460, 13.8, 11.2, and 0.00155 s for H2P, ZnP, CdP, and HgP, respectively, with the corresponding transition

  11. Four-Component Damped Density Functional Response Theory Study of UV/Vis Absorption Spectra and Phosphorescence Parameters of Group 12 Metal-Substituted Porphyrins.

    PubMed

    Fransson, Thomas; Saue, Trond; Norman, Patrick

    2016-05-10

    The influences of group 12 (Zn, Cd, Hg) metal-substitution on the valence spectra and phosphorescence parameters of porphyrins (P) have been investigated in a relativistic setting. In order to obtain valence spectra, this study reports the first application of the damped linear response function, or complex polarization propagator, in the four-component density functional theory framework [as formulated in Villaume et al. J. Chem. Phys. 2010 , 133 , 064105 ]. It is shown that the steep increase in the density of states as due to the inclusion of spin-orbit coupling yields only minor changes in overall computational costs involved with the solution of the set of linear response equations. Comparing single-frequency to multifrequency spectral calculations, it is noted that the number of iterations in the iterative linear equation solver per frequency grid-point decreases monotonously from 30 to 0.74 as the number of frequency points goes from one to 19. The main heavy-atom effect on the UV/vis-absorption spectra is indirect and attributed to the change of point group symmetry due to metal-substitution, and it is noted that substitutions using heavier atoms yield small red-shifts of the intense Soret-band. Concerning phosphorescence parameters, the adoption of a four-component relativistic setting enables the calculation of such properties at a linear order of response theory, and any higher-order response functions do not need to be considered-a real, conventional, form of linear response theory has been used for the calculation of these parameters. For the substituted porphyrins, electronic coupling between the lowest triplet states is strong and results in theoretical estimates of lifetimes that are sensitive to the wave function and electron density parametrization. With this in mind, we report our best estimates of the phosphorescence lifetimes to be 460, 13.8, 11.2, and 0.00155 s for H2P, ZnP, CdP, and HgP, respectively, with the corresponding transition

  12. Targeted Protein Degradation of Outer Membrane Decaheme Cytochrome MtrC Metal Reductase in Shewanella oneidensis MR-1 Measured Using Biarsenical Probe CrAsH-EDT2

    SciTech Connect

    Xiong, Yijia; Chen, Baowei; Shi, Liang; Fredrickson, Jim K.; Bigelow, Diana J.; Squier, Thomas C.

    2011-10-14

    Development of efficient microbial biofuel cells requires an ability to exploit interfacial electron transfer reactions to external electron acceptors, such as metal oxides; such reactions occur in the facultative anaerobic gram-negative bacterium Shewanella oneidensis MR-1 through the catalytic activity of the outer membrane decaheme c-type cytochrome MtrC. Central to the utility of this pathway to synthetic biology is an understanding of cellular mechanisms that maintain optimal MtrC function, cellular localization, and renewal by degradation and resynthesis. In order to monitor trafficking to the outer membrane, and the environmental sensitivity of MtrC, we have engineered a tetracysteine tag (i.e., CCPGCC) at its C-terminus that permits labeling by the cell impermeable biarsenical fluorophore, carboxy-FlAsH (CrAsH) of MtrC at the surface of living Shewanella oneidensis MR-1 cells. In comparison, the cell permeable reagent FlAsH permits labeling of the entire population of MtrC, including proteolytic fragments resulting from incorrect maturation. We demonstrate specific labeling by CrAsH of engineered MtrC which is dependent on the presence of a functional type-2 secretion system (T2S), as evidenced by T2S system gspD or gspG deletion mutants which are incapable of CrAsH labeling. Under these latter conditions, MtrC undergoes proteolytic degradation to form a large 35-38 kDa fragment; this degradation product is also resolved during normal turnover of the CrAsH-labeled MtrC protein. No MtrC protein is released into the medium during turnover, suggesting the presence of cellular turnover systems involving MtrC reuptake and degradation. The mature MtrC localized on the outer membrane is a long-lived protein, with a turnover rate of 0.043 hr-1 that is insensitive to O2 concentration. Maturation of MtrC is relatively inefficient, with substantial rates of turnover of the immature protein prior to export to the outer membrane (i.e., 0.028 hr-1) that are consistent

  13. A quantitatively accurate theory of stable crack growth in single phase ductile metal alloys under the influence of cyclic loading

    NASA Astrophysics Data System (ADS)

    Huffman, Peter oel

    Although fatigue has been a well studied phenomenon over the past century and a half, there has yet to be found a quantitative link between fatigue crack growth rates and materials properties. This work serves to establish that link, in the case of well behaved, single phase, ductile metals. The primary mechanisms of fatigue crack growth are identified in general terms, followed by a description of the dependence of the stress intensity factor range on those mechanisms. A method is presented for calculating the crack growth rate for an ideal, linear elastic, non-brittle material, which is assumed to be similar to the crack growth rate for a real material at very small crack growth rate values. The threshold stress intensity factor is discussed as a consequence of "crack tip healing". Residual stresses are accounted for in the form of an approximated residual stress intensity factor. The results of these calculations are compared to data available in the literature. It is concluded that this work presents a new way to consider crack growth with respect to cyclic loading which is quantitatively accurate, and introduces a new way to consider fracture mechanics with respect to the relatively small, cyclic loads, normally associated with fatigue.

  14. A Thermodynamic Model for Predicting Phosphorus Partition between CaO-based Slags and Hot Metal during Hot Metal Dephosphorization Pretreatment Process Based on the Ion and Molecule Coexistence Theory

    NASA Astrophysics Data System (ADS)

    Yang, Xue-min; Li, Jin-yan; Chai, Guo-ming; Duan, Dong-ping; Zhang, Jian

    2016-08-01

    A thermodynamic model for predicting phosphorus partition L P between a CaO-based slags and hot metal during hot metal dephosphorization pretreatment process has been developed based on the ion and molecule coexistence theory (IMCT), i.e., the IMCT- L P model. The reaction abilities of structural units or ion couples in the CaO-based slags have been represented by the calculated mass action concentrations N i through the developed IMCT- N i model based on the IMCT. The developed IMCT- L P model has been verified to be valid through comparing with the measured L P as well as the predicted L P by two reported L P models from the literature. Besides the total phosphorus partition L P between the CaO-based slag and hot metal, the respective phosphorus partitions L P, i of nine dephosphorization products as P2O5, 3FeO·P2O5, 4FeO·P2O5, 2CaO·P2O5, 3CaO·P2O5, 4CaO·P2O5, 2MgO·P2O5, 3MgO·P2O5, and 3MnO·P2O5 can also be accurately predicted by the developed IMCT- L P model. The formed 3CaO·P2O5 accounts for 99.20 pct of dephosphorization products comparing with the generated 4CaO·P2O5 for 0.08 pct. The comprehensive effect of CaO+Fe t O, which can be described by the mass percentage ratio (pct Fe t O)/(pct CaO) or the mass action concentration ratio N_{Fe}t O/N_{Fe}t O N_{CaO}. N_{CaO}} as well as the mass percentage product (pct Fe t O) × (pct CaO) or the mass action concentration product N_{{{{Fe}}t {{O}}}}5 × N_{{CaO}}3 , controls dephosphorization ability of the CaO-based slags. A linear relationship of L P against (pct Fe t O)/(pct CaO) can be correlated compared with a parabolic relationship of L P against N_{Fe}t O/N_{Fe}t O N_{CaO}. N_{CaO}, while the linear relationship of L P against (pct Fe t O) × (pct CaO) or N_{Fe}t O5 × N_{CaO}3 can be established. Thus, the mass percentage product (pct Fe t O) × (pct CaO) and the mass action concentration product N_{Fe}t O5 × N_{CaO}3 are recommended to represent the comprehensive effect of CaO+Fe t O on

  15. Processes for the production of ultra-pure metals from oxide and their cold rolling to ultra-thin foils for use as targets and as reference materials

    NASA Astrophysics Data System (ADS)

    Clifford, S.; Guo-ji, Xu; Ingelbrecht, C.; Pomeroy, M. J.

    2002-03-01

    A wide variety of metals have been reduced from their oxides with high (>90%) yields using metallothermic reduction, hydrogen reduction or electrowinning. The high yields during metallothermic reduction were achieved by careful design of the collector and crucible orifice. Whilst each of the three techniques gave rise to reasonably (>99%) pure metals, subsequent carefully controlled vacuum distillation, using a system with especially designed crucible, baffle and collector systems, resulted in ultra-high-purity metals being produced. Using a stainless steel pack rolling technique, metals derived either directly from the reduction routes or following subsequent distillation could be rolled to foils thinner than previously reported in the literature in the majority of cases.

  16. Simulating Ru L3-Edge X-ray Absorption Spectroscopy with Time-Dependent Density Functional Theory: Model Complexes and Electron Localization in Mixed-Valence Metal Dimers

    SciTech Connect

    Kuiken, Benjamin E. Van; Valiev, Marat; Daifuku, Stephanie L.; Bannan, Caitlin; Strader, Matthew L.; Cho, Hana; Huse, Nils; Schoenlein, Robert W.; Govind, Niranjan; Khalil, Munira

    2013-04-26

    Ruthenium L3-edge X-ray absorption (XA) spectroscopy probes unoccupied 4d orbitals of the metal atom and is increasingly being used to investigate the local electronic structure in ground and excited electronic states of Ru complexes. The simultaneous development of computational tools for simulating Ru L3-edge spectra is crucial for interpreting the spectral features at a molecular level. This study demonstrates that time-dependent density functional theory (TDDFT) is a viable and predictive tool for simulating ruthenium L3-edge XA spectroscopy. We systematically investigate the effects of exchange correlation functional and implicit and explicit solvent interactions on a series of RuII and RuIII complexes in their ground and electronic excited states. The TDDFT simulations reproduce all of the experimentally observed features in Ru L3-edge XA spectra within the experimental resolution (0.4 eV). Our simulations identify ligand-specific charge transfer features in complicated Ru L3-edge spectra of [Ru(CN)6]4- and RuII polypyridyl complexes illustrating the advantage of using TDDFT in complex systems. We conclude that the B3LYP functional most accurately predicts the transition energies of charge transfer features in these systems. We use our TDDFT approach to simulate experimental Ru L3-edge XA spectra of transition metal mixed-valence dimers of the form [(NC)5MII-CN-RuIII(NH3)5] (where M = Fe or Ru) dissolved in water. Our study determines the spectral signatures of electron delocalization in Ru L3-edge XA spectra. We find that the inclusion of explicit solvent molecules is necessary for reproducing the spectral features and the experimentally determined valencies in these mixed-valence complexes. This study validates the use of TDDFT for simulating Ru 2p excitations using popular quantum chemistry codes and providing a powerful interpretive tool for equilibrium and ultrafast Ru L3-edge XA spectroscopy.

  17. Carbon K-edge X-ray absorption spectroscopy and time-dependent density functional theory examination of metal-carbon bonding in metallocene dichlorides.

    PubMed

    Minasian, Stefan G; Keith, Jason M; Batista, Enrique R; Boland, Kevin S; Kozimor, Stosh A; Martin, Richard L; Shuh, David K; Tyliszczak, Tolek; Vernon, Louis J

    2013-10-01

    Metal-carbon covalence in (C5H5)2MCl2 (M = Ti, Zr, Hf) has been evaluated using carbon K-edge X-ray absorption spectroscopy (XAS) as well as ground-state and time-dependent hybrid density functional theory (DFT and TDDFT). Differences in orbital mixing were determined experimentally using transmission XAS of thin crystalline material with a scanning transmission X-ray microscope (STXM). Moving down the periodic table (Ti to Hf) has a marked effect on the experimental transition intensities associated with the low-lying antibonding 1a1* and 1b2* orbitals. The peak intensities, which are directly related to the M-(C5H5) orbital mixing coefficients, increase from 0.08(1) and 0.26(3) for (C5H5)2TiCl2 to 0.31(3) and 0.75(8) for (C5H5)2ZrCl2, and finally to 0.54(5) and 0.83(8) for (C5H5)2HfCl2. The experimental trend toward increased peak intensity for transitions associated with 1a1* and 1b2* orbitals agrees with the calculated TDDFT oscillator strengths [0.10 and 0.21, (C5H5)2TiCl2; 0.21 and 0.73, (C5H5)2ZrCl2; 0.35 and 0.69, (C5H5)2HfCl2] and with the amount of C 2p character obtained from the Mulliken populations for the antibonding 1a1* and 1b2* orbitals [8.2 and 23.4%, (C5H5)2TiCl2; 15.3 and 39.7%, (C5H5)2ZrCl2; 20.1 and 50.9%, (C5H5)2HfCl2]. The excellent agreement between experiment, theory, and recent Cl K-edge XAS and DFT measurements shows that C 2p orbital mixing is enhanced for the diffuse Hf (5d) and Zr (4d) atomic orbitals in relation to the more localized Ti (3d) orbitals. These results provide insight into how changes in M-Cl orbital mixing within the metallocene wedge are correlated with periodic trends in covalent bonding between the metal and the cyclopentadienide ancillary ligands.

  18. Square-antiprismatic eight-coordinate complexes of divalent first-row transition metal cations: a density functional theory exploration of the electronic-structural landscape.

    PubMed

    Conradie, Jeanet; Patra, Ashis K; Harrop, Todd C; Ghosh, Abhik

    2015-02-16

    Density functional theory (in the form of the PW91, BP86, OLYP, and B3LYP exchange-correlation functionals) has been used to map out the low-energy states of a series of eight-coordinate square-antiprismatic (D2d) first-row transition metal complexes, involving Mn(II), Fe(II), Co(II), Ni(II), and Cu(II), along with a pair of tetradentate N4 ligands. Of the five complexes, the Mn(II) and Fe(II) complexes have been synthesized and characterized structurally and spectroscopically, whereas the other three are as yet unknown. Each N4 ligand consists of a pair of terminal imidazole units linked by an o-phenylenediimine unit. The imidazole units are the strongest ligands in these complexes and dictate the spatial disposition of the metal three-dimensional orbitals. Thus, the dx(2)-y(2) orbital, whose lobes point directly at the coordinating imidazole nitrogens, has the highest orbital energy among the five d orbitals, whereas the dxy orbital has the lowest orbital energy. In general, the following orbital ordering (in order of increasing orbital energy) was found to be operative: dxy < dxz = dyz ≤ dz(2) < dx(2)-y(2). The square-antiprism geometry does not lead to large energy gaps between the d orbitals, which leads to an S = 2 ground state for the Fe(II) complex. Nevertheless, the dxy orbital has significantly lower energy relative to that of the dxz and dyz orbitals. Accordingly, the ground state of the Fe(II) complex corresponds unambiguously to a dxy(2)dxz(1)dyz(1)dz(2)(1)dx(2)-y(2)(1) electronic configuration. Unsurprisingly, the Mn(II) complex has an S = 5/2 ground state and no low-energy d-d excited states within 1.0 eV of the ground state. The Co(II) complex, on the other hand, has both a low-lying S = 1/2 state and multiple low-energy S = 3/2 states. Very long metal-nitrogen bonds are predicted for the Ni(II) and Cu(II) complexes; these bonds may be too fragile to survive in solution or in the solid state, and the complexes may therefore not be isolable

  19. Square-antiprismatic eight-coordinate complexes of divalent first-row transition metal cations: a density functional theory exploration of the electronic-structural landscape.

    PubMed

    Conradie, Jeanet; Patra, Ashis K; Harrop, Todd C; Ghosh, Abhik

    2015-02-16

    Density functional theory (in the form of the PW91, BP86, OLYP, and B3LYP exchange-correlation functionals) has been used to map out the low-energy states of a series of eight-coordinate square-antiprismatic (D2d) first-row transition metal complexes, involving Mn(II), Fe(II), Co(II), Ni(II), and Cu(II), along with a pair of tetradentate N4 ligands. Of the five complexes, the Mn(II) and Fe(II) complexes have been synthesized and characterized structurally and spectroscopically, whereas the other three are as yet unknown. Each N4 ligand consists of a pair of terminal imidazole units linked by an o-phenylenediimine unit. The imidazole units are the strongest ligands in these complexes and dictate the spatial disposition of the metal three-dimensional orbitals. Thus, the dx(2)-y(2) orbital, whose lobes point directly at the coordinating imidazole nitrogens, has the highest orbital energy among the five d orbitals, whereas the dxy orbital has the lowest orbital energy. In general, the following orbital ordering (in order of increasing orbital energy) was found to be operative: dxy < dxz = dyz ≤ dz(2) < dx(2)-y(2). The square-antiprism geometry does not lead to large energy gaps between the d orbitals, which leads to an S = 2 ground state for the Fe(II) complex. Nevertheless, the dxy orbital has significantly lower energy relative to that of the dxz and dyz orbitals. Accordingly, the ground state of the Fe(II) complex corresponds unambiguously to a dxy(2)dxz(1)dyz(1)dz(2)(1)dx(2)-y(2)(1) electronic configuration. Unsurprisingly, the Mn(II) complex has an S = 5/2 ground state and no low-energy d-d excited states within 1.0 eV of the ground state. The Co(II) complex, on the other hand, has both a low-lying S = 1/2 state and multiple low-energy S = 3/2 states. Very long metal-nitrogen bonds are predicted for the Ni(II) and Cu(II) complexes; these bonds may be too fragile to survive in solution or in the solid state, and the complexes may therefore not be isolable

  20. Density Functional Theory-Derived Group Additivity and Linear Scaling Methods for Prediction of Oxygenate Stability on Metal Catalysts. Adsorption of Open-Ring Alcohol and Polyol Dehydrogenation Intermediates on Pt-Based Metals

    SciTech Connect

    Salciccioli, Michael; Chen, Ying; Vlachos, Dion G.

    2010-11-09

    Semiempirical methods for prediction of thermochemical properties of adsorbed oxygenates are developed. Periodic density functional theory calculations are used to study the relative stability of ethanol, ethylene glycol, isopropyl alcohol, and glycerol dehydrogenation intermediates on Pt(111). For ethylene glycol dehydrogenation intermediates, it is found that the thermodynamically favored intermediates at each level of dehydrogenation are as follows: HOCH2CHOH, HOCHCHOH, HOCHCOH, HOCCOH ≈ HOCHCO, HOCCO, OCCO. Structural and energetic patterns emerge from these C2HxO2 adsorption calculations that lead to the formation of group additive properties for thermochemical property prediction of oxygenates on Pt(111). Finally, linear scaling relationships of atomic binding energy are used to predict the binding energy of the C2HxO2 species on the Ni(111) surface and Ni-Pt-Pt(111) bimetallic surface. It is shown that the linear scaling relationships can accurately predict the binding energy of larger oxygenates as well as of oxygenates on bimetallic catalysts. Corrections for ring strain and weak oxygen-metal and hydrogen-bonding interactions are added to increase the accuracy of group additivity and linear scaling relationships.

  1. CO2 capture properties of alkaline earth metal oxides and hydroxides: A combined density functional theory and lattice phonon dynamics study

    NASA Astrophysics Data System (ADS)

    Duan, Yuhua; Sorescu, Dan C.

    2010-08-01

    By combining density functional theory and lattice phonon dynamics, the thermodynamic properties of CO2 absorption/desorption reactions with alkaline earth metal oxides MO and hydroxides M(OH)2 (where M=Be,Mg,Ca,Sr,Ba) are analyzed. The heats of reaction and the chemical potential changes of these solids upon CO2 capture reactions have been calculated and used to evaluate the energy costs. Relative to CaO, a widely used system in practical applications, MgO and Mg(OH)2 systems were found to be better candidates for CO2 sorbent applications due to their lower operating temperatures (600-700 K). In the presence of H2O, MgCO3 can be regenerated into Mg(OH)2 at low temperatures or into MgO at high temperatures. This transition temperature depends not only on the CO2 pressure but also on the H2O pressure. Based on our calculated results and by comparing with available experimental data, we propose a general computational search methodology which can be used as a general scheme for screening a large number of solids for use as CO2 sorbents.

  2. Adsorption and ring-opening of lactide on the chiral metal surface Pt(321){sup S} studied by density functional theory

    SciTech Connect

    Franke, J.-H.; Kosov, D. S.

    2015-01-28

    We study the adsorption and ring-opening of lactide on the naturally chiral metal surface Pt(321){sup S}. Lactide is a precursor for polylactic acid ring-opening polymerization, and Pt is a well known catalyst surface. We study, here, the energetics of the ring-opening of lactide on a surface that has a high density of kink atoms. These sites are expected to be present on a realistic Pt surface and show enhanced catalytic activity. The use of a naturally chiral surface also enables us to study potential chiral selectivity effects of the reaction at the same time. Using density functional theory with a functional that includes the van der Waals forces in a first-principles manner, we find modest adsorption energies of around 1.4 eV for the pristine molecule and different ring-opened states. The energy barrier to be overcome in the ring-opening reaction is found to be very small at 0.32 eV and 0.30 eV for LL- and its chiral partner DD-lactide, respectively. These energies are much smaller than the activation energy for a dehydrogenation reaction of 0.78 eV. Our results thus indicate that (a) ring-opening reactions of lactide on Pt(321) can be expected already at very low temperatures, and Pt might be a very effective catalyst for this reaction; (b) the ring-opening reaction rate shows noticeable enantioselectivity.

  3. Cumulant Approximated Second-Order Perturbation Theory Based on the Density Matrix Renormalization Group for Transition Metal Complexes: A Benchmark Study.

    PubMed

    Phung, Quan Manh; Wouters, Sebastian; Pierloot, Kristine

    2016-09-13

    The complete active space second order perturbation theory (CASPT2) can be extended to larger active spaces by using the density matrix renormalization group (DMRG) as solver. Two variants are commonly used: the costly DMRG-CASPT2 with exact 4-particle reduced density matrix (4-RDM) and the cheaper DMRG-cu(4)-CASPT2 in which the 4-cumulant is discarded. To assess the accuracy and limitations of the latter variant DMRG-cu(4)-CASPT2 we study the spin state energetics of iron porphyrin Fe(P) and its model compound FeL2, a model for the active center of NiFe hydrogenase, and manganese-oxo porphyrin MnO(P)(+); a series of excited states of chromium hexacarbonyl Cr(CO)6; and the interconversion of two Cu2O2(2+) isomers. Our results clearly show that PT2 on top of DMRG is essential in order to obtain quantitative results for transition metal complexes. Good results were obtained with DMRG-cu(4)-CASPT2 as compared to full CASPT2 and DMRG-CASPT2 in calculations with small- and medium-sized active spaces. In calculations with large-sized active spaces (∼30 active orbitals), the performance of DMRG-cu(4)-CASPT2 is less impressive due to the errors originating from both the finite number of renormalized states m and the 4-RDM approximation. PMID:27547847

  4. Metal Preferences and Metallation*

    PubMed Central

    Foster, Andrew W.; Osman, Deenah; Robinson, Nigel J.

    2014-01-01

    The metal binding preferences of most metalloproteins do not match their metal requirements. Thus, metallation of an estimated 30% of metalloenzymes is aided by metal delivery systems, with ∼25% acquiring preassembled metal cofactors. The remaining ∼70% are presumed to compete for metals from buffered metal pools. Metallation is further aided by maintaining the relative concentrations of these pools as an inverse function of the stabilities of the respective metal complexes. For example, magnesium enzymes always prefer to bind zinc, and these metals dominate the metalloenzymes without metal delivery systems. Therefore, the buffered concentration of zinc is held at least a million-fold below magnesium inside most cells. PMID:25160626

  5. The Cost of Economic Literacy: How Well Does a Literacy-Targeted Principles of Economics Course Prepare Students for Intermediate Theory Courses?

    ERIC Educational Resources Information Center

    Gilleskie, Donna B.; Salemi, Michael K.

    2012-01-01

    In a typical economics principles course, students encounter a large number of concepts. In a literacy-targeted course, students study a "short list" of concepts that they can use for the rest of their lives. While a literacy-targeted principles course provides better education for nonmajors, it may place economic majors at a disadvantage in…

  6. Evaluating the Outcomes and Implementation of a TaMHS (Targeting Mental Health in Schools) Project in Four West Midlands (UK) Schools Using Activity Theory

    ERIC Educational Resources Information Center

    Cane, Fiona Eloise; Oland, Louise

    2015-01-01

    Government guidance in 2008 endorsed the "Targeting Mental Health in Schools" (TaMHS) agenda, which sets out to promote mental health in schools through the delivery of universal and targeted interventions. This paper initially defines mental health and outlines the TaMHS initiative. It then offers empirical findings from four focus…

  7. Incineration of doped sludges in fluidized bed. Fate and partitioning of six targeted heavy metals. I. Pilot plant used and results.

    PubMed

    Corella, J; Toledo, J M

    2000-12-30

    Incineration of sewage sludge doped with several heavy metals was studied at small pilot plant scale in a bubbling fluidized bed of 15cm i.d. and 5.2m height. Some ceramic and metallic filters were tested at a relatively high temperature (600-700 degrees C) to check their usefulness for partitioning of heavy metals in the flue gas. The work was focused on the fate of six selected heavy metals (Cr, Cd, Ni, Zn, Cu, Pb). In this process, there were four exit flows or discharges for these metals: bottom ash, coarse fly ash, cake filter or fine fly ash and flue exit gas. The distribution or partitioning of each heavy metal (HM) among these four exit flows was studied. Only cadmium and sometimes lead showed any difference between the different HMs considered. All other HMs seems to have the same fate, distribution or partitioning. Such distribution is governed or ruled by the fluid dynamics in the incinerator, cyclone and ceramic filter. Most of the HMs do not have enough residence time in this incinerator type to diffuse out of the ash particle and so remain in the particle. The amount of each HM in each exit flow in this process is governed by fluid dynamics and kinetics and not at all by thermodynamics.

  8. Inertial Confinement fusion targets

    NASA Technical Reports Server (NTRS)

    Hendricks, C. D.

    1982-01-01

    Inertial confinement fusion (ICF) targets are made as simple flat discs, as hollow shells or as complicated multilayer structures. Many techniques were devised for producing the targets. Glass and metal shells are made by using drop and bubble techniques. Solid hydrogen shells are also produced by adapting old methods to the solution of modern problems. Some of these techniques, problems, and solutions are discussed. In addition, the applications of many of the techniques to fabrication of ICF targets is presented.

  9. HYDROGEN ISOTOPE TARGETS

    DOEpatents

    Ashley, R.W.

    1958-08-12

    The design of targets for use in the investigation of nuclear reactions of hydrogen isotopes by bombardment with accelerated particles is described. The target con struction eomprises a backing disc of a metal selected from the group consisting of molybdenunn and tungsten, a eoating of condensed titaniunn on the dise, and a hydrogen isotope selected from the group consisting of deuterium and tritium absorbed in the coatiag. The proeess for preparing these hydrogen isotope targets is described.

  10. Critical assessment of chelant-enhanced metal phytoextraction.

    PubMed

    Nowack, Bernd; Schulin, Rainer; Robinson, Brett H

    2006-09-01

    Chelant-enhanced phytoextraction has received a lot of attention in the past decade. In theory, this technique could cleanse metal polluted soils by solubilizing contaminating metals, allowing them to be taken up by plants that would subsequently be removed from the site. We review the processes of metal solubilization, uptake by plants, and leaching during chelant-enhanced phytoextraction. A large excess of chelant is required to solubilize the target metal due to the co-solubilization of Ca and Fe. Chelated metals are taken up via the apoplastic pathway. Disruption of the Casparian Band is required to achieve the high shoot concentrations needed for phytoextraction. Therefore, adding chelants to a soil increases not only the total dissolved metal concentration but also changes the primary route of plant metal-uptake from the symplastic to the apoplastic pathway. Depending on metal, plant species, and chelant concentration, significant increases in metal uptake are likely. Soil solution chelate concentrations of at least several mM are required to induce appreciable shoot concentrations. A simple calculation reveals that at such soil solution concentrations plants will remove only a small fraction of the solubilized metals. Leaching, exacerbated by preferential flow processes, is unavoidable. Chelant-enhanced phytoextraction is therefore limited to areas where the connection with groundwater has been broken, orwhere leaching is unimportant. Chelant-enhanced phytoextraction may nonetheless have a role in enhancing the uptake of essential trace metals. Such a role warrants further investigations into the use of biodegradable chelants such as ethylenediaminedisuccinic acid (EDDS).

  11. Medical CT image reconstruction accuracy in the presence of metal objects using x-rays up to 1 MeV with x-ray targets of beryllium, carbon, aluminum, copper, and tungsten

    NASA Astrophysics Data System (ADS)

    Clayton, James; Ganguly, Arundhuti; Virshup, Gary

    2012-04-01

    Flat panels imagers based on amorphous silicon technology (a-Si) for digital radiography have been accepted by the medical community as having several advantages over film-based systems. Radiotherapy treatment planning systems employ computed tomographic (CT) data sets and projection images to delineate tumor targets and normal structures that are to be spared from radiation treatment. The accuracy of CT numbers is crucial for radiotherapy dose calculations. Conventional CT scanners operating at kilovoltage X-ray energies typically exhibit significant image reconstruction artifacts in the presence of metal implants in human body. Megavoltage X-ray energies have problems maintaining contrast sensitivity for the same dose as kV X-ray systems. We intend to demonstrate significant improvement in metal artifact reductions and electron density measurements using an amorphous silicon a-Si imager obtained with an X-ray source that can operate at energies up to 1 MeV. We will investigate the ability to maintain contrast sensitivity at this higher X-ray energy by using targets with lower atomic numbers and appropriate amounts of Xray filtration than are typically used as X-ray production targets and filters.

  12. An investigation of chlorine ligands in transition-metal complexes via ³⁵Cl solid-state NMR and density functional theory calculations.

    PubMed

    O'Keefe, Christopher A; Johnston, Karen E; Sutter, Kiplangat; Autschbach, Jochen; Gauvin, Régis; Trébosc, Julien; Delevoye, Laurent; Popoff, Nicolas; Taoufik, Mostafa; Oudatchin, Konstantin; Schurko, Robert W

    2014-09-15

    Chlorine ligands in a variety of diamagnetic transition-metal (TM) complexes in common structural motifs were studied using (35)Cl solid-state NMR (SSNMR), and insight into the origin of the observed (35)Cl NMR parameters was gained through first-principles density functional theory (DFT) calculations. The WURST-CPMG pulse sequence and the variable-offset cumulative spectrum (VOCS) methods were used to acquire static (35)Cl SSNMR powder patterns at both standard (9.4 T) and ultrahigh (21.1 T) magnetic field strengths, with the latter affording higher signal-to-noise ratios (S/N) and reduced experimental times (i.e., <1 h). Analytical simulations were performed to extract the (35)Cl electric field gradient (EFG) tensor and chemical shift (CS) tensor parameters. It was found that the chlorine ligands in various bonding environments (i.e., bridging, terminal-axial, and terminal-equatorial) have drastically different (35)Cl EFG tensor parameters, suggesting that (35)Cl SSNMR is ideal for characterizing chlorine ligands in TM complexes. A detailed localized molecular orbital (LMO) analysis was completed for NbCl5. It was found that the contributions of individual molecular orbitals must be considered to fully explain the observed EFG parameters, thereby negating simple arguments based on comparison of bond lengths and angles. Finally, we discuss the application of (35)Cl SSNMR for the structural characterization of WCl6 that has been grafted onto a silica support material. The resulting tungsten-chloride surface species is shown to be structurally distinct from the parent compound. PMID:25162702

  13. Influence of the reactive atmosphere on the formation of nanoparticles in the plasma plume induced by nanosecond pulsed laser irradiation of metallic targets at atmospheric pressure and high repetition rate

    NASA Astrophysics Data System (ADS)

    Girault, M.; Le Garrec, J.-L.; Mitchell, J. B. A.; Jouvard, J.-M.; Carvou, E.; Menneveux, J.; Yu, J.; Ouf, F.-X.; Carles, S.; Potin, V.; Pillon, G.; Bourgeois, S.; Perez, J.; Marco de Lucas, M. C.; Lavisse, L.

    2016-06-01

    The influence of a reactive atmosphere on the formation of nanoparticles (NPs) in the plasma plume generated by nanosecond pulsed laser irradiation of metal targets (Ti, Al, Ag) was probed in situ using Small Angle X-ray Scattering (SAXS). Air and different O2-N2 gas mixtures were used as reactive gas within atmospheric pressure. SAXS results showed the formation of NPs in the plasma-plume with a mean radius varying in the 2-5 nm range. A decrease of the NPs size with increasing the O2 percentage in the O2-N2 gas mixture was also showed. Ex situ observations by transmission electron microscopy and structural characterizations by X-ray diffraction and Raman spectroscopy were also performed for powders collected in experiments done using air as ambient gas. The stability of the different metal oxides is discussed as being a key parameter influencing the formation of NPs in the plasma-plume.

  14. Extending DFT-based genetic algorithms by atom-to-place re-assignment via perturbation theory: a systematic and unbiased approach to structures of mixed-metallic clusters.

    PubMed

    Weigend, Florian

    2014-10-01

    Energy surfaces of metal clusters usually show a large variety of local minima. For homo-metallic species the energetically lowest can be found reliably with genetic algorithms, in combination with density functional theory without system-specific parameters. For mixed-metallic clusters this is much more difficult, as for a given arrangement of nuclei one has to find additionally the best of many possibilities of assigning different metal types to the individual positions. In the framework of electronic structure methods this second issue is treatable at comparably low cost at least for elements with similar atomic number by means of first-order perturbation theory, as shown previously [F. Weigend, C. Schrodt, and R. Ahlrichs, J. Chem. Phys. 121, 10380 (2004)]. In the present contribution the extension of a genetic algorithm with the re-assignment of atom types to atom sites is proposed and tested for the search of the global minima of PtHf12 and [LaPb7Bi7](4-). For both cases the (putative) global minimum is reliably found with the extended technique, which is not the case for the "pure" genetic algorithm.

  15. Extending DFT-based genetic algorithms by atom-to-place re-assignment via perturbation theory: A systematic and unbiased approach to structures of mixed-metallic clusters

    SciTech Connect

    Weigend, Florian

    2014-10-07

    Energy surfaces of metal clusters usually show a large variety of local minima. For homo-metallic species the energetically lowest can be found reliably with genetic algorithms, in combination with density functional theory without system-specific parameters. For mixed-metallic clusters this is much more difficult, as for a given arrangement of nuclei one has to find additionally the best of many possibilities of assigning different metal types to the individual positions. In the framework of electronic structure methods this second issue is treatable at comparably low cost at least for elements with similar atomic number by means of first-order perturbation theory, as shown previously [F. Weigend, C. Schrodt, and R. Ahlrichs, J. Chem. Phys. 121, 10380 (2004)]. In the present contribution the extension of a genetic algorithm with the re-assignment of atom types to atom sites is proposed and tested for the search of the global minima of PtHf{sub 12} and [LaPb{sub 7}Bi{sub 7}]{sup 4−}. For both cases the (putative) global minimum is reliably found with the extended technique, which is not the case for the “pure” genetic algorithm.

  16. Human health risks from metals and metalloid via consumption of food animals near gold mines in Tarkwa, Ghana: estimation of the daily intakes and target hazard quotients (THQs).

    PubMed

    Bortey-Sam, Nesta; Nakayama, Shouta M M; Ikenaka, Yoshinori; Akoto, Osei; Baidoo, Elvis; Yohannes, Yared Beyene; Mizukawa, Hazuki; Ishizuka, Mayumi

    2015-01-01

    Heavy metal and metalloid contamination in food resulting from mining is of major concern due to the potential risk involved. Food consumption is the most likely route of human exposure to metals. This study was therefore to assess metals in different organs and different animal species near gold mines used for human consumption (free-range chicken, goat and sheep) in Tarkwa, Ghana, and to estimate the daily intake and health risk. The concentrations of Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Cd, and Pb were measured with an inductively coupled plasma-mass spectrometer and Hg analysis was done using the mercury analyzer. Principal component analysis of the results showed a clear separation between chicken, grouped on one side, and the ruminants clustered on another side in both offal and muscle. Interestingly, As, Cd, Hg, Mn and Pb made one cluster in the offal of chicken. Chicken muscle also showed similar distribution with As, Hg and Pb clustered together. The daily intake of metals (μg/kg body weight/day) were in the following ranges; As [0.002 (kidneys of goat and sheep)-0.19 (chicken gizzard)], Cd [0.003 (chicken muscle)-0.55 (chicken liver)], Hg [0.002 (goat muscle)-0.29 (chicken liver)], Pb [0.01 (muscles and kidneys of goat and sheep)-0.96 (chicken gizzard)] and Mn [0.13 (goat kidney)-8.92 (sheep liver)]. From the results, daily intakes of As, Cd, Hg, Pb and Mn in these food animals were low compared to the provisional tolerable daily intake guidelines. The THQs although less than one, indicated that contributions of chicken gizzard and liver to toxic metal exposure in adults and especially children could be significant.

  17. Ethanol and Water Adsorption on Transition-Metal 13-Atom Clusters: A Density Functional Theory Investigation within van der Waals Corrections.

    PubMed

    Zibordi-Besse, Larissa; Tereshchuk, Polina; Chaves, Anderson S; Da Silva, Juarez L F

    2016-06-23

    Transition-metal (TM) nanoparticles supported on oxides or carbon black have attracted much attention as potential catalysts for ethanol steam reforming reactions for hydrogen production. To improve the performance of nanocatalysts, a fundamental understanding of the interaction mechanism between water and ethanol with finite TM particles is required. In this article, we employed first-principles density functional theory with van der Waals (vdW) corrections to investigate the interaction of ethanol and water with TM13 clusters, where TM = Ni, Cu, Pd, Ag, Pt, and Au. We found that both water and ethanol bind via the anionic O atom to onefold TM sites, while at higher-energy structures, ethanol binds also via the H atom from the CH2 group to the TM sites, which can play an important role at real catalysts. The putative global minimum TM13 configurations are only slightly affected upon the adsorption of water or ethanol; however, for few systems, the compact higher-energy icosahedron structure changes its configuration upon ethanol or water adsorption. That is, those configurations are only shallow local minimums in the phase space. Except few deviations, we found similar trends for the magnitude of the adsorption energies of water and ethanol, that is, Ni13 > Pt13 > Pd13 and Cu13 > Au13 > Ag13, which is enhanced by the addition of the vdW correction (i.e., from 4% to 62%); however, the trend is the same. We found that the magnitude of the adsorption energy increases by shifting the center of gravity of the d-states toward the highest occupied molecular orbital. On the basis of the Mulliken and Hirshfeld charge analysis, as well as electron density differences, we identified the location of the charge redistribution and a tiny charge transfer (from 0.01 e to 0.19 e) from the molecules to the TM13 clusters. Our vibrational analysis indicates the red shifts in the OH modes upon binding of both water and ethanol molecules to the TM13 clusters, suggesting a weakening of

  18. Ethanol and Water Adsorption on Transition-Metal 13-Atom Clusters: A Density Functional Theory Investigation within van der Waals Corrections.

    PubMed

    Zibordi-Besse, Larissa; Tereshchuk, Polina; Chaves, Anderson S; Da Silva, Juarez L F

    2016-06-23

    Transition-metal (TM) nanoparticles supported on oxides or carbon black have attracted much attention as potential catalysts for ethanol steam reforming reactions for hydrogen production. To improve the performance of nanocatalysts, a fundamental understanding of the interaction mechanism between water and ethanol with finite TM particles is required. In this article, we employed first-principles density functional theory with van der Waals (vdW) corrections to investigate the interaction of ethanol and water with TM13 clusters, where TM = Ni, Cu, Pd, Ag, Pt, and Au. We found that both water and ethanol bind via the anionic O atom to onefold TM sites, while at higher-energy structures, ethanol binds also via the H atom from the CH2 group to the TM sites, which can play an important role at real catalysts. The putative global minimum TM13 configurations are only slightly affected upon the adsorption of water or ethanol; however, for few systems, the compact higher-energy icosahedron structure changes its configuration upon ethanol or water adsorption. That is, those configurations are only shallow local minimums in the phase space. Except few deviations, we found similar trends for the magnitude of the adsorption energies of water and ethanol, that is, Ni13 > Pt13 > Pd13 and Cu13 > Au13 > Ag13, which is enhanced by the addition of the vdW correction (i.e., from 4% to 62%); however, the trend is the same. We found that the magnitude of the adsorption energy increases by shifting the center of gravity of the d-states toward the highest occupied molecular orbital. On the basis of the Mulliken and Hirshfeld charge analysis, as well as electron density differences, we identified the location of the charge redistribution and a tiny charge transfer (from 0.01 e to 0.19 e) from the molecules to the TM13 clusters. Our vibrational analysis indicates the red shifts in the OH modes upon binding of both water and ethanol molecules to the TM13 clusters, suggesting a weakening of

  19. Metallic Hydrogen

    NASA Astrophysics Data System (ADS)

    Silvera, Isaac; Zaghoo, Mohamed; Salamat, Ashkan

    2015-03-01

    Hydrogen is the simplest and most abundant element in the Universe. At high pressure it is predicted to transform to a metal with remarkable properties: room temperature superconductivity, a metastable metal at ambient conditions, and a revolutionary rocket propellant. Both theory and experiment have been challenged for almost 80 years to determine its condensed matter phase diagram, in particular the insulator-metal transition. Hydrogen is predicted to dissociate to a liquid atomic metal at multi-megabar pressures and T =0 K, or at megabar pressures and very high temperatures. Thus, its predicted phase diagram has a broad field of liquid metallic hydrogen at high pressure, with temperatures ranging from thousands of degrees to zero Kelvin. In a bench top experiment using static compression in a diamond anvil cell and pulsed laser heating, we have conducted measurements on dense hydrogen in the region of 1.1-1.7 Mbar and up to 2200 K. We observe a first-order phase transition in the liquid phase, as well as sharp changes in optical transmission and reflectivity when this phase is entered. The optical signature is that of a metal. The mapping of the phase line of this transition is in excellent agreement with recent theoretical predictions for the long-sought plasma phase transition to metallic hydrogen. Research supported by the NSF, Grant DMR-1308641, the DOE Stockpile Stewardship Academic Alliance Program, Grant DE-FG52-10NA29656, and NASA Earth and Space Science Fellowship Program, Award NNX14AP17H.

  20. Low substrate temperature fabrication of high-performance metal oxide thin-film by magnetron sputtering with target self-heating

    SciTech Connect

    Yang, W. F.; Liu, Z. G.; Wu, Z. Y.; Hong, M. H.; Wang, C. F.; Lee, Alex Y. S.; Gong, H.

    2013-03-18

    Al-doped ZnO (AZO) films with high transmittance and low resistivity were achieved on low temperature substrates by radio frequency magnetron sputtering using a high temperature target. By investigating the effect of target temperature (T{sub G}) on electrical and optical properties, the origin of electrical conduction is verified as the effect of the high T{sub G}, which enhances crystal quality that provides higher mobility of electrons as well as more effective activation for the Al dopants. The optical bandgap increases from 3.30 eV for insulating ZnO to 3.77 eV for conducting AZO grown at high T{sub G}, and is associated with conduction-band filling up to 1.13 eV due to the Burstein-Moss effect.

  1. Assessment of the "6-31+G** + LANL2DZ" Mixed Basis Set Coupled with Density Functional Theory Methods and the Effective Core Potential: Prediction of Heats of Formation and Ionization Potentials for First-Row-Transition-Metal Complexes

    NASA Astrophysics Data System (ADS)

    Yang, Yue; Weaver, Michael N.; Merz, Kenneth M.

    2009-08-01

    Computational chemists have long demonstrated great interest in finding ways to reliably and accurately predict the molecular properties for transition-metal-containing complexes. This study is a continuation of our validation efforts of density functional theory (DFT) methods when applied to transition-metal-containing systems (Riley, K.E.; Merz, K. M., Jr. J. Phys. Chem. 2007, 111, 6044-6053). In our previous work we examined DFT using all-electron basis sets, but approaches incorporating effective core potentials (ECPs) are effective in reducing computational expense. With this in mind, our efforts were expanded to include evaluation of the performance of the basis set derived to approximate such an approach as well on the same set of density functionals. Indeed, employing an ECP basis such as LANL2DZ (Los Alamos National Laboratory 2 double ζ) for transition metals, while using all-electron basis sets for all other non-transition-metal atoms, has become more and more popular in computations on transition-metal-containing systems. In this study, we assess the performance of 12 different DFT functionals, from the GGA (generalized gradient approximation), hybrid-GGA, meta-GGA, and hybrid-meta-GGA classes, respectively, along with the 6-31+G** + LANL2DZ (on the transition metal) mixed basis set in predicting two important molecular properties, heats of formation and ionization potentials, for 94 and 58 systems containing first-row transition metals from Ti to Zn, which are all in the third row of the periodic table. An interesting note is that the inclusion of the exact exchange term in density functional methods generally increases the accuracy of ionization potential prediction for the hybrid-GGA methods but decreases the reliability of determining the heats of formation for transition-metal-containing complexes for all hybrid density functional methods. The hybrid-GGA functional B3LYP gives the best performance in predicting the ionization potentials, while the

  2. Key Beliefs for Targeted Interventions to Increase Physical Activity in Children: Analyzing Data from an Extended Version of the Theory of Planned Behaviour

    PubMed Central

    Bélanger-Gravel, A.; Godin, G.

    2010-01-01

    Given the high prevalence of overweight and low levels of physical activity among children, a better understanding of physical activity behaviour is an important step in intervention planning. This study, based on the theory of planned behaviour, was conducted among 313 fifth graders and their parents. Children completed a computer-based questionnaire to evaluate theoretical constructs and behaviour. Additional information was obtained from parents by means of a questionnaire. Correlates of children's physical activity were intention and self-identity. Determinants of intention were self-efficacy, self-identity, and attitude. Parental variables were mediated through cognitions. Among girls, practicing sedentary activities was an additional negative determinant of intention. Key beliefs of boys and girls were related to time management and difficulties associated with physical activity. For girls, social identification as an active girl was another important belief related to positive intention. This study provides theory-based information for the development of more effective interventions aimed at promoting physical activity among children. PMID:20652005

  3. Fusion Energy Science Joint Facilities and Theory Research Target 2011: Final Report for the Period October 1, 2010 through September 30, 2011

    SciTech Connect

    Groebner, R. J.; Chang, C. S.; Diamond, P. H.; Hughes, J. W.; Maingi, R.; Snyder, P. B.; Xu, X. Q.

    2011-10-01

    Briefly stated, the goal of this combined experiment/theory milestone was to improve our knowledge of the physics processes that control the H-mode pedestal by applying models of these mechanisms to experimental data. A concerted and coordinated effort of experimental, theory and modeling activities has examined several physics mechanisms of interest, and has met the goals of the milestone. A few noteworthy results will be noted here. The activity has applied peeling-ballooning theory to all three machines, and increased confidence that the theory predicts the ultimate limits to pedestal height in an ELMing plasma. The activity has expanded the range of conditions for testing of the EPED model, and increased confidence in the ability of the model to compute the pedestal pressure height in medium aspect ratio tokamaks. Kinetic neoclassical models have been used to verify that an important analytic model for the pedestal bootstrap current has good accuracy in many regimes of interest but needs correction at high collisionality. A benchmarking effort between electromagnetic gyrokinetic codes has provided increased understanding of how to use these codes in the pedestal, and has laid the groundwork for using these codes to study linear stability of gyrokinetic modes in and on top of the pedestal. Comparisons of data and models have led to successful simulations of a quasi-coherent mode in C-Mod and to the tentative identification of a high frequency mode in DIII-D. A kinetic neoclassical model qualitatively agrees with some features of pedestal density profiles. A paleoclassical transport model quantitatively predicts some features of the electron temperature profiles in NSTX and DIII-D. The milestone activity also laid the groundwork for future advancements in understanding and predicting the pedestal. All three machines obtained a wealth of pedestal data under a wide variety of operating conditions. Some of these data have been analyzed already, and the analysis and

  4. A structural equation model of soil metal bioavailability to earthworms: confronting causal theory and observations using a laboratory exposure to field-contaminated soils.

    PubMed

    Beaumelle, Léa; Vile, Denis; Lamy, Isabelle; Vandenbulcke, Franck; Gimbert, Frédéric; Hedde, Mickaël

    2016-11-01

    Structural equation models (SEM) are increasingly used in ecology as multivariate analysis that can represent theoretical variables and address complex sets of hypotheses. Here we demonstrate the interest of SEM in ecotoxicology, more precisely to test the three-step concept of metal bioavailability to earthworms. The SEM modeled the three-step causal chain between environmental availability, environmental bioavailability and toxicological bioavailability. In the model, each step is an unmeasured (latent) variable reflected by several observed variables. In an exposure experiment designed specifically to test this SEM for Cd, Pb and Zn, Aporrectodea caliginosa was exposed to 31 agricultural field-contaminated soils. Chemical and biological measurements used included CaC12-extractable metal concentrations in soils, free ion concentration in soil solution as predicted by a geochemical model, dissolved metal concentration as predicted by a semi-mechanistic model, internal metal concentrations in total earthworms and in subcellular fractions, and several biomarkers. The observations verified the causal definition of Cd and Pb bioavailability in the SEM, but not for Zn. Several indicators consistently reflected the hypothetical causal definition and could thus be pertinent measurements of Cd and Pb bioavailability to earthworm in field-contaminated soils. SEM highlights that the metals present in the soil solution and easily extractable are not the main source of available metals for earthworms. This study further highlights SEM as a powerful tool that can handle natural ecosystem complexity, thus participating to the paradigm change in ecotoxicology from a bottom-up to a top-down approach.

  5. Superconductivity in bad metals

    SciTech Connect

    Emery, V.J.; Kivelson, S.A.

    1995-12-31

    It is argued that many synthetic metals, including high temperature superconductors are ``bad metals`` with such a poor conductivity that the usual mean-field theory of superconductivity breaks down because of anomalously large classical and quantum fluctuations of the phase of the superconducting order parameter. Some consequences for high temperature superconductors are described.

  6. Thermodynamic prediction of glass formation tendency, cluster-in-jellium model for metallic glasses, ab initio tight-binding calculations, and new density functional theory development for systems with strong electron correlation

    SciTech Connect

    Yao, Yongxin

    2009-01-01

    Solidification of liquid is a very rich and complicated field, although there is always a famous homogeneous nucleation theory in a standard physics or materials science text book. Depending on the material and processing condition, liquid may solidify to single crystalline, polycrystalline with different texture, quasi-crystalline, amorphous solid or glass (Glass is a kind of amorphous solid in general, which has short-range and medium-range order). Traditional oxide glass may easily be formed since the covalent directional bonded network is apt to be disturbed. In other words, the energy landcape of the oxide glass is so complicated that system need extremely long time to explore the whole configuration space. On the other hand, metallic liquid usually crystalize upon cooling because of the metallic bonding nature. However, Klement et.al., (1960) reported that Au-Si liquid underwent an amorphous or “glassy” phase transformation with rapid quenching. In recent two decades, bulk metallic glasses have also been found in several multicomponent alloys[Inoue et al., (2002)]. Both thermodynamic factors (e.g., free energy of various competitive phase, interfacial free energy, free energy of local clusters, etc.) and kinetic factors (e.g., long range mass transport, local atomic position rearrangement, etc.) play important roles in the metallic glass formation process. Metallic glass is fundamentally different from nanocrystalline alloys. Metallic glasses have to undergo a nucleation process upon heating in order to crystallize. Thus the short-range and medium-range order of metallic glasses have to be completely different from crystal. Hence a method to calculate the energetics of different local clusters in the undercooled liquid or glasses become important to set up a statistic model to describe metalllic glass formation. Scattering techniques like x-ray and neutron have widely been used to study the structues of metallic glasses. Meanwhile, computer simulation

  7. Theory of the formation and decomposition of N-heterocyclic aminooxycarbenes through metal-assisted [2+3]-dipolar cycloaddition/retro-cycloaddition.

    PubMed

    Novikov, Alexander S; Kuznetsov, Maxim L; Pombeiro, Armando J L

    2013-02-18

    The theoretical background of the formation of N-heterocyclic oxadiazoline carbenes through a metal-assisted [2+3]-dipolar cycloaddition (CA) reaction of nitrones R(1)CH=N(R(2))O to isocyanides C≡NR and the decomposition of these carbenes to imines R(1)CH=NR(2) and isocyanates O=C=NR is discussed. Furthermore, the reaction mechanisms and factors that govern these processes are analyzed in detail. In the absence of a metal, oxadiazoline carbenes should not be accessible due to the high activation energy of their formation and their low thermodynamic stability. The most efficient promotors that could assist the synthesis of these species should be "carbenophilic" metals that form a strong bond with the oxadiazoline heterocycle, but without significant involvement of π-back donation, namely, Au(I), Au(III), Pt(II), Pt(IV), Re(V), and Pd(II) metal centers. These metals, on the one hand, significantly facilitate the coupling of nitrones with isocyanides and, on the other hand, stabilize the derived carbene heterocycles toward decomposition. The energy of the LUMO(CNR) and the charge on the N atom of the C≡N group are principal factors that control the cycloaddition of nitrones to isocyanides. The alkyl-substituted nitrones and isocyanides are predicted to be more active in the CA reaction than the aryl-substituted species, and the N,N,C-alkyloxadiazolines are more stable toward decomposition relative to the aryl derivatives. PMID:23296691

  8. Metal/dielectric thermal interfacial transport considering cross-interface electron-phonon coupling: Theory, two-temperature molecular dynamics, and thermal circuit

    NASA Astrophysics Data System (ADS)

    Lu, Zexi; Wang, Yan; Ruan, Xiulin

    2016-02-01

    The standard two-temperature equations for electron-phonon coupled thermal transport across metal/nonmetal interfaces are modified to include the possible coupling between metal electrons with substrate phonons. The previous two-temperature molecular dynamics (TT-MD) approach is then extended to solve these equations numerically at the atomic scale, and the method is demonstrated using Cu/Si interface as an example. A key parameter in TT-MD is the nonlocal coupling distance of metal electrons and nonmetal phonons, and here we use two different approximations. The first is based on Overhauser's "joint-modes" concept, while we use an interfacial reconstruction region as the length scale of joint region rather than the phonon mean-free path as in Overhauser's original model. In this region, the metal electrons can couple to the joint phonon modes. The second approximation is the "phonon wavelength" concept where electrons couple to phonons nonlocally within the range of one phonon wavelength. Compared with the original TT-MD, including the cross-interface electron-phonon coupling can slightly reduce the total thermal boundary resistance. Whether the electron-phonon coupling within the metal block is nonlocal or not does not make an obvious difference in the heat transfer process. Based on the temperature profiles from TT-MD, we construct a new mixed series-parallel thermal circuit. We show that such a thermal circuit is essential for understanding metal/nonmetal interfacial transport, while calculating a single resistance without solving temperature profiles as done in most previous studies is generally incomplete. As a comparison, the simple series circuit that neglects the cross-interface electron-phonon coupling could overestimate the interfacial resistance, while the simple parallel circuit in the original Overhauser's model underestimates the total interfacial resistance.

  9. A structural equation model of soil metal bioavailability to earthworms: confronting causal theory and observations using a laboratory exposure to field-contaminated soils.

    PubMed

    Beaumelle, Léa; Vile, Denis; Lamy, Isabelle; Vandenbulcke, Franck; Gimbert, Frédéric; Hedde, Mickaël

    2016-11-01

    Structural equation models (SEM) are increasingly used in ecology as multivariate analysis that can represent theoretical variables and address complex sets of hypotheses. Here we demonstrate the interest of SEM in ecotoxicology, more precisely to test the three-step concept of metal bioavailability to earthworms. The SEM modeled the three-step causal chain between environmental availability, environmental bioavailability and toxicological bioavailability. In the model, each step is an unmeasured (latent) variable reflected by several observed variables. In an exposure experiment designed specifically to test this SEM for Cd, Pb and Zn, Aporrectodea caliginosa was exposed to 31 agricultural field-contaminated soils. Chemical and biological measurements used included CaC12-extractable metal concentrations in soils, free ion concentration in soil solution as predicted by a geochemical model, dissolved metal concentration as predicted by a semi-mechanistic model, internal metal concentrations in total earthworms and in subcellular fractions, and several biomarkers. The observations verified the causal definition of Cd and Pb bioavailability in the SEM, but not for Zn. Several indicators consistently reflected the hypothetical causal definition and could thus be pertinent measurements of Cd and Pb bioavailability to earthworm in field-contaminated soils. SEM highlights that the metals present in the soil solution and easily extractable are not the main source of available metals for earthworms. This study further highlights SEM as a powerful tool that can handle natural ecosystem complexity, thus participating to the paradigm change in ecotoxicology from a bottom-up to a top-down approach. PMID:27378153

  10. LAT1 targeted delivery of methionine based imaging probe derived from M(III) metal ions for early diagnosis of proliferating tumours using molecular imaging modalities.

    PubMed

    Hazari, Puja Panwar; Prakash, Surbhi; Meena, Virendra K; Jaswal, Ambika; Khurana, Harleen; Mishra, Surabhi Kirti; Bhonsle, Hemanth Kumar; Singh, Lokendra; Mishra, Anil K

    2015-01-01

    We investigated the potential of DTPA-bis(Methionine), a target specific amino acid based probe for detection of L-type amino acid transporters (LAT1) known to over express in proliferating tumours using multimodality imaging. The ligand, DTPA-bis(Met) was readily converted to lanthanide complexes and was found capable of targeting cancer cells using multimodality imaging. DTPA-bis(Met) complexes were synthesized and characterized by mass spectroscopy. MR longitudinal relaxivity, r₁ = 4.067 ± 0.31 mM⁻¹s⁻¹ and transverse relaxivity, r₂ = 8.61 ± 0.07 mM⁻¹s⁻¹ of Gd(III)-DTPA-bis(Met) were observed at pH 7.4 at 7 T. Bright, localized fluorescence of Eu(III)-DTPA-bis(Met) was observed with standard microscopy and displacement studies indicated ligand functionality. K(D) value determined for Eu(III)-DTPA-bis(Met) on U-87 MG cells was found to be 17.3 pM and showed appreciable fluorescence within the cells. Radio HPLC showed a radiochemical purity more than 95% (specific activity = 400-500 MBq/μmol, labelling efficiency 78 %) for ⁶⁸Ga(III)-DTPA-bis(Met). Pre-treatment of xenografted U-87 MG athymic mice with ⁶⁸Ga(III)-DTPA-bis(Met) following unlabelled L-methionine administration reduced tumour uptake by 10-folds in Micro PET. These data support the specific binding of ⁶⁸Ga(III)-DTPA-bis(Met) to the LAT1 transporter. To summarize, this agent possesses high stability in biological environment and exhibits effective interaction with its LAT1 transporters giving high accumulation in tumour area, excellent tumour/non-tumour ratio and low non-specific retention in vivo. PMID:25329672

  11. LAT1 targeted delivery of methionine based imaging probe derived from M(III) metal ions for early diagnosis of proliferating tumours using molecular imaging modalities.

    PubMed

    Hazari, Puja Panwar; Prakash, Surbhi; Meena, Virendra K; Jaswal, Ambika; Khurana, Harleen; Mishra, Surabhi Kirti; Bhonsle, Hemanth Kumar; Singh, Lokendra; Mishra, Anil K

    2015-01-01

    We investigated the potential of DTPA-bis(Methionine), a target specific amino acid based probe for detection of L-type amino acid transporters (LAT1) known to over express in proliferating tumours using multimodality imaging. The ligand, DTPA-bis(Met) was readily converted to lanthanide complexes and was found capable of targeting cancer cells using multimodality imaging. DTPA-bis(Met) complexes were synthesized and characterized by mass spectroscopy. MR longitudinal relaxivity, r₁ = 4.067 ± 0.31 mM⁻¹s⁻¹ and transverse relaxivity, r₂ = 8.61 ± 0.07 mM⁻¹s⁻¹ of Gd(III)-DTPA-bis(Met) were observed at pH 7.4 at 7 T. Bright, localized fluorescence of Eu(III)-DTPA-bis(Met) was observed with standard microscopy and displacement studies indicated ligand functionality. K(D) value determined for Eu(III)-DTPA-bis(Met) on U-87 MG cells was found to be 17.3 pM and showed appreciable fluorescence within the cells. Radio HPLC showed a radiochemical purity more than 95% (specific activity = 400-500 MBq/μmol, labelling efficiency 78 %) for ⁶⁸Ga(III)-DTPA-bis(Met). Pre-treatment of xenografted U-87 MG athymic mice with ⁶⁸Ga(III)-DTPA-bis(Met) following unlabelled L-methionine administration reduced tumour uptake by 10-folds in Micro PET. These data support the specific binding of ⁶⁸Ga(III)-DTPA-bis(Met) to the LAT1 transporter. To summarize, this agent possesses high stability in biological environment and exhibits effective interaction with its LAT1 transporters giving high accumulation in tumour area, excellent tumour/non-tumour ratio and low non-specific retention in vivo.

  12. Targets and targeting.

    PubMed

    Will, E

    2001-08-01

    Using the vocabulary of ballistics in medicine for emphasis can result in misleading exaggeration and semantic confusion. The dual meaning of target as either aiming point (aim at) or outcome (aim to achieve) creates a muddle in the efforts to comply with quality assurance initiatives. Disentangling the two meanings allows new approaches to the clinical technology required in a modern health care environment. An example can be shown in new strategies for the management of renal anemia with iron and erythropoietin. The potential to shape outcome distributions through validated, preemptive intervention thresholds offers the predictable results required by patients and payers. Using the management of patient cohorts as a platform for outcomes creates no necessary conflict with individualized clinical care. Future guideline statements should include the likely characteristics of compliant outcome populations, as a prompt to clinical goals and as an indication of the necessary cost and effort of compliance with treatment standards. Overemphasis in language is no substitute for considered clinical methodology.

  13. The Elusive Bose Metal

    NASA Astrophysics Data System (ADS)

    Phillips, Philip; Dalidovich, Denis

    2003-10-01

    The conventional theory of metals is in crisis. In the past 15 years, there has been an unexpected sprouting of metallic states in low-dimensional systems, directly contradicting conventional wisdom. For example, bosons are thought to exist in one of two ground states: condensed in a superconductor or localized in an insulator. However, several experiments on thin metal-alloy films have observed that a metallic phase disrupts the direct transition between the superconductor and the insulator. We analyze the experiments on the insulator-superconductor transition and argue that the intervening metallic phase is bosonic. All relevant theoretical proposals for the Bose metal are discussed, particularly the recent idea that the metallic phase is glassy. The implications for the putative vortex-glass state in the copper oxide superconductors are examined.

  14. Search for Two Categories of Target Produces Fewer Fixations to Target-Color Items

    ERIC Educational Resources Information Center

    Menneer, Tamaryn; Stroud, Michael J.; Cave, Kyle R.; Li, Xingshan; Godwin, Hayward J.; Liversedge, Simon P.; Donnelly, Nick

    2012-01-01

    Searching simultaneously for metal threats (guns and knives) and improvised explosive devices (IEDs) in X-ray images is less effective than 2 independent single-target searches, 1 for metal threats and 1 for IEDs. The goals of this study were to (a) replicate this dual-target cost for categorical targets and to determine whether the cost remains…

  15. Theory of the dissociation dynamics of small molecules on metal surfaces: Finite temperature studies. Annual progress report, July 1, 1991--June 30, 1992

    SciTech Connect

    Jackson, B.E.

    1992-02-01

    The goal of this study is to gain a better understanding of metal- catalyzed reactions via a detailed examination of the dynamics of molecule-metal interactions. Much effort has focused on treating the molecule as quantum mechanically as possible, and including the effects of finite surface temperature. Recently developed time dependent quantum techniques have been used to compute the dissociative sticking probability of H{sub 2} on various metal surfaces. All molecular degrees of freedom are included either quantum mechanically or classically. The dependence upon translational and internal molecular energy, the angle and site of the surface impact, and the details of the molecule-metal interaction potential were examined. Similar techniques have been used to study the Eley-Rideal mechanism for the recombinative desorption of adsorbed H atoms with gas phase H atoms. Extremely accurate methods for coupling the molecule to the thermal vibrations of the solid have been developed. They are being used in a general study of sticking, as well as to examine the trapping of H{sub 2} and other diatomics in weakly bound molecular precursors to dissociative adsorption.

  16. A copper metallochaperone for photosynthesis and respiration reveals metal-specific targets, interaction with an importer, and alternative sites for copper acquisition.

    PubMed

    Tottey, Stephen; Rondet, Sabine A M; Borrelly, Gilles P M; Robinson, Pamela J; Rich, Peter R; Robinson, Nigel J

    2002-02-15

    A bacterial two-hybrid assay revealed interaction between a protein now designated bacterial Atx1 and amino-terminal domains of copper-transporting ATPases CtaA (cellular import) and PacS (thylakoid import) but not the related zinc (ZiaA) or cobalt (CoaT) transporters from the same organism (Synechocystis PCC 6803). The specificity of metallochaperone interactions coincides with metal specificity. After reconstitution in a N(2) atmosphere, bacterial Atx1 bound 1 mol of copper mol(-1), and apoPacS(N) acquired copper from copper-Atx1. Copper was displaced from Atx1 by p-(hydroxymercuri)phenylsulfonate, indicative of thiol ligands, and two cysteine residues were obligatory for two-hybrid interaction with PacS(N). This organism contains compartments (thylakoids) where the copper proteins plastocyanin and cytochrome oxidase reside. In copper super-supplemented mutants, photooxidation of cytochrome c(6) was greater in Deltaatx1DeltactaA than in DeltactaA, showing that Atx1 contributes to efficient switching from iron in cytochrome c(6) to copper in plastocyanin for photosynthetic electron transport. Cytochrome oxidase activity was also less in membranes purified from low [copper]-grown Deltaatx1 or DeltapacS, compared with wild-type, but the double mutant Deltaatx1DeltapacS was non-additive, consistent with Atx1 acting via PacS. Conversely, activity in Deltaatx1DeltactaA was less than in either respective single mutant, revealing that Atx1 can function without the major copper importer and consistent with a role in recycling endogenous copper.

  17. Zeolitic polyoxometalate-based metal-organic frameworks (Z-POMOFs): computational evaluation of hypothetical polymorphs and the successful targeted synthesis of the redox-active Z-POMOF1.

    PubMed

    Rodriguez-Albelo, L Marleny; Ruiz-Salvador, A Rabdel; Sampieri, Alvaro; Lewis, Dewi W; Gómez, Ariel; Nohra, Brigitte; Mialane, Pierre; Marrot, Jérôme; Sécheresse, Francis; Mellot-Draznieks, Caroline; Ngo Biboum, Rosa; Keita, Bineta; Nadjo, Louis; Dolbecq, Anne

    2009-11-11

    The targeted design and simulation of a new family of zeolitic metal-organic frameworks (MOFs) based on benzenedicarboxylate (BDC) as the ligand and epsilon-type Keggin polyoxometalates (POMs) as building units, named here Z-POMOFs, have been performed. A key feature is the use of the analogy between the connectivity of silicon in dense minerals and zeolites with that of the epsilon-type Keggin POMs capped with Zn(II) ions. Handling the epsilon-Keggin as a building block, a selection of 21 zeotype structures, together with a series of dense minerals were constructed and their relative stabilities computed. Among these Z-POMOFs, the cristobalite-like structure was predicted to be the most stable structure. This prediction has been experimentally validated by the targeted synthesis of the first experimental Z-POMOF structure, which was strikingly found to possess the cristobalite topology, with three interpenetrated networks. Crystals of [NBu(4)](3)[PMo(V)(8)Mo(VI)(4)O(36)(OH)(4)Zn(4)(BDC)(2)].2H(2)O (Z-POMOF1) have been isolated under hydrothermal conditions from the reduction of ammonium heptamolybdate in the presence of phosphorous acid and Zn(II) ions. Tetrabutylammonium cations play the role of counterions and space-filling agents in this tridimensional interpenetrated framework. Moreover, the electrochemistry of the epsilon-Keggin POM is maintained and can be exploited in the insoluble Z-POMOF1 framework, as demonstrated by the electrocatalytic reduction of bromate.

  18. Valence-Bond Concepts in Coordination Chemistry and the Nature of Metal-Metal Bonds.

    ERIC Educational Resources Information Center

    Pauling, Linus; Herman, Zelek S.

    1984-01-01

    Discusses the valence-bond method, applying it to some coordination compounds of metals, especially those involving metal-metal bonds. Suggests that transition metals can form as many as nine covalent bonds, permitting valence-theory to be extended to transition metal compounds in a more effective way than has been possible before. (JN)

  19. Molecular orbital (SCF-Xα-SW) theory of metal-metal charge transfer processes in minerals - II. Application to Fe2+ --> Ti4+ charge transfer transitions in oxides and silicates

    USGS Publications Warehouse

    Sherman, David M.

    1987-01-01

    A molecular orbital description, based on Xα-Scattered wave calculations on a (FeTiO10)14− cluster, is given for Fe2+ → Ti4+ charge transfer transitions in minerals. The calculated energy for the lowest Fe2+ → Ti4+ metal-metal charge transfer transition is 18040 cm−1 in reasonable agreement with energies observed in the optical spectra of Fe-Ti oxides and silicates. As in the case of Fe2+ → Fe3+ charge transfer in mixed-valence iron oxides and silicates, Fe2+ → Ti4+ charge transfer is associated with Fe-Ti bonding across shared polyhedral edges. Such bonding results from the overlap of the Fe(t 2g ) and Ti(t 2g ) 3d orbitals.

  20. Preclinical evaluation of multistep targeting of diasialoganglioside GD2 using an IgG-scFv bispecific antibody with high affinity for GD2 and DOTA metal complex.

    PubMed

    Cheal, Sarah M; Xu, Hong; Guo, Hong-fen; Zanzonico, Pat B; Larson, Steven M; Cheung, Nai-Kong

    2014-07-01

    Bispecific antibodies (BsAb) have proven to be useful targeting vectors for pretargeted radioimmunotherapy (PRIT). We sought to overcome key PRIT limitations such as high renal radiation exposure and immunogenicity (e.g., of streptavidin-antibody fusions), to advance clinical translation of this PRIT strategy for diasialoganglioside GD2-positive [GD2(+)] tumors. For this purpose, an IgG-scFv BsAb was engineered using the sequences for the anti-GD2 humanized monoclonal antibody hu3F8 and C825, a murine scFv antibody with high affinity for the chelator 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) complexed with β-particle-emitting radiometals such as (177)Lu and (90)Y. A three-step regimen, including hu3F8-C825, a dextran-based clearing agent, and p-aminobenzyl-DOTA radiolabeled with (177)Lu (as (177)Lu-DOTA-Bn; t1/2 = 6.71 days), was optimized in immunocompromised mice carrying subcutaneous human GD2(+) neuroblastoma (NB) xenografts. Absorbed doses for tumor and normal tissues were approximately 85 cGy/MBq and ≤3.7 cGy/MBq, respectively, with therapeutic indices (TI) of 142 for blood and 23 for kidney. A therapy study (n = 5/group; tumor volume, 240 ± 160 mm(3)) with three successive PRIT cycles (total (177)Lu: ∼33 MBq; tumor dose ∼3,400 cGy), revealed complete tumor response in 5 of 5 animals, with no recurrence up to 28 days after treatment. Tumor ablation was confirmed histologically in 4 of 5 mice, and normal organs showed minimal overall toxicities. All nontreated mice required sacrifice within 12 days (>1.0-cm(3) tumor volume). We conclude that this novel anti-GD2 PRIT approach has sufficient TI to successfully ablate subcutaneous GD2(+)-NB in mice while sparing kidney and bone marrow.

  1. Effect of metal in M3(btc)2 and M2(dobdc) MOFs for O2/N2 separations: A combined density functional theory and experimental study

    SciTech Connect

    Parkes, Marie V.; Sava Gallis, Dorina F.; Greathouse, Jeffery A.; Nenoff, Tina M.

    2015-03-02

    Computational screening of metal-organic framework (MOF) materials for selective oxygen adsorption from air could lead to new sorbents for the oxyfuel combustion process feedstock streams. A comprehensive study on the effect of MOF metal chemistry on gas binding energies in two common but structurally disparate metal-organic frameworks has been undertaken. Dispersion-corrected density functional theory methods were used to calculate the oxygen and nitrogen binding energies with each of fourteen metals, respectively, substituted into two MOF series, M2(dobdc) and M3(btc)2. The accuracy of DFT methods was validated by comparing trends in binding energy with experimental gas sorption measurements. A periodic trend in oxygen binding energies was found, with greater oxygen binding energies for early transition-metal-substituted MOFs compared to late transition metal MOFs; this was independent of MOF structural type. The larger binding energies were associated with oxygen binding in a side-on configuration to the metal, with concomitant lengthening of the O-O bond. In contrast, nitrogen binding energies were similar across the transition metal series, regardless of both MOF structural type and metal identity. Altogether, these findings suggest that early transition metal MOFs are best suited to separating oxygen from nitrogen, and that the MOF structural type is less important than the metal identity.

  2. Computational Study of Vibrational Dynamics of Binary Mg0.70Zn0.30 Metallic Glass by a Pseudopotential Theory

    NASA Astrophysics Data System (ADS)

    Vora, Aditya M.

    2008-11-01

    The vibrational dynamics of Mg70Zn30 metallic glass has been studied at room temperature in terms of phonon eigen-frequencies of longitudinal and transverse modes employing three different approaches proposed by Hubbard-Beeby (HB), Takeno-Goda (TG) and Bhatia-Singh (BS). The well-recognized model potential is employed successfully to explain electron-ion interaction in the metallic glass; instead of using experimental values of the pair correlation function g(r), which is generated from the computed pair potential. The present findings of phonon dispersion curve are found in fair agreement with available theoretical as well as experimental data. The thermodynamic properties obtained by HB and TG approaches are found much lower than those obtained by BS approach. The pseudo-alloy-atom (PAA) model is applied for the first time instead of Vegard's Law.

  3. Preclinical evaluation of multistep targeting of diasialoganglioside GD2 using a IgG-scFv bispecific antibody with high affinity for GD2 and DOTA metal complex

    PubMed Central

    Cheal, Sarah M.; Xu, Hong; Guo, Hong-fen; Zanzonico, Pat B.; Larson, Steven M.; Cheung, Nai-Kong

    2014-01-01

    Bispecific antibodies (BsAb) have proven to be useful targeting vectors for pretargeted radioimmunotherapy (PRIT). We sought to overcome key PRIT limitations such as high renal radiation exposure and immunogenicity (e.g. of streptavidin-antibody fusions), to advance clinical translation of this PRIT strategy for diasialoganglioside GD2-positive (GD2(+)) tumors. For this purpose, a IgG-scFv BsAb was engineered using the sequences for the anti-GD2 humanized monoclonal antibody hu3F8 (1) and C825, a murine scFv antibody with high affinity for the chelator 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) complexed with beta-particle emitting radiometals such as 177Lu and 90Y (2, 3). A three-step regimen including hu3F8-C825, a dextran-based clearing agent, and p-aminobenzyl-DOTA radiolabeled with 177Lu (as 177Lu-DOTA-Bn; t1/2 = 6.71 days (d)) was optimized in immunocompromised mice carrying subcutaneous (s.c.) human GD2(+) neuroblastoma (NB) xenografts. Absorbed doses for tumor and normal tissues were ∼85 cGy/MBq and ≤3.7 cGy/MBq, respectively, with therapeutic indicies (TI) of 142 for blood and 23 for kidney. A therapy study (n = 5 per group; tumor volume: 240 ± 160 mm3) with three successive PRIT cycles (total 177Lu: ∼33 MBq; tumor dose ∼3400 cGy), revealed complete tumor response in 5/5 animals, with no recurrence up to 28 d post-treatment. Tumor ablation was confirmed histologically in 4/5 mice, and normal organs showed minimal overall toxicities. All non-treated mice required sacrifice within 12 d (>1.0 cm3 tumor volume). We conclude that this novel anti-GD2 PRIT approach has sufficient TI to successfully ablate s.c. GD2(+)–NB in mice while sparing kidney and bone marrow. PMID:24944121

  4. Thick target D-T neutron yield measurements using metal occluders of scandium, titanium, yttrium, zirconium, gadolinium, erbium, hafnium, and tantalum at energies from 25 to 200 keV

    SciTech Connect

    Malbrough, D.J.; Molloy, J.T. Jr.; Becker, R.H.

    1990-11-19

    Deuterium-Tritium (D-T) neutron yields from thick films of scandium, titanium, yttrium, zirconium, gadolinium, erbium, hafnium, and tantalum were measured by the associated particle technique using the 200-keV accelerator at the Pinellas Plant. The neutron yields were measured for all targets at energies from 25 to 200 keV in 5-keV steps with an average uncertainty of {plus_minus}6.8%. Tabulated results are presented with yield versus energy curves for each target. Yield curves for D-D neutrons from earlier measurements are also presented with the D-T neutron yield curves. Good fits to the data were found for both D-D and D-T with theoretical calculations that were adjusted by smooth functions of the form: A{sub 0} + A{sub 1}E + A{sub 2}E{sup 2}. The results of the fits strongly suggest that disagreement between measurement and theory is due mainly to inaccuracies in currently available stopping power data. Comparisons with earlier theoretical calculations for titanium and erbium are also presented. 27 refs., 10 figs., 4 tabs.

  5. Mitochondria-targeted antioxidants.

    PubMed

    Oyewole, Anne O; Birch-Machin, Mark A

    2015-12-01

    Redox homeostasis is maintained by the antioxidant defense system, which is responsible for eliminating a wide range of oxidants, including reactive oxygen species (ROS), lipid peroxides, and metals. Mitochondria-localized antioxidants are widely studied because the mitochondria, the major producers of intracellular ROS, have been linked to the cause of aging and other chronic diseases. Mitochondria-targeted antioxidants have shown great potential because they cross the mitochondrial phospholipid bilayer and eliminate ROS at the heart of the source. Growing evidence has identified mitochondria-targeted antioxidants, such as MitoQ and tiron, as potentially effective antioxidant therapies against the damage caused by enhanced ROS generation. This literature review summarizes the current knowledge on mitochondria-targeted antioxidants and their contribution to the body's antioxidant defense system. In addition to addressing the concerns surrounding current antioxidant strategies, including difficulties in targeting antioxidant treatment to sites of pathologic oxidative damage, we discuss promising therapeutic agents and new strategic approaches.

  6. Sputter target

    DOEpatents

    Gates, Willard G.; Hale, Gerald J.

    1980-01-01

    The disclosure relates to an improved sputter target for use in the deposition of hard coatings. An exemplary target is given wherein titanium diboride is brazed to a tantalum backing plate using a gold-palladium-nickel braze alloy.

  7. Mass Producing Targets for Nuclear Fusion

    NASA Technical Reports Server (NTRS)

    Wang, T. G.; Elleman, D. D.; Kendall, J. M.

    1983-01-01

    Metal-encapsulating technique advances prospects of controlling nuclear fusion. Prefilled fusion targets form at nozzle as molten metal such as tin flows through outer channel and pressurized deuterium/tritium gas flows through inner channel. Molten metal completely encloses gas charge as it drops off nozzle.

  8. Whole-Cell Bioreporters for the Detection of Bioavailable Metals

    NASA Astrophysics Data System (ADS)

    Hynninen, Anu; Virta, Marko

    Whole-cell bioreporters are living microorganisms that produce a specific, quantifiable output in response to target chemicals. Typically, whole-cell bioreporters combine a sensor element for the substance of interest and a reporter element coding for an easily detectable protein. The sensor element is responsible for recognizing the presence of an analyte. In the case of metal bioreporters, the sensor element consists of a DNA promoter region for a metal-binding transcription factor fused to a promoterless reporter gene that encodes a signal-producing protein. In this review, we provide an overview of specific whole-cell bioreporters for heavy metals. Because the sensing of metals by bioreporter microorganisms is usually based on heavy metal resistance/homeostasis mechanisms, the basis of these mechanisms will also be discussed. The goal here is not to present a comprehensive summary of individual metal-specific bioreporters that have been constructed, but rather to express views on the theory and applications of metal-specific bioreporters and identify some directions for future research and development.

  9. Activation of X-H and X-D bonds (X = O, N, C) by alkaline-earth metal monoxide cations: experiment and theory.

    PubMed

    Bozović, Andrea; Bohme, Diethard K

    2009-07-28

    Experimental investigations are reported for reactions of MO (+) (M = Ca, Sr, and Ba) with elemental hydrides water, ammonia and methane proceeding in the gas phase at 295 +/- 3 K in helium buffer gas at a pressure of 0.35 +/- 0.01 Torr. Measurements were taken with an inductively-coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer and a novel electrospray ion source/ion selection quadrupole/selected-ion flow tube/triple quadrupole (ESI/qQ/SIFT/QqQ) mass spectrometer. All three alkaline-earth metal oxide ions exclusively abstract a H-atom from the three hydrides with rate coefficients > 1 x 10(-11) cm(3) molecule(-1) s(-1). Formation of metal hydroxide ion was followed by sequential addition of water or ammonia, but not methane. Density functional calculations have provided potential energy surfaces for the X-H bond activations leading to H-atom abstraction as well as those for O-atom transfer and H(2)O elimination (with ammonia and methane). A comparison of experimental and theoretical isotope effects points toward a mechanism involving the direct atom transfer from XH and XD to O in MO (+)via a three-centered transition structure. PMID:19588017

  10. Nuclear target development

    SciTech Connect

    Greene, J.P.; Thomas, G.E.

    1995-08-01

    The Physics Division operates a target development laboratory that produces thin foil targets needed for experiments performed at the ATLAS and Dynamitron accelerators. Targets are not only produced for the Physics Division but also for other divisions and occasionally for other laboratories and universities. In the past year, numerous targets were fabricated by vacuum evaporation either as self-supporting foils or on various substrates. Targets produced included Ag, Au, {sup 10,11}B, {sup 138}Ba, Be, {sup 12}C, {sup 40}Ca, {sup 116}Cd, {sup 155,160}Gd, {sup 76}Ge, In, LID, {sup 6}LiH, Melamine, Mg, {sup 142,150}Nd, {sup 58}Ni, {sup 206,208}Pb, {sup 194}Pt, {sup 28}Si, {sup 144,148}Sm, {sup 120,122,124}Sn, Ta, {sup 130}Te, ThF{sub 4}, {sup 46,50}Ti, TiH, U, UF{sub 4}, {sup 182}W and {sup 170}Yb. Polypropylene and aluminized polypropylene, along with metallized Mylar were produced for experiments at ATLAS. A number of targets of {sup 11}B of various thickness were made for the DEP 2-MeV Van de Graff accelerator. An increased output of foils fabricated using our small rolling mill included targets of Au, C, {sup 50}Cr, Cu, {sup 155,160}Gd, Mg, {sup 58}Ni, {sup 208}Pb, {sup 105,110}Pd. Sc, Ti, and {sup 64,66}Zn.

  11. Unifying Theory of Low-Energy Nuclear Reaction and Transmutation Processes in Deuterated/hydrogenated Metals, Acoustic Cavitation, Glow Discharge, and Deuteron Beam Experiments

    NASA Astrophysics Data System (ADS)

    Kim, Yeong E.; Zubarev, Alexander L.

    The most basic theoretical challenge for understanding low-energy nuclear reaction (LENR) and transmutation reaction (LETR) in condensed matters is to find mechanisms by which the large Coulomb barrier between fusing nuclei can be overcome. A unifying theory of LENR and LETR has been developed to provide possible mechanisms for the LENR and LETR processes in matters based on high-density nano-scale and micro-scale quantum plasmas. It is shown that recently developed theoretical models based on Bose-Einstein Fusion (BEF) mechanism and Quantum Plasma Nuclear Fusion (QPNF) mechanism are applicable to the results of many different types of LENR and LETR experiments.

  12. The effect of basis set and exchange-correlation functional on time-dependent density functional theory calculations within the Tamm-Dancoff approximation of the x-ray emission spectroscopy of transition metal complexes.

    PubMed

    Roper, Ian P E; Besley, Nicholas A

    2016-03-21

    The simulation of X-ray emission spectra of transition metal complexes with time-dependent density functional theory (TDDFT) is investigated. X-ray emission spectra can be computed within TDDFT in conjunction with the Tamm-Dancoff approximation by using a reference determinant with a vacancy in the relevant core orbital, and these calculations can be performed using the frozen orbital approximation or with the relaxation of the orbitals of the intermediate core-ionised state included. Both standard exchange-correlation functionals and functionals specifically designed for X-ray emission spectroscopy are studied, and it is shown that the computed spectral band profiles are sensitive to the exchange-correlation functional used. The computed intensities of the spectral bands can be rationalised by considering the metal p orbital character of the valence molecular orbitals. To compute X-ray emission spectra with the correct energy scale allowing a direct comparison with experiment requires the relaxation of the core-ionised state to be included and the use of specifically designed functionals with increased amounts of Hartree-Fock exchange in conjunction with high quality basis sets. A range-corrected functional with increased Hartree-Fock exchange in the short range provides transition energies close to experiment and spectral band profiles that have a similar accuracy to those from standard functionals.

  13. Quantum theory of IR spectroscopy of dipole-forbidden vibrational modes of adsorbed molecules on the surface of a metal in the frequency range of the anomalous skin effect

    SciTech Connect

    Volokitin, A.I.; Persson, B.N.J.

    1995-09-01

    A completely quantum-mechanical calculation of the IR spectrum for the dipole-forbidden vibrational modes of adsorbed molecules on a metal surface is performed. IT is shown for broad-band metals with a simple band structure that the asymmetry of the line shape is determined by nonlocal effects, while the nonadiabaticity makes a small contribution. In the region of the limiting anomalous skin effect ({omega}/{omega}{sub 1}{much_lt} 1, where {omega} is the frequency of the IR radiation, {omega}{sub 1}={upsilon}{sub F}/{delta}, {upsilon}{sub F} is the Fermi velocity, {delta}=c/{omega}{sub p} is the depth of the skin layer, and {omega}{sub p} is the plasma frequency) the broad-band absorption spectrum caused by the adsorbed molecules has an asymptotic limit {omega}{sup O}. The theory is compared with new absolute measurements of the IR spectrum of the CO/Cu(100) system. 20 refs., 2 figs.

  14. Theory of Josephson effect in Sr 2RuO 4/diffusive normal metal/Sr 2RuO 4 junctions

    NASA Astrophysics Data System (ADS)

    Sawa, Y.; Yokoyama, T.; Tanaka, Y.; Golubov, A. A.

    2007-10-01

    We derive a generalized Nazarov's boundary condition for diffusive normal metal (DN)/chiral p-wave superconductor (CP) interface including the macroscopic phase of the superconductor. The Josephson effect is studied in CP/DN/CP junctions solving the Usadel equations under the above boundary condition. We find that, enhancement of a critical current at low temperature is small compared with that in px-wave /DN/px-wave junctions. As a result, temperature dependence of the critical current in these junctions is similar to that in conventional junctions. The result is consistent with the experiment in Sr2RuO4-Sr3RuO7 eutectic junctions. Similar feature is also found in current-phase relation.

  15. A Metal and Base-Free Chemoselective Primary Amination of Boronic Acids Using Cyanamidyl/Arylcyanamidyl Radical as Aminating Species: Synthesis and Mechanistic Studies by Density Functional Theory.

    PubMed

    Chatterjee, Nachiketa; Arfeen, Minhajul; Bharatam, Prasad V; Goswami, Avijit

    2016-06-17

    An efficient, metal and base-free, chemoselective synthesis of aryl-, heteroaryl-, and alkyl primary amines from the corresponding boronic acids has been achieved at ambient temperature mediated by [bis(trifluoroacetoxy)iodo]benzene (PIFA) and N-bromosuccinimide (NBS) using cyanamidyl/arylcyanamidyl radicals as the aminating species. The primary amine compounds were initially obtained as their corresponding ammonium trifluoroacetate salts which, on treatment with aq NaOH, provide the free amines. Finally, the primary amines were isolated through column chromatography over silica-gel using hexane-EtOAc solvent system as the eluent. The reactions are sufficiently fast, completing within 1 h. Quantum chemical calculations in combination with experimental observations validate that the ipso amination of substituted boronic acids involves the formation of cyanamidyl/arylcyanamidyl radical, followed by regiospecific interaction of its nitrile-N center with boron atom of the boronic acids, leading to chemoselective primary amination.

  16. Spin-rotational-invariant theory of transition-metal magnetism at finite temperatures: Systematic study of a single-site model

    NASA Astrophysics Data System (ADS)

    Pastor, G. M.; Dorantes-Dávila, J.

    2016-06-01

    A spin-rotational-invariant approach to the spin-fluctuation theory of itinerant-electron magnetism is proposed and evaluated in the framework of a d -band model Hamiltonian including intra-atomic exchange interactions J and the coupling to a local magnetic field B . Using a vector-field Hubbard-Stratonovich transformation, we obtain a static approximation to the density matrix operator from which the equilibrium properties are directly derived. The method is applied to a single-site model taking Fe as a representative example. Exact and approximate analytical results are given for the local magnetic moments, their longitudinal and transversal components, the field-induced magnetizations, entropy, and heat capacity. Goals and limitations of various approximations are discussed as a function of J ,B , and temperature. The quantum-mechanical origin of some important drawbacks found in previous vector-field static approaches is identified. The significant improvements achieved with the static density operator are demonstrated.

  17. Water-soluble polymers for recovery of metal ions from aqueous streams

    DOEpatents

    Smith, Barbara F.; Robison, Thomas W.

    1998-01-01

    A process of selectively separating a target metal contained in an aqueous solution by contacting the aqueous solution containing a target metal with an aqueous solution including a water-soluble polymer capable of binding with the target metal for sufficient time whereby a water-soluble polymer-target metal complex is formed, and, separating the solution including the water-soluble polymer-target metal complex from the solution is disclosed.

  18. String Theory and Gauge Theories

    SciTech Connect

    Maldacena, Juan

    2009-02-20

    We will see how gauge theories, in the limit that the number of colors is large, give string theories. We will discuss some examples of particular gauge theories where the corresponding string theory is known precisely, starting with the case of the maximally supersymmetric theory in four dimensions which corresponds to ten dimensional string theory. We will discuss recent developments in this area.

  19. Benchmarking density functional theory predictions of framework structures and properties in a chemically diverse test set of metal-organic frameworks

    SciTech Connect

    Nazarian, Dalar; Ganesh, P.; Sholl, David S.

    2015-09-30

    We compiled a test set of chemically and topologically diverse Metal–Organic Frameworks (MOFs) with high accuracy experimentally derived crystallographic structure data. The test set was used to benchmark the performance of Density Functional Theory (DFT) functionals (M06L, PBE, PW91, PBE-D2, PBE-D3, and vdW-DF2) for predicting lattice parameters, unit cell volume, bonded parameters and pore descriptors. On average PBE-D2, PBE-D3, and vdW-DF2 predict more accurate structures, but all functionals predicted pore diameters within 0.5 Å of the experimental diameter for every MOF in the test set. The test set was also used to assess the variance in performance of DFT functionals for elastic properties and atomic partial charges. The DFT predicted elastic properties such as minimum shear modulus and Young's modulus can differ by an average of 3 and 9 GPa for rigid MOFs such as those in the test set. Moreover, we calculated the partial charges by vdW-DF2 deviate the most from other functionals while there is no significant difference between the partial charges calculated by M06L, PBE, PW91, PBE-D2 and PBE-D3 for the MOFs in the test set. We find that while there are differences in the magnitude of the properties predicted by the various functionals, these discrepancies are small compared to the accuracy necessary for most practical applications.

  20. Effect of physisorbed molecules and an external external fields on the metallic Shockley surface state of Cu(111): A density functional theory study

    NASA Astrophysics Data System (ADS)

    Berland, Kristian; Einstein, T. L.; Hyldgaard, Per

    2012-02-01

    To manipulate the Cu(111) partially-filled Shockley surface state, we study its response to an external fieldootnotetextKB, TLE, PH; arXiv 1109:6706 E and physisorbed PAHs and quinone molecules. We use density-functional theory calculations with periodic-boundary conditions. The van der Waals density functional version vdW-DF2 accounts for the molecular adsorption. The issue that the Kohn-Sham wave functions couple to both sides of the Cu slab is handled with a decoupling scheme based on a rotation in Hilbert space. A convergence study reveals that to obtain a proper Shockley surface state, 6 Cu layers is sufficient, while 15 is optimal. We use 6 layers for the response to the molecules and 15 to external field. We find that the surface state displays isotropic dispersion (up to order k^6), free-electron like until the Fermi wave vector but with a significant quartic component beyond. The shift in band minimum and effective mass depend linearly on E, with a smaller fractional change in the latter. Charge transfer occurs beyond the outermost copper atoms, and most of the screening is due to bulk electrons. We find that the molecular physisorption increases the band minimum, with the effect the of a quinone being much stronger than the corresponding PAH.

  1. Pressure-induced loss of electronic interlayer state and metallization in the ionic solid Li[subscript 3]N: Experiment and theory

    SciTech Connect

    Lazicki, A.; Yoo, C.W.; Evans, W.J.; Hu, M.Y.; Chow, P.; Pickett, W.E.

    2008-12-08

    Results of x-ray diffraction and nitrogen K-edge x-ray Raman scattering (XRS) investigations of the crystal and electronic structure of ionic compound Li{sub 3}N across two high-pressure phase transitions [A. Lazicki et al., Phys. Rev. Lett. 95, 165503 (2005)] are interpreted using density-functional theory. A low-energy peak in the XRS spectrum which is observed in both low-pressure hexagonal phases of Li3N and absent in the high-pressure cubic phase is found to originate from an interlayer band similar to the important free-electron-like state present in the graphite and graphite intercalated systems, but not observed previously in ionic insulators. XRS detection of the interlayer state is made possible because of its strong hybridization with the nitrogen p bands. A pressure-induced increase in the band gap of the high-pressure cubic phase of Li{sub 3}N is explained by the differing pressure dependencies of different quantum-number bands and is shown to be a feature of several low-Z closed-shell ionic materials.

  2. Metal aminoboranes

    DOEpatents

    Burrell, Anthony K.; Davis, Benjamin J.; Thorn, David L.; Gordon, John C.; Baker, R. Thomas; Semelsberger, Troy Allen; Tumas, William; Diyabalanage, Himashinie Vichalya Kaviraj; Shrestha, Roshan P.

    2010-05-11

    Metal aminoboranes of the formula M(NH.sub.2BH.sub.3).sub.n have been synthesized. Metal aminoboranes are hydrogen storage materials. Metal aminoboranes are also precursors for synthesizing other metal aminoboranes. Metal aminoboranes can be dehydrogenated to form hydrogen and a reaction product. The reaction product can react with hydrogen to form a hydrogen storage material. Metal aminoboranes can be included in a kit.

  3. Anticancer Activity of Metal Complexes: Involvement of Redox Processes

    PubMed Central

    Jungwirth, Ute; Kowol, Christian R.; Keppler, Bernhard K.; Hartinger, Christian G.; Berger, Walter; Heffeter, Petra

    2012-01-01

    Cells require tight regulation of the intracellular redox balance and consequently of reactive oxygen species for proper redox signaling and maintenance of metal (e.g., of iron and copper) homeostasis. In several diseases, including cancer, this balance is disturbed. Therefore, anticancer drugs targeting the redox systems, for example, glutathione and thioredoxin, have entered focus of interest. Anticancer metal complexes (platinum, gold, arsenic, ruthenium, rhodium, copper, vanadium, cobalt, manganese, gadolinium, and molybdenum) have been shown to strongly interact with or even disturb cellular redox homeostasis. In this context, especially the hypothesis of “activation by reduction” as well as the “hard and soft acids and bases” theory with respect to coordination of metal ions to cellular ligands represent important concepts to understand the molecular modes of action of anticancer metal drugs. The aim of this review is to highlight specific interactions of metal-based anticancer drugs with the cellular redox homeostasis and to explain this behavior by considering chemical properties of the respective anticancer metal complexes currently either in (pre)clinical development or in daily clinical routine in oncology. PMID:21275772

  4. Benchmarking density functional theory predictions of framework structures and properties in a chemically diverse test set of metal-organic frameworks

    DOE PAGES

    Nazarian, Dalar; Ganesh, P.; Sholl, David S.

    2015-09-30

    We compiled a test set of chemically and topologically diverse Metal–Organic Frameworks (MOFs) with high accuracy experimentally derived crystallographic structure data. The test set was used to benchmark the performance of Density Functional Theory (DFT) functionals (M06L, PBE, PW91, PBE-D2, PBE-D3, and vdW-DF2) for predicting lattice parameters, unit cell volume, bonded parameters and pore descriptors. On average PBE-D2, PBE-D3, and vdW-DF2 predict more accurate structures, but all functionals predicted pore diameters within 0.5 Å of the experimental diameter for every MOF in the test set. The test set was also used to assess the variance in performance of DFT functionalsmore » for elastic properties and atomic partial charges. The DFT predicted elastic properties such as minimum shear modulus and Young's modulus can differ by an average of 3 and 9 GPa for rigid MOFs such as those in the test set. Moreover, we calculated the partial charges by vdW-DF2 deviate the most from other functionals while there is no significant difference between the partial charges calculated by M06L, PBE, PW91, PBE-D2 and PBE-D3 for the MOFs in the test set. We find that while there are differences in the magnitude of the properties predicted by the various functionals, these discrepancies are small compared to the accuracy necessary for most practical applications.« less

  5. Search for two categories of target produces fewer fixations to target-color items.

    PubMed

    Menneer, Tamaryn; Stroud, Michael J; Cave, Kyle R; Li, Xingshan; Godwin, Hayward J; Liversedge, Simon P; Donnelly, Nick

    2012-12-01

    Searching simultaneously for metal threats (guns and knives) and improvised explosive devices (IEDs) in X-ray images is less effective than 2 independent single-target searches, 1 for metal threats and 1 for IEDs. The goals of this study were to (a) replicate this dual-target cost for categorical targets and to determine whether the cost remains when X-ray images overlap, (b) determine the role of attentional guidance in this dual-target cost by measuring eye movements, and (c) determine the effect of practice on guidance. Untrained participants conducted 5,376 trials of visual search of X-ray images, each specializing in single-target search for metal threats, single-target search for IEDs, or dual-target search for both. In dual-target search, only 1 target (metal threat or IED) at most appeared on any 1 trial. Eye movements, response time, and accuracy were compared across single-target and dual-target searches. Results showed a dual-target cost in response time, accuracy, and guidance, with fewer fixations to target-color objects and disproportionately more to non-target-color objects, compared with single-target search. Such reduction in guidance explains why targets are missed in dual-target search, which was particularly noticeable when objects overlapped. After extensive practice, accuracy, response time, and guidance remained better in single-target search than in dual-target search. The results indicate that, when 2 different target representations are required for search, both representations cannot be maintained as accurately as in separate single-target searches. They suggest that baggage X-ray security screeners should specialize in one type of threat, or be trained to conduct 2 independent searches, 1 for each threat item.

  6. Geographical Theories.

    ERIC Educational Resources Information Center

    Golledge, Reginald G.

    1996-01-01

    Discusses the origin of theories in geography and particularly the development of location theories. Considers the influence of economic theory on agricultural land use, industrial location, and geographic location theories. Explores a set of interrelated activities that show how the marketing process illustrates process theory. (MJP)

  7. Targeting metalloproteins by fragment-based lead discovery.

    PubMed

    Johnson, Sherida; Barile, Elisa; Farina, Biancamaria; Purves, Angela; Wei, Jun; Chen, Li-Hsing; Shiryaev, Sergey; Zhang, Ziming; Rodionova, Irina; Agrawal, Arpita; Cohen, Seth M; Osterman, Andrei; Strongin, Alex; Pellecchia, Maurizio

    2011-08-01

    It has been estimated that nearly one-third of functional proteins contain a metal ion. These constitute a wide variety of possible drug targets including metalloproteinases, dehydrogenases, oxidoreductases, hydrolases, deacetylases, or many others in which the metal ion is either of catalytic or of structural nature. Despite the predominant role of a metal ion in so many classes of drug targets, current high-throughput screening techniques do not usually produce viable hits against these proteins, likely due to the lack of proper metal-binding pharmacophores in the current screening libraries. Herein, we describe a novel fragment-based drug discovery approach using a metal-targeting fragment library that is based on a variety of distinct classes of metal-binding groups designed to reliably anchor the fragments at the target's metal ions. We show that the approach can effectively identify novel, potent and selective agents that can be readily developed into metalloprotein-targeted therapeutics.

  8. Density Functional Theory in Transition-Metal Chemistry: Relative Energies of Low-Lying States of Iron Compounds and the Effect of Spatial Symmetry Breaking

    SciTech Connect

    Sorkin, Anastassia; Iron, Mark A.; Truhlar, Donald G.

    2008-02-01

    The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. The ground and lower excited states of Fe2, Fe2 -, and FeO+ were studied using a number of density functional theory (DFT) methods. Specific attention was paid to the relative state energies, the internuclear distances (re), and the harmonic vibrational frequencies (öe). A number of factors influencing the calculated values of these properties were examined. These include basis sets, the nature of the density functional chosen, the percentage of Hartree- Fock exchange in the density functional, and constraints on orbital symmetry. A number of different types of generalized gradient approximation (GGA) density functionals (straight GGA, hybrid GGA, meta-GGA, and hybrid meta-GGA) were examined, and it was found that the best results were obtained with hybrid GGA or hybrid meta-GGA functionals that contain nonzero fractions of HF exchange; specifically, the best overall results were obtained with B3LYP, M05, and M06, closely followed by B1LYP. One significant observation was the effect of enforcing symmetry on the orbitals. When a degenerate orbital (ð or ä) is partially occupied in the 4¼ excited state of FeO+, reducing the enforced symmetry (from C6v to C4v to C2v) results in a lower energy since these degenerate orbitals are split in the lower symmetries. The results obtained were compared to higher level ab initio results from the literature and to recent PBE+U plane wave results by Kulik et al. (Phys. Rev. Lett. 2006, 97, 103001). It was found that some of the improvements that were afforded by the semiempirical +U correction can also be accomplished by improving the form of the DFT functional and, in one case, by not enforcing high symmetry on the orbitals.

  9. Targets and processes for fabricating same

    DOEpatents

    Cowan, Thomas; Malekos, Steven; Korgan, Grant; Adams, Jesse; Sentoku, Yasuhiko; Le Galloudec, Nathalie; Fuchs, Julien

    2012-07-24

    In particular embodiments, the present disclosure provides targets including a metal layer and defining a hollow inner surface. The hollow inner surface has an internal apex. The distance between at least two opposing points of the internal apex is less than about 15 .mu.m. In particular examples, the distance is less than about 1 .mu.m. Particular implementations of the targets are free standing. The targets have a number of disclosed shaped, including cones, pyramids, hemispheres, and capped structures. The present disclosure also provides arrays of such targets. Also provided are methods of forming targets, such as the disclosed targets, using lithographic techniques, such as photolithographic techniques. In particular examples, a target mold is formed from a silicon wafer and then one or more sides of the mold are coated with a target material, such as one or more metals.

  10. Targets and processes for fabricating same

    DOEpatents

    Cowna, Thomas; Malekos, Steven; Korgan, Grant; Adams, Jesse; Sentoku, Yasuhiko; LeGalloudec, Nathalie

    2014-06-10

    In particular embodiments, the present disclosure provides targets including a metal layer and defining a hollow inner surface. The hollow inner surface has an internal apex. The distance between at least two opposing points of the internal apex is less than about 15 .mu.m. In particular examples, the distance is less than about 1 .mu.m. Particular implementations of the targets are free standing. The targets have a number of disclosed shaped, including cones, pyramids, hemispheres, and capped structures. The present disclosure also provides arrays of such targets. Also provided are methods of forming targets, such as the disclosed targets, using lithographic techniques, such as photolithographic techniques. In particular examples, a target mold is formed from a silicon wafer and then one or more sides of the mold are coated with a target material, such as one or more metals.

  11. Targets and processes for fabricating same

    DOEpatents

    Adams, Jesse D; Malekos, Steven; Le Galloudec, Nathalie; Korgan, Grant; Cowan, Thomas; Sentoku, Yasuhiko

    2016-05-17

    In particular embodiments, the present disclosure provides targets including a metal layer and defining a hollow inner surface. The hollow inner surface has an internal apex. The distance between at least two opposing points of the internal apex is less than about 15 .mu.m. In particular examples, the distance is less than about 1 .mu.m. Particular implementations of the targets are free standing. The targets have a number of disclosed shaped, including cones, pyramids, hemispheres, and capped structures. The present disclosure also provides arrays of such targets. Also provided are methods of forming targets, such as the disclosed targets, using lithographic techniques, such as photolithographic techniques. In particular examples, a target mold is formed from a silicon wafer and then one or more sides of the mold are coated with a target material, such as one or more metals.

  12. Spin Density Distribution in Open-Shell Transition Metal Systems: A Comparative Post-Hartree-Fock, Density Functional Theory, and Quantum Monte Carlo Study of the CuCl2 Molecule.

    PubMed

    Caffarel, Michel; Giner, Emmanuel; Scemama, Anthony; Ramírez-Solís, Alejandro

    2014-12-01

    We present a comparative study of the spatial distribution of the spin density of the ground state of CuCl2 using Density Functional Theory (DFT), quantum Monte Carlo (QMC), and post-Hartree-Fock wave function theory (WFT). A number of studies have shown that an accurate description of the electronic structure of the lowest-lying states of this molecule is particularly challenging due to the interplay between the strong dynamical correlation effects in the 3d shell and the delocalization of the 3d hole over the chlorine atoms. More generally, this problem is representative of the difficulties encountered when studying open-shell metal-containing molecular systems. Here, it is shown that qualitatively different results for the spin density distribution are obtained from the various quantum-mechanical approaches. At the DFT level, the spin density distribution is found to be very dependent on the functional employed. At the QMC level, Fixed-Node Diffusion Monte Carlo (FN-DMC) results are strongly dependent on the nodal structure of the trial wave function. Regarding wave function methods, most approaches not including a very high amount of dynamic correlation effects lead to a much too high localization of the spin density on the copper atom, in sharp contrast with DFT. To shed some light on these conflicting results Full CI-type (FCI) calculations using the 6-31G basis set and based on a selection process of the most important determinants, the so-called CIPSI approach (Configuration Interaction with Perturbative Selection done Iteratively) are performed. Quite remarkably, it is found that for this 63-electron molecule and a full CI space including about 10(18) determinants, the FCI limit can almost be reached. Putting all results together, a natural and coherent picture for the spin distribution is proposed. PMID:26583212

  13. Spin Density Distribution in Open-Shell Transition Metal Systems: A Comparative Post-Hartree-Fock, Density Functional Theory, and Quantum Monte Carlo Study of the CuCl2 Molecule.

    PubMed

    Caffarel, Michel; Giner, Emmanuel; Scemama, Anthony; Ramírez-Solís, Alejandro

    2014-12-01

    We present a comparative study of the spatial distribution of the spin density of the ground state of CuCl2 using Density Functional Theory (DFT), quantum Monte Carlo (QMC), and post-Hartree-Fock wave function theory (WFT). A number of studies have shown that an accurate description of the electronic structure of the lowest-lying states of this molecule is particularly challenging due to the interplay between the strong dynamical correlation effects in the 3d shell and the delocalization of the 3d hole over the chlorine atoms. More generally, this problem is representative of the difficulties encountered when studying open-shell metal-containing molecular systems. Here, it is shown that qualitatively different results for the spin density distribution are obtained from the various quantum-mechanical approaches. At the DFT level, the spin density distribution is found to be very dependent on the functional employed. At the QMC level, Fixed-Node Diffusion Monte Carlo (FN-DMC) results are strongly dependent on the nodal structure of the trial wave function. Regarding wave function methods, most approaches not including a very high amount of dynamic correlation effects lead to a much too high localization of the spin density on the copper atom, in sharp contrast with DFT. To shed some light on these conflicting results Full CI-type (FCI) calculations using the 6-31G basis set and based on a selection process of the most important determinants, the so-called CIPSI approach (Configuration Interaction with Perturbative Selection done Iteratively) are performed. Quite remarkably, it is found that for this 63-electron molecule and a full CI space including about 10(18) determinants, the FCI limit can almost be reached. Putting all results together, a natural and coherent picture for the spin distribution is proposed.

  14. Raman and infrared spectroscopic investigations on aqueous alkali metal phosphate solutions and density functional theory calculations of phosphate-water clusters.

    PubMed

    Rudolph, Wolfram W; Irmer, Gert

    2007-12-01

    Phosphate (PO(4)(3-)) solutions in water and heavy water have been studied by Raman and infrared spectroscopy over a broad concentration range (0.0091-5.280 mol/L) including a hydrate melt at 23 degrees C. In the low wavenumber range, spectra in R-format have been constructed and the R normalization procedure has been briefly discussed. The vibrational modes of the tetrahedral PO(4)(3-)(aq) (T(d) symmetry) have been assigned and compared to the calculated values derived from the density functional theory (DFT) method for the unhydrated PO(4)(3-)(T(d)) and phosphate-water clusters: PO(4)(3-).H(2)O (C(2v)), PO(4)(3-).2H(2)O (D(2d)), PO(4)(3-).4H(2)O (D(2d)), PO(4)(3-).6H(2)O (T(d)), and PO(4)(3-).12H(2)O (T), a cluster with a complete first hydration sphere of water molecules. A cluster with a second hydration sphere of 12 water molecules and 6 in the first sphere, PO(4)(3-).18H(2)O (T), has also been calculated. Agreement between measured and calculated vibrational modes is best in the case of the PO(4)(3-).12H(2)O cluster and the PO(4)(3-).18H(2)O cluster but far less so in the case of the unhydrated PO(4)(3-) or phosphate-water cluster with a lower number of water molecules than 12. The asymmetric, broad band shape of v(1)(a(1)) PO(4)(3-) in aqueous solutions has been measured as a function of concentration and the asymmetric and broad band shape was explained. However, the same mode in heavy water has only half the full width at half-height compared to the mode in normal water. The PO(4)(3-) is strongly hydrated in aqueous solutions. This has been verified by Raman spectroscopy comparing v(2)(H(2)O), the deformation mode of water, and the stretching modes, the v(1)OH and v(3)OH of water, in K(3)PO(4) solutions as a function of concentration and comparison with the same modes in pure water. A mode at approximately 240 cm(-1) (isotropic R spectrum) has been detected and assigned to the restricted translational mode of the strong hydrogen bonds formed between

  15. Different effects of electronic excitation on metals and semiconductors

    NASA Astrophysics Data System (ADS)

    Yan, Gai-Qin; Cheng, Xin-Lu; Zhang, Hong; Zhu, Zhi-Yang; Ren, Da-Hua

    2016-06-01

    We study the electronic excitation effect upon ultrafast and intense laser irradiation on the stability of target materials, using density functional perturbation theory. The target materials include metals (Li, Na, Mg, Al, K, W, Au), Bi as a semimetal, and Si as a semiconductor. We found that the electronic excitation had different effects on the two distinct materials. For metals, the electronic pressure induces an increase in the shear modulus and presents a negative effect on the phonon entropy, which increases the lattice vibration frequency and melting temperature, leading to a higher stability for the close-packed structure (Al, Au, Mg). Conversely, the electronic pressure induces a decreasing trend in all these quantities, leading to a lower degree of stability and even a structural destabilization in the case of bcc-structured metals (W, Na, K, and Li). For semimetals and semiconductors, the internal pressure induces a completely opposite behavior with respect to close-packed structure metals. This can lead to structural destabilization for semimetals and even collapse for semiconductors. Finally, a shift of the Raman and infrared active modes is revealed for semimetals and semiconductors.

  16. Triple Point Topological Metals

    NASA Astrophysics Data System (ADS)

    Zhu, Ziming; Winkler, Georg W.; Wu, QuanSheng; Li, Ju; Soluyanov, Alexey A.

    2016-07-01

    Topologically protected fermionic quasiparticles appear in metals, where band degeneracies occur at the Fermi level, dictated by the band structure topology. While in some metals these quasiparticles are direct analogues of elementary fermionic particles of the relativistic quantum field theory, other metals can have symmetries that give rise to quasiparticles, fundamentally different from those known in high-energy physics. Here, we report on a new type of topological quasiparticles—triple point fermions—realized in metals with symmorphic crystal structure, which host crossings of three bands in the vicinity of the Fermi level protected by point group symmetries. We find two topologically different types of triple point fermions, both distinct from any other topological quasiparticles reported to date. We provide examples of existing materials that host triple point fermions of both types and discuss a variety of physical phenomena associated with these quasiparticles, such as the occurrence of topological surface Fermi arcs, transport anomalies, and topological Lifshitz transitions.

  17. A theory of single-electron non-adiabatic tunneling through a small metal nanoparticle with due account of the strong interaction of valence electrons with phonons of the condensed matter environment.

    PubMed

    Medvedev, Igor G

    2011-11-01

    A theory of electrochemical behavior of small metal nanoparticles (NPs) which is governed both by the charging effect and the effect of the solvent reorganization on the dynamic of the electron transfer (ET) is considered under ambient conditions. The exact expression for the rate constant of ET from an electrode to NP which is valid for all values of the reorganization free energy E(r), bias voltage, and overpotential is obtained in the non-adiabatic limit. The tunnel current/overpotential relations are studied and calculated for different values of the bias voltage and E(r). The effect of E(r) on the full width at half maximum of the charging peaks is investigated at different values of the bias voltage. The differential conductance/bias voltage and the tunnel current/bias voltage dependencies are also studied and calculated. It is shown that, at room temperature, the pronounced Coulomb blockade oscillations in the differential conductance/bias voltage curves and the noticeable Coulomb staircase in the tunnel current/bias voltage relations are observed only at rather small values of E(r) in the case of the strongly asymmetric tunneling contacts.

  18. Preparing Zr65Al7.5Ni10Cu17.5 bulk metallic glasses based on point-line-face-body theory.

    PubMed

    Chang, Zexin; Wang, Wenxian; Ge, Yaqiong

    2016-05-10

    Zr65Al7.5Ni10Cu17.5 bulk metallic glasses (BMGs) were prepared based on point-line-face-body (PLFB) theory with the pre-laid powder method from laser processing. The thickness of the prepared bulk amorphous alloy was about 1.6 mm. The microstructure evolution, phase composition, chemical component distribution, and corrosion behavior of the bulk amorphous alloy were investigated. The results showed that the amorphization ratio increased with the increase of the thickness of Zr65Al7.5Ni10Cu17.5 BMGs; furthermore, the volume fraction of the amorphous phase in the bottom layer (first layer), the middle layer (fourth layer), and the surface layer (seventh layer) was approximately 52%, 66%, and 74%, respectively. Due to different thermal cycles during the PLFB-forming process, the amorphous and crystallization coexisted in the deposited layers. For the corrosion property, the experiments of potentiodynamic polarization plots, Nyquist plots, and the equivalent circuits were performed in 3.5 wt. % sodium chloride solution. The seventh layer exhibits better corrosion-resistance performance than the other layers, which can be attributed to a higher amorphization ratio in the surface layer. PMID:27168294

  19. Mitochondria-targeting particles

    PubMed Central

    Wongrakpanich, Amaraporn; Geary, Sean M; Joiner, Mei-ling A; Anderson, Mark E; Salem, Aliasger K

    2015-01-01

    Mitochondria are a promising therapeutic target for the detection, prevention and treatment of various human diseases such as cancer, neurodegenerative diseases, ischemia-reperfusion injury, diabetes and obesity. To reach mitochondria, therapeutic molecules need to not only gain access to specific organs, but also to overcome multiple barriers such as the cell membrane and the outer and inner mitochondrial membranes. Cellular and mitochondrial barriers can be potentially overcome through the design of mitochondriotropic particulate carriers capable of transporting drug molecules selectively to mitochondria. These particulate carriers or vectors can be made from lipids (liposomes), biodegradable polymers, or metals, protecting the drug cargo from rapid elimination and degradation in vivo. Many formulations can be tailored to target mitochondria by the incorporation of mitochondriotropic agents onto the surface and can be manufactured to desired sizes and molecular charge. Here, we summarize recently reported strategies for delivering therapeutic molecules to mitochondria using various particle-based formulations. PMID:25490424

  20. Hydrogen interactions with metals

    NASA Technical Reports Server (NTRS)

    Mclellan, R. B.; Harkins, C. G.

    1975-01-01

    Review of the literature on the nature and extent of hydrogen interactions with metals and the role of hydrogen in metal failure. The classification of hydrogen-containing systems is discussed, including such categories as covalent hydrides, volatile hydrides, polymeric hydrides, and transition metal hydride complexes. The use of electronegativity as a correlating parameter in determining hydride type is evaluated. A detailed study is made of the thermodynamics of metal-hydrogen systems, touching upon such aspects as hydrogen solubility, the positions occupied by hydrogen atoms within the solvent metal lattice, the derivation of thermodynamic functions of solid solutions from solubility data, and the construction of statistical models for hydrogen-metal solutions. A number of theories of hydrogen-metal bonding are reviewed, including the rigid-band model, the screened-proton model, and an approach employing the augmented plane wave method to solve the one-electron energy band problem. Finally, the mechanism of hydrogen embrittlement is investigated on the basis of literature data concerning stress effects and the kinetics of hydrogen transport to critical sites.

  1. Tackling Targets.

    ERIC Educational Resources Information Center

    Further Education Unit, London (England).

    This document is designed to help British training and enterprise councils (TECs) and further education (FE) colleges develop and implement strategies for achieving the National Targets for Education and Training (NTET), which were developed by the Confederation of British Industry in 1992 and endorsed by the British government. The findings from…

  2. What Is Theory?

    ERIC Educational Resources Information Center

    Stewart, Jim; Harte, Victoria; Sambrook, Sally

    2011-01-01

    Purpose: The aim of the paper is to examine the meaning and value of the notion of theory as a basis for other papers in the special issue which examine facets of theorising HRD. Design/methodology/approach: A small scale and targeted literature review was conducted which focused on writings in the philosophy and sociology of science in order to…

  3. Metal inks

    DOEpatents

    Ginley, David S; Curtis, Calvin J; Miedaner, Alex; van Hest, Marinus Franciscus Antonius Maria; Kaydanova, Tatiana

    2014-02-04

    Self-reducing metal inks and systems and methods for producing and using the same are disclosed. In an exemplary embodiment, a method may comprise selecting metal-organic (MO) precursor, selecting a reducing agent, and dissolving the MO precursor and the reducing agent in an organic solvent to produce a metal ink that remains in a liquid phase at room temperature. Metal inks, including self-reducing and fire-through metal inks, are also disclosed, as are various applications of the metal inks.

  4. Supported Molten Metal Membranes for Hydrogen Separation

    SciTech Connect

    Datta, Ravindra; Ma, Yi Hua; Yen, Pei-Shan; Deveau, Nicholas; Fishtik, Ilie; Mardilovich, Ivan

    2013-09-30

    We describe here our results on the feasibility of a novel dense metal membrane for hydrogen separation: Supported Molten Metal Membrane, or SMMM.1 The goal in this work was to develop these new membranes based on supporting thin films of low-melting, non- precious group metals, e.g., tin (Sn), indium (In), gallium (Ga), or their alloys, to provide a flux and selectivity of hydrogen that rivals the conventional but substantially more expensive palladium (Pd) or Pd alloy membranes, which are susceptible to poisoning by the many species in the coal-derived syngas, and further possess inadequate stability and limited operating temperature range. The novelty of the technology presented numerous challenges during the course of this project, however, mainly in the selection of appropriate supports, and in the fabrication of a stable membrane. While the wetting instability of the SMMM remains an issue, we did develop an adequate understanding of the interaction between molten metal films with porous supports that we were able to find appropriate supports. Thus, our preliminary results indicate that the Ga/SiC SMMM at 550 ºC has a permeance that is an order of magnitude higher than that of Pd, and exceeds the 2015 DOE target. To make practical SMM membranes, however, further improving the stability of the molten metal membrane is the next goal. For this, it is important to better understand the change in molten metal surface tension and contact angle as a function of temperature and gas-phase composition. A thermodynamic theory was, thus, developed, that is not only able to explain this change in the liquid-gas surface tension, but also the change in the solid-liquid surface tension as well as the contact angle. This fundamental understanding has allowed us to determine design characteristics to maintain stability in the face of changing gas composition. These designs are being developed. For further progress, it is also important to understand the nature of solution and

  5. Target assembly

    DOEpatents

    Lewis, Richard A.

    1980-01-01

    A target for a proton beam which is capable of generating neutrons for absorption in a breeding blanket includes a plurality of solid pins formed of a neutron emissive target material disposed parallel to the path of the beam and which are arranged axially in a plurality of layers so that pins in each layer are offset with respect to pins in all other layers, enough layers being used so that each proton in the beam will strike at least one pin with means being provided to cool the pins. For a 300 mA, 1 GeV beam (300 MW), stainless steel pins, 12 inches long and 0.23 inches in diameter are arranged in triangular array in six layers with one sixth of the pins in each layer, the number of pins being such that the entire cross sectional area of the beam is covered by the pins with minimum overlap of pins.

  6. METAL PHTHALOCYANINES

    DOEpatents

    Frigerio, N.A.

    1962-03-27

    A process is given for preparing heavy metal phthalocyanines, sulfonated or not. The process comprises mixing an inorganic metal salt with dimethyl formamide or methyl sulfoxide; separating the metal complex formed from the solution; mixing the complex with an equimolar amount of sodium, potassium, lithium, magnesium, or beryllium sulfonated or unsulfonated phthalocyanine whereby heavy-metal phthalocyanine crystals are formed; and separating the crystals from the solution. Uranyl, thorium, lead, hafnium, and lanthanide rare earth phthalocyanines can be produced by the process. (AEC)

  7. Canonical density matrix perturbation theory.

    PubMed

    Niklasson, Anders M N; Cawkwell, M J; Rubensson, Emanuel H; Rudberg, Elias

    2015-12-01

    Density matrix perturbation theory [Niklasson and Challacombe, Phys. Rev. Lett. 92, 193001 (2004)] is generalized to canonical (NVT) free-energy ensembles in tight-binding, Hartree-Fock, or Kohn-Sham density-functional theory. The canonical density matrix perturbation theory can be used to calculate temperature-dependent response properties from the coupled perturbed self-consistent field equations as in density-functional perturbation theory. The method is well suited to take advantage of sparse matrix algebra to achieve linear scaling complexity in the computational cost as a function of system size for sufficiently large nonmetallic materials and metals at high temperatures. PMID:26764847

  8. Canonical density matrix perturbation theory.

    PubMed

    Niklasson, Anders M N; Cawkwell, M J; Rubensson, Emanuel H; Rudberg, Elias

    2015-12-01

    Density matrix perturbation theory [Niklasson and Challacombe, Phys. Rev. Lett. 92, 193001 (2004)] is generalized to canonical (NVT) free-energy ensembles in tight-binding, Hartree-Fock, or Kohn-Sham density-functional theory. The canonical density matrix perturbation theory can be used to calculate temperature-dependent response properties from the coupled perturbed self-consistent field equations as in density-functional perturbation theory. The method is well suited to take advantage of sparse matrix algebra to achieve linear scaling complexity in the computational cost as a function of system size for sufficiently large nonmetallic materials and metals at high temperatures.

  9. Silicone metalization

    DOEpatents

    Maghribi, Mariam N.; Krulevitch, Peter; Hamilton, Julie

    2008-12-09

    A system for providing metal features on silicone comprising providing a silicone layer on a matrix and providing a metal layer on the silicone layer. An electronic apparatus can be produced by the system. The electronic apparatus comprises a silicone body and metal features on the silicone body that provide an electronic device.

  10. Silicone metalization

    DOEpatents

    Maghribi, Mariam N.; Krulevitch, Peter; Hamilton, Julie

    2006-12-05

    A system for providing metal features on silicone comprising providing a silicone layer on a matrix and providing a metal layer on the silicone layer. An electronic apparatus can be produced by the system. The electronic apparatus comprises a silicone body and metal features on the silicone body that provide an electronic device.

  11. Metallic glasses.

    PubMed

    Greer, A L

    1995-03-31

    Amorphous metallic alloys, relative newcomers to the world of glasses, have properties that are unusual for solid metals. The metallic glasses, which exist in a very wide variety of compositions, combine fundamental interest with practical applications. They also serve as precursors for exciting new nanocrystalline materials. Their magnetic (soft and hard) and mechanical properties are of particular interest.

  12. Electron screening in metals

    NASA Astrophysics Data System (ADS)

    Gajević, J.; Lipoglavšek, M.; Likar, A.; Petrovič, T.; Pelicon, P.; Sánchez Ortiz, A.; Cvetinović, A.

    2016-01-01

    In order to further investigate electron screening effect we studied proton induced nuclear reactions over an energy range from 0.8 to 2.6 MeV for different environments: Mn and Cd metals and MnO and CdO insulators. Shifts in resonance energy for metallic relative to insulator targets were not observed. No large electron screening could be deduced for (p,γ) and (p,n) reactions in Mn. Moreover, no large electron screening can be deduced with certainty for the (p,n) reaction in Cd.

  13. Adhesion at metal interfaces

    NASA Technical Reports Server (NTRS)

    Banerjea, Amitava; Ferrante, John; Smith, John R.

    1991-01-01

    A basic adhesion process is defined, the theory of the properties influencing metallic adhesion is outlined, and theoretical approaches to the interface problem are presented, with emphasis on first-principle calculations as well as jellium-model calculations. The computation of the energies of adhesion as a function of the interfacial separation is performed; fully three-dimensional calculations are presented, and universality in the shapes of the binding energy curves is considered. An embedded-atom method and equivalent-crystal theory are covered in the framework of issues involved in practical adhesion.

  14. Electronic structure study of seven-coordinate first-row transition metal complexes derived from 1,10-diaza-15-crown-5: a successful marriage of theory with experiment.

    PubMed

    Platas-Iglesias, Carlos; Vaiana, Lea; Esteban-Gómez, David; Avecilla, Fernando; Real, José Antonio; de Blas, Andrés; Rodríguez-Blas, Teresa

    2005-12-26

    A detailed study of the electronic structure of seven-coordinate Mn(II), Co(II), and Ni(II) complexes with the lariat ether N,N'-bis(2-aminobenzyl)-1,10-diaza-15-crown-5 (L(1)) is presented. These complexes represent new examples of structurally characterized seven-coordinate (pentagonal bipyramidal) complexes for the Mn(II), Co(II), and Ni(II) ions. The X-ray crystal structures of the Mn(II) and Co(II) complexes show C(2) symmetries for the [M(L(1))](2+) cations, whereas the structures of the Ni(II) complexes show a more distorted coordination environment. The magnetic properties of the Mn(II) complex display a characteristic Curie law, whereas those of the Co(II) and Ni(II) ions show the occurrence of zero-field splitting of the S = 3/2 and 1 ground states, respectively. Geometry optimizations of the [M(L(1))](2+) systems (M = Mn, Co, or Ni) at the DFT (B3LYP) level of theory provide theoretical structures in good agreement with the experimental data. Electronic structure calculations predict a similar ordering of the metal-based beta spin frontier MO for the Mn(II) and Co(II) complexes. This particular ordering of the frontier MO leads to a pseudodegenerate ground state for the d(8) Ni(II) ion. The distortion of the C(2) symmetry in [Ni(L(1))](2+) is consistent with a Jahn-Teller effect that removes this pseudodegeneracy. Our electronic structure calculations predict that the binding strength of L(1) should follow the trend Co(II) approximately Mn(II) > Ni(II), in agreement with experimental data obtained from spectrophotometric titrations.

  15. Auditory target detection in reverberation

    NASA Astrophysics Data System (ADS)

    Zurek, Patrick M.; Freyman, Richard L.; Balakrishnan, Uma

    2004-04-01

    Measurements and theoretical predictions of auditory target detection in simulated reverberant conditions are reported. The target signals were pulsed 13-octave bands of noise and the masker signal was a continuous wideband noise. Target and masker signals were passed through a software simulation of a reverberant room with a rigid sphere modeling a listener's head. The location of the target was fixed while the location of the masker was varied in the simulated room. Degree of reverberation was controlled by varying the uniform acoustic absorption of the simulated room's surfaces. The resulting target and masker signals were presented to the listeners over headphones in monaural-left, monaural-right, or binaural listening modes. Changes in detection performance in the monaural listening modes were largely predictable from the changes in target-to-masker ratio in the target band, but with a few dB of extra masking in reverberation. Binaural detection performance was generally well predicted by applying Durlach's [in Foundations of Modern Auditory Theory (Academic, New York, 1972)] equalization-cancellation theory to the direct-plus-reverberant ear signals. Predictions in all cases were based on a statistical description of room acoustics and on acoustic diffraction by a sphere. The success of these detection models in the present well-controlled reverberant conditions suggests that they can be used to incorporate listening mode and source location as factors in speech-intelligibility predictions.

  16. Chemistry of carcinogenic metals.

    PubMed Central

    Martell, A E

    1981-01-01

    The periodic distribution of known and suspected carcinogenic metal ions is described, and the chemical behavior of various types of metal ions is explained in terms of the general theory of hard and soft acids and bases. The chelate effect is elucidated, and the relatively high stability of metal chelates in very dilute solutions is discussed. The concepts employed for the chelate effect are extended to explain the high stabilities of macrocyclic and cryptate complexes. Procedures for the use of equilibrium data to determine the speciation of metal ions and complexes under varying solution conditions are described. Methods for assessing the interferences by hydrogen ion, competing metal ions, hydrolysis, and precipitation are explained, and are applied to systems containing iron(III) chelates of fourteen chelating agents designed for effective binding of the ferric ion. The donor groups available for the building up of multidentate ligands are presented, and the ways in which they may be combined to achieve high affinity and selectivity for certain types of metal ions are explained. PMID:6791915

  17. Accelerator target

    DOEpatents

    Schlyer, D.J.; Ferrieri, R.A.; Koehler, C.

    1999-06-29

    A target includes a body having a depression in a front side for holding a sample for irradiation by a particle beam to produce a radioisotope. Cooling fins are disposed on a backside of the body opposite the depression. A foil is joined to the body front side to cover the depression and sample therein. A perforate grid is joined to the body atop the foil for supporting the foil and for transmitting the particle beam therethrough. A coolant is circulated over the fins to cool the body during the particle beam irradiation of the sample in the depression. 5 figs.

  18. Accelerator target

    DOEpatents

    Schlyer, David J.; Ferrieri, Richard A.; Koehler, Conrad

    1999-01-01

    A target includes a body having a depression in a front side for holding a sample for irradiation by a particle beam to produce a radioisotope. Cooling fins are disposed on a backside of the body opposite the depression. A foil is joined to the body front side to cover the depression and sample therein. A perforate grid is joined to the body atop the foil for supporting the foil and for transmitting the particle beam therethrough. A coolant is circulated over the fins to cool the body during the particle beam irradiation of the sample in the depression.

  19. Packaging Theory.

    ERIC Educational Resources Information Center

    Williams, Jeffrey

    1994-01-01

    Considers the recent flood of anthologies of literary criticism and theory as exemplifications of the confluence of pedagogical concerns, economics of publishing, and other historical factors. Looks specifically at how these anthologies present theory. Cites problems with their formatting theory and proposes alternative ways of organizing theory…

  20. Zinc metalloproteins as medicinal targets.

    PubMed

    Anzellotti, A I; Farrell, N P

    2008-08-01

    Zinc bioinorganic chemistry has emphasized the role of the metal ion on the structure and function of the protein. There is, more recently, an increasing appreciation of the role of zinc proteins in a variety of human diseases. This critical review, aimed at both bioinorganic and medicinal chemists, shows how apparently widely-diverging diseases share the common mechanistic approaches of targeting the essential function of the metal ion to inhibit activity. Protein structure and function is briefly summarized in the context of its clinical relevance. The status of current and potential inhibitors is discussed along with the prospects for future developments (162 references).