Solar concentrator with restricted exit angles

DOEpatents

Rabl, Arnulf; Winston, Roland

1978-12-19

A device is provided for the collection and concentration of radiant energy and includes at least one reflective side wall. The wall directs incident radiant energy to the exit aperture thereof or onto the surface of energy absorber positioned at the exit aperture so that the angle of incidence of radiant energy at the exit aperture or on the surface of the energy absorber is restricted to desired values.

Commensurate comparisons of models with energy budget observations reveal consistent climate sensitivities

NASA Astrophysics Data System (ADS)

Armour, K.

2017-12-01

Global energy budget observations have been widely used to constrain the effective, or instantaneous climate sensitivity (ICS), producing median estimates around 2°C (Otto et al. 2013; Lewis & Curry 2015). A key question is whether the comprehensive climate models used to project future warming are consistent with these energy budget estimates of ICS. Yet, performing such comparisons has proven challenging. Within models, values of ICS robustly vary over time, as surface temperature patterns evolve with transient warming, and are generally smaller than the values of equilibrium climate sensitivity (ECS). Naively comparing values of ECS in CMIP5 models (median of about 3.4°C) to observation-based values of ICS has led to the suggestion that models are overly sensitive. This apparent discrepancy can partially be resolved by (i) comparing observation-based values of ICS to model values of ICS relevant for historical warming (Armour 2017; Proistosescu & Huybers 2017); (ii) taking into account the "efficacies" of non-CO2 radiative forcing agents (Marvel et al. 2015); and (iii) accounting for the sparseness of historical temperature observations and differences in sea-surface temperature and near-surface air temperature over the oceans (Richardson et al. 2016). Another potential source of discrepancy is a mismatch between observed and simulated surface temperature patterns over recent decades, due to either natural variability or model deficiencies in simulating historical warming patterns. The nature of the mismatch is such that simulated patterns can lead to more positive radiative feedbacks (higher ICS) relative to those engendered by observed patterns. The magnitude of this effect has not yet been addressed. Here we outline an approach to perform fully commensurate comparisons of climate models with global energy budget observations that take all of the above effects into account. We find that when apples-to-apples comparisons are made, values of ICS in models are consistently in good agreement with values of ICS inferred from global energy budget constraints. This suggests that the current generation of coupled climate models are not overly sensitive. However, since global energy budget observations do not constrain ECS, it is less certain whether model ECS values are realistic.

Calculation of surface enthalpy of solids from an ab initio electronegativity based model: case of ice.

PubMed

Douillard, J M; Henry, M

2003-07-15

A very simple route to calculation of the surface energy of solids is proposed because this value is very difficult to determine experimentally. The first step is the calculation of the attractive part of the electrostatic energy of crystals. The partial charges used in this calculation are obtained by using electronegativity equalization and scales of electronegativity and hardness deduced from physical characteristics of the atom. The lattice energies of the infinite crystal and of semi-infinite layers are then compared. The difference is related to the energy of cohesion and then to the surface energy. Very good results are obtained with ice, if one compares with the surface energy of liquid water, which is generally considered a good approximation of the surface energy of ice.

Atomistic simulations of bulk, surface and interfacial polymer properties

NASA Astrophysics Data System (ADS)

Natarajan, Upendra

In chapter I, quasi-static molecular mechanics based simulations are used to estimate the activation energy of phenoxy rings flips in the amorphous region of a semicrystalline polyimide. Intra and intermolecular contributions to the flip activation energy, the torsional cooperativity accompanying the flip, and the effect of the flip on the motion in the glassy bulk state, are looked at. Also, comparison of the weighted mean activation energy is made with experimental data from solid state NMR measurements; the simulated value being 17.5 kcal/mol., while the experimental value was observed to be 10.5 kcal/mol. Chapter II deals with construction of random copolymer thin films of styrene-butadiene (SB) and styrene-butadiene-acrylonitrile (SBA). The structure and properties of the free surfaces presented by these thin films are analysed by, the atom mass density profiles, backbone bond orientation function, and the spatial distribution of acrylonitrile groups and styrene rings. The surface energies of SB and SBA are calculated using an atomistic equation and are compared with experimental data in the literature. In chapter III, simulations of polymer-polymer interfaces between like and unlike polymers, specifically cis-polybutadiene (PBD) and atatic polypropylene (PP), are presented. The structure of an incompatible polymer-polymer interface, and the estimation of the thermodynamic work of adhesion and interfacial energy between different incompatible polymers, form the focus here. The work of adhesion is calculated using an atomistic equation and is further used in a macroscopic equation to estimate the interfacial energy. The interfacial energy is compared with typical values for other immiscible systems in the literature. The interfacial energy compared very well with interfacial energy values for a few other immiscible hydrocarbon pairs. In chapter IV, the study proceeds to look at the interactions between nonpolar and polar small molecules with SB and SBA thin film surfaces. Toluene, hexadecane and water molecules are separately simulated to interact with SB and SBA surfaces in vacuum. The energetics of interaction are calculated atomistically and used in the atomistic equation to calculate the interfacial energy or the interaction energy. Comparisons with experimental data are not made due to the small concentrations of the molecules on the polymer surface. However, fundamental understanding of the structure of the system and the breakup of the energetics are provided by such a study.

New measurements of the sticking coefficient and binding energy of molecules on non-porous amorphous solid water in the submonolayer regime

NASA Astrophysics Data System (ADS)

He, Jiao; Acharyya, Kinsuk; Emtiaz, S. M.; Vidali, Gianfranco

2016-06-01

Sticking and adsorption of molecules on dust grains are two important processes in gas-grain interactions. We accurately measured both the sticking coefficient and the binding energy of several key molecules on the surface of amorphous solid water as a function of coverage.A time-resolved scattering technique was used to measure sticking coefficient of H2, D2, N2, O2, CO, CH4, and CO2 on non-porous amorphous solid water (np-ASW) in the low coverage limit over a wide range of surface temperatures. We found that the time-resolved scattering technique is advantageous over the conventional King-Wells method that underestimates the sticking coefficient. Based on the measured values we suggest a useful general formula of the sticking coefficient as a function of grain temperature and molecule-surface binding energy.We measured the binding energy of N2, CO, O2, CH4, and CO2 on np-ASW, and of N2 and CO on porous amorphous solid water (p-ASW). We were able to measure binding energies down to a fraction of 1% of a layer, thus making these measurements more appropriate for astrochemistry than the existing values. We found that CO2 forms clusters on np-ASW surface even at very low coverage; this may help in explaining the segregation of CO2 in ices. The binding energies of N2, CO, O2, and CH4 on np-ASW decrease with coverage in the submonolayer regime. Their values in the low coverage limit are much higher than what is commonly used in gas-grain models. An empirical formula was used to describe the coverage dependence of the binding energies. We used the newly determined binding energy distributions in a simulation of gas-grain chemistry for cold dense clouds and hot core models. We found that owing to the higher value of desorption energy in the sub-monlayer regime a fraction of all these ices stays much longer and to higher temperature on the grain surface compared to the case using single value energies as currently done in astrochemical models.This work was supported in part by a grant to GV from NSF --- Astronomy & Astrophysics Division (#1311958)

The use of inverse phase gas chromatography to study the change of surface energy of amorphous lactose as a function of relative humidity and the processes of collapse and crystallisation.

PubMed

Newell, H E; Buckton, G; Butler, D A; Thielmann, F; Williams, D R

2001-04-17

The purpose of this study was to assess the effect of relative humidity (RH) on the surface energy of amorphous lactose. Two samples of amorphous lactose were investigated; a spray dried 100% amorphous material and a ball milled sample of crystalline lactose. The milled sample had less than 1% amorphous content by mass, but on investigation at 0% RH, yielded surface energies comparable to those obtained from the 100% amorphous material, indicating that the surface was amorphous. The effect of increasing humidity was to reduce the dispersive surface energy of the two samples from 36.0 +/- 0.14 and 41.6 +/- 1.4 mJ m(-2) at 0% RH for the spray dried and milled samples respectively, to a value comparable to that obtained for the crystalline alpha-lactose monohydrate of 31.3 +/- 0.41 mJ m(-2). The change in surface energy due to water sorption was only reversible up to 20% RH; after exposure to higher RH values subsequent drying did not result in a return to the original surface energy of the amorphous form. This shows that the surface is reorganising as the glass transition temperature (Tg) is reduced, even though the sample has not collapsed or crystallised. It was possible to follow the collapse behaviour in the column with ease, using a number of different methods.

Surface energy and radiation balance systems - General description and improvements

NASA Technical Reports Server (NTRS)

Fritschen, Leo J.; Simpson, James R.

1989-01-01

Surface evaluation of sensible and latent heat flux densities and the components of the radiation balance were desired for various vegetative surfaces during the ASCOT84 experiment to compare with modeled results and to relate these values to drainage winds. Five battery operated data systems equipped with sensors to determine the above values were operated for 105 station days during the ASCOT84 experiment. The Bowen ratio energy balance technique was used to partition the available energy into the sensible and latent heat flux densities. A description of the sensors and battery operated equipment used to collect and process the data is presented. In addition, improvements and modifications made since the 1984 experiment are given. Details of calculations of soil heat flow at the surface and an alternate method to calculate sensible and latent heat flux densities are provided.

Thermodynamics of surface defects at the aspirin/water interface

NASA Astrophysics Data System (ADS)

Schneider, Julian; Zheng, Chen; Reuter, Karsten

2014-09-01

We present a simulation scheme to calculate defect formation free energies at a molecular crystal/water interface based on force-field molecular dynamics simulations. To this end, we adopt and modify existing approaches to calculate binding free energies of biological ligand/receptor complexes to be applicable to common surface defects, such as step edges and kink sites. We obtain statistically accurate and reliable free energy values for the aspirin/water interface, which can be applied to estimate the distribution of defects using well-established thermodynamic relations. As a show case we calculate the free energy upon dissolving molecules from kink sites at the interface. This free energy can be related to the solubility concentration and we obtain solubility values in excellent agreement with experimental results.

A surface physicochemical rationale for calculus formation in the oral cavity

NASA Astrophysics Data System (ADS)

Busscher, Henk J.; White, Don J.; Kamminga-Rasker, Hannetta J.; van der Mei, Henny C.

2004-01-01

Surface free energies of dental hard tissues, including salivary conditioning films on enamel, play a crucial role in mineralization, dissolution and adhesion processes at the tooth surface. These mineralization reactions at oral surfaces control the development and progression of various diseases. In this paper, we compare the surface free energies, as derived from measured contact angles with liquids, of salivary conditioning films on enamel after exposure to dentifrices with and without anti-calculus additives, such as hexametaphosphate, pyrophosphate or zinc citrate trihydrate. Measured contact angles were converted to surface free energies using the concept of Lifshitz-Van der Waals and Lewis acid-base components. Nearly all dentifrices yield film properties with a negative interfacial tension against an aqueous phase, which thermodynamically opposes mineralization. Concurrent with negative interfacial tensions, are positive values of the interfacial free energy of adhesion for octacalcium-phosphate (OCP) to the film surfaces, indicating that adhesion of newly mineralized, calcium-phosphate rich phases is thermodynamically unfavorable. Interestingly, two out of the three dentifrices with anti-calculus additives containing hexametaphosphate and pyrophosphate cause most positive interfacial free energies for OCP adhesion of 5.8 and 2.6 mJ/m 2, respectively. In summary, surface thermodynamical analyses indicate that anti-calculus effects of commercial dentifrice formulations are consistent with more negative interfacial tensions of salivary conditioning films on enamel surfaces and thus with more positive values for the interfacial free energy of adhesion toward newly formed mineral phases. A dentifrice containing hexametaphosphate yielded thermodynamic properties of salivary conditioning films most unfavorable for calculus formation.

Communication: Local energetic analysis of the interfacial and surface energies of graphene from the single layer to graphite

NASA Astrophysics Data System (ADS)

Kocherlakota, Lakshmi S.; Krajina, Brad A.; Overney, René M.

2015-12-01

Recent advances in scanning probe methods that provide direct access to the surface free energy of inorganic layered materials in terms of the Hamaker constant yield energetic values for monolayer graphene that differ substantially, by a factor of around 0.4, from bulk graphite. The onset of bulk deviating energy values was observed at a multilayer slab thickness of ˜3 nm, corresponding to a layer number of 10. The findings, complemented with extractions from water contact angle measurements and calculated interlayer binding energies, find short-range ordinary van der Waals interactions to be most prominently affected by dimensional constraints and many-body interactions.

Communication: Local energetic analysis of the interfacial and surface energies of graphene from the single layer to graphite.

PubMed

Kocherlakota, Lakshmi S; Krajina, Brad A; Overney, René M

2015-12-28

Recent advances in scanning probe methods that provide direct access to the surface free energy of inorganic layered materials in terms of the Hamaker constant yield energetic values for monolayer graphene that differ substantially, by a factor of around 0.4, from bulk graphite. The onset of bulk deviating energy values was observed at a multilayer slab thickness of ∼3 nm, corresponding to a layer number of 10. The findings, complemented with extractions from water contact angle measurements and calculated interlayer binding energies, find short-range ordinary van der Waals interactions to be most prominently affected by dimensional constraints and many-body interactions.

A one-layer satellite surface energy balance for estimating evapotranspiration rates and crop water stress indexes.

PubMed

Barbagallo, Salvatore; Consoli, Simona; Russo, Alfonso

2009-01-01

Daily evapotranspiration fluxes over the semi-arid Catania Plain area (Eastern Sicily, Italy) were evaluated using remotely sensed data from Landsat Thematic Mapper TM5 images. A one-source parameterization of the surface sensible heat flux exchange using satellite surface temperature has been used. The transfer of sensible and latent heat is described by aerodynamic resistance and surface resistance. Required model inputs are brightness, temperature, fractional vegetation cover or leaf area index, albedo, crop height, roughness lengths, net radiation, air temperature, air humidity and wind speed. The aerodynamic resistance (r(ah)) is formulated on the basis of the Monin-Obukhov surface layer similarity theory and the surface resistance (r(s)) is evaluated from the energy balance equation. The instantaneous surface flux values were converted into evaporative fraction (EF) over the heterogeneous land surface to derive daily evapotranspiration values. Remote sensing-based assessments of crop water stress (CWSI) were also made in order to identify local irrigation requirements. Evapotranspiration data and crop coefficient values obtained from the approach were compared with: (i) data from the semi-empirical approach "K(c) reflectance-based", which integrates satellite data in the visible and NIR regions of the electromagnetic spectrum with ground-based measurements and (ii) surface energy flux measurements collected from a micrometeorological tower located in the experiment area. The expected variability associated with ET flux measurements suggests that the approach-derived surface fluxes were in acceptable agreement with the observations.

Effects of surface stability on the morphological transformation of metals and metal oxides as investigated by first-principles calculations.

PubMed

Andrés, Juan; Gracia, Lourdes; Gouveia, Amanda Fernandes; Ferrer, Mateus Meneghetti; Longo, Elson

2015-10-09

Morphology is a key property of materials. Owing to their precise structure and morphology, crystals and nanocrystals provide excellent model systems for joint experimental and theoretical investigations into surface-related properties. Faceted polyhedral crystals and nanocrystals expose well-defined crystallographic planes depending on the synthesis method, which allow for thoughtful investigations into structure-reactivity relationships under practical conditions. This feature article introduces recent work, based on the combined use of experimental findings and first-principles calculations, to provide deeper knowledge of the electronic, structural, and energetic properties controlling the morphology and the transformation mechanisms of different metals and metal oxides: Ag, anatase TiO2, BaZrO3, and α-Ag2WO4. According to the Wulff theorem, the equilibrium shapes of these systems are obtained from the values of their respective surface energies. These investigations are useful to gain further understanding of how to achieve morphological control of complex three-dimensional crystals by tuning the ratio of the surface energy values of the different facets. This strategy allows the prediction of possible morphologies for a crystal and/or nanocrystal by controlling the relative values of surface energies.

Constraining the surface properties of effective Skyrme interactions

NASA Astrophysics Data System (ADS)

Jodon, R.; Bender, M.; Bennaceur, K.; Meyer, J.

2016-08-01

Background: Deformation energy surfaces map how the total binding energy of a nuclear system depends on the geometrical properties of intrinsic configurations, thereby providing a powerful tool to interpret nuclear spectroscopy and large-amplitude collective-motion phenomena such as fission. The global behavior of the deformation energy is known to be directly connected to the surface properties of the effective interaction used for its calculation. Purpose: The precise control of surface properties during the parameter adjustment of an effective interaction is key to obtain a reliable and predictive description of nuclear properties. The most relevant indicator is the surface-energy coefficient asurf. There are several possibilities for its definition and estimation, which are not fully equivalent and require a computational effort that can differ by orders of magnitude. The purpose of this study is threefold: first, to identify a scheme for the determination of asurf that offers the best compromise between robustness, precision, and numerical efficiency; second, to analyze the correlation between values for asurf and the characteristic energies of the fission barrier of 240Pu; and third, to lay out an efficient and robust procedure for how the deformation properties of the Skyrme energy density functional (EDF) can be constrained during the parameter fit. Methods: There are several frequently used possibilities to define and calculate the surface energy coefficient asurf of effective interactions built for the purpose of self-consistent mean-field calculations. The most direct access is provided by the model system of semi-infinite nuclear matter, but asurf can also be extracted from the systematics of binding energies of finite nuclei. Calculations can be carried out either self-consistently [Hartree-Fock (HF)], which incorporates quantal shell effects, or in one of the semiclassical extended Thomas-Fermi (ETF) or modified Thomas-Fermi (MTF) approximations. The latter is of particular interest because it provides asurf as a numerical integral without the need to solve self-consistent equations. Results for semi-infinite nuclear matter obtained with the HF, ETF, and MTF methods will be compared with one another and with asurf, as deduced from ETF calculations of very heavy fictitious nuclei. Results: The surface energy coefficient of 76 parametrizations of the Skyrme EDF have been calculated. Values obtained with the HF, ETF, and MTF methods are not identical, but differ by fairly constant systematic offsets. By contrast, extracting asurf from the binding energy of semi-infinite matter or of very large nuclei within the same method gives the same result within the numerical uncertainties. Conclusions: Despite having some drawbacks compared to the other methods studied here, the MTF approach provides sufficiently precise values for asurf such that it can be used as a very robust constraint on surface properties during a parameter fit at negligible additional cost. While the excitation energy of superdeformed states and the height of fission barriers is obviously strongly correlated to asurf, the presence of shell effects prevents a one-to-one correspondence between them. As in addition the value of asurf providing realistic fission barriers depends on the choices made for corrections for spurious motion, its "best value" (within a given scheme to calculate it) depends on the fit protocol. Through the construction of a series of eight parametrizations SLy5s1-SLy5s8 of the standard Skyrme EDF with systematically varied asurf value, it is shown how to arrive at a fit with realistic deformation properties.

Displacement energy of the surface layers of tungsten

NASA Astrophysics Data System (ADS)

Han, Longtao; Krstic, Predrag

2015-11-01

A molecular dynamics study with BOP potential is used to calculate the threshold displacement energy (ED) of primary knock-on atoms in the surface layers of the tungsten bcc crystal lattice at 300 K and at various crystallographic directions. Depending on the direction, ED is 10% to 75% smaller from the bulk value at the first layer, interfacing vacuum, while it reaches close to the bulk value already at the third tungsten layer. Supported by IACS of SBU and LDRD of PPPL.

The Probable Explanation for the Low Friction of Natural Joints.

PubMed

Pawlak, Zenon; Urbaniak, Wieslaw; Hagner-Derengowska, Magdalena; Hagner, Wojciech

2015-04-01

The surface of an articular cartilage, coated with phospholipid (PL) bilayers, plays an important role in its lubrication and movement. Intact (normal) and depleted surfaces of the joint were modelled and the pH influence on the surface interfacial energy, wettability and friction were investigated. In the experiments, the deterioration of the PL bilayer was controlled by its wettability and the applied friction. The surrounding fluid of an undamaged articular cartilage, the synovial fluid, has a pH value of approximately 7.4. Buffer solutions were formulated to represent the synovial fluid with various pH values. It was found that the surface interfacial energy was stabilised at its lowest values when the pH varied between 6.5 and 9.5. These results suggested that as the PL bilayers deteriorated, the hydration repulsion mechanism became less effective as friction increased. The decreased number of bilayers changed the wettability and lowered PL lubricant properties.

A new mathematical modeling approach for the energy of threonine molecule

NASA Astrophysics Data System (ADS)

Sahiner, Ahmet; Kapusuz, Gulden; Yilmaz, Nurullah

2017-07-01

In this paper, we propose an improved new methodology in energy conformation problems for finding optimum energy values. First, we construct the Bezier surfaces near local minimizers based on the data obtained from Density Functional Theory (DFT) calculations. Second, we blend the constructed surfaces in order to obtain a single smooth model. Finally, we apply the global optimization algorithm to find two torsion angles those make the energy of the molecule minimum.

Comparison of gas-solid chromatography and MM2 force field molecular binding energies for greenhouse gases on a carbonaceous surface.

PubMed

Rybolt, Thomas R; Bivona, Kevin T; Thomas, Howard E; O'Dell, Casey M

2009-10-01

Gas-solid chromatography was used to determine B(2s) (gas-solid virial coefficient) values for eight molecular adsorbates interacting with a carbon powder (Carbopack B, Supelco). B(2s) values were determined by multiple size variant injections within the temperature range of 313-553 K. The molecular adsorbates included: carbon dioxide (CO(2)); tetrafluoromethane (CF(4)); hexafluoroethane (C(2)F(6)); 1,1-difluoroethane (C(2)H(4)F(2)); 1-chloro-1,1-difluoroethane (C(2)H(3)ClF(2)); dichlorodifluoromethane (CCl(2)F(2)); trichlorofluoromethane (CCl(3)F); and 1,1,1-trichloroethane (C(2)H(3)Cl(3)). Two of these molecules are of special interest because they are "super greenhouse gases". The global warming potential, GWP, for CF(4) is 6500 and for C(2)F(6) is 9200 relative to the reference value of 1 for CO(2). The GWP index considers both radiative blocking and molecular lifetime. For these and other industrial greenhouse gases, adsorptive trapping on a carbonaceous solid, which depends on molecule-surface binding energy, could avoid atmospheric release. The temperature variations of the gas-solid virial coefficients in conjunction with van't Hoff plots were used to find the experimental adsorption energy or binding energy values (E(*)) for each adsorbate. A molecular mechanics based, rough-surface model was used to calculate the molecule-surface binding energy (Ecal(*)) using augmented MM2 parameters. The surface model consisted of parallel graphene layers with two separated nanostructures each containing 17 benzene rings arranged in linear strips. The separation of the parallel nanostructures had been optimized in a prior study to appropriately represent molecule-surface interactions for Carbopack B. Linear regressions of E(*) versus Ecal(*) for the current data set of eight molecules and the same surface model gave E(*)=0.926 Ecal(*) and r(2)=0.956. A combined set of the current and prior Carbopack B adsorbates studied (linear alkanes, branched alkanes, cyclic alkanes, ethers, and halogenated hydrocarbons) gave a data set with 33 molecules and a regression of E(*)=0.991 Ecal(*) and r(2)=0.968. These results indicated a good correlation between the experimental and the MM2 computed molecule-surface binding energies.

Surface structure and stability of partially hydroxylated silica surfaces

DOE PAGES

Rimsza, J. M.; Jones, R. E.; Criscenti, L. J.

2017-04-04

Surface energies of silicates influence crack propagation during brittle fracture and decrease with surface relaxation caused by annealing and hydroxylation. Molecular-level simulations are particularly suited for the investigation of surface processes. In this work, classical MD simulations of silica surfaces are performed with two force fields (ClayFF and ReaxFF) to investigate the effect of force field reactivity on surface structure and energy as a function of surface hydroxylation. An unhydroxylated fracture surface energy of 5.1 J/m 2 is calculated with the ClayFF force field, and 2.0 J/m 2 is calculated for the ReaxFF force field. The ClayFF surface energies aremore » consistent with the experimental results from double cantilever beam fracture tests (4.5 J/m 2), whereas ReaxFF underestimated these surface energies. Surface relaxation via annealing and hydroxylation was performed by creating a low-energy equilibrium surface. Annealing condensed neighboring siloxane bonds increased the surface connectivity, and decreased the surface energies by 0.2 J/m 2 for ClayFF and 0.8 J/m 2 for ReaxFF. Posthydroxylation surface energies decreased further to 4.6 J/m 2 with the ClayFF force field and to 0.2 J/m 2 with the ReaxFF force field. Experimental equilibrium surface energies are ~0.35 J/m 2, consistent with the ReaxFF force field. Although neither force field was capable of replicating both the fracture and equilibrium surface energies reported from experiment, each was consistent with one of these conditions. Furthermore, future computational investigations that rely on accurate surface energy values should consider the surface state of the system and select the appropriate force field.« less

Investigation of the surface free energy of the ITO thin films deposited under different working pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Özen, Soner, E-mail: osoner@ogu.edu.tr; Pat, Suat; Korkmaz, Şadan

This study discusses the influence of working pressure on the surface energy of the ITO thin films produced by radio frequency magnetron sputtering method. Optical tensiometer (Attension Theta Lite) is used for evaluating wetting behavior of the water droplet on the film surface and Equation of State method was selected to determine surface free energy for this study. Equation of state method does not divide the surface tension into different components such as polar, dispersive, acid-base. It is calculated the surfaces’ free energy measuring the contact angle with a single liquid. The surface free energy value was in the rangemore » of 15-31 mN/m. Also, the transmittances were determined in the wavelength range between 200 and 1000 nm using the UNICO 4802 UV-Vis double beam spectrophotometer. Transmittances of the produced ITO thin films are greater than %70 in the visible range.« less

Surface pretreatment of plastics with an atmospheric pressure plasma jet - Influence of generator power and kinematics

NASA Astrophysics Data System (ADS)

Moritzer, E.; Leister, C.

2014-05-01

The industrial use of atmospheric pressure plasmas in the plastics processing industry has increased significantly in recent years. Users of this treatment process have the possibility to influence the target values (e.g. bond strength or surface energy) with the help of kinematic and electrical parameters. Until now, systematic procedures have been used with which the parameters can be adapted to the process or product requirements but only by very time-consuming methods. For this reason, the relationship between influencing values and target values will be examined based on the example of a pretreatment in the bonding process with the help of statistical experimental design. Because of the large number of parameters involved, the analysis is restricted to the kinematic and electrical parameters. In the experimental tests, the following factors are taken as parameters: gap between nozzle and substrate, treatment velocity (kinematic data), voltage and duty cycle (electrical data). The statistical evaluation shows significant relationships between the parameters and surface energy in the case of polypropylene. An increase in the voltage and duty cycle increases the polar proportion of the surface energy, while a larger gap and higher velocity leads to lower energy levels. The bond strength of the overlapping bond is also significantly influenced by the voltage, velocity and gap. The direction of their effects is identical with those of the surface energy. In addition to the kinematic influences of the motion of an atmospheric pressure plasma jet, it is therefore especially important that the parameters for the plasma production are taken into account when designing the pretreatment processes.

Analysis of surface sputtering on a quantum statistical basis

NASA Technical Reports Server (NTRS)

Wilhelm, H. E.

1975-01-01

Surface sputtering is explained theoretically by means of a 3-body sputtering mechanism involving the ion and two surface atoms of the solid. By means of quantum-statistical mechanics, a formula for the sputtering ratio S(E) is derived from first principles. The theoretical sputtering rate S(E) was found experimentally to be proportional to the square of the difference between incident ion energy and the threshold energy for sputtering of surface atoms at low ion energies. Extrapolation of the theoretical sputtering formula to larger ion energies indicates that S(E) reaches a saturation value and finally decreases at high ion energies. The theoretical sputtering ratios S(E) for wolfram, tantalum, and molybdenum are compared with the corresponding experimental sputtering curves in the low energy region from threshold sputtering energy to 120 eV above the respective threshold energy. Theory and experiment are shown to be in good agreement.

H(D) → D(H) + Cu(111) collision system: Molecular dynamics study of surface temperature effects

PubMed Central

Vurdu, Can D.; Güvenç, Ziya B.

2011-01-01

All the channels of the reaction dynamics of gas-phase H (or D) atoms with D (or H) atoms adsorbed onto a Cu(111) surface have been studied by quasiclassical constant energy molecular dynamics simulations. The surface is flexible and is prepared at different temperature values, such as 30 K, 94 K, and 160 K. The adsorbates were distributed randomly on the surface to create 0.18 ML, 0.28 ML, and 0.50 ML of coverages. The multi-layer slab is mimicked by a many-body embedded-atom potential energy function. The slab atoms can move according to the exerted external forces. Treating the slab atoms non-rigid has an important effect on the dynamics of the projectile atom and adsorbates. Significant energy transfer from the projectile atom to the surface lattice atoms takes place especially during the first impact that modifies significantly the details of the dynamics of the collisions. Effects of the different temperatures of the slab are investigated in this study. Interaction between the surface atoms and the adsorbates is modeled by a modified London–Eyring–Polanyi–Sato (LEPS) function. The LEPS parameters are determined by using the total energy values which were calculated by a density functional theory and a generalized gradient approximation for an exchange-correlation energy for many different orientations, and locations of one- and two-hydrogen atoms on the Cu(111) surface. The rms value of the fitting procedure is about 0.16 eV. Many different channels of the processes on the surface have been examined, such as inelastic reflection of the incident hydrogen, subsurface penetration of the incident projectile and adsorbates, sticking of the incident atom on the surface. In addition, hot-atom and Eley-Rideal direct processes are investigated. The hot-atom process is found to be more significant than the Eley-Rideal process. Furthermore, the rate of subsurface penetration is larger than the sticking rate on the surface. In addition, these results are compared and analyzed as a function of the surface temperatures. PMID:21528959

H(D) → D(H) + Cu(111) collision system: molecular dynamics study of surface temperature effects.

PubMed

Vurdu, Can D; Güvenç, Ziya B

2011-04-28

All the channels of the reaction dynamics of gas-phase H (or D) atoms with D (or H) atoms adsorbed onto a Cu(111) surface have been studied by quasiclassical constant energy molecular dynamics simulations. The surface is flexible and is prepared at different temperature values, such as 30 K, 94 K, and 160 K. The adsorbates were distributed randomly on the surface to create 0.18 ML, 0.28 ML, and 0.50 ML of coverages. The multi-layer slab is mimicked by a many-body embedded-atom potential energy function. The slab atoms can move according to the exerted external forces. Treating the slab atoms non-rigid has an important effect on the dynamics of the projectile atom and adsorbates. Significant energy transfer from the projectile atom to the surface lattice atoms takes place especially during the first impact that modifies significantly the details of the dynamics of the collisions. Effects of the different temperatures of the slab are investigated in this study. Interaction between the surface atoms and the adsorbates is modeled by a modified London-Eyring-Polanyi-Sato (LEPS) function. The LEPS parameters are determined by using the total energy values which were calculated by a density functional theory and a generalized gradient approximation for an exchange-correlation energy for many different orientations, and locations of one- and two-hydrogen atoms on the Cu(111) surface. The rms value of the fitting procedure is about 0.16 eV. Many different channels of the processes on the surface have been examined, such as inelastic reflection of the incident hydrogen, subsurface penetration of the incident projectile and adsorbates, sticking of the incident atom on the surface. In addition, hot-atom and Eley-Rideal direct processes are investigated. The hot-atom process is found to be more significant than the Eley-Rideal process. Furthermore, the rate of subsurface penetration is larger than the sticking rate on the surface. In addition, these results are compared and analyzed as a function of the surface temperatures.

Estimation of soil hydraulic properties with microwave techniques

NASA Technical Reports Server (NTRS)

Oneill, P. E.; Gurney, R. J.; Camillo, P. J.

1985-01-01

Useful quantitative information about soil properties may be obtained by calibrating energy and moisture balance models with remotely sensed data. A soil physics model solves heat and moisture flux equations in the soil profile and is driven by the surface energy balance. Model generated surface temperature and soil moisture and temperature profiles are then used in a microwave emission model to predict the soil brightness temperature. The model hydraulic parameters are varied until the predicted temperatures agree with the remotely sensed values. This method is used to estimate values for saturated hydraulic conductivity, saturated matrix potential, and a soil texture parameter. The conductivity agreed well with a value measured with an infiltration ring and the other parameters agreed with values in the literature.

Predicting the quality of powders for inhalation from surface energy and area.

PubMed

Cline, David; Dalby, Richard

2002-09-01

To correlate the surface energy of active and carrier components in an aerosol powder to in vitro performance of a passive dry powder inhaler. Inverse gas chromatography (IGC) was used to assess the surface energy of active (albuterol and ipratropium bromide) and carrier (lactose monohydrate, trehalose dihydrate and mannitol) components of a dry powder inhaler formulation. Blends (1%w/w) of drug and carrier were prepared and evaluated for dry powder inhaler performance by cascade impaction. The formulations were tested with either of two passive dry powder inhalers, Rotahaler (GlaxoSmithKline) or Handihaler (Boehringer Ingelheim). In vitro performance of the powder blends was strongly correlated to surface energy interaction between active and carrier components. Plotting fine particle fraction vs. surface energy interaction yielded an R2 value of 0.9283. Increasing surface energy interaction between drug and carrier resulted in greater fine particle fraction of drug. A convincing relationship, potentially useful for rapid formulation design and screening, was found between the surface energy and area parameters derived from IGC and dry powder inhaler performance.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rimsza, J. M.; Jones, R. E.; Criscenti, L. J.

Surface energies of silicates influence crack propagation during brittle fracture and decrease with surface relaxation caused by annealing and hydroxylation. Molecular-level simulations are particularly suited for the investigation of surface processes. In this work, classical MD simulations of silica surfaces are performed with two force fields (ClayFF and ReaxFF) to investigate the effect of force field reactivity on surface structure and energy as a function of surface hydroxylation. An unhydroxylated fracture surface energy of 5.1 J/m 2 is calculated with the ClayFF force field, and 2.0 J/m 2 is calculated for the ReaxFF force field. The ClayFF surface energies aremore » consistent with the experimental results from double cantilever beam fracture tests (4.5 J/m 2), whereas ReaxFF underestimated these surface energies. Surface relaxation via annealing and hydroxylation was performed by creating a low-energy equilibrium surface. Annealing condensed neighboring siloxane bonds increased the surface connectivity, and decreased the surface energies by 0.2 J/m 2 for ClayFF and 0.8 J/m 2 for ReaxFF. Posthydroxylation surface energies decreased further to 4.6 J/m 2 with the ClayFF force field and to 0.2 J/m 2 with the ReaxFF force field. Experimental equilibrium surface energies are ~0.35 J/m 2, consistent with the ReaxFF force field. Although neither force field was capable of replicating both the fracture and equilibrium surface energies reported from experiment, each was consistent with one of these conditions. Furthermore, future computational investigations that rely on accurate surface energy values should consider the surface state of the system and select the appropriate force field.« less

Influence of temporary cement contamination on the surface free energy and dentine bond strength of self-adhesive cements.

PubMed

Takimoto, Masayuki; Ishii, Ryo; Iino, Masayoshi; Shimizu, Yusuke; Tsujimoto, Akimasa; Takamizawa, Toshiki; Ando, Susumu; Miyazaki, Masashi

2012-02-01

The surface free energy and dentine bond strength of self-adhesive cements were examined after the removal of temporary cements. The labial dentine surfaces of bovine mandibular incisors were wet ground with #600-grit SiC paper. Acrylic resin blocks were luted to the prepared dentine surfaces using HY Bond Temporary Cement Hard (HY), IP Temp Cement (IP), Fuji TEMP (FT) or Freegenol Temporary Cement (TC), and stored for 1 week. After removal of the temporary cements with an ultrasonic tip, the contact angle values of five specimens per test group were determined for the three test liquids, and the surface-energy parameters of the dentine surfaces were calculated. The dentine bond strengths of the self-adhesive cements were measured after removal of the temporary cements in a shear mode at a crosshead speed of 1.0mm/min. The data were subjected to one-way analysis of variance (ANOVA) followed by Tukey's HSD test. For all surfaces, the value of the estimated surface tension component γ(S)(d) (dispersion) was relatively constant at 41.7-43.3 mJm(-2). After removal of the temporary cements, the value of the γ(S)(h) (hydrogen-bonding) component decreased, particularly with FT and TC. The dentine bond strength of the self-adhesive cements was significantly higher for those without temporary cement contamination (8.2-10.6 MPa) than for those with temporary cement contamination (4.3-7.1 MPa). The γ(S) values decreased due to the decrease of γ(S)(h) values for the temporary cement-contaminated dentine. Contamination with temporary cements led to lower dentine bond strength. The presence of temporary cement interferes with the bonding performance of self-adhesive cements to dentine. Care should be taken in the methods of removal of temporary cement when using self-adhesive cements. Copyright © 2011 Elsevier Ltd. All rights reserved.

Surface studies of praseodymium by electron spectroscopies

NASA Astrophysics Data System (ADS)

Krawczyk, Mirosław; Pisarek, Marcin; Lisowski, Wojciech; Jablonski, Aleksander

2016-12-01

Electron transport properties in praseodymium (Pr) foil samples were studied by elastic-peak electron spectroscopy (EPES). Prior to EPES measurements, the Pr sample surface was pre-sputtered by Ar ions with ion energy of 2-3 keV. After such treatment, the Pr sample still contained about 10 at.% of residual oxygen in the surface region, as detected by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) analyses. The inelastic mean free path (IMFP), characterizing electron transport within this region (4 nm-thick), was evaluated from EPES using both Ni and Au standards as a function of energy in the range of 0.5-2 keV. Experimental IMFPs, λ, were approximated by the simple function λ = kEp, where E is energy (in eV), and k = 0.1549 and p = 0.7047 were the fitted parameters. These values were compared with IMFPs for the praseodymium surface in which the presence of oxygen was tentatively neglected, and also with IMFPs resulting from the TPP-2M predictive equation for bulk praseodymium. We found that the measured IMFP values to be only slightly affected by neglect of oxygen in calculations. The fitted function applied here was consistent with the energy dependence of the EPES-measured IMFPs. Additionally, the measured IMFPs were found to be from 2% to 4.2% larger than the predicted IMFPs for praseodymium in the energy range of 500-1000 eV. For electron energies of 1500 eV and 2000 eV, there was an inverse correlation between these values, and then the resulting deviations of -0.4% and -2.7%, respectively, were calculated.

Topography and surface energy dependent calcium phosphate formation on Sol-Gel derived TiO2 coatings.

PubMed

Järn, Mikael; Areva, Sami; Pore, Viljami; Peltonen, Jouko; Linden, Mika

2006-09-12

Heterogeneous nucleation and growth of calcium phosphate (CaP) on sol-gel derived TiO(2) coatings was investigated in terms of surface topography and surface energy. The topography of the coatings was derived from AFM measurements, while the surface energy was determined with contact angle measurements. The degree of precipitation was examined with scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The precipitation of CaP was found to be dependent on both topography and surface energy. A high roughness value when combining the RMS roughness parameter S(q) with the number of local maxima per unit area parameter S(ds) enhances CaP formation. The hydrophilicity of the coating was also found to be of importance for CaP formation. We suggest that the water contact angle, which is a direct measure of the hydrophilicity of the surface, may be used to evaluate the surface energy dependent precipitation kinetics rather than using the often applied Lewis base parameter.

Investigation of the effect of sealed surfaces on local climate in urban areas

NASA Astrophysics Data System (ADS)

Weihs, Philipp; Hasel, Stefan; Mursch-Radlgruber, Erich; Gützer, Christian; Krispel, Stefan; Peyerl, Martin; Trimmel, Heidi

2015-04-01

Local climate is driven by the interaction between energy balance and energy transported by advected air. Short-wave and long-wave radiation are major components in this interaction. Some few studies (e.g. Santamouris et al.) showed that adjusting the grade of reflection of surfaces is an efficient way to influence temperature. The present study investigates the influence of high albedo concrete surfaces on local climate. The first step of the study consisted of experimental investigations: routine measurements of the short and longwave radiation balance, of the ground and of the air temperature and humidity at different heights above 6 different types of sealed surfaces were performed. During this measurement campaign the above mentioned components were measured over a duration of 4 months above two conventional asphalt surfaces, one conventional concrete and three newly developed concrete surfaces with increased reflectances. Measured albedo values amounted to 0.12±0.02 for the asphalt surfaces and to maximum values of 0.56 for high albedo concrete. The maximum difference in surface temperature between the asphalt surfaces and the high albedo concrete surfaces amounted to 15°C. In addition the emission constants of the different sealed surfaces were also determined and were compared to values from literature.. In a second step the urban energy balance model Envi_Met was used to simulate the surface temperature of the six surfaces. The simulated surface temperatures were compared to the measured surface temperatures and statements as to uncertainties of the model simulations were made In a third step, Envi_Met was used to simulate the local climate of an urban district in Vienna. The surface and air temperature and the SW, LW fluxes were calculated for different types of sealed surfaces. By performing calculations of thermal stress indices (UTCI, PMV), statements as to the influence of the type of sealed surface on thermal stress on humans was made.

Inferring the microscopic surface energy of protein-protein interfaces from mutation data.

PubMed

Moal, Iain H; Dapkūnas, Justas; Fernández-Recio, Juan

2015-04-01

Mutations at protein-protein recognition sites alter binding strength by altering the chemical nature of the interacting surfaces. We present a simple surface energy model, parameterized with empirical ΔΔG values, yielding mean energies of -48 cal mol(-1) Å(-2) for interactions between hydrophobic surfaces, -51 to -80 cal mol(-1) Å(-2) for surfaces of complementary charge, and 66-83 cal mol(-1) Å(-2) for electrostatically repelling surfaces, relative to the aqueous phase. This places the mean energy of hydrophobic surface burial at -24 cal mol(-1) Å(-2) . Despite neglecting configurational entropy and intramolecular changes, the model correlates with empirical binding free energies of a functionally diverse set of rigid-body interactions (r = 0.66). When used to rerank docking poses, it can place near-native solutions in the top 10 for 37% of the complexes evaluated, and 82% in the top 100. The method shows that hydrophobic burial is the driving force for protein association, accounting for 50-95% of the cohesive energy. The model is available open-source from http://life.bsc.es/pid/web/surface_energy/ and via the CCharpPPI web server http://life.bsc.es/pid/ccharppi/. © 2015 Wiley Periodicals, Inc.

Streptococcus mutans adhesion on nickel titanium (NiTi) and copper-NiTi archwires: A comparative prospective clinical study.

PubMed

Abraham, Kirubaharan S; Jagdish, Nithya; Kailasam, Vignesh; Padmanabhan, Sridevi

2017-05-01

To compare the adhesion of Streptococcus mutans to nickel titanium (NiTi) and copper-NiTi (Cu-NiTi) archwires and to correlate the adhesion to surface characteristics (surface free energy and surface roughness) of these wires. A total of 16 patients undergoing orthodontic treatment with preadjusted edgewise appliances were included in the study. 0.016" and 0.016" × 0.022" NiTi and Cu-NiTi archwires in as-received condition and after 4 weeks of intraoral use were studied for S mutans adhesion using real-time polymerase chain reaction. Surface roughness and surface free energy were studied by three-dimensional surface profilometry and dynamic contact angle analysis, respectively. S mutans adhesion was more in Cu-NiTi archwires. These wires exhibited rougher surface and higher surface free energy when compared to NiTi archwires. S mutans adhesion, surface roughness, and surface free energy were greater in Cu-NiTi than NiTi archwires. Surface roughness and surface free energy increased after 4 weeks of intraoral exposure for all of the archwires studied. A predominantly negative correlation was seen between the cycle threshold value of adherent bacteria and surface characteristics.

Satellite remote sensing of surface energy and mass balance - Results from FIFE

NASA Technical Reports Server (NTRS)

Hall, F. G.; Markham, B. J.; Wang, J. R.; Huemmrich, F.; Sellers, P. J.; Strebel, D. E.; Kanemasu, E. T.; Kelly, Robert D.; Blad, Blaine L.

1991-01-01

Results obtained from the FIFE experiments conducted in 1987 and 1989 are summarized. Data analyses indicate that the hypotheses linking energy balance components to surface biology and remote sensing are reasonable at a point level, and that satellite remote sensing can potentially provide useful estimates of the surface energy budget. An investigation of atmospheric scattering and absorption effects on satellite remote sensing of surface radiance shows that the magnitude of atmospheric opacity variations within the FIFE site and with season can have a large effect on satellite measured values of surface radiances. Comparisons of atmospherically corrected TM radiances with surface measured radiances agreed to within about two percent at the visible and near-infrared wavelengths and to 6 percent in the midinfrared.

Determination of the mean solid-liquid interface energy of pivalic acid

NASA Technical Reports Server (NTRS)

Singh, N. B.; Gliksman, M. E.

1989-01-01

A high-confidence solid-liquid interfacial energy is determined for an anisotropic material. A coaxial composite having a cylindrical specimen chamber geometry provides a thermal gradient with an axial heating wire. The surface energy is derived from measurements of grain boundary groove shapes. Applying this method to pivalic acid, a surface energy of 2.84 erg/sq cm was determined with a total systematic and random error less than 10 percent. The value of interfacial energy corresponds to 24 percent of the latent heat of fusion per molecule.

The response of surface mass and energy balance of a continental glacier to climate variability, western Qilian Mountains, China

NASA Astrophysics Data System (ADS)

Sun, Weijun; Qin, Xiang; Wang, Yetang; Chen, Jizu; Du, Wentao; Zhang, Tong; Huai, Baojuan

2017-08-01

To understand how a continental glacier responds to climate change, it is imperative to quantify the surface energy fluxes and identify factors controlling glacier mass balance using surface energy balance (SEB) model. Light absorbing impurities (LAIs) at the glacial surface can greatly decrease surface albedo and increase glacial melt. An automatic weather station was set up and generated a unique 6-year meteorological dataset for the ablation zone of Laohugou Glacier No. 12. Based on these data, the surface energy budget was calculated and an experiment on the glacial melt process was carried out. The effect of reduced albedo on glacial melting was analyzed. Owing to continuous accumulation of LAIs, the ablation zone had been darkening since 2010. The mean value of surface albedo in melt period (June through September) dropped from 0.52 to 0.43, and the minimum of daily mean value was as small as 0.1. From the records of 2010-2015, keeping the clean ice albedo fixed in the range of 0.3-0.4, LAIs caused an increase of +7.1 to +16 W m-2 of net shortwave radiation and an removal of 1101-2663 mm water equivalent. Calculation with the SEB model showed equivalent increases in glacial melt were obtained by increasing air temperature by 1.3 and 3.2 K, respectively.

Trajectories and energy transfer of saltating particles onto rock surfaces : application to abrasion and ventifact formation on Earth and Mars

NASA Technical Reports Server (NTRS)

Bridges, Nathan T.; Phoreman, James; White, Bruce R.; Greeley, Ronald; Eddlemon, Eric E.; Wilson, Gregory R.; Meyer, Christine J.

2005-01-01

The interaction between saltating sand grains and rock surfaces is assessed to gauge relative abrasion potential as a function of rock shape, wind speed, grain size, and planetary environment. Many kinetic energy height profiles for impacts exhibit a distinctive increase, or kink, a few centimeters above the surface, consistent with previous field, wind tunnel, and theoretical investigations. The height of the kink observed in natural and wind tunnel settings is greater than predictions by a factor of 2 or more, probably because of enhanced bouncing off hard ground surfaces. Rebounded grains increase the effective flux and relative kinetic energy for intermediate slope angles. Whether abrasion occurs, as opposed to simple grain impact with little or no mass lost from the rock, depends on whether the grain kinetic energy (EG) exceeds a critical value (EC), as well as the flux of grains with energies above EC. The magnitude of abrasion and the shape change of the rock over time depends on this flux and the value of EG > EC. Considering the potential range of particle sizes and wind speeds, the predicted kinetic energies of saltating sand hitting rocks overlap on Earth and Mars. However, when limited to the most likely grain sizes and threshold conditions, our results agree with previous work and show that kinetic energies are about an order of magnitude greater on Mars.

A project summary: Water and energy budget assessment for a non-tidal wetland in the Sacramento-San Joaquin delta

USGS Publications Warehouse

Anderson, Frank E.; Snyder, R.L.; Paw, U.K.T.; Drexler, Judith Z.

2004-01-01

The methods used to obtain universal cover coefficient (Kc) values for a non-tidal restored wetland in the Sacramento-San Joaquin river delta, US, during the summer of the year 2002 and to investigate possible differences during changing wind patterns are described. A micrometeorological tower over the wetland was established to quantify actual evapotranspiration (ETa) rates and surface energy fluxes for water and energy budget analysis. The eddy-covariance (EC) system was used to measure the surface energy budget data in the period from May 23 to November 6, 2002. The results show that K c values should be lower during westerly than northerly wind events during the midseason period due to the reduced vapor pressure deficit.

Interaction of dyes CD–1 and SD–1 with the surface of oligodimethysiloxane

NASA Astrophysics Data System (ADS)

Chausov, D. N.

2018-03-01

We carried out the modeling orientation of the dyes CD–1 and SD–1 relative to the surface of oligodimethysiloxane using the atom–atom potentials method. We have discovered the dependence of the interaction energy in dyes molecules on the angles which characterizes their orientation relative to the surface of the oligodimethysiloxane crystal. It was found out that the obtained energy value of interaction with the surface can explain weak adhesive qualities of the dyes and the orientation type relative to the surface. We identified the break– loose force for the dyes on the oligodimethysiloxane crystal surface.

Interactions of satellite-speed helium atoms with satellite surfaces. 3: Drag coefficients from spatial and energy distributions of reflected helium atoms

NASA Technical Reports Server (NTRS)

Sharma, P. K.; Knuth, E. L.

1977-01-01

Spatial and energy distributions of helium atoms scattered from an anodized 1235-0 aluminum surface as well as the tangential and normal momentum accommodation coefficients calculated from these distributions are reported. A procedure for calculating drag coefficients from measured values of spatial and energy distributions is given. The drag coefficient calculated for a 6061 T-6 aluminum sphere is included.

Molecular Dynamics Simulations of Adhesion at Epoxy Interfaces

NASA Technical Reports Server (NTRS)

Frankland, Sarah-Jane V.; Clancy, Thomas C.; Hinkley, J. A.; Gates. T. S.

2008-01-01

The effect of moisture on adhesives used in aerospace applications can be modeled with chemically specific techniques such as molecular dynamics simulation. In the present study, the surface energy and work of adhesion are calculated for epoxy surfaces and interfaces, respectively, by using molecular dynamics simulation. Modifications are made to current theory to calculate the work of adhesion at the epoxy-epoxy interface with and without water. Quantitative agreement with experimental values is obtained for the surface energy and work of adhesion at the interface without water. The work of adhesion agrees qualitatively with the experimental values for the interface with water: the magnitude is reduced 15% with respect to the value for the interface without water. A variation of 26% in the magnitude is observed depending on the water configuration at a concentration of 1.6 wt%. The methods and modifications to the method that are employed to obtain these values are expected to be applicable for other epoxy adhesives to determine the effects of moisture uptake on their work of adhesion.

The surface reactivity of chalk (biogenic calcite) with hydrophilic and hydrophobic functional groups

NASA Astrophysics Data System (ADS)

Okhrimenko, D. V.; Dalby, K. N.; Skovbjerg, L. L.; Bovet, N.; Christensen, J. H.; Stipp, S. L. S.

2014-03-01

The surface properties of calcium carbonate minerals play an important role in a number of industrial and biological processes. Properties such as wettability and adsorption control liquid-solid interface behaviour and thus have a strong influence on processes such as biomineralisation, remediation of aquifers and oil recovery. We investigated how two model molecules of different polarity, namely water and ethanol, interact with reservoir and outcrop chalk samples and we compared their behaviour with that of pure, inorganically precipitated calcite. Thermodynamic quantities, such as the work of wetting, surface energy and isosteric adsorption enthalpy, were determined from vapour adsorption isotherms. The chalks were studied fresh and after extraction of organic residues that were originally present in these samples. The work of wetting correlates with the amount of organic matter present in the chalk samples but we observed a fundamental difference between the adsorption properties of chalk and pure, inorganically precipitated calcite toward the less polar, ethanol molecule. Further analysis of the chemical composition of the organic matter extracted from the chalk samples was made by gas chromatography (GC-MS). Monitoring surface composition by X-ray photoelectron spectroscopy (XPS) before and after extraction of the organic material, and with atomic force microscopy (AFM), showed that nanometer sized clay crystals observed on the chalk particle surfaces could be an important part of the reason for the differences. Removal of the extractable portion of the hydrocarbons liberates adsorption sites that have different wetting properties than the rest of the chalk and these have an energy distribution that is similar to clays. Thus, the results exemplify the complexity of biogenic calcite adsorption behaviour and demonstrate that chalk wetting in drinking water aquifers as well as oil reservoirs is controlled partly by the nanoparticles of clay that have grown on the chalk surfaces and partly by adsorbed organic material. GS < GS after extraction < WS < WS after extraction < Ålborg after extraction ⩽ Ålborg. The increase of spreading work for WS chalk for ethanol is 21 mN/m and for water is 26 mN/m, a ratio of 21/26 = 0.81. The increase of spreading work for GS chalk for ethanol and water are 36 and 42 mN/m, a ratio of 36/42 = 0.86. The similarity between these ratios leads us to conclude, that the surface that was produced by extraction of the organic material is quite similar for these two samples.The total surface energy increase, after the extraction of organics, for GS and WS was 67 and 49 mJ/m2. Further separation of surface energy into polar and dispersive parts showed that, for both samples, removing organic matter by extraction preferably increases the dispersive component of the surface energy. The contribution from dispersive surface energy to the increase in total surface energy was 87% for GS and 73% for WS chalk. A high relative proportion of dispersive component in the total surface energy is also typical for clay minerals (Chassin et al., 1986; Jouany and Chassin, 1987; Kádár et al., 2006).This demonstrates that the additional adsorption sites that are exposed by the extraction procedure are less polar than the sites originally exposed. Based on these results, we can conclude that chalk particles have surface sites of different polarity and that organic compounds preferentially adsorb at the less polar sites. These additional sites have quite similar surface properties for both North Sea chalk samples with an energy distribution that is similar to clays, that are described in the literature (Chassin et al., 1986; Jouany and Chassin, 1987; Kádár et al., 2006).The Ålborg chalk initially has minimal adsorbed organic material and the work of wetting changes very little after the treatment for extracting organic material. Considering the lower reproducibility of the results on Ålborg chalk, the differences in surface energies before and after extraction are considered insignificant and we conclude that the sample is not affected by the extraction procedure.The absolute values for the dispersive component of surface energy for North Sea chalks determined here are consistent with data obtained earlier by inverse gas chromatography (IGC) (Skovbjerg et al., 2013). Skovbjerg and colleagues reported values of γd for GS and WS chalk equal to 36.3 and 47.0 mJ/m2. The values reported for the polar components of the surface energy are, however, much lower. This difference is probably associated with the differences in the theoretical background for the two techniques. IGC measures surface interaction with vapours at close to zero coverage, using the Good-van Oss approach (van Oss et al., 1988), whereas the results obtained here are for surfaces fully covered by several layers of adsorbate and use the Owens-Wendt approach (Owens and Wendt, 1969). Our probe molecules (water and ethanol) are also more polar than the probe molecules used for the IGC experiments (dichloromethane and ethyl acetate), which probably leads to overestimation of values for the polar component of the surface energy.The total surface energy of the calcite samples that we obtained is close to reports for marble (Janczuk et al., 1983) and calcite (Goujon and Mutaftschiev, 1976; Okayama et al., 1997). There are, however, considerable differences in the values reported by different groups and in one case (Douillard et al., 1995), values reported are three times higher than our observations. We propose that the history of the samples, thus what is adsorbed on the surfaces, has a great deal to do with the surface tension measured.

Estimating envelope thermal characteristics from single point in time thermal images

NASA Astrophysics Data System (ADS)

Alshatshati, Salahaldin Faraj

Energy efficiency programs implemented nationally in the U.S. by utilities have rendered savings which have cost on average 0.03/kWh. This cost is still well below generation costs. However, as the lowest cost energy efficiency measures are adopted, this the cost effectiveness of further investment declines. Thus there is a need to more effectively find the most opportunities for savings regionally and nationally, so that the greatest cost effectiveness in implementing energy efficiency can be achieved. Integral to this process. are at scale energy audits. However, on-site building energy audits process are expensive, in the range of US1.29/m2-$5.37/m2 and there are an insufficient number of professionals to perform the audits. Energy audits that can be conducted at-scale and at low cost are needed. Research is presented that addresses at community-wide scales characterization of building envelope thermal characteristics via drive-by and fly-over GPS linked thermal imaging. A central question drives this research: Can single point-in-time thermal images be used to infer U-values and thermal capacitances of walls and roofs? Previous efforts to use thermal images to estimate U-values have been limited to rare steady exterior weather conditions. The approaches posed here are based upon the development two models first is a dynamic model of a building envelope component with unknown U-value and thermal capacitance. The weather conditions prior to the thermal image are used as inputs to the model. The model is solved to determine the exterior surface temperature, ultimately predicted the temperature at the thermal measurement time. The model U-value and thermal capacitance are tuned in order to force the error between the predicted surface temperature and the measured surface temperature from thermal imaging to be near zero. This model is developed simply to show that such a model cannot be relied upon to accurately estimate the U-value. The second is a data-based methodology. This approach integrates the exterior surface temperature measurements, historical utility data, and easily accessible or potentially easily accessible housing data. A Random Forest model is developed from a training subset of residences for which the envelope U-value is known. This model is used to predict the envelope U-value for a validation set of houses with unknown U-value. Demonstrated is an ability to estimate the wall/roof U-value with an R-squared value in the range of 0.97 and 0.96 respectively, using as few as 9 and 24 training houses for respectively wall and ceiling U-value estimation. The implication of this research is significant, offering the possibility of auditing residences remotely at-scale via aerial and drive-by thermal imaging.

Instantaneous and daily values of the surface energy balance over agricultural fields using remote sensing and a reference field in an arid environment

USGS Publications Warehouse

Kustas, William P.; Moran, M.S.; Jackson, R. D.; Gay, L.W.; Duell, L.F.W.; Kunkel, K.E.; Matthias, A.D.

1990-01-01

Remotely sensed surface temperature and reflectance in the visible and near infrared wavebands along with ancilliary meteorological data provide the capability of computing three of the four surface energy balance components (i.e., net radiation, soil heat flux, and sensible heat flux) at different spatial and temporal scales. As a result, under nonadvective conditions, this enables the estimation of the remaining term (i.e., the latent heat flux). One of the practical applications with this approach is to produce evapotranspiration (ET) maps for agricultural regions which consist of an array of fields containing different crops at varying stages of growth and soil moisture conditions. Such a situation exists in the semiarid southwest at the University of Arizona Maricopa Agricultural Center, south of Phoenix. For one day (14 June 1987), surface temperature and reflectance measurements from an aircraft 150 m above ground level (agl) were acquired over fields from zero to nearly full cover at four times between 1000 MST and 1130 MST. The diurnal pattern of the surface energy balance was measured over four fields, which included alfalfa at 60% cover, furrowed cotton at 20% and 30% cover, and partially plowed what stubble. Instantaneous and daily values of ET were estimated for a representative area around each flux site with an energy balance model that relies on a reference ET. This reference value was determined with remotely sensed data and several meteorological inputs. The reference ET was adjusted to account for the different surface conditions in the other fields using only remotely sensed variables. A comparison with the flux measurements suggests the model has difficulties with partial canopy conditions, especially related to the estimation of the sensible heat flux. The resulting errors for instantaneous ET were on the order of 100 W m-2 and for daily values of order 2 mm day-1. These findings suggest future research should involve development of methods to account for the variability of meteorological parameters brought about by changes in surface conditions and improvements in the modeling of sensible heat transfer across the surface-atmosphere interface for partial canopy conditions using remote sensing information. ?? 1990.

Influence of the "surface effect" on the segregation parameters of S in Fe(100): A multi-scale modelling and Auger Electron Spectroscopy study

NASA Astrophysics Data System (ADS)

Barnard, P. E.; Terblans, J. J.; Swart, H. C.

2015-12-01

The article takes a new look at the process of atomic segregation by considering the influence of surface relaxation on the segregation parameters; the activation energy (Q), segregation energy (ΔG), interaction parameter (Ω) and the pre-exponential factor (D0). Computational modelling, namely Density Functional Theory (DFT) and the Modified Darken Model (MDM) in conjunction with Auger Electron Spectroscopy (AES) was utilized to study the variation of the segregation parameters for S in the surface region of Fe(100). Results indicate a variation in each of the segregation parameters as a function of the atomic layer under consideration. Values of the segregation parameters varied more dramatically as the surface layer is approached, with atomic layer 2 having the largest deviations in comparison to the bulk values. This atomic layer had the highest Q value and formed the rate limiting step for the segregation of S towards the Fe(100) surface. It was found that the segregation process is influenced by two sets of segregation parameters, those of the surface region formed by atomic layer 2, and those in the bulk material. This article is the first to conduct a full scale investigation on the influence of surface relaxation on segregation and labelled it the "surface effect".

Using a Nondirect Product Basis to Compute J > 0 Rovibrational States of H3+

NASA Astrophysics Data System (ADS)

Jaquet, Ralph; Carrington, Tucker

2013-10-01

We have used a Lanczos algorithm with a nondirect product basis to compute energy levels of H3+ with J values as large as 46. Energy levels computed on the potential surface of M. Pavanello, et al. (J. Chem. Phys. 2012, 136, 184303) agree well with previous calculations for low J values.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moritzer, E., E-mail: elmar.moritzer@ktp.upb.de; Leister, C., E-mail: elmar.moritzer@ktp.upb.de

The industrial use of atmospheric pressure plasmas in the plastics processing industry has increased significantly in recent years. Users of this treatment process have the possibility to influence the target values (e.g. bond strength or surface energy) with the help of kinematic and electrical parameters. Until now, systematic procedures have been used with which the parameters can be adapted to the process or product requirements but only by very time-consuming methods. For this reason, the relationship between influencing values and target values will be examined based on the example of a pretreatment in the bonding process with the help ofmore » statistical experimental design. Because of the large number of parameters involved, the analysis is restricted to the kinematic and electrical parameters. In the experimental tests, the following factors are taken as parameters: gap between nozzle and substrate, treatment velocity (kinematic data), voltage and duty cycle (electrical data). The statistical evaluation shows significant relationships between the parameters and surface energy in the case of polypropylene. An increase in the voltage and duty cycle increases the polar proportion of the surface energy, while a larger gap and higher velocity leads to lower energy levels. The bond strength of the overlapping bond is also significantly influenced by the voltage, velocity and gap. The direction of their effects is identical with those of the surface energy. In addition to the kinematic influences of the motion of an atmospheric pressure plasma jet, it is therefore especially important that the parameters for the plasma production are taken into account when designing the pretreatment processes.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hong, Mina; Moreland, K. Trent; Chen, Jiajun

Here, we investigated the roles of three proteins associated with the formation of otoconia including fetuin A, osteopontin (OPN), and otoconin 90 (OC90). In situ atomic force microscopy (AFM) studies of the effects of these proteins on the growth of atomic steps on calcite surfaces were performed to obtain insight into their effects on the growth kinetics. We also used scanning electron microscopy to examine the effects of these proteins on crystal morphology. All three proteins were found to be potent inhibitors of calcite growth, although fetuin A promoted growth at concentrations below about 40 nM and only became anmore » inhibitor at higher concentrations. We then used in situ optical microscopy to observe calcite nucleation on films of these proteins adsorbed onto mica surfaces. By measuring the calcite nucleation rate as a function of supersaturation, the value of the interfacial energy that controls the free energy barrier to heterogeneous nucleation was determined for each protein. OPN and OC90 films led to significantly reduced interfacial energies as compared to the value for homogeneous calcite nucleation in bulk solution. The value for fetuin A was equal to that for bulk solution within experimental error. Zeta potential measurements showed all of the proteins possessed negative surface charge and varied in magnitude according to sequence fetuin A > OC90 > OPN. In addition, the interfacial energies exhibited an inverse scaling with the zeta potential. In analogy to previous measurements on polysaccharide films, this scaling indicates the differences between the proteins arise from the effect of protein surface charge on the solution–substrate interfacial energy.« less

Small Au clusters on a defective MgO(1 0 0) surface

NASA Astrophysics Data System (ADS)

Barcaro, Giovanni; Fortunelli, Alessandro

2008-05-01

The lowest energy structures of small T]>rndm where rndm is a random number (Metropolis criterion), the new configuration is accepted, otherwise the old configuration is kept, and the process is iterated. For each size we performed 3-5 BH runs, each one composed of 20-25 Monte Carlo steps, using a value of 0.5 eV as kT in the Metropolis criterion. Previous experience [13-15] shows that this is sufficient to single out the global minimum for adsorbed clusters of this size, and that the BH approach is more efficient as a global optimization algorithm than other techniques such as simulated annealing [18]. The MgO support was described via an (Mg 12O 12) cluster embedded in an array of ±2.0 a.u. point charges and repulsive pseudopotentials on the positive charges in direct contact with the cluster (see Ref. [15] for more details on the method). The atoms of the oxide cluster and the point charges were located at the lattice positions of the MgO rock-salt bulk structure using the experimental lattice constant of 4.208 Å. At variance with the ), evaluated by subtracting the energy of the oxide surface and of the metal cluster, both frozen in their interacting configuration, from the value of the total energy of the system, and by taking the absolute value; (ii) the binding energy of the metal cluster (E), evaluated by subtracting the energy of the isolated metal atoms from the total energy of the metal cluster in its interacting configuration, and by taking the absolute value; (iii) the metal cluster distortion energy (E), which corresponds to the difference between the energy of the metal cluster in the configuration interacting with the surface minus the energy of the cluster in its lowest-energy gas-phase configuration (a positive quantity); (iv) the oxide distortion energy (ΔE), evaluated subtracting the energy of the relaxed isolated defected oxide from the energy of the isolated defected oxide in the interacting configuration; and (v) the total binding energy (E), which is the sum of the binding energy of the metal cluster, the adhesion energy and the oxide distortion energy (E=E+E-ΔE). Note that the total binding energy of gas-phase clusters in their global minima can be obtained by summing E+E.

Diurnal centroid of ecosystem energy and carbon fluxes at FLUXNET sites

Treesearch

Kell B. Wilson; Dennis Baldocchi; Eva Falge; Marc Aubinet; Paul Berbigier; Christian Bernhofer; Han Dolman; Chris Field; Allen Goldstein; Andre Granier; Dave Hollinger; Gabriel Katul; B.E. Law; Tilden Meyers; John Moncrieff; Russ Monson; John Tenhunen; Riccardo Valentini; Shashi Verma; Steve Wofsy

2003-01-01

Data from a network of eddy covariance stations in Europe and North America (FLUXNET) were analyzed to examine the diurnal patterns of surface energy and carbon fluxes during the summer period across a range of ecosystems and climates. Diurnal trends were quantified by assessing the time of day surface fluxes and meteorological variable reached peak values, using the...

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Lu; Hanson, David E

Here we present the results on the study of surface properties of {beta}-HMX crystal utilizing molecular simulations. The surface polarity of three principal crystal surfaces are investigated by measuring the water contact angles. The calculated contact angles agree excellently with the values measured by experiment and show that the surface polarity of three crystal surfaces are different. The free energies and forces of detaching an Estane chain with and without nitroplasticizer from the three principal crystal surfaces were calculated using umbrella sampling technique. We find that the detaching free energy/force increases with the increasing HMX surface polarity. In addition, ourmore » results also show that nitroplasticizer plays an important role in the adhesion forces between Estane and HMX surfaces.« less

A Measurement and Analysis of Buildup Region Dose for Open Field Photon Beams (Cobalt-60 through 24 MV)

DOE Office of Scientific and Technical Information (OSTI.GOV)

McCullough, Edwin C.

2015-01-15

The central axis depth dose in the build-up region (surface to d{sub max}) of single open field photon beams (cobalt-60 through 24 MV) has been measured utilizing parallel plate and extrapolation chamber methodology. These data were used to derive, for a prescription dose of 100 cGy, values of surface dose, the maximum value of dose along the central axis (D{sub max}) and the depth (nearest the surface) at which 90% of the prescription dose occurs (d{sub 90}). For both single and parallel opposed pair (POP) open field configurations, data are presented at field sizes of 5 × 5, 15 ×more » 15 and 25 × 25 cm{sup 2} for prescription depths of 10, 15 and 20 cm (midplane for POP). For the treatment machines, field sizes, and prescription depths studied, it is possible to conclude that: for single open field irradiation, surface dose values (as a percentage of the prescription dose) can be either low (<10%) or comparable to the prescription dose itself; for POP open fields, surface dose values are relatively independent of photon energy and midplane depth, and range between 30% and 70% of prescription dose, being principally dependent on field size; the depth of the initial 90 cGy point for a prescription dose of 100 cGy, d{sub 90}, was larger for POP fields. For either single or POP open field treatments, d{sub 90} was always less than 22 mm, while for 6 MV or less, values of d{sub 90} were less than 4 mm; D{sub max} values can be very large (e.g., above 300 cGy) for certain treatment situations and are reduced significantly for POP treatments; for open field POP treatments, the percent reduction in D{sub max} with each increment in beam energy above 10 MV is reduced over that seen at 10 MV or less and, possibly, this further reduction may be clinically insignificant; for open field POP treatments, changes in surface dose, d{sub 90} and D{sub max} with beam energy above 10 MV do not suggest, with regard to these specific build-up curve parameters, any obvious advantage for treatment with beam energies greater than 10 MV for the specific machines and situations studied.« less

Communication: A new ab initio potential energy surface for HCl-H2O, diffusion Monte Carlo calculations of D0 and a delocalized zero-point wavefunction.

PubMed

Mancini, John S; Bowman, Joel M

2013-03-28

We report a global, full-dimensional, ab initio potential energy surface describing the HCl-H2O dimer. The potential is constructed from a permutationally invariant fit, using Morse-like variables, to over 44,000 CCSD(T)-F12b∕aug-cc-pVTZ energies. The surface describes the complex and dissociated monomers with a total RMS fitting error of 24 cm(-1). The normal modes of the minima, low-energy saddle point and separated monomers, the double minimum isomerization pathway and electronic dissociation energy are accurately described by the surface. Rigorous quantum mechanical diffusion Monte Carlo (DMC) calculations are performed to determine the zero-point energy and wavefunction of the complex and the separated fragments. The calculated zero-point energies together with a De value calculated from CCSD(T) with a complete basis set extrapolation gives a D0 value of 1348 ± 3 cm(-1), in good agreement with the recent experimentally reported value of 1334 ± 10 cm(-1) [B. E. Casterline, A. K. Mollner, L. C. Ch'ng, and H. Reisler, J. Phys. Chem. A 114, 9774 (2010)]. Examination of the DMC wavefunction allows for confident characterization of the zero-point geometry to be dominant at the C(2v) double-well saddle point and not the C(s) global minimum. Additional support for the delocalized zero-point geometry is given by numerical solutions to the 1D Schrödinger equation along the imaginary-frequency out-of-plane bending mode, where the zero-point energy is calculated to be 52 cm(-1) above the isomerization barrier. The D0 of the fully deuterated isotopologue is calculated to be 1476 ± 3 cm(-1), which we hope will stand as a benchmark for future experimental work.

Theoretical model of droplet wettability on a low-surface-energy solid under the influence of gravity.

PubMed

Yonemoto, Yukihiro; Kunugi, Tomoaki

2014-01-01

The wettability of droplets on a low surface energy solid is evaluated experimentally and theoretically. Water-ethanol binary mixture drops of several volumes are used. In the experiment, the droplet radius, height, and contact angle are measured. Analytical equations are derived that incorporate the effect of gravity for the relationships between the droplet radius and height, radius and contact angle, and radius and liquid surface energy. All the analytical equations display good agreement with the experimental data. It is found that the fundamental wetting behavior of the droplet on the low surface energy solid can be predicted by our model which gives geometrical information of the droplet such as the contact angle, droplet radius, and height from physical values of liquid and solid.

Study of silicon crystal surface formation based on molecular dynamics simulation results

NASA Astrophysics Data System (ADS)

Barinovs, G.; Sabanskis, A.; Muiznieks, A.

2014-04-01

The equilibrium shape of <110>-oriented single crystal silicon nanowire, 8 nm in cross-section, was found from molecular dynamics simulations using LAMMPS molecular dynamics package. The calculated shape agrees well to the shape predicted from experimental observations of nanocavities in silicon crystals. By parametrization of the shape and scaling to a known value of {111} surface energy, Wulff form for solid-vapor interface was obtained. The Wulff form for solid-liquid interface was constructed using the same model of the shape as for the solid-vapor interface. The parameters describing solid-liquid interface shape were found using values of surface energies in low-index directions known from published molecular dynamics simulations. Using an experimental value of the liquid-vapor interface energy for silicon and graphical solution of Herring's equation, we constructed angular diagram showing relative equilibrium orientation of solid-liquid, liquid-vapor and solid-vapor interfaces at the triple phase line. The diagram gives quantitative predictions about growth angles for different growth directions and formation of facets on the solid-liquid and solid-vapor interfaces. The diagram can be used to describe growth ridges appearing on the crystal surface grown from a melt. Qualitative comparison to the ridges of a Float zone silicon crystal cone is given.

Wang and Yau’s quasi-local energy for an extreme Kerr spacetime

NASA Astrophysics Data System (ADS)

Miller, Warner A.; Ray, Shannon; Wang, Mu-Tao; Yau, Shing-Tung

2018-03-01

There exist constant radial surfaces, S , that may not be globally embeddable in {R}3 for Kerr spacetimes with a>\\sqrt{3}M/2 . To compute the Brown and York (B–Y) quasi-local energy (QLE), one must isometrically embed S into {R}3 . On the other hand, the Wang and Yau (W–Y) QLE embeds S into Minkowski space. In this paper, we examine the W–Y QLE for surfaces that may or may not be globally embeddable in {R}3 . We show that their energy functional, E[τ] , has a critical point at τ=0 for all constant radial surfaces in t=constant hypersurfaces using Boyer–Lindquist coordinates. For τ=0 , the W–Y QLE reduces to the B–Y QLE. To examine the W–Y QLE in these cases, we write the functional explicitly in terms of τ under the assumption that τ is only a function of θ. We then use a Fourier expansion of τ(θ) to explore the values of E[τ(θ)] in the space of coefficients. From our analysis, we discovered an open region of complex values for E[τ(θ)] . We also study the physical properties of the smallest real value of E[τ(θ)] , which lies on the boundary separating real and complex energies.

Estimating the actual ET from a pecan farm using the OPEC energy-balance and Penman- Monteith methods

NASA Astrophysics Data System (ADS)

Debele, B.; Bawazir, S. A.

2006-12-01

Accurate estimation of ET from field crops/orchards is the basis for better irrigation water management. In areas like Mesilla Valley, NM, where water is scarce, it is even more important to precisely determine the crop ET. An OPEC energy balance system was run for 117 days (June 22 October 14, 2001) in a matured pecan farm at Mesilla Valley, NM. The actual evapotranspiration (ET) from pecan orchards was determined from the surface energy balance as a residual, having measured the net radiation, soil heat flux, and sensible heat components using the OPEC method. Since pecans are large trees, we have also examined the effect of including thermal energies stored in the air (Ga) and plant canopy (Gc), on top of the commonly used thermal energy stored in the soil (Gs), on surface energy balance, and hence ET. The results indicate that incorporating thermal energies stored in the air and canopy has a significant effect on total energy storage for shorter temporal resolutions, such as 30-minutes and an hour. Conversely, for longer temporal resolutions (e.g., diurnal and monthly averages), the effect of including thermal energies stored in the air and vegetation on total thermal energy storage is negligible. Our results also showed that the bulk of the total thermal energy storage (G = Gs + Ga + Gc) in the surface energy balance was stored in the soil (Gs). In addition, we have also determined the crop coefficient (Kc) of pecan by combining the actual ET obtained from the OPEC method and potential ET (ET0) calculated using weather data in the surrounding area. Our average pecan Kc values were comparable with the ones reported by other researchers using different methods. We conclude that the OPEC energy balance method can be used to calculate Kc values for pecan whereby farmers and extension agents use the calculated Kc values in combination with ET0 to determine the consumptive use of pecan trees.

Energy Level Alignment at the Interface between Linear-Structured Benzenediamine Molecules and Au(111) Surface

NASA Astrophysics Data System (ADS)

Li, Guo; Rangel, Tonatiuh; Liu, Zhenfei; Cooper, Valentino; Neaton, Jeffrey

Using density functional theory with model self-energy corrections, we calculate the adsorption energetics and geometry, and the energy level alignment of benzenediamine (BDA) molecules adsorbed on Au(111) surfaces. Our calculations show that linear structures of BDA, stabilized via hydrogen bonds between amine groups, are energetically more favorable than monomeric phases. Moreover, our self-energy-corrected calculations of energy level alignment show that the highest occupied molecular orbital energy of the BDA linear structure is deeper relative to the Fermi level relative to the isolated monomer and agrees well with the values measured with photoemission spectroscopy. This work supported by DOE.

Quantitative structure-property relationships for octanol-water partition coefficients of polybrominated diphenyl ethers.

PubMed

Li, Linnan; Xie, Shaodong; Cai, Hao; Bai, Xuetao; Xue, Zhao

2008-08-01

Theoretical molecular descriptors were tested against logK(OW) values for polybrominated diphenyl ethers (PBDEs) using the Partial Least-Squares Regression method which can be used to analyze data with many variables and few observations. A quantitative structure-property relationship (QSPR) model was successfully developed with a high cross-validated value (Q(cum)(2)) of 0.961, indicating a good predictive ability and stability of the model. The predictive power of the QSPR model was further cross-validated. The values of logK(OW) for PBDEs are mainly governed by molecular surface area, energy of the lowest unoccupied molecular orbital and the net atomic charges on the oxygen atom. All these descriptors have been discussed to interpret the partitioning mechanism of PBDE chemicals. The bulk property of the molecules represented by molecular surface area is the leading factor, and K(OW) values increase with the increase of molecular surface area. Higher energy of the lowest unoccupied molecular orbital and higher net atomic charge on the oxygen atom of PBDEs result in smaller K(OW). The energy of the lowest unoccupied molecular orbital and the net atomic charge on PBDEs oxygen also play important roles in affecting the partition of PBDEs between octanol and water by influencing the interactions between PBDEs and solvent molecules.

[Caloric value and energy allocation of Chloris virgata in northeast grassland].

PubMed

Guo, J; Wang, R; Wang, W

2001-06-01

The rules of seasonal changes in caloric values of individual plant, stem, and leaves of Chloris virgata were similar, which had two peak values from early July to early August, and then decreased gradually. Those of inflorescence assumed U shape, and had two peak values in early August and middle September, respectively. The seasonal changes in caloric values of dead standing were irregular, and the maximum value was appeared in early August. The seasonal changes in existent energy value of the aboveground parts in Chloris virgata population presented double peak curve. The two peak values were appeared in early August and early September respectively, and the maximum value was 7381.27 kJ.m-2 in early September. The energy allocation in different seasons was leaf > stem in early July, stem > leaf > dead standing in middle July, stem > leaf > inflorescence > dead standing in August, stem > inflorescence > leaf > dead standing in early September, and stem > inflorescence > dead standing > leaf in middle September. The vertical structure of energy in the aboveground parts was that the energy value gradually increased from the earth's surface to 20 cm high, and then decreased. The maximum value, which accounted for 25.75% of energy in the aboveground parts, was appeared in the layer of 10-20 cm high. In the underground parts, the energy value progressively decreased with the increase of depth, and the maximum value, which accounted for 74.21% of energy in the underground parts, was appeared in the layer of 0-10 cm depth.

Contribution of the hydrostatic pressure to the shape of silver island particles

NASA Astrophysics Data System (ADS)

Anno, E.; Hoshino, R.

1984-09-01

We have investigated the shape change of silver island particles caused by the surface energy reduction. When the surface energy was reduced by the reaction with hydrogen sulfide, the flattening of the particles was observed. As is well known, the similar shape change takes place when the particle size increases. Therefore, the particle shape is considered to depend both on the surface energy and the particle size. From this consideration, we predict the contribution of the hydrostatic pressure P to the particle shape. As evidence of this contribution, we consider the existence of the critical size below which P is larger than the adhesive force FA between deposit and substrate surface. Investigating the influence of the flattening due to the surface energy reduction on the size distribution, the critical size is found and estimated to be about 80 Å in diameter. This value is comparable with that estimated from the condition P = FA.

Step free energies at faceted solid surfaces: Theory and atomistic calculations for steps on the Cu(111) surface

NASA Astrophysics Data System (ADS)

Freitas, Rodrigo; Frolov, Timofey; Asta, Mark

2017-04-01

A theory for the thermodynamic properties of steps on faceted crystalline surfaces is presented. The formalism leads to the definition of step excess quantities, including an excess step stress that is the step analogy of surface stress. The approach is used to develop a relationship between the temperature dependence of the step free energy (γst) and step excess quantities for energy and stress that can be readily calculated by atomistic simulations. We demonstrate the application of this formalism in thermodynamic-integration (TI) calculations of the step free energy, based on molecular-dynamics simulations, considering <110 > steps on the {111 } surface of a classical potential model for elemental Cu. In this application we employ the Frenkel-Ladd approach to compute the reference value of γst for the TI calculations. Calculated results for excess energy and stress show relatively weak temperature dependencies up to a homologous temperature of approximately 0.6, above which these quantities increase strongly and the step stress becomes more isotropic. From the calculated excess quantities we compute γst over the temperature range from zero up to the melting point (Tm). We find that γst remains finite up to Tm, indicating the absence of a roughening temperature for this {111 } surface facet, but decreases by roughly fifty percent from the zero-temperature value. The strongest temperature dependence occurs above homologous temperatures of approximately 0.6, where the step becomes configurationally disordered due to the formation of point defects and appreciable capillary fluctuations.

Influences of the third and fourth nearest neighbouring interactions on the surface anisotropy of face-centred-cubic metals

NASA Astrophysics Data System (ADS)

Luo, Yongkun; Qin, Rongshan

2014-06-01

The structure and the anisotropic properties of the surfaces of face-centred-cubic (FCC) metals have been studied using the broken-bond model while considering the third and fourth nearest neighbouring (3rd and 4th NN) interactions. The pair potential expressions are obtained using the Rose-Vinet universal potential equation. The model is suitable for calculation of the property of a surface with arbitrary crystallographic orientations and can provide absolute unrelaxed surface energy values using three input parameters, namely the lattice constant, bulk modulus and cohesive energy. These parameters are available for the majority of FCC metals. The numerical results for 7 FCC metals have been obtained and compared with these obtained from ab initio calculations and experimental measurements. Good agreement is observed between the two. Taking into account up to the 4th NN interactions, the overall surface energy anisotropy for FCC metals was found to be between 12% to 16%, and the ratio between the surface energies at (100) and (111) planes was found to be 1.05. These values are less than those reported by conventional calculations but more similar to experimental measurements. It is found that the strength of 3rd and 4th NN interactions differs from one element to another, the Ni and Cu interactions being the most significant while the Au, Pt and Pb interactions are the least significant. This suggests that the polar diagrams of the surface energy of Ni and Cu are different from those of Au, Pt and Pb by showing cusps of the unconventional {110} and high-index {210}, {311} and possibly {135} poles. This provides explanations to the recent experimental observations of the {110}, {210}, {311} and {135} facets in equilibrated Ni and Cu crystallines.

Atomic and molecular adsorption on Au(111)

DOE PAGES

Santiago-Rodriguez, Yohaselly; Herron, Jeffrey A.; Curet-Arana, Maria C.; ...

2014-05-02

Periodic self-consistent density functional theory (DFT-GGA) calculations were used to study the adsorption of several atomic species, molecular species and molecular fragments on the Au(111) surface with a coverage of 1/4 monolayer (ML). Binding geometries, binding energies, and diffusion barriers were calculated for 27 species. Furthermore, we calculated the surface deformation energy associated with the binding events. The binding strength for all the analyzed species can be ordered as follows: NH 3 < NO < CO < CH 3 < HCO < NH 2 < COOH < OH < HCOO < CNH 2 < H < N < NH

Effect of size on bulk and surface cohesion energy of metallic nano-particles

NASA Astrophysics Data System (ADS)

Yaghmaee, M. S.; Shokri, B.

2007-04-01

The knowledge of nano-material properties not only helps us to understand the extreme behaviour of small-scale materials better (expected to be different from what we observe from their bulk value) but also helps us to analyse and design new advanced functionalized materials through different nano technologies. Among these fundamental properties, the cohesion (binding) energy mainly describes most behaviours of materials in different environments. In this work, we discuss this fundamental property through a nano-thermodynamical approach using two algorithms, where in the first approach the size dependence of the inner (bulk) cohesion energy is studied, and in the second approach the surface cohesion energy is considered too. The results, which are presented through a computational demonstration (for four different metals: Al, Ga, W and Ag), can be compared with some experimental values for W metallic nano-particles.

The new view of hydrophobic free energy.

PubMed

Baldwin, Robert L

2013-04-17

In the new view, hydrophobic free energy is measured by the work of solute transfer of hydrocarbon gases from vapor to aqueous solution. Reasons are given for believing that older values, measured by solute transfer from a reference solvent to water, are not quantitatively correct. The hydrophobic free energy from gas-liquid transfer is the sum of two opposing quantities, the cavity work (unfavorable) and the solute-solvent interaction energy (favorable). Values of the interaction energy have been found by simulation for linear alkanes and are used here to find the cavity work, which scales linearly with molar volume, not accessible surface area. The hydrophobic free energy is the dominant factor driving folding as judged by the heat capacity change for transfer, which agrees with values for solvating hydrocarbon gases. There is an apparent conflict with earlier values of hydrophobic free energy from studies of large-to-small mutations and an explanation is given. Copyright © 2013 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

Derivation of Hamaker Dispersion Energy of Amorphous Carbon Surfaces in Contact with Liquids Using Photoelectron Energy-Loss Spectra

NASA Astrophysics Data System (ADS)

Godet, Christian; David, Denis

2017-12-01

Hamaker interaction energies and cutoff distances have been calculated for disordered carbon films, in contact with purely dispersive (diiodomethane) or polar (water) liquids, using their experimental dielectric functions ɛ ( q, ω) obtained over a broad energy range. In contrast with previous works, a q-averaged < ɛ ( q, ω) > q is derived from photoelectron energy-loss spectroscopy (XPS-PEELS) where the energy loss function (ELF) < Im[-1/ ɛ ( q, ω)] > q is a weighted average over allowed transferred wave vector values, q, given by the physics of bulk plasmon excitation. For microcrystalline diamond and amorphous carbon films with a wide range of (sp3/sp2 + sp3) hybridization, non-retarded Hamaker energies, A 132 ( L < 1 nm), were calculated in several configurations, and distance and wavenumber cutoff values were then calculated based on A 132 and the dispersive work of adhesion obtained from contact angles. A geometric average approximation, H 0 CVL = ( H 0 CVC H 0 LVL )1/2, holds for the cutoff separation distances obtained for carbon-vacuum-liquid (CVL), carbon-vacuum-carbon (CVC) and liquid-vacuum-liquid (LVL) equilibrium configurations. The linear dependence found for A CVL, A CLC and A CLV values as a function of A CVC, for each liquid, allows predictive relationships for Hamaker energies (in any configuration) using experimental determination of the dispersive component of the surface tension, {γ}_{CV}^d , and a guess value of the cutoff distance H 0 CVC of the solid. [Figure not available: see fulltext.

The ground state tunneling splitting and the zero point energy of malonaldehyde: a quantum Monte Carlo determination.

PubMed

Viel, Alexandra; Coutinho-Neto, Maurício D; Manthe, Uwe

2007-01-14

Quantum dynamics calculations of the ground state tunneling splitting and of the zero point energy of malonaldehyde on the full dimensional potential energy surface proposed by Yagi et al. [J. Chem. Phys. 1154, 10647 (2001)] are reported. The exact diffusion Monte Carlo and the projection operator imaginary time spectral evolution methods are used to compute accurate benchmark results for this 21-dimensional ab initio potential energy surface. A tunneling splitting of 25.7+/-0.3 cm-1 is obtained, and the vibrational ground state energy is found to be 15 122+/-4 cm-1. Isotopic substitution of the tunneling hydrogen modifies the tunneling splitting down to 3.21+/-0.09 cm-1 and the vibrational ground state energy to 14 385+/-2 cm-1. The computed tunneling splittings are slightly higher than the experimental values as expected from the potential energy surface which slightly underestimates the barrier height, and they are slightly lower than the results from the instanton theory obtained using the same potential energy surface.

Effect of otoconial proteins fetuin A, osteopontin, and otoconin 90 on the nucleation and growth of calcite

DOE PAGES

Hong, Mina; Moreland, K. Trent; Chen, Jiajun; ...

2014-10-30

Here, we investigated the roles of three proteins associated with the formation of otoconia including fetuin A, osteopontin (OPN), and otoconin 90 (OC90). In situ atomic force microscopy (AFM) studies of the effects of these proteins on the growth of atomic steps on calcite surfaces were performed to obtain insight into their effects on the growth kinetics. We also used scanning electron microscopy to examine the effects of these proteins on crystal morphology. All three proteins were found to be potent inhibitors of calcite growth, although fetuin A promoted growth at concentrations below about 40 nM and only became anmore » inhibitor at higher concentrations. We then used in situ optical microscopy to observe calcite nucleation on films of these proteins adsorbed onto mica surfaces. By measuring the calcite nucleation rate as a function of supersaturation, the value of the interfacial energy that controls the free energy barrier to heterogeneous nucleation was determined for each protein. OPN and OC90 films led to significantly reduced interfacial energies as compared to the value for homogeneous calcite nucleation in bulk solution. The value for fetuin A was equal to that for bulk solution within experimental error. Zeta potential measurements showed all of the proteins possessed negative surface charge and varied in magnitude according to sequence fetuin A > OC90 > OPN. In addition, the interfacial energies exhibited an inverse scaling with the zeta potential. In analogy to previous measurements on polysaccharide films, this scaling indicates the differences between the proteins arise from the effect of protein surface charge on the solution–substrate interfacial energy.« less

Dispersion Energy Analysis of Rayleigh and Love Waves in the Presence of Low-Velocity Layers in Near-Surface Seismic Surveys

NASA Astrophysics Data System (ADS)

Mi, Binbin; Xia, Jianghai; Shen, Chao; Wang, Limin

2018-03-01

High-frequency surface-wave analysis methods have been effectively and widely used to determine near-surface shear (S) wave velocity. To image the dispersion energy and identify different dispersive modes of surface waves accurately is one of key steps of using surface-wave methods. We analyzed the dispersion energy characteristics of Rayleigh and Love waves in near-surface layered models based on numerical simulations. It has been found that if there is a low-velocity layer (LVL) in the half-space, the dispersion energy of Rayleigh or Love waves is discontinuous and ``jumping'' appears from the fundamental mode to higher modes on dispersive images. We introduce the guided waves generated in an LVL (LVL-guided waves, a trapped wave mode) to clarify the complexity of the dispersion energy. We confirm the LVL-guided waves by analyzing the snapshots of SH and P-SV wavefield and comparing the dispersive energy with theoretical values of phase velocities. Results demonstrate that LVL-guided waves possess energy on dispersive images, which can interfere with the normal dispersion energy of Rayleigh or Love waves. Each mode of LVL-guided waves having lack of energy at the free surface in some high frequency range causes the discontinuity of dispersive energy on dispersive images, which is because shorter wavelengths (generally with lower phase velocities and higher frequencies) of LVL-guided waves cannot penetrate to the free surface. If the S wave velocity of the LVL is higher than that of the surface layer, the energy of LVL-guided waves only contaminates higher mode energy of surface waves and there is no interlacement with the fundamental mode of surface waves, while if the S wave velocity of the LVL is lower than that of the surface layer, the energy of LVL-guided waves may interlace with the fundamental mode of surface waves. Both of the interlacements with the fundamental mode or higher mode energy may cause misidentification for the dispersion curves of surface waves.

Beam impingement angle effects on secondary electron emission characteristics of textured pyrolytic graphite

NASA Technical Reports Server (NTRS)

Curren, A. N.; Jensen, K. A.

1984-01-01

Experimentally determined values of true secondary electron emission and relative values of reflected primary electron yield for untreated and ion-textured pyrolytic graphite over a range of primary electron energy levels and electron beam impingement angles are presented. Information required to develop high efficiency multistage depressed collectors (MDC's) for microwave amplifier traveling-wave tubes for space communication and aircraft applications is provided. To attain the highest possible MDC efficiencies, the electrode surfaces must have low secondary electron emission characteristics. Pyrolytic graphite, a chemically vapor-deposited material, is a particularly promising candidate for this application. The pyrolytic graphite surfaces studied were tested over a range of primary electron beam energies and beam impingement angles from 200 to 2000 eV and direct (0 deg) to near-grazing angles (85 deg), respectively. Surfaces both parallel to and normal to the planes of material deposition were examined. The true secondary electron emission and reflected primary electron yield characteristics of the pyrolytic graphite surfaces are compared to those of sooted control surfaces.

Measurement of conformability and adhesion energy of polymeric ultrathin film to skin model

NASA Astrophysics Data System (ADS)

Sugano, Junki; Fujie, Toshinori; Iwata, Hiroyasu; Iwase, Eiji

2018-06-01

We measured the conformability and adhesion energy of a polymeric ultrathin film “nanosheet” with hundreds of nanometer thickness to a skin model with epidermal depressions. To compare the confirmability of the nanosheets with different thicknesses and/or under different attaching conditions, we proposed a measurement method using skin models with the same surface profile and defined the surface strain εS as the quantified value of the conformability. Then, we measured the adhesion energy of the nanosheet at each conformability through a vertical tensile test. Experimental results indicate that the adhesion energy does not depend on the liquid used in wetting the nanosheet before attaching to the skin model and increases monotonously as the surface strain εS increases.

LCGTO-Xα model cluster study for the chemisorption of CO on twofold sites of Ni surfaces

NASA Astrophysics Data System (ADS)

Jörg, H.; Rösch, N.

The cluster Ni 2CO is studied as a simplified model for the chemisorption of CO on twofold bridging sites of transition metal surfaces. Using the LCGTO-Xα method we have calculated the potential energy surface for the totally symmetric stretching motion keeping the Ni-Ni distance fixed at the bulk value. The minimum energy is found at a Ni-C distance of 1.72 Å and a C-O bond length of 1.19 Å. The vibrational frequency for the CO bond (1850 cm -1) shows reasonable agreement with EELS data (1810, 1870 cm -1), whereas the (Ni 2)-C frequency of 495 cm -1 is remarkably higher than the experimental values (380, 400 cm -1) indicating an overestimation of the chemisorption bond strength in this simple cluster model. The bonding between CO and Ni is analyzed using orbital correlations, ionization energies and Mulliken population analysis. Important bonding contributions from π backdonation are identified while the a 1 orbital manifold exhibits strong antibonding effects.

LCGTO-Xα model cluster study for the chemisorption of CO on twofold sites of Ni surfaces

NASA Astrophysics Data System (ADS)

Jörg, H.; Rösch, N.

1985-11-01

The cluster Ni 2CO is studied as a simplified model for the chemisorption of CO on twofold bridging sites of transition metal surfaces. Using the LCGTO-Xα method we have calculated the potential energy surface for the totally symmetric stretching motion keeping the NiNi distance fixed at the bulk value. The minimum energy is found at a NiC distance of 1.72 Å and a CO bond length of 1.19 Å. The vibrational frequency for the CO bond (1850 cm -1) shows reasonable agreement with EELS data (1810, 1870 cm -1), whereas the (Ni 2)C frequency of 495 cm -1 is remarkably higher than the experimental values (380, 400 cm -1) indicating an overestimation of the chemisorption bond strength in this simple cluster model. The bonding between CO and Ni is analyzed using orbital correlations, ionization energies and Mulliken population analysis. Important bonding contributions from π backdonation are identified while the a 1orbital manifold exhibits strong antibonding effects.

Theory of nanobubble formation and induced force in nanochannels

NASA Astrophysics Data System (ADS)

Arai, Noriyoshi; Koishi, Takahiro; Ebisuzaki, Toshikazu

2017-10-01

This paper presents a fundamental theory of nanobubble formation and induced force in confined nanochannels. It is shown that nanobubble formation between hydrophobic plates can be predicted from their surface tension and geometry, with estimated values for the surface free energy and the force acting on the plates in good agreement with the results of molecular dynamics simulation and experimentation. When a bubble is formed between two plates, vertical attractive force and horizontal retract force due to the shifted plates are applied to the plates. The net force exerted on the plates is not dependent on the distance between them. The short-range force between hydrophobic surfaces due to hydrophobic interaction appears to correspond to the force estimated by our theory. We compared between experimental and theoretical values for the binding energy of a molecular motor system to validate our theory. The tendency that the binding energy increases as the size of the protein increases is consistent with the theory.

Denaturation of RNA secondary and tertiary structure by urea: simple unfolded state models and free energy parameters account for measured m-values

PubMed Central

Lambert, Dominic; Draper, David E.

2012-01-01

To investigate the mechanism by which urea destabilizes RNA structure, urea-induced unfolding of four different RNA secondary and tertiary structures was quantified in terms of an m-value, the rate at which the free energy of unfolding changes with urea molality. From literature data and our osmometric study of a backbone analog, we derived average interaction potentials (per Å2 of solvent accessible surface) between urea and three kinds of RNA surfaces: phosphate, ribose, and base. Estimates of the increases in solvent accessible surface areas upon RNA denaturation were based on a simple model of unfolded RNA as a combination of helical and single strand segments. These estimates, combined with the three interaction potentials and a term to account for urea interactions with released ions, yield calculated m-values in good agreement with experimental values (200 mm monovalent salt). Agreement was obtained only if single-stranded RNAs were modeled in a highly stacked, A form conformation. The primary driving force for urea induced denaturation is the strong interaction of urea with the large surface areas of bases that become exposed upon denaturation of either RNA secondary or tertiary structure, though urea interactions with backbone and released ions may account for up to a third of the m-value. Urea m-values for all four RNA are salt-dependent, which we attribute to an increased extension (or decreased charge density) of unfolded RNAs with increased urea concentration. The sensitivity of the urea m-value to base surface exposure makes it a potentially useful probe of the conformations of RNA unfolded states. PMID:23088364

Prediction of the interaction site on the surface of an isolated protein structure by analysis of side chain energy scores.

PubMed

Liang, Shide; Zhang, Jian; Zhang, Shicui; Guo, Huarong

2004-11-15

We show that residues at the interfaces of protein-protein complexes have higher side-chain energy than other surface residues. Eight different sets of protein complexes were analyzed. For each protein pair, the complex structure was used to identify the interface residues in the unbound monomer structures. Side-chain energy was calculated for each surface residue in the unbound monomer using our previously developed scoring function.1 The mean energy was calculated for the interface residues and the other surface residues. In 15 of the 16 monomers, the mean energy of the interface residues was higher than that of other surface residues. By decomposing the scoring function, we found that the energy term of the buried surface area of non-hydrogen-bonded hydrophilic atoms is the most important factor contributing to the high energy of the interface regions. In spite of lacking hydrophilic residues, the interface regions were found to be rich in buried non-hydrogen-bonded hydrophilic atoms. Although the calculation results could be affected by the inaccuracy of the scoring function, patch analysis of side-chain energy on the surface of an isolated protein may be helpful in identifying the possible protein-protein interface. A patch was defined as 20 residues surrounding the central residue on the protein surface, and patch energy was calculated as the mean value of the side-chain energy of all residues in the patch. In 12 of the studied monomers, the patch with the highest energy overlaps with the observed interface. The results are more remarkable when only three residues with the highest energy in a patch are averaged to derive the patch energy. All three highest-energy residues of the top energy patch belong to interfacial residues in four of the eight small protomers. We also found that the residue with the highest energy score on the surface of a small protomer is very possibly the key interaction residue. (c) 2004 Wiley-Liss, Inc.

Interaction of slow highly charged ions with a metal surface covered with a thin dielectric film. The role of the neutralization energy in the nanostructures formation

NASA Astrophysics Data System (ADS)

Majkić, M. D.; Nedeljković, N. N.; Dojčilović, R. J.

2017-09-01

We consider the slow highly charged ions impinging upon a metal surface covered with a thin dielectric film, and formation of the surface nanostructures (craters) from the standpoint of the required energy. For the moderate ionic velocities, the size of the surface features depends on the deposited kinetic energy of the projectile and the ionic neutralization energy. The neutralization energy is calculated by employing the recently developed quasi-resonant two-state vector model for the intermediate Rydberg state population and the micro-staircase model for the cascade neutralization. The electron interactions with the ionic core, polarized dielectric and charge induced on the metal surface are modelled by the appropriate asymptotic expressions and the method for calculation of the effective ionic charges in the dielectric is proposed. The results are presented for the interaction of \\text{X}{{\\text{e}}Z+} ions (velocity v=0.25 a.u.; 25) with the metal surface (Co) covered with a thin dielectric film, for model values of dielectric constant inside the interaction region. In the absence of dielectric film, the neutralization energy is lower than the potential (ionization) energy due to the incomplete neutralization. The presence of dielectric film additionally decreases the neutralization energy. We calculate the projectile neutralization energy in the perturbed dielectric (perturbation is caused by the ionic motion and the surface structure formation). We correlate the neutralization energy added to the deposited kinetic energy with the experimentally obtained energy necessary for the formation of the nano-crater of a given depth.

Energy dissipation in micron- and submicron-thick single crystal diamond mechanical resonators

NASA Astrophysics Data System (ADS)

Liao, Meiyong; Toda, Masaya; Sang, Liwen; Hishita, Shunichi; Tanaka, Shuji; Koide, Yasuo

2014-12-01

The authors report the resonance frequency and the energy dissipation of single crystal diamond cantilevers with different dimensions, which were fabricated by ion implantation assisted technique. The resonance frequency well followed the inverse power law relationship with the length of the cantilevers and exhibited a high reproducibility with varying the dimensions. The energy dissipation decreased with increasing the cantilever length and saturated or reduced at a certain value. For the shorter cantilevers, clamping loss governed the energy dissipation. As the cantilever length increased to a certain value, defects relaxation or surface effect became dominant. The possible origins for these energy dissipations were discussed.

Symmetry energy III: Isovector skins

NASA Astrophysics Data System (ADS)

Danielewicz, Paweł; Singh, Pardeep; Lee, Jenny

2017-02-01

Isoscalar density is a sum of neutron and proton densities and isovector is a normalized difference. Here, we report the experimental evidence for the displacement of the isovector and isoscalar surfaces in nuclei, by ∼ 0.9 fm from each other. We analyze data on quasielastic (QE) charge exchange (p,n) reactions, concurrently with proton and neutron elastic scattering data for the same target nuclei, following the concepts of the isoscalar and isovector potentials combined into Lane optical potential. The elastic data largely probe the geometry of the isoscalar potential and the (p,n) data largely probe a relation between the geometries of the isovector and isoscalar potentials. The targets include 48Ca, 90Zr, 120Sn and 208Pb and projectile incident energy values span the range of (10-50) MeV. In our fit to elastic and QE charge-exchange data, we allow the values of isoscalar and isovector radii, diffusivities and overall potential normalizations to float away from those in the popular Koning and Delaroche parametrization. We find that the best-fit isovector radii are consistently larger than isoscalar and the best-fit isovector surfaces are steeper. Upon identifying the displacement of the potential surfaces with the displacement of the surfaces for the densities in the Skyrme-Hartree-Fock calculations, and by supplementing the results with those from analyzing excitation energies to isobaric analog states in the past, we arrive at the slope and value of the symmetry energy at normal density of 70 < L < 101 MeV and 33.5 < aaV < 36.4 MeV, respectively.

Erosive potential of commonly used beverages, medicated syrup, and their effects on dental enamel with and without restoration: An in vitro study

PubMed Central

Trivedi, Krishna; Bhaskar, Vijay; Ganesh, Mahadevan; Venkataraghavan, Karthik; Choudhary, Prashant; Shah, Shalin; Krishnan, Ramesh

2015-01-01

Aim: This study evaluates erosive potential of commonly used beverages, medicated syrup, and their effects on dental enamel with and without restoration in vitro. Materials and Methods: Test medias used in this study included carbonated beverage, noncarbonated beverage, high-energy sports drink medicated cough syrup, distilled water as the control. A total of 110 previously extracted human premolar teeth were selected for the study. Teeth were randomly divided into two groups. Test specimens were randomly distributed to five beverages groups and comprised 12 specimens per group. Surface roughness (profilometer) readings were performed at baseline and again, following immersion for 14 days (24 h/day). Microleakage was evaluated. The results obtained were analyzed for statistical significance using SPSS-PC package using the multiple factor ANOVA at a significance level of P < 0.05. Paired t-test, Friedman test ranks, and Wilcoxon signed ranks test. Results: For surface roughness high-energy sports drink and noncarbonated beverage showed the highly significant difference with P values of 0.000 and 0.000, respectively compared to other test media. For microleakage high-energy sports drink had significant difference in comparison to noncarbonated beverage (P = 0.002), medicated syrup (P = 0.000), and distilled water (P = 0.000). Conclusion: High-energy sports drink showed highest surface roughness value and microleakage score among all test media and thus greater erosive potential to enamel while medicated syrup showed least surface roughness value and microleakage among all test media. PMID:26538901

Validation of a Novel Technique and Evaluation of the Surface Free Energy of Food

PubMed Central

Senturk Parreidt, Tugce; Schmid, Markus; Hauser, Carolin

2017-01-01

Characterizing the physical properties of a surface is largely dependent on determining the contact angle exhibited by a liquid. Contact angles on the surfaces of rough and irregularly-shaped food samples are difficult to measure using a contact angle meter (goniometer). As a consequence, values for the surface energy and its components can be mismeasured. The aim of this work was to use a novel contact angle measurement method, namely the snake-based ImageJ program, to accurately measure the contact angles of rough and irregular shapes, such as food samples, and so enable more accurate calculation of the surface energy of food materials. In order to validate the novel technique, the contact angles of three different test liquids on four different smooth polymer films were measured using both the ImageJ software with the DropSnake plugin and the widely used contact angle meter. The distributions of the values obtained by the two methods were different. Therefore, the contact angles, surface energies, and polar and dispersive components of plastic films obtained using the ImageJ program and the Drop Shape Analyzer (DSA) were interpreted with the help of simple linear regression analysis. As case studies, the superficial characteristics of strawberry and endive salad epicarp were measured with the ImageJ program and the results were interpreted with the Drop Shape Analyzer equivalent according to our regression models. The data indicated that the ImageJ program can be successfully used for contact angle determination of rough and strongly hydrophobic surfaces, such as strawberry epicarp. However, for the special geometry of droplets on slightly hydrophobic surfaces, such as salad leaves, the program code interpolation part can be altered. PMID:28425932

Energy budget of the volcano Stromboli, Italy

NASA Technical Reports Server (NTRS)

Mcgetchin, T. R.; Chouet, B. A.

1979-01-01

The results of the analyses of movies of eruptions at Stromboli, Italy, and other available data are used to discuss the question of its energy partitioning among various energy transport mechanisms. Energy is transported to the surface from active volcanoes in at least eight modes, viz. conduction (and convection) of the heat through the surface, radiative heat transfer from the vent, acoustical radiation in blast and jet noise, seismic radiation, thermal energy of ejected particles, kinetic energy of ejected particles, thermal energy of ejected gas, and kinetic energy of ejected gas. Estimated values of energy flux from Stromboli by these eight mechanisms are tabulated. The energy budget of Stromboli in its normal mode of activity appears to be dominated by heat conduction (and convection) through the ground surface. Heat carried by eruption gases is the most important of the other energy transfer modes. Radiated heat from the open vent and heat carried by ejected lava particles also contribute to the total flux, while seismic energy accounts for about 0.5% of the total. All other modes are trivial by comparison.

Efficient Means of Detecting Neutral Atoms in Space

NASA Astrophysics Data System (ADS)

Zinicola, W. N.

2006-12-01

This summer, The Society of Physics Students granted me the opportunity to participate in an internship for The National Aeronautics and Space Administration (NASA) and The University of Maryland. Our chief interest was analyzing low energy neutral atoms that were created from random interactions of ions in space plasma. From detecting these neutrals one can project a image of what the plasma's composition is, and how this plasma changes through interactions with the solar wind. Presently, low energy neutral atom detectors have poor efficiency, typically in the range of 1%. Our goal was to increase this efficiency. To detect low energy neutrals we must first convert them from neutral molecules to negatively charged ions. Once converted, these "new" negatively charged ions can be easily detected and completely analyzed giving us information about their energy, mass, and instantaneous direction. The efficiency of the detector is drastically affected by the surface used for converting these neutrals. My job was first to create thin metal conversion surfaces. Then, using an X-ray photoelectron spectrometer, analyze atomic surface composition and gather work function values. Once the work function values were known we placed the surfaces in our neutral detector and measured their conversion efficiencies. Finally, a relation between the work function of the metal surface an its conversion efficiency was generated. With this relationship accurately measured one could use this information to help give suggestions on what surface would be the best to increase our detection efficiency. If we could increase the efficiency of these low energy neutral atom detectors by even 1% we would be able to decrease the size of the detector therefore making it cheaper and more applicable for space exploration.* * A special thanks to Dr. Michael Coplan of the University of Maryland for his support and guidance through all my research.

Role of surface energy on the morphology and optical properties of GaP micro & nano structures grown on polar and non-polar substrates

NASA Astrophysics Data System (ADS)

Roychowdhury, R.; Kumar, Shailendra; Wadikar, A.; Mukherjee, C.; Rajiv, K.; Sharma, T. K.; Dixit, V. K.

2017-10-01

Role of surface energy on the morphology, crystalline quality, electronic structure and optical properties of GaP layer grown on Si (001), Si (111), Ge (111) and GaAs (001) is investigated. GaP layers are grown on four different substrates under identical growth kinetics by metal organic vapour phase epitaxy. The atomic force microscopy images show that GaP layer completely covers the surface of GaAs substrate. On the other hand, the surfaces of Si (001), Si (111), Ge (111) substrates are partially covered with crystallographically morphed GaP island type micro and nano-structures. Origin of these crystallographically morphed GaP island is explained by the theoretical calculation of surface energy of the layer and corresponding substrates respectively. The nature of GaP island type micro and nano-structures and layers are single crystalline with existence of rotational twins on Si and Ge (111) substrates which is confirmed by the phi, omega and omega/2theta scans of high resolution x-ray diffraction. The electronic valence band offsets between the GaP and substrates have been determined from the valence band spectra of ultraviolet photoelectron spectroscopy. The valence electron plasmon of GaP are investigated by studying the energy values of Ga (3d) core level along with loss peaks in the energy dependent photoelectron spectra. The peak observed within the range of 3-6 eV from the Ga (3d) core level in the photoelectron spectra are associated to inter band transitions as their energy values are estimated from the pseudo dielectric function by the spectroscopic ellipsometry.

The Statistical Mechanics of Solar Wind Hydroxylation at the Moon, Within Lunar Magnetic Anomalies, and at Phobos

NASA Technical Reports Server (NTRS)

Farrell, W. M.; Hurley, D. M.; Esposito, V. J.; Mclain, J. L.; Zimmerman, M. I.

2017-01-01

We present a new formalism to describe the outgassing of hydrogen initially implanted by the solar wind protons into exposed soils on airless bodies. The formalism applies a statistical mechanics approach similar to that applied recently to molecular adsorption onto activated surfaces. The key element enabling this formalism is the recognition that the interatomic potential between the implanted H and regolith-residing oxides is not of singular value but possess a distribution of trapped energy values at a given temperature, F(U,T). All subsequent derivations of the outward diffusion and H retention rely on the specific properties of this distribution. We find that solar wind hydrogen can be retained if there are sites in the implantation layer with activation energy values exceeding 0.5eV. We especially examine the dependence of H retention applying characteristic energy values found previously for irradiated silica and mature lunar samples. We also apply the formalism to two cases that differ from the typical solar wind implantation at the Moon. First, we test for a case of implantation in magnetic anomaly regions where significantly lower-energy ions of solar wind origin are expected to be incident with the surface. In magnetic anomalies, H retention is found to be reduced due to the reduced ion flux and shallower depth of implantation. Second, we also apply the model to Phobos where the surface temperature range is not as extreme as the Moon. We find the H atom retention in this second case is higher than the lunar case due to the reduced thermal extremes (that reduces outgassing).

Measurement of the adsorption energy difference between ortho- and para-D2 on an amorphous ice surface.

PubMed

Amiaud, L; Momeni, A; Dulieu, F; Fillion, J H; Matar, E; Lemaire, J-L

2008-02-08

Molecular hydrogen interaction on water ice surfaces is a major process taking place in interstellar dense clouds. By coupling laser detection and classical thermal desorption spectroscopy, it is possible to study the effect of rotation of D(2) on adsorption on amorphous solid water ice surfaces. The desorption profiles of ortho- and para-D(2) are different. This difference is due to a shift in the adsorption energy distribution of the two lowest rotational states. Molecules in J''=1 rotational state are on average more strongly bound to the ice surface than those in J''=0 rotational state. This energy difference is estimated to be 1.4+/-0.3 meV. This value is in agreement with previous calculation and interpretation. The nonspherical wave function J'' =1 has an interaction with the asymmetric part of the adsorption potential and contributes positively in the binding energy.

Recent Progress in Bionic Condensate Microdrop Self-Propelling Surfaces.

PubMed

Gong, Xiaojing; Gao, Xuefeng; Jiang, Lei

2017-12-01

Bionic condensate microdrop self-propelling (CMDSP) surfaces are attracting increased attention as novel, low-adhesivity superhydrophobic surfaces due to their value in fundamental research and technological innovation, e.g., for enhancing heat transfer, energy-effective antifreezing, and electrostatic energy harvesting. Here, the focus is on recent progress in bionic CMDSP surfaces. Metal-based CMDSP surfaces, which are the most promising in their respective fields, are highlighted for use in future applications. The selected topics are divided into four sections: biological prototypes, mechanism and construction rules, fabrication, and applications of metal-based CMDSP surfaces. Finally, the challenges and future development trends in bionic CMDSP surfaces are envisioned, especially the utilization of potential bionic inspiration in the design of more advanced CMDSP surfaces. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Interaction of ammonia with semiconducting oxide surfaces

NASA Astrophysics Data System (ADS)

Nigam, Sandeep; Sahoo, Suman Kalyan; Majumder, Chiranjib

2018-04-01

Using density functional theory (DFT) we have investigated the adsorption of NH3 molecule on the rutile SnO2(110) and mixed Sn0.5Ti0.5O2(110) surfaces. NH3 molecule gets absorbed on the 5-coordinated Sn atom (Sn5c) of the surface in tilted mode having an additional hydrogen bond with nearby surface bridged oxygen (Obr) atom. After adsorption, 3a1 molecular orbital of ammonia undergo significant dispersal as it donates its electron to surface atoms. The adsorption energy is found to be 1.4-1.6eV. Inclusion of Ti atoms in the SnO2 lattice leads to decrease in the adsorption energy value.

Application of self-preservation in the diurnal evolution of the surface energy budget to determine daily evaporation

NASA Technical Reports Server (NTRS)

Brutsaert, Wilfried; Sugita, Michiaki

1992-01-01

Evaporation from natural land surfaces often exhibits a strong variation during the course of a day, mostly in response to the daily variation of radiative energy input at the surface. This makes it difficult to derive the total daily evaporation, when only one or a few instantaneous estimates of evaporation are available. It is often possible to resolve this difficulty by assuming self-preservation in the diurnal evolution of the surface energy budget. Thus if the relative partition of total incoming energy flux among the different components remains the same, the ratio of latent heat flux and any other flux component can be taken as constant through the day. This concept of constant flux ratios is tested by means of data obtained during the First ISLSCP Field Experiment; the instantaneous evaporation values were calculated by means of the atmospheric boundary layer bulk similarity approach with radiosonde profiles and radiative surface temperatures. Good results were obtained for evaporative flux ratios with available energy flux, with net radiation, and with incoming shortwave radiation.

Density dependence of the saturated velocity in graphene

NASA Astrophysics Data System (ADS)

Ferry, D. K.

2016-11-01

The saturated velocity of a semiconductor is an important measure in bench-marking performance for either logic or microwave applications. Graphene has been of interest for such applications due to its apparently high value of the saturated velocity. Recent experiments have suggested that this value is very density dependent and can even exceed the band limiting Fermi velocity. Some of these measurements have also suggested that the scattering is dominated by the low energy surface polar mode of the SiO2 substrate. Here, we show that the saturated velocity of graphene on SiO2 is relatively independent of the density and that the scattering is dominated by the high energy surface polar mode of the substrate.

The importance of particle size in porous titanium and nonporous counterparts for surface energy and its impact on apatite formation.

PubMed

Chen, Xiao-Bo; Li, Yun-Cang; Hodgson, Peter D; Wen, Cuie

2009-07-01

The importance of particle size in titanium (Ti) fabricated by powder metallurgy for the surface energy and its impact on the apatite formation was investigated. Four sorts of Ti powders of different mean particle size were realized through 20min, 2h, 5h and 8h of ball milling, respectively. Each sort of Ti powder was used to fabricate porous Ti and its nonporous counterparts sharing similar surface morphology, grain size and chemical composition, and then alkali-heat treatment was conducted on them. Surface energy was measured on the surfaces of the nonporous Ti counterparts due to the difficulty in measuring the porous surfaces directly. The surface energy increase on the alkali-heat-treated porous and nonporous Ti was observed due to the decrease in the particle size of the Ti powders and the presence of Ti-OH groups brought by the alkali-heat treatment. The apatite-inducing ability of the alkali-heat-treated porous and nonporous Ti with different surface energy values was evaluated in modified simulated body fluid and results indicated that there was a strong correlation between the apatite-inducing ability and the surface energy. The alkali-heat-treated porous and nonporous Ti discs prepared from the powders with an average particle size of 5.89+/-0.76microm possessed the highest surface energy and the best apatite-inducing ability when compared to the samples produced from the powders with the average particle size varying from 19.79+/-0.31 to 10.25+/-0.39microm.

Assessment of Global Annual Atmospheric Energy Balance from Satellite Observations

NASA Technical Reports Server (NTRS)

Lin, Bing; Stackhouse, Paul; Minnis, Patrick; Wielicki, Bruce A.; Hu, Yongxiang; Sun, Wenbo; Fan, Tai-Fang (Alice); Hinkelman, Laura

2008-01-01

Global atmospheric energy balance is one of the fundamental processes for the earth's climate system. This study uses currently available satellite data sets of radiative energy at the top of atmosphere (TOA) and surface and latent and sensible heat over oceans for the year 2000 to assess the global annual energy budget. Over land, surface radiation data are used to constrain assimilated results and to force the radiation, turbulent heat, and heat storage into balance due to a lack of observation-based turbulent heat flux estimations. Global annual means of the TOA net radiation obtained from both direct measurements and calculations are close to zero. The net radiative energy fluxes into the surface and the surface latent heat transported into the atmosphere are about 113 and 86 Watts per square meter, respectively. The estimated atmospheric and surface heat imbalances are about -8 9 Watts per square meter, values that are within the uncertainties of surface radiation and sea surface turbulent flux estimates and likely systematic biases in the analyzed observations. The potential significant additional absorption of solar radiation within the atmosphere suggested by previous studies does not appear to be required to balance the energy budget the spurious heat imbalances in the current data are much smaller (about half) than those obtained previously and debated at about a decade ago. Progress in surface radiation and oceanic turbulent heat flux estimations from satellite measurements significantly reduces the bias errors in the observed global energy budgets of the climate system.

Modified energetics and growth kinetics on H-terminated GaAs (110)

NASA Astrophysics Data System (ADS)

Galiana, B.; Benedicto, M.; Díez-Merino, L.; Lorbek, S.; Hlawacek, G.; Teichert, C.; Tejedor, P.

2013-10-01

Atomic hydrogen modification of the surface energy of GaAs (110) epilayers, grown at high temperatures from molecular beams of Ga and As4, has been investigated by friction force microscopy (FFM). The reduction of the friction force observed with longer exposures to the H beam has been correlated with the lowering of the surface energy originated by the progressive de-relaxation of the GaAs (110) surface occurring upon H chemisorption. Our results indicate that the H-terminated GaAs (110) epilayers are more stable than the As-stabilized ones, with the minimum surface energy value of 31 meV/Å2 measured for the fully hydrogenated surface. A significant reduction of the Ga diffusion length on the H-terminated surface irrespective of H coverage has been calculated from the FFM data, consistent with the layer-by-layer growth mode and the greater As incorporation coefficient determined from real-time reflection high-energy electron diffraction studies. Arsenic incorporation through direct dissociative chemisorption of single As4 molecules mediated by H on the GaAs (110) surface has been proposed as the most likely explanation for the changes in surface kinetics observed.

Influence of Curing Mode on the Surface Energy and Sorption/Solubility of Dental Self-Adhesive Resin Cements

PubMed Central

Kim, Hyun-Jin; Bagheri, Rafat; Kim, Young Kyung; Son, Jun Sik; Kwon, Tae-Yub

2017-01-01

This study investigated the influence of curing mode (dual- or self-cure) on the surface energy and sorption/solubility of four self-adhesive resin cements (SARCs) and one conventional resin cement. The degree of conversion (DC) and surface energy parameters including degree of hydrophilicity (DH) were determined using Fourier transform infrared spectroscopy and contact angle measurements, respectively (n = 5). Sorption and solubility were assessed by mass gain or loss after storage in distilled water or lactic acid for 60 days (n = 5). A linear regression model was used to correlate between the results (%DC vs. DH and %DC/DH vs. sorption/solubility). For all materials, the dual-curing consistently produced significantly higher %DC values than the self-curing (p < 0.05). Significant negative linear regressions were established between the %DC and DH in both curing modes (p < 0.05). Overall, the SARCs showed higher sorption/solubility values, in particular when immersed in lactic acid, than the conventional resin cement. Linear regression revealed that %DC and DH were negatively and positively correlated with the sorption/solubility values, respectively. Dual-curing of SARCs seems to lower the sorption and/or solubility in comparison with self-curing by increased %DC and occasionally decreased hydrophilicity. PMID:28772489

Surface nanocrystalline and hardening effects of Ti-Al-V alloy by electropulsing ultrasonic shock

NASA Astrophysics Data System (ADS)

Ye, Xiaoxin

2015-04-01

The effect of electropulsing ultrasonic shock (EUS) on the surface hardening and microstructure of Ti6Al4V alloy was studied. It was found that electropulsing improved the microhardness dramatically both in the influential depth and maximum value, compared with the only ultrasonic-shocked sample. It's indicated that refined surface layer with nanocrystalline and improved microhardness were obtained on account of surface severe plastic deformation, dynamic recrystallization (DRX) and phase change, which was implemented at relative low temperature and high strain rate/capacity due to the coupling of the thermal and athermal effects of EUS. It's different from conventional experiments and theory. It's discussed that the positive contributions of EPT in the thermodynamics and kinetics of microstructure and properties change were attributed to the reduction of nucleation energy barrier and acceleration of atomic diffusion. Therefore, it's supposed that EUS is an energy-saving and high-efficiency method of surface treatment technique with the help of high-energy electropulses, which is promising in cost reduction of the surface engineering and energy management.

Influence of radiant energy exchange on the determination of convective heat transfer rates to Orbiter leeside surfaces during entry

NASA Technical Reports Server (NTRS)

Throckmorton, D. A.

1982-01-01

Temperatures measured at the aerodynamic surface of the Orbiter's thermal protection system (TPS), and calorimeter measurements, are used to determine heating rates to the TPS surface during atmospheric entry. On the Orbiter leeside, where convective heating rates are low, it is possible that a significant portion of the total energy input may result from solar radiation, and for the wing, cross radiation from the hot (relatively) Orbiter fuselage. In order to account for the potential impact of these sources, values of solar- and cross-radiation heat transfer are computed, based upon vehicle trajectory and attitude information and measured surface temperatures. Leeside heat-transfer data from the STS-2 mission are presented, and the significance of solar radiation and fuselage-to-wing cross-radiation contributions to total energy input to Orbiter leeside surfaces is assessed.

Application of microdynamics and lattice mechanics to problems in plastic flow and fracture. Final report, 1 April 1973--31 March 1978

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bilello, J C; Liu, J M

Progress in an investigation of the application of microdynamics and lattice mechanics to the problems in plastic flow and fracture is described. The research program consisted of both theoretical formulations and experimental measurements of a number of intrinsic material parameters in bcc metals and alloys including surface energy, phonon-dispersion curves for dislocated solids, dislocation-point defect interaction energy, slip initiation and microplastic flow behavior. The study has resulted in an improved understanding in the relationship among the experimentally determined fracture surface energy, the intrinsic cohesive energy between atomic planes, and the plastic deformation associated with the initial stages of crack propagation.more » The values of intrinsic surface energy of tungsten, molybdenum, niobium and niobium-molybdenum alloys, deduced from the measurements, serve as a starting point from which fracture toughness of these materials in engineering service may be intelligently discussed.« less

Ab initio intermolecular potential energy surface for the CO2—N2 system and related thermophysical properties

NASA Astrophysics Data System (ADS)

Crusius, Johann-Philipp; Hellmann, Robert; Castro-Palacio, Juan Carlos; Vesovic, Velisa

2018-06-01

A four-dimensional potential energy surface (PES) for the interaction between a rigid carbon dioxide molecule and a rigid nitrogen molecule was constructed based on quantum-chemical ab initio calculations up to the coupled-cluster level with single, double, and perturbative triple excitations. Interaction energies for a total of 1893 points on the PES were calculated using the counterpoise-corrected supermolecular approach and basis sets of up to quintuple-zeta quality with bond functions. The interaction energies were extrapolated to the complete basis set limit, and an analytical site-site potential function with seven sites for carbon dioxide and five sites for nitrogen was fitted to the interaction energies. The CO2—N2 cross second virial coefficient as well as the dilute gas shear viscosity, thermal conductivity, and binary diffusion coefficient of CO2—N2 mixtures were calculated for temperatures up to 2000 K to validate the PES and to provide reliable reference values for these important properties. The calculated values are in very good agreement with the best experimental data.

Global Surface Solar Energy Anomalies Including El Nino and La Nina Years

NASA Technical Reports Server (NTRS)

Whitlock, C. H.; Brown, D. E.; Chandler, W. S.; DiPasquale, R. C.; Ritchey, Nancy A.; Gupta, Shashi K.; Wilber, Anne C.; Kratz, David P.; Stackhouse, Paul W.

2001-01-01

This paper synthesizes past events in an attempt to define the general magnitude, duration, and location of large surface solar anomalies over the globe. Surface solar energy values are mostly a function of solar zenith angle, cloud conditions, column atmospheric water vapor, aerosols, and surface albedo. For this study, solar and meteorological parameters for the 10-yr period July 1983 through June 1993 are used. These data were generated as part of the Release 3 Surface meteorology and Solar Energy (SSE) activity under the NASA Earth Science Enterprise (ESE) effort. Release 3 SSE uses upgraded input data and methods relative to previous releases. Cloud conditions are based on recent NASA Version-D International Satellite Cloud Climatology Project (ISCCP) global satellite radiation and cloud data. Meteorological inputs are from Version-I Goddard Earth Observing System (GEOS) reanalysis data that uses both weather station and satellite information. Aerosol transmission for different regions and seasons are for an 'average' year based on historic solar energy data from over 1000 ground sites courtesy of Natural Resources Canada (NRCan). These data are input to a new Langley Parameterized Shortwave Algorithm (LPSA) that calculates surface albedo and surface solar energy. That algorithm is an upgraded version of the 'Staylor' algorithm. Calculations are performed for a 280X280 km equal-area grid system over the globe based on 3-hourly input data. A bi-linear interpolation process is used to estimate data output values on a 1 X 1 degree grid system over the globe. Maximum anomalies are examined relative to El Nino and La Nina events in the tropical Pacific Ocean. Maximum year-to-year anomalies over the globe are provided for a 10-year period. The data may assist in the design of systems with increased reliability. It may also allow for better planning for emergency assistance during some atypical events.

First-principle modelling of forsterite surface properties: Accuracy of methods and basis sets.

PubMed

Demichelis, Raffaella; Bruno, Marco; Massaro, Francesco R; Prencipe, Mauro; De La Pierre, Marco; Nestola, Fabrizio

2015-07-15

The seven main crystal surfaces of forsterite (Mg2 SiO4 ) were modeled using various Gaussian-type basis sets, and several formulations for the exchange-correlation functional within the density functional theory (DFT). The recently developed pob-TZVP basis set provides the best results for all properties that are strongly dependent on the accuracy of the wavefunction. Convergence on the structure and on the basis set superposition error-corrected surface energy can be reached also with poorer basis sets. The effect of adopting different DFT functionals was assessed. All functionals give the same stability order for the various surfaces. Surfaces do not exhibit any major structural differences when optimized with different functionals, except for higher energy orientations where major rearrangements occur around the Mg sites at the surface or subsurface. When dispersions are not accounted for, all functionals provide similar surface energies. The inclusion of empirical dispersions raises the energy of all surfaces by a nearly systematic value proportional to the scaling factor s of the dispersion formulation. An estimation for the surface energy is provided through adopting C6 coefficients that are more suitable than the standard ones to describe O-O interactions in minerals. A 2 × 2 supercell of the most stable surface (010) was optimized. No surface reconstruction was observed. The resulting structure and surface energy show no difference with respect to those obtained when using the primitive cell. This result validates the (010) surface model here adopted, that will serve as a reference for future studies on adsorption and reactivity of water and carbon dioxide at this interface. © 2015 Wiley Periodicals, Inc.

Gas-liquid nucleation at large metastability: unusual features and a new formalism

NASA Astrophysics Data System (ADS)

Santra, Mantu; Singh, Rakesh S.; Bagchi, Biman

2011-03-01

Nucleation at large metastability is still largely an unsolved problem, even though it is a problem of tremendous current interest, with wide-ranging practical value, from atmospheric research to materials science. It is now well accepted that the classical nucleation theory (CNT) fails to provide a qualitative picture and gives incorrect quantitative values for such quantities as activation-free energy barrier and supersaturation dependence of nucleation rate, especially at large metastability. In this paper, we present an alternative formalism to treat nucleation at large supersaturation by introducing an extended set of order parameters in terms of the kth largest liquid-like clusters, where k = 1 is the largest cluster in the system, k = 2 is the second largest cluster and so on. At low supersaturation, the size of the largest liquid-like cluster acts as a suitable order parameter. At large supersaturation, the free energy barrier for the largest liquid-like cluster disappears. We identify this supersaturation as the one at the onset of kinetic spinodal. The kinetic spinodal is system-size-dependent. Beyond kinetic spinodal many clusters grow simultaneously and competitively and hence the nucleation and growth become collective. In order to describe collective growth, we need to consider the full set of order parameters. We derive an analytic expression for the free energy of formation of the kth largest cluster. The expression predicts that, at large metastability (beyond kinetic spinodal), the barrier of growth for several largest liquid-like clusters disappears, and all these clusters grow simultaneously. The approach to the critical size occurs by barrierless diffusion in the cluster size space. The expression for the rate of barrier crossing predicts weaker supersaturation dependence than what is predicted by CNT at large metastability. Such a crossover behavior has indeed been observed in recent experiments (but eluded an explanation till now). In order to understand the large numerical discrepancy between simulation predictions and experimental results, we carried out a study of the dependence on the range of intermolecular interactions of both the surface tension of an equilibrium planar gas-liquid interface and the free energy barrier of nucleation. Both are found to depend significantly on the range of interaction for the Lennard-Jones potential, both in two and three dimensions. The value of surface tension and also the free energy difference between the gas and the liquid phase increase significantly and converge only when the range of interaction is extended beyond 6-7 molecular diameters. We find, with the full range of interaction potential, that the surface tension shows only a weak dependence on supersaturation, so the reason for the breakdown of CNT (with simulated values of surface tension and free energy gap) cannot be attributed to the supersaturation dependence of surface tension. This remains an unsettled issue at present because of the use of the value of surface tension obtained at coexistence.

Unsteady Convection Flow and Heat Transfer over a Vertical Stretching Surface

PubMed Central

Cai, Wenli; Su, Ning; Liu, Xiangdong

2014-01-01

This paper investigates the effect of thermal radiation on unsteady convection flow and heat transfer over a vertical permeable stretching surface in porous medium, where the effects of temperature dependent viscosity and thermal conductivity are also considered. By using a similarity transformation, the governing time-dependent boundary layer equations for momentum and thermal energy are first transformed into coupled, non-linear ordinary differential equations with variable coefficients. Numerical solutions to these equations subject to appropriate boundary conditions are obtained by the numerical shooting technique with fourth-fifth order Runge-Kutta scheme. Numerical results show that as viscosity variation parameter increases both the absolute value of the surface friction coefficient and the absolute value of the surface temperature gradient increase whereas the temperature decreases slightly. With the increase of viscosity variation parameter, the velocity decreases near the sheet surface but increases far away from the surface of the sheet in the boundary layer. The increase in permeability parameter leads to the decrease in both the temperature and the absolute value of the surface friction coefficient, and the increase in both the velocity and the absolute value of the surface temperature gradient. PMID:25264737

Unsteady convection flow and heat transfer over a vertical stretching surface.

PubMed

Cai, Wenli; Su, Ning; Liu, Xiangdong

2014-01-01

This paper investigates the effect of thermal radiation on unsteady convection flow and heat transfer over a vertical permeable stretching surface in porous medium, where the effects of temperature dependent viscosity and thermal conductivity are also considered. By using a similarity transformation, the governing time-dependent boundary layer equations for momentum and thermal energy are first transformed into coupled, non-linear ordinary differential equations with variable coefficients. Numerical solutions to these equations subject to appropriate boundary conditions are obtained by the numerical shooting technique with fourth-fifth order Runge-Kutta scheme. Numerical results show that as viscosity variation parameter increases both the absolute value of the surface friction coefficient and the absolute value of the surface temperature gradient increase whereas the temperature decreases slightly. With the increase of viscosity variation parameter, the velocity decreases near the sheet surface but increases far away from the surface of the sheet in the boundary layer. The increase in permeability parameter leads to the decrease in both the temperature and the absolute value of the surface friction coefficient, and the increase in both the velocity and the absolute value of the surface temperature gradient.

[Energy accumulation and allocation of main plant populations in Aneurolepidium chinense grassland in Songnen Plain].

PubMed

Qu, Guohui; Wen, Mingzhang; Guo, Jixun

2003-05-01

The calorific value of plants is dependent on their biological characteristics and energy-containing materials. The allocation of calorific value in different organs of Aneurolepidium chinese, Calamagrostic epigejos, Puccinellia tenuiflora and Chloris virgata was inflorescence > leaf > stem > dead standing. The seasonal dynamics of standing crop energy of aboveground part of four plant populations showed single-peak curve, and the energy production was Aneurolepidium chinense > Calamagrostic epigejos > Chloris virgata > Puccinellia tenuiflora. Energy increasing rate showed double-peak curve, with the first peak at heading stage and the second peak at maturing stage of seeds. Energy increasing rate was negative at the final stage of growth. The horizontal distribution of energy of aboveground part was that the allocation ratio of different organs at different growth stages was different. There existed a similar trend for vertical distribution of energy among four plant populations, i.e., was the vertical distribution of energy of aboveground part showed a tower shape, with the maximum value in 10-30 cm height. The vertical distribution of energy of underground part showed an inverted tower shape from soil surface to deeper layer, with the maximum value in 0-10 cm depth. The standing crop energy of underground part was about 3-4 times than that of aboveground part.

Atmospheric heat engines on earth and Mars

NASA Astrophysics Data System (ADS)

Philip, J. R.

1987-06-01

The character of the earth's atmospheric heat engine depends, inter alia, on the relatively tight linkage between surface fluxes of energy and of H2O. On Mars, on the other hand, H2O-based latent heat fluxes are only a trivial fraction of total surface energy fluxes, and the dominant component of the working fluid is CO2. These considerations are made quantitative through evaluation of Lambda, the equivalent temperature excess at the surface for a particular component of the working fluid. The very different values (and latitudinal distribution) of Lambda on the two planets signalize vividly their different meteorology. Preliminary study of the climatology of Lambda on earth brings out, in particular, the tightness of the H2O-energy linkage in the tropics.

Modeling of thin film GaAs growth

NASA Technical Reports Server (NTRS)

Heinbockel, J. H.

1982-01-01

A potential scaling Monte Carlo model of crystal growth is developed. The model is a modification of the solid-on-solid method for studying crystal growth in that potentials at surface sites are continuously updated on a time scale reflecting the surface events of migration, incorporation and evaporation. The model allows for B on A type of crystal growth and lattice disregistry by the assignment of potential values at various surface sites. The surface adatoms are periodically assigned a random energy from a Boltzmann distribution and this energy determines whether the adatoms evaporate, migrate or remain stationary during the sampling interval. For each addition or migration of an adatom, the surface potentials are adjusted to reflect the adsorption, migration or desorption potential changes.

Optimal reconstruction of the folding landscape using differential energy surface analysis

NASA Astrophysics Data System (ADS)

La Porta, Arthur; Denesyuk, Natalia A.; de Messieres, Michel

2013-03-01

In experiments and in simulations, the free energy of a state of a system can be determined from the probability that the state is occupied. However, it is often necessary to impose a biasing potential on the system so that high energy states are sampled with sufficient frequency. The unbiased energy is typically obtained from the data using the weighted histogram analysis method (WHAM). Here we present differential energy surface analysis (DESA), in which the gradient of the energy surface, dE/dx, is extracted from data taken with a series of harmonic biasing potentials. It is shown that DESA produces a maximum likelihood estimate of the folding landscape gradient. DESA is demonstrated by analyzing data from a simulated system as well as data from a single-molecule unfolding experiment in which the end-to-end distance of a DNA hairpin is measured. It is shown that the energy surface obtained from DESA is indistinguishable from the energy surface obtained when WHAM is applied to the same data. Two criteria are defined which indicate whether the DESA results are self-consistent. It is found that these criteria can detect a situation where the energy is not a single-valued function of the measured reaction coordinate. The criteria were found to be satisfied for the experimental data analyzed, confirming that end-to-end distance is a good reaction coordinate for the experimental system. The combination of DESA and the optical trap assay in which a structure is disrupted under harmonic constraint facilitates an extremely accurate measurement of the folding energy surface.

The relative energy of fcc and hcp foams

NASA Astrophysics Data System (ADS)

Whyte, D.; Weaire, D.; Drenckhan, W.; Hutzler, S.

2015-06-01

The energies of face-centred cubic (fcc) and hexagonal close-packed (hcp) monodisperse foams, associated with their total surface area, are equal in the wet and dry limits, in the usual model. We prove that for all intermediate values of liquid fraction, hcp has lower energy. Energy considerations are thus not sufficient to explain the observed preference for crystallization into fcc over hcp in experiments using monodisperse bubbles.

Bernoulli potential in type-I and weak type-II superconductors: II. Surface dipole

NASA Astrophysics Data System (ADS)

Lipavský, P.; Morawetz, K.; Koláček, J.; Mareš, J. J.; Brandt, E. H.; Schreiber, M.

2004-09-01

The Budd-Vannimenus theorem is modified to apply to superconductors in the Meissner state. The obtained identity links the surface value of the electrostatic potential to the density of free energy at the surface which allows one to evaluate the electrostatic potential observed via the capacitive pickup without the explicit solution of the charge profile.

An ab initio potential energy surface for the formic acid dimer: zero-point energy, selected anharmonic fundamental energies, and ground-state tunneling splitting calculated in relaxed 1-4-mode subspaces.

PubMed

Qu, Chen; Bowman, Joel M

2016-09-14

We report a full-dimensional, permutationally invariant potential energy surface (PES) for the cyclic formic acid dimer. This PES is a least-squares fit to 13475 CCSD(T)-F12a/haTZ (VTZ for H and aVTZ for C and O) energies. The energy-weighted, root-mean-square fitting error is 11 cm -1 and the barrier for the double-proton transfer on the PES is 2848 cm -1 , in good agreement with the directly-calculated ab initio value of 2853 cm -1 . The zero-point vibrational energy of 15 337 ± 7 cm -1 is obtained from diffusion Monte Carlo calculations. Energies of fundamentals of fifteen modes are calculated using the vibrational self-consistent field and virtual-state configuration interaction method. The ground-state tunneling splitting is computed using a reduced-dimensional Hamiltonian with relaxed potentials. The highest-level, four-mode coupled calculation gives a tunneling splitting of 0.037 cm -1 , which is roughly twice the experimental value. The tunneling splittings of (DCOOH) 2 and (DCOOD) 2 from one to three mode calculations are, as expected, smaller than that for (HCOOH) 2 and consistent with experiment.

The two-dimensional hybrid surface plasma micro-cavity

NASA Astrophysics Data System (ADS)

Kai, Tong; Mei-yu, Wang; Fu-cheng, Wang; Jia, Guo

2018-07-01

A hybrid surface plasma micro-cavity structure with a defect cavity is formed based on the two-dimensional surface plasmon resonance photonic crystal waveguide structure. A cell defect is introduced in the centre of the photonic crystal layer to build the hybrid surface plasma micro-cavity structure. This work is numerical based on the finite-difference time-domain method. The photon energy is confined to the micro-cavity and the photon energy is strongest at the interface between the insulating layer and the metal layer. The micro-cavity structure has a very small mode volume of sub-wavelength scale in the 1550 nm communication band. The value of Q/V is up to 7132.08 λ/n-3.

The energy balance of an urban area: Examining temporal and spatial variability through measurements, remote sensing and modeling

NASA Astrophysics Data System (ADS)

Offerle, Brian

Urban environmental problems related to air quality, thermal stress, issues of water demand and quality, all of which are linked directly or indirectly to urban climate, are emerging as major environmental concerns at the start of the 21st century. Thus there are compelling social, political and economic, and scientific reasons that make the study and understanding of the fundamental causes of urban climates critically important. This research addresses these topics through an intensive study of the surface energy balance of Lodz, Poland. The research examines the temporal variability in long-term measurements of urban surface-atmosphere exchange at a downtown location and the spatial variability of this exchange over distinctly different neighborhoods using shorter-term observations. These observations provide the basis for an evaluation of surface energy balance models. Monthly patterns in energy exchange are consistent from year-to-year with variability determined by net radiation and the timing and amount of precipitation. Spatial variability can be determined from plan area fractions of vegetation and impervious surface, though heat storage exerts a strong control on shorter term variability of energy exchange, within and between locations in an urban area. Anthropogenic heat fluxes provide most of the energy driving surface-atmosphere exchange in winter, From a modeling perspective, sensible heat fluxes can be reliably determined from radiometrically sensed surface temperatures and spatially representative surface-atmosphere exchange in an urban area can be determined from satellite remote sensing products. Models of the urban surface energy balance showed good agreement with mean values of energy exchange and under most conditions represented the temporal variability due to synoptic and shorter time scale forcing well.

Comparing Multiple Evapotranspiration-calculating Methods, Including Eddy Covariance and Surface Renewal, Using Empirical Measurements from Alfalfa Fields in the Sacramento-San Joaquin River Delta

NASA Astrophysics Data System (ADS)

Clay, J.; Kent, E. R.; Leinfelder-Miles, M.; Lambert, J. J.; Little, C.; Paw U, K. T.; Snyder, R. L.

2016-12-01

Eddy covariance and surface renewal measurements were used to estimate evapotranspiration (ET) over a variety of crop fields in the Sacramento-San Joaquin River Delta during the 2016 growing season. However, comparing and evaluating multiple measurement systems and methods for determining ET was focused upon at a single alfalfa site. The eddy covariance systems included two systems for direct measurement of latent heat flux: one using a separate sonic anemometer and an open path infrared gas analyzer and another using a combined system (Campbell Scientific IRGASON). For these methods, eddy covariance was used with measurements from the Campbell Scientific CSAT3, the LI-COR 7500a, the Campbell Scientific IRGASON, and an additional R.M. Young sonic anemometer. In addition to those direct measures, the surface renewal approach included several energy balance residual methods in which net radiation, ground heat flux, and sensible heat flux (H) were measured. H was measured using several systems and different methods, including using multiple fast-response thermocouple measurements and using the temperatures measured by the sonic anemometers. The energy available for ET was then calculated as the residual of the surface energy balance equation. Differences in ET values were analyzed between the eddy covariance and surface renewal methods, using the IRGASON-derived values of ET as the standard for accuracy.

Effects of structure of fatty acid collectors on the adsorption of fluorapatite (0 0 1) surface: A first-principles calculations

NASA Astrophysics Data System (ADS)

Xie, Jun; Li, Xianhai; Mao, Song; Li, Longjiang; Ke, Baolin; Zhang, Qin

2018-06-01

Effects of carbon chain length, carbon chain isomerism, Cdbnd C double bonds number on fatty acid adsorption on FAP (0 0 1) surface have been investigated based on DFT. The results revealed that fatty acid collector can form stable adsorption configuration at Ca1 (surf) site. Chemical adsorption was formed between O (mole) of fatty acid collector and the Ca1 (surf) of fluorapatite (0 0 1) surface; hydrogen bond adsorption was formed between the H (mole) of fatty acid and the O (surf) of-[PO4]- of FAP (0 0 1) surface. Fatty acid collectors and FAP (0 0 1) surface are bonding by means of the hybridization of O (mole) 2p and Ca (surf) 4d orbitals, H (mole) 1s and O (surf) 2p orbital. The analysis of adsorption energy, DOS, electron density, Mulliken charge population and Mulliken bond population revealed that with the carbon chain growing within certain limits, the absolute value of the adsorption energy and the overlapping area between the DOS curve of O (mole) and Ca (surf) was greater, while that of H (mole) 1s and O (surf) 2p basically remained unchanged. As Cdbnd C double bonds of fatty acids increased within certain limits, the adsorption energy and the overlapping area between the state density curve of O (mole) and Ca (surf), H (mole) and O (surf) basically remained unchanged. The substituent groups of fatty acid changed, the absolute value of the adsorption energy and the overlapping area between the state density curve had a major change. The influence of fatty acids adsorption on FAP (0 0 1) surface depends mainly on the interaction between O (mole) and Ca (surf).

A theoretical prediction of the paradoxical surface free energy for FCC metallic nanosolids

NASA Astrophysics Data System (ADS)

Abdul-Hafidh, Esam H.; Aïssa, Brahim

2016-08-01

We report on the development of an efficient and simple method to calculate the surface free energy (surface tension) of a general-shaped metallic nanosolid. Both nanoparticles and nanostructures that account for the crystal structure and size were considered. The surface free energy of a face-centered cubic structure of a metallic nanoparticles was found to decrease as the size decreases, for a shape factor equal to 1.0 (i.e., spherical). However, when the shape factor exceeds this value, which includes disk-like, regular tetrahedral, regular hexahedral, regular octahedral, nanorod, and regular quadrangular structures, the behavior of the surface free energy was found to reverse, especially for small nanoparticles and then increases as the size decreases. Moreover, this behavior was systematically recorded for large nanoparticles when the mechanical distortion was appreciable. As a matter of fact, this model was also applied to the noble transition metals, including gold and silver nanoparticles. This work is a clear step forward establishing a systematic mechanism for controlling the mechanical properties of nanoscale particles by controlling the shape, size and structure.

Properties of real metallic surfaces: Effects of density functional semilocality and van der Waals nonlocality

PubMed Central

Patra, Abhirup; Bates, Jefferson E.; Sun, Jianwei; Perdew, John P.

2017-01-01

We have computed the surface energies, work functions, and interlayer surface relaxations of clean (111), (100), and (110) surfaces of Al, Cu, Ru, Rh, Pd, Ag, Pt, and Au. We interpret the surface energy from liquid metal measurements as the mean of the solid-state surface energies over these three lowest-index crystal faces. We compare experimental (and random phase approximation) reference values to those of a family of nonempirical semilocal density functionals, from the basic local density approximation (LDA) to our most advanced general purpose meta-generalized gradient approximation, strongly constrained and appropriately normed (SCAN). The closest agreement is achieved by the simplest density functional LDA, and by the most sophisticated one, SCAN+rVV10 (Vydrov–Van Voorhis 2010). The long-range van der Waals interaction, incorporated through rVV10, increases the surface energies by about 10%, and increases the work functions by about 3%. LDA works for metal surfaces through two known error cancellations. The Perdew–Burke–Ernzerhof generalized gradient approximation tends to underestimate both surface energies (by about 24%) and work functions (by about 4%), yielding the least-accurate results. The amount by which a functional underestimates these surface properties correlates with the extent to which it neglects van der Waals attraction at intermediate and long range. Qualitative arguments are given for the signs of the van der Waals contributions to the surface energy and work function. A standard expression for the work function in Kohn–Sham (KS) theory is shown to be valid in generalized KS theory. Interlayer relaxations from different functionals are in reasonable agreement with one another, and usually with experiment. PMID:29042509

The reversibility of virus attachment to mineral surfaces

USGS Publications Warehouse

Loveland, J.P.; Ryan, J.N.; Amy, G.L.; Harvey, R.W.

1996-01-01

Virus transport through groundwater is limited by attachment to mineral surfaces and inactivation. Current virus transport models do not consider the implications of the reversibility of virus attachment to minerals. To explore the reversibility of virus attachment to mineral surfaces, we attached PRD1, a bacteriophage considered to be a good model of enteric viruses, to quartz and ferric oxyhydroxide-coated quartz surfaces over a range of pH values in equilibrium 'static columns'. Following attachment, we detached the viruses by replacing the pore solution with solutions of equal and higher pH. The extent of virus attachment followed an attachment 'edge' that occurred at a pH value about 2.5-3.5 pH units above the pH(IEP) of the mineral surfaces. Viruses attached below this edge were irreversibly attached until the pH of the detachment solution exceeded the pH value of the attachment edge. Viruses attached above this edge were reversibly attached. Derjaguin-Landau-Verwey-Overbeek (DEVO) potential energy calculations showed that the attachment edge occurred at the pH at which the potential energy of the primary minimum was near zero, implying that the position of the primary minimum (attractive or repulsive) controlled the equilibrium distribution of the viruses. The results suggest that the reversibility of virus attachment must be considered in virus transport models for accurate predictions of virus travel time.

Effect of surface treatment on the corrosion properties of magnesium-based fibre metal laminate

NASA Astrophysics Data System (ADS)

Zhang, X.; Zhang, Y.; Ma, Q. Y.; Dai, Y.; Hu, F. P.; Wei, G. B.; Xu, T. C.; Zeng, Q. W.; Wang, S. Z.; Xie, W. D.

2017-02-01

The surface roughness, weight of phosphating film and wettability of magnesium alloy substrates after abrasion and phosphating treatment were investigated in this work. The interfacial bonding and corrosion properties of a magnesium-based fibre metal laminate (MgFML) were analysed. The results showed that the wettability of the magnesium alloy was greatly influenced by the surface roughness, and the rough surface possessed a larger surface energy and better wettability. The surface energy and wettability of the magnesium alloy were significantly improved by the phosphating treatment. After phosphating for 5 min, a phosphating film with a double-layer structure was formed on the magnesium substrate, and the weight of the phosphating film and the surface energy reached their maximum values. The surface energies of the phosphated substrate after abrasion with #120 and #3000 grit abrasive papers were 84.31 mJ/m2 and 83.65 mJ/m2, respectively. The wettability of the phosphated magnesium was significantly better than the abraded magnesium. The phosphated AZ31B sheet had a better corrosion resistance than the abraded AZ31B sheet within short times. The corrosion resistance of the magnesium alloy was greatly increased by being composited with glass fibre/epoxy prepregs.

Structure Determination of Au on Pt(111) Surface: LEED, STM and DFT Study

PubMed Central

Krupski, Katarzyna; Moors, Marco; Jóźwik, Paweł; Kobiela, Tomasz; Krupski, Aleksander

2015-01-01

Low-energy electron diffraction (LEED), scanning tunneling microscopy (STM) and density functional theory (DFT) calculations have been used to investigate the atomic and electronic structure of gold deposited (between 0.8 and 1.0 monolayer) on the Pt(111) face in ultrahigh vacuum at room temperature. The analysis of LEED and STM measurements indicates two-dimensional growth of the first Au monolayer. Change of the measured surface lattice constant equal to 2.80 Å after Au adsorption was not observed. Based on DFT, the distance between the nearest atoms in the case of bare Pt(111) and Au/Pt(111) surface is equal to 2.83 Å, which gives 1% difference in comparison with STM values. The first and second interlayer spacing of the clean Pt(111) surface are expanded by +0.87% and contracted by −0.43%, respectively. The adsorption energy of the Au atom on the Pt(111) surface is dependent on the adsorption position, and there is a preference for a hollow fcc site. For the Au/Pt(111) surface, the top interlayer spacing is expanded by +2.16% with respect to the ideal bulk value. Changes in the electronic properties of the Au/Pt(111) system below the Fermi level connected to the interaction of Au atoms with Pt(111) surface are observed.

Distributions of phytoplankton carbohydrate, protein and lipid in the world oceans from satellite ocean colour.

PubMed

Roy, Shovonlal

2018-06-01

Energy value of phytoplankton regulates the growth of higher trophic species, affecting the tropic balance and sustainability of marine food webs. Therefore, developing our capability to estimate and monitor, on a global scale, the concentrations of macromolecules that determine phytoplankton energy value, would be invaluable. Reported here are the first estimates of carbohydrate, protein, lipid, and overall energy value of phytoplankton in the world oceans, using ocean-colour data from satellites. The estimates are based on a novel bio-optical method that utilises satellite-derived bio-optical fingerprints of living phytoplankton combined with allometric relationships between phytoplankton cells and cellular macromolecular contents. The annually averaged phytoplankton energy value, per cubic metre of sub-surface ocean, varied from less than 0.1 kJ in subtropical gyres, to 0.5-1.0 kJ in parts of the equatorial, northern and southern latitudes, and rising to >10 kJ in certain coastal and optically complex waters. The annually averaged global stocks of carbohydrate, protein and lipid were 0.044, 0.17 and 0.108 gigatonnes, respectively, with monthly stocks highest in September and lowest in June, over 1997-2013. The fractional contributions of phytoplankton size classes e.g., picoplankton, nanoplankton and microplankton to surface concentrations and global stocks of macromolecules varied considerably across marine biomes classified as Longhurst provinces. Among these provinces, the highest annually averaged surface concentrations of carbohydrate, protein, and lipid were in North-East Atlantic Coastal Shelves, whereas, the lowest concentration of carbohydrate or lipid were in North Atlantic Tropical Gyral, and that of protein was in North Pacific Subtropical Gyre West. The regional accuracy of the estimates and their sensitivity to satellite inputs are quantified from the bio-optical model, which show promise for possible operational monitoring of phytoplankton energy value from satellite ocean colour. Adequate in situ measurements of macromolecules and improved retrievals of inherent optical properties from high-resolution satellite images, would be required to validate these estimates at local sites, and to further improve their accuracy in the world oceans.

Growth of AlGaN under the conditions of significant gallium evaporation: Phase separation and enhanced lateral growth

NASA Astrophysics Data System (ADS)

Mayboroda, I. O.; Knizhnik, A. A.; Grishchenko, Yu. V.; Ezubchenko, I. S.; Zanaveskin, Maxim L.; Kondratev, O. A.; Presniakov, M. Yu.; Potapkin, B. V.; Ilyin, V. A.

2017-09-01

The growth kinetics of AlGaN in NH3 MBE under significant Ga desorption was studied. It was found that the addition of gallium stimulates 2D growth and provides better morphology of films compared to pure AlN. The effect was experimentally observed at up to 98% desorption of the impinging gallium. We found that under the conditions of significant thermal desorption, larger amounts of gallium were retained at lateral boundaries of 3D surface features than at flat terraces because of the higher binding energy of Ga atoms at specific surface defects. The selective accumulation of gallium resulted in an increase in the lateral growth component through the formation of the Ga-enriched AlGaN phase at boundaries of 3D surface features. We studied the temperature dependence of AlGaN growth rate and developed a kinetic model analytically describing this dependence. As the model was in good agreement with the experimental data, we used it to estimate the increase in the binding energy of Ga atoms at surface defects compared to terrace surface sites using data on the Ga content in different AlGaN phases. We also applied first-principles calculations to the thermodynamic analysis of stable configurations on the AlN surface and then used these surface configurations to compare the binding energy of Ga atoms at terraces and steps. Both first-principles calculations and analytical estimations of the experimental results gave similar values of difference in binding energies; this value is 0.3 eV. Finally, it was studied experimentally whether gallium can act as a surfactant in AlN growth by NH3 MBE at elevated temperatures. Gallium application has allowed us to grow a 300 nm thick AlN film with a RMS surface roughness of 2.2 Å over an area of 10 × 10 μm and a reduced density of screw dislocations.

Jump rates for surface diffusion of large molecules from first principles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shea, Patrick, E-mail: patrick.shea@dal.ca; Kreuzer, Hans Jürgen

2015-04-21

We apply a recently developed stochastic model for the surface diffusion of large molecules to calculate jump rates for 9,10-dithioanthracene on a Cu(111) surface. The necessary input parameters for the stochastic model are calculated from first principles using density functional theory (DFT). We find that the inclusion of van der Waals corrections to the DFT energies is critical to obtain good agreement with experimental results for the adsorption geometry and energy barrier for diffusion. The predictions for jump rates in our model are in excellent agreement with measured values and show a marked improvement over transition state theory (TST). Wemore » find that the jump rate prefactor is reduced by an order of magnitude from the TST estimate due to frictional damping resulting from energy exchange with surface phonons, as well as a rotational mode of the diffusing molecule.« less

Surface nanocrystalline and hardening effects of Ti-Al-V alloy by electropulsing ultrasonic shock

NASA Astrophysics Data System (ADS)

Ye, Xiaoxin; Tang, Guoyi

2015-03-01

The effect of electropulsing ultrasonic shock (EUS) on the surface hardening and microstructure of Ti6Al4V alloy was studied. It was found that electropulsing improved the microhardness dramatically both in the influential depth and maximum value, compared with the only ultrasonic-shocked sample. It's indicated that refined surface layer with nanocrystalline and improved microhardness were obtained on account of surface severe plastic deformation, dynamic recrystallization (DRX) and phase change, which was implemented at relative low temperature and high strain rate/capacity due to the coupling of the thermal and athermal effects of EUS. It's different from conventional experiments and theory. It's discussed that the positive contributions of EPT in the thermodynamics and kinetics of microstructure and properties change were attributed to the reduction of nucleation energy barrier and acceleration of atomic diffusion. Therefore, it's supposed that EUS is an energy-saving and high-efficiency method of surface treatment technique with the help of high-energy electropulses, which is promising in cost reduction of the surface engineering and energy management. The work is supported by National Natural Science Foundation of China (No. 50571048) and Shenzhen science and technology research funding project of China (No. SGLH20121008144756946).

Hartree-Fock theory of the inhomogeneous electron gas at a jellium metal surface: Rigorous upper bounds to the surface energy and accurate work functions

NASA Astrophysics Data System (ADS)

Sahni, V.; Ma, C. Q.

1980-12-01

The inhomogeneous electron gas at a jellium metal surface is studied in the Hartree-Fock approximation by Kohn-Sham density functional theory. Rigorous upper bounds to the surface energy are derived by application of the Rayleigh-Ritz variational principle for the energy, the surface kinetic, electrostatic, and nonlocal exchange energy functionals being determined exactly for the accurate linear-potential model electronic wave functions. The densities obtained by the energy minimization constraint are then employed to determine work-function results via the variationally accurate "displaced-profile change-in-self-consistent-field" expression. The theoretical basis of this non-self-consistent procedure and its demonstrated accuracy for the fully correlated system (as treated within the local-density approximation for exchange and correlation) leads us to conclude these results for the surface energies and work functions to be essentially exact. Work-function values are also determined by the Koopmans'-theorem expression, both for these densities as well as for those obtained by satisfaction of the constraint set on the electrostatic potential by the Budd-Vannimenus theorem. The use of the Hartree-Fock results in the accurate estimation of correlation-effect contributions to these surface properties of the nonuniform electron gas is also indicated. In addition, the original work and approximations made by Bardeen in this attempt at a solution of the Hartree-Fock problem are briefly reviewed in order to contrast with the present work.

Copoly(imide siloxane) Abhesive Materials with Varied Siloxane Oligomer Length

NASA Technical Reports Server (NTRS)

Wohl, Christoper J.; Atkins, Brad M.; Lin, Yi; Belcher, Marcus A.; Connell, John W.

2010-01-01

In this work, low surface energy copoly(imide siloxane)s were synthesized with various siloxane segment lengths. Characterization of these materials revealed that domain formation of the low surface energy component within the matrix was more prevalent for longer siloxane segments as indicated by increased opacity, decreased mechanical properties, and variation of the Tg. Incorporation of siloxanes lowered the polymer s surface energy as indicated by water contact angle values. Topographical modification of these materials by laser ablation patterning further reduced the surface energy, even generating superhydrophobic surfaces. Combined, the contact angle data and particle adhesion testing indicated that copoly(imide siloxane) materials may provide greater mitigation to particulate adhesion than polyimide materials alone. These enhanced surface properties for abhesive applications did result in a reduction of the tensile moduli of the copolymers. It is possible that lower siloxane loading levels would result in retention of the mechanical properties of the polyimide while still affording abhesive surface properties. This hypothesis is currently being investigated. Laser ablation patterning offers further reduction in particle retention as the available surface area for particle adhesion is reduced. Pattern variation and size dependencies are currently being evaluated. For the purposes of lunar dust adhesion mitigation, it is likely that this approach, termed passive due to the lack of input from an external energy source, would not be sufficient to mitigate surface contamination or clean contaminated surfaces for some lunar applications. It is feasible to combine these materials with active mitigation strategies - methods that utilize input from external energy sources - would broaden the applicability of such materials for abhesive purposes. Collaborative efforts along these lines have been initiated with researchers at NASA Kennedy Space Center where experiments are being conducted involving a series of embedded electrodes within polymeric matrices.

Assessment of land surface temperature and heat fluxes over Delhi using remote sensing data.

PubMed

Chakraborty, Surya Deb; Kant, Yogesh; Mitra, Debashis

2015-01-15

Surface energy processes has an essential role in urban weather, climate and hydrosphere cycles, as well in urban heat redistribution. The research was undertaken to analyze the potential of Landsat and MODIS data in retrieving biophysical parameters in estimating land surface temperature & heat fluxes diurnally in summer and winter seasons of years 2000 and 2010 and understanding its effect on anthropogenic heat disturbance over Delhi and surrounding region. Results show that during years 2000-2010, settlement and industrial area increased from 5.66 to 11.74% and 4.92 to 11.87% respectively which in turn has direct effect on land surface temperature (LST) and heat fluxes including anthropogenic heat flux. Based on the energy balance model for land surface, a method to estimate the increase in anthropogenic heat flux (Has) has been proposed. The settlement and industrial areas has higher amounts of energy consumed and has high values of Has in all seasons. The comparison of satellite derived LST with that of field measured values show that Landsat estimated values are in close agreement within error of ±2 °C than MODIS with an error of ±3 °C. It was observed that, during 2000 and 2010, the average change in surface temperature using Landsat over settlement & industrial areas of both seasons is 1.4 °C & for MODIS data is 3.7 °C. The seasonal average change in anthropogenic heat flux (Has) estimated using Landsat & MODIS is up by around 38 W/m(2) and 62 W/m(2) respectively while higher change is observed over settlement and concrete structures. The study reveals that the dynamic range of Has values has increased in the 10 year period due to the strong anthropogenic influence over the area. The study showed that anthropogenic heat flux is an indicator of the strength of urban heat island effect, and can be used to quantify the magnitude of the urban heat island effect. Copyright © 2013 Elsevier Ltd. All rights reserved.

A two-step framework for reconstructing remotely sensed land surface temperatures contaminated by cloud

NASA Astrophysics Data System (ADS)

Zeng, Chao; Long, Di; Shen, Huanfeng; Wu, Penghai; Cui, Yaokui; Hong, Yang

2018-07-01

Land surface temperature (LST) is one of the most important parameters in land surface processes. Although satellite-derived LST can provide valuable information, the value is often limited by cloud contamination. In this paper, a two-step satellite-derived LST reconstruction framework is proposed. First, a multi-temporal reconstruction algorithm is introduced to recover invalid LST values using multiple LST images with reference to corresponding remotely sensed vegetation index. Then, all cloud-contaminated areas are temporally filled with hypothetical clear-sky LST values. Second, a surface energy balance equation-based procedure is used to correct for the filled values. With shortwave irradiation data, the clear-sky LST is corrected to the real LST under cloudy conditions. A series of experiments have been performed to demonstrate the effectiveness of the developed approach. Quantitative evaluation results indicate that the proposed method can recover LST in different surface types with mean average errors in 3-6 K. The experiments also indicate that the time interval between the multi-temporal LST images has a greater impact on the results than the size of the contaminated area.

Cooptimization of Adhesion and Power Conversion Efficiency of Organic Solar Cells by Controlling Surface Energy of Buffer Layers.

PubMed

Lee, Inhwa; Noh, Jonghyeon; Lee, Jung-Yong; Kim, Taek-Soo

2017-10-25

Here, we demonstrate the cooptimization of the interfacial fracture energy and power conversion efficiency (PCE) of poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT)-based organic solar cells (OSCs) by surface treatments of the buffer layer. The investigated surface treatments of the buffer layer simultaneously changed the crack path and interfacial fracture energy of OSCs under mechanical stress and the work function of the buffer layer. To investigate the effects of surface treatments, the work of adhesion values were calculated and matched with the experimental results based on the Owens-Wendt model. Subsequently, we fabricated OSCs on surface-treated buffer layers. In particular, ZnO layers treated with poly[(9,9-bis(3'-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN) simultaneously satisfied the high mechanical reliability and PCE of OSCs by achieving high work of adhesion and optimized work function.

Emission of dimers from a free surface of heated water

NASA Astrophysics Data System (ADS)

Bochkarev, A. A.; Polyakova, V. I.

2014-09-01

The emission rate of water dimers from a free surface and a wetted solid surface in various cases was calculated by a simplified Monte Carlo method with the use of the binding energy of water molecules. The binding energy of water molecules obtained numerically assuming equilibrium between the free surface of water and vapor in the temperature range of 298-438 K corresponds to the coordination number for liquid water equal to 4.956 and is close to the reference value. The calculation results show that as the water temperature increases, the free surface of water and the wetted solid surface become sources of free water dimers. At a temperature of 438 K, the proportion of dimers in the total flow of water molecules on its surface reaches 1%. It is found that in the film boiling mode, the emission rate of dimers decreases with decreasing saturation vapor. Two mechanisms of the emission are described.

Surface roughness effects on bidirectional reflectance

NASA Technical Reports Server (NTRS)

Smith, T. F.; Hering, R. G.

1972-01-01

An experimental study of surface roughness effects on bidirectional reflectance of metallic surfaces is presented. A facility capable of irradiating a sample from normal to grazing incidence and recording plane of incidence bidirectional reflectance measurements was developed. Samples consisting of glass, aluminum alloy, and stainless steel materials were selected for examination. Samples were roughened using standard grinding techniques and coated with a radiatively opaque layer of pure aluminum. Mechanical surface roughness parameters, rms heights and rms slopes, evaluated from digitized surface profile measurements are less than 1.0 micrometers and 0.28, respectively. Rough surface specular, bidirectional, and directional reflectance measurements for selected values of polar angle of incidence and wavelength of incident energy within the spectral range of 1 to 14 micrometers are reported. The Beckmann bidirectional reflectance model is compared with reflectance measurements to establish its usefulness in describing the magnitude and spatial distribution of energy reflected from rough surfaces.

A highly accurate ab initio potential energy surface for methane.

PubMed

Owens, Alec; Yurchenko, Sergei N; Yachmenev, Andrey; Tennyson, Jonathan; Thiel, Walter

2016-09-14

A new nine-dimensional potential energy surface (PES) for methane has been generated using state-of-the-art ab initio theory. The PES is based on explicitly correlated coupled cluster calculations with extrapolation to the complete basis set limit and incorporates a range of higher-level additive energy corrections. These include core-valence electron correlation, higher-order coupled cluster terms beyond perturbative triples, scalar relativistic effects, and the diagonal Born-Oppenheimer correction. Sub-wavenumber accuracy is achieved for the majority of experimentally known vibrational energy levels with the four fundamentals of (12)CH4 reproduced with a root-mean-square error of 0.70 cm(-1). The computed ab initio equilibrium C-H bond length is in excellent agreement with previous values despite pure rotational energies displaying minor systematic errors as J (rotational excitation) increases. It is shown that these errors can be significantly reduced by adjusting the equilibrium geometry. The PES represents the most accurate ab initio surface to date and will serve as a good starting point for empirical refinement.

Effective cluster interactions at alloy surfaces and charge self-consistency: Surface segregation in Ni-10 at. % Al and Cu-Ni

NASA Astrophysics Data System (ADS)

Schulthess, T.; Monnier, R.; Crampin, S.

1994-12-01

First-principles results are presented for the effective cluster interactions at the surface of a random Ni-10 at. % Al alloy. The derivation is based on an extension of the generalized perturbation method to semi-infinite inhomogeneous binary alloys, using a layer version of the Korringa-Kohn-Rostocker multiple-scattering approach in conjunction with the single-site coherent potential approximation to compute the self-consistent electronic structure of the system. When applied to the bulk, the method yields effective pair interactions that have the full point-group symmetry of the lattice to a very high level of numerical accuracy, despite the fact that intra- and interlayer couplings (scattering-path operators) are treated differently, and which are in perfect agreement with those of a recent three-dimensional treatment. Besides the pair terms, a selected class of triplet and quadruplet interactions are calculated, as well as the point interactions induced by the presence of the surface. The value of the latter in the first lattice plane is strongly exaggerated in our approach, leading to a complete segregation of the minority species to the surface. Using a value corresponding to the difference in the surface energies of the pure components for this term leads to the observed Al concentration of ~=25% at the surface. Possible reasons for the shortcomings of the theory are analyzed, and test calculations for the well studied Cu-Ni system show that the free energy of the semi-infinite alloy cannot be approximated by the sum over the single-particle band energies, once charge self-consistency is enforced at the surface.

Elasticity dominated surface segregation of small molecules in polymer mixtures

NASA Astrophysics Data System (ADS)

Croce, Salvatore; Krawczyk, Jaroslaw; McLeish, Tom; Chakrabarti, Buddhapriya

When a binary polymer mixture with mobile components is left to equilibrate, the low molecular weight component migrates to the free surface. A balance between loss of translational entropy and gain in surface energy dictates the equilibrium partitioning ratio and the migrant fraction. Despite its ubiquity and several theoretical and experimental investigations, the phenomenon is not fully understood. Further, methods by which migration can be controlled are in its nascent stage of development. We propose a new phenomenological free energy functional that incorporates the elasticity of bulk polymer mixtures (reticulated networks and gels) and show (using mean field and self-consistent field theories) that the migrant fraction decreases with increasing the bulk modulus of the system. Further, a wetting transition observed otherwise for large values of miscibility parameter and polymerization index can be avoided by increasing the elastic modulus of the system. Estimated values of moduli (for the effect to be observable) are akin to those of rubbery polymers. Our work paves the way for controlling surface migration in complex industrial formulations with polymeric ingredients where this effect leads to decreased product stability and performance.

Methods, computer readable media, and graphical user interfaces for analysis of frequency selective surfaces

DOEpatents

Kotter, Dale K [Shelley, ID; Rohrbaugh, David T [Idaho Falls, ID

2010-09-07

A frequency selective surface (FSS) and associated methods for modeling, analyzing and designing the FSS are disclosed. The FSS includes a pattern of conductive material formed on a substrate to form an array of resonance elements. At least one aspect of the frequency selective surface is determined by defining a frequency range including multiple frequency values, determining a frequency dependent permittivity across the frequency range for the substrate, determining a frequency dependent conductivity across the frequency range for the conductive material, and analyzing the frequency selective surface using a method of moments analysis at each of the multiple frequency values for an incident electromagnetic energy impinging on the frequency selective surface. The frequency dependent permittivity and the frequency dependent conductivity are included in the method of moments analysis.

On the nano-hillock formation induced by slow highly charged ions on insulator surfaces

NASA Astrophysics Data System (ADS)

Lemell, C.; El-Said, A. S.; Meissl, W.; Gebeshuber, I. C.; Trautmann, C.; Toulemonde, M.; Burgdörfer, J.; Aumayr, F.

2007-10-01

We discuss the creation of nano-sized protrusions on insulating surfaces using slow highly charged ions. This method holds the promise of forming regular structures on surfaces without inducing defects in deeper lying crystal layers. We find that only projectiles with a potential energy above a critical value are able to create hillocks. Below this threshold no surface modification is observed. This is similar to the track and hillock formation induced by swift (˜GeV) heavy ions. We present a model for the conversion of potential energy stored in the projectiles into target-lattice excitations (heat) and discuss the possibility to create ordered structures using the guiding effect observed in insulating conical structures.

Veneer Ceramic to Y-TZP Bonding: Comparison of Different Surface Treatments.

PubMed

Kirmali, Omer; Kapdan, Alper; Kustarci, Alper; Er, Kursat

2016-06-01

The purpose of this study was to evaluate the effects of various surface-treatment techniques for enhancing the bond strength between veneering ceramic and yttria-stabilized tetragonal zirconia polycrystals (Y-TZP). Pre-sintered Y-TZP specimens were divided into eight groups (n = 10) according to the surface-treatment technique used: (a) untreated (control); (b) air abrasion with aluminum oxide particles; (c) erbium, chromium:yttrium-scandium-gallium-garnet (Er,Cr:YSGG) laser irradiation at different energy intensities (1 to 6 W). All specimens were then sintered and veneered with veneering ceramic according to the manufacturer's instructions. The obtained zirconia-ceramic specimens were immersed in 37°C distilled water for 24 hours before a shear bond strength test using a universal testing device at a 1 mm/min crosshead speed. The average values were calculated. After debonding, the Y-TZP surfaces were examined under a stereomicroscope to determine their fracture pattern, and the surface topography was evaluated with scanning electron microscopy after surface treatments. The bond strength ranged from 13.24 to 20.54 MPa. All surface treatments increased the bond strength between the veneering ceramic and Y-TZP; however, the value for the 6 W irradiation group was significantly different from the values for other groups (p ˂ 0.05). The present study's findings showed that higher energy densities were needed for the laser irradiation to improve the bond strength between the veneering ceramic and zirconia. Y-TZP is commonly used as a core material in fixed restorations. The bond strength between zirconia and the veneering ceramic can be affected by various surface treatments. © 2015 by the American College of Prosthodontists.

A full-dimensional ab initio potential energy surface and rovibrational energies of the Ar–HF complex

NASA Astrophysics Data System (ADS)

Huang, Jing; Zhou, Yanzi; Xie, Daiqian

2018-04-01

We report a new full-dimensional ab initio potential energy surface for the Ar-HF van der Waals complex at the level of coupled-cluster singles and doubles with noniterative inclusion of connected triples levels [CCSD(T)] using augmented correlation-consistent quintuple-zeta basis set (aV5Z) plus bond functions. Full counterpoise correction was employed to correct the basis-set superposition error. The hypersurface was fitted using artificial neural network method with a root mean square error of 0.1085 cm-1 for more than 8000 ab initio points. The complex was found to prefer a linear Ar-H-F equilibrium structure. The three-dimensional discrete variable representation method and the Lanczos propagation algorithm were then employed to calculate the rovibrational states without separating inter- and intra- molecular nuclear motions. The calculated vibrational energies of Ar-HF differ from the experiment values within about 1 cm-1 on the first four HF vibrational states, and the predicted pure rotational energies on (0000) and (1000) vibrational states are deviated from the observed value by about 1%, which shows the accuracy of our new PES.

Effective surface Debye temperature for NiMnSb(100) epitaxial films

NASA Astrophysics Data System (ADS)

Borca, C. N.; Komesu, Takashi; Jeong, Hae-kyung; Dowben, P. A.; Ristoiu, D.; Hordequin, Ch.; Pierre, J.; Nozières, J. P.

2000-07-01

The surface Debye temperature of the NiMnSb (100) epitaxial films has been obtained using low energy electron diffraction, inverse photoemission, and core-level photoemission. The normal dynamic motion of the (100) surface results in a value for the effective surface Debye temperature of 145±13 K. This is far smaller than the bulk Debye temperature of 312±5 K obtained from wave vector dependent inelastic neutron scattering. The large difference between these measures of surface and bulk dynamic motion indicates a soft and compositionally different (100) surface.

Mapping apparent stress and energy radiation over fault zones of major earthquakes

USGS Publications Warehouse

McGarr, A.; Fletcher, Joe B.

2002-01-01

Using published slip models for five major earthquakes, 1979 Imperial Valley, 1989 Loma Prieta, 1992 Landers, 1994 Northridge, and 1995 Kobe, we produce maps of apparent stress and radiated seismic energy over their fault surfaces. The slip models, obtained by inverting seismic and geodetic data, entail the division of the fault surfaces into many subfaults for which the time histories of seismic slip are determined. To estimate the seismic energy radiated by each subfault, we measure the near-fault seismic-energy flux from the time-dependent slip there and then multiply by a function of rupture velocity to obtain the corresponding energy that propagates into the far-field. This function, the ratio of far-field to near-fault energy, is typically less than 1/3, inasmuch as most of the near-fault energy remains near the fault and is associated with permanent earthquake deformation. Adding the energy contributions from all of the subfaults yields an estimate of the total seismic energy, which can be compared with independent energy estimates based on seismic-energy flux measured in the far-field, often at teleseismic distances. Estimates of seismic energy based on slip models are robust, in that different models, for a given earthquake, yield energy estimates that are in close agreement. Moreover, the slip-model estimates of energy are generally in good accord with independent estimates by others, based on regional or teleseismic data. Apparent stress is estimated for each subfault by dividing the corresponding seismic moment into the radiated energy. Distributions of apparent stress over an earthquake fault zone show considerable heterogeneity, with peak values that are typically about double the whole-earthquake values (based on the ratio of seismic energy to seismic moment). The range of apparent stresses estimated for subfaults of the events studied here is similar to the range of apparent stresses for earthquakes in continental settings, with peak values of about 8 MPa in each case. For earthquakes in compressional tectonic settings, peak apparent stresses at a given depth are substantially greater than corresponding peak values from events in extensional settings; this suggests that crustal strength, inferred from laboratory measurements, may be a limiting factor. Lower bounds on shear stresses inferred from the apparent stress distribution of the 1995 Kobe earthquake are consistent with tectonic-stress estimates reported by Spudich et al. (1998), based partly on slip-vector rake changes.

Impact of Dust on Mars Surface Albedo and Energy Flux with LMD General Circulation Model

NASA Astrophysics Data System (ADS)

Singh, D.; Flanner, M.; Millour, E.; Martinez, G.

2015-12-01

Mars, just like Earth experience different seasons because of its axial tilt (about 25°). This causes growth and retreat of snow cover (primarily CO2) in Martian Polar regions. The perennial caps are the only place on the planet where condensed H2O is available at surface. On Mars, as much as 30% atmospheric CO2 deposits in each hemisphere depending upon the season. This leads to a significant variation on planet's surface albedo and hence effecting the amount of solar flux absorbed or reflected at the surface. General Circulation Model (GCM) of Laboratoire de Météorologie Dynamique (LMD) currently uses observationally derived surface albedo from Thermal Emission Spectrometer (TES) instrument for the polar caps. These TES albedo values do not have any inter-annual variability, and are independent of presence of any dust/impurity on surface. Presence of dust or other surface impurities can significantly reduce the surface albedo especially during and right after a dust storm. This change will also be evident in the surface energy flux interactions. Our work focuses on combining earth based Snow, Ice, and Aerosol Radiation (SNICAR) model with current state of GCM to incorporate the impact of dust on Martian surface albedo, and hence the energy flux. Inter-annual variability of surface albedo and planet's top of atmosphere (TOA) energy budget along with their correlation with currently available mission data will be presented.

Anisotropic Eliashberg theory of MgB 2: Tc, isotope effects, superconducting energy gaps, quasiparticles, and specific heat

NASA Astrophysics Data System (ADS)

Choi, Hyoung Joon; Cohen, Marvin L.; Louie, Steven G.

2003-03-01

The anisotropic Eliashberg formalism, employing results from the ab initio pseudopotential density functional calculations, is applied to study the superconducting properties of MgB 2. It is shown that the relatively high transition temperature of MgB 2 originates from strong electron-phonon coupling of the hole states in the boron σ-bonds although the coupling strength averaged over the Fermi surface is moderate, and the reduction of the isotope effect arises from the large anharmonicity of the relevant phonons. The superconducting energy gap is nodeless but its value varies strongly on different pieces of the Fermi surface. The gap values Δ( k) cluster into two groups at low temperature, a small value of ∼2 meV and a large value of ∼7 meV, resulting in two thresholds in the quasiparticle density of states and an increase in the specific heat at low temperature due to quasiparticle excitations over the small gap. All of these results are in good agreement with corresponding experiments and support the view that MgB 2 is a phonon-mediated multiple-gap superconductor.

Secondary electron emission characteristics of ion-textured copper and high-purity isotropic graphite surfaces

NASA Technical Reports Server (NTRS)

Curren, A. N.; Jensen, K. A.

1984-01-01

Experimentally determined values of true secondary electron emission and relative values of reflected primary electron yield for untreated and ion textured oxygen free high conductivity copper and untreated and ion textured high purity isotropic graphite surfaces are presented for a range of primary electron beam energies and beam impingement angles. This investigation was conducted to provide information that would improve the efficiency of multistage depressed collectors (MDC's) for microwave amplifier traveling wave tubes in space communications and aircraft applications. For high efficiency, MDC electrode surfaces must have low secondary electron emission characteristics. Although copper is a commonly used material for MDC electrodes, it exhibits relatively high levels of secondary electron emission if its surface is not treated for emission control. Recent studies demonstrated that high purity isotropic graphite is a promising material for MDC electrodes, particularly with ion textured surfaces. The materials were tested at primary electron beam energies of 200 to 2000 eV and at direct (0 deg) to near grazing (85 deg) beam impingement angles. True secondary electron emission and relative reflected primary electron yield characteristics of the ion textured surfaces were compared with each other and with those of untreated surfaces of the same materials. Both the untreated and ion textured graphite surfaces and the ion treated copper surface exhibited sharply reduced secondary electron emission characteristics relative to those of untreated copper. The ion treated graphite surface yielded the lowest emission levels.

Remote estimation of the surface characteristics and energy balance over an urban-rural area and the effects of surface heat flux on plume spread and concentration. M.S. Thesis; [St. Louis, Missouri, the Land Between the Lakes, Kentucky and Clarksville, Tennessee

NASA Technical Reports Server (NTRS)

Dicristofaro, D. C. (Principal Investigator)

1980-01-01

A one dimensional boundary layer model was used in conjunction with satellite derived infrared surface temperatures to deduce values of moisture availability, thermal inertia, heat and evaporative fluxes. The Penn State satellite image display system, a sophisticated image display facility, was used to remotely sense these various parameters for three cases: St. Louis, Missouri; the Land Between the Lakes, Kentucky; and Clarksville, Tennessee. The urban centers displayed the maximum daytime surface temperatures which correspond to the minimum values of moisture availability. The urban center of St. Louis and the bodies of water displayed the maximum nighttime surface temperatures which correspond to the maximum thermal inertia values. It is shown that moisture availability and thermal inertia are very much responsible for the formation of important temperature variations over the urban rural complex.

Elasticity Dominated Surface Segregation of Small Molecules in Polymer Mixtures

NASA Astrophysics Data System (ADS)

Krawczyk, Jarosław; Croce, Salvatore; McLeish, T. C. B.; Chakrabarti, Buddhapriya

2016-05-01

We study the phenomenon of migration of the small molecular weight component of a binary polymer mixture to the free surface using mean field and self-consistent field theories. By proposing a free energy functional that incorporates polymer-matrix elasticity explicitly, we compute the migrant volume fraction and show that it decreases significantly as the sample rigidity is increased. A wetting transition, observed for high values of the miscibility parameter can be prevented by increasing the matrix rigidity. Estimated values of the bulk modulus suggest that the effect should be observable experimentally for rubberlike materials. This provides a simple way of controlling surface migration in polymer mixtures and can play an important role in industrial formulations, where surface migration often leads to decreased product functionality.

Absolute single-ion solvation free energy scale in methanol determined by the lithium cluster-continuum approach.

PubMed

Pliego, Josefredo R; Miguel, Elizabeth L M

2013-05-02

Absolute solvation free energy of the lithium cation in methanol was calculated by the cluster-continuum quasichemical theory of solvation. Clusters with up to five methanol molecules were investigated using X3LYP, MP2, and MP4 methods with DZVP, 6-311+G(2df,2p), TZVPP+diff, and QZVPP+diff basis sets and including the cluster solvation through the PCM and SMD continuum models. Our calculations have determined a value of -118.1 kcal mol(-1) for the solvation free energy of the lithium, in close agreement with a value of -116.6 kcal mol(-1) consistent with the TATB assumption. Using data of solvation and transfer free energy of a pair of ions, electrode potentials and pKa, we have obtained the solvation free energy of 25 ions in methanol. Our analysis leads to a value of -253.6 kcal mol(-1) for the solvation free energy of the proton, which can be compared with the value of -263.5 kcal mol(-1) obtained by Kelly et al. using the cluster pair approximation. Considering that this difference is due to the methanol surface potential, we have estimated that it corresponds to -0.429 V.

A study of radiometric surface temperatures: Their fluctuations, distribution and meaning. [Voves, France

NASA Technical Reports Server (NTRS)

Perrier, A.; Itier, B.; Boissard, P. (Principal Investigator); Goillot, C.; Belluomo, P.; Valery, P.

1980-01-01

A consecutive night and day flight and measurements on the ground, were made in the region of Voves, south of Chartres. The statistical analysis of the thermal scanner data permitted the establishment of criteria for the homogeneity of surfaces. These criteria were used in defining the surface temperature values which are most representative for use in an energy balance approach to evapotranspiration (day) and heat balance (night). For a number of maize fields that airborne thermal scanner data permitted a detailed energy analysis of different fields of a same crop to be carried out. Such a detailed analysis was not necessary for a calculation of crop evapotranspiration which could be evaluated from the mean temperature of the crop surface. A differential analysis day night is of interest for enhancing the contrast between types of surfaces, as well as for a better definition of the daily energy balance. It should be stressed that, for a homogeneous region, a study such as the present one, could be carried out on a relatively small part of the total surface, as the results for a surface of 2.5 x 2 sq km were not significantly different from those obtained from a surface three times larger.

A semiflexible alternating copolymer chain adsorption on a flat and a fluctuating surface.

PubMed

Mishra, Pramod Kumar

2010-04-21

A lattice model of a directed self-avoiding walk is used to investigate adsorption properties of a semiflexible alternating copolymer chain on an impenetrable flat and fluctuating surface in two (square, hexagonal and rectangular lattice) and three dimensions (cubic lattice). In the cubic lattice case the surface is two-dimensional impenetrable flat and in two dimensions the surface is a fluctuating impenetrable line (hexagonal lattice) and also flat impenetrable line (square and rectangular lattice). Walks of the copolymer chains are directed perpendicular to the plane of the surface and at a suitable value of monomer surface attraction, the copolymer chain gets adsorbed on the surface. To calculate the exact value of the monomer surface attraction, the directed walk model has been solved analytically using the generating function method to discuss results when one type of monomer of the copolymer chain has attractive, repulsive or no interaction with the surface. Results obtained in the flat surface case show that, for a stiffer copolymer chain, adsorption transition occurs at a smaller value of monomer surface attraction than a flexible copolymer chain while in the case of a fluctuating surface, the adsorption transition point is independent of bending energy of the copolymer chain. These features are similar to that of a semiflexible homopolymer chain adsorption.

Characterization of land surface energy fluxes in a tropical lowland rice paddy

NASA Astrophysics Data System (ADS)

Chatterjee, Dibyendu; Tripathi, Rahul; Chatterjee, Sumanta; Debnath, Manish; Shahid, Mohammad; Bhattacharyya, Pratap; Swain, Chinmaya Kumar; Tripathy, Rojalin; Bhattacharya, Bimal K.; Nayak, Amaresh Kumar

2018-04-01

A field experiment was conducted in 2015 to study the land surface energy fluxes from tropical lowland rice paddy in eastern India with an objective to determine the mass, momentum, and energy exchange rates between rice paddies and the atmosphere. All the land surface energy fluxes were measured by eddy covariance (EC) system (make Campbell Scientific) in dry season (DS, 1-125 Julian days), dry fallow (DF, 126-181 Julian days), wet season (WS, 182-324 Julian days), and wet fallow (WF, 325-365 Julian days). The rice was cultivated in dry season (January-May) and wet season (July-November) in low wet lands and the ground is kept fallow during the remainder of the year. Results showed that albedo varied from 0.09 to 0.24 and showed positive value from morning 6:00 h until evening 18:00 h. Mean soil temperature (T g) was highest in DF, while the skin temperature (T s) was highest in WS. Average Bowen ratio (B) ranged from 0.21 to 0.64 and large variation in B was observed during the fallow periods as compared to the cropping seasons. The magnitude of aerodynamic, canopy, and climatological resistances increased with the progress of cropping season and their magnitudes decreased during the end of both cropping seasons and found minimum during the fallow periods. At a constant vapor pressure deficit (VPD) at 0.16, 0.18, 0.15, and 0.43 kPa, latent heat flux (LE) initially increased, but later it tended to level off with an increase in VPD. The actual evapotranspiration (ETa) during both the cropping seasons was higher than the fallow period. This study can be used as a source of default values for many land surface energy fluxes which are required in various meteorological or air-quality models for rice paddies. A larger imbalance of energy was observed during the wet season as the energy is stored and perhaps advected in the fresh water.

[Can the local energy minimization refine the PDB structures of different resolution universally?].

PubMed

Godzi, M G; Gromova, A P; Oferkin, I V; Mironov, P V

2009-01-01

The local energy minimization was statistically validated as the refinement strategy for PDB structure pairs of different resolution. Thirteen pairs of structures with the only difference in resolution were extracted from PDB, and the structures of 11 identical proteins obtained by different X-ray diffraction techniques were represented. The distribution of RMSD value was calculated for these pairs before and after the local energy minimization of each structure. The MMFF94 field was used for energy calculations, and the quasi-Newton method was used for local energy minimization. By comparison of these two RMSD distributions, the local energy minimization was proved to statistically increase the structural differences in pairs so that it cannot be used for refinement purposes. To explore the prospects of complex refinement strategies based on energy minimization, randomized structures were obtained by moving the initial PDB structures as far as the minimized structures had been moved in a multidimensional space of atomic coordinates. For these randomized structures, the RMSD distribution was calculated and compared with that for minimized structures. The significant differences in their mean values proved the energy surface of the protein to have only few minima near the conformations of different resolution obtained by X-ray diffraction for PDB. Some other results obtained by exploring the energy surface near these conformations are also presented. These results are expected to be very useful for the development of new protein refinement strategies based on energy minimization.

Influence of an external electric field on the potential-energy surface of alkali-metal-decorated C60

NASA Astrophysics Data System (ADS)

De, Deb Sankar; Saha, Santanu; Genovese, Luigi; Goedecker, Stefan

2018-06-01

We present a fully ab initio, unbiased structure search of the configurational space of decorated C60 fullerenes in the presence of an electric field. We observed that the potential-energy surface is significantly perturbed by an external electric field and that the energetic ordering of low-energy isomers differs with and without electric field. We identify the energetically lowest configuration for a varying number of decorating atoms (1 ≤n ≤12 ) for Li and (1 ≤n ≤6 ) for K on the C60 surface at different electric-field strengths. Using the correct geometric ground state in the electric field for the calculation of the dipole we obtain better agreement with the experimentally measured values than previous calculations based on the ground state in absence of an electric field. Since the lowest-energy structures are typically nearly degenerate in energy, a combination of different structures is expected to be found at room temperature. The experimentally measured dipole is therefore also expected to contain significant contributions from several low-energy structures.

Nanoparticle Decoration of Carbon Nanotubes by Sputtering

DTIC Science & Technology

2013-02-01

subsequent coalescence as the mechanism of growth, but focused on per- formance of the metallized arrays rather than processing- structure relationships...dictates its wet- ting behavior; if the interfacial energy is comparable to the surface energy, the metal will avoid contact with the sub- strate and...form an isolated island to minimize interfacial en- ergy. Significantly lower interfacial energy values will drive the metal to spread on the surface—for

Ro-vibrational averaging of the isotropic hyperfine coupling constant for the methyl radical

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adam, Ahmad Y.; Jensen, Per, E-mail: jensen@uni-wuppertal.de; Yachmenev, Andrey

2015-12-28

We present the first variational calculation of the isotropic hyperfine coupling constant of the carbon-13 atom in the CH{sub 3} radical for temperatures T = 0, 96, and 300 K. It is based on a newly calculated high level ab initio potential energy surface and hyperfine coupling constant surface of CH{sub 3} in the ground electronic state. The ro-vibrational energy levels, expectation values for the coupling constant, and its temperature dependence were calculated variationally by using the methods implemented in the computer program TROVE. Vibrational energies and vibrational and temperature effects for coupling constant are found to be in verymore » good agreement with the available experimental data. We found, in agreement with previous studies, that the vibrational effects constitute about 44% of the constant’s equilibrium value, originating mainly from the large amplitude out-of-plane bending motion and that the temperature effects play a minor role.« less

Symmetry Energy and Its Components in Finite Nuclei

NASA Astrophysics Data System (ADS)

Antonov, A. N.; Gaidarov, M. K.; Kadrev, D. N.; Sarriguren, P.; Moya de Guerra, E.

2018-05-01

We derive the volume and surface components of the nuclear symmetry energy (NSE) and their ratio within the coherent density fluctuation model. The estimations use the results of the model for the NSE in finite nuclei based on the Brueckner and Skyrme energy-density functionals for nuclear matter. The obtained values of the volume and surface contributions to the NSE and their ratio for the Ni, Sn, and Pb isotopic chains are compared with estimations of other approaches which have used available experimental data on binding energies, neutron-skin thicknesses, and excitation energies to isobaric analog states (IAS). Apart from the density dependence investigated in our previous works, we study also the temperature dependence of the symmetry energy in finite nuclei in the framework of the local density approximation combining it with the self-consistent Skyrme-HFB method using the cylindrical transformed deformed harmonic-oscillator basis. The results for the thermal evolution of the NSE in the interval T = 0–4 MeV show that its values decrease with temperature. The investigations of the T-dependence of the neutron and proton root-mean-square radii and the corresponding neutron skin thickness point out that the effect of temperature leads mainly to a substantial increase of the neutron radii and skins, especially in nuclei which are more rich of neutrons.

Real single ion solvation free energies with quantum mechanical simulation

DOE PAGES

Duignan, Timothy T.; Baer, Marcel D.; Schenter, Gregory K.; ...

2017-07-04

Single ion solvation free energies are one of the most important properties of electrolyte solutions and yet there is ongoing debate about what these values are. Only the values for neutral ion pairs are known. Here, we use DFT interaction potentials with molecular dynamics simulation (DFT-MD) combined with a modified version of the quasi-chemical theory (QCT) to calculate these energies for the lithium and fluoride ions. A method to correct for the error in the DFT functional is developed and very good agreement with the experimental value for the lithium fluoride pair is obtained. Moreover, this method partitions the energiesmore » into physically intuitive terms such as surface potential, cavity and charging energies which are amenable to descriptions with reduced models. Here, our research suggests that lithium's solvation free energy is dominated by the free energetics of a charged hard sphere, whereas fluoride exhibits significant quantum mechanical behavior that cannot be simply described with a reduced model.« less

Real single ion solvation free energies with quantum mechanical simulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duignan, Timothy T.; Baer, Marcel D.; Schenter, Gregory K.

Single ion solvation free energies are one of the most important properties of electrolyte solutions and yet there is ongoing debate about what these values are. Only the values for neutral ion pairs are known. Here, we use DFT interaction potentials with molecular dynamics simulation (DFT-MD) combined with a modified version of the quasi-chemical theory (QCT) to calculate these energies for the lithium and fluoride ions. A method to correct for the error in the DFT functional is developed and very good agreement with the experimental value for the lithium fluoride pair is obtained. Moreover, this method partitions the energiesmore » into physically intuitive terms such as surface potential, cavity and charging energies which are amenable to descriptions with reduced models. Here, our research suggests that lithium's solvation free energy is dominated by the free energetics of a charged hard sphere, whereas fluoride exhibits significant quantum mechanical behavior that cannot be simply described with a reduced model.« less

Development of a tuned interfacial force field parameter set for the simulation of protein adsorption to silica glass.

PubMed

Snyder, James A; Abramyan, Tigran; Yancey, Jeremy A; Thyparambil, Aby A; Wei, Yang; Stuart, Steven J; Latour, Robert A

2012-12-01

Adsorption free energies for eight host-guest peptides (TGTG-X-GTGT, with X = N, D, G, K, F, T, W, and V) on two different silica surfaces [quartz (100) and silica glass] were calculated using umbrella sampling and replica exchange molecular dynamics and compared with experimental values determined by atomic force microscopy. Using the CHARMM force field, adsorption free energies were found to be overestimated (i.e., too strongly adsorbing) by about 5-9 kcal/mol compared to the experimental data for both types of silica surfaces. Peptide adsorption behavior for the silica glass surface was then adjusted using a modified version of the CHARMM program, which we call dual force-field CHARMM, which allows separate sets of nonbonded parameters (i.e., partial charge and Lennard-Jones parameters) to be used to represent intra-phase and inter-phase interactions within a given molecular system. Using this program, interfacial force field (IFF) parameters for the peptide-silica glass systems were corrected to obtain adsorption free energies within about 0.5 kcal/mol of their respective experimental values, while IFF tuning for the quartz (100) surface remains for future work. The tuned IFF parameter set for silica glass will subsequently be used for simulations of protein adsorption behavior on silica glass with greater confidence in the balance between relative adsorption affinities of amino acid residues and the aqueous solution for the silica glass surface.

Development of a Tuned Interfacial Force Field Parameter Set for the Simulation of Protein Adsorption to Silica Glass

PubMed Central

Snyder, James A.; Abramyan, Tigran; Yancey, Jeremy A.; Thyparambil, Aby A.; Wei, Yang; Stuart, Steven J.; Latour, Robert A.

2012-01-01

Adsorption free energies for eight host–guest peptides (TGTG-X-GTGT, with X = N, D, G, K, F, T, W, and V) on two different silica surfaces [quartz (100) and silica glass] were calculated using umbrella sampling and replica exchange molecular dynamics and compared with experimental values determined by atomic force microscopy. Using the CHARMM force field, adsorption free energies were found to be overestimated (i.e., too strongly adsorbing) by about 5–9 kcal/mol compared to the experimental data for both types of silica surfaces. Peptide adsorption behavior for the silica glass surface was then adjusted using a modified version of the CHARMM program, which we call dual force-field CHARMM, which allows separate sets of nonbonded parameters (i.e., partial charge and Lennard-Jones parameters) to be used to represent intra-phase and inter-phase interactions within a given molecular system. Using this program, interfacial force field (IFF) parameters for the peptide-silica glass systems were corrected to obtain adsorption free energies within about 0.5 kcal/mol of their respective experimental values, while IFF tuning for the quartz (100) surface remains for future work. The tuned IFF parameter set for silica glass will subsequently be used for simulations of protein adsorption behavior on silica glass with greater confidence in the balance between relative adsorption affinities of amino acid residues and the aqueous solution for the silica glass surface. PMID:22941539

Modeling the Effect of Summertime Heating on Urban Runoff Temperature

NASA Astrophysics Data System (ADS)

Thompson, A. M.; Gemechu, A. L.; Norman, J. M.; Roa-Espinosa, A.

2007-12-01

Urban impervious surfaces absorb and store thermal energy, particularly during warm summer months. During a rainfall/runoff event, thermal energy is transferred from the impervious surface to the runoff, causing it to become warmer. As this higher temperature runoff enters receiving waters, it can be harmful to coldwater habitat. A simple model has been developed for the net energy flux at the impervious surfaces of urban areas to account for the heat transferred to runoff. Runoff temperature is determined as a function of the physical characteristics of the impervious areas, the weather, and the heat transfer between the moving film of runoff and the heated impervious surfaces that commonly exist in urban areas. Runoff from pervious surfaces was predicted using the Green- Ampt Mein-Larson infiltration excess method. Theoretical results were compared to experimental results obtained from a plot-scale field study conducted at the University of Wisconsin's West Madison Agricultural Research Station. Surface temperatures and runoff temperatures from asphalt and sod plots were measured throughout 15 rainfall simulations under various climatic conditions during the summers of 2004 and 2005. Average asphalt runoff temperatures ranged from 23.2°C to 37.1°C. Predicted asphalt runoff temperatures were in close agreement with measured values for most of the simulations (average RMSE = 4.0°C). Average pervious runoff temperatures ranged from 19.7° to 29.9°C and were closely approximated by the rainfall temperature (RMSE = 2.8°C). Predicted combined asphalt and sod runoff temperatures using a flow-weighted average were in close agreement with observed values (average RMSE = 3.5°C).

HCl dissociating on a rigid Au(111) surface: A six-dimensional quantum mechanical study on a new potential energy surface based on the RPBE functional.

PubMed

Liu, Tianhui; Fu, Bina; Zhang, Dong H

2017-04-28

The dissociative chemisorption of HCl on the Au(111) surface has recently been an interesting and important subject, regarding the discrepancy between the theoretical dissociation probabilities and the experimental sticking probabilities. We here constructed an accurate full-dimensional (six-dimensional (6D)) potential energy surface (PES) based on the density functional theory (DFT) with the revised Perdew-Burke-Ernzerhof (RPBE) functional, and performed 6D quantum mechanical (QM) calculations for HCl dissociating on a rigid Au(111) surface. The effects of vibrational excitations, rotational orientations, and site-averaging approximation on the present RPBE PES are investigated. Due to the much higher barrier height obtained on the RPBE PES than on the PW91 PES, the agreement between the present theoretical and experimental results is greatly improved. In particular, at the very low kinetic energy, the QM-RPBE dissociation probability agrees well with the experimental data. However, the computed QM-RPBE reaction probabilities are still markedly different from the experimental values at most of the energy regions. In addition, the QM-RPBE results achieve good agreement with the recent ab initio molecular dynamics calculations based on the RPBE functional at high kinetic energies.

Protein surface roughness accounts for binding free energy of Plasmepsin II-ligand complexes.

PubMed

Valdés-Tresanco, Mario E; Valdés-Tresanco, Mario S; Valiente, Pedro A; Cocho, Germinal; Mansilla, Ricardo; Nieto-Villar, J M

2018-01-01

The calculation of absolute binding affinities for protein-inhibitor complexes remains as one of the main challenges in computational structure-based ligand design. The present work explored the calculations of surface fractal dimension (as a measure of surface roughness) and the relationship with experimental binding free energies of Plasmepsin II complexes. Plasmepsin II is an attractive target for novel therapeutic compounds to treat malaria. However, the structural flexibility of this enzyme is a drawback when searching for specific inhibitors. Concerning that, we performed separate explicitly solvated molecular dynamics simulations using the available high-resolution crystal structures of different Plasmepsin II complexes. Molecular dynamics simulations allowed a better approximation to systems dynamics and, therefore, a more reliable estimation of surface roughness. This constitutes a novel approximation in order to obtain more realistic values of fractal dimension, because previous works considered only x-ray structures. Binding site fractal dimension was calculated considering the ensemble of structures generated at different simulation times. A linear relationship between binding site fractal dimension and experimental binding free energies of the complexes was observed within 20 ns. Previous studies of the subject did not uncover this relationship. Regression model, coined FD model, was built to estimate binding free energies from binding site fractal dimension values. Leave-one-out cross-validation showed that our model reproduced accurately the absolute binding free energies for our training set (R 2  = 0.76; <|error|> =0.55 kcal/mol; SD error  = 0.19 kcal/mol). The fact that such a simple model may be applied raises some questions that are addressed in the article. Copyright © 2017 John Wiley & Sons, Ltd.

Correlation between surface chemistry and ion energy dependence of the etch yield in multicomponent oxides etching

NASA Astrophysics Data System (ADS)

Bérubé, P.-M.; Poirier, J.-S.; Margot, J.; Stafford, L.; Ndione, P. F.; Chaker, M.; Morandotti, R.

2009-09-01

The influence of surface chemistry in plasma etching of multicomponent oxides was investigated through measurements of the ion energy dependence of the etch yield. Using pulsed-laser-deposited CaxBa(1-x)Nb2O6 (CBN) and SrTiO3 thin films as examples, it was found that the etching energy threshold shifts toward values larger or smaller than the sputtering threshold depending on whether or not ion-assisted chemical etching is the dominant etching pathway and whether surface chemistry is enhancing or inhibiting desorption of the film atoms. In the case of CBN films etched in an inductively coupled Cl2 plasma, it is found that the chlorine uptake is inhibiting the etching reaction, with the desorption of nonvolatile NbCl2 and BaCl2 compounds being the rate-limiting step.

Thermodynamic properties of adsorption and micellization of n-oktyl-β-D-glucopiranoside.

PubMed

Mańko, Diana; Zdziennicka, Anna; Jańczuk, Bronisław

2014-02-01

Measurements of the surface tension, density and viscosity of aqueous solutions of n-oktyl-β-D-glucopiranoside (OGP) were made at 293 K. From the obtained results the Gibbs surface excess concentration of OGP at the water-air interface and its critical micelle concentration were determined. The Gibbs surface excess concentration of OGP used in the Gu and Zhu isotherm equation allowed us to determine the Gibbs standard free energy of OGP adsorption at the water-air interface. The Gibbs standard free energy of OGP adsorption was also determined on the basis of the Langmuir, Szyszkowski, Gamboa and Olea equations as well the surface tension of "hydrophobic" part of OGP and "hydrophobic" part-water interface tension. It appeared that there is an agreement between the values of Gibbs standard free energy of OGP adsorption at the water-air interface determined by using all the above mentioned methods. It also proved that standard free energy of OGP micellization determined from CMC is consistent with that obtained on the basis of the free energy of the interactions between the "hydrophobic" part of the OPG through the water phase. Copyright © 2013 Elsevier B.V. All rights reserved.

Surface properties of calcium and magnesium oxide nanopowders grafted with unsaturated carboxylic acids studied with inverse gas chromatography.

PubMed

Maciejewska, Magdalena; Krzywania-Kaliszewska, Alicja; Zaborski, Marian

2012-09-28

Inverse gas chromatography (IGC) was applied at infinite dilution to evaluate the surface properties of calcium and magnesium oxide nanoparticles and the effect of surface grafted unsaturated carboxylic acid on the nanopowder donor-acceptor characteristics. The dispersive components (γ(s)(D)) of the free energy of the nanopowders were determined by Gray's method, whereas their tendency to undergo specific interactions was estimated based on the electron donor-acceptor approach presented by Papirer. The calcium and magnesium oxide nanoparticles exhibited high surface energies (79 mJ/m² and 74 mJ/m², respectively). Modification of nanopowders with unsaturated carboxylic acids decreased their specific adsorption energy. The lowest value of γ(s)(D) was determined for nanopowders grafted with undecylenic acid, approximately 55 mJ/m². The specific interactions were characterised by the molar free energy (ΔG(A)(SP)) and molar enthalpy (ΔH(A)(SP)) of adsorption as well as the donor and acceptor interaction parameters (K(A), K(D)). Copyright © 2012 Elsevier B.V. All rights reserved.

Ablation experiment and threshold calculation of titanium alloy irradiated by ultra-fast pulse laser

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng, Buxiang; Jiang, Gedong; Wang, Wenjun, E-mail: wenjunwang@mail.xjtu.edu.cn

The interaction between an ultra-fast pulse laser and a material's surface has become a research hotspot in recent years. Micromachining of titanium alloy with an ultra-fast pulse laser is a very important research direction, and it has very important theoretical significance and application value in investigating the ablation threshold of titanium alloy irradiated by ultra-fast pulse lasers. Irradiated by a picosecond pulse laser with wavelengths of 1064 nm and 532 nm, the surface morphology and feature sizes, including ablation crater width (i.e. diameter), ablation depth, ablation area, ablation volume, single pulse ablation rate, and so forth, of the titanium alloymore » were studied, and their ablation distributions were obtained. The experimental results show that titanium alloy irradiated by a picosecond pulse infrared laser with a 1064 nm wavelength has better ablation morphology than that of the green picosecond pulse laser with a 532 nm wavelength. The feature sizes are approximately linearly dependent on the laser pulse energy density at low energy density and the monotonic increase in laser pulse energy density. With the increase in energy density, the ablation feature sizes are increased. The rate of increase in the feature sizes slows down gradually once the energy density reaches a certain value, and gradually saturated trends occur at a relatively high energy density. Based on the linear relation between the laser pulse energy density and the crater area of the titanium alloy surface, and the Gaussian distribution of the laser intensity on the cross section, the ablation threshold of titanium alloy irradiated by an ultra-fast pulse laser was calculated to be about 0.109 J/cm{sup 2}.« less

The Role of Glottal Surface Adhesion on Vocal Folds Biomechanics

PubMed Central

Bhattacharya, Pinaki; Siegmund, Thomas

2014-01-01

The airway surface liquid (ASL) is a very thin mucus layer and covers the vocal fold (VF) surface. Adhesion mediated by the ASL occurs during phonation as the VFs separate after collision. Such adhesion is hypothesized to determine voice quality and health. However, biomechanical insights into the adhesive processes during VF oscillation are lacking. Here, a computational study is reported on self-sustained VF vibration involving contact and adhesion. The VF structural model and the glottal airflow are considered fully three-dimensional. The mechanical behavior of the ASL is described through a constitutive traction–separation law where mucosal cohesive strength, cohesive energy and rupture length enter. Cohesive energy values considered are bound below by the cohesive energy of water at standard temperature and pressure. Cohesive strength values considered are bound above by prior reported data on the adhesive strength of mucosal surface of rat small intestine. This model introduces a mechanical length scale into the analysis. The sensitivity of various aspects of VF dynamics such as flow-declination rate, VF separation under adhesive condition and formation of multiple local fluid bridges is determined in relation to specific ASL adhesive properties. It is found that for the ASL considered here, the characteristics of the VF separation process are of debond type. Instabilities lead to the breakup of the bond area into several smaller bond patches. Such finding is consistent with in-vivo observations. PMID:25034504

New boundary conditions for fluid interaction with hydrophobic surface

NASA Astrophysics Data System (ADS)

Pochylý, František; Fialová, Simona; Havlásek, Michal

2018-06-01

Solution of both laminar and turbulent flow with consideration of hydrophobic surface is based on the original Navier assumption that the shear stress on the hydrophobic surface is directly proportional to the slipping velocity. In the previous work a laminar flow analysis with different boundary conditions was performed. The shear stress value on the tube walls directly depends on the pressure gradient. In the solution of the turbulent flow by the k-ɛ model, the occurrence of the fluctuation components of velocity on the hydrophobic surface is considered. The fluctuation components of the velocity affect the size of the adhesive forces. We assume that the boundary condition for ɛ depending on the velocity gradients will not need to be changed. When the liquid slips over the surface, non-zero fluctuation velocity components occur in the turbulent flow. These determine the non-zero value of the turbulent kinetic energy K. In addition, the fluctuation velocity components also influence the value of the adhesive forces, so it is necessary to include these in the formulation of new boundary conditions for turbulent flow on the hydrophobic surface.

Microplastic deformation of polycrystalline iron and molybdenum subjected to high-current electron-beam irradiation

NASA Astrophysics Data System (ADS)

Dudarev, E. F.; Pochivalova, G. P.; Proskurovskii, D. I.; Rotshtein, V. P.; Markov, A. B.

1996-03-01

A technique for determination of residual stresses at various distances from the irradiated surface is proposed. It is established for iron and molybdenum that compressive stresses are set up under irradiation by low-energy high-current electron beams and that their values decrease sharply with increasing distance from the surface. The residual stresses are much smaller in absolute magnitude than those operating during irradiation. It is shown that the change in resistance to microplastic deformation on irradiation with low-energy high-current electron beams is governed not only by formation of a gradient dislocation substructure in the surface layer, but also by the residual stresses and the appearance of the Bauschinger effect.

A first-principles study of methyl lactate adsorption on the chiral Cu (643) surface

NASA Astrophysics Data System (ADS)

Yuk, Simuck F.; Asthagiri, Aravind

2014-11-01

We used dispersion-corrected density function theory (DFT) to investigate the enantiospecific adsorption of R- and S-methyl lactate on the chiral Cu (643)R surface. Initial study of methyl lactate adsorbed on the Cu (111) surface revealed that the most strongly bound states are associated with interaction of the hydroxyl and alkoxide group with the surface. Using dispersion-corrected DFT-derived pre-factors and desorption energies within the Redhead analysis predicts peak temperatures that are in relatively good agreement with experimental values for molecular methyl lactate desorption from both the Cu (111) and Cu (643)R surface. The global minimum of S-methyl lactate is more firmly bound by 9.5 kJ/mol over its enantiomer on the Cu (643)R surface, with a peak temperature difference of 25 K versus an experimental value of 12 K.

Surface instability of an imperfectly bonded thin elastic film under surface van der Waals forces

NASA Astrophysics Data System (ADS)

Wang, Xu; Jing, Rong

2017-02-01

This paper studies surface instability of a thin elastic film imperfectly bonded to a rigid substrate interacting with a rigid contactor through van der Waals forces under plane strain conditions. The film-substrate interface is modeled as a linear spring with vanishing thickness described in terms of the normal and tangential interface parameters. Depending on the ratio of the two imperfect interface parameters, the critical value of the Poisson's ratio for the occurrence of surface wrinkling in the absence of surface energy can be greater than, equal to, or smaller than 0.25, which is the critical Poisson's ratio for a perfect film-substrate interface. The critical surface energy for the inhibition of the surface wrinkling is also obtained. Finally, we propose a very simple and effective method to study the surface instability of a multilayered elastic film with imperfect interfaces interacting with a rigid contactor or with another multilayered elastic film (or a multilayered simply supported plate) with imperfect interfaces.

Secondary flows in turbulent boundary layers over longitudinal surface roughness

NASA Astrophysics Data System (ADS)

Hwang, Hyeon Gyu; Lee, Jae Hwa

2018-01-01

Direct numerical simulations of turbulent boundary layers over longitudinal surface roughness are performed to investigate the impact of the surface roughness on the mean flow characteristics related to counter-rotating large-scale secondary flows. By systematically changing the two parameters of the pitch (P) and width (S) for roughness elements in the ranges of 0.57 ≤P /δ ≤2.39 and 0.15 ≤S /δ ≤1.12 , where δ is the boundary layer thickness, we find that the size of the secondary flow in each case is mostly determined by the value of P - S, i.e., the valley width, over the ridge-type roughness. However, the strength of the secondary flows on the cross-stream plane relative to the flow is increased when the value of P increases or when the value of S decreases. In addition to the secondary flows, additional tertiary and quaternary flows are observed both above the roughness crest and in the valley as the values of P and S increase further. Based on an analysis using the turbulent kinetic energy transport equation, it is shown that the secondary flow over the ridge-type roughness is both driven and sustained by the anisotropy of turbulence, consistent with previous observations of a turbulent boundary layer over strip-type roughness [Anderson et al., J. Fluid Mech. 768, 316 (2015), 10.1017/jfm.2015.91]. Careful inspection of the turbulent kinetic energy budget reveals that the opposite rotational sense of the secondary flow between the ridge- and strip-type roughness elements is primarily attributed to the local imbalance of energy budget created by the strong turbulent transport term over the ridge-type roughness. The active transport of the kinetic energy over the ridge-type roughness is closely associated with the upward deflection of spanwise motions in the valley, mostly due to the roughness edge.

Forces and Holes in Liquid Surfaces and Soap Films: A Simple Measurement of a Not-So-Simple Effect

ERIC Educational Resources Information Center

Gratton, Luigi M.; Oss, Stefano

2004-01-01

In this article we show how to verify that in a fluid surface or film the value of the surface tension (i.e. the free energy per unit area) does not depend on the area of the film itself. The experimental evidence discussed can be obtained extremely simply yet with great accuracy. This experiment is important in that it leads to a deeper…

Full-dimensional quantum calculations of the dissociation energy, zero-point, and 10 K properties of H7+/D7+ clusters using an ab initio potential energy surface.

PubMed

Barragán, Patricia; Pérez de Tudela, Ricardo; Qu, Chen; Prosmiti, Rita; Bowman, Joel M

2013-07-14

Diffusion Monte Carlo (DMC) and path-integral Monte Carlo computations of the vibrational ground state and 10 K equilibrium state properties of the H7 (+)/D7 (+) cations are presented, using an ab initio full-dimensional potential energy surface. The DMC zero-point energies of dissociated fragments H5 (+)(D5 (+))+H2(D2) are also calculated and from these results and the electronic dissociation energy, dissociation energies, D0, of 752 ± 15 and 980 ± 14 cm(-1) are reported for H7 (+) and D7 (+), respectively. Due to the known error in the electronic dissociation energy of the potential surface, these quantities are underestimated by roughly 65 cm(-1). These values are rigorously determined for first time, and compared with previous theoretical estimates from electronic structure calculations using standard harmonic analysis, and available experimental measurements. Probability density distributions are also computed for the ground vibrational and 10 K state of H7 (+) and D7 (+). These are qualitatively described as a central H3 (+)/D3 (+) core surrounded by "solvent" H2/D2 molecules that nearly freely rotate.

Study on two operating conditions of a full-scale oxidation ditch for optimization of energy consumption and effluent quality by using CFD model.

PubMed

Yang, Yin; Yang, Jiakuan; Zuo, Jiaolan; Li, Ye; He, Shu; Yang, Xiao; Zhang, Kai

2011-05-01

The operating condition of an oxidation ditch (OD) has significant impact on energy consumption and effluent quality of wastewater treatment plants (WWTPs). An experimentally validated numerical tool, based on computational fluid dynamics (CFD) model, was proposed to optimize the operating condition by considering two important factors: flow field and dissolved oxygen (DO) concentration profiles. The model is capable of predicting flow pattern and oxygen mass transfer characteristics in ODs equipped with surface aerators and submerged impellers. Performance demonstration and comparison of two operating conditions (existing and improved) were carried out in two full-scale Carrousel ODs at the Ping Dingshan WWTP in Henan, China. A moving wall model and a fan model were designed to simulate surface aerators and submerged impellers, respectively. Oxygen mass transfer in the ditch was predicted by using a unit analysis method. In aeration zones, the mass inlets representing the surface aerators were set as one source of DO. In the whole straight channel, the oxygen consumption was modeled by using modified BOD-DO model. The following results were obtained: (1) the CFD model characterized flow pattern and DO concentration profiles in the full-scale OD. The predicted flow field values were within 1.98 ± 4.28% difference from the actual measured values while the predicted DO concentration values were within -4.71 ± 4.15% of the measured ones, (2) a surface aerator should be relocated to around 15m from the curve bend entrance to reduce energy loss caused by fierce collisions at the wall of the curve bend, and (3) DO concentration gradients in the OD under the improved operating condition were more favorable for occurrence of simultaneous nitrification and denitrification (SND). Copyright © 2011 Elsevier Ltd. All rights reserved.

Inelastic scattering matrix elements for the nonadiabatic collision B(2P1/2)+H2(1Sigmag+,j)<-->B(2P3/2)+H2(1Sigmag+,j').

PubMed

Weeks, David E; Niday, Thomas A; Yang, Sang H

2006-10-28

Inelastic scattering matrix elements for the nonadiabatic collision B(2P1/2)+H2(1Sigmag+,j)<-->B(2P3/2)+H2(1Sigmag+,j') are calculated using the time dependent channel packet method (CPM). The calculation employs 1 2A', 2 2A', and 1 2A" adiabatic electronic potential energy surfaces determined by numerical computation at the multireference configuration-interaction level [M. H. Alexander, J. Chem. Phys. 99, 6041 (1993)]. The 1 2A' and 2 2A', adiabatic electronic potential energy surfaces are transformed to yield diabatic electronic potential energy surfaces that, when combined with the total B+H2 rotational kinetic energy, yield a set of effective potential energy surfaces [M. H. Alexander et al., J. Chem. Phys. 103, 7956 (1995)]. Within the framework of the CPM, the number of effective potential energy surfaces used for the scattering matrix calculation is then determined by the size of the angular momentum basis used as a representation. Twenty basis vectors are employed for these calculations, and the corresponding effective potential energy surfaces are identified in the asymptotic limit by the H2 rotor quantum numbers j=0, 2, 4, 6 and B electronic states 2Pja, ja=1/2, 3/2. Scattering matrix elements are obtained from the Fourier transform of the correlation function between channel packets evolving in time on these effective potential energy surfaces. For these calculations the H2 bond length is constrained to a constant value of req=1.402 a.u. and state to state scattering matrix elements corresponding to a total angular momentum of J=1/2 are discussed for j=0<-->j'=0,2,4 and 2P1/2<-->2P1/2, 2P3/2 over a range of total energy between 0.0 and 0.01 a.u.

Ab initio calculation of reaction energies. III. Basis set dependence of relative energies on the FH2 and H2CO potential energy surfaces

NASA Astrophysics Data System (ADS)

Frisch, Michael J.; Binkley, J. Stephen; Schaefer, Henry F., III

1984-08-01

The relative energies of the stationary points on the FH2 and H2CO nuclear potential energy surfaces relevant to the hydrogen atom abstraction, H2 elimination and 1,2-hydrogen shift reactions have been examined using fourth-order Møller-Plesset perturbation theory and a variety of basis sets. The theoretical absolute zero activation energy for the F+H2→FH+H reaction is in better agreement with experiment than previous theoretical studies, and part of the disagreement between earlier theoretical calculations and experiment is found to result from the use of assumed rather than calculated zero-point vibrational energies. The fourth-order reaction energy for the elimination of hydrogen from formaldehyde is within 2 kcal mol-1 of the experimental value using the largest basis set considered. The qualitative features of the H2CO surface are unchanged by expansion of the basis set beyond the polarized triple-zeta level, but diffuse functions and several sets of polarization functions are found to be necessary for quantitative accuracy in predicted reaction and activation energies. Basis sets and levels of perturbation theory which represent good compromises between computational efficiency and accuracy are recommended.

Synoptic, Global Mhd Model For The Solar Corona

NASA Astrophysics Data System (ADS)

Cohen, Ofer; Sokolov, I. V.; Roussev, I. I.; Gombosi, T. I.

2007-05-01

The common techniques for mimic the solar corona heating and the solar wind acceleration in global MHD models are as follow. 1) Additional terms in the momentum and energy equations derived from the WKB approximation for the Alfv’en wave turbulence; 2) some empirical heat source in the energy equation; 3) a non-uniform distribution of the polytropic index, γ, used in the energy equation. In our model, we choose the latter approach. However, in order to get a more realistic distribution of γ, we use the empirical Wang-Sheeley-Arge (WSA) model to constrain the MHD solution. The WSA model provides the distribution of the asymptotic solar wind speed from the potential field approximation; therefore it also provides the distribution of the kinetic energy. Assuming that far from the Sun the total energy is dominated by the energy of the bulk motion and assuming the conservation of the Bernoulli integral, we can trace the total energy along a magnetic field line to the solar surface. On the surface the gravity is known and the kinetic energy is negligible. Therefore, we can get the surface distribution of γ as a function of the final speed originating from this point. By interpolation γ to spherically uniform value on the source surface, we use this spatial distribution of γ in the energy equation to obtain a self-consistent, steady state MHD solution for the solar corona. We present the model result for different Carrington Rotations.

Reaction pathways of biomass-derived oxygenates on noble metal surfaces

NASA Astrophysics Data System (ADS)

McManus, Jesse R.

As the global demand for energy continues to rise, the environmental concerns associated with increased fossil fuel consumption have motivated the use of biomass as an alternative, carbon-renewable energy feedstock. Controlling reactive chemistry of the sugars that comprise biomass through the use of catalysis becomes essential in effectively producing green fuels and value-added chemicals. Recent work on biomass conversion catalysts have demonstrated the efficacy of noble metal catalyst systems for the reforming of biomass to hydrogen fuel, and the hydrodeoxygenation of biomass-derived compounds to value-added chemicals. In particular, Pt and Pd surfaces have shown considerable promise as reforming catalysts in preliminary aqueous phase reforming studies. It becomes important to understand the mechanisms by which these molecules react on the catalyst surfaces in order to determine structure-activity relationships and bond scission energetics as to provide a framework for engineering more active and selective catalysts. Fundamental surface science techniques provide the tools to do this; however, work in this field has been so far limited to simple model molecules like ethanol and ethylene glycol. Herein, temperature programmed desorption and high resolution electron energy loss spectroscopy are utilized in an ultra-high vacuum surface science study of the biomass-derived sugar glucose on Pt and Pd single crystal catalysts. Overall, it was determined that the aldehyde function of a ring-open glucose molecule plays an integral part in the initial bonding and reforming reaction pathway, pointing to the use of aldoses glycolaldehyde and glyceraldehyde as the most appropriate model compounds for future studies. Furthermore, the addition of adatom Zn to a Pt(111) surface was found to significantly decrease the C-H and C-C bond scission activity in aldehyde containing compounds, resulting in a preferred deoxygenation pathway in opposition to the decarbonylation pathway common on clean Pt(111). This has implications in the hydrodeoxygenation of biomass-derived compounds for the production of value-added chemicals like 2-methylfuran from furfural, or the catalytic upgrading of sugars. Ultimately, identification of the reactive mechanisms of biomass-derived molecules on different unique surfaces has lead to a greater understanding for what makes a more selective catalyst for specific chemical pathways.

Quantum size effects on the (0001) surface of double hexagonal close packed americium

NASA Astrophysics Data System (ADS)

Gao, D.; Ray, A. K.

2007-01-01

Electronic structures of double hexagonal close-packed americium and the (0001) surface have been studied via full-potential all-electron density-functional calculations with a mixed APW+lo/LAPW basis. The electronic and geometric properties of bulk dhcp Am as well as quantum size effects in the surface energies and the work functions of the dhcp Am (0001) ultra thin films up to seven layers have been examined at nonmagnetic, ferromagnetic, and antiferromagnetic configurations with and without spin orbit coupling. The anti-ferromagnetic state including spin-orbit coupling is found to be the ground state of dhcp Am with the 5f electrons primarily localized. Our results show that both magnetic configurations and spin-orbit coupling play important roles in determining the equilibrium lattice constant, the bulk modulus as well as the localized feature of 5f electrons for dhcp Am. Our calculated equilibrium lattice constant and bulk modulus at the ground state are in good agreement with the experimental values respectively. The work function of dhcp Am (0001) 7-layer surface at the ground state is predicted to be 2.90 eV. The surface energy for dhcp Am (0001) semi-infinite surface energy at the ground state is predicted to be 0.84 J/m2. Quantum size effects are found to be more pronounced in work functions than in surface energies.

Electronic and total energy properties of ternary and quaternary semiconductor compounds, alloys, and superlattices: Theoretical study of Cu/graphite bonding

NASA Technical Reports Server (NTRS)

Lambrecht, Walter R. L.

1992-01-01

The goals of the research were to provide a fundamental science basis for why the bonding of Cu to graphite is weak, to critically evaluate the previous analysis of the wetting studies with particular regard to the values used for the surface energies of Cu and graphite, and to make recommendations for future experiments or other studies which could advance the understanding and solution of this technological problem. First principles electronic structure calculations were used to study the problem. These are based on density functional theory in the local density approximation and the use of the linear muffin-tin orbital band structure method. Calculations were performed for graphite monolayers, single crystal graphite with the hexagonal AB stacking, bulk Cu, Cu(111) surface, and Cu/graphite superlattices. The study is limited to the basal plane of graphite because this is the graphite plane exposed to Cu and graphite surface energies and combined with the measured contact angles to evaluate the experimental adhesion energy.

Polarized reflectance and transmittance properties of windblown sea surfaces.

PubMed

Mobley, Curtis D

2015-05-20

Generation of random sea surfaces using wave variance spectra and Fourier transforms is formulated in a way that guarantees conservation of wave energy and fully resolves wave height and slope variances. Monte Carlo polarized ray tracing, which accounts for multiple scattering between light rays and wave facets, is used to compute effective Mueller matrices for reflection and transmission of air- or water-incident polarized radiance. Irradiance reflectances computed using a Rayleigh sky radiance distribution, sea surfaces generated with Cox-Munk statistics, and unpolarized ray tracing differ by 10%-18% compared with values computed using elevation- and slope-resolving surfaces and polarized ray tracing. Radiance reflectance factors, as used to estimate water-leaving radiance from measured upwelling and sky radiances, are shown to depend on sky polarization, and improved values are given.

Analysis methods for polarization state and energy transmission of rays propagating in optical systems

NASA Astrophysics Data System (ADS)

Liu, Chao; Liu, Qiangsheng; Cen, Zhaofeng; Li, Xiaotong

2010-11-01

Polarization state of only completely polarized light can be analyzed by some software, ZEMAX for example. Based on principles of geometrical optics, novel descriptions of the light with different polarization state are provided in this paper. Differential calculus is well used for saving the polarization state and amplitudes of sampling rays when ray tracing. The polarization state changes are analyzed in terms of several typical circumstances, such as Brewster incidence, total reflection. Natural light and partially polarized light are discussed as an important aspect. Further more, a computing method including composition and decomposition of sampling rays at each surface is also set up to analyze the energy transmission of the rays for optical systems. Adopting these analysis methods mentioned, not only the polarization state changes of the incident rays can be obtained, but also the energy distributions can be calculated. Since the energy distributions are obtained, the surface with the most energy loss will be found in the optical system. The energy value and polarization state of light reaching the image surface will also be available. These analysis methods are very helpful for designing or analyzing optical systems, such as analyzing the energy of stray light in high power optical systems, researching the influences of optical surfaces to rays' polarization state in polarization imaging systems and so on.

Influence of inhomogeneous surface heat capacity on the estimation of radiative response coefficients in a two-zone energy balance model

NASA Astrophysics Data System (ADS)

Park, Jungmin; Choi, Yong-Sang

2018-04-01

Observationally constrained values of the global radiative response coefficient are pivotal to assess the reliability of modeled climate feedbacks. A widely used approach is to measure transient global radiative imbalance related to surface temperature changes. However, in this approach, a potential error in the estimate of radiative response coefficients may arise from surface inhomogeneity in the climate system. We examined this issue theoretically using a simple two-zone energy balance model. Here, we dealt with the potential error by subtracting the prescribed radiative response coefficient from those calculated within the two-zone framework. Each zone was characterized by the different magnitude of the radiative response coefficient and the surface heat capacity, and the dynamical heat transport in the atmosphere between the zones was parameterized as a linear function of the temperature difference between the zones. Then, the model system was forced by randomly generated monthly varying forcing mimicking time-varying forcing like an observation. The repeated simulations showed that inhomogeneous surface heat capacity causes considerable miscalculation (down to -1.4 W m-2 K-1 equivalent to 31.3% of the prescribed value) in the global radiative response coefficient. Also, the dynamical heat transport reduced this miscalculation driven by inhomogeneity of surface heat capacity. Therefore, the estimation of radiative response coefficients using the surface temperature-radiation relation is appropriate for homogeneous surface areas least affected by the exterior.

Negative optical absorption and up-energy conversion in dendrites of nanostructured silver grafted with α/β-poly(vinylidene fluoride) in small hierarchical structures

NASA Astrophysics Data System (ADS)

Phule, A. D.; Ram, S.; Shinde, S. K.; Choi, J. H.; Tyagi, A. K.

2018-04-01

We report that a negative optical absorption arises in a sharp band at 325 nm (energy hν2) in a nanostructured silver (n-Ag) doped poly(vinylidene fluoride) (PVF2) in a hybrid nanocomposite of films (∼100 μm thickness). Two polymorphs α- and β-PVF2 are co-stretched through the n-Ag crystallites in dendrites of hierarchical structures. A critical 0.5 wt% n-Ag dosage promotes this band of extinction coefficient to be enhanced by as much as 2.009 × 103, i.e. a 30% value in the Ag-surface plasmon band 350-650 nm (hν1). An electron donor Ag (4d105s1) bonds to an electron accepter moiety CF2 of PVF2, it tunes a dielectric field and sets up an up-energy conversion of the plasmon band. The FESEM and HRTEM images reveal fcc-Ag dendrites entangled with in-built PVF2 surface layers (2-3 nm thickness). The IR phonon bands show how a α → β-PVF2 transformation propagates onto a nascent n-Ag surface and how it is raised-up in small steps of 0.1 wt% and up to 5.0 wt%. In a model scheme, we illustrate how a rigid core-shell of a capsule conducts a new transfer mechanism of the energy to a cold surface plasmon (core) in a coherent collision, so as to balance a net value hν2 = h(ν3 - ν1). It absorbs light in a weak band at 210 nm (hν3) in a π → π* electron transition in the Cdbnd C bonds of the PVF2 (shell), and results in a negative absorption in a coherent excitation of the energy-carriers. A light-emitter on absorption over a wide range of wavelengths (200-650 nm) offers a unique type of energy-converter.

Textured carbon on copper: A novel surface with extremely low secondary electron emission characteristics

NASA Technical Reports Server (NTRS)

Curren, A. N.; Jensen, K. A.

1985-01-01

Experimentally determined values of true secondary electron emission and relative values of reflected primary electron yield for a range of primary electron beam energies and beam impingement angles are presented for a series of novel textured carbon surfaces on copper substrates. (All copper surfaces used in this study were oxygen-free, high-conductivity grade). The purpose of this investigation is to provide information necessary to develop high-efficiency multistage depressed collectors (MDC's) for microwave amplifier traveling-wave tubes (TWT's) for communications and aircraft applications. To attain the highest TWT signal quality and overall efficiency, the MDC electrode surface must have low secondary electron emission characteristics. While copper is the material most commonly used for MDC electrodes, it exhibits relatively high levels of secondary electron emission unless its surface is treated for emission control. The textured carbon surface on copper substrate described in this report is a particularly promising candidate for the MDC electrode application. Samples of textured carbon surfaces on copper substrates typical of three different levels of treatment are prepared and tested for this study. The materials are tested at primary electron beam energies of 200 to 2000 eV and at direct (0 deg) to near-grazing (85 deg) beam impingement angles. True secondary electron emission and relative reflected primary electron yield characteristics of the textured surfaces are compared with each other and with those of untreated copper. All the textured carbon surfaces on copper substrate tested exhibited sharply lower secondary electron emission characteristics than those of an untreated copper surface.

Surface diffusion of a carbon-adatom on Au(110) surfaces

NASA Astrophysics Data System (ADS)

Kim, E.; Safavi-Naini, A.; Hite, D. A.; McKay, K. S.; Pappas, D. P.; Weck, P. F.; Sadeghpour, H. R.

We have investigated the surface diffusion of carbon-adatom on gold surfaces using density functional theory and detailed scanning probe microscopy. The decoherence of trapped-ion quantum gates due to heating of their motional modes is a fundamental science and engineering problem. In an effort to understand heating at the trap-electrode surfaces, we investigate the possible source of noise by focusing on the diffusion of carbon-containing adsorbates onto the Au(110) surface. In this study, we show how the diffusive motion of carbon adatom on gold surface significantly affects the energy landscape and adatom dipole moment variation. A simple model for the diffusion noise, which varies quadratically with the variation of the dipole moment, qualitatively reproduces the measured noise spectrum, and the estimate of the noise spectral density is in accord with measured values. Sandia National Laboratories is a multiprogram laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the United States Department of Energy's NNSA under Contract DE-AC04-94AL85000.

Climatic variability of a fire-weather index based on turbulent kinetic energy and the Haines Index

Treesearch

Warren E. Heilman; Xindi Bian

2010-01-01

Combining the Haines Index (HI) with near-surface turbulent kinetic energy (TKEs) through a product of the two values (HITKEs) has shown promise as an indicator of the atmospheric potential for extreme and erratic fire behavior in the U.S. Numerical simulations of fire-weather evolution during past wildland fire episodes in...

Density functional theory study of defect energies and space charge distribution at a solid-oxide electrolyte surface

NASA Astrophysics Data System (ADS)

Han, Chu; Bongiorno, Angelo

2014-03-01

Yttrium-doped barium zirconate (BZY) is a proton conducting electrolyte forming a class of novel materials for new generation of solid oxide fuel cells, for hydrogen separation and purification, and for electrolysis of water. Here we use density functional theory calculations to compute the energy of protons and oxygen vacancies at the surface and in the bulk of lightly Y-doped BZY materials. We found that protons are energetically more stable at the surface termination than in the bulk of BZY by about 1 eV. In contrast, doubly-positively charged oxygen vacancies are found to form iso-energetic defects at both the terminal surface layer and in the bulk of BZY, while in the sub-surface region the defect energy raises by about 1 eV with respect to the value in the bulk. The energetic behavior of protons and oxygen vacancies in the near surface region of BZY is attributed to the competition of strain and electrostatic effects. Lattice model representations of BZY surfaces are then used in combination with Monte Carlo simulations to solve the Poisson-Boltzmann equation and investigate the implication of the results above on the structure of the space charge region at the surface of BZY materials.

Accurate collision-induced line-coupling parameters for the fundamental band of CO in He - Close coupling and coupled states scattering calculations

NASA Technical Reports Server (NTRS)

Green, Sheldon; Boissoles, J.; Boulet, C.

1988-01-01

The first accurate theoretical values for off-diagonal (i.e., line-coupling) pressure-broadening cross sections are presented. Calculations were done for CO perturbed by He at thermal collision energies using an accurate ab initio potential energy surface. Converged close coupling, i.e., numerically exact values, were obtained for coupling to the R(0) and R(2) lines. These were used to test the coupled states (CS) and infinite order sudden (IOS) approximate scattering methods. CS was found to be of quantitative accuracy (a few percent) and has been used to obtain coupling values for lines to R(10). IOS values are less accurate, but, owing to their simplicity, may nonetheless prove useful as has been recently demonstrated.

Redox process catalysed by growing crystal-strengite, FePO4,2H2O, crystallizing from solution with iron(II) and hydroxylamine

NASA Astrophysics Data System (ADS)

Lundager Madsen, Hans Erik

2014-09-01

In an attempt to grow pure crystals of the iron(II) phosphate vivianite, Fe3(PO4)2,8H2O, from a solution of Mohr's salt, Fe(NH4)2(SO4)2,6H2O, added to a solution of ammonium phosphate, hydroxylammonium chloride, NH3OHCl, was added to the iron(II) stock solution to eliminate oxidation of iron(II) by oxygen from the air. However, the effect turned out to be the opposite of the expected: whereas hydroxylamine reduces iron(III) in bulk solution, it acted as a strong oxidant in the presence of growing iron phosphate crystals, causing the crystallization of the iron(III) phosphate strengite, FePO4,2H2O, as the only solid phase. Evidently the crystal surface catalyses oxidation of iron(II) by hydroxylamine. The usual composite kinetics of spiral growth and surface nucleation was found. The surface-nucleation part yielded edge free energy λ in the range 12-45 pJ/m, virtually independent of temperature and in the range typical for phosphates of divalent metals. The scatter of values for λ presumably arises from contributions from different crystal forms to the overall growth rate. The low mean value points to strong adsorption of iron(II), which is subsequently oxidized at the crystal surface, forming strengite. The state of the system did not tend to thermodynamic equilibrium, but to a metastable state, presumably controlled by the iron(II) rich surface layer of the crystal. In addition to crystal growth, it was possible to measure nucleation kinetics by light scattering (turbidimetry). A point of transition from heterogeneous to homogeneous nucleation was found, and from the results for the homogeneous domain a rather precise value of crystal surface free energy γ=55 mJ/m2 was found. This is a relatively low value as well, indicating that the redox process plays a role already at the nucleation stage.

Surface photovoltage in exciton absorption range in CdS

NASA Technical Reports Server (NTRS)

Morawski, A.; Banisch, R.; Lagowski, J.

1977-01-01

The high resolution, intrinsic spectra of surface photovoltage are reported for semiconducting n-type CdS single crystals. At reduced temperatures (120-160 K) the spectra exhibit three sharp maxima due to A, B and C free exciton transitions. Energy positions of these lines and valence band parameters (spin-orbit and crystal field splittings) estimated from surface photovoltage are in good agreement with values obtained by other methods. The excitonic transitions are very sensitive to surface treatment, i.e. polishing, etching, background illumination and surface doping. The mechanism of direct interaction of free excitons with surface states is proposed to explain exciton lines in surface photovoltage.

Newton’s Rotating Water Bucket: A Simple Model

DTIC Science & Technology

2013-01-01

surface of the water must be an equipotential relative to the sum of the gravitational and centrifugal potential energies [9].) The value of z0 can be...twisted and the bucket is then released, it begins to spin and the surface of the water acquires a paraboloidal shape. In this paper, the parabolic...adopts a curved surface . Ernst Mach, for example, postulated that the parabolic shape must be due to the existence of matter in the universe

The effect of defect types on the electronic and optical properties of graphene nanoflakes physisorbed by ionic liquids.

PubMed

Shakourian-Fard, Mehdi; Kamath, Ganesh

2017-02-08

Defect engineering and non-covalent interaction strategies allow for dramatically tuning the optoelectronic properties of graphene. Using ab initio density functional theory (M06-2X/cc-pVDZ), we find that the nature of defects on the graphene nanoflakes (GNFs) and the size of defective GNF (DGNF) surfaces affect the binding energy (ΔE b ) of ionic liquids (ILs) and the UV-Vis absorption spectra of DGNFIL complexes. Further, our results indicate that increasing the size of DGNFs affects the geometrical structure of the surfaces and increases the binding energy of ILs by about 10%. Analysis based on AIM and EDA shows that the interactions between ILs and DGNFs are non-covalent in nature (dispersion energy being dominant) and associated with charge transfer between the IL and nanoflakes. A comparison between the ΔE b values of ILs on DGNFs, GNFs, and h-BN nanoflakes (h-BNNF) shows that the presence of defects on the GNF surfaces increases the binding energy values as follows: DGNFIL > pristine GNFIL > h-BNNFIL. Our calculations indicate that increasing the size of DGNF surfaces leads to a decrease in the HOMO-LUMO energy gap (E g ) of the DGNF surfaces. Orbital energy and density of state calculations show that the E g of DV(SW)-GNFs decreases upon IL adsorption and their Fermi energy level is shifted depending on the type of IL, thus enabling better conductivity. Reactivity descriptors generally indicate that the chemical potential (μ) and chemical hardness (η) of nanoflakes decrease upon IL adsorption, whereas the electrophilicity index (ω) increases. The UV-Vis absorption spectrum of DV-GNF and SW-GNF shows four bands in the visible spectrum which correspond to π → π* transitions with the absorption bands of SW-GNF appearing at higher wavelengths than those of DV-GNF. The most intense absorption bands in DV-GNF (λ = 348 nm) and SW-GNF (λ = 375 nm) are associated with electronic transitions HOMO-1 → LUMO+2 and HOMO → LUMO+1, respectively. In addition, these absorption bands undergo a red-shift by both increasing the size of the DV(SW)-GNF surfaces and IL adsorption. We also observe that the energy gaps and absorption spectra can be altered by varying the defect types and the type of IL adsorbate, where the defect types affect the spectral shapes of the bands and adsorbates at the first absorption peak, thus having potential application for light-emitting devices.

The influence of repellent coatings on surface free energy of glass plate and cotton fabric

NASA Astrophysics Data System (ADS)

Černe, Lidija; Simončič, Barbara; Željko, Matjaž

2008-08-01

The aim of this research was to determine the influence of chemical finishes on the surface properties of glass plate, considered as a model homogeneous smooth surface and cotton fabric as a non-ideal heterogeneous rough surface. Microscopic slides and 100% cotton fabric in plain weave were coated with fluorocarbon polymers (FCP), paraffin waxes with zirconium salts (PWZ), methylolmelamine derivatives (MMD), polysiloxanes with side alkyldimethylammonium groups (PSAAC) and aminofunctional polysiloxanes (AFPS). From the goniometer contact angle measurements of different liquids, the surface free energy of the coated glass plates was calculated according to approaches by Owens-Wendt-Kaelble, Wu, van Oss-Chaudhury-Good, and Li-Neumann-Kwok. The results showed that all the coatings decreased the surface free energy of the substrate, which was also influenced by the liquid combination and the theoretical approach used. In spite of the fact that the liquid contact angles were much higher on the coated fabric samples than on glass plates and resulted in the lower values of work of adhesion, a very good correlation between the coatings deposited on both substrates was obtained. The presence of repellent coatings FCP, PWZ and MMD converted the solid surface from polar to highly apolar by masking the functional groups of glass and cellulose. PSAAC and AFPS coatings did not decrease the solid surface free energy to such an extent as the former three coatings due to their monopolar character.

Investigation on preferably oriented abnormal growth of CdSe nanorods along (0002) plane synthesized by henna leaf extract-mediated green synthesis

NASA Astrophysics Data System (ADS)

Iyyappa Rajan, P.; Judith Vijaya, J.; Jesudoss, S. K.; Kaviyarasu, K.; Lee, Seung-Cheol; John Kennedy, L.; Jothiramalingam, R.; Al-Lohedan, Hamad A.; Mahamad Abdullah, M.

2018-03-01

The theme of this work is to highlight the significance of green plant extracts in the synthesis of nanostructures. In asserting this statement, herein, we report our obtained results on the synthesis of hexagonal CdSe nanorods preferably oriented along (0002) plane through henna leaf extract-mediated reaction along with a discussion about the structural, morphological and optical properties of the synthesized nanorods. The possible mechanism for the synthesis of CdSe nanorods was explored. The formation of nanorods along (0002) plane was confirmed by the relatively high intensity of the (0002) peak in X-ray diffraction pattern. To account for the experimentally realistic condition, we have calculated the surface energies of hexagonal CdSe surface slabs along the low indexed (0002), (10 1 ¯ 0 ) and (11 2 ¯ 0 ) plane surfaces using density functional theory approach and the calculated surface energy value for (0002) surface is 802.7 mJ m-2, which is higher than (11 2 ¯ 0 ) and (10 1 ¯ 0 ) surfaces. On realizing the calculated surface energies of these slabs, we determined that the combination of (11 2 ¯ 0 ) and (10 1 ¯ 0 ) planes with lower surface energies will lead to the formation of CdSe nanorods growth along (0002) orientation. Finally, we argue that the design of new greener route for the synthesis of novel functional nanomaterials is highly desired.

Implementing displacement damage calculations for electrons and gamma rays in the Particle and Heavy-Ion Transport code System

NASA Astrophysics Data System (ADS)

Iwamoto, Yosuke

2018-03-01

In this study, the Monte Carlo displacement damage calculation method in the Particle and Heavy-Ion Transport code System (PHITS) was improved to calculate displacements per atom (DPA) values due to irradiation by electrons (or positrons) and gamma rays. For the damage due to electrons and gamma rays, PHITS simulates electromagnetic cascades using the Electron Gamma Shower version 5 (EGS5) algorithm and calculates DPA values using the recoil energies and the McKinley-Feshbach cross section. A comparison of DPA values calculated by PHITS and the Monte Carlo assisted Classical Method (MCCM) reveals that they were in good agreement for gamma-ray irradiations of silicon and iron at energies that were less than 10 MeV. Above 10 MeV, PHITS can calculate DPA values not only for electrons but also for charged particles produced by photonuclear reactions. In DPA depth distributions under electron and gamma-ray irradiations, build-up effects can be observed near the target's surface. For irradiation of 90-cm-thick carbon by protons with energies of more than 30 GeV, the ratio of the secondary electron DPA values to the total DPA values is more than 10% and increases with an increase in incident energy. In summary, PHITS can calculate DPA values for all particles and materials over a wide energy range between 1 keV and 1 TeV for electrons, gamma rays, and charged particles and between 10-5 eV and 1 TeV for neutrons.

A continuum model for meltwater flow through compacting snow

NASA Astrophysics Data System (ADS)

Meyer, Colin R.; Hewitt, Ian J.

2017-12-01

Meltwater is produced on the surface of glaciers and ice sheets when the seasonal energy forcing warms the snow to its melting temperature. This meltwater percolates into the snow and subsequently runs off laterally in streams, is stored as liquid water, or refreezes, thus warming the subsurface through the release of latent heat. We present a continuum model for the percolation process that includes heat conduction, meltwater percolation and refreezing, as well as mechanical compaction. The model is forced by surface mass and energy balances, and the percolation process is described using Darcy's law, allowing for both partially and fully saturated pore space. Water is allowed to run off from the surface if the snow is fully saturated. The model outputs include the temperature, density, and water-content profiles and the surface runoff and water storage. We compare the propagation of freezing fronts that occur in the model to observations from the Greenland Ice Sheet. We show that the model applies to both accumulation and ablation areas and allows for a transition between the two as the surface energy forcing varies. The largest average firn temperatures occur at intermediate values of the surface forcing when perennial water storage is predicted.

Surface Properties of PEMFC Gas Diffusion Layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

WoodIII, David L; Rulison, Christopher; Borup, Rodney

2010-01-01

The wetting properties of PEMFC Gas Diffusion Layers (GDLs) were quantified by surface characterization measurements and modeling of material properties. Single-fiber contact-angle and surface energy (both Zisman and Owens-Wendt) data of a wide spectrum of GDL types is presented to delineate the effects of hydrophobic post-processing treatments. Modeling of the basic sessile-drop contact angle demonstrates that this value only gives a fraction of the total picture of interfacial wetting physics. Polar forces are shown to contribute 10-20 less than dispersive forces to the composite wetting of GDLs. Internal water contact angles obtained from Owens-Wendt analysis were measured at 13-19 highermore » than their single-fiber counterparts. An inverse relationship was found between internal contact angle and both Owens-Wendt surface energy and % polarity of the GDL. The most sophisticated PEMFC mathematical models use either experimentally measured capillary pressures or the standard Young-Laplace capillary-pressure equation. Based on the results of the Owens-Wendt analysis, an advancement to the Young-Laplace equation is proposed for use in these mathematical models, which utilizes only solid surface energies and fractional surface coverage of fluoropolymer. Capillary constants for the spectrum of analyzed GDLs are presented for the same purpose.« less

Calculation of a solid/liquid surface tension: A methodological study

NASA Astrophysics Data System (ADS)

Dreher, T.; Lemarchand, C.; Soulard, L.; Bourasseau, E.; Malfreyt, P.; Pineau, N.

2018-01-01

The surface tension of a model solid/liquid interface constituted of a graphene sheet surrounded by liquid methane has been computed using molecular dynamics in the Kirkwood-Buff formalism. We show that contrary to the fluid/fluid case, the solid/liquid case can lead to different structurations of the first fluid layer, leading to significantly different values of surface tension. Therefore we present a statistical approach that consists in running a series of molecular simulations of similar systems with different initial conditions, leading to a distribution of surface tensions from which an average value and uncertainty can be extracted. Our results suggest that these distributions converge as the system size increases. Besides we show that surface tension is not particularly sensitive to the choice of the potential energy cutoff and that long-range corrections can be neglected contrary to what we observed in the liquid/vapour interfaces. We have not observed the previously reported commensurability effect.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hayat, T.; Nonlinear Analysis and Applied Mathematics; Muhammad, Taseer

Development of human society greatly depends upon solar energy. Heat, electricity and water from nature can be obtained through solar power. Sustainable energy generation at present is a critical issue in human society development. Solar energy is regarded one of the best sources of renewable energy. Hence the purpose of present study is to construct a model for radiative effects in three-dimensional of nanofluid. Flow of second grade fluid by an exponentially stretching surface is considered. Thermophoresis and Brownian motion effects are taken into account in presence of heat source/sink and chemical reaction. Results are derived for the dimensionless velocities,more » temperature and concentration. Graphs are plotted to examine the impacts of physical parameters on the temperature and concentration. Numerical computations are presented to examine the values of skin-friction coefficients, Nusselt and Sherwood numbers. It is observed that the values of skin-friction coefficients are more for larger values of second grade parameter. Moreover the radiative effects on the temperature and concentration are quite reverse.« less

Estimation of equilibrium surface precipitation constants for trivalent metal sorption onto hydrous ferric oxide and calcite

NASA Astrophysics Data System (ADS)

Ragavan, Anpalaki J.; Adams, Dean V.

2009-06-01

Equilibrium constants for modeling surface precipitation of trivalent metal cations ( M) onto hydrous ferric oxide and calcite were estimated from linear correlations of standard state Gibbs free energies of formation, ( ΔGf,MvX(ss)0) of the surface precipitates. The surface precipitation reactions were derived from Farley et. al. [K.J. Farley, D.A. Dzombak, F.M.M. Morel, J. Colloid Interface Sci. 106 (1985) 226] surface precipitation model, which are based on surface complexation model coupled with solid solution representation for surface precipitation on the solid surface. The ΔGf,MvX(ss)0 values were correlated through the following linear free energy relations ΔGf,M(OH)3(ss)0-791.70r=0.1587ΔGn,M0-1273.07 and ΔGf,M2(CO3)3(ss)0-197.241r=0.278ΔGn,M0-1431.27 where 'ss' stands for the end-member solid component of surface precipitate, ΔGf,MvX(ss)0 is in kJ/mol, r is the Shannon-Prewitt radius of M in a given coordination state (nm), and ΔGn,M0 is the non-solvation contribution to the Gibbs free energy of formation of the aqueous M ion. Results indicate that the above surface precipitation correlations are useful tools where experimental data are not available.

Excess Li-Ion Storage on Reconstructed Surfaces of Nanocrystals To Boost Battery Performance

DOE PAGES

Duan, Yandong; Zhang, Bingkai; Zheng, Jiaxin; ...

2017-08-03

Because of their enhanced kinetic properties, nanocrystallites have received much attention as potential electrode materials for energy storage. However, because of the large specific surface areas of nanocrystallites, they usually suffer from decreased energy density, cycling stability, and effective electrode capacity. Here, in this work, we report a size-dependent excess capacity beyond theoretical value (170 mA h g -1) by introducing extra lithium storage at the reconstructed surface in nanosized LiFePO 4 (LFP) cathode materials (186 and 207 mA h g -1 in samples with mean particle sizes of 83 and 42 nm, respectively). Moreover, this LFP composite also showsmore » excellent cycling stability and high rate performance. Our multimodal experimental characterizations and ab initio calculations reveal that the surface extra lithium storage is mainly attributed to the charge passivation of Fe by the surface C–O–Fe bonds, which can enhance binding energy for surface lithium by compensating surface Fe truncated symmetry to create two types of extra positions for Li-ion storage at the reconstructed surfaces. Such surface reconstruction nanotechnology for excess Li-ion storage makes full use of the large specific surface area of the nanocrystallites, which can maintain the fast Li-ion transport and greatly enhance the capacity. Finally, this discovery and nanotechnology can be used for the design of high-capacity and efficient lithium ion batteries.« less

Excess Li-Ion Storage on Reconstructed Surfaces of Nanocrystals To Boost Battery Performance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duan, Yandong; Zhang, Bingkai; Zheng, Jiaxin

Because of their enhanced kinetic properties, nanocrystallites have received much attention as potential electrode materials for energy storage. However, because of the large specific surface areas of nanocrystallites, they usually suffer from decreased energy density, cycling stability, and effective electrode capacity. Here, in this work, we report a size-dependent excess capacity beyond theoretical value (170 mA h g -1) by introducing extra lithium storage at the reconstructed surface in nanosized LiFePO 4 (LFP) cathode materials (186 and 207 mA h g -1 in samples with mean particle sizes of 83 and 42 nm, respectively). Moreover, this LFP composite also showsmore » excellent cycling stability and high rate performance. Our multimodal experimental characterizations and ab initio calculations reveal that the surface extra lithium storage is mainly attributed to the charge passivation of Fe by the surface C–O–Fe bonds, which can enhance binding energy for surface lithium by compensating surface Fe truncated symmetry to create two types of extra positions for Li-ion storage at the reconstructed surfaces. Such surface reconstruction nanotechnology for excess Li-ion storage makes full use of the large specific surface area of the nanocrystallites, which can maintain the fast Li-ion transport and greatly enhance the capacity. Finally, this discovery and nanotechnology can be used for the design of high-capacity and efficient lithium ion batteries.« less

Potential energy surface and quantum dynamics study of rovibrational states for HO(3) (X (2)A'').

PubMed

Braams, Bastiaan J; Yu, Hua-Gen

2008-06-07

An analytic potential energy surface has been constructed by fitting to about 28 thousand energy points for the electronic ground-state (X (2)A'') of HO(3). The energy points are calculated using a hybrid density functional HCTH and a large basis set aug-cc-pVTZ, i.e., a HCTH/aug-cc-pVTZ density functional theory (DFT) method. The DFT calculations show that the trans-HO(3) isomer is the global minimum with a potential well depth of 9.94 kcal mol(-1) with respect to the OH + O(2) asymptote. The equilibrium geometry of the cis-HO(3) conformer is located 1.08 kcal mol(-1) above that of the trans-HO(3) one with an isomerization barrier of 2.41 kcal mol(-1) from trans- to cis-HO(3). By using this surface, a rigorous quantum dynamics (QD) study has been carried out for computing the rovibrational energy levels of HO(3). The calculated results determine a dissociation energy of 6.15 kcal mol(-1), which is in excellent agreement with the experimental value of Lester et al. [J. Phys. Chem. A, 2007, 111, 4727.].

Analytical ab initio potential-energy surfaces for the ground and the first singlet excited states of HeH 2

NASA Astrophysics Data System (ADS)

Farantos, Stavros C.; Murrell, J. N.; Carter, S.

1984-07-01

Analytical potential-energy surfaces have been constructed for the ground and the first excited states of HeH 2. The functions fit ab initio MRD CI calculations with standard deviations of 0.05 and 0.13 eV for the ground and the excited surface respectively. Classical trajectory calculations for collisions of 4Hc with HD(B 1Σ u+, υ = 3, J = 2) at the temperature T = 297 K yields the electronic quenching cross section σ Q = 6.5 A 2 and the vibrational cross section σ 3→2 = 3.8 A 2. The results are in qualitative agreement with the experimental values of Fink, Akins and Moore.

SSE Temporarily Unavailable

Atmospheric Science Data Center

2013-09-08

... SSE, POWER, and MY NASA DATA websites are public domain and free of charge. You may use them in your research, publications, and ... dataset -> Atmosphere -> Surface Meteorology and Solar Energy . Here you can select the Monthly or Annual values for various ...

Scattering of surface water waves involving semi-infinite floating elastic plates on water of finite depth

NASA Astrophysics Data System (ADS)

Chakrabarti, Aloknath; Mohapatra, Smrutiranjan

2013-09-01

Two problems of scattering of surface water waves involving a semi-infinite elastic plate and a pair of semi-infinite elastic plates, separated by a gap of finite width, floating horizontally on water of finite depth, are investigated in the present work for a two-dimensional time-harmonic case. Within the frame of linear water wave theory, the solutions of the two boundary value problems under consideration have been represented in the forms of eigenfunction expansions. Approximate values of the reflection and transmission coefficients are obtained by solving an over-determined system of linear algebraic equations in each problem. In both the problems, the method of least squares as well as the singular value decomposition have been employed and tables of numerical values of the reflection and transmission coefficients are presented for specific choices of the parameters for modelling the elastic plates. Our main aim is to check the energy balance relation in each problem which plays a very important role in the present approach of solutions of mixed boundary value problems involving Laplace equations. The main advantage of the present approach of solutions is that the results for the values of reflection and transmission coefficients obtained by using both the methods are found to satisfy the energy-balance relations associated with the respective scattering problems under consideration. The absolute values of the reflection and transmission coefficients are presented graphically against different values of the wave numbers.

Work-function calculations for a symmetrical total-charge-density profile at the metallic surface

NASA Astrophysics Data System (ADS)

Wojciechowski, K. F.; Sobańska-Nowotnik, M.

1983-07-01

It is shown that, if the total-charge-density profile nT(x) at the surface of jellium satisfies the Budd-Vannimenus constraint and also is a symmetrical function of x, relative to the ordinate axis, then the work-function variation versus the Wigner-Seitz radius rs does not depend on the form of nT(x). Also the simple linear-density profile is used to calculate the work function by application of the variational principle for the energy, including the first and second density-gradient corrections to the kinetic energy and the first gradient correction to the exchange and correlation energy. The results for the work function are in good agreement with the polycrystalline values for low-density metals.

Copoly(Imide Siloxane) Abhesive Materials with Varied Siloxane Oligomer Length

NASA Technical Reports Server (NTRS)

Wohl, Christopher J.; Atkins, Brad M.; Belcher, Marcus A.; Connell, John W.

2010-01-01

Incorporation of PDMS moieties into a polyimide matrix lowered the surface energy resulting in enhanced adhesive interactions. Polyimide siloxane materials were generated using amine-terminated PDMS oligomers of different lengths to study changes in surface migration behavior, phase segregation, mechanical, thermal, and optical properties. These materials were characterized using contact angle goniometry, tensile testing, and differential scanning calorimetry. The surface migration behavior of the PDMS component depended upon the siloxane molecular weight as indicated by distinct relationships between PDMS chain length and advancing water contact angles. Similar correlations were observed for percent elongation values obtained from tensile testing, while the addition of PDMS reduced the modulus. High fidelity topographical modification via laser ablation patterning further reduced the polyimide siloxane surface energy. Initial particulate adhesion testing experiments demonstrated that polyimide siloxane materials exhibited greater abhesive interactions relative to their respective homopolyimides.

Quantifying the Terrestrial Surface Energy Fluxes Using Remotely-Sensed Satellite Data

NASA Astrophysics Data System (ADS)

Siemann, Amanda Lynn

The dynamics of the energy fluxes between the land surface and the atmosphere drive local and regional climate and are paramount to understand the past, present, and future changes in climate. Although global reanalysis datasets, land surface models (LSMs), and climate models estimate these fluxes by simulating the physical processes involved, they merely simulate our current understanding of these processes. Global estimates of the terrestrial, surface energy fluxes based on observations allow us to capture the dynamics of the full climate system. Remotely-sensed satellite data is the source of observations of the land surface which provide the widest spatial coverage. Although net radiation and latent heat flux global, terrestrial, surface estimates based on remotely-sensed satellite data have progressed, comparable sensible heat data products and ground heat flux products have not progressed at this scale. Our primary objective is quantifying and understanding the terrestrial energy fluxes at the Earth's surface using remotely-sensed satellite data with consistent development among all energy budget components [through the land surface temperature (LST) and input meteorology], including validation of these products against in-situ data, uncertainty assessments, and long-term trend analysis. The turbulent fluxes are constrained by the available energy using the Bowen ratio of the un-constrained products to ensure energy budget closure. All final products are within uncertainty ranges of literature values, globally. When validated against the in-situ estimates, the sensible heat flux estimates using the CFSR air temperature and constrained with the products using the MODIS albedo produce estimates closest to the FLUXNET in-situ observations. Poor performance over South America is consistent with the largest uncertainties in the energy budget. From 1984-2007, the longwave upward flux increase due to the LST increase drives the net radiation decrease, and the decrease in the available energy balances the decrease in the sensible heat flux. These datasets are useful for benchmarking climate models and LSM output at the global annual scale and the regional scale subject to the regional uncertainties and performance. Future work should improve the input data, particularly the temperature gradient and Zilitinkevich empirical constant, to reduce uncertainties.

Properties of hydrophobic free energy found by gas–liquid transfer

PubMed Central

Baldwin, Robert L.

2013-01-01

The hydrophobic free energy in current use is based on transfer of alkane solutes from liquid alkanes to water, and it has been argued recently that these values are incorrect and should be based instead on gas–liquid transfer data. Hydrophobic free energy is measured here by gas–liquid transfer of hydrocarbon gases from vapor to water. The new definition reduces more than twofold the values of the apparent hydrophobic free energy. Nevertheless, the newly defined hydrophobic free energy is still the dominant factor that drives protein folding as judged by ΔCp, the change in heat capacity, found from the free energy change for heat-induced protein unfolding. The ΔCp for protein unfolding agrees with ΔCp values for solvating hydrocarbon gases and disagrees with ΔCp for breaking peptide hydrogen bonds, which has the opposite sign. The ΔCp values for the enthalpy of liquid–liquid and gas–liquid transfer are similar. The plot of free energy against the apparent solvent-exposed surface area is given for linear alkanes, but only for a single conformation, the extended conformation, of these flexible-chain molecules. The ability of the gas–liquid hydrophobic factor to predict protein stability is tested and reasonable agreement is found, using published data for the dependences on temperature of the unfolding enthalpy of ribonuclease T1 and the solvation enthalpies of the nonpolar and polar groups. PMID:23319615

Properties of hydrophobic free energy found by gas-liquid transfer.

PubMed

Baldwin, Robert L

2013-01-29

The hydrophobic free energy in current use is based on transfer of alkane solutes from liquid alkanes to water, and it has been argued recently that these values are incorrect and should be based instead on gas-liquid transfer data. Hydrophobic free energy is measured here by gas-liquid transfer of hydrocarbon gases from vapor to water. The new definition reduces more than twofold the values of the apparent hydrophobic free energy. Nevertheless, the newly defined hydrophobic free energy is still the dominant factor that drives protein folding as judged by ΔCp, the change in heat capacity, found from the free energy change for heat-induced protein unfolding. The ΔCp for protein unfolding agrees with ΔCp values for solvating hydrocarbon gases and disagrees with ΔCp for breaking peptide hydrogen bonds, which has the opposite sign. The ΔCp values for the enthalpy of liquid-liquid and gas-liquid transfer are similar. The plot of free energy against the apparent solvent-exposed surface area is given for linear alkanes, but only for a single conformation, the extended conformation, of these flexible-chain molecules. The ability of the gas-liquid hydrophobic factor to predict protein stability is tested and reasonable agreement is found, using published data for the dependences on temperature of the unfolding enthalpy of ribonuclease T1 and the solvation enthalpies of the nonpolar and polar groups.

Facile preparation in two steps of highly hydrophobic coatings on polypropylene surface

NASA Astrophysics Data System (ADS)

Petcu, Cristian; Nistor, Cristina Lavinia; Purcar, Violeta; Cinteză, Ludmila Otilia; Spătaru, Cătălin-Ilie; Ghiurea, Marius; Ianchiş, Raluca; Anastasescu, Mihai; Stoica, Mihai

2015-08-01

Monolayer and bilayer coatings deposited on polypropylene (PP) surface were prepared by sol-gel process at room temperature. Monolayer coatings were produced from sol-gel acidic solutions, containing tetraethylorthosilicate (TEOS) and different co-precursors such as phenyltriethoxysilane (PhTES), octylmethyldimethoxysilane (OMDMS) and dodecyltriethoxysilane (DOTES). Bilayer coatings consist of one layer prepared in a similar way described for monolayer coatings, followed by a second layer, obtained from fluorinated silica nanoparticles dispersion. The fluorinated group has been confirmed by the presence of Csbnd F bonds along with network Sisbnd Osbnd Si vibrational mode. Water contact angle values registered for bilayer-coated polypropylene are higher, comparing with the reference (pristine PP) and with the monolayer-coated substrate, and varies as a function of the hydrophobic functional groups of the silica co-precursors: phenyl < octyl < dodecyl. The fluorooctyl functions lead to a significant decrease in the surface energy values for bilayer coating, with very small values of polar component.

First-principles study of metallic iron interfaces

NASA Astrophysics Data System (ADS)

Hung, A.; Yarovsky, I.; Muscat, J.; Russo, S.; Snook, I.; Watts, R. O.

2002-04-01

Adhesion between clean, bulk-terminated bcc Fe(1 0 0) and Fe(1 1 0) matched and mismatched surfaces was simulated within the theoretical framework of the density functional theory. The generalized-gradient spin approximation exchange-correlation functional was used in conjunction with a plane wave-ultrasoft pseudopotential representation. The structure and properties of bulk bcc Fe were calculated in order to establish the reliability of the methodology employed, as well as to determine suitably converged values of computational parameters to be used in subsequent surface calculations. Interfaces were modelled using a single supercell approach, with the interfacial separation distance manipulated by the size of vacuum separation between vertically adjacent surface cells. The adhesive energies at discrete interfacial separations were calculated for each interface and the resulting data fitted to the universal binding energy relation (UBER) of Rose et al. [Phys. Rev. Lett. 47 (1981) 675]. An interpretation of the values of the fitted UBER parameters for the four Fe interfaces studied is given. In addition, a discussion on the validity of the employed computational methodology is presented.

Quasilocal energy and surface geometry of Kerr spacetime

NASA Astrophysics Data System (ADS)

Yu, Chengjie; Liu, Jian-Liang

2017-04-01

We study the quasilocal energy (QLE) and the surface geometry for Kerr spacetime in the Boyer-Lindquist coordinates without taking the slow rotation approximation. We also consider in the region r ≤2 m , which is inside the ergosphere. For a certain region, r >rk(a ) , the Gaussian curvature of the surface with constant t , r is positive, and for r >√{3 }a the critical value of the QLE is positive. We found that the three curves: the outer horizon r =r+(a ), r =rk(a ) and r =√{3 }a intersect at the point a =√{3 }m /2 , which is the limit for the horizon to be isometrically embedded into R3. The numerical result indicates that the Kerr QLE is monotonically decreasing to the ADM m from the region inside the ergosphere to large r . Based on the second law of black hole dynamics, the QLE is increasing with respect to the irreducible mass Mir. From the results of Chen-Wang-Yau, we conclude that in a certain region, r >rh(a ), the critical value of the Kerr QLE is a global minimum.

A study of the Merritt Island, Florida sea breeze flow regimes and their effect on surface heat and moisture fluxes

NASA Technical Reports Server (NTRS)

Rubes, M. T.; Cooper, H. J.; Smith, E. A.

1993-01-01

Data collected during the Convective and Precipitation/Electrification Experiment were analyzed as part of an investigation of the sea breeze in the vicinity of Merritt Island, Florida. Analysis of near-surface divergence fields shows that the classical 24-hour oscillation in divergence over the island due to the direct sea breeze circulation is frequently disrupted and exhibits two distinct modes: the classical sea breeze pattern and deviations from that pattern. A comparison of clear day surface energy fluxes with fluxes on other days indicates that changes in magnitudes were dominated by the presence or absence of clouds. Non-classical sea breeze days tended to lose more available energy in the morning than classical sea breeze days due to earlier development of small cumulus over the island. A composite storm of surface winds, surface energy fluxes, rainfall, and satellite visible data was constructed. A spectral transmittance over the visible wavelengths for the cloud cover resulting from the composite storm was calculated. It is shown that pre-storm transmittances of 0.8 fall to values near 0.1 as the downdraft moves directly over the site. It is also found that under post-composite storm conditions of continuous clear sky days, 3.5 days are required to evaporate back into the atmosphere the latent heat energy lost to the surface by rainfall.

Understanding pH Effects on Trichloroethylene and Perchloroethylene Adsorption to Iron in Permeable Reactive Barriers for Groundwater Remediation.

PubMed

Luo, Jing; Farrell, James

2013-01-01

Metallic iron filings are becoming increasing used in permeable reactive barriers for remediating groundwater contaminated by chlorinated solvents. Understanding solution pH effects on rates of reductive dechlorination in permeable reactive barriers is essential for designing remediation systems that can meet treatment objectives under conditions of varying groundwater properties. The objective of this research was to investigate how the solution pH value affects adsorption of trichloroethylene (TCE) and perchloroethylene (PCE) on metallic iron surfaces. Because adsorption is first required before reductive dechlorination can occur, pH effects on halocarbon adsorption energies may explain pH effects on dechlorination rates. Adsorption energies for TCE and PCE were calculated via molecular mechanics simulations using the Universal force field and a self-consistent reaction field charge equilibration scheme. A range in solution pH values was simulated by varying the amount of atomic hydrogen adsorbed on the iron. The potential energies associated TCE and PCE complexes were dominated by electrostatic interactions, and complex formation with the surface was found to result in significant electron transfer from the iron to the adsorbed halocarbons. Adsorbed atomic hydrogen was found to lower the energies of TCE complexes more than those for PCE. Attractions between atomic hydrogen and iron atoms were more favorable when TCE versus PCE was adsorbed to the iron surface. These two findings are consistent with the experimental observation that changes in solution pH affect TCE reaction rates more than those for PCE.

Density functional theory study of nitrogen atoms and molecules interacting with Fe(1 1 1) surfaces

NASA Astrophysics Data System (ADS)

Nosir, M. A.; Martin-Gondre, L.; Bocan, G. A.; Díez Muiño, R.

2016-09-01

We present Density functional theory (DFT) calculations for the investigation of the structural relaxation of Fe(1 1 1), as well as for the study of the interaction of nitrogen atoms and molecules with this surface. We perform spin polarized DFT calculations using VASP (Vienna Ab-initio Simulation Package) code. We use the supercell approach and up to 19 slab layers for the relaxation of the Fe(1 1 1) surface. We find a contraction of the first two interlayer distances with a relative value of Δ12 = - 7.8 % and Δ23 = - 21.7 % with respect to the bulk reference. The third interlayer distance is however expanded with a relative change of Δ34 = 9.7 % . Early experimental studies of the surface relaxation using Low Energy Electron Diffraction (LEED) and Medium Energy Ion Scattering (MEIS) showed contradictory results, even on the relaxation general trend. Our current theoretical results support the LEED conclusions and are consistent qualitatively with other recent theoretical calculations. In addition, we study the interaction energy of nitrogen atoms and molecules on the Fe(1 1 1) surface. The nitrogen atoms are adsorbed in the hollow site of the unit cell, with an adsorption energy consistent with the one found in previous studies. In addition, we find the three molecularly adsorbed states that are observed experimentally. Two of them correspond to the adsorbed molecule oriented normal to the surface and a third one corresponds to the molecule adsorbed parallel to the surface. We conclude that our results are accurate enough to be used to build a full six-dimensional potential energy surface for the N2 system.

Surface shift of the occupied and unoccupied 4f levels of the rare-earth metals

NASA Astrophysics Data System (ADS)

Aldén, M.; Johansson, B.; Skriver, H. L.

1995-02-01

The surface energy shifts of the occupied and unoccupied 4f levels for the lanthanide metals have been calculated from first principles by means of a Green's-function technique within the tight-binding linear muffin-tin orbitals method. We use the concept of complete screening to identify the occupied and unoccupied 4f energy level shifts as the surface segregation energy of a 4fn-1 and 4fn+1 impurity atom, respectively, in a 4fn host metal. The calculations include both initial- and final-state effects and give values that are considerably lower than those measured on polycrystalline samples as well as those found in previous initial-state model calculations. The present theory agrees well with very recent high-resolution, single-crystal film measurements for Gd, Tb, Dy, Ho, Er, Tm, and Lu. We furthermore utilize the unique possibility offered by the lanthanide metals to clarify the roles played by the initial and the different final states of the core-excitation process, permitted by the fact that the so-called initial-state effect is identical upon 4f removal and 4f addition. Surface energy and work function calculations are also reported.

A new approach to estimating evaporation from lakes and reservoirs based on energy balance and remote sensing data

NASA Astrophysics Data System (ADS)

Majidi, Maysam; Sadeghi, Morteza; Shafiei, Mojtaba; Alizadeh, Amin; Farid, Alireza; Azad, Mohammadreza; Vazifedoust, Majid

2016-04-01

Estimating evaporation from water bodies such as lakes and reservoirs is commonly a difficult task, especially due to the lack of reliable and available ground data. Remote sensing (RS) data has shown a great potential for filling the gap. Nonetheless, interpretation of the RS data (e.g. optical reflectance, thermal emission, etc.) for estimating water evaporation has remained as a challenge. In this paper, we present a novel approach for estimating water evaporation based on satellite RS data and some readily measurable ground data. In the proposed approach, named as "Reference and Water surface Energy Balance (RWEB)", we define a reference surface and then solve the energy balance equation simultaneously for the reference surfaces and water surface. This approach was tested over the Doosti dam reservoir (north east of Iran) using whether station and RS data as well as water temperature measured biweekly along the study. Accuracy of the RWEB algorithm was examined by comparison to the standard "Bowen Ratio Energy Balance (BREB)" RS algorithm. The RMSD value of 0.047 mm/year indicated a good agreement between RWEB and BREB algorithms, while RWEB provides an easier-to-use approach regarding its required input variables.

Properties of natural and synthetic hydroxyapatite and their surface free energy determined by the thin-layer wicking method

NASA Astrophysics Data System (ADS)

Szcześ, Aleksandra; Yan, Yingdi; Chibowski, Emil; Hołysz, Lucyna; Banach, Marcin

2018-03-01

Surface free energy is one of the parameters accompanying interfacial phenomena, occurring also in the biological systems. In this study the thin layer wicking method was used to determine surface free energy and its components for synthetic hydroxyapatite (HA) and natural one obtained from pig bones. The Raman, FTIR and X-Ray photoelectron spectroscopy, X-ray diffraction techniques and thermal analysis showed that both samples consist of carbonated hydroxyapatite without any organic components. Surface free energy and its apolar and polar components were found to be similar for both investigated samples and equalled γSTOT = 52.4 mJ/m2, γSLW = 40.2 mJ/m2 and γSAB = 12.3 mJ/m2 for the synthetic HA and γSTOT = 54.6 mJ/m2, γSLW = 40.3 mJ/m2 and γSAB = 14.3 mJ/m2 for the natural one. Both HA samples had different electron acceptor (γs+) and electron donor (γs-) parameters. The higher value of the electron acceptor was found for the natural HA whereas the electron donor one was higher for the synthetic HA

Surface modification of montmorillonite on surface Acid-base characteristics of clay and thermal stability of epoxy/clay nanocomposites.

PubMed

Park, Soo-Jin; Seo, Dong-Il; Lee, Jae-Rock

2002-07-01

In this work, the effect of surface treatments on smectitic clay was investigated in surface energetics and thermal behaviors of epoxy/clay nanocomposites. The pH values, X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR) were used to analyze the effect of cation exchange on clay surface and the exfoliation phenomenon of clay interlayer. The surface energetics of clay and thermal properties of epoxy/clay nanocomposites were investigated in contact angles and thermogravimetric analysis (TGA), respectively. From the experimental results, the surface modification of clay by dodecylammonium chloride led to the increases in both distance between silicate layers of about 8 A and surface acid values, as well as in the electron acceptor component (gamma(+)(s)) of surface free energy, resulting in improved interfacial adhesion between basic (or electron donor) epoxy resins and acidic (electron acceptor) clay interlayers. Also, the thermal stability of nanocomposites was highly superior to pure epoxy resin due to the presence of the well-dispersed clay nanolayer, which has a barrier property in a composite system.

Location of the adsorption transition for lattice polymers

NASA Astrophysics Data System (ADS)

Madras, Neal

2017-02-01

We consider various lattice models of polymers: lattice trees, lattice animals, and self-avoiding walks. The polymer interacts with a surface (hyperplane), receiving an energy reward of β for each site in the surface. It is known that there is an adsorption transition at a critical value of β. We present a new proof of the result of Hammersley et al (1982 J. Phys. A: Math. Gen. 15 539-71) that the transition occurs at a strictly positive value of β when the surface is impenetrable, i.e. when the polymer is restricted to a half-space. In contrast, for a penetrable surface, it is an open problem to prove that the transition occurs at β =0 . We reduce this problem to proving that the fraction of N-site polymers whose span is less than N/{{log}2}N is not too small.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Uryupin, S A; Frolov, A A

We have developed a theory of generation of low-frequency radiation and surface waves under the pondermotive action of a femtosecond laser pulse irradiating a conductor along the normal and focused by a cylindrical lens. It is shown that for the chosen focusing method and specified values of laser pulse duration and flux density it is possible to significantly increase the total energy of both surface waves and low-frequency radiation. (terahertz radiation)

Relationships between aerodynamic roughness and land use and land cover in Baltimore, Maryland

USGS Publications Warehouse

Nicholas, F.W.; Lewis, J.E.

1980-01-01

Urbanization changes the radiative, thermal, hydrologic, and aerodynamic properties of the Earth's surface. Knowledge of these surface characteristics, therefore, is essential to urban climate analysis. Aerodynamic or surface roughness of urban areas is not well documented, however, because of practical constraints in measuring the wind profile in the presence of large buildings. Using an empirical method designed by Lettau, and an analysis of variance of surface roughness values calculated for 324 samples averaging 0.8 hectare (ha) of land use and land cover sample in Baltimore, Md., a strong statistical relation was found between aerodynamic roughness and urban land use and land cover types. Assessment of three land use and land cover systems indicates that some of these types have significantly different surface roughness characteristics. The tests further indicate that statistically significant differences exist in estimated surface roughness values when categories (classes) from different land use and land cover classification systems are used as surrogates. A Level III extension of the U.S. Geological Survey Level II land use and land cover classification system provided the most reliable results. An evaluation of the physical association between the aerodynamic properties of land use and land cover and the surface climate by numerical simulation of the surface energy balance indicates that changes in surface roughness within the range of values typical of the Level III categories induce important changes in the surface climate.

Properties of Diamond and Diamond-Like Clusters in Nanometric Dimensions

NASA Technical Reports Server (NTRS)

Halicioglu, Timur; Langhoff, Stephen R. (Technical Monitor)

1996-01-01

Variations in materials properties of small clusters of nanometric dimensions were investigated. Investigations were carried out for diamond and diamond-like particles in spherical shapes. Calculations were performed for clusters containing over 1000 carbon atoms. Results indicate that as the cluster size diminishes, (i) the average cohesive energy becomes weaker, (ii) the excess surface energy increases, and (iii) the value for stiffness decreases.

Structural, optical and thermal characterization of PVC/SnO2 nanocomposites

NASA Astrophysics Data System (ADS)

Taha, T. A.; Ismail, Z.; Elhawary, M. M.

2018-04-01

The structural, optical, and thermal properties of PVC/SnO2 nanocomposites were investigated. XRD patterns were used to explore the structures of these prepared samples. Optical UV-Vis measurements were analyzed to calculate the spectroscopic optical constants of the prepared PVC/SnO2 nanocomposites. Both direct and indirect optical band gaps decreased with increasing SnO2 content. The refractive index, high frequency dielectric constant, plasma frequency, and optical conductivity values increased with SnO2. The single oscillator energy increased from 5.64 to 10.97 eV and the dispersion energy increased from 6.35 to 19.80 eV with the addition of SnO2. The other optical parameters such as optical moments, single oscillator strength, volume energy loss, and surface energy loss were calculated for different SnO2 concentrations. Raman spectra of the PVC/SnO2 nanocomposite films revealed the characteristic vibrational modes of PVC and surface phonon modes of SnO2. The thermal stability of PVC/SnO2 nanocomposite films was studied using DTA and thermogravimetric analysis. The glass transition ( T g) values abruptly changed from 46 °C for PVC to an average value of 59 °C for the polymer films doped with 2.0, 4.0, and 6.0 wt% SnO2. The weight loss decreased as the SnO2 concentration increased in the temperature range of 350-500 °C, corresponding to enhanced thermal stability.

Energy theorem for (2+1)-dimensional gravity.

NASA Astrophysics Data System (ADS)

Menotti, P.; Seminara, D.

1995-05-01

We prove a positive energy theorem in (2+1)-dimensional gravity for open universes and any matter energy-momentum tensor satisfying the dominant energy condition. We consider on the space-like initial value surface a family of widening Wilson loops and show that the energy-momentum of the enclosed subsystem is a future directed time-like vector whose mass is an increasing function of the loop, until it reaches the value 1/4G corresponding to a deficit angle of 2π. At this point the energy-momentum of the system evolves, depending on the nature of a zero norm vector appearing in the evolution equations, either into a time-like vector of a universe which closes kinematically or into a Gott-like universe whose energy momentum vector, as first recognized by Deser, Jackiw, and 't Hooft (1984) is space-like. This treatment generalizes results obtained by Carroll, Fahri, Guth, and Olum (1994) for a system of point-like spinless particle, to the most general form of matter whose energy-momentum tensor satisfies the dominant energy condition. The treatment is also given for the anti-de Sitter (2+1)-dimensional gravity.

Albedo and land surface temperature shift in hydrocarbon seepage potential area, case study in Miri Sarawak Malaysia

NASA Astrophysics Data System (ADS)

Suherman, A.; Rahman, M. Z. A.; Busu, I.

2014-02-01

The presence of hydrocarbon seepage is generally associated with rock or mineral alteration product exposures, and changes of soil properties which manifest with bare development and stress vegetation. This alters the surface thermodynamic properties, changes the energy balance related to the surface reflection, absorption and emission, and leads to shift in albedo and LST. Those phenomena may provide a guide for seepage detection which can be recognized inexpensively by remote sensing method. District of Miri is used for study area. Available topographic maps of Miri and LANDSAT ETM+ were used for boundary construction and determination albedo and LST. Three land use classification methods, namely fixed, supervised and NDVI base classifications were employed for this study. By the intensive land use classification and corresponding statistical comparison was found a clearly shift on albedo and land surface temperature between internal and external seepage potential area. The shift shows a regular pattern related to vegetation density or NDVI value. In the low vegetation density or low NDVI value, albedo of internal area turned to lower value than external area. Conversely in the high vegetation density or high NDVI value, albedo of internal area turned to higher value than external area. Land surface temperature of internal seepage potential was generally shifted to higher value than external area in all of land use classes. In dense vegetation area tend to shift the temperature more than poor vegetation area.

An approach to enhance the conservation-compatibility of solar energy development.

PubMed

Cameron, D Richard; Cohen, Brian S; Morrison, Scott A

2012-01-01

The rapid pace of climate change poses a major threat to biodiversity. Utility-scale renewable energy development (>1 MW capacity) is a key strategy to reduce greenhouse gas emissions, but development of those facilities also can have adverse effects on biodiversity. Here, we examine the synergy between renewable energy generation goals and those for biodiversity conservation in the 13 M ha Mojave Desert of the southwestern USA. We integrated spatial data on biodiversity conservation value, solar energy potential, and land surface slope angle (a key determinant of development feasibility) and found there to be sufficient area to meet renewable energy goals without developing on lands of relatively high conservation value. Indeed, we found nearly 200,000 ha of lower conservation value land below the most restrictive slope angle (<1%); that area could meet the state of California's current 33% renewable energy goal 1.8 times over. We found over 740,000 ha below the highest slope angle (<5%)--an area that can meet California's renewable energy goal seven times over. Our analysis also suggests that the supply of high quality habitat on private land may be insufficient to mitigate impacts from future solar projects, so enhancing public land management may need to be considered among the options to offset such impacts. Using the approach presented here, planners could reduce development impacts on areas of higher conservation value, and so reduce trade-offs between converting to a green energy economy and conserving biodiversity.

An Approach to Enhance the Conservation-Compatibility of Solar Energy Development

PubMed Central

Cameron, D. Richard; Cohen, Brian S.; Morrison, Scott A.

2012-01-01

The rapid pace of climate change poses a major threat to biodiversity. Utility-scale renewable energy development (>1 MW capacity) is a key strategy to reduce greenhouse gas emissions, but development of those facilities also can have adverse effects on biodiversity. Here, we examine the synergy between renewable energy generation goals and those for biodiversity conservation in the 13 M ha Mojave Desert of the southwestern USA. We integrated spatial data on biodiversity conservation value, solar energy potential, and land surface slope angle (a key determinant of development feasibility) and found there to be sufficient area to meet renewable energy goals without developing on lands of relatively high conservation value. Indeed, we found nearly 200,000 ha of lower conservation value land below the most restrictive slope angle (<1%); that area could meet the state of California’s current 33% renewable energy goal 1.8 times over. We found over 740,000 ha below the highest slope angle (<5%) – an area that can meet California’s renewable energy goal seven times over. Our analysis also suggests that the supply of high quality habitat on private land may be insufficient to mitigate impacts from future solar projects, so enhancing public land management may need to be considered among the options to offset such impacts. Using the approach presented here, planners could reduce development impacts on areas of higher conservation value, and so reduce trade-offs between converting to a green energy economy and conserving biodiversity. PMID:22685568

Highly variable aerodynamic roughness length (z0) for a hummocky debris-covered glacier

NASA Astrophysics Data System (ADS)

Miles, Evan S.; Steiner, Jakob F.; Brun, Fanny

2017-08-01

The aerodynamic roughness length (z0) is an essential parameter in surface energy balance studies, but few literature values exist for debris-covered glaciers. We use microtopographic and aerodynamic methods to assess the spatial variability of z0 for Lirung Glacier, Nepal. We apply structure from motion to produce digital elevation models for three nested domains: five 1 m2 plots, a 21,300 m2 surface depression, and the lower 550,000 m2 of the debris-mantled tongue. Wind and temperature sensor towers were installed in the vicinity of the plots within the surface depression in October 2014. We calculate z0 according to a variety of transect-based microtopographic parameterizations for each plot, then develop a grid version of the algorithms by aggregating data from all transects. This grid approach is applied to the surface depression digital elevation model to characterize z0 spatial variability. The algorithms reproduce the same variability among transects and plots, but z0 estimates vary by an order of magnitude between algorithms. Across the study depression, results from different algorithms are strongly correlated. Using Monin-Obukov similarity theory, we derive z0 values from the meteorological data. Using different stability criteria, we derive median values of z0 between 0.03 m and 0.05 m, but with considerable uncertainty due to the glacier's complex topography. Considering estimates from these algorithms, results suggest that z0 varies across Lirung Glacier between ˜0.005 m (gravels) to ˜0.5 m (boulders). Future efforts should assess the importance of such variable z0 values in a distributed energy balance model.

Parameterizing atmosphere-land surface exchange for climate models with satellite data: A case study for the Southern Great Plains CART site

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, W.

High-resolution satellite data provide detailed, quantitative descriptions of land surface characteristics over large areas so that objective scale linkage becomes feasible. With the aid of satellite data, Sellers et al. and Wood and Lakshmi examined the linearity of processes scaled up from 30 m to 15 km. If the phenomenon is scale invariant, then the aggregated value of a function or flux is equivalent to the function computed from aggregated values of controlling variables. The linear relation may be realistic for limited land areas having no large surface contrasts to cause significant horizontal exchange. However, for areas with sharp surfacemore » contrasts, horizontal exchange and different dynamics in the atmospheric boundary may induce nonlinear interactions, such as at interfaces of land-water, forest-farm land, and irrigated crops-desert steppe. The linear approach, however, represents the simplest scenario, and is useful for developing an effective scheme for incorporating subgrid land surface processes into large-scale models. Our studies focus on coupling satellite data and ground measurements with a satellite-data-driven land surface model to parameterize surface fluxes for large-scale climate models. In this case study, we used surface spectral reflectance data from satellite remote sensing to characterize spatial and temporal changes in vegetation and associated surface parameters in an area of about 350 {times} 400 km covering the southern Great Plains (SGP) Cloud and Radiation Testbed (CART) site of the US Department of Energy`s Atmospheric Radiation Measurement (ARM) Program.« less

Influence of the Surface and Cloud Nonuniformities in the Solar Energy Fluxes in the Arctic

NASA Technical Reports Server (NTRS)

Rozwadowska, A.; Cahalan, R. F.; Einaudi, Franco (Technical Monitor)

2000-01-01

Solar energy fluxes reaching the surface and absorbed by it are basic components of the energy balance of the Arctic. They depend mainly on the solar zenith angle, a state of the atmosphere, especially the cloudiness, and the surface albedo. However, they can also be modified by variabilities in the surface albedo and cloud optical thickness. The surface of the Arctic can be highly nonuniform. The surface of the Arctic Ocean, which covers the huge part of the Arctic can be view as a mosaic of sea water, sea ice, snow and, in the melting period, melting ponds. In our paper, results are presented of Monte Carlo simulations of the expected influence of nonuniform cloud structure and nonuniform surface albedo on radiative fluxes at the Arctic surface. In particular, the plane parallel biases in the surface absorptance and atmospheric transmittance are studied. The bias is defined as the difference between the real absorptance or transmittance (i.e. nonuniform conditions) averaged over a given area, and the uniform or plane parallel case with the same mean cloud optical thickness and the same mean surface albedo. The dependence of the biases is analysed with respect to the following: domain averaged values of the cloud optical thickness and surface albedo, scales of their spatial variabilities, correlation between cloud optical thickness and cloud albedo variabilities, cloud height, and the solar zenith angle. Ranges of means and standard deviations of the input parameters typical of Arctic conditions are obtained from the SHEBA experiment.

Theoretical characterization of the surface composition of ruthenium nanoparticles in equilibrium with syngas

NASA Astrophysics Data System (ADS)

Cusinato, Lucy; Martínez-Prieto, Luis M.; Chaudret, Bruno; Del Rosal, Iker; Poteau, Romuald

2016-05-01

A deeper understanding of the relationship between experimental reaction conditions and the surface composition of nanoparticles is crucial in order to elucidate mechanisms involved in nanocatalysis. In the framework of the Fischer-Tropsch synthesis, a resolution of this complex puzzle requires a detailed understanding of the interaction of CO and H with the surface of the catalyst. In this context, the single- and co-adsorption of CO and H to the surface of a 1 nm ruthenium nanoparticle has been investigated with density functional theory. Using several indexes (d-band center, crystal overlap Hamilton population, density of states), a systematic analysis of the bond properties and of the electronic states has also been done, in order to bring an understanding of structure/property relationships at the nanoscale. The H : CO surface composition of this ruthenium nanoparticle exposed to syngas has been evaluated according to a thermodynamic model fed with DFT energies. Such ab initio thermodynamic calculations give access to the optimal H : CO coverage values under a wide range of experimental conditions, through the construction of free energy phase diagrams. Surprisingly, under the Fischer-Tropsch synthesis experimental conditions, and in agreement with new experiments, only CO species are adsorbed at the surface of the nanoparticle. These findings shed new light on the possible reaction pathways underlying the Fischer-Tropsch synthesis, and specifically the initiation of the reaction. It is finally shown that the joint knowledge of the surface composition and energy descriptors can help to identify possible reaction intermediates.A deeper understanding of the relationship between experimental reaction conditions and the surface composition of nanoparticles is crucial in order to elucidate mechanisms involved in nanocatalysis. In the framework of the Fischer-Tropsch synthesis, a resolution of this complex puzzle requires a detailed understanding of the interaction of CO and H with the surface of the catalyst. In this context, the single- and co-adsorption of CO and H to the surface of a 1 nm ruthenium nanoparticle has been investigated with density functional theory. Using several indexes (d-band center, crystal overlap Hamilton population, density of states), a systematic analysis of the bond properties and of the electronic states has also been done, in order to bring an understanding of structure/property relationships at the nanoscale. The H : CO surface composition of this ruthenium nanoparticle exposed to syngas has been evaluated according to a thermodynamic model fed with DFT energies. Such ab initio thermodynamic calculations give access to the optimal H : CO coverage values under a wide range of experimental conditions, through the construction of free energy phase diagrams. Surprisingly, under the Fischer-Tropsch synthesis experimental conditions, and in agreement with new experiments, only CO species are adsorbed at the surface of the nanoparticle. These findings shed new light on the possible reaction pathways underlying the Fischer-Tropsch synthesis, and specifically the initiation of the reaction. It is finally shown that the joint knowledge of the surface composition and energy descriptors can help to identify possible reaction intermediates. Electronic supplementary information (ESI) available: Energies, detailed description of the hapticity and of the bridging character of the surface ligands and geometries for isomers; additional phase diagrams (without ZPE corrections). See DOI: 10.1039/C6NR01191H

Behavior of pentacene initial nucleation on various dielectrics and its effect on carrier transport in organic field-effect transistor.

PubMed

Qi, Qiong; Yu, Aifang; Wang, Liangmin; Jiang, Chao

2010-11-01

The influence of dielectric surface energy on the initial nucleation and the growth of pentacene films as well as the electrical properties of the pentacene-based field-effect transistors are investigated. We have examined a range of organic and inorganic dielectrics with different surface energies, such as polycarbonate/SiO2, polystyrene/SiO2, and PMMA/SiO2 bi-layered dielectrics and also the bare SiO2 dielectric. Atomic force microscopy measurements of sub-monolayer and thick pentacene films indicated that the growth of pentacene film was in Stranski-Kranstanow growth mode on all the dielectrics. However, the initial nucleation density and the size of the first-layered pentacene islands deposited on different dielectrics are drastically influenced by the dielectric surface energy. With the increasing of the surface energy, the nucleation density increased and thus the average size of pentacene islands for the first mono-layer deposition decreased. The performance of fabricated pentacene-based thin film transistors was found to be highly related to nucleation density and the island size of deposited Pentacene film, and it had no relationship to the final particle size of the thick pentacene film. The field effect mobility of the thin film transistor could be achieved as high as 1.38 cm2Ns with on/off ratio over 3 x 10(7) on the PS/SiO2 where the lowest surface energy existed among all the dielectrics. For comparison, the values of mobility and on/off ratio were 0.42 cm2Ns and 1 x 10(6) for thin film transistor deposited directly on bare SiO2 having the highest surface energy.

Adhesion of protein residues to substituted (111) diamond surfaces: an insight from density functional theory and classical molecular dynamics simulations.

PubMed

Borisenko, Konstantin B; Reavy, Helen J; Zhao, Qi; Abel, Eric W

2008-09-15

Protein-repellent diamond coatings have great potential value for surface coatings on implants and surgical instruments. The design of these coatings relies on a fundamental understanding of the intermolecular interactions involved in the adhesion of proteins to surfaces. To get insight into these interactions, adhesion energies of glycine to pure and Si and N-doped (111) diamond surfaces represented as clusters were calculated in the gas phase, using density functional theory (DFT) at the B3LYP/6-31G* level. The computed adhesion energies indicated that adhesion of glycine to diamond surface may be modified by introducing additional elements into the surface. The adhesion was also found to induce considerable change in the conformation of glycine when compared with the lowest-energy conformer of the free molecule. In the Si and N-substituted diamond clusters, notable changes in the structures involving the substituents atoms when compared with smaller parent molecules, such as 1-methyl-1-silaadamantane and 1-azaadamantane, were detected. Adhesion free energy differences were estimated for a series of representative peptides (hydrophobic Phe-Gly-Phe, amphiphilic Arg-Gly-Phe, and hydrophilic Arg-Gly-Arg) to a (111) diamond surface substituted with different amounts of N, Si, or F, using molecular dynamics simulations in an explicit water environment employing a Dreiding force field. The calculations were in agreement with the DFT results in that adsorption of the studied peptides to diamond surface is influenced by introducing additional elements to the surface. It has been shown that, in general, substitution will enhance electrostatic interactions between a surface and surrounding water, leading to a weaker adhesion of the studied peptides.

Monte Carlo calculation model for heat radiation of inclined cylindrical flames and its application

NASA Astrophysics Data System (ADS)

Chang, Zhangyu; Ji, Jingwei; Huang, Yuankai; Wang, Zhiyi; Li, Qingjie

2017-07-01

Based on Monte Carlo method, a calculation model and its C++ calculating program for radiant heat transfer from an inclined cylindrical flame are proposed. In this model, the total radiation energy of the inclined cylindrical flame is distributed equally among a certain number of energy beams, which are emitted randomly from the flame surface. The incident heat flux on a surface is calculated by counting the number of energy beams which could reach the surface. The paper mainly studies the geometrical evaluation criterion for validity of energy beams emitted by inclined cylindrical flames and received by other surfaces. Compared to Mudan's formula results for a straight cylinder or a cylinder with 30° tilt angle, the calculated view factors range from 0.0043 to 0.2742 and the predicted view factors agree well with Mudan's results. The changing trend and values of incident heat fluxes computed by the model is consistent with experimental data measured by Rangwala et al. As a case study, incident heat fluxes on a gasoline tank, both the side and the top surface are calculated by the model. The heat radiation is from an inclined cylindrical flame generated by another 1000 m3 gasoline tank 4.6 m away from it. The cone angle of the flame to the adjacent oil tank is 45° and the polar angle is 0°. The top surface and the side surface of the tank are divided into 960 and 5760 grids during the calculation, respectively. The maximum incident heat flux on the side surface is 39.64 and 51.31 kW/m2 on the top surface. Distributions of the incident heat flux on the surface of the oil tank and on the ground around the fire tank are obtained, too.

Shapes and stability of algebraic nuclear models

NASA Technical Reports Server (NTRS)

Lopez-Moreno, Enrique; Castanos, Octavio

1995-01-01

A generalization of the procedure to study shapes and stability of algebraic nuclear models introduced by Gilmore is presented. One calculates the expectation value of the Hamiltonian with respect to the coherent states of the algebraic structure of the system. Then equilibrium configurations of the resulting energy surface, which depends in general on state variables and a set of parameters, are classified through the Catastrophe theory. For one- and two-body interactions in the Hamiltonian of the interacting Boson model-1, the critical points are organized through the Cusp catastrophe. As an example, we apply this Separatrix to describe the energy surfaces associated to the Rutenium and Samarium isotopes.

New ab initio potential surfaces and three-dimensional quantum dynamics for transition state spectroscopy in ozone photodissociation

NASA Astrophysics Data System (ADS)

Yamashita, Koichi; Morokuma, Keiji; Le Quéré, Frederic; Leforestier, Claude

1992-04-01

New ab initio potential energy surfaces (PESs) of the ground and B ( 1B 2) states of ozone have been calculated with the CASSCF-SECI/DZP method to describe the three-dimensional photodissociation process. The dissociation energy of the ground state and the vertical barrier height of the B PES are obtained to be 0.88 and 1.34 eV, respectively, in better agreement with the experimental values than the previous calculation. The photodissociation autocorrelation function, calculated on the new B PES, based on exact three-dimensional quantum dynamics, reproduces well the main recurrence feature extracted from the experimental spectra.

Energy Balance Bowen Ratio (EBBR) Handbook

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cook, D. R.

2016-01-01

The Energy Balance Bowen Ratio (EBBR) system produces 30-minute estimates of the vertical fluxes of sensible and latent heat at the local surface. Flux estimates are calculated from observations of net radiation, soil surface heat flux, and the vertical gradients of temperature and relative humidity (RH). Meteorological data collected by the EBBR are used to calculate bulk aerodynamic fluxes, which are used in the Bulk Aerodynamic Technique (BA) EBBR value-added product (VAP) to replace sunrise and sunset spikes in the flux data. A unique aspect of the system is the automatic exchange mechanism (AEM), which helps to reduce errors frommore » instrument offset drift.« less

Energy Balance Bowen Ratio Station (EBBR) Handbook

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cook, DR

2011-02-23

The energy balance Bowen ratio (EBBR) system produces 30-minute estimates of the vertical fluxes of sensible and latent heat at the local surface. Flux estimates are calculated from observations of net radiation, soil surface heat flux, and the vertical gradients of temperature and relative humidity (RH). Meteorological data collected by the EBBR are used to calculate bulk aerodynamic fluxes, which are used in the Bulk Aerodynamic Technique (BA) EBBR value-added product (VAP) to replace sunrise and sunset spikes in the flux data. A unique aspect of the system is the automatic exchange mechanism (AEM), which helps to reduce errors frommore » instrument offset drift.« less

Nanoscale Phase Stability Reversal During the Nucleation and Growth of Titanium Oxide Minerals

NASA Astrophysics Data System (ADS)

Hummmer, D. R.; Heaney, P. J.; Kubicki, J. D.; Kent, P. R.; Post, J. E.

2008-12-01

Fine-grained titanium oxide minerals are important in soils, where they affect a variety of geochemical processes. They are also industrially important as catalysts, pigments, food additives, and dielectrics. Recent research has indicated an apparent reversal of thermodynamic stability between TiO2 phases at the nanoscale thought to be caused by an increased contribution of surface energy to the total free energy. Time-resolved X-ray diffraction (XRD) experiments in which titanium oxides crystallize from aqueous TiCl4 solutions confirm that anatase, a metastable phase, is always the first phase to nucleate under our range of initial conditions. Rutile peaks are observed only minutes after the first appearance of anatase, after which anatase abundance slowly decreases while rutile continues to form. Whole pattern refinement of diffraction data reveals that lattice constants of both phases increase throughout the crystallization process. In addition, transmission electron microscope (TEM) observations and kinetic modeling indicate that anatase does not undergo a solid-state transformation to the rutile structure as once thought. Instead, anatase appears to re-dissolve and then feed the growth of already nucleated rutile nanocrystals. Density functional theory (DFT) calculations were employed to model 1, 2, and 3 nm particles of both mineral phases. The total surface energies calculated from these models did yield lower values for anatase than for rutile by 8-13 kJ/mol depending on particle size, indicating that surface free energy is sufficient to account for stability reversal. However, these whole-particle surface energies were much higher than the sum of energies of each particle's constituent crystallographic surfaces. We attribute the excess energy to defects associated with the edges and corners of nanoparticles, which are not present on a 2-D periodic surface. This previously unreported edge and corner energy may play a dominant role in the stability reversal of nanocrystalline titanium oxides, as well as other mineral systems susceptible to reversals in phase stability at the nanoscale.

The surface stability of Cr 2O 3 (0 0 0 1)

DOE PAGES

Cao, Shi; Wu, Ning; Echtenkamp, William; ...

2015-05-28

The surface of chromia (Cr 2O 3) has a surface electronic structure distinct from the bulk and a packing density distinct from the bulk. More than a demarcation between the solid and the vacuum, the surface differs from the bulk of chromia, not just because of a partial occupancy of chromium sites, but also because of an increased number of unoccupied surface oxygen sites (vacancy sites), evident in angle-resolved core level photoemission. In spite of the structural differences that exist at the surface, there is, as yet, no evidence that these complications affect the surface Debye temperature beyond the mostmore » simple of assumptions regarding the lower coordination of the surface. Using low-energy electron diffraction (LEED), the effective surface Debye temperature (similar to 490 K) is found to be lower than the bulk (similar to 645 K) Debye temperature of Cr 2O 3(0 0 0 1). This surface effective Debye temperature, indicative of vibrations along the surface normal, uncorrected for anharmonic effects, has a value reduced from the effective bulk Debye temperature yet close to the value root 2 expected from a simple mean field argument.« less

Encoding photonic angular momentum information onto surface plasmon polaritons with plasmonic lens.

PubMed

Liu, Aiping; Rui, Guanghao; Ren, Xifeng; Zhan, Qiwen; Guo, Guangcan; Guo, Guoping

2012-10-22

Both spin angular momentum (SAM) and orbital angular momentum (OAM) can be used to carry information in classical optics and quantum optics. In this paper, the encoding of angular momentum (AM) information of photons onto surface plasmon polaritons (SPPs) is demonstrated using a nano-ring plasmonic lens. Near-field energy distribution on the metal surface is measured using a near-field scanning optical microscope (NSOM) when the plasmonic lens is excited by photons with different combinations of SAM and OAM. It is found that both the SAM and OAM can influence the near field energy distribution of SPPs. More interestingly, numerical and experimental studies reveal that the energy distribution on the plasmonic lens surface is determined by the absolute value of the total AM. This gives direct evidences that SPPs can be encoded with the photonic SAM and OAM information simultaneously and the spin degeneracy of the photons can be removed using the interactions between photonic OAM and plasmonic lens. The findings are useful not only for the fundamental understanding of the photonic AM but also for the future design of plasmonic quantum optics devices and systems.

Effect of surface ionic screening on the polarization reversal scenario in ferroelectric thin films: Crossover from ferroionic to antiferroionic states

DOE PAGES

Morozovska, Anna N.; Eliseev, Eugene A.; Kurchak, Anatolii I.; ...

2017-12-08

Nonlinear electrostatic interaction between the surface ions of electrochemical nature and ferroelectric dipoles gives rise to the coupled ferroionic states in nanoscale ferroelectrics. Here, we investigated the role of the surface ions formation energy value on the polarization states and polarization reversal mechanisms, domain structure and corresponding phase diagrams of ferroelectric thin films. Using 3D finite elements modeling we analyze the distribution and hysteresis loops of ferroelectric polarization and ionic charge, and dynamics of the domain states. These calculations performed over large parameter space delineate the regions of single- and poly- domain ferroelectric, ferroionic, antiferroionic and non-ferroelectric states as amore » function of surface ions formation energy, film thickness, applied voltage and temperature. We further map the analytical theory for 1D system onto effective Landau-Ginzburg free energy and establish the correspondence between the 3D numerical and 1D analytical results. In conclusion, this approach allows performing the overview of the ferroionic system phase diagrams and exploring the specifics of switching and domain evolution phenomena.« less

Effect of surface ionic screening on the polarization reversal scenario in ferroelectric thin films: Crossover from ferroionic to antiferroionic states

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morozovska, Anna N.; Eliseev, Eugene A.; Kurchak, Anatolii I.

Nonlinear electrostatic interaction between the surface ions of electrochemical nature and ferroelectric dipoles gives rise to the coupled ferroionic states in nanoscale ferroelectrics. Here, we investigated the role of the surface ions formation energy value on the polarization states and polarization reversal mechanisms, domain structure and corresponding phase diagrams of ferroelectric thin films. Using 3D finite elements modeling we analyze the distribution and hysteresis loops of ferroelectric polarization and ionic charge, and dynamics of the domain states. These calculations performed over large parameter space delineate the regions of single- and poly- domain ferroelectric, ferroionic, antiferroionic and non-ferroelectric states as amore » function of surface ions formation energy, film thickness, applied voltage and temperature. We further map the analytical theory for 1D system onto effective Landau-Ginzburg free energy and establish the correspondence between the 3D numerical and 1D analytical results. In conclusion, this approach allows performing the overview of the ferroionic system phase diagrams and exploring the specifics of switching and domain evolution phenomena.« less

Surface-slip equations for multicomponent nonequilibrium air flow

NASA Technical Reports Server (NTRS)

Gupta, R. N.; Scott, C. D.; Moss, J. N.

1985-01-01

Equations are presented for the surface-slip (or jump) values of species concentration, pressure, velocity, and temperature in the low-Reynolds number, high-altitude flight regime of a space vehicle. The equations are obtained from closed form solutions of the mass, momentum, and energy flux equations using the Chapman-Enskog velocity distribution function. This function represents a solution of the Boltzmann equation in the Navier-Stokes approximation. The analysis, obtained for nonequilibrium multicomponent air flow, includes the finite-rate surface catalytic recombination and changes in the internal energy during reflection from the surface. Expressions for the various slip quantities were obtained in a form which can be employed in flowfield computations. A consistent set of equations is provided for multicomponent, binary, and single species mixtures. Expression is also provided for the finite-rate, species-concentration boundary condition for a multicomponent mixture in absence of slip.

Surface-slip equations for multicomponent, nonequilibrium air flow

NASA Technical Reports Server (NTRS)

Gupta, Roop N.; Scott, Carl D.; Moss, James N.; Goglia, Gene

1985-01-01

Equations are presented for the surface slip (or jump) values of species concentration, pressure, velocity, and temperature in the low-Reynolds-number, high-altitude flight regime of a space vehicle. These are obtained from closed-form solutions of the mass, momentum, and energy flux equations using the Chapman-Enskog velocity distribution function. This function represents a solution of the Boltzmann equation in the Navier-Stokes approximation. The analysis, obtained for nonequilibrium multicomponent air flow, includes the finite-rate surface catalytic recombination and changes in the internal energy during reflection from the surface. Expressions for the various slip quantities have been obtained in a form which can readily be employed in flow-field computations. A consistent set of equations is provided for multicomponent, binary, and single species mixtures. Expression is also provided for the finite-rate species-concentration boundary condition for a multicomponent mixture in absence of slip.

A conceptual design study of point focusing thin-film solar concentrators

NASA Technical Reports Server (NTRS)

1981-01-01

Candidates for reflector panel design concepts, including materials and configurations, were identified. The large list of candidates was screened and reduced to the five most promising ones. Cost and technical factors were used in making the final choices for the panel conceptual design, which was a stiffened steel skin substrate with a bonded, acrylic overcoated, aluminized polyester film reflective surface. Computer simulations were run for the concentrator optics using the selected panel design, and experimentally determined specularity and reflectivity values. Intercept factor curves and energy to the aperture curves were produced. These curves indicate that surface errors of 2 mrad (milliradians) or less would be required to capture the desired energy for a Brayton cycle 816 C case. Two test panels were fabricated to demonstrate manufacturability and optically tested for surface error. Surface errors in the range of 1.75 mrad and 2.2 mrad were measured.

Simulation of oceanic whitecaps and their reflectance characteristics in the short wavelength infrared.

PubMed

Schwenger, Frédéric; Repasi, Endre

2017-02-20

The knowledge of the spatial energy (or power) distribution of light beams reflected at the dynamic sea surface is of great practical interest in maritime environments. For the estimation of the light energy reflected into a specific spatial direction a lot of parameters need to be taken into account. Both whitecap coverage and its optical properties have a large impact upon the calculated value. In published literature, for applications considering vertical light propagation paths, such as bathymetric lidar, the reflectance of sea surface and whitecaps are approximated by constant values. For near-horizontal light propagation paths the optical properties of the sea surface and the whitecaps must be considered in greater detail. The calculated light energy reflected into a specific direction varies statistically and depends largely on the dynamics of the wavy sea surface and the dynamics of whitecaps. A 3D simulation of the dynamic sea surface populated with whitecaps is presented. The simulation considers the evolution of whitecaps depending on wind speed and fetch. The radiance calculation of the maritime scene (open sea/clear sky) populated with whitecaps is done in the short wavelength infrared spectral band. Wave hiding and shadowing, especially occurring at low viewing angles, are considered. The specular reflection of a light beam at the sea surface in the absence of whitecaps is modeled by an analytical statistical bidirectional reflectance distribution function (BRDF) of the sea surface. For whitecaps, a specific BRDF is used by taking into account their shadowing function. To ensure the credibility of the simulation, the whitecap coverage is determined from simulated image sequences for different wind speeds and compared to whitecap coverage functions from literature. The impact of whitecaps on the radiation balance for bistatic configuration of light source and receiver is calculated for a different incident (zenith/azimuth angles) of the light beam and is presented for two different wind speeds.

Experimental Study and Fractal Analysis on the Anisotropic Performance of Explosively Welded Interfaces of 304 Stainless Steel/245 Carbon Steel

NASA Astrophysics Data System (ADS)

Fu, Yanshu; Qiu, Yaohui; Li, Yulong

2018-03-01

The mechanical anisotropy of an explosive welding composite plate made of 304 stainless steel/245 steel was studied through shear experiments performed on explosively welded wavy interfaces along several orientation angles. The results indicated that the strength and the fracture energy of samples significantly varied with the orientation angles. The fracture surfaces of all samples were observed using a scanning electron microscope and through three-dimensional structure microscopy. The periodic features of all the fracture surfaces were clearly shown in different fracture modes. The fractal dimension of the fracture surfaces was calculated based on the fractal geometry by the box-counting method in MATLAB. The cohesive element model was used to analyze the fracture energy according to the physical dependence of the fractal dimension on thermodynamic entropy and interface separation energy. The fracture energy was an exponential function of the fractal dimension value, which was in good agreement with the experimental results. All results were validated for effective use in the application of anisotropy analysis to the welded interface and structural optimization of explosively welded composite plates.

Theoretical studies of potential energy surface and rotational spectra of Xe -H2O van der Waals complex

NASA Astrophysics Data System (ADS)

Wang, Lin; Yang, Minghui

2008-11-01

In this work we report an ab initio intermolecular potential energy surface and theoretical spectroscopic studies for Xe -H2O complex. The ab initio energies are calculated with CCSD(T) method and large basis sets (aug-cc-pVQZ for H and O and aug-cc-pVQZ-PP for Xe) augmented by a {3s3p2d2f1g} set of bond functions. This potential energy surface has a global minimum corresponding to a planar and nearly linear hydrogen bonded configuration with a well depth of 192.5cm-1 at intermolecular distance of 4.0Å, which is consistent with the previous determined potential by Wen and Jäger [J. Phys. Chem. A 110, 7560 (2006)]. The bound state calculations have been performed for the complex by approximating the water molecule as a rigid rotor. The theoretical rotational transition frequencies, isotopic shifts, nuclear quadrupole coupling constants, and structure parameters are in good agreement with the experimental observed values. The wavefunctions are analyzed to understand the dynamics of the ground and the first excited states.

Experimental Study and Fractal Analysis on the Anisotropic Performance of Explosively Welded Interfaces of 304 Stainless Steel/245 Carbon Steel

NASA Astrophysics Data System (ADS)

Fu, Yanshu; Qiu, Yaohui; Li, Yulong

2018-05-01

The mechanical anisotropy of an explosive welding composite plate made of 304 stainless steel/245 steel was studied through shear experiments performed on explosively welded wavy interfaces along several orientation angles. The results indicated that the strength and the fracture energy of samples significantly varied with the orientation angles. The fracture surfaces of all samples were observed using a scanning electron microscope and through three-dimensional structure microscopy. The periodic features of all the fracture surfaces were clearly shown in different fracture modes. The fractal dimension of the fracture surfaces was calculated based on the fractal geometry by the box-counting method in MATLAB. The cohesive element model was used to analyze the fracture energy according to the physical dependence of the fractal dimension on thermodynamic entropy and interface separation energy. The fracture energy was an exponential function of the fractal dimension value, which was in good agreement with the experimental results. All results were validated for effective use in the application of anisotropy analysis to the welded interface and structural optimization of explosively welded composite plates.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wagner, Albert F., E-mail: wagner@anl.gov; Dawes, Richard; Continetti, Robert E.

The measured H(D)OCO survival fractions of the photoelectron-photofragment coincidence experiments by the Continetti group are qualitatively reproduced by tunneling calculations to H(D) + CO{sub 2} on several recent ab initio potential energy surfaces for the HOCO system. The tunneling calculations involve effective one-dimensional barriers based on steepest descent paths computed on each potential energy surface. The resulting tunneling probabilities are converted into H(D)OCO survival fractions using a model developed by the Continetti group in which every oscillation of the H(D)-OCO stretch provides an opportunity to tunnel. Four different potential energy surfaces are examined with the best qualitative agreement with experimentmore » occurring for the PIP-NN surface based on UCCSD(T)-F12a/AVTZ electronic structure calculations and also a partial surface constructed for this study based on CASPT2/AVDZ electronic structure calculations. These two surfaces differ in barrier height by 1.6 kcal/mol but when matched at the saddle point have an almost identical shape along their reaction paths. The PIP surface is a less accurate fit to a smaller ab initio data set than that used for PIP-NN and its computed survival fractions are somewhat inferior to PIP-NN. The LTSH potential energy surface is the oldest surface examined and is qualitatively incompatible with experiment. This surface also has a small discontinuity that is easily repaired. On each surface, four different approximate tunneling methods are compared but only the small curvature tunneling method and the improved semiclassical transition state method produce useful results on all four surfaces. The results of these two methods are generally comparable and in qualitative agreement with experiment on the PIP-NN and CASPT2 surfaces. The original semiclassical transition state theory method produces qualitatively incorrect tunneling probabilities on all surfaces except the PIP. The Eckart tunneling method uses the least amount of information about the reaction path and produces too high a tunneling probability on PIP-NN surface, leading to survival fractions that peak at half their measured values.« less

Quantum chemical investigation on the role of Li adsorbed on anatase (101) surface nano-materials on the storage of molecular hydrogen.

PubMed

Srinivasadesikan, V; Raghunath, P; Lin, M C

2015-06-01

Lithiation of TiO2 has been shown to enhance the storage of hydrogen up to 5.6 wt% (Hu et al. J Am Chem Soc 128:11740-11741, 2006). The mechanism for the process is still unknown. In this work we have carried out a study on the adsorption and diffusion of Li atoms on the surface and migration into subsurface layers of anatase (101) by periodic density functional theory calculations implementing on-site Coulomb interactions (DFT+U). The model consists of 24 [TiO2] units with 11.097 × 7.655 Å(2) surface area. Adsorption energies have been calculated for different Li atoms (1-14) on the surface. A maximum of 13 Li atoms can be accommodated on the surface at two bridged O, Ti-O, and Ti atom adsorption sites, with 83 kcal mol(-1) adsorption energy for a single Li atom adsorbed between two bridged O atoms from where it can migrate into the subsurface layer with 27 kcal mol(-1) energy barrier. The predicted adsorption energies for H2 on the lithiated TiO2 (101) surface with 1-10 Li atoms revealed that the highest adsorption energies occurred on 1-Li, 5-Li, and 9-Li surfaces with 3.5, 4.4, and 7.6 kcal mol(-1), respectively. The values decrease rapidly with additional H2 co-adsorbed on the lithiated surfaces; the maximum H2 adsorption on the 9Li-TiO2(a) surface was estimated to be only 0.32 wt% under 100 atm H2 pressure at 77 K. The result of Bader charge analysis indicated that the reduction of Ti occurred depending on the Li atoms covered on the TiO2 surface.

Surface Charge-Transfer Doping of Graphene Nanoflakes Containing Double-Vacancy (5-8-5) and Stone-Wales (55-77) Defects through Molecular Adsorption.

PubMed

Shakourian-Fard, Mehdi; Jamshidi, Zahra; Kamath, Ganesh

2016-10-18

The adsorption of six electron donor-acceptor (D/A) organic molecules on various sizes of graphene nanoflakes (GNFs) containing two common defects, double-vacancy (5-8-5) and Stone-Wales (55-77), are investigated by means of ab initio DFT [M06-2X(-D3)/cc-pVDZ]. Different D/A molecules adsorb on a defect graphene (DG) surface with binding energies (ΔE b ) of about -12 to -28 kcal mol -1 . The ΔE b values for adsorption of molecules on the Stone-Wales GNF surface are higher than those on the double vacancy GNF surface. Moreover, binding energies increase by about 10 % with an increase in surface size. The nature of cooperative weak interactions is analyzed based on quantum theory of atoms in molecules, noncovalent interactions plot, and natural bond order analyses, and the dominant interaction is compared for different molecules. Electron density population analysis is used to explain the n- and p-type character of defect graphene nanoflakes (DGNFs) and also the change in electronic properties and reactivity parameters of DGNFs upon adsorption of different molecules and with increasing DGNF size. Results indicate that the HOMO-LUMO energy gap (E g ) of DGNFs decreases upon adsorption of molecules. However, by increasing the size of DGNFs, the E g and chemical hardness of all complexes decrease and the electrophilicity index increases. Furthermore, the values of the chemical potential of acceptor-DGNF complexes decrease with increasing size, whereas those of donor-DGNF complexes increase. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

MCTDH on-the-fly: Efficient grid-based quantum dynamics without pre-computed potential energy surfaces

NASA Astrophysics Data System (ADS)

Richings, Gareth W.; Habershon, Scott

2018-04-01

We present significant algorithmic improvements to a recently proposed direct quantum dynamics method, based upon combining well established grid-based quantum dynamics approaches and expansions of the potential energy operator in terms of a weighted sum of Gaussian functions. Specifically, using a sum of low-dimensional Gaussian functions to represent the potential energy surface (PES), combined with a secondary fitting of the PES using singular value decomposition, we show how standard grid-based quantum dynamics methods can be dramatically accelerated without loss of accuracy. This is demonstrated by on-the-fly simulations (using both standard grid-based methods and multi-configuration time-dependent Hartree) of both proton transfer on the electronic ground state of salicylaldimine and the non-adiabatic dynamics of pyrazine.

New ab initio adiabatic potential energy surfaces and bound state calculations for the singlet ground X˜ 1A1 and excited C˜ 1B2(21A') states of SO2

NASA Astrophysics Data System (ADS)

Kłos, Jacek; Alexander, Millard H.; Kumar, Praveen; Poirier, Bill; Jiang, Bin; Guo, Hua

2016-05-01

We report new and more accurate adiabatic potential energy surfaces (PESs) for the ground X˜ 1A1 and electronically excited C˜ 1B2(21A') states of the SO2 molecule. Ab initio points are calculated using the explicitly correlated internally contracted multi-reference configuration interaction (icMRCI-F12) method. A second less accurate PES for the ground X ˜ state is also calculated using an explicitly correlated single-reference coupled-cluster method with single, double, and non-iterative triple excitations [CCSD(T)-F12]. With these new three-dimensional PESs, we determine energies of the vibrational bound states and compare these values to existing literature data and experiment.

Lunar Thermal Wadis and Exploration Rovers: Outpost Productivity and Participatory Exploration

NASA Technical Reports Server (NTRS)

Sacksteder, Kurt; Wegeng, Robert; Suzuki, Nantel

2009-01-01

The presentation introduces the concept of a thermal wadi, an engineered source of thermal energy that can be created using native material on the moon or elsewhere to store solar energy for use by various lunar surface assets to survive the extremely cold environment of the lunar night. A principal benefit of this approach to energy storage is the low mass requirement for transportation from Earth derived from the use of the lunar soil, or regolith, as the energy storage medium. The presentation includes a summary of the results of a feasibility study involving the numerical modeling of the performance of a thermal wadi including a manufactured thermal mass, a solar energy reflector, a nighttime thermal energy reflector and a lunar surface rover. The feasibility study shows that sufficient thermal energy can be stored using unconcentrated solar flux to keep a lunar surface rover sufficiently warm throughout a 354 hour lunar night at the lunar equator, and that similar approaches can be used to sustain surface assets during shorter dark periods that occur at the lunar poles. The presentation includes descriptions of a compact lunar rover concept that could be used to manufacture a thermal wadi and could alternatively be used to conduct a variety of high-value tasks on the lunar surface. Such rovers can be produced more easily because the capability for surviving the lunar night is offloaded to the thermal wadi infrastructure. The presentation also includes several concepts for operational scenarios that could be implemented on the moon using the thermal wadi and compact rover concepts in which multiple affordable rovers, operated by multiple terrestrial organizations, can conduct resource prospecting and human exploration site preparation tasks.

Sampling saddle points on a free energy surface

NASA Astrophysics Data System (ADS)

Samanta, Amit; Chen, Ming; Yu, Tang-Qing; Tuckerman, Mark; E, Weinan

2014-04-01

Many problems in biology, chemistry, and materials science require knowledge of saddle points on free energy surfaces. These saddle points act as transition states and are the bottlenecks for transitions of the system between different metastable states. For simple systems in which the free energy depends on a few variables, the free energy surface can be precomputed, and saddle points can then be found using existing techniques. For complex systems, where the free energy depends on many degrees of freedom, this is not feasible. In this paper, we develop an algorithm for finding the saddle points on a high-dimensional free energy surface "on-the-fly" without requiring a priori knowledge the free energy function itself. This is done by using the general strategy of the heterogeneous multi-scale method by applying a macro-scale solver, here the gentlest ascent dynamics algorithm, with the needed force and Hessian values computed on-the-fly using a micro-scale model such as molecular dynamics. The algorithm is capable of dealing with problems involving many coarse-grained variables. The utility of the algorithm is illustrated by studying the saddle points associated with (a) the isomerization transition of the alanine dipeptide using two coarse-grained variables, specifically the Ramachandran dihedral angles, and (b) the beta-hairpin structure of the alanine decamer using 20 coarse-grained variables, specifically the full set of Ramachandran angle pairs associated with each residue. For the alanine decamer, we obtain a detailed network showing the connectivity of the minima obtained and the saddle-point structures that connect them, which provides a way to visualize the gross features of the high-dimensional surface.

Quantifying Additive Interactions of the Osmolyte Proline with Individual Functional Groups of Proteins: Comparisons with Urea and Glycine Betaine, Interpretation of m-Values

PubMed Central

Diehl, Roger C.; Guinn, Emily J.; Capp, Michael W.; Tsodikov, Oleg V.; Record, M. Thomas

2013-01-01

To quantify interactions of the osmolyte L-proline with protein functional groups and predict its effects on protein processes, we use vapor pressure osmometry to determine chemical potential derivatives dµ2/dm3 = µ23 quantifying preferential interactions of proline (component 3) with 21 solutes (component 2) selected to display different combinations of aliphatic or aromatic C, amide, carboxylate, phosphate or hydroxyl O, and/or amide or cationic N surface. Solubility data yield µ23 values for 4 less-soluble solutes. Values of µ23 are dissected using an ASA-based analysis to test the hypothesis of additivity and obtain α-values (proline interaction potentials) for these eight surface types and three inorganic ions. Values of µ23 predicted from these α-values agree with experiment, demonstrating additivity. Molecular interpretation of α-values using the solute partitioning model yields partition coefficients (Kp) quantifying the local accumulation or exclusion of proline in the hydration water of each functional group. Interactions of proline with native protein surface and effects of proline on protein unfolding are predicted from α-values and ASA information and compared with experimental data, with results for glycine betaine and urea, and with predictions from transfer free energy analysis. We conclude that proline stabilizes proteins because of its unfavorable interactions with (exclusion from) amide oxygens and aliphatic hydrocarbon surface exposed in unfolding, and that proline is an effective in vivo osmolyte because of the osmolality increase resulting from its unfavorable interactions with anionic (carboxylate and phosphate) and amide oxygens and aliphatic hydrocarbon groups on the surface of cytoplasmic proteins and nucleic acids. PMID:23909383

Investigating the impact of surface wave breaking on modeling the trajectories of drifters in the northern Adriatic Sea during a wind-storm event

USGS Publications Warehouse

Carniel, S.; Warner, J.C.; Chiggiato, J.; Sclavo, M.

2009-01-01

An accurate numerical prediction of the oceanic upper layer velocity is a demanding requirement for many applications at sea and is a function of several near-surface processes that need to be incorporated in a numerical model. Among them, we assess the effects of vertical resolution, different vertical mixing parameterization (the so-called Generic Length Scale -GLS- set of k-??, k-??, gen, and the Mellor-Yamada), and surface roughness values on turbulent kinetic energy (k) injection from breaking waves. First, we modified the GLS turbulence closure formulation in the Regional Ocean Modeling System (ROMS) to incorporate the surface flux of turbulent kinetic energy due to wave breaking. Then, we applied the model to idealized test cases, exploring the sensitivity to the above mentioned factors. Last, the model was applied to a realistic situation in the Adriatic Sea driven by numerical meteorological forcings and river discharges. In this case, numerical drifters were released during an intense episode of Bora winds that occurred in mid-February 2003, and their trajectories compared to the displacement of satellite-tracked drifters deployed during the ADRIA02-03 sea-truth campaign. Results indicted that the inclusion of the wave breaking process helps improve the accuracy of the numerical simulations, subject to an increase in the typical value of the surface roughness z0. Specifically, the best performance was obtained using ??CH = 56,000 in the Charnok formula, the wave breaking parameterization activated, k-?? as the turbulence closure model. With these options, the relative error with respect to the average distance of the drifter was about 25% (5.5 km/day). The most sensitive factors in the model were found to be the value of ??CH enhanced with respect to a standard value, followed by the adoption of wave breaking parameterization and the particular turbulence closure model selected. ?? 2009 Elsevier Ltd.

One-year response of American sycamore (Platanus occidentalis L.) and black locust (Robinia pseudoacacia L.) to granular fertilizer applications on a reclaimed surface mine in eastern Kentucky

Treesearch

Josh Brinks; John Lhotka; Chris. Barton

2011-01-01

The establishment of intensively managed woody energy crops on reclaimed surface mine lands provides an opportunity to diversify domestic biomass sources, while increasing the productivity and economic value of underutilized land. Our objective is to test the effect of fertilization on the growth and biomass accumulation of American sycamore (Platanus...

Oxygen adsorption on the Al₉Co₂(001) surface: first-principles and STM study.

PubMed

Villaseca, S Alarcón; Loli, L N Serkovic; Ledieu, J; Fournée, V; Gille, P; Dubois, J-M; Gaudry, E

2013-09-04

Atomic oxygen adsorption on a pure aluminum terminated Al9Co2(001) surface is studied by first-principle calculations coupled with STM measurements. Relative adsorption energies of oxygen atoms have been calculated on different surface sites along with the associated STM images. The local electronic structure of the most favourable adsorption site is described. The preferential adsorption site is identified as a 'bridge' type site between the cluster entities exposed at the (001) surface termination. The Al-O bonding between the adsorbate and the substrate presents a covalent character, with s-p hybridization occurring between the states of the adsorbed oxygen atom and the aluminum atoms of the surface. The simulated STM image of the preferential adsorption site is in agreement with experimental observations. This work shows that oxygen adsorption generates important atomic relaxations of the topmost surface layer and that sub-surface cobalt atoms strongly influence the values of the adsorption energies. The calculated Al-O distances are in agreement with those reported in Al2O and Al2O3 oxides and for oxygen adsorption on Al(111).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Capurro, O. A.; Niello, J. O. Fernandez; Pacheco, A. J.

We have investigated experimental quasielastic cross sections measured at backward angles and at deep sub-barrier energies for the {sup 35}Cl+{sup 105,106,110}Pd and {sup 32}S+{sup 110}Pd systems. Since coupling effects are almost negligible at very low bombarding energies, the quasielastic data allow one to determine the diffuseness parameter of the ion-ion potential. For the analyzed reactions we have obtained a surface diffuseness parameter value around 0.58{+-}0.04 fm.

Evaluation of the most suitable threshold value for modelling snow glacier melt through T- index approach: the case study of Forni Glacier (Italian Alps)

NASA Astrophysics Data System (ADS)

Senese, Antonella; Maugeri, Maurizio; Vuillermoz, Elisa; Smiraglia, Claudio; Diolaiuti, Guglielmina

2014-05-01

Glacier melt occurs whenever the surface temperature is null (273.15 K) and the net energy budget is positive. These conditions can be assessed by analyzing meteorological and energy data acquired by a supraglacial Automatic Weather Station (AWS). In the case this latter is not present at the glacier surface the assessment of actual melting conditions and the evaluation of melt amount is difficult and degree-day (also named T-index) models are applied. These approaches require the choice of a correct temperature threshold. In fact, melt does not necessarily occur at daily air temperatures higher than 273.15 K, since it is determined by the energy budget which in turn is only indirectly affected by air temperature. This is the case of the late spring period when ablation processes start at the glacier surface thus progressively reducing snow thickness. In this study, to detect the most indicative air temperature threshold witnessing melt conditions in the April-June period, we analyzed air temperature data recorded from 2006 to 2012 by a supraglacial AWS (at 2631 m a.s.l.) on the ablation tongue of the Forni Glacier (Italy), and by a weather station located nearby the studied glacier (at Bormio, 1225 m a.s.l.). Moreover we evaluated the glacier energy budget (which gives the actual melt, Senese et al., 2012) and the snow water equivalent values during this time-frame. Then the ablation amount was estimated both from the surface energy balance (MEB from supraglacial AWS data) and from degree-day method (MT-INDEX, in this latter case applying the mean tropospheric lapse rate to temperature data acquired at Bormio changing the air temperature threshold) and the results were compared. We found that the mean tropospheric lapse rate permits a good and reliable reconstruction of daily glacier air temperature conditions and the major uncertainty in the computation of snow melt from degree-day models is driven by the choice of an appropriate air temperature threshold. Then, to assess the most suitable threshold, we firstly analyzed hourly MEB values to detect if ablation occurs and how long this phenomenon takes (number of hours per day). The largest part of the melting (97.7%) resulted occurring on days featuring at least 6 melting hours thus suggesting to consider their minimum average daily temperature value as a suitable threshold (268.1 K). Then we ran a simple T-index model applying different threshold values. The threshold which better reproduces snow melting results the value 268.1 K. Summarizing using a 5.0 K lower threshold value (with respect to the largely applied 273.15 K) permits the best reconstruction of glacier melt and it results in agreement with findings by van den Broeke et al. (2010) in Greenland ice sheet. Then probably the choice of a 268 K value as threshold for computing degree days amount could be generalized and applied not only on Greenland glaciers but also on Mid latitude and Alpine ones. This work was carried out under the umbrella of the SHARE Stelvio Project funded by the Lombardy Region and managed by FLA and EvK2-CNR Committee.

A study of the determination of grain boundary diffusivity and energy through the thermally grown oxide ridges on a Fe-22Cr alloy surface

NASA Astrophysics Data System (ADS)

Lin, Yu; Laughlin, David E.; Zhu, Jingxi

2017-03-01

The grain boundaries (GBs) present in polycrystalline materials are important with respect to materials behaviour and properties. During the transient stage of oxidation, the higher GB diffusivity results in heterogeneous oxidation structures in the form of oxide ridges that emerge along the alloy GBs. In an attempt to delve into the more fundamental aspects of the GBs, such as GB energy, the size of the oxide ridges was quantitatively measured by atomic force microscopy on the post oxidation surface of a Fe-22 wt % Cr alloy after an oxidation exposure at 800 °C in dry air. The GB diffusivity was calculated utilising the ridge size data and the relationship between the GB diffusivity and the GB characteristics was determined. Furthermore, the GB energy was calculated from the GB diffusivity data, also to make comparison with the data available in the literature. The absolute value of the calculated GB energy was quite close to the values reported in the literature. However, compared to the extremely low temperature (0 K) data-set from the literature, the data-set obtained from this study showed much less spread. The smaller variation range may be attributed to the higher temperature condition (1073 K) in this study.

Energy balance in the watershed of Ipê, Northwestern São Paulo State, Brazil

NASA Astrophysics Data System (ADS)

Feitosa, Diego G.; T. Hernandez, Fernando B.; Franco, Renato A. M.; Teixeira, Antonio H. C.; Neale, Christopher M.

2016-10-01

The region of Ilha Solteira, in the Northwestern of São Paulo State, has been undergoing significant changes in agricultural land use and cover since 2006, as pasture fields have been replaced by sugarcane crop. This drastic change can lead to a disturbance in the energy balance, affecting the local climate. The aim of this paper was to assess some parameters related to the energy balance of Ipê's watershed, that changed since no sugarcane cultivation in 2006 to 2,164 hectares in 2011, occupying 31% of the catchment area with this important energy crop for the economy and the environment of Brazil. This study was carried out using remote sensing combined with weather data and using the SAFER (Simple Algorithm for Retrieving Evapotranspiration) model applied in 9 Landsat images collected between 2003 and 2011. The results showed a wide variation between the components of energy balance and when considering only the sugarcane crop were verified the increase values of ETa (Actual Evapotranspiration), H/Rn (Sensible Heat Flux/Net Radiation), TS (Surface Temperature), Rl↑ (Emitted longwave), Rl↓ (Incidente longwave) and surface albedo after the sugarcane production over these years. On the other hand, the NDVI, λE/Rn (Latent Heat Flux/Net Radiation) and Rn values (data) decreased in the same period. Also there was satisfactory correlation between NDVI and ETa. The SAFER model showed satisfactory results for studies of energy balance applied in the Northwestern of São Paulo State.

Global shortwave energy budget at the earth's surface from ERBE observations

NASA Technical Reports Server (NTRS)

Breon, Francois-Marie; Frouin, Robert

1994-01-01

A method is proposed to compute the net solar (shortwave) irradiance at the earth's surface from Earth Radiation Budget Experiment (ERBE) data in the S4 format. The S4 data are monthly averaged broadband planetary albedo collected at selected times during the day. Net surface shortwave irradiance is obtained from the shortwave irradiance incident at the top of the atmosphere (known) by subtracting both the shortwave energy flux reflected by the earth-atmosphere system (measured) and the energy flux absorbed by the atmosphere (modeled). Precalculated atmospheric- and surface-dependent functions that characterize scattering and absorption in the atmosphere are used, which makes the method easily applicable and computationally efficient. Four surface types are distinguished, namely, ocean, vegetation, desert, and snow/ice. Over the tropical Pacific Ocean, the estimates based on ERBE data compare well with those obtained from International Satellite Cloud Climatology Project (ISCCP) B3 data. For the 9 months analyzed the linear correlation coefficient and the standard difference between the two datasets are 0.95 and 14 W/sq m (about 6% of the average shortwave irradiance), respectively, and the bias is 15 W/sq m (higher ERBE values). The bias, a strong function of ISCCP satellite viewing zenith angle, is mostly in the ISCCP-based estimates. Over snow/ice, vegetation, and desert no comparison is made with other satellite-based estimates, but theoretical calculations using the discrete ordinate method suggest that over highly reflective surfaces (snow/ice, desert) the model, which accounts crudely for multiple reflection between the surface and clouds, may substantially overestimate the absorbed solar energy flux at the surface, especially when clouds are optically thick. The monthly surface shortwave irradiance fields produced for 1986 exhibit the main features characteristic of the earth's climate. As found in other studies, our values are generally higher than Esbensen and Kushnir's by as much as 80 W/sq m in the tropical oceans. A cloud parameter, defined as the difference between clear-sky and actual irradiances normalized to top-of-atmosphere clear-sky irradiance, is also examined. This parameter, minimally affected by sun zenith angle, is higher in the midlatitude regions of storm tracks than in the intertropical convergence zone (ITCZ), suggesting that, on average, the higher cloud coverage in midlatitudes is more effective at reducing surface shortwave irradiance than opaque, convective, yet sparser clouds in the ITCZ. Surface albedo estimates are realistic, generally not exceeding 0.06 in the ocean, as high as 0.9 in polar regions, and reaching 0.5 in the Sahara and Arabian deserts.

Extreme Maximum Land Surface Temperatures.

NASA Astrophysics Data System (ADS)

Garratt, J. R.

1992-09-01

There are numerous reports in the literature of observations of land surface temperatures. Some of these, almost all made in situ, reveal maximum values in the 50°-70°C range, with a few, made in desert regions, near 80°C. Consideration of a simplified form of the surface energy balance equation, utilizing likely upper values of absorbed shortwave flux (1000 W m2) and screen air temperature (55°C), that surface temperatures in the vicinity of 90°-100°C may occur for dry, darkish soils of low thermal conductivity (0.1-0.2 W m1 K1). Numerical simulations confirm this and suggest that temperature gradients in the first few centimeters of soil may reach 0.5°-1°C mm1 under these extreme conditions. The study bears upon the intrinsic interest of identifying extreme maximum temperatures and yields interesting information regarding the comfort zone of animals (including man).

Assessing the urban solar energy resource potential of Davao City, Philippines, using LiDAR Digital Surface Model (DSM) and GRASS GIS

NASA Astrophysics Data System (ADS)

Teves, Justine; Sola, Eula Fae; Pintor, Ben Hur; Ang, Ma. Rosario Concepcion

2016-10-01

Solar energy is emerging as one of the top options for renewable energy sources in the Philippines, with largescale solar photovoltaic (PV) farms being built all over the country. Solar energy resource in the urban environment has great potential in making a city self-sustaining, but has not been fully explored for the country. In order to represent its potential, reliable resource assessment should be done. This study aims to assess the available solar energy resource in Davao City, a trade and commerce hub in southern Philippines. The functions of GRASS GIS, specifically the r.sun module, in modelling incoming solar radiation is discussed, along with the use of a one-meter LiDAR Digital Surface Model (DSM) and Linke Turbidity coefficients as inputs. The average Julian day of each month was used to compute the Global Horizontal Irradiation (GHI) values under clear-sky or cloudless conditions. To account for the effects of the clouds in the study area, the clear-sky indices (Kc) were computed using data from solar recording stations of the Bureau of Soils and Water Management (BSWM) found within and around the region. These were multiplied to the modelled clear-sky GHI rasters to get the real-sky GHI. The results show that the city's average GHI potential ranges from 2693.79 Wh/m2 and 4453.13 Wh/m2. Average values are particularly higher around the months of March and April, while lower values are seen in the months of November and January. Areas with higher potential are seen in the southern portion of the city, consistent in built-up areas.

Quantum study of Eley-Rideal reaction and collision induced desorption of hydrogen atoms on a graphite surface. II. H-physisorbed case.

PubMed

Martinazzo, Rocco; Tantardini, Gian Franco

2006-03-28

Following previous investigation of collision induced (CI) processes involving hydrogen atoms chemisorbed on graphite [R. Martinazzo and G. F. Tantardini, J. Chem. Phys. 124, 124702 (2006)], the case in which the target hydrogen atom is initially physisorbed on the surface is considered here. Several adsorbate-substrate initial states of the target H atom in the physisorption well are considered, and CI processes are studied for projectile energies up to 1 eV. Results show that (i) Eley-Rideal cross sections at low collision energies may be larger than those found in the H-chemisorbed case but they rapidly decrease as the collision energy increases; (ii) product hydrogen molecules are vibrationally very excited; (iii) collision induced desorption cross sections rapidly increase, reaching saturation values greater than 10 A2; (iv) trapping of the incident atoms is found to be as efficient as the Eley-Rideal reaction at low energies and remains sizable (3-4 A2) at high energies. The latter adsorbate-induced trapping results mainly in formation of metastable hot hydrogen atoms, i.e., atoms with an excess energy channeled in the motion parallel to the surface. These atoms might contribute in explaining hydrogen formation on graphite.

Simulation Study of Near-Surface Coupling of Nuclear Devices vs. Equivalent High-Explosive Charges

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fournier, Kevin B; Walton, Otis R; Benjamin, Russ

2014-09-29

A computational study was performed to examine the differences in near-surface ground-waves and air-blast waves generated by high-explosive energy sources and those generated by much higher energy - density low - yield nuclear sources. The study examined the effect of explosive-source emplacement (i.e., height-of-burst, HOB, or depth-of-burial, DOB) over a range from depths of -35m to heights of 20m, for explosions with an explosive yield of 1-kt . The chemical explosive was modeled by a JWL equation-of-state model for a ~14m diameter sphere of ANFO (~1,200,000kg – 1 k t equivalent yield ), and the high-energy-density source was modeled asmore » a one tonne (1000 kg) plasma of ‘Iron-gas’ (utilizing LLNL’s tabular equation-of-state database, LEOS) in a 2m diameter sphere, with a total internal-energy content equivalent to 1 k t . A consistent equivalent-yield coupling-factor approach was developed to compare the behavior of the two sources. The results indicate that the equivalent-yield coupling-factor for air-blasts from 1 k t ANFO explosions varies monotonically and continuously from a nearly perfec t reflected wave off of the ground surface for a HOB ≈ 20m, to a coupling factor of nearly zero at DOB ≈ -25m. The nuclear air - blast coupling curve, on the other hand, remained nearly equal to a perfectly reflected wave all the way down to HOB’s very near zero, and then quickly dropped to a value near zero for explosions with a DOB ≈ -10m. The near - surface ground - wave traveling horizontally out from the explosive source region to distances of 100’s of meters exhibited equivalent - yield coupling - factors t hat varied nearly linearly with HOB/DOB for the simulated ANFO explosive source, going from a value near zero at HOB ≈ 5m to nearly one at DOB ≈ -25m. The nuclear-source generated near-surface ground wave coupling-factor remained near zero for almost all HOB’s greater than zero, and then appeared to vary nearly - linearly with depth-of-burial until it reached a value of one at a DOB between 15m and 20m. These simulations confirm the expected result that the variation of coupling to the ground, or the air, change s much more rapidly with emplacement location for a high-energy-density (i.e., nuclear-like) explosive source than it does for relatively low - energy - density chemical explosive sources. The Energy Partitioning, Energy Coupling (EPEC) platform at LLNL utilizes laser energy from one quad (i.e. 4-laser beams) of the 192 - beam NIF Laser bank to deliver ~10kJ of energy to 1mg of silver in a hohlraum creating an effective small-explosive ‘source’ with an energy density comparable to those in low-yield nuclear devices. Such experiments have the potential to provide direct experimental confirmation of the simulation results obtained in this study, at a physical scale (and time-scale) which is a factor of 1000 smaller than the spatial- or temporal-scales typically encountered when dealing with nuclear explosions.« less

Numerical modeling of the energy storage and release in solar flares

NASA Technical Reports Server (NTRS)

Wu, S. T.; Weng, F. S.

1993-01-01

This paper reports on investigation of the photospheric magnetic field-line footpoint motion (usually referred to as shear motion) and magnetic flux emerging from below the surface in relation to energy storage in a solar flare. These causality relationships are demonstrated by using numerical magnetohydrodynamic simulations. From these results, one may conclude that the energy stored in solar flares is in the form of currents. The dynamic process through which these currents reach a critical value is discussed as well as how these currents lead to energy release, such as the explosive events of solar flares.

Binding energies from diffusion Monte Carlo for the MB-pol H{sub 2}O and D{sub 2}O dimer: A comparison to experimental values

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mallory, Joel D.; Mandelshtam, Vladimir A.

2015-10-14

The diffusion Monte Carlo (DMC) method is applied to compute the ground state energies of the water monomer and dimer and their D{sub 2}O isotopomers using MB-pol; the most recent and most accurate ab inito-based potential energy surface (PES). MB-pol has already demonstrated excellent agreement with high level electronic structure data, as well as agreement with some experimental, spectroscopic, and thermodynamic data. Here, the DMC binding energies of (H{sub 2}O){sub 2} and (D{sub 2}O){sub 2} agree with the corresponding values obtained from velocity map imaging within, respectively, 0.01 and 0.02 kcal/mol. This work adds two more valuable data points thatmore » highlight the accuracy of the MB-pol PES.« less

Remote Sensing of Evapotranspiration and Carbon Uptake at Harvard Forest

NASA Technical Reports Server (NTRS)

Min, Qilong; Lin, Bing

2005-01-01

A land surface vegetation index, defined as the difference of microwave land surface emissivity at 19 and 37 GHz, was calculated for a heavily forested area in north central Massachusetts. The microwave emissivity difference vegetation index (EDVI) was estimated from satellite SSM/I measurements at the defined wavelengths and used to estimate land surface turbulent fluxes. Narrowband visible and infrared measurements and broadband solar radiation observations were used in the EDVI retrievals and turbulent flux estimations. The EDVI values represent physical properties of crown vegetation such as vegetation water content of crown canopies. The collocated land surface turbulent and radiative fluxes were empirically linked together by the EDVI values. The EDVI values are statistically sensitive to evapotranspiration fractions (EF) with a correlation coefficient (R) greater than 0.79 under all-sky conditions. For clear skies, EDVI estimates exhibit a stronger relationship with EF than normalized difference vegetation index (NDVI). Furthermore, the products of EDVI and input energy (solar and photosynthetically-active radiation) are statistically significantly correlated to evapotranspiration (R=0.95) and CO2 uptake flux (R=0.74), respectively.

Communication: THz absorption spectrum of the CO2-H2O complex: observation and assignment of intermolecular van der Waals vibrations.

PubMed

Andersen, J; Heimdal, J; Mahler, D W; Nelander, B; Larsen, R Wugt

2014-03-07

Terahertz absorption spectra have been recorded for the weakly bound CO2-H2O complex embedded in cryogenic neon matrices at 2.8 K. The three high-frequency van der Waals vibrational transitions associated with out-of-plane wagging, in-plane rocking, and torsional motion of the isotopic H2O subunit have been assigned and provide crucial observables for benchmark theoretical descriptions of this systems' flat intermolecular potential energy surface. A (semi)-empirical value for the zero-point energy of 273 ± 15 cm(-1) from the class of intermolecular van der Waals vibrations is proposed and the combination with high-level quantum chemical calculations provides a value of 726 ± 15 cm(-1) for the dissociation energy D0.

Energy spectra and E2 transition rates of 124—130Ba

NASA Astrophysics Data System (ADS)

Sabri, H.; Seidi, M.

2016-10-01

In this paper, we have studied the energy spectra and B(E2) values of 124—130Ba isotopes in the shape phase transition region between the spherical and gamma unstable deformed shapes. We have used a transitional interacting Boson model (IBM), Hamiltonian which is based on affine SU(1,1) Lie algebra in the both IBM-1 and 2 versions and also the Catastrophe theory in combination with a coherent state formalism to generate energy surfaces and determine the exact values of control parameters. Our results for control parameters suggest a combination of U(5) and SO(6) dynamical symmetries in this isotopic chain. Also, the theoretical predictions can be rather well reproduce the experimental counterparts, when the control parameter is approached to the SO(6) limit.

Evidence for phase separation of ethanol-water mixtures at the hydrogen terminated nanocrystalline diamond surface.

PubMed

Janssens, Stoffel D; Drijkoningen, Sien; Saitner, Marc; Boyen, Hans-Gerd; Wagner, Patrick; Larsson, Karin; Haenen, Ken

2012-07-28

Interactions between ethanol-water mixtures and a hydrophobic hydrogen terminated nanocrystalline diamond surface, are investigated by sessile drop contact angle measurements. The surface free energy of the hydrophobic surface, obtained with pure liquids, differs strongly from values obtained by ethanol-water mixtures. Here, a model which explains this difference is presented. The model suggests that, due to a higher affinity of ethanol for the hydrophobic surface, when compared to water, a phase separation occurs when a mixture of both liquids is in contact with the H-terminated diamond surface. These results are supported by a computational study giving insight in the affinity and related interaction at the liquid-solid interface.

PyVCI: A flexible open-source code for calculating accurate molecular infrared spectra

NASA Astrophysics Data System (ADS)

Sibaev, Marat; Crittenden, Deborah L.

2016-06-01

The PyVCI program package is a general purpose open-source code for simulating accurate molecular spectra, based upon force field expansions of the potential energy surface in normal mode coordinates. It includes harmonic normal coordinate analysis and vibrational configuration interaction (VCI) algorithms, implemented primarily in Python for accessibility but with time-consuming routines written in C. Coriolis coupling terms may be optionally included in the vibrational Hamiltonian. Non-negligible VCI matrix elements are stored in sparse matrix format to alleviate the diagonalization problem. CPU and memory requirements may be further controlled by algorithmic choices and/or numerical screening procedures, and recommended values are established by benchmarking using a test set of 44 molecules for which accurate analytical potential energy surfaces are available. Force fields in normal mode coordinates are obtained from the PyPES library of high quality analytical potential energy surfaces (to 6th order) or by numerical differentiation of analytic second derivatives generated using the GAMESS quantum chemical program package (to 4th order).

SEP events and wake region lunar dust charging with grain radii

NASA Astrophysics Data System (ADS)

Chandran, S. B. Rakesh; Rajesh, S. R.; Abraham, A.; Renuka, G.; Venugopal, Chandu

2017-01-01

Our lunar surface is exposed to all kinds of radiations from the Sun, since it lacks a global magnetic field. Like lunar surface, dust particles are also exposed to plasmas and UV radiation and, consequently they carry electrostatic charges. During Solar Energetic Particle events (SEPs) secondary electron emission plays a vital role in charging of lunar dusts. To study the lunar dust charging during SEPs on lunar wake region, we derived an expression for lunar dust potential and analysed how it varies with different electron temperatures and grain radii. Because of high energetic solar fluxes, secondary yield (δ) values reach up to 2.3 for 0.5 μm dust grain. We got maximum yield at an energy of 550 eV which is in well agreement with lunar sample experimental observation (Anderegg et al., 1972). It is observed that yield value increases with electron energy, reaches to a maximum value and then decreases. During SEPs heavier dust grains show larger yield values because of the geometry of the grains. On the wake region, the dust potential reaches up to -497 V for 0.5 μm dust grain. The electric field of these grains could present a significant threat to manned and unmanned missions to the Moon.

The influence of internal variability on Earth's energy balance framework and implications for estimating climate sensitivity

NASA Astrophysics Data System (ADS)

Dessler, Andrew E.; Mauritsen, Thorsten; Stevens, Bjorn

2018-04-01

Our climate is constrained by the balance between solar energy absorbed by the Earth and terrestrial energy radiated to space. This energy balance has been widely used to infer equilibrium climate sensitivity (ECS) from observations of 20th-century warming. Such estimates yield lower values than other methods, and these have been influential in pushing down the consensus ECS range in recent assessments. Here we test the method using a 100-member ensemble of the Max Planck Institute Earth System Model (MPI-ESM1.1) simulations of the period 1850-2005 with known forcing. We calculate ECS in each ensemble member using energy balance, yielding values ranging from 2.1 to 3.9 K. The spread in the ensemble is related to the central assumption in the energy budget framework: that global average surface temperature anomalies are indicative of anomalies in outgoing energy (either of terrestrial origin or reflected solar energy). We find that this assumption is not well supported over the historical temperature record in the model ensemble or more recent satellite observations. We find that framing energy balance in terms of 500 hPa tropical temperature better describes the planet's energy balance.

SU-E-T-577: Obliquity Factor and Surface Dose in Proton Beam Therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Das, I; Andersen, A; Coutinho, L

2015-06-15

Purpose: The advantage of lower skin dose in proton beam may be diminished creating radiation related sequalae usually seen with photon and electron beams. This study evaluates the surface dose as a complex function of beam parameters but more importantly the effect of beam angle. Methods: Surface dose in proton beam depends on the beam energy, source to surface distance, the air gap between snout and surface, field size, material thickness in front of surface, atomic number of the medium, beam angle and type of nozzle (ie double scattering, (DS), uniform scanning (US) or pencil beam scanning (PBS). Obliquity factormore » (OF) is defined as ratio of surface dose in 0° to beam angle Θ. Measurements were made in water phantom at various beam angles using very small microdiamond that has shown favorable beam characteristics for high, medium and low proton energy. Depth dose measurements were performed in the central axis of the beam in each respective gantry angle. Results: It is observed that surface dose is energy dependent but more predominantly on the SOBP. It is found that as SSD increases, surface dose decreases. In general, SSD, and air gap has limited impact in clinical proton range. High energy has higher surface dose and so the beam angle. The OF rises with beam angle. Compared to OF of 1.0 at 0° beam angle, the value is 1.5, 1.6, 1,7 for small, medium and large range respectively for 60 degree angle. Conclusion: It is advised that just like range and SOBP, surface dose should be clearly understood and a method to reduce the surface dose should be employed. Obliquity factor is a critical parameter that should be accounted in proton beam therapy and a perpendicular beam should be used to reduce surface dose.« less

Variations in debris distribution and thickness on Himalayan debris-covered glaciers

NASA Astrophysics Data System (ADS)

Gibson, Morgan; Rowan, Ann; Irvine-Fynn, Tristram; Quincey, Duncan; Glasser, Neil

2016-04-01

Many Himalayan glaciers are characterised by extensive supraglacial debris coverage; in Nepal 33% of glaciers exhibit a continuous layer of debris covering their ablation areas. The presence of such a debris layer modulates a glacier's response to climatic change. However, the impact of this modulation is poorly constrained due to inadequate quantification of the impact of supraglacial debris on glacier surface energy balance. Few data exist to describe spatial and temporal variations in parameters such as debris thickness, albedo and surface roughness in energy balance calculations. Consequently, improved understanding of how debris affects Himalayan glacier ablation requires the assessment of surface energy balance model sensitivity to spatial and temporal variability in these parameters. Measurements of debris thickness, surface temperature, reflectance and roughness were collected across Khumbu Glacier during the pre- and post-monsoon seasons of 2014 and 2015. The extent of the spatial variation in each of these parameters are currently being incorporated into a point-based glacier surface energy balance model (CMB-RES, Collier et al., 2014, The Cryosphere), applied on a pixel-by-pixel basis to the glacier surface, to ascertain the sensitivity of glacier surface energy balance and ablation values to these debris parameters. A time series of debris thickness maps have been produced for Khumbu Glacier over a 15-year period (2000-2015) using Mihalcea et al.'s (2008, Cold Reg. Sci. Technol.) method, which utilised multi-temporal ASTER thermal imagery and our in situ debris surface temperature and thickness measurements. Change detection between these maps allowed the identification of variations in debris thickness that could be compared to discrete measurements, glacier surface velocity and morphology of the debris-covered area. Debris thickness was found to vary spatially between 0.1 and 4 metres within each debris thickness map, and temporally on the order of 1 to 2 m. Temporal variability was a result of differential surface lowering, spatial variability in glacier surface velocities and intermittent input of debris to the glacier surface through mass movement. Most debris thickening is seen in initially thin areas of debris (< 0.4 m) or within ~1 km of the glacier terminus. Surface energy balance modelling is currently underway to determine the effect of these variations in debris thickness, and other parameters mentioned previously. Future work will be to calculate debris transport flux on the surface of Khumbu Glacier using the time series of debris thickness maps. Debris flux and refined energy balance calculations will then be incorporated into a 3-D ice flow model to determine the response of Khumbu Glacier to debris transport and climatic changes.

Diaphragm correction factors for the FAC-IR-300 free-air ionization chamber.

PubMed

Mohammadi, Seyed Mostafa; Tavakoli-Anbaran, Hossein

2018-02-01

A free-air ionization chamber FAC-IR-300, designed by the Atomic Energy Organization of Iran, is used as the primary Iranian national standard for the photon air kerma. For accurate air kerma measurements, the contribution from the scattered photons to the total energy released in the collecting volume must be eliminated. One of the sources of scattered photons is the chamber's diaphragm. In this paper, the diaphragm scattering correction factor, k dia , and the diaphragm transmission correction factor, k tr , were introduced. These factors represent corrections to the measured charge (or current) for the photons scattered from the diaphragm surface and the photons penetrated through the diaphragm volume, respectively. The k dia and k tr values were estimated by Monte Carlo simulations. The simulations were performed for the mono-energetic photons in the energy range of 20 - 300keV. According to the simulation results, in this energy range, the k dia values vary between 0.9997 and 0.9948, and k tr values decrease from 1.0000 to 0.9965. The corrections grow in significance with increasing energy of the primary photons. Copyright © 2017 Elsevier Ltd. All rights reserved.

Exploring the Effect of Climate Perturbations on Water Availability for Renewable Energy Development in the Indian Wells Valley, California

NASA Astrophysics Data System (ADS)

Rey, David M.

Energy and water are connected through the water-use cycle (e.g. obtaining, transporting, and treating water) and thermoelectric energy generation, which converts heat to electricity via steam-driven turbines. As the United States implements more renewable energy technologies, quantifying the relationships between energy, water, and land-surface impacts of these implementations will provide policy makers the strengths and weaknesses of different renewable energy options. In this study, a MODFLOW model of the Indian Wells Valley (IWV), in California, was developed to capture the water, energy, and land-surface impacts of potential proposed 1) solar, 2) wind, and 3) biofuel implementations. The model was calibrated to pre-existing groundwater head data from 1985 to present to develop a baseline model before running two-year predictive scenarios for photovoltaic (PV), concentrating solar power (CSP), wind, and biofuel implementations. Additionally, the baseline model was perturbed by decreasing mountain front recharge values by 5%, 10%, and 15%, simulating potential future system perturbations under a changing climate. These potential future conditions were used to re-run each implementation scenario. Implementation scenarios were developed based on population, typical energy use per person, existing land-use and land-cover type within the IWV, and previously published values for water use, surface-area use, and energy-generation potential for each renewable fuel type. The results indicate that the quantity of water needed, localized drawdown from pumping water to meet implementation demands, and generation efficiency are strongly controlled by the fuel type, as well as the energy generating technology and thermoelectric technologies implemented. Specifically, PV and wind-turbine (WT) implementations required less than 1% of the estimated annual aquifer recharge, while technologies such as biofuels and CSP, which rely on thermoelectric generation, ranged from 3% to 20%. As modeled groundwater elevations declined in the IWV, the net generation (i.e. energy produced - energy used) of each renewable energy implementation decreased due a higher energy cost for pumping groundwater. The loss in efficiency was minimal for PV and wind solutions, with maximum changes in the drawdown being less than 10 m; however, for CSP and biofuel implementations drawdowns over 50 m were observed at the pumping well, resulting in electrical generation efficiency losses between 4% and 50% over a two-year period. It was concluded that PV would be the best balance between water and land-use for the IWV, or other groundwater dependent Basin and Range settings. In areas with limited water resources but abundant available land for implementation, WT solutions would have the smallest hydrologic impact. The impact of renewable scenarios was highly variable across and within differing fuel types, with the potential for larger negative impacts under a changing climate in areas with no perennial surface water.

The Plumbing of Land Surface Models: Is Poor Performance a Result of Methodology or Data Quality?

NASA Technical Reports Server (NTRS)

Haughton, Ned; Abramowitz, Gab; Pitman, Andy J.; Or, Dani; Best, Martin J.; Johnson, Helen R.; Balsamo, Gianpaolo; Boone, Aaron; Cuntz, Matthais; Decharme, Bertrand;

Effect of electrolyte on surface free energy components of feldspar minerals using thin-layer wicking method.

PubMed

Karagüzel, C; Can, M F; Sönmez, E; Celik, M S

2005-05-01

Application of the thin-layer wicking (TLW) technique on powdered minerals is useful for characterizing their surfaces. Albite (Na-feldspar) and orthoclase (K-feldspar) are feldspar minerals which are frequently found in the same matrix. Despite similarities in their physicochemical properties, separation of these minerals from each other by flotation is generally possible in the presence of monovalent salts such as NaCl. Both albite and orthoclase exhibit the same microflotation properties and rather close electrokinetic profiles in the absence of salt. In this study, contact angles of albite and orthoclase determined by the TLW technique yielded close values in the absence and presence of amine collector. While the calculated surface energies and their components determined using contact angle data reveal that the energy terms remain farther apart in the absence of the collector, the differences narrow down at collector concentrations where full flotation recoveries are obtained. However, the effect of addition of NaCl on contact angles and surface free energy components at constant amine concentration indicates that albite is significantly affected by salt addition, whereas orthoclase remains marginally affected. This interesting finding is explained on the basis of ion-exchange properties, the stability of the interface, flotation data, and zeta potential data in the presence of NaCl.

COHESION OF AMORPHOUS SILICA SPHERES: TOWARD A BETTER UNDERSTANDING OF THE COAGULATION GROWTH OF SILICATE DUST AGGREGATES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kimura, Hiroshi; Wada, Koji; Senshu, Hiroki

2015-10-10

Adhesion forces between submicrometer-sized silicate grains play a crucial role in the formation of silicate dust agglomerates, rocky planetesimals, and terrestrial planets. The surface energy of silicate dust particles is the key to their adhesion and rolling forces in a theoretical model based on contact mechanics. Here we revisit the cohesion of amorphous silica spheres by compiling available data on the surface energy for hydrophilic amorphous silica in various circumstances. It turned out that the surface energy for hydrophilic amorphous silica in a vacuum is a factor of 10 higher than previously assumed. Therefore, the previous theoretical models underestimated themore » critical velocity for the sticking of amorphous silica spheres, as well as the rolling friction forces between them. With the most plausible value of the surface energy for amorphous silica spheres, theoretical models based on the contact mechanics are in harmony with laboratory experiments. Consequently, we conclude that silicate grains with a radius of 0.1 μm could grow to planetesimals via coagulation in a protoplanetary disk. We argue that the coagulation growth of silicate grains in a molecular cloud is advanced either by organic mantles rather than icy mantles or, if there are no mantles, by nanometer-sized grain radius.« less

Characterization of a Laser Surface-Treated Martensitic Stainless Steel.

PubMed

Al-Sayed, S R; Hussein, A A; Nofal, A A; Hassab Elnaby, S I; Elgazzar, H

2017-05-29

Laser surface treatment was carried out on AISI 416 machinable martensitic stainless steel containing 0.225 wt.% sulfur. Nd:YAG laser with a 2.2-KW continuous wave was used. The aim was to compare the physical and chemical properties achieved by this type of selective surface treatment with those achieved by the conventional treatment. Laser power of different values (700 and 1000 W) with four corresponding different laser scanning speeds (0.5, 1, 2, and 3 m•min-1) was adopted to reach the optimum conditions for impact toughness, wear, and corrosion resistance for laser heat treated (LHT) samples. The 0 °C impact energy of LHT samples indicated higher values compared to the conventionally heat treated (CHT) samples. This was accompanied by the formation of a hard surface layer and a soft interior base metal. Microhardness was studied to determine the variation of hardness values with respect to the depth under the treated surface. The wear resistance at the surface was enhanced considerably. Microstructure examination was characterized using optical and scanning electron microscopes. The corrosion behavior of the LHT samples was also studied and its correlation with the microstructures was determined. The corrosion data was obtained in 3.5% NaCl solution at room temperature by means of a potentiodynamic polarization technique.

Characterization of a Laser Surface-Treated Martensitic Stainless Steel

PubMed Central

Al-Sayed, S. R.; Hussein, A. A.; Nofal, A. A.; Hassab Elnaby, S. I.; Elgazzar, H.

2017-01-01

Laser surface treatment was carried out on AISI 416 machinable martensitic stainless steel containing 0.225 wt.% sulfur. Nd:YAG laser with a 2.2-KW continuous wave was used. The aim was to compare the physical and chemical properties achieved by this type of selective surface treatment with those achieved by the conventional treatment. Laser power of different values (700 and 1000 W) with four corresponding different laser scanning speeds (0.5, 1, 2, and 3 m·min−1) was adopted to reach the optimum conditions for impact toughness, wear, and corrosion resistance for laser heat treated (LHT) samples. The 0 °C impact energy of LHT samples indicated higher values compared to the conventionally heat treated (CHT) samples. This was accompanied by the formation of a hard surface layer and a soft interior base metal. Microhardness was studied to determine the variation of hardness values with respect to the depth under the treated surface. The wear resistance at the surface was enhanced considerably. Microstructure examination was characterized using optical and scanning electron microscopes. The corrosion behavior of the LHT samples was also studied and its correlation with the microstructures was determined. The corrosion data was obtained in 3.5% NaCl solution at room temperature by means of a potentiodynamic polarization technique. PMID:28772955

The condensation and vaporization behavior of ices containing SO2, H2S, and CO2 - Implications for Io

NASA Astrophysics Data System (ADS)

Sandford, Scott A.; Allamandola, Louis J.

1993-12-01

The present compilation of measurements of the physical and IR spectral properties of ices whose molecular compositions are relevant to the case of Io encompasses ice systems containing SO2, H2S, and CO2. Surface-binding energies used to calculate the residence times of molecules on a surface as a function of temperature furnish crucially important parameters for models attending to the transport of such molecules to the surface of Io. The values thus derived show that SO2 frosts anneal rapidly.

Performance of five surface energy balance models for estimating daily evapotranspiration in high biomass sorghum

NASA Astrophysics Data System (ADS)

Wagle, Pradeep; Bhattarai, Nishan; Gowda, Prasanna H.; Kakani, Vijaya G.

2017-06-01

Robust evapotranspiration (ET) models are required to predict water usage in a variety of terrestrial ecosystems under different geographical and agrometeorological conditions. As a result, several remote sensing-based surface energy balance (SEB) models have been developed to estimate ET over large regions. However, comparison of the performance of several SEB models at the same site is limited. In addition, none of the SEB models have been evaluated for their ability to predict ET in rain-fed high biomass sorghum grown for biofuel production. In this paper, we evaluated the performance of five widely used single-source SEB models, namely Surface Energy Balance Algorithm for Land (SEBAL), Mapping ET with Internalized Calibration (METRIC), Surface Energy Balance System (SEBS), Simplified Surface Energy Balance Index (S-SEBI), and operational Simplified Surface Energy Balance (SSEBop), for estimating ET over a high biomass sorghum field during the 2012 and 2013 growing seasons. The predicted ET values were compared against eddy covariance (EC) measured ET (ETEC) for 19 cloud-free Landsat image. In general, S-SEBI, SEBAL, and SEBS performed reasonably well for the study period, while METRIC and SSEBop performed poorly. All SEB models substantially overestimated ET under extremely dry conditions as they underestimated sensible heat (H) and overestimated latent heat (LE) fluxes under dry conditions during the partitioning of available energy. METRIC, SEBAL, and SEBS overestimated LE regardless of wet or dry periods. Consequently, predicted seasonal cumulative ET by METRIC, SEBAL, and SEBS were higher than seasonal cumulative ETEC in both seasons. In contrast, S-SEBI and SSEBop substantially underestimated ET under too wet conditions, and predicted seasonal cumulative ET by S-SEBI and SSEBop were lower than seasonal cumulative ETEC in the relatively wetter 2013 growing season. Our results indicate the necessity of inclusion of soil moisture or plant water stress component in SEB models for the improvement of their performance, especially under too dry or wet environments.

Theoretical studies of thermionic conversion of solar energy with graphene as emitter and collector

NASA Astrophysics Data System (ADS)

Olawole, Olukunle C.; De, Dilip Kumar

2018-01-01

Thermionic energy conversion (TEC) using nanomaterials is an emerging field of research. It is known that graphene can withstand temperatures as high as 4600 K in vacuum, and it has been shown that its work function can be engineered from a high value (for monolayer/bilayer) of 4.6 eV to as low as 0.7 eV. Such attractive electronic properties (e.g., good electrical conductivity and high dielectric constant) make engineered graphene a good candidate as an emitter and collector in a thermionic energy converter for harnessing solar energy efficiently. We have used a modified Richardson-Dushman equation and have adopted a model where the collector temperature could be controlled through heat extraction in a calculated amount and a magnet can be attached on the back surface of the collector for future control of the space-charge effect. Our work shows that the efficiency of solar energy conversion also depends on power density falling on the emitter surface, and that a power conversion efficiency of graphene-based solar TEC as high as 55% can be easily achieved (in the absence of the space-charge effect) through proper choice of work functions, collector temperature, and emissivity of emitter surfaces. Such solar energy conversion would reduce our dependence on silicon solar panels and offers great potential for future renewable energy utilization.

Energy levels of a quantum particle on a cylindrical surface with non-circular cross-section in electric and magnetic fields

NASA Astrophysics Data System (ADS)

Cruz, Philip Christopher S.; Bernardo, Reginald Christian S.; Esguerra, Jose Perico H.

2017-04-01

We calculate the energy levels of a quantum particle on a cylindrical surface with non-circular cross-section in uniform electric and magnetic fields. Using separation of variables method and a change of independent variable, we show that the problem can be reduced to a one-dimensional Schrödinger equation for a periodic potential. The effects of varying the shape of the cross-section while keeping the same perimeter and the strengths of the electric and magnetic fields are investigated for elliptical, corrugated, and nearly-rectangular tubes with radial dimensions of the order of a nanometer. The geometric potential has minima at the angular positions where there is a significant amount of curvature. For the elliptical and corrugated tubes, it is shown that as the tube departs from the circular shape of cross-section the double-degeneracy between the energy levels is lifted. For the nearly-rectangular tube, it is shown that energy level crossings occur as the horizontal dimension of the tube is varied while keeping the same perimeter and radius of circular corners. The interplay between the curvature and the strength of the electric and magnetic fields determines the overall behavior of the energy levels. As the strength of the electric field increases, the overall potential gets skewed creating a potential well on the side corresponding to the more negative electric potential. The energy levels of the first few excited states approach more positive values while the ground state energy level approaches a more negative value. For large electric fields, all bound state energy levels tend to more negative values. The contribution of weak magnetic fields to the overall potential behaves in the same way as the electric field contribution but with its sign depending on the direction of the component of the momentum parallel to the cylindrical axis. Large magnetic fields lead to pairing of energy levels reminiscent of 2D Landau levels for the elliptical and nearly-rectangular tubes.

Energy levels of a quantum particle on a cylindrical surface with non-circular cross-section in electric and magnetic fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cruz, Philip Christopher S., E-mail: pscruz1@up.edu.ph; Bernardo, Reginald Christian S., E-mail: rcbernardo@nip.upd.edu.ph; Esguerra, Jose Perico H., E-mail: jesguerra@nip.upd.edu.ph

We calculate the energy levels of a quantum particle on a cylindrical surface with non-circular cross-section in uniform electric and magnetic fields. Using separation of variables method and a change of independent variable, we show that the problem can be reduced to a one-dimensional Schrödinger equation for a periodic potential. The effects of varying the shape of the cross-section while keeping the same perimeter and the strengths of the electric and magnetic fields are investigated for elliptical, corrugated, and nearly-rectangular tubes with radial dimensions of the order of a nanometer. The geometric potential has minima at the angular positions wheremore » there is a significant amount of curvature. For the elliptical and corrugated tubes, it is shown that as the tube departs from the circular shape of cross-section the double-degeneracy between the energy levels is lifted. For the nearly-rectangular tube, it is shown that energy level crossings occur as the horizontal dimension of the tube is varied while keeping the same perimeter and radius of circular corners. The interplay between the curvature and the strength of the electric and magnetic fields determines the overall behavior of the energy levels. As the strength of the electric field increases, the overall potential gets skewed creating a potential well on the side corresponding to the more negative electric potential. The energy levels of the first few excited states approach more positive values while the ground state energy level approaches a more negative value. For large electric fields, all bound state energy levels tend to more negative values. The contribution of weak magnetic fields to the overall potential behaves in the same way as the electric field contribution but with its sign depending on the direction of the component of the momentum parallel to the cylindrical axis. Large magnetic fields lead to pairing of energy levels reminiscent of 2D Landau levels for the elliptical and nearly-rectangular tubes.« less

Solar Cell Polymer Based Active Ingredients PPV and PCBM

NASA Astrophysics Data System (ADS)

Hardeli, H.; Sanjaya, H.; Resikarnila, R.; Nitami H, R.

2018-04-01

A polymer solar cell is a solar cell based on a polymer bulk heterojunction structure using the method of thin film, which can convert solar energy into electrical energy. Absorption of light is carried by active material layer PPV: PCBM. This study aims to make solar cells tandem and know the value of converting solar energy into electrical energy and increase the value of efficiency generated through morphological control, ie annealing temperature and the ratio of active layer mixture. The active layer is positioned above the PEDOT:PSS layer on ITO glass substrate. The characterization results show the surface morphology of the PPV:PCBM active layer is quite evenly at annealing temperature of 165 ° C. The result of conversion of electrical energy with a UV light source in annealing samples with temperature 165 ° C is 0.03 mA and voltage of 4.085 V with an efficiency of 2.61% and mixed ratio variation was obtained in comparison of P3HT: PCBM is 1: 3

Diabatic Definition of Geometric Phase Effects.

PubMed

Izmaylov, Artur F; Li, Jiaru; Joubert-Doriol, Loïc

2016-11-08

Electronic wave functions in the adiabatic representation acquire nontrivial geometric phases (GPs) when corresponding potential energy surfaces undergo conical intersection (CI). These GPs have profound effects on the nuclear quantum dynamics and cannot be eliminated in the adiabatic representation without changing the physics of the system. To define dynamical effects arising from the GP presence, the nuclear quantum dynamics of the CI containing system is compared with that of the system with artificially removed GP. We explore a new construction of the system with removed GP via a modification of the diabatic representation for the original CI containing system. Using an absolute value function of diabatic couplings, we remove the GP while preserving adiabatic potential energy surfaces and CI. We assess GP effects in dynamics of a two-dimensional linear vibronic coupling model both for ground and excited state dynamics. Results are compared with those obtained with a conventional removal of the GP by ignoring double-valued boundary conditions of the real electronic wave functions. Interestingly, GP effects appear similar in two approaches only for the low energy dynamics. In contrast with the conventional approach, the new approach does not have substantial GP effects in the ultrafast excited state dynamics.

Interannual variability in energy exchange and evapotranspiration over two semi-arid grasslands in Arizona

NASA Astrophysics Data System (ADS)

Meyers, T. P.; Krishnan, P.; Scott, R. L.; Kennedy, L.; Heuer, M.

2011-12-01

Continuous eddy correlation measurements of energy and water vapour above two semi-arid grasslands in southern Arizona, USA during 2004 to 2007 were examined to explain the factors controlling the seasonal and interannual variability in energy exchange and evapotranspiration (E). The study sites, a post-fire site (AG) and an unburned site (KG), received 43% to 87% of the annual precipitation (P) during the North American monsoon season (July-September) with the lowest values in the drought years of 2004 and 2005. Irrespective of the differences in temperature, surface albedo, vegetation cover and soil characteristics both sites responded similarly to changes in environmental conditions. The seasonal and interannual variations in the partitioning of net radiation to turbulent fluxes were mainly controlled by P and associated changes in soil water content (θ) and vegetation growth. Drastic changes in albedo, vegetation growth, energy fluxes occurred following the onset of the monsoon season in July. During dry or cold periods of autumn, winter and spring, sensible heat flux was the major component of energy balance whereas latent heat flux dominated during the warm and wet periods of summer. The July-September values of P, E, Priestly-Taylor coefficient and canopy surface conductance reached their lowest and the Bowen ratio reached its highest values in 2004 at AG and in 2005 at KG. During July-September, monthly E was linearly correlated to the monthly mean θ and the broadband normalized vegetation index (NDVI), whereas during May-June the relationship between NDVI and E were not significant. Annual E varied from 264 to 322 mm at AG and from 196 to 284 mm at KG with the lowest value during the severe drought year at the site. July-September E had positive correlation with total P, NDVI and the number of growing season days during that period. Annual P explained more than 80% of the variance in annual E. The study suggested strong coupling between soil water conditions and vegetation on energy exchange and E.

The fracture energy and some mechanical properties of a polyurethane elastomer.

NASA Technical Reports Server (NTRS)

Mueller, H. K.; Knauss, W. G.

1971-01-01

The energy required to form a unit of new surface in the fracture of a polyurethane elastomer is determined. The rate sensitivity of the material has been reduced by swelling it in toluene. This paper primarily describes the experimental work of measuring the lower limit of the fracture energy. With this value and the creep compliance as a basis, the rate dependence of fracture energy for the unswollen material has been determined. It is thus shown that the dependence of the fracture energy on the rate of crack propagation can be explained by energy dissipation around the tip of the crack. Good agreement between the theoretically and experimentally determined relationships for the rate-sensitive fracture energy is demonstrated.

Adsorption of 6-mercaptopurine and 6-mercaptopurine riboside on silver colloid: a pH dependent surface enhanced Raman spectroscopy and density functional theory study. Part I. 6-Mercaptopurine

NASA Astrophysics Data System (ADS)

Szeghalmi, A. V.; Leopold, L.; Pînzaru, S.; Chis, V.; Silaghi-Dumitrescu, I.; Schmitt, M.; Popp, J.; Kiefer, W.

2005-02-01

Surface enhanced Raman spectroscopy (SERS) on silver colloid has been applied to characterize the interaction of 6-mercaptopurine (6MP), an active drug used in chemotherapy of acute lymphoblastic leukemia, with a model biological substrate at therapeutical concentrations and as function of the pH value. The adsorption active sites and molecular orientation on the metal surface have been determined on the basis of SERS 'surface selection rules' subsequent to a detailed vibrational analysis of the 6MP tautomeric forms. Therefore, DFT calculations (vibrational wavenumbers, Raman scattering activities, partial atomic charges) of the optimized tautomers and potential energy distribution calculations have been performed. Around neutral pH value reorientation of the molecule has been observed. Under basic conditions the 6MP molecule is probably adsorbed on the silver colloid through the N1 atom of the purine ring and possibly the S atom, and adopts a tilted orientation to the surface. A reduction in the number of adsorbed molecules under basic conditions is proposed, since the SERS spectrum recorded at 10-6 M concentration at neutral pH value resembles the SERS spectra obtained under basic conditions at 10-5 M concentration. At acidic pH values a stronger interaction through the N9 and N3 atoms is suggested with an end-on orientation.

From clusters to bulk: A relativistic density functional investigation on a series of gold clusters Aun, n=6,…,147

NASA Astrophysics Data System (ADS)

Häberlen, Oliver D.; Chung, Sai-Cheong; Stener, Mauro; Rösch, Notker

1997-03-01

A series of gold clusters spanning the size range from Au6 through Au147 (with diameters from 0.7 to 1.7 nm) in icosahedral, octahedral, and cuboctahedral structure has been theoretically investigated by means of a scalar relativistic all-electron density functional method. One of the main objectives of this work was to analyze the convergence of cluster properties toward the corresponding bulk metal values and to compare the results obtained for the local density approximation (LDA) to those for a generalized gradient approximation (GGA) to the exchange-correlation functional. The average gold-gold distance in the clusters increases with their nuclearity and correlates essentially linearly with the average coordination number in the clusters. An extrapolation to the bulk coordination of 12 yields a gold-gold distance of 289 pm in LDA, very close to the experimental bulk value of 288 pm, while the extrapolated GGA gold-gold distance is 297 pm. The cluster cohesive energy varies linearly with the inverse of the calculated cluster radius, indicating that the surface-to-volume ratio is the primary determinant of the convergence of this quantity toward bulk. The extrapolated LDA binding energy per atom, 4.7 eV, overestimates the experimental bulk value of 3.8 eV, while the GGA value, 3.2 eV, underestimates the experiment by almost the same amount. The calculated ionization potentials and electron affinities of the clusters may be related to the metallic droplet model, although deviations due to the electronic shell structure are noticeable. The GGA extrapolation to bulk values yields 4.8 and 4.9 eV for the ionization potential and the electron affinity, respectively, remarkably close to the experimental polycrystalline work function of bulk gold, 5.1 eV. Gold 4f core level binding energies were calculated for sites with bulk coordination and for different surface sites. The core level shifts for the surface sites are all positive and distinguish among the corner, edge, and face-centered sites; sites in the first subsurface layer show still small positive shifts.

Giant Enhancement in Radiative Heat Transfer in Sub-30 nm Gaps of Plane Parallel Surfaces.

PubMed

Fiorino, Anthony; Thompson, Dakotah; Zhu, Linxiao; Song, Bai; Reddy, Pramod; Meyhofer, Edgar

2018-06-13

Radiative heat transfer rates that exceed the blackbody limit by several orders of magnitude are expected when the gap size between plane parallel surfaces is reduced to the nanoscale. To date, experiments have only realized enhancements of ∼100 fold as the smallest gap sizes in radiative heat transfer studies have been limited to ∼50 nm by device curvature and particle contamination. Here, we report a 1,200-fold enhancement with respect to the far-field value in the radiative heat flux between parallel planar silica surfaces separated by gaps as small as ∼25 nm. Achieving such small gap sizes and the resultant dramatic enhancement in near-field energy flux is critical to achieve a number of novel near-field based nanoscale energy conversion systems that have been theoretically predicted but remain experimentally unverified.

Topology of surfaces for molecular Stark energy, alignment, and orientation generated by combined permanent and induced electric dipole interactions.

PubMed

Schmidt, Burkhard; Friedrich, Bretislav

2014-02-14

We show that combined permanent and induced electric dipole interactions of linear polar and polarizable molecules with collinear electric fields lead to a sui generis topology of the corresponding Stark energy surfaces and of other observables - such as alignment and orientation cosines - in the plane spanned by the permanent and induced dipole interaction parameters. We find that the loci of the intersections of the surfaces can be traced analytically and that the eigenstates as well as the number of their intersections can be characterized by a single integer index. The value of the index, distinctive for a particular ratio of the interaction parameters, brings out a close kinship with the eigenproperties obtained previously for a class of Stark states via the apparatus of supersymmetric quantum mechanics.

Machine Learning of Accurate Energy-Conserving Molecular Force Fields

NASA Astrophysics Data System (ADS)

Chmiela, Stefan; Tkatchenko, Alexandre; Sauceda, Huziel; Poltavsky, Igor; Schütt, Kristof; Müller, Klaus-Robert; GDML Collaboration

Efficient and accurate access to the Born-Oppenheimer potential energy surface (PES) is essential for long time scale molecular dynamics (MD) simulations. Using conservation of energy - a fundamental property of closed classical and quantum mechanical systems - we develop an efficient gradient-domain machine learning (GDML) approach to construct accurate molecular force fields using a restricted number of samples from ab initio MD trajectories (AIMD). The GDML implementation is able to reproduce global potential-energy surfaces of intermediate-size molecules with an accuracy of 0.3 kcal/mol for energies and 1 kcal/mol/Å for atomic forces using only 1000 conformational geometries for training. We demonstrate this accuracy for AIMD trajectories of molecules, including benzene, toluene, naphthalene, malonaldehyde, ethanol, uracil, and aspirin. The challenge of constructing conservative force fields is accomplished in our work by learning in a Hilbert space of vector-valued functions that obey the law of energy conservation. The GDML approach enables quantitative MD simulations for molecules at a fraction of cost of explicit AIMD calculations, thereby allowing the construction of efficient force fields with the accuracy and transferability of high-level ab initio methods.

Climate Inferences From Geothermal Measurements in South America

NASA Astrophysics Data System (ADS)

Gurza Fausto, Edmundo; Harris, Robert; Montenegro, Alvaro; Tassara, Andrés; Beltrami, Hugo

2013-04-01

We present the data and analysis of 26 borehole temperature logs from South America. The dataset consists of a combination of 15 new borehole logs measured during 2012 distributed between three sites in Chile. These sites are located near Vallenar, Sierra Gorda and Sierra Limon Verde. Six temperature logs were measured during 1994 at sites near Michilla, Mansa Mina and the region of El Loa (Springer et al., Tectonophysics, 1998). Four logs were obtained from the NOAA Paleoclimatology Borehole Database located in Villa Staff, Toquepala and Talara in Peru. These data were analyzed for climate variability signals of the surface temperature and changes in the earth's surface energy balance. The analysis suggests regionalized temperature changes in ground surface temperatures with anomalies ranging from -0.1 to -0.3 K for Vallenar, -0.2 to -0.9 K in Sierra Gorda and 0.0 to 0.5 K for Sierra Limon Verde. We place the results within the context of surface air temperature yearly means obtained from existing meteorological and proxy paleoclimatic data between Peru and Northern Chile. The use of geothermal measurements for climate variability studies provides a further understanding of the climatic and energy cycles of the Southern Hemisphere, where meteorological data can be scarce to non-existent. Analysis of borehole temperature data have contributed significantly to estimating the last millennium surface temperature changes. Additionally, recent analysis have contributed to evaluate the Earth's energy balance by providing a quantitative value for the energy absorbed by the continents in the later part of the 20th century. Knowledge of the surface energy flux is important for understanding the solid Earth - atmosphere boundary condition, land cover changes, and their impact on regional and global climate models.

Zero-point energy conservation in classical trajectory simulations: Application to H2CO

NASA Astrophysics Data System (ADS)

Lee, Kin Long Kelvin; Quinn, Mitchell S.; Kolmann, Stephen J.; Kable, Scott H.; Jordan, Meredith J. T.

2018-05-01

A new approach for preventing zero-point energy (ZPE) violation in quasi-classical trajectory (QCT) simulations is presented and applied to H2CO "roaming" reactions. Zero-point energy may be problematic in roaming reactions because they occur at or near bond dissociation thresholds and these channels may be incorrectly open or closed depending on if, or how, ZPE has been treated. Here we run QCT simulations on a "ZPE-corrected" potential energy surface defined as the sum of the molecular potential energy surface (PES) and the global harmonic ZPE surface. Five different harmonic ZPE estimates are examined with four, on average, giving values within 4 kJ/mol—chemical accuracy—for H2CO. The local harmonic ZPE, at arbitrary molecular configurations, is subsequently defined in terms of "projected" Cartesian coordinates and a global ZPE "surface" is constructed using Shepard interpolation. This, combined with a second-order modified Shepard interpolated PES, V, allows us to construct a proof-of-concept ZPE-corrected PES for H2CO, Veff, at no additional computational cost to the PES itself. Both V and Veff are used to model product state distributions from the H + HCO → H2 + CO abstraction reaction, which are shown to reproduce the literature roaming product state distributions. Our ZPE-corrected PES allows all trajectories to be analysed, whereas, in previous simulations, a significant proportion was discarded because of ZPE violation. We find ZPE has little effect on product rotational distributions, validating previous QCT simulations. Running trajectories on V, however, shifts the product kinetic energy release to higher energy than on Veff and classical simulations of kinetic energy release should therefore be viewed with caution.

Climatic data for Williams Lake, Hubbard County, Minnesota, 1982

USGS Publications Warehouse

Rosenberry, D.O.; Sturrock, A.M.; Scarborough, J.L.; Winter, T.C.

1988-01-01

Research on the hydrology of Williams Lake, north-central Minnesota includes study of evaporation. Those climatic data needed for energy budget and mass transfer studies are presented , including: water surface temperature, dry-bulb and wet-bulb air temperatures, wind speed, precipitation, and solar and atmospheric radiation. Some calculated values necessary for these studies are also presented, such as vapor pressure and Bowen-ratio values. Data are collected at raft and land stations.

Assessment of the water and energy budget simulation of three land surface models: CLM4.5, CoLM2014, and CoLM2005

NASA Astrophysics Data System (ADS)

Li, C.; Lu, H.; Wen, X.

2015-12-01

Land surface model (LSM), which simulates energy, water and momentum exchanges between land and atmosphere, is an important component of Earth System Models (ESM). As shown in CMIP5, different ESMs usually use different LSMs and represent various land surface status. In order to select a land surface model which could be embedded into the ESM developed in Tsinghua University, we firstly evaluate the performance of three LSMs: Community Land Model (CLM4.5) and two different versions of Common Land Model (CoLM2005 and CoLM2014). All of three models were driven by CRUNCEP data and simulation results from 1980 to 2010 were used in this study. Diagnostic data provided by NCAR, global latent and sensible heat flux map estimated by Jung, net radiation from SRB, and in situ observation collected from FluxNet were used as reference data. Two variables, surface runoff and snow depth, were used for evaluating the model performance in water budget simulation, while three variables including net radiation, sensible heat, and latent heat were used for assessing energy budget simulation. For 30 years averaged runoff, global average value of Colm2014 is 0.44mm/day and close to the diagnostic value of 0.75 mm/day, while that of Colm2005 is 0.44mm/day and that of CLM is 0.20mm/day. For snow depth simulation, three models all have overestimation in the Northern Hemisphere and underestimation in the Southern Hemisphere compare to diagnostic data. For 30 years energy budget simulation, at global scale, CoLM2005 performs best in latent heat estimation, CoLM2014 performs best in sensible heat simulation, and CoLM2005 and CoLM2014 make similar performance in net radiation estimation but is still better than CLM. At regional and local scale, comparing to the four years average of flux tower observation, RMSE of CoLM2005 is the smallest for latent heat (9.717 W/m2) , and for sensible heat simulation, RMSE of CoLM2005 (13.048 W/m2) is slightly greater than CLM(10.767 W/m2) but still better than CoLM2014(30.085 W/m2). Our analysis shows that both CoLM 2005 and CoLM 2014 are able to reproduce comparable land surface water and energy fluxes. It implies that the ESM developed in Tsinghua University may use CoLM, a LSM developed and maintained in China, as the land surface component. .

Extra-thermodynamic study on surface diffusion in reversed-phase liquid chromatography using silica gels bonded with alkyl ligands of different chain lengths

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miyabe, Kanji; Guiochon, Georges A

2005-06-01

Surface diffusion on adsorbents made of silica gels bonded to C{sub 1}, C{sub 4}, C{sub 8}, and C{sub 18} alkyl ligands was studied in reversed-phase liquid chromatography (RPLC) from the viewpoints of two extrathermodynamic relationships: enthalpy-entropy compensation (EEC) and linear free-energy relationship (LFER). First, the values of the surface diffusion coefficient (D{sub s}), normalized by the density of the alkyl ligands, were analyzed with the modified Arrhenius equation, following the four approaches proposed in earlier research. This showed that an actual EEC resulting from substantial physicochemical effects occurs for surface diffusion and suggested a mechanistic similarity of molecular migration bymore » surface diffusion, irrespective of the alkyl chain length. Second, a new model based on EEC was derived to explain the LFER between the logarithms of D{sub s} measured under different RPLC conditions. This showed that the changes of free energy, enthalpy, and entropy of surface diffusion are linearly correlated with the carbon number in the alkyl ligands of the bonded phases and that the contribution of the C{sub 18} ligand to the changes of the thermodynamic parameters corresponds to that of the C{sub 10} ligand. The new LFER model correlates the slope and intercept of the LFER to the compensation temperatures derived from the EEC analyses and to several parameters characterizing the molecular contributions to the changes in enthalpy and entropy. Finally, the new model was used to estimate D{sub s} under various RPLC conditions. The values of D{sub s} that were estimated from only two original experimental D{sub s} data were in agreement with corresponding experimental D{sub s} values, with relative errors of {approx}20%, irrespective of some RPLC conditions.« less

Novel pathways for elimination of chlorine atoms from growing Si(100) surfaces in CVD reactors

NASA Astrophysics Data System (ADS)

Kunioshi, Nílson; Hagino, Sho; Fuwa, Akio; Yamaguchi, Katsunori

2018-05-01

Reactions leading to elimination of chlorine atoms from growing Si(100) surfaces were simulated using clusters of silicon atoms of different sizes and shapes, and at the UB3LYP/6-31 g(d,p) level of theory. The reactions of type SiCl2(s) + 2 H2(g), where (s) indicates an adsorbed species at the surface and (g) a gas-phase species, were found to proceed in two steps: SiCl2(s) + H2(g) → SiHCl(s) + HCl(g) and SiHCl(s) + H2(g) → SiH2(s) + HCl(g), each having activation energies around 55 kcal/mol, a value which is comparable to experimental values published in the literature. In addition, the results suggested that H-passivation of Si(100) surfaces support reactions leading to canonical epitaxial growth, providing a plausible explanation for the convenience of passivating the surfaces prior to silicon deposition. The reactions analyzed here can therefore be seen as important steps in the mechanism of epitaxial growth of Si(100) surfaces.

Effects of leaf area index on the coupling between water table, land surface energy fluxes, and planetary boundary layer at the regional scale

NASA Astrophysics Data System (ADS)

Lu, Y.; Rihani, J.; Langensiepen, M.; Simmer, C.

2013-12-01

Vegetation plays an important role in the exchange of moisture and energy at the land surface. Previous studies indicate that vegetation increases the complexity of the feedbacks between the atmosphere and subsurface through processes such as interception, root water uptake, leaf surface evaporation, and transpiration. Vegetation cover can affect not only the interaction between water table depth and energy fluxes, but also the development of the planetary boundary layer. Leaf Area Index (LAI) is shown to be a major factor influencing these interactions. In this work, we investigate the sensitivity of water table, surface energy fluxes, and atmospheric boundary layer interactions to LAI as a model input. We particularly focus on the role LAI plays on the location and extent of transition zones of strongest coupling and how this role changes over seasonal timescales for a real catchment. The Terrestrial System Modelling Platform (TerrSysMP), developed within the Transregional Collaborative Research Centre 32 (TR32), is used in this study. TerrSysMP consists of the variably saturated groundwater model ParFlow, the land surface model Community Land Model (CLM), and the regional climate and weather forecast model COSMO (COnsortium for Small-scale Modeling). The sensitivity analysis is performed over a range of LAI values for different vegetation types as extracted from the Moderate Resolution Imaging Spectroradiometer (MODIS) dataset for the Rur catchment in Germany. In the first part of this work, effects of vegetation structure on land surface energy fluxes and their connection to water table dynamics are studied using the stand-alone CLM and the coupled subsurface-surface components of TerrSysMP (ParFlow-CLM), respectively. The interconnection between LAI and transition zones of strongest coupling are investigated and analyzed through a subsequent set of subsurface-surface-atmosphere coupled simulations implementing the full TerrSysMP model system.

Energy balance studies and plasma catecholamine values for patients with healed burns.

PubMed

Wallace, B H; Cone, J B; Caldwell, F T

1991-01-01

We report heat balance studies and plasma catecholamine values for 49 children and young adults with healed burn wounds (age range 0.6 to 31 years and burn range 1% to 82% body surface area burned; mean 41%). All measurements were made during the week of discharge. Heat production for patients with healed burns was not significantly different from predicted normal values. However, compartmented heat loss demonstrated a persistent increment in evaporative heat loss that was secondary to continued elevation of cutaneous water vapor loss immediately after wound closure. A reciprocal decrement in dry heat loss was demonstrated (as a result of a cooler average surface temperature, 0.84 degree C cooler than the average integrated skin temperature of five normal volunteers who were studied in our unit under similar environmental conditions). Mean values for plasma catecholamines were in the normal range: epinephrine = 56 +/- 37 pg/ml, norepinephrine = 385 +/- 220 pg/ml, and dopamine = 34 +/- 29 pg/ml. In conclusion, patients with freshly healed burn wounds have normal rates of heat production; however, there is a residual increment in transcutaneous water vapor loss, which produces surface cooling and decreased average surface temperature, which in turn lowers dry heat loss by an approximately equivalent amount.

A Comparative Study of Molecular Structure, pKa, Lipophilicity, Solubility, Absorption and Polar Surface Area of Some Antiplatelet Drugs.

PubMed

Remko, Milan; Remková, Anna; Broer, Ria

2016-03-19

Theoretical chemistry methods have been used to study the molecular properties of antiplatelet agents (ticlopidine, clopidogrel, prasugrel, elinogrel, ticagrelor and cangrelor) and several thiol-containing active metabolites. The geometries and energies of most stable conformers of these drugs have been computed at the Becke3LYP/6-311++G(d,p) level of density functional theory. Computed dissociation constants show that the active metabolites of prodrugs (ticlopidine, clopidogrel and prasugrel) and drugs elinogrel and cangrelor are completely ionized at pH 7.4. Both ticagrelor and its active metabolite are present at pH = 7.4 in neutral undissociated form. The thienopyridine prodrugs ticlopidine, clopidogrel and prasugrel are lipophilic and insoluble in water. Their lipophilicity is very high (about 2.5-3.5 logP values). The polar surface area, with regard to the structurally-heterogeneous character of these antiplatelet drugs, is from very large interval of values of 3-255 Ų. Thienopyridine prodrugs, like ticlopidine, clopidogrel and prasugrel, with the lowest polar surface area (PSA) values, exhibit the largest absorption. A high value of polar surface area (PSA) of cangrelor (255 Ų) results in substantial worsening of the absorption in comparison with thienopyridine drugs.

A Comparative Study of Molecular Structure, pKa, Lipophilicity, Solubility, Absorption and Polar Surface Area of Some Antiplatelet Drugs

PubMed Central

Remko, Milan; Remková, Anna; Broer, Ria

2016-01-01

Theoretical chemistry methods have been used to study the molecular properties of antiplatelet agents (ticlopidine, clopidogrel, prasugrel, elinogrel, ticagrelor and cangrelor) and several thiol-containing active metabolites. The geometries and energies of most stable conformers of these drugs have been computed at the Becke3LYP/6-311++G(d,p) level of density functional theory. Computed dissociation constants show that the active metabolites of prodrugs (ticlopidine, clopidogrel and prasugrel) and drugs elinogrel and cangrelor are completely ionized at pH 7.4. Both ticagrelor and its active metabolite are present at pH = 7.4 in neutral undissociated form. The thienopyridine prodrugs ticlopidine, clopidogrel and prasugrel are lipophilic and insoluble in water. Their lipophilicity is very high (about 2.5–3.5 logP values). The polar surface area, with regard to the structurally-heterogeneous character of these antiplatelet drugs, is from very large interval of values of 3–255 Å2. Thienopyridine prodrugs, like ticlopidine, clopidogrel and prasugrel, with the lowest polar surface area (PSA) values, exhibit the largest absorption. A high value of polar surface area (PSA) of cangrelor (255 Å2) results in substantial worsening of the absorption in comparison with thienopyridine drugs. PMID:27007371

Interaction between amphiphilic ionic liquid 1-butyl-3-methylimidazolium octyl sulfate and anionic polymer of sodium polystyrene sulfonate in aqueous medium

NASA Astrophysics Data System (ADS)

Barhoumi, Z.; Saini, M.; Amdouni, N.; Pal, A.

2016-09-01

The micellization of an aqueous solution of the surface active ionic liquid (SAIL), 1-butyl-3-methylimidazolium octylsufate (C4mim)(C8OSO3) and its interaction with an anionic polymer sodium polystyrene sulfonate, (NaPSS) were studied using conductimetry, tensiometry and fluorimetry. Surface tension profile shows a more dramatic increase in the value of surface tension of aqueous (C4mim)(C8OSO3) before the critical micelle concentration (cmc) of IL. The critical micelle concentration (cmc) value of this surfactant was found out from conductance measurements. The thermodynamic parameters, i.e., Gibb's free energy, enthalpy, and entropy of micellization of the IL in aqueous solution have been calculated. Behavior of fluorescence probe confirms the binding interactions between SAIL and the polyelectrolyte.

Assessing the sensitivity of a land-surface scheme to the parameter values using a single column model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pitman, A.J.

The sensitivity of a land-surface scheme (the Biosphere Atmosphere Transfer Scheme, BATS) to its parameter values was investigated using a single column model. Identifying which parameters were important in controlling the turbulent energy fluxes, temperature, soil moisture, and runoff was dependent upon many factors. In the simulation of a nonmoisture-stressed tropical forest, results were dependent on a combination of reservoir terms (soil depth, root distribution), flux efficiency terms (roughness length, stomatal resistance), and available energy (albedo). If moisture became limited, the reservoir terms increased in importance because the total fluxes predicted depended on moisture availability and not on the ratemore » of transfer between the surface and the atmosphere. The sensitivity shown by BATS depended on which vegetation type was being simulated, which variable was used to determine sensitivity, the magnitude and sign of the parameter change, the climate regime (precipitation amount and frequency), and soil moisture levels and proximity to wilting. The interactions between these factors made it difficult to identify the most important parameters in BATS. Therefore, this paper does not argue that a particular set of parameters is important in BATS, rather it shows that no general ranking of parameters is possible. It is also emphasized that using `stand-alone` forcing to examine the sensitivity of a land-surface scheme to perturbations, in either parameters or the atmosphere, is unreliable due to the lack of surface-atmospheric feedbacks.« less

A composition dependent energy scale and the determination of the cosmic ray primary mass in the ankle region

NASA Astrophysics Data System (ADS)

Supanitsky, A. D.; Etchegoyen, A.; Melo, D.; Sanchez, F.

2015-08-01

At present there are still several open questions about the origin of the ultra high energy cosmic rays. However, great progress in this area has been made in recent years due to the data collected by the present generation of ground based detectors like the Pierre Auger Observatory and Telescope Array. In particular, it is believed that the study of the composition of the cosmic rays as a function of energy can play a fundamental role for the understanding of the origin of the cosmic rays. The observatories belonging to this generation are composed of arrays of surface detectors and fluorescence telescopes. The duty cycle of the fluorescence telescopes is ∼10% in contrast with the ∼100% of the surface detectors. Therefore, the energy calibration of the events observed by the surface detectors is performed by using a calibration curve obtained from a set of high quality events observed in coincidence by both types of detectors. The advantage of this method is that the reconstructed energy of the events observed by the surface detectors becomes almost independent of simulations of the showers because just a small part of the reconstructed energy (the missing energy), obtained from the fluorescence telescopes, comes from simulations. However, the calibration curve obtained in this way depends on the composition of the cosmic rays, which can introduce biases in composition analyses when parameters with a strong dependence on primary energy are considered. In this work we develop an analytical method to study these effects. We consider AMIGA (Auger Muons and Infill for the Ground Array), the low energy extension of the Pierre Auger Observatory corresponding to the surface detectors, to illustrate the use of the method. In particular, we study the biases introduced by an energy calibration dependent on composition on the determination of the mean value of the number of muons, at a given distance to the showers axis, which is one of the parameters most sensitive to primary mass and has an almost linear dependence with primary energy.

An Investigation on the role of Planetary Boundary Layer Parameterization scheme on the performance of a hydrostatic atmospheric model over a Coastal Region

NASA Astrophysics Data System (ADS)

Anurose, J. T.; Subrahamanyam, Bala D.

2012-07-01

As part of the ocean/land-atmosphere interaction, more than half of the total kinetic energy is lost within the lowest part of atmosphere, often referred to as the planetary boundary layer (PBL). A comprehensive understanding of the energetics of this layer and turbulent processes responsible for dissipation of kinetic energy within the PBL require accurate estimation of sensible and latent heat flux and momentum flux. In numerical weather prediction (NWP) models, these quantities are estimated through different surface-layer and PBL parameterization schemes. This research article investigates different factors influencing the accuracy of a surface-layer parameterization scheme used in a hydrostatic high-resolution regional model (HRM) in the estimation of surface-layer turbulent fluxes of heat, moisture and momentum over the coastal regions of the Indian sub-continent. Results obtained from this sensitivity study of a parameterization scheme in HRM revealed the role of surface roughness length (z_{0}) in conjunction with the temperature difference between the underlying ground surface and atmosphere above (ΔT = T_{G} - T_{A}) in the estimated values of fluxes. For grid points over the land surface where z_{0} is treated as a constant throughout the model integration time, ΔT showed relative dominance in the estimation of sensible heat flux. In contrast to this, estimation of sensible and latent heat flux over ocean were found to be equally sensitive on the method adopted for assigning the values of z_{0} and also on the magnitudes of ΔT.

Superhydrophobic floatability of a hydrophilic object driven by edge effect

NASA Astrophysics Data System (ADS)

Chang, Feng-Ming; Sheng, Yu-Jane; Tsao, Heng-Kwong

2009-11-01

It is generally believed that a water-repellent surface is necessary for small insects to stand on water. Through a combined experimental and theoretical study, we demonstrate that an object with hydrophilic surface can float with apparent contact angle greater than 90° due to edge effect. The apparent contact angle rises with increasing loading even to a value typically displayed only by superhydrophobic surfaces. On the basis of free energy minimization, two regimes are identified. When buoyancy controls, the meniscus meets the object with the intrinsic contact angle. As surface tension dominates, however, contact angle is regulated by total force balance.

Substrate effect on the growth of Sn thin films

NASA Astrophysics Data System (ADS)

Chakraborty, Suvankar; Menon, Krishnakumar S. R.

2018-05-01

Growth of tin (Sn) on Ag(001), Ag(111) and W(110) substrate has been studied at elevated temperatures (473 K) using x-ray photoemission spectroscopy (XPS) and low energy electron diffraction (LEED). For Sn growth on silver substrates, it is noticed that both Sn 3d and Ag 3d core-level spectra shift in the higher binding energy direction due to the formation of surface alloy with the substrate. In both cases, surface alloy finally transforms into bulk alloy finally reaching bulk Sn value. For Sn growth on W(110) only Sn 3d core-level spectra shift in the higher binding energy direction due to surface core-level effect whereas no shift for tungsten core-level was noticed confirming no alloy formation. Sn is incorporated into the surface of substrate silver layer by removing every alternate or every third silver atoms to relieve the surface tensile stress as confirmed by LEED. On the other hand, tungsten being hard, Sn forms an overlayer structure by sitting in different energetically available positions rather than forming an alloy as energetically also it is not possible. Sn forms alloy with soft substrate silver and form overlayer films with tungsten. These studies are important in understanding the growth mechanism of Sn films on metal substrates.

Quantum chemical calculations of glycine glutaric acid

NASA Astrophysics Data System (ADS)

Arioǧlu, ćaǧla; Tamer, Ömer; Avci, Davut; Atalay, Yusuf

2017-02-01

Density functional theory (DFT) calculations of glycine glutaric acid were performed by using B3LYP levels with 6-311++G(d,p) basis set. The theoretical structural parameters such as bond lengths and bond angles are in a good agreement with the experimental values of the title compound. HOMO and LUMO energies were calculated, and the obtained energy gap shows that charge transfer occurs in the title compound. Vibrational frequencies were calculated and compare with experimental ones. 3D molecular surfaces of the title compound were simulated using the same level and basis set. Finally, the 13C and 1H NMR chemical shift values were calculated by the application of the gauge independent atomic orbital (GIAO) method.

Thermal desorption of formamide and methylamine from graphite and amorphous water ice surfaces

NASA Astrophysics Data System (ADS)

Chaabouni, H.; Diana, S.; Nguyen, T.; Dulieu, F.

2018-04-01

Context. Formamide (NH2CHO) and methylamine (CH3NH2) are known to be the most abundant amine-containing molecules in many astrophysical environments. The presence of these molecules in the gas phase may result from thermal desorption of interstellar ices. Aims: The aim of this work is to determine the values of the desorption energies of formamide and methylamine from analogues of interstellar dust grain surfaces and to understand their interaction with water ice. Methods: Temperature programmed desorption (TPD) experiments of formamide and methylamine ices were performed in the sub-monolayer and monolayer regimes on graphite (HOPG) and non-porous amorphous solid water (np-ASW) ice surfaces at temperatures 40-240 K. The desorption energy distributions of these two molecules were calculated from TPD measurements using a set of independent Polanyi-Wigner equations. Results: The maximum of the desorption of formamide from both graphite and ASW ice surfaces occurs at 176 K after the desorption of H2O molecules, whereas the desorption profile of methylamine depends strongly on the substrate. Solid methylamine starts to desorb below 100 K from the graphite surface. Its desorption from the water ice surface occurs after 120 K and stops during the water ice sublimation around 150 K. It continues to desorb from the graphite surface at temperatures higher than160 K. Conclusions: More than 95% of solid NH2CHO diffuses through the np-ASW ice surface towards the graphitic substrate and is released into the gas phase with a desorption energy distribution Edes = 7460-9380 K, which is measured with the best-fit pre-exponential factor A = 1018 s-1. However, the desorption energy distribution of methylamine from the np-ASW ice surface (Edes = 3850-8420 K) is measured with the best-fit pre-exponential factor A = 1012 s-1. A fraction of solid methylamine monolayer of roughly 0.15 diffuses through the water ice surface towards the HOPG substrate. This small amount of methylamine desorbs later with higher binding energies (5050-8420 K) that exceed that of the crystalline water ice (Edes = 4930 K), which is calculated with the same pre-exponential factor A = 1012 s-1. The best wetting ability of methylamine compared to H2O molecules makes CH3NH2 molecules a refractory species for low coverage. Other binding energies of astrophysical relevant molecules are gathered and compared, but we could not link the chemical functional groups (amino, methyl, hydroxyl, and carbonyl) with the binding energy properties. Implications of these high binding energies are discussed.

Surface correlations of hydrodynamic drag for transitionally rough engineering surfaces

NASA Astrophysics Data System (ADS)

Thakkar, Manan; Busse, Angela; Sandham, Neil

2017-02-01

Rough surfaces are usually characterised by a single equivalent sand-grain roughness height scale that typically needs to be determined from laboratory experiments. Recently, this method has been complemented by a direct numerical simulation approach, whereby representative surfaces can be scanned and the roughness effects computed over a range of Reynolds number. This development raises the prospect over the coming years of having enough data for different types of rough surfaces to be able to relate surface characteristics to roughness effects, such as the roughness function that quantifies the downward displacement of the logarithmic law of the wall. In the present contribution, we use simulation data for 17 irregular surfaces at the same friction Reynolds number, for which they are in the transitionally rough regime. All surfaces are scaled to the same physical roughness height. Mean streamwise velocity profiles show a wide range of roughness function values, while the velocity defect profiles show a good collapse. Profile peaks of the turbulent kinetic energy also vary depending on the surface. We then consider which surface properties are important and how new properties can be incorporated into an empirical model, the accuracy of which can then be tested. Optimised models with several roughness parameters are systematically developed for the roughness function and profile peak turbulent kinetic energy. In determining the roughness function, besides the known parameters of solidity (or frontal area ratio) and skewness, it is shown that the streamwise correlation length and the root-mean-square roughness height are also significant. The peak turbulent kinetic energy is determined by the skewness and root-mean-square roughness height, along with the mean forward-facing surface angle and spanwise effective slope. The results suggest feasibility of relating rough-wall flow properties (throughout the range from hydrodynamically smooth to fully rough) to surface parameters.

SU-F-T-376: The Efficiency of Calculating Photonuclear Reaction On High-Energy Photon Therapy by Monte Carlo Method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hirayama, S; Fujibuchi, T

Purpose: Secondary-neutrons having harmful influences to a human body are generated by photonuclear reaction on high-energy photon therapy. Their characteristics are not known in detail since the calculation to evaluate them takes very long time. PHITS(Particle and Heavy Ion Transport code System) Monte Carlo code since versions 2.80 has the new parameter “pnimul” raising the probability of occurring photonuclear reaction forcibly to make the efficiency of calculation. We investigated the optimum value of “pnimul” on high-energy photon therapy. Methods: The geometry of accelerator head based on the specification of a Varian Clinac 21EX was used for PHITS ver. 2.80. Themore » phantom (30 cm * 30 cm * 30 cm) filled the composition defined by ICRU(International Commission on Radiation Units) was placed at source-surface distance 100 cm. We calculated the neutron energy spectra in the surface of ICRU phantom with “pnimal” setting 1, 10, 100, 1000, 10000 and compared the total calculation time and the behavior of photon using PDD(Percentage Depth Dose) and OCR(Off-Center Ratio). Next, the cutoff energy of photon, electron and positron were investigated for the calculation efficiency with 4, 5, 6 and 7 MeV. Results: The calculation total time until the errors of neutron fluence become within 1% decreased as increasing “pnimul”. PDD and OCR showed no differences by the parameter. The calculation time setting the cutoff energy like 4, 5, 6 and 7 MeV decreased as increasing the cutoff energy. However, the errors of photon become within 1% did not decrease by the cutoff energy. Conclusion: The optimum values of “pnimul” and the cutoff energy were investigated on high-energy photon therapy. It is suggest that using the optimum “pnimul” makes the calculation efficiency. The study of the cutoff energy need more investigation.« less

The Unprecedented 2016-2017 Arctic Sea Ice Growth Season: The Crucial Role of Atmospheric Rivers and Longwave Fluxes

NASA Astrophysics Data System (ADS)

Hegyi, Bradley M.; Taylor, Patrick C.

2018-05-01

The 2016-2017 Arctic sea ice growth season (October-March) exhibited one of the lowest values for end-of-season sea ice volume and extent of any year since 1979. An analysis of Modern-Era Retrospective Analysis for Research and Applications, Version 2 atmospheric reanalysis data and Clouds and the Earth's Radiant Energy System radiative flux data reveals that a record warm and moist Arctic atmosphere supported the reduced sea ice growth. Numerous regional episodes of increased atmospheric temperature and moisture, transported from lower latitudes, increased the cumulative energy input from downwelling longwave surface fluxes. In those same episodes, the efficiency of the atmosphere cooling radiatively to space was reduced, increasing the amount of energy retained in the Arctic atmosphere and reradiated back toward the surface. Overall, the Arctic radiative cooling efficiency shows a decreasing trend since 2000. The results presented highlight the increasing importance of atmospheric forcing on sea ice variability demonstrating that episodic Arctic atmospheric rivers, regions of elevated poleward water vapor transport, and the subsequent surface energy budget response is a critical mechanism actively contributing to the evolution of Arctic sea ice.

A compact and accurate semi-global potential energy surface for malonaldehyde from constrained least squares regression

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mizukami, Wataru, E-mail: wataru.mizukami@bristol.ac.uk; Tew, David P., E-mail: david.tew@bristol.ac.uk; Habershon, Scott, E-mail: S.Habershon@warwick.ac.uk

2014-10-14

We present a new approach to semi-global potential energy surface fitting that uses the least absolute shrinkage and selection operator (LASSO) constrained least squares procedure to exploit an extremely flexible form for the potential function, while at the same time controlling the risk of overfitting and avoiding the introduction of unphysical features such as divergences or high-frequency oscillations. Drawing from a massively redundant set of overlapping distributed multi-dimensional Gaussian functions of inter-atomic separations we build a compact full-dimensional surface for malonaldehyde, fit to explicitly correlated coupled cluster CCSD(T)(F12*) energies with a root mean square deviations accuracy of 0.3%–0.5% up tomore » 25 000 cm{sup −1} above equilibrium. Importance-sampled diffusion Monte Carlo calculations predict zero point energies for malonaldehyde and its deuterated isotopologue of 14 715.4(2) and 13 997.9(2) cm{sup −1} and hydrogen transfer tunnelling splittings of 21.0(4) and 3.2(4) cm{sup −1}, respectively, which are in excellent agreement with the experimental values of 21.583 and 2.915(4) cm{sup −1}.« less

Strain localization parameters of AlCu4MgSi processed by high-energy electron beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lunev, A. G., E-mail: agl@ispms.ru; Nadezhkin, M. V., E-mail: mvn@ispms.ru; National Research Tomsk Polytechnic University, Tomsk, 634050

2015-10-27

The influence of the electron beam surface treatment of AlCu4MgSi on the strain localization parameters and on the critical strain value of the Portevin–Le Chatelier effect has been considered. The strain localization parameters were measured using speckle imaging of the specimens subjected to the constant strain rate uniaxial tension at a room temperature. Impact of the surface treatment on the Portevin–Le Chatelier effect has been investigated.

Influence of application method on surface free-energy and bond strength of universal adhesive systems to enamel.

PubMed

Imai, Arisa; Takamizawa, Toshiki; Sai, Keiichi; Tsujimoto, Akimasa; Nojiri, Kie; Endo, Hajime; Barkmeier, Wayne W; Latta, Mark A; Miyazaki, Masashi

2017-10-01

The aim of the present study was to determine the influence of different adhesive application methods and etching modes on enamel bond effectiveness of universal adhesives using shear bond strength (SBS) testing and surface free-energy (SFE) measurements. The adhesives Scotchbond Universal, All-Bond Universal, Adhese Universal, and G-Premio Bond were used. Prepared bovine enamel specimens were divided into four groups, based on type of adhesive, and subjected to the following surface treatments: (i) total-etch mode with active application; (ii) total-etch mode with inactive application; (iii) self-etch mode with active application; and (iv) self-etch mode with inactive application. Bonded specimens were subjected to SBS testing. The SFE of the enamel surfaces with adhesive was measured after rinsing with acetone and water. The SBS values in total-etch mode were significantly higher than those in self-etch mode. In total-etch mode, significantly lower SBS values were observed with active application compared with inactive application; in contrast, in self-etch mode there were no significant differences in SBS between active and inactive applications. A reduction in total SFE was observed for active application compared with inactive application. The interaction between etching mode and application method was statistically significant, and the application method significantly affected enamel bond strength in total-etch mode. © 2017 Eur J Oral Sci.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meisner, L. L., E-mail: llm@ispms.tsc.ru; Meisner, S. N., E-mail: msn@ispms.tsc.ru; National Research Tomsk State University, Tomsk, 634050

This work comprises a study of the influence of the pulse number of low-energy high-current electron beam (LEHCEB) exposure on the value and character of distribution of residual elastic stresses, texturing effects and the relationship between structural-phase states and physical and mechanical properties of the modified surface layers of TiNi alloy. LEHCEB processing of the surface of TiNi samples was carried out using a RITM-SP [3] installation. Energy density of electron beam was constant at E{sub s} = 3.9 ± 0.5 J/cm{sup 2}; pulse duration was 2.8 ± 0.3 μs. The number of pulses in the series was changeable, (n =more » 2–128). It was shown that as the result of multiple LEHCEB processing of TiNi samples, hierarchically organized multilayer structure is formed in the surface layer. The residual stress field of planar type is formed in the modified surface layer as following: in the direction of the normal to the surface the strain component ε{sub ⊥} < 0 (compressing strain), and in a direction parallel to the surface, the strain component ε{sub ||} > 0 (tensile deformation). Texturing effects and the level of residual stresses after LEHCEB processing of TiNi samples with equal energy density of electron beam (∼3.8 J/cm{sup 2}) depend on the number of pulses and increase with the rise of n > 10.« less

An accurate full-dimensional potential energy surface for H-Au(111): Importance of nonadiabatic electronic excitation in energy transfer and adsorption.

PubMed

Janke, Svenja M; Auerbach, Daniel J; Wodtke, Alec M; Kandratsenka, Alexander

2015-09-28

We have constructed a potential energy surface (PES) for H-atoms interacting with fcc Au(111) based on fitting the analytic form of the energy from Effective Medium Theory (EMT) to ab initio energy values calculated with density functional theory. The fit used input from configurations of the H-Au system with Au atoms at their lattice positions as well as configurations with the Au atoms displaced from their lattice positions. It reproduces the energy, in full dimension, not only for the configurations used as input but also for a large number of additional configurations derived from ab initio molecular dynamics (AIMD) trajectories at finite temperature. Adiabatic molecular dynamics simulations on this PES reproduce the energy loss behavior of AIMD. EMT also provides expressions for the embedding electron density, which enabled us to develop a self-consistent approach to simulate nonadiabatic electron-hole pair excitation and their effect on the motion of the incident H-atoms. For H atoms with an energy of 2.7 eV colliding with Au, electron-hole pair excitation is by far the most important energy loss pathway, giving an average energy loss ≈3 times that of the adiabatic case. This increased energy loss enhances the probability of the H-atom remaining on or in the Au slab by a factor of 2. The most likely outcome for H-atoms that are not scattered also depends prodigiously on the energy transfer mechanism; for the nonadiabatic case, more than 50% of the H-atoms which do not scatter are adsorbed on the surface, while for the adiabatic case more than 50% pass entirely through the 4 layer simulation slab.

Distribution of the near-inertial kinetic energy inside mesoscale eddies: Observations in the Gulf of Mexico

NASA Astrophysics Data System (ADS)

Ixetl Garcia Gomez, Beatriz; Pallas Sanz, Enric; Candela Perez, Julio

2017-04-01

The near-inertial oscillations (NIOs), generated by the wind stress on the surface mixed layer, are the inertia gravity waves with the lowest frequency and the highest kinetic energy. NIOs are important because they drive vertical mixing in the interior ocean during wave breaking events. Although the interaction between NIOs and mesoscale eddies has been reported by several authors, these studies are mostly analytical and numerical, and only few observational studies have attempted to show the differences in near-inertial kinetic energy (KEi) between anticyclonic and cyclonic eddies. In this work the spatial structure of the KEi inside the mesoscale eddies is computed using daily satellite altimetry and observations of horizontal velocity from 23 moorings equipped with acoustic Doppler current profilers in the western Gulf of Mexico. Consistent to theory, the obtained four-year KEi-composites show two times more KEi inside the anticyclonic eddies than inside the cyclonic ones. The vertical and horizontal cross-sections of the KEi-composites show that the KEi is mainly located near to the surface of the cyclonic eddies (positive vorticity), whereas the KEi in anticyclonic eddies (negative vorticity) is maximum in the eddy's center near to the base of the eddy where the NIOs become more inertial, are trapped, and amplified. The mean vertical profiles show that the cyclonic eddies present a maximum of KEi near to the surface at 50, while the maximum of KEi in the anticyclonic eddies occurs between 900 and 1100 m. Inside anticyclonic eddies another two relative maximums are observed, one in the mixed layer and the second at 300 m. In contrast, the mean profile of KEi outside the mesoscale eddies has the maximum value at the surface ( 50 m), with high values of KEi in the first 200 m and negligible energy beneath that depth. A different mean distribution of the KEi is observed depending on the type of wind generator: tropical storms or unidirectional wind.

The hydrogen abstraction reaction O({sup 3}P) + CH{sub 4}: A new analytical potential energy surface based on fit to ab initio calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

González-Lavado, Eloisa; Corchado, Jose C.; Espinosa-Garcia, Joaquin, E-mail: joaquin@unex.es

2014-02-14

Based exclusively on high-level ab initio calculations, a new full-dimensional analytical potential energy surface (PES-2014) for the gas-phase reaction of hydrogen abstraction from methane by an oxygen atom is developed. The ab initio information employed in the fit includes properties (equilibrium geometries, relative energies, and vibrational frequencies) of the reactants, products, saddle point, points on the reaction path, and points on the reaction swath, taking especial caution respecting the location and characterization of the intermediate complexes in the entrance and exit channels. By comparing with the reference results we show that the resulting PES-2014 reproduces reasonably well the whole setmore » of ab initio data used in the fitting, obtained at the CCSD(T) = FULL/aug-cc-pVQZ//CCSD(T) = FC/cc-pVTZ single point level, which represents a severe test of the new surface. As a first application, on this analytical surface we perform an extensive dynamics study using quasi-classical trajectory calculations, comparing the results with recent experimental and theoretical data. The excitation function increases with energy (concave-up) reproducing experimental and theoretical information, although our values are somewhat larger. The OH rotovibrational distribution is cold in agreement with experiment. Finally, our results reproduce experimental backward scattering distribution, associated to a rebound mechanism. These results lend confidence to the accuracy of the new surface, which substantially improves the results obtained with our previous surface (PES-2000) for the same system.« less

Dark matter sterile neutrinos in stellar collapse: Alteration of energy/lepton number transport, and a mechanism for supernova explosion enhancement

NASA Astrophysics Data System (ADS)

Hidaka, Jun; Fuller, George M.

2006-12-01

We investigate matter-enhanced Mikheyev-Smirnov-Wolfenstein (MSW) active-sterile neutrino conversion in the νe⇌νs channel in the collapse of the iron core of a presupernova star. For values of sterile neutrino rest mass ms and vacuum mixing angle θ (specifically, 0.5keV5×10-12) which include those required for viable sterile neutrino dark matter, our one-zone in-fall phase collapse calculations show a significant reduction in core lepton fraction. This would result in a smaller homologous core and therefore a smaller initial shock energy, disfavoring successful shock reheating and the prospects for an explosion. However, these calculations also suggest that the MSW resonance energy can exhibit a minimum located between the center and surface of the core. In turn, this suggests a post-core-bounce mechanism to enhance neutrino transport and neutrino luminosities at the core surface and thereby augment shock reheating: (1) scattering-induced or coherent MSW νe→νs conversion occurs deep in the core, at the first MSW resonance, where νe energies are large (˜150MeV); (2) the high energy νs stream outward at near light speed; (3) they deposit their energy when they encounter the second MSW resonance νs→νe just below the proto-neutron star surface.

Surface polarity of beta-HMX crystal and the related adhesive forces with Estane binder.

PubMed

Yang, Lu

2008-12-02

Here I present the results on the study of surface properties of beta-HMX crystal utilizing molecular dynamics simulations. The surface polarity of three principal crystal surfaces, (011), (010), and (110), is investigated by measuring the water contact angles. The calculated contact angles are in excellent agreement with the values measured by experiment and show that the surface polarity of three crystal surfaces are different. The free energies and forces of detaching an Estane chain (with and without surrounding nitroplasticizer molecules) from the three principal crystal surfaces are also calculated using the umbrella sampling method. I find that the force for Estane detachment increases with the increasing HMX surface polarity. In addition, my results show that the nitroplasticizer also plays an important role in the adhesion between Estane and HMX surfaces.

Quantifying the Uncertainty in Estimates of Surface Atmosphere Fluxes by Evaluation of SEBS and SCOPE Models

NASA Astrophysics Data System (ADS)

Timmermans, J.; van der Tol, C.; Verhoef, A.; Wang, L.; van Helvoirt, M.; Verhoef, W.; Su, Z.

2009-11-01

An earth observation based evapotranspiration (ET) product is essential to achieving the GEWEX CEOP science objectives and to achieve the GEOSS water resources societal benefit areas. Conventional techniques that employ point measurements to estimate the components of the energy balance are only representative for local scales and cannot be extended to large areas because of the heterogeneity of the land surface and the dynamic nature of heat transfer processes.The objective of this research is to quantify the uncertainties of evapotranspiration estimates by the Surface Energy Balance System (SEBS) algorithm through validation against the detailed Soil Canopy Observation, Photochemistry and Energy fluxes process (SCOPE) model with site optimized parameters. This SCOPE model takes both radiative processes and biochemical processes into account; it combines the SAIL radiative transfer model with the energy balance at leaf level to simulate the interaction between surface and atmosphere. In this paper the validation results are presented for a semi long term dataset in Reading on 2002.The comparison between the two models showed a high correlation over the complete growth of maize capturing the daily variation to good extent. The absolute values of the SEBS model are however much lower compared to those of the SCOPE model. This is due to the fact the SEBS model uses a surface resistance parameterization that is unable to account of high vegetation. An update of the SEBS model will resolve this problem.

Hotplate precipitation gauge calibrations and field measurements

NASA Astrophysics Data System (ADS)

Zelasko, Nicholas; Wettlaufer, Adam; Borkhuu, Bujidmaa; Burkhart, Matthew; Campbell, Leah S.; Steenburgh, W. James; Snider, Jefferson R.

2018-01-01

First introduced in 2003, approximately 70 Yankee Environmental Systems (YES) hotplate precipitation gauges have been purchased by researchers and operational meteorologists. A version of the YES hotplate is described in Rasmussen et al. (2011; R11). Presented here is testing of a newer version of the hotplate; this device is equipped with longwave and shortwave radiation sensors. Hotplate surface temperature, coefficients describing natural and forced convective sensible energy transfer, and radiative properties (longwave emissivity and shortwave reflectance) are reported for two of the new-version YES hotplates. These parameters are applied in a new algorithm and are used to derive liquid-equivalent accumulations (snowfall and rainfall), and these accumulations are compared to values derived by the internal algorithm used in the YES hotplates (hotplate-derived accumulations). In contrast with R11, the new algorithm accounts for radiative terms in a hotplate's energy budget, applies an energy conversion factor which does not differ from a theoretical energy conversion factor, and applies a surface area that is correct for the YES hotplate. Radiative effects are shown to be relatively unimportant for the precipitation events analyzed. In addition, this work documents a 10 % difference between the hotplate-derived and new-algorithm-derived accumulations. This difference seems consistent with R11's application of a hotplate surface area that deviates from the actual surface area of the YES hotplate and with R11's recommendation for an energy conversion factor that differs from that calculated using thermodynamic theory.

Theoretical/experimental comparison of deep tunneling decay of quasi-bound H(D)OCO to H(D) + CO₂.

PubMed

Wagner, Albert F; Dawes, Richard; Continetti, Robert E; Guo, Hua

2014-08-07

The measured H(D)OCO survival fractions of the photoelectron-photofragment coincidence experiments by the Continetti group are qualitatively reproduced by tunneling calculations to H(D) + CO2 on several recent ab initio potential energy surfaces for the HOCO system. The tunneling calculations involve effective one-dimensional barriers based on steepest descent paths computed on each potential energy surface. The resulting tunneling probabilities are converted into H(D)OCO survival fractions using a model developed by the Continetti group in which every oscillation of the H(D)-OCO stretch provides an opportunity to tunnel. Four different potential energy surfaces are examined with the best qualitative agreement with experiment occurring for the PIP-NN surface based on UCCSD(T)-F12a/AVTZ electronic structure calculations and also a partial surface constructed for this study based on CASPT2/AVDZ electronic structure calculations. These two surfaces differ in barrier height by 1.6 kcal/mol but when matched at the saddle point have an almost identical shape along their reaction paths. The PIP surface is a less accurate fit to a smaller ab initio data set than that used for PIP-NN and its computed survival fractions are somewhat inferior to PIP-NN. The LTSH potential energy surface is the oldest surface examined and is qualitatively incompatible with experiment. This surface also has a small discontinuity that is easily repaired. On each surface, four different approximate tunneling methods are compared but only the small curvature tunneling method and the improved semiclassical transition state method produce useful results on all four surfaces. The results of these two methods are generally comparable and in qualitative agreement with experiment on the PIP-NN and CASPT2 surfaces. The original semiclassical transition state theory method produces qualitatively incorrect tunneling probabilities on all surfaces except the PIP. The Eckart tunneling method uses the least amount of information about the reaction path and produces too high a tunneling probability on PIP-NN surface, leading to survival fractions that peak at half their measured values.

Comparison of Hard Surface and Soft Soil Impact Performance of a Crashworthy Composite Fuselage Concept

NASA Technical Reports Server (NTRS)

Sareen, Ashish K.; Sparks, Chad; Mullins, B. R., Jr.; Fasanella, Edwin; Jackson, Karen

2002-01-01

A comparison of the soft soil and hard surface impact performance of a crashworthy composite fuselage concept has been performed. Specifically, comparisons of the peak acceleration values, pulse duration, and onset rate at specific locations on the fuselage were evaluated. In a prior research program, the composite fuselage section was impacted at 25 feet per second onto concrete at the Impact Dynamics Research Facility (IDRF) at NASA Langley Research Center. A soft soil test was conducted at the same impact velocity as a part of the NRTC/RITA Crashworthy and Energy Absorbing Structures project. In addition to comparisons of soft soil and hard surface test results, an MSC. Dytran dynamic finite element model was developed to evaluate the test analysis correlation. In addition, modeling parameters and techniques affecting test analysis correlation are discussed. Once correlated, the analytical methodology will be used in follow-on work to evaluate the specific energy absorption of various subfloor concepts for improved crash protection during hard surface and soft soil impacts.

Decomposition pathways of C2 oxygenates on Rh-modified tungsten carbide surfaces

DOE PAGES

Kelly, Thomas G.; Ren, Hui; Chen, Jingguang G.

2015-03-27

Ethanol decomposition on tungsten monocarbide (WC) and Rh-modified WC was investigated using ultrahigh vacuum (UHV) surface science experiments and density functional theory (DFT) calculations. DFT calculations indicated that the binding energies of ethanol and its decomposition intermediates on WC(0001) were modified by Rh, with Rh/WC(0001) showing similar values to those on Rh(111). Through temperature-programmed desorption (TPD) experiments on polycrystalline WC and Rh-modified WC, it was shown that the selectivity for ethanol decomposition was different on these surfaces. On WC, the C-O bond of ethanol was preferentially broken to produce ethylene; on Rh-modified WC, the C-C bond was broken to producemore » carbon monoxide and methane. In addition, high-resolution electron energy loss spectroscopy (HREELS) was used to determine likely surface intermediates. On Rh-modified WC, ethanol first formed ethoxy through O-H scission, then reacted through an aldehyde intermediate to form the C1 products.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yadav, Praveen Kumar, E-mail: praveenyadav@rrcat.gov.in; Nayak, Maheswar; Rai, Sanjay Kumar

The authors report the effect of argon ion to molybdenum atom ratio (r) on the microstructure of low energy (70 eV) argon ion assisted electron beam evaporated Mo thin films. Surface roughness, morphology, and crystallinity of Mo films are found to strongly depend on “r.” Increase of “r” from 0 to 100 induces gradual loss in crystallinity, reduction in surface roughness and systematic increase in density of the film. For “r” ∼ 100, average atomic density of the film approaches the bulk value (97%) with lowest surface roughness. Further, increasing “r” up to 170 reduces the atomic density, increases roughness, and increase inmore » crystallinity induced by low energy Ar ion beam. The observed surface roughness and grain size determined by x-ray reflectivity and glancing incidence x-ray diffraction correlate well with atomic force microscopy measurements. This study demonstrates that for r = 100 one gets lowest roughness Mo film with highest density and nearly amorphous microstructure. The growth model is discussed by structural zone model.« less

Potential energy function for CH3+CH3 ⇆ C2H6: Attributes of the minimum energy path

NASA Astrophysics Data System (ADS)

Robertson, S. H.; Wardlaw, D. M.; Hirst, D. M.

1993-11-01

The region of the potential energy surface for the title reaction in the vicinity of its minimum energy path has been predicted from the analysis of ab initio electronic energy calculations. The ab initio procedure employs a 6-31G** basis set and a configuration interaction calculation which uses the orbitals obtained in a generalized valence bond calculation. Calculated equilibrium properties of ethane and of isolated methyl radical are compared to existing theoretical and experimental results. The reaction coordinate is represented by the carbon-carbon interatomic distance. The following attributes are reported as a function of this distance and fit to functional forms which smoothly interpolate between reactant and product values of each attribute: the minimum energy path potential, the minimum energy path geometry, normal mode frequencies for vibrational motion orthogonal to the reaction coordinate, a torsional potential, and a fundamental anharmonic frequency for local mode, out-of-plane CH3 bending (umbrella motion). The best representation is provided by a three-parameter modified Morse function for the minimum energy path potential and a two-parameter hyperbolic tangent switching function for all other attributes. A poorer but simpler representation, which may be satisfactory for selected applications, is provided by a standard Morse function and a one-parameter exponential switching function. Previous applications of the exponential switching function to estimate the reaction coordinate dependence of the frequencies and geometry of this system have assumed the same value of the range parameter α for each property and have taken α to be less than or equal to the ``standard'' value of 1.0 Å-1. Based on the present analysis this is incorrect: The α values depend on the property and range from ˜1.2 to ˜1.8 Å-1.

Crystal Structures, Surface Stability, and Water Adsorption Energies of La-Bastnäsite via Density Functional Theory and Experimental Studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Srinivasan, Sriram Goverapet; Shivaramaiah, Radha; Kent, Paul R. C.

2016-07-11

Bastnasite is a fluoro-carbonate mineral that is the largest source of rare earth elements such as Y, La and Ce. With increasing demand for REE in many emerging technologies, there is an urgent need for improving the efficiency of ore beneficiation by froth flotation. In order to design improved flotation agents that can selectively bind to the mineral surface, a fundamental understanding of the bulk and surface properties of bastnasite is essential. Density functional theory calculations using the PBEsol exchange correlation functional and the DFT-D3 dispersion correction reveal that the most stable form of La bastnsite is isomorphic to themore » structure of Ce bastnasite belonging to the P2c space group, while the Inorganic Crystal Structure Database structure in the P2m space group is ca. 11.3 kJ/mol higher in energy per LaFCO 3 formula unit. We report powder X-ray diffraction measurements on synthetic of La bastnasite to support these theoretical findings. Six different surfaces are studied by DFT, namely [100], [0001], [101], [102], [104] and [112]. Among these, the [100] surface is the most stable with a surface energy of 0.73 J/m 2 in vacuum and 0.45 J/m 2 in aqueous solution. We predicted the shape of a La bastnasite nanoparticle via thermodynamic Wulff construction to be a hexagonal prism with [100] and [0001] facets, chiseled at its ends by the [101] and [102] facets. The average surface energy of the nanoparticle in the gas phase is estimated to be 0.86 J/m 2, in good agreement with a value of 1.11 J/m 2 measured by calorimetry. The calculated adsorption energy of a water molecule varies widely with the surface plane and specific adsorption sites on a given surface. Moreover, the first layer of water molecules is predicted to adsorb strongly on the La-bastnasite surface, in agreement with water adsorption calorimetry experiments. Our work provides an important step towards a detailed atomistic understanding of the bastnasite water interface and designing collector molecules that can bind specifically to bastnasite.« less

An observational analysis of a derecho in South China

NASA Astrophysics Data System (ADS)

Xia, Rudi; Wang, Donghai; Sun, Jianhua; Wang, Gaili; Xia, Guancong

2012-12-01

Derechos occur frequently in Europe and the United States, but reports of derechos in China are scarce. In this paper, radar, satellite, and surface observation data are used to analyze a derecho event in South China on 17 April 2011. A derecho-producing mesoscale convective system formed in an environment with medium convective available energy, strong vertical wind shear, and a dry layer in the middle troposphere, and progressed southward in tandem with a front and a surface wind convergence line. The windstorm can be divided into two stages according to differences in the characteristics of the radar echo and the causes of the gale. One stage was a supercell stage, in which the sinking rear inflow of a high-precipitation supercell with a bow-shaped radar echo induced a Fujita F0 class gale. The other stage was a non-supercell stage (the echo was sequentially kidney-shaped, foot-shaped, and an ordinary single cell), in which downbursts induced a gale in Fujita F1 class. This derecho event had many similarities with derechos observed in western countries. For example, the windstorm was perpendicular to the mean flow, the gale was located in the bulging portion of the bow echo, and the derecho moved southward along with the surface front. Some differences were observed as well. The synoptic-scale forcing was weak in the absence of an advancing high-amplitude midlevel trough and an accompanying strong surface cyclone; however, the vertical wind shear was very strong, a characteristic typical of derechos associated with strong synoptic-scale forcing. Extremely high values of convective available potential energy and downdraft convective available potential energy have previously been considered necessary to the formation of weak-forcing archetype and hybrid derechos; however, these values were much less than 2000 J during this derecho event.

Wetting characteristics and blood clotting on surfaces of copoly(gamma-Benzyl-L-glutamate, gamma-hydroxyethyl-L-glutamine).

PubMed

Yano, E; Komai, T; Kawasaki, T; Kaifu, K; Atsuta, T; Kubo, Y; Fujiwara, Y

1985-09-01

The film surface of poly(gamma-benzyl-L-glutamate) (PBLG) was modified with 2-aminoethanol to enhance its hydrophilicity. Controlling the reaction conditions of PBLG and 2-aminoethanol, various types of copoly(gamma-benzyl-L-glutamate, gamma-hydroxyethyl-L-glutamine) film surfaces were obtained. Surface free energy (gamma sv), the dispersive component of gamma sv (gamma dsv), the nondispersive component of gamma sv (gamma psv), and the interfacial free energy of polymer surface with water (gamma sw), which were obtained by using the contact angle measurement and calculation method proposed by Andrade et al., were changed remarkably by the aminolysis. The gamma sv value increased after 2 h of aminolysis from 48.2 (PBLG) to 65.3 dyn/cm and gradually increased to around 70 dyn/cm after 12 h reaction. (gamma dsv) and (gamma psv) changed from 31.0 and 17.2 dyn/cm (PBLG) to 26.5 and 44.3 dyn/cm, respectively. These parameters of the material surfaces, modified over 12 h reaction, were found to be similar to those of the surfaces of canine aorta, vein, and human fibrin membrane. Blood clotting times on these polymer surfaces were comparatively longer than on siliconized glass surfaces.

Surface Passivation of GaN Nanowires for Enhanced Photoelectrochemical Water-Splitting.

PubMed

Varadhan, Purushothaman; Fu, Hui-Chun; Priante, Davide; Retamal, Jose Ramon Duran; Zhao, Chao; Ebaid, Mohamed; Ng, Tien Khee; Ajia, Idirs; Mitra, Somak; Roqan, Iman S; Ooi, Boon S; He, Jr-Hau

2017-03-08

Hydrogen production via photoelectrochemical water-splitting is a key source of clean and sustainable energy. The use of one-dimensional nanostructures as photoelectrodes is desirable for photoelectrochemical water-splitting applications due to the ultralarge surface areas, lateral carrier extraction schemes, and superior light-harvesting capabilities. However, the unavoidable surface states of nanostructured materials create additional charge carrier trapping centers and energy barriers at the semiconductor-electrolyte interface, which severely reduce the solar-to-hydrogen conversion efficiency. In this work, we address the issue of surface states in GaN nanowire photoelectrodes by employing a simple and low-cost surface treatment method, which utilizes an organic thiol compound (i.e., 1,2-ethanedithiol). The surface-treated photocathode showed an enhanced photocurrent density of -31 mA/cm 2 at -0.2 V versus RHE with an incident photon-to-current conversion efficiency of 18.3%, whereas untreated nanowires yielded only 8.1% efficiency. Furthermore, the surface passivation provides enhanced photoelectrochemical stability as surface-treated nanowires retained ∼80% of their initial photocurrent value and produced 8000 μmol of gas molecules over 55 h at acidic conditions (pH ∼ 0), whereas the untreated nanowires demonstrated only <4 h of photoelectrochemical stability. These findings shed new light on the importance of surface passivation of nanostructured photoelectrodes for photoelectrochemical applications.

Full-dimensional quantum calculations of ground-state tunneling splitting of malonaldehyde using an accurate ab initio potential energy surface

NASA Astrophysics Data System (ADS)

Wang, Yimin; Braams, Bastiaan J.; Bowman, Joel M.; Carter, Stuart; Tew, David P.

2008-06-01

Quantum calculations of the ground vibrational state tunneling splitting of H-atom and D-atom transfer in malonaldehyde are performed on a full-dimensional ab initio potential energy surface (PES). The PES is a fit to 11 147 near basis-set-limit frozen-core CCSD(T) electronic energies. This surface properly describes the invariance of the potential with respect to all permutations of identical atoms. The saddle-point barrier for the H-atom transfer on the PES is 4.1 kcal/mol, in excellent agreement with the reported ab initio value. Model one-dimensional and ``exact'' full-dimensional calculations of the splitting for H- and D-atom transfer are done using this PES. The tunneling splittings in full dimensionality are calculated using the unbiased ``fixed-node'' diffusion Monte Carlo (DMC) method in Cartesian and saddle-point normal coordinates. The ground-state tunneling splitting is found to be 21.6 cm-1 in Cartesian coordinates and 22.6 cm-1 in normal coordinates, with an uncertainty of 2-3 cm-1. This splitting is also calculated based on a model which makes use of the exact single-well zero-point energy (ZPE) obtained with the MULTIMODE code and DMC ZPE and this calculation gives a tunneling splitting of 21-22 cm-1. The corresponding computed splittings for the D-atom transfer are 3.0, 3.1, and 2-3 cm-1. These calculated tunneling splittings agree with each other to within less than the standard uncertainties obtained with the DMC method used, which are between 2 and 3 cm-1, and agree well with the experimental values of 21.6 and 2.9 cm-1 for the H and D transfer, respectively.

Full-dimensional quantum calculations of ground-state tunneling splitting of malonaldehyde using an accurate ab initio potential energy surface.

PubMed

Wang, Yimin; Braams, Bastiaan J; Bowman, Joel M; Carter, Stuart; Tew, David P

2008-06-14

Quantum calculations of the ground vibrational state tunneling splitting of H-atom and D-atom transfer in malonaldehyde are performed on a full-dimensional ab initio potential energy surface (PES). The PES is a fit to 11 147 near basis-set-limit frozen-core CCSD(T) electronic energies. This surface properly describes the invariance of the potential with respect to all permutations of identical atoms. The saddle-point barrier for the H-atom transfer on the PES is 4.1 kcalmol, in excellent agreement with the reported ab initio value. Model one-dimensional and "exact" full-dimensional calculations of the splitting for H- and D-atom transfer are done using this PES. The tunneling splittings in full dimensionality are calculated using the unbiased "fixed-node" diffusion Monte Carlo (DMC) method in Cartesian and saddle-point normal coordinates. The ground-state tunneling splitting is found to be 21.6 cm(-1) in Cartesian coordinates and 22.6 cm(-1) in normal coordinates, with an uncertainty of 2-3 cm(-1). This splitting is also calculated based on a model which makes use of the exact single-well zero-point energy (ZPE) obtained with the MULTIMODE code and DMC ZPE and this calculation gives a tunneling splitting of 21-22 cm(-1). The corresponding computed splittings for the D-atom transfer are 3.0, 3.1, and 2-3 cm(-1). These calculated tunneling splittings agree with each other to within less than the standard uncertainties obtained with the DMC method used, which are between 2 and 3 cm(-1), and agree well with the experimental values of 21.6 and 2.9 cm(-1) for the H and D transfer, respectively.

Surface Morphologies of Ti and Ti-Al-V Bombarded by 1.0-MeV Au+ Ions

NASA Astrophysics Data System (ADS)

Garcia, M. A.; Rickards, J.; Cuerno, R.; Trejo-Luna, R.; Cañetas-Ortega, J.; de la Vega, L. R.; Rodríguez-Fernández, L.

2017-12-01

Ion implantation is known to enhance the mechanical properties of biomaterials such as, e.g., the wear resistance of orthopedic joints. Increasing the surface area of implants may likewise improve their integration with, e.g., bone tissue, which requires surface features with sizes in the micron range. Ion implantation of biocompatible metals has recently been demonstrated to induce surface ripples with wavelengths of a few microns. However, the physical mechanisms controlling the formation and characteristics of these patterns are yet to be understood. We bombard Ti and Ti-6Al-4V surfaces with 1.0-MeV Au+ ions. Analysis by scanning electron and atomic force microscopies shows the formation of surface ripples with typical dimensions in the micron range, with potential indeed for biomedical applications. Under the present specific experimental conditions, the ripple properties are seen to strongly depend on the fluence of the implanted ions while being weakly dependent on the target material. Moreover, by examining experiments performed for incidence angle values θ =8 ° , 23°, 49°, and 67°, we confirm the existence of a threshold incidence angle for (ripple) pattern formation. Surface indentation is also used to study surface features under additional values of θ , agreeing with our single-angle experiments. All properties of the surface structuring process are very similar to those found in the production of surface nanopatterns under low-energy ion bombardment of semiconductor targets, in which the stopping power is dominated by nuclear contributions, as in our experiments. We consider a continuum model that combines the effects of various physical processes as originally developed in that context, with parameters that we estimate under a binary-collision approximation. Notably, reasonable agreement with our experimental observations is achieved, even under our high-energy conditions. Accordingly, in our system, ripple formation is determined by mass-redistribution currents reinforced by ion-implantation effects, which compete with an unstable curvature dependence of the sputtering yield.

Response surface methodology to simplify calculation of wood energy potency from tropical short rotation coppice species

NASA Astrophysics Data System (ADS)

Haqiqi, M. T.; Yuliansyah; Suwinarti, W.; Amirta, R.

2018-04-01

Short Rotation Coppice (SRC) system is an option to provide renewable and sustainable feedstock in generating electricity for rural area. Here in this study, we focussed on application of Response Surface Methodology (RSM) to simplify calculation protocols to point out wood chip production and energy potency from some tropical SRC species identified as Bauhinia purpurea, Bridelia tomentosa, Calliandra calothyrsus, Fagraea racemosa, Gliricidia sepium, Melastoma malabathricum, Piper aduncum, Vernonia amygdalina, Vernonia arborea and Vitex pinnata. The result showed that the highest calorific value was obtained from V. pinnata wood (19.97 MJ kg-1) due to its high lignin content (29.84 %, w/w). Our findings also indicated that the use of RSM for estimating energy-electricity of SRC wood had significant term regarding to the quadratic model (R2 = 0.953), whereas the solid-chip ratio prediction was accurate (R2 = 1.000). In the near future, the simple formula will be promising to calculate energy production easily from woody biomass, especially from SRC species.

Cellular dosimetry calculations for Strontium-90 using Monte Carlo code PENELOPE.

PubMed

Hocine, Nora; Farlay, Delphine; Boivin, Georges; Franck, Didier; Agarande, Michelle

2014-11-01

To improve risk assessments associated with chronic exposure to Strontium-90 (Sr-90), for both the environment and human health, it is necessary to know the energy distribution in specific cells or tissue. Monte Carlo (MC) simulation codes are extremely useful tools for calculating deposition energy. The present work was focused on the validation of the MC code PENetration and Energy LOss of Positrons and Electrons (PENELOPE) and the assessment of dose distribution to bone marrow cells from punctual Sr-90 source localized within the cortical bone part. S-values (absorbed dose per unit cumulated activity) calculations using Monte Carlo simulations were performed by using PENELOPE and Monte Carlo N-Particle eXtended (MCNPX). Cytoplasm, nucleus, cell surface, mouse femur bone and Sr-90 radiation source were simulated. Cells are assumed to be spherical with the radii of the cell and cell nucleus ranging from 2-10 μm. The Sr-90 source is assumed to be uniformly distributed in cell nucleus, cytoplasm and cell surface. The comparison of S-values calculated with PENELOPE to MCNPX results and the Medical Internal Radiation Dose (MIRD) values agreed very well since the relative deviations were less than 4.5%. The dose distribution to mouse bone marrow cells showed that the cells localized near the cortical part received the maximum dose. The MC code PENELOPE may prove useful for cellular dosimetry involving radiation transport through materials other than water, or for complex distributions of radionuclides and geometries.

Effect of Wigner energy on the symmetry energy coefficient in nuclei

NASA Astrophysics Data System (ADS)

Tian, Jun-Long; Cui, Hai-Tao; Gao, Teng; Wang, Ning

2016-09-01

The nuclear symmetry energy coefficient (including the coefficient of the I4 term) of finite nuclei is extracted by using the differences of available experimental binding energies of isobaric nuclei. It is found that the extracted symmetry energy coefficient decreases with increasing isospin asymmetry I, which is mainly caused by Wigner correction, since is the summation of the traditional symmetry energy esym and the Wigner energy eW. We obtain the optimal values J = 30.25 ± 0.10 MeV, ass = 56.18 ± 1.25 MeV, and the Wigner parameter x = 2.38 ± 0.12 through a polynomial fit to 2240 measured binding energies for nuclei with 20 ⩽ A ⩽ 261 with an rms deviation of 23.42 keV. We also find that the volume symmetry coefficient J ≃ 30 MeV is insensitive to the value x, whereas the surface symmetry coefficient ass and the coefficient are very sensitive to the value of x in the range 1 ⩽ x ⩽ 4. The contribution of the term increases rapidly with increasing isospin asymmetry I. For very neutron-rich nuclei, the contribution of the term will play an important role. Supported by National Natural Science Foundation of China (11475004, 11275052, 11305003, 11375094 and 11465005), Natural Science Foundation of He'nan Educational Committee (2011A140001 and 2011GGJS-147), Open Project Program of State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences (Y4KF041CJ1)

Energy and mass balance observations on La Mare Glacier (Ortles-Cevedale, European Alps)

NASA Astrophysics Data System (ADS)

Carturan, L.; Cazorzi, F.; Dalla Fontana, G.

2009-04-01

An experimental site was setup in 2005 on the ablation area of La Mare Glacier, at 2990 m a.s.l., to study the energy and mass balance exchanges between the glacier surface and the atmosphere and to investigate the climatic sensitivity of this particular glacier. An Automatic Weather Station was operated, in the framework of a monitoring network which has been implemented in the Upper Val de La Mare experimental watershed (Trentino, Italy). This basin was selected for a study of climate change effects on cryosphere and hydrology at high-altitude catchments. The 36.2 km2 wide basin has an average altitude of 2906 m a.s.l. and at present the 25% of its surface is glacierized; the annual runoff regime is dominated by snow and ice melt. Direct mass balance measurements have been performed since 1967 on Careser glacier (2.83 km2) and since 2003 on La Mare glacier (3.97 km2). The AWS is mounted on a tripod which stands freely on the glacier surface and is solar-powered. The variables measured are: air temperature and relative humidity, wind speed and direction, shortwave and longwave incoming and outgoing radiation, precipitation and surface height. All the data are sampled at five-minute intervals as average values, with the exception of surface height which is sampled at hourly intervals, as instantaneous values. The collected data were used to calculate the point energy and mass balance and to compare the results with similar investigations carried out on glaciers and available in literature. In particular, our attention has been focussed on some processes which regulate the response to climate changes. The relative importance of the energy balance components was examined and a clear predominance of shortwave radiation inputs was found to exist during melt conditions. Given the relevance of the shortwave net balance, the ice albedo temporal variability (values ranging from 0.1 to 0.5) has been investigated and correlated with meteorological variables. Furthermore, a distinct diurnal cycle of cloud cover was found to control the actual radiation received by the surface, with a minimum coverage at morning and a maximum at late afternoon, due to thermal convection. In addition, the energy available for melt is affected by the glacier cooling effect, which produces a persistent katabatic wind and lead to a reduced climatic sensitivity with respect to the "free atmosphere". The magnitude of the cooling effect has proved to be comparable with the findings of similar studies conducted in other European glaciers. Finally, the data of the first winter highlighted a very low accumulation on the AWS site, due to strong wind erosion of freshly fallen dry and cold snow. Accumulation became significant only in spring, with the deposition of snow in higher temperature conditions and absence of post-event strong northerly winds.

“Feathered” fractal surfaces to minimize secondary electron emission for a wide range of incident angles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Swanson, Charles; Kaganovich, Igor D.

Complex structures on a material surface can significantly reduce the total secondary electron emission from that surface. The reduction occurs due to the capture of low-energy, true secondary electrons emitted at one point of the structure and intersecting another. We performed Monte Carlo calculations to demonstrate that fractal surfaces can reduce net secondary electron emission produced by the surface as compared to the flat surface. Specifically, we describe one surface, a “feathered” surface, which reduces the secondary electron emission yield more effectively than other previously considered configurations. Specifically, feathers grown onto a surface suppress secondary electron emission from shallow anglesmore » of incidence more effectively than velvet. Here, we find that, for the surface simulated, secondary electron emission yield remains below 20% of its un-suppressed value, even for shallow incident angles, where the velvet-only surface gives reduction factor of only 50%.« less

“Feathered” fractal surfaces to minimize secondary electron emission for a wide range of incident angles

DOE PAGES

Swanson, Charles; Kaganovich, Igor D.

2017-07-24

Complex structures on a material surface can significantly reduce the total secondary electron emission from that surface. The reduction occurs due to the capture of low-energy, true secondary electrons emitted at one point of the structure and intersecting another. We performed Monte Carlo calculations to demonstrate that fractal surfaces can reduce net secondary electron emission produced by the surface as compared to the flat surface. Specifically, we describe one surface, a “feathered” surface, which reduces the secondary electron emission yield more effectively than other previously considered configurations. Specifically, feathers grown onto a surface suppress secondary electron emission from shallow anglesmore » of incidence more effectively than velvet. Here, we find that, for the surface simulated, secondary electron emission yield remains below 20% of its un-suppressed value, even for shallow incident angles, where the velvet-only surface gives reduction factor of only 50%.« less

"Feathered" fractal surfaces to minimize secondary electron emission for a wide range of incident angles

NASA Astrophysics Data System (ADS)

Swanson, Charles; Kaganovich, Igor D.

2017-07-01

Complex structures on a material surface can significantly reduce the total secondary electron emission from that surface. The reduction occurs due to the capture of low-energy, true secondary electrons emitted at one point of the structure and intersecting another. We performed Monte Carlo calculations to demonstrate that fractal surfaces can reduce net secondary electron emission produced by the surface as compared to the flat surface. Specifically, we describe one surface, a "feathered" surface, which reduces the secondary electron emission yield more effectively than other previously considered configurations. Specifically, feathers grown onto a surface suppress secondary electron emission from shallow angles of incidence more effectively than velvet. We find that, for the surface simulated, secondary electron emission yield remains below 20% of its un-suppressed value, even for shallow incident angles, where the velvet-only surface gives reduction factor of only 50%.

Experimental determination of ice sublimation energies

NASA Astrophysics Data System (ADS)

Luna, R.; Canto, J.; Satorre, M. A.; Domingo, M.

2011-11-01

In Astrophysics, the study of ices is important due to the wide range of scenarios in which they are present. Their physical and chemical characteristics play an important role in the study of the interstellar medium (ISM). The assessment of the energy of sublimation allows us to improve our understanding of physical and/or chemical processes that take place where ices are present. The energy of sublimation E_sub is defined as the change of energy between solid and gas phase of certain molecule. This value is important to determinate other thermodynamical parameters such as the reticular energy of ionic compounds, the energy of formation in gas phase from the energy of formation in condensed phase, or to estimate the sublimation rate, which is very important in determining the evolution of surfaces of astrophysical objects.

Spatially Complete Global Spectral Surface Albedos: Value-Added Datasets Derived from Terra MODIS Land Products

NASA Technical Reports Server (NTRS)

Moody, Eric G.; King, Michael D.; Platnick, Steven; Schaaf, Crystal B.; Gao, Feng

2004-01-01

Land surface albedo is an important parameter in describing the radiative properties of the earth s surface as it represents the amount of incoming solar radiation that is reflected from the surface. The amount and type of vegetation of the surface dramatically alters the amount of radiation that is reflected; for example, croplands that contain leafy vegetation will reflect radiation very differently than blacktop associated with urban areas. In addition, since vegetation goes through a growth, or phenological, cycle, the amount of radiation that is reflected changes over the course of a year. As a result, albedo is both temporally and spatially dependant upon global location as there is a distribution of vegetated surface types and growing conditions. Land surface albedo is critical for a wide variety of earth system research projects including but not restricted to remote sensing of atmospheric aerosol and cloud properties from space, ground-based analysis of aerosol optical properties from surface-based sun/sky radiometers, biophysically-based land surface modeling of the exchange of energy, water, momentum, and carbon for various land use categories, and surface energy balance studies. These projects require proper representation of the surface albedo s spatial, spectral, and temporal variations, however, these representations are often lacking in datasets prior to the latest generation of land surface albedo products.

Surface layer characteristics derived from fast-response micrometeorological observations over a mountain peak in the central Himalayas

NASA Astrophysics Data System (ADS)

Solanki, Raman; Dhaka, Surendra; Rajeev, Kunjukrishnapillai; Singh, Narendra; Nadimpally, Kirankumar

Diurnal evolution of atmospheric boundary layer over hilly terrains is highly complex and least understood. Fast-response micrometeorological observations carried out at Manora Peak, Nainital (29.2°N, 79.3°E, 1960 m ASL), a hill station located in the Central Himalayas during March-2013 to February-2014 has been used to investigate diurnal variations in the surface layer characteristics, energy budget and atmospheric circulation over complex terrains. This study mainly employs tower-based sonic anemometer observations (25 Hz) carried out at two levels (12 m and 27 m above the ground level) which are used to derive the variations of zonal, meridional and vertical winds, virtual temperature, momentum flux, turbulent kinetic energy, and Monin-Obukhov stability parameter during fair-weather conditions. In general, this station is manifested by warm and dry conditions as well as relatively high wind speed during pre-monsoon season (March-May); while highly moist conditions prevail during the summer monsoon season (June-September). The sensible heat flux (SHF) undergoes a prominent diurnal variation during winter and pre-monsoon seasons with peak values (200 to 400 Wm-2) occurring between 11-15 Local Time (LT) and weakly negative values (typically -20 Wm-2) during night, the latter indicating a downward transfer of heat from atmosphere to surface. The noon-time peak values systematically increases from winter to pre-monsoon season. Remarkably, the large noon-time values of SHF observed during the pre-monsoon season over this station (peak SHF of more than 400 Wm-2 during May) arise from the forced lifting of air masses, caused by the prevailing horizontal winds that blow perpendicular to the mountain. The intricate details of the surface layer parameters and fluxes over this site will assist in investigating how such a complex topography influences the flux generation process.

Characterization of initial events in bacterial surface colonization by two Pseudomonas species using image analysis.

PubMed

Mueller, R F; Characklis, W G; Jones, W L; Sears, J T

1992-05-01

The processes leading to bacterial colonization on solid-water interfaces are adsorption, desorption, growth, and erosion. These processes have been measured individually in situ in a flowing system in real time using image analysis. Four different substrata (copper, silicon, 316 stainless-steel and glass) and 2 different bacterial species (Pseudomonas aeruginosa and Pseudomonas fluorescens) were used in the experiments. The flow was laminar (Re = 1.4) and the shear stress was kept constant during all experiments at 0.75 N m(-2). The surface roughness varied among the substrata from 0.002 microm (for silicon) to 0.015 microm (for copper). Surface free energies varied from 25.1 dynes cm(-1) for silicon to 31.2 dynes cm(-1) for copper. Cell curface hydrophobicity, reported as hydrocarbon partitioning values, ranged from 0.67 for Ps. fluorescens to 0.97 for Ps. aeruginosa.The adsorption rate coefficient varied by as much as a factor of 10 among the combinations of bacterial strain and substratum material, and was positively correlated with surface free energy, the surface roughness of the substratum, and the hydrophobicity of the cells. The probability of desorption decreased with increasing surface free energy and surface roughness of the substratum. Cell growth was inhibited on copper, but replication of cells overlying an initial cell layer was observed with increased exposure time to the cell-containing bulk water. A mathematical model describing cell accumulation on a substratum is presented.

Surface-and bulk-properties of EPDM rubber modified by electron beam irradiation

NASA Astrophysics Data System (ADS)

Majumder, Papiya Sen; Bhowmick, Anil K.

1999-01-01

Electron beam initiated grafting of trimethylol propane triacrylate (TMPTA) onto ethylene propylene diene monomer (EPDM) has been carried out over a wide range of irradiation doses (0-200 kGy) using a fixed concentration (10%) of TMPTA. The samples have been both surface and bulk modified. Infrared (IR) studies indicate increased peak absorbances at 1730, 1260, 1120 and 1019 cm -1 upto 50 kGy and hence increased CO and C-O-C concentrations. The results are further supported by X-ray photoelectron spectroscopy (XPS) studies. The surface energy of EPDM increases from 46.5 to 60.7 mJ/m 2 on irradiation of the surface modified samples to 50 kGy dose, due to increased contribution of γSAB and γS(-). The results have been explained with the help of IR and XPS data. The values of tensile strength of the surface modified samples have not changed very significantly, while the moduli values have increased at the cost of the elongation at break. DMTA studies have shown changes in Tg and tan δmax on modification of the surface. The surface morphology of the modified and irradiated samples reveals acrylate flow marks at high magnification.

Surface Mediated Protein Disaggregation

NASA Astrophysics Data System (ADS)

Radhakrishna, Mithun; Kumar, Sanat K.

2014-03-01

Preventing protein aggregation is of both biological and industrial importance. Biologically these aggregates are known to cause amyloid type diseases like Alzheimer's and Parkinson's disease. Protein aggregation leads to reduced activity of the enzymes in industrial applications. Inter-protein interactions between the hydrophobic residues of the protein are known to be the major driving force for protein aggregation. In the current paper we show how surface chemistry and curvature can be tuned to mitigate these inter-protein interactions. Our results calculated in the framework of the Hydrophobic-Polar (HP) lattice model show that, inter-protein interactions can be drastically reduced by increasing the surface hydrophobicity to a critical value corresponding to the adsorption transition of the protein. At this value of surface hydrophobicity, proteins lose inter-protein contacts to gain surface contacts and thus the surface helps in reducing the inter-protein interactions. Further, we show that the adsorption of the proteins inside hydrophobic pores of optimal sizes are most efficient both in reducing inter-protein contacts and simultaneously retaining most of the native-contacts due to strong protein-surface interactions coupled with stabilization due to the confinement. Department of Energy (Grant No DE-FG02-11ER46811).

Essays in the Economics of Energy Development and Disamenities

NASA Astrophysics Data System (ADS)

Rakitan, Timothy J.

This dissertation consists of three essays broadly themed around evaluating the impact of energy infrastructure on local consumers and industries. Taken together, they characterize ways in which the presence of energy activity is reflected in local land and labor market conditions, with a particular focus on the deployment of wind energy generation and shale resource extraction. The first chapter examines the relationship between the placement of wind energy infrastructure and house values and incomes in Iowa. The results suggest that income growth offsets some of the negative house-value effects commonly observed in the evaluation literature, but also that income gains reported in the literature are geographically distributed away from wind farm locations. I conclude that proximity to wind turbines does not increase the real incomes of local residents. The second chapter applies a regional model to county-level wage, house value, employment and energy production data to characterize the economic impact of the U.S. shale boom of the mid-2000s. While the boom has been responsible for wage and employment gains in counties located within the bounds of U.S. shale oil and gas plays, the net effect on house values has been negative. Within the set of energy-producing counties, however, house value declines are mitigated during the boom period as willingness-to-pay for residential space can overcome some of the negative impacts of energy industry activity. I conclude that shale energy extraction is a disamenity at the local level. The third chapter extends the analysis of the impact of the shale boom by examining possible spillovers in agriculture. Using parcel-level data from North Dakota, I analyze rental rates to assess the extent to which oil industry activity affects the returns to agricultural land. While "on-shale" parcels lease at lower rates than parcels located outside the oil fields, I cannot reject the hypothesis that proximity to an oil well has no impact on returns to agricultural land. Since my data examine agricultural surface rents with no associated mineral rights, my results imply that fracking-related house value declines reported in the literature may be due to aesthetic and nuisance considerations rather than lasting local environmental damage.

Optical, mechanical and surface properties of amorphous carbonaceous thin films obtained by plasma enhanced chemical vapor deposition and plasma immersion ion implantation and deposition

NASA Astrophysics Data System (ADS)

Turri, Rafael G.; Santos, Ricardo M.; Rangel, Elidiane C.; da Cruz, Nilson C.; Bortoleto, José R. R.; Dias da Silva, José H.; Antonio, César Augusto; Durrant, Steven F.

2013-09-01

Diverse amorphous hydrogenated carbon-based films (a-C:H, a-C:H:F, a-C:H:N, a-C:H:Cl and a-C:H:Si:O) were obtained by radiofrequency plasma enhanced chemical vapor deposition (PECVD) and plasma immersion ion implantation and deposition (PIIID). The same precursors were used in the production of each pair of each type of film, such as a-C:H, using both PECVD and PIIID. Optical properties, namely the refractive index, n, absorption coefficient, α, and optical gap, ETauc, of these films were obtained via transmission spectra in the ultraviolet-visible near-infrared range (wavelengths from 300 to 3300 nm). Film hardness, elastic modulus and stiffness were obtained as a function of depth using nano-indentation. Surface energy values were calculated from liquid drop contact angle data. Film roughness and morphology were assessed using atomic force microscopy (AFM). The PIIID films were usually thinner and possessed higher refractive indices than the PECVD films. Determined refractive indices are consistent with literature values for similar types of films. Values of ETauc were increased in the PIIID films compared to the PECVD films. An exception was the a-C:H:Si:O films, for which that obtained by PIIID was thicker and exhibited a decreased ETauc. The mechanical properties - hardness, elastic modulus and stiffness - of films produced by PECVD and PIIID generally present small differences. An interesting effect is the increase in the hardness of a-C:H:Cl films from 1.0 to 3.0 GPa when ion implantation is employed. Surface energy correlates well with surface roughness. The implanted films are usually smoother than those obtained by PECVD.

Real-time first-principles simulations of thermionic emission from N-doped diamond surfaces

NASA Astrophysics Data System (ADS)

Shinozaki, Tomoki; Hagiwara, Satoshi; Morioka, Naoya; Kimura, Yuji; Watanabe, Kazuyuki

2018-06-01

We investigate thermionic emission from N-doped C(100) surfaces terminated with H or Li atoms using finite-temperature real-time density functional theory simulations. The current–temperature characteristics are found to follow the Richardson–Dushman (RD) equation, which was derived from a semiclassical theory. However, the Richardson constants are two orders of magnitude smaller than the ideal values from the RD theory. This considerable reduction is attributed primarily to the extremely low transmission probability of electrons from the surfaces toward the vacuum. The present method enables straightforward evaluation of the ideal efficiency of a thermionic energy converter.

The Application of Optimum Value Engineering Design and Construction Techniques to the United States Navy’s Housing Construction Contract Request for Proposal.

DTIC Science & Technology

1988-05-01

thick asphalt pavement and a unit cost of $10/sy for subbase, binder and wearing courses (22), the following costs can be considered: Road Width Cofts...on exposed surfaces, whereas concrete and asphalt absorb and then transmit heat. This is the same rationale used in selecting a white roof over a...Surfaces Item Avg±L !9PRe± M! Trees 80 Grass Lawn i11 Wall Surface 130 ... Asphalt 160 (From Energy Efficient Site Desgn) What constitutes a good site

Multi-Terrain Impact Testing and Simulation of a Composite Energy Absorbing Fuselage Section

NASA Technical Reports Server (NTRS)

Fasanella, Edwin L.; Jackson, Karen E.; Lyle, Karen H.; Sparks, Chad E.; Sareen, Ashish K.

2007-01-01

Comparisons of the impact performance of a 5-ft diameter crashworthy composite fuselage section were investigated for hard surface, soft soil, and water impacts. The fuselage concept, which was originally designed for impacts onto a hard surface only, consisted of a stiff upper cabin, load bearing floor, and an energy absorbing subfloor. Vertical drop tests were performed at 25-ft/s onto concrete, soft-soil, and water at NASA Langley Research Center. Comparisons of the peak acceleration values, pulse durations, and onset rates were evaluated for each test at specific locations on the fuselage. In addition to comparisons of the experimental results, dynamic finite element models were developed to simulate each impact condition. Once validated, these models can be used to evaluate the dynamic behavior of subfloor components for improved crash protection for hard surface, soft soil, and water impacts.

Multi-Terrain Impact Testing and Simulation of a Composite Energy Absorbing Fuselage Section

NASA Technical Reports Server (NTRS)

Fasanella, Edwin L.; Lyle, Karen H.; Sparks, Chad E.; Sareen, Ashish K.

2004-01-01

Comparisons of the impact performance of a 5-ft diameter crashworthy composite fuselage section were investigated for hard surface, soft soil, and water impacts. The fuselage concept, which was originally designed for impacts onto a hard surface only, consisted of a stiff upper cabin, load bearing floor, and an energy absorbing subfloor. Vertical drop tests were performed at 25-ft/s onto concrete, soft-soil, and water at NASA Langley Research Center. Comparisons of the peak acceleration values, pulse durations, and onset rates were evaluated for each test at specific locations on the fuselage. In addition to comparisons of the experimental results, dynamic finite element models were developed to simulate each impact condition. Once validated, these models can be used to evaluate the dynamic behavior of subfloor components for improved crash protection for hard surface, soft soil, and water impacts.

Simulation studies for surfaces and materials strength

NASA Technical Reports Server (NTRS)

Halicioglu, T.

1985-01-01

From intermolecular force studies, it is now known that the overall non-additive contribution to the lattice enegy is positive so that analysis based on only pairwise additivity suggests a shallower intermolecular potential than the true value. Two body contributions alone are also known to be categorically unable to even qualitatively describe some configurations of molecular clusters in the gas phase or the general relaxation and reconstruction of fcc crystal surfaces. In addition, the many-body contribution was shown to play a key role in the stability of certain crystal structures. In these recent analyses, a relatively simple potential energy function (PEF), comprising only a two-body Mie-type potential plus a three-body Axilrod-Teller-type potential, was found to be extremely effective. This same parametric PEF is applied to describe the bulk stability and surface energy for the diamond cubic structure. To test the stability condition, the FCC, BCC, diamond cubic, graphite and beta-tin structures were considered.

Development of a Silicon Drift Detector Array: An X-Ray Fluorescence Spectrometer for Remote Surface Mapping

NASA Technical Reports Server (NTRS)

Gaskin, Jessica A.; Carini, Gabriella A.; Wei, Chen; Elsner, Ronald F.; Kramer, Georgiana; De Geronimo, Gianluigi; Keister, Jeffrey W.; Zheng, Li; Ramsey, Brian D.; Rehak, Pavel;

Use of principle velocity patterns in the analysis of structural acoustic optimization.

PubMed

Johnson, Wayne M; Cunefare, Kenneth A

2007-02-01

This work presents an application of principle velocity patterns in the analysis of the structural acoustic design optimization of an eight ply composite cylindrical shell. The approach consists of performing structural acoustic optimizations of a composite cylindrical shell subject to external harmonic monopole excitation. The ply angles are used as the design variables in the optimization. The results of the ply angle design variable formulation are interpreted using the singular value decomposition of the interior acoustic potential energy. The decomposition of the acoustic potential energy provides surface velocity patterns associated with lower levels of interior noise. These surface velocity patterns are shown to correspond to those from the structural acoustic optimization results. Thus, it is demonstrated that the capacity to design multi-ply composite cylinders for quiet interiors is determined by how well the cylinder be can designed to exhibit particular surface velocity patterns associated with lower noise levels.

Surface excitations in electron spectroscopy. Part I: dielectric formalism and Monte Carlo algorithm

PubMed Central

Salvat-Pujol, F; Werner, W S M

2013-01-01

The theory describing energy losses of charged non-relativistic projectiles crossing a planar interface is derived on the basis of the Maxwell equations, outlining the physical assumptions of the model in great detail. The employed approach is very general in that various common models for surface excitations (such as the specular reflection model) can be obtained by an appropriate choice of parameter values. The dynamics of charged projectiles near surfaces is examined by calculations of the induced surface charge and the depth- and direction-dependent differential inelastic inverse mean free path (DIIMFP) and stopping power. The effect of several simplifications frequently encountered in the literature is investigated: differences of up to 100% are found in heights, widths, and positions of peaks in the DIIMFP. The presented model is implemented in a Monte Carlo algorithm for the simulation of the electron transport relevant for surface electron spectroscopy. Simulated reflection electron energy loss spectra are in good agreement with experiment on an absolute scale. Copyright © 2012 John Wiley & Sons, Ltd. PMID:23794766

3-Hz postural tremor in multiple system atrophy cerebellar type (MSA-C)-a static posturography study.

PubMed

Li, Xiaodi; Wang, Yuzhou; Wang, Zhanhang; Xu, Yan; Zheng, Wenhua

2018-01-01

The objective of the study is to evaluate postural dysfunction of multiple system atrophy-parkinsonian type (MSA-P) and cerebellar type (MSA-C) by static posturography exam. A total of 29 MSA-P patients, 40 MSA-C patients, and 23 healthy controls (HC) were recruited and engaged in a sensory organization test (SOT). The amplitude of the postural sway was measured and transformed into energy value by Fourier analyzer. SOT scores, frequency of falls and typical 3-Hz postural tremors during the four stance tasks, and energy value in three different frequency bands were recorded and compared. Compared with HC, SOT scores were significantly lower in MSA groups (P < 0.01). Compared with MSA-P, the vestibular scores were further reduced in MSA-C patients (P < 0.05). Falls were more frequent in MSA groups, especially in SOT4 task (foam surface with eyes closed) or in MSA-C group (P < 0.05). Typical 3-Hz postural tremor was observed in 97.5% MSA-C patients, in 24.1% MSA-P patients but in none of the HC (P < 0.05). Compared with HC, much more energy was consumed in every task, every direction, and nearly every frequency band in MSA groups. Energy value of MSA-C group was significantly higher than that of MSA-P, especially in higher frequency band (2 ~ 20 Hz) or in more difficult stance tasks (SOT 3 ~ 4, foam surface with eyes open or closed) (P < 0.05). Both MSA-P and MSA-C were characterized by severe static postural dysfunction. However, typical 3-Hz postural tremor was predominant in MSA-C and was very useful in the differential diagnosis between MSA-P and MSA-C.

Empirical correlation between hydrophobic free energy and aqueous cavity surface area

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reynolds, J.A.; Gilbert, D.B.; Tanford, C.

1974-08-01

The unitary free energy of transfer of a hydrocarbon molecule from a hydrocarbon solvent to an aqueous medium is a measure of the hydrophobic interaction in the aqueous medium. We have reexamined available data on this phenomenon and have confirmed that the free energy for saturated hydrocarbons is proportional to the surface area of the cavity created by the solute in the aqueous solution, with the same proportionality constant for linear, branched, and cyclic hydrocarbon molecules. The numerical value of the proportionality constant is uncertain because absolute and self-consistent area measurements are not available. We estimate that it falls betweenmore » 20 and 25 cal/mole per Angstrom/sup 2/ at 25/sup 0/ (for areas measured at the distance of closest approach of water molecules), which is significantly less than the figure of 33 cal/mole per Angstrom/sup 2/ that has been assigned to the same parameter by Hermann.« less

Accurate quantum wave packet calculations for the F + HCl → Cl + HF reaction on the ground 1(2)A' potential energy surface.

PubMed

Bulut, Niyazi; Kłos, Jacek; Alexander, Millard H

2012-03-14

We present converged exact quantum wave packet calculations of reaction probabilities, integral cross sections, and thermal rate coefficients for the title reaction. Calculations have been carried out on the ground 1(2)A' global adiabatic potential energy surface of Deskevich et al. [J. Chem. Phys. 124, 224303 (2006)]. Converged wave packet reaction probabilities at selected values of the total angular momentum up to a partial wave of J = 140 with the HCl reagent initially selected in the v = 0, j = 0-16 rovibrational states have been obtained for the collision energy range from threshold up to 0.8 eV. The present calculations confirm an important enhancement of reactivity with rotational excitation of the HCl molecule. First, accurate integral cross sections and rate constants have been calculated and compared with the available experimental data.

Parametric and energy consumption optimization of Basic Red 2 removal by electrocoagulation/egg shell adsorption coupling using response surface methodology in a batch system.

PubMed

de Carvalho, Helder Pereira; Huang, Jiguo; Zhao, Meixia; Liu, Gang; Yang, Xinyu; Dong, Lili; Liu, Xingjuan

2016-01-01

In this study, response surface methodology (RSM) model was applied for optimization of Basic Red 2 (BR2) removal using electrocoagulation/eggshell (ES) coupling process in a batch system. Central composite design was used to evaluate the effects and interactions of process parameters including current density, reaction time, initial pH and ES dosage on the BR2 removal efficiency and energy consumption. The analysis of variance revealed high R(2) values (≥85%) indicating that the predictions of RSM models are adequately applicable for both responses. The optimum conditions when the dye removal efficiency of 93.18% and energy consumption of 0.840 kWh/kg were observed were 11.40 mA/cm(2) current density, 5 min and 3 s reaction time, 6.5 initial pH and 10.91 g/L ES dosage.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Christensen, C.; Horowitz, S.

In subdivisions, house orientations are largely determined by street layout. The resulting house orientations affect energy consumption (annual and on-peak) for heating and cooling, depending on window area distributions and shading from neighboring houses. House orientations also affect energy production (annual and on-peak) from solar thermal and photovoltaic systems, depending on available roof surfaces. Therefore, house orientations fundamentally influence both energy consumption and production, and an appropriate street layout is a prerequisite for taking full advantage of energy efficiency and renewable energy opportunities. The potential influence of street layout on solar performance is often acknowledged, but solar and energy issuesmore » must compete with many other criteria and constraints that influence subdivision street layout. When only general guidelines regarding energy are available, these factors may be ignored or have limited effect. Also, typical guidelines are often not site-specific and do not account for local parameters such as climate and the time value of energy. For energy to be given its due consideration in subdivision design, energy impacts need to be accurately quantified and displayed interactively to facilitate analysis of design alternatives. This paper describes a new computerized Subdivision Energy Analysis Tool being developed to allow users to interactively design subdivision street layouts while receiving feedback about energy impacts based on user-specified building design variants and availability of roof surfaces for photovoltaic and solar water heating systems.« less

Evaluation of surface topography of zirconia ceramic after Er:YAG laser etching.

PubMed

Turp, Volkan; Akgungor, Gokhan; Sen, Deniz; Tuncelli, Betul

2014-10-01

The aim of this study is to evaluate the effect of Erbium: yttrium-aluminum-garnet (Er:YAG) laser with different pulse lengths on the surface roughness of zirconia ceramic and airborne particle abrasion. Er:YAG laser treatment is expected to be an alternative surface treatment method for zirconia ceramics; however, the parameters and success of the application are not clear. One hundred and forty zirconia discs (diameter, 10 mm; thickness, 1.2 mm) were prepared by a computer-aided design and computer-aided manufacturing (CAD/CAM) system according to the manufacturer's instructions. Specimens were divided into 14 groups (n=10). One group was left as polished control, one group was air-particle abraded with Al2O3 particles. For the laser treatment groups, laser irradiation was applied at three different pulse energy levels (100, 200, and 300 mJ) and for each energy level at four different pulse lengths; 50, 100, 300, and 600 μs. Surface roughness was evaluated with an optical profilometer and specimens were evaluated with scanning electron microscopy (SEM). Data was analyzed with one way ANOVA and Tukey multiple comparison tests (α=0.05). For the 100 and 200 mJ laser etching groups, 50 and 100 μs laser duration resulted in significantly higher surface roughness compared with air-particle abrasion (p<0.05). The difference among Ra values of 300 μs, 600 μs, and air-particle abrasion groups were not statistically significant (p>0.05). For the 300 mJ laser etching groups; there was no statistically significant difference among the Ra values of 50 μs, 100 μs, 300 μs, 600 μs, and air-particle abrasion groups (p>0.05). In order to increase surface roughness and promote better bonding to resin luting agents, Er:YAG laser etching may be an alternative to air-particle abrasion for zirconia ceramics. However, high levels of pulse energy and longer pulse length may have an adverse effect on micromechanical locking properties, because of a decrease in surface roughness.

High-tensile strength sticking induced by ArF excimer laser surface treatment of poly(tetrafluoroethylene)

NASA Astrophysics Data System (ADS)

Hopp, Bela; Revesz, K.; Bor, Zsolt

1998-07-01

A successful enhancement of sticking of PTFE is demonstrated using ArF excimer laser irradiation in the presence of novel photoreagents. The applied laser fluence was very low at the sample - photoreagent liquid interface compared to the energy density applied in earlier investigations. After the treatment the PTFE films were glued by epoxy resin. It was found that at low doses the tensile strength of the sticking increased rapidly with the UV pulse number and the reached a saturation value, which was 6.66 MPa for triethylamine, 5.56 MPa in the case of 1,2-diaminoethane and 4.64 MPa for triethylene-tetramine. These are around two hundred times higher than the value of the untreated surface. It was found that this procedure makes the metallization and painting of PTFE surface also possible. A photoinduced electron transfer mechanism was suggested to describe the photoreaction, which is responsible for the increase of adhesion features on PTFE surface.

Dielectric capacitors with three-dimensional nanoscale interdigital electrodes for energy storage.

PubMed

Han, Fangming; Meng, Guowen; Zhou, Fei; Song, Li; Li, Xinhua; Hu, Xiaoye; Zhu, Xiaoguang; Wu, Bing; Wei, Bingqing

2015-10-01

Dielectric capacitors are promising candidates for high-performance energy storage systems due to their high power density and increasing energy density. However, the traditional approach strategies to enhance the performance of dielectric capacitors cannot simultaneously achieve large capacitance and high breakdown voltage. We demonstrate that such limitations can be overcome by using a completely new three-dimensional (3D) nanoarchitectural electrode design. First, we fabricate a unique nanoporous anodic aluminum oxide (AAO) membrane with two sets of interdigitated and isolated straight nanopores opening toward opposite planar surfaces. By depositing carbon nanotubes in both sets of pores inside the AAO membrane, the new dielectric capacitor with 3D nanoscale interdigital electrodes is simply realized. In our new capacitors, the large specific surface area of AAO can provide large capacitance, whereas uniform pore walls and hemispheric barrier layers can enhance breakdown voltage. As a result, a high energy density of 2 Wh/kg, which is close to the value of a supercapacitor, can be achieved, showing promising potential in high-density electrical energy storage for various applications.

Dielectric capacitors with three-dimensional nanoscale interdigital electrodes for energy storage

PubMed Central

Han, Fangming; Meng, Guowen; Zhou, Fei; Song, Li; Li, Xinhua; Hu, Xiaoye; Zhu, Xiaoguang; Wu, Bing; Wei, Bingqing

2015-01-01

Dielectric capacitors are promising candidates for high-performance energy storage systems due to their high power density and increasing energy density. However, the traditional approach strategies to enhance the performance of dielectric capacitors cannot simultaneously achieve large capacitance and high breakdown voltage. We demonstrate that such limitations can be overcome by using a completely new three-dimensional (3D) nanoarchitectural electrode design. First, we fabricate a unique nanoporous anodic aluminum oxide (AAO) membrane with two sets of interdigitated and isolated straight nanopores opening toward opposite planar surfaces. By depositing carbon nanotubes in both sets of pores inside the AAO membrane, the new dielectric capacitor with 3D nanoscale interdigital electrodes is simply realized. In our new capacitors, the large specific surface area of AAO can provide large capacitance, whereas uniform pore walls and hemispheric barrier layers can enhance breakdown voltage. As a result, a high energy density of 2 Wh/kg, which is close to the value of a supercapacitor, can be achieved, showing promising potential in high-density electrical energy storage for various applications. PMID:26601294

Apparatus and method for investigation of energy consumption of microwave assisted drying systems.

PubMed

Göllei, Attila; Vass, András; Magyar, Attila; Pallai, Elisabeth

2009-10-01

Convective, hot air drying by itself is relatively efficient for removing water from the surface environment of agricultural seed products. However, moving internal moisture to the surface needs rather a long time, as a rule. The major research aim of the authors was to decrease the processing time and processing costs, to improve the quality of the dried product, and to increase drying efficiency. For this reason their research activities focused on the development of a special drying apparatus and a method suitable for measuring of energy conditions in a hybrid (microwave and convective) dryer. Experimental investigations were made with moistened wheat as model material. Experiments were carried out in microwave, convective and hybrid drying systems. The microwave drying alone was more efficient than the convective method. The lowest energy consumption and shortest drying time were obtained by the use of a hybrid method in which the waste energy of magnetron was utilized and the temperature was controlled. In this way, it was possible to keep the temperature of the dried product at a constant and safe value and to considerably decrease the energy consumption.

Investigation of the highest bound ro-vibrational states of H+ 3, DH+ 2, HD+ 2, D+ 3, and T+ 3: use of a non-direct product basis to compute the highest allowed J > 0 states

NASA Astrophysics Data System (ADS)

Jaquet, Ralph

2013-09-01

A Lanczos algorithm with a non-direct product basis was used to compute energy levels of H+ 3, H2D+, D2H+, D+ 3, and T+ 3 with J values as large as 46, 53, 66, 66, and 81. The energy levels are based on a modified potential surface of M. Pavanello et al. that is better adapted to the ab initio energies near the dissociation limit.

Theoretical study of adsorption of amino acids on graphene and BN sheet in gas and aqueous phase with empirical DFT dispersion correction.

PubMed

Singla, Preeti; Riyaz, Mohd; Singhal, Sonal; Goel, Neetu

2016-02-21

Understanding interactions of biomolecules with nanomaterials at the molecular level is crucial to design new materials for practical use. In the present study, adsorption of three distinct types of amino acids, namely, valine, arginine and aspartic acid, over the surface of structurally analogous but chemically different graphene and BN nanosheets has been explored within the formalism of DFT. The explicit dispersion correction incorporated in the computational methodology improves the accuracy of the results by accounting for long range van der Waals interactions and is essential for agreement with experimental values. The real biological environment has been mimicked by re-optimizing all the model structures in an aqueous medium. The study provides ample evidence in terms of adsorption energy, solvation energy, separation distance and charge analysis to conclude that both the nano-surfaces adsorb the amino acids with release of energy and there are no bonded interactions between the two. The polarity of the BN nanosheet provides it an edge over the graphene surface to have more affinity towards amino acids.

Experimental determination of positron-related surface characteristics of 6H-SiC

NASA Astrophysics Data System (ADS)

Nangia, A.; Kim, J. H.; Weiss, A. H.; Brauer, G.

2002-03-01

The positron work function of 6H-SiC was determined to be -2.1±0.1 eV from an analysis of the energy spectrum of positrons reemitted from the surface. The positron reemission yield, highest in the sample inserted into vacuum after atmospheric exposure and cleaning with ethanol, was significantly reduced after sputtering with 3 keV, 125 μA min Ne+ ions. The yield was not recovered even after annealing at 900 °C, presumably due to the stability of sputter induced defects. Sputtering at lower energies caused a smaller decrease in the reemission yield that was largely recovered after annealing at 850 °C. Analysis using electron induced Auger electron spectroscopy and positron-annihilation-induced Auger electron spectroscopy indicated that the surface was Si enriched after sputtering and C enriched after subsequent annealing. Values of positron diffusion length and mobility in the unsputtered material were extracted from the dependence of the reemission yield on the beam energy. The application of SiC as a field-assisted positron moderator is discussed.

Kinetics of the sorption of triterpene saponin by hypercrosslinked polystyrene

NASA Astrophysics Data System (ADS)

Mironenko, N. V.; Brezhneva, T. A.; Selemenev, V. F.

2013-03-01

The kinetics of sorption of triterpene saponin by the polymer sorbent NM-200 is considered. The influence of the surface activity of glycoside on the rate of formation and structure of the adsorption layer on the sorbent's surface is established. The rate-determining step of sorption is found to be diffusion into the sorbent grain. The value of the activation energy demonstrates the determining role of dispersion forces in the interaction between triterpene saponin and the polymer sorbent MN-200.

Application of classical thermodynamic principles to the study of oceanic overturning circulation

NASA Astrophysics Data System (ADS)

Gade, Herman G.; Gustafsson, Karin E.

2004-08-01

Stationary deep-reaching overturning circulation in the ocean is studied by means of classical thermodynamic methods employing closed cycles in pV-space (p, pressure; V, volume). From observed (or computed) density fields, the pV-method may be used to infer the power required for driving a circulation with a given mass flux, or, if the available power is known, the resulting mass flux of the circulation may be assessed. Here, the circulation is assumed to be driven by diapycnal mixing caused by internal disturbances of meteorological and tidal origin and from transfer of geothermal heat through the ocean bottom. The analysis is developed on the basis that potential energy produced by any of these mechanisms is available for driving a circulation of the water masses above its level of generation. The method also takes into account secondary generated potential energy resulting from turbulence developed by the ensuing circulation.Models for different types of circulation are developed and applied to four types of hemispheric circulation with deep-water formation, convection and sinking in an idealized North Atlantic. Our calculations show that the energy input must exceed 15 J kg1 for a cycle to the bottom to exist. An energy supply of 2 TW would in that case support a constant vertical mass flux of 3.2 G kg s1 (3.1 Sv). Computed mass fluxes reaching the surface in the subtropics, corresponding to the same energy input, range between 2.3 5.2 G kg s1, depending on the type of convection/sinking involved. Much higher flux values ensue with ascending water masses reaching the surface at higher geographical latitudes.The study reveals also that compressibility of sea water does not enhance the circulation. An incompressible system, operating within the same mass flux and temperature range, would require about 25% less energy supply, provided that the circulation comprises the same water masses. It is furthermore shown that the meridional distribution of surface salinity, with higher values in the tropics and lower values in regions of deep-water formation, actually enhances the circulation in comparison with one of a more uniform surface salinity. With a homohaline North Atlantic, operating within the same temperature range as presently observed, an increase of 66% of power supply would be required in order that the mass flux of the overturning circulation should remain the same.

Multi-objective optimization on laser solder jet bonding process in head gimbal assembly using the response surface methodology

NASA Astrophysics Data System (ADS)

Deeying, J.; Asawarungsaengkul, K.; Chutima, P.

2018-01-01

This paper aims to investigate the effect of laser solder jet bonding parameters to the solder joints in Head Gimbal Assembly. Laser solder jet bonding utilizes the fiber laser to melt solder ball in capillary. The molten solder is transferred to two bonding pads by nitrogen gas. The response surface methodology have been used to investigate the effects of laser energy, wait time, nitrogen gas pressure, and focal position on the shear strength of solder joints and the change of pitch static attitude (PSA). The response surface methodology is employed to establish the reliable mathematical relationships between the laser soldering parameters and desired responses. Then, multi-objective optimization is conducted to determine the optimal process parameters that can enhance the joint shear strength and minimize the change of PSA. The validation test confirms that the predicted value has good agreement with the actual value.

Optimization of Energy Consumption and Mass Transfer Parameters in a Surface Aeration Vessel.

PubMed

Mohammadpour, A; AkhavanBehabadi, M A; Ebrahimzadeh, M; Raisee, M; MajdiNasab, A R; Nosrati, M; Mousavi, S M

2016-04-01

This paper reports tests on a lab-scale surface aeration vessel was equipped with a Rushton turbine to examine its performance in terms of standard aeration efficiency (SAE), mixing time, and void fraction characteristics. These characteristics were investigated by tests using variations of rotor speed, impeller immersion depth, and water level. Results showed that variation of impeller immersion depth had a greater effect on the SAE compared to variation of water level. Moreover, the SAE increased with rotor speeds up to about 150 to 200 rpm and then decreased. In addition, void fraction improved by impeller immersion depth and rotor speed enhancement; however, mixing time and power number were reduced as rotor speed increased. According to the response surface methodology statistical optimizations, optimum values for rotor speed, impeller immersion depth, and water level were 168.90 rpm, 25 mm, and 30 cm, respectively, to achieve the maximum value of SAE.

An investigation of the normal momentum transfer for gases on tungsten

NASA Technical Reports Server (NTRS)

Moskal, E. J.

1971-01-01

The near monoenergetic beam of neutral helium and argon atoms impinged on a single crystal tungsten target, with the (100) face exposed to the beam. The target was mounted on a torsion balance. The rotation of this torsion balance was monitored by an optical lever, and this reading was converted to a measurement of the momentum exchange between the beam and the target. The tungsten target was flashed to a temperature in excess of 2000 C before every clean run, and the vacuum levels in the final chamber were typically between 0.5 and 1 ntorr. The momentum exchange for the helium-tungsten surface and the argon-tungsten surface combination was obtained over approximately a decade of incoming energy (for the argon gas) at angles of incidence of 0, 30, and 41 deg on both clean and dirty (gas covered) surfaces. The results exhibited a significant variation in momentum transfer between the data obtained for the clean and dirty surfaces. The values of normal momentum accommodation coefficient for the clean surface were found to be lower than the values previously reported.

Homogenous Surface Nucleation of Solid Polar Stratospheric Cloud Particles

NASA Technical Reports Server (NTRS)

Tabazadeh, A.; Hamill, P.; Salcedo, D.; Gore, Warren J. (Technical Monitor)

2002-01-01

A general surface nucleation rate theory is presented for the homogeneous freezing of crystalline germs on the surfaces of aqueous particles. While nucleation rates in a standard classical homogeneous freezing rate theory scale with volume, the rates in a surface-based theory scale with surface area. The theory is used to convert volume-based information on laboratory freezing rates (in units of cu cm, seconds) of nitric acid trihydrate (NAT) and nitric acid dihydrate (NAD) aerosols into surface-based values (in units of sq cm, seconds). We show that a surface-based model is capable of reproducing measured nucleation rates of NAT and NAD aerosols from concentrated aqueous HNO3 solutions in the temperature range of 165 to 205 K. Laboratory measured nucleation rates are used to derive free energies for NAT and NAD germ formation in the stratosphere. NAD germ free energies range from about 23 to 26 kcal mole, allowing for fast and efficient homogeneous NAD particle production in the stratosphere. However, NAT germ formation energies are large (greater than 26 kcal mole) enough to prevent efficient NAT particle production in the stratosphere. We show that the atmospheric NAD particle production rates based on the surface rate theory are roughly 2 orders of magnitude larger than those obtained from a standard volume-based rate theory. Atmospheric volume and surface production of NAD particles will nearly cease in the stratosphere when denitrification in the air exceeds 40 and 78%, respectively. We show that a surface-based (volume-based) homogeneous freezing rate theory gives particle production rates, which are (not) consistent with both laboratory and atmospheric data on the nucleation of solid polar stratospheric cloud particles.

Investigation of pH response and photo-control of wettability on spiropyran-derivatized surfaces

NASA Astrophysics Data System (ADS)

Park, Choong-Do

2009-12-01

One promising method to control a liquid drop on a surface for microfluidic devices is to use the surface tension gradient on a photo-responsive surface by light irradiation. A photo-switchable spiropyran monolayer was prepared on smooth glass or silicon wafers via 3-aminopropylmethyldiethoxysilane linkages. The pH response of the surface-bound spiropyran was investigated by measuring contact angle as a function of pH, since the pH value of the liquids applied to a microfluidic system can vary widely. Based on the contact angle titration and UV-Vis spectroscopic data, a protonation and deprotonation mechanism of the surface-bound spiropyran was proposed. The advancing contact angles under UV and under visible light irradiation at high pH values were about 100 smaller than those at low pH values. The decrease in contact angle under UV light with decreasing pH value was assigned to the protonation of open merocyanine (MC) to MC-OH+. Meanwhile, the decrease in contact angle under visible light was attributed to the protonation of the closed spiropryan (SP), generating a mixed state of MC-OH+ in equilibrium with N-protonated SP-NH+. In order to examine the possibility of light-induced liquid drop motion on the spiropyran-derivatized smooth surfaces, the light-induced surface tension change between SP and MC was estimated using the contact angle hysteresis (CAH) and the Lifshitz---van der Waals/Acid-Base (LWAB) approaches based on the contact angle data. The average light-induced surface energy change between the two isomers under UV and visible light exposure was 1.4 mJ/m 2, implying that the small change in surface tension is not sufficient to move a liquid droplet on the surface. Liquid drop motion requires that the light-induced switching angle be greater than the contact angle hysteresis. However, the light-induced switching angle of the spiropyran-derivatized surface was significantly smaller than the hysteresis. Thus, in order to achieve liquid drop motion on the spiropyran-derivatized surface, a new surface design which employs a combination of chemical modification of a hydrophobic organosilane and micropatterned rough surface morphology was suggested.

Intrinsic map dynamics exploration for uncharted effective free-energy landscapes

PubMed Central

Covino, Roberto; Coifman, Ronald R.; Gear, C. William; Georgiou, Anastasia S.; Kevrekidis, Ioannis G.

2017-01-01

We describe and implement a computer-assisted approach for accelerating the exploration of uncharted effective free-energy surfaces (FESs). More generally, the aim is the extraction of coarse-grained, macroscopic information from stochastic or atomistic simulations, such as molecular dynamics (MD). The approach functionally links the MD simulator with nonlinear manifold learning techniques. The added value comes from biasing the simulator toward unexplored phase-space regions by exploiting the smoothness of the gradually revealed intrinsic low-dimensional geometry of the FES. PMID:28634293

Verification of land-atmosphere coupling in forecast models, reanalyses and land surface models using flux site observations.

PubMed

Dirmeyer, Paul A; Chen, Liang; Wu, Jiexia; Shin, Chul-Su; Huang, Bohua; Cash, Benjamin A; Bosilovich, Michael G; Mahanama, Sarith; Koster, Randal D; Santanello, Joseph A; Ek, Michael B; Balsamo, Gianpaolo; Dutra, Emanuel; Lawrence, D M

2018-02-01

We confront four model systems in three configurations (LSM, LSM+GCM, and reanalysis) with global flux tower observations to validate states, surface fluxes, and coupling indices between land and atmosphere. Models clearly under-represent the feedback of surface fluxes on boundary layer properties (the atmospheric leg of land-atmosphere coupling), and may over-represent the connection between soil moisture and surface fluxes (the terrestrial leg). Models generally under-represent spatial and temporal variability relative to observations, which is at least partially an artifact of the differences in spatial scale between model grid boxes and flux tower footprints. All models bias high in near-surface humidity and downward shortwave radiation, struggle to represent precipitation accurately, and show serious problems in reproducing surface albedos. These errors create challenges for models to partition surface energy properly and errors are traceable through the surface energy and water cycles. The spatial distribution of the amplitude and phase of annual cycles (first harmonic) are generally well reproduced, but the biases in means tend to reflect in these amplitudes. Interannual variability is also a challenge for models to reproduce. Our analysis illuminates targets for coupled land-atmosphere model development, as well as the value of long-term globally-distributed observational monitoring.

Countermeasures to Microbiofouling in Simulated Ocean Thermal Energy Conversion Heat Exchangers with Surface and Deep Ocean Waters in Hawaii

PubMed Central

Berger, Leslie Ralph; Berger, Joyce A.

1986-01-01

Countermeasures to biofouling in simulated ocean thermal energy conversion heat exchangers have been studied in single-pass flow systems, using cold deep and warm surface ocean waters off the island of Hawaii. Manual brushing of the loops after free fouling periods removed most of the biofouling material. However, over a 2-year period a tenacious film formed. Daily free passage of sponge rubber balls through the tubing only removed the loose surface biofouling layer and was inadequate as a countermeasure in both titanium and aluminum alloy tubes. Chlorination at 0.05, 0.07, and 0.10 mg liter-1 for 1 h day-1 lowered biofouling rates. Only at 0.10 mg liter-1 was chlorine adequate over a 1-year period to keep film formation and heat transfer resistance from rising above the maximum tolerated values. Lower chlorination regimens led to the buildup of uneven or patchy films which produced increased flow turbulence. The result was lower heat transfer resistance values which did not correlate with the amount of biofouling. Surfaces which were let foul and then treated with intermittent or continuous chlorination at 0.10 mg of chlorine or less per liter were only partially or unevenly cleaned, although heat transfer measurements did not indicate that fact. It took continuous chlorination at 0.25 mg liter-1 to bring the heat transfer resistance to zero and eliminate the fouling layer. Biofouling in deep cold seawater was much slower than in the warm surface waters. Tubing in one stainless-steel loop had a barely detectable fouling layer after 1 year in flow. With aluminum alloys sufficient corrosion and biofouling material accumulated to require that some fouling coutermeasure be used in long-term operation of an ocean thermal energy conversion plant. Images PMID:16347076

The influence of variations of vegetation and soil moisture on surface weather and atmospheric circulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, R.

1992-01-01

The influence of variations of vegetation and soil moisture on surface weather and atmospheric circulation is studied through the use of the Simple Biosphere Model (SiB) and the Center for Ocean-Land-Atmosphere interactions (COLA) GCM. Tests for the SiB sensitivity to the conversion of the forest to other short vegetation or bare soil were performed at Amazonian and Great Plains sites, and a North Wales spruce forest site respectively. The results show that deforestation has a significant influence on the local surface energy budget and surface weather. The influence is especially prominent at the Amazon and Great Plains sites, and largermore » in summer than in other seasons. The influence on the partitioning of surface incoming radiative energy is generally constrained by the local atmospheric boundary condition. The sensitivity of the COLA GCM to changes in initial soil wetness (ISW) is determined by repeating three 10-day model integrations with the same initial and boundary conditions as the control runs except the values of ISW, which are revised at 69 model grid points covering much of the continental U.S. It is found that the relations between the changes in the 5-day mean forecast surface air temperature/surface specific humidity and the changes in ISW depend upon vegetation type and the values of ISW, and can be approximated by regression equations. These relations are also confirmed with independent data. With the ISW revised based on these regression equations the surface forecasts of the revised runs are consistently improved. The spatial scale of the ISW anomaly determines the degree and range of the influence. The influence of a small regional ISW change is mainly confined to the local region and to low atmospheric levels. The influence on surface fluxes is strong and persists for more than one month, but the effects on precipitation are relatively weak, changeable, and complex, particularly when an interactive cloud scheme is used.« less

A strategic approach to physico-chemical analysis of bis (thiourea) lead chloride - A reliable semi-organic nonlinear optical crystal

NASA Astrophysics Data System (ADS)

Rajagopalan, N. R.; Krishnamoorthy, P.; Jayamoorthy, K.

2017-03-01

Good quality crystals of bis thiourea lead chloride (BTLC) have been grown by slow evaporation method from aqueous solution. Orthorhombic structure and Pna21 space group of the crystals have been identified by single crystal X-ray diffraction. Studies on nucleation kinetics of grown BTLC has been carried out from which meta-stable zone width, induction period, free energy change, critical radius, critical number and growth rate have been calculated. The experimental values of interfacial surface energy for the crystal growth process have been compared with theoretical models. Ultra violet transmittance studies resulted in a high transmittance and wide band gap energy suggested the required optical transparency of the crystal. The second harmonic generation (SHG) and phase matching nature of the crystal have been justified by Kurtz-Perry method. The SHG nature of the crystal has been further attested by the higher values of theoretical hyper polarizability. The dielectric nature of the crystals at different temperatures with varying frequencies has been thoroughly studied. The activation energy values of the electrical process have been calculated from ac conductivity study. Solid state parameters including valence electron plasma energy, Penn gap, Fermi energy and polarisability have been unveiled by theoretical approach and correlated with the crystal's SHG efficiency. The values of hardness number, elastic stiffness constant, Meyer's Index, minimum level of indentation load, load dependent constant, fracture toughness, brittleness index and corrected hardness obtained from Vicker's hardness test clearly showed that the BTLC crystal has good mechanical stability required for NLO device fabrication.

Design of control laws for flutter suppression based on the aerodynamic energy concept and comparisons with other design methods

NASA Technical Reports Server (NTRS)

Nissim, Eli

1990-01-01

The aerodynamic energy method is used to synthesize control laws for NASA's drone for aerodynamic and structural testing-aerodynamic research wing 1 (DAST-ARW1) mathematical model. The performance of these control laws in terms of closed-loop flutter dynamic pressure, control surface activity, and robustness is compared with other control laws that relate to the same model. A control law synthesis technique that makes use of the return difference singular values is developed. It is based on the aerodynamic energy approach and is shown to yield results that are superior to those results given in the literature and are based on optimal control theory. Nyquist plots are presented, together with a short discussion regarding the relative merits of the minimum singular value as a measure of robustness as compared with the more traditional measure involving phase and gain margins.

Design of control laws for flutter suppression based on the aerodynamic energy concept and comparisons with other design methods

NASA Technical Reports Server (NTRS)

Nissim, E.

1989-01-01

The aerodynamic energy method is used in this paper to synthesize control laws for NASA's Drone for Aerodynamic and Structural Testing-Aerodynamic Research Wing 1 (DAST-ARW1) mathematical model. The performance of these control laws in terms of closed-loop flutter dynamic pressure, control surface activity, and robustness is compared against other control laws that appear in the literature and relate to the same model. A control law synthesis technique that makes use of the return difference singular values is developed in this paper. it is based on the aerodynamic energy approach and is shown to yield results superior to those given in the literature and based on optimal control theory. Nyquist plots are presented together with a short discussion regarding the relative merits of the minimum singular value as a measure of robustness, compared with the more traditional measure of robustness involving phase and gain margins.

Impact of P/In flux ratio and epilayer thickness on faceting for nanoscale selective area growth of InP by molecular beam epitaxy.

PubMed

Fahed, M; Desplanque, L; Coinon, C; Troadec, D; Wallart, X

2015-07-24

The impact of the P/In flux ratio and the deposited thickness on the faceting of InP nanostructures selectively grown by molecular beam epitaxy (MBE) is reported. Homoepitaxial growth of InP is performed inside 200 nm wide stripe openings oriented either along a [110] or [1-10] azimuth in a 10 nm thick SiO2 film deposited on an InP(001) substrate. When varying the P/In flux ratio, no major shape differences are observed for [1-10]-oriented apertures. On the other hand, the InP nanostructure cross sections strongly evolve for [110]-oriented apertures for which (111)B facets are more prominent and (001) ones shrink for large P/In flux ratio values. These results show that the growth conditions allow tailoring the nanocrystal shape. They are discussed in the framework of the equilibrium crystal shape model using existing theoretical calculations of the surface energies of different low-index InP surfaces as a function of the phosphorus chemical potential, directly related to the P/In ratio. Experimental observations strongly suggest that the relative (111)A surface energy is probably smaller than the calculated value. We also discuss the evolution of the nanostructure shape with the InP-deposited thickness.

Quantification of Staphylococcus aureus adhesion forces on various dental restorative materials using atomic force microscopy

NASA Astrophysics Data System (ADS)

Merghni, Abderrahmen; Kammoun, Dorra; Hentati, Hajer; Janel, Sébastien; Popoff, Michka; Lafont, Frank; Aouni, Mahjoub; Mastouri, Maha

2016-08-01

In the oral cavity dental restorative biomaterials can act as a reservoir for infection with opportunistic Staphylococcus aureus pathogen, which can lead to the occurrence of secondary caries and treatment failures. Our aim was to evaluate the adhesion forces by S. aureus on four dental restorative biomaterials and to correlate this finding to differences in specific surface characteristics. Additionally, the influence of salivary conditioning films in exerted adhesion forces was investigated. The substrate hydrophobicity was measured by goniometer and the surface free energy was calculated using the equilibrium advancing contact angle values of water, formamide, and diiodomethane on the tested surfaces. The surface roughness was determined using atomic force microscope (AFM). Additionally, cell force spectroscopy was achieved to quantify the forces that drive cell-substrate interactions. S. aureus bacterium exerted a considerable adhesion forces on various dental restorative materials, which decreased in the presence of saliva conditioning film. The influence of the surface roughness and free energy in initial adhesion appears to be more important than the effect of hydrophobicity, either in presence or absence of saliva coating. Hence, control of surface properties of dental restorative biomaterials is of crucial importance in preventing the attachment and subsequent the biofilm formation.

Facile synthesis of stable superhydrophobic nanocomposite based on multi-walled carbon nanotubes

NASA Astrophysics Data System (ADS)

Mokarian, Zahra; Rasuli, Reza; Abedini, Yousefali

2016-04-01

A facile approach to fabricate a stable superhydrophobic composite comprising multi-walled carbon nanotubes and silicone rubber has been reported. Contact angle of de-ionized water droplets on the prepared surface was measured with the value of near 159°; while water droplets easily rolled off and bounced on it. Surface free energy of the superhydrophobic coating was examined by three methods about 26 mJ/m2. The prepared film shows good stability under high stress conditions such as ultraviolet exposure, heating, pencil hardness test, attacking with different pH value and ionic-strength solutions. In addition, remarkable stability of the coating was observed after soaking in condensed hydrochloric acid, 5 wt.% NaCl aqueous solution, boiling water and tape test.

Light-extraction efficiency and forward voltage in GaN-based light-emitting diodes with different patterns of V-shaped pits

NASA Astrophysics Data System (ADS)

Wang, Min-Shuai; Huang, Xiao-Jing

2013-08-01

We present a new method of making a textured V-pit surface for improving the light extraction efficiency in GaN-based light-emitting diodes and compare it with the usual low-temperature method for p-GaN V-pits. Three types of GaN-based light-emitting diodes (LEDs) with surface V-pits in different densities and regions were grown by metal—organic chemical vapor deposition. We achieved the highest output power and lowest forward voltage values with the p-InGaN V-pit LED. The V-pits enhanced the light output power values by 1.45 times the values of the conventional LED owing to an enhancement of the light scattering probability and an effective reduction of Mg-acceptor activation energy. Moreover, this new technique effectively solved the higher forward voltage problem of the usual V-pit LED.

Self-energy and self-force in the space-time of a thick cosmic string

NASA Astrophysics Data System (ADS)

Khusnutdinov, N. R.; Bezerra, V. B.

2001-10-01

We calculate the self-energy and self-force for an electrically charged particle at rest in the background of Gott-Hiscock cosmic string space-time. We find the general expression for the self-energy which is expressed in terms of the S matrix of the scattering problem. The self-energy continuously falls down outward from the string's center with the maximum at the origin of the string. The self-force is repulsive for an arbitrary position of the particle. It tends to zero in the string's center and also far from the string and it has a maximum value at the string's surface. The plots of the numerical calculations of the self-energy and self-force are shown.

Characterization and attenuation study on tannin-added Rhizophora spp. particleboard at high energy photon and electron

NASA Astrophysics Data System (ADS)

Yusof, Mohd Fahmi Mohd; Hamid, Puteri Nor Khatijah Abd; Tajuddin, Abd Aziz; Abdullah, Reduan; Hashim, Rokiah; Bauk, Sabar; Isa, Norriza Mohd; Isa, Muhammad Jamal Md

2017-01-01

The effective atomic number of tannin-added Rhizophora spp. particleboards was determined based on elemental composition using Energy Dispersive X-ray Analysis (EDXA). The value of mass attenuation coefficients were measured using 137Cs and 60Co gamma energies. The attenuation properties of PDD curves and beam profile of tannin-added Rhizophora spp. particleboards were investigated using Gafchromic EBT2 film at 6 MV photon and 6 MeV electrons and compared to the value in water and solid water phantoms. The results showed that tannin-added Rhizophora spp. particleboards having effective atomic number close to the value of water. The mass attenuation coefficients were near to the value of water with χ2 values of 0.018 and 0.357 to 137Cs and 60Co gamma energies respectively. The PDD of tannin-added Rhizophora spp. particleboards at 6 MV photons showed good agreement within 3.21 and 5.91% to that in solid water phantoms and water respectively. The PDD at 6 MeV electrons showed a good agreement within 3.32 and 3.12% to that in solid water phantoms and water respectively. The depth of R50 and R90 in tannin-added Rhizophora spp. also showed a good agreement to that in water and solid water pahtoms. Lower surface dose was observed in tannin-added Rhizophora spp. particleboards at electron beams in comparison to solid water phantoms and water.

Application of thin layer activation technique for surface wear studies in Zr based materials using charged particle induced nuclear reactions

NASA Astrophysics Data System (ADS)

Chowdhury, D. P.; Pal, Sujit; Parthasarathy, R.; Mathur, P. K.; Kohli, A. K.; Limaye, P. K.

1998-09-01

Thin layer activation (TLA) technique has been developed in Zr based alloy materials, e.g., zircaloy II, using 40 MeV α-particles from Variable Energy Cyclotron Centre at Calcutta. A brief description of the methodology of TLA technique is presented to determine the surface wear. The sensitivity of the measurement of surface wear in zircaloy material is found to be 0.22±0.05 μm. The surface wear is determined by TLA technique in zircaloy material which is used in pressurised heavy water reactor and the values have been compared with that obtained by conventional technique for the analytical validation of the TLA technique.

Selected bibliography on atomic collisions: Data collections, bibliographies, review articles, books, and papers of particular tutorial value

DOE Office of Scientific and Technical Information (OSTI.GOV)

McDaniel, E.W.; Flannery, M.R.; Thomas, E.W.

This bibliography deals mainly with binary and ternary collisions involving electrons, photons, and heavy particles (i.e., atoms, molecules, and ions). The energy range covered for each kind of collision is such that the interactions might be described as electronic, atomic, or chemical--higher-energy collisions involving nuclear forces are not treated. Also covered are particle and photon impact on surfaces, the passage of particles and radiation through bulk matter, and transport phenomena in gases. Practically all of the references cited are data compilations, other bibliographies, review articles, or books. The main objective is to provide easy access to atomic collision data, althoughmore » some references are included principally for their tutorial value.« less

Surface energy balance estimates at local and regional scales using optical remote sensing from an aircraft platform and atmospheric data collected over semiarid rangelands

USGS Publications Warehouse

Kustas, William P.; Moran, M.S.; Humes, K.S.; Stannard, D.I.; Pinter, P. J.; Hipps, L.E.; Swiatek, E.; Goodrich, D.C.

1994-01-01

Remotely sensed data in the visible, near-infrared, and thermal-infrared wave bands were collected from a low-flying aircraft during the Monsoon '90 field experiment. Monsoon '90 was a multidisciplinary experiment conducted in a semiarid watershed. It had as one of its objectives the quantification of hydrometeorological fluxes during the “monsoon” or wet season. The remote sensing observations along with micrometeprological and atmospheric boundary layer (ABL) data were used to compute the surface energy balance over a range of spatial scales. The procedure involved averaging multiple pixels along transects flown over the meteorological and flux (METFLUX) stations. Average values of the spectral reflectance and thermal-infrared temperatures were computed for pixels of order 10−1 to 101 km in length and were used with atmospheric data for evaluating net radiation (Rn), soil heat flux (G), and sensible (H) and latent (LE) heat fluxes at these same length scales. The model employs a single-layer resistance approach for estimating H that requires wind speed and air temperature in the ABL and a remotely sensed surface temperature. The values of Rn and G are estimated from remote sensing information together with near-surface observations of air temperature, relative humidity, and solar radiation. Finally, LE is solved as the residual term in the surface energy balance equation. Model calculations were compared to measurements from the METFLUX network for three days having different environmental conditions. Average percent differences for the three days between model and the METFLUX estimates of the local fluxes were about 5% for Rn, 20% for Gand H, and 15% for LE. Larger differences occurred during partly cloudy conditions because of errors in interpreting the remote sensing data and the higher spatial and temporal variation in the energy fluxes. Minor variations in modeled energy fluxes were observed when the pixel size representing the remote sensing inputs changed from 0.2 to 2 km. Regional scale estimates of the surface energy balance using bulk ABL properties for the model parameters and input variables and the 10-km pixel data differed from the METFLUX network averages by about 4% for Rn, 10% for G and H, and 15% for LE. Model sensitivity in calculating the turbulent fluxes H and LE to possible variations in key model parameters (i.e., the roughness lengths for heat and momentum) was found to be fairly significant. Therefore the reliability of the methods for estimating key model parameters and potential errors needs further testing over different ecosystems and environmental conditions.

Defining the Post-Machined Sub-surface in Austenitic Stainless Steels

NASA Astrophysics Data System (ADS)

Srinivasan, N.; Sunil Kumar, B.; Kain, V.; Birbilis, N.; Joshi, S. S.; Sivaprasad, P. V.; Chai, G.; Durgaprasad, A.; Bhattacharya, S.; Samajdar, I.

2018-04-01

Austenitic stainless steels grades, with differences in chemistry, stacking fault energy, and thermal conductivity, were subjected to vertical milling. Anodic potentiodynamic polarization was able to differentiate (with machining speed/strain rate) between different post-machined sub-surfaces in SS 316L and Alloy A (a Cu containing austenitic stainless steel: Sanicroe 28™), but not in SS 304L. However, such differences (in the post-machined sub-surfaces) were revealed in surface roughness, sub-surface residual stresses and misorientations, and in the relative presence of sub-surface Cr2O3 films. It was shown, quantitatively, that higher machining speed reduced surface roughness and also reduced the effective depths of the affected sub-surface layers. A qualitative explanation on the sub-surface microstructural developments was provided based on the temperature-dependent thermal conductivity values. The results herein represent a mechanistic understanding to rationalize the corrosion performance of widely adopted engineering alloys.

Defining the Post-Machined Sub-surface in Austenitic Stainless Steels

NASA Astrophysics Data System (ADS)

Srinivasan, N.; Sunil Kumar, B.; Kain, V.; Birbilis, N.; Joshi, S. S.; Sivaprasad, P. V.; Chai, G.; Durgaprasad, A.; Bhattacharya, S.; Samajdar, I.

2018-06-01

Austenitic stainless steels grades, with differences in chemistry, stacking fault energy, and thermal conductivity, were subjected to vertical milling. Anodic potentiodynamic polarization was able to differentiate (with machining speed/strain rate) between different post-machined sub-surfaces in SS 316L and Alloy A (a Cu containing austenitic stainless steel: Sanicroe 28™), but not in SS 304L. However, such differences (in the post-machined sub-surfaces) were revealed in surface roughness, sub-surface residual stresses and misorientations, and in the relative presence of sub-surface Cr2O3 films. It was shown, quantitatively, that higher machining speed reduced surface roughness and also reduced the effective depths of the affected sub-surface layers. A qualitative explanation on the sub-surface microstructural developments was provided based on the temperature-dependent thermal conductivity values. The results herein represent a mechanistic understanding to rationalize the corrosion performance of widely adopted engineering alloys.

The use of remote sensing and linear wave theory to model local wave energy around Alphonse Atoll, Seychelles

NASA Astrophysics Data System (ADS)

Hamylton, S.

2011-12-01

This paper demonstrates a practical step-wise method for modelling wave energy at the landscape scale using GIS and remote sensing techniques at Alphonse Atoll, Seychelles. Inputs are a map of the benthic surface (seabed) cover, a detailed bathymetric model derived from remotely sensed Compact Airborne Spectrographic Imager (CASI) data and information on regional wave heights. Incident energy at the reef crest around the atoll perimeter is calculated as a function of its deepwater value with wave parameters (significant wave height and period) hindcast in the offshore zone using the WaveWatch III application developed by the National Oceanographic and Atmospheric Administration. Energy modifications are calculated at constant intervals as waves transform over the forereef platform along a series of reef profile transects running into the atoll centre. Factors for shoaling, refraction and frictional attenuation are calculated at each interval for given changes in bathymetry and benthic coverage type and a nominal reduction in absolute energy is incorporated at the reef crest to account for wave breaking. Overall energy estimates are derived for a period of 5 years and related to spatial patterning of reef flat surface cover (sand and seagrass patches).

The X-ray reflectivity of the AXAF VETA-I optics

NASA Technical Reports Server (NTRS)

Kellogg, E.; Chartas, G.; Graessle, D.; Hughes, J. P.; Van Speybroeck, L.; Zhao, Ping; Weisskopf, M. C.; Elsner, R. F.; O'Dell, S. L.

1993-01-01

The study measures the X-ray reflectivity of the AXAF VETA-I optic and compares it with theoretical predictions. Measurements made at energies of 0.28, 0.9, 1.5, 2.1, and 2.3 keV are compared with predictions based on ray trace calculations. Results on the variation of the reflectivity with energy as well as the absolute value of the reflectivity are presented. A synchrotron reflectivity measurement with a high-energy resolution over the range 0.26 to 1.8 keV on a flat Zerodur sample is also reported. Evidence is found for contamination of the flat by a thin layer of carbon on the surface, and the possibility of alteration of the surface composition of the VETA-I mirror, perhaps by the polishing technique. The overall agreement between the measured and calculated effective area of VETA-I is between 2.6 and 10 percent. Measurements at individual energies deviate from the best-fitting calculation to 0.3 to 0.8 percent, averaging 0.6 percent at energies below the high energy cutoff of the mirror reflectivity, and are as high as 20.7 percent at the cutoff.

Physical condition for elimination of ambiguity in conditionally convergent lattice sums

NASA Astrophysics Data System (ADS)

Young, K.

1987-02-01

The conditional convergence of the lattice sum defining the Madelung constant gives rise to an ambiguity in its value. It is shown that this ambiguity is related, through a simple and universal integral, to the average charge density on the crystal surface. The physically correct value is obtained by setting the charge density to zero. A simple and universally applicable formula for the Madelung constant is derived as a consequence. It consists of adding up dipole-dipole energies together with a nontrivial correction term.

Assimilation of Satellite-Derived Skin Temperature Observations into Land Surface Models

NASA Technical Reports Server (NTRS)

Reichle, Rolf H.; Kumar, Sujay V.; Mahanama, P. P.; Koster, Randal D.; Liu, Q.

2010-01-01

Land surface (or "skin") temperature (LST) lies at the heart of the surface energy balance and is a key variable in weather and climate models. Here we assimilate LST retrievals from the International Satellite Cloud Climatology Project (ISCCP) into the Noah and Catchment (CLSM) land surface models using an ensemble-based, off-line land data assimilation system. LST is described very differently in the two models. A priori scaling and dynamic bias estimation approaches are applied because satellite and model LST typically exhibit different mean values and variability. Performance is measured against 27 months of in situ measurements from the Coordinated Energy and Water Cycle Observations Project at 48 stations. LST estimates from Noah and CLSM without data assimilation ("open loop") are comparable to each other and superior to that of ISCCP retrievals. For LST, RMSE values are 4.9 K (CLSM), 5.6 K (Noah), and 7.6 K (ISCCP), and anomaly correlation coefficients (R) are 0.62 (CLSM), 0.61 (Noah), and 0.52 (ISCCP). Assimilation of ISCCP retrievals provides modest yet statistically significant improvements (over open loop) of up to 0.7 K in RMSE and 0.05 in anomaly R. The skill of surface turbulent flux estimates from the assimilation integrations is essentially identical to the corresponding open loop skill. Noah assimilation estimates of ground heat flux, however, can be significantly worse than open loop estimates. Provided the assimilation system is properly adapted to each land model, the benefits from the assimilation of LST retrievals are comparable for both models.

The Effect of Bond Albedo on Venus' Atmospheric and Surface Temperatures

NASA Astrophysics Data System (ADS)

Bullock, M. A.; Limaye, S. S.; Grinspoon, D. H.; Way, M.

2017-12-01

In spite of Venus' high planetary albedo, sufficient solar energy reaches the surface to drive a powerful greenhouse effect. The surface temperature is three times higher than it would be without an atmosphere. However, the details of the energy balance within Venus' atmosphere are poorly understood. Half of the solar energy absorbed within the clouds, where most of the solar energy is absorbed, is due to an unknown agent. One of the challenges of modeling Venus' atmosphere has been to account for all the sources of opacity sufficient to generate a globally averaged surface temperature of 735 K, when only 2% of the incoming solar energy is deposited at the surface. The wavelength and spherically integrated albedo, or Bond albedo, has typically been cited as between 0.7 and 0.82 (Colin 1983). Yet, recent photometry of Venus at extended phase angles between 2 and 179° indicate a Bond albedo of 0.90 (Mallama et al., 2006). The authors note an increase in cloud top brightness at phase angles < 2°, which effectively increases the spherically integrated albedo. They suggest that forward scattering by the H2SO4/H2O aerosols of the upper cloud is responsible for Venus' high albedo at very low phase angles. The present work investigates the implications of such a high albedo for understanding and modeling the energy balance of Venus' atmosphere. Using the successful 1D radiative transfer model SimVenus that incorporates the opacity due to 9 major gases in Venus' atmosphere, as well as multiple scattering calculations of radiation within the clouds, the sensitivity of surface temperature was studied as a function of Bond albedo. Results of these model calculations are shown in Fig. 1. Figure 1a (left). Venus' atmospheric temperature profile for different values of Bond albedo. The structure and radiative effects of the clouds are fixed. Figure 1b (right). Venus surface temperature as Bond Albedo changes. Radiative-convective equilibrium models predict the correct globally averaged surface temperature at a=0.81. Calculations here show that a Bond albedo of a=0.9 would yield a surface temperature of 666.4 K, about 70 K too low, unless there is additional thermal absorption within the atmosphere that is not understood. Colin, L.,, Venus, University of Arizona Press, Tucson, 1983, pp 10-26. Mallama, A., et al., 2006. Icarus. 182, 10-22.

Energy balance in high-quality cutting of steel by fiber and CO2 lasers

NASA Astrophysics Data System (ADS)

Fomin, V. M.; Golyshev, A. A.; Orishich, A. M.; Shulyat'ev, V. B.

2017-03-01

The energy balance of laser cutting of low-carbon and stainless steel sheets with the minimum roughness of the cut surface is experimentally studied. Experimental data obtained in wide ranges of cutting parameters are generalized with the use of dimensionless parameters (Peclet number and absorbed laser energy). It is discovered for the first time that the minimum roughness is ensured at a certain value of energy per unit volume of the melt (approximately 26 J/mm3), regardless of the gas type (oxygen or nitrogen) and laser type (fiber laser with a wavelength of 1.07 μm or CO2 laser with a wavelength of 10.6 μm).

Higher Order Multipole Potentials and Electrostatic Screening Effects on Cohesive Energy and Bulk Modulus of Metallic Nanoparticles

NASA Astrophysics Data System (ADS)

Barakat, T.

2011-12-01

Higher order multipole potentials and electrostatic screening effects are introduced to incorporate the dangling bonds on the surface of a metallic nanopaticle and to modify the coulomb like potential energy terms, respectively. The total interaction energy function for any metallic nanoparticle is represented in terms of two- and three-body potentials. The two-body part is described by dipole-dipole interaction potential, and in the three-body part, triple-dipole (DDD) and dipole-dipole-quadrupole (DDQ) terms are included. The size-dependent cohesive energy and bulk modulus are observed to decrease with decreasing sizes, a result which is in good agreement with the experimental values of Mo and W nanoparticles.

Intercalating cobalt between graphene and iridium (111): Spatially dependent kinetics from the edges

NASA Astrophysics Data System (ADS)

Vlaic, Sergio; Rougemaille, Nicolas; Kimouche, Amina; Burgos, Benito Santos; Locatelli, Andrea; Coraux, Johann

2017-10-01

Using low-energy electron microscopy, we image in real time the intercalation of a cobalt monolayer between graphene and the (111) surface of iridium. Our measurements reveal that the edges of a graphene flake represent an energy barrier to intercalation. Based on a simple description of the growth kinetics, we estimate this energy barrier and find small, but substantial, local variations. These local variations suggest a possible influence of the graphene orientation with respect to its substrate and of the graphene edge termination on the energy value of the barrier height. Besides, our measurements show that intercalated cobalt is energetically more favorable than cobalt on bare iridium, indicating a surfactant role of graphene.

On the surface trapping parameters of polytetrafluoroethylene block

NASA Astrophysics Data System (ADS)

Zhang, Guan-Jun; Yang, Kai; Zhao, Wen-Bin; Yan, Zhang

2006-12-01

Surface flashover phenomena under high electric field are closely related to the surface characteristics of a solid insulating material between energized electrodes. Based on measuring the surface potential decaying curve of polytetrafluoroethylene (PTFE) block charged by a needle-plane corona discharge, its surface trapping parameters are calculated with the isothermal current theory, and the correlative curve between the surface trap density and its energy level is obtained. The maximum density of electron traps and hole traps in the surface layer of PTFE presents a similar value of ∼2.7 × 1017 eV-1 m-3, and the energy level of its electron and hole traps is of about 0.85-1.0 eV and 0.80-0.90 eV, respectively. Via the X-ray photoelectron spectroscopy (XPS) technique, the F, C, K and O elements are detected on the surface of PTFE samples, and F shows a remarkable atom proportion of ∼73.3%, quite different from the intrinsic distribution corresponding to its chemical formula. The electron traps are attributed to quantities of F atoms existing on the surface of PTFE due to its molecular chain with C atoms surrounded by F atoms spirally. It is considered that the distortions of chemical and electronic structure on solid surface are responsible for the flashover phenomena occurring at a low applied voltage.

Bulk-surface relationship of an electronic structure for high-throughput screening of metal oxide catalysts

NASA Astrophysics Data System (ADS)

Kweun, Joshua Minwoo; Li, Chenzhe; Zheng, Yongping; Cho, Maenghyo; Kim, Yoon Young; Cho, Kyeongjae

2016-05-01

Designing metal-oxides consisting of earth-abundant elements has been a crucial issue to replace precious metal catalysts. To achieve efficient screening of metal-oxide catalysts via bulk descriptors rather than surface descriptors, we investigated the relationship between the electronic structure of bulk and that of the surface for lanthanum-based perovskite oxides, LaMO3 (M = Ti, V, Cr, Mn, Fe, Co, Ni, Cu). Through density functional theory calculations, we examined the d-band occupancy of the bulk and surface transition-metal atoms (nBulk and nSurf) and the adsorption energy of an oxygen atom (Eads) on (001), (110), and (111) surfaces. For the (001) surface, we observed strong correlation between the nBulk and nSurf with an R-squared value over 94%, and the result was interpreted in terms of ligand field splitting and antibonding/bonding level splitting. Moreover, the Eads on the surfaces was highly correlated with the nBulk with an R-squared value of more than 94%, and different surface relaxations could be explained by the bulk electronic structure (e.g., LaMnO3 vs. LaTiO3). These results suggest that a bulk-derived descriptor such as nBulk can be used to screen metal-oxide catalysts.

Carbon-Water-Energy Relations for Selected River Basins

NASA Technical Reports Server (NTRS)

Choudhury, B. J.

1998-01-01

A biophysical process-based model was run using satellite, assimilated and ancillary data for four years (1987-1990) to calculate components of total evaporation (transpiration, interception, soil and snow evaporation), net radiation, absorbed photosynthetically active radiation and net primary productivity over the global land surface. Satellite observations provided fractional vegetation cover, solar and photosynthetically active radiation incident of the surface, surface albedo, fractional cloud cover, air temperature and vapor pressure. The friction velocity and surface air pressure are obtained from a four dimensional data assimilation results, while precipitation is either only surface observations or a blended product of surface and satellite observations. All surface and satellite data are monthly mean values; precipitation has been disaggregated into daily values. All biophysical parameters of the model are prescribed according to published records. From these global land surface calculations results for river basins are derived using digital templates of basin boundaries. Comparisons with field observations (micrometeorologic, catchment water balance, biomass production) and atmospheric water budget analysis for monthly evaporation from six river basins have been done to assess errors in the calculations. Comparisons are also made with previous estimates of zonal variations of evaporation and net primary productivity. Efficiencies of transpiration, total evaporation and radiation use, and evaporative fraction for selected river basins will be presented.

Relativistic Thomas-Fermi treatment of compressed atoms and compressed nuclear matter cores of stellar dimensions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rotondo, M.; Rueda, Jorge A.; Xue, S.-S.

The Feynman-Metropolis-Teller treatment of compressed atoms is extended to the relativistic regimes. Each atomic configuration is confined by a Wigner-Seitz cell and is characterized by a positive electron Fermi energy. The nonrelativistic treatment assumes a pointlike nucleus and infinite values of the electron Fermi energy can be attained. In the relativistic treatment there exists a limiting configuration, reached when the Wigner-Seitz cell radius equals the radius of the nucleus, with a maximum value of the electron Fermi energy (E{sub e}{sup F}){sub max}, here expressed analytically in the ultrarelativistic approximation. The corrections given by the relativistic Thomas-Fermi-Dirac exchange term are alsomore » evaluated and shown to be generally small and negligible in the relativistic high-density regime. The dependence of the relativistic electron Fermi energies by compression for selected nuclei are compared and contrasted to the nonrelativistic ones and to the ones obtained in the uniform approximation. The relativistic Feynman-Metropolis-Teller approach here presented overcomes some difficulties in the Salpeter approximation generally adopted for compressed matter in physics and astrophysics. The treatment is then extrapolated to compressed nuclear matter cores of stellar dimensions with A{approx_equal}(m{sub Planck}/m{sub n}){sup 3}{approx}10{sup 57} or M{sub core}{approx}M{sub {circle_dot}}. A new family of equilibrium configurations exists for selected values of the electron Fermi energy varying in the range 0

The frequency-domain method of calculation for the pulsed electromagnetic field in a conductive ferromagnetic plate

NASA Astrophysics Data System (ADS)

Nosov, G. V.; Kuleshova, E. O.; Lefebvre, S.; Plyusnin, A. A.; Tokmashev, D. M.

2017-02-01

The technique for parameters determination of magnetic skin effect on ferromagnetic plate at a specified pulse of magnetic field intensity on the plate surface is proposed. It is based on a frequency-domain method and could be applied for a pulsing transformer, a dynamoelectric pulse generator and a commutating inductor that contains an imbricated core. Due to this technique, such plate parameters as specific heat loss energy, the average power of this energy and the plate temperature raise, the magnetic flux attenuation factor and the plate q-factor could be calculated. These parameters depend on the steel type, the amplitude, the rms value, the duration and the form of the magnetic field intensity impulse on the plate surface. The plate thickness is defined by the value of the flux attenuation factor and the plate q-factor that should be maximal. The reliability of the proposed technique is built on a common frequency-domain usage applicable for pulse transient study under zero boundary conditions of the electric circuit and the conformity of obtained results with the sinusoidal steady-state mode.

Production of biodiesel from coastal macroalgae (Chara vulgaris) and optimization of process parameters using Box-Behnken design.

PubMed

Siddiqua, Shaila; Mamun, Abdullah Al; Enayetul Babar, Sheikh Md

2015-01-01

Renewable biodiesels are needed as an alternative to petroleum-derived transport fuels, which contribute to global warming and are of limited availability. Algae biomass, are a potential source of renewable energy, and they can be converted into energy such as biofuels. This study introduces an integrated method for the production of biodiesel from Chara vulgaris algae collected from the coastal region of Bangladesh. The Box-Behnken design based on response surface methods (RSM) used as the statistical tool to optimize three variables for predicting the best performing conditions (calorific value and yield) of algae biodiesel. The three parameters for production condition were chloroform (X1), sodium chloride concentration (X2) and temperature (X3). Optimal conditions were estimated by the aid of statistical regression analysis and surface plot chart. The optimal condition of biodiesel production parameter for 12 g of dry algae biomass was observed to be 198 ml chloroform with 0.75 % sodium chloride at 65 °C temperature, where the calorific value of biodiesel is 9255.106 kcal/kg and yield 3.6 ml.

Experimental comparison of laser energy losses in high-quality laser-oxygen cutting of low-carbon steel using radiation from fibre and CO{sub 2} lasers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Golyshev, A A; Malikov, A G; Orishich, A M

We report a comparative experimental study of laseroxygen cutting of low-carbon steel using a fibre laser with a wavelength of 1.07 μm and a CO{sub 2} laser with a wavelength of 10.6 μm at the sheet thickness of 3 – 16 mm. For the two lasers we have measured the dependence of the cutting speed on the radiation power and determined the cutting speed at which the surface roughness is minimal. The coefficient of laser radiation absorption in the laser cutting process is measured for these lasers at different values of the cutting speed and radiation power. It is foundmore » that the minimal roughness of the cut surface is reached at the absorbed laser energy per unit volume of the removed material, equal to 11 – 13 J mm{sup -3}; this value is the same for the two lasers and does not depend on the sheet thickness. (laser technologies)« less

Optimization of intermittent microwave–convective drying using response surface methodology

PubMed Central

Aghilinategh, Nahid; Rafiee, Shahin; Hosseinpur, Soleiman; Omid, Mahmoud; Mohtasebi, Seyed Saeid

2015-01-01

In this study, response surface methodology was used for optimization of intermittent microwave–convective air drying (IMWC) parameters with employing desirability function. Optimization factors were air temperature (40–80°C), air velocity (1–2 m/sec), pulse ratio) PR ((2–6), and microwave power (200–600 W) while responses were rehydration ratio, bulk density, total phenol content (TPC), color change, and energy consumption. Minimum color change, bulk density, energy consumption, maximum rehydration ratio, and TPC were assumed as criteria for optimizing drying conditions of apple slices in IMWC. The optimum values of process variables were 1.78 m/sec air velocity, 40°C air temperature, PR 4.48, and 600 W microwave power that characterized by maximum desirability function (0.792) using Design expert 8.0. The air temperature and microwave power had significant effect on total responses, but the role of air velocity can be ignored. Generally, the results indicated that it was possible to obtain a higher desirability value if the microwave power and temperature, respectively, increase and decrease. PMID:26286706

Impact of implementation of spaceborne lidar-retrieved canopy height in the WRF model

NASA Astrophysics Data System (ADS)

Lee, Junhong; Hong, Jinkyu

2017-04-01

Canopy height is closely related to biomass and aerodynamic properties, which regulate turbulent transfer of energy and mass at the soil-vegetation-atmosphere continuum. However, this key information has been prescribed as a constant value in a fixed plant functional type in atmospheric models. This presentation reports impacts of using realistic forest canopy height, retrieved from spaceborne LiDAR, on regional climate simulation in the Weather Research and Forecasting (WRF) model's land surface model. Numerical simulations were conducted over the Amazon Basin and East Asia during summer season. Over these regions, the LiDAR-retrieved canopy heights were higher than the default values used in the WRF,which are dependent only on plant functional type. By modifying roughness length and zero-plane displacement height, the change of canopy height resulted in changes in surface energy balance by regulating aerodynamic conductances and vertical temperature gradient, thus modifying the lifting condensation level and equivalent potential temperature in the atmospheric boundary layer. Our analysis also showed that the WRF model better reproduced the observed precipitation when LiDAR-retrieved canopy height was used over the Amazon Basin.

Implementation of spaceborne lidar-retrieved canopy height in the WRF model

NASA Astrophysics Data System (ADS)

Lee, Junhong; Hong, Jinkyu

2016-06-01

Canopy height is closely related to biomass and aerodynamic properties, which regulate turbulent transfer of energy and mass at the soil-vegetation-atmosphere continuum. However, this key information has been prescribed as a constant value in a fixed plant functional type in atmospheric models. This paper is the first to report impacts of using realistic forest canopy height, retrieved from spaceborne lidar, on regional climate simulation by using the canopy height data in the Weather Research and Forecasting (WRF) model's land surface model. Numerical simulations were conducted over the Amazon Basin during summer season. Over this region, the lidar-retrieved canopy heights were higher than the default values used in the WRF, which are dependent only on plant functional type. By modifying roughness length and zero-plane displacement height, the change of canopy height resulted in changes in surface energy balance by regulating aerodynamic conductances and vertical temperature gradient, thus modifying the lifting condensation level and equivalent potential temperature in the atmospheric boundary layer. Our analysis also showed that the WRF model better reproduced the observed precipitation when lidar-retrieved canopy height was used over the Amazon Basin.

Ligand reorganization and activation energies in nonadiabatic electron transfer reactions

NASA Astrophysics Data System (ADS)

Zhu, Jianjun; Wang, Jianji; Stell, George

2006-10-01

The activation energy and ligand reorganization energy for nonadiabatic electron transfer reactions in chemical and biological systems are investigated in this paper. The free energy surfaces and the activation energy are derived exactly in the general case in which the ligand vibration frequencies are not equal. The activation energy is derived by free energy minimization at the transition state. Our formulation leads to the Marcus-Hush [J. Chem. Phys. 24, 979 (1956); 98, 7170 (1994); 28, 962 (1958)] results in the equal-frequency limit and also generalizes the Marcus-Sumi [J. Chem. Phys. 84, 4894 (1986)] model in the context of studying the solvent dynamic effect on electron transfer reactions. It is found that when the ligand vibration frequencies are different, the activation energy derived from the Marcus-Hush formula deviates by 5%-10% from the exact value. If the reduced reorganization energy approximation is introduced in the Marcus-Hush formula, the result is almost exact.

Quest for Casimir repulsion between Chern-Simons surfaces

NASA Astrophysics Data System (ADS)

Fialkovsky, Ignat; Khusnutdinov, Nail; Vassilevich, Dmitri

2018-04-01

In this paper we critically reconsider the Casimir repulsion between surfaces that carry the Chern-Simons interaction (corresponding to the Hall-type conductivity). We present a derivation of the Lifshitz formula valid for arbitrary planar geometries and discuss its properties. This analysis allows us to resolve some contradictions in the previous literature. We compute the Casimir energy for two surfaces that have constant longitudinal and Hall conductivities. The repulsion is possible only if both surfaces have Hall conductivities of the same sign. However, there is a critical value of the longitudinal conductivity above which the repulsion disappears. We also consider a model where both parity odd and parity even terms in the conductivity are produced by the polarization tensor of surface modes. In contrast to the previous publications [L. Chen and S.-L. Wan, Phys. Rev. B 84, 075149 (2011), 10.1103/PhysRevB.84.075149; Phys. Rev. B 85, 115102 (2012), 10.1103/PhysRevB.85.115102], we include the parity anomaly term. This term ensures that the conductivities vanish for infinitely massive surface modes. We find that at least for a single mode, regardless of the sign and value of its mass, there is no Casimir repulsion.

Mild chemical strategy to grow micro-roses and micro-woolen like arranged CuO nanosheets for high performance supercapacitors

NASA Astrophysics Data System (ADS)

Dubal, Deepak P.; Gund, Girish S.; Holze, Rudolf; Lokhande, Chandrakant D.

2013-11-01

The hierarchical structures of nanosheets, micro-roses and micro-woolen like CuO nanosheets were directly fabricated on stainless steel via surfactant-free and inexpensive chemical bath deposition (CBD) method. Further, these CuO nanostructures demonstrate excellent surface properties like uniform surface morphology, high surface area and uniform pore size distribution of CuO samples. The electrochemical properties of CuO nanostructures have been investigated by cyclic voltammetry, charge-discharge and electrochemical impedance spectroscopy techniques. The electrochemical studies of the CuO samples show obvious influence of surface properties on the pseudocapacitance performance. The maximum specific capacitances of nanosheets, micro-roses and micro-woolen like CuO nanosheets are found to be 303 Fg-1, 279 Fg-1 and 346 Fg-1, respectively at 5 mV s-1 scan rate. Further, the EIS analysis shows lower ESR value, high power performance, excellent rate as well as frequency response of micro-woolen like CuO sample. The Ragone plot ascertains better power and energy densities of all three CuO nanostructured samples than other electrical energy storage devices. The long-term cycling performance of CuO is examined at different scan rates and the morphology changes of the electrode materials were studied. Present investigation suggests the inexpensive CBD approach for fine-tuning surface properties of oxide materials for energy storage applications.

Interfacial Surgery Determination of Succinonitrile and Succinonitrile-Acetone Alloy Using Surface Light Scattering Spectrometer

NASA Technical Reports Server (NTRS)

Tin, Padetha; Frate, David T.; deGroh, Henry C., III

2001-01-01

The objectives of this ground based research is to measure the liquid/vapor interfacial surface energies of succinonitrile (SCN) and alloys of succinonitrile and acetone using Surface Light Scattering Spectrometer. Liquid/vapor interfacial energy measurements will be made near and above the melting point and are the primary goal of this proposal. A measurement of viscosity also results from the Surface Light Scattering technique employed. Interfacial free energies between the phases enters into many analysis of phase transformation and flow, including nucleation, dendritic growth, interface stability, Ostwald ripening, and Marangoni flow. Succirionitrile (SCN) is useful as a model for the study of metal solidification, although it is an organic material, it has a BCC crystal structure and solidifies dendriticly like a metal. It is also transparent and has a low melting point (58.08 C). Succinonitrile has been and is being used extensively in NASAs Microgravity Materials Science and Fluid Physics programs and as well as in several ground-based and microgravity studies including the Isothermal Dendritic Growth Experiment (IDGE) due to Glicksman and coworkers and subsequently in several theoretical and numerical studies of dendritic growth. Previous measurements of succinonitrile (SCN) and alloys of succinonitrile and acetone surface tensions are extremely limited. We believe the data sought through this proposal have significant basic physical property data value and thus the work proposed will provide needed data in support of NASAs Microgravity program research.

Isotopic Enrichment of Boron in the Sputtering of Boron Nitride with Xenon Ions

NASA Technical Reports Server (NTRS)

Ray, P. K.; Shutthanandan, V.

1998-01-01

An experimental study is described to measure the isotopic enrichment of boron. Xenon ions from 100 eV to 1.5 keV were used to sputter a boron nitride target. An ion gun was used to generate the ion beam. The ion current density at the target surface was approximately 30 microA/sq cm. Xenon ions impinged on the target surface at 50 deg angle to the surface normal. Since boron nitride is an insulator, a flood electron gun was used in our experiments to neutralize the positive charge buildup on the target surface. The sputtered secondary ions of boron were detected by a quadrupole mass spectrometer. The spectrometer entrance aperture was located perpendicular to the ion beam direction and 10 mm away from the target surface. The secondary ion flux was observed to be enriched in the heavy isotopes at lower ion energies. The proportion of heavy isotopes in the sputtered secondary ion flux was found to decrease with increasing primary ion energy from 100 to 350 eV. Beyond 350 eV, light isotopes were sputtered preferentially. The light isotope enrichment factor was observed to reach an asymptotic value of 1.27 at 1.5 keV. This trend is similar to that of the isotopic enrichment observed earlier when copper was sputtered with xenon ions in the same energy range.

Reactivity of O2 on Pd/Ru(0001) and PdRu/Ru(0001) surface alloys

NASA Astrophysics Data System (ADS)

Farías, D.; Minniti, M.; Miranda, R.

2017-05-01

The reactivity of a Pd monolayer epitaxially grown on Ru(0001) toward O2 has been investigated by molecular beam techniques. O2 initial sticking coefficients were determined using the King and Wells method in the incident energy range of 40-450 meV and for sample temperatures of 100 K and 300 K, and compared to the corresponding values measured on the clean Ru(0001) and Pd(111) surfaces. In contrast to the high reactivity shown by Ru(0001) at 100 K, the Pd/Ru(0001) system exhibits a monotonic decrease in the sticking probability of O2 as a function of normal incident energy. At room temperature, the system was found to be inert. Thermal desorption measurements show that O2 is adsorbed molecularly at 100 K. A completely different behaviour has been measured for the Pd0.95Ru0.05/Ru(0001) surface alloy. On this surface, the O2 sticking probability increases with incident energy and resembles the one observed on the clean Ru(0001) surface, even at 300 K. Thermal desorption measurements point to dissociative adsorption of O2 in this system. Both the charge transfer from the Pd to the Ru substrate and the compressive strain on the Pd monolayer contribute to decrease in the reactivity of the Pd/Ru(0001) system well below those of both Ru(0001) and Pd(111).

On the Size Dependence of Molar and Specific Properties of Independent Nano-phases and Those in Contact with Other Phases

NASA Astrophysics Data System (ADS)

Kaptay, George

2018-05-01

Nano-materials are materials with at least one nano-phase. A nano-phase is a phase with at least one of its dimensions below 100 nm. It is shown here that nano-phases have at least 1% of their atoms along their surface layer. The ratio of surface atoms is proportional to the specific surface area of the phase, defined as the ratio of its surface area to its volume. Each specific/molar property has its bulk value and its surface value for the given phase, being always different, as the energetic states of the atoms in the bulk and in the surface layer of a phase are different. The average specific/molar property of a nano-phase is modeled here as a linear combination of the bulk and surface values of the same property, scaled with the ratio of the surface atoms. That makes the performance of all nano-phases proportional to their specific surface area. As the characteristic size of the nano-phase is inversely proportional to its specific surface area, all specific/molar properties of nano-phases are inversely proportional to the characteristic size of the phase. This is applied to the size dependence of the molar Gibbs energy of the nano-phase, which appears to be in agreement with the thermodynamics of Gibbs. This agreement proves the general validity of the present model on the size dependence of the specific/molar properties of independent nano-phases. It is shown that the properties of nano-phases are different for independent nano-phases (surrounded only by their equilibrium vapor phase) and for nano-phases in multi-phase situations, such as a liquid nano-droplet in the sessile drop configuration.

Superhydrophilic TiO2 thin film by nanometer scale surface roughness and dangling bonds

NASA Astrophysics Data System (ADS)

Bharti, Bandna; Kumar, Santosh; Kumar, Rajesh

2016-02-01

A remarkable enhancement in the hydrophilic nature of titanium dioxide (TiO2) films is obtained by surface modification in DC-glow discharge plasma. Thin transparent TiO2 films were coated on glass substrate by sol-gel dip coating method, and exposed in DC-glow discharge plasma. The plasma exposed TiO2 film exhibited a significant change in its wetting property contact angle, which is a representative of wetting property, has reduced to considerable limits 3.02° and 1.85° from its initial value 54.40° and 48.82° for deionized water and ethylene glycol, respectively. It is elucidated that the hydrophilic property of plasma exposed TiO2 films dependent mainly upon nanometer scale surface roughness. Variation, from 4.6 nm to 19.8 nm, in the film surface roughness with exposure time was observed by atomic force microscopy (AFM). Analysis of variation in the values of contact angle and surface roughness with increasing plasma exposure time reveal that the surface roughness is the main factor which makes the modified TiO2 film superhydrophilic. However, a contribution of change in the surface states, to the hydrophilic property, is also observed for small values of the plasma exposure time. Based upon nanometer scale surface roughness and dangling bonds, a variation in the surface energy of TiO2 film from 49.38 to 88.92 mJ/m2 is also observed. X-ray photoelectron spectroscopy (XPS) results show change in the surface states of titanium and oxygen. The observed antifogging properties are the direct results of the development of the superhydrophilic wetting characteristics to TiO2 films.

Core-level spectra and binding energies of transition metal nitrides by non-destructive x-ray photoelectron spectroscopy through capping layers

NASA Astrophysics Data System (ADS)

Greczynski, G.; Primetzhofer, D.; Lu, J.; Hultman, L.

2017-02-01

We present the first measurements of x-ray photoelectron spectroscopy (XPS) core level binding energies (BE:s) for the widely-applicable group IVb-VIb polycrystalline transition metal nitrides (TMN's) TiN, VN, CrN, ZrN, NbN, MoN, HfN, TaN, and WN as well as AlN and SiN, which are common components in the TMN-based alloy systems. Nitride thin film samples were grown at 400 °C by reactive dc magnetron sputtering from elemental targets in Ar/N2 atmosphere. For XPS measurements, layers are either (i) Ar+ ion-etched to remove surface oxides resulting from the air exposure during sample transfer from the growth chamber into the XPS system, or (ii) in situ capped with a few nm thick Cr or W overlayers in the deposition system prior to air-exposure and loading into the XPS instrument. Film elemental composition and phase content is thoroughly characterized with time-of-flight elastic recoil detection analysis (ToF-E ERDA), Rutherford backscattering spectrometry (RBS), and x-ray diffraction. High energy resolution core level XPS spectra acquired with monochromatic Al Kα radiation on the ISO-calibrated instrument reveal that even mild etching conditions result in the formation of a nitrogen-deficient surface layer that substantially affects the extracted binding energy values. These spectra-modifying effects of Ar+ ion bombardment increase with increasing the metal atom mass due to an increasing nitrogen-to-metal sputter yield ratio. The superior quality of the XPS spectra obtained in a non-destructive way from capped TMN films is evident from that numerous metal peaks, including Ti 2p, V 2p, Zr 3d, and Hf 4f, exhibit pronounced satellite features, in agreement with previously published spectra from layers grown and analyzed in situ. In addition, the N/metal concentration ratios are found to be 25-90% higher than those obtained from the corresponding ion-etched surfaces, and in most cases agree very well with the RBS and ToF-E ERDA values. The N 1 s BE:s extracted from capped TMN films, thus characteristic of a native surface, show a systematic trend, which contrasts with the large BE spread of literature "reference" values. Hence, non-destructive core level XPS employing capping layers provides an opportunity to obtain high-quality spectra, characteristic of virgin in situ grown and analyzed TMN films, although with larger versatility, and allows for extracting core level BE values that are more reliable than those obtained from sputter-cleaned N-deficient surfaces. Results presented here, recorded from a consistent set of binary TMN's grown under the same conditions and analyzed in the same instrument, provide a useful reference for future XPS studies of multinary materials systems allowing for true deconvolution of complex core level spectra.

Impact of initial surface parameters on the final quality of laser micro-polished surfaces

NASA Astrophysics Data System (ADS)

Chow, Michael; Bordatchev, Evgueni V.; Knopf, George K.

2012-03-01

Laser micro-polishing (LμP) is a new laser-based microfabrication technology for improving surface quality during a finishing operation and for producing parts and surfaces with near-optical surface quality. The LμP process uses low power laser energy to melt a thin layer of material on the previously machined surface. The polishing effect is achieved as the molten material in the laser-material interaction zone flows from the elevated regions to the local minimum due to surface tension. This flow of molten material then forms a thin ultra-smooth layer on the top surface. The LμP is a complex thermo-dynamic process where the melting, flow and redistribution of molten material is significantly influenced by a variety of process parameters related to the laser, the travel motions and the material. The goal of this study is to analyze the impact of initial surface parameters on the final surface quality. Ball-end micromilling was used for preparing initial surface of samples from H13 tool steel that were polished using a Q-switched Nd:YAG laser. The height and width of micromilled scallops (waviness) were identified as dominant parameter affecting the quality of the LμPed surface. By adjusting process parameters, the Ra value of a surface, having a waviness period of 33 μm and a peak-to-valley value of 5.9 μm, was reduced from 499 nm to 301 nm, improving the final surface quality by 39.7%.

Absolute proton hydration free energy, surface potential of water, and redox potential of the hydrogen electrode from first principles: QM/MM MD free-energy simulations of sodium and potassium hydration.

PubMed

Hofer, Thomas S; Hünenberger, Philippe H

2018-06-14

The absolute intrinsic hydration free energy G H + ,wat ◦ of the proton, the surface electric potential jump χ wat ◦ upon entering bulk water, and the absolute redox potential V H + ,wat ◦ of the reference hydrogen electrode are cornerstone quantities for formulating single-ion thermodynamics on absolute scales. They can be easily calculated from each other but remain fundamentally elusive, i.e., they cannot be determined experimentally without invoking some extra-thermodynamic assumption (ETA). The Born model provides a natural framework to formulate such an assumption (Born ETA), as it automatically factors out the contribution of crossing the water surface from the hydration free energy. However, this model describes the short-range solvation inaccurately and relies on the choice of arbitrary ion-size parameters. In the present study, both shortcomings are alleviated by performing first-principle calculations of the hydration free energies of the sodium (Na + ) and potassium (K + ) ions. The calculations rely on thermodynamic integration based on quantum-mechanical molecular-mechanical (QM/MM) molecular dynamics (MD) simulations involving the ion and 2000 water molecules. The ion and its first hydration shell are described using a correlated ab initio method, namely resolution-of-identity second-order Møller-Plesset perturbation (RIMP2). The next hydration shells are described using the extended simple point charge water model (SPC/E). The hydration free energy is first calculated at the MM level and subsequently increased by a quantization term accounting for the transformation to a QM/MM description. It is also corrected for finite-size, approximate-electrostatics, and potential-summation errors, as well as standard-state definition. These computationally intensive simulations provide accurate first-principle estimates for G H + ,wat ◦ , χ wat ◦ , and V H + ,wat ◦ , reported with statistical errors based on a confidence interval of 99%. The values obtained from the independent Na + and K + simulations are in excellent agreement. In particular, the difference between the two hydration free energies, which is not an elusive quantity, is 73.9 ± 5.4 kJ mol -1 (K + minus Na + ), to be compared with the experimental value of 71.7 ± 2.8 kJ mol -1 . The calculated values of G H + ,wat ◦ , χ wat ◦ , and V H + ,wat ◦ (-1096.7 ± 6.1 kJ mol -1 , 0.10 ± 0.10 V, and 4.32 ± 0.06 V, respectively, averaging over the two ions) are also in remarkable agreement with the values recommended by Reif and Hünenberger based on a thorough analysis of the experimental literature (-1100 ± 5 kJ mol -1 , 0.13 ± 0.10 V, and 4.28 ± 0.13 V, respectively). The QM/MM MD simulations are also shown to provide an accurate description of the hydration structure, dynamics, and energetics.

Adhesion, friction, and wear behavior of clean metal-ceramic couples

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa

1995-01-01

When a clean metal is brought into contact with a clean, harder ceramic in ultrahigh vacuum, strong bonds form between the two materials. The interfacial bond strength between the metal and ceramic surfaces in sliding contact is generally greater than the cohesive bond strength in the metal. Thus, fracture of the cohesive bonds in the metal results when shearing occurs. These strong interfacial bonds and the shearing fracture in the metal are the main causes of the observed wear behavior and the transfer of the metal to the ceramic. In the literature, the surface energy (bond energy) per unit area of the metal is shown to be related to the degree of interfacial bond strength per unit area. Because the two materials of a metal-ceramic couple have markedly different ductilities, contact can cause considerable plastic deformation of the softer metal. It is the ductility of the metal, then, that determines the real area of contact. In general, the less ductile the metal, the smaller the real area of contact. The coefficient of friction for clean surfaces of metal-ceramic couples correlates with the metals total surface energy in the real area of contact gamma A (which is the product of the surface energy per unit area of the metal gamma and the real area of contact (A)). The coefficient of friction increases as gamma A increases. Furthermore, gamma A is associated with the wear and transfer of the metal at the metal-ceramic interface: the higher the value of gamma A, the greater the wear and transfer of the metal.

Atomisti modeling of the microstructure and transport properties of lead-free solder alloys

NASA Astrophysics Data System (ADS)

Sellers, Michael S.

Damage mechanics models of lead-free solder joints in nanoelectronics continue to improve, and in doing so begin to utilize quantitative values describing processes at the atomic level, governing phenomena like electromigration and thermomigration. In particular, knowledge of the transport properties of specific microstructures helps continuum level models fully describe these larger-scale damage phenomena via multi-scale analysis. For example, diffusivities for different types of grain boundaries (fast diffusion paths for solvent and solute atoms, and vacancies), and a description of the boundary structure as a function of temperature, are critical in modeling solder microstructure evolution and, consequently, joint behavior under extreme temperature and electric current. Moreover, for damage that develops at larger length scales, surface energies and diffusivities play important roles in characterizing void stability and morphology. Unfortunately, experiments that investigate these kind of damage phenomena in the atomistic realm are often inconsistent or unable to directly quantify important parameters. One case is the particular transport and structural properties of grain boundaries in Sn (the main component in lead-free solder alloys) and their behavior in the presence of Ag and Cu impurities. This information is crucial in determining accurate diffusivity values for the common SnAgCu (SAC) type solder. Although an average grain boundary diffusivity has been reported for polycrystalline Sn in several works, the value for grain boundary width is estimated and specific diffusivities for boundaries known to occur in Sn have not been reported, to say nothing of solute effects on Sn diffusivity and grain boundary structure. Similarly, transport properties of Sn surfaces remain relatively uninvestigated as well. These gaps and inconsistencies in atomistic data must be remedied for micro- and macro-scale modeling to improve. As a complement to experimental work and possessing the ability to fill in the gaps, molecular simulation serves to reinforce experimental predictions and provide insight into the atomistic processes that govern studied phenomena. In the present body of work, we employ molecular statics and dynamics simulations in the characterization and computation of betaSn surface energies and surface diffusivities, the determination of diffusivities and structural properties of specific betaSn grain boundaries, and the investigation of Cu and Ag solute effects on betaSn grain boundaries. In our study of betaSn surfaces, energies for low number Miller index surfaces are computed and the (100) plane is found to have the lowest un-relaxed energy. We then find that two simple hopping mechanisms dominate adatom diffusion transitions on this surface. For each, we determine hopping rates of the adatom and compute its tracer diffusivity. Our work on grain boundaries investigates the self-diffusion properties and structure of several betaSn symmetric tilt grain boundaries using molecular dynamics simulations. We find that larger diffusive widths are exhibited by higher excess potential energy grain boundaries. Diffusivities in the directions parallel to the interface plane are also computed and activation energies are found with the Arrhenius relation. These are shown to agree well with experimental data. Finally, we examine the effect that solute atoms of Ag and Cu have on the microstructure of betaSn. Excess energies of the (101) symmetric tilt betaSn grain boundary are computed as a function of solute concentration at the interface, and we show that Ag lowers the energy at a greater rate than Cu. We also quantify segregation enthalpies and critical solute concentrations (where the excess energy of the boundary is reduced to zero). The effect of solute type on shear stress is also examined, and we show that solute has a strong effect on the stabilization of higher energy grain boundaries under shear stress. We then look at the self-diffusivity of Sn in the (101) symmetric tilt betaSn grain boundary and show that adding both Ag or Cu decrease the grain boundary self-diffusivity of Sn as solute amount in the interface increases. Effects of larger concentrations of Cu in particular are also investigated.

Cloud Effects on Meridional Atmospheric Energy Budget Estimated from Clouds and the Earth's Radiant Energy System (CERES) Data

NASA Technical Reports Server (NTRS)

Kato, Seiji; Rose, Fred G.; Rutan, David A.; Charlock, Thomas P.

2008-01-01

The zonal mean atmospheric cloud radiative effect, defined as the difference of the top-of-atmosphere (TOA) and surface cloud radiative effects, is estimated from three years of Clouds and the Earth's Radiant Energy System (CERES) data. The zonal mean shortwave effect is small, though it tends to be positive (warming). This indicates that clouds increase shortwave absorption in the atmosphere, especially in midlatitudes. The zonal mean atmospheric cloud radiative effect is, however, dominated by the longwave effect. The zonal mean longwave effect is positive in the tropics and decreases with latitude to negative values (cooling) in polar regions. The meridional gradient of cloud effect between midlatitude and polar regions exists even when uncertainties in the cloud effect on the surface enthalpy flux and in the modeled irradiances are taken into account. This indicates that clouds increase the rate of generation of mean zonal available potential energy. Because the atmospheric cooling effect in polar regions is predominately caused by low level clouds, which tend to be stationary, we postulate that the meridional and vertical gradients of cloud effect increase the rate of meridional energy transport by dynamics in the atmosphere from midlatitude to polar region, especially in fall and winter. Clouds then warm the surface in polar regions except in the Arctic in summer. Clouds, therefore, contribute in increasing the rate of meridional energy transport from midlatitude to polar regions through the atmosphere.

Lithium effects on the mechanical and electronic properties of germanium nanowires

NASA Astrophysics Data System (ADS)

González-Macías, A.; Salazar, F.; Miranda, A.; Trejo-Baños, A.; Pérez, L. A.; Carvajal, E.; Cruz-Irisson, M.

2018-04-01

Semiconductor nanowire arrays promise rapid development of a new generation of lithium (Li) batteries because they can store more Li atoms than conventional crystals due to their large surface areas. During the charge-discharge process, the electrodes experience internal stresses that fatigue the material and limit the useful life of the battery. The theoretical study of electronic and mechanical properties of lithiated nanowire arrays allows the designing of electrode materials that could improve battery performance. In this work, we present a density functional theory study of the electronic band structure, formation energy, binding energy, and Young’s modulus (Y) of hydrogen passivated germanium nanowires (H-GeNWs) grown along the [111] and [001] crystallographic directions with surface and interstitial Li atoms. The results show that the germanium nanowires (GeNWs) with surface Li atoms maintain their semiconducting behavior but their energy gap size decreases when the Li concentration grows. In contrast, the GeNWs can have semiconductor or metallic behavior depending on the concentration of the interstitial Li atoms. On the other hand, Y is an indicator of the structural changes that GeNWs suffer due to the concentration of Li atoms. For surface Li atoms, Y stays almost constant, whereas for interstitial Li atoms, the Y values indicate important structural changes in the GeNWs.

Surface free energy analysis of oil palm empty fruit bunches fiber reinforced biocomposites

NASA Astrophysics Data System (ADS)

Suryadi, G. S.; Nikmatin, S.; Sudaryanto; Irmansyah; Sukaryo, S. G.

2017-05-01

Study of the size effect of natural fiber from oil palm empty fruit bunches (OPEFB) as filler, onto the contact angle and surface free energy of fiber reinforced biocomposites has been done. The OPEFB fibers were prepared by mechanical milling and sieving to obtain various sizes of fiber (long-fiber, medium-fiber, short-fiber, and microparticle). The biocomposites has been produced by extrusion using single-screw extruder with EFB fiber as filler, recycled Acrylonitrile Butadiene Styrene (ABS) polymer as matrix, and primary antioxidant, acid scavanger, and coupling agent as additives. The obtained biocomposites in form of granular, were made into test piece by injection molding method. Contact angles of water, methanol, and hexane on the surface of biocomposites at room temperature were measured using Phoenix 300 Contact Angle Analyzer. The surface free energy (SFE) and their components were calculated using three previous known methods (Girifalco-Good-Fowkes-Young (GGFY), Owens-Wendt, and van Oss-Chaudhury-Good (vOCG)). The results showed that total SFE of Recycled ABS as control was about 24.38 mJ/m2, and SFE of biocomposites was lower than control, decreased with decreasing of EFB fiber size as biocomposites filler. The statistical analysis proved that there are no statistically significant differences in the value of the SFE calculated with the three different methods.

Preparation and Evaluation of Surface Modified Lactose Particles for Improved Performance of Fluticasone Propionate Dry Powder Inhaler.

PubMed

Singh, Deepak J; Jain, Rajesh R; Soni, P S; Abdul, Samad; Darshana, Hegde; Gaikwad, Rajiv V; Menon, Mala D

2015-08-01

Dry powder inhalers (DPI) are generally formulated by mixing micronized drug particles with coarse lactose carrier particles to assist powder handling during the manufacturing and powder aerosol delivery during patient use. In the present study, surface modified lactose (SML) particles were produced using force control agents, and their in vitro performance on dry powder inhaler (DPI) formulation of Fluticasone propionate was studied. With a view to reduce surface passivation of high surface free energy sites on the most commonly used DPI carrier, α- lactose monohydrate, effects of various force control agents such as Pluronic F-68, Cremophor RH 40, glyceryl monostearate, polyethylene glycol 6000, magnesium stearate, and soya lecithin were studied. DPI formulations prepared with SML showed improved flow properties, and atomic force microscopy (AFM) studies revealed decrease in surface roughness. The DSC and X-ray diffraction patterns of SML showed no change in the crystal structure and thermal behavior under the experimental conditions. The fine particle fraction (FPF) values of lactose modified with Pluronic F-68, Cremophor RH 40, glyceryl monostearate were improved, with increase in concentration up to 0.5%. Soya lecithin and PEG 6000 modified lactose showed decrease in FPF value with increase in concentration. Increase in FPF value was observed with increasing concentration of magnesium stearate. Two different DPI devices, Rotahaler(®) and Diskhaler(®), were compared to evaluate the performance of SML formulations. FPF value of all SML formulations were higher using both devices as compared to the same formulations prepared using untreated lactose. One month stability of SML formulations at 40°C/75% RH, in permeable polystyrene tubes did not reveal any significant changes in FPF values. SML particles can help in reducing product development hindrances and improve inhalational properties of DPI.

Adsorption equilibrium and thermodynamics of CO2 and CH4 on carbon molecular sieves

NASA Astrophysics Data System (ADS)

Song, Xue; Wang, Li'ao; Ma, Xu; Zeng, Yunmin

2017-02-01

Carbon molecular sieves (CMS) are widely used in the separation of dioxide carbon and methane. In this research, three commercial CMS were utilized to analyze the pore structure and chemical properties. The adsorption isotherms of CO2 and CH4 were studied at 298 K, 308 K and 318 K over the pressure range of 0-1 MPa by an Intelligent Gravimetric analysis (IGA-100B, UK). Langmuir model was adopted to fit the experimental data. The working capacity and selectivity were employed to evaluate the adsorbents. The adsorption thermodynamics were discussed. The adsorbed amounts of both CO2 and CH4 are found to be highly related with the BET specific surface area and the volume of micropores, and also are interrelated with the total pore volume and micropore surface area. The standard enthalpy change (ΔHΘ), standard Gibbs free energy (ΔGΘ) and standard entropy change (ΔSΘ) at zero surface loading are negative, manifesting the adsorption process is exothermic and spontaneous, and the system tends to be ordered. With the increasing surface coverage, the absolute values of Gibbs free energy (ΔG) decrease whereas the absolute values of enthalpy change (ΔH) and entropy change(ΔS) increase. This indicates that as the adsorbed amount increases, the degree of the spontaneity reduces, the intermolecular forces among the adsorbate molecules increase, the orderliness of the system improves and the adsorbed amount approaches the maximum adsorbed capacity.

Constrained Surface Complexation Modeling: Rutile in RbCl, NaCl, and NaCF 3SO 3 Media to 250 °C

DOE PAGES

Machesky, Michael L.; Předota, Milan; Ridley, Moira K.; ...

2015-06-01

In this paper, a comprehensive set of molecular-level results, primarily from classical molecular dynamics (CMD) simulations, are used to constrain CD-MUSIC surface complexation model (SCM) parameters describing rutile powder titrations conducted in RbCl, NaCl, and NaTr (Tr = triflate, CF 3SO 3 –) electrolyte media from 25 to 250 °C. Rb + primarily occupies the innermost tetradentate binding site on the rutile (110) surface at all temperatures (25, 150, 250 °C) and negative charge conditions (-0.1 and -0.2 C/m 2) probed via CMD simulations, reflecting the small hydration energy of this large, monovalent cation. Consequently, variable SCM parameters (Stern-layer capacitancemore » values and intrinsic Rb + binding constants) were adjusted relatively easily to satisfactorily match the CMD and titration data. The larger hydration energy of Na + results in a more complex inner-sphere distribution, which shifts from bidentate to tetradentate binding with increasing negative charge and temperature, and this distribution was not matched well for both negative charge conditions, which may reflect limitations in the CMD and/or SCM approaches. Finally, in particular, the CMD axial density profiles for Rb + and Na + reveal that peak binding distances shift toward the surface with increasing negative charge, suggesting that the CD-MUSIC framework may be improved by incorporating CD or Stern-layer capacitance values that vary with charge.« less

Constrained Surface Complexation Modeling: Rutile in RbCl, NaCl, and NaCF 3SO 3 Media to 250 °C

DOE Office of Scientific and Technical Information (OSTI.GOV)

Machesky, Michael L.; Předota, Milan; Ridley, Moira K.

In this paper, a comprehensive set of molecular-level results, primarily from classical molecular dynamics (CMD) simulations, are used to constrain CD-MUSIC surface complexation model (SCM) parameters describing rutile powder titrations conducted in RbCl, NaCl, and NaTr (Tr = triflate, CF 3SO 3 –) electrolyte media from 25 to 250 °C. Rb + primarily occupies the innermost tetradentate binding site on the rutile (110) surface at all temperatures (25, 150, 250 °C) and negative charge conditions (-0.1 and -0.2 C/m 2) probed via CMD simulations, reflecting the small hydration energy of this large, monovalent cation. Consequently, variable SCM parameters (Stern-layer capacitancemore » values and intrinsic Rb + binding constants) were adjusted relatively easily to satisfactorily match the CMD and titration data. The larger hydration energy of Na + results in a more complex inner-sphere distribution, which shifts from bidentate to tetradentate binding with increasing negative charge and temperature, and this distribution was not matched well for both negative charge conditions, which may reflect limitations in the CMD and/or SCM approaches. Finally, in particular, the CMD axial density profiles for Rb + and Na + reveal that peak binding distances shift toward the surface with increasing negative charge, suggesting that the CD-MUSIC framework may be improved by incorporating CD or Stern-layer capacitance values that vary with charge.« less

Molecular-dynamics study on characteristics of energy and tangential momentum accommodation coefficients

NASA Astrophysics Data System (ADS)

Yamaguchi, Hiroki; Matsuda, Yu; Niimi, Tomohide

2017-07-01

Gas-surface interaction is studied by the molecular dynamics method to investigate qualitatively characteristics of accommodation coefficients. A large number of trajectories of gas molecules colliding to and scattering from a surface are statistically analyzed to calculate the energy (thermal) accommodation coefficient (EAC) and the tangential momentum accommodation coefficient (TMAC). Considering experimental measurements of the accommodation coefficients, the incident velocities are stochastically sampled to represent a bulk condition. The accommodation coefficients for noble gases show qualitative coincidence with experimental values. To investigate characteristics of these accommodation coefficients in detail, the gas-surface interaction is parametrically studied by varying the molecular mass of gas, the gas-surface interaction strength, and the molecular size of gas, one by one. EAC increases with increasing every parameter, while TMAC increases with increasing the interaction strength, but decreases with increasing the molecular mass and the molecular size. Thus, contradictory results in experimentally measured TMAC for noble gases could result from the difference between the surface conditions employed in the measurements in the balance among the effective parameters of molecular mass, interaction strength, and molecular size, due to surface roughness and/or adsorbed molecules. The accommodation coefficients for a thermo-fluid dynamics field with a temperature difference between gas and surface and a bulk flow at the same time are also investigated.

Ionic liquids at the surface of graphite: Wettability and structure

NASA Astrophysics Data System (ADS)

Bordes, Emilie; Douce, Laurent; Quitevis, Edward L.; Pádua, Agílio A. H.; Costa Gomes, Margarida

2018-05-01

The aim of this work is to provide a better understanding of the interface between graphite and different molecular and ionic liquids. Experimental measurements of the liquid surface tension and of the graphite-liquid contact angle for sixteen ionic liquids and three molecular liquids are reported. These experimental values allowed the calculation of the solid/liquid interfacial energy that varies, for the ionic liquids studied, between 14.5 mN m-1 for 1-ethyl-3-methylimidazolium dicyanamide and 37.8 mN m-1 for 3-dodecyl-1-(naphthalen-1-yl)-1H-imidazol-3-ium tetrafluoroborate. Imidazolium-based ionic liquids with large alkyl side-chains or functionalized with benzyl groups seem to interact more favourably with freshly peeled graphite surfaces. Even if the interfacial energy seems a good descriptor to assess the affinity of a liquid for a carbon-based solid material, we conclude that both the surface tension of the liquid and the contact angle between the liquid and the solid can be significant. Molecular dynamics simulations were used to investigate the ordering of the ions near the graphite surface. We conclude that the presence of large alkyl side-chains in the cations increases the ordering of ions at the graphite surface. Benzyl functional groups in the cations lead to a large affinity towards the graphite surface.

A Bayesian Framework for Coupled Estimation of Key Unknown Parameters of Land Water and Energy Balance Equations

NASA Astrophysics Data System (ADS)

Farhadi, L.; Abdolghafoorian, A.

2015-12-01

The land surface is a key component of climate system. It controls the partitioning of available energy at the surface between sensible and latent heat, and partitioning of available water between evaporation and runoff. Water and energy cycle are intrinsically coupled through evaporation, which represents a heat exchange as latent heat flux. Accurate estimation of fluxes of heat and moisture are of significant importance in many fields such as hydrology, climatology and meteorology. In this study we develop and apply a Bayesian framework for estimating the key unknown parameters of terrestrial water and energy balance equations (i.e. moisture and heat diffusion) and their uncertainty in land surface models. These equations are coupled through flux of evaporation. The estimation system is based on the adjoint method for solving a least-squares optimization problem. The cost function consists of aggregated errors on state (i.e. moisture and temperature) with respect to observation and parameters estimation with respect to prior values over the entire assimilation period. This cost function is minimized with respect to parameters to identify models of sensible heat, latent heat/evaporation and drainage and runoff. Inverse of Hessian of the cost function is an approximation of the posterior uncertainty of parameter estimates. Uncertainty of estimated fluxes is estimated by propagating the uncertainty for linear and nonlinear function of key parameters through the method of First Order Second Moment (FOSM). Uncertainty analysis is used in this method to guide the formulation of a well-posed estimation problem. Accuracy of the method is assessed at point scale using surface energy and water fluxes generated by the Simultaneous Heat and Water (SHAW) model at the selected AmeriFlux stations. This method can be applied to diverse climates and land surface conditions with different spatial scales, using remotely sensed measurements of surface moisture and temperature states

Drag coefficient Variability and Thermospheric models

NASA Astrophysics Data System (ADS)

Moe, Kenneth

Satellite drag coefficients depend upon a variety of factors: The shape of the satellite, its altitude, the eccentricity of its orbit, the temperature and mean molecular mass of the ambient atmosphere, and the time in the sunspot cycle. At altitudes where the mean free path of the atmospheric molecules is large compared to the dimensions of the satellite, the drag coefficients can be determined from the theory of free-molecule flow. The dependence on altitude is caused by the concentration of atomic oxygen which plays an important role by its ability to adsorb on the satellite surface and thereby affect the energy loss of molecules striking the surface. The eccentricity of the orbit determines the satellite velocity at perigee, and therefore the energy of the incident molecules relative to the energy of adsorption of atomic oxygen atoms on the surface. The temperature of the ambient atmosphere determines the extent to which the random thermal motion of the molecules influences the momentum transfer to the satellite. The time in the sunspot cycle affects the ambient temperature as well as the concentration of atomic oxygen at a particular altitude. Tables and graphs will be used to illustrate the variability of drag coefficients. Before there were any measurements of gas-surface interactions in orbit, Izakov and Cook independently made an excellent estimate that the drag coefficient of satellites of compact shape would be 2.2. That numerical value, independent of altitude, was used by Jacchia to construct his model from the early measurements of satellite drag. Consequently, there is an altitude dependent bias in the model. From the sparce orbital experiments that have been done, we know that the molecules which strike satellite surfaces rebound in a diffuse angular distribution with an energy loss given by the energy accommodation coefficient. As more evidence accumulates on the energy loss, more realistic drag coefficients are being calculated. These improved drag coefficients help evaluate the biases in present models. Moreover, they make possible the derivation of accurate densities from accelerometer measurements.

Formation of plasmon pulses in the cooperative decay of excitons of quantum dots near a metal surface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shesterikov, A. B.; Gubin, M. Yu.; Gladush, M. G.

The formation of pulses of surface electromagnetic waves at a metal–dielectric boundary is considered in the process of cooperative decay of excitons of quantum dots distributed near a metal surface in a dielectric layer. It is shown that the efficiency of exciton energy transfer to excited plasmons can, in principle, be increased by selecting the dielectric material with specified values of the complex permittivity. It is found that in the mean field approximation, the semiclassical model of formation of plasmon pulses in the system under study is reduced to the pendulum equation with the additional term of nonlinear losses.

Surface Dangling-Bond States and Band Lineups in Hydrogen-Terminated Si, Ge, and Ge/Si Nanowires

NASA Astrophysics Data System (ADS)

Kagimura, R.; Nunes, R. W.; Chacham, H.

2007-01-01

We report an ab initio study of the electronic properties of surface dangling-bond (SDB) states in hydrogen-terminated Si and Ge nanowires with diameters between 1 and 2 nm, Ge/Si nanowire heterostructures, and Si and Ge (111) surfaces. We find that the charge transition levels ɛ(+/-) of SDB states behave as a common energy reference among Si and Ge wires and Si/Ge heterostructures, at 4.3±0.1eV below the vacuum level. Calculations of ɛ(+/-) for isolated atoms indicate that this nearly constant value is a periodic-table atomic property.

Charge dynamics of MgO single crystals subjected to KeV electron irradiation

NASA Astrophysics Data System (ADS)

Boughariou, A.; Blaise, G.; Braga, D.; Kallel, A.

2004-04-01

A scanning electron microscope has been equipped to study the fundamental aspects of charge trapping in insulating materials, by measuring the secondary electron emission (SEE) yield σ with a high precision (a few percent), as a function of energy, electron current density, and dose. The intrinsic secondary electron emission yield σ0 of uncharged MgO single crystals annealed at 1000 °C, 2 h, has been studied at four energies 1.1, 5, 15, and 30 keV on three different crystal orientations (100), (110), and (111). At low energies (1.1 and 5 keV) σ0 depends on the crystalline orientation wheras at high energies (30 keV) no differentiation occurs. It is shown that the value of the second crossover energy E2, for which the intrinsic SEE yield σ0=1, is extremely delicate to measure with precision. It is about 15 keV±500 eV for the (100) orientation, 13.5 keV±500 eV for the (110), and 18.5 keV±500 eV for the (111) one. At low current density J⩽105 pA/cm2, the variation of σ with the injected dose makes possible the observation of a self-regulated regime characterized by a steady value of the SEE yield σst=1. At low energies 1.1 and 5 keV, there is no current density effects in MgO, but at high energies ≈30 keV, apparent current density effects come from a bad collect of secondary electrons, due to very high negative surface potential. At 30 keV energy, an intense erratic electron exoemission was observed on the MgO (110) orientation annealed at 1500 °C. This phenomenon is the result of a disruptive process similar to flashover, which takes place at the surface of the material.

Electronic structure and fundamental absorption edges of KPb2Br5, K0.5Rb0.5Pb2Br5, and RbPb2Br5 single crystals

NASA Astrophysics Data System (ADS)

Tarasova, A. Yu.; Isaenko, L. I.; Kesler, V. G.; Pashkov, V. M.; Yelisseyev, A. P.; Denysyuk, N. M.; Khyzhun, O. Yu.

2012-05-01

X-ray photoelectron core-level and valence-band spectra for pristine and Ar+-ion irradiated (001) surfaces of KPb2Br5, K0.5Rb0.5Pb2Br5, and RbPb2Br5 single crystals grown by the Bridgman method have been measured and fundamental absorption edges of the ternary bromides have been recorded in the polarized light at 300 K and 80 K. The present X-ray photoelectron spectroscopy (XPS) results reveal high chemical stability of (001) surfaces of KxRb1-xPb2Br5 (x=0, 0.5, and 1.0) single crystals. Substitution of potassium for rubidium in KxRb1-xPb2Br5 does not cause any changes of binding energy values and shapes of the XPS constituent element core-level spectra. Measurements of the fundamental absorption edges indicate that band gap energy, Eg, increases by about 0.14 and 0.19 eV when temperature decreases from 300 K to 80 K in KPb2Br5 and RbPb2Br5, respectively. Furthermore, there is no dependence of the Eg value for KPb2Br5 upon the light polarization, whilst the band gap energy value for RbPb2Br5 is bigger by 0.03-0.05 eV in the case of E‖c compared to those in the cases of E‖a and E‖b.

Intermolecular configurations dominated by quadrupole-quadrupole electrostatic interactions: explicit correlation treatment of the five-dimensional potential energy surface and infrared spectra for the CO-N2 complex.

PubMed

Liu, Jing-Min; Zhai, Yu; Zhang, Xiao-Long; Li, Hui

2018-01-17

A thorough understanding of the intermolecular configurations of van der Waals complexes is a great challenge due to their weak interactions, floppiness and anharmonic nature. Although high-resolution microwave or infrared spectroscopy provides one of the most direct and precise pieces of experimental evidence, the origin and key role in determining such intermolecular configurations of a van der Waals system strongly depend on its highly accurate potential energy surface (PES) and a detailed analysis of its ro-vibrational wavefunctions. Here, a new five-dimensional potential energy surface for the van der Waals complex of CO-N 2 which explicitly incorporates the dependence on the stretch coordinate of the CO monomer is generated using the explicitly correlated couple cluster (CCSD(T)-F12) method in conjunction with a large basis set. Analytic four-dimensional PESs are obtained by the least-squares fitting of vibrationally averaged interaction energies for v = 0 and v = 1 to the Morse/Long-Range potential mode (V MLR ). These fits to 7966 points have root-mean-square deviations (RMSD) of 0.131 cm -1 and 0.129 cm -1 for v = 0 and v = 1, respectively, with only 315 parameters. Energy decomposition analysis is carried out, and it reveals that the dominant factor in controlling intermolecular configurations is quadrupole-quadrupole electrostatic interactions. Moreover, the rovibrational levels and wave functions are obtained for the first time. The predicted infrared transitions and intensities for the ortho-N 2 -CO complex as well as the calculated energy levels for para-N 2 -CO are in good agreement with the available experimental data with RMSD discrepancies smaller than 0.068 cm -1 . The calculated infrared band origin shift associated with the fundamental band frequency of CO is -0.721 cm -1 for ortho-N 2 -CO which is in excellent agreement with the experimental value of -0.739 cm -1 . The agreement with experimental values validates the high quality of the PESs and enhances our confidence to explain the observed mystery lines around 2163 cm -1 .

Structure and binding energy of the H2S dimer at the CCSD(T) complete basis set limit.

PubMed

Lemke, Kono H

2017-06-21

This study presents results for the binding energy and geometry of the H 2 S dimer which have been computed using Møller-Plesset perturbation theory (MP2, MP4) and coupled cluster (CCSD, CCSD(T)) calculations with basis sets up to aug-cc-pV5Z. Estimates of D e , E ZPE , D o , and dimer geometry have been obtained at each level of theory by taking advantage of the systematic convergence behavior toward the complete basis set (CBS) limit. The CBS limit binding energy values of D e are 1.91 (MP2), 1.75 (MP4), 1.41 (CCSD), and 1.69 kcal/mol (CCSD[T]). The most accurate values for the equilibrium S-S distance r SS (without counterpoise correction) are 4.080 (MP2/aug-cc-pV5Z), 4.131 (MP4/aug-cc-pVQZ), 4.225 (CCSD/aug-cc-pVQZ), and 4.146 Å (CCSD(T)/aug-cc-pVQZ). This study also evaluates the effect of counterpoise correction on the H 2 S dimer geometry and binding energy. As regards the structure of (H 2 S) 2 , MPn, CCSD, and CCSD(T) level values of r SS , obtained by performing geometry optimizations on the counterpoise-corrected potential energy surface, converge systematically to CBS limit values of 4.099 (MP2), 4.146 (MP4), 4.233 (CCSD), and 4.167 Å (CCSD(T)). The corresponding CBS limit values of the equilibrium binding energy D e are 1.88 (MP2), 1.76 (MP4), 1.41 (CCSD), and 1.69 kcal/mol (CCSD(T)), the latter in excellent agreement with the measured binding energy value of 1.68 ± 0.02 kcal/mol reported by Ciaffoni et al. [Appl. Phys. B 92, 627 (2008)]. Combining CBS electronic binding energies D e with E ZPE predicted by CCSD(T) vibrational second-order perturbation theory calculations yields D o = 1.08 kcal/mol, which is around 0.6 kcal/mol smaller than the measured value of 1.7 ± 0.3 kcal/mol. Overall, the results presented here demonstrate that the application of high level calculations, in particular CCSD(T), in combination with augmented correlation consistent basis sets provides valuable insight into the structure and energetics of the hydrogen sulfide dimer.

Structure and binding energy of the H2S dimer at the CCSD(T) complete basis set limit

NASA Astrophysics Data System (ADS)

Lemke, Kono H.

2017-06-01

This study presents results for the binding energy and geometry of the H2S dimer which have been computed using Møller-Plesset perturbation theory (MP2, MP4) and coupled cluster (CCSD, CCSD(T)) calculations with basis sets up to aug-cc-pV5Z. Estimates of De, EZPE, Do, and dimer geometry have been obtained at each level of theory by taking advantage of the systematic convergence behavior toward the complete basis set (CBS) limit. The CBS limit binding energy values of De are 1.91 (MP2), 1.75 (MP4), 1.41 (CCSD), and 1.69 kcal/mol (CCSD[T]). The most accurate values for the equilibrium S-S distance rSS (without counterpoise correction) are 4.080 (MP2/aug-cc-pV5Z), 4.131 (MP4/aug-cc-pVQZ), 4.225 (CCSD/aug-cc-pVQZ), and 4.146 Å (CCSD(T)/aug-cc-pVQZ). This study also evaluates the effect of counterpoise correction on the H2S dimer geometry and binding energy. As regards the structure of (H2S)2, MPn, CCSD, and CCSD(T) level values of rSS, obtained by performing geometry optimizations on the counterpoise-corrected potential energy surface, converge systematically to CBS limit values of 4.099 (MP2), 4.146 (MP4), 4.233 (CCSD), and 4.167 Å (CCSD(T)). The corresponding CBS limit values of the equilibrium binding energy De are 1.88 (MP2), 1.76 (MP4), 1.41 (CCSD), and 1.69 kcal/mol (CCSD(T)), the latter in excellent agreement with the measured binding energy value of 1.68 ± 0.02 kcal/mol reported by Ciaffoni et al. [Appl. Phys. B 92, 627 (2008)]. Combining CBS electronic binding energies De with EZPE predicted by CCSD(T) vibrational second-order perturbation theory calculations yields Do = 1.08 kcal/mol, which is around 0.6 kcal/mol smaller than the measured value of 1.7 ± 0.3 kcal/mol. Overall, the results presented here demonstrate that the application of high level calculations, in particular CCSD(T), in combination with augmented correlation consistent basis sets provides valuable insight into the structure and energetics of the hydrogen sulfide dimer.

Carbon-based supercapacitors produced by activation of graphene.

PubMed

Zhu, Yanwu; Murali, Shanthi; Stoller, Meryl D; Ganesh, K J; Cai, Weiwei; Ferreira, Paulo J; Pirkle, Adam; Wallace, Robert M; Cychosz, Katie A; Thommes, Matthias; Su, Dong; Stach, Eric A; Ruoff, Rodney S

2011-06-24

Supercapacitors, also called ultracapacitors or electrochemical capacitors, store electrical charge on high-surface-area conducting materials. Their widespread use is limited by their low energy storage density and relatively high effective series resistance. Using chemical activation of exfoliated graphite oxide, we synthesized a porous carbon with a Brunauer-Emmett-Teller surface area of up to 3100 square meters per gram, a high electrical conductivity, and a low oxygen and hydrogen content. This sp(2)-bonded carbon has a continuous three-dimensional network of highly curved, atom-thick walls that form primarily 0.6- to 5-nanometer-width pores. Two-electrode supercapacitor cells constructed with this carbon yielded high values of gravimetric capacitance and energy density with organic and ionic liquid electrolytes. The processes used to make this carbon are readily scalable to industrial levels.

Carbon-Based Supercapacitors Produced by Activation of Graphene

NASA Astrophysics Data System (ADS)

Zhu, Yanwu; Murali, Shanthi; Stoller, Meryl D.; Ganesh, K. J.; Cai, Weiwei; Ferreira, Paulo J.; Pirkle, Adam; Wallace, Robert M.; Cychosz, Katie A.; Thommes, Matthias; Su, Dong; Stach, Eric A.; Ruoff, Rodney S.

2011-06-01

Supercapacitors, also called ultracapacitors or electrochemical capacitors, store electrical charge on high-surface-area conducting materials. Their widespread use is limited by their low energy storage density and relatively high effective series resistance. Using chemical activation of exfoliated graphite oxide, we synthesized a porous carbon with a Brunauer-Emmett-Teller surface area of up to 3100 square meters per gram, a high electrical conductivity, and a low oxygen and hydrogen content. This sp2-bonded carbon has a continuous three-dimensional network of highly curved, atom-thick walls that form primarily 0.6- to 5-nanometer-width pores. Two-electrode supercapacitor cells constructed with this carbon yielded high values of gravimetric capacitance and energy density with organic and ionic liquid electrolytes. The processes used to make this carbon are readily scalable to industrial levels.

Linking Thermodynamics to Pollutant Reduction Kinetics by Fe2+ Bound to Iron Oxides.

PubMed

Stewart, Sydney M; Hofstetter, Thomas B; Joshi, Prachi; Gorski, Christopher A

2018-05-15

Numerous studies have reported that pollutant reduction rates by ferrous iron (Fe 2+ ) are substantially enhanced in the presence of an iron (oxyhydr)oxide mineral. Developing a thermodynamic framework to explain this phenomenon has been historically difficult due to challenges in quantifying reduction potential ( E H ) values for oxide-bound Fe 2+ species. Recently, our group demonstrated that E H values for hematite- and goethite-bound Fe 2+ can be accurately calculated using Gibbs free energy of formation values. Here, we tested if calculated E H values for oxide-bound Fe 2+ could be used to develop a free energy relationship capable of describing variations in reduction rate constants of substituted nitrobenzenes, a class of model pollutants that contain reducible aromatic nitro groups, using data collected here and compiled from the literature. All the data could be described by a single linear relationship between the logarithms of the surface-area-normalized rate constant ( k SA ) values and E H and pH values [log( k SA ) = - E H /0.059 V - pH + 3.42]. This framework provides mechanistic insights into how the thermodynamic favorability of electron transfer from oxide-bound Fe 2+ relates to redox reaction kinetics.

Highly surface-roughened quasi-spherical silver powders in back electrode paste for silicon solar cells

NASA Astrophysics Data System (ADS)

Yin, Peng; Liu, Shouchao; Li, Qiuying; Chen, Xiaolei; Guo, Weihong; Wu, Chifei

2017-08-01

In our work, highly surface-roughened quasi-spherical silver powders with controllable size and superior dispersibility, which have narrow size distribution and relatively high tap density, were successfully prepared by reducing silver nitrate with ascorbic acid in aqueous solutions. Gum arabic (AG) was selected as dispersant to prevent the agglomeration of silver particles. Furthermore, the effects of preparation conditions on the characteristics of the powders were systematically investigated. By varying the concentration of the reactants, dosage of dispersant, the feeding modes, synthesis temperature and the pH value of the mixture solution of silver nitrate and AG, the resulted silver particles displayed controllable size, different morphologies and surface roughness. The spherical silver powder with mean particle size of 1.20 µm, tap density of 4.1 g cm-3 and specific area value of 0.46 m2 g-1 was prepared by adjusting preparation conditions. The AG absorbed on the surface preventing the silver particles from diffusion and aggregation was proved by the ultraviolet spectra. Observations of SEM images showed that the as-prepared silver powders were relatively monodisperse silver spheres with highly roughened surface and the particle size was controllable from 1 µm to 5 µm, specific surface area value from approximately 0.2 m2 g-1 to 0.8 m2 g-1. X-ray diffraction (XRD) patterns, energy dispersive spectroscopy (EDS), x-ray photoelectron spectra (XPS) and thermal gravity analysis (TGA) demonstrated high crystallinity and purity of the obtained silver powders.

Surface characterization of nickel titanium orthodontic arch wires

PubMed Central

Krishnan, Manu; Seema, Saraswathy; Tiwari, Brijesh; Sharma, Himanshu S.; Londhe, Sanjay; Arora, Vimal

2015-01-01

Background Surface roughness of nickel titanium orthodontic arch wires poses several clinical challenges. Surface modification with aesthetic/metallic/non metallic materials is therefore a recent innovation, with clinical efficacy yet to be comprehensively evaluated. Methods One conventional and five types of surface modified nickel titanium arch wires were surface characterized with scanning electron microscopy, energy dispersive analysis, Raman spectroscopy, Atomic force microscopy and 3D profilometry. Root mean square roughness values were analyzed by one way analysis of variance and post hoc Duncan's multiple range tests. Results Study groups demonstrated considerable reduction in roughness values from conventional in a material specific pattern: Group I; conventional (578.56 nm) > Group V; Teflon (365.33 nm) > Group III; nitride (301.51 nm) > Group VI (i); rhodium (290.64 nm) > Group VI (ii); silver (252.22 nm) > Group IV; titanium (229.51 nm) > Group II; resin (158.60 nm). It also showed the defects with aesthetic (resin/Teflon) and nitride surfaces and smooth topography achieved with metals; titanium/silver/rhodium. Conclusions Resin, Teflon, titanium, silver, rhodium and nitrides were effective in decreasing surface roughness of nickel titanium arch wires albeit; certain flaws. Findings have clinical implications, considering their potential in lessening biofilm adhesion, reducing friction, improving corrosion resistance and preventing nickel leach and allergic reactions. PMID:26843749

Effect of electrode contact area on the information content of the recorded electrogastrograms: An analysis based on Rényi entropy and Teager-Kaiser Energy

NASA Astrophysics Data System (ADS)

Alagumariappan, Paramasivam; Krishnamurthy, Kamalanand; Kandiah, Sundravadivelu; Ponnuswamy, Mannar Jawahar

2017-06-01

Electrogastrograms (EGG) are electrical signals originating from the digestive system, which are closely correlated with its mechanical activity. Electrogastrography is an efficient non-invasive method for examining the physiological and pathological states of the human digestive system. There are several factors such as fat conductivity, abdominal thickness, change in electrode surface area etc, which affects the quality of the recorded EGG signals. In this work, the effect of variations in the contact area of surface electrodes on the information content of the measured electrogastrograms is analyzed using Rényi entropy and Teager-Kaiser Energy (TKE). Two different circular cutaneous electrodes with approximate contact areas of 201.14 mm2 and 283.64 mm2, have been adopted and EGG signals were acquired using the standard three electrode protocol. Further, the information content of the measured EGG signals were analyzed using the computed values of entropy and energy. Results demonstrate that the information content of the measured EGG signals increases by 6.72% for an increase in the contact area of the surface electrode by 29.09%. Further, it was observed that the average energy increases with increase in the contact surface area. This work appears to be of high clinical significance since the accurate measurement of EGG signals without loss in its information content, is highly useful for the design of diagnostic assistance tools for automated diagnosis and mass screening of digestive disorders.

Aberrated surface soliton formation in a nonlinear 1D and 2D photonic crystal

PubMed Central

Lysak, Tatiana M.; Trykin, Evgenii M.

2018-01-01

We discuss a novel type of surface soliton—aberrated surface soliton—appearance in a nonlinear one dimensional photonic crystal and a possibility of this surface soliton formation in two dimensional photonic crystal. An aberrated surface soliton possesses a nonlinear distribution of the wavefront. We show that, in one dimensional photonic crystal, the surface soliton is formed at the photonic crystal boundary with the ambient medium. Essentially, that it occupies several layers at the photonic crystal boundary and penetrates into the ambient medium at a distance also equal to several layers, so that one can infer about light energy localization at the lateral surface of the photonic crystal. In the one dimensional case, the surface soliton is formed from an earlier formed soliton that falls along the photonic crystal layers at an angle which differs slightly from the normal to the photonic crystal face. In the two dimensional case, the soliton can appear if an incident Gaussian beam falls on the photonic crystal face. The influence of laser radiation parameters, optical properties of photonic crystal layers and ambient medium on the one dimensional surface soliton formation is investigated. We also discuss the influence of two dimensional photonic crystal configuration on light energy localization near the photonic crystal surface. It is important that aberrated surface solitons can be created at relatively low laser pulse intensity and for close values of alternating layers dielectric permittivity which allows their experimental observation. PMID:29558497

The condensation and vaporization behavior of ices containing SO2, H2S, and CO2: Implications for Io

NASA Technical Reports Server (NTRS)

Sandford, Scott A.; Allamandola, Louis J.

1993-01-01

In an extension of previously reported work on ices containing CO, CO2, H2O, CH3OH, NH3, and H2, measurements of the physical and infrared spectral properties of ices containing molecules relevant to Jupiter's moon Io are presented. These include studies on ice systems containing SO2, H2S, and CO2. The condensation and sublimation behaviors of each ice system and surface binding energies of their components are discussed. The surface binding energies can be used to calculate the residence times of the molecules on a surface as a function of temperature and thus represent important parameters for any calculation that attempts to model the transport of these molecules on Io's surface. The derived values indicate that SO2 frosts on Io are likely to anneal rapidly, resulting in less fluffy, 'glassy' ices and that H2S can be trapped in the SO2 ices of Io during night-time hours provided that SO2 deposition rates are on the order of 5 micrometers/hr or larger.

Electrochemical oxidation of ampicillin antibiotic at boron-doped diamond electrodes and process optimization using response surface methodology.

PubMed

Körbahti, Bahadır K; Taşyürek, Selin

2015-03-01

Electrochemical oxidation and process optimization of ampicillin antibiotic at boron-doped diamond electrodes (BDD) were investigated in a batch electrochemical reactor. The influence of operating parameters, such as ampicillin concentration, electrolyte concentration, current density, and reaction temperature, on ampicillin removal, COD removal, and energy consumption was analyzed in order to optimize the electrochemical oxidation process under specified cost-driven constraints using response surface methodology. Quadratic models for the responses satisfied the assumptions of the analysis of variance well according to normal probability, studentized residuals, and outlier t residual plots. Residual plots followed a normal distribution, and outlier t values indicated that the approximations of the fitted models to the quadratic response surfaces were very good. Optimum operating conditions were determined at 618 mg/L ampicillin concentration, 3.6 g/L electrolyte concentration, 13.4 mA/cm(2) current density, and 36 °C reaction temperature. Under response surface optimized conditions, ampicillin removal, COD removal, and energy consumption were obtained as 97.1 %, 92.5 %, and 71.7 kWh/kg CODr, respectively.

Positron annihilation on the surfaces of SiO 2 films thermally grown on single crystal of Cz-Si

NASA Astrophysics Data System (ADS)

Deng, Wen; Yue, Li; Zhang, Wei; Cheng, Xu-xin; Zhu, Yan-yan; Huang, Yu-yang

2009-09-01

Two-detector coincidence system and mono-energetic slow positron beam has been applied to measure the Doppler broadening spectra for single crystals of SiO2, SiO2 films with different thickness thermally grown on single crystal of Cz-Si, and single crystal of Si without oxide film. Oxygen is recognized as a peak at about 11.85 × 10-3m0c on the ratio curves. The S parameters decrease with the increase of positron implantation energy for the single crystal of SiO2 and Si without oxide film. However, for the thermally grown SiO2-Si sample, the S parameters in near surface of the sample increase with positron implantation energy. It is due to the formation of silicon oxide at the surface, which lead to lower S value. S and W parameters vary with positron implantation depth indicate that the SiO2-Si system consist of a surface layer, a SiO2 layer, a SiO2-Si interface layer and a semi-infinite Si substrate.

Fundamental data on the desorption of pure interstellar ices

NASA Astrophysics Data System (ADS)

Brown, Wendy A.; Bolina, Amandeep S.

2007-01-01

The desorption of molecular ices from grain surfaces is important in a number of astrophysical environments including dense molecular clouds, cometary nuclei and the surfaces and atmospheres of some planets. With this in mind, we have performed a detailed investigation of the desorption of pure water, pure methanol and pure ammonia ices from a model dust-grain surface. We have used these results to determine the desorption energy, order of desorption and the pre-exponential factor for the desorption of these molecular ices from our model surface. We find good agreement between our desorption energies and those determined previously; however, our values for the desorption orders, and hence also the pre-exponential factors, are different to those reported previously. The kinetic parameters derived from our data have been used to model desorption on time-scales relevant to astrophysical processes and to calculate molecular residence times, given in terms of population half-life as a function of temperature. These results show the importance of laboratory data for the understanding of astronomical situations whereby icy mantles are warmed by nearby stars and by other dynamical events.

Forcing and Responses of the Surface Energy Budget at Summit, Greenland

NASA Astrophysics Data System (ADS)

Miller, Nathaniel B.

Energy exchange at the Greenland Ice Sheet surface governs surface temperature variability, a factor critical for representing increasing surface melt extent, which portends a rise in global sea level. A comprehensive set of cloud, tropospheric, near-surface and sub-surface measurements at Summit Station is utilized to determine the driving forces and subsequent responses of the surface energy budget (SEB). This budget includes radiative, turbulent, and ground heat fluxes, and ultimately controls the evolution of surface temperature. At Summit Station, clouds radiatively warm the surface in all months with an annual average cloud radiative forcing value of 33 W m -2, largely driven by the occurrence of liquid-bearing clouds. The magnitude of the surface temperature response is dependent on how turbulent and ground heat fluxes modulate changes to radiative forcing. Relationships between forcing terms and responding surface fluxes show that changes in the upwelling longwave radiation compensate for 65-85% (50- 60%) of the total change in radiative forcing in the winter (summer). The ground heat flux is the second largest response term (16% annually), especially during winter. Throughout the annual cycle, the sensible heat flux response is comparatively constant (9%) and latent heat flux response is only 1.5%, becoming more of a factor in modulating surface temperature responses during the summer. Combining annual cycles of these responses with cloud radiative forcing results, clouds warm the surface by an estimated 7.8°C annually. A reanalysis product (ERA-I), operational model (CFSv2), and climate model (CESM) are evaluated utilizing the comprehensive set of SEB observations and process-based relationships. Annually, surface temperatures in each model are warmer than observed with overall poor representation of the coldest surface temperatures. Process-based relationships between different SEB flux terms offer insight into how well a modeling framework represents physical processes and the ability to distinguish errors in forcing versus those in physical representation. Such relationships convey that all three models underestimate the response of surface temperatures to changes in radiative forcing. These results provide a method to expose model deficiencies and indicate the importance of representing surface, sub-surface and boundary-layer processes when portraying cloud impacts on surface temperature variability.

Two decision-support tools for assessing the potential effects of energy development on hydrologic resources as part of the Energy and Environment in the Rocky Mountain Area interactive energy atlas

USGS Publications Warehouse

Linard, Joshua I.; Matherne, Anne Marie; Leib, Kenneth J.; Carr, Natasha B.; Diffendorfer, James E.; Hawkins, Sarah J.; Latysh, Natalie; Ignizio, Drew A.; Babel, Nils C.

2014-01-01

The U.S. Geological Survey project—Energy and Environment in the Rocky Mountain Area (EERMA)—has developed a set of virtual tools in the form of an online interactive energy atlas for Colorado and New Mexico to facilitate access to geospatial data related to energy resources, energy infrastructure, and natural resources that may be affected by energy development. The interactive energy atlas currently (2014) consists of three components: (1) a series of interactive maps; (2) downloadable geospatial datasets; and (3) decison-support tools, including two maps related to hydrologic resources discussed in this report. The hydrologic-resource maps can be used to examine the potential effects of energy development on hydrologic resources with respect to (1) groundwater vulnerability, by using the depth to water, recharge, aquifer media, soil media, topography, impact of the vadose zone, and hydraulic conductivity of the aquifer (DRASTIC) model, and (2) landscape erosion potential, by using the revised universal soil loss equation (RUSLE). The DRASTIC aquifer vulnerability index value for the two-State area ranges from 48 to 199. Higher values, indicating greater relative aquifer vulnerability, are centered in south-central Colorado, areas in southeastern New Mexico, and along riparian corridors in both States—all areas where the water table is relatively close to the land surface and the aquifer is more susceptible to surface influences. As calculated by the RUSLE model, potential mean annual erosion, as soil loss in units of tons per acre per year, ranges from 0 to 12,576 over the two-State area. The RUSLE model calculated low erosion potential over most of Colorado and New Mexico, with predictions of highest erosion potential largely confined to areas of mountains or escarpments. An example is presented of how a fully interactive RUSLE model could be further used as a decision-support tool to evaluate the potential hydrologic effects of energy development on a site-specific basis and to explore the effectiveness of various mitigation practices.

Optimization of permeate flux produced by solar energy driven membrane distillation process using central composite design approach.

PubMed

Bouguecha, Salah T; Boubakri, Ali; Aly, Samir E; Al-Beirutty, Mohammad H; Hamdi, Mohamed M

2016-01-01

Membrane distillation (MD) is considered as a relatively high-energy requirement. To overcome this drawback, it is recommended to couple the MD process with solar energy as the renewable energy source in order to provide heat energy required to optimize its performance to produce permeate flux. In the present work, an original solar energy driven direct contact membrane distillation (DCMD) pilot plant was built and tested under actual weather conditions at Jeddah, KSA, in order to model and optimize permeate flux. The dependency of permeate flux on various operating parameters such as feed temperature (46.6-63.4°C), permeate temperature (6.6-23.4°C), feed flow rate (199-451L/h) and permeate flow rate (199-451L/h) was studied by response surface methodology based on central composite design approach. The analysis of variance (ANOVA) confirmed that all independent variables had significant influence on the model (where P-value <0.05). The high coefficient of determination (R(2) = 0.9644 and R(adj)(2) = 0.9261) obtained by ANOVA demonstrated good correlation between experimental and predicted values of the response. The optimized conditions, determined using desirability function, were T(f) = 63.4°C, Tp = 6.6°C, Q(f) = 451L/h and Q(p) = 451L/h. Under these conditions, the maximum permeate flux of 6.122 kg/m(2).h was achieved, which was close to the predicted value of 6.398 kg/m(2).h.

NH3 adsorption on anatase-TiO2(101)

NASA Astrophysics Data System (ADS)

Koust, Stig; Adamsen, Kræn C.; Kolsbjerg, Esben Leonhard; Li, Zheshen; Hammer, Bjørk; Wendt, Stefan; Lauritsen, Jeppe V.

2018-03-01

The adsorption of ammonia on anatase TiO2 is of fundamental importance for several catalytic applications of TiO2 and for probing acid-base interactions. Utilizing high-resolution scanning tunneling microscopy (STM), synchrotron X-ray photoelectron spectroscopy, temperature-programmed desorption (TPD), and density functional theory (DFT), we identify the adsorption mode and quantify the adsorption strength on the anatase TiO2(101) surface. It was found that ammonia adsorbs non-dissociatively as NH3 on regular five-fold coordinated titanium surface sites (5f-Ti) with an estimated exothermic adsorption energy of 1.2 eV for an isolated ammonia molecule. For higher adsorbate coverages, the adsorption energy progressively shifts to smaller values, due to repulsive intermolecular interactions. The repulsive adsorbate-adsorbate interactions are quantified using DFT and autocorrelation analysis of STM images, which both showed a repulsive energy of ˜50 meV for nearest neighbor sites and a lowering in binding energy for an ammonia molecule in a full monolayer of 0.28 eV, which is in agreement with TPD spectra.

Photo-catalyzed surface hydrolysis of iridium(iii) ions on semiconductors: a facile method for the preparation of semiconductor/IrOx composite photoanodes toward oxygen evolution reaction.

PubMed

Wu, Qingyong; Xu, Di; Xue, Ning; Liu, Tengyi; Xiang, Min; Diao, Peng

2016-12-21

We previously reported that the hydrolysis of Ir 3+ in homogeneous solution could be triggered by irradiation with light whose energy was larger than a threshold value. In this work, we demonstrated that, by introducing Fe 2 O 3 particles into solution, the incident light energy-restriction for the photo-catalyzed hydrolysis could be broken and the hydrolysis occurred at the Fe 2 O 3 /solution interface. The photo-generated holes on the Fe 2 O 3 surface played a key role in oxidizing Ir(iii) to Ir(iv) species and triggered the deposition of IrO x . We showed that this photo-catalyzed surface hydrolysis is a universal phenomenon that takes place on the surface of many n-type semiconductors such as Fe 2 O 3 , TiO 2 , and Ag 3 PO 4 . As IrO x is an efficient catalyst for oxygen evolution reaction, surface hydrolysis is a general, facile and efficient strategy to prepare semiconductor/IrO x composites, which can be used as anodic materials for photoelectrochemical water splitting.

Fast interaction of atoms with crystal surfaces: coherent lighting

NASA Astrophysics Data System (ADS)

Gravielle, M. S.

2017-11-01

Quantum coherence of incident waves results essential for the observation of interference patterns in grazing incidence fast atom diffraction (FAD). In this work we investigate the influence of the impact energy and projectile mass on the transversal length of the surface area that is coherently illuminated by the atomic beam, after passing through a collimating aperture. Such a transversal coherence length controls the general features of the interference structures, being here derived by means of the Van Cittert-Zernike theorem. The coherence length is then used to build the initial coherent wave packet within the Surface Initial Value Representation (SIVR) approximation. The SIVR approach is applied to fast He and Ne atoms impinging grazingly on a LiF(001) surface along a low-indexed crystallographic direction. We found that with the same collimating setup, by varying the impact energy we would be able to control the interference mechanism that prevails in FAD patterns, switching between inter-cell and unit-cell interferences. These findings are relevant to use FAD spectra adequately as a surface analysis tool, as well as to choose the appropriate collimating scheme for the observation of interference effects in a given collision system.

Melting of SiC powders preplaced duplex stainless steel using TIG welding

NASA Astrophysics Data System (ADS)

Maleque, M. A.; Afiq, M.

2018-01-01

TIG torch welding technique is a conventional melting technique for the cladding of metallic materials. Duplex stainless steels (DSS) show decrease in performance under aggressive environment which may lead to unanticipated failure due to poor surface properties. In this research, surface modification is done by using TIG torch method where silicon carbide (SiC) particles are fused into DSS substrate in order to form a new intermetallic compound at the surface. The effect of particle size, feed rate of SiC preplacement, energy input and shielding gas flow rate on surface topography, microstructure, microstructure and hardness are investigated. Deepest melt pool (1.237 mm) is produced via TIG torch with highest energy input of 1080 J/mm. Observations of surface topography shows rippling marks which confirms that re-solidification process has taken place. Melt microstructure consist of dendritic and globular carbides precipitate as well as partially melted silicon carbides (SiC) particles. Micro hardness recorded at value ranging from 316 HV0.5 to 1277 HV0.5 which shows increment from base hardness of 260 HV0.5kgf. The analyzed result showed that incorporation of silicon carbide particles via TIG Torch method increase the hardness of DSS.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duan, Yandong; Zhang, Bingkai; Zheng, Jiaxin

Abstract. Due to the enhanced kinetic properties, nanocrystallites have received much attention as potential electrode materials for energy storage. However, because of the large specific surface areas of nanocrystallites, they usually suffer from decreased energy density, reduced cycling stability and total electrode capacity. In this work, we report a size-dependent excess capacity beyond the theoretical value of 170 mAhg-1 in a special carbon coated LiFePO4 composite cathode material, which delivers capacities of 191.2 and 213.5 mAhg-1 with the mean particle sizes of 83 nm and 42 nm, respectively. Moreover, this LiFePO4 composite also shows excellent cycling stability and high ratemore » performance. Our further experimental tests and ab initio calculations reveal that the excess capacity comes from the charge passivation for which the C-O-Fe bonds would lead to charge redistribution on the surface of LiFePO4 and hence to enhance the bonding interaction between surface O atoms and Li-ions. The surface reconstruction for excess Li-ion storage makes full use of the large specific surface area for the nanocrystallites, which can maintain the fast Li-ion transport and enhance the capacity greatly that the nanocrystallites usually suffers.« less

Impact of Viscous Droplets on Superamphiphobic Surfaces

NASA Astrophysics Data System (ADS)

Zhao, Binyu; Chen, Longquan; Deng, Xu

2016-11-01

Superamphiphobic coating is promising for various applications in industry, e.g. self-cleaning windows, where the impingement of droplets on surfaces is commonly encountered. In this work, we experimentally investigated the impact of droplets with similar surface tension (63-72 mN/m) but much different viscosity (1-150 mPa s) on superamphiphobic surfaces. We found that droplets can rebound from the superamphiphobic surfaces when the impact velocity is larger than a critical value, which linearly increases with the liquid viscosity. Droplet with higher viscosity spreads, retracts slower, and eventually rebounds lower and fewer times than that of low viscous droplet. These findings have important implications for surface engineers to use superamphiphobic coatings. Furthermore, we measured the maximum spreading factors for droplet impact on superamphiphobic surfaces and proposed a simple model based on energy conversation to describe its relationship to the Weber number and Reynolds number.