Quantum Dynamics Study of the Potential Energy Minima Effect on Energy Efficiency for the F- + CH3Cl → FCH3 + Cl- Reaction.

PubMed

Li, Yida; Wang, Yuping; Wang, Dunyou

2017-04-13

The Polanyi rules on the energy efficiency on reactivity are summarized solely from the locations of barriers on the potential energy surfaces. Here, our quantum dynamics study for the F - + CH 3 Cl → FCH 3 + Cl - reaction shows that the two potential energy minima in the entrance channel on the potential energy surface play an essential role in energy efficiency on reactivity. The reactivity of this reaction is dominated by the low collision energies where two distinctive reaction mechanisms involve the two minima in the entrance channel. Overall, the Cl-CH 3 stretching motion and C-H 3 umbrella motion both are more efficient than the translational motion in promoting this reaction. Although this reaction has a negative energy barrier, our study shows that it is the minima in the entrance channel, together with the energy barrier relative to these minima, that determine the energy efficacy on reactivity.

Anomalous Seebeck coefficient observed in silicon nanowire micro thermoelectric generator

NASA Astrophysics Data System (ADS)

Hashimoto, S.; Asada, S.; Xu, T.; Oba, S.; Himeda, Y.; Yamato, R.; Matsukawa, T.; Matsuki, T.; Watanabe, T.

2017-07-01

We have found experimentally an anomalous thermoelectric characteristic of an n-type Si nanowire micro thermoelectric generator (μTEG). The μTEG is fabricated on a silicon-on-insulator wafer by electron beam lithography and dry etching, and its surface is covered with a thermally grown silicon dioxide film. The observed thermoelectric current is opposite to what is expected from the Seebeck coefficient of n-type Si. The result is understandable by considering a potential barrier in the nanowire. Upon the application of the temperature gradient across the nanowire, the potential barrier impedes the diffusion of thermally activated majority carriers into the nanowire, and it rather stimulates the injection of thermally generated minority carriers. The most plausible origin of the potential barrier is negative charges trapped at the interface between the Si nanowire and the oxide film. We practically confirmed that the normal Seebeck coefficient of the n-type Si nanowire is recovered after the hydrogen forming gas annealing. This implies that the interface traps are diminished by the hydrogen termination of bonding defects. The present results show the importance of the surface inactivation treatment of μTEGs to suppress the potential barrier and unfavorable contribution of minority carriers.

A New Potential Energy Surface for N+O2: Is There an NOO Minimum?

NASA Technical Reports Server (NTRS)

Walch, Stephen P.

1995-01-01

We report a new calculation of the N+02 potential energy surface using complete active space self-consistent field internally contracted configuration interaction with the Dunning correlation consistent basis sets. The peroxy isomer of N02 is found to be a very shallow minimum separated from NO+O by a barrier of only 0.3 kcal/mol (excluding zero-point effects). The entrance channel barrier height is estimated to be 8.6 kcal/mol for ICCI+Q calculations correlating all but the Ols and N1s electrons with a cc-p VQZ basis set.

Theoretical studies of the potential surface for the F - H2 greater than HF + H reaction

NASA Technical Reports Server (NTRS)

Bauschlicher, Charles W., Jr.; Walch, Stephen, P.; Langhoff, Stephen R.; Taylor, Peter R.; Jaffe, Richard L.

1987-01-01

The F + H2 yields HF + H potential energy hypersurface was studied in the saddle point and entrance channel regions. Using a large (5s 5p 3d 2f 1g/4s 3p 2d) atomic natural orbital basis set, a classical barrier height of 1.86 kcal/mole was obtained at the CASSCF/multireference CI level (MRCI) after correcting for basis set superposition error and including a Davidson correction (+Q) for higher excitations. Based upon an analysis of the computed results, the true classical barrier is estimated to be about 1.4 kcal/mole. The location of the bottleneck on the lowest vibrationally adiabatic potential curve was also computed and the translational energy threshold determined from a one-dimensional tunneling calculation. Using the difference between the calculated and experimental threshold to adjust the classical barrier height on the computed surface yields a classical barrier in the range of 1.0 to 1.5 kcal/mole. Combining the results of the direct estimates of the classical barrier height with the empirical values obtained from the approximation calculations of the dynamical threshold, it is predicted that the true classical barrier height is 1.4 + or - 0.4 kcal/mole. Arguments are presented in favor of including the relatively large +Q correction obtained when nine electrons are correlated at the CASSCF/MRCI level.

Surface potential barrier in m-plane GaN studied by contactless electroreflectance

NASA Astrophysics Data System (ADS)

Janicki, Lukasz; Misiewicz, Jan; Cywiński, Grzegorz; Sawicka, Marta; Skierbiszewski, Czeslaw; Kudrawiec, Robert

2016-02-01

Contactless electroreflectance (CER) is used to study the surface potential barrier in m-plane GaN UN+ [GaN (d = 20,30,50,70 nm)/GaN:Si] structures grown by using molecular beam epitaxy. Clear bandgap-related transitions followed by Franz-Keldysh oscillations (FKO) have been observed in the CER spectra of all samples at room temperature. The built-in electric fields in the undoped cap layers have been determined from the FKO period. From the built-in electric field and the undoped GaN layer thickness, the Fermi level location at the air-exposed m-plane GaN surface has been estimated as 0.42 ± 0.05 eV below the conduction band.

Two-layer thermal barrier coating for turbine airfoils - furnace and burner rig test results

NASA Technical Reports Server (NTRS)

Stecura, S.

1976-01-01

A simple, two-layer plasma-sprayed thermal barrier coating system was developed which has the potential for protecting high temperature air-cooled gas turbine components. Of those coatings initially examined, the most promising system consisted of a Ni-16Cr-6Al-0.6Y (in wt%) thermal barrier coating (about 0.005 to 0.010 cm thick) and a ZrO2-12Y2O3 (in wt%) thermal barrier coating (about 0.025 to 0.064 cm thick). This thermal barrier substantially lowered the metal temperature of an air-cooled airfoil. The coating withstood 3,200 cycles (80 sec at 1,280 C surface temperature) and 275 cycles (1 hr at 1,490 C surface temperature) without cracking or spalling. No separation of the thermal barrier from the bond coating or the bond coating from the substrate was observed.

Radiation-tolerant imaging device

DOEpatents

Colella, N.J.; Kimbrough, J.R.

1996-11-19

A barrier at a uniform depth for an entire wafer is used to produce imaging devices less susceptible to noise pulses produced by the passage of ionizing radiation. The barrier prevents charge created in the bulk silicon of a CCD detector or a semiconductor logic or memory device from entering the collection volume of each pixel in the imaging device. The charge barrier is a physical barrier, a potential barrier, or a combination of both. The physical barrier is formed by an SiO{sub 2} insulator. The potential barrier is formed by increasing the concentration of majority carriers (holes) to combine with the electron`s generated by the ionizing radiation. A manufacturer of CCD imaging devices can produce radiation-tolerant devices by merely changing the wafer type fed into his process stream from a standard wafer to one possessing a barrier beneath its surface, thus introducing a very small added cost to his production cost. An effective barrier type is an SiO{sub 2} layer. 7 figs.

Radiation-tolerant imaging device

DOEpatents

Colella, Nicholas J.; Kimbrough, Joseph R.

1996-01-01

A barrier at a uniform depth for an entire wafer is used to produce imaging devices less susceptible to noise pulses produced by the passage of ionizing radiation. The barrier prevents charge created in the bulk silicon of a CCD detector or a semiconductor logic or memory device from entering the collection volume of each pixel in the imaging device. The charge barrier is a physical barrier, a potential barrier, or a combination of both. The physical barrier is formed by an SiO.sub.2 insulator. The potential barrier is formed by increasing the concentration of majority carriers (holes) to combine with the electron's generated by the ionizing radiation. A manufacturer of CCD imaging devices can produce radiation-tolerant devices by merely changing the wafer type fed into his process stream from a standard wafer to one possessing a barrier beneath its surface, thus introducing a very small added cost to his production cost. An effective barrier type is an SiO.sub.2 layer.

Energy Levels in Quantum Wells.

NASA Astrophysics Data System (ADS)

Zang, Jan Xin

Normalized analytical equations for eigenstates of an arbitrary one-dimensional configuration of square potentials in a well have been derived. The general formulation is used to evaluate the energy levels of a particle in a very deep potential well containing seven internal barriers. The configuration can be considered as a finite superlattice sample or as a simplified model for a sample with only several atom layers. The results are shown in graphical forms as functions of the height and width of the potential barriers and as functions of the ratio of the effective mass in barrier to the mass in well. The formation of energy bands and surface eigenstates from eigenstates of a deep single well, the coming close of two energy bands and a surface state which are separate ordinarily, and mixing of the wave function of a surface state with the bulk energy bands are seen. Then the normalized derivation is extended to study the effect of a uniform electric field applied across a one-dimensional well containing an internal configuration of square potentials The general formulation is used to calculate the electric field dependence of the energy levels of a deep well with five internal barriers. Typical results are shown in graphical forms as functions of the barrier height, barrier width, barrier effective mass and the field strength. The formation of Stark ladders and surface states from the eigenstates of a single deep well in an electric field, the localization process of wave functions with changing barrier height, width, and field strength and their anticrossing behaviors are seen. The energy levels of a hydrogenic impurity in a uniform medium and in a uniform magnetic field are calculated with variational methods. The energy eigenvalues for the eigenstates with major quantum number less than or equal to 3 are obtained. The results are consistent with previous results. Furthermore, the energy levels of a hydrogenic impurity at the bottom of a one-dimensional parabolic quantum well with a magnetic field normal to the plane of the well are calculated with the finite-basis-set variational method. The limit of small radial distance and the limit of great radial distance are considered to choose a set of proper basis functions. It is found that the energy levels increase with increasing parabolic parameter alpha and increase with increasing normalized magnetic field strength gamma except those levels with magnetic quantum number m < 0 at small gamma.

Material Barriers to Diffusive Mixing

NASA Astrophysics Data System (ADS)

Haller, George; Karrasch, Daniel

2017-11-01

Transport barriers, as zero-flux surfaces, are ill-defined in purely advective mixing in which the flux of any passive scalar is zero through all material surfaces. For this reason, Lagrangian Coherent Structures (LCSs) have been argued to play the role of mixing barriers as most repelling, attracting or shearing material lines. These three kinematic concepts, however, can also be defined in different ways, both within rigorous mathematical treatments and within the realm of heuristic diagnostics. This has lead to a an ever-growing number of different LCS methods, each generally identifying different objects as transport barriers. In this talk, we examine which of these methods have actual relevance for diffusive transport barriers. The latter barriers are arguably the practically relevant inhibitors in the mixing of physically relevant tracers, such as temperature, salinity, vorticity or potential vorticity. We demonstrate the role of the most effective diffusion barriers in analytical examples and observational data. Supported in part by the DFG Priority Program on Turbulent Superstructures.

IPE : EVALUATION OF ORTHOTROPIC ELASTIC PROPERTIES AND ITS APPLICATION IN ROADSIDE BARRIERS

DOT National Transportation Integrated Search

2017-12-24

Roadside barriers are the primary structural safety devices on surface roads. They can be made from any material as long as they can absorb the energy involved in an impact scenario. One material that has that potential is Ipe, which is a hardwood ma...

THE SIZE AND SURFACE COATING OF NANOSILVER DIFFERENTIALLY AFFECTS BIOLOGICAL ACTIVITY IN BLOOD BRAIN BARRIER (RBEC4) CELLS.

EPA Science Inventory

Linking the physical properties of nanoparticles with differences in their biological activity is critical for understanding their potential toxicity and mode of action. The influence of aggregate size, surface coating, and surface charge on nanosilver's (nanoAg) movement through...

Quantal Study of the Exchange Reaction for N + N2 using an ab initio Potential Energy Surface

NASA Technical Reports Server (NTRS)

Wang, Dunyou; Stallcop, James R.; Huo, Winifred M.; Dateo, Christopher E.; Schwenke, David W.; Partridge, Harry; Kwak, Dochan (Technical Monitor)

2002-01-01

The N + N2 exchange rate is calculated using a time-dependent quantum dynamics method on a newly determined ab initio potential energy surface (PES) for the ground A" state. This ab initio PES shows a double barrier feature in the interaction region with the barrier height at 47.2 kcal/mol, and a shallow well between these two barriers, with the minimum at 43.7 kcal/mol. A quantum dynamics wave packet calculation has been carried out using the fitted PES to compute the cumulative reaction probability for the exchange reaction of N + N2(J=O). The J - K shift method is then employed to obtain the rate constant for this reaction. The calculated rate constant is compared with experimental data and a recent quasi-classical calculation using a LEPS PES. Significant differences are found between the present and quasiclassical results. The present rate calculation is the first accurate 3D quantal dynamics study for N + N2 reaction system and the ab initio PES reported here is the first such surface for N3.

The vibrationally adiabatic torsional potential energy surface of trans-stilbene

NASA Astrophysics Data System (ADS)

Chowdary, Praveen D.; Martinez, Todd J.; Gruebele, Martin

2007-05-01

The effect of vibrational Zero Point Energy (ZPE) on the torsional barriers of trans-stilbene is studied in the adiabatic approximation. The two torsional modes corresponding to phenyl rotation are explicitly separated, and the remaining modes are treated as normal coordinates. ZPE reduces the adiabatic barrier along the in-phase torsion from 198 to 13 cm -1. A one-dimensional adiabatic potential for the anti-phase torsion, including the ZPE of the in-phase torsion, reduces the adiabatic barrier from 260 to 58 cm -1. Comparison with recent electronic structure benchmark calculations suggests that vibrational corrections play a significant role in trans-stilbene's experimentally observed planar structure.

Prediction of large negative shaded-side spacecraft potentials

NASA Technical Reports Server (NTRS)

Prokopenko, S. M. L.; Laframboise, J. G.

1977-01-01

A calculation by Knott, for the floating potential of a spherically symmetric synchronous-altitude satellite in eclipse, was adapted to provide simple calculations of upper bounds on negative potentials which may be achieved by electrically isolated shaded surfaces on spacecraft in sunlight. Large (approximately 60 percent) increases in predicted negative shaded-side potentials are obtained. To investigate effective potential barrier or angular momentum selection effects due to the presence of less negative sunlit-side or adjacent surface potentials, these expressions were replaced by the ion random current, which is a lower bound for convex surfaces when such effects become very severe. Further large increases in predicted negative potentials were obtained, amounting to a doubling in some cases.

Conformation and dynamics of polymer chains on dirty surfaces: A discrete-to-continuum approach

NASA Astrophysics Data System (ADS)

Foo, Grace M.; Pandey, R. B.

1998-07-01

A discrete-to-continuum (DC) simulation approach is introduced to study the statics and dynamics of polymer chains in two dimensions with quenched barriers, a dirty surface. In our DC hybrid approach, the large-scale relaxation of polymer chains on a discrete disordered lattice is followed by off-lattice simulation using a bead-spring chain model with a finitely extensible nonlinear elastic (FENE) potential for covalent bonds and Lennard-Jones (LJ) potential for nonbonded interactions. Segregation/folding of chains, which occurs at low temperatures (T=0.2, 1.0) with LJ interaction, becomes more difficult as the concentration of barriers increases, due to a screening effect of the barriers. In contrast to the chains' contraction at high temperature (i.e., T=5) and their collapse in athermal systems, chains are elongated on increasing the barrier concentration—a barrier-induced stretching. Variations of the root-mean-square (rms) displacements of the center of mass (Rcm) of the chains and their center node (Rcn) with time (t) show power-law behaviors (Rcm˜tν1, Rcn˜tν2) with nonuniversal exponents in the range ν1≃0.40-0.05 and ν2≃0.30-0.05, respectively, depending on temperature and barrier concentration. The radius of gyration (Rg) and the average bond length () expand on increasing the barrier concentration at low temperature and contract at high temperature, which is consistent with the variation of the width of the radial distribution function.

Multidimensionally constrained relativistic mean-field study of triple-humped barriers in actinides

NASA Astrophysics Data System (ADS)

Zhao, Jie; Lu, Bing-Nan; Vretenar, Dario; Zhao, En-Guang; Zhou, Shan-Gui

2015-01-01

Background: Potential energy surfaces (PES's) of actinide nuclei are characterized by a two-humped barrier structure. At large deformations beyond the second barrier, the occurrence of a third barrier was predicted by macroscopic-microscopic model calculations in the 1970s, but contradictory results were later reported by a number of studies that used different methods. Purpose: Triple-humped barriers in actinide nuclei are investigated in the framework of covariant density functional theory (CDFT). Methods: Calculations are performed using the multidimensionally constrained relativistic mean field (MDC-RMF) model, with the nonlinear point-coupling functional PC-PK1 and the density-dependent meson exchange functional DD-ME2 in the particle-hole channel. Pairing correlations are treated in the BCS approximation with a separable pairing force of finite range. Results: Two-dimensional PES's of 226,228,230,232Th and 232,235,236,238U are mapped and the third minima on these surfaces are located. Then one-dimensional potential energy curves along the fission path are analyzed in detail and the energies of the second barrier, the third minimum, and the third barrier are determined. The functional DD-ME2 predicts the occurrence of a third barrier in all Th nuclei and 238U . The third minima in 230 ,232Th are very shallow, whereas those in 226 ,228Th and 238U are quite prominent. With the functional PC-PK1 a third barrier is found only in 226 ,228 ,230Th . Single-nucleon levels around the Fermi surface are analyzed in 226Th, and it is found that the formation of the third minimum is mainly due to the Z =90 proton energy gap at β20≈1.5 and β30≈0.7 . Conclusions: The possible occurrence of a third barrier on the PES's of actinide nuclei depends on the effective interaction used in multidimensional CDFT calculations. More pronounced minima are predicted by the DD-ME2 functional, as compared to the functional PC-PK1. The depth of the third well in Th isotopes decreases with increasing neutron number. The origin of the third minimum is due to the proton Z =90 shell gap at relevant deformations.

Molecular switches from benzene derivatives adsorbed on metal surfaces

PubMed Central

Liu, Wei; Filimonov, Sergey N.; Carrasco, Javier; Tkatchenko, Alexandre

2013-01-01

Transient precursor states are often experimentally observed for molecules adsorbing on surfaces. However, such precursor states are typically rather short-lived, quickly yielding to more stable adsorption configurations. Here we employ first-principles calculations to systematically explore the interaction mechanism for benzene derivatives on metal surfaces, enabling us to selectively tune the stability and the barrier between two metastable adsorption states. In particular, in the case of the tetrachloropyrazine molecule, two equally stable adsorption states are identified with a moderate and conceivably reversible barrier between them. We address the feasibility of experimentally detecting the predicted bistable behaviour and discuss its potential usefulness in a molecular switch. PMID:24157660

Roadblocks in the gut: barriers to enteric infection.

PubMed

Gill, Navkiran; Wlodarska, Marta; Finlay, B Brett

2011-05-01

This review discusses the barriers an enteric pathogen encounters when establishing an infection in the intestinal tract. There are potential barriers in the lumen that increase competition for nutrients and space. The role of mucus layer, and the antimicrobial peptides and secretory IgA sequestered within it, are also significant barriers. After overcoming these defences, the pathogen encounters the epithelial layer. This layer can be broken down into various protective components including enterocytes, Paneth cells, goblet cells, M cells and pathogen recognition receptors. Collectively, these intestinal defences constitute significant barriers that pathogens must overcome to successfully colonize this important mucosal surface. © 2011 Blackwell Publishing Ltd.

Surface diffusion on SrTiO3 (100): A temperature accelerated dynamics and first principles study

NASA Astrophysics Data System (ADS)

Hong, Minki; Wohlwend, Jennifer L.; Behera, Rakesh K.; Phillpot, Simon R.; Sinnott, Susan B.; Uberuaga, Blas P.

2013-11-01

Temperature accelerated dynamics (TAD) with an empirical potential is used to predict diffusion mechanisms and energy barriers associated with surface diffusion of adatoms and surface vacancies on (100) SrTiO3 (STO). Specifically, Sr, O, and Ti adatoms and vacancies are investigated on each termination - SrO and TiO2 - of the SrTiO3 surface. We find that the empirical potential predicts different surface mobility of adatoms depending on the surface termination: they are mobile with relatively low diffusion barriers on the SrO-terminated surface, whereas they are largely immobile on the TiO2-terminated surface. One important finding is that, of the two binding sites on the SrO-terminated surface, one is typically very close in energy to the saddle point. Thus, one of the two sites is a good estimator of the migration energy of the adatom, a conclusion supported by select density functional theory (DFT) calculations. Motivated by this result, we calculate the migration energies for a number of metal elements on the SrO-terminated surface: Ti, Ba, La, and Al. The DFT results also reveal that the details of the migration mechanism depend on the charge state of the diffusing species and that the ability of the empirical potential to properly estimate the migration mechanism depends on the magnitude and variability of the charge transfer between the adatom and the surface.

Investigation of ultrahigh sensitivity in GaInAsP nanolaser biosensor

NASA Astrophysics Data System (ADS)

Saijo, Yoshito; Watanabe, Takumi; Hasegawa, Yu; Nishijima, Yoshiaki; Baba, Toshihiko

2018-02-01

We have developed GaInAsP semiconductor photonic crystal nanolaser biosensor and demonstrated the detection of ultralow-concentration (fM to aM) proteins and deoxyribonucleic acids (DNAs) adsorbed on the device surface. In general, this type of photonic sensors exploiting optical resonance has been considered to detect the refractive index of biomolecules via the wavelength shift. However, this principle cannot explain the detection of such ultralowconcentration. Therefore, we investigated another candidate principle, i.e., ion sensitivity. We consider such a process that 1) the electric charge of biomolecules changes the nanolaser's surface charge, 2) the Schottky barrier near the semiconductor surface is increased or decreased, 3) the distribution of photopumped carriers is modified by the barrier, 4) the refractive index of the semiconductor is changed by the carrier effects, and 5) the laser wavelength shifts. To confirm this process, we electrochemically measured the zeta and flatband potentials when charged electrolyte polymers were adsorbed in water. We clearly observed that these potentials temporally behaved consistently with that of the laser wavelength, which suggests that polymers significantly acted on the Schottky barrier. The same behaviors were also observed for the adsorption of 1 fM DNA. We consider that a limited number of charged DNA changed the surface functional group of the entire device surface. Such charge effects will be the key that achieves the ultrahigh sensitivity in the nanolaser biosensor.

Theory of vibrationally assisted tunneling for hydroxyl monomer flipping on Cu(110)

NASA Astrophysics Data System (ADS)

Gustafsson, Alexander; Ueba, Hiromu; Paulsson, Magnus

2014-10-01

To describe vibrationally mediated configuration changes of adsorbates on surfaces we have developed a theory to calculate both reaction rates and pathways. The method uses the T-matrix to describe excitations of vibrational states by the electrons of the substrate, adsorbate, and tunneling electrons from a scanning tunneling probe. In addition to reaction rates, the theory also provides the reaction pathways by going beyond the harmonic approximation and using the full potential energy surface of the adsorbate which contains local minima corresponding to the adsorbates different configurations. To describe the theory, we reproduce the experimental results in [T. Kumagai et al., Phys. Rev. B 79, 035423 (2009), 10.1103/PhysRevB.79.035423], where the hydrogen/deuterium atom of an adsorbed hydroxyl (OH/OD) exhibits back and forth flipping between two equivalent configurations on a Cu(110) surface at T =6 K. We estimate the potential energy surface and the reaction barrier, ˜160 meV, from DFT calculations. The calculated flipping processes arise from (i) at low bias, tunneling of the hydrogen through the barrier, (ii) intermediate bias, tunneling electrons excite the vibrations increasing the reaction rate although over the barrier processes are rare, and (iii) higher bias, overtone excitations increase the reaction rate further.

Role of constant value of surface diffuseness in alpha decay half-lives of superheavy nuclei

NASA Astrophysics Data System (ADS)

Dehghani, V.; Alavi, S. A.; Benam, Kh.

2018-05-01

By using WKB method and considering deformed Woods-Saxon nuclear potential, deformed Coulomb potential, and centrifugal potential, the alpha decay half-lives of 68 superheavy alpha emitters have been calculated. The effect of the constant value of surface diffuseness parameter in the range of 0.1 ≤ a ≤ 0.9 (fm) on the potential barrier, tunneling probability, assault frequency, and alpha decay half-lives has been investigated. Significant differences were observed for alpha decay half-lives and decay quantities in this range of surface diffuseness. Good agreement between calculated half-lives with fitted surface diffuseness parameter a = 0.54 (fm) and experiment was observed.

Free energy barrier for melittin reorientation from a membrane-bound state to a transmembrane state.

PubMed

Irudayam, Sheeba J; Pobandt, Tobias; Berkowitz, Max L

2013-10-31

An important step in a phospholipid membrane pore formation by melittin antimicrobial peptide is a reorientation of the peptide from a surface into a transmembrane conformation. Experiments measure the fraction of peptides in the surface state and the transmembrane state, but no computational study exists that quantifies the free energy curve for the reorientation. In this work we perform umbrella sampling simulations to calculate the potential of mean force (PMF) for the reorientation of melittin from a surface-bound state to a transmembrane state and provide a molecular level insight in understanding the peptide-lipid properties that influence the existence of the free energy barrier. The PMFs were calculated for a peptide to lipid (P/L) ratio of 1/128 and 4/128. We observe that the free energy barrier is reduced when the P/L ratio increases. In addition, we study the cooperative effect; specifically we investigate if the reorientation barrier is smaller for a second melittin, given that another neighboring melittin was already in the transmembrane orientation. We observe that indeed the barrier of the PMF curve is reduced in this case, thus confirming the presence of a cooperative effect.

Study of Fission Barrier Heights of Uranium Isotopes by the Macroscopic-Microscopic Method

NASA Astrophysics Data System (ADS)

Zhong, Chun-Lai; Fan, Tie-Shuan

2014-09-01

Potential energy surfaces of uranium nuclei in the range of mass numbers 229 through 244 are investigated in the framework of the macroscopic-microscopic model and the heights of static fission barriers are obtained in terms of a double-humped structure. The macroscopic part of the nuclear energy is calculated according to Lublin—Strasbourg-drop (LSD) model. Shell and pairing corrections as the microscopic part are calculated with a folded-Yukawa single-particle potential. The calculation is carried out in a five-dimensional parameter space of the generalized Lawrence shapes. In order to extract saddle points on the potential energy surface, a new algorithm which can effectively find an optimal fission path leading from the ground state to the scission point is developed. The comparison of our results with available experimental data and others' theoretical results confirms the reliability of our calculations.

Influence of deformed surface diffuseness on alpha decay half-lives of actinides and lanthanides

NASA Astrophysics Data System (ADS)

Dahmardeh, S.; Alavi, S. A.; Dehghani, V.

2017-07-01

By using semiclassical WKB method and taking into account the Bohr-Sommerfeld quantization condition, the alpha decay half-lives of some deformed lanthanide (with 151 ≤ A ≤ 160 and 66 ≤ Z ≤ 73) and rare-earth nuclei (with 217 ≤ A ≤ 261 and 92 ≤ Z ≤ 104) have been calculated. The effective potential has been considered as sum of deformed Woods-Saxon nuclear potential, deformed Coulomb potential, and centrifugal potential. The influence of deformed surface diffuseness on the potential barrier, transmission coefficient at each angle, assault frequency, and alpha decay half-lives has been investigated. Good agreement between calculated half-lives with deformed surface diffuseness and experiment is observed. Relative differences between calculated half-lives with deformed surface diffuseness and with constant surface diffuseness were significant.

Effect of Electronic Excitation on Hydrogen Atom Transfer (Tautomerization) Reactions for the DNA Base Adenine

NASA Technical Reports Server (NTRS)

Chaban, Galina M.; Salter, Latasha M.; Kwak, Dochan (Technical Monitor)

2002-01-01

Geometrical structures and energetic properties for four different tautomers of adenine are calculated in this study, using multi-configurational wave functions. Both the ground and the lowest single excited state potential energy surface are studied. The energetic order of the tautomers on the ground state potential surface is 9H less than 7H less than 3H less than 1H, while on the excited state surface this order is found to be different: 3H less than 1H less than 9H less than 7H. Minimum energy reaction paths are obtained for hydrogen atom transfer (9 yields 3 tautomerization) reactions in the ground and the lowest excited electronic state. It is found that the barrier heights and the shapes of the reaction paths are different for the ground and the excited electronic state, suggesting that the probability of such tautomerization reaction is higher on the excited state potential energy surface. The barrier for this reaction in the excited state may become very low in the presence of water or other polar solvent molecules, and therefore such tautomerization reaction may play an important role in the solution phase photochemistry of adenine.

Shallow Geologic Framework and Geomorphic Evolution of a Paleo-barrier Shoreline, Terrebonne and Timbalier Bay, Louisiana, USA.

NASA Astrophysics Data System (ADS)

Culling, D. P.; Allison, M. A.; Kulp, M. A.; Georgiou, I. Y.; Weathers, H. D., III

2016-12-01

The Louisiana coast is an invaluable asset to the nation's human, economic, and ecological welfare. However, due to the combined effects of coastal erosion, subsidence, and sea level rise, Louisiana is losing on average 25 km2 of its valuable coastal wetlands per year. Terrebonne- Timbalier Bay and the associated Lafourche deltaic lobe headland is a critical section of this coast for wetlands and infrastructure protection and restoration in the State's Master Plan. Historical imagery and bathymetry clearly show the rapid transgression and erosional degradation of both sets of headland-flanking barrier island shorelines due to wave attack and relative sea level rise in the past 150 y. The focus of the present study is a barrier island system: an ocean-fronting modern-barrier shoreline and a paleo-deltaic headland barrier arc inland of the active barrier. The evolution of the modern barrier arc is closely tied to the shallow geologic framework over which it is transgressing, and specifically the sand re-activation capacity of the antecedent geology once erosional forces are introduced. To understand the evolution of these barrier systems and how to address their protection and re-nourishment, it is important to quantify (1) the depositional facies geometry and (2) the volume of sand in these back-barrier sandy lithosomes. Here we present new observations from CHIRP sub-bottom seismic multibeam bathymetry and LIDAR topography, and surface grab and vibracore sampling in an effort to quantify the sediment availability within the underlying geologic framework and reconstruct the geomorphic evolution of these barrier shorelines. Preliminary results show the morphologic expression of antecedent geology, which is evident in seismic and bathymetric patterns, and the presence of near-surface and surface sandy stratigraphy within the back barrier bay. Observations of sandy units agree with results from Kulp et al. (2005), who showed the presence and extent of sandy lithofacies within 3 m of the surface proximal to the Raccoon Pass tidal-inlet. We suggest this sand is an important potential resource for the longevity of proximal sandy barriers as transgression continues; one identified lithesome alone is estimated to contain 5.25 km3 of fine-grained sand.

Vented Cavity Radiant Barrier Assembly And Method

DOEpatents

Dinwoodie, Thomas L.; Jackaway, Adam D.

2000-05-16

A vented cavity radiant barrier assembly (2) includes a barrier (12), typically a PV module, having inner and outer surfaces (18, 22). A support assembly (14) is secured to the barrier and extends inwardly from the inner surface of the barrier to a building surface (14) creating a vented cavity (24) between the building surface and the barrier inner surface. A low emissivity element (20) is mounted at or between the building surface and the barrier inner surface. At least part of the cavity exit (30) is higher than the cavity entrance (28) to promote cooling air flow through the cavity.

Schottky-barrier-free contacts with two-dimensional semiconductors by surface-engineered MXenes

DOE PAGES

Liu, Yuanyue; Xiao, Hai; Goddard, III, William A.

2016-11-22

Two-dimensional (2D) metal carbides and nitrides, called MXenes, have attracted great interest for applications such as energy storage. Here we demonstrate their potential as Schottky-barrier-free metal contacts to 2D semiconductors, providing a solution to the contact-resistance problem in 2D electronics. Based on first principles calculations, we find that the surface chemistry strongly affects the Fermi level of MXenes: O termination always increases the work function with respect to that of bare surface, OH always decreases it, while F exhibits either trend depending on the specific material. This phenomenon originates from the effect of surface dipoles, which together with the weakmore » Fermi level pinning, enable Schottky-barrier-free hole (or electron) injection into 2D semiconductors through van der Waals junctions with some of the O-terminated (or all the OH-terminated) MXenes. Furthermore, we suggest synthetic routes to control the surface terminations based on the calculated formation energies. Finally, this study enhances the understanding of the correlation between surface chemistry and electronic/transport properties of 2D materials, and also gives practical predictions for improving 2D electronics.« less

Proceedings of the Flat-plate Solar Array Project Research Forum on High-efficiency Crystalline Silicon Solar Cells

NASA Technical Reports Server (NTRS)

Kachare, R.

1985-01-01

The high-efficiency crystalline silicon solar cells research forum addressed high-efficiency concepts, surface-interface effects, bulk effects, modeling and device processing. The topics were arranged into six interactive sessions, which focused on the state-of-the-art of device structures, identification of barriers to achieve high-efficiency cells and potential ways to overcome these barriers.

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

Hydrogen generation due to water splitting on Si - terminated 4H-Sic(0001) surfaces

NASA Astrophysics Data System (ADS)

Li, Qingfang; Li, Qiqi; Yang, Cuihong; Rao, Weifeng

2018-02-01

The chemical reactions of hydrogen gas generation via water splitting on Si-terminated 4H-SiC surfaces with or without C/Si vacancies were studied by using first-principles. We studied the reaction mechanisms of hydrogen generation on the 4H-SiC(0001) surface. Our calculations demonstrate that there are major rearrangements in surface when H2O approaches the SiC(0001) surface. The first H splitting from water can occur with ground-state electronic structures. The second H splitting involves an energy barrier of 0.65 eV. However, the energy barrier for two H atoms desorbing from the Si-face and forming H2 gas is 3.04 eV. In addition, it is found that C and Si vacancies can form easier in SiC(0001)surfaces than in SiC bulk and nanoribbons. The C/Si vacancies introduced can enhance photocatalytic activities. It is easier to split OH on SiC(0001) surface with vacancies compared to the case of clean SiC surface. H2 can form on the 4H-SiC(0001) surface with C and Si vacancies if the energy barriers of 1.02 and 2.28 eV are surmounted, respectively. Therefore, SiC(0001) surface with C vacancy has potential applications in photocatalytic water-splitting.

On the enhanced sampling over energy barriers in molecular dynamics simulations.

PubMed

Gao, Yi Qin; Yang, Lijiang

2006-09-21

We present here calculations of free energies of multidimensional systems using an efficient sampling method. The method uses a transformed potential energy surface, which allows an efficient sampling of both low and high energy spaces and accelerates transitions over barriers. It allows efficient sampling of the configuration space over and only over the desired energy range(s). It does not require predetermined or selected reaction coordinate(s). We apply this method to study the dynamics of slow barrier crossing processes in a disaccharide and a dipeptide system.

Protein adsorption capability on polyurethane and modified-polyurethane membrane for periodontal guided tissue regeneration applications.

PubMed

Sheikh, Zeeshan; Khan, Abdul Samad; Roohpour, Nima; Glogauer, Michael; Rehman, Ihtesham U

2016-11-01

Periodontal disease if left untreated can result in creation of defects within the alveolar ridge. Barrier membranes are frequently used with or without bone replacement graft materials for achieving periodontal guided tissue regeneration (GTR). Surface properties of barrier membranes play a vital role in their functionality and clinical success. In this study polyetherurethane (PEU) membranes were synthesized by using 4,4'-methylene-diphenyl diisocyanate (MDI), polytetramethylene oxide (PTMO) and 1,4-butane diol (BDO) as a chain extender via solution polymerization. Hydroxyl terminated polydimethylsiloxane (PDMS) due to having inherent surface orientation towards air was used for surface modification of PEU on one side of the membranes. This resulting membranes had one surface being PEU and the other being PDMS coated PEU. The prepared membranes were treated with solutions of bovine serum albumin (BSA) in de-ionized water at 37°C at a pH of 7.2. The surface protein adsorptive potential of PEU membranes was observed using Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR), Raman spectroscopy and Confocal Raman spectroscopy. The contact angle measurement, tensile strength and modulus of prepared membranes were also evaluated. PEU membrane (89.86±1.62°) exhibited less hydrophobic behavior than PEU-PDMS (105.87±3.16°). The ultimate tensile strength and elastic modulus of PEU (27±1MPa and 14±2MPa) and PEU-PDMS (8±1MPa and 26±1MPa) membranes was in required range. The spectral analysis revealed adsorption of BSA proteins on the surface of non PDMS coated PEU surface. The PDMS modified PEU membranes demonstrated a lack of BSA adsorption. The non PDMS coated side of the membrane which adsorbs proteins could potentially be used facing towards the defect attracting growth factors for periodontal tissue regeneration. Whereas, the PDMS coated side could serve as an occlusive barrier for preventing gingival epithelial cells from proliferating and migrating into the defect space by facing the soft tissue flaps. This study demonstrates the potential of a dual natured PEU barrier membrane for use in periodontal tissue engineering applications and further investigations are required. Copyright © 2016 Elsevier B.V. All rights reserved.

Exploration for the stabilities of CHN7 and CN7-: A theoretical study on the formation and dissociation mechanisms

NASA Astrophysics Data System (ADS)

Yu, Tao; Liu, Ying-Zhe; Lai, Wei-Peng

2018-03-01

CHN7 and CN7- are meta-stable species. In order to study on the relationship between thermodynamic and kinetic stabilities, the potential energy surfaces of CHN7 and CN7- were scanned at the B3LYP/aug-cc-pVDZ level. After the analysis of potential energy surfaces, the optimum pathways were got to conclude the dissociation and formation mechanisms. The dissociation barriers of 5-azido-1H-tetrazole and 5-azido-2H-tetrazole are about 150 kJ mol-1. They are sufficient to keep the two azidotetrazoles stable. The reaction between cyanogen azide and azide anion cannot produce azidotetrazolate anion, but produce the linear CN7- with a lower barrier. The reaction between cyanogen azide and hydrazoic acid preferentially produce 5-azido-1H-tetrazole. The decyclization barriers of 1H-tetrazolo[1,5-d]tetrazole and tetrazolo[1,5-d]tetrazolate anion are 44.7 and 81.6 kJ mol-1, respectively. The deprotoned anion is more available than the neutral compound. Heptaazacubane and heptaazacubanide anion with cubic geometries are highly unstable.

The reaction mechanism with free energy barriers at constant potentials for the oxygen evolution reaction at the IrO 2 (110) surface

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

Ping, Yuan; Nielsen, Robert J.; Goddard, William A.

How to efficiently oxidize H 2O to O 2 (oxygen evolution reaction, OER) in photoelectrochemical cells (PEC) is a great challenge due to its complex charge transfer process, high overpotential, and corrosion. So far no OER mechanism has been fully explained atomistically with both thermodynamic and kinetics. IrO 2 is the only known OER catalyst with both high catalytic activity and stability in acidic conditions. This is important because PEC experiments often operate at extreme pH conditions. In this work, we performed first-principles calculations integrated with implicit solvation at constant potentials to examine the detailed atomistic reaction mechanism of OERmore » at the IrO 2 (110) surface. We determined the surface phase diagram, explored the possible reaction pathways including kinetic barriers, and computed reaction rates based on the microkinetic models. Furthermore, this allowed us to resolve several long-standing puzzles about the atomistic OER mechanism.« less

The reaction mechanism with free energy barriers at constant potentials for the oxygen evolution reaction at the IrO 2 (110) surface

DOE PAGES

Ping, Yuan; Nielsen, Robert J.; Goddard, William A.

2016-12-09

How to efficiently oxidize H 2O to O 2 (oxygen evolution reaction, OER) in photoelectrochemical cells (PEC) is a great challenge due to its complex charge transfer process, high overpotential, and corrosion. So far no OER mechanism has been fully explained atomistically with both thermodynamic and kinetics. IrO 2 is the only known OER catalyst with both high catalytic activity and stability in acidic conditions. This is important because PEC experiments often operate at extreme pH conditions. In this work, we performed first-principles calculations integrated with implicit solvation at constant potentials to examine the detailed atomistic reaction mechanism of OERmore » at the IrO 2 (110) surface. We determined the surface phase diagram, explored the possible reaction pathways including kinetic barriers, and computed reaction rates based on the microkinetic models. Furthermore, this allowed us to resolve several long-standing puzzles about the atomistic OER mechanism.« less

Focused ultrasound delivery of Raman nanoparticles across the blood-brain barrier: Potential for targeting experimental brain tumors

PubMed Central

Diaz, Roberto Jose; McVeigh, Patrick Z.; O’Reilly, Meaghan A.; Burrell, Kelly; Bebenek, Matthew; Smith, Christian; Etame, Arnold; Zadeh, Gelareh; Hynynen, Kullervo; Wilson, Brian C.; Rutka, James T.

2014-01-01

Spectral mapping of nanoparticles with surface enhanced Raman scattering (SERS) capability in the near-infrared range is an emerging molecular imaging technique. We used magnetic resonance image-guided transcranial focused ultrasound (TcMRgFUS) to reversibly disrupt the blood-brain barrier (BBB) adjacent to brain tumor margins in rats. Glioma cells were found to internalize SERS capable nanoparticles of 50 nm or 120 nm physical diameter. Surface coating with anti-epidermal growth factor receptor antibody or non-specific human immunoglobulin G, resulted in enhanced cell uptake of nanoparticles in-vitro compared to nanoparticles with methyl terminated 12-unit polyethylene glycol surface. BBB disruption permitted the delivery of SERS capable spherical 50 or 120 nm gold nanoparticles to the tumor margins. Thus, nanoparticles with SERS imaging capability can be delivered across the BBB non-invasively using TcMRgFUS and have the potential to be used as optical tracking agents at the invasive front of malignant brain tumors. PMID:24374363

Exploring a potential energy surface by machine learning for characterizing atomic transport

NASA Astrophysics Data System (ADS)

Kanamori, Kenta; Toyoura, Kazuaki; Honda, Junya; Hattori, Kazuki; Seko, Atsuto; Karasuyama, Masayuki; Shitara, Kazuki; Shiga, Motoki; Kuwabara, Akihide; Takeuchi, Ichiro

2018-03-01

We propose a machine-learning method for evaluating the potential barrier governing atomic transport based on the preferential selection of dominant points for atomic transport. The proposed method generates numerous random samples of the entire potential energy surface (PES) from a probabilistic Gaussian process model of the PES, which enables defining the likelihood of the dominant points. The robustness and efficiency of the method are demonstrated on a dozen model cases for proton diffusion in oxides, in comparison with a conventional nudge elastic band method.

Directional mass transport in an atmospheric pressure surface barrier discharge.

PubMed

Dickenson, A; Morabit, Y; Hasan, M I; Walsh, J L

2017-10-25

In an atmospheric pressure surface barrier discharge the inherent physical separation between the plasma generation region and downstream point of application reduces the flux of reactive chemical species reaching the sample, potentially limiting application efficacy. This contribution explores the impact of manipulating the phase angle of the applied voltage to exert a level of control over the electrohydrodynamic forces generated by the plasma. As these forces produce a convective flow which is the primary mechanism of species transport, the technique facilitates the targeted delivery of reactive species to a downstream point without compromising the underpinning species generation mechanisms. Particle Imaging Velocimetry measurements are used to demonstrate that a phase shift between sinusoidal voltages applied to adjacent electrodes in a surface barrier discharge results in a significant deviation in the direction of the plasma induced gas flow. Using a two-dimensional numerical air plasma model, it is shown that the phase shift impacts the spatial distribution of the deposited charge on the dielectric surface between the adjacent electrodes. The modified surface charge distribution reduces the propagation length of the discharge ignited on the lagging electrode, causing an imbalance in the generated forces and consequently a variation in the direction of the resulting gas flow.

Finite Element Model Characterization Of Nano-Composite Thermal And Environmental Barrier Coatings

NASA Technical Reports Server (NTRS)

Yamada, Yoshiki; Zhu, Dongming

2011-01-01

Thermal and environmental barrier coatings have been applied for protecting Si based ceramic matrix composite components from high temperature environment in advanced gas turbine engines. It has been found that the delamination and lifetime of T/EBC systems generally depend on the initiation and propagation of surface cracks induced by the axial mechanical load in addition to severe thermal loads. In order to prevent T/EBC systems from surface cracking and subsequent delamination due to mechanical and thermal stresses, T/EBC systems reinforced with nano-composite architectures have showed promise to improve mechanical properties and provide a potential crack shielding mechanism such as crack bridging. In this study, a finite element model (FEM) was established to understand the potential beneficial effects of nano-composites systems such as SiC nanotube-reinforced oxide T/EBC systems.

Effect of a direct current bias on the electrohydrodynamic performance of a surface dielectric barrier discharge actuator for airflow control

NASA Astrophysics Data System (ADS)

Yan, Huijie; Yang, Liang; Qi, Xiaohua; Ren, Chunsheng

2015-02-01

The effect of a DC bias on the electrohydrodynamics (EHD) force induced by a surface dielectric barrier AC discharge actuator for airflow control at the atmospheric pressure is investigated. The measurement of the surface potential due to charge deposition at different DC biases is carried out by using a special designed corona like discharge potential probe. From the surface potential data, the plasma electromotive force is shown not affected much by the DC biases except for some reduction of the DC bias near the exposed electrode edge for the sheath-like configuration. The total thrust is measured by an analytical balance, and an almost linear relationship to the potential voltage at the exposed electrode edge is found for the direct thrust force. The temporally averaged ionic wind characteristics are investigated by Pitot tube sensor and schlieren visualization system. It is found that the ionic wind velocity profiles with different DC biases are almost the same in the AC discharge plasma area but gradually diversified in the further downstream area as well as the upper space away from the discharge plasma area. Also, the DC bias can significantly modify the topology of the ionic wind produced by the AC discharge actuator. These results can provide an insight into how the DC biases to affect the force generation.

Thermoelectric properties of nano-granular indium-tin-oxide within modified electron filtering model with chemisorption-type potential barriers

NASA Astrophysics Data System (ADS)

Brinzari, V.; Nika, D. L.; Damaskin, I.; Cho, B. K.; Korotcenkov, G.

2016-07-01

In this work, an approach to the numerical study of the thermoelectric parameters of nanoscale indium tin oxide (ITO, Sn content<10 at%) based on an electron filtering model (EFM) was developed. Potential barriers at grain boundaries were assumed to be responsible for a filtering effect. In the case of the dominant inelastic scattering of electrons, the maximal distance between potential barriers was limited in this modified model. The algorithm for such characteristic length calculation was proposed, and its value was evaluated for ITO. In addition, the contributions of different scattering mechanisms (SMs) in electron transport were examined. It was confirmed that in bulk ITO, the scattering on polar optical phonons (POPs) and ionized impurities dominates, limiting electron transport. In the framework of the filtering model, the basic thermoelectric parameters (i.e., electrical conductivity, mobility, Seebeck coefficient, and power factor (PF)) were calculated for ITO in the temperature range of 100-500 °C as a function of potential barrier height. The results demonstrated a sufficient rise of the Seebeck coefficient with an increase in barrier height and specific behavior of PF. It was found that PF is very sensitive to barrier height, and at its optimal value for granular ITO, it may exceed the PF for bulk ITO by 3-5 times. The PF maximum was achieved by band bending, slightly exceeding Fermi energy. The nature of surface potential barriers in nano-granular ITO with specific grains is due to the oxygen chemisorption effect, and this can be observed despite of the degeneracy of the conduction band (CB). This hypothesis and the corresponding calculations are in good agreement with recent experimental studies [Brinzari et al. Thin Solid Films 552 (2014) 225].

Nanocrystalline cellulose-dispersed AKD emulsion for enhancing the mechanical and multiple barrier properties of surface-sized paper.

PubMed

Yang, Luming; Lu, Sheng; Li, Juanjuan; Zhang, Fengshan; Cha, Ruitao

2016-01-20

In this study, we employed nanocrystalline cellulose (NCC) as an efficient dispersant to perpare alkyl ketene dimer (AKD) emulsion. The particle size and zeta potential of AKD/NCC emulsion were measured, which were approximately 5 μm and -50 mV, respectively. The surface-sized paper possessed multiple barriers properties. The air permeability of surface-sized paper was 0.29 μm/Pas and the sizing degree reached 42 s when the amount of sizing was 12.58 g/m(2) with a 96.83% decrease and a 40.00%, increase, respectively. Furthermore, the mechanical properties were optimal when the amount of sizing was about 8 g/m(2). AKD/NCC emulsion acted as a good reinforcing agent in surface-sized paper. Copyright © 2015 Elsevier Ltd. All rights reserved.

Morphological characteristics and barrier properties of thermoplastic starch/chitosan blown film.

PubMed

Dang, Khanh Minh; Yoksan, Rangrong

2016-10-05

Fabrication of starch-based edible film using blown film extrusion is challenging and interesting because this process provides continuous operation with shorter production time and lower energy consumption, is less labor intensive, and results in higher productivity than the conventional solution casting technique. Previously, we reported on the preparation and some properties of thermoplastic starch/chitosan (TPS/CTS) blown films; however, their morphological characteristics and barrier properties had not yet been elucidated. The present work thus aims to investigate the effect of chitosan (0.37-1.45%) on morphological characteristics, water vapor and oxygen barrier properties as well as hydrophilicity of the TPS and TPS/CTS films. The relationship between morphological characteristics and properties of the films was also discussed. Scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM) and X-ray photoelectron spectroscopy (XPS) confirmed the distribution and deposition of chitosan on the film surface. The existence of chitosan on the surface imparted the improved water vapor and oxygen barrier properties and the reduced surface hydrophilicity to the film. The results suggest that this biodegradable bio-based TPS/CTS film could potentially be used as an edible film for food and pharmaceutical applications. Copyright © 2016 Elsevier Ltd. All rights reserved.

Controlling the electronic and geometric structures of 2D insertions to realize high performance metal/insertion-MoS2 sandwich interfaces.

PubMed

Su, Jie; Feng, Liping; Zeng, Wei; Liu, Zhengtang

2017-06-08

Metal/insertion-MoS 2 sandwich interfaces are designed to reduce the Schottky barriers at metal-MoS 2 interfaces. The effects of geometric and electronic structures of two-dimensional (2D) insertion materials on the contact properties of metal/insertion-MoS 2 interfaces are comparatively studied by first-principles calculations. Regardless of the geometric and electronic structures of 2D insertion materials, Fermi level pinning effects and charge scattering at the metal/insertion-MoS 2 interface are weakened due to weak interactions between the insertion and MoS 2 layers, no gap states and negligible structural deformations for MoS 2 layers. The Schottky barriers at metal/insertion-MoS 2 interfaces are induced by three interface dipoles and four potential steps that are determined by the charge transfers and structural deformations of 2D insertion materials. The lower the electron affinities of 2D insertion materials, the more are the electrons lost from the Sc surface, resulting in lower n-type Schottky barriers at Sc/insertion-MoS 2 interfaces. The larger the ionization potentials and the thinner the thicknesses of 2D insertion materials, the fewer are the electrons that accumulate at the Pt surface, leading to lower p-type Schottky barriers at Pt/insertion-MoS 2 interfaces. All Sc/insertion-MoS 2 interfaces exhibited ohmic characters. The Pt/BN-MoS 2 interface exhibits the lowest p-type Schottky barrier of 0.52 eV due to the largest ionization potential (∼6.88 eV) and the thinnest thickness (single atomic layer thickness) of BN. These results in this work are beneficial to understand and design high performance metal/insertion-MoS 2 interfaces through 2D insertion materials.

Barrier inhomogeneities limited current and 1/f noise transport in GaN based nanoscale Schottky barrier diodes

PubMed Central

Kumar, Ashutosh; Heilmann, M.; Latzel, Michael; Kapoor, Raman; Sharma, Intu; Göbelt, M.; Christiansen, Silke H.; Kumar, Vikram; Singh, Rajendra

2016-01-01

The electrical behaviour of Schottky barrier diodes realized on vertically standing individual GaN nanorods and array of nanorods is investigated. The Schottky diodes on individual nanorod show highest barrier height in comparison with large area diodes on nanorods array and epitaxial film which is in contrast with previously published work. The discrepancy between the electrical behaviour of nanoscale Schottky diodes and large area diodes is explained using cathodoluminescence measurements, surface potential analysis using Kelvin probe force microscopy and 1ow frequency noise measurements. The noise measurements on large area diodes on nanorods array and epitaxial film suggest the presence of barrier inhomogeneities at the metal/semiconductor interface which deviate the noise spectra from Lorentzian to 1/f type. These barrier inhomogeneities in large area diodes resulted in reduced barrier height whereas due to the limited role of barrier inhomogeneities in individual nanorod based Schottky diode, a higher barrier height is obtained. PMID:27282258

Barrier Coatings for Refractory Metals and Superalloys

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

SM Sabol; BT Randall; JD Edington

2006-02-23

In the closed working fluid loop of the proposed Prometheus space nuclear power plant (SNPP), there is the potential for reaction of core and plant structural materials with gas phase impurities and gas phase transport of interstitial elements between superalloy and refractory metal alloy components during service. Primary concerns are surface oxidation, interstitial embrittlement of refractory metals and decarburization of superalloys. In parallel with kinetic investigations, this letter evaluates the ability of potential coatings to prevent or impede communication between reactor and plant components. Key coating requirements are identified and current technology coating materials are reviewed relative to these requirements.more » Candidate coatings are identified for future evaluation based on current knowledge of design parameters and anticipated environment. Coatings were identified for superalloys and refractory metals to provide diffusion barriers to interstitial transport and act as reactive barriers to potential oxidation. Due to their high stability at low oxygen potential, alumina formers are most promising for oxidation protection given the anticipated coolant gas chemistry. A sublayer of iridium is recommended to provide inherent diffusion resistance to interstitials. Based on specific base metal selection, a thin film substrate--coating interdiffusion barrier layer may be necessary to meet mission life.« less

Photoemission into water adsorbed on metals: Probing dissociative electron transfer using theory

NASA Astrophysics Data System (ADS)

Zhang, Yu; Whitten, J. L.

The photoinduced dissociation of water adsorbed on a silver nanoparticle is explored using theory to probe reaction pathways that produce hydrogen. Ab initio configuration theory is used to describe the systems. A formulation that allows excited electronic states embedded in a near continuum of lower energy states to be calculated accurately is described. Electron attachment of a photoemitted electron to adsorbed water can lead to the formation of H2 at a very low energy barrier with oxygen remaining on the Ag surface. A large energy barrier to form H2 plus adsorbed O is found for the ground state. The excited state has a much smaller barrier to OH stretch; however, to dissociate, the system must cross over from the excited state to the ground state potential energy surface. The cross over point is near the transition state for a ground state process. A characteristic feature of the excited state potential curve is an increase in energy in the early stages of OH stretch as the charge transfer state evolves from a state with considerable Rydberg character to one that has a typical OH antibonding molecular orbital. Another pathway releases a H atom leaving OH on the surface. Effects due to doping of a Ag nanoparticle with a K electron donor atom are compared with those caused by a Fermi level shift due to an applied potential. Results are also reported for electron transfer to a solvated lithium ion, Li(H2O) 6+, near the surface of a silver particle. A steering mechanism is found that involves the interaction of a hydridic hydrogen formed after electron transfer with an acidic hydrogen of a second solvated water molecule.

Tunnel barrier schottky

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

Chu, Rongming; Cao, Yu; Li, Zijian

2018-02-20

A diode includes: a semiconductor substrate; a cathode metal layer contacting a bottom of the substrate; a semiconductor drift layer on the substrate; a graded aluminum gallium nitride (AlGaN) semiconductor barrier layer on the drift layer and having a larger bandgap than the drift layer, the barrier layer having a top surface and a bottom surface between the drift layer and the top surface, the barrier layer having an increasing aluminum composition from the bottom surface to the top surface; and an anode metal layer directly contacting the top surface of the barrier layer.

NANOSILVER MOVEMENT THROUGH BIOLOGICAL BARRIERS RELATES TO PHYSICOCHEMICAL PROPERTIES

EPA Science Inventory

Linking the physicochemical (PC) properties of engineered nanomaterials (NM) to their biological activity is critical for identifying their (toxic) mode of action, and developing appropriate and effective risk assessment guidelines. Particle surface charge (zeta potential), surfa...

A double-layer based model of ion confinement in electron cyclotron resonance ion source.

PubMed

Mascali, D; Neri, L; Celona, L; Castro, G; Torrisi, G; Gammino, S; Sorbello, G; Ciavola, G

2014-02-01

The paper proposes a new model of ion confinement in ECRIS, which can be easily generalized to any magnetic configuration characterized by closed magnetic surfaces. Traditionally, ion confinement in B-min configurations is ascribed to a negative potential dip due to superhot electrons, adiabatically confined by the magneto-static field. However, kinetic simulations including RF heating affected by cavity modes structures indicate that high energy electrons populate just a thin slab overlapping the ECR layer, while their density drops down of more than one order of magnitude outside. Ions, instead, diffuse across the electron layer due to their high collisionality. This is the proper physical condition to establish a double-layer (DL) configuration which self-consistently originates a potential barrier; this "barrier" confines the ions inside the plasma core surrounded by the ECR surface. The paper will describe a simplified ion confinement model based on plasma density non-homogeneity and DL formation.

Gold-Based Magneto/Optical Nanostructures: Challenges for In Vivo Applications in Cancer Diagnostics and Therapy.

PubMed

Melancon, Marites; Lu, Wei; Li, Chun

2009-06-01

Nanoparticles with gold shell and iron core have unique optical and magnetic properties which can be utilized for simultaneous detection and treatment strategies. Several nanoparticles have been synthesized and shown to mediate a variety of potential applications in biomedicine, including cancer molecular optical and magnetic resonance imaging, controlled drug delivery, and photothermal ablation therapy. However, to be effective, these nanoparticles must be delivered efficiently into their targets. In this review, we will provide an updated summary of the gold-shelled magnetic nanoparticles that have been synthesized, methods for characterization, and their potential for cancer diagnosis and treatment. We will also discuss the biological barriers that need to be overcome for the effective delivery of these nanoparticles. The desired nanoparticle characteristics needed to evade these biological barriers were also explained. Hopefully, this review will help researchers in designing nanoparticles by carefully choosing the optimum size, shape, surface charge, and surface coating.

Selected hydrologic data for the field demonstration of three permeable reactive barriers near Fry Canyon, Utah, 1996-2000

USGS Publications Warehouse

Wilkowske, Chris D.; Rowland, Ryan C.; Naftz, David L.

2001-01-01

Three permeable reactive barriers (PRBs) were installed near Fry Canyon, Utah, in August 1997 to demonstrate the use of PRBs to control the migration of uranium in ground water. Reactive material included (1) bone-char phosphate, (2) zero-valent iron pellets, and (3) amorphous ferric oxyhydroxide coated gravel. An extensive monitoring network was installed in and around each PRB for collection of water samples, analysis of selected water-quality parameters, and monitoring of water levels. Water temperature, specific conductance, pH, Eh (oxidation-reduction potential), and dissolved oxygen were measured continuously within three different barrier materials, and in two monitoring wells. Water temperature and water level below land surface were electronically recorded every hour with pressure transducers. Data were collected from ground-water monitoring wells installed in and around the PRBs during 1996-98 and from surface-water sites in Fry Creek.

Ab initio study of C + H3+ reactions

NASA Technical Reports Server (NTRS)

Talbi, D.; DeFrees, D. J.

1991-01-01

The reaction C + H3+ --> CH(+) + H2 is frequently used in models of dense interstellar cloud chemistry with the assumption that it is fast, i.e. there are no potential energy barriers inhibiting it. Ab initio molecular orbital study of the triplet CH3+ potential energy surface (triplet because the reactant carbon atom is a ground state triplet) supports this hypothesis. The reaction product is 3 pi CH+; the reaction is to exothermic even though the product is not in its electronic ground state. No path has been found on the potential energy surface for C + H3+ --> CH2(+) + H reaction.

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.

Spacecraft charging and ion wake formation in the near-Sun environment

NASA Astrophysics Data System (ADS)

Ergun, R. E.; Malaspina, D. M.; Bale, S. D.; McFadden, J. P.; Larson, D. E.; Mozer, F. S.; Meyer-Vernet, N.; Maksimovic, M.; Kellogg, P. J.; Wygant, J. R.

2010-07-01

A three-dimensional, self-consistent code is employed to solve for the static potential structure surrounding a spacecraft in a high photoelectron environment. The numerical solutions show that, under certain conditions, a spacecraft can take on a negative potential in spite of strong photoelectron currents. The negative potential is due to an electrostatic barrier near the surface of the spacecraft that can reflect a large fraction of the photoelectron flux back to the spacecraft. This electrostatic barrier forms if (1) the photoelectron density at the surface of the spacecraft greatly exceeds the ambient plasma density, (2) the spacecraft size is significantly larger than local Debye length of the photoelectrons, and (3) the thermal electron energy is much larger than the characteristic energy of the escaping photoelectrons. All of these conditions are present near the Sun. The numerical solutions also show that the spacecraft's negative potential can be amplified by an ion wake. The negative potential of the ion wake prevents secondary electrons from escaping the part of spacecraft in contact with the wake. These findings may be important for future spacecraft missions that go nearer to the Sun, such as Solar Orbiter and Solar Probe Plus.

What is the most efficient respiratory organ for the loricariid air-breathing fish Pterygoplichthys anisitsi, gills or stomach? A quantitative morphological study.

PubMed

da Cruz, André Luis; Fernandes, Marisa Narciso

2016-12-01

The purpose of the present study was to evaluate the morphometric respiratory potential of gills compared to the stomach in obtaining oxygen for aerobic metabolism in Pterygoplichthys anisitsi, a facultative air-breathing fish. The measurements were done using stereological methods. The gills showed greater total volume, volume-to-body mass ratio, potential surface area, and surface-to-volume ratio than the stomach. The water-blood diffusion barrier of the gills is thicker than the air-blood diffusion barrier of the stomach. Taken together, the surface area, the surface-to-volume ratio and the diffusion distance for O 2 transfer from the respiratory medium to blood yield a greater diffusing capacity for gills than for the stomach, suggesting greater importance of aquatic respiration in this species. On the other hand, water breathing is energetically more expensive than breathing air. Under severe hypoxic conditions, O 2 uptake by the stomach is more efficient than by the gills, although the stomach has a much lower diffusing capacity. Thus, P. anisitsi uses gills under normoxic conditions but the stomach may also support aerobic metabolism depending on environmental conditions. Copyright © 2016 Elsevier GmbH. All rights reserved.

Passengers, Crew, Life Support, and Insurance Considerations

NASA Technical Reports Server (NTRS)

ONeil, Daniel A.; Young, Lawrence R.

1999-01-01

This section describes the key issues, barriers, opportunities, and potential trip packages related to the needs and expectations of initial space adventure travelers. A variety of ideas to overcome barriers is presented that address financial, psychological, and sociological problems expected to be encountered in establishing a general PST and tourism business. Tour package descriptions range from near-term surface training facilities to far-term lunar ones. Recommendations include requirements pertaining to human factors in design and needed technology.

Conformational transition free energy profiles of an adsorbed, lattice model protein by multicanonical Monte Carlo simulation

NASA Astrophysics Data System (ADS)

Castells, Victoria; Van Tassel, Paul R.

2005-02-01

Proteins often undergo changes in internal conformation upon interacting with a surface. We investigate the thermodynamics of surface induced conformational change in a lattice model protein using a multicanonical Monte Carlo method. The protein is a linear heteropolymer of 27 segments (of types A and B) confined to a cubic lattice. The segmental order and nearest neighbor contact energies are chosen to yield, in the absence of an adsorbing surface, a unique 3×3×3 folded structure. The surface is a plane of sites interacting either equally with A and B segments (equal affinity surface) or more strongly with the A segments (A affinity surface). We use a multicanonical Monte Carlo algorithm, with configuration bias and jump walking moves, featuring an iteratively updated sampling function that converges to the reciprocal of the density of states 1/Ω(E), E being the potential energy. We find inflection points in the configurational entropy, S(E)=klnΩ(E), for all but a strongly adsorbing equal affinity surface, indicating the presence of free energy barriers to transition. When protein-surface interactions are weak, the free energy profiles F(E)=E-TS(E) qualitatively resemble those of a protein in the absence of a surface: a free energy barrier separates a folded, lowest energy state from globular, higher energy states. The surface acts in this case to stabilize the globular states relative to the folded state. When the protein surface interactions are stronger, the situation differs markedly: the folded state no longer occurs at the lowest energy and free energy barriers may be absent altogether.

Low Dielectric Permittivity of Water at the Membrane Interface: Effect on the Energy Coupling Mechanism in Biological Membranes

PubMed Central

Cherepanov, Dmitry A.; Feniouk, Boris A.; Junge, Wolfgang; Mulkidjanian, Armen Y.

2003-01-01

Protonmotive force (the transmembrane difference in electrochemical potential of protons, \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} \\begin{equation*}{\\Delta}{\\tilde {{\\mu}}}_{{\\mathrm{H}}^{+}}\\end{equation*}\\end{document}) drives ATP synthesis in bacteria, mitochondria, and chloroplasts. It has remained unsettled whether the entropic (chemical) component of \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} \\begin{equation*}{\\Delta}{\\tilde {{\\mu}}}_{{\\mathrm{H}}^{+}}\\end{equation*}\\end{document} relates to the difference in the proton activity between two bulk water phases (ΔpHB) or between two membrane surfaces (ΔpHS). To scrutinize whether ΔpHS can deviate from ΔpHB, we modeled the behavior of protons at the membrane/water interface. We made use of the surprisingly low dielectric permittivity of interfacial water as determined by O. Teschke, G. Ceotto, and E. F. de Souza (O. Teschke, G. Ceotto, and E. F. de Sousa, 2001, Phys. Rev. E. 64:011605). Electrostatic calculations revealed a potential barrier in the water phase some 0.5–1 nm away from the membrane surface. The barrier was higher for monovalent anions moving toward the surface (0.2–0.3 eV) than for monovalent cations (0.1–0.15 eV). By solving the Smoluchowski equation for protons spreading away from proton “pumps” at the surface, we found that the barrier could cause an elevation of the proton concentration at the interface. Taking typical values for the density of proton pumps and for their turnover rate, we calculated that a potential barrier of 0.12 eV yielded a steady-state pHS of ∼6.0; the value of pHS was independent of pH in the bulk water phase under neutral and alkaline conditions. These results provide a rationale to solve the long-lasting problem of the seemingly insufficient protonmotive force in mesophilic and alkaliphilic bacteria. PMID:12885673

Polyacrylamide sorption opportunity on interlayer and external pore surfaces of contaminant barrier clays.

PubMed

Inyang, Hilary I; Bae, Sunyoung

2005-01-01

Physico-chemical interactions among polymer molecules in aqueous solution and clay mineralogical/textural characteristics influence the sorption of polymer molecules on clay barrier minerals. Amendment of potentially unstable barrier clays with aqueous polymers can improve barrier material resistance to environmental stresses during service. In this research, the ability of molecular coils of polyacrylamide (PAM) to overlap in solution and to enter interlayer space in Na-montmorillonite (specific surface=31.82+/-0.22 m2 g(-1)) and kaolinite (specific surface=18+/-2 m2 g(-1)) were analyzed theoretically and experimentally, using solution viscosity measurements, and X-ray diffractometry. Experimental data on two theoretical indices: relative size ratio (RSR); and molecular availability (Ma) that are formulated to scale polymer molecular sorption on clay interlayer, indicate that the sorption of PAM A (Mw=4000000) and PAM B (Mw=7000000) does not produce any significant change in the d-spacing of both clay minerals. Although the negative Ma values of -3.51 g l(-1) for PAM A and -3.88 g l(-1) for PAM B indicate high levels of entanglement of polymer molecular coils in solution, sorption data confirm that the entangled coils are still able to sorb onto Na-montmorillonite highly and kaolinite to a lesser extent.

Substrate Vibrations as Promoters of Chemical Reactivity on Metal Surfaces.

PubMed

Campbell, Victoria L; Chen, Nan; Guo, Han; Jackson, Bret; Utz, Arthur L

2015-12-17

Studies exploring how vibrational energy (Evib) promotes chemical reactivity most often focus on molecular reagents, leaving the role of substrate atom motion in heterogeneous interfacial chemistry underexplored. This combined theoretical and experimental study of methane dissociation on Ni(111) shows that lattice atom motion modulates the reaction barrier height during each surface atom's vibrational period, which leads to a strong variation in the reaction probability (S0) with surface temperature (Tsurf). State-resolved beam-surface scattering studies at Tsurf = 90 K show a sharp threshold in S0 at translational energy (Etrans) = 42 kJ/mol. When Etrans decreases from 42 kJ/mol to 34 kJ/mol, S0 decreases 1000-fold at Tsurf = 90 K, but only 2-fold at Tsurf = 475 K. Results highlight the mechanism for this effect, provide benchmarks for DFT calculations, and suggest the potential importance of surface atom induced barrier height modulation in heterogeneously catalyzed reactions, particularly on structurally labile nanoscale particles and defect sites.

Methane Oxidation on Pd-Ceria. A DFT Study of the Combustion Mechanism over Pd, PdO and Pd-ceria Sites

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

Mayernick, Adam D.; Janik, Michael J.

2010-12-24

Palladium/ceria exhibits unique catalytic activity for hydrocarbon oxidation; however, the chemical and structural properties of active sites on the palladium–ceria surface are difficult to characterize. Strong interactions between palladium and the ceria support stabilize oxidized Pd δ+ species, which may contribute to the significant activity of Pd/ceria for methane oxidation. We present a density functional theory (DFT + U) investigation into methane oxidation over Pd/ceria and quantify the activity of the Pd xCe 1-xO 2(1 1 1) mixed oxide surface in comparison with the PdO(1 0 0) and Pd(1 1 1) surfaces. The methane activation barrier is lowest over themore » Pd xCe 1-xO 2(1 1 1) surface, even lower than over the Pd(1 1 1) surface or low coordinated stepped or kinked Pd sites. Subsequent reaction steps in complete oxidation, including product desorption and vacancy refilling, are considered to substantiate that methane activation remains the rate-limiting step despite the low barrier over Pd xCe 1-xO 2(1 1 1). The low barrier over the Pd xCe 1-xO 2(1 1 1) surface demonstrates that mixed ceria-noble metal oxides offer the potential for improved hydrocarbon oxidation performance with respect to dispersed noble metal particles on ceria.« less

Methane oxidation on Pd–Ceria: A DFT study of the mechanism over PdxCe1-xO2, Pd, and PdO

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

Mayernick, Adam D.; Janik, Michael J.

2011-02-14

Palladium/ceria exhibits unique catalytic activity for hydrocarbon oxidation; however, the chemical and structural properties of active sites on the palladium–ceria surface are difficult to characterize. Strong interactions between palladium and the ceria support stabilize oxidized Pdδ+ species, which may contribute to the significant activity of Pd/ceria for methane oxidation. We present a density functional theory (DFT + U) investigation into methane oxidation over Pd/ceria and quantify the activity of the Pd xCe 1-xO 2(1 1 1) mixed oxide surface in comparison with the PdO(1 0 0) and Pd(1 1 1) surfaces. The methane activation barrier is lowest over the Pdmore » xCe 1-xO 2(1 1 1) surface, even lower than over the Pd(1 1 1) surface or low coordinated stepped or kinked Pd sites. Subsequent reaction steps in complete oxidation, including product desorption and vacancy refilling, are considered to substantiate that methane activation remains the rate-limiting step despite the low barrier over Pd xCe 1-xO 2(1 1 1). The low barrier over the Pd xCe 1-xO 2(1 1 1) surface demonstrates that mixed ceria-noble metal oxides offer the potential for improved hydrocarbon oxidation performance with respect to dispersed noble metal particles on ceria.« less

Potential barrier heights at metal on oxygen-terminated diamond interfaces

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

Muret, P., E-mail: pierre.muret@neel.cnrs.fr; Traoré, A.; Maréchal, A.

2015-11-28

Electrical properties of metal-semiconductor (M/SC) and metal/oxide/SC structures built with Zr or ZrO{sub 2} deposited on oxygen-terminated surfaces of (001)-oriented diamond films, comprised of a stack of lightly p-doped diamond on a heavily doped layer itself homoepitaxially grown on an Ib substrate, are investigated experimentally and compared to different models. In Schottky barrier diodes, the interfacial oxide layer evidenced by high resolution transmission electron microscopy and electron energy losses spectroscopy before and after annealing, and barrier height inhomogeneities accounts for the measured electrical characteristics until flat bands are reached, in accordance with a model which generalizes that by Tung [Phys.more » Rev. B 45, 13509 (1992)] and permits to extract physically meaningful parameters of the three kinds of interface: (a) unannealed ones, (b) annealed at 350 °C, (c) annealed at 450 °C with the characteristic barrier heights of 2.2–2.5 V in case (a) while as low as 0.96 V in case (c). Possible models of potential barriers for several metals deposited on well defined oxygen-terminated diamond surfaces are discussed and compared to experimental data. It is concluded that interface dipoles of several kinds present at these compound interfaces and their chemical evolution due to annealing are the suitable ingredients that are able to account for the Mott-Schottky behavior when the effect of the metal work function is ignored, and to justify the reverted slope observed regarding metal work function, in contrast to the trend always reported for all other metal-semiconductor interfaces.« less

Thermal barriers for compartments

DOEpatents

Kreutzer, Cory J.; Lustbader, Jason A.

2017-10-17

An aspect of the present disclosure is a thermal barrier that includes a core layer having a first surface, a second surface, and a first edge, and a first outer layer that includes a third surface and a second edge, where the third surface substantially contacts the first surface, the core layer is configured to minimize conductive heat transfer through the barrier, and the first outer layer is configured to maximize reflection of light away from the barrier.

Isomerization reaction dynamics and equilibrium at the liquid-vapor interface of water. A molecular-dynamics study

NASA Technical Reports Server (NTRS)

Benjamin, Ilan; Pohorille, Andrew

1993-01-01

The gauche-trans isomerization reaction of 1,2-dichloroethane at the liquid-vapor interface of water is studied using molecular-dynamics computer simulations. The solvent bulk and surface effects on the torsional potential of mean force and on barrier recrossing dynamics are computed. The isomerization reaction involves a large change in the electric dipole moment, and as a result the trans/gauche ratio is considerably affected by the transition from the bulk solvent to the surface. Reactive flux correlation function calculations of the reaction rate reveal that deviation from the transition-state theory due to barrier recrossing is greater at the surface than in the bulk water. This suggests that the system exhibits non-Rice-Ramsperger-Kassel-Marcus behavior due to the weak solvent-solute coupling at the water liquid-vapor interface.

Surface Desorption Dielectric-Barrier Discharge Ionization Mass Spectrometry.

PubMed

Zhang, Hong; Jiang, Jie; Li, Na; Li, Ming; Wang, Yingying; He, Jing; You, Hong

2017-07-18

A variant of dielectric-barrier discharge named surface desorption dielectric-barrier discharge ionization (SDDBDI) mass spectrometry was developed for high-efficiency ion transmission and high spatial resolution imaging. In SDDBDI, a tungsten nanotip and the inlet of the mass spectrometer are used as electrodes, and a piece of coverslip is used as a sample plate as well as an insulating dielectric barrier, which simplifies the configuration of instrument and thus the operation. Different from volume dielectric-barrier discharge (VDBD), the microdischarges are generated on the surface at SDDBDI, and therefore the plasma density is extremely high. Analyte ions are guided directly into the MS inlet without any deflection. This configuration significantly improves the ion transmission efficiency and thus the sensitivity. The dependence of sensitivity and spatial resolution of the SDDBDI on the operation parameters were systematically investigated. The application of SDDBDI was successfully demonstrated by analysis of multiple species including amino acids, pharmaceuticals, putative cancer biomarkers, and mixtures of both fatty acids and hormones. Limits of detection (S/N = 3) were determined to be 0.84 and 0.18 pmol, respectively, for the analysis of l-alanine and metronidazole. A spatial resolution of 22 μm was obtained for the analysis of an imprinted cyclophosphamide pattern, and imaging of a "T" character was successfully demonstrated under ambient conditions. These results indicate that SDDBDI has high-efficiency ion transmission, high sensitivity, and high spatial resolution, which render it a potential tool for mass spectrometry imaging.

Kinetics and dynamics of the C(3P) + H2O reaction on a full-dimensional accurate triplet state potential energy surface.

PubMed

Li, Jun; Xie, Changjian; Guo, Hua

2017-08-30

A full dimensional accurate potential energy surface (PES) for the C( 3 P) and H 2 O reaction is developed based on ∼34 000 data points calculated at the level of the explicitly correlated unrestricted coupled cluster method with single, double, and perturbative triple excitations with the augmented correlation-consistent polarized triple zeta basis set (CCSD(T)-F12a/AVTZ). The PES is invariant with respect to the permutation of the two hydrogen atoms and the total root mean square error (RMSE) of the fit is only 0.31 kcal mol -1 . The PES features two barriers in the entrance channel and several potential minima, as well as multiple product channels. The rate coefficients of this reaction calculated using a transition-state theory and quasi-classical trajectory (QCT) method are small near room temperature, consistent with experiments. The reaction dynamics is also investigated with QCT on the new PES, which found that the reactivity is constrained by the entrance barriers and the final product branching is not statistical.

The rate of the reaction between CN and C2H2 at interstellar temperatures.

PubMed

Woon, D E; Herbst, E

1997-03-01

The rate coefficient for the important interstellar reaction between CN and C2H2 has been calculated as a function of temperature between 10 and 300 K. The potential surface for this reaction has been determined through ab initio quantum chemical techniques; the potential exhibits no barrier in the entrance channel but does show a small exit channel barrier, which lies below the energy of reactants. Phase-space calculations for the reaction dynamics, which take the exit channel barrier into account, show the same unusual temperature dependence as determined by experiment, in which the rate coefficient at first increases as the temperature is reduced below room temperature and then starts to decrease as the temperature drops below 50-100 K. The agreement between theory and experiment provides strong confirmation that the reaction occurs appreciably at cool interstellar temperatures.

Clusterin Seals the Ocular Surface Barrier in Mouse Dry Eye

PubMed Central

Bauskar, Aditi; Mack, Wendy J.; Mauris, Jerome; Argüeso, Pablo; Heur, Martin; Nagel, Barbara A.; Kolar, Grant R.; Gleave, Martin E.; Nakamura, Takahiro; Kinoshita, Shigeru; Moradian-Oldak, Janet; Panjwani, Noorjahan; Pflugfelder, Stephen C.; Wilson, Mark R.; Fini, M. Elizabeth; Jeong, Shinwu

2015-01-01

Dry eye is a common disorder caused by inadequate hydration of the ocular surface that results in disruption of barrier function. The homeostatic protein clusterin (CLU) is prominent at fluid-tissue interfaces throughout the body. CLU levels are reduced at the ocular surface in human inflammatory disorders that manifest as severe dry eye, as well as in a preclinical mouse model for desiccating stress that mimics dry eye. Using this mouse model, we show here that CLU prevents and ameliorates ocular surface barrier disruption by a remarkable sealing mechanism dependent on attainment of a critical all-or-none concentration. When the CLU level drops below the critical all-or-none threshold, the barrier becomes vulnerable to desiccating stress. CLU binds selectively to the ocular surface subjected to desiccating stress in vivo, and in vitro to the galectin LGALS3, a key barrier component. Positioned in this way, CLU not only physically seals the ocular surface barrier, but it also protects the barrier cells and prevents further damage to barrier structure. These findings define a fundamentally new mechanism for ocular surface protection and suggest CLU as a biotherapeutic for dry eye. PMID:26402857

Clusterin Seals the Ocular Surface Barrier in Mouse Dry Eye.

PubMed

Bauskar, Aditi; Mack, Wendy J; Mauris, Jerome; Argüeso, Pablo; Heur, Martin; Nagel, Barbara A; Kolar, Grant R; Gleave, Martin E; Nakamura, Takahiro; Kinoshita, Shigeru; Moradian-Oldak, Janet; Panjwani, Noorjahan; Pflugfelder, Stephen C; Wilson, Mark R; Fini, M Elizabeth; Jeong, Shinwu

2015-01-01

Dry eye is a common disorder caused by inadequate hydration of the ocular surface that results in disruption of barrier function. The homeostatic protein clusterin (CLU) is prominent at fluid-tissue interfaces throughout the body. CLU levels are reduced at the ocular surface in human inflammatory disorders that manifest as severe dry eye, as well as in a preclinical mouse model for desiccating stress that mimics dry eye. Using this mouse model, we show here that CLU prevents and ameliorates ocular surface barrier disruption by a remarkable sealing mechanism dependent on attainment of a critical all-or-none concentration. When the CLU level drops below the critical all-or-none threshold, the barrier becomes vulnerable to desiccating stress. CLU binds selectively to the ocular surface subjected to desiccating stress in vivo, and in vitro to the galectin LGALS3, a key barrier component. Positioned in this way, CLU not only physically seals the ocular surface barrier, but it also protects the barrier cells and prevents further damage to barrier structure. These findings define a fundamentally new mechanism for ocular surface protection and suggest CLU as a biotherapeutic for dry eye.

Installation Restoration Program. Phase I. Records Search, Hazardous Materials Disposal Sites. Myrtle Beach Air Force Base, South Carolina.

DTIC Science & Technology

1981-10-01

Geography 3-1 Topography 3-. Drainage 3-1 ii Page Surface Geology 3-3 Barrier Sediments 3-3 Myrtle Beach Backbarrier Sediments 3-3 soils 3-5 Subsurface...Beach AFB Surface Drainage and Surface Water Sampling Points 3-2 3.2 Myrtle Beach AFB Surface Soils 3-4 3.3 Myrtle Beach AFB Location of Geologic Cross...has created a potential contamination problem. This situation is compounded by the site’s sandy soil and shallow ground water table. b.) Weathering Pit

Butyrophenone on O-TiO2(110): one-dimensional motion in a weakly confined potential well.

PubMed

Jensen, Stephen C; Shank, Alex; Madix, Robert J; Friend, Cynthia M

2012-04-24

We demonstrate the one-dimensional confinement of weakly bound butyrophenone molecules between strongly bound complexes formed via reaction with oxygen on TiO(2)(110). Butyrophenone weakly bound to Ti rows through the carbonyl oxygen diffuses freely in one dimension along the rows even at 55 K, persisting for many minutes before hopping out of the 1-D well. Quantitative analysis yields an estimate of the migration barrier of 0.11 eV and a frequency factor of 6.5 × 10(9) Hz. These studies demonstrate that weakly bound organic molecules can be confined on a surface by creating molecular barriers, potentially altering their assembly.

Pressure Injury Prevention in a Saudi Arabian Intensive Care Unit: Registered Nurse Attitudes Toward Prevention Strategies and Perceived Facilitators and Barriers to Evidence Implementation.

PubMed

Tayyib, Nahla; Coyer, Fiona; Lewis, Peter

2016-01-01

The purpose of this study was to examine RNs' attitudes toward pressure injury (PI) prevention strategies. Barriers and facilitators perceived by RNs to potentially impact on the adoption and implementation of PI prevention interventions in the intensive care unit (ICU) were examined. Descriptive cross-sectional survey. The target population was RNs practicing in an intensive care unit (ICU) of a major tertiary hospital, King Abdul-Aziz, Mecca, in Saudi Arabia. Fifty-six of the available 60 ICU RNs participated in this study. Data were collected via survey using the Attitude towards Pressure injury Prevention instrument, which included 13 items rated with 4-point Likert scale, and the modified Barriers and Facilitators tool, which included 27 items. The survey was organized into 3 parts: demographic information, potential barriers to optimal skin care, and potential facilitators to skin care. The survey took 10 to 15 minutes to complete. Data were analyzed with descriptive-correlation statistics and multiple regression analysis. Thematic analysis was undertaken for qualitative data. Participants demonstrated positive attitudes toward PI prevention (μ = 38.19/52; 73.44%). No significant differences were found between demographic characteristics of the participants with the RNs' Attitude subscale and perceived barriers and facilitators associated with implementing PI prevention in the critical care setting. Several barriers influenced the ability of RNs to implement PI prevention strategies including time demands (β = .388; P = .011), limitation of RNs' knowledge (β = -.632; P = .022), and current documentation format (β = .344; P = .046). Statistically significant facilitating factors that increased respondents ability to undertake PI prevention were ease of obtaining pressure-reduction surfaces (β = -.388; P = .007), collaboration with interdisciplinary teams (β = .37; P = .02), and availability of appropriate skin care products (β = .44; P = .015). Thematic analysis of open-ended questions highlighted workload as a barrier that impedes the implementation of care specific to PI prevention. Findings from this study highlighted that ICU RNs had a positive attitude toward PI prevention. This study also identified perceived factors influencing PI prevention in the ICU, both facilitators and barriers. Perceived facilitators included availability of pressure-relieving support surfaces and appropriate skin care products and collaboration with the healthcare professional team. However, perceived barriers included limited PI prevention knowledge of the nurse and RN workflow (time demands and documentation format). Findings from this study provide important information identifying context-specific factors that may influence the adoption and implementation of PI prevention interventions in the ICU.

A mechanism study of sound wave-trapping barriers.

PubMed

Yang, Cheng; Pan, Jie; Cheng, Li

2013-09-01

The performance of a sound barrier is usually degraded if a large reflecting surface is placed on the source side. A wave-trapping barrier (WTB), with its inner surface covered by wedge-shaped structures, has been proposed to confine waves within the area between the barrier and the reflecting surface, and thus improve the performance. In this paper, the deterioration in performance of a conventional sound barrier due to the reflecting surface is first explained in terms of the resonance effect of the trapped modes. At each resonance frequency, a strong and mode-controlled sound field is generated by the noise source both within and in the vicinity outside the region bounded by the sound barrier and the reflecting surface. It is found that the peak sound pressures in the barrier's shadow zone, which correspond to the minimum values in the barrier's insertion loss, are largely determined by the resonance frequencies and by the shapes and losses of the trapped modes. These peak pressures usually result in high sound intensity component impinging normal to the barrier surface near the top. The WTB can alter the sound wave diffraction at the top of the barrier if the wavelengths of the sound wave are comparable or smaller than the dimensions of the wedge. In this case, the modified barrier profile is capable of re-organizing the pressure distribution within the bounded domain and altering the acoustic properties near the top of the sound barrier.

Water organization between oppositely charged surfaces: Implications for protein sliding along DNA a)

NASA Astrophysics Data System (ADS)

Marcovitz, Amir; Naftaly, Aviv; Levy, Yaakov

2015-02-01

Water molecules are abundant in protein-DNA interfaces, especially in their nonspecific complexes. In this study, we investigated the organization and energetics of the interfacial water by simplifying the geometries of the proteins and the DNA to represent them as two equally and oppositely charged planar surfaces immersed in water. We found that the potential of mean force for bringing the two parallel surfaces into close proximity comprises energetic barriers whose properties strongly depend on the charge density of the surfaces. We demonstrated how the organization of the water molecules into discretized layers and the corresponding energetic barriers to dehydration can be modulated by the charge density on the surfaces, salt, and the structure of the surfaces. The 1-2 layers of ordered water are tightly bound to the charged surfaces representing the nonspecific protein-DNA complex. This suggests that water might mediate one-dimensional diffusion of proteins along DNA (sliding) by screening attractive electrostatic interactions between the positively charged molecular surface on the protein and the negatively charged DNA backbone and, in doing so, reduce intermolecular friction in a manner that smoothens the energetic landscape for sliding, and facilitates the 1D diffusion of the protein.

Barrier coated drug layered particles for enhanced performance of amorphous solid dispersion dosage form.

PubMed

Puri, Vibha; Dantuluri, Ajay K; Bansal, Arvind K

2012-01-01

Amorphous solid dispersions (ASDs) may entail tailor-made dosage form design to exploit their solubility advantage. Surface phenomena dominated the performance of amorphous celecoxib solid dispersion (ACSD) comprising of amorphous celecoxib (A-CLB), polyvinylpyrrolidone, and meglumine (7:2:1, w/w). ACSD cohesive interfacial interactions hindered its capsule dosage form dissolution (Puri V, Dhantuluri AK, Bansal AK 2011. J Pharm Sci 100:2460-2468). Furthermore, ACSD underwent significant devitrification under environmental stress. In the present study, enthalpy relaxation studies revealed its free surface to contribute to molecular mobility. Based on all these observations, barrier coated amorphous CLB solid dispersion layered particles (ADLP) were developed by Wurster process, using microcrystalline cellulose as substrate and polyvinyl alcohol (PVA), inulin, and polyvinyl acetate phthalate (PVAP) as coating excipients. Capsule formulations of barrier coated-ADLP could achieve rapid dispersibility and high drug release. Evaluation under varying temperature and RH conditions suggested the crystallization inhibitory efficiency in order of inulin < PVA ≈ PVAP; however, under only temperature treatment, crystallization inhibition increased with increase in T(g) of the coating material. Simulated studies using DSC evidenced drug-polymer mixing at the interface as a potential mechanism for surface stabilization. In conclusion, surface modification yielded a fast dispersing robust high drug load ASD based dosage form. Copyright © 2011 Wiley-Liss, Inc.

Modulating the Surface State of SiC to Control Carrier Transport in Graphene/SiC.

PubMed

Jia, Yuping; Sun, Xiaojuan; Shi, Zhiming; Jiang, Ke; Liu, Henan; Ben, Jianwei; Li, Dabing

2018-05-28

Silicon carbide (SiC) with epitaxial graphene (EG/SiC) shows a great potential in the applications of electronic and photoelectric devices. The performance of devices is primarily dependent on the interfacial heterojunction between graphene and SiC. Here, the band structure of the EG/SiC heterojunction is experimentally investigated by Kelvin probe force microscopy. The dependence of the barrier height at the EG/SiC heterojunction to the initial surface state of SiC is revealed. Both the barrier height and band bending tendency of the heterojunction can be modulated by controlling the surface state of SiC, leading to the tuned carrier transport behavior at the EG/SiC interface. The barrier height at the EG/SiC(000-1) interface is almost ten times that of the EG/SiC(0001) interface. As a result, the amount of carrier transport at the EG/SiC(000-1) interface is about ten times that of the EG/SiC(0001) interface. These results offer insights into the carrier transport behavior at the EG/SiC heterojunction by controlling the initial surface state of SiC, and this strategy can be extended in all devices with graphene as the top layer. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Computing the Free Energy Barriers for Less by Sampling with a Coarse Reference Potential while Retaining Accuracy of the Target Fine Model.

PubMed

Plotnikov, Nikolay V

2014-08-12

Proposed in this contribution is a protocol for calculating fine-physics (e.g., ab initio QM/MM) free-energy surfaces at a high level of accuracy locally (e.g., only at reactants and at the transition state for computing the activation barrier) from targeted fine-physics sampling and extensive exploratory coarse-physics sampling. The full free-energy surface is still computed but at a lower level of accuracy from coarse-physics sampling. The method is analytically derived in terms of the umbrella sampling and the free-energy perturbation methods which are combined with the thermodynamic cycle and the targeted sampling strategy of the paradynamics approach. The algorithm starts by computing low-accuracy fine-physics free-energy surfaces from the coarse-physics sampling in order to identify the reaction path and to select regions for targeted sampling. Thus, the algorithm does not rely on the coarse-physics minimum free-energy reaction path. Next, segments of high-accuracy free-energy surface are computed locally at selected regions from the targeted fine-physics sampling and are positioned relative to the coarse-physics free-energy shifts. The positioning is done by averaging the free-energy perturbations computed with multistep linear response approximation method. This method is analytically shown to provide results of the thermodynamic integration and the free-energy interpolation methods, while being extremely simple in implementation. Incorporating the metadynamics sampling to the algorithm is also briefly outlined. The application is demonstrated by calculating the B3LYP//6-31G*/MM free-energy barrier for an enzymatic reaction using a semiempirical PM6/MM reference potential. These modifications allow computing the activation free energies at a significantly reduced computational cost but at the same level of accuracy compared to computing full potential of mean force.

Computing the Free Energy Barriers for Less by Sampling with a Coarse Reference Potential while Retaining Accuracy of the Target Fine Model

PubMed Central

2015-01-01

Proposed in this contribution is a protocol for calculating fine-physics (e.g., ab initio QM/MM) free-energy surfaces at a high level of accuracy locally (e.g., only at reactants and at the transition state for computing the activation barrier) from targeted fine-physics sampling and extensive exploratory coarse-physics sampling. The full free-energy surface is still computed but at a lower level of accuracy from coarse-physics sampling. The method is analytically derived in terms of the umbrella sampling and the free-energy perturbation methods which are combined with the thermodynamic cycle and the targeted sampling strategy of the paradynamics approach. The algorithm starts by computing low-accuracy fine-physics free-energy surfaces from the coarse-physics sampling in order to identify the reaction path and to select regions for targeted sampling. Thus, the algorithm does not rely on the coarse-physics minimum free-energy reaction path. Next, segments of high-accuracy free-energy surface are computed locally at selected regions from the targeted fine-physics sampling and are positioned relative to the coarse-physics free-energy shifts. The positioning is done by averaging the free-energy perturbations computed with multistep linear response approximation method. This method is analytically shown to provide results of the thermodynamic integration and the free-energy interpolation methods, while being extremely simple in implementation. Incorporating the metadynamics sampling to the algorithm is also briefly outlined. The application is demonstrated by calculating the B3LYP//6-31G*/MM free-energy barrier for an enzymatic reaction using a semiempirical PM6/MM reference potential. These modifications allow computing the activation free energies at a significantly reduced computational cost but at the same level of accuracy compared to computing full potential of mean force. PMID:25136268

Focused ultrasound delivery of Raman nanoparticles across the blood-brain barrier: potential for targeting experimental brain tumors.

PubMed

Diaz, Roberto Jose; McVeigh, Patrick Z; O'Reilly, Meaghan A; Burrell, Kelly; Bebenek, Matthew; Smith, Christian; Etame, Arnold B; Zadeh, Gelareh; Hynynen, Kullervo; Wilson, Brian C; Rutka, James T

2014-07-01

Spectral mapping of nanoparticles with surface enhanced Raman scattering (SERS) capability in the near-infrared range is an emerging molecular imaging technique. We used magnetic resonance image-guided transcranial focused ultrasound (TcMRgFUS) to reversibly disrupt the blood-brain barrier (BBB) adjacent to brain tumor margins in rats. Glioma cells were found to internalize SERS capable nanoparticles of 50nm or 120nm physical diameter. Surface coating with anti-epidermal growth factor receptor antibody or non-specific human immunoglobulin G, resulted in enhanced cell uptake of nanoparticles in-vitro compared to nanoparticles with methyl terminated 12-unit polyethylene glycol surface. BBB disruption permitted the delivery of SERS capable spherical 50 or 120nm gold nanoparticles to the tumor margins. Thus, nanoparticles with SERS imaging capability can be delivered across the BBB non-invasively using TcMRgFUS and have the potential to be used as optical tracking agents at the invasive front of malignant brain tumors. This study demonstrates the use of magnetic resonance image-guided transcranial focused ultrasound to open the BBB and enable spectral mapping of nanoparticles with surface enhanced Raman scattering (SERS)-based molecular imaging for experimental tumor tracking. Copyright © 2014 Elsevier Inc. All rights reserved.

Computed potential energy surfaces for chemical reactions

NASA Technical Reports Server (NTRS)

Walch, Stephen P.

1988-01-01

The minimum energy path for the addition of a hydrogen atom to N2 is characterized in CASSCF/CCI calculations using the (4s3p2d1f/3s2p1d) basis set, with additional single point calculations at the stationary points of the potential energy surface using the (5s4p3d2f/4s3p2d) basis set. These calculations represent the most extensive set of ab initio calculations completed to date, yielding a zero point corrected barrier for HN2 dissociation of approx. 8.5 kcal mol/1. The lifetime of the HN2 species is estimated from the calculated geometries and energetics using both conventional Transition State Theory and a method which utilizes an Eckart barrier to compute one dimensional quantum mechanical tunneling effects. It is concluded that the lifetime of the HN2 species is very short, greatly limiting its role in both termolecular recombination reactions and combustion processes.

Anticorrosion efficiency of ultrasonically deposited silica coatings on titanium

NASA Astrophysics Data System (ADS)

Ertaş, Fatma Sinem; Kaş, Recep; Mikó, Annamária; Birer, Özgür

2013-07-01

We utilized high intensity ultrasound to prepare coatings of silica and organically modified silica composed of multiple layers of densely packed nanoparticles. Ultrasound was used to collide nanoparticles onto an activated titanium surface with high speed. Large areas could be homogeneously coated by this method. These coatings were characterized by spectroscopy and microscopy methods and the anticorrosion efficiency in NaCl solution was evaluated by electrochemical measurements. The results indicated that the composite coatings provided good quality barrier layer on bare titanium and decreased the anodic corrosion rate. It was found that increase in the organic content of the coating shifted the passivation potential towards more positive direction. The comparison of the impedance results recorded at the corrosion potential pointed out that in each case a good quality barrier layer was formed on the titanium surface. The outstanding corrosion resistance of the composite coatings with only ~200 nm thickness shows that ultrasound assisted deposition can be a competitive method to obtain corrosion protective layers.

Excited state conformational dynamics in carotenoids: dark intermediates and excitation energy transfer.

PubMed

Beck, Warren F; Bishop, Michael M; Roscioli, Jerome D; Ghosh, Soumen; Frank, Harry A

2015-04-15

A consideration of the excited state potential energy surfaces of carotenoids develops a new hypothesis for the nature of the conformational motions that follow optical preparation of the S2 (1(1)Bu(+)) state. After an initial displacement from the Franck-Condon geometry along bond length alternation coordinates, it is suggested that carotenoids pass over a transition-state barrier leading to twisted conformations. This hypothesis leads to assignments for several dark intermediate states encountered in femtosecond spectroscopic studies. The Sx state is assigned to the structure reached upon the onset of torsional motions near the transition state barrier that divides planar and twisted structures on the S2 state potential energy surface. The X state, detected recently in two-dimensional electronic spectra, corresponds to a twisted structure well past the barrier and approaching the S2 state torsional minimum. Lastly, the S(∗) state is assigned to a low lying S1 state structure with intramolecular charge transfer character (ICT) and a pyramidal conformation. It follows that the bent and twisted structures of carotenoids that are found in photosynthetic light-harvesting proteins yield excited-state structures that favor the development of an ICT character and optimized energy transfer yields to (bacterio)chlorophyll acceptors. Copyright © 2015 Elsevier Inc. All rights reserved.

Mechanism and kinetics of the electrocatalytic reaction responsible for the high cost of hydrogen fuel cells.

PubMed

Cheng, Tao; Goddard, William A; An, Qi; Xiao, Hai; Merinov, Boris; Morozov, Sergey

2017-01-25

The sluggish oxygen reduction reaction (ORR) is a major impediment to the economic use of hydrogen fuel cells in transportation. In this work, we report the full ORR reaction mechanism for Pt(111) based on Quantum Mechanics (QM) based Reactive metadynamics (RμD) simulations including explicit water to obtain free energy reaction barriers at 298 K. The lowest energy pathway for 4 e - water formation is: first, *OOH formation; second, *OOH reduction to H 2 O and O*; third, O* hydrolysis using surface water to produce two *OH and finally *OH hydration to water. Water formation is the rate-determining step (RDS) for potentials above 0.87 Volt, the normal operating range. Considering the Eley-Rideal (ER) mechanism involving protons from the solvent, we predict the free energy reaction barrier at 298 K for water formation to be 0.25 eV for an external potential below U = 0.87 V and 0.41 eV at U = 1.23 V, in good agreement with experimental values of 0.22 eV and 0.44 eV, respectively. With the mechanism now fully understood, we can use this now validated methodology to examine the changes upon alloying and surface modifications to increase the rate by reducing the barrier for water formation.

Combined valence bond-molecular mechanics potential-energy surface and direct dynamics study of rate constants and kinetic isotope effects for the H + C2H6 reaction.

PubMed

Chakraborty, Arindam; Zhao, Yan; Lin, Hai; Truhlar, Donald G

2006-01-28

This article presents a multifaceted study of the reaction H+C(2)H(6)-->H(2)+C(2)H(5) and three of its deuterium-substituted isotopologs. First we present high-level electronic structure calculations by the W1, G3SX, MCG3-MPWB, CBS-APNO, and MC-QCISD/3 methods that lead to a best estimate of the barrier height of 11.8+/-0.5 kcal/mol. Then we obtain a specific reaction parameter for the MPW density functional in order that it reproduces the best estimate of the barrier height; this yields the MPW54 functional. The MPW54 functional, as well as the MPW60 functional that was previously parametrized for the H+CH(4) reaction, is used with canonical variational theory with small-curvature tunneling to calculate the rate constants for all four ethane reactions from 200 to 2000 K. The final MPW54 calculations are based on curvilinear-coordinate generalized-normal-mode analysis along the reaction path, and they include scaled frequencies and an anharmonic C-C bond torsion. They agree with experiment within 31% for 467-826 K except for a 38% deviation at 748 K; the results for the isotopologs are predictions since these rate constants have never been measured. The kinetic isotope effects (KIEs) are analyzed to reveal the contributions from subsets of vibrational partition functions and from tunneling, which conspire to yield a nonmonotonic temperature dependence for one of the KIEs. The stationary points and reaction-path potential of the MPW54 potential-energy surface are then used to parametrize a new kind of analytical potential-energy surface that combines a semiempirical valence bond formalism for the reactive part of the molecule with a standard molecular mechanics force field for the rest; this may be considered to be either an extension of molecular mechanics to treat a reactive potential-energy surface or a new kind of combined quantum-mechanical/molecular mechanical (QM/MM) method in which the QM part is semiempirical valence bond theory; that is, the new potential-energy surface is a combined valence bond molecular mechanics (CVBMM) surface. Rate constants calculated with the CVBMM surface agree with the MPW54 rate constants within 12% for 534-2000 K and within 23% for 200-491 K. The full CVBMM potential-energy surface is now available for use in variety of dynamics calculations, and it provides a prototype for developing CVBMM potential-energy surfaces for other reactions.

An Investigation of the Effects of Self-Assembled Monolayers on Protein Crystallisation

PubMed Central

Zhang, Chen-Yan; Shen, He-Fang; Wang, Qian-Jin; Guo, Yun-Zhu; He, Jin; Cao, Hui-Ling; Liu, Yong-Ming; Shang, Peng; Yin, Da-Chuan

2013-01-01

Most protein crystallisation begins from heterogeneous nucleation; in practice, crystallisation typically occurs in the presence of a solid surface in the solution. The solid surface provides a nucleation site such that the energy barrier for nucleation is lower on the surface than in the bulk solution. Different types of solid surfaces exhibit different surface energies, and the nucleation barriers depend on the characteristics of the solid surfaces. Therefore, treatment of the solid surface may alter the surface properties to increase the chance to obtain protein crystals. In this paper, we propose a method to modify the glass cover slip using a self-assembled monolayer (SAM) of functional groups (methyl, sulfydryl and amino), and we investigated the effect of each SAM on protein crystallisation. The results indicated that both crystallisation success rate in a reproducibility study, and crystallisation hits in a crystallisation screening study, were increased using the SAMs, among which, the methyl-modified SAM demonstrated the most significant improvement. These results illustrated that directly modifying the crystallisation plates or glass cover slips to create surfaces that favour heterogeneous nucleation can be potentially useful in practical protein crystallisation, and the utilisation of a SAM containing a functional group can be considered a promising technique for the treatment of the surfaces that will directly contact the crystallisation solution. PMID:23749116

Patterning of a-C DLC films: exploration of an aqueous electro-oxidative mechanism

NASA Astrophysics Data System (ADS)

Mühl, Thomas; Myhra, Sverre

2007-06-01

Conducting ion-beam assisted CVD deposited a-C type DLC films can be patterned electro-oxidatively by masked and maskless probe-induced STM-based lithography. The former constitutes a parallel rapid processing technology, with the tip acting as a distant stationary electrode. The latter is a higher spatial resolution serial technology, with the tip defining a travelling local electro-chemical cell. The mechanism is based on electro-oxidative conversion of solid carbon to gaseous CO or CO2 in the presence of an aqueous phase, either as a bulk fluid or as a thin adsorbed film. The process is constrained kinetically in the early stages by limitations on charge transport through the surface barrier at the fluid-to-solid interface and subsequently by the availability of oxidants and by their transport to reactive sites. The as-received surface is terminated by chemisorbed oxygen, leading to the formation of an insulating surface barrier. The threshold potential for initiation of conversion depends on the width of the barrier. The results may have implications for new technologies exploiting the properties of carbon-based materials, but may also add to the present understanding of the electrochemistry of carbon solids.

Protecting High Energy Barriers: A New Equation to Regulate Boost Energy in Accelerated Molecular Dynamics Simulations.

PubMed

Sinko, William; de Oliveira, César Augusto F; Pierce, Levi C T; McCammon, J Andrew

2012-01-10

Molecular dynamics (MD) is one of the most common tools in computational chemistry. Recently, our group has employed accelerated molecular dynamics (aMD) to improve the conformational sampling over conventional molecular dynamics techniques. In the original aMD implementation, sampling is greatly improved by raising energy wells below a predefined energy level. Recently, our group presented an alternative aMD implementation where simulations are accelerated by lowering energy barriers of the potential energy surface. When coupled with thermodynamic integration simulations, this implementation showed very promising results. However, when applied to large systems, such as proteins, the simulation tends to be biased to high energy regions of the potential landscape. The reason for this behavior lies in the boost equation used since the highest energy barriers are dramatically more affected than the lower ones. To address this issue, in this work, we present a new boost equation that prevents oversampling of unfavorable high energy conformational states. The new boost potential provides not only better recovery of statistics throughout the simulation but also enhanced sampling of statistically relevant regions in explicit solvent MD simulations.

Significant improvement in the electrical characteristics of Schottky barrier diodes on molecularly modified Gallium Nitride surfaces

NASA Astrophysics Data System (ADS)

Garg, Manjari; Naik, Tejas R.; Pathak, C. S.; Nagarajan, S.; Rao, V. Ramgopal; Singh, R.

2018-04-01

III-Nitride semiconductors face the issue of localized surface states, which causes fermi level pinning and large leakage current at the metal semiconductor interface, thereby degrading the device performance. In this work, we have demonstrated the use of a Self-Assembled Monolayer (SAM) of organic molecules to improve the electrical characteristics of Schottky barrier diodes (SBDs) on n-type Gallium Nitride (n-GaN) epitaxial films. The electrical characteristics of diodes were improved by adsorption of SAM of hydroxyl-phenyl metallated porphyrin organic molecules (Zn-TPPOH) onto the surface of n-GaN. SAM-semiconductor bonding via native oxide on the n-GaN surface was confirmed using X-ray photoelectron spectroscopy measurements. Surface morphology and surface electronic properties were characterized using atomic force microscopy and Kelvin probe force microscopy. Current-voltage characteristics of different metal (Cu, Ni) SBDs on bare n-GaN were compared with those of Cu/Zn-TPPOH/n-GaN and Ni/Zn-TPPOH/n-GaN SBDs. It was found that due to the molecular monolayer, the surface potential of n-GaN was decreased by ˜350 mV. This caused an increase in the Schottky barrier height of Cu and Ni SBDs from 1.13 eV to 1.38 eV and 1.07 eV to 1.22 eV, respectively. In addition to this, the reverse bias leakage current was reduced by 3-4 orders of magnitude for both Cu and Ni SBDs. Such a significant improvement in the electrical performance of the diodes can be very useful for better device functioning.

Carbonation of wollastonite(001) competing hydration: microscopic insights from ion spectroscopy and density functional theory.

PubMed

Longo, Roberto C; Cho, Kyeongjae; Brüner, Philipp; Welle, Alexander; Gerdes, Andreas; Thissen, Peter

2015-03-04

In this paper, we report about the influence of the chemical potential of water on the carbonation reaction of wollastonite (CaSiO3) as a model surface of cement and concrete. Total energy calculations based on density functional theory combined with kinetic barrier predictions based on nudge elastic band method show that the exposure of the water-free wollastonite surface to CO2 results in a barrier-less carbonation. CO2 reacts with the surface oxygen and forms carbonate (CO3(2-)) complexes together with a major reconstruction of the surface. The reaction comes to a standstill after one carbonate monolayer has been formed. In case one water monolayer is covering the wollastonite surface, the carbonation is no more barrier-less, yet ending in a localized monolayer. Covered with multilayers of water, the thermodynamic ground state of the wollastonite completely changes due to a metal-proton exchange reaction (also called early stage hydration) and Ca(2+) ions are partially removed from solid phase into the H2O/wollastonite interface. Mobile Ca(2+) reacts again with CO2 and forms carbonate complexes, ending in a delocalized layer. By means of high-resolution time-of-flight secondary-ion mass spectrometry images, we confirm that hydration can lead to a partially delocalization of Ca(2+) ions on wollastonite surfaces. Finally, we evaluate the impact of our model surface results by the meaning of low-energy ion-scattering spectroscopy combined with careful discussion about the competing reactions of carbonation vs hydration.

In situ clay formation : evaluation of a proposed new technology for stable containment barriers.

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

Nagy, Kathryn L.; DiGiovanni, Anthony Albert; Fredrich, Joanne T.

2004-03-01

Containment of chemical wastes in near-surface and repository environments is accomplished by designing engineered barriers to fluid flow. Containment barrier technologies such as clay liners, soil/bentonite slurry walls, soil/plastic walls, artificially grouted sediments and soils, and colloidal gelling materials are intended to stop fluid transport and prevent plume migration. However, despite their effectiveness in the short-term, all of these barriers exhibit geochemical or geomechanical instability over the long-term resulting in degradation of the barrier and its ability to contain waste. No technologically practical or economically affordable technologies or methods exist at present for accomplishing total remediation, contaminant removal, or destruction-degradationmore » in situ. A new type of containment barrier with a potentially broad range of environmental stability and longevity could result in significant cost-savings. This report documents a research program designed to establish the viability of a proposed new type of containment barrier derived from in situ precipitation of clays in the pore space of contaminated soils or sediments. The concept builds upon technologies that exist for colloidal or gel stabilization. Clays have the advantages of being geologically compatible with the near-surface environment and naturally sorptive for a range of contaminants, and further, the precipitation of clays could result in reduced permeability and hydraulic conductivity, and increased mechanical stability through cementation of soil particles. While limited success was achieved under certain controlled laboratory conditions, the results did not warrant continuation to the field stage for multiple reasons, and the research program was thus concluded with Phase 2.« less

Monitoring the Vadose Zone Moisture Regime Below a Surface Barrier

NASA Astrophysics Data System (ADS)

Zhang, Z. F.; Strickland, C. E.; Field, J. G.

2009-12-01

A 6000 m2 interim surface barrier has been constructed over a portion of the T Tank Farm in the Depart of Energy’s Hanford site. The purpose of using a surface barrier was to reduce or eliminate the infiltration of meteoric precipitation into the contaminated soil zone due to past leaks from Tank T-106 and hence to reduce the rate of movement of the plume. As part of the demonstration effort, vadose zone moisture is being monitored to assess the effectiveness of the barrier on the reduction of soil moisture flow. A vadose zone monitoring system was installed to measure soil water conditions at four horizontal locations (i.e., instrument Nests A, B, C, and D) outside, near the edge of, and beneath the barrier. Each instrument nest consists of a capacitance probe with multiple sensors, multiple heat-dissipation units, and a neutron probe access tube used to measure soil-water content and soil-water pressure. Nest A serves as a control by providing subsurface conditions outside the influence of the surface barrier. Nest B provides subsurface measurements to assess barrier edge effects. Nests C and D are used to assess the impact of the surface barrier on soil-moisture conditions beneath it. Monitoring began in September 2006 and continues to the present. To date, the monitoring system has provided high-quality data. Results show that the soil beneath the barrier has been draining from the shallower depth. The lack of climate-caused seasonal variation of soil water condition beneath the barrier indicates that the surface barrier has minimized water exchange between the soil and the atmosphere.

Surface pre-treatment for barrier coatings on polyethylene terephthalate

NASA Astrophysics Data System (ADS)

Bahre, H.; Bahroun, K.; Behm, H.; Steves, S.; Awakowicz, P.; Böke, M.; Hopmann, Ch; Winter, J.

2013-02-01

Polymers have favourable properties such as light weight, flexibility and transparency. Consequently, this makes them suitable for food packaging, organic light-emitting diodes and flexible solar cells. Nonetheless, raw plastics do not possess sufficient barrier functionality against oxygen and water vapour, which is of paramount importance for most applications. A widespread solution is to deposit thin silicon oxide layers using plasma processes. However, silicon oxide layers do not always fulfil the requirements concerning adhesion and barrier performance when deposited on films. Thus, plasma pre-treatment is often necessary. To analyse the influence of a plasma-based pre-treatment on barrier performance, different plasma pre-treatments on three reactor setups were applied to a very smooth polyethylene terephthalate film before depositing a silicon oxide barrier layer. In this paper, the influence of oxygen and argon plasma pre-treatments towards the barrier performance is discussed examining the chemical and topological change of the film. It was observed that a short one-to-ten-second plasma treatment can reduce the oxygen transmission rate by a factor of five. The surface chemistry and the surface topography change significantly for these short treatment times, leading to an increased surface energy. The surface roughness rises slowly due to the development of small spots in the nanometre range. For very long treatment times, surface roughness of the order of the barrier layer's thickness results in a complete loss of barrier properties. During plasma pre-treatment, the trade-off between surface activation and roughening of the surface has to be carefully considered.

F + H/sub 2/ potential energy surface: the ecstasy and the agony

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

Schaefer, H.F. III

1985-12-05

This account surveys 14 years of more or less continuing theoretical research on the FH/sub 2/ potential energy hypersurface. Early encouragement concerning the ability of theory to reliably characterize the entrance barrier for F + H/sub 2/ ..-->.. FH + H has more recently been sobered by the realization that very high levels of theory are required for this task. The importance of zero-point vibrational corrections and tunneling corrections in reliable predictions of the same activation energy is discussed. In contrast, the barrier height of H + FH ..-->.. HF + H three-center exchange stands as a prominent early successmore » of ab initio molecular electronic structure theory. 90 references, 4 figures, 6 tables.« less

Orientation dependent ionization potential of In2O3: a natural source for inhomogeneous barrier formation at electrode interfaces in organic electronics.

PubMed

Hohmann, Mareike V; Ágoston, Péter; Wachau, André; Bayer, Thorsten J M; Brötz, Joachim; Albe, Karsten; Klein, Andreas

2011-08-24

The ionization potentials of In(2)O(3) films grown epitaxially by magnetron sputtering on Y-stabilized ZrO(2) substrates with (100) and (111) surface orientation are determined using photoelectron spectroscopy. Epitaxial growth is verified using x-ray diffraction. The observed ionization potentials, which directly affect the work functions, are in good agreement with ab initio calculations using density functional theory. While the (111) surface exhibits a stable surface termination with an ionization potential of ∼ 7.0 eV, the surface termination and the ionization potential of the (100) surface depend strongly on the oxygen chemical potential. With the given deposition conditions an ionization potential of ∼ 7.7 eV is obtained, which is attributed to a surface termination stabilized by oxygen dimers. This orientation dependence also explains the lower ionization potentials observed for In(2)O(3) compared to Sn-doped In(2)O(3) (ITO) (Klein et al 2009 Thin Solid Films 518 1197-203). Due to the orientation dependent ionization potential, a polycrystalline ITO film will exhibit a laterally varying work function, which results in an inhomogeneous charge injection into organic semiconductors when used as electrode material. The variation of work function will become even more pronounced when oxygen plasma or UV-ozone treatments are performed, as an oxidation of the surface is only possible for the (100) surface. The influence of the deposition technique on the formation of stable surface terminations is also discussed. © 2011 IOP Publishing Ltd

Fission barriers at the end of the chart of the nuclides

NASA Astrophysics Data System (ADS)

Möller, Peter; Sierk, Arnold J.; Ichikawa, Takatoshi; Iwamoto, Akira; Mumpower, Matthew

2015-02-01

We present calculated fission-barrier heights for 5239 nuclides for all nuclei between the proton and neutron drip lines with 171 ≤A ≤330 . The barriers are calculated in the macroscopic-microscopic finite-range liquid-drop model with a 2002 set of macroscopic-model parameters. The saddle-point energies are determined from potential-energy surfaces based on more than 5 000 000 different shapes, defined by five deformation parameters in the three-quadratic-surface shape parametrization: elongation, neck diameter, left-fragment spheroidal deformation, right-fragment spheroidal deformation, and nascent-fragment mass asymmetry. The energy of the ground state is determined by calculating the lowest-energy configuration in both the Nilsson perturbed-spheroid (ɛ ) and the spherical-harmonic (β ) parametrizations, including axially asymmetric deformations. The lower of the two results (correcting for zero-point motion) is defined as the ground-state energy. The effect of axial asymmetry on the inner barrier peak is calculated in the (ɛ ,γ ) parametrization. We have earlier benchmarked our calculated barrier heights to experimentally extracted barrier parameters and found average agreement to about 1 MeV for known data across the nuclear chart. Here we do additional benchmarks and investigate the qualitative and, when possible, quantitative agreement and/or consistency with data on β -delayed fission, isotope generation along prompt-neutron-capture chains in nuclear-weapons tests, and superheavy-element stability. These studies all indicate that the model is realistic at considerable distances in Z and N from the region of nuclei where its parameters were determined.

Cashew gum and gelatin blend for food packaging application

USDA-ARS?s Scientific Manuscript database

Cashew gum (CG) and gelatin (G) films were developed using the casting method and response surface methodology. The objective was produce packaging films from CG/G blends that exhibit effective barrier properties. A study of zeta potential versus pH was first carried out to determine the isoelectric...

"Green" synthesized and coated nanaosilver alters the membrance permeability of barrier (intestinal, brain, endothelial) cells and stimulates oxidative stress pathways in neurons.

EPA Science Inventory

Nanosilver's (nanoAg) use in medical applications and consumer products is increasing. Because of this, its "green" synthesis and surface modification with beneficial coatings are desirable. Given nanoAg's potential exposure routes (e.g., dermal, intestin...

Stability diagrams for the surface patterns of GaN(0001bar) as a function of Schwoebel barrier height

NASA Astrophysics Data System (ADS)

Krzyżewski, Filip; Załuska-Kotur, Magdalena A.

2017-01-01

Height and type of Schwoebel barriers (direct or inverse) decides about the character of the surface instability. Different surface morphologies are presented. Step bunches, double steps, meanders, mounds and irregular patterns emerge at the surface as a result of step (Schwoebel) barriers at some temperature or miscut values. The study was carried out on the two-component kinetic Monte Carlo (kMC) model of GaN(0001bar) surface grown in nitrogen rich conditions. Diffusion of gallium adatoms over N-polar surface is slow and nitrogen adatoms are almost immobile. We show that in such conditions surfaces remain smooth when gallium adatoms diffuse in the presence of low inverse Schwoebel barrier. It is illustrated by adequate stability diagrams for surface morphologies.

Efficient multidimensional free energy calculations for ab initio molecular dynamics using classical bias potentials

NASA Astrophysics Data System (ADS)

VandeVondele, Joost; Rothlisberger, Ursula

2000-09-01

We present a method for calculating multidimensional free energy surfaces within the limited time scale of a first-principles molecular dynamics scheme. The sampling efficiency is enhanced using selected terms of a classical force field as a bias potential. This simple procedure yields a very substantial increase in sampling accuracy while retaining the high quality of the underlying ab initio potential surface and can thus be used for a parameter free calculation of free energy surfaces. The success of the method is demonstrated by the applications to two gas phase molecules, ethane and peroxynitrous acid, as test case systems. A statistical analysis of the results shows that the entire free energy landscape is well converged within a 40 ps simulation at 500 K, even for a system with barriers as high as 15 kcal/mol.

Adsorption, dissociation and diffusion of hydrogen on the ZrCo surface and subsurface: A comprehensive study using first principles approach

NASA Astrophysics Data System (ADS)

Chattaraj, D.; Kumar, Nandha; Ghosh, Prasenjit; Majumder, C.; Dash, Smruti

2017-11-01

With increasing demand for hydrogen economy driven world, the fundamental research of hydrogen-metal interactions has gained momentum. In this work we report a systematic theoretical study of the stability of different surfaces of intermetallic ZrCo that is a possible candidate as a getter bed for tritium. Our first principles ab initio thermodynamic calculations predict that amongst the (100), (110) and (111) surfaces, the stoichiometric (110) surface is the most stable one over a wide range of Co chemical potential. We have also studied adsorption, dissociation and diffusion of hydrogen on the (110) surface. On the basis of total energy, it is seen that adsorption of molecular hydrogen (H2) on the surface is much weaker than atomic hydrogen. The H2 decomposition on ZrCo surface can easily take place and the dissociation barrier is calculated to be 0.70 eV. The strength of binding of H atom on the surface is more or less independent of surface coverage till 1.0 ML of H. The thermodynamic stability of atomic H adsorbed on the surface, in subsurface and bulk decreases from surface to bulk to subsurface. Though the H atoms are mobile on the surface, their diffusion to the subsurface involves a barrier of about 0.79 eV.

Hydrogen bonding and interparticle forces in platelet alpha-Al2O3 dispersions: yield stress and zeta potential.

PubMed

Khoo, Kay-Sen; Teh, E-Jen; Leong, Yee-Kwong; Ong, Ban Choon

2009-04-09

Adsorbed phosphate on smooth platelet alpha-Al2O3 particles at saturation surface coverage gives rise to strong interparticle attractive forces in dispersion. The maximum yield stress at the point of zero charge was increased by 2-fold. This was attributed to a high density of intermolecular hydrogen bonding between the adsorbed phosphate layers of the interacting particles. Adsorbed citrate at saturation surface coverage, however, reduced the maximum yield stress by 50%. It adsorbed to form a very effective steric barrier as intramolecular hydrogen bonding between -OH and the free terminal carboxylic group prevented strong interactions with other adsorbed citrate molecules residing on the second interacting particle. This steric barrier kept the interacting platelet particles further apart, thereby weakening the van der Waals attraction. The platelet alpha-Al2O3 dispersions were flocculated at all pH level. These dispersions displayed a maximum yield stress at the point of zero zeta potential at the pH approximately 8.0. They also obeyed the yield stress-DLVO force model as characterized by a linear decrease in the yield stress with the square of the zeta potential.

Optically controlled resonant tunneling in a double-barrier diode

NASA Astrophysics Data System (ADS)

Kan, S. C.; Wu, S.; Sanders, S.; Griffel, G.; Yariv, A.

1991-03-01

The resonant tunneling effect is optically enhanced in a GaAs/GaAlAs double-barrier structure that has partial lateral current confinement. The peak current increases and the valley current decreases simultaneously when the device surface is illuminated, due to the increased conductivity of the top layer of the structure. The effect of the lateral current confinement on the current-voltage characteristic of a double-barrier resonant tunneling structure was also studied. With increased lateral current confinement, the peak and valley current decrease at a different rate such that the current peak-to-valley ratio increases up to three times. The experimental results are explained by solving the electrostatic potential distribution in the structure using a simple three-layer model.

Advanced Environmental Barrier Coatings Developed for SiC/SiC Composite Vanes

NASA Technical Reports Server (NTRS)

Lee, Kang N.; Fox, Dennis S.; Eldridge, Jeffrey I.; Zhu, Dongming; Bansal, Narottam P.; Miller, Robert A.

2003-01-01

Ceramic components exhibit superior high-temperature strength and durability over conventional component materials in use today, signifying the potential to revolutionize gas turbine engine component technology. Silicon-carbide fiber-reinforced silicon carbide ceramic matrix composites (SiC/SiC CMCs) are prime candidates for the ceramic hotsection components of next-generation gas turbine engines. A key barrier to the realization of SiC/SiC CMC hot-section components is the environmental degradation of SiC/SiC CMCs in combustion environments. This is in the form of surface recession due to the volatilization of silica scale by water vapor. An external environmental barrier coating (EBC) is a logical approach to achieve protection and long-term durability.

The Effects of Fire on the Function of the 200-BP-1 Engineered Surface Barrier

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

Ward, Anderson L.; Link, Steven O.; Hasan, Nazmul

2009-09-01

A critical unknown in use of barrier technology for long-term waste isolation is performance after a major disturbance especially when institutional controls are intact, but there are no resources to implement corrective actions. The objective of this study was to quantify the effects of wild fire on alterations the function of an engineered barrier. A controlled burn September 26, 2008 was used to remove all the vegetation from the north side of the barrier. Flame heights exceeded 9 m and temperatures ranged from 250 oC at 1.5 cm below the surface to over 700 oC at 1 m above themore » surface. Post-fire analysis of soil properties show significant decreases in wettability, hydraulic conductivity, air entry pressure, organic matter, and porosity relative to pre-fire conditions whereas dry bulk density increased. Decreases in hydraulic conductivity and wettabilty immediately after the fire are implicated in a surface runoff event that occurred in January 2009, the first in 13 years. There was a significant increase in macro-nutrients, pH, and electrical conductivity. After one year, hydrophobicity has returned to pre-burn levels with only 16% of samples still showing signs of decreased wettability. Over the same period, hydraulic conductivity and air entry pressure returned to pre-burn levels at one third of the locations but remained identical to values recorded immediately after the fire at the other two thirds. Soil nutrients, pH, and electrical conductivity remain elevated after 1 year. Species composition on the burned surface changed markedly from prior years and relative to the unburned surface and two analog sites. An increase in the proportion of annuals and biennials is characteristic of burned surfaces that have become dominated by ruderal species. Greenhouse seedling emergence tests conducted to assess the seed bank of pre- and post-burn soils and of two analog sites at the McGee Ranch show no difference in the number of species emerging from soils collected before and after the fire. However, there were fewer species emerging from the seed bank on the side slopes and more species emerging from two analog sites. Leaf area index measures confirmed the substantial differences in plant communities after fire. Xylem pressure potential were considerably higher on the burned half of the barrier in September 2009 suggesting that not all the water in the soil profile will be removed before the fall rains begin. The results of this study are expected to contribute to a better understanding of barrier performance after major disturbances in a post-institutional control environment. Such an understanding is needed to enhance stakeholder acceptance regarding the long-term efficacy of engineered barriers. This study will also support improvements in the design of evapotranspiration (ET) and hybrid (ET + capacitive) barriers and the performance monitoring systems.« less

Reactivity of Ala-Gly dipeptide with β-turn secondary structure

NASA Astrophysics Data System (ADS)

Yu, Craig P.; Gerlei, Klára Z.; Rágyanszki, Anita; Jensen, Svend J. Knak; Viskolcz, Béla; Csizmadia, Imre G.

2018-01-01

The conformational space of β-turns of Ala-Gly dipeptide is analyzed theoretically using quantum mechanical methods. A number of potential minima are obtained and characterized. The potential energy surface suggests that β-turn conformers are susceptible to rapid radical formation, which leads to potential L and D epimerization. The calculated thermodynamics show that the radical mediated epimerization is possible and that the estimated barrier height for hydrogen abstraction on the Cα is the lowest for the Gly residue.

Experimental study of interfacial fracture toughness in a SiN(x)/PMMA barrier film.

PubMed

Kim, Yongjin; Bulusu, Anuradha; Giordano, Anthony J; Marder, Seth R; Dauskardt, Reinhold; Graham, Samuel

2012-12-01

Organic/inorganic multilayer barrier films play an important role in the semihermetic packaging of organic electronic devices. With the rise in use of flexible organic electronics, there exists the potential for mechanical failure due to the loss of adhesion/cohesion when exposed to harsh environmental operating conditions. Although barrier performance has been the predominant metric for evaluating these encapsulation films, interfacial adhesion between the organic/inorganic barrier films and factors that influence their mechanical strength and reliability has received little attention. In this work, we present the interfacial fracture toughness of a model organic/inorganic multilayer barrier (SiN(x)-PMMA). Data from four point bending (FPB) tests showed that adhesive failure occurred between the SiN(x) and PMMA, and that the adhesion increased from 4.8 to 10 J/m(2) by using a variety of chemical treatments to vary the surface energy at the interface. Moreover, the adhesion strength increased to 28 J/m(2) by creating strong covalent bonds at the interface. Overall, three factors were found to have the greatest impact on the interfacial fracture toughness which were (a) increasing the polar component of the surface energy, (b) creating strong covalent bonds at the organic/inorganic interface, and (c) by increasing the plastic zone size at the crack tip by increasing the thickness of the PMMA layer.

Layer Dependence and Light Tuning Surface Potential of 2D MoS2 on Various Substrates.

PubMed

Li, Feng; Qi, Junjie; Xu, Minxuan; Xiao, Jiankun; Xu, Yuliang; Zhang, Xiankun; Liu, Shuo; Zhang, Yue

2017-04-01

Here surface potential of chemical vapor deposition (CVD) grown 2D MoS 2 with various layers is reported, and the effect of adherent substrate and light illumination on surface potential of monolayer MoS 2 are investigated. The surface potential of MoS 2 on Si/SiO 2 substrate decreases from 4.93 to 4.84 eV with the increase in the number of layer from 1 to 4 or more. Especially, the surface potentials of monolayer MoS 2 are strongly dependent on its adherent substrate, which are determined to be 4.55, 4.88, 4.93, 5.10, and 5.50 eV on Ag, graphene, Si/SiO 2 , Au, and Pt substrates, respectively. Light irradiation is introduced to tuning the surface potential of monolayer MoS 2 , with the increase in light intensity, the surface potential of MoS 2 on Si/SiO 2 substrate decreases from 4.93 to 4.74 eV, while increases from 5.50 to 5.56 eV on Pt substrate. The I-V curves on vertical of monolayer MoS 2 /Pt heterojunction show the decrease in current with the increase of light intensity, and Schottky barrier height at MoS 2 /Pt junctions increases from 0.302 to 0.342 eV. The changed surface potential can be explained by trapped charges on surface, photoinduced carriers, charge transfer, and local electric field. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

On the Existence of Our Metals-Based Civilization: I. Phase Space Analysis

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

D.D. Macdonald

2005-06-22

The stability of the barrier layers of bilayer passive films that form on metal and alloy surfaces, when in contact with oxidizing aqueous environments, is explored within the framework of the Point Defect Model (PDM) using phase-space analysis (PSA), in which the rate of growth of the barrier layer into the metal, (dL{sup +}/dt), and the barrier layer dissolution rate, (dL{sup -}/dt), are plotted simultaneously against the barrier layer thickness. A point of intersection of dL{sup -}/dt with dL{sup +}/dt indicates the existence of a metastable barrier layer with a steady state thickness greater than zero. If dL{sup -}/dt >more » (dL{sup +}/dt){sub L=0}, where the latter quantity is the barrier layer growth rate at zero barrier layer thickness, the barrier layer cannot exist, even as a metastable phase, as the resulting thickness would be negative. Under these conditions, the surface is depassivated and the metal may corrode at a rapid rate. Depassivation may result from a change in the oxidation state of the cation upon dissolution of the barrier layer, such that the dissolution rate becomes highly potential dependent (as in the case of transpassive dissolution of chromium-containing alloys, for example, in which the reaction Cr{sub 2}O{sub 3} + 5H{sub 2}O {yields} 2CrO{sub 4}{sup 2-} + 10H {sup +} + 6e{sup -} results in the destruction of the film), or by the action of some solution-phase species (e.g., H{sup +}, Cl{sup -}) that enhances the dissolution rate to the extent that dL{sup -}/dt > (dL{sup +}/dt){sub L=0}. The boundaries for depassivation may be plotted in potential-pH space to develop Kinetic Stability Diagrams (KSDs) as alternatives to the classical Pourbaix diagrams for describing the conditions under which metals or alloys exist in contact with an aqueous environment. The advantage of KSDs is that they provide kinetic descriptions of the state of a metal or alloy that is in much closer concert with the kinetic phenomenon of passivity and depassivation than are equilibrium thermodynamic diagrams. Thus, KSDs more accurately account for the limits of passivity in highly acidic systems, where acid depassivation occurs, and at high potentials, where transition to the transpassive state may occur in some systems. In any event, phase space analysis of the PDM permits specification of the conditions over which reactive metals will remain passive in contact with aqueous systems and hence of the conditions that must be met for the existence of our metals-based civilization.« less

DFT study of CO2 conversion on InZr3(110) surface.

PubMed

Zhang, Minhua; Dou, Maobin; Yu, Yingzhe

2017-11-01

Methanol and methane synthesis from CO 2 hydrogenation on a InZr 3 (110) surface has been studied using density functional theory calculations. The CO 2 can be chemically adsorbed via a polydentated configuration and the H 2 molecule can dissociate to H atoms spontaneously. The methanol is primarily formed via the HCOO route instead of the RWGS route, due to its higher activation barrier of 1.35 eV for HCO hydrogenation. In the HCOO route, the adsorbed CO 2 consecutively hydrogenates to form HCOO, H 2 COO and the H 3 CO species. The H 3 COH is produced via the reaction of H 3 CO with a surface OH group. Furthermore, the C-O bonds of CO, CHO, CH 2 O and CH 3 O species prefer to dissociate to C, CH, CH 2 CH 3 and surface O species. Methane is formed via the hydrogenation of CH x (x = 0-3) monomers with the highest activation barrier of 1.19 eV for CH 3 hydrogenation, which is higher than that of the hydrogenation of H 2 COO in methanol synthesis via the HCOO route. The surface O species formed during CO 2 hydrogenation reacts with the adsorbed H 2 molecule to produce an OH group which reacts with a surface H atom to form H 2 O with an activation barrier of 1.13 eV, which then desorbs to the gas phase. Our calculated results indicate that the InZr 3 alloy is a potential candidate catalyst for CO 2 utilization and conversion.

The potential for use of steam at atmospheric pressure to decontaminate or sterilize parenteral filling lines incorporating barrier isolation technology.

PubMed

Lysfjord, J P; Haas, P J; Melgaard, H L; Pflug, I J

1995-01-01

Barrier isolators that enclose aseptic filling equipment are being proposed as a means of: (1) assisting in achieving a 10(-6) sterility assurance level (SAL) in the filling area and (2) minimizing the clean environment required in the manufacturing area. The need for operator and maintenance access to the interior of the barrier isolators presents difficulties in achieving the above goals. Several methods are available for reducing the microbial level inside the isolation barrier. If the objective is the decontamination of all surfaces inside the enclosure, saturated steam at atmospheric pressure can be used. If the objective is to sterilize the inside of the enclosure, saturated steam at atmospheric pressure with added H2O2 can be used. Test data and practical interface considerations relative to various methodologies will be reviewed.

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.

Poromechanical behaviour of a surficial geological barrier during fluid injection into an underlying poroelastic storage formation

PubMed Central

Selvadurai, A. P. S.; Kim, Jueun

2016-01-01

A competent low permeability and chemically inert geological barrier is an essential component of any strategy for the deep geological disposal of fluidized hazardous material and greenhouse gases. While the processes of injection are important to the assessment of the sequestration potential of the storage formation, the performance of the caprock is important to the containment potential, which can be compromised by the development of cracks and other defects that might be activated during and after injection. This paper presents a mathematical modelling approach that can be used to assess the state of stress in a surficial caprock during injection of a fluid to the interior of a poroelastic storage formation. Important information related to time-dependent evolution of the stress state and displacements of the surficial caprock with injection rates, and the stress state in the storage formation can be obtained from the theoretical developments. Most importantly, numerical results illustrate the influence of poromechanics on the development of adverse stress states in the geological barrier. The results obtained from the mathematical analysis illustrate that the surface heave increases as the hydraulic conductivity of the caprock decreases, whereas the surface heave decreases as the shear modulus of the caprock increases. The results also illustrate the influence of poromechanics on the development of adverse stress states in the caprock. PMID:27118906

Poromechanical behaviour of a surficial geological barrier during fluid injection into an underlying poroelastic storage formation.

PubMed

Selvadurai, A P S; Kim, Jueun

2016-03-01

A competent low permeability and chemically inert geological barrier is an essential component of any strategy for the deep geological disposal of fluidized hazardous material and greenhouse gases. While the processes of injection are important to the assessment of the sequestration potential of the storage formation, the performance of the caprock is important to the containment potential, which can be compromised by the development of cracks and other defects that might be activated during and after injection. This paper presents a mathematical modelling approach that can be used to assess the state of stress in a surficial caprock during injection of a fluid to the interior of a poroelastic storage formation. Important information related to time-dependent evolution of the stress state and displacements of the surficial caprock with injection rates, and the stress state in the storage formation can be obtained from the theoretical developments. Most importantly, numerical results illustrate the influence of poromechanics on the development of adverse stress states in the geological barrier. The results obtained from the mathematical analysis illustrate that the surface heave increases as the hydraulic conductivity of the caprock decreases, whereas the surface heave decreases as the shear modulus of the caprock increases. The results also illustrate the influence of poromechanics on the development of adverse stress states in the caprock.

Wetting transitions on patterned surfaces with diffuse interaction potentials embedded in a Young-Laplace formulation

NASA Astrophysics Data System (ADS)

Pashos, G.; Kokkoris, G.; Papathanasiou, A. G.; Boudouvis, A. G.

2016-01-01

The Minimum Energy Paths (MEPs) of wetting transitions on pillared surfaces are computed with the Young-Laplace equation, augmented with a pressure term that accounts for liquid-solid interactions. The interactions are smoothed over a short range from the solid phase, therefore facilitating the numerical solution of problems concerning wetting on complex surface patterns. The patterns may include abrupt geometric features, e.g., arrays of rectangular pillars, where the application of the unmodified Young-Laplace is not practical. The MEPs are obtained by coupling the augmented Young-Laplace with the modified string method from which the energy barriers of wetting transitions are eventually extracted. We demonstrate the method on a wetting transition that is associated with the breakdown of superhydrophobic behavior, i.e., the transition from the Cassie-Baxter state to the Wenzel state, taking place on a superhydrophobic pillared surface. The computed energy barriers quantify the resistance of the system to these transitions and therefore, they can be used to evaluate superhydrophobic performance or provide guidelines for optimal pattern design.

Ocean barrier layers' effect on tropical cyclone intensification.

PubMed

Balaguru, Karthik; Chang, Ping; Saravanan, R; Leung, L Ruby; Xu, Zhao; Li, Mingkui; Hsieh, Jen-Shan

2012-09-04

Improving a tropical cyclone's forecast and mitigating its destructive potential requires knowledge of various environmental factors that influence the cyclone's path and intensity. Herein, using a combination of observations and model simulations, we systematically demonstrate that tropical cyclone intensification is significantly affected by salinity-induced barrier layers, which are "quasi-permanent" features in the upper tropical oceans. When tropical cyclones pass over regions with barrier layers, the increased stratification and stability within the layer reduce storm-induced vertical mixing and sea surface temperature cooling. This causes an increase in enthalpy flux from the ocean to the atmosphere and, consequently, an intensification of tropical cyclones. On average, the tropical cyclone intensification rate is nearly 50% higher over regions with barrier layers, compared to regions without. Our finding, which underscores the importance of observing not only the upper-ocean thermal structure but also the salinity structure in deep tropical barrier layer regions, may be a key to more skillful predictions of tropical cyclone intensities through improved ocean state estimates and simulations of barrier layer processes. As the hydrological cycle responds to global warming, any associated changes in the barrier layer distribution must be considered in projecting future tropical cyclone activity.

Ocean barrier layers’ effect on tropical cyclone intensification

PubMed Central

Balaguru, Karthik; Chang, Ping; Saravanan, R.; Leung, L. Ruby; Xu, Zhao; Li, Mingkui; Hsieh, Jen-Shan

2012-01-01

Improving a tropical cyclone’s forecast and mitigating its destructive potential requires knowledge of various environmental factors that influence the cyclone’s path and intensity. Herein, using a combination of observations and model simulations, we systematically demonstrate that tropical cyclone intensification is significantly affected by salinity-induced barrier layers, which are “quasi-permanent” features in the upper tropical oceans. When tropical cyclones pass over regions with barrier layers, the increased stratification and stability within the layer reduce storm-induced vertical mixing and sea surface temperature cooling. This causes an increase in enthalpy flux from the ocean to the atmosphere and, consequently, an intensification of tropical cyclones. On average, the tropical cyclone intensification rate is nearly 50% higher over regions with barrier layers, compared to regions without. Our finding, which underscores the importance of observing not only the upper-ocean thermal structure but also the salinity structure in deep tropical barrier layer regions, may be a key to more skillful predictions of tropical cyclone intensities through improved ocean state estimates and simulations of barrier layer processes. As the hydrological cycle responds to global warming, any associated changes in the barrier layer distribution must be considered in projecting future tropical cyclone activity. PMID:22891298

Ocean Barrier Layers’ Effect on Tropical Cyclone Intensification

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

Balaguru, Karthik; Chang, P.; Saravanan, R.

2012-09-04

Improving a tropical cyclone's forecast and mitigating its destructive potential requires knowledge of various environmental factors that influence the cyclone's path and intensity. Herein, using a combination of observations and model simulations, we systematically demonstrate that tropical cyclone intensification is significantly affected by salinity-induced barrier layers, which are 'quasi-permanent' features in the upper tropical oceans. When tropical cyclones pass over regions with barrier layers, the increased stratification and stability within the layer reduce storm-induced vertical mixing and sea surface temperature cooling. This causes an increase in enthalpy flux from the ocean to the atmosphere and, consequently, an intensification of tropicalmore » cyclones. On average, the tropical cyclone intensification rate is nearly 50% higher over regions with barrier layers, compared to regions without. Our finding, which underscores the importance of observing not only the upper-ocean thermal structure but also the salinity structure in deep tropical barrier layer regions, may be a key to more skillful predictions of tropical cyclone intensities through improved ocean state estimates and simulations of barrier layer processes. As the hydrological cycle responds to global warming, any associated changes in the barrier layer distribution must be considered in projecting future tropical cyclone activity.« less

Early Stages of Interface Formation at Compound Semiconductor Surfaces Studied by Scanning Tunneling Microscopy

DTIC Science & Technology

1991-10-01

classical image potential in an ideal creasing gap separation, that is specific to the form of the metal- insulator -semiconductor (MIS) junction...with which one can precisely adjust s, and hence continuously vary the vacvuum barrier, is a potentially valuable tool for investigating this effect- By... insulator -semiconductor (MIS) junction similar to that shown in Fig. I diverge at the semiconductor-vacuum and vacuum-metal interfaces [7,81. These

Theoretical determination of the ionization potential and the electron affinity of organic semiconductors

NASA Astrophysics Data System (ADS)

Yanagisawa, Susumu

2017-11-01

Ionization potential and electron affinity of organic semicondutors are important quantities, which are relevant to charge injection barriers. The electrostatic and dynamical contributions to the polarization energies for the injected charges in pentacene polymorphs were investigated. While the dynamical polarization induced narrowing of the energy gap, the electrostatic effect shifted up or down the frontier energy levels, which is sensitive to the molecular orientation at the surface.

Theoretical and Experimental Studies in Reactive Scattering.

DTIC Science & Technology

1986-08-11

dynamics 3. Three-dimensional reaction dynamics 4. Anisotropic potentials for He + C02, OCS, CS2 .. 5. Production of a high intensity-high energy beam of...involving beams of He atoms, H atoms and metastable H molecules aimed at the determination of potential energy surfaces involving these systems. 2... energy of 0.3 ’, Kcal/mole below the top of the barrier, the reaction probability from ground S"t vibrational state reagent to ground vibrational

Collective phenomena in volume and surface barrier discharges

NASA Astrophysics Data System (ADS)

Kogelschatz, U.

2010-11-01

Barrier discharges are increasingly used as a cost-effective configuration to produce non-equilibrium plasmas at atmospheric pressure. This way, copious amounts of electrons, ions, free radicals and excited species can be generated without significant heating of the background gas. In most applications the barrier is made of dielectric material. Major applications utilizing mainly dielectric barriers include ozone generation, surface cleaning and modification, polymer and textile treatment, sterilization, pollution control, CO2 lasers, excimer lamps, plasma display panels (flat TV screens). More recent research efforts are devoted to biomedical applications and to plasma actuators for flow control. Sinusoidal feeding voltages at various frequencies as well as pulsed excitation schemes are used. Volume as well as surface barrier discharges can exist in the form of filamentary, regularly patterned or diffuse, laterally homogeneous discharges. The physical effects leading to collective phenomena in volume and surface barrier discharges are discussed in detail. Special attention is paid to self-organization of current filaments and pattern formation. Major similarities of the two types of barrier discharges are elaborated.

Far-infrared response of spherical quantum dots: Dielectric effects and the generalized Kohn's theorem

NASA Astrophysics Data System (ADS)

Movilla, J. L.; Planelles, J.

2007-05-01

The influence of the dielectric environment on the far-infrared (FIR) absorption spectra of two-electron spherical quantum dots is theoretically studied. Effective mass and envelope function approaches with realistic steplike confining potentials are used. Special attention is paid to absorptions that are induced by the electron-electron interaction. High confining barriers make the FIR absorption coefficients almost independent of the quantum dot dielectric environment. Low barrier heights and strong dielectric mismatches preserve the strong fundamental (Kohn) mode but yield the cancellation of excited absorptions, thus monitoring dielectrically induced phase transitions from volume to surface states.

Method and apparatus for measuring on-line failure of turbine thermal barrier coatings

DOEpatents

Zombo, Paul J.; Lemieux, Dennis; Diatzikis, Evangelos

2010-04-06

A method of remotely monitoring the radiant energy (6) emitted from a turbine component such as a turbine blade (1) having a low-reflective surface coating (3) which may be undergoing potential degradation is used to determine whether erosion, spallation, delamination, or the like, of the coating (3) is occurring.

A new ab initio potential energy surface of LiClH (1A') system and quantum dynamics calculation for Li + HCl (v = 0, j = 0-2) → LiCl + H reaction

NASA Astrophysics Data System (ADS)

Tan, Rui Shan; Zhai, Huan Chen; Yan, Wei; Gao, Feng; Lin, Shi Ying

2017-04-01

A new ab initio potential energy surface (PES) for the ground state of Li + HCl reactive system has been constructed by three-dimensional cubic spline interpolation of 36 654 ab initio points computed at the MRCI+Q/aug-cc-pV5Z level of theory. The title reaction is found to be exothermic by 5.63 kcal/mol (9 kcal/mol with zero point energy corrections), which is very close to the experimental data. The barrier height, which is 2.99 kcal/mol (0.93 kcal/mol for the vibrationally adiabatic barrier height), and the depth of van der Waals minimum located near the entrance channel are also in excellent agreement with the experimental findings. This study also identified two more van der Waals minima. The integral cross sections, rate constants, and their dependence on initial rotational states are calculated using an exact quantum wave packet method on the new PES. They are also in excellent agreement with the experimental measurements.

The Ehrlich-Schwoebel barrier on an oxide surface: a combined Monte-Carlo and in situ scanning tunneling microscopy approach.

PubMed

Gianfrancesco, Anthony G; Tselev, Alexander; Baddorf, Arthur P; Kalinin, Sergei V; Vasudevan, Rama K

2015-11-13

The controlled growth of epitaxial films of complex oxides requires an atomistic understanding of key parameters determining final film morphology, such as termination dependence on adatom diffusion, and height of the Ehrlich-Schwoebel (ES) barrier. Here, through an in situ scanning tunneling microscopy study of mixed-terminated La5/8Ca3/8MnO3 (LCMO) films, we image adatoms and observe pile-up at island edges. Image analysis allows determination of the population of adatoms at the edge of islands and fractions on A-site and B-site terminations. A simple Monte-Carlo model, simulating the random walk of adatoms on a sinusoidal potential landscape using Boltzmann statistics is used to reproduce the experimental data, and provides an estimate of the ES barrier as ∼0.18 ± 0.04 eV at T = 1023 K, similar to those of metal adatoms on metallic surfaces. These studies highlight the utility of in situ imaging, in combination with basic Monte-Carlo methods, in elucidating the factors which control the final film growth in complex oxides.

The Ehrlich-Schwoebel barrier on an oxide surface: a combined Monte-Carlo and in situ scanning tunneling microscopy approach

NASA Astrophysics Data System (ADS)

Gianfrancesco, Anthony G.; Tselev, Alexander; Baddorf, Arthur P.; Kalinin, Sergei V.; Vasudevan, Rama K.

2015-11-01

The controlled growth of epitaxial films of complex oxides requires an atomistic understanding of key parameters determining final film morphology, such as termination dependence on adatom diffusion, and height of the Ehrlich-Schwoebel (ES) barrier. Here, through an in situ scanning tunneling microscopy study of mixed-terminated La5/8Ca3/8MnO3 (LCMO) films, we image adatoms and observe pile-up at island edges. Image analysis allows determination of the population of adatoms at the edge of islands and fractions on A-site and B-site terminations. A simple Monte-Carlo model, simulating the random walk of adatoms on a sinusoidal potential landscape using Boltzmann statistics is used to reproduce the experimental data, and provides an estimate of the ES barrier as ˜0.18 ± 0.04 eV at T = 1023 K, similar to those of metal adatoms on metallic surfaces. These studies highlight the utility of in situ imaging, in combination with basic Monte-Carlo methods, in elucidating the factors which control the final film growth in complex oxides.

Our life is protected by the Earth's atmosphere and magnetic field: what aurora research tells us.

PubMed

Kamide, Y

2001-01-01

Our sun is an average middle-aged star. Without the sun, there would be no atmosphere, no water, and no life on the Earth. The sun is constantly changing, providing the Earth with energy through a complicated chain of processes that occur in space surrounding the Earth. This paper demonstrates that life on Earth is protected by two barriers, i.e., the atmosphere and the magnetic field, against otherwise menacing events in space. Because of these shielding effects, we, peacefully sitting on the Earth's surface, are not aware of a number of critical and potentially dangerous episodes that are taking place only 100 km above the Earth's surface. The aurora, which dances in the polar sky also because of the two barriers, is sending us a crucial hint about what is happening in space.

Controlled modulation of hard and soft X-ray induced tunneling currents utilizing coaxial metal-insulator-metal probe tips

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

Cummings, Marvin; Shirato, Nozomi; Kersell, Heath

Here, the effect of a local external electric field on the barrier potential of a tunneling gap is studied utilizing an emerging technique, synchrotron x-ray scanning tunneling microscopy. Here, we demonstrate that the shape of the potential barrier in the tunneling gap can be altered by a localized external electric field, generated by voltages placed on the metallic outer shield of a nanofabricated coaxial metal-insulator-metal tip, resulting in a controlled linear modulation of the tunneling current. Experiments at hard and soft x-ray synchrotron beamlines reveal that both the chemical contrast and magnetic contrast signals measured by the tip can bemore » drastically enhanced, resulting in improved local detection of chemistry and magnetization at the surface.« less

Controlled modulation of hard and soft X-ray induced tunneling currents utilizing coaxial metal-insulator-metal probe tips

DOE PAGES

Cummings, Marvin; Shirato, Nozomi; Kersell, Heath; ...

2017-01-05

Here, the effect of a local external electric field on the barrier potential of a tunneling gap is studied utilizing an emerging technique, synchrotron x-ray scanning tunneling microscopy. Here, we demonstrate that the shape of the potential barrier in the tunneling gap can be altered by a localized external electric field, generated by voltages placed on the metallic outer shield of a nanofabricated coaxial metal-insulator-metal tip, resulting in a controlled linear modulation of the tunneling current. Experiments at hard and soft x-ray synchrotron beamlines reveal that both the chemical contrast and magnetic contrast signals measured by the tip can bemore » drastically enhanced, resulting in improved local detection of chemistry and magnetization at the surface.« less

Robust Superhydrophobic Graphene-Based Composite Coatings with Self-Cleaning and Corrosion Barrier Properties.

PubMed

Nine, Md J; Cole, Martin A; Johnson, Lucas; Tran, Diana N H; Losic, Dusan

2015-12-30

Superhydrophobic surfaces for self-cleaning applications often suffer from mechanical instability and do not function well after abrasion/scratching. To address this problem, we present a method to prepare graphene-based superhydrophobic composite coatings with robust mechanical strength, self-cleaning, and barrier properties. A suspension has been formulated that contains a mixture of reduced graphene oxide (rGO) and diatomaceous earth (DE) modified with polydimethylsiloxane (PDMS) that can be applied on any surface using common coating methods such as spraying, brush painting, and dip coating. Inclusion of TiO2 nanoparticles to the formulation shows further increase in water contact angle (WCA) from 159 ± 2° to 170 ± 2° due to the structural improvement with hierarchical surface roughness. Mechanical stability and durability of the coatings has been achieved by using a commercial adhesive to bond the superhydrophobic "paint" to various substrates. Excellent retention of superhydrophobicity was observed even after sandpaper abrasion and crosscut scratching. A potentiodynamic polarization study revealed excellent corrosion resistance (96.78%) properties, and an acid was used to provide further insight into coating barrier properties. The ease of application and remarkable properties of this graphene-based composite coating show considerable potential for broad application as a self-cleaning and protective layer.

Theoretical Study of Tautomerization Reactions for the Ground and First Excited Electronic States of Adenine

NASA Technical Reports Server (NTRS)

Salter, Latasha M.; Chaban, Galina M.; Kwak, Dochan (Technical Monitor)

2002-01-01

Geometrical structures and energetic properties for different tautomers of adenine are calculated in this study, using multi-configurational wave functions. Both the ground and the lowest singlet excited state potential energy surfaces are studied. Four tautomeric forms are considered, and their energetic order is found to be different on the ground and the excited state potential energy surfaces. Minimum energy reaction paths are obtained for hydrogen atom transfer (tautomerization) reactions in the ground and the lowest excited electronic states. It is found that the barrier heights and the shapes of the reaction paths are different for the ground and the excited electronic states, suggesting that the probability of such tautomerization reaction is higher on the excited state potential energy surface. This tautomerization process should become possible in the presence of water or other polar solvent molecules and should play an important role in the photochemistry of adenine.

Hydrogen isotopic substitution of solid methylamine through atomic surface reactions at low temperatures: A potential contribution to the D/H ratio of methylamine in molecular clouds

NASA Astrophysics Data System (ADS)

Oba, Yasuhiro; Chigai, Takeshi; Osamura, Yoshihiro; Watanabe, Naoki; Kouchi, Akira

2014-01-01

We experimentally studied hydrogen (H)-deuterium (D) substitution reactions of solid methylamine (CH3NH2) under astrophysically relevant conditions. We also calculated the potential energy surface for the H-D substitution reactions of methylamine isotopologues using quantum chemical methods. Despite the relatively large energy barrier of more than 18 kJ mol-1, CH3NH2 reacted with D atoms to yield deuterated methylamines at 10 K, suggesting that the H-D substitution reaction proceeds through quantum tunneling. Deuterated methylamines reacted with H atoms as well. On the basis of present results, we propose that methylamine has potential for D enrichment through atomic surface reactions on interstellar grains at very low temperatures in molecular clouds. D enrichment would occur in particular in the methyl group of methylamine.

Test Plan to Assess Fire Effects on the Function of an Engineered Surface Barrier

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

Ward, Anderson L.; Berlin, Gregory T.; Cammann, Jerry W.

2008-09-29

Wildfire is a frequent perturbation in shrub steppe ecosystems, altering the flora, fauna, atmosphere, and soil of these systems. Research on the fire effects has focused mostly on natural ecosystems with essentially no attention on engineered systems like surface barriers. The scope of the project is to use a simulated wildfire to induce changes in an engineered surface barrier and document the effects on barrier performance. The main objective is to quantify the effects of burning and the resulting post-fire conditions on alterations in soil physical properties; hydrologic response, particularly the water balance; geochemical properties; and biological properties. A secondarymore » objective is to use the lessons learned to maximize fire protection in the design of long-term monitoring systems based on electronic sensors. A simulated wildfire will be initiated, controlled and monitored at the 200-BP-1 barrier in collaboration with the Hanford Fire Department during the fall of 2008. The north half of the barrier will be divided into nine 12 x 12 m plots, each of which will be randomly assigned a fuel load of 2 kg m-2 or 4 kg m-2. Each plot will be ignited around the perimeter and flames allowed to carry to the centre. Any remaining unburned vegetation will be manually burned off using a drip torch. Progress of the fire and its effects will be monitored using point measurements of thermal, hydrologic, and biotic variables. Three measures of fire intensity will be used to characterize fire behavior: (1) flame height, (2) the maximum temperature at three vertical profile levels, and (3) total duration of elevated temperature at these levels. Pre-burn plant information, including species diversity, plant height, and canopy diameter will be measured on shrubs from the plots to be burned and from control plots at the McGee ranch. General assessments of shrub survival, recovery, and recruitment will be made after the fire. Near-surface soil samples will be collected pre- and post-burn to determine changes in the gravel content of the surface layer so as to quantify inflationary or deflationary responses to fire and to reveal the ability of the surface to resist post-fire erosive stresses. Measures of bulk density, water repellency, water retention, and hydraulic conductivity will be used to characterize changes in infiltration rates and water storage capacity following the fire. Samples will also be analyzed to quantify geochemical changes including changes in soil pH, cation exchange capacity, specific surface area, and the concentration of macro nutrients (e.g. N, P, K) and other elements such as Na, Mg, Ca, that are critical to the post-fire recovery revegetation. Soil CO2 emissions will be measured monthly for one year following the burn to document post-fire stimulation of carbon turnover and soil biogenic emissions. Surface and subsurface temperature measurements at and near monitoring installations will be used to document fire effects on electronic equipment. The results of this study will be used to bridge the gaps in knowledge on the effects of fire on engineered ecosystems (e.g. surface barriers), particularly the hydrologic and biotic characteristics that govern the water and energy balance. These results will also support the development of practical fire management techniques for barriers that are compatible with wildfire suppression strategies. Furthermore, lessons learned will be use to develop installation strategies needed to protect electronic monitoring equipment from the intense heat of fire and the potential damaging effects of smoke and fire extinguishing agents. Such information is needed to better understand long-term barrier performance under extreme conditions, especially if site maintenance and operational funding is lost for activities such as barrier revegetation.« less

Phase space barriers and dividing surfaces in the absence of critical points of the potential energy: Application to roaming in ozone

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

Mauguière, Frédéric A. L., E-mail: frederic.mauguiere@bristol.ac.uk; Collins, Peter, E-mail: peter.collins@bristol.ac.uk; Wiggins, Stephen, E-mail: stephen.wiggins@mac.com

We examine the phase space structures that govern reaction dynamics in the absence of critical points on the potential energy surface. We show that in the vicinity of hyperbolic invariant tori, it is possible to define phase space dividing surfaces that are analogous to the dividing surfaces governing transition from reactants to products near a critical point of the potential energy surface. We investigate the problem of capture of an atom by a diatomic molecule and show that a normally hyperbolic invariant manifold exists at large atom-diatom distances, away from any critical points on the potential. This normally hyperbolic invariantmore » manifold is the anchor for the construction of a dividing surface in phase space, which defines the outer or loose transition state governing capture dynamics. We present an algorithm for sampling an approximate capture dividing surface, and apply our methods to the recombination of the ozone molecule. We treat both 2 and 3 degrees of freedom models with zero total angular momentum. We have located the normally hyperbolic invariant manifold from which the orbiting (outer) transition state is constructed. This forms the basis for our analysis of trajectories for ozone in general, but with particular emphasis on the roaming trajectories.« less

Fission barriers at the end of the chart of the nuclides

DOE PAGES

Möller, Peter; Sierk, Arnold J.; Ichikawa, Takatoshi; ...

2015-02-12

We present calculated fission-barrier heights for 5239 nuclides for all nuclei between the proton and neutron drip lines with 171 ≤ A ≤ 330. The barriers are calculated in the macroscopic-microscopic finite-range liquid-drop (FRLDM) with a 2002 set of macroscopic-model parameters. The saddle-point energies are determined from potential-energy surfaces based on more than five million different shapes, defined by five deformation parameters in the three-quadratic-surface shape parametrization: elongation, neck diameter, left-fragment spheroidal deformation, right-fragment spheroidal deformation, and nascent-fragment mass asymmetry. The energy of the ground state is determined by calculating the lowest-energy configuration in both the Nilsson perturbed-spheroid (ϵ) andmore » the spherical-harmonic (β) parametrizations, including axially asymmetric deformations. The lower of the two results (correcting for zero-point motion) is defined as the ground-state energy. The effect of axial asymmetry on the inner barrier peak is calculated in the (ϵ,γ) parametrization. We have earlier benchmarked our calculated barrier heights to experimentally extracted barrier parameters and found average agreement to about one MeV for known data across the nuclear chart. Here we do additional benchmarks and investigate the qualitative and, when possible, quantitative agreement and/or consistency with data on β-delayed fission, isotope generation along prompt-neutron-capture chains in nuclear-weapons tests, and superheavy-element stability. In addition these studies all indicate that the model is realistic at considerable distances in Z and N from the region of nuclei where its parameters were determined.« less

Reconfiguration of a smart surface using heteroclinic connections

PubMed Central

McInnes, Colin R.; Xu, Ming

2017-01-01

A reconfigurable smart surface with multiple equilibria is presented, modelled using discrete point masses and linear springs with geometric nonlinearity. An energy-efficient reconfiguration scheme is then investigated to connect equal-energy unstable (but actively controlled) equilibria. In principle, zero net energy input is required to transition the surface between these unstable states, compared to transitions between stable equilibria across a potential barrier. These transitions between equal-energy unstable states, therefore, form heteroclinic connections in the phase space of the problem. Moreover, the smart surface model developed can be considered as a unit module for a range of applications, including modules which can aggregate together to form larger distributed smart surface systems. PMID:28265191

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.

Evaluation of biofilm performance as a protective barrier against biocorrosion using an enzyme electrode.

PubMed

Soleimani, S; Ormeci, B; Isgor, O B; Papavinasam, S

2011-01-01

Sulfide is known to be an important factor in microbiologically influenced corrosion (MIC) of metals and concrete deterioration in wastewater treatment structures and sewer pipelines. A sulfide biosensor was used to determine the effectiveness of Escherichia coli DH5 alpha biofilm as a protective barrier against MIC. The biofilm was shown to be effective in protecting surfaces from sulfide and helping to reduce MIC using amperometric measurements. The results also indicated that the growth conditions of E. coli DH5 alpha may have an impact on the performance of the biofilm as a sulfide barrier. The simple method provided in this work enables the comparison of several microbial biofilms and selection of the ones with potential to prevent MIC in a relatively short time.

Production of atmospheric pressure diffuse nanosecond pulsed dielectric barrier discharge using the array needles-plate electrode in air

NASA Astrophysics Data System (ADS)

Yang, De-zheng; Wang, Wen-chun; Jia, Li; Nie, Dong-xia; Shi, Heng-chao

2011-04-01

In this paper, a bidirectional high pulse voltage with 20 ns rising time is employed to generate an atmospheric pressure diffuse dielectric barrier discharge using the array needles-plate electrode configuration. Both double needle and multiple needle electrode configurations nanosecond pulsed dielectric barrier discharges are investigated. It is found that a diffuse discharge plasma with low gas temperature can be obtained, and the plasma volume increases with the increase of the pulse peak voltage, but remains almost constant with the increase of the pulse repetition rate. In addition to showing the potential application on a topographically nonuniform surface treatment of the discharge, the multiple needle-plate electrode configuration with different needle-plate electrode gaps are also employed to generate diffuse discharge plasma.

Constructing a multidimensional free energy surface like a spider weaving a web.

PubMed

Chen, Changjun

2017-10-15

Complete free energy surface in the collective variable space provides important information of the reaction mechanisms of the molecules. But, sufficient sampling in the collective variable space is not easy. The space expands quickly with the number of the collective variables. To solve the problem, many methods utilize artificial biasing potentials to flatten out the original free energy surface of the molecule in the simulation. Their performances are sensitive to the definitions of the biasing potentials. Fast-growing biasing potential accelerates the sampling speed but decreases the accuracy of the free energy result. Slow-growing biasing potential gives an optimized result but needs more simulation time. In this article, we propose an alternative method. It adds the biasing potential to a representative point of the molecule in the collective variable space to improve the conformational sampling. And the free energy surface is calculated from the free energy gradient in the constrained simulation, not given by the negative of the biasing potential as previous methods. So the presented method does not require the biasing potential to remove all the barriers and basins on the free energy surface exactly. Practical applications show that the method in this work is able to produce the accurate free energy surfaces for different molecules in a short time period. The free energy errors are small in the cases of various biasing potentials. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Chemical solution deposition method of fabricating highly aligned MgO templates

DOEpatents

Paranthaman, Mariappan Parans [Knoxville, TN; Sathyamurthy, Srivatsan [Knoxville, TN; Aytug, Tolga [Knoxville, TN; Arendt, Paul N [Los Alamos, NM; Stan, Liliana [Los Alamos, NM; Foltyn, Stephen R [Los Alamos, NM

2012-01-03

A superconducting article includes a substrate having an untextured metal surface; an untextured barrier layer of La.sub.2Zr.sub.2O.sub.7 or Gd.sub.2Zr.sub.2O.sub.7 supported by and in contact with the surface of the substrate; a biaxially textured buffer layer supported by the untextured barrier layer; and a biaxially textured superconducting layer supported by the biaxially textured buffer layer. Moreover, a method of forming a buffer layer on a metal substrate includes the steps of: providing a substrate having an untextured metal surface; coating the surface of the substrate with a barrier layer precursor; converting the precursor to an untextured barrier layer; and depositing a biaxially textured buffer layer above and supported by the untextured barrier layer.

High-Sensitive Two-Layer Photoresistors Based on p-Cd x Hg1- x Te with a Converted Near-Surface Layer

NASA Astrophysics Data System (ADS)

Ismailov, N. D.; Talipov, N. Kh.; Voitsekhovskii, A. V.

2018-04-01

The results of an experimental study of photoelectric characteristics of two-layer photoresistors based on p-Cd x Hg1- x Te (x = 0.24-0.28) with a thin near-surface layer of n-type obtained by treatment in atmospheric gas plasma are presented. It is shown that the presence of a potential barrier between the p- and n-regions causes high photosensitivity and speed of operation of such photoresistors at T = 77 K

High-Sensitive Two-Layer Photoresistors Based on p-Cd x Hg1-x Te with a Converted Near-Surface Layer

NASA Astrophysics Data System (ADS)

Ismailov, N. D.; Talipov, N. Kh.; Voitsekhovskii, A. V.

2018-04-01

The results of an experimental study of photoelectric characteristics of two-layer photoresistors based on p-Cd x Hg1-x Te (x = 0.24-0.28) with a thin near-surface layer of n-type obtained by treatment in atmospheric gas plasma are presented. It is shown that the presence of a potential barrier between the p- and n-regions causes high photosensitivity and speed of operation of such photoresistors at T = 77 K

Spatial nonuniformity of current flow and its consideration in determination of characteristics of surface illuminated InAsSbP/InAs-based photodiodes

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

Zotova, N. V.; Karandashev, S. A.; Matveev, B. A., E-mail: Bmat@iropt3.ioffe.ru

Current-voltage characteristics of surface-irradiated photodiodes based on the InAsSbP/InAs structures are analyzed using experimental data on the distribution of electroluminescence intensity over the diode surface and taking into account thickening the current streamlines near the contacts. The influence of the potential barrier associated with the N-InAsSbP/n-InAs junction in double heterostructures on the differential resistance of diodes under zero bias, the value of the reverse current, and spreading of the forward current is discussed.

A scanning probe mounted on a field-effect transistor: Characterization of ion damage in Si.

PubMed

Shin, Kumjae; Lee, Hoontaek; Sung, Min; Lee, Sang Hoon; Shin, Hyunjung; Moon, Wonkyu

2017-10-01

We have examined the capabilities of a Tip-On-Gate of Field-Effect Transistor (ToGoFET) probe for characterization of FIB-induced damage in Si surface. A ToGoFET probe is the SPM probe which the Field Effect Transistor(FET) is embedded at the end of a cantilever and a Pt tip was mounted at the gate of FET. The ToGoFET probe can detect the surface electrical properties by measuring source-drain current directly modulated by the charge on the tip. In this study, a Si specimen whose surface was processed with Ga+ ion beam was prepared. Irradiation and implantation with Ga+ ions induce highly localized modifications to the contact potential. The FET embedded on ToGoFET probe detected the surface electric field profile generated by schottky contact between the Pt tip and the sample surface. Experimentally, it was shown that significant differences of electric field due to the contact potential barrier in differently processed specimens were observed using ToGOFET probe. This result shows the potential that the local contact potential difference can be measured by simple working principle with high sensitivity. Copyright © 2017 Elsevier Ltd. All rights reserved.

200-BP-1 Prototype Hanford Barrier Annual Monitoring Report for Fiscal Year 2004

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

Ward, Andy L.; Linville, Jenifer K.; Keller, Jason M.

2005-01-03

In FY 2004, monitoring of the prototype Hanford barrier focused on barrier stability, vegetative cover, evidence of plant and animal intrusion, and the main components of the water balance. Monitored water-balance components included precipitation, runoff, storage, drainage, and deep percolation. Precipitation in FY 2004 was 26 percent less than in FY 2003 but was still higher than normal. The seasonal distribution in precipitation was also different from the previous year with a 43 percent reduction in spring precipitation and a 46 percent increase in summer precipitation. The cumulative amount of water received from October 1994, through September 2004, was 2,559.58more » mm on the northern half of the barrier, which is the formerly irrigated treatment, and 1,886.71 mm on the southern non-irrigated treatments. Water storage continued to show a cyclic pattern, increasing in the winter and declining in the spring and summer to a lower limit of about 100 mm in response to evapotranspiration. The 600-mm design storage has never been exceeded. Total drainage from the soil-covered plots range from 2.9E-4 mm to 0.22 mm or 0.003 6 0.004 percent of precipitation. Side-slope drainage was much higher at 20.9 6 2.3 percent of precipitation from the gravel and 18.6 6 5.1 percent from the riprap. There was no runoff from the barrier, but runoff from the BY tank farm following a thunderstorm in May eroded a 45-inch-deep channel into the structural fill at the toe of the riprap slope. Above-asphalt and below-asphalt moisture measurements show no evidence of deep percolation of water. Topographic surveys were conducted on the barrier surface, including the two settlement gauges and 12 creep gauges on the riprap slope using aerial photogrammetry (AP) and a global positioning system (GPS). Comparing the aerial photogrammetry (AP) and global positioning system (GPS) surveys with the traditional survey shows the barrier and side slopes to be stable. Both AP and GPS show potential for considerable cost savings without any loss in accuracy. A relatively high coverage of native plants still persists after the initial revegetation in 1994. The formerly irrigated treatments continue to show greater cover of grasses and litter than the non-irrigated treatments. On the formerly irrigated treatments, the mean cover class was 25 to 50 percent for both grasses and shrubs. On the non-irrigated treatments, the mean cover class was 5 to 25 percent from grasses and 25 to 50 percent for shrubs. Species diversity of the vegetative community appears to have stabilized over the past several years. In addition to 12 of 17 species present in 2003 being present in 2004, two additional species were encountered. Sagebrush continues to flourish with shrubs along the perimeter showing higher biomass yield than the interior shrubs. There is evidence of sagebrush seedlings recruitment but not of rabbitbrush; the presence of gray rabbitbrush appears is declining as the barrier surface continues to stabilize. Use of the barrier surface by insects and small mammals is also evident. Small mammal burrowing on the barrier surface has become more prevalent in recent years, suggesting that the restored barrier surface is beginning to function as a recovering ecosystem. Small-mammal burrowing on the top and sides of the barrier is most prevalent on the finer-grained and disturbed soils while active ant mounds were observed on the northern and western slopes.« less

Collective Phenomena In Volume And Surface Barrier Discharges

NASA Astrophysics Data System (ADS)

Kogelschatz, U.

2010-07-01

Barrier discharges are increasingly used as a cost-effective means to produce non-equilibrium plasmas at atmospheric pressure. This way, copious amounts of electrons, ions, free radicals and excited species can be generated without appreciable gas heating. In most applications the barrier is made of dielectric material. In laboratory experiments also the use of resistive, ferroelectric and semiconducting materials has been investigated, also porous ceramic layers and dielectric barriers with controlled surface conductivity. Major applications utilizing mainly dielectric barriers include ozone generation, surface cleaning and modification, polymer and textile treatment, sterilization, pollution control, CO2 lasers, excimer lamps, plasma display panels (flat TV screens). More recent research efforts are also devoted to biomedical applications and to plasma actuators for flow control. Sinu- soidal feeding voltages at various frequencies as well as pulsed excitation schemes are used. Volume as well as surface barrier discharges can exist in the form of filamentary, regularly patterned or laterally homogeneous discharges. Reviews of the subject and the older literature on barrier discharges were published by Kogelschatz (2002, 2003), by Wagner et al. (2003) and by Fridman et al. (2005). A detailed discussion of various properties of barrier discharges can also be found in the recent book "Non-Equilibrium Air Plasmas at Atmospheric Pressure" by Becker et al. (2005). The physical effects leading to collective phenomena in volume and surface barrier discharges will be discussed in detail. Special attention will be given to self-organization of current filaments. Main similarities and differences of the two types of barrier discharges will be elaborated.

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

Möller, Peter; Sierk, Arnold J.; Ichikawa, Takatoshi

We present calculated fission-barrier heights for 5239 nuclides for all nuclei between the proton and neutron drip lines with 171 ≤ A ≤ 330. The barriers are calculated in the macroscopic-microscopic finite-range liquid-drop (FRLDM) with a 2002 set of macroscopic-model parameters. The saddle-point energies are determined from potential-energy surfaces based on more than five million different shapes, defined by five deformation parameters in the three-quadratic-surface shape parametrization: elongation, neck diameter, left-fragment spheroidal deformation, right-fragment spheroidal deformation, and nascent-fragment mass asymmetry. The energy of the ground state is determined by calculating the lowest-energy configuration in both the Nilsson perturbed-spheroid (ϵ) andmore » the spherical-harmonic (β) parametrizations, including axially asymmetric deformations. The lower of the two results (correcting for zero-point motion) is defined as the ground-state energy. The effect of axial asymmetry on the inner barrier peak is calculated in the (ϵ,γ) parametrization. We have earlier benchmarked our calculated barrier heights to experimentally extracted barrier parameters and found average agreement to about one MeV for known data across the nuclear chart. Here we do additional benchmarks and investigate the qualitative and, when possible, quantitative agreement and/or consistency with data on β-delayed fission, isotope generation along prompt-neutron-capture chains in nuclear-weapons tests, and superheavy-element stability. In addition these studies all indicate that the model is realistic at considerable distances in Z and N from the region of nuclei where its parameters were determined.« less

Disentangle the Causes of the Road Barrier Effect in Small Mammals through Genetic Patterns.

PubMed

Ascensão, Fernando; Mata, Cristina; Malo, Juan E; Ruiz-Capillas, Pablo; Silva, Catarina; Silva, André P; Santos-Reis, Margarida; Fernandes, Carlos

2016-01-01

Road barrier effect is among the foremost negative impacts of roads on wildlife. Knowledge of the factors responsible for the road barrier effect is crucial to understand and predict species' responses to roads, and to improve mitigation measures in the context of management and conservation. We built a set of hypothesis aiming to infer the most probable cause of road barrier effect (traffic effect or road surface avoidance), while controlling for the potentially confounding effects road width, traffic volume and road age. The wood mouse Apodemus sylvaticus was used as a model species of small and forest-dwelling mammals, which are more likely to be affected by gaps in cover such as those resulting from road construction. We confront genetic patterns from opposite and same roadsides from samples of three highways and used computer simulations to infer migration rates between opposite roadsides. Genetic patterns from 302 samples (ca. 100 per highway) suggest that the highway barrier effect for wood mouse is due to road surface avoidance. However, from the simulations we estimated a migration rate of about 5% between opposite roadsides, indicating that some limited gene flow across highways does occur. To reduce highway impact on population genetic diversity and structure, possible mitigation measures could include retrofitting of culverts and underpasses to increase their attractiveness and facilitate their use by wood mice and other species, and setting aside roadside strips without vegetation removal to facilitate establishment and dispersal of small mammals.

Disentangle the Causes of the Road Barrier Effect in Small Mammals through Genetic Patterns

PubMed Central

Ascensão, Fernando; Mata, Cristina; Malo, Juan E.; Ruiz-Capillas, Pablo; Silva, Catarina; Silva, André P.; Santos-Reis, Margarida; Fernandes, Carlos

2016-01-01

Road barrier effect is among the foremost negative impacts of roads on wildlife. Knowledge of the factors responsible for the road barrier effect is crucial to understand and predict species’ responses to roads, and to improve mitigation measures in the context of management and conservation. We built a set of hypothesis aiming to infer the most probable cause of road barrier effect (traffic effect or road surface avoidance), while controlling for the potentially confounding effects road width, traffic volume and road age. The wood mouse Apodemus sylvaticus was used as a model species of small and forest-dwelling mammals, which are more likely to be affected by gaps in cover such as those resulting from road construction. We confront genetic patterns from opposite and same roadsides from samples of three highways and used computer simulations to infer migration rates between opposite roadsides. Genetic patterns from 302 samples (ca. 100 per highway) suggest that the highway barrier effect for wood mouse is due to road surface avoidance. However, from the simulations we estimated a migration rate of about 5% between opposite roadsides, indicating that some limited gene flow across highways does occur. To reduce highway impact on population genetic diversity and structure, possible mitigation measures could include retrofitting of culverts and underpasses to increase their attractiveness and facilitate their use by wood mice and other species, and setting aside roadside strips without vegetation removal to facilitate establishment and dispersal of small mammals. PMID:26978779

In Situ Experiments To Reveal the Role of Surface Feature Sidewalls in the Cassie–Wenzel Transition

PubMed Central

2014-01-01

Waterproof and self-cleaning surfaces continue to attract much attention as they can be instrumental in various different technologies. Such surfaces are typically rough, allowing liquids to contact only the outermost tops of their asperities, with air being entrapped underneath. The formed solid–liquid–air interface is metastable and, hence, can be forced into a completely wetted solid surface. A detailed understanding of the wetting barrier and the dynamics of this transition is critically important for the practical use of the related surfaces. Toward this aim, wetting transitions were studied in situ at a set of patterned perfluoropolyether dimethacrylate (PFPEdma) polymer surfaces exhibiting surface features with different types of sidewall profiles. PFPEdma is intrinsically hydrophobic and exhibits a refractive index very similar to water. Upon immersion of the patterned surfaces into water, incident light was differently scattered at the solid–liquid–air and solid–liquid interface, which allows for distinguishing between both wetting states by dark-field microscopy. The wetting transition observed with this methodology was found to be determined by the sidewall profiles of the patterned structures. Partial recovery of the wetting was demonstrated to be induced by abrupt and continuous pressure reductions. A theoretical model based on Laplace’s law was developed and applied, allowing for the analytical calculation of the transition barrier and the potential to revert the wetting upon pressure reduction. PMID:25496232

Technological capabilities of surface layers formation on implant made of Ti-6Al-4V ELI alloy.

PubMed

Kiel-Jamrozik, Marta; Szewczenko, Janusz; Basiaga, Marcin; Nowińska, Katarzyna

2015-01-01

The aim of the presented research was to find a combination of surface modification methods of implants made of the Ti-6Al-4V ELI alloy, that lead to formation of effective barrier for metallic ions that may infiltrate into solution. To this end, the following tests were carried out: roughness measurement, the voltamperometric tests (potentiodynamic and potentiostatic), and the ion infiltration test. The electropolishing process resulted in the lowering of surface roughness in comparison with mechanical treatment of the surface layer. The anodization process and steam sterilization increased corrosion resistance regardless of the mechanical treatment or electropolishing. The crevice corrosion tests revealed that independent of the modification method applied, the Ti-6Al-4V ELI alloy has excellent crevice corrosion resistance. The smallest quantity of ions infiltrated to the solution was observed for surface modification consisting in the mechanical treatment and anodization with the potential of 97 V. Electric parameters deter- mined during studies were the basis for effectiveness estimation of particular surface treatment methods. The research has shown that the anodization process significantly influences the pitting corrosion resistance of the Ti-6Al-4V ELI alloy independent of the previous surface treatment methods (mechanical and electrochemical). The surface layer after such modification is a protective barrier for metallic ions infiltrated to solution and protects titanium alloy against corrosive environment influence.

Energy of the Isolated Metastable Iron-Nickel FCC Nanocluster with a Carbon Atom in the Tetragonal Interstice.

PubMed

Bondarenko, Natalya V; Nedolya, Anatoliy V

2017-12-01

The energy of the isolated iron-nickel nanocluster was calculated by molecular mechanics method using Lennard-Jones potential. The cluster included a carbon atom that drifted from an inside octahedral interstice to a tetrahedral interstice in [Formula: see text] direction and after that in <222> direction to the surface. In addition, one of 14 iron atoms was replaced by a nickel atom, the position of which was changing during simulation.The energy of the nanocluster was estimated at the different interatomic distances. As a result of simulation, the optimal interatomic distances of Fe-Ni-C nanocluster was chosen for the simulation, in which height of the potential barrier was maximal and face-centered cubic (FCC) nanocluster was the most stable.It is shown that there were three main positions of a nickel atom that significantly affected nanocluster's energy.The calculation results indicated that position of the carbon atom in the octahedral interstice was more energetically favorable than tetrahedral interstice in the case of FCC nanocluster. On the other side, the potential barrier was smaller in the direction [Formula: see text] than in the direction <022>.This indicates that there are two ways for carbon atom to drift to the surface of the nanocluster.

Deliquescence and efflorescence of small particles.

PubMed

McGraw, Robert; Lewis, Ernie R

2009-11-21

We examine size-dependent deliquescence/efflorescence phase transformation for particles down to several nanometers in size. Thermodynamic properties of inorganic salt particles, coated with aqueous solution layers of varying thickness and surrounded by vapor, are analyzed. A thin layer criterion (TLC) is introduced to define a limiting deliquescence relative humidity (RH(D)) for small particles. This requires: (1) equality of chemical potentials between salt in an undissolved core, and thin adsorbed solution layer, and (2) equality of chemical potentials between water in the thin layer and vapor phase. The usual bulk deliquescence conditions are recovered in the limit of large dry particle size. Nanosize particles are found to deliquesce at relative humidity just below the RH(D) on crossing a nucleation barrier, located at a critical solution layer thickness. This barrier vanishes precisely at the RH(D) defined by the TLC. Concepts and methods from nucleation theory including the kinetic potential, self-consistent nucleation theory, nucleation theorems, and the Gibbs dividing surface provide theoretical foundation and point to unifying features of small particle deliquescence/efflorescence processes. These include common thermodynamic area constructions, useful for interpretation of small particle water uptake measurements, and a common free-energy surface, with constant RH cross sections describing deliquescence and efflorescence related through the nucleation theorem.

Cellular interactions and biomechanical properties of a unique vascular-derived scaffold for periodontal tissue regeneration.

PubMed

Goktas, Selda; Pierre, Nicolas; Abe, Koki; Dmytryk, John; McFetridge, Peter S

2010-03-01

These investigations describe the development of a novel ex vivo three-dimensional scaffold derived from the human umbilical vein (HUV), and its potential as a regenerative matrix for tissue regeneration. Unique properties associated with the vascular wall have shown potential to function as a surgical barrier for guided tissue regeneration, particularly with the regeneration of periodontal tissues. HUV was isolated from umbilical cords using a semiautomated machining technology, decellularized using 1% sodium dodecyl sulfate, and then opened longitudinally to form tissue sheets. Uniaxial tensile testing, stress relaxation, and suture retention tests were performed on the acellular matrix to evaluate the HUV's biomechanical properties, followed by an evaluation of cellular interactions by seeding human gingival fibroblasts to assess adhesion, metabolic function, and proliferation on the scaffold. The scaffold's biomechanical properties were shown to display anisotropic behavior, which is attributed to the ex vivo material's composite structure. Detailed results indicated that the ultimate tensile strength of the longitudinal strips was significantly higher than that of the circumferential strips (p < 0.001). The HUV also exhibited significantly higher stress relaxation response in the longitudinal direction than in the circumferential orientation (p < 0.05). The ablumenal and lumenal surfaces of the material were also shown to differentially influence cell proliferation and metabolic activity, with both cellular functions significantly increased on the ablumenal surface (p < 0.05). Human gingival fibroblast migration into the scaffold was also influenced by the organization of extracellular matrix components, where the lumenal surface inhibits cell migration, acting as a barrier, while the ablumenal surface, which is proposed to interface with the wound site, promotes cellular invasion. These results show the HUV bioscaffold to be a promising naturally derived surgical barrier that may function well as a resorbable guided tissue regeneration membrane as well as in other clinical applications.

A radio frequency coaxial feedthrough

DOEpatents

Owens, T.L.

1987-12-07

An improved radio frequency coaxial transmission line vacuum feedthrough is provided based on the use of a half-wavelength annular dielectric pressure barrier disk, or multiple disks comprising an effective half wavelength structure to eliminate reflection from the barrier surfaces. Gas-tight seals are formed about the outer and inner diameter surfaces of the barrier disk using a sealing technique which generates radial forces sufficient to form seals by forcing the conductor walls against the surfaces of the barrier disks in a manner which does not deform the radii of the inner and outer conductors, thereby preventing enhancement of the electric field at the barrier faces which limits the voltage and power handling capabilities of a feedthrough.

Radio frequency coaxial feedthrough

DOEpatents

Owens, Thomas L.

1989-01-17

An improved radio frequency coaxial transmission line vacuum feed-through provided based on the use of a half-wavelength annular dielectric pressure barrier disk, or multiple disks comprising an effective half wavelength structure to eliminate reflections from the barrier surfaces. Gas-tight seals are formed about the outer and inner diameter surfaces of the barrier disk using a sealing technique which generates radial forces sufficient to form seals by forcing the conductor walls against the surfaces of the barrier disks in a manner which does not deform the radii of the inner and outer conductors, thereby preventing enhancement of the electric field at the barrier faces which limits voltage and power handling capabilities of a feedthrough.

Biomimetic thermal barrier coating in jet engine to resist volcanic ash deposition

NASA Astrophysics Data System (ADS)

Song, Wenjia; Major, Zsuzsanna; Schulz, Uwe; Muth, Tobias; Lavallée, Yan; Hess, Kai-Uwe; Dingwell, Donald B.

2017-04-01

The threat of volcanic ash to aviation safety is attracting extensive attention when several commercial jet aircraft were damaged after flying through volcanic ash clouds from the May 1980 eruptions of Mount St. Helen in Washington, U.S. and especially after the air traffic disruption in 2010 Eyjafjallajökull eruption. A major hazard presented by volcanic ash to aircraft is linked to the wetting and spreading of molten ash droplets on engine component surfaces. Due to the fact ash has a lower melting point, around 1100 °C, than the gas temperature in the hot section (between 1400 to 2000 °C), this cause the ash to melt and potentially stick to the internal components (e.g., combustor and turbine blades), this cause the ash to melt and potentially stick to the internal components of the engine creating, substantial damage or even engine failure after ingestion. Here, inspiring form the natural surface of lotus leaf (exhibiting extreme water repellency, known as 'lotus effect'), we firstly create the multifunctional surface thermal barrier coatings (TBCs) by producing a hierarchical structure with femtosecond laser pulses. In detail, we investigate the effect of one of primary femtosecond laser irradiation process parameter (scanning speed) on the hydrophobicity of water droplets onto the two kinds of TBCs fabricated by electron-beam physical vapor deposition (EB-PVD) and air plasma spray (APS), respectively as well as their corresponding to morphology. It is found that, comparison with the original surface (without femtosecond laser ablation), all of the irradiated samples demonstrate more significant hydrophobic properties due to nanostructuring. On the basis of these preliminary room-temperature results, the wettability of volcanic ash droplets will be analysed at the high temperature to constrain the potential impact of volcanic ash on the jet engines.

Noninvasive ocular drug delivery: potential transcorneal and other alternative delivery routes for therapeutic molecules in glaucoma.

PubMed

Foldvari, Marianna

2014-01-01

Drug delivery to the eye is made difficult by multiple barriers (such as the tear film, cornea, and vitreous) between the surface of the eye and the treatment site. These barriers are difficult to surmount for the purposes of drug delivery without causing toxicity. Using nanotechnology tools to control, manipulate, and study delivery systems, new approaches to delivering drugs, genes, and antigens that are effective and safe can be developed. Topical administration to the ocular surface would be the safest method for delivery, as it is noninvasive and painless compared with other delivery methods. However, there is only limited success using topical delivery methods, especially for gene therapy. Current thinking on treatments of the future enabled by nanodelivery systems and the identification of target specificity parameters that require deeper understanding to develop successful topical delivery systems for glaucoma is highlighted.

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.

Achieving DFT accuracy with a machine-learning interatomic potential: Thermomechanics and defects in bcc ferromagnetic iron

NASA Astrophysics Data System (ADS)

Dragoni, Daniele; Daff, Thomas D.; Csányi, Gábor; Marzari, Nicola

2018-01-01

We show that the Gaussian Approximation Potential (GAP) machine-learning framework can describe complex magnetic potential energy surfaces, taking ferromagnetic iron as a paradigmatic challenging case. The training database includes total energies, forces, and stresses obtained from density-functional theory in the generalized-gradient approximation, and comprises approximately 150,000 local atomic environments, ranging from pristine and defected bulk configurations to surfaces and generalized stacking faults with different crystallographic orientations. We find the structural, vibrational, and thermodynamic properties of the GAP model to be in excellent agreement with those obtained directly from first-principles electronic-structure calculations. There is good transferability to quantities, such as Peierls energy barriers, which are determined to a large extent by atomic configurations that were not part of the training set. We observe the benefit and the need of using highly converged electronic-structure calculations to sample a target potential energy surface. The end result is a systematically improvable potential that can achieve the same accuracy of density-functional theory calculations, but at a fraction of the computational cost.

Accelerated molecular dynamics: A promising and efficient simulation method for biomolecules

NASA Astrophysics Data System (ADS)

Hamelberg, Donald; Mongan, John; McCammon, J. Andrew

2004-06-01

Many interesting dynamic properties of biological molecules cannot be simulated directly using molecular dynamics because of nanosecond time scale limitations. These systems are trapped in potential energy minima with high free energy barriers for large numbers of computational steps. The dynamic evolution of many molecular systems occurs through a series of rare events as the system moves from one potential energy basin to another. Therefore, we have proposed a robust bias potential function that can be used in an efficient accelerated molecular dynamics approach to simulate the transition of high energy barriers without any advance knowledge of the location of either the potential energy wells or saddle points. In this method, the potential energy landscape is altered by adding a bias potential to the true potential such that the escape rates from potential wells are enhanced, which accelerates and extends the time scale in molecular dynamics simulations. Our definition of the bias potential echoes the underlying shape of the potential energy landscape on the modified surface, thus allowing for the potential energy minima to be well defined, and hence properly sampled during the simulation. We have shown that our approach, which can be extended to biomolecules, samples the conformational space more efficiently than normal molecular dynamics simulations, and converges to the correct canonical distribution.

Direct control and characterization of a Schottky barrier by scanning tunneling microscopy

NASA Technical Reports Server (NTRS)

Bell, L. D.; Kaiser, W. J.; Hecht, M. H.; Grunthaner, F. J.

1988-01-01

Scanning tunneling microscopy (STM) methods are used to directly control the barrier height of a metal tunnel tip-semiconductor tunnel junction. Barrier behavior is measured by tunnel current-voltage spectroscopy and compared to theory. A unique surface preparation method is used to prepare a low surface state density Si surface. Control of band bending with this method enables STM investigation of semiconductor subsurface properties.

Effect of a multi-layer infection control barrier on the micro-hardness of a composite resin

PubMed Central

HWANG, In-Nam; HONG, Sung-Ok; LEE, Bin-Na; HWANG, Yun-Chan; OH, Won-Mann; CHANG, Hoon-Sang

2012-01-01

Objective The aim of this study was to evaluate the effect of multiple layers of an infection control barrier on the micro-hardness of a composite resin. Material and Methods One, two, four, and eight layers of an infection control barrier were used to cover the light guides of a high-power light emitting diode (LED) light curing unit (LCU) and a low-power halogen LCU. The composite specimens were photopolymerized with the LCUs and the barriers, and the micro-hardness of the upper and lower surfaces was measured (n=10). The hardness ratio was calculated by dividing the bottom surface hardness of the experimental groups by the irradiated surface hardness of the control groups. The data was analyzed by two-way ANOVA and Tukey's HSD test. Results The micro-hardness of the composite specimens photopolymerized with the LED LCU decreased significantly in the four- and eight-layer groups of the upper surface and in the two-, four-, and eight-layer groups of the lower surface. The hardness ratio of the composite specimens was <80% in the eight-layer group. The micro-hardness of the composite specimens photopolymerized with the halogen LCU decreased significantly in the eight-layer group of the upper surface and in the two-, four-, and eight-layer groups of the lower surface. However, the hardness ratios of all the composite specimens photopolymerized with barriers were <80%. Conclusions The two-layer infection control barrier could be used on high-power LCUs without decreasing the surface hardness of the composite resin. However, when using an infection control barrier on the low-power LCUs, attention should be paid so as not to sacrifice the polymerization efficiency. PMID:23138746

The Infant Skin Barrier: Can We Preserve, Protect, and Enhance the Barrier?

PubMed Central

Telofski, Lorena S.; Morello, A. Peter; Mack Correa, M. Catherine; Stamatas, Georgios N.

2012-01-01

Infant skin is different from adult in structure, function, and composition. Despite these differences, the skin barrier is competent at birth in healthy, full-term neonates. The primary focus of this paper is on the developing skin barrier in healthy, full-term neonates and infants. Additionally, a brief discussion of the properties of the skin barrier in premature neonates and infants with abnormal skin conditions (i.e., atopic dermatitis and eczema) is included. As infant skin continues to mature through the first years of life, it is important that skin care products (e.g., cleansers and emollients) are formulated appropriately. Ideally, products that are used on infants should not interfere with skin surface pH or perturb the skin barrier. For cleansers, this can be achieved by choosing the right type of surfactant, by blending surfactants, or by blending hydrophobically-modified polymers (HMPs) with surfactants to increase product mildness. Similarly, choosing the right type of oil for emollients is important. Unlike some vegetable oils, mineral oil is more stable and is not subject to oxidation and hydrolysis. Although emollients can improve the skin barrier, more studies are needed to determine the potential long-term benefits of using emollients on healthy, full-term neonates and infants. PMID:22988452

Scattering on a rectangular potential barrier in nodal-line Weyl semimetals

NASA Astrophysics Data System (ADS)

Khokhlov, D. A.; Rakhmanov, A. L.; Rozhkov, A. V.

2018-06-01

We investigate single-particle ballistic scattering on a rectangular barrier in the nodal-line Weyl semimetals. Since the system under study has a crystallographic anisotropy, the scattering properties are dependent on mutual orientation of the crystalline axis and the barrier. To account for the anisotropy, we examine two different barrier orientations. It is demonstrated that, for certain angles of incidence, the incoming particle passes through the barrier with probability of unity. This is a manifestation of the Klein tunneling, a familiar phenomenon in the context of graphene and semimetals with Weyl points. However, the Klein tunneling in the Weyl-ring systems is observed when the angle of incidence differs from 90∘, unlike the cases of graphene and Weyl-point semimetals. The reflectionless transmission also occurs for the so-called "magic angles." The values of the magic angles are determined by geometrical resonances between the barrier width and the de Broglie length of the scattered particle. In addition, we show that under certain conditions the wave function of the transmitted and reflected particles may be a superposition of two plane waves with unequal momenta. Such a feature is a consequence of the nontrivial structure of the isoenergy surfaces of the nodal-line semimetals. Conductance of the barrier is briefly discussed.

Noble magnetic barriers in the ASDEX UG tokamak

NASA Astrophysics Data System (ADS)

Ali, Halima; Punjabi, Alkesh; Vazquez, Justin

2010-02-01

The second-order perturbation method of creating invariant tori inside chaos in Hamiltonian systems (Ali, H.; Punjabi, A. Plasma Phys. Contr. F. 2007, 49, 1565-1582) is applied to the axially symmetric divertor experiment upgrade (ASDEX UG) tokamak to build noble irrational magnetic barriers inside chaos created by resonant magnetic perturbations (m, n)=(3, 2)+(4, 3), with m and n the poloidal and toroidal mode numbers of the Fourier expansion of the magnetic perturbation. The radial dependence of the Fourier modes is ignored. The modes are considered to be locked and have the same amplitude δ. A symplectic mathematical mapping in magnetic coordinates is used to integrate magnetic field line trajectories in the ASDEX UG. Tori with noble irrational rotational transform are the last ones to be destroyed by perturbation in Hamiltonian systems. For this reason, noble irrational magnetic barriers are built inside chaos, and the strongest noble irrational barrier is identified. Three candidate locations for the strongest noble barrier in ASDEX UG are selected. All three candidate locations are chosen to be roughly midway between the resonant rational surfaces ψ32 and ψ43. ψ is the magnetic coordinate of the flux surface. The three candidate surfaces are the noble irrational surfaces close to the surface with q value that is a mediant of q=3/2 and 4/3, q value of the physical midpoint of the two resonant surfaces, and the q value of the surface where the islands of the two perturbing modes just overlap. These q values of the candidate surfaces are denoted by q MED, q MID, and q OVERLAP. The strongest noble barrier close to q MED has the continued fraction representation (CFR) [1;2,2,1∞] and exists for δ≤2.6599×10-4; the strongest noble barrier close to q MID has CFR [1;2,2,2,1∞] and exists for δ≤4.6311×10-4; and the strongest noble barrier close to q OVERLAP has CFR [1;2,2,6,2,1∞] and exists for δ≤1.367770×10-4. From these results, the strongest noble barrier is found to be close to the surface that is located physically exactly in the middle of the two resonant surfaces.

Borate cross-linked graphene oxide-chitosan as robust and high gas barrier films

NASA Astrophysics Data System (ADS)

Yan, Ning; Capezzuto, Filomena; Lavorgna, Marino; Buonocore, Giovanna G.; Tescione, Fabiana; Xia, Hesheng; Ambrosio, Luigi

2016-05-01

Chitosan (CS) is one of the most promising polymers due to its biocompatibility, biodegradability, and natural abundance. However, its poor mechanical and barrier properties make it difficult to satisfy a wide range of applications. Herein, borate ions, originating from the hydrolysis of sodium tetraborate decahydrate (borax), have been used to crosslink chitosan and graphene oxide (GO) nanocomposites. Chitosan films consisting of 1.0 wt% boron and 1.0 wt% GO exhibit a significant improvement in both the toughness and oxygen barrier properties compared to pristine chitosan. In particular the tensile strength of the samples after thermal treatment increases by ~160% compared to pristine chitosan, whereas their oxygen permeability reduces by ~90%. This is ascribed to the chemical crosslinking between chitosan and GO nanoplatelets through borate ions, as well as the formation of a layered morphology with graphene nanoplatelets oriented parallel to the sample surface. The exceptional robust and high gas barrier film has promising application in the packaging industry. The borate-crosslinking chemistry represents the potential strategy for improving properties of other polymer nanocomposites.Chitosan (CS) is one of the most promising polymers due to its biocompatibility, biodegradability, and natural abundance. However, its poor mechanical and barrier properties make it difficult to satisfy a wide range of applications. Herein, borate ions, originating from the hydrolysis of sodium tetraborate decahydrate (borax), have been used to crosslink chitosan and graphene oxide (GO) nanocomposites. Chitosan films consisting of 1.0 wt% boron and 1.0 wt% GO exhibit a significant improvement in both the toughness and oxygen barrier properties compared to pristine chitosan. In particular the tensile strength of the samples after thermal treatment increases by ~160% compared to pristine chitosan, whereas their oxygen permeability reduces by ~90%. This is ascribed to the chemical crosslinking between chitosan and GO nanoplatelets through borate ions, as well as the formation of a layered morphology with graphene nanoplatelets oriented parallel to the sample surface. The exceptional robust and high gas barrier film has promising application in the packaging industry. The borate-crosslinking chemistry represents the potential strategy for improving properties of other polymer nanocomposites. Electronic supplementary information (ESI) available: Detailed characterization methods and survey XPS spectra. See DOI: 10.1039/c6nr00377j

Potential barrier classification by short-time measurement

NASA Astrophysics Data System (ADS)

Granot, Er'El; Marchewka, Avi

2006-03-01

We investigate the short-time dynamics of a delta-function potential barrier on an initially confined wave packet. There are mainly two conclusions: (A) At short times the probability density of the first particles that passed through the barrier is unaffected by it. (B) When the barrier is absorptive (i.e., its potential is imaginary) it affects the transmitted wave function at shorter times than a real potential barrier. Therefore, it is possible to distinguish between an imaginary and a real potential barrier by measuring its effect at short times only on the transmitting wave function.

Influence of the Cell Wall on Intracellular Delivery to Algal Cells by Electroporation and Sonication

PubMed Central

Azencott, Harold R.; Peter, Gary F.; Prausnitz, Mark R.

2007-01-01

To assess the cell wall’s role as a barrier to intracellular delivery, wild-type Chlamydomonas reinhardtii algal cells and mutant cells lacking a cell wall were exposed to electroporation or sonication. Flow cytometry determined intracellular uptake of calcein and bovine serum albumin (BSA) and loss of cell viability as functions of electroporation transmembrane potential and acoustic energy. Electroporation of wild-type cells increased calcein uptake with increasing transmembrane potential, but delivered much less BSA. Electroporation of wall-deficient cells had similar effects on calcein uptake, but increased BSA uptake as much as 7.5-fold relative to wild-type cells, which indicated that the cell wall was a significant barrier to BSA delivery during electroporation. Sonication of wild-type cells caused calcein and BSA uptake at similar levels. This suggests that the cell wall barrier to BSA delivery can be overcome by sonication. Increased electroporation transmembrane potential or acoustic energy also caused increased loss of cell viability, where wall-deficient cells were especially susceptible to lysis. Overall, we believe this is the first study to compare the effects of electroporation and sonication in a direct fashion in any cell type. Specifically, these findings suggest that electroporation primarily transports molecules across the plasma membrane, because its mechanism is specific to lipid bilayer disruption, whereas sonication transports molecules across both the plasma membrane and cell wall, because it non-specifically disrupts cell-surface barriers. PMID:17602827

Nanoprobe studies: Electrical transport in carbon nanotubes and crystal structure of aluminum nitride surfaces

NASA Astrophysics Data System (ADS)

Biswas, Sujit Kumar

Nanoprobes are an extraordinary set of experimental tools that allow fabrication, manipulation, and measurement in nano-scale systems. The primary use of a nanoprobe for imaging tiny objects is supplemented by powerful electrical techniques, namely scanning surface potential microscopy and current sensing atomic force microscopy. They allow us to measure potential, and current in carbon nanotube circuits. Nanoprobes are superior to conventional two- or four-probe measurements because they can provide spatial information of local electronic properties. This makes them highly attractive in studying junctions and contacts with carbon nanotubes. We have studied single-walled carbon nanotube circuits, forming junctions to other nanotubes. The experimental results indicate that these junctions act like potential barriers of about 50 meV that can confine electrons with an effective mass of 0.003 me , within nanotube channels of length 0.5 mum lying in-between two such potential barriers. This leads to quantization of the channel, forming a resonant tunneling structure. We have also found that single-walled nanotubes have phase coherence lengths of the order of 1 mum. This leads to situations where the electron interference effects at scattering centers need to be considered. We have seen direct evidence of this, in the non-linear resistance increase within nanotubes with few defects. Ambipolar transistor behavior was measured in a p-type single-walled nanotube circuit that showed electron injection across the Schottky junction at high positive bias. We have also studied multi-walled carbon nanotube circuits using scanning potential microscopy, and found that a back gate potential can vary the resistance of the channel. Vertical nanotube arrays, suitable for interconnects, were also measured. These hollow multi-walled nanotube channels were about 45 nm in diameter, and 50 mum in length, fabricated in an anodized alumina template. We found that these structures could sustain current densities greater than 105 A/cm2. Conventional use of nanoprobes in imaging aluminum nitride surfaces displayed curious step bunching structures. We have used an innovative analysis technique with which the bulk lattice constant of the crystal was measured to an accuracy of about 4% of X-ray crystallography value of 0.497 nm. In addition, this technique showed that there were regions on the surface that had a larger lattice parameter of 0.64 nm, which we interpreted to be due to a variation in the chemical composition of the surface such as oxide formation. We believe that this technique may prove useful as a study of chemical-composition variations on a surface as well as relaxation of the surface layer.

Outer brain barriers in rat and human development

PubMed Central

Brøchner, Christian B.; Holst, Camilla B.; Møllgård, Kjeld

2015-01-01

Complex barriers at the brain's surface, particularly in development, are poorly defined. In the adult, arachnoid blood-cerebrospinal fluid (CSF) barrier separates the fenestrated dural vessels from the CSF by means of a cell layer joined by tight junctions. Outer CSF-brain barrier provides diffusion restriction between brain and subarachnoid CSF through an initial radial glial end feet layer covered with a pial surface layer. To further characterize these interfaces we examined embryonic rat brains from E10 to P0 and forebrains from human embryos and fetuses (6–21st weeks post-conception) and adults using immunohistochemistry and confocal microscopy. Antibodies against claudin-11, BLBP, collagen 1, SSEA-4, MAP2, YKL-40, and its receptor IL-13Rα2 and EAAT1 were used to describe morphological characteristics and functional aspects of the outer brain barriers. Claudin-11 was a reliable marker of the arachnoid blood-CSF barrier. Collagen 1 delineated the subarachnoid space and stained pial surface layer. BLBP defined radial glial end feet layer and SSEA-4 and YKL-40 were present in both leptomeningeal cells and end feet layer, which transformed into glial limitans. IL-13Rα2 and EAAT1 were present in the end feet layer illustrating transporter/receptor presence in the outer CSF-brain barrier. MAP2 immunostaining in adult brain outlined the lower border of glia limitans; remnants of end feet were YKL-40 positive in some areas. We propose that outer brain barriers are composed of at least 3 interfaces: blood-CSF barrier across arachnoid barrier cell layer, blood-CSF barrier across pial microvessels, and outer CSF-brain barrier comprising glial end feet layer/pial surface layer. PMID:25852456

Outer brain barriers in rat and human development.

PubMed

Brøchner, Christian B; Holst, Camilla B; Møllgård, Kjeld

2015-01-01

Complex barriers at the brain's surface, particularly in development, are poorly defined. In the adult, arachnoid blood-cerebrospinal fluid (CSF) barrier separates the fenestrated dural vessels from the CSF by means of a cell layer joined by tight junctions. Outer CSF-brain barrier provides diffusion restriction between brain and subarachnoid CSF through an initial radial glial end feet layer covered with a pial surface layer. To further characterize these interfaces we examined embryonic rat brains from E10 to P0 and forebrains from human embryos and fetuses (6-21st weeks post-conception) and adults using immunohistochemistry and confocal microscopy. Antibodies against claudin-11, BLBP, collagen 1, SSEA-4, MAP2, YKL-40, and its receptor IL-13Rα2 and EAAT1 were used to describe morphological characteristics and functional aspects of the outer brain barriers. Claudin-11 was a reliable marker of the arachnoid blood-CSF barrier. Collagen 1 delineated the subarachnoid space and stained pial surface layer. BLBP defined radial glial end feet layer and SSEA-4 and YKL-40 were present in both leptomeningeal cells and end feet layer, which transformed into glial limitans. IL-13Rα2 and EAAT1 were present in the end feet layer illustrating transporter/receptor presence in the outer CSF-brain barrier. MAP2 immunostaining in adult brain outlined the lower border of glia limitans; remnants of end feet were YKL-40 positive in some areas. We propose that outer brain barriers are composed of at least 3 interfaces: blood-CSF barrier across arachnoid barrier cell layer, blood-CSF barrier across pial microvessels, and outer CSF-brain barrier comprising glial end feet layer/pial surface layer.

Fusion and elastic scattering of 6Li + 58Ni at low energies

NASA Astrophysics Data System (ADS)

Aguilera, Elí F.; Amador-Valenzuela, Paulina; Martinez-Quiroz, Enrique; Lizcano, David; Garcia-Flores, Araceli; Kolata, James J.

2017-11-01

Sub-barrier fusion cross sections (σfus) for the 6Li + 58Ni system, obtained from the respective evaporation protons, are examined in the present work. With respect to expectations of a simple one-dimensional barrier penetration model, a large enhancement of the data is observed. Good consistency with equivalent data reported previously for similar systems is found. A comparison with total reaction cross sections (σR), deduced from elastic scattering measurements reported previously, indicates that σfus is close to σR within the measured energy range. To estimate the contribution of complete fusion (CF), an optical model analysis of the elastic scattering data is performed where CF is identified with the absorption in a short range volume potential. A surface polarization potential is added to the bare nuclear potential to simulate the effect of peripheral reactions. The results obtained indicate that other mechanisms different from CF may be dominant, especially in the lower energy region.

First-Principles Study of the Band Diagrams and Schottky-Type Barrier Heights of Aqueous Ta3N5 Interfaces.

PubMed

Watanabe, Eriko; Ushiyama, Hiroshi; Yamashita, Koichi

2017-03-22

The photo(electro)chemical production of hydrogen by water splitting is an efficient and sustainable method for the utilization of solar energy. To improve photo(electro)catalytic activity, a Schottky-type barrier is typically useful to separate excited charge carriers in semiconductor electrodes. Here, we focused on studying the band diagrams and the Schottky-type barrier heights of Ta 3 N 5 , which is one of the most promising materials as a photoanode for water splitting. The band alignments of the undoped and n-type Ta 3 N 5 with adsorbents in a vacuum were examined to determine how impurities and adsorbents affect the band positions and Fermi energies. The band edge positions as well as the density of surface states clearly depended on the density of O N impurities in the bulk and surface regions. Finally, the band diagrams of the n-type Ta 3 N 5 /water interfaces were calculated with an improved interfacial model to include the effect of electrode potential with explicit water molecules. We observed partial Fermi level pinning in our calculations at the Ta 3 N 5 /water interface, which affects the driving force for charge separation.

Laser Ablation Electrodynamic Ion Funnel for In Situ Mass Spectrometry on Mars

NASA Technical Reports Server (NTRS)

Johnson, Paul V.; Hodyss, Robert P.; Tang, Keqi; Smith, Richard D.

2012-01-01

A front-end instrument, the laser ablation ion funnel, was developed, which would ionize rock and soil samples in the ambient Martian atmosphere, and efficiently transport the product ions into a mass spectrometer for in situ analysis. Laser ablation creates elemental ions from a solid with a high-power pulse within ambient Mars atmospheric conditions. Ions are captured and focused with an ion funnel into a mass spectrometer for analysis. The electrodynamic ion funnel consists of a series of axially concentric ring-shaped electrodes whose inside diameters (IDs) decrease over the length of the funnel. DC potentials are applied to each electrode, producing a smooth potential slope along the axial direction. Two radio-frequency (RF) AC potentials, equal in amplitude and 180 out of phase, are applied alternately to the ring electrodes. This creates an effective potential barrier along the inner surface of the electrode stack. Ions entering the funnel drift axially under the influence of the DC potential while being restricted radially by the effective potential barrier created by the applied RF. The net result is to effectively focus the ions as they traverse the length of the funnel.

Water Adsorption and Dissociation on Ceria-Supported Single-Atom Catalysts: A First-Principles DFT+U Investigation.

PubMed

Han, Zhong-Kang; Gao, Yi

2016-02-01

Single-atom catalysts have attracted wide attention owing to their extremely high atom efficiency and activities. In this paper, we applied density functional theory with the inclusion of the on-site Coulomb interaction (DFT+U) to investigate water adsorption and dissociation on clean CeO 2 (111) surfaces and single transition metal atoms (STMAs) adsorbed on the CeO 2 (111) surface. It is found that the most stable water configuration is molecular adsorption on the clean CeO 2 (111) surface and dissociative adsorption on STMA/CeO 2 (111) surfaces, respectively. In addition, our results indicate that the more the electrons that transfer from STMA to the ceria substrate, the stronger the binding energies between the STMA and ceria surfaces. A linear relationship is identified between the water dissociation barriers and the d band centers of STMA, known as the generalized Brønsted-Evans-Polanyi principle. By combining the oxygen spillovers, single-atom dispersion stabilities, and water dissociation barriers, Zn, Cr, and V are identified as potential candidates for the future design of ceria-supported single-atom catalysts for reactions in which the dissociation of water plays an important role, such as the water-gas shift reaction. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Chemical reaction CO+OH • → CO 2+H • autocatalyzed by carbon dioxide: Quantum chemical study of the potential energy surfaces

DOE PAGES

Masunov, Artem E.; Wait, Elizabeth; Vasu, Subith S.

2016-06-28

The supercritical carbon dioxide medium, used to increase efficiency in oxy combustion fossil energy technology, may drastically alter both rates and mechanisms of chemical reactions. Here we investigate potential energy surface of the second most important combustion reaction with quantum chemistry methods. Two types of effects are reported: formation of the covalent intermediates and formation of van der Waals complexes by spectator CO 2 molecule. While spectator molecule alter the activation barrier only slightly, the covalent bonding opens a new reaction pathway. The mechanism includes sequential covalent binding of CO 2 to OH radical and CO molecule, hydrogen transfer frommore » oxygen to carbon atoms, and CH bond dissociation. This reduces the activation barrier by 11 kcal/mol at the rate-determining step and is expected to accelerate the reaction rate. The finding of predicted catalytic effect is expected to play an important role not only in combustion but also in a broad array of chemical processes taking place in supercritical CO 2 medium. Furthermore, tt may open a new venue for controlling reaction rates for chemical manufacturing.« less

Effect of La3+ substitution with Gd3+ on the resistive switching properties of La0.7Sr0.3MnO3 thin films

NASA Astrophysics Data System (ADS)

Lee, Hong-Sub; Park, Chang-Sun; Park, Hyung-Ho

2014-05-01

This study demonstrated that the resistive switching voltage of perovskite manganite material could be controlled by A-site cation substitution in "A" MnO3 perovskite manganite structure. A partial substitution of La3+ in La0.7Sr0.3MnO3 with smaller cation Gd3+ induced A-site vacancy of the largest Sr2+ cation with surface segregation of SrOy due to ionic size mismatch, and the induced vacancies reduced migration energy barrier. The operating voltage decreased from 3.5 V to 2.5 V due to a favorable condition for electrochemical migration and redox of oxygen ions. Moreover, surface-segregated SrOy was enhanced with Gd-substitution and the SrOy reduced Schottky-like barrier height and resistive switching ratio from the potential drop and screening effect. The relationship between A-site vacancy generation resulting in surface segregation of SrOy and resistive switching behavior was also investigated by energy resolved x-ray photoelectron spectroscopy, O 1s near edge x-ray absorption spectroscopy, and current voltage measurement.

Elimination of diazinon insecticide from cucumber surface by atmospheric pressure air-dielectric barrier discharge plasma.

PubMed

Dorraki, Naghme; Mahdavi, Vahideh; Ghomi, Hamid; Ghasempour, Alireza

2016-12-06

The food industry is in a constant search for new technologies to improve the commercial sterilization process of agricultural commodities. Plasma treatment may offer a novel and efficient method for pesticide removal from agricultural product surfaces. To study the proposed technique of plasma food treatment, the degradation behavior of diazinon insecticide by air-dielectric barrier discharge (DBD) plasma was investigated. The authors studied the effect of different plasma powers and treatment times on pesticide concentration in liquid form and coated on the surface of cucumbers, where the diazinon residue was analyzed with mass spectroscopy gas chromatography. Our results suggest that atmospheric pressure air-DBD plasma is potentially effective for the degradation of diazinon insecticide, and mainly depends on related operating parameters, including plasma treatment time, discharge power, and pesticide concentrations. Based on the interaction between reactive oxygen species and electrons in the plasma with the diazinon molecule, two degradation pathway of diazinon during plasma treatment are proposed. It was also found that produced organophosphate pesticides are harmless and less hazardous compounds than diazinon.

Bi-functional anodic TiO2 oxide: Nanotubes for wettability control and barrier oxide for uniform coloring

NASA Astrophysics Data System (ADS)

Kim, Sunkyu; Jung, Minkyeong; Kim, Moonsu; Choi, Jinsub

2017-06-01

A uniformly colored TiO2, on which the surface is functionalized with nanotubes to control wettability, was prepared by a two-step anodization; the first anodization was carried out to prepare nanotubes for a super-hydrophilic or -hydrophobic surface and the second anodization was performed to fabricate a thin film barrier oxide to ensure uniform coloring. The effect of the nanotubes on barrier oxide coloring was examined by spectrophotometry and UV-vis-IR spectroscopy. We found four different regimes governing the color changes in terms of anodization voltage, indicating that the color of the duplex TiO2 was primarily determined by the thickness of the barrier oxide layer formed during the second anodization step. The surface wettability, as confirmed by the water contact angle, revealed that the single barrier TiO2 yielded 74.6° ± 2.1, whereas the nanotubes on the barrier oxide imparted super-hydrophilic properties as a result of increasing surface roughness as well as imparting a higher hydrophobicity after organic acid treatment.

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

Yuan, Bing; Bernstein, Elliot R., E-mail: erb@Colostate.edu

Unimolecular decomposition of nitrogen-rich energetic salt molecules bis(ammonium)5,5′-bistetrazolate (NH{sub 4}){sub 2}BT and bis(triaminoguanidinium) 5,5′-azotetrazolate TAGzT, has been explored via 283 nm laser excitation. The N{sub 2} molecule, with a cold rotational temperature (<30 K), is observed as an initial decomposition product, subsequent to UV excitation. Initial decomposition mechanisms for the two electronically excited salt molecules are explored at the complete active space self-consistent field (CASSCF) level. Potential energy surface calculations at the CASSCF(12,8)/6-31G(d) ((NH{sub 4}){sub 2}BT) and ONIOM (CASSCF/6-31G(d):UFF) (TAGzT) levels illustrate that conical intersections play an essential role in the decomposition mechanism as they provide non-adiabatic, ultrafast radiationless internalmore » conversion between upper and lower electronic states. The tetrazole ring opens on the S{sub 1} excited state surface and, through conical intersections (S{sub 1}/S{sub 0}){sub CI}, N{sub 2} product is formed on the ground state potential energy surface without rotational excitation. The tetrazole rings open at the N2—N3 ring bond with the lowest energy barrier: the C—N ring bond opening has a higher energy barrier than that for any of the N—N ring bonds: this is consistent with findings for other nitrogen-rich neutral organic energetic materials. TAGzT can produce N{sub 2} either by the opening of tetrazole ring or from the N=N group linking its two tetrazole rings. Nonetheless, opening of a tetrazole ring has a much lower energy barrier. Vibrational temperatures of N{sub 2} products are hot based on theoretical predictions. Energy barriers for opening of the tetrazole ring for all the nitrogen-rich energetic materials studied thus far, including both neutral organic molecules and salts, are in the range from 0.31 to 2.71 eV. Energy of the final molecular structure of these systems with dissociated N{sub 2} product is in the range from −1.86 to 3.11 eV. The main difference between energetic salts and neutral nitrogen-rich energetic material is that energetic salts usually have lower excitation energy.« less

Thermal effect of Zn quantum dots grown on Si(111): competition between relaxation and reconstraint

NASA Astrophysics Data System (ADS)

Kao, Li-Chi; Huang, Bo-Jia; Zheng, Yu-En; Tu, Kai-Teng; Chiu, Shang-Jui; Ku, Ching-Shun; Lo, Kuang Yao

2018-01-01

Zn dots are potential solutions for metal contacts in future nanodevices. The metastable states that exist at the interface between Zn quantum dots and oxide-free Si(111) surfaces can suppress the development of the complete relaxation and increase the size of Zn dots. In this work, the actual heat consumption of the structural evolution of Zn dots resulting from extrinsic thermal effect was analyzed. Zn dots were coherently grown on oxide-free Si(111) through magnetron RF sputtering. A compensative optical method combined with reflective second harmonic generation and synchrotron x-ray diffraction (XRD) was developed to statistically analyze the thermal effect on the Zn dot system. Pattern matching (3 m) between the Zn and oxide-free Si(111) surface enabled Si(111) to constrain Zn dots from a liquid to solid phase. Annealing under vacuum induced smaller, loose Zn dots to be reconstrained by Si(111). When the size of the Zn dots was in the margin of complete relaxation, the Zn dot was partially constrained by potential barriers (metastable states) between Zn(111) and one of the six in-planes of Si〈110〉. The thermal disturbance exerted by annealing would enable partially constrained ZnO/Zn dots to overcome the potential barrier and be completely relaxed, which is obvious on the transition between Zn(111) and Zn(002) peak in synchrotron XRD. Considering the actual irradiated surface area of dots array in a wide-size distribution, the competition between reconstrained and relaxed Zn dots on Si(111) during annealing was statistically analyzed.

Development of Spray on Bag for manufacturing of large composites parts: Diffusivity analysis

NASA Astrophysics Data System (ADS)

Dempah, Maxime Joseph

Bagging materials are utilized in many composites manufacturing processes. The selection is mainly driven by cost, temperature requirements, chemical compatibility and tear properties of the bag. The air barrier properties of the bag are assumed to be adequate or in many cases are not considered at all. However, the gas barrier property of a bag is the most critical parameter, as it can negatively affect the quality of the final laminate. The barrier property is a function of the bag material, uniformity, thickness and temperature. Improved barrier properties are needed for large parts, high pressure consolidated components and structures where air stays entrapped on the part surface. The air resistance property of the film is defined as permeability and is investigated in this thesis. A model was developed to evaluate the gas transport through the film and an experimental cell was implemented to characterize various commercial films. Understanding and characterizing the transport phenomena through the film allows optimization of the bagging material for various manufacturing processes. Spray-on-Bag is a scalable alternative bagging method compared to standard films. The approach allows in-situ fabrication of the bag on large and complex geometry structures where optimization of the bag properties can be varied on a local level. An experimental setup was developed and implemented using a six axis robot and an automated spraying system. Experiments were performed on a flat surface and specimens were characterized and compared to conventional films. Air barrier properties were within range of standard film approaches showing the potential to fabricate net shape bagging structures in an automated process.

Evaporation of tiny water aggregation on solid surfaces with different wetting properties.

PubMed

Wang, Shen; Tu, Yusong; Wan, Rongzheng; Fang, Haiping

2012-11-29

The evaporation of a tiny amount of water on the solid surface with different wettabilities has been studied by molecular dynamics simulations. From nonequilibrium MD simulations, we found that, as the surface changed from hydrophobic to hydrophilic, the evaporation speed did not show a monotonic decrease as intuitively expected, but increased first, and then decreased after it reached a maximum value. The analysis of the simulation trajectory and calculation of the surface water interaction illustrate that the competition between the number of water molecules on the water-gas surface from where the water molecules can evaporate and the potential barrier to prevent those water molecules from evaporating results in the unexpected behavior of the evaporation. This finding is helpful in understanding the evaporation on biological surfaces, designing artificial surfaces of ultrafast water evaporating, or preserving water in soil.

Effects of ultrathin oxides in conducting MIS structures on GaAs

NASA Technical Reports Server (NTRS)

Childs, R. B.; Ruths, J. M.; Sullivan, T. E.; Fonash, S. J.

1978-01-01

Schottky barrier-type GaAs baseline devices (semiconductor surface etched and then immediately metalized) and GaAs conducting metal oxide-semiconductor devices are fabricated and characterized. The baseline surfaces (no purposeful oxide) are prepared by a basic or an acidic etch, while the surface for the MIS devices are prepared by oxidizing after the etch step. The metallizations used are thin-film Au, Ag, Pd, and Al. It is shown that the introduction of purposeful oxide into these Schottky barrier-type structures examined on n-type GaAs modifies the barrier formation, and that thin interfacial layers can modify barrier formation through trapping and perhaps chemical reactions. For Au- and Pd-devices, enhanced photovoltaic performance of the MIS configuration is due to increased barrier height.

Design and performance evaluation of a 1000-year evapotranspiration-capillary surface barrier.

PubMed

Zhang, Zhuanfang Fred; Strickland, Christopher E; Link, Steven O

2017-02-01

Surface barrier technology is used to isolate radioactive waste and to reduce or eliminate recharge water to the waste zone for 1000 years or longer. However, the design and evaluation of such a barrier is challenging because of the extremely long design life. After establishing a set of design and performance objectives, a package of design solutions was developed for 1000-year surface barriers over nuclear waste sites. The Prototype Hanford Barrier (PHB) was then constructed in 1994 in the field over an existing waste site as a demonstration. The barrier was tested to evaluate surface-barrier design and performance at the field scale under conditions of enhanced and natural precipitation and of no vegetation. The monitoring data demonstrate that the barrier satisfied nearly all objectives in the past two decades. The PHB far exceeded the Resource Conservation and Recovery Act criteria, functioned in Hanford's semiarid climate, limited drainage to well below the 0.5 mm yr -1 performance criterion, limited runoff, and minimized erosion and bio-intrusion. Given the two-decade record of successful performance and consideration of the processes and mechanisms that could affect barrier stability and hydrology in the future, the results suggest the PHB is very likely to perform for its 1000-year design life. This conclusion is based on two assumptions: (1) the exposed subgrade receives protection against erosion and (2) institutional controls prevent inadvertent human activity at the barrier. The PHB design can serve as the basis for site-specific barriers over waste sites containing underground nuclear waste, uranium mine tailings, and hazardous mine waste. Copyright © 2016 Elsevier Ltd. All rights reserved.

Effect of barrier height on friction behavior of the semiconductors silicon and gallium arsenide in contact with pure metals

NASA Technical Reports Server (NTRS)

Mishina, H.; Buckley, D. H.

1984-01-01

Friction experiments were conducted for the semiconductors silicon and gallium arsenide in contact with pure metals. Polycrystalline titanium, tantalum, nickel, palladium, and platinum were made to contact a single crystal silicon (111) surface. Indium, nickel, copper, and silver were made to contact a single crystal gallium arsenide (100) surface. Sliding was conducted both in room air and in a vacuum of 10 to the minus 9th power torr. The friction of semiconductors in contact with metals depended on a Schottky barrier height formed at the metal semiconductor interface. Metals with a higher barrier height on semiconductors gave lower friction. The effect of the barrier height on friction behavior for argon sputtered cleaned surfaces in vacuum was more specific than that for the surfaces containing films in room air. With a silicon surface sliding on titanium, many silicon particles back transferred. In contrast, a large quantity of indium transferred to the gallium arsenide surface.

First principles calculations on the influence of solute elements and chlorine adsorption on the anodic corrosion behavior of Mg (0001) surface

NASA Astrophysics Data System (ADS)

Luo, Zhe; Zhu, Hong; Ying, Tao; Li, Dejiang; Zeng, Xiaoqin

2018-06-01

The influences of solute atoms (Li, Al, Mn, Zn, Fe, Ni, Cu, Y, Zr) and Cl adsorption on the anodic corrosion performance on Mg (0001) surface have been investigated based on first-principles calculations, which might be useful for the design of corrosion-resistant Mg alloys. Work function and local electrode potential shift are chosen as descriptors since they quantify the barrier for charge transfer and anodic stability. We found that at 25% surface doping rate, Y decreased the work function of Mg, while the impact of remaining doping elements on the work function of Mg was trivial due to the small surface dipole moment change. The adsorption of Cl destabilized the Mg atoms at surface by weakening the bonding between surface Mg atoms. We find that a stronger hybridization of d orbits of alloying elements (e.g. Zr) with the orbits of Mg can greatly increase the local electrode potential,which even overbalances the negative effect introduced by Cl adsorbates and hence improves the corrosion resistance of Mg alloys.

Adding EUV reflectance to aluminum-coated mirrors for space-based observation

NASA Astrophysics Data System (ADS)

Allred, David D.; Turley, R. Steven; Thomas, Stephanie M.; Willett, Spencer G.; Greenburg, Michael J.; Perry, Spencer B.

2017-09-01

Protective layers on aluminum mirror surfaces which can be removed via the use of atomic hydrogen or hydrogen plasmas at the point of use in space may allow an expansion of broad-band mirrors into the EUV. LUVOIR (large, UV-optical-IR telescope) is a potential NASA flagship space-based observatory of the 2020's or 30's. It would utilize the largest mirrors ever flown1 . Their reflective coating will almost certainly be aluminum, since such telescopes would profit from truly broad-band mirrors. To achieve reflectance over the broadest band, the top surface of such aluminum mirrors, however, needs to be bare, without the oxide layers that naturally form in air. This will open the 11 to 15 eV band. Since thin aluminum films are largely transparent between 15 and 70 eV an EUV mirror under the aluminum could make EUV bands such as 30.4 nm available for space-based astrophysics without sacrificing mirror IR, visible and UV reflectance. The local space environment for the observatory is sufficiently oxygen-free that the surface should remain bare for decades. We discuss protecting as-deposited aluminum mirrors with robust, oxygenimpenetrable, barrier layers applied in vacuo to the aluminum immediately after deposition and before air contact. The goal is that the barrier could also be cleanly, and relatively easily, removed once the mirror is in space. We propose hydrogen atoms as the means for removing the overcoat, since they can be expected to meet the criteria that the means is gentle enough to not roughen the mirror surface, and does not redeposit material on the mirror or other spacecraft components. We have investigated both organic and inorganic (such as, a-Si) hydrogen-removable films that can be applied to the aluminum immediately after its deposition have been investigated. We also examined the REVAP technique, using Cd and Zn. Agglomeration limited their effectiveness as barrier layers. That and dealing with the reevaporated atoms may limit their utility as barrier materials.

A first principle study for the adsorption and absorption of carbon atom and the CO dissociation on Ir(100) surface

NASA Astrophysics Data System (ADS)

Erikat, I. A.; Hamad, B. A.

2013-11-01

We employ density functional theory to examine the adsorption and absorption of carbon atom as well as the dissociation of carbon monoxide on Ir(100) surface. We find that carbon atoms bind strongly with Ir(100) surface and prefer the high coordination hollow site for all coverages. In the case of 0.75 ML coverage of carbon, we obtain a bridging metal structure due to the balance between Ir-C and Ir-Ir interactions. In the subsurface region, the carbon atom prefers the octahedral site of Ir(100) surface. We find large diffusion barrier for carbon atom into Ir(100) surface (2.70 eV) due to the strong bonding between carbon atom and Ir(100) surface, whereas we find a very small segregation barrier (0.22 eV) from subsurface to the surface. The minimum energy path and energy barrier for the dissociation of CO on Ir(100) surface are obtained by using climbing image nudge elastic band. The energy barrier of CO dissociation on Ir(100) surface is found to be 3.01 eV, which is appreciably larger than the association energy (1.61 eV) of this molecule.

A first principle study for the adsorption and absorption of carbon atom and the CO dissociation on Ir(100) surface.

PubMed

Erikat, I A; Hamad, B A

2013-11-07

We employ density functional theory to examine the adsorption and absorption of carbon atom as well as the dissociation of carbon monoxide on Ir(100) surface. We find that carbon atoms bind strongly with Ir(100) surface and prefer the high coordination hollow site for all coverages. In the case of 0.75 ML coverage of carbon, we obtain a bridging metal structure due to the balance between Ir-C and Ir-Ir interactions. In the subsurface region, the carbon atom prefers the octahedral site of Ir(100) surface. We find large diffusion barrier for carbon atom into Ir(100) surface (2.70 eV) due to the strong bonding between carbon atom and Ir(100) surface, whereas we find a very small segregation barrier (0.22 eV) from subsurface to the surface. The minimum energy path and energy barrier for the dissociation of CO on Ir(100) surface are obtained by using climbing image nudge elastic band. The energy barrier of CO dissociation on Ir(100) surface is found to be 3.01 eV, which is appreciably larger than the association energy (1.61 eV) of this molecule.

Analysis of the topochemical effects of dielectric-barrier discharge on cellulosic fibers

Treesearch

Lorraine C. Vander Wielen; Thomas Elder; Arthur J. Ragauskas

2005-01-01

This study investigates the fundamental topochemical effects of dielectric-barrier discharge treatment on bleached chemical pulp and unbleached mechanical pulp fiber surfaces. Fibers were treated with various levels of dielectric-barrier discharge treatment ranging from 0 to 9.27 kw/m2/min. Changes to the fiber surface topochemistry were investigated by atomic force...

Unoccupied Electron States and the Formation of Interface between Films of Dimethyl-Substituted Thiophene-Phenylene Coolygomers and Oxidized Silicon Surface

NASA Astrophysics Data System (ADS)

Komolov, A. S.; Lazneva, E. F.; Gerasimova, N. B.; Panina, Yu. A.; Zashikhin, G. D.; Pshenichnyuk, S. A.; Borshchev, O. V.; Ponomarenko, S. A.; Handke, B.

2018-05-01

The unoccupied electron states and the boundary potential barrier during deposition of ultrathin films of dimethyl-substituted thiophene-phenylene coolygomers of the type of CH3-phenylene-thiophene-thiophene-phenylene-CH3 (CH3-PTTP-CH3) on an oxidized silicon surface have been studied. The electronic characteristics have been measured in the energy range from 5 to 20 eV above the Fermi level using total current spectroscopy (TCS). The structure of the CH3-PTTP-CH3 film surfaces has been studied by atomic force microscopy (AFM), and the atomic compositions of the films have been studied by X-ray photoelectron spectroscopy (XPS). The changes in the maximum intensities measured by the TCS method obtained from the deposited CH3-PTTP-CH3 film and from the substrate during increasing in the organic coating thickness to 6 nm is discussed. The formation of the boundary potential barrier in the n-Si/SiO2/CH3-PTTP-CH3 is accompanied by the decrease in the surface work function from 4.2 ± 0.1 to 4.0 ± 0.1 eV as the organic coating thickness increases to 3 nm. The ratio of atomic concentrations C: S in the CH3-PTTP-CH3 films well corresponds to the chemical formula of CH3-PTTP-CH3 molecules. The roughness of the CH3-PTTP-CH3 coating surface was not higher than 10 nm on the 10 × 10 μm areas as the total CH3-PTTP-CH3-layer thickness was about 100 nm.

Surface States in the AlxGa1-xN Barrier in AlxGa1-xN/GaN Heterostructures

NASA Astrophysics Data System (ADS)

Liu, Jie; Shen, Bo; Wang, Mao-Jun; Zhou, Yu-Gang; Chen, Dun-Jun; Zhang, Rong; Shi, Yi; Zheng, You-Dou

2004-01-01

Frequency-dependent capacitance-voltage (C-V) measurements have been performed on modulation-doped Al0.22 Ga0.78N/GaN heterostructures to investigate the characteristics of the surface states in the AlxGa1-xN barrier. Numerical fittings based on the experimental data indicate that there are surface states with high density locating on the AlxGa1-xN barrier. The density of the surface states is about 1012 cm-2eV-1, and the time constant is about 1 mus. It is found that an insulating layer (Si3N4) between the metal contact and the surface of AlxGa1-xN can passivate the surface states effectively.

Tracking the Effect of Adatom Electronegativity on Systematically Modified AlGaN/GaN Schottky Interfaces.

PubMed

Reiner, Maria; Pietschnig, Rudolf; Ostermaier, Clemens

2015-10-21

The influence of surface modifications on the Schottky barrier height for gallium nitride semiconductor devices is frequently underestimated or neglected in investigations thereof. We show that a strong dependency of Schottky barrier heights for nickel/aluminum-gallium nitride (0001) contacts on the surface terminations exists: a linear correlation of increasing barrier height with increasing electronegativity of superficial adatoms is observed. The negatively charged adatoms compete with the present nitrogen over the available gallium (or aluminum) orbital to form an electrically improved surface termination. The resulting modification of the surface dipoles and hence polarization of the surface termination causes observed band bending. Our findings suggest that the greatest Schottky barrier heights are achieved by increasing the concentration of the most polarized fluorine-gallium (-aluminum) bonds at the surface. An increase in barrier height from 0.7 to 1.1 eV after a 15% fluorine termination is obtained with ideality factors of 1.10 ± 0.05. The presence of surface dipoles that are changing the surface energy is proven by the sessile drop method as the electronegativity difference and polarization influences the contact angle. The extracted decrease in the Lifshitz-van-der-Waals component from 48.8 to 40.4 mJ/m(2) with increasing electronegativity and concentration of surface adatoms confirms the presence of increasing surface dipoles: as the polarizability of equally charged anions decreases with increasing electronegativity, the diiodomethane contact angles increase significantly from 14° up to 39° after the 15% fluorine termination. Therefore, a linear correlation between increasing anion electronegativity of the (Al)GaN termination and total surface energy within a 95% confidence interval is obtained. Furthermore, our results reveal a generally strong Lewis basicity of (Al)GaN surfaces explaining the high chemical inertness of the surfaces.

Origin of the Energy Barrier to Chemical Reactions of O2 on Al(111): Evidence for Charge Transfer, Not Spin Selection

DTIC Science & Technology

2012-11-08

change of O2 spin, at the barrier [Fig. 3]; i.e., the corresponding diabatic surfaces cross. Far from the Al surface, the triplet state is...previous theoretical models, in particular nonadiabatic [17] or diabatic [16] approaches, which also find an energy barrier consistent with experiment...crossings of different diabatic O2 spin configuration sur- faces are accommodated by small spin fluctuations within the metal surface. For parallel

Oxygen-Barrier Coating for Titanium

NASA Technical Reports Server (NTRS)

Clark, Ronald K.; Unnam, Jalaiah

1987-01-01

Oxygen-barrier coating for titanium developed to provide effective and low-cost means for protecting titanium alloys from oxygen in environment when alloys used in high-temperature mechanical or structural applications. Provides protective surface layer, which reduces extent of surface oxidation of alloy and forms barrier to diffusion of oxygen, limiting contamination of substrate alloy by oxygen. Consists of submicron layer of aluminum deposited on surface of titanium by electron-beam evaporation, with submicron layer of dioxide sputtered onto aluminum to form coat.

Durable, Low-Surface-Energy Treatments

NASA Technical Reports Server (NTRS)

Willis, Paul B.; Mcelroy, Paul M.; Hickey, Gregory S.

1992-01-01

Chemical treatment for creation of durable, low-surface-energy coatings for glass, ceramics and other protonated surfaces easily applied, and creates very thin semipermanent film with extremely low surface tension. Exhibits excellent stability; surfaces retreated if coating becomes damaged or eroded. Uses include water-repellent surfaces, oil-repellent surfaces, antimigration barriers, corrosion barriers, mold-release agents, and self-cleaning surfaces. Film resists wetting by water, alcohols, hydrocarbon solvents, and silicone oil. Has moderate resistance to abrasion, such as rubbing with cloths, and compression molding to polymers and composite materials.

InGaN/GaN multilayer quantum dots yellow-green light-emitting diode with optimized GaN barriers.

PubMed

Lv, Wenbin; Wang, Lai; Wang, Jiaxing; Hao, Zhibiao; Luo, Yi

2012-11-07

InGaN/GaN multilayer quantum dot (QD) structure is a potential type of active regions for yellow-green light-emitting diodes (LEDs). The surface morphologies and crystalline quality of GaN barriers are critical to the uniformity of InGaN QD layers. While GaN barriers were grown in multi-QD layers, we used improved growth parameters by increasing the growth temperature and switching the carrier gas from N2 to H2 in the metal organic vapor phase epitaxy. As a result, a 10-layer InGaN/GaN QD LED is demonstrated successfully. The transmission electron microscopy image shows the uniform multilayer InGaN QDs clearly. As the injection current increases from 5 to 50 mA, the electroluminescence peak wavelength shifts from 574 to 537 nm.

Dynamical approach to fusion-fission process in superheavy mass region

NASA Astrophysics Data System (ADS)

Aritomo, Y.; Hinde, D. J.; Wakhle, A.; du Rietz, R.; Dasgupta, M.; Hagino, K.; Chiba, S.; Nishio, K.

2012-10-01

In order to describe heavy-ion fusion reactions around the Coulomb barrier with an actinide target nucleus, we propose a model which combines the coupled-channels approach and a fluctuation-dissipation model for dynamical calculations. This model takes into account couplings to the collective states of the interacting nuclei in the penetration of the Coulomb barrier and the subsequent dynamical evolution of a nuclear shape from the contact configuration. In the fluctuation-dissipation model with a Langevin equation, the effect of nuclear orientation at the initial impact on the prolately deformed target nucleus is considered. Fusion-fission, quasifission and deep quasifission are separated as different Langevin trajectories on the potential energy surface. Using this model, we analyze the experimental data for the mass distribution of fission fragments (MDFF) in the reaction of 36S+238U at several incident energies around the Coulomb barrier.

InGaN/GaN multilayer quantum dots yellow-green light-emitting diode with optimized GaN barriers

PubMed Central

2012-01-01

InGaN/GaN multilayer quantum dot (QD) structure is a potential type of active regions for yellow-green light-emitting diodes (LEDs). The surface morphologies and crystalline quality of GaN barriers are critical to the uniformity of InGaN QD layers. While GaN barriers were grown in multi-QD layers, we used improved growth parameters by increasing the growth temperature and switching the carrier gas from N2 to H2 in the metal organic vapor phase epitaxy. As a result, a 10-layer InGaN/GaN QD LED is demonstrated successfully. The transmission electron microscopy image shows the uniform multilayer InGaN QDs clearly. As the injection current increases from 5 to 50 mA, the electroluminescence peak wavelength shifts from 574 to 537 nm. PMID:23134721

Controlled surface oxidation of multi-layered graphene anode to increase hole injection efficiency in organic electronic devices

NASA Astrophysics Data System (ADS)

Han, Tae-Hee; Kwon, Sung-Joo; Seo, Hong-Kyu; Lee, Tae-Woo

2016-03-01

Ultraviolet ozone (UVO) surface treatment of graphene changes its sp2-hybridized carbons to sp3-bonded carbons, and introduces oxygen-containing components. Oxidized graphene has a finite energy band gap, so UVO modification of the surface of a four-layered graphene anode increases its surface ionization potential up to ∼5.2 eV and improves the hole injection efficiency (η) in organic electronic devices by reducing the energy barrier between the graphene anode and overlying organic layers. By controlling the conditions of the UVO treatment, the electrical properties of the graphene can be tuned to improve η. This controlled surface modification of the graphene will provide a way to achieve efficient and stable flexible displays and solid-state lighting.

Numerical study of the effects of surface topography and chemistry on the wetting transition using the string method.

PubMed

Zhang, Yanan; Ren, Weiqing

2014-12-28

Droplets on a solid surface patterned with microstructures can exhibit the composite Cassie-Baxter (CB) state or the wetted Wenzel state. The stability of the CB state is determined by the energy barrier separating it from the wetted state. In this work, we study the CB to Wenzel transition using the string method [E et al., J. Chem. Phys. 126, 164103 (2007); W. Ren and E. Vanden-Eijnden, J. Chem. Phys. 138, 134105 (2013)]. We compute the transition states and energy barriers for a three-dimensional droplet on patterned surfaces. The liquid-vapor coexistence is modeled using the mean field theory. Numerical results are obtained for surfaces patterned with straight pillars and nails, respectively. It is found that on both type of surfaces, wetting occurs via infiltration of the liquid in a single groove. The reentrant geometry of nails creates large energy barrier for the wetting of the solid surface compared to straight pillars. We also study the effect of surface chemistry, pillar height, and inter-pillar spacing on the energy barrier and compare it with nails.

Numerical study of the effects of surface topography and chemistry on the wetting transition using the string method

NASA Astrophysics Data System (ADS)

Zhang, Yanan; Ren, Weiqing

2014-12-01

Droplets on a solid surface patterned with microstructures can exhibit the composite Cassie-Baxter (CB) state or the wetted Wenzel state. The stability of the CB state is determined by the energy barrier separating it from the wetted state. In this work, we study the CB to Wenzel transition using the string method [E et al., J. Chem. Phys. 126, 164103 (2007); W. Ren and E. Vanden-Eijnden, J. Chem. Phys. 138, 134105 (2013)]. We compute the transition states and energy barriers for a three-dimensional droplet on patterned surfaces. The liquid-vapor coexistence is modeled using the mean field theory. Numerical results are obtained for surfaces patterned with straight pillars and nails, respectively. It is found that on both type of surfaces, wetting occurs via infiltration of the liquid in a single groove. The reentrant geometry of nails creates large energy barrier for the wetting of the solid surface compared to straight pillars. We also study the effect of surface chemistry, pillar height, and inter-pillar spacing on the energy barrier and compare it with nails.

Multiscale Investigations of the Early Stage Oxidation on Cu Surfaces

NASA Astrophysics Data System (ADS)

Zhu, Qing; Xiao, Penghao; Lian, Xin; Yang, Shen-Che; Henkelman, Grame; Saidi, Wissam; Yang, Judith; University of Pittsburgh Team; University of Texas at Austin Team

Previous in situ TEM experiments have shown that the oxidation of the three low index Cu surfaces (100), (110) and (111) exhibit different oxide nucleation rates, and the resulting oxides have 3-dimensional (3D) island shapes or 2D rafts under different conditions. In order to better understand these results, we have investigated the early stages of Cu oxidation using a multiscale computational approach that employs density functional theory (DFT), reactive force field (ReaxFF), and kinetic Mote Carlo (KMC). With DFT calculation, we have compared O2 dissociation barriers on Cu (100), (110) and (111) surfaces at high oxygen coverage to evaluate the kinetic barrier of sublayer oxidization. We found that O2 dissociation barriers on Cu(111) surface are all lower than those on (110) and (100) surfaces. This trend agrees with experimental observations that (111) surface is easier to oxidize. These DFT calculated energy barriers are then incorporated into KMC simulations. The large scale ReaxFF molecular dynamics and KMC simulations detail the oxidation dynamics of the different Cu surfaces, and show the formation of various oxide morphologies that are consistent with experimental observations.

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

Hughes, Michael John; McConnaughhay, Johnie Franklin

A combustor includes a tube bundle that extends radially across at least a portion of the combustor. The tube bundle includes an upstream surface axially separated from a downstream surface, and a plurality of tubes extend from the upstream surface through the downstream surface to provide fluid communication through the tube bundle. A barrier extends radially inside the tube bundle between the upstream and downstream surfaces, and a baffle extends axially inside the tube bundle between the upstream surface and the barrier.

Current from a nano-gap hyperbolic diode using shape-factors: Theory

NASA Astrophysics Data System (ADS)

Jensen, Kevin L.; Shiffler, Donald A.; Peckerar, Martin; Harris, John R.; Petillo, John J.

2017-08-01

Quantum tunneling by field emission from nanoscale features or sharp field emission structures for which the anode-cathode gap is nanometers in scale ("nano diodes") experience strong deviations from the planar image charge lowered tunneling barrier used in the Murphy and Good formulation of the Fowler-Nordheim equation. These deviations alter the prediction of total current from a curved surface. Modifications to the emission barrier are modeled using a hyperbolic (prolate spheroidal) geometry to determine the trajectories along which the Gamow factor in a WKB-like treatment is undertaken; a quadratic equivalent potential is determined, and a method of shape factors is used to evaluate the corrected total current from a protrusion or wedge geometry.

Weather in Mountainous Terrain (Overcoming Scientific Barriers to Weather Support)

DTIC Science & Technology

2011-02-15

been more effective. Similarly, profiler data is more effective than surface observations. The satellite data are potentially valuable as an... Satellite data can play an important role in model validation, but accuracy has been an issue. Turbulence 1. The classical parameterizations for... data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this

Universal functions of nuclear proximity potential for Skyrme nucleus-nucleus interaction in a semiclassical approach

NASA Astrophysics Data System (ADS)

Gupta, Raj K.; Singh, Dalip; Kumar, Raj; Greiner, Walter

2009-07-01

The universal function of the nuclear proximity potential is obtained for the Skyrme nucleus-nucleus interaction in the semiclassical extended Thomas-Fermi (ETF) approach. This is obtained as a sum of the spin-orbit-density-independent and spin-orbit-density-dependent parts of the Hamiltonian density, since the two terms behave differently, the spin-orbit-density-independent part mainly attractive and the spin-orbit-density-dependent part mainly repulsive. The semiclassical expansions of kinetic energy density and spin-orbit density are allowed up to second order, and the two-parameter Fermi density, with its parameters fitted to experiments, is used for the nuclear density. The universal functions or the resulting nuclear proximity potential reproduce the 'exact' Skyrme nucleus-nucleus interaction potential in the semiclassical approach, within less than ~1 MeV of difference, both at the maximum attraction and in the surface region. An application of the resulting interaction potential to fusion excitation functions shows clearly that the parameterized universal functions of nuclear proximity potential substitute completely the 'exact' potential in the Skyrme energy density formalism based on the semiclassical ETF method, including also the modifications of interaction barriers at sub-barrier energies in terms of modifying the constants of the universal functions.

Association of Cell Surface Mucins with Galectin-3 Contributes to the Ocular Surface Epithelial Barrier*

PubMed Central

Argüeso, Pablo; Guzman-Aranguez, Ana; Mantelli, Flavio; Cao, Zhiyi; Ricciuto, Jessica; Panjwani, Noorjahan

2009-01-01

Maintenance of an intact mucosal barrier is critical to preventing damage to and infection of wet-surfaced epithelia. The mechanism of defense has been the subject of much investigation, and there is evidence now implicating O-glycosylated mucins on the epithelial cell surface. Here we investigate a new role for the carbohydrate-binding protein galectin-3 in stabilizing mucosal barriers through its interaction with mucins on the apical glycocalyx. Using the surface of the eye as a model system, we found that galectin-3 colocalized with two distinct membrane-associated mucins, MUC1 and MUC16, on the apical surface of epithelial cells and that both mucins bound to galectin-3 affinity columns in a galactose-dependent manner. Abrogation of the mucin-galectin interaction in four different mucosal epithelial cell types using competitive carbohydrate inhibitors of galectin binding, β-lactose and modified citrus pectin, resulted in decreased levels of galectin-3 on the cell surface with concomitant loss of barrier function, as indicated by increased permeability to rose bengal diagnostic dye. Similarly, down-regulation of mucin O-glycosylation using a stable tetracycline-inducible RNA interfering system to knockdown c1galt1 (T-synthase), a critical galactosyltransferase required for the synthesis of core 1 O-glycans, resulted in decreased cell surface O-glycosylation, reduced cell surface galectin-3, and increased epithelial permeability. Taken together, these results suggest that galectin-3 plays a key role in maintaining mucosal barrier function through carbohydrate-dependent interactions with cell surface mucins. PMID:19556244

Synchrotron Radiation and the Far-Infrared and Mid-Infrared Spectra of Ncncs

NASA Astrophysics Data System (ADS)

Winnewisser, Manfred; Winnewisser, Brenda P.; De Lucia, Frank C.; Tokaryk, Dennis; Ross, Stephen Cary; Billinghurst, Brant E.

2014-06-01

The large-amplitude in-plane bending vibration of NCNCS at 85 wn has a potential energy function which includes a barrier to linearity with a height of about 285 wn. The topology of the surface of the space defined by this two-dimensional potential function exhibits non-trivial monodromy. Therefore an energy/momentum map for a quantum system with its motion determined by such a potential takes the form of a lattice which contains a defect associated with the top of the barrier. In NCNCS, the wavenumber values of the fundamental vibrational excitation and the barrier height mean that easily accessible energy levels allow us to observe 3 bending vibrational levels below and 3 above the barrier, yet still below all of the other vibrational levels, allowing the study of all the levels in the neighborhood of the defect. In three measuring campaigns at the Canadian Light Source in May of the years 2011, 2012, and 2013 we have now obtained 8 of the 9 fundamental vibrational band systems of NCNCS in high resolution, in particular that of the large-amplitude bend in the FIR. So far only a-type spectra have been assigned. Thus we have now determined the Δvb = 1, and ΔKa = 0 vibrational intervals (using bent molecule notation) but do not yet have experimental values for either rotational ΔKa = +/- 1 intervals nor ro-vibrational Δvb = 1, ΔKa = +/- 1 intervals. In May of 2014 we will have our last measuring campaign and hope to observe the more elusive b-type transitions.

Polyurethane membranes for surgical gown applications

NASA Astrophysics Data System (ADS)

Ukpabi, Pauline Ozoemena

The Occupational Safety and Health Administration (OSHA) recently issued a directive requiring all employers to supply personnel protective equipment to employees who are at risk of exposure to blood or other potentially infectious body fluids. For the healthcare worker, a wide variety of surgical gowns is available commercially but there are concerns over their barrier effectiveness and/or wearer comfort. To successfully create a barrier fabric which combines resistance to fluid penetration with comfort, a complete understanding of the relationship between membrane structure and functional properties is required. In this study, we investigated the surface properties of hydrophilicity and hydrophobicity in polyurethane membranes intended for use in surgical gowns. The polyurethane membranes were grafted with side chains of varying lengths, polyethylene glycol (PEG) being used for the hydrophilic modifications and perfluoroalkyl compounds (a monofunctional acid and a difunctional amino alcohol) for the hydrophobic modifications. The hydrophilic treatment was intended to improve the comfort properties of monolithic membranes without adversely affecting their barrier properties. The hydrophobic treatment, on the other hand, was intended to improve the fluid repellency and hence barrier properties of microporous membranes without adversely affecting their comfort properties. Reflection infrared spectroscopy showed that fluorine was successfully grafted onto the polyurethane backbone during the hydrophobic modification, but was not sensitive enough to detect PEG grafting in leached polyethylene glycol-treated polyurethanes. X-ray photoelectron spectroscopy showed that the perfluoroalkylated polyurethanes contained up to 40% fluorine on their surfaces and the PEG-treated polyurethanes showed an increase in their C-O content over the unmodified polyurethane. Scanning electron microscopy not only showed that perfluoroalkylation yielded polyurethane membranes with very rough surfaces compared to the unmodified membrane, it also showed varying degrees of surface roughness on the perfluoroalkylated polyurethanes depending on whether the monofunctional acid or the difunctional amino alcohol was used as modifier. The PEG-treated samples exhibited smooth surfaces under the SEM. Perfluoroalkylation yielded samples with slightly higher contact angles than the untreated polyurethane while the PEG treatment resulted in polyurethanes with lower contact angles than the untreated polyurethane. The perfluoroalkylated materials were more thermally stable than the unmodified polyurethanes.

T Tank Farm Interim Surface Barrier Demonstration - Vadose Zone Monitoring FY09 Report

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

Zhang, Z. F.; Strickland, Christopher E.; Field, Jim G.

2010-01-01

DOE’s Office of River Protection constructed a temporary surface barrier over a portion of the T Tank Farm as part of the T Farm Interim Surface Barrier Demonstration Project. As part of the demonstration effort, vadose zone moisture is being monitored to assess the effectiveness of the barrier at reducing soil moisture. A solar-powered system was installed to continuously monitor soil water conditions at four locations (i.e., instrument Nests A, B, C, and D) beneath the barrier and outside the barrier footprint as well as site meteorological conditions. Nest A is placed in the area outside the barrier footprint andmore » serves as a control, providing subsurface conditions outside the influence of the surface barrier. Nest B provides subsurface measurements to assess surface-barrier edge effects. Nests C and D are used to assess changes in soil-moisture conditions beneath the interim surface barrier. Each instrument nest is composed of a capacitance probe (CP) with multiple sensors, multiple heat-dissipation units (HDUs), and a neutron probe (NP) access tube. The monitoring results in FY09 are summarized below. The solar panels functioned normally and could provide sufficient power to the instruments. The CP in Nest C after September 20, 2009, was not functional. The CP sensors in Nest B after July 13 and the 0.9-m CP sensor in Nest D before June 10 gave noisy data. Other CPs were functional normally. All the HDUs were functional normally but some pressure-head values measured by HDUs were greater than the upper measurement-limit. The higher-than-upper-limit values might be due to the very wet soil condition and/or measurement error but do not imply the malfunction of the sensors. Similar to FY07 and FY08, in FY09, the soil under natural conditions (Nest A) was generally recharged during the winter period (October-March) and discharged during the summer period (April-September). Soil water conditions above about 1.5-m to 2-m depth from all three types of measurements (i.e., CP, NP and HDU) showed relatively large variation during the seasonal wetting-drying cycle. For the soil below 2-m depth, the seasonal variation of soil water content was relatively small. The construction of the surface barrier was completed in April 2008. In the soil below the surface barrier (Nests C and D), the CP measurements showed that water content at the soil between 0.6-m and 2.3-m depths was very stable, indicating no climatic impacts on soil water condition beneath the barrier. The NP-measured water content showed that soil water drainage seemed occurring in the soil between about 3.4 m (11 ft) and 9.1 m (30 ft) in FY09. The HDU-measured water pressure decreased consistently in the soil above 5-m depth, indicating soil water drainage at these depths of the soil. In the soil below the edge of the surface barrier (Nest B), the CP-measured water content was relatively stable through the year except at the 0.9-m depth; the NP-measured water content showed that soil water drainage was occurring in the soil between about 3.4 m (11 ft) and 9.1 m (30 ft) but at a slightly smaller magnitude than those in Nests C and D; the HDU-measurements show that the pressure head changes in FY09 in Nest B were less than those for C and D but more than those for A. The soil-water-pressure head was more sensitive to soil water regime changes under dry conditions. In the soil beneath the barrier, the theoretical steady-state values of pressure head is equal to the negative of the distance to groundwater table. Hence, it is expected that, in the future, while the water content become stable, the pressure head will keep decreasing for a long time (e.g., many years). These results indicate that the T Tank Farm surface barrier was performing as expected by intercepting the meteoric water from infiltrating into the soil and the soil was becoming drier gradually. The barrier also has some effects on the soil below the barrier edge but at a reduced magnitude.« less

Optimization of micro-fabricated porous membranes for intestinal epithelial cell culture and in vitro modeling of the human intestinal barrier

NASA Astrophysics Data System (ADS)

Nair Gourikutty Sajay, Bhuvanendran; Yin, Chiam Su; Ramadan, Qasem

2017-12-01

In vitro modeling of organs could provide a controlled platform for studying physiological events and has great potential in the field of pharmaceutical development. Here, we describe the characterization of in vitro modeling of the human intestinal barrier mimicked using silicon porous membranes as a substrate. To mimic an intestinal in vivo setup as closely as possible, a porous substrate is required in a dynamic environment for the cells to grow rather than a static setup with an impermeable surface such as a petri dish. In this study, we focus on the detailed characterization of Caco-2 cells cultured on a silicon membrane with different pore sizes as well as the effect of dynamic fluid flow on the model. The porous silicon membrane together with continuous perfusion of liquid applying shear stress on the cells enhances the differentiation of polarized cells by providing access to the both their basal and apical surfaces. Membranes with pore sizes of 0.5-3 µm were used and a shear stress of ~0.03 dyne cm-2 was created by applying a low flow rate of 20 nl s-1. By providing these optimized conditions, cells were able to differentiate with columnar morphology, which developed microvilli structures on their apical side and tight junctions between adjacent cells like those in a healthy human intestinal barrier. In this setup, it is possible to study the important cellular functions of the intestine such as transport, absorption and secretion, and thus this model has great potential in drug screening.

Assessment of skin barrier function and biochemical changes of ex vivo human skin in response to physical and chemical barrier disruption.

PubMed

Döge, Nadine; Avetisyan, Araks; Hadam, Sabrina; Pfannes, Eva Katharina Barbosa; Rancan, Fiorenza; Blume-Peytavi, Ulrike; Vogt, Annika

2017-07-01

Topical dermatotherapy is intended to be used on diseased skin. Novel drug delivery systems even address differences between intact and diseased skin underlining the need for pre-clinical assessment of different states of barrier disruption. Herein, we studied how short-term incubation in culture media compared to incubation in humidified chambers affects human skin barrier function and viability. On both models we assessed different types and intensities of physical and chemical barrier disruption methods with regard to structural integrity, biophysical parameters and cytokine levels. Tissue degeneration and proliferative activity limited the use of tissue cultures to 48h. Viability is better preserved in cultured tissue. Tape-stripping (50×TS) and 4h sodium lauryl sulfate (SLS) pre-treatment were identified as highly reproducible and effective procedures for barrier disruption. Transepidermal water loss (TEWL) values reproducibly increased with the intensity of disruption while sebum content and skin surface pH were of limited value. Interleukin (IL)-6/8 and various chemokines and proteases were increased in tape-stripped skin which was more pronounced in SLS-treated skin tissue extracts. Thus, albeit limited to 48h, cultured full-thickness skin maintained several barrier characteristics and responded to different intensities of barrier disruption. Potentially, these models can be used to assess pre-clinically the efficacy and penetration of anti-inflammatory compounds. Copyright © 2016 Elsevier B.V. All rights reserved.

Simulation study of free-energy barriers in the wetting transition of an oily fluid on a rough surface with reentrant geometry.

PubMed

Savoy, Elizabeth S; Escobedo, Fernando A

2012-11-20

When in contact with a rough solid surface, fluids with low surface tension, such as oils and alkanes, have their lowest free energy in the fully wetted state. For applications where nonwetting by these phillic fluids is desired, some barrier must be introduced to maintain the nonwetted composite state. One way to create this free-energy barrier is to fabricate roughness with reentrant geometry, but the question remains as to whether the free-energy barrier is sufficiently high to prevent wetting. Our goal is to quantify the free-energy landscape for the wetting transition of an oily fluid on a surface of nails and identify significant surface features and conditions that maximize the wetting free-energy barrier (ΔGfwd*). This is a departure from most work on wetting, which focuses on the equilibrium composite and wetted states. We use boxed molecular dynamics (BXD) (Glowacki, D. R.; Paci, E.; Shalashilin, D. V. J. Phys. Chem. B2009, 113, 16603-16611) with a modified control scheme to evaluate both the thermodynamics and kinetics of the transition over a range of surface affinities (chemistry). We find that the reentrant geometry of the nails does create a free-energy barrier to transition for phillic chemistry whereas a corresponding system on straight posts wets spontaneously and, that doubling the nail height more than doubles ΔGfwd*. For neutral to phillic chemistry, the dewetting free-energy barrier is at least an order of magnitude higher than that for wetting, indicating an essentially irreversible wetting transition. Transition rates from BXD simulations and the associated trends agree well with those in our previous study that used forward flux sampling to compute transition rates for similar systems.

Efficient sampling over rough energy landscapes with high barriers: A combination of metadynamics with integrated tempering sampling.

PubMed

Yang, Y Isaac; Zhang, Jun; Che, Xing; Yang, Lijiang; Gao, Yi Qin

2016-03-07

In order to efficiently overcome high free energy barriers embedded in a complex energy landscape and calculate overall thermodynamics properties using molecular dynamics simulations, we developed and implemented a sampling strategy by combining the metadynamics with (selective) integrated tempering sampling (ITS/SITS) method. The dominant local minima on the potential energy surface (PES) are partially exalted by accumulating history-dependent potentials as in metadynamics, and the sampling over the entire PES is further enhanced by ITS/SITS. With this hybrid method, the simulated system can be rapidly driven across the dominant barrier along selected collective coordinates. Then, ITS/SITS ensures a fast convergence of the sampling over the entire PES and an efficient calculation of the overall thermodynamic properties of the simulation system. To test the accuracy and efficiency of this method, we first benchmarked this method in the calculation of ϕ - ψ distribution of alanine dipeptide in explicit solvent. We further applied it to examine the design of template molecules for aromatic meta-C-H activation in solutions and investigate solution conformations of the nonapeptide Bradykinin involving slow cis-trans isomerizations of three proline residues.

Efficient sampling over rough energy landscapes with high barriers: A combination of metadynamics with integrated tempering sampling

NASA Astrophysics Data System (ADS)

Yang, Y. Isaac; Zhang, Jun; Che, Xing; Yang, Lijiang; Gao, Yi Qin

2016-03-01

In order to efficiently overcome high free energy barriers embedded in a complex energy landscape and calculate overall thermodynamics properties using molecular dynamics simulations, we developed and implemented a sampling strategy by combining the metadynamics with (selective) integrated tempering sampling (ITS/SITS) method. The dominant local minima on the potential energy surface (PES) are partially exalted by accumulating history-dependent potentials as in metadynamics, and the sampling over the entire PES is further enhanced by ITS/SITS. With this hybrid method, the simulated system can be rapidly driven across the dominant barrier along selected collective coordinates. Then, ITS/SITS ensures a fast convergence of the sampling over the entire PES and an efficient calculation of the overall thermodynamic properties of the simulation system. To test the accuracy and efficiency of this method, we first benchmarked this method in the calculation of ϕ - ψ distribution of alanine dipeptide in explicit solvent. We further applied it to examine the design of template molecules for aromatic meta-C—H activation in solutions and investigate solution conformations of the nonapeptide Bradykinin involving slow cis-trans isomerizations of three proline residues.

Efficient sampling over rough energy landscapes with high barriers: A combination of metadynamics with integrated tempering sampling

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

Yang, Y. Isaac; Zhang, Jun; Che, Xing

2016-03-07

In order to efficiently overcome high free energy barriers embedded in a complex energy landscape and calculate overall thermodynamics properties using molecular dynamics simulations, we developed and implemented a sampling strategy by combining the metadynamics with (selective) integrated tempering sampling (ITS/SITS) method. The dominant local minima on the potential energy surface (PES) are partially exalted by accumulating history-dependent potentials as in metadynamics, and the sampling over the entire PES is further enhanced by ITS/SITS. With this hybrid method, the simulated system can be rapidly driven across the dominant barrier along selected collective coordinates. Then, ITS/SITS ensures a fast convergence ofmore » the sampling over the entire PES and an efficient calculation of the overall thermodynamic properties of the simulation system. To test the accuracy and efficiency of this method, we first benchmarked this method in the calculation of ϕ − ψ distribution of alanine dipeptide in explicit solvent. We further applied it to examine the design of template molecules for aromatic meta-C—H activation in solutions and investigate solution conformations of the nonapeptide Bradykinin involving slow cis-trans isomerizations of three proline residues.« less

Extension of the general thermal field equation for nanosized emitters

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

Kyritsakis, A., E-mail: akyritsos1@gmail.com; Xanthakis, J. P.

2016-01-28

During the previous decade, Jensen et al. developed a general analytical model that successfully describes electron emission from metals both in the field and thermionic regimes, as well as in the transition region. In that development, the standard image corrected triangular potential barrier was used. This barrier model is valid only for planar surfaces and therefore cannot be used in general for modern nanometric emitters. In a recent publication, the authors showed that the standard Fowler-Nordheim theory can be generalized for highly curved emitters if a quadratic term is included to the potential model. In this paper, we extend thismore » generalization for high temperatures and include both the thermal and intermediate regimes. This is achieved by applying the general method developed by Jensen to the quadratic barrier model of our previous publication. We obtain results that are in good agreement with fully numerical calculations for radii R > 4 nm, while our calculated current density differs by a factor up to 27 from the one predicted by the Jensen's standard General-Thermal-Field (GTF) equation. Our extended GTF equation has application to modern sharp electron sources, beam simulation models, and vacuum breakdown theory.« less

Method of Suppressing Sublimation in Advanced Thermoelectric Devices

NASA Technical Reports Server (NTRS)

Sakamoto, Jeffrey S. (Inventor); Caillat, Thierry (Inventor); Fleurial, Jean-Pierre (Inventor); Snyder, G. Jeffrey (Inventor)

2009-01-01

A method of applying a physical barrier to suppress thermal decomposition near a surface of a thermoelectric material including applying a continuous metal foil to a predetermined portion of the surface of the thermoelectric material, physically binding the continuous metal foil to the surface of the thermoelectric material using a binding member, and heating in a predetermined atmosphere the applied and physically bound continuous metal foil and the thermoelectric material to a sufficient temperature in order to promote bonding between the continuous metal foil and the surface of the thermoelectric material. The continuous metal foil forms a physical barrier to enclose a predetermined portion of the surface. Thermal decomposition is suppressed at the surface of the thermoelectric material enclosed by the physical barrier when the thermoelectric element is in operation.

Mechanically expandable annular seal

DOEpatents

Gilmore, R.F.

1983-07-19

A mechanically expandable annular reusable seal assembly to form an annular hermetic barrier between two stationary, parallel, and planar containment surfaces is described. A rotatable ring, attached to the first surface, has ring wedges resembling the saw-tooth array of a hole saw. Matching seal wedges are slidably attached to the ring wedges and have their motion restricted to be perpendicular to the second surface. Each seal wedge has a face parallel to the second surface. An annular elastomer seal has a central annular region attached to the seal wedges' parallel faces and has its inner and outer circumferences attached to the first surface. A rotation of the ring extends the elastomer seal's central region perpendicularly towards the second surface to create the fluid tight barrier. A counter rotation removes the barrier. 6 figs.

Comparative research on activation technique for GaAs photocathodes

NASA Astrophysics Data System (ADS)

Chen, Liang; Qian, Yunsheng; Chang, Benkang; Chen, Xinlong; Yang, Rui

2012-03-01

The properties of GaAs photocathodes mainly depend on the material design and activation technique. In early researches, high-low temperature two-step activation has been proved to get more quantum efficiency than high-temperature single-step activation. But the variations of surface barriers for two activation techniques have not been well studied, thus the best activation temperature, best Cs-O ratio and best activation time for two-step activation technique have not been well found. Because the surface photovoltage spectroscopy (SPS) before activation is only in connection with the body parameters for GaAs photocathode such as electron diffusion length and the spectral response current (SRC) after activation is in connection with not only body parameters but also surface barriers, thus the surface escape probability (SEP) can be well fitted through the comparative research between SPS before activation and SEP after activation. Through deduction for the tunneling process of surface barriers by Schrödinger equation, the width and height for surface barrier I and II can be well fitted through the curves of SEP. The fitting results were well proved and analyzed by quantitative analysis of angle-dependent X-ray photoelectron spectroscopy (ADXPS) which can also study the surface chemical compositions, atomic concentration percentage and layer thickness for GaAs photocathodes. This comparative research method for fitting parameters of surface barriers through SPS before activation and SRC after activation shows a better real-time in system method for the researches of activation techniques.

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.

Surface Dielectric Barrier Discharge Jet for Skin Disinfection

NASA Astrophysics Data System (ADS)

Creyghton, Yves; Meijer, Rogier; Verweij, Paul; van der Zanden, Frank; Leenders, Paul

A consortium consisting of the research institute TNO, the medical ­university and hospital St Radboud and two industrial enterprises is working on a non-thermal plasma treatment method for hand disinfection. The group is seeking for cooperation, in particular in the field of validation methods and potential ­standardization for plasma based disinfection procedures. The present paper describes technical progress in plasma source development together with initial microbiological data. Particular properties of the sheet shaped plasma volume are the possibility of treating large irregular surfaces in a short period of time, effective plasma produced species transfer to the surface together with high controllability of the nature of plasma species by means of temperature conditioning.

Trajectories and traversal times in quantum tunneling

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

Huang, Zhi Hong.

1989-01-01

The classical concepts of trajectories and traversal times applied to quantum tunneling are discussed. By using the Wentzel-Kramers-Brillouin approximation, it is found that in a forbidden region of a multidimensional space the wave function can be described by two sets of trajectories, or equivalently by two sets of wave fronts. The trajectories belonging to different sets are mutually orthogonal. An extended Huygens construction is proposed to determine these wave fronts and trajectories. In contrast to the classical results in the allowed region, these trajectories couple to each other. However, if the incident wave is normal to the turning surface, themore » trajectories are found to be independent and can be determined by Newton's equations of motion with inverted potential and energy. The multidimensional tunneling theory is then applied to the scanning tunneling microscope to calculate the current density distribution and to derive the expressions for the lateral resolution and the surface corrugation amplitude. The traversal time in quantum tunneling, i.e. tunneling time, is found to depend on model calculations and simulations. Computer simulation of a wave packet tunneling through a square barrier is performed. Several approaches, including the phase method, Larmor clock, and time-dependent barrier model, are investigated. For a square barrier, two characteristic times are found: One is equal to the barrier width divided by the magnitude of the imaginary velocity; the other is equal to the decay length divided by the incident velocity. It is believed that the tunneling time can only be defined operationally.« less

Ion Exchange Method - Diffusion Barrier Investigations

NASA Astrophysics Data System (ADS)

Pielak, G.; Szustakowski, M.; Kiezun, A.

1990-01-01

Ion exchange method is used to GRIN-rod lenses manufacturing. In this process the ion exchange occurs between bulk glass (rod) and a molten salt. It was find that diffusion barrier exists on a border of glass surface and molten salt. The investigations of this barrier show that it value varies with ion exchange time and process temperature. It was find that in the case when thalium glass rod was treated in KNO3, bath, the minimum of the potential after 24 h was in temperature of 407°C, after 48 h in 422°C, after 72 h in 438°C and so on. So there are the possibility to keep the minimum of diffusion barrier by changing the temperature of the process and then the effectiveness of ion exchange process is the most effective. The time needed to obtain suitable refractive index distribution in a process when temperature was linearly changed from 400°C to 460°C was shorter of about 30% compare with the process in which temperature was constant and equal 450°C.

Theory of C2Hx species on Pt{110} (1×2): Reaction pathways for dehydrogenation

NASA Astrophysics Data System (ADS)

Anghel, A. T.; Wales, D. J.; Jenkins, S. J.; King, D. A.

2007-01-01

A complete reaction sequence for molecular dissociation at a surface has been characterized using density functional theory. The barriers for sequential ethane dehydrogenation on Pt{110} are found to fall into distinct energy sets: very low barriers, with values in the range of 0.29-0.42eV, for the initial ethane dissociation to ethene and ethylidene at the surface; medium barriers, in the range of 0.72-1.10eV, for dehydrogenation of C2H4 fragments to vinylidene and ethyne; and high barriers, requiring more than 1.45eV, for further dehydrogenation. For dissociation processes where more than one pathway has been found, the lowest energetic route links the most stable reactant adsorbed state at the surface to a product state involving the hydrocarbon moiety adsorbed in its most stable configuration at the surface. Hence there is a clear link between surface stability and kinetics for these species.

Theoretical study on the potential energy surfaces of CaNC and CaCN

NASA Astrophysics Data System (ADS)

Ishii, Keisaku; Taketsugu, Tetsuya; Hirano, Tsuneo

2003-06-01

The potential energy surfaces of CaNC ( overlineX2Σ+) and CaCN ( overlineX2Σ+) have been investigated by the highly correlated ab initio molecular orbital methods. The bending potential for CaNC is shallow, and shows quite anharmonic and anomalous character, which can explain why the centrifugal distortion constants up to the tenth order were required for the analysis of its rotational spectrum. The reaction path for the isomerization reaction of CaNC and CaCN was also determined: The activation barrier is 2111 cm -1 from the CaNC side, and 602 cm -1 from the CaCN side. Core-core and core-valence correlation contributions of Ca M-shell electrons make the Ca-N (for CaNC) and Ca-C (for CaCN) bond lengths shorter by 0.05 and 0.04 Å, respectively, which indicates the significance of these core-correlation effects.

Applying a potential difference to minimise damage to carbon fibres during carbon nanotube grafting by chemical vapour deposition.

PubMed

Anthony, David B; Qian, Hui; Clancy, Adam J; Greenhalgh, Emile S; Bismarck, Alexander; Shaffer, Milo S P

2017-07-28

The application of an in situ potential difference between carbon fibres and a graphite foil counter electrode (300 V, generating an electric field ca 0.3-0.7 V μm -1 ), during the chemical vapour deposition synthesis of carbon nanotube (CNT) grafted carbon fibres, significantly improves the uniformity of growth without reducing the tensile properties of the underlying carbon fibres. Grafted CNTs with diameters 55 nm ± 36 nm and lengths around 10 μm were well attached to the carbon fibre surface, and were grown without the requirement for protective barrier coatings. The grafted CNTs increased the surface area to 185 m 2 g -1 compared to the as-received sized carbon fibre 0.24 m 2 g -1 . The approach is not restricted to batch systems and has the potential to improve CNT grafted carbon fibre production for continuous processing.

Applying a potential difference to minimise damage to carbon fibres during carbon nanotube grafting by chemical vapour deposition

NASA Astrophysics Data System (ADS)

Anthony, David B.; Qian, Hui; Clancy, Adam J.; Greenhalgh, Emile S.; Bismarck, Alexander; Shaffer, Milo S. P.

2017-07-01

The application of an in situ potential difference between carbon fibres and a graphite foil counter electrode (300 V, generating an electric field ca 0.3-0.7 V μm-1), during the chemical vapour deposition synthesis of carbon nanotube (CNT) grafted carbon fibres, significantly improves the uniformity of growth without reducing the tensile properties of the underlying carbon fibres. Grafted CNTs with diameters 55 nm ± 36 nm and lengths around 10 μm were well attached to the carbon fibre surface, and were grown without the requirement for protective barrier coatings. The grafted CNTs increased the surface area to 185 m2 g-1 compared to the as-received sized carbon fibre 0.24 m2 g-1. The approach is not restricted to batch systems and has the potential to improve CNT grafted carbon fibre production for continuous processing.

Calculation of smooth potential energy surfaces using local electron correlation methods

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

Mata, Ricardo A.; Werner, Hans-Joachim

2006-11-14

The geometry dependence of excitation domains in local correlation methods can lead to noncontinuous potential energy surfaces. We propose a simple domain merging procedure which eliminates this problem in many situations. The method is applied to heterolytic bond dissociations of ketene and propadienone, to SN2 reactions of Cl{sup -} with alkylchlorides, and in a quantum mechanical/molecular mechanical study of the chorismate mutase enzyme. It is demonstrated that smooth potentials are obtained in all cases. Furthermore, basis set superposition error effects are reduced in local calculations, and it is found that this leads to better basis set convergence when computing barriermore » heights or weak interactions. When the electronic structure strongly changes between reactants or products and the transition state, the domain merging procedure leads to a balanced description of all structures and accurate barrier heights.« less

DFT study of adsorption and dissociation of thiophene molecules on Ni(1 1 0)

NASA Astrophysics Data System (ADS)

Morin, C.; Eichler, A.; Hirschl, R.; Sautet, P.; Hafner, J.

2003-08-01

The different adsorption possibilities of thiophene (C 4H 4S) on the Ni(1 1 0) surface have been studied using first principle local-density-functional calculations, with the Vienna ab initio simulation package, which is based on a plane wave basis set and projector augmented wave potentials. For each configuration, a geometric optimisation has been performed. A detailed analysis of the structural and electronic properties of the molecule and the surface in the most stable conformations is presented, showing the combined roles of the molecular distortion and the interactions between the molecule and the surface. Three structures with comparatively large adsorption energies are identified, all with the molecule plane parallel to the surface. Starting from these stabilised structures, various scenarios for the desulfurisation process have been envisaged. While, for the most stable structure, the formation of an adsorbed thiol is an activated process, with an energetic barrier of 0.70 eV, the two structures which are just a bit less stable can dissociate to a C 4H 4 species and a sulfur atom with barriers as low as 0.07 eV. A description of the different transition states and a kinetic analysis of the desulfurisation reaction is also presented.

Single-electron population and depopulation of an isolated quantum dot using a surface-acoustic-wave pulse.

PubMed

Kataoka, M; Schneble, R J; Thorn, A L; Barnes, C H W; Ford, C J B; Anderson, D; Jones, G A C; Farrer, I; Ritchie, D A; Pepper, M

2007-01-26

We use a pulse of surface acoustic waves (SAWs) to control the electron population and depopulation of a quantum dot. The barriers between the dot and reservoirs are set high to isolate the dot. Within a time scale of approximately 100 s the dot can be set to a nonequilibrium charge state, where an empty (occupied) level stays below (above) the Fermi energy. A pulse containing a fixed number of SAW periods is sent through the dot, controllably changing the potential, and hence the tunneling probability, to add (remove) an electron to (from) the dot.

Small-scale barriers mitigate desertification processes and enhance plant recruitment in a degraded semiarid grassland

USGS Publications Warehouse

Fick, Stephen E; Decker, Cheryl E.; Duniway, Michael C.; Miller, Mark E.

2016-01-01

Anthropogenic desertification is a problem that plagues drylands globally; however, the factors which maintain degraded states are often unclear. In Canyonlands National Park on the Colorado Plateau of southeastern Utah, many degraded grasslands have not recovered structure and function >40 yr after release from livestock grazing pressure, necessitating active restoration. We hypothesized that multiple factors contribute to the persistent degraded state, including lack of seed availability, surficial soil-hydrological properties, and high levels of spatial connectivity (lack of perennial vegetation and other surface structure to retain water, litter, seed, and sediment). In combination with seeding and surface raking treatments, we tested the effect of small barrier structures (“ConMods”) designed to disrupt the loss of litter, seed and sediment in degraded soil patches within the park. Grass establishment was highest when all treatments (structures, seed addition, and soil disturbance) were combined, but only in the second year after installation, following favorable climatic conditions. We suggest that multiple limiting factors were ameliorated by treatments, including seed limitation and microsite availability, seed removal by harvester ants, and stressful abiotic conditions. Higher densities of grass seedlings on the north and east sides of barrier structures following the summer months suggest that structures may have functioned as artificial “nurse-plants”, sheltering seedlings from wind and radiation as well as accumulating wind-blown resources. Barrier structures increased the establishment of both native perennial grasses and exotic annuals, although there were species-specific differences in mortality related to spatial distribution of seedlings within barrier structures. The unique success of all treatments combined, and even then only under favorable climatic conditions and in certain soil patches, highlights that restoration success (and potentially, natural regeneration) often is contingent on many interacting factors.

Characterization of Textiles Used in Chefs' Uniforms for Protection Against Thermal Hazards Encountered in the Kitchen Environment.

PubMed

Zhang, Han; McQueen, Rachel H; Batcheller, Jane C; Ehnes, Briana L; Paskaluk, Stephen A

2015-10-01

Within the kitchen the potential for burn injuries arising from contact with hot surfaces, flames, hot liquid, and steam hazards is high. The chef's uniform can potentially offer some protection against such burns by providing a protective barrier between the skin and the thermal hazard, although the extent to which can provide some protection is unknown. The purpose of this study was to examine whether fabrics used in chefs' uniforms were able to provide some protection against thermal hazards encountered in the kitchen. Fabrics from chefs' jackets and aprons were selected. Flammability of single- and multiple-layered fabrics was measured. Effect of jacket type, apron and number of layers on hot surface, hot water, and steam exposure was also measured. Findings showed that all of the jacket and apron fabrics rapidly ignited when exposed to a flame. Thermal protection against hot surfaces increased as layers increased due to more insulation. Protection against steam and hot water improved with an impermeable apron in the system. For wet thermal hazards increasing the number of permeable layers can decrease the level of protection due to stored thermal energy. As the hands and arms are most at risk of burn injury increased insulation and water-impermeable barrier in the sleeves would improve thermal protection with minimal compromise to overall thermal comfort. © The Author 2015. Published by Oxford University Press on behalf of the British Occupational Hygiene Society.

Monte Carlo simulations on atropisomerism of thienotriazolodiazepines applicable to slow transition phenomena using potential energy surfaces by ab initio molecular orbital calculations.

PubMed

Morikami, Kenji; Itezono, Yoshiko; Nishimoto, Masahiro; Ohta, Masateru

2014-01-01

Compounds with a medium-sized flexible ring often show atropisomerism that is caused by the high-energy barriers between long-lived conformers that can be isolated and often have different biological properties to each other. In this study, the frequency of the transition between the two stable conformers, aS and aR, of thienotriazolodiazepine compounds with flexible 7-membered rings was estimated computationally by Monte Carlo (MC) simulations and validated experimentally by NMR experiments. To estimate the energy barriers for transitions as precisely as possible, the potential energy (PE) surfaces used in the MC simulations were calculated by molecular orbital (MO) methods. To accomplish the MC simulations with the MO-based PE surfaces in a practical central processing unit (CPU) time, the MO-based PE of each conformer was pre-calculated and stored before the MC simulations, and then only referred to during the MC simulations. The activation energies for transitions calculated by the MC simulations agreed well with the experimental ΔG determined by the NMR experiments. The analysis of the transition trajectories of the MC simulations revealed that the transition occurred not only through the transition states, but also through many different transition paths. Our computational methods gave us quantitative estimates of atropisomerism of the thienotriazolodiazepine compounds in a practical period of time, and the method could be applicable for other slow-dynamics phenomena that cannot be investigated by other atomistic simulations.

CH4 dehydrogenation on Cu(1 1 1), Cu@Cu(1 1 1), Rh@Cu(1 1 1) and RhCu(1 1 1) surfaces: A comparison studies of catalytic activity

NASA Astrophysics Data System (ADS)

Zhang, Riguang; Duan, Tian; Ling, Lixia; Wang, Baojun

2015-06-01

In the CVD growth of graphene, the reaction barriers of the dehydrogenation for hydrocarbon molecules directly decide the graphene CVD growth temperature. In this study, density functional theory method has been employed to comparatively probe into CH4 dehydrogenation on four types of Cu(1 1 1) surface, including the flat Cu(1 1 1) surface (labeled as Cu(1 1 1)) and the Cu(1 1 1) surface with one surface Cu atom substituted by one Rh atom (labeled as RhCu(1 1 1)), as well as the Cu(1 1 1) surface with one Cu or Rh adatom (labeled as Cu@Cu(1 1 1) and Rh@Cu(1 1 1), respectively). Our results show that the highest barrier of the whole CH4 dehydrogenation process is remarkably reduced from 448.7 and 418.4 kJ mol-1 on the flat Cu(1 1 1) and Cu@Cu(1 1 1) surfaces to 258.9 kJ mol-1 on RhCu(1 1 1) surface, and to 180.0 kJ mol-1 on Rh@Cu(1 1 1) surface, indicating that the adsorbed or substituted Rh atom on Cu catalyst can exhibit better catalytic activity for CH4 complete dehydrogenation; meanwhile, since the differences for the highest barrier between Cu@Cu(1 1 1) and Cu(1 1 1) surfaces are smaller, the catalytic behaviors of Cu@Cu(1 1 1) surface are very close to the flat Cu(1 1 1) surface, suggesting that the morphology of Cu substrate does not obviously affect the dehydrogenation of CH4, which accords with the reported experimental observations. As a result, the adsorbed or substituted Rh atom on Cu catalyst exhibit a better catalytic activity for CH4 dehydrogenation compared to the pure Cu catalyst, especially on Rh-adsorbed Cu catalyst, we can conclude that the potential of synthesizing high-quality graphene with the help of Rh on Cu foils may be carried out at relatively low temperatures. Meanwhile, the adsorbed Rh atom is the reaction active center, namely, the CVD growth can be controlled by manipulating the graphene nucleation position.

Electron mobility enhancement in metalorganic-vapor-phase-epitaxy-grown InAlN high-electron-mobility transistors by control of surface morphology of spacer layer

NASA Astrophysics Data System (ADS)

Yamada, Atsushi; Ishiguro, Tetsuro; Kotani, Junji; Nakamura, Norikazu

2018-01-01

We demonstrated low-sheet-resistance metalorganic-vapor-phase-epitaxy-grown InAlN high-electron-mobility transistors using AlGaN spacers with excellent surface morphology. We systematically investigated the effects of AlGaN spacer growth conditions on surface morphology and electron mobility. We found that the surface morphology of InAlN barriers depends on that of AlGaN spacers. Ga desorption from AlGaN spacers was suppressed by increasing the trimethylaluminum (TMA) supply rate, resulting in the small surface roughnesses of InAlN barriers and AlGaN spacers. Moreover, we found that an increase in the NH3 supply rate also improved the surface morphologies of InAlN barriers and AlGaN spacers as long as the TMA supply rate was high enough to suppress the degradation of GaN channels. Finally, we realized a low sheet resistance of 185.5 Ω/sq with a high electron mobility of 1210 cm2 V-1 s-1 by improving the surface morphologies of AlGaN spacers and InAlN barriers.

Numerical study of the effects of surface topography and chemistry on the wetting transition using the string method

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

Zhang, Yanan, E-mail: ynzhang@suda.edu.cn; Ren, Weiqing, E-mail: matrw@nus.edu.sg; Institute of High Performance Computing, Singapore 138632

2014-12-28

Droplets on a solid surface patterned with microstructures can exhibit the composite Cassie-Baxter (CB) state or the wetted Wenzel state. The stability of the CB state is determined by the energy barrier separating it from the wetted state. In this work, we study the CB to Wenzel transition using the string method [E et al., J. Chem. Phys. 126, 164103 (2007); W. Ren and E. Vanden-Eijnden, J. Chem. Phys. 138, 134105 (2013)]. We compute the transition states and energy barriers for a three-dimensional droplet on patterned surfaces. The liquid-vapor coexistence is modeled using the mean field theory. Numerical results aremore » obtained for surfaces patterned with straight pillars and nails, respectively. It is found that on both type of surfaces, wetting occurs via infiltration of the liquid in a single groove. The reentrant geometry of nails creates large energy barrier for the wetting of the solid surface compared to straight pillars. We also study the effect of surface chemistry, pillar height, and inter-pillar spacing on the energy barrier and compare it with nails.« less

Surface potential based modeling of charge, current, and capacitances in DGTFET including mobile channel charge and ambipolar behaviour

NASA Astrophysics Data System (ADS)

Jain, Prateek; Yadav, Chandan; Agarwal, Amit; Chauhan, Yogesh Singh

2017-08-01

We present a surface potential based analytical model for double gate tunnel field effect transistor (DGTFET) for the current, terminal charges, and terminal capacitances. The model accounts for the effect of the mobile charge in the channel and captures the device physics in depletion as well as in the strong inversion regime. The narrowing of the tunnel barrier in the presence of mobile charges in the channel is incorporated via modeling of the inverse decay length, which is constant under channel depletion condition and bias dependent under inversion condition. To capture the ambipolar current behavior in the model, tunneling at the drain junction is also included. The proposed model is validated against TCAD simulation data and it shows close match with the simulation data.

Drop-wise and film-wise water condensation processes occurring on metallic micro-scaled surfaces

NASA Astrophysics Data System (ADS)

Starostin, Anton; Valtsifer, Viktor; Barkay, Zahava; Legchenkova, Irina; Danchuk, Viktor; Bormashenko, Edward

2018-06-01

Water condensation was studied on silanized (superhydrophobic) and fluorinated (superoleophobic) micro-rough aluminum surfaces of the same topography. Condensation on superhydrophobic surfaces occurred via film-wise mechanism, whereas on superoleophobic surfaces it was drop-wise. The difference in the pathways of condensation was attributed to the various energy barriers separating the Cassie and Wenzel wetting states on the investigated surfaces. The higher barriers inherent for superoleophobic surfaces promoted the drop-wise condensation. Triple-stage kinetics of growth of droplets condensed on superoleophobic surfaces is reported and discussed.

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.

Ketamine nano-delivery based on poly-lactic-co-glycolic acid (PLGA) nanoparticles

NASA Astrophysics Data System (ADS)

Hirano, Sota; Bovi, Michele; Romeo, Alessandro; Guzzo, Flavia; Chiamulera, Cristiano; Perduca, Massimiliano

2018-04-01

This work describes a novel method for the generation of a ketamine nano-delivery, to improve brain blood barrier permeability and increase drug therapeutic window as anaesthetic, analgesic and potential antidepressant. The approach herein described is based on ketamine-loaded poly-lactic-co-glycolic acid (PLGA) nanoparticles coupled to an apolipoprotein E (ApoE) peptide for delivery to the central nervous system. PLGA particles were synthesized with amount of drug, coupled with the ApoE peptide on the surface, and validated by physical characterization. The produced nanodevice showed a good colloidal stability in water, confirmed by zeta potential measurements, with a diameter in the range of 185-205 nm. The ketamine encapsulation was verified by liquid chromatography-mass spectrometry analyses obtaining an encapsulation efficiency up to 21.2 ± 3.54%. Once the occurrence of ApoE peptide functionalization was confirmed with fluorescence spectroscopy, the thermal stability and morphological information were obtained by differential scanning calorimetry and further dynamic light scattering measurements. The spherical shape and a rough nanoparticles surface were observed by atomic force microscopy. The reliability of this approach may be further developed as a protocol to be used to generate PLGA nanoparticles greater than 100 nm able to better penetrate blood brain barrier and release a neuroactive molecule at lower doses.

Active species delivered by dielectric barrier discharge filaments to bacteria biofilms on the surface of apple

NASA Astrophysics Data System (ADS)

Cheng, He; Liu, Xin; Lu, Xinpei; Liu, Dawei

2016-07-01

The atmospheric pressure non-equilibrium plasma has shown a significant potential as a novel food decontamination technology. In this paper, we report a computational study of the intersection of negative streamer produced by air dielectric barrier discharge with bacteria biofilm on an apple surface. The structure, conductivities, and permittivities of bacteria biofilm have been considered in the Poisson's equations and transportation equations of charge and neutral species to realize self-consistent transportation of plasma between electrode and charging surfaces of apple. We find that the ionization near the biofilm facilitates the propagation of negative streamer when the streamer head is 1 mm from the biofilm. The structure of the biofilm results in the non-uniform distribution of ROS and RNS captured by flux and time fluence of these reactive species. The mean free path of charged species in μm scale permitted the plasma penetrate into the cavity of the biofilm, therefore, although the density of ROS and RNS decrease by 6-7 order of magnitude, the diffusion results in the uniform distribution of ROS and RNS inside the cavity during the pulse off period.

Effects of thermally induced denaturation on technological-functional properties of whey protein isolate-based films.

PubMed

Schmid, M; Krimmel, B; Grupa, U; Noller, K

2014-09-01

This study examined how and to what extent the degree of denaturation affected the technological-functional properties of whey protein isolate (WPI)-based coatings. It was observed that denaturation affected the material properties of WPI-coated films significantly. Surface energy decreased by approximately 20% compared with native coatings. Because the surface energy of a coating should be lower than that of the substrate, this might result in enhanced wettability characteristics between WPI-based solution and substrate surface. Water vapor barrier properties increased by about 35% and oxygen barrier properties increased by approximately 33%. However, significant differences were mainly observed between coatings made of fully native WPI and ones with a degree of denaturation of 25%. Higher degrees of denaturation did not lead to further improvement of material properties. This observation offers cost-saving potential: a major share of denatured whey proteins may be replaced by fully native ones that are not exposed to energy-intensive heat treatment. Furthermore, native WPI solutions can be produced with higher dry matter content without gelatinizing. Hence, less moisture has to be removed through drying, resulting in reduced energy consumption. Copyright © 2014 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

The Possible Emergence of Life and Differentiation of a Shallow Biosphere on Irradiated Icy Worlds: The Example of Europa

NASA Astrophysics Data System (ADS)

Russell, Michael J.; Murray, Alison E.; Hand, Kevin P.

2017-12-01

Irradiated ice-covered ocean worlds with rocky mafic mantles may provide the conditions needed to drive the emergence and maintenance of life. Alkaline hydrothermal springs - relieving the geophysical, thermal, and chemical disequilibria between oceans and tidally stressed crusts - could generate inorganic barriers to the otherwise uncontrolled and kinetically disfavored oxidation of hydrothermal hydrogen and methane. Ionic gradients imposed across these inorganic barriers, comprising iron oxyhydroxides and sulfides, could drive the hydrogenation of carbon dioxide and the oxidation of methane through thermodynamically favorable metabolic pathways leading to early life-forms. In such chemostatic environments, fuels may eventually outweigh oxidants. Ice-covered oceans are primarily heated from below, creating convection that could transport putative microbial cells and cellular cooperatives upward to congregate beneath an ice shell, potentially giving rise to a highly focused shallow biosphere. It is here where electron acceptors, ultimately derived from the irradiated surface, could be delivered to such life-forms through exchange with the icy surface. Such zones would act as "electron disposal units" for the biosphere, and occupants might be transferred toward the surface by buoyant diapirs and even entrained into plumes.

Efficacy of atmospheric pressure dielectric barrier discharge for inactivating airborne pathogens

DOE PAGES

Romero-Mangado, Jaione; Dey, Avishek; Diaz-Cartagena, Diana C.; ...

2017-07-05

Atmospheric pressure plasmas have gained attention in recent years for several environmental applications. This technology could potentially be used to deactivate airborne microorganisms, surface-bound microorganisms, and biofilms. Here, the authors explore the efficacy of the atmospheric pressure dielectric barrier discharge (DBD) to inactivate airborne Staphylococcus epidermidis and Aspergillus niger that are opportunistic pathogens associated with nosocomial infections. This technology uses air as the source of gas and does not require any process gas such as helium, argon, nitrogen, or hydrogen. Moreover, the effect of DBD was studied on aerosolized S. epidermidis and aerosolized A. niger spores via scanning electron microscopymore » (SEM). The morphology observed on the SEM micrographs showed deformations in the cellular structure of both microorganisms. Cell structure damage upon interaction with the DBD suggests leakage of vital cellular materials, which is a key mechanism for microbial inactivation. The chemical structure of the cell surface of S. epidermidis was also analyzed by near edge x-ray absorption fine structure spectroscopy before and after DBD exposure. Our results from surface analysis revealed that reactive oxygen species from the DBD discharge contributed to alterations on the chemistry of the cell membrane/cell wall of S. epidermidis.« less

Highly sensitive hydrogen sensor based on graphite-InP or graphite-GaN Schottky barrier with electrophoretically deposited Pd nanoparticles

PubMed Central

2011-01-01

Depositions on surfaces of semiconductor wafers of InP and GaN were performed from isooctane colloid solutions of palladium (Pd) nanoparticles (NPs) in AOT reverse micelles. Pd NPs in evaporated colloid and in layers deposited electrophoretically were monitored by SEM. Diodes were prepared by making Schottky contacts with colloidal graphite on semiconductor surfaces previously deposited with Pd NPs and ohmic contacts on blank surfaces. Forward and reverse current-voltage characteristics of the diodes showed high rectification ratio and high Schottky barrier heights, giving evidence of very small Fermi level pinning. A large increase of current was observed after exposing diodes to flow of gas blend hydrogen in nitrogen. Current change ratio about 700,000 with 0.1% hydrogen blend was achieved, which is more than two orders-of-magnitude improvement over the best result reported previously. Hydrogen detection limit of the diodes was estimated at 1 ppm H2/N2. The diodes, besides this extremely high sensitivity, have been temporally stable and of inexpensive production. Relatively more expensive GaN diodes have potential for functionality at high temperatures. PMID:21831273

Efficacy of atmospheric pressure dielectric barrier discharge for inactivating airborne pathogens

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

Romero-Mangado, Jaione; Dey, Avishek; Diaz-Cartagena, Diana C.

Atmospheric pressure plasmas have gained attention in recent years for several environmental applications. This technology could potentially be used to deactivate airborne microorganisms, surface-bound microorganisms, and biofilms. Here, the authors explore the efficacy of the atmospheric pressure dielectric barrier discharge (DBD) to inactivate airborne Staphylococcus epidermidis and Aspergillus niger that are opportunistic pathogens associated with nosocomial infections. This technology uses air as the source of gas and does not require any process gas such as helium, argon, nitrogen, or hydrogen. Moreover, the effect of DBD was studied on aerosolized S. epidermidis and aerosolized A. niger spores via scanning electron microscopymore » (SEM). The morphology observed on the SEM micrographs showed deformations in the cellular structure of both microorganisms. Cell structure damage upon interaction with the DBD suggests leakage of vital cellular materials, which is a key mechanism for microbial inactivation. The chemical structure of the cell surface of S. epidermidis was also analyzed by near edge x-ray absorption fine structure spectroscopy before and after DBD exposure. Our results from surface analysis revealed that reactive oxygen species from the DBD discharge contributed to alterations on the chemistry of the cell membrane/cell wall of S. epidermidis.« less

Surface modification of electrospun PVA/chitosan nanofibers by dielectric barrier discharge plasma at atmospheric pressure and studies of their mechanical properties and biocompatibility.

PubMed

Das, Punamshree; Ojah, Namita; Kandimalla, Raghuram; Mohan, Kiranjyoti; Gogoi, Dolly; Dolui, Swapan Kumar; Choudhury, Arup Jyoti

2018-03-22

In this paper, surface of electrospun PVA/Cs nanofibers is modified using dielectric barrier discharge (DBD) plasma and the relationship between the observed mechanical properties and biocompatibility of the nanofibers and plasma-induced surface properties is discussed. Plasma treatment of electrospun PVA/Cs nanofibers is carried out with both inert (argon, Ar) and reactive (oxygen, O 2 ) gases at atmospheric pressure. Incorporation of oxygen-containing polar functional groups on the surface of Ar-plasma treated (PVA/Cs/Ar) and O 2 -plasma treated (PVA/Cs/O 2 ) nanofibers and increase in surface roughness contribute to the improvement of surface wettability and the decrease of contact angle with water of the nanofibers. Both PVA/Cs/Ar and PVA/Cs/O 2 nanofibers show high tensile strength (11.6-15.6%) and Young's modulus (33.8-37.3%) as compared to the untreated one. Experimental results show that in terms of haemolytic activity the PVA/Cs/Ar and PVA/Cs/O 2 nanofibers do not cause structural changes of blood cells and meet the biocompatibility requirements for blood-contacting polymeric materials. MTT cell viability results further reveals improvement in biocompatibility of PVA/Cs nanofibers after Ar and O 2 plasma treatment. The results suggest that DBD plasma treated electrospun PVA/Cs nanofibers have the potential to be used as wound dressing and scaffolds for tissue engineering. Copyright © 2018 Elsevier B.V. All rights reserved.

The cold and atmospheric-pressure air surface barrier discharge plasma for large-area sterilization applications

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

Wang Dacheng; Department of Aeronautics, Fujian Key Laboratory for Plasma and Magnetic Resonance, School of Physics and Mechanical and Electrical Engineering, Xiamen University, Xiamen, Fujian 361005; Zhao Di

2011-04-18

This letter reports a stable air surface barrier discharge device for large-area sterilization applications at room temperature. This design may result in visually uniform plasmas with the electrode area scaled up (or down) to the required size. A comparison for the survival rates of Escherichia coli from air, N{sub 2} and O{sub 2} surface barrier discharge plasmas is presented, and the air surface plasma consisting of strong filamentary discharges can efficiently kill Escherichia coli. Optical emission measurements indicate that reactive species such as O and OH generated in the room temperature air plasmas play a significant role in the sterilizationmore » process.« less

The surface emissions trap: a new approach in indoor air purification.

PubMed

Markowicz, Pawel; Larsson, Lennart

2012-11-01

A new device for stopping or reducing potentially irritating or harmful emissions from surfaces indoors is described. The device is a surface emissions trap prototype and consists of an adsorbent sheet with a semipermeable barrier surrounded by two thin nonwoven layers. The trap may be applied directly at the source of the emissions e.g. at moisture-affected floors and walls, surfaces contaminated by chemical spills etc. This results in an immediate stop or reduction of the emitting pollutants. The trap has a very low water vapor resistance thus allowing drying of wet surfaces. In laboratory experiments typically 98% reduction of air concentrations of volatile organic compounds and a virtually total reduction of mold particle-associated mycotoxins was observed. The surface emissions trap may represent a convenient and efficient way of restoring indoor environments polluted by microbial and other moisture-associated emissions. Copyright © 2012 Elsevier B.V. All rights reserved.

Overview of thermal barrier coatings in diesel engines

NASA Technical Reports Server (NTRS)

Yonushonis, Thomas M.

1995-01-01

An understanding of delamination mechanisms in thermal barrier coatings has been developed for diesel engine applications through rig tests, structural analysis modeling, nondestructive evaluation, and engine evaluation of various thermal barrier coatings. This knowledge has resulted in improved thermal barrier coatings which survive abusive cyclic fatigue tests in high output diesel engines. Although much conflicting literature now exists regarding the impact of thermal barrier coatings on engine performance and fuel consumption, the changes in fuel consumption appear to be less than a few percent and can be negative for state-of-the-art diesel engines. The ability of the thermal barrier coating to improve fuel economy tends to be dependent on a number of factors including the fuel injection system, combustion chamber design, and the initial engine fuel economy. Limited investigations on state-of-the-art diesel engines have indicated that the surface connected porosity and coating surface roughness may influence engine fuel economy. Current research efforts on thermal barrier coatings are primarily directed at reducing in-cylinder heat rejection, thermal fatigue protection of underlying metal surfaces and a possible reduction in diesel engine emissions. Significant efforts are still required to improve the plasma spray processing capability and the economics for complex geometry diesel engine components.

Covering solid, film cooled surfaces with a duplex thermal barrier coating

NASA Technical Reports Server (NTRS)

Liebert, C. H. (Inventor)

1983-01-01

Thermal barrier coating systems were applied to hardware having passageways in the walls connecting apertures in the surface to a gas supply for film cooling. An inert gas, such as argon, is discharged through the apertures during the application of the thermal barrier coating system by plasma spraying. This flow of inert gas reduces both blocking of the holes and base metal oxidation during the coating operation.

Circularly polarized antennas for active holographic imaging through barriers

DOEpatents

McMakin, Douglas L [Richland, WA; Severtsen, Ronald H [Richland, WA; Lechelt, Wayne M [West Richland, WA; Prince, James M [Kennewick, WA

2011-07-26

Circularly-polarized antennas and their methods of use for active holographic imaging through barriers. The antennas are dielectrically loaded to optimally match the dielectric constant of the barrier through which images are to be produced. The dielectric loading helps to remove barrier-front surface reflections and to couple electromagnetic energy into the barrier.

Effect of hydrogen adsorption on the formation and annealing of Stone-Wales defects in graphene

NASA Astrophysics Data System (ADS)

Podlivaev, A. I.; Openov, L. A.

2015-12-01

The heights of energy barriers preventing the formation and annealing of Stone-Wales defects in graphene with a hydrogen atom adsorbed on the defect or in its immediate vicinity have been calculated using the atomistic computer simulation. It has been shown that, in the presence of hydrogen, both barriers are significantly lower than those in the absence of hydrogen. Based on the analysis of the potential energy surface, the frequency factors have been calculated for two different paths of the Stone-Wales transformation, and the temperature dependences of the corresponding annealing times of the defects have been found. The results obtained have been compared with the first-principles calculations and molecular dynamics data.

DFT studies on the mechanism of the reaction of C2H5S with NO2

NASA Astrophysics Data System (ADS)

Tang, Yi-Zhen; Sun, Hao; Pan, Ya-Ru; Pan, Xiu-Mei; Wang, Rong-Shun

The mechanisms for the reaction of C2H5S with NO2 are investigated at the QCISD(T)/6-311++G(d, p)//B3LYP/6-311++G(d, p) level on both single and triple potential energy surfaces. The geometries, vibrational frequencies and zero-point energy (ZPE) corrections of all stationary points involved in the title reaction are calculated at the B3LYP/6-311++G(d, p) level. The results show that the reaction is more predominant on the single potential energy surface, while it is negligible on the triple potential energy surface. Without barrier height in the whole process, the major channel is R ? C2H5SONO (IM1 and IM2) ? P1 (C2H5SO+NO). With much heat released in the formation of C2H5SNO2 (IM3) and the transition state involved in the subsequent step more stable than reactants, P4 (CH3CHS + t-HONO) is subdominant product energetically.

Lithium diffusion at Si-C interfaces in silicon-graphene composites

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

Odbadrakh, Khorgolkhuu; McNutt, N. W.; Nicholson, D. M.

2014-08-04

Models of intercalated Li and its diffusion in Si-Graphene interfaces are investigated using density functional theory. Results suggest that the presence of interfaces alters the energetics of Li binding and diffusion significantly compared to bare Si or Graphene surfaces. Our results show that cavities along reconstructed Si surface provide diffusion paths for Li. Diffusion barriers calculated along these cavities are significantly lower than penetration barriers to bulk Si. Interaction with Si surface results in graphene defects, creating Li diffusion paths that are confined along the cavities but have still lower barrier than in bulk Si.

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

Kawamoto, Shuhei; Shinoda, Wataru, E-mail: w.shinoda@apchem.nagoya-u.ac.jp; Klein, Michael L.

The effects of membrane curvature on the free energy barrier for membrane fusion have been investigated using coarse-grained molecular dynamics (CG-MD) simulations, assuming that fusion takes place through a stalk intermediate. Free energy barriers were estimated for stalk formation as well as for fusion pore formation using the guiding potential method. Specifically, the three different geometries of two apposed membranes were considered: vesicle–vesicle, vesicle–planar, and planar–planar membranes. The free energy barriers for the resulting fusion were found to depend importantly on the fusing membrane geometries; the lowest barrier was obtained for vesicular membranes. Further, lipid sorting was observed in fusionmore » of the mixed membranes of dimyristoyl phosphatidylcholine and dioleoyl phosphatidylethanolamine (DOPE). Specifically, DOPE molecules were found to assemble around the stalk to support the highly negative curved membrane surface. A consistent result for lipid sorting was observed when a simple continuum model (CM) was used, where the Helfrich energy and mixing entropy of the lipids were taken into account. However, the CM predicts a much higher free energy barrier than found using CG-MD. This discrepancy originates from the conformational changes of lipids, which were not considered in the CM. The results of the CG-MD simulations reveal that a large conformational change in the lipid takes place around the stalk region, which results in a reduction of free energy barriers along the stalk mechanism of membrane fusion.« less

Mismatch between cuticle deposition and area expansion in fruit skins allows potentially catastrophic buildup of elastic strain.

PubMed

Lai, Xiaoting; Khanal, Bishnu Prasad; Knoche, Moritz

2016-11-01

The continuous deposition of cutin and wax during leaf and fruit growth is crucial to alleviate elastic strain of the cuticle, minimize the risk of failure and maintain its barrier functions. The cuticular membrane (CM) is a lipoidal biopolymer that covers primary surfaces of terrestrial plants. CMs have barrier functions in water and solute transfer and pathogen invasion. These require intact CMs throughout growth. This is a challenge particularly for fruit, because they increase in area from initiation through to maturity. Our paper investigates the effects of cutin and wax deposition on strain buildup in the CM. We use developing fruits and leaves of apple (Malus × domestica) and sweet cherry (Prunus avium) as models. The hypothesis was that the continuous deposition of the CM prevents the buildup of excessive elastic strain in fruit and leaves. Strains were quantified from decreases in surface area of CMs after isolation from epidermal discs, after wax extraction and from increases in surface area during development. Cuticle mass per unit area increased throughout development in apple fruit, and leaves of apple and sweet cherry. In sweet cherry fruit, however, CM mass increased only initially, but thereafter decreased as the surface expanded rapidly. The release of strain on CM isolation was low in apple fruit and leaves and sweet cherry leaves, but high in sweet cherry fruit. Conversely, strains fixed by the deposition of wax and cutin were high in apple fruit and leaves and sweet cherry leaves, but low in sweet cherry fruit. Our results indicate that in expanding organs, deposition of cutin and wax in the CM allows conversion of elastic to plastic strain. Hence, any lack of such deposition allows buildup of high, potentially catastrophic, elastic strain.

Active cooling-based surface confinement system for thermal soil treatment

DOEpatents

Aines, R.D.; Newmark, R.L.

1997-10-28

A thermal barrier is disclosed for surface confinement with active cooling to control subsurface pressures during thermal remediation of shallow (5-20 feet) underground contaminants. If steam injection is used for underground heating, the actively cooled thermal barrier allows the steam to be injected into soil at pressures much higher (20-60 psi) than the confining strength of the soil, while preventing steam breakthrough. The rising steam is condensed to liquid water at the thermal barrier-ground surface interface. The rapid temperature drop forced by the thermal barrier drops the subsurface pressure to below atmospheric pressure. The steam and contaminant vapors are contained by the thermal blanket, which can be made of a variety of materials such as steel plates, concrete slabs, membranes, fabric bags, or rubber bladders. 1 fig.

Active cooling-based surface confinement system for thermal soil treatment

DOEpatents

Aines, Roger D.; Newmark, Robin L.

1997-01-01

A thermal barrier is disclosed for surface confinement with active cooling to control subsurface pressures during thermal remediation of shallow (5-20 feet) underground contaminants. If steam injection is used for underground heating, the actively cooled thermal barrier allows the steam to be injected into soil at pressures much higher (20-60 psi) than the confining strength of the soil, while preventing steam breakthrough. The rising steam is condensed to liquid water at the thermal barrier-ground surface interface. The rapid temperature drop forced by the thermal barrier drops the subsurface pressure to below atmospheric pressure. The steam and contaminant vapors are contained by the thermal blanket, which can be made of a variety of materials such as steel plates, concrete slabs, membranes, fabric bags, or rubber bladders.

First principles study of the atomic layer deposition of alumina by TMA-H2O-process.

PubMed

Weckman, Timo; Laasonen, Kari

2015-07-14

Atomic layer deposition (ALD) is a coating technology used to produce highly uniform thin films. Aluminiumoxide, Al2O3, is mainly deposited using trimethylaluminium (TMA) and water as precursors and is the most studied ALD-process to date. However, only few theoretical studies have been reported in the literature. The surface reaction mechanisms and energetics previously reported focus on a gibbsite-like surface model but a more realistic description of the surface can be achieved when the hydroxylation of the surface is taken into account using dissociatively adsorbed water molecules. The adsorbed water changes the structure of the surface and reaction energetics change considerably when compared to previously studied surface model. Here we have studied the TMA-H2O process using density functional theory on a hydroxylated alumina surface and reproduced the previous results for comparison. Mechanisms and energetics during both the TMA and the subsequent water pulse are presented. TMA is found to adsorb exothermically onto the surface. The reaction barriers for the ligand-exchange reactions between the TMA and the surface hydroxyl groups were found to be much lower compared to previously presented results. TMA dissociation on the surface is predicted to saturate at monomethylaluminium. Barriers for proton diffusion between surface sites are observed to be low. TMA adsorption was also found to be cooperative with the formation of methyl bridges between the adsorbants. The water pulse was studied using single water molecules reacting with the DMA and MMA surface species. Barriers for these reactions were found to reasonable in the process conditions. However, stabilizing interactions amongst water molecules were found to lower the reaction barriers and the dynamical nature of water is predicted to be of importance. It is expected that these calculations can only set an upper limit for the barriers during the water pulse.

Formation and decay analysis of Cd *48 98 ,104 isotopes in 40Ca20-induced reactions

NASA Astrophysics Data System (ADS)

Gautam, Manjeet Singh; Kaur, Amandeep; Sharma, Manoj K.

2015-11-01

We have analyzed the fusion dynamics of Ca4020+Ni 28 58 ,64 reactions by using the energy dependent Woods-Saxon potential (EDWSP) model and coupled channel model and subsequently the decay patterns of Cd *48 98 ,104 nuclei are governed via the dynamical cluster-decay model (DCM). The influence of intrinsic degrees of freedom of colliding pairs, such as low lying surface vibrations and neutron transfer channels, are entertained within the context of coupled channel calculations. Interestingly, the energy dependence in the Woods-Saxon potential induces barrier modification effects (barrier height, barrier position, barrier curvature) in a somewhat similar way as that for coupled channel approach, hence adequately explains the observed fusion dynamics of Ca4020+Ni 28 58 ,64 reactions. In addition, the decay analysis of compound nuclei formed in the fusion of Ca4020+Ni 28 58 ,64 reactions is investigated by using DCM. The calculations are done for quadrupole (β2) deformed fragments having optimum orientations for hot configurations. The experimental data for evaporation residues lying within the wide range of center of mass energy (Ec .m .) of 64 -88 MeV is nicely addressed using the collective clusterization approach of the DCM. The comparative analysis of decay profiles of Cd *48 98 ,104 is worked out by introducing angular momentum and temperature effects in the fragmentation potential and preformation factor.

Oblique wave trapping by vertical permeable membrane barriers located near a wall

NASA Astrophysics Data System (ADS)

Koley, Santanu; Sahoo, Trilochan

2017-12-01

The effectiveness of a vertical partial flexible porous membrane wave barrier located near a rigid vertical impermeable seawall for trapping obliquely incident surface gravity waves are analyzed in water of uniform depth under the assumption of linear water wave theory and small amplitude membrane barrier response. From the general formulation of the submerged membrane barrier, results for bottom-standing and surface-piercing barriers are computed and analyzed in special cases. Using the eigenfunction expansion method, the boundary-value problems are converted into series relations and then the required unknowns are obtained using the least squares approximation method. Various physical quantities of interests like reflection coefficient, wave energy dissipation, wave forces acting on the membrane barrier and the seawall are computed and analyzed for different values of the wave and structural parameters. The study will be useful in the design of the membrane wave barrier for the creation of tranquility zone in the lee side of the barrier to protect the seawall.

Barriers and dispersal surfaces in minimum-time interception

NASA Technical Reports Server (NTRS)

Rajan, N.; Ardema, M. D.

1982-01-01

Minimum time interception of a target moving in a horizontal plane is analyzed as a one-player differential game. Dispersal points and points on the barrier are located for a class of pursuit evasion and interception problems. These points are determined by constructing cross sections of the isochrones and hence obtaining the barrier, dispersal, and control level surfaces. The game solution maps the controls as a function of the state within the capture region.

Modeling electron emission and surface effects from diamond cathodes

NASA Astrophysics Data System (ADS)

Dimitrov, D. A.; Smithe, D.; Cary, J. R.; Ben-Zvi, I.; Rao, T.; Smedley, J.; Wang, E.

2015-02-01

We developed modeling capabilities, within the Vorpal particle-in-cell code, for three-dimensional simulations of surface effects and electron emission from semiconductor photocathodes. They include calculation of emission probabilities using general, piece-wise continuous, space-time dependent surface potentials, effective mass, and band bending field effects. We applied these models, in combination with previously implemented capabilities for modeling charge generation and transport in diamond, to investigate the emission dependence on applied electric field in the range from approximately 2 MV/m to 17 MV/m along the [100] direction. The simulation results were compared to experimental data. For the considered parameter regime, conservation of transverse electron momentum (in the plane of the emission surface) allows direct emission from only two (parallel to [100]) of the six equivalent lowest conduction band valleys. When the electron affinity χ is the only parameter varied in the simulations, the value χ = 0.31 eV leads to overall qualitative agreement with the probability of emission deduced from experiments. Including band bending in the simulations improves the agreement with the experimental data, particularly at low applied fields, but not significantly. Using surface potentials with different profiles further allows us to investigate the emission as a function of potential barrier height, width, and vacuum level position. However, adding surface patches with different levels of hydrogenation, modeled with position-dependent electron affinity, leads to the closest agreement with the experimental data.

The Influence of High-Energy Electrons Irradiation on Surface of n-GaP and on Au/n-GaP/Al Schottky Barrier Diode

NASA Astrophysics Data System (ADS)

Demir, K. Çinar; Kurudirek, S. V.; Oz, S.; Biber, M.; Aydoğan, Ş.; Şahin, Y.; Coşkun, C.

We fabricated 25 Au/n-GaP/Al Schottky devices and investigated the influence of high electron irradiation, which has 12MeV on the devices, at room temperature. The X-ray diffraction patterns, scanning electron microscopic images and Raman spectra of a gallium phosphide (GaP) semiconductor before and after electron irradiation have been analyzed. Furthermore, some electrical measurements of the devices were carried out through the current-voltage (I-V) and capacitance-voltage (C-V) measurements. From the I-V characteristics, experimental ideality factor n and barrier height Φ values of these Schottky diodes have been determined before and after irradiation, respectively. The results have also been analyzed statically, and a gauss distribution has been obtained. The built-in potential Vbi, barrier height Φ, Fermi level EF and donor concentration Nd values have been determined from the reverse bias C-V and C-2-V curves of Au/n-GaP/Al Schottky barrier diodes at 100kHz before and after 12MeV electron irradiation. Furthermore, we obtained the series resistance values of Au/n-GaP/Al Schottky barrier diodes with the help of different methods. Experimental results confirmed that the electrical characterization of the device changed with the electron irradiation.

Bilayer Poly(Lactic-co-glycolic acid)/Nano-Hydroxyapatite Membrane with Barrier Function and Osteogenesis Promotion for Guided Bone Regeneration

PubMed Central

Fu, Li; Wang, Zhanfeng; Dong, Shujun; Cai, Yan; Ni, Yuxin; Zhang, Tianshou; Wang, Lin; Zhou, Yanmin

2017-01-01

Guided bone regeneration (GBR) is one such treatment that reconstructs neo-bone tissue by using a barrier membrane to prevent the invasion of soft tissue and to create a space for guiding new bone growth into the bone defect. Herein, we report a novel functionally graded bilayer membrane (FGBM) for GBR application. To fabricate the novel membrane, the composites of poly(lactic-co-glycolic acid) and nano-hydroxyapatite were prepared by phase inversion for the dense layer and by electrospinning for another porous layer, and their corresponding properties were evaluated including surface morphology, mechanics, degradability, cell barrier function, and in vitro osteogenic bioactivity. The results showed that PLGA with 5% nHA in dense layer could meet the requirement of mechanical strength and have excellent barrier function even on condition of post-degradation. Furthermore, PLGA with 30% nHA in porous layer could achieve the good physical and chemical properties. In addition, 30% nHA incorporation would enhance the in vitro mineralization, and have superior capabilities of cell adhesion, proliferation and differentiation compared to other groups. Therefore, the designed FGBM could potentially serve as a barrier for preferential tissue ingrowth and achieve a desirable therapeutic result for bone tissue regeneration. PMID:28772618

Free energy barriers to evaporation of water in hydrophobic confinement.

PubMed

Sharma, Sumit; Debenedetti, Pablo G

2012-11-08

We use umbrella sampling Monte Carlo and forward and reverse forward flux sampling (FFS) simulation techniques to compute the free energy barriers to evaporation of water confined between two hydrophobic surfaces separated by nanoscopic gaps, as a function of the gap width, at 1 bar and 298 K. The evaporation mechanism for small (1 × 1 nm(2)) surfaces is found to be fundamentally different from that for large (3 × 3 nm(2)) surfaces. In the latter case, the evaporation proceeds via the formation of a gap-spanning tubular cavity. The 1 × 1 nm(2) surfaces, in contrast, are too small to accommodate a stable vapor cavity. Accordingly, the associated free energy barriers correspond to the formation of a critical-sized cavity for sufficiently large confining surfaces, and to complete emptying of the gap region for small confining surfaces. The free energy barriers to evaporation were found to be of O(20kT) for 14 Å gaps, and to increase by approximately ~5kT with every 1 Å increase in the gap width. The entropy contribution to the free energy of evaporation was found to be independent of the gap width.

Preparation and High-temperature Anti-adhesion Behavior of a Slippery Surface on Stainless Steel.

PubMed

Zhang, Pengfei; Huawei, Chen; Liu, Guang; Zhang, Liwen; Zhang, Deyuan

2018-03-29

Anti-adhesion surfaces with high-temperature resistance have a wide application potential in electrosurgical instruments, engines, and pipelines. A typical anti-wetting superhydrophobic surface easily fails when exposed to a high-temperature liquid. Recently, Nepenthes-inspired slippery surfaces demonstrated a new way to solve the adhesion problem. A lubricant layer on the slippery surface can act as a barrier between the repelled materials and the surface structure. However, the slippery surfaces in previous studies rarely showed high-temperature resistance. Here, we describe a protocol for the preparation of slippery surfaces with high-temperature resistance. A photolithography-assisted method was used to fabricate pillar structures on stainless steel. By functionalizing the surface with saline, a slippery surface was prepared by adding silicone oil. The prepared slippery surface maintained the anti-wetting property for water, even when the surface was heated to 300 °C. Also, the slippery surface exhibited great anti-adhesion effects on soft tissues at high temperatures. This type of slippery surface on stainless steel has applications in medical devices, mechanical equipment, etc.

Geophysical Assessment of the Control of a Jetty on a Barrier Beach and Estuary System

NASA Astrophysics Data System (ADS)

Ulrich, C.; Hubbard, S.; Delaney, C.; Seymour, D.; Blom, K.; Black, W.

2013-12-01

An evaluation is underway at the Goat Rock State Beach, which is located at the mouth of the Russian River near Jenner, CA. The study focuses on quantifying the influence of a man made jetty on the functioning of a barrier beach and associated implications for estuary fish habitat and flood control. Flow through the beach results from water level differences between the estuary and the ocean. When the estuary is closed or perched, one of the potential major sources of outflow from the lagoon is seepage flow through the barrier beach. The location and design of the jetty could be altering subsurface flow paths through the jetty and possibly impeding or enhancing subsurface flow where the jetty is still intact. This will result in unnatural connectivity between the ocean and the estuary leading to atypical surface water elevations and possibly salinity imbalance. Results of the assessment will enable the Sonoma County Water Agency to understand how the jetty affects formation of the barrier beach and water surface elevations within the estuary. As one aspect of the evaluation, we are using geophysical methods to monitor seepage through the jetty as well as through the beach berm. We are using multiple surface geophysical methods, including: electrical resistivity, seismic refraction, ground penetrating radar, and electromagnetic methods. In general, seismic data are being used to characterize deeper bedrock controls on beach barrier functioning such as, channeling of estuarine water beneath the barrier beach. Electrical and electromagnetic methods are being used to characterize the beach sediment layers that could contribute to preferential flow paths during tide cycles in addition to preferential flow paths created by the jetty structure. Time-lapse electrical and electromagnetic data are being used to monitor moisture changes and mixing of saline and fresh water within the beach berm. Ground penetrating radar data are being used to delineate the geometry of the (often buried) jetty. All data are being integrated with topography, tidal and hydrological information, and electrical conductivity and temperature data from monitoring wells. These results are expected to improve the overall understanding of the jetty's effects on beach permeability and will better improve the understanding of the jetty's influence on estuary habitats and flood risk.

Chemical dynamics between wells across a time-dependent barrier: Self-similarity in the Lagrangian descriptor and reactive basins.

PubMed

Junginger, Andrej; Duvenbeck, Lennart; Feldmaier, Matthias; Main, Jörg; Wunner, Günter; Hernandez, Rigoberto

2017-08-14

In chemical or physical reaction dynamics, it is essential to distinguish precisely between reactants and products for all times. This task is especially demanding in time-dependent or driven systems because therein the dividing surface (DS) between these states often exhibits a nontrivial time-dependence. The so-called transition state (TS) trajectory has been seen to define a DS which is free of recrossings in a large number of one-dimensional reactions across time-dependent barriers and thus, allows one to determine exact reaction rates. A fundamental challenge to applying this method is the construction of the TS trajectory itself. The minimization of Lagrangian descriptors (LDs) provides a general and powerful scheme to obtain that trajectory even when perturbation theory fails. Both approaches encounter possible breakdowns when the overall potential is bounded, admitting the possibility of returns to the barrier long after the trajectories have reached the product or reactant wells. Such global dynamics cannot be captured by perturbation theory. Meanwhile, in the LD-DS approach, it leads to the emergence of additional local minima which make it difficult to extract the optimal branch associated with the desired TS trajectory. In this work, we illustrate this behavior for a time-dependent double-well potential revealing a self-similar structure of the LD, and we demonstrate how the reflections and side-minima can be addressed by an appropriate modification of the LD associated with the direct rate across the barrier.

2D halide perovskite-based van der Waals heterostructures: contact evaluation and performance modulation

NASA Astrophysics Data System (ADS)

Guo, Yaguang; Saidi, Wissam A.; Wang, Qian

2017-09-01

Halide perovskites and van der Waals (vdW) heterostructures are both of current interest owing to their novel properties and potential applications in nano-devices. Here, we show the great potential of 2D halide perovskite sheets (C4H9NH3)2PbX4 (X  =  Cl, Br and I) that were synthesized recently (Dou et al 2015 Science 349 1518-21) as the channel materials contacting with graphene and other 2D metallic sheets to form van der Waals heterostructures for field effect transistor (FET). Based on state-of-the-art theoretical simulations, we show that the intrinsic properties of the 2D halide perovskites are preserved in the heterojunction, which is different from the conventional contact with metal surfaces. The 2D halide perovskites form a p-type Schottky barrier (Φh) contact with graphene, where tunneling barrier exists, and a negative band bending occurs at the lateral interface. We demonstrate that the Schottky barrier can be turned from p-type to n-type by doping graphene with nitrogen atoms, and a low-Φh or an Ohmic contact can be realized by doping graphene with boron atoms or replacing graphene with other high-work-function 2D metallic sheets such as ZT-MoS2, ZT-MoSe2 and H-NbS2. This study not only predicts a 2D halide perovskite-based FETs, but also enhances the understanding of tuning Schottky barrier height in device applications.

Torsion-wagging tunneling and vibrational states in hydrazine determined from its ab initio potential energy surface

NASA Astrophysics Data System (ADS)

Łodyga, Wiesław; Makarewicz, Jan

2012-05-01

Geometries, anharmonic vibrations, and torsion-wagging (TW) multiplets of hydrazine and its deuterated species are studied using high-level ab initio methods employing the second-order Møller-Plesset perturbation theory (MP2) as well as the coupled cluster singles and doubles model including connected triple corrections, CCSD(T), in conjunction with extended basis sets containing diffuse and core functions. To describe the splitting patterns caused by tunneling in TW states, the 3D potential energy surface (PES) for the large-amplitude TW modes is constructed. Stationary points in the 3D PES, including equivalent local minima and saddle points are characterized. Using this 3D PES, a flexible Hamiltonian is built numerically and then employed to solve the vibrational problem for TW coupled motion. The calculated ground state rav structure is expected to be more reliable than the experimental one that has been determined using a simplified structural model. The calculated fundamental frequencies allowed resolution of the assignment problems discussed earlier in the literature. The determined energy barriers, including the contributions from the small-amplitude vibrations, to the tunneling of the symmetric and antisymmetric wagging mode of 1997 cm-1 and 3454 cm-1, respectively, are in reasonable agreement with the empirical estimates of 2072 cm-1 and 3312 cm-1, respectively [W. Łodyga et al. J. Mol. Spectrosc. 183, 374 (1997), 10.1006/jmsp.1997.7271]. However, the empirical torsion barrier of 934 cm-1 appears to be overestimated. The ab initio calculations yield two torsion barriers: cis and trans of 744 cm-1 and 2706 cm-1, respectively. The multiplets of the excited torsion states are predicted from the refined 3D PES.

Landfill disposal systems.

PubMed

Slimak, K M

1978-12-01

The current status of landfill disposal of hazardous wastes in the United States is indicated by presenting descriptions of six operating landfills. These landfills illustrate the variety of techniques that exist in landfill disposal of hazardous wastes. Although some landfills more effectively isolate hazardous waste than others, all landfills must deal with the following problems. Leachate from hazardous waste landfills is generally highly polluted. Most landfills attempt to contain leachate at the site and prevent its discharge to surface or groundwaters. To retain leachate within a disposal area, subsurface barriers of materials such as concrete, asphalt, butyl rubber, vinyl, and clay are used. It is difficult to assure that these materials can seal a landfill indefinitely. When a subsurface barrier fails, the leachate enters the groundwater in a concentrated, narrow band which may bypass monitoring wells. Once a subsurface barrier has failed, repairs are time-consuming and costly, since the waste above the repair site may have to be removed. The central problem in landfill disposal is leachate control. Recent emphasis has been on developing subsurface barriers to contain the wastes and any leachate. Future emphasis should also be on techniques for removing water from hazardous wastes before they are placed in landfills, and on methods for preventing contact of the wastes with water during and after disposal operations. When leachate is eliminated, the problems of monitoring, and subsurface barrier failure and repair can be addressed, and a waste can be effectively isolated.A surface seal landfill design is recommended for maintaining the dry state of solid hazardous wastes and for controlling leachate. Any impervious liner is utilized over the top of the landfill to prevent surface water from seeping into the waste. The surface barrier is also the site where monitoring and maintenance activities are focused. Barrier failure can be detected by visual inspections and any repairs can be made without disturbing the waste. The surface seal landfill does not employ a subsurface barrier. The surface seal landfill successfully addresses each of the four environmental problems listed above, provided that this landfill design is utilized for dry wastes only and is located at a site which provides protection from groundwater and temporary perched water tables.

Analysis of differential and active charging phenomena on ATS-5 and ATS-6

NASA Technical Reports Server (NTRS)

Olsen, R. C.; Whipple, E. C., Jr.

1980-01-01

Spacecraft charging on the differential charging and artificial particle emission experiments on ATS 5 and ATS 6 were studied. Differential charging of spacecraft surfaces generated large electrostatic barriers to spacecraft generated electrons, from photoemission, secondary emission, and thermal emitters. The electron emitter could partially or totally discharge the satellite, but the mainframe recharged negatively in a few 10's of seconds. The time dependence of the charging behavior was explained by the relatively large capacitance for differential charging in comparison to the small spacecraft to space capacitance. A daylight charging event on ATS 6 was shown to have a charging behavior suggesting the dominance of differential charging on the absolute potential of the mainframe. Ion engine operations and plasma emission experiments on ATS 6 were shown to be an effective means of controlling the spacecraft potential in eclipse and sunlight. Elimination of barrier effects around the detectors and improving the quality of the particle data are discussed.

ZMappTM Reinforces the Airway Mucosal Barrier Against Ebola Virus.

PubMed

Yang, Bing; Schaefer, Alison; Wang, Ying-Ying; McCallen, Justin; Lee, Phoebe; Newby, Jay M; Arora, Harendra; Kumar, Priya A; Zeitlin, Larry; Whaley, Kevin J; McKinley, Scott A; Fischer, William A; Harit, Dimple; Lai, Samuel K

2018-04-24

Filoviruses, including Ebola, have the potential to be transmitted via virus-laden droplets deposited onto mucus membranes. Protecting against such emerging pathogens will require understanding how they may transmit at mucosal surfaces and developing strategies to reinforce the airway mucus barrier.Here, we prepared Ebola pseudovirus (with Zaire strain glycoproteins) and employed high resolution multiple particle tracking to track the motions of hundreds of individual pseudoviruses in fresh and undiluted human airway mucus isolated from extubated endotracheal tubes.We found that Ebola pseudovirus readily penetrate human airway mucus. Addition of ZMappTM, a cocktail of Ebola-binding IgG antibodies, effectively reduced mobility of Ebola pseudovirus in the same mucus secretions. Topical delivery of ZMappTM to the mouse airways also facilitated rapid elimination of Ebola pseudovirus.Our work demonstrates that antibodies can immobilize virions in airway mucus and reduce access to the airway epithelium, highlighting topical delivery of pathogen-specific antibodies to the lungs as a potential prophylactic or therapeutic approach against emerging viruses or biowarfare agents.

Barrier-free subsurface incorporation of 3 d metal atoms into Bi(111) films

DOE PAGES

Klein, C.; Vollmers, N. J.; Gerstmann, U.; ...

2015-05-27

By combining scanning tunneling microscopy with density functional theory it is shown that the Bi(111) surface provides a well-defined incorporation site in the first bilayer that traps highly coordinating atoms such as transition metals (TMs) or noble metals. All deposited atoms assume exactly the same specific sevenfold coordinated subsurface interstitial site while the surface topography remains nearly unchanged. Notably, 3 d TMs show a barrier-free incorporation. The observed surface modification by barrier-free subsorption helps to suppress aggregation in clusters. Thus, it allows a tuning of the electronic properties not only for the pure Bi(111) surface, but may also be observedmore » for topological insulators formed by substrate-stabilized Bi bilayers.« less

Bone conditioned media (BCM) improves osteoblast adhesion and differentiation on collagen barrier membranes.

PubMed

Fujioka-Kobayashi, Masako; Caballé-Serrano, Jordi; Bosshardt, Dieter D; Gruber, Reinhard; Buser, Daniel; Miron, Richard J

2016-07-04

The use of autogenous bone chips during guided bone regeneration procedures has remained the gold standard for bone grafting due to its excellent combination of osteoconduction, osteoinduction and osteogenesis. Recent protocols established by our group have characterized specific growth factors and cytokines released from autogenous bone that have the potential to be harvested and isolated into bone conditioned media (BCM). Due to the advantageous osteo-promotive properties of BCM, the aims of the present study was to pre-coat collagen barrier membranes with BCM and investigate its effect on osteoblast adhesion, proliferation and differentiation for possible future clinical use. Scanning electron microscopy (SEM) was first used to qualitative assess BCM protein accumulation on the surface of collagen membranes. Thereafter, undifferentiated mouse ST2 stromal bone marrow cells were seeded onto BioGide porcine derived collagen barrier membranes (control) or barrier membranes pre-coated with BCM (test group). Control and BCM samples were compared for cell adhesion at 8 h, cell proliferation at 1, 3 and 5 days and real-time PCR at 5 days for osteoblast differentiation markers including Runx2, alkaline phosphatase (ALP), osteocalcin (OCN) and bone sialoprotein (BSP). Mineralization was further assessed with alizarin red staining at 14 days post seeding. SEM images demonstrated evidence of accumulated proteins found on the surface of collagen membranes following coating with BCM. Analysis of total cell numbers revealed that the additional pre-coating with BCM markedly increased cell attachment over 4 fold when compared to cells seeded on barrier membranes alone. No significant difference could be observed for cell proliferation at all time points. BCM significantly increased mRNA levels of osteoblast differentiation markers including ALP, OCN and BSP at 5 days post seeding. Furthermore, barrier membranes pre-coated with BCM demonstrated a 5-fold increase in alizarin red staining at 14 days. The results from the present study suggest that the osteoconductive properties of porcine-derived barrier membranes could be further improved by BCM by significantly increasing cell attachment, differentiation and mineralization of osteoblasts in vitro. Future animal testing is required to fully characterize the additional benefits of BCM for guided bone regeneration.

Saltwater-barrier line in Florida : concepts, considerations, and site examples

USGS Publications Warehouse

Hughes, Jerry L.

1979-01-01

Construction of canals and enlargement of streams in Florida has been mostly to alleviate impact of floods and to drain wetlands for development. Land drainage and heavy pumpage from coastal water-table aquifers has degraded potable ground and surface water with saltwater. Control of saltwater intrusion is possible through implementation of certain hydrologic principles. State of Florida statute 373.033 provides for a saltwater-barrier line in areas of saltwater intrusion along canals. A saltwater-barrier line is defined as the allowable landward limit that a canal shall be constructed or enlarged or a stream deepened or enlarged without a salinity-control structure seaward of the saltwater-barrier line. The salinity control structure controls saltwater intrusion along a surface-water channel and assists in controlling saltwater intrusion into shallow aquifers. This report briefly reviews the fundamentals of saltwater intrusion in surface-water channels and associated coastal aquifers, describes the effects of established saltwater-barrier lines in Florida, and gives a history of the use and benefits of salinity-control structures. (Woodard-USGS).

Design and performance evaluation of a 1000-year evapotranspiration-capillary surface barrier

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

Zhang, Zhuanfang Fred; Strickland, Christopher E.; Link, Steven O.

Surface barrier technology is used to isolate radioactive waste and to reduce or eliminate recharge water to the waste zone for 1000 years or longer. However, the design and evaluation of such a barrier is challenging because of the extremely long design life. The Prototype Hanford Barrier (PHB) was designed as a 1000-year barrier with pre-determined design and performance objectives and demonstrated in field from 1994 to present. The barrier was tested to evaluate surface-barrier design and performance at the field scale under conditions of enhanced and natural precipitation and of no vegetation. The monitoring data demonstrate that the barriermore » satisfied nearly all key objectives. The PHB far exceeded the Resource Conservation and Recovery Act criteria, functioned in Hanford’s semiarid climate, limited drainage to well below the 0.5 mm yr-1 performance criterion, limited runoff, and minimized erosion. Given the two-decade record of successful performance and consideration of all the processes and mechanisms that could degrade the stability and hydrology in the future, the results suggest the PHB is very likely to perform for its 1000-year design life. This conclusion is based on two assumptions: (1) the exposed subgrade receives protection against erosion and (2) institutional controls prevent inadvertent human activity at the barrier. The PHB design can serve as the base for site-specific barriers over waste sites containing underground nuclear waste, uranium mine tailings, and hazardous mine waste.« less

Tests of potential functional barriers for laminated multilayer food packages. Part I: Low molecular weight permeants.

PubMed

Simal-Gándara, J; Sarria-Vidal, M; Koorevaar, A; Rijk, R

2000-08-01

The advent of the functional barrier concept in food packaging has brought with it a requirement for fast tests of permeation through potential barrier materials. In such tests it would be convenient for both foodstuffs and materials below the functional barrier (sub-barrier materials) to be represented by standard simulants. By means of inverse gas chromatography, liquid paraffin spiked with appropriate permeants was considered as a potential simulant of sub-barrier materials based on polypropylene (PP) or similar polyolefins. Experiments were performed to characterize the kinetics of the permeation of low molecular weight model permeants (octene, toluene and isopropanol) from liquid paraffin, through a surrogate potential functional barrier (25 microns-thick oriented PP) into the food stimulants olive oil and 3% (w/v) acetic acid. These permeation results were interpreted in terms of three permeation kinetic models regarding the solubility of a particular model permeant in the post-barrier medium (i.e. the food simulant). The results obtained justify the development and evaluation of liquid sub-barrier simulants that would allow flexible yet rigorous testing of new laminated multilayer packaging materials.

Navigation Effects on Asian Carp Movement Past Electric Barrier, Chicago Sanitary and Ship Canal

DTIC Science & Technology

2016-02-01

model was necessary to better address the potential mechanisms for transport of Asian carp. In addition to primarily modeling stunned fish , this...model fish positions that varied within the water column to include bottom, near-surface, and mid-depth placement. As additional information was...in the image represents an identified model fish . In addition , fish could be tracked from one frame to the next frame to calculate their velocity

Multinucleon transfer dynamics in heavy-ion collisions near Coulomb-barrier energies

NASA Astrophysics Data System (ADS)

Niu, Fei; Chen, Peng-Hui; Guo, Ya-Fei; Ma, Chun-Wang; Feng, Zhao-Qing

2017-12-01

Multinucleon transfer reactions near barrier energies have been investigated with a multistep model based on the dinuclear system (DNS) concept, in which the capture of two colliding nuclei, the transfer dynamics, and the deexcitation process of primary fragments are described by an analytical formula, diffusion theory, and a statistical model, respectively. The nucleon transfer takes place after forming the DNS and is coupled to the dissipation of relative motion energy and angular momentum by solving a set of microscopically derived master equations within the potential energy surface. Specific reactions of Ca,4840+124Sn , 40Ca(40Ar,58Ni)+232Th , 40Ca(58Ni)+238U , and Ca,4840(58Ni)+248Cm near barrier energies are investigated. It is found that fragments are produced by multinucleon transfer reactions with maximal yields along the β -stability line. The isospin relaxation is particularly significant in the process of fragment formation. The incident energy dependence of heavy target-like fragments in the reaction of 58Ni+248Cm is analyzed thoroughly.

An all-carbon vdW heterojunction composed of penta-graphene and graphene: Tuning the Schottky barrier by electrostatic gating or nitrogen doping

NASA Astrophysics Data System (ADS)

Guo, Yaguang; Wang, Fancy Qian; Wang, Qian

2017-08-01

The non-zero band gap together with other unique properties endows penta-graphene with potential for device applications. Here, we study the performance of penta-graphene as the channel material contacting with graphene to form a van der Waals heterostructure. Based on first-principles calculations, we show that the intrinsic properties of penta-graphene are preserved in the heterojunction, which is different from the conventional contact with metal surfaces. The stacked system forms an n-type Schottky barrier (Φe) at the vertical interface, while a negative band bending occurs at the lateral interface in a current-in-plane model. From the device point of view, we further demonstrate that a low-Φe or an Ohmic contact can be realized by applying an external electric field or doping graphene with nitrogen atoms. This allows the control of the Schottky barrier height, which is essential in fabricating penta-graphene-based nanotransistors.

Evaluating the long-term hydrology of an evapotranspiration-capillary barrier with a 1000 year design life

NASA Astrophysics Data System (ADS)

Zhang, Z. Fred

2016-06-01

A surface barrier is a commonly used technology for isolation of subsurface contaminants. Surface barriers for isolating radioactive waste are expected to perform for centuries to millennia, yet there are very few data for field-scale surface barriers for periods approaching a decade or longer. The Prototype Hanford Barrier (PHB) with a design life of 1000 years was constructed over an existing radioactive waste site in 1994 to demonstrate its long-term performance. The primary element of the PHB is an evapotranspiration-capillary (ETC) barrier in which precipitation water is stored in a fine-textured soil layer and later released to the atmosphere via evapotranspiration. To address the barrier performance under extreme conditions, this study included an enhanced precipitation stress test from 1995 to 1997 to determine barrier response to extreme precipitation events. During this period a 1000 year 24 h return rainstorm was simulated in March every year. The loss of vegetation on barrier hydrology was tested with a controlled fire test in 2008. The 19 year monitoring record shows that the store-and-release mechanism worked as well as or better than the design criterion. Average drainage from the ETC barrier amounted to an average of 0.005 mm yr-1, which is well below the design criterion of 0.5 mm yr-1. After a simulated wildfire, the naturally reestablished vegetation and increased evaporation combined to release the stored water and summer precipitation to the atmosphere such that drainage did not occur in the 5 years subsequent to the fire.

Additive impairment of the barrier function and irritation by biogenic amines and sodium lauryl sulphate: a controlled in vivo tandem irritation study.

PubMed

Fluhr, J W; Kelterer, D; Fuchs, S; Kaatz, M; Grieshaber, R; Kleesz, P; Elsner, P

2005-01-01

Biogenic amines are potential irritants e.g. in fish-, meat-, milk- and egg-processing professions like cooks, butchers and bakers. The aim of this study was to test the irritative and barrier-disrupting properties of the biogenic amines ammonium hydroxide (AM), dimethylamine (DMA) and trimethylamine (TMA). A repeated sequential irritation of 30 min twice per day was performed over a total of 4 days (tandem repeated irritation test) on the back of 20 healthy volunteers of both sexes with AM, DMA, TMA and sodium lauryl sulphate (SLS). The epidermal barrier function was assessed with a Tewameter TM 210, stratum corneum surface pH was measured with a Skin-pH-Meter 900, inflammation was assessed with a Chromameter CR-300 on the a* axis for redness and a visual score was recorded. All tested biogenic amines (AM, DMA and TMA) induced a barrier disruption and a pH increase paralleled with a 1-day-delayed onset of inflammatory signs. These effects were further enhanced and accelerated by a sequential application of SLS together with the biogenic amines, and inflammation occurred earlier than with the single compounds. Acetic acid (AA) in contrast did only show mild barrier disruption and no significant inflammatory signs. Our system allowed a ranking of the different compounds in their irritative potential in the tandem irritation with SLS: SLS > NaOH > TMA > AA > AM > DMA. The results are suggestive that in the food-processing industry the simultaneous contact with biogenic amines and harmful detergents like SLS should be minimized. Copyright 2005 S. Karger AG, Basel.

Method of making dense, conformal, ultra-thin cap layers for nanoporous low-k ILD by plasma assisted atomic layer deposition

DOEpatents

Jiang, Ying-Bing [Albuquerque, NM; Cecchi, Joseph L [Albuquerque, NM; Brinker, C Jeffrey [Albuquerque, NM

2011-05-24

Barrier layers and methods for forming barrier layers on a porous layer are provided. The methods can include chemically adsorbing a plurality of first molecules on a surface of the porous layer in a chamber and forming a first layer of the first molecules on the surface of the porous layer. A plasma can then be used to react a plurality of second molecules with the first layer of first molecules to form a first layer of a barrier layer. The barrier layers can seal the pores of the porous material, function as a diffusion barrier, be conformal, and/or have a negligible impact on the overall ILD k value of the porous material.

Epidermal Permeability Barrier Recovery Is Delayed in Vitiligo-Involved Sites

PubMed Central

Liu, J.; Man, W.Y.; Lv, C.Z.; Song, S.P.; Shi, Y.J.; Elias, P.M.; Man, M.Q.

2010-01-01

Background/Objectives Prior studies have demonstrated that both the skin surface pH and epidermal permeability barrier function vary with skin pigmentation types. Although melanin deficiency is the main feature of vitiligo, alterations in cutaneous biophysical properties in vitiligo have not yet been well defined. In the present study, stratum corneum (SC) hydration, the skin surface pH and epidermal permeability barrier function in vitiligo were evaluated. Methods A total of 30 volunteers with vitiligo comprising 19 males and 11 females aged 13–51 years (mean age: 27.91 ± 2.06 years) were enrolled in this study. The skin surface pH, SC hydration, melanin/erythema index and transepidermal water loss (TEWL) were measured by respective probes connected to a Courage-Khazaka MPA5. SC integrity was determined by measuring the TEWL following each D-Squame application. The barrier recovery rate was assessed at 5 h following barrier disruption by repeated tape stripping. Results In addition to SC hydration, both melanin and erythema index were significantly lower in vitiligo lesions than in contralateral, nonlesional sites, while no difference in skin surface pH between vitiligo-involved and uninvolved areas was observed. In addition, neither the basal TEWL nor SC integrity in the involved areas differed significantly from that in the uninvolved areas. However, barrier recovery in vitiligo-involved sites was significantly delayed in comparison with uninvolved sites (40.83 ± 5.39% vs. 58.30 ± 4.71%; t = 2.441; p < 0.02). Conclusion Barrier recovery following tape stripping of the SC is delayed in vitiligo. Therefore, improvement in epidermal permeability barrier function may be an important unrecognized factor to be considered in treating patients with vitiligo. PMID:20185976

Characterization and Application of a Planar Radio - Inductively-Coupled Plasma Source for the Production of Barrier Coatings.

NASA Astrophysics Data System (ADS)

Mahoney, Leonard Joseph

A planar radio-frequency (rf) inductively-coupled plasma (ICP) source is used to produce fluorocarbon discharges (CF_4/Ar) to fluorinate the surface of high-density polyethylene (HDPE). Using this system, concurrent studies of discharge characteristics, permeation properties of treated polymers and polymer surface characteristics are conducted to advance the use of plasma-fluorinated polymer surfaces as a barrier layer for automotive applications. Langmuir probes are used to determine spatial distribution of charged-particle and space-potential characteristics in Ar and CF_4/Ar discharges and to show the influence of the spatial distribution of the heating regions and the reactor boundaries on the discharge uniformity. Langmuir probes are also used to identify rf anisotropic drift motion of electrons in the heating regions of the source and transient high-energy electron features in pulsed discharges. These latter features allow pulsed ICP sources to be operated at low time-averaged powers that are necessary to treat thermally sensitive polymers. Fourier Transform Infrared (FITR) spectroscopy is used to measure the dissociation of fluorocarbon gases and to explore differences between pulsed- and continuous -power operation. Dissociation levels of CF_4 (50-85%) using pulsed-power operation are as high as that for continuous operation, even though the net time -averaged power is far less with pulsed operation. The result suggests that pulsed fluorocarbon discharges possess high concentrations of chemically-active species needed for rapid surface fluorination. A gravimetric permeation cup method is used to measure the permeation rate of test fuels through HDPE membranes, and electron spectroscopy for chemical analysis (ESCA) studies are performed to determine the stoichiometry and thickness of the barrier layer. From these studies we find that a 50-70 A thick, polar, fluoro-hydrocarbon over layer reduces the permeation of isooctane/toluene/methanol mixtures by a factor of 4. To increase the permeation resistance for automotive applications, this result points towards the deposition of a 1000 A thick fluoro-hydrocarbon barrier coating with stoichiometry and bond structures similar to the CF_4/Ar treated HDPE.

Methane dissociation on Ni(111): A fifteen-dimensional potential energy surface using neural network method

NASA Astrophysics Data System (ADS)

Shen, Xiangjian; Chen, Jun; Zhang, Zhaojun; Shao, Kejie; Zhang, Dong H.

2015-10-01

In the present work, we develop a highly accurate, fifteen-dimensional potential energy surface (PES) of CH4 interacting on a rigid flat Ni(111) surface with the methodology of neural network (NN) fit to a database consisted of about 194 208 ab initio density functional theory (DFT) energy points. Some careful tests of the accuracy of the fitting PES are given through the descriptions of the fitting quality, vibrational spectrum of CH4 in vacuum, transition state (TS) geometries as well as the activation barriers. Using a 25-60-60-1 NN structure, we obtain one of the best PESs with the least root mean square errors: 10.11 meV for the entrance region and 17.00 meV for the interaction and product regions. Our PES can reproduce the DFT results very well in particular for the important TS structures. Furthermore, we present the sticking probability S0 of ground state CH4 at the experimental surface temperature using some sudden approximations by Jackson's group. An in-depth explanation is given for the underestimated sticking probability.

Negative collision energy dependence of Br formation in the OH + HBr reaction.

PubMed

Che, Dock-Chil; Matsuo, Takashi; Yano, Yuya; Bonnet, Laurent; Kasai, Toshio

2008-03-14

The reaction between HBr and OH leading to H(2)O and Br in its ground state is studied by means of a crossed molecular beam experiment for a collision energy varying from 0.05 to 0.26 eV, the initial OH being selected in the state |JOmega> = |3/2 3/2> by an electrostatic hexapole field. The reaction cross-section is found to decrease with increasing collision energy. This negative dependence suggests that there is no barrier on the potential energy surface for the formation pathway considered. The experimental results are compared with the previously reported quantum scattering calculations of Clary et al. (D. C. Clary, G. Nyman and R. Hernandez, J. Phys. Chem., 1994, 101, 3704), and briefly discussed in the light of skewed potential energy surfaces associated with heavy-light-heavy type reactions.

Electronic field emission models beyond the Fowler-Nordheim one

NASA Astrophysics Data System (ADS)

Lepetit, Bruno

2017-12-01

We propose several quantum mechanical models to describe electronic field emission from first principles. These models allow us to correlate quantitatively the electronic emission current with the electrode surface details at the atomic scale. They all rely on electronic potential energy surfaces obtained from three dimensional density functional theory calculations. They differ by the various quantum mechanical methods (exact or perturbative, time dependent or time independent), which are used to describe tunneling through the electronic potential energy barrier. Comparison of these models between them and with the standard Fowler-Nordheim one in the context of one dimensional tunneling allows us to assess the impact on the accuracy of the computed current of the approximations made in each model. Among these methods, the time dependent perturbative one provides a well-balanced trade-off between accuracy and computational cost.

Computationally Efficient Characterization of Potential Energy Surfaces Based on Fingerprint Distances

NASA Astrophysics Data System (ADS)

Schaefer, Bastian; Goedecker, Stefan; Goedecker Group Team

Based on Lennard-Jones, Silicon, Sodium-Chloride and Gold clusters, it was found that uphill barrier energies of transition states between directly connected minima tend to increase with increasing structural differences of the two minima. Based on this insight it also turned out that post-processing minima hopping data at a negligible computational cost allows to obtain qualitative topological information on potential energy surfaces that can be stored in so called qualitative connectivity databases. These qualitative connectivity databases are used for generating fingerprint disconnectivity graphs that allow to obtain a first qualitative idea on thermodynamic and kinetic properties of a system of interest. This research was supported by the NCCR MARVEL, funded by the Swiss National Science Foundation. Computer time was provided by the Swiss National Supercomputing Centre (CSCS) under Project ID No. s499.

The role of the microbiota in shaping infectious immunity

PubMed Central

Hand, Timothy W.

2016-01-01

Humans are meta-organisms that maintain a diverse population of microorganisms on their barrier surfaces, collectively named the microbiota. Since most pathogens either cross or inhabit barrier surfaces, the microbiota plays a critical and often protective role during infections, both by modulating immune system responses and by mediating colonization resistance. However, the microbiota can also act as a reservoir for opportunistic micro-organisms that can ‘bloom’, significantly complicating diseases of barrier surfaces by contributing to inflammatory immune responses. Here, we review our current understanding of the complex interactions between the host, its microbiota and pathogenic organisms, focusing in particular on the intestinal mucosa. PMID:27616558

Fracture-induced amorphization of polycrystalline SiO2 stishovite: a potential platform for toughening in ceramics

PubMed Central

Nishiyama, Norimasa; Wakai, Fumihiro; Ohfuji, Hiroaki; Tamenori, Yusuke; Murata, Hidenobu; Taniguchi, Takashi; Matsushita, Masafumi; Takahashi, Manabu; Kulik, Eleonora; Yoshida, Kimiko; Wada, Kouhei; Bednarcik, Jozef; Irifune, Tetsuo

2014-01-01

Silicon dioxide has eight stable crystalline phases at conditions of the Earth's rocky parts. Many metastable phases including amorphous phases have been known, which indicates the presence of large kinetic barriers. As a consequence, some crystalline silica phases transform to amorphous phases by bypassing the liquid via two different pathways. Here we show a new pathway, a fracture-induced amorphization of stishovite that is a high-pressure polymorph. The amorphization accompanies a huge volume expansion of ~100% and occurs in a thin layer whose thickness from the fracture surface is several tens of nanometers. Amorphous silica materials that look like strings or worms were observed on the fracture surfaces. The amount of amorphous silica near the fracture surfaces is positively correlated with indentation fracture toughness. This result indicates that the fracture-induced amorphization causes toughening of stishovite polycrystals. The fracture-induced solid-state amorphization may provide a potential platform for toughening in ceramics. PMID:25297473

Fracture-induced amorphization of polycrystalline SiO2 stishovite: a potential platform for toughening in ceramics.

PubMed

Nishiyama, Norimasa; Wakai, Fumihiro; Ohfuji, Hiroaki; Tamenori, Yusuke; Murata, Hidenobu; Taniguchi, Takashi; Matsushita, Masafumi; Takahashi, Manabu; Kulik, Eleonora; Yoshida, Kimiko; Wada, Kouhei; Bednarcik, Jozef; Irifune, Tetsuo

2014-10-09

Silicon dioxide has eight stable crystalline phases at conditions of the Earth's rocky parts. Many metastable phases including amorphous phases have been known, which indicates the presence of large kinetic barriers. As a consequence, some crystalline silica phases transform to amorphous phases by bypassing the liquid via two different pathways. Here we show a new pathway, a fracture-induced amorphization of stishovite that is a high-pressure polymorph. The amorphization accompanies a huge volume expansion of ~100% and occurs in a thin layer whose thickness from the fracture surface is several tens of nanometers. Amorphous silica materials that look like strings or worms were observed on the fracture surfaces. The amount of amorphous silica near the fracture surfaces is positively correlated with indentation fracture toughness. This result indicates that the fracture-induced amorphization causes toughening of stishovite polycrystals. The fracture-induced solid-state amorphization may provide a potential platform for toughening in ceramics.

Classical vs. non-classical pathways of mineral formation (Invited)

NASA Astrophysics Data System (ADS)

De Yoreo, J. J.

2013-12-01

Recent chemical analyses, microscopy studies and computer simulations suggest many minerals nucleate through aggregation of pre-nucleation clusters and grow by particle-mediated processes that involve amorphous or disordered precursors. Still other analyses, both experimental and computational, conclude that even simple mineral systems like calcium carbonate form via a barrier-free process of liquid-liquid separation, which is followed by dehydration of the ion-rich phase to form the solid products. However, careful measurements of calcite nucleation rates on a variety of ionized surfaces give results that are in complete agreement with the expectations of classical nucleation theory, in which clusters growing through ion-by-ion addition overcome a free energy barrier through the natural microscopic density fluctuations of the system. Here the challenge of integrating these seemingly disparate observations and analyses into a coherent picture of mineral formation is addressed by considering the energy barriers to calcite formation predicted by the classical theory and the changes in those barriers brought about by the introduction of interfaces and clusters, both stable and metastable. Results from a suite of in situ TEM, AFM, and optical experiments combined with simulations are used to illustrate the conclusions. The analyses show that the expected barrier to homogeneous calcite nucleation is prohibitive even at concentrations exceeding the solubility limit of amorphous calcium carbonate. However, as demonstrated by experiments on self-assembled monolayers, the introduction of surfaces that moderately decrease the interfacial energy associated with the forming nucleus can reduce the magnitude of the barrier to a level that is easily surmounted under typical laboratory conditions. In the absence of such surfaces, experiments that proceed by continually increasing supersaturation with time can easily by-pass direct nucleation of calcite and open up pathways through all other solid phases, as well as dense liquid phases associated with a spinodal. Simulations predict that this phase boundary lies within the region of the calcium carbonate - water phase diagram accessible at room temperature. AFM and TEM analyses of other mineral systems, particularly calcium phosphate, suggest cluster aggregation can play important roles both in modifying barriers and in biasing pathways towards or away from amorphous phases. Most importantly, analysis of the energetic changes shows that barriers are only reduced if the clusters are metastable relative to the free ions and that the reduction is naturally accompanied by a bias towards formation of amorphous precursors. Finally, results from in situ TEM observations of nanoparticle interactions are used to understand the mechanisms controlling particle-mediated growth following formation of primary nuclei of either crystalline phases or disordered precursors. Measurements of the particle speeds and accelerations are used to estimate the magnitude of the attractive potential that drives particle-particle aggregation.

Stacked mechanical nanogenerator comprising piezoelectric semiconducting nanostructures and Schottky conductive contacts

DOEpatents

Wang, Zhong L [Marietta, GA; Xu, Sheng [Atlanta, GA

2011-08-23

An electric power generator includes a first conductive layer, a plurality of semiconducting piezoelectric nanostructures, a second conductive layer and a plurality of conductive nanostructures. The first conductive layer has a first surface from which the semiconducting piezoelectric nanostructures extend. The second conductive layer has a second surface and is parallel to the first conductive layer so that the second surface faces the first surface of the first conductive layer. The conductive nanostructures depend downwardly therefrom. The second conductive layer is spaced apart from the first conductive layer at a distance so that when a force is applied, the semiconducting piezoelectric nanostructures engage the conductive nanostructures so that the piezoelectric nanostructures bend, thereby generating a potential difference across the at semiconducting piezoelectric nanostructures and also thereby forming a Schottky barrier between the semiconducting piezoelectric nanostructures and the conductive nanostructures.

Fundamental Pathways for the Adsorption and Transport of Hydrogen on TiO2 Surfaces: Origin for Effective Sensing at about Room Temperature.

PubMed

Wang, Zhuo; Xia, Xiaohong; Guo, Meilan; Shao, Guosheng

2016-12-28

Effective detection of hydrogen at lowered temperature is highly desirable in promoting safety in using this abundant gas as a clean energy source. Through first-principle calculations in the framework of density functional theory, we find that the high-energy (002) surface for rutile TiO 2 is significantly more effective in adsorbing hydrogen atoms through dissociating hydrogen molecules. The pathways for the dissociation of hydrogen molecules and sequential migration of hydrogen atoms are identified through searching along various transitional states. Pathways of low potential barriers indicate promise for hydrogen sensing, even close to room temperature. This has been proven through sensors made of thin films of well-aligned rutile nanorods, wherein the high-energy (002) surface dictates the top surface of the active layer of the sensors.

Accelerated barrier recovery and enhancement of the barrier integrity and properties by topical application of a pH 4 compared to a pH 5.8 w/o emulsion in aged skin.

PubMed

Angelova-Fischer, I; Fischer, T W; Abels, C; Zillikens, D

2018-03-25

Increased skin surface pH is an important host-related factor for deteriorated barrier function in the aged. We investigated whether restoration of the skin pH through topical application of a water-in-oil (w/o) emulsion with pH 4 improved the barrier homeostasis in aged skin and compared the effects to an identical galenic formulation with pH 5.8. The effects of the test formulations on the barrier recovery were investigated by repeated measurements of transepidermal water loss (TEWL) and skin pH 3 h, 6 h and 24 h after acetone-induced impairment of the barrier function in aged skin. The long-term effects of the pH 4 and pH 5.8 emulsions were analyzed by investigation of the barrier integrity/cohesion, the skin surface pH and the skin roughness and scaliness before and after a 4-week, controlled application of the formulations. The application of the pH 4 emulsion accelerated the barrier recovery in aged skin: 3 h and 6 h after acetone-induced barrier disruption the differences in the TEWL recovery between the pH4-treated and acetone control field were significant. Furthermore, the long-term application of the pH 4 formulation resulted in significantly decreased skin pH, enhanced barrier integrity and reduced skin surface roughness and scaliness. At the same time points, the pH 5.8 formulation exerted only minor effects on the barrier function parameters. Exogenous acidification through topical application of a w/o emulsion with pH 4 leads to improvement of the barrier function and maintenance of the barrier homeostasis in aged skin. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

Insights on finite size effects in ab initio study of CO adsorption and dissociation on Fe 110 surface

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

Chakrabarty, Aurab, E-mail: aurab.chakrabarty@qatar.tamu.edu; Bouhali, Othmane; Mousseau, Normand

Adsorption and dissociation of hydrocarbons on metallic surfaces represent crucial steps on the path to carburization, eventually leading to dusting corrosion. While adsorption of CO molecules on Fe surface is a barrier-less exothermic process, this is not the case for the dissociation of CO into C and O adatoms and the diffusion of C beneath the surface that are found to be associated with large energy barriers. In practice, these barriers can be affected by numerous factors that combine to favour the CO-Fe reaction such as the abundance of CO and other hydrocarbons as well as the presence of structuralmore » defects. From a numerical point of view, studying these factors is challenging and a step-by-step approach is necessary to assess, in particular, the influence of the finite box size on the reaction parameters for adsorption and dissociation of CO on metal surfaces. Here, we use density functional theory (DFT) total energy calculations with the climbing-image nudged elastic band method to estimate the adsorption energies and dissociation barriers for different CO coverages with surface supercells of different sizes. We further compute the effect of periodic boundary condition for DFT calculations and find that the contribution from van der Waals interaction in the computation of adsorption parameters is important as they contribute to correcting the finite-size error in small systems. The dissociation process involves carbon insertion into the Fe surface causing a lattice deformation that requires a larger surface system for unrestricted relaxation. We show that, in the larger surface systems associated with dilute CO-coverages, C-insertion is energetically more favourable, leading to a significant decrease in the dissociation barrier. This observation suggests that a large surface system with dilute coverage is necessary for all similar metal-hydrocarbon reactions in order to study their fundamental electronic mechanisms, as an isolated phenomenon, free from finite-size effects.« less

Insights on finite size effects in ab initio study of CO adsorption and dissociation on Fe 110 surface

NASA Astrophysics Data System (ADS)

Chakrabarty, Aurab; Bouhali, Othmane; Mousseau, Normand; Becquart, Charlotte S.; El-Mellouhi, Fedwa

2016-08-01

Adsorption and dissociation of hydrocarbons on metallic surfaces represent crucial steps on the path to carburization, eventually leading to dusting corrosion. While adsorption of CO molecules on Fe surface is a barrier-less exothermic process, this is not the case for the dissociation of CO into C and O adatoms and the diffusion of C beneath the surface that are found to be associated with large energy barriers. In practice, these barriers can be affected by numerous factors that combine to favour the CO-Fe reaction such as the abundance of CO and other hydrocarbons as well as the presence of structural defects. From a numerical point of view, studying these factors is challenging and a step-by-step approach is necessary to assess, in particular, the influence of the finite box size on the reaction parameters for adsorption and dissociation of CO on metal surfaces. Here, we use density functional theory (DFT) total energy calculations with the climbing-image nudged elastic band method to estimate the adsorption energies and dissociation barriers for different CO coverages with surface supercells of different sizes. We further compute the effect of periodic boundary condition for DFT calculations and find that the contribution from van der Waals interaction in the computation of adsorption parameters is important as they contribute to correcting the finite-size error in small systems. The dissociation process involves carbon insertion into the Fe surface causing a lattice deformation that requires a larger surface system for unrestricted relaxation. We show that, in the larger surface systems associated with dilute CO-coverages, C-insertion is energetically more favourable, leading to a significant decrease in the dissociation barrier. This observation suggests that a large surface system with dilute coverage is necessary for all similar metal-hydrocarbon reactions in order to study their fundamental electronic mechanisms, as an isolated phenomenon, free from finite-size effects.

Giant tunnelling electroresistance in metal/ferroelectric/semiconductor tunnel junctions by engineering the Schottky barrier

PubMed Central

Xi, Zhongnan; Ruan, Jieji; Li, Chen; Zheng, Chunyan; Wen, Zheng; Dai, Jiyan; Li, Aidong; Wu, Di

2017-01-01

Recently, ferroelectric tunnel junctions have attracted much attention due to their potential applications in non-destructive readout non-volatile memories. Using a semiconductor electrode has been proven effective to enhance the tunnelling electroresistance in ferroelectric tunnel junctions. Here we report a systematic investigation on electroresistance of Pt/BaTiO3/Nb:SrTiO3 metal/ferroelectric/semiconductor tunnel junctions by engineering the Schottky barrier on Nb:SrTiO3 surface via varying BaTiO3 thickness and Nb doping concentration. The optimum ON/OFF ratio as great as 6.0 × 106, comparable to that of commercial Flash memories, is achieved in a device with 0.1 wt% Nb concentration and a 4-unit-cell-thick BaTiO3 barrier. With this thinnest BaTiO3 barrier, which shows a negligible resistance to the tunnelling current but is still ferroelectric, the device is reduced to a polarization-modulated metal/semiconductor Schottky junction that exhibits a more efficient control on the tunnelling resistance to produce the giant electroresistance observed. These results may facilitate the design of high performance non-volatile resistive memories. PMID:28513590

Giant tunnelling electroresistance in metal/ferroelectric/semiconductor tunnel junctions by engineering the Schottky barrier

NASA Astrophysics Data System (ADS)

Xi, Zhongnan; Ruan, Jieji; Li, Chen; Zheng, Chunyan; Wen, Zheng; Dai, Jiyan; Li, Aidong; Wu, Di

2017-05-01

Recently, ferroelectric tunnel junctions have attracted much attention due to their potential applications in non-destructive readout non-volatile memories. Using a semiconductor electrode has been proven effective to enhance the tunnelling electroresistance in ferroelectric tunnel junctions. Here we report a systematic investigation on electroresistance of Pt/BaTiO3/Nb:SrTiO3 metal/ferroelectric/semiconductor tunnel junctions by engineering the Schottky barrier on Nb:SrTiO3 surface via varying BaTiO3 thickness and Nb doping concentration. The optimum ON/OFF ratio as great as 6.0 × 106, comparable to that of commercial Flash memories, is achieved in a device with 0.1 wt% Nb concentration and a 4-unit-cell-thick BaTiO3 barrier. With this thinnest BaTiO3 barrier, which shows a negligible resistance to the tunnelling current but is still ferroelectric, the device is reduced to a polarization-modulated metal/semiconductor Schottky junction that exhibits a more efficient control on the tunnelling resistance to produce the giant electroresistance observed. These results may facilitate the design of high performance non-volatile resistive memories.

Low Barrier Methyl Rotation in 3-PENTYN-1-OL as Observed by Microwave Spectroscopy

NASA Astrophysics Data System (ADS)

Eibl, Konrad; Kannengießer, Raphaela; Stahl, Wolfgang; Nguyen, Ha Vinh Lam; Kleiner, Isabelle

2016-06-01

It is known that the barrier to internal rotation of the methyl groups in ethane (1) is about 1000 wn. If a C-C-triple bond is inserted between the methyl groups as a spacer (2), the torsional barrier is assumed to be dramatically lower, which is a common feature of ethinyl groups in general. To study this effect of almost free internal rotation, we measured the rotational spectrum of 3-pentyn-1-ol (3) by pulsed jet Fourier transform microwave spectroscopy in the frequency range from 2 to 26.5 GHz. Quantum chemical calculations at the MP2/6-311++G(d,p) level of theory yielded five stable conformers on the potential energy surface. The most stable conformer, which possesses C1 symmetry, was assigned and fitted using two theoretical approaches treating internal rotations, the rho axis method (BELGI-C1) and the combined axis method (XIAM). The molecular parameters as well as the internal rotation parameters were determined. A very low barrier to internal rotation of the methyl group of only 9.4545(95) wn was observed. R. M. Pitzer, Acc. Chem. Res., 1983, 16, 207-210

Nucleophilic substitution at silicon (SN2@Si) via a central reaction barrier.

PubMed

Bento, A Patrícia; Bickelhaupt, F Matthias

2007-03-16

It is textbook knowledge that nucleophilic substitution at carbon (SN2@C) proceeds via a central reaction barrier which disappears in the corresponding nucleophilic substitution reaction at silicon (SN2@Si). Here, we address the question why the central barrier disappears from SN2@C to SN2@Si despite the fact that these processes are isostructural and isoelectronic. To this end, we have explored and analyzed the potential energy surfaces (PES) of various Cl-+CR3Cl (R=H, CH3) and Cl-+SiR3Cl model reactions (R=H, CH3, C2H5, and OCH3). Our results show that the nature of the SN2 reaction barrier is in essence steric, but that it can be modulated by electronic factors. Thus, simply by increasing the steric demand of the substituents R around the silicon atom, the SN2@Si mechanism changes from its regular single-well PES (with a stable intermediate transition complex, TC), via a triple-well PES (with a pre- and a post-TS before and after the central TC), to a double-well PES (with a TS; R=OCH3), which is normally encountered for SN2@C reactions.

Clustering on Magnesium Surfaces - Formation and Diffusion Energies.

PubMed

Chu, Haijian; Huang, Hanchen; Wang, Jian

2017-07-12

The formation and diffusion energies of atomic clusters on Mg surfaces determine the surface roughness and formation of faulted structure, which in turn affect the mechanical deformation of Mg. This paper reports first principles density function theory (DFT) based quantum mechanics calculation results of atomic clustering on the low energy surfaces {0001} and [Formula: see text]. In parallel, molecular statics calculations serve to test the validity of two interatomic potentials and to extend the scope of the DFT studies. On a {0001} surface, a compact cluster consisting of few than three atoms energetically prefers a face-centered-cubic stacking, to serve as a nucleus of stacking fault. On a [Formula: see text], clusters of any size always prefer hexagonal-close-packed stacking. Adatom diffusion on surface [Formula: see text] is high anisotropic while isotropic on surface (0001). Three-dimensional Ehrlich-Schwoebel barriers converge as the step height is three atomic layers or thicker. Adatom diffusion along steps is via hopping mechanism, and that down steps is via exchange mechanism.

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

Yan, Wei; Liu, Hongtao, E-mail: liuht100@126.com; Sun, Qinghe

A facile and quick fabrication method was proposed to prepare superhydrophobic surfaces on iron substrate by chemical immersion and subsequent stearic acid modification. The association between wettability and surface morphology was studied through altering the copper ion concentration and immersion time. Surface tension instrument, scanning electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and electrochemical workstation were used to characterize the wettability, physical morphology, chemical composition, and corrosion resistance ability of the prepared film. Results showed that both the rough micro/nanostructures and low surface energy material play critical roles in surface wettability. The superhydrophobic film achieved a better anticorrosion property comparedmore » to barrier iron by analysis of open circuit potential, potentiodynamic polarization curves, and Nyquist plots. In addition, the superhydrophobic surface showed excellent performance of acid and alkali resistance, anti-icing, and self-cleaning through a series of environmental tests. This study provides a valid method for quick-preparation of the stable superhydrophobic surfaces, which has a promising application in steel buildings and facilities.« less

Nanostructured Surfaces for Drug Delivery and Anti-Fibrosis

NASA Astrophysics Data System (ADS)

Kam, Kimberly Renee

Effective and cost-efficient healthcare is at the forefront of public discussion; on both personal and policy levels, technologies that improve therapeutic efficacy without the use of painful hypodermic needle injections or the use of harsh chemicals would prove beneficial to patients. Nanostructured surfaces as structure-mediated permeability enhancers introduce a potentially revolutionary approach to the field of drug delivery. Parental administration routes have been the mainstay technologies for delivering biologics because these therapeutics are too large to permeate epithelial barriers. However, there is a significant patient dislike for hypodermic needles resulting in reduced patient compliance and poor therapeutic results. We present an alternative strategy to harness the body's naturally occurring biological processes and transport mechanisms to enhance the drug transport of biologics across the epithelium. Our strategy offers a paradigm shift from traditional biochemical drug delivery vehicles by using nanotopography to loosen the epithelial barrier. Herein, we demonstrate that nanotopographical cues can be used to enable biologics > 66 kDa to be transported across epithelial monolayers by increasing paracellular transport. When placed in contact with epithelial cells, nanostructured films significantly increase the transport of albumin, IgG, and a model therapeutic, etanercept. Our work highlights the potential to use drug delivery systems which incorporate nanotopographical cues to increase the transport of biologics across epithelial tissue. Furthermore, we describe current advancements in nano- and microfabrication for applications in anti-fibrosis and wound healing. Influencing cellular responses to biomaterials is crucial in the field of tissue engineering and regenerative medicine. Since cells are surrounded by extracellular matrix features that are on the nanoscale, identifying nanostructures for imparting desirable cellular function could greatly impact the field. Due to the rise in micro and nanofabrication techniques borrowed from the advances in the microelectronics industry, previously unattainable nanostructured surfaces on a variety of biomaterials can be generated. We investigated how nanostructured surfaces with varying nanofeature aspect ratios can influence fibrosis. Thus, nanostructured surfaces show substantial progress for therapeutic applications in drug delivery and wound healing.

Multilayer coatings for flexible high-barrier materials

NASA Astrophysics Data System (ADS)

Vaško, Karol; Noller, Klaus; Mikula, Milan; Amberg-Schwab, Sabine; Weber, Ulrike

2009-06-01

A multilayer, flexible, and transparent high-barrier system based on flexible plastic foils, polyethyleneterephthalate (PET) and ethylene-tetrafluoroethylene-copolymer (ETFE), combined with vacuum-deposited, inorganic SiOx layers and hybrid ORMOCER® varnish layers were prepared in different orders on a semiproduction level. Barrier properties of prepared systems, as water vapour transmission (WVTR) and oxygen transmission (OTR), were measured and studied in connection with surface energy, surface topography, and water vapour adsorption properties. Correlations among layers sequence, barrier properties, and other parameters are presented, including some basic principles of permeation of substances through multilayer barrier systems. A combination of several inorganic and hybrid varnish layers is necessary to achieve the technological demands from a barrier standpoint. It is easier to suppress the oxygen transport than the water transport, due to the additional active penetration of water through hydrogen bonds and silanol creations at oxide interfaces, capillary condensation, and swelling with high internal pressure, leading to new defects.

Interference phenomena in the refraction of a surface polariton by vertical dielectric barriers

NASA Technical Reports Server (NTRS)

Shen, T. P.; Wallis, R. F.; Maradudin, A. A.; Stegeman, G. I.

1984-01-01

A normal mode analysis is used to calculate the transmission and reflection coefficients for a surface polariton propagating along the interface between a surface active medium and a dielectric and incident normally on a vertical dielectric barrier of finite thickness or a thin dielectric film of finite length. The efficiencies of conversion of the surface polariton into transmitted and reflected bulk waves are also determined. The radiation patterns associated with the latter waves are presented.

Transient thermography testing of unpainted thermal barrier coating surfaces

NASA Astrophysics Data System (ADS)

Ptaszek, Grzegorz; Cawley, Peter; Almond, Darryl; Pickering, Simon

2013-01-01

This paper has investigated the effects of uneven surface discolouration of a thermal barrier coating (TBC) and of its IR translucency on the thermal responses observed by using mid and long wavelength IR cameras. It has been shown that unpainted blades can be tested satisfactorily by using a more powerful flash heating system and a long wavelength IR camera. The problem of uneven surface emissivity can be overcome by applying 2nd derivative processing of the log-log surface cooling curves.

Ozone dissociation to oxygen affected by Criegee intermediate.

PubMed

Wei, Wen-Mei; Zheng, Ren-Hui; Pan, Yue-Li; Wu, Yun-Kai; Yang, Fan; Hong, Shi

2014-03-06

The detailed potential energy surfaces for the reactions of Criegee intermediate (CI, H2COO) and formaldehyde (H2CO) with ozone (O3) have been investigated at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-311++G(2d,2p) level of theory, respectively. New alternative reaction mechanisms, to the one previously proposed (J. Phys. Chem. Lett. 2013, 4, 2525) have been found. The lower barrier of the new mechanism shows that it is easy for H2COO + O3 to dissociate to formaldehyde and oxygen. For the reactions of H2CO with O3 to produce H2COO and O2, we find relatively high energy barriers, which makes the ozone dissociation to oxygen unlikely to be catalyzed by CI.

Kinetic and mechanisms of methanimine reactions with singlet and triplet molecular oxygen: Substituent and catalyst effects

NASA Astrophysics Data System (ADS)

Asgharzadeh, Somaie; Vahedpour, Morteza

2018-06-01

Methanimine reaction with O2 on singlet and triplet potential energy surfaces are investigated using B3PW91, M06-2X, MP2 and CCSD(T) methods. Thermodynamic and kinetic parameters are calculated at M06-2X method. The most favorable channel involves H-abstraction of CH2NH+O2 to the formation of HCN + H2O2 products via low level energy barrier. The catalytic effect of water molecule on HCN + H2O2 products pathway are investigated. Result shows that contribution of water molecule using complex formation with methanimine can decreases barrier energy of transition state and the reaction rate increases. Also, substituent effect of fluorine atom as deactivating group are investigated on the main reaction pathway.

Charge optimized many body (COMB) potentials for Pt and Au.

PubMed

Antony, A C; Akhade, S A; Lu, Z; Liang, T; Janik, M J; Phillpot, S R; Sinnott, S B

2017-06-07

Interatomic potentials for Pt and Au are developed within the third generation charge optimized many-body (COMB3) formalism. The potentials are capable of reproducing phase order, lattice constants, and elastic constants of Pt and Au systems as experimentally measured or calculated by density functional theory. We also fit defect formation energies, surface energies and stacking fault energies for Pt and Au metals. The resulting potentials are used to map a 2D contour of the gamma surface and simulate the tensile test of 16-grain polycrystalline Pt and Au structures at 300 K. The stress-strain behaviour is investigated and the primary slip systems {1 1 1}〈1 [Formula: see text] 0〉 are identified. In addition, we perform high temperature (1800 K for Au and 2300 K for Pt) molecular dynamics simulations of 30 nm Pt and Au truncated octahedron nanoparticles and examine morphological changes of each particle. We further calculate the activation energy barrier for surface diffusion during simulations of several nanoseconds and report energies of [Formula: see text] eV for Pt and [Formula: see text] eV for Au. This initial parameterization and application of the Pt and Au potentials demonstrates a starting point for the extension of these potentials to multicomponent systems within the COMB3 framework.

Conjugate heat transfer investigation on the cooling performance of air cooled turbine blade with thermal barrier coating

NASA Astrophysics Data System (ADS)

Ji, Yongbin; Ma, Chao; Ge, Bing; Zang, Shusheng

2016-08-01

A hot wind tunnel of annular cascade test rig is established for measuring temperature distribution on a real gas turbine blade surface with infrared camera. Besides, conjugate heat transfer numerical simulation is performed to obtain cooling efficiency distribution on both blade substrate surface and coating surface for comparison. The effect of thermal barrier coating on the overall cooling performance for blades is compared under varied mass flow rate of coolant, and spatial difference is also discussed. Results indicate that the cooling efficiency in the leading edge and trailing edge areas of the blade is the lowest. The cooling performance is not only influenced by the internal cooling structures layout inside the blade but also by the flow condition of the mainstream in the external cascade path. Thermal barrier effects of the coating vary at different regions of the blade surface, where higher internal cooling performance exists, more effective the thermal barrier will be, which means the thermal protection effect of coatings is remarkable in these regions. At the designed mass flow ratio condition, the cooling efficiency on the pressure side varies by 0.13 for the coating surface and substrate surface, while this value is 0.09 on the suction side.

Protection of SK-N-MC cells against β-amyloid peptide-induced degeneration using neuron growth factor-loaded liposomes with surface lactoferrin.

PubMed

Kuo, Yung-Chih; Wang, Cheng-Ting

2014-07-01

A liposomal system with surface lactoferrin (Lf) was developed for delivering neuron growth factor (NGF) across the blood-brain barrier (BBB) and improving the viability of neuron-like SK-N-MC cells with deposited β-amyloid peptide (Aβ). The Lf-grafted liposomes carrying NGF (Lf/NGF-liposomes) were applied to a monolayer of human brain-microvascular endothelial cells (HBMECs) regulated by human astrocytes (HAs) and to fibrillar Aβ1-42-insulted SK-N-MC cells. An increase in cholesterol mole percentage enhanced the particle size, absolute value of zeta potential, and physical stability, however, reduced the entrapment efficiency and release rate of NGF. In addition, an increase in Lf concentration increased the particle size, surface nitrogen percentage, NGF permeability across the BBB, and viability of HBMECs, HAs, and SK-N-MC cells, however, decreased the absolute value of zeta potential, surface phosphorus percentage, and loading efficiency of Lf. After treating with Lf/NGF-liposomes, a higher Aβ concentration yielded a lower survival of SK-N-MC cells. The current Lf/NGF-liposomes are efficacious drug carriers to target the BBB and inhibit the Aβ-induced neurotoxicity as potential pharmacotherapy for Alzheimer's disease. Copyright © 2014 Elsevier Ltd. All rights reserved.

Hindered rotation and nuclear spin isomers separation of molecularly chemisorbed H2 on Pd(210)

NASA Astrophysics Data System (ADS)

Arguelles, Elvis F.; Kasai, Hideaki

2018-03-01

We investigated the hindered rotation and nuclear spin isomer separation of H2 on Pd(210) for various pre-adsorbed atomic hydrogen coverages (Θ), by total energy calculations based on density functional theory. Our results revealed that H2 is in the molecularly chemisorbed state and the adsorption is characterized by a highly anisotropic potential energy surface. Further, we found that J = 1 degenerate level splitting is insensitive to the increase in Θ from 1 to 2 ML. This is due to the comparable potential strengths hindering/restricting the polar rotations in both coverages. On a fully H passivated (3 ML) Pd(210), H2 is in a weakly physisorbed state with a negligible potential anisotropy. Our findings suggest that the activation barrier for polar rotational motion does not strongly depend on the adsorption energy but rather on the surface-molecule bond. The estimated rotational state desorption energies show a separation of ortho and para isomers by around 7.0 meV.

Magnetically responsive nanoparticles for drug delivery applications using low magnetic field strengths.

PubMed

McGill, Shayna L; Cuylear, Carla L; Adolphi, Natalie L; Osiński, Marek; Smyth, Hugh D C

2009-03-01

The purpose of this study is to investigate the potential of magnetic nanoparticles for enhancing drug delivery using a low oscillating magnetic field (OMF) strength. We investigated the ability of magnetic nanoparticles to cause disruption of a viscous biopolymer barrier to drug delivery and the potential to induce triggered release of drug conjugated to the surfaces of these particles. Various magnetic nanoparticles were screened for thermal response under a 295-kHz OMF with an amplitude of 3.1 kA/m. Based on thermal activity of particles screened, we selected the nanoparticles that displayed desired characteristics for evaluation in a simplified model of an extracellular barrier to drug delivery, using lambda DNA/HindIII. Results indicate that nanoparticles could be used to induce DNA breakage to enhance local diffusion of drugs, despite low temperatures of heating. Additional studies showed increased diffusion of quantum dots in this model by single-particle tracking methods. Bimane was conjugated to the surface of magnetic nanoparticles. Fluorescence and transmission electron microscope images of the conjugated nanoparticles indicated little change in the overall appearance of the nanoparticles. A release study showed greater drug release using OMF, while maintaining low bulk heating of the samples (T = 30 degrees C). This study indicates that lower magnetic field strengths may be successfully utilized for drug delivery applications as a method for drug delivery transport enhancement and drug release switches.

Free energy surface of two- and three-dimensional transitions of Au 12 nanoclusters obtained by ab initio metadynamics

NASA Astrophysics Data System (ADS)

Santarossa, Gianluca; Vargas, Angelo; Iannuzzi, Marcella; Baiker, Alfons

2010-05-01

The description of the conformational space generated by metal nanoparticles is a fundamental issue for the study of their physicochemical properties. In this investigation, an exhaustive exploration and a unified view of the conformational space of a gold nanocluster is provided using a Au 12 cluster as an example. Such system is characterized by coexisting planar/quasiplanar and tridimensional conformations separated by high-energy barriers. The conformational space of Au 12 has been explored by means of Born-Oppenheimer ab initio metadynamics, i.e., a molecular dynamics simulation coupled with a history dependent potential to accelerate events that might occur on a long time scale compared to the time step used in the simulations (rare events). The sampled conformations have complex, in general not intuitive topologies that we have classified as planar/quasiplanar or tridimensional, belonging to different regions of the free energy surface. Three conformational free energy basins were identified, one for the planar/quasiplanar and two for the tridimensional structures. At thermodynamic equilibrium, the planar/quasi-planar and tridimensional conformations were found to coexist, to be fluxional and to be separated by high-free-energy barriers. The comparison between the free energy and the potential energy revealed the relevance of the entropic contribution in the equilibrium distribution of the conformations of the cluster.

Electrochemical studies of Copper, Tantalum and Tantalum Nitride surfaces in aqueous solutions for applications in chemical-mechanical and electrochemical-mechanical planarization

NASA Astrophysics Data System (ADS)

Sulyma, Christopher Michael

This report will investigate fundamental properties of materials involved in integrated circuit (IC) manufacturing. Individual materials (one at a time) are studied in different electrochemical environmental solutions to better understand the kinetics associated with the polishing process. Each system tries to simulate a real CMP environment in order to compare our findings with what is currently used in industry. To accomplish this, a variety of techniques are used. The voltage pulse modulation technique is useful for electrochemical processing of metal and alloy surfaces by utilizing faradaic reactions like electrodeposition and electrodissolution. A theoretical framework is presented in chapter 4 to facilitate quantitative analysis of experimental data (current transients) obtained in this approach. A typical application of this analysis is demonstrated for an experimental system involving electrochemical removal of copper surface layers, a relatively new process for abrasive-free electrochemical mechanical planarization of copper lines used in the fabrication of integrated circuits. Voltage pulse modulated electrodissolution of Cu in the absence of mechanical polishing is activated in an acidic solution of oxalic acid and hydrogen peroxide. The current generated by each applied voltage step shows a sharp spike, followed by a double-exponential decay, and eventually attains the rectangular shape of the potential pulses. For the second system in chapter 5, open-circuit potential measurements, cyclic voltammetry and Fourier transform impedance spectroscopy have been used to study pH dependent surface reactions of Cu and Ta rotating disc electrodes (RDEs) in aqueous solutions of succinic acid (SA, a complexing agent), hydrogen peroxide (an oxidizer), and ammonium dodecyl sulfate (ADS, a corrosion inhibitor for Cu). The surface chemistries of these systems are relevant for the development of a single-slurry approach to chemical mechanical planarization (CMP) of Cu lines and Ta barriers in the fabrication of semiconductor devices. It is shown that in non-alkaline solutions of H2O2, the SA-promoted surface complexes of Cu and Ta can potentially support chemically enhanced material removal in low-pressure CMP of surface topographies overlying fragile low-k dielectrics. ADS can suppress Cu dissolution without significantly affecting the surface chemistry of Ta. Chapter 6 discusses anodic corrosion of Ta, which is examined as a possible route to voltage induced removal of Ta for potential applications in electrochemical mechanical planarization (ECMP) of diffusion barriers. This strategy involves electro-oxidation of Ta in the presence of NO3- anions to form mechanically weak surface oxide films, followed by removal of the oxide layers by moderate mechanical abrasion. This NO3 - system is compared with a reference solution of Br -. In both electrolytes, the voltammetric currents of anodic oxidation exhibit oscillatory behaviors in the initial cycles of slow (5 mV s-1) voltage scans. The frequencies of these current oscillations are show signature attributes of localized pitting or general surface corrosion caused by Br- or NO3 -, respectively. Scanning electron microscopy, cyclic voltammetry, polarization resistance measurements, and time resolved Fourier transform impedance spectroscopy provide additional details about these corrosion mechanism. Apart from their relevance in the context of ECMP, the results also address certain fundamental aspects of pitting and general corrosions. The general protocols necessary to combine and analyze the results of D.C. and A.C. electrochemical measurements involving such valve metal corrosion systems are discussed in detail. In chapter 7 potassium salts of certain oxyanions (nitrate, sulfate and phosphate in particular) are shown to serve as effective surface-modifying agents in chemically enhanced, low-pressure chemical mechanical planarization (CMP) of Ta and TaN barrier layers for interconnect structures. The surface reactions that form the basis of this CMP strategy are investigated here in detail using the electrochemical techniques of cyclic voltammetry, open circuit potential analysis, polarization resistance measurements, and Fourier transform impedance spectroscopy. The results suggest that forming structurally weak oxide layers on the CMP samples is a key to achieving the goal of chemically controlled CMP of Ta/TaN at low down-pressures. (Abstract shortened by UMI.)

The properties and performance of moisture/oxygen barrier layers deposited by remote plasma sputtering

NASA Astrophysics Data System (ADS)

Brown, Hayley Louise

The development of flexible lightweight OLED devices requires oxygen/moisture barrier layer thin films with water vapour transmission rates (WVTR) of < 10-6 g/m2/day. This thesis reports on single and multilayer architecture barrier layers (mostly based on SiO2, Al2O3 and TiO2) deposited onto glass, Si and polymeric substrates using remote plasma sputtering. The reactive sputtering depositions were performed on Plasma Quest S500 based sputter systems and the morphology, nanostructure and composition of the coatings have been examined using SEM, EDX, STEM, XPS, XRD and AFM. The WVTR has been determined using industry standard techniques (e.g. MOCON) but, for rapid screening of the deposited layers, an in-house permeation test was also developed. SEM, XRD and STEM results showed that the coatings exhibited a dense, amorphous structure with no evidence of columnar growth. However, all of the single and multilayer coatings exhibited relatively poor WVTRs of > 1 x 10-1 g/m2/day at 38 °C and 85 % RH. Further characterisation indicated that the barrier films were failing due to the presence of substrate asperities and airborne particulates. Different mechanisms were investigated in an attempt to reduce the density of film defects including incorporation of a getter layer, modification of growth kinetics, plasma treatment and polymer planarising, but none were successful in lowering the WVTR. Review of this issue indicated that the achievement of good barrier layers was likely to be problematic in commercial practice due to the cost implications of adequately reducing particulate density and the need to cover deliberately non-planar surfaces and fabricated 3D structures. Conformal coverage would therefore be required to bury surface structures and to mitigate particulate issues. Studies of the remote plasma system showed that it both inherently delivered an ionised physical vapour deposition (IPVD) process and was compatible with bias re-sputtering of substrates. Accordingly, a process using RF substrate bias to conformally coat surfaces was developed to encapsulate surface particulates and seal associated permeation paths. An order of magnitude improvement in WVTR (6.7 x 10-2 g/m2/day) was measured for initial Al2O3 coatings deposited with substrate bias. The development of substrate bias to enhance conformal coverage provides significant new commercial benefit. Furthermore, conformal coverage of 5:1 aspect ratio structures have been demonstrated by alternating the substrate bias between -222 V and -267 V, with a 50 % dwell time at each voltage. Further development and optimisation of the substrate bias technique is required to fully explore the potential for further improving barrier properties and conformal coverage of high aspect ratio and other 3D structures.

The Possible Emergence of Life and Differentiation of a Shallow Biosphere on Irradiated Icy Worlds: The Example of Europa.

PubMed

Russell, Michael J; Murray, Alison E; Hand, Kevin P

2017-12-01

Irradiated ice-covered ocean worlds with rocky mafic mantles may provide the conditions needed to drive the emergence and maintenance of life. Alkaline hydrothermal springs-relieving the geophysical, thermal, and chemical disequilibria between oceans and tidally stressed crusts-could generate inorganic barriers to the otherwise uncontrolled and kinetically disfavored oxidation of hydrothermal hydrogen and methane. Ionic gradients imposed across these inorganic barriers, comprising iron oxyhydroxides and sulfides, could drive the hydrogenation of carbon dioxide and the oxidation of methane through thermodynamically favorable metabolic pathways leading to early life-forms. In such chemostatic environments, fuels may eventually outweigh oxidants. Ice-covered oceans are primarily heated from below, creating convection that could transport putative microbial cells and cellular cooperatives upward to congregate beneath an ice shell, potentially giving rise to a highly focused shallow biosphere. It is here where electron acceptors, ultimately derived from the irradiated surface, could be delivered to such life-forms through exchange with the icy surface. Such zones would act as "electron disposal units" for the biosphere, and occupants might be transferred toward the surface by buoyant diapirs and even entrained into plumes. Key Words: Biofilms-Europa-Extraterrestrial life-Hydrothermal systems. Astrobiology 17, 1265-1273.

The Possible Emergence of Life and Differentiation of a Shallow Biosphere on Irradiated Icy Worlds: The Example of Europa

PubMed Central

Murray, Alison E.; Hand, Kevin P.

2017-01-01

Abstract Irradiated ice-covered ocean worlds with rocky mafic mantles may provide the conditions needed to drive the emergence and maintenance of life. Alkaline hydrothermal springs—relieving the geophysical, thermal, and chemical disequilibria between oceans and tidally stressed crusts—could generate inorganic barriers to the otherwise uncontrolled and kinetically disfavored oxidation of hydrothermal hydrogen and methane. Ionic gradients imposed across these inorganic barriers, comprising iron oxyhydroxides and sulfides, could drive the hydrogenation of carbon dioxide and the oxidation of methane through thermodynamically favorable metabolic pathways leading to early life-forms. In such chemostatic environments, fuels may eventually outweigh oxidants. Ice-covered oceans are primarily heated from below, creating convection that could transport putative microbial cells and cellular cooperatives upward to congregate beneath an ice shell, potentially giving rise to a highly focused shallow biosphere. It is here where electron acceptors, ultimately derived from the irradiated surface, could be delivered to such life-forms through exchange with the icy surface. Such zones would act as “electron disposal units” for the biosphere, and occupants might be transferred toward the surface by buoyant diapirs and even entrained into plumes. Key Words: Biofilms—Europa—Extraterrestrial life—Hydrothermal systems. Astrobiology 17, 1265–1273. PMID:29016193

Method and apparatus for determining minority carrier diffusion length in semiconductors

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

Moore, A.R.

1984-02-21

Method and apparatus are provided for determining the diffusion length of minority carriers in semiconductor material, particularly amorphous silicon, which has a significantly small minority carrier diffusion length using the constant magnitude surface-photovoltage (SPV) method. Steady or modulated illumination at several wavelengths provides the light excitation on the surface of the material to generate the SPV. A manually controlled or automatic servo system maintains a constant predetermined value of the SPB for each wavelength. A probe electrode immersed in an electrolyte solution containing redox couples (preferably quinhydrone) having an oxidation-reduction potential (E) in the order of +0.6 to -1.65 voltsmore » couples the SPV to a measurement system. The redox couple solution functions to create a liquid Schottky barrier at the surface of the material. The Schottky barrier is contacted by merely placing the probe in the solution. The redox solution is placed over and in contact with the material to be tested and light is passed through the solution to generate the SPV. To compensate for colored redox solutions a portion of the redox solution not over the material is also illuminated for determining the color compensated light intensity. Steady red light is also used as an optical bias to reduce deleterious space-charge effects that occur in amorphous silicon.« less

Method and apparatus for determining minority carrier diffusion length in semiconductors

DOEpatents

Moore, Arnold R.

1984-02-21

Method and apparatus are provided for determining the diffusion length of minority carriers in semiconductor material, particularly amorphous silicon, which has a significantly small minority carrier diffusion length using the constant magnitude surface-photovoltage (SPV) method. Steady or modulated illumination at several wavelengths provides the light excitation on the surface of the material to generate the SPV. A manually controlled or automatic servo system maintains a constant predetermined value of the SPV for each wavelength. A probe electrode immersed in an electrolyte solution containing redox couples (preferably quinhydrone) having an oxidation-reduction potential (E) in the order of +0.6 to -1.65 volts couples the SPV to a measurement system. The redox couple solution functions to create a liquid Schottky barrier at the surface of the material. The Schottky barrier is contacted by merely placing the probe in the solution. The redox solution is placed over and in contact with the material to be tested and light is passed through the solution to generate the SPV. To compensate for colored redox solutions a portion of the redox solution not over the material is also illuminated for determining the color compensated light intensity. Steady red light is also used as an optical bias to reduce deleterious space-charge effects that occur in amorphous silicon.

Large-scale, thick, self-assembled, nacre-mimetic brick-walls as fire barrier coatings on textiles

NASA Astrophysics Data System (ADS)

Das, Paramita; Thomas, Helga; Moeller, Martin; Walther, Andreas

2017-01-01

Highly loaded polymer/clay nanocomposites with layered structures are emerging as robust fire retardant surface coatings. However, time-intensive sequential deposition processes, e.g. layer-by-layer strategies, hinders obtaining large coating thicknesses and complicates an implementation into existing technologies. Here, we demonstrate a single-step, water-borne approach to prepare thick, self-assembling, hybrid fire barrier coatings of sodium carboxymethyl cellulose (CMC)/montmorillonite (MTM) with well-defined, bioinspired brick-wall nanostructure, and showcase their application on textile. The coating thickness on the textile is tailored using different concentrations of CMC/MTM (1-5 wt%) in the coating bath. While lower concentrations impart conformal coatings of fibers, thicker continuous coatings are obtained on the textile surface from highest concentration. Comprehensive fire barrier and fire retardancy tests elucidate the increasing fire barrier and retardancy properties with increasing coating thickness. The materials are free of halogen and heavy metal atoms, and are sourced from sustainable and partly even renewable building blocks. We further introduce an amphiphobic surface modification on the coating to impart oil and water repellency, as well as self-cleaning features. Hence, our study presents a generic, environmentally friendly, scalable, and one-pot coating approach that can be introduced into existing technologies to prepare bioinspired, thick, fire barrier nanocomposite coatings on diverse surfaces.

Enhanced methanol utilization in direct methanol fuel cell

DOEpatents

Ren, Xiaoming; Gottesfeld, Shimshon

2001-10-02

The fuel utilization of a direct methanol fuel cell is enhanced for improved cell efficiency. Distribution plates at the anode and cathode of the fuel cell are configured to distribute reactants vertically and laterally uniformly over a catalyzed membrane surface of the fuel cell. A conductive sheet between the anode distribution plate and the anodic membrane surface forms a mass transport barrier to the methanol fuel that is large relative to a mass transport barrier for a gaseous hydrogen fuel cell. In a preferred embodiment, the distribution plate is a perforated corrugated sheet. The mass transport barrier may be conveniently increased by increasing the thickness of an anode conductive sheet adjacent the membrane surface of the fuel cell.

Isotopic dependence of fusion enhancement of various heavy ion systems using energy dependent Woods-Saxon potential

NASA Astrophysics Data System (ADS)

Gautam, Manjeet Singh

2015-01-01

In the present work, the fusion of symmetric and asymmetric projectile-target combinations are deeply analyzed within the framework of energy dependent Woods-Saxon potential model (EDWSP model) in conjunction with one dimensional Wong formula and the coupled channel code CCFULL. The neutron transfer channels and the inelastic surface excitations of collision partners are dominating mode of couplings and the coupling of relative motion of colliding nuclei to such relevant internal degrees of freedom produces a significant fusion enhancement at sub-barrier energies. It is quite interesting that the effects of dominant intrinsic degrees of freedom such as multi-phonon vibrational states, neutron transfer channels and proton transfer channels can be simulated by introducing the energy dependence in the nucleus-nucleus potential (EDWSP model). In the EDWSP model calculations, a wide range of diffuseness parameter ranging from a = 0.85 fm to a = 0.97 fm, which is much larger than a value (a = 0.65 fm) extracted from the elastic scattering data, is needed to reproduce sub-barrier fusion data. However, such diffuseness anomaly, which might be an artifact of some dynamical effects, has been resolved by trajectory fluctuation dissipation (TFD) model wherein the resulting nucleus-nucleus potential possesses normal diffuseness parameter.

Exploring chemical reaction mechanisms through harmonic Fourier beads path optimization.

PubMed

Khavrutskii, Ilja V; Smith, Jason B; Wallqvist, Anders

2013-10-28

Here, we apply the harmonic Fourier beads (HFB) path optimization method to study chemical reactions involving covalent bond breaking and forming on quantum mechanical (QM) and hybrid QM∕molecular mechanical (QM∕MM) potential energy surfaces. To improve efficiency of the path optimization on such computationally demanding potentials, we combined HFB with conjugate gradient (CG) optimization. The combined CG-HFB method was used to study two biologically relevant reactions, namely, L- to D-alanine amino acid inversion and alcohol acylation by amides. The optimized paths revealed several unexpected reaction steps in the gas phase. For example, on the B3LYP∕6-31G(d,p) potential, we found that alanine inversion proceeded via previously unknown intermediates, 2-iminopropane-1,1-diol and 3-amino-3-methyloxiran-2-ol. The CG-HFB method accurately located transition states, aiding in the interpretation of complex reaction mechanisms. Thus, on the B3LYP∕6-31G(d,p) potential, the gas phase activation barriers for the inversion and acylation reactions were 50.5 and 39.9 kcal∕mol, respectively. These barriers determine the spontaneous loss of amino acid chirality and cleavage of peptide bonds in proteins. We conclude that the combined CG-HFB method further advances QM and QM∕MM studies of reaction mechanisms.

The Barrier Properties of PET Coated DLC Film Deposited by Microwave Surface-Wave PECVD

NASA Astrophysics Data System (ADS)

Yin, Lianhua; Chen, Qiang

2017-12-01

In this paper we report the investigation of diamond-like carbon (DLC) deposited by microwave surface-wave plasma enhanced chemical vapor deposition (PECVD) on the polyethylene terephthalate (PET) web for the purpose of the barrier property improvement. In order to characterize the properties of DLC coatings, we used several substrates, silicon wafer, glass, and PET web and KBr tablet. The deposition rate was obtained by surface profiler based on the DLC deposited on glass substrates; Fourier transform infrared spectroscope (FTIR) was carried out on KBr tablets to investigate chemical composition and bonding structure; the morphology of the DLC coating was analyzed by atomic force microscope (AFM) on Si substrates. For the barrier properties of PET webs, we measured the oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) after coated with DLC films. We addressed the film barrier property related to process parameters, such as microwave power and pulse parameter in this work. The results show that the DLC coatings can greatly improve the barrier properties of PET webs.

Revival of cloaking effect in a driven bilayer graphene vector barrier

NASA Astrophysics Data System (ADS)

Maiti, S.; Panigrahi, A.; Biswas, R.; Sinha, C.

2018-05-01

Transmission profiles in bilayer graphene are studied theoretically through a rectangular vector potential (magnetic) barrier with and without the presence of an oscillatory potential. Unlike the electrostatic barrier, the Fano resonances (FR) are noted in the transmission spectra both for normal and glancing incidences due to non-conservation of chirality for a static vector barrier. The results for normal incidence indicate that the cloaking effect is a manifestation of the chirality conservation in charge transport through bilayer graphene scalar barriers. It is also noted that the aforesaid FR for a static vector barrier might disappear (photon induced electronic cloaking effect) due to the predominant photon exchange processes in presence of an external oscillating potential. The study of Fano resonances in transmission spectrum is in high demand in respect of localization of charge carriers in graphene nano structures for its potential applications in digital device fabrications.

Orbital Debris Impact Damage to Reusable Launch Vehicles

NASA Technical Reports Server (NTRS)

Robinson, Jennifer H.

1998-01-01

In an effort by the National Aeronautics and Space Administration (NASA), hypervelocity impact tests were performed on thermal protection systems (TPS) applied on the external surfaces of reusable launch vehicles (RLV) to determine the potential damage from orbital debris impacts. Three TPS types were tested, bonded to composite structures representing RLV fuel tank walls. The three heat shield materials tested were Alumina-Enhanced Thermal Barrier-12 (AETB-12), Flexible Reusable Surface Insulation (FRSI), and Advanced Flexible Reusable Surface Insulation (AFRSI). Using this test data, predictor equations were developed for the entry hole diameters in the three TPS materials, with correlation coefficients ranging from 0.69 to 0.86. Possible methods are proposed for approximating damage occurring at expected orbital impact velocities higher than tested, with references to other published work.

Proton Transfer and Low-Barrier Hydrogen Bonding: a Shifting Vibrational Landscape Dictated by Large Amplitude Tunneling

NASA Astrophysics Data System (ADS)

Vealey, Zachary; Foguel, Lidor; Vaccaro, Patrick

2017-06-01

Our fundamental understanding of synergistic hydrogen-bonding and proton-transfer phenomena has been advanced immensely by studies of model systems in which the coherent transduction of hydrons is mediated by two degenerate equilibrium configurations that are isolated from one another by a potential barrier of substantial height. This topography advantageously affords unambiguous signatures for the underlying state-resolved dynamics in the form of tunneling-induced spectral bifurcations, the magnitudes of which encode both the overall efficacy and the detailed mechanism of the unimolecular transformation. As a prototypical member of this class of compounds, 6-hydroxy-2-formylfulvene (HFF) supports an unusual quasi-linear O-H...O \\leftrightarrow O...H-O reaction coordinate that presents a minimal impediment to proton migration - a situation commensurate with the concepts of low-barrier hydrogen bonding (which are characterized by great strength, short distance, and a vanishingly small barrier for hydron migration). A variety of fluorescence-based, laser-spectroscopic probes have been deployed in a cold supersonic free-jet expansion to explore the vibrational landscape and anomalously large tunneling-induced shifts that dominate the ˜{X}^{1}A_{1} potential-energy surface of HFF, thus revealing the most rapid proton tunneling ever reported for a molecular ground state (τ_{pt}≤120fs). The surprising efficiency of such tunneling-mediated processes stems from proximity of the zero-point level to the barrier crest and produces a dramatic alteration in the canonical pattern of vibrational features that reflects, in part, the subtle transition from quantum-mechanical barrier penetration to classical over-the-barrier dynamics. The ultrafast proton-transfer regime that characterizes the ˜{X}^{1}A_{1} manifold will be juxtaposed against analogous findings for the lowest-lying singlet excited state ˜{A}^{1}B_{2} (π*←π), where a marked change in the nature of the reaction coordinate leads to the near-complete quenching of proton transfer. Experimental results, as well as complementary quantum-chemical analyses, will be discussed and contrasted with those obtained for related hydron-migration systems in an effort to highlight the unique bonding motifs and reaction propensities evinced by HFF.

Effect of phosphate on U(VI) sorption to montmorillonite: Ternary complexation and precipitation barriers

NASA Astrophysics Data System (ADS)

Troyer, Lyndsay D.; Maillot, Fabien; Wang, Zheming; Wang, Zimeng; Mehta, Vrajesh S.; Giammar, Daniel E.; Catalano, Jeffrey G.

2016-02-01

Phosphate addition is a potential treatment method to lower the solubility of U(VI) in soil and groundwater systems by causing U(VI) phosphate precipitation as well as enhancing adsorption. Previous work has shown that iron oxide surfaces may facilitate the nucleation of U(VI) phosphate minerals and, that under weakly acidic conditions, phosphate also enhances U(VI) adsorption to such phases. Like iron oxides, clays are important reactive phases in the subsurface but little is known about the interaction of U(VI) and phosphate with these minerals. The effect of aqueous phosphate on U(VI) binding to Wyoming montmorillonite (SWy-2) in air-equilibrated systems was investigated. Equilibrium U(VI) uptake to montmorillonite was determined at pH 4, 6 and 8 at discrete initial phosphate concentrations between 0 and 100 μM. The observed behavior of U(VI) indicates a transition from adsorption to precipitation with increasing total uranium and phosphate concentrations at all pH values. At the highest phosphate concentration examined at each pH value, a barrier to U(VI) phosphate nucleation is observed. At lower concentrations, phosphate has no effect on macroscopic U(VI) adsorption. To assess the mechanisms of U(VI)-phosphate interactions on smectite surfaces, U(VI) speciation was investigated under selected conditions using laser-induced fluorescence spectroscopy (LIFS) and extended X-ray absorption fine-structure (EXAFS) spectroscopy. Samples above the precipitation threshold display EXAFS and LIFS spectral signatures consistent with the autunite family of U(VI) phosphate minerals. However, at lower U(VI) concentrations, changes in LIFS spectra upon phosphate addition suggest that U(VI)-phosphate ternary surface complexes form on the montmorillonite surface at pH 4 and 6 despite the lack of a macroscopic effect on adsorption. The speciation of solid-associated U(VI) below the precipitation threshold at pH 8 is dominated by U(VI)-carbonate surface complexes. This work reveals that ternary complexation may occur without a macroscopic signature, which is attributed to phosphate not appreciably binding to smectite in the absence of U(VI), with U(VI) surface complexes serving as the sole reactive surface sites for phosphate. This study shows that phosphate does not enhance U(VI) adsorption to smectite clay minerals, unlike oxide phases, and that a barrier to homogeneous nucleation of U(VI) phosphates was not affected by the presence of the smectite surface.

Silicon surface barrier detectors used for liquid hydrogen density measurement

NASA Technical Reports Server (NTRS)

James, D. T.; Milam, J. K.; Winslett, H. B.

1968-01-01

Multichannel system employing a radioisotope radiation source, strontium-90, radiation detector, and a silicon surface barrier detector, measures the local density of liquid hydrogen at various levels in a storage tank. The instrument contains electronic equipment for collecting the density information, and a data handling system for processing this information.

Molecular assemblies as protective barriers and adhesion promotion interlayer

DOEpatents

King, David E.; Czanderna, Alvin W.; Kennedy, Cheryl E.

1996-01-01

A protective diffusion barrier having adhesive qualifies for metalized surfaces is provided by a passivating agent having the formula HS--(CH.sub.2).sub.11 --COOH Which forms a very dense, transparent organized molecular assembly or layer that is impervious to water, alkali, and other impurities and corrosive substances that typically attack metal surfaces.

Modeling electron emission and surface effects from diamond cathodes

DOE PAGES

Dimitrov, D. A.; Smithe, D.; Cary, J. R.; ...

2015-02-05

We developed modeling capabilities, within the Vorpal particle-in-cell code, for three-dimensional (3D) simulations of surface effects and electron emission from semiconductor photocathodes. They include calculation of emission probabilities using general, piece-wise continuous, space-time dependent surface potentials, effective mass and band bending field effects. We applied these models, in combination with previously implemented capabilities for modeling charge generation and transport in diamond, to investigate the emission dependence on applied electric field in the range from approximately 2 MV/m to 17 MV/m along the [100] direction. The simulation results were compared to experimental data. For the considered parameter regime, conservation of transversemore » electron momentum (in the plane of the emission surface) allows direct emission from only two (parallel to [100]) of the six equivalent lowest conduction band valleys. When the electron affinity χ is the only parameter varied in the simulations, the value χ = 0.31 eV leads to overall qualitative agreement with the probability of emission deduced from experiments. Including band bending in the simulations improves the agreement with the experimental data, particularly at low applied fields, but not significantly. In this study, using surface potentials with different profiles further allows us to investigate the emission as a function of potential barrier height, width, and vacuum level position. However, adding surface patches with different levels of hydrogenation, modeled with position-dependent electron affinity, leads to the closest agreement with the experimental data.« less

Exploring the mechanisms of DNA hybridization on a surface

NASA Astrophysics Data System (ADS)

Schmitt, Terry J.; Rogers, J. Brandon; Knotts, Thomas A.

2013-01-01

DNA microarrays are a potentially disruptive technology in the medical field, but their use in such settings is limited by poor reliability. Microarrays work on the principle of hybridization and can only be as reliable as this process is robust, yet little is known at the molecular level about how the surface affects the hybridization process. This work uses advanced molecular simulation techniques and an experimentally parameterized coarse-grain model to determine the mechanism by which hybridization occurs on surfaces. The results show that hybridization proceeds through a mechanism where the untethered (target) strand often flips orientation. For evenly lengthed strands, the surface stabilizes hybridization (compared to the bulk system) by reducing the barriers involved in the flipping event. For unevenly lengthed strands, the surface destabilizes hybridization compared to the bulk, but the degree of destabilization is dependent on the location of the matching sequence. Taken as a whole, the results offer an unprecedented view into the hybridization process on surfaces and provide some insights as to the poor reproducibility exhibited by microarrays.

Evaluation of the constant potential method in simulating electric double-layer capacitors

NASA Astrophysics Data System (ADS)

Wang, Zhenxing; Yang, Yang; Olmsted, David L.; Asta, Mark; Laird, Brian B.

2014-11-01

A major challenge in the molecular simulation of electric double layer capacitors (EDLCs) is the choice of an appropriate model for the electrode. Typically, in such simulations the electrode surface is modeled using a uniform fixed charge on each of the electrode atoms, which ignores the electrode response to local charge fluctuations in the electrolyte solution. In this work, we evaluate and compare this Fixed Charge Method (FCM) with the more realistic Constant Potential Method (CPM), [S. K. Reed et al., J. Chem. Phys. 126, 084704 (2007)], in which the electrode charges fluctuate in order to maintain constant electric potential in each electrode. For this comparison, we utilize a simplified LiClO4-acetonitrile/graphite EDLC. At low potential difference (ΔΨ ⩽ 2 V), the two methods yield essentially identical results for ion and solvent density profiles; however, significant differences appear at higher ΔΨ. At ΔΨ ⩾ 4 V, the CPM ion density profiles show significant enhancement (over FCM) of "inner-sphere adsorbed" Li+ ions very close to the electrode surface. The ability of the CPM electrode to respond to local charge fluctuations in the electrolyte is seen to significantly lower the energy (and barrier) for the approach of Li+ ions to the electrode surface.

[Corrosion resistant properties of different anodized microtopographies on titanium surfaces].

PubMed

Fangjun, Huo; Li, Xie; Xingye, Tong; Yueting, Wang; Weihua, Guo; Weidong, Tian

2015-12-01

To investigate the corrosion resistant properties of titanium samples prepared by anodic oxidation with different surface morphologies. Pure titanium substrates were treated by anodic oxidation to obtain porous titanium films in micron, submicron, and micron-submicron scales. The surface morphologies, coating cross-sectional morphologies, crystalline structures, and surface roughness of these samples were characterized. Electrochemical technique was used to measure the corrosion potential (Ecorr), current density of corrosion (Icorr), and polarization resistance (Rp) of these samples in a simulated body fluid. Pure titanium could be modified to exhibit different surface morphologies by the anodic oxidation technique. The Tafel curve results showed that the technique can improve the corrosion resistance of pure titanium. Furthermore, the corrosion resistance varied with different surface morphologies. The submicron porous surface sample demonstrated the best corrosion resistance, with maximal Ecorr and Rp and minimal Icorr. Anodic oxidation technology can improve the corrosion resistance of pure titanium in a simulated body fluid. The submicron porous surface sample exhibited the best corrosion resistance because of its small surface area and thick barrier layer.

Article Including Environmental Barrier Coating System

NASA Technical Reports Server (NTRS)

Lee, Kang N. (Inventor)

2015-01-01

An enhanced environmental barrier coating for a silicon containing substrate. The enhanced barrier coating may include a bond coat doped with at least one of an alkali metal oxide and an alkali earth metal oxide. The enhanced barrier coating may include a composite mullite bond coat including BSAS and another distinct second phase oxide applied over said surface.

Diffusion Barriers to Increase the Oxidative Life of Overlay Coatings

NASA Technical Reports Server (NTRS)

Nesbitt, James A.; Lei, Jih-Fen

1999-01-01

Currently, most blades and vanes in the hottest section of aero gas turbine engines require some type of coating for oxidation protection. Newly developed single crystal superalloys have the mechanical potential to operate at increasingly higher component temperatures. However, at these elevated temperatures, coating/substrate interdiffusion can shorten the protective life of the coating. Diffusion barriers between overlay coatings and substrates are being examined to extend the protective life of the coating. A previously- developed finite-difference diffusion model has been modified to predict the oxidative life enhancement due to use of a diffusion barrier. The original diffusion model, designated COSIM, simulates Al diffusion in the coating to the growing oxide scale as well as Al diffusion into the substrate. The COSIM model incorporates an oxide growth and spalling model to provide the rate of Al consumption during cyclic oxidation. Coating failure is predicted when the Al concentration at the coating surface drops to a defined critical level. The modified COSIM model predicts the oxidative life of an overlay coating when a diffusion barrier is present eliminating diffusion of Al from the coating into the substrate. Both the original and the modified diffusion models have been used to predict the effectiveness of a diffusion barrier in extending the protective life of a NiCrAl overlay coating undergoing cyclic oxidation at 1100 C.

Reaction paths of alane dissociation on the Si(0 0 1) surface

NASA Astrophysics Data System (ADS)

Smith, Richard; Bowler, David R.

2018-03-01

Building on our earlier study, we examine the kinetic barriers to decomposition of alane, AlH3, on the Si(0 0 1) surface, using the nudged elastic band approach within density functional theory. We find that the initial decomposition to AlH with two H atoms on the surface proceeds without a significant barrier. There are several pathways available to lose the final hydrogen, though these present barriers of up to 1 eV. Incorporation is more challenging, with the initial structures less stable in several cases than the starting structures, just as was found for phosphorus. We identify a stable route for Al incorporation following selective surface hydrogen desorption (e.g. by scanning tunneling microscope tip). The overall process parallels PH3, and indicates that atomically precise acceptor doping should be possible.

Pathways to dewetting in hydrophobic confinement.

PubMed

Remsing, Richard C; Xi, Erte; Vembanur, Srivathsan; Sharma, Sumit; Debenedetti, Pablo G; Garde, Shekhar; Patel, Amish J

2015-07-07

Liquid water can become metastable with respect to its vapor in hydrophobic confinement. The resulting dewetting transitions are often impeded by large kinetic barriers. According to macroscopic theory, such barriers arise from the free energy required to nucleate a critical vapor tube that spans the region between two hydrophobic surfaces--tubes with smaller radii collapse, whereas larger ones grow to dry the entire confined region. Using extensive molecular simulations of water between two nanoscopic hydrophobic surfaces, in conjunction with advanced sampling techniques, here we show that for intersurface separations that thermodynamically favor dewetting, the barrier to dewetting does not correspond to the formation of a (classical) critical vapor tube. Instead, it corresponds to an abrupt transition from an isolated cavity adjacent to one of the confining surfaces to a gap-spanning vapor tube that is already larger than the critical vapor tube anticipated by macroscopic theory. Correspondingly, the barrier to dewetting is also smaller than the classical expectation. We show that the peculiar nature of water density fluctuations adjacent to extended hydrophobic surfaces--namely, the enhanced likelihood of observing low-density fluctuations relative to Gaussian statistics--facilitates this nonclassical behavior. By stabilizing isolated cavities relative to vapor tubes, enhanced water density fluctuations thus stabilize novel pathways, which circumvent the classical barriers and offer diminished resistance to dewetting. Our results thus suggest a key role for fluctuations in speeding up the kinetics of numerous phenomena ranging from Cassie-Wenzel transitions on superhydrophobic surfaces, to hydrophobically driven biomolecular folding and assembly.

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.].

Chirality of weakly bound complexes: The potential energy surfaces for the hydrogen-peroxide−noble-gas interactions

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

Roncaratti, L. F., E-mail: lz@fis.unb.br; Leal, L. A.; Silva, G. M. de

2014-10-07

We consider the analytical representation of the potential energy surfaces of relevance for the intermolecular dynamics of weakly bound complexes of chiral molecules. In this paper we study the H{sub 2}O{sub 2}−Ng (Ng=He, Ne, Ar, Kr, and Xe) systems providing the radial and the angular dependence of the potential energy surface on the relative position of the Ng atom. We accomplish this by introducing an analytical representation which is able to fit the ab initio energies of these complexes in a wide range of geometries. Our analysis sheds light on the role that the enantiomeric forms and the symmetry ofmore » the H{sub 2}O{sub 2} molecule play on the resulting barriers and equilibrium geometries. The proposed theoretical framework is useful to study the dynamics of the H{sub 2}O{sub 2} molecule, or other systems involving O–O and S–S bonds, interacting by non-covalent forces with atoms or molecules and to understand how the relative orientation of the O–H bonds changes along collisional events that may lead to a hydrogen bond formation or even to selectivity in chemical reactions.« less

Method for construction of a biased potential for hyperdynamic simulation of atomic systems

NASA Astrophysics Data System (ADS)

Duda, E. V.; Kornich, G. V.

2017-10-01

An approach to constructing a biased potential for hyperdynamic simulation of atomic systems is considered. Using this approach, the diffusion of an atom adsorbed on the surface of a two-dimensional crystal and a vacancy in the bulk of the crystal are simulated. The influence of the variation in the potential barriers due to thermal vibrations of atoms on the results of calculations is discussed. It is shown that the bias of the potential in the hyperdynamic simulation makes it possible to obtain statistical samples of transitions of atomic systems between states, similar to those given by classical molecular dynamics. However, hyperdynamics significantly accelerates computations in comparison with molecular dynamics in the case of temperature-activated transitions and the associated processes in atomic systems.

A generalized force-modified potential energy surface (G-FMPES) for mechanochemical simulations

DOE PAGES

Subramanian, Gopinath; Mathew, Nithin; Leiding, Jeffery A.

2015-10-05

We describe the modifications that a spatially varying external load produces on a Born-Oppenheimer potential energy surface (PES) by calculating static quantities of interest. The effects of the external loads are exemplified using electronic structure calculations (at the HF/6-31G** level) of two different molecules: ethane and hexahydro-1,3,5-trinitro-s-triazine (RDX). The calculated transition states and The Hessian matrices of stationary points show that spatially varying external loads shift the stationary points and modify the curvature of the PES, thereby affecting the harmonic transition rates by altering both the energy barrier as well as the prefactor. The harmonic spectra of both molecules aremore » blue-shifted with increasing compressive “pressure.” Some stationary points on the RDX-PES disappear under application of the external load, indicating the merging of an energy minimum with a saddle point.« less

Surface-structure dependence of healing radiation-damage mechanism in nanoporous tungsten

NASA Astrophysics Data System (ADS)

Duan, Guohua; Li, Xiangyan; Sun, Jingjing; Hao, Congyu; Xu, Yichun; Zhang, Yange; Liu, Wei; Liu, C. S.

2018-01-01

Under nuclear fusion environments, displacement damage in tungsten (W) is usually caused by neutrons irradiation through producing large quantities of vacancies (Vs) and self-interstitial atoms (SIAs). These defects not only affect the mechanical properties of W, but also act as the trap sites for implanted hydrogen isotopes and helium. Nano-porous (NP) W with a high fraction of free surfaces has been developed to mitigate the radiation damage. However, the mechanism of the surface reducing defects accumulation is not well understood. By using multi-scale simulation methods, we investigated the interaction of the SIA and V with different surfaces on across length and time scales. We found that, at a typical operation temperature of 1000 K, surface (1 1 0) preferentially heals radiation damage of W compared with surface (1 0 0) and boundary (3 1 0). On surface (1 1 0), the diffusion barrier for the SIA is only 0.68 eV. The annihilation of the SIA-V happens via the coupled motion of the V segregation towards the surface from the bulk and the two-dimensional diffusion of the SIA on the surface. Such mechanism makes the surface (1 1 0) owe better healing capability. On surface (1 0 0), the diffusion energy barrier for the SIA is 2.48 eV, higher than the diffusion energy barrier of the V in bulk. The annihilation of the SIA-V occurs via the V segregation and recombination. The SIA was found to migrate one-dimensionally along a boundary (3 1 0) with a barrier of 0.21 eV, leading to a lower healing efficiency in the boundary. This study suggested that the on-surface process plays an important role in healing radiation damage of NP W in addition to surface-enhanced diffusion and annihilation near the surface. A certain surface structure renders nano-structured W more radiation-tolerant.

The long-term effects of the micrometeoroid and orbital debris environments on materials used in space

NASA Technical Reports Server (NTRS)

Cour-Palais, Burton G.

1989-01-01

The long-term effects of the orbital debris and micrometeoroid environments on materials that are current candidates for use on space vehicles are discussed. In addition, the limits of laboratory testing to determine these effects are defined and the need for space-based data is delineated. The impact effects discussed are divided into primary and secondary surfaces. Primary surfaces are those that are subject to erosion, pitting, the degradation and delamination of optical coatings, perforation of atomic oxygen erosion barriers, vapor coating of optics and the production of secondary ejecta particles. Secondary surfaces are those that are affected by the result of the perforation of primary surfaces, for example, vapor deposition on electronic components and other sensitive equipment, and the production of fragments with damage potential to internal pressurized elements. The material properties and applications that are required to prevent or lessen the effects described, are defined.

Photo-induced persistent inversion of germanium in a 200-nm-deep surface region.

PubMed

Prokscha, T; Chow, K H; Stilp, E; Suter, A; Luetkens, H; Morenzoni, E; Nieuwenhuys, G J; Salman, Z; Scheuermann, R

2013-01-01

The controlled manipulation of the charge carrier concentration in nanometer thin layers is the basis of current semiconductor technology and of fundamental importance for device applications. Here we show that it is possible to induce a persistent inversion from n- to p-type in a 200-nm-thick surface layer of a germanium wafer by illumination with white and blue light. We induce the inversion with a half-life of ~12 hours at a temperature of 220 K which disappears above 280 K. The photo-induced inversion is absent for a sample with a 20-nm-thick gold capping layer providing a Schottky barrier at the interface. This indicates that charge accumulation at the surface is essential to explain the observed inversion. The contactless change of carrier concentration is potentially interesting for device applications in opto-electronics where the gate electrode and gate oxide could be replaced by the semiconductor surface.

Thermodynamics and kinetics of graphene chemistry: a graphene hydrogenation prototype study.

PubMed

Pham, Buu Q; Gordon, Mark S

2016-12-07

The thermodynamic and kinetic controls of graphene chemistry are studied computationally using a graphene hydrogenation reaction and polyaromatic hydrocarbons to represent the graphene surface. Hydrogen atoms are concertedly chemisorped onto the surface of graphene models of different shapes (i.e., all-zigzag, all-armchair, zigzag-armchair mixed edges) and sizes (i.e., from 16-42 carbon atoms). The second-order Z-averaged perturbation theory (ZAPT2) method combined with Pople double and triple zeta basis sets are used for all calculations. It is found that both the net enthalpy change and the barrier height of graphene hydrogenation at graphene edges are lower than at their interior surfaces. While the thermodynamic product distribution is mainly determined by the remaining π-islands of functionalized graphenes (Phys. Chem. Chem. Phys., 2013, 15, 3725-3735), the kinetics of the reaction is primarily correlated with the localization of the electrostatic potential of the graphene surface.

A stepwise mechanism for the permeation of phloretin through a lipid bilayer

PubMed Central

1982-01-01

The thermodynamics of interactions between phloretin and a phosphatidylcholine (PC) vesicle membrane are characterized using equilibrium spectrophotometric titration, stopped-flow, and temperature- jump techniques. Binding of phloretin to a PC vesicle membrane is diffusion limited, with an association rate constant greater than 10(8) M-1s-1, and an interfacial activation free energy of less than 2 kcal/mol. Equilibrium binding of phloretin to a vesicle membrane is characterized by a single class of high-affinity (8 micro M), noninteracting sites. Binding is enthalpy driven (delta H = -4.9 kcal/mol) at 23 degrees C. Analysis of amplitudes of kinetic processes shows that 66 +/- 3% of total phloretin binding sites are exposed at the external vesicle surface. The rate of phloretin movement between binding sites located near the external and internal interfaces is proportional to the concentration of un-ionized phloretin, with a rate constant of 5.7 X 10(4) M-1s-1 at 23 degrees C. The rate of this process is limited by a large enthalpic (9 kcal/mol) and entropic (-31 entropy units) barrier. An analysis of the concentration dependence of the rate of transmembrane movement suggests the presence of multiple intramembrane potential barriers. Permeation of phloretin through a lipid bilayer is modeled quantitatively in terms of discrete steps: binding to a membrane surface, translocation across a series of intramembrane barriers, and dissociation from the opposite membrane surface. The permeability coefficient for phloretin is calculated as 1.9 X 10(-3) cm/s on the basis of the model presented. Structure- function relationships are examined for a number of phloretin analogues. PMID:7142954

FY04 LDRD Final Report: Interaction of Viruses with Membranes and Soil Materials

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

Schaldach, C M

2005-02-08

The influence of ionic strength on the electrostatic interaction of viruses with environmentally relevant surfaces was determined for three viruses, MS2, Q{beta} and Norwalk. The environmental surface is modeled as charged Gouy-Chapman plane with and without a finite atomistic region (patch) of opposite charge. The virus is modeled as a particle comprised of ionizable amino acid residues in a shell surrounding a spherical RNA core of negative charge, these charges being compensated for by a Coulomb screening due to intercalated ions. Surface potential calculations for each of the viruses show excellent agreement with electrophoretic mobility and zeta potential measurements asmore » a function of pH. The results indicate that the electrostatic interaction between the virus and the planar surface, mitigated by the ionic strength of the solute, is dependent upon the spatial distribution of the amino acid residues in the different viruses. Specifically, the order of interaction energies with the patch (MS2 greatest at 5 mM; Norwalk greatest at 20 mM) is dependent upon the ionic strength of the fluid as a direct result of the viral coat amino acid distributions. We have developed an atomistic-scale method of calculation of the binding energy of viruses to surfaces including electrostatic, van der Waals, electron-overlap repulsion, surface charge polarization (images), and hydrophobic effects. The surface is treated as a Gouy-Chapman plane allowing inclusion of pH and ionic strength effects on the electrostatic potential at each amino acid charge. Van der Waals parameters are obtained from the DREIDING force field and from Hamaker constant measurements. We applied this method to the calculation of the Cowpea Mosaic Virus (CPMV), a negatively charged virus at a pH of 7.0, and find that the viral-gold surface interaction is very long range for both signs of surface potential, a result due to the electrostatic forces. For a negative (Au) surface potential of -0.05 volts, a nearly 4 eV barrier must be overcome to reach 1 nm from the surface.« less

Influence of rotational energy barriers to the conformational search of protein loops in molecular dynamics and ranking the conformations.

PubMed

Tappura, K

2001-08-15

An adjustable-barrier dihedral angle potential was added as an extension to a novel, previously presented soft-core potential to study its contribution to the efficacy of the search of the conformational space in molecular dynamics. As opposed to the conventional soft-core potential functions, the leading principle in the design of the new soft-core potential, as well as of its extension, the soft-core and adjustable-barrier dihedral angle (SCADA) potential (referred as the SCADA potential), was to maintain the main equilibrium properties of the original force field. This qualifies the methods for a variety of a priori modeling problems without need for additional restraints typically required with the conventional soft-core potentials. In the present study, the different potential energy functions are applied to the problem of predicting loop conformations in proteins. Comparison of the performance of the soft-core and SCADA potential showed that the main hurdles for the efficient sampling of the conformational space of (loops in) proteins are related to the high-energy barriers caused by the Lennard-Jones and Coulombic energy terms, and not to the rotational barriers, although the conformational search can be further enhanced by lowering the rotational barriers of the dihedral angles. Finally, different evaluation methods were studied and a few promising criteria found to distinguish the near-native loop conformations from the wrong ones.

Analysis of leaf surfaces using scanning ion conductance microscopy.

PubMed

Walker, Shaun C; Allen, Stephanie; Bell, Gordon; Roberts, Clive J

2015-05-01

Leaf surfaces are highly complex functional systems with well defined chemistry and structure dictating the barrier and transport properties of the leaf cuticle. It is a significant imaging challenge to analyse the very thin and often complex wax-like leaf cuticle morphology in their natural state. Scanning electron microscopy (SEM) and to a lesser extent Atomic force microscopy are techniques that have been used to study the leaf surface but their remains information that is difficult to obtain via these approaches. SEM is able to produce highly detailed and high-resolution images needed to study leaf structures at the submicron level. It typically operates in a vacuum or low pressure environment and as a consequence is generally unable to deal with the in situ analysis of dynamic surface events at submicron scales. Atomic force microscopy also possess the high-resolution imaging required and can follow dynamic events in ambient and liquid environments, but can over exaggerate small features and cannot image most leaf surfaces due to their inherent roughness at the micron scale. Scanning ion conductance microscopy (SICM), which operates in a liquid environment, provides a potential complementary analytical approach able to address these issues and which is yet to be explored for studying leaf surfaces. Here we illustrate the potential of SICM on various leaf surfaces and compare the data to SEM and atomic force microscopy images on the same samples. In achieving successful imaging we also show that SICM can be used to study the wetting of hydrophobic surfaces in situ. This has potentially wider implications than the study of leaves alone as surface wetting phenomena are important in a range of fundamental and applied studies. © 2015 The Authors Journal of Microscopy © 2015 Royal Microscopical Society.

Resonant interaction of electromagnetic wave with plasma layer and overcoming the radiocommunication blackout problem

NASA Astrophysics Data System (ADS)

Bogatskaya, A. V.; Klenov, N. V.; Tereshonok, M. V.; Adjemov, S. S.; Popov, A. M.

2018-05-01

We present an analysis of the possibility of penetrating electromagnetic waves through opaque media using an optical-mechanical analogy. As an example, we consider the plasma sheath surrounding the vehicle as a potential barrier and analyze the overcoming of radiocommunication blackout problem. The idea is to embed a «resonator» between the surface on the vehicle and plasma sheath which is supposed to provide an effective tunneling of the signal to the receiving antenna. We discuss the peculiarities of optical mechanical analogy applicability and analyze the radio frequency wave tunneling regime in detail. The cases of normal and oblique incidence of radiofrequency waves on the vehicle surface are studied.

Condensation on superhydrophobic surfaces: the role of local energy barriers and structure length scale.

PubMed

Enright, Ryan; Miljkovic, Nenad; Al-Obeidi, Ahmed; Thompson, Carl V; Wang, Evelyn N

2012-10-09

Water condensation on surfaces is a ubiquitous phase-change process that plays a crucial role in nature and across a range of industrial applications, including energy production, desalination, and environmental control. Nanotechnology has created opportunities to manipulate this process through the precise control of surface structure and chemistry, thus enabling the biomimicry of natural surfaces, such as the leaves of certain plant species, to realize superhydrophobic condensation. However, this "bottom-up" wetting process is inadequately described using typical global thermodynamic analyses and remains poorly understood. In this work, we elucidate, through imaging experiments on surfaces with structure length scales ranging from 100 nm to 10 μm and wetting physics, how local energy barriers are essential to understand non-equilibrium condensed droplet morphologies and demonstrate that overcoming these barriers via nucleation-mediated droplet-droplet interactions leads to the emergence of wetting states not predicted by scale-invariant global thermodynamic analysis. This mechanistic understanding offers insight into the role of surface-structure length scale, provides a quantitative basis for designing surfaces optimized for condensation in engineered systems, and promises insight into ice formation on surfaces that initiates with the condensation of subcooled water.

Impact of humidity on functionality of on-paper printed electronics.

PubMed

Bollström, Roger; Pettersson, Fredrik; Dolietis, Peter; Preston, Janet; Osterbacka, Ronald; Toivakka, Martti

2014-03-07

A multilayer coated paper substrate, combining barrier and printability properties was manufactured utilizing a pilot-scale slide curtain coating technique. The coating structure consists of a thin mineral pigment layer coated on top of a barrier layer. The surface properties, i.e. smoothness and surface porosity, were adjusted by the choice of calendering parameters. The influence of surface properties on the fine line printability and conductivity of inkjet-printed silver lines was studied. Surface roughness played a significant role when printing narrow lines, increasing the risk of defects and discontinuities, whereas for wider lines the influence of surface roughness was less critical. A smooth, calendered surface resulted in finer line definition, i.e. less edge raggedness. Dimensional stability and its influence on substrate surface properties as well as on the functionality of conductive tracks and transistors were studied by exposure to high/low humidity cycles. The barrier layer of the multilayer coated paper reduced the dimensional changes and surface roughness increase caused by humidity and helped maintain the conductivity of the printed tracks. Functionality of a printed transistor during a short, one hour humidity cycle was maintained, but a longer exposure to humidity destroyed the non-encapsulated transistor.

Molecular assemblies as protective barriers and adhesion promotion interlayer

DOEpatents

King, D.E.; Czanderna, A.W.; Kennedy, C.E.

1996-01-30

A protective diffusion barrier having adhesive qualities for metalized surfaces is provided by a passivating agent having the formula HS--(CH{sub 2}){sub 11}--COOH which forms a very dense, transparent organized molecular assembly or layer that is impervious to water, alkali, and other impurities and corrosive substances that typically attack metal surfaces. 8 figs.

Dielectric Surface Effects on Transient Arcs in Lightning Arrester Devices

DTIC Science & Technology

2011-06-01

pp. 816– 823, 1971. [13] V. I. Gibalov and G. J. Pietsch , “The development of dielectric barrier discharges in gas gaps and on surfaces,” J. Phys. D...Appl. Phys., vol. 33, p. 2618, 2000. [14] D. Braun, V. Gibalov, and G. Pietsch , “Two-dimensional modelling of the dielectric barrier discharge in air

Anisotropic capillary barrier for waste site surface covers

DOEpatents

Stormont, J.C.

1996-08-27

Waste sites are capped or covered upon closure. The cover structure incorporates a number of different layers each having a contributory function. One such layer is the barrier layer. Traditionally the barriers have been compacted soil and geosynthetics. These types of barriers have not been successfully implemented in unsaturated ground conditions like those found in dry climates. Capillary barriers have been proposed as barrier layers in dry environments, but the divergence length of these barriers has been found to be inadequate. An alternative to the capillary barrier is a anisotropic capillary barrier. An anisotropic capillary barrier has an increased divergence length which results in more water being diverted laterally preventing the majority of water from percolating in a downward direction through the barrier. 10 figs.

Anisotropic capillary barrier for waste site surface covers

DOEpatents

Stormont, John C.

1996-01-01

Waste sites are capped or covered upon closure. The cover structure incorporates a number of different layers each having a contributory function. One such layer is the barrier layer. Traditionally the barriers have been compacted soil and geosynthetics. These types of barriers have not been successfully implemented in unsaturated ground conditions like those found in dry climates. Capillary barriers have been proposed as barrier layers in dry environments, but the divergence length of these barriers has been found to be inadequate. An alternative to the capillary barrier is a anisotropic capillary barrier. An anisotropic capillary barrier has an increased divergence length which results in more water being diverted laterally preventing the majority of water from percolating in a downward direction through the barrier.

The torsional barriers of two equivalent methyl internal rotations in 2,5-dimethylfuran investigated by microwave spectroscopy

NASA Astrophysics Data System (ADS)

Van, Vinh; Bruckhuisen, Jonas; Stahl, Wolfgang; Ilyushin, Vadim; Nguyen, Ha Vinh Lam

2018-01-01

The microwave spectrum of 2,5-dimethylfuran was recorded using two pulsed molecular jet Fourier transform microwave spectrometers which cover the frequency range from 2 to 40 GHz. The internal rotations of two equivalent methyl tops with a barrier height of approximately 439.15 cm-1 introduce torsional splittings of all rotational transitions in the spectrum. For the spectral analysis, two different computer programs were applied and compared, the PAM-C2v-2tops code based on the principal axis method which treats several torsional states simultaneously, and the XIAM code based on the combined axis method, yielding accurate molecular parameters. The experimental work was supplemented by quantum chemical calculations. Two-dimensional potential energy surfaces depending on the torsional angles of both methyl groups were calculated and parametrized.

Thermal barrier coatings

DOEpatents

Alvin, Mary Anne [Pittsburg, PA

2010-06-22

This disclosure addresses the issue of providing a metallic-ceramic overlay coating that potentially serves as an interface or bond coat layer to provide enhanced oxidation resistance to the underlying superalloy substrate via the formation of a diffusion barrier regime within the supporting base material. Furthermore, the metallic-ceramic coating is expected to limit the growth of a continuous thermally grown oxide (TGO) layer that has been primarily considered to be the principal cause for failure of existing TBC systems. Compositional compatibility of the metallic-ceramic with traditional yttria-stabilized zirconia (YSZ) top coats is provided to further limit debond or spallation of the coating during operational use. A metallic-ceramic architecture is disclosed wherein enhanced oxidation resistance is imparted to the surface of nickel-based superalloy or single crystal metal substrate, with simultaneous integration of the yttria stabilized zirconia (YSZ) within the metallic-ceramic overlayer.

Conductance and refraction across a Barrier in Phosphorene

NASA Astrophysics Data System (ADS)

Dahal, Dipendra; Gumbs, Godfrey

The transmission coefficient and ballistic conductance for monolayer black phosphorene is calculated when a potential step or square barrier is present. The Landauer-B¨uttiker formalism is employed in our calculations of the conductance. We obtain the refractive index for the step potential barrier when an incident beam of electron travel along different paths so as to observe what role the anisotropy of the energy bands plays. Numerical results are presented for various potential heights and barrier widths and these are compared with those for gapless and gapped graphene.

Ab initio study of Ga-GaN system: Transition from adsorbed metal atoms to a metal–semiconductor junction

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

Witczak, Przemysław; Kempisty, Pawel; Strak, Pawel

2015-11-15

Ab initio studies of a GaN(0001)-Ga system with various thicknesses of a metallic Ga layer were undertaken. The studied systems extend from a GaN(0001) surface with a fractional coverage of gallium atoms to a Ga-GaN metal–semiconductor (m–s) contact. Electronic properties of the system are simulated using density functional theory calculations for different doping of the bulk semiconductor. It is shown that during transition from a bare GaN(0001) surface to a m–s heterostructure, the Fermi level stays pinned at a Ga-broken bond highly dispersive surface state to Ga–Ga states at the m–s interface. Adsorption of gallium leads to an energy gainmore » of about 4 eV for a clean GaN(0001) surface and the energy decreases to 3.2 eV for a thickly Ga-covered surface. The transition to the m–s interface is observed. For a thick Ga overlayer such interface corresponds to a Schottky contact with a barrier equal to 0.9 and 0.6 eV for n- and p-type, respectively. Bond polarization-related dipole layer occurring due to an electron transfer to the metal leads to a potential energy jump of 1.5 eV, independent on the semiconductor doping. Additionally high electron density in the Ga–Ga bond region leads to an energy barrier about 1.2 eV high and 4 Å wide. This feature may adversely affect the conductivity of the n-type m–s system.« less

Surface decorations of poly(amidoamine) dendrimer by various pendant moieties for improved delivery of nucleic acid materials.

PubMed

Dehshahri, Ali; Sadeghpour, Hossein

2015-08-01

In recent years, the discovery of novel nucleic acid-based drug candidates (e.g., siRNA and miRNA) and the groundbreaking studies for somatic cell reprogramming into a state of pluripotency have led to reconsideration for the use of human gene therapy as a new paradigm with great therapeutic potential. However, the success of gene therapy is dependent on overcoming intra- and extracellular barriers hampering the efficient delivery of nucleic acid therapeutics into the target cells or tissues. Despite relatively low transfection efficiency, great attention has been directed to cationic polymers and dendrimers due to their ability to condense DNA and RNA molecules into nano-sized particles which is a necessary prerequisite for efficient transfer of nucleic acids into cells. These gene carriers show remarkable adaptability and significant capacity to transfer larger sizes of nucleic acid materials. Polyamidoamine (PAMAM) dendrimer has been employed as non-viral gene carrier due to its globular shape and well-defined structure containing abundant amino surface groups which provide possibility for surface decoration of the dendrimer via the conjugation of various moieties. In this review, we have brought out the various functionalization strategies of the PAMAM surface amines using different pendant moieties such as amino acids, proteins, cyclodextrins, and hydrophobic units in order to overcome intra- and extracellular barriers. These surface-decorated dendrimers possessing favorable properties provide substantial information and insight for redesigning existing dendrimers and polymers. By understanding the role played by the conjugated moieties, more efficient and novel designs of gene vehicles may be possible. Copyright © 2015 Elsevier B.V. All rights reserved.

Suppression of Lateral Diffusion and Surface Leakage Currents in nBn Photodetectors Using an Inverted Design

NASA Astrophysics Data System (ADS)

Du, X.; Savich, G. R.; Marozas, B. T.; Wicks, G. W.

2018-02-01

Surface leakage and lateral diffusion currents in InAs-based nBn photodetectors have been investigated. Devices fabricated using a shallow etch processing scheme that etches through the top contact and stops at the barrier exhibited large lateral diffusion current but undetectably low surface leakage. Such large lateral diffusion current significantly increased the dark current, especially in small devices, and causes pixel-to-pixel crosstalk in detector arrays. To eliminate the lateral diffusion current, two different approaches were examined. The conventional solution utilized a deep etch process, which etches through the top contact, barrier, and absorber. This deep etch processing scheme eliminated lateral diffusion, but introduced high surface current along the device mesa sidewalls, increasing the dark current. High device failure rate was also observed in deep-etched nBn structures. An alternative approach to limit lateral diffusion used an inverted nBn structure that has its absorber grown above the barrier. Like the shallow etch process on conventional nBn structures, the inverted nBn devices were fabricated with a processing scheme that only etches the top layer (the absorber, in this case) but avoids etching through the barrier. The results show that inverted nBn devices have the advantage of eliminating the lateral diffusion current without introducing elevated surface current.

Impact of electrode geometry on an atmospheric pressure surface barrier discharge

NASA Astrophysics Data System (ADS)

Hasan, M. I.; Morabit, Y.; Dickenson, A.; Walsh, J. L.

2017-06-01

Several of the key characteristics of an atmospheric pressure surface barrier discharge (SBD) are heavily dependent on the geometrical configuration of the plasma generating electrodes. This paper reveals that increasing the surface area of an SBD device by reducing the gaps within the electrodes can have major and unforeseen consequence on the discharge properties. It is experimentally demonstrated that a critical limit exists when reducing the diameter of a circular electrode gap below 5 mm, beyond which the required breakdown voltage increases exponentially and the power deposited in the discharge is impeded. Using a numerical model, it is shown that a reduced electrode gap diameter yields a decrease in the voltage difference between the electrode and dielectric surface, thus lowering the maximum electric field. This study indicates a link between the electrode geometry and the nature of the reactive chemistry produced in the plasma, findings which have wide-reaching implications for many applications where multiple closely packed surface barrier discharges are employed to achieve uniform and large area plasma processing.

Electrical measurement of the hydration state of the skin surface in vivo.

PubMed

Tagami, H

2014-09-01

Healthy skin surface is smooth and soft, because it is covered by the properly hydrated stratum corneum (SC), an extremely thin and soft barrier membrane produced by the underlying normal epidermis. By contrast, the skin surfaces covering pathological lesions exhibit dry and scaly changes and the SC shows poor barrier function. The SC barrier function has been assessed in vivo by instrumentally measuring transepidermal water loss (TEWL). However, there was a lack of any appropriate method for evaluating the hydration state of the skin surface in vivo until 1980 when we reported the feasibility of employing high-frequency conductance or capacitance to evaluate it quickly and accurately. With such measurements, we can assess easily the moisturizing efficacy of various topical agents in vivo as well as the distribution pattern of water in the SC by combining it with a serial tape-stripping procedure of the skin surface. © 2014 The Author BJD © 2014 British Association of Dermatologists.

Permeable reactive barrier of surface hydrophobic granular activated carbon coupled with elemental iron for the removal of 2,4-dichlorophenol in water.

PubMed

Yang, Ji; Cao, Limei; Guo, Rui; Jia, Jinping

2010-12-15

Granular activated carbon was modified with dimethyl dichlorosilane to improve its surface hydrophobicity, and therefore to improve the performance of permeable reactive barrier constructed with the modified granular activated carbon and elemental iron. X-ray photoelectron spectroscopy shows that the surface silicon concentration of the modified granular activated carbon is higher than that of the original one, leading to the increased surface hydrophobicity. Although the specific surface area decreased from 895 to 835 m(2)g(-1), the modified granular activated carbon could adsorb 20% more 2,4-dichlorophenol than the original one did in water. It is also proven that the permeable reactive barrier with the modified granular activated carbon is more efficient at 2,4-dichlorophenol dechlorination, in which process 2,4-dichlorophenol is transformed to 2-chlorophenol or 4-chlorophenol then to phenol, or to phenol directly. Copyright © 2010 Elsevier B.V. All rights reserved.

Secondary electron emission influenced by oxidation on the aluminum surface: the roles of the chemisorbed oxygen and the oxide layer

NASA Astrophysics Data System (ADS)

Li, Jiangtao; Hoekstra, Bart; Wang, Zhen-Bin; Qiu, Jie; Pu, Yi-Kang

2018-04-01

A relationship between the apparent secondary electron yield ({γ }{{se}}) and the oxygen coverage/oxide layer thickness on an aluminum cathode is obtained in an experiment under a controlled environment. The apparent secondary electron yield ({γ }{{se}}) is deduced from the breakdown voltage between two parallel plate electrodes in a 360 mTorr argon environment using a simple Townsend breakdown model with the assumption that the variation of the apparent secondary electron yield is dominated by the variation of the argon ion induced processes. The oxygen coverage/oxide layer thickness on the aluminum cathode is measured by a semi in situ x-ray photoemission spectroscopy equipment which is directly attached to the discharge chamber. It is found that three phases exist: (1) in the monomonolayer regime, as the oxygen coverage increases from 0 to 0.3, {γ }{{se}} decreases by nearly 40 % , (2) as the oxygen coverage increases from 0.3 to 1, {γ }{{se}} keeps nearly constant, (3) as the oxide layer thickness increases from about 0.3 nm to about 1.1 nm, {γ }{{se}} increases by 150 % . We propose that, in the submonolayer regime, the chemisorbed oxygen on the aluminum surface causes the decrease of {γ }{{se}} by creating a local potential barrier, which reduces the Auger neutralization rate and the energy gained by the Auger electrons. In the multilayer regime, as the oxide layer grows in thickness, there are three proposed mechanisms which cause the increase of {γ }{{se}}: (1) the work function decreases; (2) resonance neutralization and Auger de-excitation may exist. This is served as another channel for secondary electron production; (3) the kinetic energy of Auger electrons is increased on average, leading to a higher probability for electrons to overcome the surface potential barrier.

Far-infrared vibration--rotation-tunneling spectroscopy of Ar--NH sub 3 : Intermolecular vibrations and effective angular potential energy surface

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

Schmuttenmaer, C.A.; Cohen, R.C.; Loeser, J.G.

Two new intermolecular vibration--rotation-tunneling (VRT) bands of Ar--NH{sub 3} have been measured using tunable far infrared laser spectroscopy. We have unambiguously assigned these and a previously measured FIR band (Gwo {ital et} {ital al}., Mol. Phys. {bold 71}, 453 (1990)) as {Pi}(1{sub 0}, {ital n}=0){l arrow}{Sigma}(0{sub 0}, {ital n}=0), {Sigma}(1{sub 0}, {ital n}=0){l arrow}{Sigma}(0{sub 0}, {ital n}=0), and {Sigma}(0{sub 0}, {ital n}=1){l arrow}{Sigma}(0{sub 0}, {ital n}=0). The three upper states of these are found to be strongly mixed by anisotropy and Coriolis effects. A simultaneous least squares fit of all transitions has yielded vibrational frequencies, rotational and centrifugal distortion constants,more » and a Coriolis parameter as well as quadrupole hyperfine coupling constants for the upper states. An effective angular potential energy surface for Ar--NH{sub 3} in its lowest stretching state has been determined from these data, after explicitly accounting for the effects of bend stretch interactions. Features of the surface include a global minimum at the near T-shaped configuration ({theta}=90{degree}), a 30 cm{sup {minus}1} to 60 cm{sup {minus}1} barrier to rotation at {theta}=180{degree} (or 0{degree}), and a very low barrier or possibly a secondary minimum at {theta}=0{degree} (or 180{degree}). Both attractive and repulsive interactions are shown to contribute significantly to the anisotropic forces in the complex. Comparison with {ital ab} {ital initio} calculations are presented.« less

Generation of Superponderomotive Electrons in Multipicosecond Interactions of Kilojoule Laser Beams with Solid-Density Plasmas.

PubMed

Sorokovikova, A; Arefiev, A V; McGuffey, C; Qiao, B; Robinson, A P L; Wei, M S; McLean, H S; Beg, F N

2016-04-15

The interaction of a multipicosecond, kilojoule laser pulse with a surface of a solid target has been shown to produce electrons with energies far beyond the free-electron ponderomotive limit m_{e}c^{2}a_{0}^{2}/2. Particle-in-cell simulations indicate that an increase in the pulse duration from 1 to 10 ps leads to the formation of a low-density shelf (about 10% of the critical density). The shelf extends over 100  μm toward the vacuum side, with a nonstationary potential barrier forming in that area. Electrons reflected from the barrier gain superponderomotive energy from the potential. Some electrons experience an even greater energy gain due to ponderomotive acceleration when their "dephasing rate" R=γ-p_{x}/m_{e}c drops well below unity, thus increasing acceleration by a factor of 1/R. Both 1D and 2D simulations indicate that these mechanisms are responsible for the generation of extensive thermal distributions with T_{e}>10  MeV and a high-energy cutoff of hundreds of MeV.

Large-scale, thick, self-assembled, nacre-mimetic brick-walls as fire barrier coatings on textiles

PubMed Central

Das, Paramita; Thomas, Helga; Moeller, Martin; Walther, Andreas

2017-01-01

Highly loaded polymer/clay nanocomposites with layered structures are emerging as robust fire retardant surface coatings. However, time-intensive sequential deposition processes, e.g. layer-by-layer strategies, hinders obtaining large coating thicknesses and complicates an implementation into existing technologies. Here, we demonstrate a single-step, water-borne approach to prepare thick, self-assembling, hybrid fire barrier coatings of sodium carboxymethyl cellulose (CMC)/montmorillonite (MTM) with well-defined, bioinspired brick-wall nanostructure, and showcase their application on textile. The coating thickness on the textile is tailored using different concentrations of CMC/MTM (1–5 wt%) in the coating bath. While lower concentrations impart conformal coatings of fibers, thicker continuous coatings are obtained on the textile surface from highest concentration. Comprehensive fire barrier and fire retardancy tests elucidate the increasing fire barrier and retardancy properties with increasing coating thickness. The materials are free of halogen and heavy metal atoms, and are sourced from sustainable and partly even renewable building blocks. We further introduce an amphiphobic surface modification on the coating to impart oil and water repellency, as well as self-cleaning features. Hence, our study presents a generic, environmentally friendly, scalable, and one-pot coating approach that can be introduced into existing technologies to prepare bioinspired, thick, fire barrier nanocomposite coatings on diverse surfaces. PMID:28054589

Distribution and Biological Effects of Nanoparticles in the Reproductive System.

PubMed

Liu, Ying; Li, Hongxia; Xiao, Kai

2016-01-01

Nanoparticles have shown great potential in biomedical applications such as imaging probes and drug delivery. However, the increasing use of nanoparticles has raised concerns about their adverse effects on human health and environment. Reproductive tissues and gametes represent highly delicate biological systems with the essential function of transmitting genetic information to the offspring, which is highly sensitive to environmental toxicants. This review aims to summarzie the penetration of physiological barriers (blood-testis barrier and placental barrier), distribution and biological effects of nanoparticles in the reproductive system, which is essential to control the beneficial effects of nanoparticles applications and to avoid their adverse effects on the reproductive system. We referred to a large number of relevant peer-reviewed research articles about the reproductive toxicity of nanoparticles. The comprehensive information was summarized into two parts: physiological barrier penetration and biological effects of nanoparticles in male or female reproductive system; distribution and metabolism of nanoparticles in the reproductive system. The representative examples were also presented in four tables. The in vitro and in vivo studies imply that some nanoparticles are able to cross the blood-testis barrier or placental barrier, and their penetration depends on the physicochemical characteristics of nanoparticles (e.g., composition, shape, particle size and surface coating). The toxicity assays indicate that nanoparticles might induce adverse physiological effects and impede fertility or embryogenesis. The barrier penetration, adverse physiological effects, distribution and metabolism are closely related to physicochemical characteristics of nanoparticles. Further systematic and mechanistic studies using well-characterized nanoparticles, relevant administration routes, and doses relevant to the expected exposure level are required to improve our understanding of biological effects of nanoparticles on the reproductive system.

Liposome-based glioma targeted drug delivery enabled by stable peptide ligands.

PubMed

Wei, Xiaoli; Gao, Jie; Zhan, Changyou; Xie, Cao; Chai, Zhilan; Ran, Danni; Ying, Man; Zheng, Ping; Lu, Weiyue

2015-11-28

The treatment of glioma is one of the most challenging tasks in clinic. As an intracranial tumor, glioma exhibits many distinctive characteristics from other tumors. In particular, various barriers including enzymatic barriers in the blood and brain capillary endothelial cells, blood-brain barrier (BBB) and blood-brain tumor barrier (BBTB) rigorously prevent drug and drug delivery systems from reaching the tumor site. To tackle this dilemma, we developed a liposomal formulation to circumvent multiple-barriers by modifying the liposome surface with proteolytically stable peptides, (D)CDX and c(RGDyK). (D)CDX is a D-peptide ligand of nicotine acetylcholine receptors (nAChRs) on the BBB, and c(RGDyK) is a ligand of integrin highly expressed on the BBTB and glioma cells. Lysosomal compartments of brain capillary endothelial cells are implicated in the transcytosis of those liposomes. However, both peptide ligands displayed exceptional stability in lysosomal homogenate, ensuring that intact ligands could exert subsequent exocytosis from brain capillary endothelial cells and glioma targeting. In the cellular uptake studies, dually labeled liposomes could target both brain capillary endothelial cells and tumor cells, effectively traversing the BBB and BBTB monolayers, overcoming enzymatic barrier and targeting three-dimensional tumor spheroids. Its targeting ability to intracranial glioma was further verified in vivo by ex vivo imaging and histological studies. As a result, doxorubicin liposomes modified with both (D)CDX and c(RGDyK) presented better anti-glioma effect with prolonged median survival of nude mice bearing glioma than did unmodified liposomes and liposomes modified with individual peptide ligand. In conclusion, the liposome suggested in the present study could effectively overcome multi-barriers and accomplish glioma targeted drug delivery, validating its potential value in improving the therapeutic efficacy of doxorubicin for glioma. Copyright © 2015 Elsevier B.V. All rights reserved.

Plasma treatment of polyethylene tubes in continuous regime using surface dielectric barrier discharge with water electrodes

NASA Astrophysics Data System (ADS)

Galmiz, Oleksandr; Zemánek, Miroslav; Pavliňák, David; Černák, Mirko

2018-05-01

Combining the surface dielectric barrier discharges generated in contact with water based electrolytes, as the discharge electrodes, we have designed a new type of surface electric discharge, generating thin layers of plasma which propagate along the treated polymer surfaces. The technique was aimed to achieve uniform atmospheric pressure plasma treatment of polymeric tubes and other hollow bodies. The results presented in this work show the possibility of such system to treat outer surface of polymer materials in a continuous mode. The technical details of experimental setup are discussed as well as results of treatment of polyethylene tubes are shown.

Effect of the charge surface distribution on the flow field induced by a dielectric barrier discharge actuator

NASA Astrophysics Data System (ADS)

Cristofolini, Andrea; Neretti, Gabriele; Borghi, Carlo A.

2013-08-01

The Electro-Hydro-Dynamics (EHD) interaction induced by a surface dielectric barrier discharge in the aerodynamic boundary layer at one atmosphere still air has been investigated. Three different geometrical configurations of the actuator have been utilized. In the first configuration, an electrode pair separated by a 2 mm dielectric sheet has been used. The second and the third configurations have been obtained by adding a third electrode on the upper side of the dielectric surface. This electrode has been placed downstream of the upper electrode and has been connected to ground or has been left floating. Three different dielectric materials have been utilized. The high voltage upper electrode was fed by an a.c. electric tension. Measurements of the dielectric surface potential generated by the charge deposition have been done. The discharge has been switched off after positive and negative phases of the plasma current (the current phase was characterized by a positive or a negative value, respectively). The measurements have been carried out after both phases. The charge distribution strongly depended on the switching off phase and was heavily affected by the geometrical configuration. A remarkable decrease of the charge deposited on the dielectric surface has been detected when the third electrode was connected to ground. Velocity profiles were obtained by using a Pitot probe. They showed that the presence of the third electrode limits the fluid dynamics performance of the actuator. A relation between the charge surface distribution and the EHD interaction phenomenon has been found. Imaging of the plasma has been done to evaluate the discharge structure and the extension of the plasma in the configurations investigated.

Effects of surface motion and electron-hole pair excitations in CO2 dissociation and scattering on Ni(100)

NASA Astrophysics Data System (ADS)

Luo, Xuan; Zhou, Xueyao; Jiang, Bin

2018-05-01

The energy transfer between different channels is an important aspect in chemical reactions at surfaces. We investigate here in detail the energy transfer dynamics in a prototypical system, i.e., reactive and nonreactive scattering of CO2 on Ni(100), which is related to heterogeneous catalytic processes with Ni-based catalysts for CO2 reduction. On the basis of our earlier nine-dimensional potential energy surface for CO2/Ni(100), dynamical calculations have been done using the generalized Langevin oscillator (GLO) model combined with local density friction approximation (LDFA), in which the former accounts for the surface motion and the latter accounts for the low-energy electron-hole pair (EHP) excitation. In spite of its simplicity, it is found that the GLO model yields quite satisfactory results, including the significant energy loss and product energy disposal, trapping, and steering dynamics, all of which agree well with the ab initio molecular dynamics ones where many surface atoms are explicitly involved with high computational cost. However, the GLO model fails to describe the reactivity enhancement due to the lattice motion because it intrinsically does not incorporate the variance of barrier height on the surface atom displacement. On the other hand, in LDFA, the energy transferred to EHPs is found to play a minor role and barely alter the dynamics, except for slightly reducing the dissociation probabilities. In addition, vibrational state-selected dissociative sticking probabilities are calculated and previously observed strong mode specificity is confirmed. Our work suggests that further improvement of the GLO model is needed to consider the lattice-induced barrier lowering.

Potential variation around grain boundaries in BaSi{sub 2} films grown on multicrystalline silicon evaluated using Kelvin probe force microscopy

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

Baba, Masakazu; Tsukahara, Daichi; Toko, Kaoru

2014-12-21

Potential variations across the grain boundaries (GBs) in a 100 nm thick undoped n-BaSi{sub 2} film on a cast-grown multicrystalline Si (mc-Si) substrate are evaluated using Kelvin probe force microscopy (KFM). The θ-2θ X-ray diffraction pattern reveals diffraction peaks, such as (201), (301), (410), and (411) of BaSi{sub 2}. Local-area electron backscatter diffraction reveals that the a-axis of BaSi{sub 2} is tilted slightly from the surface normal, depending on the local crystal plane of the mc-Si. KFM measurements show that the potentials are not significantly disordered in the grown BaSi{sub 2}, even around the GBs of mc-Si. The potentials are highermore » at GBs of BaSi{sub 2} around Si GBs that are formed by grains with a Si(111) face and those with faces that deviate slightly from Si(111). Thus, downward band bending occurs at these BaSi{sub 2} GBs. Minority carriers (holes) undergo a repelling force near the GBs, which may suppress recombination as in the case of undoped n-BaSi{sub 2} epitaxial films on a single crystal Si(111) substrate. The barrier height for hole transport across the GBs varies in the range from 10 to 55 meV. The potentials are also higher at the BaSi{sub 2} GBs grown around Si GBs composed of grains with Si(001) and Si(111) faces. The barrier height for hole transport ranges from 5 to 55 meV. These results indicate that BaSi{sub 2} GBs formed on (111)-dominant Si surfaces do not have a negative influence on the minority-carrier properties, and thus BaSi{sub 2} formed on underlayers, such as (111)-oriented Si or Ge and on (111)-oriented mc-Si, can be utilized as a solar cell active layer.« less

Layout designs of surface barrier coatings for boosting the capability of oxygen/vapor obstruction utilized in flexible electronics

NASA Astrophysics Data System (ADS)

Lee, Chang-Chun; Huang, Pei-Chen; He, Jing-Yan

2018-04-01

Organic light-emitting diode-based flexible and rollable displays have become a promising candidate for next-generation flexible electronics. For this reason, the design of surface multi-layered barriers should be optimized to enhance the long-term mechanical reliability of a flexible encapsulation that prevents the penetration of oxygen and vapor. In this study, finite element-based stress simulation was proposed to estimate the mechanical reliability of gas/vapor barrier design with low-k/silicon nitride (low-k/SiNx) stacking architecture. Consequently, stress-induced failure of critical thin films within the flexible display under various bending conditions must be considered. The feasibility of one pair SiO2/SiNx barrier design, which overcomes the complex lamination process, and the critical bending radius, which is decreased to 1.22 mm, were also examined. In addition, the influence of distance between neutral axes to the concerned layer surface dominated the induced-stress magnitude rather than the stress compliant mechanism provided from stacked low-k films.

Growth of quaternary InAlGaN barrier with ultrathin thickness for HEMT application

NASA Astrophysics Data System (ADS)

Li, Zhonghui; Li, Chuanhao; Peng, Daqing; Zhang, Dongguo; Dong, Xun; Pan, Lei; Luo, Weike; Li, Liang; Yang, Qiankun

2018-06-01

Quaternary InAlGaN barriers with thickness of 7 nm for HEMT application were grown on 3-inch semi-insulating 4H-SiC substrates by metal organic chemical vapor deposition (MOCVD). Focused on growth mechanism of the InAlGaN barrier, the surface morphology and characteristics of InAlGaN/AlN/GaN heterostructures were studied with different growth parameters, including the temperature, Al/Ga ratio and chamber pressure. Among the as-grown samples, high electron mobility is consistent with smooth surface morphology, while high crystalline quality of the quaternary barrier is confirmed by measurements of Photoluminescence (PL) and Mercury-probe Capacity-Voltage (C-V). The recommended heterostructures without SiN passivation is characterized by mobility of 1720 cm2/(V·s), 2DEG density of 1.71*1013 cm-2, sheet resistance of about 210 Ω/□ with a smooth surface morphology and moderate tensile state, specially applied for microwave devices.

Shingle System And Method

DOEpatents

Dinwoodie, Thomas L.

2005-04-26

A barrier, such as a PV module, is secured to a base by a support to create a shingle assembly with a venting region defined between the barrier and base for temperature regulation. The bottom edges of the barriers of one row may overlap the top edges of the barriers of another row. The shingle assemblies may be mounted by first mounting the bases to an inclined surface; the barriers may be then secured to the bases using the supports to create rows of shingle assemblies defining venting regions between the barriers and the bases for temperature regulation.

Mechanism of atomic layer deposition of SiO2 on the silicon (100)-2×1 surface using SiCl4 and H2O as precursors

NASA Astrophysics Data System (ADS)

Kang, Jeung Ku; Musgrave, Charles B.

2002-03-01

We use density functional theory to investigate atomic layer deposition (ALD) mechanism of silicon dioxide on the Si(100)-2×1 surface from the precursors SiCl4 and H2O. First, we explore the reaction mechanism of water with the bare Si(100)-2×1 surface to produce surface hydroxyl groups. We find that this reaction proceeds through a two-step pathway with an overall barrier of 33.3 kcal/mol. Next, we investigate the ALD mechanism for the binary reaction sequence: the SiCl4 half reaction and the H2O half reaction. For the SiCl4 half reaction, SiCl4 first forms a σ-bond with the oxygen of the surface OH group and then releases an HCl molecule. The predicted barrier for this process is 15.8 kcal/mol. Next, adsorbed SiCl3 reacts with a neighboring OH group to form bridged SiCl2 with a barrier of 22.6 kcal/mol. The H2O half reaction also proceeds through two sequential steps with an overall barrier of 19.1 kcal/mol for the reaction of H2O with bridged SiCl2 to form bridged Si(OH)2. The predicted barrier of 22.6 kcal/mol for the rate-limiting step of the ALD binary reaction mechanism is consistent with the experimental value of 22.0 kcal/mol. In addition, we find that the calculated frequencies are in good agreement with the experimentally measured IR spectra.

1,3,5-trinitro-1,3,5-triazine decomposition and chemisorption on Al(111) surface: first-principles molecular dynamics study.

PubMed

Umezawa, Naoto; Kalia, Rajiv K; Nakano, Aiichiro; Vashista, Priya; Shimojo, Fuyuki

2007-06-21

We have investigated the decomposition and chemisorption of a 1,3,5-trinitro-1,3,5-triazine (RDX) molecule on Al(111) surface using molecular dynamics simulations, in which interatomic forces are computed quantum mechanically in the framework of the density functional theory (DFT). The real-space DFT calculations are based on higher-order finite difference and norm-conserving pseudopotential methods. Strong attractive forces between oxygen and aluminum atoms break N-O and N-N bonds in the RDX and, subsequently, the dissociated oxygen atoms and NO molecules oxidize the Al surface. In addition to these Al surface-assisted decompositions, ring cleavage of the RDX molecule is also observed. These reactions occur spontaneously without potential barriers and result in the attachment of the rest of the RDX molecule to the surface. This opens up the possibility of coating Al nanoparticles with RDX molecules to avoid the detrimental effect of oxidation in high energy density material applications.

A trajectory planning scheme for spacecraft in the space station environment. M.S. Thesis - University of California

NASA Technical Reports Server (NTRS)

Soller, Jeffrey Alan; Grunwald, Arthur J.; Ellis, Stephen R.

1991-01-01

Simulated annealing is used to solve a minimum fuel trajectory problem in the space station environment. The environment is special because the space station will define a multivehicle environment in space. The optimization surface is a complex nonlinear function of the initial conditions of the chase and target crafts. Small permutations in the input conditions can result in abrupt changes to the optimization surface. Since no prior knowledge about the number or location of local minima on the surface is available, the optimization must be capable of functioning on a multimodal surface. It was reported in the literature that the simulated annealing algorithm is more effective on such surfaces than descent techniques using random starting points. The simulated annealing optimization was found to be capable of identifying a minimum fuel, two-burn trajectory subject to four constraints which are integrated into the optimization using a barrier method. The computations required to solve the optimization are fast enough that missions could be planned on board the space station. Potential applications for on board planning of missions are numerous. Future research topics may include optimal planning of multi-waypoint maneuvers using a knowledge base to guide the optimization, and a study aimed at developing robust annealing schedules for potential on board missions.

NOx Direct Decomposition: Potentially Enhanced Thermodynamics and Kinetics on Chemically Modified Ferroelectric Surfaces

NASA Astrophysics Data System (ADS)

Kakekhani, Arvin; Ismail-Beigi, Sohrab

2014-03-01

NOx are regulated pollutants produced during automotive combustion. As part of an effort to design catalysts for NOx decomposition that operate in oxygen rich environment and permit greater fuel efficiency, we study chemistry of NOx on (001) ferroelectric surfaces. Changing the polarization at such surfaces modifies electronic properties and leads to switchable surface chemistry. Using first principles theory, our previous work has shown that addition of catalytic RuO2 monolayer on ferroelectric PbTiO3 surface makes direct decomposition of NO thermodynamically favorable for one polarization. Furthermore, the usual problem of blockage of catalytic sites by strong oxygen binding is overcome by flipping polarization that helps desorb the oxygen. We describe a thermodynamic cycle for direct NO decomposition followed by desorption of N2 and O2. We provide energy barriers and transition states for key steps of the cycle as well as describing their dependence on polarization direction. We end by pointing out how a switchable order parameter of substrate,in this case ferroelectric polarization, allows us to break away from some standard compromises for catalyst design(e.g. the Sabatier principle). This enlarges the set of potentially catalytic metals. Primary support from Toyota Motor Engineering and Manufacturing, North America, Inc.

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.

Bobcats ( Lynx rufus) as a Model Organism to Investigate the Effects of Roads on Wide-Ranging Carnivores

NASA Astrophysics Data System (ADS)

Litvaitis, John A.; Reed, Gregory C.; Carroll, Rory P.; Litvaitis, Marian K.; Tash, Jeffrey; Mahard, Tyler; Broman, Derek J. A.; Callahan, Catherine; Ellingwood, Mark

2015-06-01

We are using bobcats ( Lynx rufus) as a model organism to examine how roads affect the abundance, distribution, and genetic structure of a wide-ranging carnivore. First, we compared the distribution of bobcat-vehicle collisions to road density and then estimated collision probabilities for specific landscapes using a moving window with road-specific traffic volume. Next, we obtained incidental observations of bobcats from the public, camera-trap detections, and locations of bobcats equipped with GPS collars to examine habitat selection. These data were used to generate a cost-surface map to investigate potential barrier effects of roads. Finally, we have begun an examination of genetic structure of bobcat populations in relation to major road networks. Distribution of vehicle-killed bobcats was correlated with road density, especially state and interstate highways. Collision models suggested that some regions may function as demographic sinks. Simulated movements in the context of the cost-surface map indicated that some major roads may be barriers. These patterns were supported by the genetic structure of bobcats. The sharpest divisions among genetically distinct demes occurred along natural barriers (mountains and large lakes) and in road-dense regions. In conclusion, our study has demonstrated the utility of using bobcats as a model organism to understand the variety of threats that roads pose to a wide-ranging species. Bobcats may also be useful as one of a group of focal species while developing approaches to maintain existing connectivity or mitigate the negative effects of roads.

Bobcats (Lynx rufus) as a Model Organism to Investigate the Effects of Roads on Wide-Ranging Carnivores.

PubMed

Litvaitis, John A; Reed, Gregory C; Carroll, Rory P; Litvaitis, Marian K; Tash, Jeffrey; Mahard, Tyler; Broman, Derek J A; Callahan, Catherine; Ellingwood, Mark

2015-06-01

We are using bobcats (Lynx rufus) as a model organism to examine how roads affect the abundance, distribution, and genetic structure of a wide-ranging carnivore. First, we compared the distribution of bobcat-vehicle collisions to road density and then estimated collision probabilities for specific landscapes using a moving window with road-specific traffic volume. Next, we obtained incidental observations of bobcats from the public, camera-trap detections, and locations of bobcats equipped with GPS collars to examine habitat selection. These data were used to generate a cost-surface map to investigate potential barrier effects of roads. Finally, we have begun an examination of genetic structure of bobcat populations in relation to major road networks. Distribution of vehicle-killed bobcats was correlated with road density, especially state and interstate highways. Collision models suggested that some regions may function as demographic sinks. Simulated movements in the context of the cost-surface map indicated that some major roads may be barriers. These patterns were supported by the genetic structure of bobcats. The sharpest divisions among genetically distinct demes occurred along natural barriers (mountains and large lakes) and in road-dense regions. In conclusion, our study has demonstrated the utility of using bobcats as a model organism to understand the variety of threats that roads pose to a wide-ranging species. Bobcats may also be useful as one of a group of focal species while developing approaches to maintain existing connectivity or mitigate the negative effects of roads.

Simulation of Nanowires on Metal Vicinal Surfaces: Effect of Growth Parameters and Energetic Barriers

NASA Astrophysics Data System (ADS)

Hamouda, Ajmi B. H.; Blel, Sonia; Einstein, T. L.

2012-02-01

Growing one-dimensional metal structures is an important task in the investigation of the electronic and magnetic properties of new devices. We used kinetic Monte-Carlo (kMC) method to simulate the formation of nanowires of several metallic and non-metallic adatoms on Cu and Pt vicinal surfaces. We found that mono-atomic chains form on step-edges due to energetic barriers (the so-called Ehrlich-shwoebel and exchange barriers) on step-edge. Creation of perfect wires is found to depend on growth parameters and binding energies. We measure the filling ratio of nanowires for different chemical species in a wide range of temperature and flux. Perfect wires were obtained at lower deposition rate for all tested adatoms, however we notice different temperature ranges. Our results were compared with experimental ones [Gambardella et al., Surf. Sci.449, 93-103 (2000), PRB 61, 2254-2262, (2000)]. We review the role of impurities in nanostructuring of surfaces [Hamouda et al., Phys. Rev. B 83, 035423, (2011)] and discuss the effect of their energetic barriers on the obtained quality of nanowires. Our work provides experimentalists with optimum growth parameters for the creation of a uniform distribution of wires on surfaces.

Clustering on Magnesium Surfaces – Formation and Diffusion Energies

DOE PAGES

Chu, Haijian; Huang, Hanchen; Wang, Jian

2017-07-12

The formation and diffusion energies of atomic clusters on Mg surfaces determine the surface roughness and formation of faulted structure, which in turn affect the mechanical deformation of Mg. This paper reports first principles density function theory (DFT) based quantum mechanics calculation results of atomic clustering on the low energy surfaces {0001} and {more » $$\\bar{1}$$011} . In parallel, molecular statics calculations serve to test the validity of two interatomic potentials and to extend the scope of the DFT studies. On a {0001} surface, a compact cluster consisting of few than three atoms energetically prefers a face-centered-cubic stacking, to serve as a nucleus of stacking fault. On a {$$\\bar{1}$$011} , clusters of any size always prefer hexagonal-close-packed stacking. Adatom diffusion on surface {$$\\bar{1}$$011} is high anisotropic while isotropic on surface (0001). Three-dimensional Ehrlich–Schwoebel barriers converge as the step height is three atomic layers or thicker. FInally, adatom diffusion along steps is via hopping mechanism, and that down steps is via exchange mechanism.« less

Clustering on Magnesium Surfaces – Formation and Diffusion Energies

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

Chu, Haijian; Huang, Hanchen; Wang, Jian

The formation and diffusion energies of atomic clusters on Mg surfaces determine the surface roughness and formation of faulted structure, which in turn affect the mechanical deformation of Mg. This paper reports first principles density function theory (DFT) based quantum mechanics calculation results of atomic clustering on the low energy surfaces {0001} and {more » $$\\bar{1}$$011} . In parallel, molecular statics calculations serve to test the validity of two interatomic potentials and to extend the scope of the DFT studies. On a {0001} surface, a compact cluster consisting of few than three atoms energetically prefers a face-centered-cubic stacking, to serve as a nucleus of stacking fault. On a {$$\\bar{1}$$011} , clusters of any size always prefer hexagonal-close-packed stacking. Adatom diffusion on surface {$$\\bar{1}$$011} is high anisotropic while isotropic on surface (0001). Three-dimensional Ehrlich–Schwoebel barriers converge as the step height is three atomic layers or thicker. FInally, adatom diffusion along steps is via hopping mechanism, and that down steps is via exchange mechanism.« less

Barrier island arcs along abandoned Mississippi River deltas

USGS Publications Warehouse

Penland, S.; Suter, J.R.; Boyd, Ron

1985-01-01

Generation of transgressive barrier island arcs along the Mississippi River delta plain and preservation of barrier shoreline facies in their retreat paths on the inner shelf is controlled by: (1) shoreface translation; (2) age of the transgression; and (3) the thickness of the barrier island arc sediment package. Barrier island arcs experience an average relative sea level rise of 0.50-1.00 cm yr-1 and shoreface retreat rates range from 5-15 m yr-1. Young barrier island arc sediment packages (Isles Dernieres) are thin and have experienced limited landward retreat of the shoreface. Older barrier island arcs (Chandeleur Islands) are thicker and have experienced significant landward movement of the shoreface because of the greater time available for retreat. If the transgressed barrier shoreline sediment package lies above the advancing ravinement surface, the entire sequence is truncated. A thin reworked sand sheet marks the shoreface retreat path. The base of the transgressive sediment package can lie below the ravinement surface in older barrier shorelines. In this setting, the superstructure of the barrier shoreline is truncated, leaving the basal portion of the transgressive sequence preserved on the inner shelf. A variety of transgressive stratigraphic sequences from sand sheets to truncated barrier islands to sand-filled tidal inlet scars have been identified by high resolution seismic profiling across the shoreface retreat paths of Mississippi delta barrier island arcs. One of these examples, the Isles Dernieres, represents a recently detached barrier island arc in the early stages of transgression. An older example, the Chandeleur Islands, represents a barrier island arc experiencing long-term shoreface retreat. This paper describes the stratigraphic character and preserved transgressive facies for the Isles Dernieres and Chandeleur Islands. ?? 1985.

Investigating the complementary value of discrete choice experiments for the evaluation of barriers and facilitators in implementation research: a questionnaire survey

PubMed Central

van Helvoort-Postulart, Debby; van der Weijden, Trudy; Dellaert, Benedict GC; de Kok, Mascha; von Meyenfeldt, Maarten F; Dirksen, Carmen D

2009-01-01

Background The potential barriers and facilitators to change should guide the choice of implementation strategy. Implementation researchers believe that existing methods for the evaluation of potential barriers and facilitators are not satisfactory. Discrete choice experiments (DCE) are relatively new in the health care sector to investigate preferences, and may be of value in the field of implementation research. The objective of our study was to investigate the complementary value of DCE for the evaluation of barriers and facilitators in implementation research. Methods Clinical subject was the implementation of the guideline for breast cancer surgery in day care. We identified 17 potential barriers and facilitators to the implementation of this guideline. We used a traditional questionnaire that was made up of statements about the potential barriers and facilitators. Respondents answered 17 statements on a five-point scale ranging from one (fully disagree) to five (fully agree). The potential barriers and facilitators were included in the DCE as decision attributes. Data were gathered among anaesthesiologists, surgical oncologists, and breast care nurses by means of a paper-and-pencil questionnaire. Results The overall response was 10%. The most striking finding was that the responses to the traditional questionnaire hardly differentiated between barriers. Forty-seven percent of the respondents thought that DCE is an inappropriate method. These respondents considered DCE too difficult and too time-consuming. Unlike the traditional questionnaire, the results of a DCE provide implementation researchers and clinicians with a relative attribute importance ranking that can be used to prioritize potential barriers and facilitators to change, and hence to better fine-tune the implementation strategies to the specific problems and challenges of a particular implementation process. Conclusion The results of our DCE and traditional questionnaire would probably lead to different implementation strategies. Although there is no 'gold standard' for prioritising potential barriers and facilitators to the implementation of change, theoretically, DCE would be the method of choice. However, the feasibility of using DCE was less favourable. Further empirical applications should investigate whether DCE can really make a valuable contribution to the implementation science. PMID:19250555

Energy shift and conduction-to-valence band transition mediated by a time-dependent potential barrier in graphene

NASA Astrophysics Data System (ADS)

Chaves, Andrey; da Costa, D. R.; de Sousa, G. O.; Pereira, J. M.; Farias, G. A.

2015-09-01

We investigate the scattering of a wave packet describing low-energy electrons in graphene by a time-dependent finite-step potential barrier. Our results demonstrate that, after Klein tunneling through the barrier, the electron acquires an extra energy which depends on the rate of change of the barrier height with time. If this rate is negative, the electron loses energy and ends up as a valence band state after leaving the barrier, which effectively behaves as a positively charged quasiparticle.

Laser surface modification of Yttria Stabilized Zirconia (YSZ) thermal barrier coating on AISI H13 tool steel substrate

NASA Astrophysics Data System (ADS)

Reza, M. S.; Aqida, S. N.; Ismail, I.

2018-03-01

This paper presents laser surface modification of plasma sprayed yttria stabilized zirconia (YSZ) coating to seal porosity defect. Laser surface modification on plasma sprayed YSZ was conducted using 300W JK300HPS Nd: YAG laser at different operating parameters. Parameters varied were laser power and pulse frequency with constant residence time. The coating thickness was measured using IM7000 inverted optical microscope and surface roughness was analysed using two-dimensional Mitutoyo Surface Roughness Tester. Surface roughness of laser surface modification of YSZ H-13 tool steel decreased significantly with increasing laser power and decreasing pulse frequency. The re-melted YSZ coating showed higher hardness properties compared to as-sprayed coating surface. These findings were significant to enhance thermal barrier coating surface integrity for dies in semi-solid processing.

Controlled thermoelectric response of a tunable Rashba coupled metal-insulator-superconductor junction

NASA Astrophysics Data System (ADS)

Kapri, Priyadarshini; Adhikary, Priyanka; Sinha, Shubham; Basu, Saurabh

2018-05-01

Thermoelectric effect for metal, insulator and the superconductor junctions has been studied with Rashba spin-orbit coupling (RSOC) being present at the interfaces via modified Blonder-Tinkham-Klapwijk (BTK) theory. We find that the thermopower, as a function of an effective barrier potential that characterizes the intermediate insulating layer, displays an oscillatory behavior. Interesting interplay between the strength of RSOC and the effective barrier potential has been carried out in details in this regard. For specific ranges of the effective barrier potential, RSOC enhances the thermopower, while the reverse happens for other values. Moreover it is found that the effective barrier potential plays a crucial role in determining the thermopower spectrum. For a tunable Rashba coupling, the thermopower of the junction can be controlled with precision, which may useful for the thermoelectric applications, at low temperatures. Further the efficiency of the system is obtained for different pairing correlations of the superconducting lead where we find that the system with a d-wave symmetry is more efficient as compared to a s-wave correlation, in some selective regions of effective barrier potential. It is found that for some selective regions of effective barrier potential, the efficiency of the system increases with RSOC and the opposite happens for other values.

Long-Term Drainage from the Riprap Side Slope of a Surface Barrier

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

Zhang, Zhuanfang

Surface barriers designed to isolate underground nuclear waste in place are expected to function for at least 1000 years. To achieve this long design life, such barriers need to be protected with side slopes against wind- and water-induced erosion and damage by natural or human activities. However, the side slopes are usually constructed with materials coarser than the barrier. Their hydrological characteristics must be understood so that any drainage from them is considered in the barrier design and will not compromise the barrier function. The Prototype Hanford Barrier, an evapotranspiration-capillary (ETC) barrier, was constructed in 1994 at the Hanford Sitemore » in southeastern Washington state, with a gravel side slope and a riprap side slope. The soil water content in the gravel side slope and drainage from both side slopes have been monitored since the completion of construction. The monitoring results show that under natural precipitation the annual drainage rates from the two types of side slopes were very similar and about 5 times the typical recharge from local soil with natural vegetation and 40 times the barrier design criterion. The higher recharge from the side slopes results in some of the drainage migrating laterally to the region beneath the ETC barrier. This edge effect of the enhanced drainage was evaluated for a period of 1000 years by numerical simulation. The edge effect was quantified by the amount of water across the barrier edges and the affecting distance of the barrier edges. These results indicate that design features can be adjusted to reduce the edge effect when necessary.« less

Synthesis, tautomeric stability, spectroscopy and computational study of a potential molecular switch of (Z)-4-(phenylamino)pent-3-en-2-one

NASA Astrophysics Data System (ADS)

Fahid, Farzaneh; Kanaani, Ayoub; Pourmousavi, Seied Ali; Ajloo, Davood

2017-04-01

The (Z)-4-(phenylamino) pent-3-en-2-one (PAPO) was synthesised applying carbon-based solid acid and described by experimental techniques. Calculated results reveal that its keto-amine form is more stable than its enol-imine form. A relaxed potential energy surface scan has been accomplished based on the optimised geometry of NH tautomeric form to depict the potential energy barrier related to intramolecular proton transfer. The spectroscopic results and theoretical calculations demonstrate that the intramolecular hydrogen bonding strength of PAPO is stronger than that in 4-amino-3-penten-2-one)APO(. In addition, molecular electrostatic potential, total and partial density of stats (TDOS, PDOS) and non-linear optical properties of the compound were studied using same theoretical calculations. Our calculations show that the title molecule has the potential to be used as molecular switch.

Modeling the light-induced electric potential difference ΔΨ across the thylakoid membrane based on the transition state rate theory.

PubMed

Lyu, Hui; Lazár, Dušan

2017-03-01

In photosynthesis, electron transport-coupled proton movement initiates the formation of the light-induced electric potential difference, ΔΨ, across the thylakoid membrane (TM). Ions are transported across the TM to counterbalance the charge of protons accumulated in the lumen. The objective of this work is to construct range of mathematical models for simulation of ΔΨ, using the transition state rate theory (TSRT) for description of movement of ions through the channels. The TSRT considers either single-ion (TSRT-SI) or multi-ion occupancy (TSRT-MI) in the channels. Movement of ions through the channel pore is described by means of energy barriers and binding sites; ions move in and out of vacant sites with rate constants that depend on the barrier heights and well depths, as well as on the interionic repulsion in TSRT-MI model. Three energy motifs are used to describe the TSRT-SI model: two-barrier one-site (2B1S), three-barrier two-site (3B2S), and four-barrier three-site (4B3S). The 3B2S energy motif is used for the TSRT-MI model. The accumulation of cations due to the TM surface negative fixed charges is also taken into account. A model employing the electro-diffusion theory instead of the TSRT is constructed for comparison. The dual wavelength transmittance signal (ΔA515-560nm) measuring the electrochromic shift (ECS) provides a proxy for experimental light-induced ΔΨ. The simulated ΔΨ traces qualitatively agree with the measured ECS traces. The models can simulate different channel conducting regimes and assess their impact on ΔΨ. The ionic flux coupling in the TSRT-MI model suggests that an increase in the internal or external K + concentration may block the outward or the inward Mg 2+ current, respectively. Copyright © 2016 Elsevier B.V. All rights reserved.

Model studies of hydrogen atom addition and abstraction processes involving ortho-, meta-, and para-benzynes.

PubMed

Clark, A E; Davidson, E R

2001-10-31

H-atom addition and abstraction processes involving ortho-, meta-, and para-benzyne have been investigated by multiconfigurational self-consistent field methods. The H(A) + H(B)...H(C) reaction (where r(BC) is adjusted to mimic the appropriate singlet-triplet energy gap) is shown to effectively model H-atom addition to benzyne. The doublet multiconfiguration wave functions are shown to mix the "singlet" and "triplet" valence bond structures of H(B)...H(C) along the reaction coordinate; however, the extent of mixing is dependent on the singlet-triplet energy gap (DeltaE(ST)) of the H(B)...H(C) diradical. Early in the reaction, the ground-state wave function is essentially the "singlet" VB function, yet it gains significant "triplet" VB character along the reaction coordinate that allows H(A)-H(B) bond formation. Conversely, the wave function of the first excited state is predominantly the "triplet" VB configuration early in the reaction coordinate, but gains "singlet" VB character when the H-atom is close to a radical center. As a result, the potential energy surface (PES) for H-atom addition to triplet H(B)...H(C) diradical is repulsive! The H3 model predicts, in agreement with the actual calculations on benzyne, that the singlet diradical electrons are not coupled strongly enough to give rise to an activation barrier associated with C-H bond formation. Moreover, this model predicts that the PES for H-atom addition to triplet benzyne will be characterized by a repulsive curve early in the reaction coordinate, followed by a potential avoided crossing with the (pi)1(sigma*)1 state of the phenyl radical. In contrast to H-atom addition, large activation barriers characterize the abstraction process in both the singlet ground state and first triplet state. In the ground state, this barrier results from the weakly avoided crossing of the dominant VB configurations in the ground-state singlet (S0) and first excited singlet (S1) because of the large energy gap between S0 and S1 early in the reaction coordinate. Because the S1 state is best described as the combination of the triplet X-H bond and the triplet H(B)...H(C) spin couplings, the activation barrier along the S0 abstraction PES will have much less dependence on the DeltaE(ST) of H(B)...H(C) than previously speculated. For similar reasons, the T1 potential surface is quite comparable to the S0 PES.

Propargyl + O 2 Reaction in Helium Droplets: Entrance Channel Barrier or Not?

DOE PAGES

Moradi, Christopher P.; Morrison, Alexander M.; Klippenstein, Stephen J.; ...

2013-09-09

A combination of liquid He droplet experiments and multireference electronic structure calculations is used to probe the potential energy surface for the reaction between the propargyl radical and O 2. Infrared laser spectroscopy is used to probe the outcome of the low temperature, liquid He-mediated reaction. Bands in the spectrum are assigned to the acetylenic CH stretch (ν 1), the symmetric CH 2 stretch (ν 2), and the antisymmetric CH 2 stretch (ν 13) of the trans-acetylenic propargyl peroxy radical (•OO—CH 2—C≡CH). The observed band origins are in excellent agreement with previously reported anharmonic frequency computations for this species. Themore » Stark spectrum of the ν 1 band provides further evidence that the reaction leads only to the trans-acetylenic species. There are no other bands in the CH 2 stretching region that can be attributed to any of the other three propargyl peroxy isomers/conformers that are predicted to be minimum energy structures ( gauche-acetylenic, cis-allenic, and trans-allenic). There is also no evidence for the kinetic stabilization of a van der Waals complex between propargyl and O 2. A combination of multireference and coupled-cluster electronic structure calculations is used to probe the potential energy surface in the neighborhood of the transition state connecting reactants with the acetylenic adduct. The multireference based evaluation of the doublet-quartet splitting added to the coupled-cluster calculated quartet state energies yields what are likely the most accurate predictions for the doublet potential curve. As a result, this calculation suggests that there is no saddle point for the addition process, in agreement with the experimental observations. Other calculations suggest the possible presence of a small submerged barrier.« less

Kinetics-Driven Crystal Facets Evolution at the Tip of Nanowires: A New Implementation of the Ostwald-Lussac Law.

PubMed

Yin, Xin; Wang, Xudong

2016-11-09

Nanocrystal facets evolution is critical for designing nanomaterial morphology and controlling their properties. In this work, we report a unique high-energy crystal facets evolution phenomenon at the tips of wurtzite zinc oxide nanowires (NWs). As the zinc vapor supersaturation decreased at the NW deposition region, the NW tip facets evolved from the (0001) surface to the {101̅3} surface and subsequently to the {112̅2} surface and eventually back to the flat (0001) surface. A series of NW tip morphology was observed in accordance to the different combinations of exposed facets. Exposure of the high-energy facets was attributed to the fluctuation of the energy barriers for the formation of different crystal facets during the layer-by-layer growth of the NW tip. The energy barrier differences between these crystal facets were quantified from the surface area ratios as a function of supersaturation. On the basis of the experimental observation and kinetics analysis, we argue that at appropriate deposition conditions exposure of the crystal facets at NW growth front is not merely determined by the surface energy. Instead, the NW may choose to expose the facets with minimal formation energy barrier, which can be determined by the Ehrlich-Schwoebel barrier variation. This empirical law for the NW tip facet formation was in analogy to the Ostwald-Lussac law of phase transformation, which brings a new insight toward nanostructure design and controlled synthesis.

Studies of Cu adatom island ripening on Cu(100) by LEEM

NASA Astrophysics Data System (ADS)

Bussmann, Ezra; Kellogg, Gary L.

2007-03-01

Simple metal surfaces are model systems for characterizing kinetic processes governing the growth and stability of nanoscale structures. It is generally presumed that diffusive transport of adatoms across terraces determines the rate of these processes. However, STM studies in the temperature range T˜330-420 K reveal that transport between step edges on the Cu(100) surface is limited by detachment barriers at the step edges, rather than by the adatom diffusion barrier.^1 This is because on the Cu(100) surface, mass transport is mediated primarily by vacancies, instead of adatoms. We have used low energy electron microscopy (LEEM) movies to characterize coarsening of Cu islands on the Cu(100) surface in the range T˜460-560 K. By measuring the temperature dependence of the island decay rate we find an activation barrier of 0.9±0.1 eV. This value is comparable to the 0.80±0.03 eV barrier found in STM studies.^1 However, we are not able to conclude that transport is entirely detachment limited at these elevated temperatures. This work serves as background to establish whether or not Pd alloying in the Cu(100) surface will slow Cu surface transport. ^2 1. C. Kl"unker, et al., PRB 58, R7556 (1998). 2. M. L. Grant, et al., PRL 86, 4588 (2001). Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the U.S. DOE NNSA, Contract No. DE-AC04-94AL85000.

Profound re-organization of cell surface proteome in equine retinal pigment epithelial cells in response to in vitro culturing.

PubMed

Szober, Christoph M; Hauck, Stefanie M; Euler, Kerstin N; Fröhlich, Kristina J H; Alge-Priglinger, Claudia; Ueffing, Marius; Deeg, Cornelia A

2012-10-31

The purpose of this study was to characterize the cell surface proteome of native compared to cultured equine retinal pigment epithelium (RPE) cells. The RPE plays an essential role in visual function and represents the outer blood-retinal barrier. We are investigating immunopathomechanisms of equine recurrent uveitis, an autoimmune inflammatory disease in horses leading to breakdown of the outer blood-retinal barrier and influx of autoreactive T-cells into affected horses' vitrei. Cell surface proteins of native and cultured RPE cells from eye-healthy horses were captured by biotinylation, analyzed by high resolution mass spectrometry coupled to liquid chromatography (LC MS/MS), and the most interesting candidates were validated by PCR, immunoblotting and immunocytochemistry. A total of 112 proteins were identified, of which 84% were cell surface membrane proteins. Twenty-three of these proteins were concurrently expressed by both cell states, 28 proteins exclusively by native RPE cells. Among the latter were two RPE markers with highly specialized RPE functions: cellular retinaldehyde-binding protein (CRALBP) and retinal pigment epithelium-specific protein 65kDa (RPE65). Furthermore, 61 proteins were only expressed by cultured RPE cells and absent in native cells. As we believe that initiating events, leading to the breakdown of the outer blood-retinal barrier, take place at the cell surface of RPE cells as a particularly exposed barrier structure, this differential characterization of cell surface proteomes of native and cultured equine RPE cells is a prerequisite for future studies.

Energy barriers, entropy barriers, and non-Arrhenius behavior in a minimal glassy model.

PubMed

Du, Xin; Weeks, Eric R

2016-06-01

We study glassy dynamics using a simulation of three soft Brownian particles confined to a two-dimensional circular region. If the circular region is large, the disks freely rearrange, but rearrangements are rarer for smaller system sizes. We directly measure a one-dimensional free-energy landscape characterizing the dynamics. This landscape has two local minima corresponding to the two distinct disk configurations, separated by a free-energy barrier that governs the rearrangement rate. We study several different interaction potentials and demonstrate that the free-energy barrier is composed of a potential-energy barrier and an entropic barrier. The heights of both of these barriers depend on temperature and system size, demonstrating how non-Arrhenius behavior can arise close to the glass transition.

Role of oceanography in shaping the genetic structure in the North Pacific hake Merluccius productus

PubMed Central

2018-01-01

Determining the relative influence of biotic and abiotic factors on genetic connectivity among populations remains a major challenge in evolutionary biology and in the management and conservation of species. North Pacific hake (Merluccius productus) inhabits upwelling regions in the California Current ecosystem from the Gulf of California to the Gulf of Alaska. In this study, we examined mitochondrial DNA (mtDNA) and microsatellite variation to estimate levels of genetic differentiation of M. productus in relation to the role of oceanographic features as potential barriers to gene flow. Samples were obtained from nine sites spanning a large part of the geographic range of the species, from Puget Sound, Washington to Costa Rica. The microsatellite results revealed three genetically discrete populations: one spanning the eastern Pacific coast, and two apparently resident populations circumscribed to the Puget Sound and the northern Gulf of California (FST = 0.032, p = 0.036). Cytochrome b sequence data indicated that isolation between the Puget Sound and northern Gulf of California populations from the coastal Pacific were recent phenomena (18.5 kyr for Puget Sound and 40 kyr for the northern Gulf of California). Oceanographic data obtained from the Gulf of California support the hypothesis that permanent fronts within the region, and strong gradients at the entrance to the Gulf of California act as barriers to gene flow. A seascape genetics approach found significant genetic–environment associations, where the daytime sea surface temperature and chlorophyll concentrations were the best predictive variables for the observed genetic differentiation. Considering the potential causes of genetic isolation among the three populations, e.g. spawning areas in different latitudes associated with upwelling processes, oceanographic barriers, asymmetric migration and specialized diet, oceanographic barriers appear to be a likely mechanism restricting gene flow. PMID:29579060

Role of oceanography in shaping the genetic structure in the North Pacific hake Merluccius productus.

PubMed

García-De León, Francisco Javier; Galván-Tirado, Carolina; Sánchez Velasco, Laura; Silva-Segundo, Claudia A; Hernández-Guzmán, Rafael; Barriga-Sosa, Irene de Los Angeles; Díaz Jaimes, Píndaro; Canino, Michael; Cruz-Hernández, Pedro

2018-01-01

Determining the relative influence of biotic and abiotic factors on genetic connectivity among populations remains a major challenge in evolutionary biology and in the management and conservation of species. North Pacific hake (Merluccius productus) inhabits upwelling regions in the California Current ecosystem from the Gulf of California to the Gulf of Alaska. In this study, we examined mitochondrial DNA (mtDNA) and microsatellite variation to estimate levels of genetic differentiation of M. productus in relation to the role of oceanographic features as potential barriers to gene flow. Samples were obtained from nine sites spanning a large part of the geographic range of the species, from Puget Sound, Washington to Costa Rica. The microsatellite results revealed three genetically discrete populations: one spanning the eastern Pacific coast, and two apparently resident populations circumscribed to the Puget Sound and the northern Gulf of California (FST = 0.032, p = 0.036). Cytochrome b sequence data indicated that isolation between the Puget Sound and northern Gulf of California populations from the coastal Pacific were recent phenomena (18.5 kyr for Puget Sound and 40 kyr for the northern Gulf of California). Oceanographic data obtained from the Gulf of California support the hypothesis that permanent fronts within the region, and strong gradients at the entrance to the Gulf of California act as barriers to gene flow. A seascape genetics approach found significant genetic-environment associations, where the daytime sea surface temperature and chlorophyll concentrations were the best predictive variables for the observed genetic differentiation. Considering the potential causes of genetic isolation among the three populations, e.g. spawning areas in different latitudes associated with upwelling processes, oceanographic barriers, asymmetric migration and specialized diet, oceanographic barriers appear to be a likely mechanism restricting gene flow.

Skin friction related behaviour of artificial turf systems.

PubMed

Tay, Sock Peng; Fleming, Paul; Hu, Xiao; Forrester, Steph

2017-08-01

The occurrence of skin friction related injuries is an issue for artificial turf sports pitches and remains a barrier to their acceptance. The purpose of this study was to evaluate the current industry standard Securisport® Sports Surface Tester that measures skin surface related frictional behaviour of artificial turf. Little research has been published about the device and its efficacy, despite its widespread use as a standard FIFA test instrument. To achieve a range of frictional behaviours, several "third generation" (3G) carpet and infill combinations were investigated; friction time profiles throughout the Securisport rotations were assessed in combination with independent measurements of skin roughness before and after friction testing via 3D surface scanning. The results indicated that carpets without infill had greatest friction (coefficients of friction 0.97-1.20) while those completely filled with sand or rubber had similar and lower values independent of carpet type (coefficient of friction (COF) ≈0.57). Surface roughness of a silicone skin (s-skin) decreased after friction testing, with the largest change on sand infilled surfaces, indicating an "abrasive" polishing effect. The combined data show that the s-skin is damaged in a surface-specific manner, thus the Securisport COF values appear to be a poor measure of the potential for skin abrasion. It is proposed that the change in s-skin roughness improves assessment of the potential for skin damage when players slide on artificial turf.

Pyridine adsorption and diffusion on Pt(111) investigated with density functional theory

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

Kolsbjerg, Esben L.; Groves, Michael N.; Hammer, Bjørk, E-mail: hammer@phys.au.dk

2016-04-28

The adsorption, diffusion, and dissociation of pyridine, C{sub 5}H{sub 5}N, on Pt(111) are investigated with van der Waals-corrected density functional theory. An elaborate search for local minima in the adsorption potential energy landscape reveals that the intact pyridine adsorbs with the aromatic ring parallel to the surface. Piecewise interconnections of the local minima in the energy landscape reveal that the most favourable diffusion path for pyridine has a barrier of 0.53 eV. In the preferred path, the pyridine remains parallel to the surface while performing small single rotational steps with a carbon-carbon double bond hinged above a single Pt atom.more » The origin of the diffusion pathway is discussed in terms of the C{sub 2}–Pt π-bond being stronger than the corresponding CN–Pt π-bond. The energy barrier and reaction enthalpy for dehydrogenation of adsorbed pyridine into an adsorbed, upright bound α-pyridyl species are calculated to 0.71 eV and 0.18 eV, respectively (both zero-point energy corrected). The calculations are used to rationalize previous experimental observations from the literature for pyridine on Pt(111).« less

Modeling of influencing parameters in active noise control on an enclosure wall

NASA Astrophysics Data System (ADS)

Tarabini, Marco; Roure, Alain

2008-04-01

This paper investigates, by means of a numerical model, the possibility of using an active noise barrier to virtually reduce the acoustic transparency of a partition wall inside an enclosure. The room is modeled with the image method as a rectangular enclosure with a stationary point source; the active barrier is set up by an array of loudspeakers and error microphones and is meant to minimize the squared sound pressure on a wall with the use of a decentralized control. Simulations investigate the effects of the enclosure characteristics and of the barrier geometric parameters on the sound pressure attenuation on the controlled partition, on the whole enclosure potential energy and on the diagonal control stability. Performances are analyzed in a frequency range of 25-300 Hz at discrete 25 Hz steps. Influencing parameters and their effects on the system performances are identified with a statistical inference procedure. Simulation results have shown that it is possible to averagely reduce the sound pressure on the controlled partition. In the investigated configuration, the surface attenuation and the diagonal control stability are mainly driven by the distance between the loudspeakers and the error microphones and by the loudspeakers directivity; minor effects are due to the distance between the error microphones and the wall, by the wall reflectivity and by the active barrier grid meshing. Room dimensions and source position have negligible effects. Experimental results point out the validity of the model and the efficiency of the barrier in the reduction of the wall acoustic transparency.

2-D modeling and analysis of short-channel behavior of a front high- K gate stack triple-material gate SB SON MOSFET

NASA Astrophysics Data System (ADS)

Banerjee, Pritha; Kumari, Tripty; Sarkar, Subir Kumar

2018-02-01

This paper presents the 2-D analytical modeling of a front high- K gate stack triple-material gate Schottky Barrier Silicon-On-Nothing MOSFET. Using the two-dimensional Poisson's equation and considering the popular parabolic potential approximation, expression for surface potential as well as the electric field has been considered. In addition, the response of the proposed device towards aggressive downscaling, that is, its extent of immunity towards the different short-channel effects, has also been considered in this work. The analytical results obtained have been validated using the simulated results obtained using ATLAS, a two-dimensional device simulator from SILVACO.

Comparison Of Reaction Barriers In Energy And Free Energy For Enzyme Catalysis

NASA Astrophysics Data System (ADS)

Andrés Cisneros, G.; Yang, Weitao

Reaction paths on potential energy surfaces obtained from QM/MM calculations of enzymatic or solution reactions depend on the starting structure employed for the path calculations. The free energies associated with these paths should be more reliable for studying reaction mechanisms, because statistical averages are used. To investigate this, the role of enzyme environment fluctuations on reaction paths has been studied with an ab initio QM/MM method for the first step of the reaction catalyzed by 4-oxalocrotonate tautomerase (4OT). Four minimum energy paths (MEPs) are compared, which have been determined with two different methods. The first path (path A) has been determined with a procedure that combines the nudged elastic band (NEB) method and a second order parallel path optimizer recently developed in our group. The second path (path B) has also been determined by the combined procedure, however, the enzyme environment has been relaxed by molecular dynamics (MD) simulations. The third path (path C) has been determined with the coordinate driving (CD) method, using the enzyme environment from path B. We compare these three paths to a previously determined path (path D) determined with the CD method. In all four cases the QM/MM-FE method (Y. Zhang et al., JCP, 112, 3483) was employed to obtain the free energy barriers for all four paths. In the case of the combined procedure, the reaction path is approximated by a small number of images which are optimized to the MEP in parallel, which results in a reduced computational cost. However, this does not allow the FEP calculation on the MEP. In order to perform FEP calculations on these paths, we introduce a modification to the NEB method that enables the addition of as many extra images to the path as needed for the FEP calculations. The calculated potential energy barriers show differences in the activation barrier between the calculated paths of as much as 5.17 kcal/mol. However, the largest free energy barrier difference is 1.58 kcal/mol. These results show the importance of the inclusion of the environment fluctuation in the calculation of enzymatic activation barriers

Radical production efficiency and electrical characteristics of a coplanar barrier discharge built by multilayer ceramic technology

NASA Astrophysics Data System (ADS)

Jõgi, Indrek; Erme, Kalev; Levoll, Erik; Stamate, Eugen

2017-11-01

The present study investigated the electrical characteristics and radical production efficiency of a coplanar barrier discharge (CBD) device manufactured by Kyocera by multilayer ceramic technology. The device consisted of a number of linear electrodes with electrode and gap widths of 0.75 mm, immersed into a ceramic dielectric barrier. A closed flow-through system necessary for the measurements was prepared by placing a quartz plate at a height of 3 mm from the ceramic barrier. The production of nitrogen radicals was determined from the removal of a trace amount of NO in pure N2 gas, while the production of oxygen radicals was determined by ozone production in pure O2 or synthetic air. The production efficiency of N and O radicals and NO oxidation in synthetic air was comparable with the efficiency of a volume barrier discharge device. The power density per unit of surface area of the CBD device was more than two times larger than that of a similar volume barrier discharge setup, which makes the CBD device a compact alternative for gas treatment. The production of ozone and different nitrogen oxides was also evaluated for the open system of the CBD which is usable for surface treatment. The ozone concentration of this system was nearly independent from the input power, while the concentration of nitrogen oxides increased with input power. The open system of the CBD was additionally tested for the treatment of a silicon surface. An increase of applied power decreased the time required to reduce the water contact angle below 10 degrees but also started to have an impact on the surface roughness.

Electric characteristics of a surface barrier discharge with a plasma induction electrode

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

Alemskii, I. N.; Lelevkin, V. M.; Tokarev, A. V.

2006-07-15

Static and dynamic current-voltage and charge-voltage characteristics of a surface barrier discharge with a plasma induction electrode have been investigated experimentally. The dependences of the discharge current on both the gas pressure in the induction electrode tube and the winding pitch of the corona electrode, as well as of the discharge power efficiency on the applied voltage, have been measured.

Method for applying a diffusion barrier interlayer for high temperature components

DOEpatents

Wei, Ronghua; Cheruvu, Narayana S.

2016-03-08

A coated substrate and a method of forming a diffusion barrier coating system between a substrate and a MCrAl coating, including a diffusion barrier coating deposited onto at least a portion of a substrate surface, wherein the diffusion barrier coating comprises a nitride, oxide or carbide of one or more transition metals and/or metalloids and a MCrAl coating, wherein M includes a transition metal or a metalloid, deposited on at least a portion of the diffusion barrier coating, wherein the diffusion barrier coating restricts the inward diffusion of aluminum of the MCrAl coating into the substrate.

Investigation of transition States in bulk and freestanding film polymer glasses.

PubMed

Jain, Tushar S; de Pablo, Juan J

2004-04-16

We have performed transition state searches on the potential energy landscape for bulk and freestanding film polymer glasses and identified connected minima. An analysis of the displacements between minima shows that the sites that undergo the greatest displacement are highly localized in space for both the bulk and the thin-film systems studied. In the case of the thin film, the clusters originate at the surface and penetrate into the center of the film thereby coupling the relaxation in the center of the film to the mobile surface layer. Furthermore, the energy barriers between minima are lower in the thin film than in the bulk system. These findings can rationalize the experimentally observed depression of the glass transition temperature in freestanding polymer films.

Crystallization of soft matter under confinement at interfaces and in wedges

NASA Astrophysics Data System (ADS)

Archer, Andrew J.; Malijevský, Alexandr

2016-06-01

The surface freezing and surface melting transitions that are exhibited by a model two-dimensional soft matter system are studied. The behaviour when confined within a wedge is also considered. The system consists of particles interacting via a soft purely repulsive pair potential. Density functional theory (DFT) is used to calculate density profiles and thermodynamic quantities. The external potential due to the confining walls is modelled via a hard wall with an additional repulsive Yukawa potential. The surface phase behaviour depends on the range and strength of this repulsion: when the repulsion is weak, the wall promotes freezing at the surface of the wall. The thickness of this frozen layer grows logarithmically as the bulk liquid-solid phase coexistence is approached. Our mean-field DFT predicts that this crystalline layer at the wall must be nucleated (i.e. there is a free energy barrier) and its formation is necessarily a first-order transition, referred to as ‘prefreezing’, by analogy with the prewetting transition. However, in contrast to the latter, prefreezing cannot terminate in a critical point, since the phase transition involves a change in symmetry. If the wall-fluid interaction is sufficiently long ranged and the repulsion is strong enough, surface melting can occur instead. Then the interface between the wall and the bulk crystalline solid is wetted by the liquid phase as the chemical potential is decreased towards the value at liquid-solid coexistence. It is observed that the finite thickness fluid film at the wall has a broken translational symmetry due to its proximity to the bulk crystal, and so the nucleation of the wetting film can be either first order or continuous. Our mean-field theory predicts that for certain wall potentials there is a premelting critical point analogous to the surface critical point for the prewetting transition. When the fluid is confined within a linear wedge, this can strongly promote freezing when the opening angle of the wedge is commensurate with the crystal lattice.

Mechanisms and energetics of hydride dissociation reactions on surfaces of plasma-deposited silicon thin films

NASA Astrophysics Data System (ADS)

Singh, Tejinder; Valipa, Mayur S.; Mountziaris, T. J.; Maroudas, Dimitrios

2007-11-01

We report results from a detailed analysis of the fundamental silicon hydride dissociation processes on silicon surfaces and discuss their implications for the surface chemical composition of plasma-deposited hydrogenated amorphous silicon (a-Si:H) thin films. The analysis is based on a synergistic combination of first-principles density functional theory (DFT) calculations of hydride dissociation on the hydrogen-terminated Si(001)-(2×1) surface and molecular-dynamics (MD) simulations of adsorbed SiH3 radical precursor dissociation on surfaces of MD-grown a-Si :H films. Our DFT calculations reveal that, in the presence of fivefold coordinated surface Si atoms, surface trihydride species dissociate sequentially to form surface dihydrides and surface monohydrides via thermally activated pathways with reaction barriers of 0.40-0.55eV. The presence of dangling bonds (DBs) results in lowering the activation barrier for hydride dissociation to 0.15-0.20eV, but such DB-mediated reactions are infrequent. Our MD simulations on a-Si :H film growth surfaces indicate that surface hydride dissociation reactions are predominantly mediated by fivefold coordinated surface Si atoms, with resulting activation barriers of 0.35-0.50eV. The results are consistent with experimental measurements of a-Si :H film surface composition using in situ attenuated total reflection Fourier transform infrared spectroscopy, which indicate that the a-Si :H surface is predominantly covered with the higher hydrides at low temperatures, while the surface monohydride, SiH(s ), becomes increasingly more dominant as the temperature is increased.

Uptake and bio-reactivity of polystyrene nanoparticles is affected by surface modifications, ageing and LPS adsorption: in vitro studies on neural tissue cells

NASA Astrophysics Data System (ADS)

Murali, Kumarasamy; Kenesei, Kata; Li, Yang; Demeter, Kornél; Környei, Zsuzsanna; Madarász, Emilia

2015-02-01

Because of their capacity of crossing an intact blood-brain barrier and reaching the brain through an injured barrier or via the nasal epithelium, nanoparticles have been considered as vehicles to deliver drugs and as contrast materials for brain imaging. The potential neurotoxicity of nanoparticles, however, is not fully explored. Using particles with a biologically inert polystyrene core material, we investigated the role of the chemical composition of particle surfaces in the in vitro interaction with different neural cell types. PS NPs within a size-range of 45-70 nm influenced the metabolic activity of cells depending on the cell-type, but caused toxicity only at extremely high particle concentrations. Neurons did not internalize particles, while microglial cells ingested a large amount of carboxylated but almost no PEGylated NPs. PEGylation reduced the protein adsorption, toxicity and cellular uptake of NPs. After storage (shelf-life >6 months), the toxicity and cellular uptake of NPs increased. The altered biological activity of ``aged'' NPs was due to particle aggregation and due to the adsorption of bioactive compounds on NP surfaces. Aggregation by increasing the size and sedimentation velocity of NPs results in increased cell-targeted NP doses. The ready endotoxin adsorption which cannot be prevented by PEG coating, can render the particles toxic. The age-dependent changes in otherwise harmless NPs could be the important sources for variability in the effects of NPs, and could explain the contradictory data obtained with ``identical'' NPs.Because of their capacity of crossing an intact blood-brain barrier and reaching the brain through an injured barrier or via the nasal epithelium, nanoparticles have been considered as vehicles to deliver drugs and as contrast materials for brain imaging. The potential neurotoxicity of nanoparticles, however, is not fully explored. Using particles with a biologically inert polystyrene core material, we investigated the role of the chemical composition of particle surfaces in the in vitro interaction with different neural cell types. PS NPs within a size-range of 45-70 nm influenced the metabolic activity of cells depending on the cell-type, but caused toxicity only at extremely high particle concentrations. Neurons did not internalize particles, while microglial cells ingested a large amount of carboxylated but almost no PEGylated NPs. PEGylation reduced the protein adsorption, toxicity and cellular uptake of NPs. After storage (shelf-life >6 months), the toxicity and cellular uptake of NPs increased. The altered biological activity of ``aged'' NPs was due to particle aggregation and due to the adsorption of bioactive compounds on NP surfaces. Aggregation by increasing the size and sedimentation velocity of NPs results in increased cell-targeted NP doses. The ready endotoxin adsorption which cannot be prevented by PEG coating, can render the particles toxic. The age-dependent changes in otherwise harmless NPs could be the important sources for variability in the effects of NPs, and could explain the contradictory data obtained with ``identical'' NPs. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr06849a

Band-selective filter in a zigzag graphene nanoribbon.

PubMed

Nakabayashi, Jun; Yamamoto, Daisuke; Kurihara, Susumu

2009-02-13

Electric transport of a zigzag graphene nanoribbon through a steplike potential and a barrier potential is investigated by using the recursive Green's function method. In the case of the steplike potential, we demonstrate numerically that scattering processes obey a selection rule for the band indices when the number of zigzag chains is even; the electrons belonging to the "even" ("odd") bands are scattered only into the even (odd) bands so that the parity of the wave functions is preserved. In the case of the barrier potential, by tuning the barrier height to be an appropriate value, we show that it can work as the "band-selective filter", which transmits electrons selectively with respect to the indices of the bands to which the incident electrons belong. Finally, we suggest that this selection rule can be observed in the conductance by applying two barrier potentials.

Bacteriophage-encoded virion-associated enzymes to overcome the carbohydrate barriers during the infection process.

PubMed

Latka, Agnieszka; Maciejewska, Barbara; Majkowska-Skrobek, Grazyna; Briers, Yves; Drulis-Kawa, Zuzanna

2017-04-01

Bacteriophages are bacterial viruses that infect the host after successful receptor recognition and adsorption to the cell surface. The irreversible adherence followed by genome material ejection into host cell cytoplasm must be preceded by the passage of diverse carbohydrate barriers such as capsule polysaccharides (CPSs), O-polysaccharide chains of lipopolysaccharide (LPS) molecules, extracellular polysaccharides (EPSs) forming biofilm matrix, and peptidoglycan (PG) layers. For that purpose, bacteriophages are equipped with various virion-associated carbohydrate active enzymes, termed polysaccharide depolymerases and lysins, that recognize, bind, and degrade the polysaccharide compounds. We discuss the existing diversity in structural locations, variable architectures, enzymatic specificities, and evolutionary aspects of polysaccharide depolymerases and virion-associated lysins (VALs) and illustrate how these aspects can correlate with the host spectrum. In addition, we present methods that can be used for activity determination and the application potential of these enzymes as antibacterials, antivirulence agents, and diagnostic tools.

Observation of H displacement and H2 elimination channels in the reaction of O(3P) with 1-butene from crossed beams and theoretical studies

NASA Astrophysics Data System (ADS)

Caracciolo, Adriana; Vanuzzo, Gianmarco; Balucani, Nadia; Stranges, Domenico; Cavallotti, Carlo; Casavecchia, Piergiorgio

2017-09-01

We report preliminary combined experimental/theoretical results on O(3P) + 1-butene reaction dynamics with focus on atomic hydrogen displacement and molecular hydrogen elimination channels. Dynamics and relative yield of the ethylvinoxy + H and ethylketene + H2 product channels are characterized in crossed beam experiments. Stationary points and energetics of triplet/singlet C4H8O potential energy surfaces (PESs) are calculated at CCSD(T)/CBS and CASPT2 level. O(3P) attack occurs on both unsaturated C-atoms with preference for the less substituted one leading, among other products, to C2H5CHCHO + H via an exit barrier on the triplet PES, and to C2H5CHCO + H2 via a very high exit barrier on the singlet PES following intersystem crossing.

Post-annealing-free, room temperature processed nanocrystalline indium tin oxide thin films for plastic electronics

NASA Astrophysics Data System (ADS)

Nyoung Jang, Jin; Jong Lee, You; Jang, YunSung; Yun, JangWon; Yi, Seungjun; Hong, MunPyo

2016-06-01

In this study, we confirm that bombardment by high energy negative oxygen ions (NOIs) is the key origin of electro-optical property degradations in indium tin oxide (ITO) thin films formed by conventional plasma sputtering processes. To minimize the bombardment effect of NOIs, which are generated on the surface of the ITO targets and accelerated by the cathode sheath potential on the magnetron sputter gun (MSG), we introduce a magnetic field shielded sputtering (MFSS) system composed of a permanent magnetic array between the MSG and the substrate holder to block the arrival of energetic NOIs. The MFSS processed ITO thin films reveal a novel nanocrystal imbedded polymorphous structure, and present not only superior electro-optical characteristics but also higher gas diffusion barrier properties. To the best of our knowledge, no gas diffusion barrier composed of a single inorganic thin film formed by conventional plasma sputtering processes achieves such a low moisture permeability.

THE STUDY OF HIGH DIELECTRIC CONSTANT MECHANISM OF La-DOPED Ba0.67Sr0.33TiO3 CERAMICS

NASA Astrophysics Data System (ADS)

Xu, Jing; He, Bo; Liu, Han Xing

It is a common and effective method to enhance the dielectric properties of BST ceramics by adding rare-earth elements. In this paper, it is important to analyze the cause of the high dielectric constant behavior of La-doped BST ceramics. The results show that proper rare earth La dopant (0.2≤x≤0.7) may greatly increase the dielectric constant of BST ceramics, and also improve the temperature stability, evidently. According to the current-voltage (J-V) characteristics, the proper La-doped BST ceramics may reach the better semiconductivity, with the decrease and increase in La doping, the ceramics are insulators. By using the Schottky barrier model and electric microstructure model to find the surface or grain boundary potential barrier height, the width of the depletion layer and grain size do play an important role in impacting the dielectric constant.

Metastability of isoformyl ions in collisions with helium and hydrogen. [in interstellar molecular clouds

NASA Technical Reports Server (NTRS)

Green, S.

1984-01-01

The stability of HOC(+) ions under conditions in interstellar molecular clouds is considered. In particular, the possibility that collisions with helium or hydrogen will induce isomerization to the stable HCO(+) form is examined theoretically. Portions of the electronic potential energy surfaces for interaction with He and H atoms are obtained from standard quantum mechanical calculations. Collisions with He atoms are found to be totally ineffective for inducing isomerization. Collisions with H atoms are found to be ineffective at low interstellar temperatures owing to a small (about 500 K) barrier in the entrance channel; at higher temperatures where this barrier can be overcome, however, collisions with hydrogen atoms do result in conversion to the stable HCO(+) form. Although detailed calculations are not presented, it is argued that low-energy collisions with H2 molecules are also ineffective in destroying the metastable ion.

Hydration of AN Acid Anhydride: the Water Complex of Acetic Sulfuric Anhydride

NASA Astrophysics Data System (ADS)

Smith, CJ; Huff, Anna; Mackenzie, Becca; Leopold, Ken

2017-06-01

The water complex of acetic sulfuric anhydride (ASA, CH_{3}COOSO_{2}OH) has been observed by pulsed nozzle Fourier transform microwave spectroscopy. ASA is formed in situ in the supersonic jet via the reaction of SO_{3} and acetic acid and subsequently forms a complex with water during the expansion. Spectra of the parent and fully deuterated form, as well as those of the species derived from CH_{3}^{13}COOH, have been observed. The fitted internal rotation barrier of the methyl group is 219.599(21), \\wn indicating the complexation with water lowers the internal rotation barrier of the methyl group by 9% relative to that of free ASA. The observed species is one of several isomers identified theoretically in which the water inserts into the intramolecular hydrogen bond of the ASA. Aspects of the intermolecular potential energy surface are discussed.

Enhancing antimicrobial activity of TiO2/Ti by torularhodin bioinspired surface modification.

PubMed

Ungureanu, Camelia; Dumitriu, Cristina; Popescu, Simona; Enculescu, Monica; Tofan, Vlad; Popescu, Marian; Pirvu, Cristian

2016-02-01

Implant-associated infections are a major cause of morbidity and mortality. This study was performed using titanium samples coated by anodization with a titanium dioxide (TiO2) shielded nanotube layer. TiO2/Ti surface was modified by simple immersion in torularhodin solution and by using a mussel-inspired method based on polydopamine as bio adhesive for torularhodin immobilization. SEM analysis revealed tubular microstructures of torularhodin and the PDA ability to function as a catchy anchor between torularhodin and TiO2 surface. Corrosion resistance was associated with TiO2 barrier oxide layer and nano-organized oxide layer and the torularhodin surface modification does not bring significant changes in resistance of the oxide layer. Our results demonstrated that the torularhodin modified TiO2/Ti surface could effectively prevent adhesion and proliferation of Escherichia coli, Staphylococcus aureus, Enterococcus faecalis, Bacillus subtilis, and Pseudomonas aeruginosa. The new modified titanium surface showed good biocompatibility and well-behaved haemocompatibility. This biomaterial with enhanced antimicrobial activity holds great potential for future biomedical applications. Copyright © 2015 Elsevier B.V. All rights reserved.

Resonant tunneling of spin-wave packets via quantized states in potential wells.

PubMed

Hansen, Ulf-Hendrik; Gatzen, Marius; Demidov, Vladislav E; Demokritov, Sergej O

2007-09-21

We have studied the tunneling of spin-wave pulses through a system of two closely situated potential barriers. The barriers represent two areas of inhomogeneity of the static magnetic field, where the existence of spin waves is forbidden. We show that for certain values of the spin-wave frequency corresponding to the quantized spin-wave states existing in the well formed between the barriers, the tunneling has a resonant character. As a result, transmission of spin-wave packets through the double-barrier structure is much more efficient than the sequent tunneling through two single barriers.

Effect of Phosphate on U(VI) Sorption to Montmorillonite: Ternary Complexation and Precipitation Barriers

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

Troyer, Lyndsay D.; Maillot, Fabien; Wang, Zheming

Phosphate addition is a potential treatment method to lower the solubility of U(VI) in soil and groundwater systems by causing U(VI) phosphate precipitation as well as enhancing adsorption. Previous work has shown that iron oxide surfaces may facilitate the nucleation of U(VI) phosphate minerals and, that under weakly acidic conditions, phosphate also enhances U(VI) adsorption to such phases. Like iron oxides, clays are important reactive phases in the subsurface but little is known about the interaction of U(VI) and phosphate with these minerals. The effect of aqueous phosphate on U(VI) binding to Wyoming montmorillonite (SWy-2) in air-equilibrated systems was investigated.more » Equilibrium U(VI) uptake to montmorillonite was determined at pH 4, 6 and 8 at discrete initial phosphate concentrations between 0 and 100 μM. The observed behavior of U(VI) indicates a transition from adsorption to precipitation with increasing total uranium and phosphate concentrations at all pH values. At the highest phosphate concentration examined at each pH value, a barrier to U(VI) phosphate nucleation is observed. At lower concentrations, phosphate has no effect on macroscopic U(VI) adsorption. To assess the mechanisms of U(VI)-phosphate interactions on smectite surfaces, U(VI) speciation was investigated under selected conditions using laser-induced fluorescence spectroscopy (LIFS) and extended X-ray absorption fine-structure (EXAFS) spectroscopy. Samples above the precipitation threshold display EXAFS and LIFS spectral signatures consistent with the autunite family of U(VI) phosphate minerals. However, at lower U(VI) concentrations, changes in LIFS spectra upon phosphate addition suggest that U(VI)-phosphate ternary surface complexes form on the montmorillonite surface at pH 4 and 6 despite the lack of a macroscopic effect on adsorption. The speciation of solid-associated U(VI) below the precipitation threshold at pH 8 is dominated by U(VI)-carbonate surface complexes. This work reveals that ternary complexation may occur without a macroscopic signature, which is attributed to phosphate not appreciably binding to smectite in the absence of U(VI), with U(VI) surface complexes serving as the sole reactive surface sites for phosphate. This study shows that phosphate does not enhance U(VI) adsorption to smectite clay minerals, unlike oxide phases, and that a barrier to homogeneous nucleation of U(VI) phosphates was not affected by the presence of the smectite surface« less

Numerical Study for a Large-Volume Droplet on the Dual-Rough Surface: Apparent Contact Angle, Contact Angle Hysteresis, and Transition Barrier.

PubMed

Dong, Jian; Jin, Yanli; Dong, He; Liu, Jiawei; Ye, Senbin

2018-06-26

The profile, apparent contact angle (ACA), contact angle hysteresis (CAH), and wetting state transmission energy barrier (WSTEB) are important static and dynamic properties of a large-volume droplet on the hierarchical surface. Understanding them can provide us with important insights into functional surfaces and promote the application in corresponding areas. In this paper, we establish three theoretical models (models 1-3) and the corresponding numerical methods, which were obtained by the free energy minimization and the nonlinear optimization algorithm, to predict the profile, ACA, CAH, and WSTEB of a large-volume droplet on the horizontal regular dual-rough surface. In consideration of the gravity, the energy barrier on the contact circle, the dual heterogeneous structures and their roughness on the surface, the models are more universal and accurate than the previous models. It showed that the predictions of the models were in good agreement with the results from the experiment or literature. The models are promising to become novel design approaches of functional surfaces, which are frequently applied in microfluidic chips, water self-catchment system, and dropwise condensation heat transfer system.

Quantum scattering in one-dimensional systems satisfying the minimal length uncertainty relation

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

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

In quantum gravity theories, when the scattering energy is comparable to the Planck energy the Heisenberg uncertainty principle breaks down and is replaced by the minimal length uncertainty relation. In this paper, the consequences of the minimal length uncertainty relation on one-dimensional quantum scattering are studied using an approach involving a recently proposed second-order differential equation. An exact analytical expression for the tunneling probability through a locally-periodic rectangular potential barrier system is obtained. Results show that the existence of a non-zero minimal length uncertainty tends to shift the resonant tunneling energies to the positive direction. Scattering through a locally-periodic potentialmore » composed of double-rectangular potential barriers shows that the first band of resonant tunneling energies widens for minimal length cases when the double-rectangular potential barrier is symmetric but narrows down when the double-rectangular potential barrier is asymmetric. A numerical solution which exploits the use of Wronskians is used to calculate the transmission probabilities through the Pöschl–Teller well, Gaussian barrier, and double-Gaussian barrier. Results show that the probability of passage through the Pöschl–Teller well and Gaussian barrier is smaller in the minimal length cases compared to the non-minimal length case. For the double-Gaussian barrier, the probability of passage for energies that are more positive than the resonant tunneling energy is larger in the minimal length cases compared to the non-minimal length case. The approach is exact and applicable to many types of scattering potential.« less

Method of manufacturing lightweight thermo-barrier material

NASA Technical Reports Server (NTRS)

Blair, Winford (Inventor)

1987-01-01

A method of manufacturing thermal barrier structures comprising at least three dimpled cores separated by flat plate material with the outer surface of the flat plate material joined together by diffusion bonding.

Probing equilibrium of molecular and deprotonated water on TiO 2 (110)

DOE PAGES

Wang, Zhi-Tao; Wang, Yang-Gang; Mu, Rentao; ...

2017-02-06

Understanding water structure and its deprotonation dynamics on oxide surfaces is key to understanding many physical and chemical processes. In this study, we directly measure the energy barriers associated with the protonation equilibrium of water on the prototypical oxide surface, rutile-TiO2(110) by a combination of a supersonic molecular beam, scanning tunneling microscopy, and ab initio molecular dynamics simulations. We show that long-range electrostatic fields emanating from the oxide lead to steering and reorientation of the molecules approaching the surface, activating the O-H bonds and inducing deprotonation. The incident energy dependent studies allow for a direct determination of the dissociation barrier.more » Temperature dependent imaging yields the reverse barrier and the equilibrium constant. Molecularly bound water is preferred by 0.035 eV over the surface-bound hydroxyls. The techniques developed in this work are readily extended to other systems where the understanding of bond-activation processes is critical.« less

A DFT study of ethanol adsorption and decomposition on α-Al2O3(0 0 0 1) surface

NASA Astrophysics Data System (ADS)

Chiang, Hsin-Ni; Nachimuthu, Santhanamoorthi; Cheng, Ya-Chin; Damayanti, Nur Pradani; Jiang, Jyh-Chiang

2016-02-01

Ethanol adsorption and decomposition on the clean α-Al2O3(0 0 0 1) surface have been systematically investigated by density functional theory calculations. The nature of the surface-ethanol bonding has studied through the density of states (DOS) and the electron density difference (EDD) contour plots. The DOS patterns confirm that the lone pair electrons of EtOH are involved in the formation of a surface Alsbnd O dative bond and the EDD plots provide evidences for the bond weakening/forming, which are consistent with the DOS analysis. Our ethanol decomposition results indicate that ethanol dehydration to ethylene (CH3CH2OH(a) → C2H4(g) + OH(a) + H(a)), is the main reaction pathway with the energy barrier of 1.46 eV. Although the cleavage of the hydroxyl group of ethanol has lower energy barrier, the further decomposition of ethoxy owns much higher energy barrier.

Development and photoelectric properties of In/p-Ag{sub 3}AsS{sub 3} surface-barrier structures

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

Rud', V. Yu., E-mail: rudvas@spbstu.ru; Rud', Yu. V.; Terukov, E. I.

2010-08-15

Homogeneous p-Ag{sub 3}AsS{sub 3} bulk single crystals with rhombic structure have been grown by planar crystallization from melts with atomic composition corresponding to this ternary compound. Photosensitive surface-barrier structures based on the interface between the surface of these crystals and thin films of pure indium are fabricated for the first time. The photosensitivity of fabricated structures is studied in natural and linearly polarized light. Photosensitivity spectra of In/p-Ag{sub 3}AsS{sub 3} structures are measured for the first time and used to determine the nature and energy of interband transitions in p-Ag{sub 3}AsS{sub 3} crystals. The phenomenon of natural photopleochroism is studiedmore » for surface-barrier structures grown on oriented p-Ag{sub 3}AsS{sub 3} single crystals. It is concluded that Ag{sub 3}AsS{sub 3} single crystals can be used in photoconverters of natural and linearly polarized light.« less

Wetting transition on patterned surfaces: transition states and energy barriers.

PubMed

Ren, Weiqing

2014-03-18

We study the wetting transition on microstructured hydrophobic surfaces. We use the string method [J. Chem. Phys. 2007, 126, 164103; J. Chem. Phys. 2013, 138, 134105] to accurately compute the transition states, the energy barriers, and the minimum energy paths for the wetting transition from the Cassie-Baxter state to the Wenzel state. Numerical results are obtained for the wetting of a hydrophobic surface textured with a square lattice of pillars. It is found that the wetting of the solid substrate occurs via infiltration of the liquid in a single groove, followed by lateral propagation of the liquid front. The propagation of the liquid front proceeds in a stepwise manner, and a zipping mechanism is observed during the infiltration of each layer. The minimum energy path for the wetting transition goes through a sequence of intermediate metastable states, whose wetted areas reflect the microstructure of the patterned surface. We also study the dependence of the energy barrier on the drop size and the gap between the pillars.

Strongly reduced Ehrlich-Schwoebel barriers at the Cu (111) stepped surface with In and Pb surfactants

NASA Astrophysics Data System (ADS)

Hao, Jialei; Zhang, Lixin

2018-01-01

A surfactant can modify the properties of the surface and induce different mode of epitaxy growth. The atomistic mechanism is not fully understood yet. In this first-principles study, taking Cu homoepitaxy along (111) direction as an example, we show that the distribution of the surfactant atoms on the surface is the key. For In and Pb, they prefer to locate at the step edges and remain isolated. Once the growth is started, the distribution can be further modified by Cu adatoms. The uniquely decorated step edges have much lowered Ehrlich-Schwoebel (ES) barriers than that of the clean edges, thus the two dimensional growth on Cu (111) surface is promoted significantly. On the other hand, for Rh, Ir, and Au, these atoms are not favored at the step edges. The ES barriers can't be affected and these metals are not surfactants. The result is very helpful for searching of the optimal surfactants in metal homoepitaxy.

Probing equilibrium of molecular and deprotonated water on TiO 2(110)

DOE PAGES

Wang, Zhi -Tao; Wang, Yang -Gang; Mu, Rentao; ...

2017-02-06

Understanding water structure and its deprotonation dynamics on oxide surfaces is key to understanding many physical and chemical processes. In this study, we directly measure the energy barriers associated with the protonation equilibrium of water on the prototypical oxide surface, rutile-TiO 2(110) by a combination of a supersonic molecular beam, scanning tunneling microscopy, and ab initio molecular dynamics simulations. We show that long-range electrostatic fields emanating from the oxide lead to steering and reorientation of the molecules approaching the surface, activating the O-H bonds and inducing deprotonation. The incident energy dependent studies allow for a direct determination of the dissociationmore » barrier. Temperature dependent imaging yields the reverse barrier and the equilibrium constant. Molecularly bound water is preferred by 0.035 eV over the surface-bound hydroxyls. In conclusion, the techniques developed in this work are readily extended to other systems where the understanding of bond-activation processes is critical.« less

Containment of a silicone fluid free surface in reduced gravity using barrier coatings

NASA Technical Reports Server (NTRS)

Pline, Alexander D.; Jacobson, Thomas P.

1988-01-01

In support of the Surface Tension Driven Convection Experiment planned for flight aboard the Space Shuttle, tests were conducted under reduced gravity in the 2.2-sec Drop Tower and the 5.0-sec Zero-G facility at the NASA Lewis Research Center. The dynamics of controlling the test fluid, a 10-cSt viscosity silicone fluid in a low gravity environment were investigated using different container designs and barrier coatings. Three container edge designs were tested without a barrier coating; a square edge, a sharp edge with a 45-deg slope, and a sawtooth edge. All three edge designs were successful in containing the fluid below the edge. G-jitter experiments were made in scaled down containers subjected to horizontal accelerations. The data showed that a barrier coating is effective in containing silicone fluid under g-levels up to 10 sup -1 sub g sub 0. In addition, a second barrier coating was found which has similar anti-wetting characteristics and is also more durable.

MOPAC Manual. A General Molecular Orbital Package. Fourth Edition.

DTIC Science & Technology

1987-10-01

RELEASE; DISTRIBUTION UNLIMITED. / -October 1987 / AIR FORCE SYSTEMS COMMAND / UNITED STATES AIR FORCE - ’,~ 7:I~82 A" A a’ FJSRL-TR-87-0006 This document...will result in a difference in H.o.F. of less than 0.1 Kcal/mole. This is only true for fairly rigid systems , e.g. I- formaldehyde and benzene. For... systems with low barriers to rotation or flat potential surfaces, e.g. aniline or water dimer, quite I large H.o.F. errors can result. *Action users can

Integration of air separation membrane and coalescing filter for use on an inlet air system of an engine

DOEpatents

Moncelle, Michael E.

2003-01-01

An intake air separation system suitable for combustion air of an internal combustion engine. An air separation device of the system includes a plurality of fibers, each fiber having a tube with a permeation barrier layer on the outer surface thereof and a coalescing layer on the inner surface thereof, to restrict fluid droplets from contacting the permeation barrier layer.

Effects of surface dielectric barrier discharge on aerodynamic characteristic of train

NASA Astrophysics Data System (ADS)

Dong, Lei; Gao, Guoqiang; Peng, Kaisheng; Wei, Wenfu; Li, Chunmao; Wu, Guangning

2017-07-01

High-speed railway today has become an indispensable means of transportation due to its remarkable advantages, including comfortability, convenience and less pollution. The increase in velocity makes the air drag become the main source of energy consumption, leading to receiving more and more concerns. The surface dielectric barrier discharge has shown some unique characteristics in terms of active airflow control. In this paper, the influences of surface dielectric barrier discharge on the aerodynamic characteristics of a scaled train model have been studied. Aspects of the discharge power consumption, the temperature distribution, the velocity of induced flow and the airflow field around the train model were considered. The applied AC voltage was set in the range of 20 kV to 28 kV, with a fixed frequency of 9 kHz. Results indicated that the discharge power consumption, the maximum temperature and the induced flow velocity increased with increasing applied voltage. Mechanisms of applied voltage influencing these key parameters were discussed from the point of the equivalent circuit. The airflow field around the train model with different applied voltages was observed by the smoke visualization experiment. Finally, the effects of surface dielectric barrier discharge on the train drag reduction with different applied voltages were analyzed.

Mechanism of H adatoms improving the O2 reduction reaction on the Zn-modified anatase TiO2 (101) surface studied by first principles calculation.

PubMed

Liu, Liangliang; Li, Chongyang; Jiang, Man; Li, Xiaodong; Huang, Xiaowei; Wang, Zhu; Jia, Yu

2018-06-05

First principles calculations were performed to cast insight into the mechanism of the improvement of O2 reduction reaction (ORR) activity by Zn and H interstitials on the anatase TiO2 (101) surface. For the Zn-modified anatase TiO2 (101) surface, both surface and subsurface Zn interstitials could contribute to O2 adsorption and dissociation, but the dissociation barriers of O2 molecules are still too high, which limits the ORR activity. After a H adatom is introduced onto the Zn-modified anatase TiO2 (101) surface, the highest energy barriers are greatly reduced compared with those of the Zn-modified surface. Meanwhile, it is observed that the dissociation barriers decrease almost linearly with the increase of the charge difference of adsorption O2 between initial and transition state configurations. Specifically, subsurface Zn and surface H interstitials facilitate O2 dissociation and subsequent oxidation reactions, and further frequency analysis shows that these dissociation processes are frequent even at the room temperature of 300 K. In a word, this work provides a theoretical support to design a high ORR activity catalyst of the TiO2 nanocrystal comparable to precious Pt catalysts.

Liposomes bi-functionalized with phosphatidic acid and an ApoE-derived peptide affect Aβ aggregation features and cross the blood-brain-barrier: implications for therapy of Alzheimer disease.

PubMed

Bana, Laura; Minniti, Stefania; Salvati, Elisa; Sesana, Silvia; Zambelli, Vanessa; Cagnotto, Alfredo; Orlando, Antonina; Cazzaniga, Emanuela; Zwart, Rob; Scheper, Wiep; Masserini, Massimo; Re, Francesca

2014-10-01

Targeting amyloid-β peptide (Aβ) within the brain is a strategy actively sought for therapy of Alzheimer's disease (AD). We investigated the ability of liposomes bi-functionalized with phosphatidic acid and with a modified ApoE-derived peptide (mApoE-PA-LIP) to affect Aβ aggregation/disaggregation features and to cross in vitro and in vivo the blood-brain barrier (BBB). Surface plasmon resonance showed that bi-functionalized liposomes strongly bind Aβ (kD=0.6 μM), while Thioflavin-T and SDS-PAGE/WB assays show that liposomes inhibit peptide aggregation (70% inhibition after 72 h) and trigger the disaggregation of preformed aggregates (60% decrease after 120 h incubation). Moreover, experiments with dually radiolabelled LIP suggest that bi-functionalization enhances the passage of radioactivity across the BBB either in vitro (permeability=2.5×10(-5) cm/min, 5-fold higher with respect to mono-functionalized liposomes) or in vivo in healthy mice. Taken together, our results suggest that mApoE-PA-LIP are valuable nanodevices with a potential applicability in vivo for the treatment of AD. From the clinical editor: Bi-functionalized liposomes with phosphatidic acid and a modified ApoE-derived peptide were demonstrated to influence Aβ aggregation/disaggregation as a potential treatment in an Alzheimer's model. The liposomes were able to cross the blood-brain barrier in vitro and in vivo. Similar liposomes may become clinically valuable nanodevices with a potential applicability for the treatment of Alzheimer's disease. Copyright © 2014 Elsevier Inc. All rights reserved.

Surfactants, not size or zeta-potential influence blood-brain barrier passage of polymeric nanoparticles.

PubMed

Voigt, Nadine; Henrich-Noack, Petra; Kockentiedt, Sarah; Hintz, Werner; Tomas, Jürgen; Sabel, Bernhard A

2014-05-01

Nanoparticles (NP) can deliver drugs across the blood-brain barrier (BBB), but little is known which of the factors surfactant, size and zeta-potential are essential for allowing BBB passage. To this end we designed purpose-built fluorescent polybutylcyanoacrylate (PBCA) NP and imaged the NP's passage over the blood-retina barrier - which is a model of the BBB - in live animals. Rats received intravenous injections of fluorescent PBCA-NP fabricated by mini-emulsion polymerisation to obtain various NP's compositions that varied in surfactants (non-ionic, anionic, cationic), size (67-464nm) and zeta-potential. Real-time imaging of retinal blood vessels and retinal tissue was carried out with in vivo confocal neuroimaging (ICON) before, during and after NP's injection. Successful BBB passage with subsequent cellular labelling was achieved if NP were fabricated with non-ionic surfactants or cationic stabilizers but not when anionic compounds were added. NP's size and charge had no influence on BBB passage and cell labelling. This transport was not caused by an unspecific opening of the BBB because control experiments with injections of unlabelled NP and fluorescent dye (to test a "door-opener" effect) did not lead to parenchymal labelling. Thus, neither NP's size nor chemo-electric charge, but particle surface is the key factor determining BBB passage. This result has important implications for NP engineering in medicine: depending on the surfactant, NP can serve one of two opposite functions: while non-ionic tensides enhance brain up-take, addition of anionic tensides prevents it. NP can now be designed to specifically enhance drug delivery to the brain or, alternatively, to prevent brain penetration so to reduce unwanted psychoactive effects of drugs or prevent environmental nanoparticles from entering tissue of the central nervous system. Copyright © 2014 Elsevier B.V. All rights reserved.

The triaxiality and Coriolis effects on the fission barrier in isovolumic nuclei with mass number A = 256 based on multidimensional total Routhian surface calculations

NASA Astrophysics Data System (ADS)

Chai, Qing-Zhen; Zhao, Wei-Juan; Wang, Hua-Lei; Liu, Min-Liang; Xu, Fu-Rong

2018-05-01

The triaxiality and Coriolis effects on the first fission barrier in even-even nuclei with A=256 have been studied in terms of the approach of multidimensional total Routhian surface calculations. The present results are compared with available data and other theories, showing a good agreement. Based on the deformation energy or Routhian curves, the first fission barriers are analyzed, focusing on their shapes, heights, and evolution with rotation. It is found that, relative to the effect on the ground-state minimum, the saddle point, at least the first one, can be strongly affected by the triaxial deformation degree of freedom and Coriolis force. The evolution trends of the macroscopic and microscopic (shell and pairing) contributions as well as the triaxial fission barriers are briefly discussed.

Engineering the Mechanical Properties of Ultrabarrier Films Grown by Atomic Layer Deposition for the Encapsulation of Printed Electronics

DOE PAGES

Bulusu, Anuradha; Singh, Ankit K.; Wang, Cheng-Yin; ...

2015-08-28

Direct deposition of barrier films by atomic layer deposition (ALD) onto printed electronics presents a promising method for packaging devices. Films made by ALD have been shown to possess desired ultrabarrier properties, but face challenges when directly grown onto surfaces with varying composition and topography. Challenges include differing nucleation and growth rates across the surface, stress concentrations from topography and coefficient of thermal expansion (CTE) mismatch, elastic mismatch, and particle contamination that may impact the performance of the ALD barrier. In such cases, a polymer smoothing layer may be needed to coat the surface prior to ALD barrier film deposition.more » We present the impact of architecture on the performance of aluminum oxide (Al2O3)/hafnium oxide (HfO2) ALD nanolaminate barrier films deposited on fluorinated polymer layer using an optical calcium (Ca) test under damp heat. It is found that with increasing polymer thickness, the barrier films with residual tensile stress are prone to cracking resulting in rapid failure of the Ca sensor at 50{degree sign}C/85% RH. Inserting a SiNx layer with residual compressive stress between the polymer and ALD layers is found to prevent cracking over a range of polymer thicknesses with more than 95% of the Ca sensor remaining after 500 h of testing. These results suggest that controlling mechanical properties and film architecture play an important role in the performance of direct deposited ALD barriers.« less

Experimental visualization of the cathode layer in AC surface dielectric barrier discharge

NASA Astrophysics Data System (ADS)

Kim, Sang-You; Lho, Taihyeop; Chung, Kyu-Sun

2018-06-01

A narrow etched polyimide line at the bottom edge of a biased electrode (BE) and a non-etched dielectric surface near the biased electrode were observed in an atmospheric AC flexible surface dielectric barrier discharge of polyimide dielectric. These findings are attributed to the bombardment of positive oxygen ions on the bottom edge of the BE and the electron breakdown trajectory not contacting the polyimide surface following the electric field lines formed between the BE edge and the surface charge layer on the dielectric. The length of the non-etched dielectric surface during the first micro-discharge was observed as 22 μm. This occurred, regardless of three different operating durations, which is in good agreement with the length of the cathode layer according to Paschen's law.

Treatment of poly(ethylene terephthalate) foils by atmospheric pressure air dielectric barrier discharge and its influence on cell growth

NASA Astrophysics Data System (ADS)

Kuzminova, Anna; Vandrovcová, Marta; Shelemin, Artem; Kylián, Ondřej; Choukourov, Andrei; Hanuš, Jan; Bačáková, Lucie; Slavínská, Danka; Biederman, Hynek

2015-12-01

In this contribution an effect of dielectric barrier discharge (DBD) sustained in air at atmospheric pressure on surface properties of poly(ethylene terephthalate) (PET) foils is studied. It is found that exposure of PET to DBD plasma leads to rapid changes of surface chemical composition, wettability, surface morphology as well as mechanical properties of PET surface. In addition, based on biological tests that were performed using two cell types (Saos-2 human osteoblast-like cells and HUVEC human umbilical vein endothelial cells), it may be concluded that DBD plasma treatment positively influences cell growth on PET. This effect was found to be connected predominantly with increased surface energy and oxygen content of the surface of treated PET foils.

Shoreline Evolution and Coastal Resiliency at Two Military Installations: Investigating the Potential for and Impacts of Loss of Protecting Barriers

DTIC Science & Technology

2014-05-01

control barrier morphology and migration (and potentially drowning). We have developed a numerical model of barrier evolution over the centennial ...required to maintain barrier geometries over centennial timescales. Long-term storm histories for each region show a consistent picture of...landward of the flood tidal delta is an area of over 40km2 that is over 9m deep, with some depressions as deep as 12m. During periods of rising sea-level

Universal potential-barrier penetration by initially confined wave packets

NASA Astrophysics Data System (ADS)

Granot, Er'El; Marchewka, Avi

2007-07-01

The dynamics of an initially sharp-boundary wave packet in the presence of an arbitrary potential barrier is investigated. It is shown that the penetration through the barrier is universal in the sense that it depends only on the values of the wave function and its derivatives at the boundary. The dependence on the derivatives vanishes at long distances from the barrier, where the dynamics is governed solely by the initial value of the wave function at the boundary.

Interaction of tetraethoxysilane with OH-terminated SiO2 (0 0 1) surface: A first principles study

NASA Astrophysics Data System (ADS)

Deng, Xiaodi; Song, Yixu; Li, Jinchun; Pu, Yikang

2014-06-01

First principles calculates have been performed to investigate the surface reaction mechanism of tetraethoxysilane (TEOS) with fully hydroxylated SiO2(0 0 1) substrate. In semiconductor industry, this is the key step to understand and control the SiO2 film growth in chemical vapor deposition (CVD) and atomic layer deposition (ALD) processes. During the calculation, we proposed a model which breaks the surface dissociative chemisorption into two steps and we calculated the activation barriers and thermochemical energies for each step. Our calculation result for step one shows that the first half reaction is thermodynamically favorable. For the second half reaction, we systematically studied the two potential reaction pathways. The comparing result indicates that the pathway which is more energetically favorable will lead to formation of crystalline SiO2 films while the other will lead to formation of disordered SiO2 films.

Observation and measurement of negative differential resistance on PtSi Schottky junctions on porous silicon.

PubMed

Banihashemian, Seyedeh Maryam; Hajghassem, Hassan; Erfanian, Alireza; Aliahmadi, Majidreza; Mohtashamifar, Mansor; Mosakazemi, Seyed Mohamadhosein

2010-01-01

Nanosize porous Si is made by two step controlled etching of Si. The first etching step is carried on the Si surface and the second is performed after deposition of 75 Å of platinum on the formed surface. A platinum silicide structure with a size of less than 25 nm is formed on the porous Si surface, as measured with an Atomic Forced Microscope (AFM). Differential resistance curve as a function of voltage in 77 K and 100 K shows a negative differential resistance and indicates the effect of quantum tunneling. In general form, the ratio of maximum to minimum tunneling current (PVR) and the number of peaks in I-V curves reduces by increasing the temperature. However, due to accumulation of carriers behind the potential barrier and superposition of several peaks, it is observed that the PVR increases at 100 K and the maximum PVR at 100 K is 189.6.

Fabricating Ohmic contact on Nb-doped SrTiO{sub 3} surface in nanoscale

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

Wang, Yuhang; National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, Chinese Academy of Engineering Physics, Mianyang, Sichuan 621999; Shi, Xiaolan

2016-05-09

Fabricating reliable nano-Ohmic contact on wide gap semiconductors is an important yet difficult step in oxide nanoelectronics. We fabricated Ohmic contact on the n-type wide gap oxide Nb-doped SrTiO{sub 3} in nanoscale by mechanically scratching the surface using an atomic force microscopy tip. Although contacted to high work function metal, the scratched area exhibits nearly linear IV behavior with low contact resistance, which maintains for hours in vacuum. In contrast, the unscratched area shows Fowler–Nordheim tunneling dominated Schottky rectifying behavior with high contact resistance. It was found that the Ohmic conductivity in the scratched area was drastically suppressed by oxygenmore » gas indicating the oxygen vacancy origin of the Ohmic behavior. The surface oxygen vacancy induced barrier width reduction was proposed to explain the phenomena. The nanoscale approach is also applicable to macroscopic devices and has potential application in all-oxide devices.« less

[ACTIVITY OF ANTIMICROBIAL NANOSTRUCTURED BARRIER LAYERS BASED ON POLYETHYLENETEREPHTHALATE IN RELATION TO CLINICAL STRAINES OF MICROORGANISMS FOR SICK PERSONS OF GASTROENTEROLOGICAL PROFILE].

PubMed

Elinson, V M; Rusanova, E V; Vasilenko, I A; Lyamin, A N; Kostyuchenko, L N

2015-01-01

Homeostasis transgressions of enteral medium including disbiotic ones are often accompanying deseases of digestive tract. Espessially it touches upon sick persons connected with probe nourishing. One of the way for solving this problem is normalization of digestion microflore by means of wares with nanotechnological modifications of walls (probes, stomic tubes) which provide them antimicrobial properties and assist to normalization of digestive microbiotis and enteral homeostasis completely. The aim to study is research of antimicrobial activity of of nanostructured barrier layers based on polyethyleneterephthalate (PET) in relation to clinical straines of microorganisms. For barrier layer creation the approach on the base of methods of ion-plasma technology was used including ion-plasma treatment (nanostructuring) of the surface by ions noble and chemically active gases and following formation nanodimensional carbon films on the surface/ For the study of antimicrobial activity in relation to clinical straines of microorganisms we used the technique which allowed to establish the influence of parting degree of microorganisms suspension and time for samples exposing and microorganisms adsorbed on the surface. In experiment clinical straines obtained from different materials were used: Staphylococcus Hly+ and Calbicans--from pharyngeal mucosa, E. coli--from feces, K.pneumoniae--from urine. Sharing out and species identification of microorganisms were fulfilled according with legasy documents. In results of the study itwas obtained not only the presence of staticticaly confirmed antimicrobial activity of PET samples with nanostructured barrier layers in relation to different stimulators of nosocomical infections but also the influence of different factors connected with formation of nanostructured layers and consequently based with them physicochemical characteristics such as, in particular, surface energy, surface relief parameters, surface charg and others, as well as influence of microorganisms nature onto the interaction of between barrier layers and microorganisms.

Tunnelling anomalous and planar Hall effects (Conference Presentation)

NASA Astrophysics Data System (ADS)

Matos-Abiague, Alex; Scharf, Benedikt; Han, Jong E.; Hankiewicz, Ewelina M.; Zutic, Igor

2016-10-01

We theoretically show how the interplay between spin-orbit coupling (SOC) and magnetism can result in a finite tunneling Hall conductance, transverse to the applied bias. For two-dimensional tunnel junctions with a ferromagnetic lead and magnetization perpendicular to the current flow, the detected anomalous Hall voltage can be used to extract information not only about the spin polarization but also about the strength of the interfacial SOC. In contrast, a tunneling current across a ferromagnetic barrier on the surface of a three-dimensional topological insulator (TI) can induce a planar Hall response even when the magnetization is oriented along the current flow[1]. The tunneling nature of the states contributing to the planar Hall conductance can be switched from the ordinary to the Klein regimes by the electrostatic control of the barrier strength. This allows for an enhancement of the transverse response and a giant Hall angle, with the tunneling planar Hall conductance exceeding the longitudinal component. Despite the simplicity of a single ferromagnetic region, the TI/ferromagnet system exhibits a variety of functionalities. In addition to a spin-valve operation for magnetic sensing and storing information, positive, negative, and negative differential conductances can be tuned by properly adjusting the barrier potential and/or varying the magnetization direction. Such different resistive behaviors in the same system are attractive for potential applications in reconfigurable spintronic devices. [1] B. Scharf, A. Matos-Abiague, J. E. Han, E. M. Hankiewicz, and I. Zutic, arXiv:1601.01009 (2016).

Barrier Island Failure During Hurricane Katrina

NASA Astrophysics Data System (ADS)

Sallenger, A.; Howd, P.; Stockdon, H.; Wright, C. W.; Fauver, L.; Guy, K.

2006-12-01

Classical models of barrier-island response to storms predict that wave runup can periodically overtop an island and transport sand from its seaside to its bayside, forcing the island to migrate landward. While this process can destroy fixed human developments, the island survives with little net change in form or dimensions. In contrast, we find that Louisiana's Chandeleur Islands during Hurricane Katrina were not periodically overtopped by waves, but were continuously inundated by storm surge. When such inundation occurs locally on a barrier island, it can force the erosion of a narrow breach that connects sea and bay. However, little is known about the response of a barrier island when it is entirely submerged. Here, we show that the Chandeleur Islands approached complete failure, losing 84% of their surface area. Their Gulf of Mexico shorelines retreated landward an average of 268 m, the largest retreat ever reported for a storm. Sand was stripped from the islands, reducing their peak elevation from >6 m to <3 m and exposing them to further degradation and potential failure by future hurricanes of less intensity than Katrina. Further, the islands that survived Katrina were marsh remnants composed of mud and vegetation that relatively small waves diminished following the storm. The Chandeleur Islands are prone to failure because of their location on the Mississippi delta where small sand supply and large sea-level rise (induced locally by land subsidence) limit natural rebuilding of the islands following a storm. The response of the delta's barrier islands during Hurricane Katrina provides a warning of how the world's barrier islands might respond to storm-surge inundation should predictions of accelerated global sea level rise prove accurate.

Mechanism for degradation of Nafion in PEM fuel cells from quantum mechanics calculations.

PubMed

Yu, Ted H; Sha, Yao; Liu, Wei-Guang; Merinov, Boris V; Shirvanian, Pezhman; Goddard, William A

2011-12-14

We report results of quantum mechanics (QM) mechanistic studies of Nafion membrane degradation in a polymer electrolyte membrane (PEM) fuel cell. Experiments suggest that Nafion degradation is caused by generation of trace radical species (such as OH(●), H(●)) only when in the presence of H(2), O(2), and Pt. We use density functional theory (DFT) to construct the potential energy surfaces for various plausible reactions involving intermediates that might be formed when Nafion is exposed to H(2) (or H(+)) and O(2) in the presence of the Pt catalyst. We find a barrier of 0.53 eV for OH radical formation from HOOH chemisorbed on Pt(111) and of 0.76 eV from chemisorbed OOH(ad), suggesting that OH might be present during the ORR, particularly when the fuel cell is turned on and off. Based on the QM, we propose two chemical mechanisms for OH radical attack on the Nafion polymer: (1) OH attack on the S-C bond to form H(2)SO(4) plus a carbon radical (barrier: 0.96 eV) followed by decomposition of the carbon radical to form an epoxide (barrier: 1.40 eV). (2) OH attack on H(2) crossover gas to form hydrogen radical (barrier: 0.04 eV), which subsequently attacks a C-F bond to form HF plus carbon radicals (barrier as low as 1.00 eV). This carbon radical can then decompose to form a ketone plus a carbon radical with a barrier of 0.86 eV. The products (HF, OCF(2), SCF(2)) of these proposed mechanisms have all been observed by F NMR in the fuel cell exit gases along with the decrease in pH expected from our mechanism. © 2011 American Chemical Society

Potential use of polymeric nanoparticles for drug delivery across the blood-brain barrier.

PubMed

Tosi, G; Bortot, B; Ruozi, B; Dolcetta, D; Vandelli, M A; Forni, F; Severini, G M

2013-01-01

Nanomedicine is certainly one of the scientific and technological challenges of the coming years. In particular, biodegradable nanoparticles formulated from poly (D,L-lactide-co-glycolide) (PLGA) have been extensively investigated for sustained and targeted delivery of different agents, including recombinant proteins, plasmid DNA, and low molecular weight compounds. PLGA NPs present some very attractive properties such as biodegradability and biocompatibility, protection of drug from degradation, possibility of sustained release, and the possibility to modify surface properties to target nanoparticles to specific organs or cells. Moreover, PLGA NPs have received the FDA and European Medicine Agency approval in drug delivery systems for parenteral administration, thus reducing the time for human clinical applications. This review in particular deals on surface modification of PLGA NPs and their possibility of clinical applications, including treatment for brain pathologies such as brain tumors and Lysosomal Storage Disorders with neurological involvement. Since a great number of pharmacologically active molecules are not able to cross the Blood-Brain Barrier (BBB) and reach the Central Nervous System (CNS), new brain targeted polymeric PLGA NPs modified with glycopeptides (g7- NPs) have been recently produced. In this review several in vivo biodistribution studies and pharmacological proof-of evidence of brain delivery of model drugs are reported, demonstrating the ability of g7-NPs to create BBB interaction and trigger an efficacious BBB crossing. Moreover, another relevant development of NPs surface engineering was achieved by conjugating to the surface of g7-NPs, some specific and selective antibodies to drive NPs directly to a specific cell type once inside the CNS parenchyma.

Effect of the δ-potential on spin-dependent electron tunneling in double barrier semiconductor heterostructure

NASA Astrophysics Data System (ADS)

Chandrasekar, L. Bruno; Gnanasekar, K.; Karunakaran, M.

2018-06-01

The effect of δ-potential was studied in GaAs/Ga0.6Al0·4As double barrier heterostructure with Dresselhaus spin-orbit interaction. The role of barrier height and position of the δ- potential in the well region was analysed on spin-dependent electron tunneling using transfer matrix method. The spin-separation between spin-resonances on energy scale depends on both height and position of the δ- potential, whereas the tunneling life time of electrons highly influenced by the position of the δ- potential and not on the height. These results might be helpful for the fabrication of spin-filters.

Dehydrogenation of benzene on Pt(111) surface

NASA Astrophysics Data System (ADS)

Gao, W.; Zheng, W. T.; Jiang, Q.

2008-10-01

The dehydrogenation of benzene on Pt(111) surface is studied by ab initio density functional theory. The minimum energy pathways for benzene dehydrogenation are found with the nudge elastic band method including several factors of the associated barriers, reactive energies, intermediates, and transient states. The results show that there are two possible parallel minimum energy pathways on the Pt(111) surface. Moreover, the tilting angle of the H atom in benzene can be taken as an index for the actual barrier of dehydrogenation. In addition, the properties of dehydrogenation radicals on the Pt(111) surface are explored through their adsorption energy, adsorption geometry, and electronic structure on the surface. The vibrational frequencies of the dehydrogenation radicals derived from the calculations are in agreement with literature data.

Dehydrogenation of benzene on Pt(111) surface.

PubMed

Gao, W; Zheng, W T; Jiang, Q

2008-10-28

The dehydrogenation of benzene on Pt(111) surface is studied by ab initio density functional theory. The minimum energy pathways for benzene dehydrogenation are found with the nudge elastic band method including several factors of the associated barriers, reactive energies, intermediates, and transient states. The results show that there are two possible parallel minimum energy pathways on the Pt(111) surface. Moreover, the tilting angle of the H atom in benzene can be taken as an index for the actual barrier of dehydrogenation. In addition, the properties of dehydrogenation radicals on the Pt(111) surface are explored through their adsorption energy, adsorption geometry, and electronic structure on the surface. The vibrational frequencies of the dehydrogenation radicals derived from the calculations are in agreement with literature data.

Generalized stacking fault energies of alloys.

PubMed

Li, Wei; Lu, Song; Hu, Qing-Miao; Kwon, Se Kyun; Johansson, Börje; Vitos, Levente

2014-07-02

The generalized stacking fault energy (γ surface) provides fundamental physics for understanding the plastic deformation mechanisms. Using the ab initio exact muffin-tin orbitals method in combination with the coherent potential approximation, we calculate the γ surface for the disordered Cu-Al, Cu-Zn, Cu-Ga, Cu-Ni, Pd-Ag and Pd-Au alloys. Studying the effect of segregation of the solute to the stacking fault planes shows that only the local chemical composition affects the γ surface. The calculated alloying trends are discussed using the electronic band structure of the base and distorted alloys.Based on our γ surface results, we demonstrate that the previous revealed 'universal scaling law' between the intrinsic energy barriers (IEBs) is well obeyed in random solid solutions. This greatly simplifies the calculations of the twinning measure parameters or the critical twinning stress. Adopting two twinnability measure parameters derived from the IEBs, we find that in binary Cu alloys, Al, Zn and Ga increase the twinnability, while Ni decreases it. Aluminum and gallium yield similar effects on the twinnability.

Access to Strong Opioid Analgesics in the Context of Legal and Regulatory Barriers in Eleven Central and Eastern European Countries.

PubMed

Vranken, Marjolein J M; Mantel-Teeuwisse, Aukje K; Schutjens, Marie-Hélène D B; Scholten, Willem K; Jünger, Saskia; Medic, Dr Rer; Leufkens, Hubert G M

2018-04-06

In 2011-2013, >95% of the global opioid analgesics consumption occurred in three regions, accounting for 15% of the world population. Despite abundant literature on barriers to access, little is known on the correlation between actual access to opioid analgesics and barriers to access, including legal and regulatory barriers. This study aimed to evaluate the correlation between access to strong opioid analgesics and barriers to access in national legislation and regulations in 11 central and eastern European countries that participated in the Access to Opioid Medication in Europe (ATOME) project. Two variables were contrasted to assess their correlation: the country level of access to strong opioid analgesics indicated by the Adequacy of Consumption Measure (ACM) and the number of potential legal and regulatory barriers identified by an external review of legislation and regulations. A linear correlation was evaluated using a squared linear correlation coefficient. Evaluation of the correlation between the ACM and the number of potential barriers produces an R 2 value of 0.023 and a correlation plot trend line gradient of -0.075, indicating no correlation between access to strong opioid analgesics and the number of potential barriers in national legislation and regulations in the countries studied. No correlation was found, which indicates that other factors besides potential legal and regulatory barriers play a critical role in withholding prescribers and patients essential pain medication in the studied countries. More research is needed toward better understanding of the complex interplay of factors that determine access to strong opioid analgesics.

Reappraisal of the sequence boundary in time and space: Case and considerations for an SU (subaerial unconformity) that is not a sediment bypass surface, a time barrier, or an unconformity

NASA Astrophysics Data System (ADS)

Holbrook, John M.; Bhattacharya, Janok P.

2012-07-01

The sequence-bounding unconformity bears the key defining traits of being "a surface separating younger from older strata, along which there is evidence of subaerial erosional truncation … or subaerial exposure, with a significant hiatus indicated (Van Wagoner et al., 1988)." This subaerial component of sequence boundaries (subaerial unconformity—SU) is also broadly considered to form as a topographic surface of sediment bypass, carved during relative sea level fall and buried by backfilling during relative sea level rise. Accordingly, the SU is commonly presumed to record an approximate time barrier, which separates older from younger strata along its full length. In this paper we show that regional composite scour (RCS) surfaces that are traditionally mapped as an integral component of the SU were never a single subaerial topographic surface characterized by sediment bypass, are not unconformities, do not record an effective time barrier, and form diachronously at the channel-belt scale over the entire fall to rise of a base-level cycle. These RCS surfaces, and by inference the SU surfaces they comprise, thus do not fully fit key defining characteristics embodied in the conceptual sequence boundary. Flume observations and field data show that the RCS is buried by fluvial sediment simultaneously as it is scoured. Accordingly, the RCS is perennially covered with stored sediment during formation, is only exposed as a subaerial topographic surface at the local place and time where it is undergoing active growth, and forms over the duration of local marine drainage during a relative sea-level cycle. This "cut-and-cover" model differs greatly from more established "bypass" models, which assume that the RCS was roughly sediment free and subaerially exposed for long durations of incision during regression and thus preserves a significant depositional hiatus upon later burial. Instead, the RCS may commonly and locally record a hiatus more typical of a facies-bounding diastem without a lacuna significantly greater than that of surfaces within the strata it binds. Fragments of fluvial strata may commonly and sporadically be preserved above the RCS that are older than underlying marine units overrun by this surface. Consequently, the RCS is not an effective time barrier. Lateral planation by migrating and avulsing channels as the RCS expands laterally after nucleation can place younger fluvial strata over much older units, which means that this surface is also composite and highly diachronous laterally at the scale of channel belts. The cut-and-cover model has additional implications not captured by the bypass model. First, significant sediments may be stored within fluvial strata above the RCS during regression that are not available for contemporary falling stage and lowstand marine shorelines. This can result in marine sediment starvation, particularly of the sand fraction, and in extreme cases can result in sand autodetachment and an absence of regressive marine reservoir sandstones. Second, cutting of the RCS co-generates a suprafluvial surface above the covering fluvial strata during regression that may be used as a mappable proxy for the conceptual maximum regressive surface (MRS). The MRS may be raised above this surface locally by low-accommodation aggradation during lowstand normal regression, but in either case preserves an approximate time line where not reworked during later transgression. Third, valley development across the RCS does not exclusively form by landward knickpoint growth, and may include complexly formed and potentially cross-cutting buffer valleys. SU valley incision can be divided into four modes, which include denudation, structural, buttress, and buffer valley components, which may work together locally and tend to have variable importance along the shore-to-hinterland profile. Although the RCS is not a good rock proxy for the conceptual sequence boundary it remains a very mappable surface which may separate facies of potentially very different origin and reservoir quality. The RCS is also inseparable from the SU and typically the only terrestrial erosional surface of extent in most short-duration sequences. Its nullification as a sequence boundary would mean abandonment of depositional sequence stratigraphy as a correlation and interpretive tool within these sections. An alternative to abandonment of the SU as a sequence boundary is to loosen the definition of a sequence boundary to 'a discrete surface of erosional truncation carved landward of contemporary shorelines that is traceable beyond the scale of a single valley or comparable local system, and its correlative surfaces of conformity and/or non-deposition', and continue its use as before.

Molecular structures and intramolecular dynamics of pentahalides

NASA Astrophysics Data System (ADS)

Ischenko, A. A.

2017-03-01

This paper reviews advances of modern gas electron diffraction (GED) method combined with high-resolution spectroscopy and quantum chemical calculations in studies of the impact of intramolecular dynamics in free molecules of pentahalides. Some recently developed approaches to the electron diffraction data interpretation, based on direct incorporation of the adiabatic potential energy surface parameters to the diffraction intensity are described. In this way, complementary data of different experimental and computational methods can be directly combined for solving problems of the molecular structure and its dynamics. The possibility to evaluate some important parameters of the adiabatic potential energy surface - barriers to pseudorotation and saddle point of intermediate configuration from diffraction intensities in solving the inverse GED problem is demonstrated on several examples. With increasing accuracy of the electron diffraction intensities and the development of the theoretical background of electron scattering and data interpretation, it has become possible to investigate complex nuclear dynamics in fluxional systems by the GED method. Results of other research groups are also included in the discussion.