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Sample records for waals potential measurements

  1. Non-additivity of molecule-surface van der Waals potentials from force measurements.

    Science.gov (United States)

    Wagner, Christian; Fournier, Norman; Ruiz, Victor G; Li, Chen; Müllen, Klaus; Rohlfing, Michael; Tkatchenko, Alexandre; Temirov, Ruslan; Tautz, F Stefan

    2014-11-26

    Van der Waals (vdW) forces act ubiquitously in condensed matter. Despite being weak on an atomic level, they substantially influence molecular and biological systems due to their long range and system-size scaling. The difficulty to isolate and measure vdW forces on a single-molecule level causes our present understanding to be strongly theory based. Here we show measurements of the attractive potential between differently sized organic molecules and a metal surface using an atomic force microscope. Our choice of molecules and the large molecule-surface separation cause this attraction to be purely of vdW type. The experiment allows testing the asymptotic vdW force law and its validity range. We find a superlinear growth of the vdW attraction with molecular size, originating from the increased deconfinement of electrons in the molecules. Because such non-additive vdW contributions are not accounted for in most first-principles or empirical calculations, we suggest further development in that direction.

  2. Measurement of van-der-Waals interaction by atom trajectory imaging

    CERN Document Server

    Thaicharoen, N; Raithel, G

    2015-01-01

    We study the repulsive van der Waals interaction of cold rubidium $70S_{1/2}$ Rydberg atoms by analysis of time-delayed pair correlation functions. After excitation, Rydberg atoms are allowed to accelerate under the influence of the van der Waals force. Their positions are then measured using a single-atom imaging technique. From the average pair correlation function of the atom positions we obtain the initial atom-pair separation and the terminal velocity, which yield the van der Waals interaction coefficient $C_{6}$. The measured $C_{6}$ value agrees well with calculations. The experimental method has been validated by simulations. The data hint at anisotropy in the overall expansion, caused by the shape of the excitation volume. Our measurement implies that the interacting entities are individual Rydberg atoms, not groups of atoms that coherently share a Rydberg excitation.

  3. Spectroscopic measurement of the titanium-helium van der Waals molecule: TiHe

    Science.gov (United States)

    Quiros, Nancy; Tariq, Naima; Weinstein, Jonathan

    2016-05-01

    Atoms that are weakly bound by the van der Waals (vdW) interaction are known as van der Waals molecules. The existence and formation of vdW molecules is favorable at low temperatures due to their weak binding energy. We have used laser ablation and helium buffer gas cooling to create the exotic vdW diatomic molecule made of titanium (Ti) and helium (He). TiHe molecules were detected through laser-induced-fluorescence spectroscopy closely blue-detuned from the a3F2 --> y3F3 atomic Ti transition at 25227 cm-1. Measurements of the binding energy of TiHe were obtained by studying its equilibrium thermodynamic properties. It is believed the molecules are formed from the constituent cold atoms through three-body recombination. Progress towards measuring the three-body recombination rate coefficient will be discussed. This material is based upon work supported by National Science Foundation under Grant No. PHY 1265905.

  4. Van der Waals potential and vibrational energy levels of the ground state radon dimer

    Science.gov (United States)

    Sheng, Xiaowei; Qian, Shifeng; Hu, Fengfei

    2017-08-01

    In the present paper, the ground state van der Waals potential of the Radon dimer is described by the Tang-Toennies potential model, which requires five essential parameters. Among them, the two dispersion coefficients C6 and C8 are estimated from the well determined dispersion coefficients C6 and C8 of Xe2. C10 is estimated by using the approximation equation that C6C10 / C82 has an average value of 1.221 for all the rare gas dimers. With these estimated dispersion coefficients and the well determined well depth De and Re the Born-Mayer parameters A and b are derived. Then the vibrational energy levels of the ground state radon dimer are calculated. 40 vibrational energy levels are observed in the ground state of Rn2 dimer. The last vibrational energy level is bound by only 0.0012 cm-1.

  5. A self-consistent GW approach to the van der Waals potential for a helium dimer.

    Science.gov (United States)

    Shoji, Toru; Kuwahara, Riichi; Ono, Shota; Ohno, Kaoru

    2016-09-21

    van der Waals interaction between two helium (He) atoms is studied by calculating the total energy as a function of the He-He distance within the self-consistent GW approximation, which is expected to behave correctly in the long wavelength limit. In the Born-Oppenheimer (BO) approximation, the pair potential curve has its minimum value at 2.87 Å, which is somewhat larger than the local density approximation result, 2.40 Å, and is closer to previous quantum chemistry results. The expectation value for the interatomic distance, calculated by solving the Schrödinger equation for the two nuclei problem using the BO potential energy curve, is 30 Å, which is smaller but of the same order as previous experimental and theoretical results.

  6. Direct measurement of the van der Waals interaction between two single atoms

    CERN Document Server

    Béguin, Lucas; Chicireanu, Radu; Lahaye, Thierry; Browaeys, Antoine

    2013-01-01

    We report on the direct measurement of the van der Waals interaction between two isolated, single Rydberg atoms separated by a controlled distance of a few micrometers. By working in a regime where the single-atom Rabi frequency of the laser used for excitation to the Rydberg state is comparable to the interaction energy, we observe a \\emph{partial} Rydberg blockade, whereby the time-dependent populations of the various two-atom states exhibit coherent oscillations with several frequencies. A quantitative comparison of the data with a simple model based on the optical Bloch equations allows us to extract the van der Waals energy, and to observe its characteristic $C_6/R^6$ dependence. The magnitude of the measured $C_6$ coefficient agrees well with an \\emph{ab-initio} theoretical calculation, and we observe its dramatic increase with the principal quantum number $n$ of the Rydberg state. Our results not only allow to test an important physical law, but also demonstrate a degree of experimental control which o...

  7. Two-atom interaction energies with one atom in an excited state: van der Waals potentials versus level shifts

    Science.gov (United States)

    Donaire, M.

    2016-05-01

    I revisit the problem of the interaction between two dissimilar atoms with one atom in an excited state, recently addressed by Berman [Phys. Rev. A 91, 042127 (2015), 10.1103/PhysRevA.91.042127], Donaire et al. [Phys. Rev. Lett. 115, 033201 (2015), 10.1103/PhysRevLett.115.033201], and Milonni and Rafsanjani [Phys. Rev. A 92, 062711 (2015), 10.1103/PhysRevA.92.062711], for which precedent approaches have given conflicting results. In the first place, I discuss to what extent these works provide equivalent results. I show that the phase-shift rate of the two-atom wave function computed by Berman, the van der Waals potential of the excited atom by Donaire et al., and the level shift of the excited atom by Milonni and Rafsanjani possess equivalent expressions in the quasistationary approximation. In addition, I show that the level shift of the ground-state atom computed by Milonni and Rafsanjani is equivalent to its van der Waals potential. A diagrammatic representation of all those quantities is provided. The equivalences among them are, however, not generic. In particular, it is found that for the case of the interaction between two identical atoms excited, the phase-shift rate and the van der Waals potentials differ. Concerning the conflicting results of previous approaches in regards to the spatial oscillation of the interactions, I conclude, in agreement with Berman and with Milonni and Rafsanjani, that they refer to different physical quantities. The impacts of free-space dissipation and finite excitation rates on the dynamics of the potentials are analyzed. In contrast with Milonni and Rafsanjani, the oscillatory versus monotonic spatial forms of the potentials of each atom are found not to be related to the reversible versus irreversible nature of the excitation transfer involved.

  8. Purification of multiwalled carbon nanotubes by annealing and extraction based on the difference in van der Waals potential.

    Science.gov (United States)

    Zhang, Hui; Sun, Cheng H; Li, Feng; Li, Hong X; Cheng, Hui M

    2006-05-18

    The potential energies of van der Waals interactions between two multiwalled carbon nanotubes (MWNTs) as well as two carbon nanoparticles (CNPs) were calculated and compared on the basis of the continuum Lennard-Jones model. The well depth of the potential is 1 order of magnitude higher for MWNTs than for CNPs, indicating that MWNTs and CNPs can be separated from each other through polymer-induced steric stabilization. On the basis of this prediction, a novel method for the purification of MWNTs was proposed. The method involves a high-temperature annealing (2600 degrees C, 1 h) followed by an extraction treatment with a selected dispersing agent. While the annealing process evaporates the metal particles, the extraction treatment removes CNPs. The quality of the nanotubes obtained after purification was examined by laser Raman, thermogravimetric analysis, and electron microscopy observations.

  9. Measuring the thermal boundary resistance of van der Waals contacts using an individual carbon nanotube.

    Science.gov (United States)

    Hirotani, Jun; Ikuta, Tatsuya; Nishiyama, Takashi; Takahashi, Koji

    2013-01-16

    Interfacial thermal transport via van der Waals interaction is quantitatively evaluated using an individual multi-walled carbon nanotube bonded on a platinum hot-film sensor. The thermal boundary resistance per unit contact area was obtained at the interface between the closed end or sidewall of the nanotube and platinum, gold, or a silicon dioxide surface. When taking into consideration the surface roughness, the thermal boundary resistance at the sidewall is found to coincide with that at the closed end. A new finding is that the thermal boundary resistance between a carbon nanotube and a solid surface is independent of the materials within the experimental errors, which is inconsistent with a traditional phonon mismatch model, which shows a clear material dependence of the thermal boundary resistance. Our data indicate the inapplicability of existing phonon models when weak van der Waals forces are dominant at the interfaces.

  10. Five-body van der Waals interactions

    Science.gov (United States)

    Han, Jianing

    2017-06-01

    We report on the five-body repulsive and attractive van der Waals interactions between the strongly dipole-dipole coupled Rydberg states. Compared to four-body van der Waals interactions, five-body van der Waals interactions show more energy levels and more potential wells caused by avoided crossings. This research bridges the few-body physics and many-body physics. Other disciplines, such as chemistry, biology, and medical fields, will also benefit from better understanding van der Waals interactions.

  11. Accurate and efficient calculation of van der Waals interactions within density functional theory by local atomic potential approach.

    Science.gov (United States)

    Sun, Y Y; Kim, Yong-Hyun; Lee, Kyuho; Zhang, S B

    2008-10-21

    Density functional theory (DFT) in the commonly used local density or generalized gradient approximation fails to describe van der Waals (vdW) interactions that are vital to organic, biological, and other molecular systems. Here, we propose a simple, efficient, yet accurate local atomic potential (LAP) approach, named DFT+LAP, for including vdW interactions in the framework of DFT. The LAPs for H, C, N, and O are generated by fitting the DFT+LAP potential energy curves of small molecule dimers to those obtained from coupled cluster calculations with single, double, and perturbatively treated triple excitations, CCSD(T). Excellent transferability of the LAPs is demonstrated by remarkable agreement with the JSCH-2005 benchmark database [P. Jurecka et al. Phys. Chem. Chem. Phys. 8, 1985 (2006)], which provides the interaction energies of CCSD(T) quality for 165 vdW and hydrogen-bonded complexes. For over 100 vdW dominant complexes in this database, our DFT+LAP calculations give a mean absolute deviation from the benchmark results less than 0.5 kcal/mol. The DFT+LAP approach involves no extra computational cost other than standard DFT calculations and no modification of existing DFT codes, which enables straightforward quantum simulations, such as ab initio molecular dynamics, on biomolecular systems, as well as on other organic systems.

  12. Potential energy surface of the CO{sub 2}–N{sub 2} van der Waals complex

    Energy Technology Data Exchange (ETDEWEB)

    Nasri, Sameh; Ajili, Yosra [Laboratoire de Spectroscopie Atomique, Moléculaire et Applications-LSAMA, Université de Tunis El Manar, Tunis (Tunisia); Université Paris-Est, Laboratoire Modélisation et Simulation Multi Echelle, MSME UMR 8208 CNRS, 5 bd Descartes, 77454 Marne-la-Vallée (France); Jaidane, Nejm-Eddine [Laboratoire de Spectroscopie Atomique, Moléculaire et Applications-LSAMA, Université de Tunis El Manar, Tunis (Tunisia); Kalugina, Yulia N. [Department of Optics and Spectroscopy, Tomsk State University, 36 Lenin Ave., Tomsk 634050 (Russian Federation); Halvick, Philippe; Stoecklin, Thierry [Institut des Sciences Moléculaires, Université de Bordeaux, CNRS UMR 5255, 33405 Talence Cedex (France); Hochlaf, Majdi, E-mail: hochlaf@univ-mlv.fr [Université Paris-Est, Laboratoire Modélisation et Simulation Multi Echelle, MSME UMR 8208 CNRS, 5 bd Descartes, 77454 Marne-la-Vallée (France)

    2015-05-07

    Four-dimensional potential energy surface (4D-PES) of the atmospherically relevant CO{sub 2}–N{sub 2} van der Waals complex is generated using the explicitly correlated coupled cluster with single, double, and perturbative triple excitation (CCSD(T)-F12) method in conjunction with the augmented correlation consistent triple zeta (aug-cc-pVTZ) basis set. This 4D-PES is mapped along the intermonomer coordinates. An analytic fit of this 4D-PES is performed. Our extensive computations confirm that the most stable form corresponds to a T-shape structure where the nitrogen molecule points towards the carbon atom of CO{sub 2}. In addition, we located a second isomer and two transition states in the ground state PES of CO{sub 2}–N{sub 2}. All of them lay below the CO{sub 2} + N{sub 2} dissociation limit. This 4D-PES is flat and strongly anisotropic along the intermonomer coordinates. This results in the possibility of the occurrence of large amplitude motions within the complex, such as the inversion of N{sub 2}, as suggested in the recent spectroscopic experiments. Finally, we show that the experimentally established deviations from the C{sub 2v} structure at equilibrium for the most stable isomer are due to the zero-point out-of-plane vibration correction.

  13. Ab initio intermolecular potential energy surfaces for the Ar-NCCN van der Waals complexes

    Science.gov (United States)

    Solimannejad, Mohammad; Jouypazadeh, Hamidreza; Farrokhpour, Hossein

    2014-11-01

    The intermolecular potential energy surface of complex pairing argon with cyanogen molecule (NCCN) was calculated using the coupled cluster with single and double and perturbative triple excitations (CCSD(T)) with aug-cc-pvdz basis set extended with a set of mid-bond (3s3p2d1f1g) functions. The interaction energies were calculated by the supermolecular approach with the full counterpoise correction for the basis set superposition error. The calculated potential energies were fitted to an analytical expression. The calculated Ar-NCCN potential energy surface shows a global minimum at 3.35 Å, the distance between argon and centre of mass of cyanogen, for the T-shaped geometry and two local minimum at distance of 5.54 Å for the linear geometry on one side of cyanogen. Finally, the interaction second virial coefficients were calculated using the fitted potential energy surface and were compared with those obtained by the parameters of the Beattie-Bridgeman equation of states of pure argon and cyanogens fluids, approximately.

  14. Potential energy surface and rovibrational energy levels of the H2-CS van der Waals complex.

    Science.gov (United States)

    Denis-Alpizar, Otoniel; Stoecklin, Thierry; Halvick, Philippe; Dubernet, Marie-Lise; Marinakis, Sarantos

    2012-12-21

    Owing to its large dipole, astrophysicists use carbon monosulfide (CS) as a tracer of molecular gas in the interstellar medium, often in regions where H(2) is the most abundant collider. Predictions of the rovibrational energy levels of the weakly bound complex CS-H(2) (not yet observed) and also of rate coefficients for rotational transitions of CS in collision with H(2) should help to interpret the observed spectra. This paper deals with the first goal, i.e., the calculation of the rovibrational energy levels. A new four-dimensional intermolecular potential energy surface for the H(2)-CS complex is presented. Ab initio potential energy calculations were carried out at the coupled-cluster level with single and double excitations and a perturbative treatment of triple excitations, using a quadruple-zeta basis set and midbond functions. The potential energy surface was obtained by an analytic fit of the ab initio data. The equilibrium structure of the H(2)-CS complex is found to be linear with the carbon pointing toward H(2) at the intermolecular separation of 8.6 a(o). The corresponding well depth is -173 cm(-1). The potential was used to calculate the rovibrational energy levels of the para-H(2)-CS and ortho-H(2)-CS complexes. The present work provides the first theoretical predictions of these levels. The calculated dissociation energies are found to be 35.9 cm(-1) and 49.9 cm(-1), respectively, for the para and ortho complexes. The second virial coefficient for the H(2)-CS pair has also been calculated for a large range of temperature. These results could be used to assign future experimental spectra and to check the accuracy of the potential energy surface.

  15. Multi-terminal transport measurements of MoS2 using a van der Waals heterostructure device platform

    DEFF Research Database (Denmark)

    Cui, Xu; Lee, Gwan-Hyoung; Kim, Young Duck

    2015-01-01

    Atomically thin two-dimensional semiconductors such as MoS2 hold great promise for electrical, optical and mechanical devices and display novel physical phenomena. However, the electron mobility of mono-and few-layer MoS2 has so far been substantially below theoretically predicted limits, which has...... in performance, including a record-high Hall mobility reaching 34,000 cm2 V-1 s-1 for six-layer MoS2 at low temperature, confirming that low-temperature performance in previous studies was limited by extrinsic interfacial impurities rather than bulk defects in the MoS2. We also observed Shubnikov-de Haas...... scattering, we have developed here a van der Waals heterostructure device platform where MoS2 layers are fully encapsulated within hexagonal boron nitride and electrically contacted in a multi-terminal geometry using gate-tunable graphene electrodes. Magneto-transport measurements show dramatic improvements...

  16. a Code for Automated Construction of Potential Energy Surfaces for Van Der Waals Systems

    Science.gov (United States)

    Quintas Sánchez, Ernesto; Dawes, Richard

    2017-06-01

    The potential energy surface (PES) constitutes a cornerstone for theoretical studies of spectroscopy and dynamics. We fit PESs using a local interpolating moving least squares (L-IMLS) approach. The L-IMLS method is interpolative and has the flexibility to fit energies or energies and gradients, where inclusion of gradient information significantly reduces the number of points required for an accurate fit. The method permits fully automated PES generation: beginning with an initial set of seed points, an automatic point selection scheme determines where new data are required and, in a series of iterations, computes new ab initio data and updates the fit until a specified accuracy is reached. We have interfaced this fitting approach to popular electronic structure codes such as Molpro and CFOUR to automatically generate ab initio 4D PESs for vdWs systems composed of two (rigid) linear fragments. We present here our freely distributed code designed to run in parallel on a computing cluster, allowing the user to specify the system (masses, interatomic equilibrium distances, symmetry, energy range of interest, etc.) through an input file. For a selection of benchmark systems, we show that PESs with fitting errors below 1 \\wn can be constructed using only a few hundred ab initio points. M. Majumder, S. Ndengue and R. Dawes, Molecular Physics 114, 1 (2016).

  17. Measuring the Managerial Potential

    OpenAIRE

    Ion Gh. Rosca; George Moldoveanu

    2009-01-01

    The paper proposes the measurement of managerial and functional capabilities of the organization, as the dimensions of managerial potential, based on the configurative theory and not on the reductionist one. The components of the managerial potential are fulfilled by the capability of building organizational culture, managerial change and defining equity as the proximate type of social responsibility. The components are described in relation with the socio-economic model, useful in the proces...

  18. Theoretical studies for the N{sub 2}–N{sub 2}O van der Waals complex: The potential energy surface, intermolecular vibrations, and rotational transition frequencies

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, Rui [Key Laboratory of Magnetic Resonance in Biological Systems, State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Centre for Magnetic Resonance, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071 (China); School of Mathematics and Information Science, North China University of Water Resources and Electric Power, Zhengzhou 450011 (China); Zheng, Limin; Yang, Minghui, E-mail: yplu@ntu.edu.sg, E-mail: yangmh@wipm.ac.cn [Key Laboratory of Magnetic Resonance in Biological Systems, State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Centre for Magnetic Resonance, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071 (China); Lu, Yunpeng, E-mail: yplu@ntu.edu.sg, E-mail: yangmh@wipm.ac.cn [Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371 (Singapore)

    2015-10-21

    Theoretical studies of the potential energy surface (PES) and bound states are performed for the N{sub 2}–N{sub 2}O van der Waals (vdW) complex. A four-dimensional intermolecular PES is constructed at the level of single and double excitation coupled-cluster method with a non-iterative perturbation treatment of triple excitations [CCSD(T)] with aug-cc-pVTZ basis set supplemented with bond functions. Two equivalent T-shaped global minima are located, in which the O atom of N{sub 2}O monomer is near the N{sub 2} monomer. The intermolecular fundamental vibrational states are assigned by inspecting the orientation of the nodal surface of the wavefunctions. The calculated frequency for intermolecular disrotation mode is 23.086 cm{sup −1}, which is in good agreement with the available experimental data of 22.334 cm{sup −1}. A negligible tunneling splitting with the value of 4.2 MHz is determined for the ground vibrational state and the tunneling splitting increases as the increment of the vibrational frequencies. Rotational levels and transition frequencies are calculated for both isotopomers {sup 14}N{sub 2}–N{sub 2}O and {sup 15}N{sub 2}–N{sub 2}O. The accuracy of the PES is validated by the good agreement between theoretical and experimental results for the transition frequencies and spectroscopic parameters.

  19. Toward transferable interatomic van der Waals potentials: The role of multipole electrostatics and many-body dispersion without electrons

    CERN Document Server

    Bereau, Tristan

    2014-01-01

    We estimate polarizabilities of atoms in molecules without electron density, using a Voronoi partitioning approach instead. The resulting atomic dispersion coefficients are calculated, as well as many-body dispersion effects on intermolecular potential energies. We also estimate contributions from multipole electrostatics and compare them to dispersion. We assess the performance of the resulting intermolecular potential from dispersion and electrostatics for more than 1,300 neutral and charged, small organic molecular dimers. Applications to water clusters, the benzene crystal, the anti-cancer drug ellipticine---intercalated between two Watson-Crick DNA base pairs, as well as six macro-molecular host-guest complexes highlight the potential of this method and help to identify points of future improvement. Overall, the method achieves an accuracy well within sophisticated empirical force fields, such as OPLS and Amber FF03, while exhibiting a simple parametrization protocol without the need for experimental inp...

  20. Calculation of the structure, potential energy surface, vibrational dynamics, and electric dipole properties for the Xe:HI van der Waals complex.

    Science.gov (United States)

    Preller, M; Grunenberg, J; Bulychev, V P; Bulanin, M O

    2011-05-07

    We report the structure and spectroscopic characteristics for the Xe:HI van der Waals binary isomers determined from variational solutions of two-dimensional and three-dimensional (3D) vibrational Schrödinger equations. The solutions are based on a potential energy surface computed at the coupled-cluster level of theory including single and double excitations and a non-iterative perturbation treatment of triple excitations [CCSD(T)]. The dipole moment surface was calculated using quadratic configuration interaction (QCISD). The global potential minimum is shown to be located at the anti-hydrogen-bonded Xe-IH isomer, 21 cm(-1) below the secondary local minimum associated with the hydrogen-bonded Xe-HI isomeric form. The dissociation energy from the global minimum is 245.9 cm(-1). 3D Schrödinger equations are solved for the rotational quantum numbers J = k = 0, 1, and 2, without invoking an adiabatic separation of high- and low-frequency degrees of freedom. The vibrational ground state resides in the Xe-HI potential well, while the first excited state, 8.59 cm(-1) above the ground, occupies the Xe-IH well. We find that intra-complex dynamics exhibits a sudden transformation upon increase of the r(HI) bond length, accompanied by abrupt changes in the geometric and dipole parameters. A similar chaotic behavior is predicted to occur for Xe:DI at a shorter r(DI) bond length, which implies stronger coupling between low- and high-frequency motions in the heavier complex. Our calculations confirm a strong enhancement for the r(HI) stretch fundamental and a significant weakening for the first overtone vibrational transitions in Xe:HI, as compared to those in the free HI molecule. A qualitative explanation of this, earlier experimentally detected effect is suggested.

  1. Theoretical investigation of potential energy surface and bound states for the van der Waals complex Ar–BrCl dimer

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, Rui [School of Mathematics and Information Science, North China University of Water Resources and Electric Power, Zhengzhou (China); Key Laboratory of Magnetic Resonance in Biological Systems, State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Centre for Magnetic Resonance, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan (China); Li, Song, E-mail: lsong@yangtzeu.edu.cn [School of Physics and Optoelectronic Engineering, Yangtze University, Jingzhou (China); Chen, Shan-Jun; Chen, Yan [School of Physics and Optoelectronic Engineering, Yangtze University, Jingzhou (China); Zheng, Li-Min [Key Laboratory of Magnetic Resonance in Biological Systems, State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Centre for Magnetic Resonance, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan (China)

    2015-09-08

    Highlights: • A two-dimensional potential for Ar–BrCl is constructed at the CCSD(T) level. • The PES is characterized by three minima and two saddle points between them. • Bound state calculations were carried out for the complex. - Abstract: The intermolecular potential energy surface (PES) of the ground electronic state for the Ar–BrCl dimer is constructed at the CCSD(T) level with the aug-cc-pVQZ basis set and mid-bond functions. The PES is characterized by three minima and two saddle points. The global minimum corresponding to a collinear Ar–BrCl configuration, which has been observed experimentally, is located at R = 4.10 Å and θ = 2.5° with a well depth of −285.207 cm{sup −1}. A nearly T-shaped structure and an anti-linear Ar–ClBr geometry is also predicted. The bound state calculations are preformed to study intermolecular vibrational modes, rotational levels and average structures for the complex. Our transition frequencies, spectroscopic constants and average structures for all isotopomers of the collinear isomer agree well with experimental data. We have also provided pure rotational transitional frequencies for both nearly T-shaped and anti-linear isomers. These results are significant for further experimental investigations of the Ar–BrCl dimer.

  2. Interatomic potentials for van der Waals complexes of group 13 metal atoms: AlAr, AlKr, and AlXe

    Science.gov (United States)

    Callender, C. L.; Mitchell, S. A.; Hackett, P. A.

    1989-05-01

    Interatomic potential parameters for the ground X1,2 2Π1/2,3/2 and excited B 2Σ+1/2 states of jet-cooled van der Waals complexes of Al atoms with rare gases have been determined from fluorescence excitation and emission spectra. Vibrational numbering in the B states is established from isotopic and rotational broadening of fluorescence excitation line shapes. Bond distances are estimated by comparison with analogous states of alkali-rare gas molecules, and by modeling observed relative emission intensities with calculated Franck-Condon factors. Morse potentials are found to adequately describe the data for the ground states, but for the excited states there are indications of departures from Morse functions at large internuclear distances. Dissociation energies De are estimated from Birge-Sponer extrapolations. Multiplet splittings in Al-rare gas complexes are compared to those in In-rare gas complexes and are discussed in terms of an empirical treatment of spin-orbit coupling, which assumes that the spin-orbit coupling constant for the molecule is the same as that for the atom. The ground X1 state of each Al-rare gas molecule is more stable than that of the analogous In complex, whereas the spin-orbit excited X2 state is less stable. This is explained by the greater mixing between the X1 state and the dissociative A 2Σ+1/2 state for indium over aluminum, caused by the greater spin-orbit coupling constant for the heavier metal.

  3. van der Waals torque

    Science.gov (United States)

    Esquivel-Sirvent, Raul; Schatz, George

    2014-03-01

    The theory of generalized van der Waals forces by Lifshtz when applied to optically anisotropic media predicts the existence of a torque. In this work we present a theoretical calculation of the van der Waals torque for two systems. First we consider two isotropic parallel plates where the anisotropy is induced using an external magnetic field. The anisotropy will in turn induce a torque. As a case study we consider III-IV semiconductors such as InSb that can support magneto plasmons. The calculations of the torque are done in the Voigt configuration, that occurs when the magnetic field is parallel to the surface of the slabs. The change in the dielectric function as the magnetic field increases has the effect of decreasing the van der Waals force and increasing the torque. Thus, the external magnetic field is used to tune both the force and torque. The second example we present is the use of the torque in the non retarded regime to align arrays of nano particle slabs. The torque is calculated within Barash and Ginzburg formalism in the nonretarded limit, and is quantified by the introduction of a Hamaker torque constant. Calculations are conducted between anisotropic slabs of materials including BaTiO3 and arrays of Ag nano particles. Depending on the shape and arrangement of the Ag nano particles the effective dielectric function of the array can be tuned as to make it more or less anisotropic. We show how this torque can be used in self assembly of arrays of nano particles. ref. R. Esquivel-Sirvent, G. C. Schatz, Phys. Chem C, 117, 5492 (2013). partial support from DGAPA-UNAM.

  4. Streaming potential measurements of biosurfaces

    Science.gov (United States)

    Van Wagenen, R. A.; Andrade, J. D.; Hibbs, J. B., Jr.

    1976-01-01

    A technique based on the measurement of streaming potentials has been developed to evaluate the electrokinetic region of the cell periphery. This approach is feasible for cell lines propagated in in-vitro cell cultures in monolayer form. The advantage of this system is that cells may be evaluated in the living state atttached to a substrate; it is not necessary to subject the cells to enzymatic, chemical, or mechanical trauma required to obtain monodisperse suspensions which are then normally evaluated by microelectrophoresis. In this manner, it should be possible to study the influence of substrate and environmental factors on the charge density and potential at the cell periphery. The apparatus and procedure are described as well as some results concerning the electrokinetic potential of borosilicate capillaries as a function of ionic strength, pH, and temperature. The effect that turbulence and entrance flow conditions have on accurate streaming-potential measurements is discussed. The electrokinetic potential of BALB/c 3T12 fibroblasts has been quantified as a function of pH, ionic strength, glutaraldehyde fixation, and Giemsa staining.

  5. Streaming potential measurements of biosurfaces

    Science.gov (United States)

    Van Wagenen, R. A.; Andrade, J. D.; Hibbs, J. B., Jr.

    1976-01-01

    A technique based on the measurement of streaming potentials has been developed to evaluate the electrokinetic region of the cell periphery. This approach is feasible for cell lines propagated in in-vitro cell cultures in monolayer form. The advantage of this system is that cells may be evaluated in the living state atttached to a substrate; it is not necessary to subject the cells to enzymatic, chemical, or mechanical trauma required to obtain monodisperse suspensions which are then normally evaluated by microelectrophoresis. In this manner, it should be possible to study the influence of substrate and environmental factors on the charge density and potential at the cell periphery. The apparatus and procedure are described as well as some results concerning the electrokinetic potential of borosilicate capillaries as a function of ionic strength, pH, and temperature. The effect that turbulence and entrance flow conditions have on accurate streaming-potential measurements is discussed. The electrokinetic potential of BALB/c 3T12 fibroblasts has been quantified as a function of pH, ionic strength, glutaraldehyde fixation, and Giemsa staining.

  6. Dynamical and non-additive atomic van der Waals phases

    CERN Document Server

    Impens, François; Neto, Paulo A Maia

    2013-01-01

    We investigate dynamical corrections to the van der Waals phase induced by the non-unitary evolution of atomic waves propagating near a perfectly conducting surface. These corrections reflect the interplay between field retardation effects and the dynamics of the external atomic degrees of freedom. The dynamical atom-surface interaction phase shift contains both local and non-local contributions. We derive the local contributions and show that they are equivalent to coarse-graining the instantaneous van der Waals potential over the time scale corresponding to the round-trip travel time of light between atom and surface. We show that the non-local phase contributions are non-additive, and propose to use this property in a multiple-path van der Waals interferometer in order to isolate them from the standard (and much larger) quasi-static van der Waals phase.

  7. Can atom-surface potential measurements test atomic structure models?

    Science.gov (United States)

    Lonij, Vincent P A; Klauss, Catherine E; Holmgren, William F; Cronin, Alexander D

    2011-06-30

    van der Waals (vdW) atom-surface potentials can be excellent benchmarks for atomic structure calculations. This is especially true if measurements are made with two different types of atoms interacting with the same surface sample. Here we show theoretically how ratios of vdW potential strengths (e.g., C₃(K)/C₃(Na)) depend sensitively on the properties of each atom, yet these ratios are relatively insensitive to properties of the surface. We discuss how C₃ ratios depend on atomic core electrons by using a two-oscillator model to represent the contribution from atomic valence electrons and core electrons separately. We explain why certain pairs of atoms are preferable to study for future experimental tests of atomic structure calculations. A well chosen pair of atoms (e.g., K and Na) will have a C₃ ratio that is insensitive to the permittivity of the surface, whereas a poorly chosen pair (e.g., K and He) will have a ratio of C₃ values that depends more strongly on the permittivity of the surface.

  8. The van der Waals potentials of MgCa, MgSr, MgBa, CaSr, CaBa, and SrBa

    Science.gov (United States)

    Wei, L. M.; Li, P.; Tang, K. T.

    2015-08-01

    Based on the facts that the potential energy curves of the homo-nuclear group 2 dimers (group IIA metal), except Be2, are conformal, and they can be described by the Tang-Toennies potential model, a set of simple combining rules are proposed for the parameters of the reduced potentials of the hetero-nuclear dimers. Together with the well-established combining rules of the range parameters of the exponential repulsion and the known dispersion coefficients, these rules enable us to determine the ground state potential energy curves of MgCa, MgSr, MgBa, CaSr, CaBa, and SrBa from those of Mg2, Ca2, Sr2, and Ba2. The determined potentials are comparable to some ab initio calculations and in excellent agreement with the experiment.

  9. van der Waals Heterostructures Grown by MBE

    Science.gov (United States)

    Hinkle, Christopher

    In this work, we demonstrate the high-quality MBE heterostructure growth of various layered 2D materials by van der Waals epitaxy (VDWE). The coupling of different types of van der Waals materials including transition metal dichalcogenide thin films (e.g., WSe2, WTe2, HfSe2) , insulating hexagonal boron nitride (h-BN), and topological insulators (e.g., Bi2Se3) allows for the fabrication of novel electronic devices that take advantage of unique quantum confinement and spin-based characteristics. The relaxed lattice-matching criteria of van der Waals epitaxy has allowed for high-quality heterostructure growth with atomically abrupt interfaces, allowing us to couple these materials based primarily on their band alignment and electronic properties. We will discuss the impact of sample preparation, surface reactivity, and lattice mismatch of various substrates (sapphire, graphene, TMDs, Bi2Se3) on the growth mode and quality of the films and will discuss our studies of substrate temperature and flux rates on the resultant growth and grain size. Structural and chemical characterization was conducted via reflection high energy electron diffraction (RHEED, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning tunneling microscopy/spectroscopy (STM/S), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Experimentally determined band alignments have been determined and compared with first-principles calculations allowing the design of novel low-power logic and magnetic memory devices. Initial results from the electrical characterization of these grown thin films and some simple devices will also be presented. These VDWE grown layered 2D materials show significant potential for fabricating novel heterostructures with tunable band alignments and magnetic properties for a variety of nanoelectronic and optoelectronic applications.

  10. Evolutionary design of interfacial phase change van der Waals heterostructures.

    Science.gov (United States)

    Kalikka, Janne; Zhou, Xilin; Behera, Jitendra; Nannicini, Giacomo; Simpson, Robert E

    2016-10-27

    We use an evolutionary algorithm to explore the design space of hexagonal Ge2Sb2Te5; a van der Waals layered two dimensional crystal heterostructure. The Ge2Sb2Te5 structure is more complicated than previously thought. Predominant features include layers of Ge3Sb2Te6 and Ge1Sb2Te4 two dimensional crystals that interact through Te-Te van der Waals bonds. Interestingly, (Ge/Sb)-Te-(Ge/Sb)-Te alternation is a common feature for the most stable structures of each generation's evolution. This emergent rule provides an important structural motif that must be included in the design of high performance Sb2Te3-GeTe van der Waals heterostructure superlattices with interfacial atomic switching capability. The structures predicted by the algorithm agree well with experimental measurements on highly oriented, and single crystal Ge2Sb2Te5 samples. By analysing the evolutionary algorithm optimised structures, we show that diffusive atomic switching is probable by Ge atoms undergoing a transition at the van der Waals interface from layers of Ge3Sb2Te6 to Ge1Sb2Te4 thus producing two blocks of Ge2Sb2Te5. Evolutionary methods present an efficient approach to explore the enormous multi-dimensional design parameter space of van der Waals bonded heterostructure superlattices.

  11. Van der Waals black hole

    Directory of Open Access Journals (Sweden)

    Aruna Rajagopal

    2014-10-01

    Full Text Available In the context of extended phase space, where the negative cosmological constant is treated as a thermodynamic pressure in the first law of black hole thermodynamics, we find an asymptotically AdS metric whose thermodynamics matches exactly that of the Van der Waals fluid. We show that as a solution of Einstein's equations, the corresponding stress energy tensor obeys (at least for certain range of metric parameters all three weak, strong, and dominant energy conditions.

  12. Investigations of the Rg-BrCl (Rg = He, Ne, Ar, Kr, Xe) binary van der Waals complexes: ab initio intermolecular potential energy surfaces, vibrational states and predicted pure rotational transition frequencies

    Science.gov (United States)

    Li, Song; Zheng, Rui; Chen, Shan-Jun; Chen, Yan; Chen, Peng

    2017-03-01

    The intermolecular potential energy surfaces (PESs) of the ground electronic state for the Rg-BrCl (Rg = He, Ne, Ar, Kr, Xe) van der Waals complexes have been constructed by using the coupled-cluster method in combination with the augmented quadruple-zeta correlation-consistent basis sets supplemented with an additional set of bond functions. The features of the anisotropic PESs for these complexes are remarkably similar, which are characterized by three minima and two saddle points between them. The global minimum corresponds to a collinear Rg-Br-Cl configuration. Two local minima, correlate with an anti-linear Rg-Cl-Br geometry and a nearly T-shaped structure, can also be located on each PES. The quantum bound state calculations enable us to investigate intermolecular vibrational states and rotational energy levels of the complexes. The transition frequencies are predicted and are fitted to obtain their corresponding spectroscopic constants. In general, the periodic trends are observed for this complex family. Comparisons with available experimental data for the collinear isomer of Ar-BrCl demonstrate reliability of our theoretical predictions, and our results for the other two isomers of Ar-BrCl as well as for other members of the complex family are also anticipated to be trustable. Except for the collinear isomer of Ar-BrCl, the data presented in this paper would be beneficial to improve our knowledge for these experimentally unknown species.

  13. Investigations of the Rg-BrCl (Rg=He, Ne, Ar, Kr, Xe) binary van der Waals complexes: ab initio intermolecular potential energy surfaces, vibrational states and predicted pure rotational transition frequencies.

    Science.gov (United States)

    Li, Song; Zheng, Rui; Chen, Shan-Jun; Chen, Yan; Chen, Peng

    2017-03-05

    The intermolecular potential energy surfaces (PESs) of the ground electronic state for the Rg-BrCl (Rg=He, Ne, Ar, Kr, Xe) van der Waals complexes have been constructed by using the coupled-cluster method in combination with the augmented quadruple-zeta correlation-consistent basis sets supplemented with an additional set of bond functions. The features of the anisotropic PESs for these complexes are remarkably similar, which are characterized by three minima and two saddle points between them. The global minimum corresponds to a collinear Rg-Br-Cl configuration. Two local minima, correlate with an anti-linear Rg-Cl-Br geometry and a nearly T-shaped structure, can also be located on each PES. The quantum bound state calculations enable us to investigate intermolecular vibrational states and rotational energy levels of the complexes. The transition frequencies are predicted and are fitted to obtain their corresponding spectroscopic constants. In general, the periodic trends are observed for this complex family. Comparisons with available experimental data for the collinear isomer of Ar-BrCl demonstrate reliability of our theoretical predictions, and our results for the other two isomers of Ar-BrCl as well as for other members of the complex family are also anticipated to be trustable. Except for the collinear isomer of Ar-BrCl, the data presented in this paper would be beneficial to improve our knowledge for these experimentally unknown species.

  14. Refined ab initio intermolecular ground-state potential energy surface for the He-C2H2 van der Waals complex

    DEFF Research Database (Denmark)

    Fernández, Berta; Henriksen, Christian; Farrelly, David

    2013-01-01

    , are fitted to a 15-parameter analytic function. The potential is characterised by minima of-24.21 cm-1 at distances between the rare gas atom and the C2H2 centre of mass of 4.3453 Å, and with the complex in a linear configuration. At intermediate distances the surface is rather similar to that developed...

  15. Van der Waals interaction between two crossed carbon nanotubes

    OpenAIRE

    Zhbanov, Alexander I.; Pogorelov, Evgeny G.; Chang, Yia-Chung

    2008-01-01

    The analytical expressions for the van der Waals potential energy and force between two crossed carbon nanotubes are presented. The Lennard-Jones potential for two carbon atoms and the method of the smeared out approximation suggested by L.A. Girifalco were used. The exact formula is expressed in terms of rational and elliptical functions. The potential and force for carbon nanotubes were calculated. The uniform potential curves for single- and multi- wall nanotubes were plotted. The equilibr...

  16. Large area molybdenum disulphide- epitaxial graphene vertical Van der Waals heterostructures

    Science.gov (United States)

    Pierucci, Debora; Henck, Hugo; Naylor, Carl H.; Sediri, Haikel; Lhuillier, Emmanuel; Balan, Adrian; Rault, Julien E.; Dappe, Yannick J.; Bertran, François; Fèvre, Patrick Le; Johnson, A. T. Charlie; Ouerghi, Abdelkarim

    2016-06-01

    Two-dimensional layered transition metal dichalcogenides (TMDCs) show great potential for optoelectronic devices due to their electronic and optical properties. A metal-semiconductor interface, as epitaxial graphene - molybdenum disulfide (MoS2), is of great interest from the standpoint of fundamental science, as it constitutes an outstanding platform to investigate the interlayer interaction in van der Waals heterostructures. Here, we study large area MoS2-graphene-heterostructures formed by direct transfer of chemical-vapor deposited MoS2 layer onto epitaxial graphene/SiC. We show that via a direct transfer, which minimizes interface contamination, we can obtain high quality and homogeneous van der Waals heterostructures. Angle-resolved photoemission spectroscopy (ARPES) measurements combined with Density Functional Theory (DFT) calculations show that the transition from indirect to direct bandgap in monolayer MoS2 is maintained in these heterostructures due to the weak van der Waals interaction with epitaxial graphene. A downshift of the Raman 2D band of the graphene, an up shift of the A1g peak of MoS2 and a significant photoluminescence quenching are observed for both monolayer and bilayer MoS2 as a result of charge transfer from MoS2 to epitaxial graphene under illumination. Our work provides a possible route to modify the thin film TDMCs photoluminescence properties via substrate engineering for future device design.

  17. The Economics of van der Waals Force Engineering

    Science.gov (United States)

    Pinto, Fabrizio

    2008-01-01

    As micro-electro-mechanical system (MEMS) fabrication continues on an ever-decreasing scale, new technological challenges must be successfully negotiated if Moore's Law is to be an even approximately valid model of the future of device miniaturization. Among the most significant obstacles is the existence of strong surface forces related to quantum mechanical van der Waals interatomic interactions, which rapidly diverge as the distance between any two neutral boundaries decreases. The van der Waals force is a contributing factor in several device failures and limitations, including, for instance, stiction and oscillator non-linearities. In the last decade, however, it has been conclusively shown that van der Waals forces are not just a MEMS limitation but can be engineered in both magnitude and sign so as to enable classes of proprietary inventions which either deliver novel capabilities or improve upon existing ones. The evolution of van der Waals force research from an almost exclusively theoretical field in quantum-electro-dynamics to an enabling nanotechnology discipline represents a useful example of the ongoing paradigm shift from government-centered to private-capital funded R&D in cutting-edge physics leading to potentially profitable products. In this paper, we discuss the reasons van der Waals force engineering may lead to the creation of thriving markets both in the short and medium terms by highlighting technical challenges that can be competitively addressed by this novel approach. We also discuss some notable obstacles to the cultural transformation of the academic research community required for the emergence of a functional van der Waals force engineering industry worldwide.

  18. Measurement of human potential in organizations

    Directory of Open Access Journals (Sweden)

    Rosa María Fuchs Ángeles

    2015-09-01

    Full Text Available Companies around the world are concerned about talent management in their organizations. The concern is to retain talented employees and this may not be possible if they are not properly identified. Performance and potential evaluations become then important. Performance evaluations qualify the historical record of the employee, so their measurement is provided. However, measuring the potential performance assesses potential future charges, therefore it is not a simple task. In this paper, characteristics evaluated in potential employees and tools that are commonly used are presented. Also, the case of four companies operating in Peru is shown.

  19. Critical and near-critical phase behavior and interplay between the thermodynamic Casimir and van der Waals forces in a confined nonpolar fluid medium with competing surface and substrate potentials

    Science.gov (United States)

    Valchev, Galin; Dantchev, Daniel

    2015-07-01

    We study, using general scaling arguments and mean-field type calculations, the behavior of the critical Casimir force and its interplay with the van der Waals force acting between two parallel slabs separated at a distance L from each other, confining some fluctuating fluid medium, say a nonpolar one-component fluid or a binary liquid mixture. The surfaces of the slabs are coated by thin layers exerting strong preference to the liquid phase of the fluid, or one of the components of the mixture, modeled by strong adsorbing local surface potentials ensuring the so-called (+,+) boundary conditions. The slabs, on the other hand, influence the fluid by long-range competing dispersion potentials, which represent irrelevant interactions in renormalization-group sense. Under such conditions, one usually expects attractive Casimir force governed by universal scaling function, pertinent to the extraordinary surface universality class of Ising type systems, to which the dispersion potentials provide only corrections to scaling. We demonstrate, however, that below a given threshold thickness of the system Lcrit for a suitable set of slabs-fluid and fluid-fluid coupling parameters the competition between the effects due to the coatings and the slabs can result in sign change of the Casimir force acting between the surfaces confining the fluid when one changes the temperature T , the chemical potential of the fluid μ , or L . The last implies that by choosing specific materials for the slabs, coatings, and the fluid for L ≲Lcrit one can realize repulsive Casimir force with nonuniversal behavior which, upon increasing L , gradually turns into an attractive one described by a universal scaling function, depending only on the relevant scaling fields related to the temperature and the excess chemical potential, for L ≫Lcrit . We present arguments and relevant data for specific substances in support of the experimental feasibility of the predicted behavior of the force. It can

  20. Structure and dynamics of small van der Waals complexes

    Energy Technology Data Exchange (ETDEWEB)

    Loreau, J. [Service de Chimie Quantique et Photophysique, Université Libre de Bruxelles (ULB) CP 160/09, 1050 Brussels (Belgium)

    2014-10-06

    We illustrate computational aspects of the calculation of the potential energy surfaces of small (up to five atoms) van der Waals complexes with high-level quantum chemistry techniques such as the CCSD(T) method with extended basis sets. We discuss the compromise between the required accuracy and the computational time. Further, we show how these potential energy surfaces can be fitted and used in dynamical calculations such as non-reactive inelastic scattering.

  1. Potentiometric Measurements of Semiconductor Nanocrystal Redox Potentials.

    Science.gov (United States)

    Carroll, Gerard M; Brozek, Carl K; Hartstein, Kimberly H; Tsui, Emily Y; Gamelin, Daniel R

    2016-04-06

    A potentiometric method for measuring redox potentials of colloidal semiconductor nanocrystals (NCs) is described. Fermi levels of colloidal ZnO NCs are measured in situ during photodoping, allowing correlation of NC redox potentials and reduction levels. Excellent agreement is found between electrochemical and optical redox-indicator methods. Potentiometry is also reported for colloidal CdSe NCs, which show more negative conduction-band-edge potentials than in ZnO. This difference is highlighted by spontaneous electron transfer from reduced CdSe NCs to ZnO NCs in solution, with potentiometry providing a measure of the inter-NC electron-transfer driving force. Future applications of NC potentiometry are briefly discussed.

  2. Jet-Cooled Infrared Laser Spectroscopy in the Umbrella νb{2} Vibration Region of NH_3: Improving the Potential Energy Surface Model of the NH_3-Ar Van Der Waals Complex

    Science.gov (United States)

    Asselin, Pierre; Jabri, Atef; Potapov, Alexey; Loreau, Jérome; van der Avoird, Ad

    2017-06-01

    Taking advantage of our sensitive laser spectrometer coupled to a pulsed slit jet, we recorded near the νb{2} vibration a series of rovibrational transitions of the NH_3-Ar van der Waals (vdW) complex. These transitions involve in the ground vibrational state several internal rotor states corresponding to the ortho{NH_3} and para{NH_3} spin modifications of the complex. They are labeled by Σ_{a}(j,k), Σ_{s}(j,k), Π_{a}(j,k) and Π_{s}(j,k) where Σ(K=0) and Π(K=1) indicate the projection K of the total rotational angular momentum J on the vdW axis, the superscripts s and a designate a symmetric or antisymmetric NH_3 inversion wave function, and j, k quantum numbers indicate the correlation between the internal-rotor state of the complex and the j, k rotational state of the free NH_3 monomer. Five bands have been identified, only one of which was partly observed before. They include transitions starting from the Σ_{a}(j=0 or j=1) state without any internal angular momentum, consequently they can be assigned from the band contour of a linear-molecule-like K=0, ΔJ=1 transition. The energies and splittings of the rovibrational levels of the νb{2}=1←0 spectrum derived from the analysis of the Π_{s}, Σ_{s}(j=1)← Σ_{a}(j=0), k=0 bands and mostly of the Σ_{s}, Π_{s} and Σ_{a}(j=1)←Σ_{a}(j=1), k=1 bands bring relevant information about the νb{2} dependence of the NH_3-Ar interaction, the rovibrational dynamics of the NH_3-Ar complex and provide a sensitive test of a recently developed 4D potential energy surface that includes explicitly its dependence on the umbrella motion. P. Asselin, Y. Berger, T. R. Huet, R. Motiyenko, L. Margulès, R. J. Hendricks, M. R. Tarbutt, S. Tokunaga, B. Darquié, PCCP 19, 4576 (2017), G. T. Fraser, A.S. Pine and W. A. Kreiner, J. Chem. Phys. 94, 7061 (1991). J. Loreau, J. Liévin, Y. Scribano and A. van der Avoird, J. Chem. Phys. 141, 224303 (2014).

  3. Van der Waals interaction between two crossed carbon nanotubes.

    Science.gov (United States)

    Zhbanov, Alexander I; Pogorelov, Evgeny G; Chang, Yia-Chung

    2010-10-26

    The analytical expressions for the van der Waals potential energy and force between two crossed carbon nanotubes are presented. The Lennard-Jones potential between pairs of carbon atoms and the smeared-out approximation suggested by L. A. Girifalco (J. Phys. Chem. 1992, 96, 858) were used. The exact formula is expressed in terms of rational and elliptical functions. The potential and force for carbon nanotubes were calculated. The uniform potential curves for single- and multiwall nanotubes were plotted. The equilibrium distance, maximal attractive force, and potential energy have been evaluated.

  4. Van der Waals and Casimir-Polder interactions between neutrons

    Directory of Open Access Journals (Sweden)

    Babb James F.

    2016-01-01

    Full Text Available We investigate the van der Waals interaction between neutrons using the theory of Casimir and Polder, wherein the potential for asymptotically large separations falls off as the inverse seventh power, and compare it to the similar interaction between a neutron and a proton, for which the asymptotic interaction falls off as the inverse fourth power. Modifications of the formalism to extend the validity to smaller separations using dynamic electric and magnetic dipole polarizability data are discussed.

  5. Bio-potential amplifier for potential gradient measurements

    Energy Technology Data Exchange (ETDEWEB)

    Bermudez, Andrea N; Spinelli, Enrique M; Muravchik, Carlos H [LEICI, Departamento de Electrotecnia, Universidad Nacional de La Plata, CC 91 (1900) La Plata (Argentina)

    2007-11-15

    This work proposes a bio-potential amplifier suitable for measurements from an electric potential gradient sensor, in electro-encephalography (EEG). The sensor is an array made by three electrodes placed on the vertices of an equilateral triangle of reduced size. Measuring the gradient requires small separation between electrodes hence, very low amplitude signals, of a few {mu}V, are obtained. Therefore, it is important to minimize amplifier noise and electromagnetic interference effects. In the proposed scheme, the first stage is a passive and balanced ac-coupling network adapted to the gradient configuration and the second stage is an 80 dB gain amplifier. The implementation requires a reduced number of components. Therefore, the circuit can be mounted just above the electrodes (active electrodes). The proposed amplifier was built and tested. It achieves a CMRR of 125dB at 50 Hz and an equivalent input noise voltage of 0,3{mu}V RMS in the band 0.5 - 500 Hz. Finally, some preliminary results in the detection of occipital alpha rhythm are presented.

  6. Measurement of Redox Potential in Nanoecotoxicological Investigations

    Directory of Open Access Journals (Sweden)

    Ratna Tantra

    2012-01-01

    Full Text Available Redox potential has been identified by the Organisation for Economic Co-operation and Development (OECD as one of the parameters that should be investigated for the testing of manufactured nanomaterials. There is still some ambiguity concerning this parameter, i.e., as to what and how to measure, particularly when in a nanoecotoxicological context. In this study the redox potentials of six nanomaterials (either zinc oxide (ZnO or cerium oxide (CeO2 dispersions were measured using an oxidation-reduction potential (ORP electrode probe. The particles under testing differed in terms of their particle size and dispersion stability in deionised water and in various ecotox media. The ORP values of the various dispersions and how they fluctuate relative to each other are discussed. Results show that the ORP values are mainly governed by the type of liquid media employed, with little contributions from the nanoparticles. Seawater was shown to have reduced the ORP value, which was attributed to an increase in the concentration of reducing agents such as sulphites or the reduction of dissolved oxygen concentration. The lack of redox potential value contribution from the particles themselves is thought to be due to insufficient interaction of the particles at the Pt electrode of the ORP probe.

  7. Van der Waals Interactions and Exciton Condensation

    Science.gov (United States)

    Handel, P. H.; Kittel, C.

    1971-01-01

    It is shown that the van der Waals interaction can lead at low temperatures to a condensed state of excitons with properties in qualitative agreement with the observations of exciton droplets. Our calculation gives a binding energy of the correct sign and magnitude for the exciton condensate. In a diclectric medium, the strong enhancement of the exciton polarizability leads to a giant van der Waals interaction, and this interaction appears to make possible a condensed exciton phase. PMID:16591958

  8. Electromagnetically induced transparency with controlled van der Waals interaction

    CERN Document Server

    Wu, Huaizhi; Shen, Li-Tuo; Chen, Rong-Xin; Yang, Zhen-Biao; Zheng, Shi-Biao

    2014-01-01

    The transmission of light through cold Rydberg atoms controlled by a second laser beam under the condition of the electromagnetically induced transparency (EIT) has been shown to exhibit highly optical nonlinearity. Here we study this effect with two individually addressed Rydberg atoms under the influence of the interatomic van der Waals interaction. We derive an effectively atomic Raman transition model that can potentially overcome the limits of applications for EIT with atoms of the ladder-type level configuration. By probing one of the atoms, we observe four doublets of absorption induced by the Autler-Townes (AT) splitting and van der Waals interaction. In particular, we find that the EIT center keeps unshifted compared with the case of interatomic interaction free, which demonstrated that the interference among the multiple transition channels is basically destructive. The EIT with controlled Rydberg-Rydberg interaction among few atoms provides a versatile tool for engineering the propagation dynamics ...

  9. Global empirical potentials from purely rotational measurements

    CERN Document Server

    Dattani, Nikesh S; Sun, Ming; Johnson, Erin R; Roy, Robert J Le; Ziurys, Lucy M

    2014-01-01

    The recent advent of chirped-pulse FTMW technology has created a plethora of pure rotational spectra for molecules for which no vibrational information is known. The growing number of such spectra demands a way to build empirical potential energy surfaces for molecules, without relying on any vibrational measurements. Using ZnO as an example, we demonstrate a powerful technique for efficiently accomplishing this. We first measure eight new ultra-high precision ($\\pm2$ kHz) pure rotational transitions in the $X$-state of ZnO. Combining them with previous high-precision ($\\pm50$ kHz) pure rotational measurements of different transitions in the same system, we have data that spans the bottom 10\\% of the well. Despite not using any vibrational information, our empirical potentials are able to determine the size of the vibrational spacings and bond lengths, with precisions that are more than three and two orders of magnitude greater, respectively, than the most precise empirical values previously known, and the mo...

  10. Van der Waals explosion of cold Rydberg clusters

    CERN Document Server

    Faoro, R; Archimi, M; Masella, G; Valado, M M; Arimondo, E; Mannella, R; Ciampini, D; Morsch, O

    2015-01-01

    We report on the direct measurement in real space of the effect of the van der Waals forces between individual Rydberg atoms on their external degrees of freedom. Clusters of Rydberg atoms with inter-particle distances of around 5 {\\mu}m are created by first generating a small number of seed excitations in a magneto-optical trap, followed by off-resonant excitation that leads to a chain of facilitated excitation events. After a variable expansion time the Rydberg atoms are field ionized, and from the arrival time distributions the size of the Rydberg cluster after expansion is calculated. Our experimental results agree well with a numerical simulation of the van der Waals explosion.

  11. Differential potential noise measurement during crack initiation

    Energy Technology Data Exchange (ETDEWEB)

    Hettiarachchi, S. [GE-Hitachi Nuclear Energy, Vallecitos Nuclear Center, Sunol, California (United States)]. E-mail: samson.hettiarachchi@gene.ge.com

    2007-07-01

    Electrochemical potential and current noise have been used over the past two decades as methods of detecting general corrosion, pitting corrosion, crevice corrosion, stress corrosion, corrosion in concrete and corrosion under coatings. The methods involved the use of self-generated potential noise/current noise or both, of the material of choice in a given environment. In a variety of these studies, data processing involved techniques such as fast fourier transforms (FFT) to generate the power spectrum that provided the unique signature associated with the type of the corrosion process. This paper deals with a more simplistic method of monitoring differential potential noise measured between two identical slow strain rate test (SSRT) specimens placed close to each other, in a high temperature aqueous environment, while one is being subjected to dynamic strain and the other maintained under static conditions. The differential potential noise (DPN) was monitored as the applied load increased on the slow strain rate test specimen. Unlike self-generated noise, differential potential noise is less affected by electrical noise in the surroundings, and is able to signal the point of oxide film cracking or crack initiation more conveniently without extensive data processing. This method also allows the in-situ detection of crack initiation without interruption of the SSRT test. The DPN signal at the crack initiation stage is different from the signals acquired as cracking progressed due to continuing dynamic strain. Furthermore, the nature of the DPN signal response depends on the type of material used in this study, Type 304 stainless steel or Inconel 182. (author)

  12. Wettability Studies Using Zeta Potential Measurements

    Directory of Open Access Journals (Sweden)

    Ghada Bassioni

    2015-01-01

    Full Text Available Wettability studies have been carried out on reservoir rocks using different techniques such as the Amott-Harvey method, the USBM method, and the contact angle method, all with limitations. In this study, the wettability is studied by discussing the surface charge using zeta potential measurements. The study relies on the finding that carbonated reservoir rocks, consisting of CaCO3 mainly, are positively charged and their surface has the potential to adsorb significant quantities of anions. Moreover, heavy fractions such as asphaltenes are reported to remain afloat depending on dispersive forces present in the oil and its various fractions. Experiments are carried out on aqueous limestone suspension with the addition of crude oil. The experiment is repeated with the use of polymeric inhibitors, A and B. The zeta potential is found to alter depending on the sequence of polymeric inhibitor in oil/water addition. The inhibitor is found to adsorb on the limestone surface, with a net negative charge, causing repulsion between crude oil and the inhibitor and, hence, preventing the deposition of heavy fractions and particularly asphaltenes. This study gives a comprehensive insight on the mechanism of polymeric inhibitor interaction with the surface and the effect of wettability on its performance.

  13. Integrable extended van der Waals model

    Science.gov (United States)

    Giglio, Francesco; Landolfi, Giulio; Moro, Antonio

    2016-10-01

    Inspired by the recent developments in the study of the thermodynamics of van der Waals fluids via the theory of nonlinear conservation laws and the description of phase transitions in terms of classical (dissipative) shock waves, we propose a novel approach to the construction of multi-parameter generalisations of the van der Waals model. The theory of integrable nonlinear conservation laws still represents the inspiring framework. Starting from a macroscopic approach, a four parameter family of integrable extended van der Waals models is indeed constructed in such a way that the equation of state is a solution to an integrable nonlinear conservation law linearisable by a Cole-Hopf transformation. This family is further specified by the request that, in regime of high temperature, far from the critical region, the extended model reproduces asymptotically the standard van der Waals equation of state. We provide a detailed comparison of our extended model with two notable empirical models such as Peng-Robinson and Soave's modification of the Redlich-Kwong equations of state. We show that our extended van der Waals equation of state is compatible with both empirical models for a suitable choice of the free parameters and can be viewed as a master interpolating equation. The present approach also suggests that further generalisations can be obtained by including the class of dispersive and viscous-dispersive nonlinear conservation laws and could lead to a new type of thermodynamic phase transitions associated to nonclassical and dispersive shock waves.

  14. Spherical and hyperspherical harmonics representation of van der Waals aggregates

    Science.gov (United States)

    Lombardi, Andrea; Palazzetti, Federico; Aquilanti, Vincenzo; Grossi, Gaia; Albernaz, Alessandra F.; Barreto, Patricia R. P.; Cruz, Ana Claudia P. S.

    2016-12-01

    The representation of the potential energy surfaces of atom-molecule or molecular dimers interactions should account faithfully for the symmetry properties of the systems, preserving at the same time a compact analytical form. To this aim, the choice of a proper set of coordinates is a necessary precondition. Here we illustrate a description in terms of hyperspherical coordinates and the expansion of the intermolecular interaction energy in terms of hypersherical harmonics, as a general method for building potential energy surfaces suitable for molecular dynamics simulations of van der Waals aggregates. Examples for the prototypical case diatomic-molecule-diatomic-molecule interactions are shown.

  15. Van der Waals universality in homonuclear atom-dimer elastic collisions

    CERN Document Server

    Giannakeas, P

    2016-01-01

    The universal aspects of atom-dimer elastic collisions are investigated within the framework of Faddeev equations. The two-body interactions between the neutral atoms are approximated by the separable potential approach. Our analysis considers a pure van der Waals potential tail as well as soft-core van der Waals interactions permitting us in this manner to address the universally general features of atom-dimer resonant spectra. In particular, we show that the atom-dimer resonances are solely associated with the {\\it excited} Efimov states. Furthermore, the positions of the corresponding resonances for a soft-core potentials with more than 5 bound states are in good agreement with the corresponding results from an infinitely deep pure van der Waals tail potential.

  16. Van der Waals forces and spatial dispersion

    OpenAIRE

    2009-01-01

    A version of the Green's functions theory of the Van der Waals forces which can be conveniently used in the presence of spatial dispersion is presented. The theory is based on the fluctuation-dissipation theorem and is valid for interacting bodies, separated by vacuum. Objections against theories acounting for the spatial dispersion are discussed.

  17. Cluster ions and van der Waals molecules

    CERN Document Server

    Smirnov, Boris M

    1992-01-01

    This review discusses current ideas in the physics and chemistry of cluster ions and Van der Waals molecules as well as presenting numerical data on their parameters and the processes involving them. It is also a detailed reference on basic data relating to many species.

  18. Quantum transport across van der Waals domain walls in bilayer graphene

    Science.gov (United States)

    Abdullah, H. M.; Van Duppen, B.; Zarenia, M.; Bahlouli, H.; Peeters, F. M.

    2017-10-01

    Bilayer graphene can exhibit deformations such that the two graphene sheets are locally detached from each other resulting in a structure consisting of domains with different van der Waals inter-layer coupling. Here we investigate how the presence of these domains affects the transport properties of bilayer graphene. We derive analytical expressions for the transmission probability, and the corresponding conductance, across walls separating different inter-layer coupling domains. We find that the transmission can exhibit a valley-dependent layer asymmetry and that the domain walls have a considerable effect on the chiral tunnelling properties of the charge carriers. We show that transport measurements allow one to obtain the strength with which the two layers are coupled. We perform numerical calculations for systems with two domain walls and find that the availability of multiple transport channels in bilayer graphene significantly modifies the conductance dependence on inter-layer potential asymmetry.

  19. Thermodynamics of Van der Waals Fluids with quantum statistics

    CERN Document Server

    Redlich, Krzysztof

    2016-01-01

    We consider thermodynamics of the van der Waals fluid of quantum systems. We derive general relations of thermodynamic functions and parameters of any ideal gas and the corresponding van der Waals fluid. This provides unambiguous generalization of the classical van der Waals theory to quantum statistical systems. As an example, we apply the van der Waals fluid with fermi statistics to characterize the liquid-gas critical point in nuclear matter. We also introduce the Bose-Einstein condensation in the relativistic van der Waals boson gas, and argue, that it exhibits two-phase structure separated in space.

  20. Van der Waals interactions and the limits of isolated atom models at interfaces.

    Science.gov (United States)

    Kawai, Shigeki; Foster, Adam S; Björkman, Torbjörn; Nowakowska, Sylwia; Björk, Jonas; Canova, Filippo Federici; Gade, Lutz H; Jung, Thomas A; Meyer, Ernst

    2016-05-13

    Van der Waals forces are among the weakest, yet most decisive interactions governing condensation and aggregation processes and the phase behaviour of atomic and molecular matter. Understanding the resulting structural motifs and patterns has become increasingly important in studies of the nanoscale regime. Here we measure the paradigmatic van der Waals interactions represented by the noble gas atom pairs Ar-Xe, Kr-Xe and Xe-Xe with a Xe-functionalized tip of an atomic force microscope at low temperature. Individual rare gas atoms were fixed at node sites of a surface-confined two-dimensional metal-organic framework. We found that the magnitude of the measured force increased with the atomic radius, yet detailed simulation by density functional theory revealed that the adsorption induced charge redistribution strengthened the van der Waals forces by a factor of up to two, thus demonstrating the limits of a purely atomic description of the interaction in these representative systems.

  1. Thermal response in van der Waals heterostructures

    Science.gov (United States)

    Naidu Gandi, Appala; Alshareef, Husam N.; Schwingenschlögl, Udo

    2017-01-01

    We solve numerically the Boltzmann transport equations of the phonons and electrons to understand the thermoelectric response in heterostructures of M2CO2 (M: Ti, Zr, Hf) MXenes with transition metal dichalcogenide monolayers. Low frequency optical phonons are found to occur as a consequence of the van der Waals bonding, contribute significantly to the thermal transport, and compensate for the reduced contributions of the acoustic phonons (increased scattering cross-sections in heterostructures), such that the thermal conductivities turn out to be similar to those of the bare MXenes. Our results indicate that the important superlattice design approach of thermoelectrics (to reduce the thermal conductivity) may be effective for two-dimensional van der Waals materials when used in conjunction with intercalation.

  2. Thermal response in van der Waals heterostructures

    KAUST Repository

    Gandi, Appala

    2016-11-21

    We solve numerically the Boltzmann transport equations of the phonons and electrons to understand the thermoelectric response in heterostructures of M2CO2 (M: Ti, Zr, Hf) MXenes with transition metal dichalcogenide monolayers. Low frequency optical phonons are found to occur as a consequence of the van der Waals bonding, contribute significantly to the thermal transport, and compensate for the reduced contributions of the acoustic phonons (increased scattering cross-sections in heterostructures), such that the thermal conductivities turn out to be similar to those of the bare MXenes. Our results indicate that the important superlattice design approach of thermoelectrics (to reduce the thermal conductivity) may be effective for two-dimensional van der Waals materials when used in conjunction with intercalation. © 2016 IOP Publishing Ltd.

  3. Near-Unity Absorption in van der Waals Semiconductors for Ultrathin Optoelectronics.

    Science.gov (United States)

    Jariwala, Deep; Davoyan, Artur R; Tagliabue, Giulia; Sherrott, Michelle C; Wong, Joeson; Atwater, Harry A

    2016-09-14

    We demonstrate near-unity, broadband absorbing optoelectronic devices using sub-15 nm thick transition metal dichalcogenides (TMDCs) of molybdenum and tungsten as van der Waals semiconductor active layers. Specifically, we report that near-unity light absorption is possible in extremely thin (<15 nm) van der Waals semiconductor structures by coupling to strongly damped optical modes of semiconductor/metal heterostructures. We further fabricate Schottky junction devices using these highly absorbing heterostructures and characterize their optoelectronic performance. Our work addresses one of the key criteria to enable TMDCs as potential candidates to achieve high optoelectronic efficiency.

  4. Observation of scalar nuclear spin-spin coupling in van der Waals molecules

    CERN Document Server

    Ledbetter, Micah; Bagno, Alessandro; Tran, Nhan; Romalis, Michael

    2011-01-01

    Scalar couplings between covalently bound nuclear spins are a ubiquitous feature in nuclear magnetic resonance (NMR) experiments, imparting valuable information to NMR spectra regarding molecular structure and conformation. Such couplings arise due to a second-order hyperfine interaction, and, in principle, the same mechanism should lead to scalar couplings between nuclear spins in unbound van der Waals complexes. Here, we report the first observation of scalar couplings between nuclei in van der Waals molecules. Our measurements are performed in a solution of hyperpolarized ${\\rm ^{129}Xe}$ and pentane, using superconducting quantum interference devices to detect NMR in 10 mG fields, and are in good agreement with calculations based on density functional theory. van der Waals forces play an important role in many physical phenomena, and hence the techniques presented here may provide a new method for probing such interactions.

  5. van der Waals interaction of a neutral atom with the surface of a metal or dielectric nanosphere

    Energy Technology Data Exchange (ETDEWEB)

    Schmidt, Regine; Chormaic, Sile Nic [Photonics Centre, Tyndall National Institute, Prospect Row, Cork (Ireland); Minogin, Vladimir G, E-mail: s.nicchormaic@ucc.ie [Institute of Spectroscopy Russ. Ac. of Sciences, 142190 Troitsk, Moscow region (Russian Federation)

    2011-01-14

    We analyse the van der Waals interaction of a neutral atom with the internal and external surfaces of either a metal or dielectric nanosphere. We derive closed analytical equations for the van der Waals interaction energy using an electrostatic approximation and show that the energy increases or decreases as a function of the atom's distance from the surface, depending on the surface curvature. For concave spherical surfaces, the van der Waals energy can increase by up to a factor of 6, while for convex surfaces it decreases by as much as a factor of 2, when compared to that obtained for a flat surface. The derived analytical equations are very simple and can be used for a comparison between theory and experimental measurements of the van der Waals constant, C{sub 3}.

  6. Kinetic Roughening and Material Optical Properties Influence on Van der Waals/Casimir Forces

    NARCIS (Netherlands)

    van Zwol, P. J.; Palasantzas, G.

    Atomic force microscopy measurements and force theory calculations using the Lifshitz theory show that van der Waals/Casimir dispersive forces have a strong dependence on surface roughness and material optical properties. It is found that at separations below 100 nm the roughness effect is

  7. Influence of dielectric properties on van der Waals/Casimir forces in solid-liquid systems

    NARCIS (Netherlands)

    van Zwol, P. J.; Palasantzas, G.; De Hosson, J. Th. M.

    In this paper, we present calculations of van der Waals/Casimir forces, described by Lifshitz theory, for the solid-liquid-solid system using measured dielectric functions of all involved materials for the wavelength range from millimeters down to subnanometers. It is shown that even if the

  8. Van der Waals Type Model for Neutron-Proton Elastic Scattering at High Energies

    Science.gov (United States)

    Aleem, F.

    1980-12-01

    The most recent measurements of the angular distribution and total cross-section for neutron-proton elastic scattering between 70< pL <400 GeV/c with squared four momentum transfer -t ≤ 3.6 (GeV/c)2 have been explained using Van der Waals type model.

  9. Critical fluctuations in models with van der Waals interactions

    CERN Document Server

    Vovchenko, V; Gorenstein, M I; Poberezhnyuk, R V; Stoecker, H

    2016-01-01

    Particle number fluctuations are considered within the van der Waals (VDW) equation, which contains both attractive (mean-field) and repulsive (eigenvolume) interactions. The VDW equation is used to calculate the scaled variance of particle number fluctuations in generic Boltzmann VDW system and in nuclear matter. The strongly intensive measures $\\Delta[E^*,N]$ and $\\Sigma[E^*,N]$ of the particle number and excitation energy fluctuations are also considered, and, similarly, show singular behavior near the critical point. The $\\Delta[E^*,N]$ measure is shown to attain both positive and negative values in the vicinity of critical point. Based on universality argument, similar behavior is expected to occur in the vicinity of the QCD critical point.

  10. Flexible ferroelectric element based on van der Waals heteroepitaxy.

    Science.gov (United States)

    Jiang, Jie; Bitla, Yugandhar; Huang, Chun-Wei; Do, Thi Hien; Liu, Heng-Jui; Hsieh, Ying-Hui; Ma, Chun-Hao; Jang, Chi-Yuan; Lai, Yu-Hong; Chiu, Po-Wen; Wu, Wen-Wei; Chen, Yi-Chun; Zhou, Yi-Chun; Chu, Ying-Hao

    2017-06-01

    We present a promising technology for nonvolatile flexible electronic devices: A direct fabrication of epitaxial lead zirconium titanate (PZT) on flexible mica substrate via van der Waals epitaxy. These single-crystalline flexible ferroelectric PZT films not only retain their performance, reliability, and thermal stability comparable to those on rigid counterparts in tests of nonvolatile memory elements but also exhibit remarkable mechanical properties with robust operation in bent states (bending radii down to 2.5 mm) and cycling tests (1000 times). This study marks the technological advancement toward realizing much-awaited flexible yet single-crystalline nonvolatile electronic devices for the design and development of flexible, lightweight, and next-generation smart devices with potential applications in electronics, robotics, automotive, health care, industrial, and military systems.

  11. EDITORIAL: Van der Waals interactions in advanced materials, in memory of David C Langreth Van der Waals interactions in advanced materials, in memory of David C Langreth

    Science.gov (United States)

    Hyldgaard, Per; Rahman, Talat S.

    2012-10-01

    forces by examining the impact their inclusion has on predictions of material properties. On the other hand, the experimental and theoretical study of Casimir forces also plays a vital role in the exploration of material behavior. vdW forces are related to the Casimir force but lack retardation effects. While the vdW bonding depends on additional effects (for example, the multipole contributions that reflect image-plane effects), the study of Casimir forces provides direct (and not indirect) measurements of the nature of interactions. Klimchitskaya et al note that to reconcile explicit measurements of the Casmir forces between semiconductor fragments within the Lifshitz description, it is relevant to question the Drude-like description of the contributions from free carriers and instead proceed with a formulation based only on optical observations of the permittivity. This optical response can be seen as a reflection of a more plasmon-like behavior. The authors suggest an experiment involving the study of the impact on the Casimir forces by a Mott transition in doped semiconductors. Such an experiment would permit explicit testing of the validity of the present model for Casimir forces and hence provide additional perspectives on the nature of dispersive interactions. There is an effort to store energy, e.g. H2 or CO2, inside a range of open cage-like structures, such as metal organics frameworks (MOF) or clathrates. The fact that the internal molecular adhesion is dominated by vdW forces suggests that the storage and retrieval costs could perhaps be lowered as compared to an approach that involves more traditional chemical compounds. Nijem et al have provided spectroscopic characterization of vdW interactions of both hydrogen molecules and CO in a specific MOF. The study includes a vdW-DF calculation of structure and a theoretical prediction of expected infrared activity. The potential applications to energy materials have motivated more theoretical characterizations

  12. Electronic structure of transferred graphene/h-BN van der Waals heterostructures with nonzero stacking angles by nano-ARPES

    Science.gov (United States)

    Wang, Eryin; Chen, Guorui; Wan, Guoliang; Lu, Xiaobo; Chen, Chaoyu; Avila, Jose; Fedorov, Alexei V.; Zhang, Guangyu; Asensio, Maria C.; Zhang, Yuanbo; Zhou, Shuyun

    2016-11-01

    In van der Waals heterostructures, the periodic potential from the Moiré superlattice can be used as a control knob to modulate the electronic structure of the constituent materials. Here we present a nanoscale angle-resolved photoemission spectroscopy (nano-ARPES) study of transferred graphene/h-BN heterostructures with two different stacking angles of 2.4° and 4.3° respectively. Our measurements reveal six replicas of graphene Dirac cones at the superlattice Brillouin zone (SBZ) centers. The size of the SBZ and its relative rotation angle to the graphene BZ are in good agreement with Moiré superlattice period extracted from atomic force microscopy (AFM) measurements. Comparison to the epitaxial graphene/h-BN with 0° stacking angles suggests that the interaction between graphene and h-BN decreases with increasing stacking angle.

  13. Inversion of Spin Signal and Spin Filtering in Ferromagnet|Hexagonal Boron Nitride-Graphene van der Waals Heterostructures

    Science.gov (United States)

    Kamalakar, M. Venkata; Dankert, André; Kelly, Paul J.; Dash, Saroj P.

    2016-02-01

    Two dimensional atomically thin crystals of graphene and its insulating isomorph hexagonal boron nitride (h-BN) are promising materials for spintronic applications. While graphene is an ideal medium for long distance spin transport, h-BN is an insulating tunnel barrier that has potential for efficient spin polarized tunneling from ferromagnets. Here, we demonstrate the spin filtering effect in cobalt|few layer h-BN|graphene junctions leading to a large negative spin polarization in graphene at room temperature. Through nonlocal pure spin transport and Hanle precession measurements performed on devices with different interface barrier conditions, we associate the negative spin polarization with high resistance few layer h-BN|ferromagnet contacts. Detailed bias and gate dependent measurements reinforce the robustness of the effect in our devices. These spintronic effects in two-dimensional van der Waals heterostructures hold promise for future spin based logic and memory applications.

  14. The role of van der waals interaction on quantum-mechanical tunneling

    Energy Technology Data Exchange (ETDEWEB)

    Takayanagi, Toshiyuki; Kurosaki, Yuzuru [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment

    1998-10-01

    We present three-dimensional quantum cumulative reaction probabilities for the F + H{sub 2}, D{sub 2}, and HD reactions with a special emphasis on resonances associated with quasi-bound states localized in the reactant van der Waals region of the potential energy surface. The accurate ab initio potential surface of Stark and Werner and the less accurate 5SEC-W surface developed by Truhlar and co-workers have been employed. (author)

  15. Interpretation of van der Waal density functionals

    CERN Document Server

    Hyldgaard, Per; Schröder, Elsebeth

    2014-01-01

    The nonlocal correlation energy in the van der Waals density functional (vdW-DF) method [Phys. Rev. Lett. 92, 246401 (2004); Phys. Rev. B 76, 125112 (2007); Phys. Rev. B 89, 035412 (2014)] can be interpreted in terms of a coupling of zero-point energies of characteristic modes of semilocal exchange-correlation (xc) holes. These xc holes reflect the internal functional in the framework of the vdW-DF method [Phys. Rev. B 82, 081101(2010)]. We explore the internal xc hole components, showing that they share properties with those of the generalized-gradient approximation. We use these results to illustrate the nonlocality in the vdW-DF description and analyze the vdW-DF formulation of nonlocal correlation.

  16. Universal curves for the van der Waals interaction between single-walled carbon nanotubes.

    Science.gov (United States)

    Pogorelov, Evgeny G; Zhbanov, Alexander I; Chang, Yia-Chung; Yang, Sung

    2012-01-17

    We report very simple and accurate algebraic expressions for the van der Waals (VDW) potentials and the forces between two parallel and crossed carbon nanotubes. The Lennard-Jones potential for two carbon atoms and the method of the smeared-out approximation suggested by Girifalco were used. It is found that the interaction between parallel and crossed tubes is described by two universal curves for parallel and crossed configurations that do not depend on the van der Waals constants, the angle between tubes, and the surface density of atoms and their nature but only on the dimensionless distance. The explicit functions for equilibrium VDW distances, well depths, and maximal attractive forces have been given. These results may be used as a guide for the analysis of experimental data to investigate the interaction between nanotubes of various natures.

  17. Two dimensional graphene nanogenerator by coulomb dragging: Moving van der Waals heterostructure

    Energy Technology Data Exchange (ETDEWEB)

    Zhong, Huikai; Li, Xiaoqiang; Wu, Zhiqian; Zhang, Shengjiao; Xu, Zhijuan [Department of Information Science and Electronic Engineering, Zhejiang University, Hangzhou 310027 (China); Chen, Hongsheng; Lin, Shisheng, E-mail: shishenglin@zju.edu.cn [Department of Information Science and Electronic Engineering, Zhejiang University, Hangzhou 310027 (China); State Key Laboratory of Modern Optical Instrumentation, Zhejiang University, Hangzhou 310027 (China)

    2015-06-15

    Harvesting energy from environment is the current focus of scientific community. Here, we demonstrate a graphene nanogenerator, which is based on moving van der Waals heterostructure formed between graphene and two dimensional (2D) graphene oxide (GO). This nanogenerator can convert mechanical energy into electricity with a voltage output of around 10 mV. Systematic experiments reveal the generated electricity originates from the coulomb interaction induced momentum transfer between 2D GO and holes in graphene. 2D boron nitride was also demonstrated to be effective in the framework of moving van der Waals heterostructure nanogenerator. This investigation of nanogenerator based on the interaction between 2D macromolecule materials will be important to understand the origin of the flow-induced potential in nanomaterials and may have great potential in practical applications.

  18. Two dimensional graphene nanogenerator by coulomb dragging: Moving van der Waals heterostructure

    Science.gov (United States)

    Zhong, Huikai; Li, Xiaoqiang; Wu, Zhiqian; Zhang, Shengjiao; Xu, Zhijuan; Chen, Hongsheng; Lin, Shisheng

    2015-06-01

    Harvesting energy from environment is the current focus of scientific community. Here, we demonstrate a graphene nanogenerator, which is based on moving van der Waals heterostructure formed between graphene and two dimensional (2D) graphene oxide (GO). This nanogenerator can convert mechanical energy into electricity with a voltage output of around 10 mV. Systematic experiments reveal the generated electricity originates from the coulomb interaction induced momentum transfer between 2D GO and holes in graphene. 2D boron nitride was also demonstrated to be effective in the framework of moving van der Waals heterostructure nanogenerator. This investigation of nanogenerator based on the interaction between 2D macromolecule materials will be important to understand the origin of the flow-induced potential in nanomaterials and may have great potential in practical applications.

  19. Van der Waals interactions in rare-gas dimers: The role of interparticle interactions

    CERN Document Server

    Chen, Yu-Ting; Chai, Jeng-Da

    2015-01-01

    We investigate the potential energy curves of rare-gas dimers with various ranges and strengths of interparticle interactions (nuclear-electron, electron-electron, and nuclear-nuclear interactions). Our investigation is based on the highly accurate coupled-cluster theory associated with those interparticle interactions. For comparison, the performance of the corresponding Hartree-Fock theory, second-order Moller-Plesset perturbation theory, and density functional theory is also investigated. Our results reveal that when the interparticle interactions retain the long-range Coulomb tails, the nature of van der Waals interactions in the rare-gas dimers remains similar. By contrast, when the interparticle interactions are sufficiently short-range, the conventional van der Waals interactions in the rare-gas dimers completely disappear, yielding purely repulsive potential energy curves.

  20. The van der Waals fluid and its role in cosmology

    Science.gov (United States)

    Jantsch, Rudinei C. S.; Christmann, Marcus H. B.; Kremer, Gilberto M.

    2016-01-01

    We analyze the properties of a generic cosmological fluid described by the van der Waals equation-of-state. Exact solutions for the energy-density evolution are found as implicit functions of the scale factor for a flat Friedmann-Robertson-Walker (FRW) spacetime. The possible values of the free parameter in the van der Waals equation are selected a posteriori, in accordance with asymptotic behaviors that are physically relevant. The stability of the model against small perturbations is studied through the hydrodynamic perturbations of the fluid for the relevant cases. It is found that a van der Waals fluid seems appropriate to describe noneternal inflationary scenarios.

  1. The van der Waals fluid and its role in cosmology

    CERN Document Server

    Jantsch, Rudinei C S; Kremer, Gilberto M

    2016-01-01

    We analyze the properties of a generic cosmological fluid described by the van der Waals equation of state. Exact solutions for the energy density evolution are found as implicit functions of the scale factor for a flat Friedmann-Robertson-Walker space-time. The possible values of the free parameter in the van der Waals equation are selected \\emph{a posteriori}, in accordance with asymptotic behaviors that are physically relevant. The stability of the model against small perturbations is studied through the hydrodynamic perturbations of the fluid for the relevant cases. It is found that a van der Waals fluid seems appropriate to describe non-eternal inflationary scenarios.

  2. The van der Waals force and gravitational force in matter

    CERN Document Server

    Zhang, Lei

    2013-01-01

    It was thought that the van der Waals force and gravitational force were distinct. Now a model is used to describe the attraction between macroscopic objects according to van der Waals interaction. The force between two objects with thermal equilibrium deviates from the law of universal gravitation slightly, and the gravity on the earth is explained approximately. We argue that the gravitational force is the van der Waals force actually. In other words, the gravitational force and mass are related to the quantum fluctuations of electron clouds in atoms, and these parameters are dictated by dielectric susceptibility.

  3. Theoretical Study of the Pyridine-Helium van der Waals Complexes

    DEFF Research Database (Denmark)

    v, Hubert; Henriksen, Christian; Fernandez, Berta

    2015-01-01

    In this study we evaluate a high-level ab initio ground-state intermolecular potential-energy surface for the pyridine–He van der Waals complex, using the CCSD(T) method and Dunning’s augmented correlation consistent polarized valence double-ζ basis set extended with a set of 3s3p2d1f1g midbond f...

  4. Automated and continuous redox potential measurements in soil.

    Science.gov (United States)

    Vorenhout, Michel; van der Geest, Harm G; van Marum, Daan; Wattel, Kees; Eijsackers, Herman J P

    2004-01-01

    Redox potential (Eh) describes the electrical state of a matrix. In soils, Eh is an important parameter controlling the persistence of many organic and inorganic compounds. A popular, but also criticized, manual measuring method makes use of a small tip of Pt placed on a copper wire that is placed in the soil; a reference electrode is placed in the same soil at a fixed distance. Fluctuations in redox potential values measured in the soil can be very large and depth-dependent. This will be overlooked when making single-point measurements. We developed the datalogger Hypnos 2.0 for continuous redox potential and temperature measurements at various depths in the soil and without disturbance of the site. Hypnos is field-deployable, relatively cheap, and runs on batteries. The datalogger can use a "sleep mode" between sampling events. In sleep mode, there is no constant voltage on the Pt wire or the reference electrode, but there is only a short pulse during sampling. We did not measure an effect of this short pulse on the measured redox potential. In sandy soils in mesocosms and in a salt marsh soil we measured changes in the Eh as large as from -400 to +100 mV within 4 d, and daily cycles of 200 mV. Both absolute redox potential values and their diurnal variations were depth-dependent. Because single redox measurements are insufficient in describing redox conditions in some soil systems, Hypnos can be a powerful tool when studying the effects of fluctuating redox conditions on metal availability and pollutant degradation.

  5. Strong Van der Waals force in the hadron physics

    CERN Document Server

    Sawada, T

    2000-01-01

    Possible strong Van der Waals interaction between hadrons is searched in the P-wave amplitude of the pi-pi scattering by removing the cut of the two-pion exchange spectrum as well as the unitarity cut.

  6. Measurements of Plasma Potential Distribution in Segmented Electrode Hall Thruster

    Energy Technology Data Exchange (ETDEWEB)

    Y. Raitses; D. Staack; N.J. Fisch

    2001-10-16

    Use of a segmented electrode placed at the Hall thruster exit can substantially reduce the voltage potential drop in the fringing magnetic field outside the thruster channel. In this paper, we investigate the dependence of this effect on thruster operating conditions and segmented electrode configuration. A fast movable emissive probe is used to measure plasma potential in a 1 kW laboratory Hall thruster with semented electrodes made of a graphite material. Relatively small probe-induced perturbations of the thruster discharge in the vicinity of the thruster exit allow a reasonable comparison of the measured results for different thruster configurations. It is shown that the plasma potential distribution is almost not sensitive to changes of the electrode potential, but depends on the magnetic field distribution and the electrode placement.

  7. Van der Waals Force Assisted Heat Transfer

    Science.gov (United States)

    Sasihithlu, K.; Pendry, J. B.; Craster, R. V.

    2017-02-01

    Phonons (collective atomic vibrations in solids) are more effective in transporting heat than photons. This is the reason why the conduction mode of heat transport in nonmetals (mediated by phonons) is dominant compared to the radiation mode of heat transport (mediated by photons). However, since phonons are unable to traverse a vacuum gap (unlike photons), it is commonly believed that two bodies separated by a gap cannot exchange heat via phonons. Recently, a mechanism was proposed [J. B. Pendry, K. Sasihithlu, and R. V. Craster, Phys. Rev. B 94, 075414 (2016)] by which phonons can transport heat across a vacuum gap - through the Van der Waals interaction between two bodies with gap less than the wavelength of light. Such heat transfer mechanisms are highly relevant for heating (and cooling) of nanostructures; the heating of the flying heads in magnetic storage disks is a case in point. Here, the theoretical derivation for modelling phonon transmission is revisited and extended to the case of two bodies made of different materials separated by a vacuum gap. Magnitudes of phonon transmission, and hence the heat transfer, for commonly used materials in the micro- and nano-electromechanical industry are calculated and compared with the calculation of conduction heat transfer through air for small gaps as well as the heat transfer calculation due to photon exchange.

  8. Van der Waals Interactions in Aspirin

    Science.gov (United States)

    Reilly, Anthony; Tkatchenko, Alexandre

    2015-03-01

    The ability of molecules to yield multiple solid forms, or polymorphs, has significance for diverse applications ranging from drug design and food chemistry to nonlinear optics and hydrogen storage. In particular, aspirin has been used and studied for over a century, but has only recently been shown to have an additional polymorphic form, known as form II. Since the two observed solid forms of aspirin are degenerate in terms of lattice energy, kinetic effects have been suggested to determine the metastability of the less abundant form II. Here, first-principles calculations provide an alternative explanation based on free-energy differences at room temperature. The explicit consideration of many-body van der Waals interactions in the free energy demonstrates that the stability of the most abundant form of aspirin is due to a subtle coupling between collective electronic fluctuations and quantized lattice vibrations. In addition, a systematic analysis of the elastic properties of the two forms of aspirin rules out mechanical instability of form II as making it metastable.

  9. A potential issue for the OPERA neutrino velocity measurement

    CERN Document Server

    Palazzo, Antonio

    2011-01-01

    We discuss what we think may be a potential issue for the OPERA neutrino velocity measurement, in connection with the statistical procedure employed for the extraction of the neutrino time of flight. We show that such a potential problem may have eluded the Monte Carlo tests performed by the collaboration. Only the collaboration has the information necessary to clarify the issue, make quantitative estimates and trace definitive conclusions.

  10. Evaluating the Measurement of Activated Sludge Foam Potential

    Directory of Open Access Journals (Sweden)

    Eoghan O’Flaherty

    2011-03-01

    Full Text Available The most widely used technique for assessing the propensity of activated sludge to suffer from biological foaming is to measure foam potential. This involves measuring the amount of foam produced from sludge under conditions of controlled aeration. Two approaches have been adopted: (1 Air is passed through specially designed columns from fine porous diffusers at a fixed rate to form uniform sized bubbles or (2 employing Alka-Seltzer™ tablets which effervesce when added to the sludge. Both tests generate foam formation which can then be quantified. Foam assessment in activated sludge is reviewed. A sintered disc aeration column was compared with the Alka-Seltzer™ test method and both methods examined under a range of different environmental conditions. Foam potential measured by the sintered disc method displayed better repeatability compared to the Alka-Seltzer test. The use of a wire cage placed over the tablets greatly improved the precision of the Alka-Seltzer test. A positive linear correlation was also found between foam potential and temperature (4–20 °C. Sludge solids concentration was also shown to influence foaming potential making comparisons between reactors problematic. Recommendations on how to improve the repeatability of foam potential measurements are given.

  11. Lifshitz theory of van der Waals pressure in dissipative media

    CERN Document Server

    Zheng, Yi

    2010-01-01

    We derive a first--principles method of determining the van der Waals or Casimir pressure in a dissipative and dispersive planar multilayered system by calculating the Maxwell stress tensor in a fictitious layer of vacuum, that is eventually made to vanish, introduced in the structure. This is illustrated by calculating the van der Waals pressure in a thin film with dissipative properties embedded between two semi--infinite media.

  12. Nano Electronics on Atomically Controlled van der Waals Quantum Heterostructures

    Science.gov (United States)

    2015-03-30

    Final 3. DATES COVERED (From - To) 14 Aug 13 to 13 Feb 15 4. TITLE AND SUBTITLE Nano Electronics on Atomically Controlled van der Waals...OMB control number. 1. REPORT DATE 14 MAY 2015 2. REPORT TYPE Final 3. DATES COVERED 14-08-2013 to 13-02-2015 4. TITLE AND SUBTITLE Nano ...AOARD Grant 134122 “ Nano Electronics on Atomically Controlled van der Waals Quantum Heterostructures” 3/30/2015 Name of Principal

  13. Van der Waals Type Model and Structure in π-p Elastic Scattering at High Energies

    Science.gov (United States)

    Aleem, F.

    1982-10-01

    The most recent measurement of the angular distribution for π-p elastic scattering at pL =50 and 200 GeV/c which show a structure near -t ≈ 4(GeV/c)2, with squared four momentum transfer -t extended to 10(GeV/c)2, and the total cross section data for 50 ≤ pL ≤ 370 GeV/c have been simultaneously explained by using Van der Waal's type model.

  14. A simplified implementation of van der Waals density functionals for first-principles molecular dynamics applications

    Science.gov (United States)

    Wu, Jun; Gygi, François

    2012-06-01

    We present a simplified implementation of the non-local van der Waals correlation functional introduced by Dion et al. [Phys. Rev. Lett. 92, 246401 (2004)] and reformulated by Román-Pérez et al. [Phys. Rev. Lett. 103, 096102 (2009)]. The proposed numerical approach removes the logarithmic singularity of the kernel function. Complete expressions of the self-consistent correlation potential and of the stress tensor are given. Combined with various choices of exchange functionals, five versions of van der Waals density functionals are implemented. Applications to the computation of the interaction energy of the benzene-water complex and to the computation of the equilibrium cell parameters of the benzene crystal are presented. As an example of crystal structure calculation involving a mixture of hydrogen bonding and dispersion interactions, we compute the equilibrium structure of two polymorphs of aspirin (2-acetoxybenzoic acid, C9H8O4) in the P21/c monoclinic structure.

  15. Bonding in Mercury-Alkali Molecules: Orbital-driven van der Waals Complexes

    Directory of Open Access Journals (Sweden)

    Dieter Cremer

    2008-06-01

    Full Text Available The bonding situation in mercury-alkali diatomics HgA (2Σ+ (A = Li, Na, K, Rb has been investigated employing the relativistic all-electron method Normalized Elimination of the Small Component (NESC, CCSD(T, and augmented VTZ basis sets. Although Hg,A interactions are typical of van der Waals complexes, trends in calculated De values can be explained on the basis of a 3-electron 2-orbital model utilizing calculated ionization potentials and the De values of HgA+(1Σ+ diatomics. HgA molecules are identified as orbital-driven van der Waals complexes. The relevance of results for the understanding of the properties of liquid alkali metal amalgams is discussed.

  16. Modified Van der Waals equation and law of corresponding states

    Science.gov (United States)

    Zhong, Wei; Xiao, Changming; Zhu, Yongkai

    2017-04-01

    It is well known that the Van der Waals equation is a modification of the ideal gas law, yet it can be used to describe both gas and liquid, and some important messages can be obtained from this state equation. However, the Van der Waals equation is not a precise state equation, and it does not give a good description of the law of corresponding states. In this paper, we expand the Van der Waals equation into its Taylor's series form, and then modify the fourth order expansion by changing the constant Virial coefficients into their analogous ones. Via this way, a more precise result about the law of corresponding states has been obtained, and the law of corresponding states can then be expressed as: in terms of the reduced variables, all fluids should obey the same equation with the analogous Virial coefficients. In addition, the system of 3 He with quantum effects has also been taken into consideration with our modified Van der Waals equation, and it is found that, for a normal system without quantum effect, the modification on ideal gas law from the Van der Waals equation is more significant than the real case, however, for a system with quantum effect, this modification is less significant than the real case, thus a factor is introduced in this paper to weaken or strengthen the modification of the Van der Waals equation, respectively.

  17. Influence of beverage composition on the results of erosive potential measurement by different measurement techniques.

    NARCIS (Netherlands)

    Jager, D.H.; Vieira, A.M.; Ruben, J.L.; Huysmans, M.C.D.N.J.M.

    2008-01-01

    The influence of beverage composition on the measurement of erosive potential is unclear. The aim of this study was to evaluate whether beverage composition influences the measurement of erosive potential and to evaluate the influence of exposure in small and large volumes. Eleven beverages were inc

  18. Influence of beverage composition on the results of erosive potential measurement by different measurement techniques

    NARCIS (Netherlands)

    Jager, D. H. J.; Vieira, A. M.; Ruben, J. L.; Huysmans, M. C. D. N. J. M.

    2008-01-01

    The influence of beverage composition on the measurement of erosive potential is unclear. The aim of this study was to evaluate whether beverage composition influences the measurement of erosive potential and to evaluate the influence of exposure in small and large volumes. Eleven beverages were inc

  19. Work function measurements by the field emission retarding potential method.

    Science.gov (United States)

    Strayer, R. W.; Mackie, W.; Swanson, L. W.

    1973-01-01

    Description of the theoretical foundation of the field electron retarding potential method, and review of its experimental application to the measurement of single crystal face work functions. The results obtained from several substrates are discussed. An interesting and useful fallout from the experimental approach described is the ability to accurately measure the elastic and inelastic reflection coefficient for impinging electrons to near zero-volt energy.

  20. Underwater adhesion of abalone: The role of van der Waals and capillary forces

    Energy Technology Data Exchange (ETDEWEB)

    Lin, A.Y.M., E-mail: albertlin22@yahoo.com [Materials Science and Engineering Program, University of California, San Diego, La Jolla, CA 92093 (United States); Brunner, R. [Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA 92093 (United States)] [Department of Nanoengineering, University of California, San Diego, La Jolla, CA 92093 (United States); Chen, P.Y. [Materials Science and Engineering Program, University of California, San Diego, La Jolla, CA 92093 (United States); Talke, F.E. [Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA 92093 (United States)] [Center for Magnetic Recording Research, University of California, San Diego, La Jolla, CA 92093 (United States); Meyers, M.A. [Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA 92093 (United States)] [Department of Nanoengineering, University of California, San Diego, La Jolla, CA 92093 (United States)] [Materials Science and Engineering Program, University of California, San Diego, La Jolla, CA 92093 (United States)

    2009-08-15

    The observation of the pedal foot of the red abalone Haliotis rufescens reveals the presence of micrometer-scaled setae terminating in nanometer-sized cylindrical fibrils, with some resemblance to those found on the gecko foot. Atomic force microscopy (AFM) pull-off force measurements on a single seta are compared with theoretical estimates for van der Waals attraction obtained through the Johnson-Kendall-Roberts (JKR) equation, approximately 600 nN, and show agreement. The use of the JKR equation is justified through an analysis of the shape of the fibril extremities (parabolic) as well as their diameter ({approx}200 nm). Measurements under varying humidity conditions indicate that additional capillary interactions play a role, since the pull-off force increases with humidity. It is proposed that both van der Waals and capillary forces play a role in the attachment mechanism of H. rufescens, effectively enabling suction to reach its theoretical limit. Bulk pull-off force measurements on entire live animals yield an average detachment stress of 115 kPa, consistent with theoretical estimates. The setae and nanoscale fibril terminations enable compliance to surfaces with a variety of roughnesses, effectively sealing the interface, in addition to providing capillary and van der Waals forces.

  1. Transient zeta-potential measurements in hydrophobic, TOPAS microfluidic substrates.

    Science.gov (United States)

    Tandon, Vishal; Bhagavatula, Sharath K; Kirby, Brian J

    2009-08-01

    We utilize time-resolved electrokinetic measurements in order to study the electrokinetic properties of silica and TOPAS microfluidic channels as a function of the time history of the fluid-solid interface. In pressure-driven flow through TOPAS microchannels, the zeta-potential as inferred from streaming potential measurements decays exponentially by a factor of 1.5 with a characteristic decay time of 3 h after the initial formation of the fluid-solid interface. A similar exponential decay is observed immediately after water is exchanged for ethanol as the solvent in the system. In electroosmotically driven flow through TOPAS microchannels, the zeta-potential as inferred through current monitoring experiments was constant in time. No electrokinetic transients were observed in silica microchannels under these flow conditions.

  2. Van der Waals equation of state revisited: importance of the dispersion correction.

    Science.gov (United States)

    de Visser, Sam P

    2011-04-28

    One of the most basic equations of state describing nonideal gases and liquids is the van der Waals equation of state, and as a consequence, it is generally taught in most first year undergraduate chemistry courses. In this work, we show that the constants a and b in the van der Waals equation of state are linearly proportional to the polarizability volume of the molecules in a gas or liquid. Using this information, a new thermodynamic one-parameter equation of state is derived that contains experimentally measurable variables and physics constants only. This is the first equation of state apart from the Ideal Gas Law that contains experimentally measurable variables and physics constants only, and as such, it may be a very useful and practical equation for the description of dilute gases and liquids. The modified van der Waals equation of state describes pV as the sum of repulsive and attractive intermolecular interaction energies that are represented by an exponential repulsion function between the electron clouds of the molecules and a London dispersion component, respectively. The newly derived equation of state is tested against experimental data for several gas and liquid examples, and the agreement is satisfactory. The description of the equation of state as a one-parameter function also has implications on other thermodynamic functions, such as critical parameters, virial coefficients, and isothermal compressibilities. Using our modified van der Waals equation of state, we show that all of these properties are a function of the molecular polarizability volume. Correlations of experimental data confirm the derived proportionalities.

  3. First principles calculations of solid-state thermionic transport in layered van der Waals heterostructures

    Science.gov (United States)

    Wang, Xiaoming; Zebarjadi, Mona; Esfarjani, Keivan

    2016-08-01

    This work aims at understanding solid-state energy conversion and transport in layered (van der Waals) heterostructures in contact with metallic electrodes via a first-principles approach. As an illustration, a graphene/phosphorene/graphene heterostructure in contact with gold electrodes is studied by using density functional theory (DFT)-based first principles calculations combined with real space Green's function (GF) formalism. We show that for a monolayer phosphorene, quantum tunneling dominates the transport. By adding more phosphorene layers, one can switch from tunneling-dominated transport to thermionic-dominated transport, resulting in transporting more heat per charge carrier, thus, enhancing the cooling coefficient of performance. The use of layered van der Waals heterostructures has two advantages: (a) thermionic transport barriers can be tuned by changing the number of layers, and (b) thermal conductance across these non-covalent structures is very weak. The phonon thermal conductance of the present van der Waals heterostructure is found to be 4.1 MW m-2 K-1 which is one order of magnitude lower than the lowest value for that of covalently-bonded interfaces. The thermionic coefficient of performance for the proposed device is 18.5 at 600 K corresponding to an equivalent ZT of 0.13, which is significant for nanoscale devices. This study shows that layered van der Waals structures have great potential to be used as solid-state energy-conversion devices.This work aims at understanding solid-state energy conversion and transport in layered (van der Waals) heterostructures in contact with metallic electrodes via a first-principles approach. As an illustration, a graphene/phosphorene/graphene heterostructure in contact with gold electrodes is studied by using density functional theory (DFT)-based first principles calculations combined with real space Green's function (GF) formalism. We show that for a monolayer phosphorene, quantum tunneling dominates the

  4. Morphodynamic responds of groyne fields to the lowering of crest level of the groynes in the Waal River, The Netherlands

    NARCIS (Netherlands)

    Busnelli, M.M.; Schuurman, F.; Sieben, A.; Wal, Maarten van der; Hector, H.

    2011-01-01

    The lowering of the crest of the groynes in the River Waal is one of the measures being applied in the Netherlands to reduce the water levels at high water conditions. A total of 750 groynes will be lowered lengthwise by 1 to 2 meters. An expected side-effect is sedimentation in the main channel, du

  5. High Energy Proton-Proton Elastic Scattering for Large Momentum Transfers and Van der Waals Type Model

    Science.gov (United States)

    Aleem, F.

    1980-03-01

    The most recent measurements of the angular distribution in proton-proton elastic scattering at sqrt{s}=27.4, 45 and 62GeV with squared four momentum transfer, -t, extending up to 14(GeV/c)2, have been explained using Van der Waals type model.

  6. Measuring surface flow velocity with smartphones: potential for citizen observatories

    Science.gov (United States)

    Weijs, Steven V.; Chen, Zichong; Brauchli, Tristan; Huwald, Hendrik

    2014-05-01

    Stream flow velocity is an important variable for discharge estimation and research on sediment dynamics. Given the influence of the latter on rating curves (stage-discharge relations), and the relative scarcity of direct streamflow measurements, surface velocity measurements can offer important information for, e.g., flood warning, hydropower, and hydrological science and engineering in general. With the growing amount of sensing and computing power in the hands of more outdoorsy individuals, and the advances in image processing techniques, there is now a tremendous potential to obtain hydrologically relevant data from motivated citizens. This is the main focus of the interdisciplinary "WeSenseIt" project, a citizen observatory of water. In this subproject, we investigate the feasibility of stream flow surface velocity measurements from movie clips taken by (smartphone-) cameras. First results from movie-clip derived velocity information will be shown and compared to reference measurements.

  7. Potential of Geo-neutrino Measurements at JUNO

    CERN Document Server

    Han, Ran; Zhan, Liang; McDonough, William F; Cao, Jun

    2015-01-01

    The flux of geoneutrinos at any point on the Earth is a function of the abundance and distribution of radioactive elements within our planet. This flux has been successfully detected by the 1-kt KamLAND and 0.3-kt Borexino detectors with these measurements being limited by their low statistics. The planned 20-kt JUNO detector will provide an exciting opportunity to obtain a high statistics measurement, which will provide data to address several questions of geological importance. This paper presents the JUNO detector design concept, the expected geo-neutrino signal and corresponding backgrounds. The precision level of geo-neutrino measurements at JUNO is obtained with the standard least-squares method. The potential of the Th/U ratio and mantle measurements is also discussed.

  8. Measuring zeta potential of protein nano-particles using electroacoustics.

    Science.gov (United States)

    Dukhin, A S; Parlia, S

    2014-09-01

    Electroacoustic spectroscopy offers a simple way for measuring the zeta potential of proteins in physiological solutions with high ionic strength. Ultrasound as a driving force does not generate the heat effects which complicate traditional electrophoretic measurements at high ionic strength. In addition, measurements can be conducted with concentrated protein dispersions without dilution, as is required by electrophoretic methods. This paper presents results for electroacoustic measurements of 5wt.% bovine serum albumin suspended in aqueous solutions. In these suspensions the proteins are not completely dissolved; they form nano-particles with a median size of about 180nm. We studied the dependence of zeta potential on ionic strength within a wide range of salt molarities, up to as high as 0.5mol/L. Dialysis was used for performing measurements at lower ionic strength range. We also conducted pH titrations of this system and titrations with Ca(2+) ions. Our results agree well with published data for samples where such data is available.

  9. Measuring the inward FDI potential of South African regions

    Directory of Open Access Journals (Sweden)

    W. Krugell

    2008-12-01

    Full Text Available Purpose: The purpose of this paper is to construct an index that captures the factors expected to affect a local economy's attractiveness to foreign investors. Problem statement: Following South Africa's reintegration into the world economy in 1994, foreign direct investment has been seen as a potential driver of growth and development. Concerns about the low investment rate in South Africa raise the possibility of augmenting domestic with foreign investment expenditure. The potential of technology spillovers and skills transfer from foreign direct investment have also been emphasised. As a result, Trade and Investment South Africa is involved in identifying, packaging and promoting investment opportunities. However, investments tend to be place-specific and this has lead to the decentralisation of foreign direct investment promotion. Currently the nine provincial development agencies are competing to attract investors and the larger local governments are also getting involved in the fray. This paper argues that some places have better potential to attract foreign investment than others. A first step to use scarce investment promotion resources more efficiently would be to measure the inward FDI potential of South African regions. Approach: This paper uses principal components analysis to construct an index that captures the factors expected to affect a local economy's attractiveness to foreign investors. This approach draws on UNCTAD's Inward FDI Potential Index and applies it to 354 magisterial districts in South Africa for the periods 1996, 2001 and 2006. The index creates a summary measure of FDI potential.Findings: The results show that different places present differential potential in urbanization and localization economies and market size. The high-potential locations are typically found in or around the major agglomerations, but there are a few smaller places on the periphery that offer FDI potential. Contribution: The index should aid

  10. Measurement of event-related potentials and placebo

    Directory of Open Access Journals (Sweden)

    Sovilj Platon

    2014-01-01

    Full Text Available ERP is common abbreviation for event-related brain potentials, which are measured and used in clinical practice as well as in research practice. Contemporary studies of placebo effect are often based on functional neuromagnetic resonance (fMRI, positron emission tomography (PET, and event related potentials (ERP. This paper considers an ERP instrumentation system used in experimental researches of placebo effect. This instrumentation system can be divided into four modules: electrodes and cables, conditioning module, digital measurement module, and PC module for stimulations, presentations, acquisition and data processing. The experimental oddball paradigm is supported by the software of the instrumentation. [Projekat Ministarstva nauke Republike Srbije, br. TR32019 and Provincial Secretariat for Science and Technological Development of Autonomous Province of Vojvodina (Republic of Serbia under research grant No. 114-451-2723

  11. FAIR VALUE MEASUREMENT IN AGRICULTURE AND THE POTENTIAL TO MISLEAD

    Directory of Open Access Journals (Sweden)

    VLADU ALINA BEATTRICE

    2013-08-01

    Full Text Available Applying fair value measurement to tangible and intangible assets in agriculture cannot be risk free. Twofoldreasons can be brought into attention for the above statement: fair value estimation and the specific of agriculturefield. The purpose of this discussion paper is to underline potential creative accounting demarches that can appear inthis context. The paper concludes based on the discussions approached in the literature. Further avenues of researchare discussed.

  12. Classifying Floating Potential Measurement Unit Data Products as Science Data

    Science.gov (United States)

    Coffey, Victoria; Minow, Joseph

    2015-01-01

    We are Co-Investigators for the Floating Potential Measurement Unit (FPMU) on the International Space Station (ISS) and members of the FPMU operations and data analysis team. We are providing this memo for the purpose of classifying raw and processed FPMU data products and ancillary data as NASA science data with unrestricted, public availability in order to best support science uses of the data.

  13. Quasi-1D van der Waals materials as high current-density local interconnects (Conference Presentation)

    Science.gov (United States)

    Stolyarov, Maxim; Aytan, Ece; Bloodgood, Matthew; Salguero, Tina T.; Balandin, Alexander A.

    2016-09-01

    The continuous downscaling of interconnect dimensions in combination with the introduction of low-k dielectrics has increased the number of heat dissipation, integration and reliability challenges in modern electronics. As a result, there is a strong need for new materials that have high current-carrying capacity for applications as nanoscale interconnects. In this presentation, we show that quasi-one-dimensional (1D) van der Waals metals such as TaSe3 have excellent breakdown current density exceeding that of 5 MA/cm2. This value is above that currently achievable in conventional copper or aluminum wires. The quasi-1D van der Waals materials are characterized by strong bonds along one dimension and weak van der Waals bonds along two other dimensions. The material for this study was grown by the chemical vapor transport (CVT) method. Both mechanical and chemical exfoliation methods were used to fabricate nanowires with lateral dimensions below 100 nm. The dimensions of the quasi-1D nanowires were verified with scanning electron microscopy (SEM) and atomic force microscopy (AFM). The metal (Ti/Au) contacts for the electrical characterization were deposited using electron beam evaporation (EBE). The measurements were conducted on a number of prototype interconnects with multiple electric contacts to ensure reproducibility. The obtained results suggest that quasi-1D van der Waals metals present a feasible alternative to conventional copper interconnects in terms of the current-carrying capacity and the breakdown current-density. This work was supported, in part, by the SRC and DARPA through STARnet Center for Function Accelerated nanoMaterial Engineering (FAME).

  14. Potential environmental effects of energy conservation measures in northwest industries

    Energy Technology Data Exchange (ETDEWEB)

    Baechler, M C; Gygi, K F; Hendrickson, P L

    1992-01-01

    The Bonneville Power Administration (Bonneville) has identified 101 plants in the Pacific Northwest that account for 80% of the region's industrial electricity consumption. These plants offer a precise target for a conservation program. PNL determined that most of these 101 plants were represented by 11 major industries. We then reviewed 36 major conservation technologies used in these 11 industrial settings to determine their potential environmental impacts. Energy efficiency technologies designed for industrial use may result in direct or indirect environmental impacts. Effects may result from the production of the conservation measure technology, changes in the working environment due to different energy and material requirements, or changes to waste streams. Industry type, work-place conditions, worker training, and environmental conditions inside and outside the plant are all key variables that may affect environmental outcomes. To address these issues this report has three objectives: Describe potential conservation measures that Bonneville may employ in industrial programs and discuss potential primary impacts. Characterize industrial systems and processes where the measure may be employed and describe general environmental issues associated with each industry type. Review environmental permitting, licensing, and other regulatory actions required for industries and summarize the type of information available from these sources for further analysis.

  15. Materials perspective on Casimir and van der Waals interactions

    Science.gov (United States)

    Woods, L. M.; Dalvit, D. A. R.; Tkatchenko, A.; Rodriguez-Lopez, P.; Rodriguez, A. W.; Podgornik, R.

    2016-10-01

    Interactions induced by electromagnetic fluctuations, such as van der Waals and Casimir forces, are of universal nature present at any length scale between any types of systems. Such interactions are important not only for the fundamental science of materials behavior, but also for the design and improvement of micro- and nanostructured devices. In the past decade, many new materials have become available, which has stimulated the need for understanding their dispersive interactions. The field of van der Waals and Casimir forces has experienced an impetus in terms of developing novel theoretical and computational methods to provide new insights into related phenomena. The understanding of such forces has far reaching consequences as it bridges concepts in materials, atomic and molecular physics, condensed-matter physics, high-energy physics, chemistry, and biology. This review summarizes major breakthroughs and emphasizes the common origin of van der Waals and Casimir interactions. Progress related to novel ab initio modeling approaches and their application in various systems, interactions in materials with Dirac-like spectra, force manipulations through nontrivial boundary conditions, and applications of van der Waals forces in organic and biological matter are examined. The outlook of the review is to give the scientific community a materials perspective of van der Waals and Casimir phenomena and stimulate the development of experimental techniques and applications.

  16. Soil moisture and potential measurements in NW Italy

    Science.gov (United States)

    Ferraris, Stefano; Canone, Davide; Previati, Maurizio

    2015-04-01

    The vertical variability of soil moisture in the rootzone is a key factor and it is not taken into account in many hydrological models. Therefore it is here proposed a novel approach that is based on the inversion of a semianalytical solution of the equation governing the infiltration and the exfiltration processes. The inversion allows keeping the information contained in the vertical spatial variability. It has been monitored with TDR measurements down to 2 meters depth. Also, the hysteresis and dynamical effects are then taken into account, with water potential measurements, in order to correctly predict the water retention both in infiltration and in drainage/exfiltration transients. References M. Baudena, I. Bevilacqua, D. Canone, S. Ferraris, M. Previati, A. Provenzale (2012). Soil water dynamics at a midlatitude test site: Field measurements and box modeling approaches. JOURNAL OF HYDROLOGY, vol. 414-415, p. 329-340, ISSN: 0022-1694, doi: 10.1016/j.jhydrol.2011.11.009

  17. Brane cosmology with a van der Waals equation of state

    CERN Document Server

    Kremer, G M

    2004-01-01

    The evolution of a Universe confined onto a 3-brane embedded in a five-dimensional space-time is investigated where the cosmological fluid on the brane is modeled by the van der Waals equation of state. It is shown that the Universe on the brane evolves in such a manner that three distinct periods concerning its acceleration field are attained: (a) an initial accelerated epoch where the van der Waals fluid behaves like a scalar field with a negative pressure; (b) a past decelerated period which has two contributions, one of them is related to the van der Waals fluid which behaves like a matter field with a positive pressure, whereas the other contribution comes from a term of the Friedmann equation on the brane which is inversely proportional to the scale factor to the fourth power and can be interpreted as a radiation field, and (c) a present accelerated phase due to a cosmological constant on the brane.

  18. A cartography of the van der Waals territories.

    Science.gov (United States)

    Alvarez, Santiago

    2013-06-28

    The distribution of distances from atoms of a particular element E to a probe atom X (oxygen in most cases), both bonded and intermolecular non-bonded contacts, has been analyzed. In general, the distribution is characterized by a maximum at short E···X distances corresponding to chemical bonds, followed by a range of unpopulated distances--the van der Waals gap--and a second maximum at longer distances--the van der Waals peak--superimposed on a random distribution function that roughly follows a d(3) dependence. The analysis of more than five million interatomic "non-bonded" distances has led to the proposal of a consistent set of van der Waals radii for most naturally occurring elements, and its applicability to other element pairs has been tested for a set of more than three million data, all of them compared to over one million bond distances.

  19. Empathy's purity, sympathy's complexities; De Waal, Darwin and Adam Smith.

    Science.gov (United States)

    van der Weele, Cor

    2011-07-01

    Frans de Waal's view that empathy is at the basis of morality directly seems to build on Darwin, who considered sympathy as the crucial instinct. Yet when we look closer, their understanding of the central social instinct differs considerably. De Waal sees our deeply ingrained tendency to sympathize (or rather: empathize) with others as the good side of our morally dualistic nature. For Darwin, sympathizing was not the whole story of the "workings of sympathy"; the (selfish) need to receive sympathy played just as central a role in the complex roads from sympathy to morality. Darwin's understanding of sympathy stems from Adam Smith, who argued that the presence of morally impure motives should not be a reason for cynicism about morality. I suggest that De Waal's approach could benefit from a more thorough alignment with the analysis of the workings of sympathy in the work of Darwin and Adam Smith.

  20. Earliest detection of magma movements by measuring transient streaming potential

    Science.gov (United States)

    Fujinawa, Yukio; Matsumoto, Takumi; Iitaka, Hiroshi; Takahashi, Kozo; Nakano, Hiroshi; Doi, Takuya; Saito, Toshiyuki; Kasai, Naoko; Sato, Sohjun

    Volcanic eruptions are generally preceded by magma intrusion. Volcanic forecasting is sure to make considerable progress if we have a practical means to detect magma movements. Electric potential variations have been observed since April 1999 at Miyake Island, a volcanic island in Japan. Measurements have been conducted by a special long vertical antenna using a steel casing pipe and a short horizontal dipole. Beginning about half a day before as well as at the time period of the largest eruption in 2000 of Miyake-jima volcano on August 18, 2000, conspicuous electric field variations were observed on the horizontal and vertical components in the frequency bands of DC, ULF and ELF/VLF. And several types of anomalies were found to occur in association with different stage of volcanic activities. We suggest that transient self-potential variations are induced by confined ground water pressure fluctuations through interaction between intruding magma and hydrothermal circulation through electro-kinetic effect. Subsurface transient self-potential measurement has been suggested to be useful means for monitoring volcanic eruption and to provide an efficient window for looking into modification of hydrothermal circulation induced by the volcanic activity.

  1. Measuring the 2HDM Scalar Potential at LHC14

    CERN Document Server

    Barger, Vernon; Jackson, Chris B; Peterson, Andrea D; Shaughnessy, Gabe

    2014-01-01

    After the extraordinary discovery of the Higgs boson at the LHC, the next goal is to pin down its underlying dynamics by measuring the Higgs self-couplings, along with its couplings to gauge and matter particles. As a prototype model of new physics in the scalar sector, we consider the Two Higgs Doublet Model (2HDM) with CP-conservation, and evaluate the prospects for measuring the trilinear scalar couplings among the CP-even Higgs bosons $h$ and $H$ ($\\lambda^{hhh}$, $\\lambda^{hhH}$, $\\lambda^{hHH}$) at LHC14. The continuum and resonant production of CP-even Higgs boson pairs, $hh$ and $hH$, offer complementary probes of the scalar potential away from the light-Higgs decoupling limit. We identify the viable search channels at LHC14 and estimate their expected discovery sensitivities.

  2. Global scale comparison of simultaneous ionospheric potential measurements

    Science.gov (United States)

    Markson, R.; Ruhnke, L. H.; Williams, E. R.

    A unique series of simultaneous ionospheric potential ( VI) balloon soundings were obtained every 3 h over 2 full days at Weston, MA and Darwin, Australia, on the other side of the earth. These comparisons were to test the assumption that the ionosphere at sub-auroral latitudes is an equipotential and that a single measurement can provide a globally representative number. Another objective was to evaluate meteorological conditions affecting the measurements in a clean dry continental atmosphere (Darwin) compared with a more variable moist less clean atmosphere (Weston). The results indicate that for the Darwin data the VI measurements were within 10% of the classic Carnegie curve diurnal variation while the Weston data were more variable and often too large. The major source of error appears to be due to hydrated aerosol at Weston causing high electric fields in the exchange layer that were not fully compensated by electric fields above the inversion. The prototype instrumentation also contributed some error. The major finding of this experiment is that a layer of low conductivity air near the ground can have an unexpectedly large effect on electric field sounding data leading to error in the estimates of VI magnitude. This finding would not have been possible if simultaneous measurements in different airmasses had not been made since the individual electric field profiles appeared normal.

  3. Lean Principles’Potential Measurement Framework for Service Organization

    Directory of Open Access Journals (Sweden)

    M. D. Vadhvani

    2016-06-01

    Full Text Available Role of service sector can be considered vital as these industries are accountable for accelerating the major functions of the secondary organizations. Hence it is a very important element of economy in enhancing competitive dimensions- quality, flexibility, cost and delivery. Improvement initiatives such as Total Quality Management, Lean Practices, and Leansigma focus on increasing the competitive dimensions. Among these Lean Practices are having the inherent principles of reducing the cost and increasing the quality by focusing the non value added activities from the value chain of the service or product. Lean Principles (LPs are being practiced since long by the organizations of secondary sectors and followed by that of the tertiary sectors. Albeit the reported improvement achieved are limited by the drawbacks such as lack of proper set of guidelines, partial features of measurable characteristics, lack of guideline for measurement. Present work proposes a measurement frame work with aids of flowchart and questionnaire for measuring the potential of LPs in service organization which help them to take accompanying initiatives to implement the LPs.

  4. Redox potential - field measurements - meassured vs. expected values

    Science.gov (United States)

    Stavělová, Monika; Kovář, Martin

    2016-04-01

    Oxidation and reduction (redox) potential is an important and theoretically very well defined parameter and can be calculated accurately. Its value is determinative for management of many electrochemical processes, chemical redox technologies as well as biotechnologies. To measure the redox value that would correspond with the accuracy level of theoretical calculations in field or operational conditions is however nearly impossible. Redox is in practice measured using combined argentochloride electrode with subsequent value conversion to standard hydrogen electrode (EH). Argentochloride electrode does not allow for precise calibration. Prior to the measurement the accuracy of measurement of particular electrode can only be verified in comparative/control solution with value corresponding with oxic conditions (25°C: +220 mV argentochloride electrode, i.e.. +427 mV after conversion to EH). A commercial product of stabile comparative solution for anoxic conditions is not available and therefore not used in every day practice - accuracy of negative redox is not verified. In this presentation results of two tests will be presented: a) monitoring during dynamic groundwater sampling from eight monitoring wells at a site contaminated by chlorinated ethenes (i.e. post-oxic to anoxic conditions) and b) laboratory test of groundwater contaminated by arsenic from two sites during reaction with highly oxidized compounds of iron (ferrates) - i.e. strongly oxic conditions. In both tests a simultaneous measurement by four argentochloride electrodes was implemented - all four electrodes were prior to the test maintained expertly. The redox values of testing electrodes in a comparative solution varied by max. 6 mV. The redox values measured by four electrodes in both anoxic and oxic variant varied by tens to a hundred mV, while with growing time of test the variance of measured redox values increased in both oxic and anoxic variant. Therefore the interpretation of measured redox

  5. Online monitoring of Mezcal fermentation based on redox potential measurements.

    Science.gov (United States)

    Escalante-Minakata, P; Ibarra-Junquera, V; Rosu, H C; De León-Rodríguez, A; González-García, R

    2009-01-01

    We describe an algorithm for the continuous monitoring of the biomass and ethanol concentrations as well as the growth rate in the Mezcal fermentation process. The algorithm performs its task having available only the online measurements of the redox potential. The procedure combines an artificial neural network (ANN) that relates the redox potential to the ethanol and biomass concentrations with a nonlinear observer-based algorithm that uses the ANN biomass estimations to infer the growth rate of this fermentation process. The results show that the redox potential is a valuable indicator of the metabolic activity of the microorganisms during Mezcal fermentation. In addition, the estimated growth rate can be considered as a direct evidence of the presence of mixed culture growth in the process. Usually, mixtures of microorganisms could be intuitively clear in this kind of processes; however, the total biomass data do not provide definite evidence by themselves. In this paper, the detailed design of the software sensor as well as its experimental application is presented at the laboratory level.

  6. Van der Waals forces in pNRQED

    Energy Technology Data Exchange (ETDEWEB)

    Shtabovenko, Vladyslav [Physik-Department, Technische Universität München, James-Franck-Str. 1, 85748 Garching (Germany)

    2016-01-22

    We report on the calculation of electromagnetic van der Waals forces [1] between two hydrogen atoms using non-relativistic effective field theories (EFTs) of QED for large and small momentum transfers with respect to the intrinsic energy scale of the hydrogen atom. Our results reproduce the well known London and Casimir-Polder forces.

  7. Higher-accuracy van der Waals density functional

    DEFF Research Database (Denmark)

    Lee, Kyuho; Murray, Éamonn D.; Kong, Lingzhu

    2010-01-01

    We propose a second version of the van der Waals density functional of Dion et al. [Phys. Rev. Lett. 92, 246401 (2004)], employing a more accurate semilocal exchange functional and the use of a large-N asymptote gradient correction in determining the vdW kernel. The predicted binding energy...

  8. Graphene on metals: A van der Waals density functional study

    DEFF Research Database (Denmark)

    Vanin, Marco; Mortensen, Jens Jørgen; Kelkkanen, Kari André;

    2010-01-01

    We use density functional theory (DFT) with a recently developed van der Waals density functional (vdW-DF) to study the adsorption of graphene on Co, Ni, Pd, Ag, Au, Cu, Pt, and Al(111) surfaces. In contrast to the local-density approximation (LDA) which predicts relatively strong binding for Ni...

  9. Electro-photo modulation of the fermi level in WSe2/graphene van der Waals heterojunction

    Science.gov (United States)

    Sun, Honghui; Yang, Hang; Fang, Liang; Zhang, Jiangwei; Wang, Zhiyuan; Jiang, Tian

    2017-04-01

    We report an electro-photo double modulation of the fermi level in a WSe2/graphene heterojunction. The heterojunction exhibits high ION/IOFF ratio ( 103) in transfer characteristic in dark and distinct rectification behavior in output characteristic under light illumination, respectively. Time-dependent photoresponse reveals that the heterojunction has a considerable potential in the application of photodetection. Interestingly, an exotic current peak is observed in transfer characteristic under light illumination. This novel behavior is attributed to the tunable fermi level at the WSe2/graphene heterojunction by electro-photo double modulation. The results may be helpful to develop tunable photovoltaic optoelectronics based on van der Waals heterojunctions.

  10. Lacunarity Measures of Potential Fields in Covered Lithology Identification

    Science.gov (United States)

    Gettings, M. E.

    2013-12-01

    Measure distributions, both multifractal and other kinds, are not unique, so spatial patterns with the same measure may have different appearances. Lacunarity analysis is a method of description of dispersion in spatial patterns across a range of scales, and is one way of descriminating clustering of similar values. Lacunarity of an image was calculated using a moving window across a range of scales as the ratio of the second moment divided by the square of the first moment for values within the window. This gives a curve of lacunarity versus resolution (scale); the curve is concave for highly clustered data, pseudolinear or convex for data with clusters at many scales such as multifractal simulations, and constant for uniformly spaced data. Breaks in slope of the curve indicate scales that are important in the structure of the spatial pattern. Gravity and magnetic field anomaly data are well known to be multifractal and thus calculated lacunarities of gridded datasets have been investigated to determine if the resulting curves are a useful measure of texture of the potential field data and helpful in identifying likely lithologies at depth beneath cover. Lacunarity is often calculated on binary data, but it can also be calculated using quantitative data. The quantitative data case lacunarity measure was computed for grids using a 25 by 25 km window moving over the grid, each window overlapping the previous one by 12.5 km. The data were the aeromagnetic and isostatic gravity anomaly grids for the state of Arizona at 0.5 km grid-interval, resulting in a lacunarity curves for gravity and aeromagnetic anomaly for each of approximately 2500 windows. The open-source software R was used for plotting a map of window center locations and lacunarity curves, and the map was loaded into Google Earth, together with maps of the gravity and magnetic field anomaly, porphyry copper deposit locations, and the geological map of Arizona. Windows were selected to compare lacunarity

  11. Measurement of the first ionization potential of lawrencium (element 103)

    CERN Document Server

    Sato, T K; Borschevsky, A; Stora, T; Sato, N; Kaneya, Y; Tsukada, K; Düllmann, Ch E; Eberhardt, K; Eliav, E; Ichikawa, S; Kaldor, U; Kratz, J V; Miyashita, S; Nagame, Y; Ooe, K; Osa, A; Renisch, D; Runke, J; Schädel, M; Thörle-Pospiech, P; Toyoshima, A; Trautmann, N

    2015-01-01

    The chemical properties of an element are primarily governed by the configuration of electrons in the valence shell. Relativistic effects influence the electronic structure of heavy elements in the sixth row of the periodic table, and these effects increase dramatically in the seventh row—including the actinides—even affecting ground-state configurations. Atomic s and p1/2 orbitals are stabilized by relativistic effects, whereas p3/2, d and f orbitals are destabilized, so that ground-state configurations of heavy elements may differ from those of lighter elements in the same group. The first ionization potential (IP1) is a measure of the energy required to remove one valence electron from a neutral atom, and is an atomic property that reflects the outermost electronic configuration. Precise and accurate experimental determination of IP1 gives information on the binding energy of valence electrons, and also, therefore, on the degree of relativistic stabilization. However, such measurements are hampered by ...

  12. A Proposed Alternative Measure for Climate Change Potential

    Science.gov (United States)

    DeGroff, F. A.

    2015-12-01

    Background/Issue There currently exists no comprehensive metric to measure and value anthropogenic changes in carbon flux between geospheric carbon sinks. We propose that changes in carbon residence time within geospheres be used as a metric to assess anthropogenic changes in carbon flux, and the term 'carbon quality' (cq) be used to describe such changes. Carbon residence time represents the inverse of carbon flux; as carbon flux increases, the corresponding cq will decrease, and vice versa. Focusing on atmospheric carbon emissions as a measure of anthropogenic activity on the environment ignores the fungible characteristics of carbon that are crucial in both the biosphere and the worldwide economy. The ubiquitous carbon molecule enables the enormous diversity in the biosphere, as well as the widespread, strategic economic presence of carbon in the world economy. Focusing on a single form of inorganic carbon as a proxy metric for the plethora of anthropogenic activity and carbon compounds will prove inadequate, convoluted, and unmanageable. A broader, more basic metric is needed to capture the breath and scope of carbon activity. Results/Conclusions We propose a logarithmic vector scale for cq to measure anthropogenic carbon flux. The distance between vector points, e.g. the starting and ending residence times, would represent the change in cq. A base-10 logarithmic scale would allow the addition and subtraction of exponents to calculate changes in cq. As carbon moves between carbon reservoirs, the change in cq is measured as: cq = b ( log10 [mean carbon residence time] ) where b represents the carbon price coefficient for a particular country. For any country, cq measures the climate change potential for any organic carbon when converted to inorganic CO2, or to any lower residence time carbon state. The greater the carbon fees for a country, the larger the b coefficient would be, and the greater the import fees would be to achieve carbon parity on imports from

  13. Spontaneous doping on high quality talc-graphene-hBN van der Waals heterostructures

    Science.gov (United States)

    Mania, E.; Alencar, A. B.; Cadore, A. R.; Carvalho, B. R.; Watanabe, K.; Taniguchi, T.; Neves, B. R. A.; Chacham, H.; Campos, L. C.

    2017-09-01

    Steady doping, added to its remarkable electronic properties, would make graphene a valuable commodity in the solar cell market, as energy power conversion could be substantially increased. Here we report a graphene van der Waals heterostructure which is able to spontaneously dope graphene (p-type) up to n ~ 2.2  ×  1013 cm-2 while providing excellent charge mobility (μ ~ 25 000 cm2 V-1 s-1). Such properties are achieved via deposition of graphene on atomically flat layered talc, a natural and abundant dielectric crystal. Raman investigation shows a preferential charge accumulation on graphene-talc van der Waals heterostructures, which are investigated through the electronic properties of talc/graphene/hBN heterostructure devices. These heterostructures preserve graphene’s good electronic quality, verified by the observation of quantum Hall effect at low magnetic fields (B  =  0.4 T) at T  =  4.2 K. In order to investigate the physical mechanisms behind graphene-on-talc p-type doping, we performed first-principles calculations of their interface structural and electronic properties. In addition to potentially improving solar cell efficiency, graphene doping via van der Waals stacking is also a promising route towards controlling the band gap opening in bilayer graphene, promoting a steady n or p type doping in graphene and, eventually, providing a new path to access superconducting states in graphene, predicted to exist only at very high doping.

  14. Biophoton Emission as a Potential Measure of Organizational Order

    Institute of Scientific and Technical Information of China (English)

    顾樵; Popp Fritz—Albert

    1994-01-01

    Beginning with the quantum theory of biophoton emission,a c-number equation character-izing the excited-state dynamics of a complex system of collective biomolecules in interaction with both the"pumping"field and the biophoton field is presented,and then the order-growth process of the system interms of both determinism and statistics is investigated.A general expression describing the order-growthdynamics of biological systems,which reduces in a limiting case to the well-known growth curve,is obtained.Then a Fokker-Planck equation for probability density function of an order parameter q of the systemhas been established.The solution predicts that the system under consideration can evolute from an arbitraryinitial state to a pure state characterized by the steady-state order parameter q1.Furthermore,the evolutionof the maximum entropy of the system is discussed,which shows that the system investigated is to keep anabsolute maximum of entropy,and at the same time,to minimize its entropy value by reducing the uncertain-ty of the order parameter.Finally,some agreements of the theoretical results with the corresponding experi-mental observations of order-growth process demonstrated by the biophoton emission are shown,which indi-cates that biophoton emission may serve as a potential measure of the organizational order.

  15. Crack Growth Monitoring in Harsh Environments by Electric Potential Measurements

    Energy Technology Data Exchange (ETDEWEB)

    Lloyd, Wilson Randolph; Reuter, Walter Graham; Weinberg, David Michael

    1999-09-01

    Electric potential measurement (EPM) technology offers an attractive alternative to conventional nondestructive evaluation (NDE) for monitoring crack growth in harsh environments. Where conventional NDE methods typically require localized human interaction, the EPM technique developed at the Idaho National Engineering and Environmental Laboratory (INEEL) can be operated remotely and automatically. Once a crack-like defect is discovered via conventional means, EPM can be applied to monitor local crack size changes. This is of particular interest in situations where an identified structural defect is not immediately rejectable from a fitness-for-service viewpoint, but due to operational and environmental conditions may grow to an unsafe size with continuing operation. If the location is in a harsh environment where periodic monitoring by normal means is either too costly or not possible, a very expensive repair may be immediately mandated. However, the proposed EPM methodology may offer a unique monitoring capability that would allow for continuing service. INEEL has developed this methodology, supporting equipment, and calibration information to apply EPM in a field environment for just this purpose. Laboratory and pilot scale tests on full-size engineering structures (pressure vessels and piping) have been successfully performed. The technique applicable is many severe environments because the sensitive equipment (electronics, operators) can be situated in a remote location, with only current and voltage probe electrical leads entering into the harsh environment. Experimental results showing the utility of the methodology are presented, and unique application concepts that have been examined by multiple experiments are discussed.

  16. Band Alignment and Minigaps in Monolayer MoS2-Graphene van der Waals Heterostructures.

    Science.gov (United States)

    Pierucci, Debora; Henck, Hugo; Avila, Jose; Balan, Adrian; Naylor, Carl H; Patriarche, Gilles; Dappe, Yannick J; Silly, Mathieu G; Sirotti, Fausto; Johnson, A T Charlie; Asensio, Maria C; Ouerghi, Abdelkarim

    2016-07-13

    Two-dimensional layered MoS2 shows great potential for nanoelectronic and optoelectronic devices due to its high photosensitivity, which is the result of its indirect to direct band gap transition when the bulk dimension is reduced to a single monolayer. Here, we present an exhaustive study of the band alignment and relativistic properties of a van der Waals heterostructure formed between single layers of MoS2 and graphene. A sharp, high-quality MoS2-graphene interface was obtained and characterized by micro-Raman spectroscopy, high-resolution X-ray photoemission spectroscopy (HRXPS), and scanning high-resolution transmission electron microscopy (STEM/HRTEM). Moreover, direct band structure determination of the MoS2/graphene van der Waals heterostructure monolayer was carried out using angle-resolved photoemission spectroscopy (ARPES), shedding light on essential features such as doping, Fermi velocity, hybridization, and band-offset of the low energy electronic dynamics found at the interface. We show that, close to the Fermi level, graphene exhibits a robust, almost perfect, gapless, and n-doped Dirac cone and no significant charge transfer doping is detected from MoS2 to graphene. However, modification of the graphene band structure occurs at rather larger binding energies, as the opening of several miniband-gaps is observed. These miniband-gaps resulting from the overlay of MoS2 and the graphene layer lattice impose a superperiodic potential.

  17. Theoretical and practical aspects of measuring market potential

    OpenAIRE

    Bešlagić Mirza; Bešlagić Amela

    2016-01-01

    The area of research in this paper refers to the theoretical, practical and methodological aspects of the assessment of market potential. It presents the main factors relevant to assessing market potential. The process of evaluating the market potential is important, first of all, for optimal adoption of future strategic decisions in business. Planning of business processes is one of the main reasons for the assessment of the market potential and managers often face, when planning, the enviro...

  18. Local Probe Spectroscopy of Two-Dimensional van der Waals Heterostructures

    Science.gov (United States)

    Yankowitz, Matthew Abraham

    A large family of materials, collectively known as "van der Waals materials", have attracted enormous research attention over the past decade following the realization that they could be isolated into individual crystalline monolayers, with charge carriers behaving effectively two-dimensionally. More recently, an even larger class of composite materials has been realized, made possible by combining the isolated atomic layers of different materials into "van der Waals heterostructures", which can exhibit electronic and optical behaviors not observed in the parent materials alone. This thesis describes efforts to characterize the atomic-scale structural and electronic properties of these van der Waals materials and heterostructures through scanning tunneling microscopy measurements. The majority of this work addresses the properties of monolayer and few-layer graphene, whose charge carriers are described by massless and massive chiral Dirac Hamiltonians, respectively. In heterostructures with hexagonal boron nitride, an insulating isomorph of graphene, we observe electronic interference patterns between the two materials which depend on their relative rotation. As a result, replica Dirac cones are formed in the valence and conduction bands of graphene, with their energy tuned by the rotation. Further, we are able to dynamically drag the graphene lattice in these heterostructures, owing to an interaction between the scanning probe tip and the domain walls formed by the electronic interference pattern. Similar dragging is observed in domain walls of trilayer graphene, whose electronic properties are found to depend on the stacking configuration of the three layers. Scanning tunneling spectroscopy provides a direct method for visualizing the scattering pathways of electrons in these materials. By analyzing the scattering, we can directly infer properties of the band structures and local environments of these heterostructures. In bilayer graphene, we map the electrically

  19. Poisson-Boltzmann Calculations: van der Waals or Molecular Surface?

    Science.gov (United States)

    Pang, Xiaodong; Zhou, Huan-Xiang

    2013-01-01

    The Poisson-Boltzmann equation is widely used for modeling the electrostatics of biomolecules, but the calculation results are sensitive to the choice of the boundary between the low solute dielectric and the high solvent dielectric. The default choice for the dielectric boundary has been the molecular surface, but the use of the van der Waals surface has also been advocated. Here we review recent studies in which the two choices are tested against experimental results and explicit-solvent calculations. The assignment of the solvent high dielectric constant to interstitial voids in the solute is often used as a criticism against the van der Waals surface. However, this assignment may not be as unrealistic as previously thought, since hydrogen exchange and other NMR experiments have firmly established that all interior parts of proteins are transiently accessible to the solvent.

  20. Persistent hysteresis in graphene-mica van der Waals heterostructures.

    Science.gov (United States)

    Mohrmann, Jens; Watanabe, Kenji; Taniguchi, Takashi; Danneau, Romain

    2015-01-09

    We report the study of electronic transport in graphene-mica van der Waals heterostructures. We have designed various graphene field-effect devices in which mica is utilized as a substrate and/or gate dielectric. When mica is used as a gate dielectric we observe a very strong positive gate voltage hysteresis of the resistance, which persists in samples that were prepared in a controlled atmosphere down to even millikelvin temperatures. In a double-gated mica-graphene-hBN van der Waals heterostructure, we found that while a strong hysteresis occurred when mica was used as a substrate/gate dielectric, the same graphene sheet on mica substrate no longer showed hysteresis when the charge carrier density was tuned through a second gate with the hBN dielectric. While this hysteretic behavior could be useful for memory devices, our findings confirm that the environment during sample preparation has to be controlled strictly.

  1. Investigation of human body potential measured by a non-contact measuring system.

    Science.gov (United States)

    Ichikawa, Norimitsu

    2016-12-07

    A human body is occasionally electrified in a room. This charged object will be a source of electrostatic accidents, including the malfunction of electronic equipment. Hence, prevention of these accidents is required. Accidents occasionally occur, even though antistatic clothes and shoes are used. One of the causes for these accidents is that there is a lack of the preventive measures. This situation occurs when using, for example, unconductive wax. In this study, human body potential (voltage) is measured using a non-contact measuring system. An investigation of the human body's voltage when using this system is conducted. The result demonstrates that the voltage of a human body wearing antistatic clothes and shoes or light clothes and slippers exceeds a malfunctioning voltage of a microelectronics device when the body walks on floors. Thus, accidents may occur even if a human body wearing the antistatic clothes walks on flooring. These results will be useful in estimating determination whether electrostatic accidents occur or not.

  2. Van der Waals interactions of parallel and concentric nanotubes

    OpenAIRE

    Schroder, Elsebeth; Hyldgaard, Per

    2003-01-01

    For sparse materials like graphitic systems and carbon nanotubes the standard density functional theory (DFT) faces significant problems because it cannot accurately describe the van der Waals interactions that are essential to the carbon-nanostructure materials behavior. While standard implementations of DFT can describe the strong chemical binding within an isolated, single-walled carbon nanotube, a new and extended DFT implementation is needed to describe the binding between nanotubes. We ...

  3. Dynamic changes of phase in a van der Waals fluid

    Science.gov (United States)

    Hagan, R.; Serrin, J.

    1984-03-01

    This paper gives sufficient conditions to guarantee the existence of a shock layer solution connecting two different equilibrium states in a van der Waals fluid. In particular, the equilibrium states can belong to two different phases of the fluid. The constitutive laws come from a modified Korteweg theory which is compatible with the Clausius Duhem inequality. The Clausius Duhem inequality in turn gives rise to a Liapunov function. The main mathematical tool is the LaSalle invariance principle.

  4. Measuring naphthenic acid corrosion potential with the Fe powder test

    Directory of Open Access Journals (Sweden)

    Hau, J. L.

    2003-12-01

    Full Text Available Results are presented of experiments performed using a new method to measure the naphthenic acid corrosion potential. The method consists of adding pure iron powder into a small autoclave containing the crude or oil sample. The test is then performed at a given temperature for one hour, after which the oil sample is filtered and the remaining liquid is sent for iron content determination (ppm. The tests are run at 7 different temperature levels, 3 more are run as repeated tests. A best-fitted curve is drawn through these 10 experimental points and the maximum point is thus determined. This becomes the main outcome of the test and it is used to give a measure of the naphthenic acid corrosion potential. The same general trends as observed in the past using the neutralization number or TAN (Total Acid Number is obtained. However, this new test seems capable oí detecting anomalous cases where oil samples having larger values of TAN exhibit less corrosivity than others having much lower values of TAN or where they show completely different corrosivity despite having similar or the same TAN.

    Se presentan los resultados de experimentos realizados con un nuevo método para medir el potencial de corrosión por ácidos nafténicos. El método consiste en añadir hierro puro en polvo a una muestra de crudo o aceite, en un autoclave pequeño. El ensayo se realiza a una temperatura dada durante una hora; luego se filtra la muestra de aceite y el líquido filtrado se envía para medir la concentración de hierro disuelto (ppm. El ensayo se reitera para siete temperaturas diferentes y se repiten tres más para determinar su reproducibilidad. Con estos 10 puntos experimentales se dibuja la mejor curva de ajuste y se determina un máximo de hierro disuelto. Este máximo se convierte en el resultado principal del ensayo y se usa para dar una medida del potencial de corrosión por ácidos nafténicos. Se obtienen las mismas tendencias generales observadas

  5. Scaling Laws for van der Waals Interactions in Nanostructured Materials

    Science.gov (United States)

    Gobre, Vivekanand; Tkatchenko, Alexandre

    2014-03-01

    Van der Waals (vdW) forces originate from interactions between fluctuating multipoles in matter and play a significant role in the structure and stability of nanostructured materials. Many models used to describe vdW interactions in nanomaterials are based on a simple pairwise-additive approximation, neglecting the strong electrodynamic response effects caused by long-range fluctuations in matter. We develop and utilize an efficient microscopic method to demonstrate that vdW interactions in nanomaterials act at distances greater than typically assumed, and can be characterized by different scaling laws depending on the dimensionality and size of the system. Specifically, we study the behaviour of vdW interactions in single-layer and multilayer graphene, fullerenes of varying size, single-wall carbon nanotubes and graphene nanoribbons. As a function of nanostructure size, the van der Waals coefficients follow unusual trends for all of the considered systems, and deviate significantly from the conventionally employed pairwise-additive picture. We propose that the peculiar van der Waals interactions in nanostructured materials could be exploited to control their self-assembly.

  6. Van der Waals Type Model and Structure in bar{p}p Elastic Scattering at High Energies

    Science.gov (United States)

    Aleem, F.

    1983-10-01

    The most recent measurements of the angular distribution for bar{p}p elastic scattering at pL=50, 100 and 200 GeV/ c which show a structure near -t=1.4 (GeV/ c)2, with squared four momentum transter -t extended to 5(GeV/ c)2, and the total cross section data for 50 <= pL <= 280GeV/ c have been simultaneously fitted by using the Van der Waals type model.

  7. Theoretical and practical aspects of measuring market potential

    Directory of Open Access Journals (Sweden)

    Bešlagić Mirza

    2016-01-01

    Full Text Available The area of research in this paper refers to the theoretical, practical and methodological aspects of the assessment of market potential. It presents the main factors relevant to assessing market potential. The process of evaluating the market potential is important, first of all, for optimal adoption of future strategic decisions in business. Planning of business processes is one of the main reasons for the assessment of the market potential and managers often face, when planning, the environmental factors that can not be influenced. Realistic and quality assessment of market potential and sales forecasting in companies becomes not only a means of gaining competitive advantage, but also a necessary condition for long-term development and survival in the market. Knowledge of the potential market increases the efficiency of business operations. To this end, the theoretical, methodological and practical problems of assessment of market potential were analyzed. The need for this is all the more pronounced because of objective, reliable and valid assessment of the market potential is a prerequisite of business improvement and long-term development of enterprises. The aim was to explain the characteristics of the market potential as one of the primary market sizes in order to carry out its assessment. In this context, it was necessary to identify the main factors influencing the assessment of market potential. Results of the study showed that factors of macro and micro environment of the company, competition and purchasing power determine the market potential of edible oil in Bosnia and Herzegovina. In the empirical part of the paper are applied most common methods of assessment of market potential.

  8. Thermodynamics of lithium intercalation into graphite studied using density functional theory calculations incorporating van der Waals correlation and uncertainty estimation

    CERN Document Server

    Pande, Vikram

    2016-01-01

    Graphite is the most widely used and among the most widely-studied anode materials for lithium-ion batteries. Lithium intercalation into graphite has been extensively studied theoretically using density functional theory (DFT) calculations, complemented by experimental studies through X-ray diffraction, spectroscopy, optical imaging and other techniques. However, previous theoretical studies have not directly included van der Waals (vdW) interactions in their density functional theory calculations and vdW interactions play a crucial role in determining the stable phases. In this work, we present a first principles based model using DFT calculations, employing Bayesian Error Estimation Functional with van der Waals (BEEF-vdW) as the exchange correlation functional, and statistical thermodynamics to determine the phase transformations and subsequently, the thermodynamic intercalation potential diagram. We explore the entire configurational phase space by determining the important interactions and applying clust...

  9. Chemical sensing by band modulation of a black phosphorus/molybdenum diselenide van der Waals hetero-structure

    Science.gov (United States)

    Feng, Zhihong; Chen, Buyun; Qian, Shuangbei; Xu, Linyan; Feng, Liefeng; Yu, Yuanyuan; Zhang, Rui; Chen, Jiancui; Li, Qianqian; Li, Quanning; Sun, Chongling; Zhang, Hao; Liu, Jing; Pang, Wei; Zhang, Daihua

    2016-09-01

    We report on a new chemical sensor based on black phosphorus/molybdenum diselenide van der Waals hetero-junctions. Due to the atomically thin nature of two-dimensional (2D) materials, surface adsorption of gas molecules can effectively modulate the band alignment at the junction interface, making the device a highly sensitive detector for chemical adsorptions. Compared to sensors made of homogeneous nanomaterials, the hetero-junction demonstrates considerably lower detection limit and higher sensitivity toward nitrogen dioxide. Kelvin probe force microscopy and finite element simulations have provided experimental and theoretical explanations for the enhanced performance, proving that chemical adsorption can induce significant changes in band alignment and carrier transport behaviors. The study demonstrates the potential of van der Waals hetero-junction as a new platform for sensing applications, and provides more insights into the interaction between gaseous molecules and 2D hetero-structures.

  10. Thermodynamics of acetylene van der Waals dimerization

    Science.gov (United States)

    Colussi, A. J.; Sander, S. P.; Friedl, R. R.

    1991-01-01

    Integrated band intensities of the 620/cm absorption in (C2H2)2 are measured by FTIR spectroscopy at constant acetylene pressure between 198 and 273 K. These data, in conjunction with ab initio results for (C2H2)2, are used for the statistical evaluation of the equilibrium constant Kp(T) for acetylene-cluster dimerization. The present results are used to clarify the role of molecular clusters in chemical systems at or near equilibrium, in particular in Titan's stratosphere.

  11. Counterpoise correction is not useful for short and Van der Waals distances but may be useful at long range.

    Science.gov (United States)

    Sheng, Xiao Wei; Mentel, Lukasz; Gritsenko, Oleg V; Baerends, Evert Jan

    2011-10-01

    This article investigates the errors in supermolecule calculations for the helium dimer. In a full CI calculation, there are two errors. One is the basis set superposition error (BSSE), the other is the basis set convergence error (BSCE). Both of the errors arise from the incompleteness of the basis set. These two errors make opposite contributions to the interaction energies. The BSCE is by far the largest error in the short range and larger than (but much closer to) BSSE around the Van der Waals minimum. Only at the long range, the BSSE becomes the larger error. The BSCE and BSSE largely cancel each other over the Van der Waals well. Accordingly, it may be recommended to not include the BSSE for the calculation of the potential energy curve from short distance till well beyond the Van der Waals minimum, but it may be recommended to include the BSSE correction if an accurate tail behavior is required. Only if the calculation has used a very large basis set, one can refrain from including the counterpoise correction in the full potential range. These results are based on full CI calculations with the aug-cc-pVXZ (X = D, T, Q, 5) basis sets.

  12. Evaluation of a density functional with account of van der Waals forces using experimental data of H2 physisorption on Cu(111)

    DEFF Research Database (Denmark)

    Lee, Kyuho; Kelkkanen, Kari André; Berland, Kristian

    2011-01-01

    Detailed experimental data for physisorption potential-energy curves of H2 on low-indexed faces of Cu challenge theory. Recently, density-functional theory has been developed to also account for nonlocal correlation effects, including van der Waals forces. We show that one functional, denoted vd...

  13. Droplet spreading driven by van der Waals force: a molecular dynamics study

    Energy Technology Data Exchange (ETDEWEB)

    Wu Congmin [Department of Mathematics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon (Hong Kong); Qian Tiezheng [Department of Mathematics and Joint KAUST-HKUST Micro/Nanofluidics Laboratory, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon (Hong Kong); Sheng Ping, E-mail: maqian@ust.h [Department of Physics and William Mong Institute of Nano Science and Technology, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon (Hong Kong)

    2010-08-18

    The dynamics of droplet spreading is investigated by molecular dynamics simulations for two immiscible fluids of equal density and viscosity. All the molecular interactions are modeled by truncated Lennard-Jones potentials and a long-range van der Waals force is introduced to act on the wetting fluid. By gradually increasing the coupling constant in the attractive van der Waals interaction between the wetting fluid and the substrate, we observe a transition in the initial stage of spreading. There exists a critical value of the coupling constant, above which the spreading is pioneered by a precursor film. In particular, the dynamically determined critical value quantitatively agrees with that determined by the energy criterion that the spreading coefficient equals zero. The latter separates partial wetting from complete wetting. In the regime of complete wetting, the radius of the spreading droplet varies with time as R(t){approx}{radical}t, a behavior also found in molecular dynamics simulations where the wetting dynamics is driven by the short-range Lennard-Jones interaction between liquid and solid.

  14. Formation and dynamics of van der Waals molecules in buffer-gas traps.

    Science.gov (United States)

    Brahms, Nathan; Tscherbul, Timur V; Zhang, Peng; Kłos, Jacek; Forrey, Robert C; Au, Yat Shan; Sadeghpour, H R; Dalgarno, A; Doyle, John M; Walker, Thad G

    2011-11-14

    We show that weakly bound He-containing van der Waals molecules can be produced and magnetically trapped in buffer-gas cooling experiments, and provide a general model for the formation and dynamics of these molecules. Our analysis shows that, at typical experimental parameters, thermodynamics favors the formation of van der Waals complexes composed of a helium atom bound to most open-shell atoms and molecules, and that complex formation occurs quickly enough to ensure chemical equilibrium. For molecular pairs composed of a He atom and an S-state atom, the molecular spin is stable during formation, dissociation, and collisions, and thus these molecules can be magnetically trapped. Collisional spin relaxation is too slow to affect trap lifetimes. However, (3)He-containing complexes can change spin due to adiabatic crossings between trapped and untrapped Zeeman states, mediated by the anisotropic hyperfine interaction, causing trap loss. We provide a detailed model for Ag(3)He molecules, using ab initio calculation of Ag-He interaction potentials and spin interactions, quantum scattering theory, and direct Monte Carlo simulations to describe formation and spin relaxation in this system. The calculated rate of spin-change agrees quantitatively with experimental observations, providing indirect evidence for molecular formation in buffer-gas-cooled magnetic traps. Finally, we discuss the possibilities for spectroscopic detection of these complexes, including a calculation of expected spectra for Ag(3)He, and report on our spectroscopic search for Ag(3)He, which produced a null result.

  15. Structural and quantum properties of van der Waals cluster near the unitary regime

    Science.gov (United States)

    Lekala, M. L.; Chakrabarti, B.; Haldar, S. K.; Roy, R.; Rampho, G. J.

    2017-07-01

    We study the structural and several quantum properties of three-dimensional bosonic cluster interacting through van der Waals potential at large scattering length. We use Faddeev-type decomposition of the many-body wave function which includes all possible two-body correlations. At large scattering length, we observe spatially extended states which exhibit the exponential dependence on the state number. The cluster ground state energy shows universal nature at large negative scattering length. We also find the existence of generalized Tjon lines for N-body clusters. Signature of universal behaviour of weakly bound clusters can be observed in experiments of ultracold Bose gases. We also study the spectral statistics of the system. We calculate both the short-range fluctuation and long-range correlation and observe semi-Poisson distribution which interpolates the Gaussian Orthogonal Ensemble (GOE) and Poisson statistics of random matrix theory. It indicates that the van der Waal cluster near the unitary becomes highly complex and correlated. However additional study of P (r) distribution (without unfolding of energy spectrum) reveals the possibility of chaos for larger cluster.

  16. Droplet spreading driven by van der Waals force: a molecular dynamics study

    KAUST Repository

    Wu, Congmin

    2010-07-07

    The dynamics of droplet spreading is investigated by molecular dynamics simulations for two immiscible fluids of equal density and viscosity. All the molecular interactions are modeled by truncated Lennard-Jones potentials and a long-range van der Waals force is introduced to act on the wetting fluid. By gradually increasing the coupling constant in the attractive van der Waals interaction between the wetting fluid and the substrate, we observe a transition in the initial stage of spreading. There exists a critical value of the coupling constant, above which the spreading is pioneered by a precursor film. In particular, the dynamically determined critical value quantitatively agrees with that determined by the energy criterion that the spreading coefficient equals zero. The latter separates partial wetting from complete wetting. In the regime of complete wetting, the radius of the spreading droplet varies with time as R(t) ∼ √t, a behavior also found in molecular dynamics simulations where the wetting dynamics is driven by the short-range Lennard-Jones interaction between liquid and solid. © 2010 IOP Publishing Ltd.

  17. Stacking sequence dependent photo-electrocatalytic performance of CVD grown MoS2/graphene van der Waals solids

    Science.gov (United States)

    Biroju, Ravi K.; Pal, Shubhadeep; Sharma, Rahul; Giri, P. K.; Narayanan, Tharangattu N.

    2017-02-01

    New layered solids by the combinatorial stacking of different atomic layers are emanating as novel candidates for energy efficient devices. Here, sequentially stacked single layer graphene-molybdenum disulfide (MoS2) van der Waals (vdW) solids are demonstrated for their efficacy in the catalysis of hydrogen evolution reaction (HER), and importance of their stacking order in tuning the photo-electrocatalytic (PEC) efficiency is unraveled. Single layer graphene and a few layered MoS2 stacked vdW solids based transparent flexible electrodes were prepared, and a particular stacking sequence where top-graphene: bottom-MoS2/polydimethylsiloxane (PDMS) geometry (MSGR) exhibited the lowest onset and over potentials and a very high exchange current density (j 0 ∼ 245 ± 1 μA cm‑2) in acidic HER in comparison to the individual layers and other stacked configuration (MoS2 on top of graphene on PDMS, GRMS). The HER studies under dark and white light illuminations were conducted to explore the PEC responses of the devices. The augmented HER performance of MSGR is further confirmed from the charge transfer resistance measurements using electrochemical impedance spectroscopy. Role of graphene plasmonics and MoS2 to graphene electron transfer were studied, and this study unravels the importance of a new factor, stacking order of vdW layers, while designing novel devices from the layered solids.

  18. Quantum Transport Detected by Strong Proximity Interaction at a Graphene-WS2 van der Waals Interface.

    Science.gov (United States)

    O'Farrell, E C T; Avsar, A; Tan, J Y; Eda, G; Özyilmaz, B

    2015-09-09

    Magnetotransport measurements demonstrate that graphene in a van der Waals heterostructure is a sensitive probe of quantum transport in an adjacent WS2 layer via strong Coulomb interactions. We observe a large low-field magnetoresistance (≫ e(2)/h) and a -ln T temperature dependence of the resistance. In-plane magnetic field resistance indicates the origin is orbital and nonclassical. We demonstrate a strong electron-hole asymmetry in the mobility and coherence length of graphene demonstrating the presence of localized Coulomb interactions with ionized donors in the WS2 substrate, which ultimately leads to screening as the Fermi level of graphene is tuned toward the conduction band of WS2. This leads us to conclude that graphene couples to quantum localization processes in WS2 via the Coulomb interaction and results in the observed signatures of quantum transport. Our results show that theoretical descriptions of the van der Waals interface should not ignore localized strong correlations.

  19. Quantitative method of measuring cancer cell urokinase and metastatic potential

    Science.gov (United States)

    Morrison, Dennis R. (Inventor)

    1993-01-01

    The metastatic potential of tumors can be evaluated by the quantitative detection of urokinase and DNA. The cell sample selected for examination is analyzed for the presence of high levels of urokinase and abnormal DNA using analytical flow cytometry and digital image analysis. Other factors such as membrane associated urokinase, increased DNA synthesis rates and certain receptors can be used in the method for detection of potentially invasive tumors.

  20. Measurement campaign for wind power potential in west Greenland

    Science.gov (United States)

    Rønnow Jakobsen, Kasper

    2013-04-01

    Experiences and results from a wind resource exploring campaign 2003- in west Greenland. Like many other countries, Greenland is trying to reduce its dependency of fossil fuel by implementing renewable energy. The main challenge is that the people live on the coast in scattered settlements, without power infrastructure. Based on this a wind power potential project was established in 2002, funded by the Greenlandic government and the Technical University of Denmark. We present results and experiences of the campaign. 1 Field campaign There were only a few climate stations in or close to settlements and due to their positioning and instrumentation, they were not usable for wind resource estimation. To establish met stations in Arctic areas with complex topography, there are some challenges to face; mast positioning in complex terrain, severe weather conditions, instrumentation, data handling, installation and maintenance budget. The terrain in the ice free and populated part, mainly consists of mountains of different heights and shapes, separated by deep fjords going from the ice cap to the sea. With a generally low wind resource the focus was on the most exposed positions close to the settlements. Data from the nearest existing climate stations was studied for background estimations of predominant wind directions and extreme wind speeds, and based on that the first 10m masts were erected in 2003. 2 Instruments The first installations used standard NRG systems with low cost NRG instruments. For most of the sites this low cost setup did a good job, but there were some problems with the first design, including instrument and boom strains. In subsequent years, the systems were updated several times to be able to operate in the extreme conditions. Different types of instruments, data logger and boom systems were tested to get better data quality and reliability. Today 11 stations with heights ranging from 10-50m are installed and equipped according to the IEC standard

  1. Measurement of sheath thickness at a floating potential

    Energy Technology Data Exchange (ETDEWEB)

    Han, Hyung-Sik; Lee, Hyo-Chang; Oh, Se-Jin; Chung, Chin-Wook, E-mail: joykang@hanyang.ac.kr [Department of Electrical Engineering, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791 (Korea, Republic of)

    2014-02-15

    In a cylindrical Langmuir probe measurement, ion current is collected from the surface of the sheath surrounded at probe tip, not at the surface of the probe tip. By using this, the sheath thickness can be obtained, if we know some unknown parameters, such as ion current, plasma density, and electron temperature. In this paper, we present a method to measure sheath thickness by using a wave cutoff method and a floating harmonic method. The measured result is in a good agreement with Allen-Boyd-Reynolds theory.

  2. Meteorological field measurements at potential and actual wind turbine sites

    Energy Technology Data Exchange (ETDEWEB)

    Renne, D.S.; Sandusky, W.F.; Hadley, D.L.

    1982-09-01

    An overview of experiences gained in a meteorological measurement program conducted at a number of locations around the United States for the purpose of site evaluation for wind energy utilization is provided. The evolution of the measurement program from its inception in 1976 to the present day is discussed. Some of the major accomplishments and areas for improvement are outlined. Some conclusions on research using data from this program are presented.

  3. Measuring spin correlations in optical lattices using superlattice potentials

    DEFF Research Database (Denmark)

    Pedersen, Kim Georg Lind; Andersen, Brian Møller; Bruun, Georg Morten;

    2011-01-01

    We suggest two experimental methods for probing both short- and long-range spin correlations of atoms in optical lattices using superlattice potentials. The first method involves an adiabatic doubling of the periodicity of the underlying lattice to probe neighboring singlet (triplet) correlations...... for fermions (bosons) by the occupation of the resulting vibrational ground state. The second method utilizes a time-dependent superlattice potential to generate spin-dependent transport by any number of prescribed lattice sites, and probes correlations by the resulting number of doubly occupied sites....... For experimentally relevant parameters, we demonstrate how both methods yield large signatures of antiferromagnetic correlations of strongly repulsive fermionic atoms in a single shot of the experiment. Lastly, we show how this method may also be applied to probe d-wave pairing, a possible ground-state candidate...

  4. Field Effect in Graphene-Based van der Waals Heterostructures

    DEFF Research Database (Denmark)

    Stradi, Daniele; Papior, Nick Rübner; Hansen, Ole

    2017-01-01

    Stacked van der Waals (vdW) heterostructures where semiconducting two-dimensional (2D) materials are contacted by overlaid graphene electrodes enable atomically thin, flexible electronics. We use first-principles quantum transport simulations of graphene-contacted MoS2 devices to show how...... the transistor effect critically depends on the stacking configuration relative to the gate electrode. We can trace this behavior to the stacking-dependent response of the contact region to the capacitive electric field induced by the gate. The contact resistance is a central parameter and our observation...

  5. Van der Waals phase transition in the framework of holography

    CERN Document Server

    Zeng, Xiao-Xiong

    2015-01-01

    Phase structure of the quintessence Reissner-Nordstr\\"{o}m-AdS black hole is probed with the nonlocal observables such as holographic entanglement entropy and two point correlation function. Our result shows that, as the case of the thermal entropy, both the observables exhibit the similar Van der Waals-like phase transition. To reinforce the conclusion, we further check the equal area law for the first order phase transition and critical exponent of the heat capacity for the second order phase transition. We also discuss the effect of the state parameter on the phase structure of the nonlocal observables.

  6. New potential for the Leitz Infinity Coordinate Measuring Machine

    CERN Document Server

    Sanz, Claude; MAINAUD DURAND , Hélène; Schneider, Jurgen; Steffens, Norbert; Morantz , Paul; Shore , Paul

    2015-01-01

    The following study is realised within the frame of the PACMAN project: a study on Particle Accelerator Components Metrology and Alignment to the Nanometre scale, which is a Marie Curie program supported by the European commission and hosted by CERN (European Organisation for Nuclear Research). The aim of this program is to develop and build a pre-alignment bench on which each component is aligned to the required level in one single step using a stretched wire. During the operation, the centre of the stretched wire is aligned with the magnetic axis of the magnet. Then, the position of the wire is measured to the highest possible accuracy using a 3D Coordinate Measuring Machine (CMM) Leitz PMM-C Infinity from HEXAGON Metrology. The research described in this paper is two-fold: on one hand we apply a strong magnetic field to the head of the CMM and evaluate its influence on the measurement accuracy; on the other hand we measure the position

  7. Scanning tunneling spectroscopy of van der Waals graphene/semiconductor interfaces: absence of Fermi level pinning

    Science.gov (United States)

    Le Quang, T.; Cherkez, V.; Nogajewski, K.; Potemski, M.; Dau, M. T.; Jamet, M.; Mallet, P.; Veuillen, J.-Y.

    2017-09-01

    We have investigated the electronic properties of two-dimensional (2D) transition metal dichalcogenides (TMDs), namely trilayer WSe2 and monolayer MoSe2, deposited on epitaxial graphene on silicon carbide, by using scanning tunneling microscopy and spectroscopy (STM/STS) in ultra-high vacuum. Depending on the number of graphene layers below the TMD flakes, we identified variations in the electronic dI/dV(V) spectra measured by the STM tip: the most salient feature is a rigid shift of the TMD spectra (i.e. of the different band onset positions) towards occupied states by about 120 mV when passing from bilayer to monolayer underlying graphene. Since both graphene phases are metallic and present a work function difference in the same energy range, our measurements point towards the absence of Fermi-level pinning for such van der Waals 2D TMD/Metal heterojunctions, following the prediction of the Schottky-Mott model.

  8. 77 FR 11119 - Request for Nominations of Children's Healthcare Quality Measures for Potential Inclusion in the...

    Science.gov (United States)

    2012-02-24

    ... Healthcare Quality Measures for Potential Inclusion in the CHIPRA 2013 Improved Core Set of Health Care... soliciting the submission of measures of children's healthcare quality for potential inclusion in the CHIPRA..., and feasibility of the measures. If a measure is selected for inclusion, more information, including a...

  9. Investigation of a potential HCHO measurement artifact from ISOPOOH

    Science.gov (United States)

    St. Clair, Jason M.; Rivera-Rios, Jean C.; Crounse, John D.; Praske, Eric; Kim, Michelle J.; Wolfe, Glenn M.; Keutsch, Frank N.; Wennberg, Paul O.; Hanisco, Thomas F.

    2016-09-01

    Recent laboratory experiments have shown that a first generation isoprene oxidation product, ISOPOOH, can decompose to methyl vinyl ketone (MVK) and methacrolein (MACR) on instrument surfaces, leading to overestimates of MVK and MACR concentrations. Formaldehyde (HCHO) was suggested as a decomposition co-product, raising concern that in situ HCHO measurements may also be affected by an ISOPOOH interference. The HCHO measurement artifact from ISOPOOH for the NASA In Situ Airborne Formaldehyde instrument (ISAF) was investigated for the two major ISOPOOH isomers, (1,2)-ISOPOOH and (4,3)-ISOPOOH, under dry and humid conditions. The dry conversion of ISOPOOH to HCHO was 3 ± 2 % and 6 ± 4 % for (1,2)-ISOPOOH and (4,3)-ISOPOOH, respectively. Under humid (relative humidity of 40-60 %) conditions, conversion to HCHO was 6 ± 4 % for (1,2)-ISOPOOH and 10 ± 5 % for (4,3)-ISOPOOH. The measurement artifact caused by conversion of ISOPOOH to HCHO in the ISAF instrument was estimated for data obtained on the 6 September 2013 flight of the Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) campaign. Prompt ISOPOOH conversion to HCHO was the source of < 4 % of the observed HCHO, including in the high-isoprene boundary layer. Time-delayed conversion, where previous exposure to ISOPOOH affects measured HCHO later in the flight, was conservatively estimated to be < 10 % of observed HCHO, and is significant only when high ISOPOOH sampling periods immediately precede periods of low HCHO.

  10. Encapsulation of organic molecules in carbon nanotubes: role of the van der Waals interactions

    Science.gov (United States)

    Dappe, Y. J.

    2014-02-01

    Carbon nanotubes are fascinating nano-objects not only from a fundamental point of view but also with respect to their remarkable properties, holding great potential in new materials design. When combined with organic molecules, these properties can be enhanced or modulated in order to fulfil the demand in domains as diverse as molecular electronics, biomaterials or even construction engineering, to name a few. To adequately conceive these hybrid materials it is essential to fully appreciate the nature of molecule-carbon nanotube interactions. In this review, we will discuss some relevant fundamental and applied research done on encapsulated molecules in carbon nanotubes. We will particularly focus on the weak and van der Waals interactions which rule the molecule-tube coupling. Therefore a small state of the art on the theoretical methods used to describe these interactions is presented here. Then, we will discuss various applications of molecular encapsulation, where we will consider structural, magnetic, charge transfer and transport, and optical properties.

  11. Efficient implementation of a van der Waals density functional: application to double-wall carbon nanotubes.

    Science.gov (United States)

    Román-Pérez, Guillermo; Soler, José M

    2009-08-28

    We present an efficient implementation of the van der Waals density functional of Dion et al. [Phys. Rev. Lett. 92, 246401 (2004)], which expresses the nonlocal correlation energy as a double spatial integral. We factorize the integration kernel and use fast Fourier transforms to evaluate the self-consistent potential, total energy, and atomic forces, in O(NlogN) operations. The resulting overhead, for medium and large systems, is a small fraction of the total computational cost, representing a dramatic speedup over the O(N(2)) evaluation of the double integral. This opens the realm of first-principles simulations to the large systems of interest in soft matter and biomolecular problems. We apply the method to calculate the binding energies and the barriers for relative translation and rotation in double-wall carbon nanotubes.

  12. Strain induced piezoelectric effect in black phosphorus and MoS2 van der Waals heterostructure.

    Science.gov (United States)

    Huang, Le; Li, Yan; Wei, Zhongming; Li, Jingbo

    2015-11-10

    The structural, electronic, transport and optical properties of black phosphorus/MoS2 (BP/MoS2) van der Waals (vdw) heterostructure are investigated by using first principles calculations. The band gap of BP/MoS2 bilayer decreases with the applied normal compressive strain and a semiconductor-to-metal transition is observed when the applied strain is more than 0.85 Å. BP/MoS2 bilayer also exhibits modulation of its carrier effective mass and carrier concentration by the applied compressive strain, suggesting that mobility engineering and good piezoelectric effect can be realized in BP/MoS2 heterostructure. Because the type-II band alignment can facilitate the separation of photo-excited electrons and holes, and it can benefit from the great absorption coefficient in ultra-violet region, the BP/MoS2 shows great potential to be a very efficient ultra-violet photodetector.

  13. Experiment and computation: a combined approach to study the van der Waals complexes

    Directory of Open Access Journals (Sweden)

    Surin L.A.

    2017-01-01

    Full Text Available A review of recent results on the millimetre-wave spectroscopy of weakly bound van der Waals complexes, mostly those which contain H2 and He, is presented. In our work, we compared the experimental spectra to the theoretical bound state results, thus providing a critical test of the quality of the M–H2 and M–He potential energy surfaces (PESs which are a key issue for reliable computations of the collisional excitation and de-excitation of molecules (M = CO, NH3, H2O in the dense interstellar medium. The intermolecular interactions with He and H2 play also an important role for high resolution spectroscopy of helium or para-hydrogen clusters doped by a probe molecule (CO, HCN. Such experiments are directed on the detection of superfluid response of molecular rotation in the He and p-H2 clusters.

  14. The T-shaped KrI2(ion-pair states) van der Waals complexes

    Science.gov (United States)

    Baturo, V. V.; Kevorkyants, R.; Lukashov, S. S.; Poretsky, S. A.; Pravilov, A. M.; Zhironkin, A. I.

    2017-09-01

    The T-shaped KrI2(E0g+) van der Waals complexes have been observed and studied for the first time. Analysis of the luminescence excitation spectra as well as luminescence spectra themselves in the spectral ranges, where the I2(E0g+ → B0u+, D0u+ → X0g+, β1g → A1u and D‧2g → A‧2u) transitions can occur, has been carried out. Branching ratios of the iodine molecule state formation and vibronic level population, as well as the potential parameters of the KrI2(E,vE = 0-8, nE) complexes have been determined. Binding energies of the KrI2(X0g+,vX = 0, nX = 0 and B0u+, vB = 19, nB = 0) complexes have been also estimated.

  15. Thermodynamic properties of van der Waals fluids from Monte Carlo simulations and perturbative Monte Carlo theory.

    Science.gov (United States)

    Díez, A; Largo, J; Solana, J R

    2006-08-21

    Computer simulations have been performed for fluids with van der Waals potential, that is, hard spheres with attractive inverse power tails, to determine the equation of state and the excess energy. On the other hand, the first- and second-order perturbative contributions to the energy and the zero- and first-order perturbative contributions to the compressibility factor have been determined too from Monte Carlo simulations performed on the reference hard-sphere system. The aim was to test the reliability of this "exact" perturbation theory. It has been found that the results obtained from the Monte Carlo perturbation theory for these two thermodynamic properties agree well with the direct Monte Carlo simulations. Moreover, it has been found that results from the Barker-Henderson [J. Chem. Phys. 47, 2856 (1967)] perturbation theory are in good agreement with those from the exact perturbation theory.

  16. Franckeite as a naturally occurring van der Waals heterostructure

    Science.gov (United States)

    Molina-Mendoza, Aday J.; Giovanelli, Emerson; Paz, Wendel S.; Niño, Miguel Angel; Island, Joshua O.; Evangeli, Charalambos; Aballe, Lucía; Foerster, Michael; van der Zant, Herre S. J.; Rubio-Bollinger, Gabino; Agraït, Nicolás; Palacios, J. J.; Pérez, Emilio M.; Castellanos-Gomez, Andres

    2017-01-01

    The fabrication of van der Waals heterostructures, artificial materials assembled by individual stacking of 2D layers, is among the most promising directions in 2D materials research. Until now, the most widespread approach to stack 2D layers relies on deterministic placement methods, which are cumbersome and tend to suffer from poor control over the lattice orientations and the presence of unwanted interlayer adsorbates. Here, we present a different approach to fabricate ultrathin heterostructures by exfoliation of bulk franckeite which is a naturally occurring and air stable van der Waals heterostructure (composed of alternating SnS2-like and PbS-like layers stacked on top of each other). Presenting both an attractive narrow bandgap (<0.7 eV) and p-type doping, we find that the material can be exfoliated both mechanically and chemically down to few-layer thicknesses. We present extensive theoretical and experimental characterizations of the material's electronic properties and crystal structure, and explore applications for near-infrared photodetectors. PMID:28194037

  17. Measuring Engagement with the Potential Consequences of Climate Change

    Science.gov (United States)

    Young, N.; Danielson, R. W.; Lombardi, D.

    2015-12-01

    Across three studies, we investigated engagement with the consequences of climate change. We drew from the conceptual change and risk analysis literatures to find the factors that determine how much people will care about future risks. Questions derived from these factors were then asked about many hypothesized consequences of climate change. These consequences were drawn from an Intergovernmental Panel on Climate Change special report (IPCC, 2012) and, in the third study, additionally from the IPCC AR5 (IPCC, 2014). The first two studies, using undergraduate students, demonstrated that some consequences were indeed considerably more engaging than others. The third study used a more representative sample of American adults, drawn from Amazon Mechanical Turk and used the Global Warming's Six Americas Screening Tool (Maibach, Leiserowitz, Roser-Renouf, Mertz, & Akerlof, 2011) in a large screening survey to find 20 participants in each of the six audiences defined by this tool. These participants were then asked about the potential consequences of climate change. Results again showed that some consequences are considered more engaging than others, and also showed the ways in which members of these six audiences perceive the consequences of climate change differently.

  18. Measuring the zeta potential. The relationships with sandstone fineness

    Directory of Open Access Journals (Sweden)

    de Luxán, M. P.

    1989-09-01

    Full Text Available The application of the zeta potential technique in the area of construction materials and Portland cement is quite recent. The initial research work involved the study of cement suspensions or suspensions of one of the components of cement, such as alite, tricalcium alumínate, in the presence of additives and, more specifically, superplasticizers. The studies of this sort were extended with the mixing of active additions into cement (fly ashes, etc.. The present study discusses the application of siliceous materials (sandstone as a basis of the research into the behaviour of sandstone mortars containing repair products.

    La aplicación de la técnica del potencial zeta en el campo de los materiales de construcción y del cemento portland es muy reciente. Las primeras investigaciones se refieren al estudio de suspensiones de cemento o de alguno de sus compuestos que lo forman como alita, aluminato tricálcico, en presencia de aditivos y, más concretamente, de superfluidificantes. Con la incorporación de adiciones activas al cemento (cenizas volantes,... se amplían los estudios de este tipo de cementos. En este trabajo se considera la aplicación a los materiales silíceos (arenisca como base para la investigación del comportamiento de los morteros de arenisca conteniendo productos de reparación.

  19. Reconstruction from one boundary measurement of a potential homogeneous of degree zero

    DEFF Research Database (Denmark)

    Cornean, Horia; Knudsen, Kim

    2006-01-01

    We consider the inverse boundary value problem concerning the determination and reconstruction of an unknown potential in a Schrödinger equation in a bounded domain from measurements on the boundary of the domain. For the special case of a small potential homogeneous of degree zero we show that one...... boundary measurement determines the potential uniquely. Moreover, we give a reconstruction procedure....

  20. Reconstruction from one boundary measurement of a potential homogeneous of degree zero

    DEFF Research Database (Denmark)

    Cornean, Horia Decebal; Knudsen, Kim

    We consider the inverse boundary value problem concerning the determination and reconstruction of an unknown potential in a Schrödinger equation in a bounded domain from measurements on the boundary of the domain. For the special case of a small potential homogeneous of degree zero we show that one...... boundary measurement determines the potential uniquely. Moreover, we give a reconstruction procedure....

  1. Endocannabinoids measurement in human saliva as potential biomarker of obesity.

    Directory of Open Access Journals (Sweden)

    Isabelle Matias

    Full Text Available BACKGROUND: The discovery of the endocannabinoid system and of its role in the regulation of energy balance has significantly advanced our understanding of the physiopathological mechanisms leading to obesity and type 2 diabetes. New knowledge on the role of this system in humans has been acquired by measuring blood endocannabinoids. Here we explored endocannabinoids and related N-acylethanolamines in saliva and verified their changes in relation to body weight status and in response to a meal or to body weight loss. METHODOLOGY/PRINCIPAL FINDINGS: Fasting plasma and salivary endocannabinoids and N-acylethanolamines were measured through liquid mass spectrometry in 12 normal weight and 12 obese, insulin-resistant subjects. Salivary endocannabinoids and N-acylethanolamines were evaluated in the same cohort before and after the consumption of a meal. Changes in salivary endocannabinoids and N-acylethanolamines after body weight loss were investigated in a second group of 12 obese subjects following a 12-weeks lifestyle intervention program. The levels of mRNAs coding for enzymes regulating the metabolism of endocannabinoids, N-acylethanolamines and of cannabinoid type 1 (CB(1 receptor, alongside endocannabinoids and N-acylethanolamines content, were assessed in human salivary glands. The endocannabinoids 2-arachidonoylglycerol (2-AG, N-arachidonoylethanolamide (anandamide, AEA, and the N-acylethanolamines (oleoylethanolamide, OEA and palmitoylethanolamide, PEA were quantifiable in saliva and their levels were significantly higher in obese than in normal weight subjects. Fasting salivary AEA and OEA directly correlated with BMI, waist circumference and fasting insulin. Salivary endocannabinoids and N-acylethanolamines did not change in response to a meal. CB(1 receptors, ligands and enzymes were expressed in the salivary glands. Finally, a body weight loss of 5.3% obtained after a 12-weeks lifestyle program significantly decreased salivary AEA

  2. Prediction of intrinsic two-dimensional ferroelectrics in In2Se3 and other III2-VI3 van der Waals materials

    Science.gov (United States)

    Ding, Wenjun; Zhu, Jianbao; Wang, Zhe; Gao, Yanfei; Xiao, Di; Gu, Yi; Zhang, Zhenyu; Zhu, Wenguang

    2017-04-01

    Interest in two-dimensional (2D) van der Waals materials has grown rapidly across multiple scientific and engineering disciplines in recent years. However, ferroelectricity, the presence of a spontaneous electric polarization, which is important in many practical applications, has rarely been reported in such materials so far. Here we employ first-principles calculations to discover a branch of the 2D materials family, based on In2Se3 and other III2-VI3 van der Waals materials, that exhibits room-temperature ferroelectricity with reversible spontaneous electric polarization in both out-of-plane and in-plane orientations. The device potential of these 2D ferroelectric materials is further demonstrated using the examples of van der Waals heterostructures of In2Se3/graphene, exhibiting a tunable Schottky barrier, and In2Se3/WSe2, showing a significant band gap reduction in the combined system. These findings promise to substantially broaden the tunability of van der Waals heterostructures for a wide range of applications.

  3. Cavitation inception of a van der Waals fluid at a sack-wall obstacle

    CERN Document Server

    Kaehler, G; Gonnella, G; Lamura, A

    2016-01-01

    Cavitation in a liquid moving past a constraint is numerically investigated by means of a free-energy lattice Boltzmann simulation based on the van der Waals equation of state. The fluid is streamed past an obstacle and, depending on the pressure drop between inlet and outlet, vapor formation underneath the corner of the sack-wall is observed. The circumstances of cavitation formation are investigated and it is found that the local bulk pressure and mean stress are insufficient to explain the phenomenon. Results obtained in this study strongly suggest that the viscous stress, interfacial contributions to the local pressure, and the Laplace pressure are relevant to the opening of a vapor cavity. This can be described by a generalization of Joseph's criterion that includes these contributions. A macroscopic investigation measuring mass flow rate behavior and discharge coefficient was also performed. As theoretically predicted, mass flow rate increases linearly with the square root of the pressure drop. However,...

  4. Equations of State: From the Ideas of van der Waals to Association Theories

    DEFF Research Database (Denmark)

    Kontogeorgis, Georgios; Economou, Ioannis G.

    2010-01-01

    The ideas of van der Waals have resulted to cubic equations of state like Soave–Redlich–Kwong (SRK) and Peng–Robinson (PR) which are widely used in the petroleum and chemical industries. It is often thought that the range of applicability of van der Waals-type models is limited to mixtures...

  5. The potential of ground gravity measurements to validate GRACE data

    Directory of Open Access Journals (Sweden)

    D. Crossley

    2003-01-01

    Full Text Available New satellite missions are returning high precision, time-varying, satellite measurements of the Earth’s gravity field. The GRACE mission is now in its calibration/- validation phase and first results of the gravity field solutions are imminent. We consider here the possibility of external validation using data from the superconducting gravimeters in the European sub-array of the Global Geodynamics Project (GGP as ‘ground truth’ for comparison with GRACE. This is a pilot study in which we use 14 months of 1-hour data from the beginning of GGP (1 July 1997 to 30 August 1998, when the Potsdam instrument was relocated to South Africa. There are 7 stations clustered in west central Europe, and one station, Metsahovi in Finland. We remove local tides, polar motion, local and global air pressure, and instrument drift and then decimate to 6-hour samples. We see large variations in the time series of 5–10µgal between even some neighboring stations, but there are also common features that correlate well over the 427-day period. The 8 stations are used to interpolate a minimum curvature (gridded surface that extends over the geographical region. This surface shows time and spatial coherency at the level of 2– 4µgal over the first half of the data and 1–2µgal over the latter half. The mean value of the surface clearly shows a rise in European gravity of about 3µgal over the first 150 days and a fairly constant value for the rest of the data. The accuracy of this mean is estimated at 1µgal, which compares favorably with GRACE predictions for wavelengths of 500 km or less. Preliminary studies of hydrology loading over Western Europe shows the difficulty of correlating the local hydrology, which can be highly variable, with large-scale gravity variations.Key words. GRACE, satellite gravity, superconducting gravimeter, GGP, ground truth

  6. Cosmological models described by a mixture of van der Waals fluid and dark energy

    CERN Document Server

    Kremer, G M

    2003-01-01

    The Universe is modeled as a binary mixture whose constituents are described by a van der Waals fluid and by a dark energy density. The dark energy density is considered either as the quintessence or as the Chaplygin gas. The irreversible processes concerning the energy transfer between the van der Waals fluid and the gravitational field are taken into account. This model can simulate: (a) an inflationary period where the acceleration grows exponentially and the van der Waals fluid behaves like an inflaton; (b) an inflationary period where the acceleration is positive but it decreases and tends to zero whereas the energy density of the van der Waals fluid decays; (c) a decelerated period which corresponds to a matter dominated period with a non-negative pressure; and (d) a present accelerated period where the dark energy density outweighs the energy density of the van der Waals fluid.

  7. Density, structure, and dynamics of water: the effect of van der Waals interactions.

    Science.gov (United States)

    Wang, Jue; Román-Pérez, G; Soler, Jose M; Artacho, Emilio; Fernández-Serra, M-V

    2011-01-14

    It is known that ab initio molecular dynamics (AIMD) simulations of liquid water at ambient conditions, based on the generalized gradient approximation (GGA) to density functional theory (DFT), with commonly used functionals fail to produce structural and diffusive properties in reasonable agreement with experiment. This is true for canonical, constant temperature simulations where the density of the liquid is fixed to the experimental density. The equilibrium density, at ambient conditions, of DFT water has recently been shown by Schmidt et al. [J. Phys. Chem. B, 113, 11959 (2009)] to be underestimated by different GGA functionals for exchange and correlation, and corrected by the addition of interatomic pair potentials to describe van der Waals (vdW) interactions. In this contribution we present a DFT-AIMD study of liquid water using several GGA functionals as well as the van der Waals density functional (vdW-DF) of Dion et al. [Phys. Rev. Lett. 92, 246401 (2004)]. As expected, we find that the density of water is grossly underestimated by GGA functionals. When a vdW-DF is used, the density improves drastically and the experimental diffusivity is reproduced without the need of thermal corrections. We analyze the origin of the density differences between all the functionals. We show that the vdW-DF increases the population of non-H-bonded interstitial sites, at distances between the first and second coordination shells. However, it excessively weakens the H-bond network, collapsing the second coordination shell. This structural problem is partially associated to the choice of GGA exchange in the vdW-DF. We show that a different choice for the exchange functional is enough to achieve an overall improvement both in structure and diffusivity.

  8. Wave packet studies of the vibrational predissociation of three and four-atom van der Waals complexes

    Energy Technology Data Exchange (ETDEWEB)

    Gray, S.K.

    1994-03-01

    Vibrational predissociation of XI{sub 2} and X{sub 2}I{sub 2} van der Waals complexes, with X = He and Ne, is studied with wave packets. Three-dimensional calculations are carried out on the three-atom systems. Suitable X{center_dot}{center_dot}I potential interactions are determined, and product distributions are predicted. Reduced dimension models of X{sub 2}I{sub 2}(v{prime}) {yields} 2X + I{sub 2}(v < v{prime}) are investigated. Comparison is made with available experimental results. Mechanistic issues, including the role of intramolecular vibrational relaxation resonances, are addressed.

  9. Hybrid van der Waals p-n Heterojunctions based on SnO and 2D MoS2

    KAUST Repository

    Wang, Zhenwei

    2016-08-30

    A p-type oxide/2D hybrid van der Waals p-n heterojunction is demonstrated for the first time between SnO (tin monoxide) (the p-type oxide) and 2D MoS2 (molybdenum disulfide), showing an ideality factor of 2 and rectification ratio up to 10(4) . The reported heterojunction is gate-tunable with typical anti-ambipolar transfer characteristics. Surface potential mapping is performed and a current model for such a heterojunction is proposed.

  10. Engineering Low Dimensional Materials with van der Waals Interaction

    Science.gov (United States)

    Jin, Chenhao

    Two-dimensional van der Waals materials grow into a hot and big field in condensed matter physics in the past decade. One particularly intriguing thing is the possibility to stack different layers together as one wish, like playing a Lego game, which can create artificial structures that do not exist in nature. These new structures can enable rich new physics from interlayer interaction: The interaction is strong, because in low-dimension materials electrons are exposed to the interface and are susceptible to other layers; and the screening of interaction is less prominent. The consequence is rich, not only from the extensive list of two-dimensional materials available nowadays, but also from the freedom of interlayer configuration, such as displacement and twist angle, which creates a gigantic parameter space to play with. On the other hand, however, the huge parameter space sometimes can make it challenging to describe consistently with a single picture. For example, the large periodicity or even incommensurability in van der Waals systems creates difficulty in using periodic boundary condition. Worse still, the huge superlattice unit cell and overwhelming computational efforts involved to some extent prevent the establishment of a simple physical picture to understand the evolution of system properties in the parameter space of interlayer configuration. In the first part of the dissertation, I will focus on classification of the huge parameter space into subspaces, and introduce suitable theoretical approaches for each subspace. For each approach, I will discuss its validity, limitation, general solution, as well as a specific example of application demonstrating how one can obtain the most important effects of interlayer interaction with little computation efforts. Combining all the approaches introduced will provide an analytic solution to cover majority of the parameter space, which will be very helpful in understanding the intuitive physical picture behind

  11. Thermohydrodynamics of boiling in a van der Waals fluid.

    Science.gov (United States)

    Laurila, T; Carlson, A; Do-Quang, M; Ala-Nissila, T; Amberg, G

    2012-02-01

    We present a modeling approach that enables numerical simulations of a boiling Van der Waals fluid based on the diffuse interface description. A boundary condition is implemented that allows in and out flux of mass at constant external pressure. In addition, a boundary condition for controlled wetting properties of the boiling surface is also proposed. We present isothermal verification cases for each element of our modeling approach. By using these two boundary conditions we are able to numerically access a system that contains the essential physics of the boiling process at microscopic scales. Evolution of bubbles under film boiling and nucleate boiling conditions are observed by varying boiling surface wettability. We observe flow patters around the three-phase contact line where the phase change is greatest. For a hydrophilic boiling surface, a complex flow pattern consistent with vapor recoil theory is observed.

  12. Heterostructures based on inorganic and organic van der Waals systems

    Directory of Open Access Journals (Sweden)

    Gwan-Hyoung Lee

    2014-09-01

    Full Text Available The two-dimensional limit of layered materials has recently been realized through the use of van der Waals (vdW heterostructures composed of weakly interacting layers. In this paper, we describe two different classes of vdW heterostructures: inorganic vdW heterostructures prepared by co-lamination and restacking; and organic-inorganic hetero-epitaxy created by physical vapor deposition of organic molecule crystals on an inorganic vdW substrate. Both types of heterostructures exhibit atomically clean vdW interfaces. Employing such vdW heterostructures, we have demonstrated various novel devices, including graphene/hexagonal boron nitride (hBN and MoS2 heterostructures for memory devices; graphene/MoS2/WSe2/graphene vertical p-n junctions for photovoltaic devices, and organic crystals on hBN with graphene electrodes for high-performance transistors.

  13. A crossover in anisotropic nanomechanochemistry of van der Waals crystals

    Energy Technology Data Exchange (ETDEWEB)

    Shimamura, Kohei [Department of Physics, Kumamoto University, Kumamoto 860-8555 (Japan); Collaboratory for Advanced Computing and Simulations, Department of Physics and Astronomy, Department of Computer Science, Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-0242 (United States); Graduate School of System Informatics, Kobe University, Kobe 657-8501 (Japan); Misawa, Masaaki [Department of Physics, Kumamoto University, Kumamoto 860-8555 (Japan); Collaboratory for Advanced Computing and Simulations, Department of Physics and Astronomy, Department of Computer Science, Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-0242 (United States); Li, Ying [Argonne Leadership Computing Facility, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya [Collaboratory for Advanced Computing and Simulations, Department of Physics and Astronomy, Department of Computer Science, Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-0242 (United States); Shimojo, Fuyuki [Department of Physics, Kumamoto University, Kumamoto 860-8555 (Japan)

    2015-12-07

    In nanoscale mechanochemistry, mechanical forces selectively break covalent bonds to essentially control chemical reactions. An archetype is anisotropic detonation of layered energetic molecular crystals bonded by van der Waals (vdW) interactions. Here, quantum molecular dynamics simulations reveal a crossover of anisotropic nanomechanochemistry of vdW crystal. Within 10{sup −13} s from the passage of shock front, lateral collision produces NO{sub 2} via twisting and bending of nitro-groups and the resulting inverse Jahn-Teller effect, which is mediated by strong intra-layer hydrogen bonds. Subsequently, as we transition from heterogeneous to homogeneous mechanochemical regimes around 10{sup −12} s, shock normal to multilayers becomes more reactive, producing H{sub 2}O assisted by inter-layer N-N bond formation. These time-resolved results provide much needed atomistic understanding of nanomechanochemistry that underlies a wider range of technologies.

  14. Band engineering in a van der Waals heterostructure using a 2D polar material and a capping layer

    Science.gov (United States)

    Cho, Sung Beom; Chung, Yong-Chae

    2016-06-01

    Van der Waals (vdW) heterostructures are expected to play a key role in next-generation electronic and optoelectronic devices. In this study, the band alignment of a vdW heterostructure with 2D polar materials was studied using first-principles calculations. As a model case study, single-sided fluorographene (a 2D polar material) on insulating (h-BN) and metallic (graphite) substrates was investigated to understand the band alignment behavior of polar materials. Single-sided fluorographene was found to have a potential difference along the out-of-plane direction. This potential difference provided as built-in potential at the interface, which shift the band alignment between h-BN and graphite. The interface characteristics were highly dependent on the interface terminations because of this built-in potential. Interestingly, this band alignment can be modified with a capping layer of graphene or BN because the capping layer triggered electronic reconstruction near the interface. This is because the bonding nature is not covalent, but van der Waals, which made it possible to avoid Fermi-level pinning at the interface. The results of this study showed that diverse types of band alignment can be achieved using polar materials and an appropriate capping layer.

  15. On Invariant Measures for the Vlasov Equation with a Regular Potential

    CERN Document Server

    Zhidkov, P E

    2003-01-01

    We consider a Vlasov equation with a smooth bounded potential of interaction between particles in a class of measure-valued solutions and construct a measure which is invariant for this problem in a sense.

  16. Electrical Transport and Thermal Expansion in van der Waals Materials: Graphene and Topological Insulator

    Science.gov (United States)

    Jing, Lei

    Novel two-dimensional materials with weak interlayer Van der Waals interaction are fantastic platforms to study novel physical phenomena. This thesis describes our investigation on two different Van der Waals materials: graphene and bismuth selenide with calcium doping (CaxBi 2-xSe3, x as the doping level) in the topological insulator family. Firstly, we characterize the electrical transport behaviors of high-quality substrate-supported bilayer graphene devices with suspended metal gates. The device exhibits a transport gap induced by external electric field with an on/off ratio of 20,000, which could be explained by variable range hoping between localized states or disordered charge puddles. At large magnetic field, the device presents quantum Hall plateau at fractional values of conductance quantum, which arises from the equilibration of edge states between differentially doped regions. Secondly, we present our study on the electronic transport of CaxBi 2-xSe3 thin films, which are three-dimensional topological insulators and coupled with superconducting leads. In these novel Josephson transistors, we observe different characteristic features by energy dispersion spectrum (EDS) and Raman spectroscopy, and the weak suppression in the critical current Ic. Thirdly, we explore the thermal expansion of suspended graphene. By in-situ scanning electron microscope (SEM), we measure the thickness-dependence of graphene's negative thermal expansion coefficient (TEC). We propose that there is a competitive relation between the intrinsic TEC and the friction from the substrate and the graphene. Lastly, in collaboration with Dr. Nikolai Kalugin from New Mexico Tech., we explore the graphene's application as a quantum Hall effect infrared photodetector. This graphene-based detector can be operated at higher temperature (liquid nitrogen) and wider frequency than the previous implementations of quantum Hall detector.

  17. Measuring Soil Water Potential for Water Management in Agriculture: A Review

    Directory of Open Access Journals (Sweden)

    Marco Bittelli

    2010-05-01

    Full Text Available Soil water potential is a soil property affecting a large variety of bio-physical processes, such as seed germination, plant growth and plant nutrition. Gradients in soil water potential are the driving forces of water movement, affecting water infiltration, redistribution, percolation, evaporation and plants’ transpiration. The total soil water potential is given by the sum of gravity, matric, osmotic and hydrostatic potential. The quantification of the soil water potential is necessary for a variety of applications both in agricultural and horticultural systems such as optimization of irrigation volumes and fertilization. In recent decades, a large number of experimental methods have been developed to measure the soil water potential, and a large body of knowledge is now available on theory and applications. In this review, the main techniques used to measure the soil water potential are discussed. Subsequently, some examples are provided where the measurement of soil water potential is utilized for a sustainable use of water resources in agriculture.

  18. Testing the distance-dependence of the van der Waals interaction between an atom and a surface through spectroscopy in a vapor nanocell

    CERN Document Server

    Laliotis, A; Todorov, P; Hamdi, I; Dutier, G; Yarovitski, A; Saltiel, S; Gorza, M P; Fichet, M; Ducloy, M; Bloch, D; Laliotis, Athanasdios; Maurin, Isabelle; Todorov, Petko; Hamdi, Ismah\\`{e}ne; Dutier, Gabriel; Yarovitski, Alexander; Saltiel, Solomon; Gorza, Marie-Pascale; Fichet, Mich\\`{e}le; Ducloy, Martial; Bloch, Daniel

    2007-01-01

    This paper presents our current measurements in a vapor nanocell aiming at a test of the distance-dependence of the atom-surface interaction, when simple asymptotic descriptions may turn to be not valid. A state-of-the-art of atom-surface interaction measurements is provided as an introduction, along with the comparison with the theory of the van der Waals (or Casimir-Polder) interaction; it is followed by a presentation of the most salient features of nanocell spectroscopy

  19. In situ potential distribution measurement in an all-vanadium flow battery.

    Science.gov (United States)

    Liu, Qinghua; Turhan, Ahmet; Zawodzinski, Thomas A; Mench, Matthew M

    2013-07-18

    An experimental method for measurement of local redox potential within multilayer electrodes was developed and applied to all-vanadium redox flow batteries (VRFBs). Through-plane measurement at the positive side reveals several important phenomena including potential distribution, concentration distribution of active species and the predominant reaction location within the porous carbon electrodes.

  20. Carbon nanotube multi-electrode array chips for noninvasive real-time measurement of dopamine, action potentials, and postsynaptic potentials.

    Science.gov (United States)

    Suzuki, Ikuro; Fukuda, Mao; Shirakawa, Keiichi; Jiko, Hideyasu; Gotoh, Masao

    2013-11-15

    Multi-electrode arrays (MEAs) can be used for noninvasive, real-time, and long-term recording of electrophysiological activity and changes in the extracellular chemical microenvironment. Neural network organization, neuronal excitability, synaptic and phenotypic plasticity, and drug responses may be monitored by MEAs, but it is still difficult to measure presynaptic activity, such as neurotransmitter release, from the presynaptic bouton. In this study, we describe the development of planar carbon nanotube (CNT)-MEA chips that can measure both the release of the neurotransmitter dopamine as well as electrophysiological responses such as field postsynaptic potentials (fPSPs) and action potentials (APs). These CNT-MEA chips were fabricated by electroplating the indium-tin oxide (ITO) microelectrode surfaces. The CNT-plated ITO electrode exhibited electrochemical response, having much higher current density compared with the bare ITO electrode. Chronoamperometric measurements using these CNT-MEA chips detected dopamine at nanomolar concentrations. By placing mouse striatal brain slices on the CNT-MEA chip, we successfully measured synaptic dopamine release from spontaneous firings with a high S/N ratio of 62. Furthermore, APs and fPSPs were measured from cultured hippocampal neurons and slices with high temporal resolution and a 100-fold greater S/N ratio. Our CNT-MEA chips made it possible to measure neurotransmitter dopamine (presynaptic activities), postsynaptic potentials, and action potentials, which have a central role in information processing in the neuronal network. CNT-MEA chips could prove useful for in vitro studies of stem cell differentiation, drug screening and toxicity, synaptic plasticity, and pathogenic processes involved in epilepsy, stroke, and neurodegenerative diseases.

  1. Density functional results for isotropic and anisotropic multipole polarizabilities and C6, C7, and C8 Van der Waals dispersion coefficients for molecules

    Science.gov (United States)

    Osinga, V. P.; van Gisbergen, S. J. A.; Snijders, J. G.; Baerends, E. J.

    1997-03-01

    The generalized gradient-approximated (GGA) energy functionals used in density functional theory (DFT) provide accurate results for many different properties. However, one of their weaknesses lies in the fact that Van der Waals forces are not described. In spite of this, it is possible to obtain reliable long-range potential energy surfaces within DFT. In this paper, we use time-dependent density functional response theory to obtain the Van der Waals dispersion coefficients C6, C7, and C8 (both isotropic and anisotropic). They are calculated from the multipole polarizabilities at imaginary frequencies of the two interacting molecules. Alternatively, one might use one of the recently-proposed Van der Waals energy functionals for well-separated systems, which provide fairly good approximations to our isotropic results. Results with the local density approximation (LDA), Becke-Perdew (BP) GGA and the Van Leeuwen-Baerends (LB94) exchange-correlation potentials are presented for the multipole polarizabilities and the dispersion coefficients of several rare gases, diatomics and the water molecule. The LB94 potential clearly performs best, due to its correct Coulombic asymptotic behavior, yielding results which are close to those obtained with many-body perturbation theory (MBPT). The LDA and BP results are systematically too high for the isotropic properties. This becomes progressively worse for the higher dispersion coefficients. The results for the relative anisotropies are quite satisfactory for all three potentials, however.

  2. Determination of Contact Potential Difference by the Kelvin Probe (Part I I. Basic Principles of Measurements

    Directory of Open Access Journals (Sweden)

    Vilitis O.

    2016-04-01

    Full Text Available Determination of electric potential difference using the Kelvin probe, i.e. vibrating capacitor technique, is one of the most sensitive measuring procedures in surface physics. Periodic modulation of distance between electrodes leads to changes in capacitance, thereby causing current to flow through the external circuit. The procedure of contactless, non-destructive determination of contact potential difference between an electrically conductive vibrating reference electrode and an electrically conductive sample is based on precise control measurement of Kelvin current flowing through a capacitor. The present research is devoted to creation of a new low-cost miniaturised measurement system to determine potential difference in real time and at high measurement resolution. Furthermore, using the electrode of a reference probe, the Kelvin method leads to both the indirect measurement of an electronic work function, or a contact potential of sample, and of a surface potential for insulator type samples.

  3. Enhanced Li capacity in functionalized graphene: A first principle study with van der Waals correction

    Science.gov (United States)

    Chouhan, Rajiv K.; Raghani, Pushpa

    2015-09-01

    We have investigated the adsorption of Li on graphene oxide using density functional theory. We show a novel and simple approach to achieve a positive lithiation potential on epoxy and hydroxyl functionalized graphene, compared to the negative lithiation potential that has been found on prestine graphene. We included the van der Waals correction into the calculation so as to get a better picture of weak interactions. A positive lithiation potential suggests a favorable adsorption of Li on graphene oxide sheets that can lead to an increase in the specific capacity, which in turn can be used as an anode material in Li-batteries. We find a high specific capacity of ˜860 mAhg-1 by functionalizing the graphene sheet. This capacity is higher than the previously reported capacities that were achieved on graphene with high concentration of Stone-Wales (75%) and divacancy (16%) defects. Creating such high density of defects can make the entire system energetically unstable, whereas graphene oxide is a naturally occurring substance.

  4. A natural orbital analysis of the long range behavior of chemical bonding and van der Waals interaction in singlet H2: the issue of zero natural orbital occupation numbers.

    Science.gov (United States)

    Sheng, X W; Mentel, Ł M; Gritsenko, O V; Baerends, E J

    2013-04-28

    This paper gives a natural orbital (NO) based analysis of the van der Waals interaction in (singlet) H2 at long distance. The van der Waals interaction, even if not leading to a distinct van der Waals well, affects the shape of the interaction potential in the van der Waals distance range of 5-9 bohrs and can be clearly distinguished from chemical bonding effects. In the NO basis the van der Waals interaction can be quantitatively covered with, apart from the ground state configurations (1σ(g))(2) and (1σ(u))(2), just the 4 configurations (2σ(g))(2) and (2σ(u))(2), and (1π(u))(2) and (1π(g))(2). The physics of the dispersion interaction requires and explains the peculiar relatively large positive CI coefficients of the doubly excited electron configurations (2σ(u))(2) and (1π(g))(2) (the occupancy amplitudes of the 2σ(u) and 1π(gx, y) NOs) in the distance range 5-9 bohrs, which have been observed before by Cioslowski and Pernal [Chem. Phys. Lett. 430, 188 (2006)]. We show that such positive occupancy amplitudes do not necessarily lead to the existence of zero occupation numbers at some H-H distances.

  5. Gastric potential difference measurements. The gastric mucosal integrity and function studied with a new method for measurement of the electric potential difference across the stomach wall

    DEFF Research Database (Denmark)

    Højgaard, L

    1991-01-01

    be reduced by allopurinol pretreatment, possibly due to the inhibition of oxygen-derived free radical formation. Gastric PD and pH were measured in volunteers and duodenal ulcer patients during Stroop's color word conflict test, in which mental stress causes sympathetic activation. A PD reduction and a p......H increase were found along with stress induction, thereby indicating an influence of mental stress on stomach mucosal function. It is concluded that gastric PD measurement may be useful in ulcer pathogenetic research, and a sufficient gastric mucosal blood flow is stressed as being important for the mucosal......PD--the electric potential difference across the gastric mucosa--is a variable used to describe the gastric mucosal integrity and function. A new, reliable, and easily applied method for gastric PD measurements corrected for the disturbing liquid junction potentials between gastric juice and the PD...

  6. Measurement of streaming potentials of mammalian blood vessels, aorta and vena cava, in vivo.

    Science.gov (United States)

    Sawyer, P N; Himmelfarb, E; Lustrin, I; Ziskind, H

    1966-09-01

    Attempts to measure streaming potentials in large rabbit blood vessels in vivo have been carried out. Streaming potentials, V(89), were measured by the introduction of microelectrodes through the wall of the blood vessel at separations greater than 1 cm. The outputs from these electrodes fed through calomel cells were amplified and recorded directly by using an Electronics for Medicine photorecorder (White Plains, N. Y.). "Effective streaming currents" were determined by running the output through a low impedence galvanometer while simultaneously measuring the resistance of the circuit V(8) were, therefore, calculated from two measurements and compared. Flow through vessels studied was measured using two different electromagnetic flowmeters. The results indicate that V(8) present in both aorta and vena cava are of the order of 5 to 10 mv. By using the Helmholtz-Smoluchowski equation into which flow was reintegrated, the numbers yield zeta potentials approximating 0.1 to 0.4 v in both aorta and vena cava. This number approaches the apparent upper limit for zeta (actually "interfacial potentials") potentials in biological systems. The measured "i.f." potential is considered as the interreaction of several physical and metabolic factors operating at the blood intimal interface. The polarity of the potential suggests that the interface is negative with respect to the blood flowing through the vessel. Interfacial potential and related V(8) are discussed in terms of their possible importance as a mechanism for maintaining vascular homeostasis in the living animal.

  7. Shaly sand formation evaluation in tight gas sands using electrochemical potential measurements

    Science.gov (United States)

    Sharma, M. M.; Jin, M.

    1991-08-01

    Equations are developed that directly relate the shaly conductivity to the electrochemical (membrane) potential (EP). The model is applied to both fully and partially saturated sands. The relationship between the resistivity index and the water saturation is also expressed in terms of a single membrane potential measurement. The Ep measured at different salinities are compared with model prediction using a single membrane potential measurement. Sigma (sub 0) versus Sigma (sub w) curves are then generated using the model equations and compared with measured curves. Experimental results are presented for electrochemical potential measurement made in the lab on 50 tight gs sand samples. It is shown that the measurements can be correlated with CEC although the CEC measured by grinding up the samples was always higher than that estimated from Ep measurements. The Ep measurements are combined with the equations for partial saturation developed in the report to obtain water saturations in a tight gas sand well. Through the example it is shown that it is possible to determine the water saturation in Shaly sands from one membrane potential measurement at a known salinity together with a set of resistivity logs. The results clearly demonstrate the applicability of the method as a practical procedure for Shaly sand information evaluation.

  8. Use of Two-Body Correlated Basis Functions with van der Waals Interaction to Study the Shape-Independent Approximation for a Large Number of Trapped Interacting Bosons

    Science.gov (United States)

    Lekala, M. L.; Chakrabarti, B.; Das, T. K.; Rampho, G. J.; Sofianos, S. A.; Adam, R. M.; Haldar, S. K.

    2017-01-01

    We study the ground-state and the low-lying excitations of a trapped Bose gas in an isotropic harmonic potential for very small (˜ 3) to very large (˜ 10^7 ) particle numbers. We use the two-body correlated basis functions and the shape-dependent van der Waals interaction in our many-body calculations. We present an exhaustive study of the effect of inter-atomic correlations and the accuracy of the mean-field equations considering a wide range of particle numbers. We calculate the ground-state energy and the one-body density for different values of the van der Waals parameter C6 . We compare our results with those of the modified Gross-Pitaevskii results, the correlated Hartree hypernetted-chain equations (which also utilize the two-body correlated basis functions), as well as of the diffusion Monte Carlo for hard sphere interactions. We observe the effect of the attractive tail of the van der Waals potential in the calculations of the one-body density over the truly repulsive zero-range potential as used in the Gross-Pitaevskii equation and discuss the finite-size effects. We also present the low-lying collective excitations which are well described by a hydrodynamic model in the large particle limit.

  9. A simple microcontroller-based sedimentation potential measurement for nanosuspension stability investigations

    Science.gov (United States)

    Joni, I. Made; Zannuary, Ilham; Hidayat, Darmawan; Panatarani, Camellia

    2016-02-01

    This paper report the development of a simple sedimentation potential measurement system to know the state of nanoparticles (NPs) dispersion stability. The state of nanoparticles dispersion stability is very important in applications of nanoparticles since the nature of NPs is easily agglomerate. The developed sedimentation potential consist of graphite electrodes, signal conditioning, microcontroller, and interface circuits provided with a data acquisition applications. The system was designed to obtained sedimentation potential in the range -200 to 200 mV with accuracy of 0.415 mV. From the measured sedimentation potential, the zeta potential can be determined. This system was applied to investigate stability of TiO2 NPS suspension in water media to obtain the performances of the system. Those zeta potentials were determined at various condition such as vary in surface charges by controlling the pH of the suspension, vary in suspension concentrations and sedimentation time. The results show that the higher concentration of the suspension, lower zeta potential of the suspension was obtained. The zeta potential was decreased by the sedimentation time indicated that the agglomeration of particles occurred. Controlling of surface charges by controlling pH also affect the values of obtained zeta potentials. It is concluded that the developed sedimentation potential measurement successfully applied for determination of zeta potential of the TiO2 NPs suspension to evaluate the stability NPs suspension.

  10. Interacting He and Ar atoms: Revised theoretical interaction potential, dipole moment, and collision-induced absorption spectra.

    Science.gov (United States)

    Meyer, Wilfried; Frommhold, Lothar

    2015-09-21

    Coupled cluster quantum chemical calculations of the potential energy surface and the induced dipole surface are reported for the He-Ar van der Waals collisional complex. Spectroscopic parameters are derived from global analytical fits while an accurate value for the long-range dipole coefficient D7 is obtained by perturbation methods. Collision-induced absorption spectra are computed quantum mechanically and compared with existing measurements.

  11. NATO Advanced Research Workshop on Dynamics of Polyatomic Van der Waals Complexes

    CERN Document Server

    Janda, Kenneth

    1991-01-01

    This publication is the Proceedings of the NATO Advanced Research Workshop (ARW) on the Dynamics of Polyatomic Van der Waals Molecules held at the Chateau de Bonas, Castera-Verduzan, France, from August 21 through August 26, 1989. Van der Waals complexes provide important model problems for understanding energy transfer and dissipation. These processes can be described in great detail for Van der Waals complexes, and the insight gained from such studies can be applied to more complicated chemical problems that are not amenable to detailed study. The workshop concentrated on the current questions and future prospects for extend­ ing our highly detailed knowledge of triatomic Van der Waals molecule dynamics to polyatomic molecules and clusters (one molecule surrounded by several, or up to sev­ eral tens of, atoms). Both experimental and theoretical studies were discussed, with particular emphasis on the dynamical behavior of dissociation as observed in the dis­ tributions of quantum states of the dissociatio...

  12. {InSe}/{GaSe} heterointerfaces prepared by Van der Waals epitaxy

    Science.gov (United States)

    Lang, O.; Klein, A.; Schlaf, R.; Löher, T.; Pettenkofer, C.; Jaegermann, W.; Chevy, A.

    1995-01-01

    Epitaxial films of layered substrates can be prepared onto layered substrates even for large lattice mismatch, when the growth is attempted with the Van der Waals surfaces opposing each other (Van der Waals epitaxy). Thin epitaxial InSe(GaSe) films are prepared onto ultrahigh vacuum (UHV) cleaved GaSe(InSe) Van der Waals (0001) surfaces. The films and the heterointerface are characterized by photoelectron spectroscopy, electron diffraction and scanning tunneling microscopy (STM). High quality and stoichiometric films are obtained by direct InSe(GaSe) evaporation from a Knudsen cell at sample temperatures between 520 and 620 K. Despite a 6% lattice mismatch the deposited films are oriented with their c- and α-axis to the hexagonal substrate. The growth mostly follows the Frank-Van der Merwe mode. This rather ideal growth behaviour is related to the specific properties of the Van der Waals plane which contains no dangling bonds.

  13. Potential of optical spectral transmission measurements for joint inflammation measurements in rheumatoid arthritis patients

    Science.gov (United States)

    Meier, A. J. Louise; Rensen, Wouter H. J.; de Bokx, Pieter K.; de Nijs, Ron N. J.

    2012-08-01

    Frequent monitoring of rheumatoid arthritis (RA) patients enables timely treatment adjustments and improved outcomes. Currently this is not feasible due to a shortage of rheumatologists. An optical spectral transmission device is presented for objective assessment of joint inflammation in RA patients, while improving diagnostic accuracy and clinical workflow. A cross-sectional, nonrandomized observational study was performed with this device. In the study, 77 proximal interphalangeal (PIP) joints in 67 patients have been analyzed. Inflammation of these PIP joints was also assessed by a rheumatologist with a score varying from 1 (not inflamed) to 5 (severely inflamed). Out of 77 measurements, 27 were performed in moderate to strongly inflamed PIP joints. Comparison between the clinical assessment and an optical measurement showed a correlation coefficient r=0.63, p<0.001, 95% CI [0.47, 0.75], and a ROC curve (AUC=0.88) that shows a relative good specificity and sensitivity. Optical spectral transmission measurements in a single joint correlate with clinical assessment of joint inflammation, and therefore might be useful in monitoring joint inflammation in RA patients.

  14. Molecular interactions in particular Van der Waals nanoclusters

    Energy Technology Data Exchange (ETDEWEB)

    Jungclas, Hartmut; Schmidt, Lothar [Marburg Univ. (Germany). Chemistry Dept.; Komarov, Viacheslav V.; Popova, Anna M. [Marburg Univ. (Germany). Chemistry Dept.; Lomonosov Moscow State Univ. (Russian Federation). Skobeltzin Inst. of Nuclear Physics

    2017-04-01

    A method is presented to analyse the interaction energies in a nanocluster, which is consisting of three neutral molecules bound by non-covalent long range Van der Waals forces. One of the molecules (M{sub 0}) in the nanocluster has a permanent dipole moment, whereas the two other molecules (M{sub 1} and M{sub 2}) are non-polar. Analytical expressions are obtained for the numerical calculation of the dispersion and induction energies of the molecules in the considered nanocluster. The repulsive forces at short intermolecular distances are taken into account by introduction of damping functions. Dispersion and induction energies are calculated for a nanocluster with a definite geometry, in which the polar molecule M{sub 0} is a linear hydrocarbon molecule C{sub 5}H{sub 10} and M{sub 1} and M{sub 2} are pyrene molecules. The calculations are done for fixed distances between the two pyrene molecules. The results show that the induction energies in the considered three-molecular nanocluster are comparable with the dispersion energies. Furthermore, the sum of induction energies in the substructure (M{sub 0}, M{sub 1}) of the considered nanocluster is much higher than the sum of induction energies in a two-molecular nanocluster with similar molecules (M{sub 0}, M{sub 1}) because of the absence of an electrostatic field in the latter case. This effect can be explained by the essential intermolecular induction in the three-molecular nanocluster.

  15. Van der Waals torque induced by external magnetic fields

    CERN Document Server

    Esquivel-Sirvent, R; Palomono-Ovando, M

    2010-01-01

    We present a method for inducing and controlling van der Waals torques between two parallel slabs using a constant magnetic field. The torque is calculated using the Barash theory of dispersive torques. In III-IV semiconductors such as $InSb$, the effect of an external magnetic field is to induce an optical anisotropy, in an otherwise isotropic material, that will in turn induce a torque. The calculations of the torque are done in the Voigt configuration, with the magnetic field parallel to the surface of the slabs. As a case study we consider a slab made of calcite and a second slab made of $InSb$. In the absence of magnetic field there is no torque. As the magnetic field increases, the optical anisotropy of $InSb$ increases and the torque becomes different from zero, increasing with the magnetic field. The resulting torque is of the same order of magnitude as that calculated using permanent anisotropic materials when the magnetic fields is close to 1 T.

  16. Van der Waals torque induced by external magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Esquivel-Sirvent, R.; Cocoletzi, G. H.; Palomino-Ovando, M.

    2010-01-01

    We present a method for inducing and controlling van der Waals torques between two parallel slabs using a constant magnetic field. The torque is calculated using the Barash theory of dispersive torques. In III–IV semiconductors such as InSb, the effect of an external magnetic field is to induce an optical anisotropy, in an otherwise isotropic material, that will in turn induce a torque. The calculations of the torque are done in the Voigt configuration, with the magnetic field parallel to the surface of the slabs. As a case study we consider a slab made of calcite and a second slab made of InSb. In the absence of magnetic field there is no torque. As the magnetic field increases, the optical anisotropy of InSb increases and the torque becomes different from zero, increasing with the magnetic field. The resulting torque is of the same order of magnitude as that calculated using permanent anisotropicmaterials when the magnetic fields is close to 1 T.

  17. Spatially Correlated Disorder in Epitaxial van der Waals Heterostructures

    Science.gov (United States)

    Laanait, Nouamane; Zhang, Zhan; Schleputz, Christian; Liu, Ying; Wojcik, Michael; Myers-Ward, Rachael; Gaskill, D. Kurt; Fenter, Paul; Li, Lian

    The structural cohesion of van der Waals (vdW) heterostructures relies upon a cooperative balance between strong intra-layer bonded interactions and weak inter-layer coupling. The confinement of extended defects to within a single vdW layer and competing interactions introduced by epitaxial constraints could generate fundamentally new structural disorders. Here we report on the presence of spatially correlated and localized disorder states that coexist with the near perfect crystallographic order along the growth direction of epitaxial vdW heterostructure of Bi2Se3/graphene/SiC grown by molecular beam epitaxy. With the depth penetration of hard X-ray diffraction microscopy and high-resolution surface scattering, we imaged local structural configurations from the atomic to mesoscopic length scales, and found that these disorder states result as a confluence of atomic scale modulations in the strength of vdW layer-layer interactions and nanoscale boundary conditions imposed by the substrate. These findings reveal a vast landscape of novel disorder states that can be manifested in epitaxial vdW heterostructures. Supported by the Wigner Fellowship program at Oak Ridge Nat'l Lab.

  18. Thermionic Energy Conversion Based on Graphene van der Waals Heterostructures

    Science.gov (United States)

    Liang, Shi-Jun; Liu, Bo; Hu, Wei; Zhou, Kun; Ang, L. K.

    2017-01-01

    Seeking for thermoelectric (TE) materials with high figure of merit (or ZT), which can directly converts low-grade wasted heat (400 to 500 K) into electricity, has been a big challenge. Inspired by the concept of multilayer thermionic devices, we propose and design a solid-state thermionic devices (as a power generator or a refrigerator) in using van der Waals (vdW) heterostructure sandwiched between two graphene electrodes, to achieve high energy conversion efficiency in the temperature range of 400 to 500 K. The vdW heterostructure is composed of suitable multiple layers of transition metal dichalcogenides (TMDs), such as MoS2, MoSe2, WS2 and WSe2. From our calculations, WSe2 and MoSe2 are identified as two ideal TMDs (using the reported experimental material’s properties), which can harvest waste heat at 400 K with efficiencies about 7% to 8%. To our best knowledge, this design is the first in combining the advantages of graphene electrodes and TMDs to function as a thermionic-based device. PMID:28387363

  19. Consistent van der Waals radii for the whole main group.

    Science.gov (United States)

    Mantina, Manjeera; Chamberlin, Adam C; Valero, Rosendo; Cramer, Christopher J; Truhlar, Donald G

    2009-05-14

    Atomic radii are not precisely defined but are nevertheless widely used parameters in modeling and understanding molecular structure and interactions. The van der Waals radii determined by Bondi from molecular crystals and data for gases are the most widely used values, but Bondi recommended radius values for only 28 of the 44 main-group elements in the periodic table. In the present Article, we present atomic radii for the other 16; these new radii were determined in a way designed to be compatible with Bondi's scale. The method chosen is a set of two-parameter correlations of Bondi's radii with repulsive-wall distances calculated by relativistic coupled-cluster electronic structure calculations. The newly determined radii (in A) are Be, 1.53; B, 1.92; Al, 1.84; Ca, 2.31; Ge, 2.11; Rb, 3.03; Sr, 2.49; Sb, 2.06; Cs, 3.43; Ba, 2.68; Bi, 2.07; Po, 1.97; At, 2.02; Rn, 2.20; Fr, 3.48; and Ra, 2.83.

  20. El Legado de Johannes Diderik van der Waals y su Conferencia Nobel The Legacy of Johannes Diderik van der Waals and his Nobel Lecture

    Directory of Open Access Journals (Sweden)

    José O Valderrama

    2010-01-01

    Full Text Available El autor presenta la conferencia que dictó Johannes Diderik van der Waals cuando recibió el premio Nobel de física el año 1910. Este trabajo es una contribución a las celebraciones que se realizan alrededor del mundo para conmemorar los cien años desde que van der Waals recibiera el máximo galardón. La conferencia resume en forma simple pero detallada algunos de sus principales logros; en particular la ecuación de estado, el principio de estados correspondientes y la teoría de mezclas. Estas pioneras ideas de van der Waals han influenciado efectivamente varias áreas de la ciencia, pero en particular estos tres conceptos, y que fueron los que motivaron su merecido premio Nobel. Este artículo concluye que aún después de 100 años del Nobel y más de 125 de la Tesis doctoral, y a pesar de muchos otros extraordinarios logros en la física y en la termodinámica, los conceptos de van der Waals siguen más vigentes que nunca.The author presents the conference that van der Waals delivered when he received the Nobel Prize for Physics in 1910. This work is a contribution to the several commemorating activities that are be-ing organized around the world to celébrate the 100 years since van der Waals was awarded the máximum prize. The conference summarizes some of the main achievements and in particular the equation of state, the principie of corresponding states and the theory of mixtures. These pioneering ideas of van der Waals have influenced several áreas of physics and thermodynamics but in particular these three concepts, which motivated his merited Nobel Prize. The paper concludes that even after a hundred years since the Nobel and more than 125 years since the doctoral thesis, and despite of many other extraordinary advances in physics and thermodynamics, the concepts of van der Waals continué more valid than ever.

  1. Measurement of soil water potential over an extended range by polymer tensiometers: comparison with other instruments

    Science.gov (United States)

    van der Ploeg, M. J.; Gooren, H. P.; Hoogendam, R. C.; Bakker, G.; Huiskes, C.; Koopal, L. K.; Kruidhof, H.; de Rooij, G. H.

    2007-12-01

    In water scarce areas, plant growth and productivity can be severely hampered by irregular precipitation and overall water shortage. Root water uptake is mainly driven by matric potential gradients, but measurement of soil water matric potential is limited by the measurement range of water-filled tensiometers (-0.085 MPa). Other measurement techniques indirectly measure soil water potential by converting soil water content with the use of the water retention curve. In dry soils, the water content measurements may become insensitive to small variations, and consequently this conversion may lead to large errors. We developed a polymer tensiometer (POT) that is able to measure matric potentials down to -2.0 MPa. The POT consists of a solid ceramic, a stainless steel cup and a pressure transducer. The ceramic consist of a support layer and a membrane with 2 nm pore-size to prevent polymer leakage. Between the ceramic membrane and the pressure transducer a tiny chamber is located, which contains the polymer solution. The polymer's osmotic potential strongly reduces the total water potential inside the polymer tensiometer, which causes build-up of osmotic pressure. Hence, the water in the polymer tensiometer will cavitate at a much lower matric potential than the nearly pure water in a conventional tensiometer. Direct observation of the potential of soil water at different locations in the root-system will yield knowledge about the ability of a plant to take up the water under conditions of water shortage or salinity stress. With this knowledge it will be possible to adjust existing unsaturated flow models accounting for root water uptake. We tested 8 POTs in an experimental setup, where we compared matric potential measurements to TDR water content measurements, matric potentials derived from measured water contents, and matric potentials measured by water-filled tensiometers. The experimental setup consisted of two evaporation boxes, one filled with sand (97.6% sand, 1

  2. Van der Waals interactions and Photoelectric Effect in Noncommutative Quantum Mechanics

    Institute of Scientific and Technical Information of China (English)

    LI Kang; CHAMOUN Nidal

    2007-01-01

    We calculate the long-range Van der Waals force and the photoelectric cross section in a noncommutative setup. It is argued that non-commutativity effects could not be discerned for the Van der Waals interactions. The result for the photoelectric effect shows deviation from the usual commutative one, which in principle can be used to put bounds on the space-space non-commutativity parameter.

  3. van der Waals energy under strong atom-field coupling in doped carbon nanotubes

    OpenAIRE

    Bondarev, Igor; Lambin, Philippe

    2004-01-01

    Using a unified macroscopic QED formalism, we derive an integral equation for the van der Waals energy of a two-level atomic system near a carbon nanotube. The equation is valid for both strong and weak atom-vacuum-field coupling. By solving it numerically, we demonstrate the inapplicability of weak-coupling-based van der Waals interaction models in a close vicinity of the nanotube surface.

  4. van der Waals energy under strong atom field coupling in doped carbon nanotubes

    Science.gov (United States)

    Bondarev, I. V.; Lambin, Ph.

    2004-10-01

    Using a unified macroscopic QED formalism, we derive an integral equation for the van der Waals energy of a two-level atomic system near a carbon nanotube. The equation is valid for both strong and weak atom-vacuum-field coupling. By solving it numerically, we demonstrate the inapplicability of weak-coupling-based van der Waals interaction models in a close vicinity of the nanotube surface.

  5. Classical ab initio van der Waals interactions from many-body dispersion and multipole machine learning models trained in chemical space

    CERN Document Server

    Bereau, Tristan; von Lilienfeld, O Anatole

    2015-01-01

    Accurate predictions of van der Waals forces require faithful models of dispersion, permanent and induced multipole-moments, as well as penetration and repulsion. We introduce a universal combined physics- and data-driven model of dispersion and multipole-moment contributions, respectively. Atomic multipoles are estimated "on-the-fly" for any organic molecule in any conformation using a machine learning approach trained on quantum chemistry results for tens of thousands of atoms in varying chemical environments drawn from thousands of organic molecules. Globally neutral, cationic, and anionic molecular charge states can be treated with individual models. Dispersion interactions are included via recently-proposed classical many-body potentials. For nearly one thousand intermolecular dimers, this approximate van der Waals model is found to reach an accuracy similar to that of state-of-the-art force fields, while bypassing the need for parametrization. Estimates of cohesive energies for the benzene crystal confi...

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

    Science.gov (United States)

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

    2014-03-01

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

  7. Communication: THz absorption spectrum of the CO{sub 2}–H{sub 2}O complex: Observation and assignment of intermolecular van der Waals vibrations

    Energy Technology Data Exchange (ETDEWEB)

    Andersen, J.; Mahler, D. W.; Larsen, R. Wugt, E-mail: rewl@kemi.dtu.dk [Department of Chemistry, Technical University of Denmark, Kemitorvet 206, 2800 Kgs. Lyngby (Denmark); Heimdal, J.; Nelander, B. [MAX-IV Laboratory, Lund University, P. O. Box 118, 22100 Lund (Sweden)

    2014-03-07

    Terahertz absorption spectra have been recorded for the weakly bound CO{sub 2}–H{sub 2}O complex embedded in cryogenic neon matrices at 2.8 K. The three high-frequency van der Waals vibrational transitions associated with out-of-plane wagging, in-plane rocking, and torsional motion of the isotopic H{sub 2}O subunit have been assigned and provide crucial observables for benchmark theoretical descriptions of this systems’ flat intermolecular potential energy surface. A (semi)-empirical value for the zero-point energy of 273 ± 15 cm{sup −1} from the class of intermolecular van der Waals vibrations is proposed and the combination with high-level quantum chemical calculations provides a value of 726 ± 15 cm{sup −1} for the dissociation energy D{sub 0}.

  8. MISCIBILITY, SOLUBILITY, AND VISCOSITY MEASUREMENTS FOR R-236EA WITH POTENTIAL LUBRICANTS

    Science.gov (United States)

    The report gives results of miscibility, solubility, and viscosity measurements of refrigerant R-236ea with three potential lubricants. (NOTE: The data were needed to determine the suitability of refrigerant/lubricant combinations for use in refrigeration systems.) The lubricants...

  9. Density-functional calculation of van der Waals forces for free-electron-like surfaces

    DEFF Research Database (Denmark)

    Hult, E.; Hyldgaard, P.; Rossmeisl, Jan;

    2001-01-01

    A recently proposed general density functional for asymptotic van der Waals forces is used to calculate van der Waals coefficients and reference-plane positions for realistic low-indexed Al surfaces. Results are given for a number of atoms and molecules outside the surfaces, as well as for the in......A recently proposed general density functional for asymptotic van der Waals forces is used to calculate van der Waals coefficients and reference-plane positions for realistic low-indexed Al surfaces. Results are given for a number of atoms and molecules outside the surfaces, as well...... as for the interaction between the surfaces themselves. The densities and static image-plane positions that are needed as input in the van der Waals functional are calculated self-consistently within density-functional theory using the generalized-gradient approximation, pseudopotentials, and plane waves. This study...... shows that the van der Waals density functional is applicable to realistic surfaces. The need for physically correct surface models, especially for open surfaces, is also illustrated. Finally the parameters for the anisotropic interaction of O-2 with Al are calculated....

  10. Mean field propagation of infinite dimensional Wigner measures with a singular two-body interaction potential

    CERN Document Server

    Ammari, Zied

    2011-01-01

    We consider the quantum dynamics of many bosons systems in the mean field limit with a singular pair-interaction potential, including the attractive or repulsive Coulombic case in three dimensions. By using a measure transportation technique, we show that Wigner measures propagate along the nonlinear Hartree flow. Such property was previously proved only for bounded potentials in our previous works with a slightly different strategy.

  11. A Student-Constructed Galvanic Cell for the Measurement of Cell Potentials at Different Temperatures

    Science.gov (United States)

    Jakubowska, Anna

    2016-01-01

    A student-made galvanic cell is proposed for temperature measurements of cell potential. This cell can be easily constructed by students, the materials needed are readily available and nontoxic, and the solution applied is in an attractive color. For this cell, the potential values are excellently reproducible at each temperature, and the…

  12. Theoretical and experimental factors affecting measurements of semiconductor mean inner potentials

    Energy Technology Data Exchange (ETDEWEB)

    Pennington, R S; Kasama, T; Boothroyd, C B; Dunin-Borkowski, R E [Center for Electron Nanoscopy, Technical University of Denmark, DK-2800 Kongens Lyngby (Denmark); Mortensen, J J, E-mail: robert.pennington@cen.dtu.d [Center for Atomic-Scale Materials Design, Technical University of Denmark, DK-2800 Kongens Lyngby (Denmark)

    2010-02-01

    We use density functional theory to explore the effect on calculations of semiconductor mean inner potentials of the presence of reconstructions, changes in lattice spacing and adsorbates on the surfaces of parallel-sided thin specimens. We also use electron holography to illustrate several factors that affect experimental measurements of mean inner potentials of semiconductor nanowires.

  13. A Student-Constructed Galvanic Cell for the Measurement of Cell Potentials at Different Temperatures

    Science.gov (United States)

    Jakubowska, Anna

    2016-01-01

    A student-made galvanic cell is proposed for temperature measurements of cell potential. This cell can be easily constructed by students, the materials needed are readily available and nontoxic, and the solution applied is in an attractive color. For this cell, the potential values are excellently reproducible at each temperature, and the…

  14. A transient method for measuring the DC streaming potential coefficient of porous and fractured rocks

    Science.gov (United States)

    Walker, E.; Glover, P. W. J.; Ruel, J.

    2014-02-01

    High-quality streaming potential coupling coefficient measurements have been carried out using a newly designed cell with both a steady state methodology and a new pressure transient approach. The pressure transient approach has shown itself to be particularly good at providing high-quality streaming potential coefficient measurements as each transient increase or decrease allows thousands of measurements to be made at different pressures to which a good linear regression can be fitted. Nevertheless, the transient method can be up to 5 times as fast as the conventional measurement approaches because data from all flow rates are taken in the same transient measurement rather than separately. Test measurements have been made on samples of Berea and Boise sandstone as a function of salinity (approximately 18 salinities between 10-5 mol/dm3 and 2 mol/dm3). The data have also been inverted to obtain the zeta potential. The streaming potential coefficient becomes greater (more negative) for fluids with lower salinities, which is consistent with existing measurements. Our measurements are also consistent with the high-salinity streaming potential coefficient measurements made by Vinogradov et al. (2010). Both the streaming potential coefficient and the zeta potential have also been modeled using the theoretical approach of Glover (2012). This modeling allows the microstructural, electrochemical, and fluid properties of the saturated rock to be taken into account in order to provide a relationship that is unique to each particular rock sample. In all cases, we found that the experimental data were a good match to the theoretical model.

  15. Optimizing Protein-Protein van der Waals Interactions for the AMBER ff9x/ff12 Force Field.

    Science.gov (United States)

    Chapman, Dail E; Steck, Jonathan K; Nerenberg, Paul S

    2014-01-14

    The quality of molecular dynamics (MD) simulations relies heavily on the accuracy of the underlying force field. In recent years, considerable effort has been put into developing more accurate dihedral angle potentials for MD force fields, but relatively little work has focused on the nonbonded parameters, many of which are two decades old. In this work, we assess the accuracy of protein-protein van der Waals interactions in the AMBER ff9x/ff12 force field. Across a test set of 44 neat organic liquids containing the moieties present in proteins, we find root-mean-square (RMS) errors of 1.26 kcal/mol in enthalpy of vaporization and 0.36 g/cm(3) in liquid densities. We then optimize the van der Waals radii and well depths for all of the relevant atom types using these observables, which lowers the RMS errors in enthalpy of vaporization and liquid density of our validation set to 0.59 kcal/mol (53% reduction) and 0.019 g/cm(3) (46% reduction), respectively. Limitations in our parameter optimization were evident for certain atom types, however, and we discuss the implications of these observations for future force field development.

  16. Tuning electronic transport in epitaxial graphene-based van der Waals heterostructures

    Science.gov (United States)

    Lin, Yu-Chuan; Li, Jun; de La Barrera, Sergio C.; Eichfeld, Sarah M.; Nie, Yifan; Addou, Rafik; Mende, Patrick C.; Wallace, Robert M.; Cho, Kyeongjae; Feenstra, Randall M.; Robinson, Joshua A.

    2016-04-01

    Two-dimensional tungsten diselenide (WSe2) has been used as a component in atomically thin photovoltaic devices, field effect transistors, and tunneling diodes in tandem with graphene. In some applications it is necessary to achieve efficient charge transport across the interface of layered WSe2-graphene, a semiconductor to semimetal junction with a van der Waals (vdW) gap. In such cases, band alignment engineering is required to ensure a low-resistance, ohmic contact. In this work, we investigate the impact of graphene electronic properties on the transport at the WSe2-graphene interface. Electrical transport measurements reveal a lower resistance between WSe2 and fully hydrogenated epitaxial graphene (EGFH) compared to WSe2 grown on partially hydrogenated epitaxial graphene (EGPH). Using low-energy electron microscopy and reflectivity on these samples, we extract the work function difference between the WSe2 and graphene and employ a charge transfer model to determine the WSe2 carrier density in both cases. The results indicate that WSe2-EGFH displays ohmic behavior at small biases due to a large hole density in the WSe2, whereas WSe2-EGPH forms a Schottky barrier junction.Two-dimensional tungsten diselenide (WSe2) has been used as a component in atomically thin photovoltaic devices, field effect transistors, and tunneling diodes in tandem with graphene. In some applications it is necessary to achieve efficient charge transport across the interface of layered WSe2-graphene, a semiconductor to semimetal junction with a van der Waals (vdW) gap. In such cases, band alignment engineering is required to ensure a low-resistance, ohmic contact. In this work, we investigate the impact of graphene electronic properties on the transport at the WSe2-graphene interface. Electrical transport measurements reveal a lower resistance between WSe2 and fully hydrogenated epitaxial graphene (EGFH) compared to WSe2 grown on partially hydrogenated epitaxial graphene (EGPH). Using low

  17. Van der Waals Interactions and Dipole Blockade in a Cold Rydberg Gas Probed by Microwave Spectroscopy

    Science.gov (United States)

    Nguyen, Thanh Long; Celistrino Teixeira, Raul; Hermann Avigliano, Carla; Cantat Moltrecht, Tigrane; Raimond, Jean Michel; Haroche, Serge; Gleyzes, Sebastiens; Brune, Michel

    2016-05-01

    Dipole-dipole interactions between Rydberg atoms are a flourishing tool for quantum information processing and for quantum simulation of complex many-body problems. Microwave spectroscopy of a dense Rydberg gas trapped close to a superconducting atom chip in the strong dipole blockade regime reveals directly the many-body atomic interaction spectrum. We present here a direct measurement of the interaction energy distribution in the strong dipole blockade regime, based on microwave spectroscopy. We first apply this method to the observation of the excitation dynamics of the Rydberg gas, conditioned by dipole-dipole interactions, in either the strong blockade regime or the so-called facilitation regime. We also observe with this method the atomic cloud expansion driven by the repulsive Van der Waals interaction after excitation. This measurement, in good agreement with Monte Carlo simulations of the excitation process and of the cloud dynamics, reveals the limits of the frozen gas approximation. This method can help investigate self-organization and dynamical phase transitions in Rydberg-atom based quantum simulators. This study thus opens a promising route for quantum simulation of many-body systems and quantum information transport in chains of strongly interacting Rydberg atom.

  18. Selection of measures for a potential with two maxima at the zero temperature limit

    CERN Document Server

    Baraviera, Alexandre T; Lopes, Artur O

    2010-01-01

    For the subshift of finite type $\\S=\\{0,1,2\\}^{\\N}$ we study the convergence at temperature zero of the Gibbs measure associated to a non-locally constant H\\"older potential which admits only two maximizing measures. These measures are Dirac measures at two different fixed points. The potential is flattest at one of these two fixed points. The question we are interested is: which of these probabilities the invariant Gibbs state will select when temperature goes to zero? We prove that on the one hand the Gibbs measure converges, and at the other hand it does not necessarily converge to the measures where the potential is the flattest. We consider a family of potentials of the above form; for some of them there is the selection of a convex combination of the two Dirac measures, and for others there is a selection of the Dirac measure associated to the flattest point. In the first case this is contrary to what was expected if we consider the analogous problem in Aubry-Mather theory by N. Anantharaman, R. Iturria...

  19. Measuring very negative water potentials with polymer tensiometers: principles, performance and applications

    NARCIS (Netherlands)

    Rooij, de G.H.; Ploeg, van der M.J.; Gooren, H.P.A.; Bakker, G.; Hoogendam, C.W.; Huiskens, C.; Kruidhof, H.; Koopal, L.K.

    2009-01-01

    In recent years, a polymer tensiometer (POT) was developed and tested to directly measure matric potentials in dry soils. By extending the measurement range to wilting point (a 20-fold increase compared to conventional, water-filled tensiometers), a myriad of previously unapproachable research quest

  20. Measurement of water potential in low-level waste management. [Shallow Land Burial

    Energy Technology Data Exchange (ETDEWEB)

    Jones, T. L.; Gee, G. W.; Kirkham, R. R.; Gibson, D. D.

    1982-08-01

    The measurement of soil water is important to the shallow land burial of low-level waste. Soil water flow is the principle mechanism of radionuclide transport, allows the establishment of stabilizing vegetation and also governs the dissolution and release rates of the waste. This report focuses on the measurement of soil water potential and provides an evaluation of several field instruments that are available for use to monitor waste burial sites located in arid region soils. The theoretical concept of water potential is introduced and its relationship to water content and soil water flow is discussed. Next, four major areas of soils research are presented in terms of their dependence on the water potential concept. There are four basic types of sensors used to measure soil water potential. These are: (1) tensiometers; (2) soil psychrometers; (3) electrical resistance blocks; and (4) heat dissipation probes. Tensiometers are designed to measure the soil water potential directly by measuring the soil water pressure. Monitoring efforts at burial sites require measurements of soil water over long time periods. They also require measurements at key locations such as waste-soil interfaces and within any barrier system installed. Electrical resistance blocks are well suited for these types of measurements. The measurement of soil water potential can be a difficult task. There are several sensors commercially available; however, each has its own limitations. It is important to carefully select the appropriate sensor for the job. The accuracy, range, calibration, and stability of the sensor must be carefully considered. This study suggests that for waste management activities, the choice of sensor will be the tensiometer for precise soil characterization studies and the electrical resistance block for long term monitoring programs. (DMC)

  1. Optical tweezers as a new biomedical tool to measure zeta potential of stored red blood cells.

    Directory of Open Access Journals (Sweden)

    Diego C N Silva

    Full Text Available During storage, red blood cells (RBCs for transfusion purposes suffer progressive deterioration. Sialylated glycoproteins of the RBC membrane are responsible for a negatively charged surface which creates a repulsive electrical zeta potential. These charges help prevent the interaction between RBCs and other cells, and especially among each RBCs. Reports in the literature have stated that RBCs sialylated glycoproteins can be sensitive to enzymes released by leukocyte degranulation. Thus, the aim of this study was, by using an optical tweezers as a biomedical tool, to measure the zeta potential in standard RBCs units and in leukocyte reduced RBC units (collected in CPD-SAGM during storage. Optical tweezers is a sensitive tool that uses light for measuring cell biophysical properties which are important for clinical and research purposes. This is the first study to analyze RBCs membrane charges during storage. In addition, we herein also measured the elasticity of RBCs also collected in CPD-SAGM. In conclusion, the zeta potential decreased 42% and cells were 134% less deformable at the end of storage. The zeta potential from leukodepleted units had a similar profile when compared to units stored without leukoreduction, indicating that leukocyte lyses were not responsible for the zeta potential decay. Flow cytometry measurements of reactive oxygen species suggested that this decay is due to membrane oxidative damages. These results show that measurements of zeta potentials provide new insights about RBCs storage lesion for transfusion purposes.

  2. Seasonal variation of redox species and redox potentials in shallow groundwater: A comparison of measured and calculated redox potentials

    Science.gov (United States)

    Ramesh Kumar, A.; Riyazuddin, P.

    2012-06-01

    SummaryThe seasonal variation of redox potential (Eh) and redox species such as As(V)/As(III), Cr(VI)/Cr(III), Fe(III)/Fe(II), NO3-/NO2-, and Se(VI)/Se(IV) were studied in a shallow groundwater for a period of three years (May, 2004-January, 2007). The study area was Chrompet area of Chennai city, India. Groundwater samples from 65 wells were monitored for pH, electrical conductivity, dissolved oxygen (DO), and major ions during pre-(May) and post-monsoon (January) seasons. The objective of the study was to gain insight into the temporal variation of the redox species due to groundwater recharge and to identify the redox reactions controlling the measured Eh of the groundwater. The study revealed that the shallow groundwater was "oxic" with DO ranging between 0.25 and 5.00 mg L-1, and between 0.38 and 5.05 mg L-1 during pre-(May, 2004) and post-monsoon (January, 2005) seasons, respectively. The measured Eh (with respect to standard hydrogen electrode, SHE) ranged between 65 and 322 mV, and between 110 and 330 mV during pre- and post-monsoon seasons, respectively. During post-monsoon seasons, DO and Eh increased in most of the wells due to groundwater recharge. The calculated Eh using the redox couples As(V)/As(III), NO3-/NO2-, O2/H2O and Se(VI)/Se(IV) neither agreed among themselves nor with the measured Eh during all the seasons. It shows that in the shallow groundwater, the various redox couples are in disequilibrium among themselves and with the Pt electrode. However, 41% (n = 122) of the Eh values calculated from Fe(III)/Fe(II) couple agreed with the measured Eh within ±30 mV, the uncertainty of Pt-electrode measurement. The post-monsoon seasons showed higher values of As(V)/As(III) and Se(VI)/Se(IV) compared to the pre-monsoon seasons, whereas Fe(III)/Fe(II) behaved in the opposite manner. This pattern of variation is consistent with the increased oxidizing nature, as shown by the higher DO and Eh values observed during post-monsoon seasons. The results

  3. Accurate potential drop sheet resistance measurements of laser-doped areas in semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Heinrich, Martin, E-mail: mh.seris@gmail.com [Solar Energy Research Institute of Singapore, National University of Singapore, Singapore 117574 (Singapore); NUS Graduate School for Integrative Science and Engineering, National University of Singapore, Singapore 117456 (Singapore); Kluska, Sven; Binder, Sebastian [Fraunhofer Institute for Solar Energy Systems (ISE), Heidenhofstrasse 2, D-79110 Freiburg (Germany); Hameiri, Ziv [The School of Photovoltaic and Renewable Energy Engineering, The University of New South Wales, Sydney NSW 2052 (Australia); Hoex, Bram [Solar Energy Research Institute of Singapore, National University of Singapore, Singapore 117574 (Singapore); Aberle, Armin G. [Solar Energy Research Institute of Singapore, National University of Singapore, Singapore 117574 (Singapore); NUS Graduate School for Integrative Science and Engineering, National University of Singapore, Singapore 117456 (Singapore); Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117456 (Singapore)

    2014-10-07

    It is investigated how potential drop sheet resistance measurements of areas formed by laser-assisted doping in crystalline Si wafers are affected by typically occurring experimental factors like sample size, inhomogeneities, surface roughness, or coatings. Measurements are obtained with a collinear four point probe setup and a modified transfer length measurement setup to measure sheet resistances of laser-doped lines. Inhomogeneities in doping depth are observed from scanning electron microscope images and electron beam induced current measurements. It is observed that influences from sample size, inhomogeneities, surface roughness, and coatings can be neglected if certain preconditions are met. Guidelines are given on how to obtain accurate potential drop sheet resistance measurements on laser-doped regions.

  4. Exact results for Casimir interactions between dielectric bodies: The weak-coupling or van der Waals Limit

    CERN Document Server

    Milton, Kimball A; Wagner, Jef

    2008-01-01

    In earlier papers we have applied multiple scattering techniques to calculate Casimir forces due to scalar fields between different bodies described by delta function potentials. When the coupling to the potentials became weak, closed-form results were obtained. We simplify this weak-coupling technique and apply it to the case of tenuous dielectric bodies, in which case the method involves the summation of van der Waals (Casimir-Polder) interactions. Once again exact results for finite bodies can be obtained. We present closed formulas describing the interaction between spheres and between cylinders, and between an infinite plate and a retangular slab of finite size. For such a slab, we consider the torque acting on it, and find non-trivial equilibrium points can occur.

  5. Van der Waals metal-semiconductor junction: Weak Fermi level pinning enables effective tuning of Schottky barrier.

    Science.gov (United States)

    Liu, Yuanyue; Stradins, Paul; Wei, Su-Huai

    2016-04-01

    Two-dimensional (2D) semiconductors have shown great potential for electronic and optoelectronic applications. However, their development is limited by a large Schottky barrier (SB) at the metal-semiconductor junction (MSJ), which is difficult to tune by using conventional metals because of the effect of strong Fermi level pinning (FLP). We show that this problem can be overcome by using 2D metals, which are bounded with 2D semiconductors through van der Waals (vdW) interactions. This success relies on a weak FLP at the vdW MSJ, which is attributed to the suppression of metal-induced gap states. Consequently, the SB becomes tunable and can vanish with proper 2D metals (for example, H-NbS2). This work not only offers new insights into the fundamental properties of heterojunctions but also uncovers the great potential of 2D metals for device applications.

  6. Van der Waals Interactions in Pyridine and Pyridine-like Molecular Crystals: An ab initio Molecular Dynamics Study

    Science.gov (United States)

    Ko, Hsin-Yu; Distasio, Robert A., Jr.; Santra, Biswajit; Car, Roberto

    2014-03-01

    Pyridine has recently been investigated as a potentially effective material for use in artificial light harvesting.In this work, we propose the use of ab initio molecular dynamics (AIMD) to gain valuable physical insight into the artificial photosynthetic processes occurring in condensed-phase pyridine, the study of which has been limited to semi-empirical force fields to date.For this purpose, we introduce an accurate and efficient AIMD method, based on density functional theory (DFT) and a self-consistent pairwise description of van der Waals (vdW) interactions, for use in finite temperature and pressure (NPT) simulations on pyridine and several pyridine-like molecular crystals (PLMCs). Utilizing this approach, we demonstrate that vdW forces play a crucial role in the theoretical prediction of the structure and density of pyridine and PLMCs, and therefore must be accounted for in studies of these potential alternative energy materials. DOE: DE-SC0008626, NSF: DMS-1065894.

  7. Vertical electron transport in van der Waals heterostructures with graphene layers

    Energy Technology Data Exchange (ETDEWEB)

    Ryzhii, V., E-mail: v-ryzhii@riec.tohoku.ac.jp [Research Institute for Electrical Communication, Tohoku University, Sendai 980-8577 (Japan); Center for Photonics and Infrared Engineering, Bauman Moscow State Technical University and Institute of Ultra High Frequency Semiconductor Electronics of RAS, Moscow 111005 (Russian Federation); Otsuji, T. [Research Institute for Electrical Communication, Tohoku University, Sendai 980-8577 (Japan); Ryzhii, M. [Department of Computer Science and Engineering, University of Aizu, Aizu-Wakamatsu 965-8580 (Japan); Aleshkin, V. Ya.; Dubinov, A. A. [Institute for Physics of Microstructures of RAS and Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod 603950 (Russian Federation); Mitin, V. [Research Institute for Electrical Communication, Tohoku University, Sendai 980-8577 (Japan); Department of Electrical Engineering, University at Buffalo, Buffalo, New York 1460-1920 (United States); Shur, M. S. [Department of Electrical, Electronics, and Systems Engineering and Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States)

    2015-04-21

    We propose and analyze an analytical model for the self-consistent description of the vertical electron transport in van der Waals graphene-layer (GL) heterostructures with the GLs separated by the barriers layers. The top and bottom GLs serve as the structure emitter and collector. The vertical electron transport in such structures is associated with the propagation of the electrons thermionically emitted from GLs above the inter-GL barriers. The model under consideration describes the processes of the electron thermionic emission from and the electron capture to GLs. It accounts for the nonuniformity of the self-consistent electric field governed by the Poisson equation which accounts for the variation of the electron population in GLs. The model takes also under consideration the cooling of electrons in the emitter layer due to the Peltier effect. We find the spatial distributions of the electric field and potential with the high-electric-field domain near the emitter GL in the GL heterostructures with different numbers of GLs. Using the obtained spatial distributions of the electric field, we calculate the current-voltage characteristics. We demonstrate that the Peltier cooling of the two-dimensional electron gas in the emitter GL can strongly affect the current-voltage characteristics resulting in their saturation. The obtained results can be important for the optimization of the hot-electron bolometric terahertz detectors and different devices based on GL heterostructures.

  8. van der Waals Interactions in Hadron Resonance Gas: From Nuclear Matter to Lattice QCD.

    Science.gov (United States)

    Vovchenko, Volodymyr; Gorenstein, Mark I; Stoecker, Horst

    2017-05-05

    An extension of the ideal hadron resonance gas (HRG) model is constructed which includes the attractive and repulsive van der Waals (VDW) interactions between baryons. This VDW-HRG model yields the nuclear liquid-gas transition at low temperatures and high baryon densities. The VDW parameters a and b are fixed by the ground state properties of nuclear matter, and the temperature dependence of various thermodynamic observables at zero chemical potential are calculated within the VDW-HRG model. Compared to the ideal HRG model, the inclusion of VDW interactions between baryons leads to a qualitatively different behavior of second and higher moments of fluctuations of conserved charges, in particular in the so-called crossover region T∼140-190  MeV. For many observables this behavior resembles closely the results obtained from lattice QCD simulations. This hadronic model also predicts nontrivial behavior of net-baryon fluctuations in the region of phase diagram probed by heavy-ion collision experiments. These results imply that VDW interactions play a crucial role in the thermodynamics of hadron gas. Thus, the commonly performed comparisons of the ideal HRG model with the lattice and heavy-ion data may lead to misconceptions and misleading conclusions.

  9. Van der Waals-like behaviour of charged black holes and hysteresis in the dual QFTs

    Directory of Open Access Journals (Sweden)

    Mariano Cadoni

    2017-05-01

    Full Text Available Using the rules of the AdS/CFT correspondence, we compute the spherical analogue of the shear viscosity, defined in terms of the retarded Green function for the stress-energy tensor for QFTs dual to five-dimensional charged black holes of general relativity with a negative cosmological constant. We show that the ratio between this quantity and the entropy density, η˜/s, exhibits a temperature-dependent hysteresis. We argue that this hysteretic behaviour can be explained by the Van der Waals-like character of charged black holes, considered as thermodynamical systems. Under the critical charge, hysteresis emerges owing to the presence of two stable states (small and large black holes connected by a meta-stable region (intermediate black holes. A potential barrier prevents the equilibrium path between the two stable states; the system evolution must occur through the meta-stable region, and a path-dependence of η˜/s is generated.

  10. Esaki Diodes in van der Waals Heterojunctions with Broken-Gap Energy Band Alignment.

    Science.gov (United States)

    Yan, Rusen; Fathipour, Sara; Han, Yimo; Song, Bo; Xiao, Shudong; Li, Mingda; Ma, Nan; Protasenko, Vladimir; Muller, David A; Jena, Debdeep; Xing, Huili Grace

    2015-09-09

    van der Waals (vdW) heterojunctions composed of two-dimensional (2D) layered materials are emerging as a solid-state materials family that exhibits novel physics phenomena that can power a range of electronic and photonic applications. Here, we present the first demonstration of an important building block in vdW solids: room temperature Esaki tunnel diodes. The Esaki diodes were realized in vdW heterostructures made of black phosphorus (BP) and tin diselenide (SnSe2), two layered semiconductors that possess a broken-gap energy band offset. The presence of a thin insulating barrier between BP and SnSe2 enabled the observation of a prominent negative differential resistance (NDR) region in the forward-bias current-voltage characteristics, with a peak to valley ratio of 1.8 at 300 K and 2.8 at 80 K. A weak temperature dependence of the NDR indicates electron tunneling being the dominant transport mechanism, and a theoretical model shows excellent agreement with the experimental results. Furthermore, the broken-gap band alignment is confirmed by the junction photoresponse, and the phosphorus double planes in a single layer of BP are resolved in transmission electron microscopy (TEM) for the first time. Our results represent a significant advance in the fundamental understanding of vdW heterojunctions and broaden the potential applications of 2D layered materials.

  11. Flexible Multiferroic Bulk Heterojunction with Giant Magnetoelectric Coupling via van der Waals Epitaxy.

    Science.gov (United States)

    Amrillah, Tahta; Bitla, Yugandhar; Shin, Kwangwoo; Yang, Tiannan; Hsieh, Ying-Hui; Chiou, Yu-You; Liu, Heng-Jui; Do, Thi Hien; Su, Dong; Chen, Yi-Chun; Jen, Shien-Uang; Chen, Long-Qing; Kim, Kee Hoon; Juang, Jenh-Yih; Chu, Ying-Hao

    2017-06-27

    Magnetoelectric nanocomposites have been a topic of intense research due to their profound potential in the applications of electronic devices based on spintronic technology. Nevertheless, in spite of significant progress made in the growth of high-quality nanocomposite thin films, the substrate clamping effect still remains a major hurdle in realizing the ultimate magnetoelectric coupling. To overcome this obstacle, an alternative strategy of fabricating a self-assembled ferroelectric-ferrimagnetic bulk heterojunction on a flexible muscovite via van der Waals epitaxy is adopted. In this study, we investigated the magnetoelectric coupling in a self-assembled BiFeO3 (BFO)-CoFe2O4 (CFO) bulk heterojunction epitaxially grown on a flexible muscovite substrate. The obtained heterojunction is composed of vertically aligned multiferroic BFO nanopillars embedded in a ferrimagnetic CFO matrix. Moreover, due to the weak interaction between the flexible substrate and bulk heterojunction, the interface is incoherent and, hence, the substrate clamping effect is greatly reduced. The phase-field simulation model also complements our results. The magnetic and electrical characterizations highlight the improvement in magnetoelectric coupling of the BFO-CFO bulk heterojunction. A magnetoelectric coupling coefficient of 74 mV/cm·Oe of this bulk heterojunction is larger than the magnetoelectric coefficient reported earlier on flexible substrates. Therefore, this study delivers a viable route of fabricating a remarkable magnetoelectric heterojunction and yet flexible electronic devices that are robust against extreme conditions with optimized performance.

  12. Optoelectronic Properties of Van Der Waals Hybrid Structures: Fullerenes on Graphene Nanoribbons

    Science.gov (United States)

    Correa, Julián David; Orellana, Pedro Alejandro; Pacheco, Mónica

    2017-01-01

    The search for new optical materials capable of absorbing light in the frequency range from visible to near infrared is of great importance for applications in optoelectronic devices. In this paper, we report a theoretical study of the electronic and optical properties of hybrid structures composed of fullerenes adsorbed on graphene and on graphene nanoribbons. The calculations are performed in the framework of the density functional theory including the van der Waals dispersive interactions. We found that the adsorption of the C60 fullerenes on a graphene layer does not modify its low energy states, but it has strong consequences for its optical spectrum, introducing new absorption peaks in the visible energy region. The optical absorption of fullerenes and graphene nanoribbon composites shows a strong dependence on photon polarization and geometrical characteristics of the hybrid systems, covering a broad range of energies. We show that an external electric field across the nanoribbon edges can be used to tune different optical transitions coming from nanoribbon–fullerene hybridized states, which yields a very rich electro-absorption spectrum for longitudinally polarized photons. We have carried out a qualitative analysis on the potential of these hybrids as possible donor-acceptor systems in photovoltaic cells. PMID:28336904

  13. Evaluating dispersion forces for optimization of van der Waals complexes using a non-empirical functional.

    Science.gov (United States)

    Arabi, Alya A

    2016-11-13

    Modelling dispersion interactions with traditional density functional theory (DFT) is a challenge that has been extensively addressed in the past decade. The exchange-dipole moment (XDM), among others, is a non-empirical add-on dispersion correction model in DFT. The functional PW86+PBE+XDM for exchange, correlation and dispersion, respectively, compromises an accurate functional for thermochemistry and for van der Waals (vdW) complexes at equilibrium and non-equilibrium geometries. To use this functional in optimizing vdW complexes, rather than computing single point energies, it is necessary to evaluate accurate forces. The purpose of this paper is to validate that, along the potential energy surface, the distance at which the energy is minimum is commensurate with the distance at which the forces vanish to zero. This test was validated for 10 rare gas diatomic molecules using various integration grids and different convergence criteria. It was found that the use of either convergence criterion, 10(-6) or 10(-8), in Gaussian09, does not affect the accuracy of computed optimal distances and binding energies. An ultra-fine grid needs to be used when computing accurate energies using generalized gradient approximation functionals.This article is part of the themed issue 'Multiscale modelling at the physics-chemistry-biology interface'. © 2016 The Author(s).

  14. How van der Waals interactions determine the unique properties of water

    CERN Document Server

    Morawietz, Tobias; Dellago, Christoph; Behler, Jörg

    2016-01-01

    While the interactions between water molecules are dominated by strongly directional hydrogen bonds (HBs), it was recently proposed that relatively weak, isotropic van der Waals (vdW) forces are essential for understanding the properties of liquid water and ice. This insight was derived from ab initio computer simulations, which provide an unbiased description of water at the atomic level and yield information on the underlying molecular forces. However, the high computational cost of such simulations prevents the systematic investigation of the influence of vdW forces on the thermodynamic anomalies of water. Here we develop efficient ab initio-quality neural network potentials and use them to demonstrate that vdW interactions are crucial for the formation of water's density maximum and its negative volume of melting. Both phenomena can be explained by the flexibility of the HB network, which is the result of a delicate balance of weak vdW forces, causing e.g. a pronounced contraction of the second solvation ...

  15. Evaluating dispersion forces for optimization of van der Waals complexes using a non-empirical functional

    Science.gov (United States)

    Arabi, Alya A.

    2016-11-01

    Modelling dispersion interactions with traditional density functional theory (DFT) is a challenge that has been extensively addressed in the past decade. The exchange-dipole moment (XDM), among others, is a non-empirical add-on dispersion correction model in DFT. The functional PW86+PBE+XDM for exchange, correlation and dispersion, respectively, compromises an accurate functional for thermochemistry and for van der Waals (vdW) complexes at equilibrium and non-equilibrium geometries. To use this functional in optimizing vdW complexes, rather than computing single point energies, it is necessary to evaluate accurate forces. The purpose of this paper is to validate that, along the potential energy surface, the distance at which the energy is minimum is commensurate with the distance at which the forces vanish to zero. This test was validated for 10 rare gas diatomic molecules using various integration grids and different convergence criteria. It was found that the use of either convergence criterion, 10-6 or 10-8, in Gaussian09, does not affect the accuracy of computed optimal distances and binding energies. An ultra-fine grid needs to be used when computing accurate energies using generalized gradient approximation functionals. This article is part of the themed issue 'Multiscale modelling at the physics-chemistry-biology interface'.

  16. Van der Waals interactions in hadron resonance gas: From nuclear matter to lattice QCD

    CERN Document Server

    Vovchenko, Volodymyr; Stoecker, Horst

    2016-01-01

    An extension of the ideal non-interacting hadron resonance gas (HRG) model is constructed which includes the attractive and repulsive van der Waals (VDW) interactions between baryons. This VDW-HRG model yields the nuclear liquid-gas transition at low temperatures and high baryon densities. The VDW parameters $a$ and $b$ are fixed by the ground state properties of nuclear matter, and the temperature dependence of various thermodynamic observables at zero chemical potential are calculated within VDW-HRG model. Compared to the ideal non-interacting HRG, the inclusion of VDW interactions between baryons leads to a qualitatively different behavior of 2nd and higher moments of fluctuations of conserved charges, in particular in the so-called crossover region $T \\sim 140 \\div 190$ MeV. For many observables this behavior resembles closely the results obtained from lattice QCD simulations. These results imply that VDW interactions play a crucial role in thermodynamics of hadron gas. Thus, the commonly performed compar...

  17. Density functional approximation for van der Waals fluids: based on hard sphere density functional approximation

    Institute of Scientific and Technical Information of China (English)

    Zhou Shi-Qi

    2007-01-01

    A universal theoretical approach is proposed which enables all hard sphere density functional approximations(DFAs) applicable to van der Waals fluids. The resultant DFA obtained by combining the universal theoretical approach with any hard sphere DFAs only needs as input a second-order direct correlation function (DCF) of a coexistence bulk fluid, and is applicable in both supercritical and subcritical temperature regions. The associated effective hard sphere density can be specified by a hard wall sum rule. It is indicated that the value of the effective hard sphere density so determined can be universal, i.e. can be applied to any external potentials different from the single hard wall. As an illustrating example, the universal theoretical approach is combined with a hard sphere bridge DFA to predict the density profile of a hard core attractive Yukawa model fluid influenced by diverse external fields; agreement between the present formalism's predictions and the corresponding simulation data is good or at least comparable to several previous DFT approaches. The primary advantage of the present theoretical approach combined with other hard sphere DFAs is discussed.

  18. Unusually efficient photocurrent extraction in monolayer van der Waals heterostructure by tunnelling through discretized barriers

    Science.gov (United States)

    Yu, Woo Jong; Vu, Quoc An; Oh, Hyemin; Nam, Hong Gi; Zhou, Hailong; Cha, Soonyoung; Kim, Joo-Youn; Carvalho, Alexandra; Jeong, Munseok; Choi, Hyunyong; Castro Neto, A. H.; Lee, Young Hee; Duan, Xiangfeng

    2016-11-01

    Two-dimensional layered transition-metal dichalcogenides have attracted considerable interest for their unique layer-number-dependent properties. In particular, vertical integration of these two-dimensional crystals to form van der Waals heterostructures can open up a new dimension for the design of functional electronic and optoelectronic devices. Here we report the layer-number-dependent photocurrent generation in graphene/MoS2/graphene heterostructures by creating a device with two distinct regions containing one-layer and seven-layer MoS2 to exclude other extrinsic factors. Photoresponse studies reveal that photoresponsivity in one-layer MoS2 is surprisingly higher than that in seven-layer MoS2 by seven times. Spectral-dependent studies further show that the internal quantum efficiency in one-layer MoS2 can reach a maximum of 65%, far higher than the 7% in seven-layer MoS2. Our theoretical modelling shows that asymmetric potential barriers in the top and bottom interfaces of the graphene/one-layer MoS2/graphene heterojunction enable asymmetric carrier tunnelling, to generate usually high photoresponsivity in one-layer MoS2 device.

  19. van der Waals Interactions in Hadron Resonance Gas: From Nuclear Matter to Lattice QCD

    Science.gov (United States)

    Vovchenko, Volodymyr; Gorenstein, Mark I.; Stoecker, Horst

    2017-05-01

    An extension of the ideal hadron resonance gas (HRG) model is constructed which includes the attractive and repulsive van der Waals (VDW) interactions between baryons. This VDW-HRG model yields the nuclear liquid-gas transition at low temperatures and high baryon densities. The VDW parameters a and b are fixed by the ground state properties of nuclear matter, and the temperature dependence of various thermodynamic observables at zero chemical potential are calculated within the VDW-HRG model. Compared to the ideal HRG model, the inclusion of VDW interactions between baryons leads to a qualitatively different behavior of second and higher moments of fluctuations of conserved charges, in particular in the so-called crossover region T ˜140 - 190 MeV . For many observables this behavior resembles closely the results obtained from lattice QCD simulations. This hadronic model also predicts nontrivial behavior of net-baryon fluctuations in the region of phase diagram probed by heavy-ion collision experiments. These results imply that VDW interactions play a crucial role in the thermodynamics of hadron gas. Thus, the commonly performed comparisons of the ideal HRG model with the lattice and heavy-ion data may lead to misconceptions and misleading conclusions.

  20. Analytical modeling of static behavior of electrostatically actuated nano/micromirrors considering van der Waals forces

    Institute of Scientific and Technical Information of China (English)

    Hamid Moeenfard; Mohammad Taghi Ahmadian

    2012-01-01

    In this paper,the effect of van der Waals (vdW)force on the pull-in behavior of electrostatically actuated nano/micromirrors is investigated.First,the minimum potential energy principle is utilized to find the equation governing the static behavior of nano/microminror under electrostatic and vdW forces.Then,the stability of static equilibrium points is analyzed using the energy method.It is found that when there exist two equilibrium points,the smaller one is stable and the larger one is unstable.The effects of different design parameters on the mirror's pull-in angle and pull-in voltage are studied and it is found that vdW force can considerably reduce the stability limit of the mirror.At the end,the nonlinear equilibrium equation is solved numerically and analytically using homotopy perturbation method (HPM).It is observed that a sixth order perturbation approximation can precisely model the mirror's behavior.The resuits of this paper can be used for stable operation design and safe fabrication of torsional nano/micro actuators.

  1. Summary of 2006 to 2010 FPMU Measurements of International Space Station Frame Potential Variations

    Science.gov (United States)

    Minow, Joseph I.; Wright, Kenneth H., Jr.; Chandler, Michael O.; Coffey, Victoria N.; Craven, Paul D.; Schneider, Todd A.; Parker, Linda N.; Ferguson, Dale C.; Koontz, Steve L.; Alred, John W.

    2010-01-01

    Electric potential variations on the International Space Station (ISS) structure in low Earth orbit are dominated by contributions from interactions of the United States (US) 160 volt solar arrays with the relatively high density, low temperature plasma environment and inductive potentials generated by motion of the large vehicle across the Earth?s magnetic field. The Floating Potential Measurement Unit (FPMU) instrument suite comprising two Langmuir probes, a plasma impedance probe, and a floating potential probe was deployed in August 2006 for use in characterizing variations in ISS potential, the state of the ionosphere along the ISS orbit and its effect on ISS charging, evaluating effects of payloads and visiting vehicles, and for supporting ISS plasma hazard assessments. This presentation summarizes observations of ISS frame potential variations obtained from the FPMU from deployment in 2006 through the current time. We first describe ISS potential variations due to current collection by solar arrays in the day time sector of the orbit including eclipse exit and entry charging events, potential variations due to plasma environment variations in the equatorial anomaly, and visiting vehicles docked to the ISS structure. Next, we discuss potential variations due to inductive electric fields generated by motion of the vehicle across the geomagnetic field and the effects of external electric fields in the ionosphere. Examples of night time potential variations at high latitudes and their possible relationship to auroral charging are described and, finally, we demonstrate effects on the ISS potential due to European Space Agency and US plasma contactor devices.

  2. Coincidence Lattices and Interlayer Twist in van der Waals Heterostructures: Application of the Coincidence Lattice Method on \\hbox {hBN/MoSe}_2 Heterobilayer Systems

    Science.gov (United States)

    Koda, Daniel S.; Bechstedt, Friedhelm; Marques, Marcelo; Teles, Lara K.

    2017-07-01

    Van der Waals heterostructures have great potential in large-scale integration devices and exploration of new physics. Experimental investigations allow flexible combinations of two-dimensional crystals in device fabrications. Theory, however, has limitations of supercell sizes and commensurability, translated into computational effort. In this work, we demonstrate the application of the coincidence lattice method to simulate two \\hbox {hBN/MoSe}_2 heterobilayers taking interlayer twist effects into account. We predict that both systems are stable upon contact and interact via van der Waals dispersions. We found that electronic properties of \\hbox {MoSe}_2 are preserved for both simulated systems, but hBN suffers from the increase of interface interactions, as evidenced by band structures and density of states calculations. Finally, band discontinuities are obtained and charge transfer arguments explain small shifts in band offsets with respect to natural alignments. We conclude that hBN is a reasonable substrate for preserving useful properties of \\hbox {MoSe}_2 for application in electronic and optoelectronic devices, and that interlayer twist angles play a significant role in the physics of van der Waals heterostructures.

  3. Rocket-borne measurements of electron temperature and density with the Electron Retarding Potential Analyzer instrument

    Science.gov (United States)

    Cohen, I. J.; Widholm, M.; Lessard, M. R.; Riley, P.; Heavisides, J.; Moen, J. I.; Clausen, L. B. N.; Bekkeng, T. A.

    2016-07-01

    Determining electron temperature in the ionosphere is a fundamentally important measurement for space science. Obtaining measurements of electron temperatures at high altitudes (>700 km) is difficult because of limitations on ground-based radar and classic spacecraft instrumentation. In light of these limitations, the rocket-borne Electron Retarding Potential Analyzer (ERPA) was developed to allow for accurate in situ measurement of ionospheric electron temperature with a simple and low-resource instrument. The compact ERPA, a traditional retarding potential analyzer with multiple baffle collimators, allows for a straightforward calculation of electron temperature. Since its first mission in 2004, it has amassed significant flight heritage and obtained data used in multiple studies investigating a myriad of phenomena related to magnetosphere-ionosphere coupling. In addition to highlighting the scientific contributions of the ERPA instrument, this paper outlines its theory and operation, the methodology used to obtain electron temperature measurements, and a comparative study suggesting that the ERPA can also provide electron density measurements.

  4. Resolution of multiple sheet-type structures in self-potential measurement

    Indian Academy of Sciences (India)

    Arkoprovo Biswas; Shashi Prakash Sharma

    2014-06-01

    The resolution of self-potential anomalies due to closely spaced multiple sheet-like bodies by the potential difference and potential gradient is studied in this paper. Self-potential anomalies due to several synthetic models were inverted through a very fast simulated annealing (VFSA) global optimization. Increase in depth to the top, polarization constant and depth extent of the body decreases resolution at a particular target separation. It has been observed that depth to the top and separation between two targets play an important role in the resolution. Vertical sheets at equal depth can be resolved in the potential difference measurement only if they are separated by at least four times their depth, while they can be resolved in the gradient method, if they are separated by twice the depth. Resolution using potential difference becomes more difficult for dipping sheets, although the potential gradient method can resolve them efficiently. Efficacy of potential gradient data in the inversion is demonstrated in the study using synthetic data as well as field measurement from South Purulia Shear Zone related with uranium investigation.

  5. Effect of surface roughness on van der Waals and Casimir-Polder/Casimir attraction energies

    Science.gov (United States)

    Makeev, Maxim A.

    2017-09-01

    A theoretical model is devised to assess effects of surface roughness on dispersion interactions between macroscopic bodies, bounded by self-affine fractal surfaces and separated by a vacuum gap. The rough-surface profiles are described statistically by the saturation values of surface width and the correlation lengths; i.e., in terms of experimentally measurable quantities. The model devised takes into account the separation distance-dependent nature of dispersive interactions. The case of non-retarded van der Waals interactions, known to operate at smaller separation distances between the bodies, and that of retarded attractions, operative at larger separation length-scales, are treated separately in this work. Analytical formulae for the roughness corrections are deduced for the two aforementioned types of attractions. The model is employed to compute roughness corrections to interactions between an extended body, bounded by a self-affine surface, and: a) a point-like adherent; and b) a planar half-space. Furthermore, the roughness-induced corrections to dispersive interaction energies between half-spaces, both bounded by self-affine surfaces, are obtained under assumption that the corresponding surface profiles are not correlated. The predictions of the model are compared with some previously reported theoretical studies and available experimental data on the theme of dispersive adhesion between macroscopic bodies.

  6. Free-standing electronic character of monolayer MoS2 in van der Waals epitaxy

    Science.gov (United States)

    Kim, HoKwon; Dumcenco, Dumitru; Frégnaux, Mathieu; Benayad, Anass; Chen, Ming-Wei; Kung, Yen-Cheng; Kis, Andras; Renault, Olivier

    2016-08-01

    We have evaluated as-grown Mo S2 crystals, epitaxially grown on a monocrystalline sapphire by chemical vapor deposition (CVD), with direct electronic band-structure measurements by energy-filtered k -space photoelectron emission microscopy performed with a conventional laboratory vacuum ultraviolet He I light source under off-normal illumination. The valence states of the epitaxial Mo S2 were mapped in momentum space down to 7 eV below the Fermi level. Despite the high nucleation density within the imaged area, the CVD Mo S2 possesses an electronic structure similar to the free-standing monolayer Mo S2 single crystal, and it exhibits hole effective masses of 2.41 ±0.05 m0 , and 0.81 ±0.05 m0 , respectively, at Γ and K high-symmetry points that are consistent with the van der Waals epitaxial growth mechanism. This demonstrates the excellent ability of the Mo S2 CVD on sapphire to yield a highly aligned growth of well-stitched grains through epitaxial registry with a strongly preferred crystallographic orientation.

  7. Efficient Oscillator-Based Approach for Polarizability and van der Waals Interactions

    Science.gov (United States)

    Gobre, Vivekanand; Distasio, Robert A., Jr.; Car, Roberto; Scheffler, Matthias; Tkatchenko, Alexandre

    2013-03-01

    The dynamic polarizability measures the response to an applied time-dependent electric field, and its accurate determination is crucial for van der Waals (vdW) interactions and other response properties. First-principles calculations of polarizabilities in principle require a computationally expensive explicit treatment of many-electron excitations, and are only applicable in practice to systems with less than about 100 atoms. In this work, we present an efficient parameter-free approach for calculating accurate frequency dependent polarizabilities for molecules with thousands of atoms, as well as periodic materials. This is achieved by the synergistic coupling of the Tkatchenko-Scheffler method, which accurately treats short-range hybridization effects, with the self-consistent screening equation from classical electrodynamics. Using only the electron density and free atom reference, we obtain an accuracy of 7% for both static polarizabilities and vdW coefficients for an extensive database of gas-phase molecules and crystals. We analyze the interplay of hybridization and long-range electrostatic screening effects on the polarizability.

  8. Measuring the Repassivation Potential of Alloy 22 Using the Potentiodynamic - Galvanostatic - Potentiostatic Method

    Energy Technology Data Exchange (ETDEWEB)

    Evans, K J; Rebak, R B

    2007-04-27

    Traditionally, the susceptibility of Alloy 22 (N06022) to suffer crevice corrosion has been measured using the Cyclic Potentiodynamic Polarization (CPP) technique (ASTM G 61). When the alloy is not very susceptible to crevice corrosion, the values of repassivation potential obtained using the CPP technique are not highly reproducible. To circumvent the large uncertainty in the values of the repassivation potential by the CPP method, the repassivation potential of Alloy 22 may be measured using a slower method that combines sequentially potentiodynamic, galvanostatic and potentiostatic treatments (this method is called the Tsujikawa-Hisamatsu Electrochemical or THE method). In the THE method the anodic charge is applied to the specimen in a more controlled manner, which avoids driving the alloy to transpassivity and therefore results in more reproducible repassivation potential values. Results using THE method under various testing conditions are presented. A new standard has been prepared for ASTM balloting for the THE method. The round robin matrix results are also discussed.

  9. Development of a Corrosion Potential Measuring System Based on the Generalization of DACS Physical Scale Modeling

    OpenAIRE

    Song Dalei; Fan Xinjian; Ma Xueyan; Shi Weiguo; Wang Xiangdong

    2015-01-01

    A feasible method in evaluating the protection effect and corrosion state of marine cathodic protection (CP) systems is collecting sufficient electric potential data around a submarine pipeline and then establishing the mapping relations between these data and corrosion states of pipelines. However, it is difficult for scientists and researchers to obtain those data accurately due to the harsh marine environments and absence of dedicated potential measurement device. In this paper, to allevia...

  10. A Complete Characterization of Potential Compensation Tests of Hicksian Welfare Measures

    OpenAIRE

    Donald Keenan; Arthur Snow

    1999-01-01

    In this paper, the authors present complete characterizations of the compensation tests for potential Pareto superiority proposed by Kaldor, Hicks, and Samuelson in terms of the aggregate Hicksian measures of income compensation, including compensating and equivalent variations. The key to obtaining these characterizations lies in recognizing that each potential compensation test entails a search over possible outcomes, rather than a comparison of only the new and original outcomes, as with s...

  11. Identifying prospective antifouling coatings for venturis: Zeta potential measurements of oxides at elevated temperatures

    Energy Technology Data Exchange (ETDEWEB)

    Jayaweera, P.; Hettiarachchi, S.; Pound, B.G. (SRI International, Menlo Park, CA (United States))

    1992-10-01

    This report describes the results of research to determine the zeta potential of oxides responsible for fouling of heat transfer, venturi, and other flow measurement device surfaces. Fouling deposits formed on these surfaces reduce mass flow rates of water, causing power reductions of as much as 3 to 4%. There is considerable evidence that deposit formation can be prevented by coating the critical surfaces with a coating material that electrostatically repels the suspended fouling particulates. The zeta potential can be used as a parameter to identify and determine the best coating material to be employed for fouling prevention. The research entailed the development of the equipment necessary for zeta potential measurements, measurement of zeta potentials of oxides and coatings of interest to nuclear power plant applications, and evaluation of candidate coating materials to prevent fouling of surfaces. By this approach, numerous metals and oxides have been identified as potential coating materials. Fouling studies revealed that magnetite does not deposit on tungsten and palladium surfaces, indicating the potential use of these metals for coating venturi surfaces used in nuclear power plants.

  12. Development of a Corrosion Potential Measuring System Based on the Generalization of DACS Physical Scale Modeling

    Directory of Open Access Journals (Sweden)

    Song Dalei

    2015-01-01

    Full Text Available A feasible method in evaluating the protection effect and corrosion state of marine cathodic protection (CP systems is collecting sufficient electric potential data around a submarine pipeline and then establishing the mapping relations between these data and corrosion states of pipelines. However, it is difficult for scientists and researchers to obtain those data accurately due to the harsh marine environments and absence of dedicated potential measurement device. In this paper, to alleviate these two problems, firstly, the theory of dimension and conductivity scaling (DACS physical scale modeling of marine impressed current cathodic protection (ICCP systems is generalized to marine CP systems, secondly, a potential measurement device is developed specially and analogue experiment is designed according to DACS physical scale modeling to verify the feasibility of the measuring system. The experimental results show that 92 percent of the measurement errors are less than 0.25mv, thereby providing an economical and feasible measuring system to get electric potential data around an actual submarine pipeline under CP.

  13. High-concentration zeta potential measurements using light-scattering techniques.

    Science.gov (United States)

    Kaszuba, Michael; Corbett, Jason; Watson, Fraser Mcneil; Jones, Andrew

    2010-09-28

    Zeta potential is the key parameter that controls electrostatic interactions in particle dispersions. Laser Doppler electrophoresis is an accepted method for the measurement of particle electrophoretic mobility and hence zeta potential of dispersions of colloidal size materials. Traditionally, samples measured by this technique have to be optically transparent. Therefore, depending upon the size and optical properties of the particles, many samples will be too concentrated and will require dilution. The ability to measure samples at or close to their neat concentration would be desirable as it would minimize any changes in the zeta potential of the sample owing to dilution. However, the ability to measure turbid samples using light-scattering techniques presents a number of challenges. This paper discusses electrophoretic mobility measurements made on turbid samples at high concentration using a novel cell with reduced path length. Results are presented on two different sample types, titanium dioxide and a polyurethane dispersion, as a function of sample concentration. For both of the sample types studied, the electrophoretic mobility results show a gradual decrease as the sample concentration increases and the possible reasons for these observations are discussed. Further, a comparison of the data against theoretical models is presented and discussed. Conclusions and recommendations are made from the zeta potential values obtained at high concentrations.

  14. Immobilization and surface functionalization of gold nanoparticles monitored via streaming current/potential measurements.

    Science.gov (United States)

    Greben, Kyrylo; Li, Pinggui; Mayer, Dirk; Offenhäusser, Andreas; Wördenweber, Roger

    2015-05-14

    A streaming current/potential method is optimized and used for the analysis of the variation of the surface potential upon chemical modifications of a complex interface consisting of different organic molecules and gold nanoparticles (AuNPs). The surfaces of Si/SiO2 substrates modified with 3-aminopropyltriethoxysilane (APTES), AuNPs, and 11-amino-1-undecanethiol (aminothiols) are analyzed via pH and time dependent ζ potential measurements that reveal the stability and modification of the surface and identify crucial parameters for each individual preparation step. For instance, surface activation and especially molecular adsorbate layers tend not to be stable in time, whereas the substrate and the AuNPs provide a stable surface potential as long as impurities are avoided. It is shown that the streaming potential/current technique represents an ideal tool to analyze and monitor the complex surfaces and their modification.

  15. Membrane potential measurements of isolated neurons using a voltage-sensitive dye.

    Directory of Open Access Journals (Sweden)

    Richard Fairless

    Full Text Available The ability to monitor changes in membrane potential is a useful tool for studying neuronal function, but there are only limited options available at present. Here, we have investigated the potential of a commercially available FLIPR membrane potential (FMP dye, developed originally for high throughput screening using a plate reader, for imaging the membrane potential of cultured cells using an epifluorescence-based single cell imaging system. We found that the properties of the FMP dye make it highly suitable for such imaging since 1 its fluorescence displayed a high signal-to-noise ratio, 2 robust signals meant only minimal exposure times of around 5 ms were necessary, and 3 bidirectional changes in fluorescence were detectable resulting from hyper- or depolarising conditions, reaching equilibrium with a time constant of 4-8 s. Measurements were possible independently of whether membrane potential changes were induced by voltage clamping, or manipulating the ionic distribution of either Na(+ or K(+. Since FMP behaves as a charged molecule which accumulates in the cytosol, equations based on the Boltzmann distribution were developed determining that the apparent charge of FMP which represents a measure of the voltage sensitivity of the dye, is between -0.62 and -0.72. Finally, we demonstrated that FMP is suitable for use in a variety of neuronal cell types and detects membrane potential changes arising from spontaneous firing of action potentials and through stimulation with a variety of excitatory and inhibitory neurotransmitters.

  16. Van der Waals interaction torque and force between dielectrically anisotropic layered media

    CERN Document Server

    Lu, Bing-Sui

    2016-01-01

    We analyse the van der Waals interaction for a pair of dielectrically anisotropic plane-layered media interacting across a dielectrically isotropic medium. We investigate the van der Waals torque and force for the following cases: (i) a pair of single anisotropic layers, (ii) a single anisotropic layer interacting with a multilayered slab consisting of alternating anisotropic and isotropic layers, and (iii) a pair of multilayered slabs each consisting of alternating anisotropic and isotropic layers, looking at the cases where the optical axes lie parallel and/or perpendicular to the plane of the layers. For the first case, the optical axes of the oppositely facing anisotropic layers of the two interacting slabs generally have an angular mismatch, and within each multilayered slab the optical axes may either be the same, or undergo constant angular increments across the anisotropic layers. In particular, we examine how the behaviors of the van der Waals torque and force can be "tuned" by adjusting the layer th...

  17. Van der Waals interaction between a microparticle and a single-wall carbon nanotube

    CERN Document Server

    Blagov, E V; Mostepanenko, V M

    2007-01-01

    The Lifshitz-type formulas describing the free energy and the force of the van der Waals interaction between an atom (molecule) and a single-wall carbon nanotube are obtained. The single-wall nanotube is considered as a cylindrical sheet carrying a two-dimensional free electron gas with appropriate boundary conditions on the electromagnetic field. The obtained formulas are used to calculate the van der Waals free energy and force between a hydrogen atom (molecule) and single-wall carbon nanotubes of different radia. Comparison studies of the van der Waals interaction of hydrogen atoms with single- and multi-wall carbon nanotubes show that depending on atom-nanotube separation distance the idealization of graphite dielectric permittivity is already applicable to nanotubes with only two or three walls.

  18. Cohesive properties of noble metals by van der Waals-corrected Density Functional Theory

    CERN Document Server

    Ambrosetti, Alberto

    2016-01-01

    The cohesive energy, equilibrium lattice constant, and bulk modulus of noble metals are computed by different van der Waals-corrected Density Functional Theory methods, including vdW-DF, vdW-DF2, vdW-DF-cx, rVV10 and PBE-D. Two specifically-designed methods are also developed in order to effectively include dynamical screening effects: the DFT/vdW-WF2p method, based on the generation of Maximally Localized Wannier Functions, and the RPAp scheme (in two variants), based on a single-oscillator model of the localized electron response. Comparison with results obtained without explicit inclusion of van der Waals effects, such as with the LDA, PBE, PBEsol, or the hybrid PBE0 functional, elucidates the importance of a suitable description of screened van der Waals interactions even in the case of strong metal bonding. Many-body effects are also quantitatively evaluated within the RPAp approach.

  19. Many-body effects in the van der Waals-Casimir interaction between graphene layers

    Science.gov (United States)

    Sarabadani, Jalal; Naji, Ali; Asgari, Reza; Podgornik, Rudolf

    2011-10-01

    Van der Waals-Casimir dispersion interactions between two apposed graphene layers, a graphene layer and a substrate, and in a multilamellar graphene system are analyzed within the framework of the Lifshitz theory. This formulation hinges on a known form of the dielectric response function of an undoped or doped graphene sheet, assumed to be of a random-phase-approximation form. In the geometry of two apposed layers, the separation dependence of the van der Waals-Casimir interaction for both types of graphene sheets is determined and critically compared with some well-known limiting cases. In a multilamellar array, the many-body effects are quantified and shown to increase the magnitude of the van der Waals-Casimir interactions.

  20. Molecular recognition by van der Waals interaction between polymers with sequence-specific polarizabilities

    CERN Document Server

    Lu, Bing-Sui; Podgornik, Rudolf

    2016-01-01

    We analyze van der Waals interactions between two rigid polymers with sequence-specific, anisotropic polarizabilities along the polymer backbones, so that the dipole moments fluctuate parallel to the polymer backbones. Assuming that each polymer has a quenched-in polarizability sequence which reflects, for example, the polynucleotide sequence of a double-stranded DNA molecule, we study the van der Waals interaction energy between a pair of such polymers with rod-like structure for the cases where their respective polarizability sequences are (i) distinct and (ii) identical, with both zero and non-zero correlation length of the polarizability correlator along the polymer backbones in the latter case. For identical polymers, we find a novel $r^{-5}$ scaling behavior of the van der Waals interaction energy for small inter-polymer separation $r$, in contradistinction to the $r^{-4}$ scaling behavior of distinct polymers, with furthermore a pronounced angular dependence favoring attraction between sufficiently ali...

  1. Van der Waals Interactions among Alkali Rydberg Atoms with Excitonic States

    CERN Document Server

    Zoubi, Hashem

    2015-01-01

    We investigate the influence of the appearance of excitonic states on van der Waals interactions among two Rydberg atoms. The atoms are assumed to be in different Rydberg states, e.g., in the $|ns\\rangle$ and $|np\\rangle$ states. The resonant dipole-dipole interactions yield symmetric and antisymmetric excitons, with energy splitting that give rise to new resonances as the atoms approach each other. Only far from these resonances the van der Waals coefficients, $C_6^{sp}$, can be defined. We calculate the $C_6$ coefficients for alkali atoms and present the results for lithium by applying perturbation theory. At short interatomic distances of several $\\mu m$, we show that the widely used simple model of two-level systems for excitons in Rydberg atoms breaks down, and the correct representation implies multi-level atoms. Even though, at larger distances one can keep the two-level systems but in including van der Waals interactions among the atoms.

  2. Electric field modulation of Schottky barrier height in graphene/MoSe{sub 2} van der Waals heterointerface

    Energy Technology Data Exchange (ETDEWEB)

    Sata, Yohta; Moriya, Rai, E-mail: moriyar@iis.u-tokyo.ac.jp, E-mail: tmachida@iis.u-tokyo.ac.jp; Morikawa, Sei; Yabuki, Naoto [Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505 (Japan); Masubuchi, Satoru; Machida, Tomoki, E-mail: moriyar@iis.u-tokyo.ac.jp, E-mail: tmachida@iis.u-tokyo.ac.jp [Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505 (Japan); Institute for Nano Quantum Information Electronics, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505 (Japan)

    2015-07-13

    We demonstrate a vertical field-effect transistor based on a graphene/MoSe{sub 2} van der Waals (vdW) heterostructure. The vdW interface between the graphene and MoSe{sub 2} exhibits a Schottky barrier with an ideality factor of around 1.3, suggesting a high-quality interface. Owing to the low density of states in graphene, the position of the Fermi level in the graphene can be strongly modulated by an external electric field. Therefore, the Schottky barrier height at the graphene/MoSe{sub 2} vdW interface is also modulated. We demonstrate a large current ON-OFF ratio of 10{sup 5}. These results point to the potential high performance of the graphene/MoSe{sub 2} vdW heterostructure for electronics applications.

  3. Modulation of electronic structures of MoSe2/WSe2 van der Waals heterostructure by external electric field

    Science.gov (United States)

    Zhang, Fang; Li, Wei; Dai, Xianqi

    2017-10-01

    By using first-principles calculations, we investigate the electronic structures of MoSe2/WSe2 van der Waals(vdW) heterostructure by applying external electric field(Eext) perpendicular to the layers. It is demonstrated that MoSe2/WSe2 heterostructure is a type-II vdW heterostructure. The band gap of MoSe2/WSe2 is significantly modulated by Eext, eventually a semiconductor-to-metal transition can be realized. The positive and negative Eext have different effects on the band gap due to the intrinsic spontaneous electric polarization in MoSe2/WSe2 heterostructure. Moreover, MoSe2/WSe2 heterobilayer experiences transitions from type-II to type-I and then to type-II under various Eext. The present study provides great application potential of ultrathin MoSe2/WSe2 heterostructure in future nano- and optoelectronics.

  4. Understanding compressible turbulence in the solar wind with multipoint density measurements derived from spacecraft potential

    Science.gov (United States)

    Roberts, Owen

    2016-04-01

    Measurements of spacecraft potential can often be used to derive the electron number density with higher time resolution than is typically available with plasma instruments. On board the Cluster spacecraft the potential is measured with the Electric Fields and Waves instrument (EFW) which consists of four booms in the spin plane of the spacecraft. Consequently the potential measurement is affected by spin and wake effects. This makes the study of frequencies larger than the spin frequency challenging. To overcome these caveats a statistical model of the potential is obtained as a function of the angle the spacecraft is facing. When this variation is known it can be removed from the potential data, resulting in a much more accurate determination of the electron density and a cleaner power spectrum. Spikes at harmonics of the spin frequency can be removed without the need to use a notch filter on the time series. The treated data can then be used as an input to the k-filtering technique, which has previously been applied to the incompressible components of the magnetic field. This allows determination of the three dimensional power distribution in wave space as well as the wavevectors and plasma frame frequencies. Results for the compressible component (using electron density and magnitude of the magnetic field as inputs) and the incompressible component (three components of the magnetic field) will be compared.

  5. A new approach to endocochlear potential and potassium ion concentration measures in mini pig models

    Institute of Scientific and Technical Information of China (English)

    Lili Ren a; Ling Zhang b; Weiwei Guo a; Wei Sun c; Shiming Yang a

    2014-01-01

    Mini pig models are large mammals and their ears are more similar with human beings in structure and development than other animals. However, the study on porcine ears is still in the initial stage and there is no description of an ideal operation approach to endocochlear potential and potassium ion concentration measurements. In this article, we describe a pre-auricular surgical approach to access the middle and inner ear for endocochlear potential and potassium ion concentration measures in mini pig models. Ten one-week old normal mini pigs were used in the study. The bulla of the temporal bone was accessed via a pre-auricular approach for endocochlear potential and potassium ion concentration measurements. The condition of the animals during the first posteexperiment 24 h was observed. One animal died during surgery. The pre-auricular approach improved protection and preservation of relevant nervous and vascular elements including the facial nerve and carotid ar-tery. So, the pre-auricular approach can be used for endocochlear potential and potassium ion concentration measurements with improved nerve and artery preservation mini pigs.

  6. Measuring Foster Parent Potential: Casey Foster Parent Inventory-Applicant Version

    Science.gov (United States)

    Orme, John G.; Cuddeback, Gary S.; Buehler, Cheryl; Cox, Mary Ellen; Le Prohn, Nicole S.

    2007-01-01

    Objective: The Casey Foster Applicant Inventory-Applicant Version (CFAI-A) is a new standardized self-report measure designed to assess the potential to foster parent successfully. The CFAI-A is described, and results concerning its psychometric properties are presented. Method: Data from a sample of 304 foster mothers from 35 states are analyzed.…

  7. On-line measurements of oscillating mitochondrial membrane potential in glucose-fermenting Saccharomyces cerevisiae

    DEFF Research Database (Denmark)

    Andersen, Ann Zahle; Poulsen, Allan K; Olsen, Lars Folke

    2007-01-01

    We employed the fluorescent cyanine dye DiOC(2)(3) to measure membrane potential in semi-anaerobic yeast cells under conditions where glycolysis was oscillating. Oscillations in glycolysis were studied by means of the naturally abundant nicotinamide adenine dinucleotide (NADH). We found that the ...

  8. Predictability of bacterial activity and denitrification in aquatic sediments with continuous measurements of redox potential.

    NARCIS (Netherlands)

    Hunting, E.R.; van der Geest, H.G.

    2011-01-01

    Redox potential has been adopted as a qualitative parameter for interpreting solubility changes of nutrients and contaminants and the biological activity within wetland systems for several decades. The majority of studies considering the redox geochemistry in sediments used measurements of bulked

  9. MISCIBILITY, SOLUBILITY, VISCOSITY, AND DENSITY MEASUREMENTS FOR R-236FA WITH POTENTIAL LUBRICANTS

    Science.gov (United States)

    The report gives results of miscibility, solubility, viscosity, and density measurements for refrigerant R-236fa and two potential lubricants . (The data are needed to determine the suitability of refrigerant/lubricant combinations for use in refrigeration systems.) The tested oi...

  10. Measurement of Donnan potentials in gels by in situ microelectrode voltammetry

    NARCIS (Netherlands)

    Davis, T.A.; Yezek, L.P.; Pinheiro, J.P.; Leeuwen, van H.P.

    2005-01-01

    This work describes the electrochemical methodology for the determination of the Donnan potential from diffusion-limited steady-state voltammograms of acrylamide gels. The technique is based upon the measurement of gel-sol systems that have reached Donnan equilibrium and contain Cd2+ as a probe ion.

  11. Surface free energy components of glass from ellipsometry and zeta potential measurements

    NARCIS (Netherlands)

    Chibowski, E.; Hołysz, L.; Kip, Gerhardus A.M.; van Silfhout, Arend; Busscher, H.J.

    1989-01-01

    Two different experimental approaches based on ellipsometry and zeta potential measurements have been employed to determine the dispersion and polar surface free energy components of glass. From ellipsometry the adsorption isotherms of n-octane and water have been determined, yielding values for the

  12. Interpretation of fast measurements of plasma potential, temperature and density in SOL of ASDEX Upgrade

    DEFF Research Database (Denmark)

    Horacek, J.; Adamek, J.; Müller, H.W.

    2010-01-01

    This paper focuses on interpretation of fast (1 µs) and local (2–4 mm) measurements of plasma density, potential and electron temperature in the edge plasma of tokamak ASDEX Upgrade. Steady-state radial profiles demonstrate the credibility of the ball-pen probe. We demonstrate that floating poten...

  13. Nineteenth century air pollution variations in Paris inferred from Eiffel Tower potential gradient measurements

    CERN Document Server

    Harrison, R G

    2003-01-01

    Early surface measurements of atmospheric Potential Gradient were made in many European cities in the nineteenth century (C19th). The data was usually obtained at hourly resolution, and good accounts of the calibration of the instruments are also often available. The PG measurements made by Chauveau on the Eiffel Tower, soon after its completion in the 1890s, are particularly notable. Atmospheric electrical proxy techniques in combination with simple boundary layer meteorology are used to determine air pollution levels. The C19th PG measurements in both polluted and clean Parisian air present a unique resource for European air pollution and atmospheric composition studies.

  14. Standard test method for measurement of corrosion potentials of Aluminum alloys

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    1997-01-01

    1.1 This test method covers a procedure for measurement of the corrosion potential (see Note 1) of an aluminum alloy in an aqueous solution of sodium chloride with enough hydrogen peroxide added to provide an ample supply of cathodic reactant. Note 1—The corrosion potential is sometimes referred to as the open-circuit solution or rest potential. 1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. 1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

  15. Measurement of the Relativistic Potential Difference Across a Rotating Dielectric Cylinder

    CERN Document Server

    Hertzberg, J B; Hummon, M T; Krause, D; Peck, S K; Hunter, L R

    2001-01-01

    According to the Special Theory of Relativity, a rotating magnetic dielectric cylinder in an axial magnetic field should exhibit a contribution to the radial electric potential that is associated with the motion of the material's magnetic dipoles. In 1913 Wilson and Wilson reported a measurement of the potential difference across a magnetic dielectric constructed from wax and steel balls. Their measurement has long been regarded as a verification of this prediction. In 1995 Pelligrini and Swift questioned the theoretical basis of experiment. In particular, they pointed out that it is not obvious that a rotating medium may be treated as if each point in the medium is locally inertial. They calculated the effect in the rotating frame and predicted a potential different from both Wilson's theory and experiment. Subsequent analysis of the experiment suggests that Wilson's experiment does not distinguish between the two predictions due to the fact that their composite steel-wax cylinder is conductive in the region...

  16. Understanding the nanoscale local buckling behavior of vertically aligned MWCNT arrays with van der Waals interactions

    Science.gov (United States)

    Li, Yupeng; Kim, Hyung-Ick; Wei, Bingqing; Kang, Junmo; Choi, Jae-Boong; Nam, Jae-Do; Suhr, Jonghwan

    2015-08-01

    The local buckling behavior of vertically aligned carbon nanotubes (VACNTs) has been investigated and interpreted in the view of a collective nanotube response by taking van der Waals interactions into account. To the best of our knowledge, this is the first report on the case of collective VACNT behavior regarding van der Waals force among nanotubes as a lateral support effect during the buckling process. The local buckling propagation and development of VACNTs were experimentally observed and theoretically analyzed by employing finite element modeling with lateral support from van der Waals interactions among nanotubes. Both experimental and theoretical analyses show that VACNTs buckled in the bottom region with many short waves and almost identical wavelengths, indicating a high mode buckling. Furthermore, the propagation and development mechanism of buckling waves follow the wave damping effect.The local buckling behavior of vertically aligned carbon nanotubes (VACNTs) has been investigated and interpreted in the view of a collective nanotube response by taking van der Waals interactions into account. To the best of our knowledge, this is the first report on the case of collective VACNT behavior regarding van der Waals force among nanotubes as a lateral support effect during the buckling process. The local buckling propagation and development of VACNTs were experimentally observed and theoretically analyzed by employing finite element modeling with lateral support from van der Waals interactions among nanotubes. Both experimental and theoretical analyses show that VACNTs buckled in the bottom region with many short waves and almost identical wavelengths, indicating a high mode buckling. Furthermore, the propagation and development mechanism of buckling waves follow the wave damping effect. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr03581c

  17. Organic richness and gas generation potential of Permian Barren Measures from Raniganj field, West Bengal, India

    Indian Academy of Sciences (India)

    Annapurna Boruah; S Ganapathi

    2015-07-01

    The organic geochemistry of shales in terms of its organic richness, hydrocarbon source potential, thermal maturity, depositional environment, etc., are essential stipulations for shale gas resources assessment. In this study, a total of 32 core samples of Permian Barren Measures from four boreholes in Raniganj field of Damodar Basin were analysed to evaluate their gas generation potential using Rock–Eval pyrolysis techniques. Petrographic analysis brings out the lithofacies of Barren Measures as carbonaceous silty shale, iron rich claystone and sand-shale intercalation. The total organic content (TOC) of the shale units of Barren Measures ranges from 3.75 to 20.9 wt%, whereas hydrogen index (HI) ranges from 58.45 to 125.34 mg HC/g TOC. Present study suggests early to late maturated (0.6–1%) organic matters in Barren Measures with gas prone type III kerogen. The study analysed the effect of burial history on the preservation and maturation of organic matters. The organic richness, kerogen type, thermal maturity and petrographic properties of Barren Measures signify fair to excellent gas generation potential.

  18. Adsorption of tannic acid on polyelectrolyte monolayers determined in situ by streaming potential measurements.

    Science.gov (United States)

    Oćwieja, M; Adamczyk, Z; Morga, M

    2015-01-15

    Physicochemical characteristics of tannic acid (tannin) suspensions comprising its stability for a wide range of ionic strength and pH were thoroughly investigated using UV-vis spectrophotometry, dynamic light scattering and microelectrophoretic measurements. These studies allowed to determine the hydrodynamic diameter of the tannic acid that was 1.63 nm for the pH range 3.5-5.5. For pH above 6.0 the hydrodynamic diameter significantly decreased as a result of the tannin hydrolysis. The electrophoretic mobility measurements confirmed that tannic acid is negatively charged for these values of pH and ionic strength 10(-4)-10(-2) M. Therefore, in order to promote adsorption of tannin molecules on negatively charged mica, the poly(allylamine hydrochloride) (PAH) supporting monolayers were first adsorbed under diffusion transport conditions. The coverage of polyelectrolyte monolayers was regulated by changing bulk concentration of PAH and the adsorption time. The electrokinetic characteristics of bare and PAH-covered mica were determined using the streaming potential measurements. The zeta potential of these PAH monolayers was highly positive, equal to 46 mV for ionic strength of 10(-2) M. The kinetics of tannin adsorption on these PAH supporting monolayers was evaluated by the in situ the streaming potential measurements. The zeta potential of PAH monolayers abruptly decreases with the adsorption of tannin molecules that was quantitatively interpreted in terms of the three-dimensional electrokinetic model. The acid-base characteristics of tannin monolayers were acquired via the streaming potential measurements for a broad range of pH. The obtained results indicate that it is possible to control adsorption of tannin on positively charged surfaces in order to designed new multilayer structures of desirable electrokinetic properties and stability.

  19. Electric field measurement using a non-perturbative method based on a calibrated electric potential sensor

    Energy Technology Data Exchange (ETDEWEB)

    Aydin, A; Stiffell, P B, E-mail: a.aydin@sussex.ac.uk [Centre for Physical Electronics and Quantum Technology, School of Engineering and Design, University of Sussex, Brighton, BN1 9QT (United Kingdom)

    2011-06-23

    We present results of finite element analysis for simple test structures which demonstrate clearly that the measurement situation is complex. The test structure consists of an open geometry parallel plate capacitor within a screened enclosure. Indeed, the presence of earthed objects, even at considerable distances, is shown to have a significant effect on the field geometry close to the source. These simulations are compared with field measurements made using an ultra-high input impedance sensor, the Electric Potential Sensor. A single experimentally determined calibration factor is all that is required to achieve excellent agreement between experimental measurements and the results of the simulations. Given this, the sensor is capable of mapping accurately, and in a non-perturbative manner, the spatial potential both within and outside of the test structure.

  20. Detection of microbial contaminations in drinking water using ATP measurements – evaluating potential for online monitoring

    DEFF Research Database (Denmark)

    Vang, Óluva Karin; Corfitzen, Charlotte B.; Albrechtsen, Hans-Jørgen

    2011-01-01

    There is an increasing call for fast and reliable methods for continuous monitoring of microbial drinking water quality in order to protect public health. The potential for Adenosine triphosphate (ATP) measurements as a real-time analysis for continuous monitoring of microbial drinking water...... quality was investigated through simulation of two contamination scenarios, i.e. drinking water contaminated with waste water and surface water at various concentrations. With ATP measurements it was possible to detect waste water diluted 1000-10,000 times in drinking water depending on sensitivity...... of reagent kit. Surface water diluted 100-1000 times was detected in drinking water with ATP measurements. ATP has the potential as an early warning tool, especially in the period when the contamination concentration is high. 2011 © American Water Works Association AWWA WQTC Conference Proceedings All Rights...

  1. Detection of microbial contaminations in drinking water using ATP measurements – evaluating potential for online monitoring

    DEFF Research Database (Denmark)

    Vang, Óluva Karin; Corfitzen, Charlotte B.; Albrechtsen, Hans-Jørgen

    2011-01-01

    There is an increasing call for fast and reliable methods for continuous monitoring of microbial drinking water quality in order to protect public health. The potential for Adenosine triphosphate (ATP) measurements as a real-time analysis for continuous monitoring of microbial drinking water...... quality was investigated through simulation of two contamination scenarios, i.e. drinking water contaminated with waste water and surface water at various concentrations. With ATP measurements it was possible to detect waste water diluted 1000-10,000 times in drinking water depending on sensitivity...... of reagent kit. Surface water diluted 100-1000 times was detected in drinking water with ATP measurements. ATP has the potential as an early warning tool, especially in the period when the contamination concentration is high. 2011 © American Water Works Association AWWA WQTC Conference Proceedings All Rights...

  2. Standard test method for measurement of oxidation-reduction potential (ORP) of soil

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    2009-01-01

    1.1 This test method covers a procedure and related test equipment for measuring oxidation-reduction potential (ORP) of soil samples removed from the ground. 1.2 The procedure in Section 9 is appropriate for field and laboratory measurements. 1.3 Accurate measurement of oxidation-reduction potential aids in the analysis of soil corrosivity and its impact on buried metallic structure corrosion rates. 1.4 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard. 1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

  3. High broad-band photoresponsivity of mechanically formed InSe-graphene van der Waals heterostructures.

    Science.gov (United States)

    Mudd, Garry W; Svatek, Simon A; Hague, Lee; Makarovsky, Oleg; Kudrynskyi, Zakhar R; Mellor, Christopher J; Beton, Peter H; Eaves, Laurence; Novoselov, Kostya S; Kovalyuk, Zakhar D; Vdovin, Evgeny E; Marsden, Alex J; Wilson, Neil R; Patanè, Amalia

    2015-07-01

    High broad-band photoresponsivity of mechanically formed InSe-graphene van der Waals heterostructures is achieved by exploiting the broad-band transparency of graphene, the direct bandgap of InSe, and the favorable band line up of InSe with graphene. The photoresponsivity exceeds that for other van der Waals heterostructures and the spectral response extends from the near-infrared to the visible spectrum. © 2015 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. A high-pressure van der Waals compound in solid nitrogen-helium mixtures

    Science.gov (United States)

    Vos, W. L.; Finger, L. W.; Hemley, R. J.; Hu, J. Z.; Mao, H. K.; Schouten, J. A.

    1992-01-01

    A detailed diamond anvil-cell study using synchrotron X-ray diffraction, Raman scattering, and optical microscopy has been conducted for the He-N system, with a view to the weakly-bound van der Waals molecule interactions that can be formed in the gas phase. High pressure is found to stabilize the formation of a stoichiometric, solid van der Waals compound of He(N2)11 composition which may exemplify a novel class of compounds found at high pressures in the interiors of the outer planets and their satellites.

  5. Anisotropic spheres with Van derWaals-type equation of state

    Indian Academy of Sciences (India)

    S Thirukkanesh; F C Ragel

    2014-07-01

    We study static spherically symmetric space-time to describe relativistic compact objects with anisotropic matter distribution and derive two classes of exact models to the Einstein–Maxwell system with a modified Van derWaals equation of state. We motivate a Van derWaals-type equation of state to physically signify a high-density domain of quark matter, and the generated exact solutions are shown to contain several classes of exact models reported previously that correspond to various physical scenarios. Geometrical analysis shows that the physical quantities are well behaved so that these models may be used to describe anisotropic charged compact spheres.

  6. Nanoscale Tail Aggregation in Ionic Liquids: Roles of Electrostatic and van der Waals Interactions

    Institute of Scientific and Technical Information of China (English)

    赵海清; 石锐; 王延颋

    2011-01-01

    Nanoscale spatial heterogeneity in ionic liquids is formed by the aggregation of cationic tail groups. The electrostatic interactions between polar groups and the collective van der Waals interactions between nonpolar tail groups both contribute to the formation of tail domains, but the degrees of their contributions were unknown. In this work, by applying a strong external electric field to effectively overpower the electrostatic interactions between polar groups, we have determined that the tail aggregation is majorly attributed to the electrostatic interactions and the van der Waals interactions only have minor influence on the spatial heterogeneity phenomenon of ionic liquids.

  7. Using computation to teach the properties of the van der Waals fluid

    Science.gov (United States)

    Swendsen, Robert H.

    2013-10-01

    The calculation of the thermodynamic properties of the van der Waals fluid is not trivial and most of its properties are rarely discussed because of mathematical difficulties. I describe a numerical approach that produces the full thermodynamic behavior of the van der Waals fluid with little effort. The numerical approach is particularly useful for showing the behavior of the specific heat, the isothermal compressibility, and the coefficient of thermal expansion at and near the critical point. The results of these computations show some surprising properties and give new insights into the mean-field description of the liquid-gas transition.

  8. Competition of van der Waals and chemical forces on gold–sulfur surfaces and nanoparticles

    DEFF Research Database (Denmark)

    Reimers, Jeffrey R.; Ford, Michael J.; Marcuccio, Sebastian M.

    2017-01-01

    Chemists generally believe that covalent and ionic bonds form much stronger links between atoms than the van der Waals force does. However, this is not always so. We present cases in which van der Waals dispersive forces introduce new competitive bonding possibilities rather than just modulating...... traditional bonding scenarios. Although the new possibilities could arise from any soft–soft chemical interaction, we focus on bonding between gold atoms and alkyl or arylsulfur ligands, RS. Consideration of all the interactions at play in sulfur-protected gold surfaces and gold nanoparticles is necessary...

  9. Interlayer Transition and Infrared Photodetection in Atomically Thin Type-II MoTe₂/MoS₂ van der Waals Heterostructures.

    Science.gov (United States)

    Zhang, Kenan; Zhang, Tianning; Cheng, Guanghui; Li, Tianxin; Wang, Shuxia; Wei, Wei; Zhou, Xiaohao; Yu, Weiwei; Sun, Yan; Wang, Peng; Zhang, Dong; Zeng, Changgan; Wang, Xingjun; Hu, Weida; Fan, Hong Jin; Shen, Guozhen; Chen, Xin; Duan, Xiangfeng; Chang, Kai; Dai, Ning

    2016-03-22

    We demonstrate the type-II staggered band alignment in MoTe2/MoS2 van der Waals (vdW) heterostructures and an interlayer optical transition at ∼1.55 μm. The photoinduced charge separation between the MoTe2/MoS2 vdW heterostructure is verified by Kelvin probe force microscopy (KPFM) under illumination, density function theory (DFT) simulations and photoluminescence (PL) spectroscopy. Photoelectrical measurements of MoTe2/MoS2 vdW heterostructures show a distinct photocurrent response in the infrared regime (1550 nm). The creation of type-II vdW heterostructures with strong interlayer coupling could improve our fundamental understanding of the essential physics behind vdW heterostructures and help the design of next-generation infrared optoelectronics.

  10. Mapping the fissure potential zones based on microtremor measurement in Denpasar City, Bali

    Science.gov (United States)

    Prabowo, U. N.; Marjiyono; Sismanto

    2016-01-01

    Denpasar City and its vicinity considered as the areas with excessive ground water exploitation and high earthquake intensity. These conditions will cause these area potential with land subsidence which is triggering ground fissures. This research aims are to mapping the fissures potential areas based on microtremor measurement in Denpasar City and its vicinity. Ground fissures will happen if the land subsidence occurs in the areas which have different bedrock height beneath its sedimentary layer. The height of bedrock is determined by reducing surface elevation with the sedimentary layer thickness. This sedimentary layer thickness obtained from microtremor measurement using HVSR method, and Shear wave velocity (VS) obtained from microtremor array measurement which is analyzed by Spatial Auto Correlation (SPAC) method. The result from HVSR method as well as Peak Ground Acceleration (PGA) value are then analyzed to get ground shear strain value, which is the soil surface strain and its effect when earthquake occurs. Based on the bedrock map, it can be estimated that the bedrock layer forms structure in the southern part of the research areas and the potential fissuring area due to the massive ground water exploitation is in the west Denpasar Subdistrict. In addition, based on the bedrock map and ground shear strain value which combined with Simple Additive Weight (SAW) method, there are two areas having Assuring potential, i.e west and south Denpasar Subdistricts.

  11. Field measurements of the ambient ozone formation potential in Beijing during winter

    Science.gov (United States)

    Crilley, Leigh; Kramer, Louisa; Thomson, Steven; Lee, James; Squires, Freya; Bloss, William

    2017-04-01

    The air quality issues in Beijing have been well-documented, and the severe air pollution levels result in a unique chemical mix in the urban boundary layer, both in terms of concentration and composition. As many of the atmospheric chemical process are non-linear and interlinked, this makes predictions difficult for species formed in atmosphere, such as ozone, requiring field measurements to understand these processes in order to guide mitigation efforts. To investigate the ozone formation potential of ambient air, we employed a custom built instrument to measure in near real time the potential for in situ ozone production, using an artificial light source. Our results are thus indicative of the ozone formation potential for the sampled ambient air mixture. Measurements were performed as part of the Air Pollution and Human Health (APHH) field campaign in November / December 2016 at a suburban site in central Beijing. We also conducted experiments to examine the ozone production sensitivity to NOx. We will present preliminarily results from ambient sampling and NOx experiments demonstrating changes in the ozone production potential during clean and haze periods in Beijing.

  12. Measurements of the SUSY Higgs self-couplings and the reconstruction of the Higgs potential

    CERN Document Server

    Boudjema, F

    2002-01-01

    We address the issue of the reconstruction of the scalar potential of a two-Higgs doublet model having in mind that of the MSSM. We first consider the general CP conserving dim-4 effective potential. To fully reconstruct this potential, we show that even if all the Higgs masses and their couplings to the standard model particles are measured one needs not only to measure certain trilinear Higgs self-couplings but some of the quartic couplings as well. We also advocate expressing the Higgs self couplings in the mass basis. We show explicitly, that in the so-called decoupling limit, the most easily accessible Higgs self-couplings are given in terms of the Higgs mass while all other dependencies on the parameters of the general effective potential are screened. This helps also easily explain how, in the MSSM, the largest radiative corrections which affect these self couplings are reabsorbed by using the corrected Higgs mass. We also extend our analysis to higher order operators in the effective Higgs potential. ...

  13. Monolayers of poly(amido amine) dendrimers on mica - In situ streaming potential measurements.

    Science.gov (United States)

    Michna, Aneta; Adamczyk, Zbigniew; Sofińska, Kamila; Matusik, Katarzyna

    2017-01-01

    The deposition of poly(amido amine) dendrimers on mica at various pHs was studied by the atomic force microscopy (AFM) and in situ streaming potential measurements. Bulk characteristics of dendrimers were acquired by using the dynamic light scattering (DLS) and the laser Doppler velocimetry (LDV). The hydrodynamic radius derived from DLS measurements was 5.2nm for the ionic strength of 10(-2)M and pH range 4-10. The electrophoretic mobility, the zeta potential and the number of electrokinetic charges per molecule were derived as a function of pH from the LDV measurements. It was revealed that the dendrimers are positively charged for pH up to 10. This promoted their deposition on negatively charged mica substrate whose kinetics was quantitatively evaluated by direct AFM imaging and streaming potential measurements interpreted in terms of the electrokinetic model. The desorption kinetics of dendrimers under flowing conditions from monolayers of various coverage was also studied. It was revealed that dendrimer deposition was partially reversible for pH above 5.8. The acid-base properties of the dendrimer monolayers deposited on mica were characterized.

  14. The Potential of Continuous, Local Atomic Clock Measurements for Earthquake Prediction and Volcanology

    CERN Document Server

    Bondarescu, Mihai; Jetzer, Philippe; Lundgren, Andrew

    2015-01-01

    Modern optical atomic clocks along with the optical fiber technology currently being developed can measure the geoid, which is the equipotential surface that extends the mean sea level on continents, to a precision that competes with existing technology. In this proceeding, we point out that atomic clocks have the potential to not only map the sea level surface on continents, but also look at variations of the geoid as a function of time with unprecedented timing resolution. The local time series of the geoid has a plethora of applications. These include potential improvement in the predictions of earthquakes and volcanoes, and closer monitoring of ground uplift in areas where hydraulic fracturing is performed.

  15. Van der Waals Epitaxy of Two-Dimensional MoS2-Graphene Heterostructures in Ultrahigh Vacuum.

    Science.gov (United States)

    Miwa, Jill A; Dendzik, Maciej; Grønborg, Signe S; Bianchi, Marco; Lauritsen, Jeppe V; Hofmann, Philip; Ulstrup, Søren

    2015-06-23

    In this work, we demonstrate direct van der Waals epitaxy of MoS2-graphene heterostructures on a semiconducting silicon carbide (SiC) substrate under ultrahigh vacuum conditions. Angle-resolved photoemission spectroscopy (ARPES) measurements show that the electronic structure of free-standing single-layer (SL) MoS2 is retained in these heterostructures due to the weak van der Waals interaction between adjacent materials. The MoS2 synthesis is based on a reactive physical vapor deposition technique involving Mo evaporation and sulfurization in a H2S atmosphere on a template consisting of epitaxially grown graphene on SiC. Using scanning tunneling microscopy, we study the seeding of Mo on this substrate and the evolution from nanoscale MoS2 islands to SL and bilayer (BL) MoS2 sheets during H2S exposure. Our ARPES measurements of SL and BL MoS2 on graphene reveal the coexistence of the Dirac states of graphene and the expected valence band of MoS2 with the band maximum shifted to the corner of the Brillouin zone at K̅ in the SL limit. We confirm the 2D character of these electronic states via a lack of dispersion with photon energy. The growth of epitaxial MoS2-graphene heterostructures on SiC opens new opportunities for further in situ studies of the fundamental properties of these complex materials, as well as perspectives for implementing them in various device schemes to exploit their many promising electronic and optical properties.

  16. Inferring the gravitational potential of the Milky Way with a few precisely measured stars

    Energy Technology Data Exchange (ETDEWEB)

    Price-Whelan, Adrian M.; Johnston, Kathryn V.; Hendel, David [Department of Astronomy, Columbia University, 550 West 120th Street, New York, NY 10027 (United States); Hogg, David W., E-mail: adrn@astro.columbia.edu [Center for Cosmology and Particle Physics, Department of Physics, New York University, 4 Washington Place, New York, NY 10003 (United States)

    2014-10-10

    The dark matter halo of the Milky Way is expected to be triaxial and filled with substructure. It is hoped that streams or shells of stars produced by tidal disruption of stellar systems will provide precise measures of the gravitational potential to test these predictions. We develop a method for inferring the Galactic potential with tidal streams based on the idea that the stream stars were once close in phase space. Our method can flexibly adapt to any form for the Galactic potential: it works in phase-space rather than action-space and hence relies neither on our ability to derive actions nor on the integrability of the potential. Our model is probabilistic, with a likelihood function and priors on the parameters. The method can properly account for finite observational uncertainties and missing data dimensions. We test our method on synthetic data sets generated from N-body simulations of satellite disruption in a static, multi-component Milky Way, including a triaxial dark matter halo with observational uncertainties chosen to mimic current and near-future surveys of various stars. We find that with just eight well-measured stream stars, we can infer properties of a triaxial potential with precisions of the order of 5%-7%. Without proper motions, we obtain 10% constraints on most potential parameters and precisions around 5%-10% for recovering missing phase-space coordinates. These results are encouraging for the goal of using flexible, time-dependent potential models combined with larger data sets to unravel the detailed shape of the dark matter distribution around the Milky Way.

  17. Dielectric Spectroscopy: noninvasive and fast method for measuring changes in the membrane potential

    Science.gov (United States)

    Bot, Corina; Prodan, Camelia; Prodan, Emil

    2008-03-01

    We present a noninvasive and fast method, dielectric spectroscopy, to measure changes in the membrane potential of live cell suspensions, in particular to E. coli. This technique can be applied virtually to any cell suspension, regardless of size or shape and is tested against the traditional one-using voltage sensitive dyes. Precise measurements of the dielectric permittivity ɛ and conductivity σ of live cells suspensions require prior elimination of the polarization errors. Polarization errors are caused by the ionic content of a buffer, and they affect the total impedance in the low frequency interval. We hereby present our approach of polarization removal in low frequency limit by fitting both real and imaginary experimental curves with an ideal impedance Z=d/iφɛ^*S, where ɛ^*=ɛ+1/iφσ. Here, ɛ and σ represent the fitting parameters; a higher weight is given to each of them for the high frequency domain (3kHz-10kHz), where polarization effects were proven negligible. Measurements were performed in a low electric field (1V/cm) and 40Hz-10kHz frequency domain. Different buffers are measured, such as HEPES, DMEM with different KCl concentrations. Adding different KCl concentration or ionophores triggers changes in the membrane potential of E. coli. Those changes are measured using dielectric spectroscopy and voltage sensitive dyes.

  18. Dielectric constant of liquids confined in the extended nanospace measured by a streaming potential method.

    Science.gov (United States)

    Morikawa, Kyojiro; Kazoe, Yutaka; Mawatari, Kazuma; Tsukahara, Takehiko; Kitamori, Takehiko

    2015-02-01

    Understanding liquid structure and the electrical properties of liquids confined in extended nanospaces (10-1000 nm) is important for nanofluidics and nanochemistry. To understand these liquid properties requires determination of the dielectric constant of liquids confined in extended nanospaces. A novel dielectric constant measurement method has thus been developed for extended nanospaces using a streaming potential method. We focused on the nonsteady-state streaming potential in extended nanospaces and successfully measured the dielectric constant of liquids within them without the use of probe molecules. The dielectric constant of water was determined to be significantly reduced by about 3 times compared to that of the bulk. This result contributes key information toward further understanding of the chemistry and fluidics in extended nanospaces.

  19. GaN: From three- to two-dimensional single-layer crystal and its multilayer van der Waals solids

    Science.gov (United States)

    Onen, A.; Kecik, D.; Durgun, E.; Ciraci, S.

    2016-02-01

    Three-dimensional (3D) GaN is a III-V compound semiconductor with potential optoelectronic applications. In this paper, starting from 3D GaN in wurtzite and zinc-blende structures, we investigated the mechanical, electronic, and optical properties of the 2D single-layer honeycomb structure of GaN (g -GaN ) and its bilayer, trilayer, and multilayer van der Waals solids using density-functional theory. Based on high-temperature ab initio molecular-dynamics calculations, we first showed that g -GaN can remain stable at high temperature. Then we performed a comparative study to reveal how the physical properties vary with dimensionality. While 3D GaN is a direct-band-gap semiconductor, g -GaN in two dimensions has a relatively wider indirect band gap. Moreover, 2D g -GaN displays a higher Poisson ratio and slightly less charge transfer from cation to anion. In two dimensions, the optical-absorption spectra of 3D crystalline phases are modified dramatically, and their absorption onset energy is blueshifted. We also showed that the physical properties predicted for freestanding g -GaN are preserved when g -GaN is grown on metallic as well as semiconducting substrates. In particular, 3D layered blue phosphorus, being nearly lattice-matched to g -GaN , is found to be an excellent substrate for growing g -GaN . Bilayer, trilayer, and van der Waals crystals can be constructed by a special stacking sequence of g -GaN , and they can display electronic and optical properties that can be controlled by the number of g -GaN layers. In particular, their fundamental band gap decreases and changes from indirect to direct with an increasing number of g -GaN layers.

  20. Electronic structure, lattice dynamics, and optical properties of a novel van der Waals semiconductor heterostructure: InGaSe2

    Science.gov (United States)

    Ibarra-Hernández, Wilfredo; Elsayed, Hannan; Romero, Aldo H.; Bautista-Hernández, Alejandro; Olguín, Daniel; Cantarero, Andrés

    2017-07-01

    There is a growing interest in the property dependence of transition metal dichalcogenides as a function of the number of layers and formation of heterostructures. Depending on the stacking, doping, edge effects, and interlayer distance, the properties can be modified, which opens the door to novel applications that require a detailed understanding of the atomic mechanisms responsible for those changes. In this work, we analyze the electronic properties and lattice dynamics of a heterostructure constructed by simultaneously stacking InSe layers and GaSe layers bounded by van der Waals forces. We have assumed the same space group of GaSe, P 6 ¯m 2 as it becomes the lower energy configuration for other considered stackings. The structural, vibrational, and optical properties of this layered compound have been calculated using density functional theory. The structure is shown to be energetically, thermally, and elastically stable, which indicates its possible chemical synthesis. A correlation of the theoretical physical properties with respect to its parent compounds is extensively discussed. One of the most interesting properties is the low thermal conductivity, which indicates its potential use in thermolectric applications. Additionally, we discuss the possibility of using electronic gap engineering methods, which can help us to tune the optical emission in a variable range close to that used in the field of biological systems (NIR). Finally, the importance of considering properly van der Waals dispersion in layered materials has been emphasized as included in the exchange correlation functional. As for the presence of atoms with important spin-orbit coupling, relativistic corrections have been included.

  1. Evaluation of a novel integrated sensor system for synchronous measurement of cardiac vibrations and cardiac potentials.

    Science.gov (United States)

    Chuo, Yindar; Tavakolian, Kouhyar; Kaminska, Bozena

    2011-08-01

    The measurement of human body vibrations as a result of heart beating, simultaneously with cardiac potentials have been demonstrated in past studies to bring additional value to diagnostic cardiology through the detection of irregularities in the mechanical movement of the heart. The equipment currently available to the medical community is either large and bulky or difficult to synchronize. To address this problem, a novel integrated sensor system has been developed to record cardiac vibration and cardiac potential simultaneously and synchronously from a single compact site on the chest. The developed sensor system is lightweight, small in size, and suitable for mounting on active moving patients. The sensor is evaluated for its adequacy in measuring cardiac vibrations and potentials. In this evaluation, 45 independent signal recording are studied from 15 volunteers, and the morphology of the recorded signals are analyzed qualitatively (by visual inspection) and quantitatively (by computational methods) against larger devices used in established cardiac vibration studies (reference devices). It is found that the cardiac vibration signals acquired by the integrated sensor has 92.37% and 81.76% identically identifiable systolic and diastolic cardiac complexes, respectively, when compared to the cardiac vibration signals recorded simultaneously from the reference device. Further, the cardiac potential signals acquired by the integrated sensor show a high correlation coefficient of 0.8912 and a high estimated signal-to-noise-ratio of 22.00 dB when compared to the reference electrocardiograph (non-standard leads) acquired through a common clinical machine. The results suggest that the tiny, wearable, integrated sensor system that synchronously measures cardiac vibrations and cardiac potentials may be practical for use as an alternative or assistive cardiac diagnostic tool.

  2. Measurement of the first ionization potential of astatine by laser ionization spectroscopy

    CERN Document Server

    Rothe, S; Antalic, S; Borschevsky, A; Capponi, L; Cocolios, T E; De Witte, H; Eliav, E; Fedorov, D V; Fedosseev, V N; Fink, D A; Fritzsche, S; Ghys, L; Huyse, M; Imai, N; Kaldor, U; Kudryavtsev, Yu; Köster, U; Lane, J; Lassen, J; Liberati, V; Lynch, K M; Marsh, B A; Nishio, K; Pauwels, D; Pershina, V; Popescu, L; Procter, T J; Radulov, D; Raeder, S; Rajabali, M M; Rapisarda, E; Rossel, R E; Sandhu, K; Seliverstov, M D; Sjödin, A M; Van den Bergh, P; Van Duppen, P; Venhart, M; Wakabayashi, Y; Wendt K D A

    2013-01-01

    The radioactive element astatine exists only in trace amounts in nature. Its properties can therefore only be explored by study of smallest quantities of artificially produced isotopes or by performing theoretical calculations. One of the most important properties influencing the chemical behaviour is the energy required to remove one electron from the valence shell, referred to as the ionization potential. Here we use laser spectroscopy to probe the optical spectrum of astatine near the ionization threshold. The observed series of Rydberg states enabled the first determination of the ionization potential of the astatine atom, 9.317510(8) eV. New ab initio calculations were performed to support the experimental result. The measured value serves as a benchmark for quantum chemistry calculations of the properties of astatine as well as for the theoretical prediction of the ionization potential of super-heavy element 117, the heaviest homologue of astatine.

  3. Recognition and measurement of potential share value of conversion for convertible bonds

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    To recognize and measure the potential share value of conversion for convertible bonds more accurately, different approaches such as the straight method, the separating method, the expected value approach and the improved approach are comparatively analyzed by taking China Merchants Bank's convertible bonds as an example. There is also a focus on the improved approach that views that convertible bond issue proceeds can be separated into accrual debt value, accrual equity value and accrual option value accor...

  4. The hot pick-up technique for batch assembly of van der Waals heterostructures

    DEFF Research Database (Denmark)

    Pizzocchero, Filippo; Gammelgaard, Lene; Jessen, Bjarke Sørensen

    2016-01-01

    The assembly of individual two-dimensional materials into van der Waals heterostructures enables the construction of layered three-dimensional materials with desirable electronic and optical properties. A core problem in the fabrication of these structures is the formation of clean interfaces bet...

  5. Dynamics of Gold Nanoparticles on Carbon Nanostructures Driven by van der Waals and Electrostatic Interactions.

    Science.gov (United States)

    La Torre, Alessandro; Gimenez-Lopez, Maria del Carmen; Fay, Michael W; Lucas, Carlos Herreros; Brown, Paul D; Khlobystov, Andrei N

    2015-06-01

    Transmission electron microscopy studies on the assembly and growth of gold nanoparticles on carbon nanotubes supported on few-layer graphene and amorphous carbon reveal a competition between van der Waals forces and electrostatic interactions, enabling controlled positioning and sizing of adsorbed nanoparticles at the nanochannels formed between the carbon nanotube and the few-layer graph-ene surface.

  6. Probing low-energy hyperbolic polaritons in van der Waals crystals with an electron microscope

    KAUST Repository

    Govyadinov, Alexander A.

    2017-07-14

    Van der Waals materials exhibit intriguing structural, electronic, and photonic properties. Electron energy loss spectroscopy within scanning transmission electron microscopy allows for nanoscale mapping of such properties. However, its detection is typically limited to energy losses in the eV range-too large for probing low-energy excitations such as phonons or mid-infrared plasmons. Here, we adapt a conventional instrument to probe energy loss down to 100 meV, and map phononic states in hexagonal boron nitride, a representative van der Waals material. The boron nitride spectra depend on the flake thickness and on the distance of the electron beam to the flake edges. To explain these observations, we developed a classical response theory that describes the interaction of fast electrons with (anisotropic) van der Waals slabs, revealing that the electron energy loss is dominated by excitation of hyperbolic phonon polaritons, and not of bulk phonons as often reported. Thus, our work is of fundamental importance for interpreting future low-energy loss spectra of van der Waals materials.Here the authors adapt a STEM-EELS system to probe energy loss down to 100 meV, and apply it to map phononic states in hexagonal boron nitride, revealing that the electron loss is dominated by hyperbolic phonon polaritons.

  7. Control of excitons in multi-layer van der Waals heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Calman, E. V., E-mail: ecalman@gmail.com; Dorow, C. J.; Fogler, M. M.; Butov, L. V. [Department of Physics, University of California at San Diego, La Jolla, California 92093-0319 (United States); Hu, S.; Mishchenko, A.; Geim, A. K. [School of Physics and Astronomy, University of Manchester, Manchester M13 9PL (United Kingdom)

    2016-03-07

    We report an experimental study of excitons in a double quantum well van der Waals heterostructure made of atomically thin layers of MoS{sub 2} and hexagonal boron nitride. The emission of neutral and charged excitons is controlled by gate voltage, temperature, and both the helicity and the power of optical excitation.

  8. Molecular interpretation of nonclassical gas dynamics of dense vapors under the van der Waals model

    NARCIS (Netherlands)

    Colonna, P.; Guardone, A.

    2006-01-01

    The van der Waals polytropic gas model is used to investigate the role of attractive and repulsive intermolecular forces and the influence of molecular complexity on the possible nonclassical gas dynamic behavior of vapors near the liquid-vapor saturation curve. The decrease of the sound speed upon

  9. Estimating spawning habitat availability in flooded areas of the river Waal, the Netherlands

    NARCIS (Netherlands)

    Wolfshaar, van de K.E.; Ruizeveld de Winter, A.C.; Straatsma, M.W.; Brink, N.G.M.; Leeuw, de J.J.

    2010-01-01

    Fish spawning habitat availability in the river Waal is significantly influenced by seasonal and annual variations in discharge. In this paper we develop habitat suitability models, based on a literature survey of spawning preferences of the commonly occurring species roach (Rutilus rutilus), bream

  10. Molecular van der Waals Space and Topological Indices from the Distance Matrix

    Directory of Open Access Journals (Sweden)

    Seiman Corina

    2004-12-01

    Full Text Available A comparative study of 36 molecular descriptors derived from the topologicaldistance matrix and van der Waals space is carried out within this paper. They arepartitioned into 16 generalized topological distance matrix indices, 11 topologicaldistance indices known in the literature (seven obtained from eigenvalues/eigenvectors ofdistance matrix, and 9 van der Waals molecular descriptors. The generalized topologicaldistance indices, kδλ (λ = 1 – 3, k = 1 – 4, are introduced in this work on the basis ofreciprocical distance matrix. Intercorrelation analysis reveals that topological distanceindices mostly contain the same type of information, while van der Waals indices can bebound to the shape or the size of molecules. Furthermore, we found that topologicaldistance indices are good for describing molecular size, and they may be viewed as bulkparameters. The most accurate QSPR models for predicting boiling point of alkanes arebased on some of the generalized, eigenvalues/eigenvectors topological distance indicesand the van der Waals descriptors of molecular size.

  11. Molecular interpretation of nonclassical gas dynamics of dense vapors under the van der Waals model

    NARCIS (Netherlands)

    Colonna, P.; Guardone, A.

    2006-01-01

    The van der Waals polytropic gas model is used to investigate the role of attractive and repulsive intermolecular forces and the influence of molecular complexity on the possible nonclassical gas dynamic behavior of vapors near the liquid-vapor saturation curve. The decrease of the sound speed upon

  12. A van der Waals Equation of State for a Dilute Boson Gas

    Science.gov (United States)

    Deeney, F. A.; O'Leary, J. P.

    2012-01-01

    An equation of state of a system is a relationship that connects the thermodynamic variables of the system such as pressure and temperature. Such equations are well known for classical gases but less so for quantum systems. In this paper we develop a van der Waals equation of state for a dilute boson gas that may be used to explain the occurrence…

  13. Theoretical investigation of van der Waals forces between solid surfaces at nanoscales

    NARCIS (Netherlands)

    Kudryavtsev, Y.V.; Gelinck, E.R.M.; Fischer, H.R.

    2009-01-01

    A theoretical investigation of van der Waals forces acting between two solid silicon surfaces at separations from zero to approximately 20 nm is presented. We focused our efforts on the analysis of different factors that can cause deviations from the classical pressure-distance dependence p ∼ 1/D3.

  14. Influence of ultrathin water layer on the van der Waals/Casimir force between gold surfaces

    NARCIS (Netherlands)

    Palasantzas, G.; Svetovoy, V. B.; van Zwol, P. J.

    In this paper we investigate the influence of ultrathin water layer (similar to 1-1.5 nm) on the van der Waals/Casimir force between gold surfaces. Adsorbed water is inevitably present on gold surfaces at ambient conditions as jump-up-to contact during adhesion experiments demonstrate. Calculations

  15. Theoretical investigation of van der Waals forces between solid surfaces at nanoscales

    NARCIS (Netherlands)

    Kudryavtsev, Y.V.; Gelinck, E.R.M.; Fischer, H.R.

    2009-01-01

    A theoretical investigation of van der Waals forces acting between two solid silicon surfaces at separations from zero to approximately 20 nm is presented. We focused our efforts on the analysis of different factors that can cause deviations from the classical pressure-distance dependence p ∼ 1/D3.

  16. van der Waals Density Functional Theory vdW-DFq for Semihard Materials

    Science.gov (United States)

    Peng, Qing; de, Suvranu

    There are a large number of materials with mild stiffness, which are not as soft as tissues and not as strong as metals. These semihard materials includes energetic materials, molecular crystals, layered materials, and van der Waals crystals. The integrity and mechanical stability are mainly determined by the interactions between instantaneously induced dipoles, the so called London dispersion force or van der Waals force. It is challenging to accurately model the structural and mechanical properties of these semihard materials in the frame of density functional theory where the non-local correlation functionals are not well known. Here we propose a van der Waals density functional named vdW-DFq to accurately model the density and geometry of semihard materials. Using β-cyclotetramethylene tetranitramine as a prototype, we adjust the enhancement factor of the exchange energy functional with generalized gradient approximations. We find this method to be simple and robust over a wide tuning range when calibrating the functional on-demand with experimental data. With a calibrated value q = 1 . 05 , the proposed vdW-DFq method shows good performance in predicting the geometries of 11 common energetic material molecular crystals and 3 typical layered van der Waals crystals. The authors would like to acknowledge the generous financial support from the Defense Threat Reduction Agency (DTRA) Grant # HDTRA1-13-1-0025.

  17. Is there a Difference in Van Der Waals Interactions between Rare Gas Atoms Adsorbed on Metallic and Semiconducting Single-Walled Carbon Nanotubes?

    Energy Technology Data Exchange (ETDEWEB)

    Chen, De-Li [Univ. of Pittsburgh, PA (United States). Dept. of Chemical and Petroleum Engineering; Mandeltort, Lynn [Univ. of Virginia, Charlottesville, VA (United States). Dept. of Chemistry; Saidi, Wissam A. [Univ. of Pittsburgh, PA (United States). Dept. of Chemical and Petroleum Engineering; Yates, John T. [Univ. of Virginia, Charlottesville, VA (United States). Dept. of Chemistry; Cole, Milton W. [Pennsylvania State Univ., University Park, PA (United States). Dept of Physics; Johnson, J. Karl [Univ. of Pittsburgh, PA (United States). Dept. of Chemical and Petroleum Engineering; National Energy Technology Lab. (NETL), Pittsburgh, PA, (United States)

    2013-03-01

    Differences in polarizabilities of metallic (M) and semiconducting (S) single-walled carbon nanotubes (SWNTs) might give rise to differences in adsorption potentials. We show from experiments and van der Waals-corrected density functional theory (DFT) that binding energies of Xe adsorbed on M- and S-SWNTs are nearly identical. Temperature programmed desorption of Xe on purified M- and S-SWNTs give similar peak temperatures, indicating that desorption kinetics and binding energies are independent of the type of SWNT. Binding energies computed from vdW-corrected DFT are in good agreement with experiments.

  18. Lennard-Jones parameters for small diameter carbon nanotubes and water for molecular mechanics simulations from van der Waals density functional calculations.

    Science.gov (United States)

    Kaukonen, M; Gulans, A; Havu, P; Kauppinen, E

    2012-03-05

    Lennard-Jones (LJ) parameters are derived for classical nonpolarizable force fields for carbon nanotubes (CNTs) and for CNT-water interaction from van der Waals (vdW) enhanced density functional calculations. The new LJ parameters for carbon-carbon interactions are of the same order as those previously used in the literature but differ significantly for CNT-water interactions. This may partially originate from the fact that in addition to pure vdW interactions the polarization and other quantum mechanics effects are embedded into the LJ-potential.

  19. Is there a difference in van der Waals interactions between rare gas atoms adsorbed on metallic and semiconducting single-walled carbon nanotubes?

    Science.gov (United States)

    Chen, De-Li; Mandeltort, Lynn; Saidi, Wissam A; Yates, John T; Cole, Milton W; Johnson, J Karl

    2013-03-29

    The differences in the polarizabilities of metallic (M) and semiconducting (S) single-walled carbon nanotubes (SWNTs) might give rise to differences in adsorption potentials. We show from experiments and van der Waals--corrected density functional theory that the binding energies of Xe adsorbed on M- and S-SWNTs are nearly identical. Temperature programed desorption experiments of Xe on purified M- and S-SWNTs give similar peak temperatures, indicating that desorption kinetics and binding energies are independent of the type of SWNT. Binding energies computed from vdW-corrected density functional theory are in good agreement with experiments.

  20. THz absorption spectrum of the CO2–H2O complex: Observation and assignment of intermolecular van der Waals vibrations

    OpenAIRE

    Andersen, Jonas; Heimdal, J.; Wallin Mahler Andersen, Denise; Nelander, B.; Larsen, René Wugt

    2014-01-01

    Terahertz absorption spectra have been recorded for the weakly bound CO2–H2O complex embedded in cryogenic neon matrices at 2.8 K. The three high-frequency van der Waals vibrational transitions associated with out-of-plane wagging, in-plane rocking, and torsional motion of the isotopic H2O subunit have been assigned and provide crucial observables for benchmark theoretical descriptions of this systems’ flat intermolecular potential energy surface. A (semi)-empirical value for the zero-point e...

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

    OpenAIRE

    Andersen, J.; Heimdal, Jimmy; Mahler, D W; Nelander, Bengt; Wugt Larsen, R

    2014-01-01

    Terahertz absorption spectra have been recorded for the weakly bound CO2-H2O complex embedded in cryogenic neon matrices at 2.8 K. The three high-frequency van der Waals vibrational transitions associated with out-of-plane wagging, in-plane rocking, and torsional motion of the isotopic H2O subunit have been assigned and provide crucial observables for benchmark theoretical descriptions of this systems' flat intermolecular potential energy surface. A (semi)-empirical value for the zero-poi...

  2. Measurement and analysis of postsynaptic potentials using a novel voltage-deconvolution method.

    Science.gov (United States)

    Richardson, Magnus J E; Silberberg, Gilad

    2008-02-01

    Accurate measurement of postsynaptic potential amplitudes is a central requirement for the quantification of synaptic strength, dynamics of short-term and long-term plasticity, and vesicle-release statistics. However, the intracellular voltage is a filtered version of the underlying synaptic signal and so a method of accounting for the distortion caused by overlapping postsynaptic potentials must be used. Here a voltage-deconvolution technique is demonstrated that defilters the entire voltage trace to reveal an underlying signal of well-separated synaptic events. These isolated events can be cropped out and reconvolved to yield a set of isolated postsynaptic potentials from which voltage amplitudes may be measured directly-greatly simplifying this common task. The method also has the significant advantage of providing a higher temporal resolution of the dynamics of the underlying synaptic signal. The versatility of the method is demonstrated by a variety of experimental examples, including excitatory and inhibitory connections to neurons with passive membranes and those with activated voltage-gated currents. The deconvolved current-clamp voltage has many features in common with voltage-clamp current measurements. These similarities are analyzed using cable theory and a multicompartment cell reconstruction, as well as direct comparison to voltage-clamp experiments.

  3. Frequency-Dependent Streaming Potential of Porous Media—Part 2: Experimental Measurement of Unconsolidated Materials

    Directory of Open Access Journals (Sweden)

    P. W. J. Glover

    2012-01-01

    Full Text Available Frequency-dependent streaming potential coefficient measurements have been made upon Ottawa sand and glass bead packs using a new apparatus that is based on an electromagnetic drive. The apparatus operates in the range 1 Hz to 1 kHz with samples of 25.4 mm diameter up to 150 mm long. The results have been analysed using theoretical models that are either (i based upon vibrational mechanics, (ii treat the geological material as a bundle of capillary tubes, or (iii treat the material as a porous medium. The best fit was provided by the Pride model and its simplification, which is satisfying as this model was conceived for porous media rather than capillary tube bundles. Values for the transition frequency were derived from each of the models for each sample and were found to be in good agreement with those expected from the independently measured effective pore radius of each material. The fit to the Pride model for all four samples was also found to be consistent with the independently measured steady-state permeability, while the value of the streaming potential coefficient in the low-frequency limit was found to be in good agreement with other steady-state streaming potential coefficient data.

  4. Bonded Paths and van der Waals Interactions in Orpiment, As2S3

    Energy Technology Data Exchange (ETDEWEB)

    Gibbs, Gerald V.; Wallace, Adam F.; Zallen, Richard; Downs, R. T.; Ross, Nancy L.; Cox, David F.; Rosso, Kevin M.

    2010-06-17

    Bond critical properties and bond paths have been calculated for the thioarsenide molecular crystal orpiment, As2S3. In addition to the intramolecular As-S bond paths and van der Waals As-S and S-S bond paths within the layers, intermolecular S-S, As-S and As-As van der Waals paths exist between the layers. The S-S bond paths between the layers are identified with the main interlayer restoring forces responsible for the vibrational internal-mode splitting and the low frequency rigid layer modes previously documented in infrared and Raman studies of orpiment. These S-S bond paths are comparable with those calculated for orthorhombic native sulfur and the As4Sn (n = 3,4,5) molecules for several arsenide molecular crystals. The As-S bond paths show that the two nonequivalent arsenic atoms are each coordinated by a highly distorted octahedral array of sulfur atoms. The octahedra consist of three As-S intramolecular bonded interactions and three longer van der Waals interactions (two intramolecular and one intermolecular). One of the arsenic atoms is also coordinated by an arsenic atom in an interlayer As-As bonded interaction. Laplacian isosurface envelopes calculated for the arsenic and sulfur atoms are comparable with those calculated for native arsenic and orthorhombic sulfur. The intermolecular As-S bond paths connect Lewis acid domains on arsenic and an Lewis base domains on sulfur. Van der Waals interactions are traditionally defined as attractive interactions other than those ascribed to bond formation. However, theoretical evidence and arguments, as well as the connection between the bond paths and the vibrational spectra, indicate that the van der Waals interactions in orpiment are directed bonded interactions in the Slater sense. The experimental bond lengths for the As-S and S-S bonded interactions decrease nonlinearly with the increasing value of the electron density at the bond critical point, concomitant with a decrease in the bonded radii of arsenic and

  5. Comparative study of van der Waals corrections to the bulk properties of graphite.

    Science.gov (United States)

    Rêgo, Celso R C; Oliveira, Luiz N; Tereshchuk, Polina; Da Silva, Juarez L F

    2015-10-21

    Graphite is a stack of honeycomb (graphene) layers bound together by nonlocal, long-range van der Waals (vdW) forces, which are poorly described by density functional theory (DFT) within local or semilocal exchange-correlation functionals. Several approximations have been proposed to add a vdW correction to the DFT total energies (Stefan Grimme (D2 and D3) with different damping functions (D3-BJ), Tkatchenko-Scheffler (TS) without and with self-consistent screening (TS  +  SCS) effects). Those corrections have remarkly improved the agreement between our results and experiment for the interlayer distance (from 3.9 to 0.6%) [corrected] and high-level random-phase approximation (RPA) calculations for interlayer binding energy (from 69.5 to 1.5%). [corrected]. We report a systematic investigation of various structural, energetic and electron properties with the aforementioned vdW corrections followed by comparison with experimental and theoretical RPA data. Comparison between the resulting relative errors shows that the TS  +  SCS correction provides the best results; the other corrections yield significantly larger errors for at least one of the studied properties. If considerations of computational costs or convergence problems rule out the TS  +  SCS approach, we recommend the D3-BJ correction. Comparison between the computed π(z)Γ-splitting and experimental results shows disagreements of 10% or more with all vdW corrections. Even the computationally more expensive hybrid PBE0 has proved unable to improve the agreement with the measured splitting. Our results indicate that improvements of the exchange-correlation functionals beyond the vdW corrections are necessary to accurately describe the band structure of graphite.

  6. Photoionisation study of Xe.CF4 and Kr.CF4 van-der-Waals molecules.

    Science.gov (United States)

    Alekseev, V A; Garcia, G A; Kevorkyants, R; Nahon, L

    2016-05-14

    We report on photoionization studies of Xe.CF4 and Kr.CF4 van-der-Waals complexes produced in a supersonic expansion and detected using synchrotron radiation and photoelectron-photoion coincidence techniques. The ionization potential of CF4 is larger than those of the Xe and Kr atoms and the ground state of the Rg.CF4 (+) ion correlates with Rg(+) ((2)P3/2) + CF4. The onset of the Rg.CF4 (+) signals was found to be only ∼0.2 eV below the Rg ionization potential. In agreement with experiment, complementary ab initio calculations show that vertical transitions originating from the potential minimum of the ground state of Rg.CF4 terminate at a part of the potential energy surfaces of Rg.CF4 (+), which are approximately 0.05 eV below the Rg(+) ((2)P3/2) + CF4 dissociation limit. In contrast to the neutral complexes, which are most stable in the face geometry, for the Rg.CF4 (+) ions, the calculations show that the minimum of the potential energy surface is in the vertex geometry. Experiments which have been performed only with Xe.CF4 revealed no Xe.CF4 (+) signal above the first ionization threshold of Xe, suggesting that the Rg.CF4 (+) ions are not stable above the first dissociation limit.

  7. Surface and interface of epitaxial CdTe film on CdS buffered van der Waals mica substrate

    Science.gov (United States)

    Yang, Y.-B.; Seewald, L.; Mohanty, Dibyajyoti; Wang, Y.; Zhang, L. H.; Kisslinger, K.; Xie, Weiyu; Shi, J.; Bhat, I.; Zhang, Shengbai; Lu, T.-M.; Wang, G.-C.

    2017-08-01

    Single crystal CdTe films are desirable for optoelectronic device applications. An important strategy of creating films with high crystallinity is through epitaxial growth on a proper single crystal substrate. We report the metalorganic chemical vapor deposition of epitaxial CdTe films on the CdS/mica substrate. The epitaxial CdS film was grown on a mica surface by thermal evaporation. Due to the weak van der Waals forces, epitaxy is achieved despite the very large interface lattice mismatch between CdS and mica (∼21-55%). The surface morphology of mica, CdS and CdTe were quantified by atomic force microscopy. The near surface structures, orientations and texture of CdTe and CdS films were characterized by the unique reflection high-energy electron diffraction surface pole figure technique. The interfaces of CdTe and CdS films and mica were characterized by X-ray pole figure technique and transmission electron microscopy. The out-of-plane and in-plane epitaxy of the heteroepitaxial films stack are determined to be CdTe(111)//CdS(0001)//mica(001) and [ 1 bar2 1 bar]CdTe//[1 bar100]CdS//[010]mica, respectively. The measured photoluminescence (PL), time resolved PL, photoresponse, and Hall mobility of the CdTe/CdS/mica indicate quality films. The use of van der Waals surface to grow epitaxial CdTe/CdS films offers an alternative strategy towards infrared imaging and solar cell applications.

  8. Defining function of lipopolysaccharide O-antigen ligase WaaL using chemoenzymatically synthesized substrates.

    Science.gov (United States)

    Han, Weiqing; Wu, Baolin; Li, Lei; Zhao, Guohui; Woodward, Robert; Pettit, Nicholas; Cai, Li; Thon, Vireak; Wang, Peng G

    2012-02-17

    The WaaL-mediated ligation of O-antigen onto the core region of the lipid A-core block is an important step in the lipopolysaccharide (LPS) biosynthetic pathway. Although the LPS biosynthesis has been largely characterized, only a limited amount of in vitro biochemical evidence has been established for the ligation reaction. Such limitations have primarily resulted from the barriers in purifying WaaL homologues and obtaining chemically defined substrates. Accordingly, we describe herein a chemical biology approach that enabled the reconstitution of this ligation reaction. The O-antigen repeating unit (O-unit) of Escherichia coli O86 was first enzymatically assembled via sequential enzymatic glycosylation of a chemically synthesized GalNAc-pyrophosphate-undecaprenyl precursor. Subsequent expression of WaaL through use of a chaperone co-expression system then enabled the demonstration of the in vitro ligation between the synthesized donor (O-unit-pyrophosphate-undecaprenyl) and the isolated lipid A-core acceptor. The previously reported ATP and divalent metal cation dependence were not observed using this system. Further analyses of other donor substrates revealed that WaaL possesses a highly relaxed specificity toward both the lipid moiety and the glycan moiety of the donor. Lastly, three conserved amino acid residues identified by sequence alignment were found essential for the WaaL activity. Taken together, the present work represents an in vitro systematic investigation of the WaaL function using a chemical biology approach, providing a system that could facilitate the elucidation of the mechanism of WaaL-catalyzed ligation reaction.

  9. Effect of sampling frequency on the measurement of phase-locked action potentials.

    Directory of Open Access Journals (Sweden)

    Go eAshida

    2010-09-01

    Full Text Available Phase-locked spikes in various types of neurons encode temporal information. To quantify the degree of phase-locking, the metric called vector strength (VS has been most widely used. Since VS is derived from spike timing information, error in measurement of spike occurrence should result in errors in VS calculation. In electrophysiological experiments, the timing of an action potential is detected with finite temporal precision, which is determined by the sampling frequency. In order to evaluate the effects of the sampling frequency on the measurement of VS, we derive theoretical upper and lower bounds of VS from spikes collected with finite sampling rates. We next estimate errors in VS assuming random sampling effects, and show that our theoretical calculation agrees with data from electrophysiological recordings in vivo. Our results provide a practical guide for choosing the appropriate sampling frequency in measuring VS.

  10. Fluid flow monitoring in oilfields using downhole measurements of electrokinetic potential

    Science.gov (United States)

    Jackson, M. D.; Saunders, J. H.; Pain, C. C.

    2006-12-01

    Permanently installed downhole sensors are increasingly being deployed to provide `real-time' reservoir data during hydrocarbon production, which helps to reduce uncertainty in the reservoir description and contributes to reservoir management decisions. Where wells are equipped with inflow control valves (so called `intelligent' wells), it is possible to develop a feedback loop between measurement and control to optimize production. We suggest that measurements of electrokinetic potential during production, using permanently installed downhole electrodes, could be used to detect water encroachment towards an intelligent oil well. Downhole electrodes mounted at the production well on the outside of insulated casing, have been successfully applied in subsurface resistivity surveys during oil production. Similar technology could be used to measure electrokinetic potential. Moreover, recent and ongoing work has changed our understanding of electrokinetic coupling under two-phase conditions. We present the results of numerical simulations of fluid movement during hydrocarbon production, using a new formulation which captures both the changing fluid distributions and the resulting electrical potentials. We suggest that encroaching water causes changes in electrokinetic potential at the production well which could be resolved above background electrical noise; indeed, changes in water saturation could be detected several 10's to 100's of metres away from the well. This contrasts with most other downhole monitoring techniques, which sample only the region immediately adjacent to the wellbore. Signal resolution is improved if the water has a relatively low salinity, and the pressure gradient into the well is large. However, significant uncertainties remain concerning the nature of electrokinetic coupling during the flow of oil and water, particularly in mixed and oil-wet reservoirs.

  11. Microscopic Measurements of Electrical Potential in Hydrogenated Nanocrystalline Silicon Solar Cells: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, C. S.; Moutinho, H. R.; Reedy, R. C.; Al-Jassim, M. M.; Yan, B.; Yue, G.; Sivec, L.; Yang, J.; Guha, S.; Tong, X.

    2012-04-01

    We report on a direct measurement of electrical potential and field profiles across the n-i-p junction of hydrogenated nanocrystalline silicon (nc-Si:H) solar cells, using the nanometer-resolution potential imaging technique of scanning Kelvin probe force microscopy (SKPFM). It was observed that the electric field is nonuniform across the i layer. It is much higher in the p/i region than in the middle and the n/i region, illustrating that the i layer is actually slightly n-type. A measurement on a nc-Si:H cell with a higher oxygen impurity concentration shows that the nonuniformity of the electric field is much more pronounced than in samples having a lower O impurity, indicating that O is an electron donor in nc-Si:H materials. This nonuniform distribution of electric field implies a mixture of diffusion and drift of carrier transport in the nc-Si:H solar cells. The composition and structure of these nc-Si:H cells were further investigated by using secondary-ion mass spectrometry and Raman spectroscopy, respectively. The effects of impurity and structural properties on the electrical potential distribution and solar cell performance are discussed.

  12. Metal Semiconductor Field-Effect Transistor with MoS2/Conducting NiO(x) van der Waals Schottky Interface for Intrinsic High Mobility and Photoswitching Speed.

    Science.gov (United States)

    Lee, Hee Sung; Baik, Seung Su; Lee, Kimoon; Min, Sung-Wook; Jeon, Pyo Jin; Kim, Jin Sung; Choi, Kyujin; Choi, Hyoung Joon; Kim, Jae Hoon; Im, Seongil

    2015-08-25

    Molybdenum disulfide (MoS2) nanosheet, one of two-dimensional (2D) semiconductors, has recently been regarded as a promising material to break through the limit of present semiconductors. With an apparent energy band gap, it certainly provides a high carrier mobility, superior subthreshold swing, and ON/OFF ratio in field-effect transistors (FETs). However, its potential in carrier mobility has still been depreciated since the field-effect mobilities have only been measured from metal-insulator-semiconductor (MIS) FETs, where the transport behavior of conducting carriers located at the insulator/MoS2 interface is unavoidably interfered by the interface traps and gate voltage. Moreover, thin MoS2 MISFETs have always shown large hysteresis with unpredictable negative threshold voltages. Here, we for the first time report MoS2-based metal semiconductor field-effect transistors (MESFETs) using NiOx Schottky electrode which makes van der Waals interface with MoS2. We thus expect that the maximum mobilities or carrier transport behavior of the Schottky devices may hardly be interfered by interface traps or an on-state gate field. Our MESFETs with a few and ∼10 layer MoS2 demonstrate intrinsic-like high mobilities of 500-1200 cm(2)/(V s) at a certain low threshold voltage between -1 and -2 V without much hysteresis. Moreover, they work as a high speed and highly sensitive phototransistor with 2 ms switching and ∼5000 A/W, respectively, supporting their high intrinsic mobility results.

  13. Efimov Physics and the Three-Body Parameter for Shallow van der Waals Potentials

    Science.gov (United States)

    Blume, D.

    2015-12-01

    Extremely weakly-bound three-boson systems are predicted to exhibit intriguing universal properties such as discrete scale invariance. Motivated by recent experimental studies of the ground and excited helium trimers, this work analyzes the three-body parameter and the structural properties of three helium atoms as the s-wave scattering length is tuned artificially. Connections with theoretical and experimental studies of the Efimov scenario as it pertains to cold atom systems are made.

  14. Environmental Signatures for Habitability: What to Measure and How to Rank the Habitability Potential of Mars

    Science.gov (United States)

    Conrad, Pamela G.; Eigenbrode, Jennifer L.; Mahaffy, Paul M.; Steele, Andrew

    2011-01-01

    The environmental signatures for habitability are not necessarily biosignatures, even though on Earth, they are definitive proof of habitability. It is the constant overprint of the chemical signatures of life that makes it difficult to recognize the chemical and physical properties of a potentially habitable environment as distinct from an inhabited one. Mars Science Laboratory (MSL) will soon embark on a mission to Mars to assess its past or present habitability, so it is useful to examine how we measure habitability on Earth and prepare for how that approach may differ for Mars. This exercise includes: (a) articulation of fundamental assumptions about habitability, (b) an inventory of factors that affect habitability, (c) development of metrics, measurement approach and implementation, and (d) a new classification scheme for planetary habitability that goes beyond the binary "yes" or "no." There may be dozens of factors that affect habitability and they can be weighted as a function of specific environment. However a robotic, in situ investigation even on Earth has constraints that prevent the measurement of every environmental factor, so metrics must be reduced to the most relevant subset, given available time, cost, technical feasibility and scientific importance. Many of the factors could be measured with a combination of orbital data and the MSL payload. We propose that, at a minimum, a designation of high habitability potential requires the following conditions be met: (a) thermally stable with respect to extremes and frequency of fluctuation, (b) has more than one energy source, (c) sufficient chemical diversity to make compounds with covalent and hydrogen bonding, (d) can moderate ionizing radiation enough to allow a stable or evolving pool of organic molecules, (e) must have water or other high quality polar solvent, (f) must be able to renew chemical resources (e.g., plate tectonics, volcanism or something else we haven't envisioned). A measurement

  15. O2, pH, and redox potential microprofiles around Potamogeton malaianus measured using microsensors.

    Directory of Open Access Journals (Sweden)

    Bin Dong

    Full Text Available This study aimed to elucidate the effects of periphyton on the microprofiles of oxygen (O2, pH, and oxidation-reduction potential around the stems and leaves of a submerged macrophyte Potamogeton malaianus and on the plant growth in the eutrophic shallow Taihu Lake, China. The microprofiles were measured using a motorized microprofiling system equipped with microsensors. The leaf age of the macrophyte and periphyton exerted significant effects on the microprofiles of O2, pH, and oxidation-reduction potential. O2 concentration and pH increased whereas the oxidation-reduction potential decreased with decreasing distance to the stem/leaf surface. The fluctuation amplitudes of O2, pH, and oxidation-reduction potential were the largest in the microprofiles of mature leaves and the lowest in senescent leaves. The periphyton increased the thickness of the broad diffusive boundary layer and fluctuation amplitudes of O2, pH, and oxidation-reduction potential. When the periphyton was removed, the thickness of the broad diffusive boundary layer in the microprofiles of stems, senescent leaves, and mature leaves reduced by 29.0%, 49.72%, and 70.34%, and the O2, pH, and oxidation-reduction potential fluctuation amplitudes also declined accordingly. Our results suggest that a thick periphyton exerted negative effects on the growth of macrophytes by providing extensive shading and creating a barrier that hindered the transport of dissolved substances such as O2, and led to premature decline in macrophytes in the eutrophic Taihu Lake. The consequent implications can help to elucidate the control mechanism of the broad diffusive boundary layer around macrophytes on nutrient cycling in eutrophic waters and to better understand the role of this layer in the Taihu Lake and other similar eutrophic waters.

  16. Surveillance indicators for potential reduced exposure products (PREPs: developing survey items to measure awareness

    Directory of Open Access Journals (Sweden)

    McNeill Ann

    2009-10-01

    Full Text Available Abstract Background Over the past decade, tobacco companies have introduced cigarettes and smokeless tobacco products (known as Potential Reduced Exposure Products, PREPs with purportedly lower levels of some toxins than conventional cigarettes and smokeless products. It is essential that public health agencies monitor awareness, interest, use, and perceptions of these products so that their impact on population health can be detected at the earliest stages. Methods This paper reviews and critiques existing strategies for measuring awareness of PREPs from 16 published and unpublished studies. From these measures, we developed new surveillance items and subjected them to two rounds of cognitive testing, a common and accepted method for evaluating questionnaire wording. Results Our review suggests that high levels of awareness of PREPs reported in some studies are likely to be inaccurate. Two likely sources of inaccuracy in awareness measures were identified: 1 the tendency of respondents to misclassify "no additive" and "natural" cigarettes as PREPs and 2 the tendency of respondents to mistakenly report awareness as a result of confusion between PREPs brands and similarly named familiar products, for example, Eclipse chewing gum and Accord automobiles. Conclusion After evaluating new measures with cognitive interviews, we conclude that as of winter 2006, awareness of reduced exposure products among U.S. smokers was likely to be between 1% and 8%, with the higher estimates for some products occurring in test markets. Recommended measurement strategies for future surveys are presented.

  17. Inferring the gravitational potential of the Milky Way with a few precisely measured stars

    CERN Document Server

    Price-Whelan, Adrian M; Johnston, Kathryn V; Hendel, David

    2014-01-01

    The dark matter halo of the Milky Way is expected to be triaxial and filled with substructure. It is hoped that streams or shells of stars produced by tidal disruption of stellar systems will provide precise measures of the gravitational potential to test these predictions. We develop a method for inferring the Galactic potential with tidal streams based on the idea that the stream stars were once close in phase space. Our method can flexibly adapt to any form for the Galactic potential: it works in phase-space rather than action-space and hence relies neither on our ability to derive actions nor on the integrability of the potential. Our model is probabilistic, with a likelihood function and priors on the parameters. The method can properly account for finite observational uncertainties and missing data dimensions. We test our method on synthetic datasets generated from N-body simulations of satellite disruption in a static, multi-component Milky Way including a triaxial dark matter halo with observational u...

  18. Iridium Oxide Nanotube Electrodes for Highly Sensitive and Prolonged Intracellular Measurement of Action Potentials

    Science.gov (United States)

    Lin, Ziliang Carter; Xie, Chong; Osakada, Yasuko; Cui, Yi; Cui, Bianxiao

    2014-01-01

    Intracellular recording of action potentials is important to understand electrically-excitable cells. Recently, vertical nanoelectrodes have been developed to achieve highly sensitive, minimally invasive, and large scale intracellular recording. It has been demonstrated that the vertical geometry is crucial for the enhanced signal detection. Here we develop nanoelectrodes made up of nanotubes of iridium oxide. When cardiomyocytes are cultured upon those nanotubes, the cell membrane not only wraps around the vertical tubes but also protrudes deep into the hollow center. We show that this geometry enhances cell-electrode coupling and results in measuring much larger intracellular action potentials. The nanotube electrodes afford much longer intracellular access and are minimally invasive, making it possible to achieve stable recording up to an hour in a single session and more than 8 days of consecutive daily recording. This study suggests that the electrode performance can be significantly improved by optimizing the electrode geometry. PMID:24487777

  19. Alpha-Glucosidase Enzyme Biosensor for the Electrochemical Measurement of Antidiabetic Potential of Medicinal Plants

    Science.gov (United States)

    Mohiuddin, M.; Arbain, D.; Islam, A. K. M. Shafiqul; Ahmad, M. S.; Ahmad, M. N.

    2016-02-01

    A biosensor for measuring the antidiabetic potential of medicinal plants was developed by covalent immobilization of α-glucosidase (AG) enzyme onto amine-functionalized multi-walled carbon nanotubes (MWCNTs-NH2). The immobilized enzyme was entrapped in freeze-thawed polyvinyl alcohol (PVA) together with p-nitrophenyl-α- d-glucopyranoside (PNPG) on the screen-printed carbon electrode at low pH to prevent the premature reaction between PNPG and AG enzyme. The enzymatic reaction within the biosensor is inhibited by bioactive compounds in the medicinal plant extracts. The capability of medicinal plants to inhibit the AG enzyme on the electrode correlates to the potential of the medicinal plants to inhibit the production of glucose from the carbohydrate in the human body. Thus, the inhibition indicates the antidiabetic potential of the medicinal plants. The performance of the biosensor was evaluated to measure the antidiabetic potential of three medicinal plants such as Tebengau ( Ehretis laevis), Cemumar ( Micromelum pubescens), and Kedondong ( Spondias dulcis) and acarbose (commercial antidiabetic drug) via cyclic voltammetry, amperometry, and spectrophotometry. The cyclic voltammetry (CV) response for the inhibition of the AG enzyme activity by Tebengau plant extracts showed a linear relation in the range from 0.423-8.29 μA, and the inhibition detection limit was 0.253 μA. The biosensor exhibited good sensitivity (0.422 μA/mg Tebengau plant extracts) and rapid response (22 s). The biosensor retains approximately 82.16 % of its initial activity even after 30 days of storage at 4 °C.

  20. Recombinant albumin adsorption on mica studied by AFM and streaming potential measurements.

    Science.gov (United States)

    Kujda, Marta; Adamczyk, Zbigniew; Morga, Maria; Sofińska, Kamila

    2015-03-01

    Recombinant human serum albumin (rHSA) in monomeric state is widely used in pharmaceutical industry as a drug excipient and for preparing coatings for medical devices. In this work the adsorption process of rHSA on model mica surface at pH 3.5 was studied using the atomic force microscopy (AFM) and in situ streaming potential measurements. The kinetics of albumin adsorption was determined by a direct enumeration of single molecules over various substrate areas. These results were consistent with streaming potential measurements carried out for the parallel-plate channel flow and with theoretical predictions derived from the random sequential adsorption (RSA) model. Desorption kinetics of albumin under flow conditions was also evaluated via the streaming potential measurements. In this way, the amount of irreversibly bound albumin was quantitatively evaluated to be 0.64 and 1.2 mg m(-2) for ionic strength of 0.01 and 0.15 M, respectively. This agrees with previous results obtained for HSA and theoretical calculations derived from the RSA model. Additionally, it was demonstrated that there existed a fraction of reversibly bound albumin that can be fully eluted within a few hours. The binding energy of these fraction of molecules was -18 kT that is consistent with the electrostatic controlled adsorption mechanism of albumin at this pH. It was concluded that the rHSA monolayers of well-defined coverage can find applications for quantitatively analyzing ligand binding and for performing efficient biomaterials and immunological tests.

  1. Are non-linear C-H⋯O contacts hydrogen bonds or Van der Waals interactions?. Establishing the limits between hydrogen bonds and Van der Waals interactions

    Science.gov (United States)

    Novoa, Juan J.; Lafuente, Pilar; Mota, Fernando

    1998-07-01

    The hydrogen bond nature of angular C-H⋯O contacts is examined to determine when these contacts are better classified as hydrogen bonds or as Van der Waals bonds. To classify the bond we propose to look at the nature of the intermolecular bond critical point present in the electron density of the complex containing the bond. The physics behind this approach is explained using a qualitative orbital overlap model aimed at describing the main changes in the electronic density of the complex produced by the C-H⋯O bending.

  2. Direct Measurements of the Ionization Potential Depression in a Dense Plasma

    Science.gov (United States)

    Ciricosta, O.; Vinko, S. M.; Chung, H.-K.; Cho, B.-I.; Brown, C. R. D.; Burian, T.; Chalupský, J.; Engelhorn, K.; Falcone, R. W.; Graves, C.; Hájková, V.; Higginbotham, A.; Juha, L.; Krzywinski, J.; Lee, H. J.; Messerschmidt, M.; Murphy, C. D.; Ping, Y.; Rackstraw, D. S.; Scherz, A.; Schlotter, W.; Toleikis, S.; Turner, J. J.; Vysin, L.; Wang, T.; Wu, B.; Zastrau, U.; Zhu, D.; Lee, R. W.; Heimann, P.; Nagler, B.; Wark, J. S.

    2012-08-01

    We have used the Linac Coherent Light Source to generate solid-density aluminum plasmas at temperatures of up to 180 eV. By varying the photon energy of the x rays that both create and probe the plasma, and observing the K-α fluorescence, we can directly measure the position of the K edge of the highly charged ions within the system. The results are found to disagree with the predictions of the extensively used Stewart-Pyatt model, but are consistent with the earlier model of Ecker and Kröll, which predicts significantly greater depression of the ionization potential.

  3. Waste explosives and other hazardous materials--hazard potential and remedial measures: an overview.

    Science.gov (United States)

    Pandey, R K; Asthana, S N; Bhattacharya, B; Tiwari, Ila; Ghole, V S

    2007-07-01

    A large amount of energetic materials including propellants, high explosives, pyrotechnics are subjected to disposal either due to expiry of their useful life or rejection in the manufacturing process. The environmental regulations do not allow the hazardous materials for open burning / detonation in view of the health hazard involved in these operations. The present paper describes the hazard potential of energetic materials and associated hazardous chemicals. It also deals with global technological status for remedial measures of hazardous chemicals along with their merits and demerits.

  4. Information Theoretic Global Measures of Dirac Equation With Morse and Trigonometric Rosen-Morse Potentials

    Science.gov (United States)

    Najafizade, S. A.; Hassanabadi, H.; Zarrinkamar, S.

    2017-09-01

    In this study, the information-theoretic measures of (1+1)-dimensional Dirac equation in both position and momentum spaces are investigated for the trigonometric Rosen-Morse and the Morse potentials. The solutions of the corresponding Dirac equation are obtained in an exact analytical manner in the first step. Next, using the Fourier transformation, the position and momentum Shannon information entropies are obtained and some features of the probability densities are analyzed. The consistency with Bialynicki-Birula-Mycielski inequality and Heisenberg uncertainty is checked.

  5. Potential of [{sup 11}C]DASB for measuring endogenous serotonin with PET: binding studies

    Energy Technology Data Exchange (ETDEWEB)

    Lundquist, Pinelopi [Division of Pharmacokinetics and Drug Therapy, Department of Pharmaceutical Biosciences, Uppsala University, SE-751 24 Uppsala (Sweden) and Hospital Pharmacy, University Hospital, SE-751 85 Uppsala (Sweden)]. E-mail: pinelopi.lundquist@farmbio.uu.se; Wilking, Helena [Uppsala Imanet, SE-751 09 Uppsala (Sweden); Hoeglund, A. Urban [Uppsala Imanet, SE-751 09 Uppsala (Sweden); Sandell, Johan [Uppsala Imanet, SE-751 09 Uppsala (Sweden); Bergstroem, Mats [Uppsala Imanet, SE-751 09 Uppsala (Sweden); Hartvig, Per [Hospital Pharmacy, University Hospital, SE-751 85 Uppsala (Sweden); Langstroem, Bengt [Uppsala Imanet, SE-751 09 Uppsala (Sweden)

    2005-02-01

    The serotonin transporter radioligand [{sup 11}C]-3-amino-4-(2-dimethylaminomethylphenylsulfanyl)-benzonitrile, or [{sup 11}C]DASB, was examined in order to assess its potential for measuring fluctuations in endogenous serotonin concentrations with positron emission tomography. Binding characteristics of [{sup 11}C]DASB and the propensity for serotonin to displace the tracer were explored in rat brain homogenates. Experiments showed that serotonin displaced [{sup 11}C]DASB in vitro. Ex vivo experiments performed after tranylcypromine injection (3 or 15 mg/kg) showed a dose-dependent trend in radioactivity uptake and suggested that serotonin may compete with [{sup 11}C]DASB for transporter binding.

  6. Measurements of the streaming potential of clay soils from tropical and subtropical regions using self-made apparatus.

    Science.gov (United States)

    Li, Zhong-Yi; Li, Jiu-Yu; Liu, Yuan; Xu, Ren-Kou

    2014-09-01

    The streaming potential has been wildly used in charged parallel plates, capillaries, and porous media. However, there have been few studies involving the ζ potential of clay soils based on streaming potential measurements. A laboratory apparatus was developed in this study to measure the streaming potential (ΔE) of bulk clay soils' coupling coefficient (C) and cell resistance (R) of saturated granular soil samples. Excellent linearity of ΔE versus liquid pressure (ΔP) ensured the validity of measurements. The obtained parameters of C and R can be used to calculate the ζ potential of bulk soils. The results indicated that the ζ potentials measured by streaming potential method were significantly correlated with the ζ potentials of soil colloids determined by electrophoresis (r (2) = 0.960**). Therefore, the streaming potential method can be used to study the ζ potentials of bulk clay soils. The absolute values of the ζ potentials of four soils followed the order: Ultisol from Jiangxi > Ultisol from Anhui > Oxisol from Guangdong > Oxisol from Hainan, and this was consistent with the cation exchange capacities of these soils. The type and concentration of electrolytes affected soil ζ potentials. The ζ potential became less negative with increased electrolyte concentration. The ζ potentials were more negative in monovalent than in divalent cationic electrolyte solutions because more divalent cations were distributed in the shear plane of the diffuse layer as counter-cations on the soil surfaces than monovalent cations at the same electrolyte concentration.

  7. In-situ epitaxial growth of graphene/h-BN van der Waals heterostructures by molecular beam epitaxy.

    Science.gov (United States)

    Zuo, Zheng; Xu, Zhongguang; Zheng, Renjing; Khanaki, Alireza; Zheng, Jian-Guo; Liu, Jianlin

    2015-10-07

    Van der Waals materials have received a great deal of attention for their exceptional layered structures and exotic properties, which can open up various device applications in nanoelectronics. However, in situ epitaxial growth of dissimilar van der Waals materials remains challenging. Here we demonstrate a solution for fabricating van der Waals heterostructures. Graphene/hexagonal boron nitride (h-BN) heterostructures were synthesized on cobalt substrates by using molecular beam epitaxy. Various characterizations were carried out to evaluate the heterostructures. Wafer-scale heterostructures consisting of single-layer/bilayer graphene and multilayer h-BN were achieved. The mismatch angle between graphene and h-BN is below 1°.

  8. Beyond measures and monitoring: Realizing the potential of feedback-informed treatment.

    Science.gov (United States)

    Miller, Scott D; Hubble, Mark A; Chow, Daryl; Seidel, Jason

    2015-12-01

    More than a dozen randomized controlled trials and several meta-analyses have provided strong empirical support for routine outcome monitoring (ROM) in clinical practice. Despite current enthusiasm, advances in implementation, and the growing belief among some proponents and policymakers that ROM represents a major revolution in the practice of psychotherapy, other research has suggested that the focus on measurement and monitoring is in danger of missing the point. Any clinical tool or technology is only as good as the therapist who uses it. Failing to attend to the therapist's contribution, the long neglected variable in psychotherapy outcome, ensures that efforts to create, research, and refine new outcome measurement systems will inevitably fall short. Research from the field of expertise and expert performance provides guidance for realizing the full potential of ROM.

  9. Photoacoustically Measured Speeds of Sound of Liquid HBO2: On Unlocking the Fuel Potential of Boron

    Energy Technology Data Exchange (ETDEWEB)

    Bastea, S; Crowhurst, J; Armstrong, M; ., N T

    2010-03-24

    Elucidation of geodynamic, geochemical, and shock induced processes is often limited by challenges to accurately determine molecular fluid equations of state (EOS). High pressure liquid state reactions of carbon species underlie physiochemical mechanisms such as differentiation of planetary interiors, deep carbon sequestration, propellant deflagration, and shock chemistry. Here we introduce a versatile photoacoustic technique developed to measure accurate and precise speeds of sound (SoS) of high pressure molecular fluids and fluid mixtures. SoS of an intermediate boron oxide, HBO{sub 2} are measured up to 0.5 GPa along the 277 C isotherm. A polarized Exponential-6 interatomic potential form, parameterized using our SoS data, enables EOS determinations and corresponding semi-empirical evaluations of > 2000 C thermodynamic states including energy release from bororganic formulations. Our thermochemical model propitiously predicts boronated hydrocarbon shock Hugoniot results.

  10. Reactor Materials Program electrochemical potential measurements by ORNL with unirradiated and irradiated stainless steel specimens

    Energy Technology Data Exchange (ETDEWEB)

    Baumann, E.W.; Caskey, G.R. Jr.

    1993-07-01

    Effect of irradiation of stainless steel on electrochemical potential (ECP) was investigated by measurements in dilute HNO{sub 3} and H{sub 2}O{sub 2} solutions, conditions simulating reactor moderator. The electrodes were made from unirradiated/irradiated, unsensitized/sensitized specimens from R-reactor piping. Results were inconclusive because of budgetary restrictions. The dose rate may have been too small to produce a significant radiolytic effect. Neither the earlier CERT corrosion susceptibility tests nor the present ECP measurements showed a pronounced effect of irradiation on susceptibility of the stainless steel to IGSCC; this is confirmed by the absence in the stainless steel of the SRS reactor tanks (except for the C Reactor tank knuckle area).

  11. The importance of measuring and accounting for potential biases in respondent-driven samples.

    Science.gov (United States)

    Rudolph, Abby E; Fuller, Crystal M; Latkin, Carl

    2013-07-01

    Respondent-driven sampling (RDS) is often viewed as a superior method for recruiting hard-to-reach populations disproportionately burdened with poor health outcomes. As an analytic approach, it has been praised for its ability to generate unbiased population estimates via post-stratified weights which account for non-random recruitment. However, population estimates generated with RDSAT (RDS Analysis Tool) are sensitive to variations in degree weights. Several assumptions are implicit in the degree weight and are not routinely assessed. Failure to meet these assumptions could result in inaccurate degree measures and consequently result in biased population estimates. We highlight potential biases associated with violating the assumptions implicit in degree weights for the RDSAT estimator and propose strategies to measure and possibly correct for biases in the analysis.

  12. Mental workload measurement: Event-related potentials and ratings of workload and fatigue

    Science.gov (United States)

    Biferno, M. A.

    1985-01-01

    Event-related potentials were elicited when a digitized word representing a pilot's call-sign was presented. This auditory probe was presented during 27 workload conditions in a 3x3x3 design where the following variables were manipulated: short-term load, tracking task difficulty, and time-on-task. Ratings of workload and fatigue were obtained between each trial of a 2.5-hour test. The data of each subject were analyzed individually to determine whether significant correlations existed between subjective ratings and ERP component measures. Results indicated that a significant number of subjects had positive correlations between: (1) ratings of workload and P300 amplitude, (2) ratings of workload and N400 amplitude, and (3) ratings of fatigue and P300 amplitude. These data are the first to show correlations between ratings of workload or fatigue and ERP components thereby reinforcing their validity as measures of mental workload and fatigue.

  13. Cognitive Evoked Potential Measurement, P300, in a group of healthy Colombian individuals

    Directory of Open Access Journals (Sweden)

    Natalia Gutiérrez Giraldo

    2013-05-01

    Full Text Available Cognitive evoked potentials are electrophysiological measurements of cognitive functions. Cognitivepotential P300 is specifically related to attention processes. Objetive: the aim of this studywas to establish reference values for latency and amplitude of P300 wave in the Colombian population and determine their variability with age, gender and education of the subjects. Methods:we studied 122 healthy subjects between 6 and 80 years, are practical potential measurementmethodology as odd-ball, in leads Cz and Pz. Results: we were able to establish reference valuesfor different age groups, and statistical significance was found with which the latency of P300wave increases with the age of individuals, and instead thereof the amplitude tends to decrease.Similarly to correlate latency and amplitude was shown an inverse relationship between them.Conclusions: no differences were found for latency and wave amplitude, gender-related or schoolsubjects as well as no difference was found when measuring the Pz derivation obtained comparedwith the wave in lead Cz.

  14. Energy performance contracting - energy saving potential of selected energy conservation measures (ECM)

    Energy Technology Data Exchange (ETDEWEB)

    Johansson, M. (Dansk Energi Analyse A/S, Frederiksberg (Denmark)); Langkilde, G.; Olesen, Bjarne W. (Technical Univ. of Denmark, ICIEE, Kgs. Lyngby (Denmark)); Moerck, O. (Cenergia Energy Consultants, Herlev (Denmark)); Sundman, O. (DONG Energy, Copenhagen (Denmark)); Engelund Thomsen, K. (Aalborg Univ., SBi, Hoersholm (Denmark))

    2008-09-15

    This report has been developed under the research project 'Etablering af grundlag for energitjenester i Danmark' (project number: ENS-33031-0185) under the Danish research programme - EFP. The objective of this project has been to contribute to the utilisation of the large potential for energy conservations in the building sector within the public, industry and service sectors through the development of a better basis for decision making for both the Energy Service Companies (ESCOes) and the building owners. The EU directive on Energy Service Contracting points at the buildings as the area where the biggest potential market for energy services and energy efficiency improvements are. The EFP-project has two parts: (1) A Danish part and (2) participation in the international cooperation project 'Holistic Assesment Tool-Kit on Energy Efficient Retrofit Measures for Government Buildings (EnERGo)', Annex 46 under the IEA R and D program 'Energy Conservation In Buildings And Community Systems' (ECBCS). This report describes the Danish contributions to the IEA projects subtask B, which has a primary objective to develop a database of energy conservation measures (ECM) with descriptions and performance characteristics of these. (au)

  15. Two Dimensional LIF Measurements and Potential Structure of Ion Beam Formation in an Argon Helicon Plasma

    Science.gov (United States)

    Aguirre, Evan; Scime, Earl; Good, Timothy

    2016-10-01

    We report 2-dimensional, spatially resolved observations of ion beam formation in an expanding helicon plasma. Previous studies found that a current free double layer (CFDL) spontaneously arises at low pressure, below 1 mT. We use Laser Induced Fluorescence (LIF), a non-perturbative diagnostic to measure the ion velocity distribution functions (IVDFs) of argon ions both parallel and perpendicular to the background magnetic field. We report ion beam formation as a function of the expansion chamber magnetic field (0-108 G). The ion beam appears peaked in the center of the expansion chamber and decays over a few centimeters radially. We also report the potential structure of the plasma obtained with a planar Langmuir probe. To obtain meaningful Langmuir probe measurements, averages of tens of current-voltage are needed to reduce the effects of large electrostatic fluctuations that arise in plasmas that generate ion beams. We report the dependence of density, electron temperature, and floating potential on radial and axial position in the expansion plume. NSF Award PHYS-1360278.

  16. Marine and Hydrokinetic Renewable Energy Technologies: Potential Navigational Impacts and Mitigation Measures

    Energy Technology Data Exchange (ETDEWEB)

    Cool, Richard, M.; Hudon, Thomas, J.; Basco, David, R.; Rondorf, Neil, E.

    2009-12-10

    On April 15, 2008, the Department of Energy (DOE) issued a Funding Opportunity Announcement for Advanced Water Power Projects which included a Topic Area for Marine and Hydrokinetic Renewable Energy Market Acceleration Projects. Within this Topic Area, DOE identified potential navigational impacts of marine and hydrokinetic renewable energy technologies and measures to prevent adverse impacts on navigation as a sub-topic area. DOE defines marine and hydrokinetic technologies as those capable of utilizing one or more of the following resource categories for energy generation: ocean waves; tides or ocean currents; free flowing water in rivers or streams; and energy generation from the differentials in ocean temperature. PCCI was awarded Cooperative Agreement DE-FC36-08GO18177 from the DOE to identify the potential navigational impacts and mitigation measures for marine hydrokinetic technologies, as summarized herein. The contract also required cooperation with the U.S. Coast Guard (USCG) and two recipients of awards (Pacific Energy Ventures and reVision) in a sub-topic area to develop a protocol to identify streamlined, best-siting practices. Over the period of this contract, PCCI and our sub-consultants, David Basco, Ph.D., and Neil Rondorf of Science Applications International Corporation, met with USCG headquarters personnel, with U.S. Army Corps of Engineers headquarters and regional personnel, with U.S. Navy regional personnel and other ocean users in order to develop an understanding of existing practices for the identification of navigational impacts that might occur during construction, operation, maintenance, and decommissioning. At these same meetings, “standard” and potential mitigation measures were discussed so that guidance could be prepared for project developers. Concurrently, PCCI reviewed navigation guidance published by the USCG and international community. This report summarizes the results of this effort, provides guidance in the form of a

  17. A tool for evaluating the potential for cost-effective outcomes measurement

    Directory of Open Access Journals (Sweden)

    Somasekhar MM

    2012-04-01

    Full Text Available Melinda M Somasekhar1, Alfred Bove2, Chris Rausch1, James Degnan3, Cathy T King1, Arnold Meyer11The Albert J Finestone, MD, Office for Continuing Medical Education, 2Section of Cardiology, Temple University School of Medicine, Philadelphia, PA, USA; 3Measurement and Research Center, Temple University, Philadelphia, PA, USAAbstract: Cost related to higher-level outcomes measurement is often very high. However, the cost burden is felt even more by smaller, less well-funded continuing medical education (CME programs. It is possible to overcome financial and participant-related barriers to measuring Level 6 outcomes, which are patient health outcomes. The Temple University School of Medicine’s Office for Continuing Medical Education developed a sequential tool for attaining cost-effective outcomes measurement for determining the likelihood of a CME intervention to produce significant changes in physician performance. The appropriate selection of the CME topic and specific practice change indictors drive this tool. This tool walks providers through a simple YES or NO decision-making list that guides them toward an accurate prediction of potential programmatic outcomes. Factors considered during the decision-making process include whether: (a the intended change(s will have a substantial impact on current practice; (b the intended practice change(s are well supported by clinical data, specialty organization/government recommendations, expert opinion, etc; (c the potential change(s affects a large population; (d external factors, such as system pressures, media pressures, financial pressures, patient pressures, safety pressures, etc, are driving this intended change in performance; (e there is a strong motivation on the part of physicians to implement the intended change(s; and (f the intended change(s is relatively easy to implement within any system of practice. If each of these questions can be responded to positively, there is a higher likelihood

  18. Tetracycline adsorption on chitosan: a mechanistic description based on mass uptake and zeta potential measurements.

    Science.gov (United States)

    Caroni, A L P F; de Lima, C R M; Pereira, M R; Fonseca, J L C

    2012-12-01

    Adsorption phenomena occurring at the solid/liquid interface of chitosan particles are of extreme importance in the kinetics of drug release/upload as well as in effluent treatment by adsorption. In this work, equilibrium and kinetic aspects of protonated tetracycline adsorption on chitosan are explored using classic solution depletion method and zeta potential measurements. Equilibrium experiments showed that for solutions with tetracycline initial concentration of ca. 1.2 g L(-1), corresponding to a pH around 3, chitosan structure disrupted, as indicated by an increase in magnitude of tetracycline sorption. Adsorption and zeta potential isotherms before disruption suggested that the process of adsorption had a Langmuir character up to a point at which subsurface was exposed to adsorption; at this point, a second mode of sorption began: zeta potential tended to an equilibrium value, following Sips isotherm and tetracycline sorption had a linear dependence on its continuous phase concentration. The kinetics of tetracycline sorption suggested that sorption of tetracycline was divided between the sorption of protonated and non-protonated tetracycline; tetracycline in its non-protonated form seemed to rule the sorption of tetracycline.

  19. Hydrophobicity, surface tension, and zeta potential measurements of glass-reinforced hydroxyapatite composites.

    Science.gov (United States)

    Lopes, M A; Monteiro, F J; Santos, J D; Serro, A P; Saramago, B

    1999-06-15

    Wettability and zeta potential studies were performed to characterize the hydrophobicity, surface tension, and surface charge of P2O5-glass-reinforced hydroxyapatite composites. Quantitative phase analysis was performed by the Rietveld method using GSAS software applied to X-ray diffractograms. Surface charge was assessed by zeta potential measurements. Protein adsorption studies were performed using vitronectin. Contact angles and surface tensions variation with time were determined by the sessile and pendent drop techniques, respectively, using ADSA-P software. The highest (-18.1 mV) and lowest (-28.7 mV) values of zeta potential were found for hydroxyapatite (HA) and beta-tricalcium phosphate (beta-TCP), respectively, with composite materials presenting values in between. All studied bioceramic materials showed similar solid surface tension. For HA and beta-TCP, solid surface tensions of 46.7 and 45.3 mJ/m2, respectively, were obtained, while composites presented intermediate surface tension values. The dispersive component of surface tension was the predominant one for all materials studied. Adhesion work values between the vitronectin solution and HA and beta-TCP were found to be 79.8 and 88.0 mJ/m2, respectively, while the 4.0 wt % glass composites showed slightly lower values than the 2.5 wt % ones. The presence of beta-TCP influenced surface charge, hydrophobicity, and protein adsorption of the glass-reinforced HA composites, and therefore indirectly affected cell-biomaterial interactions.

  20. Mechanisms of fibrinogen adsorption on latex particles determined by zeta potential and AFM measurements.

    Science.gov (United States)

    Adamczyk, Zbigniew; Bratek-Skicki, Anna; Dąbrowska, Paulina; Nattich-Rak, Małgorzata

    2012-01-10

    The adsorption of fibrinogen on polystyrene latex particles was studied using the concentration depletion method combined with the AFM detection of residual protein after adsorption. Measurements were carried out for a pH range of 3.5-11 and an ionic strength range of 10(-3)-0.15 M NaCl. First, the bulk physicochemical properties of fibrinogen and the latex particle suspension were characterized for this range of pH and ionic strength. The zeta potential and the number of uncompensated (electrokinetic) charges on the protein were determined from microelectrophoretic measurements. It was revealed that fibrinogen molecules exhibited amphoteric characteristics, being on average positively charged for pH adsorption of fibrinogen on latex for pH below 11. It was also proven that fibrinogen adsorption was irreversible, with the maximum surface concentration varying between 2.5 and 5 × 10(3) μm(-2) (weight concentration of a bare molecule was 1.4 to 2.8 mg m(-2)). These measurements revealed two main adsorption mechanisms of fibrinogen: (i) the unoriented (random) mechanism prevailing for lower ionic strength, where adsorbing molecules significantly penetrate the fuzzy polymeric layer on the latex core and (ii) the side-on adsorption mechanism prevailing for pH > 5.8 and a higher ionic strength of 0.15 M. It was also shown that in the latter case, variations in the zeta potential with the protein coverage could be adequately described in terms of the electrokinetic model, previously formulated for planar substrate adsorption. On the basis of these experimental data, an efficient procedure of preparing fibrinogen-covered latex particles of controlled monolayer structure and coverage was envisaged.

  1. Porous media matric potential and water content measurements during parabolic flight

    Science.gov (United States)

    Norikane, Joey H.; Jones, Scott B.; Steinberg, Susan L.; Levine, Howard G.; Or, Dani

    2005-01-01

    Control of water and air in the root zone of plants remains a challenge in the microgravity environment of space. Due to limited flight opportunities, research aimed at resolving microgravity porous media fluid dynamics must often be conducted on Earth. The NASA KC-135 reduced gravity flight program offers an opportunity for Earth-based researchers to study physical processes in a variable gravity environment. The objectives of this study were to obtain measurements of water content and matric potential during the parabolic profile flown by the KC-135 aircraft. The flight profile provided 20-25 s of microgravity at the top of the parabola, while pulling 1.8 g at the bottom. The soil moisture sensors (Temperature and Moisture Acquisition System: Orbital Technologies, Madison, WI) used a heat-pulse method to indirectly estimate water content from heat dissipation. Tensiometers were constructed using a stainless steel porous cup with a pressure transducer and were used to measure the matric potential of the medium. The two types of sensors were placed at different depths in a substrate compartment filled with 1-2 mm Turface (calcined clay). The ability of the heat-pulse sensors to monitor overall changes in water content in the substrate compartment decreased with water content. Differences in measured water content data recorded at 0, 1, and 1.8 g were not significant. Tensiometer readings tracked pressure differences due to the hydrostatic force changes with variable gravity. The readings may have been affected by changes in cabin air pressure that occurred during each parabola. Tensiometer porous membrane conductivity (function of pore size) and fluid volume both influence response time. Porous media sample height and water content influence time-to-equilibrium, where shorter samples and higher water content achieve faster equilibrium. Further testing is needed to develop these sensors for space flight applications.

  2. Similarity Laws for the Lines of Ideal Free Energy and Chemical Potential in Supercritical Fluids.

    Science.gov (United States)

    Apfelbaum, E M; Vorob'ev, V S

    2017-09-21

    We have found the curves on the density-temperature plane, along which the values of free energy and chemical potential correspond to ideal gas quantities. At first, we have applied the van der Waals equation to construct them and to derive their equations. Then we have shown that the same lines for real substances (Ar, N2, CH4, SF6, H2, H2O) and for the model Lennard-Jones system constructed on the basis of the measurements data and calculations are well matched with the derived equations. The validity and deviations from the obtained similarity laws are discussed.

  3. Formation and dynamics of van der Waals molecules in buffer-gas traps

    CERN Document Server

    Brahms, Nathan; Zhang, Peng; Kłos, Jacek; Forrey, Robert C; Au, Yat Shan; Sadeghpour, H R; Dalgarno, A; Doyle, John M; Walker, Thad G

    2011-01-01

    We show that weakly bound He-containing van der Waals molecules can be produced and magnetically trapped in buffer-gas cooling experiments, and provide a general model for the formation and dynamics of these molecules. Our analysis shows that, at typical experimental parameters, thermodynamics favors the formation of van der Waals complexes composed of a helium atom bound to most open-shell atoms and molecules, and that complex formation occurs quickly enough to ensure chemical equilibrium. For molecular pairs composed of a He atom and an S-state atom, the molecular spin is stable during formation, dissociation, and collisions, and thus these molecules can be magnetically trapped. Collisional spin relaxations are too slow to affect trap lifetimes. However, helium-3-containing complexes can change spin due to adiabatic crossings between trapped and untrapped Zeeman states, mediated by the anisotropic hyperfine interaction, causing trap loss. We provide a detailed model for Ag3He molecules, using ab initio calc...

  4. Exfoliation of natural van der Waals heterostructures to a single unit cell thickness

    Science.gov (United States)

    Velický, Matěj; Toth, Peter S.; Rakowski, Alexander M.; Rooney, Aidan P.; Kozikov, Aleksey; Woods, Colin R.; Mishchenko, Artem; Fumagalli, Laura; Yin, Jun; Zólyomi, Viktor; Georgiou, Thanasis; Haigh, Sarah J.; Novoselov, Kostya S.; Dryfe, Robert A. W.

    2017-02-01

    Weak interlayer interactions in van der Waals crystals facilitate their mechanical exfoliation to monolayer and few-layer two-dimensional materials, which often exhibit striking physical phenomena absent in their bulk form. Here we utilize mechanical exfoliation to produce a two-dimensional form of a mineral franckeite and show that the phase segregation of chemical species into discrete layers at the sub-nanometre scale facilitates franckeite's layered structure and basal cleavage down to a single unit cell thickness. This behaviour is likely to be common in a wider family of complex minerals and could be exploited for a single-step synthesis of van der Waals heterostructures, as an alternative to artificial stacking of individual two-dimensional crystals. We demonstrate p-type electrical conductivity and remarkable electrochemical properties of the exfoliated crystals, showing promise for a range of applications, and use the density functional theory calculations of franckeite's electronic band structure to rationalize the experimental results.

  5. Cl-intercalated graphene on SiC: Influence of van der Waals forces

    KAUST Repository

    Cheng, Yingchun

    2013-01-01

    The atomic and electronic structures of Cl-intercalated epitaxial graphene on SiC are studied by first-principles calculations. By increasing the Cl concentration, doping levels from n-type to slightly p-type are achieved on the SiC(0001) surface, while a wider range of doping levels is possible on the SiC(0001̄) surface. We find that the Cl atoms prefer bonding to the substrate rather than to the graphene. By varying the Cl concentration the doping level can be tailored. Consideration of van der Waals forces improves the distance between the graphene and the substrate as well as the binding energy, but it is not essential for the formation energy. For understanding the doping mechanism the introduction of non-local van der Waals contributions to the exchange correlation functional is shown to be essential. Copyright © EPLA, 2013.

  6. Finite-size nanowire at a surface: Unconventional power laws of the van der Waals interaction

    Science.gov (United States)

    Makhnovets, K. A.; Kolezhuk, A. K.

    2017-09-01

    We study the van der Waals interaction of a metallic or narrow-gap semiconducting nanowire with a surface, in the regime of intermediate wire-surface distances (vF/c )L ≪d ≪L or L ≪d ≪(c /vF)L , where L is the nanowire length, d is the distance to the surface, and vF is the characteristic velocity of nanowire electrons (for a metallic wire, it is the Fermi velocity). Our approach, based on the Luttinger liquid framework, allows one to analyze the dependence of the interaction on the interplay between the nanowire length, wire-surface distance, and characteristic length scales related to the spectral gap and temperature. We show that this interplay leads to nontrivial modifications of the power law that governs van der Waals forces, in particular to a nonmonotonic dependence of the power-law exponent on the wire-surface separation.

  7. Electrical and optical properties of SnS2/WSe2 van der Waals Heterojunction FETs

    Science.gov (United States)

    Zubair, Ahmad; Nourbakhsh, Amirhasan; Dresselhaus, Mildred; Palacios, Tomas

    Two dimensional crystals based on atomically thin films of transition metal dichalcogenides offer an exciting platform for various optoelectronic applications. Their unique crystal properties make them particularly attractive for van der Waals heterostructures which open up an additional degree of freedom to tailor the material properties into new physics and device applications. In this work, we explore, for the first time, the optoelectronic properties of van der Waals SnS2/WSe2 heterojunction. WSe2 is an ambipolar semiconductor while SnS2 is an n-type wide bandgap semiconductor. We use the pickup and dry transfer methods to fabricate SnS2/WSe2 heterojunction transistors (hetero-FETs). We observe negative differential transconductance in the SnS2/WSe2 hetero-FET. Also, the heterostructure couples strongly to incident light and shows high photovoltaic responsivity which can find applications in nano-devices such as photo-detectors and solar cells.

  8. Steady dynamics of exothermic chemical wave fronts in van der Waals fluids

    Science.gov (United States)

    Dumazer, G.; Antoine, C.; Lemarchand, A.; Nowakowski, B.

    2009-12-01

    We study the steady dynamics of an exothermic Fisher-Kolmogorov-Petrovsky-Piskunov chemical wave front traveling in a one-dimensional van der Waals fluid. The propagating wave is initiated by a nonuniformity in reactant concentration contrary to usual combustion ignition processes. The heat release and activation energy of the reaction play the role of control parameters. We recently proved that the propagation of an exothermic chemical wave front in a perfect gas displays a forbidden interval of stationary wave front speeds [G. Dumazer, M. Leda, B. Nowakowski, and A. Lemarchand, Phys. Rev. E 78, 016309 (2008)]. We examine how this result is modified for nonideal fluids and determine the effect of the van der Waals parameters and fluid density on the bifurcation between diffusion flames and Chapman-Jouguet detonation waves as heat release increases. Analytical predictions are confirmed by the numerical solution of the hydrodynamic equations including reaction kinetics.

  9. Holographic Van der Waals-like phase transition in the Gauss–Bonnet gravity

    Energy Technology Data Exchange (ETDEWEB)

    He, Song, E-mail: hesong17@gmail.com [Max Planck Institute for Gravitational Physics (Albert Einstein Institute), Am Mühlenberg 1, 14476 Golm (Germany); State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100190 (China); Li, Li-Fang, E-mail: lilf@itp.ac.cn [Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing 100190 (China); Zeng, Xiao-Xiong, E-mail: xxzeng@itp.ac.cn [State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100190 (China); School of Material Science and Engineering, Chongqing Jiaotong University, Chongqing 400074 (China)

    2017-02-15

    The Van der Waals-like phase transition is observed in temperature–thermal entropy plane in spherically symmetric charged Gauss–Bonnet–AdS black hole background. In terms of AdS/CFT, the non-local observables such as holographic entanglement entropy, Wilson loop, and two point correlation function of very heavy operators in the field theory dual to spherically symmetric charged Gauss–Bonnet–AdS black hole have been investigated. All of them exhibit the Van der Waals-like phase transition for a fixed charge parameter or Gauss–Bonnet parameter in such gravity background. Further, with choosing various values of charge or Gauss–Bonnet parameter, the equal area law and the critical exponent of the heat capacity are found to be consistent with phase structures in temperature–thermal entropy plane.

  10. Van der Waals force: a dominant factor for reactivity of graphene.

    Science.gov (United States)

    Lee, Jong Hak; Avsar, Ahmet; Jung, Jeil; Tan, Jun You; Watanabe, K; Taniguchi, T; Natarajan, Srinivasan; Eda, Goki; Adam, Shaffique; Castro Neto, Antonio H; Özyilmaz, Barbaros

    2015-01-14

    Reactivity control of graphene is an important issue because chemical functionalization can modulate graphene's unique mechanical, optical, and electronic properties. Using systematic optical studies, we demonstrate that van der Waals interaction is the dominant factor for the chemical reactivity of graphene on two-dimensional (2D) heterostructures. A significant enhancement in the chemical stability of graphene is achieved by replacing the common SiO2 substrate with 2D crystals such as an additional graphene layer, WS2, MoS2, or h-BN. Our theoretical and experimental results show that its origin is a strong van der Waals interaction between the graphene layer and the 2D substrate. This results in a high resistive force on graphene toward geometric lattice deformation. We also demonstrate that the chemical reactivity of graphene can be controlled by the relative lattice orientation with respect to the substrates and thus can be used for a wide range of applications including hydrogen storage.

  11. Henry constants in polymer solutions with the van der Waals equation of state

    DEFF Research Database (Denmark)

    Bithas, Sotiris; Kalospiros, Nikolaos; Kontogeorgis, Georgios

    1996-01-01

    The simple der Waals equation of state, as extended to polymer systems, is applied to the correlation and prediction of Henry constants in polymer solutions comprising five polymers and many nonpolar and polar solvents, including supercritical gases. The correlation achieved with one adjustable...... parameter is satisfactory, with typical errors within the experimental uncertainty and comparable to those with the more complex Perturbed Hard Chain Theory-based equations of state with the same number of adjustable parameters. A predictive scheme for calculating Henry constants is also presented, which...... is a corresponding-states correlation for a dimensionless Henry constant defined based on the van der Waals equation of state. Satisfactory results-often close to the ones from the one-parameter correlation-are obtained for all systems investigated in this work. Compared with literature models that have been applied...

  12. van der Waals binding and band structure effects in graphene overlayers and graphane multilayers

    Science.gov (United States)

    Hyldgaard, Per; Rohrer, Jochen

    2011-03-01

    We study graphene formation (by selective Si evaporation) and adhesion on SiC surfaces as well as stacking and binding of graphane multilayers using a number of versions of the van der Waals Density Functional (vdW-DF) method and plane-wave density functional theory calculations. For the graphene/SiC systems and for the graphane multilayers we document that the bonding is entirely dominated by van der Waals (vdW) forces. At the same time we find that dispersive forces acting on the layers produce significant modifications in the graphene and graphane band structure. We interpret the changes and discuss a competition between wave function hybridization and interaction with the charge enhancement (between the layers) that results from density overlap. Supported by Svenska Vetenskapsrådet VR #621-2008-4346.

  13. Holographic Van der Waals-like phase transition in the Gauss-Bonnet gravity

    Science.gov (United States)

    He, Song; Li, Li-Fang; Zeng, Xiao-Xiong

    2017-02-01

    The Van der Waals-like phase transition is observed in temperature-thermal entropy plane in spherically symmetric charged Gauss-Bonnet-AdS black hole background. In terms of AdS/CFT, the non-local observables such as holographic entanglement entropy, Wilson loop, and two point correlation function of very heavy operators in the field theory dual to spherically symmetric charged Gauss-Bonnet-AdS black hole have been investigated. All of them exhibit the Van der Waals-like phase transition for a fixed charge parameter or Gauss-Bonnet parameter in such gravity background. Further, with choosing various values of charge or Gauss-Bonnet parameter, the equal area law and the critical exponent of the heat capacity are found to be consistent with phase structures in temperature-thermal entropy plane.

  14. Review-evaluating the molecular assays for measuring the oxidative potential of particulate matter

    Directory of Open Access Journals (Sweden)

    Hedayat F.

    2015-01-01

    Full Text Available Several cell-free assays are currently used to quantify and detect the Reactive Oxygen Species (ROS. All of them have certain limitations, do not provide direct comparison of results and, to date, none of these assays have been acknowledged as the most suitable acellular assay and none has yet been adopted for investigation of potential PM toxicity. These assays include DTT, ascorbic acid, DCFHDA and PFN assays which have been used in measurements of the particles generated from various combustion sources such as diesel engine, wood smoke (or biomass burning and cigarette smoke, as well as for outdoor measurements. All the probes use different units for expressing redox properties of PM. Also, their reactivity is being triggered by different types of ROS. This limits the direct comparison of the results that are reporting the toxicity of the same aerosol type measured with various probes. This study is evaluating and comparing the various assays in order to develop deeper understanding of their capabilities, selectivity as well as improve understanding of the underlying chemical mechanisms.

  15. Measurement error potential and control when quantifying volatile hydrocarbon concentrations in soils

    Energy Technology Data Exchange (ETDEWEB)

    Siegrist, R.L.

    1990-01-01

    Due to their widespread use throughout commerce and industry, volatile hydrocarbons such as toluene, trichloroethene and 1,1,1-trichloroethene routinely appear as principal pollutants in contaminated sites throughout the US and abroad. As a result, quantitative determination of soil system hydrocarbons is necessary to confirm the presence of contamination and its nature and extent; to assess site risks and the need for cleanup; to evaluate remedial technologies; and to verify the performance of a selected alternative. Decisions regarding these issues have far-reaching impacts and ideally should be based on accurate measurements of soil hydrocarbon concentrations. Unfortunately, quantification of volatile hydrocarbons in soils is extremely difficult and there is normally little understanding of the accuracy and precision of these measurements. Rather, the assumption is often implicitly made that the hydrocarbon data are sufficiently accurate for the intended purpose. This paper presents a discussion of measurement error potential when quantifying volatile hydrocarbons in soils and outlines some methods for understanding and managing these errors. 11 refs., 1 fig., 4 tabs.

  16. Diaphragm compound muscle action potential measured with magnetic stimulation and chest wall surface electrodes.

    Science.gov (United States)

    Luo, Y M; Mustfa, N; Lyall, R A; Man, W D C; Glérant, J C; Polkey, M I; Moxham, J

    2002-06-01

    To seek a method to reliably measure phrenic nerve conduction time (PNCT) with magnetic stimulation we investigated two stimulus sites, placing the magnetic coil at the cricoid cartilage (high position) or close to the clavicle (low position). We also compared compound muscle action potential (CMAP) recorded from three different sites: in the sixth to eighth intercostal spaces in the anterior axillary line (Ant-a); in the 8th intercostal space close to the midclavicular line; and with one electrode at the lower sternum and the other at the costal margin. Fourteen normal subjects were studied. The PNCT measured by magnetic stimulation in the high position recorded from (Ant-a) was 7.6+/-0.6 on the left side and 8.4+/-0.7 on the right. The PNCT recorded from all three sites become much shorter when the magnetic coil was moved from the high to the low position. Our results show that PNCT can be accurately measured with magnetic stimulation when care is taken to avoid coactivation of the brachial plexus.

  17. A Case of Functional (Psychogenic Monocular Hemianopia Analyzed by Measurement of Hemifield Visual Evoked Potentials

    Directory of Open Access Journals (Sweden)

    Tsuyoshi Yoneda

    2013-12-01

    Full Text Available Purpose: Functional monocular hemianopia is an extremely rare condition, for which measurement of hemifield visual evoked potentials (VEPs has not been previously described. Methods: A 14-year-old boy with functional monocular hemianopia was followed up with Goldmann perimetry and measurement of hemifield and full-field VEPs. Results: The patient had a history of monocular temporal hemianopia of the right eye following headache, nausea and ague. There was no relative afferent pupillary defect, and a color perception test was normal. Goldmann perimetry revealed a vertical monocular temporal hemianopia of the right eye; the hemianopia on the right was also detected with a binocular visual field test. Computed tomography, magnetic resonance imaging (MRI and MR angiography of the brain including the optic chiasm as well as orbital MRI revealed no abnormalities. On the basis of these results, we diagnosed the patient's condition as functional monocular hemianopia. Pattern VEPs according to the International Society for Clinical Electrophysiology of Vision (ISCEV standard were within the normal range. The hemifield pattern VEPs for the right eye showed a symmetrical latency and amplitude for nasal and temporal hemifield stimulation. One month later, the visual field defect of the patient spontaneously disappeared. Conclusions: The latency and amplitude of hemifield VEPs for a patient with functional monocular hemianopia were normal. Measurement of hemifield VEPs may thus provide an objective tool for distinguishing functional hemianopia from hemifield loss caused by an organic lesion.

  18. Surface properties of a single perfluoroalkyl group on water surfaces studied by surface potential measurements.

    Science.gov (United States)

    Shimoaka, Takafumi; Tanaka, Yuki; Shioya, Nobutaka; Morita, Kohei; Sonoyama, Masashi; Amii, Hideki; Takagi, Toshiyuki; Kanamori, Toshiyuki; Hasegawa, Takeshi

    2016-12-01

    A discriminative study of a single perfluoroalkyl (Rf) group from a bulk material is recently recognized to be necessary toward the total understanding of Rf compounds based on a primary chemical structure. The single molecule and the bulk matter have an interrelationship via an intrinsic two-dimensional (2D) aggregation property of an Rf group, which is theorized by the stratified dipole-arrays (SDA) theory. Since an Rf group has dipole moments along many C-F bonds, a single Rf group would possess a hydrophilic-like character on the surface. To reveal the hydration character of a single Rf group, in the present study, surface potential (ΔV) measurements are performed for Langmuir monolayers of Rf-containing compounds. From a comparative study with a monolayer of a normal hydrocarbon compound, the hydration/dehydration dynamics of a lying Rf group on water has first been monitored by ΔV measurements, through which a single Rf group has been revealed to have a unique "dipole-interactive" character, which enables the Rf group interacted with the water 'surface.' In addition, the SDA theory proves to be useful to predict the 2D aggregation property across the phase transition temperature of 19°C by use of the ΔV measurements.

  19. Evaluation of the potential of benchmarking to facilitate the measurement of chemical persistence in lakes.

    Science.gov (United States)

    Zou, Hongyan; MacLeod, Matthew; McLachlan, Michael S

    2014-01-01

    The persistence of chemicals in the environment is rarely measured in the field due to a paucity of suitable methods. Here we explore the potential of chemical benchmarking to facilitate the measurement of persistence in lake systems using a multimedia chemical fate model. The model results show that persistence in a lake can be assessed by quantifying the ratio of test chemical and benchmark chemical at as few as two locations: the point of emission and the outlet of the lake. Appropriate selection of benchmark chemicals also allows pseudo-first-order rate constants for physical removal processes such as volatilization and sediment burial to be quantified. We use the model to explore how the maximum persistence that can be measured in a particular lake depends on the partitioning properties of the test chemical of interest and the characteristics of the lake. Our model experiments demonstrate that combining benchmarking techniques with good experimental design and sensitive environmental analytical chemistry may open new opportunities for quantifying chemical persistence, particularly for relatively slowly degradable chemicals for which current methods do not perform well.

  20. Toward Best Practices For Assessing Near Surface Sensor Fouling: Potential Correction Approaches Using Underway Ferry Measurements

    Science.gov (United States)

    Sastri, A. R.; Dewey, R. K.; Pawlowicz, R.; Krogh, J.

    2016-02-01

    Data from long term deployments of sensors on autonomous, mobile and cabled observation platforms suffer potential quality issues associated with bio-fouling. This issue is of particular concern for optical sensors, such as fluorescence and/or absorbance-based instruments for which light emitting/receiving surfaces are prone to fouling due constant contact with the marine environment. Here we examine signal quality for backscatter, chlorophyll and CDOM fluorescence from a single triplet instrument installed in a ferry box system (nominal depth of 3m) operated by Ocean Networks Canada. The time series consists of 22 months of 8-10 daily transits across the productive waters of the Strait of Georgia, British Columbia, Canada (Nanaimo on Vancouver Island and Vancouver on mainland BC). Instruments were cleaned every 2 weeks since all three instruments experienced significant signal attenuation during that period throughout the year. We experimented with a variety of pre- and post-cleaning measurements in an effort to develop `correction factors' with which to account for the effects of fouling. We found that CDOM fluorescence was especially sensitive to fouling and that correction factors derived from measurements of the fluorescence of standardized solutions successfully accounted for fouling. Similar results were found for chlorophyll fluorescence. Here we present results from our measurements and assess the efficacy of each of these approaches using comparisons against additional instruments less prone to signal attenuation over short periods.

  1. Early Seizure Detection Using Neuronal Potential Similarity: A Generalized Low-Complexity and Robust Measure.

    Science.gov (United States)

    Bandarabadi, Mojtaba; Rasekhi, Jalil; Teixeira, Cesar A; Netoff, Theoden I; Parhi, Keshab K; Dourado, Antonio

    2015-08-01

    A novel approach using neuronal potential similarity (NPS) of two intracranial electroencephalogram (iEEG) electrodes placed over the foci is proposed for automated early seizure detection in patients with refractory partial epilepsy. The NPS measure is obtained from the spectral analysis of space-differential iEEG signals. Ratio between the NPS values obtained from two specific frequency bands is then investigated as a robust generalized measure, and reveals invaluable information about seizure initiation trends. A threshold-based classifier is subsequently applied on the proposed measure to generate alarms. The performance of the method was evaluated using cross-validation on a large clinical dataset, involving 183 seizure onsets in 1785 h of long-term continuous iEEG recordings of 11 patients. On average, the results show a high sensitivity of 86.9% (159 out of 183), a very low false detection rate of 1.4 per day, and a mean detection latency of 13.1 s from electrographic seizure onsets, while in average preceding clinical onsets by 6.3 s. These high performance results, specifically the short detection latency, coupled with the very low computational cost of the proposed method make it adequate for using in implantable closed-loop seizure suppression systems.

  2. Effects of the van der Waals Force on the Dynamics Performance for a Micro Resonant Pressure Sensor

    Directory of Open Access Journals (Sweden)

    Lizhong Xu

    2016-01-01

    Full Text Available The micro resonant pressure sensor outputs the frequency signals where the distortion does not take place in a long distance transmission. As the dimensions of the sensor decrease, the effects of the van der Waals forces should be considered. Here, a coupled dynamic model of the micro resonant pressure sensor is proposed and its coupled dynamic equation is given in which the van der Waals force is considered. By the equation, the effects of the van der Waals force on the natural frequencies and vibration amplitudes of the micro resonant pressure sensor are investigated. Results show that the natural frequency and the vibrating amplitudes of the micro resonant pressure sensor are affected significantly by van der Waals force for a small clearance between the film and the base plate, a small initial tension stress of the film, and some other conditions.

  3. In situ soil moisture and matrix potential - what do we measure?

    Science.gov (United States)

    Jackisch, Conrad; Durner, Wolfgang

    2017-04-01

    Soil moisture and matric potential are often regarded as state variables that are simple to monitor at the Darcy-scale. At the same time unproven believes about the capabilities and reliabilities of specific sensing methods or sensor systems exist. A consortium of ten institutions conducted a comparison study of currently available sensors for soil moisture and matrix potential at a specially homogenised field site with sandy loam soil, which was kept free of vegetation. In total 57 probes of 15 different systems measuring soil moisture, and 50 probes of 14 different systems measuring matric potential have been installed in a 0.5 meter grid to monitor the moisture state in 0.2 meter depth. The results give rise to a series of substantial questions about the state of the art in hydrological monitoring, the heterogeneity problem and the meaning of soil water retention at the field scale: A) For soil moisture, most sensors recorded highly plausible data. However, they do not agree in absolute values and reaction timing. For matric potential, only tensiometers were able to capture the quick reactions during rainfall events. All indirect sensors reacted comparably slowly and thus introduced a bias with respect to the sensing of soil water state under highly dynamic conditions. B) Under natural field conditions, a better homogeneity than in our setup can hardly be realised. While the homogeneity assumption held for the first weeks, it collapsed after a heavy storm event. The event exceeded the infiltration capacity, initiated the generation of redistribution networks at the surface, which altered the local surface properties on a very small scale. If this is the reality at a 40 m2 plot, what representativity have single point observations referencing the state of whole basins? C) A comparison of in situ and lab-measured retention curves marks systematic differences. Given the general practice of soil water retention parameterisation in almost any hydrological model this

  4. Van der Waals and Casimir interactions between atoms and carbon nanotubes

    OpenAIRE

    Klimchitskaya, G. L.(Central Astronomical Observatory at Pulkovo of the Russian Academy of Sciences, 196140, St. Petersburg, Russia); Blagov, E. V.; Mostepanenko, V. M.

    2008-01-01

    The van der Waals and Casimir interactions of a hydrogen atom (molecule) with a single-walled and a multiwalled carbon nanotubes are compared. It is shown that the macroscopic concept of graphite dielectric permittivity is already applicable for nanotubes with only two or three walls. The absorption of hydrogen atoms by a nanotube at separations below one nanometer is considered. The lateral force due to exchange repulsion moves the atom to a position above the cell center, where it is absorb...

  5. van der Waals epitaxy and photoresponse of two-dimensional CdSe plates

    Science.gov (United States)

    Zhu, Dan-Dan; Xia, Jing; Wang, Lei; Li, Xuan-Ze; Tian, Li-Feng; Meng, Xiang-Min

    2016-06-01

    Here we demonstrate the first growth of two-dimensional (2D) single-crystalline CdSe plates on mica substrates via van der Waals epitaxy. The as-synthesized 2D plates exhibit hexagonal, truncated triangular and triangular shapes with the lateral size around several microns. Photodetectors based on 2D CdSe plates present a fast response time of 24 ms, revealing that 2D CdSe is a promising building block for ultrathin optoelectronic devices.

  6. Moire superlattice effects in graphene/boron-nitride van der Waals heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Wallbank, John R.; Chen, Xi; Fal' ko, Vladimir I. [Department of Physics, Lancaster University, Lancaster (United Kingdom); Mucha-Kruczynski, Marcin [Department of Physics, University of Bath (United Kingdom)

    2015-06-15

    Van der Waals heterostructures of graphene and hexagonal boron nitride feature a moire superlattice for graphene's Dirac electrons. Here, we review the effects generated by this superlattice, including a specific miniband structure featuring gaps and secondary Dirac points, and a fractal spectrum of magnetic minibands known as Hofstadter's butterfly. (copyright 2015 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  7. Van der Waals epitaxial double heterostructure: InAs/single-layer graphene/InAs.

    Science.gov (United States)

    Hong, Young Joon; Yang, Jae Won; Lee, Wi Hyoung; Ruoff, Rodney S; Kim, Kwang S; Fukui, Takashi

    2013-12-17

    Van der Waals (vdW) epitaxial double heterostructures have been fabricated by vdW epitaxy of InAs nanostructures on both sides of graphene. InAs nanostructures diametrically form on/underneath graphene exclusively along As-polar direction, indicating polarity inversion of the double heterostructures. First-principles and density functional calculations demonstrate how and why InAs easily form to be double heterostructures with polarity inversion.

  8. First-principles study of two-dimensional van der Waals heterojunctions

    OpenAIRE

    Hu, Wei; Yang, Jinlong

    2015-01-01

    Research on graphene and other two-dimensional (2D) materials, such as silicene, germanene, phosphorene, hexagonal boron nitride (h-BN), graphitic carbon nitride (g-C3N4), graphitic zinc oxide (g-ZnO) and molybdenum disulphide (MoS2), has recently received considerable interest owing to their outstanding properties and wide applications. Looking beyond this field, combining the electronic structures of 2D materials in ultrathin van der Waals heterojunctions has also emerged to widely study th...

  9. Van der Waals density functional study of water binding in metal-organic frameworks

    Science.gov (United States)

    Lee, Kyuho; Smit, Berend; Neaton, Jeffrey B.

    2013-03-01

    Metal-organic frameworks (MOFs) are promising candidate materials for gas storage, gas separation and catalysis. However, MOFs are vulnerable to humid air and effective surface area drops dramatically on an exposure to water. In this theoretical study, we investigate the interaction of single water molecule with MOF-74 on different binding sites by using van der Waals density functionals. We also explore how different type of metal cations affect the interaction.

  10. Effect of van der Waals interactions on the structural and elastic properties of black phosphorus

    DEFF Research Database (Denmark)

    Appalakondaiah, S.; Vaitheeswaran, G.; Lebègue, S.;

    2012-01-01

    The structural and elastic properties of orthorhombic black phosphorus have been investigated using first-principles calculations based on density functional theory. The structural parameters have been calculated using the local density approximation (LDA), the generalized gradient approximation...... (GGA), and with several dispersion corrections to include van der Waals interactions. It is found that the dispersion corrections improve the lattice parameters over LDA and GGA in comparison with experimental results. The calculations reproduce well the experimental trends under pressure and show...

  11. Determination of Contact Potential Difference by the Kelvin Probe (Part II) 2. Measurement System by Involving the Composite Bucking Voltage

    Science.gov (United States)

    Vilitis, O.; Rutkis, M.; Busenbergs, J.; Merkulovs, D.

    2016-12-01

    The present research is devoted to creation of a new low-cost miniaturised measurement system for determination of potential difference in real time and with high measurement resolution. Furthermore, using the electrode of the reference probe, Kelvin method leads to both an indirect measurement of electronic work function or contact potential of the sample and measurement of a surface potential for insulator type samples. The bucking voltage in this system is composite and comprises a periodically variable component. The necessary steps for development of signal processing and tracking are described in detail.

  12. Impact of local environmental conditions on atmospheric electrical potential gradient measurements

    Science.gov (United States)

    Buzás, Attila; Barta, Veronika; Steinbach, Péter; Bór, József

    2017-04-01

    The atmospheric electrical potential gradient (PG) is a fundamental parameter of the global electric circuit (GEC) which comprises all large scale quasi-static electrical processes occurring in between the surface of the Earth and the lower ionosphere. The observation of PG near the Earth's surface plays a pivotal role in surveying our atmospheric electrical environment. The PG shows high variability in different temporal and spatial scales and it is especially sensitive to local effects. Therefore, obtaining a PG value which represents the general state of the GEC over a larger area rather than various effects due to measuring site-specific local factors is a challenging task. PG measurements are going on in the Széchenyi István Geophysical Observatory (NCK, 47°38' N, 16°43' E) of the Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences near Nagycenk, Hungary since 1961. PG sensors are set up in NCK in an open area surrounded by buildings and trees within 20 m distance. The effect of the changing vegetation on the long-term trend observed in the PG variation at NCK has been subject of debates [1,2,3]. In order to examine the possible bias in the measured PG values due to the relatively close buildings and trees at NCK, two sets of simultaneous PG measurements from two EFM-100 field mills were compared. One field mill was kept at a fixed location while the other was moved to grid points covering the open area around the fixed field mill. The measurement was done in fair weather conditions in summer and was repeated during the winter. The poster demonstrates the performance of this method in surveying the effect of various objects and the state of vegetation on the measured PG values by comparing the measured PG differences to those obtained from electrostatic models calculated by the finite element method using the FEMM 4.2 software package. [1] F. Märcz and R. G. Harrison, 2003, Annales Gephysicae, 21: 2193-2200 [2] F. Märcz and R

  13. Strong pressure-energy correlations in van der Waals liquids

    DEFF Research Database (Denmark)

    Pedersen, Ulf Rørbæk; Bailey, Nicholas; Schrøder, Thomas

    2008-01-01

    Strong correlations between equilibrium fluctuations of the configurational parts of pressure and energy are found in computer simulations of the Lennard-Jones liquid and other simple liquids, but not for hydrogen-bonding liquids such as methanol and water. The correlations that are present also...... in the crystal and glass phases reflect an effective inverse power-law repulsive potential dominating fluctuations, even at zero and slightly negative pressure. In experimental data for supercritical argon, the correlations are found to be approximately 96%. Consequences for viscous liquid dynamics are discussed....

  14. Spooky correlations and unusual van der Waals forces between gapless and near-gapless molecules

    CERN Document Server

    Dobson, John F; Angyan, Janos G; Liu, Ru-Fen

    2016-01-01

    We consider the zero-temperature van der Waals interaction between two molecules, each of which has a zero or near-zero electronic gap between a groundstate and the first excited state, using a toy model molecule ( equilateral H3) as an example. We show that the van der Waals energy between two groundstate molecules falls off as D^(-3) instead of the usual D^(-6) dependence, when the molecules are separated by distance D: We show that this is caused by perfect "spooky" correlation between the two fluctuating electric dipoles. The phenomenon is related to, but not the same as, the "resonant" interaction between an electronically excited and a groundstate molecule introduced by Eisenschitz and London in 1930. It is also an example of "type C van der Waals non- additivity" recently introduced by one of us ( Int. J. Quantum Chem. 114, 1157 (2014)). Our toy molecule H3 is not stable, but symmetry considerations suggest that a similar vdW phenomenon may be observable, despite Jahn-Teller effects, in molecules with ...

  15. Molecular recognition by van der Waals interaction between polymers with sequence-specific polarizabilities

    Science.gov (United States)

    Lu, Bing-Sui; Naji, Ali; Podgornik, Rudolf

    2015-06-01

    We analyze van der Waals interactions between two rigid polymers with sequence-specific, anisotropic polarizabilities along the polymer backbones, so that the dipole moments fluctuate parallel to the polymer backbones. Assuming that each polymer has a quenched-in polarizability sequence which reflects, for example, the polynucleotide sequence of a double-stranded DNA molecule, we study the van der Waals interaction energy between a pair of such polymers with rod-like structure for the cases where their respective polarizability sequences are (i) distinct and (ii) identical, with both zero and non-zero correlation length of the polarizability correlator along the polymer backbones in the latter case. For identical polymers, we find a novel r-5 scaling behavior of the van der Waals interaction energy for small inter-polymer separation r, in contradistinction to the r-4 scaling behavior of distinct polymers, with furthermore a pronounced angular dependence favoring attraction between sufficiently aligned identical polymers. Such behavior can assist the molecular recognition between polymers.

  16. Study of van der Waals bonding and interactions in metal organic framework materials.

    Science.gov (United States)

    Zuluaga, Sebastian; Canepa, Pieremanuele; Tan, Kui; Chabal, Yves J; Thonhauser, Timo

    2014-04-02

    Metal organic framework (MOF) materials have attracted a lot of attention due to their numerous applications in fields such as hydrogen storage, carbon capture and gas sequestration. In all these applications, van der Waals forces dominate the interaction between the small guest molecules and the walls of the MOFs. In this review article, we describe how a combined theoretical and experimental approach can successfully be used to study those weak interactions and elucidate the adsorption mechanisms important for various applications. On the theory side, we show that, while standard density functional theory is not capable of correctly describing van der Waals interactions, functionals especially designed to include van der Waals forces exist, yielding results in remarkable agreement with experiment. From the experimental point of view, we show examples in which IR adsorption and Raman spectroscopy are essential to study molecule/MOF interactions. Importantly, we emphasize throughout this review that a combination of theory and experiment is crucial to effectively gain further understanding. In particular, we review such combined studies for the adsorption mechanism of small molecules in MOFs, the chemical stability of MOFs under humid conditions, water cluster formation inside MOFs, and the diffusion of small molecules into MOFs. The understanding of these phenomena is critical for the rational design of new MOFs with desired properties.

  17. Li intercalation in graphite: A van der Waals density-functional study

    Science.gov (United States)

    Hazrati, E.; de Wijs, G. A.; Brocks, G.

    2014-10-01

    Modeling layered intercalation compounds from first principles poses a problem, as many of their properties are determined by a subtle balance between van der Waals interactions and chemical or Madelung terms, and a good description of van der Waals interactions is often lacking. Using van der Waals density functionals we study the structures, phonons and energetics of the archetype layered intercalation compound Li-graphite. Intercalation of Li in graphite leads to stable systems with calculated intercalation energies of -0.2 to -0.3 eV/Li atom, (referred to bulk graphite and Li metal). The fully loaded stage 1 and stage 2 compounds LiC6 and Li1 /2C6 are stable, corresponding to two-dimensional √{3 }×√{3 } lattices of Li atoms intercalated between two graphene planes. Stage N >2 structures are unstable compared to dilute stage 2 compounds with the same concentration. At elevated temperatures dilute stage 2 compounds easily become disordered, but the structure of Li3 /16C6 is relatively stable, corresponding to a √{7 }×√{7 } in-plane packing of Li atoms. First-principles calculations, along with a Bethe-Peierls model of finite temperature effects, allow for a microscopic description of the observed voltage profiles.

  18. The hot pick-up technique for batch assembly of van der Waals heterostructures.

    Science.gov (United States)

    Pizzocchero, Filippo; Gammelgaard, Lene; Jessen, Bjarke S; Caridad, José M; Wang, Lei; Hone, James; Bøggild, Peter; Booth, Timothy J

    2016-06-16

    The assembly of individual two-dimensional materials into van der Waals heterostructures enables the construction of layered three-dimensional materials with desirable electronic and optical properties. A core problem in the fabrication of these structures is the formation of clean interfaces between the individual two-dimensional materials which would affect device performance. We present here a technique for the rapid batch fabrication of van der Waals heterostructures, demonstrated by the controlled production of 22 mono-, bi- and trilayer graphene stacks encapsulated in hexagonal boron nitride with close to 100% yield. For the monolayer devices, we found semiclassical mean-free paths up to 0.9 μm, with the narrowest samples showing clear indications of the transport being affected by boundary scattering. The presented method readily lends itself to fabrication of van der Waals heterostructures in both ambient and controlled atmospheres, while the ability to assemble pre-patterned layers paves the way for complex three-dimensional architectures.

  19. Spooky correlations and unusual van der Waals forces between gapless and near-gapless molecules

    Science.gov (United States)

    Dobson, John F.; Savin, Andreas; Ángyán, János G.; Liu, Ru-Fen

    2016-11-01

    We consider the zero-temperature van der Waals (vdW) interaction between two molecules, each of which has a zero or near-zero electronic gap between a ground state and the first excited state, using a toy model molecule (equilateral H3) as an example. We show that the van der Waals energy between two ground state molecules falls off as D-3 instead of the usual D-6 dependence, when the molecules are separated by distance D. We show that this is caused by a perfect "spooky" correlation between the two fluctuating electric dipoles. The phenomenon is related to, but not the same as, the "resonant" interaction between an electronically excited and a ground state molecule introduced by Eisenschitz and London in 1930. It is also an example of "type C van der Waals non-additivity" recently introduced by one of us [J. F. Dobson, Int. J. Quantum Chem. 114, 1157 (2014)]. Our toy molecule H3 is not stable, but symmetry considerations suggest that a similar vdW phenomenon may be observable, despite Jahn-Teller effects, in molecules with a discrete rotational symmetry and broken inversion symmetry, such as certain metal atom clusters. The motion of the nuclei will need to be included for a definitive analysis of such cases, however.

  20. Measuring microchannel electroosmotic mobility and zeta potential by the current monitoring method.

    Science.gov (United States)

    Shao, Chenren; Devoe, Don L

    2013-01-01

    Electroosmotic flow (EOF) is an electrokinetic flow control technique widely used in microfluidic systems for applications including direct electrokinetic pumping, hydrodynamic pressure generation, and counterflow for microfluidic separations. During EOF, an electric field is applied along the length of a microchannel containing an electrolyte, with mobile ions near the charged microchannel walls experiencing a Coulomb force due to electrostatic interactions with the applied electric field that leads to bulk solution movement. The goal of this laboratory is to experimentally determine the fixed channel surface charge (zeta potential) and electroosmotic mobility associated with a given microchannel substrate material and buffer solution, using a simple current monitoring method to measure the average flow velocity within the microchannel. It is a straightforward experiment designed to help students understand EOF physics while gaining hands-on experience with basic world-to-chip interfacing. It is well suited to a 90-min laboratory session for up to 12 students with minimal infrastructure requirements.

  1. Potential contributions of noncontact atomic force microscopy for the future Casimir force measurements

    CERN Document Server

    Kim, W J

    2010-01-01

    Surface electric noise, i.e., the non-uniform distribution of charges and potentials on a surface, poses a great experimental challenge in modern precision force measurements. Such a challenge is encountered in a number of different experimental circumstances. The scientists employing atomic force microscopy (AFM) have long focused their efforts to understand the surface-related noise issues via variants of AFM techniques, such as Kelvin probe force microscopy or electric force microscopy. Recently, the physicists investigating quantum vacuum fluctuation phenomena between two closely-spaced objects have also begun to collect experimental evidence indicating a presence of surface effects neglected in their previous analyses. It now appears that the two seemingly disparate science communities are encountering effects rooted in the same surface phenomena. In this report, we suggest specific experimental tasks to be performed in the near future that are crucial not only for fostering needed collaborations between...

  2. Direct measurements of the ozone formation potential from livestock and poultry waste emissions.

    Science.gov (United States)

    Howard, Cody J; Kumar, Anuj; Mitloehner, Frank; Stackhouse, Kimberly; Green, Peter G; Flocchini, Robert G; Kleeman, Michael J

    2010-04-01

    The global pattern of expanding urban centers and increasing agricultural intensity is leading to more frequent interactions between air pollution emissions from urban and agricultural sources. The confluence of these emissions that traditionally have been separated by hundreds of kilometers is creating new air quality challenges in numerous regions across the United States. An area of particular interest is California's San Joaquin Valley (SJV), which has an agricultural output higher than many countries, a rapidly expanding human population, and ozone concentrations that are already higher than many dense urban areas. New regulations in the SJV restrict emissions of reactive organic gases (ROGs) from animal sources in an attempt to meet Federal and State ozone standards designed to protect human health. The objective of this work is to directly measure the ozone formation potential (OFP) of agricultural animal plus waste sources in representative urban and rural atmospheres using a transportable "smog" chamber. Four animal types were examined: beef cattle, dairy cattle, swine, and poultry. Emissions from each animal plus waste type were captured in a 1 m(3) Teflon bag, mixed with representative background NO(x) and ROG concentrations, and then exposed to UV radiation so that ozone formation could be quantified. The emitted ROG composition was also measured so that the theoretical incremental reactivity could be calculated for a variety of atmospheres and directly compared with the measured OFP under the experimental conditions. The results demonstrate that OFP associated with waste ROG emissions from swine (0.39 +/- 0.04 g-O(3) per g-ROG), beef cattle (0.51 +/- 0.10 g-O(3) per g-ROG), and dairy cattle (0.42 +/- 0.07 g-O(3) per g-ROG) are lower than OFP associated with ROG emissions from gasoline powered light-duty vehicles (LDV) (0.69 +/- 0.05 g-O(3) per g-ROG). The OFP of ROG emitted from poultry waste (1.35 +/- 0.73 g-O(3) per g-ROG) is approximately double the

  3. Measurement of Electroretinograms and Visually Evoked Potentials in Awake Moving Mice.

    Directory of Open Access Journals (Sweden)

    Yusuke Tomiyama

    Full Text Available The development of new treatments for intractable retinal diseases requires reliable functional assessment tools for animal models. In vivo measurements of neural activity within visual pathways, including electroretinogram (ERG and visually evoked potential (VEP recordings, are commonly used for such purposes. In mice, the ERG and VEPs are usually recorded under general anesthesia, a state that may alter sensory transduction and neurotransmission, but seldom in awake freely moving mice. Therefore, it remains unknown whether the electrophysiological assessment of anesthetized mice accurately reflects the physiological function of the visual pathway. Herein, we describe a novel method to record the ERG and VEPs simultaneously in freely moving mice by immobilizing the head using a custom-built restraining device and placing a rotatable cylinder underneath to allow free running or walking during recording. Injection of the commonly used anesthetic mixture xylazine plus ketamine increased and delayed ERG oscillatory potentials by an average of 67.5% and 36.3%, respectively, compared to unanesthetized mice, while having minimal effects on the a-wave and b-wave. Similarly, components of the VEP were enhanced and delayed by up to 300.2% and 39.3%, respectively, in anesthetized mice. Our method for electrophysiological recording in conscious mice is a sensitive and robust means to assess visual function. It uses a conventional electrophysiological recording system and a simple platform that can be built in any laboratory at low cost. Measurements using this method provide objective indices of mouse visual function with high precision and stability, unaffected by anesthetics.

  4. Temporal dynamics of visual attention measured with event-related potentials.

    Directory of Open Access Journals (Sweden)

    Yoshiyuki Kashiwase

    Full Text Available How attentional modulation on brain activities determines behavioral performance has been one of the most important issues in cognitive neuroscience. This issue has been addressed by comparing the temporal relationship between attentional modulations on neural activities and behavior. Our previous study measured the time course of attention with amplitude and phase coherence of steady-state visual evoked potential (SSVEP and found that the modulation latency of phase coherence rather than that of amplitude was consistent with the latency of behavioral performance. In this study, as a complementary report, we compared the time course of visual attention shift measured by event-related potentials (ERPs with that by target detection task. We developed a novel technique to compare ERPs with behavioral results and analyzed the EEG data in our previous study. Two sets of flickering stimulus at different frequencies were presented in the left and right visual hemifields, and a target or distracter pattern was presented randomly at various moments after an attention-cue presentation. The observers were asked to detect targets on the attended stimulus after the cue. We found that two ERP components, P300 and N2pc, were elicited by the target presented at the attended location. Time-course analyses revealed that attentional modulation of the P300 and N2pc amplitudes increased gradually until reaching a maximum and lasted at least 1.5 s after the cue onset, which is similar to the temporal dynamics of behavioral performance. However, attentional modulation of these ERP components started later than that of behavioral performance. Rather, the time course of attentional modulation of behavioral performance was more closely associated with that of the concurrently recorded SSVEPs analyzed. These results suggest that neural activities reflected not by either the P300 or N2pc, but by the SSVEPs, are the source of attentional modulation of behavioral performance.

  5. Towards an extension of 1905 relativistic dynamics with a variable rest mass measuring potential energy

    CERN Document Server

    Hidalgo-Gato, Rafael A Valls

    2012-01-01

    From a rigorous historic analysis of 1686 I. Newton and 1905 A. Einstein works where the last derived the universal mass-energy relationship, it is concluded that rest mass measures potential energy. From the same formula used to obtain that relation, it is derived the ratio Total Energy/Potential Energy is equal to the gamma relativistic factor. It is derived a formula for the variation of a body rest mass with its position in a gravity field, explaining with it the behavior of an atomic clock. It is revised the bodies free fall in a gravitational field, finding that a constant total mass is equal to the gravitational mass, while the variable rest mass is equal to the inertial mass, maintaining all an identical behavior independent of their masses. A revision of the E\\"otv\\"os experiment concludes that it is unable to detect the found difference between inertial and gravitational mass. Applying the extended 1905 relativistic dynamics to Mercury, its perihelion shift is determined; it is concluded with the co...

  6. Driving Distance to Telemedicine Units in Northern Ontario as a Measure of Potential Access to Healthcare.

    Science.gov (United States)

    O'Gorman, Laurel D; Hogenbirk, John C

    2016-04-01

    The Ontario Telemedicine Network (OTN) uses technology to help make medical services more accessible to people in medically underserved rural and remote parts of Ontario, Canada. We examined access to OTN-enabled health and medical services in Northern Ontario, which has 775,000 people in communities scattered across an area of 803,000 km(2). We used ArcGIS Network Analyst (Esri, Redlands, CA) to conduct a service area analysis with travel time as a measure of potential access to care. We used road distance and speed limits to estimate travel time between Northern Ontario communities and the nearest OTN unit. In 2014 there were 2,331 OTN units, of which 552 (24%) were located in Northern Ontario. All seven communities in Northern Ontario with a population of 10,000 or greater had OTN units. Almost 97% of the 59 communities with 1,000-10,000 people were within 30 min of an OTN unit. The percentage of communities within 30 min steadily decreased with decreasing population size, to 58% for communities with fewer than 50 people. In total, 86% (690/802) of Northern Ontario communities were within an hour's drive of an OTN unit. This study showed that most Northern Ontario communities were within an hour's drive of an OTN unit. The current distribution of OTN units has the potential to increase access to medical services and to reduce the need for medically related travel for residents of these communities.

  7. Antarctic subglacial groundwater: measurement concept and potential influence on ice flow

    Science.gov (United States)

    Kulessa, Bernd; Siegert, Martin; Bougamont, Marion; Christoffersen, Poul; Key, Kerry; Andersen, Kristoffer; Booth, Adam; Smith, Andrew

    2017-04-01

    Is groundwater abundant in Antarctica and does it modulate ice flow? Answering this question matters because ice streams flow by gliding over a wet substrate of till. Water fed to ice-stream beds thus influences ice-sheet dynamics and, potentially, sea-level rise. It is recognised that both till and the sedimentary basins from which it originates are porous and could host a reservoir of mobile groundwater that interacts with the subglacial interfacial system. According to recent numerical modelling up to half of all water available for basal lubrication, and time lags between hydrological forcing and ice-sheet response as long as millennia, may have been overlooked in models of ice flow. Here, we review evidence in support of Antarctic groundwater and propose how it can be measured to ascertain the extent to which it modulates ice flow. We present new seismoelectric soundings of subglacial till, and new magnetotelluric and transient electromagnetic forward models of subglacial groundwater reservoirs. We demonstrate that multi-facetted and integrated geophysical datasets can detect, delineate and quantify the groundwater contents of subglacial sedimentary basins and, potentially, monitor groundwater exchange rates between subglacial till layers. We thus describe a new area of glaciological investigation and how it should progress in future.

  8. Design of a Computerised Flight Mill Device to Measure the Flight Potential of Different Insects.

    Science.gov (United States)

    Martí-Campoy, Antonio; Ávalos, Juan Antonio; Soto, Antonia; Rodríguez-Ballester, Francisco; Martínez-Blay, Victoria; Malumbres, Manuel Pérez

    2016-04-07

    Several insect species pose a serious threat to different plant species, sometimes becoming a pest that produces significant damage to the landscape, biodiversity, and/or the economy. This is the case of Rhynchophorus ferrugineus Olivier (Coleoptera: Dryophthoridae), Semanotus laurasii Lucas (Coleoptera: Cerambycidae), and Monochamus galloprovincialis Olivier (Coleoptera: Cerambycidae), which have become serious threats to ornamental and productive trees all over the world such as palm trees, cypresses, and pines. Knowledge about their flight potential is very important for designing and applying measures targeted to reduce the negative effects from these pests. Studying the flight capability and behaviour of some insects is difficult due to their small size and the large area wherein they can fly, so we wondered how we could obtain information about their flight capabilities in a controlled environment. The answer came with the design of flight mills. Relevant data about the flight potential of these insects may be recorded and analysed by means of a flight mill. Once an insect is attached to the flight mill, it is able to fly in a circular direction without hitting walls or objects. By adding sensors to the flight mill, it is possible to record the number of revolutions and flight time. This paper presents a full description of a computer monitored flight mill. The description covers both the mechanical and the electronic parts in detail. The mill was designed to easily adapt to the anatomy of different insects and was successfully tested with individuals from three species R. ferrugineus, S. laurasii, and M. galloprovincialis.

  9. Measurements of water potential and water content in unsaturated crystalline rock

    Science.gov (United States)

    Schneebeli, Martin; Flühler, Hannes; Gimmi, Thomas; Wydler, Hannes; LäSer, Hans-Peter; Baer, Toni

    1995-08-01

    A water desaturation zone develops around a tunnel in water-saturated rock when the evaporative water loss at the rock surface is larger than the water flow from the surrounding saturated region of restricted permeability. We describe the methods with which such water desaturation processes in rock materials can be quantified. The water retention characteristic θ (ψ) of crystalline rock samples was determined with a pressure membrane apparatus. The negative water potential, identical to the capillary pressure, ψ, below the tensiometric range (ψ drilled into the granodiorite as a measuring chamber. The water potentials observed in a cylindrical granodiorite monolith ranged between -0.1 and -3.0 MPa; those near the wall in a ventilated tunnel between -0.1 and -2.2 MPa. Two types of three-rod TDR probes were used, one as a depth probe inserted into the rock, the other as a surface probe using three copper stripes attached to the surface for detecting water content changes in the rock-to-air boundary. The TDR signal was smoothed with a low-pass filter, and the signal length determined based on the first derivative of the trace. Despite the low porosity of crystalline rock these standard methods are applicable to describe the unsaturated zone in solid rock and may also be used in other consolidated materials such as concrete.

  10. Silver ion impregnated composite biomaterial optimally prepared using zeta potential measurements.

    Science.gov (United States)

    Sakthivel, N; Socrates, R; Shanthini, G M; Rajaram, A; Kalkura, S Narayana

    2015-02-01

    Biodegradable, antimicrobial composite of various silver ion concentrations was synthesized using zeta potential and isoelectric point measurements, for a controlled release of silver ions, and in addition to assess the effect of protein adsorption with the increase of the silver ion concentration. The interaction between hydroxyapatite (HAp) and silver incorporated hydroxyapatite (AgHAp) with gelatin was increased by optimally adjusting the zeta potential and isoelectric point of the ceramic (HAp and AgHAp), and bio-polymer individually. The electrostatic interactions between the ceramic and biopolymer were confirmed, through shifts in N-H stretching, decrease in the swelling ratio, and increase in the degradation temperature observed by the derivative thermo-gravimetric analysis (DTG). These results substantiate that, the zeta potential is a novel tool to increase the ceramic-biopolymer interaction. Increasing electrostatic interaction between the biopolymer and ceramic, decreases the release of silver ions in the simulated body fluid, due to the controlled degradation of the biopolymer. The isoelectric point decreases with the increase of the silver ion concentration, which evidenced the change in the net surface charge. With the increase of the silver ion concentration, the protein adsorption decreases due to an increase in hydrophilic character of the composite. This study examines the minimum concentration of silver ion essential for maximum protein adsorption, antimicrobial and hemocompatibility. This study provides a novel route to control the release of silver ions by enhancing the ceramic-polymer interaction and estimate the silver ion concentration suitable for protein adsorption. The prepared composite is nontoxic, degradable, and antimicrobial, with the controlled release of silver ions in the simulated body fluid.

  11. Monitoring the Effects of Acupoint Antioxidant Intervention by Measuring Electrical Potential Difference along the Meridian

    Directory of Open Access Journals (Sweden)

    Ming-Ming Xu

    2015-01-01

    Full Text Available Previous studies suggest that superoxide anions are possibly traveling along acupuncture meridians. The electrical potential difference (EPD between acupoints may be related to the movement. To test the above hypothesis, we conducted a study investigating the effects of acupoint antioxidant interventions on the meridian EPD. Firstly, ST39 (L and ST44 (L were screened out for the EPD detection along the stomach meridian, and ST36 (L was selected for interventions including acumassage with the control cream, as well as the TAT-SOD cream for 30 minutes, or injection with reduced glutathione sodium. The EPD between ST39 and ST44 was recorded for 80 minutes and measured again 48 h later. While the EPD increased during the acumassage, the acumassage with TAT-SOD cream and the glutathione injection generated waves of EPD increased, indicating the migration or removal from the visceral organ of a greater quantity of superoxide. Remarkably lower EPD readings 48 h later with both antioxidant acupoint interventions than the mere acumassage imply a more complete superoxide flushing out due to the restored superoxide pathway at the acupoint after interventions. The results confirm superoxide transportation along the meridians and demonstrate a possibility of acupoint EPD measurement as a tool to monitor changes in the meridians and acupoints.

  12. Measurement of ADP–ATP Exchange in Relation to Mitochondrial Transmembrane Potential and Oxygen Consumption

    Science.gov (United States)

    Chinopoulos, Christos; Kiss, Gergely; Kawamata, Hibiki; Starkov, Anatoly A.

    2015-01-01

    We have previously described a fluorometric method to measure ADP–ATP exchange rates in mitochondria of permeabilized cells, in which several enzymes that consume substantial amounts of ATP and other competing reactions interconverting adenine nucleotides are present. This method relies on recording changes in free extramitochondrial Mg2+ with the Mg2+-sensitive fluorescent indicator Magnesium Green (MgGr)™, exploiting the differential affinity of ADP and ATP for Mg2+. In particular, cells are permeabilized with digitonin in the presence of BeF3− and Na3VO4, inhibiting all ATP- and ADP-utilizing reactions but mitochondrial exchange of ATP with ADP catalyzed by the adenine nucleotide translocase. The rate of ATP appearing in the medium upon the addition of ADP to energized mitochondria is then calculated from the rate of change in free extramitochondrial Mg2+ using standard binding equations. Here, we describe a variant of this method involving an improved calibration step. This step minimizes errors that may be introduced during the conversion of the MgGr™ signal into free extramitochondrial [Mg2+] and ATP. Furthermore, we describe an approach for combining this methodology with the measurement of mitochondrial membrane potential and oxygen consumption in the same sample. The method described herein is useful for the study of malignant cells, which are known to thrive in hypoxic environments and to harbor mitochondria with profound functional alterations. PMID:24862274

  13. Measurement of ADP-ATP exchange in relation to mitochondrial transmembrane potential and oxygen consumption.

    Science.gov (United States)

    Chinopoulos, Christos; Kiss, Gergely; Kawamata, Hibiki; Starkov, Anatoly A

    2014-01-01

    We have previously described a fluorometric method to measure ADP-ATP exchange rates in mitochondria of permeabilized cells, in which several enzymes that consume substantial amounts of ATP and other competing reactions interconverting adenine nucleotides are present. This method relies on recording changes in free extramitochondrial Mg(2+) with the Mg(2+)-sensitive fluorescent indicator Magnesium Green (MgGr)™, exploiting the differential affinity of ADP and ATP for Mg(2+). In particular, cells are permeabilized with digitonin in the presence of BeF3(-) and Na3VO4, inhibiting all ATP- and ADP-utilizing reactions but mitochondrial exchange of ATP with ADP catalyzed by the adenine nucleotide translocase. The rate of ATP appearing in the medium upon the addition of ADP to energized mitochondria is then calculated from the rate of change in free extramitochondrial Mg(2+) using standard binding equations. Here, we describe a variant of this method involving an improved calibration step. This step minimizes errors that may be introduced during the conversion of the MgGr™ signal into free extramitochondrial [Mg(2+)] and ATP. Furthermore, we describe an approach for combining this methodology with the measurement of mitochondrial membrane potential and oxygen consumption in the same sample. The method described herein is useful for the study of malignant cells, which are known to thrive in hypoxic environments and to harbor mitochondria with profound functional alterations. © 2014 Elsevier Inc. All rights reserved.

  14. Potential for a Tensor Asymmetry Azz Measurement in the x > 1 Region at Jefferson Lab

    Energy Technology Data Exchange (ETDEWEB)

    Long, Elena [UNH

    2014-10-01

    The tensor asymmetry A(zz) in the quasi-elastic region through the tensor polarized D(e, e')X channel is sensitive to the nucleon-nucleon potential. Previous measurements of A(zz) have been used to extract b(1) in the DIS region and T(20) in the elastic region. In the quasielastic region, A(zz) can be used to compare light cone calculations with variation nucleon- nucleon calculations, and is an important quantity to determine for understanding tensor effects, such as the dominance of pn correlations in nuclei. In the quasi-elastic region, A(zz) was first calculated in 1988 by Frankfurt and Strikman using the Hamada-Johnstone and Reid soft-core wave functions [1]. Recent calculations by M. Sargsian revisit A(zz) in the x > 1 range using virtual-nucleon and light-cone methods, which differ by up to a factor of two [2]. Discussed in these proceedings, a study has been completed that determines the feasibility of measuring A(zz) in the quasi-elastic x > 1 region at Jefferson Lab's Hall C.

  15. A new total antioxidant potential measurements using RP-HPLC assay with fluorescence detection.

    Science.gov (United States)

    Głód, Bronisław K; Piszcz, Paweł; Czajka, Katarzyna; Zarzycki, Paweł K

    2011-05-01

    In this paper, an improved total antioxidant potential (TAP) estimation using high-performance liquid chromatographic (HPLC) assay with fluorometric detection has been described. The principle of this method is based on the hydroxyl radicals generated in the Fenton-like reaction and subsequently detected using hydroxyterephthalic acid (HTPA), which is a reaction product of hydroxyl radicals and terephthalic acid (TPA), working as a sensing compound. HTPA quantity in the samples was measured by fluorescence detector working at excitation and emission wavelengths equal to 312 and 428 nm, respectively. A number of key experimental conditions including the influence of the reaction (incubation) time on the surface areas of HTPA peaks, concentration of Fe(II) ions as well as the influence of concentration of TPA on the surface area of the chromatographic peak of HTPA were optimized to the characteristic feature of TAP measurements. The elaborated assay has been used to evaluate TAP values of selected low-molecular mass compounds like pyrogallol, tryptamine, and n-alcohols (methanol, ethanol, and n-propanol) as well as chlorogenic and ascorbic acids and benzoic acid derivatives, which are commonly present in the food samples.

  16. Combining density functional and incremental post-Hartree-Fock approaches for van der Waals dominated adsorbate-surface interactions: Ag2/graphene

    Science.gov (United States)

    de Lara-Castells, María Pilar; Mitrushchenkov, Alexander O.; Stoll, Hermann

    2015-09-01

    A combined density functional (DFT) and incremental post-Hartree-Fock (post-HF) approach, proven earlier to calculate He-surface potential energy surfaces [de Lara-Castells et al., J. Chem. Phys. 141, 151102 (2014)], is applied to describe the van der Waals dominated Ag2/graphene interaction. It extends the dispersionless density functional theory developed by Pernal et al. [Phys. Rev. Lett. 103, 263201 (2009)] by including periodic boundary conditions while the dispersion is parametrized via the method of increments [H. Stoll, J. Chem. Phys. 97, 8449 (1992)]. Starting with the elementary cluster unit of the target surface (benzene), continuing through the realistic cluster model (coronene), and ending with the periodic model of the extended system, modern ab initio methodologies for intermolecular interactions as well as state-of-the-art van der Waals-corrected density functional-based approaches are put together both to assess the accuracy of the composite scheme and to better characterize the Ag2/graphene interaction. The present work illustrates how the combination of DFT and post-HF perspectives may be efficient to design simple and reliable ab initio-based schemes in extended systems for surface science applications.

  17. Combining density functional and incremental post-Hartree-Fock approaches for van der Waals dominated adsorbate-surface interactions: Ag{sub 2}/graphene

    Energy Technology Data Exchange (ETDEWEB)

    Lara-Castells, María Pilar de, E-mail: Pilar.deLara.Castells@csic.es [Instituto de Física Fundamental (C.S.I.C.), Serrano 123, E-28006 Madrid (Spain); Mitrushchenkov, Alexander O. [Université Paris-Est, Laboratoire Modélisation et Simulation Multi Echelle, MSME UMR 8208 CNRS, 5 bd Descartes, 77454 Marne-la-Vallée (France); Stoll, Hermann [Institut für Theoretische Chemie, Universität Stuttgart, D-70550 Stuttgart (Germany)

    2015-09-14

    A combined density functional (DFT) and incremental post-Hartree-Fock (post-HF) approach, proven earlier to calculate He-surface potential energy surfaces [de Lara-Castells et al., J. Chem. Phys. 141, 151102 (2014)], is applied to describe the van der Waals dominated Ag{sub 2}/graphene interaction. It extends the dispersionless density functional theory developed by Pernal et al. [Phys. Rev. Lett. 103, 263201 (2009)] by including periodic boundary conditions while the dispersion is parametrized via the method of increments [H. Stoll, J. Chem. Phys. 97, 8449 (1992)]. Starting with the elementary cluster unit of the target surface (benzene), continuing through the realistic cluster model (coronene), and ending with the periodic model of the extended system, modern ab initio methodologies for intermolecular interactions as well as state-of-the-art van der Waals-corrected density functional-based approaches are put together both to assess the accuracy of the composite scheme and to better characterize the Ag{sub 2}/graphene interaction. The present work illustrates how the combination of DFT and post-HF perspectives may be efficient to design simple and reliable ab initio-based schemes in extended systems for surface science applications.

  18. Measurement of individual intracellular pH and membrane potential values in living cells

    Science.gov (United States)

    Slavik, Jan; Lanz, Edvard; Cimprich, Petr

    1999-07-01

    It was assumed that each cell is a homogeneous suspension may have a slightly different pH and membrane potential. A wide range of pH-sensitive fluorescent dyes BCECF, SNARF, FITC, carboxyfluorescein, fluorescein and pyranine have been carefully tested for the accuracy and reliability of their pH-response inside living cells. The intracellular milieu was simulated by a series of mineral buffers with addition of proteins. The pH values have been determined from the excitation ratios 490/435 nm for BCECF, FITC, carboxyfluorescein and fluorescein, and 450/400 nm for pyranine, emission ratios 518/529 nm for BCECF and 635/590 nm for SNARF. The spectrally determined values were then compared with the pH values of buffers measured by a glass electrode. Using the data from the calibration procedure, we evaluated individual intracellular pH values of a large number of cells within one cell population. The confocal ratio fluorescence microscopy revealed pH maps from which both cytoplasmic and vacuolar pH values could be determine, flow cytometry gave enormous amount of average intracellular pH values of individual cells of a whole cell population. Each cell population exhibited significant differences in both cytoplasmic pH values among individual cells. The pH distribution of a typical cell population appeared to fit a Gaussian curve. In yeast it was a Gaussian curve with half- width values around 0.4 pH unit. The men pH values depended on the growth phase, H-ATPase activity and external pH values. The preliminary result with the new membrane potential dye tetramethylrhodamine methyl ester indicated that similarly to pH values, there is a heterogeneity in membrane potential values among cell sin one cell population. The data presented above suggest that each ell behaves as an individual with an individual set up of its metabolism. This 'fine tuning' of the metabolism result in slightly higher or lower pH or membrane potential values that can be detected by fluorescence

  19. Multivariate evaluation of brain function by measuring regional cerebral blood flow and event-related potentials

    Energy Technology Data Exchange (ETDEWEB)

    Koga, Yoshihiko; Mochida, Masahiko; Shutara, Yoshikazu; Nakagawa, Kazumi [Kyorin Univ., Mitaka, Tokyo (Japan). School of Medicine; Nagata, Ken

    1998-07-01

    To measure the effect of events on human cognitive function, effects of odors by measurement regional cerebral blood flow (rCBF) and P300 were evaluated during the auditory odd-ball exercise. PET showed the increase in rCBF on the right hemisphere of the brain by coffee aroma. rCBF was measured by PET in 9 of right-handed healthy adults men, and P300 was by event-related potential (ERP) in each sex of 20 right-handed healthy adults. ERP showed the difference of the P300 amplitude between men and women, and showed the tendency, by odors except the lavender oil, that women had higher in the P300 amplitude than men. These results suggest the presence of effects on the cognitive function through emotional actions. Next, the relationship between rCBF and ERP were evaluated. The subjects were 9 of the right-handed healthy adults (average: 25.6{+-}3.4 years old). rCBF by PET and P300 amplitude by ERP were simultaneously recorded during the auditory odd-ball exercise using the tone-burst method (2 kHz of the low frequency aimed stimuli and 1 kHz of the high frequency non-aimed stimuli). The rCBF value was the highest at the transverse gyrus of Heschl and the lowest at the piriform cortex among 24 regions of interest (ROI) from both sides. The difference of P300 peak latent time among ROI was almost the same. The brain waves from Cz and Pz were similar and the average amplitude was highest at Pz. We found the high correlation in the right piriform cortex (Fz), and right (Fz, Cz) and left (Cz, Pz) transverse gyrus of Heschl between the P300 amplitude and rCBF. (K.H.)

  20. The adhesive potential of dentin bonding systems assessed using cuspal deflection measurements and cervical microleakage scores.

    Science.gov (United States)

    Sultan, Ahmed; Moorthy, Advan; Fleming, Garry J P

    2014-10-01

    To assess the cuspal deflection and cervical microleakage of standardized mesio-occluso-distal (MOD) cavities restored with a dimethacrylate resin-based-composite (RBC) placed with one 3-step, one 2-step and three 1-step bonding systems and compared with the unbound condition. Forty-eight sound maxillary premolar teeth with standardized MOD cavities were randomly allocated to six groups. Restoration was performed in eight oblique increments using a quartz-tungsten-halogen (QTH) light curing unit (LCU) with the bonding condition as the dependent variable. Buccal and palatal cuspal deflections were recorded post-irradiation using a twin channel deflection measuring gauge at 0, 30, 60 and 180s. Following restoration, the teeth were thermocycled, immersed in a 0.2% basic fuchsin dye for 24h, sectioned and examined for cervical microleakage assessment. The mean total cuspal deflection measurements with the one 3-step, one 2-step and three 1-step bonding systems were 11.26 (2.56), 10.95 (2.16), 10.03 (2.05) (Futurabond(®) DC SingleDose), 6.37 (1.37) (Adper™ Prompt™ L-Pop™), 8.98 (1.34) μm (All-Bond SE(®)), respectively when compared with the unbound condition (6.46 (1.88) μm) The one-way ANOVA of the total cuspal deflection measurements identified statistical differences (pbonding system although differences between the bonding systems were evident (pbonding technologies available to practitioners for RBCs. Poorly performing adhesives can be identified which indicated the technique may be useful as a screening tool for assessing existing and new bonding technologies which offers the potential to limit complications routinely encountered with Class II RBC restorations. Copyright © 2014 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

  1. Gastric potential difference measurements. The gastric mucosal integrity and function studied with a new method for measurement of the electric potential difference across the stomach wall

    DEFF Research Database (Denmark)

    Højgaard, L

    1991-01-01

    be reduced by allopurinol pretreatment, possibly due to the inhibition of oxygen-derived free radical formation. Gastric PD and pH were measured in volunteers and duodenal ulcer patients during Stroop's color word conflict test, in which mental stress causes sympathetic activation. A PD reduction and a p...

  2. A Method for Measuring Fast Time Evolutions of the Plasma Potential by Means of a Simple Emissive Probe

    DEFF Research Database (Denmark)

    Iizuka, S.; Michelsen, Poul; Juul Rasmussen, Jens;

    1981-01-01

    A method is presented for obtaining the temporal evolution of the plasma potential, which is assumed to be given by the floating potential of a simple emissive probe. The construction of the probe is also described. The method avoids the slow time response of the usual technique where the floating...... potential is measured across a high resistance. During each sweep of the probe voltage, the changing of the sign of the probe current, which is sampled at a specific time, gives rise to a negative pulse, driving the pen-lift of an X-Y recorder. Since the real floating potential is measured where the probe...

  3. Global Warming Potential and Eutrophication Potential of Biofuel Feedstock Crops Produced in Florida, Measured Under Different Scenarios

    Energy Technology Data Exchange (ETDEWEB)

    Izursa, Jose-Luis; Hanlon, Edward; Amponsah, Nana; Capece, John

    2013-02-15

    The agriculture sector is in a growing need to develop greenhouse gas (GHG) mitigation techniques to reduce the enhanced greenhouse effect. The challenge to the sector is not only to reduce net emissions but also increase production to meet growing demands for food, fiber, and biofuel. This study focuses on the changes in the GHG balance of three biofuel feedstock (biofuel sugarcane, energy-cane and sweet sorghum) considering changes caused by the adoption of conservationist practices such as reduced tillage, use of controlled-release fertilizers or when cultivation areas are converted from burned harvest to green harvest. Based on the Intergovernmental Panel on Climate Change (IPCC) (2006) balance and the Tools for the Reduction and Assessment of Chemical and Other Environmental Impacts (TRACI) characterization factors published by the EPA, the annual emission balance includes use energy (diesel and electricity), equipment, and ancillary materials, according to the mean annual consumption of supplies per hectare. The total amounts of GWP were 2740, 1791, and 1910 kg CO2e ha-1 y-1 for biofuel sugarcane, energy-cane and sweet sorghum, respectively, when produced with conventional tillage and sugarcane was burned prior to harvesting. Applying reduced tillage practices, the GHG emissions reduced to 13% for biofuel sugarcane, 23% for energy-cane and 8% for sweet sorghum. A similar decrease occurs when a controlled-release fertilizer practice is adopted, which helps reduce the total emission balance in 5%, 12% and 19% for biofuel sugarcane, energy-cane and sweet sorghum, respectively and a 31% average reduction in eutrophication potential. Moreover, the GHG emissions for biofuel sugarcane, with the adoption of green harvest, would result in a smaller GHG balance of 1924 kg CO2e ha-1 y-1, providing an effect strategy for GHG mitigation while still providing a profitable yield in Florida.

  4. Role of Lewis basicity and van der Waals forces in adhesion of silica MFI zeolites (010) with polyimides.

    Science.gov (United States)

    Lee, Jung-Hyun; Thio, Beng Joo Reginald; Bae, Tae-Hyun; Meredith, J Carson

    2009-08-18

    Adhesion between zeolites and polymers is a central factor in achieving defect-free mixed-matrix membranes for energy-efficient gas separations. In this work, atomic force microscopy (AFM) was used to measure adhesion forces between a pure silica MFI (ZSM-5: Zeolite Socony Mobil-Five) (010) zeolite probe and a series of polyimide (Matrimid 5218, 6FDA-DAM, 6FDA-6FpDA, and 6FDA-DAM:DABA (3:2)) and polyetherimide (Ultem 1000) polymers in air. Combined with measurements of surface energy of the polymer surfaces, the dependence of adhesion on polymer structure was determined. Adhesion force was strongly dependent on the Lewis basicity component of polymer surface energy and was less dependent on van der Waals (VDW) components, by a factor of about 6. Hydrogen bonding likely occurs between the acidic (electron acceptor) component of the zeolite surface (silanols or adsorbed water) and the basic (electron donor) component of the polymer surface. Adhesion force was strongly correlated with the mole fraction of carbonyls per monomer. We conclude that differences in adhesion as a function of polymer structure were primarily controlled by the polymer's Lewis basicity, contributed primarily by carbonyl groups.

  5. Design of a Computerised Flight Mill Device to Measure the Flight Potential of Different Insects

    Directory of Open Access Journals (Sweden)

    Antonio Martí-Campoy

    2016-04-01

    Full Text Available Several insect species pose a serious threat to different plant species, sometimes becoming a pest that produces significant damage to the landscape, biodiversity, and/or the economy. This is the case of Rhynchophorus ferrugineus Olivier (Coleoptera: Dryophthoridae, Semanotus laurasii Lucas (Coleoptera: Cerambycidae, and Monochamus galloprovincialis Olivier (Coleoptera: Cerambycidae, which have become serious threats to ornamental and productive trees all over the world such as palm trees, cypresses, and pines. Knowledge about their flight potential is very important for designing and applying measures targeted to reduce the negative effects from these pests. Studying the flight capability and behaviour of some insects is difficult due to their small size and the large area wherein they can fly, so we wondered how we could obtain information about their flight capabilities in a controlled environment. The answer came with the design of flight mills. Relevant data about the flight potential of these insects may be recorded and analysed by means of a flight mill. Once an insect is attached to the flight mill, it is able to fly in a circular direction without hitting walls or objects. By adding sensors to the flight mill, it is possible to record the number of revolutions and flight time. This paper presents a full description of a computer monitored flight mill. The description covers both the mechanical and the electronic parts in detail. The mill was designed to easily adapt to the anatomy of different insects and was successfully tested with individuals from three species R. ferrugineus, S. laurasii, and M. galloprovincialis.

  6. Transmission potential of chikungunya virus and control measures: the case of Italy.

    Directory of Open Access Journals (Sweden)

    Piero Poletti

    Full Text Available During summer 2007 Italy has experienced an epidemic caused by Chikungunya virus - the first large outbreak documented in a temperate climate country - with approximately 161 laboratory confirmed cases concentrated in two bordering villages in North-Eastern Italy comprising 3,968 inhabitants. The seroprevalence was recently estimated to be 10.2%. In this work we provide estimates of the transmission potential of the virus and we assess the efficacy of the measures undertaken by public health authorities to control the epidemic spread. To such aim, we developed a model describing the temporal dynamics of the competent vector, known as Aedes albopictus, explicitly depending on climatic factors, coupled to an epidemic transmission model describing the spread of the epidemic in both humans and mosquitoes. The cumulative number of notified cases predicted by the model was 185 on average (95% CI 117-278, in good agreement with observed data. The probability of observing a major outbreak after the introduction of an infective human case was estimated to be in the range of 32%-76%. We found that the basic reproduction number was in the range of 1.8-6 but it could have been even larger, depending on the density of mosquitoes, which in turn depends on seasonal meteorological effects, besides other local abiotic factors. These results confirm the increasing risk of tropical vector-borne diseases in temperate climate countries, as a consequence of globalization. However, our results show that an epidemic can be controlled by performing a timely intervention, even if the transmission potential of Chikungunya virus is sensibly high.

  7. Dependence of receptor potential and redox state of mitochondrial cytochromes on oxygen fraction measured in the blowfly eye in vivo

    NARCIS (Netherlands)

    Smits, R.P.; Jansonius, N.M.; Stavenga, D.G.

    1. The dependence of dark-adapted fly (Calliphora vicina) photoreceptors on oxygen was investigated by measuring the electroretinogram (ERG), the receptor potential, and the redox states of the mitochondrial cytochromes. The redox states were determined via reflection microspectrophotometry on

  8. The direct-to-indirect band gap crossover in two-dimensional van der Waals Indium Selenide crystals

    Science.gov (United States)

    Mudd, G. W.; Molas, M. R.; Chen, X.; Zólyomi, V.; Nogajewski, K.; Kudrynskyi, Z. R.; Kovalyuk, Z. D.; Yusa, G.; Makarovsky, O.; Eaves, L.; Potemski, M.; Fal’Ko, V. I.; Patanè, A.

    2016-12-01

    The electronic band structure of van der Waals (vdW) layered crystals has properties that depend on the composition, thickness and stacking of the component layers. Here we use density functional theory and high field magneto-optics to investigate the metal chalcogenide InSe, a recent addition to the family of vdW layered crystals, which transforms from a direct to an indirect band gap semiconductor as the number of layers is reduced. We investigate this direct-to-indirect bandgap crossover, demonstrate a highly tuneable optical response from the near infrared to the visible spectrum with decreasing layer thickness down to 2 layers, and report quantum dot-like optical emissions distributed over a wide range of energy. Our analysis also indicates that electron and exciton effective masses are weakly dependent on the layer thickness and are significantly smaller than in other vdW crystals. These properties are unprecedented within the large family of vdW crystals and demonstrate the potential of InSe for electronic and photonic technologies.

  9. Direct Measurement of Surface Dissolution Rates in Potential Nuclear Waste Forms: The Example of Pyrochlore.

    Science.gov (United States)

    Fischer, Cornelius; Finkeldei, Sarah; Brandt, Felix; Bosbach, Dirk; Luttge, Andreas

    2015-08-19

    The long-term stability of ceramic materials that are considered as potential nuclear waste forms is governed by heterogeneous surface reactivity. Thus, instead of a mean rate, the identification of one or more dominant contributors to the overall dissolution rate is the key to predict the stability of waste forms quantitatively. Direct surface measurements by vertical scanning interferometry (VSI) and their analysis via material flux maps and resulting dissolution rate spectra provide data about dominant rate contributors and their variability over time. Using pyrochlore (Nd2Zr2O7) pellet dissolution under acidic conditions as an example, we demonstrate the identification and quantification of dissolution rate contributors, based on VSI data and rate spectrum analysis. Heterogeneous surface alteration of pyrochlore varies by a factor of about 5 and additional material loss by chemo-mechanical grain pull-out within the uppermost grain layer. We identified four different rate contributors that are responsible for the observed dissolution rate range of single grains. Our new concept offers the opportunity to increase our mechanistic understanding and to predict quantitatively the alteration of ceramic waste forms.

  10. Measurment of threshold friction velocities at potential dust sources in semi-arid regions

    Science.gov (United States)

    King, Matthew A.

    The threshold friction velocities of potential dust sources in the US Southwest were measured in the field using a Portable Wind Tunnel, which is based on the Desert Research Institute's Portable In-Situ Wind Erosion Laboratory (PI-SWERL). A mix of both disturbed and undisturbed surfaces were included in this study. It was found that disturbed surfaces, such as those at the Iron King Mine tailings site, which is part of the EPA's Superfund program and contains surface concentrations of arsenic and lead reaching as high as 0.5% (w/w), had lower threshold friction velocities (0.32 m s -1 to 0.40 m s-1) in comparison to those of undisturbed surfaces (0.48 to 0.61 m s-1). Surface characteristics, such as particle size distribution, had effects on the threshold friction velocity (smaller grain sized distributions resulted in lower threshold friction velocities). Overall, the threshold friction velocities of disturbed surfaces were within the range of natural wind conditions, indicating that surfaces disturbed by human activity are more prone to causing windblown dust.

  11. Estimation of the Postmortem Interval by Measuring Blood Oxidation-reduction Potential Values

    Directory of Open Access Journals (Sweden)

    Zhuqing Jiang

    2016-01-01

    Full Text Available Accurate estimation of the postmortem interval (PMI is an important task in forensic practice. In the last half-century, the use of postmortem biochemistry has become an important ancillary method in determining the time of death. The present study was carried out to determine the correlation between blood oxidation-reduction potential (ORP values and PMIs, and to develop a three-dimensional surface equation to estimate the PMI under various temperature conditions. A total of 48 rabbits were placed into six groups and sacrificed by air embolism. Blood was obtained from the right ventricle of each rabbit, and specimens were stored at 10°C, 15°C, 20°C, 25°C, 30°C, and 35°C. At different PMIs (once every 4 h, the blood ORP values were measured using a PB-21 electrochemical analyzer. Statistical analysis and curve fitting of the data yielded cubic polynomial regression equations and a surface equation at different temperatures. Result: The results showed that there was a strong positive correlation between the blood ORP values at different temperatures and the PMI. This study provides another example of using a three-dimensional surface equation as a tool to estimate the PMI at various temperature conditions.

  12. Soil radon measurements as a potential tracer of tectonic and volcanic activity

    Science.gov (United States)

    Neri, Marco; Ferrera, Elisabetta; Giammanco, Salvatore; Currenti, Gilda; Cirrincione, Rosolino; Patanè, Giuseppe; Zanon, Vittorio

    2016-04-01

    In Earth Sciences there is a growing interest in studies concerning soil-radon activity, due to its potential as a tracer of numerous natural phenomena. Our work marks an advance in the comprehension of the interplay between tectonic activity, volcanic eruptions and gas release through faults. Soil-radon measurements, acquired on Mt. Etna volcano in 2009–2011, were analyzed. Our radon probe is sensitive to changes in both volcanic and seismic activity. Radon data were reviewed in light of the meteorological parameters. Soil samples were analyzed to characterize their uranium content. All data have been summarized in a physical model which identifies the radon sources, highlights the mechanism of radon transport and envisages how such a mechanism may change as a consequence of seismicity and volcanic events. In the NE of Etna, radon is released mainly from a depth of 50 m/day. Three periods of anomalous gas release were found (February 2010, January and February 2011). The trigger of the first anomaly was tectonic, while the second and third had a volcanic origin. These results mark a significant step towards a better understanding of the endogenous mechanisms that cause changes in soil-radon emission at active volcanoes.

  13. Soil radon measurements as a potential tracer of tectonic and volcanic activity.

    Science.gov (United States)

    Neri, Marco; Ferrera, Elisabetta; Giammanco, Salvatore; Currenti, Gilda; Cirrincione, Rosolino; Patanè, Giuseppe; Zanon, Vittorio

    2016-04-15

    In Earth Sciences there is a growing interest in studies concerning soil-radon activity, due to its potential as a tracer of numerous natural phenomena. Our work marks an advance in the comprehension of the interplay between tectonic activity, volcanic eruptions and gas release through faults. Soil-radon measurements, acquired on Mt. Etna volcano in 2009-2011, were analyzed. Our radon probe is sensitive to changes in both volcanic and seismic activity. Radon data were reviewed in light of the meteorological parameters. Soil samples were analyzed to characterize their uranium content. All data have been summarized in a physical model which identifies the radon sources, highlights the mechanism of radon transport and envisages how such a mechanism may change as a consequence of seismicity and volcanic events. In the NE of Etna, radon is released mainly from a depth of 50 m/day. Three periods of anomalous gas release were found (February 2010, January and February 2011). The trigger of the first anomaly was tectonic, while the second and third had a volcanic origin. These results mark a significant step towards a better understanding of the endogenous mechanisms that cause changes in soil-radon emission at active volcanoes.

  14. Exploring the potential of the cosmic-ray neutron method to measure interception storage dynamics

    Science.gov (United States)

    Jakobi, Jannis; Bogena, Heye; Huisman, Johan Alexander; Diekkrüger, Bernd; Vereecken, Harry

    2017-04-01

    Cosmic-ray neutron soil moisture probes are an emerging technology that relies on the negative correlation between near-surface fast neutron counts and soil moisture content. Hydrogen atoms in the soil, which are mainly present as water, moderate the secondary neutrons on the way back to the surface. Any application of this method needs to consider the sensitivity of the neutron counts to additional sources of hydrogen (e.g. above- and below-ground biomass, humidity of the lower atmosphere, lattice water of the soil minerals, organic matter and water in the litter layer, intercepted water in the canopy, and soil organic matter). In this study, we analyzed the effects of canopy-intercepted water on the cosmic-ray neutron counts. For this, an arable field cropped with sugar beet was instrumented with several cosmic-ray neutron probes and a wireless sensor network with more than 140 in-situ soil moisture sensors. Additionally rainfall interception was estimated using a new approach coupling throughfall measurements and leaf wetness sensors. The derived interception storage was used to correct for interception effects on cosmic ray neutrons to enhance soil water content prediction. Furthermore, the potential for a simultaneous prediction of above- and below-ground biomass, soil moisture and interception was tested.

  15. Transmission potential and design of adequate control measures for Marburg hemorrhagic fever.

    Directory of Open Access Journals (Sweden)

    Marco Ajelli

    Full Text Available Marburg hemorrhagic fever is rare yet among the most severe diseases affecting humans, with case fatality ratio even higher than 80%. By analyzing the largest documented Marburg hemorrhagic fever epidemic, which occurred in Angola in 2005 and caused 329 deaths, and data on viral load over time in non-human primates, we make an assessment of transmissibility and severity of the disease. We also give insight into the control of new Marburg hemorrhagic fever epidemics to inform appropriate health responses. We estimated the distribution of the generation time to have mean 9 days (95%CI: 8.2-10 days and standard deviation 5.4 days (95%CI: 3.9-8.6 days, and the basic reproduction number to be R(0 = 1.59 (95%CI: 1.53-1.66. Model simulations suggest that a timely isolation of cases, starting no later than 2-3 days after symptoms onset, is sufficient to contain an outbreak. Our analysis reveals that Marburg hemorrhagic fever is characterized by a relatively small reproduction number and by a relatively long generation time. Such factors, along with the extremely high severity and fatality, support the rare occurrence of large epidemics in human populations. Our results also support the effectiveness of social distancing measures--case isolation in particular--to contain or at least to mitigate an emerging outbreak. This work represents an advance in the knowledge required to manage a potential Marburg hemorrhagic fever epidemic.

  16. Auditory evoked potentials in patients with major depressive disorder measured by Emotiv system.

    Science.gov (United States)

    Wang, Dongcui; Mo, Fongming; Zhang, Yangde; Yang, Chao; Liu, Jun; Chen, Zhencheng; Zhao, Jinfeng

    2015-01-01

    In a previous study (unpublished), Emotiv headset was validated for capturing event-related potentials (ERPs) from normal subjects. In the present follow-up study, the signal quality of Emotiv headset was tested by the accuracy rate of discriminating Major Depressive Disorder (MDD) patients from the normal subjects. ERPs of 22 MDD patients and 15 normal subjects were induced by an auditory oddball task and the amplitude of N1, N2 and P3 of ERP components were specifically analyzed. The features of ERPs were statistically investigated. It is found that Emotiv headset is capable of discriminating the abnormal N1, N2 and P3 components in MDD patients. Relief-F algorithm was applied to all features for feature selection. The selected features were then input to a linear discriminant analysis (LDA) classifier with leave-one-out cross-validation to characterize the ERP features of MDD. 127 possible combinations out of the selected 7 ERP features were classified using LDA. The best classification accuracy was achieved to be 89.66%. These results suggest that MDD patients are identifiable from normal subjects by ERPs measured by Emotiv headset.

  17. Oxygen potential measurements in high burnup LWR U0 2 fuel

    Science.gov (United States)

    Matzke, Hj.

    1995-05-01

    A miniature solid state galvanic cell was used to measure the oxygen potential Δ overlineG( O2) of reactor irradiated U0 2 fuel at different burnups in the range of 28 to ⩾ 150 GWd d/t M. This very high burnup was achieved in the rim region of a fuel with a cross section average burnup of 75 GWd d/t M. The fuels had different enrichments and therefore different contributions of fission of 235U and 239Pu. The temperature range covered was 900 to 1350 K. None of the fuels showed a significant oxidation. Rather, if allowance is made for the dissolved rare earth fission products and the Pu formed during irradiation, some of the fuels were very slightly substoichiometric and the highest possible degree of oxidation corresponded to U0 2.001. In general, the Δ overlineG( O2) at 750°C was about -400 kJ/mol, corresponding to the Δ overlineG( O2) of the reaction Mo + O 2 → MoO 2. The implication of these results which are in contrast to commonly assumed ideas that U0 2 fuel oxidizes due to burnup, are discussed and the importance of the fission product Mo and of the zircaloy clad as oxygen buffers is outlined.

  18. Manifest variable path analysis: potentially serious and misleading consequences due to uncorrected measurement error.

    Science.gov (United States)

    Cole, David A; Preacher, Kristopher J

    2014-06-01

    Despite clear evidence that manifest variable path analysis requires highly reliable measures, path analyses with fallible measures are commonplace even in premier journals. Using fallible measures in path analysis can cause several serious problems: (a) As measurement error pervades a given data set, many path coefficients may be either over- or underestimated. (b) Extensive measurement error diminishes power and can prevent invalid models from being rejected. (c) Even a little measurement error can cause valid models to appear invalid. (d) Differential measurement error in various parts of a model can change the substantive conclusions that derive from path analysis. (e) All of these problems become increasingly serious and intractable as models become more complex. Methods to prevent and correct these problems are reviewed. The conclusion is that researchers should use more reliable measures (or correct for measurement error in the measures they do use), obtain multiple measures for use in latent variable modeling, and test simpler models containing fewer variables.

  19. Discovery of intrinsic ferromagnetism in two-dimensional van der Waals crystals

    Science.gov (United States)

    Gong, Cheng; Li, Lin; Li, Zhenglu; Ji, Huiwen; Stern, Alex; Xia, Yang; Cao, Ting; Bao, Wei; Wang, Chenzhe; Wang, Yuan; Qiu, Z. Q.; Cava, R. J.; Louie, Steven G.; Xia, Jing; Zhang, Xiang

    2017-06-01

    The realization of long-range ferromagnetic order in two-dimensional van der Waals crystals, combined with their rich electronic and optical properties, could lead to new magnetic, magnetoelectric and magneto-optic applications. In two-dimensional systems, the long-range magnetic order is strongly suppressed by thermal fluctuations, according to the Mermin-Wagner theorem; however, these thermal fluctuations can be counteracted by magnetic anisotropy. Previous efforts, based on defect and composition engineering, or the proximity effect, introduced magnetic responses only locally or extrinsically. Here we report intrinsic long-range ferromagnetic order in pristine Cr2Ge2Te6 atomic layers, as revealed by scanning magneto-optic Kerr microscopy. In this magnetically soft, two-dimensional van der Waals ferromagnet, we achieve unprecedented control of the transition temperature (between ferromagnetic and paramagnetic states) using very small fields (smaller than 0.3 tesla). This result is in contrast to the insensitivity of the transition temperature to magnetic fields in the three-dimensional regime. We found that the small applied field leads to an effective anisotropy that is much greater than the near-zero magnetocrystalline anisotropy, opening up a large spin-wave excitation gap. We explain the observed phenomenon using renormalized spin-wave theory and conclude that the unusual field dependence of the transition temperature is a hallmark of soft, two-dimensional ferromagnetic van der Waals crystals. Cr2Ge2Te6 is a nearly ideal two-dimensional Heisenberg ferromagnet and so will be useful for studying fundamental spin behaviours, opening the door to exploring new applications such as ultra-compact spintronics.

  20. Effect of adsorption of charged macromolecules on streaming and membrane potential values measured with a microporous polysulfone membrane

    DEFF Research Database (Denmark)

    Benavente, J.; Jonsson, Gunnar Eigil

    1997-01-01

    Changes in streaming and membrane potentials measured across a commercial microporous polysulfone membrane as a result of the adsorption of differently charged macromolecules were studied. Measurements were carried out with different NaCl solutions (10(-3) M to 5 x 10(-2) M) and their mixtures...

  1. Atomically thin resonant tunnel diodes built from synthetic van der Waals heterostructures

    Science.gov (United States)

    Lin, Yu-Chuan; Ghosh, Ram Krishna; Addou, Rafik; Lu, Ning; Eichfeld, Sarah M.; Zhu, Hui; Li, Ming-Yang; Peng, Xin; Kim, Moon J.; Li, Lain-Jong; Wallace, Robert M.; Datta, Suman; Robinson, Joshua A.

    2015-06-01

    Vertical integration of two-dimensional van der Waals materials is predicted to lead to novel electronic and optical properties not found in the constituent layers. Here, we present the direct synthesis of two unique, atomically thin, multi-junction heterostructures by combining graphene with the monolayer transition-metal dichalcogenides: molybdenum disulfide (MoS2), molybdenum diselenide (MoSe2) and tungsten diselenide (WSe2). The realization of MoS2-WSe2-graphene and WSe2-MoS2-graphene heterostructures leads to resonant tunnelling in an atomically thin stack with spectrally narrow, room temperature negative differential resistance characteristics.

  2. Influence of van der Waals forces on the adsorption structure of benzene on silicon

    CERN Document Server

    Johnston, Karen; Lundqvist, Bengt I; Nieminen, Risto M

    2008-01-01

    Two different adsorption configurations of benzene on the Si(001)-(2x1) surface, the tight-bridge and butterfly structures, were studied using density functional theory. Several exchange and correlation functionals were used, including the recently developed vdW-DF functional, which accounts for the effect of van der Waals forces. In contrast to the PBE, revPBE and other GGA functionals, the vdW-DF functional finds that, for most coverages, the adsorption energy of the butterfly structure is greater than that of the tight-bridge structure.

  3. Bond paths and van der Waals interactions in orpiment, As2S3.

    Science.gov (United States)

    Gibbs, G V; Wallace, A F; Zallen, R; Downs, R T; Ross, N L; Cox, D F; Rosso, K M

    2010-06-17

    The calculated electron density distribution for orpiment, As(2)S(3), reveals that As-S, S-S, and As-As bond paths are associated with the experimental interlayer directed bonded interactions detected in a combined infrared and Raman study. The successful modeling of the infrared- and Raman-determined interlayer bonded interactions together with bond paths and the structuralization of a variety of inorganic molecules in terms of "key-lock" bond path mainstays support the argument that van der Waals forces in inorganic molecular crystals are directional.

  4. Protein Adsorption into Mesopores: A Combination of Electrostatic Interaction, Counterion Release and van der Waals Forces

    CERN Document Server

    Moerz, Sebastian T

    2015-01-01

    Bovine heart cytochrome c has been immobilized into the mesoporous silica host material SBA-15 in both its native folded and urea-unfolded state. The comparison of the two folding states' behavior casts doubt on the commonly used explanation of cytochrome c adsorption, i.e. the electrostatic interaction model. A detailed investigation of the protein binding as a function of pH and ionic strength of the buffer solution reveals the complex nature of the protein-silica interaction. Electrostatic interaction, van der Waals forces and entropic contributions by counterion release each contribute to adsorption on the silica pore walls.

  5. Droplet evaporation in one-component fluids: Dynamic van der Waals theory

    OpenAIRE

    Teshigawara, Ryohei; Onuki, Akira

    2008-01-01

    In a one-component fluid, we investigate evaporation of a small axysymmetric liquid droplet in the partial wetting condition on a heated wall at $T\\sim 0.9 T_c$. In the dynamic van der Waals theory (Phys. Rev. E {\\bf 75}, 036304 (2007)), we take into account the latent heat transport from liquid to gas upon evaporation. Along the gas-liquid interface, the temperature is nearly equal to the equilibrium coexisting temperature away from the substrate, but it rises sharply to the wall temperature...

  6. Field effect in graphene-based van der Waals heterostructures: Stacking sequence matters.

    Science.gov (United States)

    Stradi, Daniele; Papior, Nick; Hansen, Ole; Brandbyge, Mads

    2017-03-06

    Stacked van der Waals (vdW) heterostructures where semi-conducting two-dimensional (2D) materials are contacted by overlayed graphene electrodes enable atomically-thin, flexible electronics. We use first-principles quantum transport simulations of graphene- contacted MoS2 devices to show how the transistor effect critically depends on the stacking configuration relative to the gate electrode. We can trace this behavior to the stacking-dependent response of the contact region to the capacitive electric field induced by the gate. The contact resistance is a central parameter and our observation establishes an important design rule for ultra-thin devices based on 2D atomic crystals.

  7. Van der Waals coefficients for alkali metal clusters and their size dependence

    Indian Academy of Sciences (India)

    Arup Banerjee; Manoj K Harbola

    2006-02-01

    In this paper we employ the hydrodynamic formulation of time-dependent density functional theory to obtain the van der Waals coefficients 6 and 8 of alkali metal clusters of various sizes including very large clusters. Such calculations become computationally very demanding in the orbital-based Kohn-Sham formalism, but are quite simple in the hydrodynamic approach. We show that for interactions between the clusters of the same sizes, 6 and 8 scale as the sixth and the eighth power of the cluster radius, respectively, and approach their classically predicted values for the large size clusters.

  8. Variations of the Lifshitz-van der Waals force between metals immersed in liquids

    CERN Document Server

    Esquivel-Sirvent, R

    2010-01-01

    We present a theoretical calculation of the Lifshitz-van der Waals force between two metallic slabs embedded in a fluid, taking into account the change of the Drude parameters of the metals when in contact with liquids of different index of refraction. For the three liquids considered in this work, water, $CCl_3F$ and $ CBr_3F$ the change in the Drude parameters of the metal imply a difference of up to 15% in the determination of the force at short separations. These variations in the force is bigger for liquids with a higher index of refraction.

  9. van der Waals interactions between nanotubes and nanoparticles for controlled assembly of composite nanostructures.

    Science.gov (United States)

    Rance, Graham A; Marsh, Dan H; Bourne, Stephen J; Reade, Thomas J; Khlobystov, Andrei N

    2010-08-24

    We have demonstrated that ubiquitous van der Waals forces are significant in controlling the interactions between nanoparticles and nanotubes. The adsorption of gold nanoparticles (AuNPs) on nanotubes (MWNTs) obeys a simple quadratic dependence on the nanotube surface area, regardless of the source of AuNPs and MWNTs. Changes in the geometric parameters of the components have pronounced effects on the affinity of nanoparticles for nanotubes, with larger, more polarizable nanostructures exhibiting stronger attractive interactions, the impact of which changes in the following order MWNT diameter > AuNP diameter > MWNT length.

  10. Stability of Multidimensional Phase Transitions in a Steady van der Waals Flow

    Institute of Scientific and Technical Information of China (English)

    Shuyi ZHANG

    2008-01-01

    In this paper,the author studies the multidimensional stability of subsonic phase transitions in a steady supersonic flow of van der Waals type.The viscosity capillarity criterion (in "Arch.Rat.Mech.Anal.,81(4),1983,301-315") is used to seek physical admissible planar waves.By showing the Lopatinski determinant being non-zero,it is proved that subsonic phase transitions are uniformly stable in the sense of Majda (in "Mem.Amer.Math.Soc.,41(275),1983,1-95") under both one dimensional and multidimensional perturbations.

  11. Controlled Synthesis of Organic/Inorganic van der Waals Solid for Tunable Light-Matter Interactions.

    Science.gov (United States)

    Niu, Lin; Liu, Xinfeng; Cong, Chunxiao; Wu, Chunyang; Wu, Di; Chang, Tay Rong; Wang, Hong; Zeng, Qingsheng; Zhou, Jiadong; Wang, Xingli; Fu, Wei; Yu, Peng; Fu, Qundong; Najmaei, Sina; Zhang, Zhuhua; Yakobson, Boris I; Tay, Beng Kang; Zhou, Wu; Jeng, Horng Tay; Lin, Hsin; Sum, Tze Chien; Jin, Chuanhong; He, Haiyong; Yu, Ting; Liu, Zheng

    2015-12-16

    High-quality organic and inorganic van der Waals (vdW) solids are realized using methylammonium lead halide (CH3 NH3 PbI3 ) as the organic part (organic perovskite) and 2D inorganic monolayers as counterparts. By stacking on various 2D monolayers, the vdW solids exhibit dramatically different light emissions. Futhermore, organic/h-BN vdW solid arrays are patterned for red-light emission. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Atomically thin resonant tunnel diodes built from synthetic van der Waals heterostructures

    KAUST Repository

    Lin, Yu-Chuan

    2015-06-19

    Vertical integration of two-dimensional van der Waals materials is predicted to lead to novel electronic and optical properties not found in the constituent layers. Here, we present the direct synthesis of two unique, atomically thin, multi-junction heterostructures by combining graphene with the monolayer transition-metal dichalcogenides: molybdenum disulfide (MoS2), molybdenum diselenide (MoSe2) and tungsten diselenide (WSe2). The realization of MoS2–WSe2–graphene and WSe2–MoS2–graphene heterostructures leads to resonant tunnelling in an atomically thin stack with spectrally narrow, room temperature negative differential resistance characteristics.

  13. Room temperature electroluminescence from mechanically formed van der Waals III–VI homojunctions and heterojunctions

    OpenAIRE

    Balakrishnan, Nilanthy; Kudrynskyi, Zakhar R.; Fay, Mike W.; Mudd, Garry W.; Svatek, Simon A; Makarovsky, Oleg; Kovalyuk, Zakhar D.; Eaves, Laurence; Peter H. Beton; Patanè, Amalia

    2014-01-01

    Room temperature electroluminescence from semiconductor junctions is demonstrated. The junctions are fabricated by the exfoliation and direct mechanical adhesion of InSe and GaSe van der Waals layered crystals. Homojunction diodes formed from layers of p- and n-type InSe exhibit electroluminescence at energies close to the bandgap energy of InSe (Eg= 1.26 eV). In contrast, heterojunction diodes formed by combining layers of p-type GaSe and n-type InSe emit photons at lower energies, which is ...

  14. Interlayer coupling effects on Schottky barrier in the arsenene-graphene van der Waals heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Xia, Congxin, E-mail: xiacongxin@htu.edu.cn; Xue, Bin; Wang, Tianxing; Peng, Yuting [Department of Physic, Henan Normal University, Xinxiang 453007 (China); Jia, Yu [School of Physics and Engineering, Zhengzhou University, Zhengzhou 450052 (China)

    2015-11-09

    The electronic characteristics of arsenene-graphene van der Waals (vdW) heterostructures are studied by using first-principles methods. The results show that a linear Dirac-like dispersion relation around the Fermi level can be quite well preserved in the vdW heterostructures. Moreover, the p-type Schottky barrier (0.18 eV) to n-type Schottky barrier (0.31 eV) transition occurs when the interlayer distance increases from 2.8 to 4.5 Å, which indicates that the Schottky barrier can be tuned effectively by the interlayer distance in the vdW heterostructures.

  15. Microwave probes Dipole Blockade and van der Waals Forces in a Cold Rydberg Gas

    CERN Document Server

    Teixeira, R Celistrino; Nguyen, Thanh Long; Cantat-Moltrecht, T; Raimond, Jean-Michel; Haroche, S; Gleyzes, S; Brune, M

    2015-01-01

    We show that microwave spectroscopy of a dense Rydberg gas trapped on a superconducting atom chip in the dipole blockade regime reveals directly the dipole-dipole many-body interaction energy spectrum. We use this method to investigate the expansion of the Rydberg cloud under the effect of repulsive van der Waals forces and the breakdown of the frozen gas approximation. This study opens a promising route for quantum simulation of many-body systems and quantum information transport in chains of strongly interacting Rydberg atoms.

  16. Silicene on MoS2: role of the van der Waals interaction

    KAUST Repository

    Jiajie Zhu,

    2015-10-13

    We demonstrate for silicene on MoS2 substrate the limitations of the predictive power of first principles calculations based on van der Waals density functional theory. Only the optB86b-vdW functional is found to give reasonable agreement with experimental results on structural properties, while for all other investigated functionals the interlayer interaction is underestimated or the charge redistribution at the interface is not described correctly so that the predicted electronic structure is qualitatively wrong. © 2015 IOP Publishing Ltd.

  17. Normal and dichromatic color discrimination measured with transient visual evoked potential.

    Science.gov (United States)

    Gomes, Bruno D; Souza, Givago S; Rodrigues, Anderson R; Saito, Cézar A; Silveira, Luiz Carlos L; da Silva Filho, Manoel

    2006-01-01

    It would be informative to have an electrophysiological method to study, in an objective way, the effects of mercury exposure and other neurotoxics on human color vision performance. The purpose of the present work was to study human color discrimination by measuring chromatic difference thresholds with visual evoked potential (VEP). Six young normal trichromats (24 +/- 1 years old) and one deutan (26 years old) were tested. The stimuli consisted of sinusoidal isoluminant chromatic gratings made from chromaticity pairs located along four different color directions centered on two reference points. Heterochromatic flicker photometry (HFP) protocol was used to obtain the isoluminance condition for every subject and for all chromaticity pairs. Spatial frequency was 2 cycles/deg. Presentation mode comprised onset (300 ms)/offset (700 ms) periods. As previously described, we found a negative deflection in the VEP which was related to the chromatic difference: as chromatic difference increased, amplitude increased and latency decreased. VEP response amplitude was plotted against distance in the CIE 1976 color space between the grating chromaticities and fitted with a regression line. We found color thresholds by extrapolating the fitting to null amplitude values. The thresholds were plotted in the CIE 1976 color space as MacAdam ellipses. In normal trichromats the ellipses had small size, low ellipticity, and were vertically oriented. In the deutan subject, the ellipses had large size, high ellipticity, and were oriented towards the deutan copunctal locus. The VEP thresholds were similar to those obtained using grating stimuli and psychophysical procedures, however smaller than those obtained using pseudoisochromatic stimuli (Mollon-Reffin method). We concluded that transient VEP amplitude as a function of contrast can be reliably used in objective studies of chromatic discrimination performance in normal and altered human subjects.

  18. Splenius capitis is a reliable target for measuring cervical vestibular evoked myogenic potentials in adults.

    Science.gov (United States)

    Camp, Aaron J; Gu, Chao; Cushing, Sharon L; Gordon, Karen A; Corneil, Brian D

    2017-02-08

    The cervical vestibular evoked myogenic potential (cVEMP) is a common and simple test of vestibulospinal reflex patency. In the clinic, cVEMPs are measured in response to loud sounds from the sternocleidomastoid (SCM) on the ventral neck, as subjects maintain an uncomfortable head posture needed to recruit SCM. Here we characterize the cVEMP in a dorsal neck turner (splenius capitis; SPL), and compare it with the SCM cVEMP. cVEMPs were recorded simultaneously via surface electromyography from SCM and SPL from 17 healthy subjects in a variety of postures, including head-turned postures adopted while either seated or standing, and the clinical posture. Like the SCM cVEMP recorded ipsilateral to the side of sound stimulation, the cVEMP on the contralateral SPL (synergistic with ipsilateral SCM) was characterized by a biphasic wave of muscle activity that began at ~ 13 ms. cVEMP reliability was higher on SPL vs. SCM in standing postures (chi-squared; P < 0.05), and equivalent results were obtained from SPL in a standing or seated posture. In 9 of the 17 subjects, we also obtained bilateral intramuscular (IM) recordings from SPL at the same time as the surface recordings. In these subjects, the initial surface response in SPL was associated with a consistent decrease in multi-unit IM SPL activity. Overall, these results demonstrate that SPL recordings offer a complimentary target for cVEMP assessments. The expression of SPL cVEMPs in simple head-turned postures may also improve the utility of cVEMP testing for vestibular assessment in children, the elderly, or non-compliant.

  19. Potential risk of malposition of nasogastric tube using nose-ear-xiphoid measurement.

    Directory of Open Access Journals (Sweden)

    Yen-Chun Chen

    Full Text Available BACKGROUND: Correct placement of nasogastric tubes provide proper functionality and maximize benefit and minimize risk. The Nose-Ear-Xiphoid (NEX body surface estimate method is a long-lasting technique, and this study was conducted to evaluate the correlation between NEX method and the secure insertion depth of nasogastric tube. MATERIALS AND METHODS: Thirty patients with nasogastric tube insertion who received whole body positron emission tomography with computerized tomography scan (PET-CT were recruited. All data were gathered in the image center, which included Nose-Ear (NE, Ear-Xiphoid (EX, Nose-Ear-Xiphoid (NEX, glabella-xiphoid (GX and glabella-umbilicus (GU lengths. The distances of the inserted portion of the nasogastric tube between the cardiac and the nostril were measured by multiplanar reconstruction algorithm. RESULTS: Only one patient successfully placed all side-holes into the stomach while using NEX method to estimate inserting depth. Twenty-nine patients (96.7% failed to place correctly. Fourteen participants had one or more side-holes in both the esophagus and the stomach sides. Fifteen patients could not pass through any side-hole across the gastroesophageal junction. They had shorter EX distances (p = 0.02, but no difference among the NE distances. Body height had the highest statistical correlation with nasogastric tube length (adjusted R(2 = 0.459, as compared with the NEX, GX and GU body surface methods. CONCLUSION: This study suggests that NEX method is inappropriate for adult patients to estimate the ideal inserting length of nasogastric tube. Physicians should realize these underinsertions with any side-hole above the gastroesophageal junctions may increase the potential risk of complications.

  20. A comparison of inflection point and floating point emissive probe techniques for electric potential measurements in a Hall thruster plasma

    Science.gov (United States)

    Sheehan, J. P.; Raitses, Yevgeny; Hershkowitz, Noah; Fisch, Nathaniel

    2010-11-01

    Theory suggests that when increasing the electron emission of an emissive probe the floating potential will saturate ˜Te/e below the plasma potential. This can introduce significant errors in plasma potential measurements in Hall thrusters where Te> 10 eV. The method of determining the plasma potential from the inflection point of emissive IV traces in the limit of zero emission may give a more accurate measurement of the plasma potential. The two methods are compared in a Hall thruster where ne˜10^11 cm-3, Te˜20 eV, and ion flows are significant. The results can be generalized to other types of plasmas.

  1. Measurements of the large-scale direct-current Earth potential and possible implications for the geomagnetic dynamo.

    Science.gov (United States)

    1985-07-05

    The magnitude of the large-scale direct-current earth potential was measured on a section of a recently laid transatlantic telecommunications cable. Analysis of the data acquired on the 4476-kilometer cable yielded a mean direct-current potential drop of less than about 0.072 +/- 0.050 millivolts per kilometer. Interpreted in terms of a generation of the potential by the earth's geodynamo, such a small value of the mean potential implies that the toroidal and poloidal magnetic fields of the dynamo are approximately equal at the core-mantle boundary.

  2. Measuring the Chemical Potential of the Martian Regolith to Generate and Sustain Life

    Science.gov (United States)

    Kounaves, S. P.; Buehler, M. G.; Kuhlman, K. R.

    1999-01-01

    such, requires an aqueous environment. Deciphering die chemical speciation of this aqueous environment is the key to recognizing therein the biosignatures of any extinct or present life forms. Identifying the soluble (ionic and nonionic) components by reacting a currently dormant environment can provide a "picture" of the thermodynamics and chemical components of a possibly bioactive environment. The only devices which can provide such information are electrochemical sensors based on the potentiometric ion selective electrodes (ISEs) and on dynamic techniques such as cyclic voltammetry (CV) and stripping voltammetry (SV). Such an array of devices can provide not only the chemical composition of a water-soluble Martian soil sample, but also several other vital chemical parameters such as pH, conductivity, redox potential, and dissolved gases. To address these issues we have been investigating the possible use of an electrochemically-based ion sensor array as a new integrated approach to quantitative analytical and chemometric electrochemical measurements. The sensor array will consist of specific and semispecific ion selective and amperometric transducers, which can simultaneously and continuously identify and semiquantitatively determine over 50 organic and inorganic analytes in water-based environments. Several individual sensors, based on the same principle, have been flight-tested and have been installed as part of the MECA instrumentation on the Mars 2001 Lander for in-situ analyses. However, the microfabrication, integration and multiplexing of such a large number of these sensors on a single substrate have not been previously attempted.

  3. Measuring the Chemical Potential of the Martian Regolith to Generate and Sustain Life

    Science.gov (United States)

    Kounaves, S. P.; Buehler, M. G.; Kuhlman, K. R.

    1999-01-01

    such, requires an aqueous environment. Deciphering die chemical speciation of this aqueous environment is the key to recognizing therein the biosignatures of any extinct or present life forms. Identifying the soluble (ionic and nonionic) components by reacting a currently dormant environment can provide a "picture" of the thermodynamics and chemical components of a possibly bioactive environment. The only devices which can provide such information are electrochemical sensors based on the potentiometric ion selective electrodes (ISEs) and on dynamic techniques such as cyclic voltammetry (CV) and stripping voltammetry (SV). Such an array of devices can provide not only the chemical composition of a water-soluble Martian soil sample, but also several other vital chemical parameters such as pH, conductivity, redox potential, and dissolved gases. To address these issues we have been investigating the possible use of an electrochemically-based ion sensor array as a new integrated approach to quantitative analytical and chemometric electrochemical measurements. The sensor array will consist of specific and semispecific ion selective and amperometric transducers, which can simultaneously and continuously identify and semiquantitatively determine over 50 organic and inorganic analytes in water-based environments. Several individual sensors, based on the same principle, have been flight-tested and have been installed as part of the MECA instrumentation on the Mars 2001 Lander for in-situ analyses. However, the microfabrication, integration and multiplexing of such a large number of these sensors on a single substrate have not been previously attempted.

  4. Van der Waals interaction between microparticle and uniaxial crystal with application to hydrogen atoms and multiwall carbon nanotubes

    CERN Document Server

    Blagov, E V; Mostepanenko, V M

    2005-01-01

    The Lifshitz theory of the van der Waals force is extended for the case of an atom (molecule) interacting with a plane surface of an uniaxial crystal or with a long solid cylinder or cylindrical shell made of isotropic material or uniaxial crystal. For a microparticle near a semispace or flat plate made of an uniaxial crystal the exact expressions for the free energy of the van der Waals and Casimir-Polder interaction are presented. An approximate expression for the free energy of microparticle- cylinder interaction is obtained which becomes precise for microparticle-cylinder separations much smaller than cylinder radius. The obtained expressions are used to investigate the van der Waals interaction between hydrogen atoms (molecules) and graphite plates or multiwall carbon nanotubes. To accomplish this the behavior of graphite dielectric permittivities along the imaginary frequency axis is found using the optical data for the complex refractive index of graphite for the ordinary and extraordinary rays. It is ...

  5. Simple model for analyzing Efimov energy and three-body recombination of three identical bosons with van der Waals interactions

    Science.gov (United States)

    Li, Jing-Lun; Hu, Xue-Jin; Han, Yong-Chang; Cong, Shu-Lin

    2016-09-01

    We construct a simple model to calculate the trimer bound state energy ET(n ) and three-body recombination rate K30 of three identical bosons with van der Waals interaction without using any two- or three-body fitting parameter. Using this simple model, we investigate the influence of the van der Waals finite-range effect on ET(n ) and K30. Our calculation shows that the finite-range effect leads to the ground trimer state energy ET(0 ) not crossing the atom-dimer threshold, and the scaled three-body recombination rate K30/a4 deviating from the universal three-body theory. The results of our simple model agree within a few percent with other theoretical works with van der Waals interaction and also the experimental data.

  6. Image method in the calculation of the van der Waals force between an atom and a conducting surface

    CERN Document Server

    Souza, Reinaldo de Melo e; Sigaud, C; Farina, C

    2012-01-01

    Initially, we make a detailed historical survey of van der Waals forces, collecting the main references on the subject. Then, we review a method recently proposed by Eberlein and Zietal to compute the dispersion van der Waals interaction between a neutral but polarizable atom and a perfectly conducting surface of arbitrary shape. This method has the advantage of relating the quantum problem to a corresponding classical one in electrostatics so that all one needs is to compute an appropriate Green function. We show how the image method of electrostatics can be conveniently used together with the Eberlein and Zietal mehtod (when the problem admits an image solution). We then illustrate this method in a couple of simple but important cases, including the atom-sphere system. Particularly, in our last example, we present an original result, namely, the van der Waals force between an atom and a boss hat made of a grounded conducting material.

  7. Image method in the calculation of the van der Waals force between an atom and a conducting surface

    Science.gov (United States)

    de Melo e Souza, Reinaldo; Kort-Kamp, W. J. M.; Sigaud, C.; Farina, C.

    2013-05-01

    After a brief survey of van der Waals forces, we review a method recently proposed by Eberlein and Zietal to compute the dispersion van der Waals interaction between a neutral but polarizable atom and a perfectly conducting surface of arbitrary shape. This method has the advantage of relating the quantum problem to a corresponding classical one in electrostatics in an enlightening way so that all one needs is to compute an appropriate Green function. We show how the image method of electrostatics can be conveniently used together with the Eberlein and Zietal method (when the image solution is known). We then illustrate this method in some simple but important cases, including the atom-sphere system. Finally, we present an original result for the van der Waals force between an atom and a boss hat made of a grounded conducting material.

  8. Event-related potentials as a measure of sleep disturbance: A tutorial review

    Directory of Open Access Journals (Sweden)

    Kenneth Campbell

    2010-01-01

    Full Text Available This article reviews event-related potentials (ERPs the minute responses of the human brain that are elicited by external auditory stimuli and how the ERPs can be used to measure sleep disturbance. ERPs consist of a series of negative- and positive-going components. A negative component peaking at about 100 ms, N1, is thought to reflect the outcome of a transient detector system, activated by change in the transient energy in an acoustic stimulus. Its output and thus the amplitude of N1 increases as the intensity level of the stimulus is increased and when the rate of presentation is slowed. When the output reaches a certain critical level, operations of the central executive are interrupted and attention is switched to the auditory channel. This switching of attention is thought to be indexed by a later positivity, P3a, peaking between 250 and 300 ms. In order to sleep, consciousness for all but the most relevant of stimuli must be prevented. Thus, during sleep onset and definitive non-rapid eye movement (NREM sleep, the amplitude of N1 diminishes to near-baseline level. The amplitude of P2, peaking from 180 to 200 ms, is however larger in NREM sleep than in wakefulness. P2 is thought to reflect an inhibitory process protecting sleep from irrelevant disturbance. As stimulus input becomes increasingly obtrusive, the amplitude of P2 also increases. With increasing obtrusiveness particularly when stimuli are presented slowly, a later large negativity, peaking at about 350 ms, N350, becomes apparent. N350 is unique to sleep, its amplitude also increasing as the stimulus becomes more obtrusive. Many authors postulate that when the N350 reaches a critical amplitude, a very large amplitude N550, a component of the K-Complex is elicited. The K-Complex can only be elicited during NREM sleep. The P2, N350 and N550 processes are thus conceived as sleep protective mechanisms, activated sequentially as the risk for disturbance increases. During REM sleep

  9. Benzene on Cu(111): I. Application of van der Waals-Density Functional Formalism to Determine Binding Sites and Energy Contour Map

    Science.gov (United States)

    Berland, Kristian; Einstein, T. L.; Hyldgaard, Per

    2010-03-01

    With a recently developed van der Waals density functional (vdW-DF)footnotetextM. Dion et al., Phys. Rev. Lett. 92 (2004) 246401 we study the adsorption of benzene on Cu(111).footnotetextKB, TLE, and PH, Phys. Rev. B 80 (2009) 155431 The vdW-DF inclusion of nonlocal correlations changes the relative stability of 8 high-symmetry binding-position options and increases the adsorption energy by over an order of magnitude, achieving good agreement with experiment. The metallic surface state survives benzene adsorption. From a contour plot of the potential energy, we find that benzene can move almost freely along a honeycomb web of ``corridors" linking fcc and hcp sites via bridge sites, consistent with the low diffusion barrier in experiment.

  10. An equal area law for the van der Waals transition of holographic entanglement entropy

    CERN Document Server

    Nguyen, Phuc H

    2015-01-01

    The Anti-de Sitter-Reissner-Nordstrom (AdS-RN) black hole in the canonical ensemble undergoes a phase transition similar to the liquid-gas phase transition. i.e. the isocharges on the entropy-temperature plane develop an unstable branch when the charge is smaller than a critical value. It was later discovered that the isocharges on the entanglement entropy-temperature plane also exhibit the same van der Waals-like structure. In this paper, we present numerical results which sharpen this similarity between entanglement entropy and black hole entropy, by showing that both of these entropies obey Maxwell's equal area law. Moreover, we checked this for two disk-shaped entangling regions of different sizes, and the conclusion seems to be valid regardless of the region's size. We checked the equal area law for AdS-RN in 4 and 5 dimensions, so that the conclusion seems to hold for any dimension. Finally, we also checked that the equal area law holds for a similar, van der Waals-like transition of the dyonic black ho...

  11. Understanding corrosion inhibition with van der Waals DFT methods: the case of benzotriazole.

    Science.gov (United States)

    Gattinoni, Chiara; Michaelides, Angelos

    2015-01-01

    The corrosion of materials is an undesirable and costly process affecting many areas of technology and everyday life. As such, considerable effort has gone into understanding and preventing it. Organic molecule based coatings can in certain circumstances act as effective corrosion inhibitors. Although they have been used to great effect for more than sixty years, how they function at the atomic-level is still a matter of debate. In this work, computer simulation approaches based on density functional theory are used to investigate benzotriazole (BTAH), one of the most widely used and studied corrosion inhibitors for copper. In particular, the structures formed by protonated and deprotonated BTAH molecules on Cu(111) have been determined and linked to their inhibiting properties. It is found that hydrogen bonding, van der Waals interactions and steric repulsions all contribute in shaping how BTAH molecules adsorb, with flat-lying structures preferred at low coverage and upright configurations preferred at high coverage. The interaction of the dehydrogenated benzotriazole molecule (BTA) with the copper surface is instead dominated by strong chemisorption via the azole moiety with the aid of copper adatoms. Structures of dimers or chains are found to be the most stable structures at all coverages, in good agreement with scanning tunnelling microscopy results. Benzotriazole thus shows a complex phase behaviour in which van der Waals forces play an important role and which depends on coverage and on its protonation state and all of these factors feasibly contribute to its effectiveness as a corrosion inhibitor.

  12. Van der Waals and resonance interactions between accelerated atoms in vacuum and the Unruh effect

    Science.gov (United States)

    Lattuca, M.; Marino, J.; Noto, A.; Passante, R.; Rizzuto, L.; Spagnolo, S.; Zhou, W.

    2017-08-01

    We discuss different physical effects related to the uniform acceleration of atoms in vacuum, in the framework of quantum electrodynamics. We first investigate the van der Waals/Casimir-Polder dispersion and resonance interactions between two uniformly accelerated atoms in vacuum. We show that the atomic acceleration significantly affects the van der Waals force, yielding a different scaling of the interaction with the interatomic distance and an explicit time dependence of the interaction energy. We argue how these results could allow for an indirect detection of the Unruh effect through dispersion interactions between atoms. We then consider the resonance interaction between two accelerated atoms, prepared in a correlated Bell-type state, and interacting with the electromagnetic field in the vacuum state, separating vacuum fluctuations and radiation reaction contributions, both in the free-space and in the presence of a perfectly reflecting plate. We show that nonthermal effects of acceleration manifest in the resonance interaction, yielding a change of the distance dependence of the resonance interaction energy. This suggests that the equivalence between temperature and acceleration does not apply to all radiative properties of accelerated atoms. To further explore this aspect, we evaluate the resonance interaction between two atoms in non inertial motion in the coaccelerated (Rindler) frame and show that in this case the assumption of an Unruh temperature for the field is not required for a complete equivalence of locally inertial and coaccelerated points of views.

  13. Thermal transport in van der Waals solids from first-principles calculations

    Science.gov (United States)

    Lindroth, Daniel O.; Erhart, Paul

    2016-09-01

    The lattice thermal expansion and conductivity in bulk Mo and W-based transition metal dichalcogenides are investigated by means of density functional and Boltzmann transport theory calculations. To this end, a recent van der Waals density functional (vdW-DF-CX) is employed, which is shown to yield excellent agreement with reference data for the structural parameters. The calculated in-plane thermal conductivity compares well with experimental room-temperature values, when phonon-phonon and isotopic scattering are included. To explain the behavior over the entire available temperature range one must, however, include additional (temperature independent) scattering mechanisms that limit the mean free path. Generally, the primary heat carrying modes have mean free paths of 1 μ m or more, which makes these materials very susceptible to structural defects. The conductivity of Mo- and W-based transition metal dichalcogenides is primarily determined by the chalcogenide species and increases in the order Te-Se-S. While for the tellurides and selenides the transition metal element has a negligible effect, the conductivity of WS2 is notably higher than for MoS2, which may be traced to the much larger phonon band gap of the former. Overall, the present study provides a consistent set of thermal conductivities that reveal chemical trends and constitute the basis for future investigations of van der Waals solids.

  14. An introduction to the Dieterici Equation and the van der Waal Equation

    Science.gov (United States)

    Sheldon, John

    2003-11-01

    The derivation of the ideal gas law by using the kinetic theory of gases is usually presented in an undergraduate physics thermodynamics texts and physical chemistry texts. Following these derivations is the introduction of nonideal effects and the empirical equations of state: the van der Waals equation and the Dieterici equation. These are sometimes are simply given without comment as to the origin of the terms in them. An introduction to a "derivation" of these equations, appropriate for the undergraduate thermodynamics course, is given herein. Empirical equations are not rigorously derived, but rather they are invented, the so-called derivation simply serves to make the empirical terms appear reasonable.The barometric equation is exploited to get an expression for the effective attractive molecular forces. The differential form of the barometric is derived using kinetic theory, then from the barometric equation we get the Dieterici Equation an expansion of the Dieterici Equation, yields the van der Waals Equation of state. The relationship between the empirical constants is also discussed

  15. van der Waals interaction energy and disjoining pressure at small separation.

    Science.gov (United States)

    White, Lee R

    2010-03-01

    The divergence of the van der Waals interaction energy E(132)(L) between plane half-spaces 1 and 2 separated by medium 3 as the separation distance L tends to zero is naively thought of as due to the overlap of the atomic polarization centers. It follows that it may therefore be prevented by properly allowing for the finite size of the atomic species which would prevent the overlap. The distance cutoff model is a simple example of such a modification. The present paper demonstrates that this is not ultimately the origin of the divergence and, that although finite atomic dimensions would alleviate the embarrassment, non-overlap does not properly address the thermodynamic restriction that pertains to the interaction energy. By allowing in an albeit approximate way for the wavelength dependence of the material dielectric response functions epsilon(i xi, k) which arise naturally in the modern Lifshitz theory for this interaction, a form for the van der Waals energy and the corresponding disjoining pressure may be derived which obey the thermodynamic constraint and remove the divergence as L-->0. The energy and disjoining pressure in this new model are compared with the classic non-retarded results and the length cutoff model.

  16. Exciton–polaritons in van der Waals heterostructures embedded in tunable microcavities

    Science.gov (United States)

    Dufferwiel, S.; Schwarz, S.; Withers, F.; Trichet, A. A. P.; Li, F.; Sich, M.; Del Pozo-Zamudio, O.; Clark, C.; Nalitov, A.; Solnyshkov, D. D.; Malpuech, G.; Novoselov, K. S.; Smith, J. M.; Skolnick, M. S.; Krizhanovskii, D. N.; Tartakovskii, A. I.

    2015-01-01

    Layered materials can be assembled vertically to fabricate a new class of van der Waals heterostructures a few atomic layers thick, compatible with a wide range of substrates and optoelectronic device geometries, enabling new strategies for control of light–matter coupling. Here, we incorporate molybdenum diselenide/hexagonal boron nitride (MoSe2/hBN) quantum wells in a tunable optical microcavity. Part-light–part-matter polariton eigenstates are observed as a result of the strong coupling between MoSe2 excitons and cavity photons, evidenced from a clear anticrossing between the neutral exciton and the cavity modes with a splitting of 20 meV for a single MoSe2 monolayer, enhanced to 29 meV in MoSe2/hBN/MoSe2 double-quantum wells. The splitting at resonance provides an estimate of the exciton radiative lifetime of 0.4 ps. Our results pave the way for room-temperature polaritonic devices based on multiple-quantum-well van der Waals heterostructures, where polariton condensation and electrical polariton injection through the incorporation of graphene contacts may be realized. PMID:26446783

  17. Soil radon measurements as potential tracer of seismic and volcanic activity at Etna

    Science.gov (United States)

    Neri, Marco; Giammanco, Salvatore; Galli, Gianfranco; Ferrera, Elisabetta

    2014-05-01

    Radon is a radioactive noble gas present in all rocks of the Earth. It's used by the scientific community as a tracer of natural phenomena related to outgassing from the soil along faults, fractures and crustal discontinuity. Recently, radon has also been used on active volcanoes such as Etna, both as a precursor of volcanic phenomena as well as in the study of the dynamics of faults. The Istituto Nazionale di Geofisica e Vulcanologia (INGV) performs discrete and continuous measurements of radon from soil at Etna since 2002. First studies concerned measurements of radon and thoron emissions from soil carried out on the E and SW flanks of Etna, in zones characterized by the presence of numerous seismogenic and aseismic faults. The statistical treatment of the geochemical data allowed recognizing anomaly thresholds, producing distribution maps that highlighted a significant spatial correlation between soil gas anomalies and tectonic lineaments. These studies confirmed that mapping the distribution of radon and thoron in soil gas can reveal hidden faults buried by recent soil cover. INGV permanent radon monitoring network was installed in July 2005. First results were obtained during the July 2006 eruption. The radon signal recorded at Torre del Filosofo (TdF, ~2950 m asl) was compared with volcanic tremor and thermal radiance data. The onset of explosive activity and a lava fountaining episode were preceded by some hours with increases in radon activity and more gradual increases in volcanic tremor. After 2006, Etna produced dozens of paroxysmal episodes from a new vent opened on the eastern flank of the Southeast Crater (summit area), that have built up a new, huge pyroclastic cone. In many cases we observed increase in radon activity some hours before the eruptive events. These observations suggest that radon emissions from the TdF zone are sensitive to the local geodynamic pressure induced by magma dynamics in the conduit systems. Other promising results were

  18. The van der Waals coefficients between carbon nanostructures and small molecules: A time-dependent density functional theory study.

    Science.gov (United States)

    Kamal, C; Ghanty, T K; Banerjee, Arup; Chakrabarti, Aparna

    2009-10-28

    We employ all-electron ab initio time-dependent density functional theory based method to calculate the long-range dipole-dipole dispersion coefficient, namely, the van der Waals (vdW) coefficient (C(6)) between fullerenes and finite-length carbon nanotubes as well as between these structures and different small molecules. Our aim is to accurately estimate the strength of the long-range vdW interaction in terms of the C(6) coefficients between these systems and also compare these values as a function of shape and size. The dispersion coefficients are obtained via Casimir-Polder relation. The calculations are carried out with the asymptotically correct exchange-correlation potential-the statistical average of orbital potential. It is observed from our calculations that the C(6) coefficients of the carbon nanotubes increase nonlinearly with length, which implies a much stronger vdW interaction between the longer carbon nanostructures compared with the shorter ones. Additionally, it is found that the values of C(6) and polarizability are about 40%-50% lower for the carbon cages when compared with the results corresponding to the quasi-one-dimensional nanotubes with equivalent number of atoms. From our calculations of the vdW coefficients between the small molecules and the carbon nanostructures, it is observed that for H(2), the C(6) value is much larger compared with that of He. It is found that the rare gas atoms have very low values of vdW coefficient with the carbon nanostructures. In contrast, it is found that other gas molecules, including the ones that are environmentally important, possess much higher C(6) values. Carbon tetrachloride as well as chlorine molecule show very high C(6) values with themselves as well as with the carbon nanostructures. This is due to the presence of the weakly bound seven electrons in the valence state for the halogen atoms, which makes these compounds much more polarizable compared with the others.

  19. 2D spatial profile measurements of potential fluctuation with heavy ion beam probe on the Large Helical Device

    Science.gov (United States)

    Shimizu, A.; Ido, T.; Nishiura, M.; Kato, S.; Ogawa, K.; Takahashi, H.; Igami, H.; Yoshimura, Y.; Kubo, S.; Shimozuma, T.

    2016-11-01

    Two-dimensional spatial profiles of potential fluctuation were measured with the heavy ion beam probe (HIBP) in the Large Helical Device (LHD). For 2D spatial profile measurements, the probe beam energy has to be changed, which requires the adjustment of many deflectors in the beam transport line to optimize the beam trajectory, since the transport line of LHD-HIBP system is long. The automatic beam adjustment system was developed, which allows us to adjust the beam trajectory easily. By analyzing coherence between potential fluctuation and magnetic probe signal, the noise level of the mode power spectrum of the potential fluctuation can be reduced. By using this method, the 2D spatial profile of potential fluctuation profile was successfully obtained.

  20. Van der Waals effect in weak adsorption affecting trends in adsorption, reactivity, and the view of substrate nobility

    DEFF Research Database (Denmark)

    Kelkkanen, Kari André; Lundqvist, Bengt; Nørskov, Jens Kehlet

    2011-01-01

    The ubiquitous van der Waals (vdW) force, particularly discernible in weak adsorption, is studied on noble and transition metals. In calculations with the vdW density functional (DF) [ M. Dion et al., Phys. Rev. Lett. 92, 246401 (2004)], the atomic structure near the adsorption site is systematic......The ubiquitous van der Waals (vdW) force, particularly discernible in weak adsorption, is studied on noble and transition metals. In calculations with the vdW density functional (DF) [ M. Dion et al., Phys. Rev. Lett. 92, 246401 (2004)], the atomic structure near the adsorption site...