The effects of van der Waals attractions on cloud droplet growth by coalescence

NASA Technical Reports Server (NTRS)

Rogers, Jan R.; Davis, Robert H.

1990-01-01

The inclusion of van der Waals attractions in the interaction between cloud droplets has been recently shown to significantly increase the collision efficiencies of the smaller droplets. In the current work, these larger values for the collision efficiencies are used in a population dynamics model of the droplet size distribution evolution with time, in hopes of at least partially resolving the long-standing paradox in cloud microphysics that predicted rates of the onset of precipitation are generally much lower than those which are observed. Evolutions of several initial cloud droplet spectra have been tracked in time. Size evolutions are compared as predicted from the use of collision efficiencies computed using two different models to allow for droplet-droplet contact: one which considers slip flow effects only, and one which considers the combined effects of van der Waals forces and slip flow. The rate at which the droplet mass density function shifts to larger droplet sizes is increased by typically 20-25 percent, when collision efficiencies which include van der Waals forces are used.

Selective Perception for Robot Driving

DTIC Science & Technology

1992-05-01

models are theories of human cognitive activity during driving. Van der Molen and Botticher recently reviewed several of these models [ van der Molen 871...how to represent driving knowledge, how to perceive traffic situations, or how to process information to obtain actions. Van der Molen and Botticher...attempted to compare the operations of various models objectively on the same task [Rothengatter 88, van der Molen 87], but the models could be

Application of Diffusion Monte Carlo to Materials Dominated by van der Waals Interactions

DOE PAGES

Benali, Anouar; Shulenburger, Luke; Romero, Nichols A.; ...

2014-06-12

Van der Waals forces are notoriously difficult to account for from first principles. We perform extensive calculation to assess the usefulness and validity of diffusion quantum Monte Carlo when applied to van der Waals forces. We present results for noble gas solids and clusters - archetypical van der Waals dominated assemblies, as well as a relevant pi-pi stacking supramolecular complex: DNA + intercalating anti-cancer drug Ellipticine.

Resonance oscillations of nonreciprocal long-range van der Waals forces between atoms in electromagnetic fields

NASA Astrophysics Data System (ADS)

Sherkunov, Yury

2018-03-01

We study theoretically the van der Waals interaction between two atoms out of equilibrium with an isotropic electromagnetic field. We demonstrate that at large interatomic separations, the van der Waals forces are resonant, spatially oscillating, and nonreciprocal due to resonance absorption and emission of virtual photons. We suggest that the van der Waals forces can be controlled and manipulated by tuning the spectrum of artificially created random light.

Implication of Two-Coupled Differential Van der Pol Duffing Oscillator in Weak Signal Detection

NASA Astrophysics Data System (ADS)

Peng, Hang-hang; Xu, Xue-mei; Yang, Bing-chu; Yin, Lin-zi

2016-04-01

The principle of the Van der Pol Duffing oscillator for state transition and for determining critical value is described, which has been studied to indicate that the application of the Van der Pol Duffing oscillator in weak signal detection is feasible. On the basis of this principle, an improved two-coupled differential Van der Pol Duffing oscillator is proposed which can identify signals under any frequency and ameliorate signal-to-noise ratio (SNR). The analytical methods of the proposed model and the construction of the proposed oscillator are introduced in detail. Numerical experiments on the properties of the proposed oscillator compared with those of the Van der Pol Duffing oscillator are carried out. Our numerical simulations have confirmed the analytical treatment. The results demonstrate that this novel oscillator has better detection performance than the Van der Pol Duffing oscillator.

Scaling laws for van der Waals interactions in nanostructured materials.

PubMed

Gobre, Vivekanand V; Tkatchenko, Alexandre

2013-01-01

Van der Waals interactions have a fundamental role in biology, physics and chemistry, in particular in the self-assembly and the ensuing function of nanostructured materials. Here we utilize an efficient microscopic method to demonstrate that van der Waals 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 van der Waals 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.

Effect of van der Waals interactions on the structural and binding properties of GaSe

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

Sarkisov, Sergey Y., E-mail: sarkisov@mail.tsu.ru; Kosobutsky, Alexey V., E-mail: kosobutsky@kemsu.ru; Kemerovo State University, Krasnaya 6, 650043 Kemerovo

The influence of van der Waals interactions on the lattice parameters, band structure, elastic moduli and binding energy of layered GaSe compound has been studied using projector-augmented wave method within density functional theory. We employed the conventional local/semilocal exchange-correlation functionals and recently developed van der Waals functionals which are able to describe dispersion forces. It is found that application of van der Waals density functionals allows to substantially increase the accuracy of calculations of the lattice constants a and c and interlayer distance in GaSe at ambient conditions and under hydrostatic pressure. The pressure dependences of the a-parameter, Ga–Ga, Ga–Semore » bond lengths and Ga–Ga–Se bond angle are characterized by a relatively low curvature, while c(p) has a distinct downward bowing due to nonlinear shrinking of the interlayer spacing. From the calculated binding energy curves we deduce the interlayer binding energy of GaSe, which is found to be in the range 0.172–0.197 eV/layer (14.2–16.2 meV/Å{sup 2}). - Highlights: • Effects of van der Waals interactions are analyzed using advanced density functionals. • Calculations with vdW-corrected functionals closely agree with experiment. • Interlayer binding energy of GaSe is estimated to be 14.2–16.2 meV/Å{sup 2}.« less

Van der Waals forces in pNRQED

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

Shtabovenko, Vladyslav

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.

Low-Voltage Complementary Electronics from Ion-Gel-Gated Vertical Van der Waals Heterostructures

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

Choi, Yongsuk; Kang, Junmo; Jariwala, Deep

2016-03-22

Low-voltage complementary circuits comprising n-type and p-type van der Waals heterojunction vertical field-effect transistors (VFETs) are demonstrated. The resulting VFETs possess high on-state current densities (>3000 A cm-2) and on/off current ratios (>104) in a narrow voltage window (<3 V).

Task modulation of the effects of brightness on reaction time and response force.

PubMed

Jaśkowski, Piotr; Włodarczyk, Dariusz

2006-08-01

Van der Molen and Keuss [van der Molen, M.W., Keuss, P.J.G., 1979. The relationship between reaction time and intensity in discrete auditory tasks. Quarterly Journal of Experimental Psychology 31, 95-102; van der Molen, M.W., Keuss, P.J.G., 1981. Response selection and the processing of auditory intensity. Quarterly Journal of Experimental Psychology 33, 177-184] showed that paradoxically long reaction times (RT) occur with extremely loud auditory stimuli when the task is difficult (e.g. needs a response choice). It was argued that this paradoxical behavior of RT is due to active suppression of response prompting to prevent false responses. In the present experiments, we demonstrated that such an effect can also occur for visual stimuli provided that they are large enough. Additionally, we showed that response force exerted by participants on response keys monotonically grew with intensity for large stimuli but was independent of intensity for small visual stimuli. Bearing in mind that only large stimuli are believed to be arousing this pattern of results supports the arousal interpretation of the negative effect of loud stimuli on RT given by van der Molen and Keuss.

Genetics Home Reference: van der Woude syndrome

MedlinePlus

... What is the prognosis of a genetic condition? Genetic and Rare Diseases Information Center Frequency Van der Woude syndrome is believed to occur in 1 in 35,000 to 1 in 100,000 people, based on data from Europe and Asia. Van der Woude syndrome ...

A New Method for Suppressing Periodic Narrowband Interference Based on the Chaotic van der Pol Oscillator

NASA Astrophysics Data System (ADS)

Lu, Jia; Zhang, Xiaoxing; Xiong, Hao

The chaotic van der Pol oscillator is a powerful tool for detecting defects in electric systems by using online partial discharge (PD) monitoring. This paper focuses on realizing weak PD signal detection in the strong periodic narrowband interference by using high sensitivity to the periodic narrowband interference signals and immunity to white noise and PD signals of chaotic systems. A new approach to removing the periodic narrowband interference by using a van der Pol chaotic oscillator is described by analyzing the motion characteristic of the chaotic oscillator on the basis of the van der Pol equation. Furthermore, the Floquet index for measuring the amplitude of periodic narrowband signals is redefined. The denoising signal processed by the chaotic van der Pol oscillators is further processed by wavelet analysis. Finally, the denoising results verify that the periodic narrowband and white noise interference can be removed efficiently by combining the theory of the chaotic van der Pol oscillator and wavelet analysis.

van der Pauw's Theorem on Sheet Resistance

ERIC Educational Resources Information Center

Bolt, Michael

2017-01-01

The sheet resistance of a conducting material of uniform thickness is analogous to the resistivity of a solid material and provides a measure of electrical resistance. In 1958, L. J. van der Pauw found an effective method for computing sheet resistance that requires taking two electrical measurements from four points on the edge of a simply…

Do apolipoprotein E genotype and educational attainment predict the rate of cognitive decline in normal aging? A 12-year follow-up of the Maastricht Aging Study.

PubMed

Van Gerven, Pascal W M; Van Boxtel, Martin P J; Ausems, Eleonora E B; Bekers, Otto; Jolles, Jelle

2012-07-01

We investigated suspected longitudinal interaction effects of apolipoprotein E (APOE) genotype and educational attainment on cognitive decline in normal aging. Our sample consisted of 571 healthy, nondemented adults aged between 49 and 82 years. Linear mixed-models analyses were performed with four measurement time points: baseline, 3-year, 6-year, and 12-year follow-up. Covariates included age at baseline, sex, and self-perceived physical and mental health. Dependent measures were global cognitive functioning (Mini-Mental State Examination; Folstein, Folstein, & McHugh, 1975), Stroop performance (Stroop Color-Word Test; Van der Elst, Van Boxtel, Van Breukelen, & Jolles, 2006a), set-shifting performance (Concept Shifting Test; Van der Elst, Van Boxtel, Van Breukelen, & Jolles, 2006b), cognitive speed (Letter-Digit Substitution Test; Van der Elst, Van Boxtel, Van Breukelen, & Jolles, 2006c), verbal learning (Verbal Learning Test: Sum of five trials; Van der Elst, Van Boxtel, Van Breukelen, & Jolles, 2005), and long-term memory (Verbal Learning Test: Delayed recall). We found only faint evidence that older, high-educated carriers of the APOE-ε4 allele (irrespective of zygosity) show a more pronounced decline than younger, low-educated carriers and noncarriers (irrespective of educational attainment). Moreover, this outcome was confined to concept-shifting performance and was especially observable between 6- and 12-year follow-ups. No protective effects of higher education were found on any of the six cognitive measures. We conclude that the combination of APOE-ε4 allele and high educational attainment may be a risk factor for accelerated cognitive decline in older age, as has been reported before, but only to a very limited extent. Moreover, we conclude that, within the cognitive reserve framework, education does not have significant protective power against age-related cognitive decline.

Investigation of Luminescent Diode Arrays for Photochromic Film Recording

DTIC Science & Technology

1969-06-30

usually measured by Hall effect and rev.istivity measurements using the Van der Pauw technique.) Ami an example, if GP is Initially 3 x i10 P type and...contacta and eettin% the specimen in a known magnetic field. The Van der Pauw technique Is used to meaeure the HAll coefficient. From the Hall coefficient...iraenuitive within 30 minutes after activation. Un~ der ultr’aviolet exposure, dark red ’Iuoro-cence occurs. When the activation properties of the film are

Photovoltaic Effect in an Electrically Tunable van der Waals Heterojunction

PubMed Central

2014-01-01

Semiconductor heterostructures form the cornerstone of many electronic and optoelectronic devices and are traditionally fabricated using epitaxial growth techniques. More recently, heterostructures have also been obtained by vertical stacking of two-dimensional crystals, such as graphene and related two-dimensional materials. These layered designer materials are held together by van der Waals forces and contain atomically sharp interfaces. Here, we report on a type-II van der Waals heterojunction made of molybdenum disulfide and tungsten diselenide monolayers. The junction is electrically tunable, and under appropriate gate bias an atomically thin diode is realized. Upon optical illumination, charge transfer occurs across the planar interface and the device exhibits a photovoltaic effect. Advances in large-scale production of two-dimensional crystals could thus lead to a new photovoltaic solar technology. PMID:25057817

DEM modeling of failure mechanisms induced by excavations on the Moon

NASA Astrophysics Data System (ADS)

jiang, mingjing; shen, zhifu; Utili, Stefano

2013-04-01

2D Discrete Element Method (DEM) analyses were performed for excavations supported by retaining walls in lunar environment. The lunar terrain is made of a layer of sand (regolith) which differs from terrestrial sands for two main features: the presence of adhesive attractive forces due to van der Waals interactions and grains being very irregular in shape leading to high interlocking. A simplified contact model based on linear elasticity and perfect plasticity was employed. The contact model includes a moment - relative rotation law to account for high interlocking among grains and a normal adhesion law to account for the van der Waals interactions. Analyses of the excavations were run under both lunar and terrestrial environments. Under lunar environment, gravity is approximately one sixth than the value on Earth and adhesion forces between grains of lunar regolith due to van der Waals interactions are not negligible. From the DEM simulations it emerged that van der Waals interactions may significantly increase the bending moment and deflection of the retaining wall, and the ground displacements. Hence this study indicates that an unsafe estimate of the wall response to an excavation on the Moon would be obtained from physical experiments performed in a terrestrial environment, i.e., considering the effect of gravity but neglecting the van der Waals interactions.

Effects of van der Waals Force and Thermal Stresses on Pull-in Instability of Clamped Rectangular Microplates.

PubMed

Batra, Romesh C; Porfiri, Maurizio; Spinello, Davide

2008-02-15

We study the influence of von Karman nonlinearity, van der Waals force, and a athermal stresses on pull-in instability and small vibrations of electrostatically actuated mi-croplates. We use the Galerkin method to develop a tractable reduced-order model for elec-trostatically actuated clamped rectangular microplates in the presence of van der Waals forcesand thermal stresses. More specifically, we reduce the governing two-dimensional nonlineartransient boundary-value problem to a single nonlinear ordinary differential equation. For thestatic problem, the pull-in voltage and the pull-in displacement are determined by solving apair of nonlinear algebraic equations. The fundamental vibration frequency corresponding toa deflected configuration of the microplate is determined by solving a linear algebraic equa-tion. The proposed reduced-order model allows for accurately estimating the combined effectsof van der Waals force and thermal stresses on the pull-in voltage and the pull-in deflectionprofile with an extremely limited computational effort.

Inter-layer and intra-layer heat transfer in bilayer/monolayer graphene van der Waals heterostructure: Is there a Kapitza resistance analogous?

NASA Astrophysics Data System (ADS)

Rajabpour, Ali; Fan, Zheyong; Vaez Allaei, S. Mehdi

2018-06-01

Van der Waals heterostructures have exhibited interesting physical properties. In this paper, heat transfer in hybrid coplanar bilayer/monolayer (BL-ML) graphene, as a model layered van der Waals heterostructure, was studied using non-equilibrium molecular dynamics (MD) simulations. The temperature profile and inter- and intra-layer heat fluxes of the BL-ML graphene indicated that, there is no fully developed thermal equilibrium between layers and the drop in the average temperature profile at the step-like BL-ML interface is not attributable to the effect of Kapitza resistance. By increasing the length of the system up to 1 μm in the studied MD simulations, the thermally non-equilibrium region was reduced to a small area near the step-like interface. All MD results were compared to a continuum model and a good match was observed between the two approaches. Our results provide a useful understanding of heat transfer in nano- and micro-scale layered materials and van der Waals heterostructures.

Layer-dependent band alignment of few layers of blue phosphorus and their van der Waals heterostructures with graphene

NASA Astrophysics Data System (ADS)

Pontes, Renato B.; Miwa, Roberto H.; da Silva, Antônio J. R.; Fazzio, Adalberto; Padilha, José E.

2018-06-01

The structural and electronic properties of few layers of blue phosphorus and their van der Waals heterostructures with graphene were investigated by means of first-principles electronic structure calculations. We study the four energetically most stable stacking configurations for multilayers of blue phosphorus. For all of them, the indirect band-gap semiconductor character, are preserved. We show that the properties of monolayer graphene and single-layer (bilayer) blue phosphorus are preserved in the van der Waals heterostructures. Further, our results reveal that under a perpendicular applied electric field, the position of the band structure of blue phosphorus with respect to that of graphene is tunable, enabling the effective control of the Schottky barrier height. Indeed, for the bilayer blue phosphorene on top of graphene, it is possible to even move the system into an Ohmic contact and induce a doping level of the blue phosphorene. All of these features are fundamental for the design of new nanodevices based on van der Waals heterostructures.

Temperature-Dependent and Gate-Tunable Rectification in a Black Phosphorus/WS2 van der Waals Heterojunction Diode.

PubMed

Dastgeer, Ghulam; Khan, Muhammad Farooq; Nazir, Ghazanfar; Afzal, Amir Muhammad; Aftab, Sikandar; Naqvi, Bilal Abbas; Cha, Janghwan; Min, Kyung-Ah; Jamil, Yasir; Jung, Jongwan; Hong, Suklyun; Eom, Jonghwa

2018-04-18

Heterostructures comprising two-dimensional (2D) semiconductors fabricated by individual stacking exhibit interesting characteristics owing to their 2D nature and atomically sharp interface. As an emerging 2D material, black phosphorus (BP) nanosheets have drawn much attention because of their small band gap semiconductor characteristics along with high mobility. Stacking structures composed of p-type BP and n-type transition metal dichalcogenides can produce an atomically sharp interface with van der Waals interaction which leads to p-n diode functionality. In this study, for the first time, we fabricated a heterojunction p-n diode composed of BP and WS 2 . The rectification effects are examined for monolayer, bilayer, trilayer, and multilayer WS 2 flakes in our BP/WS 2 van der Waals heterojunction diodes and also verified by density function theory calculations. We report superior functionalities as compared to other van der Waals heterojunction, such as efficient gate-dependent static rectification of 2.6 × 10 4 , temperature dependence, thickness dependence of rectification, and ideality factor of the device. The temperature dependence of Zener breakdown voltage and avalanche breakdown voltage were analyzed in the same device. Additionally, superior optoelectronic characteristics such as photoresponsivity of 500 mA/W and external quantum efficiency of 103% are achieved in the BP/WS 2 van der Waals p-n diode, which is unprecedented for BP/transition metal dichalcogenides heterostructures. The BP/WS 2 van der Waals p-n diodes have a profound potential to fabricate rectifiers, solar cells, and photovoltaic diodes in 2D semiconductor electronics and optoelectronics.

Size Effects in Epitaxial Films of Magnetite

DTIC Science & Technology

2002-06-03

van Eemeren , J. aan de Stegge, 1727. WJ.M. de Jonge, Surf. Sci. 373 (1997) 85. [38] J.L. Dormann, T. Merceron, P. Renaudin, VA.M. Brabers, J. [20] S.A...Metals and Semiconductors, Trans Tech, Switzerland, 1994, p. __221. [4] G.A. Prinz, Phys. Today 48 (1995) 58. 100 - [5] P.J. van der Zaag. P.J.H...Bloemen. J.M. Gaines, R.M. Wolf, -10 -8 -6 -4 -2 0 2 4 6 8 10 P.A.A. van der Heijden, R.J.M. van de Veerdonk, W.J.M. velocity [mm/s] de Jonge, J. Magn. Magn

Modeling Subsurface Storm and Tile Drain Systems in GSSHA with SUPERLINK

DTIC Science & Technology

2014-09-01

side is computed as . ( )e Kq d m m L   2 0 01 2 (7) de is defined as ( van der Molen and Wesseling (1991)) ERDC/CHL TR-14-11 15...Conservation Service. Van der Molen , W.H., and J. Wesseling. 1991. A solution in closed form and a series solution to replace the tables for thickness of...effective lateral hydraulic conductivity (cm hr-1) C = 1 in the present version. Hooghoudt ( van Schilfgaarde 1974) characterized flow to cylindrical

Dynamical property analysis of fractionally damped van der pol oscillator and its application

NASA Astrophysics Data System (ADS)

Zhong, Qiuhui; Zhang, Chunrui

2012-01-01

In this paper, the fractionally damped van der pol equation was studied. Firstly, the fractionally damped van der pol equation was transformed into a set of integer order equations. Then the Lyapunov exponents diagram was given. Secondly, it was transformed into a set of fractional integral equations and solved by a predictor-corrector method. The time domain diagrams and phase trajectory were used to describe the dynamic behavior. Finally, the fractionally damped van der pol equation was used to detect a weak signal.

A notable difference between ideal gas and infinite molar volume limit of van der Waals gas

NASA Astrophysics Data System (ADS)

Liu, Q. H.; Shen, Y.; Bai, R. L.; Wang, X.

2010-05-01

The van der Waals equation of state does not sufficiently represent a gas unless a thermodynamic potential with two proper and independent variables is simultaneously determined. The limiting procedures under which the behaviour of the van der Waals gas approaches that of an ideal gas are letting two van der Waals coefficients be zero rather than letting the molar volume become infinitely large; otherwise, the partial derivative of internal energy with respect to pressure at a fixed temperature does not vanish.

Jacobus Schroeder van der Kolk (1797-1862): his resistance against materialism.

PubMed

Eling, P

1998-07-01

Schroeder van der Kolk is regarded as the founder of Dutch psychiatry and neurology. This paper describes his vitalistic views on the relation between body and soul, as formulated by him in a series of lectures. These lectures were intended to counteract the materialistic tendencies of some of Schroeder van der Kolk's French and German contemporaries. It is argued that Schroeder van der Kolk can be regarded as the transition in Holland from the "Naturphilosophie" approach to the modern experimental approach in physiology. Copyright 1998 Academic Press.

Van der Waals interaction mediated by an optically uniaxial layer

NASA Astrophysics Data System (ADS)

Šarlah, A.; Žumer, S.

2001-11-01

We study the van der Waals interaction between macroscopic bodies separated by a thin anisotropic film with a uniaxial permittivity tensor. We describe the effect of anisotropy of the media on the magnitude and sign of the interaction. The resulting differences in the van der Waals interaction are especially important for the stability of strongly confined liquid crystals, and nanostructures characterized by highly uniaxial macroscopic molecular arrangement, such as in self-assemblies of long organic molecules forming films, membranes, colloids, etc. We introduce an improved expression for the Hamaker constant which takes into account the uniaxial symmetry of a medium. In special cases neglecting the optical anisotropy even leads to an incorrect sign of the interaction.

Building Cultural Capability for Full-Spectrum Operations

DTIC Science & Technology

2008-01-01

Mol, Born, Willemsen, & Van der Molen , 2005; Caligiuri & Day, 2000). In addition to these broad traits, antecedents to cross-cultural competence...510-517. 18 Mol, S. T., Born, M. P., Willemsen, M. E., & Van Der Molen , H. T. (2005). Predicting expatriate job performance for selection purposes: A...et al., 2003). In addition, self-regulation has been shown to be critical for adjustment (Matsumoto et al., 2003; van Oudenhoven, Mol, & Van der Zee

Theory of coherent van der Waals matter.

PubMed

Kulić, Igor M; Kulić, Miodrag L

2014-12-01

We explain in depth the previously proposed theory of the coherent van der Waals (cvdW) interaction, the counterpart of van der Waals (vdW) force, emerging in spatially coherently fluctuating electromagnetic fields. We show that cvdW driven matter is dominated by many-body interactions, which are significantly stronger than those found in standard van der Waals (vdW) systems. Remarkably, the leading two- and three-body interactions are of the same order with respect to the distance (∝R(-6)), in contrast to the usually weak vdW three-body effects (∝R(-9)). From a microscopic theory we show that the anisotropic cvdW many-body interactions drive the formation of low-dimensional structures such as chains, membranes, and vesicles with very unusual, nonlocal properties. In particular, cvdW chains display a logarithmically growing stiffness with the chain length, while cvdW membranes have a bending modulus growing linearly with their size. We argue that the cvdW anisotropic many-body forces cause local cohesion but also a negative effective "surface tension." We conclude by deriving the equation of state for cvdW materials and propose experiments to test the theory, in particular the unusual three-body nature of cvdW.

Theory of coherent van der Waals matter

NASA Astrophysics Data System (ADS)

Kulić, Igor M.; Kulić, Miodrag L.

2014-12-01

We explain in depth the previously proposed theory of the coherent van der Waals (cvdW) interaction, the counterpart of van der Waals (vdW) force, emerging in spatially coherently fluctuating electromagnetic fields. We show that cvdW driven matter is dominated by many-body interactions, which are significantly stronger than those found in standard van der Waals (vdW) systems. Remarkably, the leading two- and three-body interactions are of the same order with respect to the distance (∝R-6) , in contrast to the usually weak vdW three-body effects (∝R-9 ). From a microscopic theory we show that the anisotropic cvdW many-body interactions drive the formation of low-dimensional structures such as chains, membranes, and vesicles with very unusual, nonlocal properties. In particular, cvdW chains display a logarithmically growing stiffness with the chain length, while cvdW membranes have a bending modulus growing linearly with their size. We argue that the cvdW anisotropic many-body forces cause local cohesion but also a negative effective "surface tension." We conclude by deriving the equation of state for cvdW materials and propose experiments to test the theory, in particular the unusual three-body nature of cvdW.

Strong electrically tunable MoTe2/graphene van der Waals heterostructures for high-performance electronic and optoelectronic devices

NASA Astrophysics Data System (ADS)

Wang, Feng; Yin, Lei; Wang, Zhenxing; Xu, Kai; Wang, Fengmei; Shifa, Tofik Ahmed; Huang, Yun; Wen, Yao; Jiang, Chao; He, Jun

2016-11-01

MoTe2 is an emerging two-dimensional layered material showing ambipolar/p-type conductivity, which makes it an important supplement to n-type two-dimensional layered material like MoS2. However, the properties based on its van der Waals heterostructures have been rarely studied. Here, taking advantage of the strong Fermi level tunability of monolayer graphene (G) and the feature of van der Waals interfaces that is free from Fermi level pinning effect, we fabricate G/MoTe2/G van der Waals heterostructures and systematically study the electronic and optoelectronic properties. We demonstrate the G/MoTe2/G FETs with low Schottky barriers for both holes (55.09 meV) and electrons (122.37 meV). Moreover, the G/MoTe2/G phototransistors show high photoresponse performances with on/off ratio, responsivity, and detectivity of ˜105, 87 A/W, and 1012 Jones, respectively. Finally, we find the response time of the phototransistors is effectively tunable and a mechanism therein is proposed to explain our observation. This work provides an alternative choice of contact for high-performance devices based on p-type and ambipolar two-dimensional layered materials.

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

NASA Astrophysics Data System (ADS)

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

2017-05-01

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.

Cosmological models constructed by van der Waals fluid approximation and volumetric expansion

NASA Astrophysics Data System (ADS)

Samanta, G. C.; Myrzakulov, R.

The universe modeled with van der Waals fluid approximation, where the van der Waals fluid equation of state contains a single parameter ωv. Analytical solutions to the Einstein’s field equations are obtained by assuming the mean scale factor of the metric follows volumetric exponential and power-law expansions. The model describes a rapid expansion where the acceleration grows in an exponential way and the van der Waals fluid behaves like an inflation for an initial epoch of the universe. Also, the model describes that when time goes away the acceleration is positive, but it decreases to zero and the van der Waals fluid approximation behaves like a present accelerated phase of the universe. Finally, it is observed that the model contains a type-III future singularity for volumetric power-law expansion.

Quantum synchronization of quantum van der Pol oscillators with trapped ions.

PubMed

Lee, Tony E; Sadeghpour, H R

2013-12-06

The van der Pol oscillator is the prototypical self-sustained oscillator and has been used to model nonlinear behavior in biological and other classical processes. We investigate how quantum fluctuations affect phase locking of one or many van der Pol oscillators. We find that phase locking is much more robust in the quantum model than in the equivalent classical model. Trapped-ion experiments are ideally suited to simulate van der Pol oscillators in the quantum regime via sideband heating and cooling of motional modes. We provide realistic experimental parameters for 171Yb+ achievable with current technology.

Isotope separation by photodissociation of Van der Waal's molecules

DOEpatents

Lee, Yuan T.

1977-01-01

A method of separating isotopes based on the dissociation of a Van der Waal's complex. A beam of molecules of a Van der Waal's complex containing, as one partner of the complex, a molecular species in which an element is present in a plurality of isotopes is subjected to radiation from a source tuned to a frequency which will selectively excite vibrational motion by a vibrational transition or through electronic transition of those complexed molecules of the molecular species which contain a desired isotope. Since the Van der Waal's binding energy is much smaller than the excitational energy of vibrational motion, the thus excited Van der Waal's complex dissociate into molecular components enriched in the desired isotope. The recoil velocity associated with vibrational to translational and rotational relaxation will send the separated molecules away from the beam whereupon the product enriched in the desired isotope can be separated from the constituents of the beam.

Communication: Determining the structure of the N{sub 2}Ar van der Waals complex with laser-based channel-selected Coulomb explosion

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

Wu, Chengyin, E-mail: cywu@pku.edu.cn; Liu, Yunquan; Gong, Qihuang

2014-04-14

We experimentally reconstructed the structure of the N{sub 2}Ar van der Waals complex with the technique of laser-based channel-selected Coulomb explosion imaging. The internuclear distance between the N{sub 2} center of mass and the Ar atom, i.e., the length of the van der Waals bond, was determined to be 3.88 Å from the two-body explosion channels. The angle between the van der Waals bond and the N{sub 2} principal axis was determined to be 90° from the three-body explosion channels. The reconstructed structure was contrasted with our high level ab initio calculations. The agreement demonstrated the potential application of laser-basedmore » Coulomb explosion in imaging transient molecular structure, particularly for floppy van der Waals complexes, whose structures remain difficult to be determined by conventional spectroscopic methods.« less

Vibration-rotation-tunneling spectroscopy of the van der Waals Bond: A new look at intermolecular forces

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

Cohen, R.C.; Saykally, R.J.

Measurements of the low-frequency van der Waals vibrations in weakly bound complexes by high-resolution laser spectroscopy provide a means to probe intermolecular forces at unprecedented levels of detail and precision. Several new methods are presently being used to record vibration/rotation-tunneling (VRT) transitions associated with the motions of the weak bonds in van der Waals clusters. The most direct measurements are those probing only the van der Waals modes themselves, which occur at far-infrared wavelengths. This article presents a review of the information on both intramolecular forces and intramolecular dynamics that has been obtained from far-infrared VRT spectra of 18 complexesmore » during the past several years. Some rotationally resolved measurements of van der Waals modes observed in combination with electronic or vibrational excitation are also discussed. 185 refs., 15 figs., 1 tab.« less

Isotope engineering of van der Waals interactions in hexagonal boron nitride

NASA Astrophysics Data System (ADS)

Vuong, T. Q. P.; Liu, S.; van der Lee, A.; Cuscó, R.; Artús, L.; Michel, T.; Valvin, P.; Edgar, J. H.; Cassabois, G.; Gil, B.

2018-02-01

Hexagonal boron nitride is a model lamellar compound where weak, non-local van der Waals interactions ensure the vertical stacking of two-dimensional honeycomb lattices made of strongly bound boron and nitrogen atoms. We study the isotope engineering of lamellar compounds by synthesizing hexagonal boron nitride crystals with nearly pure boron isotopes (10B and 11B) compared to those with the natural distribution of boron (20 at% 10B and 80 at% 11B). On the one hand, as with standard semiconductors, both the phonon energy and electronic bandgap varied with the boron isotope mass, the latter due to the quantum effect of zero-point renormalization. On the other hand, temperature-dependent experiments focusing on the shear and breathing motions of adjacent layers revealed the specificity of isotope engineering in a layered material, with a modification of the van der Waals interactions upon isotope purification. The electron density distribution is more diffuse between adjacent layers in 10BN than in 11BN crystals. Our results open perspectives in understanding and controlling van der Waals bonding in layered materials.

Isotope engineering of van der Waals interactions in hexagonal boron nitride.

PubMed

Vuong, T Q P; Liu, S; Van der Lee, A; Cuscó, R; Artús, L; Michel, T; Valvin, P; Edgar, J H; Cassabois, G; Gil, B

2018-02-01

Hexagonal boron nitride is a model lamellar compound where weak, non-local van der Waals interactions ensure the vertical stacking of two-dimensional honeycomb lattices made of strongly bound boron and nitrogen atoms. We study the isotope engineering of lamellar compounds by synthesizing hexagonal boron nitride crystals with nearly pure boron isotopes ( 10 B and 11 B) compared to those with the natural distribution of boron (20 at% 10 B and 80 at% 11 B). On the one hand, as with standard semiconductors, both the phonon energy and electronic bandgap varied with the boron isotope mass, the latter due to the quantum effect of zero-point renormalization. On the other hand, temperature-dependent experiments focusing on the shear and breathing motions of adjacent layers revealed the specificity of isotope engineering in a layered material, with a modification of the van der Waals interactions upon isotope purification. The electron density distribution is more diffuse between adjacent layers in 10 BN than in 11 BN crystals. Our results open perspectives in understanding and controlling van der Waals bonding in layered materials.

Charge carrier mobility in thin films of organic semiconductors by the gated van der Pauw method

PubMed Central

Rolin, Cedric; Kang, Enpu; Lee, Jeong-Hwan; Borghs, Gustaaf; Heremans, Paul; Genoe, Jan

2017-01-01

Thin film transistors based on high-mobility organic semiconductors are prone to contact problems that complicate the interpretation of their electrical characteristics and the extraction of important material parameters such as the charge carrier mobility. Here we report on the gated van der Pauw method for the simple and accurate determination of the electrical characteristics of thin semiconducting films, independently from contact effects. We test our method on thin films of seven high-mobility organic semiconductors of both polarities: device fabrication is fully compatible with common transistor process flows and device measurements deliver consistent and precise values for the charge carrier mobility and threshold voltage in the high-charge carrier density regime that is representative of transistor operation. The gated van der Pauw method is broadly applicable to thin films of semiconductors and enables a simple and clean parameter extraction independent from contact effects. PMID:28397852

Nanotechnology-Enabled Optical Molecular Imaging of Breast Cancer

DTIC Science & Technology

2013-09-01

Jacobus J M van Der Hoeven, Elsken van Der Wall, Petra van Der Groep, Paul J van Diest, Emile F I Comans, Urvi Joshi, et al. 2002. “Biologic...Leigh G Seamon, William B Farrar, and Edward W Martin . 2008. “Novel perioperative imaging with 18F-FDG PET/CT and intraoperative 18F-FDG detection...www.springerlink.com/content/n752170246r84660/. Hall, Nathan C, Stephen P Povoski, Douglas A Murrey, Michael V Knopp, and Edward W Martin . 2007. “Combined

Submaximal Exercise Testing Treadmill and Floor Walking.

DTIC Science & Technology

1978-05-01

Amputations," Archives of Physical Medicine and Rehabilitation, 56:67-71, 1975. 36. van der Walt, W. H., and Wyndham, C. H,, "An Equation for...C. H., van Renaburg, A. J., Rogr, G. G., Greyson, J. S.. and van der Walt, V. H., "Walk or Jog for Health: I, The Energy Cost of Walking or Running at...G., Greyson, J. S., and van der Walt, V. H., "Walk or Jog for Health: II, Iatimating the Maximi Aerobic Capacity for Exercise,* South &frIca Kedical

Active Masks and Active Inhibition: A Comment on Lleras and Enns (2004) and on Verleger, Jaskowski, Aydemir, van der Lubbe, and Groen (2004)

ERIC Educational Resources Information Center

Schlaghecken, Friederike; Eimer, Martin

2006-01-01

Verleger, Jaskowski, Aydemir, van der Lubbe, and Groen (see record 2004-21166-002) and Lleras and Enns (see record 2004-21166-001) have argued that negative compatibility effects (NCEs) obtained with masked primes do not reflect self-inhibition processes in motor control. Instead, NCEs are assumed to reflect activation of the response opposite to…

Estimation of Some Parameters from Morse-Morse-Spline-Van Der Waals Intermolecular Potential

NASA Astrophysics Data System (ADS)

Coroiu, I.

2007-04-01

Some parameters such as transport cross-sections and isotopic thermal diffusion factor have been calculated from an improved intermolecular potential, Morse-Morse-Spline-van der Waals (MMSV) potential proposed by R.A. Aziz et al. The treatment was completely classical and no corrections for quantum effects were made. The results would be employed for isotope separations of different spherical and quasi-spherical molecules.

van der Waals epitaxial ZnTe thin film on single-crystalline graphene

NASA Astrophysics Data System (ADS)

Sun, Xin; Chen, Zhizhong; Wang, Yiping; Lu, Zonghuan; Shi, Jian; Washington, Morris; Lu, Toh-Ming

2018-01-01

Graphene template has long been promoted as a promising host to support van der Waals flexible electronics. However, van der Waals epitaxial growth of conventional semiconductors in planar thin film form on transferred graphene sheets is challenging because the nucleation rate of film species on graphene is significantly low due to the passive surface of graphene. In this work, we demonstrate the epitaxy of zinc-blende ZnTe thin film on single-crystalline graphene supported by an amorphous glass substrate. Given the amorphous nature and no obvious remote epitaxy effect of the glass substrate, this study clearly proves the van der Waals epitaxy of a 3D semiconductor thin film on graphene. X-ray pole figure analysis reveals the existence of two ZnTe epitaxial orientational domains on graphene, a strong X-ray intensity observed from the ZnTe [ 1 ¯ 1 ¯ 2] ǁ graphene [10] orientation domain, and a weaker intensity from the ZnTe [ 1 ¯ 1 ¯ 2] ǁ graphene [11] orientation domain. Furthermore, this study systematically investigates the optoelectronic properties of this epitaxial ZnTe film on graphene using temperature-dependent Raman spectroscopy, steady-state and time-resolved photoluminescence spectroscopy, and fabrication and characterization of a ZnTe-graphene photodetector. The research suggests an effective approach towards graphene-templated flexible electronics.

Perception for Outdoor Navigation

DTIC Science & Technology

1991-12-01

are theories of human cognitive activity during driving. Van der Molen and Botticher recently reviewed several of these models [40]. The models...represent driving knowledge, how to perceive traffic situations, or how to process information to obtain actions. Van der Molen and Botticher attempted to...Conference on Robotics and Automation. IEEE, 1987. [40] van der Molen , H.H., and Botticher, A.M.T. Risk Models for Traffic Participants: A Concerted

Network approach towards understanding the crazing in glassy amorphous polymers

NASA Astrophysics Data System (ADS)

Venkatesan, Sudarkodi; Vivek-Ananth, R. P.; Sreejith, R. P.; Mangalapandi, Pattulingam; Hassanali, Ali A.; Samal, Areejit

2018-04-01

We have used molecular dynamics to simulate an amorphous glassy polymer with long chains to study the deformation mechanism of crazing and associated void statistics. The Van der Waals interactions and the entanglements between chains constituting the polymer play a crucial role in crazing. Thus, we have reconstructed two underlying weighted networks, namely, the Van der Waals network and the entanglement network from polymer configurations extracted from the molecular dynamics simulation. Subsequently, we have performed graph-theoretic analysis of the two reconstructed networks to reveal the role played by them in the crazing of polymers. Our analysis captured various stages of crazing through specific trends in the network measures for Van der Waals networks and entanglement networks. To further corroborate the effectiveness of network analysis in unraveling the underlying physics of crazing in polymers, we have contrasted the trends in network measures for Van der Waals networks and entanglement networks in the light of stress-strain behaviour and voids statistics during deformation. We find that the Van der Waals network plays a crucial role in craze initiation and growth. Although, the entanglement network was found to maintain its structure during craze initiation stage, it was found to progressively weaken and undergo dynamic changes during the hardening and failure stages of crazing phenomena. Our work demonstrates the utility of network theory in quantifying the underlying physics of polymer crazing and widens the scope of applications of network science to characterization of deformation mechanisms in diverse polymers.

Binding and Diffusion of Lithium in Graphite: Quantum Monte Carlo Benchmarks and Validation of van der Waals Density Functional Methods

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

Ganesh, P.; Kim, Jeongnim; Park, Changwon

2014-11-03

In highly accurate diffusion quantum Monte Carlo (QMC) studies of the adsorption and diffusion of atomic lithium in AA-stacked graphite are compared with van der Waals-including density functional theory (DFT) calculations. Predicted QMC lattice constants for pure AA graphite agree with experiment. Pure AA-stacked graphite is shown to challenge many van der Waals methods even when they are accurate for conventional AB graphite. Moreover, the highest overall DFT accuracy, considering pure AA-stacked graphite as well as lithium binding and diffusion, is obtained by the self-consistent van der Waals functional vdW-DF2, although errors in binding energies remain. Empirical approaches based onmore » point charges such as DFT-D are inaccurate unless the local charge transfer is assessed. Our results demonstrate that the lithium carbon system requires a simultaneous highly accurate description of both charge transfer and van der Waals interactions, favoring self-consistent approaches.« less

Nanotechnology-Enabled Optical Molecular Imaging of Breast Cancer

DTIC Science & Technology

2012-07-01

Jacobus J M van Der Hoeven, Elsken van Der Wall, Petra van Der Groep, Paul J van Diest, Emile F I Comans, Urvi Joshi, et al. 2002. “Biologic correlates...William B Farrar, and Edward W Martin . 2008. “Novel perioperative imaging with 18F-FDG PET/CT and intraoperative 18F-FDG detection using a handheld gamma...n752170246r84660/. Hall, Nathan C, Stephen P Povoski, Douglas A Murrey, Michael V Knopp, and Edward W Martin . 2007. “Combined approach of perioperative 18F-FDG PET

Colossal terahertz nonlinearity of tunneling van der Waals gap (Conference Presentation)

NASA Astrophysics Data System (ADS)

Bahk, Young-Mi; Kang, Bong Joo; Kim, Yong Seung; Kim, Joon-Yeon; Kim, Won Tae; Kim, Tae Yun; Kang, Taehee; Rhie, Ji Yeah; Han, Sanghoon; Park, Cheol-Hwan; Rotermund, Fabian; Kim, Dai-Sik

2016-09-01

We manufactured an array of three angstrom-wide, five millimeter-long van der Waals gaps of copper-graphene-copper composite, in which unprecedented nonlinearity was observed. To probe and manipulate van der Waals gaps with long wavelength electromagnetic waves such as terahertz waves, one is required to fabricate vertically oriented van der Waals gaps sandwiched between two metal planes with an infinite length in the sense of being much larger than any of the wavelengths used. By comparison with the simple vertical stacking of metal-graphene-metal structure, in our structure, background signals are completely blocked enabling all the light to squeeze through the gap without any strays. When the angstrom-sized van der Waals gaps are irradiated with intense terahertz pulses, the transient voltage across the gap reaches up to 5 V with saturation, sufficiently strong to deform the quantum barrier of angstrom gaps. The large transient potential difference across the gap facilitates electron tunneling through the quantum barrier, blocking terahertz waves completely. This negative feedback of electron tunneling leads to colossal nonlinear optical response, a 97% decrease in the normalized transmittance. Our technology for infinitely long van der Waals gaps can be utilized for other atomically thin materials than single layer graphene, enabling linear and nonlinear angstrom optics in a broad spectral range.

Materials perspective on Casimir and van der Waals interactions

NASA Astrophysics Data System (ADS)

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.

The Economics of van der Waals Force Engineering

NASA Astrophysics Data System (ADS)

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.

A review on data and predictions of water dielectric spectra for calculations of van der Waals surface forces.

PubMed

Wang, Jianlong; Nguyen, Anh V

2017-12-01

Van der Waals forces are one of the important components of intermolecular, colloidal and surface forces governing many phenomena and processes. The latest examples include the colloidal interactions between hydrophobic colloids and interfaces in ambient (non-degassed) water in which dissolved gases and nanobubbles are shown to affect the van der Waals attractions significantly. The advanced computation of van der Waals forces in aqueous systems by the Lifshitz theory requires reliable data for water dielectric spectra. In this paper we review the available predictions of water dielectric spectra for calculating colloidal and surface van der Waals forces. Specifically, the available experimental data for the real and imaginary parts of the complex dielectric function of liquid water in the microwave, IR and UV regions and various corresponding predictions of the water spectra are critically reviewed. The data in the UV region are critical, but the available predictions are still based on the outdated data obtained in 1974 (for frequency only up to 25.5eV). We also reviewed and analysed the experimental data obtained for the UV region in 2000 (for frequency up to 50eV) and 2015 (for frequency up to 100eV). The 1974 and 2000 data require extrapolations to higher frequencies needed for calculating the van der Waals forces but remain inaccurate. Our analysis shows that the latest data of 2015 do not require the extrapolation and can be used to reliably calculate van der Waals forces. The most recent water dielectric spectra gives the (non-retarded) Hamaker constant, A=5.20×10 -20 J, for foam films of liquid water. This review provides the most updated and reliable water dielectric spectra to compute van der Waals forces in aqueous systems. Copyright © 2017 Elsevier B.V. All rights reserved.

Beam-dynamic effects at the CMS BRIL van der Meer scans

NASA Astrophysics Data System (ADS)

Babaev, A.

2018-03-01

The CMS Beam Radiation Instrumentation and Luminosity Project (BRIL) is responsible for the simulation and measurement of luminosity, beam conditions and radiation fields in the CMS experiment. The project is engaged in operating and developing new detectors (luminometers), adequate for the experimental conditions associated with high values of instantaneous luminosity delivered by the CERN LHC . BRIL operates several detectors based on different physical principles and technologies. Precise and accurate measurements of the delivered luminosity is of paramount importance for the CMS physics program. The absolute calibration of luminosity is achieved by the van der Meer method, which is carried out under specially tailored conditions. This paper presents models used to simulate of beam-dynamic effects arising due to the electromagnetic interaction of colliding bunches. These effects include beam-beam deflection and dynamic-β effect. Both effects are important to luminosity measurements and influence calibration constants at the level of 1-2%. The simulations are carried out based on 2016 CMS van der Meer scan data for proton-proton collisions at a center-of-mass energy of 13 TeV.

Hybrid, Gate-Tunable, van der Waals p–n Heterojunctions from Pentacene and MoS 2

DOE PAGES

Jariwala, Deep; Howell, Sarah L.; Chen, Kan-Sheng; ...

2015-12-18

The recent emergence of a wide variety of two-dimensional (2D) materials has created new opportunities for device concepts and applications. In particular, the availability of semiconducting transition metal dichalcogenides, in addition to semimetallic graphene and insulating boron nitride, has enabled the fabrication of “all 2D” van der Waals heterostructure devices. Furthermore, the concept of van der Waals heterostructures has the potential to be significantly broadened beyond layered solids. For example, molecular and polymeric organic solids, whose surface atoms possess saturated bonds, are also known to interact via van der Waals forces and thus offer an alternative for scalable integration withmore » 2D materials. Here, we demonstrate the integration of an organic small molecule p-type semiconductor, pentacene, with a 2D n-type semiconductor, MoS2. The resulting p–n heterojunction is gate-tunable and shows asymmetric control over the antiambipolar transfer characteristic. In addition, the pentacene/MoS2 heterojunction exhibits a photovoltaic effect attributable to type II band alignment, which suggests that MoS2 can function as an acceptor in hybrid solar cells.« less

Hybrid, Gate-Tunable, van der Waals p–n Heterojunctions from Pentacene and MoS 2

DOE PAGES

Jariwala, Deep; Howell, Sarah L.; Chen, Kan -Sheng; ...

2015-12-10

Here, the recent emergence of a wide variety of two-dimensional (2D) materials has created new opportunities for device concepts and applications. In particular, the availability of semiconducting transition metal dichalcogenides, in addition to semimetallic graphene and insulating boron nitride, has enabled the fabrication of “all 2D” van der Waals heterostructure devices. Furthermore, the concept of van der Waals heterostructures has the potential to be significantly broadened beyond layered solids. For example, molecular and polymeric organic solids, whose surface atoms possess saturated bonds, are also known to interact via van der Waals forces and thus offer an alternative for scalable integrationmore » with 2D materials. Here, we demonstrate the integration of an organic small molecule p-type semiconductor, pentacene, with a 2D n-type semiconductor, MoS 2. The resulting p–n heterojunction is gate-tunable and shows asymmetric control over the antiambipolar transfer characteristic. In addition, the pentacene/MoS 2 heterojunction exhibits a photovoltaic effect attributable to type II band alignment, which suggests that MoS 2 can function as an acceptor in hybrid solar cells.« less

Hybrid, Gate-Tunable, van der Waals p–n Heterojunctions from Pentacene and MoS 2

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

Jariwala, Deep; Howell, Sarah L.; Chen, Kan -Sheng

Here, the recent emergence of a wide variety of two-dimensional (2D) materials has created new opportunities for device concepts and applications. In particular, the availability of semiconducting transition metal dichalcogenides, in addition to semimetallic graphene and insulating boron nitride, has enabled the fabrication of “all 2D” van der Waals heterostructure devices. Furthermore, the concept of van der Waals heterostructures has the potential to be significantly broadened beyond layered solids. For example, molecular and polymeric organic solids, whose surface atoms possess saturated bonds, are also known to interact via van der Waals forces and thus offer an alternative for scalable integrationmore » with 2D materials. Here, we demonstrate the integration of an organic small molecule p-type semiconductor, pentacene, with a 2D n-type semiconductor, MoS 2. The resulting p–n heterojunction is gate-tunable and shows asymmetric control over the antiambipolar transfer characteristic. In addition, the pentacene/MoS 2 heterojunction exhibits a photovoltaic effect attributable to type II band alignment, which suggests that MoS 2 can function as an acceptor in hybrid solar cells.« less

Simon van der Meer (1925-2011):. A Modest Genius of Accelerator Science

NASA Astrophysics Data System (ADS)

Chohan, Vinod C.

2011-02-01

Simon van der Meer was a brilliant scientist and a true giant of accelerator science. His seminal contributions to accelerator science have been essential to this day in our quest for satisfying the demands of modern particle physics. Whether we talk of long base-line neutrino physics or antiproton-proton physics at Fermilab or proton-proton physics at LHC, his techniques and inventions have been a vital part of the modern day successes. Simon van der Meer and Carlo Rubbia were the first CERN scientists to become Nobel laureates in Physics, in 1984. Van der Meer's lesserknown contributions spanned a whole range of subjects in accelerator science, from magnet design to power supply design, beam measurements, slow beam extraction, sophisticated programs and controls.

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

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

Zhong, Huikai; Li, Xiaoqiang; Wu, Zhiqian

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 betweenmore » 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.« less

A theoretical approach for estimation of ultimate size of bimetallic nanocomposites synthesized in microemulsion systems

NASA Astrophysics Data System (ADS)

Salabat, Alireza; Saydi, Hassan

2012-12-01

In this research a new idea for prediction of ultimate sizes of bimetallic nanocomposites synthesized in water-in-oil microemulsion system is proposed. In this method, by modifying Tabor Winterton approximation equation, an effective Hamaker constant was introduced. This effective Hamaker constant was applied in the van der Waals attractive interaction energy. The obtained effective van der Waals interaction energy was used as attractive contribution in the total interaction energy. The modified interaction energy was applied successfully to predict some bimetallic nanoparticles, at different mass fraction, synthesized in microemulsion system of dioctyl sodium sulfosuccinate (AOT)/isooctane.

van der Waals Interactions on the Mesoscale: Open-Science Implementation, Anisotropy, Retardation, and Solvent Effects.

PubMed

Dryden, Daniel M; Hopkins, Jaime C; Denoyer, Lin K; Poudel, Lokendra; Steinmetz, Nicole F; Ching, Wai-Yim; Podgornik, Rudolf; Parsegian, Adrian; French, Roger H

2015-09-22

The self-assembly of heterogeneous mesoscale systems is mediated by long-range interactions, including van der Waals forces. Diverse mesoscale architectures, built of optically and morphologically anisotropic elements such as DNA, collagen, single-walled carbon nanotubes, and inorganic materials, require a tool to calculate the forces, torques, interaction energies, and Hamaker coefficients that govern assembly in such systems. The mesoscale Lifshitz theory of van der Waals interactions can accurately describe solvent and temperature effects, retardation, and optically and morphologically anisotropic materials for cylindrical and planar interaction geometries. The Gecko Hamaker open-science software implementation of this theory enables new and sophisticated insights into the properties of important organic/inorganic systems: interactions show an extended range of magnitudes and retardation rates, DNA interactions show an imprint of base pair composition, certain SWCNT interactions display retardation-dependent nonmonotonicity, and interactions are mapped across a range of material systems in order to facilitate rational mesoscale design.

Cross-Cultural Skills for Deployed Air Force Personnel: Defining Cross-Cultural Performance

DTIC Science & Technology

2009-01-01

Van Der Molen , 2005). However, other research shows that as a person’s fluency in a for- eign language increases, so do the expectations that the...and Van Der Molen , 2005). Changing behavior to fit cultural context. Changing behavior to fit cultural context involves adapting one’s behavior to...2003); it has also been shown to relate to job performance (Mol, Born, Willemsen, and Van Der Molen , 2005). The relationship between this behavior

Naval Research Logistics Quarterly. Volume 28, Number 4,

DTIC Science & Technology

1981-12-01

Fan [31 and an observation by Meijerink and van der Vorst [181 guarantee that after pivoting on any diagonal element of a diagonally dominant M- matrix...Science, 3, 255-269 (1957). 1181 Meijerink, J. and H. Van der Vorst, "An Iterative Solution Method for Linear Systems of which the Coefficient Matrix Is a...Hee, K., A. Hordijk and J. Van der Wal, "Successive Approximations for Convergent Dynamic Programming," in Markov Decision Theory, H. Tijms and J

Materials perspective on Casimir and van der Waals interactions

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

Woods, L. M.; Dalvit, D. A. R.; Tkatchenko, A.

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. In such interactions these 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 insightsmore » 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. Our 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. Finally, 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.« less

Materials perspective on Casimir and van der Waals interactions

DOE PAGES

Woods, L. M.; Dalvit, D. A. R.; Tkatchenko, A.; ...

2016-11-02

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. In such interactions these 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 insightsmore » 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. Our 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. Finally, 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.« less

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

PubMed

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

2017-04-07

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 In 2 Se 3 and other III 2 -VI 3 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 In 2 Se 3 /graphene, exhibiting a tunable Schottky barrier, and In 2 Se 3 /WSe 2 , 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.

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

PubMed Central

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

2017-01-01

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. PMID:28387225

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

NASA Astrophysics Data System (ADS)

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.

A generalized linear factor model approach to the hierarchical framework for responses and response times.

PubMed

Molenaar, Dylan; Tuerlinckx, Francis; van der Maas, Han L J

2015-05-01

We show how the hierarchical model for responses and response times as developed by van der Linden (2007), Fox, Klein Entink, and van der Linden (2007), Klein Entink, Fox, and van der Linden (2009), and Glas and van der Linden (2010) can be simplified to a generalized linear factor model with only the mild restriction that there is no hierarchical model at the item side. This result is valuable as it enables all well-developed modelling tools and extensions that come with these methods. We show that the restriction we impose on the hierarchical model does not influence parameter recovery under realistic circumstances. In addition, we present two illustrative real data analyses to demonstrate the practical benefits of our approach. © 2014 The British Psychological Society.

Passivation of Black Phosphorus via Self-Assembled Organic Monolayers by van der Waals Epitaxy.

PubMed

Zhao, Yinghe; Zhou, Qionghua; Li, Qiang; Yao, Xiaojing; Wang, Jinlan

2017-02-01

An effective passivation approach to protect black phosphorus (BP) from degradation based on multi-scale simulations is proposed. The self-assembly of perylene-3,4,9,10-tetracarboxylic dianhydride monolayers via van der Waals epitaxy on BP does not break the original electronic properties of BP. The passivation layer thickness is only 2 nm. This study opens up a new pathway toward fine passivation of BP. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Holographic Van der Waals phase transition of the higher-dimensional electrically charged hairy black hole

NASA Astrophysics Data System (ADS)

Li, Hui-Ling; Feng, Zhong-Wen; Zu, Xiao-Tao

2018-01-01

With motivation by holography, employing black hole entropy, two-point connection function and entanglement entropy, we show that, for the higher-dimensional Anti-de Sitter charged hairy black hole in the fixed charged ensemble, a Van der Waals-like phase transition can be observed. Furthermore, based on the Maxwell equal-area construction, we check numerically the equal-area law for a first order phase transition in order to further characterize the Van der Waals-like phase transition.

van der Waals-Tonks-type equations of state for hard-hypersphere fluids in four and five dimensions

NASA Astrophysics Data System (ADS)

Wang, Xian-Zhi

2004-04-01

Recently, we developed accurate van der Waals-Tonks-type equations of state for hard-disk and hard-sphere fluids by using the known virial coefficients. In this paper, we derive the van der Waals-Tonks-type equations of state. We further apply these equations of state to hard-hypersphere fluids in four and five dimensions. In the low-density fluid regime, these equations of state are in good agreement with the simulation results and existing equations of state.

Graphene Substrate for van der Waals Epitaxy of Layer-Structured Bismuth Antimony Telluride Thermoelectric Film.

PubMed

Kim, Eun Sung; Hwang, Jae-Yeol; Lee, Kyu Hyoung; Ohta, Hiromichi; Lee, Young Hee; Kim, Sung Wng

2017-02-01

Graphene as a substrate for the van der Waals epitaxy of 2D layered materials is utilized for the epitaxial growth of a layer-structured thermoelectric film. Van der Waals epitaxial Bi 0.5 Sb 1.5 Te 3 film on graphene synthesized via a simple and scalable fabrication method exhibits good crystallinity and high thermoelectric transport properties comparable to single crystals. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Concrete Block Pavements

DTIC Science & Technology

1983-03-01

concrete paving block ( Van der Vlist 1980). The concrete paving block was readily accepted as a substitute for the scarce paving brick and today has...seen in Figure 4, its growth.has been steady ( Van der Vlist 1980). 20 15 0< 0. n 10 1𔃺 978 960 1 62 63 64 65 66 67 68 6970 71 72 73 74 7678 7778 79...Figure 4. Concrete paving block production in the Netherlands ( Van der Vlist 1980) 8. The use of concrete paving block in the Netherlands developedI

Theory of Solid Surfaces.

DTIC Science & Technology

1976-05-01

of low—energy e~1ectrons by ti ght—bi ndimg electrons ”. 3. Phys. C 8, 1087—1098. 39. IN CLESF IELD , J . E . and WIKBORG , E. “The van der Waals...very good numerical results. An alternative nt~ erical scheme which holds out promise is by Van der Avoird ’s group at T~ megen, Netherlands , where...with Van der 1~aals interactions between metals and using the experience gained at surfaces to help produc e a more consistent many body potential

Calculation of Hamaker constants in non-aqueous fluid media

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

BELL,NELSON S.; DIMOS,DUANE B.

2000-05-09

Calculations of the Hamaker constants representing the van der Waals interactions between conductor, resistor and dielectric materials are performed using Lifshitz theory. The calculation of the parameters for the Ninham-Parsegian relationship for several non-aqueous liquids has been derived based on literature dielectric data. Discussion of the role of van der Waals forces in the dispersion of particles is given for understanding paste formulation. Experimental measurements of viscosity are presented to show the role of dispersant truncation of attractive van der Waals forces.

Accurate van der Waals coefficients from density functional theory

PubMed Central

Tao, Jianmin; Perdew, John P.; Ruzsinszky, Adrienn

2012-01-01

The van der Waals interaction is a weak, long-range correlation, arising from quantum electronic charge fluctuations. This interaction affects many properties of materials. A simple and yet accurate estimate of this effect will facilitate computer simulation of complex molecular materials and drug design. Here we develop a fast approach for accurate evaluation of dynamic multipole polarizabilities and van der Waals (vdW) coefficients of all orders from the electron density and static multipole polarizabilities of each atom or other spherical object, without empirical fitting. Our dynamic polarizabilities (dipole, quadrupole, octupole, etc.) are exact in the zero- and high-frequency limits, and exact at all frequencies for a metallic sphere of uniform density. Our theory predicts dynamic multipole polarizabilities in excellent agreement with more expensive many-body methods, and yields therefrom vdW coefficients C6, C8, C10 for atom pairs with a mean absolute relative error of only 3%. PMID:22205765

Porous silicon film formation from silicon-nanoparticle inks: The possibility of effects of van der Waals interactions on uniform film formation

NASA Astrophysics Data System (ADS)

Tanaka, Kazuki; Nagoya, Wataru; Moriki, Kazuya; Sato, Seiichi

2018-02-01

Porous Si films were formed on electrically insulative, semiconductive, and conductive substrates by depositing aqueous and nonaqueous Si nanoparticle inks. In this study, we focused on whether the Si ink deposition resulted in the formation of uniform porous Si films on various substrates. As a result of the experiments, we found that the inks showing better substrate wettabilities did not necessarily result in more uniform film formation on the substrates. This implies that the ink-solvent wettability and the nanoparticle-substrate interactions play important roles in the uniform film formation. As one of the interactions, we discussed the influence of van der Waals interactions by calculating the Hamaker constants. The calculation results indicated that the uniform film formation was hampered when the nanoparticle surface had a repulsive van der Waals interaction with the substrate.

Polynomial-interpolation algorithm for van der Pauw Hall measurement in a metal hydride film

NASA Astrophysics Data System (ADS)

Koon, D. W.; Ares, J. R.; Leardini, F.; Fernández, J. F.; Ferrer, I. J.

2008-10-01

We apply a four-term polynomial-interpolation extension of the van der Pauw Hall measurement technique to a 330 nm Mg-Pd bilayer during both absorption and desorption of hydrogen at room temperature. We show that standard versions of the van der Pauw DC Hall measurement technique produce an error of over 100% due to a drifting offset signal and can lead to unphysical interpretations of the physical processes occurring in this film. The four-term technique effectively removes this source of error, even when the offset signal is drifting by an amount larger than the Hall signal in the time interval between successive measurements. This technique can be used to increase the resolution of transport studies of any material in which the resistivity is rapidly changing, particularly when the material is changing from metallic to insulating behavior.

Aqueous gating of van der Waals materials on bilayer nanopaper.

PubMed

Bao, Wenzhong; Fang, Zhiqiang; Wan, Jiayu; Dai, Jiaqi; Zhu, Hongli; Han, Xiaogang; Yang, Xiaofeng; Preston, Colin; Hu, Liangbing

2014-10-28

In this work, we report transistors made of van der Waals materials on a mesoporous paper with a smooth nanoscale surface. The aqueous transistor has a novel planar structure with source, drain, and gate electrodes on the same surface of the paper, while the mesoporous paper is used as an electrolyte reservoir. These transistors are enabled by an all-cellulose paper with nanofibrillated cellulose (NFC) on the top surface that leads to an excellent surface smoothness, while the rest of the microsized cellulose fibers can absorb electrolyte effectively. Based on two-dimensional van der Waals materials, including MoS2 and graphene, we demonstrate high-performance transistors with a large on-off ratio and low subthreshold swing. Such planar transistors with absorbed electrolyte gating can be used as sensors integrated with other components to form paper microfluidic systems. This study is significant for future paper-based electronics and biosensors.

Giant magnetic splitting inducing near-unity valley polarization in van der Waals heterostructures.

PubMed

Nagler, Philipp; Ballottin, Mariana V; Mitioglu, Anatolie A; Mooshammer, Fabian; Paradiso, Nicola; Strunk, Christoph; Huber, Rupert; Chernikov, Alexey; Christianen, Peter C M; Schüller, Christian; Korn, Tobias

2017-11-16

Monolayers of semiconducting transition metal dichalcogenides exhibit intriguing fundamental physics of strongly coupled spin and valley degrees of freedom for charge carriers. While the possibility of exploiting these properties for information processing stimulated concerted research activities towards the concept of valleytronics, maintaining control over spin-valley polarization proved challenging in individual monolayers. A promising alternative route explores type II band alignment in artificial van der Waals heterostructures. The resulting formation of interlayer excitons combines the advantages of long carrier lifetimes and spin-valley locking. Here, we demonstrate artificial design of a two-dimensional heterostructure enabling intervalley transitions that are not accessible in monolayer systems. The resulting giant effective g factor of -15 for interlayer excitons induces near-unity valley polarization via valley-selective energetic splitting in high magnetic fields, even after nonselective excitation. Our results highlight the potential to deterministically engineer novel valley properties in van der Waals heterostructures using crystallographic alignment.

Terahertz vibration-rotation-tunneling (VRT) spectroscopy of the d6-water trimer: Complete characterization of the 2.94 THz torsional band ( kn = ±2 1 ← 0 0)

NASA Astrophysics Data System (ADS)

Han, Jia-xiang; Takahashi, Lynelle K.; Lin, Wei; Lee, Eddy; Keutsch, Frank N.; Saykally, Richard J.

2006-06-01

We report the measurement and analysis of the complete perpendicular kn = ±2 1 ← 0 0 (D 2O) 3 torsional band (origin 2940.9376(3) GHz), the upper state of which is the highest-energy (98.09912 cm -1) torsional state yet observed. All known torsional transitions were included in a new global analysis of the six observed torsional bands, using the effective Hamiltonians derived by van der Avoird et al. [M. R. Viant, M. G. Brown, J. D. Cruzan, R. J. Saykally, M. Geleijns, A. van der Avoird, J. Chem. Phys. 110 (1999) 4369; A. van der Avoird, E. H. T. Olthof, P. E. S. Wormer, J. Chem. Phys. 105 (1996) 8034]. The experimental results will facilitate the descriptions of three-body interactions in water intermolecular potential energy surfaces (IPSs).

Reale Gase, tiefe Temperaturen

NASA Astrophysics Data System (ADS)

Heintze, Joachim

Wir werden uns in diesem Kapitel zunächst mit der van der Waals'schen Zustandsgleichung befassen. In dieser Gleichung wird versucht, die Abweichungen, die reale Gase vom Verhalten idealer Gase zeigen, durch physikalisch motivierte Korrekturterme zu berücksichtigen. Es zeigt sich, dass die van derWaals-Gleichung geeignet ist, nicht nur die Gasphase, sondern auch die Phänomene bei der Verflüssigung von Gasen und den kritischen Punkt zu beschreiben.

Li intercalation in graphite: A van der Waals density-functional study

NASA Astrophysics Data System (ADS)

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.

Quality of Life for Adults with Asthma in a Military Setting

DTIC Science & Technology

1998-05-01

Tilley, Havstead, & Zoratti, 1997). More recently, van der Molen , et al. (1997) conducted a study comparing discriminative aspects of two generic...Symptom Management Faculty Group, UCSF. (1994). IMAGE: Journal of Nursing Scholarship, 26(4), 272-276. van der Molen , T., Postma, D., Schreuers, A...the most important (Earwood, 1996, Rutten- Van Molken, Van Doorslaer, & Rutten, 1992). Purpose of the Study When patients clarify their perceptions of

De Ontwikkeling van een PBPK Model voor VX; Stand van Zaken V013-813 en 207C (The Development of a PBPK Model for VX: Status Report)

DTIC Science & Technology

2006-02-01

ing. H.C. Trap, dr. ir. M.J. van der werd zes maal gesproken over de Schans, ing. L.F. Chau, B.). Lander, invulling en de voortgang van het I.A. Cordia ...dr. ir. M.J. van der Schans, ing. L.F. Chau, J.P. Oostdijk, B.J. Lander, l.A. Cordia 25 TNO Defensie en Veiligheid, vestiging Rijswijk, Marketing en

Concurrent Van der Woude syndrome and Turner syndrome: A case report.

PubMed

Los, Evan; Baines, Hayley; Guttmann-Bauman, Ines

2017-01-01

Most cases of Van der Woude syndrome are caused by a mutation to interferon regulatory factor 6 on chromosome 1. Turner syndrome is caused by complete or partial absence of the second sex chromosome in girls. We describe a unique case of the two syndromes occurring concurrently though apparently independently in a girl with Van der Woude syndrome diagnosed at birth and Turner syndrome at 14 years 9 months. Short stature was initially misattributed to Van der Woude syndrome and pituitary insufficiency associated with clefts before correctly diagnosing Turner syndrome. We discuss the prevalence of delayed diagnosis of Turner syndrome, the rarity of reports of concurrent autosomal chromosome mutation and sex chromosome deletion, as well as the need to consider the diagnosis of Turner syndrome in all girls with short stature regardless of prior medical history.

Should We Stop Developing Heuristics and Only Rely on Mixed Integer Programming Solvers in Automated Test Assembly? A Rejoinder to van der Linden and Li (2016).

PubMed

Chen, Pei-Hua

2017-05-01

This rejoinder responds to the commentary by van der Linden and Li entiled "Comment on Three-Element Item Selection Procedures for Multiple Forms Assembly: An Item Matching Approach" on the article "Three-Element Item Selection Procedures for Multiple Forms Assembly: An Item Matching Approach" by Chen. Van der Linden and Li made a strong statement calling for the cessation of test assembly heuristics development, and instead encouraged embracing mixed integer programming (MIP). This article points out the nondeterministic polynomial (NP)-hard nature of MIP problems and how solutions found using heuristics could be useful in an MIP context. Although van der Linden and Li provided several practical examples of test assembly supporting their view, the examples ignore the cases in which a slight change of constraints or item pool data might mean it would not be possible to obtain solutions as quickly as before. The article illustrates the use of heuristic solutions to improve both the performance of MIP solvers and the quality of solutions. Additional responses to the commentary by van der Linden and Li are included.

First description and bionomic notes for the final-instar larva and pupa of an Oriental dobsonfly species, Neoneuromus sikkimmensis (van der Weele, 1907) (Megaloptera: Corydalidae).

PubMed

Cao, Chengquan; Tong, Chao; Chen, Shengzhi; Liu, Zhiwei; Xu, Faqiong; Liu, Qian; Liu, Xingyue

2016-10-31

Neoneuromus van der Weele, 1909, a member of megalopteran subfamily Corydalinae, is a common and widespread dobsonfly genus of the Oriental Region. The adult taxonomy of Neoneuromus is relatively well-known but the larvae and pupae are undescribed. In this paper we describe the last-instar larva and the pupa of N. sikkimmensis (van der Weele, 1907), representing the first detailed description of any immature stage of Neoneuromus. Information on the bionomics of this species is also reported.

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

NASA Technical Reports Server (NTRS)

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.

Bell's palsy before Bell: Cornelis Stalpart van der Wiel's observation of Bell's palsy in 1683.

PubMed

van de Graaf, Robert C; Nicolai, Jean-Philippe A

2005-11-01

Bell's palsy is named after Sir Charles Bell (1774-1842), who has long been considered to be the first to describe idiopathic facial paralysis in the early 19th century. However, it was discovered that Nicolaus Anton Friedreich (1761-1836) and James Douglas (1675-1742) preceded him in the 18th century. Recently, an even earlier account of Bell's palsy was found, as observed by Cornelis Stalpart van der Wiel (1620-1702) from The Hague, The Netherlands in 1683. Because our current knowledge of the history of Bell's palsy before Bell is limited to a few documents, it is interesting to discuss Stalpart van der Wiel's description and determine its additional value for the history of Bell's palsy. It is concluded that Cornelis Stalpart van der Wiel was the first to record Bell's palsy in 1683. His manuscript provides clues for future historical research.

The role of van der Waals interaction in the tilted binding of amine molecules to the Au(111) surface

NASA Astrophysics Data System (ADS)

Le, Duy; Aminpour, Maral; Kiejna, Adam; Rahman, Talat S.

2012-06-01

We present the results of ab initio electronic structure calculations for the adsorption characteristics of three amine molecules on Au(111), which show that the inclusion of van der Waals interactions between the isolated molecule and the surface leads in general to good agreement with experimental data on the binding energies. Each molecule, however, adsorbs with a small tilt angle (between -5 and 9°). For the specific case of 1,4-diaminobenzene (BDA) our calculations reproduce the larger tilt angle (close to 24°) measured by photoemission experiments, when intermolecular (van der Waals) interactions (for about 8% coverage) are included. These results point not only to the important contribution of van der Waals interactions to molecule-surface binding energy, but also that of intermolecular interactions, often considered secondary to that between the molecule and the surface, in determining the adsorption geometry and pattern formation.

Spectral asymmetry of atoms in the van der Waals potential of an optical nanofiber

NASA Astrophysics Data System (ADS)

Patterson, B. D.; Solano, P.; Julienne, P. S.; Orozco, L. A.; Rolston, S. L.

2018-03-01

We measure the modification of the transmission spectra of cold 87Rb atoms in the proximity of an optical nanofiber (ONF). Van der Waals interactions between the atoms an the ONF surface decrease the resonance frequency of atoms closer to the surface. An asymmetric spectra of the atoms holds information of their spatial distribution around the ONF. We use a far-detuned laser beam coupled to the ONF to thermally excite atoms at the ONF surface. We study the change of transmission spectrum of these atoms as a function of heating laser power. A semiclassical phenomenological model for the thermal excitation of atoms in the atom-surface van der Waals bound states is in good agreement with the measurements. This result suggests that van der Waals potentials could be used to trap and probe atoms at few nanometers from a dielectric surface, a key tool for hybrid photonic-atomic quantum systems.

Van der Waals epitaxial growth and optoelectronics of large-scale WSe2/SnS2 vertical bilayer p-n junctions.

PubMed

Yang, Tiefeng; Zheng, Biyuan; Wang, Zhen; Xu, Tao; Pan, Chen; Zou, Juan; Zhang, Xuehong; Qi, Zhaoyang; Liu, Hongjun; Feng, Yexin; Hu, Weida; Miao, Feng; Sun, Litao; Duan, Xiangfeng; Pan, Anlian

2017-12-04

High-quality two-dimensional atomic layered p-n heterostructures are essential for high-performance integrated optoelectronics. The studies to date have been largely limited to exfoliated and restacked flakes, and the controlled growth of such heterostructures remains a significant challenge. Here we report the direct van der Waals epitaxial growth of large-scale WSe 2 /SnS 2 vertical bilayer p-n junctions on SiO 2 /Si substrates, with the lateral sizes reaching up to millimeter scale. Multi-electrode field-effect transistors have been integrated on a single heterostructure bilayer. Electrical transport measurements indicate that the field-effect transistors of the junction show an ultra-low off-state leakage current of 10 -14 A and a highest on-off ratio of up to 10 7 . Optoelectronic characterizations show prominent photoresponse, with a fast response time of 500 μs, faster than all the directly grown vertical 2D heterostructures. The direct growth of high-quality van der Waals junctions marks an important step toward high-performance integrated optoelectronic devices and systems.

Interlayer coupling effects on Schottky barrier in the arsenene-graphene van der Waals heterostructures

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

Xia, Congxin, E-mail: xiacongxin@htu.edu.cn; Xue, Bin; Wang, Tianxing

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.

Electric-field switching of two-dimensional van der Waals magnets

NASA Astrophysics Data System (ADS)

Jiang, Shengwei; Shan, Jie; Mak, Kin Fai

2018-05-01

Controlling magnetism by purely electrical means is a key challenge to better information technology1. A variety of material systems, including ferromagnetic (FM) metals2-4, FM semiconductors5, multiferroics6-8 and magnetoelectric (ME) materials9,10, have been explored for the electric-field control of magnetism. The recent discovery of two-dimensional (2D) van der Waals magnets11,12 has opened a new door for the electrical control of magnetism at the nanometre scale through a van der Waals heterostructure device platform13. Here we demonstrate the control of magnetism in bilayer CrI3, an antiferromagnetic (AFM) semiconductor in its ground state12, by the application of small gate voltages in field-effect devices and the detection of magnetization using magnetic circular dichroism (MCD) microscopy. The applied electric field creates an interlayer potential difference, which results in a large linear ME effect, whose sign depends on the interlayer AFM order. We also achieve a complete and reversible electrical switching between the interlayer AFM and FM states in the vicinity of the interlayer spin-flip transition. The effect originates from the electric-field dependence of the interlayer exchange bias.

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

PubMed

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.

van der Waals interactions between nanostructures: Some analytic results from series expansions

NASA Astrophysics Data System (ADS)

Stedman, T.; Drosdoff, D.; Woods, L. M.

2014-01-01

The van der Waals force between objects of nontrivial geometries is considered. A technique based on a perturbation series approach is formulated in the dilute limit. We show that the dielectric response and object size can be decoupled and dominant contributions in terms of object separations can be obtained. This is a powerful method, which enables straightforward calculations of the interaction for different geometries. Our results for planar structures, such as thin sheets, infinitely long ribbons, and ribbons with finite dimensions, may be applicable for nanostructured devices where the van der Waals interaction plays an important role.

Nano-RDX Electrostatic Stabilization Mechanism Investigation Using Derjaguin-Landau and Verwey-Overbeek (DLVO) Theory

DTIC Science & Technology

2017-01-20

is the same order of magnitude as the van der Waals attraction (fig. 1). At ionic strenghs (0.1 mol/ L ), the thickness is less than 1 nm. In that...c) At concentration 0.1 m/ L , the van der Waals attraction force is dominant. This explain why most charged nanoparticles agglomerate when...60 -40 -20 0 20 40 60 80 0 5 10 15 20 To ta l i nt er ac tio n En er gy in u ni ts o f k bT Distance between nanoparticles (nm) Van der Waals

Anyon black holes

NASA Astrophysics Data System (ADS)

Aghaei Abchouyeh, Maryam; Mirza, Behrouz; Karimi Takrami, Moein; Younesizadeh, Younes

2018-05-01

We propose a correspondence between an Anyon Van der Waals fluid and a (2 + 1) dimensional AdS black hole. Anyons are particles with intermediate statistics that interpolates between a Fermi-Dirac statistics and a Bose-Einstein one. A parameter α (0 < α < 1) characterizes this intermediate statistics of Anyons. The equation of state for the Anyon Van der Waals fluid shows that it has a quasi Fermi-Dirac statistics for α >αc, but a quasi Bose-Einstein statistics for α <αc. By defining a general form of the metric for the (2 + 1) dimensional AdS black hole and considering the temperature of the black hole to be equal with that of the Anyon Van der Waals fluid, we construct the exact form of the metric for a (2 + 1) dimensional AdS black hole. The thermodynamic properties of this black hole is consistent with those of the Anyon Van der Waals fluid. For α <αc, the solution exhibits a quasi Bose-Einstein statistics. For α >αc and a range of values of the cosmological constant, there is, however, no event horizon so there is no black hole solution. Thus, for these values of cosmological constants, the AdS Anyon Van der Waals black holes have only quasi Bose-Einstein statistics.

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

PubMed

Govyadinov, Alexander A; Konečná, Andrea; Chuvilin, Andrey; Vélez, Saül; Dolado, Irene; Nikitin, Alexey Y; Lopatin, Sergei; Casanova, Fèlix; Hueso, Luis E; Aizpurua, Javier; Hillenbrand, Rainer

2017-07-21

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.

Efimov states near a Feshbach resonance and the limits of van der Waals universality at finite background scattering length

NASA Astrophysics Data System (ADS)

Langmack, Christian; Schmidt, Richard; Zwerger, Wilhelm

2018-03-01

We calculate the spectrum of three-body Efimov bound states near a Feshbach resonance within a model which accounts both for the finite range of interactions and the presence of background scattering. The latter may be due to direct interactions in an open channel or a second overlapping Feshbach resonance. It is found that background scattering gives rise to substantial changes in the trimer spectrum as a function of the detuning away from a Feshbach resonance, in particular in the regime where the background channel supports Efimov states on its own. Compared to the situation with negligible background scattering, the regime where van der Waals universality applies is shifted to larger values of the resonance strength if the background scattering length is positive. For negative background scattering lengths, in turn, van der Waals universality extends to even small values of the resonance strength parameter, consistent with experimental results on Efimov states in 39K. Within a simple model, we show that short-range three-body forces do not affect van der Waals universality significantly. Repulsive three-body forces may, however, explain the observed variation between around -8 and -10 of the ratio between the scattering length where the first Efimov trimer appears and the van der Waals length.

Dipole-dipole interaction in cavity QED: The weak-coupling, nondegenerate regime

NASA Astrophysics Data System (ADS)

Donaire, M.; Muñoz-Castañeda, J. M.; Nieto, L. M.

2017-10-01

We compute the energies of the interaction between two atoms placed in the middle of a perfectly reflecting planar cavity, in the weak-coupling nondegenerate regime. Both inhibition and enhancement of the interactions can be obtained by varying the size of the cavity. We derive exact expressions for the dyadic Green's function of the cavity field which mediates the interactions and apply time-dependent quantum perturbation theory in the adiabatic approximation. We provide explicit expressions for the van der Waals potentials of two polarizable atomic dipoles and the electrostatic potential of two induced dipoles. We compute the van der Waals potentials in three different scenarios: two atoms in their ground states, two atoms excited, and two dissimilar atoms with one of them excited. In addition, we calculate the phase-shift rate of the two-atom wave function in each case. The effect of the two-dimensional confinement of the electromagnetic field on the dipole-dipole interactions is analyzed. This effect depends on the atomic polarization. For dipole moments oriented parallel to the cavity plates, both the electrostatic and the van der Waals interactions are exponentially suppressed for values of the cavity width much less than the interatomic distance, whereas for values of the width close to the interatomic distance, the strength of both interactions is higher than their values in the absence of cavity. For dipole moments perpendicular to the plates, the strength of the van der Waals interaction decreases for values of the cavity width close to the interatomic distance, while it increases for values of the width much less than the interatomic distance with respect to its strength in the absence of cavity. We illustrate these effects by computing the dipole-dipole interactions between two alkali atoms in circular Rydberg states.

Interaction-component analysis of the hydration and urea effects on cytochrome c

NASA Astrophysics Data System (ADS)

Yamamori, Yu; Ishizuka, Ryosuke; Karino, Yasuhito; Sakuraba, Shun; Matubayasi, Nobuyuki

2016-02-01

Energetics was analyzed for cytochrome c in pure-water solvent and in a urea-water mixed solvent to elucidate the solvation effect in the structural variation of the protein. The solvation free energy was computed through all-atom molecular dynamics simulation combined with the solution theory in the energy representation, and its correlations were examined over sets of protein structures against the electrostatic and van der Waals components in the average interaction energy of the protein with the solvent and the excluded-volume component in the solvation free energy. It was observed in pure-water solvent that the solvation free energy varies in parallel to the electrostatic component with minor roles played by the van der Waals and excluded-volume components. The effect of urea on protein structure was then investigated in terms of the free-energy change upon transfer of the protein solute from pure-water solvent to the urea-water mixed solvent. The decomposition of the transfer free energy into the contributions from urea and water showed that the urea contribution is partially canceled by the water contribution and governs the total free energy of transfer. When correlated against the change in the solute-solvent interaction energy upon transfer and the corresponding changes in the electrostatic, van der Waals, and excluded-volume components, the transfer free energy exhibited strong correlations with the total change in the solute-solvent energy and its van der Waals component. The solute-solvent energy was decomposed into the contributions from the protein backbone and side chain, furthermore, and neither of the contributions was seen to be decisive in the correlation to the transfer free energy.

Beta-catenin: A Potential Survival Marker of Breast Cancer Stem Cells

DTIC Science & Technology

2006-09-01

T. C., Alexander, C. M., Georges-Labouesse, E., Van der Neut , R., Kreidberg, J. A., Jones, C. J., Sonnenberg, A. and Streuli, C. H. (2001...de Lau, W., Oving, I., Hurlstone, A., van der Horn, K., Batlle, E., Coudreuse, D., Haramis, A. P., Tjon-Pon-Fong, M., Moerer, P., van den Born, M...Scherer, D. C., Willert, K., Hintz, L., Nusse, R. & Weissman, I. L. (2003) Nature 423, 409-14. 36. van de Wetering, M., Sancho, E., Verweij, C

van der Waals torque

NASA Astrophysics Data System (ADS)

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.

Chesapeake Bay Sediment Flux Model

DTIC Science & Technology

1993-06-01

1988; Van der Molen , -88- 1991; Yoshida, 1981.) The model developed below is based on both of these approaches. It incorporates the diagenetic...288: pp. 289-333. Van der Molen , D.T. (1991): A simple, dynamic model for the simulation of the release of phosphorus from sediments in shallow...1974; Berner, 1980; van Cappellen and Berner, 1988). These relate the diagenetic production of phosphate to the resulting pore water concentration

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

PubMed Central

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

2016-01-01

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. PMID:27174162

Dynamics of three coupled van der Pol oscillators with application to circadian rhythms

NASA Astrophysics Data System (ADS)

Rompala, Kevin; Rand, Richard; Howland, Howard

2007-08-01

In this work we study a system of three van der Pol oscillators. Two of the oscillators are identical, and are not directly coupled to each other, but rather are coupled via the third oscillator. We investigate the existence of the in-phase mode in which the two identical oscillators have the same behavior. To this end we use the two variable expansion perturbation method (also known as multiple scales) to obtain a slow flow, which we then analyze using the computer algebra system MACSYMA and the numerical bifurcation software AUTO. Our motivation for studying this system comes from the presence of circadian rhythms in the chemistry of the eyes. We model the circadian oscillator in each eye as a van der Pol oscillator. Although there is no direct connection between the two eyes, they are both connected to the brain, especially to the pineal gland, which is here represented by a third van der Pol oscillator.

Accurate van der Waals force field for gas adsorption in porous materials.

PubMed

Sun, Lei; Yang, Li; Zhang, Ya-Dong; Shi, Qi; Lu, Rui-Feng; Deng, Wei-Qiao

2017-09-05

An accurate van der Waals force field (VDW FF) was derived from highly precise quantum mechanical (QM) calculations. Small molecular clusters were used to explore van der Waals interactions between gas molecules and porous materials. The parameters of the accurate van der Waals force field were determined by QM calculations. To validate the force field, the prediction results from the VDW FF were compared with standard FFs, such as UFF, Dreiding, Pcff, and Compass. The results from the VDW FF were in excellent agreement with the experimental measurements. This force field can be applied to the prediction of the gas density (H 2 , CO 2 , C 2 H 4 , CH 4 , N 2 , O 2 ) and adsorption performance inside porous materials, such as covalent organic frameworks (COFs), zeolites and metal organic frameworks (MOFs), consisting of H, B, N, C, O, S, Si, Al, Zn, Mg, Ni, and Co. This work provides a solid basis for studying gas adsorption in porous materials. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Uncovering Droop Control Laws Embedded Within the Nonlinear Dynamics of Van der Pol Oscillators

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

Sinha, Mohit; Dorfler, Florian; Johnson, Brian B.

This paper examines the dynamics of power-electronic inverters in islanded microgrids that are controlled to emulate the dynamics of Van der Pol oscillators. The general strategy of controlling inverters to emulate the behavior of nonlinear oscillators presents a compelling time-domain alternative to ubiquitous droop control methods which presume the existence of a quasistationary sinusoidal steady state and operate on phasor quantities. We present two main results in this paper. First, by leveraging the method of periodic averaging, we demonstrate that droop laws are intrinsically embedded within a slower time scale in the nonlinear dynamics of Van der Pol oscillators. Second,more » we establish the global convergence of amplitude and phase dynamics in a resistive network interconnecting inverters controlled as Van der Pol oscillators. Furthermore, under a set of nonrestrictive decoupling approximations, we derive sufficient conditions for local exponential stability of desirable equilibria of the linearized amplitude and phase dynamics.« less

Tunable Schottky barrier in van der Waals heterostructures of graphene and g-GaN

NASA Astrophysics Data System (ADS)

Sun, Minglei; Chou, Jyh-Pin; Ren, Qingqiang; Zhao, Yiming; Yu, Jin; Tang, Wencheng

2017-04-01

Using first-principles calculations, we systematically investigated the electronic properties of graphene/g-GaN van der Waals (vdW) heterostructures. We discovered that the Dirac cone of graphene could be quite well preserved in the vdW heterostructures. Moreover, a transition from an n-type to p-type Schottky contact at the graphene/g-GaN interface was induced with a decreased interlayer distance from 4.5 to 2.5 Å. This relationship is expected to enable effective control of the Schottky barrier, which is an important development in the design of Schottky devices.

Observation of novel photochemistry in the multiphoton ionization of Mo(CO) sub 6 van der Waals clusters

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

Peifer, W.R.; Garvey, J.F.

1989-07-27

van der Waals clusters of Mo(CO){sub 6} generated in the free-jet expansion of a pulsed beam of seeded helium are subjected to multiphoton ionization and the product ions analyzed by quadrupole mass spectrometry. Oxomolybdenum and dioxomolybdenum ions are observed to be produced with high efficiency. This behavior is in striking contrast to that of metal carbonyl monomers and covalently bound cluster carbonyls, which under complete ligand loss prior to ionization. The observed photochemistry is ascribed to reactions between a photoproduced molybdenum atom and the ligands of neighboring Mo(CO){sub 6} solvent molecules within the van der Waals cluster.

European Symposium on X-Ray Topography and High Resolution Diffraction (2nd) Held in Berlin, Germany on 5-7 September 1994. Programme and Abstracts

DTIC Science & Technology

1994-09-07

RELAXATION OF NANOSTRUCTURED SIGE/SI PILLARS BY HIGH-RESOLUTION X-RAY DIFFRACTION P. van der Sluis and C.W.T. Bull.-Lieuwma PLillps Research Laboratories...whereas the lattice is fully strained in large (10xlO mm2) pillars. (1] P.B. Fischer and S.Y. Chou, Appl. Phys. Lett. 62, 1414 (1993) (2) P. van der ...tIn, hi&ttttV (Thl)ttLtl Of epitaxial layers of 111I-V compoutnds, J1. Cl’ybll GIVILth, Vol. 44:1)1.5113 :-517, 1978. (2) P. van der Sluls Determination

A statistical model of the human core-temperature circadian rhythm

NASA Technical Reports Server (NTRS)

Brown, E. N.; Choe, Y.; Luithardt, H.; Czeisler, C. A.

2000-01-01

We formulate a statistical model of the human core-temperature circadian rhythm in which the circadian signal is modeled as a van der Pol oscillator, the thermoregulatory response is represented as a first-order autoregressive process, and the evoked effect of activity is modeled with a function specific for each circadian protocol. The new model directly links differential equation-based simulation models and harmonic regression analysis methods and permits statistical analysis of both static and dynamical properties of the circadian pacemaker from experimental data. We estimate the model parameters by using numerically efficient maximum likelihood algorithms and analyze human core-temperature data from forced desynchrony, free-run, and constant-routine protocols. By representing explicitly the dynamical effects of ambient light input to the human circadian pacemaker, the new model can estimate with high precision the correct intrinsic period of this oscillator ( approximately 24 h) from both free-run and forced desynchrony studies. Although the van der Pol model approximates well the dynamical features of the circadian pacemaker, the optimal dynamical model of the human biological clock may have a harmonic structure different from that of the van der Pol oscillator.

The formation of quasi-alicyclic rings in alkyl-aromatic compounds

NASA Astrophysics Data System (ADS)

Straka, Pavel; Buryan, Petr; Bičáková, Olga

2018-02-01

The alkyl side chains of n-alkyl phenols, n-alkyl benzenes and n-alkyl naphthalenes are cyclised, as demonstrated by GC measurements, FTIR spectroscopy and molecular mechanics calculations. Cyclisation occurs due to the intramolecular interaction between an aromatic ring (-δ) and a hydrogen of the terminal methyl group (+δ) of an alkyl chain. In fact, conventional molecules are not aliphatic-aromatic, but quasi-alicyclic-aromatic. With the aromatic molecules formed with a quasi-alicyclic ring, the effect of van der Waals attractive forces increases not only intramolecularly but also intermolecularly. This effect is strong in molecules with propyl and higher alkyl substituents. The increase of intermolecular van der Waals attractive forces results in bi-linearity in the GC retention time of the compounds in question, observed in the dependence of the logarithm of the relative retention time on the number of carbons in a molecule in both polar and nonpolar stationary phases with both capillary and packed columns. The role of van der Waals forces has been demonstrated using the potential energies of covalent and noncovalent interactions for 2-n-alkyl phenols, n-alkyl benzenes and 1-n-alkyl- and 2-n-alkyl naphthalenes.

Generalization of the van der Pauw relationship derived from electrostatics

NASA Astrophysics Data System (ADS)

Weiss, Jonathan D.

2011-08-01

In an earlier paper, this author, along with two others Weiss et al. (2008) [1], demonstrated that the original van der Pauw relationship could be derived from three-dimensional electrostatics, as opposed to van der Pauw's use of conformal mapping. The earlier derivation was done for a conducting material of rectangular cross section with contacts placed at the corners. Presented here is a generalization of the previous work involving a square sample and a square array of electrodes that are not confined to the corners, since this measurement configuration could be a more convenient one. As in the previous work, the effects of non-zero sample thickness and contact size have been investigated. Buehler and Thurber derived a similar relationship using an infinite series of current images on a large and thin conducting sheet to satisfy the conditions at the boundary of the sample. The results presented here agree with theirs numerically, but analytic agreement could not be shown using any of the perused mathematical literature. By simply equating the two solutions, it appears that, as a byproduct of this work, a new mathematical relationship has been uncovered. Finally, the application of this methodology to the Hall Effect is discussed.

Atomically thin p-n junctions with van der Waals heterointerfaces.

PubMed

Lee, Chul-Ho; Lee, Gwan-Hyoung; van der Zande, Arend M; Chen, Wenchao; Li, Yilei; Han, Minyong; Cui, Xu; Arefe, Ghidewon; Nuckolls, Colin; Heinz, Tony F; Guo, Jing; Hone, James; Kim, Philip

2014-09-01

Semiconductor p-n junctions are essential building blocks for electronic and optoelectronic devices. In conventional p-n junctions, regions depleted of free charge carriers form on either side of the junction, generating built-in potentials associated with uncompensated dopant atoms. Carrier transport across the junction occurs by diffusion and drift processes influenced by the spatial extent of this depletion region. With the advent of atomically thin van der Waals materials and their heterostructures, it is now possible to realize a p-n junction at the ultimate thickness limit. Van der Waals junctions composed of p- and n-type semiconductors--each just one unit cell thick--are predicted to exhibit completely different charge transport characteristics than bulk heterojunctions. Here, we report the characterization of the electronic and optoelectronic properties of atomically thin p-n heterojunctions fabricated using van der Waals assembly of transition-metal dichalcogenides. We observe gate-tunable diode-like current rectification and a photovoltaic response across the p-n interface. We find that the tunnelling-assisted interlayer recombination of the majority carriers is responsible for the tunability of the electronic and optoelectronic processes. Sandwiching an atomic p-n junction between graphene layers enhances the collection of the photoexcited carriers. The atomically scaled van der Waals p-n heterostructures presented here constitute the ultimate functional unit for nanoscale electronic and optoelectronic devices.

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

NASA Astrophysics Data System (ADS)

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.

Review of Radar Absorbing Materials

DTIC Science & Technology

2005-01-01

Symposium, 1990. AP-S. Merging technologies for the 90’s. Digest 1990, 3, 1212. (30) Nortier, J. R., Van der Neut , C.A., Baker, D.E. Microwave Journal...1987, 219. (31) Kasevich, R. S.; Broderick, F., US Patent 5223849. 1993. (32) Van Der Plas, G., Barel, A., Schweicher, E. Antennas and Propagation

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

PubMed Central

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

2017-01-01

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

Nonlinearity of resistive impurity effects on van der Pauw measurements

NASA Astrophysics Data System (ADS)

Koon, D. W.

2006-09-01

The dependence of van der Pauw resistivity measurements on local macroscopic inhomogeneities is shown to be nonlinear. A resistor grid network models a square laminar specimen, enabling the investigation of both positive and negative local perturbations in resistivity. The effect of inhomogeneity is measured both experimentally, for an 11×11 grid, and computationally, for both 11×11 and 101×101 grids. The maximum "shortlike" perturbation produces 3.1±0.2 times the effect predicted by the linear approximation, regardless of its position within the specimen, while all "openlike" perturbations produce a smaller effect than predicted. An empirical nonlinear correction for f(x ,y) is presented which provides excellent fit over the entire range of both positive and negative perturbations for the entire specimen.

Finite element and analytical solutions for van der Pauw and four-point probe correction factors when multiple non-ideal measurement conditions coexist

NASA Astrophysics Data System (ADS)

Reveil, Mardochee; Sorg, Victoria C.; Cheng, Emily R.; Ezzyat, Taha; Clancy, Paulette; Thompson, Michael O.

2017-09-01

This paper presents an extensive collection of calculated correction factors that account for the combined effects of a wide range of non-ideal conditions often encountered in realistic four-point probe and van der Pauw experiments. In this context, "non-ideal conditions" refer to conditions that deviate from the assumptions on sample and probe characteristics made in the development of these two techniques. We examine the combined effects of contact size and sample thickness on van der Pauw measurements. In the four-point probe configuration, we examine the combined effects of varying the sample's lateral dimensions, probe placement, and sample thickness. We derive an analytical expression to calculate correction factors that account, simultaneously, for finite sample size and asymmetric probe placement in four-point probe experiments. We provide experimental validation of the analytical solution via four-point probe measurements on a thin film rectangular sample with arbitrary probe placement. The finite sample size effect is very significant in four-point probe measurements (especially for a narrow sample) and asymmetric probe placement only worsens such effects. The contribution of conduction in multilayer samples is also studied and found to be substantial; hence, we provide a map of the necessary correction factors. This library of correction factors will enable the design of resistivity measurements with improved accuracy and reproducibility over a wide range of experimental conditions.

Finite element and analytical solutions for van der Pauw and four-point probe correction factors when multiple non-ideal measurement conditions coexist.

PubMed

Reveil, Mardochee; Sorg, Victoria C; Cheng, Emily R; Ezzyat, Taha; Clancy, Paulette; Thompson, Michael O

2017-09-01

This paper presents an extensive collection of calculated correction factors that account for the combined effects of a wide range of non-ideal conditions often encountered in realistic four-point probe and van der Pauw experiments. In this context, "non-ideal conditions" refer to conditions that deviate from the assumptions on sample and probe characteristics made in the development of these two techniques. We examine the combined effects of contact size and sample thickness on van der Pauw measurements. In the four-point probe configuration, we examine the combined effects of varying the sample's lateral dimensions, probe placement, and sample thickness. We derive an analytical expression to calculate correction factors that account, simultaneously, for finite sample size and asymmetric probe placement in four-point probe experiments. We provide experimental validation of the analytical solution via four-point probe measurements on a thin film rectangular sample with arbitrary probe placement. The finite sample size effect is very significant in four-point probe measurements (especially for a narrow sample) and asymmetric probe placement only worsens such effects. The contribution of conduction in multilayer samples is also studied and found to be substantial; hence, we provide a map of the necessary correction factors. This library of correction factors will enable the design of resistivity measurements with improved accuracy and reproducibility over a wide range of experimental conditions.

Interlayer excitons in a bulk van der Waals semiconductor.

PubMed

Arora, Ashish; Drüppel, Matthias; Schmidt, Robert; Deilmann, Thorsten; Schneider, Robert; Molas, Maciej R; Marauhn, Philipp; Michaelis de Vasconcellos, Steffen; Potemski, Marek; Rohlfing, Michael; Bratschitsch, Rudolf

2017-09-21

Bound electron-hole pairs called excitons govern the electronic and optical response of many organic and inorganic semiconductors. Excitons with spatially displaced wave functions of electrons and holes (interlayer excitons) are important for Bose-Einstein condensation, superfluidity, dissipationless current flow, and the light-induced exciton spin Hall effect. Here we report on the discovery of interlayer excitons in a bulk van der Waals semiconductor. They form due to strong localization and spin-valley coupling of charge carriers. By combining high-field magneto-reflectance experiments and ab initio calculations for 2H-MoTe 2 , we explain their salient features: the positive sign of the g-factor and the large diamagnetic shift. Our investigations solve the long-standing puzzle of positive g-factors in transition metal dichalcogenides, and pave the way for studying collective phenomena in these materials at elevated temperatures.Excitons, quasi-particles of bound electron-hole pairs, are at the core of the optoelectronic properties of layered transition metal dichalcogenides. Here, the authors unveil the presence of interlayer excitons in bulk van der Waals semiconductors, arising from strong localization and spin-valley coupling of charge carriers.

On possible microscopic origins of the swelling of neutral lipid bilayers induced by simple salts.

PubMed

Manciu, Marian; Ruckenstein, Eli

2007-05-01

It was recently suggested that the swelling of neutral multilipid bilayers upon addition of a salt can be simply explained only by the electrolyte screening of the van der Waals attractions, while assuming that the hydration force and the repulsion due to thermal undulations of membranes are unaffected by the salt. While we agree that the screening of the van der Waals interactions plays a role, we suggest that the increase in the hydration force upon addition of a salt has also to be taken into account. In a statistical model, which accounts for the membrane undulations, parameters could be found to explain the multibilayer swelling even when the van der Waals attraction is considered unaffected by the electrolyte screening. These results point out that the decrease by a factor of three of the Hamaker constant upon addition of a salt, suggested recently to be responsible for the swelling of neutral multilipid bilayers, is perhaps too large, and a smaller decrease in Hamaker constant, coupled with the above mentioned effects might explain the swelling.

Combat Casualty Hand Burns: Evaluating Impairment and Disability during Recovery

DTIC Science & Technology

2008-06-01

impairment guidelines would correlate with disability as mea- sured by the DASH. However, a study by Mink van der Molen et al. found only a weak correlation (r...Mink van der Molen AB, Ettema AM, Hovius SER. Outcome of hand trauma: the hand injury severity scoring system (HISS) and subsequent impairment and...0.38) between AMA and DASH scores at six months after hand trauma.16 In another study, van Oosterom et al. reported no statistically significant

Control of excitons in multi-layer van der Waals heterostructures

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

Calman, E. V., E-mail: ecalman@gmail.com; Dorow, C. J.; Fogler, M. M.

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.

Combined Task and Physical Demands Analyses towards a Comprehensive Human Work Model

DTIC Science & Technology

2014-09-01

new equipment or modifying tasks and providing training (van der Molen, Sluiter, Hulshof , Vink, & Frings-Dresen, 2005). List the Job Duties (the...00 1/SV, Defence Research and Development Canada. van der Molen, H. F., Sluiter, J. K., Hulshof , C. T. J. , Vink, P., & Frings-Dresen, M. H. W

Optimal Item Pool Design for a Highly Constrained Computerized Adaptive Test

ERIC Educational Resources Information Center

He, Wei

2010-01-01

Item pool quality has been regarded as one important factor to help realize enhanced measurement quality for the computerized adaptive test (CAT) (e.g., Flaugher, 2000; Jensema, 1977; McBride & Wise, 1976; Reckase, 1976; 2003; van der Linden, Ariel, & Veldkamp, 2006; Veldkamp & van der Linden, 2000; Xing & Hambleton, 2004). However, studies are…

Inflationary universe in terms of a van der Waals viscous fluid

NASA Astrophysics Data System (ADS)

Brevik, I.; Elizalde, E.; Odintsov, S. D.; Timoshkin, A. V.

The inflationary expansion of our early-time universe is considered in terms of the van der Waals equation, as equation of state for the cosmic fluid, where a bulk viscosity contribution is assumed to be present. The corresponding gravitational equations for the energy density in a homogeneous and isotropic Friedmann-Lemaître-Robertson-Walker universe are solved, and an analytic expression for the scale factor is obtained. Attention is paid, specifically, to the role of the viscosity term in the accelerated expansion; the values of the slow-roll parameters, the spectral index, and the tensor-to-scalar ratio for the van der Waals model are calculated and compared with the most recent astronomical data from the Planck satellite. By imposing reasonable restrictions on the parameters of the van der Waals equation, in the presence of viscosity, it is shown to be possible for this model to comply quite precisely with the observational data. One can therefore conclude that the inclusion of viscosity in the theory of the inflationary epoch may definitely improve the cosmological models.

Supersonic minimum length nozzle design for dense gases

NASA Technical Reports Server (NTRS)

Aldo, Andrew C.; Argrow, Brian M.

1993-01-01

Recently, dense gases have been investigated for many engineering applications such as for turbomachinery and wind tunnels. Supersonic nozzle design for these gases is complicated by their nonclassical behavior in the transonic flow regime. In this paper a method of characteristics (MOC) is developed for two-dimensional (planar) and, primarily, axisymmetric flow of a van der Waals gas. Using a straight aortic line assumption, a centered expansion is used to generate an inviscid wall contour of minimum length. The van der Waals results are compared to previous perfect gas results to show the real gas effects on the flow properties and inviscid wall contours.

Nonadditivity of van der Waals forces on liquid surfaces

NASA Astrophysics Data System (ADS)

Venkataram, Prashanth S.; Whitton, Jeremy D.; Rodriguez, Alejandro W.

2016-09-01

We present an approach for modeling nanoscale wetting and dewetting of textured solid surfaces that exploits recently developed, sophisticated techniques for computing exact long-range dispersive van der Waals (vdW) or (more generally) Casimir forces in arbitrary geometries. We apply these techniques to solve the variational formulation of the Young-Laplace equation and predict the equilibrium shapes of liquid-vacuum interfaces near solid gratings. We show that commonly employed methods of computing vdW interactions based on additive Hamaker or Derjaguin approximations, which neglect important electromagnetic boundary effects, can result in large discrepancies in the shapes and behaviors of liquid surfaces compared to exact methods.

Dependence of Radar Backscatter on the Energetics of the Air-Sea Interface

DTIC Science & Technology

1990-07-01

14 3 Figure 41a. Shematic Spectrum of Wind Speed Near the Ground Estimated from a Study of Van der Hoven (1957...O.O0 Figure 41a. Schematic Spectrum of Wind Speed Near the Ground Estimated from a Study of Van der Hoven (1957) (from Lumley and Panofsky, 1964) The...resolved is 0.6 to 8.0s. Following Der (1976), the sensors are capacitance transduction devices which produce output voltage signals proportional to surface

Finite-Size Effects on the Behavior of the Susceptibility in van der Waals Films Bounded by Strongly Absorbing Substrates

NASA Technical Reports Server (NTRS)

Dantchev, Daniel; Rudnick, Joseph; Barmatz, M.

2007-01-01

We study critical point finite-size effects in the case of the susceptibility of a film in which interactions are characterized by a van der Waals-type power law tail. The geometry is appropriate to a slab-like system with two bounding surfaces. Boundary conditions are consistent with surfaces that both prefer the same phase in the low temperature, or broken symmetry, state. We take into account both interactions within the system and interactions between the constituents of the system and the material surrounding it. Specific predictions are made with respect to the behavior of 3He and 4He films in the vicinity of their respective liquid-vapor critical points.

Quantum Monte Carlo calculations of van der Waals interactions between aromatic benzene rings

NASA Astrophysics Data System (ADS)

Azadi, Sam; Kühne, T. D.

2018-05-01

The magnitude of finite-size effects and Coulomb interactions in quantum Monte Carlo simulations of van der Waals interactions between weakly bonded benzene molecules are investigated. To that extent, two trial wave functions of the Slater-Jastrow and Backflow-Slater-Jastrow types are employed to calculate the energy-volume equation of state. We assess the impact of the backflow coordinate transformation on the nonlocal correlation energy. We found that the effect of finite-size errors in quantum Monte Carlo calculations on energy differences is particularly large and may even be more important than the employed trial wave function. In addition to the cohesive energy, the singlet excitonic energy gap and the energy gap renormalization of crystalline benzene at different densities are computed.

Effective elastic properties of a van der Waals molecular monolayer at a metal surface

NASA Astrophysics Data System (ADS)

Sun, Dezheng; Kim, Dae-Ho; Le, Duy; Borck, Øyvind; Berland, Kristian; Kim, Kwangmoo; Lu, Wenhao; Zhu, Yeming; Luo, Miaomiao; Wyrick, Jonathan; Cheng, Zhihai; Einstein, T. L.; Rahman, Talat S.; Hyldgaard, Per; Bartels, Ludwig

2010-11-01

Adsorbing anthracene on a Cu(111) surface results in a wide range of complex and intriguing superstructures spanning a coverage range from 1 per 17 to 1 per 15 substrate atoms. In accompanying first-principles density-functional theory calculations we show the essential role of van der Waals interactions in estimating the variation in anthracene adsorption energy and height across the sample. We can thereby evaluate the compression of the anthracene film in terms of continuum elastic properties, which results in an effective Young’s modulus of 1.5 GPa and a Poisson ratio ≈0.1 . These values suggest interpretation of the molecular monolayer as a porous material—in marked congruence with our microscopic observations.

Dutch Minister of Science Visits ESO Facilities in Chile

NASA Astrophysics Data System (ADS)

2005-05-01

Mrs. Maria van der Hoeven, the Dutch Minister of Education, Culture and Science, who travelled to the Republic of Chile, arrived at the ESO Paranal Observatory on Friday afternoon, May 13, 2005. The Minister was accompanied, among others, by the Dutch Ambassador to Chile, Mr. Hinkinus Nijenhuis, and Mr. Cornelis van Bochove, the Dutch Director of Science. The distinguished visitors were able to acquaint themselves with one of the foremost European research facilities, the ESO Very Large Telescope (VLT), during an overnight stay at this remote site, and later, with the next major world facility in sub-millimetre and millimetre astronomy, the Atacama Large Millimeter Array (ALMA). At Paranal, the guests were welcomed by the ESO Director General, Dr. Catherine Cesarsky; the ESO Council President, Prof. Piet van der Kruit; the ESO Representative in Chile, Prof. Felix Mirabel; the Director of the La Silla Paranal Observatory, Dr. Jason Spyromilio; by one of the Dutch members of the ESO Council, Prof. Tim de Zeeuw; by the renowned astrophysicist from Leiden, Prof. Ewine van Dishoek, as well as by ESO staff members. The visitors were shown the various high-tech installations at the observatory, including many of the large, front-line VLT astronomical instruments that have been built in collaboration between ESO and European research institutes. Explanations were given by ESO astronomers and engineers and the Minister gained a good impression of the wide range of exciting research programmes that are carried out with the VLT. Having enjoyed the spectacular sunset over the Pacific Ocean from the Paranal deck, the Minister visited the VLT Control Room from where the four 8.2-m Unit Telescopes and the VLT Interferometer (VLTI) are operated. Here, the Minister was invited to follow an observing sequence at the console of the Kueyen (UT2) and Melipal (UT3) telescopes. "I was very impressed, not just by the technology and the science, but most of all by all the people involved," expressed Mrs. Maria van der Hoeven during her visit. "An almost unique level of international cooperation is achieved at ESO, and everything is done by those who can do it best, irrespective of their country or institution. This spirit of excellence is an example for all Europe, notably for the new European Research Council." Catherine Cesarsky, ESO Director General, remarked that Dutch astronomers have been part of ESO from the beginning: "The Dutch astronomy community and industry play a major role in various aspects of the Very Large Telescope, and more particularly in its interferometric mode. With their long-based expertise in radio astronomy, Dutch astronomers greatly contribute in this field, and are now also playing a major role in the construction of ALMA. It is thus a particularly great pleasure to receive Her Excellency, Mrs. Maria van der Hoeven." ESO PR Photo 16d/05 ESO PR Photo 16d/05 Dutch Minister Maria van der Hoeven at Chajnantor - I [Preview - JPEG: 400 x 480 pix - 207k] [Normal - JPEG: 800 x 959 pix - 617k] ESO PR Photo 16e/05 ESO PR Photo 16e/05 Dutch Minister Maria van der Hoeven at Chajnantor - II [Preview - JPEG: 400 x 605 pix - 179k] [Normal - JPEG: 800 x 1210 pix - 522k] Caption: ESO PR Photo 16d/05: In front of the APEX antenna at Chajnantor. From left to right: Prof. Piet van der Kruit, Mrs. Maria van der Hoeven, Prof. Tim de Zeeuw, and Prof. Ewine van Dishoeck. ESO PR Photo 16e/05 shows the Delegation on the 5000m high Llano de Chajnantor plateau. From left to right: Dr. Leo Le Duc, Prof. Felix Mirabel, Prof. Tim de Zeeuw, Prof. Ewine van Dishoeck, Dr. Cornelius van Bochove, Mrs. Maria van der Hoeven, Mr. Hans van der Vlies, Dr. Joerg Eschwey, Mr. Hinkinus Nijenhuis, Prof. Piet van der Kruit, Mr. Hans van den Broek, and Mr. Eduardo Donoso. The delegation spent the night at the Observatory before heading further North in the Chilean Andes to San Pedro de Atacama and from there to the Operation Support Facility of the future ALMA Observatory. On Sunday, May 15, the delegation went to the 5000m Llano de Chajnantor, the future site of the large array of 12m antennas that is being build there and should be completed by 2013. The Minister in particular could visit the 12m APEX (Atacama Pathfinder Experiment) telescope and see the technical infrastructure. "I am fully confident that the worldwide cooperation in ALMA will be equally successful as the VLT, and I am convinced that the discoveries to be made here are meaningful for the Earth we live in", said Mrs. van der Hoeven. "History and future are coming together in the north of Chile, in a very special way," she added. "In the region of the ancient Atacamenos, scientists from all over the world are discovering more and more about the universe and the birth and death of stars. They even find new planets. They do that on Paranal with the VLT and soon will be doing that on the ALMA site." The Minister and her delegation left for Santiago in the afternoon.

The Forced van der Pol Equation

ERIC Educational Resources Information Center

Fay, Temple H.

2009-01-01

We report on a study of the forced van der Pol equation x + [epsilon](x[superscript 2] - 1)x + x = F cos[omega]t, by solving numerically the differential equation for a variety of values of the parameters [epsilon], F and [omega]. In doing so, many striking and interesting trajectories can be discovered and phenomena such as frequency entrainment,…

A New Statistic for Detection of Aberrant Answer Changes

ERIC Educational Resources Information Center

Sinharay, Sandip; Duong, Minh Q.; Wood, Scott W.

2017-01-01

As noted by Fremer and Olson, analysis of answer changes is often used to investigate testing irregularities because the analysis is readily performed and has proven its value in practice. Researchers such as Belov, Sinharay and Johnson, van der Linden and Jeon, van der Linden and Lewis, and Wollack, Cohen, and Eckerly have suggested several…

Heterogeneous nucleation of polymorphs on polymer surfaces: polymer-molecule interactions using a Coulomb and van der Waals model.

PubMed

Wahlberg, Nanna; Madsen, Anders Ø; Mikkelsen, Kurt V

2018-06-09

The nucleation processes of acetaminophen on poly(methyl methacrylate) and poly(vinyl acetate) have been investigated and the mechanisms of the processes are studied. This is achieved by a combination of theoretical models and computational investigations within the framework of a modified QM/MM method; a Coulomb-van der Waals model. We have combined quantum mechanical computations and electrostatic models at the atomistic level for investigating the stability of different orientations of acetaminophen on the polymer surfaces. Based on the Coulomb-van der Waals model, we have determined the most stable orientation to be a flat orientation, and the strongest interaction is seen between poly(vinyl acetate) and the molecule in a flat orientation in vacuum.

Application of mixed-mode, solid-phase extraction in environmental and clinical chemistry. Combining hydrogen-bonding, cation-exchange and Van der Waals interactions

USGS Publications Warehouse

Mills, M.S.; Thurman, E.M.; Pedersen, M.J.

1993-01-01

Silica- and styrene-divinylbenzene-based mixed-mode resins that contain C8, C18 and sulphonated cation-exchange groups were compared for their efficiency in isolation of neutral triazine compounds from water and of the basic drug, benzoylecgonine, from urine. The triazine compounds were isolated by a combination of Van der Waals and hydrogen-bonding interactions, and benzoylecgonine was isolated by Van der Waals interactions and cation exchange. All analytes were eluted with a polar organic solvent contaning 2% ammonium hydroxide. Larger recoveries (95%) were achieved on copolymerized mixed-mode resins where C18 and sulfonic acid are in closer proximity than on 'blended' mixed-mode resins (60-70% recovery).

Atomic layer MoS2-graphene van der Waals heterostructure nanomechanical resonators.

PubMed

Ye, Fan; Lee, Jaesung; Feng, Philip X-L

2017-11-30

Heterostructures play significant roles in modern semiconductor devices and micro/nanosystems in a plethora of applications in electronics, optoelectronics, and transducers. While state-of-the-art heterostructures often involve stacks of crystalline epi-layers each down to a few nanometers thick, the intriguing limit would be hetero-atomic-layer structures. Here we report the first experimental demonstration of freestanding van der Waals heterostructures and their functional nanomechanical devices. By stacking single-layer (1L) MoS 2 on top of suspended single-, bi-, tri- and four-layer (1L to 4L) graphene sheets, we realize an array of MoS 2 -graphene heterostructures with varying thickness and size. These heterostructures all exhibit robust nanomechanical resonances in the very high frequency (VHF) band (up to ∼100 MHz). We observe that fundamental-mode resonance frequencies of the heterostructure devices fall between the values of graphene and MoS 2 devices. Quality (Q) factors of heterostructure resonators are lower than those of graphene but comparable to those of MoS 2 devices, suggesting interface damping related to interlayer interactions in the van der Waals heterostructures. This study validates suspended atomic layer heterostructures as an effective device platform and provides opportunities for exploiting mechanically coupled effects and interlayer interactions in such devices.

Interaction-component analysis of the effects of urea and its alkylated derivatives on the structure of T4-lysozyme

NASA Astrophysics Data System (ADS)

Yamamori, Yu; Matubayasi, Nobuyuki

2017-06-01

The effects of urea and its alkylated derivatives on the structure of T4-lysozyme were analyzed from the standpoint of energetics. Molecular dynamics simulations were conducted with explicit solvent, and the energy-representation method was employed to compute the free energy of transfer of the protein from pure-water solvent to the mixed solvents of water with urea, methylurea, 1,1-dimethylurea, and isopropylurea. Through the decomposition of the transfer free energy into the cosolvent and water contributions, it was observed that the former is partially cancelled by the latter and governs the total free energy of transfer. To determine the interaction component responsible for the transfer energetics, the correlations of the transfer free energy were also examined against the change in the solute-solvent interaction energy upon transfer and the corresponding changes in the electrostatic, van der Waals, and excluded-volume components. It was then found over the set of protein structures ranging from native to (partially) unfolded ones that the transfer free energy changes in parallel with the van der Waals component even when the cosolvent is alkylated. The electrostatic and excluded-volume components play minor roles in the structure modification of the protein, and the denaturing ability of alkylurea is brought by the van der Waals interaction.

Effects of van der Waals interaction and electric field on the electronic structure of bilayer MoS2.

PubMed

Xiao, Jin; Long, Mengqiu; Li, Xinmei; Zhang, Qingtian; Xu, Hui; Chan, K S

2014-10-08

The modification of the electronic structure of bilayer MoS2 by an external electric field can have potential applications in optoelectronics and valleytronics. Nevertheless, the underlying physical mechanism is not clearly understood, especially the effects of the van der Waals interaction. In this study, the spin orbit-coupled electronic structure of bilayer MoS2 has been investigated using the first-principle density functional theory. We find that the van der Waals interaction as well as the interlayer distance has significant effects on the band structure. When the interlayer distance of bilayer MoS2 increases from 0.614 nm to 0.71 nm, the indirect gap between the Γ and Λ points increases from 1.25 eV to 1.70 eV. Meanwhile, the energy gap of bilayer MoS2 transforms from an indirect one to a direct one. An external electric field can shift down (up) the energy bands of the bottom (top) MoS2 layer and also breaks the inversion symmetry of bilayer MoS2. As a result, the electric field can affect the band gaps, the spin-orbit interaction and splits the valance bands into two groups. The present study can help us understand more about the electronic structures of MoS2 materials for potential applications in electronics and optoelectronics.

Correlated insulator behaviour at half-filling in magic-angle graphene superlattices

NASA Astrophysics Data System (ADS)

Cao, Yuan; Fatemi, Valla; Demir, Ahmet; Fang, Shiang; Tomarken, Spencer L.; Luo, Jason Y.; Sanchez-Yamagishi, Javier D.; Watanabe, Kenji; Taniguchi, Takashi; Kaxiras, Efthimios; Ashoori, Ray C.; Jarillo-Herrero, Pablo

2018-04-01

A van der Waals heterostructure is a type of metamaterial that consists of vertically stacked two-dimensional building blocks held together by the van der Waals forces between the layers. This design means that the properties of van der Waals heterostructures can be engineered precisely, even more so than those of two-dimensional materials. One such property is the ‘twist’ angle between different layers in the heterostructure. This angle has a crucial role in the electronic properties of van der Waals heterostructures, but does not have a direct analogue in other types of heterostructure, such as semiconductors grown using molecular beam epitaxy. For small twist angles, the moiré pattern that is produced by the lattice misorientation between the two-dimensional layers creates long-range modulation of the stacking order. So far, studies of the effects of the twist angle in van der Waals heterostructures have concentrated mostly on heterostructures consisting of monolayer graphene on top of hexagonal boron nitride, which exhibit relatively weak interlayer interaction owing to the large bandgap in hexagonal boron nitride. Here we study a heterostructure consisting of bilayer graphene, in which the two graphene layers are twisted relative to each other by a certain angle. We show experimentally that, as predicted theoretically, when this angle is close to the ‘magic’ angle the electronic band structure near zero Fermi energy becomes flat, owing to strong interlayer coupling. These flat bands exhibit insulating states at half-filling, which are not expected in the absence of correlations between electrons. We show that these correlated states at half-filling are consistent with Mott-like insulator states, which can arise from electrons being localized in the superlattice that is induced by the moiré pattern. These properties of magic-angle-twisted bilayer graphene heterostructures suggest that these materials could be used to study other exotic many-body quantum phases in two dimensions in the absence of a magnetic field. The accessibility of the flat bands through electrical tunability and the bandwidth tunability through the twist angle could pave the way towards more exotic correlated systems, such as unconventional superconductors and quantum spin liquids.

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

PubMed

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.

Minimum Weight Design of Cylindrical Shell with Multiple Stiffener Sizes Under Buckling Constraint

DTIC Science & Technology

1977-10-01

i.i.iiJ.i |..l.l.ll|l,«p»l|HII.I|lllB.I. SECTION I INTRODUCTION Since van der Neut (Reference 1) demonstrated the influtnce of eccentricity of...o:neral conclusions. ■■’ ■ ■■■—^-’—--^ ■ „J..,.....^ .... .a. a,-^,.,.,.. —..-.., mmmmmmmmm**** "■ REFERENCES 1. Van der Neut , A., "The General...Kicher, T. P., "Structural Synthesis of Integrally Stiffened Cylin- ders ", Journal of Spacecraft and Rockets, Vol. 5, Jan. 1968, pp. 62-67. Schmit

The effect of the London-van der Waals dispersion force on interline heat transfer

NASA Technical Reports Server (NTRS)

Wayner, P. C., Jr.

1978-01-01

A theoretical procedure to determine the heat transfer characteristics of the interline region (junction of liquid-solid-vapor) from the macroscopic optical and thermophysical properties of the system is outlined. The analysis is based on the premise that the interline transport processes are controlled by the London-van der Waals dispersion force between condensed phases (solid and liquid). Numerical values of the dispersion constant are presented. The procedure is used to compare the relative size of the interline heat sink of various systems using a constant heat flux mode. This solution demonstrates the importance of the interline heat flow number, which is evaluated for various systems.

Enhanced van der Waals epitaxy via electron transfer enabled interfacial dative bond formation

DOE PAGES

Xie, Weiyu; Lu, Toh -Ming; Wang, Gwo -Ching; ...

2017-11-14

Enhanced van der Waals (vdW) epitaxy of semiconductors on a layered vdW substrate is identified as the formation of dative bonds. For example, despite that NbSe 2 is a vdW layeredmaterial, first-principles calculations reveal that the bond strength at a CdTe-NbSe 2 interface is five times as large as that of vdW interactions at a CdTe-graphene interface. Finally, the unconventional chemistry here is enabled by an effective net electron transfer from Cd dangling-bond states at a CdTe surface to metallic nonbonding NbSe 2 states, which is a necessary condition to activate the Cd for enhanced binding with Se.

On the crystallization of polymer composites with inorganic fullerene-like particles.

PubMed

Enyashin, Andrey N; Glazyrina, Polina Yu

2012-05-21

The effect of a sulfide fullerene-like particle embedded into a polymer has been studied by molecular dynamics simulations on the nanosecond time scale using a mesoscopic Van der Waals force field evaluated for the case of a spherical particle. Even in this approach, neglecting the atomistic features of the surface, the inorganic particle acts as a nucleation agent facilitating the crystallization of the polymeric sample. A consideration of the Van der Waals force field of multi-walled sulfide nanoparticles suggests that in the absence of chemical interactions the size of the nanoparticle is dominating for the adhesion strength, while the number of sulfide layers composing the cage does not play a role.

Enhanced van der Waals epitaxy via electron transfer enabled interfacial dative bond formation

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

Xie, Weiyu; Lu, Toh -Ming; Wang, Gwo -Ching

Enhanced van der Waals (vdW) epitaxy of semiconductors on a layered vdW substrate is identified as the formation of dative bonds. For example, despite that NbSe 2 is a vdW layeredmaterial, first-principles calculations reveal that the bond strength at a CdTe-NbSe 2 interface is five times as large as that of vdW interactions at a CdTe-graphene interface. Finally, the unconventional chemistry here is enabled by an effective net electron transfer from Cd dangling-bond states at a CdTe surface to metallic nonbonding NbSe 2 states, which is a necessary condition to activate the Cd for enhanced binding with Se.

Structural Equation Model Approach to the Use of Response Times for Improving Estimation in Item Response Models

ERIC Educational Resources Information Center

Sen, Rohini

2012-01-01

In the last five decades, research on the uses of response time has extended into the field of psychometrics (Schnikpe & Scrams, 1999; van der Linden, 2006; van der Linden, 2007), where interest has centered around the usefulness of response time information in item calibration and person measurement within an item response theory. framework.…

Geometrothermodynamics of Van der Waals black hole

NASA Astrophysics Data System (ADS)

Hu, Yumin; Chen, Juhua; Wang, Yongjiu

2017-12-01

We study the geometrothermodynamics of a special asymptotically AdS black hole, i.e. Van der Waals ( VdW) black hole, in the extended phase space where the negative cosmological constant Λ can be regarded as thermodynamic pressure. Analysing some special conditions of this black hole with geometrothermodynamical method, we find a good correlation with ordinary cases according to the state equation.

The first record of Pyxidium tardigradum Van der Land, 1964 (Ciliophora) in Romania.

PubMed

Ciobanu, Daniel Adrian; Roszkowska, Milena; Moglan, Ioan; Kaczmarek, Łukasz

2015-04-02

In three lichen samples collected from eastern part of Romania, three populations of Ramazzottius cf. oberhaeuseri (Doyère, 1840) infested by Pyxidium tardigradum Van der Land 1964 were found. In this short correspondence we present a first record of P. tardigradum in Romania and infestation rates in studied populations according to the different life stages.

Theoretical Foundation of Zisman's Empirical Equation for Wetting of Liquids on Solid Surfaces

ERIC Educational Resources Information Center

Zhu, Ruzeng; Cui, Shuwen; Wang, Xiaosong

2010-01-01

Theories of wetting of liquids on solid surfaces under the condition that van der Waals force is dominant are briefly reviewed. We show theoretically that Zisman's empirical equation for wetting of liquids on solid surfaces is a linear approximation of the Young-van der Waals equation in the wetting region, and we express the two parameters in…

Publisher Correction: Discordant congenital Zika syndrome twins show differential in vitro viral susceptibility of neural progenitor cells.

PubMed

Caires-Júnior, Luiz Carlos; Goulart, Ernesto; Melo, Uirá Souto; Araujo, Bruno Henrique Silva; Alvizi, Lucas; Soares-Schanoski, Alessandra; de Oliveira, Danyllo Felipe; Kobayashi, Gerson Shigeru; Griesi-Oliveira, Karina; Musso, Camila Manso; Amaral, Murilo Sena; daSilva, Lucas Ferreira; Astray, Renato Mancini; Suárez-Patiño, Sandra Fernanda; Ventini, Daniella Cristina; da Silva, Sérgio Gomes; Yamamoto, Guilherme Lopes; Ezquina, Suzana; Naslavsky, Michel Satya; Telles-Silva, Kayque Alves; Weinmann, Karina; van der Linden, Vanessa; van der Linden, Helio; de Oliveira, João Ricardo Mendes; Arrais, Nivia Maria Rodrigues; Melo, Adriana; Figueiredo, Thalita; Santos, Silvana; Meira, Joanna Goes Castro; Passos, Saulo Duarte; de Almeida, Roque Pacheco; Bispo, Ana Jovina Barreto; Cavalheiro, Esper Abrão; Kalil, Jorge; Cunha-Neto, Edécio; Nakaya, Helder; Andreata-Santos, Robert; de Souza Ferreira, Luis Carlos; Verjovski-Almeida, Sergio; Ho, Paulo Lee; Passos-Bueno, Maria Rita; Zatz, Mayana

2018-03-13

The original PDF version of this Article contained errors in the spelling of Luiz Carlos Caires-Júnior, Uirá Souto Melo, Bruno Henrique Silva Araujo, Alessandra Soares-Schanoski, Murilo Sena Amaral, Kayque Alves Telles-Silva, Vanessa van der Linden, Helio van der Linden, João Ricardo Mendes de Oliveira, Nivia Maria Rodrigues Arrais, Joanna Goes Castro Meira, Ana Jovina Barreto Bispo, Esper Abrão Cavalheiro, and Robert Andreata-Santos, which were incorrectly given as Luiz Carlos de Caires Jr., UiráSouto Melo, Bruno Silva Henrique Araujo, Alessandra Soares Schanoski, MuriloSena Amaral, Kayque Telles Alves Silva, Vanessa Van der Linden, Helio Van der Linden, João Mendes Ricardo de Oliveira, Nivia Rodrigues Maria Arrais, Joanna Castro Goes Meira, Ana JovinaBarreto Bispo, EsperAbrão Cavalheiro, and Robert Andreata Santos. Furthermore, in both the PDF and HTML versions of the Article, the top panel of Fig. 3e was incorrectly labeled '10608-1' and should have been '10608-4', and financial support from CAPES and DECIT-MS was inadvertently omitted from the Acknowledgements section. These errors have now been corrected in both the PDF and HTML versions of the Article.

Thermodynamics of higher dimensional black holes with higher order thermal fluctuations

NASA Astrophysics Data System (ADS)

Pourhassan, B.; Kokabi, K.; Rangyan, S.

2017-12-01

In this paper, we consider higher order corrections of the entropy, which coming from thermal fluctuations, and find their effect on the thermodynamics of higher dimensional charged black holes. Leading order thermal fluctuation is logarithmic term in the entropy while higher order correction is proportional to the inverse of original entropy. We calculate some thermodynamics quantities and obtain the effect of logarithmic and higher order corrections of entropy on them. Validity of the first law of thermodynamics investigated and Van der Waals equation of state of dual picture studied. We find that five-dimensional black hole behaves as Van der Waals, but higher dimensional case have not such behavior. We find that thermal fluctuations are important in stability of black hole hence affect unstable/stable black hole phase transition.

Enhanced photocatalytic hydrogen evolution from in situ formation of few-layered MoS2/CdS nanosheet-based van der Waals heterostructures.

PubMed

Iqbal, Shahid; Pan, Ziwei; Zhou, Kebin

2017-05-25

Here we report for the first time that the H 2 bubbles generated by photocatalytic water splitting are effective in the layer-by-layer exfoliation of MoS 2 nanocrystals (NCs) into few layers. The as-obtained few layers can be in situ assembled with CdS nanosheets (NSs) into van der Waals heterostructures (vdWHs) of few-layered MoS 2 /CdS NSs which, in turn, are effective in charge separation and transfer, leading to enhanced photocatalytic H 2 production activity. The few-layered MoS 2 /CdS vdWHs exhibited a H 2 evolution rate of 140 mmol g (CdS) -1 h -1 and achieved an apparent quantum yield of 66% at 420 nm.

Probing the Interlayer Exciton Physics in a MoS2/MoSe2/MoS2 van der Waals Heterostructure.

PubMed

Baranowski, M; Surrente, A; Klopotowski, L; Urban, J M; Zhang, N; Maude, D K; Wiwatowski, K; Mackowski, S; Kung, Y C; Dumcenco, D; Kis, A; Plochocka, P

2017-10-11

Stacking atomic monolayers of semiconducting transition metal dichalcogenides (TMDs) has emerged as an effective way to engineer their properties. In principle, the staggered band alignment of TMD heterostructures should result in the formation of interlayer excitons with long lifetimes and robust valley polarization. However, these features have been observed simultaneously only in MoSe 2 /WSe 2 heterostructures. Here we report on the observation of long-lived interlayer exciton emission in a MoS 2 /MoSe 2 /MoS 2 trilayer van der Waals heterostructure. The interlayer nature of the observed transition is confirmed by photoluminescence spectroscopy, as well as by analyzing the temporal, excitation power, and temperature dependence of the interlayer emission peak. The observed complex photoluminescence dynamics suggests the presence of quasi-degenerate momentum-direct and momentum-indirect bandgaps. We show that circularly polarized optical pumping results in long-lived valley polarization of interlayer exciton. Intriguingly, the interlayer exciton photoluminescence has helicity opposite to the excitation. Our results show that through a careful choice of the TMDs forming the van der Waals heterostructure it is possible to control the circular polarization of the interlayer exciton emission.

Adsorption of thiophene on transition metal surfaces with the inclusion of van der Waals effects

NASA Astrophysics Data System (ADS)

Malone, Walter; Matos, Jeronimo; Kara, Abdelkader

2018-03-01

We use density functional theory with the inclusion of the van der Waals interaction to study the adsorption of thiophene, C4H4S, on Pt, Rh, Pd, Au, and Ag (100) surfaces. The five van der Waals (vdW) inclusive functionals we employ are optB86b-vdW, optB88-vdW, optPBE-vdW, revPBE-vdW, and rPW86-vdW2. For comparison we also run calculations with the GGA- Perdew Burke and Ernzerhof (PBE) functional. We examine several adsorption sites with the plane of the molecule parallel or perpendicular to the surface. The most stable configuration on all metals was the site where the center of the thiophene lies over a 4-fold hollow site with the sulfur atom lying close to a top site. Furthermore, we examine several electronic and geometric properties of the adsorbate including charge transfer, modification of the d-band, adsorption energy, tilt angle, and adsorption height. For the coinage metals PBE gives the lowest adsorption energy. For reactive transition metal substrates, revPBE-vdW and rPW86-vdW2 give lower adsorption energies than PBE.

van der Waals forces in density functional theory: a review of the vdW-DF method.

PubMed

Berland, Kristian; Cooper, Valentino R; Lee, Kyuho; Schröder, Elsebeth; Thonhauser, T; Hyldgaard, Per; Lundqvist, Bengt I

2015-06-01

A density functional theory (DFT) that accounts for van der Waals (vdW) interactions in condensed matter, materials physics, chemistry, and biology is reviewed. The insights that led to the construction of the Rutgers-Chalmers van der Waals density functional (vdW-DF) are presented with the aim of giving a historical perspective, while also emphasizing more recent efforts which have sought to improve its accuracy. In addition to technical details, we discuss a range of recent applications that illustrate the necessity of including dispersion interactions in DFT. This review highlights the value of the vdW-DF method as a general-purpose method, not only for dispersion bound systems, but also in densely packed systems where these types of interactions are traditionally thought to be negligible.

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

PubMed

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

2014-03-07

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

The Average IQ of Sub-Saharan Africans: Comments on Wicherts, Dolan, and van der Maas

ERIC Educational Resources Information Center

Lynn, Richard; Meisenberg, Gerhard

2010-01-01

Wicherts, Dolan, and van der Maas (2009) contend that the average IQ of sub-Saharan Africans is about 80. A critical evaluation of the studies presented by WDM shows that many of these are based on unrepresentative elite samples. We show that studies of 29 acceptably representative samples on tests other than the Progressive Matrices give a…

Economic Aspects of a Therapy and Support Service for People with Long-Term Stroke and Aphasia

ERIC Educational Resources Information Center

van der Gaag, Anna; Brooks, Richard

2008-01-01

Background: This paper considers some economic aspects of a therapy and support service for people with stroke and aphasia. This material was part of a broader evaluation of the service, which is reported elsewhere (van der Gaag et al. 2005, van der Gaag and Mowles 2005). Aims: The purpose of this part of the study was to investigate the…

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

ERIC Educational Resources Information Center

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…

Adhesion mechanisms on solar glass: Effects of relative humidity, surface roughness, and particle shape and size

DOE PAGES

Moutinho, Helio R.; Jiang, Cun -Sheng; To, Bobby; ...

2017-07-27

To better understand and quantify soiling rates on solar panels, we are investigating the adhesion mechanisms between dust particles and solar glass. In this work, we report on two of the fundamental adhesion mechanisms: van der Waals and capillary adhesion forces. The adhesion was determined using force versus distance (F-z) measurements performed with an atomic force microscope (AFM). To emulate dust interacting with the front surface of a solar panel, we measured how oxidized AFM tips, SiO 2 glass spheres, and real dust particles adhered to actual solar glass. The van der Waals forces were evaluated by measurements performed withmore » zero relative humidity in a glove box, and the capillary forces were measured in a stable environment created inside the AFM enclosure with relative humidity values ranging from 18% to 80%. To simulate topographic features of the solar panels caused by factors such as cleaning and abrasion, we induced different degrees of surface roughness in the solar glass. As a result, we were able to 1) identify and quantify both the van der Waals and capillary forces, 2) establish the effects of surface roughness, relative humidity, and particle size on the adhesion mechanisms, and 3) compare adhesion forces between well-controlled particles (AFM tips and glass spheres) and real dust particles.« less

Generalization of the van der Pauw Method: Analyzing Longitudinal Magnetoresistance Asymmetry to Quantify Doping Gradients

NASA Astrophysics Data System (ADS)

Grayson, M.; Zhou, Wang; Yoo, Heun-Mo; Prabhu-Gaunkar, S.; Tiemann, L.; Reichl, C.; Wegscheider, W.

A longitudinal magnetoresistance asymmetry (LMA) between a positive and negative magnetic field is known to occur in both the extreme quantum limit and the classical Drude limit in samples with a nonuniform doping density. By analyzing the current stream function in van der Pauw measurement geometry, it is shown that the electron density gradient can be quantitatively deduced from this LMA in the Drude regime. Results agree with gradients interpolated from local densities calibrated across an entire wafer, establishing a generalization of the van der Pauw method to quantify density gradients. Results will be shown of various semoconductor systems where this method is applied, from bulk doped semiconductors, to exfoliated 2D materials. McCormick Catalyst Award from Northwestern University, EECS Bridge Funding, and AFOSR FA9550-15-1-0247.

van der Waals forces in density functional theory: a review of the vdW-DF method

DOE PAGES

Berland, Kristian; Cooper, Valentino R.; Lee, Kyuho; ...

2015-05-15

We review a density functional theory (DFT) that accounts for van der Waals (vdW) interactions in condensed matter, materials physics, chemistry, and biology. The insights that led to the construction of the Rutgers–Chalmers van der Waals density functional (vdW-DF) are presented with the aim of giving a historical perspective, while also emphasizing more recent efforts which have sought to improve its accuracy. In addition to technical details, we discuss a range of recent applications that illustrate the necessity of including dispersion interactions in DFT. This review highlights the value of the vdW-DF method as a general-purpose method, not only formore » dispersion bound systems, but also in densely packed systems where these types of interactions are traditionally thought to be negligible.« less

Van der Waals model for phase transitions in thermoresponsive surface films.

PubMed

McCoy, John D; Curro, John G

2009-05-21

Phase transitions in polymeric surface films are studied with a simple model based on the van der Waals equation of state. Each chain is modeled by a single bead attached to the surface by an entropic-Hooke's law spring. The surface coverage is controlled by adjusting the chemical potential, and the equilibrium density profile is calculated with density functional theory. The interesting feature of this model is the multivalued nature of the density profile seen at low temperature. This van der Waals loop behavior is resolved with a Maxwell construction between a high-density phase near the wall and a low-density phase in a "vertical" phase transition. Signatures of the phase transition in experimentally measurable quantities are then found. Numerical calculations are presented for isotherms of surface pressure, for the Poisson ratio, and for the swelling ratio.

Effect of van der Waals interactions on the stability of SiC polytypes

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

Kawanishi, Sakiko, E-mail: s-kawa@tagen.tohoku.ac.jp; Mizoguchi, Teruyasu

2016-05-07

Density functional theory calculations with a correction of the long-range dispersion force, namely, the van der Waals (vdW) force, are performed for SiC polytypes. The lattice parameters are in good agreement with those obtained from the experiments. Furthermore, the stability of the polytypes in the experiments, which show 3C-SiC as the most stable, is reproduced by the present calculations. The effects of the vdW force on the electronic structure and the stability of polytypes are discussed. We observe that the vdW interaction is more sensitive to the cubic site than the hexagonal site. Thus, the influence of the vdW forcemore » increases with decreasing the hexagonality of the polytype, which results in the confirmation that the most stable polytype is 3C-SiC.« less

van der Waals heterostructures of germanene, stanene, and silicene with hexagonal boron nitride and their topological domain walls

NASA Astrophysics Data System (ADS)

Wang, Maoyuan; Liu, Liping; Liu, Cheng-Cheng; Yao, Yugui

2016-04-01

We investigate van der Waals (vdW) heterostructures made of germanene, stanene, or silicene with hexagonal boron nitride (h-BN). The intriguing topological properties of these buckled honeycomb materials can be maintained and further engineered in the heterostructures, where the competition between the substrate effect and external electric fields can be used to control the tunable topological phase transitions. Using such heterostructures as building blocks, various vdW topological domain walls (DW) are designed, along which there exist valley polarized quantum spin Hall edge states or valley-contrasting edge states which are protected by valley(spin)- resolved topological charges and can be tailored by the patterning of the heterojunctions and by external fields.

The Average IQ of Sub-Saharan Africans Assessed by the Progressive Matrices: A Reply to Wicherts, Dolan, Carlson & van der Maas

ERIC Educational Resources Information Center

Lynn, Richard

2010-01-01

Wicherts, Dolan, Carlson & van der Maas (WDCM) (2010) contend that the average IQ in sub-Saharan Africa is about 76 in relation to a British mean of 100 and sd of 15. This result is achieved by including many studies of unrepresentative elite samples. Studies of acceptably representative samples indicate a sub-Saharan Africa IQ of…

Thin Film Evaporation Model with Retarded Van Der Waals Interaction (Postprint)

DTIC Science & Technology

2013-11-01

Waals interaction. The retarded van der Waals interaction is derived from Hamaker theory, the summation of retarded pair potentials for all molecules...interaction is derived from Hamaker theory, the summation of retarded pair potentials for all molecules for a given geometry. When combined, the governing...interaction force is the negative derivative with respect to distance of the interaction energy. The method due to Hamaker essentially sums all pair

Self-Aligned van der Waals Heterojunction Diodes and Transistors.

PubMed

Sangwan, Vinod K; Beck, Megan E; Henning, Alex; Luo, Jiajia; Bergeron, Hadallia; Kang, Junmo; Balla, Itamar; Inbar, Hadass; Lauhon, Lincoln J; Hersam, Mark C

2018-02-14

A general self-aligned fabrication scheme is reported here for a diverse class of electronic devices based on van der Waals materials and heterojunctions. In particular, self-alignment enables the fabrication of source-gated transistors in monolayer MoS 2 with near-ideal current saturation characteristics and channel lengths down to 135 nm. Furthermore, self-alignment of van der Waals p-n heterojunction diodes achieves complete electrostatic control of both the p-type and n-type constituent semiconductors in a dual-gated geometry, resulting in gate-tunable mean and variance of antiambipolar Gaussian characteristics. Through finite-element device simulations, the operating principles of source-gated transistors and dual-gated antiambipolar devices are elucidated, thus providing design rules for additional devices that employ self-aligned geometries. For example, the versatility of this scheme is demonstrated via contact-doped MoS 2 homojunction diodes and mixed-dimensional heterojunctions based on organic semiconductors. The scalability of this approach is also shown by fabricating self-aligned short-channel transistors with subdiffraction channel lengths in the range of 150-800 nm using photolithography on large-area MoS 2 films grown by chemical vapor deposition. Overall, this self-aligned fabrication method represents an important step toward the scalable integration of van der Waals heterojunction devices into more sophisticated circuits and systems.

Graded Interface Models for more accurate Determination of van der Waals-London Dispersion Interactions across Grain Boundaries

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

van Benthem, Klaus; Tan, Guolong; French, Roger H

2006-01-01

Attractive van der Waals V London dispersion interactions between two half crystals arise from local physical property gradients within the interface layer separating the crystals. Hamaker coefficients and London dispersion energies were quantitatively determined for 5 and near- 13 grain boundaries in SrTiO3 by analysis of spatially resolved valence electron energy-loss spectroscopy (VEELS) data. From the experimental data, local complex dielectric functions were determined, from which optical properties can be locally analysed. Both local electronic structures and optical properties revealed gradients within the grain boundary cores of both investigated interfaces. The obtained results show that even in the presence ofmore » atomically structured grain boundary cores with widths of less than 1 nm, optical properties have to be represented with gradual changes across the grain boundary structures to quantitatively reproduce accurate van der Waals V London dispersion interactions. London dispersion energies of the order of 10% of the apparent interface energies of SrTiO3 were observed, demonstrating their significance in the grain boundary formation process. The application of different models to represent optical property gradients shows that long-range van der Waals V London dispersion interactions scale significantly with local, i.e atomic length scale property variations.« less

van der Waals torque and force between dielectrically anisotropic layered media.

PubMed

Lu, Bing-Sui; Podgornik, Rudolf

2016-07-28

We analyse van der Waals interactions between a pair of dielectrically anisotropic plane-layered media interacting across a dielectrically isotropic solvent medium. We develop a general formalism based on transfer matrices to investigate the van der Waals torque and force in the limit of weak birefringence and dielectric matching between the ordinary axes of the anisotropic layers and the solvent. We apply this formalism to study the following systems: (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 optic axes lie parallel and/or perpendicular to the plane of the layers. For the first case, the optic axes of the oppositely facing anisotropic layers of the two interacting slabs generally possess an angular mismatch, and within each multilayered slab the optic 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 thicknesses, the relative angular increment within each slab, and the angular mismatch between the slabs.

Fast Determination of the Element Excitation of an Active Phased Array Antenna

DTIC Science & Technology

1991-03-01

elementenexcitatie te, bepalen: de amplitude en fase van het elektrische ven-e veld moeten gemeten warden in slechts I richting in het verre veld van de ...Page 3 rapport no FEL-91-BO38 titel Een snelle bepaling van de excitatie van de elenienten van cen actieve phased array antenne auteur(s) I. J.G. van...van der Spek Onderzoek uItgevoerd door Ir. J.G. van Hezewijk SAMENVATIING (ONGERUBRICEERD) Het verre veld stralingsdiagram van een actieve phased array

Van der Waals heterojunction diode composed of WS2 flake placed on p-type Si substrate

NASA Astrophysics Data System (ADS)

Aftab, Sikandar; Farooq Khan, M.; Min, Kyung-Ah; Nazir, Ghazanfar; Afzal, Amir Muhammad; Dastgeer, Ghulam; Akhtar, Imtisal; Seo, Yongho; Hong, Suklyun; Eom, Jonghwa

2018-01-01

P-N junctions represent the fundamental building blocks of most semiconductors for optoelectronic functions. This work demonstrates a technique for forming a WS2/Si van der Waals junction based on mechanical exfoliation. Multilayered WS2 nanoflakes were exfoliated on the surface of bulk p-type Si substrates using a polydimethylsiloxane stamp. We found that the fabricated WS2/Si p-n junctions exhibited rectifying characteristics. We studied the effect of annealing processes on the performance of the WS2/Si van der Waals p-n junction and demonstrated that annealing improved its electrical characteristics. However, devices with vacuum annealing have an enhanced forward-bias current compared to those annealed in a gaseous environment. We also studied the top-gate-tunable rectification characteristics across the p-n junction interface in experiments as well as density functional theory calculations. Under various temperatures, Zener breakdown occurred at low reverse-bias voltages, and its breakdown voltage exhibited a negative coefficient of temperature. Another breakdown voltage was observed, which increased with temperature, suggesting a positive coefficient of temperature. Therefore, such a breakdown can be assigned to avalanche breakdown. This work demonstrates a promising application of two-dimensional materials placed directly on conventional bulk Si substrates.

Thermal electron attachment to van der Waals molecules containing O/sub 2/

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

Huo, W.M.; Fessenden, R.W.; Bauschlicher C.W. Jr.

1984-12-15

Calculations on O/sub 2/xN/sub 2/ and O/sup -//sub 2/xN/sub 2/ have been carried out to explain the large enhancement in the attachment rate of thermal electrons found in van der Waals molecules containing O/sub 2/. Two geometries, T-shape and linear, are used. SCF wave functions are used to represent both the neutral molecule and the ion. The incoming electron is approximated by a plane wave. The width is determined using a shielded polarization potential. The effect of additional vibrational structures of the van der Waals molecule on the attachment process is investigated by studying the O/sub 2/--N/sub 2/ stretching modemore » using Lennard-Jones potentials. Symmetry breaking, which allows the molecule to attach a p wave electron, is shown to play a primary role. The lowering of resonance energy, due to a deeper Lennard-Jones potential of O/sup -//sub 2/xN/sub 2/ in comparison with O/sub 2/xN/sub 2/, furthers the enhancement. The calculated attachment rate is comparable to that determined by Shimamori and Fessenden, but differs from the recent values obtained by Toriumi and Hatano, who used a different set of reactions to interpret their data.« less

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

Moutinho, Helio R.; Jiang, Cun -Sheng; To, Bobby

To better understand and quantify soiling rates on solar panels, we are investigating the adhesion mechanisms between dust particles and solar glass. In this work, we report on two of the fundamental adhesion mechanisms: van der Waals and capillary adhesion forces. The adhesion was determined using force versus distance (F-z) measurements performed with an atomic force microscope (AFM). To emulate dust interacting with the front surface of a solar panel, we measured how oxidized AFM tips, SiO 2 glass spheres, and real dust particles adhered to actual solar glass. The van der Waals forces were evaluated by measurements performed withmore » zero relative humidity in a glove box, and the capillary forces were measured in a stable environment created inside the AFM enclosure with relative humidity values ranging from 18% to 80%. To simulate topographic features of the solar panels caused by factors such as cleaning and abrasion, we induced different degrees of surface roughness in the solar glass. As a result, we were able to 1) identify and quantify both the van der Waals and capillary forces, 2) establish the effects of surface roughness, relative humidity, and particle size on the adhesion mechanisms, and 3) compare adhesion forces between well-controlled particles (AFM tips and glass spheres) and real dust particles.« less

Novel algebraic aspects of Liouvillian integrability for two-dimensional polynomial dynamical systems

NASA Astrophysics Data System (ADS)

Demina, Maria V.

2018-05-01

The general structure of irreducible invariant algebraic curves for a polynomial dynamical system in C2 is found. Necessary conditions for existence of exponential factors related to an invariant algebraic curve are derived. As a consequence, all the cases when the classical force-free Duffing and Duffing-van der Pol oscillators possess Liouvillian first integrals are obtained. New exact solutions for the force-free Duffing-van der Pol system are constructed.

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

PubMed

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.

Pattern-free thermal modulator via thermal radiation between Van der Waals materials

NASA Astrophysics Data System (ADS)

Liu, Xianglei; Shen, Jiadong; Xuan, Yimin

2017-10-01

Modulating heat flux provides a platform for a plethora of emerging devices such as thermal diodes, thermal transistors, and thermal memories. Here, a pattern-free noncontact thermal modulator is proposed based on the mechanical rotation between two Van der Waals films with optical axes parallel to the surfaces. A modulation contrast can reach a value higher than 5 for hexagonal Boron Nitride (hBN) films separated by a nanoscale gap distance. The dominant radiative heat exchange comes from the excitation of both Type I and Type II hyperbolic surface phonon polaritons (HSPhPs) at the vacuum-hBN interface for different orientations, while the large modulation contrast is mainly attributed to the mismatching Type I HSPhPs induced by rotation. This work opens the possibility to design cheap thermal modulators without relying on nanofabrication techniques, and paves the way to apply natural Van der Waals materials in manipulating heat currents in an active way.

Ionic liquids: dissecting the enthalpies of vaporization.

PubMed

Köddermann, Thorsten; Paschek, Dietmar; Ludwig, Ralf

2008-03-14

We calculate the heats of vaporisation for imidazolium-based ionic liquids [C(n)mim][NTf(2)] with n=1, 2, 4, 6, 8 by means of molecular dynamics (MD) simulations and discuss their behavior with respect to temperature and the alkyl chain length. We use a force field developed recently. The different cohesive energies contributing to the overall heats of vaporisations are discussed in detail. With increasing alkyl chain length, the Coulomb contribution to the heat of vaporisation remains constant at around 80 kJ mol(-1), whereas the van der Waals interaction increases continuously. The calculated increase of about 4.7 kJ mol(-1) per CH(2)-group of the van der Waals contribution in the ionic liquid exactly coincides with the increase in the heats of vaporisation for n-alcohols and n-alkanes, respectively. The results support the importance of van der Waals interactions even in systems completely composed of ions.

Spin-Flavor van der Waals Forces and NN interaction

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

Alvaro Calle Cordon, Enrique Ruiz Arriola

A major goal in Nuclear Physics is the derivation of the Nucleon-Nucleon (NN) interaction from Quantum Chromodynamics (QCD). In QCD the fundamental degrees of freedom are colored quarks and gluons which are confined to form colorless strongly interacting hadrons. Because of this the resulting nuclear forces at sufficiently large distances correspond to spin-flavor excitations, very much like the dipole excitations generating the van der Waals (vdW) forces acting between atoms. We study the Nucleon-Nucleon interaction in the Born-Oppenheimer approximation at second order in perturbation theory including the Delta resonance as an intermediate state. The potential resembles strongly chiral potentials computedmore » either via soliton models or chiral perturbation theory and has a van der Waals like singularity at short distances which is handled by means of renormalization techniques. Results for the deuteron are discussed.« less

van der Waals interaction between a moving nano-cylinder and a liquid thin film.

PubMed

Ledesma-Alonso, René; Raphaël, Elie; Salez, Thomas; Tordjeman, Philippe; Legendre, Dominique

2017-05-24

We study the static and dynamic interaction between a horizontal cylindrical nano-probe and a thin liquid film. The effects of the physical and geometrical parameters, with a special focus on the film thickness, the probe speed, and the distance between the probe and the free surface are analyzed. Deformation profiles have been computed numerically from a Reynolds lubrication equation, coupled to a modified Young-Laplace equation, which takes into account the probe/liquid and the liquid/substrate non-retarded van der Waals interactions. We have found that the film thickness and the probe speed have a significant effect on the threshold separation distance below which the jump-to-contact instability is triggered. These results encourage the use of horizontal cylindrical nano-probes to scan thin liquid films, in order to determine either the physical or geometrical properties of the latter, through the measurement of interaction forces.

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

PubMed Central

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

2016-01-01

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. PMID:27152360

Effect of adding Te to layered GaSe crystals to increase the van der Waals bonding force

NASA Astrophysics Data System (ADS)

Tanabe, Tadao; Zhao, Shu; Sato, Yohei; Oyama, Yutaka

2017-10-01

The interplanar binding strength of layered GaSe1-xTex crystals was directly measured using a tensile testing machine. The GaSe1-xTex crystals were grown by a low temperature liquid phase solution method under a controlled Se vapor pressure. The stoichiometry-controlled GaSe1-xTex crystal has the ɛ-polytype structure of GaSe, where the Te atoms are substituted for some of the Se atoms in the GaSe crystal. The effect of adding Te on the bonding strength between the GaSe layers was determined from direct measurements of the van der Waals bonding energy. The bonding energy was increased from 0.023 × 106 N/m2 for GaSe to 0.16 × 106 N/m2 for GaSe1-xTex (x = 0.106).

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

DOE PAGES

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

2016-04-22

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 vanishmore » 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.« less

Chemical free device fabrication of two dimensional van der Waals materials based transistors by using one-off stamping

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

Lee, Young Tack, E-mail: 023273@kist.re.kr, E-mail: stunalren@gmail.com; Choi, Won Kook; Materials and Life Science Research Division, Korea Institute of Science and Technology

We report on a chemical free one-off imprinting method to fabricate two dimensional (2D) van der Waals (vdWs) materials based transistors. Such one-off imprinting technique is the simplest and effective way to prevent unintentional chemical reaction or damage of 2D vdWs active channel during device fabrication process. 2D MoS{sub 2} nanosheets based transistors with a hexagonal-boron-nitride (h-BN) passivation layer, prepared by one-off imprinting, show negligible variations of transfer characteristics after chemical vapor deposition process. In addition, this method enables the fabrication of all 2D MoS{sub 2} transistors consisting of h-BN gate insulator, and graphene source/drain and gate electrodes without anymore » chemical damage.« less

Strong van der Waals attractive forces in nanotechnology

NASA Astrophysics Data System (ADS)

Reimers, Jeffrey

The Dobson classification scheme for failure of London-like expressions for describing dispersion is reviewed. New ways to measure using STM data and calculate by first principles free energies of organic self-assembly processes from solution will be discussed, considering tetraalkylporphyrins on graphite. How strong van der Waals forces can compete against covalent bonding to produce new molecular isomers and reaction pathways will also be demonstrated, focusing on golds-sulfur bonds for sensors and stabilizing nanoparticles.

Vygotsky's Fragile Genius in Time and Place: Essay Review of "Understanding Vygotsky: A Quest for Synthesis" by Rene van der Veer and Jaan Valsiner.

ERIC Educational Resources Information Center

Youniss, James

1994-01-01

Briefly summarizes Vygotsky's life, the appeal and subsequent abandonment of his ideas in the 1960s, and renewal of interest in the 1970s and 1980s (often at the expense of Piaget). Praises van der Veer and Valsinger's book as a realistic picture of Vygotsky's background, life, and work, of the scientific and political context in Russia and of his…

Calculations of predissociative lifetimes of RG...Hal2 Van der Waals complexes

NASA Astrophysics Data System (ADS)

Buchachenko, Alexei A.; Stepanov, N. F.

1992-07-01

Good examples of combined energy- and time-resolved techniques linked by the theoretical solution of a nuclear problem may be found in investigations of the dynamics of weakly bound Van der Waals (VdW) complexes, such as Ar-OH and He-stilbene. Our report concerns only the theoretical aspect of this complex approach. However, we shall stress the importance of energy-resolved spectroscopy for the dynamics and try to illustrate this with some numerical results.

A Van der Waals-like theory of plasma double layers

NASA Technical Reports Server (NTRS)

Katz, Ira; Davis, V. A.

1989-01-01

A theory describing plasma double layers in terms of multiple roots of the charge density expression is presented. The theory presented uses the fact that equilibrium plasmas shield small potential perturbations linearly; for high potentials, the shielding decreases. The approach is analogous to Van der Waals' theory of simple fluids in which inclusion of approximate expressions for both excluded volume and long range attractive forces sufficiently describes the first-order liquid-gas phase transition.

Nuclear spin-spin coupling in a van der Waals-bonded system: xenon dimer.

PubMed

Vaara, Juha; Hanni, Matti; Jokisaari, Jukka

2013-03-14

Nuclear spin-spin coupling over van der Waals bond has recently been observed via the frequency shift of solute protons in a solution containing optically hyperpolarized (129)Xe nuclei. We carry out a first-principles computational study of the prototypic van der Waals-bonded xenon dimer, where the spin-spin coupling between two magnetically non-equivalent isotopes, J((129)Xe - (131)Xe), is observable. We use relativistic theory at the four-component Dirac-Hartree-Fock and Dirac-density-functional theory levels using novel completeness-optimized Gaussian basis sets and choosing the functional based on a comparison with correlated ab initio methods at the nonrelativistic level. J-coupling curves are provided at different levels of theory as functions of the internuclear distance in the xenon dimer, demonstrating cross-coupling effects between relativity and electron correlation for this property. Calculations on small Xe clusters are used to estimate the importance of many-atom effects on J((129)Xe - (131)Xe). Possibilities of observing J((129)Xe - (131)Xe) in liquid xenon are critically examined, based on molecular dynamics simulation. A simplistic spherical model is set up for the xenon dimer confined in a cavity, such as in microporous materials. It is shown that the on the average shorter internuclear distance enforced by the confinement increases the magnitude of the coupling as compared to the bulk liquid case, rendering J((129)Xe - (131)Xe) in a cavity a feasible target for experimental investigation.

Energy and charge transfer effects in two-dimensional van der Waals hybrid nanostructures on periodic gold nanopost array

NASA Astrophysics Data System (ADS)

Kim, Jun Young; Kim, Sun Gyu; Youn, Jong Won; Lee, Yongjun; Kim, Jeongyong; Joo, Jinsoo

2018-05-01

Two-dimensional (2D) semiconducting MoS2 and WSe2 flakes grown by chemical vapor deposition were mechanically hybridized. A hexagonal boron nitride (h-BN) dielectric flake was inserted between MoS2 and WSe2 flakes to investigate the nanoscale optical properties of 2D van der Waals hybrid nanostructures. The fabricated MoS2/WSe2 and MoS2/h-BN/WSe2 van der Waals hybrid nanostructures were loaded on a periodic gold nanopost (Au-NPo) array to study energy and charge transfer effects at the surface plasmon resonance (SPR) condition. Nanoscale photoluminescence (PL) spectra of the 2D hybrid nanostructures were measured using a high-resolution laser confocal microscope (LCM). A shift of the LCM PL peak of the MoS2/WSe2 n-p hybrid nanostructures was observed owing to the charge transfer. In contrast, the shift of the LCM PL peak of the MoS2/h-BN/WSe2 n-insulator-p hybrid nanostructure was not considerable, as the inserted h-BN dielectric layer prevented the charge transfer. The intensity of the LCM PL peak of the MoS2/h-BN/WSe2 hybrid nanostructure considerably increased once the nanostructure was loaded on the Au-NPo array, owing to the energy transfer between the 2D materials and the Au-NPo array at the SPR condition, which was confirmed by the increase in the LCM Raman intensity.

Antiferromagnetism in the van der Waals layered spin-lozenge semiconductor CrTe 3

DOE PAGES

McGuire, Michael A.; Garlea, V. Ovidiu; KC, Santosh; ...

2017-04-14

We have investigated the crystallographic, magnetic, and transport properties of the van der Waals bonded, layered compound CrTe 3 on single-crystal and polycrystalline materials. Furthermore, the crystal structure contains layers made up of lozenge-shaped Cr 4 tetramers. Electrical resistivity measurements show the crystals to be semiconducting, with a temperature dependence consistent with a band gap of 0.3 eV. The magnetic susceptibility exhibits a broad maximum near 300 K characteristic of low dimensional magnetic systems. Weak anomalies are observed in the susceptibility and heat capacity near 55 K, and single-crystal neutron diffraction reveals the onset of long-range antiferromagnetic order at thismore » temperature. Strongly dispersive spin waves are observed in the ordered state. Significant magnetoelastic coupling is indicated by the anomalous temperature dependence of the lattice parameters and is evident in structural optimization in van der Waals density functional theory calculations for different magnetic configurations. The cleavability of the compound is apparent from its handling and is confirmed by first-principles calculations, which predict a cleavage energy 0.5 J / m 2 , similar to graphite. Based on our results, CrTe 3 is identified as a promising compound for studies of low dimensional magnetism in bulk crystals as well as magnetic order in monolayer materials and van der Waals heterostructures.« less

Hermite Functional Link Neural Network for Solving the Van der Pol-Duffing Oscillator Equation.

PubMed

Mall, Susmita; Chakraverty, S

2016-08-01

Hermite polynomial-based functional link artificial neural network (FLANN) is proposed here to solve the Van der Pol-Duffing oscillator equation. A single-layer hermite neural network (HeNN) model is used, where a hidden layer is replaced by expansion block of input pattern using Hermite orthogonal polynomials. A feedforward neural network model with the unsupervised error backpropagation principle is used for modifying the network parameters and minimizing the computed error function. The Van der Pol-Duffing and Duffing oscillator equations may not be solved exactly. Here, approximate solutions of these types of equations have been obtained by applying the HeNN model for the first time. Three mathematical example problems and two real-life application problems of Van der Pol-Duffing oscillator equation, extracting the features of early mechanical failure signal and weak signal detection problems, are solved using the proposed HeNN method. HeNN approximate solutions have been compared with results obtained by the well known Runge-Kutta method. Computed results are depicted in term of graphs. After training the HeNN model, we may use it as a black box to get numerical results at any arbitrary point in the domain. Thus, the proposed HeNN method is efficient. The results reveal that this method is reliable and can be applied to other nonlinear problems too.

Van der Pol and the history of relaxation oscillations: Toward the emergence of a concept

NASA Astrophysics Data System (ADS)

Ginoux, Jean-Marc; Letellier, Christophe

2012-06-01

Relaxation oscillations are commonly associated with the name of Balthazar van der Pol via his paper (Philosophical Magazine, 1926) in which he apparently introduced this terminology to describe the nonlinear oscillations produced by self-sustained oscillating systems such as a triode circuit. Our aim is to investigate how relaxation oscillations were actually discovered. Browsing the literature from the late 19th century, we identified four self-oscillating systems in which relaxation oscillations have been observed: (i) the series dynamo machine conducted by Gérard-Lescuyer (1880), (ii) the musical arc discovered by Duddell (1901) and investigated by Blondel (1905), (iii) the triode invented by de Forest (1907), and (iv) the multivibrator elaborated by Abraham and Bloch (1917). The differential equation describing such a self-oscillating system was proposed by Poincaré for the musical arc (1908), by Janet for the series dynamo machine (1919), and by Blondel for the triode (1919). Once Janet (1919) established that these three self-oscillating systems can be described by the same equation, van der Pol proposed (1926) a generic dimensionless equation which captures the relevant dynamical properties shared by these systems. Van der Pol's contributions during the period of 1926-1930 were investigated to show how, with Le Corbeiller's help, he popularized the "relaxation oscillations" using the previous experiments as examples and, turned them into a concept.

Defect mediated van der Waals epitaxy of hexagonal boron nitride on graphene

NASA Astrophysics Data System (ADS)

Heilmann, M.; Bashouti, M.; Riechert, H.; Lopes, J. M. J.

2018-04-01

Van der Waals heterostructures comprising of hexagonal boron nitride and graphene are promising building blocks for novel two-dimensional devices such as atomically thin transistors or capacitors. However, demonstrators of those devices have been so far mostly fabricated by mechanical assembly, a non-scalable and time-consuming method, where transfer processes can contaminate the surfaces. Here, we investigate a direct growth process for the fabrication of insulating hexagonal boron nitride on high quality epitaxial graphene using plasma assisted molecular beam epitaxy. Samples were grown at varying temperatures and times and studied using atomic force microscopy, revealing a growth process limited by desorption at high temperatures. Nucleation was mostly commencing from morphological defects in epitaxial graphene, such as step edges or wrinkles. Raman spectroscopy combined with x-ray photoelectron measurements confirm the formation of hexagonal boron nitride and prove the resilience of graphene against the nitrogen plasma used during the growth process. The electrical properties and defects in the heterostructures were studied with high lateral resolution by tunneling current and Kelvin probe force measurements. This correlated approach revealed a nucleation apart from morphological defects in epitaxial graphene, which is mediated by point defects. The presented results help understanding the nucleation and growth behavior during van der Waals epitaxy of 2D materials, and point out a route for a scalable production of van der Waals heterostructures.

Antiferromagnetism in the van der Waals layered spin-lozenge semiconductor CrTe 3

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

McGuire, Michael A.; Garlea, V. Ovidiu; KC, Santosh

We have investigated the crystallographic, magnetic, and transport properties of the van der Waals bonded, layered compound CrTe 3 on single-crystal and polycrystalline materials. Furthermore, the crystal structure contains layers made up of lozenge-shaped Cr 4 tetramers. Electrical resistivity measurements show the crystals to be semiconducting, with a temperature dependence consistent with a band gap of 0.3 eV. The magnetic susceptibility exhibits a broad maximum near 300 K characteristic of low dimensional magnetic systems. Weak anomalies are observed in the susceptibility and heat capacity near 55 K, and single-crystal neutron diffraction reveals the onset of long-range antiferromagnetic order at thismore » temperature. Strongly dispersive spin waves are observed in the ordered state. Significant magnetoelastic coupling is indicated by the anomalous temperature dependence of the lattice parameters and is evident in structural optimization in van der Waals density functional theory calculations for different magnetic configurations. The cleavability of the compound is apparent from its handling and is confirmed by first-principles calculations, which predict a cleavage energy 0.5 J / m 2 , similar to graphite. Based on our results, CrTe 3 is identified as a promising compound for studies of low dimensional magnetism in bulk crystals as well as magnetic order in monolayer materials and van der Waals heterostructures.« less

The potential for fast van der Waals computations for layered materials using a Lifshitz model

NASA Astrophysics Data System (ADS)

Zhou, Yao; Pellouchoud, Lenson A.; Reed, Evan J.

2017-06-01

Computation of the van der Waals (vdW) interactions plays a crucial role in the study of layered materials. The adiabatic-connection fluctuation-dissipation theorem within random phase approximation (ACFDT-RPA) has been empirically reported to be the most accurate of commonly used methods, but it is limited to small systems due to its computational complexity. Without a computationally tractable vdW correction, fictitious strains are often introduced in the study of multilayer heterostructures, which, we find, can change the vdW binding energy by as much as 15%. In this work, we employed for the first time a defined Lifshitz model to provide the vdW potentials for a spectrum of layered materials orders of magnitude faster than the ACFDT-RPA for representative layered material structures. We find that a suitably defined Lifshitz model gives the correlation component of the binding energy to within 8-20% of the ACFDT-RPA calculations for a variety of layered heterostructures. Using this fast Lifshitz model, we studied the vdW binding properties of 210 three-layered heterostructures. Our results demonstrate that the three-body vdW effects are generally small (10% of the binding energy) in layered materials for most cases, and that non-negligible second-nearest neighbor layer interaction and three-body effects are observed for only those cases in which the middle layer is atomically thin (e.g. BN or graphene). We find that there is potential for particular combinations of stacked layers to exhibit repulsive three-body van der Waals effects, although these effects are likely to be much smaller than two-body effects.

Inventory of Materials to be Used in Explosive Effects Mitigating Structures (Inventarisatie van materialen te gebruiken in constructies ter afscherming van explosie-effecten)

DTIC Science & Technology

2008-11-01

F +31 15 284 39 91 info-DenV@tno.nl TNO-rapportnummer TNO-DV 2008 A357 Opdrachtnummer Datum november 2008 Auteur (s) ir. O.C. van der Jagt...een keramisch materiaal (ZrSiO.*). TNO-rapport | TNO-DV 2008 A357 32/44 K, 04 035 0.3 0 25 02 0 15 01 005 0 O a 0 X A • • Theory ...47] Molinari. A., et al., Modeling plastic shocks in periodic laminates with gradient plasticity theories . Journal of the Mechanics and Physics of

The role of collective motion in the ultrafast charge transfer in van der Waals heterostructures

DOE PAGES

Wang, Han; Bang, Junhyeok; Sun, Yiyang; ...

2016-05-10

Here, the success of van der Waals (vdW) heterostructures, made of graphene, metal dichalcogenides, and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications. In contrast to conventional heterostructures, where a strong interfacial coupling is essential to charge transfer, recent experimental findings indicate that vdW heterostructues can exhibit ultra-fast charge transfer despite the weak binding of the heterostructure. Using time-dependent density functional theory molecular dynamics, we identify a strong dynamic coupling between the vdW layers associated with charge transfer. This dynamic coupling results in rapid nonlinear coherentmore » charge oscillations which constitute a purely electronic phenomenon and are shown to be a general feature of vdW heterostructures provided they have a critical minimum dipole coupling. Application to MoS2/WS2 heterostructure yields good agreement with experiment, indicating near complete charge transfer within a timescale of 100 fs.The success of van der Waals heterostructures made of graphene, metal dichalcogenides and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications. In contrast to conventional heterostructures, where a strong interfacial coupling is essential to charge transfer, recent experimental findings indicate that van der Waals heterostructues can exhibit ultrafast charge transfer despite the weak binding of these heterostructures. Here we find, using time-dependent density functional theory molecular dynamics, that the collective motion of excitons at the interface leads to plasma oscillations associated with optical excitation. By constructing a simple model of the van der Waals heterostructure, we show that there exists an unexpected criticality of the oscillations, yielding rapid charge transfer across the interface. Application to the MoS2/WS2 heterostructure yields good agreement with experiments, indicating near complete charge transfer within a timescale of 100 fs.« less

The role of collective motion in the ultrafast charge transfer in van der Waals heterostructures

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

Wang, Han; Bang, Junhyeok; Sun, Yiyang

Here, the success of van der Waals (vdW) heterostructures, made of graphene, metal dichalcogenides, and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications. In contrast to conventional heterostructures, where a strong interfacial coupling is essential to charge transfer, recent experimental findings indicate that vdW heterostructues can exhibit ultra-fast charge transfer despite the weak binding of the heterostructure. Using time-dependent density functional theory molecular dynamics, we identify a strong dynamic coupling between the vdW layers associated with charge transfer. This dynamic coupling results in rapid nonlinear coherentmore » charge oscillations which constitute a purely electronic phenomenon and are shown to be a general feature of vdW heterostructures provided they have a critical minimum dipole coupling. Application to MoS2/WS2 heterostructure yields good agreement with experiment, indicating near complete charge transfer within a timescale of 100 fs.The success of van der Waals heterostructures made of graphene, metal dichalcogenides and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications. In contrast to conventional heterostructures, where a strong interfacial coupling is essential to charge transfer, recent experimental findings indicate that van der Waals heterostructues can exhibit ultrafast charge transfer despite the weak binding of these heterostructures. Here we find, using time-dependent density functional theory molecular dynamics, that the collective motion of excitons at the interface leads to plasma oscillations associated with optical excitation. By constructing a simple model of the van der Waals heterostructure, we show that there exists an unexpected criticality of the oscillations, yielding rapid charge transfer across the interface. Application to the MoS2/WS2 heterostructure yields good agreement with experiments, indicating near complete charge transfer within a timescale of 100 fs.« less

Development of a picture of the van der Waals interaction energy between clusters of nanometer-range particles

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

Arunachalam, V.; Marlow, W.H.; Lu, J.X.

1998-09-01

The importance of the long-range Lifshitz{endash}van der Waals interaction energy between condensed bodies is well known. However, its implementation for interacting bodies that are highly irregular and separated by distances varying from contact to micrometers has received little attention. As part of a study of collisions of irregular aerosol particles, an approach based on the Lifshitz theory of van der Waals interaction has been developed to compute the interaction energy between a sphere and an aggregate of spheres at all separations. In the first part of this study, the iterated sum-over-dipole interactions between pairs of approximately spherical molecular clusters aremore » compared with the Lifshitz and Lifshitz-Hamaker interaction energies for continuum spheres of radii equal to those of the clusters{close_quote} circumscribed spheres and of the same masses as the clusters. The Lifshitz energy is shown to converge to the iterated dipolar energy for quasispherical molecular clusters for sufficiently large separations, while the energy calculated by using the Lifshitz-Hamaker approach does not. Next, the interaction energies between a contacting pair of these molecular clusters and a third cluster in different relative positions are calculated first by coupling all molecules in the three-cluster system and second by ignoring the interactions between the molecules of the adhering clusters. The error calculated by this omission is shown to be very small, and is an indication of the error in computing the long-range interaction energy between a pair of interacting spheres and a third sphere as a simple sum over the Lifshitz energies between individual, condensed-matter spheres. This Lifshitz energy calculation is then combined with the short-separation, nonsingular van der Waals energy calculation of Lu, Marlow, and Arunachalam, to provide an integrated picture of the van der Waals energy from large separations to contact. {copyright} {ital 1998} {ital The American Physical Society}« less

Analysis of Gas-Particle Flows through Multi-Scale Simulations

NASA Astrophysics Data System (ADS)

Gu, Yile

Multi-scale structures are inherent in gas-solid flows, which render the modeling efforts challenging. On one hand, detailed simulations where the fine structures are resolved and particle properties can be directly specified can account for complex flow behaviors, but they are too computationally expensive to apply for larger systems. On the other hand, coarse-grained simulations demand much less computations but they necessitate constitutive models which are often not readily available for given particle properties. The present study focuses on addressing this issue, as it seeks to provide a general framework through which one can obtain the required constitutive models from detailed simulations. To demonstrate the viability of this general framework in which closures can be proposed for different particle properties, we focus on the van der Waals force of interaction between particles. We start with Computational Fluid Dynamics (CFD) - Discrete Element Method (DEM) simulations where the fine structures are resolved and van der Waals force between particles can be directly specified, and obtain closures for stress and drag that are required for coarse-grained simulations. Specifically, we develop a new cohesion model that appropriately accounts for van der Waals force between particles to be used for CFD-DEM simulations. We then validate this cohesion model and the CFD-DEM approach by showing that it can qualitatively capture experimental results where the addition of small particles to gas fluidization reduces bubble sizes. Based on the DEM and CFD-DEM simulation results, we propose stress models that account for the van der Waals force between particles. Finally, we apply machine learning, specifically neural networks, to obtain a drag model that captures the effects from fine structures and inter-particle cohesion. We show that this novel approach using neural networks, which can be readily applied for other closures other than drag here, can take advantage of the large amount of data generated from simulations, and therefore offer superior modeling performance over traditional approaches.

van der Waals-type forces in spontaneously broken supersymmetries

NASA Astrophysics Data System (ADS)

Radescu, E. E.

1983-03-01

In spontaneously broken rigid supersymmetry, Goldstone-fermion pair exchange should lead to a universal interaction between massive bodies uniquely fixed by the existing low-energy theorem. The resulting van der Waals-type potential is shown to be V(r)=-Mmπ-3F-4r-7+O(r-8), where M and m are the masses of the interacting bodies while F is the scale of the breaking. The change in the situation when the supersymmetry is promoted to a local symmetry is briefly discussed.

Grippers Based on Opposing Van Der Waals Adhesive Pads

NASA Technical Reports Server (NTRS)

Parness, Aaron (Inventor); Kennedy, Brett A. (Inventor); Heverly, Matthew C (Inventor); Cutkosky, Mark R. (Inventor); Hawkes, Elliot Wright (Inventor)

2016-01-01

Novel gripping structures based on van der Waals adhesive forces are disclosed. Pads covered with fibers can be activated in pairs by opposite forces, thereby enabling control of the adhesive force in an ON or OFF state. Pads can be used in groups, each comprising a group of opposite pads. The adhesive structures enable anchoring forces that can resist adverse forces from different directions. The adhesive structures can be used to enable the operation of robots on surfaces of space vehicles.

Effects of van der Waals density functional corrections on trends in furfural adsorption and hydrogenation on close-packed transition metal surfaces

NASA Astrophysics Data System (ADS)

Liu, Bin; Cheng, Lei; Curtiss, Larry; Greeley, Jeffrey

2014-04-01

The hydrogenation of furfural to furfuryl alcohol on Pd(111), Cu(111) and Pt(111) is studied with both standard Density Functional Theory (DFT)-GGA functionals and with van der Waals-corrected density functionals. VdW-DF functionals, including optPBE, optB88, optB86b, and Grimme's method, are used to optimize the adsorption configurations of furfural, furfuryl alcohol, and related intermediates resulting from hydrogenation of furfural, and the results are compared to corresponding values determined with GGA functionals, including PW91 and PBE. On Pd(111) and Pt(111), the adsorption geometries of the intermediates are not noticeably different between the two classes of functionals, while on Cu(111), modest changes are seen in both the perpendicular distance and the orientation of the aromatic ring with respect to the planar surface. In general, the binding energies increase substantially in magnitude as a result of van der Waals contributions on all metals. In contrast, however, dispersion effects on the kinetics of hydrogenation are relatively small. It is found that activation barriers are not significantly affected by the inclusion of dispersion effects, and a Brønsted-Evans-Polanyi relationship developed solely from PW91 calculations on Pd(111) is capable of describing corresponding results on Cu(111) and Pt(111), even when the dispersion effects are included. Finally, the reaction energies and barriers derived from the dispersion-corrected and pure GGA calculations are used to plot simple potential energy profiles for furfural hydrogenation to furfuryl alcohol on the three considered metals, and an approximately constant downshift of the energetics due to the dispersion corrections is observed.

Surface stress induced by interactions of adsorbates and its effect on deformation and frequency of microcantilever sensors

NASA Astrophysics Data System (ADS)

Yi, X.; Duan, H. L.

2009-08-01

Surface stress is widely used to characterize the adsorption effect on the mechanical response of nanomaterials and nanodevices. However, quantitative relations between continuum-level descriptions of surface stress and molecular-level descriptions of adsorbate interactions are not well established. In this paper, we first obtain the relations between the adsorption-induced surface stress and the van der Waals and Coulomb interactions in terms of the physical and chemical interactions between adsorbates and solid surfaces. Then, we present a theoretical framework to predict the deflection and resonance frequencies of microcantilevers with the simultaneous effects of the eigenstrain, surface stress and adsorption mass. Finally, the adsorption-induced deflection and resonance frequency shift of microcantilevers are numerically analyzed for the van der Waals and Coulomb interactions. The present theoretical framework quantifies the mechanisms of the adsorption-induced surface stress, and thus provides guidelines to the analysis of the sensitivities, and the identification of the detected substance in the design and application of micro- and nanocantilever sensors.

Structural Dynamics Investigation of Human Family 1 & 2 Cystatin-Cathepsin L1 Interaction: A Comparison of Binding Modes.

PubMed

Nandy, Suman Kumar; Seal, Alpana

2016-01-01

Cystatin superfamily is a large group of evolutionarily related proteins involved in numerous physiological activities through their inhibitory activity towards cysteine proteases. Despite sharing the same cystatin fold, and inhibiting cysteine proteases through the same tripartite edge involving highly conserved N-terminal region, L1 and L2 loop; cystatins differ widely in their inhibitory affinity towards C1 family of cysteine proteases and molecular details of these interactions are still elusive. In this study, inhibitory interactions of human family 1 & 2 cystatins with cathepsin L1 are predicted and their stability and viability are verified through protein docking & comparative molecular dynamics. An overall stabilization effect is observed in all cystatins on complex formation. Complexes are mostly dominated by van der Waals interaction but the relative participation of the conserved regions varied extensively. While van der Waals contacts prevail in L1 and L2 loop, N-terminal segment chiefly acts as electrostatic interaction site. In fact the comparative dynamics study points towards the instrumental role of L1 loop in directing the total interaction profile of the complex either towards electrostatic or van der Waals contacts. The key amino acid residues surfaced via interaction energy, hydrogen bonding and solvent accessible surface area analysis for each cystatin-cathepsin L1 complex influence the mode of binding and thus control the diverse inhibitory affinity of cystatins towards cysteine proteases.

Fabrication of functional ultrathin single-crystal nanowires from quasi-one dimensional van der Waals crystals Ta2(Pd or Pt)3Se8

NASA Astrophysics Data System (ADS)

Liu, Xue; Liu, Jinyu; Hu, Jin; Yue, Chunlei; Mao, Zhiqiang; Wei, Jiang; Zhu, Yibo; Sanchez, Ana; Antipina, Liubov; Sorokin, Pavel

Micromechanical exfoliation or wet exfoliation of two-dimensional van der Waals materials has triggered an explosive interest in 2D material research. In our work, we extend this idea to 1D van der Waals material. By using micromechanical exfoliation or wet exfoliation, 1D nanowire with size as small as six molecular ribbons can be readily achieved in the Ta2(Pd or Pt)3Se8 system. The semiconducting properties of exfoliated Ta2Pd3Se8 nanowires show n-type, whereas Ta2Pt3Se8 nanowires are p-type. Our electronic band structure calculation for Ta2Pd3Se8 nanowire reveals that from multi-ribbon to single-ribbon the band gap evolves from indirect 0.5eV in bulk to direct 1eV in single-ribbon. A functional ``NOT'' gate consisting of field-effect transistors based on these two types of complementary nanowires has also been successfully realized. Moreover, the photocurrent response of Ta2Pd3Se8 nanowire transistors has been studied as well. Ta2(Pd or Pt)3Se8 system, as an intrinsic quasi-1D material, provides a viable platform for the study of low dimensional condensed matter physics. We acknowledge the financial support from DOE and BoRSF.

Strong interlayer coupling in phosphorene/graphene van der Waals heterostructure: A first-principles investigation

NASA Astrophysics Data System (ADS)

Hu, Xue-Rong; Zheng, Ji-Ming; Ren, Zhao-Yu

2018-04-01

Based on first-principles calculations within the framework of density functional theory, we study the electronic properties of phosphorene/graphene heterostructures. Band gaps with different sizes are observed in the heterostructure, and charges transfer from graphene to phosphorene, causing the Fermi level of the heterostructure to shift downward with respect to the Dirac point of graphene. Significantly, strong coupling between two layers is discovered in the band spectrum even though it has a van der Waals heterostructure. A tight-binding Hamiltonian model is used to reveal that the resonance of the Bloch states between the phosphorene and graphene layers in certain K points combines with the symmetry matching between band states, which explains the reason for the strong coupling in such heterostructures. This work may enhance the understanding of interlayer interaction and composition mechanisms in van der Waals heterostructures consisting of two-dimensional layered nanomaterials, and may indicate potential reference information for nanoelectronic and optoelectronic applications.

Existence of quasi-periodic solutions of fast excited van der Pol-Mathieu-Duffing equation

NASA Astrophysics Data System (ADS)

Lu, Lin; Li, Xuemei

2015-12-01

The van der Pol-Mathieu-Duffing equation x ̈ + ( Ω0 2 + h 1 cos Ω 1 t + h 2 cos Ω 2 t ) x - ( α - β x 2 ) x ˙ - h 3 x 3 = h 4 Ω3 2 cos x cos Ω 3 t is considered in this paper, where α, β, h1, h2, h3, h4, Ω1, Ω2 are small parameters, α, β > 0, the frequency Ω3 is large compared to Ω1 and Ω2, the above parameters are real. For ∀α, β > 0, we use KAM (Kolmogorov-Arnold-Moser) theory to prove that the van der Pol-Mathieu-Duffing equation possesses quasi-periodic solutions for most of the parameters Ω0, Ω1, Ω2, Ω3, it verifies some phenomenon of Fahsi and Belhaq [Commun. Nonlinear Sci. 14, 244-253 (2009)] and can be regarded as a extension of Abouhazim et al. [Nonlinear Dyn. 39, 395-409 (2005)].

Out-of-plane heat transfer in van der Waals stacks through electron-hyperbolic phonon coupling

NASA Astrophysics Data System (ADS)

Tielrooij, Klaas-Jan; Hesp, Niels C. H.; Principi, Alessandro; Lundeberg, Mark B.; Pogna, Eva A. A.; Banszerus, Luca; Mics, Zoltán; Massicotte, Mathieu; Schmidt, Peter; Davydovskaya, Diana; Purdie, David G.; Goykhman, Ilya; Soavi, Giancarlo; Lombardo, Antonio; Watanabe, Kenji; Taniguchi, Takashi; Bonn, Mischa; Turchinovich, Dmitry; Stampfer, Christoph; Ferrari, Andrea C.; Cerullo, Giulio; Polini, Marco; Koppens, Frank H. L.

2018-01-01

Van der Waals heterostructures have emerged as promising building blocks that offer access to new physics, novel device functionalities and superior electrical and optoelectronic properties1-7. Applications such as thermal management, photodetection, light emission, data communication, high-speed electronics and light harvesting8-16 require a thorough understanding of (nanoscale) heat flow. Here, using time-resolved photocurrent measurements, we identify an efficient out-of-plane energy transfer channel, where charge carriers in graphene couple to hyperbolic phonon polaritons17-19 in the encapsulating layered material. This hyperbolic cooling is particularly efficient, giving picosecond cooling times for hexagonal BN, where the high-momentum hyperbolic phonon polaritons enable efficient near-field energy transfer. We study this heat transfer mechanism using distinct control knobs to vary carrier density and lattice temperature, and find excellent agreement with theory without any adjustable parameters. These insights may lead to the ability to control heat flow in van der Waals heterostructures.

van der Waals three-body force shell model (VTSM) for the lattice dynamical studies of thallous bromide

NASA Astrophysics Data System (ADS)

Tiwari, Sarvesh K.; Pandey, L. K.; Shukla, Lal Ji; Upadhyaya, K. S.

2009-12-01

The van der Waals three-body force shell model (VTSM) has been developed by modifying the three-body force shell model (TSM) for the lattice dynamics of ionic crystals with cesium chloride (CsCl) structure. This new model incorporates van der Waals interactions along with long-range Coulomb interactions, three-body interactions and short-range second neighbour interactions in the framework of a rigid shell model (RSM). In the present paper, VTSM has been used to study the lattice dynamics of thallous bromide (TlBr), from which adequacy of VTSM has been established. A comparative study of the dynamical behaviour of TlBr has also been done between the present model and TSM, the model over which modification has been made to obtain the present model VTSM. Good agreement has been observed between the theoretical and experimental results, which give confidence that it is an appropriate model for the complete description of ionic crystals with CsCl structure.

A variation-perturbation method for atomic and molecular interactions. I - Theory. II - The interaction potential and van der Waals molecule for Ne-HF

NASA Astrophysics Data System (ADS)

Gallup, G. A.; Gerratt, J.

1985-09-01

The van der Waals energy between the two parts of a system is a very small fraction of the total electronic energy. In such cases, calculations have been based on perturbation theory. However, such an approach involves certain difficulties. For this reason, van der Waals energies have also been directly calculated from total energies. But such a method has definite limitations as to the size of systems which can be treated, and recently ab initio calculations have been combined with damped semiempirical long-range dispersion potentials to treat larger systems. In this procedure, large basis set superposition errors occur, which must be removed by the counterpoise method. The present investigation is concerned with an approach which is intermediate between the previously considered procedures. The first step in the new approach involves a variational calculation based upon valence bond functions. The procedure includes also the optimization of excited orbitals, and an approximation of atomic integrals and Hamiltonian matrix elements.

Franckeite as a naturally occurring van der Waals heterostructure

PubMed Central

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

Exfoliation and van der Waals heterostructure assembly of intercalated ferromagnet Cr1/3TaS2

NASA Astrophysics Data System (ADS)

Yamasaki, Yuji; Moriya, Rai; Arai, Miho; Masubuchi, Satoru; Pyon, Sunseng; Tamegai, Tsuyoshi; Ueno, Keiji; Machida, Tomoki

2017-12-01

Ferromagnetic van der Waals (vdW) materials are in demand for spintronic devices with all-two-dimensional-materials heterostructures. Here, we demonstrate mechanical exfoliation of magnetic-atom-intercalated transition metal dichalcogenide Cr1/3TaS2 from its bulk crystal; previously such intercalated materials were thought difficult to exfoliate. Magnetotransport in exfoliated tens-of-nanometres-thick flakes revealed ferromagnetic ordering below its Curie temperature T C ~ 110 K as well as strong in-plane magnetic anisotropy; these are identical to its bulk properties. Further, van der Waals heterostructure assembly of Cr1/3TaS2 with another intercalated ferromagnet Fe1/4TaS2 is demonstrated using a dry-transfer method. The fabricated heterojunction composed of Cr1/3TaS2 and Fe1/4TaS2 with a native Ta2O5 oxide tunnel barrier in between exhibits tunnel magnetoresistance (TMR), revealing possible spin injection and detection with these exfoliatable ferromagnetic materials through the vdW junction.

Recent progress in the assembly of nanodevices and van der Waals heterostructures by deterministic placement of 2D materials.

PubMed

Frisenda, Riccardo; Navarro-Moratalla, Efrén; Gant, Patricia; Pérez De Lara, David; Jarillo-Herrero, Pablo; Gorbachev, Roman V; Castellanos-Gomez, Andres

2018-01-02

Designer heterostructures can now be assembled layer-by-layer with unmatched precision thanks to the recently developed deterministic placement methods to transfer two-dimensional (2D) materials. This possibility constitutes the birth of a very active research field on the so-called van der Waals heterostructures. Moreover, these deterministic placement methods also open the door to fabricate complex devices, which would be otherwise very difficult to achieve by conventional bottom-up nanofabrication approaches, and to fabricate fully-encapsulated devices with exquisite electronic properties. The integration of 2D materials with existing technologies such as photonic and superconducting waveguides and fiber optics is another exciting possibility. Here, we review the state-of-the-art of the deterministic placement methods, describing and comparing the different alternative methods available in the literature, and we illustrate their potential to fabricate van der Waals heterostructures, to integrate 2D materials into complex devices and to fabricate artificial bilayer structures where the layers present a user-defined rotational twisting angle.

Evaluation of van der Waals density functionals for layered materials

NASA Astrophysics Data System (ADS)

Tawfik, Sherif Abdulkader; Gould, Tim; Stampfl, Catherine; Ford, Michael J.

2018-03-01

In 2012, Björkman et al. posed the question "Are we van der Waals ready?" [T. Björkman et al., J. Phys.: Condens. Matter 24, 424218 (2012), 10.1088/0953-8984/24/42/424218] about the ability of ab initio modeling to reproduce van der Waals (vdW) dispersion forces in layered materials. The answer at that time was no, however. Here we report on a new generation of vdW dispersion models and show that one, i.e., the fractionally ionic atom theory with many-body dispersions, offers close to quantitative predictions for layered structures. Furthermore, it does so from a qualitatively correct picture of dispersion forces. Other methods, such as D3 and optB88vdW, also work well, albeit with some exceptions. We thus argue that we are nearly vdW ready and that some modern dispersion methods are accurate enough to be used for nanomaterial prediction, albeit with some caution required.

Quantum Monte Carlo Simulation of condensed van der Waals Systems

NASA Astrophysics Data System (ADS)

Benali, Anouar; Shulenburger, Luke; Romero, Nichols A.; Kim, Jeongnim; Anatole von Lilienfeld, O.

2012-02-01

Van der Waals forces are as ubiquitous as infamous. While post-Hartree-Fock methods enable accurate estimates of these forces in molecules and clusters, they remain elusive for dealing with many-electron condensed phase systems. We present Quantum Monte Carlo [1,2] results for condensed van der Waals systems. Interatomic many-body contributions to cohesive energies and bulk modulus will be discussed. Numerical evidence is presented for crystals of rare gas atoms, and compared to experiments and methods [3]. Sandia National Laboratories is a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. DoE's National Nuclear Security Administration under Contract No. DE-AC04-94AL85000.[4pt] [1] J. Kim, K. Esler, J. McMinis and D. Ceperley, SciDAC 2010, J. of Physics: Conference series, Chattanooga, Tennessee, July 11 2011 [0pt] [2] QMCPACK simulation suite, http://qmcpack.cmscc.org (unpublished)[0pt] [3] O. A. von Lillienfeld and A. Tkatchenko, J. Chem. Phys. 132 234109 (2010)

Strain-engineered diffusive atomic switching in two-dimensional crystals

PubMed Central

Kalikka, Janne; Zhou, Xilin; Dilcher, Eric; Wall, Simon; Li, Ju; Simpson, Robert E.

2016-01-01

Strain engineering is an emerging route for tuning the bandgap, carrier mobility, chemical reactivity and diffusivity of materials. Here we show how strain can be used to control atomic diffusion in van der Waals heterostructures of two-dimensional (2D) crystals. We use strain to increase the diffusivity of Ge and Te atoms that are confined to 5 Å thick 2D planes within an Sb2Te3–GeTe van der Waals superlattice. The number of quintuple Sb2Te3 2D crystal layers dictates the strain in the GeTe layers and consequently its diffusive atomic disordering. By identifying four critical rules for the superlattice configuration we lay the foundation for a generalizable approach to the design of switchable van der Waals heterostructures. As Sb2Te3–GeTe is a topological insulator, we envision these rules enabling methods to control spin and topological properties of materials in reversible and energy efficient ways. PMID:27329563

Domain Hierarchy and closed Loops (DHcL): a server for exploring hierarchy of protein domain structure

PubMed Central

Koczyk, Grzegorz; Berezovsky, Igor N.

2008-01-01

Domain hierarchy and closed loops (DHcL) (http://sitron.bccs.uib.no/dhcl/) is a web server that delineates energy hierarchy of protein domain structure and detects domains at different levels of this hierarchy. The server also identifies closed loops and van der Waals locks, which constitute a structural basis for the protein domain hierarchy. The DHcL can be a useful tool for an express analysis of protein structures and their alternative domain decompositions. The user submits a PDB identifier(s) or uploads a 3D protein structure in a PDB format. The results of the analysis are the location of domains at different levels of hierarchy, closed loops, van der Waals locks and their interactive visualization. The server maintains a regularly updated database of domains, closed loop and van der Waals locks for all X-ray structures in PDB. DHcL server is available at: http://sitron.bccs.uib.no/dhcl. PMID:18502776

Strong room-temperature ferromagnetism in VSe2 monolayers on van der Waals substrates

NASA Astrophysics Data System (ADS)

Bonilla, Manuel; Kolekar, Sadhu; Ma, Yujing; Diaz, Horacio Coy; Kalappattil, Vijaysankar; Das, Raja; Eggers, Tatiana; Gutierrez, Humberto R.; Phan, Manh-Huong; Batzill, Matthias

2018-04-01

Reduced dimensionality and interlayer coupling in van der Waals materials gives rise to fundamentally different electronic1, optical2 and many-body quantum3-5 properties in monolayers compared with the bulk. This layer-dependence permits the discovery of novel material properties in the monolayer regime. Ferromagnetic order in two-dimensional materials is a coveted property that would allow fundamental studies of spin behaviour in low dimensions and enable new spintronics applications6-8. Recent studies have shown that for the bulk-ferromagnetic layered materials CrI3 (ref. 9) and Cr2Ge2Te6 (ref. 10), ferromagnetic order is maintained down to the ultrathin limit at low temperatures. Contrary to these observations, we report the emergence of strong ferromagnetic ordering for monolayer VSe2, a material that is paramagnetic in the bulk11,12. Importantly, the ferromagnetic ordering with a large magnetic moment persists to above room temperature, making VSe2 an attractive material for van der Waals spintronics applications.

Study of interaction in silica glass via model potential approach

NASA Astrophysics Data System (ADS)

Mann, Sarita; Rani, Pooja

2016-05-01

Silica is one of the most commonly encountered substances in daily life and in electronics industry. Crystalline SiO2 (in several forms: quartz, cristobalite, tridymite) is an important constituent of many minerals and gemstones, both in pure form and mixed with related oxides. Cohesive energy of amorphous SiO2 has been investigated via intermolecular potentials i.e weak Van der Waals interaction and Morse type short-range interaction. We suggest a simple atom-atom based Van der Waals as well as Morse potential to find cohesive energy of glass. It has been found that the study of silica structure using two different model potentials is significantly different. Van der Waals potential is too weak (P.E =0.142eV/molecule) to describe the interaction between silica molecules. Morse potential is a strong potential, earlier given for intramolecular bonding, but if applied for intermolecular bonding, it gives a value of P.E (=-21.92eV/molecule) to appropriately describe the structure of silica.

Investigation for Molecular Attraction Impact Between Contacting Surfaces in Micro-Gears

NASA Astrophysics Data System (ADS)

Yang, Ping; Li, Xialong; Zhao, Yanfang; Yang, Haiying; Wang, Shuting; Yang, Jianming

2013-10-01

The aim of this research work is to provide a systematic method to perform molecular attraction impact between contacting surfaces in micro-gear train. This method is established by integrating involute profile analysis and molecular dynamics simulation. A mathematical computation of micro-gear involute is presented based on geometrical properties, Taylor expression and Hamaker assumption. In the meantime, Morse potential function and the cut-off radius are introduced with a molecular dynamics simulation. So a hybrid computational method for the Van Der Waals force between the contacting faces in micro-gear train is developed. An example is illustrated to show the performance of this method. The results show that the change of Van Der Waals force in micro-gear train has a nonlinear characteristic with parameters change such as the modulus of the gear and the tooth number of gear etc. The procedure implies a potential feasibility that we can control the Van Der Waals force by adjusting the manufacturing parameters for gear train design.

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

NASA Astrophysics Data System (ADS)

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.

Sub-bandgap Voltage Electroluminescence and Magneto-oscillations in a WSe2 Light-Emitting van der Waals Heterostructure.

PubMed

Binder, Johannes; Withers, Freddie; Molas, Maciej R; Faugeras, Clement; Nogajewski, Karol; Watanabe, Kenji; Taniguchi, Takashi; Kozikov, Aleksey; Geim, Andre K; Novoselov, Kostya S; Potemski, Marek

2017-03-08

We report on experimental investigations of an electrically driven WSe 2 based light-emitting van der Waals heterostructure. We observe a threshold voltage for electroluminescence significantly lower than the corresponding single particle band gap of monolayer WSe 2 . This observation can be interpreted by considering the Coulomb interaction and a tunneling process involving excitons, well beyond the picture of independent charge carriers. An applied magnetic field reveals pronounced magneto-oscillations in the electroluminescence of the free exciton emission intensity with a 1/B periodicity. This effect is ascribed to a modulation of the tunneling probability resulting from the Landau quantization in the graphene electrodes. A sharp feature in the differential conductance indicates that the Fermi level is pinned and allows for an estimation of the acceptor binding energy.

A crossover in anisotropic nanomechanochemistry of van der Waals crystals

NASA Astrophysics Data System (ADS)

Shimamura, Kohei; Misawa, Masaaki; Li, Ying; Kalia, Rajiv K.; Nakano, Aiichiro; Shimojo, Fuyuki; Vashishta, Priya

2015-12-01

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 10-13 s from the passage of shock front, lateral collision produces NO2 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 10-12 s, shock normal to multilayers becomes more reactive, producing H2O 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.

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

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

Sata, Yohta; Moriya, Rai, E-mail: moriyar@iis.u-tokyo.ac.jp, E-mail: tmachida@iis.u-tokyo.ac.jp; Morikawa, Sei

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 ofmore » the graphene/MoSe{sub 2} vdW heterostructure for electronics applications.« less

A Diverging View of Role Modeling in Medical Education

ERIC Educational Resources Information Center

Sandhu, Gurjit; Rich, Jessica V.; Magas, Christopher; Walker, G. Ross

2015-01-01

Research in the area of role modeling has primarily focused on the qualities and attributes of exceptional role models, and less attention has been given to the act of role modeling itself (Elzubeir & Rizk, 2001; Jochemsen-van der Leeuw, van Dijk, van Etten-Jamaludin, & Wieringa-de Waard, 2013; Wright, 1996; Wright, Wong, & Newill,…

On the stability analysis of a pair of van der Pol oscillators with delayed self-connection, position and velocity couplings

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

Hu, Kun; Department of Mathematics, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon; Chung, Kwok-wai, E-mail: makchung@cityu.edu.hk

2013-11-15

In this paper, we perform a stability analysis of a pair of van der Pol oscillators with delayed self-connection, position and velocity couplings. Bifurcation diagram of the damping, position and velocity coupling strengths is constructed, which gives insight into how stability boundary curves come into existence and how these curves evolve from small closed loops into open-ended curves. The van der Pol oscillator has been considered by many researchers as the nodes for various networks. It is inherently unstable at the zero equilibrium. Stability control of a network is always an important problem. Currently, the stabilization of the zero equilibriummore » of a pair of van der Pol oscillators can be achieved only for small damping strength by using delayed velocity coupling. An interesting question arises naturally: can the zero equilibrium be stabilized for an arbitrarily large value of the damping strength? We prove that it can be. In addition, a simple condition is given on how to choose the feedback parameters to achieve such goal. We further investigate how the in-phase mode or the out-of-phase mode of a periodic solution is related to the stability boundary curve that it emerges from a Hopf bifurcation. Analytical expression of a periodic solution is derived using an integration method. Some illustrative examples show that the theoretical prediction and numerical simulation are in good agreement.« less

Magnetic behavior and spin-lattice coupling in cleavable van der Waals layered CrCl 3 crystals

DOE PAGES

McGuire, Michael A.; Clark, Genevieve; KC, Santosh; ...

2017-06-19

CrCl 3 is a layered insulator that undergoes a crystallographic phase transition below room temperature and orders antiferromagnetically at low temperature. Weak van der Waals bonding between the layers and ferromagnetic in-plane magnetic order make it a promising material for obtaining atomically thin magnets and creating van der Waals heterostructures. In this work we have grown crystals of CrCl 3, revisited the structural and thermodynamic properties of the bulk material, and explored mechanical exfoliation of the crystals. We find two distinct anomalies in the heat capacity at 14 and 17 K confirming that the magnetic order develops in two stagesmore » on cooling, with ferromagnetic correlations forming before long-range antiferromagnetic order develops between them. This scenario is supported by magnetization data. A magnetic phase diagram is constructed from the heat capacity and magnetization results. We also find an anomaly in the magnetic susceptibility at the crystallographic phase transition, indicating some coupling between the magnetism and the lattice. First-principles calculations accounting for van der Waals interactions also indicate spin-lattice coupling, and find multiple nearly degenerate crystallographic and magnetic structures consistent with the experimental observations. Lastly, we demonstrate that monolayer and few-layer CrCl 3 specimens can be produced from the bulk crystals by exfoliation, providing a path for the study of heterostructures and magnetism in ultrathin crystals down to the monolayer limit.« less

Magnetic behavior and spin-lattice coupling in cleavable van der Waals layered CrCl 3 crystals

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

McGuire, Michael A.; Clark, Genevieve; KC, Santosh

CrCl 3 is a layered insulator that undergoes a crystallographic phase transition below room temperature and orders antiferromagnetically at low temperature. Weak van der Waals bonding between the layers and ferromagnetic in-plane magnetic order make it a promising material for obtaining atomically thin magnets and creating van der Waals heterostructures. In this work we have grown crystals of CrCl 3, revisited the structural and thermodynamic properties of the bulk material, and explored mechanical exfoliation of the crystals. We find two distinct anomalies in the heat capacity at 14 and 17 K confirming that the magnetic order develops in two stagesmore » on cooling, with ferromagnetic correlations forming before long-range antiferromagnetic order develops between them. This scenario is supported by magnetization data. A magnetic phase diagram is constructed from the heat capacity and magnetization results. We also find an anomaly in the magnetic susceptibility at the crystallographic phase transition, indicating some coupling between the magnetism and the lattice. First-principles calculations accounting for van der Waals interactions also indicate spin-lattice coupling, and find multiple nearly degenerate crystallographic and magnetic structures consistent with the experimental observations. Lastly, we demonstrate that monolayer and few-layer CrCl 3 specimens can be produced from the bulk crystals by exfoliation, providing a path for the study of heterostructures and magnetism in ultrathin crystals down to the monolayer limit.« less

Engineering Low Dimensional Materials with van der Waals Interaction

NASA Astrophysics Data System (ADS)

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 the consequence of interlayer interaction, as well as its systematic evolution in the parameter space. Experimentally, optical spectroscopy is a powerful tool to investigate properties of materials, owing to its insusceptibility to extrinsic effects like defects, capability of obtaining information in large spectral range, and the sensitivity to not only density of states but also wavefunction through transition matrix element. Following the classification of interlayer interaction, I will present optical spectroscopy studies of three van der Waals systems: Two-dimensional few layer phosphorene, one-dimensional double-walled nanotubes, and two-dimensional graphene/hexagonal Boron Nitride heterostructure. Experimental results exhibit rich and distinctively different effects of interlayer interaction in these systems, as a demonstration of the colorful physics from the large parameter space. On the other hand, all these cases can be well-described by the methods developed in the theory part, which explains experimental results quantitatively through only a few parameters each with clear physical meaning. Therefore, the formalism given here, both from theoretical and experimental aspects, offers a generally useful methodology to study, understand and design van der Waals materials for both fascinating physics and novel applications.

Workforce Development.

ERIC Educational Resources Information Center

1999

This document contains four symposium papers on work force development. "Effects of Two Different Learning Paths on School-to-Work Transition" (Esther Van Der Schoot) discusses a Dutch study documenting that the following items make a difference in the school-to-work transition: learning path, curriculum characteristics, individual…

Critical lines for an unequal size of molecules in a binary gas-liquid mixture around the van Laar point using the combination of the Tompa model and the van der Waals equation.

PubMed

Gençaslan, Mustafa; Keskin, Mustafa

2012-02-14

We combine the modified Tompa model with the van der Waals equation to study critical lines for an unequal size of molecules in a binary gas-liquid mixture around the van Laar point. The van Laar point is coined by Meijer and it is the only point at which the mathematical double point curve is stable. It is the intersection of the tricritical point and the double critical end point. We calculate the critical lines as a function of χ(1) and χ(2), the density of type I molecules and the density of type II molecules for various values of the system parameters; hence the global phase diagrams are presented and discussed in the density-density plane. We also investigate the connectivity of critical lines at the van Laar point and its vicinity and discuss these connections according to the Scott and van Konynenburg classifications. It is also found that the critical lines and phase behavior are extremely sensitive to small modifications in the system parameters. © 2012 American Institute of Physics

Characterization of van der Waals type bimodal,- lambda,- meta- and spinodal phase transitions in liquid mixtures, solid suspensions and thin films.

PubMed

Rosenholm, Jarl B

2018-03-01

The perfect gas law is used as a reference when selecting state variables (P, V, T, n) needed to characterize ideal gases (vapors), liquids and solids. Van der Waals equation of state is used as a reference for models characterizing interactions in liquids, solids and their mixtures. Van der Waals loop introduces meta- and unstable states between the observed gas (vapor)-liquid P-V transitions at low T. These intermediate states are shown to appear also between liquid-liquid, liquid-solid and solid-solid phase transitions. First-order phase transitions are characterized by a sharp discontinuity of first-order partial derivatives (P, S, V) of Helmholtz and Gibbs free energies. Second-order partial derivatives (K T , B, C V , C P , E) consist of a static contribution relating to second-order phase transitions and a relaxation contribution representing the degree of first-order phase transitions. Bimodal (first-order) and spinodal (second-order) phase boundaries are used to separate stable phases from metastable and unstable phases. The boundaries are identified and quantified by partial derivatives of molar Gibbs free energy or chemical potentials with respect to P, S, V and composition (mole fractions). Molecules confined to spread Langmuir monolayers or adsorbed Gibbs monolayers are characterized by equation of state and adsorption isotherms relating to a two-dimensional van der Waals equation of state. The basic work of two-dimensional wetting (cohesion, adsorption, spreading, immersion), have to be adjusted by a horizontal surface pressure in the presence of adsorbed vapor layers. If the adsorption is extended to liquid films a vertical surface pressure (Π) may be added to account for the lateral interaction, thus restoring PV = ΠAh dependence of thin films. Van der Waals attraction, Coulomb repulsion and structural hydration forces contribute to the vertical surface pressure. A van der Waals type coexistence of ordered (dispersed) and disordered (aggregated) phases is shown to exist when liquid vapor is confined in capillaries (condensation-liquefaction-evaporation and flux). This pheno-menon can be experimentally illustrated with suspended nano-sized particles (flocculation-coagulation-peptisation of colloidal sols) being confined in sample holders of varying size. The self-assembled aggregates represent critical self-similar equilibrium structures corres-ponding to rate determining complexes in kinetics. Overall, a self-consistent thermodynamic framework is established for the characterization of two- and three-dimensional phase separations in one-, two- and three-component systems. Copyright © 2018 Elsevier B.V. All rights reserved.

Job Oriented Training: Onderwijskundige Grondslag en Onderbouwing (Job Oriented Training: Foundation and Empirical Support)

DTIC Science & Technology

2008-07-01

die binmen defensie tot aanzien van de effecten van JOT onderwijs met het nieuwe leren terug te dan toe in gebruik waren bij het theorie - voeren is op...problemen in de uitvoerings- onderwijs; toepassing van JOT impliceerde Grondslag praktijk van datzeltde regulier onderwijs. dat er geen theorie meer...het rechte eind Opdrachtnummer Datum PROGRAMMA PROJECT juli 2008 Program mabegeleider Projectbegeleider Auteur (s) IkolP.M.. Bonen,dr. A.H. van der

Layer-dependent ferromagnetism in a van der Waals crystal down to the monolayer limit.

PubMed

Huang, Bevin; Clark, Genevieve; Navarro-Moratalla, Efrén; Klein, Dahlia R; Cheng, Ran; Seyler, Kyle L; Zhong, Ding; Schmidgall, Emma; McGuire, Michael A; Cobden, David H; Yao, Wang; Xiao, Di; Jarillo-Herrero, Pablo; Xu, Xiaodong

2017-06-07

Since the discovery of graphene, the family of two-dimensional materials has grown, displaying a broad range of electronic properties. Recent additions include semiconductors with spin-valley coupling, Ising superconductors that can be tuned into a quantum metal, possible Mott insulators with tunable charge-density waves, and topological semimetals with edge transport. However, no two-dimensional crystal with intrinsic magnetism has yet been discovered; such a crystal would be useful in many technologies from sensing to data storage. Theoretically, magnetic order is prohibited in the two-dimensional isotropic Heisenberg model at finite temperatures by the Mermin-Wagner theorem. Magnetic anisotropy removes this restriction, however, and enables, for instance, the occurrence of two-dimensional Ising ferromagnetism. Here we use magneto-optical Kerr effect microscopy to demonstrate that monolayer chromium triiodide (CrI 3 ) is an Ising ferromagnet with out-of-plane spin orientation. Its Curie temperature of 45 kelvin is only slightly lower than that of the bulk crystal, 61 kelvin, which is consistent with a weak interlayer coupling. Moreover, our studies suggest a layer-dependent magnetic phase, highlighting thickness-dependent physical properties typical of van der Waals crystals. Remarkably, bilayer CrI 3 displays suppressed magnetization with a metamagnetic effect, whereas in trilayer CrI 3 the interlayer ferromagnetism observed in the bulk crystal is restored. This work creates opportunities for studying magnetism by harnessing the unusual features of atomically thin materials, such as electrical control for realizing magnetoelectronics, and van der Waals engineering to produce interface phenomena.

Layer-dependent ferromagnetism in a van der Waals crystal down to the monolayer limit

DOE PAGES

Huang, Bevin; Clark, Genevieve; Navarro-Moratalla, Efrén; ...

2017-06-07

Since the celebrated discovery of graphene, the family of two-dimensional (2D) materials has grown to encompass a broad range of electronic properties. Recent additions include spin-valley coupled semiconductors, Ising superconductors that can be tuned into a quantum metal, possible Mott insulators with tunable charge-density waves, and topological semi-metals with edge transport. Despite this progress, there is still no 2D crystal with intrinsic magnetism, which would be useful for many technologies such as sensing, information, and data storage. Theoretically, magnetic order is prohibited in the 2D isotropic Heisenberg model at finite temperatures by the Mermin-Wagner theorem. However, magnetic anisotropy removes thismore » restriction and enables, for instance, the occurrence of 2D Ising ferromagnetism. Here, we use magneto-optical Kerr effect (MOKE) microscopy to demonstrate that monolayer chromium triiodide (CrI 3) is an Ising ferromagnet with out-of-plane spin orientation. Its Curie temperature of 45 K is only slightly lower than the 61 K of the bulk crystal, consistent with a weak interlayer coupling. Moreover, our studies suggest a layer-dependent magnetic phases, showcasing the hallmark thickness dependent physical properties typical of van der Waals crystals. Remarkably, bilayer CrI3 displays suppressed magnetization with a metamagnetic effect, while in trilayer the interlayer ferromagnetism observed in the bulk crystal is restored. Our work creates opportunities for studying magnetism by harnessing the unique features of atomically-thin materials, such as electrical control for realizing magnetoelectronics, and van der Waals engineering for novel interface phenomena.« less

Layer-dependent ferromagnetism in a van der Waals crystal down to the monolayer limit

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

Huang, Bevin; Clark, Genevieve; Navarro-Moratalla, Efrén

Since the celebrated discovery of graphene, the family of two-dimensional (2D) materials has grown to encompass a broad range of electronic properties. Recent additions include spin-valley coupled semiconductors, Ising superconductors that can be tuned into a quantum metal, possible Mott insulators with tunable charge-density waves, and topological semi-metals with edge transport. Despite this progress, there is still no 2D crystal with intrinsic magnetism, which would be useful for many technologies such as sensing, information, and data storage. Theoretically, magnetic order is prohibited in the 2D isotropic Heisenberg model at finite temperatures by the Mermin-Wagner theorem. However, magnetic anisotropy removes thismore » restriction and enables, for instance, the occurrence of 2D Ising ferromagnetism. Here, we use magneto-optical Kerr effect (MOKE) microscopy to demonstrate that monolayer chromium triiodide (CrI 3) is an Ising ferromagnet with out-of-plane spin orientation. Its Curie temperature of 45 K is only slightly lower than the 61 K of the bulk crystal, consistent with a weak interlayer coupling. Moreover, our studies suggest a layer-dependent magnetic phases, showcasing the hallmark thickness dependent physical properties typical of van der Waals crystals. Remarkably, bilayer CrI3 displays suppressed magnetization with a metamagnetic effect, while in trilayer the interlayer ferromagnetism observed in the bulk crystal is restored. Our work creates opportunities for studying magnetism by harnessing the unique features of atomically-thin materials, such as electrical control for realizing magnetoelectronics, and van der Waals engineering for novel interface phenomena.« less

Quantum 1/f Noise in Solid State Devices in Particular Hg(1-x)Cd(x)Te N(+)-P Diodes

DTIC Science & Technology

1989-05-15

1 / f noise in pentodes. 3. A. van der Ziel, P. H. Handel, X. C. Zhu, and K. H. Duh, "A theory of the Hooge parameters of solid-state...the progress reports 12. P. H. Hardel and A. van der Ziel, "Relativistic correction of the Hooge parameter for Umklapp 1 / f noise ," Physica, vol. 141B... Hooge parameter and of fundamental 1 / f noise sources. As a side result many quantum 1 / f noise formulas are verified

USAF Summer Faculty Research Program. 1981 Research Reports. Volume II.

DTIC Science & Technology

1981-10-01

Research Associate 17 (A) Spect roscop i( Analysis anld Opt. i n1iZaLtol on 1 Di. Larry R. Dalton the oxygen/ I od ine Chemica (tILase r and (8...theory appear in Fig. 7 where the inverse temper- ature dependence reflects the dominant influence of the van der Waals 2.7 attraction. Note that the...colinear geometry. Coltrin obtains a 13 depth of 6.9 kcal/mol vs. 2.7 kcal/mol obtained by Wilkins. Thus we expect more Coltrin trajectories to form van der

Rapid estimation of the electron correlation energy for van der Waals complexes RgX (Rg = Kr, Xe, X = Br, I)

NASA Astrophysics Data System (ADS)

Xinying, Li; Yongfang, Zhao; Xiaogong, Jing; Fengli, Liu; Fengyou, Hao

2006-01-01

We present the rules of electron correlation energies for RgX (Rg = Kr, Xe, X = Br, I) van der Waals (vdW) complex systems at CCSD(T) theoretical level with SDB-cc-pVQZ basis set by the Gaussian 98 program. A new method to derive the dispersion coefficient C6 by fitting the intermonomer electron correlation energies to C6R-6 function is introduced. The present C6 values are compared with the corresponding theoretical ones.

Anisotropic contribution to the van der Waals and the Casimir-Polder energies for CO2 and CH4 molecules near surfaces and thin films

NASA Astrophysics Data System (ADS)

Thiyam, Priyadarshini; Parashar, Prachi; Shajesh, K. V.; Persson, Clas; Schaden, Martin; Brevik, Iver; Parsons, Drew F.; Milton, Kimball A.; Malyi, Oleksandr I.; Boström, Mathias

2015-11-01

In order to understand why carbon dioxide (CO2) and methane (CH4) molecules interact differently with surfaces, we investigate the Casimir-Polder energy of a linearly polarizable CO2 molecule and an isotropically polarizable CH4 molecule in front of an atomically thin gold film and an amorphous silica slab. We quantitatively analyze how the anisotropy in the polarizability of the molecule influences the van der Waals contribution to the binding energy of the molecule.

Synchronous Oscillations in Van Der Pol Generator with Modulated Natural Frequency

NASA Astrophysics Data System (ADS)

Nimets, A. Yu.; Vavriv, D. M.

2015-12-01

The synchronous operation of Van Der Pole generator with the low-frequency modulated natural frequency has been investigated. The presence of low-frequency modulation is shown to lead to formation of additional synchronization regions. The appearance of such regions is found to be caused by threefrequency resonances resulted from the interaction between oscillations of the generator natural frequency, modulation frequency and synchronized signal frequency. Characteristics of synchronous oscillations due to the below mentioned three-frequency interaction are obtained and comparison with the case of synchronization of oscillator on the main mode made.

Effects of van der Waals Interactions in the Adsorption of Isooctane and Ethanol on Fe(100) Surfaces

PubMed Central

2014-01-01

van der Waals (vdW) forces play a fundamental role in the structure and behavior of diverse systems. Because of development of functionals that include nonlocal correlation, it is possible to study the effects of vdW interactions in systems of industrial and tribological interest. Here we simulated within the framework of density functional theory (DFT) the adsorption of isooctane (2,2,4-trimethylpentane) and ethanol on an Fe(100) surface, employing various exchange–correlation functionals to take vdW forces into account. In particular, this paper discusses the effect of vdW forces on the magnitude of adsorption energies, equilibrium geometries, and their role in the binding mechanism. According to our calculations, vdW interactions increase the adsorption energies and reduce the equilibrium distances. Nevertheless, they do not influence the spatial configuration of the adsorbed molecules. Their effect on the electronic density is a nonisotropic, delocalized accumulation of charge between the molecule and the slab. In conclusion, vdW forces are essential for the adsorption of isooctane and ethanol on a bcc Fe(100) surface. PMID:25126156

Theory of gas hydrates: effect of the approximation of rigid water lattice.

PubMed

Pimpalgaonkar, Hrushikesh; Veesam, Shivanand K; Punnathanam, Sudeep N

2011-08-25

One of the assumptions of the van der Waals and Platteeuw theory for gas hydrates is that the host water lattice is rigid and not distorted by the presence of guest molecules. In this work, we study the effect of this approximation on the triple-point lines of the gas hydrates. We calculate the triple-point lines of methane and ethane hydrates via Monte Carlo molecular simulations and compare the simulation results with the predictions of van der Waals and Platteeuw theory. Our study shows that even if the exact intermolecular potential between the guest molecules and water is known, the dissociation temperatures predicted by the theory are significantly higher. This has serious implications to the modeling of gas hydrate thermodynamics, and in spite of the several impressive efforts made toward obtaining an accurate description of intermolecular interactions in gas hydrates, the theory will suffer from the problem of robustness if the issue of movement of water molecules is not adequately addressed. © 2011 American Chemical Society

Two-dimensional n -InSe/p -GeSe(SnS) van der Waals heterojunctions: High carrier mobility and broadband performance

NASA Astrophysics Data System (ADS)

Xia, Cong-xin; Du, Juan; Huang, Xiao-wei; Xiao, Wen-bo; Xiong, Wen-qi; Wang, Tian-xing; Wei, Zhong-ming; Jia, Yu; Shi, Jun-jie; Li, Jing-bo

2018-03-01

Recently, constructing van der Waals (vdW) heterojunctions by stacking different two-dimensional (2D) materials has been considered to be effective strategy to obtain the desired properties. Here, through first-principles calculations, we find theoretically that the 2D n -InSe/p -GeSe(SnS) vdW heterojunctions are the direct-band-gap semiconductor with typical type-II band alignment, facilitating the effective separation of photogenerated electron and hole pairs. Moreover, they possess the high optical absorption strength (˜105 ), broad spectrum width, and excellent carrier mobility (˜103c m2V-1s-1 ). Interestingly, under the influences of the interlayer coupling and external electric field, the characteristics of type-II band alignment is robust, while the band-gap values and band offset are tunable. These results indicate that 2D n -InSe/p -GeSe(SnS) heterojunctions possess excellent optoelectronic and transport properties, and thus can become good candidates for next-generation optoelectronic nanodevices.

Speed Measuring System (Detectoren en Signaalbewerking Voor Het Snelheidsmeetsysteem 4-01)

DTIC Science & Technology

1989-03-01

een hogere nauwkeurigheid te halen dan san de voet van bet signasi mogelijk is bij een grote signaalaniplitude, Wanneer de S/L < 6 is wordt de drempel...snelheidsmeetsysteem 4-01 Niets Uilf deze ultgave mag worden vermenigvuldigd en of openbaar gemaakt door mlddel van druk fotokope microfilm autour~s): of op welke...andere wijze dan 006 zonder voorafgaarode toestemming van TNO J. van der Haven Hetlter I zage geven van net TNO-rappoit aan direct belanghebbenoen is

Anisotropic instability of a stretching film

NASA Astrophysics Data System (ADS)

Xu, Bingrui; Li, Minhao; Deng, Daosheng

2017-11-01

Instability of a thin liquid film, such as dewetting arising from Van der Waals force, has been well studied, and is typically characterized by formation of many droplets. Interestingly, a thin liquid film subjected to an applied stretching during a process of thermal drawing is evolved into an array of filaments, i.e., continuity is preserved along the direction of stretching while breakup occurs exclusively in the plane of cross section. Here, to understand this anisotropic instability, we build a physical model by considering both Van der Waals force and the effect of stretching. By using the linear instability analysis method and then performing a numerical calculation, we find that the growth rate of perturbations at the cross section is larger than that along the direction of stretching, resulting in the anisotropic instability of the stretching film. These results may provide theoretical guidance to achieve more diverse structures for nanotechnology.

Multidisciplinary management of a patient with van der Woude syndrome: A case report.

PubMed

Tehranchi, Azita; Behnia, Hossein; Nadjmi, Nasser; Yassaee, Vahid Reza; Ravesh, Zeinab; Mina, Morteza

2017-01-01

Van der Woude syndrome (VWS) is the most frequent form of syndromic cleft lip and palate (SCLP) accounting for 2% of all patients with CLP. We describe the orthodontic treatment of a girl diagnosed with VWS referred by her family dentist for her cosmetic concerns. Comprehensive orthodontic treatment, secondary bone graft, distraction osteogenesis (for a deficient maxilla), secondary palatoplasty and excision of lower lip pits, as well as orthodontic and prosthetic procedures may provide a satisfactory outcome. Genetic testing showed a known putative splice site mutation (c.174+1G/A) as the prime cause of VWS in our patient and her family. SCLP has significant effects on facial aesthetics and the psychosocial status. Parents should be assessed and counseled appropriately. This condition is treatable in the absence of life threatening systemic anomalies. An interdisciplinary team approach is advocated. Copyright © 2016 The Author(s). Published by Elsevier Ltd.. All rights reserved.

Thermodynamics and phase transition of charged AdS black holes with a global monopole

NASA Astrophysics Data System (ADS)

Deng, Gao-Ming; Fan, Jinbo; Li, Xinfei; Huang, Yong-Chang

2018-01-01

Thermodynamical properties of charged AdS black holes with a global monopole still remain obscure. In this paper, we investigate the thermodynamics and phase transition of the black holes in the extended phase space. It is shown that thermodynamical quantities of the black holes exhibit an interesting dependence on the internal global monopole, and they perfectly satisfy both the first law of thermodynamics and Smarr relation. Furthermore, analysis of the local and the global thermodynamical stability manifests that the charged AdS black hole undergoes an elegant phase transition at critical point. Of special interest, critical behaviors of the black holes resemble a Van der Waals liquid-gas system. Our results not only reveal the effect of a global monopole on thermodynamics of AdS black holes, but also further support that Van der Waals-like behavior of the black holes is a universal phenomenon.

Crystal-phase intergradation in InAs nanostructures grown by van der Waals heteroepitaxy on graphene

NASA Astrophysics Data System (ADS)

Choi, Ji Eun; Yoo, Jinkyoung; Lee, Donghwa; Hong, Young Joon; Fukui, Takashi

2018-04-01

This study demonstrates the crystal-phase intergradation of InAs nanostructures grown on graphene via van der Waals epitaxy. InAs nanostructures with diverse diameters are yielded on graphene. High-resolution transmission electron microscopy (HR-TEM) reveals two crystallographic features of (i) wurtzite (WZ)-to-zinc blende (ZB) intergradation along the growth direction of InAs nanostructures and (ii) an increased mean fraction of ZB according to diameter increment. Based on the HR-TEM observations, a crystal-phase intergradation diagram is depicted. We discuss how the formation of a WZ-rich phase during the initial growth stage is an effective way of releasing heterointerfacial stress endowed by the lattice mismatch of InAs/graphene for energy minimization in terms of less in-plane lattice mismatching between WZ-InAs and graphene. The WZ-to-ZB evolution is responsible for the attenuation of the bottom-to-top surface charge interaction as growth proceeds.

Investigation of a van der Waals complex with C 1 symmetry: the free-jet rotational spectrum of 1,2-difluoroethane-Ar

NASA Astrophysics Data System (ADS)

Melandri, Sonia; Velino, Biagio; Favero, Paolo G.; Dell'Erba, Adele; Caminati, Walther

2000-04-01

The van der Waals complex between Ar and 1,2-difluoroethane has been investigated by free-jet absorption millimeter-wave spectroscopy in the frequency range 60-78 GHz. The analysis of the spectroscopic constants derived from the rotational spectrum allowed the determination of the dimer's structure. 1,2-Difluoroethane is in the gauche conformation and the Ar atom is in a position stabilized by the interaction with one fluorine and the two carbon atoms. The distance between Ar and the center of mass (CM) of the monomer is 3.968 Å, the angle between the Ar-CM line and the C-C bond is 65° and the dihedral angle Ar-CM-C-C is 99°. From centrifugal distortion effects the dissociation energy of the complex has been estimated to be 2.1 kJ/mol.

Analytical theory of the hydrophobic effect of solutes in water.

PubMed

Urbic, Tomaz; Dill, Ken A

2017-09-01

We develop an analytical statistical-mechanical model for hydrophobic solvation in water. In this three-dimensional Mercedes-Benz-like model, two neighboring waters have three possible interaction states: a radial van der Waals interaction, a tetrahedral orientation-dependent hydrogen-bonding interaction, or no interaction. Nonpolar solutes are modeled as van der Waals particles of different radii. The model is sufficiently simple that we can calculate the partition function and thermal and volumetric properties of solvation versus temperature, pressure, and solute radius. Predictions are in good agreement with results of Monte Carlo simulations. And their trends agree with experiments on hydrophobic solute insertion. The theory shows that first-shell waters are more highly structured than bulk waters, because of hydrogen bonding, and that that structure melts out faster with temperature than it does in bulk waters. Because the theory is analytical, it can explore a broad range of solvation properties and anomalies of water, at minimal computational expense.

Analytical theory of the hydrophobic effect of solutes in water

NASA Astrophysics Data System (ADS)

Urbic, Tomaz; Dill, Ken A.

2017-09-01

We develop an analytical statistical-mechanical model for hydrophobic solvation in water. In this three-dimensional Mercedes-Benz-like model, two neighboring waters have three possible interaction states: a radial van der Waals interaction, a tetrahedral orientation-dependent hydrogen-bonding interaction, or no interaction. Nonpolar solutes are modeled as van der Waals particles of different radii. The model is sufficiently simple that we can calculate the partition function and thermal and volumetric properties of solvation versus temperature, pressure, and solute radius. Predictions are in good agreement with results of Monte Carlo simulations. And their trends agree with experiments on hydrophobic solute insertion. The theory shows that first-shell waters are more highly structured than bulk waters, because of hydrogen bonding, and that that structure melts out faster with temperature than it does in bulk waters. Because the theory is analytical, it can explore a broad range of solvation properties and anomalies of water, at minimal computational expense.

Controlling the electronic properties of van der Waals heterostructures by applying electrostatic design

NASA Astrophysics Data System (ADS)

Winkler, Christian; Harivyasi, Shashank S.; Zojer, Egbert

2018-07-01

Van der Waals heterostructures based on the heteroassembly of 2D materials represent a recently developed class of materials with promising properties especially for optoelectronic applications. The alignment of electronic energy bands between consecutive layers of these heterostructures crucially determines their functionality. In the present paper, relying on dispersion-corrected density-functional theory calculations, we present electrostatic design as a promising tool for manipulating this band alignment. The latter is achieved by inserting a layer of aligned polar molecules between consecutive transition-metal dichalcogenide (TMD) sheets. As a consequence, collective electrostatic effects induce a shift of as much as 0.3 eV in the band edges of successive TMD layers. Building on that, the proposed approach can be used to design electronically more complex systems, like quantum cascades or quantum wells, or to change the type of band lineup between type II and type I.

Electronic cooling via interlayer Coulomb coupling in multilayer epitaxial graphene

PubMed Central

Mihnev, Momchil T.; Tolsma, John R.; Divin, Charles J.; Sun, Dong; Asgari, Reza; Polini, Marco; Berger, Claire; de Heer, Walt A.; MacDonald, Allan H.; Norris, Theodore B.

2015-01-01

In van der Waals bonded or rotationally disordered multilayer stacks of two-dimensional (2D) materials, the electronic states remain tightly confined within individual 2D layers. As a result, electron–phonon interactions occur primarily within layers and interlayer electrical conductivities are low. In addition, strong covalent in-plane intralayer bonding combined with weak van der Waals interlayer bonding results in weak phonon-mediated thermal coupling between the layers. We demonstrate here, however, that Coulomb interactions between electrons in different layers of multilayer epitaxial graphene provide an important mechanism for interlayer thermal transport, even though all electronic states are strongly confined within individual 2D layers. This effect is manifested in the relaxation dynamics of hot carriers in ultrafast time-resolved terahertz spectroscopy. We develop a theory of interlayer Coulomb coupling containing no free parameters that accounts for the experimentally observed trends in hot-carrier dynamics as temperature and the number of layers is varied. PMID:26399955

Chaotic Oscillations of Second Order Linear Hyperbolic Equations with Nonlinear Boundary Conditions: A Factorizable but Noncommutative Case

NASA Astrophysics Data System (ADS)

Li, Liangliang; Huang, Yu; Chen, Goong; Huang, Tingwen

If a second order linear hyperbolic partial differential equation in one-space dimension can be factorized as a product of two first order operators and if the two first order operators commute, with one boundary condition being the van der Pol type and the other being linear, one can establish the occurrence of chaos when the parameters enter a certain regime [Chen et al., 2014]. However, if the commutativity of the two first order operators fails to hold, then the treatment in [Chen et al., 2014] no longer works and significant new challenges arise in determining nonlinear boundary conditions that engenders chaos. In this paper, we show that by incorporating a linear memory effect, a nonlinear van der Pol boundary condition can cause chaotic oscillations when the parameter enters a certain regime. Numerical simulations illustrating chaotic oscillations are also presented.

A semi-floating gate memory based on van der Waals heterostructures for quasi-non-volatile applications

NASA Astrophysics Data System (ADS)

Liu, Chunsen; Yan, Xiao; Song, Xiongfei; Ding, Shijin; Zhang, David Wei; Zhou, Peng

2018-05-01

As conventional circuits based on field-effect transistors are approaching their physical limits due to quantum phenomena, semi-floating gate transistors have emerged as an alternative ultrafast and silicon-compatible technology. Here, we show a quasi-non-volatile memory featuring a semi-floating gate architecture with band-engineered van der Waals heterostructures. This two-dimensional semi-floating gate memory demonstrates 156 times longer refresh time with respect to that of dynamic random access memory and ultrahigh-speed writing operations on nanosecond timescales. The semi-floating gate architecture greatly enhances the writing operation performance and is approximately 106 times faster than other memories based on two-dimensional materials. The demonstrated characteristics suggest that the quasi-non-volatile memory has the potential to bridge the gap between volatile and non-volatile memory technologies and decrease the power consumption required for frequent refresh operations, enabling a high-speed and low-power random access memory.

Giant tunneling magnetoresistance in spin-filter van der Waals heterostructures

DOE PAGES

Song, Tiancheng; Cai, Xinghan; Tu, Matisse Wei-Yuan; ...

2018-05-03

Magnetic multilayer devices that exploit magnetoresistance are the backbone of magnetic sensing and data storage technologies. Here, we report multiple-spin-filter magnetic tunnel junctions (sf-MTJs) based on van der Waals (vdW) heterostructures in which atomically thin chromium triiodide (CrI3) acts as a spin-filter tunnel barrier sandwiched between graphene contacts. We demonstrate tunneling magnetoresistance which is drastically enhanced with increasing CrI 3 layer thickness, reaching a record 19,000% for magnetic multilayer structures using four-layer sf-MTJs at low temperatures. Using magnetic circular dichroism measurements, we attribute these effects to the intrinsic layer-by-layer antiferromagnetic ordering of the atomically thin CrI 3. In conclusion, ourmore » work reveals the possibility to push magnetic information storage to the atomically thin limit and highlights CrI 3 as a superlative magnetic tunnel barrier for vdW heterostructure spintronic devices.« less

Giant tunneling magnetoresistance in spin-filter van der Waals heterostructures

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

Song, Tiancheng; Cai, Xinghan; Tu, Matisse Wei-Yuan

Magnetic multilayer devices that exploit magnetoresistance are the backbone of magnetic sensing and data storage technologies. Here, we report multiple-spin-filter magnetic tunnel junctions (sf-MTJs) based on van der Waals (vdW) heterostructures in which atomically thin chromium triiodide (CrI3) acts as a spin-filter tunnel barrier sandwiched between graphene contacts. We demonstrate tunneling magnetoresistance which is drastically enhanced with increasing CrI 3 layer thickness, reaching a record 19,000% for magnetic multilayer structures using four-layer sf-MTJs at low temperatures. Using magnetic circular dichroism measurements, we attribute these effects to the intrinsic layer-by-layer antiferromagnetic ordering of the atomically thin CrI 3. In conclusion, ourmore » work reveals the possibility to push magnetic information storage to the atomically thin limit and highlights CrI 3 as a superlative magnetic tunnel barrier for vdW heterostructure spintronic devices.« less

van der Waals criticality in AdS black holes: A phenomenological study

NASA Astrophysics Data System (ADS)

Bhattacharya, Krishnakanta; Majhi, Bibhas Ranjan; Samanta, Saurav

2017-10-01

Anti-de Sitter black holes exhibit van der Waals-type phase transition. In the extended phase-space formalism, the critical exponents for any spacetime metric are identical to the standard ones. Motivated by this fact, we give a general expression for the Helmholtz free energy near the critical point, which correctly reproduces these exponents. The idea is similar to the Landau model, which gives a phenomenological description of the usual second-order phase transition. Here, two main inputs are taken into account for the analysis: (a) black holes should have van der Waals-like isotherms, and (b) free energy can be expressed solely as a function of thermodynamic volume and horizon temperature. Resulting analysis shows that the form of Helmholtz free energy correctly encapsulates the features of the Landau function. We also discuss the isolated critical point accompanied by nonstandard values of critical exponents. The whole formalism is then extended to two other criticalities, namely, Y -X and T -S (based on the standard; i.e., nonextended phase space), where X and Y are generalized force and displacement, whereas T and S are the horizon temperature and entropy. We observe that in the former case Gibbs free energy plays the role of Landau function, whereas in the later case, that role is played by the internal energy (here, it is the black hole mass). Our analysis shows that, although the existence of a van der Waals phase transition depends on the explicit form of the black hole metric, the values of the critical exponents are universal in nature.

Ultrafast Interlayer Electron Transfer in Incommensurate Transition Metal Dichalcogenide Homobilayers.

PubMed

Li, Yuanyuan; Cui, Qiannan; Ceballos, Frank; Lane, Samuel D; Qi, Zeming; Zhao, Hui

2017-11-08

Two-dimensional materials, such as graphene, transition metal dichalcogenides, and phosphorene, can be used to construct van der Waals multilayer structures. This approach has shown potentials to produce new materials that combine novel properties of the participating individual layers. One key requirement for effectively harnessing emergent properties of these materials is electronic connection of the involved atomic layers through efficient interlayer charge or energy transfer. Recently, ultrafast charge transfer on a time scale shorter than 100 fs has been observed in several van der Waals bilayer heterostructures formed by two different materials. However, information on the transfer between two atomic layers of the same type is rare. Because these homobilayers are essential elements in constructing multilayer structures with desired optoelectronic properties, efficient interlayer transfer is highly desired. Here we show that electron transfer between two monolayers of MoSe 2 occurs on a picosecond time scale. Even faster transfer was observed in homobilayers of WS 2 and WSe 2 . The samples were fabricated by manually stacking two exfoliated monolayer flakes. By adding a graphene layer as a fast carrier recombination channel for one of the two monolayers, the transfer of the photoexcited carriers from the populated to the drained monolayers was time-resolved by femtosecond transient absorption measurements. The observed efficient interlayer carrier transfer indicates that such homobilayers can be used in van der Waals multilayers to enhance their optical absorption without significantly compromising the interlayer transport performance. Our results also provide valuable information for understanding interlayer charge transfer in heterostructures.

van der Waals epitaxy of Ge films on mica

NASA Astrophysics Data System (ADS)

Littlejohn, A. J.; Xiang, Y.; Rauch, E.; Lu, T.-M.; Wang, G.-C.

2017-11-01

To date, many materials have been successfully grown on substrates through van der Waals epitaxy without adhering to the constraint of lattice matching as is required for traditional chemical epitaxy. However, for elemental semiconductors such as Ge, this has been challenging and therefore it has not been achieved thus far. In this paper, we report the observation of Ge epitaxially grown on mica at a narrow substrate temperature range around 425 °C. Despite the large lattice mismatch (23%) and the lack of high in-plane symmetry in the mica surface, an epitaxial Ge film with [111] out-of-plane orientation is observed. Crystallinity and electrical properties degrade upon deviation from the ideal growth temperature, as shown by Raman spectroscopy, X-ray diffraction, and Hall effect measurements. X-ray pole figure analysis reveals that there exist multiple rotational domains in the epitaxial Ge film with dominant in-plane orientations between Ge [" separators="|1 ¯10 ] and mica[100] of (20 n )°, where n = 0, 1, 2, 3, 4, 5. A superlattice area mismatch model was used to account for the likelihood of the in-plane orientation formation and was found to be qualitatively consistent with the observed dominant orientations. Our observation of Ge epitaxy with one out-of-plane growth direction through van der Waals forces is a step toward the growth of single crystal Ge films without the constraint in the lattice and symmetry matches with the substrates.

Structural Dynamics Investigation of Human Family 1 & 2 Cystatin-Cathepsin L1 Interaction: A Comparison of Binding Modes

PubMed Central

Nandy, Suman Kumar; Seal, Alpana

2016-01-01

Cystatin superfamily is a large group of evolutionarily related proteins involved in numerous physiological activities through their inhibitory activity towards cysteine proteases. Despite sharing the same cystatin fold, and inhibiting cysteine proteases through the same tripartite edge involving highly conserved N-terminal region, L1 and L2 loop; cystatins differ widely in their inhibitory affinity towards C1 family of cysteine proteases and molecular details of these interactions are still elusive. In this study, inhibitory interactions of human family 1 & 2 cystatins with cathepsin L1 are predicted and their stability and viability are verified through protein docking & comparative molecular dynamics. An overall stabilization effect is observed in all cystatins on complex formation. Complexes are mostly dominated by van der Waals interaction but the relative participation of the conserved regions varied extensively. While van der Waals contacts prevail in L1 and L2 loop, N-terminal segment chiefly acts as electrostatic interaction site. In fact the comparative dynamics study points towards the instrumental role of L1 loop in directing the total interaction profile of the complex either towards electrostatic or van der Waals contacts. The key amino acid residues surfaced via interaction energy, hydrogen bonding and solvent accessible surface area analysis for each cystatin-cathepsin L1 complex influence the mode of binding and thus control the diverse inhibitory affinity of cystatins towards cysteine proteases. PMID:27764212

Probing hydrogen bond potentials via combination band spectroscopy: A near infrared study of the geared bend/van der Waals stretch intermolecular modes in (HF)2

NASA Astrophysics Data System (ADS)

Anderson, David T.; Davis, Scott; Nesbitt, David J.

1996-04-01

High resolution near infrared spectra of the two lowest frequency intermolecular modes in HF-stretch excited states of (HF)2 have been characterized using a slit-jet infrared spectrometer. In the spectral region surveyed, ten vibration-rotation-tunneling (VRT) bands are observed and assigned to the low frequency ``van der Waals stretch'' (ν4) and ``geared bend'' (ν5) intermolecular modes, in combination with either the hydrogen bond acceptor (ν1) or donor (ν2) high-frequency intramolecular HF stretches. Analysis of the rotationally resolved spectra provide intermolecular frequencies, rotational constants, tunneling splittings, and predissociation rates for the ν4/ν5 intermolecular excited states. The intermolecular vibrational frequencies in the combination states display a systematic dependence on intramolecular redshift that allows far-IR intermolecular frequencies to be reliably extrapolated from the near-IR data. Approximately tenfold increases in the hydrogen bond interconversion tunneling splittings with either ν4 or ν5 excitation indicate that both intermolecular modes correlate strongly to the tunneling coordinate. The high resolution VRT line shapes reveal mode specific predissociation broadening sensitive predominantly to intramolecular excitation, with weaker but significant additional effects due to low frequency intermolecular excitation. Analysis of the high resolution spectroscopic data for these ν4 and ν5 combination bands suggests strong state mixing between what has previously been considered van der Waals stretch and geared bend degrees of freedom.

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

NASA Astrophysics Data System (ADS)

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

2017-09-01

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

Combination Rules for Morse-Based van der Waals Force Fields.

PubMed

Yang, Li; Sun, Lei; Deng, Wei-Qiao

2018-02-15

In traditional force fields (FFs), van der Waals interactions have been usually described by the Lennard-Jones potentials. Conventional combination rules for the parameters of van der Waals (VDW) cross-termed interactions were developed for the Lennard-Jones based FFs. Here, we report that the Morse potentials were a better function to describe VDW interactions calculated by highly precise quantum mechanics methods. A new set of combination rules was developed for Morse-based FFs, in which VDW interactions were described by Morse potentials. The new set of combination rules has been verified by comparing the second virial coefficients of 11 noble gas mixtures. For all of the mixed binaries considered in this work, the combination rules work very well and are superior to all three other existing sets of combination rules reported in the literature. We further used the Morse-based FF by using the combination rules to simulate the adsorption isotherms of CH 4 at 298 K in four covalent-organic frameworks (COFs). The overall agreement is great, which supports the further applications of this new set of combination rules in more realistic simulation systems.

Optical spectroscopy of excited exciton states in MoS2 monolayers in van der Waals heterostructures

NASA Astrophysics Data System (ADS)

Robert, C.; Semina, M. A.; Cadiz, F.; Manca, M.; Courtade, E.; Taniguchi, T.; Watanabe, K.; Cai, H.; Tongay, S.; Lassagne, B.; Renucci, P.; Amand, T.; Marie, X.; Glazov, M. M.; Urbaszek, B.

2018-01-01

The optical properties of MoS2 monolayers are dominated by excitons, but for spectrally broad optical transitions in monolayers exfoliated directly onto SiO2 substrates detailed information on excited exciton states is inaccessible. Encapsulation in hexagonal boron nitride (hBN) allows approaching the homogenous exciton linewidth, but interferences in the van der Waals heterostructures make direct comparison between transitions in optical spectra with different oscillator strength more challenging. Here we reveal in reflectivity and in photoluminescence excitation spectroscopy the presence of excited states of the A exciton in MoS2 monolayers encapsulated in hBN layers of calibrated thickness, allowing us to extrapolate an exciton binding energy of ≈220 meV. We theoretically reproduce the energy separations and oscillator strengths measured in reflectivity by combining the exciton resonances calculated for a screened two-dimensional Coulomb potential with transfer matrix calculations of the reflectivity for the van der Waals structure. Our analysis shows a very different evolution of the exciton oscillator strength with principal quantum number for the screened Coulomb potential as compared to the ideal two-dimensional hydrogen model.

Tunable two-dimensional interfacial coupling in molecular heterostructures

DOE PAGES

Xu, Beibei; Chakraborty, Himanshu; Yadav, Vivek K.; ...

2017-08-22

Two-dimensional van der Waals heterostructures are of considerable interest for the next generation nanoelectronics because of their unique interlayer coupling and optoelectronic properties. Here, we report a modified Langmuir–Blodgett method to organize twodimensional molecular charge transfer crystals into arbitrarily and vertically stacked heterostructures, consisting of bis(ethylenedithio)tetrathiafulvalene (BEDT–TTF)/C 60 and poly (3-dodecylthiophene-2,5-diyl) (P3DDT)/C 60 nanosheets. A strong and anisotropic interfacial coupling between the charge transfer pairs is demonstrated. The van der Waals heterostructures exhibit pressure dependent sensitivity with a high piezoresistance coefficient of -4.4 × 10 -6 Pa -1, and conductance and capacitance tunable by external stimuli (ferroelectric field and magneticmore » field). Density functional theory calculations confirm charge transfer between the n-orbitals of the S atoms in BEDT–TTF of the BEDT–TTF/C 60 layer and the π* orbitals of C atoms in C 60 of the P3DDT/C 60 layer contribute to the inter-complex CT. Thus, the two-dimensional molecular van der Waals heterostructures with tunable optical–electronic–magnetic coupling properties are promising for flexible electronic applications.« less

Exciton–polaritons in van der Waals heterostructures embedded in tunable microcavities

PubMed Central

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

Ultra-confined surface phonon polaritons in molecular layers of van der Waals dielectrics.

PubMed

Dubrovkin, Alexander M; Qiang, Bo; Krishnamoorthy, Harish N S; Zheludev, Nikolay I; Wang, Qi Jie

2018-05-02

Improvements in device density in photonic circuits can only be achieved with interconnects exploiting highly confined states of light. Recently this has brought interest to highly confined plasmon and phonon polaritons. While plasmonic structures have been extensively studied, the ultimate limits of phonon polariton squeezing, in particular enabling the confinement (the ratio between the excitation and polariton wavelengths) exceeding 10 2 , is yet to be explored. Here, exploiting unique structure of 2D materials, we report for the first time that atomically thin van der Waals dielectrics (e.g., transition-metal dichalcogenides) on silicon carbide substrate demonstrate experimentally record-breaking propagating phonon polaritons confinement resulting in 190-times squeezed surface waves. The strongly dispersive confinement can be potentially tuned to greater than 10 3 near the phonon resonance of the substrate, and it scales with number of van der Waals layers. We argue that our findings are a substantial step towards infrared ultra-compact phonon polaritonic circuits and resonators, and would stimulate further investigations on nanophotonics in non-plasmonic atomically thin interface platforms.

Enhancing Student Motivation: A Longitudinal Intervention Study Based on Future Time Perspective Theory

ERIC Educational Resources Information Center

Schuitema, Jaap; Peetsma, Thea; van der Veen, Ineke

2014-01-01

The authors investigated the effects of an intervention developed to enhance student motivation in the first years of secondary education. The intervention, based on future time perspective (FTP) theory, has been found to be effective in prevocational secondary education (T. T. D. Peetsma & I. Van der Veen, 2008, 2009). The authors extend the…

Self-similarity and scaling transitions during rupture of thin free films of Newtonian fluids

NASA Astrophysics Data System (ADS)

Thete, Sumeet Suresh; Anthony, Christopher; Doshi, Pankaj; Harris, Michael T.; Basaran, Osman A.

2016-09-01

Rupture of thin liquid films is crucial in many industrial applications and nature such as foam stability in oil-gas separation units, coating flows, polymer processing, and tear films in the eye. In some of these situations, a liquid film may have two free surfaces (referred to here as a free film or a sheet) as opposed to a film deposited on a solid substrate that has one free surface. The rupture of such a free film or a sheet of a Newtonian fluid is analyzed under the competing influences of inertia, viscous stress, van der Waals pressure, and capillary pressure by solving a system of spatially one-dimensional evolution equations for film thickness and lateral velocity. The dynamics close to the space-time singularity where the film ruptures is asymptotically self-similar and, therefore, the problem is also analyzed by reducing the transient partial differential evolution equations to a corresponding set of ordinary differential equations in similarity space. For sheets with negligible inertia, it is shown that the dominant balance of forces involves solely viscous and van der Waals forces, with capillary force remaining negligible throughout the thinning process in a viscous regime. On the other hand, for a sheet of an inviscid fluid for which the effect of viscosity is negligible, it is shown that the dominant balance of forces is between inertial, capillary, and van der Waals forces as the film evolves towards rupture in an inertial regime. Real fluids, however, have finite viscosity. Hence, for real fluids, it is further shown that the viscous and the inertial regimes are only transitory and can only describe the initial thinning dynamics of highly viscous and slightly viscous sheets, respectively. Moreover, regardless of the fluid's viscosity, it is shown that for sheets that initially thin in either of these two regimes, their dynamics transition to a late stage or final inertial-viscous regime in which inertial, viscous, and van der Waals forces balance each other while capillary force remains negligible, in accordance with the results of Vaynblat, Lister, and Witelski.

Self-Directed Workplace Learning.

ERIC Educational Resources Information Center

1998

This document contains four papers from a symposium on self-directed workplace learning. "Self-Directed Work Teams: Implementation and Performance" (Marcel van der Klink, Hilde ter Horst) discusses the results of a study examining the implementation and effects of self-directed work teams in a land register office and the role of the…

Investigating Intermolecular Interactions via Scanning Tunneling Microscopy: An Experiment for the Physical Chemistry Laboratory

ERIC Educational Resources Information Center

Pullman, David; Peterson, Karen I.

2004-01-01

A scanning tunneling microscope (STM) project designed as a module for the undergraduate physical chemistry laboratory is described. The effects of van der Waals interactions on the condensed-phase structure are examined by the analysis of the pattern of the monolayer structures.

Analysis of defect structure in silicon. Effect of grain boundary density on carrier mobility in UCP material

NASA Technical Reports Server (NTRS)

Dunn, J.; Stringfellow, G. B.; Natesh, R.

1982-01-01

The relationships between hole mobility and grain boundary density were studied. Mobility was measured using the van der Pauw technique, and grain boundary density was measured using a quantitative microscopy technique. Mobility was found to decrease with increasing grain boundary density.

Toward an Operational Definition of Cross-Cultural Competence from the Literature

DTIC Science & Technology

2008-01-01

Journal of Applied Psychology, 73, 410-420. Mol, S. T., Born, M. P., Willemsen, M. E., & Van Der Molen , H. T. (2005). Predicting expatriate job...decision-making processes (Ang, Van Dyne, Koh, & Ng, 2004; Ang, Van Dyne, & Koh, 2007). Because the CQ has demonstrated validity and covers the...empirical foundation. U.S. Army Research Institute for the Behavioral and Social Sciences, Study Report 2008-1. Arlington, VA: ARI. Ang, S., Van Dyne, L

Decoupling interface effect on the phase stability of CdS thin films by van der Waals heteroepitaxy

NASA Astrophysics Data System (ADS)

Sun, Xin; Wang, Yiping; Seewald, Lucas J.; Chen, Zhizhong; Shi, Jian; Washington, Morris A.; Lu, Toh-Ming

2017-01-01

Wurtzite (W) and zinc-blende (ZB) polytypism has long been observed in epitaxial CdS thin films. The present work, based on van der Waals epitaxial CdS thin films, is an attempt to explain which crystal modification, W or ZB, is favored under different growth conditions. In this van der Waals epitaxy system where the substrate influence is considered weak, it is found that the substrate temperature plays a crucial role in determining the crystal modification of CdS, that is, W and ZB CdS are more stable at low and high ends of substrate temperature, respectively. We attribute this temperature effect to the entropy difference (SW < SZB), a conclusion well supported by the thermodynamic hard sphere model formulation of the entropy difference between hexagonal close-packed and face-centered cubic structures. By summarizing other works, we find that the entropy difference model can also be applied to large mismatched (≳3%) CdS-substrate chemical epitaxy systems but not for small mismatched (≲3%) ones. In the latter case, the energy benefit in terms of high density of bonding contributed by the substrate-film interface is believed to be too overwhelming for the intrinsic entropy difference to overcome. Furthermore, the deposition rate is found to affect the crystalline quality and strain level in CdS films but not the crystal modification of the CdS films. Last, Raman and photoluminescence spectroscopies reveal the strain behaviors in the films. The phase change from W to ZB CdS is well-correlated with the observed peak shifts in Raman and photoluminescence spectroscopies.

Van der Waals pressure sensors using reduced graphene oxide composites

NASA Astrophysics Data System (ADS)

Jung, Ju Ra; Ahn, Sung Il

2018-04-01

Reduced graphene oxide (RGO) films intercalated with various polymers were fabricated by reaction-based self-assembly, and their characteristics as vacuum pressure sensors based on van der Waals interactions were studied. At low temperature, the electrical resistances of the samples decrease linearly with increasing vacuum pressure, whereas at high temperature the variation of the electrical resistance shows secondary order curves. Among all samples, the poly vinyl alcohol intercalated RGO shows the highest sensitivity, being almost two times more sensitive than reference RGO. All samples show almost the same signal for repetitive sudden pressure changes, indicating reasonable reproducibility and durability.

Electromagnetic Saturation of Angstrom-Sized Quantum Barriers at Terahertz Frequencies

NASA Astrophysics Data System (ADS)

Bahk, Young-Mi; Kang, Bong Joo; Kim, Yong Seung; Kim, Joon-Yeon; Kim, Won Tae; Kim, Tae Yun; Kang, Taehee; Rhie, Jiyeah; Han, Sanghoon; Park, Cheol-Hwan; Rotermund, Fabian; Kim, Dai-Sik

2015-09-01

Metal-graphene-metal hybrid structures allow angstrom-scale van der Waals gaps, across which electron tunneling occurs. We squeeze terahertz electromagnetic waves through these λ /10 000 000 gaps, accompanied by giant field enhancements. Unprecedented transmission reduction of 97% is achieved with the transient voltage across the gap saturating at 5 V. Electron tunneling facilitated by the transient electric field strongly modifies the gap index, starting a self-limiting process related to the barrier height. Our work enables greater interplay between classical optics and quantum tunneling, and provides optical indices to the van der Waals gaps.

Quality assurance in radiotherapy.

PubMed

Kouloulias, V E

2003-03-01

In 1999, the European Organisation for Research and Treatment of Cancer (EORTC), being a European pioneer in the field of cancer research as well as in quality assurance (QA), launched an Emmanuel van der Schueren fellowship for QA in radiotherapy. In this paper, the work that has been done during the first E. van der Schueren fellowship is reported, focusing on four phase III EORTC clinical trials: 22921 for rectal cancer, 22961 and 22991 for prostate cancer and 22922 for breast cancer. A historical review of the QA programme of the EORTC Radiotherapy group during the past 20 years is included.

Synchronisation Induced by Repulsive Interactions in a System of van der Pol Oscillators

NASA Astrophysics Data System (ADS)

Martins, T. V.; Toral, R.

2011-09-01

We consider a system of identical van der Pol oscillators, globally coupled through their velocities, and study how the presence of competitive interactions affects its synchronisation properties. We will address the question from two points of view. Firstly, we will investigate the role of competitive interactions on the synchronisation among identical oscillators. Then, we will show that the presence of a fraction of repulsive links results in the appearance of macroscopic oscillations at that signal's rhythm, in regions where the individual oscillator is unable to synchronise with a weak external signal.

Proceedings of Biological Actions of Extracellular ATP Conference Held in Philadelphia, Pennsylvania on 27-19 November 1990. (Annals of the New York Academy of Sciences. Volume 603)

DTIC Science & Technology

1990-12-16

Uncomplexed with Divalent Cations Activate a Receptor Coupled to Phosphoinositidase C in iitar Cells. By J. S. DAVIDsoN, 1. WAKEFIEL, P. A. VAN DER ...selective antagonist, at least over a limited concentration range)." ’ Studies of the pharma - cological actions of isopolar phosphonate analogues of...139 VAN DER MERWE, F A, 1. K WAKEFIELD, I FINE, R, P. MILLAR & 3. S. DAVIDSON, 1989 FEltS Lell 243: 333-336. 140 HARDEN, T K, J L BOYER, It A BROWN

Thermally programmable gas storage and release in single crystals of an organic van der Waals host.

PubMed

Enright, Gary D; Udachin, Konstantin A; Moudrakovski, Igor L; Ripmeester, John A

2003-08-20

A single crystal of a low density form of guest-free p-tert-butylcalix[4]arene can take up and release small guest molecules by controlling the temperature and pressure without changing the structure. Using NMR spectroscopy with flowing hyperpolarized xenon, we have shown that at room temperature access of xenon to the pore system is difficult, whereas it is relatively easy at 100 degrees C. There are good prospects for simple van der Waals materials such as the title material to be used as programmable zeolite mimics.

Atomically thin resonant tunnel diodes built from synthetic van der Waals heterostructures.

PubMed

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

2015-06-19

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.

Granular fountains: convection cascade in a compartmentalized granular gas.

PubMed

van der Meer, Devaraj; van der Weele, Ko; Reimann, Peter

2006-06-01

This paper extends the two-compartment granular fountain [D. van der Meer, P. Reimann, K. van der Weele, and D. Lohse, Phys. Rev. Lett. 92, 184301 (2004)] to an arbitrary number of compartments: the tendency of a granular gas to form clusters is exploited to generate spontaneous convective currents, with particles going down in the well-filled compartments and going up in the diluted ones. We focus upon the bifurcation diagram of the general -compartment system, which is constructed using a dynamical flux model and which proves to agree quantitatively with results from molecular dynamics simulations.

Peeling off an elastica from a smooth attractive substrate

NASA Astrophysics Data System (ADS)

Oyharcabal, Xabier; Frisch, Thomas

2005-03-01

Using continuum mechanics, we study theoretically the unbinding of an inextensible rod with free ends attracted by a smooth substrate and submitted to a vertical force. We use the elastica model in a medium-range van der Waals potential. We numerically solve a nonlinear boundary value problem and obtain the force-stretching relation at zero temperature. We obtain the critical force for which the rod unbinds from the substrate as a function of three dimensionless parameters, and we find two different regimes of adhesion. We study analytically the contact potential case as the van der Waals radius goes to zero.

Van der Waals corrected DFT study of adsorption of groups VA and VIA hydrides on graphene monoxide

NASA Astrophysics Data System (ADS)

Notash, M. Yaghoobi; Ebrahimzadeh, A. Rastkar

2016-06-01

Adsorption properties of H2O, H2S, NH3 and PH3 on graphene monoxide (GMO) nano flack are investigated using density functional theory (DFT). Calculations were carried out by van der Waals correction and general gradient approximation. The adsorption energies and charge transfer between species are obtained and discussed for the considered positions of adsorbate molecules. Charge transfer analysis show that the gas molecules act as an electron acceptor in all cases. The analysis of the adsorption energies suggest GMO can be a good candidate for the adsorption of these molecules.

Van der Woude syndrome: Management in the mixed dentition.

PubMed

Agarwal, Sonahita; Dinesh, M R; Dharma, R M; Amarnath, B C

2013-01-01

This article presents the case of a patient with Van der Woude syndrome treated with orthodontic and orthopedic intervention in the mixed dentition stage. The patient had a bilateral cleft of the lip and alveolus accompanied by lip pits on the lower lip. Intra-orally, there was bilateral anterior and posterior cross-bite with a collapsed maxilla. The maxillary transverse deficiency was managed with orthopedic expansion and the second phase of treatment involved secondary alveolar bone grafting followed by retention with functional regulator-3. The mild maxillary retrognathia and deficient lip support was managed with dental compensation.

Van der Woude syndrome: Management in the mixed dentition

PubMed Central

Agarwal, Sonahita; Dinesh, M. R.; Dharma, R. M.; Amarnath, B. C.

2013-01-01

This article presents the case of a patient with Van der Woude syndrome treated with orthodontic and orthopedic intervention in the mixed dentition stage. The patient had a bilateral cleft of the lip and alveolus accompanied by lip pits on the lower lip. Intra-orally, there was bilateral anterior and posterior cross-bite with a collapsed maxilla. The maxillary transverse deficiency was managed with orthopedic expansion and the second phase of treatment involved secondary alveolar bone grafting followed by retention with functional regulator-3. The mild maxillary retrognathia and deficient lip support was managed with dental compensation. PMID:23853466

Merlon-type density waves in a compartmentalized conveyor system

NASA Astrophysics Data System (ADS)

Kanellopoulos, G.; van derWeele, K.

2016-09-01

Multi-particle flow through a cyclic array of K connected compartments with a preferential direction is known to be able to organize itself in the form of density waves [Kanellopoulos, Van der Meer, and Van der Weele, Phys. Rev. E 92, 022205 (2015)]. In this brief note we focus on the intriguing shape these waves take when K is even, in which case they travel through alternatingly dense and diluted compartments. We call them "merlon waves", since the sequence of high and low densities is reminiscent of the merlons and crenels on the battlements of medieval castles.

Van der Waals heterostructure of phosphorene and graphene: tuning the Schottky barrier and doping by electrostatic gating.

PubMed

Padilha, J E; Fazzio, A; da Silva, Antônio J R

2015-02-13

In this Letter, we study the structural and electronic properties of single-layer and bilayer phosphorene with graphene. We show that both the properties of graphene and phosphorene are preserved in the composed heterostructure. We also show that via the application of a perpendicular electric field, it is possible to tune the position of the band structure of phosphorene with respect to that of graphene. This leads to control of the Schottky barrier height and doping of phosphorene, which are important features in the design of new devices based on van der Waals heterostructures.

Electromagnetic Saturation of Angstrom-Sized Quantum Barriers at Terahertz Frequencies.

PubMed

Bahk, Young-Mi; Kang, Bong Joo; Kim, Yong Seung; Kim, Joon-Yeon; Kim, Won Tae; Kim, Tae Yun; Kang, Taehee; Rhie, Jiyeah; Han, Sanghoon; Park, Cheol-Hwan; Rotermund, Fabian; Kim, Dai-Sik

2015-09-18

Metal-graphene-metal hybrid structures allow angstrom-scale van der Waals gaps, across which electron tunneling occurs. We squeeze terahertz electromagnetic waves through these λ/10 000 000 gaps, accompanied by giant field enhancements. Unprecedented transmission reduction of 97% is achieved with the transient voltage across the gap saturating at 5 V. Electron tunneling facilitated by the transient electric field strongly modifies the gap index, starting a self-limiting process related to the barrier height. Our work enables greater interplay between classical optics and quantum tunneling, and provides optical indices to the van der Waals gaps.

Optical properties of metal-hydride switchable films

NASA Astrophysics Data System (ADS)

Griessen, Ronald

2001-03-01

In 1996 we discovered that yttrium-, lanthanum-, and rare-earth-hydride (REHx) films [1] protected by a thin palladium layer, exhibit spectacular changes in their optical properties when the hydrogen concentration x is increased from 2 to 3. For example, a 500 nm thick YH2 film is metallic and shiny while YH3 is yellowish and transparent. The transition is reversible, fast [2, 3], and can simply be induced by adding or removing hydrogen from the gas phase, an electrolyte or from an H containing liquid. The optical switching that occurs near the metal-insulator transition of these hydrides is remarkably robust as it is not affected by structural or compositional disorder. It occurs in polycrystalline and epitaxial films, in alloys with cubic or hexagonal crystal structures,and deuterides [4] switch as well as hydrides. At small length scales epitaxial YHx films exhibit surprising structural properties which open the way to pixel-by-pixel optical switching [5]. Colour-neutral switchable mirrors based on RE-Mg alloys [6] can be used in all-solid-state switchable devices. Newest results for Rare-Earth free switchable mirrors will be presented. [1] J. N. Huiberts, R. Griessen, J. H. Rector, R. J. Wijngaarden, J. P. Dekker, D. G. de Groot and N. J. Koeman, Nature 380 (1996) 231; [2] S. J. van der Molen, J. W. J. Kerssemakers, J. H. Rector, N. J. Koeman, B. Dam, R. Griessen, J. Appl. Phys. 86 (1999) 6107; [3] F. J. A. den Broeder, S. J. van der Molen, et al., Nature 394 (1998)656; [4] A. T. M. van Gogh, E. S. Kooij, R. Griessen, Phys. Rev. Lett. 83 (1999) 4614; [5] J. W. J. Kerssemakers, S. J. van der Molen and R. Griessen, Nature 406 (2000) 489; [6] P. van der Sluis, M. Ouwerkerk and P. A. Duine, Appl. Phys. Lett. 70 (1997) 3356.

Analysis of Regional Phases Using Three-Component Data

DTIC Science & Technology

1989-11-20

and Sen- gbush, 1953; Cholet and Richards, 1954; Uhrig and Van Melle, 1955; de Segonzac and Laherrere, 1959; Richards, 1960; Gretener , 1961; Van der...1963, Elastische Anisotropie in tektonisch verformten Sedimentgesteinen, Geophys. Prospecting, 1,, 423-458. Gretener , P.E.F., 1961, An analysis of

How does a tidal embayment morphodynamically react on sea level rise?

NASA Astrophysics Data System (ADS)

van der Wegen, Mick

2010-05-01

Conditions for (assumed) equilibrium in tidal embayments have been studied extensively in the past years with morphodynamic 1D models (Van Dongeren and De Vriend, 1994; Schuttelaars and de Swart, 1996, 2000; Lanzoni and Seminara, 2002) and 2D models (Hibma et al. [2003], Van der Wegen and Roelvink [2008]) Van der Wegen et al 2008). The current research addresses the impact of sea level rise on tidal embayments. Although effects of sea level rise may only become apparent after decades, the character of the embayment can change considerably. Examples are the (dis)appearance or re-allocation of intertidal flats, increased tidal resonance, shift from sediment export to import, deepening of channel area and other related (ecological) parameters. The research applies a 2D morphodynamic model (Delft3D) in an idealized environment. The model is based on the 2 D shallow water equations, the Engelund -Hansen transport formula and includes bed slope effects, drying and flooding procedures and an advanced morphodynamic update scheme (Roelvink 2006). The initial condition of the bathymetry is generated by 3000 years of morphodynamic calculations in a 80 km long and 2.5 km wide rectangular tidal embayment under constant M2 tidal forcing conditions (Van der Wegen and Roelvink [2008]). After this period sea level rise gradually developing towards a rate of 0.4 m/century is added to the boundary conditions. Model results describe development towards less intertidal area and a transition from an exporting system to a importing system. Model results are evaluated in terms of M2, M4 and M6 tidal constituents as well as against Vs/Vc (shoal volume over channel volume) versus a/h (amplitude over water depth) relationship as proposed by Friedrichs and Aubrey (1988). Although the model describes morphodynamic development in a strongly idealized environment the results can provide an excellent tool to systematically study the impact of sea level rise in tidal embayments as well as the time scales of dominant underlying resulting transport mechanisms and processes. DISSANAYAKE, D.M.P.K; RANASINGHE, R. and ROELVINK, J.A., 2009. Effect of Sea Level Rise in tidal inlet evolution: a numerical modelling approach. Journal of Coastal Research, SI 56 (Proceedings of the 10th International Coastal Symposium), pg - pg. Lisbon, Portugal. Friedrichs, C. T., and D. G. Aubrey (1988), Non-linear tidal distortion in shallow well mixed estuaries: A synthesis, Estuarine Coastal Shelf Sci.,27, 521- 545, doi:10.1016/0272-7714(88)90082-0. Hibma, A., H.M. Schuttelaars, and H. J. de Vriend (2003b), Initial formation and long-term evolution of channel-shoal patterns in estuaries, in Proc. 3rd RCEM conf.edited by A. Sánchez -Acrilla and A. Bateman, pp. 740-760, IAHR., Barcelona, Spain. Lanzoni, S., and G. Seminara (2002), Long-term evolution and morphodynamic equilibrium of tidal channels, J. Geophys. Res., 107(C1), 3001, doi:10.1029/2000JC000468. Roelvink, J. A. (2006), Coastal morphodynamic evolution techniques, J. Coastal Eng., 53, 177-187. Schuttelaars, H. M., and H. E. De Swart (1996), An idealized long termmorphodynamic model of a tidal embayment, Eur. J. Mech. B Fluids, 15(1), 55-80. Schuttelaars, H. M., and H. E. De Swart (2000), Multiple morphodynamic equilibria in tidal embayments, J. Geophys. Res., 105(C10), 24,105 - 24,118. Van Dongeren, A. D., and H. J. De Vriend (1994), A model of morphological behaviour of tidal basins, Coastal Eng., 22, 287- 310. van der Wegen, M., and J. A. Roelvink (2008), Long-term morphodynamic evolution of a tidal embayment using a twodimensional, process-based model, J. Geophys. Res., 113, C03016, doi:10.1029/2006JC003983 van der Wegen, M., Z. B. Wang, H. H. G. Savenije, and J. A. Roelvink (2008), Long-term morphodynamic evolution and energy dissipation in a coastal plain, tidal embayment, J. Geophys. Res., 113, F03001, doi:10.1029/2007JF000898

Mixed Dimensional Van der Waals Heterostructures for Opto-Electronics.

NASA Astrophysics Data System (ADS)

Jariwala, Deep

The isolation of a growing number of two-dimensional (2D) materials has inspired worldwide efforts to integrate distinct 2D materials into van der Waals (vdW) heterostructures. While a tremendous amount of research activity has occurred in assembling disparate 2D materials into ``all-2D'' van der Waals heterostructures, this concept is not limited to 2D materials alone. Given that any passivated, dangling bond-free surface will interact with another via vdW forces, the vdW heterostructure concept can be extended to include the integration of 2D materials with non-2D materials that adhere primarily through noncovalent interactions. In the first part of this talk I will present our work on emerging mixed-dimensional (2D + nD, where n is 0, 1 or 3) heterostructure devices performed at Northwestern University. I will present two distinct examples of gate-tunable p-n heterojunctions 1. Single layer n-type MoS2\\ (2D) combined with p-type semiconducting single walled carbon nanotubes (1D) and 2. Single layer MoS2 combined with 0D molecular semiconductor, pentacene. I will present the unique electrical properties, underlying charge transport mechanisms and photocurrent responses in both the above systems using a variety of scanning probe microscopy techniques as well as computational analysis. This work shows that van der Waals interactions are robust across different dimensionalities of materials and can allow fabrication of semiconductor devices with unique geometries and properties unforeseen in bulk semiconductors. Finally, I will briefly discuss our recent work from Caltech on near-unity absorption in atomically-thin photovoltaic devices. This work is supported by the Materials Research Center at Northwestern University, funded by the National Science Foundation (NSF DMR-1121262) and the Resnick Sustainability Institute at Caltech.

Holographic Jet Shapes and their Evolution in Strongly Coupled Plasma

NASA Astrophysics Data System (ADS)

Brewer, Jasmine; Rajagopal, Krishna; Sadofyev, Andrey; van der Schee, Wilke

2017-11-01

Recently our group analyzed how the probability distribution for the jet opening angle is modified in an ensemble of jets that has propagated through an expanding cooling droplet of plasma [K. Rajagopal, A. V. Sadofyev, W. van der Schee, Phys. Rev. Lett. 116 (2016) 211603]. Each jet in the ensemble is represented holographically by a string in the dual 4+1- dimensional gravitational theory with the distribution of initial energies and opening angles in the ensemble given by perturbative QCD. In [K. Rajagopal, A. V. Sadofyev, W. van der Schee, Phys. Rev. Lett. 116 (2016) 211603], the full string dynamics were approximated by assuming that the string moves at the speed of light. We are now able to analyze the full string dynamics for a range of possible initial conditions, giving us access to the dynamics of holographic jets just after their creation. The nullification timescale and the features of the string when it has nullified are all results of the string evolution. This emboldens us to analyze the full jet shape modification, rather than just the opening angle modification of each jet in the ensemble as in [K. Rajagopal, A. V. Sadofyev, W. van der Schee, Phys. Rev. Lett. 116 (2016) 211603]. We find the result that the jet shape scales with the opening angle at any particular energy. We construct an ensemble of dijets with energies and energy asymmetry distributions taken from events in proton-proton collisions, opening angle distribution as in [K. Rajagopal, A. V. Sadofyev, W. van der Schee, Phys. Rev. Lett. 116 (2016) 211603], and jet shape taken from proton-proton collisions and scaled according to our result. We study how these observables are modified after we send the ensemble of dijets through the strongly-coupled plasma.

Light-matter interaction in transition metal dichalcogenides and their heterostructures

NASA Astrophysics Data System (ADS)

Wurstbauer, Ursula; Miller, Bastian; Parzinger, Eric; Holleitner, Alexander W.

2017-05-01

The investigation of two-dimensional (2D) van der Waals materials is a vibrant, fast-moving and still growing interdisciplinary area of research. These materials are truly 2D crystals with strong covalent in-plane bonds and weak van der Waals interaction between the layers, and have a variety of different electronic, optical and mechanical properties. Transition metal dichalcogenides are a very prominent class of 2D materials, particularly the semiconducting subclass. Their properties include bandgaps in the near-infrared to the visible range, decent charge carrier mobility together with high (photo-) catalytic and mechanical stability, and exotic many-body phenomena. These characteristics make the materials highly attractive for both fundamental research as well as innovative device applications. Furthermore, the materials exhibit a strong light-matter interaction, providing a high sunlight absorbance of up to 15% in the monolayer limit, strong scattering cross section in Raman experiments, and access to excitonic phenomena in van der Waals heterostructures. This review focuses on the light-matter interaction in MoS2, WS2, MoSe2 and WSe2, which is dictated by the materials’ complex dielectric functions, and on the multiplicity of studying the first-order phonon modes by Raman spectroscopy to gain access to several material properties such as doping, strain, defects and temperature. 2D materials provide an interesting platform for stacking them into van der Waals heterostructures without the limitation of lattice mismatch, resulting in novel devices for applications but also to enable the study of exotic many-body interaction phenomena such as interlayer excitons. Future perspectives of semiconducting transition metal dichalcogenides and their heterostructures for applications in optoelectronic devices will be examined, and routes to study emergent fundamental problems and many-body quantum phenomena under excitations with photons will be discussed.

A mechanistic study on Decontamination of Methyl Orange Dyes from Aqueous Phase by Mesoporous Pulp Waste and Polyaniline

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

Li, Donglin; Yang, Yonggang; Li, Chaozheng

2017-04-15

The dispersion-corrected density functional theory (DFT-D3) is used to investigate the mechanism of mesoporous pulp waste (MPW) and polyaniline (PANI) adsorptive removal methyl orange (MO) dye from their aqueous solutions. The results are absolutely reliable because of the sufficiently accurate method although such big systems are studied. It is demonstrated that hydrogen bond and Van Der Waals interactions play a significant role in MO adsorption by MPW and PANI. For MO adsorption by MPW, hydrogen bond and Van Der Waals interactions are both weakened in S{sub 1} state. In contrast, hydrogen bond and Van Der Waals interactions between PANI andmore » MO are both enhanced in S{sub 1} state. The thermodynamic parameters such as enthalpy and free energy change reveal that the MO adsorption by MPW and PANI are spontaneous and exothermic. The adsorption of MO on MPW is less favorable in S{sub 1} state and the adsorption of MO on PANI is more favorable in S{sub 1} state. Therefore, the photoexcitation should be controlled during the MO adsorption by MPW and applied for MO adsorption by PANI. - Highlights: • The hydrogen bond and Van Der Waals interactions play a significant role in MO adsorption by MPW and PANI. • The influence of photoexcitation on adsorption has been studied firstly in our work. • The adsorption of MO on MPW is less favorable in S{sub 1} state and the adsorption of MO on PANI is more favorable in S{sub 1} state. • The MO adsorption by MPW and PANI are spontaneous and exothermic.« less

Nanoscale measurement of Nernst effect in two-dimensional charge density wave material 1T-TaS 2

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

Wu, Stephen M.; Luican-Mayer, Adina; Bhattacharya, Anand

Advances in nanoscale material characterization on two-dimensional van der Waals layered materials primarily involve their optical and electronic properties. The thermal properties of these materials are harder to access due to the difficulty of thermal measurements at the nanoscale. In this work, we create a nanoscale magnetothermal device platform to access the basic out-of-plane magnetothermal transport properties of ultrathin van der Waals materials. Specifically, the Nernst effect in the charge density wave transition metal dichalcogenide 1T-TaS 2 is examined on nano-thin flakes in a patterned device structure. It is revealed that near the commensurate charge density wave (CCDW) to nearlymore » commensurate charge density wave (NCCDW) phase transition, the polarity of the Nernst effect changes. Since the Nernst effect is especially sensitive to changes in the Fermi surface, this suggests that large changes are occurring in the out-of-plane electronic structure of 1T-TaS 2, which are otherwise unresolved in just in-plane electronic transport measurements. This may signal a coherent evolution of out-of-plane stacking in the CCDW! NCCDW transition.« less

The Spatial Influence of Apartheid on the South African City

ERIC Educational Resources Information Center

Schoeman, Thea

2018-01-01

Maps and satellite images can be used effectively to identify and compare settlement patterns. Spatial cognition and interpretation are important to further map literacy (Larangeira and Van der Merwe 2016). Although Apartheid ended in 1994 in South Africa, the legacy of this "separate development" system is still very noticeable in South…

Communication: Accurate higher-order van der Waals coefficients between molecules from a model dynamic multipole polarizability

DOE PAGES

Tao, Jianmin; Rappe, Andrew M.

2016-01-20

Due to the absence of the long-range van der Waals (vdW) interaction, conventional density functional theory (DFT) often fails in the description of molecular complexes and solids. In recent years, considerable progress has been made in the development of the vdW correction. However, the vdW correction based on the leading-order coefficient C 6 alone can only achieve limited accuracy, while accurate modeling of higher-order coefficients remains a formidable task, due to the strong non-additivity effect. Here, we apply a model dynamic multipole polarizability within a modified single-frequency approximation to calculate C 8 and C 10 between small molecules. We findmore » that the higher-order vdW coefficients from this model can achieve remarkable accuracy, with mean absolute relative deviations of 5% for C 8 and 7% for C 10. As a result, inclusion of accurate higher-order contributions in the vdW correction will effectively enhance the predictive power of DFT in condensed matter physics and quantum chemistry.« less

MoS2 /Rubrene van der Waals Heterostructure: Toward Ambipolar Field-Effect Transistors and Inverter Circuits.

PubMed

He, Xuexia; Chow, WaiLeong; Liu, Fucai; Tay, BengKang; Liu, Zheng

2017-01-01

2D transition metal dichalcogenides are promising channel materials for the next-generation electronic device. Here, vertically 2D heterostructures, so called van der Waals solids, are constructed using inorganic molybdenum sulfide (MoS 2 ) few layers and organic crystal - 5,6,11,12-tetraphenylnaphthacene (rubrene). In this work, ambipolar field-effect transistors are successfully achieved based on MoS 2 and rubrene crystals with the well balanced electron and hole mobilities of 1.27 and 0.36 cm 2 V -1 s -1 , respectively. The ambipolar behavior is explained based on the band alignment of MoS 2 and rubrene. Furthermore, being a building block, the MoS 2 /rubrene ambipolar transistors are used to fabricate CMOS (complementary metal oxide semiconductor) inverters that show good performance with a gain of 2.3 at a switching threshold voltage of -26 V. This work paves a way to the novel organic/inorganic ultrathin heterostructure based flexible electronics and optoelectronic devices. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

CMMI Roadmaps

DTIC Science & Technology

2008-11-01

Attendees of the SPIder Workshop D. Bierhuizen—Medis Medical Imaging Systems L. Braafhart—LogicaCMG Nederland H.J.J. Cannegieter—SYSQA W. den...Dekker—LogicaCMG Nederland L. Delmelk—LogicaCMG België A.J. Donderman—Transfer Solutions G.H.M. Friedhoff—SYSQA L.L. van der Giessen—ABN AMRO M...Mechelen—Compuware Nederland M.P.H.M. Mermans—Philips Medical Systems C. Michielsen—ITIB N. van Mourik—SYSQA E.M. Oostveen—Advanced M.H.M. van

Establishing conditions for simulating hydrophobic solutes in electric fields by molecular dynamics: effects of the long-range van der Waals treatment on the apparent particle mobility.

PubMed

Miličević, Zoran; Marrink, Siewert J; Smith, Ana-Sunčana; Smith, David M

2014-08-01

Despite considerable effort over the last decade, the interactions between solutes and solvents in the presence of electric fields have not yet been fully understood. A very useful manner in which to study these systems is through the application of molecular dynamics (MD) simulations. However, a number of MD studies have shown a tremendous sensitivity of the migration rate of a hydrophobic solute to the treatment of the long range part of the van der Waals interactions. While the origin of this sensitivity was never explained, the mobility is currently regarded as an artifact of an improper simulation setup. We explain the spread in observed mobilites by performing extensive molecular dynamics simulations using the GROMACS software package on a system consisting of a model hydrophobic object (Lennard-Jones particle) immersed in water both in the presence and absence of a static electric field. We retrieve a unidirectional field-induced mobility of the hydrophobic object when the forces are simply truncated. Careful analysis of the data shows that, only in the specific case of truncated forces, a non-zero van der Waals force acts, on average, on the Lennard-Jones particle. Using the Stokes law we demonstrate that this force yields quantitative agreement with the field-induced mobility found within this setup. In contrast, when the treatment of forces is continuous, no net force is observed. In this manner, we provide a simple explanation for the previously controversial reports.

Probing the probe: AFM tip-profiling via nanotemplates to determine Hamaker constants from phase-distance curves.

PubMed

Rodriguez, Raul D; Lacaze, Emmanuelle; Jupille, Jacques

2012-10-01

A method to determine the van der Waals forces from phase-distance curves recorded by atomic force microscopy (AFM) in tapping mode is presented. The relationship between the phase shift and the tip-sample distance is expressed as a function of the product of the Hamaker constant by tip radius. Silica-covered silicon tips are used to probe silica-covered silicon substrate in dry conditions to avoid capillary effects. Tips being assumed spherical, radii are determined in situ by averaging profiles recorded in different directions on hematite nanocrystals acting as nanotemplates, thus accounting for tip anisotropy. Through a series of reproducible measurements performed with tips of various radii (including the in-situ characterization of a damaged tip), a value of (6.3±0.4)×10(-20) J is found for the Hamaker constant of interacting silica surfaces in air, in good agreement with tabulated data. The results demonstrate that the onset of the tip-surface interaction is dominated by the van der Waals forces and that the total force can be modeled in the framework of the harmonic approximation. Based on the tip radius and the Hamaker constant associated to the tip-substrate system, the model is quite flexible. Once the Hamaker constant is known, a direct estimate of the tip size can be achieved whereas when the tip size is known, a quantitative evaluation of the van der Waals force becomes possible on different substrates with a spatial resolution at the nanoscale. Copyright © 2012 Elsevier B.V. All rights reserved.

International Hydrogenase Conference (7th) Held at the University of Reading on August 24th to 29th 2004.

DTIC Science & Technology

2004-08-19

Johannes Hackstein [ PB GIO rNovel Fe-hydrogenases from the rumen ciliate metagenome . :12.50 :114.00 -1 Lunch [ 114.00 1 7.00 1 Poster Session 2...d.r.o’ g’.e n-.a-.s.e..s from the rumnen ciliate metagenome . p36 Severing, E., Boxma, B., van Alen, T.A., Ricard, G., van Hoek, A.H.A.M., Moon-van...hydrogenases from the rumen ciliate metagenome . Severing, E.’, Boxma, B.1, van Alen, T.A.’, Ricard, G.z, van Hoek, A.H.A.M.’, Moon-van der Staay, S.Y

A Look at Psychometrics in the Netherlands.

ERIC Educational Resources Information Center

Hambleton, Ronald K.; Swaminathan, H.

Comments are made on the review papers presented by six Dutch psychometricians: Ivo Molenaar, Wim van der Linden, Ed Roskam, Arnold Van den Wollenberg, Gideon Mellenbergh, and Dato de Gruijter. Molenaar has embraced a pragmatic viewpoint on Bayesian methods, using both empirical and pure approaches to solve educational research problems. Molenaar…

Hilbert's sixth problem and the failure of the Boltzmann to Euler limit

NASA Astrophysics Data System (ADS)

Slemrod, Marshall

2018-04-01

This paper addresses the main issue of Hilbert's sixth problem, namely the rigorous passage of solutions to the mesoscopic Boltzmann equation to macroscopic solutions of the Euler equations of compressible gas dynamics. The results of the paper are that (i) in general Hilbert's program will fail because of the appearance of van der Waals-Korteweg capillarity terms in a macroscopic description of motion of a gas, and (ii) the van der Waals-Korteweg theory itself might satisfy Hilbert's quest for a map from the `atomistic view' to the laws of motion of continua. This article is part of the theme issue `Hilbert's sixth problem'.

Amplitude and phase fluctuations of Van der Pol oscillator under external random forcing

NASA Astrophysics Data System (ADS)

Singh, Aman K.; Yadava, R. D. S.

2018-05-01

The paper presents an analytical study of noise in Van der Pol oscillator output subjected to an external force noise assumed to be characterized by delta function (white noise). The external fluctuations are assumed to be small in comparison to the average response of the noise free system. The autocorrelation function and power spectrum are calculated under the condition of weak nonlinearity. The latter ensures limit cycle oscillations. The total spectral power density is dominated by the contributions from the phase fluctuations. The amplitude fluctuations are at least two orders of magnitude smaller. The analysis is shown to be useful to interpretation microcantilever based biosensing data.

On coagulation mechanisms of charged nanoparticles produced by combustion of hydrocarbon and metallized fuels

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

Savel'ev, A. M.; Starik, A. M.

2009-02-15

The contributions of van der Waals, Coulomb, and polarization interactions between nanometersized particles to the particle coagulation rate in both free-molecular and continuum regimes are analyzed for particle charges of various magnitudes and signs. Analytical expressions are obtained for the coagulation rate constant between particles whose interaction in the free-molecular regime is described by a singular potential. It is shown that van der Waals and polarization forces significantly increase the coagulation rate between a neutral and a charged particle (by a factor of up to 10) and can even suppress the Coulomb repulsion between like-charged particles of widely different sizes.

Precise, Self-Limited Epitaxy of Ultrathin Organic Semiconductors and Heterojunctions Tailored by van der Waals Interactions.

PubMed

Wu, Bing; Zhao, Yinghe; Nan, Haiyan; Yang, Ziyi; Zhang, Yuhan; Zhao, Huijuan; He, Daowei; Jiang, Zonglin; Liu, Xiaolong; Li, Yun; Shi, Yi; Ni, Zhenhua; Wang, Jinlan; Xu, Jian-Bin; Wang, Xinran

2016-06-08

Precise assembly of semiconductor heterojunctions is the key to realize many optoelectronic devices. By exploiting the strong and tunable van der Waals (vdW) forces between graphene and organic small molecules, we demonstrate layer-by-layer epitaxy of ultrathin organic semiconductors and heterostructures with unprecedented precision with well-defined number of layers and self-limited characteristics. We further demonstrate organic p-n heterojunctions with molecularly flat interface, which exhibit excellent rectifying behavior and photovoltaic responses. The self-limited organic molecular beam epitaxy (SLOMBE) is generically applicable for many layered small-molecule semiconductors and may lead to advanced organic optoelectronic devices beyond bulk heterojunctions.

Spherical and hyperspherical harmonics representation of van der Waals aggregates

NASA Astrophysics Data System (ADS)

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.

Application of Van Der Waals Density Functional Theory to Study Physical Properties of Energetic Materials

NASA Astrophysics Data System (ADS)

Conroy, M. W.; Budzevich, M. M.; Lin, Y.; Oleynik, I. I.; White, C. T.

2009-12-01

An empirical correction to account for van der Waals interactions based on the work of Neumann and Perrin [J. Phys. Chem. B 109, 15531 (2005)] was applied to density functional theory calculations of energetic molecular crystals. The calculated equilibrium unit-cell volumes of FOX-7, β-HMX, solid nitromethane, PETN-I, α-RDX, and TATB show a significant improvement in the agreement with experimental results. Hydrostatic-compression simulations of β-HMX, PETN-I, and α-RDX were also performed. The isothermal equations of state calculated from the results show increased agreement with experiment in the pressure intervals studied.

Atomically thin resonant tunnel diodes built from synthetic van der Waals heterostructures

PubMed Central

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.

2015-01-01

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. PMID:26088295

Combined Tongue-Palate Fusion With Alveolar Bands in a Patient With Pierre Robin Sequence and Van der Woude Syndrome.

PubMed

Robbins, Alexa; Zarate, Yuri A; Hartzell, Larry D

2018-01-01

This report describes the presentation of a newborn male with circumferential tongue-palate fusion associated with cleft palate and alveolar bands. After intraoral adhesions lysis, the patient was diagnosed with Pierre Robin sequence. A family history of cleft lip and palate was noted, and interferon regulatory factor 6 ( IRF6) sequencing revealed a heterozygous variant, confirming the diagnosis of van der Woude syndrome. The disruption of IRF6 resulted in abnormal orofacial development including micrognathia and intraoral adhesions as well as tongue-palate fusion, then resulting in glossoptosis with airway obstruction and cleft palate.

Ab-initio study of structural and electronic properties of WS2/h-BN van der Waals heterostructure

NASA Astrophysics Data System (ADS)

Ghasemi majd, Zahra; Amiri, Peiman; Taghizadeh, Seyed Fardin

2018-06-01

First-principle calculations with different exchange-correlation functionals, including LDA, GGA, semi-empirical and ab-initio van der Waals in the forms of vdW-DF2B86R and vdW-DF2 were performed to evaluate the performance of different functionals in describing the bonding mechanism, adsorption energy and interlayer distance of WS2 monolayer on and between h-BN layers. The finding was that the vdW-DF2B86R seems to be the approach best lending itself to this purpose. In order to include the van der Waals (vdW) interactions in our calculations, we used the DFT-D2 and vdW methods, which gave rise to a physical adsorption with no net charge transfer between the WS2 layer and the corresponding substrates. In addition, we investigated the electronic and structural properties of WS2 and h-BN heterolayers, using vdW-DF2B86R functional. Based on density functional theory calculations, WS2 on and between h-BN layers showed a direct band gap at the K-point, which was experimentally observed.

Two-dimensional antimonene single crystals grown by van der Waals epitaxy.

PubMed

Ji, Jianping; Song, Xiufeng; Liu, Jizi; Yan, Zhong; Huo, Chengxue; Zhang, Shengli; Su, Meng; Liao, Lei; Wang, Wenhui; Ni, Zhenhua; Hao, Yufeng; Zeng, Haibo

2016-11-15

Unlike the unstable black phosphorous, another two-dimensional group-VA material, antimonene, was recently predicted to exhibit good stability and remarkable physical properties. However, the synthesis of high-quality monolayer or few-layer antimonenes, sparsely reported, has greatly hindered the development of this new field. Here, we report the van der Waals epitaxy growth of few-layer antimonene monocrystalline polygons, their atomical microstructure and stability in ambient condition. The high-quality, few-layer antimonene monocrystalline polygons can be synthesized on various substrates, including flexible ones, via van der Waals epitaxy growth. Raman spectroscopy and transmission electron microscopy reveal that the obtained antimonene polygons have buckled rhombohedral atomic structure, consistent with the theoretically predicted most stable β-phase allotrope. The very high stability of antimonenes was observed after aging in air for 30 days. First-principle and molecular dynamics simulation results confirmed that compared with phosphorene, antimonene is less likely to be oxidized and possesses higher thermodynamic stability in oxygen atmosphere at room temperature. Moreover, antimonene polygons show high electrical conductivity up to 10 4  S m -1 and good optical transparency in the visible light range, promising in transparent conductive electrode applications.

Two-dimensional antimonene single crystals grown by van der Waals epitaxy

PubMed Central

Ji, Jianping; Song, Xiufeng; Liu, Jizi; Yan, Zhong; Huo, Chengxue; Zhang, Shengli; Su, Meng; Liao, Lei; Wang, Wenhui; Ni, Zhenhua; Hao, Yufeng; Zeng, Haibo

2016-01-01

Unlike the unstable black phosphorous, another two-dimensional group-VA material, antimonene, was recently predicted to exhibit good stability and remarkable physical properties. However, the synthesis of high-quality monolayer or few-layer antimonenes, sparsely reported, has greatly hindered the development of this new field. Here, we report the van der Waals epitaxy growth of few-layer antimonene monocrystalline polygons, their atomical microstructure and stability in ambient condition. The high-quality, few-layer antimonene monocrystalline polygons can be synthesized on various substrates, including flexible ones, via van der Waals epitaxy growth. Raman spectroscopy and transmission electron microscopy reveal that the obtained antimonene polygons have buckled rhombohedral atomic structure, consistent with the theoretically predicted most stable β-phase allotrope. The very high stability of antimonenes was observed after aging in air for 30 days. First-principle and molecular dynamics simulation results confirmed that compared with phosphorene, antimonene is less likely to be oxidized and possesses higher thermodynamic stability in oxygen atmosphere at room temperature. Moreover, antimonene polygons show high electrical conductivity up to 104 S m−1 and good optical transparency in the visible light range, promising in transparent conductive electrode applications. PMID:27845327

Isobaric first-principles molecular dynamics of liquid water with nonlocal van der Waals interactions

NASA Astrophysics Data System (ADS)

Miceli, Giacomo; de Gironcoli, Stefano; Pasquarello, Alfredo

2015-01-01

We investigate the structural properties of liquid water at near ambient conditions using first-principles molecular dynamics simulations based on a semilocal density functional augmented with nonlocal van der Waals interactions. The adopted scheme offers the advantage of simulating liquid water at essentially the same computational cost of standard semilocal functionals. Applied to the water dimer and to ice Ih, we find that the hydrogen-bond energy is only slightly enhanced compared to a standard semilocal functional. We simulate liquid water through molecular dynamics in the NpH statistical ensemble allowing for fluctuations of the system density. The structure of the liquid departs from that found with a semilocal functional leading to more compact structural arrangements. This indicates that the directionality of the hydrogen-bond interaction has a diminished role as compared to the overall attractions, as expected when dispersion interactions are accounted for. This is substantiated through a detailed analysis comprising the study of the partial radial distribution functions, various local order indices, the hydrogen-bond network, and the selfdiffusion coefficient. The explicit treatment of the van der Waals interactions leads to an overall improved description of liquid water.

Problems of low-parameter equations of state

NASA Astrophysics Data System (ADS)

Petrik, G. G.

2017-11-01

The paper focuses on the system approach to problems of low-parametric equations of state (EOS). It is a continuation of the investigations in the field of substantiated prognosis of properties on two levels, molecular and thermodynamic. Two sets of low-parameter EOS have been considered based on two very simple molecular-level models. The first one consists of EOS of van der Waals type (a modification of van der Waals EOS proposed for spheres). The main problem of these EOS is a weak connection with the micro-level, which raise many uncertainties. The second group of EOS has been derived by the author independently of the ideas of van der Waals based on the model of interacting point centers (IPC). All the parameters of the EOS have a meaning and are associated with the manifestation of attractive and repulsive forces. The relationship between them is found to be the control parameter of the thermodynamic level. In this case, EOS IPC passes into a one-parameter family. It is shown that many EOS of vdW-type can be included in the framework of the PC model. Simultaneously, all their parameters acquire a physical meaning.

Molecular dynamics simulation of the interactions between EHD1 EH domain and multiple peptides.

PubMed

Yu, Hua; Wang, Mao-jun; Xuan, Nan-xia; Shang, Zhi-cai; Wu, Jun

2015-10-01

To provide essential information for peptide inhibitor design, the interactions of Eps15 homology domain of Eps15 homology domain-containing protein 1 (EHD1 EH domain) with three peptides containing NPF (asparagine-proline-phenylalanine), DPF (aspartic acid-proline-phenylalanine), and GPF (glycine-proline-phenylalanine) motifs were deciphered at the atomic level. The binding affinities and the underlying structure basis were investigated. Molecular dynamics (MD) simulations were performed on EHD1 EH domain/peptide complexes for 60 ns using the GROMACS package. The binding free energies were calculated and decomposed by molecular mechanics/generalized Born surface area (MM/GBSA) method using the AMBER package. The alanine scanning was performed to evaluate the binding hot spot residues using FoldX software. The different binding affinities for the three peptides were affected dominantly by van der Waals interactions. Intermolecular hydrogen bonds provide the structural basis of contributions of van der Waals interactions of the flanking residues to the binding. van der Waals interactions should be the main consideration when we design peptide inhibitors of EHD1 EH domain with high affinities. The ability to form intermolecular hydrogen bonds with protein residues can be used as the factor for choosing the flanking residues.

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

PubMed

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.

When 2D Materials Meet Molecules: Opportunities and Challenges of Hybrid Organic/Inorganic van der Waals Heterostructures.

PubMed

Gobbi, Marco; Orgiu, Emanuele; Samorì, Paolo

2018-05-01

van der Waals heterostructures, composed of vertically stacked inorganic 2D materials, represent an ideal platform to demonstrate novel device architectures and to fabricate on-demand materials. The incorporation of organic molecules within these systems holds an immense potential, since, while nature offers a finite number of 2D materials, an almost unlimited variety of molecules can be designed and synthesized with predictable functionalities. The possibilities offered by systems in which continuous molecular layers are interfaced with inorganic 2D materials to form hybrid organic/inorganic van der Waals heterostructures are emphasized. Similar to their inorganic counterpart, the hybrid structures have been exploited to put forward novel device architectures, such as antiambipolar transistors and barristors. Moreover, specific molecular groups can be employed to modify intrinsic properties and confer new capabilities to 2D materials. In particular, it is highlighted how molecular self-assembly at the surface of 2D materials can be mastered to achieve precise control over position and density of (molecular) functional groups, paving the way for a new class of hybrid functional materials whose final properties can be selected by careful molecular design. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The physics behind Van der Burgh's empirical equation, providing a new predictive equation for salinity intrusion in estuaries

NASA Astrophysics Data System (ADS)

Zhang, Zhilin; Savenije, Hubert H. G.

2017-07-01

The practical value of the surprisingly simple Van der Burgh equation in predicting saline water intrusion in alluvial estuaries is well documented, but the physical foundation of the equation is still weak. In this paper we provide a connection between the empirical equation and the theoretical literature, leading to a theoretical range of Van der Burgh's coefficient of 1/2 < K < 2/3 for density-driven mixing which falls within the feasible range of 0 < K < 1. In addition, we developed a one-dimensional predictive equation for the dispersion of salinity as a function of local hydraulic parameters that can vary along the estuary axis, including mixing due to tide-driven residual circulation. This type of mixing is relevant in the wider part of alluvial estuaries where preferential ebb and flood channels appear. Subsequently, this dispersion equation is combined with the salt balance equation to obtain a new predictive analytical equation for the longitudinal salinity distribution. Finally, the new equation was tested and applied to a large database of observations in alluvial estuaries, whereby the calibrated K values appeared to correspond well to the theoretical range.

Transport and deposition of cohesive pharmaceutical powders in human airway

NASA Astrophysics Data System (ADS)

Wang, Yuan; Chu, Kaiwei; Yu, Aibing

2017-06-01

Pharmaceutical powders used in inhalation therapy are in the size range of 1-5 microns and are usually cohesive. Understanding the cohesive behaviour of pharmaceutical powders during their transportation in human airway is significant in optimising aerosol drug delivery and targeting. In this study, the transport and deposition of cohesive pharmaceutical powders in a human airway model is simulated by a well-established numerical model which combines computational fluid dynamics (CFD) and discrete element method (DEM). The van der Waals force, as the dominant cohesive force, is simulated and its influence on particle transport and deposition behaviour is discussed. It is observed that even for dilute particle flow, the local particle concentration in the oral to trachea region can be high and particle aggregation happens due to the van der Waals force of attraction. It is concluded that the deposition mechanism for cohesive pharmaceutical powders, on one hand, is dominated by particle inertial impaction, as proven by previous studies; on the other hand, is significantly affected by particle aggregation induced by van der Waals force. To maximum respiratory drug delivery efficiency, efforts should be made to avoid pharmaceutical powder aggregation in human oral-to-trachea airway.

Marginal Structural Models with Counterfactual Effect Modifiers.

PubMed

Zheng, Wenjing; Luo, Zhehui; van der Laan, Mark J

2018-06-08

In health and social sciences, research questions often involve systematic assessment of the modification of treatment causal effect by patient characteristics. In longitudinal settings, time-varying or post-intervention effect modifiers are also of interest. In this work, we investigate the robust and efficient estimation of the Counterfactual-History-Adjusted Marginal Structural Model (van der Laan MJ, Petersen M. Statistical learning of origin-specific statically optimal individualized treatment rules. Int J Biostat. 2007;3), which models the conditional intervention-specific mean outcome given a counterfactual modifier history in an ideal experiment. We establish the semiparametric efficiency theory for these models, and present a substitution-based, semiparametric efficient and doubly robust estimator using the targeted maximum likelihood estimation methodology (TMLE, e.g. van der Laan MJ, Rubin DB. Targeted maximum likelihood learning. Int J Biostat. 2006;2, van der Laan MJ, Rose S. Targeted learning: causal inference for observational and experimental data, 1st ed. Springer Series in Statistics. Springer, 2011). To facilitate implementation in applications where the effect modifier is high dimensional, our third contribution is a projected influence function (and the corresponding projected TMLE estimator), which retains most of the robustness of its efficient peer and can be easily implemented in applications where the use of the efficient influence function becomes taxing. We compare the projected TMLE estimator with an Inverse Probability of Treatment Weighted estimator (e.g. Robins JM. Marginal structural models. In: Proceedings of the American Statistical Association. Section on Bayesian Statistical Science, 1-10. 1997a, Hernan MA, Brumback B, Robins JM. Marginal structural models to estimate the causal effect of zidovudine on the survival of HIV-positive men. 2000;11:561-570), and a non-targeted G-computation estimator (Robins JM. A new approach to causal inference in mortality studies with sustained exposure periods - application to control of the healthy worker survivor effect. Math Modell. 1986;7:1393-1512.). The comparative performance of these estimators is assessed in a simulation study. The use of the projected TMLE estimator is illustrated in a secondary data analysis for the Sequenced Treatment Alternatives to Relieve Depression (STAR*D) trial where effect modifiers are subject to missing at random.

Generalized closed form solutions for feasible dimension limit and pull-in characteristics of nanocantilever under the Influences of van der Waals and Casimir forces

NASA Astrophysics Data System (ADS)

Mukherjee, Banibrata; Sen, Siddhartha

2018-04-01

This paper presents generalized closed form expressions for determining the dimension limit for the basic design parameters as well as the pull-in characteristics of a nanocantilever beam under the influences of van der Waals and Casimir forces. The coupled nonlinear electromechanical problem of electrostatic nanocantilever is formulated in nondimensional form with Galerkin’s approximation considering the effects of these intermolecular forces and fringe field. The resulting integrals and higher order polynomials are solved numerically to derive the closed form expressions for maximum permissible detachment length, minimum feasible gap spacing and critical pull-in limit. The derived expressions are compared and validated as well with several reported literature showing reasonable agreement. The major advantages of the proposed closed form expressions are that, they do not contain any complex mathematical term or operation unlike in reported literature and thus they will serve as convenient tools for the NEMS community in successful design of various electrostatically actuated nanosystems.

Electrochemical tuning of vertically aligned MoS2 nanofilms and its application in improving hydrogen evolution reaction

PubMed Central

Wang, Haotian; Lu, Zhiyi; Xu, Shicheng; Kong, Desheng; Cha, Judy J.; Zheng, Guangyuan; Hsu, Po-Chun; Yan, Kai; Bradshaw, David; Prinz, Fritz B.; Cui, Yi

2013-01-01

The ability to intercalate guest species into the van der Waals gap of 2D layered materials affords the opportunity to engineer the electronic structures for a variety of applications. Here we demonstrate the continuous tuning of layer vertically aligned MoS2 nanofilms through electrochemical intercalation of Li+ ions. By scanning the Li intercalation potential from high to low, we have gained control of multiple important material properties in a continuous manner, including tuning the oxidation state of Mo, the transition of semiconducting 2H to metallic 1T phase, and expanding the van der Waals gap until exfoliation. Using such nanofilms after different degree of Li intercalation, we show the significant improvement of the hydrogen evolution reaction activity. A strong correlation between such tunable material properties and hydrogen evolution reaction activity is established. This work provides an intriguing and effective approach on tuning electronic structures for optimizing the catalytic activity. PMID:24248362

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

NASA Astrophysics Data System (ADS)

Wang, Xu; Jing, Rong

2017-02-01

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

Role of ligand-ligand vs. core-core interactions in gold nanoclusters.

PubMed

Milowska, Karolina Z; Stolarczyk, Jacek K

2016-05-14

The controlled assembly of ligand-coated gold nanoclusters (NCs) into larger structures paves the way for new applications ranging from electronics to nanomedicine. Here, we demonstrate through rigorous density functional theory (DFT) calculations employing novel functionals accounting for van der Waals forces that the ligand-ligand interactions determine whether stable assemblies can be formed. The study of NCs with different core sizes, symmetry forms, ligand lengths, mutual crystal orientations, and in the presence of a solvent suggests that core-to-core van der Waals interactions play a lesser role in the assembly. The dominant interactions originate from combination of steric effects, augmented by ligand bundling on NC facets, and related to them changes in electronic properties induced by neighbouring NCs. We also show that, in contrast to standard colloidal theory approach, DFT correctly reproduces the surprising experimental trends in the strength of the inter-particle interaction observed when varying the length of the ligands. The results underpin the importance of understanding NC interactions in designing gold NCs for a specific function.

Schottky barrier tuning of the graphene/SnS2 van der Waals heterostructures through electric field

NASA Astrophysics Data System (ADS)

Zhang, Fang; Li, Wei; Ma, Yaqiang; Dai, Xianqi

2018-03-01

Combining the electronic structures of two-dimensional monolayers in ultrathin hybrid nanocomposites is expected to display new properties beyond their single components. The effects of external electric field (Eext) on the electronic structures of monolayer SnS2 with graphene hybrid heterobilayers are studied by using the first-principle calculations. It is demonstrated that the intrinsic electronic properties of SnS2 and graphene are quite well preserved due to the weak van der Waals (vdW) interactions. We find that the n-type Schottky contacts with the significantly small Schottky barrier are formed at the graphene/SnS2 interface. In the graphene/SnS2 heterostructure, the vertical Eext can control not only the Schottky barriers (n-type and p-type) but also contact types (Schottky contact or Ohmic contact) at the interface. The present study would open a new avenue for application of ultrathin graphene/SnS2 heterostructures in future nano- and optoelectronics.

van der Waals Interactions and Hadron Resonance Gas: Role of resonance widths modeling on conserved charges fluctuations

NASA Astrophysics Data System (ADS)

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

2018-02-01

The quantum van der Waals (QvdW) extension of the ideal hadron resonance gas (HRG) model which includes the attractive and repulsive interactions between baryons - the QvdW-HRG model - is applied to study the behavior of the baryon number related susceptibilities in the crossover temperature region. Inclusion of the QvdW interactions leads to a qualitatively different behavior of susceptibilities, in many cases resembling lattice QCD simulations. It is shown that for some observables, in particular for χBQ11/χB2, effects of the QvdW interactions essentially cancel out. It is found that the inclusion of the finite resonance widths leads to an improved description of χB2, but it also leads to a worse description of χBQ11/χB2, as compared to the lattice data. On the other hand, inclusion of the extra, unconfirmed baryons into the hadron list leads to a simultaneous improvement in the description of both observables.

Van der Waals Interactions in Aspirin

NASA Astrophysics Data System (ADS)

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.

Signatures of van der Waals binding: A coupling-constant scaling analysis

NASA Astrophysics Data System (ADS)

Jiao, Yang; Schröder, Elsebeth; Hyldgaard, Per

2018-02-01

The van der Waals (vdW) density functional (vdW-DF) method [Rep. Prog. Phys. 78, 066501 (2015), 10.1088/0034-4885/78/6/066501] describes dispersion or vdW binding by tracking the effects of an electrodynamic coupling among pairs of electrons and their associated exchange-correlation holes. This is done in a nonlocal-correlation energy term Ecnl, which permits density functional theory calculation in the Kohn-Sham scheme. However, to map the nature of vdW forces in a fully interacting materials system, it is necessary to also account for associated kinetic-correlation energy effects. Here, we present a coupling-constant scaling analysis, which permits us to compute the kinetic-correlation energy Tcnl that is specific to the vdW-DF account of nonlocal correlations. We thus provide a more complete spatially resolved analysis of the electrodynamical-coupling nature of nonlocal-correlation binding, including vdW attraction, in both covalently and noncovalently bonded systems. We find that kinetic-correlation energy effects play a significant role in the account of vdW or dispersion interactions among molecules. Furthermore, our mapping shows that the total nonlocal-correlation binding is concentrated to pockets in the sparse electron distribution located between the material fragments.

Investigation of Gene Expression Correlating With Centrosome Amplification in Development and Progression of Breast Cancer

DTIC Science & Technology

2004-09-01

M. A., Broerse, J. J., deVries, J. B., vandenBerg, K. K., Knaan, 33. Papa, D., Li, S. A. & Li, J. J. (2003) Mol. Carcinog. 38, 97-105. S. & van der ...Veer LI, Dai H, van de Vijver MJ, et al. Gene (n = 84). These data are similar to those of van de expression profiling predicts clinical outcome of...breast Vijver et al,"O who demonstrated a significant cancer. Nature 2002;415:530-536. correlation between outcome and expression of 70 10 van de Vijver

A theoretical study of optical contact of vitreous silica

NASA Technical Reports Server (NTRS)

Barber, T. D.

1972-01-01

Optical contact has been proposed as a method of bonding quartz parts of the Stanford relativity satellite. The theory of the van der Waals force is outlined and applied to the problem of optical contact. The effect of various contaminations is discussed and a program of experimentation for further study of the problem is presented.

Roles of additives and surface control in slurry atomization

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

Tsai, S.C.

1990-03-01

This quarterly report describes a quantitative correlation between the flow behavior index of a micronized coal slurry and the interparticular van der Waals attraction force as measured by the Hamaker constant. Preliminary results on the effects of interparticular electrostatic repulsion and the liquid viscosity on both the flow behavior and the relative viscosity are also presented.

A Monte Carlo Study of Skewed Theta Distributions on DIF Indices.

ERIC Educational Resources Information Center

Monaco, Malina

The effects of skewed theta distributions on indices of differential item functioning (DIF) were studied, comparing Mantel Haenszel (N. Mantel and W. Haenszel, 1959) and DFIT (N. S. Raju, W. J. van der Linden, and P. F. Fleer) (noncompensatory DIF). The significance of the study is that in educational and psychological data, the distributions one…

Versatile van der Waals Density Functional Based on a Meta-Generalized Gradient Approximation

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

Peng, Haowei; Yang, Zeng-Hui; Perdew, John P.

A “best-of-both-worlds” van der Waals (vdW) density functional is constructed, seamlessly supplementing the strongly constrained and appropriately normed (SCAN) meta-generalized gradient approximation for short- and intermediate-range interactions with the long-range vdW interaction from r VV 10 , the revised Vydrov–van Voorhis nonlocal correlation functional. The resultant SCAN + r VV 10 is the only vdW density functional to date that yields excellent interlayer binding energies and spacings, as well as intralayer lattice constants in 28 layered materials. Its versatility for various kinds of bonding is further demonstrated by its good performance for 22 interactions between molecules; the cohesive energies andmore » lattice constants of 50 solids; the adsorption energy and distance of a benzene molecule on coinage-metal surfaces; the binding energy curves for graphene on Cu(111), Ni(111), and Co(0001) surfaces; and the rare-gas solids. We argue that a good semilocal approximation should (as SCAN does) capture the intermediate-range vdW through its exchange term. We have found an effective range of the vdW interaction between 8 and 16 Å for systems considered here, suggesting that this interaction is negligibly small at the larger distances where it reaches its asymptotic power-law decay.« less

Versatile van der Waals Density Functional Based on a Meta-Generalized Gradient Approximation

DOE PAGES

Peng, Haowei; Yang, Zeng-Hui; Perdew, John P.; ...

2016-10-12

A “best-of-both-worlds” van der Waals (vdW) density functional is constructed, seamlessly supplementing the strongly constrained and appropriately normed (SCAN) meta-generalized gradient approximation for short- and intermediate-range interactions with the long-range vdW interaction from r VV 10 , the revised Vydrov–van Voorhis nonlocal correlation functional. The resultant SCAN + r VV 10 is the only vdW density functional to date that yields excellent interlayer binding energies and spacings, as well as intralayer lattice constants in 28 layered materials. Its versatility for various kinds of bonding is further demonstrated by its good performance for 22 interactions between molecules; the cohesive energies andmore » lattice constants of 50 solids; the adsorption energy and distance of a benzene molecule on coinage-metal surfaces; the binding energy curves for graphene on Cu(111), Ni(111), and Co(0001) surfaces; and the rare-gas solids. We argue that a good semilocal approximation should (as SCAN does) capture the intermediate-range vdW through its exchange term. We have found an effective range of the vdW interaction between 8 and 16 Å for systems considered here, suggesting that this interaction is negligibly small at the larger distances where it reaches its asymptotic power-law decay.« less

Photoionization of rare gas clusters

NASA Astrophysics Data System (ADS)

Zhang, Huaizhen

This thesis concentrates on the study of photoionization of van der Waals clusters with different cluster sizes. The goal of the experimental investigation is to understand the electronic structure of van der Waals clusters and the electronic dynamics. These studies are fundamental to understand the interaction between UV-X rays and clusters. The experiments were performed at the Advanced Light Source at Lawrence Berkeley National Laboratory. The experimental method employs angle-resolved time-of-flight photoelectron spectrometry, one of the most powerful methods for probing the electronic structure of atoms, molecules, clusters and solids. The van der Waals cluster photoionization studies are focused on probing the evolution of the photoelectron angular distribution parameter as a function of photon energy and cluster size. The angular distribution has been known to be a sensitive probe of the electronic structure in atoms and molecules. However, it has not been used in the case of van der Waals clusters. We carried out outer-valence levels, inner-valence levels and core-levels cluster photoionization experiments. Specifically, this work reports on the first quantitative measurements of the angular distribution parameters of rare gas clusters as a function of average cluster sizes. Our findings for xenon clusters is that the overall photon-energy-dependent behavior of the photoelectrons from the clusters is very similar to that of the corresponding free atoms. However, distinct differences in the angular distribution point at cluster-size-dependent effects were found. For krypton clusters, in the photon energy range where atomic photoelectrons have a high angular anisotropy, our measurements show considerably more isotropic angular distributions for the cluster photoelectrons, especially right above the 3d and 4p thresholds. For the valence electrons, a surprising difference between the two spin-orbit components was found. For argon clusters, we found that the angular distribution parameter values of the two-spin-orbit components from Ar 2p clusters are slightly different. When comparing the beta values for Ar between atoms and clusters, we found different results between Ar 3s atoms and clusters, and between Ar 3p atoms and clusters. Argon cluster resonance from surface and bulk were also measured. Furthermore, the angular distribution parameters of Ar cluster photoelectrons and Ar atom photoelectrons in the 3s → np ionization region were obtained.

Forces dictating colloidal interactions between viruses and soil

USGS Publications Warehouse

Chattopadhyay, Sandip; Puls, Robert W.

2000-01-01

The fate and transport of viruses in soil and aquatic environments were studied with respect to the different forces involved in the process of sorption of these viruses on soil particles. In accordance with the classical DLVO theory, we have calculated the repulsive electrostatic forces and the attractive van der Waals forces. Bacteriophages have been used as model sorbates, while different clays have been used as model sorbents. The equations used for the determination of the change in free energy for the process (ΔG) takes into consideration the roughness of the sorbent surfaces. Results indicate that attractive van der Waals forces predominate the process of sorption of the selected bacteriophages on clays.

Experimental study of complex mixed-mode oscillations generated in a Bonhoeffer-van der Pol oscillator under weak periodic perturbation

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

Shimizu, Kuniyasu, E-mail: kuniyasu.shimizu@it-chiba.ac.jp; Sekikawa, Munehisa; Inaba, Naohiko

2015-02-15

Bifurcations of complex mixed-mode oscillations denoted as mixed-mode oscillation-incrementing bifurcations (MMOIBs) have frequently been observed in chemical experiments. In a previous study [K. Shimizu et al., Physica D 241, 1518 (2012)], we discovered an extremely simple dynamical circuit that exhibits MMOIBs. Our model was represented by a slow/fast Bonhoeffer-van der Pol circuit under weak periodic perturbation near a subcritical Andronov-Hopf bifurcation point. In this study, we experimentally and numerically verify that our dynamical circuit captures the essence of the underlying mechanism causing MMOIBs, and we observe MMOIBs and chaos with distinctive waveforms in real circuit experiments.

Some new exact solitary wave solutions of the van der Waals model arising in nature

NASA Astrophysics Data System (ADS)

Bibi, Sadaf; Ahmed, Naveed; Khan, Umar; Mohyud-Din, Syed Tauseef

2018-06-01

This work proposes two well-known methods, namely, Exponential rational function method (ERFM) and Generalized Kudryashov method (GKM) to seek new exact solutions of the van der Waals normal form for the fluidized granular matter, linked with natural phenomena and industrial applications. New soliton solutions such as kink, periodic and solitary wave solutions are established coupled with 2D and 3D graphical patterns for clarity of physical features. Our comparison reveals that the said methods excel several existing methods. The worked-out solutions show that the suggested methods are simple and reliable as compared to many other approaches which tackle nonlinear equations stemming from applied sciences.

A Scalable Implementation of Van der Waals Density Functionals

NASA Astrophysics Data System (ADS)

Wu, Jun; Gygi, Francois

2010-03-01

Recently developed Van der Waals density functionals[1] offer the promise to account for weak intermolecular interactions that are not described accurately by local exchange-correlation density functionals. In spite of recent progress [2], the computational cost of such calculations remains high. We present a scalable parallel implementation of the functional proposed by Dion et al.[1]. The method is implemented in the Qbox first-principles simulation code (http://eslab.ucdavis.edu/software/qbox). Application to large molecular systems will be presented. [4pt] [1] M. Dion et al. Phys. Rev. Lett. 92, 246401 (2004).[0pt] [2] G. Roman-Perez and J. M. Soler, Phys. Rev. Lett. 103, 096102 (2009).

Layered uranium(VI) hydroxides: structural and thermodynamic properties of dehydrated schoepite α-UO₂(OH)₂.

PubMed

Weck, Philippe F; Kim, Eunja

2014-12-07

The structure of dehydrated schoepite, α-UO2(OH)2, was investigated using computational approaches that go beyond standard density functional theory and include van der Waals dispersion corrections (DFT-D). Thermal properties of α-UO2(OH)2, were also obtained from phonon frequencies calculated with density functional perturbation theory (DFPT) including van der Waals dispersion corrections. While the isobaric heat capacity computed from first-principles reproduces available calorimetric data to within 5% up to 500 K, some entropy estimates based on calorimetric measurements for UO3·0.85H2O were found to overestimate by up to 23% the values computed in this study.

Electrostatics of electron-hole interactions in van der Waals heterostructures

NASA Astrophysics Data System (ADS)

Cavalcante, L. S. R.; Chaves, A.; Van Duppen, B.; Peeters, F. M.; Reichman, D. R.

2018-03-01

The role of dielectric screening of electron-hole interaction in van der Waals heterostructures is theoretically investigated. A comparison between models available in the literature for describing these interactions is made and the limitations of these approaches are discussed. A simple numerical solution of Poisson's equation for a stack of dielectric slabs based on a transfer matrix method is developed, enabling the calculation of the electron-hole interaction potential at very low computational cost and with reasonable accuracy. Using different potential models, direct and indirect exciton binding energies in these systems are calculated within Wannier-Mott theory, and a comparison of theoretical results with recent experiments on excitons in two-dimensional materials is discussed.

Density, structure, and dynamics of water: The effect of van der Waals interactions

NASA Astrophysics Data System (ADS)

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

2011-01-01

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.

Scanning Probe Microscopy and Electrical Transport Studies of Ferroelectric Thin Films and 2D van der Waals Materials

NASA Astrophysics Data System (ADS)

Xiao, Zhiyong

In this dissertation, I present the scanning microscopy and electrical transport studies of ferroelectric thin films and ferroic/2D van der Waals heterostructures. Based on the conducting probe atomic force microscopy and piezo-response force microscopy (PFM) studies of the static and dynamic behavior of ferroelectric domain walls (DW), we found that the ferroelectric polymer poly(vinylidene-fluoride-trifluorethylene) P(VDF-TrFE) is composed of two-dimensional (2D) ferroelectric monolayers (MLs) that are weakly coupled to each other. We also observed polarization asymmetry in epitaxial thin films of ferroelectric Pb(Zr,Ti)O3, which is attributed to the screening properties of the underlying conducting oxide. PFM studies also reveal ferroelectric relaxor-type behavior in ultrathin Sr(Zr,Ti)O3 films epitaxially deposited on Ge. We exploited scanning-probe-controlled domain patterning in a P(VDF-TrFE) top layer to induce nonvolatile modulation of the conduction characteristic of ML molybdenum disulfide (MoS2) between a transistor and a junction state. In the presence of a DW, MoS2 exhibits rectified Ids-Vds (IV) characteristics that are well described by the thermionic emission model. This approach can be applied to a wide range of van der Waals materials to design various functional homojunctions and nanostructures. We also studied the interfacial charge transfer effect between graphene and magnetoelectric Cr2O3 via electrostatic force microscopy and Kelvin probe force microscopy, which reveal p-type doping with up to 150 meV shift of the Fermi level. The graphene/Cr2O3 heterostructure is promising for developing magnetoelectric graphene transistors for spintronic applications.

Mechanical deformation of carbon nanotube nano-rings on flat substrate

NASA Astrophysics Data System (ADS)

Zheng, Meng; Ke, Changhong

2011-04-01

We present a numerical analysis of the mechanical deformation of carbon nanotube (CNT) nano-rings on flat graphite substrates, which is motivated by our recent experimental findings on the elastic deformation of CNT nano-rings. Our analysis considers a perfectly circular CNT ring formed by bending a straight individual or bundled single-walled nanotube to connect its two ends. The seamless CNT ring is placed vertically on a flat graphite substrate and its respective deformation curvatures under zero external force, compressive, and tensile forces are determined using a continuum model based on nonlinear elastica theory. Our results show that the van der Waals interaction between the CNT ring and the substrate has profound effects on the deformation of the CNT ring, and that the interfacial binding interaction between the CNT ring and the substrate is strongly modulated by the ring deformation. Our results demonstrate that the CNT ring in force-free conditions has a flat ring segment in contact with the substrate if the ring radius R ≥√EI/2Wvdw , in which EI is the flexural rigidity of the nanotube and Wvdw is the per-unit-length van der Waals energy between the flat ring segment and the substrate. Our results reveal that the load-deformation profiles of the CNT ring under tensile loadings exhibit bifurcation behavior, which is ascribed to its van der Waals interaction with the substrate and is dependent on its relaxed conformation on the substrate. Our work suggests that CNT nano-rings are promising for a number of applications, such as ultrasensitive force sensors and stretchable and flexible structural components in nanoscale mechanical and electromechanical systems.

Bandgap engineering in van der Waals heterostructures of blue phosphorene and MoS{sub 2}: A first principles calculation

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

Zhang, Z.Y.; Si, M.S., E-mail: sims@lzu.edu.cn; Peng, S.L.

2015-11-15

Blue phosphorene (BP) was theoretically predicted to be thermally stable recently. Considering its similar in-layer hexagonal lattice to MoS{sub 2}, MoS{sub 2} could be an appropriate substrate to grow BP in experiments. In this work, the van der Waals (vdW) heterostructures are constructed by stacking BP on top of MoS{sub 2}. The thermal stability and electronic structures are evaluated based on first principles calculations with vdW-corrected exchange-correlation functional. The formation of the heterostructures is demonstrated to be exothermic and the most stable stacking configuration is confirmed. The heterostructures BP/MoS{sub 2} preserve both the properties of BP and MoS{sub 2} butmore » exhibit relatively narrower bandgaps due to the interlayer coupling effect. The band structures can be further engineered by applying external electric fields. An indirect–direct bandgap transition in bilayer BP/MoS{sub 2} is demonstrated to be controlled by the symmetry property of the built-in electric dipole fields. - Graphical abstract: An indirect-direct band gap transition occurs in van der Waals heterostructure of MoS{sub 2}/BP under external electric fields which is demonstrated to be controlled by the symmetry of the built-in electric dipole fields. - Highlights: • The stacking of heterostructures of BP/MoS{sub 2} is demonstrated to be exothermic. • This suggests that it is possible to grow BP using MoS{sub 2} as the substrate. • The band structures of the heterostructures are exploited. • It realizes an indirect–direct gap transition under external electric fields. • The symmetry of the built-in electric dipole fields controls such gap transition.« less

Corresponding-states laws for protein solutions.

PubMed

Katsonis, Panagiotis; Brandon, Simon; Vekilov, Peter G

2006-09-07

The solvent around protein molecules in solutions is structured and this structuring introduces a repulsion in the intermolecular interaction potential at intermediate separations. We use Monte Carlo simulations with isotropic, pair-additive systems interacting with such potentials. We test if the liquid-liquid and liquid-solid phase lines in model protein solutions can be predicted from universal curves and a pair of experimentally determined parameters, as done for atomic and colloid materials using several laws of corresponding states. As predictors, we test three properties at the critical point for liquid-liquid separation: temperature, as in the original van der Waals law, the second virial coefficient, and a modified second virial coefficient, all paired with the critical volume fraction. We find that the van der Waals law is best obeyed and appears more general than its original formulation: A single universal curve describes all tested nonconformal isotropic pair-additive systems. Published experimental data for the liquid-liquid equilibrium for several proteins at various conditions follow a single van der Waals curve. For the solid-liquid equilibrium, we find that no single system property serves as its predictor. We go beyond corresponding-states correlations and put forth semiempirical laws, which allow prediction of the critical temperature and volume fraction solely based on the range of attraction of the intermolecular interaction potential.

The relationship between crystal structure and methyl and t-butyl group dynamics in van der Waals organic solids

NASA Astrophysics Data System (ADS)

Beckmann, Peter A.; Paty, Carol; Allocco, Elizabeth; Herd, Maria; Kuranz, Carolyn; Rheingold, Arnold L.

2004-03-01

We report x-ray diffractometry in a single crystal of 2-t-butyl-4-methylphenol (TMP) and low-frequency solid state nuclear magnetic resonance (NMR) proton relaxometry in a polycrystalline sample of TMP. The x-ray data show TMP to have a monoclinic, P21/c, structure with eight molecules per unit cell and two crystallographically inequivalent t-butyl group (C(CH3)3) sites. The proton spin-lattice relaxation rates were measured between 90 and 310 K at NMR frequencies of 8.50, 22.5, and 53.0 MHz. The relaxometry data is fitted with two models characterizing the dynamics of the t-butyl groups and their constituent methyl groups, both of which are consistent with the determined x-ray structure. In addition to presenting results for TMP, we review previously reported x-ray diffractometry and low-frequency NMR relaxometry in two other van der Waals solids which have a simpler structure. In both cases, a unique model for the reorientational dynamics was found. Finally, we review a similar previously reported analysis in a van der Waals solid with a very complex structure in which case fitting the NMR relaxometry requires very many parameters and serves mainly as a flag for a careful x-ray diffraction study.

The generalized van der Waals theory of pure fluids and mixtures: Annual report for September 1985 to November 1986

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

Sandler, S.I.

1986-01-01

The objective of the work is to use the generalized van der Waals theory, as derived earlier (''The Generalized van der Waals Partition Function I. Basic Theory'' by S.I. Sandler, Fluid Phase Equilibria 19, 233 (1985)) to: (1) understand the molecular level assumptions inherent in current thermodynamic models; (2) use theory and computer simulation studies to test these assumptions; and (3) develop new, improved thermodynamic models based on better molecular level assumptions. From such a fundamental study, thermodynamic models will be developed that will be applicable to mixtures of molecules of widely different size and functionality, as occurs in themore » processing of heavy oils, coal liquids and other synthetic fuels. An important aspect of our work is to reduce our fundamental theoretical developments to engineering practice through extensive testing and evaluation with experimental data on real mixtures. During the first year of this project important progress was made in the areas specified in the original proposal, as well as several subsidiary areas identified as the work progressed. Some of this work has been written up and submitted for publication. Manuscripts acknowledging DOE support, together with a very brief description, are listed herein.« less

Excitons in one-dimensional van der Waals materials: Sb2S3 nanoribbons

NASA Astrophysics Data System (ADS)

Caruso, Fabio; Filip, Marina R.; Giustino, Feliciano

2015-09-01

Antimony sulphide Sb2S3 has emerged as a promising material for a variety of energy applications ranging from solar cells to thermoelectrics and solid-state batteries. The most distinctive feature of Sb2S3 is its crystal structure, which consists of parallel 1-nm-wide ribbons held together by weak van der Waals forces. This structure clearly suggests that it should be possible to isolate individual Sb2S3 ribbons using micromechanical or liquid-phase exfoliation techniques. However, it is not clear yet how to identify the ribbons postexfoliation using standard optical probes. Using state-of-the-art first-principles calculations based on many-body perturbation theory, here we show that individual ribbons of Sb2S3 carry optical signatures clearly distinct from those of bulk Sb2S3 . In particular, we find a large blueshift of the optical absorption edge (from 1.38 to 2.30 eV) resulting from the interplay between a reduced screening and the formation of bound excitons. In addition, we observe a transition from an indirect band gap to a direct gap, suggesting an enhanced photoluminescence in the green. These unique fingerprints will enable extending the research on van der Waals materials to the case of one-dimensional chalchogenides.

Molecular dynamics simulation of the interactions between EHD1 EH domain and multiple peptides* #

PubMed Central

Yu, Hua; Wang, Mao-Jun; Xuan, Nan-Xia; Shang, Zhi-Cai; Wu, Jun

2015-01-01

Objective: To provide essential information for peptide inhibitor design, the interactions of Eps15 homology domain of Eps15 homology domain-containing protein 1 (EHD1 EH domain) with three peptides containing NPF (asparagine-proline-phenylalanine), DPF (aspartic acid-proline-phenylalanine), and GPF (glycine-proline-phenylalanine) motifs were deciphered at the atomic level. The binding affinities and the underlying structure basis were investigated. Methods: Molecular dynamics (MD) simulations were performed on EHD1 EH domain/peptide complexes for 60 ns using the GROMACS package. The binding free energies were calculated and decomposed by molecular mechanics/generalized Born surface area (MM/GBSA) method using the AMBER package. The alanine scanning was performed to evaluate the binding hot spot residues using FoldX software. Results: The different binding affinities for the three peptides were affected dominantly by van der Waals interactions. Intermolecular hydrogen bonds provide the structural basis of contributions of van der Waals interactions of the flanking residues to the binding. Conclusions: van der Waals interactions should be the main consideration when we design peptide inhibitors of EHD1 EH domain with high affinities. The ability to form intermolecular hydrogen bonds with protein residues can be used as the factor for choosing the flanking residues. PMID:26465136

Efficient Carrier-to-Exciton Conversion in Field Emission Tunnel Diodes Based on MIS-Type van der Waals Heterostack.

PubMed

Wang, Shunfeng; Wang, Junyong; Zhao, Weijie; Giustiniano, Francesco; Chu, Leiqiang; Verzhbitskiy, Ivan; Zhou Yong, Justin; Eda, Goki

2017-08-09

We report on efficient carrier-to-exciton conversion and planar electroluminescence from tunnel diodes based on a metal-insulator-semiconductor (MIS) van der Waals heterostack consisting of few-layer graphene (FLG), hexagonal boron nitride (hBN), and monolayer tungsten disulfide (WS 2 ). These devices exhibit excitonic electroluminescence with extremely low threshold current density of a few pA·μm -2 , which is several orders of magnitude lower compared to the previously reported values for the best planar EL devices. Using a reference dye, we estimate the EL quantum efficiency to be ∼1% at low current density limit, which is of the same order of magnitude as photoluminescence quantum yield at the equivalent excitation rate. Our observations reveal that the efficiency of our devices is not limited by carrier-to-exciton conversion efficiency but by the inherent exciton-to-photon yield of the material. The device characteristics indicate that the light emission is triggered by injection of hot minority carriers (holes) to n-doped WS 2 by Fowler-Nordheim tunneling and that hBN serves as an efficient hole-transport and electron-blocking layer. Our findings offer insight into the intelligent design of van der Waals heterostructures and avenues for realizing efficient excitonic devices.

A comparative morphological revision of the aphid genus Myzaphis van der Goot, 1913 (Insecta: Hemiptera: Aphididae) revealed a new genus and three new species

PubMed Central

Barjadze, Shalva; Jensen, Andrew S.; Wieczorek, Karina

2018-01-01

The aphid genus Myzaphis van der Goot, 1913 from the tribe Macrosiphini is revised to include eight species. Apterous and alate viviparous females, known fundatrices and known sexual morphs (oviparous females and males) of Myzaphis bucktoni, M. juchnevitschae, M. rosarum, M. tianshanica and M. turanica are re-described and illustrated. Lectotype and paralectotypes of Myzaphis bucktoni and M. turanica are designated. The status of M. komatsubarae nomen dubium is discussed. Myzaphis avariolosa is regarded as a species belonging to the genus Ericaphis. Three new species: M. oezdemirae Kanturski & Barjadze sp. nov., M. tuatayae Kanturski & Barjadze sp. nov. from Turkey and M. rezwanii Kanturski & Barjadze sp. nov. from Iran are described and illustrated. Myzaphis bucktoni is recorded from Portugal for the first time. Diagnosis of the genus Myzaphis van der Goot, 1913 is redefined and a new genus Richardsaphis Kanturski & Barjadze gen. nov. is erected with the type species R. canadensis (Richards) comb. nov. Richardsaphis is for the first time recorded from the USA and hitherto unknown oviparous female and alate male are described and illustrated. Original keys to species of the genus Myzaphis and aphid genera of the tribe Macrosiphini with 2-2-2 first tarsal chaetotaxy are also provided. PMID:29543813

Combining density functional and incremental post-Hartree-Fock approaches for van der Waals dominated adsorbate-surface interactions: Ag{sub 2}/graphene

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

Lara-Castells, María Pilar de, E-mail: Pilar.deLara.Castells@csic.es; Mitrushchenkov, Alexander O.; Stoll, Hermann

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), andmore » 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.« less

Stability of selected volatile contact allergens in different patch test chambers under different storage conditions.

PubMed

Mose, Kristian F; Andersen, Klaus E; Christensen, Lars Porskjaer

2012-04-01

Patch test preparations of volatile substances may evaporate during storage, thereby giving rise to reduced patch test concentrations. To investigate the stability of selected acrylates/methacrylates and fragrance allergens in three different test chambers under different storage conditions. Petrolatum samples of methyl methacrylate (MMA), 2-hydroxyethyl methacrylate (2-HEMA), 2-hydroxypropyl acrylate (2-HPA), cinnamal and eugenol in patch test concentrations were stored in three different test chambers (IQ chamber™, IQ Ultimate™, and Van der Bend® transport container) at room temperature and in a refrigerator. The samples were analysed in triplicate with high-performance liquid chromatography. The decrease in concentration was substantial for all five allergens under both storage conditions in IQ chamber™ and IQ Ultimate™, with the exception of 2-HEMA during storage in the refrigerator. For these two chamber systems, the contact allergen concentration dropped below the stability limit in the following order: MMA, cinnamal, 2-HPA, eugenol, and 2-HEMA. In the Van der Bend® transport container, the contact allergens exhibited acceptable stability under both storage conditions, whereas MMA and 2-HPA required cool storage for maintenance of the limit. The Van der Bend® transport container was the best device for storage of samples of volatile contact allergens. © 2012 John Wiley & Sons A/S.

Cheatgrass facilitates spillover of a seed bank pathogen onto native grass species

Treesearch

Julie Beckstead; Susan E. Meyer; Brian M. Connolly; Michael B. Huck; Laura E. Street

2010-01-01

Attack by pathogens can have ecological consequences for plants at many scales, such as the individual, population and community scale, although the latter is the least studied. Community-level consequences of disease in natural plant communities can drive facilitation in succession (Van der Putten, Van Dijk & Peters 1993), maintain species diversity in...

In situ Van der Pauw measurements of the Ni/YSZ anode during exposure to syngas with phosphine contaminant

NASA Astrophysics Data System (ADS)

Demircan, Oktay; Xu, Chunchuan; Zondlo, John; Finklea, Harry O.

Solid oxide fuel cells (SOFCs) represent an option to provide a bridging technology for energy conversion (coal syngas) as well as a long-term technology (hydrogen from biomass). Whether the fuel is coal syngas or hydrogen from biomass, the effect of impurities on the performance of the anode is a vital question. The anode resistivity during SOFC operation with phosphine-contaminated syngas was studied using the in situ Van der Pauw method. Commercial anode-supported solid oxide fuel cells (Ni/YSZ composite anodes, YSZ electrolytes) were exposed to a synthetic coal syngas mixture (H 2, H 2O, CO, and CO 2) at a constant current and their performance evaluated periodically with electrochemical methods (cyclic voltammetry, impedance spectroscopy, and polarization curves). In one test, after 170 h of phosphine exposure, a significant degradation of cell performance (loss of cell voltage, increase of series resistance and increase of polarization resistance) was evident. The rate of voltage loss was 1.4 mV h -1. The resistivity measurements on Ni/YSZ anode by the in situ Van der Pauw method showed that there were no significant changes in anode resistivity both under clean syngas and syngas with 10 ppm PH 3. XRD analysis suggested that Ni 5P 2 and P 2O 5 are two compounds accumulated on the anode. XPS studies provided support for the presence of two phosphorus phases with different oxidation states on the external anode surface. Phosphorus, in a positive oxidation state, was observed in the anode active layer. Based on these observations, the effect of 10 ppm phosphine impurity (or its reaction products with coal syngas) is assigned to the loss of performance of the Ni/YSZ active layer next to the electrolyte, and not to any changes in the thick Ni/YSZ support layer.

Cosmology with an interacting van der Waals fluid

NASA Astrophysics Data System (ADS)

Elizalde, E.; Khurshudyan, M.

A model for the late-time accelerated expansion of the Universe is considered where a van der Waals fluid interacting with matter plays the role of dark energy. The transition towards this phase in the cosmic evolution history is discussed in detail and, moreover, a complete classification of the future finite-time singularities is obtained for six different possible forms of the nongravitational interaction between dark energy (the van der Waals fluid) and dark matter. This study shows, in particular, that a Universe with a noninteracting three-parameter van der Waals fluid can evolve into a Universe characterized by a type IV (generalized sudden) singularity. On the other hand, for certain values of the parameters, exit from the accelerated expanding phase is possible in the near future, what means that the expansion of the Universe in the future could become decelerated - to our knowledge, this interesting situation is not commonplace in the literature. On the other hand, our study shows that space can be divided into different regions. For some of them, in particular, the nongravitational interactions Q = 3Hbρde, Q = 3Hbρdm and Q = 3Hb(ρde + ρde) may completely suppress future finite-time singularity formation, for sufficiently high values of b. On the other hand, for some other regions of the parameter space, the mentioned interactions would not affect the singularity type, namely the type IV singularity generated in the case of the noninteracting model would be preserved. A similar conclusion has been archived for the cases of Q = 3bHρdeρdm/(ρde + ρdm), Q = 3bHρdm2/(ρ de + ρdm) and Q = 3bHρde2/(ρ de + ρdm) nongravitational interactions, with only one difference: the Q = 3bHρdm2/(ρ de + ρdm) interaction will change the type IV singularity of the noninteracting model into a type II (the sudden) singularity.

The Study of the Intramolecular Heavy Atom Effect in 9,10-Dichlorophenanthrene and 1,2,3,4-Tetrachloronaphthalene Using PMDR Techniques.

DTIC Science & Technology

1978-06-30

Inc . , 1974. 4. C. T. u n , Thesis , UCLA, 1974. 5. N. A. El-Sayed, Acta Phys. Polonica , XXXIV , 649(1968). 6. N. A. El-Sayed , Proceedings for the m...See Refs. 11 ,15 A. de Groot and 3. H. van der Waals, Physica 19, 1128 (1963). L

Roles of additives and surface control in slurry atomization

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

Tsai, S.C.

1990-03-01

This quartery report describes a quantitative correlation between the flow behavior index of a micronized coal slurry and the interparticular van der Waals attraction force a measured by the Hamaker constant. Preliminary results on the effects of interparticular electrostatic repulsion and the liquid viscosity on both the flow behavior and the relative viscosity are also presented. 4 refs., 2 figs., 1 tab.

Roles of additives and surface control in slurry atomization. Quarterly report, April 5, 1990

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

Tsai, S.C.

1990-03-01

This quarterly report describes a quantitative correlation between the flow behavior index of a micronized coal slurry and the interparticular van der Waals attraction force as measured by the Hamaker constant. Preliminary results on the effects of interparticular electrostatic repulsion and the liquid viscosity on both the flow behavior and the relative viscosity are also presented.

Correlational Effects of the Molecular-Tilt Configuration and the Intermolecular van der Waals Interaction on the Charge Transport in the Molecular Junction.

PubMed

Shin, Jaeho; Gu, Kyungyeol; Yang, Seunghoon; Lee, Chul-Ho; Lee, Takhee; Jang, Yun Hee; Wang, Gunuk

2018-06-25

Molecular conformation, intermolecular interaction, and electrode-molecule contacts greatly affect charge transport in molecular junctions and interfacial properties of organic devices by controlling the molecular orbital alignment. Here, we statistically investigated the charge transport in molecular junctions containing self-assembled oligophenylene molecules sandwiched between an Au probe tip and graphene according to various tip-loading forces ( F L ) that can control the molecular-tilt configuration and the van der Waals (vdW) interactions. In particular, the molecular junctions exhibited two distinct transport regimes according to the F L dependence (i.e., F L -dependent and F L -independent tunneling regimes). In addition, the charge-injection tunneling barriers at the junction interfaces are differently changed when the F L ≤ 20 nN. These features are associated to the correlation effects between the asymmetry-coupling factor (η), the molecular-tilt angle (θ), and the repulsive intermolecular vdW force ( F vdW ) on the molecular-tunneling barriers. A more-comprehensive understanding of these charge transport properties was thoroughly developed based on the density functional theory calculations in consideration of the molecular-tilt configuration and the repulsive vdW force between molecules.

Influence of sleep deprivation and auditory intensity on reaction time and response force.

PubMed

Włodarczyk, Dariusz; Jaśkowski, Piotr; Nowik, Agnieszka

2002-06-01

Arousal and activation are two variables supposed to underlie change in response force. This study was undertaken to explain these roles, specifically, for strong auditory stimuli and sleep deficit. Loud auditory stimuli can evoke phasic overarousal whereas sleep deficit leads to general underarousal. Moreover, Van der Molen and Keuss (1979, 1981) showed that paradoxically long reaction times occurred with extremely strong auditory stimuli when the task was difficult, e.g., choice reaction or Simon paradigm. It was argued that this paradoxical behavior related to reaction time is due to active disconnecting of the coupling between arousal and activation to prevent false responses. If so, we predicted that for extremely loud stimuli and for difficult tasks, the lengthening of reaction time should be associated with reduction of response force. The effects of loudness and sleep deficit on response time and force were investigated in three different tasks: simple response, choice response, and Simon paradigm. According to our expectation, we found a detrimental effect of sleep deficit on reaction time and on response force. In contrast to Van der Molen and Keuss, we found no increase in reaction time for loud stimuli (up to 110 dB) even on the Simon task.

Probabilistic analysis for identifying the driving force of protein folding

NASA Astrophysics Data System (ADS)

Tokunaga, Yoshihiko; Yamamori, Yu; Matubayasi, Nobuyuki

2018-03-01

Toward identifying the driving force of protein folding, energetics was analyzed in water for Trp-cage (20 residues), protein G (56 residues), and ubiquitin (76 residues) at their native (folded) and heat-denatured (unfolded) states. All-atom molecular dynamics simulation was conducted, and the hydration effect was quantified by the solvation free energy. The free-energy calculation was done by employing the solution theory in the energy representation, and it was seen that the sum of the protein intramolecular (structural) energy and the solvation free energy is more favorable for a folded structure than for an unfolded one generated by heat. Probabilistic arguments were then developed to determine which of the electrostatic, van der Waals, and excluded-volume components of the interactions in the protein-water system governs the relative stabilities between the folded and unfolded structures. It was found that the electrostatic interaction does not correspond to the preference order of the two structures. The van der Waals and excluded-volume components were shown, on the other hand, to provide the right order of preference at probabilities of almost unity, and it is argued that a useful modeling of protein folding is possible on the basis of the excluded-volume effect.

All-Electrical Spin Field Effect Transistor in van der Waals Heterostructures at Room Temperature

NASA Astrophysics Data System (ADS)

Dankert, André; Dash, Saroj

Spintronics aims to exploit the spin degree of freedom in solid state devices for data storage and information processing. Its fundamental concepts (creation, manipulation and detection of spin polarization) have been demonstrated in semiconductors and spin transistor structures using electrical and optical methods. However, an unsolved challenge is the realization of all-electrical methods to control the spin polarization in a transistor manner at ambient temperatures. Here we combine graphene and molybdenum disulfide (MoS2) in a van der Waals heterostructure to realize a spin field-effect transistor (spin-FET) at room temperature. These two-dimensional crystals offer a unique platform due to their contrasting properties, such as weak spin-orbit coupling (SOC) in graphene and strong SOC in MoS2. The gate-tuning of the Schottky barrier at the MoS2/graphene interface and MoS2 channel yields spins to interact with high SOC material and allows us to control the spin polarization and lifetime. This all-electrical spin-FET at room temperature is a substantial step in the field of spintronics and opens a new platform for testing a plethora of exotic physical phenomena, which can be key building blocks in future device architectures.

Binding mechanisms of DNA/RNA nucleobases adsorbed on graphene under charging: first-principles van der Waals study

NASA Astrophysics Data System (ADS)

Gürel, Hikmet Hakan; Salmankurt, Bahadır

2017-06-01

Graphene is a 2D material that has attracted much attention due to its outstanding properties. Because of its high surface area and unique chemical and physical properties, graphene is a good candidate for biological applications. For this reason, a deep understanding of the mechanism of interaction of graphene with biomolecules is required. In this study, theoretical investigation of van der Waals effects has been conducted using density functional theory. Here we show that the order of the binding energies of five nucleobases with graphene is G  >  A  >  T  >  C  >   U. This trend is in good agreement with most of the theoretical and experimental data. Also, the effects of charging on the electronic and structural properties of the graphene-nucleubase systems are studied for the first time. We show that the binding energy can be changed by adding or removing an electron from the system. The results presented in this work provide fundamental insights into the quantum interactions of DNA with carbon-based nanostructures and will be useful for developments in biotechnology and nanotechnology.

Nonlocal van der Waals functionals: The case of rare-gas dimers and solids

NASA Astrophysics Data System (ADS)

Tran, Fabien; Hutter, Jürg

2013-05-01

Recently, the nonlocal van der Waals (vdW) density functionals [M. Dion, H. Rydberg, E. Schröder, D. C. Langreth, and B. I. Lundqvist, Phys. Rev. Lett. 92, 246401 (2004), 10.1103/PhysRevLett.92.246401] have attracted considerable attention due to their good performance for systems where weak interactions are important. Since the physics of dispersion is included in these functionals, they are usually more accurate and show less erratic behavior than the semilocal and hybrid methods. In this work, several variants of the vdW functionals have been tested on rare-gas dimers (from He2 to Kr2) and solids (Ne, Ar, and Kr) and their accuracy compared to standard semilocal approximations, supplemented or not by an atom-pairwise dispersion correction [S. Grimme, J. Antony, S. Ehrlich, and H. Krieg, J. Chem. Phys. 132, 154104 (2010), 10.1063/1.3382344]. An analysis of the results in terms of energy decomposition is also provided.

Infrared hyperbolic metasurface based on nanostructured van der Waals materials

NASA Astrophysics Data System (ADS)

Li, Peining; Dolado, Irene; Alfaro-Mozaz, Francisco Javier; Casanova, Fèlix; Hueso, Luis E.; Liu, Song; Edgar, James H.; Nikitin, Alexey Y.; Vélez, Saül; Hillenbrand, Rainer

2018-02-01

Metasurfaces with strongly anisotropic optical properties can support deep subwavelength-scale confined electromagnetic waves (polaritons), which promise opportunities for controlling light in photonic and optoelectronic applications. We developed a mid-infrared hyperbolic metasurface by nanostructuring a thin layer of hexagonal boron nitride that supports deep subwavelength-scale phonon polaritons that propagate with in-plane hyperbolic dispersion. By applying an infrared nanoimaging technique, we visualize the concave (anomalous) wavefronts of a diverging polariton beam, which represent a landmark feature of hyperbolic polaritons. The results illustrate how near-field microscopy can be applied to reveal the exotic wavefronts of polaritons in anisotropic materials and demonstrate that nanostructured van der Waals materials can form a highly variable and compact platform for hyperbolic infrared metasurface devices and circuits.

Direction-specific van der Waals attraction between rutile TiO2 nanocrystals

NASA Astrophysics Data System (ADS)

Zhang, Xin; He, Yang; Sushko, Maria L.; Liu, Jia; Luo, Langli; De Yoreo, James J.; Mao, Scott X.; Wang, Chongmin; Rosso, Kevin M.

2017-04-01

Mutual lattice orientations dictate the types and magnitudes of forces between crystalline particles. When lattice polarizability is anisotropic, the van der Waals dispersion attraction can, in principle, contribute to this direction dependence. We report measurement of this attraction between rutile nanocrystals, as a function of their mutual orientation and surface hydration extent. At tens of nanometers of separation, the attraction is weak and shows no dependence on azimuthal alignment or surface hydration. At separations of approximately one hydration layer, the attraction is strongly dependent on azimuthal alignment and systematically decreases as intervening water density increases. Measured forces closely agree with predictions from Lifshitz theory and show that dispersion forces can generate a torque between particles interacting in solution and between grains in materials.

Calculation of noncontact forces between silica nanospheres.

PubMed

Sun, Weifu; Zeng, Qinghua; Yu, Aibing

2013-02-19

Quantification of the interactions between nanoparticles is important in understanding their dynamic behaviors and many related phenomena. In this study, molecular dynamics simulation is used to calculate the interaction potentials (i.e., van der Waals attraction, Born repulsion, and electrostatic interaction) between two silica nanospheres of equal radius in the range of 0.975 to 5.137 nm. The results are compared with those obtained from the conventional Hamaker approach, leading to the development of modified formulas to calculate the van der Waals attraction and Born repulsion between nanospheres, respectively. Moreover, Coulomb's law is found to be valid for calculating the electrostatic potential between nanospheres. The developed formulas should be useful in the study of the dynamic behaviors of nanoparticle systems under different conditions.

Flexible ferroelectric element based on van der Waals heteroepitaxy.

PubMed

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.

Ab-initio adsorption study of chitosan on functionalized graphene: critical role of van der Waals interactions.

PubMed

Rahman, R; Mazumdar, D

2012-03-01

We investigate the adsorption process of an organic biomolecule (chitosan) on epoxy-functionalized graphene using ab-initio density functional methods incorporating van-der-waals (vdW) interactions. The role of London dispersion force on the cohesive energy and conformal preference of the molecule is quantitatively elucidated. Functionalizing graphene with epoxy leads to weak hydrogen-bond interactions with chitosan. Binding energy values increase by over an order of magnitude after including vdW corrections, implying that dispersive interactions dominate the physisorption process. Conformal study show binding upto 30 kcal/mol when the molecule is oriented with the hydroxyl group approaching the functionalized graphene. Our study advances the promise of functionalized graphene for a variety of applications.

Superconducting Ga/GaSe layers grown by van der Waals epitaxy

NASA Astrophysics Data System (ADS)

Desrat, W.; Moret, M.; Briot, O.; Ngo, T.-H.; Piot, B. A.; Jabakhanji, B.; Gil, B.

2018-04-01

We report on the growth of GaSe films by molecular beam epitaxy on both (111)B GaAs and sapphire substrates. X-ray diffraction reveals the perfect crystallinity of GaSe with the c-axis normal to the substrate surface. The samples grown under Ga rich conditions possess an additional gallium film on top of the monochalcogenide layer. This metallic film shows two normal-to-superconducting transitions which are detected at T c ≈ 1.1 K and 6.0 K. They correspond likely to the β and α-phases of gallium in the form of bulk and droplets respectively. Our results demonstrate that van der Waals epitaxy can lead to future high quality hybrid superconductor/monochalcogenide heterostructures.

Flexible ferroelectric element based on van der Waals heteroepitaxy

PubMed Central

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

2017-01-01

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. PMID:28630922

Distal Communication by Chimpanzees (Pan troglodytes): Evidence for Common Ground?

PubMed Central

Leavens, David A.; Reamer, Lisa A.; Mareno, Mary Catherine; Russell, Jamie L.; Wilson, Daniel; Schapiro, Steven J.; Hopkins, William D.

2015-01-01

van der Goot et al. (2014) proposed that distal, deictic communication indexed the appreciation of the psychological state of a common ground between a signaler and a receiver. In their study, great apes did not signal distally, which they construed as evidence for the human uniqueness of a sense of common ground. This study exposed 166 chimpanzees to food and an experimenter, at an angular displacement, to ask, “Do chimpanzees display distal communication?” Apes were categorized as (a) proximal or (b) distal signalers on each of four trials. The number of chimpanzees who communicated proximally did not statistically differ from the number who signaled distally. Therefore, contrary to the claim by van der Goot et al., apes do communicate distally. PMID:26292996

Crystalline multiwall carbon nanotubes and their application as a field emission electron source.

PubMed

Liu, Peng; Zhou, Duanliang; Zhang, Chunhai; Wei, Haoming; Yang, Xinhe; Wu, Yang; Li, Qingwei; Liu, Changhong; Du, Bingchu; Liu, Liang; Jiang, Kaili; Fan, Shoushan

2018-05-18

Using super-aligned carbon nanotube (CNT) film, we have fabricated van der Waals crystalline multiwall CNTs (MWCNT) by adopting high pressure and high temperature processing. The CNTs keep parallel to each other and are distributed uniformly. X-ray diffraction characterization shows peaks at the small angle range, which can be assigned to the spacing of the MWCNT crystals. The mechanical, electrical and thermal properties are all greatly improved compared with the original CNT film. The field emission properties of van der Waals crystalline MWCNTs are tested and they show a better surface morphology stability for the large emission current. We have further fabricated a field emission x-ray tube and demonstrated a precise resolution imaging ability.

International Conference on Coordination Chemistry (23rd) Held at Boulder, Colorado on 29 July - 3 August 1984. Abstracts of Paper.

DTIC Science & Technology

1984-08-03

KlausS Gr er let Krebs MWd Gerald lNe" Anorganlach-Chemlaches Institut der Uivesitat Maopse Corrensstr. 36, D4MO M~nster, Federal Republic of Germany In...chelates previously prepared in theme Laboratories. Also, an intense, low energy band (360 cm-1 ) in the ir spectra of all od the chloro der - ivatives...PLAnIND(II) Luther 9. Erickson, Douglas R. Wright, and Gregory S. Vignoul Grinnell College, GrIonll. lam, USA, 50112 Van der Poel, et &I.* have succeeded

A Connectionist Model of a Continuous Developmental Transition in the Balance Scale Task

ERIC Educational Resources Information Center

Schapiro, Anna C.; McClelland, James L.

2009-01-01

A connectionist model of the balance scale task is presented which exhibits developmental transitions between "Rule I" and "Rule II" behavior [Siegler, R. S. (1976). Three aspects of cognitive development. "Cognitive Psychology," 8, 481-520.] as well as the "catastrophe flags" seen in data from Jansen and van der Maas [Jansen, B. R. J., & van der…

Is It that Difficult to Find a Good Preference Order for the Incremental Algorithm?

ERIC Educational Resources Information Center

Krahmer, Emiel; Koolen, Ruud; Theune, Mariet

2012-01-01

In a recent article published in this journal (van Deemter, Gatt, van der Sluis, & Power, 2012), the authors criticize the Incremental Algorithm (a well-known algorithm for the generation of referring expressions due to Dale & Reiter, 1995, also in this journal) because of its strong reliance on a pre-determined, domain-dependent Preference Order.…

Stochastic responses of Van der Pol vibro-impact system with fractional derivative damping excited by Gaussian white noise.

PubMed

Xiao, Yanwen; Xu, Wei; Wang, Liang

2016-03-01

This paper focuses on the study of the stochastic Van der Pol vibro-impact system with fractional derivative damping under Gaussian white noise excitation. The equations of the original system are simplified by non-smooth transformation. For the simplified equation, the stochastic averaging approach is applied to solve it. Then, the fractional derivative damping term is facilitated by a numerical scheme, therewith the fourth-order Runge-Kutta method is used to obtain the numerical results. And the numerical simulation results fit the analytical solutions. Therefore, the proposed analytical means to study this system are proved to be feasible. In this context, the effects on the response stationary probability density functions (PDFs) caused by noise excitation, restitution condition, and fractional derivative damping are considered, in addition the stochastic P-bifurcation is also explored in this paper through varying the value of the coefficient of fractional derivative damping and the restitution coefficient. These system parameters not only influence the response PDFs of this system but also can cause the stochastic P-bifurcation.

Microscopic Description of Thermodynamics of Lipid Membrane at Liquid-Gel Phase Transition

NASA Astrophysics Data System (ADS)

Kheyfets, B.; Galimzyanov, T.; Mukhin, S.

2018-05-01

A microscopic model of the lipid membrane is constructed that provides analytically tractable description of the physical mechanism of the first order liquid-gel phase transition. We demonstrate that liquid-gel phase transition is cooperative effect of the three major interactions: inter-lipid van der Waals attraction, steric repulsion and hydrophobic tension. The model explicitly shows that temperature-dependent inter-lipid steric repulsion switches the system from liquid to gel phase when the temperature decreases. The switching manifests itself in the increase of lateral compressibility of the lipids as the temperature decreases, making phase with smaller area more preferable below the transition temperature. The model gives qualitatively correct picture of abrupt change at transition temperature of the area per lipid, membrane thickness and volume per hydrocarbon group in the lipid chains. The calculated dependence of phase transition temperature on lipid chain length is in quantitative agreement with experimental data. Steric repulsion between the lipid molecules is shown to be the only driver of the phase transition, as van der Waals attraction and hydrophobic tension are weakly temperature dependent.

The direct-to-indirect band gap crossover in two-dimensional van der Waals Indium Selenide crystals

PubMed Central

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.

2016-01-01

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. PMID:28008964

The direct-to-indirect band gap crossover in two-dimensional van der Waals Indium Selenide crystals.

PubMed

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

2016-12-23

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.

Modulation of surface flatness and van der Waals bonding of two-dimensional materials to reduce contact resistance.

NASA Astrophysics Data System (ADS)

Yue, Dewu; Yoo, Won Jong

Despite that the novel quantum mechanical properties of two-dimension (2D) materials are well explored theoretically, their electronic performance is limited by the contact resistance of the metallic interface and therefore their inherent novel properties are rarely realized experimentally. In this study, we demonstrate that we can largely reduce the contact resistance induced between metal and 2D materials, by controlling the surface condition of 2D materials, eg. surface flatness and van der Waals bonding. To induce the number of more effective carrier conducting modes, we engineer the surface roughness and dangling bonds of the 2D interface in contact with metal. As a result, electrical contact resistance of the metal interface is significantly reduced and carrier mobility in the device level is enhanced correspondingly. This work was supported by the Global Research Laboratory and Global Frontier R&D Programs at the Center for Hybrid Interface Materials, both funded by the Ministry of Science, ICT & Future Planning via the National Research Foundation of Korea (NRF).

Density functional studies of the defect-induced electronic structure modifications in bilayer boronitrene

NASA Astrophysics Data System (ADS)

Ukpong, A. M.; Chetty, N.

2012-05-01

The van der Waals interaction-corrected density functional theory is used in this study to investigate the formation, energetic stability, and inter-layer cohesion in bilayer hexagonal boronitrene. The effect of inter-layer separation on the electronic structure is systematically investigated. The formation and energetic stability of intrinsic defects are also investigated at the equilibrium inter-layer separation. It is found that nonstoichiometric defects, and their complexes, that induce excess nitrogen or excess boron, in each case, are relatively more stable in the atmosphere that corresponds to the excess atomic species. The modifications of the electronic structure due to formation of complexes are also investigated. It is shown that van der Waals density functional theory gives an improved description of the cohesive properties but not the electronic structure in bilayer boronitrene compared to other functionals. We identify energetically favourable topological defects that retain the energy gap in the electronic structure, and discuss their implications for band gap engineering in low-n layer boronitrene insulators. The relative strengths and weaknesses of the functionals in predicting the properties of bilayer boronitrene are also discussed.

Importance of van der Waals interaction on structural, vibrational, and thermodynamic properties of NaCl

NASA Astrophysics Data System (ADS)

Marcondes, Michel L.; Wentzcovitch, Renata M.; Assali, Lucy V. C.

2018-05-01

Thermal equations of state (EOS) are essential in several scientific domains. However, experimental determination of EOS parameters may be limited at extreme conditions, therefore, ab initio calculations have become an important method to obtain them. Density functional theory (DFT) and its extensions with various degrees of approximations for the exchange and correlation (XC) energy is the method of choice, but large errors in the EOS parameters are still common. The alkali halides have been problematic from the onset of this field and the quest for appropriate DFT functionals for such ionic and relatively weakly bonded systems has remained an active topic of research. Here we use DFT + van der Waals functionals to calculate vibrational properties, thermal EOS, thermodynamic properties, and the B1 to B2 phase boundary of NaCl with high precision. Our results reveal a remarkable improvement over the performance of standard local density approximation and generalized gradient approximation functionals for all these properties and phase transition boundary, as well as great sensitivity of anharmonic effects on the choice of XC functional.

Resistive sensitivity functions for van der Pauw astroid and rounded crosses and cloverleafs

NASA Astrophysics Data System (ADS)

Koon, Daniel; Hansen, Ole

2014-03-01

We have calculated the sensitivity of van der Pauw resistances to local resistive variations for circular, square and astroid discs of infinitesimal thickness, as well as for the families of rounded crosses and cloverleafs, as a function of specimen parameters, using the direct formulas of our recent paper (Koon et al. 2013 J. Appl. Phys.114 163710) applied to ``reciprocally dual geometries'' (swapped Dirichlet and Neumann boundary conditions) described by Mareš et al.(2012 Meas. Sci. Technol. 23 045004). These results show that (a) the product of any such sensitivity function times differential area, and thus (b) the ratio of any two sensitivities, is invariant under conformal mapping, allowing for the pointwise determination of the conformal mapping function. The family of rounded crosses, which is bounded in parameter space by the square, the astroid and an ``infinitesimally thin'' cross, seems to represent the best geometry for focusing transport measurements on the center of the specimen while minimizing errors due to edge- or contact-effects. Made possible by an SLU Faculty research grant.

Stochastic responses of Van der Pol vibro-impact system with fractional derivative damping excited by Gaussian white noise

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

Xiao, Yanwen; Xu, Wei, E-mail: weixu@nwpu.edu.cn; Wang, Liang

2016-03-15

This paper focuses on the study of the stochastic Van der Pol vibro-impact system with fractional derivative damping under Gaussian white noise excitation. The equations of the original system are simplified by non-smooth transformation. For the simplified equation, the stochastic averaging approach is applied to solve it. Then, the fractional derivative damping term is facilitated by a numerical scheme, therewith the fourth-order Runge-Kutta method is used to obtain the numerical results. And the numerical simulation results fit the analytical solutions. Therefore, the proposed analytical means to study this system are proved to be feasible. In this context, the effects onmore » the response stationary probability density functions (PDFs) caused by noise excitation, restitution condition, and fractional derivative damping are considered, in addition the stochastic P-bifurcation is also explored in this paper through varying the value of the coefficient of fractional derivative damping and the restitution coefficient. These system parameters not only influence the response PDFs of this system but also can cause the stochastic P-bifurcation.« less

Oscillations and Rolling for Duffing's Equation

NASA Astrophysics Data System (ADS)

Aref'eva, I. Ya.; Piskovskiy, E. V.; Volovich, I. V.

2013-01-01

The Duffing equation has been used to model nonlinear dynamics not only in mechanics and electronics but also in biology and in neurology for the brain process modeling. Van der Pol's method is often used in nonlinear dynamics to improve perturbation theory results when describing small oscillations. However, in some other problems of nonlinear dynamics particularly in case of Duffing-Higgs equation in field theory, for the Einsten-Friedmann equations in cosmology and for relaxation processes in neurology not only small oscillations regime is of interest but also the regime of slow rolling. In the present work a method for approximate solution to nonlinear dynamics equations in the rolling regime is developed. It is shown that in order to improve perturbation theory in the rolling regime it turns out to be effective to use an expansion in hyperbolic functions instead of trigonometric functions as it is done in van der Pol's method in case of small oscillations. In particular the Duffing equation in the rolling regime is investigated using solution expressed in terms of elliptic functions. Accuracy of obtained approximation is estimated. The Duffing equation with dissipation is also considered.

Interfacial interactions between plastic particles in plastics flotation.

PubMed

Wang, Chong-qing; Wang, Hui; Gu, Guo-hua; Fu, Jian-gang; Lin, Qing-quan; Liu, You-nian

2015-12-01

Plastics flotation used for recycling of plastic wastes receives increasing attention for its industrial application. In order to study the mechanism of plastics flotation, the interfacial interactions between plastic particles in flotation system were investigated through calculation of Lifshitz-van der Waals (LW) function, Lewis acid-base (AB) Gibbs function, and the extended Derjaguin-Landau-Verwey-Overbeek potential energy profiles. The results showed that van der Waals force between plastic particles is attraction force in flotation system. The large hydrophobic attraction, caused by the AB Gibbs function, is the dominant interparticle force. Wetting agents present significant effects on the interfacial interactions between plastic particles. It is found that adsorption of wetting agents promotes dispersion of plastic particles and decreases the floatability. Pneumatic flotation may improve the recovery and purity of separated plastics through selective adsorption of wetting agents on plastic surface. The relationships between hydrophobic attraction and surface properties were also examined. It is revealed that there exists a three-order polynomial relationship between the AB Gibbs function and Lewis base component. Our finding provides some insights into mechanism of plastics flotation. Copyright © 2015 Elsevier Ltd. All rights reserved.

Anomalous van der Waals-Casimir interactions on graphene: A concerted effect of temperature, retardation, and non-locality

NASA Astrophysics Data System (ADS)

Ambrosetti, Alberto; Silvestrelli, Pier Luigi

2018-04-01

Dispersion forces play a major role in graphene, largely influencing adhesion of adsorbate moieties and stabilization of functional multilayered structures. However, the reliable prediction of dispersion interactions on graphene up to the relevant ˜10 nm scale is an extremely challenging task: in fact, electromagnetic retardation effects and the highly non-local character of π electrons can imply sizeable qualitative variations of the interaction with respect to known pairwise approaches. Here we address both issues, determining the finite-temperature van der Waals (vdW)-Casimir interaction for point-like and extended adsorbates on graphene, explicitly accounting for the non-local dielectric permittivity. We find that temperature, retardation, and non-locality play a crucial role in determining the actual vdW scaling laws and the stability of both atomic and larger molecular adsorbates. Our results highlight the importance of these effects for a proper description of systems of current high interest, such as graphene interacting with biomolecules, and self-assembly of complex nanoscale structures. Due to the generality of our approach and the observed non-locality of other 2D materials, our results suggest non-trivial vdW interactions from hexagonal mono-layered materials from group 14 of the periodic table, to transition metal dichalcogenides.

Anomalous van der Waals-Casimir interactions on graphene: A concerted effect of temperature, retardation, and non-locality.

PubMed

Ambrosetti, Alberto; Silvestrelli, Pier Luigi

2018-04-07

Dispersion forces play a major role in graphene, largely influencing adhesion of adsorbate moieties and stabilization of functional multilayered structures. However, the reliable prediction of dispersion interactions on graphene up to the relevant ∼10 nm scale is an extremely challenging task: in fact, electromagnetic retardation effects and the highly non-local character of π electrons can imply sizeable qualitative variations of the interaction with respect to known pairwise approaches. Here we address both issues, determining the finite-temperature van der Waals (vdW)-Casimir interaction for point-like and extended adsorbates on graphene, explicitly accounting for the non-local dielectric permittivity. We find that temperature, retardation, and non-locality play a crucial role in determining the actual vdW scaling laws and the stability of both atomic and larger molecular adsorbates. Our results highlight the importance of these effects for a proper description of systems of current high interest, such as graphene interacting with biomolecules, and self-assembly of complex nanoscale structures. Due to the generality of our approach and the observed non-locality of other 2D materials, our results suggest non-trivial vdW interactions from hexagonal mono-layered materials from group 14 of the periodic table, to transition metal dichalcogenides.

Investigation of the electronic structure of Be2+He and Be+He, and static dipole polarisabilities of the helium atom

NASA Astrophysics Data System (ADS)

Dhiflaoui, J.; Bejaoui, M.; Farjallah, M.; Berriche, H.

2018-05-01

The potential energy and spectroscopic constants of the ground and many excited states of the Be+He van der Waals system have been investigated using a one-electron pseudo-potential approach, which is used to replace the effect of the Be2+ core and the electron-He interactions by effective potentials. Furthermore, the core-core interactions are incorporated. This permits the reduction of the number of active electrons of the Be+He van der Waals system to only one electron. Therefore, the potential energy of the ground state as well as the excited states is performed at the SCF level and considering the spin-orbit interaction. The core-core interaction for Be2+He ground state is included using accurate CCSD (T) calculations. Then, the spectroscopic properties of the Be+He electronic states are extracted and compared with the previous theoretical and experimental studies. This comparison has shown a very good agreement for the ground and the first excited states. Moreover, the transition dipole moment has been determined for a large and dense grid of internuclear distances including the spin orbit effect. In addition, a vibrational spacing analysis for the Be2+He and Be+He ground states is performed to extract the He atomic polarisability.

Chemotherapy drugs form ion pores in membranes due to physical interactions with lipids.

PubMed

Ashrafuzzaman, Mohammad; Tseng, Chih-Yuan; Duszyk, Marek; Tuszynski, Jack A

2012-12-01

We demonstrate the effects on membrane of the tubulin-binding chemotherapy drugs: thiocolchicoside and taxol. Electrophysiology recordings across lipid membranes in aqueous phases containing drugs were used to investigate the drug effects on membrane conductance. Molecular dynamics simulation of the chemotherapy drug-lipid complexes was used to elucidate the mechanism at an atomistic level. Both drugs are observed to induce stable ion-flowing pores across membranes. Discrete pore current-time plots exhibit triangular conductance events in contrast to rectangular ones found for ion channels. Molecular dynamics simulations indicate that drugs and lipids experience electrostatic and van der Waals interactions for short periods of time when found within each other's proximity. The energies from these two interactions are found to be similar to the energies derived theoretically using the screened Coulomb and the van der Waals interactions between peptides and lipids due to mainly their charge properties while forming peptide-induced ion channels in lipid bilayers. Experimental and in silico studies together suggest that the chemotherapy drugs induce ion pores inside lipid membranes due to drug-lipid physical interactions. The findings reveal cytotoxic effects of drugs on the cell membrane, which may aid in novel drug development for treatment of cancer and other diseases. © 2012 John Wiley & Sons A/S.

Towards understanding the effects of van der Waals strengths on the electric double-layer structures and capacitive behaviors

NASA Astrophysics Data System (ADS)

Yang, Huachao; Bo, Zheng; Yang, Jinyuan; Yan, Jianhua; Cen, Kefa

2017-10-01

Solid-liquid interactions are considered to play a crucial role in charge storage capability of electric double-layer capacitors (EDLCs). In this work, effects of van der Waals (VDW) strengths on the EDL structures and capacitive performances within two representative electrolytes of solvated aqueous solutions and solvent-free ionic liquids are illuminated by molecular dynamics simulations. Single crystalline metals with similar lattice constant but diverse VDW potentials are employed as electrodes. Upon enhancing VDW strengths, capacitance of aqueous electrolytes first increases conspicuously by ∼34.0% and then descends, manifesting a non-monotonic trend, which goes beyond traditional perspectives. Such unusual observation is interpreted by the excluded-volume effects stemmed from ion-solvent competitions. Stimulated by predominant coulombic interactions, more ions are aggregated at the interface despite of the increasing VDW potentials, facilitating superior screening efficiency and capacitance. However, further enhancing strengths preferentially attracts more solvents instead of ions to the electrified surface, which in turn strikingly repels ions from Helmholtz layers, deteriorating electrode capacitance. An essentially similar feather is also recognized for ionic liquids, while the corresponding mechanisms are prominently ascribed to the suppressed ionic separations issued from cation-anion competitions. We highlight that constructing electrode materials with a moderate-hydrophilicity could further advance the performances of EDLCs.

Micromorphology in unconsolidated landslide sediments - investigating mass movement deposits at a different scale

NASA Astrophysics Data System (ADS)

Jaeger, Daniel; Menzies, John

2015-04-01

In order to reliably reconstruct a landslide event, its triggers, movements and the main factors of influence, a profound knowledge of the slide masses' inner architecture and their internal processes is of great importance. As van der Meer (1996) states, micromorphology permits a complete examination of particles, matrix and all components contained in unconsolidated sediments, as well as an insight into their internal arrangement. So far, thin sections and micromorphology are mainly used for studying marine, periglacial and glacial sediments (e.g. Maltman 1988; van der Meer 1993, Menzies 2000, van Fliet-Lanoe 2010, van der Meer & Menzies 2011). Comparatively little work has been carried out with a focus on landslides (e.g. Bertran & Texier 1999). Therefore, our work is a first attempt at investigating unconsolidated deposits of landslides in the low mountain areas of southern Germany using micromorphological tools. The objective was to observe sedimentary microstructures in order to gain an understanding of the sediments' internal movement, deformation etc. during a slide event. On the investigated landslides near Ebermannstadt (Franconian Alb), Gailnau (Frankenhöhe region) and Talheim (Swabian Alb) samples were taken from small pits or outcrops (depths between 50 cm - 300 cm below the surface) in the upper, central and lower part (foot) of the slide mass. The thin section analyses revealed several differences between the three environments and within the specific landslides themselves. Most prominently, several structures (e.g. water-escape-structures, flow-noses and rotational structures) indicate a crucial impact of water in all three slide masses. Furthermore, the thin sections showed heterogeneous compositions of different sediment materials and aggregates, presumably transported, mixed together and deformed during the slide movement. In Ebermannstadt and Talheim, several ductile and brittle deformation structures (rotational structures, marbled structures, fractures, crushed grains) were obvious in those deposits, proving a rather turbulent mass movement with pervasive pressure and stress and varying phases of deformation. In contrast, thin sections from Gailnau only provided very slight deformation structures, which lead to the assumption of a completely different and steadier type of movement with less pressure. Downslope, samples from all landslides showed accumulations of broken fragments with plasma filling out (parts of) the joints, while samples from the front areas (foot) revealed plasma-dominated, structureless, homogenized sediments with varying amounts of sand particles but with few fragments in it. This leads to the assumption of water-saturated plasma being squeezed out of the main accumulation body during its deposition, creating a flow-type movement in the foremost part of both landslides. The results significantly improved the understanding of the behavior of the landslides as several details in terms of processes and structures could be revealed. The micromorphological analyses also helped to validate presumptions gathered from geomorphological mapping and geophysical soundings. Although continuing research into the microstructure of landslide deposits is necessary, our investigations already illustrate the potential value of micromorphology in this environment. References - Bertran, P. & Texier, J.-P. (1999). Facies and microfacies of slope deposits. Catena 35: 99-121. - Maltman, A. J. (1988). The importance of shear zones in naturally deformed wet sediments. Tectonophysics 145: 163-175. - Menzies, J. (2000). Micromorphological analyses of microfabrics and microstructures, indicative of deformation processes. In: Maltman, A. J. Hubbard, B., Hambrey, M.J. (Eds.): Deformations of Glacial Materials. Geological Society, London, 245-258. - van der Meer, J. J. M. (1993). Microscopic evidence of subglacial deformation. Quaternary Science Reviews 12: 553-587. - van der Meer, J.J.M. (1996): Micromorphology. In: Menzies, J. (Ed.): Past Glacial Environments - Sediments, Forms and Techniques. Butterworth-Heinemann, Oxford, 335-356. - van der Meer, J. J. M. & Menzies, J. (2011). The micromorphology of unconsolidated sediments. Sedimentary Geology 238: 213-232. - van Fliet-Lanoe, B. (2010). Frost action. In: Stoops, G. Marcelino, V., Mees, F.: Interpretation of micromorphological features of soils and regoliths. Elsevier, Amsterdam, 81-108.

Effect of Phenol Molecular Structure on Bacterial Transformation Rate Constants in Pond and River Samples

PubMed Central

Paris, Doris F.; Wolfe, N. Lee; Steen, William C.; Baughman, George L.

1983-01-01

Microbial transformation rate constants for a series of phenols were correlated with a property of the substituents, van der Waal's radius. Transformation products were the corresponding catechols, with the exception of p-hydroxybenzoic acid, the product of p-acetylphenol. A different product suggested a different pathway; p-acetylphenol, therefore, was deleted from the data base. PMID:16346236

An Experiential-Based Learning Method Aiming to Improve Spatial Awareness Utilizing GPS, Geocaching, and Geo-Selfies

ERIC Educational Resources Information Center

Flynn, K. Colton; Popp, Jennie

2016-01-01

Many educators have suggested that spatial awareness is vital in the foundation of geography curricula, as well as the ability to utilize geospatial technologies (National Research Council 2006; Kerski 2008; Lee and Bednarz 2009; Favier and Van der Schee 2014). The purpose of this research was to identify a low-cost and effective method to improve…

Observing Imperfection in Atomic Interfaces for van der Waals Heterostructures.

PubMed

Rooney, Aidan P; Kozikov, Aleksey; Rudenko, Alexander N; Prestat, Eric; Hamer, Matthew J; Withers, Freddie; Cao, Yang; Novoselov, Kostya S; Katsnelson, Mikhail I; Gorbachev, Roman; Haigh, Sarah J

2017-09-13

Vertically stacked van der Waals heterostructures are a lucrative platform for exploring the rich electronic and optoelectronic phenomena in two-dimensional materials. Their performance will be strongly affected by impurities and defects at the interfaces. Here we present the first systematic study of interfaces in van der Waals heterostructure using cross-sectional scanning transmission electron microscope (STEM) imaging. By measuring interlayer separations and comparing these to density functional theory (DFT) calculations we find that pristine interfaces exist between hBN and MoS 2 or WS 2 for stacks prepared by mechanical exfoliation in air. However, for two technologically important transition metal dichalcogenide (TMDC) systems, MoSe 2 and WSe 2 , our measurement of interlayer separations provide the first evidence for impurity species being trapped at buried interfaces with hBN interfaces that are flat at the nanometer length scale. While decreasing the thickness of encapsulated WSe 2 from bulk to monolayer we see a systematic increase in the interlayer separation. We attribute these differences to the thinnest TMDC flakes being flexible and hence able to deform mechanically around a sparse population of protruding interfacial impurities. We show that the air sensitive two-dimensional (2D) crystal NbSe 2 can be fabricated into heterostructures with pristine interfaces by processing in an inert-gas environment. Finally we find that adopting glovebox transfer significantly improves the quality of interfaces for WSe 2 compared to processing in air.

Ultrafast Exciton Dissociation and Long-Lived Charge Separation in a Photovoltaic Pentacene-MoS2 van der Waals Heterojunction.

PubMed

Bettis Homan, Stephanie; Sangwan, Vinod K; Balla, Itamar; Bergeron, Hadallia; Weiss, Emily A; Hersam, Mark C

2017-01-11

van der Waals heterojunctions between two-dimensional (2D) layered materials and nanomaterials of different dimensions present unique opportunities for gate-tunable optoelectronic devices. Mixed-dimensional p-n heterojunction diodes, such as p-type pentacene (0D) and n-type monolayer MoS 2 (2D), are especially interesting for photovoltaic applications where the absorption cross-section and charge transfer processes can be tailored by rational selection from the vast library of organic molecules and 2D materials. Here, we study the kinetics of excited carriers in pentacene-MoS 2 p-n type-II heterojunctions by transient absorption spectroscopy. These measurements show that the dissociation of MoS 2 excitons occurs by hole transfer to pentacene on the time scale of 6.7 ps. In addition, the charge-separated state lives for 5.1 ns, up to an order of magnitude longer than the recombination lifetimes from previously reported 2D material heterojunctions. By studying the fractional amplitudes of the MoS 2 decay processes, the hole transfer yield from MoS 2 to pentacene is found to be ∼50%, with the remaining holes undergoing trapping due to surface defects. Overall, the ultrafast charge transfer and long-lived charge-separated state in pentacene-MoS 2 p-n heterojunctions suggest significant promise for mixed-dimensional van der Waals heterostructures in photovoltaics, photodetectors, and related optoelectronic technologies.

A model to estimate the size of nanoparticle agglomerates in gas-solid fluidized beds

NASA Astrophysics Data System (ADS)

de Martín, Lilian; van Ommen, J. Ruud

2013-11-01

The estimation of nanoparticle agglomerates' size in fluidized beds remains an open challenge, mainly due to the difficulty of characterizing the inter-agglomerate van der Waals force. The current approach is to describe micron-sized nanoparticle agglomerates as micron-sized particles with 0.1-0.2-μm asperities. This simplification does not capture the influence of the particle size on the van der Waals attraction between agglomerates. In this paper, we propose a new description where the agglomerates are micron-sized particles with nanoparticles on the surface, acting as asperities. As opposed to previous models, here the van der Waals force between agglomerates decreases with an increase in the particle size. We have also included an additional force due to the hydrogen bond formation between the surfaces of hydrophilic and dry nanoparticles. The average size of the fluidized agglomerates has been estimated equating the attractive force obtained from this method to the weight of the individual agglomerates. The results have been compared to 54 experimental values, most of them collected from the literature. Our model approximates without a systematic error the size of most of the nanopowders, both in conventional and centrifugal fluidized beds, outperforming current models. Although simple, the model is able to capture the influence of the nanoparticle size, particle density, and Hamaker coefficient on the inter-agglomerate forces.

Dual-Gated MoTe2/MoS2 van der Waals Heterojunction p-n Diode

NASA Astrophysics Data System (ADS)

Rai, Amritesh; Movva, Hema C. P.; Kang, Sangwoo; Larentis, Stefano; Roy, Anupam; Tutuc, Emanuel; Banerjee, Sanjay K.

2D materials are promising for future electronic and optoelectronic applications. In this regard, it is important to realize p-n diodes, the most fundamental building block of all modern semiconductor devices, based on these 2D materials. While it is challenging to achieve homojunction diodes in 2D semiconductors due to lack of reliable selective doping techniques, it is relatively easier to achieve diode-like behavior in van der Waals (vdW) heterostructures comprising different 2D semiconductors. Here, we demonstrate dual-gated vdW heterojunction p-n diodes based on p-type MoTe2 and n-type MoS2, with hBN as the top and bottom gate dielectric. The heterostructure stack is assembled using a polymer-based `dry-transfer' technique. Pt contact is used for hole injection in MoTe2, whereas Ag is used for electron injection in MoS2. The dual-gates allow for independent electrostatic tuning of the carriers in MoTe2 and MoS2. Room temperature interlayer current-voltage characteristics reveal a strong gate-tunable rectification behavior. At low temperatures, the diode turn-on voltage increases, whereas the reverse saturation current decreases, in accordance with conventional p-n diode behavior. Dual-Gated MoTe2/MoS2 van der Waals Heterojunction p-n Diode.

On the Computation of Finite Invariant Sets of Mappings.

DTIC Science & Technology

1988-02-01

for the calculation of such invariant cycles. We refer here only to Doedel [1], looss et al [3], Kevrekidis et al [4], Van Veldhuizen ,[6], where further... van Veldhuizen , On Polygonal Approximations of an Invariant Curve, Dept.of Mathem. and Comp. Science, Vrije Universiteit Amsterdam, Techni- cal Report 1987, Math. Comp. to appear DATE Fl .LMED ...of van der Pol’s equation " x2) x - A(l - x ) X’ + x - 0 (16) As shown, for example in [2], the solution satisfies x - 2 cos(wt)+ A (0.75 sin(wt

An Evolutionary Algorithm to Generate Ellipsoid Detectors for Negative Selection

DTIC Science & Technology

2005-03-21

of Congress on Evolutionary Computation. Honolulu,. 58. Lamont, Gary B., Robert E. Marmelstein, and David A. Van Veldhuizen . A Distributed Architecture...antibody and an antigen is a function of several processes including electrostatic interactions, hydrogen bonding, van der Waals interaction, and others [20...Kelly, Patrick M., Don R. Hush, and James M. White. “An Adaptive Algorithm for Modifying Hyperellipsoidal Decision Surfaces”. Journal of Artificial

[A year's review of the treatment of lymphedema of the extremities with the Lymphapress (preliminary note)].

PubMed

Gruffaz, J

1981-01-01

Lymphoedema of the limbs constitutes a chronic disorder. Its form may vary but its treatment is now well-established and medical and surgical therapies have been perfected. We have tried out the Lymphapress as a replacement of Van der Molen's treatment used successfully since 1968. After a brief anatomopathological resume based on Foldi's theory, we recall the various therapeutic indications and the observation of a patient with lymphoedema of the limbs following surgery and Cobalt for seminoma, which we treated using the Lymphapress. The results are analysed. 17 patients were treated between April and June 1979. The method of treatment is not detailed here. This technique does not dispense with secondary compression; it replaces the "piping" used by Van der Molen in major lymphoedema.

A bi-stable nanoelectromechanical non-volatile memory based on van der Waals force

NASA Astrophysics Data System (ADS)

Soon, Bo Woon; Jiaqiang Ng, Eldwin; Qian, You; Singh, Navab; Julius Tsai, Minglin; Lee, Chengkuo

2013-07-01

By using complementary-metal-oxide-semiconductor processes, a silicon based bi-stable nanoelectromechanical non-volatile memory is fabricated and characterized. The main feature of this device is an 80 nm wide and 3 μm high silicon nanofin (SiNF) of a high aspect ratio (1:35). The switching mechanism is realized by electrostatic actuation between two lateral electrodes, i.e., terminals. Bi-stable hysteresis behavior is demonstrated when the SiNF maintains its contact to one of the two terminals by leveraging on van der Waals force even after voltage bias is turned off. The compelling results indicate that this design is promising for realization of high density non-volatile memory application due to its nano-scale footprint and zero on-hold power consumption.

Rarefaction waves in van der Waals fluids with an arbitrary number of degrees of freedom

DOE PAGES

Yuen, Albert; Barnard, John J.

2015-09-30

The isentropic expansion of an instantaneously and homogeneously heated foil is calculated using a 1D fluid model. The initial temperature and density are assumed to be in the vicinity of the critical temperature and solid density, respectively. The fluid is assumed to satisfy the van der Waals equation of state with an arbitrary number of degrees of freedom. Self-similar Riemann solutions are found. With a larger number of degrees of freedom f, depending on the initial dimensionless entropymore » $$˜\\atop{s_0}$$, a richer family of foil expansion behaviors have been found. We calculate the domain in parameter space where these behaviors occur. In total, eight types of rarefaction waves are found and described.« less

Shape matters: The case for Ellipsoids and Ellipsoidal Water

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

Tillack, Andreas F.; Robinson, Bruce H.

We describe the shape potentials used for the van der Waals interactions between soft-ellipsoids used to coarse-grain molecular moieties in our Metropolis Monte-Carlo simulation software. The morphologies resulting from different expressions for these van der Waals interaction potentials are discussed for the case of a prolate spheroid system with a strong dipole at the ellipsoid center. We also show that the calculation of ellipsoids is, at worst, only about fivefold more expensive computationally when compared to a simple Lennard- Jones sphere. Finally, as an application of the ellipsoidal shape we parametrize water from the original SPC water model and observemore » – just through the difference in shape alone – a significant improvement of the O-O radial distribution function when compared to experimental data.« less

Semi-empirical correlation for binary interaction parameters of the Peng-Robinson equation of state with the van der Waals mixing rules for the prediction of high-pressure vapor-liquid equilibrium.

PubMed

Fateen, Seif-Eddeen K; Khalil, Menna M; Elnabawy, Ahmed O

2013-03-01

Peng-Robinson equation of state is widely used with the classical van der Waals mixing rules to predict vapor liquid equilibria for systems containing hydrocarbons and related compounds. This model requires good values of the binary interaction parameter kij . In this work, we developed a semi-empirical correlation for kij partly based on the Huron-Vidal mixing rules. We obtained values for the adjustable parameters of the developed formula for over 60 binary systems and over 10 categories of components. The predictions of the new equation system were slightly better than the constant-kij model in most cases, except for 10 systems whose predictions were considerably improved with the new correlation.

An exact solution of the van der Waals interaction between two ground-state hydrogen atoms

NASA Astrophysics Data System (ADS)

Koga, Toshikatsu; Matsumoto, Shinya

1985-06-01

A momentum space treatment shows that perturbation equations for the H(1s)-H(1s) van der Waals interaction can be exactly solved in their Schrödinger forms without invoking any variational methods. Using the Fock transformation, which projects the momentum vector of an electron from the three-dimensional hyperplane onto the four-dimensional hypersphere, we solve the third order integral-type perturbation equation with respect to the reciprocal of the internuclear distance R. An exact third order wave function is found as a linear combination of infinite number of four-dimensional spherical harmonics. The result allows us to evaluate the exact dispersion energy E6R-6, which is completely determined by the first three coefficients of the above linear combination.

Revisiting the adsorption of copper-phthalocyanine on Au(111) including van der Waals corrections.

PubMed

Lüder, Johann; Eriksson, Olle; Sanyal, Biplab; Brena, Barbara

2014-03-28

We have studied the adsorption of copper-phthalocyanine on Au(111) by means of van der Waals corrected density functional theory using the Tkatchenko-Scheffler method. We have compared the element and site resolved adsorption distances to recent experimental normal-incident X-ray standing wave measurements. The measured adsorption distances could be reproduced within a deviation of 1% for the Cu atom, 1% for the C atoms, and 2% for the N atoms. The molecule was found to have a magnetic moment of 1 μB distributed over the Cu and the N atoms of the pyrrole ring. Simulated scanning tunnel microscopy images based on the total and on the spin-resolved differential charge densities are provided for bias voltages of -1.45 and 1.45 eV.

Molecular adsorption on metal surfaces with van der Waals density functionals

NASA Astrophysics Data System (ADS)

Li, Guo; Tamblyn, Isaac; Cooper, Valentino R.; Gao, Hong-Jun; Neaton, Jeffrey B.

2012-03-01

The adsorption of 1,4-benzenediamine (BDA) on Au(111) and azobenzene on Ag(111) is investigated using density functional theory (DFT) with the nonlocal van der Waals density functional (vdW-DF) and the semilocal Perdew-Burke-Ernzerhof functional. For BDA on Au(111), the inclusion of London dispersion interactions not only dramatically enhances the molecule-substrate binding, resulting in adsorption energies consistent with experimental results, but also significantly alters the BDA binding geometry. For azobenzene on Ag(111), vdW-DFs produce superior adsorption energies compared to those obtained with other dispersion-corrected DFT approaches. These results provide evidence for the applicability of the vdW-DF approach and serve as practical benchmarks for the investigation of molecules adsorbed on noble-metal surfaces.

Efficiency of Launching Highly Confined Polaritons by Infrared Light Incident on a Hyperbolic Material.

PubMed

Dai, Siyuan; Ma, Qiong; Yang, Yafang; Rosenfeld, Jeremy; Goldflam, Michael D; McLeod, Alex; Sun, Zhiyuan; Andersen, Trond I; Fei, Zhe; Liu, Mengkun; Shao, Yinming; Watanabe, Kenji; Taniguchi, Takashi; Thiemens, Mark; Keilmann, Fritz; Jarillo-Herrero, Pablo; Fogler, Michael M; Basov, D N

2017-09-13

We investigated phonon-polaritons in hexagonal boron nitride-a naturally hyperbolic van der Waals material-by means of the scattering-type scanning near-field optical microscopy. Real-space nanoimages we have obtained detail how the polaritons are launched when the light incident on a thin hexagonal boron nitride slab is scattered by various intrinsic and extrinsic inhomogeneities, including sample edges, metallic nanodisks deposited on its top surface, random defects, and surface impurities. The scanned tip of the near-field microscope is itself a polariton launcher whose efficiency proves to be superior to all the other types of polariton launchers we studied. Our work may inform future development of polaritonic nanodevices as well as fundamental studies of collective modes in van der Waals materials.

Two-probe versus van der Pauw method in studying the piezoresistivity of single-wall carbon nanotube thin films

NASA Astrophysics Data System (ADS)

Yao, Yanbo; Duan, Xiaoshuang; Luo, Jiangjiang; Liu, Tao

2017-11-01

The use of the van der Pauw (VDP) method for characterizing and evaluating the piezoresistive behavior of carbon nanomaterial enabled piezoresistive sensors have not been systematically studied. By using single-wall carbon nanotube (SWCNT) thin films as a model system, herein we report a coupled electrical-mechanical experimental study in conjunction with a multiphysics finite element simulation as well as an analytic analysis to compare the two-probe and VDP testing configuration in evaluating the piezoresistive behavior of carbon nanomaterial enabled piezoresistive sensors. The key features regarding the sample aspect ratio dependent piezoresistive sensitivity or gauge factor were identified for the VDP testing configuration. It was found that the VDP test configuration offers consistently higher piezoresistive sensitivity than the two-probe testing method.

The analysis of solutions behaviour of Van der Pol Duffing equation describing local brain hemodynamics

NASA Astrophysics Data System (ADS)

Cherevko, A. A.; Bord, E. E.; Khe, A. K.; Panarin, V. A.; Orlov, K. J.

2017-10-01

This article proposes the generalized model of Van der Pol — Duffing equation for describing the relaxation oscillations in local brain hemodynamics. This equation connects the velocity and pressure of blood flow in cerebral vessels. The equation is individual for each patient, since the coefficients are unique. Each set of coefficients is built based on clinical data obtained during neurosurgical operation in Siberian Federal Biomedical Research Center named after Academician E. N. Meshalkin. The equation has solutions of different structure defined by the coefficients and right side. We investigate the equations for different patients considering peculiarities of their vessel systems. The properties of approximate analytical solutions are studied. Amplitude-frequency and phase-frequency characteristics are built for the small-dimensional solution approximations.

Origin of band gaps in graphene on hexagonal boron nitride

PubMed Central

Jung, Jeil; DaSilva, Ashley M.; MacDonald, Allan H.; Adam, Shaffique

2015-01-01

Recent progress in preparing well-controlled two-dimensional van der Waals heterojunctions has opened up a new frontier in materials physics. Here we address the intriguing energy gaps that are sometimes observed when a graphene sheet is placed on a hexagonal boron nitride substrate, demonstrating that they are produced by an interesting interplay between structural and electronic properties, including electronic many-body exchange interactions. Our theory is able to explain the observed gap behaviour by accounting first for the structural relaxation of graphene’s carbon atoms when placed on a boron nitride substrate, and then for the influence of the substrate on low-energy π-electrons located at relaxed carbon atom sites. The methods we employ can be applied to many other van der Waals heterojunctions. PMID:25695638

Piezotronic effect in 1D van der Waals solid of elemental tellurium nanobelt for smart adaptive electronics

NASA Astrophysics Data System (ADS)

Gao, Shengjie; Wang, Yixiu; Wang, Ruoxing; Wu, Wenzhuo

2017-10-01

Emerging technologies in wearable systems demand that functional devices can adaptively interact with the human body, where mechanical stimuli are ubiquitous and abundant. However, the electrical manipulation of charge carriers underpins the operations of state-of-the-art devices, and the effective control of interfacial energetics for charge carriers by the dynamic mechanical stimuli is still a relatively unexplored degree of freedom for semiconductor nanodevices. Piezotronic effect in nanostructured piezoelectric semiconductors offers exciting opportunities in addressing the above challenges. Here we report the first experimental exploration of piezotronic effect in 1D van der Waals solid of p-type tellurium nanobelt and systematically investigate the strain-gated charge carriers transport properties. The strain-induced polarization charges at the [10\\bar{1}0] surfaces of Te nanobelt can modulate the electronic transport through the interfacial effect on the Schottky contacts and the volumetric effect on the conducting channel. The competing phenomenon between interfacial and volumetric effects has been studied for the first time in piezotronics. Our research allows the access to a broad range of characterization and application of Te nanomaterials for piezotronics and could guide the future study of piezotronic effect in other materials. This progress in piezotronics, together with emerging methods for deterministic production and assembly of nanomaterials, leads to compelling opportunities for research from basic studies of piezoelectricity and semiconductor properties in functional nanomaterials to the development of ‘smarter’ electronics and optoelectronics.

What correlation effects are covered by density functional theory?

NASA Astrophysics Data System (ADS)

He, Yuan; Grafenstein, Jurgen; Kraka, Elfi; Cremer, Dieter

The electron density distribution rho(r) generated by a DFT calculation was systematically studied by comparison with a series of reference densities obtained by wavefunction theory (WFT) methods that cover typical electron correlation effects. As a sensitive indicator for correlation effects the dipole moment of the CO molecule was used. The analysis reveals that typical LDA and GGA exchange functionals already simulate effects that are actually reminiscent of pair and three-electron correlation effects covered by MP2, MP4, and CCSD(T) in WFT. Correlation functionals contract the density towards the bond and the valence region thus taking negative charge out of the van der Waals region. It is shown that these improvements are relevant for the description of van der Waals interactions. Similar to certain correlated single-determinant WFT methods, BLYP and other GGA functionals underestimate ionic terms needed for a correct description of polar bonds. This is compensated for in hybrid functionals by mixing in HF exchange. The balanced mixing of local and non-local exchange and correlation effects leads to the correct description of polar bonds as in the B3LYP description of the CO molecule. The density obtained with B3LYP is closer to CCSD and CCSD(T) than to MP2 or MP4, which indicates that the B3LYP hybrid functional mimics those pair and three-electron correlation effects, which in WFT are only covered by coupled cluster methods.

The effects of intermolecular interactions on the physical properties of organogels in edible oils.

PubMed

Lupi, Francesca R; Greco, Valeria; Baldino, Noemi; de Cindio, Bruno; Fischer, Peter; Gabriele, Domenico

2016-12-01

The microstructure of organogels based on monoglycerides of fatty acids (MAGs) and policosanol and on different edible oils was investigated by using different techniques (calorimetry, nuclear magnetic resonance, infrared spectroscopy, rheology, polarized light microscopy) towards a better understanding and control of the oil gelation phenomena. Dynamic moduli were related via a fractal model to microstructural information such as solid content and fractal dimension. Infrared spectroscopy evidenced that network structure in MAGs gel is mainly due to hydrogen bonding, whereas in policosanol system is mainly given by van der Waals interactions. Because of the different relative contribution of molecular interactions, the investigated organogelators exhibit a distinguished macroscopic behavior. MAGs are sensitive to the utilized oil and structuration occurs quickly, even though at a temperature lower than policosanol. Policosanol organogels exhibit a behavior independent of the used oil and a slower gelation rate, as a result of the weaker van der Waals interactions. Nevertheless, at lower concentration a stronger final gel is obtained, probably due to of the large number of interactions arising among the long alkyl chains of the fatty alcohols. Obtained results evidenced that policosanol is very effective in gelation of different oils and seems promising for potential commercial uses. Copyright © 2016 Elsevier Inc. All rights reserved.

Electrodynamics of Lipid Membrane Interactions in the Presence of Zwitterionic Buffers

PubMed Central

Koerner, Megan M.; Palacio, Luis A.; Wright, Johnnie W.; Schweitzer, Kelly S.; Ray, Bruce D.; Petrache, Horia I.

2011-01-01

Due to thermal motion and molecular polarizability, electrical interactions in biological systems have a dynamic character. Zwitterions are dipolar molecules that typically are highly polarizable and exhibit both a positive and a negative charge depending on the pH of the solution. We use multilamellar structures of common lipids to identify and quantify the effects of zwitterionic buffers that go beyond the control of pH. We use the fact that the repeat spacing of multilamellar lipid bilayers is a sensitive and accurate indicator of the force balance between membranes. We show that common buffers can in fact charge up neutral membranes. However, this electrostatic effect is not immediately recognized because of the concomitant modification of dispersion (van der Waals) forces. We show that although surface charging can be weak, electrostatic forces are significant even at large distances because of reduced ionic screening and reduced van der Waals attraction. The zwitterionic interactions that we identify are expected to be relevant for interfacial biological processes involving lipid bilayers, and for a wide range of biomaterials, including amino acids, detergents, and pharmaceutical drugs. An appreciation of zwitterionic electrodynamic character can lead to a better understanding of molecular interactions in biological systems and in soft materials in general. PMID:21767488

Elucidation of the binding mechanism of renin using a wide array of computational techniques and biological assays.

PubMed

Tzoupis, Haralambos; Leonis, Georgios; Avramopoulos, Aggelos; Reis, Heribert; Czyżnikowska, Żaneta; Zerva, Sofia; Vergadou, Niki; Peristeras, Loukas D; Papavasileiou, Konstantinos D; Alexis, Michael N; Mavromoustakos, Thomas; Papadopoulos, Manthos G

2015-11-01

We investigate the binding mechanism in renin complexes, involving three drugs (remikiren, zankiren and enalkiren) and one lead compound, which was selected after screening the ZINC database. For this purpose, we used ab initio methods (the effective fragment potential, the variational perturbation theory, the energy decomposition analysis, the atoms-in-molecules), docking, molecular dynamics, and the MM-PBSA method. A biological assay for the lead compound has been performed to validate the theoretical findings. Importantly, binding free energy calculations for the three drug complexes are within 3 kcal/mol of the experimental values, thus further justifying our computational protocol, which has been validated through previous studies on 11 drug-protein systems. The main elements of the discovered mechanism are: (i) minor changes are induced to renin upon drug binding, (ii) the three drugs form an extensive network of hydrogen bonds with renin, whilst the lead compound presented diminished interactions, (iii) ligand binding in all complexes is driven by favorable van der Waals interactions and the nonpolar contribution to solvation, while the lead compound is associated with diminished van der Waals interactions compared to the drug-bound forms of renin, and (iv) the environment (H2O/Na(+)) has a small effect on the renin-remikiren interaction. Copyright © 2015 Elsevier Inc. All rights reserved.

Strong magnetization and Chern insulators in compressed graphene/CrI 3 van der Waals heterostructures

NASA Astrophysics Data System (ADS)

Zhang, Jiayong; Zhao, Bao; Zhou, Tong; Xue, Yang; Ma, Chunlan; Yang, Zhongqin

2018-02-01

Graphene-based heterostructures are a promising material system for designing the topologically nontrivial Chern insulating devices. Recently, a two-dimensional monolayer ferromagnetic insulator CrI3 was successfully synthesized in experiments [B. Huang et al., Nature (London) 546, 270 (2017), 10.1038/nature22391]. Here, these two interesting materials are proposed to build a heterostructure (Gr /CrI3). Our first-principles calculations show that the system forms a van der Waals (vdW) heterostructure, which is relatively facilely fabricated in experiments. A Chern insulating state is acquired in the Gr /CrI3 heterostructure if the vdW gap is compressed to a distance between about 3.3 and 2.4 Å, corresponding to a required external pressure between about 1.4 and 18.3 GPa. Amazingly, very strong magnetization (about 150 meV) is found in graphene, induced by the substrate CrI3, despite the vdW interactions between them. A low-energy effective model is employed to understand the mechanism. The work functions, contact types, and band alignments of the Gr /CrI3 heterostructure system are also studied. Our work demonstrates that the Gr /CrI3 heterostructure is a promising system to observe the quantum anomalous Hall effect at high temperatures (up to 45 K) in experiments.

Van der Waals Interactions Involving Proteins

NASA Technical Reports Server (NTRS)

Roth, Charles M.; Neal, Brian L.; Lenhoff, Abraham M.

1996-01-01

Van der Waals (dispersion) forces contribute to interactions of proteins with other molecules or with surfaces, but because of the structural complexity of protein molecules, the magnitude of these effects is usually estimated based on idealized models of the molecular geometry, e.g., spheres or spheroids. The calculations reported here seek to account for both the geometric irregularity of protein molecules and the material properties of the interacting media. Whereas the latter are found to fall in the generally accepted range, the molecular shape is shown to cause the magnitudes of the interactions to differ significantly from those calculated using idealized models. with important consequences. First, the roughness of the molecular surface leads to much lower average interaction energies for both protein-protein and protein-surface cases relative to calculations in which the protein molecule is approximated as a sphere. These results indicate that a form of steric stabilization may be an important effect in protein solutions. Underlying this behavior is appreciable orientational dependence, one reflection of which is that molecules of complementary shape are found to exhibit very strong attractive dispersion interactions. Although this has been widely discussed previously in the context of molecular recognition processes, the broader implications of these phenomena may also be important at larger molecular separations, e.g., in the dynamics of aggregation, precipitation, and crystal growth.

Numerical estimation of ultrasonic production of hydrogen: Effect of ideal and real gas based models.

PubMed

Kerboua, Kaouther; Hamdaoui, Oualid

2018-01-01

Based on two different assumptions regarding the equation describing the state of the gases within an acoustic cavitation bubble, this paper studies the sonochemical production of hydrogen, through two numerical models treating the evolution of a chemical mechanism within a single bubble saturated with oxygen during an oscillation cycle in water. The first approach is built on an ideal gas model, while the second one is founded on Van der Waals equation, and the main objective was to analyze the effect of the considered state equation on the ultrasonic hydrogen production retrieved by simulation under various operating conditions. The obtained results show that even when the second approach gives higher values of temperature, pressure and total free radicals production, yield of hydrogen does not follow the same trend. When comparing the results released by both models regarding hydrogen production, it was noticed that the ratio of the molar amount of hydrogen is frequency and acoustic amplitude dependent. The use of Van der Waals equation leads to higher quantities of hydrogen under low acoustic amplitude and high frequencies, while employing ideal gas law based model gains the upper hand regarding hydrogen production at low frequencies and high acoustic amplitudes. Copyright © 2017 Elsevier B.V. All rights reserved.

The role of the van der Waals interactions in the adsorption of anthracene and pentacene on the Ag(111) surface

NASA Astrophysics Data System (ADS)

Morbec, Juliana M.; Kratzer, Peter

2017-01-01

Using first-principles calculations based on density-functional theory (DFT), we investigated the effects of the van der Waals (vdW) interactions on the structural and electronic properties of anthracene and pentacene adsorbed on the Ag(111) surface. We found that the inclusion of vdW corrections strongly affects the binding of both anthracene/Ag(111) and pentacene/Ag(111), yielding adsorption heights and energies more consistent with the experimental results than standard DFT calculations with generalized gradient approximation (GGA). For anthracene/Ag(111) the effect of the vdW interactions is even more dramatic: we found that "pure" DFT-GGA calculations (without including vdW corrections) result in preference for a tilted configuration, in contrast to the experimental observations of flat-lying adsorption; including vdW corrections, on the other hand, alters the binding geometry of anthracene/Ag(111), favoring the flat configuration. The electronic structure obtained using a self-consistent vdW scheme was found to be nearly indistinguishable from the conventional DFT electronic structure once the correct vdW geometry is employed for these physisorbed systems. Moreover, we show that a vdW correction scheme based on a hybrid functional DFT calculation (HSE) results in an improved description of the highest occupied molecular level of the adsorbed molecules.

Corrigendum: Cultural Relativity in Perceiving Emotion From Vocalizations.

PubMed

2014-12-01

Gendron, M., Roberson, D., van der Vyver, J. M., & Barrett, L. F. (2014). Cultural relativity in perceiving emotion from vocalizations. Psychological Science, 25, 911-920. (Original DOI: 10.1177/0956797613517239 ).

Geophysicist in the ranks

NASA Astrophysics Data System (ADS)

President Clinton has tapped Gregory van der Vink, director of planning of the Incorporated Research Institutions for Seismology,to serve on the Scientific and Policy Advisory Committee of the Arms Control and Disarmament Agency.

Critical behavior and microscopic structure of charged AdS black holes via an alternative phase space

NASA Astrophysics Data System (ADS)

Dehyadegari, Amin; Sheykhi, Ahmad; Montakhab, Afshin

2017-05-01

It has been argued that charged Anti-de Sitter (AdS) black holes have similar thermodynamic behavior as the Van der Waals fluid system, provided one treats the cosmological constant as a thermodynamic variable (pressure) in an extended phase space. In this paper, we disclose the deep connection between charged AdS black holes and Van der Waals fluid system from an alternative point of view. We consider the mass of an AdS black hole as a function of square of the charge Q2 instead of the standard Q, i.e. M = M (S ,Q2 , P). We first justify such a change of view mathematically and then ask if a phase transition can occur as a function of Q2 for fixed P. Therefore, we write the equation of state as Q2 =Q2 (T , Ψ) where Ψ (conjugate of Q2) is the inverse of the specific volume, Ψ = 1 / v. This allows us to complete the analogy of charged AdS black holes with Van der Waals fluid system and derive the phase transition as well as critical exponents of the system. We identify a thermodynamic instability in this new picture with real analogy to Van der Waals fluid with physically relevant Maxwell construction. We therefore study the critical behavior of isotherms in Q2- Ψ diagram and deduce all the critical exponents of the system and determine that the system exhibits a small-large black hole phase transition at the critical point (Tc , Qc2 ,Ψc). This alternative view is important as one can imagine such a change for a given single black hole i.e. acquiring charge which induces the phase transition. Finally, we disclose the microscopic properties of charged AdS black holes by using thermodynamic geometry. Interestingly, we find that scalar curvature has a gap between small and large black holes, and this gap becomes exceedingly large as one moves away from the critical point along the transition line. Therefore, we are able to attribute the sudden enlargement of the black hole to the strong repulsive nature of the internal constituents at the phase transition.

Van der Waals Epitaxy of Functional Oxide Heterostructures

NASA Astrophysics Data System (ADS)

Chu, Ying-Hao

In the diligent pursuit of low-power consumption, multifunctional, and environmentally friendly electronics, more sophisticated requirements on functional materials are on demand. Recently, the discovery of 2D layered materials has created a revolution to this field. Pioneered by graphene, these new 2D materials exhibit abundant unusual physical phenomena that is undiscovered in bulk forms. These materials are characterized with their layer form and almost pure 2D electronic behavior. The confinement of charge and heat transport at such ultrathin planes offers possibilities to overcome the bottleneck of present device development in thickness limitation, and thus push the technologies into next generation. Van der Waals epitaxy, an epitaxial growth method to combine 2D and 3D materials, is one of current reliable manufacturing processes to fabricate 2D materials by growing these 2D materials epitaxially on 3D materials. Then, transferring the 2D materials to the substrates for practical applications. In the mean time, van der Waals epitaxy has also been used to create free-standing 3D materials by growing 3D materials on 2D materials and then removing them from 2D materials since the interfacial boding between 2D and 3D materials should be weak van der Waals bonds. In this study, we intend to take the same concept, but to integrate a family of functional materials in order to open new avenue to flexible electronics. Due to the interplay of lattice, charge, orbital, and spin degrees of freedom, correlated electrons in oxides generate a rich spectrum of competing phases and physical properties. Recently, lots of studies have suggested that oxide heterostructures provide a powerful route to create and manipulate the degrees of freedom and offer new possibilities for next generation devices, thus create a new playground for researchers to investigate novel physics and the emergence of fascinating states of condensed matter. In this talk, we use a 2D layered material as the substrate. And we take several oxides as examples to demonstrate a pathway to integrate 3D functional oxides on 2D layered materials.

Stereospecific olefin polymerization catalysts

DOEpatents

Bercaw, John E.; Herzog, Timothy A.

1998-01-01

A metallocene catalyst system for the polymerization of .alpha.-olefins to yield stereospecific polymers including syndiotactic, and isotactic polymers. The catalyst system includes a metal and a ligand of the formula ##STR1## wherein: R.sup.1, R.sup.2, and R.sup.3 are independently selected from the group consisting of hydrogen, C.sub.1 to C.sub.10 alkyl, 5 to 7 membered cycloalkyl, which in turn may have from 1 to 3 C.sub.1 to C.sub.10 alkyls as a substituent, C.sub.6 to C.sub.15 aryl or arylalkyl in which two adjacent radicals may together stand for cyclic groups having 4 to 15 carbon atoms which in turn may be substituted, or Si(R.sup.8).sub.3 where R.sup.8 is selected from the group consisting of C.sub.1 to C.sub.10 alkyl, C.sub.6 to C.sub.15 aryl or C.sub.3 to C.sub.10 cycloalkyl; R.sup.4 and R.sup.6 are substituents both having van der Waals radii larger than the van der Waals radii of groups R.sup.1 and R.sup.3 ; R.sup.5 is a substituent having a van der Waals radius less than about the van der Waals radius of a methyl group; E.sup.1, E.sup.2 are independently selected from the group consisting of Si(R.sup.9).sub.2, Si(R.sup.9).sub.2 --Si(R.sup.9).sub.2, Ge(R.sup.9).sub.2, Sn(R.sup.9).sub.2, C(R.sup.9).sub.2, C(R.sup.9).sub.2 --C(R.sup.9).sub.2, where R.sup.9 is C.sub.1 to C.sub.10 alkyl, C.sub.6 to C.sub.15 aryl or C.sub.3 to C.sub.10 cycloalkyl; and the ligand may have C.sub.S or C.sub.1 -symmetry. Preferred metals are selected from the group consisting of group III, group IV, group V or lanthanide group elements. The catalysts are used to prepare stereoregular polymers including polypropylene from .alpha.-olefin monomers.

Stereospecific olefin polymerization catalysts

DOEpatents

Bercaw, J.E.; Herzog, T.A.

1998-01-13

A metallocene catalyst system is described for the polymerization of {alpha}-olefins to yield stereospecific polymers including syndiotactic, and isotactic polymers. The catalyst system includes a metal and a ligand of the formula shown wherein: R{sup 1}, R{sup 2}, and R{sup 3} are independently selected from the group consisting of hydrogen, C{sub 1} to C{sub 10} alkyl, 5 to 7 membered cycloalkyl, which in turn may have from 1 to 3 C{sub 1} to C{sub 10} alkyls as a substituent, C{sub 6} to C{sub 15} aryl or arylalkyl in which two adjacent radicals may together stand for cyclic groups having 4 to 15 carbon atoms which in turn may be substituted, or Si(R{sup 8}){sub 3} where R{sup 8} is selected from the group consisting of C{sub 1} to C{sub 10} alkyl, C{sub 6} to C{sub 15} aryl or C{sub 3} to C{sub 10} cycloalkyl; R{sup 4} and R{sup 6} are substituents both having van der Waals radii larger than the van der Waals radii of groups R{sup 1} and R{sup 3}; R{sup 5} is a substituent having a van der Waals radius less than about the van der Waals radius of a methyl group; E{sup 1}, E{sup 2} are independently selected from the group consisting of Si(R{sup 9}){sub 2}, Si(R{sup 9}){sub 2}--Si(R{sup 9}){sub 2}, Ge(R{sup 9}){sub 2}, Sn(R{sup 9}){sub 2}, C(R{sup 9}){sub 2}, C(R{sup 9}){sub 2}--C(R{sup 9}){sub 2}, where R{sup 9} is C{sub 1} to C{sub 10} alkyl, C{sub 6} to C{sub 15} aryl or C{sub 3} to C{sub 10} cycloalkyl; and the ligand may have C{sub S} or C{sub 1}-symmetry. Preferred metals are selected from the group consisting of group III, group IV, group V or lanthanide group elements. The catalysts are used to prepare stereoregular polymers including polypropylene from {alpha}-olefin monomers.

Properties of Organic Liquids when Simulated with Long-Range Lennard-Jones Interactions.

PubMed

Fischer, Nina M; van Maaren, Paul J; Ditz, Jonas C; Yildirim, Ahmet; van der Spoel, David

2015-07-14

In order to increase the accuracy of classical computer simulations, existing methodologies may need to be adapted. Hitherto, most force fields employ a truncated potential function to model van der Waals interactions, sometimes augmented with an analytical correction. Although such corrections are accurate for homogeneous systems with a long cutoff, they should not be used in inherently inhomogeneous systems such as biomolecular and interface systems. For such cases, a variant of the particle mesh Ewald algorithm (Lennard-Jones PME) was already proposed 20 years ago (Essmann et al. J. Chem. Phys. 1995, 103, 8577-8593), but it was implemented only recently (Wennberg et al. J. Chem. Theory Comput. 2013, 9, 3527-3537) in a major simulation code (GROMACS). The availability of this method allows surface tensions of liquids as well as bulk properties to be established, such as density and enthalpy of vaporization, without approximations due to truncation. Here, we report on simulations of ≈150 liquids (taken from a force field benchmark: Caleman et al. J. Chem. Theory Comput. 2012, 8, 61-74) using three different force fields and compare simulations with and without explicit long-range van der Waals interactions. We find that the density and enthalpy of vaporization increase for most liquids using the generalized Amber force field (GAFF, Wang et al. J. Comput. Chem. 2004, 25, 1157-1174) and the Charmm generalized force field (CGenFF, Vanommeslaeghe et al. J. Comput. Chem. 2010, 31, 671-690) but less so for OPLS/AA (Jorgensen and Tirado-Rives, Proc. Natl. Acad. Sci. U.S.A. 2005, 102, 6665-6670), which was parametrized with an analytical correction to the van der Waals potential. The surface tension increases by ≈10(-2) N/m for all force fields. These results suggest that van der Waals attractions in force fields are too strong, in particular for the GAFF and CGenFF. In addition to the simulation results, we introduce a new version of a web server, http://virtualchemistry.org, aimed at facilitating sharing and reuse of input files for molecular simulations.

Quantum-Mechanical Definition of Atoms and Chemical Bonds in Molecules

DTIC Science & Technology

2015-01-01

properties into atomic and bonding contributions, continue to be a focus of considerable attention, dating from early studies of Slater [12], Van Vleck [13...theory employing (Eisenschitz-London) spectral products of atomic eigenstates, familiar from early combined studies of covalent and van der Waals...of atoms and bonds in molecules provided by the present study , rather than to report highly accurate potential curves for the H3 molecule obtained

High quality NMR structures: a new force field with implicit water and membrane solvation for Xplor-NIH.

PubMed

Tian, Ye; Schwieters, Charles D; Opella, Stanley J; Marassi, Francesca M

2017-01-01

Structure determination of proteins by NMR is unique in its ability to measure restraints, very accurately, in environments and under conditions that closely mimic those encountered in vivo. For example, advances in solid-state NMR methods enable structure determination of membrane proteins in detergent-free lipid bilayers, and of large soluble proteins prepared by sedimentation, while parallel advances in solution NMR methods and optimization of detergent-free lipid nanodiscs are rapidly pushing the envelope of the size limit for both soluble and membrane proteins. These experimental advantages, however, are partially squandered during structure calculation, because the commonly used force fields are purely repulsive and neglect solvation, Van der Waals forces and electrostatic energy. Here we describe a new force field, and updated energy functions, for protein structure calculations with EEFx implicit solvation, electrostatics, and Van der Waals Lennard-Jones forces, in the widely used program Xplor-NIH. The new force field is based primarily on CHARMM22, facilitating calculations with a wider range of biomolecules. The new EEFx energy function has been rewritten to enable OpenMP parallelism, and optimized to enhance computation efficiency. It implements solvation, electrostatics, and Van der Waals energy terms together, thus ensuring more consistent and efficient computation of the complete nonbonded energy lists. Updates in the related python module allow detailed analysis of the interaction energies and associated parameters. The new force field and energy function work with both soluble proteins and membrane proteins, including those with cofactors or engineered tags, and are very effective in situations where there are sparse experimental restraints. Results obtained for NMR-restrained calculations with a set of five soluble proteins and five membrane proteins show that structures calculated with EEFx have significant improvements in accuracy, precision, and conformation, and that structure refinement can be obtained by short relaxation with EEFx to obtain improvements in these key metrics. These developments broaden the range of biomolecular structures that can be calculated with high fidelity from NMR restraints.

Comment on `Banana-doughnut kernels and mantle tomography' by van der Hilst and de Hoop

NASA Astrophysics Data System (ADS)

Montelli, R.; Nolet, G.; Dahlen, F. A.

2006-12-01

E debbasi considerare come non è cosa più difficile a trattare, né più dubbia a riuscire, nè più pericolosa a maneggiare, che farsi capo ad introdurre nuovi ordini. Perché lo introduttore ha per nimici tutti quelli che delli ordini vecchi fanno bene, et ha tepidi defensori tutti quelli che delli ordini nuovi farebbono bene.† Machiavelli, Il Principe The claim by van der Hilst and de Hoop that finite-frequency (FF) inversion of seismic traveltimes does not result in measurable improvements in tomographic images is misguided, and based upon a biased selection of images in the upper mantle, where wave front healing effects are indeed small, and where our models are generally poorly resolved because we primarily used teleseismic waves that travel steeply in the upper mantle; and upon an improper application of statistics to the better-resolved anomalies in the lower mantle. If station corrections for long-period P waves are computed using ray theory, as we do, unmodelled FF effects may be responsible for slow anomalies of up to 0.3 per cent beneath very small island stations, but these effects are negligible for larger islands such as Reunion and Kerguelen. The presence of a plume beneath these islands is the most probable explanation for the observed low velocities.

Changes in materials properties explain the effects of humidity on gecko adhesion.

PubMed

Puthoff, Jonathan B; Prowse, Michael S; Wilkinson, Matt; Autumn, Kellar

2010-11-01

Geckos owe their remarkable stickiness to millions of dry setae on their toes, and the mechanism of adhesion in gecko setae has been the topic of scientific scrutiny for over two centuries. Previously, we demonstrated that van der Waals forces are sufficient for strong adhesion and friction in gecko setae, and that water-based capillary adhesion is not required. However, recent studies demonstrated that adhesion increases with relative humidity (RH) and proposed that surface hydration and capillary water bridge formation is important or even necessary. In this study, we confirmed a significant effect of RH on gecko adhesion, but rejected the capillary adhesion hypothesis. While contact forces of isolated tokay gecko setal arrays increased with humidity, the increase was similar on hydrophobic and hydrophilic surfaces, inconsistent with a capillary mechanism. Contact forces increased with RH even at high shear rates, where capillary bridge formation is too slow to affect adhesion. How then can a humidity-related increase in adhesion and friction be explained? The effect of RH on the mechanical properties of setal β-keratin has escaped consideration until now. We discovered that an increase in RH softens setae and increases viscoelastic damping, which increases adhesion. Changes in setal materials properties, not capillary forces, fully explain humidity-enhanced adhesion, and van der Waals forces remain the only empirically supported mechanism of adhesion in geckos.

Epilepsy Surgery for Individuals with TSC

MedlinePlus

... AC, van der Grond J (2003) Diffusion-weighted magnetic resonance imaging and identification of the epileptogenic tuber ... tuberous sclerosis complex. Epilepsy Behav 20:561-565 Shields WD (2004) Surgical Treatment of Refractory Epilepsy. Curr ...

Management Development from a Dutch Perspective.

ERIC Educational Resources Information Center

Paauwe, Jaap, Ed.; Williams, Roger, Ed.

2001-01-01

Includes "Seven Key Issues for Management Development" (Paauwe, Williams); "Typology of Management Development" (Jansen, van der Velde, Mul); "Management Development at Royal Dutch/Shell" (Mahieu); "Management Development in Unilever" (Reitsma); "International Co-ordination and Management…

REMPI detection of singlet oxygen 1O2 arising from UV-photodissociation of van der Waals complex isoprene-oxygen C5H8-O2

NASA Astrophysics Data System (ADS)

Bogomolov, Alexandr S.; Dozmorov, Nikolay V.; Kochubei, Sergei A.; Baklanov, Alexey V.

2018-01-01

The one-laser two-color resonance enhanced multiphoton ionization REMPI [(1 + 1‧) + 1] and velocity map imaging have been applied to investigate formation of molecular oxygen in excited singlet O2(a1Δg) and ground O2(X3Σg-) states in the photodissociation of van der Waals complex isoprene-oxygen C5H8-O2. These molecules were found to appear in the different rotational states with translational energy varied from a value as low as ∼1 meV to a distribution with temperature of about 940 K. The observed traces of electron recoil in the images of photoions reveal participation of several ionization pathways of the resonantly excited intermediate states of O2.

Dynamical analysis of an n‑H‑T cosmological quintessence real gas model with a general equation of state

NASA Astrophysics Data System (ADS)

Ivanov, Rossen I.; Prodanov, Emil M.

2018-01-01

The cosmological dynamics of a quintessence model based on real gas with general equation of state is presented within the framework of a three-dimensional dynamical system describing the time evolution of the number density, the Hubble parameter and the temperature. Two global first integrals are found and examples for gas with virial expansion and van der Waals gas are presented. The van der Waals system is completely integrable. In addition to the unbounded trajectories, stemming from the presence of the conserved quantities, stable periodic solutions (closed orbits) also exist under certain conditions and these represent models of a cyclic Universe. The cyclic solutions exhibit regions characterized by inflation and deflation, while the open trajectories are characterized by inflation in a “fly-by” near an unstable critical point.

Revisiting the phase transition of AdS-Maxwell-power-Yang-Mills black holes via AdS/CFT tools

NASA Astrophysics Data System (ADS)

El Moumni, H.

2018-01-01

In the present work we investigate the Van der Waals-like phase transition of AdS black hole solution in the Einstein-Maxwell-power-Yang-Mills gravity (EMPYM) via different approaches. After reconsidering this phase structure in the entropy-thermal plane, we recall the nonlocal observables such as holographic entanglement entropy and two point correlation function to show that the both observables exhibit a Van der Waals-like behavior as the case of the thermal entropy. By checking the Maxwell's equal area law and calculating the critical exponent for different values of charge C and nonlinearity parameter q we confirm that the first and the second order phases persist in the holographic framework. Also the validity of the Maxwell law is governed by the proximity to the critical point.

Taxonomic notes on the species of the genus Anterhynchium de Saussure, 1863 (Hymenoptera: Vespidae: Eumeninae) from Vietnam, with description of a new species.

PubMed

Nguyen, Lien Thi Phuong

2015-02-02

A taxonomic study on the solitary wasps in the vespid genus Anterhynchium de Saussure, 1863, from Vietnam is presented. One species previously identified as A. (Anterhynchium) abdominale abdominale (Illiger, 1802) is described as new, namely A. punctatum Nguyen, sp. nov. Antechynchium (Dirhynchium) flavolineatum flavolineatum (Smith, 1857) and A. (Dirhynchium) flavomarginatum flavomarginatum (Smith, 1852) are newly recorded from Vietnam. New synonymy is proposed for A. flavolineatum flavolineatum (Smith, 1857) =A. flavolineatum malaisei van der Vecht, 1963, syn. nov. A. coracinum van der Vecht sensu Girish Kumar (2013) is a misidentification of A. f. flavomarginatum (Smith), and the record of this species from Pakistan and India belongs to A. f. flavolineatum. A key to species of the genus from Vietnam is provided. 

Distal Communication by Chimpanzees (Pan troglodytes): Evidence for Common Ground?

PubMed

Leavens, David A; Reamer, Lisa A; Mareno, Mary Catherine; Russell, Jamie L; Wilson, Daniel; Schapiro, Steven J; Hopkins, William D

2015-01-01

van der Goot et al. (2014) proposed that distal, deictic communication indexed the appreciation of the psychological state of a common ground between a signaler and a receiver. In their study, great apes did not signal distally, which they construed as evidence for the human uniqueness of a sense of common ground. This study exposed 166 chimpanzees to food and an experimenter, at an angular displacement, to ask, "Do chimpanzees display distal communication?" Apes were categorized as (a) proximal or (b) distal signalers on each of four trials. The number of chimpanzees who communicated proximally did not statistically differ from the number who signaled distally. Therefore, contrary to the claim by van der Goot et al., apes do communicate distally. © 2015 The Authors. Child Development © 2015 Society for Research in Child Development, Inc.

Iterative combining rules for the van der Waals potentials of mixed rare gas systems

NASA Astrophysics Data System (ADS)

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

2017-05-01

An iterative procedure is introduced to make the results of some simple combining rules compatible with the Tang-Toennies potential model. The method is used to calculate the well locations Re and the well depths De of the van der Waals potentials of the mixed rare gas systems from the corresponding values of the homo-nuclear dimers. When the ;sizes; of the two interacting atoms are very different, several rounds of iteration are required for the results to converge. The converged results can be substantially different from the starting values obtained from the combining rules. However, if the sizes of the interacting atoms are close, only one or even no iteration is necessary for the results to converge. In either case, the converged results are the accurate descriptions of the interaction potentials of the hetero-nuclear dimers.

A combining rule calculation of the ground-state van der Waals potentials of the magnesium rare-gas complexes

NASA Astrophysics Data System (ADS)

Saidi, Samah; Alharzali, Nissrin; Berriche, Hamid

2017-04-01

The potential energy curves and spectroscopic constants of the ground-state of the Mg-Rg (Rg = He, Ne, Ar, Kr, and Xe) van der Waals complexes are generated by the Tang-Toennies potential model and a set of derived combining rules. The parameters of the model are calculated from the potentials of the homonuclear magnesium and rare-gas dimers. The predicted spectroscopic constants are comparable to other available theoretical and experimental results, except in the case of Mg-He, we note that there are large differences between various determinations. Moreover, in order to reveal relative differences between species more obviously we calculated the reduced potential of these five systems. The curves are clumped closely together, but at intermediate range the Mg-He reduced potential is clearly very different from the others.

[Energetics of complex formation of the DNA hairpin structure d(GCGAAGC) with aromatic ligands].

PubMed

Kostiukov, V V

2011-01-01

The energy contributions of various physical interactions to the total Gibbs energy of complex formation of the biologically important DNA hairpin d(GCGAAGC) with aromatic antitumor antibiotics daunomycin and novantron and the mutagens ethidium and proflavine have been calculated. It has been shown that the relatively small value of the total energy of binding of the ligands to the hairpin is the sum of components great in absolute value and different in sign. The contributions of van der Waals interactions and both intra- and intermolecular hydrogen bonds and bonds with aqueous environment have been studied. According to the calculations, the hydrophobic and van der Waals components are energetically favorable in complex formation of the ligands with the DNA pairpin d(GCGAAGC), whereas the electrostatic (with consideration of hydrogen bonds) and entropic components are unfavorable.

Novel size-dependent chemistry within ionized van der Waals clusters of 1,1-difluoroethane

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

Coolbaugh, M.T.; Peifer, W.R.; Garvey, J.F.

1990-02-22

The authors present in this paper evidence for size-dependent cluster chemistry occurring in van der Waals clusters of 1,1-difluoroethane. Clusters of C{sub 2}H{sub 4}F{sub 2} are produced from a neat adiabatic expansion and are ionized via electron impact. In addition to the anticipated fragment ions, we observe ions with the general empirical formula of M{sub n}H{sup +} (where n {ge} 4). The reactive process that generates this species cannot be rationalized in terms of intramolecular analogues of known gas-phase bimolecular ion-molecular reactions. Hence, we fell the production of this product cluster ion represents an additional example of a brand newmore » class of ion-molecule reactions that can only occur within the unique solvated environment of the cluster.« less

Direction-specific van der Waals attraction between rutile TiO2 nanocrystals.

PubMed

Zhang, Xin; He, Yang; Sushko, Maria L; Liu, Jia; Luo, Langli; De Yoreo, James J; Mao, Scott X; Wang, Chongmin; Rosso, Kevin M

2017-04-28

Mutual lattice orientations dictate the types and magnitudes of forces between crystalline particles. When lattice polarizability is anisotropic, the van der Waals dispersion attraction can, in principle, contribute to this direction dependence. We report measurement of this attraction between rutile nanocrystals, as a function of their mutual orientation and surface hydration extent. At tens of nanometers of separation, the attraction is weak and shows no dependence on azimuthal alignment or surface hydration. At separations of approximately one hydration layer, the attraction is strongly dependent on azimuthal alignment and systematically decreases as intervening water density increases. Measured forces closely agree with predictions from Lifshitz theory and show that dispersion forces can generate a torque between particles interacting in solution and between grains in materials. Copyright © 2017, American Association for the Advancement of Science.

Macroscopic self-reorientation of interacting two-dimensional crystals

PubMed Central

Woods, C. R.; Withers, F.; Zhu, M. J.; Cao, Y.; Yu, G.; Kozikov, A.; Ben Shalom, M.; Morozov, S. V.; van Wijk, M. M.; Fasolino, A.; Katsnelson, M. I.; Watanabe, K.; Taniguchi, T.; Geim, A. K.; Mishchenko, A.; Novoselov, K. S.

2016-01-01

Microelectromechanical systems, which can be moved or rotated with nanometre precision, already find applications in such fields as radio-frequency electronics, micro-attenuators, sensors and many others. Especially interesting are those which allow fine control over the motion on the atomic scale because of self-alignment mechanisms and forces acting on the atomic level. Such machines can produce well-controlled movements as a reaction to small changes of the external parameters. Here we demonstrate that, for the system of graphene on hexagonal boron nitride, the interplay between the van der Waals and elastic energies results in graphene mechanically self-rotating towards the hexagonal boron nitride crystallographic directions. Such rotation is macroscopic (for graphene flakes of tens of micrometres the tangential movement can be on hundreds of nanometres) and can be used for reproducible manufacturing of aligned van der Waals heterostructures. PMID:26960435

Assembly, Thermodynamics, and Structure of a Two-Wheeled Composite of a Dumbbell-Shaped Molecule and Cylindrical Molecules with Different Edges.

PubMed

Matsuno, Taisuke; Kamata, Sho; Sato, Sota; Yokoyama, Atsutoshi; Sarkar, Parantap; Isobe, Hiroyuki

2017-11-20

A carbonaceous dumbbell was able to spontaneously glue two tubular receptors to form a unique two-wheeled composite through van der Waals interactions, thus forcing the wheel components into contact with each other at the edges. In the present study, two tubular receptors with enantiomeric carbon networks were assembled on the dumbbell joint, and the handedness of the receptors was discriminated, thus leading to the self-sorting of homomeric receptors from a mixture of enantiomeric tubes. The crystal structures of the composites revealed the structural origins of the molecular recognition driven by van der Waals forces as well as the presence of a columnar array of C 120 molecules in a 1:1 composite. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Direction-specific van der Waals attraction between rutile TiO 2 nanocrystals

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

Zhang, Xin; He, Yang; Sushko, Maria L.

Mutual lattice orientations dictate the types and magnitudes of forces between crystalline particles. When lattice polarizability is anisotropic, the van der Waals dispersion attraction can, in principle, contribute to this direction dependence. Here we report direct measurement of this attraction between rutile nanocrystals, as a function of their mutual orientation and surface hydration extent. At tens of nanometers of separation the attraction is weak and shows no dependence on azimuthal alignment nor surface hydration. At separations of approximately one hydration layer the attraction is strongly dependent on azimuthal alignment, and systematically decreases as intervening water density increases. Measured forces aremore » in close agreement with predictions from Lifshitz theory, and show that dispersion forces are capable of generating a torque between particles interacting in solution and between grains in materials.« less

Revisiting the adsorption of copper-phthalocyanine on Au(111) including van der Waals corrections

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

Lüder, Johann; Eriksson, Olle; Sanyal, Biplab

2014-03-28

We have studied the adsorption of copper-phthalocyanine on Au(111) by means of van der Waals corrected density functional theory using the Tkatchenko-Scheffler method. We have compared the element and site resolved adsorption distances to recent experimental normal-incident X-ray standing wave measurements. The measured adsorption distances could be reproduced within a deviation of 1% for the Cu atom, 1% for the C atoms, and 2% for the N atoms. The molecule was found to have a magnetic moment of 1 μ{sub B} distributed over the Cu and the N atoms of the pyrrole ring. Simulated scanning tunnel microscopy images based onmore » the total and on the spin-resolved differential charge densities are provided for bias voltages of −1.45 and 1.45 eV.« less

Understanding interactions in the adsorption of gaseous organic compounds to indoor materials.

PubMed

Ongwandee, Maneerat; Chatsuvan, Thabtim; Suksawas Na Ayudhya, Wichitsawat; Morris, John

2017-02-01

We studied adsorption of organic compounds to a wide range of indoor materials, including plastics, gypsum board, carpet, and many others, under various relative humidity conditions by applying a conceptual model of the free energy of interfacial interactions of both van der Waals and Lewis acid-base (e-donor/acceptor) types. Data used for the analyses were partitioning coefficients of adsorbates between surface and gas phase obtained from three sources: our sorption experiments and two other published studies. Target organic compounds included apolars, monopolars, and bipolars. We established correlations of partitioning coefficients of adsorbates for a considered surface with the corresponding hexadecane/air partitioning coefficients of the adsorbates which are used as representative of a van der Waals descriptor instead of vapor pressure. The logarithmic adsorption coefficients of the apolars and weak bases, e.g., aliphatics and aromatics, to indoor materials linearly correlates well with the logarithmic hexadecane/air partitioning coefficients regardless of the surface polarity. The surface polarity in terms of e-donor/acceptor interactions becomes important for adsorption of the strong bases and bipolars, e.g., amines, phenols, and alcohols, to unpainted gypsum board. Under dry or humid conditions, the adsorption to flat plastic materials still linearly correlates well with the van der Waals interactions of the adsorbates, but no correlations were observed for the adsorption to fleecy or plush materials, e.g., carpet. Adsorption of highly bipolar compounds, e.g., phenol and isopropanol, is strongly affected by humidity, attributed to Lewis acid-base interactions with modified surfaces.

pH and generation dependent morphologies of PAMAM dendrimers on a graphene substrate.

PubMed

Gosika, Mounika; Maiti, Prabal K

2018-03-07

The adsorption of PAMAM dendrimers at solid/water interfaces has been extensively studied, and is mainly driven by electrostatic and van der Waals interactions between the substrate and the dendrimers. However, the pH dependence of the adsorption driven predominantly by the van der Waals interactions is poorly explored, although it is crucial for investigating the potentiality of these dendrimers in supercapacitors and surface patterning. Motivated by this aspect, we have studied the adsorption behavior of PAMAM dendrimers of generations 2 (G2) to 5 (G5) with pH and salt concentration variation, on a charge neutral graphene substrate, using fully atomistic molecular dynamics simulations. The instantaneous snapshots from our simulations illustrate that the dendrimers deform significantly from their bulk structures. Based on various structural property calculations, we classify the adsorbed dendrimer morphologies into five categories and map them to a phase diagram. Interestingly, the morphologies we report here have striking analogies with those reported in star-polymer adsorption studies. From the fractional contacts and other structural property analyses we find that the deformations are more pronounced at neutral pH as compared to high and low pH. Higher generation dendrimers resist deformation following the deformation trend, G2 > G3 > G4 > G5 at any given pH level. As the adsorption here is mainly driven by van der Waals interactions, we observe no desorption of the dendrimers as the salt molarity is increased, unlike that reported in the electrostatically driven adsorption studies.

Surface and interface of epitaxial CdTe film on CdS buffered van der Waals mica substrate

NASA Astrophysics Data System (ADS)

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.

Hydration free energies of cyanide and hydroxide ions from molecular dynamics simulations with accurate force fields

USGS Publications Warehouse

Lee, M.W.; Meuwly, M.

2013-01-01

The evaluation of hydration free energies is a sensitive test to assess force fields used in atomistic simulations. We showed recently that the vibrational relaxation times, 1D- and 2D-infrared spectroscopies for CN(-) in water can be quantitatively described from molecular dynamics (MD) simulations with multipolar force fields and slightly enlarged van der Waals radii for the C- and N-atoms. To validate such an approach, the present work investigates the solvation free energy of cyanide in water using MD simulations with accurate multipolar electrostatics. It is found that larger van der Waals radii are indeed necessary to obtain results close to the experimental values when a multipolar force field is used. For CN(-), the van der Waals ranges refined in our previous work yield hydration free energy between -72.0 and -77.2 kcal mol(-1), which is in excellent agreement with the experimental data. In addition to the cyanide ion, we also study the hydroxide ion to show that the method used here is readily applicable to similar systems. Hydration free energies are found to sensitively depend on the intermolecular interactions, while bonded interactions are less important, as expected. We also investigate in the present work the possibility of applying the multipolar force field in scoring trajectories generated using computationally inexpensive methods, which should be useful in broader parametrization studies with reduced computational resources, as scoring is much faster than the generation of the trajectories.

Stability of a thin elastic film close to a rigid plate

NASA Astrophysics Data System (ADS)

Chen, Yi-chao; Fried, Eliot; Tortorelli, Daniel A.

2012-05-01

We introduce and study a variational model for the formation of patterns induced by bringing the surface of a rigid plate into contact proximity with the surface of a polymeric film strongly bonded to a substrate. We treat the film as a homogeneous, isotropic, hyperelastic solid and account for both attractive and repulsive van der Waals interactions between the film surface and the proximate contractor. Aside from confirming the intuitive expectation that the presence of a repulsive contribution to the van der Waals potential should stabilize patterns that form on the film surface, we elucidate the role of repulsive interactions at the onset of instability. For a recently proposed van der Waals potential involving two parameters, the Hamaker constant A and the equilibrium spacing de, our results include estimates for the critical gap dc at which undulations appear on the film surface, the corresponding wavenumber kc of the undulations, and a lower bound fm for the attractive force needed to induce the undulations. To leading order, dc˜(Ah/μ), kc˜1/h, and fm˜(μ3A/h3), where h and μ denote the thickness and infinitesimal shear modulus of the film. Correction terms due to repulsive interactions indicate that, while kc may be influenced by μ and A, dc may also be influenced by de. Granted knowledge of μ and A, our results also suggest a simple experimental protocol for determining de.

Molecular dynamics simulation of water in and around carbon nanotubes: A coarse-grained description

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

Pantawane, Sanwardhini; Choudhury, Niharendu, E-mail: nihcho@barc.gov.in

2016-05-23

In the present study, we intend to investigate behaviour of water in and around hydrophobic open ended carbon nanotubes (CNTs) using a coarse-grained, core-softened model potential for water. The model potential considered here for water has recently been shown to successfully reproduce dynamic, thermodynamic and structural anomalies of water. The epitome of the study is to understand the incarceration of this coarse-grained water in a single-file carbon nanotube. In order to examine the effect of fluid-water van der Waals interaction on the structure of fluid in and around the nanotube, we have simulated three different CNT-water systems with varying degreemore » of solute-water dispersion interaction. The analyses of the radial one-particle density profiles reveal varying degree of permeation and wetting of the CNT interior depending on the degree of fluid-solute attractive van der Waals interaction. A peak in the radial density profile slightly off the nanotube axis signifies a zigzag chain of water molecule around the CNT axis. The average numbers of water molecules inside the CNT have been shown to increase with the increase in fluid-water attractive dispersion interaction.« less

Interface bonding in silicon oxide nanocontacts: interaction potentials and force measurements.

PubMed

Wierez-Kien, M; Craciun, A D; Pinon, A V; Roux, S Le; Gallani, J L; Rastei, M V

2018-04-01

The interface bonding between two silicon-oxide nanoscale surfaces has been studied as a function of atomic nature and size of contacting asperities. The binding forces obtained using various interaction potentials are compared with experimental force curves measured in vacuum with an atomic force microscope. In the limit of small nanocontacts (typically <10 3 nm 2 ) measured with sensitive probes the bonding is found to be influenced by thermal-induced fluctuations. Using interface interactions described by Morse, embedded atom model, or Lennard-Jones potential within reaction rate theory, we investigate three bonding types of covalent and van der Waals nature. The comparison of numerical and experimental results reveals that a Lennard-Jones-like potential originating from van der Waals interactions captures the binding characteristics of dry silicon oxide nanocontacts, and likely of other nanoscale materials adsorbed on silicon oxide surfaces. The analyses reveal the importance of the dispersive surface energy and of the effective contact area which is altered by stretching speeds. The mean unbinding force is found to decrease as the contact spends time in the attractive regime. This contact weakening is featured by a negative aging coefficient which broadens and shifts the thermal-induced force distribution at low stretching speeds.

Structure and properties of fullerene molecular crystals with linear-scaling van der Waals density functional theory

NASA Astrophysics Data System (ADS)

Mostofi, Arash; Andrinopoulos, Lampros; Hine, Nicholas

2014-03-01

Fullerene molecular crystals are of technological promise for their use in heterojunction photovoltaic cells. An improved theoretical understanding of their structure and properties would be a step towards the rational design of new devices. Simulations based on density-functional theory (DFT) are invaluable for developing such insight, but standard semi-local functionals do not capture the important inter-molecular van der Waals (vdW) interactions in fullerene crystals. Furthermore the computational cost associated with the large unit cells needed are at the limit or beyond the capabilities of traditional DFT methods. In this work we overcome these limitations by using our implementation of a number of vdW-DFs in the ONETEP linear-scaling DFT code to study the structural properties of C60 molecular crystals. Powder neutron diffraction shows that the low-temperature Pa-3 phase is orientationally ordered with individual C60 units rotated around the [111] direction. We fully explore the energy landscape associated with the rotation angle and find two stable structures that are energetically very close, one of which corresponds to the experimentally observed structure. We further consider the effect of orientational disorder in very large supercells of thousands of atoms.

Free Vibration Analysis of DWCNTs Using CDM and Rayleigh-Schmidt Based on Nonlocal Euler-Bernoulli Beam Theory

PubMed Central

2014-01-01

The free vibration response of double-walled carbon nanotubes (DWCNTs) is investigated. The DWCNTs are modelled as two beams, interacting between them through the van der Waals forces, and the nonlocal Euler-Bernoulli beam theory is used. The governing equations of motion are derived using a variational approach and the free frequencies of vibrations are obtained employing two different approaches. In the first method, the two double-walled carbon nanotubes are discretized by means of the so-called “cell discretization method” (CDM) in which each nanotube is reduced to a set of rigid bars linked together by elastic cells. The resulting discrete system takes into account nonlocal effects, constraint elasticities, and the van der Waals forces. The second proposed approach, belonging to the semianalytical methods, is an optimized version of the classical Rayleigh quotient, as proposed originally by Schmidt. The resulting conditions are solved numerically. Numerical examples end the paper, in which the two approaches give lower-upper bounds to the true values, and some comparisons with existing results are offered. Comparisons of the present numerical results with those from the open literature show an excellent agreement. PMID:24715807

Including screening in van der Waals corrected density functional theory calculations: the case of atoms and small molecules physisorbed on graphene.

PubMed

Silvestrelli, Pier Luigi; Ambrosetti, Alberto

2014-03-28

The Density Functional Theory (DFT)/van der Waals-Quantum Harmonic Oscillator-Wannier function (vdW-QHO-WF) method, recently developed to include the vdW interactions in approximated DFT by combining the quantum harmonic oscillator model with the maximally localized Wannier function technique, is applied to the cases of atoms and small molecules (X=Ar, CO, H2, H2O) weakly interacting with benzene and with the ideal planar graphene surface. Comparison is also presented with the results obtained by other DFT vdW-corrected schemes, including PBE+D, vdW-DF, vdW-DF2, rVV10, and by the simpler Local Density Approximation (LDA) and semilocal generalized gradient approximation approaches. While for the X-benzene systems all the considered vdW-corrected schemes perform reasonably well, it turns out that an accurate description of the X-graphene interaction requires a proper treatment of many-body contributions and of short-range screening effects, as demonstrated by adopting an improved version of the DFT/vdW-QHO-WF method. We also comment on the widespread attitude of relying on LDA to get a rough description of weakly interacting systems.

Van der Waals epitaxy and photoresponse of hexagonal tellurium nanoplates on flexible mica sheets.

PubMed

Wang, Qisheng; Safdar, Muhammad; Xu, Kai; Mirza, Misbah; Wang, Zhenxing; He, Jun

2014-07-22

Van der Waals epitaxy (vdWE) is of great interest due to its extensive applications in the synthesis of ultrathin two-dimensional (2D) layered materials. However, vdWE of nonlayered functional materials is still not very well documented. Here, although tellurium has a strong tendency to grow into one-dimensional nanoarchitecture due to its chain-like structure, we successfully realize 2D hexagonal tellurium nanoplates on flexible mica sheets via vdWE. Chemically inert mica surface is found to be crucial for the lateral growth of hexagonal tellurium nanoplates since it (1) facilitates the migration of tellurium adatoms along mica surface and (2) allows a large lattice mismatch. Furthermore, 2D tellurium hexagonal nanoplates-based photodetectors are in situ fabricated on flexible mica sheets. Efficient photoresponse is obtained even after bending the device for 100 times, indicating 2D tellurium hexagonal nanoplates-based photodetectors on mica sheets have a great application potential in flexible and wearable optoelectronic devices. We believe the fundamental understanding of vdWE effect on the growth of 2D tellurium hexagonal nanoplate can pave the way toward leveraging vdWE as a useful channel to realize the 2D geometry of other nonlayered materials.

Interface bonding in silicon oxide nanocontacts: interaction potentials and force measurements

NASA Astrophysics Data System (ADS)

Wierez-Kien, M.; Craciun, A. D.; Pinon, A. V.; Le Roux, S.; Gallani, J. L.; Rastei, M. V.

2018-04-01

The interface bonding between two silicon-oxide nanoscale surfaces has been studied as a function of atomic nature and size of contacting asperities. The binding forces obtained using various interaction potentials are compared with experimental force curves measured in vacuum with an atomic force microscope. In the limit of small nanocontacts (typically <103 nm2) measured with sensitive probes the bonding is found to be influenced by thermal-induced fluctuations. Using interface interactions described by Morse, embedded atom model, or Lennard-Jones potential within reaction rate theory, we investigate three bonding types of covalent and van der Waals nature. The comparison of numerical and experimental results reveals that a Lennard-Jones-like potential originating from van der Waals interactions captures the binding characteristics of dry silicon oxide nanocontacts, and likely of other nanoscale materials adsorbed on silicon oxide surfaces. The analyses reveal the importance of the dispersive surface energy and of the effective contact area which is altered by stretching speeds. The mean unbinding force is found to decrease as the contact spends time in the attractive regime. This contact weakening is featured by a negative aging coefficient which broadens and shifts the thermal-induced force distribution at low stretching speeds.

Quantum defect theory for the orbital Feshbach resonance

NASA Astrophysics Data System (ADS)

Cheng, Yanting; Zhang, Ren; Zhang, Peng

2017-01-01

In the ultracold gases of alkali-earth-metal-like atoms, a new type of Feshbach resonance, i.e., the orbital Feshbach resonance (OFR), has been proposed and experimentally observed in ultracold 173Yb atoms [R. Zhang et al., Phys. Rev. Lett. 115, 135301 (2015), 10.1103/PhysRevLett.115.135301]. When the OFR of the 173Yb atoms occurs, the energy gap between the open and closed channels is smaller by two orders of magnitude than the van der Waals energy. As a result, quantitative accurate results for the low-energy two-body problems can be obtained via multichannel quantum defect theory (MQDT), which is based on the exact solution of the Schrödinger equation with the van der Waals potential. In this paper we use MQDT to calculate the two-atom scattering length, effective range, and binding energy of two-body bound states for the systems with OFR. With these results we further study the clock-transition spectrum for the two-body bound states, which can be used to experimentally measure the binding energy. Our results are helpful for the quantitative theoretical and experimental research for the ultracold gases of alkali-earth-metal-like atoms with OFR.

Multifunctional tunneling devices based on graphene/h-BN/MoSe2 van der Waals heterostructures

NASA Astrophysics Data System (ADS)

Cheng, Ruiqing; Wang, Feng; Yin, Lei; Xu, Kai; Ahmed Shifa, Tofik; Wen, Yao; Zhan, Xueying; Li, Jie; Jiang, Chao; Wang, Zhenxing; He, Jun

2017-04-01

The vertically stacked devices based on van der Waals heterostructures (vdWHs) of two-dimensional layered materials (2DLMs) have attracted considerable attention due to their superb properties. As a typical structure, graphene/hexagonal boron nitride (h-BN)/graphene vdWH has been proved possible to make tunneling devices. Compared with graphene, transition metal dichalcogenides possess intrinsic bandgap, leading to high performance of electronic devices. Here, tunneling devices based on graphene/h-BN/MoSe2 vdWHs are designed for multiple functions. On the one hand, the device shows a typical tunneling field-effect transistor behavior. A high on/off ratio of tunneling current (5 × 103) and an ultrahigh current rectification ratio (7 × 105) are achieved, which are attributed to relatively small electronic affinity of MoSe2 and optimized thickness of h-BN. On the other hand, the same structure also realizes 2D non-volatile memory with a high program/erase current ratio (>105), large memory window (˜150 V from ±90 V), and good retention characteristic. These results could enhance the fundamental understanding of tunneling behavior in vdWHs and contribute to the design of ultrathin rectifiers and memory based on 2DLMs.