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Sample records for van der voort

  1. A Reply to van der Voort's Response to Welch's Review of "Urihi A: A Terra‐ Floresta Yanomami"

    Directory of Open Access Journals (Sweden)

    James R. Welch

    2011-02-01

    Full Text Available A Reply to van der Voort's Response to Welch's Review of Urihi A: A Terra‐ Floresta Yanomami. Bruce Albert and William Milliken with Gale Goodwin Gomez. São Paulo: Instituto Socioambiental, 2009. 207 pp., illustrations, tables, bibliography, appendices, index. Paperback ISBN: 978‐85 85994‐72‐3.

  2. DS. DIRK VAN DER HOFF EN DIE VOORTREKKER-IDEAAL. Ds ...

    African Journals Online (AJOL)

    Test

    vluchtsoord wierd voor menig va!schen !eeraar — en wie zoude bij zu!k een treurig vooruitzigt, op zu!k een !osse voet voortwer ken? en den eenig veiligen grond om voort te gaan beschouwt de. Heer Neethling te zijn: de verbindtenis in 't geeste!ijk van deze gemeenten aan de Synode der Gereformeerde Kerk van Zuid-.

  3. van der Waals

    Indian Academy of Sciences (India)

    University education was beyond reach for van der Waals as he had to work for earning his daily bread ... languages, which was a prerequisite for entering a University those days. van der Waals worked as a school ... take academic examinations at the University yet, van der Waals continued studying at Leiden. University ...

  4. De bodemgesteldheid van bosreservaten in Nederland; deel 9 bosreservaat Leyduin-Vinkenduin (NH), bosreservaat Bunderbos (L), bosreservaat Ossenbos (G), bosreservaat Heloma- en Bleekerspolder(Fr), bosreservaat Achter de Voort (Ov), bosreservaat De Slikken van Flakkee (Z)

    NARCIS (Netherlands)

    Mekkink, P.

    2004-01-01

    In de bosreservaten Leyduin-Vinkenduin, Bunderbos, Ossenbos, Heloma- en Bleekerspolder, Achter de Voort en Slikken van Flakkee komen Tertiaire, Pleistocene en Holocene afzettingen voor. Het zijn veengronden, moerige gronden, zandgronden, rivierkleigronden en lössgronden met daarin vlietveengronden,

  5. B. J. van der Merwe . Pentateugtradisies in die prediking van ...

    African Journals Online (AJOL)

    B. J. van der Merwe . Pentateugtradisies in die prediking van Deuterojesaja. Proefschrift ter verkrijging van de graad van Doctor in de Godgeleerdheid aan de Rijkuniversiteit te Groningen. Uitg. J. B. Wolters, Groningen, Djakarta. 1955. 280 bls.

  6. Simon van der Meer retires

    International Nuclear Information System (INIS)

    Anon.

    1991-01-01

    CERN's big Auditorium was packed on Friday 23 November for a 'Simon van der Meer Feest' to mark the formal retirement of the gifted Dutch accelerator physicist who has made so many valuable contributions to his field and to CERN's success

  7. Van der Waals black hole

    Directory of Open Access Journals (Sweden)

    Aruna Rajagopal

    2014-10-01

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

  8. Rememorant a Mies van der Rohe

    OpenAIRE

    Gómez Montenegro, Carlos

    1999-01-01

    Imatges del primer gratacels de Mies Van Der Rohe a través dels mitjans tècnics actuals. Imágenes del primer rascacielos de Mies Van Der Rohe através de los medios técnicos actuales. Peer Reviewed

  9. Molecule Matters van der Waals Molecules

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 14; Issue 12. Molecule Matters van der Waals Molecules - Noble Gas Clusters are London Molecules! E Arunan. Feature Article Volume 14 Issue 12 December 2009 pp 1210-1222 ...

  10. Dispersion (van der Waals) Forces and TDDFT

    Science.gov (United States)

    Dobson, John F.

    A semi-pedagogic discussion is given of the use of response theory and Time Dependent Density Functional Theory to describe van der Waals (dispersion) energies, within the context of Adiabatic Connection and the Fluctuation-Dissipation theorem.

  11. Professor Willem van der Angeliaan / Aive Sarjas

    Index Scriptorium Estoniae

    Sarjas, Aive

    2010-01-01

    Läänemaal Koluvere hooldekodus kord nädalas tegevusteraapia teenust osutavast väikesest šetlandi tõugu ruunast Willem van der Angeliaanist ning tegevusterapeudi Moonika Salumaa tegevusteraapias kasutatavatest teooriatest ja meetoditest

  12. De rode jonker : De eeuw van Marinus van der Goes van Naters (1900-2005)

    NARCIS (Netherlands)

    Mreijen, Anne-Marie Francine

    2018-01-01

    Marinus van der Goes van Naters (1900-2005). A Biography The history of the twentieth century is reflected in the life of the Dutch politician and lawyer Marinus (‘Dup’) van der Goes of Naters, also known as the ‘Red Squire’. He was a flamboyant and idiosyncratic politician, who during his lifetime

  13. Salient signature of van der Waals interactions

    Science.gov (United States)

    Via-Nadal, Mireia; Rodríguez-Mayorga, Mauricio; Matito, Eduard

    2017-11-01

    van der Waals interactions govern the physics of a plethora of molecular structures. It is well known that the leading term in the distance-based London expansion of the van der Waals energy for atomic and molecular dimers decays as 1 /R6 , where R is the dimer distance. Using perturbation theory, we find the leading term in the distance-based expansion of the intracule pair density at the interatomic distance. Our results unveil a universal 1 /R3 decay, which is less prone to numerical errors than the 1 /R6 dependency, and it is confirmed numerically in H2 and He2 molecules. This signature of van der Waals interactions can be directly used in the construction of approximate pair density and energy functionals including vdW corrections.

  14. Electron attachment to Van der Waals molecules

    International Nuclear Information System (INIS)

    Hatano, Y.

    1986-01-01

    A survey is given of recent experimental studies of low-energy electron attachment to O 2 , N 2 O and other molecules in dense gases and in sonic nozzle beams with emphasis on the important role of pre-existing van der Waals molecules in the attachment mechanism. The experimental results particularly for O 2 are compared with recent theories. A survey is also given briefly of recent studies on electron solvation and localization in the condensed phase from the viewpoint of the studies on electron interaction with van der Waals molecules. (Auth.)

  15. Walter van der Cruijsen / Walter van der Cruijsen ; interv. Tilman Baumgärtel

    Index Scriptorium Estoniae

    Cruijsen, Walter van der

    2006-01-01

    1997. a. Berliinis tehtud intervjuu hollandi maali, võrgu- ja installatsioonikunstniku Walter van der Cruijseniga (sünd. 1958), kes kuulub Euroopa ühe edukama 1990-ndatel loodud võrguprojekti De Digitale Stad Amsterdam loojate hulka

  16. Molecule Matters van der Waals Molecules

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 15; Issue 7. Molecule Matters van der Waals Molecules - Rg•••HF Complexes are Debye Molecules! E Arunan. Feature Article Volume 15 Issue 7 July 2010 pp 667-674. Fulltext. Click here to view fulltext PDF. Permanent link:

  17. Strain engineering of van der Waals heterostructures

    NARCIS (Netherlands)

    Vermeulen, Paul A.; Mulder, Jefta; Momand, Jamo; Kooi, Bart J.

    2018-01-01

    Modifying the strain state of solids allows control over a plethora of functional properties. The weak interlayer bonding in van der Waals (vdWaals) materials such as graphene, hBN, MoS2, and Bi2Te3 might seem to exclude strain engineering, since strain would immediately relax at the vdWaals

  18. Cluster ions and van der Waals molecules

    CERN Document Server

    Smirnov, Boris M

    1992-01-01

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

  19. Molecule Matters van der Waals Molecules

    Indian Academy of Sciences (India)

    1884-03-24

    Petrus Josephus Wilhelmus Debije (Peter Joseph Williams Debye) was born on March 24, 1884 in Maastricht, Netherlands, which is. 167.5 km from Leiden, where van der Waals was born 37 years earlier [1,2]. Debye had his early education in maths and physics and got a degree in electrical engineering in 1905. Debye ...

  20. Molecule Matters van der Waals Molecules

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 14; Issue 12. Molecule Matters van der Waals Molecules - Noble Gas Clusters are London Molecules! E Arunan ... Author Affiliations. E Arunan1. Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India.

  1. Molecule Matters van der Waals Molecules

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 15; Issue 7. Molecule Matters van der Waals Molecules - Rg•••HF Complexes are Debye Molecules! E Arunan ... Author Affiliations. E Arunan1. Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India.

  2. Electron attachment to Van der Waals clusters

    International Nuclear Information System (INIS)

    Stamatovic, A.

    1988-01-01

    This paper deals with attachment of thermal electrons to Van der Waals clusters at zero energy. The underlying theory is treated briefly. Three different major types of experiments for studying thermal electron attachment to molecules and clusters: swarm experiments, beam experiments and collisions with Rydberg atoms, are described and some results are reviewed. 42 refs.; 5 figs

  3. Van der Waals and Molecular Science

    International Nuclear Information System (INIS)

    Kox, A J

    1997-01-01

    For many years it has been a source of amazement to scientists and historians of science that no serious scientific biography of J D van der Waals existed. When, more than ten years ago, I became engaged in a correspondence with the Russian historian of science B E Yavelow on the topic of van der Waals, whose biography he was writing, I was both pleased and a bit puzzled. It was clear that Yavelow had not done any archival research in the Netherlands himself, yet he was intimately familiar with many obscure facts from the life of van der Waals. Naturally, I was very curious to see the end result, which appeared in 1985, but although the Amsterdam University Library obtained a copy, my limited knowledge of Russian kept me from forming a judgement on the book. Finally, after more than ten years, an English edition has appeared. The two original Russian authors have joined forces with the well known scientist J S Rowlinson (who earlier edited an English translation of van der Waals's dissertation) to produce a revised and enlarged English version of the Russian original. Now that I have finally been able to study this work, I must admit to being much impressed. Both the life and the work of van der Waals are dealt with in an exemplary way: the authors' command of primary and secondary sources is impressive, as is their understanding of the Dutch social and educational circumstances in the last century. Teaching and research at the newly-founded University of Amsterdam, as well as activities in the Academy of Sciences, are discussed in great and interesting detail. Van der Waals's education and rise from a simple teacher to one of the foremost theoretical physicists in Europe teaches us much about his personality as well as about the opportunities offered by the Dutch educational system. In their discussion of the development of van der Waals's ideas and their impact (including an interesting chapter on the reception in Russia) the authors are not afraid to go into

  4. Thermal response in van der Waals heterostructures

    KAUST Repository

    Gandi, Appala

    2016-11-21

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

  5. Dr Jacob van der Land, marine biologist extraordinary

    NARCIS (Netherlands)

    Bruggen, van A.C.

    2001-01-01

    This contribution is an attempt to sketch the life and works of Dr Jacob van der Land, curator of worms and chief marine biologist of the National Museum of Natural History, on the occasion of his official retirement. Born in 1935, Jacob van der Land read biology at Leiden University (1958-1964),

  6. Genetic heterogeneity in Van der Woude syndrome: Identification of ...

    Indian Academy of Sciences (India)

    Priyanka

    IRF6 for VWS and highlights genetic heterogeneity of this disorder, in the Indian population. Key Words: Van der Woude syndrome, NOL4, IRF6, Genome wide linkage, NGS. Introduction. Van der .... down of the mapped regions, linkage was attempted through 15 microsatellite markers from the 3 high LOD regions on ...

  7. Photoresponse of Natural van der Waals Heterostructures.

    Science.gov (United States)

    Ray, Kyle; Yore, Alexander E; Mou, Tong; Jha, Sauraj; Smithe, Kirby K H; Wang, Bin; Pop, Eric; Newaz, A K M

    2017-06-27

    Van der Waals heterostructures consisting of two-dimensional materials offer a platform to obtain materials by design and are very attractive owing to unique electronic states. Research on 2D van der Waals heterostructures (vdWH) has so far been focused on fabricating individually stacked atomically thin unary or binary crystals. Such systems include graphene, hexagonal boron nitride, and members of the transition metal dichalcogenide family. Here we present our experimental study of the optoelectronic properties of a naturally occurring vdWH, known as franckeite, which is a complex layered crystal composed of lead, tin, antimony, iron, and sulfur. We present here that thin film franckeite (60 nm power-resolved and temperature-resolved photocurrent measurements reveal that the photocarrier generation and recombination are dominated by continuously distributed trap states within the band gap. To understand wavelength-resolved photocurrent, we also calculated the optical absorption properties via density functional theory. Finally, we have shown that the device has a fast photoresponse with a rise time as fast as ∼1 ms. Our study provides a fundamental understanding of the optoelectronic behavior in a complex naturally occurring vdWH, and may pave an avenue toward developing nanoscale optoelectronic devices with tailored properties.

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

    Science.gov (United States)

    2018-02-19

    AFRL-AFOSR-JP-TR-2018-0012 Nano Electronics on Atomically Controlled van der Waals Quantum Heterostructures PHILIP Kim HARVARD COLLEGE PRESIDENT... Atomically Controlled van der Waals Quantum Heterostructures 5a.  CONTRACT NUMBER 5b.  GRANT NUMBER FA2386-15-1-4003 5c.  PROGRAM ELEMENT NUMBER 61102F...Final Report for AOARD Grant FA2386-15-1-4003 “Nano Electronics on Atomically Controlled van der Waals Quantum Heterostructures” 2/18/2018 Name of

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

    Science.gov (United States)

    Zhong, Wei; Xiao, Changming; Zhu, Yongkai

    2017-04-01

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

  10. Simon van der Meer (1925-2011)

    CERN Multimedia

    2011-01-01

    Simon van der Meer was a true giant of modern particle physics, though a gentle one. His contributions to accelerator science remain vital for the operation of accelerators such as the LHC today. Simon was an electrical engineer who grew up in The Hague, moving on to Delft University to study electrical engineering. After a short stint with Philips, he came to CERN in 1956, just two years after the lab opened, and remained with us until his retirement in 1990.   Simon was an incredibly inventive man. When confronted with a problem, he would sink into deep reflection, rarely emerging until he had a solution. One of us, Steve Myers, remembers him as a man who did not suffer fools gladly, and who was extremely taciturn. Simon would never use two words where one would suffice. But that one word would invariably be the right one. Simon is best known for his contribution to the SPS collider project, for which he was awarded the Nobel Prize, jointly with Carlo Rubbia, in 1984. Stochastic cooling, the in...

  11. Van der Waals Interactions in Aspirin

    Science.gov (United States)

    Reilly, Anthony; Tkatchenko, Alexandre

    2015-03-01

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

  12. Editorial | van der Merwe | Stellenbosch Papers in Linguistics Plus

    African Journals Online (AJOL)

    Antoinette van der Merwe, Alta van Rensburg, Rose Richards, Sharifa Daniels, Rufus Gouws. Abstract. No Abstract. Full Text: EMAIL FREE FULL TEXT EMAIL FREE FULL TEXT · DOWNLOAD FULL TEXT DOWNLOAD FULL TEXT · AJOL African Journals Online. HOW TO USE AJOL... for Researchers · for Librarians ...

  13. A cartography of the van der Waals territories.

    Science.gov (United States)

    Alvarez, Santiago

    2013-06-28

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

  14. van der Waals interactions in a magnetodielectric medium

    International Nuclear Information System (INIS)

    Spagnolo, S.; Dalvit, D. A. R.; Milonni, P. W.

    2007-01-01

    The van der Waals interaction between two ground-state atoms is calculated for two electrically or magnetically polarizable particles embedded in a dispersive magnetodielectric medium. Unlike previous calculations which infer the atom-atom interaction from the dilute-medium limit of the macroscopic, many-body van der Waals interaction, the interaction is calculated directly for the system of two atoms in a magnetodielectric medium. Two approaches are presented, the first based on the quantized electromagnetic field in a dispersive medium without absorption and the second on Green functions that allow for absorption. We show that the correct van der Waals interactions are obtained regardless of whether absorption in the host medium is explicitly taken into account

  15. Wat is het geheim van ammonium? (interview met Bram van der Maas)

    NARCIS (Netherlands)

    Maas, van der A.A.

    2013-01-01

    Beter meten is meer weten. Dat is het uitgangspunt van de 'ion selectieve meter' die Horticoop en CleanGrow bezig zijn te ontwikkelen. Daarmee zijn zes elementen te controleren. Maar wat zegt bijvoorbeeld het gehalte ammonium over een gewas? Onderzoeker Bram van der Maas: 'Met ammonium is misschien

  16. Effective field theories for van der Waals interactions

    Science.gov (United States)

    Brambilla, Nora; Shtabovenko, Vladyslav; Tarrús Castellà, Jaume; Vairo, Antonio

    2017-06-01

    Van der Waals interactions between two neutral but polarizable systems at a separation R much larger than the typical size of the systems are at the core of a broad sweep of contemporary problems in settings ranging from atomic, molecular and condensed matter physics to strong interactions and gravity. In this paper, we reexamine the dispersive van der Waals interactions between two hydrogen atoms. The novelty of the analysis resides in the usage of nonrelativistic effective field theories of quantum electrodynamics. In this framework, the van der Waals potential acquires the meaning of a matching coefficient in an effective field theory, dubbed van der Waals effective field theory, suited to describe the low-energy dynamics of an atom pair. It may be computed systematically as a series in R times some typical atomic scale and in the fine-structure constant α . The van der Waals potential gets short-range contributions and radiative corrections, which we compute in dimensional regularization and renormalize here for the first time. Results are given in d space-time dimensions. One can distinguish among different regimes depending on the relative size between 1 /R and the typical atomic bound-state energy, which is of order m α2. Each regime is characterized by a specific hierarchy of scales and a corresponding tower of effective field theories. The short-distance regime is characterized by 1 /R ≫m α2 and the leading-order van der Waals potential is the London potential. We also compute next-to-next-to-next-to-leading-order corrections. In the long-distance regime we have 1 /R ≪m α2. In this regime, the van der Waals potential contains contact terms, which are parametrically larger than the Casimir-Polder potential that describes the potential at large distances. In the effective field theory, the Casimir-Polder potential counts as a next-to-next-to-next-to-leading-order effect. In the intermediate-distance regime, 1 /R ˜m α2, a significantly more complex

  17. Oscillator representation and generalized van der Waals Hamiltonians

    International Nuclear Information System (INIS)

    Dinejkhan, M.

    1996-01-01

    The method called the oscillator representation is extended to calculate the energy spectrum of bound state described by axially symmetrical potentials in the parabolic system coordinates. In particular, the method is applied to calculate the energy of the ground and excited states of the hydrogen atom in the uniform electric field and van der Waals field. The method gives the perturbation formulas for the analytic spectrum of the hydrogen atom in the generalized van der Waals field and defined oscillator strengths for transitions from the ground state to the perturbed manifold n=10, m=0. 14 refs., 1 fig

  18. Eglon Hendrik van der Neer (1635/36 - 1703) : Zijn leven en werk

    NARCIS (Netherlands)

    Schavemaker, E.

    2009-01-01

    Eglon van der Neer. His Life and His Work In his own time Eglon van der Neer was highly successful. His acclaim endured throughout the eighteenth century. Nowadays he is rated as a second-rate master. Van der Neer was born in Amsterdam in 1635 or 1636 as the son of the now more famous landscape

  19. Van Der Woude Syndrome – A Report Of Two Cases | Umweni ...

    African Journals Online (AJOL)

    Two cases of Van der Woude syndrome, which presented in a mother and son are reported. The occurrence of isolated cleft palate in a sibling supports the evidence that Van der Woude syndrome is associated with a dominant autosomic gene of high penetrance and variable expressively. The occurrence of Van der ...

  20. THE PORTRAITS OF SIMON VAN DER STEL, FIRST GOVERNOR ...

    African Journals Online (AJOL)

    The Stichting moreover reported that in its opinion the subject of the portrait was not Willem (Adriaan), but his father Simon van der Stel, and the youth on the horse, one of the latter's children. This hypothesis was based not exclusively on the date assigned to the painting, but also on the outward appearance of its subject.

  1. Van Der Woude syndrome: report of a case | Newman | Ghana ...

    African Journals Online (AJOL)

    A rare case of Van Der Woude Syndrome, which is characterized by pits in the lower lip and bilateral cleft of the lip and cleft palate is presented. A multidisciplinary approach to treatment produced an aesthetically pleasing and functional outcome. Ghana Medical Journal Vol. 39(2) 2005: 68-70 ...

  2. Šveitsi hommage Mies van der Rohele / Kai Lobjakas

    Index Scriptorium Estoniae

    Lobjakas, Kai, 1975-

    1999-01-01

    Šveitsi väikelinna Buschi ehitatud voolava ruumilahendusega maja meenutab Mies van der Rohe kujundatud saksa paviljoni maailmanäitusel Barcelonas. Materjalideks betoon, puit, klaas. Loodud on palju erineva kõrgusega pindu maja ja seda ümbritseva müüri vahel. Interjööris punakas tammepuit. Arhitekt: Peter+Christian Frei, Architekten.

  3. Genetic heterogeneity in Van der Woude syndrome: identification of ...

    Indian Academy of Sciences (India)

    PRIYANKA KUMARI

    2018-03-03

    Mar 3, 2018 ... Abstract. Van der Woude syndrome (VWS) shows an autosomal dominant pattern of inheritance with two known candidate genes, IRF6 and GRHL3. In this study, by employing genome-wide linkage analyses on two VWS affected families, we report the cosegregation of an intronic rare variant in NOL4 in ...

  4. Genetic heterogeneity in Van der Woude syndrome: Identification of ...

    Indian Academy of Sciences (India)

    Priyanka

    Genetic heterogeneity in Van der Woude syndrome: Identification of NOL4 and IRF6 haplotype from the noncoding region as candidates in two families. Priyanka Kumari1, Akhtar Ali2, Subodh Kumar Singh3, Amit Chaurasia4, Rajiva Raman1. 1Cytogenetics Laboratory, Department of Zoology, Institute of Science, Banaras ...

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

    DEFF Research Database (Denmark)

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

    2010-01-01

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

  6. (AJST) ANALYSIS OF VAN DER WAAL EQUATION NEAR THE ...

    African Journals Online (AJOL)

    ABSTRACT:- The van der Waal equation of state is redefined in a functional manner that reveals some additional critical ... The law of corresponding states is also shown to apply to the lower limits of reduced temperatures. .... This is a cubic function Vmc(b) in and would in general have three solutions. Graphically, the ...

  7. Somatotropin physiology - a review | van der Walt | South African ...

    African Journals Online (AJOL)

    South African Journal of Animal Science. Journal Home · ABOUT THIS JOURNAL · Advanced Search · Current Issue · Archives · Journal Home > Vol 24, No 1 (1994) >. Log in or Register to get access to full text downloads. Username, Password, Remember me, or Register. Somatotropin physiology - a review. JG van der ...

  8. Franckeite as a naturally occurring van der Waals heterostructure

    NARCIS (Netherlands)

    Molina-Mendoza, Aday J.; Giovanelli, Emerson; Paz, Wendel S.; Ninõ, Miguel Angel; Island, J.O.; Evangeli, Charalambos; Aballe, Luciá; Foerster, Michael; Van Der Zant, Herre S.J.; Rubio-Bollinger, Gabino; Agraït, Nicolás; Palacios, JJ; 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

  9. Mies van der Rohe preemia 2011 / Karen Jagodin

    Index Scriptorium Estoniae

    Jagodin, Karen, 1982-

    2011-01-01

    20. juunil antakse Barcelonas inglise arhitektile Sir David Chipperfieldile Berliini Neues Museumi restaureerimise eest üle 2011. aasta Mies van der Rohe arhitektuuripreemia. Nimetatud võidutöö viis suuremat konkurenti, varem preemia pälvinud hooneid ja nende autoreid. Sir David Chipperfieldist, Berliini Neues Muuseumi restaureerimisest. Loetletud preemia nominendid Eestist

  10. R. E. van der Ross (1921–2017)

    African Journals Online (AJOL)

    19 Mrt. 2018 ... Sedert sy jeug het Richard Ernest van der Ross. (1921–2017) 'n belangrike rol in die breë Kaapse ge- meenskap gespeel. Hy het hom onderskei as 'n anti- apartheidsaktivis, 'n opvoedkundige, 'n geskied- skrywer en openbare intellektueel, 'n vakbondmens,. 'n gemeenskapsbouer, 'n maatskappydirekteur ...

  11. Augmented van der Waals Equations of State: SAFT-VR versus Yukawa Based van der Waals Equation

    Czech Academy of Sciences Publication Activity Database

    Nezbeda, Ivo; Melnyk, R.; Trokhymchuk, A.

    2011-01-01

    Roč. 309, č. 2 (2011), s. 174-178 ISSN 0378-3812 R&D Projects: GA AV ČR IAA400720710 Institutional research plan: CEZ:AV0Z40720504 Keywords : perturbation theory * SAFT-VR * augmented van der Waals Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.139, year: 2011

  12. Die funksies en toepassings van retoriese vrae | van der Merwe ...

    African Journals Online (AJOL)

    Dit kan byvoorbeeld in ekspressiewe funksie aangewend word ter be- klemtoning, ter oorreding en ter uiting van emosies. Hierdie soort vrae kom voor in mondelinge kommunikasie (bv. toesprake, didaktiese redevoering en gemoedelike gesprekvoering) en geskrewe taal (bv. in die media en die letterkunde). Die retoriese ...

  13. Accurate van der Waals coefficients from density functional theory

    Science.gov (United States)

    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

  14. Quark confinement potential and color Van der Waals force

    International Nuclear Information System (INIS)

    Zheng Yuming; Hua Daping; Liu Zuhua

    1985-01-01

    The color-analog Van der Waals force between two hadrons is studied by use of the coupling channel resonating group method in the framework of the Gaussian-type quark confinement potential. The problem of the boundary values for the two channel coupling differential equations is changed to the problem of the initial values. The equations are solved numerically by use of the Gear mehtod. The calculated results show that there is no color Van der Waals force between hadrons in the confinement potential model. This indicates that the confinement potential model not only can describe the internal structure of hadrons but also can be used to calculate the hadron-hadron interactions if the quark confinement potential is chosen properly

  15. Hopf Bifurcation of Compound Stochastic van der Pol System

    Directory of Open Access Journals (Sweden)

    Shaojuan Ma

    2016-01-01

    Full Text Available Hopf bifurcation analysis for compound stochastic van der Pol system with a bound random parameter and Gaussian white noise is investigated in this paper. By the Karhunen-Loeve (K-L expansion and the orthogonal polynomial approximation, the equivalent deterministic van der Pol system can be deduced. Based on the bifurcation theory of nonlinear deterministic system, the critical value of bifurcation parameter is obtained and the influence of random strength δ and noise intensity σ on stochastic Hopf bifurcation in compound stochastic system is discussed. At last we found that increased δ can relocate the critical value of bifurcation parameter forward while increased σ makes it backward and the influence of δ is more sensitive than σ. The results are verified by numerical simulations.

  16. The dependence of scattering length on van der Waals interaction ...

    Indian Academy of Sciences (India)

    2016-06-16

    Jun 16, 2016 ... DOI 10.1007/s12043-016-1221-y. The dependence of scattering length on van der Waals interaction and reduced mass of the system in two-atomic collision at cold energies. HASI RAY1,2,3,4. 1Study Centre, S-1/407/6, B.P. Township, Kolkata 700 094, India. 2Department of Physics, New Alipore College, ...

  17. Evidence for van der Waals adhesion in gecko setae

    OpenAIRE

    Autumn, Kellar; Sitti, Metin; Liang, Yiching A.; Peattie, Anne M.; Hansen, Wendy R.; Sponberg, Simon; Kenny, Thomas W.; Fearing, Ronald; Israelachvili, Jacob N.; Full, Robert J.

    2002-01-01

    Geckos have evolved one of the most versatile and effective adhesives known. The mechanism of dry adhesion in the millions of setae on the toes of geckos has been the focus of scientific study for over a century. We provide the first direct experimental evidence for dry adhesion of gecko setae by van der Waals forces, and reject the use of mechanisms relying on high surface polarity, including capillary adhesion. The toes of live Tokay geckos were highly hydrophobic, and adhered equally well ...

  18. Strong van der Waals attractive forces in nanotechnology

    Science.gov (United States)

    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.

  19. Grippers Based on Opposing Van Der Waals Adhesive Pads

    Science.gov (United States)

    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.

  20. 'N OU LIED WAT MET DIE KOMS VAN Ds. D. VAN DER HOFF ...

    African Journals Online (AJOL)

    Test

    Toe ds. D. van der Hoff begin Augustus 1853 op Rustenburg verwelkom is, is die volgende lied vir hierdie geleentheid vervaardig om gesing te word: Toi de Gemeenfe. De daagraad lang door ons verwacht. Is eindelijk aangebroken! Verdrongen is de duistre nacht: Gods heilig woord wordt weer gesproken. W ij hebben ...

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

    Science.gov (United States)

    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.

  2. Disaini ja rahvaste saatusest / Daniel Van der Velden ; intervjueerinud Kristjan Mändmaa

    Index Scriptorium Estoniae

    Van der Velden, Daniel

    2011-01-01

    17.-27. X 2008 oli Eesti Kunstiakadeemias näitus "Marsilt. Omaalgatuslikud projektid graafilises disainis". Kuraatorid: tšehhi disainerid Adam Machacek ja Radim Peshko. 17. X esinesid EKA saalis loengutega James Goggin Londoni firmast Practice ja Daniel van der Velden Hollandi disainikollektiivist Metahaven. 16. V osales D. van der Velden Eesti Disainiinstituudi korraldatud kohabrändingu-teemalises ümarlauas. D. van der Velden disaini, poliitika ja kohabrändingu tulevikust, Metahaveni disainitöödest

  3. Disaini ja rahvaste saatusest / Daniel Van der Velden ; interv. Kristjan Mändmaa

    Index Scriptorium Estoniae

    Van der Velden, Daniel

    2008-01-01

    17.-27. X 2008 oli Eesti Kunstiakadeemias näitus "Marsilt. Omaalgatuslikud projektid graafilises disainis". Kuraatorid: tšehhi disainerid Adam Machacek ja Radim Peshko. 17. X esinesid EKA saalis loengutega James Goggin Londoni firmast Practice ja Daniel van der Velden Hollandi disainikollektiivist Metahaven. 16. V osales D. van der Velden Eesti Disainiinstituudi korraldatud kohabrändingu-teemalises ümarlauas. D. van der Velden disaini, poliitika ja kohabrändingu tulevikust, Metahaveni disainitöödest

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

    Science.gov (United States)

    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.

  5. Coincident-site lattice matching during van der Waals epitaxy

    OpenAIRE

    Boschker, Jos E.; Galves, Lauren A.; Flissikowski, Timur; Lopes, Joao Marcelo J.; Riechert, Henning; Calarco, Raffaella

    2015-01-01

    Van der Waals (vdW) epitaxy is an attractive method for the fabrication of vdW heterostructures. Here Sb2Te3 films grown on three different kind of graphene substrates (monolayer epitaxial graphene, quasi freestanding bilayer graphene and the SiC (6?3???6?3)R30? buffer layer) are used to study the vdW epitaxy between two 2-dimensionally (2D) bonded materials. It is shown that the Sb2Te3 /graphene interface is stable and that coincidence lattices are formed between the epilayers and substrate ...

  6. Layered van der Waals crystals with hyperbolic light dispersion

    DEFF Research Database (Denmark)

    Gjerding, Morten Niklas; Petersen, R.; Pedersen, T.G.

    2017-01-01

    -infrared to the ultraviolet. Combined with the emerging field of van der Waals heterostructuring, we demonstrate how the hyperbolic properties can be further controlled by stacking different two-dimensional crystals opening new perspectives for atomic-scale design of photonic metamaterials. As an application, we identify...... candidates for Purcell factor control of emission from diamond nitrogen-vacancy centers.Natural hyperbolic materials retain the peculiar optical properties of traditional metamaterials whilst not requiring artificial structuring. Here, the authors perform a theoretical screening of a large class of natural...

  7. VPLIV VAN DER WAALSOVIH SIL NA TVORBO ASOCIIRANIH MOLEKUL

    OpenAIRE

    Kuster, Bernarda

    2014-01-01

    Namen diplomske naloge je preučiti vpliv van der Waalsovih sil na tvorbo asociiranih molekul. V ta namen smo izbrali površinsko aktivne snovi, ki imajo amfifilne lastnosti in vplivajo na povšinske in medfazne napetosti ter pri določeni koncentraciji, imenovani kritična micelna koncentracija (CMC), tvorijo molekulske skupke, ki jim pravimo micele. Kritično micelno koncentracijo smo določili trem površinsko aktivnim snovem: heksadeciltrimetilamonijevemu bromidu, tetradeciltrimetilamonijevemu b...

  8. Simon van der Meer in the AA Control Room

    CERN Multimedia

    CERN PhotoLab

    1984-01-01

    Simon van der Meer, spiritus rector of the Antiproton Accumulator, in the AA Control Room. Inventor of stochastic cooling, on which the AA was based, and of the magnetic horn, with which the antiprotons were focused, he also wrote most of the software with which the AA was controlled, and spent uncountable numbers of hours in this chair to tickle the AA to top performance. 8 months after this picture was taken, he received, in October 1984, the Nobel prize, together with Carlo Rubbia, the moving force behind the whole Proton-Antiproton Collider project that led to the discovery, in 1983, of the W and Z intermediate bosons.

  9. Capillary pressure of van der Waals liquid nanodrops

    Science.gov (United States)

    Tsekov, R.; Toshev, B. V.

    2012-04-01

    The dependence of the surface tension on a nanodrop radius is important for the new-phase formation process. It is demonstrated that the famous Tolman formula is not unique and the size-dependence of the surface tension can distinct for different systems. The analysis is based on a relationship between the surface tension and disjoining pressure in nanodrops. It is shown that the van der Waals interactions do not affect the new-phase formation thermodynamics since the effect of the disjoining pressure and size-dependent component of the surface tension cancel each other.

  10. Capillary pressure of van der Waals liquid nanodrops

    OpenAIRE

    Tsekov, R.; Toshev, B. V.

    2011-01-01

    The dependence of the surface tension on a nanodrop radius is important for the new-phase formation process. It is demonstrated that the famous Tolman formula is not unique and the size-dependence of the surface tension can distinct for different systems. The analysis is based on a relationship between the surface tension and disjoining pressure in nanodrops. It is shown that the van der Waals interactions do not affect the new-phase formation thermodynamics since the effect of the disjoining...

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

    Directory of Open Access Journals (Sweden)

    Xiao-Xiong Zeng

    2017-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Zeng, Xiao-Xiong, E-mail: xxzeng@itp.ac.cn [State School of Material Science and Engineering, Chongqing Jiaotong University, Chongqing 400074 (China); Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100190 (China); Li, Li-Fang, E-mail: lilf@itp.ac.cn [State Key Laboratory of Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing 100190 (China)

    2017-01-10

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

  13. J.T. van der Kemp and Eighteenth century coded subjectivity | Smit ...

    African Journals Online (AJOL)

    It then proceeds to an analysis of the impact of J.T. van der Kemp, 1799-1804. Theoretically I draw on the distinction between morality and ethics by Michel Foucault as well as his theorising of eighteenth century representational thought. Keywords: J.T. van der Kemp, morality, ethics, models for missionary engagement, ...

  14. Bartholomeus van der Helst (1613-1670): een studie naar zijn leven en zijn werk

    NARCIS (Netherlands)

    van Gent, J.F.J.M.|info:eu-repo/dai/nl/135067243

    2011-01-01

    Bartholomeus van der Helst was a leading portrait painter in the Northern Netherlands in the 17th century. This monograph reconstructs his career and his circle of patrons based on the surviving works and documents. Van der Helst was born in Haarlem around 1613. In the early 1630s he moved to

  15. Analysis of van der waal equation near the critical point | Awuor ...

    African Journals Online (AJOL)

    The van der Waal equation of state is redefined in a functional manner that reveals some additional critical parameters and presents the ideal gas temperature as a lower limit to the van der Waal gas temperature. The law of corresponding states is also shown to apply to the lower limits of reduced temperatures.

  16. Anisotropic spheres with Van der Waals-type equation of state

    Indian Academy of Sciences (India)

    2014-07-02

    Jul 2, 2014 ... Abstract. We study static spherically symmetric space-time to describe relativistic compact ob- jects with anisotropic matter distribution and derive two classes of exact models to the Einstein–. Maxwell system with a modified Van der Waals equation of state. We motivate a Van der Waals-type equation of ...

  17. Mihkelson paljastas van der Lindeni ärihuvid Venemaal / Helga Koger

    Index Scriptorium Estoniae

    Koger, Helga, 1945-

    2007-01-01

    Riigikogu EL asjade komisjoni esimees Marko Mihkelson tutvustas materjale, mis viitavad hiljuti Eestit kritiseerinud Euroopa Nõukogu Parlamentaarse Assamblee presidendi Rene van der Linderi ärihuvile Venemaal. Mihkelsoni sõnade järgi võivad van der Lindenil olla majandushuvid seoses Vladimiri oblasti Sobinski rajooni rajatava tööstuspargiga

  18. Oscillation death in a coupled van der Pol–Mathieu system

    Indian Academy of Sciences (India)

    Abstract. We report an investigation of the oscillation death (OD) of a parametrically excited cou- pled van der Pol–Mathieu (vdPM) system. The system can be considered as a pair of harmonically forced van der Pol oscillators under a double-well potential. The two oscillators are coupled with a cubic nonlinearity. We have ...

  19. Evidence for van der Waals adhesion in gecko setae.

    Science.gov (United States)

    Autumn, Kellar; Sitti, Metin; Liang, Yiching A; Peattie, Anne M; Hansen, Wendy R; Sponberg, Simon; Kenny, Thomas W; Fearing, Ronald; Israelachvili, Jacob N; Full, Robert J

    2002-09-17

    Geckos have evolved one of the most versatile and effective adhesives known. The mechanism of dry adhesion in the millions of setae on the toes of geckos has been the focus of scientific study for over a century. We provide the first direct experimental evidence for dry adhesion of gecko setae by van der Waals forces, and reject the use of mechanisms relying on high surface polarity, including capillary adhesion. The toes of live Tokay geckos were highly hydrophobic, and adhered equally well to strongly hydrophobic and strongly hydrophilic, polarizable surfaces. Adhesion of a single isolated gecko seta was equally effective on the hydrophobic and hydrophilic surfaces of a microelectro-mechanical systems force sensor. A van der Waals mechanism implies that the remarkable adhesive properties of gecko setae are merely a result of the size and shape of the tips, and are not strongly affected by surface chemistry. Theory predicts greater adhesive forces simply from subdividing setae to increase surface density, and suggests a possible design principle underlying the repeated, convergent evolution of dry adhesive microstructures in gecko, anoles, skinks, and insects. Estimates using a standard adhesion model and our measured forces come remarkably close to predicting the tip size of Tokay gecko seta. We verified the dependence on size and not surface type by using physical models of setal tips nanofabricated from two different materials. Both artificial setal tips stuck as predicted and provide a path to manufacturing the first dry, adhesive microstructures.

  20. Van der Waals interactions: Corrections from radiation in fluids

    Directory of Open Access Journals (Sweden)

    Magnus H. Waage

    2013-02-01

    Full Text Available We consider induced van der Waals interactions with corrections due to radiation in fluids consisting of polarizable hard spheres. The fluctuating polarizations are quantized while the positions of particles are treated classically. First the well known result for the induced Casimir free energy for a pair of particles is used to establish the resulting free energy at low density. The Casimir interaction includes the full effect of the quantized radiating electromagnetic field. Then the situation with electrostatic dipole-dipole interactions is considered for general density. For this situation the induced interactions are the van der Waals interactions, and we evaluate numerically the free energy based upon analytic results obtained earlier. These analytic results were obtained by extending methods of classical statistical mechanics to the path integral of quantum mechanics. We have realized that these methods can be extended to time-dependent interactions too. Thus we here also make the extension to the radiating dipole-dipole interaction between pairs of particles to obtain explicit results for more arbitrary fluid densities, and radiation corrections to the induced free energy are found both analytically and numerically.

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

    DEFF Research Database (Denmark)

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

    2001-01-01

    A recently proposed general density functional for asymptotic van der Waals forces is used to calculate van der Waals coefficients and reference-plane positions for realistic low-indexed Al surfaces. Results are given for a number of atoms and molecules outside the surfaces, as well as for the in......A recently proposed general density functional for asymptotic van der Waals forces is used to calculate van der Waals coefficients and reference-plane positions for realistic low-indexed Al surfaces. Results are given for a number of atoms and molecules outside the surfaces, as well...... as for the interaction between the surfaces themselves. The densities and static image-plane positions that are needed as input in the van der Waals functional are calculated self-consistently within density-functional theory using the generalized-gradient approximation, pseudopotentials, and plane waves. This study...

  2. Leeft het wilde paard voort in Engeland?

    NARCIS (Netherlands)

    Hovens, H.

    2009-01-01

    Lange tijd werd gedacht dat het Przewalskipaard het enige niet uitgestorven wilde paard van Europa was, maar mogelijk is er nog een tweede: de Exmoorpony. Hans Hovens gaat in het nieuwste nummer van Zoogdier op zoek naar bewijzen.

  3. Van Der Waals Friction: a Hamiltonian Test-Bed

    Science.gov (United States)

    Barton, Gabriel

    2012-07-01

    In the van der Waals regime (neglecting relativity and retardation), we find the power P generated by friction between two Drude-modelled dissipative half-spaces, at fixed separation and relative speed u, admitting only low u and low temperatures. This requires only elementary quantum mechanics; but the results can serve as partial checks on calculations in the fully retarded Casimir regime. They also raise questions regarding (i) the frequency-distribution of P; (ii) the status of predictions about Casimir forces generally, insofar as they feature parameters like conductivities with their empirical temperature-dependence; and (iii) calculations of heat transfer, insofar as they assume fluctuations in the two bodies to be uncorrelated.

  4. Layered van der Waals crystals with hyperbolic light dispersion

    DEFF Research Database (Denmark)

    Gjerding, Morten Niklas; Petersen, R.; Pedersen, T.G.

    2017-01-01

    candidates for Purcell factor control of emission from diamond nitrogen-vacancy centers.Natural hyperbolic materials retain the peculiar optical properties of traditional metamaterials whilst not requiring artificial structuring. Here, the authors perform a theoretical screening of a large class of natural......Compared to artificially structured hyperbolic metamaterials, whose performance is limited by the finite size of the metallic components, the sparse number of naturally hyperbolic materials recently discovered are promising candidates for the next generation of hyperbolic materials. Using first......-infrared to the ultraviolet. Combined with the emerging field of van der Waals heterostructuring, we demonstrate how the hyperbolic properties can be further controlled by stacking different two-dimensional crystals opening new perspectives for atomic-scale design of photonic metamaterials. As an application, we identify...

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

    Directory of Open Access Journals (Sweden)

    Gwan-Hyoung Lee

    2014-09-01

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

  6. Entanglement growth during Van der Waals like phase transition

    Directory of Open Access Journals (Sweden)

    Hao Xu

    2017-09-01

    Full Text Available We address the problem of describing the coexistence state of two different black holes and Van der Waals like phase transition in Reissner–Nordström–AdS space–time. We start by a small charged black hole, then introduce a collapsing neutral thin-shell described by Vaidya metric to form a large one. The formation of the large black hole does not change the temperature and free energy of the initial state. We discuss the entanglement growing during the phase transition. The transition is always continuous and the saturation time is determined by the final state. It opens a possibility for studying the holography from excited states to excited states.

  7. Nonlinearity of resistive impurity effects on van der Pauw measurements

    Science.gov (United States)

    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.

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

    Science.gov (United States)

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

    2012-02-01

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

  9. Infrared hyperbolic metasurface based on nanostructured van der Waals materials

    Science.gov (United States)

    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.

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

    Science.gov (United States)

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

    2017-06-01

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

  11. Multifunctional high-performance van der Waals heterostructures

    Science.gov (United States)

    Huang, Mingqiang; Li, Shengman; Zhang, Zhenfeng; Xiong, Xiong; Li, Xuefei; Wu, Yanqing

    2017-12-01

    A range of novel two-dimensional materials have been actively explored for More Moore and More-than-Moore device applications because of their ability to form van der Waals heterostructures with unique electronic properties. However, most of the reported electronic devices exhibit insufficient control of multifunctional operations. Here, we leverage the band-structure alignment properties of narrow-bandgap black phosphorus and large-bandgap molybdenum disulfide to realize vertical heterostructures with an ultrahigh rectifying ratio approaching 106 and on-off ratio up to 107. Furthermore, we design and fabricate tunable multivalue inverters, in which the output logic state and window of the mid-logic can be controlled by specific pairs of channel length and, most importantly, by the electric field, which shifts the band-structure alignment across the heterojunction. Finally, high gains over 150 are achieved in the inverters with optimized device geometries, showing great potential for future logic applications.

  12. Theory of electron attachment to van der Waals clusters

    International Nuclear Information System (INIS)

    Fabrikant, Ilya I

    2005-01-01

    A theory of electron collisions with van der Waals clusters is developed which is capable of describing the vibrational Feshbach resonances (VFRs) recently observed in electron attachment to CO 2 clusters. VFRs appear below vibrational excitation thresholds of one molecular unit and their energy decreases with the increase of the cluster size. The selectivity observed in vibrational excitation of individual components of a Fermi dyad is substantially reduced in the attachment spectra. We also calculate elastic electron scattering and vibrational excitation (VE) of one molecular unit in a cluster environment and demonstrate a strong influence of the VFRs on the VE cross sections. Theoretically predicted VFRs are much narrower than observed. We explain the VFR broadening by contribution of several neutral precursors, contribution of different cluster conformations and the dependence of the resonance energy on the position of the molecular unit in the cluster. A model is developed to describe the latter effect quantitatively

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

    Science.gov (United States)

    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.

  14. Equilibrium shape of a suspended graphene sheet under electrostatic and van der Waals forces

    Science.gov (United States)

    Inui, Norio

    2018-03-01

    The equilibrium shape of a graphene sheet suspended over a silicon substrate with a narrow gap is investigated by introducing a continuum model. The displacement of the suspended graphene sheet, subject to electrostatic and van der Waals forces, was obtained by solving the equation of motion including the dissipation terms. The van der Waals force was calculated based on the quantum theory by considering the unique optical properties of graphene and their temperature dependence. The van der Waals force has a large effect on the equilibrium shape near the threshold value, below which a pull-in phenomenon occurs.

  15. Strange attractors and synchronization dynamics of coupled Van der Pol-Duffing oscillators

    International Nuclear Information System (INIS)

    Yamapi, R.; Filatrella, G.

    2006-07-01

    We consider in this paper the dynamics and synchronization of coupled chaotic Van der Pol-Duffing systems. The stability of the synchronization process between two coupled autonomous Van der Pol model is first analyzed analytically and numerically, before following the problem of synchronizing chaos both on the same and different chaotic orbits of two coupled Van der Pol-Duffing systems. The stability boundaries of the synchronization process are derived and the effects of the amplitude of the periodic perturbation of the coupling parameter on these boundaries are analyzed. The results are provided on the stability map in the (q, K) plane. (author)

  16. Average and extreme multi-atom Van der Waals interactions: Strong coupling of multi-atom Van der Waals interactions with covalent bonding

    Directory of Open Access Journals (Sweden)

    Finkelstein Alexei V

    2007-07-01

    Full Text Available Abstract Background The prediction of ligand binding or protein structure requires very accurate force field potentials – even small errors in force field potentials can make a 'wrong' structure (from the billions possible more stable than the single, 'correct' one. However, despite huge efforts to optimize them, currently-used all-atom force fields are still not able, in a vast majority of cases, even to keep a protein molecule in its native conformation in the course of molecular dynamics simulations or to bring an approximate, homology-based model of protein structure closer to its native conformation. Results A strict analysis shows that a specific coupling of multi-atom Van der Waals interactions with covalent bonding can, in extreme cases, increase (or decrease the interaction energy by about 20–40% at certain angles between the direction of interaction and the covalent bond. It is also shown that on average multi-body effects decrease the total Van der Waals energy in proportion to the square root of the electronic component of dielectric permittivity corresponding to dipole-dipole interactions at small distances, where Van der Waals interactions take place. Conclusion The study shows that currently-ignored multi-atom Van der Waals interactions can, in certain instances, lead to significant energy effects, comparable to those caused by the replacement of atoms (for instance, C by N in conventional pairwise Van der Waals interactions.

  17. The scholar and the state: in search of van der Waerden

    CERN Document Server

    Soifer, Alexander

    2015-01-01

    Bartel Leendert van der Waerden made major contributions to algebraic geometry, abstract algebra, quantum mechanics, and other fields. He liberally published on the history of mathematics. His 2-volume work Modern Algebra is one of the most influential and popular mathematical books ever written. It is therefore surprising that no monograph has been dedicated to his life and work. Van der Waerden’s record is complex. In attempting to understand his life, the author assembled thousands of documents from numerous archives in Germany, the Netherlands, Switzerland and the United States which revealed fascinating and often surprising new information about van der Waerden. Soifer traces Van der Waerden’s early years in a family of great Dutch public servants, his life as professor in Leipzig during the entire Nazi period, and his personal and professional friendship with one of the great physicists Werner Heisenberg. We encounter heroes and villains and a much more numerous group in between these two extremes. ...

  18. ENPA juht usub Vene arengusse / Rene van der Linden ; interv. Erkki Bahovski

    Index Scriptorium Estoniae

    Linden, Rene van der

    2006-01-01

    Vt. ka Postimees : na russkom jazõke 2. juuni lk. 7. Euroopa Nõukogu Parlamentaarse Assamblee president Rene van der Linden Euroopa Nõukogu (EN) rollist, Venemaa ja Eesti arengutest EN-i liikmena. Lisa: Euroopa parlamentide kogu

  19. The scholar and the state in search of van der Waerden

    CERN Document Server

    Soifer, Alexander

    2015-01-01

    Bartel Leendert van der Waerden made major contributions to algebraic geometry, abstract algebra, quantum mechanics, and other fields. He liberally published on the history of mathematics. His 2-volume work Modern Algebra is one of the most influential and popular mathematical books ever written. It is therefore surprising that no monograph has been dedicated to his life and work. Van der Waerden’s record is complex. In attempting to understand his life, the author assembled thousands of documents from numerous archives in Germany, the Netherlands, Switzerland and the United States which revealed fascinating and often surprising new information about van der Waerden. Soifer traces Van der Waerden’s early years in a family of great Dutch public servants, his life as professor in Leipzig during the entire Nazi period, and his personal and professional friendship with one of the great physicists Werner Heisenberg. We encounter heroes and villains and a much more numerous group in between these two extremes. ...

  20. Jazõk do demokrati ne dovedjot / Max van der Stoel

    Index Scriptorium Estoniae

    Stoel, Max van der, 1924-2011

    1999-01-01

    OSCE vähemusrahvuste ülemkomissari Max van der Stoeli pöördumine Lennart Meri poole seoses riigikeele oskuse nõude sisseviimisega Riigikogu valimise ja kohaliku omavalitsuse volikogu valimise seadusesse

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

    CERN Document Server

    Janda, Kenneth

    1991-01-01

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

  2. Van der Waals interactions and photoelectric effect in noncommutative quantum mechanics

    International Nuclear Information System (INIS)

    Li Kang; Chamoun, N.

    2007-01-01

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

  3. A modified van der Pol equation with delay in a description of the heart action

    OpenAIRE

    Zduniak Beata; Bodnar Marek; Foryś Urszula

    2014-01-01

    In this paper, a modified van der Pol equation is considered as a description of the heart action. This model has a number of interesting properties allowing reconstruction of phenomena observed in physiological experiments as well as in Holter electrocardiographic recordings. Our aim is to study periodic solutions of the modified van der Pol equation and take into consideration the influence of feedback and delay which occur in the normal heart action mode as well as in pathological modes. U...

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

    Science.gov (United States)

    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.

  5. Marriage Aspects of Minangkabau Matrilineal Systems in Hamka's Tenggelamnya Kapal Van Der Wijck

    OpenAIRE

    BAHRI, SYAMSUL

    2014-01-01

    This study explores the cultural elements found in the literary work of Tenggelamnya Kapal Van Der Wijck in the form of Novel written by Buya Hamka. It utilizes an extrinsic approach in which there are some interpretations and explanations about cultural elements in Hamka's Tenggelamnya Kapal Van Der Wijck. It describes the aspects of marriage based on Minangkabau custom especially practiced in Batipuh, West Sumatera that still hold fast to the tradition and culture very much concerned to t...

  6. De mens in zijn totaliteit. De antropologische benadering in het werk van Lammert van der Horst (1893-1978

    Directory of Open Access Journals (Sweden)

    Bart Karstens

    2010-09-01

    Full Text Available The totality of man. The anthropological approach to psychiatry in the work of Lammert van der Horst (1893-1978 The anthropological approach was one of the new approaches to psychiatry that emerged in the interbellum. In the Netherlands professor Van der Horst (VU-university Amsterdam and the municipal University of Amsterdam was its most prominent proponent. The general idea of the anthropological approach was to integrate the various ways of knowing then available. A psychiatric disease was seen as the result of a failure in the self-realisation of the individual person. This required to consider all relevant aspects relating to the patient’s existence. How to tailor these ideas to concrete forms of diagnosis and methods of treatment was no easy matter and Van der Horst devoted himself all his life to this task. He first sought to classify man in three or four types of character inspired by the works of Heymans and Kretschmer. Then he tried to give the specific human aspect its place in psychiatry by introducing a ‘pneumatic’ dimension in his analysis of persons. He also connected this dimension to Calvinism, the church he belonged to. In the 1940’s he made a turn towards existentialism and tried to connect this philosophy to anthropological psychiatry. In spite of its fragmentary appearance I believe it is possible to discern a degree of continuity in the work of Van der Horst. The concern with the specifically human was always central to him. Moreover Van der Horst saw no strict divide between addressing questions in psychiatry and thinking about the greater questions of life which provides an explanation for his meandering thoughts. The dissertation of J.H. van den Berg which appeared in 1946 offers an interesting contrast to Van der Horst. To Van den Berg the anthropological approach was no more than a method best developed by Binswanger. Van den Berg tested this method and concluded that the approach could offer hermeneutic

  7. Ingredienten voor kwaliteitsborging van modelonderzoek

    NARCIS (Netherlands)

    Grinsven JJM van; Haan BJ de; Braat LC; MNV; LBG; CIM

    1995-01-01

    In dit rapport wordt een aanzet gepresenteerd tot harmonisatie van de kwaliteitsborging van modelonderzoek in het RIVM. Het rapport komt voort uit initiatieven van leden van het Intersectoraal Modellen Overleg. Het rapport is in eerste instantie bedoeld voor onderzoekers die modellen

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

    Science.gov (United States)

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

    2009-05-14

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

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

    Science.gov (United States)

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

    2017-04-01

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

  10. Rotational dissociation of impulsively aligned van der Waals complexes.

    Science.gov (United States)

    Søndergaard, Anders A; Zillich, Robert E; Stapelfeldt, Henrik

    2017-08-21

    The nonadiabatic alignment dynamics of weakly bound molecule-atom complexes, induced by a moderately intense 300 fs nonresonant laser pulse, is calculated by direct numerical solution of the time-dependent Schrödinger equation. Our method propagates the wave function according to the coupled channel equations for the complex, which can be done in a very efficient and stable manner out to large times. We present results for two van der Waal complexes, CS 2 -He and HCCH-He, as respective examples of linear molecules with large and small moments of inertia. Our main result is that at intensities typical of nonadiabatic alignment experiments, these complexes rapidly dissociate. In the case of the CS 2 -He complex, the ensuing rotational dynamics resembles that of isolated molecules, whereas for the HCCH-He complex, the detachment of the He atom severely perturbs and essentially quenches the subsequent rotational motion. At intensities of the laser pulse ≲2.0 × 10 12 W/cm 2 , it is shown that the molecule-He complex can rotate and align without breaking apart. We discuss the implications of our findings for recent experiments on iodine molecules solvated in helium nanodroplets.

  11. LA CASA CON PATIO EN MIES VAN DER ROHE / House with patio from Mies van der Rohe

    Directory of Open Access Journals (Sweden)

    José Altés Bustelo

    2013-05-01

    Full Text Available RESUMEN Una revisión del tema Casa con Patio, con especial atención a los planteamientos desarrollados por Mies van der Rohe durante sus últimos años en Berlín, a propósito del conocido dibujo denominado “Casa con tres patios”. Se explora su pensamiento arquitectónico a partir de los datos historiográficos de su trayectoria, más los que se pueden deducir del análisis de los dibujos y croquis previos del arquitecto. El conjunto de proyectos en que aparece el tema es muy amplio durante ese tiempo y los dibujos conservados ofrecen múltiples reflexiones. Sobre ese soporte se examinan conceptos relativos a la definición espacial y formal, donde aparecen cuestiones que ligan esa definición con los sistemas y materiales constructivos. Malla estructural, muro, pared de vidrio y patio vividero, vinculados necesariamente a sus respectivas cualidades tectónicas, adquieren el sentido de materiales de proyecto utilizados para definir un particular modo de entender la arquitectura en el que el usuario está presente siempre como destinatario de la misma. Finalmente, se plantea la utilidad didáctica del análisis de esos dibujos para el progreso del conocimiento en el proyecto arquitectónico.SUMMARY A review of the theme, House with Patio, with special reference to the plans developed by Mies van der Rohe during his last years in Berlin, in relation to the well–known drawing called: “House with three patios”. His architectural thoughts are explored through the historiographic data of his career, plus those that can be deduced from the analysis of the architect’s previous drawings and sketches. The group of projects, in which the theme appears is prolific from that time, and the preserved drawings offer multiple opportunities for reflection. Concepts on that medium are examined, relative to spatial and formal definition, where questions appear that link that definition with the constructive systems and materials. Structural mesh

  12. van't Hoff-van der Waals osmotic pressure and energy transformers

    Science.gov (United States)

    Zener, Clarence; Levenson, William

    1983-01-01

    We find the van't Hoff relations between osmotic pressure, freezing point depression, and boiling point elevation provide a clue on how, by using salt solutions, one may lower the cost of extracting power from low-grade heat sources. In particular, the ratio of 7 between the heat of evaporation and the heat of freezing of pure water suggests a chemical system that raises 7-fold the temperature difference between heat source and heat sink, while decreasing by the same factor the heat flux. Heat exchangers dominate the cost of heat engines operating upon low-grade heat. Their area for a fixed power output is inversely proportional to the available temperature differential. Herein lies the potential for a great cost reduction. We show that the simple van der Waals concept of a gas of hard elastic spheres suffices to understand the colligative properties of salt solutions, at least up to the concentration of the eutectic composition. This concept enables us to physically interpret the thermodynamic processes during the concentration of salt solutions by evaporation and during the mixing of ice and solid salt hydrates at their eutectic temperature. These are identical to the thermodynamic processes taking place during the isothermal compression and expansion of gases in pumps and in turbines. PMID:16593343

  13. van't Hoff-van der Waals osmotic pressure and energy transformers.

    Science.gov (United States)

    Zener, C; Levenson, W

    1983-07-01

    We find the van't Hoff relations between osmotic pressure, freezing point depression, and boiling point elevation provide a clue on how, by using salt solutions, one may lower the cost of extracting power from low-grade heat sources. In particular, the ratio of 7 between the heat of evaporation and the heat of freezing of pure water suggests a chemical system that raises 7-fold the temperature difference between heat source and heat sink, while decreasing by the same factor the heat flux. Heat exchangers dominate the cost of heat engines operating upon low-grade heat. Their area for a fixed power output is inversely proportional to the available temperature differential. Herein lies the potential for a great cost reduction. We show that the simple van der Waals concept of a gas of hard elastic spheres suffices to understand the colligative properties of salt solutions, at least up to the concentration of the eutectic composition. This concept enables us to physically interpret the thermodynamic processes during the concentration of salt solutions by evaporation and during the mixing of ice and solid salt hydrates at their eutectic temperature. These are identical to the thermodynamic processes taking place during the isothermal compression and expansion of gases in pumps and in turbines.

  14. Quantum Coulomb Systems: Recombination, Screening, and van der Waals Forces

    International Nuclear Information System (INIS)

    Alastuey, A.

    2009-01-01

    Under standard Earth conditions, and also in many astrophysical situations, the properties of matter result from the interplay between non-relativistic quantum mechanics and Coulomb interactions. In that context, the derivation of exact results for equilibrium properties of quantum Coulomb systems is of crucial importance. First, I briefly review rigorous proofs about either stability or limiting behaviours, as well as various asymptotic expansions specific to almost fully ionized situations. Then, I present the Feynman-Kac path integral representation which is the most efficient tool for dealing with both recombination and screening. Within that representation, the grand-canonical partition function for a system of quantum particles with two-body interactions is shown to be equal to its equivalent counterpart for a system of classical loops. Equilibrium quantities for the gas of loops are then represented by straightforward generalizations of standard Mayer diagrammatics. Because of the Coulomb-like long range of the two-body loop potential, every Mayer graph diverges. Such divergences are first removed via systematic chain resummations, which amount to introduce an effective potential φ, the quantum analogue of Debye potential. In a second step, the whole resumed diagrammatical series is exactly reorganized in terms of graphs where particle clusters are connected by bonds built with φ. The corresponding screened cluster representation is particularly useful for studying partially ionized gases, as illustrated by its application to hydrogen in the atomic regime. Exact asymptotic expansions for thermodynamics are derived beyond familiar Saha theory. Also, the screening of van der Waals forces between two hydrogen atoms by ionized protons and ionized electrons is shown to be only partial. (author)

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

    DEFF Research Database (Denmark)

    Kontogeorgis, Georgios; Economou, Ioannis G.

    2010-01-01

    The ideas of van der Waals have resulted to cubic equations of state like Soave–Redlich–Kwong (SRK) and Peng–Robinson (PR) which are widely used in the petroleum and chemical industries. It is often thought that the range of applicability of van der Waals-type models is limited to mixtures...... of compounds relatively similar in size. We employ in this work an approach for investigating the various terms of cubic equations of state by looking at the excess Gibbs energy and activity coefficient expressions which are derived from these equations of state. We illustrate that the results of cubic...... equations of state are sensitive to the mixing and combining rules used. Moreover, it is shown that previously reported deficiencies for size-asymmetric systems are more related to the van der Waals one fluid mixing rules used rather than the functionality of the cubic equation of state itself. Improved...

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

    Science.gov (United States)

    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.

  17. Professor Bennie van der Walt: a bridge between white Afrikaners and black Africans

    Directory of Open Access Journals (Sweden)

    Y. Turaki

    2010-07-01

    Full Text Available This article honours Professor Bennie van der Walt as a bridge builder between white Afrikaners and black Africans as well as a renowned Christian scholar. Historical Western colonialism in South Africa divided its citizens against each other by means of white racism and apartheid. The whites in general were pitched against the blacks on the basis of white racism and its doctrine of apartheid. This doctrine of separation of races kept the white Afrikaners from the Bantu Africans. However, apartheid as a form of political, social, cultural and religious racism is now history in South Africa. The role which Professor Van der Walt played in bridging the gap between this racial divide is highly commendable and needs to be acknowledged and appreciated, hence the primary objective of this article in honour of his 71st birthday. Furthermore, the article discusses the immense contributions of Professor Bennie van der Walt to Christian scholarship in Africa.

  18. Maria van der Hoeven, the Netherlands minister for education, culture and science, visited CERN

    CERN Multimedia

    maximilien Brice

    2005-01-01

    On 21 April, the Netherlands Minister for Education, Culture and Science, Mrs Maria van der Hoeven, was welcomed to CERN by the Director-General, Robert Aymar, and the Chief Scientific Officer, Jos Engelen. Minister van der Hoeven visited the ATLAS installations, the LHC tunnel and the magnet assembly and test hall before meeting a group of young scientists from the Netherlands. Picture 05 : from left to right, Frank Linde, Director of the Netherlands National Institute for Nuclear Physics and High Energy Physics (NIKHEF), Jos Engelen, CERN's Chief Scientific Officer, Maria van der Hoeven, Netherlands Minister for Education, Culture and Science, and Herman Ten Kate, Head of the ATLAS magnet project, visiting the ATLAS assembly hall.Picture 09 ; Here she talks with, from left to right, Jos Engelen, CERN's chief scientific officer, Peter Jenni, the ATLAS spokesman, Herman Ten Kate, head of the ATLAS magnet project, and Frank Linde, director of the Netherlands National Institute for Nuclear Physics and High Ener...

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

    Science.gov (United States)

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

    2015-09-14

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

  20. From Canards of Folded Singularities to Torus Canards in a Forced van der Pol Equation

    DEFF Research Database (Denmark)

    Burke, John; Desroches, Mathieu; Granados, Albert

    2016-01-01

    In this article, we study canard solutions of the forced van der Pol equation in the relaxation limit for low-, intermediate-, and high-frequency periodic forcing. A central numerical observation made herein is that there are two branches of canards in parameter space which extend across all...... of the secondary canards turn around in the intermediate-frequency regime, instead of continuing into the high-frequency regime. Also, we identify the mechanism responsible for this turning. Finally, we show that the forced van der Pol equation is a normal form-type equation for a class of single...

  1. A modified van der Pol equation with delay in a description of the heart action

    Directory of Open Access Journals (Sweden)

    Zduniak Beata

    2014-12-01

    Full Text Available In this paper, a modified van der Pol equation is considered as a description of the heart action. This model has a number of interesting properties allowing reconstruction of phenomena observed in physiological experiments as well as in Holter electrocardiographic recordings. Our aim is to study periodic solutions of the modified van der Pol equation and take into consideration the influence of feedback and delay which occur in the normal heart action mode as well as in pathological modes. Usage of certain values for feedback and delay parameters allows simulating the heart action when an accessory conducting pathway is present (Wolff-Parkinson-White syndrome.

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

    DEFF Research Database (Denmark)

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

    2016-01-01

    The assembly of individual two-dimensional materials into van der Waals heterostructures enables the construction of layered three-dimensional materials with desirable electronic and optical properties. A core problem in the fabrication of these structures is the formation of clean interfaces...... between the individual two-dimensional materials which would affect device performance. We present here a technique for the rapid batch fabrication of van der Waals heterostructures, demonstrated by the controlled production of 22 mono-, bi- and trilayer graphene stacks encapsulated in hexagonal boron...

  3. Estructura portante y estructura formal: Mies Van Der Rohe y su influencia sobre la arquitectura paulista

    OpenAIRE

    Mahfuz, Edson da Cunha

    2014-01-01

    El artículo trata de la posible influencia de Mies van der Rohe sobre la arquitectura paulista. Su característica más evidente es el rol de la estructura portante en la construcción de la forma. El uso de un número reducido de soportes busca liberar el suelo para actividades colectivas. The article describes the possible influence of Mies van der Rohe on the architecture practiced in São Paulo. Its most noticeable feature is the role of the structure on the definition of the overall art...

  4. Beam-Beam effects at the CMS BRIL van-der-Meer scans

    CERN Document Server

    CMS Collaboration

    2017-01-01

    The CMS Beam Radiation Instrumentation and Luminosity Project (BRIL) is devoted to the simulation and measurement of luminosity, beam conditions and radiation fields in the CMS Experiment at CERN. The project is engaged in operating and developing new detectors, compatible with the high luminosity experimental environments at the LHC. BRIL operates several detectors based on different physical principles and technologies. The detectors are calibrated using van-der-Meer scans to measure the luminosity that is a fundamental quantity of the LHC beam. In van-der-Meer scans the count rate in a detector is measured as a function of the distance between beams in the plane perpendicular to beam direction, to extract the underlying beam overlap area. The goal of the van-der-Meer scans is to obtain the calibration constant for each luminometer to be used at calibration then in physics data taking runs. The note presents the overview of beam-beam effects at the van-der-Meer scan and the corresponding corrections that sh...

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

    NARCIS (Netherlands)

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

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

  6. Optical properties and kinetic roughening influence on dispersive casimir and van der Waals forces

    NARCIS (Netherlands)

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

    2010-01-01

    Casimir and van der Waals dispersive forces between real material surfaces can be strongly influenced by surface roughness and the frequency dependent dielectric functions of the interacting materials. The Lifshitz theory allows calculations of these forces between two flat plates if the frequency

  7. Optical Properties and Kinetic Roughening Influence on Dispersive Casimir and van der Waals Forces

    NARCIS (Netherlands)

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

    2010-01-01

    Casimir and van der Waals dispersive forces between real material surfaces can be strongly influenced by surface roughness and the frequency dependent dielectric functions of the interacting materials. The Lifshitz theory allows calculations of these forces between two flat plates if the frequency

  8. J.T. van der Kemp and his Critique of the Settler Farmers on the ...

    African Journals Online (AJOL)

    Theoretically, I draw on some insights from works of Michel Foucault, especially with regard to eighteenth and early nineteenth century 'representational thought', where 'idea' and 'object' are directly related. Keywords: J.T. van der Kemp, settler farmers, frontier, patriot, rebellion, slavery, baptism, cruelty, Black Circuit Court ...

  9. Dynamical screening of the van der Waals interaction between graphene layers.

    Science.gov (United States)

    Dappe, Y J; Bolcatto, P G; Ortega, J; Flores, F

    2012-10-24

    The interaction between graphene layers is analyzed combining local orbital DFT and second order perturbation theory. For this purpose we use the linear combination of atomic orbitals-orbital occupancy (LCAO-OO) formalism, that allows us to separate the interaction energy as the sum of a weak chemical interaction between graphene layers plus the van der Waals interaction (Dappe et al 2006 Phys. Rev. B 74 205434). In this work, the weak chemical interaction is calculated by means of corrected-LDA calculations using an atomic-like sp(3)d(5) basis set. The van der Waals interaction is calculated by means of second order perturbation theory using an atom-atom interaction approximation and the atomic-like-orbital occupancies. We also analyze the effect of dynamical screening in the van der Waals interaction using a simple model. We find that this dynamical screening reduces by 40% the van der Waals interaction. Taking this effect into account, we obtain a graphene-graphene interaction energy of 70 ± 5 meV/atom in reasonable agreement with the experimental evidence.

  10. Far infrared study of the Argon-HCl van der Waals molecule

    NARCIS (Netherlands)

    Boom, E.W.; Frenkel, D.; Elsken, J. van der

    1977-01-01

    Results of far infrared measurements on the system HCl–Ar at low density and temperature are presented. Distinct spectral features are observed that must be attributed to Ar–HCl van der Waals molecules. Possible explanations of the observed spectra in terms of a simple picture of the internal motion

  11. David van der Linden, Experiencing Exile: Huguenot Refugees in the Dutch Republic 1680-1700

    Directory of Open Access Journals (Sweden)

    Matthew Glozier

    2016-04-01

    Full Text Available David van der Linden, Experiencing Exile: Huguenot Refugees in the Dutch Republic 1680-1700 (PhD Universiteit Utrecht 2013; Politics and Culture in Europe, 1650-1750; Farnham: Ashgate, 2015, xx + 289 pp., ISBN 978 14 7242 927 8.

  12. Anisotropic spheres with Van der Waals-type equation of state

    Indian Academy of Sciences (India)

    2014-07-02

    Jul 2, 2014 ... viewed as a relativistic Fermi gas of quark at the extremes of densities necessary for colour deconfinement to ... nuclear forces mediated by multigluon exchange lead to a short-range force, which is considered to be in analogy with the effective Van der Waals force due to multiphoton exchange interaction ...

  13. I:\\AA-TYPESET\\CHEM\\2005\\van der Westhuyzen.vp

    African Journals Online (AJOL)

    NJD

    Saharan Africa.2 A million people die annually from the disease. At this time, the only class of compounds against which the ... mode of action was proved incorrect by Krishna and Eckstein-Ludwig,8 ... C.W. van der Westhuyzen and C.J. Parkinson,.

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

    NARCIS (Netherlands)

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

    2009-01-01

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

  15. Van der Woude syndrome: A review of 11 cases seen at the Lagos ...

    African Journals Online (AJOL)

    Background: Van der Woude syndrome (VWS), an autosomal dominant condition associated with clefts of the lip and/or palate and lower lip pits and is caused by mutations in interferon regulatory factor six gene. It is reported to be the most common syndromic cleft worldwide. Non-penetrance for the lip pit phenotype is ...

  16. El pabellón de Mies Van Der Rohe en Barcelona

    Directory of Open Access Journals (Sweden)

    Eduardo Meissner Grebe

    1989-06-01

    Full Text Available Circunstancias especiales me han llevado, una vez más, a Barcelona, ciudad de manifiestas afinidades electivas. Me espera un afán especial, la venida al recientemente reconstruido Pabellón de Exposiciones, de Mies van der Rohe.

  17. Holography does not account for goodness: A critical review of Van der Helm and Leeuwenberg .

    NARCIS (Netherlands)

    Olivers, C.N.L.; Chater, N.; Watson, D.G.

    2004-01-01

    P. A. van der Helm and E. L. J. Leeuwenberg (1996) outlined a holographic account of figural goodness of a perceptual stimulus. The theory is mathematically precise and can be applied to a broad spectrum of empirical data. The authors argue, however, that the account is inadequate on both

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

    KAUST Repository

    Govyadinov, Alexander A.

    2017-07-14

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Yongsuk [SKKU Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University, Suwon 440-746 Korea; Department of Materials Science and Engineering, Northwestern University, Evanston IL 60208 USA; Kang, Junmo [Department of Materials Science and Engineering, Northwestern University, Evanston IL 60208 USA; Jariwala, Deep [Department of Materials Science and Engineering, Northwestern University, Evanston IL 60208 USA; Kang, Moon Sung [Department of Chemical Engineering, Soongsil University, Seoul 156-743 Korea; Marks, Tobin J. [Department of Materials Science and Engineering, Northwestern University, Evanston IL 60208 USA; Department of Chemistry, Northwestern University, Evanston IL 60208 USA; Hersam, Mark C. [Department of Materials Science and Engineering, Northwestern University, Evanston IL 60208 USA; Department of Chemistry, Northwestern University, Evanston IL 60208 USA; Department of Electrical Engineering and Computer Science, Northwestern University, Evanston IL 60208 USA; Cho, Jeong Ho [SKKU Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University, Suwon 440-746 Korea; Department of Materials Science and Engineering, Northwestern University, Evanston IL 60208 USA; School of Chemical Engineering, Sungkyunkwan University, Suwon 440-746 Korea

    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).

  20. The Hopf-van der Pol system: Failure of a homotopy method

    NARCIS (Netherlands)

    Meijer, Hil Gaétan Ellart; Kalmár-Nagy, T.

    2012-01-01

    The purpose of this article to provide an explicit example where continuation based on the homotopy method fails. The example is a one-parameter homotopy for periodic orbits between two well-known nonlinear systems, the normal form of the Hopf bifurcation and the van der Pol system. Our analysis

  1. The mediator's moral dilemma: An essay in memory of H.W. van der ...

    African Journals Online (AJOL)

    Several important ecumenical declarations in the 1980s emphasised the moral and theological imperative for believers to take sides with the oppressed and poor.2 Van der Merwe's grounding of the integrity of mediation in religious faith was therefore highly relevant in the context of the time. This short essay re-visits two ...

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

    Energy Technology Data Exchange (ETDEWEB)

    Sarkisov, Sergey Y., E-mail: sarkisov@mail.tsu.ru [Tomsk State University, Lenin Avenue 36, 634050 Tomsk (Russian Federation); Kosobutsky, Alexey V., E-mail: kosobutsky@kemsu.ru [Tomsk State University, Lenin Avenue 36, 634050 Tomsk (Russian Federation); Kemerovo State University, Krasnaya 6, 650043 Kemerovo (Russian Federation); Shandakov, Sergey D. [Kemerovo State University, Krasnaya 6, 650043 Kemerovo (Russian Federation)

    2015-12-15

    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–Se 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}.

  3. The van der Waals Equation of State and the Law of Corresponding States: A Spreadsheet Experiment

    NARCIS (Netherlands)

    Schaink, H.M.; Venema, P.

    2007-01-01

    In normal physical chemistry courses the student is told how the van der Waals equation works. The mathematics needed for making a Maxwell construction is difficult for the average chemistry student. This makes it difficult to show how the liquid-gas digram is obtained from the equation of state.

  4. Blades Forced Vibration Under Aero-Elastic Excitation Modeled by Van der Pol

    Czech Academy of Sciences Publication Activity Database

    Půst, Ladislav; Pešek, Luděk

    2017-01-01

    Roč. 27, č. 11 (2017), č. článku 1750166. ISSN 0218-1274 R&D Projects: GA ČR GA16-04546S Institutional support: RVO:61388998 Keywords : ade vibration * aero-elastic force * self-excitation * van der Pol Subject RIV: BI - Acoustics OBOR OECD: Applied mechanics Impact factor: 1.329, year: 2016

  5. Lithium ions in the van der Waals gap of Bi2Se3 single crystals

    Czech Academy of Sciences Publication Activity Database

    Bludská, Jana; Jakubec, Ivo; Karamazov, S.; Horák, Jaromír; Uher, C.

    2010-01-01

    Roč. 183, č. 12 (2010), s. 2813-2817 ISSN 0022-4596 Institutional research plan: CEZ:AV0Z40320502 Keywords : intercalation * van Der Waals gap * Bi2Se3 crystals Subject RIV: CG - Electrochemistry Impact factor: 2.261, year: 2010

  6. Semi-analytical stochastic analysis of the generalized van der Pol system

    Czech Academy of Sciences Publication Activity Database

    Náprstek, Jiří; Fischer, Cyril

    (2018) ISSN 1802-680X R&D Projects: GA ČR(CZ) GA15-01035S Institutional support: RVO:68378297 Keywords : stochastic stability * generalized van der Pol system * stochastic averaging * limit cycles Subject RIV: JM - Building Engineering OBOR OECD: Construction engineering, Municipal and structural engineering https://www.kme.zcu.cz/acm/acm/article/view/407

  7. Weyl-van der Waerden spinor technic for spin-3/2 fermions

    International Nuclear Information System (INIS)

    Novaes, S.F.; Spehler, D.

    1991-09-01

    We use the Weyl-van der Waerden spinor technic to construct helicity wave functions for massless and massive spin-3/2 fermions. We apply our formalism to evaluate helicity amplitudes taking into account some phenomenological couplings involving these particles. (author)

  8. Van der Waals coefficients for alkali metal clusters and their size ...

    Indian Academy of Sciences (India)

    . 1000 atoms) easily, thereby allowing us to study the evolution of van der Waals coefficients with the size of the clusters. For details of the ETF method and its application to study alkali–metal cluster, we refer the reader to [9,10,27–29]. In the.

  9. Field Effect in Graphene-Based van der Waals Heterostructures: Stacking Sequence Matters

    DEFF Research Database (Denmark)

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

    2017-01-01

    Stacked van der Waals (vdW) heterostructures where semiconducting two-dimensional (2D) materials are contacted by overlaid graphene electrodes enable atomically thin, flexible electronics. We use first-principles quantum transport simulations of graphene-contacted MoS2 devices to show how the tra...

  10. Van der Waals coefficients for alkali metal clusters and their size

    Indian Academy of Sciences (India)

    In this paper we employ the hydrodynamic formulation of time-dependent density functional theory to obtain the van der Waals coefficients 6 and 8 of alkali metal clusters of various sizes including very large clusters. Such calculations become computationally very demanding in the orbital-based Kohn-Sham formalism, ...

  11. Holography Does Not Account for Goodness: A Critique of van der Helm and Leeuwenberg (1996)

    Science.gov (United States)

    Olivers, Christian N. L.; Chater, Nick; Watson, Derrick G.

    2004-01-01

    P. A. van der Helm and E. L. J. Leeuwenberg (1996; see record 1996-01780-002) outlined a holographic account of figural goodness of a perceptual stimulus. The theory is mathematically precise and can be applied to a broad spectrum of empirical data. The authors argue, however, that the account is inadequate on both theoretical and empirical…

  12. Between Looking and Making: Unravelling Dom Hans van der Laan’s Plastic Number

    Directory of Open Access Journals (Sweden)

    Caroline Voet

    2016-01-01

    Full Text Available Between 1920 and 1991, the Dutch Benedictine monk and architect Dom Hans van der Laan (1904–91 developed his own proportional system based on the ratio 3:4, or the irrational number 1.3247. . ., which he called the plastic number. According to him, this ratio directly grew from discernment, the human ability to differentiate sizes, and as such would be an improvement over the golden ratio. To put his theories to the test, he developed an architectural language, which can best be described as elementary architecture. His oeuvre — four convents and a house — is published on an international scale. His buildings have become pilgrimage sites for practicing architects and institutions that want to study and experience his spaces. His 1977 book 'Architectonic Space: Fifteen Lessons on the Disposition of the Human Habitat', translated into English, French, German and Italian, still inspires architects today, as does his biography, 'Modern Primitive', written by the architect Richard Padovan in 1994. But beyond the inspiration of his writings and realisations, the actual application of the plastic number in Van der Laan’s designs is unclear. Moreover, Van der Laan’s theories seem to be directed towards one goal only: to present the plastic number as the only possible means by which eminent architecture can be achieved, making them a target for suspicion and critique. To understand and evaluate Van der Laan’s application of the plastic number, this paper approaches it as a practical design tool. It analyses its genealogy and defines its key concepts. From that framework, Van der Laan’s architectonic space is interpreted as a design methodology that combines antique tectonic theories reminiscent of writers from Plato to Vitruvius with more recent atectonic approaches towards space through experience and movement.

  13. "Neue Liebe, neues Leben" - Ein Goethe-Gedicht in der Vertonung durch Ludwig van Beethoven

    Directory of Open Access Journals (Sweden)

    Körndle, Franz

    2001-12-01

    Full Text Available Ludwig van Beethoven composed two versions of Goethe's poem „Neue Liebe, neues Leben" in 1798/99 and 1810 respectively. A comparison of both versions reveals a change in the composer's intention. At first in several passages he followed the more traditional technique of transferring single words of the text directly into musical figures. Later on he seemed more intent on expressing the general mood and eliminated some of the rather simplistic details in favour of a more subjective rendering of the poems content.

    [de] Ludwig van Beethoven vertonte das Goethe-Gedicht „Neue Liebe, neues Leben" in zwei Fassungen 1798/99 und 1810. Der Vergleich der beiden Fassungen ergibt, daß sich in der Zeit zwischen diesen beiden Fassungen die Vorstellungen des Komponisten von der musikalischen Umsetzung teilweise gewandelt haben müssen. Zunächst scheint Beethoven eher nach der traditionellen Méthode einer direkten Übertragung von Begriffen aus dem Text komponiert zu haben. Später war er dann aber eher an einer subjektiven Darstellung des Inhalts interessiert und drângte drängte zu einfach gerate Einzelheiten zugunsten der - nunmehr freilich recht differenziert gestalteten - Gesamtstimmung zurück.

  14. De betekenis van Johan Buitendags stellingname in theologie der ...

    African Journals Online (AJOL)

    29 juli 2016 ... zich aan ons voordoet (Kants 'Wirklichkeit als Erscheinung'), maar over het geheel der dingen. 'soos dit kwansuis is' (Buitendag 2013:1). In Buitendags visie betekent dit dat systematische theologie probeert te begrijpen hoe de werkelijkheid in elkaar steekt wanneer wij daarmee geconfronteerd worden.

  15. Klinisch statistisch onderzoek van de resultaten der prostatectomie

    NARCIS (Netherlands)

    Wymenga, Jan Hendrik

    1958-01-01

    Om een indruk te krijgen in welke frequentie prostaathypertrophie en carcinoom in Nederland een primaire of secundaire doodsoorzaak vormden in de na-oorlogse jaren, en tevens na te gaan of er in de loop der jaren ook opvallende verschillen hierin waren ontstaan, hebben wij ons gewend tot het

  16. Goiter in paintings by Rogier van der Weyden (1399-1464).

    Science.gov (United States)

    Lazzeri, Davide; Pozzilli, Paolo; Zhang, Yi Xin; Persichetti, Paolo

    2015-05-01

    Figures affected by goiter were only sparsely depicted by Peter Paul Rubens and Albrecht Dürer among Flemish artists, because obvious goiter was not common in regions such as the Netherlands and Belgium. However, the recent observation of two figures with a goiter elegantly depicted by Rogier van der Weyden has raised our interest in this topic. When taking a close look at the paintings of this Flemish Renaissance painter, it is interesting to note that 16 portrayed subjects show an abnormal profile of the neck with swelling, suggestive of a presumptive medico-artistic diagnosis of goiter. Van der Weyden travelled to Italy where he soon acquired great fame and was second only to the other Flemish painter of the time, Jan Van Eyck. It is very likely that in Italy he had the opportunity to look at several female figures depicted with goiter, which may have influenced his paintings. Van der Weyden was appreciated because of his style to mix realistic details with idealized softened features to increase the beauty and appeal of his models. It is also likely that the integration of the goiter may have been part of the Renaissance tendency toward a more realistic and precise representation of subjects. The fact that in almost all cases the goiter was a low-to-moderate grade enlargement of the thyroid may confirm our speculation that perhaps the painter used the same model or the template derived from one model for subsequent paintings.

  17. The toluene-Ar complex: S0 and S1 van der Waals modes, changes to methyl rotation, and torsion-van der Waals vibration coupling

    Science.gov (United States)

    Gascooke, Jason R.; Lawrance, Warren D.

    2013-02-01

    The methyl rotor and van der Waals vibrational levels in the S1 and S0 states of toluene-Ar have been investigated by the technique of two-dimensional laser induced fluorescence (2D-LIF). The S0 van der Waals and methyl rotor levels are reported for the first time, while improved S1 values are presented. The correlations seen in the 2D-LIF images between the S0 and S1 states lead to a reassignment of key features in the S1 ← S0 excitation spectrum. This reassignment reveals that there are significant changes in the methyl rotor levels in the complex compared with those in bare toluene, particularly at low m. The observed rotor energies are explained by the introduction of a three-fold, V3, term in the torsion potential (this term is zero in toluene) and a reduction in the height of the six-fold, V6, barriers in S0 and S1 from their values in bare toluene. The V3 term is larger in magnitude than the V6 term in both S0 and S1. The constants determined are |V3(S1)| = 33.4 ± 1.0 cm-1, |V3(S0)| = 20.0 ± 1.0 cm-1, V6(S1) = -10.7 ± 1.0 cm-1, and V6(S0) = -1.7 ± 1.0 cm-1. The methyl rotor is also found to couple with van der Waals vibration; specifically, the m″ = 2 rotor state couples with the combination level involving one quantum of the long axis bend and m″ = 1. The coupling constant is determined to be 1.9 cm-1, which is small compared with the values typically reported for torsion-vibration coupling involving ring modes.

  18. Book Review: Woordenboek van de Drentse Dialecten, A-L | van der ...

    African Journals Online (AJOL)

    Book Title: Woordenboek van de Drentse Dialecten, A-L. Book Authors: G.H. Kocks (Samesteller), J.P. Vording, A. Beugels, H. Bloemhof. 1996, LXIX + 706 pp. ISBN 90-232-3176-7. Assen: Van Gorcum. Full Text: EMAIL FREE FULL TEXT EMAIL FREE FULL TEXT · DOWNLOAD FULL TEXT DOWNLOAD FULL TEXT.

  19. Fragmentation of neutral van der Waals clusters with visible laser light: A new variant of the Raman effect?

    International Nuclear Information System (INIS)

    Stamatovic, A.; Howorka, F.; Scheier, P.; Maerk, T.D.

    1989-01-01

    We have observed strong photodissociation (using visible laser light) of neutral van der Waals clusters (Ar, N 2 , O 2 , CO 2 , SO 2 , NH 3 ) produced by supersonic expansion and detected by electron ionization/mass spectrometer. Several tests were performed, all of them supporting this surprising discovery. We suggest that Raman induced photodissociation (RIP) is responsible for this phenomenon. This first observation of Raman induced photodissociation provides a new technique for the study of neutral van der Waals clusters. (orig.)

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

    Science.gov (United States)

    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.

  1. The nonlinear effect of resistive inhomogeneities on van der Pauw measurements

    Science.gov (United States)

    Koon, Daniel W.

    2005-03-01

    The resistive weighting function [D. W. Koon and C. J. Knickerbocker, Rev. Sci. Instrum. 63, 207 (1992)] quantifies the effect of small local inhomogeneities on van der Pauw resistivity measurements, but assumes such effects to be linear. This talk will describe deviations from linearity for a square van der Pauw geometry, modeled using a 5 x 5 grid network of discrete resistors and introducing both positive and negative perturbations to local resistors, covering nearly two orders of magnitude in -δρ/ρ or -δσ/σ. While there is a relatively modest quadratic nonlinearity for inhomogeneities of decreasing conductivity, the nonlinear term for inhomogeneities of decreasing resistivity is approximately cubic and can exceed the linear term.

  2. Massive Dirac fermions and Hofstadter butterfly in a van der Waals heterostructure.

    Science.gov (United States)

    Hunt, B; Sanchez-Yamagishi, J D; Young, A F; Yankowitz, M; LeRoy, B J; Watanabe, K; Taniguchi, T; Moon, P; Koshino, M; Jarillo-Herrero, P; Ashoori, R C

    2013-06-21

    van der Waals heterostructures constitute a new class of artificial materials formed by stacking atomically thin planar crystals. We demonstrated band structure engineering in a van der Waals heterostructure composed of a monolayer graphene flake coupled to a rotationally aligned hexagonal boron nitride substrate. The spatially varying interlayer atomic registry results in both a local breaking of the carbon sublattice symmetry and a long-range moiré superlattice potential in the graphene. In our samples, this interplay between short- and long-wavelength effects resulted in a band structure described by isolated superlattice minibands and an unexpectedly large band gap at charge neutrality. This picture is confirmed by our observation of fractional quantum Hall states at ± 5/3 filling and features associated with the Hofstadter butterfly at ultrahigh magnetic fields.

  3. Cl-intercalated graphene on SiC: Influence of van der Waals forces

    KAUST Repository

    Cheng, Yingchun

    2013-01-01

    The atomic and electronic structures of Cl-intercalated epitaxial graphene on SiC are studied by first-principles calculations. By increasing the Cl concentration, doping levels from n-type to slightly p-type are achieved on the SiC(0001) surface, while a wider range of doping levels is possible on the SiC(0001̄) surface. We find that the Cl atoms prefer bonding to the substrate rather than to the graphene. By varying the Cl concentration the doping level can be tailored. Consideration of van der Waals forces improves the distance between the graphene and the substrate as well as the binding energy, but it is not essential for the formation energy. For understanding the doping mechanism the introduction of non-local van der Waals contributions to the exchange correlation functional is shown to be essential. Copyright © EPLA, 2013.

  4. The van der Waals interactions in rare-gas dimers: the role of interparticle interactions.

    Science.gov (United States)

    Chen, Yu-Ting; Hui, Kerwin; Chai, Jeng-Da

    2016-01-28

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

  5. The Symbol of Modern Architecture. About the Barcelona Pavilion by Mies van der Rohe

    Directory of Open Access Journals (Sweden)

    Ilya Lezhava

    2016-08-01

    Full Text Available The article reviews peculiarities of the architectural and spatial organization of the Barcelona Pavilion designed by Mies van der Rohe and the reasons for its rehabilitation after a long period of oblivion. The analysis of the display shows that the only exhibit item of the Barcelona Pavilion is its architecture and furniture compositions designed by the author. The characteristics of partitions, screens, glass surfaces and the position of transparent walls of this construction are of special interest. The style of the building designed by Mies van der Rohe may be referred to formalism, rather than the traditional European functionalism. The article shows a special role of this construction in the architect’s creative work

  6. Chaos control of chaotic limit cycles of real and complex van der Pol oscillators

    Energy Technology Data Exchange (ETDEWEB)

    Mahmoud, Gamal M. E-mail: gmahmoud@uaeu.ac.ae; Farghaly, Ahmed A.M. E-mail: ahmed_1_66@yahoo.com

    2004-08-01

    Chaos control and nonlinear dynamics of both real and complex nonlinear oscillators constitutes some of the most fascinating developments in applied sciences. The chaos control of chaotic unstable limit cycles of real and complex (or coupled) nonlinear van der Pol oscillators is investigated in this paper. These oscillators appear in many important applications in engineering, for example, vacuum tube circuits. The presence of chaotic limit cycles is verified by calculating largest Lyapunov exponent and the power spectrum. The problem of chaos control of these limit cycles is studied using a feedback control method, which is based on the construction of a special form of a time-continuous perturbation. Our investigation of both real and complex (or coupled) van der Pol oscillators enriches the nonlinear dynamical systems.

  7. High External Quantum Efficiency in van der Waals Heterostructures for Ultrathin Photovoltaics

    Science.gov (United States)

    Wong, Joeson; Jariwala, Deep; Tat, Kevin; Tagliabue, Giulia; Davoyan, Artur; Sherrott, Michelle; Atwater, Harry

    High external radiative efficiency and high external quantum efficiency are prerequisites for an efficient photovoltaic cell. In transition metal dichalcogenides (TMDCs), previous work has demonstrated that near-unity external radiative efficiency is possible through superacid passivation. Yet, near-unity external quantum efficiency has remained elusive. In this work, we experimentally demonstrate that high external quantum efficiencies (>50%) are possible in vertical van der Waals heterostructures consisting of graphene, tungsten diselenide, and molybdenum disulfide, on metallic substrates. We achieve near-unity absorption in ultrathin (internal quantum efficiency, a measure of the carrier collection efficiency. Moreover, the internal quantum efficiency is shown to exhibit exciton resonances with peak efficiencies >70%. In summary, our results presented here will serve as design considerations and principles towards achieving near-unity external quantum efficiency in van der Waals materials.

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

    Directory of Open Access Journals (Sweden)

    Dieter Cremer

    2008-06-01

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

  9. Electrical and optical properties of SnS2/WSe2 van der Waals Heterojunction FETs

    Science.gov (United States)

    Zubair, Ahmad; Nourbakhsh, Amirhasan; Dresselhaus, Mildred; Palacios, Tomas

    Two dimensional crystals based on atomically thin films of transition metal dichalcogenides offer an exciting platform for various optoelectronic applications. Their unique crystal properties make them particularly attractive for van der Waals heterostructures which open up an additional degree of freedom to tailor the material properties into new physics and device applications. In this work, we explore, for the first time, the optoelectronic properties of van der Waals SnS2/WSe2 heterojunction. WSe2 is an ambipolar semiconductor while SnS2 is an n-type wide bandgap semiconductor. We use the pickup and dry transfer methods to fabricate SnS2/WSe2 heterojunction transistors (hetero-FETs). We observe negative differential transconductance in the SnS2/WSe2 hetero-FET. Also, the heterostructure couples strongly to incident light and shows high photovoltaic responsivity which can find applications in nano-devices such as photo-detectors and solar cells.

  10. Holographic Van der Waals-like phase transition in the Gauss–Bonnet gravity

    Energy Technology Data Exchange (ETDEWEB)

    He, Song, E-mail: hesong17@gmail.com [Max Planck Institute for Gravitational Physics (Albert Einstein Institute), Am Mühlenberg 1, 14476 Golm (Germany); State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100190 (China); Li, Li-Fang, E-mail: lilf@itp.ac.cn [Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing 100190 (China); Zeng, Xiao-Xiong, E-mail: xxzeng@itp.ac.cn [State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100190 (China); School of Material Science and Engineering, Chongqing Jiaotong University, Chongqing 400074 (China)

    2017-02-15

    The Van der Waals-like phase transition is observed in temperature–thermal entropy plane in spherically symmetric charged Gauss–Bonnet–AdS black hole background. In terms of AdS/CFT, the non-local observables such as holographic entanglement entropy, Wilson loop, and two point correlation function of very heavy operators in the field theory dual to spherically symmetric charged Gauss–Bonnet–AdS black hole have been investigated. All of them exhibit the Van der Waals-like phase transition for a fixed charge parameter or Gauss–Bonnet parameter in such gravity background. Further, with choosing various values of charge or Gauss–Bonnet parameter, the equal area law and the critical exponent of the heat capacity are found to be consistent with phase structures in temperature–thermal entropy plane.

  11. Polymorphism and thermodynamic ground state of Silver fulminate studied from van der Waals density functional calculations

    OpenAIRE

    Yedukondalu, N.; Vaitheeswaran, G.

    2014-01-01

    Silver fulminate (AgCNO) is a primary explosive, which exists in two polymorphic phases namely orthorhombic (\\emph{Cmcm}) and trigonal (\\emph{R$\\bar{3}$}) forms at ambient conditions. In the present study, we have investigated the effect of pressure and temperature on relative phase stability of the polymorphs using planewave pseudopotential approaches based on Density Functional Theory (DFT). van der Waals interactions play a significant role in predicting the phase stability and they can be...

  12. Switching phase states in two van der Pol oscillators coupled by ttochastically time-varying resistor

    OpenAIRE

    Uwate, Y; Nishio, Y; Stoop, R

    2009-01-01

    We explore the synchronization and switching behavior of a system of two identical van der Pol oscillators coupled by a stochastically timevarying resistor. Triggered by the time-varying resistor, the system of oscillators switches between synchronized and anti-synchronized behavior. We find that the preference of the synchronized/antisynchronized state is determined by the ratio of the probabilities of the two resistor states. The length of the phases of maintained resistor states, however, ...

  13. Supersonic molecular beam electric resonance spectroscopy and van der Waals molecules

    International Nuclear Information System (INIS)

    Luftman, H.S.

    1982-09-01

    A supersonic molecular beam electric resonance (MBER) spectrometer was built to study the radiofrequency spectra of weakly bound gas phase van der Waals molecules. The instrument and its operating characteristics are described in detail. Sample mass spectra of Ar-ClF gas mixtures are also presented as an illustration of the synthesis of van der Waals molecules. The Stark focusing process for linear polar molecules is discussed and computer-simulated using both second order perturbation and variational methods. Experimental refocusing spectra of OCS and ClF are studied and compared with these trajectory calculations. Though quantitative fitting is poor, there are strong qualitative indicators that the central part of a supersonic beam consists of molecules with a significantly greater population in the lowest energy rotational states than generally assumed. Flop in as opposed to flop out resonance signals for OCS are also numerically predicted and observed. The theoretical properties of the MBER spectrum for linear molecules are elaborated upon with special emphasis on line shape considerations. MBER spectra of OCS and ClF under a variety of conditions are presented and discussed in context to these predictions. There is some uncertainty expressed both in our own modeling and in the manner complex MBER spectra have been analyzed in the past. Finally, an electrostatic potential model is used to quantitatively describe the class of van der Waals molecules Ar-MX, where MX is an alkali halide. Energetics and equilibrium geometries are calculated. The validity of using an electrostatic model to predict van der Waals bond properties is critically discussed

  14. Etude de l'oscillateur de van der pol generalise par la methode du ...

    African Journals Online (AJOL)

    La méthode du groupe de renormalisation est l'une des méthodes de perturbation singulière utilisée dans la recherche des comportements asymptotiques de solution des équations différentielles ordinaires. Dans ce papier, l'équation de l'oscillateur de VAN der Pol généralisé qui modélise beaucoup de phénomènes ...

  15. Retardation-enhanced van der Waals force between thin metal films

    OpenAIRE

    Boström, Mathias; Sernelius, Bo

    2000-01-01

    We recently investigated the van der Waals force between thin metal films. Under certain conditions this force decrease with separation to a fractional power. In the present work we use optical data of metals and the zero-temperature Lifshitz formalism to demonstrate a retardation effect. The retarded attraction between thin metal films may be larger than the nonretarded attraction. This property is related to a comparatively weak retardation dependence of the energy that originates from the ...

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

    Science.gov (United States)

    de Visser, Sam P

    2011-04-28

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

  17. Dynamic anomalies at the glass transition of the van der Waals glass tri-α-naphthylbenzene

    International Nuclear Information System (INIS)

    Bartsch, E.; Debus, O.; Fujara, F.; Kiebel, M.; Sillescu, H.; Petry, W.; Magill, J.H.

    1992-01-01

    The Debye-Waller factor of the van der Waals glass tri-α-naphthylbenzene, measured by high resolution incoherent quasielastic neutron scattering, shows a cusp at Tc = 407 ± 5 K signaling the existence of a critical instability as has been predicted by mode coupling theory to occur in supercooled glass forming liquids. At temperatures above Tc structural relaxation is observed to obey the time-temperature superposition principle. (orig.)

  18. Physisorption of nucleobases on graphene: a comparative van der Waals study

    International Nuclear Information System (INIS)

    Le, Duy; Kara, Abdelkader; Rahman, Talat S; Schröder, Elsebeth; Hyldgaard, Per

    2012-01-01

    The physisorption of the nucleobases adenine (A), cytosine (C), guanine (G), thymine (T), and uracil (U) on graphene is studied using several variants of the density functional theory (DFT): the generalized gradient approximation with the inclusion of van der Waals interaction (vdW) based on the TS approach (Tkatchenko and Scheffer 2009 Phys. Rev. Lett. 102 073005) and our simplified version of this approach (here called sTS), the van der Waals density functional vdW-DF (Dion et al 2004 Phys. Rev. Lett. 92 246401) and vdW-DF2 (Lee et al 2010 Phys. Rev. B 82 081101), and DFT-D2 (Grimme 2006 J. Comput. Chem. 27 1787) and DFT-D3 (Grimme et al 2010 J. Chem. Phys. 132 154104) methods. The binding energies of nucleobases on graphene are found to be in the following order: G > A > T > C > U within TS, sTS, vdW-DF, and DFT-D2, and in the following order: G > A > T ∼ C > U within DFT-D3 and vdW-DF2. The binding separations are found to be different within different methods and in the following order: DFT-D2 < TS < DFT-D3 ∼ vdW-DF2 < vdW-DF. We also comment on the efficiency of combining the DFT-D approach and vdW-DF to study systems with van der Waals interactions.

  19. Physisorption of nucleobases on graphene: a comparative van der Waals study.

    Science.gov (United States)

    Le, Duy; Kara, Abdelkader; Schröder, Elsebeth; Hyldgaard, Per; Rahman, Talat S

    2012-10-24

    The physisorption of the nucleobases adenine (A), cytosine (C), guanine (G), thymine (T), and uracil (U) on graphene is studied using several variants of the density functional theory (DFT): the generalized gradient approximation with the inclusion of van der Waals interaction (vdW) based on the TS approach (Tkatchenko and Scheffer 2009 Phys. Rev. Lett. 102 073005) and our simplified version of this approach (here called sTS), the van der Waals density functional vdW-DF (Dion et al 2004 Phys. Rev. Lett. 92 246401) and vdW-DF2 (Lee et al 2010 Phys. Rev. B 82 081101), and DFT-D2 (Grimme 2006 J. Comput. Chem. 27 1787) and DFT-D3 (Grimme et al 2010 J. Chem. Phys. 132 154104) methods. The binding energies of nucleobases on graphene are found to be in the following order: G > A > T > C > U within TS, sTS, vdW-DF, and DFT-D2, and in the following order: G > A > T ~ C > U within DFT-D3 and vdW-DF2. The binding separations are found to be different within different methods and in the following order: DFT-D2 DFT-D3 ~ vdW-DF2 DFT-D approach and vdW-DF to study systems with van der Waals interactions.

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

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

    International Nuclear Information System (INIS)

    Lin, A.Y.M.; Brunner, R.; Chen, P.Y.; Talke, F.E.; Meyers, M.A.

    2009-01-01

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

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

  6. Relatieve klaring van een aantal eiwitten in de urine bij verschillende vormen van proteinurie

    NARCIS (Netherlands)

    Vermeer, Gerrit

    1966-01-01

    Dit onderzoek kwam voort uit de waarneming van HARDWICKE en SOOTHILL, dat er verschillen bestaan in de klaringen van een aantal eiwitten in de urine bij patienten met proteinurie. Deze verschillen leken samen te hangen met variaties in het histologische beeld van de glomerulus. Voor betere

  7. Het werk van een klerk: een stylometrische verkenning van het auteurschap achter 'Der ystorien bloeme'

    NARCIS (Netherlands)

    Hogenbirk, M.; Kestemont, M.

    2013-01-01

    Der ystorien bloeme is a rhymed Middle Dutch adaptation (ca. 1300?) of the Legenda aurea by Jacobus de Voragine. The anonymous author identifies himself as a ‘clerk’. The ystorien only survive in a single - possible incomplete - early fourteenth-century copy in the convoluted manuscript Leiden,

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    Hyldgaard, Per; Rahman, Talat S.

    2012-10-01

    The past decade has seen a dramatic rise in interest in exploring the role that van der Waals (vdW) or dispersion forces play in materials and in material behavior. Part of this stems from the obvious fact that vdW interactions (and other weak forces, such as Casimir) underpin molecular recognition, i.e., nature's approach to search for a match between genes and anti-genes and hence enable biological function. Less obvious is the recognition that vdW interactions affect a multitude of properties of a vast variety of materials in general, some of which also have strong technological applications. While for two atom- or orbital-sized material fragments the dispersive contributions to binding are small compared to those from the better known forms (ionic, covalent, metallic), those between sparse materials (spread over extended areas) can be of paramount importance. For example, an understanding of binding in graphite cannot arise solely from a study of the graphene layers individually, but also requires insight from inter-sheet graphene vdW bonding. It is the extended-area vdW bonding that provides sufficient cohesion to make graphite a robust, naturally occurring material. In fact, it is the vdW-bonded graphite, and not the all-covalently bonded diamond, that is the preferred form of pure carbon under ambient conditions. Also important is the understanding that vdW attraction can attain a dramatic relevance even if the material fragments, the building blocks, are not necessarily parallel from the outset or smooth when viewed in isolation (such as a graphene sheet or a carbon nanotube). This can happen if the building blocks have some softness and flexibility and allow an internal relative alignment to emerge. The vdW forces can then cause increasingly larger parts of the interacting fragments to line up at sub-nanometer separations and thus beget more areas with a sizable vdW bonding contribution. The gecko can scale a wall because it can bring its flexible hairs

  10. Van der Vyver’s analysis of rights: a case study drawn from thirteenth-century canon law

    Directory of Open Access Journals (Sweden)

    Charles J. Reid, Jr.

    1999-03-01

    Full Text Available In an important article published in 1988, Johan Van der Vyver challenged the prevailing reliance on Wesley Hohfeld’s taxonomy of rights. Hohfeld's division of rights into claims, powers, privileges and immunities, Van der Vyver stresses, is excessively concerned with "inter-individual legal relations” at the expense of the right-holder's relationship to the object of the right. Van der Vyver proposes instead that an assertion of right involves three distinct juridic aspects:• legal capacity, which is "the competence to occupy the offices of legal subject;• legal claim, which "comprises claims of a legal subject as against other persons to a legal object";• legal entitlement, which specifies the boundaries of the right-holder's ability to use, enjoy, consume, destroy or alienate the right in question.This article applies Van der Vyver’s taxonomy to the operations of thirteenthcentury canon law, and demonstrates that Van der Vyver’s analysis provides greater depth than Hohfeld's, in that it considers both the relationship of the person claiming a particular right and the object of that right.

  11. Nonlocal van der Waals functionals: the case of rare-gas dimers and solids.

    Science.gov (United States)

    Tran, Fabien; Hutter, Jürg

    2013-05-28

    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)] 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)]. An analysis of the results in terms of energy decomposition is also provided.

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

    Science.gov (United States)

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

    2017-09-01

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

  13. van't Hoff-van der Waals osmotic pressure and energy transformers

    OpenAIRE

    Zener, Clarence; Levenson, William

    1983-01-01

    We find the van't Hoff relations between osmotic pressure, freezing point depression, and boiling point elevation provide a clue on how, by using salt solutions, one may lower the cost of extracting power from low-grade heat sources. In particular, the ratio of 7 between the heat of evaporation and the heat of freezing of pure water suggests a chemical system that raises 7-fold the temperature difference between heat source and heat sink, while decreasing by the same factor the heat flux. Hea...

  14. Silicene on MoS2: role of the van der Waals interaction

    KAUST Repository

    Jiajie Zhu,

    2015-10-13

    We demonstrate for silicene on MoS2 substrate the limitations of the predictive power of first principles calculations based on van der Waals density functional theory. Only the optB86b-vdW functional is found to give reasonable agreement with experimental results on structural properties, while for all other investigated functionals the interlayer interaction is underestimated or the charge redistribution at the interface is not described correctly so that the predicted electronic structure is qualitatively wrong. © 2015 IOP Publishing Ltd.

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

    KAUST Repository

    Lin, Yu-Chuan

    2015-06-19

    Vertical integration of two-dimensional van der Waals materials is predicted to lead to novel electronic and optical properties not found in the constituent layers. Here, we present the direct synthesis of two unique, atomically thin, multi-junction heterostructures by combining graphene with the monolayer transition-metal dichalcogenides: molybdenum disulfide (MoS2), molybdenum diselenide (MoSe2) and tungsten diselenide (WSe2). The realization of MoS2–WSe2–graphene and WSe2–MoS2–graphene heterostructures leads to resonant tunnelling in an atomically thin stack with spectrally narrow, room temperature negative differential resistance characteristics.

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

    Energy Technology Data Exchange (ETDEWEB)

    Xia, Congxin, E-mail: xiacongxin@htu.edu.cn; Xue, Bin; Wang, Tianxing; Peng, Yuting [Department of Physic, Henan Normal University, Xinxiang 453007 (China); Jia, Yu [School of Physics and Engineering, Zhengzhou University, Zhengzhou 450052 (China)

    2015-11-09

    The electronic characteristics of arsenene-graphene van der Waals (vdW) heterostructures are studied by using first-principles methods. The results show that a linear Dirac-like dispersion relation around the Fermi level can be quite well preserved in the vdW heterostructures. Moreover, the p-type Schottky barrier (0.18 eV) to n-type Schottky barrier (0.31 eV) transition occurs when the interlayer distance increases from 2.8 to 4.5 Å, which indicates that the Schottky barrier can be tuned effectively by the interlayer distance in the vdW heterostructures.

  17. Olefin-borane "van der Waals complexes": intermediates in frustrated Lewis pair addition reactions.

    Science.gov (United States)

    Zhao, Xiaoxi; Stephan, Douglas W

    2011-08-17

    The nature of the borane-olefin interactions that take place prior to frustrated Lewis pair addition reactions has been probed employing a Lewis acidic borane tethered to a vinyl group through an alkyl chain. (1)H{(19)F} HOESY spectral data obtained at -50 °C demonstrated the spatial proximity of the boryl and vinyl groups and computational data support the initial formation of a van der Waals borane-olefin complex. Such species serve as intermediates undergoing facile addition reactions with phosphine bases to afford cyclic zwitterionic products.

  18. Nucleon-nucleon interaction with quark exchanges and prediction to colour van der Waals potential

    International Nuclear Information System (INIS)

    Osman, A.

    1985-11-01

    The nucleon-nucleon interaction is considered by including the colour nucleon clusters. The nucleon-nucleon system is treated as a six-quark system. The obtained local potentials reduce the short-range repulsion. The resulted nucleon-nucleon potential by using a quark-quark potential well agrees with the central-force potentials. The phase shifts calculated by using these local potentials are in good agreement with those obtained from other methods. Introducing the quark-quark potential in the nucleon-nucleon interaction, leads to a colour van der Waals potential very strong compared with that predicted by experiments. (author)

  19. Spectroscopic Signatures for Interlayer Coupling in MoS2-WSe2 van der Waals Stacking

    Science.gov (United States)

    2014-09-07

    REPORT NUMBER 19a. NAME OF RESPONSIBLE PERSON 19b. TELEPHONE NUMBER Pullickel Ajayan Ming -Hui Chiu, Ming -Yang Li, Wengjing Zhang, Wei-Ting Hsu, Wen...2014 C 2014 American Chemical Society Spectroscopic Signatures for Interlayer Coupling in MoS2WSe2 van der Waals Stacking Ming -Hui Chiu,†,X Ming -Yang...www.acsnano.org 9655 7. Jones, A. M.; Yu, H.; Ghimire, N. J.; Wu, S.; Aivazian, G.; Ross, J. S.; Zhao, B.; Yan, J.; Mandrus, D. G.; Xiao , D.; et al. Optical

  20. Multicomponent van der Waals equation of state: Applications in nuclear and hadronic physics

    Science.gov (United States)

    Vovchenko, Volodymyr; Motornenko, Anton; Alba, Paolo; Gorenstein, Mark I.; Satarov, Leonid M.; Stoecker, Horst

    2017-10-01

    A generalization of the quantum van der Waals equation of state for a multicomponent system in the grand-canonical ensemble is proposed. The model includes quantum statistical effects and allows us to specify the parameters characterizing repulsive and attractive forces for each pair of particle species. The model is applied to the description of asymmetric nuclear matter and also for mixtures of interacting nucleons and nuclei. Applications of the model to the equation of state of an interacting hadron resonance gas are discussed.

  1. On van der Waals-like forces in spontaneously broken supersymmetries

    International Nuclear Information System (INIS)

    Radescu, E.E.

    1982-12-01

    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-like potential is shown to be V(r)=Mmπ -3 F -4 r -7 +O(r -8 ), where M,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 one is briefly discussed. (author)

  2. Period-doubling cascades of canards from the extended Bonhoeffer-van der Pol oscillator

    Energy Technology Data Exchange (ETDEWEB)

    Sekikawa, Munehisa, E-mail: sekikawa@dove.kuee.kyoto-u.ac.j [Department of Electrical Engineering, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo, Kyoto, 615-8510 (Japan); Inaba, Naohiko [Department of Electronics and Bioinformatics, Meiji University, 1-1-1 Higashi-Mita, Tama-ku, Kawasaki, 214-8571 (Japan); Yoshinaga, Tetsuya [Institute of Health Biosciences, The University of Tokushima, 3-18-15 Kuramoto-cho, Tokushima, 770-8509 (Japan); Hikihara, Takashi [Department of Electrical Engineering, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo, Kyoto, 615-8510 (Japan)

    2010-08-09

    This Letter investigates the period-doubling cascades of canards, generated in the extended Bonhoeffer-van der Pol oscillator. Canards appear by Andronov-Hopf bifurcations (AHBs) and it is confirmed that these AHBs are always supercritical in our system. The cascades of period-doubling bifurcation are followed by mixed-mode oscillations. The detailed two-parameter bifurcation diagrams are derived, and it is clarified that the period-doubling bifurcations arise from a narrow parameter value range at which the original canard in the non-extended equation is observed.

  3. Virtual Resonance and Frequency Difference Generation by van der Waals Interaction

    Science.gov (United States)

    Tetard, L.; Passian, A.; Eslami, S.; Jalili, N.; Farahi, R. H.; Thundat, T.

    2011-05-01

    The ability to explore the interior of materials for the presence of inhomogeneities was recently demonstrated by mode synthesizing atomic force microscopy [L. Tetard, A. Passian, and T. Thundat, Nature Nanotech. 5, 105 (2009).NNAABX1748-338710.1038/nnano.2009.454]. Proposing a semiempirical nonlinear force, we show that difference frequency ω- generation, regarded as the simplest synthesized mode, occurs optimally when the force is tuned to van der Waals form. From a parametric study of the probe-sample excitation, we show that the predicted ω- oscillation agrees well with experiments. We then introduce the concept of virtual resonance to show that probe oscillations at ω- can efficiently be enhanced.

  4. Ionization and fragmentation of isomeric van der Waals complexes embedded in helium nanodroplets

    Science.gov (United States)

    Lewis, William K.; Lindsay, C. Michael; Miller, Roger E.

    2008-11-01

    The ionization and charge transfer processes, which occur when a doped helium droplet undergoes electron impact, are studied for droplets doped with van der Waals complexes with various structures and electrostatic moments. The mass spectra of the two isomers of hydrogen cyanide complexed with either cyanoacetylene or acetylene in helium droplets were obtained using optically selected mass spectrometry, and show that the structure of the complex has a large effect on the fragmentation pattern. The resulting fragmentation pattern is consistent with an ionization process in which charge steering strongly influences the site of initial ionization. The observed dissociation products may also be subject to caging by the helium matrix.

  5. A Fractionally Ionic Approach to Polarizability and van der Waals Many-Body Dispersion Calculations.

    Science.gov (United States)

    Gould, Tim; Lebègue, Sébastien; Ángyán, János G; Bučko, Tomáš

    2016-12-13

    By explicitly including fractionally ionic contributions to the polarizability of a many-component system, we are able to significantly improve on previous atom-wise many-body van der Waals approaches with essentially no extra numerical cost. For nonionic systems, our method is comparable in accuracy to existing approaches. However, it offers substantial improvements in ionic solids, e.g., producing better polarizabilities by over 65% in some cases. It has particular benefits for two-dimensional transition metal dichalcogenides and interactions of H 2 with modified coronenes, ionic systems of nanotechnological interest. It thus offers an efficient improvement on existing approaches, valid for a wide range of systems.

  6. Sindrome de Van der Knaap megalencefalia com leucodistrofia: a respeito de dois casos na mesma família Van Der Knaap syndrome (megalencephaly with leukodystrophy: report of two cases in the same family

    Directory of Open Access Journals (Sweden)

    CARLOS EDUARDO CAVALCANTI

    2000-03-01

    Full Text Available Relatamos os casos de dois irmãos, com quatro e seis anos de idade, com achados característicos da síndrome de Van Der Knaap. Discutimos os seus aspectos clínicos e radiológicos, assim como suas peculiaridades. Comparamos aos dados da literatura e analisamos os possíveis mecanismos etiopatogênicos envolvidos.We report on two brothers, aged four and six years-old, evidencing the Van Der Knaap syndrome. Clinical and radiological aspects are discussed as well their peculiarities. Data are compared with related literature, as etiopathogenic mechanisms possibly involved.

  7. The treasure trove of yeast genera and species described by Johannes van der Walt (1925-2011).

    Science.gov (United States)

    Smith, Maudy Th; Groenewald, Marizeth

    2012-12-01

    Yeast taxonomy and systematics have in recent years been dealt with intensively primarily by a small group of individual researchers with particular expertise. Amongst these was Johannes P. van der Walt, who had a major role in shaping our current understanding of yeast biodiversity and taxonomy. Van der Walt based his taxonomic studies not only on available cultures, but also by going into the field to isolate yeasts from various substrates. This pioneering work led to the discovery of many new genera and species, which were deposited in the Centraalbureau voor Schimmelcultures (CBS) collections for future studies in taxonomy, genomics, and industrial uses. These treasures collected during more than 60 years provide an outstanding legacy to the yeast community and will continue to exist in his absence. This contribution provides a comprehensive overview of the current nomenclatural and taxonomic status of the yeast genera and species introduced by van der Walt during his career.

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

    Science.gov (United States)

    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)].

  9. van der Waals Solids from Self-Assembled Nanoscale Building Blocks.

    Science.gov (United States)

    Choi, Bonnie; Yu, Jaeeun; Paley, Daniel W; Trinh, M Tuan; Paley, Maria V; Karch, Jessica M; Crowther, Andrew C; Lee, Chul-Ho; Lalancette, Roger A; Zhu, Xiaoyang; Kim, Philip; Steigerwald, Michael L; Nuckolls, Colin; Roy, Xavier

    2016-02-10

    Traditional atomic van der Waals materials such as graphene, hexagonal boron-nitride, and transition metal dichalcogenides have received widespread attention due to the wealth of unusual physical and chemical behaviors that arise when charges, spins, and vibrations are confined to a plane. Though not as widespread as their atomic counterparts, molecule-based two-dimensional (2D) layered solids offer significant benefits; their structural flexibility will enable the development of materials with tunable properties. Here we describe a layered van der Waals solid self-assembled from a structure-directing building block and C60 fullerene. The resulting crystalline solid contains a corrugated monolayer of neutral fullerenes and can be mechanically exfoliated. The absorption spectrum of the bulk solid shows an optical gap of 390 ± 40 meV that is consistent with thermal activation energy obtained from electrical transport measurement. We find that the dimensional confinement of fullerenes significantly modulates the optical and electronic properties compared to the bulk solid.

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

    KAUST Repository

    Wu, Congmin

    2010-07-07

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

  11. From the Cover: Evidence for van der Waals adhesion in gecko setae

    Science.gov (United States)

    Autumn, Kellar; Sitti, Metin; Liang, Yiching A.; Peattie, Anne M.; Hansen, Wendy R.; Sponberg, Simon; Kenny, Thomas W.; Fearing, Ronald; Israelachvili, Jacob N.; Full, Robert J.

    2002-09-01

    Geckos have evolved one of the most versatile and effective adhesives known. The mechanism of dry adhesion in the millions of setae on the toes of geckos has been the focus of scientific study for over a century. We provide the first direct experimental evidence for dry adhesion of gecko setae by van der Waals forces, and reject the use of mechanisms relying on high surface polarity, including capillary adhesion. The toes of live Tokay geckos were highly hydrophobic, and adhered equally well to strongly hydrophobic and strongly hydrophilic, polarizable surfaces. Adhesion of a single isolated gecko seta was equally effective on the hydrophobic and hydrophilic surfaces of a microelectro-mechanical systems force sensor. A van der Waals mechanism implies that the remarkable adhesive properties of gecko setae are merely a result of the size and shape of the tips, and are not strongly affected by surface chemistry. Theory predicts greater adhesive forces simply from subdividing setae to increase surface density, and suggests a possible design principle underlying the repeated, convergent evolution of dry adhesive microstructures in gecko, anoles, skinks, and insects. Estimates using a standard adhesion model and our measured forces come remarkably close to predicting the tip size of Tokay gecko seta. We verified the dependence on size and not surface type by using physical models of setal tips nanofabricated from two different materials. Both artificial setal tips stuck as predicted and provide a path to manufacturing the first dry, adhesive microstructures.

  12. Imaging of Interlayer Coupling in van der Waals Heterostructures Using a Bright-Field Optical Microscope.

    Science.gov (United States)

    Alexeev, Evgeny M; Catanzaro, Alessandro; Skrypka, Oleksandr V; Nayak, Pramoda K; Ahn, Seongjoon; Pak, Sangyeon; Lee, Juwon; Sohn, Jung Inn; Novoselov, Kostya S; Shin, Hyeon Suk; Tartakovskii, Alexander I

    2017-09-13

    Vertically stacked atomic layers from different layered crystals can be held together by van der Waals forces, which can be used for building novel heterostructures, offering a platform for developing a new generation of atomically thin, transparent, and flexible devices. The performance of these devices is critically dependent on the layer thickness and the interlayer electronic coupling, influencing the hybridization of the electronic states as well as charge and energy transfer between the layers. The electronic coupling is affected by the relative orientation of the layers as well as by the cleanliness of their interfaces. Here, we demonstrate an efficient method for monitoring interlayer coupling in heterostructures made from transition metal dichalcogenides using photoluminescence imaging in a bright-field optical microscope. The color and brightness in such images are used here to identify mono- and few-layer crystals and to track changes in the interlayer coupling and the emergence of interlayer excitons after thermal annealing in heterobilayers composed of mechanically exfoliated flakes and as a function of the twist angle in atomic layers grown by chemical vapor deposition. Material and crystal thickness sensitivity of the presented imaging technique makes it a powerful tool for characterization of van der Waals heterostructures assembled by a wide variety of methods, using combinations of materials obtained through mechanical or chemical exfoliation and crystal growth.

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

    Science.gov (United States)

    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.

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

    International Nuclear Information System (INIS)

    Wu Congmin; Qian Tiezheng; Sheng Ping

    2010-01-01

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

  15. Effect of van der Waals interaction on the properties of SnS2 layered semiconductor

    International Nuclear Information System (INIS)

    Seminovski, Y.; Palacios, P.; Wahnón, P.

    2013-01-01

    Nowadays, dispersion correction applied on layered semiconductors is a topic of interest. Among the known layered semiconductors, SnS 2 polytypes are wide gap semiconductors with a van der Waals interaction between their layers, which could form good materials to be used in photovoltaic applications. The present work gives an approach to the SnS 2 geometrical and electronic characterization using an empirical dispersion correction added to the Perdew–Burke–Ernzerhof functional and subsequent actualization of the electronic charge density using the screened hybrid Heyd–Scuseria–Ernzerhof functional using a density functional code. The obtained interlayer distance and band-gap are in good agreement with experimental values when van der Waals dispersion forces are included. - Highlights: ► Tin disulphide (SnS 2 ) has been calculated using density functional theory methods. ► A dispersion correction was also applied for two different SnS 2 polytypes. ► Geometrical parameters and band-gaps were obtained using both approaches. ► Our calculations give a good agreement of the computed band gap with experiment

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

    Science.gov (United States)

    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.

  17. The Dutch Connection: Johanna van der Meulen’s Contribution to Russian Symbolism

    Directory of Open Access Journals (Sweden)

    Magnus Ljunggren

    2017-09-01

    Full Text Available The Symbolist Ėllis’ (Lev Kobylinskij writings during his Moscow period emphasize the split, the division and dichotomy between material reality and celestial vision. His works written in exile in Locarno-Monti in Switzerland are devoted to resolving these antitheses by building bridges on all levels: between Catholicism and Orthodoxy, between culture and religion, between worldly and otherworldly, ultimately between East and West. From being a poet and critic he became a translator and culturologist: “Dr. Leo Kobilinski-Ellis.” The Dutch medium Johanna van der Meulen — whom he had met in 1911 in Rudolf Steiner’s Theosophical, soon Anthroposophical colony — played a crucial role in this fundamental metamorphosis. With her he lived in a thirty-five-year-long creative symbiosis that proved extremely beneficial to the two of them. Van der Meulen developed a mystical doctrine of her own, “Cosmosophy”, based on a Gnostic world view, strongly influenced by Russian religious philosophy. As she had finished her work in four parts Dr. Kobilinski-Ellis published his summary and interpretation of her teachings, in which he defines the core of Cosmosophy as a synthesis of the “Johannian” element in the meditative wisdom of the Eastern Church and the “Petrine” component in the energetic faith of Catholicism.

  18. Contribution of van der Waals forces to the plasticity of magnesium

    International Nuclear Information System (INIS)

    Ding, Zhigang; Liu, Wei; Li, Shuang; Zhang, Dalong; Zhao, Yonghao; Lavernia, Enrique J.; Zhu, Yuntian

    2016-01-01

    The accurate determination of stacking fault energies (SFE) and associated restoring forces is important for understanding plastic deformation, especially the dislocation emission and motion in metals. In this work, we use density-functional theory (DFT) calculations to, systematically study the all-dimension relaxed atomic models of Mg crystal slip, with a special focus on the “subslip modes” in prismatic and pyramidal slip systems. We find that slip systems with large interplanar distances are readily activated, which agrees well with experimental observations. Inclusion of the ubiquitous van der Waals (vdW) interactions results in lower generalized stacking fault energy curves. Remarkably, the unstable SFE value of pyramidal-II system is strongly reduced by up to 69 mJ/m 2 , and the related restoring stress is lowered by 0.74 GPa after taking into account the vdW energy. Our calculations indicate significant effect of vdW forces on the plasticity of Mg. - Graphical abstract: By using density-functional theory calculations, we systematically study the generalized stacking fault energy for pure Mg, and demonstrated pronounced contributions of van der Waals forces to the plasticity of Mg.

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

    Science.gov (United States)

    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.

  20. Electronic Properties and Device Applications of van-der-Waals Thin Films

    Science.gov (United States)

    Renteria, Jacqueline de Dios

    Successful exfoliation of graphene and discoveries of its unique electrical and thermal properties have motivated searches for other quasi two-dimensional (2D) materials with interesting properties. The layered van der Waals materials can be cleaved mechanically or exfoliated chemically by breaking the relatively weak bonding between the layers. In this dissertation research I addressed a special group of inorganic van der Waals materials -- layered transition metal dichalcogenides (MX2, where M=Mo, W, Nb, Ta or Ti and X=S, Se or Te). The focus of the investigation was electronic properties of thin films of TaSe2 and MoS2 and their device applications. In the first part of the dissertation, I describe the fabrication and performance of all-metallic three-terminal devices with the TaSe2 thin-film conducting channel. The layers of 2H-TaSe2 were exfoliated mechanically from single crystals grown by the chemical vapor transport method. It was established that devices with nanometer-scale thickness channels exhibited strongly non-linear current-voltage characteristics, unusual optical response, and electrical gating at room temperature. It was found that the drain-source current in thin-film 2H-TaSe2--Ti/Au devices reproducibly shows an abrupt transition from a highly resistive to a conductive state, with the threshold tunable via the gate voltage. Such current-voltage characteristics can be used, in principle, for implementing radiation-hard all-metallic logic circuits. In the second part of the dissertation, I describe the fabrication, electrical testing and measurements of the low-frequency 1/f noise in three-terminal devices with the MoS2 thin-film channel (f is the frequency). Analysis of the experimental data allowed us to distinguish channel and contact noise contributions for both as fabricated and aged devices. The noise characteristics of MoS 2--Ti/Au devices are in agreement with the McWhorter model description. The latter is contrary to what is observed in

  1. Van-der-Waals interaction of atoms in dipolar Rydberg states

    Science.gov (United States)

    Kamenski, Aleksandr A.; Mokhnenko, Sergey N.; Ovsiannikov, Vitaly D.

    2018-02-01

    An asymptotic expression for the van-der-Waals constant C 6( n) ≈ -0.03 n 12 K p ( x) is derived for the long-range interaction between two highly excited hydrogen atoms A and B in their extreme Stark states of equal principal quantum numbers n A = n B = n ≫ 1 and parabolic quantum numbers n 1(2) = n - 1, n 2(1) = m = 0 in the case of collinear orientation of the Stark-state dipolar electric moments and the interatomic axis. The cubic polynomial K 3( x) in powers of reciprocal values of the principal quantum number x = 1/ n and quadratic polynomial K 2( y) in powers of reciprocal values of the principal quantum number squared y = 1/ n 2 were determined on the basis of the standard curve fitting polynomial procedure from the calculated data for C 6( n). The transformation of attractive van-der-Waals force ( C 6 > 0) for low-energy states n observed from the results of numerical calculations based on the second-order perturbation theory for the operator of the long-range interaction between neutral atoms. This transformation is taken into account in the asymptotic formulas (in both cases of p = 2, 3) by polynomials K p tending to unity at n → ∞ ( K p (0) = 1). The transformation from low- n attractive van-der-Waals force into high- n repulsive force demonstrates the gradual increase of the negative contribution to C 6( n) from the lower-energy two-atomic states, of the A(B)-atom principal quantum numbers n'A(B) = n-Δ n (where Δ n = 1, 2, … is significantly smaller than n for the terms providing major contribution to the second-order series), which together with the states of n″B(A) = n+Δ n make the joint contribution proportional to n 12. So, the hydrogen-like manifold structure of the energy spectrum is responsible for the transformation of the power-11 asymptotic dependence C 6( n) ∝ n 11of the low-angular-momenta Rydberg states in many-electron atoms into the power-12 dependence C 6( n) ∝ n 12 for the dipolar states of the Rydberg manifold.

  2. No support for a General Factor of Personality in a reanalysis of Van der Linden et al.

    NARCIS (Netherlands)

    de Vries, R.E.

    2011-01-01

    Reanalysis of data (N= 512) of Van der Linden, Scholte, Cillessen, Te Nijenhuis, and Segers (2010) does not provide support for the existence of a General Factor of Personality (GFP) and of its relation with likeability and popularity among adolescent classmates. First of all, it was impossible to

  3. First-principles study of van der Waals interactions and lattice mismatch at MoS2/metal interfaces

    NARCIS (Netherlands)

    Farmanbar Gelepordsari, M.; Brocks, G.

    2016-01-01

    We explore the adsorption of MoS 2 on a range of metal substrates by means of first-principles density functional theory calculations. Including van der Waals forces in the density functional is essential to capture the interaction between MoS 2 and a metal surface, and obtain reliable interface

  4. Some simple bifurcation sets of an extended Van der Pol model and their relation to chemical oscillators

    Science.gov (United States)

    Koper, Marc T. M.

    1995-04-01

    Some typical bifurcation sets of a generalized autonomous Van der Pol-type model are discussed as archetypes of phase diagrams occurring in nonlinear dynamical systems. The relevance of the obtained bifurcation sets is exemplified by several experimental and numerical results from the literature of oscillating chemical reactions.

  5. A 900 electrostatic prism for microparticle beam steering on a 2 MV van der Graaff dust accelerator

    International Nuclear Information System (INIS)

    Dixon, D.G.; Clarke, C.D.; McDonnell, J.A.M.; Dickason, R.E.; Flavill, R.P.

    1984-01-01

    The design and construction of a 90 0 electrostatic prism is described. The device is used to deflect hypervelocity dust particles produced in a horizontal van der Graaff accelerator to simulate micrometeoroid impacts on dusty lunar and asteroidal surfaces where vertical incidence must be provided. (author)

  6. Ab initio determination of polarizabilities and van der Waals coefficients of Li atoms using the relativistic coupled-cluster method

    NARCIS (Netherlands)

    Wansbeek, L. W.; Sahoo, B. K.; Timmermans, R. G. E.; Das, B. P.; Mukherjee, D.

    We report on a technique to determine the van der Waals coefficients of lithium (Li) atoms based on relativistic coupled-cluster theory. These quantities are determined using the imaginary parts of the scalar dipole and quadrupole polarizabilities, which are evaluated using an approach that we have

  7. Influence of van der Waals forces on the adsorption structure of benzene on silicon studied using density functional theory

    DEFF Research Database (Denmark)

    Johnston, Karen; Kleis, Jesper; Lundqvist, Bengt

    2008-01-01

    Two different adsorption configurations of benzene on the Si(001)-(2×1) surface, the tight-bridge and butterfly structures, were studied using density functional theory. Several exchange and correlation functionals were used, including the recently developed van der Waals density functional (vd...

  8. Formation and physical characteristics of van der Waals molecules, cations, and anions: Estimates of complete basis set values

    Czech Academy of Sciences Publication Activity Database

    Zahradník, Rudolf; Šroubková, Libuše

    2005-01-01

    Roč. 104, č. 1 (2005), s. 52-63 ISSN 0020-7608 Institutional research plan: CEZ:AV0Z40400503 Keywords : intermolecular complexes * van der Waals species * ab initio calculations * complete basis set values * estimates Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.192, year: 2005

  9. Sacred History And Sacred Texts In Early Judaism : A Symposium In Honour Of A.s. Van Der Woude

    NARCIS (Netherlands)

    Bremmer, J.N.; García Martínez, F.

    1992-01-01

    After a long and distinguished career Adam S. van der Woude will retire on Reformation Day (October 31) from the Chair of Old Testament Studies and Intertestamental Literature of the Faculty of Theology of the Rijksuniversiteit Groningen. In order not to let this occasion go unnoticed, the Center of

  10. Reconstructing the Middle Ages. Dirck van Bleyswijck’s Beschryvinge der stadt Delft and its uneasy relationship with the past

    Directory of Open Access Journals (Sweden)

    Marcin Polkowski

    2013-12-01

    Full Text Available Dirck van Bleyswijck's Beschryvinge der stadt Delft presents an ambiguous and problematic attitude to the medieval history of Delft, which makes it interesting to scholars wishing to explore the perception of the Middle Ages as it crystallized during the early modern period. The aim of this contribution is to determine the intellectual origins of Van Bleyswijck's work as a historian in the context of his perception of the medieval past. The analysis of Van Bleyswijck's performance as a historian is based on a case study derived from the narrative: quotations from source texts and commentary about the life of the medieval Delft beguine Geertruyd van Oosten will be compared. Van Bleyswijck's representation of the Middle Ages was formed by a combination of humanist and proto-Enlightenment concepts, which entailed a critical reaction to forms of religious culture known to medieval society.

  11. Direction-specific van der Waals attraction between rutile TiO 2 nanocrystals

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Xin; He, Yang; Sushko, Maria L.; Liu, Jia; Luo, Langli; De Yoreo, James J.; Mao, Scott X.; Wang, Chongmin; Rosso, Kevin M.

    2017-04-27

    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 are 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.

  12. Interfacial adhesion between graphene and silicon dioxide by density functional theory with van der Waals corrections

    International Nuclear Information System (INIS)

    Gao, Wei; Liechti, Kenneth M; Huang, Rui; Xiao, Penghao; Henkelman, Graeme

    2014-01-01

    Interfacial adhesion between graphene and a SiO 2 substrate is studied by density functional theory (DFT) with dispersion corrections. The results demonstrate the van der Waals (vdW) interaction as the predominant mechanism at the graphene/SiO 2 interface. It is found that the interaction strength is strongly influenced by changes of the SiO 2 surface structures due to surface reactions with water. The adhesion energy is reduced when the reconstructed SiO 2 surface is hydroxylated, and further reduced when covered by a monolayer of adsorbed water molecules. Moreover, it is noted that vdW forces are required to accurately model the graphene/SiO 2 interface with DFT and that the adhesion energy is underestimated by empirical force fields commonly used in atomistic simulations. (paper)

  13. Production Methods of Van der Waals Heterostructures Based on Transition Metal Dichalcogenides

    Directory of Open Access Journals (Sweden)

    Haimei Qi

    2018-01-01

    Full Text Available Two dimensional (2D materials have gained significant attention since the discovery of graphene in 2004. Layered transition metal dichalcogenides (TMDs have become the focus of 2D materials in recent years due to their wide range of chemical compositions and a variety of properties. These TMDs layers can be artificially integrated with other layered materials into a monolayer (lateral or a multilayer stack (vertical heterostructures. The resulting heterostructures provide new properties and applications beyond their component 2D atomic crystals and many exciting experimental results have been reported during the past few years. In this review, we present the various synthesis methods (mechanical exfoliation, physical vapor transport, chemical vapor deposition, and molecular beam epitaxy method on van der Waals heterostructures based on different TMDs as well as an outlook for future research.

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

    Energy Technology Data Exchange (ETDEWEB)

    Kawanishi, Sakiko, E-mail: s-kawa@tagen.tohoku.ac.jp; Mizoguchi, Teruyasu [Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505 (Japan)

    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 force increases with decreasing the hexagonality of the polytype, which results in the confirmation that the most stable polytype is 3C-SiC.

  15. Rotational study on the van der Waals complex 1-chloro-1,1-difluoroethane-argon.

    Science.gov (United States)

    Wang, Juan; Chen, Junhua; Feng, Gang; Xia, Zhining; Gou, Qian

    2018-03-15

    The rotational spectrum of the van der Waals complex formed between 1-chloro-1,1-difluoroethane and argon has been investigated by using a pulsed jet Fourier transform microwave spectrometer. Only one set of rotational transitions belonging to the lowest energy conformer has been observed and assigned, although theoretical calculations suggest six stable conformers that might be observed. The observed conformer, according to the experimental evidence from two isotopologues ( 35 Cl and 37 Cl), adopts a configuration in which the argon atom is located, close to the CF 2 Cl top, between the CCF and CCCl planes (the dihedral angle ∠ArCCCl is 65.2°). The distance between argon atom and the center of mass of CH 3 CF 2 Cl is 3.949(2) Å. The dissociation energy, with pseudo diatomic approximation, is evaluated to be 2.4kJmol -1 . Copyright © 2017 Elsevier B.V. All rights reserved.

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

    CERN Document Server

    Babaev, Anton

    2017-01-01

    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-beta effect. Both effects are important to luminosity measurements and influence calibrat...

  17. Generalized Fourier series and limit cycles of generalized van der Pol oscillators

    Science.gov (United States)

    Garcia-Margallo, J.; Bejarano, J. D.

    1990-02-01

    A very simple generalization, using Jacobian elliptic functions, of the usual Fourier series, appropriate for non-linear systems, is used to study the first order approximate solution of the generalized van der Pol oscillators Ẍ+AX+2BX 3+ɛ(z 3+z 2X 2+z 1X 4) dotX=0 . A generalized harmonic balance method is used to determine the limit cycles. The cases A > 0, B > 0 and A 0 are considered in some detail. For given values of the parameters zi, the values of A and B for which limit cycles exist are found as functions of m. Numerical values for the radius, frequency, and energy of the limit cycles are given. The presence of zero, one, two, three or four limit cycles depends on the value of the parameters of the equation. Stability, bifurcations of fixed points, and the limit cycle stability are studied qualitatively.

  18. The analysis of solutions behaviour of Van der Pol Duffing equation describing local brain hemodynamics

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    Sheng, Xiaowei; Qian, Shifeng; Hu, Fengfei

    2017-08-01

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

  20. Electrostatics of electron-hole interactions in van der Waals heterostructures

    Science.gov (United States)

    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.

  1. Research for Coupled van der Pol Systems with Parametric Excitation and Its Application

    Science.gov (United States)

    Qian, Y. H.; Fu, H. X.

    2017-10-01

    In this article, we study the primary resonances of van der Pol systems with parametric excitation using the multiple scales method (MSM) and the homotopy analysis method (HAM). First, we study the nonlinear dynamic response of a coupled system with parametric excitation when the ratio of internal resonances are different, and obtain the four-dimensional average equation of the rectangular coordinate form using the MSM, thereby periodic motions are found in the system. Second, using the HAM, we obtain the four periodic solutions, in which there are two sets of in-phase periodic solutions and two sets of out-of-phase periodic solutions. Finally, we obtain the frequency response curves using the MSM and the HAM, in which it is found that the differences could be ignored.

  2. Methods for determining assimilable organic carbon and some factors affecting the van der Kooij method. [EUROPE

    Energy Technology Data Exchange (ETDEWEB)

    Huck, P.M.; Fedorak, P.M.; Anderson, W.B. (Univ. of Alberta, Edmonton (Canada))

    It has been demonstrated in many advanced European drinking water facilities that the application of ozone in conjunction with a subsequent granular activated carbon (GAC) treatment step results in reduced distribution system disinfectant demand. This is due, in large measure, to the removal of biodegradable organic substances by miroorganisms colonizing the activated carbon. The concentration of easily biodegradable or assimilable caron (AOC) can be measured in various ways. This paper compares available methods for measuring AOC or bacterial regrowth, and presents pilot plant results showing some factors affecting the van der Kooij method. Difficulties with the survival of Pseudomonas aeruginosa P17 strain following sedimentation are attributed to the use of polyaluminum chloride as a coagulant. This effect was, however, not evident at low doses of polyaluminum chloride. Incidents of inhibition of P17 following ozonation have been observed but, as of yet, not explained. Filtration of samples through cellulose/acetate filters will increase the concentration of AOC determined significantly.

  3. Van Der Waals Heterostructures between Small Organic Molecules and Layered Substrates

    Directory of Open Access Journals (Sweden)

    Han Huang

    2016-09-01

    Full Text Available Two dimensional atomic crystals, like grapheme (G and molybdenum disulfide (MoS2, exhibit great interest in electronic and optoelectronic applications. The excellent physical properties, such as transparency, semiconductivity, and flexibility, make them compatible with current organic electronics. Here, we review recent progress in the understanding of the interfaces of van der Waals (vdW heterostructures between small organic molecules (pentacene, copper phthalocyanine (CuPc, perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA, and dioctylbenzothienobenzothiophene (C8-BTBT and layered substrates (G, MoS2 and hexagonal boron nitride (h-BN. The influences of the underlying layered substrates on the molecular arrangement, electronic and vibrational properties will be addressed.

  4. Two-Dimensional Semiconductor Optoelectronics Based on van der Waals Heterostructures

    Directory of Open Access Journals (Sweden)

    Jae Yoon Lee

    2016-10-01

    Full Text Available Two-dimensional (2D semiconductors such as transition metal dichalcogenides (TMDCs and black phosphorous have drawn tremendous attention as an emerging optical material due to their unique and remarkable optical properties. In addition, the ability to create the atomically-controlled van der Waals (vdW heterostructures enables realizing novel optoelectronic devices that are distinct from conventional bulk counterparts. In this short review, we first present the atomic and electronic structures of 2D semiconducting TMDCs and their exceptional optical properties, and further discuss the fabrication and distinctive features of vdW heterostructures assembled from different kinds of 2D materials with various physical properties. We then focus on reviewing the recent progress on the fabrication of 2D semiconductor optoelectronic devices based on vdW heterostructures including photodetectors, solar cells, and light-emitting devices. Finally, we highlight the perspectives and challenges of optoelectronics based on 2D semiconductor heterostructures.

  5. Impact of momentum mismatch on 2D van der Waals tunnel field-effect transistors

    Science.gov (United States)

    Cao, Jiang; Logoteta, Demetrio; Pala, Marco G.; Cresti, Alessandro

    2018-02-01

    We numerically investigate electron quantum transport in 2D van der Waals tunnel field-effect-transistors in the presence of lateral momentum mismatch induced by lattice mismatch or rotational misalignment between the two-dimensional layers. We show that a small momentum mismatch induces a threshold voltage shift without altering the subthreshold swing. On the contrary, a large momentum mismatch produces significant potential variations and ON-current reduction. Short-range scattering, such as that due to phonons or system edges, enables momentum variations, thus enhancing interlayer tunneling. The coupling of electrons with acoustic phonons is shown to increase the ON current without affecting the subthreshold swing. In the case of optical phonons, the ON-current increase is accompanied by a subthreshold swing degradation due to the inelastic nature of the scattering.

  6. Mechanism of electron attachment to van der Waals clusters: Application to carbon dioxide clusters

    International Nuclear Information System (INIS)

    Tsukada, M.; Shima, N.; Tsuneyuki, S.; Kageshima, H.; Kondow, T.

    1987-01-01

    A theory on the attachment of very slow electrons to van der Waals clusters was developed on the basis of the electronic structure theory, and was applied to clarify the mechanism of the collisional electron transfer from a high-Rydberg atom to a CO 2 cluster. The strong coupled electron--phonon model is found to afford a reasonable mechanism of the attachment. The equilibrium geometry of (CO 2 )/sub N/ (2≤N≤13) clusters are determined and their vertical affinity levels are obtained by the DV-X α-transition state method. Using this information, as well as some plausible assumptions on the values of the coupling constants, the attachment cross section σ is evaluated as a function of the energy of the incident electron. The theory predicts the existence of the threshold cluster size for the attachment and a sharp decrease of σ with the energy, which are consistent with the experimental results

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

    Directory of Open Access Journals (Sweden)

    Surin L.A.

    2017-01-01

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

  8. Tunable Schottky contacts in the antimonene/graphene van der Waals heterostructures

    Science.gov (United States)

    Li, Wei; Wang, Xinlian; Dai, Xianqi

    2017-03-01

    Electronic structures modulation in the antimonene/graphene van der Waals(vdW) heterostructure with an external electric field(Eext) are investigated by density functional theory calculations. It is demonstrated that weak vdW interactions dominate between antimonene and graphene with their intrinsic electronic properties preserved. Furthermore, the vertical Eext can control not only the Schottky barrier but also the Schottky contacts (n-type and p-type) and Ohmic contacts (n-type) at the antimonene/graphene interface. Meanwhile, the negative Eext can shifts the Dirac point of graphene above the Fermi level, resulting in p-type doping in graphene because electrons can easily transfer from the Dirac point of graphene to the conduction band of antimonene. The present study would open a new avenue for application of ultrathin antimonene/graphene heterostructures in future nano- and optoelectronics.

  9. Tuning the Schottky barrier in the arsenene/graphene van der Waals heterostructures by electric field

    Science.gov (United States)

    Li, Wei; Wang, Tian-Xing; Dai, Xian-Qi; Wang, Xiao-Long; Ma, Ya-Qiang; Chang, Shan-Shan; Tang, Ya-Nan

    2017-04-01

    Using density functional theory calculations, we investigate the electronic properties of arsenene/graphene van der Waals (vdW) heterostructures by applying external electric field perpendicular to the layers. It is demonstrated that weak vdW interactions dominate between arsenene and graphene with their intrinsic electronic properties preserved. We find that an n-type Schottky contact is formed at the arsenene/graphene interface with a Schottky barrier of 0.54 eV. Moreover, the vertical electric field can not only control the Schottky barrier height but also the Schottky contacts (n-type and p-type) and Ohmic contacts (n-type) at the interface. Tunable p-type doping in graphene is achieved under the negative electric field because electrons can transfer from the Dirac point of graphene to the conduction band of arsenene. The present study would open a new avenue for application of ultrathin arsenene/graphene heterostructures in future nano- and optoelectronics.

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

    Science.gov (United States)

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

    2011-01-14

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

  11. Lithium ions in the van der Waals gap of Bi2Se3 single crystals

    International Nuclear Information System (INIS)

    Bludska, J.; Jakubec, I.; Karamazov, S.; Horak, J.; Uher, C.

    2010-01-01

    Insertion/extraction of lithium ions into/from Bi 2 Se 3 crystals was investigated by means of cyclic voltammetry. The process of insertion is reflected in the appearance of two bands on voltammograms at ∼1.7 and ∼1.5 V, corresponding to the insertion of Li + ions into octahedral and tetrahedral sites of the van der Waals gap of these layered crystals. The process of extraction of Li + ions from the gap results in the appearance of four bands on the voltammograms. The bands 1 and 2 at ∼2.1 and ∼2.3 V correspond to the extraction of a part of Li + guest ions from the octahedral and tetrahedrals sites and this extraction has a character of a reversible intercalation/deintercalation process. A part of Li + ions is bound firmly in the crystal due to the formation of negatively charged clusters of the (LiBiSe 2 .Bi 3 Se 4 - ) type. A further extraction of Li + ions from the van der Waals gap is associated with the presence of bands 3 and 4 placed at ∼2.5 and ∼2.7 V on the voltammograms as their extraction needs higher voltage due to the influence of negative charges localized on these clusters. -- Graphical abstract: Insertion/extraction of lithium ions into/from Bi 2 Se 3 layered crystals was investigated by cyclic voltammetry. The extraction of Li + results in the appearance of four bands on the voltammograms. The first two bands have a character of a reversible process. A part of Li + ions is bound firmly in the crystal due to the formation of negatively charged clusters of the (LiBiSe 2 .Bi 3 Se 4 - ) type. Their extraction needs higher voltage due to the negative charge. Display Omitted

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

    Science.gov (United States)

    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

    2017-06-01

    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 (CrI3) 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 CrI3 displays suppressed magnetization with a metamagnetic effect, whereas in trilayer CrI3 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.

  13. 2D halide perovskite-based van der Waals heterostructures: contact evaluation and performance modulation

    Science.gov (United States)

    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.

  14. Jet-Cooled High Resolution Infrared Spectroscopy of Small Van Der Waals SF_6 Clusters

    Science.gov (United States)

    Asselin, Pierre; Boudon, Vincent; Potapov, Alexey; Bruel, Laurent; Gaveau, Marc-André; Mons, Michel

    2016-06-01

    Using a pulsed slit nozzle multipass absorption spectrometer with a tunable quantum cascade laser we investigated van der Waals clusters involving sulfur hexafluoride in the spectral range near the νb{3} stretching vibration. Different sized homo-complexes were generated in a planar supersonic expansion with typically 0,5 % SF_6 diluted in 6 bar He. Firstly, several rotationally resolved parallel and perpendicular bands of (SF_6)_2, at 934,0 and 956,1 wn (#1 structure) in agreement with Takami et al. but also one band at 933,6 wn (#2 structure) never observed previously, were analyzed in light of a recent theoretical study predicting three nearly isoenergetic isomers of D2d, C2h and C_2 symmetry for the dimer. Furthermore, some broader bands were detected around 938 and 964 wn and assigned to (SF_6)_3 and (SF_6)_4 clusters on the grounds of concentration effects and/or ab initio calculations. Lastly, with 0,5 % rare gas Rg (Rg = Ne, Ar, Kr and Xe) added to the SF_6:He gas mixture, a series of van der Waals (SF_6)_2-Rg hetero-trimers were observed, which display a remarkable linear dependence of the vibrational shift with the polarizability of the rare gas atom provided that the initial SF_6 dimer structure is #2 . In the same time no transitions belonging to the binary complexes SF_6-Rg were found near the νb{3} monomer band. This result suggests a complex thermodynamics within the pulsed supersonic expansion leading to the preponderance of (SF_6)_2-Rg clusters over SF_6-Rg binary systems. R. D. Urban and M. Takami, J. Chem. Phys. 103, 9132 (1995). T. Vazhappily, A. Marjolin and K. D. Jordan, J. Phys. Chem. B, DOI: 10.1021/acs.jpcb.5b09419 (2015).

  15. El todo en el fragmento. Arquitectura y Bankunst en Mies Van der Rohe = The whole in the fragment. Mies van der Rohe´s Architecture and Bankunst

    Directory of Open Access Journals (Sweden)

    Antonio Juárez Chicote

    2013-10-01

    Full Text Available ResumenEl texto pretende asomarse a la mirada interior de Ludwig Mies van der Rohe y tomar conciencia del ejercicio visual y mental que la noción de ‘construcción’ tiene para el arquitecto. A partir de los ejercicios de adiestramiento visual (visual training propuestos en el IIT de Chicago a partir de 1938 propuestos por Mies van der Rohe y desarrollados por Walter Perterhans, y de los collage realizados por Mies para ilustrar su obra de arquitectura, como los realizados para el edificio de oficinas Bacardí en Santiago de Cuba el texto disecciona el universo mental de Mies.El adiestramiento del ojo propuesto por Mies en el IIT supone un adiestramiento en el orden de lo visual de enorme complejidad, pues el orden de la percepción no coincide con el orden de la construcción.Este desfase entre ambos universos plantea problemas casi irresolubles entre los que se debate el arquitecto y que el artículo, tras las lecturas que William Jordy, Robin Evans y Colin Rowe han realizado de la obra miesiana, pretende sintetizar y clarificar.El texto pretende asomarse a la tensión interna que, en la propia mente del arquitecto, alcanzan algunas de sus piezas, en un equilibrio altamente inestable, en el que la estructura superpuesta de la piel del edificio –la ‘representación de la estructura’– no puede sino anunciar con nostalgia el esplendor perdido del primer orden jerárquico estructural, que es de acero recubierto de hormigón, quedando, de esta manera a la vista, su condición inestable que se debate entre ser muro y ser esqueleto.Se proponen algunos conceptos clave extraídos de los cursos de Adiestramiento Visual y de algunos aspectos de la obra europea y americana de Mies a la luz de los cuales se puede hacer una relectura global de su obra: horizonte / obstáculo, textura / estructura, paisaje / material, percepción / construcción, totalidad / fragmento.Palabras claveforma, estructura, textura, percepción, construcci

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

    Directory of Open Access Journals (Sweden)

    Haowei Peng

    2016-10-01

    Full Text Available 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 rVV10, the revised Vydrov–van Voorhis nonlocal correlation functional. The resultant SCAN+rVV10 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 and 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.

  17. 17 Resensies 03 van Coller WEB.pmd

    African Journals Online (AJOL)

    Owner

    die erfopvolging, foto's en grafte nie, maar selfs in die voorkoms van spoke wat, gewoond aan hul heerskappy, hulle eiendom nie kan agterlaat nie. Voorts is die tipiese hoofpersoon 'n man wat trekke van die mitiese heldefiguur vertoon. Hierdie hooffigure in die tradisionele plaasroman vertoon deur die bank stereo-.

  18. Mr. Jan van der Boon, Leader personnel division (PE) from 01.04.99 to 31.03.02. CERN Council 2000, new position, Mr. Jan van der Boon was nominated Director of Admnistration from 01.01.01 to 31.12.03.

    CERN Multimedia

    Paulo Pascoal

    1999-01-01

    Mr. Jan van der Boon, Leader personnel division (PE) from 01.04.99 to 31.03.02. CERN Council 2000, new position, Mr. Jan van der Boon was nominated Director of Admnistration from 01.01.01 to 31.12.03.

  19. Differentiële effecten van het werken in kleine groepen: theorie, hypothesen en onderzoek

    NARCIS (Netherlands)

    Terwel, J.; Van den Eeden, P.

    1992-01-01

    Dit artikel betreft de vraag naar de differentiële effecten van het werken in kleine groepen bij wiskunde in de eerste fase van het voortgezet onderwijs.Uit verschillende onderzoekingen blijkt dat ‘cooperative learning’een positief effect heeft op de leerresultaten van de leerlingen. Voorts zijn er

  20. Middeleeuwse tandheelkunde in de Lage Landen 6: "Van enen ontbonden tant ende van die vuyle verve der tanden"

    NARCIS (Netherlands)

    Jonkman, E.J.; Eijkman, M.A.J.

    2015-01-01

    Professoren waren vroeger - en zijn dat wellicht nog - dol op rijtjes, bijvoorbeeld van symptomen en therapieën, die dan op een tentamen gevraagd konden worden. Dat is niets nieuws onder de zon. Ook de middeleeuwse chirurgen structureerden meestal hun betoog om een rij van oorzaken en een rij van

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

    Science.gov (United States)

    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.

  2. Effects of Interlayer Distance and van der Waals Energy on Electrochemical Activation of Partially Reduced Graphite Oxide

    International Nuclear Information System (INIS)

    Yoo, Hyun Deog; Jang, Jong Hyun; Cho, Kyeongjae; Zheng, Yongping; Park, Yuwon; Ryu, Ji Heon; Oh, Seung M.

    2015-01-01

    Partially reduced graphite oxide (GOpr) inherits expanded interlayer distance from the parent, graphite oxide (GO), and electronic conductivity from the grandparent, graphite. Indebted to the dual properties, GOpr shows unique behavior so-called electrochemical activation in organic electrolytes; when GOpr is polarized over a certain electrode potential, graphitic layers in GOpr are injected by solvated ions and become ion adsorbing sites permanently. Resultant gravimetric or volumetric capacitance (up to 200 F g −1 or 150 F ml −1 ) exceeds that of commercially available activated carbon electrodes for electric double-layer capacitor (EDLC). Previous literatures have reported that larger interlayer distance (d) lowers the on-set potential of electrochemical activation of graphitic carbons. However, the reason of this phenomenon has not yet been studied. In this paper, we combined experimental and theoretical approaches to reveal the effect of interlayer distance and van der Waals energy (U vdW ) on the electrochemical activation of graphitic carbon. More specifically, we compared the energy for the electrochemical activation (U EA ) and the van der Waals energy with respect to the interlayer distance. For this purpose, we devised an experimental method to measure U EA from cyclic voltammogram, and this method was verified by in-situ electrochemical dilatometry. The theoretical value of U vdW was calculated by semi-empirical density functional theory (DFT) and those experimental and theoretical values were linearly in accordance with each other. This finding signifies that (1) the electrochemical activation of graphitic carbon occurs by overcoming van der Waals energy to expand the interlayer distance, (2) and the on-set potential for electrochemical activation is varied by the interlayer distance because of the different van der Waals energy

  3. A Componentwise Convex Splitting Scheme for Diffuse Interface Models with Van der Waals and Peng--Robinson Equations of State

    KAUST Repository

    Fan, Xiaolin

    2017-01-19

    This paper presents a componentwise convex splitting scheme for numerical simulation of multicomponent two-phase fluid mixtures in a closed system at constant temperature, which is modeled by a diffuse interface model equipped with the Van der Waals and the Peng-Robinson equations of state (EoS). The Van der Waals EoS has a rigorous foundation in physics, while the Peng-Robinson EoS is more accurate for hydrocarbon mixtures. First, the phase field theory of thermodynamics and variational calculus are applied to a functional minimization problem of the total Helmholtz free energy. Mass conservation constraints are enforced through Lagrange multipliers. A system of chemical equilibrium equations is obtained which is a set of second-order elliptic equations with extremely strong nonlinear source terms. The steady state equations are transformed into a transient system as a numerical strategy on which the scheme is based. The proposed numerical algorithm avoids the indefiniteness of the Hessian matrix arising from the second-order derivative of homogeneous contribution of total Helmholtz free energy; it is also very efficient. This scheme is unconditionally componentwise energy stable and naturally results in unconditional stability for the Van der Waals model. For the Peng-Robinson EoS, it is unconditionally stable through introducing a physics-preserving correction term, which is analogous to the attractive term in the Van der Waals EoS. An efficient numerical algorithm is provided to compute the coefficient in the correction term. Finally, some numerical examples are illustrated to verify the theoretical results and efficiency of the established algorithms. The numerical results match well with laboratory data.

  4. Analysis of the quasiperiodic response of a generalized van der Pol nonlinear system in the resonance zone

    Czech Academy of Sciences Publication Activity Database

    Náprstek, Jiří; Fischer, Cyril

    -, - (2018), , , --- ISSN 0045-7949 R&D Projects: GA ČR(CZ) GA15-01035S Institutional support: RVO:68378297 Keywords : nonlinear dynamics * generalized van der Pol system * quasiperiodic response * synchronization effects * stability of auto-oscillation Subject RIV: JM - Building Engineering OBOR OECD: Mechanical engineering Impact factor: 2.847, year: 2016 http://www. science direct.com/ science /article/pii/S004579491730278X

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

    Energy Technology Data Exchange (ETDEWEB)

    Jariwala, Deep [Department of Materials Science and Engineering and ‡Department of; Howell, Sarah L. [Department of Materials Science and Engineering and ‡Department of; Chen, Kan-Sheng [Department of Materials Science and Engineering and ‡Department of; Kang, Junmo [Department of Materials Science and Engineering and ‡Department of; Sangwan, Vinod K. [Department of Materials Science and Engineering and ‡Department of; Filippone, Stephen A. [Department of Materials Science and Engineering and ‡Department of; Turrisi, Riccardo [Department of Materials Science and Engineering and ‡Department of; Marks, Tobin J. [Department of Materials Science and Engineering and ‡Department of; Lauhon, Lincoln J. [Department of Materials Science and Engineering and ‡Department of; Hersam, Mark C. [Department of Materials Science and Engineering and ‡Department of

    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 with 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.

  6. Multiple critical points and liquid-liquid equilibria from the van der Waals like equations of state

    International Nuclear Information System (INIS)

    Artemenko, Sergey; Lozovsky, Taras; Mazur, Victor

    2008-01-01

    The principal aim of this work is a comprehensive analysis of the phase diagram of water via the van der Waals like equations of state (EoSs) which are considered as superpositions of repulsive and attractive forces. We test more extensively the modified van der Waals EoS (MVDW) proposed by Skibinski et al (2004 Phys. Rev. E 69 061206) and refine this model by introducing instead of the classical van der Waals repulsive term a very accurate hard sphere EoS over the entire stable and metastable regions (Liu 2006 Preprint cond-mat/0605392). It was detected that the simplest form of MVDW EoS displays a complex phase behavior, including three critical points, and identifies four fluid phases (gas, low density liquid (LDL), high density liquid (HDL), and very high density liquid (VHDL)). Moreover the experimentally observed (Mallamace et al 2007 Proc. Natl Acad. Sci. USA 104 18387) anomalous behavior of the density of water in the deeply supercooled region (a density minimum) is reproduced by the MWDW EoS. An improvement of the repulsive part does not change the topological picture of the phase behavior of water in the wide range of thermodynamic variables. The new parameters set for second and third critical points are recognized by thorough analysis of experimental data for the loci of thermodynamic response function extrema

  7. Multiple critical points and liquid-liquid equilibria from the van der Waals like equations of state

    Energy Technology Data Exchange (ETDEWEB)

    Artemenko, Sergey; Lozovsky, Taras; Mazur, Victor [Thermodynamics Department, Academy of Refrigeration, 65082 Odessa (Ukraine)

    2008-06-18

    The principal aim of this work is a comprehensive analysis of the phase diagram of water via the van der Waals like equations of state (EoSs) which are considered as superpositions of repulsive and attractive forces. We test more extensively the modified van der Waals EoS (MVDW) proposed by Skibinski et al (2004 Phys. Rev. E 69 061206) and refine this model by introducing instead of the classical van der Waals repulsive term a very accurate hard sphere EoS over the entire stable and metastable regions (Liu 2006 Preprint cond-mat/0605392). It was detected that the simplest form of MVDW EoS displays a complex phase behavior, including three critical points, and identifies four fluid phases (gas, low density liquid (LDL), high density liquid (HDL), and very high density liquid (VHDL)). Moreover the experimentally observed (Mallamace et al 2007 Proc. Natl Acad. Sci. USA 104 18387) anomalous behavior of the density of water in the deeply supercooled region (a density minimum) is reproduced by the MWDW EoS. An improvement of the repulsive part does not change the topological picture of the phase behavior of water in the wide range of thermodynamic variables. The new parameters set for second and third critical points are recognized by thorough analysis of experimental data for the loci of thermodynamic response function extrema.

  8. Recent progress in predicting structural and electronic properties of organic solids with the van der Waals density functional

    Energy Technology Data Exchange (ETDEWEB)

    Yanagisawa, Susumu, E-mail: shou@sci.u-ryukyu.ac.jp [Department of Physics and Earth Sciences, Faculty of Science, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213 (Japan); Okuma, Koji; Inaoka, Takeshi [Department of Physics and Earth Sciences, Faculty of Science, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213 (Japan); Hamada, Ikutaro, E-mail: Hamada.Ikutaro@nims.go.jp [International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), Tsukuba 305-0044 (Japan)

    2015-10-01

    Highlights: • Review of theoretical studies on organic solids with the density-functional methods. • van der Waals (vdW)-inclusive methods to predict cohesive properties of oligoacenes. • A variant of the vdW density functional describes the structures accurately. • The molecular configuration and conformation crucially affects the band dispersion. - Abstract: We review recent studies on electronic properties of the organic solids with the first-principles electronic structure methods, with the emphasis on the roles of the intermolecular van der Waals (vdW) interaction in electronic properties of the organic semiconductors. After a brief summary of the recent vdW inclusive first-principle theoretical methods, we discuss their performance in predicting cohesive properties of oligoacene crystals as examples of organic crystals. We show that a variant of the van der Waals density functional describes structure and energetics of organic crystals accurately. In addition, we review our recent study on the zinc phthalocyanine crystal and discuss the importance of the intermolecular distance and orientational angle in the band dispersion. Finally, we draw some general conclusions and the future perspectives.

  9. Direct observation of interlayer hybridization and Dirac relativistic carriers in graphene/MoS₂ van der Waals heterostructures.

    Science.gov (United States)

    Diaz, Horacio Coy; Avila, José; Chen, Chaoyu; Addou, Rafik; Asensio, Maria C; Batzill, Matthias

    2015-02-11

    Artificial heterostructures assembled from van der Waals materials promise to combine materials without the traditional restrictions in heterostructure-growth such as lattice matching conditions and atom interdiffusion. Simple stacking of van der Waals materials with diverse properties would thus enable the fabrication of novel materials or device structures with atomically precise interfaces. Because covalent bonding in these layered materials is limited to molecular planes and the interaction between planes are very weak, only small changes in the electronic structure are expected by stacking these materials on top of each other. Here we prepare interfaces between CVD-grown graphene and MoS2 and report the direct measurement of the electronic structure of such a van der Waals heterostructure by angle-resolved photoemission spectroscopy. While the Dirac cone of graphene remains intact and no significant charge transfer doping is detected, we observe formation of band gaps in the π-band of graphene, away from the Fermi-level, due to hybridization with states from the MoS2 substrate.

  10. Novel electronic properties of 2D MoS2/TiO2 van der Waals heterostructure

    Science.gov (United States)

    Li, Yanhua; Cai, Congzhong; Sun, Baoguang; Chen, Jianjun

    2017-10-01

    Two different exchange-correlation functionals with van der Waals correction are employed to investigate the electronic properties of 2D {MoS}}2/{TiO}}2 heterostructure with a special configuration of Moiré pattern. It is found that, for both PBE and HSE06 functional, the new van der Waals heterostructure that consists of monolayer {MoS}}2 and 2D lepidocrocite-type {TiO}}2 exhibits a type-II band alignment between the {MoS}}2 and {TiO}}2 layers, and the electronic structures of monolayer {MoS}}2 and 2D {TiO}}2 are well retained in their respective layers due to a weak interlaminar coupling, which indicates that the new heterostructure may have potential applications in many fields such as photocatalysis, photoelectric devices, solar cells, etc. Furthermore, a novel design scheme based on the new 2D {MoS}}2/{TiO}}2 van der Waals heterostructure is proposed for a solar cell, and the corresponding power conversion efficiency is estimated to be about 8%.

  11. Van der Waals potentials between metal clusters and helium atoms obtained with density functional theory and linear response methods

    International Nuclear Information System (INIS)

    Liebrecht, M.

    2014-01-01

    The importance of van der Waals interactions in many diverse research fields such as, e. g., polymer science, nano--materials, structural biology, surface science and condensed matter physics created a high demand for efficient and accurate methods that can describe van der Waals interactions from first principles. These methods should be able to deal with large and complex systems to predict functions and properties of materials that are technologically and biologically relevant. Van der Waals interactions arise due to quantum mechanical correlation effects and finding appropriate models an numerical techniques to describe this type of interaction is still an ongoing challenge in electronic structure and condensed matter theory. This thesis introduces a new variational approach to obtain intermolecular interaction potentials between clusters and helium atoms by means of density functional theory and linear response methods. It scales almost linearly with the number of electrons and can therefore be applied to much larger systems than standard quantum chemistry techniques. The main focus of this work is the development of an ab-initio method to account for London dispersion forces, which are purely attractive and dominate the interaction of non--polar atoms and molecules at large distances. (author) [de

  12. Density functional study of the adsorption and van der Waals binding of aromatic and conjugated compounds on the basal plane of MoS2

    DEFF Research Database (Denmark)

    Moses, Poul Georg; Mortensen, Jens Jørgen; Lundqvist, Bengt

    2009-01-01

    der Waals interactions are essential for binding energies on MoS2 surfaces and that DFT with a recently developed exchange-correlation functional (vdW-DF) accurately calculates the van der Waals energy. Values are calculated for the adsorption energies of butadiene, thiophene, benzothiophene, pyridine...

  13. van der Waals torque and force between anisotropic topological insulator slabs

    Science.gov (United States)

    Lu, Bing-Sui

    2018-01-01

    We investigate the character of the van der Waals (vdW) torque and force between two coplanar and dielectrically anisotropic topological insulator (TI) slabs separated by a vacuum gap in the nonretardation regime, where the optic axes of the slabs are each perpendicular to the normal direction to the slab-gap interface and also generally differently oriented from each other. We find that in addition to the magnetoelectric coupling strength, the anisotropy can also influence the sign of the vdW force, viz., a repulsive vdW force can become attractive if the anisotropy is increased sufficiently. In addition, the vdW force oscillates as a function of the angular difference between the optic axes of the TI slabs, being most repulsive/least attractive (least repulsive/most attractive) for angular differences that are integer (half-integer) multiples of π . Our third finding is that the vdW torque for TI slabs is generally weaker than that for ordinary dielectric slabs. Our work provides an instance in which the vector potential appears in a calculation of the vdW interaction for which the limit is nonretarded or static.

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

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

    2017-05-05

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

  16. van der Waals epitaxy of CdS thin films on single-crystalline graphene

    Science.gov (United States)

    Sun, Xin; Lu, Zonghuan; Xie, Weiyu; Wang, Yiping; Shi, Jian; Zhang, Shengbai; Washington, Morris A.; Lu, Toh-Ming

    2017-04-01

    van der Waals epitaxy (vdWE) of three-dimensional CdS thin films on both single-crystalline graphene/Cu(111)/spinel(111) and single-crystalline graphene/SiO2/Si substrates is achieved via thermal evaporation. X-ray and electron backscatter diffraction pole figures reveal that the CdS films are a Wurtzite structure with a weak epitaxy on graphene and accompanied with a fiber texture background. The epitaxial alignment between CdS and graphene is observed to be an unusual non-parallel epitaxial relationship with a 30° rotation between the unit vectors of CdS and graphene. A geometrical model based on the minimization of superlattice area mismatch is employed to calculate possible interface lattice arrangement. It is found that the 30° rotation between CdS and graphene is indeed the most probable interface epitaxial lattice alignment. The vdWE of CdS on graphene, transferrable to arbitrary substrates, may represent a step forward for the growth of quality CdS thin films on arbitrary substrates through a graphene buffer.

  17. Tunable quasiparticle band gap in few-layer GaSe/graphene van der Waals heterostructures

    Science.gov (United States)

    Ben Aziza, Zeineb; Pierucci, Debora; Henck, Hugo; Silly, Mathieu G.; David, Christophe; Yoon, Mina; Sirotti, Fausto; Xiao, Kai; Eddrief, Mahmoud; Girard, Jean-Christophe; Ouerghi, Abdelkarim

    2017-07-01

    Two-dimensional (2D) materials have recently been the focus of extensive research. By following a similar trend as graphene, other 2D materials, including transition metal dichalcogenides (M X2 ) and metal mono-chalcogenides (MX), show great potential for ultrathin nanoelectronic and optoelectronic devices. Despite the weak nature of interlayer forces in semiconducting MX materials, their electronic properties are highly dependent on the number of layers. Using scanning tunneling microscopy and spectroscopy, we demonstrate the tunability of the quasiparticle energy gap of few-layered gallium selenide (GaSe) directly grown on a bilayer graphene substrate by molecular beam epitaxy. Our results show that the band gap is about 3.50 ± 0.05 eV for single-tetralayer, 3.00 ±0.05 eV for bi-tetralayer, and 2.30 ±0.05 eV for tri-tetralayer GaSe. This band-gap evolution of GaSe, particularly the shift of the valence band with respect to the Fermi level, was confirmed by angle-resolved photoemission spectroscopy (ARPES) measurements and our theoretical calculations. Moreover, we observed a charge transfer in the GaSe/graphene van der Waals (vdW) heterostructure using ARPES. These findings demonstrate the high impact on the GaSe electronic band structure and electronic properties that can be obtained by the control of 2D materials layer thickness and the graphene induced doping.

  18. The role of van der Waals interactions in the adsorption of noble gases on metal surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Chen, De-Li; Al-Saidi, W A; Johnson, J Karl

    2012-10-03

    Adsorption of noble gases on metal surfaces is determined by weak interactions. We applied two versions of the nonlocal van der Waals density functional (vdW-DF) to compute adsorption energies of Ar, Kr, and Xe on Pt(111), Pd(111), Cu(111), and Cu(110) metal surfaces. We have compared our results with data obtained using other density functional approaches, including the semiempirical vdW corrected DFT-D2. The vdW-DF results show considerable improvements in the description of adsorption energies and equilibrium distances over other DFTbased methods, giving good agreement with experiments. We have also calculated perpendicular vibrational energies for noble gases on the metal surfaces using vdWDF data and found excellent agreement with available experimental results. Our vdW-DF calculations show that adsorption of noble gases on low-coordination sites is energetically favored over high-coordination sites, but only by a few meV. Analysis of the 2-dimensional potential energy surface shows that the high-coordination sites are local maxima on the 2-dimensional potential energy surface and therefore unlikely to be observed in experiments, which provides an explanation of the experimental observations. The DFT-D2 approach with the standard parameterization was found to overestimate the dispersion interactions, and to give the wrong adsorption site preference for four of the nine systems we studied.

  19. Ab initio study of the Br(2P)-HBr van der Waals complex.

    Science.gov (United States)

    Toboła, R; Chałasiński, G; Kłos, J; Szcześniak, M M

    2009-05-14

    This study reports an ab initio characterization of a prereactive van der Waals complex between an open-shell atom Br((2)P) and a closed shell molecule HBr. The three adiabatic potential surfaces 1 (2)A('), 2 (2)A('), and 1 (2)A("), which result from the splitting of degenerate P state of Br are obtained from coupled cluster calculations. The coupling between same-symmetry states is calculated by multireference configuration-interaction method. A transformation to a diabatic representation and inclusion of the spin-orbit coupling effects on the interactions are also discussed. Bound states are calculated using an adiabatic bender model. The global minimum on the lowest adiabatic potential surface corresponds to a T-shaped geometry and has a well depth of D(e)=762.5 cm(-1) at R(e)=3.22 A. A secondary minimum occurs for a hydrogen-bonded geometry with D(e)=445.3 cm(-1) at R(e)=4.24 A. Upon inclusion of spin-orbit coupling the hydrogen-bonded minimum remains at the same depth, but the T-shaped minimum washes out to less than half of its spin-free value. The lowest bound state is localized in the linear minimum. The spin-orbit coupling plays a very important role in shaping of the potential energy surfaces of Br-HBr.

  20. Van der Waals bond in dimers: H2Ne, H2Ar, H2Kr

    International Nuclear Information System (INIS)

    Waaijer, M.

    1981-01-01

    The H 2 -inert gas dimers H 2 X, and particularly H 2 Ne, H 2 Ar and H 2 Kr, form the subject of this thesis and are loosely bound van der Waals complexes, which is reflected in the low number of bound states and the small anisotropic interaction. The H 2 X dimers studied are formed in a supersonic nozzle expansion, in which the internal energy is converted into the macroscopic flow energy, establishing an internal temperature drop to 3 K, which favours dimer formation. Because of this cooling the H 2 X dimers relax to the lowest rotational states. The hyperfine transitions have been measured using magnetic beam resonance and yield information about the isotropic as well as the anisotropic intermolecular potential in the range between the classical turning points and in the adjacent part of the repulsive branch. The sensitivity of the method is very high and slight changes in the intermolecular potential cause significant effects. The analysis of the measured hyperfine transitions incorporates all interacting states of the molecule, bound as well as unbound (continuum) states. For H 2 Ne, which is the best studied H 2 -inert gas system from the experimental point of view, the author succeeded in establishing an intermolecular potential, that provides a solid ground for comparison with future ab initio calculations. (Auth.)

  1. Thermal stability and thermal conductivity of phosphorene in phosphorene/graphene van der Waals heterostructures.

    Science.gov (United States)

    Pei, Qing-Xiang; Zhang, Xiaoliang; Ding, Zhiwei; Zhang, Ying-Yan; Zhang, Yong-Wei

    2017-07-14

    Phosphorene, a new two-dimensional (2D) semiconducting material, has attracted tremendous attention recently. However, its structural instability under ambient conditions poses a great challenge to its practical applications. A possible solution for this problem is to encapsulate phosphorene with more stable 2D materials, such as graphene, forming van der Waals heterostructures. In this study, using molecular dynamics simulations, we show that the thermal stability of phosphorene in phosphorene/graphene heterostructures can be enhanced significantly. By sandwiching phosphorene between two graphene sheets, its thermally stable temperature is increased by 150 K. We further study the thermal transport properties of phosphorene and find surprisingly that the in-plane thermal conductivity of phosphorene in phosphorene/graphene heterostructures is much higher than that of the free-standing one, with a net increase of 20-60%. This surprising increase in thermal conductivity arises from the increase in phonon group velocity and the extremely strong phonon coupling between phosphorene and the graphene substrate. Our findings have an important meaning for the practical applications of phosphorene in nanodevices.

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

    DEFF Research Database (Denmark)

    v, Hubert; Henriksen, Christian; Fernandez, Berta

    2015-01-01

    In this study we evaluate a high-level ab initio ground-state intermolecular potential-energy surface for the pyridine–He van der Waals complex, using the CCSD(T) method and Dunning’s augmented correlation consistent polarized valence double-ζ basis set extended with a set of 3s3p2d1f1g midbond...... functions. The potential is characterized by two symmetric global minima of −93.2 cm–1 that correspond to geometries where the distance between the helium atom and the pyridine center of mass is 3.105 Å and the angle with respect to the pyridine c rotational axis is 3.9°. Six local minima can be observed...... for geometries with the helium atom in the plane cotaining the pyridine molecule. To further analyze the nature of the intermolecular interactions in the complex, we use symmetry-adapted perturbation theory (SAPT). Additional consideration of the pyridine–He2 complex provides a better insight into many...

  3. Resistive sensitivity functions for van der Pauw astroid and rounded crosses and cloverleafs

    Science.gov (United States)

    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.

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

    Science.gov (United States)

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

    2015-09-09

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

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

    Directory of Open Access Journals (Sweden)

    Mariano Cadoni

    2017-05-01

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

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

    Science.gov (United States)

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

    2014-11-01

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

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

    Science.gov (United States)

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

    2014-11-26

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

  8. CO2 adsorption on the copper surfaces: van der Waals density functional and TPD studies

    Science.gov (United States)

    Muttaqien, Fahdzi; Hamamoto, Yuji; Hamada, Ikutaro; Inagaki, Kouji; Shiozawa, Yuichiro; Mukai, Kozo; Koitaya, Takanori; Yoshimoto, Shinya; Yoshinobu, Jun; Morikawa, Yoshitada

    2017-09-01

    We investigated the adsorption of CO2 on the flat, stepped, and kinked copper surfaces from density functional theory calculations as well as the temperature programmed desorption and X-ray photoelectron spectroscopy. Several exchange-correlation functionals have been considered to characterize CO2 adsorption on the copper surfaces. We used the van der Waals density functionals (vdW-DFs), i.e., the original vdW-DF (vdW-DF1), optB86b-vdW, and rev-vdW-DF2, as well as the Perdew-Burke-Ernzerhof (PBE) with dispersion correction (PBE-D2). We have found that vdW-DF1 and rev-vdW-DF2 functionals slightly underestimate the adsorption energy, while PBE-D2 and optB86b-vdW functionals give better agreement with the experimental estimation for CO2 on Cu(111). The calculated CO2 adsorption energies on the flat, stepped, and kinked Cu surfaces are 20-27 kJ/mol, which are compatible with the general notion of physisorbed species on solid surfaces. Our results provide a useful insight into appropriate vdW functionals for further investigation of related CO2 activation on Cu surfaces such as methanol synthesis and higher alcohol production.

  9. Subharmonic Resonance of Van Der Pol Oscillator with Fractional-Order Derivative

    Directory of Open Access Journals (Sweden)

    Yongjun Shen

    2014-01-01

    Full Text Available The subharmonic resonance of van der Pol (VDP oscillator with fractional-order derivative is studied by the averaging method. At first, the first-order approximate solutions are obtained by the averaging method. Then the definitions of equivalent linear damping coefficient (ELDC and equivalent linear stiffness coefficient (ELSC for subharmonic resonance are established, and the effects of the fractional-order parameters on the ELDC, the ELSC, and the dynamical characteristics of system are also analysed. Moreover, the amplitude-frequency equation and phase-frequency equation of steady-state solution for subharmonic resonance are established. The corresponding stability condition is presented based on Lyapunov theory, and the existence condition for subharmonic resonance (ECSR is also obtained. At last, the comparisons of the fractional-order and the traditional integer-order VDP oscillator are fulfilled by the numerical simulation. The effects of the parameters in fractional-order derivative on the steady-state amplitude, the amplitude-frequency curves, and the system stability are also studied.

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

    Science.gov (United States)

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

    2017-01-01

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

  11. Size-tunable band alignment and optoelectronic properties of transition metal dichalcogenide van der Waals heterostructures

    Science.gov (United States)

    Zhao, Yipeng; Yu, Wangbing; Ouyang, Gang

    2018-01-01

    2D transition metal dichalcogenide (TMDC)-based heterostructures exhibit several fascinating properties that can address the emerging market of energy conversion and storage devices. Current achievements show that the vertical stacked TMDC heterostructures can form type II band alignment and possess significant optoelectronic properties. However, a detailed analytical understanding of how to quantify the band alignment and band offset as well as the optimized power conversion efficiency (PCE) is still lacking. Herein, we propose an analytical model to exhibit the PCEs of TMDC van der Waals (vdW) heterostructures and explore the intrinsic mechanism of photovoltaic conversion based on the detailed balance principle and atomic-bond-relaxation correlation mechanism. We find that the PCE of monolayer MoS2/WSe2 can be up to 1.70%, and that of the MoS2/WSe2 vdW heterostructures increases with thickness, owing to increasing optical absorption. Moreover, the results are validated by comparing them with the available evidence, providing realistic efficiency targets and design principles. Highlights • Both electronic and optoelectronic models are developed for vertical stacked MoS2/WSe2 heterostructures. • The underlying mechanism on size effect of electronic and optoelectronic properties for vertical stacked MoS2/WSe2 heterostructures is clarified. • The macroscopically measurable quantities and the microscopical bond identities are connected.

  12. Tunable band gaps in graphene/GaN van der Waals heterostructures

    International Nuclear Information System (INIS)

    Huang, Le; Kang, Jun; Li, Yan; Li, Jingbo; Yue, Qu

    2014-01-01

    Van der Waals (vdW) heterostructures consisting of graphene and other two-dimensional materials provide good opportunities for achieving desired electronic and optoelectronic properties. Here, we focus on vdW heterostructures composed of graphene and gallium nitride (GaN). Using density functional theory, we perform a systematic study on the structural and electronic properties of heterostructures consisting of graphene and GaN. Small band gaps are opened up at or near the Γ point of the Brillouin zone for all of the heterostructures. We also investigate the effect of the stacking sequence and electric fields on their electronic properties. Our results show that the tunability of the band gap is sensitive to the stacking sequence in bilayer-graphene-based heterostructures. In particular, in the case of graphene/graphene/GaN, a band gap of up to 334 meV is obtained under a perpendicular electric field. The band gap of bilayer graphene between GaN sheets (GaN/graphene/graphene/GaN) shows similar tunability, and increases to 217 meV with the perpendicular electric field reaching 0.8 V Å  − 1 . (paper)

  13. Approximate scheme for calculating van der Waals interactions between finite cylindrical volume elements.

    Science.gov (United States)

    Jaiswal, Ravi P; Beaudoin, Stephen P

    2012-06-05

    A successful approach to calculating van der Waals (vdW) forces between irregular bodies is to divide the bodies into small cylindrical volume elements and integrate the vdW interactions between opposing elements. In this context it has been common to use Hamaker's expression for parallel plates to approximate the vdW interactions between the opposing elements. This present study shows that Hamaker's vdW expression for parallel plates does not accurately describe the vdW interactions for co-axial cylinders having a ratio of cylinder radius to separation distance (R/D) of 10 or less. This restricts the systems that can be simulated using this technique and explicitly excludes consideration of topographical or compositional variations at the nanoscale for surfaces that are in contact or within a few nm of contact. To address this limitation, approximate analytical expressions for nonretarded vdW forces between finite cylinders in different orientations are derived and are shown to produce a high level of agreement with forces calculated using full numerical solutions of the corresponding Hamaker's equations. The expressions developed here allow accurate calculation of vdW forces in systems where particles are in contact or within a few nm of contact with surfaces and the particles and/or surfaces have heterogeneous nanoscale morphology or composition. These calculations can be performed at comparatively low computational cost compared to the full numerical solution of Hamaker's equations.

  14. Fluctuations of the van der Waals attraction force between macroscopic bodies

    Energy Technology Data Exchange (ETDEWEB)

    Kogan, A. S. (Aleksandr Semenovich)

    2003-01-01

    The tliccry of the fluctuations of the van der Waals (vdW) attractive force between macroscopic bodies is developed. A general equation for the spectral density of the fluctuating surface Maxwell stress (force per unit mea.) in va,cuurn nea,r the surface of a body is derived under the assumption that, inside the bodies, the random La.ngevin sources of the electric and magnetic fields (charges, polarizations, currents) are Gaussian. This spectral density of stress is an integral over frequencies of a sum of terms each of which is a product of Fourier amplitudes of two field components' correlation functions. For metallic bodies, the contribution of free electrons to the vdW force (at frequencies up to the frequency of electron scattering) is calculated. This contribution to the force and its noise grows with temperature. Application of noiseless voltage to two interacting metals across the vacuum gap between them generates an additional force noise. This additional noise is proportional to the volta.ge squared and to the spectral density of the random electric field at the frequency of noise measurement. The theoretical qualitative conclusions are in good agreement with experirncnts.

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

    Science.gov (United States)

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

    2017-03-20

    The search for new optical materials capable of absorbing light in the frequency range from visible to near infrared is of great importance for applications in optoelectronic devices. In this paper, we report a theoretical study of the electronic and optical properties of hybrid structures composed of fullerenes adsorbed on graphene and on graphene nanoribbons. The calculations are performed in the framework of the density functional theory including the van der Waals dispersive interactions. We found that the adsorption of the C 60 fullerenes on a graphene layer does not modify its low energy states, but it has strong consequences for its optical spectrum, introducing new absorption peaks in the visible energy region. The optical absorption of fullerenes and graphene nanoribbon composites shows a strong dependence on photon polarization and geometrical characteristics of the hybrid systems, covering a broad range of energies. We show that an external electric field across the nanoribbon edges can be used to tune different optical transitions coming from nanoribbon-fullerene hybridized states, which yields a very rich electro-absorption spectrum for longitudinally polarized photons. We have carried out a qualitative analysis on the potential of these hybrids as possible donor-acceptor systems in photovoltaic cells.

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

    Directory of Open Access Journals (Sweden)

    Julián David Correa

    2017-03-01

    Full Text Available The search for new optical materials capable of absorbing light in the frequency range from visible to near infrared is of great importance for applications in optoelectronic devices. In this paper, we report a theoretical study of the electronic and optical properties of hybrid structures composed of fullerenes adsorbed on graphene and on graphene nanoribbons. The calculations are performed in the framework of the density functional theory including the van der Waals dispersive interactions. We found that the adsorption of the C 60 fullerenes on a graphene layer does not modify its low energy states, but it has strong consequences for its optical spectrum, introducing new absorption peaks in the visible energy region. The optical absorption of fullerenes and graphene nanoribbon composites shows a strong dependence on photon polarization and geometrical characteristics of the hybrid systems, covering a broad range of energies. We show that an external electric field across the nanoribbon edges can be used to tune different optical transitions coming from nanoribbon–fullerene hybridized states, which yields a very rich electro-absorption spectrum for longitudinally polarized photons. We have carried out a qualitative analysis on the potential of these hybrids as possible donor-acceptor systems in photovoltaic cells.

  17. Pauli Repulsion Versus van der Waals: Interaction of Indenocorannulene with a Cu(111) Surface.

    Science.gov (United States)

    Zoppi, Laura; Stöckl, Quirin; Mairena, Anaïs; Allemann, Oliver; Siegel, Jay S; Baldridge, Kim K; Ernst, Karl-Heinz

    2018-01-18

    Modification of metal electrode surfaces with functional organic molecules is an important step toward organic electronics. The interaction of the buckybowl indenocorannulene with a Cu(111) surface and the two-dimensional self-assembly on the same surface was studied by means of scanning tunneling microscopy and dispersion-enabled density functional theory. Based on the conjecture of maximizing van der Waals interaction with the surface one would expect the indeno group to be aligned parallel to the surface. Theoretical investigations predict a nonparallel arrangement with the benzo ring of the indeno group located higher above the surface than the bowl rim connected to the indeno group. This adsorbate geometry is due to strong electronic interaction between molecule and surface, including substantial Pauli repulsion. The long-range ordered monolayer shows differences for two molecules of the unit cell in scanning tunneling microscopy contrast, suggesting either different polar alignments, and therefore a different tilt of the indeno group, or occupation of different adsorption sites.

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

    Science.gov (United States)

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

    2017-06-27

    Magnetoelectric nanocomposites have been a topic of intense research due to their profound potential in the applications of electronic devices based on spintronic technology. Nevertheless, in spite of significant progress made in the growth of high-quality nanocomposite thin films, the substrate clamping effect still remains a major hurdle in realizing the ultimate magnetoelectric coupling. To overcome this obstacle, an alternative strategy of fabricating a self-assembled ferroelectric-ferrimagnetic bulk heterojunction on a flexible muscovite via van der Waals epitaxy is adopted. In this study, we investigated the magnetoelectric coupling in a self-assembled BiFeO 3 (BFO)-CoFe 2 O 4 (CFO) bulk heterojunction epitaxially grown on a flexible muscovite substrate. The obtained heterojunction is composed of vertically aligned multiferroic BFO nanopillars embedded in a ferrimagnetic CFO matrix. Moreover, due to the weak interaction between the flexible substrate and bulk heterojunction, the interface is incoherent and, hence, the substrate clamping effect is greatly reduced. The phase-field simulation model also complements our results. The magnetic and electrical characterizations highlight the improvement in magnetoelectric coupling of the BFO-CFO bulk heterojunction. A magnetoelectric coupling coefficient of 74 mV/cm·Oe of this bulk heterojunction is larger than the magnetoelectric coefficient reported earlier on flexible substrates. Therefore, this study delivers a viable route of fabricating a remarkable magnetoelectric heterojunction and yet flexible electronic devices that are robust against extreme conditions with optimized performance.

  19. Van der Waals enhancement of optical atom potentials via resonant coupling to surface polaritons.

    Science.gov (United States)

    Kerckhoff, Joseph; Mabuchi, Hideo

    2009-08-17

    Contemporary experiments in cavity quantum electrodynamics (cavity QED) with gas-phase neutral atoms rely increasingly on laser cooling and optical, magneto-optical or magnetostatic trapping methods to provide atomic localization with sub-micron uncertainty. Difficult to achieve in free space, this goal is further frustrated by atom-surface interactions if the desired atomic placement approaches within several hundred nanometers of a solid surface, as can be the case in setups incorporating monolithic dielectric optical resonators such as microspheres, microtoroids, microdisks or photonic crystal defect cavities. Typically in such scenarios, the smallest atom-surface separation at which the van der Waals interaction can be neglected is taken to be the optimal localization point for associated trapping schemes, but this sort of conservative strategy generally compromises the achievable cavity QED coupling strength. Here we suggest a new approach to the design of optical dipole traps for atom confinement near surfaces that exploits strong surface interactions, rather than avoiding them, and present the results of a numerical study based on (39)K atoms and indium tin oxide (ITO). Our theoretical framework points to the possibility of utilizing nanopatterning methods to engineer novel modifications of atom-surface interactions. (c) 2009 Optical Society of America

  20. van der Knaap syndrome: MR imaging findings including FLAIR, diffusion imaging, and proton MR spectroscopy

    International Nuclear Information System (INIS)

    Sener, R.N.

    2000-01-01

    A patient is reported with diffuse leukoencephalopathy associated with cystic degeneration of the white matter of the brain (van der Knaap syndrome). The changes were studied by fluid attenuated inversion recovery (FLAIR), and diffusion-weighted MR imaging. The FLAIR sequence revealed suppressed signal of the cysts, and widespread high-signal white matter changes associated with thinned cortices. On diffusion-weighted MR imaging, apparent diffusion coefficient (ADC) values ranged from 3.0 x 10 -3 to 2.7 x 10 -3 mm 2 /s in the temporal cysts, similar to that of CSF. The ADC values within the parenchyma ranged between 2 x 10 -3 and 2.1 x 10 -3 mm 2 /s, a value falling between normal parenchyma and cerebrospinal fluid, compared with a control group of three healthy subjects. The changes were also evaluated by proton MR spectroscopy, and were compared with a control group of 12 cases. Magnetic resonance spectroscopy revealed apparently increased NAA/Cr ratios in most parts of the brain. The NAA/Cho ratios were either high or low, and the Cho/Cr ratios were increased or normal in different regions. (orig.)

  1. An oscillation free shock-capturing method for compressible van der Waals supercritical fluid flows

    International Nuclear Information System (INIS)

    Pantano, C.; Saurel, R.; Schmitt, T.

    2017-01-01

    Numerical solutions of the Euler equations using real gas equations of state (EOS) often exhibit serious inaccuracies. The focus here is the van der Waals EOS and its variants (often used in supercritical fluid computations). The problems are not related to a lack of convexity of the EOS since the EOS are considered in their domain of convexity at any mesh point and at any time. The difficulties appear as soon as a density discontinuity is present with the rest of the fluid in mechanical equilibrium and typically result in spurious pressure and velocity oscillations. This is reminiscent of well-known pressure oscillations occurring with ideal gas mixtures when a mass fraction discontinuity is present, which can be interpreted as a discontinuity in the EOS parameters. We are concerned with pressure oscillations that appear just for a single fluid each time a density discontinuity is present. As a result, the combination of density in a nonlinear fashion in the EOS with diffusion by the numerical method results in violation of mechanical equilibrium conditions which are not easy to eliminate, even under grid refinement.

  2. Stabilization of thin liquid films by repulsive van der waals force

    KAUST Repository

    Li, Erqiang

    2014-05-13

    Using high-speed video recording of bubble rise experiments, we study the stability of thin liquid films trapped between a rising bubble and a surfactant-free liquid-liquid meniscus interface. Using different combinations of nonpolar oils and water that are all immiscible, we investigate the extent to which film stability can be predicted by attractive and repulsive van der Waals (vdW) interactions that are indicated by the relative magnitude of the refractive indices of the liquid combinations, for example, water (refractive index, n = 1.33), perfluorohexane (n = 1.23), and tetradecane (n = 1.43). We show that, when the film-forming phase was oil (perfluorohexane or tetradecane), the stability of the film could always be predicted from the sign of the vdW interaction, with a repulsive vdW force resulting in a stable film and an attractive vdW force resulting in film rupture. However, if aqueous electrolyte is the film-forming bulk phase between the rising air bubble and the upper oil phase, the film always ruptured, even when a repulsive vdW interaction was predicted. We interpret these results as supporting the hypothesis that a short-ranged hydrophobic attraction determines the stability of the thin water film formed between an air phase and a nonpolar oil phase. © 2014 American Chemical Society.

  3. Mobility Engineering in Vertical Field Effect Transistors Based on Van der Waals Heterostructures.

    Science.gov (United States)

    Shin, Yong Seon; Lee, Kiyoung; Kim, Young Rae; Lee, Hyangsook; Lee, I Min; Kang, Won Tae; Lee, Boo Heung; Kim, Kunnyun; Heo, Jinseong; Park, Seongjun; Lee, Young Hee; Yu, Woo Jong

    2018-03-01

    Vertical integration of 2D layered materials to form van der Waals heterostructures (vdWHs) offers new functional electronic and optoelectronic devices. However, the mobility in vertical carrier transport in vdWHs of vertical field-effect transistor (VFET) is not yet investigated in spite of the importance of mobility for the successful application of VFETs in integrated circuits. Here, the mobility in VFET of vdWHs under different drain biases, gate biases, and metal work functions is first investigated and engineered. The traps in WSe 2 are the main source of scattering, which influences the vertical mobility and three distinct transport mechanisms: Ohmic transport, trap-limited transport, and space-charge-limited transport. The vertical mobility in VFET can be improved by suppressing the trap states by raising the Fermi level of WSe 2 . This is achieved by increasing the injected carrier density by applying a high drain voltage, or decreasing the Schottky barrier at the graphene/WSe 2 and metal/WSe 2 junctions by applying a gate bias and reducing the metal work function, respectively. Consequently, the mobility in Mn vdWH at +50 V gate voltage is about 76 times higher than the initial mobility of Au vdWH. This work enables further improvements in the VFET for successful application in integrated circuits. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Electric-field tunable electronic structure in WSe2/arsenene van der Waals heterostructure

    Science.gov (United States)

    Zhang, Fang; Li, Wei; Dai, Xianqi

    2017-04-01

    The electronic properties of WSe2/arsenene van der Waals (vdW) heterostructure with an external electric field (Eext) are investigated by density functional theory (DFT). It is demonstrated that the WSe2/arsenene heterobilayer is a type-II vdW heterostructure, and thus electrons and holes are spatially separated. The WSe2/arsenene heterobilayer undergoes a transition from semiconductor to metal when subjected to an Eext. The positive and negative Eext have different effects on the band gap due to the spontaneous electric polarization in WSe2/arsenene heterostructure. The variation of band edges as a function of Eext provides further insight to the linear variation of the band gap. Moreover, the WSe2/arsenene vdW heterostructure experiences transitions from type-II to type-I and then from type-I to type-II with an increasing negative Eext. The present study would open a new avenue for application of ultrathin WSe2/arsenene heterobilayer in future nano- and optoelectronics.

  5. Van der Waals interactions between planar substrate and tubular lipid membranes undergoing pearling instability

    Science.gov (United States)

    Valchev, G. S.; Djondjorov, P. A.; Vassilev, V. M.; Dantchev, D. M.

    2017-10-01

    In the current article we study the behavior of the van der Waals force between a planar substrate and an axisymmetric bilayer lipid membrane undergoing pearling instability, caused by uniform hydrostatic pressure difference. To do so, the recently suggested "surface integration approach" is used, which can be considered a generalization of the well known and widely used Derjaguin approximation. The static equilibrium shape after the occurrence of the instability is described in the framework of Helfrich's spontaneous curvature model. Some specific classes of exact analytical solutions to the corresponding shape equation are considered, and the components of the respective position vectors given in terms of elliptic integrals and Jacobi elliptic functions. The mutual orientation between the interacting objects is chosen such that the axis of revolution of the distorted cylinder be parallel to the plane bounding the substrate. Based on the discussed models and approaches we made some estimations for the studied force in real experimentally realizable systems, thus showing the possibility of pearling as an useful technique for reduction of the adhesion in variety of industrial processes using lipid membranes as carriers.

  6. Two-dimensional laser induced fluorescence spectroscopy of van der Waals complexes: fluorobenzene-Ar(n) (n = 1,2).

    Science.gov (United States)

    Gascooke, Jason R; Alexander, Ula N; Lawrance, Warren D

    2012-04-07

    The technique of two-dimensional laser induced fluorescence (2D-LIF) spectroscopy has been used to observe the van der Waals complexes fluorobenzene-Ar and fluorobenzene-Ar(2) in the region of their S(1)-S(0) electronic origins. The 2D-LIF spectral images reveal a number of features assigned to the van der Waals vibrations in S(0) and S(1). An advantage of 2D-LIF spectroscopy is that the LIF spectrum associated with a particular species may be extracted from an image. This is illustrated for fluorobenzene-Ar. The S(1) van der Waals modes observed in this spectrum are consistent with previous observations using mass resolved resonance enhanced multiphoton ionisation techniques. For S(0), the two bending modes previously observed using a Raman technique were observed along with three new levels. These agree exceptionally well with ab initio calculations. The Fermi resonance between the stretch and bend overtone has been analysed in both the S(0) and S(1) states, revealing that the coupling is stronger in S(0) than in S(1). For fluorobenzene-Ar(2) the 2D-LIF spectral image reveals the S(0) symmetric stretch van der Waals vibration to be 35.0 cm(-1), closely matching the value predicted based on the fluorobenzene-Ar van der Waals stretch frequency. Rotational band contour analysis has been performed on the fluorobenzene-Ar 0(0)(0) transition to yield a set of S(1) rotational constants A' = 0.05871 ± 0.00014 cm(-1), B' = 0.03803 ± 0.00010 cm(-1), and C' = 0.03103 ± 0.00003 cm(-1). The rotational constants imply that in the S(1) 0(0) level the Ar is on average 3.488 Å from the fluorobenzene centre of mass and displaced from it towards the centre of the ring at an angle of ~6° to the normal. The rotational contour for fluorobenzene-Ar(2) was predicted using rotational constants calculated on the basis of the fluorobenzene-Ar geometry and compared with the experimental contour. The comparison is poor which, while due in part to expected saturation effects, suggests

  7. Energiezuinige teeltsturing bij paprika : proof of principle : testen van dynamische optimalisatie als methode om doelgerichte sturing van de teelt te combineren met energiebesparing

    NARCIS (Netherlands)

    Buwalda, F.; Zwart, de H.F.; Henten, van E.J.; Gelder, de A.; Hemming, J.; Bontsema, J.; Lagas, P.; Mark, van der C.

    2009-01-01

    De noodzaak om efficiënt met energie om te gaan en de uitstoot van CO2 te beperken, wordt niet alleen door de maatschappij aan de sector opgelegd, maar komt ook voort uit economische noodzaak. In verschillende proeven is aangetoond dat winst valt te behalen door af te wijken van de gangbare

  8. Groenblauwe dooradering van het landelijk gebied; een overzicht van waarden, functies, functiecombinaties, opties tot vermarkting, subsidies, regelingen ruimtelijke ordening en meer

    NARCIS (Netherlands)

    Henkens, R.J.H.G.; Raffe, van J.K.

    2002-01-01

    Deze studie komt voort uit het project Kwaliteitsimpuls landelijk gebied, dat tot doel had de kwaliteit en identiteit van het landelijk gebied te versterken door de aanleg, het herstel en het beheer van 40 000 ha aan landschapselementen. Deze landschapselementen kunnen functies vervullen op het

  9. Polymorphism and thermodynamic ground state of silver fulminate studied from van der Waals density functional calculations

    Science.gov (United States)

    Yedukondalu, N.; Vaitheeswaran, G.

    2014-06-01

    Silver fulminate (AgCNO) is a primary explosive, which exists in two polymorphic phases, namely, orthorhombic (Cmcm) and trigonal (Rbar{3}) forms at ambient conditions. In the present study, we have investigated the effect of pressure and temperature on relative phase stability of the polymorphs using planewave pseudopotential approaches based on Density Functional Theory (DFT). van der Waals interactions play a significant role in predicting the phase stability and they can be effectively captured by semi-empirical dispersion correction methods in contrast to standard DFT functionals. Based on our total energy calculations using DFT-D2 method, the Cmcm structure is found to be the preferred thermodynamic equilibrium phase under studied pressure and temperature range. Hitherto Cmcm and Rbar{3} phases denoted as α- and β-forms of AgCNO, respectively. Also a pressure induced polymorphic phase transition is seen using DFT functionals and the same was not observed with DFT-D2 method. The equation of state and compressibility of both polymorphic phases were investigated. Electronic structure and optical properties were calculated using full potential linearized augmented plane wave method within the Tran-Blaha modified Becke-Johnson potential. The calculated electronic structure shows that α, β phases are indirect bandgap insulators with a bandgap values of 3.51 and 4.43 eV, respectively. The nature of chemical bonding is analyzed through the charge density plots and partial density of states. Optical anisotropy, electric-dipole transitions, and photo sensitivity to light of the polymorphs are analyzed from the calculated optical spectra. Overall, the present study provides an early indication to experimentalists to avoid the formation of unstable β-form of AgCNO.

  10. Quasi van der Waals epitaxy of copper thin film on single-crystal graphene monolayer buffer

    Science.gov (United States)

    Lu, Zonghuan; Sun, Xin; Washington, Morris A.; Lu, Toh-Ming

    2018-03-01

    Quasi van der Waals epitaxial growth of face-centered cubic Cu (~100 nm) thin films on single-crystal monolayer graphene is demonstrated using thermal evaporation at an elevated substrate temperature of 250 °C. The single-crystal graphene was transferred to amorphous (glass) and crystalline (quartz) SiO2 substrates for epitaxy study. Raman analysis showed that the thermal evaporation method had minimal damage to the graphene lattice during the Cu deposition. X-ray diffraction and electron backscatter diffraction analyses revealed that both Cu films are single-crystal with (1 1 1) out-of-plane orientation and in-plane Σ3 twin domains of 60° rotation. The crystallinity of the SiO2 substrates has a negligible effect on the Cu crystal orientation during the epitaxial growth, implying the strong screening effect of graphene. We also demonstrate the epitaxial growth of polycrystalline Cu on a commercial polycrystalline monolayer graphene consisting of two orientation domains offset 30° to each other. It confirms that the crystal orientation of the epitaxial Cu film follows that of graphene, i.e. the Cu film consists of two orientation domains offset 30° to each other when deposited on polycrystalline graphene. Finally, on the contrary to the report in the literature, we show that the direct current and radio frequency flip sputtering method causes significant damage to the graphene lattice during the Cu deposition process, and therefore neither is a suitable method for Cu epitaxial growth on graphene.

  11. Electrical conductance sensitivity functions for square and circular cloverleaf van der Pauw geometries

    Science.gov (United States)

    Koon, Daniel W.; Heřmanová, Martina; Náhlík, Josef

    2015-11-01

    We have undertaken the first systematic computational and experimental study of the sensitivity of charge transport measurement to local physical defects for van der Pauw circular and square cloverleafs with rounded internal corners and unclovered geometries, using copper-foil specimens. Cloverleafs with rounded internal corners are in common use and reduce sampling of the material near their boundaries, an advantage over sharp corners. We have defined two parameters for these cloverleafs, one of which, the ‘admittance’, is the best predictor of the sensitivity at the center of these specimens, with this sensitivity depending only weakly on the central ‘core’ size when its diameter is less than about 60% of the specimen’s lateral size. Resistive measurement errors in all four geometries are linear in areas for errors up to about 50% in sheet resistance, and superlinear above. An ASTM-based ‘standard’ cloverleaf geometry, in which the central core diameter of the specimen is 1/5 the overall length and the slit widths are 1/10 the overall length, narrows the effective area sampled by the resistive measurement by a factor of about 16  ×  in the small-hole limit and over 40  ×  for larger holes, relative to unclovered goemetries, whether square or circular, with a smooth transition in these numbers for geometries intermediate between the standard cloverleaf and unclovered specimens. We believe that this work will allow materials scientists to better estimate the impact of factors such as the uniformity of film thickness and of material purity on their measurements, and allow sensor designers to better choose an optimal specimen geometry.

  12. PENELITIAN SPESIES SIBLING NYAMUK ANOPHELES BARBIROSTRIS VAN DER WULP DI INDONESIA

    Directory of Open Access Journals (Sweden)

    S. Sukowati

    2012-11-01

    Full Text Available Malaria continues to be a public health problem of high priority in the majority of malaria endemic countries of the South East Asia region, such as Indonesia. Vector control remain the most effective measure to prevent malaria transmission. The study of mosquito species complexes and the understanding of the biology, evolution as well as epidemiology of malaria transmission and the possibly of development of efficient control measures against malaria have been subjects of greatly increased interest in recent years. Natural populations of Anopheles barbirostris Van der Wulp were sampled from 5 geographically isolated populations in Indonesia: (1 Ambarawa, Central Java. (2 Tara-Tara, North Sulawesi, (3 Boru-Boru, (4 Konga and (5 Tanjung Bunga, the last three in Flores, East Nusa Tenggara. Analysis of larval mitotic chromosomes had been made from F I progeny of isofemale lines derived from these 5 populations. Specimens from these populations appear to share a similar mitotic karyotype (2n=6 consisting of two pairs of autosomes and one pair of sex chromosomes. The Giemsa staining of mitotic chromosomes of the An. barbirostris complex showed considerable variation in the amount and distribution of constitutive heterochromatin in sex chromosomes. These cytological differences have led to the recognation of 4 distinct cytological forms within the taxon An. barbirostris, viz., form A (X1,X2,X3,Y1, form B (X1,X2,X3,Y2 form C (X2,X3,Y3 and form D (X2,X3,Y4. Form A is widely distributed in Indonesia, while, form Band D have been found in sympatric association with form A in Tara-tara 2, North Sulawesi; Konga, Flores and Tanjung Bunga, Form C, however, has been found only in Boru-Boru, and sympatric with forms A and B. Keywords: Anopheles barbirostris, malaria, mitotic chromosome, sibling species

  13. Origin of the size-dependence of the equilibrium van der Waals binding between nanostructures

    Science.gov (United States)

    Tao, Jianmin; Perdew, John P.; Tang, Hong; Shahi, Chandra

    2018-02-01

    Nanostructures can be bound together at equilibrium by the van der Waals (vdW) effect, a small but ubiquitous many-body attraction that presents challenges to density functional theory. How does the binding energy depend upon the size or number of atoms in one of a pair of identical nanostructures? To answer this question, we treat each nanostructure as a whole object, not as a collection of atoms. Our calculations start from an accurate static dipole polarizability for each considered nanostructure, and an accurate equilibrium center-to-center distance for the pair (the latter from experiment or from the vdW-DF-cx functional). We consider the competition in each term -C2k/d2k (k = 3, 4, 5) of the long-range vdW series for the interaction energy, between the size dependence of the vdW coefficient C2k and that of the 2kth power of the center-to-center distance d. The damping of these vdW terms can be negligible, but in any case, it does not affect the size dependence for a given term in the absence of non-vdW binding. To our surprise, the vdW energy can be size-independent for quasi-spherical nanoclusters bound to one another by vdW interaction, even with strong nonadditivity of the vdW coefficient, as demonstrated for fullerenes. We also show that, for low-dimensional systems, the vdW interaction yields the strongest size-dependence, in stark contrast to that of fullerenes. We illustrate this with parallel planar polycyclic aromatic hydrocarbons. The size dependences of other morphologies or bonding types lie between, as shown by sodium clusters.

  14. Van der Waals Epitaxy of GaSe/Graphene Heterostructure: Electronic and Interfacial Properties.

    Science.gov (United States)

    Ben Aziza, Zeineb; Henck, Hugo; Pierucci, Debora; Silly, Mathieu G; Lhuillier, Emmanuel; Patriarche, Gilles; Sirotti, Fausto; Eddrief, Mahmoud; Ouerghi, Abdelkarim

    2016-10-07

    Stacking two-dimensional materials in so-called van der Waals (vdW) heterostructures, like the combination of GaSe and graphene, provides the ability to obtain hybrid systems which are suitable to design optoelectronic devices. Here, we report the structural and electronic properties of the direct growth of multilayered GaSe by Molecular beam Epitaxy (MBE) on graphene. Reflection high-energy electron diffraction (RHEED) images exhibited sharp streaky features indicative of high quality GaSe layer produced via a vdW epitaxy. Micro-Raman spectroscopy showed that, after the vdW hetero-interface formation, the Raman signature of pristine graphene is preserved. However, the GaSe film tuned the charge density of graphene layer by shifting the Dirac point by about 80 meV toward lower binding energies, attesting an electron transfer from graphene to GaSe. Angle-resolved photoemission spectroscopy (ARPES) measurements showed that the maximum of the valence band of few layers of GaSe are located at the Γ point at a binding energy of about -0.73 eV relatively to the Fermi level (p-type doping). From the ARPES measurements, a hole effective mass defined along the ΓM direction and equal to about m*/m0 = -1.1 was determined. By coupling the ARPES data with high resolution X-ray photoemission spectroscopy (HR-XPS) measurements, the Schottky interface barrier height was estimated to be 1.2 eV. These findings allow deeper understanding of the interlayer interactions and the electronic structure of GaSe/graphene vdW heterostructure.

  15. Calculated carrier mobility of h-BN/γ-InSe/h-BN van der Waals heterostructures

    Science.gov (United States)

    Kang, P.; Michaud-Rioux, V.; Kong, X.-H.; Yu, G.-H.; Guo, H.

    2017-12-01

    Recent experiments reported excellent transport properties of two-dimensional (2D) van der Waals (vdW) heterostructures made of atomically thin InSe layers encapsulated by two hBN capping layers (ISBN). The carrier mobility of the ISBN films exceeded μ ˜ 1.2× {{10}4} \\text{c}{{\\text{m}}2} {{\\text{V}}-1} {{\\text{s}}-1} at low temperature, much higher than that of pristine InSe films. It has been puzzling why the relatively inert hBN capping layer could so drastically enhance mobility of the ISBN composite. Using a state-of-the-art first principles method, we have calculated phonon limited carrier mobility of 18 different ISBN films and 6 pristine InSe films with different thicknesses, the largest system containing 2212 atoms. The hBN capping layer significantly alters the elastic stiffness coefficient as compared with pure InSe—thus the acoustic phonons in the ISBN composite—giving rise to the observed large mobility of ISBN films. Of the 18 calculated ISBN films, the ones with no strain at the hBN/InSe interface possess the highest electron mobility, reaching 4340~\\text{c}{{\\text{m}}2}~{{\\text{V}}-1}~{{\\text{s}}-1} at room temperature, which could easily go over {{10}4}~\\text{c}{{\\text{m}}2}~{{\\text{V}}-1}~{{\\text{s}}-1} at low temperatures. We conclude that the mechanical properties of the composite 2D vdW ISBN material play the crucial role for inducing the large carrier mobility, a principle that could be applied to many other 2D vdW heterostructures.

  16. Origin of the size-dependence of the equilibrium van der Waals binding between nanostructures.

    Science.gov (United States)

    Tao, Jianmin; Perdew, John P; Tang, Hong; Shahi, Chandra

    2018-02-21

    Nanostructures can be bound together at equilibrium by the van der Waals (vdW) effect, a small but ubiquitous many-body attraction that presents challenges to density functional theory. How does the binding energy depend upon the size or number of atoms in one of a pair of identical nanostructures? To answer this question, we treat each nanostructure as a whole object, not as a collection of atoms. Our calculations start from an accurate static dipole polarizability for each considered nanostructure, and an accurate equilibrium center-to-center distance for the pair (the latter from experiment or from the vdW-DF-cx functional). We consider the competition in each term -C 2k /d 2k (k = 3, 4, 5) of the long-range vdW series for the interaction energy, between the size dependence of the vdW coefficient C 2k and that of the 2kth power of the center-to-center distance d. The damping of these vdW terms can be negligible, but in any case, it does not affect the size dependence for a given term in the absence of non-vdW binding. To our surprise, the vdW energy can be size-independent for quasi-spherical nanoclusters bound to one another by vdW interaction, even with strong nonadditivity of the vdW coefficient, as demonstrated for fullerenes. We also show that, for low-dimensional systems, the vdW interaction yields the strongest size-dependence, in stark contrast to that of fullerenes. We illustrate this with parallel planar polycyclic aromatic hydrocarbons. The size dependences of other morphologies or bonding types lie between, as shown by sodium clusters.

  17. A fully automated temperature-dependent resistance measurement setup using van der Pauw method

    Science.gov (United States)

    Pandey, Shivendra Kumar; Manivannan, Anbarasu

    2018-03-01

    The van der Pauw (VDP) method is widely used to identify the resistance of planar homogeneous samples with four contacts placed on its periphery. We have developed a fully automated thin film resistance measurement setup using the VDP method with the capability of precisely measuring a wide range of thin film resistances from few mΩ up to 10 GΩ under controlled temperatures from room-temperature up to 600 °C. The setup utilizes a robust, custom-designed switching network board (SNB) for measuring current-voltage characteristics automatically at four different source-measure configurations based on the VDP method. Moreover, SNB is connected with low noise shielded coaxial cables that reduce the effect of leakage current as well as the capacitance in the circuit thereby enhancing the accuracy of measurement. In order to enable precise and accurate resistance measurement of the sample, wide range of sourcing currents/voltages are pre-determined with the capability of auto-tuning for ˜12 orders of variation in the resistances. Furthermore, the setup has been calibrated with standard samples and also employed to investigate temperature dependent resistance (few Ω-10 GΩ) measurements for various chalcogenide based phase change thin films (Ge2Sb2Te5, Ag5In5Sb60Te30, and In3SbTe2). This setup would be highly helpful for measurement of temperature-dependent resistance of wide range of materials, i.e., metals, semiconductors, and insulators illuminating information about structural change upon temperature as reflected by change in resistances, which are useful for numerous applications.

  18. Determination of silicon and chromium content in gray cast iron by the Van der Pauw method; Determinacion del contenido de silicio y cromo en fundiciones grises mediante el metodo de Van der Pauw

    Energy Technology Data Exchange (ETDEWEB)

    Tremps, E.; Enrique, J. L.; Moron, C.; Garcia, A.; Gomez, A.

    2013-07-01

    In this paper we show a system based on the resistivity measurement of samples of gray cast iron by the Van der Pauw method to calculate the silicon content in the samples. Twenty five trials have been carried out, studying resistive and metallographic characteristics of the samples. This has demonstrated that it is possible to obtain, by this method, the silicon content in molten flat with low content of alloying elements, also the content of chromium in series smelters where the rate of silicon remains constant. (Author)

  19. São Paulo Miesiana: a influência de Mies van der Rohe na Arquitetura Moderna Paulista

    Directory of Open Access Journals (Sweden)

    Patricia Pereira Fernandes

    2017-06-01

    The in-depth study of his interaction with modern Brazilian architectural production will be developed through successive steps of approaching the theme, from the general to the particular. In the first place, more general aspects related to the figure of Mies van der Rohe and his practices will be analyzed. Subsequently, the intercurrent relations between the master and the Brazilian architectural panorama will be investigated. And the subsequent stage will involve a detailed study of works considered emblematic of the influence of the architect in the São Paulo range.

  20. Horseshoes chaos and stability of a delayed van der Pol-Duffing oscillator under a bounded double well potential

    International Nuclear Information System (INIS)

    Kwuimy, C.A. Kitio; Woafo, P.

    2009-06-01

    In this paper a van der Pol-Duffing oscillator with a bounded double well potential and a delayed (positive and negative) position and velocity feedback is considered. Attention is focussed on the effects of time delay on stability, escape motion and horseshoes chaos. Using Forde and Nelson's theorem, harmonic balance and Melnikov criterion for chaos, the boundary conditions for such phenomena are derived. It appears that, time delay can be used as simple switch to avoid and/or create complex behavior of the model. (author)

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

    KAUST Repository

    Wang, Zhenwei

    2016-08-30

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

  2. Nature and strength of bonding in a crystal of semiconducting nanotubes: van der Waals density functional calculations and analytical results

    DEFF Research Database (Denmark)

    Kleis, Jesper; Schröder, Elsebeth; Hyldgaard, Per

    2008-01-01

    for the nanotube-crystal binding energy can be approximated by a sum of nanotube-pair interactions when these are calculated in vdW-DR This observation suggests a framework for an efficient implementation of quantum-physical modeling of the carbon nanotube bundling in more general nanotube bundles, including...... nanotube yarn and rope structures.......The dispersive interaction between nanotubes is investigated through ab initio theory calculations and in an analytical approximation. A van der Waals density functional (vdW-DF) [M. Dion et al., Phys. Rev. Lett. 92, 246401 (2004)] is used to determine and compare the binding of a pair of nanotubes...

  3. Connection between fragility, mean-squared displacement and shear modulus in two van der Waals bonded glass-forming liquids

    DEFF Research Database (Denmark)

    Hansen, Henriette Wase; Frick, Bernhard; Hecksher, Tina

    2017-01-01

    The temperature dependence of the high-frequency shear modulus measured in the kHz range is compared with the mean-squared displacement measured in the nanosecond range for the two van der Waals bonded glass-forming liquids cumene and 5-polyphenyl ether. This provides an experimental test...... for the assumption connecting two versions of the shoving model for the non-Arrhenius temperature dependence of the relaxation time in glass formers. The two versions of the model are also tested directly and both are shown to work well for these liquids....

  4. All-carbon vertical van der Waals heterostructures: Non-destructive functionalization of graphene for electronic applications

    OpenAIRE

    Woszczyna, Miroslaw; Winter, Andreas; Grothe, Miriam; Willunat, Annika; Wundrack, Stefan; Stosch, Rainer; Weimann, Thomas; Ahlers, Franz; Turchanin, Andrey

    2014-01-01

    We present a route to non-destructive functionalization of graphene via assembly of vertical all-carbon van der Waals heterostructures. To this end, we employ singlelayer graphene (SLG) sheets grown by low-pressure methane CVD on Cu foils and large-area dielectric ~1 nm thick amino-terminated carbon nanomembranes (NH2-CNMs) generated by electron-beam-induced crosslinking of aromatic self-assembled monolayers. We encapsulate SLG sheets on oxidized silicon wafers with NH2-CNMs via mechanical st...

  5. Electromagnetic-energy-density distribution around a ground-state hydrogen atom and connection with van der Waals forces

    International Nuclear Information System (INIS)

    Passante, R.; Power, E.A.

    1987-01-01

    A spinless hydrogen atom coupled to the electromagnetic field is considered within the context of nonrelativistic quantum electrodynamics. The atom-field interaction is taken in the minimal-coupling form and the Coulomb gauge is used. When the coupled system is in its ground state the electromagnetic field fluctuates away from the vacuum state and the atom has virtual admixtures from its uncoupled lowest eigenstate. The electric- and magnetic-field-energy densities that arise from the fluctuations are determined as functions of the distance from the atom. The relationship between these field-energy densities and the retarded long-range van der Waals forces is also discussed

  6. Density functional for van der Waals forces accounts for hydrogen bond in benchmark set of water hexamers

    DEFF Research Database (Denmark)

    Kelkkanen, Kari André; Lundqvist, Bengt; Nørskov, Jens Kehlet

    2009-01-01

    A recent extensive study has investigated how various exchange-correlation (XC) functionals treat hydrogen bonds in water hexamers and has shown traditional generalized gradient approximation and hybrid functionals used in density-functional (DF) theory to give the wrong dissociation-energy trend...... of low-lying isomers and van der Waals (vdW) dispersion forces to give key contributions to the dissociation energy. The question raised whether functionals that incorporate vdW forces implicitly into the XC functional predict the correct lowest-energy structure for the water hexamer and yield accurate...

  7. Seks & Drugs & Boeremusiek: Die memoires van 'n volksverraaier ...

    African Journals Online (AJOL)

    Die eerste uitgawe het voorts 'n foto van. Kombuis in Istanboel op die buiteblad terwyl die tweede 'n tekenontwerp het. Die drie telefoonpale wat soos kruise lyk in laasgenoemde, herinner aan Kombuis se gelukkige getal wat drie is en onder andere verwys na drie aktiwiteite waar- mee hy hom besig gehou het in sy lewe:.

  8. Charge Versus Energy Transfer in Atomically Thin Graphene-Transition Metal Dichalcogenide van der Waals Heterostructures

    Science.gov (United States)

    Froehlicher, Guillaume; Lorchat, Etienne; Berciaud, Stéphane

    2018-01-01

    Made from stacks of two-dimensional materials, van der Waals heterostructures exhibit unique light-matter interactions and are promising for novel optoelectronic devices. The performance of such devices is governed by near-field coupling through, e.g., interlayer charge and/or energy transfer. New concepts and experimental methodologies are needed to properly describe two-dimensional heterointerfaces. Here, we report an original study of interlayer charge and energy transfer in atomically thin metal-semiconductor [i.e., graphene-transition metal dichalcogenide (TMD, here molybdenum diselenide, MoSe2 )] heterostructures using a combination of microphotoluminescence and Raman scattering spectroscopies. The photoluminescence intensity in graphene /MoSe2 is quenched by more than 2 orders of magnitude and rises linearly with the incident photon flux, demonstrating a drastically shortened (about 1 ps) room-temperature MoSe2 exciton lifetime. Key complementary insights are provided from a comprehensive analysis of the graphene and MoSe2 Raman modes, which reveals net photoinduced electron transfer from MoSe2 to graphene and hole accumulation in MoSe2 . Remarkably, the steady-state Fermi energy of graphene saturates at 290 ±15 meV above the Dirac point. This reproducible behavior is observed both in ambient air and in vacuum and is discussed in terms of intrinsic factors (i.e., band offsets) and environmental effects. In this saturation regime, balanced photoinduced flows of electrons and holes may transfer to graphene, a mechanism that effectively leads to energy transfer. Using a broad range of incident photon fluxes and diverse environmental conditions, we find that the presence of net photoinduced charge transfer has no measurable impact on the near-unity photoluminescence quenching efficiency in graphene /MoSe2 . This absence of correlation strongly suggests that energy transfer to graphene (either in the form of electron exchange or dipole-dipole interaction) is the

  9. Charge Versus Energy Transfer in Atomically Thin Graphene-Transition Metal Dichalcogenide van der Waals Heterostructures

    Directory of Open Access Journals (Sweden)

    Guillaume Froehlicher

    2018-01-01

    Full Text Available Made from stacks of two-dimensional materials, van der Waals heterostructures exhibit unique light-matter interactions and are promising for novel optoelectronic devices. The performance of such devices is governed by near-field coupling through, e.g., interlayer charge and/or energy transfer. New concepts and experimental methodologies are needed to properly describe two-dimensional heterointerfaces. Here, we report an original study of interlayer charge and energy transfer in atomically thin metal-semiconductor [i.e., graphene-transition metal dichalcogenide (TMD, here molybdenum diselenide, MoSe_{2}] heterostructures using a combination of microphotoluminescence and Raman scattering spectroscopies. The photoluminescence intensity in graphene/MoSe_{2} is quenched by more than 2 orders of magnitude and rises linearly with the incident photon flux, demonstrating a drastically shortened (about 1 ps room-temperature MoSe_{2} exciton lifetime. Key complementary insights are provided from a comprehensive analysis of the graphene and MoSe_{2} Raman modes, which reveals net photoinduced electron transfer from MoSe_{2} to graphene and hole accumulation in MoSe_{2}. Remarkably, the steady-state Fermi energy of graphene saturates at 290±15  meV above the Dirac point. This reproducible behavior is observed both in ambient air and in vacuum and is discussed in terms of intrinsic factors (i.e., band offsets and environmental effects. In this saturation regime, balanced photoinduced flows of electrons and holes may transfer to graphene, a mechanism that effectively leads to energy transfer. Using a broad range of incident photon fluxes and diverse environmental conditions, we find that the presence of net photoinduced charge transfer has no measurable impact on the near-unity photoluminescence quenching efficiency in graphene/MoSe_{2}. This absence of correlation strongly suggests that energy transfer to graphene (either in the form of electron

  10. Redox levels in aqueous solution: Effect of van der Waals interactions and hybrid functionals.

    Science.gov (United States)

    Ambrosio, Francesco; Miceli, Giacomo; Pasquarello, Alfredo

    2015-12-28

    We investigate redox levels in aqueous solution using a combination of ab initio molecular dynamics (MD) simulations and thermodynamic integration methods. The molecular dynamics are performed with both the semilocal Perdew-Burke-Ernzerhof functional and a nonlocal functional (rVV10) accounting for van der Waals (vdW) interactions. The band edges are determined through three different schemes, namely, from the energy of the highest occupied and of the lowest unoccupied Kohn-Sham states, from total-energy differences, and from a linear extrapolation of the density of states. It is shown that the latter does not depend on the system size while the former two are subject to significant finite-size effects. For the redox levels, we provide a formulation in analogy to the definition of charge transition levels for defects in crystalline materials. We consider the H(+)/H2 level defining the standard hydrogen electrode, the OH(-)/OH(∗) level corresponding to the oxidation of the hydroxyl ion, and the H2O/OH(∗) level for the dehydrogenation of water. In spite of the large structural modifications induced in liquid water, vdW interactions do not lead to any significant structural effect on the calculated band gap and band edges. The effect on the redox levels is also small since the solvation properties of ionic species are little affected by vdW interactions. Since the electronic properties are not significantly affected by the underlying structural properties, it is justified to perform hybrid functional calculations on the configurations of our MD simulations. The redox levels calculated as a function of the fraction α of Fock exchange are found to remain constant, reproducing a general behavior previously observed for charge transition levels of defects. Comparison with experimental values shows very good agreement. At variance, the band edges and the band gap evolve linearly with α. For α ≃ 0.40, we achieve a band gap, band-edge positions, and redox levels in

  11. Durabilidad natural y descripción anatómica de la madera de la especie Caryodaphnopsis cogolloi Van der Werf

    OpenAIRE

    César Polanco Tapia; Jenny Caicedo Velásquez; Diego Beltrán Hernandez

    2014-01-01

    Se realizó la descripción anatómica de la madera de la especie Caryodaphnopsis cogolloi van der Werff., describiendo las principales características xilológicas de la especie, identificadas en los planos transversal y longitudinal (tangencial y radial) de la madera. Además, se determinó la durabilidad natural de la especie Caryodaphnopsis cogolloi Van der Werff mediante el ensayo acelerado de laboratorio, utilizando las metodologías soil block, establecida por la norma NTC 1127, y agar block,...

  12. Using the van der Waals broadening of the spectral atomic lines to measure the gas temperature of an argon microwave plasma at atmospheric pressure

    International Nuclear Information System (INIS)

    Yubero, C.; Dimitrijevic, M.S.; Garcia, M.C.; Calzada, M.D.

    2007-01-01

    The ro-vibrational emission spectra of the molecular species are usually used to measure the gas temperature of a discharge at atmospheric pressure. However, under some experimental conditions, it is difficult to detect them. In order to overcome this difficulty and obtain the temperature, there are methods based on the relation between the gas temperature and the van der Waals broadening of argon atomic spectral lines with a Stark contribution negligible. In this work, we propose a method based on this relation but for lines with a Stark broadening comparable with the van der Waals one

  13. A critical engagement with BJ van der Walt’s reformational approach towards African culture and world view / Isaac Njaramba Mutua

    OpenAIRE

    Mutua, Isaac Njaramba

    2014-01-01

    This research interrogates Bennie van der Walt’s third way as a solution for the “divided soul” of the African people - a divided soul that creates a false dilemma. This division is the creation of political colonialism and neo-colonialism, which impacts negatively on the African socio-economic and political structure. The myth of the superiority of Western culture propagates this vice. Van der Walt’s clarification of the concepts of a world view and culture are depicted in chapter 1. He w...

  14. Sliding Dynamics of Parallel Graphene Sheets: Effect of Geometry and Van Der Waals Interactions on Nano-Spring Behavior

    Directory of Open Access Journals (Sweden)

    Alessandro Crisafulli

    2018-03-01

    Full Text Available Graphene and carbon nanotubes are promising materials for nanoelectromechanical systems. Among other aspects, a proper understanding of the sliding dynamics of parallel graphene sheets or concentric nanotubes is of crucial importance for the design of nano-springs. Here, we analytically investigate the sliding dynamics between two parallel, rigid graphene sheets. In particular, the analysis focuses on configurations in which the distance between the sheets is kept constant and lower than the equilibrium interlayer spacing of graphite (unstable configurations. The aim is to understand how the interlayer force due to van der Waals interactions along the sliding direction changes with the geometrical characteristics of the configuration, namely size and interlayer spacing. Results show metastable equilibrium positions with completely faced sheets, namely a null force along the sliding direction, whereas net negative/positive forces arise when the sheets are approaching/leaving each other. This behavior resembles a molecular spring, being able to convert kinetic into potential energy (van der Waals potential, and viceversa. The amplitude of both storable energy and entrance/exit forces is found to be proportional to the sheet size, and inversely proportional to their interlayer spacing. This model could also be generalized to describe the behavior of configurations made of concentric carbon nanotubes, therefore allowing a rational design of some elements of carbon-based nanoelectromechanical systems.

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

    Science.gov (United States)

    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.

  16. A van der Waals DFT study of PtH{sub 2} systems absorbed on pristine and defective graphene

    Energy Technology Data Exchange (ETDEWEB)

    López-Corral, Ignacio [Instituto de Química del Sur (INQUISUR), UNS-CONICET, Av. Alem 1253, B8000 Bahía Blanca (Argentina); Departamento de Química, Universidad Nacional del Sur, Av. Alem 1253, B8000 Bahía Blanca (Argentina); Piriz, Sebastián; Faccio, Ricardo [Centro NanoMat/DETEMA, Facultad de Química, Universidad de la República, Montevideo (Uruguay); Centro Interdisciplinario de Nanotecnología, Química y Física de Materiales (CINQUIFIMA), Facultad de Química, Universidad de la República, Montevideo (Uruguay); Juan, Alfredo, E-mail: cajuan@uns.edu.ar [Instituto de Física del Sur (IFISUR), UNS-CONICET, Av. Alem 1253, B8000 Bahía Blanca (Argentina); Departamento de Física, Universidad Nacional del Sur, Av. Alem 1253, B8000 Bahía Blanca (Argentina); Avena, Marcelo [Instituto de Química del Sur (INQUISUR), UNS-CONICET, Av. Alem 1253, B8000 Bahía Blanca (Argentina); Departamento de Química, Universidad Nacional del Sur, Av. Alem 1253, B8000 Bahía Blanca (Argentina)

    2016-09-30

    Highlights: • We performed DFT calculations including van der Waals interactions. • Kubas-type Pt-H2 complex is stable on defective graphene. • Carbon vacancy decreases the reactivity of the metal decoration. • The interaction between σ-H and π-C states favors the Kubas-type complex. - Abstract: We used a density functional that incorporates van der Waals interactions to study hydrogen adsorption onto Pt atoms attached to carbon-vacancies on graphene layers, considering molecular and dissociated hydrogen-platinum coordination structures. PtH{sub 2} complexes adsorbed on several sites of pristine graphene were also studied for comparison. Our results indicate that both a Kubas-type dihydrogen complex and a classic hydride without H−H bond are the preferential PtH{sub 2} systems on the vacancy site of graphene. In contrast, the Kubas complex is unstable onto pristine graphene and the hydride is obtained at all adsorption sites. Our simulations suggest that the C-vacancy decreases the reactivity of the metal decoration, allowing a non-dissociative hydrogen adsorption. The H{sub 2} molecule is oriented almost perpendicular to the outermost C−Pt bond, interacting also with the graphene surface through σ-H and π-C states. This stabilization of the Kubas-type complex could play a very important role for hydrogen storage in Pt-decorated carbon adsorbents with vacancies.

  17. A van der Waals DFT study of PtH2 systems absorbed on pristine and defective graphene

    International Nuclear Information System (INIS)

    López-Corral, Ignacio; Piriz, Sebastián; Faccio, Ricardo; Juan, Alfredo; Avena, Marcelo

    2016-01-01

    Highlights: • We performed DFT calculations including van der Waals interactions. • Kubas-type Pt-H2 complex is stable on defective graphene. • Carbon vacancy decreases the reactivity of the metal decoration. • The interaction between σ-H and π-C states favors the Kubas-type complex. - Abstract: We used a density functional that incorporates van der Waals interactions to study hydrogen adsorption onto Pt atoms attached to carbon-vacancies on graphene layers, considering molecular and dissociated hydrogen-platinum coordination structures. PtH 2 complexes adsorbed on several sites of pristine graphene were also studied for comparison. Our results indicate that both a Kubas-type dihydrogen complex and a classic hydride without H−H bond are the preferential PtH 2 systems on the vacancy site of graphene. In contrast, the Kubas complex is unstable onto pristine graphene and the hydride is obtained at all adsorption sites. Our simulations suggest that the C-vacancy decreases the reactivity of the metal decoration, allowing a non-dissociative hydrogen adsorption. The H 2 molecule is oriented almost perpendicular to the outermost C−Pt bond, interacting also with the graphene surface through σ-H and π-C states. This stabilization of the Kubas-type complex could play a very important role for hydrogen storage in Pt-decorated carbon adsorbents with vacancies.

  18. Van der Waals molecular dimers (He2)2 in solutions of the quantum liquids He3-He II

    International Nuclear Information System (INIS)

    Bashkin, E.P.

    1980-01-01

    Bound states of a pair of impurity He 3 quasiparticles produced as a result of van der Waals attraction at the free surface, in thin films, in narrow capillaries and at vortex filaments in superfluid He 4 are investigated. The contribution of bound states to the thermodynamics of the solution becomes predominant on lowering of the temperature. The inelastic absorption coefficient of first sound due to decay of the bound state in the field of an acoustic wave is calculated. For a system of impurity excitations in narrow capillaries or vortex filaments the existence of a resonance singularity (at a frequency corresponding to the threshold for bound state splitting) is predicted for which the absorption coefficient for monochromatic sound becomes infinite. The gas-liquid phase transition temperature and superfluid transition temperature are calculated for a Bose system of van der Waals (He 3 ) 2 pairs at the surface or in thin He II films. It is shown that the superfluid transition temperature may be of the order of 35 mK

  19. Nonlinear response of a forced van der Pol-Duffing oscillator at non-resonant bifurcations of codimension two

    International Nuclear Information System (INIS)

    Ji, J.C.; Zhang, N.

    2009-01-01

    Non-resonant bifurcations of codimension two may appear in the controlled van der Pol-Duffing oscillator when two critical time delays corresponding to a double Hopf bifurcation have the same value. With the aid of centre manifold theorem and the method of multiple scales, the non-resonant response and two types of primary resonances of the forced van der Pol-Duffing oscillator at non-resonant bifurcations of codimension two are investigated by studying the possible solutions and their stability of the four-dimensional ordinary differential equations on the centre manifold. It is shown that the non-resonant response of the forced oscillator may exhibit quasi-periodic motions on a two- or three-dimensional (2D or 3D) torus. The primary resonant responses admit single and mixed solutions and may exhibit periodic motions or quasi-periodic motions on a 2D torus. Illustrative examples are presented to interpret the dynamics of the controlled system in terms of two dummy unfolding parameters and exemplify the periodic and quasi-periodic motions. The analytical predictions are found to be in good agreement with the results of numerical integration of the original delay differential equation.

  20. Multimodal Nonlinear Optical Imaging of MoS₂ and MoS₂-Based van der Waals Heterostructures.

    Science.gov (United States)

    Li, Dawei; Xiong, Wei; Jiang, Lijia; Xiao, Zhiyong; Golgir, Hossein Rabiee; Wang, Mengmeng; Huang, Xi; Zhou, Yunshen; Lin, Zhe; Song, Jingfeng; Ducharme, Stephen; Jiang, Lan; Silvain, Jean-Francois; Lu, Yongfeng

    2016-03-22

    van der Waals layered structures, notably the transitional metal dichalcogenides (TMDs) and TMD-based heterostructures, have recently attracted immense interest due to their unique physical properties and potential applications in electronics, optoelectronics, and energy harvesting. Despite the recent progress, it is still a challenge to perform comprehensive characterizations of critical properties of these layered structures, including crystal structures, chemical dynamics, and interlayer coupling, using a single characterization platform. In this study, we successfully developed a multimodal nonlinear optical imaging method to characterize these critical properties of molybdenum disulfide (MoS2) and MoS2-based heterostructures. Our results demonstrate that MoS2 layers exhibit strong four-wave mixing (FWM), sum-frequency generation (SFG), and second-harmonic generation (SHG) nonlinear optical characteristics. We believe this is the first observation of FWM and SFG from TMD layers. All three kinds of optical nonlinearities are sensitive to layer numbers, crystal orientation, and interlayer coupling. The combined and simultaneous SHG/SFG-FWM imaging not only is capable of rapid evaluation of crystal quality and precise determination of odd-even layers but also provides in situ monitoring of the chemical dynamics of thermal oxidation in MoS2 and interlayer coupling in MoS2-graphene heterostructures. This method has the advantages of versatility, high fidelity, easy operation, and fast imaging, enabling comprehensive characterization of van der Waals layered structures for fundamental research and practical applications.

  1. Effect of van der Waals interaction on the properties of SnS{sub 2} layered semiconductor

    Energy Technology Data Exchange (ETDEWEB)

    Seminovski, Y. [Instituto de Energía Solar, Universidad Politécnica de Madrid, Ciudad Universitaria, 28040 Madrid (Spain); Dpt. TEAT, ETSI Telecomunicacion, Universidad Politecnica de Madrid, Ciudad Universitaria, 28040 Madrid (Spain); Palacios, P., E-mail: pablo.palacios@upm.es [Instituto de Energía Solar, Universidad Politécnica de Madrid, Ciudad Universitaria, 28040 Madrid (Spain); Dpt. FyQATA, EIAE, Universidad Politécnica de Madrid, Pz. Cardenal Cisneros, 3, 28040 Madrid (Spain); Wahnón, P. [Instituto de Energía Solar, Universidad Politécnica de Madrid, Ciudad Universitaria, 28040 Madrid (Spain); Dpt. TEAT, ETSI Telecomunicacion, Universidad Politecnica de Madrid, Ciudad Universitaria, 28040 Madrid (Spain)

    2013-05-01

    Nowadays, dispersion correction applied on layered semiconductors is a topic of interest. Among the known layered semiconductors, SnS{sub 2} polytypes are wide gap semiconductors with a van der Waals interaction between their layers, which could form good materials to be used in photovoltaic applications. The present work gives an approach to the SnS{sub 2} geometrical and electronic characterization using an empirical dispersion correction added to the Perdew–Burke–Ernzerhof functional and subsequent actualization of the electronic charge density using the screened hybrid Heyd–Scuseria–Ernzerhof functional using a density functional code. The obtained interlayer distance and band-gap are in good agreement with experimental values when van der Waals dispersion forces are included. - Highlights: ► Tin disulphide (SnS{sub 2}) has been calculated using density functional theory methods. ► A dispersion correction was also applied for two different SnS{sub 2} polytypes. ► Geometrical parameters and band-gaps were obtained using both approaches. ► Our calculations give a good agreement of the computed band gap with experiment.

  2. Film Thickness Formation in Nanoscale due to Effects of Elastohydrodynamic, Electrostatic and Surface force of Solvation and Van der Waals

    Directory of Open Access Journals (Sweden)

    M.F. Abd Al-Samieh

    2017-03-01

    Full Text Available The mechanism of oil film with a thickness in the nanoscale is discussed in this paper. A polar lubricant of propylene carbonate is used as the intervening liquid between contiguous bodies in concentrated contacts. A pressure caused by the hydrodynamic viscous action in addition to double layer electrostatic force, Van der Waals inter-molecular forces, and solvation pressure due to inter-surface forces is considered in calculating the ultrathin lubricating films. The numerical solution has been carried out, using the Newton-Raphson iteration technique, applied for the convergence of the hydrodynamic pressure. The results show that, at separations beyond about five molecular diameters of the intervening liquid, the formation of a lubricant film thickness is governed by combined effects of viscous action and surface force of an attractive Van der Waals force and a repulsive double layer force. At smaller separations below about five molecular diameters of the intervening liquid, the effect of solvation force is dominant in determining the oil film thickness

  3. Over den invloed van insuline op de permeabiliteit der weefsels voor glucose

    NARCIS (Netherlands)

    Hamburger, Rudolf Jacobus

    1930-01-01

    In het voorafgaande overzicht van de literatuur, hebben wij gezien, dat vooral vele proeven in vivo, erop wijzen, dat bij diabetes, zoowel van den mensch als bij door pancreasextirpatie diabetisch gemaakte proefdieren minder glucose in de weefsels voorkomt en eveneens minder glucose daarin wordt

  4. Ruimteclub NASA doet spectaculaire vondst (interview met Prof. Dr. John van der Oost)

    NARCIS (Netherlands)

    Vreede, de J.; Oost, van der J.

    2010-01-01

    De Amerikaanse ruimtevaartorganisatie NASA heeft een bijzondere bacterie ontdekt, die gedijt op het giftige arsenicum, oftewel rattengif. De ontdekking vergroot de kans dat op andere planeten vormen van primitief leven voorkomt.

  5. Using the minimum principle for the Helmholtz free energy in the analysis of the equilibria of a van der Waals fluid

    International Nuclear Information System (INIS)

    Ascoli, Sergio; Malvestuto, Vincenzo

    2004-01-01

    For a fluid system, obeying a state equation of the van der Waals type, the gas and the liquid phases can coexist in equilibrium, at a given temperature, only if the volume of the system is kept fixed. Thus, in order to study the two-phase equilibria of a fluid system, it seemed quite natural to choose the molar volume as the independent variable, and, consequently, the Helmholtz free energy as the proper thermodynamic potential for the application of the minimum principle. Specific computations are here carried out for a single van der Waals fluid, namely, pure water at 300 0 C. As a result, the present treatment indicates a simple and effective way to identify the whole range of molar volumes where the equilibrium preferred by the system is a two-phase equilibrium. This range results to be wider than the interval of strict instability of the van der Waals isotherm. Finally, it is pointed out that all the results, obtained here for the van der Waals state equation, can be extended to all the state equations of the same type

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

    DEFF Research Database (Denmark)

    Andersen, Jonas; Heimdal, J.; Wallin Mahler Andersen, Denise

    2014-01-01

    Terahertz absorption spectra have been recorded for the weakly bound CO2–H2O complex embedded in cryogenic neon matrices at 2.8 K. The three high-frequency van der Waals vibrational transitions associated with out-of-plane wagging, in-plane rocking, and torsional motion of the isotopic H2O subunit...

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

    Science.gov (United States)

    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…

  8. Comparative DFT study of van der Waals complexes: rare-gas dimers, alkaline-earth dimers, zinc dimer, and zinc-rare-gas dimers.

    Science.gov (United States)

    Zhao, Yan; Truhlar, Donald G

    2006-04-20

    Recent interest in the application of density functional theory prompted us to test various functionals for the van der Waals interactions in the rare-gas dimers, the alkaline-earth metal dimers, zinc dimer, and zinc-rare-gas dimers. In the present study, we report such tests for 18 DFT functionals, including both some very recent functionals and some well-established older ones. We draw the following conclusions based on the mean errors in binding energies and complex geometries: (1) B97-1 gives the best performance for predicting the geometry of rare-gas dimers, whereas M05-2X and B97-1 give the best energetics for rare-gas dimers. (2) PWB6K gives the best performance for the prediction of the geometry of the alkaline-earth metal dimers, zinc dimers, and zinc-rare-gas dimers. M05-2X gives the best energetics for the metal dimers, whereas B97-1 gives the best energetics for the zinc-rare-gas dimers. (3) The M05 functional is unique in providing good accuracy for both covalent transition-metal dimers and van der Waals metal dimers. (4) The combined mean percentage unsigned error in geometries and energetics shows that M05-2X and MPWB1K are the overall best methods for the prediction of van der Waals interactions in metal and rare-gas van der Waals dimers.

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

    DEFF Research Database (Denmark)

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

    2011-01-01

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

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

    DEFF Research Database (Denmark)

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

    2015-01-01

    scattering, we have developed here a van der Waals heterostructure device platform where MoS2 layers are fully encapsulated within hexagonal boron nitride and electrically contacted in a multi-terminal geometry using gate-tunable graphene electrodes. Magneto-transport measurements show dramatic improvements...

  11. LA IDEA MATERIALIZADA EN EL ESPACIO CONSTRUIDO. LA MUESTRA ‘DIE WHONUNG UNSERER ZEIT’ DE MIES VAN DER ROHE / The idea represented in the exhibition Die Wohnung unserer Zeit of Mies van der Rohe

    Directory of Open Access Journals (Sweden)

    Laura Lizondo Sevilla, José Santatecla Fayos, Nuria Salvador Luján, Ignacio Bosch Reig

    2013-05-01

    Full Text Available RESUMEN El artículo analiza la muestra Die Wohnung unserer Zeit (La Vivienda de Nuestro Tiempo, perteneciente a la Deutsche Bauausstellung (Exposición de la Construcción Alemana de 1931, e indaga en las posibilidades de experimentación arquitectónica que desempeñaron este tipo de arquitecturas en el desarrollo profesional de Mies van der Rohe. El discurso constata el potencial de esta exposición para actuar como campo de experimentación efímero, capaz de dar forma construida a una idea o concepto; una arquitectura temporal que rompió con los convencionalismos expositivos del momento, convirtiéndose en un evento de relevancia a nivel cultural, histórico y arquitectónico. La muestra materializó, físicamente y a escala 1.1, la idea que un grupo de arquitectos del Movimiento Moderno tenían sobre la vivienda del futuro; una vivienda pensada y diseñada con ideas basadas en el hipotético individuo de la nueva época.SUMMARY The article analyses the exhibition Die Wohnung unserer Zeit (The House of Our Time, pertaining to the Deutsche Bauausstellung (1931 German Construction Exhibition, and explores the possibilities of architectural experimentation that such architecture played in the professional development of Mies van der Rohe. It discusses the potential of this exhibition to act as an ephemeral testing ground, capable of giving constructed form to an idea or concept; an architecture that broke with the expository conventionalisms of the time, becoming an important event in the cultural, historical and architectural sense. The exhibition presented, physically, and on a scale of 1 to 1, the idea that a group of architects of the Modern Movement had about the house of the future, a house conceived and designed with ideas based on the hypothetical individual of the new age.

  12. Ab initio van der waals interactions in simulations of water alter structure from mainly tetrahedral to high-density-like

    DEFF Research Database (Denmark)

    Møgelhøj, Andreas; Kelkkanen, Kari André; Wikfeldt, K Thor

    2011-01-01

    The structure of liquid water at ambient conditions is studied in ab initio molecular dynamics simulations in the NVE ensemble using van der Waals (vdW) density-functional theory, i.e., using the new exchange-correlation functionals optPBE-vdW and vdW-DF2, where the latter has softer nonlocal...... protocol could cause the deviation. An O-O PCF consisting of a linear combination of 70% from vdW-DF2 and 30% from low-density liquid water, as extrapolated from experiments, reproduces near-quantitatively the experimental O-O PCF for ambient water. This suggests the possibility that the new functionals...... shows some resemblance with experiment for high-density water ( Soper , A. K. and Ricci , M. A. Phys. Rev. Lett. 2000 , 84 , 2881 ), but not directly with experiment for ambient water. Considering the accuracy of the new functionals for interaction energies, we investigate whether the simulation...

  13. Michel Van der Yeught, L’anglais de la bourse et de la finance : description et recherche

    OpenAIRE

    Azuelos, Martine

    2013-01-01

    Cet ouvrage est le premier de la collection « Langues de spécialité » dirigée par Michel Van der Yeught aux éditions Ophrys en partenariat avec le GERAS et le LERMA (EA 853) de l’Université d’Aix-Marseille. Son intérêt réside donc tout autant dans la présentation de la langue de spécialité sur laquelle portent sa deuxième et sa troisième partie (l’anglais de la bourse et de la finance) que dans la vingtaine de pages introductives consacrées à la présentation de la collection et du cadre théor...

  14. Spectroscopic Signatures for Interlayer Coupling in MoS 2 –WSe 2 van der Waals Stacking

    KAUST Repository

    Chiu, Ming-Hui

    2014-09-23

    Stacking of MoS2 and WSe2 monolayers is conducted by transferring triangular MoS2 monolayers on top of WSe2 monolayers, all grown by chemical vapor deposition (CVD). Raman spectroscopy and photoluminescence (PL) studies reveal that these mechanically stacked monolayers are not closely coupled, but after a thermal treatment at 300 degrees C, it is possible to produce van der Waals solids consisting of two interacting transition metal dichalcogenide (TMD) monolayers. The layer-number sensitive Raman out-of-plane mode A(1g)(2) for WSe2 (309 cm(-1)) is found sensitive to the coupling between two TMD monolayers. The presence of interlayer excitonic emissions and the changes in other intrinsic Raman modes such as E \\'\\' for MoS2 at 286 cm(-1) and A(1g)(2) for MoS2 at around 463 cm(-1) confirm the enhancement of the interlayer coupling.

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

    Science.gov (United States)

    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).

  16. Semiempirical calculation of van der Waals coefficients for alkali-metal and alkaline-earth-metal atoms

    International Nuclear Information System (INIS)

    Mitroy, J.; Bromley, M.W.J.

    2003-01-01

    The van der Waals coefficients, C 6 , C 8 , and C 10 for the alkali-metal (Li, Na, K, and Rb) and alkaline-earth-metal (Be, Mg, Ca, and Sr) atoms are estimated by a combination of ab initio and semiempirical methods. Polarizabilities and atom-wall coefficients are given as a diagnostic check, and the lowest order nonadiabatic dispersion coefficient, D 8 and the three-body coefficient, C 9 are also presented. The dispersion coefficients are in agreement with the available relativistic many-body perturbation theory calculations. The contribution from the core was included by using constrained sum rules involving the core polarizability and Hartree-Fock expectation values to estimate the f-value distribution

  17. Long-Range van der Waals Correction to a Semilocal Density Functional: The Tail Need Not Wag the Dog

    Science.gov (United States)

    Perdew, John P.

    The SCAN (strongly constrained and appropriately normed) meta-generalized gradient approximation satisfies all 17 exact constraints that a semilocal functional can. Without being fitted to any bonded system, it correctly describes most kinds of bonding, including intermediate-range van der Waals (vdW) interaction. It can be supplemented [3.4] with a long-range vdW correction such as D3 or rVV10, which have the flexibility to exclude any intermediate-range contribution. Accurate results are found for free molecules, for molecules weakly bound to metal surfaces, and for interlayer binding energies of layered materials. Despite being a pair-interaction model, the rVV10 correction to SCAN also gives a random-phase-approximation-like long-range contribution to the binding energy curve for graphene on a nickel surface. Supported by DOE BES and NSF DMR.

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

    Science.gov (United States)

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

    2016-11-09

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

  19. A modified hybrid Van der Pol-Duffing-Rayleigh oscillator for modelling the lateral walking force on a rigid floor

    Science.gov (United States)

    Kumar, Prakash; Kumar, Anil; Erlicher, Silvano

    2017-11-01

    The paper proposes a single degree of freedom oscillator in order to accurately represent the lateral force acting on a rigid floor due to human walking. As a pedestrian produces itself the energy required to maintain its motion, it can be modelled as a self-sustained oscillator that is able to produce: (i) self-sustained motion; (ii) a lateral periodic force signal; and (iii) a stable limit cycle. The proposed oscillator is a modification of hybrid Van der Pol-Duffing-Rayleigh oscillator, by introducing an additional nonlinear hardening term. Stability analysis of the proposed oscillator has been performed by using the energy balance method and the Lindstedt-Poincare perturbation technique. Model parameters were identified from the experimental force signals of ten pedestrians using the least squares identification technique. The experimental and the model generated lateral forces show a good agreement.

  20. Van der Waals epitaxial growth of MoS2 on SiO2/Si by chemical vapor deposition

    KAUST Repository

    Cheng, Yingchun

    2013-01-01

    Recently, single layer MoS2 with a direct band gap of 1.9 eV has been proposed as a candidate for two dimensional nanoelectronic devices. However, the synthetic approach to obtain high-quality MoS2 atomic thin layers is still problematic. Spectroscopic and microscopic results reveal that both single layers and tetrahedral clusters of MoS2 are deposited directly on the SiO2/Si substrate by chemical vapor deposition. The tetrahedral clusters are mixtures of 2H- and 3R-MoS2. By ex situ optical analysis, both the single layers and tetrahedral clusters can be attributed to van der Waals epitaxial growth. Due to the similar layered structures we expect the same growth mechanism for other transition-metal disulfides by chemical vapor deposition. © 2013 The Royal Society of Chemistry.

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

    Science.gov (United States)

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

    2017-07-01

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

  2. Bandgap engineering in van der Waals heterostructures of blue phosphorene and MoS{sub 2}: A first principles calculation

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Z.Y. [Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000 (China); Si, M.S., E-mail: sims@lzu.edu.cn [Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000 (China); Peng, S.L. [Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000 (China); Zhang, F. [Key Lab of Photovoltaic Materials of Henan Province, Henan University, Kaifeng 475001 (China); Wang, Y.H.; Xue, D.S. [Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000 (China)

    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} but 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.

  3. Application of Solution-blown 20-50 nm Nanofibers in Filtration of Nanoparticles: The Efficient van der Waals Collectors

    Science.gov (United States)

    Sinha-Ray, Sumit; Sinha-Ray, Suman; Yarin, Alexander; Pourdeyhimi, Behnam

    2015-11-01

    Filtration efficiency of commercially available filter media with fiber/pore sizes on the scale of 10 μm can be dramatically increased by adding a layer of ultrafine supersonically-blown 20-50 nm nanofibers. Different commercial filters were modified with (i) electrospun nanofibers alone, (ii) solution-blown 20-50 nm alone, and (iii) the dual coating with electrospun nanofibers deposited first and the solution-blown 20-50 nm nanofibers deposited on top of them. Detailed observations of nanoparticle removal revealed that the above-mentioned modified filters, especially those with the dual nanofiber coating with the 20-50 nm nanofibers deposited on top, are the most effective in removing the below-200 nm Cu nanoparticles/clusters from aqueous suspensions, in particular at the lowest concentrations of 0.2-0.5 ppm. The theory developed in the present work dealing with convective transport of nanoparticles in the fluid flow along with diffusion of nanoparticles and the van der Waals attraction explains and describes how the smallest solution-blown nanofibers introduce a novel physical mechanism of nanoparticle interception (the attractive van der Waals forces) and become significantly more efficient collectors compared to the larger electrospun nanofibers. The theory also elucidates the morphology of the nanoparticle clusters being accumulated at the smallest nanofiber surfaces, including the clusters growing at the windward side, or in some cases also on the leeward side of a nanofiber. This work is supported by the Nonwovens Cooperative Research Center (NCRC), grant No. 12-144SB.

  4. One-dimensional Fermi accelerator model with moving wall described by a nonlinear van der Pol oscillator.

    Science.gov (United States)

    Botari, Tiago; Leonel, Edson D

    2013-01-01

    A modification of the one-dimensional Fermi accelerator model is considered in this work. The dynamics of a classical particle of mass m, confined to bounce elastically between two rigid walls where one is described by a nonlinear van der Pol type oscillator while the other one is fixed, working as a reinjection mechanism of the particle for a next collision, is carefully made by the use of a two-dimensional nonlinear mapping. Two cases are considered: (i) the situation where the particle has mass negligible as compared to the mass of the moving wall and does not affect the motion of it; and (ii) the case where collisions of the particle do affect the movement of the moving wall. For case (i) the phase space is of mixed type leading us to observe a scaling of the average velocity as a function of the parameter (χ) controlling the nonlinearity of the moving wall. For large χ, a diffusion on the velocity is observed leading to the conclusion that Fermi acceleration is taking place. On the other hand, for case (ii), the motion of the moving wall is affected by collisions with the particle. However, due to the properties of the van der Pol oscillator, the moving wall relaxes again to a limit cycle. Such kind of motion absorbs part of the energy of the particle leading to a suppression of the unlimited energy gain as observed in case (i). The phase space shows a set of attractors of different periods whose basin of attraction has a complicated organization.

  5. De Staart der Cetacea en eenige Gevallen van lintvormige Staarten bij Phocaena phocoena (L.)

    NARCIS (Netherlands)

    Deinse, van A.B.

    1945-01-01

    Bij de beschrijving en (of) de determinatie van Cetacea speelt de staart geen belangrijke rol. Toch is er een vertegenwoordiger dier orde te noemen, waarbij de staart er zoo karakteristiek uitziet, dat hierdoor alleen reeds geslacht en soort volkomen zijn bepaald. Ik bedoel Megaptera novaeangliae

  6. van G elderen , De boeken der Koningen, opnieuw uit de grondtekst ...

    African Journals Online (AJOL)

    Test

    ... en verontwaardiging, veral waar dit hier die werk betref van 'n geleerde wie se lesings ons self 'n paar jaar gevolg het en wie se nagedagtenis ons wil eer. Nou stuur die manne, in wie se hande blykbaar sy letterkundige nalatenskap berus, dit die wéreld in met bv. 'n bibliografie wat nie verder as die jaar 1931 reik nie!

  7. De paradox van het verlichte gelijkheidsdiscours. Beschouwingen over De uitvinding der mensheid door Siep Stuurman

    NARCIS (Netherlands)

    van Eijnatten, J.

    2011-01-01

    The paradox of Enlightened equality. Some considerations on Siep Stuurman’s De uitvinding van de mensheid Jesus praised the Good Samaritan who, according to the parable, understood that the stranger we encounter in daily life is, in fact, our neighbour. For Siep Stuurman, the tale of the Samaritan

  8. Dr. Hans Chang, Director, Physics Research Committee, Stichting voor Fundamenteel Onderzoek der Materie (FOM), Dr. Joris Van Enst, Head of Science Policy Division, Ministry of Education, Culture and S cience, Dr. Jan Bezemer, NL Delegate CERN, Netherlands

    CERN Multimedia

    Patrice Loiez

    1999-01-01

    Dr. Hans Chang, Director, Physics Research Committee, Stichting voor Fundamenteel Onderzoek der Materie (FOM), Dr. Joris Van Enst, Head of Science Policy Division, Ministry of Education, Culture and S cience, Dr. Jan Bezemer, NL Delegate CERN, Netherlands

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

    Science.gov (United States)

    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).

  10. Substrate induced tuning of compressive strain and phonon modes in large area MoS2 and WS2 van der Waals epitaxial thin films

    Science.gov (United States)

    Sahu, Rajib; Radhakrishnan, Dhanya; Vishal, Badri; Negi, Devendra Singh; Sil, Anomitra; Narayana, Chandrabhas; Datta, Ranjan

    2017-07-01

    Large area MoS2 and WS2 van der Waals epitaxial thin films with control over number of layers including monolayer is grown by pulsed laser deposition utilizing slower growth kinetics. The films grown on c-plane sapphire show stiffening of A1g and E12g phonon modes with decreasing number of layers for both MoS2 and WS2. The observed stiffening translate into the compressive strain of 0.52% & 0.53% with accompanying increase in fundamental direct band gap to 1.74 and 1.68 eV for monolayer MoS2 and WS2, respectively. The strain decays with the number of layers. HRTEM imaging directly reveals the nature of atomic registry of van der Waals layers with the substrate and the associated compressive strain. The results demonstrate a practical route to stabilize and engineer strain for this class of material over large area device fabrication.

  11. Application of the van der Waals equation of state to polymers .4. Correlation and prediction of lower critical solution temperatures for polymer solutions

    DEFF Research Database (Denmark)

    Goncalves, Ana Saraiva; Kontogeorgis, Georgios; Harismiadis, Vassilis I.

    1996-01-01

    and has been successfully used for the prediction of upper critical solution temperatures for various binary polymer solutions. In this work, we demonstrate and explain some of the problems which cubic equations of state exhibit in describing the lower critical solution behavior for polymer solutions......The van der Waals equation of state is used for the correlation and the prediction of the lower critical solution behavior or mixtures including a solvent and a polymer. The equation of state parameters for the polymer are estimated from experimental volumetric data at low pressures. The equation...... of state parameters for the solvent are estimated via the classical Soave method, i.e. using the critical properties and a generalized equation for the energy parameter. When extended to mixtures, the van der Waals one-fluid mixing rules along with the Berthelot combining rule for the molecular cross...

  12. Bifurcations of new multi soliton solutions of the van der Waals normal form for fluidized granular matter via six different methods

    Directory of Open Access Journals (Sweden)

    Dianchen Lu

    Full Text Available In this article, we study one of the most popular models in nature and also industrial which is the van der Waals normal form for the fluidized granular matter. Understanding of static and dynamic property for these kinds of the models is very important in many aspects of industrial from pharmaceuticals to civil engineering and also some basic physical phenomena like those studied in geophysics. This model explains the phase separation phenomenon. We apply six different methods for this model to obtained the traveling and solitary wave solutions. We make the comparison between obtained solutions with each of them and also with obtained solutions with different methods. Keywords: The van der Waals normal form for fluidized granular matter, Modified simple equation method, The improved mapping approach and variable separation method, Traveling wave solutions, Solitary wave solutions, Mathematical physics

  13. Using the van der Waals broadening of spectral atomic lines to measure the gas temperature of an argon-helium microwave plasma at atmospheric pressure

    International Nuclear Information System (INIS)

    Munoz, J.; Dimitrijevic, M.S.; Yubero, C.; Calzada, M.D.

    2009-01-01

    The applications of plasmas generated with gas mixtures have become increasingly common in different scientific and technological fields. In order to understand the advantages of these discharges, for instance in chemical analysis, it is necessary to know the gas temperature (T g , kinetic energy of the heavy particles) since it has a great influence on the atomization reactions of the molecules located in the discharge, along with the dependence of the reaction rate on this parameter. The ro-vibrational emission spectra of the molecular species are usually used to measure the gas temperature of a discharge at atmospheric pressure although under some experimental conditions, these are difficult to detect. In such cases, the gas temperature can be determined from the van der Waals broadening of the emitted atomic spectral lines related to this parameter. The method proposed is based on the van der Waals broadening taking into account two perturbers

  14. WSe2/MoS2 and MoTe2/SnSe2 van der Waals heterostructure transistors with different band alignment

    Science.gov (United States)

    Li, Chao; Yan, Xiao; Song, Xiongfei; Bao, Wenzhong; Ding, Shijin; Zhang, David Wei; Zhou, Peng

    2017-10-01

    Heterostructure field-effect transistors (hetero-FETs) are experimentally demonstrated, consisting of van der Waals heterostructure channels based on a 2D semiconductor. By optimally selecting the band alignment of the heterostructure channels, different output characteristics of the hetero-FETs were achieved. In atomically thin WSe2/MoS2 hetero-FET with staggered energy band, the oscillating transfer characteristic and negative transconductance were realized. With near-broken-gap alignment in the MoTe2/SnSe2 heterostructure channel, a superior reverse-biased current was obtained in the hetero-FETs, which can be analyzed as typical tunneling current. Our study on the hetero-FET-based atomically thin van der Waals heterostructure channel, provides significant inspiration and reference to novel heterostructure FETs.

  15. The influence of van der Waals forces on the state of water in the shallow subsurface of Mars

    Science.gov (United States)

    Möhlmann, Diedrich T. F.

    2008-05-01

    Microscopic liquid layers of water can evolve via adsorption on grain and mineral surfaces at and in the soil of the surface of Mars. The upper parts of these layers will start to freeze at temperatures clearly below the freezing point of bulk water (freezing point depression). A sandwich structure with layers of ice (top), liquid water (in between) and mineral surface (bottom) can evolve. The properties of the interfacial water (of adsorption water and premelted ice) on grain surfaces are described by a sandwich-model of a layer of liquid-like adsorption water between the adsorbing mineral surface layer and an upper ice layer. It is shown that the thickness or number of mono-layers of the interfacial water (of adsorption water and premelted ice) depends on temperature and atmospheric relative humidity. The derived equations for the sandwich model fit well to a known phenomenological relation between thickness of the liquid layer and relative humidity, and can be a tool to estimate or to determine for appropriate materials Hamaker's constant for van der Waals interactions on grains and in porous media. The curvature of grain surfaces is shown to have no remarkable effects for particles in the μm-range and larger. The application of these equations to thermo-physical conditions on Mars shows that the thickness of frost-layers, which can evolve over several hours on cooling surface parts of Mars, is typically of the order or a few tenths of one millimeter or less. This is in agreement with observations. Furthermore, an equation is derived, which relates the freezing point depression for van der Waals force governed interfacial water to the value of the Hamaker constant, to the latent heat of solidification, to the mass density of water ice, and to the thickness of the liquid-like layer. Again, this equation fits well to a known phenomenological relation between freezing point depression and thickness of the liquid-like layer. The derived equation shows that the

  16. Quasi-periodic bifurcations of four-frequency tori in the ring of five coupled van der Pol oscillators with different types of dissipative coupling

    Science.gov (United States)

    Stankevich, N. V.; Kuznetsov, A. P.; Seleznev, E. P.

    2017-06-01

    Five van der Pol oscillators connected into a ring have been investigated numerically. We have considered different types of coupling: dissipative and active, as well as dissipative and active with a single coupling sign reversal. Bifurcations observed upon a transition from a five- to four-frequency torus have been investigated. The possibility of quasi-periodic Hopf bifurcation in this system has been established.

  17. Repliek op Van der Watt se artikel oor ‘Intertekstualiteit en oorinterpretasie: Verwysings na Genesis 28:12 in Johannes 1:51?’

    Directory of Open Access Journals (Sweden)

    Hennie F. Stander

    2017-10-01

    Full Text Available A response to Van der Watt’s article on ‘Intertextuality and over-interpretation: References to Genesis 28:12 in John 1:51?’ This article is a response to an article of Van der Watt titled ‘Intertextuality and over-interpretation: References to Genesis 28:12 in John 1:51?’ (2016. He states in this article that his aim is ‘to illustrate the dangers of over-interpretation when dealing with intertextual relations between texts, especially when allusion is assumed’. He then gives a brief survey of different interpretations of John 1:51. Van der Watt shows in his article how theologians use themes from Genesis 28:12 (like the ladder, Jacob or Bethel, which are not mentioned in John 1:51 in their expositions of John 1:51. Van der Watt regards some of these expositions as examples of over-interpretation. The aim of my article is to show how Church Fathers interpreted Genesis 28:12 and John 1:51. I show in my article that the Church Fathers saw several parallels between these two sections from the Bible. Furthermore, I suggest that the early theologians’ interpretations formed a tradition that probably influenced modern interpreters of the Bible. I also discuss the role of typology in the history of interpretation, specifically also in the case of Genesis 28:12 and John 1:51. I then argue that it is perhaps not so far-fetched to see an intertextual relation between Genesis 28:12 and John 1:51.

  18. Investigating the effect of Casimir and van der Waals attractions on the electrostatic pull-in instability of nano-actuators

    International Nuclear Information System (INIS)

    Soroush, R; Koochi, A; Haddadpour, H; Kazemi, A S; Noghrehabadi, A; Abadyan, M

    2010-01-01

    This paper investigates the effect of dispersion (van der Waals and Casimir) forces on the pull-in instability of cantilever nano-actuators by considering their range of application. Adomian decomposition is introduced to obtain an analytical solution of the distributed parameter model. Dispersion forces decrease the pull-in deflection and voltage of a nano-actuator. However, the fringing field increases the pull-in deflection while decreasing the pull-in voltage of the actuator. The minimum initial gap and the detachment length of the actuator that does not stick to the substrate due to van der Waals and Casimir attractions were determined. Furthermore, the proposed approach is capable of determining the stress distribution of the actuator at the onset of instability. It is seen that Casimir and van der Waals attractions effectively reduce the maximum value of stress resultants at the onset of instability. The results indicate that Adomian decomposition is a reliable method for simulating nano-structures at submicrometer ranges.

  19. Political Storytelling on Instagram: Key Aspects of Alexander Van der Bellen’s Successful 2016 Presidential Election Campaign

    Directory of Open Access Journals (Sweden)

    Karin Liebhart

    2017-12-01

    Full Text Available This article addresses the strategic use of Instagram in election campaigns for the office of the Austrian Federal President in 2016. Based on a comprehensive visual analysis of 504 Instagram posts from Green-backed but independent presidential candidate Alexander Van der Bellen, who resulted as winner after almost one year of campaigning, this contribution reconstructs key aspects of digital storytelling on Instagram. By identifying relevant image types central to the self-representation of the candidate, this article shows how a politician makes use of a digital platform in order to project and manage desired images. The salience of image types allows for the reconstruction of underlying visual strategies: (1 the highlighting of the candidate’s biography (biographical strategy, (2 the presentation of his campaign team (team strategy, and (3 the presentation of the candidate as a legitimate office holder (incumbent strategy. The article thus sheds light on visual aspects of digital storytelling as relevant factor of political communication.

  20. Layer-dependent electronic properties of phosphorene-like materials and phosphorene-based van der Waals heterostructures.

    Science.gov (United States)

    Huang, Y C; Chen, X; Wang, C; Peng, L; Qian, Q; Wang, S F

    2017-06-29

    Black phosphorus is a layered semiconducting allotrope of phosphorus with high carrier mobility. Its monolayer form, phosphorene, is an extremely fashionable two-dimensional material which has promising potential in transistors, optoelectronics and electronics. However, phosphorene-like analogues, especially phosphorene-based heterostructures and their layer-controlled electronic properties, are rarely systematically investigated. In this paper, the layer-dependent structural and electronic properties of phosphorene-like materials, i.e., mono- and few-layer MXs (M = Sn, Ge; X = S, Se), are first studied via first-principles calculations, and then the band edge position of these MXs as well as mono- and few-layer phosphorene are aligned. It is revealed that van der Waals heterostructures with a Moiré superstructure formed by mutual coupling among MXs and among MXs and few-layer phosphorene are able to show type-I or type-II characteristics and a I-II or II-I transition can be induced by adjusting the number of layers. Our work is expected to yield a new family of phosphorene-based semiconductor heterostructures with tunable electronic properties through altering the number of layers of the composite.

  1. Electronic structures and enhanced optical properties of blue phosphorene/transition metal dichalcogenides van der Waals heterostructures

    Science.gov (United States)

    Peng, Qiong; Wang, Zhenyu; Sa, Baisheng; Wu, Bo; Sun, Zhimei

    2016-01-01

    As a fast emerging topic, van der Waals (vdW) heterostructures have been proposed to modify two-dimensional layered materials with desired properties, thus greatly extending the applications of these materials. In this work, the stacking characteristics, electronic structures, band edge alignments, charge density distributions and optical properties of blue phosphorene/transition metal dichalcogenides (BlueP/TMDs) vdW heterostructures were systematically studied based on vdW corrected density functional theory. Interestingly, the valence band maximum and conduction band minimum are located in different parts of BlueP/MoSe2, BlueP/WS2 and BlueP/WSe2 heterostructures. The MoSe2, WS2 or WSe2 layer can be used as the electron donor and the BlueP layer can be used as the electron acceptor. We further found that the optical properties under visible-light irradiation of BlueP/TMDs vdW heterostructures are significantly improved. In particular, the predicted upper limit energy conversion efficiencies of BlueP/MoS2 and BlueP/MoSe2 heterostructures reach as large as 1.16% and 0.98%, respectively, suggesting their potential applications in efficient thin-film solar cells and optoelectronic devices. PMID:27553787

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

    Science.gov (United States)

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

    2018-04-09

    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 10 6 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.

  3. Nuclear molecular halo: the ubiquitous occurrence of van der Waals molecular states near threshold in molecular, nuclear and particle physics

    International Nuclear Information System (INIS)

    Gai, Moshe

    1999-01-01

    The observation of large E1 strength near threshold in the electromagnetic dissociation of 11 Li poses a fundamental question: Is the large E1 strength due to the threshold or is it due to a low lying E1 state? Such molecular cluster states were observed in 18 O and in several nuclei near the drip line. We discuss the nature of the threshold effect as well as review the situation in Molecular (and Particle Physics) where such Molecular States are observed near the dissociation limit. We suggest that the situation in 11 Li is reminiscent of the argon-benzene molecule where the argon atom is loosely bound by a polarization (van der Waals) mechanism and thus leads to a very extended object lying near the dissociation limit. Such states are also suggested to dominate the structure of mesons [α 0 (980), f 0 (975)] and baryons [λ(1405)] with proposed Kaon molecular structure (Dalitz) near threshold. The inspection of such states throughout Physics allows us to gain insight into this phenomenon and suggest that a new collective Molecular Dipole Degree of Freedom plays a major role in the structure of hadrons (halo nuclei, mesons and baryons), and that quantitative tools such as the E1 Molecular Sum Rule are useful for elucidating the nature of the observed low lying E1 strength in halo nuclei. (author)

  4. A van der Waals DFT study of PtH2 systems absorbed on pristine and defective graphene

    Science.gov (United States)

    López-Corral, Ignacio; Piriz, Sebastián; Faccio, Ricardo; Juan, Alfredo; Avena, Marcelo

    2016-09-01

    We used a density functional that incorporates van der Waals interactions to study hydrogen adsorption onto Pt atoms attached to carbon-vacancies on graphene layers, considering molecular and dissociated hydrogen-platinum coordination structures. PtH2 complexes adsorbed on several sites of pristine graphene were also studied for comparison. Our results indicate that both a Kubas-type dihydrogen complex and a classic hydride without Hsbnd H bond are the preferential PtH2 systems on the vacancy site of graphene. In contrast, the Kubas complex is unstable onto pristine graphene and the hydride is obtained at all adsorption sites. Our simulations suggest that the C-vacancy decreases the reactivity of the metal decoration, allowing a non-dissociative hydrogen adsorption. The H2 molecule is oriented almost perpendicular to the outermost Csbnd Pt bond, interacting also with the graphene surface through σ-H and π-C states. This stabilization of the Kubas-type complex could play a very important role for hydrogen storage in Pt-decorated carbon adsorbents with vacancies.

  5. A combining rule calculation of the ground state van der Waals potentials of the mercury rare-gas complexes.

    Science.gov (United States)

    Sheng, X W; Li, P; Tang, K T

    2009-05-07

    The ground state van der Waals potentials of the Hg-RG (RG = He,Ne,Ar,Kr,Xe) systems are generated by the Tang-Toennies potential model. The parameters of the model are calculated from the potentials of the homonuclear mercury and rare-gas dimers with combining rules. The predicted spectroscopic parameters for these mercury rare-gas complexes are in good agreement with available experimental values, except for Hg-He. In the repulsive and potential well regions, the predicted potential energy curves agree with the available experimental hybrid potentials, but they differ in the long range part of the potential. On the other hand, the present potentials are in agreement with the ab initio CCSD(T) calculations in the long range part of the potential, but there are some differences in the short repulsive regions. According to the present theory, the reduced potential curves of these five systems, including Hg-He, are almost identical to each other. This reduced potential curve can also describe, within a few percent, the five reduced potentials obtained from the ab initio CCSD(T) calculations. These reduced potentials have a potential bowl that is wider than that of the rare-gas dimers, but narrower than the mercury dimer.

  6. Rigorous analysis of Casimir and van der Waals forces on a silicon nano-optomechanical device actuated by optical forces.

    Science.gov (United States)

    Rodrigues, Janderson R; Gusso, Andre; Rosa, Felipe S S; Almeida, Vilson R

    2018-02-22

    Nano-optomechanical devices have enabled a lot of interesting scientific and technological applications. However, due to their nanoscale dimensions, they are vulnerable to the action of Casimir and van der Waals (dispersion) forces. This work presents a rigorous analysis of the dispersion forces on a nano-optomechanical device based on a silicon waveguide and a silicon dioxide substrate, surrounded by air and driven by optical forces. The dispersion forces are calculated using a modified Lifshitz theory with experimental optical data and validated by means of a rigorous 3D FDTD simulation. The mechanical nonlinearity of the nanowaveguide is taken into account and validated using a 3D FEM simulation. The results show that it is possible to attain a no pull-in critical point due to only the optical forces; however, the dispersion forces usually impose a pull-in critical point to the device and establish a minimal initial gap between the waveguide and the substrate. Furthermore, it is shown that the geometric nonlinearity effect may be exploited in order to avoid or minimize the pull-in and, therefore, the device collapse.

  7. Unified many-body approach to van der Waals interactions based on semi-local polarizability functional

    Science.gov (United States)

    Hermann, Jan; Scheffler, Matthias; Tkatchenko, Alexandre

    Electromagnetic coupling of charge fluctuations leads to van der Waals (vdW) attraction in systems ranging from metal nanoparticles to dielectric materials. In this regard, broadly applicable and accurate description of vdW interactions in complex materials is an elusive and unsolved puzzle. Many promising approaches model various subsets of this general problem, but are limited in scope by the underlying parametrization (atomic models), in accuracy due to missing many-body interactions (nonlocal density functionals), or in efficiency by working with virtual orbital space (e.g., random-phase approximation). Here, we present a unifying method that combines key elements from different theories and accurately describes vdW interactions in covalent, ionic, and metallic systems. In particular, we employ a semi-local polarizability functional of the electron density and its gradient to parametrize material response and its coupling within the many-body dispersion framework, and demonstrate the generality of the method on binding in molecular dimers and crystals, carbon-based nanomaterials, oxides, and salts, as well as on adsorption of molecules on metal surfaces. Our approach allows consistent modelling of a wide spectrum of materials as well as hybrid materials with mixed bond types.

  8. Binding mechanisms of DNA/RNA nucleobases adsorbed on graphene under charging: first-principles van der Waals study

    Science.gov (United States)

    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.

  9. Hybrid van der Waals SnO/MoS2 Heterojunctions for Thermal and Optical Sensing Applications

    KAUST Repository

    Wang, Zhenwei

    2017-11-10

    Emerging van der Waals heterojunctions (vdWH) containing 2D materials have shown exciting functionalities that surpass those of traditional devices based on bulk materials. In this Communication, a report on the properties of a 2D sulfide/oxide hybrid vdWH based on n-type molybdenum disulfide (MoS2) and p-type tin monoxide (SnO) is presented, with promising rectification, thermal-sensing, and photosensing performance. Specifically, the hybrid SnO/MoS2 vdWH shows static rectification ratio of 2 × 102 with ideality factor of 2.3, and can operate at 100 Hz with good stability. The vdWH shows good temperature stability with reversible and reproducible current levels up to 110 °C, indicating its potential for thermal sensing applications. The sensitivity of current variation is calculated to be 0.0144 dec °C−1. Finally, maximum responsivity of 8.17 mA W−1 and external quantum efficiency of 2.14% have been achieved in photovoltaic measurements. The results suggest that MoS2–SnO hybrid vdWH are promising for various sensing applications.

  10. Rearrangement of van der Waals stacking and formation of a singlet state at T = 90 K in a cluster magnet

    Energy Technology Data Exchange (ETDEWEB)

    Sheckelton, John P.; Plumb, Kemp W.; Trump, Benjamin A.; Broholm, Collin L.; McQueen, Tyrel M.

    2017-01-01

    Insulating Nb3Cl8 is a layered chloride consisting of two-dimensional triangular layers of Seff = 1/2 Nb3Cl13 clusters at room temperature. Magnetic susceptibility measurement show a sharp, hysteretic drop to a temperature independent value below T = 90 K. Specific heat measurements show that the transition is first order, with ΔS ≈ 5 J K-1 mol-1 f.u.-1, and a low temperature T-linear contribution originating from defect spins. Neutron and X-ray diffraction show a lowering of symmetry from trigonal P[3 with combining macron]m1 to monoclinic C2/m symmetry, with a change in layer stacking from –AB–AB– to –AB'–BC'–CA'– and no observed magnetic order. This lowering of symmetry and rearrangement of successive layers evades geometric magnetic frustration to form a singlet ground state. It is the lowest temperature at which a change in stacking sequence is known to occur in a van der Waals solid, occurs in the absence of orbital degeneracies, and suggests that designer 2-D heterostructures may be able to undergo similar phase transitions.

  11. Piezotronic effect in 1D van der Waals solid of elemental tellurium nanobelt for smart adaptive electronics

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

  14. Significant decrease in thermal conductivity of multi-walled carbon nanotube induced by inter-wall van der Waals interactions

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Xue; Zhou, Wu-Xing, E-mail: wuxingzhou@hnu.edu.cn; Chen, Xue-Kun; Liu, Yue-Yang; Chen, Ke-Qiu, E-mail: keqiuchen@hnu.edu.cn

    2016-05-06

    The thermal transport properties of multi-walled carbon nanotubes (MWCNTs) were investigated by using non-equilibrium molecular dynamics simulation. The results show that the thermal conductivity of MWCNTs decreases significantly comparing to that of single-walled carbon nanotubes (SWCNTs) due to the inter-wall van der Waals interactions. The more interesting is a fact that the thermal conductance of MWCNTs is significantly greater than the thermal conductance summation of each SWCNTs. This is because the thermal conductance of a carbon nanotube protected by an outer tube is much larger than that of one that is not protected. Moreover, we also studied the thermal flux distribution of MWCNTs, and found that the outer tube plays a dominant role in heat energy transfer. - Highlights: • Significant decrease in thermal conductivity of multi-walled carbon nanotube induced by inter-wall interactions. • The thermal conductivity of the inner tube is increased significantly due to protected by outer tube. • The outer tube plays a dominant role in heat energy transfer in multi-walled carbon nanotube.

  15. Quantitative relationships for the prediction of the vapor pressure of some hydrocarbons from the van der Waals molecular surface

    Directory of Open Access Journals (Sweden)

    Olariu Tudor

    2015-01-01

    Full Text Available A quantitative structure - property relationship (QSPR modeling of vapor pressure at 298.15 K, expressed as log (VP / Pa was performed for a series of 84 hydrocarbons (63 alkanes and 21 cycloalkanes using the van der Waals (vdW surface area, SW/Å2, calculated by the Monte Carlo method, as the molecular descriptor. The QSPR model developed from the subset of 63 alkanes (C1-C16, deemed as the training set, was successfully used for the prediction of the log (VP / Pa values of the 21 cycloalkanes, which was the external prediction (test subset. A QSPR model was also developed for a series composed of all 84 hydrocarbons. Both QSPR models were statistically tested for their ability to fit the data and for prediction. The results showed that the vdW molecular surface used as molecular descriptor (MD explains the variance of the majority of the log (VP / Pa values in this series of 84 hydrocarbons. This MD describes very well the intermolecular forces that hold neutral molecules together. The clear physical meaning of the molecular surface values, SW/Å2, could explain the success of the QSPR models obtained with a single structural molecular descriptor.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-05-07

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

  17. VAN DER WAALS MIXING RULES FOR THE REDLICH-KWONG EQUATION OF STATE. APPLICATION FOR SUPERCRITICAL SOLUBILITY MODELING

    Directory of Open Access Journals (Sweden)

    Ratnawati Ratnawati

    2012-02-01

    Full Text Available A solid-supercritical fluid system is highly asymmetric in terms of the size and energy differences of the components. The key point in extending a cubic equation of state to such system is on the choice of proper mixing rules. New mixing rules for the Redlich-Kwong equation of state are developed. The developement is based on the statistical-mechanical theory of the van der Waals mixing rules. The Redlich Kwong equation of state with the proposed mixing rules along with the original ones is used to predict solubilities of solids in supercritical fluid. The prediction is done with kij equal zero, as well as with optimized kij.  The results show superiority of the proposed mixing rules over the original ones. For most of the systems considered, the proposed mixing rules with the kij equal zero are closer to the experimental data than the original ones do. For 28 systems with 521 data points taken from various sources, the original and the proposed mixing rules give the overall AAD of 13.4%, while the original mixing rules give 45.9%.

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

    Science.gov (United States)

    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.

  19. A MODIFIED VAN DER PAUW SETUP FOR MEASURING THE RESISTIVITY AND THERMOPOWER OF THERMOELECTRIC MATERIALS OF VARYING THICKNESSES

    KAUST Repository

    HITCHCOCK, DALE

    2013-10-01

    In the investigation of thermoelectric (TE) materials as a practical, and efficient, means of power generation/ refrigeration nearly ninety percent of the possible high-efficient binary compounds have been evaluated. But only a few proved to be useful such as Bi2Te3 alloys, PbTe and SiGe to name the most important materials. Therefore, in order to expand the research of high-efficiency TE materials new compounds and methods of efficiency optimization must be explored. There currently exist a vast number of uninvestigated ternary and quaternary materials that could be potential high-efficiency thermoelectric materials. The device and methodology discussed herein deal with rapidly measuring both the electrical resistivity and the Seebeck coefficient of thermoelectric materials, at a set temperature of T ≈ 300 K. Using nontraditional resistivity measurements and rapid, room-temperature thermopower measurements, a reliable and time-efficient means of gauging the power factor (defined below) values of newly synthesized thermoelectric materials is achievable. Furthermore, the efficacy of the van der Pauw technique for measuring the resistivity of thermoelectric materials has been verified. © World Scientific Publishing Company.

  20. Modulation of interfacial electronic properties in PbI2 and BN van der Waals heterobilayer via external electric field

    Science.gov (United States)

    Ma, Yaqiang; Zhao, Xu; Niu, Mengmeng; Dai, Xianqi; Li, Wei; Wang, Xiaolong; Zhao, Mingyu; Wang, Tianxing; Tang, Yanan

    2017-07-01

    The interfacial electronic properties of PbI2 and BN van der Waals (vdW) heterobilayer are explored by using density functional theory (DFT) method. An intrinsic type-II heterostructure with a wide bandgap is demonstrated. The spatial separation of the lowest energy electron-hole pairs can be actualised and make PbI2/BN heterostructure as a good candidate for applications in optoelectronics and solar cell. A simulation of Efield is actualized to modify its electronic properties. Band alignment converts from type-II to type-I heterostructure separated by a forward voltage with the value of about 0.07 V/Å. Three regions implying different Efield-sensitive properties are obtained from the variations of bandgap with Efield. The charge redistribution with an Efield is mainly on the surface of PbI2 and BN layers as well as the amount of electrons depends on the strength of Efield. In addition, the PbI2/BN heterobilayer exhibits more outstanding optical conductivity capability. Our results could bring forward a new perspective on sensor and shed light on the design of novel nano- and optoelectronics based on the PbI2/BN vdW heterostructure.

  1. Effect of the van der Waals interaction on the electron energy-loss near edge structure theoretical calculation.

    Science.gov (United States)

    Katsukura, Hirotaka; Miyata, Tomohiro; Tomita, Kota; Mizoguchi, Teruyasu

    2017-07-01

    The effect of the van der Waals (vdW) interaction on the simulation of the electron energy-loss near edge structure (ELNES) by a first-principles band-structure calculation is reported. The effect of the vdW interaction is considered by the Tkatchenko-Scheffler scheme, and the change of the spectrum profile and the energy shift are discussed. We perform calculations on systems in the solid, liquid and gaseous states. The transition energy shifts to lower energy by approximately 0.1eV in the condensed (solid and liquid) systems by introducing the vdW effect into the calculation, whereas the energy shift in the gaseous models is negligible owing to the long intermolecular distance. We reveal that the vdW interaction exhibits a larger effect on the excited state than the ground state owing to the presence of an excited electron in the unoccupied band. Moreover, the vdW effect is found to depend on the local electron density and the molecular coordination. In addition, this study suggests that the detection of the vdW interactions exhibited within materials is possible by a very stable and high resolution observation. Copyright © 2016 Elsevier B.V. All rights reserved.

  2. L.J. van der Veen et S. Bodinga-bwa-Bodinga. Gedandedi sa Geviya/ Dictionnaire Geviya?Fran?ais

    Directory of Open Access Journals (Sweden)

    P.A. Mavoungou

    2011-10-01

    Full Text Available La parution aux ?ditions Peeters de l'ouvrage de r?f?rence lexicographique intitul? Gedandedi sa Geviya/Dictionnaire Geviya?Fran?ais (en abr?g? DGF dans les reste de l'article a ?t? accueilli avec joie et fiert? aussi bien par les locuteurs geviya1 en particulier que par les Gabonais en g?n?ral. Ce dictionnaire, r?sultat d'une longue et fructueuse collaboration scientifique entre Lolke van der Veen et S?bastien Bodinga-bwa-Bodinga, marque le d?but d'une nouvelle ?re dans la r?daction des dictionnaires au Gabon. En effet, la majorit? des ouvrages de r?f?rence lexicographique disponibles dans les langues gabonaises sont des dictionnaires bilingues r?dig?s par les missionnaires catholiques et protestants ou par les administrateurs coloniaux dans la p?riode allant de 1800 ? 1960, date de l'accession du Gabon ? la souverainet? internationale (Nyangone Assam et Mavoungou 2000, Mavoungou 2001.

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

    Science.gov (United States)

    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

  4. Single Photon Ionization Mass Spectroscopy of Hydrogen Bonded and van der Waals Cluster Systems Using a Capillary Discharge Soft X-Ray Laser

    Science.gov (United States)

    Heinbuch, S.; Dong, F.; Bernstein, E. R.; Rocca, J. J.

    We report the first use of a soft x-ray laser in photochemistry studies. A 46.9 nm capillary discharge soft x-ray laser was used to study hydrogen bonded and van der Waals cluster systems. The study of van der Waals cluster formation and growth in the gas phase can contribute to the understanding of solvation processes, solvation dynamics, and the nucleation and growth of small clusters. The comparative investigation of water, methanol, and ammonia clusters is of importance because these clusters demonstrate a wide range of van der Waals interactions and hydrogen bonding: water clusters are very strongly and dominantly hydrogen bonded; methanol clusters somewhat less so; and ammonia clusters perhaps not at all. Sulfur dioxide is the major contributor to acid rain and a generator of soot. The process of SO2 and water forming acid rain has been studied for some time in order to determine the atmospheric mechanism for this environmental issue. Carbon dioxide is the major gas phase pollutant responsible for the "green house effect" of the atmosphere. Many experiments employing supersonic expansion coupled with mass spectroscopic detection have been conducted in order to study monomeric and clustered structure and behavior of each of these systems. Spectroscopic and photochemical properties of the systems should be related to cluster structure. However, one of the most serious problems in the investigation of the distribution of neutral hydrogen-bonded and van der Waals clusters is the fragmentation or the intra-cluster ion-molecule reactions to the protonated cluster ions. Electron Impact (EI) ionization usually suffers considerably from fragmentation of parent cluster ions on account of the large excess energies during the ionization process. Multiphoton ionization (MPI) processes result in the predissociation of the neutral clusters before ionization. Single photon ionization is a more "gentle" way to study hydrogen-bonded and Van der Waals clusters since less

  5. [Dentistry in the Middle Ages in the low lands 6. "Van enen ontbonden tant ende van die vuyle verve der tanden"].

    Science.gov (United States)

    Jonkman, E J; Eijkman, M A J

    2015-06-01

    Professoren waren vroeger – en zijn dat wellicht nog – dol op rijtjes, bijvoorbeeld van symptomen en therapieën, die dan op een tentamen gevraagd konden worden. Dat is niets nieuws onder de zon. Ook de middeleeuwse chirurgen structureerden meestal hun betoog om een rij van oorzaken en een rij van therapeutische mogelijkheden. Zo ook bij de ontbonden, dat wil zeggen de loszittende, tand. In moderne termen lijkt hier de parodontologie aan de orde te komen.

  6. Thermodynamics of hydrogen bonding and van der Waals interactions of organic solutes in solutions of imidazolium based ionic liquids: “Structure-property” relationships

    International Nuclear Information System (INIS)

    Varfolomeev, Mikhail A.; Khachatrian, Artashes A.; Akhmadeev, Bulat S.; Solomonov, Boris N.

    2016-01-01

    Highlights: • Solution enthalpies of organic solutes in imidazolium based ionic liquids were measured. • van der Waals interactions scale of imidazolium based ionic liquids was proposed. • Enthalpies of solvation of organic solutes in ionic liquids were determined. • Hydrogen bond enthalpies of organic solutes with ionic liquids were calculated. • Relationships between structure of ionic liquids and thermochemical data were obtained. - Abstract: In the present work thermochemistry of intermolecular interactions of organic compounds in solutions of imidazolium based ionic liquids (ILs) has been studied using solution calorimetry method. Enthalpies of solution at infinite dilution of non-polar (alkanes, aromatic hydrocarbons) and polar (alcohols, amides, and etc.) organic solutes in two ionic liquids 1-butyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium trifluoromethanesulfonate were measured at 298.15 K. The scale of van der Waals interactions of imidazolium based ILs has been proposed on the basis of solution enthalpies of n-alkanes in their media. The effect of the cation and anion structure of ILs on the enthalpies of solvation was analyzed. Enthalpies of hydrogen bonding of organic solutes with imidazolium based ILs were determined. It has been shown that these values are close to zero for proton acceptor solutes. At the same time, enthalpies of hydrogen bonding of proton donor solutes with ionic liquids are increased depending the anion: tetrafluoroborate ≈ bis(trifluoromethylsulfonyl)imide < 2-(2-methoxyethoxy)ethyl sulfate < trifluoromethanesulfonate. Enthalpies of van der Waals interactions and hydrogen bonding in the solutions of imidazolium based ionic liquids were compared with the same data for molecular solvents.

  7. Bifurcations of new multi soliton solutions of the van der Waals normal form for fluidized granular matter via six different methods

    Science.gov (United States)

    Lu, Dianchen; Seadawy, Aly R.; Khater, Mostafa M. A.

    In this article, we study one of the most popular models in nature and also industrial which is the van der Waals normal form for the fluidized granular matter. Understanding of static and dynamic property for these kinds of the models is very important in many aspects of industrial from pharmaceuticals to civil engineering and also some basic physical phenomena like those studied in geophysics. This model explains the phase separation phenomenon. We apply six different methods for this model to obtained the traveling and solitary wave solutions. We make the comparison between obtained solutions with each of them and also with obtained solutions with different methods.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-03-01

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

  9. Output-only parameter identification of a colored-noise-driven Van-der-Pol oscillator: Thermoacoustic instabilities as an example

    Science.gov (United States)

    Bonciolini, Giacomo; Boujo, Edouard; Noiray, Nicolas

    2017-06-01

    The problem of output-only parameter identification for nonlinear oscillators forced by colored noise is considered. In this context, it is often assumed that the forcing noise is white, since its actual spectral content is unknown. The impact of this white-noise forcing assumption upon parameter identification is quantitatively analyzed. First, a Van-der-Pol oscillator forced by an Ornstein-Uhlenbeck process is considered. Second, the practical case of thermoacoustic limit cycles in combustion chambers with turbulence-induced forcing is investigated. It is shown that in both cases, the system parameters are accurately identified if time signals are appropriately band-pass-filtered around the oscillator eigenfrequency.

  10. Effect of temperature and density fluctuations on the spatially heterogeneous dynamics of glass-forming Van der Waals liquids under high pressure.

    Science.gov (United States)

    Koperwas, K; Grzybowski, A; Grzybowska, K; Wojnarowska, Z; Sokolov, A P; Paluch, M

    2013-09-20

    In this Letter, we show how temperature and density fluctuations affect the spatially heterogeneous dynamics at ambient and elevated pressures. By using high-pressure experimental data for van der Waals liquids, we examine contributions of the temperature and density fluctuations to the dynamics heterogeneity. We show that the dynamic heterogeneity decreases significantly with increasing pressure at a constant structural relaxation time (isochronal condition), while the broadening of the relaxation spectrum remains constant. This observation questions the relationship between spectral broadening and dynamic heterogeneity.

  11. Representation of phase equilibria and densities for complex systems using a van der Waals volume translated equation of state with a UNIFAC mixing rule

    Directory of Open Access Journals (Sweden)

    Osvaldo Chiavone-Filho

    2014-09-01

    Full Text Available This work investigated the applicability of the van der Waals cubic equation of state (EoS with volume translation (vdWt, using the modified Huron-Vidal (MHV2 mixing rule with the UNIFAC (UNIQUAC Functional Activity Coefficients model for describing phase equi-librium and density data for a series of complex systems over wide ranges of temperature (T and pressure (P. Some limitations were identified in the prediction of the experimental data collected, e.g., systems with highly associating components, but in general, the EoS vdWt+MHV was able to satisfactorily represent both phase equilibrium and volumetric behavior.

  12. Chaotic oscillations of the Klein-Gordon equation with distributed energy pumping and van der Pol boundary regulation and distributed time-varying coefficients

    Directory of Open Access Journals (Sweden)

    Bo Sun

    2014-09-01

    Full Text Available Consider the Klein-Gordon equation with variable coefficients, a van der Pol cubic nonlinearity in one of the boundary conditions and a spatially distributed antidamping term, we use a variable-substitution technique together with the analogy with the 1-dimensional wave equation to prove that for the Klein-Gordon equation chaos occurs for a class of equations and boundary conditions when system parameters enter a certain regime. Chaotic and nonchaotic profiles of solutions are illustrated by computer graphics.

  13. Behavior of quasinormal modes and Van der Waals-like phase transition of charged AdS black holes in massive gravity

    Energy Technology Data Exchange (ETDEWEB)

    Zou, De-Cheng; Yue, Ruihong [Yangzhou University, Center for Gravitation and Cosmology, College of Physical Science and Technology, Yangzhou (China); Liu, Yunqi [Huazhong University of Science and Technology, School of Physics, Wuhan (China)

    2017-06-15

    In this work, we utilize the quasinormal modes (QNMs) of a massless scalar perturbation to probe the Van der Waals-like small and large black holes (SBH/LBH) phase transition of charged topological Anti-de Sitter (AdS) black holes in four-dimensional massive gravity. We find that the signature of this SBH/LBH phase transition is detected in the isobaric as well as in the isothermal process. This further supports the idea that the QNMs can be an efficient tool to investigate the thermodynamical phase transition. (orig.)

  14. New distribution records of the gall crab Opecarcinus cathyae van der Meij, 2014 (Decapoda: Brachyura: Cryptochiridae) from the Red Sea, Maldives and Japan

    KAUST Repository

    Meij, Sancia E. T.

    2016-11-12

    The gall crab Opecarcinus cathyae van der Meij, 2014 has been reported from various localities in Indonesia and Malaysia. Recent surveys in the Red Sea, Maldives and Japan yielded additional specimens of O. cathyae, considerably expanding the known distribution range of this species to the east and west. The identity of O. cathyae was confirmed based on COI sequence data, revealing identical haplotypes for the Red Sea, Maldivian and Japanese material and three haplotypes in the Indonesian material. Opecarcinus cathyae has one of the widest known recorded distribution ranges for all gall crab species.

  15. Generation of “bastard” molecular ions from van der Waals clusters: Arn(C2Cl4)m+ ions, suspected interlopers in collection of solar neutrinos

    OpenAIRE

    Buelow, S. J.; Worsnop, D. R.; Herschbach, D. R.

    1981-01-01

    Gaseous molecular ions containing argon and perchlorethylene, Arn(C2Cl4)m+ in which n ≥ 1-29 and m ≥ 1-4, are produced by electron bombardment of van der Waals clusters formed by expanding an Ar/C2Cl4 mixture through a supersonic nozzle. Previous attempts to observe such ions in a high-pressure mass spectrometer were not successful, as with many other (“bastard”) ions that similarly lack a stable chemically bound neutral parent molecule. This is probably due to dissociation induced by the lar...

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

    DEFF Research Database (Denmark)

    Fernández, Berta; Henriksen, Christian; Farrelly, David

    2013-01-01

    A refined CCSD(T) intermolecular potential energy surface is developed for the He-C2H2 van der Waals complex. For this, 206 points on the intermolecular potential energy surface, evaluated using the CCSD(T) method and the aug-cc-pVQZ basis set extended with a set of 3s3p2d1f1g midbond functions...... previously by Munteanu and Fernández (J. Chem. Phys., 123, 014309, 2005) but differs notably at short range. The improved potential energy surface should, therefore, be particularly useful for computations of collision line broadening. Dynamical calculations of a number of rovibrational bound state energies...

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

    Science.gov (United States)

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

    2012-03-05

    Lennard-Jones (LJ) parameters are derived for classical nonpolarizable force fields for carbon nanotubes (CNTs) and for CNT-water interaction from van der Waals (vdW) enhanced density functional calculations. The new LJ parameters for carbon-carbon interactions are of the same order as those previously used in the literature but differ significantly for CNT-water interactions. This may partially originate from the fact that in addition to pure vdW interactions the polarization and other quantum mechanics effects are embedded into the LJ-potential. Copyright © 2012 Wiley Periodicals, Inc.

  18. Comments on the paper "A statistical assessment of differences and equivalences between genetically modified and reference plant varieties" by van der Voet et al. 2011

    Directory of Open Access Journals (Sweden)

    Ward Keith J

    2012-04-01

    Full Text Available Abstract van der Voet et al. (2011 describe statistical methodology that the European Food Safety Authority expects an applicant to adopt when making a GM crop regulatory submission. Key to their proposed methodology is the inclusion of reference varieties in the experimental design to provide a measure of natural variation amongst commercially grown crops. While taking proper account of natural variation amongst commercial varieties in the safety assessment of GM plants makes good sense, the methodology described by the authors is shown here to be fundamentally flawed and consequently cannot be considered fit for purpose in its current form.

  19. Comments on the paper "A statistical assessment of differences and equivalences between genetically modified and reference plant varieties" by van der Voet et al. 2011.

    Science.gov (United States)

    Ward, Keith J; Nemeth, Margaret A; Brownie, Cavell; Hong, Bonnie; Herman, Rod A; Oberdoerfer, Regina

    2012-04-25

    van der Voet et al. (2011) describe statistical methodology that the European Food Safety Authority expects an applicant to adopt when making a GM crop regulatory submission. Key to their proposed methodology is the inclusion of reference varieties in the experimental design to provide a measure of natural variation amongst commercially grown crops. While taking proper account of natural variation amongst commercial varieties in the safety assessment of GM plants makes good sense, the methodology described by the authors is shown here to be fundamentally flawed and consequently cannot be considered fit for purpose in its current form.

  20. Graphene-supported small transition-metal clusters: A density functional theory investigation within van der Waals corrections

    Science.gov (United States)

    Rêgo, Celso R. C.; Tereshchuk, Polina; Oliveira, Luiz N.; Da Silva, Juarez L. F.

    2017-06-01

    Transition-metal nanoparticles adsorbed on graphene are of great interest due to the unique catalytic and magnetic properties resulting from nanoparticles-graphene interactions. Comparison between the physical properties of such systems and those of the same nanoparticles in the gas phase is especially important. Here we report a systematic density functional investigation of the structural, energetic, and magnetic properties of small Nin, Pdn, and Ptn clusters, comprising from n =1 to 6 atoms, in the gas phase and adsorbed on a graphene monolayer. Our results show that the Ni adatom binds to the graphene hollow site, with -1.47 -meV adsorption energy, while Pd and Pt prefer the bridge sites, with -1.14 - and -1.62 -meV adsorption energies, respectively. This difference is determined by a competition between quantum and classical forces. Ni2 and Pt2 dimers bind perpendicularly on hollow and bridge sites, respectively, while Pd2 lies parallel to the graphene sheet, with each adatom on a bridge site. For larger TMn (TM = Ni , Pd , Pt ; n =3 -6 ) clusters, either two or three atoms bind to bridge graphene sites. In almost all cases the adsorbed clusters retain their gas-phase structures. The exceptions are Ni5 and Pt4, which acquire more compact structures with effective coordination number 12 and 19 % larger than in the gas phase, respectively. As the number of atoms grows, the cluster binds more weakly to the graphene, while its binding energy mounts up. Van der Waals corrections to the plain density functional theory (DFT) total energy raise the adsorption energy, but leave the cluster structure unchanged, in the gas phase or upon adsorption. Bader charge analysis shows that adsorption causes minor charge redistribution: the TM atoms bound to C atoms become positively charged, while the remaining metal atoms acquire negative charge. We have derived an approximate analytical expression for the local densities of states for the d orbitals of Ni , Pd , and Pt adatoms

  1. Combining density functional and incremental post-Hartree-Fock approaches for van der Waals dominated adsorbate-surface interactions: Ag2/graphene

    International Nuclear Information System (INIS)

    Lara-Castells, María Pilar de; Mitrushchenkov, Alexander O.; Stoll, Hermann

    2015-01-01

    A combined density functional (DFT) and incremental post-Hartree-Fock (post-HF) approach, proven earlier to calculate He-surface potential energy surfaces [de Lara-Castells et al., J. Chem. Phys. 141, 151102 (2014)], is applied to describe the van der Waals dominated Ag 2 /graphene interaction. It extends the dispersionless density functional theory developed by Pernal et al. [Phys. Rev. Lett. 103, 263201 (2009)] by including periodic boundary conditions while the dispersion is parametrized via the method of increments [H. Stoll, J. Chem. Phys. 97, 8449 (1992)]. Starting with the elementary cluster unit of the target surface (benzene), continuing through the realistic cluster model (coronene), and ending with the periodic model of the extended system, modern ab initio methodologies for intermolecular interactions as well as state-of-the-art van der Waals-corrected density functional-based approaches are put together both to assess the accuracy of the composite scheme and to better characterize the Ag 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

  2. Ab initio and semi-empirical van der Waals study of graphene-boron nitride interaction from a molecular point of view.

    Science.gov (United States)

    Caciuc, Vasile; Atodiresei, Nicolae; Callsen, Martin; Lazić, Predrag; Blügel, Stefan

    2012-10-24

    We have performed a systematic semi-empirical and ab initio van der Waals study to investigate the bonding mechanism of benzene (C(6)H(6)), triazine (C(3)N(3)H(3)) and borazine (B(3)N(3)H(6)) adsorbed on graphene and a single boron nitride (BN) sheet. The two semi-empirical approaches used to include the van der Waals (vdW) interactions in our density functional theory (DFT) calculations suggest that the strength of the molecule-surface interaction corresponds to a strong physisorption with no net charge transfer between the molecules and the corresponding substrates. This observation is strengthened by the use of first-principles non-local correlation vdW-DF functionals which provide a sound physical basis to include vdW interactions in DFT calculations. In particular we have employed two flavors of vdW-DF functionals which enabled us to determine the role of the non-local correlation effects in the molecule-surface bonding mechanism which cannot be assessed by using only semi-empirical vdW methods. Our study also reveals that the strength of the molecule-surface interaction can be influenced by the electronegativity of the B, C and N atoms.

  3. Combining density functional and incremental post-Hartree-Fock approaches for van der Waals dominated adsorbate-surface interactions: Ag2/graphene.

    Science.gov (United States)

    de Lara-Castells, María Pilar; Mitrushchenkov, Alexander O; Stoll, Hermann

    2015-09-14

    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 Ag2/graphene interaction. It extends the dispersionless density functional theory developed by Pernal et al. [Phys. Rev. Lett. 103, 263201 (2009)] by including periodic boundary conditions while the dispersion is parametrized via the method of increments [H. Stoll, J. Chem. Phys. 97, 8449 (1992)]. Starting with the elementary cluster unit of the target surface (benzene), continuing through the realistic cluster model (coronene), and ending with the periodic model of the extended system, modern ab initio methodologies for intermolecular interactions as well as state-of-the-art van der Waals-corrected density functional-based approaches are put together both to assess the accuracy of the composite scheme and to better characterize the Ag2/graphene interaction. The present work illustrates how the combination of DFT and post-HF perspectives may be efficient to design simple and reliable ab initio-based schemes in extended systems for surface science applications.

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

    Science.gov (United States)

    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.

  5. A comparative morphological revision of the aphid genus Myzaphis van der Goot, 1913 (Insecta: Hemiptera: Aphididae) revealed a new genus and three new species.

    Science.gov (United States)

    Kanturski, Mariusz; 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.

  6. WOMEN’S VIEW ON MEN’S SUCCESS: IN F. SCOTT FIRZTGERALD’S THE GREAT GATSBY AND HAMKA’S TENGGELAMNYA KAPAL VAN DER WIJCK

    Directory of Open Access Journals (Sweden)

    Itsna Syahadatud Dinurriyah

    2015-12-01

    Full Text Available Marriage is a very important step in women’s life. A woman must be sure that the groom she has chosen is the right man for her entirely life, and she must be ready for the consequence of her choice for the rest of her life. Having a handsome, well-known and prosperous husband, is a part of women’s esteem. When all those things gone, it is a condition in which a wife must show her integrity and faith to her husband. In some parts of the world, there is a belief related to the culture that when a woman gets married, she has to set her life as a house wife with high integrity since it is her dignity. She will lose her pride when she decides to be a widow by divorce. The Great Gatsby and Tenggelamnya Kapal Van Der Wijck are the literary works that propose the idea of women’s choice in marriage. They agreed to choose the different men to be their husbands because of the success they see at the time. Both works explore women’s problem when their husbands are not as success as their previous boyfriends. The word ‘choice’ then becomes very important since she cannot take what she has given back because her condition before and after marriage is different. Keywords: marriage, women’s view, men’s success, The Great Gatsby, Tenggelamnya Kapal Van Der Wijck

  7. Combining density functional and incremental post-Hartree-Fock approaches for van der Waals dominated adsorbate-surface interactions: Ag{sub 2}/graphene

    Energy Technology Data Exchange (ETDEWEB)

    Lara-Castells, María Pilar de, E-mail: Pilar.deLara.Castells@csic.es [Instituto de Física Fundamental (C.S.I.C.), Serrano 123, E-28006 Madrid (Spain); Mitrushchenkov, Alexander O. [Université Paris-Est, Laboratoire Modélisation et Simulation Multi Echelle, MSME UMR 8208 CNRS, 5 bd Descartes, 77454 Marne-la-Vallée (France); Stoll, Hermann [Institut für Theoretische Chemie, Universität Stuttgart, D-70550 Stuttgart (Germany)

    2015-09-14

    A combined density functional (DFT) and incremental post-Hartree-Fock (post-HF) approach, proven earlier to calculate He-surface potential energy surfaces [de Lara-Castells et al., J. Chem. Phys. 141, 151102 (2014)], is applied to describe the van der Waals dominated Ag{sub 2}/graphene interaction. It extends the dispersionless density functional theory developed by Pernal et al. [Phys. Rev. Lett. 103, 263201 (2009)] by including periodic boundary conditions while the dispersion is parametrized via the method of increments [H. Stoll, J. Chem. Phys. 97, 8449 (1992)]. Starting with the elementary cluster unit of the target surface (benzene), continuing through the realistic cluster model (coronene), and ending with the periodic model of the extended system, modern ab initio methodologies for intermolecular interactions as well as state-of-the-art van der Waals-corrected density functional-based approaches are put together both to assess the accuracy of the composite scheme and to better characterize the Ag{sub 2}/graphene interaction. The present work illustrates how the combination of DFT and post-HF perspectives may be efficient to design simple and reliable ab initio-based schemes in extended systems for surface science applications.

  8. Many-body study of van der Waals interaction involving lithium and rare-gas atoms and its contribution to hyperfine shifts

    International Nuclear Information System (INIS)

    Rao, B.K.; Das, T.P.

    1982-01-01

    Using linked cluster many-body perturbation theory, the frequency-dependent dipole polarizabilities a(ω) has been calculated for the lithium atom. The value of a(ω) at the static limit (169.04 a 0 3 ) matches well with other available theoretical values and experimental results. These values have been used to calculate the van der Waals constants for interactions of lithium, helium and neon atoms. The values of the van der Waals constants for dipole-dipole interaction in atomic units are -22.9, -44.8, -1465.8, 184950.0, 2011.8, 3896.5, 30.3, 59.0 and 115.1 for Li-He, Li-Ne, Li-Li, Li-Li-Li, Li-Li-He, Li-Li-Ne, Li-He-He, Li-He-Ne and Li-Ne-Ne interactions respectively. Obtaining the suitable response functions for lithium and helium atoms, the long range contribution to Δa(r)/a 0 in the study of fractional frequency shift in hyperfine pressure and temperature shift measurements is obtained as -541 atomic units. (author)

  9. Angela van der Berg

    African Journals Online (AJOL)

    MJM Venter

    weather events, droughts, floods, extreme hailstorms, gales, fires, earthquakes and the occurrence of sinkholes .... planning, storm-water management systems, gas and electricity regulation, firefighting services, environmental .... likely to occur in the municipal area, and their effects;56 a system of incentives that will promote.

  10. De beteekenis der persoonsnamen voor onze kennis van het leven en denken der oude babyloniërs en assyriërs

    NARCIS (Netherlands)

    Gemser, Berend

    1924-01-01

    a. Antiek Naamsbegrip. Als GOETHE in de Faust den hoofdpersoon, sprekende met Margarete in Marthe's tuin over God, zeggen laat: "Nenn es dann, wie du willst,.... Gefühl ist alles; Name is Schall und Rauch, umnebelnd Himmelsglut", dan is dit modern en niet antiek gevoeld. Voor den mensch van de

  11. Nutrientsamenstelling van voedingsmiddelen en berekening van opname van voedingsstoffen ten behoeve van een patient-controle onderzoek naar der ol van voeding bij het ontstaan van kanker deel 3: Aanvullingen en correcties bij nutrientwaarden behorende bij rapport nr. V 84/320/080156 CIVO/TNO

    NARCIS (Netherlands)

    Runia S; Bueno de Mesquita HB

    1989-01-01

    Ten behoeve van het internationale patient-controle onderzoek naar de relatie tussen voeding en kanker van pancreas, galblaas en galwegen (SEARCH-project IARC, Lyon) is het noodzakelijk een voedingsmiddelentabel samen te stellen, hierna te noemen SEARCH tabel, bestaande uit nutrienten die voor het

  12. Reply to "Basal buoyancy and fast-moving glaciers: in defense of analytic force balance" by C. J. van der Veen (2016)

    Science.gov (United States)

    Hughes, Terence J.

    2017-07-01

    Two approaches to ice-sheet modeling are available. Analytical modeling is the traditional approach (Van der Veen, 2016). It solves the force (momentum), mass, and energy balances to obtain three-dimensional solutions over time, beginning with the Navier-Stokes equations for the force balance. Geometrical modeling employs simple geometry to solve the force and mass balance in one dimension along ice flow (Hughes, 2012a). It is useful primarily to provide the first-order physical basis of ice-sheet modeling for students with little background in mathematics. The geometric approach uses changes in ice-bed coupling along flow to calculate changes in ice elevation and thickness, using a floating fraction ϕ along a flow line or flow band, where ϕ = 0 for sheet flow, 0 < ϕ < 1 for stream flow, and ϕ = 1 for shelf flow. An attempt is made to reconcile the two approaches.

  13. Influence of van der Waals contact forces on the deformation mechanics of thin flexible membranes assembled from metallic or semiconducting single-wall carbon nanotubes

    Science.gov (United States)

    Hobbie, Erik K.; Harris, John; Iyer, Swathi; Huh, Ji Yeon; Fagan, Jeffrey A.; Hudson, Steven D.; Stafford, Christopher M.

    2011-03-01

    Thin membranes of single-wall carbon nanotubes (SWCNTs) assembled from either metallic or semiconducting SWCNTs are subjected to the compressive strains imposed by a stretched elastic substrate, and the mechanical characteristics of the membranes are inferred from the topography of the wrinkling instability that emerges. By depositing comparable films on quartz, we also use optical (UV-Vis-NIR) absorption spectroscopy to compute the effective London dispersion spectra of the purified materials, and from these we compute the attractive part of the van der Waals potential between nanotubes of identical electronic type as a function of separation and relative orientation. We find significant differences in the strength and shape of the contact potential depending on electronic type, which in turn are evident in the modulus and yield strain measured from the deformation of the films. Supported by the NSF through CMMI-0969155 and the DOE through DE-FG36-08GO88160.

  14. Las casas patio de Mies van der Rohe: un jardín de la modernidad. Una lectura desde el concepto de pluralidad y desde la tercera naturaleza

    Directory of Open Access Journals (Sweden)

    Germán Ramírez

    2016-12-01

    Full Text Available En este artículo, el proyecto de las casas patio de Mies van der Rohe se plantea como un jardín de la modernidad; en sentido alegórico, como un espacio trascendente que supera el sentido de utilidad. Este singular y emblemático proyecto se comprende en contraposición a una visión positivista y economicista que también ha absorbido la práctica arquitectónica. La lectura que se propone de este proyecto hace una particular mediación con el concepto de pluralidad, de Hannah Arendt en su crítica a la emergencia del Mundo Moderno, y al concepto de la tercera naturaleza o el jardín como arquitectura del paisaje.

  15. Size effects in van der Waals clusters studied by spin and angle-resolved electron spectroscopy and multi-coincidence ion imaging

    International Nuclear Information System (INIS)

    Rolles, D; Pesic, Z D; Zhang, H; Bilodeau, R C; Bozek, J D; Berrah, N

    2007-01-01

    We have studied the valence and inner-shell photoionization of free rare-gas clusters by means of angle and spin resolved photoelectron spectroscopy and momentum resolving electron-multi-ion coincidence spectroscopy. The electron measurements probe the evolution of the photoelectron angular distribution and spin polarization parameters as a function of photon energy and cluster size, and reveal a strong cluster size dependence of the photoelectron angular distributions in certain photon energy regions. In contrast, the spin polarization parameter of the cluster photoelectrons is found to be very close to the atomic value for all covered photon energies and cluster sizes. The ion imaging measurements, which probe the fragmentation dynamics of multiply charged van der Waals clusters, also exhibit a pronounced cluster size dependence

  16. Effect of van der Waals interaction on energetics and transport properties of a single anthracene molecule adsorbed or confined inside a carbon nanotube

    Science.gov (United States)

    Debbichi, L.; Dappe, Y. J.; Alouani, M.

    2012-01-01

    The energetics and transport properties of a single aromatic molecule (C14H10) in interaction with a metallic single-walled carbon nanotube (SWCNT) have been studied using state-of-the-art density functional calculations. In both adsorption and encapsulation configurations, we show that the fundamental importance of the weak van der Waals (vdW) interactions is to stabilize the position of the molecule. These interactions have been treated through the ab initio linear combination of atomic orbitals (LCAO-S2) method including the vdW weak interactions. Moreover, we show that the electric conductance of the SWCNT, calculated within a nonequilibrium Green's-function formalism, is very sensitive to the position of the molecule with respect to the nanotube. The change of the conductance is explained in terms of charge transfer strength between the nanotube and the molecule.

  17. Accurate approximate analytical solutions for multi-degree-of-freedom coupled van der Pol-Duffing oscillators by homotopy analysis method

    Science.gov (United States)

    Qian, Youhua; Chen, Shengmin

    2010-10-01

    In this paper, the homotopy analysis method (HAM) is presented to establish the accurate approximate analytical solutions for multi-degree-of-freedom (MDOF) nonlinear coupled oscillators. The periodic solutions for the three-degree-of-freedom (3DOF) coupled van der Pol-Duffing oscillators are applied to illustrate the validity and great potential of this method. For given physical parameters of nonlinear systems and with different initial conditions, the frequency ω , displacements x1 (t),x2 (t) and x3 (t) can be explicitly obtained. In addition, comparisons are conducted between the results obtained by the HAM and the numerical integration (i.e. Runge-Kutta) method. It is shown that the analytical solutions of the HAM are in excellent agreement with respect to the numerical integration solutions, even if time t progresses to a certain large domain in the time history responses. Finally, the homotopy Pade technique is used to accelerate the convergence of the solutions.

  18. Sequence-specific recognition of DNA by phenanthrenequinone diimine complexes of rhodium(III): importance of steric and van der Waals interactions.

    Science.gov (United States)

    Sitlani, A; Barton, J K

    1994-10-11

    The importance of steric and van der Waals interactions in the sequence-specific recognition of DNA by [Rh(phi)]3+ complexes has been explored through the synthesis and application of a series of Rh(phi)3+ (phi: 9,10-phenanthrenequinone diimine) derivatives. [Rh(phi)]3+ complexes intercalate in the major groove of DNA via the phi ligand and promote strand scission in the presence of UV light. The complexes reported here are derivatives of the parent molecules [Rh(phi)2bpy]3+ and [Rh(bpy)2phi]3+ (bpy: 2,2'-bipyridyl). The [Rh(phi)]3+ complexes have comparable photoefficiencies; therefore, their different photocleavage patterns on 32P-end-labeled DNA fragments reflect their unique sequence-specific recognition characteristics. The shapes of the [Rh(phi)]3+ complexes are found to govern DNA recognition and reaction. Importantly and generally, the more sterically bulky complexes, containing methyl or phenyl groups on the ancillary ligands, cleave DNA at a subset of sequences recognized by their parent molecules. [Rh-(diphenylbpy)2phi]3+ specifically targets the site 5'-CTCTAGAG-3'. Furthermore, chiral discrimination in site selectivity is observed; the different isomers target different sites. delta- and lambda-[Rh(5,5'-dimethylbpy)2phi]3+ cleave specifically at sites that are defined by the consensus sequences 5'-C-T-N-G-3' and 5'-A-C/G-T-C/G-3', respectively. The sequence selectivities may be understood on the basis of both negative steric clashes and positive van der Waals interactions between methyl groups on the metal complex and thymine methyl groups in the DNA major groove.

  19. Revisiting van der Waals like behavior of f(R AdS black holes via the two point correlation function

    Directory of Open Access Journals (Sweden)

    Jie-Xiong Mo

    2017-05-01

    Full Text Available Van der Waals like behavior of f(R AdS black holes is revisited via two point correlation function, which is dual to the geodesic length in the bulk. The equation of motion constrained by the boundary condition is solved numerically and both the effect of boundary region size and f(R gravity are probed. Moreover, an analogous specific heat related to δL is introduced. It is shown that the T−δL graphs of f(R AdS black holes exhibit reverse van der Waals like behavior just as the T−S graphs do. Free energy analysis is carried out to determine the first order phase transition temperature T⁎ and the unstable branch in T−δL curve is removed by a bar T=T⁎. It is shown that the first order phase transition temperature is the same at least to the order of 10−10 for different choices of the parameter b although the values of free energy vary with b. Our result further supports the former finding that charged f(R AdS black holes behave much like RN-AdS black holes. We also check the analogous equal area law numerically and find that the relative errors for both the cases θ0=0.1 and θ0=0.2 are small enough. The fitting functions between log⁡|T−Tc| and log⁡|δL−δLc| for both cases are also obtained. It is shown that the slope is around 3, implying that the critical exponent is about 2/3. This result is in accordance with those in former literatures of specific heat related to the thermal entropy or entanglement entropy.

  20. De Spieghel in beeld. Hendrik Herps Spieghel der volcomenheit in Jezus en de ziel van Jan Luyken

    NARCIS (Netherlands)

    Dietz, F.M.; Müller, J.

    2012-01-01

    This article focuses on an unknown source of Jan Luyken’s religious emblem book Jezus en de ziel (1678): the Spieghel der volcomenheit by the medieval mystic Hendrik Herp. Luyken reuses the Spieghel in a literal but creative way; Biblical quotes and themes from the Spieghel are combined with new

  1. Die invloed van doelwitstelling op prestasie

    Directory of Open Access Journals (Sweden)

    J. G. A. Louw

    1985-11-01

    Ofskoon die meeste navorsing Locke se doelwitstellingsteorie ondersteun, is bepaalde afwykings teengekom wat nie op 'n bevredigende wyse verklaar kan word nie. Die resultate van hierdie studie dui daarop dat 'n toename in doelwitmoeilikheidsgraad nie altyd tot ‘n ooreenstemmende toename in prestasie lei nie. Hierdie resultaat kon ook nie op grond van 'n gebrek aan doelwitaanvaarding verklaar word nie. Daar is voorts gevind dat die wyse waarop 'n nie-spesifieke doelwit gestel word, 'n beduidende invloed op prestasie kan hê. Finansiële aansporings blyk ook 'n onafhanklike invloed op prestasie te hê. Bepaalde aspekte van Locke se teorie word dus deur bogenoemde resultate bevraagteken. Aanbevelings vir verdere navorsing word ten slotte gedoen.

  2. Genetiese parameters van speenkafrf^ eienskappe by ...

    African Journals Online (AJOL)

    Genetiese en. Omgewingsparameters van 'n VIeisraskudde. Ph.D.-tesis,. Univ. van die Oranje-Vrystaat. VAN MARLE, J., 1964. Untersuchungen tiber Einfltisse von. Umwelt und Erbanlage auf die Gewichtsentwicklung von. Fleischrinden unter extensiven Weidebedingungen der. Versuchstation Armoedsvlakte in Stidafrika.

  3. Zeeland geeft glastuinbouw belangrijke rol in Biopark Terneuzen (Bram van der Maas: "Ontzorgd telen is het uitgangspunt")

    NARCIS (Netherlands)

    Staalduinen, van J.; Maas, van der A.A.

    2008-01-01

    Biopark Terneuzen is een ambitieus plan voor integrale gebiedsontwikkeling, waarin industrie en glastuinbouw centraal staan. De industrie voorziet 160 ha kassen van restwarmte en CO2 wat de milieubelasting vermindert. Het draagvlak voor de plannen is groot en zo'n twintig telers hebben concrete

  4. Photochemistry of xenon-halogen Van der Waals complexes (X2 = Cl2, Br2, I2): evidence for the intermediate states in the (Xe-X2)*→ XeX* + X reaction

    International Nuclear Information System (INIS)

    Boivineau, Michel

    1987-01-01

    This research thesis addresses the reactivity of excited states of xenon-halogen Van der Waals complexes (Cl 2 , Br 2 , I 2 ) submitted to a multi-photonic excitation. The objective of this study is, by means of a specific experimental approach, to highlight the R*+ X 2 *- to better understand the reaction mechanism, and to study the reactivity of rare gas/halogen systems depending on the halogen nature. After having reported a bibliographical study on each studied system, the author describes the experimental system, reports and discusses experimental results obtained on the different complex systems (chlorine-, bromine- or iodine-based). He finally comments a possible and original application of these works in the development of an excimer laser with a new active medium (the rare gas/halogen Van der Waals complex) which would allow a continuous operation and an easy discharge production [fr

  5. Durabilidad natural y descripción anatómica de la madera de la especie Caryodaphnopsis cogolloi Van der Werf

    Directory of Open Access Journals (Sweden)

    César Polanco Tapia

    2014-06-01

    Full Text Available Se realizó la descripción anatómica de la madera de la especie Caryodaphnopsis cogolloi van der Werff., describiendo las principales características xilológicas de la especie, identificadas en los planos transversal y longitudinal (tangencial y radial de la madera. Además, se determinó la durabilidad natural de la especie Caryodaphnopsis cogolloi Van der Werff mediante el ensayo acelerado de laboratorio, utilizando las metodologías soil block, establecida por la norma NTC 1127, y agar block, establecida por la norma EN 350-1, y los hongos de pudrición Trametes versicolor y Gloeophyllum trabeum. La durabilidad fue determinada mediante pérdida de peso y estudio de las características de degradación de los hongos durante cuatro meses de incubación en la madera, estudiando cada mes el mecanismo de colonización, el desarrollo de los hongos y sus características de crecimiento, así como sus efectos sobre la pared celular. Al finalizar el periodo de exposición se determinó que la madera es muy resistente tanto al ataque del hongo de pudrición blanca como al de pudrición marrón, reportando pérdidas de peso promedio en soil block de 5.1 % para el primer hongo y 6.1 % para el segundo, y de 5.9 % para los dos hongos en agar block. Los patrones de degradación de los hongos en la madera mostraron que T. versicolor erosionó la pared celular y generó el ensanchamiento de las punteaduras en algunas células, mientras que G. trabeum produjo la disminución del espesor de las paredes celulares en pocas células. Este estudio se reporta como el primero en durabilidad natural para la especie C. cogolloi.

  6. Tapices de Escenas mitológicas tejidos en los talleres bruselenses de Jacques van der Borcht (h. 1650-h.1709-1713 y Albert Auwercx (1629-1709: Nueva documentación

    Directory of Open Access Journals (Sweden)

    García Calvo, Margarita

    2016-09-01

    Full Text Available This article is based on previously unpublished documentation for two tapestries of mythological scenes woven in the well-known workshops of Albert Auwercx and Jacques van der Borcht. A set of tapestries signed by van der Borcht in the Kunsthistorisches Museum, Vienna, corresponds for the most part with those described in this document, which also provides interesting information concerning the painters who participated in designing the models for this series.En este artículo se aporta una documentación inédita sobre dos tapicerías de Escenas mitológicas tejidas en las conocidas manufacturas de Albert Auwercx y de Jacques van der Borcht. Con la firma de este segundo tejedor se conserva en Viena (Kunsthistorisches Museum un conjunto de tapices, que se corresponde en su mayoría con los descritos en este documento, que proporciona además interesantes novedades acerca de los pintores que participaron en el diseño de los modelos de esta serie.

  7. Ultrastructural analysis of glands located in the wall of the congenital fistulae of the lower lip of patients with Van der Woude syndrome Análise ultra-estrutural das glândulas localizadas na parede da fístula congênita de lábio inferior de pacientes com a síndrome de Van der Woude

    Directory of Open Access Journals (Sweden)

    Mirian Aparecida Onofre

    2003-09-01

    Full Text Available The objective of the present study was to evaluate the glands of wall of congenital fistulae of the lower lip with the transmission electron microscope in order to characterize their microstructural pattern. Thin section of Araldite resin embedded congenital fistulae of the lower lip of four patients with Van der Woude syndrome from the Hospital de Reabilitação de Anomalias Craniofaciais da Universidade de São Paulo, Bauru, SP, were analyzed with a transmission electron microscope. The results showed that the glands were mostly made by typical mucous acini exhibiting, with certain frequency, myoepithelial cells surrounding them. In some of lobules, a few acini smaller than the typical mucous, showed granules of moderate electron density or containing a dense core or exhibiting small dense spherule and predominance granular material. These granules resemble to described recently by others in various human minor salivary glands. We concluded that glands associated with congenital fistula of lower lip of patients with Van der Woude syndrome, in spite of being located in vermilion border of the lip, showed at the transmission electron microscope characteristics of labial minor salivary gland, i.e, are mostly mucous with a few seromucous units, while typical seromucous demilunes are not present.O objetivo do presente estudo foi avaliar a ultraestrutura de glândulas da parede de fístula congênita de lábio inferior ao microscópio eletrônico de transmissão para caracterizar seu padrão microestrutural. Deste modo, as fístulas congênitas de 4 pacientes com a síndrome de Van der Woude do Hospital de Reabilitação de Anomalias Craniofaciais da Universidade de Sâo Paulo, Bauru, SP, foram processadas para inclusão em resina Araldite e os cortes finos foram analisados no microscópio eletrônico de transmissão. Os resultados mostraram que as glândulas estavam constituídas por ácinos mucosos típicos exibindo com certa freqüência c

  8. Sosiaal-wetenskaplike kritiese eksegese van Nuwe-Testamentiese ...

    African Journals Online (AJOL)

    p1243322

    kritiese eksegese van Nuwe-Testamentiese tekste (Van Aarde 2007a:49-79;. 1 Andries G van Aarde is .... 6 Kyk veral die werk van die Nederlandse praktiese teoloog Johannes A van der Ven (kyk o a Van der. Ven 1993:489; vgl ook ... As mens op 30,000 voet in 'n vliegtuig vlieg, kan mens slegs die groter kenmerke van die ...

  9. Including screening in van der Waals corrected density functional theory calculations: The case of atoms and small molecules physisorbed on graphene

    International Nuclear Information System (INIS)

    Silvestrelli, Pier Luigi; Ambrosetti, Alberto

    2014-01-01

    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, H 2 , H 2 O) 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

  10. The inherent transport anisotropy of rutile tin dioxide (SnO2) determined by van der Pauw measurements and its consequences for applications

    Science.gov (United States)

    Bierwagen, Oliver; Galazka, Zbigniew

    2018-02-01

    The anisotropic electron mobility of unintentionally doped, single crystalline, bulk, rutile SnO2(100) and (110) wafers is investigated by van der Pauw-Hall measurements. The room temperature average Hall electron mobility of μ ≈ 220 cm2/V s at a Hall electron concentration of n ≈ 1018 cm-3 suggests high-quality samples. The extracted 1.26 times higher mobility in the c-direction than perpendicular to it is in very good agreement with the corresponding anisotropy of the effective electron mass, which is 1.28 times higher perpendicular to c than parallel to c, suggesting rather isotropic scattering mechanisms. At temperatures below 100 K, a higher mobility anisotropy is found and tentatively attributed to low-angle grain boundaries with a surprisingly low energy barrier. Thus, the efficiency of mobility-sensitive applications, such as field effect transistors, increases by aligning the transport direction with the c-direction of the crystal. For transparent contact applications, such as Sb- or F-doped SnO2 (termed "ATO" or "FTO," respectively), this benefit is expected to be even larger due to the increasing effective mass anisotropy with the increasing electron concentration.

  11. Efficient band structure modulations in two-dimensional MnPSe3/CrSiTe3 van der Waals heterostructures

    Science.gov (United States)

    Pei, Qi; Wang, Xiaocha; Zou, Jijun; Mi, Wenbo

    2018-05-01

    As a research upsurge, van der Waals (vdW) heterostructures give rise to numerous combined merits and novel applications in nanoelectronics fields. Here, we systematically investigate the electronic structure of MnPSe3/CrSiTe3 vdW heterostructures with various stacking patterns. Then, particular attention of this work is paid on the band structure modulations in MnPSe3/CrSiTe3 vdW heterostructures via biaxial strain or electric field. Under a tensile strain, the relative band edge positions of heterostructures transform from type-I (nested) to type-II (staggered). The relocation of conduction band minimum also brings about a transition from indirect to direct band gap. Under a compressive strain, the electronic properties change from semiconducting to metallic. The physical mechanism of strain-dependent band structure may be ascribed to the shifts of the energy bands impelled by different superposition of atomic orbitals. Meanwhile, our calculations manifest that band gap values of MnPSe3/CrSiTe3 heterostructures are insensitive to the electric field. Even so, by applying a suitable intensity of negative electric field, the band alignment transition from type-I to type-II can also be realized. The efficient band structure modulations via external factors endow MnPSe3/CrSiTe3 heterostructures with great potential in novel applications, such as strain sensors, photocatalysis, spintronic and photoelectronic devices.

  12. Reactivity of phosphorene with a 3d element trioxide (CrO3) considering van der Waals molecular interactions: a DFT-D2 study.

    Science.gov (United States)

    Rubio-Pereda, Pamela; Cocoletzi, Gregorio H

    2017-02-01

    First-principle calculations are performed to investigate the interaction between clean black phosphorene and the CrO 3 molecule which is known to be a powerful oxidizer and a suspected carcinogen. Van der Waals forces are included in all calculations through empirical corrections. Energetics studies are first done to determine the structural stability. Then charge density, Löwdin population analysis and electronic states are evaluated. Results show that the CrO 3 molecule, with an acceptor electron character, is chemisorbed on the phosphorene surface inducing minimal geometrical distortions, however, after adsorption, a partial charge gradient is produced between the P atoms located at the phosphorene upper and lower planes. Furthermore, variations on the CrO 3 concentration causes different interaction strengths. At high concentrations of adsorbed CrO 3 molecules, the interaction with the surface becomes stronger due to an increased steric effect between neighboring molecules. Nevertheless, this effect along with the geometrical distortions produced on the phosphorene structure, due to the large number of molecules adsorbed, leads to a decrement on the adsorption energy. It is expected that the reported results may render phosphorene as a promising material for application as a gas sensor.

  13. Centimeter Scale Patterned Growth of Vertically Stacked Few Layer Only 2D MoS2/WS2 van der Waals Heterostructure.

    Science.gov (United States)

    Choudhary, Nitin; Park, Juhong; Hwang, Jun Yeon; Chung, Hee-Suk; Dumas, Kenneth H; Khondaker, Saiful I; Choi, Wonbong; Jung, Yeonwoong

    2016-05-05

    Two-dimensional (2D) van der Waal (vdW) heterostructures composed of vertically-stacked multiple transition metal dichalcogenides (TMDs) such as molybdenum disulfide (MoS2) and tungsten disulfide (WS2) are envisioned to present unprecedented materials properties unobtainable from any other material systems. Conventional fabrications of these hybrid materials have relied on the low-yield manual exfoliation and stacking of individual 2D TMD layers, which remain impractical for scaled-up applications. Attempts to chemically synthesize these materials have been recently pursued, which are presently limited to randomly and scarcely grown 2D layers with uncontrolled layer numbers on very small areas. Here, we report the chemical vapor deposition (CVD) growth of large-area (>2 cm(2)) patterned 2D vdW heterostructures composed of few layer, vertically-stacked MoS2 and WS2. Detailed structural characterizations by Raman spectroscopy and high-resolution/scanning transmission electron microscopy (HRTEM/STEM) directly evidence the structural integrity of two distinct 2D TMD layers with atomically sharp vdW heterointerfaces. Electrical transport measurements of these materials reveal diode-like behavior with clear current rectification, further confirming the formation of high-quality heterointerfaces. The intrinsic scalability and controllability of the CVD method presented in this study opens up a wide range of opportunities for emerging applications based on the unconventional functionalities of these uniquely structured materials.

  14. Research Update: Van-der-Waals epitaxy of layered chalcogenide Sb2Te3 thin films grown by pulsed laser deposition

    Directory of Open Access Journals (Sweden)

    Isom Hilmi

    2017-05-01

    Full Text Available An attempt to deposit a high quality epitaxial thin film of a two-dimensionally bonded (layered chalcogenide material with van-der-Waals (vdW epitaxy is of strong interest for non-volatile memory application. In this paper, the epitaxial growth of an exemplary layered chalcogenide material, i.e., stoichiometric Sb2Te3 thin films, is reported. The films were produced on unreconstructed highly lattice-mismatched Si(111 substrates by pulsed laser deposition (PLD. The films were grown by vdW epitaxy in a two-dimensional mode. X-ray diffraction measurements and transmission electron microscopy revealed that the films possess a trigonal Sb2Te3 structure. The single atomic Sb/Te termination layer on the Si surface was formed initializing the thin film growth. This work demonstrates a straightforward method to deposit vdW-epitaxial layered chalcogenides and, at the same time, opens up the feasibility to fabricate chalcogenide vdW heterostructures by PLD.

  15. Free volume from positron lifetime and pressure-volume-temperature experiments in relation to structural relaxation of van der Waals molecular glass-forming liquids.

    Science.gov (United States)

    Dlubek, G; Shaikh, M Q; Rätzke, K; Paluch, M; Faupel, F

    2010-06-16

    Positron annihilation lifetime spectroscopy (PALS) is employed to characterize the temperature dependence of the free volume in two van der Waals liquids: 1, 1'-bis(p-methoxyphenyl)cyclohexane (BMPC) and 1, 1'-di(4-methoxy-5-methylphenyl)cyclohexane (BMMPC). From the PALS spectra analysed with the routine LifeTime9.0, the size (volume) distribution of local free volumes (subnanometer size holes), its mean, [v(h)], and mean dispersion, σ(h), were calculated. A comparison with the macroscopic volume from pressure-volume-temperature (PV T) experiments delivered the hole density and the specific hole free volume and a complete characterization of the free volume microstructure in that sense. These data are used in correlation with structural (α) relaxation data from broad-band dielectric spectroscopy (BDS) in terms of the Cohen-Grest and Cohen-Turnbull free volume models. An extension of the latter model allows us to quantify deviations between experiments and theory and an attempt to systematize these in terms of T(g) or of the fragility. The experimental data for several fragile and less fragile glass formers are involved in the final discussion. It was concluded that, for large differences in the fragility of different glass formers, the positron lifetime mirrors clearly the different character of these materials. For small differences in the fragility, additional properties like the character of bonds and chemical structure of the material may affect size, distribution and thermal behaviour of the free volume.

  16. Association study between Van der Woude Syndrome causative gene GRHL3 and nonsyndromic cleft lip with or without cleft palate in a Chinese cohort.

    Science.gov (United States)

    Wang, Yirui; Sun, Yimin; Huang, Yongqing; Pan, Yongchu; Jia, Zhonglin; Ma, Lijuan; Ma, Lan; Lan, Feifei; Zhou, Yuxi; Shi, Jiayu; Yang, Xiong; Zhang, Lei; Jiang, Hongbing; Jiang, Min; Yin, Aihua; Cheng, Jing; Wang, Lin; Yang, Yinxue; Shi, Bing

    2016-08-15

    Cleft lip with or without cleft palate (CL/P) is one of the most common birth defects worldwide and is characterized by abnormalities of the orofacial structure. Syndromic CL/P is mainly caused by Mendelian disorders such as Van der Woude Syndrome (VWS). However, >70% of CL/P cases are nonsyndromic, characterized by isolated orofacial cleft without any known syndrome. The etiology of nonsyndromic CL/P (NSCL/P) remains elusive, but it has been suggested that causative genes of syndromic CL/P might also contribute to NSCL/P. As such, the VWS causative gene IRF6 has been extensively studied in NSCL/P. Recently, GRHL3 was identified as another VWS causative gene. Thus, it may be a novel candidate gene for NSCL/P. In the present study, we genotyped 10 tag SNPs covering GRHL3 and performed association analysis with NSCL/P in 504 cases and 455 healthy controls. Our preliminary results identified rs10903078, rs4638975, and a haplotype rs10903078-rs6659209 of GRHL3 that exceeded the significance threshold (p<0.05), though none survived Bonferroni correction for multiple comparisons. As the first study between GRHL3 and NSCL/P, the contribution of this gene to NSCL/P etiology should be interpreted with caution based on existing evidence. Further, the robustness of association between GRHL3 and NSCL/P should be further validated in expanded cohorts. Copyright © 2016. Published by Elsevier B.V.

  17. Anatomic Severity, Midfacial Growth, and Speech Outcomes in Van der Woude/Popliteal Pterygium Syndromes Compared to Nonsyndromic Cleft Lip/Palate.

    Science.gov (United States)

    Reardon, Jeffrey B; Brustowicz, Katherine A; Marrinan, Eileen M; Mulliken, John B; Padwa, Bonnie L

    2015-11-01

    To summarize the clinical characteristics and surgical and speech outcomes for patients with Van der Woude/popliteal pterygium syndromes (VWS/PPS) and to compare them with a historic cohort of patients with nonsyndromic cleft lip/cleft palate (CL/P). Retrospective chart review. Tertiary care center. All patients with VWS/PPS seen at Boston Children's Hospital from 1979 to 2012: 28 patients with VWS (n = 21)/PPS (n = 7) whose mean age was 17.3 ± 10.4 years, including 18 females (64%) and 10 males (36%); 18 patients (64%) had a family history of VWS/PPS. Cleft type, operative procedures, speech, and midfacial growth. Data were compared with historic cohorts of patients with nonsyndromic CL/P treated at one tertiary care center. There were 24 patients (86%) with CP±L, Veau types I (n = 4, 17%), II (n = 4, 17%), III (n = 5, 21%), and IV (n = 11, 46%). Nine patients (38%) had palatal fistula after palatoplasty. Fourteen of 23 (61%) patients with CL/P age 5 years or older had midfacial retrusion, and 10 (43%) required a pharyngeal flap for velopharyngeal insufficiency. Fisher's exact test demonstrated higher frequencies of Veau type IV CP±L (P = .0016), bilateral CL±P (P = .0001), and complete CL±P (P palatal fistula (P clefting and higher incidences of midfacial retrusion, palatal fistula, and velopharyngeal insufficiency following primary repair as compared with nonsyndromic CL/P.

  18. Rotational spectra of the Xe-(H2O)2 van der Waals trimer: xenon as a probe of electronic structure and dynamics.

    Science.gov (United States)

    Wen, Qing; Jäger, Wolfgang

    2007-03-22

    Rotational spectra of three isotopomers of the Xe-(H2O)2 van der Waals trimer were recorded using a pulsed-nozzle, Fourier transform microwave spectrometer. Nine [nine, four] a-type and twelve [eleven, seven] b-type transitions were measured for the 132Xe-(H2O)2 [129Xe-(H2O)2, 131Xe-(H2O)2] isotopomer. The determined rotational and centrifugal distortion constants were used to extract information about the structure and vibrational motions of the complex. The nuclear quadrupole hyperfine structures due to the 131Xe (nuclear spin quantum number I=3/2) nucleus were also detected. The large value of the off-diagonal nuclear quadrupole coupling constant chiab in particular provides detailed insight into the electronic environment of the xenon atom and the orientations of the water molecules within the complex. An effective structure that best reproduces the experimental 131Xe nuclear quadrupole coupling constants is rationalized by ab initio calculations. An overall goal of this line of work is to determine how the successive solvation of a xenon atom with water molecules affects the xenon electron distribution and its intermolecular interactions. The results may provide molecular level interpretations of 129Xe NMR data from, for example, imaging experiments.

  19. A kinetic Monte Carlo simulation method of van der Waals epitaxy for atomistic nucleation-growth processes of transition metal dichalcogenides.

    Science.gov (United States)

    Nie, Yifan; Liang, Chaoping; Cha, Pil-Ryung; Colombo, Luigi; Wallace, Robert M; Cho, Kyeongjae

    2017-06-07

    Controlled growth of crystalline solids is critical for device applications, and atomistic modeling methods have been developed for bulk crystalline solids. Kinetic Monte Carlo (KMC) simulation method provides detailed atomic scale processes during a solid growth over realistic time scales, but its application to the growth modeling of van der Waals (vdW) heterostructures has not yet been developed. Specifically, the growth of single-layered transition metal dichalcogenides (TMDs) is currently facing tremendous challenges, and a detailed understanding based on KMC simulations would provide critical guidance to enable controlled growth of vdW heterostructures. In this work, a KMC simulation method is developed for the growth modeling on the vdW epitaxy of TMDs. The KMC method has introduced full material parameters for TMDs in bottom-up synthesis: metal and chalcogen adsorption/desorption/diffusion on substrate and grown TMD surface, TMD stacking sequence, chalcogen/metal ratio, flake edge diffusion and vacancy diffusion. The KMC processes result in multiple kinetic behaviors associated with various growth behaviors observed in experiments. Different phenomena observed during vdW epitaxy process are analysed in terms of complex competitions among multiple kinetic processes. The KMC method is used in the investigation and prediction of growth mechanisms, which provide qualitative suggestions to guide experimental study.

  20. Charge Transfer Effects in Naturally Occurring van der Waals Heterostructures (PbSe )1.16(TiSe2 )m (m =1 , 2)

    Science.gov (United States)

    Yao, Q.; Shen, D. W.; Wen, C. H. P.; Hua, C. Q.; Zhang, L. Q.; Wang, N. Z.; Niu, X. H.; Chen, Q. Y.; Dudin, P.; Lu, Y. H.; Zheng, Y.; Chen, X. H.; Wan, X. G.; Feng, D. L.

    2018-03-01

    van der Waals heterostructures (VDWHs) exhibit rich properties and thus has potential for applications, and charge transfer between different layers in a heterostructure often dominates its properties and device performance. It is thus critical to reveal and understand the charge transfer effects in VDWHs, for which electronic structure measurements have proven to be effective. Using angle-resolved photoemission spectroscopy, we studied the electronic structures of (PbSe )1.16(TiSe2 )m (m =1 , 2), which are naturally occurring VDWHs, and discovered several striking charge transfer effects. When the thickness of the TiSe2 layers is halved from m =2 to m =1 , the amount of charge transferred increases unexpectedly by more than 250%. This is accompanied by a dramatic drop in the electron-phonon interaction strength far beyond the prediction by first-principles calculations and, consequently, superconductivity only exists in the m =2 compound with strong electron-phonon interaction, albeit with lower carrier density. Furthermore, we found that the amount of charge transferred in both compounds is nearly halved when warmed from below 10 K to room temperature, due to the different thermal expansion coefficients of the constituent layers of these misfit compounds. These unprecedentedly large charge transfer effects might widely exist in VDWHs composed of metal-semiconductor contacts; thus, our results provide important insights for further understanding and applications of VDWHs.

  1. Understanding the role of vibrations, exact exchange, and many-body van der Waals interactions in the cohesive properties of molecular crystals

    Science.gov (United States)

    Reilly, Anthony M.; Tkatchenko, Alexandre

    2013-07-01

    The development and application of computational methods for studying molecular crystals, particularly density-functional theory (DFT), is a large and ever-growing field, driven by their numerous applications. Here we expand on our recent study of the importance of many-body van der Waals interactions in molecular crystals [A. M. Reilly and A. Tkatchenko, J. Phys. Chem. Lett. 4, 1028 (2013), 10.1021/jz400226x], with a larger database of 23 molecular crystals. Particular attention has been paid to the role of the vibrational contributions that are required to compare experiment sublimation enthalpies with calculated lattice energies, employing both phonon calculations and experimental heat-capacity data to provide harmonic and anharmonic estimates of the vibrational contributions. Exact exchange, which is rarely considered in DFT studies of molecular crystals, is shown to have a significant contribution to lattice energies, systematically improving agreement between theory and experiment. When the vibrational and exact-exchange contributions are coupled with a many-body approach to dispersion, DFT yields a mean absolute error (3.92 kJ/mol) within the coveted "chemical accuracy" target (4.2 kJ/mol). The role of many-body dispersion for structures has also been investigated for a subset of the database, showing good performance compared to X-ray and neutron diffraction crystal structures. The results show that the approach employed here can reach the demanding accuracy of crystal-structure prediction and organic material design with minimal empiricism.

  2. Ionic Intercalation in Two-Dimensional van der Waals Materials: In Situ Characterization and Electrochemical Control of the Anisotropic Thermal Conductivity of Black Phosphorus.

    Science.gov (United States)

    Kang, Joon Sang; Ke, Ming; Hu, Yongjie

    2017-03-08

    Two-dimensional van der Waals materials have shown novel fundamental properties and promise for wide applications. Here, we report for the first time an experimental demonstration of the in situ characterization and highly reversible control of the anisotropic thermal conductivity of black phosphorus. We develop a novel platform based on lithium ion batteries that integrates ultrafast optical spectroscopy and electrochemical control to investigate the interactions between lithium ions and the lattices of the black phosphorus electrode. We discover a strong dependence of the thermal conductivity on battery charge states (lithium concentrations) during the discharge/charge process. The thermal conductivity of black phosphorus is reversibly tunable over a wide range of 2.45-3.86, 62.67-85.80, and 21.66-27.58 W·m -1 ·K -1 in the cross-plan, zigzag, and armchair directions, respectively. The modulation in thermal conductivity is attributed to phonon scattering introduced by the ionic intercalation in between the interspacing layers and shows anisotropic phonon scattering mechanism based on semiclassical model. At the fully discharged state (x ∼ 3 in Li x P), a dramatic reduction of thermal conductivity by up to 6 times from that of the pristine crystal has been observed. This study provides a unique approach to explore the fundamental energy transport involving lattices and ions in the layered structures and may open up new opportunities in controlling energy transport based on novel operation mechanisms and the rational design of nanostructures.

  3. Origin of n-type conductivity in two-dimensional InSe: In atoms from surface adsorption and van der Waals gap

    Science.gov (United States)

    Wang, Hui; Shi, Jun-jie; Huang, Pu; Ding, Yi-min; Wu, Meng; Cen, Yu-lang; Yu, Tongjun

    2018-04-01

    Recently, two-dimensional (2D) InSe nanosheet becomes a promising material for electronic and optoelectronic nano-devices due to its excellent electron transport, wide bandgap tunability and good metal contact. The inevitable native point defects are essential in determining its characteristics and device performance. Here we investigate the defect formation energy and thermodynamic transition levels for the most important native defects and clarify the physical origin of n-type conductivity in unintentionally doped 2D InSe by using the powerful first-principles calculations. We find that both surface In adatom and Se vacancy are the key defects, and the In adatom, donated 0.65 electrons to the host, causes the n-type conductivity in monolayer InSe under In-rich conditions. For bilayer or few-layer InSe, the In interstitial within the van der Waals gap, transferred 0.68 electrons to InSe, is found to be the most stable donor defect, which dominates the n-type character. Our results are significant for understanding the defect nature of 2D InSe and improving the related nano-device performance.

  4. van der Waals interactions govern C-β-d-glucopyranosyl triazoles' nM inhibitory potency in human liver glycogen phosphorylase.

    Science.gov (United States)

    Kantsadi, Anastassia L; Stravodimos, George A; Kyriakis, Efthimios; Chatzileontiadou, Demetra S M; Solovou, Theodora G A; Kun, Sándor; Bokor, Éva; Somsák, László; Leonidas, Demetres D

    2017-07-01

    3-(C-Glucopyranosyl)-5aryl-1,2,4-triazoles with an aryl moiety larger than phenyl have been shown to have strong inhibitory potency (K i values in the range of upper nM) for human liver glycogen phosphorylase (hlGP), a pharmacologically relevant target for diabetes type 2. In this study we investigate in a comparative manner the inhibitory effect of the above triazoles and their respective imidazoles on hlGPa. Kinetic studies show that the imidazole derivatives are 6-8 times more potent than their corresponding triazoles. We also seek to answer how the type of the aryl moiety affects the potency in hlGPa, and by determination of the crystal structure of rmGPb in complex with the triazole derivatives the structural basis of their inhibitory efficacy is also elucidated. Our studies revealed that the van der Waals interactions between the aryl moiety and residues in a hydrophobic pocket within the active site are mainly responsible for the variations in the potency of these inhibitors. Copyright © 2017 Elsevier Inc. All rights reserved.

  5. Geskiedenis van die Geneeskunde in Pretoria*

    African Journals Online (AJOL)

    31 Jul 1971 ... Elandspoort het aan Andries van der WaIt behoort en. Daspoort aan Joggem Tweeduim Prinsloo. ... Van der Hoff en die Vierkleur, ook deur horn ontwerp, word vir die eerste keer gehys. Die eerste ... met net 'n ketting van 50 voet, en 'n verkyker tot sy beskikking. Al die strate was 80 voet breed behalwe ...

  6. OM LYNING VAN DIEREPRODUKSIESTRATEGTEd

    African Journals Online (AJOL)

    gegee het. Ek wil ook hulde bring aan wyle prof Jan. Swart, aan prof J H R Bisschop, prof F N Bonsma, prof. J W Groenewald, wyle prof A M Gericke, wyle J A. (Koos) van der Merwe, mnr Danie van Wyk, wyle Koot. Kotze, dr W A Verbeek en baie ander. Die boere van. Suid-Afrika was gelukkig dat hulle sterk leiding kon kry.

  7. Direct comparison of time-resolved Terahertz spectroscopy and Hall Van der Pauw methods for measurement of carrier conductivity and mobility in bulk semiconductors.

    Science.gov (United States)

    Alberding, Brian G; Thurber, W Robert; Heilweil, Edwin J

    2017-07-01

    Charge carrier conductivity and mobility for various semiconductor wafers and crystals were measured by ultrafast above bandgap, optically excited Time-Resolved Terahertz Spectroscopy (TRTS) and Hall Van der Pauw contact methods to directly compare these approaches and validate the use of the non-contact optical approach for future materials and in-situ device analyses. Undoped and doped silicon (Si) wafers with resistances varying over six orders of magnitude were selected as model systems since contact Hall measurements are reliably made on this material. Conductivity and mobility obtained at room temperature by terahertz transmission and TRTS methods yields the sum of electron and hole mobility which agree very well with either directly measured or literature values for corresponding atomic and photo-doping densities. Careful evaluation of the optically-generated TRTS frequency-dependent conductivity also shows it is dominated by induced free-carrier absorption rather than small probe pulse phase shifts, which is commonly ascribed to changes in the complex conductivity from sample morphology and evaluation of carrier mobility by applying Drude scattering models. Thus, in this work, the real-valued, frequency-averaged conductivity was used to extract sample mobility without application of models. Examinations of germanium (Ge), gallium arsenide (GaAs), gallium phosphide (GaP) and zinc telluride (ZnTe) samples were also made to demonstrate the general applicability of the TRTS method, even for materials that do not reliably make good contacts (e.g., GaAs, GaP, ZnTe). For these cases, values for the sum of the electron and hole mobility also compare very favorably to measured or available published data.

  8. Symmetry-adapted perturbation theory based on unrestricted Kohn-Sham orbitals for high-spin open-shell van der Waals complexes.

    Science.gov (United States)

    Hapka, Michał; Żuchowski, Piotr S; Szczęśniak, Małgorzata M; Chałasiński, Grzegorz

    2012-10-28

    Two open-shell formulations of the symmetry-adapted perturbation theory are presented. They are based on the spin-unrestricted Kohn-Sham (SAPT(UKS)) and unrestricted Hartree-Fock (SAPT(UHF)) descriptions of the monomers, respectively. The key reason behind development of SAPT(UKS) is that it is more compatible with density functional theory (DFT) compared to the previous formulation of open-shell SAPT based on spin-restricted Kohn-Sham method of Żuchowski et al. [J. Chem. Phys. 129, 084101 (2008)]. The performance of SAPT(UKS) and SAPT(UHF) is tested for the following open-shell van der Waals complexes: He···NH, H(2)O···HO(2), He···OH, Ar···OH, Ar···NO. The results show an excellent agreement between SAPT(UKS) and SAPT(ROKS). Furthermore, for the first time SAPT based on DFT is shown to be suitable for the treatment of interactions involving Π-state radicals (He···OH, Ar···OH, Ar···NO). In the interactions of transition metal dimers ((3)Σ(u)(+))Au(2) and ((13)Σ(g)(+))Cr(2) we show that SAPT is incompatible with the use of effective core potentials. The interaction energies of both systems expressed instead as supermolecular UHF interaction plus dispersion from SAPT(UKS) result in reasonably accurate potential curves.

  9. [Bodies and souls of Maxence van der Meersch. The gaze of a writer on medicine in France on the eve of the Second World War].

    Science.gov (United States)

    Vercel, R

    1997-01-01

    Maxence Van der Meersch, got the Prix Goncourt in 1937. He was an important writer between the two world wars, by his inspiration and his realism he was related to the naturalism school. His works reflect his life, from 1937, after having discovered the christian faith, he devoted his live to it and militated through his writing for his convictions. "Corps et âmes", published in 1943 is a painting of the medicine in France at the end of the thirties. When he was published the book raised up a sharp polemic, badly accepted by medical world because of its realism without concession, on another hand it was welcome by general public and litterary critics. In an university town the author stages physicians, students, nurses, administrators, politicians and many other characters to paint a vast fresco of medical world and society, during this time. In whole he gives a greater share to mental pathology with the advent of new therapeutics and to tuberculosis wich had a great medico-social importance. Taking a fancy for doctor Carton's neo hippocratics theories, he fully bound himself in his book to broadcast that he thinks to be a new medical truth and then was led to contest scientific medicine which had, for him, lost his humanity. Suffering of lung tuberculosis, holding fast to his convictions he rejected any therapeutics except his diets and died January the 13th 1951. Beside his spiritual and bound features, "Corps et âmes" the quality of documentation and the accuracy of descriptions remains a testimony about physicians and medicine at second world war eve.

  10. Spectroscopic features of the low-lying electronic states of some sodium-helium and potassium-helium van der Waals systems

    Science.gov (United States)

    Chattopadhyay, Anjan

    2011-08-01

    Configuration interaction studies on MHe and MHe2 (where M = Na, K) systems have revealed several interesting characteristics in the properties of their low-lying electronic states. Binding energy values of the 12Π1/2, 3/2 states in MHe systems are found to be lower than the values of 12Πu (1/2, 3/2) states in the He-M-He systems by a margin of more than 200 cm-1, indicating better exciplex stabilities of the latter systems. Excited states of the other variety of the linear MHe2 (M-He-He) systems are almost repulsive. The characteristic energy barrier of the first excited spin-orbit state of alkali metal-helium systems is found to be only 15 cm-1 in KHe and 19 cm-1 in He-K-He. For the Na*He and K*He exciplexes, predicted radiative lifetime values of 18.5 ns and 29.8 ns, respectively, are in excellent agreement with the experimental values. The red-tail portions of their emission bands are contributed by M*He2 exciplexes with relatively high radiative lifetimes. The repulsive excited state of 2Σ+1/2 (or 2Σ+g,1/2) symmetry in these van der Waals systems is likely to play an important role in the pumping of the blue side of the ns2S1/2 → np2P3/2 transition, which eventually may give rise to the np2P1/2 → ns2S1/2 lasing transition.

  11. A new model approach for the near-critical point region: 1. Construction of the generalized van der Waals equation of state.

    Science.gov (United States)

    Lee, Sukbae; Jeon, Joonhyeon; Kim, Wonsoo; Chair, Tong-Seek

    2008-12-11

    To date, it has been considered that all classical equations of state (EOS) have failed to describe the properties of fluids near the critical region, where the density fluctuations have a significant influence on fluid properties. In this paper, we suggest a newly constructed equation for fluid states, the generalized van der Waals (GvdW) EOS with the highly simplified Dieterici's form P = [RT/(V - b)] - a(b/V)c by a new model potential construction describing intermolecular interactions. On the basis of the model potential construction, it is shown that the a, b, and c parameters have physical interpretations as an internal pressure, a void volume, and a dimensionless value that represents an inharmonic intermolecular cell potential, respectively. As an illustration of our model approach, we initially apply it to near the critical point (cp) region, where all classical EOS descriptions have been incorporated with experimental thermodynamic data, and we obtain a table of three parameters for 12 pure normal fluids, which precisely describes thermodynamic critical values. On the basis of the basic relations between pressure and volume at the critical point, we express the corresponding EOS in terms of the c parameter, and by this means, we also obtain a theoretical vapor-liquid equilibrium (VLE) line, which closely coincides with the experimental data for several pure normal fluids near the critical region. As a result, we show that thermodynamic properties near the critical region can be described analytically by only three parameters. In addition, to validate our EOS for the temperature-differential derivatives, we show that the calculated isochoric heat capacity (Cv) of saturated argon closely coincides with the experimental data. Moreover, the possibility of a precise description with respect to the entire fluid region is also argued, in terms of the physical cases from the triple point to the ideal gas region.

  12. Investigation of the range of validity of the pairwise summation method applied to the calculation of the surface roughness correction to the van der Waals force

    Science.gov (United States)

    Gusso, André; Burnham, Nancy A.

    2016-09-01

    It has long been recognized that stochastic surface roughness can considerably change the van der Waals (vdW) force between interacting surfaces and particles. However, few analytical expressions for the vdW force between rough surfaces have been presented in the literature. Because they have been derived using perturbative methods or the proximity force approximation the expressions are valid when the roughness correction is small and for a limited range of roughness parameters and surface separation. In this work, a nonperturbative approach, the effective density method (EDM) is proposed to circumvent some of these limitations. The method simplifies the calculations of the roughness correction based on pairwise summation (PWS), and allows us to derive simple expressions for the vdW force and energy between two semispaces covered with stochastic rough surfaces. Because the range of applicability of PWS and, therefore, of our results, are not known a priori, we compare the predictions based on the EDM with those based on the multilayer effective medium model, whose range of validity can be defined more properly and which is valid when the roughness correction is comparatively large. We conclude that the PWS can be used for roughness characterized by a correlation length of the order of its rms amplitude, when this amplitude is of the order of or smaller than a few nanometers, and only for typically insulating materials such as silicon dioxide, silicon nitride, diamond, and certain glasses, polymers and ceramics. The results are relevant for the correct modeling of systems where the vdW force can play a significant role such as micro and nanodevices, for the calculation of the tip-sample force in atomic force microscopy, and in problems involving adhesion.

  13. Modulation of interfacial electronic properties in PbI{sub 2} and BN van der Waals heterobilayer via external electric field

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Yaqiang [College of Physics and Materials Science, Henan Normal University, Xinxiang 453007 (China); Zhao, Xu, E-mail: zhaoxu@htu.cn [College of Physics and Materials Science, Henan Normal University, Xinxiang 453007 (China); Niu, Mengmeng [College of Physics and Materials Science, Henan Normal University, Xinxiang 453007 (China); Dai, Xianqi, E-mail: xqdai@htu.cn [College of Physics and Materials Science, Henan Normal University, Xinxiang 453007 (China); School of Physics and Electronic Engineering, Zhengzhou Normal University, Zhengzhou, Henan 450044 (China); Li, Wei [College of Physics and Materials Science, Henan Normal University, Xinxiang 453007 (China); Wang, Xiaolong [College of Physics and Materials Science, Henan Normal University, Xinxiang 453007 (China); State Key Laboratory of Information Photonics and Optical Communication, Beijing University Posts and Telecommunications, Beijing 100876 (China); Zhao, Mingyu; Wang, Tianxing [College of Physics and Materials Science, Henan Normal University, Xinxiang 453007 (China); Tang, Yanan [School of Physics and Electronic Engineering, Zhengzhou Normal University, Zhengzhou, Henan 450044 (China)

    2017-07-31

    Highlights: • An atomically type-II heterobilayer which is suitable for optoelectronics and solar cell with wide bandgap was formed. • The charge redistribution is mainly on the surface and the amount of electrons depends on the strength of E{sub field}. • The bandgaps varying with E{sub field} can be divided into three ranges indicating different E{sub field}-sensitive which may possess potential in sensor. • Increasing the E{sub field} upon 0.07 V/Å, the band alignment converts from type-II to type-I heterojunction. - Abstract: The interfacial electronic properties of PbI{sub 2} and BN van der Waals (vdW) heterobilayer are explored by using density functional theory (DFT) method. An intrinsic type-II heterostructure with a wide bandgap is demonstrated. The spatial separation of the lowest energy electron-hole pairs can be actualised and make PbI{sub 2}/BN heterostructure as a good candidate for applications in optoelectronics and solar cell. A simulation of E{sub field} is actualized to modify its electronic properties. Band alignment converts from type-II to type-I heterostructure separated by a forward voltage with the value of about 0.07 V/Å. Three regions implying different E{sub field}-sensitive properties are obtained from the variations of bandgap with E{sub field}. The charge redistribution with an E{sub field} is mainly on the surface of PbI{sub 2} and BN layers as well as the amount of electrons depends on the strength of E{sub field}. In addition, the PbI{sub 2}/BN heterobilayer exhibits more outstanding optical conductivity capability. Our results could bring forward a new perspective on sensor and shed light on the design of novel nano- and optoelectronics based on the PbI{sub 2}/BN vdW heterostructure.

  14. Trends on band alignments: Validity of Anderson's rule in SnS2- and SnSe2-based van der Waals heterostructures

    Science.gov (United States)

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

    2018-04-01

    Van der Waals (vdW) heterostructures are promising candidates for building blocks in novel electronic and optoelectronic devices with tailored properties, since their electronic action is dominated by the band alignments upon their contact. In this work, we analyze 10 vdW heterobilayers based on tin dichalcogenides by first-principles calculations. Structural studies show that all systems are stable, and that commensurability leads to smaller interlayer distances. Using hybrid functional calculations, we derive electronic properties and band alignments for all the heterosystems and isolated two-dimensional (2D) crystals. Natural band offsets are derived from calculated electron affinities and ionization energies of 11 freestanding 2D crystals. They are compared with band alignments in true heterojunctions, using a quantum mechanical criterion, and available experimental data. For the hBN/SnSe 2 system, we show that hBN suffers an increase in band gap, while leaving almost unchanged the electronic properties of SnSe2. Similarly, MX2 (M = Mo, W; X = S, Se) over SnX2 preserve the natural discontinuities from each side of the heterobilayer. Significant charge transfer occurs in junctions with graphene, which becomes p-doped and forms an Ohmic contact with SnX2. Zirconium and hafnium dichalcogenides display stronger interlayer interactions, leading to larger shifts in band alignments with tin dichalcogenides. Significant orbital overlap is found, which creates zero conduction band offset systems. The validity of the Anderson electron affinity rule is discussed. Failures of this model are traced back to interlayer interaction, band hybridization, and quantum dipoles. The systematic work sheds light on interfacial engineering for future vdW electronic and optoelectronic devices.

  15. Cálculo do Volume Molar de um Gás de van der Waals em SCILAB: o Método Newton-Raphson na Resolução de um Problema Físico-Químico

    Directory of Open Access Journals (Sweden)

    Diogenes Filho

    2014-07-01

    Full Text Available The use of software in chemical calculations is a constant reality in both laboratories as well as in simulation processes of chemical transformations. Around addition, this publication discusses the use of the computer program in Scilab problems of chemical origin, especially in the case of calculating the molar volume of gas van der Waals forces. Discussions on the results of the use of this program with a view to the tools available for the calculation of a polynomial provide satisfactory conclusions on the use of mathematical methods in Physical Chemistry, especially the Newton-Raphson method.

  16. De Glorious Revolution van 1688 herdacht

    Directory of Open Access Journals (Sweden)

    G. Groenhuis

    1990-01-01

    Full Text Available A.G.H Bachrach, Willem III, de stadhouder-koning en zijn tijd R. Bastiaanse, H. Bots, Glorieuze Revolutie. De wereld van Willem & Mary. Glorious Revolution. The world of William & Mary M. van Doorn, Koning-stadhouder Willem III, triomfator. De triomfale intocht in Den Haag in 1691 D. Jacques, A.J. van der Horst, De tuinen van Willem en Mary A. van der Kuijl, Glorieuze overtocht. De expeditie van Willem III naar Engeland in 1688 J. Kuijpers, A.D. Renting, Boeken van Oranje. De Oranje-Nassaubibliotheek ten tijde van Willem III R. van Leeuwen, Paintings from England. William III and the Royal Collections R.P. Maccubbin, M. Hamilton-Philips, The age of William III & Mary II. Power, politics and patronage 1688-1702. A reference encyclopedia and exhibition catalogue K. Ottenheym, Daniel Marot. Vormgever van een deftig bestaan. Architectuur en interieurs van Haagse stadspaleizen S. van Raay, In het gevolg van Willem III & Mary. Huizen en tuinen uit hun tijd D. Swetschinski, L. Schönduve, De familie Lopes Suasso, financiers van Willem III H. van der Zee, B. van der Zee, 1688. Revolution in the family H. van der Zee, B. van der Zee, William and Mary J.D. Hunt, The Anglo-Dutch garden in the age of William and Mary. De gouden eeuw van de Hollandse tuinkunst R. Turner, G. de Bruin, A.H. Huussen jr., [Koning-stadhouder Willem III triomfator] R. Hatton, W. Troost, W.F. Leemans, Oranje-Nassau museum jaarboek 1988

  17. Influence of the van der Waals interaction in the dissociation dynamics of N{sub 2} on W(110) from first principles

    Energy Technology Data Exchange (ETDEWEB)

    Martin-Gondre, L. [Institut UTINAM-CNRS UMR 6213, Université de Franche-Comté, 16 Route de Gray, 25030 Besançon Cedex (France); Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, 20018 Donostia-San Sebastián (Spain); Juaristi, J. I. [Departamento de Física de Materiales, Facultad de Químicas (UPV/EHU), Apartado 1072, 20080 Donostia-San Sebastián (Spain); Centro de Física de Materiales CFM/MPC (CSIC-UPV/EHU), Paseo Manuel de Lardizabal 5, 20018 Donostia-San Sebastián (Spain); Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, 20018 Donostia-San Sebastián (Spain); Blanco-Rey, M. [Departamento de Física de Materiales, Facultad de Químicas (UPV/EHU), Apartado 1072, 20080 Donostia-San Sebastián (Spain); Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, 20018 Donostia-San Sebastián (Spain); Díez Muiño, R.; Alducin, M. [Centro de Física de Materiales CFM/MPC (CSIC-UPV/EHU), Paseo Manuel de Lardizabal 5, 20018 Donostia-San Sebastián (Spain); Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, 20018 Donostia-San Sebastián (Spain)

    2015-02-21

    Using ab initio molecular dynamics (AIMD) calculations, we investigate the role of the van der Waals (vdW) interaction in the dissociative adsorption of N{sub 2} on W(110). Hitherto, existing classical dynamics calculations performed on six-dimensional potential energy surfaces based on density functional theory (DFT), and the semi-local PW91 and RPBE [Hammer et al. Phys. Rev. B 59, 7413 (1999)] exchange-correlation functionals were unable to fully describe the dependence of the initial sticking coefficient on the molecular beam incidence conditions as found in experiments. N{sub 2} dissociation on W(110) was shown to be very sensitive not only to short molecule-surface distances but also to large distances where the vdW interaction, not included in semilocal-DFT, should dominate. In this work, we perform a systematic study on the dissociative adsorption using a selection of existing non-local functionals that include the vdW interaction (vdW-functionals). Clearly, the inclusion of the non-local correlation term contributes in all cases to correct the unrealistic energy barriers that were identified in the RPBE at large molecule-surface distances. Among the tested vdW-functionals, the original vdW-DF by Dion et al. [Phys. Rev. Lett. 92, 246401 (2004)] and the ulterior vdW-DF2 give also an adequate description of the N{sub 2} adsorption energy and energy barrier at the transition state, i.e., of the properties that are commonly used to verify the quality of any exchange-correlation functional. However, the results of our AIMD calculations, which are performed at different incidence conditions and hence extensively probe the multi-configurational potential energy surface of the system, do not seem as satisfactory as the preliminary static analysis suggested. When comparing the obtained dissociation probabilities with existing experimental data, none of the used vdW-functionals seems to provide altogether an adequate description of the N{sub 2}/W(110) interaction at

  18. Factorisation of beams in van der Meer scans and measurements of the $\\phi^*_{\\eta}$ distribution of $Z\\rightarrow e^+e^-$ events in pp collisions at $\\sqrt{s}=8$ TeV with the ATLAS detector

    CERN Document Server

    Webb, Samuel Nathan

    Two analyses of data recorded in proton-proton collisions at the ATLAS detector in 2012 are presented in this thesis. The first pertains to the beam separation (van der Meer) scans required to calibrate the absolute luminosity. An estimate is made for the size of the correction needed to the standard van der Meer calibration method, which assumes that the proton bunch density profiles are factorisable. This is done by observing and modelling the evolution of various beam spot phenomena during the separation scans. The second analysis described is a series of measurements of the $Z/\\gamma$ cross-section, differential in the $\\phi^*_{\\eta}$ observable, for different ranges of the boson invariant mass and absolute rapidity. In particular the events in which the boson decays to electron-positron pairs are considered. The $\\phi^*_{\\eta}$ observable is defined in terms of the well-measured lepton directions and enables a probe of initial state gluon radiation in the non-perturbative regime of QCD.

  19. In silico carbon molecular beam epitaxial growth of graphene on the h-BN substrate: carbon source effect on van der Waals epitaxy

    Science.gov (United States)

    Lee, Jonghoon; Varshney, Vikas; Park, Jeongho; Farmer, Barry L.; Roy, Ajit K.

    2016-05-01

    Against the presumption that hexagonal boron-nitride (h-BN) should provide an ideal substrate for van der Waals (vdW) epitaxy to grow high quality graphene films, carbon molecular beam epitaxy (CMBE) techniques using solid carbon sublimation have reported relatively poor quality of the graphene. In this article, the CMBE growth of graphene on the h-BN substrate is numerically studied in order to identify the effect of the carbon source on the quality of the graphene film. The carbon molecular beam generated by the sublimation of solid carbon source materials such as graphite and glassy carbon is mostly composed of atomic carbon, carbon dimers and carbon trimers. Therefore, the graphene film growth becomes a complex process involving various deposition characteristics of a multitude of carbon entities. Based on the study of surface adsorption and film growth characteristics of these three major carbon entities comprising graphite vapour, we report that carbon trimers convey strong traits of vdW epitaxy prone to high quality graphene growth, while atomic carbon deposition is a surface-reaction limited process accompanied by strong chemisorption. The vdW epitaxial behaviour of carbon trimers is found to be substantial enough to nucleate and develop into graphene like planar films within a nanosecond of high flux growth simulation, while reactive atomic carbons tend to impair the structural integrity of the crystalline h-BN substrate upon deposition to form an amorphous interface between the substrate and the growing carbon film. The content of reactive atomic carbons in the molecular beam is suspected to be the primary cause of low quality graphene reported in the literature. A possible optimization of the molecular beam composition towards the synthesis of better quality graphene films is suggested.Against the presumption that hexagonal boron-nitride (h-BN) should provide an ideal substrate for van der Waals (vdW) epitaxy to grow high quality graphene films, carbon

  20. Mies van der Rohe Award

    Index Scriptorium Estoniae

    2001-01-01

    Euroopa Komisjoni loodud arhitektuuripreemia statuut. 2001. a. preemia pälvis hispaania arhitekt Rafael Moneo. Eripreemia pälvis sakslane Florian Nagler. Eestist esitati preemia saamiseks Andres Alveri ja Tiit Trummali De la Gardie kaubamaja

  1. Reliability of hypertrophy of the contralateral testis in prediction of ...

    African Journals Online (AJOL)

    6 Goede J, Hack WWM, Sijstermans K, van der Voort-Doedens LM,. Van der Ploeg T, Meij-de Vries A, et al. Normative values for testicular volume measured by ultrasonography in a normal population from infancy to adolescence. Horm Res Paediatr 2011; 76:56. 7 Shehata S, Shalaby R, Ismail M, Abouheba M, Elrouby A.

  2. De behandeling van prostatisme met diathermie volgens Remijnse

    NARCIS (Netherlands)

    Okker, Jacob Jacobus

    1942-01-01

    Bij de bestudeering van de geschiedenis van de therapie der prostaathypertrophie blijkt, dat deze zich eerst aan het einde van de vorige en aan het begin van deze eeuw heeft ontwikkeld. Fuller en Freyer waren de grondleggers van de transvesicale operatie. Young propageerde de perineale

  3. Verticillium : Status quo van een miljoenenverslindende bodemziekte : Kansen en oplossingen bij bestrijding en beheer van verwelkingsziekte

    NARCIS (Netherlands)

    Hiemstra, J.A.; Sluis, van der B.J.

    2013-01-01

    Verwelkingsziekte bedreigt al jaren de boomkwekerij, m.n. in de teelt van laanbomen en rozen. Onderzoek naar deze bodemziekte is daarom hard nodig. Jelle Hiemstra en Bart van der Sluis geven in dit artikel een overview van de stand van zaken met betrekking tot onderzoek naar dit probleem.

  4. Boekbespreking | van Aarde | HTS Teologiese Studies / Theological ...

    African Journals Online (AJOL)

    The Bible and stress. Van der Westhuizen, H.G. - Kirk, J.A. 1990. Liberation theology in brief. Van Wyk, D.J.C - Kritzinger, J.N.J & Saayman, W.A 1990. Mission in creative tension: A dialogue with David Bosch. Van Wyk, D.J.C - Pass, D.B 1990. Music and the church: A theology of church music. Van Wyk, D.J.C - Van Elderen, ...

  5. Découverte d’une culture africaine et fantasmes d’un missionnaire. Le Dictionnaire français-kirundi du Père Van der Burgt (1903 entre ethnographie, exégèse biblique et orientalisme

    Directory of Open Access Journals (Sweden)

    Jean-Pierre Chrétien

    2010-04-01

    Full Text Available Un des premiers regards extérieurs portés sur l’Afrique des Grands Lacs nous vient du Père blanc hollandais Van der Burgt, missionnaire au Burundi. En 1903 il publie un dictionnaire encyclopédique français‑kirundi, dont l’influence sera durable auprès des lettrés de ce pays. Or cet ouvrage est autant nourri d’une érudition ethnographique, historique et biblique mal contrôlée que d’enquêtes sur le terrain. Il exprime une obsession raciale, celle de la quête des origines orientales des populations noires et, en particulier, de l’assimilation de la catégorie tutsi à une souche hamito‑sémitique. Il est même tenté par des formes ésotériques de l’orientalisme qui le mènent jusqu’en Inde, en Polynésie ou aux révélations de la mystique allemande Catherine Emmerich. La culture burundaise se retrouve capturée par cet imaginaire venu des bibliothèques européennes et elle est décrite comme le fruit d’une dégénérescence, prolongeant le mythe de la malédiction de Cham.One of the first exogenous looks on the Great Lakes region of Africa came from a missionary in Burundi, the Dutch White Father Van der Burgt. He published in 1903 a French‑Kirundi encyclopaedic dictionary, which left a lasting influence on that countries scholarship. This book was both based on fieldwork and poorly‑controlled ethnographic, historical and biblical scholarship. It expressed a peculiar racial obsession : the quest for the Oriental origins of African populations and particularly the inclusion of the Tutsi category into a Hamito‑Semitic stock. Van der Burgt was even influenced by esoteric forms of orientalism, which drove his thoughts as far as India, Polynesia, or the revelations of the German mystic Catherine Emmerich. The Burundese culture was thus trapped by this imagination born out of the European libraries and it was described as the result of degeneration, based on the myth of the curse of Ham.

  6. Die nabyheid van die Koninkryk

    Directory of Open Access Journals (Sweden)

    W.J. Snyman

    1963-03-01

    Full Text Available Vanweë die belangrikheid daarvan volg hier ’n breër bespreking van die proefskrif van dr. Tjaart van der Walt oor die nabyheid van die Koninkryk as wat in ’n gewone resensie kan geskied. Die vraagstuk wat onder oë gesien word is so oud as die kerk en die teologie, soms minder en soms meer op die voorgrond. Tans kan gesê word, staan dit in die middelpunt. Daarby is dit nie maar ’n akademiese vraagstuk nie, maar ’n vraagstuk waarvoor elke nadenkende leser van die Skrif te staan kom.

  7. The intercombination Cd line 326.1 nm and van der Waals potential coefficients {Delta}C{sub 6}{sup 0}and{Delta}C{sub 6}{sup 1} for pure Cd and Cd-inert gas systems

    Energy Technology Data Exchange (ETDEWEB)

    Roston, G.D., E-mail: Gamal_daniel@yahoo.com [Department of Physics, Faculty of Science, Alexandria University, Alexandria (Egypt); Helmi, M.S. [Department of Physics, Faculty of Science, Alexandria University, Alexandria (Egypt)

    2009-03-30

    The absorption profiles of the Cd 326.1 nm line for pure Cd and Cd-inert gases (Xe, Kr, Ar, Ne and He) have been carefully studied from the line center to 700 cm{sup -1} in the red wing using a high resolution double beam spectrometer. The density of Cd was about 5.108 x 10{sup 18} atoms cm{sup -3}. The temperature dependences of the red wings of these profiles were analysed in the frame work of the Unified Frank Condon (UFC) treatment of pressure broadening of spectral lines developed by Szudy and Baylis. The van der Waals potential coefficient differences {Delta}C{sub 6}{sup 0} and {Delta}C{sub 6}{sup 1} between the ground {sup 1}0{sup +} state and the two excited states {sup 3}0{sup +} and {sup 3}1 were obtained using Kuhn's law.

  8. Die invloed van doelwitstelling op prestasie

    Directory of Open Access Journals (Sweden)

    J. G. A. Louw

    1985-11-01

    Full Text Available Although a number of research studies support Locke's goal setting theory, conflicting results are encountered in the Literature which suggest further investigation into the subtleties of the theory. The results of this study indicate that an increase in goal-difficulty does not always lead to a corresponding increase in performance. The latter could also not be explained in terms of the degree of goal-acceptance as an intervening variable. It was found that financial incentives and the way in which a nonspecific goal is formulated could have a significant effect on performance. Recommendations are made for future research.OpsommingOfskoon die meeste navorsing Locke se doelwitstellingsteorie ondersteun, is bepaalde afwykings teengekom wat nie op 'n bevredigende wyse verklaar kan word nie. Die resultate van hierdie studie dui daarop dat 'n toename in doelwitmoeilikheidsgraad nie altyd tot ‘n ooreenstemmende toename in prestasie lei nie. Hierdie resultaat kon ook nie op grond van 'n gebrek aan doelwitaanvaarding verklaar word nie. Daar is voorts gevind dat die wyse waarop 'n nie-spesifieke doelwit gestel word, 'n beduidende invloed op prestasie kan hê. Finansiële aansporings blyk ook 'n onafhanklike invloed op prestasie te hê. Bepaalde aspekte van Locke se teorie word dus deur bogenoemde resultate bevraagteken. Aanbevelings vir verdere navorsing word ten slotte gedoen.

  9. HISTORIESE OORSIG VAN DIE ONTSTAAN EN ONTWIKKELING ...

    African Journals Online (AJOL)

    toe Orville op die 17de Desember 120 voet in 12 sekondes gevlieg het! Met :iil~ koms van die vliegtuig het die ... 2 Die ontwikkeling vall die militere lugvaart ell die ontstaan van selfstandiRe lugmagte met besondere venvysing na ..... as General der Flieger, sy tegnici e.a. te voorskyn. Goering was deur die Minister van ...

  10. 'Kerk' en 'volk' uit die hoek van moderne samelewíngsteologieë

    African Journals Online (AJOL)

    Om na die kerk en volk te kyk vanuit die gesigspunt van die hedendaagse same- lewingsteologie, vra 'n kort verduideliking van wat .... der uitgebrei met die voorstel van 'verantwoordelike mense wat deelneem aan 'n wêreldgemeenskap waarin almal die ..... A Huf & F van der Heijden. Baarn: Bosch & Keuning. Cranston, M ...

  11. Prediction of phase equilibrium for gas hydrate in the presence of organic inhibitors and electrolytes by using an explicit pressure-dependent Langmuir adsorption constant in the van der Waals–Platteeuw model

    International Nuclear Information System (INIS)

    Chin, Huai-Ying; Hsieh, Min-Kang; Chen, Yan-Ping; Chen, Po-Chun; Lin, Shiang-Tai; Chen, Li-Jen

    2013-01-01

    Highlights: • The hydrate phase is described by the van der Waals and Platteeuw model. • An explicit pressure-dependent Langmuir adsorption constant is used in our model. • Phase behavior of gas hydrates with organic inhibitors and electrolytes predicted. • Our model well predicts phase behavior of gas hydrates at high pressures. -- Abstract: A new approach is developed for the prediction of the melting curve of gas hydrate with single or multiple additives, including organic inhibitors and electrolytes. This is made possible by combining a predictive equation of state for the fluid phase, the Peng–Robinson–Stryjek–Vera equation of state (PRSV EoS) combined with the COSMO-SAC activity coefficient model through the first order modified Huron–Vidal (MHV1) mixing rule, and a modified van der Waals–Platteeuw model for the hydrate phase. We have examined this method for the change of the melting condition of gas hydrate upon addition of single organic inhibitor, single electrolyte, and a mixture of organic and electrolyte. The absolute average relative deviation in temperature (AARD-T) for these three types of systems are 0.79% (695 data points, T from 230.2 K to 294.0 K, P from 0.10 MPa to 33.9 MPa), 0.16% (810 data points, T from 259.5 K to 299.1 K, P from 0.13 MPa to 71.56 MPa), and 1.56% (316 data points, T from 248.2 K to 292.9 K, P from 0.90 MPa to 73.28 MPa), respectively. We believe that the proposed model is useful for the exploitation of natural or synthetic gas hydrates with multiple additives

  12. Arbeidsongeschiktheid in een post-industriële economie. De gevolgen van maatschappelijke veranderingen voor de grondslagen van een stelsel van sociale zekerheid

    NARCIS (Netherlands)

    van der Veen, Romke

    2003-01-01

    Romke van der Veen laat zien dat de jachtigheid van de samenleving tegenwoordig een belangrijke risicofactor is om in de WAO te belanden. Omdat mensen zelf voor een deel verantwoordelijk zijn voor of ze zich wel of niet door de jachtigheid van de samenleving en de eisen van de cultuur laten

  13. die nasionalisering van waterregte in suid- afrika: ontneming of ...

    African Journals Online (AJOL)

    Administrator

    ondersoek word of die staat, deur die bepalings van die Nasionale. Waterwet ... word nie.14. In die uitspraak van Watermeyer CJ in Commissioner for Inland. Revenue v Estate Crewe15 blyk dit duidelik dat die begrip eiendom reeds van vroeg af ..... Van der Walt "Moving towards recognition of constructive expropriation?

  14. M erw e . Pentateugtradisies in die prediking van Deuterojesaja ...

    African Journals Online (AJOL)

    Test

    B. J. van der M erw e . Pentateugtradisies in die prediking van Deuterojesaja. Proefschrift ter verkrijging van de graad van Doctor in de God geleerdheid aan de Rijkuniversiteit te Groningen. Uitg. J. B. Wolters,. Groningen, Djakarta. 1955. 280 bis. Met hierdie deur die uitgewer in verskillende duidelike lettertipes.

  15. Te schepe waert. Overwegingen bij de reconstructie van een zot polyfoon lied van Clemens non Papa

    NARCIS (Netherlands)

    Grijp, L.P.; van Maas e.a., S.

    2012-01-01

    Clemens non Papa's vierstemmige 'Te schepe waert' is het eerste lied van de bundel Niewe Duytsche Liedekens, uitgegeven in Maastricht 1554 door Jacob Baethen. Van deze bundel ontbreekt de sopraanpartij. Louis Grijp heeft samen met Nico van der Meel de sopraan gereconstrueerd en hoopt de aldus

  16. Emotionalisierung der Nachhaltigkeitskommunikation

    DEFF Research Database (Denmark)

    Pedersen, Anne Grethe Julius

    emotional (mehr als rational) angesprochen - Welche Emotionalisierungsstrategien werden benutzt - Inwieweit unterscheidet sich die deutschsprachige Nachhaltigkeitskommunikation von der dänischsprachigen. Das Textkorpus umfasst online verfügbare Nachhaltigkeitskommunikation auf Websites und in neuen Medien......, Charakteristika und Herausforderungen. Wiesbaden: Gabler. Kress, G./ van Leuwen, T. (1995): Reading images: grammar of visual design, London: Routledge. Kress.G. (2010): Multimodality: Exploring Contemporary Methods of Communication, London: Routledge. Martin, J.R./ White. P. R.R. (2005): The Language...

  17. Der Fachbereich Fertigungstechnik der Zukunft

    DEFF Research Database (Denmark)

    Alting, Leo

    1998-01-01

    Forscher sowie für eine industrielle Zusammenarbeit/Beratung eine attraktive Umgebung zu bieten.Im vorliegenden Papier wird ein internes Entwicklungsprojekt, genannt "Der Fachberich der Zukunft", beschrieben. Ausgehend von den Bedürfnissen und Erwartungen der Kunden (Studierende, Einrichtungen der...

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

    Science.gov (United States)

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

    2017-06-01

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

  19. De ontwikkeling van een feedbacksysteem voor toetsvragenmakers

    NARCIS (Netherlands)

    Reinders, J J; Cohen-Schotanus, J; Molenaar, W M

    2005-01-01

    Door de Groningse Faculteit der Medische Wetenschappen is een feedbacksysteem voor toetsvragenmakers ontwikkeld. Het systeem is onder andere gebaseerd op een statistische analyse van de toetsresultaten. Uit een eerste peiling onder toetsvragenmakers blijken de respondenten overwegend positief te

  20. Nieuwe vondsten van zeldzame planten in 2005, 2006 en ten dele 2007

    NARCIS (Netherlands)

    Holverda, Wout; Moorsel, van René C.M.J.; Duistermaat, Leni H.

    2009-01-01

    Op 27 april 2007 overleed onze dierbare collega en NHN-staflid Ruud van der Meijden, sinds vele jaren auteur van de ‘Lijst van zeldzame planten’. Zijn plaats bij het samenstellen van deze publicatie zal worden ingenomen door degene die ook zijn werk aan de Heukels’ Flora van Nederland zal