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  1. Umsetzung der Unternehmensstrategie mit der Balanced Scorecard

    NASA Astrophysics Data System (ADS)

    Crespo, Isabel; Bergmann, Lars; Portmann, Stefan; Lacker, Thomas; Lacker, Michael; Fleischmann, Jürgen; Kozó, Hans

    Die Balanced Scorecard (BSC) ist ein Ansatz zum strategischen Management, der neben der Ausrichtung des Unternehmens auf finanzielle Zielwerte ebenso großes Gewicht auf so genannte weiche Faktoren legt, die den wirtschaftlichen Erfolg eines Unternehmens erst ermöglichen. Das entscheidende Merkmal der Balanced Scorecard ist dabei, dass sie ein ausgewogenes System strategischer Ziele herstellt, welches das Unternehmen hinsichtlich der vier Perspektiven Finanzen, Kunden, interne Prozesse und Mitarbeiter und Potenziale strategisch ausrichtet (Kaplan u. Norton 1997).

  2. Lehrbuch der Mathematischen Physik

    NASA Astrophysics Data System (ADS)

    Thirring, Walter

    Aus den Besprechungen der ersten Auflage: "... Das Buch wendet sich nicht nur an Studierende der Physik und Mathematik in höheren Semestern, sondern ist auch für fertige Physiker und Mathematiker äußerst anregend. Ein besonderes Lob möchte ich für die zahlreichen Illustrationen des Stoffes mit relevanten, anwendungsbezogenen Beispielen aussprechen." Zeitschrift für Angewandte Mathematik und Physik#1 "W. Thirring hat mit seinem Lehrbuch für Mathematische Physik das erstemal den Versuch unternommen, eine spezifische Bearbeitung der gesamten mathematischen Physik einzuleiten und damit ein "Lehrbuch" der wissenschaftlichen Fachwelt vorzulegen, das in seiner Art sicher als neuartig zu bezeichnen ist. Es zeigt neben der Klarheit und Übersichtlichkeit aber auch eine tiefe Kenntnis der Pädagogik, um ein so schwieriges und abstraktes Gebiet darzustellen." Acta Physica Austriaca#2 "Der Leser kann hier Mathematische Physik in einer Form kennenlernen, wie sie sich einem in der akutuellen Forschung stehenden theoretischen Physiker darstellt, der andererseits auch mit der Entwicklung der modernen mathematischen Methoden wohlvertraut ist. Trotz der anspruchsvollen mathematischen Fundierung gerät der Verfasser an keiner Stelle des Buches in die Gefahr, Mathematische Physik im Sinne einer rein mathematischen Disziplin zu verfremden ... Wer heute wissen will, was "Mathematische Physik" ist und sein soll, wird an diesem Buch nicht vorbeigehen können und Antwort und Gewinn davontragen..." ZAMM#3

  3. Lehrbuch der Mathematischen Physik

    NASA Astrophysics Data System (ADS)

    Thirring, Walter

    Aus den Besprechungen der ersten Auflage: "...Das Buch wendet sich nicht nur an Studierende der Physik und Mathematik in höheren Semestern, sondern ist auch für fertige Physiker und Mathematiker äußerst anregend. Ein besonderes Lob möchte ich für die zahlreichen Illustrationen des Stoffes mit relevanten, anwendungsbezogenen Beispielen aussprechen." Zeitschrift für Angewandte Mathematik und Physik#1 "...W. Thirring hat mit seinem Lehrbuch für mathematische Physik das erstemal den Versuch unternommen, eine spezifische Bearbeitung der gesamten mathematischen Physik einzuleiten und damit ein 'Lehrbuch' der wissenschaftlichen Fachwelt vorzulegen, das in seiner Art sicher als neuartig zu bezeichnen ist. Es zeigt neben der Klarheit und Übersichtlichkeit aber auch eine tiefe Kenntnis der Pädagogik, um ein so schwieriges und abstraktes Gebiet darzustellen..." Acta Physica Austriaca#2 "... Der Leser kann hier Mathematische Physik in einer Form kennenlernen, wie sie sich einem in der aktuellen Forschung stehenden theoretischen Physiker darstellt, der andererseits auch mit der Entwicklung der modernen mathematischen Methoden wohlvertraut ist. Trotz der anspruchsvollen mathematischen Fundierung gerät der Verfasser an keiner Stelle des Buches in die Gefahr, Mathematische Physik im Sinne einer rein mathematischen Disziplin zu verfremden...Wer heute wissen will, was 'Mathematische Physik'ist und sein soll, wird an diesem Buch nicht vorbeigehen können und Antwort und Gewinn davontragen..." ZAMM#3

  4. Grundlagen der Mechatronik

    NASA Astrophysics Data System (ADS)

    Roddeck, Werner

    Der Begriff Mechatronik ist ein Kunstwort, welches durch Eindeutschung des englischen Wortes "Mechatronics“ entstanden ist. Dieses ist wiederum eine Zusammenziehung der englischen Bezeichnungen für "Mechanics“ (Maschinenbau) und "Electronics“ (Elektrotechnik). Der Begriff wurde durch einen japanischen Ingenieur 1969 geprägt und durch eine japanische Firma bis 1972 als Warenzeichen gehalten.

  5. Der II. Hauptsatz der Wärmelehre

    NASA Astrophysics Data System (ADS)

    Heintze, Joachim

    Wir haben in (4.44) den II. Hauptsatz als empirische Tatsache folgendermaßen formuliert: (i) Wärmeenergie geht von selbst nur von einem wärmeren Körper auf einen kälteren über, niemals in der umgekehrten Richtung. Nun werden wir beweisen, dass sich aus diesem Prinzip folgende äquivalente Formulierungen für den II. Hauptsatz ableiten lassen: (ii) Es ist unmöglich, ein Perpetuum mobile zweiter Art zu bauen, d. h. eine Maschine, die fortlaufend Wärmeenergie vollständig in mechanische Arbeit umsetzen kann. Eine Wärmekraftmaschine, die einen Kreisprozess mit der höchsten Temperatur Tw und der niedrigsten Temperatur Tk durchläuft, hat höchstens den Carnotschen Wirkungsgrad c = (Tw - Tk)/Tw. Wenn in der Maschine nur reversible Prozesse ablaufen, die gesamte Wärmezufuhr bei der Temperatur Tw erfolgt und ausschließlich bei der Temperatur Tw gekühlt wird, ist ihr Wirkungsgrad = C. Es gibt keine Wärmekraftmaschine, die eine bessere Ausnutzung der Wärmeenergie ermöglicht. (iv) In jedem thermodynamischen System existiert die Zustandsgröße Entropie, definiert durch ihr Differential dS = (dQrev)/T . Entropie kann erzeugt, aber nicht vernichtet werden. Bei Zustandsänderungen, die in einem abgeschlossenen System ablaufen, nimmt die Entropie entweder zu (irreversible Prozesse), oder sie bleibt konstant (reversible Prozesse). Im Anschluss an (iii) werden wir zur Definition der thermodynamischen Temperatur und bei der Diskussion von (iv) zu einem tieferen Verständnis der Entropie gelangen. Es zeigt sich, dass die Entropie das eigentliche Bindeglied zwischen Mechanik und Wärmelehre darstellt. Am Ende des Kapitels werden wir einige Anwendungen des II. Hauptsatzes betrachten.

  6. Kants Theorie der Sonne: Physikgeschichte

    NASA Astrophysics Data System (ADS)

    Jacobi, Manfred

    2005-01-01

    Im Rahmen seiner Kosmogonie entwickelte der junge Immanuel Kant eine Theorie der Sonne. Sie ist ein einzigartiges Zeugnis seiner intuitiven Vorstellungskraft und beweist auch die Leistungsfähigkeit der damaligen, vorwiegend von Newton geprägten Weltsicht. Entstehung, Aufbau und Dynamik der Sonne werden in Kants Theorie ebenso erklärt wie etwa das Phänomen der Sonnenflecken.

  7. Strahlungsfeldbedingungen bei der Ionisationsdosimetrie

    NASA Astrophysics Data System (ADS)

    Krieger, Hanno

    Bei der Dosimetrie von Photonenstrahlungen mit luftgefüllten Ionisationskammern werden in diesem Kapitel zwei Grenzfälle unterschieden. Der eine Fall ist die Bedingung des so genannten Sekundärelektronengleichwichts im Kammervolumen. In diesem Fall bestimmen ausschließlich die Photonen im Messvolumen die dosimetrische Anzeige. Der zweite Grenzfall ist gegeben, wenn das Luftvolumen und die Kammer das Strahlungsfeld im Phantom so wenig stören, dass der Sekundärelektronenfluss unverändert bleibt. Diese Bedingungen nennt man BRAGG-GRAY-Bedingungen. Beide Grenzfälle sind in der Praxis nur näherungsweise zu verwirklichen. Abweichungen müssen durch entsprechende Korrekturen oder Kalibrierungen berücksichtigt werden.

  8. Theoretische Konzepte der Physik

    NASA Astrophysics Data System (ADS)

    Longair, Malcolm S.; Simon, B.; Simon, H.

    "Dies ist kein Lehrbuch der theoretischen Physik, auch kein Kompendium der Physikgeschichte ... , vielmehr eine recht anspruchsvolle Sammlung historischer Miniaturen zur Vergangenheit der theoretischen Physik - ihrer "Sternstunden", wenn man so will. Frei vom Zwang, etwas Erschöpfendes vorlegen zu müssen, gelingt dem Autor etwas Seltenes: einen "lebendigen" Zugang zum Ideengebäude der modernen Physik freizulegen, ... zu zeigen, wie Physik in praxi entsteht... Als Vehikel seiner Absichten dienen dem Autor geschichtliche Fallstudien, insgesamt sieben an der Zahl. Aus ihnen extrahiert er das seiner Meinung nach Lehrhafte, dabei bestrebt, mathematische Anachronismen womöglich zu vermeiden... Als Student hätte ich mir diese gescheiten Essays zum Werden unserer heutigen physikalischen Weltsicht gewünscht. Sie sind originell, didaktisch klug und genieren sich auch nicht, von der Faszination zu sprechen, die ... von der Physik ausgeht. Unnötig darauf hinzuweisen, das sie ein gründliches "konventionelles" Studium weder ersetzen wollen noch können, sie vermögen aber, dazu zu ermuntern." #Astronomische Nachrichten (zur englischen Ausgabe)#1

  9. Nomogramme der Sickerwasserprognose

    NASA Astrophysics Data System (ADS)

    Schneider, Wilfried; Stöfen, Heinke

    Kurzfassung Modelle zur Sickerwasserprognose stehen in unterschiedlicher Komplexität zur Verfügung. Komplexe Modelle werden aufgrund der schwierigen Handhabung und des enormen Eingabedatenumfangs in der Praxis kaum angewandt. Grobe Abschätzmethoden sind dagegen nicht ausreichend wissenschaftlich fundiert, um damit justiziable Ergebnisse erzielen zu können. Um die Kluft zwischen komplexer und einfacher, jedoch justiziabler sowie wissenschaftlich fundierter Methode zu schmälern, wurden Nomogramme für Sickerwasserprognosen zur Berücksichtigung der Endlichkeit der Quelle entwickelt. Mithilfe der Nomogramme können ohne Modellierungserfahrung schnell und einfach die zu erwartenden Schadstoffkonzentrationen am Ort der Beurteilung abgeschätzt werden, falls die Endlichkeit der Quelle der hauptsächlich zur Abminderung führende Prozess ist. Die Nomogramme basieren auf analytischen Lösungen der eindimensionalen Advektions-Dispersions-Gleichung. Sie berücksichtigen die Prozesse Advektion, Diffusion in Bodenwasser und -luft, Dispersion, lineare Sorption, Abbau 1. Ordnung innerhalb einer aus mehreren Bodenschichten bestehenden Sickerwasserzone, wobei die Endlichkeit der Schadstoffmasse in der Bodenkontamination einbezogen wird. Die Genauigkeit der Nomogramme wird dargestellt. Models of different complexity are available for groundwater risk assessment. In practice complex models are hardly used, due to their difficult handling and large data requirement. Rough estimation methods are not sufficiently scientifically founded to produce justiciable results. To reduce the gap between complex and easy to use but justiciable and scientifically founded methods we developed nomograms for groundwater risk assessment which take into account the finite mass of contaminant in the source. With the help of the nomograms the expected concentrations at the point of compliance (transition between the unsaturated and saturated zone) can be estimated easily, fast and without any

  10. Geologie der terrestrischen Planeten und Monde.

    NASA Astrophysics Data System (ADS)

    Stöffler, D.

    Contents: 1. Inhalt und Aufgabe der Planetologie. 2. Aufbau des Sonnensystems. 3. Methoden der Exploration und Analyse der Planeten und Monde. 4. Geologische Grundprozesse auf den terrestrischen Planeten und Monden. 5. Geologische Formationen der planetaren Oberflächen. 6. Gesteine und Mineralien der planetaren Krusten. 7. Der innere Aufbau der terrestrischen planetaren Körper. 8. Vergleichende geologische Entwicklungsgeschichte der terrestrischen Planeten und des Mondes. 9. Ursprung und Entstehung der terrestrischen planetaren Körper.

  11. Die Zeitung der Zukunft

    NASA Astrophysics Data System (ADS)

    Wieser, Christoph; Schaffert, Sebastian

    Schon lange wird spekuliert, wie wir in Zukunft Zeitung lesen werden. Werden wir am Frühstückstisch wie gewohnt in einer Zeitung aus Papier schmökern oder werden wir die Zeitung als biegsame Folie beschrieben mit elektronischer Tinte in Händen halten? Wird die Zeitung mit anderen Medien wie Radio und Fernsehen verschmelzen? Viele Varianten sind denkbar. Heute lässt sich schon ein Trend ablesen: Immer mehr Leser entdecken die Online-Zeitung als Informationsmedium, eine Voraussetzung für die Nutzung neuer Technologien in der Zeitung der Zukunft. In diesem Kapitel stellen wir Entwicklungsmöglichkeiten der Online-Zeitung dar, wie sie im Social Semantic Web möglich werden.

  12. Zum Stellenwert der Unterdruck-Instillationstherapie in der Dermatologie.

    PubMed

    Müller, Cornelia Sigrid Lissi; Burgard, Barbara; Zimmerman, Monika; Vogt, Thomas; Pföhler, Claudia

    2016-08-01

    Die Methoden zur Behandlung akuter und chronischer Wunden unterliegen einer steten Weiterentwicklung, Reevaluierung und Anwendung innovativer Therapieformen. Die Vakuumtherapie zur Wundbehandlung gehört zu den etablierten Behandlungsmodalitäten. Ein innovatives Verfahren kombiniert die Vakuumtherapie mit der automatisierten, kontrollierten Zufuhr und Drainage wirkstoffhaltiger Lösungen zur topischen Wundbehandlung im Wundbett und auch wirkstofffrei durch Instillation physiologischer Kochsalzlösung (Unterdruck-Instillationstherapie). Hierdurch können die Effekte der konventionellen Vakuumtherapie mit denen der lokalen Antisepsis kombiniert werden. Hierdurch kommt es zu einer Reduktion der Wundfläche, einer Induktion von Granulationsgewebe sowie einer Reduktion der Keimbesiedelung der Wunden. Bisher publizierte Studien konzentrieren sich auf die Anwendung dieses Therapieverfahrens zur Behandlung orthopädisch-chirurgischer Krankheiten. Die Datenlage bezüglich der Vakuum-Instillationstherapie in der Dermatochirurgie beschränkt sich derzeit auf Fallberichte und Einzelfallerfahrungen. Randomisierte, prospektive Studien zum Vergleich der Vakuum-Instillationstherapie zur Behandlung dermatologischer Krankheitsbilder existieren bislang nicht. Ziele des vorliegenden Artikels sind die Vorstellung der Vakuumtherapie mit Instillation einschließlich ihres Wirkprinzips, deren mögliche Komplikationen, die Diskussion erdenklicher Kontraindikationen sowie eine Übersicht über die aktuell verfügbare Datenlage. Zusammenfassend scheint sich die Evidenz zu verdichten, dass mittels Unterdruck-Instillationstherapie sowohl einfache als auch komplizierte Wunden effizient behandelt werden können, was sich in einer deutlichen Beschleunigung der Wundgranulation mit konsekutiv früher möglichem Defektverschluss äußert. PMID:27509413

  13. Van der Waals Forces

    NASA Astrophysics Data System (ADS)

    Parsegian, V. Adrian

    2006-03-01

    This should prove to be the definitive work explaining van der Waals forces, how to calculate them and take account of their impact under any circumstances and conditions. These weak intermolecular forces are of truly pervasive impact, and biologists, chemists, physicists and engineers will profit greatly from the thorough grounding in these fundamental forces that this book offers. Parsegian has organized his book at three successive levels of mathematical sophistication, to satisfy the needs and interests of readers at all levels of preparation. The Prelude and Level 1 are intended to give everyone an overview in words and pictures of the modern theory of van der Waals forces. Level 2 gives the formulae and a wide range of algorithms to let readers compute the van der Waals forces under virtually any physical or physiological conditions. Level 3 offers a rigorous basic formulation of the theory. Author is among the most highly respected biophysicists Van der Waals forces are significant for a wide range of questions and problems in the life sciences, chemistry, physics, and engineering, ranging up to the macro level No other book that develops the subject vigorously, and this book also makes the subject intuitively accessible to students who had not previously been mathematically sophisticated enough to calculate them

  14. Das mechatronische Fahrwerk der Zukunft

    NASA Astrophysics Data System (ADS)

    Rieth, Peter

    Technologiesprünge gab es immer wieder in der Geschichte der Automobiltechnologie, so auch in der Kraftfahrzeugbremse, die seit ihren Anfängen eine stete Weiterentwicklung erfahren hat (Bild 40-1). So erlangten schon mechanische Bremsen durchaus ein hohes Niveau, ehe die Hydraulik Mitte der zwanziger Jahre für Komfort und Sicherheit vollkommen neue Perspektiven eröffnete, welche durch Einführung der Hilfskraft(servo)bremsanlagen Mitte des letzten Jahrhunderts noch erweitert wurden. Den wichtigsten Technologiesprung, den der Kunde als Fortschritt erkennt und dementsprechend honoriert, ermöglichte die Elektronik Mitte der siebziger Jahre. ABS, ASR, EBV und nicht zuletzt ESC wären ohne sie nicht vorstellbar.

  15. Evaluation der zentralen TUM-Lernplattform

    NASA Astrophysics Data System (ADS)

    Schulze, Elvira; Baume, Matthias; Graf, Stephan; Gergintchev, Ivan

    Die Notwendigkeit der Qualitätssicherung und -kontrolle für innovative universitäre Lehr-/Lernszenarien ist in der Praxis unbestritten. Die Wirksamkeit der Einführung der zentralen Lernplattform CLIX Campus der imc AG an der TUM wurde mittels quantitativer und qualitativer Evaluation überprüft. Als statistische Bewertungsgrundlage wurde der Erreichungsgrad bestimmter Projektziele herangezogen. Aufbauend auf den theoretischen Grundlagen der Evaluation von Bildungsangeboten gibt diese Studie Aufschluss über die Ergebnisse der Datenerhebungen sowie die Einschätzung der Plattform aus Nutzersicht und belegt die wesentliche Bedeutung der durchgängigen IT-Infrastruktur und speziell der einheitlichen Verfügbarkeit der eLearning Angebote.

  16. Haftung in der Medizintechnik

    NASA Astrophysics Data System (ADS)

    Müller, Ute; Lücker, Volker

    Die Unversehrtheit von Leib und Leben ist das größte Rechtsgut unserer Gesellschaft. Dies macht schon das Grundgesetz in Art. 2 Abs. Satz 1 GG deutlich. Die Öffentlichkeit zeigt daher größtes Interesse an Produkten, welche der Gesundheit dienen und Leben retten oder erhalten. Dieses Interesse gilt einerseits der Entwicklung und Bereitstellung leistungsfähiger Medizinprodukte, andererseits zielt es auf deren Sicherheit. Um vor allem letztere zu gewährleisten, nimmt der Gesetzgeber alle Beteiligten in die Pflicht, die auftretenden Risiken auf das geringstmögliche Maß zu begrenzen. Dies spiegelt sich in den rechtlichen Vorgaben ebenso wie in den Haftungsfolgen, die bei Verletzung dieser Vorgaben greifen, wieder. Diese Folgen können dementsprechend gravierend ausfallen, von Geldstrafen bis zu Freiheitsstrafen, von Bußgeldzahlungen bis zum Schadenersatzansprüchen, die schnell ein wirtschaftliches Aus bedeuten können. Den Beteiligten, allen voran den Herstellern, muss deshalb daran gelegen sein, nicht nur die Produkte, sondern auch deren Sicherheit stetig weiter zu entwickeln.

  17. Der Forsch-Frosch Fred

    NASA Astrophysics Data System (ADS)

    Kaibel, Volker

    Bewegt man sich auf der Suche nach Informationen zu einem bestimmten Thema immer neuen Links folgend durch das World-Wide-Web, so stellt man in der Regel nach einer gewissen Zeit fest, dass man auf manchen Seiten immer wieder gelandet ist. Diese Seiten stellen sich oft als wichtig heraus. Suchmaschinen wie Google machen sich dieses Phänomen zu Nutze, um die Wichtigkeit einzelner Web-Seiten zu bewerten. Dazu lassen sie auf einer beliebigen Web-Seite einen imaginären Surfer starten, der immer zufällig einen der auf seiner aktuell besuchten Seite vorgefundenen Links verfolgt. Der Surfer vollführt einen Random Walk im Netzwerk der Web-Seiten.

  18. van der Waals torque

    NASA Astrophysics Data System (ADS)

    Esquivel-Sirvent, Raul; Schatz, George

    2014-03-01

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

  19. Zeit im Wandel der Zeit.

    NASA Astrophysics Data System (ADS)

    Aichelburg, P. C.

    Contents: Einleitung(P. C. Aichelburg). 1. Über Zeit, Bewegung und Veränderung (Aristoteles). 2. Ewigkeit und Zeit (Plotin). 3. Was ist die Zeit? (Augustinus). 4. Von der Zeit (Immanuel Kant). 5. Newtons Ansichten über Zeit, Raum und Bewegung (Ernst Mach). 6. Über die mechanische Erklärung irreversibler Vorgänge (Ludwig Boltzmann). 7. Das Maß der Zeit (Henri Poincaré). 8. Dauer und Intuition (Henri Bergson). 9. Die Geschichte des Unendlichkeitsproblems (Bertrand Russell). 10. Raum und Zeit (Hermann Minkowski). 11. Der Unterschied von Zeit und Raum (Hans Reichenbach). 12. Newtonscher und Bergsonscher Zeitbegriff (Norbert Wiener). 13. Die Bildung des Zeitbegriffs beim Kinde (JeanPiaget).14. Eine Bemerkung über die Beziehungen zwischen Relativitätstheorie und der idealistischen Philosophie (Kurt Gödel). 15. Der zweite Hauptsatz und der Unterschied von Vergangenheit und Zukunft (Carl Friedrich v. Weizsäcker). 16. Zeit als physikalischer Begriff (Friedrich Hund). 17. Zeitmessung und Zeitbegriff in der Astronomie (Otto Heckmann). 18. Kann die Zeit rückwärts gehen? (Martin Gardner). 19. Zeit und Zeiten (Ilya Prigogine, Isabelle Stengers). 20. Zeit als dynamische Größe in der Relativitätstheorie (P. C. Aichelburg).

  20. Das Lob der Sternkunst. Astronomie in der deutschen Aufklärung.

    NASA Astrophysics Data System (ADS)

    Baasner, R.

    Contents: 1. Einleitung. 2. Die Astronomie im Rahmen der Aufklärungs-Physik. 3. Das Lob der Sternkunst. 4. Ein Blick auf die Sternwarten. 5. Allgemeine Darstellungen der Sternkunde. 6. Schleppende Rezeption: Das kopernikanische Weltbild. 7. Himmelsphysik: Die Debatte um die causa gravitatis. 8. Theorie der Himmelskörper. 9. Die Erde als Gegenstand der Astronomie. 10. Die Sonne. 11. Der Mond. 12. Die Planeten. 13. Die Kometen. 14. Die Fixsterne. 15. Die Entstehung der Welt. 16. Beiträge der Astrotheologie. 17. Der Kampf gegen die Astrologen.

  1. Biochips und ihr Einsatz in der Lebensmittelanalytik

    NASA Astrophysics Data System (ADS)

    Huber, Ingrid; Zeltz, Patric

    Mit der Verbreitung des Begriffes "Biochip“ in den biotechnologischen Medien wurde Ende der 1990er-Jahre zunächst der Eindruck erweckt, dass die Computerelektronik in die molekularbiologischen Anwendungen eingestiegen ist [18]. In nur wenigen Jahren hat sich die Biochiptechnologie zu einem Verfahren entwickelt, das aus der molekularbiologischen Grundlagenforschung nicht mehr wegzudenken ist und über eine Vielzahl von Einsatzbereichen verfügt. Die Biochiptechnologie ermöglicht die Miniaturisierung von DNA-, RNA- bzw. Proteinanalytik in hochparallelen Formaten. Dieser hohe Parallelisierungsgrad ist einer der wesentlichen Vorteile dieser Technik gegenüber klassischen molekularbiologischen Methoden. Sie wird heutzutage vor allem in der Genomforschung eingesetzt, für Genexpressionsstudien, zum Screening von single nucleotide polymorphisms (SNPs), in der pharmakogenetischen Forschung sowie in der Erforschung von Erbkrankheiten und in der Krebsforschung [1, 7, 19]. Neben vielen weiteren Bereichen finden Biochips auch spezielle Anwendungen in der Lebensmittelanalytik.

  2. Dialektischer Materialismus in der Quantentheorie

    NASA Astrophysics Data System (ADS)

    Fuchs, Klaus

    Der absolute Determinismus der klassischen Mechanik bietet keine Ansatzpunkte für eine befriedigende Naturphilosophie. Mit der Quantenmechanik werden nicht lediglich die Unzulänglichkeiten einzelner klassischer Begriffe, sondern die des gesamten klassischen Begriffssystems beseitigt.Translated AbstractDialectical Materialism in Quantum TheoryThe absolute determinism of classical mechanics does not provide any base for a satisfactory philosophy of nature. In quantum mechanics the shortcomings of not only some single classical concepts but of the classical description as a whole are removed.

  3. Der evolutionäre Naturalismus in der Ethik

    NASA Astrophysics Data System (ADS)

    Kaiser, Marie I.

    Charles Darwin hat eindrucksvoll gezeigt, dass der Mensch ebenso wie alle anderen Lebewesen ein Produkt der biologischen Evolution ist. Die sich an Darwin anschließende Forschung hat außerdem plausibel gemacht, dass sich nicht nur viele der körperlichen Merkmale des Menschen, sondern auch (zumindest einige) seiner Verhaltensdispositionen in adaptiven Selektionsprozessen herausgebildet haben. Die Vorstellung, dass auch die menschliche Moralität evolutionär bedingt ist, scheint daher auf den ersten Blick ganz überzeugend. Schließlich hat die Evolutionstheorie in den vergangenen Jahrzehnten in vielen Bereichen (auch außerhalb der Biologie) ihre weitreichende Bedeutung unter Beweis gestellt. Warum sollte, so könnte man beispielsweise fragen, gerade die Fähigkeit des Menschen, moralische Normen aufzustellen und gemäß ihnen zu handeln, nicht evolutionär erklärt werden können? Und warum sollte eine solche evolutionäre Erklärung der menschlichen Moralität irrelevant für die Rechtfertigung moralischer Normen sein? Warum sollte die Ethik eine Bastion der Philosophen bleiben, für die evolutionsbiologische Forschungsergebnisse über den Menschen und seine nächsten Verwandten keinerlei Relevanz besitzen?

  4. Der Physik-Nobelpreis vor 100 Jahren Eine neue Eigenschaft der Materie

    NASA Astrophysics Data System (ADS)

    Jacobi, Manfred

    2003-11-01

    Im Jahre 1903 erhielten Henri Becquerel sowie Marie und Pierre Curie den Physik-Nobelpreis für die Entdeckung der Radioaktivität. Schon damals stellte Pierre Curie die Frage nach Nutzen und Gefahr dieser neuen Eigenschaft von Materie. Er war der Überzeugung, dass der Fortschritt letztlich mehr zum Nutzen als zum Schaden der Menschen beitrage.

  5. Physik gestern und heute Der Spion, der die Wärme untersuchte

    NASA Astrophysics Data System (ADS)

    Heering, Peter

    2003-11-01

    Der in Massachusetts geborene Benjamin Thompson, der ab 1792 auch den Titel eines Grafen von Rumford führte, ist eine der schillerndsten Figuren der Physikgeschichte. Berühmt wurde er insbesondere wegen seiner Experimente zur Wärmetheorie.http://www.famousamericans.net/benjaminthompsonrumford

  6. Coronellis Cosmos in der Melker Stiftsbibliothek.

    NASA Astrophysics Data System (ADS)

    Glaßner, Gottfried; Pärr, Nora

    2009-06-01

    Die Melker Stiftsbibliothek besitzt ein Globenpaar des berühmten venezianischen Globenbauers Vincenzo Coronelli (1650-1718), einen Erdglobus von 1688 und einen Himmelsglobus von 1693. Wie und wann die beiden Globen nach Melk gekommen sind, ist nicht bekannt. Dass sie zur ursprünglichen Ausstattung der 1735 fertig gestellten Barockbibliothek gehörten, wird aber aus der zentralen Stellung deutlich, die dem Globus (Erdglobus und Armillarphäre) in dem von Paul Troger 1732 gemalten Deckenfresko zukommt. Mehrfach begegnet das Motiv des Globus als Attribut der Weisheit bzw. Philosophie, der Geographie bzw. Geometrie und der Astronomie in den beiden Hauptsälen wie auch in der Deckenmalerei von Johann Bergl in der Oberen Bibliothek (1768) und in der Kuppel des Gartenpavillons (1764).

  7. Historisches Rätsel Der rastlose Amerikaner

    NASA Astrophysics Data System (ADS)

    Loos, Andreas

    2004-09-01

    In der Schule, die er mit acht Jahren zum ersten Mal von innen sah, hielt man ihn nicht für allzu helle - schließlich hinkte der Kleine oft hinter der Klasse her. Und es hat etwas Tragisches, wenn der wohl berühmteste Erfinder aller Zeiten und Halter von 2000 Patenten im Alter über seinen Vater sagt: Er dachte, ich sei dumm. Und ich meinte schon fast selbst, ich sei ein Dummkopf.

  8. [The 'van der Linden' retainer].

    PubMed

    van der Linden, F P

    2003-11-01

    Normally, only the anterior teeth have to be retained after an orthodontic treatment. For that purpose, a lingually bonded wire is preferred in the mandible and a removable plate in the maxilla. The design of the Van der Linden-retainer is based on theoretical considerations and secures rigid fixation of the six anterior teeth with solid anchorage in that region. A retention plate should not be used to move anterior teeth. However, with instant corrections small improvements can be realized. The fabrication and clinical use of the Van der Linden-retainer is explained and illustrated. PMID:14669487

  9. Der Begriff der Verständlichkeit in der modernen Physik (1948).

    PubMed

    Feyerabend, Paul K

    2016-06-01

    This is a critical transcription of Paul Feyerabend's earliest extant essay "Der Begriff der Verständlichkeit in der modernen Physik" (1948) recovered from the European Forum Alpbach archives. In it, Feyerabend defends positivism as a progressive framework for scientific research in certain stages of scientific development. He argues that in physics visualizability (Anschaulichkeit) and intelligibility (Verständlichkeit) are time-conditioned concepts: what is deemed visualizable in the development of physical theories is relative to a specific historical context and changes over time. He concludes that from time to time the abandonment of visualizability is crucial for progress in physics, as it is conducive to major theory change, illustrating the point on the basis of advances in atomic theory. PMID:27269264

  10. Ancillary Services Provided from DER

    SciTech Connect

    Campbell, J.B.

    2005-12-21

    Distributed energy resources (DER) are quickly making their way to industry primarily as backup generation. They are effective at starting and then producing full-load power within a few seconds. The distribution system is aging and transmission system development has not kept up with the growth in load and generation. The nation's transmission system is stressed with heavy power flows over long distances, and many areas are experiencing problems in providing the power quality needed to satisfy customers. Thus, a new market for DER is beginning to emerge. DER can alleviate the burden on the distribution system by providing ancillary services while providing a cost adjustment for the DER owner. This report describes 10 types of ancillary services that distributed generation (DG) can provide to the distribution system. Of these 10 services the feasibility, control strategy, effectiveness, and cost benefits are all analyzed as in the context of a future utility-power market. In this market, services will be provided at a local level that will benefit the customer, the distribution utility, and the transmission company.

  11. Ressourceneinsatzplanung In der Energie- und Verfahrenstechnik

    NASA Astrophysics Data System (ADS)

    Engell, Sebastian; Handschin, Edmund; Rehtanz, Christian; Schultz, Rüdiger

    Der ökologisch nachhaltige, wirtschaftlich effiziente und politisch faire Umgang mit den Ressourcen der Erde ist eine der größten Herausforderungen an die Menschheit im 21. Jahrhundert und impliziert Paradigmenwechsel in allen Bereichen des gesellschaftlichen Lebens. Energie- und Verfahrenstechnik sind traditionell Bereiche, in denen der optimale Umgang mit kostbaren und beschränkt verfügbaren Ressourcen von erstrangiger Bedeutung ist. Zur Lösung der damit verbundenen komplexen Entscheidungsprobleme sind mathematische Methoden schon seit längerem im Einsatz. Hierbei können aber noch längst nicht alle bislang aufgetretenen Probleme fundiert angegangen werden. Der wachsende wirtschaftliche und ökologische Druck auf die Effizienz der Produktions-und Versorgungssysteme sowie stärkere Schwankungen von Angebot und Nachfrage führen zu neuen Herausforderungen, für die neue mathematische Methoden und Algorithmen entwickelt werden müssen.

  12. Das Neutron, der Kosmos und die Kräfte: Neutronen in der Teilchenphysik

    NASA Astrophysics Data System (ADS)

    Soldner, Torsten

    2003-05-01

    Das Neutron besitzt eine einzigartige Kombination von Eigenschaften. Sie ermöglicht die Untersuchung aller vier elementaren Kräfte. Dabei wurden beeindruckende Resultate erzielt, wie die Präzisionsmessungen der elektrischen Ladung des Neutrons oder der Feinstrukturkonstante zeigen. Die genaue Bestimmung der schwachen Wechselwirkungsstärke der Nukleonen liefert der Astrophysik wichtige Daten. Die Messung eines von Null verschiedenen elektrischen Dipolmoments des Neutrons könnte einen entscheidenden Hinweis über die Physik jenseits des Standardmodells der Teilchenphysik geben. Doch auch zur Aufklärung von Unsicherheiten innerhalb des Standardmodells selbst tragen Neutronen bei.

  13. Verbesserung der Prozessbedingungen beim Einlippentiefbohren durch unterschiedliche Formen der Vorschubmodulation

    NASA Astrophysics Data System (ADS)

    Eisseler, Rocco

    Das Tiefbohren mit Einlippenwerkzeugen ist bei vielen Anwendungen das Verfahren der ersten Wahl, vor allem wenn kleine und kleinste Bohrungsdurchmesser, ein sehr großes Verhältnis zwischen Bohrtiefe und Durchmesser (l/D) und eine hohe Bearbeitungsqualität gefordert werden. Der erreichbare Durchmesserbereich des Verfahrens liegt zwischen D = 0,5 mm und 40 mm, wobei die möglichen Bohrtiefen von l = 3 x D bis 250 x D reichen. Diese Werte beziehen sich auf das Vollbohren, beim Aufbohren können noch größere Durchmesser erreicht werden [1]. Die erreichbare Oberflächenqualität ist so hoch, dass in den meisten Fällen auf eine nachfolgende Feinbearbeitung verzichtet werden kann.

  14. Aufgaben und Genauigkeit der klinischen Dosimetrie

    NASA Astrophysics Data System (ADS)

    Krieger, Hanno

    In diesem Kapitel werden die Aufgaben der klinischen Dosimetrie für die verschiedenen radiologischen Disziplinen zusammengestellt. Die wichtigste Aufgabe ist die Messung der im bestrahlten Medium entstandenen Energiedosis für die verschiedenen Strahlungsquellen. Die am weitesten verbreitete dazu verwendete Methode ist die Dosismessung mit gasgefüllten Ionisationskammern. Im zweiten Teil des Kapitels werden die Genauigkeitsanforderungen der klinischen Dosimetrie diskutiert.

  15. Friedrich Möglich - sein Beitrag zum Aufbau der Physik in der DDR. Friedrich Möglich - langjähriger Mitherausgeber und Chefredakteur der Annalen der Physik

    NASA Astrophysics Data System (ADS)

    Rompe, Robert

    Friedrich Möglich, ein Schüler von Max von Laue und Erwin Schrödinger, übernahm 1947 die Chefredaktion der Annalen der Physik.Translated AbstractFriedrich Möglich - His Contributions to the Formation of Physics in GDRFriedrich Möglich a student of Max von Laue and Erwin Schrödinger took over as editor in chief of Annalen der Physik in 1947.

  16. Tycho Brahe - Instrumentenbauer und Meister der Beobachtungstechnik

    NASA Astrophysics Data System (ADS)

    Wolfschmidt, Gudrun

    Vor der Erfindung des Fernrohrs war der dänische Astronom Tycho Brahe (1546 - 1601) der bedeutendste beobachtende Astronom. Von seinem Observatorium Uraniborg auf der - damals dänischen - Insel Hven ist heute noch der Grundriß erkennbar, von Stjerneborg sind die Fundamente erhalten, die Kuppeln in den 1950er Jahren ergänzt. In der Astronomie-Ausstellung im Deutschen Museum gibt es ein Modell der Sternwarte Uraniborg und der zugehörigen Instrumente (Maßstab 1:10); das größere Modell wurde dem Technischen Museum in Malmö geschenkt. Die Instrumente, die er in den Observatorien Uraniborg und Stjerneborg benutzte, sind nicht erhalten. Aber es gibt gute Beschreibungen der Instrumente (Halbkreis, Quadranten, Sextanten, Armillarsphären, Triquetrum, Himmelsglobus) in seinem Buch Astronomiae instauratae mechanica (Wandsbek 1598). Eine Nachbildung des großen hölzernen Quadranten kann man im Runden Turm in Kopenhagen sehen. Zwei Sextanten, hergestellt für Tycho um 1600 von Jost Bürgi und Erasmus Habermel, gibt es noch im Nationalmuseum für Technik in Prag. Ähnlichkeiten von Tychos Instrumenten mit Groß-Instrumenten aus dem islamischen Kulturkreis sind auffällig. Tycho Brahes Meßgeräte markieren einen großen Fortschritt in der Entwicklung astronomischer Instrumente und Meßtechniken und bilden die Grundlage für den weiteren Fortschritt der Positionsastronomie und der damit verbundenen Tabellenwerke. Die Nachwirkungen sind bis ins 17. und 18. Jahrhundert nachweisbar.

  17. Untersuchung der Richtwirkung der Einkopplung von ebenen Wellen in eine Leitung

    NASA Astrophysics Data System (ADS)

    Magdowski, M.; Vick, R.

    2013-07-01

    Elektrische Leitungen und Kabel stellen häufig die Haupteinfallstore für elektromagnetische Felder in die daran angeschlossenen Geräte und Systeme dar. Für die Einkopplung einer ebenen Welle kann der in eine Leitung eingekoppelte Strom unter bestimmten Voraussetzungen mit Hilfe der Leitungstheorie sehr effizient bestimmt werden. Er hängt dabei von den Abmessungen der Leitung, den Leitungsabschlüssen sowie der Amplitude, der Wellenlänge und der Einfallsrichtung der ebenen Welle ab. In dieser Arbeit wird die Abhängigkeit der Einkopplung von der Einfallsrichtung näher untersucht. Dazu werden Richtdiagramme der Einkopplung berechnet, dargestellt und hinsichtlich der mittleren und maximalen Einkopplung über alle Einfallsrichtungen und Polarisationen ausgewertet. Die Ergebnisse werden genutzt, um die maximale Direktivität der Einkopplung in eine Leitung zu bestimmen. Fasst man die Einkopplung externer Felder in eine Leitung als einen Störfestigkeitstest auf, so kann die maximale Direktivität benutzt werden, um einen Vergleich zwischen unterschiedlichen Messumgebungen wie Absorberhallen und Modenverwirbelungskammern herzustellen.

  18. Von Humboldt bis Einstein. Berlin als Weltzentrum der exakten Wissenschaften.

    NASA Astrophysics Data System (ADS)

    Meschkowski, H.

    Contents: 1. Die Anfänge. 2. Die Ära Dirichlet-Jacobi. 3. Der Ausbau der experimentellen Naturwissenschaften. 4. Alexander von Humboldt. 5. Berlin wird "Weltzentrum" der Mathematik. 6. Die Ära Helmholtz. 7. Neue Arbeitsweisen der Astronomie. 8. Chemie: Forschung und Industrie. 9. Max Planck. 10. Ins technische Zeitalter. 11. Zur Mathematik der zwanziger Jahre. 12. Albert Einstein. 13. Fortschritte der Grundlagenforschung. 14. Erwin Schrödinger: Physiker, Philosoph und Poet. 15. Zum Schluß.

  19. Werner Heisenberg zum 100. Geburtstag: Pionier der Quantenmechanik

    NASA Astrophysics Data System (ADS)

    Jacobi, Manfred

    2001-11-01

    Werner Heisenberg war eine der prägendsten Gestalten der Physik des 20. Jahrhunderts. Zu seinen wichtigsten Verdiensten gehören die Grundlegung der Quantenmechanik, die Formulierung der Unschärferelationen sowie die Beteiligung an der Ausarbeitung der Kopenhagener Deutung der Quantenmechanik. Darüber hinaus lieferte er Arbeiten von fundamentalem Charakter zur Theorie des Atomkerns, zur kosmischen Strahlung und zur Quantenfeldtheorie. Während des Krieges war er an den Arbeiten des Uranvereins beteiligt, der die Möglichkeit einer Entwicklung von Kernwaffen untersuchte, jedoch über Vorarbeiten zur Reaktorphysik nicht hinauskam. Wegen dieser Tätigkeit wurde er bei Kriegsende für einige Monate in England interniert. Nach seiner Rückkehr widmete er sich vor allem dem Aufbau der Physik in Deutschland, die während der NS-Zeit nahezu ihrer gesamten Substanz beraubt worden war.

  20. ARPES studies of van der Waals heterostructure

    NASA Astrophysics Data System (ADS)

    Wang, Eryin; Lu, Xiaobo; Chen, Guorui; Fedorov, Alexei V.; Zhang, Yuanbo; Zhang, Guangyu; Zhou, Shuyun

    Van der Waals heterostructures are a novel class of ``materials by design'' which are formed by stacking different two-dimensional crystals together via van der Waals interaction. The periodic potential by the Moir é superlattice can be used as a control knob for tuning the electronic properties of two dimensional materials and can induce various novel quantum phenomena. Here we report direct electronic structure studies the of a model van der Waals heterostructure using angle-resolved photoemission spectroscopy (ARPES). This work is supported by the National Natural Science Foundation of China and Ministry of Education of China.

  1. Qualitätsmanagement in der Lebensmittelindustrie

    NASA Astrophysics Data System (ADS)

    Thorn, Volker

    Die wesentlichen Kunden der Lebensmittelindustrie sind der Einzel- und Großhandel und die Verbraucher. Jedes Unternehmen kann mittel- und langfristig nur existieren, wenn seine Kunden zufrieden sind. Kunden sind zufrieden, wenn ihre Erwartungen, die sie an Produkt, Service und Preis stellen, erfüllt werden. Also die bestimmte erwartete Qualität (Leistung) sichergestellt wird. Trotz aller Bemühungen und Anstrengungen der Anbieter, Qualitätsprodukte auf den Markt zu bringen, kames in den letzten Jahren immer wieder zu Lebensmittelskandalen.

  2. Wie entsteht Bewusstsein?: Einfache Modelle der Selbstwahrnehmung

    NASA Astrophysics Data System (ADS)

    Schuster, Heinz Georg

    2003-07-01

    Was ist die funktionale Basis der Entstehung des Bewusstseins? Warum bringt dieses in der Evolution einen Vorteil? Diese Fragen werden anhand von drei Spielen untersucht, in denen die Spieler mathematisch modelliert sind. Im ersten Spiel lernt ein Spieler, seine Stellung in einer Hierarchie aus der Interaktion mit anderen zu erraten. Im zweiten Spiel macht ein Zuwachs des Gedächtnisses einen Spieler zum Gewinner: Das ermöglicht ihm einen Spiel entscheidenden Überblick über sein eigenes Verhalten und das seines Gegners. Im dritten Spiel müssen die Spieler die Farbe des Hutes auf dem eigenen Kopf aus der Reaktion des Gegners erraten. Hier ist die Fähigkeit von Vorteil, Inhalte aus dem Langzeit- und Kurzzeitgedächtnis im Geist abbilden und manipulieren zu können.

  3. Genetics Home Reference: van der Woude syndrome

    MedlinePlus

    ... people with this disorder are born with a cleft lip , a cleft palate (an opening in the roof ... People with van der Woude syndrome who have cleft lip and/or palate, like other individuals with these ...

  4. Checkpoint-Inhibitoren in der Immuntherapie: Ein Meilenstein in der Behandlung des malignen Melanoms.

    PubMed

    Wilden, Sophia M; Lang, Berenice M; Mohr, Peter; Grabbe, Stephan

    2016-07-01

    Seit Jahrzehnten ist bekannt, dass Tumoren vom Immunsystem erkannt und zerstört werden können. Diese, vor allem in Tierversuchen gewonnene Erkenntnis konnte jedoch in der Vergangenheit nicht zum Nutzen unserer Patienten umgesetzt werden, da immunonkologische Therapieansätze in den letzten Jahrzehnten in der Anwendung beim Menschen stets versagt haben. Daher hat, mit Ausnahme der adjuvanten Interferontherapie, keines dieser Verfahren den Einzug in die klinische Versorgung gefunden. Langzeitüberleben unter guter Lebensqualität war dabei sehr wenigen Patienten vorbehalten. Mit den neuen immunologischen Therapieansätzen wird jedoch sowohl das Langzeitüberleben als auch die Lebensqualität onkologischer Patienten neu definiert. Auf die neuen "Immun-Checkpoint-Inhibitoren" spricht erstmals ein relevanter Teil der behandelten Patienten an und diese zeigen in der Regel langandauernde Remissionen bis hin zur Heilung. Schon jetzt ist klar, dass die Immuntherapie in Zukunft eine der wesentlichen Therapiesäulen bei der Behandlung des metastasierten Melanoms und auch vieler anderer fortgeschrittener Tumoren bilden wird. In dieser Übersicht werden die wichtigsten neuen Therapiemodalitäten besprochen und sowohl deren Wirkprinzip als auch klinische Daten zum Therapieansprechen und zu erwartenden Nebenwirkungen der Therapie referiert. PMID:27373243

  5. Wie wissenschaftlich ist der Evolutionsgedanke?

    NASA Astrophysics Data System (ADS)

    Vollmer, Gerhard

    Darwin war ein besonnener Mann; alles Aufsehen war ihm zuwider. Trotzdem hat er eine Revolution ausgelöst, deren Wirkung nicht auf die Biologie beschränkt blieb. Seine Theorie lässt sich in fünf Teiltheorien zerlegen, die sich durch die Begriffe Artenwandel, Verwandtschaft alles Lebendigen und gemeinsamer Ursprung, Artenaufspaltung und Artenvielfalt, Gradualismus, natürliche Auslese charakterisieren lassen. Dadurch wurden mehrere religiöse und weitere weltanschauliche Überzeugungen in Frage gestellt. Deshalb wird die Evolutionstheorie auch heute noch vielfach kritisiert, ja bekämpft. Die Vorwürfe lassen sich ordnen nach den Kriterien, mit denen wir erfahrungswissenschaftliche Theorien beurteilen. Haltbar ist daran nur, dass es für die Evolutionstheorie zwar beliebig viele Bestätigungen gibt, aber nur wenige Widerlegungsmöglichkeiten. Durch die neuerdings entwickelten und durchgeführten Evolutionsexperimente ist die empirische Situation allerdings deutlich besser geworden. Am (erfahrungs)wissenschaftlichen Charakter der Evolutionstheorie besteht deshalb kein Zweifel.

  6. Historisches Rätsel Ein Pionier der Raumfahrt

    NASA Astrophysics Data System (ADS)

    Loos, Andreas

    2004-05-01

    Geschichten über seine Person muss man in der Regel mit Vorsicht genießen. Schließlich war der gesuchte Raketenforscher ein begabter Selbstdarsteller, der schon seine ersten größeren Versuche zu öffentlichen Flugschauen machte - und dafür Eintrittsgeld nahm.

  7. TÜV - Zertifizierungen in der Life Science Branche

    NASA Astrophysics Data System (ADS)

    Schaff, Peter; Gerbl-Rieger, Susanne; Kloth, Sabine; Schübel, Christian; Daxenberger, Andreas; Engler, Claus

    Life Sciences [1] (Lebenswissenschaften) sind ein globales Innovationsfeld mit Anwendungen der Bio- und Medizinwissenschaften, der Pharma-, Chemie-, Kosmetik- und Lebensmittelindustrie. Diese Branche zeichnet sich durch eine stark interdisziplinäre Ausrichtung aus, mit Anwendung wissenschaftlicher Erkenntnisse und Einsatz von Ausgangsstoffen aus der modernen Biologie, Chemie und Humanmedizin sowie gezielter marktwirtschaftlich orientierter Arbeit.

  8. Darwin, Engels und die Rolle der Arbeit in der biologischen und kulturellen Evolution des Menschen

    NASA Astrophysics Data System (ADS)

    Reichholf, Josef H.

    Im Jahre 1876, 5 Jahre nach Erscheinen von Darwins Buch über die Evolution des Menschen und die sexuelle Selektion (Darwin 1871), veröffentlichte Friedrich Engels den berühmt gewordenen Essay "Anteil der Arbeit an der Menschwerdung des Affen“ (Engels 1876). Die Kernfrage darin lautet in Kurzform: Warum hat der Mensch eigentlich ein Bedürfnis nach Arbeit? Engels Antwort wird nachfolgend näher betrachtet und vom gegenwärtigen Kenntnisstand aus beurteilt. Wie sich zeigen wird, beantworten seine Überlegungen die Frage nicht wirklich. Sie ist weiterhin offen. Es können lediglich einige zusätzliche Anhaltspunkte zur Diskussion gestellt werden. Angesichts des drängenden Problems millionenfacher Arbeitslosigkeit und der Forderungen nach einem "Grundrecht auf Arbeit“ kommt den Überlegungen zum möglichen Ursprung des Bedürfnisses nach Arbeit mehr als nur akademisches Interesse zu.

  9. Energetische Müllverwertung

    NASA Astrophysics Data System (ADS)

    Zahoransky, Richard; Allelein, Hans-Josef; Bollin, Elmar; Oehler, Helmut; Schelling, Udo

    In den 1970er Jahren entstand in der Bundesrepublik Deutschland das Bewusstsein für die Problematik von Mülldeponien mit ihren Sickerwässern und entweichenden Gasen. Die lokalen Müllkippen wurden zugunsten weniger zentraler, überwachter Anlagen geschlossen (Faustregel: Eine Zentraldeponie pro Landkreis).

  10. The Forced van der Pol Equation

    ERIC Educational Resources Information Center

    Fay, Temple H.

    2009-01-01

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

  11. Obituary for Jan van der Pers

    Technology Transfer Automated Retrieval System (TEKTRAN)

    After a short but valiant struggle against cancer, Jan van der Pers died on 29 April, 2006 in the hospital in Hilversum, The Netherlands, close to his home. Our conversations with Jan during the last months of his life showed the remarkable strength and positive attitude typical of him. Discussions...

  12. Die Evolution der Religiosität

    NASA Astrophysics Data System (ADS)

    Voland, Eckart

    Ein konsequent darwinischer Blick auf den Menschen bedeutet, auch im Denken, Fühlen und Handeln biologische Anpassungsgeschichte zu suchen, denn auch die psychischen und mentalen Eigenheiten des Homo sapiens unterliegen der natürlichen Selektion. Lässt sich die religiöse Lebenspraxis von Menschen daher auch aus einer Fitnessperspektive betrachten?

  13. Auf der Suche nach extrasolaren Transitplaneten

    NASA Astrophysics Data System (ADS)

    Heller, René

    2010-06-01

    Planeten um andere Sonnen, die von der Erde aus gesehen einmal während ihres Orbits vor ihrem Zentralstern vorbeiziehen, eröffnen eine bis vor Kurzem ungeahnte Palette an Möglichkeiten zu ihrer Untersuchung. Nur: Wo am Himmel lassen sich diese Kandidaten für Sternbedeckungen eigentlich finden?

  14. Chirurgische Behandlung von Melanomen in der Schwangerschaft: eine praktische Anleitung.

    PubMed

    Crisan, Diana; Treiber, Nicolai; Kull, Thomas; Widschwendter, Peter; Adolph, Oliver; Schneider, Lars Alexander

    2016-06-01

    Als ein Tumor, der primär eine chirurgische Behandlung erfordert, ist ein neu diagnostiziertes oder vorbestehendes Melanom in der Schwangerschaft eine klinische Rarität. In solchen Fällen steht der Chirurg vor der Herausforderung, ein geeignetes therapeutisches Vorgehen festlegen zu müssen. Auf der Grundlage unserer klinischen Erfahrung und einer Übersicht über die Literatur geben wir in der vorliegenden Arbeit eine Anleitung für das praktische Vorgehen bei dieser seltenen klinischen Konstellation. Unserer Erfahrung nach müssen schwangere Melanom-Patientinnen im Hinblick auf ihre therapeutischen Optionen ausführlich beraten werden. Naturgemäß setzen sie ihr ungeborenes Kind an die erste Stelle und zögern, der erforderlichen Operation zuzustimmen, obwohl bei ihnen eine möglicherweise lebensbedrohliche Erkrankung diagnostiziert worden ist. Daher ist es entscheidend, diese Patientinnen klar darüber zu informieren, dass, wie die vorliegenden medizinischen Erfahrungen zeigen, eine Schwangerschaft per se kein Grund ist, eine notwendige Melanom-Operation aufzuschieben. Jedoch müssen bei einigen Parametern wie den präoperativen Bildgebungsverfahren, der Positionierung auf dem Operationstisch, der Überwachung, Anästhesie und der perioperativen Medikation bestimmte Anpassungen vorgenommen werden, um der speziellen Situation Rechnung zu tragen. PMID:27240063

  15. Die neogene Hebungsgeschichte der Patagonischen Anden im Kontext der Subduktion eines aktiven Spreizungszentrums

    NASA Astrophysics Data System (ADS)

    Warkus, Frank

    2002-05-01

    Das Phänomen der Subduktion eines aktiven Spreizungszentrums an der Südspitze Südamerikas ist seit langem bekannt. Eine Vielzahl von geologischen Beobachtungen wurden mit diesem Phänomen in Verbindung gebracht, trotzdem ist der genaue Mechanismus der Beeinflussung des aktiven Kontinentalrandes weitgehend unbekannt. Die Zusammenhänge zwischen den Subduktionsprozessen und der Entwicklung der patagonischen Anden zwischen 47°S und 48°S stehen im Mittelpunkt der Untersuchungen. Um eine detaillierte zeitliche Auflösung der zugrunde liegenden Prozesse untersuchen zu können, wurde die Entwicklung der Vorlandsedimentation, die thermische Entwicklung und die Heraushebung der Oberkruste des andinen Orogens untersucht und diese in Bezug zur Subduktion des Chile-Rückens gesetzt. Im Bereich von 47°30′S wurden die synorogenen Vorlandsedimente der Santa Cruz Formation sedimentologisch untersucht. Diese fluviatilen Sedimente wurden in einem reliefarmen Vorlandgebiet durch häufige Rinnenverlagerung und dem Aufbau von Rinnenumlagerungsgürteln in Kombination mit assoziierten groräumigen Überflutungsablagerungen akkumuliert. Sie stehen in einem engen Zusammenhang mit der orogenen Entwicklung im andinen Liefergebiet. Dies spiegelt sich in dem nach oben gröber werdenden Zyklus der Santa Cruz Formation wider. Die magnetostratigraphischen Untersuchungen einer 270 m mächtigen Sequenz aus der Basis der Santa Cruz Formation, die mit 329 Einzelproben aus 96 Probenpunkten beprobt wurde, ergab 7 Umkehrungen der geomagnetischen Feldrichtung. Mit Hilfe der geomagnetischen Polaritätszeitskala (CANDE AND KENT, 1995) konnte der untersuchte Abschnitt der Santa Cruz Formation zwischen 16.2 und 18.5 Ma datiert werden. Als Träger der Sedimentations-Remanenz konnten überwiegend Pseudoeinbereichs-Magentitpartikel und untergeordnet Hämatitpartikel identifiziert werden. An drei Profilen der Santa Cruz Formation wurden aus Sandsteinlagen unterschiedlicher stratigraphischer Position

  16. Über die Methode der physikalischen Naturbeschreibung [33

    NASA Astrophysics Data System (ADS)

    Wenn es zu den Aufgaben der Philosophie und der wissensehaftlicher Theologie gehört, das Warum und Wie unserer Existenz und ihrer Umwelt zu ergründen, so muss als ihr Ausgangspunkt eine vollständige und möglichst übersichtliche Beschreibung unserer Empfindungen vorliegen. Einen Teil dieser Empfindungen fassen wir unter dem Namen Sinnesempfindungen zusammen. Ob ein solcher Aussehnitt genau abgegrenzt werden kann, soll hier nicht untersucht werden. Es kann sogar mit gewisser Berechtigung behauptet werden, dass eine Unterteilung gar nicht streng durchführbar ist. Der schon in der Philosophie der Antike uns entgegentretende Gedanke, dass die Welt nur in ihrer Gesamtheit rerständlich sein kann, kommt sicherlich der Wahrheit näher als die philosophischen Systeme des verflossenen Jahrhunderts, welche glaubten, dass alies aus unseren materialistischen Erkenntnissen heraus erklärt werden könne. Die Entstehung dieser Systeme, ich denke z. Â. an den Monisimis Haeckels, erklärt sich aus der Hybris, welche die Reaktion der Philosophie auf die bedeutenden Erfolge der exakten Naturwissenschaften war. Die ebenfalls nicht zu imterschätzenden Fortschritte unserer heutigen Kenntnisse auf diesem Gebiete zwingen din Naturforschung eher zu einer immer steigenden Bescheidenheit den "Welträtseln" gegenüber, deren letzte Konsequenz vielleicht darin liegen wird, dass sie die eingangs der Philosophie und Theologie zugewiesene Aufgabe als unlosbar bezeichnen muss..

  17. Resonance broadening and van der waals broadening

    NASA Astrophysics Data System (ADS)

    Mashonkina, L.

    2010-11-01

    Resonance broadening is important for the hydrogen lines in the spectra of F-type and later stars. In the corresponding temperature regime, the extended wings of the Balmer lines are used as a stellar effective temperature indicator. We show the effect of the use of two broadening theories, Ali & Griem (1965, 1966) and Barklem et al. (2000a, 2000b), on the effective temperature derived in non-LTE from Hα and Hβ in the Sun and the metal-poor star HD19445. Van der Waals broadening is important for strong spectral lines in the atmospheres of F-type and later stars. For the selected transitions in Ca I and Ca II, line profile comparisons are made between applying the van der Waals damping constants from laboratory measurements, the ABO perturbation theory, and the classic Unsöld approximation.

  18. van der Waals Forces between Cylinders

    PubMed Central

    Mitchell, D. J.; Ninham, B. W.; Richmond, P.

    1973-01-01

    We derive the retarded van der Waals interaction between two long thin parallel dielectric cylinders immersed in a solvent. The result shows that the ultraviolet interactions which may be responsible for the specificity of macromolecular interactions do not operate strongly over distances R ≥ 50 Å. For greater distances the contribution of these frequencies ξ is damped by a factor ∞ e-ξR/c. PMID:4696763

  19. Mehr Mathematik Wagen in der Medizin

    NASA Astrophysics Data System (ADS)

    Deuflhard, Peter; Dössel, Olaf; Louis, Alfred K.; Zachow, Stefan

    In diesem Artikel wird an drei Erfolgsmodellen dargestellt, wie das Zusammenwirken von Mathematik und Medizin eine Entwicklung hin zu patientenspezifischen Modellen auf Basis moderner medizinischer Bildgebung angestoßen hat, die in naher Zukunft dynamisch weiter Raum greifen wird. Dabei existiert ein Gleichklang der Interessen von Medizin und Mathematik: Beide Disziplinen wollen die Resultate schnell und zuverlässig. Für die Klinik heißt dies, dass notwendige Rechnungen in möglichst kurzer Zeit, und zwar auf dem PC, ablaufen müssen und dass die Resultate so genau und belastbar sein müssen, dass medizinische Entscheidungen darauf aufbauen können. Für die Mathematik folgt daraus, dass höchste Anforderungen an die Effizienz der verwendeten Algorithmen und die darauf aufbauende Software in Numerik und Visualisierung zu stellen sind. Allerdings ist es noch ein weiter Weg, bis anatomische und medizinisch brauchbare funktionelle Modelle auch nur für die wichtigsten Körperteile und die häufigsten Krankheitsfälle verfügbar sein werden. Führende Universitätskliniken könnten, als Zentren einer interdisziplinären Kooperation von Medizinern, Ingenieuren und Mathematikern, eine Vorreiterrolle dabei übernehmen, mehr Mathematik in der Medizin zu wagen. Dies wäre zweifellos ein wichtiger Schritt in Richtung auf eine individuelle quantitative Medizin, bei dem Deutschland die besten Voraussetzungen hätte, die Rolle des "Schrittmachers“ zu übernehmen.

  20. Zellulare Nichtlineare Netzwerke: Anwendungen in der Informationstechnologie

    NASA Astrophysics Data System (ADS)

    Tetzlaff, R.

    2007-06-01

    Zellulare Nichtlineare Netzwerke (CNN) wurden 1988 von Chua und Yang (Chua und Yang, 1988) eingeführt. Diese Netzwerke sind dadurch gekennzeichnet, dass eine Zelle, die die kleinste Einheit eines CNN darstellt, nur mit Zellen innerhalb einer bestimmten Umgebung verbunden ist. üblicherweise sind Art und Stärke der Wechselwirkung zwischen zwei Zellen eines CNN translationsinvariant, d.h. sie hängen nur von der relativen Lage beider Zellen zueinander ab. Im Vordergrund aktueller Arbeiten stehen auf derartigen Netzwerken basierende schaltungstechnische Realisierungen mit bis zu 176x144 Zellen, die eine direkte Verbindung zu zweidimensionalen optischen Sensor-Anordnungen aufweisen. Über einen separaten Speicherbereich können die Zellkopplungen eines Netzwerks verändert werden, wodurch eine adaptive Verarbeitung von mehrdimensionalen Sensorsignalen ermöglicht wird. Das kürzlich vorgestellte so genannte EyeRis System (Anafocus Ltd.) enthält zusätzlich noch einen Standardprozessor und stellt (bei einer Größe vergleichbar mit der einer Kreditkarte) daher ein vollständiges superschnelles System zur Informationsverarbeitung dar. In diesem Beitrag sollen, nach einem kurzen Überblick über die Eigenschaften von CNN, aktuelle Realisierungen und exemplarisch eine neuere eigene Anwendung vorgestellt und besprochen werden.

  1. Der Telemanipulator daVinci als mechanisches Trackingsystem

    NASA Astrophysics Data System (ADS)

    Käst, Johannes; Neuhaus, Jochen; Nickel, Felix; Kenngott, Hannes; Engel, Markus; Short, Elaine; Reiter, Michael; Meinzer, Hans-Peter; Maier-Hein, Lena

    Der Telemanipulator daVinci (Intuitive Surgical, Sunnyvale, Kalifornien) ist ein M aster-Slave System für roboterassistierte minimalinvasive Chirurgie. Da er über integrierte Gelenksensoren verfügt, kann er unter Verwendung der daVinci-API als mechanisches Trackingsystem verwendet werden. In dieser Arbeit evaluieren wir die Präzision und Genauigkeit eines daVinci mit Hilfe eines Genauigkeitsphantoms mit bekannten Maßen. Der ermittelte Positionierungsfehler liegt in der Größenordnung von 6 mm und ist somit für einen Großteil der medizinischen Fragestellungen zu hoch. Zur Reduktion des Fehlers schlagen wir daher eine Kalibrierung der Gelenksensoren vor.

  2. Zum Wissenschaftsverständnis der modernen Evolutionsbiologie

    NASA Astrophysics Data System (ADS)

    Sommer, Ralf J.

    Die moderne Evolutionsbiologie hat ihren Ursprung in den Arbeiten von Charles Darwin und Alfred Wallace (Darwin 1963). Der gemeinsame Ausgangspunkt des Evolutionsgedanken ist dabei die Beobachtung, dass die biologische Welt nicht konstant ist. Biologische Systeme und alle darin lebenden Organismen unterliegen über längere Zeiträume hinweg einer stetigen Veränderung. Diese grundlegende Eigenschaft biologischer Systeme macht die Biologie zu einer historischen Wissenschaft und stellt einen wichtigen Gegensatz zu großen Teilen der Physik dar. Obwohl die Aussage von der Veränderlichkeit der Arten heute trivial klingt, war sie im 19. Jahrhundert eine Revolution, da die Konstanz der Arten und der Welt eine vorherrschende Stellung im damaligen Weltbild hatte (Amundson 2005).

  3. Jahre Entwicklung der Instandhaltung - von der ausfallorientierten Instandhaltung zum gemeinsamen TPM und RCM

    NASA Astrophysics Data System (ADS)

    Iske, Friedhelm

    Zur Einleitung meines Beitrages möchte ich von einem Gespräch mit einem Mitarbeiter berichten, das ich als junger Vorgesetzter einer Instandhaltungsgruppe 1988 führte. Der engagierte Mitarbeiter feierte damals sein vierzigjähriges Dienstjubiläum und war stolz auf das von ihm Geleistete sowie auf den besonderen Einsatz seiner Altersgruppe, die nach dem Zweiten Weltkrieg das Werk wieder aufgebaut hatte. Auf meine Frage, was denn damals die erste Aufgabe in der Firma war, bekam ich kurz und knapp und mit einer Selbstverständlichkeit die selbstbewusste Antwort: "Unser Pferd füttern und mit dem Pferd die innerbetrieblichen Transporte erledigen“. Als junger, technisch orientierter Vorgesetzter war ich über diese Antwort sehr überrascht. Gedanklich weit entfernt war die Vorstellung, dass in der Vergangenheit Transporte mit einem Pferd erledigt wurden.

  4. Bereits nach Ablauf der Halbwertszeit droht der vollständige Zerfall Die britische Atomic Scientists’ Association, die Ideologie der „objektiven” Wissenschaft und die H-Bombe

    NASA Astrophysics Data System (ADS)

    Laucht, Christoph

    Präsident Harry Trumans Verlautbarung vom 31.1.1950, seine Regierung wolle die Entwicklung der Wasserstoffbombe vorantreiben, fand große Beachtung in den britischen Medien. Die illustrierte Zeitschrift Picture Post widmete der HBombe einen Artikel, der unter anderem kurze Stellungnahmen der britischen Atomwissenschaftler Eric Burhop, Kathleen Lonsdale, Harrie Massey, Rudolf Peierls und Maurice Pryce enthielt, die alle Mitglieder der Atomic Scientists' Association (ASA) waren.

  5. Information Interaction Study for DER and DMS Interoperability

    NASA Astrophysics Data System (ADS)

    Liu, Haitao; Lu, Yiming; Lv, Guangxian; Liu, Peng; Chen, Yu; Zhang, Xinhui

    The Common Information Model (CIM) is an abstract data model that can be used to represent the major objects in Distribution Management System (DMS) applications. Because the Common Information Model (CIM) doesn't modeling the Distributed Energy Resources (DERs), it can't meet the requirements of DER operation and management for Distribution Management System (DMS) advanced applications. Modeling of DER were studied based on a system point of view, the article initially proposed a CIM extended information model. By analysis the basic structure of the message interaction between DMS and DER, a bidirectional messaging mapping method based on data exchange was proposed.

  6. Phänomenologische Grundlagen der Wärmelehre

    NASA Astrophysics Data System (ADS)

    Heintze, Joachim

    Die Physik der Wärme lässt sich auf zweierlei Weise formulieren: Einmal als Mechanik eines Systems, das eine enorm große Zahl von Teilchen enthält (statistische Mechanik), und einmal mit Hilfe von ad hoc eingeführten Größen, den sogenannten Zustandsgrößen, die geeignet sind, das Verhalten eines solchen Systems zu beschreiben, ohne dass man die Teilchen selbst und ihre Bewegungen betrachten muss (Thermodynamik). Wir werden beide Ansätze in ihrer einfachsten und anschaulichsten Ausprägung in Kap. 5 (kinetische Gastheorie) bzw. in Kap. 8 (Grundbegriffe der Thermodynamik) behandeln. Obgleich sich die volle Durchführung des Programms als begrifflich und mathematisch recht schwierig erweist - die Vorlesung "Thermodynamik und Statistik" steht gewöhnlich am Ende der Kursvorlesungen über theoretische Physik - werden wir doch auf der Grundlage der Kap. 5 und 8 eine Menge über die Physik der Wärme lernen können. Den Ausgangspunkt der Wärmelehre bilden jedoch allemal die Naturerscheinungen, die wir hier in Kap. 4 behandeln wollen: Wärme, Kälte, Temperaturausgleich. Wir werden untersuchen, wie man diese Begriffe quantifizieren kann, und was bei der Erwärmung oder Abkühlung eines Körpers vor sich geht. Dabei werden wir auf den I. und II. Hauptsatz der Wärmelehre stoßen.

  7. Biological activity of recombinant Der p 2, Der p 5 and Der p 7 allergens of the house-dust mite Dermatophagoides pteronyssinus.

    PubMed

    Lynch, N R; Thomas, W R; Garcia, N M; Di Prisco, M C; Puccio, F A; L'opez, R I; Hazell, L A; Shen, H D; Lin, K L; Chua, K Y

    1997-09-01

    Der p 2, Der p 5 and Der p 7 are three allergens of the house-dust mite Dermatophagoides pteronyssinus that have been cloned and expressed in Escherichia coli as fusion proteins with glutathione-S-transferase (GST). We showed that these recombinant allergens produced immediate hypersensitivity skin-test reactions in 70, 60 and 52% respectively of a group of mite-sensitive allergic patients who were strongly positive to whole mite extract (WME). Comparable positivities were found for serum levels of specific IgE antibody against these allergens, as measured by the radioallergosorbant test (RAST). Overall, for the group of allergic patients that we evaluated, the serum IgE antibody concentrations against Der p 2, 5 and 7 were calculated to represent about one third, one quarter and one fifth respectively of the levels measured against the WME. However, for some patients the activity determined against the separate allergens was far higher than that detected against the WME, thus indicating that the concentration of these can be limiting in the WME. We found no significant correlations between the RAST levels against Derp 2 and either Derp 5 or 7, and RAST-inhibition tests indicated a lack of cross-reactivity between Der p 2 and the other two allergens. In contrast, the RAST results revealed the existence of a significant immunological relationship between Der p 5 and 7. Although a certain degree of reactivity against the GST fusion partner was found in the allergic patients studied, this was not a significant influence in determining the positivity against the recombinant allergens. These results confirm the in vivo biological activity of recombinant Der p 2, 5 and 7, and indicate that whilst Der p 2 is undoubtedly a major mite allergen, both Der p 5 and 7 make important contributions toward the overall allergenic activity of house-dust mites. PMID:9303332

  8. Die Deutsche Statistische Gesellschaft in der Weimarer Republik und während der Nazidiktatur

    NASA Astrophysics Data System (ADS)

    Wilke, Jürgen

    Nach anfänglichen Schwierigkeiten durch den 1. Weltkrieg erlangte die Deutsche Statistische Gesellschaft (DStatG) unter dem renommierten Statistiker und Vorsitzenden der DStatG, Friedrich Zahn, durch eine Vielzahl von Aktivitäten hohes Ansehen. Es gab Bestrebungen, Statistiker aus allen Arbeitsfeldern der Statistik in die DStatG zu integrieren, wobei die "Mathematische Statistik" nur zögerlich akzeptiert wurde (Konjunkturforschung, Zeitreihenanalyse). Nach der Machtübernahme 1933 durch Adolf Hitler geriet die DStatG in das Fahrwasser nationalsozialistischer Ideologie und Politik (Führerprinzip, Gleichschaltung des Vereinswesens). Damit war eine personelle Umstrukturierung in der DStatG verbunden. Politisch Missliebige und rassisch Verfolgte mussten die DStatG verlassen (Bernstein, Freudenberg, Gumbel u.a.). Unter den Statistikern gab es alle Abstufungen im Verhalten zum Regime von Ablehnung und zwangsweiser Anpassung über bereitwilliges Mitläufertum bis zu bewusster Täterschaft. Besonders die Bevölkerungsstatistik wurde durch die NS- Rassenpolitik auf lange Sicht diskreditiert. Im Rahmen von Wirtschaftsplanung und Aufrüstung wurden neue zukunftsträchtige statistische Modelle (Grünig, Bramstedt, Leisse) entwickelt.

  9. van der Waals Heterostructures Grown by MBE

    NASA Astrophysics Data System (ADS)

    Hinkle, Christopher

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

  10. Kanban - der Weg ist das Ziel

    NASA Astrophysics Data System (ADS)

    Aull, Florian; Berlak, Joachim; Dickmann, Eva; Dickmann, Philipp; Fischäder, Holm; Gerlach, Joachim; Henneberg, Jens; Kapalla, Klaus; Kress, Oliver; Kuttler, Robert; Schneider, Herfried M.; Schürle, Philipp; Stellpflug, Franz-Josef; Wannenwetsch, Ralph; Wulz, Johannes; Zäh, Michael F.

    Wenn man aktuell Produktionsbereiche in Deutschland und Europa besucht, fallen im Zusammenhang mit modernen Produktionsmethoden immer öfter die Begriffe Kanban (jap. Karte, Signal) und Pull-Produktion, und dies nicht ohne Stolz, da diese mit dem schillernden Vorbild des Toyota Produktionssystems in Zusammenhang stehen. Tatsächlich ist Kanban ein integraler Bestandteil moderner Produktionssysteme. Blickt man aber im Rahmen von Prozessanalysen hinter die Fassaden", d. h. in die tägliche Praxis der Arbeitsprozesse, wird man schnell desillusioniert - die viel gepriesenen klassischen Kanban-Regeln werden im Tagesgeschäft nicht eingehalten.

  11. Komplexität der Geographie

    NASA Astrophysics Data System (ADS)

    Diekert, Volker; Hertrampf, Ulrich

    Das allgemein als Prototyp eines PSPACE-vollständigen Spiels gesehene Geographiespiel wird bezüglich seiner Komplexität genauer untersucht. Das Interesse der theoretischen Informatik an diesem Spiel wurde sehr durch die Darstellung in dem Lehrbuch von Papadimitriou [Pap94] gefördert. Allerdings bestimmt dieses Lehrbuch nicht die Komplexität des Standardspiels sondern verwendet eine Verallgemeinerung. Die Aussage in dem Lehrbuch bleibt damit etwas unbefriedigend und hinter den Möglichkeiten. Wir zeigen hier, dass die komplexitätstheoretische Charakterisierung schon für die Standardvariante des Spiels gilt.

  12. Physik gestern und heute: Visualisierung mit der Schlierenmethode

    NASA Astrophysics Data System (ADS)

    Heering, Peter

    2006-07-01

    Der Name des österreichischen Forschers Ernst Mach ist heute noch mit der Schallgeschwindigkeit verbunden. Diese Auszeichnung resultiert aus Machs Untersuchungen, wie sich Projektile mit Überschallgeschwindigkeit durch die Luft bewegen. Gerade in jüngster Zeit hat die Anwendung derartiger Methoden durch technische Modifikationen wieder einen Aufschwung erfahren.

  13. Modellierung des Einflusses der Landnutzung auf die Hochwasserentstehung in der Mesoskala

    NASA Astrophysics Data System (ADS)

    Niehoff, Daniel

    2001-10-01

    Seit 1990 waren mehrere der großen Flussgebiete Mitteleuropas wiederholt von extremen Hochwassern betroffen. Da sowohl die Landoberfläche als auch die Flusssysteme weiter Teile Mitteleuropas in der Vergangenheit weitreichenden Eingriffen ausgesetzt gewesen sind, wird bei der Suche nach den Ursachen für diese Häufung von Extremereignissen auch die Frage nach der Verantwortung des Menschen hierfür diskutiert. Gewässerausbau, Flächenversiegelung, intensive landwirtschaftliche Bodenbearbeitung, Flurbereinigung und Waldschäden sind nur einige Beispiele und Folgen der anthropogenen Eingriffe in die Landschaft. Aufgrund der Vielfalt der beteiligten Prozesse und deren Wechselwirkungen gibt es allerdings bislang nur Schätzungen darüber, wie sehr sich die Hochwassersituation hierdurch verändert hat. Vorrangiges Ziel dieser Arbeit ist es, mit Hilfe eines hydrologischen Modells systematisch darzustellen, in welcher Weise, in welcher Größenordnung und unter welchen Umständen die Art der Landnutzung auf die Hochwasserentstehung Einfluss nimmt. Dies wird anhand exemplarischer Modellanwendungen in der hydrologischen Mesoskala untersucht. Zu diesem Zweck wurde das deterministische und flächendifferenzierte hydrologische Modell wasim-eth ausgewählt, das sich durch eine ausgewogene Mischung aus physikalisch begründeten und konzeptionellen Ansätzen auszeichnet. Das Modell wurde im Rahmen dieser Arbeit um verschiedene Aspekte erweitert, die für die Charakterisierung des Einflusses der Landnutzung auf die Hochwasserentstehung wichtig sind: (1) Bevorzugtes Fließen in Makroporen wird durch eine Zweiteilung des Bodens in Makroporen und Bodenmatrix dargestellt, die schnelle Infiltration und Perkolation jenseits der hydraulischen Leitfähigkeit der Bodenmatrix ermöglicht. (2) Verschlämmung äußert sich im Modell abhängig von Niederschlagsintensität und Vegetationsbedeckungsgrad als Verschlechterung der Infiltrationsbedingungen an der Bodenoberfläche. (3) Das

  14. Evaluation of Distribution Analysis Software for DER Applications

    SciTech Connect

    Staunton, RH

    2003-01-23

    The term ''Distributed energy resources'' or DER refers to a variety of compact, mostly self-contained power-generating technologies that can be combined with energy management and storage systems and used to improve the operation of the electricity distribution system, whether or not those technologies are connected to an electricity grid. Implementing DER can be as simple as installing a small electric generator to provide backup power at an electricity consumer's site. Or it can be a more complex system, highly integrated with the electricity grid and consisting of electricity generation, energy storage, and power management systems. DER devices provide opportunities for greater local control of electricity delivery and consumption. They also enable more efficient utilization of waste heat in combined cooling, heating and power (CHP) applications--boosting efficiency and lowering emissions. CHP systems can provide electricity, heat and hot water for industrial processes, space heating and cooling, refrigeration, and humidity control to improve indoor air quality. DER technologies are playing an increasingly important role in the nation's energy portfolio. They can be used to meet base load power, peaking power, backup power, remote power, power quality, as well as cooling and heating needs. DER systems, ranging in size and capacity from a few kilowatts up to 50 MW, can include a number of technologies (e.g., supply-side and demand-side) that can be located at or near the location where the energy is used. Information pertaining to DER technologies, application solutions, successful installations, etc., can be found at the U.S. Department of Energy's DER Internet site [1]. Market forces in the restructured electricity markets are making DER, both more common and more active in the distribution systems throughout the US [2]. If DER devices can be made even more competitive with central generation sources this trend will become unstoppable. In response, energy

  15. Endoskopie, minimal invasive chirurgische und navigierte Verfahren in der Urologie

    NASA Astrophysics Data System (ADS)

    Grosse, Joachim; von Walter, Matthias; Jakse, Gerhard

    Betrachtet man die letzten 100 Jahre der Urologie in Deutschland seit Gründung ihrer Fachgesellschaft 1906 in Stuttgart, so sind sicherlich die letzten 25 Jahre von umfassenden Entwicklungen mit z. T. vollständigen Umwälzungen bisheriger Therapien und Methoden auf urologischen Fachgebiet gekennzeichnet. In erster Linie handelte es sich dabei um minimal invasive endoskopische Techniken wie perkutane Nierenchirurgie, Ureterorenoskopie, videoendoskopisch unterstütze transurethrale Elektroresektionen der Prostata und von Blasentumore sowie die Laparoskopie. Sie führten zu besseren operativen Ergebnissen und einer deutlichen Senkung der Morbidität der entsprechenden Behandlung urologischer Krankheitsbilder, mit der Konsequenz, dass einige bisher als Standard gültige offene Operationsverfahren abgelöst wurden.

  16. Vollautomatische Segmentierung der Prostata aus 3D-Ultraschallbildern

    NASA Astrophysics Data System (ADS)

    Heimann, Tobias; Simpfendörfer, Tobias; Baumhauer, Matthias; Meinzer, Hans-Peter

    Diese Arbeit beschreibt ein modellbasiertes Verfahren zur Segmentierung der Prostata aus 3D-Ultraschalldaten. Kern der Methode ist ein statistisches Formmodell, das auf Beispieldaten der Prostata trainiert wird. Erster Schritt der Segmentierung ist ein evolutionärer Algorithmus, mit dem das Modell grob im zu segmentierenden Bild positioniert wird. Für die darauf folgende lokale Suche wurden mehrere Varianten des Algorithmus evaluiert, unter anderem Ausreißer-Unterdrückung, freie Deformation und Gewichtung der verwendeten Erscheinungsmodelle nach ihrer Zuverlässigkeit. Alle Varianten wurden auf 35 Ultraschallbildern getestet und mit manuellen Referenzsegmentierungen verglichen. Die beste Variante erreichte eine durchschnittliche Oberflächenabweichung von 1.1 mm.

  17. elecTUM: Umsetzung der eLearning-Strategie der Technischen Universität München

    NASA Astrophysics Data System (ADS)

    Rathmayer, Sabine; Gergintchev, Ivan

    An der TUM wurde ein umfassendes und integriertes eLearning-Konzept umgesetzt, welches Präsenzstudium und eLearning in allen Leistungsbereichen der Universität miteinander verzahnt. Ein besonderer Schwerpunkt lag dabei in der Schaffung einer effizienten und wettbewerbsfähigen integrierten eLearning Infrastruktur in Hinblick auf die noch weiter steigenden Studienanfängerzahlen ab dem Jahr 2011 sowie die Umsetzung von eBologna. Die Etablierung einer hochschulweiten Lernplattform stellte eine wesentliche Basis für die Umsetzung der eLearning-Strategie dar. Die wissenschaftliche und wirtschaftliche Anschlussfähigkeit im Hinblick auf eine Verwertung der Projektergebnisse wurde durch die aktive Beteiligung an einer Vielzahl hochschulübergreifender Arbeitskreise, Fachtagungen und Kooperationen, vor allem über Organisations- und Dienstleistungsmodelle sowie innovative technische Entwicklungen, sichergestellt.

  18. Werner-Syndrom. Eine prototypische Form der segmentalen Progerie

    PubMed Central

    Lessel, D.; Oshima, J.; Kubisch, C.

    2013-01-01

    Das Werner-Syndrom ist eine segmental progeroide Erkrankung mit Beginn in der Adoleszenz oder im frühen Erwachsenenalter. Typische Symptome, die zum vorgealterten Phänotyp beitragen, sind ein post-pubertär auftretender Kleinwuchs, Katarakte, eine vorzeitige Ergrauung/Ausdünnung des Haupthaars, sklerodermieähnliche Hautveränderungen und eine regionale Atrophie des subkutanen Fettgewebes. Darüber hinaus kommt es früh und gehäuft zu „Alterserkrankungen“ wie z. B. einem Diabetes mellitus Typ 2, einer Osteoporose, einer Atherosklerose sowie verschiedenen malignen Tumoren. Das Werner-Syndrom wird autosomal- rezessiv vererbt und ist durch Mutationen im Werner-Gen (WRN) bedingt. Es wurden bis heute mehr als 70 über das gesamte Gen verteilte Mutationen identifiziert, die typischerweise zu einem Verlust der Genfunktion führen. WRN kodiert für eine RecQ-Typ- Helikase, die u. a. an der DNA-Reparatur und der Aufrechterhaltung der DNA-Integrität beteiligt ist, was sich in einer erhöhten genetischen Instabilität in Patientenzellen wider-spiegelt. Trotz der relativen Seltenheit ist die Analyse des Werner-Syndroms von allgemeiner Bedeutung, um die Rolle der DNA-Stabilität und Integrität für das Altern sowie die Entwicklung altersassoziierter Erkrankungen besser zu verstehen. PMID:25309043

  19. Echtzeitfähigkeit von Satellitenkompassen in der Binnenschifffahrt

    NASA Astrophysics Data System (ADS)

    Haberkamp, G.; Zöbel, D.

    In der maritimen Schifffahrt finden Satellitenkompasse schon seit längerem Verwendung. Nachdem diese Geräte immer erschwinglicher werden, stellt sich die Frage, ob sie auch als Multisensoren für Telematikanwendungen in der Binnenschifffahrt geeignet sind. Im Rahmen einer umfassenden Untersuchung wurde auch die Fragestellung untersucht, wie zeitnah die Sensorinformationen verfügbar werden. Es wurde ein Versuchsaufbau entwickelt, der es ermöglicht, Satellitenkompasse auf ihre Echtzeitfähigkeit hin zu überprüfen. Das vorliegende Papier beschreibt den entwickelten Versuchsaufbau, dokumentiert die Ergebnisse und gibt einen Ausblick auf Verbesserungspotenziale.

  20. Nanophysik: Wärmeübertrag auf der Nanometerskala

    NASA Astrophysics Data System (ADS)

    Kittel, Achim

    2006-01-01

    Gegen Ende des 19. Jahrhunderts waren die grundlegenden Prozesse des Wärmeaustauschs verstanden. Die Gesetze dienten dann als Grundlage für die Quantenmechanik. Doch gelten diese Gesetze auch auf der Nanometerskala? In den 1970er-Jahren wurde eine Theorie für den Wärmeübertrag im atomaren Bereich entwickelt. Physiker der Universität Oldenburg überprüften deren Vorhersagen und stießen dabei auf signifikante Abweichungen, welche auf einen Zusammenbruch der klassischen, makroskopischen Elektrodynamik hindeuten.

  1. Kernschmelze Der nachhaltige Einfluss von Nuklearwaffen auf Politik und Wirtschaft

    NASA Astrophysics Data System (ADS)

    Greiner, Bernd

    "Was sollen wir von einer Kultur halten, der die Ethik stets als wesentliches Element des menschlichen Lebens galt, die aber - außer in fachlicher oder spieltheoretischer Terminologie - nicht in der Lage war, über die Möglichkeit zu sprechen, nahezu alle Menschen zu töten?" Der Fragesteller gehört zu den berühmtesten Physikern des 20. Jahrhunderts und zu den nach wie vor Umstrittensten. über ihn wurde in den 1960er Jahren ein international viel beachtetes Theaterstück geschrieben, vor wenigen Jahren gar eine Oper.

  2. Trends in der IT-Sicherheit

    NASA Astrophysics Data System (ADS)

    Eckert, Claudia

    Ich möchte Ihnen einen Überblick geben über Trends, Challenges, offene Fragestellungen sowie Lösungsansätze aus dem Bereich der IT-Sicherheit. Meine Vorredner haben mir schon eine wunderbare Basis dafür geschaffen, indem sie wichtige Trends im Bereich IT bereits angesprochen haben. Deshalb werde ich auf diese Trends, nämlich das Internet of Things and Services nur noch einmal kurz eingehen, um daran dann die IT-Sicherheitsthemen, die sich aus diesen IT-Trends ergeben, zu skizzieren und anschließend Lösungen vorstellen, die insbesondere im Forschungsumfeld entwickelt werden, aber schon reif sind, auch in die unternehmerische Praxis übernommen zu werden.

  3. Tunnelling in van der Waals heterostructures

    NASA Astrophysics Data System (ADS)

    Mishchenko, Artem; Novoselov, Kostya; Geim, Andre; Eaves, Laurence; Falko, Vladimir

    When graphene and other conductive two-dimensional (2D) materials are separated by an atomically thin insulating 2D crystal, quantum mechanical tunnelling leads to appreciable current between two 2D conductors due to the overlap of their wavefunctions. These tunnel devices demonstrate interesting physics and potential for applications: such effects as resonant tunnelling, negative differential conductance, light emission and detection have already been demonstrated. In this presentation we will outline the current status and perspectives of tunnelling transistors based on 2D materials assembled into van der Waals heterostructures. Particularly, we will present results on mono- and bilayer graphene tunnelling, tunnelling in 2D crystal-based quantum wells, and tunnelling in superconducting 2D materials. Such effects as momentum and chirality conservation, phonon- and impurity-assisted tunnelling will also be discussed. Finally, we will ponder the implications of discovered effects for practical applications.

  4. Melker Meilensteine auf dem Weg in ein naturwissenschaftliches Zeitalter - Glanzlichter der Ausstellung zum Internationalen Astronomiejahr 2009 in der Melker Stiftsbibliothek.

    NASA Astrophysics Data System (ADS)

    Beck, Paul G.; Zotti, Georg

    2009-06-01

    Das Mittelalter wird weithin als die dunkle Epoche in der Geschichte der Europäischen Wissenschaften betrachtet, und insbesondere das Leben in den Klöstern galt lange Zeit als frei von jeglichem Interesse für Naturwissenschaften abseits der Medizin. Im Mittelalter galt die Astronomie bloß als Mittel zum Zweck, um religiöse und zivile Kalender erstellen zu können. Durch den Bestand der Handschriftenkammer der Melker Stiftsbibliothek eröffnet sich uns eine neue Sichtweise auf das gegen Ende des Mittelalters wachsende Interesse an den Naturwissenschaften. Dies wurde durch die starke Aufwertung der Klosterbibliothek im Rahmen der 'Melker Reform' im 15. Jahrhundert noch weiter verstärkt. Diese Epoche fällt mit der Frühphase der Universität Wien und der 'ersten Wiener Schule der Astronomie' zusammen. Dieser Artikel beleuchtet ausgewählte astronomischen Werke in der Melker Stiftsbibliothek zwischen dem frühen 9 und dem 18. Jahrhundert. Einen Schwerpunkt stellt das Wirken der Wiener Schule der Astronomie dar, wobei wir u.a. die Melker Abschrift von Peuerbachs Gutachten über den Kometen von 1456 sowie die im Stift Melk durchgeführte Beobachtung der Mondfinsternis von 1457 durch Regiomontanus und Peuerbach beleuchten. Dieser Beitrag ist der einführende Übersichtsartikel zum Ausstellungsprojekt in der Melker Stiftsbibliothek im Rahmen des Internationalen Jahres der Astronomie 2009. The medieval period is commonly seen as a dark epoch for science in Europe. Especially monasteries were seen as institutions without interest in natural sciences except for medicine. Astronomy was allegedly only a tool to construct religious and civil calendars. The inventory of the medieval manuscript collection of the library of the Abbey of Melk allows a new view on the growing interest in the exact sciences towards the end of the medieval ages. This interest was intensified through the increased importance of the monastery library due to the monastery reform

  5. Isotope separation by photodissociation of Van der Waal's molecules

    DOEpatents

    Lee, Yuan T.

    1977-01-01

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

  6. Die Anfaenge der Melker Bibliothek - Neue Erkenntnisse zu Handschriften und Fragmenten aus der Zeit vor 1200

    NASA Astrophysics Data System (ADS)

    Glaßner, Christine; Haidinger, Alois

    1996-04-01

    Shortly after Benedictine monks started monastic life in Melk in 1089 the scriptorium was flourishing under abbot Erchenfried (1121-1164). Noteworthy is Cod. 391, a manuscript written in its main part in 1123, but used by the monks as a yearbook with handwritten entries up to the 16th century. This manuscript was also an important source for the publication which dealt with the history of the scriptorium in 12th century. By examining the entries in this book the period of the activity of at least three unknwon writers in this era could be identified. It was the first time that not only the intact volumes but also the manuscripts preserved as fragments in the binding were examined. At the beginning of th 13th century the number of books held in the collection according to the result of this examination was 68. Another remarkable point of the exhibition and of the publication refering to the exhibition was Cod. 412, the oldest manuscript of the monastery, written in early 9th century and containing texts on natural sciences and astronomy by Venerable Bede. Three copies of this manuscript were done during 12th century, one of them probably in Melk, all of them with nearly identical consistency except the catalogue of signs of the zodiac which was ascribed erroneously to Venerable Bede in the Middle Ages: Vatican, Cod. Vat. lat. 643, Zwettl, Cod. 296 (copy of the Vatican manuscript), Klosterneuburg, Cod. 685 (copy of the Zwettl manuscript done in Klosterneuburg). Kurz nach Einführung der Benediktiner in Melk im Jahr 1089 erlebte das Melker Skriptorium unter Abt Erchenfried (1121-1163) seine erste Blüte. Hervorzuheben ist eine im Jahr 1123 angelegte Chronik, die bis in das 16. Jahrhundert durch Annaleneintragungen und andere wichtige Texte zur Geschichte des Klosters ergänzt wurde (Cod. 391). Diese Handschrift ist zugleich eine der wichtigsten Quellen zur Geschichte des Melker Skriptoriums im 12. Jahrhundert, dem sich die Publikation widmet. Mit Hilfe einer genaueren

  7. Picosecond photoresponse in van der Waals heterostructures.

    PubMed

    Massicotte, M; Schmidt, P; Vialla, F; Schädler, K G; Reserbat-Plantey, A; Watanabe, K; Taniguchi, T; Tielrooij, K J; Koppens, F H L

    2016-01-01

    Two-dimensional crystals such as graphene and transition-metal dichalcogenides demonstrate a range of unique and complementary optoelectronic properties. Assembling different two-dimensional materials in vertical heterostructures enables the combination of these properties in one device, thus creating multifunctional optoelectronic systems with superior performance. Here, we demonstrate that graphene/WSe2/graphene heterostructures ally the high photodetection efficiency of transition-metal dichalcogenides with a picosecond photoresponse comparable to that of graphene, thereby optimizing both speed and efficiency in a single photodetector. We follow the extraction of photoexcited carriers in these devices using time-resolved photocurrent measurements and demonstrate a photoresponse time as short as 5.5 ps, which we tune by applying a bias and by varying the transition-metal dichalcogenide layer thickness. Our study provides direct insight into the physical processes governing the detection speed and quantum efficiency of these van der Waals heterostuctures, such as out-of-plane carrier drift and recombination. The observation and understanding of ultrafast and efficient photodetection demonstrate the potential of hybrid transition-metal dichalcogenide-based heterostructures as a platform for future optoelectronic devices. PMID:26436565

  8. Van der Waals Interactions Involving Proteins

    NASA Technical Reports Server (NTRS)

    Roth, Charles M.; Neal, Brian L.; Lenhoff, Abraham M.

    1996-01-01

    Van der Waals (dispersion) forces contribute to interactions of proteins with other molecules or with surfaces, but because of the structural complexity of protein molecules, the magnitude of these effects is usually estimated based on idealized models of the molecular geometry, e.g., spheres or spheroids. The calculations reported here seek to account for both the geometric irregularity of protein molecules and the material properties of the interacting media. Whereas the latter are found to fall in the generally accepted range, the molecular shape is shown to cause the magnitudes of the interactions to differ significantly from those calculated using idealized models. with important consequences. First, the roughness of the molecular surface leads to much lower average interaction energies for both protein-protein and protein-surface cases relative to calculations in which the protein molecule is approximated as a sphere. These results indicate that a form of steric stabilization may be an important effect in protein solutions. Underlying this behavior is appreciable orientational dependence, one reflection of which is that molecules of complementary shape are found to exhibit very strong attractive dispersion interactions. Although this has been widely discussed previously in the context of molecular recognition processes, the broader implications of these phenomena may also be important at larger molecular separations, e.g., in the dynamics of aggregation, precipitation, and crystal growth.

  9. Supercurrent in van der Waals Josephson junction

    PubMed Central

    Yabuki, Naoto; Moriya, Rai; Arai, Miho; Sata, Yohta; Morikawa, Sei; Masubuchi, Satoru; Machida, Tomoki

    2016-01-01

    Supercurrent flow between two superconductors with different order parameters, a phenomenon known as the Josephson effect, can be achieved by inserting a non-superconducting material between two superconductors to decouple their wavefunctions. These Josephson junctions have been employed in fields ranging from digital to quantum electronics, yet their functionality is limited by the interface quality and use of non-superconducting material. Here we show that by exfoliating a layered dichalcogenide (NbSe2) superconductor, the van der Waals (vdW) contact between the cleaved surfaces can instead be used to construct a Josephson junction. This is made possible by recent advances in vdW heterostructure technology, with an atomically flat vdW interface free of oxidation and inter-diffusion achieved by eliminating all heat treatment during junction preparation. Here we demonstrate that this artificially created vdW interface provides sufficient decoupling of the wavefunctions of the two NbSe2 crystals, with the vdW Josephson junction exhibiting a high supercurrent transparency. PMID:26830754

  10. Van der Waals interactions involving proteins.

    PubMed Central

    Roth, C M; Neal, B L; Lenhoff, A M

    1996-01-01

    Van der Waals (dispersion) forces contribute to interactions of proteins with other molecules or with surfaces, but because of the structural complexity of protein molecules, the magnitude of these effects is usually estimated based on idealized models of the molecular geometry, e.g., spheres or spheroids. The calculations reported here seek to account for both the geometric irregularity of protein molecules and the material properties of the interacting media. Whereas the latter are found to fall in the generally accepted range, the molecular shape is shown to cause the magnitudes of the interactions to differ significantly from those calculated using idealized models, with important consequences. First, the roughness of the molecular surface leads to much lower average interaction energies for both protein-protein and protein-surface cases relative to calculations in which the protein molecule is approximated as a sphere. These results indicate that a form of steric stabilization may be an important effect in protein solutions. Underlying this behavior is appreciable orientational dependence, one reflection of which is that molecules of complementary shape are found to exhibit very strong attractive dispersion interactions. Although this has been widely discussed previously in the context of molecular recognition processes, the broader implications of these phenomena may also be important at larger molecular separations, e.g., in the dynamics of aggregation, precipitation, and crystal growth. Images FIGURE 3 PMID:8789115

  11. Modern theory of van der Waals interactions

    NASA Astrophysics Data System (ADS)

    Dobson, John

    2014-03-01

    van der Waals (vdW, dispersion) interactions are important in diverse areas such as colloid, surface and nano science, cohesion of molecular crystals, and biomolecular science. They also provide competition in experiments to discover the fifth fundamental force.While vdW interactions have been understood in principle for a century, their quantitative first-principles prediction and modelling down to chemical contact separations have proven stubbornly difficult because the quantal many-electron problem is involved. After some brief historical material, the current state of the art will be discussed with particular reference to several approaches: pairwise additive, perturbative quantum chemical, vdW-DF, Lifshitz-like scattering, RPA-like, Adiabatic Connection Fluctuation Dissipation / Time Dependent DFT based etc.. A potentially useful classification will be introduced to aid in understanding the physical causes of departures from pairwise additivity, that is from the usual sum of C6R-6 contributions. These departures result in non-standard power law decays of nanostructure vdW interactions as a function of separation D, as well as surprising dependences of the attraction on the number, N, of atoms within each vdW-interacting fragment. Some further recent results on non-additivity will also be presented. Work supported by an Australian Research Council Discovery Grant.

  12. Picosecond photoresponse in van der Waals heterostructures

    NASA Astrophysics Data System (ADS)

    Massicotte, M.; Schmidt, P.; Vialla, F.; Schädler, K. G.; Reserbat-Plantey, A.; Watanabe, K.; Taniguchi, T.; Tielrooij, K. J.; Koppens, F. H. L.

    2016-01-01

    Two-dimensional crystals such as graphene and transition-metal dichalcogenides demonstrate a range of unique and complementary optoelectronic properties. Assembling different two-dimensional materials in vertical heterostructures enables the combination of these properties in one device, thus creating multifunctional optoelectronic systems with superior performance. Here, we demonstrate that graphene/WSe2/graphene heterostructures ally the high photodetection efficiency of transition-metal dichalcogenides with a picosecond photoresponse comparable to that of graphene, thereby optimizing both speed and efficiency in a single photodetector. We follow the extraction of photoexcited carriers in these devices using time-resolved photocurrent measurements and demonstrate a photoresponse time as short as 5.5 ps, which we tune by applying a bias and by varying the transition-metal dichalcogenide layer thickness. Our study provides direct insight into the physical processes governing the detection speed and quantum efficiency of these van der Waals heterostuctures, such as out-of-plane carrier drift and recombination. The observation and understanding of ultrafast and efficient photodetection demonstrate the potential of hybrid transition-metal dichalcogenide-based heterostructures as a platform for future optoelectronic devices.

  13. Supercurrent in van der Waals Josephson junction

    NASA Astrophysics Data System (ADS)

    Yabuki, Naoto; Moriya, Rai; Arai, Miho; Sata, Yohta; Morikawa, Sei; Masubuchi, Satoru; Machida, Tomoki

    2016-02-01

    Supercurrent flow between two superconductors with different order parameters, a phenomenon known as the Josephson effect, can be achieved by inserting a non-superconducting material between two superconductors to decouple their wavefunctions. These Josephson junctions have been employed in fields ranging from digital to quantum electronics, yet their functionality is limited by the interface quality and use of non-superconducting material. Here we show that by exfoliating a layered dichalcogenide (NbSe2) superconductor, the van der Waals (vdW) contact between the cleaved surfaces can instead be used to construct a Josephson junction. This is made possible by recent advances in vdW heterostructure technology, with an atomically flat vdW interface free of oxidation and inter-diffusion achieved by eliminating all heat treatment during junction preparation. Here we demonstrate that this artificially created vdW interface provides sufficient decoupling of the wavefunctions of the two NbSe2 crystals, with the vdW Josephson junction exhibiting a high supercurrent transparency.

  14. Van der Waals Interactions in Aspirin

    NASA Astrophysics Data System (ADS)

    Reilly, Anthony; Tkatchenko, Alexandre

    2015-03-01

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

  15. Dielectric Genome of van der Waals Heterostructures.

    PubMed

    Andersen, Kirsten; Latini, Simone; Thygesen, Kristian S

    2015-07-01

    Vertical stacking of two-dimensional (2D) crystals, such as graphene and hexagonal boron nitride, has recently lead to a new class of materials known as van der Waals heterostructures (vdWHs) with unique and highly tunable electronic properties. Ab initio calculations should in principle provide a powerful tool for modeling and guiding the design of vdWHs, but in their traditional form such calculations are only feasible for commensurable structures with a few layers. Here we show that the dielectric properties of realistic, incommensurable vdWHs comprising hundreds of layers can be efficiently calculated using a multiscale approach where the dielectric functions of the individual layers (the dielectric building blocks) are computed ab initio and coupled together via the long-range Coulomb interaction. We use the method to illustrate the 2D-3D transition of the dielectric function of multilayer MoS2 crystals, the hybridization of quantum plasmons in thick graphene/hBN heterostructures, and to demonstrate the intricate effect of substrate screening on the non-Rydberg exciton series in supported WS2. The dielectric building blocks for a variety of 2D crystals are available in an open database together with the software for solving the coupled electrodynamic equations. PMID:26047386

  16. Supercurrent in van der Waals Josephson junction.

    PubMed

    Yabuki, Naoto; Moriya, Rai; Arai, Miho; Sata, Yohta; Morikawa, Sei; Masubuchi, Satoru; Machida, Tomoki

    2016-01-01

    Supercurrent flow between two superconductors with different order parameters, a phenomenon known as the Josephson effect, can be achieved by inserting a non-superconducting material between two superconductors to decouple their wavefunctions. These Josephson junctions have been employed in fields ranging from digital to quantum electronics, yet their functionality is limited by the interface quality and use of non-superconducting material. Here we show that by exfoliating a layered dichalcogenide (NbSe2) superconductor, the van der Waals (vdW) contact between the cleaved surfaces can instead be used to construct a Josephson junction. This is made possible by recent advances in vdW heterostructure technology, with an atomically flat vdW interface free of oxidation and inter-diffusion achieved by eliminating all heat treatment during junction preparation. Here we demonstrate that this artificially created vdW interface provides sufficient decoupling of the wavefunctions of the two NbSe2 crystals, with the vdW Josephson junction exhibiting a high supercurrent transparency. PMID:26830754

  17. Advanced Communication and Control Solutions of Distributed Energy Resources (DER)

    SciTech Connect

    Asgeirsson, Haukur; Seguin, Richard; Sherding, Cameron; de Bruet, Andre, G.; Broadwater, Robert; Dilek, Murat

    2007-01-10

    This report covers work performed in Phase II of a two phase project whose objective was to demonstrate the aggregation of multiple Distributed Energy Resources (DERs) and to offer them into the energy market. The Phase I work (DE-FC36-03CH11161) created an integrated, but distributed, system and procedures to monitor and control multiple DERs from numerous manufacturers connected to the electric distribution system. Procedures were created which protect the distribution network and personnel that may be working on the network. Using the web as the communication medium for control and monitoring of the DERs, the integration of information and security was accomplished through the use of industry standard protocols such as secure SSL,VPN and ICCP. The primary objective of Phase II was to develop the procedures for marketing the power of the Phase I aggregated DERs in the energy market, increase the number of DER units, and implement the marketing procedures (interface with ISOs) for the DER generated power. The team partnered with the Midwest Independent System Operator (MISO), the local ISO, to address the energy market and demonstrate the economic dispatch of DERs in response to market signals. The selection of standards-based communication technologies offers the ability of the system to be deployed and integrated with other utilities’ resources. With the use of a data historian technology to facilitate the aggregation, the developed algorithms and procedures can be verified, audited, and modified. The team has demonstrated monitoring and control of multiple DERs as outlined in phase I report including procedures to perform these operations in a secure and safe manner. In Phase II, additional DER units were added. We also expanded on our phase I work to enhance communication security and to develop the market model of having DERs, both customer and utility owned, participate in the energy market. We are proposing a two-part DER energy market model--a utility

  18. Structure-based design and screening of inhibitors for an essential bacterial GTPase, Der.

    PubMed

    Hwang, Jihwan; Tseitin, Vladimir; Ramnarayan, Kal; Shenderovich, Mark D; Inouye, Masayori

    2012-05-01

    Der is an essential and widely conserved GTPase that assists assembly of a large ribosomal subunit in bacteria. Der associates specifically with the 50S subunit in a GTP-dependent manner and the cells depleted of Der accumulate the structurally unstable 50S subunit, which dissociates into an aberrant subunit at a lower Mg(2+) concentration. As Der is an essential and ubiquitous protein in bacteria, it may prove to be an ideal cellular target against which new antibiotics can be developed. In the present study, we describe our attempts to identify novel antibiotics specifically targeting Der GTPase. We performed the structure-based design of Der inhibitors using the X-ray crystal structure of Thermotoga maritima Der (TmDer). Virtual screening of commercially available chemical library retrieved 257 small molecules that potentially inhibit Der GTPase activity. These 257 chemicals were tested for their in vitro effects on TmDer GTPase and in vivo antibacterial activities. We identified three structurally diverse compounds, SBI-34462, -34566 and -34612, that are both biologically active against bacterial cells and putative enzymatic inhibitors of Der GTPase homologs. We also presented the possible interactions of each compound with the Der GTP-binding site to understand the mechanism of inhibition. Therefore, our lead compounds inhibiting Der GTPase provide scaffolds for the development of novel antibiotics against antibiotic-resistant pathogenic bacteria. PMID:22377538

  19. Van der Waals interaction in uniaxial anisotropic media

    NASA Astrophysics Data System (ADS)

    Kornilovitch, Pavel E.

    2013-01-01

    Van der Waals interactions between flat surfaces in uniaxial anisotropic media are investigated in the nonretarded limit. The main focus is the effect of nonzero tilt between the optical axis and the surface normal on the strength of the van der Waals attraction. General expressions for the van der Waals free energy are derived using the surface mode method and the transfer-matrix formalism. To facilitate numerical calculations a temperature-dependent three-band parameterization of the dielectric tensor of the liquid crystal 5CB is developed. A solid slab immersed in a liquid crystal experiences a van der Waals torque that aligns the surface normal relative to the optical axis of the medium. The preferred orientation is different for different materials. Two solid slabs in close proximity experience a van der Waals attraction that is strongest for homeotropic alignment of the intervening liquid crystal for all the materials studied. The results have implications for the stability of plate-like colloids in liquid crystal hosts.

  20. Van der Waals interaction in uniaxial anisotropic media.

    PubMed

    Kornilovitch, Pavel E

    2013-01-23

    Van der Waals interactions between flat surfaces in uniaxial anisotropic media are investigated in the nonretarded limit. The main focus is the effect of nonzero tilt between the optical axis and the surface normal on the strength of the van der Waals attraction. General expressions for the van der Waals free energy are derived using the surface mode method and the transfer-matrix formalism. To facilitate numerical calculations a temperature-dependent three-band parameterization of the dielectric tensor of the liquid crystal 5CB is developed. A solid slab immersed in a liquid crystal experiences a van der Waals torque that aligns the surface normal relative to the optical axis of the medium. The preferred orientation is different for different materials. Two solid slabs in close proximity experience a van der Waals attraction that is strongest for homeotropic alignment of the intervening liquid crystal for all the materials studied. The results have implications for the stability of plate-like colloids in liquid crystal hosts. PMID:23234868

  1. van der Waals interactions between excited atoms in generic environments

    NASA Astrophysics Data System (ADS)

    Barcellona, Pablo; Passante, Roberto; Rizzuto, Lucia; Buhmann, Stefan Yoshi

    2016-07-01

    We consider the van der Waals force involving excited atoms in general environments, constituted by magnetodielectric bodies. We develop a dynamical approach studying the dynamics of the atoms and the field, mutually coupled. When only one atom is excited, our dynamical theory suggests that for large distances the van der Waals force acting on the ground-state atom is monotonic, while the force acting in the excited atom is spatially oscillating. We show how this latter force can be related to the known oscillating Casimir-Polder force on an excited atom near a (ground-state) body. Our force also reveals a population-induced dynamics: for times much larger that the atomic lifetime the atoms will decay to their ground states leading to the van der Waals interaction between ground-state atoms.

  2. Spontaneous stacking faults in van der Waals heterostructures

    NASA Astrophysics Data System (ADS)

    Boussinot, G.

    2016-08-01

    The rapid developments in the manipulation of two-dimensional monoatomic layers such as graphene or h-BN allow one to create heterostructures consisting of possibly many chemically different layers, stacked owing to van der Waals attraction. We propose a Frenkel-Kontorova model including a transverse degree of freedom in order to describe local deformations in these heterostructures. We study the case where two dissimilar monolayers are alternatively stacked, and find that stacking faults may emerge spontaneously for a large enough number of stacked layers as a result of the competition between adhesion and elastic energies. This symmetry-breaking transition should become of fundamental importance for the description of three-dimensional van der Waals heterostructures as soon as a precise control on the lattice orientation of the van der Waals layers is achieved.

  3. Biokompatible Implantate und Neuentwicklungen in der Gynäkologie

    NASA Astrophysics Data System (ADS)

    Jacobs, Volker R.; Kiechle, Marion

    Für den Einsatz in der Gynäkologie stehen heute eine Vielzahl unterschiedlicher, biokompatibler Materialien und Implantate zur Verfügung. Auf eine Auswahl soll hier näher eingegangen werden, die die verschiedenen Materialien und Bauweisen repräsentieren. So sind Brustimplantate seit fast vier Jahrzehnten im Gebrauch für die Brustvergrösserung und den Brustwiederaufbau. Material, Bauweisen und medizinische Aspekte einschliesslich der kontroversen Diskussion um Silikon werden im folgenden erläutert. Neuere Entwicklungen von Verhütungstechniken für permanente Sterilisation wie den Filshie ClipTM für transabdominalen und den STOPTM für intraluminalen Verschluss der Eileiter oder die intrauterin plazierte Hormonspirale MirenaTM für zeitlich begrenzte Verhütung werden beschrieben. Eine neue Perspektive zur Verhinderung postoperativer intraabdominaler Adhäsionen stellt Spray-GelTM, ein Zweikomponenten Hydrogel aus Polyethylenglykol, dar.

  4. Van der Waals stacked 2D layered materials for optoelectronics

    NASA Astrophysics Data System (ADS)

    Zhang, Wenjing; Wang, Qixing; Chen, Yu; Wang, Zhuo; Wee, Andrew T. S.

    2016-06-01

    The band gaps of many atomically thin 2D layered materials such as graphene, black phosphorus, monolayer semiconducting transition metal dichalcogenides and hBN range from 0 to 6 eV. These isolated atomic planes can be reassembled into hybrid heterostructures made layer by layer in a precisely chosen sequence. Thus, the electronic properties of 2D materials can be engineered by van der Waals stacking, and the interlayer coupling can be tuned, which opens up avenues for creating new material systems with rich functionalities and novel physical properties. Early studies suggest that van der Waals stacked 2D materials work exceptionally well, dramatically enriching the optoelectronics applications of 2D materials. Here we review recent progress in van der Waals stacked 2D materials, and discuss their potential applications in optoelectronics.

  5. Van der Woude Syndrome with Short Review of the Literature

    PubMed Central

    Deshmukh, Pallavi K.; Deshmukh, Kiran; Mangalgi, Anand; Patil, Subhash; Hugar, Deepa; Kodangal, Saraswathi Fakirappa

    2014-01-01

    Van der Woude syndrome (VWS) is a rare autosomal dominant condition with high penetrance and variable expression. Clinical manifestation of this autosomal dominant clefting syndrome includes bilateral midline lower lip pits, cleft lip, and cleft palate along with hypodontia. These congenital lip pits appear as a malformation in the vermilion border of the lip, with or without excretion. Discomfort caused by spontaneous or induced drainage of saliva/mucus when pressure is applied or during a meal as well as poor aesthetic match is one of the main complaints of patients with congenital lip fistula. The pits are treated by surgical resection. Dentists should be aware of the congenital lip pits as in Van der Woude syndrome because they have been reported to be associated with a variety of malformations or other congenital disorders. Here, the authors report a rare case of Van der Woude syndrome with short review of the literature. PMID:25050184

  6. Collisional stabilization of van der Waals states of ozone

    NASA Astrophysics Data System (ADS)

    Ivanov, Mikhail V.; Babikov, Dmitri

    2011-05-01

    The mixed quantum-classical theory developed earlier [M. Ivanov and D. Babikov, J. Chem. Phys. 134, 144107 (2011)] is employed to treat the collisional energy transfer and the ro-vibrational energy flow in a recombination reaction that forms ozone. Assumption is that the van der Waals states of ozone are formed in the O + O2 collisions, and then stabilized into the states of covalent well by collisions with bath gas. Cross sections for collision induced dissociation of van der Waals states of ozone, for their stabilization into the covalent well, and for their survival in the van der Waals well are computed. The role these states may play in the kinetics of ozone formation is discussed.

  7. Molekulare Nanomaschinen unter der Lupe: Proteindynamik-Simulationen

    NASA Astrophysics Data System (ADS)

    de Groot, Bert L.; Böckmann, Rainer A.; Grubmüller, Helmut

    2006-01-01

    Moderne computergestützte Simulationsverfahren erlauben tiefe Einblicke in biologische Funktionsprozesse. Sie zeigen in atomarer Auflösung, wie Proteine als biologische Nanomaschinen funktionieren. Entscheidend ist dabei deren dynamisches Verhalten. Die Strukturaufklärung liefert meist nur statische Bilder der eingefrorenen räumlichen Gestalt der Proteine. Molekulardynamik-Simulationen machen dagegen Bewegungen sichtbar. Sie konnten zum Beispiel offen legen, wie das Protein F-ATP-Synthase das Adenosintriphosphat (ATP) synthetisiert, den zentralen Energieträger des Körpers. Die F-ATP-Synthase arbeitet dabei wie ein mechano-chemischer Dreizylindermotor. Sie ist die kleinste bekannte Nanomaschine der Welt. Ein anderes Beispiel ist die Simulation des komplexen Mechanismus, mit dem das Protein Aquaporin Wassermoleküle durch Zellmembranen schleust.

  8. The Economics of van der Waals Force Engineering

    NASA Astrophysics Data System (ADS)

    Pinto, Fabrizio

    2008-01-01

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

  9. Einsteins Traum. Expeditionen an die Grenzen der Raumzeit.

    NASA Astrophysics Data System (ADS)

    Hawking, S. W.

    This book is a German translation, by H. Kober, of the English original "Black holes and baby universes and other essays" published in 1993. It is a collection of articles written by the author between 1976 and 1992. Contents: 1. Kindheit. 2. Oxford und Cambridge. 3. Meine Erfahrung mit ALS. 4. Öffentliche Einstellungen zur Wissenschaft. 5. Eine kurze Geschichte der Kurzen Geschichte. 6. Mein Standpunkt. 7. Einsteins Traum. 8. Der Ursprung des Universums. 9. Die Quantenmechanik Schwarzer Löcher. 10. Schwarze Löcher und Baby-Universen. 11. Ist alles vorherbestimmt? 12. Die Zukunft des Universums. 13. Desert Island Discs, ein Interview.

  10. Curves of growth for van der Waals broadened spectral lines

    NASA Technical Reports Server (NTRS)

    Park, C.

    1980-01-01

    Curves of growth are evaluated for a spectral line broadened by the van der Waals interactions during collisions. The growth of the equivalent widths of such lines is shown to be dependent on the product of the perturber density and the 6/10 power of the van der Waals potential coefficient. When the parameter is small, the widths grow as the 1/2 power of the optical depth as they do for the Voigt profile: but when the parameter is large, they grow as 2/3 power and, hence, faster than the Voigt profile. An approximate analytical expression for the computed growth characteristics is given.

  11. Notes on Van der Meer scan for absolute luminosity measurement

    NASA Astrophysics Data System (ADS)

    Balagura, Vladislav

    2011-10-01

    The absolute luminosity can be measured in an accelerator by sweeping beams transversely across each other in the so-called van der Meer scan. We prove that the method can be applied in the general case of arbitrary beam directions and a separation scan plane. A simple method to develop an image of the beam in its transverse plane from spatial distributions of interaction vertexes is also proposed. From the beam images one can determine their overlap and the absolute luminosity. This provides an alternative way of the luminosity measurement during van der Meer scan.

  12. Thermal effects on van der Waals adhesive forces

    NASA Astrophysics Data System (ADS)

    Pinon, A. V.; Wierez-Kien, M.; Craciun, A. D.; Beyer, N.; Gallani, J. L.; Rastei, M. V.

    2016-01-01

    We present an experimental and theoretical study on how thermal energy alters van der Waals adhesion forces in nanoscale contacts stretched by mechanical probes. The force follows a distribution whose density function is an asymmetric bell-shaped curve presenting a temperature-dependent negative skewness. With increasing temperature the asymmetry increases whereas the most probable force value decreases. Using a 2-8 Lennard-Jones interaction potential within the reaction rate theory, we offer a theoretical framework permitting an evaluation of the microscopic parameters governing adhesion in a van der Waals nanocontact subjected to mechanical fluctuations.

  13. Modelling and bioinformatics analysis of the dimeric structure of house dust mite allergens from families 5 and 21: Der f 5 could dimerize as Der p 5.

    PubMed

    Khemili, Souad; Kwasigroch, Jean Marc; Hamadouche, Tarik; Gilis, Dimitri

    2012-01-01

    Allergy represents an increasing thread to public health in both developed and emerging countries and the dust mites Dermatophagoides pteronyssinus (Der p), Blomia tropicalis (Blo t), Dermatophagoides farinae (Der f), Lepidoglyphus destructor (Lep d) and Suidasia medanensis (Sui m) strongly contribute to this problem. Their allergens are classified in several families among which families 5 and 21 which are the subject of this work. Indeed, their biological function as well as the mechanism or epitopes by which they are contributing to the allergic response remain unknown and their tridimensional structures have not been resolved experimentally except for Blo t 5 and Der p 5. Blo t 5 is a monomeric three helical bundle, whereas Der p 5 shows a three helical bundle with a kinked N-terminal helix that assembles in an entangled dimeric structure with a large hydrophobic cavity. This cavity could be involved in the binding of hydrophobic ligands, which in turn could be responsible for the shift of the immune response from tolerance to allergic inflammation. We used molecular modelling approaches to bring out if other house dust mite allergens of families 5 and 21 (Der f 5, Sui m 5, Lep d 5, Der p 21 and Der f 21) could dimerize and form a large cavity in the same way as Der p 5. Monomeric models were first performed with MODELLER using the experimental structures of Der p 5 and Blo t 5 as templates. The ClusPro server processed the selected monomers in order to assess their capacity to form dimeric structures with a positive result for Der p 5 and Der f 5 only. The other allergens (Blo t 5, Sui m 5, Lep d 5, Der p 21 and Der f 21) did not present such a propensity. Moreover, we identified mutations that should destabilize and/or prevent the formation of the Der p 5 dimeric structure. The production of these mutated proteins could help us to understand the role of the dimerization process in the allergic response induced by Der p 5, and if Der p 5 and Der f 5 behave

  14. Excited nucleon as a van der Waals system of partons

    SciTech Connect

    Jenkovszky, L. L.; Muskeyev, A. O. Yezhov, S. N.

    2012-06-15

    Saturation in deep inelastic scattering (DIS) and deeply virtual Compton scattering (DVCS) is associated with a phase transition between the partonic gas, typical of moderate x and Q{sup 2}, and partonic fluid appearing at increasing Q{sup 2} and decreasing Bjorken x. We suggest the van der Waals equation of state to describe properly this phase transition.

  15. Statistical complexity, virial expansion, and van der Waals equation

    NASA Astrophysics Data System (ADS)

    Pennini, F.; Plastino, A.

    2016-09-01

    We investigate the notion of LMC statistical complexity with regards to a real gas and in terms of the second virial coefficient. The ensuing results are applied to the van der Waals equation. Interestingly enough, one finds a complexity-interpretation for the associated phase transition.

  16. Einstellung und Wissen von Lehramtsstudierenden zur Evolution - ein Vergleich zwischen Deutschland und der Türkei

    NASA Astrophysics Data System (ADS)

    Graf, Dittmar; Soran, Haluk

    Es wird eine Untersuchung vorgestellt, in der Wissen und Überzeugungen von Lehramtsstudierenden aller Fächer zum Thema Evolution an zwei Universitäten in Deutschland und der Türkei erhoben worden sind. Die Befragung wurde in Dortmund und in Ankara durchgeführt. Es stellte sich heraus, dass ausgeprägte Defizite im Verständnis der Evolutionsmechanismen herrschen. Viele Studierende, insbesondere aus der Türkei, sind nicht von der Faktizität der Evolution überzeugt. Dies gilt sowohl für Studierende mit Fach Biologie als auch für Studierende mit anderen Fächern. Näher untersucht worden sind die Faktoren, die die Überzeugungen zur Evolution beeinflussen können, was ja in Anbetracht der hohen Ablehnungsrate der Evolution von besonderem Interesse ist. Das Vertrauen in die Wissenschaft spielt hierbei eine besondere Rolle: Wer der Wissenschaft vertraut, ist auch eher von der Evolution überzeugt, als diejenigen, die skeptisch gegenüber der Wissenschaft sind.

  17. Von der Prägeometrie zur Topologischen Komplexität.

    NASA Astrophysics Data System (ADS)

    Kurth, D.

    Der Autor macht in seinem Beitrag gegen das vorherrschende reduktionistische Selbstverständnis der modernen Physik geltend, daß eine umfassende Theorie von Allem (TOE) nicht schon durch eine Alles vereinheitlichende Theorie als Abschluß des reduktionistischen Programms der Elementarteilchenphysik gegeben sein kann. Zum einen muß der initialen Kontingenz unseres Universums durch eine entsprechende quantenkosmologische Theorie Rechnung getragen werden, zum anderen muß auch die in dieser Kontingenz begründete Geschichtlichkeit unseres Universums, d.h. die Emergenz von Komplexität, von einer angemessenen TOE erklärt werden können. Der Autor zeigt, daß ein solcher Anspruch nicht mit den üblichen Komplexitätsmaßen der heutigen Komplexitätstheorien eingelöst werden kann, und schlägt als Alternative einen unmittelbar emergenztheoretisch begründeten Komplexitätsbegriff, den der Topologischen Komplexität vor.

  18. Minimalinvasive endovaskuläre Stent-Therapie bei Erkrankungen in der thorakalen Aorta

    NASA Astrophysics Data System (ADS)

    Voss, Bernhard; Bauernschmitt, Robert; Brockmann, Gernot; Lange, Rüdiger

    Die Inzidenz der Aortenerkrankungen nimmt aufgrund der Überalterung der Bevölkerung stetig zu und hat sich innerhalb der letzten 20 Jahre von 2,9 auf 10,9 pro 100.000 Einwohner mehr als verdreifacht [1]. Bei Aortenerkrankungen muss zwischen Aneurysmen und Dissektionen unterschieden werden. Der Begriff Aneurysma (Abb. 62.1) bezeichnet die Ausweitung eines arteriellen Blutgefäßes. Sind dabei alle Wandschichten, also innere Schicht (Intima), mittlere Schicht (Media) und äußere Schicht (Adventitia) betroffen, so spricht man von einem echten Aneurysma (Aneurysma verum). Besteht die Aneurysmawand nur aus adventitiellem Gewebe, spricht man von einem falschen Aneurysma. Ursache für ein Aneurysma ist eine Schwächung der elastischen Kräfte der Media, die dann dem intravaskulären Druck nicht mehr standhalten kann.

  19. Expression, purification and characterization of Der f 27, a new allergen from dermatophagoides farinae

    PubMed Central

    Lin, Jianli; Li, Meng; Liu, Yulin; Jiang, Congli; Wu, Yulan; Wang, Yuanyuan; Gao, Anjian; Liu, Zhigang; Yang, Pingchang; Liu, Xiaoyu

    2016-01-01

    The house dust mite (HDM), Dermatophagoidesfarinae (D. farina), is one of the most important indoor allergen sources and a major elicitor of allergic asthma; itscharacterization is important in the diagnosis and immunotherapy of mite allergen-relevant diseases. This study aims to characterize a novel allergen, the D. farinaederived serpin (Der f 27). In this study, the total RNA of D. farinae was extracted, and the Der f 27 gene was cloned and expressed. The allergenicity of recombinant Der f 27 protein was determined by enzyme-linked immunosorbent assay, and Western-blotting with the sera of asthma patients, and skin prick test (SPT) in allergic human subjects. A r-Der f 27 allergic asthma mouse model was established. The cloned Der f 27 gene has been presented at the Gene Bank with an accession number of KM009995. The IgE levels of r-Der f 27 in the serum from r-Der f 27 SPT positive allergic patients were 3 folds more than healthy subjects. The Der f 27 SPT positive ratewas 42.1% in 19 DM-SPT positive patients. Airway hyperresponsiveness, serum specific IgE, and levels of interleukin-4 in the spleen cell culture supernatant were significantly increased in allergic asthma mice sensitized to r-Der f 27. In conclusion, Der f 27 is a new subtype of house mite allergen. PMID:27347356

  20. Characterization of arginine kinase, anovel allergen of dermatophagoides farinae (Der f 20)

    PubMed Central

    Xing, Peng; Yu, Haiqiong; Li, Meng; Xiao, Xiaojun; Jiang, Congli; Mo, Lihua; Zhang, Min; Yang, Pingchang; Liu, Zhigang

    2015-01-01

    Objective: To characterize a novel allergen, the Dermatophagoides farinae-derived arginine kinase (Der f 20). Methods: The protein of Der f 20 was synthesized by genetic engineering approaches. The allergenicity of Der f 20 was tested by enzyme-linked immunosorbent assay and an airway allergy mouse model. Results: The Der f 20 gene was cloned andpresented in the Gene Bank with an accession number of AAP57094. The Der f 20 is an arginine kinase (AK), whichshowed a close relationship with D. pteronyssinus AK and Aleuroglyphusovatus AK. Western-blot and ELISA studies showed the IgE binding capacity of Der f 20 was 66.7% in the sera from 6 dust mite allergic patients. Immune inhibition assayresults showed the IgE cross-reactivity between Der f 20 and DME (Dust mite extract). Positive responses to Der f 20 were 41.2% as shown by skin prick tests in 17 DME-allergic patients. In vitro experimental results showed that Der f 20 induced Th2 cell differentiation and the expression of T cell Ig mucin domain molecule-4 (TIM4) in DCs. Conclusions; The Der f 20 protein is a novel subtype of thedust mite allergen. PMID:26885278

  1. Zu einer inhaltsorientierten Theorie des Lernens und Lehrens der biologischen Evolution

    NASA Astrophysics Data System (ADS)

    Wallin, Anita

    Der Zweck dieser Studie (zwecks Überblick siehe dazu Abb. 9.1) war zu untersuchen, wie die Schüler der Sekundarstufe II ein Verständnis von der Theorie der biologischen Evolution entwickeln. Vom Ausgangspunkt "Vorurteile der Schüler“ ausgehend wurden Unterrichtssequenzen entwickelt und drei verschiedene Lernexperimente in einem zyklischen Prozess durchgeführt. Das Wissen der Schüler wurde vor, während und nach den Unterrichtssequenzen mit Hilfe von schriftlichen Tests, Interviews und Diskussionsrunden in kleinen Gruppen abgefragt. Etwa 80 % der Schüler hatten vor dem Unterricht alternative Vorstellungen von Evolution, und in dem Nachfolgetest erreichten circa 75 % ein wissenschaftliches Niveau. Die Argumentation der Schüler in den verschiedenen Tests wurde sorgfältig unter Rücksichtnahme auf Vorurteile, der konzeptionellen Struktur der Theorie der Evolution und den Zielen des Unterrichts analysiert. Daraus konnten Einsichten in solche Anforderungen an Lehren und Lernen gewonnen werden, die Herausforderungen an Schüler und Lehrer darstellen, wenn sie anfangen, evolutionäre Biologie zu lernen oder zu lehren. Ein wichtiges Ergebnis war, dass das Verständnis existierender Variation in einer Population der Schlüssel zum Verständnis von natürlicher Selektion ist. Die Ergebnisse sind in einer inhaltsorientierten Theorie zusammengefasst, welche aus drei verschiedenen Aspekten besteht: 1) den inhaltsspezifischen Aspekten, die einzigartig für jedes wissenschaftliche Feld sind; 2) den Aspekten, die die Natur der Wissenschaft betreffen; und 3) den allgemeinen Aspekten. Diese Theorie kann in neuen Experimenten getestet und weiter entwickelt werden.

  2. Romanistik ohne Latein? Zu einer Empfehlung der Konferenz der Romanischen Seminare (Romance Studies without Latin? On a Recommendation from the Conference of Romance Seminars)

    ERIC Educational Resources Information Center

    Neumeister, Sebastian

    1973-01-01

    Reaction to a February 19, 1972 recommendation of the Konferenz der Romanischen Seminare der Bundesrepublik Deutschland und West-Berlins in Deutschen Romanistenverband'' (Conference of Romance Seminars of the Federal Republic of Germany and West Berlin of the German Association of Romance Philologists) to discontinue the Latin prerequisite for…

  3. Photovoltaic Effect in an Electrically Tunable van der Waals Heterojunction

    PubMed Central

    2014-01-01

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

  4. Cyber-Physical Systems - Wissenschaftliche Herausforderungen Bei Der Entwicklung

    NASA Astrophysics Data System (ADS)

    Broy, Manfred

    Cyber-Physical Systems adressieren die enge Verbindung eingebetteter Systeme zur Überwachung und Steuerung physikalischer Vorgänge mittels Sensoren und Aktuatoren über Kommunikationseinrichtungen mit den globalen digitalen Netzen (dem Cyberspace"). Dieser Typus von Systemen ermöglicht über Wirkketten eine Verbindung zwischen Vorgängen der physischen Realität und den heute verfügbaren digitalen Netzinfrastrukturen. Dies erlaubt vielfältige Applikationen mit hohem wirtschaftlichen Potential, und mit starker Innovationskraft. Die vollständige Ausschöpfung des Potentials erfordert aber gezielte wissenschaftliche Anstrengungen bei der Entwicklung solcher Systeme im Hinblick auf Methodik, Technologie, Kostenbeherrschung und funktionale Angemessenheit.

  5. Aqueous gating of van der Waals materials on bilayer nanopaper.

    PubMed

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

    2014-10-28

    In this work, we report transistors made of van der Waals materials on a mesoporous paper with a smooth nanoscale surface. The aqueous transistor has a novel planar structure with source, drain, and gate electrodes on the same surface of the paper, while the mesoporous paper is used as an electrolyte reservoir. These transistors are enabled by an all-cellulose paper with nanofibrillated cellulose (NFC) on the top surface that leads to an excellent surface smoothness, while the rest of the microsized cellulose fibers can absorb electrolyte effectively. Based on two-dimensional van der Waals materials, including MoS2 and graphene, we demonstrate high-performance transistors with a large on-off ratio and low subthreshold swing. Such planar transistors with absorbed electrolyte gating can be used as sensors integrated with other components to form paper microfluidic systems. This study is significant for future paper-based electronics and biosensors. PMID:25283598

  6. Charge Transfer Excitons at van der Waals Interfaces.

    PubMed

    Zhu, Xiaoyang; Monahan, Nicholas R; Gong, Zizhou; Zhu, Haiming; Williams, Kristopher W; Nelson, Cory A

    2015-07-01

    The van der Waals interfaces of molecular donor/acceptor or graphene-like two-dimensional (2D) semiconductors are central to concepts and emerging technologies of light-electricity interconversion. Examples include, among others, solar cells, photodetectors, and light emitting diodes. A salient feature in both types of van der Waals interfaces is the poorly screened Coulomb potential that can give rise to bound electron-hole pairs across the interface, i.e., charge transfer (CT) or interlayer excitons. Here we address common features of CT excitons at both types of interfaces. We emphasize the competition between localization and delocalization in ensuring efficient charge separation. At the molecular donor/acceptor interface, electronic delocalization in real space can dictate charge carrier separation. In contrast, at the 2D semiconductor heterojunction, delocalization in momentum space due to strong exciton binding may assist in parallel momentum conservation in CT exciton formation. PMID:26001297

  7. Plasmakristalle an Bord der ISS: Komplexe Plasmen in Schwerelosigkeit

    NASA Astrophysics Data System (ADS)

    Thomas, Hubertus M.; Morfill, Gregor E.

    2005-03-01

    Das deutsch-russische Experiment PKE-Nefedov erforscht komplexe Plasmen in Schwerelosigkeit. Seit 2001 arbeitet es auf der internationalen Raumstation ISS. Komplexe Plasmen bestehen aus einem teilweise ionisierten Gas, das Mikropartikel enthält. Diese Partikel laden sich im Strom der Elektronen und Ionen elektrisch auf. Ihr Verhalten beeinflussen vor allem abgeschirmte Coulomb-Kräfte und Reibungskräfte im Gas. Sie können sich sogar zu einem Plasma-Kristall anordnen. Diese reguläre, dreidimensionale Struktur hat viele Eigenschaften eines echten Kristallgitters. Sie ist jedoch makroskopisch, also klassisch, und die einzelnen Partikel sind viel besser beobachtbar als etwa Atome in kondensierter Materie. Das macht sie zu idealen Modellsystemen für die Erforschung von Kristallen, Phasenübergängen oder von Flüssigkeiten. Komplexe Plasmen zeigen darüber hinaus ganz neue Eigenschaften.

  8. Generalized van der Waals density functional theory for nonuniform polymers

    SciTech Connect

    Patra, Chandra N.; Yethiraj, Arun

    2000-01-15

    A density functional theory is presented for the effect of attractions on the structure of polymers at surfaces. The theory treats the ideal gas functional exactly, and uses a weighted density approximation for the hard chain contribution to the excess free energy functional. The attractive interactions are treated using a van der Waals approximation. The theory is in good agreement with computer simulations for the density profiles at surfaces for a wide range of densities and temperatures, except for low polymer densities at low temperatures where it overestimates the depletion of chains from the surface. This deficiency is attributed to the neglect of liquid state correlations in the van der Waals term of the free energy functional. (c) 2000 American Institute of Physics.

  9. Millimeter-wave rubidium Rydberg van der Waals spectroscopy

    SciTech Connect

    Han Jianing; Gallagher, T. F.

    2009-05-15

    We have observed the diatomic nsns{yields}ns(n+1)s{yields}(n+1)s(n+1)s microwave transitions of pairs of cold Rb Rydberg atoms for 36der Waals shift due to its near degeneracy with the nearby np{sub 3/2}np{sub 3/2} state. In fact, the energy difference and the van der Waals shift change sign at n=38 and we observe shifts of both signs. The combined excitation of the ns(n+1)s and (n+1)s(n+1)s states leads to an unusual line shape which can be described by a three-level Floquet model.

  10. Van der Waals density functional applied to adsorption systems

    NASA Astrophysics Data System (ADS)

    Hamada, Ikutaro

    2013-03-01

    The van der Waals density functional (vdW-DF) is a promising density functional to describe the van der Waals forces within density functional theory. However, despite the recent efforts, there is still room for further improvement, especially for describing molecular adsorption on metal surfaces. I will show that by choosing appropriate exchange and nonlocal correlation functionals, it is possible to calculate geometries and electronic structures for adsorption systems accurately within the framework of vdW-DF. Applicability of the present approach will be illustrated with its applications to graphene/metal, fullerene/metal, and water/graphene interfaces. This work is partly supported by a Grant-in-Aid for Scientific Research on Innovative Area (No. 23104501). AIMR was established by the World Premier International Research Center Initiative (WPI), MEXT, Japan.

  11. Van der Waals interaction-tuned heat transfer in nanostructures

    NASA Astrophysics Data System (ADS)

    Sun, Tao; Wang, Jianxiang; Kang, Wei

    2012-12-01

    Interfaces usually impede heat transfer in heterogeneous structures. Recent experiments show that van der Waals (vdW) interactions can significantly enhance thermal conductivity parallel to the interface of a bundle of nanoribbons compared to a single layer of freestanding nanoribbon. In this paper, by simulating heat transfer in nanostructures based on a model of nonlinear one-dimensional lattices interacting via van der Waals interactions, we show that the vdW interface interaction can adjust the thermal conductivity parallel to the interface. The efficiency of the adjustment depends on the intensity of interactions and temperature. The nonlinear dependence of the conductivity on the intensity of interactions agrees well with experimental results for carbon nanotube bundles, multi-walled carbon nanotubes, multi-layer graphene, and nanoribbons.

  12. van der Waals explosion of cold Rydberg clusters

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  13. Spin-Flavor van der Waals Forces and NN interaction

    SciTech Connect

    Alvaro Calle Cordon, Enrique Ruiz Arriola

    2011-12-01

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

  14. Quantum field theory of van der Waals friction

    SciTech Connect

    Volokitin, A. I.; Persson, B. N. J.

    2006-11-15

    van der Waals friction between two semi-infinite solids, and between a small neutral particle and semi-infinite solid is studied using thermal quantum field theory in the Matsubara formulation. We show that the friction to linear order in the sliding velocity can be obtained from the equilibrium Green functions and that our treatment can be extended for bodies with complex geometry. The calculated friction agrees with the friction obtained using a dynamical modification of the Lifshitz theory, which is based on the fluctuation-dissipation theorem. We show that it should be possible to measure the van der Waals friction in noncontact friction experiment using state-of-the-art equipment.

  15. A van der Waals free energy in electrolytes revisited

    NASA Astrophysics Data System (ADS)

    Jancovici, B.

    2006-01-01

    A system of three electrolytes separated by two parallel planes is considered. Each region is described by a dielectric constant and a Coulomb fluid in the Debye-Hückel regime. In their book Dispersion Forces, Mahanty and Ninham have given the van der Waals free energy of this system. We rederive this free energy by a different method, using linear response theory and the electrostatic Maxwell stress tensor for obtaining the dispersion force.

  16. Structure and dynamics of small van der Waals complexes

    SciTech Connect

    Loreau, J.

    2014-10-06

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

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

    NASA Astrophysics Data System (ADS)

    Babb, James F.; Hussein, Mahir S.

    2016-03-01

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

  18. Twilight of the gods: John Henry Mackay's Der Unschuldige.

    PubMed

    Kennedy, H

    1993-01-01

    The writings of the Scotch-German John Henry Mackay are important for the early cultural history of the modern gay movement. This article recalls this unjustly neglected anarchist writer and advocate of man/boy love by tracing his biography and pointing out his contacts with others in the movement. His late novella Der Unschuldige is analyzed to show that Mackay has encoded homosexuality there in a unique and individual way. PMID:8113599

  19. Nonadiabatic Van der Pol oscillations in molecular transport

    NASA Astrophysics Data System (ADS)

    Kartsev, Alexey; Verdozzi, Claudio; Stefanucci, Gianluca

    2014-01-01

    The force exerted by the electrons on the nuclei of a current-carrying molecular junction can be manipulated to engineer nanoscale mechanical systems. In the adiabatic regime a peculiarity of these forces is negative friction, responsible for Van der Pol oscillations of the nuclear coordinates. In this work we study the robustness of the Van der Pol oscillations against high-frequency sources. For this purpose we go beyond the adiabatic approximation and perform full Ehrenfest dynamics simulations. The numerical scheme implements a mixed quantum-classical algorithm for open systems and is capable to deal with arbitrary time-dependent driving fields. We find that the Van der Pol oscillations are extremely stable. The nonadiabatic electron dynamics distorts the trajectory in the momentum-coordinate phase space but preserves the limit cycles in an average sense. We further show that high-frequency fields change both the oscillation amplitudes and the average nuclear positions. By switching the fields off at different times one obtains cycles of different amplitudes which attain the limit cycle only after considerably long times.

  20. Laboratory tests of IEC DER object models for grid applications.

    SciTech Connect

    Blevins, John D.; Menicucci, David F.; Byrd, Thomas, Jr.; Gonzalez, Sigifredo; Ginn, Jerry W.; Ortiz-Moyet, Juan

    2007-02-01

    This report describes a Cooperative Research and Development Agreement (CRADA) between Salt River Project Agricultural Improvement and Power District (SRP) and Sandia National Laboratories to jointly develop advanced methods of controlling distributed energy resources (DERs) that may be located within SRP distribution systems. The controls must provide a standardized interface to allow plug-and-play capability and should allow utilities to take advantage of advanced capabilities of DERs to provide a value beyond offsetting load power. To do this, Sandia and SRP field-tested the IEC 61850-7-420 DER object model (OM) in a grid environment, with the goal of validating whether the model is robust enough to be used in common utility applications. The diesel generator OM tested was successfully used to accomplish basic genset control and monitoring. However, as presently constituted it does not enable plug-and-play functionality. Suggestions are made of aspects of the standard that need further development and testing. These problems are far from insurmountable and do not imply anything fundamentally unsound or unworkable in the standard.

  1. Dynamisierung und Erstarrung in der modernen Gesellschaft - Das Beschleunigungsphänomen

    NASA Astrophysics Data System (ADS)

    Rosa, Hartmut

    Dass die Geschichte der Moderne die Geschichte einer ungeheuren Beschleunigung "des Lebens“, "der Kultur“, "der Geschichte“ oder gar "der Zeit selbst“ sei, ist eine Behauptung, der man in Büchern über die Moderne - gelehrten wie ungelehrten - so häufig begegnet, dass sie geradezu als eine Binsenweisheit gelten kann. Völlig unklar bleibt dabei jedoch in aller Regel, was sich dabei wirklich beschleunigt hat und welcher Begriff von Beschleunigung dieser Auffassung zugrunde liegt. Ich will im Folgenden zunächst einen wissenschaftlich vertretbaren Begriff von Beschleunigung entwickeln, um danach mit Hilfe dieses Instruments zu überprüfen, inwieweit die Geschichte der Moderne wirklich als eine Beschleunigungsgeschichte aufgefasst werden kann.

  2. Application of diffusion Monte Carlo to materials dominated by van der Waals interactions

    SciTech Connect

    Benali, Anouar; Shulenburger, Luke; Romero, Nichols; Kim, Jeongnim; Von Lilienfeld, Anatole

    2014-01-01

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

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

    DOE PAGESBeta

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

    2014-06-12

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

  4. Von Ringplaneten und schwarzen Löchern. Die Top-Themen der Astronomie

    NASA Astrophysics Data System (ADS)

    Keller, Hans-Ulrich

    Die spannendsten Monatsthemen der letzten Jahre. Wie alt ist das Universum? Woher kommen die Sterne? Beeinflusst der Mond das irdische Leben? Fast jeder mag sich diese und ähnliche Fragen schon einmal gestellt haben. Kurzweilig berichtet Hans-Ulrich Keller von alten Weisheiten und neuen Erkenntnissen aus der Wissenschaft. Mit vielen farbigen Bildern und Illustrationen sind diese "astronomischen Kurzgeschichten" Lesevergnügen und Informationsquelle zugleich. In über 20 Artikeln erfahren Sie z. B. etwas über: Das feurige Schicksal unseres Sonnensystems. Das Rätsel der dunklen Materie. Die Suche nach außerirdischen Intelligenzen.

  5. Bewertung von Fahrerassistenzsystemen mittels der Vehicle in the Loop-Simulation

    NASA Astrophysics Data System (ADS)

    Bock, Thomas

    Mit der Vehicle in the Loop-Simulation hat Audi eine Test- und Simulationsumgebung für Fahrerassistenzsysteme entwickelt, welche die Vorzüge eines realen Versuchsfahrzeugs mit der Sicherheit und Reproduzierbarkeit von Fahrsimulatoren kombiniert. Virtueller Fremdverkehr, Straßenbegrenzungen oder sonstige simulierte Gegenstände werden durch ein "Optical see through Head Mounted Display“ während der Fahrt realitätsnah und kontaktanalog für den Fahrer eingeblendet. Besonders bei der Erprobung aktiver Fahrerassistenzsysteme eröffnen sich durch das Konzept des virtuellen Fremdverkehrs im realen Versuchsfahrzeug neue Möglichkeiten.

  6. Analyse der Plasmakoma des Kometen P/Halley mittels Bildverarbeitung der Bochumer Photoplatten

    NASA Astrophysics Data System (ADS)

    Voelzke, M. R.

    1993-12-01

    Photographic and photoeletric observations of comet P/Halley's ion gas coma from CO+ at 4250 A were part of the Bochum Halley Monitoring Program, conducted from 1986 February 17, to April 17 at the European Southern Observatory on La Silla (Chile). In this spectral range it is possible to watch the continuous formation, motion and expansion of plasma structures. To observe the morphology of these structures 32 CO+ photos (glass plates) from P/Halley's comet have been analysed. They have a field of view of 28.6 X 28.6 degrees and were obtained from 1986 March 29, to April 17 with exposure times between 20 and 120 minutes. All photos were digitized with a PDS 2020 GM (Photometric Data System) microdensitometer at the Astronomisches Institut der Westfalischen Wilhelms-Universitaet in Muenster (one pixel = 25 X 25 microns approximately 46.88 X 46.88 arcsec). After digitization the data were reduced to relative intensities, and the part with proper calibrations were also converted to absolute intensities, expressed in terms of column densities using the image data systems MIDAS (Munich Image Data Analysis System; ESO - Image Processing Group, 1988) and IHAP (Image Handling And Processing; Middleburg, 1983). With the help of the Stellingwerf-Theta-Minimum-Method (Stellingwerf, 1978) a period of (2.22 +/- 0.09) days result from analysis of structures in the plasma-coma by subtracting subsequent images. The idea behind subtracting subsequent images is that rotation effects are only 10% phenomena on gas distribution. Difference images are than used to supress the static component of the gas cloud. The CO+ column density data (in molecules cm^-2) were compared with the data of CN column density from Schulz (1990) in all common days. The results show that the relations between CO+ and CN in average column density values (N_CO^+/N_CN) are 11.6 for a circular slit with average diameter (Phi) of 6.1 arcminute which corresponds to a distance from the nucleus (rho) equal to 6.3 X

  7. Schröder Triangles, Paths, and Parallelogram Polyominoes

    NASA Astrophysics Data System (ADS)

    Pergola, Elisa; Sulanke, Robert A.

    1998-05-01

    This paper considers combinatorial interpretations for two triangular recurrence arrays containing the Schröder numbers s_n = 1, 1, 3, 11, 45 197, ... and r_n = 1, 2, 6, 22, 90, 394, ... , for n = 0, 1, 2, .... These interpretations involve the enumeration of constrained lattice paths and bicolored parallelogram polyominoes, called zebras. In addition to two recent inductive constructions of zebras and their associated generating trees, we present two new ones and a bijection between zebras and constrained lattice paths. We use the constructions with generating function methods to count sets of zebras with respect to natural parameters.

  8. Ionized van-der-Waals systems: Structure and interactions

    SciTech Connect

    Zuelicke, L.

    1996-12-31

    Ions of molecular systems with internal interactions partly of van-der-Waals type differ significantly from their neutral parent species in binding, structure and dynamics. Theoretical knowledge is still rather scarce. The paper discusses some recent advances from theoretical work in the field concerning (i) electronic and geometric structure of triatomic rare-gas containing cations like Ar{sub 3}{sup +} and ArHCI{sup +}, in ground and excited electronic states; (ii) potential energy surfaces for the interaction of H{sup +} or H{sup -} with diatomic molecules, in ground and excited electronic states; (iii) some features of the dynamics of these systems.

  9. Impact of van der Waals Interactions on Single Asperity Friction

    NASA Astrophysics Data System (ADS)

    Lessel, Matthias; Loskill, Peter; Hausen, Florian; Gosvami, Nitya Nand; Bennewitz, Roland; Jacobs, Karin

    2013-07-01

    Single asperity measurements on Si wafers with variable SiO2 layer thickness, yet identical roughness, revealed the influence of van der Waals (vdW) interactions on friction: on thin (1 nm) SiO2 layers, higher friction and jump-off forces were observed as compared to thick (150 nm) SiO2 layers. The vdW interactions were additionally controlled by a set of silanized Si wafers, exhibiting the same trend. The experimental results demonstrate the influence of the subsurface material and are quantitatively described by combining calculations of interactions of the involved materials and the Derjaguin-Müller-Toporov model.

  10. Impact of van der Waals interactions on single asperity friction.

    PubMed

    Lessel, Matthias; Loskill, Peter; Hausen, Florian; Gosvami, Nitya Nand; Bennewitz, Roland; Jacobs, Karin

    2013-07-19

    Single asperity measurements on Si wafers with variable SiO(2) layer thickness, yet identical roughness, revealed the influence of van der Waals (vdW) interactions on friction: on thin (1 nm) SiO(2) layers, higher friction and jump-off forces were observed as compared to thick (150 nm) SiO(2) layers. The vdW interactions were additionally controlled by a set of silanized Si wafers, exhibiting the same trend. The experimental results demonstrate the influence of the subsurface material and are quantitatively described by combining calculations of interactions of the involved materials and the Derjaguin-Müller-Toporov model. PMID:23909336

  11. Mit Mathematik zu Mehr Intelligenz in der Logistik

    NASA Astrophysics Data System (ADS)

    Möhring, Rolf H.; Schenk, Michael

    Die Lösung logistischer Probleme ist ein wichtiger Aspekt menschlichen Handelns seit Menschen gemeinsam zielgerichtet tätig wurden. Die Grundlagen dessen, was wir heute Logistik nennen, entstammen dem militärischen Bereich. So basierte z. B. das römische Imperium in starkem Maße auf militärisch-logistischen Glanzleistungen. Ob damals bereits mathematische Überlegungen eine Rolle spielten, wissen wir heute nicht. Jedoch versuchte z. B. Napoleon, der mit den bedeutendsten Mathematikern seiner Zeit befreundet war, den Transport seiner Truppen und die Verbreitung von Informationen zu optimieren und strategisch einzusetzen.1,2

  12. Hybrid Meson Potentials and the Gluonic van der Waals Force

    SciTech Connect

    O. Lakhina; E.S. Swanson

    2004-03-01

    The chromoelectric polarizability of mesons governs the strength of the gluonic van der Waals force and therefore of non-quark-exchange processes in hadronic physics. We compute the polarizability of heavy mesons with the aid of lattice gauge theory and the Born--Oppenheimer adiabatic expansion. We find that the operator product expansion breaks down at surprisingly large quarks masses due to nonperturbative gluodynamics and that previous conclusions concerning J/{psi}--nuclear matter interactions and J/{psi} dissociation in the quark-gluon plasma must be substantially modified.

  13. Phonons in nonlocal van der Waals density functional theory

    NASA Astrophysics Data System (ADS)

    Sabatini, Riccardo; Küçükbenli, Emine; Pham, Cong Huy; de Gironcoli, Stefano

    2016-06-01

    We extend the formulation of density functional perturbation theory to treat nonlocal density functionals, accounting for van der Waals interactions, in a rigorous and efficient way. We provide a general formalism, suitable for any functional in this family, and give specific equations for the most widely used ones. We then study the lattice dynamics of graphite, comparing several nonlocal functionals and the local density approximation, showing that our recent revision of the VV10 functional [R. Sabatini et al., Phys. Rev. B 87, 041108(R) (2013), 10.1103/PhysRevB.87.041108] gives the best comparison with experiments.

  14. Creatio ex zero. Ursprungs-Konzepte in der mathematischen Naturphilosophie des 19. Jahrhunderts.

    NASA Astrophysics Data System (ADS)

    Heuser, M.-L.

    Die Autorin zeigt in ihrem Beitrag, daß Ansätze der heutigen Selbstorganisationstheorien, die diese in Richtung einer vereinheitlichten dynamischen Theorie verallgemeinern wollen, zumindest in konzeptueller Hinsicht, schon in der Mathematik und Naturphilosophie des 19. Jahrhunderts gewisse Vorläufer finden könnten.

  15. 49 CFR 40.35 - What information about the DER must employers provide to collectors?

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... provide to collectors? 40.35 Section 40.35 Transportation Office of the Secretary of Transportation... What information about the DER must employers provide to collectors? As an employer, you must provide to collectors the name and telephone number of the appropriate DER (and C/TPA, where applicable)...

  16. 49 CFR 40.35 - What information about the DER must employers provide to collectors?

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... provide to collectors? 40.35 Section 40.35 Transportation Office of the Secretary of Transportation... What information about the DER must employers provide to collectors? As an employer, you must provide to collectors the name and telephone number of the appropriate DER (and C/TPA, where applicable)...

  17. 49 CFR 40.35 - What information about the DER must employers provide to collectors?

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... provide to collectors? 40.35 Section 40.35 Transportation Office of the Secretary of Transportation... What information about the DER must employers provide to collectors? As an employer, you must provide to collectors the name and telephone number of the appropriate DER (and C/TPA, where applicable)...

  18. 49 CFR 40.35 - What information about the DER must employers provide to collectors?

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... provide to collectors? 40.35 Section 40.35 Transportation Office of the Secretary of Transportation... What information about the DER must employers provide to collectors? As an employer, you must provide to collectors the name and telephone number of the appropriate DER (and C/TPA, where applicable)...

  19. Opportunities and challenges of 2D magnetic van der Waals materials: magnetic graphene?

    NASA Astrophysics Data System (ADS)

    Park, Je-Geun

    2016-08-01

    There has been a huge increase of interests in two-dimensional van der Waals materials over the past ten years or so with the conspicuous absence of one particular class of materials: magnetic van der Waals systems. In this Viewpoint, we point it out and illustrate how we might be able to benefit from exploring these so-far neglected materials.

  20. Flexible DER Utility Interface System: Final Report, September 2004--May 2006

    SciTech Connect

    Lynch, J.; John, V.; Danial, S. M.; Benedict, E.; Vihinen, I.; Kroposki, B.; Pink, C.

    2006-08-01

    In an effort to accelerate deployment of Distributed Energy Resources (DER) such as wind, solar, and conventional backup generators to our nation's electrical grid, Northern Power Systems (NPS), the California Energy Commission (CEC), and the National Renewable Energy Laboratory (NREL) collaborated to create a prototype universal interconnect device called the DER Switch.

  1. Schönheit und andere Provokationen - Eine neue evolutionsbiologische Theorie der Kunst

    NASA Astrophysics Data System (ADS)

    Junker, Thomas

    Die Evolution hat viele spektakuläre Phänomene hervorgebracht - von der Eleganz des Vogelflugs über die gigantischen Körper der Dinosaurier und die farbenprächtige Vielfalt der Korallenriffe bis hin zu ihrem jüngsten Geniestreich - der menschlichen Kunst. Die schönen Künste - Malerei, Bildhauerei und Architektur, Theater, Tanz, Oper und Filmkunst, Musik und Literatur - Produkte der Evolution? Diese Vorstellung mutet vielen Menschen fremd an, aber wie könnte es anders sein? Denn wenn Charles Darwin recht hat, dann sind nicht nur die körperlichen Merkmale der Menschen als Antworten auf die Erfordernisse des Lebens entstanden, sondern auch ihre geistigen Fähigkeiten und Verhaltensweisen. Im Jahr 1859 hatte er auf den letzten Seiten seines berühmten Buches über die Entstehung der Arten eine kühne Prophezeiung gemacht: Durch die Evolutionstheorie werde es "zu einer bemerkenswerten Revolution in der Naturwissenschaft kommen […]. Die Psychologie wird auf die neue Grundlage gestellt, dass jede geistige Kraft und Fähigkeit notwendigerweise durch graduelle Übergänge erworben wird“ (Darwin 1859, S. 484, 488; Junker 2008).

  2. Unterstützung der IT-Service-Management-Prozesse an der Technischen Universität München durch eine Configuration-Management-Database

    NASA Astrophysics Data System (ADS)

    Knittl, Silvia

    Hochschulprozesse in Lehre und Verwaltung erfordern durch die steigende Integration und IT-Unterstützung ein sogenanntes Business Alignment der IT und damit auch ein professionelleres IT-Service-Management (ITSM). Die IT Infrastructure Library (ITIL) mit ihrer Beschreibung von in der Praxis bewährten Prozessen hat sich zum de-facto Standard im ITSM etabliert. Ein solcher Prozess ist das Konfigurationsmanagement. Es bildet die IT-Infrastruktur als Konfigurationselemente und deren Beziehungen in einem Werkzeug, genannt Configuration Management Database (CMDB), ab und unterstützt so das ITSM. Dieser Bericht beschreibt die Erfahrungen mit der prototypischen Einführung einer CMDB an der Technischen Universität München.

  3. Der neue Kosmos. Einführung in die Astronomie und Astrophysik

    NASA Astrophysics Data System (ADS)

    Unsöld, Albrecht; Baschek, Bodo

    Der neue Kosmos bietet in überschaubarem Umfang eine zusammenhängende Einführung in das Gesamtgebiet der Astronomie und Astrophysik. Aus den Bereichen: Klassische Astronomie und Planetensystem, Instrumente und Beobachtungsverfahren, Sonne und Sterne, Milchstraße und Galaxien, Kosmologie, Entstehung des Planetensystems, Entwicklung der Erde und des Lebens werden die Beobachtungsmethoden und die Ergebnisse astronomischer Forschung sowie deren theoretische Grundlagen und wechselseitigen Zusammenhänge vermittelt. Die aktualisierte 7. Auflage berücksichtigt den raschen Fortschritt astronomischer Forschung der letzten drei Jahre von unserem Planetensystem und den Entdeckungen zahlreicher Planeten bei anderen Sternen, über die fernsten Galaxien und Quasare bis zur Entwicklung der modernen Kosmologie.

  4. Ludwig Boltzmann als Experimentalphysiker: Frühe Bestätigung der Maxwell-Theorie

    NASA Astrophysics Data System (ADS)

    Rumpf, Klemens; Granitzer, Petra

    2006-09-01

    Am Beispiel von Boltzmanns Experimenten zur Bestätigung der Maxwell-Theorie wird dessen hervorragende Begabung auch als Experimentalphysiker deutlich. Die dargestellten Arbeiten fanden etwa 15 Jahre vor den Hertzschen Experimenten statt, zu einem Zeitpunkt also, als die noch junge Maxwell-Theorie dringend experimenteller Bestätigung bedurfte. Boltzmann konnte mit seinen experimentellen Untersuchungen eine direkte Konsequenz der Maxwellschen elektromagnetischen Theorie, die so genannte Maxwell-Relation, bestätigen. Seine Experimente stellten nicht nur lange Zeit den stärksten Beleg für die Richtigkeit der Maxwellschen Lichttheorie dar, sondern waren eine experimentelle Spitzenleistung an der Grenze des damals Möglichen. Besonders Boltzmanns Bestimmung der Dielektrizitätskonstanten von Gasen fand noch Jahrzehnte später Erwähnung in namhaften Lehrbüchern.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  6. Van der Waals Epitaxy of Ultrathin Halide Perovkistes

    NASA Astrophysics Data System (ADS)

    Wang, Yiping; Shi, Yunfeng; Shi, Jian

    We present our understanding, with CH3NH3PbX3 as a model system, on the 2D van der Waals growth and kinetics of 3D parent materials. We show the successful synthesis of ultrathin (sub-10 nm), large scale (a few tens of μm) single crystalline 2D perovskite thin films on layered mica substrate by van der Waals (VDW) epitaxy. Classical nucleation and growth model explaining conventional epitaxy has been modified to interpret the unique 2D results under VDW mechanism. The generalization of our model shows that a 3D crystal with low cohesive energy tends to favor the 2D growth while the one with strong cohesive energy has less kinetic window. With Monte Carlo simulations, we show that the fractal 2D morphology in perovskite precisely manifests the kinetic competition between VDW diffusivity and thermodynamic driving force, a unique phenomenon to VDW growth, suggesting a fundamental limit on the morphology stability of the 2D form of a 3D material. On the other hand, our single crystal thin film growth results and subsequent cryogenic study in the iodide perovskite provide a perfect resource for the exploration of its complex optical and electronic properties and unveiling the origins of its popularity in the energy conversion field.

  7. Synthesis and Investigation of van der Waals Heterostructures

    NASA Astrophysics Data System (ADS)

    McCreary, Kathleen; Hanbicki, Aubrey; Culbertson, James; Currie, Marc; Jonker, Berend

    2015-03-01

    The recent isolation of single layers of transition metal dichalcogenides (TMD) has demonstrated that reducing dimensionality can alter the material properties. In particular, MoS2, MoSe2, WS2, and WSe2 exhibit an abrupt transition from indirect to direct bandgap semiconductors at monolayer thickness. Monolayer TMDs are promising materials for electronic components due to their high mobility, high on/off ratio, and low standby power dissipation. Additionally, selective layer-by-layer stacking to form van der Waals (vdW) heterostructures may provide the ability to controllably engineer electronic, optic, and spintronic properties. Recently, several methods were investigated to achieve vdW heterostructures including sequential exfoliation, stacking of chemical vapor deposition (CVD) grown monolayers, and epitaxial growth of bilayers. We detail our CVD synthesis of the monolayer TMDs (MoS2, MoSe2, WS2 and WSe2) and the subsequent fabrication and characterization of vdW heterostructures. In our heterostructures, we observe a dramatic decrease in PL intensity compared to the monolayer constituents. The Raman spectra exhibit clear and distinct differences from a superposition of monolayer spectra, demonstrating that interactions across the van der Waals interface in these heterostructures may significantly modify the net electronic properties. We find the observed behaviors are influenced by many factors, including charge transfer, substrate effects, stacking sequence, as well as intra- and inter-layer exciton formation, which will be discussed here.

  8. Herschel und die Zukunft der Fern-Infrarot-Astronomie

    NASA Astrophysics Data System (ADS)

    Linz, Hendrik

    2015-06-01

    Schon lange ist die beobachtende Astronomie den engen Grenzen des optisch Sichbaren entwachsen und hat fast alle Bereiche des elektromagnetischen Spektrums für sich dienstbar gemacht. Im sogenannten nahen und mittleren Infrarot (Wellenlängen zwischen 1-30 μm) sowie im Millimeter- und Radio-Regime (Wellenlängen zwischen 1 mm und 10 m) ist die Erdatmosphäre relativ gut durchlässig für elektromagnetische Signale oder hat zumindest eine Vielzahl von spektral begrenzten Transmissionsfenstern, die astronomische Beobachtungen zumindest von höheren Bergen aus möglich machen. Allerdings ist das sogenannte Ferne Infrarot (FIR, 30-300 μm Wellenlänge) von der Erde aus fast völlig unzugänglich für astronomische Beobachtungen. Selbst für die besten Beobachtungsplätze der Erde bleibt die atmosphärische Transmission durch die immense Wasserdampf- Absorption auf ein absolutes Minimum beschränkt. Jedoch erlaubt uns das FIR Zugang zu Informationen, die sehr nützlich sind für die astrophysikalische Forschung und komplementär zu anderen Wellenlängen-Bereichen.

  9. Two-dimensional van der Waals C60 molecular crystal

    PubMed Central

    Reddy, C. D.; Gen Yu, Zhi; Zhang, Yong-Wei

    2015-01-01

    Two-dimensional (2D) atomic crystals, such as graphene and transition metal dichalcogenides et al. have drawn extraordinary attention recently. For these 2D materials, atoms within their monolayer are covalently bonded. An interesting question arises: Can molecules form a 2D monolayer crystal via van der Waals interactions? Here, we first study the structural stability of a free-standing infinite C60 molecular monolayer using molecular dynamic simulations, and find that the monolayer is stable up to 600 K. We further study the mechanical properties of the monolayer, and find that the elastic modulus, ultimate tensile stress and failure strain are 55–100 GPa, 90–155 MPa, and 1.5–2.3%, respectively, depending on the stretching orientation. The monolayer fails due to shearing and cavitation under uniaxial tensile loading. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the monolayer are found to be delocalized and as a result, the band gap is reduced to only 60% of the isolated C60 molecule. Interestingly, this band gap can be tuned up to ±30% using strain engineering. Owing to its thermal stability, low density, strain-tunable semi-conducting characteristics and large bending flexibility, this van der Waals molecular monolayer crystal presents aplenty opportunities for developing novel applications in nanoelectronics. PMID:26183501

  10. Epigenetische Aspekte bei Karzinomen der Kopf-Hals-Region

    PubMed Central

    Schmezer, Peter; Plass, Christoph

    2009-01-01

    Zusammenfassung Plattenepithelkarzinome der Kopf-Hals-Region (HNSCC) zählen seit Jahren zu den weltweit häufigsten Krebsarten. Trotz vieler Bemühungen hat sich das 5-Jahres-Überleben bei Patienten mit HNSCC kaum verbessert. Um einen Fortschritt zu erzielen, ist es notwendig, die der Erkrankung zugrunde liegenden biologischen Prozesse besser zu verstehen. Neben den bekannten genetischen Veränderungen haben molekular-zytogenetische Untersuchungen bei HNSCC gezeigt, dass es weitere Veränderungen gibt, die mit Vermehrung und Verlust chromosomaler Bereiche einhergehen, für die jedoch die krankheitsverursachenden Gene bisher nicht identifiziert wurden. Darüberhinaus haben jüngste Forschungsergebnisse verdeutlicht, dass epigenetische Modifikationen wie die DNA Methylierung eine wichtige Rolle spielen. So konnte gezeigt werden, dass bei HNSCC eine Reihe von Genen (z.B. das Tumorsuppressorgen CDKN2A sowie DAPK1, MGMT, TIMP3, TCF21, und C/EBPα) hypermethylierte Bereiche in regulatorischen DNA Sequenzen aufweisen, wodurch ihre Expression verringert oder unterbunden wird. Die Hypermethylierung solcher Gene könnte als Biomarker zur Früherkennung von HNSCC genutzt werden und nicht zuletzt dadurch zur Verbesserung von Prävention und Therapieerfolg beitragen. PMID:18483718

  11. van der Waals forces influencing adhesion of cells

    PubMed Central

    Kendall, K.; Roberts, A. D.

    2015-01-01

    Adhesion molecules, often thought to be acting by a ‘lock and key’ mechanism, have been thought to control the adhesion of cells. While there is no doubt that a coating of adhesion molecules such as fibronectin on a surface affects cell adhesion, this paper aims to show that such surface contamination is only one factor in the equation. Starting from the baseline idea that van der Waals force is a ubiquitous attraction between all molecules, and thereby must contribute to cell adhesion, it is clear that effects from geometry, elasticity and surface molecules must all add on to the basic cell attractive force. These effects of geometry, elasticity and surface molecules are analysed. The adhesion force measured between macroscopic polymer spheres was found to be strongest when the surfaces were absolutely smooth and clean, with no projecting protruberances. Values of the measured surface energy were then about 35 mJ m−2, as expected for van der Waals attractions between the non-polar molecules. Surface projections such as abrasion roughness or dust reduced the molecular adhesion substantially. Water cut the measured surface energy to 3.4 mJ m−2. Surface active molecules lowered the adhesion still further to less than 0.3 mJ m−2. These observations do not support the lock and key concept. PMID:25533101

  12. Two-dimensional van der Waals C60 molecular crystal

    NASA Astrophysics Data System (ADS)

    Reddy, C. D.; Gen Yu, Zhi; Zhang, Yong-Wei

    2015-07-01

    Two-dimensional (2D) atomic crystals, such as graphene and transition metal dichalcogenides et al. have drawn extraordinary attention recently. For these 2D materials, atoms within their monolayer are covalently bonded. An interesting question arises: Can molecules form a 2D monolayer crystal via van der Waals interactions? Here, we first study the structural stability of a free-standing infinite C60 molecular monolayer using molecular dynamic simulations, and find that the monolayer is stable up to 600 K. We further study the mechanical properties of the monolayer, and find that the elastic modulus, ultimate tensile stress and failure strain are 55-100 GPa, 90-155 MPa, and 1.5-2.3%, respectively, depending on the stretching orientation. The monolayer fails due to shearing and cavitation under uniaxial tensile loading. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the monolayer are found to be delocalized and as a result, the band gap is reduced to only 60% of the isolated C60 molecule. Interestingly, this band gap can be tuned up to ±30% using strain engineering. Owing to its thermal stability, low density, strain-tunable semi-conducting characteristics and large bending flexibility, this van der Waals molecular monolayer crystal presents aplenty opportunities for developing novel applications in nanoelectronics.

  13. van der Waals interaction as a summable asymptotic series

    NASA Astrophysics Data System (ADS)

    Perdew, John P.; Ruzsinszky, Adrienn; Sun, Jianwei; Glindmeyer, Stephen; Csonka, Gabor I.

    2012-12-01

    The dynamic multipole polarizabilities and thus the second-order van der Waals coefficients C2k of all orders are known exactly for the interaction between two classical spherical conducting shells, each of uniform electron density ρ with outer radius R and thickness t. The result is C2k=-ck(t/R)4πρ[(2R)2]k. The ck approach a limiting constant value, so the infinite series for the van der Waals interaction at separation d, -C6/d6-C8/d8-⋯, can be summed analytically, diverging only for d≤2R. This divergence can be removed without changing the asymptotic series. Real quasispherical objects like nanoclusters, fullerenes, and even atoms can be approximated by this spherical-shell model, with R fixed by the true static dipole polarizability. Once t/R is fixed, all the higher coefficients are determined by just C6 and C8. Finally, we compare the exact C2k to those from a pair interaction model, which works for solid spheres (t=R) but not for fullerenes.

  14. Quantum Monte Carlo Simulation of condensed van der Waals Systems

    NASA Astrophysics Data System (ADS)

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

    2012-02-01

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

  15. Ontogenic Caste Differences in the Van der Vecht Organ of Primitively Eusocial Neotropical Paper Wasps.

    PubMed

    de Souza, André Rodrigues; Petrocelli, Iacopo; Lino-Neto, José; Santos, Eduardo Fernando; Noll, Fernando Barbosa; Turillazzi, Stefano

    2016-01-01

    Recent studies have reported incipient morphological caste dimorphism in the Van der Vecht organ size of some temperate Polistes paper wasps. Whether species other than the temperate ones show a similar pattern remains elusive. Here, we have studied some Neotropical Polistes species. By comparing females collected through the year, we showed caste related differences in the size of the Van der Vecht organ in P. ferreri (body size corrected Van der Vech organ size of queens = 0.45 ± 0.06, workers = 0.38 ± 0.07 mm2, p = 0.0021), P. versicolor (body size corrected Van der Vech organ size of queens = 0.54 ± 0.11, workers = 0.46 ± 0.09 mm2, p = 0.010), but not P. simillimus (body size corrected Van der Vech organ size of queens = 0.52 ± 0.05, workers = 0.49 ± 0.06 mm2, p = 0.238). Therefore, it seems that queens and workers of some Neotropical Polistes have diverged in their ontogenic trajectory of the Van der Vecht organ size, providing clear evidence for incipient morphological caste dimorphism. As Polistes are distributed mostly in the tropics, we propose that physical caste differences may be widespread in the genus. Also, we highlight that morphological divergence in the queen-worker phenotypes may have started through differential selection of body structures, like the Van der Vecht organ. PMID:27167514

  16. Characterization of Der f 29, a new allergen from dermatophagoides farinae

    PubMed Central

    Jiang, Congli; Fan, Xiaoqin; Li, Meng; Xing, Peng; Liu, Xiaoyu; Wu, Yulan; Zhang, Min; Yang, Pingchang; Liu, Zhigang

    2015-01-01

    More than 30 allergens have been identified from Dermatophagoides farina (D. farina), which is one of the main species of house dust mites. The mite allergens are an important factor contributing to allergic disease in the world. As the detection and identification of new allergens is critical for the diagnosis or treatment of allergic diseases, we sought to characterize the profilin of D. farina (Der f 29) in this study. The results showed that 21% of allergic patients displayed positive results in skin prick test with recombinant Der f 29 (rDer f 29) as the specific allergen; specific IgE reactivity to rDer f 29 was shown by Western Blot and ELISA. In addition, rDer f 29 induced bone marrow-derived dendritic cells (DC) to produce T cells immunoglobulin domain and mucin domain protein 4 (TIM4). Moreover, an allergic asthma mouse model was established by challenging with rDer f 29. Airway hyperresponsiveness, serum specific IgE, IgG1, eosinophil infiltration in the allergic mice bronchoalveolar lavage fluid, the cytokines interleukin-4 (IL-4) and interferon-γ (INF-γ) from spleen cells were markedly increased; the histology showed severe inflammation in the lung. In conclusion, Der f 29 is identified as a new type of the house dust mite allergen. PMID:26328014

  17. Ontogenic Caste Differences in the Van der Vecht Organ of Primitively Eusocial Neotropical Paper Wasps

    PubMed Central

    de Souza, André Rodrigues; Petrocelli, Iacopo; Lino-Neto, José; Santos, Eduardo Fernando; Noll, Fernando Barbosa; Turillazzi, Stefano

    2016-01-01

    Recent studies have reported incipient morphological caste dimorphism in the Van der Vecht organ size of some temperate Polistes paper wasps. Whether species other than the temperate ones show a similar pattern remains elusive. Here, we have studied some Neotropical Polistes species. By comparing females collected through the year, we showed caste related differences in the size of the Van der Vecht organ in P. ferreri (body size corrected Van der Vech organ size of queens = 0.45 ± 0.06, workers = 0.38 ± 0.07 mm2, p = 0.0021), P. versicolor (body size corrected Van der Vech organ size of queens = 0.54 ± 0.11, workers = 0.46 ± 0.09 mm2, p = 0.010), but not P. simillimus (body size corrected Van der Vech organ size of queens = 0.52 ± 0.05, workers = 0.49 ± 0.06 mm2, p = 0.238). Therefore, it seems that queens and workers of some Neotropical Polistes have diverged in their ontogenic trajectory of the Van der Vecht organ size, providing clear evidence for incipient morphological caste dimorphism. As Polistes are distributed mostly in the tropics, we propose that physical caste differences may be widespread in the genus. Also, we highlight that morphological divergence in the queen–worker phenotypes may have started through differential selection of body structures, like the Van der Vecht organ. PMID:27167514

  18. Band Gap Engineering of PbI2 by Incommensurate Van der Waals Epitaxy

    NASA Astrophysics Data System (ADS)

    Wang, Yiping; Shi, Jian

    Van der Waals epitaxial growth had been thought to have trivial contribution on inducing substantial epitaxial strain in thin films due to its weak nature of Van der Waals interfacial energy. Due to this, electrical and optical structure engineering via Van der Waals epitaxial strain has been rarely studied. However, by appropriate film-substrate selection, we show that significant band structure engineering could be achieved in a soft thin film material PbI2 via Van der Waals epitaxy. The thickness dependent photoluminescence of single crystal PbI2 flakes was studied and attributed to the substrate-film coupling effect via incommensurate Van der Waals epitaxy. It is proposed that the Van der Waals strain is resulted from the soft nature of PbI2 and large Van der Waals interaction due to the involvement of heavy elements. Such strain plays vital roles in modifying the band gap of PbI2. The deformation potential theory is used to quantitatively unveil the correlation between thickness, strain and band gap change. Our hypothesis is confirmed by the subsequent mechanical bending test and Raman characterization.

  19. Wie verstehen Schülerinnen und Schüler den Begriff der Unendlichkeit?

    NASA Astrophysics Data System (ADS)

    Schimmöller, Tabea

    Wie Hilbert bereits feststellte, wirkt die Idee der Unendlichkeit, wie keine andere, schon seit Zeiten sehr anregend und fruchtbar auf den Verstand und bewegt das Gemüt der Menschen. Der Begriff der Unendlichkeit bedarf aber auch, wie kein anderer, der Aufklärung, denn mit ihm eröffnet sich ein weites Feld, welches nicht nur aus vielen verschiedenen Definitionen besteht, sondern auch aus völlig unterschiedlichen Disziplinen. Physiker suchen immer dringender nach einer "Theorie für Alles" oder einer "Weltformel", Kosmologen beschäftigen sich unter anderem mit der Ewigkeit des Universums, Theologen interessiert eher die Unendlichkeit Gottes, Philosophen diskutieren unter anderem Grenzfragen zwischen Naturwissenschaft und Philosophie und die Mathematiker versuchen den Paradoxien des Unendlichen einen Sinn zu geben. Und so wird ersichtlich, dass nichts abstrakter ist als das Unendliche: Obwohl die Unendlichkeit für die unterschiedlichsten Wissenschaften von großer Bedeutung ist, "[ist] in der Wirklichkeit das Unendliche nirgends zu finden, [egal] was für Erfahrungen und Beobachtungen und welcherlei Wissenschaft wir auch heranziehen".

  20. Das singuläre Modell der über der Oberfläche von Kryodielektrikas lokalisierten Elektronenzustände

    NASA Astrophysics Data System (ADS)

    Dorofeyev, O. F.; Lysov, B. A.; Pavlova, O. S.; Ternov, I. M.

    Wir schlagen ein neues Modell zur Beschreibung der in der Nähe der Oberfläche von Kryodielektrika lokalisierten Elektronenzustände vor. Dabei wird die Nichteindeutigkeit der selbstadjungierten Erweiterung des Hamilton-Operators der elektrostatischen Bildkräfte an der flachen Grenze Dielektrikum-Vakuum benutzt. Im Unterschied zum bekannten Modell von Grimes enthält das von uns vorgeschlagene Modell nur einen einzigen phänomenologischen Parameter, den Vermischungswinkel. Es zeigt sich, daß die entsprechende Wahl des Vermischungswinkels es erlaubt, die spektroskopischen Daten von elektrischen Dipolübergängen zwischen den Einteilchen-Elektronenzuständen, die über der Oberfläche flüssigen 4He und 3He sowie festen Wasserstoffe lokalisiert sind, vollständig zu beschreiben.Translated AbstractA Singular Model of Electronic States, Localized over the Surface of Cryogenized DielectricA new model for the description of localized electronic states near the surface of a cryogenized dielectric is proposed. In this model an ambiguity of the self-adjoined extention of the Hamiltonian for the problem of the motion of an electron in the field of the electrostatic image at flat boundary dielectric-vacuum is used. The proposed model, in contrast with the well known model of Grimes, contains as only phenomenological parameter the mixing angle. It is shown that the proper choise of the mixing angle makes it possible to completely account for the spectroscopic data on electric dipole transitions between singleparticle electronic states localized over the surfaces of 4He, 3He and also solid hydrogen.

  1. Van der Waals Epitaxy of Functional Oxide Heterostructures

    NASA Astrophysics Data System (ADS)

    Chu, Ying-Hao

    In the diligent pursuit of low-power consumption, multifunctional, and environmentally friendly electronics, more sophisticated requirements on functional materials are on demand. Recently, the discovery of 2D layered materials has created a revolution to this field. Pioneered by graphene, these new 2D materials exhibit abundant unusual physical phenomena that is undiscovered in bulk forms. These materials are characterized with their layer form and almost pure 2D electronic behavior. The confinement of charge and heat transport at such ultrathin planes offers possibilities to overcome the bottleneck of present device development in thickness limitation, and thus push the technologies into next generation. Van der Waals epitaxy, an epitaxial growth method to combine 2D and 3D materials, is one of current reliable manufacturing processes to fabricate 2D materials by growing these 2D materials epitaxially on 3D materials. Then, transferring the 2D materials to the substrates for practical applications. In the mean time, van der Waals epitaxy has also been used to create free-standing 3D materials by growing 3D materials on 2D materials and then removing them from 2D materials since the interfacial boding between 2D and 3D materials should be weak van der Waals bonds. In this study, we intend to take the same concept, but to integrate a family of functional materials in order to open new avenue to flexible electronics. Due to the interplay of lattice, charge, orbital, and spin degrees of freedom, correlated electrons in oxides generate a rich spectrum of competing phases and physical properties. Recently, lots of studies have suggested that oxide heterostructures provide a powerful route to create and manipulate the degrees of freedom and offer new possibilities for next generation devices, thus create a new playground for researchers to investigate novel physics and the emergence of fascinating states of condensed matter. In this talk, we use a 2D layered material as

  2. Tuning the van der Waals Interaction of Graphene with Molecules via Doping.

    PubMed

    Huttmann, Felix; Martínez-Galera, Antonio J; Caciuc, Vasile; Atodiresei, Nicolae; Schumacher, Stefan; Standop, Sebastian; Hamada, Ikutaro; Wehling, Tim O; Blügel, Stefan; Michely, Thomas

    2015-12-01

    We use scanning tunneling microscopy to visualize and thermal desorption spectroscopy to quantitatively measure that the binding of naphthalene molecules to graphene, a case of pure van der Waals interaction, strengthens with n and weakens with p doping of graphene. Density-functional theory calculations that include the van der Waals interaction in a seamless, ab initio way accurately reproduce the observed trend in binding energies. Based on a model calculation, we propose that the van der Waals interaction is modified by changing the spatial extent of graphene's π orbitals via doping. PMID:26684126

  3. Tuning the van der Waals Interaction of Graphene with Molecules via Doping

    NASA Astrophysics Data System (ADS)

    Huttmann, Felix; Martínez-Galera, Antonio J.; Caciuc, Vasile; Atodiresei, Nicolae; Schumacher, Stefan; Standop, Sebastian; Hamada, Ikutaro; Wehling, Tim O.; Blügel, Stefan; Michely, Thomas

    2015-12-01

    We use scanning tunneling microscopy to visualize and thermal desorption spectroscopy to quantitatively measure that the binding of naphthalene molecules to graphene, a case of pure van der Waals interaction, strengthens with n and weakens with p doping of graphene. Density-functional theory calculations that include the van der Waals interaction in a seamless, ab initio way accurately reproduce the observed trend in binding energies. Based on a model calculation, we propose that the van der Waals interaction is modified by changing the spatial extent of graphene's π orbitals via doping.

  4. Body-assisted van der Waals interaction between two atoms

    SciTech Connect

    Safari, Hassan; Buhmann, Stefan Yoshi; Welsch, Dirk-Gunnar; Ho Trung Dung

    2006-10-15

    Using fourth-order perturbation theory, a general formula for the van der Waals potential of two neutral, unpolarized, ground-state atoms in the presence of an arbitrary arrangement of dispersing and absorbing magnetodielectric bodies is derived. The theory is applied to two atoms in bulk material and in front of a planar multilayer system, with special emphasis on the cases of a perfectly reflecting plate and a semi-infinite half space. It is demonstrated that the enhancement and reduction of the two-atom interaction due to the presence of a perfectly reflecting plate can be understood, at least in the nonretarded limit, by using the method of image charges. For the semi-infinite half space, both analytical and numerical results are presented.

  5. Characterization of rarefaction waves in van der Waals fluids

    NASA Astrophysics Data System (ADS)

    Yuen, Albert; Barnard, John J.

    2015-12-01

    We calculate the isentropic evolution of an instantaneously heated foil, assuming a van der Waals equation of state with the Maxwell construction. The analysis by Yuen and Barnard [Phys. Rev. E 92, 033019 (2015), 10.1103/PhysRevE.92.033019] is extended for the particular case of three degrees of freedom. We assume heating to temperatures in the vicinity of the critical point. The self-similar profiles of the rarefaction waves describing the evolution of the foil display plateaus in density and temperature due to a phase transition from the single-phase to the two-phase regime. The hydrodynamic equations are expressed in a dimensionless form and the solutions form a set of universal curves, depending on a single parameter: the dimensionless initial entropy. We characterize the rarefaction waves by calculating how the plateau length, density, pressure, temperature, velocity, internal energy, and sound speed vary with dimensionless initial entropy.

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

    SciTech Connect

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

    2014-09-01

    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 MoS{sub 2} heterostructures for memory devices; graphene/MoS{sub 2}/WSe{sub 2}/graphene vertical p-n junctions for photovoltaic devices, and organic crystals on hBN with graphene electrodes for high-performance transistors.

  7. Grundlagen und Vollzug der amtlichen Lebensmittelkontrolle in Deutschland

    NASA Astrophysics Data System (ADS)

    Neuhaus, Annette

    Für Menschen besteht ein täglicher Bedarf an Lebensmitteln, die gesundheitlich unbedenklich, allgemein zum Verzehr geeignet und unverfälscht sein sollen. Lebensmittel sind vergängliche Naturprodukte und bergen in sich Gefahren, die mit dem natürlichen Verderbnisvorgang verbunden sind. Zusätzlich bestehen Risiken durch eine unsachgemäße Herstellung, Behandlung oder Verarbeitung, zum Beispiel durch ungeeignete Zutaten oder technologische Verfahren, falsche Lagertemperaturen oder Verwendung ungeeigneter Behältnisse. So lange wie Lebensmittel zum Zweck der Gewinnerzielung an andere abgegeben werden, besteht darüber hinaus die Versuchung, Kunden durch Verfälschung oder andere Manipulation zu übervorteilen.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    In nanoscale mechanochemistry, mechanical forces selectively break covalent bonds to essentially control chemical reactions. An archetype is anisotropic detonation of layered energetic molecular crystals bonded by van der Waals (vdW) interactions. Here, quantum molecular dynamics simulations reveal a crossover of anisotropic nanomechanochemistry of vdW crystal. Within 10-13 s from the passage of shock front, lateral collision produces NO2 via twisting and bending of nitro-groups and the resulting inverse Jahn-Teller effect, which is mediated by strong intra-layer hydrogen bonds. Subsequently, as we transition from heterogeneous to homogeneous mechanochemical regimes around 10-12 s, shock normal to multilayers becomes more reactive, producing H2O assisted by inter-layer N-N bond formation. These time-resolved results provide much needed atomistic understanding of nanomechanochemistry that underlies a wider range of technologies.

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

    SciTech Connect

    Koon, D. W.

    2006-09-15

    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 11x11 grid, and computationally, for both 11x11 and 101x101 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.

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

    SciTech Connect

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

    2015-12-07

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

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

    PubMed Central

    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 that depend on the size of the surface unit cell. This demonstrates that there is a significant, although relatively weak, interfacial interaction between the two materials. Lattice matching is thus relevant for vdW epitaxy with two 2D bonded materials and a fundamental design parameter for vdW heterostructures. PMID:26658715

  12. Van der Waals Interactions in Density Functional Theory: Intermolecular Complexes

    NASA Astrophysics Data System (ADS)

    Kannemann, Felix; Becke, Axel

    2010-03-01

    Conventional density functional theory (GGA and hybrid functionals) fails to account for dispersion interactions and is therefore not applicable to systems where van der Waals interactions play a dominant role, such as intermolecular complexes and biomolecules. The exchange-hole dipole moment (XDM) dispersion model of Becke and Johnson [A. D. Becke and E. R. Johnson, J. Chem. Phys. 127, 154108 (2007)] corrects for this deficiency. We have previously shown that the XDM dispersion model can be combined with standard GGA functionals (PW86 for exchange and PBE for correlation) to give accurate binding energy curves for rare-gas diatomics [F. O. Kannemann and A. D. Becke, J. Chem. Theory Comput. 5, 719 (2009)]. Here we present further tests of the GGA-XDM method using benchmark sets including hydrogen bonding, electrostatic, dispersion and stacking interactions, and systems ranging from rare-gas diatomics to biomolecular complexes.

  13. Van der Waals Density Functional Theory with Applications

    NASA Astrophysics Data System (ADS)

    Langreth, David C.

    2004-03-01

    We discuss the development of electronic density functionals that are applicable for weakly bound systems where the van der Waals interaction and its ramifications become important. Our current functionals approach the correct asymptotic dependence at large distances and are seamless at small distances. The first form of the functional, appropriate for layered systems, has been recently applied to graphite, boron nitride, and molybdenum sulfide [H. Rydberg et al., Phys. Rev. Lett. 91, 126402 (2003) and D. C. Langreth, Int. J. Quant. Chem. (submitted), see http//:www.physics.rutgers.edu/ ˜langreth/preprints/dft2003.pdf]. The second form of the functional [M. Dion it et al. (to be published)] is appropriate for arbitrary geometries. Recent results on rare gas dimers and the benzene dimer suggest promise for this method as well.

  14. Characterization of rarefaction waves in van der Waals fluids.

    PubMed

    Yuen, Albert; Barnard, John J

    2015-12-01

    We calculate the isentropic evolution of an instantaneously heated foil, assuming a van der Waals equation of state with the Maxwell construction. The analysis by Yuen and Barnard [Phys. Rev. E 92, 033019 (2015)] is extended for the particular case of three degrees of freedom. We assume heating to temperatures in the vicinity of the critical point. The self-similar profiles of the rarefaction waves describing the evolution of the foil display plateaus in density and temperature due to a phase transition from the single-phase to the two-phase regime. The hydrodynamic equations are expressed in a dimensionless form and the solutions form a set of universal curves, depending on a single parameter: the dimensionless initial entropy. We characterize the rarefaction waves by calculating how the plateau length, density, pressure, temperature, velocity, internal energy, and sound speed vary with dimensionless initial entropy. PMID:26764692

  15. Regenerative Energieträger im Aufwind: Entwicklung der erneuerbaren Energien

    NASA Astrophysics Data System (ADS)

    Kohl, Harald

    2006-05-01

    2005 kam 4,6 % des deutschen Primär-Energieverbrauchs aus erneuerbaren Energiequellen, bei der Stromproduktion lag ihr Anteil bei 10,2 %. Wesentliche Ursache ist der Boom bei der Windkraft, die vor allem durch Offshore-Windparks auf See weiter ausbaubar ist. Die Wasserkraft lieferte in Deutschland traditionell einen großen Beitrag zur Stromerzeugung, doch ihr Ausbaupotenzial ist gering. Die Photovoltaik, die solar- und die geothermische Stromerzeugung spielen derzeit noch eine kleine Rolle. Den deutschen Bedarf an Wärmeenergie deckten 2004 die erneuerbaren Energien zu 5,4 %, vor allem aus Biomasse. Die solarthermische Wärmeerzeugung hat sich gegenüber 2000 mehr als verdoppelt. Im Straßenverkehr spielen biogene Kraftstoffe mit 5,4 % noch eine untergeordnete Rolle. Bis 2050 könnte in Deutschland der Anteil regenerativer Energien am Primär-Energieverbrauch die Fünfzigprozentmarke überschreiten.

  16. NetCoDer: A Retransmission Mechanism for WSNs Based on Cooperative Relays and Network Coding.

    PubMed

    Valle, Odilson T; Montez, Carlos; Medeiros de Araujo, Gustavo; Vasques, Francisco; Moraes, Ricardo

    2016-01-01

    Some of the most difficult problems to deal with when using Wireless Sensor Networks (WSNs) are related to the unreliable nature of communication channels. In this context, the use of cooperative diversity techniques and the application of network coding concepts may be promising solutions to improve the communication reliability. In this paper, we propose the NetCoDer scheme to address this problem. Its design is based on merging cooperative diversity techniques and network coding concepts. We evaluate the effectiveness of the NetCoDer scheme through both an experimental setup with real WSN nodes and a simulation assessment, comparing NetCoDer performance against state-of-the-art TDMA-based (Time Division Multiple Access) retransmission techniques: BlockACK, Master/Slave and Redundant TDMA. The obtained results highlight that the proposed NetCoDer scheme clearly improves the network performance when compared with other retransmission techniques. PMID:27258280

  17. NetCoDer: A Retransmission Mechanism for WSNs Based on Cooperative Relays and Network Coding

    PubMed Central

    Valle, Odilson T.; Montez, Carlos; Medeiros de Araujo, Gustavo; Vasques, Francisco; Moraes, Ricardo

    2016-01-01

    Some of the most difficult problems to deal with when using Wireless Sensor Networks (WSNs) are related to the unreliable nature of communication channels. In this context, the use of cooperative diversity techniques and the application of network coding concepts may be promising solutions to improve the communication reliability. In this paper, we propose the NetCoDer scheme to address this problem. Its design is based on merging cooperative diversity techniques and network coding concepts. We evaluate the effectiveness of the NetCoDer scheme through both an experimental setup with real WSN nodes and a simulation assessment, comparing NetCoDer performance against state-of-the-art TDMA-based (Time Division Multiple Access) retransmission techniques: BlockACK, Master/Slave and Redundant TDMA. The obtained results highlight that the proposed NetCoDer scheme clearly improves the network performance when compared with other retransmission techniques. PMID:27258280

  18. Der Physik-Nobelpreis vor 100 Jahren Die Entdeckung des trägen Gases

    NASA Astrophysics Data System (ADS)

    Jacobi, Manfred

    2004-11-01

    Im Jahr 1904 erhielt der britische Physiker Lord Rayleigh (John William Strutt, 1842 bis 1919) den Nobelpreis für seine Untersuchungen über die Dichte von Gasen und die Entdeckung des Edelgases Argon.

  19. Optimizing Distributed Energy Resources and building retrofits with the strategic DER-CAModel

    DOE PAGESBeta

    Stadler, M.; Groissböck, M.; Cardoso, G.; Marnay, C.

    2014-08-05

    The pressuring need to reduce the import of fossil fuels as well as the need to dramatically reduce CO2 emissions in Europe motivated the European Commission (EC) to implement several regulations directed to building owners. Most of these regulations focus on increasing the number of energy efficient buildings, both new and retrofitted, since retrofits play an important role in energy efficiency. Overall, this initiative results from the realization that buildings will have a significant impact in fulfilling the 20/20/20-goals of reducing the greenhouse gas emissions by 20%, increasing energy efficiency by 20%, and increasing the share of renewables to 20%,more » all by 2020. The Distributed Energy Resources Customer Adoption Model (DER-CAM) is an optimization tool used to support DER investment decisions, typically by minimizing total annual costs or CO2 emissions while providing energy services to a given building or microgrid site. This document shows enhancements made to DER-CAM to consider building retrofit measures along with DER investment options. Specifically, building shell improvement options have been added to DER-CAM as alternative or complementary options to investments in other DER such as PV, solar thermal, combined heat and power, or energy storage. The extension of the mathematical formulation required by the new features introduced in DER-CAM is presented and the resulting model is demonstrated at an Austrian Campus building by comparing DER-CAM results with and without building shell improvement options. Strategic investment results are presented and compared to the observed investment decision at the test site. Results obtained considering building shell improvement options suggest an optimal weighted average U value of about 0.53 W/(m2K) for the test site. This result is approximately 25% higher than what is currently observed in the building, suggesting that the retrofits made in 2002 were not optimal. Furthermore, the results obtained with

  20. Optimizing Distributed Energy Resources and building retrofits with the strategic DER-CAModel

    SciTech Connect

    Stadler, M.; Groissböck, M.; Cardoso, G.; Marnay, C.

    2014-08-05

    The pressuring need to reduce the import of fossil fuels as well as the need to dramatically reduce CO2 emissions in Europe motivated the European Commission (EC) to implement several regulations directed to building owners. Most of these regulations focus on increasing the number of energy efficient buildings, both new and retrofitted, since retrofits play an important role in energy efficiency. Overall, this initiative results from the realization that buildings will have a significant impact in fulfilling the 20/20/20-goals of reducing the greenhouse gas emissions by 20%, increasing energy efficiency by 20%, and increasing the share of renewables to 20%, all by 2020. The Distributed Energy Resources Customer Adoption Model (DER-CAM) is an optimization tool used to support DER investment decisions, typically by minimizing total annual costs or CO2 emissions while providing energy services to a given building or microgrid site. This document shows enhancements made to DER-CAM to consider building retrofit measures along with DER investment options. Specifically, building shell improvement options have been added to DER-CAM as alternative or complementary options to investments in other DER such as PV, solar thermal, combined heat and power, or energy storage. The extension of the mathematical formulation required by the new features introduced in DER-CAM is presented and the resulting model is demonstrated at an Austrian Campus building by comparing DER-CAM results with and without building shell improvement options. Strategic investment results are presented and compared to the observed investment decision at the test site. Results obtained considering building shell improvement options suggest an optimal weighted average U value of about 0.53 W/(m2K) for the test site. This result is approximately 25% higher than what is currently observed in the building, suggesting that the retrofits made in 2002 were not optimal. Furthermore

  1. Intraoperative Schnellschnittuntersuchungen parapylorischer Lymphknoten bei der pyloruserhaltenden Pankreaskopfresektion: Gibt es eine klinische Relevanz?

    PubMed Central

    Riediger, Hartwig; Schulz, Antje; Adam, Ulrich; Krüger, Colin M.

    2014-01-01

    Zusammenfassung Hintergrund Die pyloruserhaltende Pankreaskopfresektion (PPPD) ist als onkologisches Standardverfahren etabliert. Lokal fortgeschrittene Tumoren können eine erweiterte Resektion erforderlich machen. Ebenso soll früheren Arbeiten zufolge bei Tumornachweis in den parapylorischen Lymphknoten (PLK) eine distale Magenresektion im Sinne einer klassischen Whipple-Operation indiziert sein. Entsprechend diesen Empfehlungen haben wir intraoperative Schnellschnittuntersuchungen der PLK in unseren Routineablauf integriert. Im Rahmen dieser Studie haben wir die klinische Relevanz dieses Vorgehens hinterfragt. Methoden Bei 105 onkologischen Patienten im Zeitraum von 2006-2012 bestand die Indikation zur PPPD. In allen Fällen erfolgte eine intraoperative Schnellschnittuntersuchung der PLK. Die Patienten wurden bezüglich Primärtumor, Anzahl der untersuchten Lymphknoten (LK) (gesamt und parapylorisch) sowie Auswirkungen auf das operative Konzept untersucht. Es handelt sich um eine retrospektive Studie, die auf prospektiv erhobenen Daten unserer Pankreasdatenbank basiert. Ergebnisse Die Primärtumoren waren 72 Pankreaskopfkarzinome und 33 extrapankreatische Karzinome (Gallengangskarzinom, Ampullenkarzinom, Duodenalkarzinom). 73 Patienten waren nodalpositiv. Insgesamt wurden 2391 LK untersucht, von denen 325 parapylorisch lokalisiert waren. Die intraoperative Schnellschnittuntersuchung erbrachte lediglich bei 4 Patienten mit Pankreaskopfkarzinom jeweils einen positiven PLK; daraufhin erfolgte eine distale Magenresektion. In keinem der distalen Magenresektate waren Tumorresiduen nachweisbar. Lokale chirurgisch-technische Probleme im Sinne von Durchblutungsstörungen des Magens ergaben sich durch die regionale Lymphadenektomie nicht. PLK waren nur beim Pankreaskarzinom positiv. In der Subgruppe der nodalpositiven Patienten mit Pankreaskopfkarzinom hatten 8% der Patienten einen positiven PLK. Schlussfolgerung Die regionale parapylorische Lymphadenektomie ist beim

  2. [Vegetarische und vegane Ernährung bei Kindern - Stand der Forschung und Forschungsbedarf].

    PubMed

    Keller, Markus; Müller, Stine

    2016-01-01

    Die Praxis vegetarischer Ernährungsformen ist in Deutschland im letzten Jahrzehnt deutlich angestiegen. Allerdings ist der Anteil vegetarischer und veganer Kinder dabei unbekannt. Studien mit Erwachsenen zeigen das präventive Potenzial, aber auch potenzielle Schwachstellen pflanzenbasierter Kostformen. Die Vorteile und Risiken einer vegetarischen bzw. veganen Ernährung im Kindesalter wurden bisher jedoch relativ selten untersucht. Außerdem lassen das unterschiedliche Alter der Kinder, das heterogene Studiendesign sowie die teilweise geringe Probandenzahl der Studien keine verbindlichen Aussagen zu. In dieser Übersichtsarbeit werden die Ergebnisse der wenigen Studien zu vegetarisch und vegan ernährten Kindern (< 12 Jahren) in Nordamerika und Europa zusammengefasst. Demnach lag die Zufuhr von Nahrungsenergie und Makronährstoffen vegetarischer und veganer Kinder meist näher an den Empfehlungen der Fachgesellschaften als die Ernährung gleichaltriger Mischkostkinder. Ebenso wiesen vegetarisch und vegan ernährte Kinder eine höhere Zufuhr von und bessere Versorgung mit verschiedenen Vitaminen und Mineralstoffen auf. Häufiger zeigten sich jedoch Defizite bei Vitamin B12, Zink, Kalzium, Eisen und Vitamin D. Das Wachstum und die Entwicklung vegetarisch und vegan ernährter Kinder entsprachen weitgehend den Referenzstandards, wobei sie dazu tendierten, leichter, schlanker und (< 5 Jahren) auch kleiner zu sein. Aufgrund der unzureichenden Studienlage besteht erheblicher Forschungsbedarf zu den Auswirkungen einer vegetarischen und veganen Ernährung im Kindesalter. PMID:27160086

  3. Untersuchung der Störwirkung von LTE auf SRD Anwendungen bei 868 MHz

    NASA Astrophysics Data System (ADS)

    Welpot, M.; Wunderlich, S.; Gaspard, I.

    2014-11-01

    Moderne Hausautomatisierungssysteme, Alarmanlagen oder auch Funk-Zugangssysteme in Haus und Automobil setzen auf frei nutzbare Frequenzen in ISM/SRD-Bändern. Die rasante Zunahme an privaten und kommerziell genutzten Applikationen im SRD-Band bei 868 MHz und der Ausbau der LTE-Mobilfunknetze im Frequenzbereich unterhalb von 1 GHz ("Digital Dividend") wirft zunehmend die Frage nach der Funkverträglichkeit dieser Systeme untereinander auf. Während die SRD-Funkmodule auf eine geringe Sendeleistung von ~ +14 dBm beschränkt sind (Ralf and Thomas, 2009), beträgt die maximale LTE-Sendeleistung im Uplink nach (ETSI-Norm, 2011) +23 dBm. Zusammen mit der Einführung von LTE im Frequenzbereich unterhalb 1 GHz als DSL-Ersatz vor allem in ländlichen Gebieten, ergibt sich damit als mögliches Störszenario, dass durch die Aussendung des LTE-Endgerätes im Bereich von ca. 850 MHz die SRD-Funkverbindungen bei 868 MHz insbesondere dann gestört werden, wenn die Antennen beider Funksysteme räumlich nahe zueinander angeordnet sind und folglich nur eine geringe zusätzliche Entkopplung der Systeme bieten. In der vorliegenden Arbeit wird das LTE-Störpotential auf SRD-Empfänger praxisnah untersucht.

  4. Molekulare Methoden zum Nachweis, zur Quantifizierung und zum Monitoring der Mykotoxinbildung lebensmittelrelevanter Pilze

    NASA Astrophysics Data System (ADS)

    Geisen, Rolf

    Schimmelpilze kommen ubiquitär vor und spielen besonders bei pflanzlichen Lebensmitteln und Rohprodukten eine besondere Rolle als Verderbsorganismen. Es wird geschätzt, dass 20-25 % der jährlichen Produktion an pflanzlichen Produkten durch Schimmelpilze verdorben werden (Smith et al., 1994). Viele der lebensmittelrelevanten Schimmelpilze sind zudem in der Lage, Mykotoxine, toxische Sekundärmetabolite, zu bilden, was das Ausmaß des Problems deutlich macht. Die wichtigsten mykotoxinbildenden Spezies gehören zu den Fusarien (Trichothecene, Fumonisine, Zearalenon), Aspergillen (Aflatoxin, Ochratoxin, Cyclopiazonsäure) und Penicillien (Patulin, Ochratoxin). Für viele Mykotoxine, wie die Aflatoxine, Ochratoxin, Fumonisine und Trichothecene sind Grenzwerte erlassen worden, die die Verkehrsfähigkeit betroffener Produkte regeln. Die Einhaltung der Grenzwerte kann sehr genau durch offizielle chemisch-analytische Methoden, wie HPLC, GC-MS etc. kontrolliert werden. Diese analytischen Methoden sind aber für die Anwendung eines HACCP-Ansatzes zur Kontrolle der Mykotoxinbildung nur bedingt geeignet, da sie Endpunktkontrollen darstellen und nur das über eine längere Zeit gebildete Mykotoxin bestimmen. Sie sagen daher nichts über die biologischen Bedingungen zur Zeit der Bildung durch den Pilz aus.

  5. Sitzungsberichte der Heidelberger Akademie der Wissenschaften> " Jahrgang 1990 Sitzungsber.Heidelberg 90 " "Gott hat die Natur einfältig gemacht, sie aber suchen viel Künste"

    NASA Astrophysics Data System (ADS)

    Zehe, Horst

    Der Aufsatz demonstriert anhand ausgiebig kommentierter zeitgenössischer Zeugnisse Goethes Reaktion auf die Arbeiten Fraunhofers, insbesondere auf die Entdeckung der dunklen Linien im Sonnenspektrum. Den Fehlurteilen Goethes werden dabei die Urteile zeitgenössischer Physiker wie Chladni und J.F.W. Herschel gegenübergestellt. Bislang noch ungedruckte Dokumente aus dem Weimarer Goethe- und Schiller-Archiv belegen, daß sich Goethe nicht nur literarisch mit Fraunhofer beschäftigte, sondern daß er auch dessen Versuche mit Hilfe des Jenaer Universitätsmechanikers Körner getreulich zu wiederholen suchte.

  6. BOOK REVIEW: Meilensteine der Astronomie - Von Aristoteles bis Hawking

    NASA Astrophysics Data System (ADS)

    Duerbeck, H. W.; Hamel, J.

    2006-12-01

    A writer, more specific a writer on the history of astronomy, might from time to time look at the collected document folders with all the research material and reprints, and might wonder: has this been all? Especially at a time when recycling is in vogue? And, perhaps with a request or an invitation to submit something, he or she might consider re-using the material before its definitive disposal. Well, such are my feelings when I looked at Jurgen Hamel's new book Milestones of Astronomy - From Aristoteles to Hawking . A slight chance for survival of medium-sized publishers like Kosmos is to offer popular books, and a title must attract potential buyers: Aristoteles means the "old" times, and as concerns the "mad scientist" of modern times, Stephen Hawking has by now dethroned Einstein. In 1998, Hamel had published a Geschichte der Astronomie - Von den Anfangen bis zur Gegenwart (History of astronomy, from the beginnings to the present), which, of course, he could not simply copy. This time, he selected some stones from his research areas - milestones, touchstones, stumbling blocks in the long road of astronomical evolution - and put them between the covers of his new book. So let us look at these (mile)stones . The reader is informed about Aristoteles on 2 pages, but his medieval interpreter Johannes de Sacrobosco gets 8 pages! Copernicus' life and achievements are described on 9 pages, closely followed by his devotee and translator Rothmann with 8 pages; Copernicus' contemporary, Peter Apian, however, gets about 13! Bessel's and Herschel's lifes and works are described on well-deserved 13 and 15 pages, while the achievements of the two Lucasian professors, Isaac Newton and Stephen Hawking, are just outlined in a single paragraph! Thus, importance is sometimes inversely proportional to text length... But let us become serious now. Why should an active historian outline, for the hundreth time, the life of Copernicus, while there are so many interesting, and often

  7. Gate tunable WSe2-BP van der Waals heterojunction devices

    NASA Astrophysics Data System (ADS)

    Chen, Peng; Zhang, Ting Ting; Zhang, Jing; Xiang, Jianyong; Yu, Hua; Wu, Shuang; Lu, Xiaobo; Wang, Guole; Wen, Fusheng; Liu, Zhongyuan; Yang, Rong; Shi, Dongxia; Zhang, Guangyu

    2016-02-01

    Due to the weak screening effect, the concentration and type of charge carriers in 2D semiconductor heterostructures can be effectively tuned by electrostatic gating, enabling us to realize different types of heterojunctions in a single device. Such `type tunable' properties are useful for designing novel electrical or optoelectrical devices. Here, we demonstrate a `type tunable' heterojunction device construct with two pieces of ambipolar 2D semiconductors: WSe2 and black phosphorus (BP). This heterojunction could be tuned to either the p-p junction or n-n junction by gate modulation. The p-p junction shows a large current rectification ratio while the n-n junction shows a negligible current rectification ratio, indicating a large valence band offset and a small conduction band offset at the WSe2/BP interface. In the optoelectrical measurements, we found the amplitude and even the polarity of photocurrent could be modulated by electrostatic gating. Our study could further enhance the understanding of designing devices based on these `type tunable' van der Waals heterojunctions. Moreover, the properties of the WSe2/BP interface were also experimentally identified through the electrical and optoelectrical measurements in our study.Due to the weak screening effect, the concentration and type of charge carriers in 2D semiconductor heterostructures can be effectively tuned by electrostatic gating, enabling us to realize different types of heterojunctions in a single device. Such `type tunable' properties are useful for designing novel electrical or optoelectrical devices. Here, we demonstrate a `type tunable' heterojunction device construct with two pieces of ambipolar 2D semiconductors: WSe2 and black phosphorus (BP). This heterojunction could be tuned to either the p-p junction or n-n junction by gate modulation. The p-p junction shows a large current rectification ratio while the n-n junction shows a negligible current rectification ratio, indicating a large valence

  8. Surface energy and wettability of van der Waals structures

    NASA Astrophysics Data System (ADS)

    Annamalai, Meenakshi; Gopinadhan, Kalon; Han, Sang A.; Saha, Surajit; Park, Hye Jeong; Cho, Eun Bi; Kumar, Brijesh; Patra, Abhijeet; Kim, Sang-Woo; Venkatesan, T.

    2016-03-01

    The wetting behaviour of surfaces is believed to be affected by van der Waals (vdW) forces; however, there is no clear demonstration of this. With the isolation of two-dimensional vdW layered materials it is possible to test this hypothesis. In this paper, we report the wetting behaviour of vdW heterostructures which include chemical vapor deposition (CVD) grown graphene, molybdenum disulfide (MoS2) and tungsten disulfide (WS2) on few layers of hexagon boron nitride (h-BN) and SiO2/Si. Our study clearly shows that while this class of two-dimensional materials are not completely wetting transparent, there seems to be a significant amount of influence on their wetting properties by the underlying substrate due to dominant vdW forces. Contact angle measurements indicate that graphene and graphene-like layered transitional metal dichalcogenides invariably have intrinsically dispersive surfaces with a dominating London-vdW force-mediated wettability.The wetting behaviour of surfaces is believed to be affected by van der Waals (vdW) forces; however, there is no clear demonstration of this. With the isolation of two-dimensional vdW layered materials it is possible to test this hypothesis. In this paper, we report the wetting behaviour of vdW heterostructures which include chemical vapor deposition (CVD) grown graphene, molybdenum disulfide (MoS2) and tungsten disulfide (WS2) on few layers of hexagon boron nitride (h-BN) and SiO2/Si. Our study clearly shows that while this class of two-dimensional materials are not completely wetting transparent, there seems to be a significant amount of influence on their wetting properties by the underlying substrate due to dominant vdW forces. Contact angle measurements indicate that graphene and graphene-like layered transitional metal dichalcogenides invariably have intrinsically dispersive surfaces with a dominating London-vdW force-mediated wettability. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr06705

  9. Structural analysis of Der p 1-antibody complexes and comparison with complexes of proteins or peptides with monoclonal antibodies

    PubMed Central

    Osinski, Tomasz; Pomés, Anna; Majorek, Karolina A.; Glesner, Jill; Offermann, Lesa R.; Vailes, Lisa D.; Chapman, Martin D.; Minor, Wladek; Chruszcz, Maksymilian

    2015-01-01

    Der p 1 is a major allergen from the house dust mite Dermatophagoides pteronyssinus that belongs to the papain-like cysteine protease family. To investigate the antigenic determinants of Der p 1, we determined two crystal structures of Der p 1 in complex with the Fab fragments of mAbs 5H8 or 10B9. Epitopes for these two Der p 1-specific antibodies are located in different, non-overlapping parts of the Der p 1 molecule. Nevertheless, surface area and identity of the amino acid residues involved in hydrogen bonds between allergen and antibody are similar. The epitope for mAb 10B9 only, showed a partial overlap with the previously reported epitope for mAb 4C1, a cross-reactive mAb that binds Der p 1 and its homolog Der f 1 from D. farinae. Upon binding to Der p 1, the Fab fragment of mAb 10B9 was found to form a very rare alpha-helix in its third CDR of the heavy chain. In order to provide an overview of the surface properties of the interfaces formed by the complexes of Der p 1-10B9 and Der p 1-5H8, along with the complexes of 4C1 with Der p 1 and Der f 1, a broad analysis of the surfaces and hydrogen bonds of all complexes of Fab-protein or Fab-peptide was performed. This work provides detailed insight into the cross-reactive and specific allergen-antibody interactions in Group 1 mite allergens. The surface data of Fab-protein and Fab-peptide interfaces can be used in the design of less potent conformational epitopes for immunotherapy. PMID:26026055

  10. Surface energy and wettability of van der Waals structures.

    PubMed

    Annamalai, Meenakshi; Gopinadhan, Kalon; Han, Sang A; Saha, Surajit; Park, Hye Jeong; Cho, Eun Bi; Kumar, Brijesh; Patra, Abhijeet; Kim, Sang-Woo; Venkatesan, T

    2016-03-14

    The wetting behaviour of surfaces is believed to be affected by van der Waals (vdW) forces; however, there is no clear demonstration of this. With the isolation of two-dimensional vdW layered materials it is possible to test this hypothesis. In this paper, we report the wetting behaviour of vdW heterostructures which include chemical vapor deposition (CVD) grown graphene, molybdenum disulfide (MoS2) and tungsten disulfide (WS2) on few layers of hexagon boron nitride (h-BN) and SiO2/Si. Our study clearly shows that while this class of two-dimensional materials are not completely wetting transparent, there seems to be a significant amount of influence on their wetting properties by the underlying substrate due to dominant vdW forces. Contact angle measurements indicate that graphene and graphene-like layered transitional metal dichalcogenides invariably have intrinsically dispersive surfaces with a dominating London-vdW force-mediated wettability. PMID:26910437

  11. Gate tunable WSe2-BP van der Waals heterojunction devices.

    PubMed

    Chen, Peng; Zhang, Ting Ting; zhang, Jing; Xiang, Jianyong; Yu, Hua; Wu, Shuang; Lu, Xiaobo; Wang, Guole; Wen, Fusheng; Liu, Zhongyuan; Yang, Rong; Shi, Dongxia; Zhang, Guangyu

    2016-02-14

    Due to the weak screening effect, the concentration and type of charge carriers in 2D semiconductor heterostructures can be effectively tuned by electrostatic gating, enabling us to realize different types of heterojunctions in a single device. Such 'type tunable' properties are useful for designing novel electrical or optoelectrical devices. Here, we demonstrate a 'type tunable' heterojunction device construct with two pieces of ambipolar 2D semiconductors: WSe2 and black phosphorus (BP). This heterojunction could be tuned to either the p-p junction or n-n junction by gate modulation. The p-p junction shows a large current rectification ratio while the n-n junction shows a negligible current rectification ratio, indicating a large valence band offset and a small conduction band offset at the WSe2/BP interface. In the optoelectrical measurements, we found the amplitude and even the polarity of photocurrent could be modulated by electrostatic gating. Our study could further enhance the understanding of designing devices based on these 'type tunable' van der Waals heterojunctions. Moreover, the properties of the WSe2/BP interface were also experimentally identified through the electrical and optoelectrical measurements in our study. PMID:26810387

  12. Helmholtz's early empiricism and the Erhaltung der Kraft.

    PubMed

    Jurkowitz, Edward

    2010-01-01

    Hermann Helmholtz has often been understood to have started research under the influence of Kant, and then to have made a transition to a later mature empiricist phase. Without claiming that in 1847 Helmholtz held the same positions that he later espoused, I suggest that already in his 1847 'Uber die Erhaltung der Kraft' one may find important aspects of his later empiricism. I highlight the ways in which, from early on, Helmholtz turned Kant to use in developing an empirical program of inquiry into possible basic natural causes. To that end, I indicate how, throughout his arguments, Helmholtz employed, sometimes explicitly, but often tacitly, an empiricist logic, one that ran contrary to any form of transcendental deduction, and even to all a priori knowledge. Instead of deriving aspects about the ultimate constituents of nature, Helmholtz aimed to define the proper project for physical natural science. The first part of the paper describes the context of discussion in which Helmholtz entered. The bulk of the paper then analyzes Helmholtz's arguments in order to make space between (1) Kantian, and other, deductions of characteristics that must be true of nature and (2) Helmholtz's delineation of empirically determinable characteristics of presumed ultimate elements of nature, ones that he meant to be specified and delimited through future experimental research. The paper highlights that throughout his discussion Helmholtz meant to define the proper project for physical natural science, a project rife with empiricist aspects. PMID:20503777

  13. Effects of van der Waals interaction on nanoparticle adsorption

    NASA Astrophysics Data System (ADS)

    Poddar, Nitun; Amar, Jacques

    2014-03-01

    The results of molecular dynamics (MD) simulations carried out using an all-atom model in order to understand the structure, diffusion, and binding of dodecanethiol (DDT)-coated Au nanoparticles (NPs) at the toluene-air interface are presented. We find that due to the strong attraction between DDT and toluene, the NP lies mainly below the interface. As a result, the coefficient for diffusion along the interface is close to the Stokes-Einstein prediction for 3D bulk diffusion. We also find that, due to the small ratio of ligand length to NP diameter, there is little spontaneous asymmetry in the NP coating. We have also used our MD results along with analytical expressions for the van der Waals (VdW) interactions to estimate corrections to the adsorption energy for DDT-coated Au NPs at the toluene-vapor interface as well as for alkanethiol-coated NPs at the water-vapor interface. In both cases, we find that the core-solvent interaction may significantly reduce the binding energy. We also find that the competition between this interaction and short-range attraction to the interface leads to well-defined activation barriers for interfacial desorption as well as for NP adsorption from the solvent. This work was supported by NSF Grant No. CHE-1012896.

  14. Jarzynski equality in van der Pol and Rayleigh oscillators

    NASA Astrophysics Data System (ADS)

    Hasegawa, Hideo

    2011-12-01

    We have studied the Jarzynski equality (JE) in van der Pol and Rayleigh oscillators, which are typical deterministic non-Hamiltonian models but not expected to rigorously satisfy the JE because they are not reversible. Our simulations that calculate the contribution to the work W of an applied ramp force with a duration τ show that the JE approximately holds for a fairly wide range of τ including τ→0 and τ→∞, except for τ˜T, where T denotes the period of relaxation oscillations in the limit cycle. The work distribution function (WDF) is shown to be non-Gaussian with the U-shaped structure for a strong damping parameter. The τ dependence of R (=-kBTln) obtained by our simulations is semiquantitatively elucidated with the use of a simple expression for limit-cycle oscillations, where the bracket <·> expresses an average over the WDF. The result obtained in self-excited oscillators is in contrast with the fact that the JE holds in the Nosé-Hoover oscillator, which also belongs to deterministic non-Hamiltonian models.

  15. Spatially Correlated Disorder in Epitaxial van der Waals Heterostructures

    NASA Astrophysics Data System (ADS)

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

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

  16. Peptide folding driven by Van der Waals interactions.

    PubMed

    Sung, Shen-Shu

    2015-09-01

    Contrary to the widespread view that hydrogen bonding and its entropy effect play a dominant role in protein folding, folding into helical and hairpin-like structures is observed in molecular dynamics (MD) simulations without hydrogen bonding in the peptide-solvent system. In the widely used point charge model, hydrogen bonding is calculated as part of the interaction between atomic partial charges. It is removed from these simulations by setting atomic charges of the peptide and water to zero. Because of the structural difference between the peptide and water, van der Waals (VDW) interactions favor peptide intramolecular interactions and are a major contributing factor to the structural compactness. These compact structures are amino acid sequence dependent and closely resemble standard secondary structures, as a consequence of VDW interactions and covalent bonding constraints. Hydrogen bonding is a short range interaction and it locks the approximate structure into the specific secondary structure when it is included in the simulation. In contrast to standard molecular simulations where the total energy is dominated by charge-charge interactions, these simulation results will give us a new view of the folding mechanism. PMID:26013298

  17. Photocurrent generation with two-dimensional van der Waals semiconductors.

    PubMed

    Buscema, Michele; Island, Joshua O; Groenendijk, Dirk J; Blanter, Sofya I; Steele, Gary A; van der Zant, Herre S J; Castellanos-Gomez, Andres

    2015-06-01

    Two-dimensional (2D) materials have attracted a great deal of interest in recent years. This family of materials allows for the realization of versatile electronic devices and holds promise for next-generation (opto)electronics. Their electronic properties strongly depend on the number of layers, making them interesting from a fundamental standpoint. For electronic applications, semiconducting 2D materials benefit from sizable mobilities and large on/off ratios, due to the large modulation achievable via the gate field-effect. Moreover, being mechanically strong and flexible, these materials can withstand large strain (>10%) before rupture, making them interesting for strain engineering and flexible devices. Even in their single layer form, semiconducting 2D materials have demonstrated efficient light absorption, enabling large responsivity in photodetectors. Therefore, semiconducting layered 2D materials are strong candidates for optoelectronic applications, especially for photodetection. Here, we review the state-of-the-art in photodetectors based on semiconducting 2D materials, focusing on the transition metal dichalcogenides, novel van der Waals materials, black phosphorus, and heterostructures. PMID:25909688

  18. Inflationary magnetogenesis, derivative couplings, and relativistic Van der Waals interactions

    NASA Astrophysics Data System (ADS)

    Giovannini, Massimo

    2015-08-01

    When the gauge fields have derivative couplings to scalars, like in the case of the relativistic theory of Van der Waals (or Casimir-Polder) interactions, conformal invariance is broken but the magnetic and electric susceptibilities are not bound to coincide. We analyze the formation of large-scale magnetic fields in slow-roll inflation and find that they are generated at the level of a few hundredths of a nG and over typical length scales between few Mpc and 100 Mpc. Using a new time parametrization that reduces to conformal time but only for coincident susceptibilities, the gauge action is quantized while the evolution equations of the corresponding mode functions are more easily solvable. The power spectra depend on the normalized rates of variation of the two susceptibilities (or of the corresponding gauge couplings) and on the absolute value of their ratio at the beginning of inflation. We pin down explicit regions in the parameter space where all the physical requirements (i.e., the backreaction constraints, the magnetogenesis bounds and the naturalness of the initial conditions of the scenario) are jointly satisfied. Weakly coupled initial data are favored if the gauge couplings are of the same order at the end of inflation. Duality is systematically used to simplify the analysis of the wide parameter space of the model.

  19. Van Der Pol model of a Cerenkov maser

    SciTech Connect

    Kleckner, M.; Ron, A.; Botton, M.

    1995-12-31

    A non-linear analysis of a Cerenkov maser is presented. The system consists of a ring configuration of a cylindrical waveguide filled with a dielectric material. A single transverse-magnetic mode is assumed to propagate in the system. A low-density pencil electron beam travels in part of the ring, confined by a strong axial magnetic field. Using the single-particle description for the beam and the wave equation for the field, we obtain a set of two coupled non-linear differential equations describing the slowly varying amplitude and phase of the electromagnetic mode. The gain per path is assumed to be small and the spatial growth of the field is neglected. The resulting time dependent amplitude includes the exponential gain of the linear stage and the saturation to its maximum value. The time dependent frequency is also calculated. The two equations are combined to a single Van Der Pol equation with a non-linear restoring force. This description demonstrates the similarities and differences between the Cerenkov maser and other lasing systems.

  20. Van der Waals interactions in density functional theory

    NASA Astrophysics Data System (ADS)

    Langreth, David C.

    2009-03-01

    The van der Waals density functional which we introduced half a decade agoootnotetextM. Dion et al. Phys. Rev. Lett. 92, 246401 (2004). and its self-consistent generalizationootnotetextT. Thonhauser et al., Phys. Rev. B 76, 125112 (2007). will be briefly reviewed. There are many collaborators in the application review that will follow, not only those who worked in the physics department at Rutgers% ootnotetextMaxime Dion, Aaron Puzder, T. Thonhauser, Valentino R. Cooper, Shen Li, Eamonn Murray, Lingzhu Kong, and Kyuho Lee. and at Chalmers,% ootnotetextHenrik Rydberg, Svetla Chakarova-K"ack, Jesper Kleis, Elsebeth Schr"oder, Per Hyldgaard, and Bengt I. Lundqvist. but also at Denmarks Technical University,% ootnotetextAndrei Kelkkanen, Poul G. Moses, Jesper Kleis, and Bengt I. Lundqvist. the chemistry department at Rutgers,% ootnotetextKonhoa Li, Jing Li, Yves Chabal, and Wilma K. Olson. and most recently at the University of Texas at Dallas.% ootnotetextNour Nijem and Yves Chabal. I will expand on our recent review article,ootnotetextD. C. Langreth et al., J. Phys. Cond. Mat. (in press). which hopefully will be published before the present talk, and include applications by other groups not listed below. If possible, I will also review results from a more recent collaboration to study nucleosomal DNA and beyond.

  1. Hemiquantal mechanics. I. Vibrational predissociation of van der Waals molecules

    NASA Astrophysics Data System (ADS)

    Halcomb, Lawrence L.; Diestler, D. J.

    1986-03-01

    The ``hemiquantal'' equations (HQE), which pertain to a system consisting of a quantally-behaving (``light'') subsystem coupled to a classically-behaving (``heavy'') one, result from a partial classical limit of Heisenberg's equations of motion. In effect, all heavy particles are required to follow precisely their classical trajectories. The HQE are applied to vibrational predissociation in a collinear model of the van der Waals molecule He ṡ ṡ ṡI2(B). Here, the vibration of I2 is the classical subsystem and the motion of He relative to the center of mass of I2 is the quantal subsystem. In this case, the HQE comprise a partial differential equation (Schrödinger's equation for the He motion) coupled to two ordinary differential equations (Hamilton's equations for the I2 vibration). These were solved numerically on the CYBER 205 supercomputer by means of an algorithm that uses a second-order predictor-corrector for Hamilton's equations and second-order time differencing for Schrödinger's equation. A scheme based on the fast Fourier transform was used to evaluate the spatial derivative of the wave function. The computed rates of vibrational predissociation are compared with the results of previous quasiclassical and fully quantal calculations and with experimental results.

  2. Synchronization of two memristively coupled van der Pol oscillators

    NASA Astrophysics Data System (ADS)

    Ignatov, M.; Hansen, M.; Ziegler, M.; Kohlstedt, H.

    2016-02-01

    The objective of this letter is to convey two essential principles of biological computing—synchronization and memory—in an electronic circuit with two van der Pol (vdP) oscillators coupled via a memristive device. The coupling was mediated by connecting the gate terminals of two programmable unijunction transistors through a resistance-capacitance network comprising an Ag-TiOx-Al memristive device. In the high resistance state the memristance was in the order of MΩ, which leads to two independent self-sustained oscillators characterized by the different frequencies f1 and f2 and no phase relation between the oscillations. Depending on the mediated pulse amplitude, the memristive device switched to the low resistance state after a few cycles and a frequency adaptation and phase locking were observed. The experimental results are underlined by theoretically considering a system of two coupled vdP equations. This experiment may pave the way to larger neuromorphic networks in which the coupling parameters (through memristive devices) can vary in time and strength and are able to remember the history of applied electrical potentials.

  3. Hochenergieröntgenspektren der akkretierenden Röntgenpulsare Vela X-1 und A 0535+26

    NASA Astrophysics Data System (ADS)

    Kretschmar, Peter

    1996-04-01

    In dieser Arbeit wurden Daten aus gemeinsamen, zeitgleichen Beobachtungen der bei- den akkretierenden Röntgenpulsare VelaX-1 und A0535+26 durch die Instrumente HEXE und TTM an Bord der Raumstation Mir ausgewertet. Die Kombination der gemeinsamen Beobachtungen erlaubte zum ersten Mal die Analyse von Lichtkurven, Pulsprofilen und Spektren dieser Quellen im breiten Energieband von 2–200 keV.Obwohl die Systemparameter und Akkretionsmechanismen der beiden Quellen recht verschieden sind, weisen sie im Röntgenbereich einige Ähnlichkeiten auf. So zeigen die Lichtkurven beider Quellen starke Puls-zu-Puls Variationen. Erst bei der Überlagerung hinreichend vieler Pulse ((geq) 10) ergeben sich die recht stabilen mittleren Pulsprofile. Das Spektrum einzelner Pulse kann deutlich vom mittleren Spektrum abweichen, es ergaben sich aber keine Hinweise auf systematische Zusammenhänge mit anderen Größen, wie z.B. dem Gesamtfluß.Die Kontinuumsspektren der beiden Röntgenpulsare werden am besten durch das “Potenzgesetz mit exponentiellem Abfall” beschrieben. “Physikalische” Spektren, die auf stark vereinfachten Modellen beruhen, wie z.B. comptonisierte Spektren, beschreiben das erstmals aus zeitgleichen Beobachtungen bestimmte Breitbandkontinuum systematisch schlechter. In beiden Quellen hängt die Form der Kontinuumsspektren von der Pulsphase ab, allerdings in unterschiedlicher Ausprägung: Für Vela X-1 ergibt sich eine signifikante Variation unterhalb des spektralen Knicks bei ˜20 keV, für A 0535+26 dagegen oberhalb.In den Spektren beider Quellen gibt es deutliche Hinweise auf Zyklotronresonanzlinien, wobei die Stärke und Signifikanz der Strukturen mit der Pulsphase variiert. A 0535+26 zeigt statistisch sehr signifikante Strukturen bei ˜50 und ˜100 keV. Die statistisch etwas weniger signifikanten Strukturen bei ˜23 und ˜45 keV in den Vela X-1 Spektren stimmen gut überein mit Ergebnissen der Ginga -Beobachtungen dieser Quelle (Mihara 1995). Die

  4. Institute for Science Education. Institut fur die Padagogik der Naturwissenschaften an der Universitat Kiel. IPN Report-in-Brief 11. 3rd Edition.

    ERIC Educational Resources Information Center

    Blansdorf, Klaus, Ed.

    The Institut fur die Padagogik der Naturwissenschaften (IPN) is the research institute for science education, with a national function in the Federal Republic of Germany. The IPN consists of biology education, chemistry education, physics education, educational science, research methodology/statistics, and administration/general services…

  5. Wirkungen biogener Amine auf die Erregungs-Sekretions-Kopplung in der Speicheldrüse von Periplaneta americana (L.)

    NASA Astrophysics Data System (ADS)

    Rietdorf, Katja

    2003-07-01

    In der vorliegenden Arbeit habe ich wichtige Teilmechanismen der Erregungs-Sekretionskopplung in der Speicheldrüse der Schabe Periplaneta americana (L.) untersucht. Die Speicheldrüse ist von dopaminergen und serotonergen Fasern innerviert (Baumann et al., 2002). Beide Transmitter stimulieren eine unterschiedliche Reaktion der Drüse: Dopamin (DA) stimuliert die P-Zellen der Acini und die Ausführgangzellen, während Serotonin (5-HT) die P- und C-Zellen der Acini stimuliert, nicht jedoch die Ausführgangzellen. Der Endspeichel ist nach einer DA-Stimulierung proteinfrei. Dagegen enthält er nach einer 5-HT-Stimulierung Proteine, die von den C-Zellen sezerniert werden (Just & Walz, 1996). Im ersten Teil meiner Arbeit habe ich mittels Kapillarelektrophoretischer Analyse (CE-Analyse) die Elektrolytkonzentrationen im Endspeichel untersucht sowie die Raten der Flüssigkeitssekretion gemessen. Damit wollte ich klären, welche Transporter an der Sekretion des Primärspeichels und an dessen Modifikation beteiligt sind. Ausserdem wollte ich die Rolle der transportaktiven Epithelzellen der Ausführgänge für die Modifikation des Primärspeichels untersuchen. Dafür habe ich einen Vergleich der Elektrolytkonzentrationen im DA- und 5-HT-stimulierten Endspeichel durchgeführt. Der Elektrolytgehalt des DA- und 5-HT-stimulierten Endspeichels unterscheidet sich nicht signifikant voneinander. Er ist nach beiden Stimulierungen hypoosmotisch zum verwendeten Ringer. Die Ausführgangzellen werden durch DA stimuliert und modifizieren den Primärspeichel durch eine netto-Ionenreabsorption. Meine Versuche zeigen jedoch, dass auch die während einer 5-HT-Stimulierung der Drüse unstimulierten Ausführgangzellen den Primärspeichel modifizieren. In einer nachfolgenden Versuchsreihe habe ich den Einfluss von Ouabain, einem Hemmstoff der Na+-K+-ATPase, und Bumetanid, einem Hemmstoff des NKCC, auf die Raten der Flüssigkeitssekretion sowie den Elektrolytgehalt des Endspeichels untersucht. Ich

  6. FORS am Very Large Telescope der Europäischen Südsternwarte

    NASA Astrophysics Data System (ADS)

    1998-09-01

    Erstes wissenschaftliches Beobachtungsinstrument liefert eindrucksvolle Bilder Entsprechend dem straffen Zeitplan wird das ESO Very Large Teleskop Projekt (VLT-Projekt) auf dem Cerro Paranal in Nord-Chile verwirklicht: die volle Betriebsbereitschaft des ersten der vier 8,2m-Einzelteleskope wird Anfang des nächsten Jahres erreicht sein. Am 15. September 1998 wurde ein weiterer wichtiger Meilenstein erfolgreich, rechtzeitig und innerhalb des Kostenplans erreicht. Nur wenige Tage nach seiner Montage am ersten 8,2m-Einzelteleskop des VLT (UT1) konnte FORS1 ( FO cal R educer and S pectrograph) als erstes einer Gruppe leistungsfähiger und komplexer wissenschaftlicher Instrumente seine Beobachtungstätigkeit beginnen. Von Anfang an konnte es eine Reihe exzellenter astronomischer Bilder aufnehmen. Dieses bedeutende Ereignis eröffnet eine Fülle neuer Möglichkeiten für die europäische Astronomie. FORS - ein Höhepunkt an Komplexität FORS1 und das zukünftige Zwillingsinstrument (FORS2) sind das Ergebnis einer der eingehendsten und fortschrittlichsten technologischen Studien, die je für ein Instrument der bodengebundenen Astronomie durchgeführt wurden. Dieses einzigartige Instrument ist nun im Cassegrain-Fokus installiert und verschwindet beinahe, trotz seiner Dimensionen von 3 x 1.5m (Gewicht 2.3t), unterhalb des riesigen 53 m 2 großen Zerodurspiegels. Um die große Spiegelfläche und die hervorragende Bildqualität von UT1 optimal auszunützen, wurde FORS speziell so konstruiert, daß es die lichtschwächsten und entferntesten Objekte im Weltall untersuchen kann. Bald wird dieses komplexe VLT-Instrument den europäischen Astronomen erlauben, die derzeitigen Beobachtungshorizonte entscheidend zu erweitern. Die beiden FORS-Instrumente sind Vielzweck-Beobachtungsinstrumente, die in mehreren unterschiedlichen Beobachtungsarten eingesetzt werden können. Beispielsweise können Bilder mit zwei verschiedenen Abbildungsmaßstäben (Vergrößerungen) sowie Spektren mit

  7. House dust mite Der p 1 downregulates defenses of the lung by inactivating elastase inhibitors.

    PubMed

    Brown, Alan; Farmer, Kinley; MacDonald, Louise; Kalsheker, Noor; Pritchard, Dave; Haslett, Chris; Lamb, Jonathan; Sallenave, J-M

    2003-09-01

    House dust mites (HDM) are the most common source of aeroallergens and in genetic susceptible individuals can cause symptoms ranging from atopic dermatitis to bronchial asthma. Der p 1, a major target of the human immune responses to HDM, through its enzymatic properties can modulate the adaptive immune system by the cleavage of CD23 and CD25. The consequences of this would be to promote allergic inflammatory responses. Furthermore, by disrupting epithelial tight junctions Der p 1 facilitates the transport of allergen across the epithelium. Here, we report that Der p 1 has additional effects on the innate defense mechanisms of the lung, by inactivating in vitro and ex vivo the elastase inhibitors human (h) alpha1-proteinase inhibitor (h-A1-Pi), mouse (m-), (but not human [h])-SLPI and h-elafin. We confirm that Der p 1 contain both cysteine and serine proteinases, and extend this finding to demonstrate for the first time that h-elafin is particularly sensitive to the biological activity of the latter. Because these elastase inhibitors have antimicrobial, as well as antielastase activity, our results suggest that inactivation of these innate components of the lung defense system by Der p 1 may increase the susceptibility of patients with allergic inflammation to infection. PMID:12689923

  8. Der p 5 Crystal Structure Provides Insight into the Group 5 Dust Mite Allergens

    SciTech Connect

    Mueller, G.; Gosavi, R; Krahn, J; Edwards, L; Cuneo, M; Glesner, J; Pomes, A; Chapman, M; London, R; Pedersen, L

    2010-01-01

    Group 5 allergens from house dust mites elicit strong IgE antibody binding in mite-allergic patients. The structure of Der p 5 was determined by x-ray crystallography to better understand the IgE epitopes, to investigate the biologic function in mites, and to compare with the conflicting published Blo t 5 structures, designated 2JMH and 2JRK in the Protein Data Bank. Der p 5 is a three-helical bundle similar to Blo t 5, but the interactions of the helices are more similar to 2JMH than 2JRK. The crystallographic asymmetric unit contains three dimers of Der p 5 that are not exactly alike. Solution scattering techniques were used to assess the multimeric state of Der p 5 in vitro and showed that the predominant state was monomeric, similar to Blo t 5, but larger multimeric species are also present. In the crystal, the formation of the Der p 5 dimer creates a large hydrophobic cavity of {approx}3000 {angstrom}{sup 3} that could be a ligand-binding site. Many allergens are known to bind hydrophobic ligands, which are thought to stimulate the innate immune system and have adjuvant-like effects on IgE-mediated inflammatory responses.

  9. Einfluss der Korrosion auf die Schirmdämpfung versilberter Gestricke und Gewebe

    NASA Astrophysics Data System (ADS)

    Tasser, M.; Wehnert, G.

    2007-06-01

    Zur Abschirmung elektromagnetischer Strahlung werden unter anderem metallisierte Gestricke eingesetzt, die versilbertes Polyamid enthalten. Solche Materialien finden beispielsweise Anwendungen als flexible Verpackungen oder als Strumpfmaterialien im medizinischen Bereich, z.B. bei der Therapie des Phantomschmerzes. Versilbertes Polyamid ist dem korrosiven Angriff schwefelhaltiger Verbindungen ausgesetzt, welche die Schirmdämpfungswirkung aufgrund der Ausbildung von Silbersulfidschichten herabsetzen. Untersucht wurde, inwieweit Silbersulfidbildung die Schirmdämpfung beeinträchtigt und ob die Silbersulfidbildung durch Schutzschichten aus Titandioxid (TiO2) verhindert werden kann. Die Silbersulfidschichten wurden mit Hilfe einer alkalischen Natriumsulfid-Lösung (Tuccillo-Nielsen-Lösung) hergestellt. Titandioxid-Schichten wurden durch ein Sol-Gel-Verfahren abgeschieden. Die untersuchten versilberten Gestricke zeigten im Bereich von 300 MHz bis 4 GHz eine weitgehend konstante Schirmdämpfung von ca. 40 dB, abhängig von der Strickart. Durch Belegung der Oberfläche mit Silbersulfid nahm die Schirmdämpfung auf ca. 5-10 dB ab. Dünne, durch Sol-Gel-Verfahren abgeschiedene TiO2 -Schichten verhinderten nicht die Ausbildung von Silbersulfidschichten. Durch Reduktion des Silbersulfids mit Aluminium in Natriumchlorid-Lösung konnte die Schirmdämpfung teilweise wiederhergestellt werden, was sich an einem Anstieg der Schirmdämpfung auf ca. 25 dB zeigte.

  10. Comparing heat exchangers of thermacoustic prime movers with a Van der Pol model

    NASA Astrophysics Data System (ADS)

    Cox, I.; Jorgensen, M.; Andersen, B.

    2010-10-01

    A thermoacoustic standing-wave prime mover is a self-sustained oscillator whose initial growth of acoustic pressure into amplitude saturation can be modeled by the Van der Pol equation. The nonlinear Van der Pol equation is calculated computationally, using 4^th order Runge-Kutta. The Van der Pol model gives quantitative loss and gain parameters, when using a best-fit with experimental data. The engines tested in this study have an average frequency of 2700 Hz, which suggests that the first second of oscillations when using the Van der Pol model can reveal information about the steady-state performance of the device. This model is applied to studying the effect of different heat exchanger sizes. All sixteen possible permutations were tested using different copper wire mesh dimensions: 24X24, 40X40, 60X60, and 80X80 for the hot and cold heat exchangers (where ##X## indicates wires per inch). Plotting the steady-state acoustic pressure as a function of the gain term divided by the loss term shows roughly, a linear relationship. The engine with the highest gain term and smallest loss term was using 80X80 for the hot heat exchanger combined with the 24X24 for the cold heat exchanger and is consistent with the highest steady-state pressure achieved. The modeling process has been very successful and fits the Van der Pol equation.

  11. Der p 1 facilitates transepithelial allergen delivery by disruption of tight junctions

    PubMed Central

    Wan, Hong; Winton, Helen L.; Soeller, Christian; Tovey, Euan R.; Gruenert, Dieter C.; Thompson, Philip J.; Stewart, Geoffrey A.; Taylor, Graham W.; Garrod, David R.; Cannell, Mark B.; Robinson, Clive

    1999-01-01

    House dust mite (HDM) allergens are important factors in the increasing prevalence of asthma. The lung epithelium forms a barrier that allergens must cross before they can cause sensitization. However, the mechanisms involved are unknown. Here we show that the cysteine proteinase allergen Der p 1 from fecal pellets of the HDM Dermatophagoides pteronyssinus causes disruption of intercellular tight junctions (TJs), which are the principal components of the epithelial paracellular permeability barrier. In confluent airway epithelial cells, Der p 1 led to cleavage of the TJ adhesion protein occludin. Cleavage was attenuated by antipain, but not by inhibitors of serine, aspartic, or matrix metalloproteinases. Putative Der p 1 cleavage sites were found in peptides from an extracellular domain of occludin and in the TJ adhesion protein claudin-1. TJ breakdown nonspecifically increased epithelial permeability, allowing Der p 1 to cross the epithelial barrier. Thus, transepithelial movement of Der p 1 to dendritic antigen-presenting cells via the paracellular pathway may be promoted by the allergen’s own proteolytic activity. These results suggest that opening of TJs by environmental proteinases may be the initial step in the development of asthma to a variety of allergens. PMID:10393706

  12. Molecular, Structural and Immunological Characterization of Der p 18, a Chitinase-Like House Dust Mite Allergen

    PubMed Central

    Resch, Yvonne; Blatt, Katharina; Malkus, Ursula; Fercher, Christian; Swoboda, Ines; Focke-Tejkl, Margit; Chen, Kuan-Wei; Seiberler, Susanne; Mittermann, Irene; Lupinek, Christian; Rodriguez-Dominguez, Azahara; Zieglmayer, Petra; Zieglmayer, René; Keller, Walter; Krzyzanek, Vladislav; Valent, Peter; Valenta, Rudolf; Vrtala, Susanne

    2016-01-01

    Background The house dust mite (HDM) allergen Der p 18 belongs to the glycoside hydrolase family 18 chitinases. The relevance of Der p 18 for house dust mite allergic patients has only been partly investigated. Objective To perform a detailed characterization of Der p 18 on a molecular, structural and immunological level. Methods Der p 18 was expressed in E. coli, purified to homogeneity, tested for chitin-binding activity and its secondary structure was analyzed by circular dichroism. Der p 18-specific IgG antibodies were produced in rabbits to localize the allergen in mites using immunogold electron microscopy and to search for cross-reactive allergens in other allergen sources (i.e. mites, crustacea, mollusca and insects). IgE reactivity of rDer p 18 was tested with sera from clinically well characterized HDM-allergic patients (n = 98) and its allergenic activity was analyzed in basophil activation experiments. Results Recombinant Der p 18 was expressed and purified as a folded, biologically active protein. It shows weak chitin-binding activity and partial cross-reactivity with Der f 18 from D. farinae but not with proteins from the other tested allergen sources. The allergen was mainly localized in the peritrophic matrix of the HDM gut and to a lower extent in fecal pellets. Der p 18 reacted with IgE from 10% of mite allergic patients from Austria and showed allergenic activity when tested for basophil activation in Der p 18-sensitized patients. Conclusion Der p 18 is a rather genus-specific minor allergen with weak chitin-binding activity but exhibits allergenic activity and therefore should be included in diagnostic test panels for HDM allergy. PMID:27548813

  13. Van der Waals coefficients beyond the classical shell model

    SciTech Connect

    Tao, Jianmin; Fang, Yuan; Hao, Pan; Scuseria, G. E.; Ruzsinszky, Adrienn; Perdew, John P.

    2015-01-14

    Van der Waals (vdW) coefficients can be accurately generated and understood by modelling the dynamic multipole polarizability of each interacting object. Accurate static polarizabilities are the key to accurate dynamic polarizabilities and vdW coefficients. In this work, we present and study in detail a hollow-sphere model for the dynamic multipole polarizability proposed recently by two of the present authors (JT and JPP) to simulate the vdW coefficients for inhomogeneous systems that allow for a cavity. The inputs to this model are the accurate static multipole polarizabilities and the electron density. A simplification of the full hollow-sphere model, the single-frequency approximation (SFA), circumvents the need for a detailed electron density and for a double numerical integration over space. We find that the hollow-sphere model in SFA is not only accurate for nanoclusters and cage molecules (e.g., fullerenes) but also yields vdW coefficients among atoms, fullerenes, and small clusters in good agreement with expensive time-dependent density functional calculations. However, the classical shell model (CSM), which inputs the static dipole polarizabilities and estimates the static higher-order multipole polarizabilities therefrom, is accurate for the higher-order vdW coefficients only when the interacting objects are large. For the lowest-order vdW coefficient C{sub 6}, SFA and CSM are exactly the same. The higher-order (C{sub 8} and C{sub 10}) terms of the vdW expansion can be almost as important as the C{sub 6} term in molecular crystals. Application to a variety of clusters shows that there is strong non-additivity of the long-range vdW interactions between nanoclusters.

  14. Arzt und Hobby-Astronom in stürmischen Zeiten Der Büchernachlass des Doktor Johannes Häringshauser, Viertelsmedicus in Mistelbach (1630-1641) in der Melker Stiftsbibliothek.

    NASA Astrophysics Data System (ADS)

    Davison, Giles; Glaßner, Gottfried

    2009-06-01

    Auf der Suche nach astronomischer Literatur stieß Giles Davison in der Melker Stiftsbibliothek auf den Namen "Doctor Johannes Häringshauser“ als Besitzer seltener und interessanter astronomischer Werke u.a. von Johannes Regiomontan, Georg von Peuerbach, Michael Mästlin, Johannes Kepler und Daniel Sennert. Weitere in den Jahren 2007-2009 durchgeführte Nachforschungen ergaben, dass es sich um den von 1630-1641 in Mistelbach, Niederösterreich, als Landschaftsarzt tätigen Vater des Melker Konventualen und Bibliothekars Sigismund Häringshauser (1631-1698) handelt. Er wurde 1603 als Sohn des aus Magdeburg stammenden Apothekers Johannes Häringshauser geboren und starb 1642 in Mistelbach. Johannes Häringshauser Sen. bekleidete von 1613-1640 eine Reihe wichtiger Ämter in der Wiener Stadtregierung und starb 1647. Der Studienaufenthalt von Dr. Johannes Häringshauser Jun. in Padua (1624-1626) dürfte das Interesse für Astronomie geweckt haben, das sich in seiner in die Bestände der Melker Stiftsbibliothek eingegangenen Privatbibliothek widerspiegelt. Der Großteil der 10 dem Fachbereich der Astronomie und Astrologie zuzuweisenden Titel wurde von ihm in den Jahren 1636 und 1637 erworben.

  15. BOOK REVIEW: Meilensteine der Astronomie - Von Aristoteles bis Hawking

    NASA Astrophysics Data System (ADS)

    Duerbeck, H. W.; Hamel, J.

    2006-12-01

    A writer, more specific a writer on the history of astronomy, might from time to time look at the collected document folders with all the research material and reprints, and might wonder: has this been all? Especially at a time when recycling is in vogue? And, perhaps with a request or an invitation to submit something, he or she might consider re-using the material before its definitive disposal. Well, such are my feelings when I looked at Jurgen Hamel's new book Milestones of Astronomy - From Aristoteles to Hawking . A slight chance for survival of medium-sized publishers like Kosmos is to offer popular books, and a title must attract potential buyers: Aristoteles means the "old" times, and as concerns the "mad scientist" of modern times, Stephen Hawking has by now dethroned Einstein. In 1998, Hamel had published a Geschichte der Astronomie - Von den Anfangen bis zur Gegenwart (History of astronomy, from the beginnings to the present), which, of course, he could not simply copy. This time, he selected some stones from his research areas - milestones, touchstones, stumbling blocks in the long road of astronomical evolution - and put them between the covers of his new book. So let us look at these (mile)stones . The reader is informed about Aristoteles on 2 pages, but his medieval interpreter Johannes de Sacrobosco gets 8 pages! Copernicus' life and achievements are described on 9 pages, closely followed by his devotee and translator Rothmann with 8 pages; Copernicus' contemporary, Peter Apian, however, gets about 13! Bessel's and Herschel's lifes and works are described on well-deserved 13 and 15 pages, while the achievements of the two Lucasian professors, Isaac Newton and Stephen Hawking, are just outlined in a single paragraph! Thus, importance is sometimes inversely proportional to text length... But let us become serious now. Why should an active historian outline, for the hundreth time, the life of Copernicus, while there are so many interesting, and often

  16. Die Pugwash Conferences on Science and World Affairs Ein Beispiel für erfolgreiche „Track-II-Diplomacy“ der Naturwissenschaftler im Kalten Krieg

    NASA Astrophysics Data System (ADS)

    Neuneck, Götz

    "Kein Zeitalter der Geschichte ist stärker von den Naturwissenschaften durchdrungen und abhängiger von ihnen als das 20. Jahrhundert" schreibt Eric Hobsbawn im Kapitel "Zauberer und Lehrlinge: Die Naturwissenschaften" seines Buches "Zeitalter der Extreme".

  17. An Insight into Lüders Deformation Using Advanced Imaging Techniques

    NASA Astrophysics Data System (ADS)

    Nagarajan, Srinivasan; Narayanaswamy, Raghu; Balasubramaniam, Venkatraman

    2013-10-01

    An investigation to explore the feasibility of simultaneous application of infrared thermography (IRT) and digital image correlation (DIC) for analysis of Lüders deformation is carried out. Physical models and proposed concepts explaining the dynamics of deformation localization associated with Lüders band phenomenon addressing band-formation mechanism, inhomogeneity in stress-strain distribution across the band front, and strain localization following band front propagation are successfully correlated with the thermal and strain evolutions obtained using IRT and DIC. The studies revealed the potential of using these techniques simultaneously in providing an enhanced understanding of micro mechanisms involved in Lüders deformation based on associated macroscopic thermal and strain evolutions in a noncontact, nondestructive manner.

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

    PubMed Central

    Wang, Han; Bang, Junhyeok; Sun, Yiyang; Liang, Liangbo; West, Damien; Meunier, Vincent; Zhang, Shengbai

    2016-01-01

    The success of van der Waals heterostructures made of graphene, metal dichalcogenides and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications. In contrast to conventional heterostructures, where a strong interfacial coupling is essential to charge transfer, recent experimental findings indicate that van der Waals heterostructues can exhibit ultrafast charge transfer despite the weak binding of these heterostructures. Here we find, using time-dependent density functional theory molecular dynamics, that the collective motion of excitons at the interface leads to plasma oscillations associated with optical excitation. By constructing a simple model of the van der Waals heterostructure, we show that there exists an unexpected criticality of the oscillations, yielding rapid charge transfer across the interface. Application to the MoS2/WS2 heterostructure yields good agreement with experiments, indicating near complete charge transfer within a timescale of 100 fs. PMID:27160484

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

    PubMed

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

    2016-01-01

    Van der Waals forces are among the weakest, yet most decisive interactions governing condensation and aggregation processes and the phase behaviour of atomic and molecular matter. Understanding the resulting structural motifs and patterns has become increasingly important in studies of the nanoscale regime. Here we measure the paradigmatic van der Waals interactions represented by the noble gas atom pairs Ar-Xe, Kr-Xe and Xe-Xe with a Xe-functionalized tip of an atomic force microscope at low temperature. Individual rare gas atoms were fixed at node sites of a surface-confined two-dimensional metal-organic framework. We found that the magnitude of the measured force increased with the atomic radius, yet detailed simulation by density functional theory revealed that the adsorption induced charge redistribution strengthened the van der Waals forces by a factor of up to two, thus demonstrating the limits of a purely atomic description of the interaction in these representative systems. PMID:27174162

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

    PubMed

    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. PMID:26242771

  1. Amerikas Einschätzung der deutschen Atomforschung: Das deutsche Uranprojekt

    NASA Astrophysics Data System (ADS)

    Walker, Mark

    2002-07-01

    Die amerikanischen Wissenschaftler und ihre emigrierten Kollegen, die am Bau der Atombombe beteiligt waren, verfügten über sehr widersprüchliche und großteils falsche Informationen über den Fortschritt des deutschen Uranprogramms. Noch nach Kriegsende lässt sich dies an Aussagen des Leiters der amerikanischen Alsos-Mission, Samuel Goudsmit, festmachen. Tatsächlich war das deutsche Programm hinsichtlich seiner wissenschaftlichen Grundlagen und des Managements nicht so unterlegen, wie vielfach behauptet wurde. Aber die deutschen Behörden waren nicht in der Lage, Geld und Ressourcen in gleichem Maße in das Uranprojekt zu investieren, wie etwa in das Peenemünder Raketenprojekt.

  2. Nano-photonic phenomena in van der Waals heterostructures (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Basov, Dmitri N.

    2015-09-01

    van der Waals (vdW) crystals consist of individual atomic planes coupled by vdW interaction, similar to graphene monolayers in bulk graphite. We investigated van der Waals heterostructures assembled from atomically thin layers of graphene and hexagonal boron nitride (hBN). We launched, detected and imaged plasmonic, phonon polaritonic and hybrid plasmon-phonon polariton waves in a setting of an antenna based nano-infrared apparatus. Hyperbolic phonon polaritons in hBN enabled sub-diffractional focusing in infrared frequencies. Because electronic, plasmonic and phonon polaritonic properties in van der Waals heterstructures are intertwined, gate voltage and/or details of layer assembly enable efficient control of nano-photonic effects.

  3. Quantum vacuum photon modes and repulsive Lifshitz-van der Waals interactions

    NASA Astrophysics Data System (ADS)

    Dellieu, Louis; Deparis, Olivier; Muller, Jérôme; Kolaric, Branko; Sarrazin, Michaël

    2015-12-01

    The bridge between quantum vacuum photon modes and properties of patterned surfaces is currently being established on solid theoretical grounds. Based on these foundations, the manipulation of quantum vacuum photon modes in a nanostructured cavity is theoretically shown to be able to change the Lifshitz-van der Waals forces from attractive to repulsive regime. Since this concept relies on surface nanopatterning instead of chemical composition changes, it drastically relaxes the usual conditions for achieving repulsive Lifshitz-van der Waals forces. As a case study, the potential interaction energy between a nanopatterned polyethylene slab and a flat polyethylene slab with water as the intervening medium is calculated. Extremely small corrugation heights (<10 nm) are shown to be able to change the Lifshitz-van der Waals force from attractive to repulsive, the interaction strength being controlled by the corrugation height. This new approach could lead to various applications in surface science.

  4. Photovoltaic DER System Could Save USPS $25,000 per Year in Marina del Rey, California

    SciTech Connect

    Not Available

    2002-11-01

    In numerous projects, government agencies are demonstrating the economic and environmental value of using distributed energy resources (DER) to provide reliable electricity for Federal facilities. These projects also show how renewable DER systems such as photovoltaics (PV) can be effectively integrated into utility power grids to provide added power during peak demand periods in populous regions and states. This four-page case study describes a recent project in which the United States Postal Service (USPS) worked with the U.S. Department of Energy (DOE) Federal Energy Management Program (FEMP), a national laboratory, the local utility, and a private company to install a PV DER system at the USPS Marina Processing and Distribution Center in Inglewood, California. This system is expected to shave 10% off the facility's 1.2-megawatt peak power demand and save more $25,000 per year in utility costs.

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

    PubMed Central

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

    2016-01-01

    Van der Waals forces are among the weakest, yet most decisive interactions governing condensation and aggregation processes and the phase behaviour of atomic and molecular matter. Understanding the resulting structural motifs and patterns has become increasingly important in studies of the nanoscale regime. Here we measure the paradigmatic van der Waals interactions represented by the noble gas atom pairs Ar–Xe, Kr–Xe and Xe–Xe with a Xe-functionalized tip of an atomic force microscope at low temperature. Individual rare gas atoms were fixed at node sites of a surface-confined two-dimensional metal–organic framework. We found that the magnitude of the measured force increased with the atomic radius, yet detailed simulation by density functional theory revealed that the adsorption induced charge redistribution strengthened the van der Waals forces by a factor of up to two, thus demonstrating the limits of a purely atomic description of the interaction in these representative systems. PMID:27174162

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

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

    NASA Astrophysics Data System (ADS)

    Rompala, Kevin; Rand, Richard; Howland, Howard

    2007-08-01

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

  8. Van der Waals interactions among alkali Rydberg atoms with excitonic states

    NASA Astrophysics Data System (ADS)

    Zoubi, Hashem

    2015-09-01

    We investigate the influence of the appearance of excitonic states on van der Waals interactions among two Rydberg atoms. The atoms are assumed to be in different Rydberg states, e.g., in the | {ns}> and | {np}> states. The resonant dipole-dipole interactions yield symmetric and antisymmetric excitons, with energy splitting that give rise to new resonances as the atoms approach each other. Only away from these resonances can the van der Waals coefficients, C6sp, be defined. We calculate the C6 coefficients for alkali atoms and present the results for lithium by applying perturbation theory. At short interatomic distances of several μ {{m}}, we show that the widely used simple model of two-level systems for excitons in Rydberg atoms breaks down, and the correct representation implies multi-level atoms. Even though, at larger distances one can keep the two-level systems but in including van der Waals interactions among the atoms .

  9. Measurement of the Hall coefficient using van der Pauw method without magnetic field reversal

    SciTech Connect

    Levy, M.; Sarachik, M. P.

    1989-07-01

    The van der Pauw geometry has been widely used for the measurement of resistivities and Hall coefficients. Although the measurement of a Hall coefficient requires a finite magnetic field, it should be noted that van der Pauw's expression is valid only in the limit of zero field; in addition to the Hall contribution, measurements in a finite magnetic field generally include a term associated with field-induced changes in the longitudinal resistivity. Although a simple solution to this problem entails taking the difference between readings in opposite field directions, there are circumstances where this may be impractical. In this note we present a straightforward extension of the van der Pauw calculation which allows a determination of the Hall coefficient from quantities measured in one field direction only.

  10. Renaturierung von Salzgrasländern bzw. Salzwiesen der Küsten

    NASA Astrophysics Data System (ADS)

    Seiberling, Stefan; Stock, Martin

    Die deutschen Meeresküsten werden im übergang vom Land zum Meer weitgehend von zwei ökosystemtypen geprägt. Auf die augenfälligeren, die Dünen, gehen wir hier nicht ein (siehe v. a.Grootjans et al. 2001, 2002, Rozé und Lemauviel 2004, Ketner-Oostra et al. 2006, Aptroot et al. 2007, Bossuyt et al. 2007). Gegenstand dieses Kapitels sind vielmehr die Salzwiesen, die im Wattenmeer der Nordsee als natürlicher Lebensraum auftreten und an der Ostseeküste — hier werden sie Salzgrasländer genannt — zu den ältesten Bestandteilen der Kulturlandschaft zählen. Naturnahe Küstensalzwiesen sind nicht nur Lebensraum für speziell angepasste Pflanzenund Tierarten, sondern tragen auch zur Regulation des marinen Stoffhaushalts und zum Küstenschutz bei.

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

    NASA Astrophysics Data System (ADS)

    Chohan, Vinod C.

    2011-02-01

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

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

    NASA Astrophysics Data System (ADS)

    Wang, Han; Bang, Junhyeok; Sun, Yiyang; Liang, Liangbo; West, Damien; Meunier, Vincent; Zhang, Shengbai

    2016-05-01

    The success of van der Waals heterostructures made of graphene, metal dichalcogenides and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications. In contrast to conventional heterostructures, where a strong interfacial coupling is essential to charge transfer, recent experimental findings indicate that van der Waals heterostructues can exhibit ultrafast charge transfer despite the weak binding of these heterostructures. Here we find, using time-dependent density functional theory molecular dynamics, that the collective motion of excitons at the interface leads to plasma oscillations associated with optical excitation. By constructing a simple model of the van der Waals heterostructure, we show that there exists an unexpected criticality of the oscillations, yielding rapid charge transfer across the interface. Application to the MoS2/WS2 heterostructure yields good agreement with experiments, indicating near complete charge transfer within a timescale of 100 fs.

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

    PubMed

    Wang, Han; Bang, Junhyeok; Sun, Yiyang; Liang, Liangbo; West, Damien; Meunier, Vincent; Zhang, Shengbai

    2016-01-01

    The success of van der Waals heterostructures made of graphene, metal dichalcogenides and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications. In contrast to conventional heterostructures, where a strong interfacial coupling is essential to charge transfer, recent experimental findings indicate that van der Waals heterostructues can exhibit ultrafast charge transfer despite the weak binding of these heterostructures. Here we find, using time-dependent density functional theory molecular dynamics, that the collective motion of excitons at the interface leads to plasma oscillations associated with optical excitation. By constructing a simple model of the van der Waals heterostructure, we show that there exists an unexpected criticality of the oscillations, yielding rapid charge transfer across the interface. Application to the MoS2/WS2 heterostructure yields good agreement with experiments, indicating near complete charge transfer within a timescale of 100 fs. PMID:27160484

  14. Measurement of the van der Waals interaction by atom trajectory imaging

    NASA Astrophysics Data System (ADS)

    Thaicharoen, N.; Schwarzkopf, A.; Raithel, G.

    2015-10-01

    We study the repulsive van der Waals interaction of cold rubidium 70 S1 /2 Rydberg atoms by analysis of time-delayed pair-correlation functions. After excitation, Rydberg atoms are allowed to accelerate under the influence of the van der Waals force. Their positions are then measured using a single-atom imaging technique. From the average pair-correlation function of the atom positions we obtain the initial atom-pair separation and the terminal velocity, which yield the van der Waals interaction coefficient C6. The measured C6 value agrees well with calculations. The experimental method has been validated by simulations. The data hint at anisotropy in the overall expansion, caused by the shape of the excitation volume. Our measurement implies that the interacting entities are individual Rydberg atoms, not groups of atoms that coherently share a Rydberg excitation.

  15. 49 CFR 40.215 - What information about the DER do employers have to provide to BATs and STTs?

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... to provide to BATs and STTs? 40.215 Section 40.215 Transportation Office of the Secretary of... Personnel § 40.215 What information about the DER do employers have to provide to BATs and STTs? As an employer, you must provide to the STTs and BATs the name and telephone number of the appropriate DER (and...

  16. 49 CFR 40.215 - What information about the DER do employers have to provide to BATs and STTs?

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... to provide to BATs and STTs? 40.215 Section 40.215 Transportation Office of the Secretary of... Personnel § 40.215 What information about the DER do employers have to provide to BATs and STTs? As an employer, you must provide to the STTs and BATs the name and telephone number of the appropriate DER (and...

  17. 49 CFR 40.215 - What information about the DER do employers have to provide to BATs and STTs?

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... to provide to BATs and STTs? 40.215 Section 40.215 Transportation Office of the Secretary of... Personnel § 40.215 What information about the DER do employers have to provide to BATs and STTs? As an employer, you must provide to the STTs and BATs the name and telephone number of the appropriate DER (and...

  18. 49 CFR 40.215 - What information about the DER do employers have to provide to BATs and STTs?

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... to provide to BATs and STTs? 40.215 Section 40.215 Transportation Office of the Secretary of... Personnel § 40.215 What information about the DER do employers have to provide to BATs and STTs? As an employer, you must provide to the STTs and BATs the name and telephone number of the appropriate DER (and...

  19. 49 CFR 40.215 - What information about the DER do employers have to provide to BATs and STTs?

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... to provide to BATs and STTs? 40.215 Section 40.215 Transportation Office of the Secretary of... Personnel § 40.215 What information about the DER do employers have to provide to BATs and STTs? As an employer, you must provide to the STTs and BATs the name and telephone number of the appropriate DER (and...

  20. Der p 11 is a major allergen for house dust mite-allergic patients suffering from atopic dermatitis.

    PubMed

    Banerjee, Srinita; Resch, Yvonne; Chen, Kuan-Wei; Swoboda, Ines; Focke-Tejkl, Margit; Blatt, Katharina; Novak, Natalija; Wickman, Magnus; van Hage, Marianne; Ferrara, Rosetta; Mari, Adriano; Purohit, Ashok; Pauli, Gabrielle; Sibanda, Elopy N; Ndlovu, Portia; Thomas, Wayne R; Krzyzanek, Vladislav; Tacke, Sebastian; Malkus, Ursula; Valent, Peter; Valenta, Rudolf; Vrtala, Susanne

    2015-01-01

    House dust mites (HDMs) belong to the most potent indoor allergen sources worldwide and are associated with allergic manifestations in the respiratory tract and the skin. Here we studied the importance of the high-molecular-weight group 11 allergen from Dermatophagoides pteronyssinus (Der p 11) in HDM allergy. Sequence analysis showed that Der p 11 has high homology to paramyosins from mites, ticks, and other invertebrates. A synthetic gene coding for Der p 11 was expressed in Escherichia coli and rDer p 11 purified to homogeneity as folded, alpha-helical protein as determined by circular dichroism spectroscopy. Using antibodies raised against rDer p 11 and immunogold electron microscopy, the allergen was localized in the muscle beneath the skin of mite bodies but not in feces. IgE reactivity of rDer p 11 was tested with sera from HDM-allergic patients from Europe and Africa in radioallergosorbent test-based dot-blot assays. Interestingly, we found that Der p 11 is a major allergen for patients suffering from atopic dermatitis (AD), whereas it is only a minor allergen for patients suffering from respiratory forms of HDM allergy. Thus, rDer p 11 might be a useful serological marker allergen for the identification of a subgroup of HDM-allergic patients suffering from HDM-associated AD. PMID:24999597

  1. Der p 11 Is a Major Allergen for House Dust Mite-Allergic Patients Suffering from Atopic Dermatitis

    PubMed Central

    Banerjee, Srinita; Resch, Yvonne; Chen, Kuan-Wei; Swoboda, Ines; Focke-Tejkl, Margit; Blatt, Katharina; Novak, Natalija; Wickman, Magnus; van Hage, Marianne; Ferrara, Rosetta; Mari, Adriano; Purohit, Ashok; Pauli, Gabrielle; Sibanda, Elopy N.; Ndlovu, Portia; Thomas, Wayne R.; Krzyzanek, Vladislav; Tacke, Sebastian; Malkus, Ursula; Valent, Peter; Valenta, Rudolf; Vrtala, Susanne

    2015-01-01

    House dust mites (HDMs) belong to the most potent indoor allergen sources worldwide and are associated with allergic manifestations in the respiratory tract and the skin. Here we studied the importance of the high-molecular-weight group 11 allergen from Dermatophagoides pteronyssinus (Der p 11) in HDM allergy. Sequence analysis showed that Der p 11 has high homology to paramyosins from mites, ticks, and other invertebrates. A synthetic gene coding for Der p 11 was expressed in Escherichia coli and rDer p 11 purified to homogeneity as folded, alpha-helical protein as determined by circular dichroism spectroscopy. Using antibodies raised against rDer p 11 and immunogold electron microscopy, the allergen was localized in the muscle beneath the skin of mite bodies but not in feces. IgE reactivity of rDer p 11 was tested with sera from HDM-allergic patients from Europe and Africa in radioallergosorbent test–based dot-blot assays. Interestingly, we found that Der p 11 is a major allergen for patients suffering from atopic dermatitis (AD), whereas it is only a minor allergen for patients suffering from respiratory forms of HDM allergy. Thus, rDer p 11 might be a useful serological marker allergen for the identification of a subgroup of HDM-allergic patients suffering from HDM-associated AD. PMID:24999597

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

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

  3. Efficacies of immunotherapy with polypeptide vaccine from ProDer f 1 in asthmatic mice

    PubMed Central

    Li, Chaopin; Li, Qiuyu; Jiang, Yuxin

    2015-01-01

    Allergic asthma is associated with the major house dust mite group 1 allergens Der p 1 and Der f 1, which belongs to the papin-like protease family and is the most potent of indoor allergens and allergen-specific immunotherapy (SIT), is seen as effective intervention for the entity. The current study was designed to verify the SIT efficacies of the enzymatic hydrolysates (papain and trypsin) in mice with asthma. We initially developed the asthmatic mouse models with ProDer f 1, and respectively applied recombinant ProDer f 1 protein and the two kinds of enzymatic hydrolysates for SIT. The results were verified by measuring the contents of IL-4, IL-10, IL-17 and IFN-γ changed in both bronchoalveolar lavage fluid (BALF) and supernatant of splenocyte culture as well as level changes of specific IgE and IgG2a in the serum. After SIT intervention, the symptoms of allergic inflammation was alleviated significantly in mice treated with ProDer f 1 protein and the two enzymatic hydrolysates via detection of the lung tissue sections, and infiltration of inflammatory cells was also notably depressed as compared with the models, though the epithelial structure in airways remained similar with the PBS group. In addition, we observed lower serum contents of the specific IgE antibody and lower levels of IL-4, IL-17 in BALF and splenic cells in mice undergone SIT, whereas specific IgG2a, IFN-γ and IL-10 in BALF and supernatant of splenocyte culture were higher as compared to the asthma group. The findings suggest the SIT using the above two kinds of hydrolysates may effectively inhibit the allergic inflammation in the airways of mouse models sensitized with ProDer f 1 protein. PMID:25932130

  4. On Attempting to Do What Lord Said Was Impossible: Commentary on van der Linden's "Some Conceptual Issues in Observed-Score Equating"

    ERIC Educational Resources Information Center

    Dorans, Neil J.

    2013-01-01

    van der Linden (this issue) uses words differently than Holland and Dorans. This difference in language usage is a source of some confusion in van der Linden's critique of what he calls equipercentile equating. I address these differences in language. van der Linden maintains that there are only two requirements for score equating. I maintain…

  5. Reduktion der Invasivität bei nadelbasierter Bewegungskompensation für navigierte Eingriffe im Abdomen

    NASA Astrophysics Data System (ADS)

    Maier-Hein, L.; Tekbas, A.; Franz, A. M.; Tetzlaff, R.; Müller, S. A.; Pianka, F.; Wolf, I.; Kauczor, H.-U.; Schmied, B. M.; Meinzer, H.-P.

    Diese Arbeit stellt eine in-vivo Genauigkeitsstudie über das Kombinieren interner und externer Marker für die Bewegungskompensation bei Leberinterventionen vor. Abhängig von der Anzahl und Anordnung der verwendeten Marker sowie der angewandten Echtzeittransformation wurde bei kontinuierlicher Atmung eine Schätzgenauigkeit der Zielposition zwischen 1 und 5 mm erreicht. Das Hinzufügen einer einzigen Hilfsnadel zu einer Menge von Hautmarkern führte zu einer Fehlerreduktion von über 50%. Die Ergebnisse dieser Studie können in der Praxis verwendet werden, um basierend auf dem Tradeoff zwischen geringer Invasivität und hoher Genauigkeit eine geeignete Kombination von internen und externen Markern für eine gegebene Fragestellung zu wählen.

  6. Anwendung von Methoden der Logistik und Netzplantechnik zur präzedenz- und ressourcenbeschränkten Ablaufplanung von Echtzeitsystemen

    NASA Astrophysics Data System (ADS)

    Gumzej, Roman; Lipičnik, Martin

    Grundlegende Zusammenhänge zwischen Logistik, Netzplantechnik und Echtzeit sowie den zugehörigen Arten der Ablaufplanung und ihrer Nutzung werden dargestellt. Das Echtzeitprinzip beinhaltet Rechtzeitigkeit von Abläufen, wobei es für eine frühzeitige Beendigung eines Ablaufs keinen Bonus gibt; im Gegensatz zum verspäteten Ablauf, dessen Konsequenzen in der Regel negativ und unabschätzbar sind. Das Just-in-Time-Prinzip gleicht dem der Echtzeit und wird vor allem in der Logistik zur Bezeichnung reibungsloser Abläufe in Beschaffungsketten verwendet. In der Netzplantechnik werden die kritischen Aktivitäten binnen eines Projektes bestimmt, die nicht verzögert werden dürfen, um das Projekt rechtzeitig zu beenden. Außerdem haben die drei Bereiche noch eine Gemeinsamkeit: um realistische Ablaufszenarien darzustellen, müssen in den Analysen auch begrenzte Ressourcen angemessen berücksichtigt werden.

  7. Observation of long-lived van der Waals molecules in an optical lattice

    NASA Astrophysics Data System (ADS)

    Kato, Shinya; Yamazaki, Rekishu; Shibata, Kosuke; Yamamoto, Ryuta; Yamada, Hirotaka; Takahashi, Yoshiro

    2012-10-01

    We observe long-lived tightly bound van der Waals molecules of ytterbium in a three-dimensional optical lattice with a lifetime of 8.0 s. The molecules, state-selectively produced by a photoassociation technique from a Bose-Einstein condensate or an atomic Mott insulator, are successfully detected with a photodissociation method where the molecules are photodissociated into two atoms and the atoms are captured by a magneto-optical trap or optical molasses, for the fluorescence detection. This work will open up various possibilities of research with van der Waals molecules in an optical lattice.

  8. General theory based on fluctuational electrodynamics for van der Waals interactions in colloidal systems

    SciTech Connect

    Yannopapas, Vassilios

    2007-12-15

    A rigorous theory for the determination of the van der Waals interactions in colloidal systems is presented. The method is based on fluctuational electrodynamics and a multiple-scattering method which provides the electromagnetic Green's tensor. In particular, expressions for the Green's tensor are presented for arbitrary, finite collections of colloidal particles, for infinitely periodic or defected crystals, as well as for finite slabs of crystals. The presented formalism allows for ab initio calculations of the van der Waals interactions in colloidal systems since it takes fully into account retardation, many-body, multipolar, and near-field effects.

  9. Automatische Segmentierung der Gewebegrenzen eines schlagenden embryonalen Hühnerherzens im 2D-Videobild

    NASA Astrophysics Data System (ADS)

    Thommes, Jan; Yelbuz, Talât Mesud

    Eine Klimakammer ermöglicht es, die Herzentwicklung bei Hühnerembryonen in einer schalenlosen Kultur über einen Zeitraum von etwa 50 Stunden visuell zu beobachten. Eine Hochgeschwindigkeits-Mikroskopkamera liefert eine Aufsicht auf das schlagende embryonale Herz. Da die für eine Analyse der Herzfunktion notwendige Segmentierung der Myokardgrenzen und des blutgefüllte Cavums manuell sehr zeitaufwändig ist, wird ein Ansatz zur kontinuierlichen, automatischen Segmentierung des schlagenden embryonalen Herzens mit Active Appearance Modellen präsentiert.

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

    PubMed

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

    2015-10-30

    A longitudinal magnetoresistance asymmetry (LMA) between a positive and negative magnetic field is known to occur in both the extreme quantum limit and the classical Drude limit in samples with a nonuniform doping density. By analyzing the current stream function in van der Pauw measurement geometry, it is shown that the electron density gradient can be quantitatively deduced from this LMA in the Drude regime. Results agree with gradients interpolated from local densities calibrated across an entire wafer, establishing a generalization of the van der Pauw method to quantify density gradients. PMID:26565488

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

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

    A longitudinal magnetoresistance asymmetry (LMA) between a positive and negative magnetic field is known to occur in both the extreme quantum limit and the classical Drude limit in samples with a nonuniform doping density. By analyzing the current stream function in van der Pauw measurement geometry, it is shown that the electron density gradient can be quantitatively deduced from this LMA in the Drude regime. Results agree with gradients interpolated from local densities calibrated across an entire wafer, establishing a generalization of the van der Pauw method to quantify density gradients.

  13. Numerical integration of nearly-Hamiltonian systems. [Van der Pol oscillator and perturbed Keplerian motion

    NASA Technical Reports Server (NTRS)

    Bond, V. R.

    1978-01-01

    The reported investigation is concerned with the solution of systems of differential equations which are derived from a Hamiltonian function in the extended phase space. The problem selected involves a one-dimensional perturbed harmonic oscillator. The van der Pol equation considered has an exact asymptotic value for its amplitude. Comparisons are made between a numerical solution and a known analytical solution. In addition to the van der Pol problem, known solutions regarding the restricted problem of three bodies are used as examples for perturbed Keplerian motion. The extended phase space Hamiltonian discussed by Stiefel and Scheifele (1971) is considered. A description is presented of two canonical formulations of the perturbed harmonic oscillator.

  14. Connecting Distributed Energy Resources to the Grid: Their Benefits to the DER Owner etc.

    SciTech Connect

    Poore, WP

    2003-07-09

    The vision of the Distributed Energy Research Program (DER) program of the U.S. Department of Energy (DOE) is that the United States will have the cleanest and most efficient and reliable energy system in the world by maximizing the use of affordable distributed energy resources. Electricity consumers will be able to choose from a diverse number of efficient, cost-effective, and environmentally friendly distributed energy options and easily connect them into the nation's energy infrastructure while providing benefits to their owners and other stakeholders. The long-term goal of this vision is that DER will achieve a 20% share of new electric capacity additions in the United States by 2010, thereby helping to make the nation's electric power generation and delivery system more efficient, reliable, secure, clean, economical, and diverse in terms of fuel use (oil, natural gas, solar, hydroelectric, etc.) and prime mover resource (solar, wind, gas turbines, etc.). Near- and mid-term goals are to develop new technologies for implementing and operating DER and address barriers associated with DER usage and then to reduce costs and emissions and improve the efficiency and reliability of DER. Numerous strategies for meeting these goals have been developed into a research, development, and demonstration (RD&D) program that supports generation and delivery systems architecture, including modeling and simulation tools. The benefits associated with DER installations are often significant and numerous. They almost always provide tangible economic benefits, such as energy savings or transmission and distribution upgrade deferrals, as well as intangible benefits, such as power quality improvements that lengthen maintenance or repair intervals for power equipment. Also, the benefits routinely are dispersed among end users, utilities, and the public. For instance, an end user may use the DER to reduce their peak demand and save money due to lower demand charges. Reduced end user

  15. „Überholen ohne einzuholen“ Die Entwicklung von Technologien für übermorgen in Kernenergie und Mikroelektronik der DDR

    NASA Astrophysics Data System (ADS)

    Barkleit, Gerhard

    Dem nuklearen Patt zwischen Ostblock und westlichem Staatenbündnis ist es nach weitgehend übereinstimmender Auffassung von Politik und Wissenschaft zu danken, dass der "Kalte Krieg" in der zweiten Hälfte des 20. Jahrhunderts nicht zum weltumfassenden Flächenbrand eskalierte. An der raschen Herstellung dieses Patts waren zwei Dresdner Physiker maßgeblich beteiligt, deren einer im Manhattan-Projekt in den USA gearbeitet hatte und später in England der Spionage für die Sowjetunion und des Verrats des Know-how der Atombombe überführt wurde.

  16. Supernumerary chromosome marker Der(22)t(11;22) resulting from a maternal balanced translocation.

    PubMed

    Hou, Jia-Woei

    2003-01-01

    Derivative 22 [der(22)] syndrome is a rare disorder associated with multiple congenital anomalies including pre-auricular skin tags or pits, conotruncal heart defects, and profound mental retardation. Der(22)t(11;22) is one of the causes of supernumerary chromosome markers (mar) in humans. We present a boy with developmental delay and multiple anomalies consistent with the supernumerary der(22) syndrome. Cytogenetic analysis showed an abnormal chromosome complement of 47, XY, +mar in all 50 cells analyzed. The karyotype of his mother showed a reciprocal translocation over the distal bands 11q23 and 22q11, respectively, i.e., 46,XX,t( 11;22)(q23.3;q11.2), and that of his father was 46,XY. Thus, the nature of the supernumerary chromosome markers was of der(22)t(11 ;22)(q23.3;q11.2). The clinical features, including craniofacial dysmorphism, hypotonia, psychomotor retardation, heart defects, and urogenital anomalies, were the combined effects of partial trisomies for both distal 11q and pericentromeric 22q. PMID:12656309

  17. 49 CFR 40.35 - What information about the DER must employers provide to collectors?

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 49 Transportation 1 2011-10-01 2011-10-01 false What information about the DER must employers provide to collectors? 40.35 Section 40.35 Transportation Office of the Secretary of Transportation PROCEDURES FOR TRANSPORTATION WORKPLACE DRUG AND ALCOHOL TESTING PROGRAMS Urine Collection Personnel §...

  18. Bewertung und Verbesserung der Zuverlässigkeit von mikroelektronischen Komponenten in mechatronischen Systemen

    NASA Astrophysics Data System (ADS)

    Wunderlich, Hans-Joachim; Elm, Melanie; Kochte, Michael

    In den letzten Jahrzehnten hat der Anteil der informationsverarbeitenden Komponenten an den Herstellungskosten mechatronischer Systeme rapide zugenommen. In den 70er Jahren machte die Informationsverarbeitung noch ca. 15% des Systems aus. Zu Beginn dieses Jahrtausends sind es bereits über 60% [8.9], wie auch aus Abb. 8.1 hervorgeht. Dieser Zuwachs in den Herstellungskosten ist auf die Zunahme der durch die Informationsverarbeitung realisierten Funktionen zurückzuführen. Sehr deutlich ist diese Zunahme im Automobil zu beobachten. Während das Antiblockiersystem und die digitale Motorsteuerung schon seit Jahren zum Standard gehören, werden nun zunehmend auch Fahrerassistenz- und Infotainmentsysteme ins Kraftfahrzeug integriert. Bei diesen Systemen beginnt die Grenze zwischen klassischer Sicherheits- und Komfortfunktion zu verschwimmen. Die Bandbreite möglichen Fehlverhaltens reicht vom Ausfall des Navigationssystems über Störungen der Zentralverriegelung bis hin zum automatischen Einleiten von Bremsmanövern bei hohen Geschwindigkeiten. Entsprechend ergeben sich hier hohe Anforderungen an die Zuverlässigkeit dieser Systeme.

  19. Generalized van der Waals Hamiltonian: periodic orbits and C1 nonintegrability.

    PubMed

    Guirao, Juan L G; Llibre, Jaume; Vera, Juan A

    2012-03-01

    The aim of this paper is to study the periodic orbits of the generalized van der Waals Hamiltonian system. The tool for studying such periodic orbits is the averaging theory. Moreover, for this Hamiltonian system we provide information on its C(1) nonintegrability, i.e., on the existence of a second first integral of class C(1). PMID:22587198

  20. First kind symmetric periodic solutions of the generalized van der Waals Hamiltonian

    NASA Astrophysics Data System (ADS)

    Alberti, Angelo; Vidal, Claudio

    2016-07-01

    The aim of this paper is to prove the existence of a new symmetric family of periodic solutions of the generalized van der Waals Hamiltonian. In fact, we prove the existence of several families of first kind symmetric periodic solutions as continuation of circular orbits of the Kepler problem in the spatial case.

  1. Characterization of a new subtype of allergen in dermatophagoides farinae—Der f 28

    PubMed Central

    Lin, Jian-Li; Wang, Yuan-Yuan; Xiao, Xiao-Jun; Wu, Yu-Lan; Sun, Bao-Qing; Gao, An-Jian; Liu, Zhi-Gang

    2015-01-01

    Background House dust mites (HDMs) are the major sources of indoor allergens which induce asthma, dermatitis, rhinitis, and some other allergic diseases. Close to 30 sub-allergens have been identified. Methods Through analyzing the full genome sequence of dust mite, a new allergen whose primary structure belongs to the heat shock protein family was identified. The sequence of this allergen was determined by cDNA cloning. The allergenicity was assayed by skin prick test, Western-blot and enzyme-linked immunosorbent assay (ELISA). Results r-Der f 28 bound to serum IgE from mite allergic patients. Positive responses to r-Der f 28 were shown in 11.5% by skin prick testing from 26 DM-allergic patients. Airway hyperresponsiveness, serum specific IgE and IL-4 were significantly increased in allergic asthma mouse model sensitized to r-Der f 28. Conclusions Der f 28 is a new subtype of allergen in dermatophagoides farinae. PMID:26623108

  2. A theoretical study of the rovibrational levels of the bosonic van der Waals neon trimer.

    PubMed

    Salci, Moses; Levin, Sergey B; Elander, Nils; Yarevsky, Evgeny

    2008-10-01

    The eigenenergies and root mean square radii of the rovibrational levels (J = 0-3) of the weakly bound bosonic van der Waals neon trimer were calculated using a full angular momentum three-dimensional finite element method. The differing results of three previous studies for zero angular momentum are discussed, explained, and compared with the results presented here. PMID:19045087

  3. Erzahlraum im virtuellen Raum: Rewriting Bernhard Schlink's "Der Vorleser" on the Web >.

    ERIC Educational Resources Information Center

    Schaumann, Caroline

    2001-01-01

    Presents a pilot course for the Collaboration in Virtual Space (CiVS) project at Middlebury College. After reading and discussing Bernhard Schlink's "Der Vorleser," students produced in collaborative groups a Web site with information on Schlink, the text's cultural-historical background, and its reception, and they developed an interactive,…

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

    ERIC Educational Resources Information Center

    Lynn, Richard; Meisenberg, Gerhard

    2010-01-01

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

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

    PubMed

    Choi, Yongsuk; Kang, Junmo; Jariwala, Deep; Kang, Moon Sung; Marks, Tobin J; Hersam, Mark C; Cho, Jeong Ho

    2016-05-01

    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 (>10(4) ) in a narrow voltage window (<3 V). PMID:27002478

  6. Bridging the Gap: A Literacy-Oriented Approach to Teaching the Graphic Novel "Der erste Fruhling"

    ERIC Educational Resources Information Center

    Bridges, Elizabeth

    2009-01-01

    This article examines the phenomenon of graphic novels generally, and in particular, their utility in second-language contexts via the example of the graphic adaptation of Klaus Kordoris "Der erste Fruhling." This text lends itself especially to bridging thematic gaps in 20th-century German literature courses, as well as the "language/literature…

  7. Comments on "Some Conceptual Issues in Observed-Score Equating" by Wim J. van der Linden

    ERIC Educational Resources Information Center

    Bradlow, Eric T.

    2013-01-01

    The van der Linden article (this issue) provides a roadmap for future research in equating. My belief is that the roadmap begins and ends with collecting auxiliary data that can be utilized to provide improved equating, especially when data are sparse or equating beyond simple moments is desired.

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

    ERIC Educational Resources Information Center

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

    2012-01-01

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

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

    PubMed

    Wang, Xiaoming; Zebarjadi, Mona; Esfarjani, Keivan

    2016-08-21

    This work aims at understanding solid-state energy conversion and transport in layered (van der Waals) heterostructures in contact with metallic electrodes via a first-principles approach. As an illustration, a graphene/phosphorene/graphene heterostructure in contact with gold electrodes is studied by using density functional theory (DFT)-based first principles calculations combined with real space Green's function (GF) formalism. We show that for a monolayer phosphorene, quantum tunneling dominates the transport. By adding more phosphorene layers, one can switch from tunneling-dominated transport to thermionic-dominated transport, resulting in transporting more heat per charge carrier, thus, enhancing the cooling coefficient of performance. The use of layered van der Waals heterostructures has two advantages: (a) thermionic transport barriers can be tuned by changing the number of layers, and (b) thermal conductance across these non-covalent structures is very weak. The phonon thermal conductance of the present van der Waals heterostructure is found to be 4.1 MW m(-2) K(-1) which is one order of magnitude lower than the lowest value for that of covalently-bonded interfaces. The thermionic coefficient of performance for the proposed device is 18.5 at 600 K corresponding to an equivalent ZT of 0.13, which is significant for nanoscale devices. This study shows that layered van der Waals structures have great potential to be used as solid-state energy-conversion devices. PMID:27314610

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

    NASA Astrophysics Data System (ADS)

    Peng, Qing; de, Suvranu

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

  11. Approximating the 3D Character of a Van Der Waals Atom-Solid Potential

    NASA Astrophysics Data System (ADS)

    Bruch, L. W.

    2016-04-01

    A truncated Fourier decomposition of the atom-substrate potential energy is developed for three-dimensional models of van der Waals systems, specifically for adsorption on the basal plane surface of graphite or the (111) face of a face-centered-cubic lattice. This provides a framework for analysis of a priori calculations of physical adsorption energies.

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

    NASA Astrophysics Data System (ADS)

    Calman, E. V.; Dorow, C. J.; Fogler, M. M.; Butov, L. V.; Hu, S.; Mishchenko, A.; Geim, A. K.

    2016-03-01

    We report an experimental study of excitons in a double quantum well van der Waals heterostructure made of atomically thin layers of MoS2 and hexagonal boron nitride. The emission of neutral and charged excitons is controlled by gate voltage, temperature, and both the helicity and the power of optical excitation.

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

    ERIC Educational Resources Information Center

    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…

  14. Maxwell's Relations for a van der Waals Gas and a Nuclear Paramagnetic System.

    ERIC Educational Resources Information Center

    Herlihy, James; And Others

    1981-01-01

    Since Maxwell's relations are derived in general form from the first to second laws, and students often wonder what they mean and how they are used, appropriate partition functions for van der Waals gas and the nuclear paramagnetic system are used to obtain entropy expressions and equations of state. (Author/SK)

  15. Comments on van der Linden's Critique and Proposal for Equating

    ERIC Educational Resources Information Center

    Holland, Paul W.

    2013-01-01

    While agreeing with van der Linden (this issue) that test equating needs better theoretical underpinnings, my comments criticize several aspects of his article. His examples are, for the most part, worthless; he does not use well-established terminology correctly; his view of 100 years of attempts to give a theoretical basis for equating is…

  16. Von Tondern nach Gotha. Der Astronom Peter Andreas Hansen, 1795 - 1874.

    NASA Astrophysics Data System (ADS)

    Strumpf, M.; Pehlemann, E.; Wolfschmidt, G.

    This companion booklet to an exposition in honor of Peter Andreas Hansen's 200th birthday contains three papers. Contents: 1. Peter Andreas Hansen - Leben und Wirken in Gotha (M. Strumpf). 2. Peter Andreas Hansens wissenschaftliches Werk (E. Pehlemann). 3. Beobachtungsinstrumente der Sternwarte Gotha zur Zeit Hansens (G. Wolfschmidt).

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

    PubMed

    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. PMID:23032606

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

    NASA Astrophysics Data System (ADS)

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

    2012-10-01

    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 sp3d5 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.

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

    PubMed

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

    2015-06-01

    Transmission electron microscopy studies on the assembly and growth of gold nanoparticles on carbon nanotubes supported on few-layer graphene and amorphous carbon reveal a competition between van der Waals forces and electrostatic interactions, enabling controlled positioning and sizing of adsorbed nanoparticles at the nanochannels formed between the carbon nanotube and the few-layer graph-ene surface. PMID:25689488

  20. Bonded Paths and van der Waals Interactions in Orpiment, As2S3

    SciTech Connect

    Gibbs, Gerald V.; Wallace, Adam F.; Zallen, Richard; Downs, R. T.; Ross, Nancy L.; Cox, David F.; Rosso, Kevin M.

    2010-06-17

    Bond critical properties and bond paths have been calculated for the thioarsenide molecular crystal orpiment, As2S3. In addition to the intramolecular As-S bond paths and van der Waals As-S and S-S bond paths within the layers, intermolecular S-S, As-S and As-As van der Waals paths exist between the layers. The S-S bond paths between the layers are identified with the main interlayer restoring forces responsible for the vibrational internal-mode splitting and the low frequency rigid layer modes previously documented in infrared and Raman studies of orpiment. These S-S bond paths are comparable with those calculated for orthorhombic native sulfur and the As4Sn (n = 3,4,5) molecules for several arsenide molecular crystals. The As-S bond paths show that the two nonequivalent arsenic atoms are each coordinated by a highly distorted octahedral array of sulfur atoms. The octahedra consist of three As-S intramolecular bonded interactions and three longer van der Waals interactions (two intramolecular and one intermolecular). One of the arsenic atoms is also coordinated by an arsenic atom in an interlayer As-As bonded interaction. Laplacian isosurface envelopes calculated for the arsenic and sulfur atoms are comparable with those calculated for native arsenic and orthorhombic sulfur. The intermolecular As-S bond paths connect Lewis acid domains on arsenic and an Lewis base domains on sulfur. Van der Waals interactions are traditionally defined as attractive interactions other than those ascribed to bond formation. However, theoretical evidence and arguments, as well as the connection between the bond paths and the vibrational spectra, indicate that the van der Waals interactions in orpiment are directed bonded interactions in the Slater sense. The experimental bond lengths for the As-S and S-S bonded interactions decrease nonlinearly with the increasing value of the electron density at the bond critical point, concomitant with a decrease in the bonded radii of arsenic and

  1. Sinn und Möglichkeiten der Theoretischen Physik. Zum 300. Jahrestag von Newtons Philosophiae Naturalis Principia Mathematica

    NASA Astrophysics Data System (ADS)

    Rompe, R.; Thiessen, P. A.; Treder, H.-J.

    Die Newtonschen Prinzipien und die aus ihnen gewonnene Erkenntnis der Existenz von Elementarkonstanten nach Planck, Einstein und Bohr erweisen sich zunehmend als tragfähiges Fundament nicht nur der Physik und ihrer Anwendung in der Technik, sondern überhaupt aller exakten Wissenschaften in breitestem Sinne des Wortes.Die physikalisch inhaltliche Klärung der Begriffe erfolgt seit Newton in engem Verbund mit der Entwicklung mathematischer Methoden. Diese Kombination erweist sich weiterhin als produktiv und sichert den Fortschritt der Physik und der exakten Wissenschaften.Wohl alle Probleme, die im Bereich der Technik Bedeutung haben können, lassen sich bei entsprechendem Aufwand bereits mit dem vorhandenen Fundus an Erkenntnissen und Methoden erfolgreich angehen.Der in der Wirklichkeit verankerte Zusammenhang von Gesetz und Zufall erweist sich als eine Manifestation der Dialektik in der Natur. Es gibt keinen absoluten Zufall. Sie kommt in allen Zweigen der Physik, nicht nur in der Thermodynamik und Quantenphysik, zutage, und muß bereits auf dem Niveau der Newtonschen Prinzipien und der Elementarkonstanten behandelt werden.Die theoretische Physik, so wie sie von Newton initiiert worden ist, wurde so angelegt, daß sie alle Seiten der Wirklichkeit, so weit sie in die Kompetenz der Physik fallen, umfaßt. Es besteht darum kein Gegensatz zwischen der klassischen Physik und der Quantenphysik. Es handelt sich lediglich um eine Differenzierung nach den unterschiedlichen physikalischen Inhalten und den angemessenen mathematischen Methoden, die natürlich von der Wahl der Probleme abhängen.Die theoretische Physik stellt eine allgemein zugängliche Zusammenfassung des gesicherten Wissens der Physik dar, das zugleich das Fundament der exakten Wissenschaften ist.Die theoretische Physik ist damit das Mittel der Verständigung innerhalb der Kooperation, die notwendig ist zur Lösung der großen komplexen Aufgaben der Wissenschaft und Technik.

  2. Band gap engineering of a soft inorganic compound PbI2 by incommensurate van der Waals epitaxy

    NASA Astrophysics Data System (ADS)

    Wang, Yiping; Sun, Yi-Yang; Zhang, Shengbai; Lu, Toh-Ming; Shi, Jian

    2016-01-01

    Van der Waals epitaxial growth had been thought to have trivial contribution on inducing substantial epitaxial strain in thin films due to its weak nature of van der Waals interfacial energy. Due to this, electrical and optical structure engineering via van der Waals epitaxial strain has been rarely studied. In this report, we show that significant band structure engineering could be achieved in a soft thin film material PbI2 via van der Waals epitaxy. The thickness dependent photoluminescence of single crystal PbI2 flakes was studied and attributed to the substrate-film coupling effect via incommensurate van der Waals epitaxy. It is proposed that the van der Waals strain is resulted from the soft nature of PbI2 and large van der Waals interaction due to the involvement of heavy elements. Such strain plays vital roles in modifying the band gap of PbI2. The deformation potential theory is used to quantitatively unveil the correlation between thickness, strain, and band gap change. Our hypothesis is confirmed by the subsequent mechanical bending test and Raman characterization.

  3. Van der Woude and Popliteal Pterygium Syndromes: Broad intrafamilial variability in a three generation family with mutation in IRF6.

    PubMed

    Busche, Andreas; Hehr, Ute; Sieg, Peter; Gillessen-Kaesbach, Gabriele

    2016-09-01

    Patients with Van der Woude syndrome typically present with cleft lip, cleft lip and palate, or with cleft palate only. In contrast to non-syndromic cleft lip and/or palate, Van der Woude syndrome typically is characterized by bilateral, paramedian lower-lip pits. Popliteal pterygium syndrome shares features with Van der Woude syndrome, but, in addition, is characterized by a popliteal pterygium, genital anomalies, cutaneous syndactyly of the fingers and the toes, and a characteristic pyramidal fold of skin overlying the nail of the hallux. In some patients oral synechiae or eyelid synechiae are present. Van der Woude Syndrome and Popliteal pterygium syndrome are autosomal dominantly inherited disorders caused by heterozygous mutations in IRF6. We present a three generation family with tremendous intrafamilial phenotypic variability. The newborn index patient had a diagnosis of Popliteal pterygium syndrome. The mother presented with a classic Van der Woude Syndrome, while the maternal grandfather had Van der Woude Syndrome as well as minor signs of Popliteal pterygium syndrome. In all three affecteds the known pathogenic mutation c.265A>G, p.Lys89Glu in IRF6 was identified. While inter- as well as intra-familial variability has been described in IRF6-related disorders, the occurrence of a typical Van der Woude Syndrome without any other anomalies as well as a diagnosis of Popliteal pterygium syndrome in the same family is rare. © 2016 Wiley Periodicals, Inc. PMID:27286731

  4. Characterization of an immunomodulatory Der p 2-FIP-fve fusion protein produced in transformed rice suspension cell culture.

    PubMed

    Su, Chin-Fen; Kuo, I-Chun; Chen, Peng-Wen; Huang, Chiung-Hui; Seow, See Voon; Chua, Kaw Yan; Yu, Su-May

    2012-02-01

    Der p 2, a major allergen of Dermatophagoides pteronyssinus mites, is one of the most clinically relevant allergens to allergic patients worldwide. FIP-fve protein (Fve) from the golden needle mushroom (Flammulina velutipes) is an immunomodulatory protein with potential Th1-skewed adjuvant properties. Here, we produced and immunologically evaluated a Der p 2-Fve fusion protein as a potential immunotherapeutic for allergic diseases. Using an inducible expression system in cultured rice suspension cells, the recombinant Der p 2-Fve fusion protein (designated as OsDp2Fve) was expressed in rice cells under the control of an α-amylase gene (αAmy8) promoter and secreted under sucrose starvation. OsDp2Fve was partially purified from the cultured medium. The conformation of Der p 2 in OsDp2Fve remains intact as reflected by its unaltered allergenicity, as assessed by human IgE ELISA and histamine release assays, compared to non-fusion Der p 2 protein. Furthermore, the Fve protein expressed in OsDp2Fve retains its in vitro lymphoproliferative activity but loses its hemagglutination and lymphoagglutination effects compared to the native protein. Notably, in vivo evaluation showed that mice administered with OsDp2Fve possessed an enhanced production of Der p 2-specific IgG antibodies without potentiating the production of Der p 2-specific IgE and Th2 effector cytokines in comparison with mice co-administered with native Fve and Der p 2 proteins. These results suggest that the recombinant Der p 2-Fve fusion protein produced in rice suspension cell cultures has a great potential for allergy immunotherapy. PMID:21556691

  5. Analysis of T-cell epitopes of Der f3 in Dermatophagoides farina

    PubMed Central

    Li, Na; Xu, Haifeng; Song, Hongyu; Wang, Kexia; Li, Chaopin

    2015-01-01

    House dust mites (HDM) are most important indoor allergens for humans. Der f3, one of the potent allergens with allergenicity, is derived from Dermatophagoides farina (D. farinae), and exhibits strong allergenicity that was confirmed in our previous work. The current study was undertaken to determine the localization of T-cell epitope of Der f3. We initially developed the T-cell fraction from BALB/c mice sensitized with recombinant Der f3 to determine the T-cell epitopes in the murine models, and performed T cell proliferation assay with 25 synthetic overlapping peptides of Der f3. The results indicated that T-cell reactive region of murine were assigned on amino acid range 41-60, 101-120, 161-180 and 201-220, respectively. In addition, we did T-cell proliferation experiment, respectively using the 4 murine T-cell epitope peptide and the human T-cell lines from three patients allergic to mite allergens in order to verify homogenous T-cell epitopes in humans. The results indicated that the amino acid sequences of 41-60, 101-120 and 161-180 had induced T cell proliferation in humans, yet 201-220 failed to. These findings suggest that T-cell epitope in Der f3 is located in the amino acid sequences of 41-60, 101-120 and 161-180, respectively. T-cell epitope localization detected in our study may provide a basis for development of animal therapeutic model and peptide vaccine for asthma. PMID:25755700

  6. Assessment of (mu)grid distributed energy resource potential using DER-CAM and GIS

    SciTech Connect

    Edwards, Jennifer L.; Marnay, Chris; Bartholomew, Emily; Ouaglal, Boubekeur; Siddiqui, Afzal S.; LaCommare, Kristina S.H.

    2002-01-01

    This report outlines an approach to assess the local potential for deployment of distributed energy resources (DER), small power-generation installations located close to the point where the energy they produce will be consumed. Although local restraints, such as zoning, building codes, and on-site physical barriers are well-known frustrations to DER deployment, no analysis method has been developed to address them within a broad economic analysis framework. The approach developed here combines established economic optimization techniques embedded in the Distributed Energy Resource Customer Adoption Model (DER-CAM) with a geographic information system (GIS) analysis of local land-use constraint. An example case in the San Diego area is developed from a strictly customer perspective, based on the premise that future development of DER may take the form of microgrids ((mu)Grids) under the control of current utility customers. Beginning with assumptions about which customer combinations h ave complementary energy loads, a GIS was used to locate specific neighborhoods in the San Diego area with promising customer combinations. A detailed energy analysis was conducted for the commercial/residential area chosen covering both electrical and heat energy requirements. Under various scenarios, different combinations of natural gas reciprocating engines were chosen by DER-CAM, ranging in size from 25 kW to 500 kW, often with heat recovery or absorption cooling. These generators typically operate throughout the day and are supplemented by purchased electricity during late-night and early-morning hours, when utility time-of-use prices are lowest. Typical (mu)Grid scenarios displaced about 80 percent of their annual gas heat load through CHP. Self-generation together with absorption cooling dramatically reduce electricity purchases, which usually only occur during nighttime hours.

  7. In-situ epitaxial growth of graphene/h-BN van der Waals heterostructures by molecular beam epitaxy

    PubMed Central

    Zuo, Zheng; Xu, Zhongguang; Zheng, Renjing; Khanaki, Alireza; Zheng, Jian-Guo; Liu, Jianlin

    2015-01-01

    Van der Waals materials have received a great deal of attention for their exceptional layered structures and exotic properties, which can open up various device applications in nanoelectronics. However, in situ epitaxial growth of dissimilar van der Waals materials remains challenging. Here we demonstrate a solution for fabricating van der Waals heterostructures. Graphene/hexagonal boron nitride (h-BN) heterostructures were synthesized on cobalt substrates by using molecular beam epitaxy. Various characterizations were carried out to evaluate the heterostructures. Wafer-scale heterostructures consisting of single-layer/bilayer graphene and multilayer h-BN were achieved. The mismatch angle between graphene and h-BN is below 1°. PMID:26442629

  8. Über die Möglichkeit der Zustandsvoraussage chaotischer Systeme

    NASA Astrophysics Data System (ADS)

    Leven, R. W.; Pompe, B.

    Deterministische chaotische Systeme reagieren empfindlich auf Störungen ihrer Bewegung. Kennt man im speziellen den Anfangszustand des Systems nicht exakt, so ist eine Voraussage über das zukünftige Verhalten des Systems nur beschränkt möglich. Die Transformation IT gibt an, wieviel Information man über einen zukünftigen Zustand hat, wenn man den Anfangszustand mit einer bestimmten Genauigkeit kennt.In dieser Arbeit werden weitere mögliche Interpretationen von IT in Hinblick auf die Beschreibung dynamischer Systeme gegeben. Für zwei einfache eindimensionale Abbildungen wird IT in Abhängigkeit von der Zeit der Voraussage (l) bestimmt: Ein System, das durch die BERNOULLI-Abbildung beschrieben wird, vergißt nach der ersten Iteration 1 bis 1,5 bit von seinem Anfangszustand. Vollständiges Vergessen tritt jedoch i. allg. erst für l ein. Bei der Logistik-Abbildung vergißt das System seinen Anfangszustand schneller, wenn der Grad des Chaos (d. h. der LJAPUNOV-Exponent) oder die äußeren Störungen zunehmen.Translated AbstractOn the Possibility of State Prediction of Chaotic SystemsDeterministic chaotic systems show a sensitive response to perturbations of their motion. In particular, if one has not exact knowledge about the initial state of the system, limits are set to the prediction of the system's future behaviour. The transinformation IT is the information obtainable about a future state, if one knows the initial state within a certain precision. In this paper further possible interpretations of IT are given with regard to the description of dynamic systems. IT is determined for different times of prediction (l) in the case of two simple one-dimensional maps: A system described by the BERNOULLI-map forgets after the first iteration 1 to 1.5 bit of its initial state. Nevertheless, in general we have complete loss of memory only for l . In the case of the logistic map the system forgets its initial state faster, if the

  9. Turbulenzübergang in der Rohrströmung: Die Lösung eines alten Rätsels

    NASA Astrophysics Data System (ADS)

    Eckhardt, Bruno; Hof, Björn; Faisst, Holger

    2006-09-01

    Die Strömung von Flüssigkeiten und Gasen durch eine Röhre kann zwei Zustände annehmen. Einer ist laminar, also gleichmäßig geordnet, einer ist zeitlich-räumlich verwirbelt und turbulent. Mit dem Übergang zur Turbulenz nimmt der Strömungswiderstand drastisch zu. Vor etwa 120 Jahren beschrieb Osborne Reynolds bereits das Verhalten der Rohrströmung sehr genau. Er beobachtete, dass der Turbulenzübergang sehr empfindlich von äußeren Störungen abhängt, was bislang rätselhaft blieb. Dieses Rätsel konnte nun mit einer Kombination aus Computerstudien, Konzepten aus der nichtlinearen Dynamik und speziell entwickelten Experimenten gelöst werden.

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

    SciTech Connect

    Ganesh, P.; Kim, Jeongnim; Park, Changwon; Yoon, Mina; Reboredo, Fernando A.; Kent, Paul R. C.

    2014-11-03

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

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

    PubMed

    Ganesh, P; Kim, Jeongnim; Park, Changwon; Yoon, Mina; Reboredo, Fernando A; Kent, Paul R C

    2014-12-01

    Highly accurate diffusion quantum Monte Carlo (QMC) studies of the adsorption and diffusion of atomic lithium in AA-stacked graphite are compared with van der Waals-including density functional theory (DFT) calculations. Predicted QMC lattice constants for pure AA graphite agree with experiment. Pure AA-stacked graphite is shown to challenge many van der Waals methods even when they are accurate for conventional AB graphite. Highest overall DFT accuracy, considering pure AA-stacked graphite as well as lithium binding and diffusion, is obtained by the self-consistent van der Waals functional vdW-DF2, although errors in binding energies remain. Empirical approaches based on point charges such as DFT-D are inaccurate unless the local charge transfer is assessed. The results demonstrate that the lithium-carbon system requires a simultaneous highly accurate description of both charge transfer and van der Waals interactions, favoring self-consistent approaches. PMID:26583215

  12. Coexisting two canards and their breakdown into chaos in the van der Pol oscillator under weak periodic perturbation

    NASA Astrophysics Data System (ADS)

    Sekikawa, Munehisa; Inaba, Naohiko; Aihara, Kazuyuki

    2007-04-01

    Two coexisting stable canards are discussed in a periodically driven singularly perturbed van der Pol equation, where the amplitude of the driving force is extremely small. Canard breakdown into chaos via period-doubling bifurcations is also observed.

  13. Grundsätze über die Anlagen neuer Sternwarten mit Beziehung auf die Sternwarte der Universität Göttingen. Von Georg Heinrich Borheck

    NASA Astrophysics Data System (ADS)

    Beuermann, Klaus; Borheck, Georg Heinrich

    Die Göttinger Sternwarte, Wirkungsstätte des berühmten Gelehrten Carl Friedrich Gauß, ist ein bedeutendes Baudenkmal. Im Jahre 2005 wird sie gemeinsam von der Georg-August-Universität und der Akademie der Wissenschaften zu Göttingen renoviert, um dann als repräsentatives Gebäude der Universität und Arbeitsstätte der Akademie zu dienen. Die Nutzung der historischen Räume für Ausstellungen macht diesen imposanten Bau erstmals der Öffentlichkeit zugänglich. Die Sternwarte war bei ihrer Errichtung vor 200 Jahren ein nach seinerzeit neuesten wissenschaftlichen Erkenntnissen konzipierter Bau, der die Universität Göttingen in eine der vordersten Stellen Europa rückte. Auch aufgrund ihrer Architektur ist sie ein großer Wurf des Göttinger Universitätsbaumeisters Georg Heinrich Borheck. Durch die Kriegswirren der Napoleonischen Zeit zerschlug sich Borhecks Versuch einer Publikation seiner Beschreibung des Baus der Göttinger Sternwarte 1805. Doch seine Schrift ist auch heute noch aktuell und wird mit diesem Band erstmals einer breiten Öffentlichkeit zugängig gemacht. Er zeigt die Grundsätze, nach denen damals öffentliche Bauten konzipiert wurden, erläutert die Bedeutung des Baus aus kunst- und wissenschaftshistorischer Sicht und informiert über die Pläne zur Restaurierung der Sternwarte in einem separaten Beitrag und im Geleitwort des Präsidenten der Georg-August Universität Prof. Dr. Dr. h. c. Kurt von Figura.

  14. Black phosphorene/monolayer transition-metal dichalcogenides as two dimensional van der Waals heterostructures: a first-principles study.

    PubMed

    You, Baiqing; Wang, Xiaocha; Zheng, Zhida; Mi, Wenbo

    2016-03-14

    The electronic structure of black phosphorene (BP)/monolayer 1H-XT2 (X = Mo, W; T = S, Se, Te) two dimensional (2D) van der Waals heterostructures have been calculated by the first-principles method. It is found that the electronic band structures of both BP and XT2 are preserved in the combined van der Waals heterostructures. The WSe2/BP van der Waals heterostructure demonstrates a type-I band alignment, but the MoS2/BP, MoSe2/BP, MoTe2/BP, WS2/BP and WTe2/BP van der Waals heterostructures demonstrate a type-II band alignment. In particular, the n-type XT2/p-type BP van der Waals heterostructures can be applied in p-n diode and logical devices. Strong spin splitting appears in all of the heterostructures when considering the spin orbital coupling. Our results play a significant role in the prediction of novel 2D van der Waals heterostructures that have potential applications in spin-filter devices, spin field effect transistors, optoelectronic devices, etc. PMID:26899350

  15. Van der Waals pressure and its effect on trapped interlayer molecules

    NASA Astrophysics Data System (ADS)

    Vasu, K. S.; Prestat, E.; Abraham, J.; Dix, J.; Kashtiban, R. J.; Beheshtian, J.; Sloan, J.; Carbone, P.; Neek-Amal, M.; Haigh, S. J.; Geim, A. K.; Nair, R. R.

    2016-07-01

    Van der Waals assembly of two-dimensional crystals continue attract intense interest due to the prospect of designing novel materials with on-demand properties. One of the unique features of this technology is the possibility of trapping molecules between two-dimensional crystals. The trapped molecules are predicted to experience pressures as high as 1 GPa. Here we report measurements of this interfacial pressure by capturing pressure-sensitive molecules and studying their structural and conformational changes. Pressures of 1.2+/-0.3 GPa are found using Raman spectrometry for molecular layers of 1-nm in thickness. We further show that this pressure can induce chemical reactions, and several trapped salts are found to react with water at room temperature, leading to two-dimensional crystals of the corresponding oxides. This pressure and its effect should be taken into account in studies of van der Waals heterostructures and can also be exploited to modify materials confined at the atomic interfaces.

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

    PubMed

    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. PMID:26738722

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

    PubMed

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

    2015-09-22

    The self-assembly of heterogeneous mesoscale systems is mediated by long-range interactions, including van der Waals forces. Diverse mesoscale architectures, built of optically and morphologically anisotropic elements such as DNA, collagen, single-walled carbon nanotubes, and inorganic materials, require a tool to calculate the forces, torques, interaction energies, and Hamaker coefficients that govern assembly in such systems. The mesoscale Lifshitz theory of van der Waals interactions can accurately describe solvent and temperature effects, retardation, and optically and morphologically anisotropic materials for cylindrical and planar interaction geometries. The Gecko Hamaker open-science software implementation of this theory enables new and sophisticated insights into the properties of important organic/inorganic systems: interactions show an extended range of magnitudes and retardation rates, DNA interactions show an imprint of base pair composition, certain SWCNT interactions display retardation-dependent nonmonotonicity, and interactions are mapped across a range of material systems in order to facilitate rational mesoscale design. PMID:25815562

  18. A cohesive law for carbon nanotube/polymer interfaces based on the van der Waals force

    NASA Astrophysics Data System (ADS)

    Jiang, L. Y.; Huang, Y.; Jiang, H.; Ravichandran, G.; Gao, H.; Hwang, K. C.; Liu, B.

    2006-11-01

    We have established the cohesive law for interfaces between a carbon nanotube (CNT) and polymer that are not well bonded and are characterized by the van der Waals force. The tensile cohesive strength and cohesive energy are given in terms of the area density of carbon nanotube and volume density of polymer, as well as the parameters in the van der Waals force. For a CNT in an infinite polymer, the shear cohesive stress vanishes, and the tensile cohesive stress depends only on the opening displacement. For a CNT in a finite polymer matrix, the tensile cohesive stress remains the same, but the shear cohesive stress depends on both opening and sliding displacements, i.e., the tension/shear coupling. The simple, analytical expressions of the cohesive law are useful to study the interaction between CNT and polymer, such as in CNT-reinforced composites. The effect of polymer surface roughness on the cohesive law is also studied.

  19. van der Waals forces in density functional theory: Perturbational long-range electron-interaction corrections

    SciTech Connect

    Angyan, Janos G.; Gerber, Iann C.; Savin, Andreas; Toulouse, Julien

    2005-07-15

    Long-range exchange and correlation effects, responsible for the failure of currently used approximate density functionals in describing van der Waals forces, are taken into account explicitly after a separation of the electron-electron interaction in the Hamiltonian into short- and long-range components. We propose a 'range-separated hybrid' functional based on a local density approximation for the short-range exchange-correlation energy, combined with a long-range exact exchange energy. Long-range correlation effects are added by a second-order perturbational treatment. The resulting scheme is general and is particularly well adapted to describe van der Waals complexes, such as rare gas dimers.

  20. Microwave spectra of van der Waals complexes of importance in planetary atmospheres

    NASA Astrophysics Data System (ADS)

    Suenram, R. D.; Lovas, F. J.

    1990-05-01

    The Fourier-transform Fabry-Perot pulsed-molecular-beam microwave spectrometer at NIST was used to study the microwave spectra of a number of molecular dimers and trimers that may be present in planetary atmospheres. The weak van der Waals bonds associated with these species usually give rise to rotational-tunneling splittings in the microwave spectra. The microwave spectrum of the water dimer species was used to illustrate the complications that can arise in the study of the rotational spectra of these loosely bound species. In addition to the water dimer species, the microwave spectra of the following hydrogen-bonded and van der Waals complexes were studied: (CO2)2-H2O, CO2-(H2O)2, CO2-H2S, N2-H2O, CO-H2O, SO2-H2O, and O3-H2O.

  1. [Heinrich Hoffmann's Der Struwwelpeter (1845/1859): a parody on the romantic cult of childhood].

    PubMed

    Wesseling, Lies

    2006-01-01

    This article analyzes the cultural dynamics of the construction and deconstruction of childhood images, by means of a case study of Heinrich Hoffmann's classic picture book, Der Struwwelpeter (1845/1859). Childhood images are the joint product of sciences (especially anthropology, pedagogy and developmental psychology) and arts (especially painting, photography and (children's) literature). These images are historically variable, because childhood is the permanent target of idealization and demystification. This article interprets Der Struwwelpeter as a demystication of Romantic idealizations of childhood as propounded by Romantic Naturphilosophie and, more specifically, the pedagogy of Friedrich Fröbel (1772-1852). In my view, this picture book satirizes the developmentalism and the pastoryl idyll which informed the Romantic image of childhood, through its verbal and visual components. As I argue at length, this satire directly bears upon leading scientific and political controversies of Hoffmann's time. PMID:20681191

  2. Elution of human granulocytes from nylon fibers by means of repulsive van der Waals forces.

    PubMed

    Absolom, D R; van Oss, C J; Neumann, A W

    1981-01-01

    A novel method for the isolation of granulocytes from nylon fibers is described. It is modification of filtration leukapheresis based on cellular surface thermodynamics. The system takes into account both electrical and van der Waals forces. The elution buffer contains a chelating agent and a surface active agent which lowers the surface tension of the liquid to a value intermediate between that of the surface tensions of the nylon fibers and of the granulocytes. Thus, the attractive van der Waals interaction between the fibers and the granulocytes becomes a repulsion. This results in a two- to threefold increase in cell yield. Phagocytosis, candicidal activity, and oxygen consumption did not appear to be affected through the isolation procedure. By both light and transmission electron microscopy the isolated granulocytes appeared to be morphologically intact. PMID:7314214

  3. Steady dynamics of exothermic chemical wave fronts in van der Waals fluids.

    PubMed

    Dumazer, G; Antoine, C; Lemarchand, A; Nowakowski, B

    2009-12-01

    We study the steady dynamics of an exothermic Fisher-Kolmogorov-Petrovsky-Piskunov chemical wave front traveling in a one-dimensional van der Waals fluid. The propagating wave is initiated by a nonuniformity in reactant concentration contrary to usual combustion ignition processes. The heat release and activation energy of the reaction play the role of control parameters. We recently proved that the propagation of an exothermic chemical wave front in a perfect gas displays a forbidden interval of stationary wave front speeds [G. Dumazer, M. Leda, B. Nowakowski, and A. Lemarchand, Phys. Rev. E 78, 016309 (2008)]. We examine how this result is modified for nonideal fluids and determine the effect of the van der Waals parameters and fluid density on the bifurcation between diffusion flames and Chapman-Jouguet detonation waves as heat release increases. Analytical predictions are confirmed by the numerical solution of the hydrodynamic equations including reaction kinetics. PMID:20365269

  4. Energetics, dynamics, and reactions of rydberg state molecules in van der Waals clusters

    SciTech Connect

    Shang, Q.Y.; Bernstein, E.R.

    1994-12-31

    In the past 10 years the study of van der Waals clusters has grown enormously; perhaps one of the best indications of this growth, in both activity and sophistication, is the advent of this review issue devoted to such research. Van der Waals clusters, synthesized one molecule or atom at a time and accessed according to size and structure, provide a molecule by molecule view of the solvation process, its energetics, solute/solvent dynamics, and eventually even unimolecular and bimolecular chemical reactions. The clusters treated most frequently and discussed in this review are of the form solute or chromophore (solvent)n, with n varying from 1 to more than 100. These clusters are most typically generated in a supersonic beam; both large and small clusters can be synthesized by controlling the expansion conditions.

  5. Direct Measurement of the van der Waals Interaction between Two Rydberg Atoms

    NASA Astrophysics Data System (ADS)

    Béguin, L.; Vernier, A.; Chicireanu, R.; Lahaye, T.; Browaeys, A.

    2013-06-01

    We report the direct measurement of the van der Waals interaction between two isolated, single Rydberg atoms separated by a controlled distance of a few micrometers. Working in a regime where the single-atom Rabi frequency for excitation to the Rydberg state is comparable to the interaction, we observe partial Rydberg blockade, whereby the time-dependent populations of the various two-atom states exhibit coherent oscillations with several frequencies. Quantitative comparison of the data with a simple model based on the optical Bloch equations allows us to extract the van der Waals energy, and observe its characteristic C6/R6 dependence. The measured C6 coefficients agree well with ab initio calculations, and we observe their dramatic increase with the principal quantum number n of the Rydberg state.

  6. Exact traveling wave solutions of the van der Waals normal form for fluidized granular matter

    NASA Astrophysics Data System (ADS)

    Abourabia, A. M.; Morad, A. M.

    2015-11-01

    Analytical solutions of the van der Waals normal form for fluidized granular media have been done to study the phase separation phenomenon by using two different exact methods. The Painlevé analysis is discussed to illustrate the integrability of the model equation. An auto-Bäcklund transformation is presented via the truncated expansion and symbolic computation. The results show that the exact solutions of the model introduce solitary waves of different types. The solutions of the hydrodynamic model and the van der Waals equation exhibit a behavior similar to the one observed in molecular dynamic simulations such that two pairs of shock and rarefaction waves appear and move away, giving rise to the bubbles. The dispersion properties and the relation between group and phase velocities of the model equation are studied using the plane wave assumption. The diagrams are drawn to illustrate the physical properties of the exact solutions, and indicate their stability and bifurcation.

  7. Diffuse-interface modeling of liquid-vapor phase separation in a van der Waals fluid

    NASA Astrophysics Data System (ADS)

    Lamorgese, A. G.; Mauri, R.

    2009-04-01

    We simulate liquid-vapor phase separation in a van der Waals fluid that is deeply quenched into the unstable range of its phase diagram. Our theoretical approach follows the diffuse-interface model, where convection induced by phase change is accounted for via a nonequilibrium (Korteweg) force expressing the tendency of the liquid-vapor system to minimize its free energy. Spinodal decomposition patterns for critical and off-critical van der Waals fluids are studied numerically, revealing the scaling laws of the characteristic length scale and composition of single-phase microdomains, together with their dependence on the Reynolds number. Unlike phase separation of viscous binary mixtures, here local equilibrium is reached almost immediately after single-phase domains start to form. In addition, as predicted by scaling laws, such domains grow in time like t2/3. Comparison between 2D and 3D results reveals that 2D simulations capture, even quantitatively, the main features of the phenomenon.

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

    SciTech Connect

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

    2015-06-15

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

  9. Microwave spectra of van der Waals complexes of importance in planetary atmospheres

    NASA Technical Reports Server (NTRS)

    Suenram, R. D.; Lovas, F. J.

    1990-01-01

    The Fourier-transform Fabry-Perot pulsed-molecular-beam microwave spectrometer at NIST was used to study the microwave spectra of a number of molecular dimers and trimers that may be present in planetary atmospheres. The weak van der Waals bonds associated with these species usually give rise to rotational-tunneling splittings in the microwave spectra. The microwave spectrum of the water dimer species was used to illustrate the complications that can arise in the study of the rotational spectra of these loosely bound species. In addition to the water dimer species, the microwave spectra of the following hydrogen-bonded and van der Waals complexes were studied: (CO2)2-H2O, CO2-(H2O)2, CO2-H2S, N2-H2O, CO-H2O, SO2-H2O, and O3-H2O.

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

    NASA Astrophysics Data System (ADS)

    Wang, Xiaoming; Zebarjadi, Mona; Esfarjani, Keivan

    2016-08-01

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

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

    NASA Astrophysics Data System (ADS)

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

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

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

    NASA Astrophysics Data System (ADS)

    Quiros, Nancy; Tariq, Naima; Weinstein, Jonathan

    2016-05-01

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

  13. Van der Waals heterostructure of phosphorene and hexagonal boron nitride: First-principles modeling

    NASA Astrophysics Data System (ADS)

    Peng, Zhang; Jing, Wang; Xiang-Mei, Duan

    2016-03-01

    We have studied the structural and electronic properties of a hybrid hexagonal boron nitride with phosphorene nanocomposite using ab initio density functional calculations. It is found that the interaction between the hexagonal boron nitride and phosphorene is dominated by the weak van der Waals interaction, with their own intrinsic electronic properties preserved. Furthermore, the band gap of the nanocomposite is dependent on the interfacial distance. Our results could shed light on the design of new devices based on van der Waals heterostructure. Projected supported by the National Natural Science Foundation of China (Grant No. 11574167), the New Century 151 Talents Project of Zhejiang Province,China, and the K. C. Wong Magna Foundation in Ningbo University, China.

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

    NASA Astrophysics Data System (ADS)

    Wu, Jun; Gygi, François

    2012-06-01

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

  15. Stochastic bifurcations induced by correlated noise in a birhythmic van der Pol system

    NASA Astrophysics Data System (ADS)

    Mbakob Yonkeu, R.; Yamapi, R.; Filatrella, G.; Tchawoua, C.

    2016-04-01

    We investigate the effects of exponentially correlated noise on birhythmic van der Pol type oscillators. The analytical results are obtained applying the quasi-harmonic assumption to the Langevin equation to derive an approximated Fokker-Planck equation. This approach allows to analytically derive the probability distributions as well as the activation energies associated to switching between coexisting attractors. The stationary probability density function of the van der Pol oscillator reveals the influence of the correlation time on the dynamics. Stochastic bifurcations are discussed through a qualitative change of the stationary probability distribution, which indicates that noise intensity and correlation time can be treated as bifurcation parameters. Comparing the analytical and numerical results, we find good agreement both when the frequencies of the attractors are about equal or when they are markedly different.

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

    PubMed

    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. PMID:23742450

  17. Nuclear spin-spin coupling anisotropy in the van der Waals-bonded 129Xe dimer.

    PubMed

    Jokisaari, Jukka; Vaara, Juha

    2013-07-21

    The spin-spin coupling constant, J, in the van der Waals-bonded (129)Xe-(129)Xe dimer cannot be determined experimentally because of the magnetic equivalence of the two nuclei. In contrast, the anisotropy of the coupling tensor, ΔJ, can be obtained from the so called effective dipole-dipole coupling determined in a solid state inclusion compound whose cages accommodate two xenon atoms. For the determination of the experimental ΔJ((129)Xe, (129)Xe) we exploited the data reported earlier in this journal. [D. H. Brouwer et al., Phys. Chem. Chem. Phys., 2007, 9, 1093.] The experimental value and the value obtained from relativistic first-principles computation are in perfect agreement. To the best of our knowledge this is the first investigation of spin-spin coupling anisotropy in a van der Waals-bonded system. PMID:23743998

  18. Klassifikation von Standardebenen in der 2D-Echokardiographie mittels 2D-3D-Bildregistrierung

    NASA Astrophysics Data System (ADS)

    Bergmeir, Christoph; Subramanian, Navneeth

    Zum Zweck der Entwicklung eines Systems, das einen unerfahrenen Anwender von Ultraschall (US) zur Aufnahme relevanter anatomischer Strukturen leitet, untersuchen wir die Machbarkeit von 2D-US zu 3D-CT Registrierung. Wir verwenden US-Aufnahmen von Standardebenen des Herzens, welche zu einem 3D-CT-Modell registriert werden. Unser Algorithmus unterzieht sowohl die US-Bilder als auch den CT-Datensatz Vorverarbeitungsschritten, welche die Daten durch Segmentierung auf wesentliche Informationen in Form von Labein für Muskel und Blut reduzieren. Anschließend werden diese Label zur Registrierung mittels der Match-Cardinality-Metrik genutzt. Durch mehrmaliges Registrieren mit verschiedenen Initialisierungen ermitteln wir die im US-Bild sichtbare Standardebene. Wir evaluierten die Methode auf sieben US-Bildern von Standardebenen. Fünf davon wurden korrekt zugeordnet.

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

    NASA Astrophysics Data System (ADS)

    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.

  20. On the pseudopotential approximation in the van der Waals density functional calculations

    NASA Astrophysics Data System (ADS)

    Hamada, Ikutaro; Callsen, Martin

    The van der Waals density functional (vdW-DF) is a density functional that is able to describe van der Waals and covalent interactions in a seamless fashion, and has been applied to a variety of systems. In practical calculations, the pseudopotential (PP) approximation has been employed, for which the PPs should be generated consistently for the chosen exchange correlation XC functional. However, usually PPs generated with a generalized gradient approximation (GGA) XC functional are used and the effect of the approximation to the XC functional applied in the PP generation is scarcely discussed. In this work, we discuss the appropriate XC functionals in the PP generation for the vdW-DF calculations. Furthermore, we compare the vdW-DF results for several systems using the PP's generated with appropriate XC and those with GGA XC.

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

    SciTech Connect

    Coroiu, I.

    2007-04-23

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

  2. van der Waals epitaxy and photoresponse of two-dimensional CdSe plates.

    PubMed

    Zhu, Dan-Dan; Xia, Jing; Wang, Lei; Li, Xuan-Ze; Tian, Li-Feng; Meng, Xiang-Min

    2016-06-01

    Here we demonstrate the first growth of two-dimensional (2D) single-crystalline CdSe plates on mica substrates via van der Waals epitaxy. The as-synthesized 2D plates exhibit hexagonal, truncated triangular and triangular shapes with the lateral size around several microns. Photodetectors based on 2D CdSe plates present a fast response time of 24 ms, revealing that 2D CdSe is a promising building block for ultrathin optoelectronic devices. PMID:27199079

  3. Complex Dynamics in a Duffing-Van der Pol Oscillator with φ6 Potential

    NASA Astrophysics Data System (ADS)

    Yu, Jun; Xie, Zhi-kun; Yu, Li-xian

    2008-11-01

    The dynamical behavior of the extended Duffing-Van der Pol oscillator is investigated numerically in some detail. Different routes to chaos such as period-doubling bifurcation and intermittency, as well as various shapes of strange attractors and rich dynamical phenomena: crisis, transient chaos, are all observed by using bifurcation diagrams, phase projections and Poincaré maps. To characterize chaotic behavior of this oscillator system, the spectrum of Lyapunov exponent and Lyapunov dimension of the strange attractor are also employed.

  4. GENERAL: Period-Doubling Cascades and Strange Attractors in Extended Duffing-Van der Pol Oscillator

    NASA Astrophysics Data System (ADS)

    Yu, Jun; Pan, Wei-Zhen; Zhang, Rong-Bo

    2009-05-01

    The dynamical behavior of the extended Duffing-Van der Pol oscillator is investigated numerically in detail. With the aid of some numerical simulation tools such as bifurcation diagrams and Poincaré maps, the different routes to chaos and various shapes of strange attractors are observed. To characterize chaotic behavior of this oscillator system, the spectrum of Lyapunov exponent and Lyapunov dimension are also employed.

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

    DOE PAGESBeta

    Wang, Han; Bang, Junhyeok; Sun, Yiyang; West, Damien; Meunier, Vincent; Zhang, Shengbai; Liang, Linagbo

    2016-05-10

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

  6. The van der Waals interaction in one, two, and three dimensions

    NASA Astrophysics Data System (ADS)

    Ipsen, A. C.; Splittorff, K.

    2015-02-01

    The van der Waals interaction between two polarizable atoms is considered. In three dimensions, the standard form with an attractive 1/R6 potential is obtained from second-order quantum perturbation theory. When the electron motion is restricted to lower dimensions (but the 1/R Coulomb potential is retained), new terms in the expansion appear and alter both the sign and the R-dependence of the interaction.

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

    SciTech Connect

    Wang, Han; Bang, Junhyeok; Sun, Yiyang; Liang, Chen; Damien, West; Meunier, Vincent; Zhang, Prof. Shengbai

    2016-01-01

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

  8. van der Waals epitaxy and photoresponse of two-dimensional CdSe plates

    NASA Astrophysics Data System (ADS)

    Zhu, Dan-Dan; Xia, Jing; Wang, Lei; Li, Xuan-Ze; Tian, Li-Feng; Meng, Xiang-Min

    2016-06-01

    Here we demonstrate the first growth of two-dimensional (2D) single-crystalline CdSe plates on mica substrates via van der Waals epitaxy. The as-synthesized 2D plates exhibit hexagonal, truncated triangular and triangular shapes with the lateral size around several microns. Photodetectors based on 2D CdSe plates present a fast response time of 24 ms, revealing that 2D CdSe is a promising building block for ultrathin optoelectronic devices.

  9. Stability analysis for periodic solutions of the Van der Pol-Duffing forced oscillator

    NASA Astrophysics Data System (ADS)

    Cui, Jifeng; Liang, Jiaming; Lin, Zhiliang

    2016-01-01

    Based on the homotopy analysis method (HAM), the high accuracy frequency response curve and the stable/unstable periodic solutions of the Van der Pol-Duffing forced oscillator with the variation of the forced frequency are obtained and studied. The stability of the periodic solutions obtained is analyzed by use of Floquet theory. Furthermore, the results are validated in the light of spectral analysis and bifurcation theory.

  10. EXPERIMENTAL AND THEORETICAL STUDIES OF THE CN-AR VAN DER WAALS COMPLEX

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The CN-Ar van der Waals complex has been observed using B2E+-X2E+ and A2II-X2E+ electronic transitions. The spectra yielded a dissociation energy of D0"=109+2 cm1 and a zero point rational constant of B0"=0.067+0.005 cm-1 for CN(x)-Ar. The dissociation energy for Cn(A)-Ar was found to be D0"=132+2...

  11. Synchronization of coupled van der pole and Kislov-Dmitriev self-oscillators

    NASA Astrophysics Data System (ADS)

    Emel'Yanova, Yu. P.; Kuznetsov, A. P.

    2011-04-01

    The problem of interaction of self-oscillating elements of different origin is considered for a coupled van der Pole oscillator and Kislov-Dmitriev generator. Domains with different types of dynamics in the space of parameters are indicated taking into account the possibility of broadband synchronization of the systems. The case of essentially different control parameters is considered. Chaos stabilization effects and the opposite effect (initiated chaos) are detected in the system under investigation for various values of parameters.

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

    NASA Astrophysics Data System (ADS)

    Artemenko, Sergey; Lozovsky, Taras; Mazur, Victor

    2008-06-01

    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.

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

    PubMed

    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. PMID:25747746

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

    PubMed Central

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

    2016-01-01

    Two-dimensional layered transition metal dichalcogenides (TMDCs) show great potential for optoelectronic devices due to their electronic and optical properties. A metal-semiconductor interface, as epitaxial graphene - molybdenum disulfide (MoS2), is of great interest from the standpoint of fundamental science, as it constitutes an outstanding platform to investigate the interlayer interaction in van der Waals heterostructures. Here, we study large area MoS2-graphene-heterostructures formed by direct transfer of chemical-vapor deposited MoS2 layer onto epitaxial graphene/SiC. We show that via a direct transfer, which minimizes interface contamination, we can obtain high quality and homogeneous van der Waals heterostructures. Angle-resolved photoemission spectroscopy (ARPES) measurements combined with Density Functional Theory (DFT) calculations show that the transition from indirect to direct bandgap in monolayer MoS2 is maintained in these heterostructures due to the weak van der Waals interaction with epitaxial graphene. A downshift of the Raman 2D band of the graphene, an up shift of the A1g peak of MoS2 and a significant photoluminescence quenching are observed for both monolayer and bilayer MoS2 as a result of charge transfer from MoS2 to epitaxial graphene under illumination. Our work provides a possible route to modify the thin film TDMCs photoluminescence properties via substrate engineering for future device design. PMID:27246929

  15. A novel nanostructured biosensor for the detection of the dust mite antigen Der p2

    PubMed Central

    Tsai, Jaw-Ji; Bau, I-Jiuan; Chen, He-Tsing; Lin, Yu-Ta; Wang, Gou-Jen

    2011-01-01

    The group 2 allergen, Der p2, has been reported to activate innate toll-like receptors (TLRs) on respiratory epithelial cells and thus aggravate respiratory diseases. In this study, a highly sensitive nanostructured biosensor based on a 3D sensing element with uniformly deposited gold nanoparticles is proposed for the detection of the dust mite antigen Der p2. The barrier layer comprises an anodic aluminum oxide (AAO) film which is used as the template in this highly sensitive nanostructured biosensor. Simple electrochemical deposition without reducing agent and stabilizer was enough to uniformly synthesize gold nanoparticles on the surface of the barrier layer. The size and the distribution density of the nanoparticles can be well controlled by the applied potential during electrochemical deposition. Following this procedure, the dust mite monoclonal antibodies (IgG) were then immobilized through the 11-MUA (11-mercaptoundecanoic acid), (1-ethyl-3-(3-dimethyl-aminopropyl)-carbodiimide)/(N-hydroxysuccinimide) self-assembled monolayer approach for the dust mite antigen Der p2 detection. The detection limit of the proposed 3D gold nanoparticle-based nanostructured biosensor was examined using electrochemical impedance spectroscopy analysis and found to be 1 pg/mL. The dynamic range was found to be 5 μg/mL. The proposed nanostructured biosensor would be useful for fast detection of rare molecules in a solution. PMID:21822382

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

    PubMed Central

    Pizzocchero, Filippo; Gammelgaard, Lene; Jessen, Bjarke S.; Caridad, José M.; Wang, Lei; Hone, James; Bøggild, Peter; Booth, Timothy J.

    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 nitride with close to 100% yield. For the monolayer devices, we found semiclassical mean-free paths up to 0.9 μm, with the narrowest samples showing clear indications of the transport being affected by boundary scattering. The presented method readily lends itself to fabrication of van der Waals heterostructures in both ambient and controlled atmospheres, while the ability to assemble pre-patterned layers paves the way for complex three-dimensional architectures. PMID:27305833

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

    SciTech Connect

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

    2009-05-15

    In this paper, we present calculations of van der Waals/Casimir forces, described by Lifshitz theory, for the solid-liquid-solid system using measured dielectric functions of all involved materials for the wavelength range from millimeters down to subnanometers. It is shown that even if the dielectric function is known over all relevant frequency ranges, the scatter in the dielectric data can lead to very large scatter in the calculated van der Waals/Casimir forces. Especially when the liquid dielectric function becomes comparable in magnitude to the dielectric function of one of the interacting solids, the associated variation in the force can be up to a factor of 2 for plate-plate separations 5-500 nm. This corresponds to an uncertainty up to 100% in the theory prediction for a specific system. As a result accuracy testing of the Lifshitz theory under these circumstances is rather questionable. Finally we discuss predictions of Lifshitz theory regarding multiple repulsive-attractive transitions with separation distance, as well as nontrivial scaling of the van der Waals/Casimir force with distance.

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

    PubMed

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

    2016-01-01

    Two-dimensional layered transition metal dichalcogenides (TMDCs) show great potential for optoelectronic devices due to their electronic and optical properties. A metal-semiconductor interface, as epitaxial graphene - molybdenum disulfide (MoS2), is of great interest from the standpoint of fundamental science, as it constitutes an outstanding platform to investigate the interlayer interaction in van der Waals heterostructures. Here, we study large area MoS2-graphene-heterostructures formed by direct transfer of chemical-vapor deposited MoS2 layer onto epitaxial graphene/SiC. We show that via a direct transfer, which minimizes interface contamination, we can obtain high quality and homogeneous van der Waals heterostructures. Angle-resolved photoemission spectroscopy (ARPES) measurements combined with Density Functional Theory (DFT) calculations show that the transition from indirect to direct bandgap in monolayer MoS2 is maintained in these heterostructures due to the weak van der Waals interaction with epitaxial graphene. A downshift of the Raman 2D band of the graphene, an up shift of the A1g peak of MoS2 and a significant photoluminescence quenching are observed for both monolayer and bilayer MoS2 as a result of charge transfer from MoS2 to epitaxial graphene under illumination. Our work provides a possible route to modify the thin film TDMCs photoluminescence properties via substrate engineering for future device design. PMID:27246929

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

    NASA Astrophysics Data System (ADS)

    Ginoux, Jean-Marc; Letellier, Christophe

    2012-06-01

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

  20. Short-range Cut-Off of the Summed-Up van der Waals Series

    NASA Astrophysics Data System (ADS)

    Patra, Abhirup; Perdew, John P.

    2015-03-01

    van der Waals interactions are important in typical van der Waals-bound systems such as noble-gas, hydrocarbon, alkali and alkaline-earth dimers. The summed-up van der Waals series works well and gives an accurate result at large separation between two atoms. But it has a strong singularity at short non-zero separation, where the two atoms touch. In this work we remove that singularity with a reasonable and physical choice of the cut-off distance. Only one fitting parameter has been introduced for the short-range cut off. The parameter in our model has been optimized for each system, and a system-averaged value has been used to get the final binding energy curves. When this correction is added to the binding energy curve from the semilocal density functional meta-GGA-MS2, we get vdW- corrected binding energy curve. These curves are compared with the results of other vdW-corrected methods such as PBE-D2 and vdW-DF2 .Binding energy curves are in reasonable agreement with those from experiment. These curves also predict reasonably good equilibrium bond length. Supported by NSF (DMR).

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

    NASA Astrophysics Data System (ADS)

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

    2012-10-01

    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.

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

    NASA Technical Reports Server (NTRS)

    Rogers, Jan R.; Davis, Robert H.

    1990-01-01

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

  3. Study of van der Waals bonding and interactions in metal organic framework materials.

    PubMed

    Zuluaga, Sebastian; Canepa, Pieremanuele; Tan, Kui; Chabal, Yves J; Thonhauser, Timo

    2014-04-01

    Metal organic framework (MOF) materials have attracted a lot of attention due to their numerous applications in fields such as hydrogen storage, carbon capture and gas sequestration. In all these applications, van der Waals forces dominate the interaction between the small guest molecules and the walls of the MOFs. In this review article, we describe how a combined theoretical and experimental approach can successfully be used to study those weak interactions and elucidate the adsorption mechanisms important for various applications. On the theory side, we show that, while standard density functional theory is not capable of correctly describing van der Waals interactions, functionals especially designed to include van der Waals forces exist, yielding results in remarkable agreement with experiment. From the experimental point of view, we show examples in which IR adsorption and Raman spectroscopy are essential to study molecule/MOF interactions. Importantly, we emphasize throughout this review that a combination of theory and experiment is crucial to effectively gain further understanding. In particular, we review such combined studies for the adsorption mechanism of small molecules in MOFs, the chemical stability of MOFs under humid conditions, water cluster formation inside MOFs, and the diffusion of small molecules into MOFs. The understanding of these phenomena is critical for the rational design of new MOFs with desired properties. PMID:24613989

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

    PubMed

    Pizzocchero, Filippo; Gammelgaard, Lene; Jessen, Bjarke S; Caridad, José M; Wang, Lei; Hone, James; Bøggild, Peter; Booth, Timothy J

    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 nitride with close to 100% yield. For the monolayer devices, we found semiclassical mean-free paths up to 0.9 μm, with the narrowest samples showing clear indications of the transport being affected by boundary scattering. The presented method readily lends itself to fabrication of van der Waals heterostructures in both ambient and controlled atmospheres, while the ability to assemble pre-patterned layers paves the way for complex three-dimensional architectures. PMID:27305833

  5. Probabilistic characteristics of noisy Van der Pol type oscillator with nonlinear damping

    NASA Astrophysics Data System (ADS)

    Dubkov, A. A.; Litovsky, I. A.

    2016-05-01

    The exact Fokker–Planck equation for the joint probability distribution of amplitude and phase of a Van der Pol oscillator perturbed by both additive and multiplicative noise sources with arbitrary nonlinear damping is first derived by the method of functional splitting of averages. We truncate this equation in the usual manner using the smallness of the damping parameter and obtain a general expression for the stationary probability density function of oscillation amplitude, which is valid for any nonlinearity in the feedback loop of the oscillator. We analyze the dependence of this stationary solution on system parameters and intensities of noise sources for two different situations: (i) Van der Pol generator with soft and hard excitation regimes; (ii) Van der Pol oscillator with negative nonlinear damping. As shown, in the first case the probability distribution of amplitude demonstrates one characteristic maximum, which indicates the presence of a stable limit cycle in the system. The non-monotonic dependence of stationary probability density function on oscillation frequency is also detected. In the second case we examine separately three situations: linear oscillator with two noise sources, nonlinear oscillator with additive noise and nonlinear oscillator with frequency fluctuations. For the last two situations, noise-induced transitions in the system under consideration are found.

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

    NASA Astrophysics Data System (ADS)

    Sarkisov, Sergey Y.; Kosobutsky, Alexey V.; Shandakov, Sergey D.

    2015-12-01

    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/Å2).

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

    NASA Astrophysics Data System (ADS)

    Pizzocchero, Filippo; Gammelgaard, Lene; Jessen, Bjarke S.; Caridad, José M.; Wang, Lei; Hone, James; Bøggild, Peter; Booth, Timothy J.

    2016-06-01

    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 nitride with close to 100% yield. For the monolayer devices, we found semiclassical mean-free paths up to 0.9 μm, with the narrowest samples showing clear indications of the transport being affected by boundary scattering. The presented method readily lends itself to fabrication of van der Waals heterostructures in both ambient and controlled atmospheres, while the ability to assemble pre-patterned layers paves the way for complex three-dimensional architectures.

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

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

    NASA Astrophysics Data System (ADS)

    Lu, Bing-Sui; Podgornik, Rudolf

    2016-07-01

    We analyse van der Waals interactions between a pair of dielectrically anisotropic plane-layered media interacting across a dielectrically isotropic solvent medium. We develop a general formalism based on transfer matrices to investigate the van der Waals torque and force in the limit of weak birefringence and dielectric matching between the ordinary axes of the anisotropic layers and the solvent. We apply this formalism to study the following systems: (i) a pair of single anisotropic layers, (ii) a single anisotropic layer interacting with a multilayered slab consisting of alternating anisotropic and isotropic layers, and (iii) a pair of multilayered slabs each consisting of alternating anisotropic and isotropic layers, looking at the cases where the optic axes lie parallel and/or perpendicular to the plane of the layers. For the first case, the optic axes of the oppositely facing anisotropic layers of the two interacting slabs generally possess an angular mismatch, and within each multilayered slab the optic axes may either be the same or undergo constant angular increments across the anisotropic layers. In particular, we examine how the behaviors of the van der Waals torque and force can be "tuned" by adjusting the layer thicknesses, the relative angular increment within each slab, and the angular mismatch between the slabs.

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

    PubMed

    Lu, Bing-Sui; Podgornik, Rudolf

    2016-07-28

    We analyse van der Waals interactions between a pair of dielectrically anisotropic plane-layered media interacting across a dielectrically isotropic solvent medium. We develop a general formalism based on transfer matrices to investigate the van der Waals torque and force in the limit of weak birefringence and dielectric matching between the ordinary axes of the anisotropic layers and the solvent. We apply this formalism to study the following systems: (i) a pair of single anisotropic layers, (ii) a single anisotropic layer interacting with a multilayered slab consisting of alternating anisotropic and isotropic layers, and (iii) a pair of multilayered slabs each consisting of alternating anisotropic and isotropic layers, looking at the cases where the optic axes lie parallel and/or perpendicular to the plane of the layers. For the first case, the optic axes of the oppositely facing anisotropic layers of the two interacting slabs generally possess an angular mismatch, and within each multilayered slab the optic axes may either be the same or undergo constant angular increments across the anisotropic layers. In particular, we examine how the behaviors of the van der Waals torque and force can be "tuned" by adjusting the layer thicknesses, the relative angular increment within each slab, and the angular mismatch between the slabs. PMID:27475386

  11. Herausforderungen für künftige Lernumgebungen am Beispiel der Fakultät für Medizin

    NASA Astrophysics Data System (ADS)

    Gergintchev, Ivan; Graf, Stephan

    Nach der weit reichenden Etablierung von eLearning in den letzten Jahren stehen nahezu alle deutschen Hochschulen vor der Aufgabe, wettbewerbsfähige hochschulübergreifende Mechanismen sowie entsprechende organisatorische Rahmenbedingungen zu schaffen. Vor allem die Umsetzung von EBologna und die Unterstützung kooperativer Bildungsangebote verstärken diese Notwendigkeit. Motiviert durch die Veränderungen im Bereich der Hochschullehre und die Herausforderungen für künftige Lernumgebungen schlagen wir eine Integrationslösung im Sinne eines Learning Gateway vor, die zur webgestützten Abwicklung von kooperativen Bildungsangeboten in heterogen Lernumgebungen eingesetzt werden kann. Ihre Praxisanwendung verdeutlichen wir anschließend im komplexen Szenario der Medizin an der TUM. Die Evaluierung der Umsetzung belegt den deutlichen Mehrwert des Ansatzes.

  12. Characterization and analysis of a cDNA coding for the group 29b (Der f 29b) allergen of Dermatophagoides farinae

    PubMed Central

    Lin, Jianli; Wang, Hui; Li, Meng; Liang, Zhilin; Jiang, Congli; Wu, Yulan; Liu, Zhigang; Yang, Pingchang; Liu, Xiaoyu

    2016-01-01

    This study aims to acquire a recombinant allergen of Der f 29b by cloning and expression, and to identify its immunogenicity. In this study, the total RNA of D. farinae was extracted, cloned and expressed based on the Der f 29b gene. The molecular characteristics of Der f 29b was analyzed by the procedures of Bioinformatics. The allergenicity of recombinant Der f 29b protein was examined by western-blotting, ELISA, Immune inhibitory assays and skin prick test. The gene of Der f 29b consisted of 495 bases, derived from its nucleic acid sequence and encoded 164 amino acids. Positive responses to r-Der f 29b were shown in 24.3% by means of skin prick testing with 37 DM-allergic patients. The immunoblotting assays demonstrated that serum IgE from allergic patients reacted to r-Der f 29b protein. The IgE reactivity of r-Der f 29b in the serum from r-Der f 29b allergic patients was increased by more than 2 folds compared with healthy subjects. Immune inhibition assays showed that the IgE cross-reactivity was between r-Der f 29b and DME. Bioinformatics analysis predicted four peptides (13-17, 67-71, 104-109 and 147-155) as the B cell epitopes and five peptides (5-14, 16-31, 35-43, 52-63 and 87-97) as the T cell epitopes. Secondary structure prediction of Der f 29b with software PSIPRED identified two α-helices and seven β-sheets in Der f 29b. In conclusion, Derf 29b protein was identified as a novel subtype of dust mite allergen. PMID:27158348

  13. An Analysis of the DER Adoption Climate in Japan UsingOptimization Results for Prototype Buildings with U.S. Comparisons

    SciTech Connect

    Zhou, Nan; Marnay, Chris; Firestone, Ryan; Gao, Weijun; Nishida,Masaru

    2006-06-16

    This research demonstrates economically optimal distributedenergy resource (DER) system choice using the DER choice and operationsoptimization program, the Distributed Energy Resources Customer AdoptionModel (DER-CAM). DER-CAM finds the optimal combination of installedequipment given prevailing utility tariffs and fuel prices, siteelectrical and thermal loads (including absorption cooling), and a menuof available equipment. It provides a global optimization, albeitidealized, that shows how site useful energy loads can be served atminimum cost. Five prototype Japanese commercial buildings are examinedand DER-CAM is applied to select the economically optimal DER system foreach. Based on the optimization results, energy and emission reductionsare evaluated. Significant decreases in fuel consumption, carbonemissions, and energy costs were seen in the DER-CAM results. Savingswere most noticeable in the prototype sports facility, followed by thehospital, hotel, and office building. Results show that DER with combinedheat and power equipment is a promising efficiency and carbon mitigationstrategy, but that precise system design is necessary. Furthermore, aJapan-U.S. comparison study of policy, technology, and utility tariffsrelevant to DER installation is presented.

  14. 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

    NASA Astrophysics Data System (ADS)

    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

  15. Crystallization and Preliminary X-ray Analysis of Der f 2, a Potent Allergen Derived from the House Dust Mite

    NASA Technical Reports Server (NTRS)

    Roeber, Dana; Achari, Aniruddha; Takai, Toshiro; Okumura, Yasushi; Scott, David L.; Curreri, Peter (Technical Monitor)

    2002-01-01

    Although a number of allergens have been identified and isolated, the underlying molecular basis for the potent immune response is poorly understood. House dust mites (Dermatophugoides sp.) are particularly ubiquitous contributors to atopy in developed countries. The rhinitis, dermatitis, and asthma associated with allergic reactions to these arthropods are often caused by relatively small (125-129 amino acids) mite proteins of unclear biological function. Der f 2, a major allergen from the mite Dermatophagoides farinae, has been recombinantly expressed and characterized. The Der f 2 protein has been crystallized in our laboratory and a native data set collected at a synchrotron source. The crystals belong to the orthorhombic space group I422 with unit cell parameters of a = 95.2 Angstroms, b = 95.2 Angstroms, and c = 103.3 Angstroms. An essentially complete (97.2%) data set has been collected to 2.4 Angstroms. Attempts to solve the crystal structure of Der f 2 by molecular replacement using the available NMR coordinates for either Der f 2 or Der p 2 (the homologous protein from D. pterovssinus) failed to reveal a creditable solution.

  16. [A Comparative Analysis of Shushi-Sanbaron and the Original German Textbook Lehrbuch der Hebammenkunst].

    PubMed

    Tsukisawa, Miyoko

    2015-12-01

    In this paper we present a comparative analysis of Shushi-Sanbaron (Japanese characters) and the original book, Lehrbuch der Hebammenkunst. After the legal reorganisation of the medical professions in Germany in the mid nineteenth century, the textbook Lehrbuch der Hebammenkunst was published for certified midwives. This book has two distinct characteristics; it was written from the physician's standpoint regarding the importance of the professional hierarchy of obstetricians and midwives, and it also served as a practical educator for midwives. Lehrbuch der Hebammenkunst was translated into Japanese for use as a textbook after the introduction of systematised education for certified midwives by the Tokyo-fu Hospital. It was published between 1877 and 1878 under title Shushi-Sanbaron. We clarify that Shushi-Sanbaron was not a literal translation of the original book, but was largely rewritten by two physicians in order to modify it to the Japanese situation after the introduction of modern medicine. Japanese physicians made serious modifications of the chapters that dealt with deviations from the regular course of birth and abnormal conditions of postpartum women and new-born babies, and they added theoretical explanations about obstetrics. As a result, Shushi-Sanbaron made two contradicting demands to midwives. On the one hand, midwives were urged to attain high-level theoretical knowledge and skill in obstetrics in order to--independently--help pregnant women and new-born babies in a crisis. On the other hand, as lower participants in the medical hierarchy, they were told to assume a dependent and uncritical attitude towards physicians. PMID:27089735

  17. Optimization of a Der p 2-based prophylactic DNA vaccine against house dust mite allergy.

    PubMed

    Pulsawat, Pinya; Pitakpolrat, Patrawadee; Prompetchara, Eakachai; Kaewamatawong, Theerayuth; Techakriengkrai, Navapon; Sirivichayakul, Sunee; Buranapraditkun, Supranee; Hannaman, Drew; Ruxrungtham, Kiat; Jacquet, Alain

    2013-03-01

    DNA vaccines encoding allergens are promising immunotherapeutics to prevent or to treat allergy through induction of allergen-specific Th1 responses. Despite anti-allergy effects observed in small rodents, DNA-based vaccines are weak immunogens in primates and humans and particularly when administered by conventional injection. The goal of the present study was to improve the immunogenicity of a prophylactic vaccine encoding the major house dust mite allergen Der p 2. In this context, we evaluated the influence of different DNA backbones including notably intron and CpG enriched sequence, the DNA dose, the in vivo delivery by electroporation as well as the heterologous prime boost regimen on the vaccine efficiency. We found that a minimal allergen expression level threshold must be reached to induce the production of specific antibodies but beyond this limit, the intensity of the immune response was independent on the DNA dose and allergen expression. The in vivo DNA delivery by electroporation drastically enhanced the production of specific antibodies but not the IFNg secretion. Vaccination of naïve mice with DNA encoding Der p 2 delivered by electroporation even at very low dose (2μg) prevented the development of house dust mite allergy through Th1-skewed immune response characterized by the drastic reduction of allergen-specific IgE, IL-5 and lung inflammation together with the induction of strong specific IgG2a titers and IFNg secretion. CpG cassette in the DNA backbone does not play a critical role in the efficient prophylaxis. Finally, comparable protective immune responses were observed when using heterologous DNA prime/protein boost or homologous DNA prime/boost. Taken together, these data suggest that the potent Th1 response induced by DNA-based vaccine encoding allergens through electroporation provides the rationale for the evaluation of DNA encoding Der p 2 into HDM allergy clinical trials. PMID:23396105

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

    NASA Astrophysics Data System (ADS)

    Yankowitz, Matthew Abraham

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

  19. The Dielectric Function for Water and Its Application to van der Waals Forces.

    PubMed

    Dagastine; Prieve; White

    2000-11-15

    The dielectric response, varepsilon(ixi), for water (which is required in Lifshitz theory to calculate the van der Waals interactions in aqueous systems) is commonly constructed, in the absence of complete spectral data, by fitting a damped-harmonic-oscillator model to absorption data. Two sets of parameters for the model have been developed corresponding to different constraints: Parsegian and Weiss (J. Colloid Interface Sci., 1981, 81, 285) and Roth and Lenhoff (J. Colloid Interface Sci., 1996, 179, 637). These different representations of the dielectric response lead to significant differences in the van der Waals force calculated from Lifshitz theory. In this work, more recent and complete spectral data for water were compiled from the literature and direct integration of the Kramers-Kronig relations was used to construct a new varepsilon(ixi) for water at 298 degrees K. This approach also allows a number of different types of spectral measurements (such as infrared spectroscopy, microwave resonance techniques, and x-ray inelastic scattering) in the compilation of absorption data over a large frequency range (on the order of 8 to 10 decades in frequency). A Kramers-Kronig integration was employed to construct the real and imaginary parts of varepsilon(omega), varepsilon'(omega), and varepsilon"(omega) for water from the different spectral measurements before calculation of varepsilon(ixi) from its integral definition. The resulting new varepsilon(ixi) is intermediate between the Parsegian-Weiss and Roth-Lenhoff representations of varepsilon(ixi), does not use a model, and treats the conversion of absorption data as rigorously as possible. We believe the varepsilon(ixi) from the present work is the most reliable construction for use in van der Waals force calculations using Lifshitz theory. The extension of the varepsilon(ixi) construction to other temperatures is also discussed. Copyright 2000 Academic Press. PMID:11049685

  20. Microwave and ab initio studies of rare gas-methane van der Waals complexes

    NASA Astrophysics Data System (ADS)

    Liu, Yaqian; Jäger, Wolfgang

    2004-05-01

    Rotational spectra of the weakly bound Kr-methane van der Waals complex were recorded using a pulsed molecular beam Fourier transform microwave spectrometer in the range from 3.5 to 18 GHz. Spectra of 25 isotopomers of Kr-methane were assigned and analyzed. For isotopomers containing CH4, 13CH4, and CD4, two sets of transitions with K=0 and one with K=1 were recorded, correlating to the j=0, 1, and 2 rotational levels of free methane, respectively (j is the rotational angular momentum quantum number of the methane monomer). For isotopomers containing CH3D and CHD3, two K=0 components were recorded, correlating to the jk=00 and 11 rotational levels of free methane (k corresponds to the projection of j onto the C3 axis of CH3D and CHD3). The obtained spectroscopic results were used to derive van der Waals bond distance R, van der Waals stretching frequency νs, and the corresponding stretching force constant ks. Nuclear spin statistical weights of individual states were obtained from molecular symmetry group analyses and were compared with the observed relative transition intensities. The tentatively assigned j=2 transitions were more intense than predicted from symmetry considerations. This is attributed to a relatively large effective dipole moment of this state, supported by ab initio dipole moment calculations. Ab initio potential energy calculations of Kr-CH4 and Ar-CH4 were done at the coupled cluster level of theory, with single and double excitations and perturbative inclusion of triple excitations, using the aug-cc-pVTZ basis set supplemented with bond functions. The theoretical results show that the angular dynamics of the dimer does not change significantly when the binding partner of methane changes from Ar to Kr. The dipole moment of Ar-CH4 was calculated at various configurations, providing a qualitative explanation for the unsuccessful spectral searches for rotational transitions of Ar-CH4.

  1. Der1-mediated preprotein import into the periplastid compartment of chromalveolates?

    PubMed

    Sommer, Maik S; Gould, Sven B; Lehmann, Petra; Gruber, Ansgar; Przyborski, Jude M; Maier, Uwe-G

    2007-04-01

    Phototrophic chromalveolates possess plastids surrounded by either 3 or 4 membranes, revealing their secondary endosymbiotic origin from an engulfed eukaryotic alga. In cryptophytes, a member of the chromalveolates, the organelle is embedded within a designated region of the host's rough endoplasmic reticulum (RER). Its eukaryotic compartments other than the plastid were reduced to the mere remains of its former cytosol, the periplastid compartment (PPC, PP space), and its nucleus, the nucleomorph, separated from the RER by its former plasma membrane, the periplast membrane (PPM). In the nucleomorph genome of the cryptophyte Guillardia theta, we identified several genes sharing homology with components of the ER-associated degradation (ERAD) machinery of yeast and higher eukaryotes, namely ORF201 and ORF477, homologs of membrane-bound proteins, Der1p (Degradation in the ER protein 1) and the RING-finger ubiquitin ligase Hrd1, and a truncated version of Udf1, a cofactor of Cdc48, a lumenal ATPase. Exemplarily, studies on the Der1-homolog ORF201 showed that this protein partially rescued a yeast deletion mutant, indicating the existence of a functional PPC-specific ERAD-like system in cryptophytes. With the noninvestigated exception of haptophytes a phylogenetically and mechanistically related system is apparently present in all chromalveolates with 4 membrane-bound plastids because amongst others, PPC-specific Derlins (Der1-like proteins), CDC48 and its cofactor Ufd1 were identified in the nuclear genomes of diatoms and apicomplexa. These proteins are equipped with the required topogenic signals to direct them into the periplastid compartment of their secondary symbionts. Based on our findings, we suggest that all chromalveolates with 4 membrane-bound plastids express an ERAD-derived machinery in the PPM of their secondary plastid, coexisting physically and systematically adjacent to the host's own ERAD system. We propose herewith that this system was functionally

  2. Das Lektin aus der Erbse Pisum sativum : Bindungsstudien, Monomer-Dimer-Gleichgewicht und Rückfaltung aus Fragmenten

    NASA Astrophysics Data System (ADS)

    Küster, Frank

    2002-11-01

    Das Lektin aus Pisum sativum, der Gartenerbse, ist Teil der Familie der Leguminosenlektine. Diese Proteine haben untereinander eine hohe Sequenzhomologie, und die Struktur ihrer Monomere, ein all-ß-Motiv, ist hoch konserviert. Dagegen gibt es innerhalb der Familie eine große Vielfalt an unterschiedlichen Quartärstrukturen, die Gegenstand kristallographischer und theoretischer Arbeiten waren. Das Erbsenlektin ist ein dimeres Leguminosenlektin mit einer Besonderheit in seiner Struktur: Nach der Faltung in der Zelle wird aus einem Loop eine kurze Aminosäuresequenz herausgeschnitten, so dass sich in jeder Untereinheit zwei unabhängige Polypeptidketten befinden. Beide Ketten sind aber stark miteinander verschränkt und bilden eine gemeinsame strukturelle Domäne. Wie alle Lektine bindet Erbsenlektin komplexe Oligosaccharide, doch sind seine physiologische Rolle und der natürliche Ligand unbekannt. In dieser Arbeit wurden Versuche zur Entwicklung eines Funktionstests für Erbsenlektin durchgeführt und seine Faltung, Stabilität und Monomer-Dimer-Gleichgewicht charakterisiert. Um die spezifische Rolle der Prozessierung für Stabilität und Faltung zu untersuchen, wurde ein unprozessiertes Konstrukt in E. coli exprimiert und mit der prozessierten Form verglichen. Beide Proteine zeigen die gleiche kinetische Stabilität gegenüber chemischer Denaturierung. Sie denaturieren extrem langsam, weil nur die isolierten Untereinheiten entfalten können und das Monomer-Dimer-Gleichgewicht bei mittleren Konzentrationen an Denaturierungsmittel auf der Seite der Dimere liegt. Durch die extrem langsame Entfaltung zeigen beide Proteine eine apparente Hysterese im Gleichgewichtsübergang, und es ist nicht möglich, die thermodynamische Stabilität zu bestimmen. Die Stabilität und die Geschwindigkeit der Assoziation und Dissoziation in die prozessierten bzw. nichtprozessierten Untereinheiten sind für beide Proteine gleich. Darüber hinaus konnte gezeigt werden, dass auch unter

  3. Sitzungsberichte der Heidelberger Akademie der Wissenschaften¬Jahrgang 1990 Sitzungsber.Heidelberg 90¬"Gott hat die Natur einfältig gemacht, sie aber suchen viel Künste"

    NASA Astrophysics Data System (ADS)

    Zehe, Horst

    Der Aufsatz demonstriert anhand ausgiebig kommentierter zeitgenössischer Zeugnisse Goethes Reaktion auf die Arbeiten Fraunhofers, insbesondere auf die Entdeckung der dunklen Linien im Sonnenspektrum. Den Fehlurteilen Goethes werden dabei die Urteile zeitgenössischer Physiker wie Chladni und J.F.W. Herschel gegenübergestellt. Bislang noch ungedruckte Dokumente aus dem Weimarer Goethe- und Schiller-Archiv belegen, daß sich Goethe nicht nur literarisch mit Fraunhofer beschäftigte, sondern daß er auch dessen Versuche mit Hilfe des Jenaer Universitätsmechanikers Körner getreulich zu wiederholen suchte.

  4. Construction of van der Waals magnetic tunnel junction using ferromagnetic layered dichalcogenide

    SciTech Connect

    Arai, Miho; Moriya, Rai Yabuki, Naoto; Masubuchi, Satoru; Ueno, Keiji; Machida, Tomoki

    2015-09-07

    We investigate the micromechanical exfoliation and van der Waals (vdW) assembly of ferromagnetic layered dichalcogenide Fe{sub 0.25}TaS{sub 2}. The vdW interlayer coupling at the Fe-intercalated plane of Fe{sub 0.25}TaS{sub 2} allows exfoliation of flakes. A vdW junction between the cleaved crystal surfaces is constructed by dry transfer method. We observe tunnel magnetoresistance in the resulting junction under an external magnetic field applied perpendicular to the plane, demonstrating spin-polarized tunneling between the ferromagnetic layered material and the vdW junction.

  5. Stability of an attractive bosonic cloud with van der Waals interaction

    SciTech Connect

    Biswas, Anindya; Das, Tapan Kumar; Salasnich, Luca; Chakrabarti, Barnali

    2010-10-15

    We investigate the structure and stability of Bose-Einstein condensates of {sup 7}Li atoms with realistic van der Waals interactions by using the potential harmonic expansion method. Besides the known low-density metastable solution with a contact {delta}-function interaction, we find a stable branch at a higher density which corresponds to the formation of an atomic cluster. Comparison with the results of a nonlocal effective interaction is also presented. We analyze the effect of trap size on the transition between the two branches of solutions. We also compute the loss rate of a Bose condensate due to two- and three-body collisions.

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

    NASA Astrophysics Data System (ADS)

    Lin, Yu-Chuan; Ghosh, Ram Krishna; Addou, Rafik; Lu, Ning; Eichfeld, Sarah M.; Zhu, Hui; Li, Ming-Yang; Peng, Xin; Kim, Moon J.; Li, Lain-Jong; Wallace, Robert M.; Datta, Suman; Robinson, Joshua A.

    2015-06-01

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

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

    NASA Astrophysics Data System (ADS)

    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.

  8. Rare and hidden attractors in Van der Pol-Duffing oscillators

    NASA Astrophysics Data System (ADS)

    Brezetskyi, S.; Dudkowski, D.; Kapitaniak, T.

    2015-07-01

    We study the dynamics of the single and coupled van der Pol-Duffing oscillators. Each oscillator is characterized by the multistability (the coexistence of attractors). Some of the coexisting attractors have very small basins of attraction (the rare ones) and some of them do not contain equilibria in their basin of attraction (the hidden ones). We perform the detailed bifurcation analysis of these attractors and investigate how this plethora of states influences the dynamics of the network of coupled oscillators. We have observed the cluster synchronization on different attractors as well as different types of chimera states.

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

    PubMed

    Lin, Yu-Chuan; Ghosh, Ram Krishna; Addou, Rafik; Lu, Ning; Eichfeld, Sarah M; Zhu, Hui; Li, Ming-Yang; Peng, Xin; Kim, Moon J; Li, Lain-Jong; Wallace, Robert M; Datta, Suman; Robinson, Joshua A

    2015-01-01

    Vertical integration of two-dimensional van der Waals materials is predicted to lead to novel electronic and optical properties not found in the constituent layers. Here, we present the direct synthesis of two unique, atomically thin, multi-junction heterostructures by combining graphene with the monolayer transition-metal dichalcogenides: molybdenum disulfide (MoS2), molybdenum diselenide (MoSe2) and tungsten diselenide (WSe2). The realization of MoS2-WSe2-graphene and WSe2-MoS2-graphene heterostructures leads to resonant tunnelling in an atomically thin stack with spectrally narrow, room temperature negative differential resistance characteristics. PMID:26088295

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

    SciTech Connect

    Xia, Congxin Xue, Bin; Wang, Tianxing; Peng, Yuting; Jia, Yu

    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.

  11. Observing the interplay between surface and bulk optical nonlinearities in thin van der Waals crystals

    PubMed Central

    Deckoff-Jones, Skylar; Zhang, Jingjing; Petoukhoff, Christopher E.; Man, Michael K.L.; Lei, Sidong; Vajtai, Robert; Ajayan, Pulickel M.; Talbayev, Diyar; Madéo, Julien; Dani, Keshav M.

    2016-01-01

    Van der Waals materials, existing in a range of thicknesses from monolayer to bulk, allow for interplay between surface and bulk nonlinearities, which otherwise dominate only at atomically-thin or bulk extremes, respectively. Here, we observe an unexpected peak in intensity of the generated second harmonic signal versus the thickness of Indium Selenide crystals, in contrast to the quadratic increase expected from thin crystals. We explain this by interference effects between surface and bulk nonlinearities, which offer a new handle on engineering the nonlinear optical response of 2D materials and their heterostructures. PMID:26936437

  12. Spectroscopy of DABCO-rare-gas and DABCO-DABCO van der Waals complexes

    NASA Astrophysics Data System (ADS)

    van den Hock, G.; Consalvo, D.; Parker, D. H.; Reuss, J.

    1993-03-01

    The excited electronic origin bands of several DABCO containing van der Waals complexes have been observed via (1+1) resonance enhanced multi-photon ionization. Sharp resonances with widths of about 3 cm-1 are seen for DABCO-Rg n=1,2,3 (Rg is Ar, Kr or Xe), for the DABCO-DABCO dimer and for DABCO-DABCO-Ar. The origins of the rare-gas complexes are blue shifted with respect to the monomer origin. Broad features originating from DABCO-Rg n complexes with high n, appear to higher energies than the complex origins, with widths of 120 cm-1.

  13. The effect of various types of periodic random excitations on the Van der Pol system

    NASA Astrophysics Data System (ADS)

    Nguyen, D. A.

    1986-02-01

    Random oscillations in a Van der Pol system characterized by random and periodic external excitation with a periodically varying natural frequency or by random and periodic parametric excitation are analyzed using the Krylov-Bogoliubov-Mitropolskii asymptotic methods and the method of Fokker-Planck-Kolmogorov equations. It is shown that in the system investigated, the integrability condition for the averaged Fokker-Planck-Kolmogorov equations is satisfied. Exact amplitude and phase probability densities are obtained, which are then used to analyze the oscillation characteristics.

  14. New species and records of Metriocnemus van der Wulp s. str. from China (Diptera, Chironomidae)

    PubMed Central

    Li, Xing; Wang, Xin-hua

    2014-01-01

    Abstract The Chinese species of Metriocnemus van der Wulp s. str., 1874 is reviewed. M. (M.) calcaneum sp. n. is described and illustrated as adult male. M. (M.) albolineatus (Meigen) is recorded from China for the first time. M. (M.) beringensis (Cranston & Oliver), M. (M.) bilobatus Makarchenko & Makarchenko, M. (M.) caudigus Sæther, M. (M.) intergerivus Sæther, M. (M.) tamaokui Sasa and M. (M.) tristellus Edwards are recorded from the Oriental Region for the first time. A key to the males of 17 Chinese Metriocnemus (Metriocnemus) species is given. PMID:24693220

  15. Families at risk: comment on Dirkzwager, Bramsen, Adèr, and van der Ploeg (2005).

    PubMed

    Fairbank, John A; Fairbank, Doreen W

    2005-06-01

    New findings from a study by A. J. E. Dirkzwager, I. Bramsen, H. Adèr, and H. M. van der Ploeg (2005; see record 2005-06518-006) provide important empirical information on the adverse psychological and functional adjustment of families of former Dutch peacekeepers suffering from posttraumatic stress disorder (PTSD). In this comment the authors consider a few methodological limitations and issues for future study, including the need for intergenerational studies of the legacy of peacekeeping-related PTSD. Attention to considering the treatment needs of families of traumatized former peacekeepers is encouraged. PMID:15982099

  16. Effects of zero van der Waals and zero electrostatic forces on droplet sedimentation

    NASA Technical Reports Server (NTRS)

    Omenyi, S. N.; Snyder, R. S.; Van Oss, C. J.; Absolom, D. R.; Neumann, A. W.

    1981-01-01

    The present investigation provides a confirmation of the dependence of droplet sedimentation on particle concentration. It is shown that it is possible to determine the maximum particle concentration which can remain stable on a given liquid from droplet sedimentation experiments. Droplet sedimentation can be reduced but not totally eliminated by the addition of appropriate amounts of dimethyl sulfoxide (DMSO) to reduce the van der Waals forces to zero. It was found that, at 12% DMSO, a maximum particle concentration of 6.3 x 10 to the 8th cells/ml of glutaraldehyde-fixed human erythrocytes suspended in physiological saline can remain stable on a D2O cushion.

  17. System for absolute measurement of electrolytic conductivity in aqueous solutions based on van der Pauw's theory

    NASA Astrophysics Data System (ADS)

    Zhang, Bing; Lin, Zhen; Zhang, Xiao; Yu, Xiang; Wei, Jiali; Wang, Xiaoping

    2014-05-01

    Based on an innovative application of van der Pauw's theory, a system was developed for the absolute measurement of electrolytic conductivity in aqueous solutions. An electrolytic conductivity meter was designed that uses a four-electrode system with an axial-radial two-dimensional adjustment structure coupled to an ac voltage excitation source and signal collecting circuit. The measurement accuracy, resolution and repeatability of the measurement system were examined through a series of experiments. Moreover, the measurement system and a high-precision electrolytic conductivity meter were compared using some actual water samples.

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

    PubMed

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

    2003-08-20

    A single crystal of a low density form of guest-free p-tert-butylcalix[4]arene can take up and release small guest molecules by controlling the temperature and pressure without changing the structure. Using NMR spectroscopy with flowing hyperpolarized xenon, we have shown that at room temperature access of xenon to the pore system is difficult, whereas it is relatively easy at 100 degrees C. There are good prospects for simple van der Waals materials such as the title material to be used as programmable zeolite mimics. PMID:12914432

  19. Ground-state van der Waals forces in planar multilayer magnetodielectrics

    SciTech Connect

    Buhmann, Stefan Yoshi; Welsch, Dirk-Gunnar; Kampf, Thomas

    2005-09-15

    Within the frame of lowest-order perturbation theory, the van der Waals potential of a ground-state atom placed within an arbitrary dispersing and absorbing magnetodielectric multilayer system is given. Examples of an atom situated in front of a magnetodielectric plate or between two such plates are studied in detail. Special emphasis is placed on the competing attractive and repulsive force components associated with the electric and magnetic matter properties, respectively, and conditions for the formation of repulsive potential walls are given. Both numerical and analytical results are presented.

  20. Observing the interplay between surface and bulk optical nonlinearities in thin van der Waals crystals

    NASA Astrophysics Data System (ADS)

    Deckoff-Jones, Skylar; Zhang, Jingjing; Petoukhoff, Christopher E.; Man, Michael K. L.; Lei, Sidong; Vajtai, Robert; Ajayan, Pulickel M.; Talbayev, Diyar; Madéo, Julien; Dani, Keshav M.

    2016-03-01

    Van der Waals materials, existing in a range of thicknesses from monolayer to bulk, allow for interplay between surface and bulk nonlinearities, which otherwise dominate only at atomically-thin or bulk extremes, respectively. Here, we observe an unexpected peak in intensity of the generated second harmonic signal versus the thickness of Indium Selenide crystals, in contrast to the quadratic increase expected from thin crystals. We explain this by interference effects between surface and bulk nonlinearities, which offer a new handle on engineering the nonlinear optical response of 2D materials and their heterostructures.

  1. Erfahrungen im Aufbau des IT Service Desks der Technischen Universität München

    NASA Astrophysics Data System (ADS)

    Vellguth, Karmela

    Durch das Projekt IntegraTUM und die darin eingebettete Einrichtung eines IT Service Desks mit 1st, 2nd und 3rd Level Support gelang eine an ITIL orientierte Neuausrichtung der internen IT-Dienstleistungen. Die vormals existierende Struktur mit einer Vielzahl an Ansprechpartnern bei auftretenden IT-Problemen wurde aufgelöst. Die Nutzer haben nun eine Anlaufstelle erhalten, die sich für die Beantwortung aller Incidents in kürzester Zeit und mit qualitativ hohem Niveau zuständig fühlt.

  2. Microwaves Probe Dipole Blockade and van der Waals Forces in a Cold Rydberg Gas.

    PubMed

    Teixeira, R Celistrino; Hermann-Avigliano, C; Nguyen, T L; Cantat-Moltrecht, T; Raimond, J M; Haroche, S; Gleyzes, S; Brune, M

    2015-07-01

    We show that microwave spectroscopy of a dense Rydberg gas trapped on a superconducting atom chip in the dipole blockade regime reveals directly the dipole-dipole many-body interaction energy spectrum. We use this method to investigate the expansion of the Rydberg cloud under the effect of repulsive van der Waals forces and the breakdown of the frozen gas approximation. This study opens a promising route for quantum simulation of many-body systems and quantum information transport in chains of strongly interacting Rydberg atoms. PMID:26182093

  3. Infrared vibrational predissociation of van der Waals clusters: applications to isotope separation

    SciTech Connect

    Philippoz, J.M.; Zellweger, J.M.; van den Bergh, H.; Monot, R.

    1984-08-30

    Isotope separation is demonstrated following the selective infrared laser-induced photodissociation of van der Waals clusters in a free jet. Irradiation of a natural abundance mixture of SF/sub 6/ isotopomers diluted in argon with a 20-W cw CO/sub 2/ laser gives overall enrichment factors in excess of 1.1. By adjusting the wavelength one can either enrich or deplete the center of the free jet in any one of the sulfur isotopes. Furthermore, unselective photodissociation of clusters can be used to enhance the separation of isotopes in a recently reported selective condensation method. 8 references, 3 figures.

  4. 3D van der Waals σ-model and its topological excitations

    NASA Astrophysics Data System (ADS)

    Bulgadaev, S. A.

    2001-09-01

    It is shown that the 3D vector van der Waals nonlinear σ-model (NSM) on a sphere S2 has two types of topological excitations: reminiscent vortices and instantons of 2D NSM. The first ones, the hedgehogs, are described by the homotopic group π2(S2) = Z and have logarithmic energies. They are an analog of 2D vortices. The second ones, corresponding to 2D instantons, are the hopfions. They are described by the homotopic group π3(S2) = Z, or the Hopf invariant HinZ, and have finite energy. The possibility of a topological phase transition in this model and its applications are briefly discussed.

  5. Nonadiabatic alignment of van der Waals--force-bound argon dimers by femtosecond laser pulses

    SciTech Connect

    Wu, J.; Vredenborg, A.; Ulrich, B.; Schmidt, L. Ph. H.; Meckel, M.; Voss, S.; Sann, H.; Kim, H.; Jahnke, T.; Doerner, R.

    2011-06-15

    We demonstrated that the weak van der Waals-force-bound argon dimer can be nonadiabatically aligned by nonresonant femtosecond laser pulses, showing periodic alignment and anti-alignment revivals after the extinction of the laser pulse. Based on the measured nonadiabatic alignment trace, the rotational constant of the argon dimer ground state is determined to be B{sub 0}= 0.05756 {+-} 0.00004 cm{sup -1}. Noticeable alignment dependence of frustrated tunneling ionization and bond-softening induced dissociation of the argon dimer are observed.

  6. Electron transport calculations with Wannier functions in van der Waals heterostructures

    NASA Astrophysics Data System (ADS)

    Dong, Wushi; Lopez-Bezanilla, Alejandro; Littlewood, Peter; Andreas Roelofs'group at Argonne National Lab Collaboration

    The vertical stacking of 2D materials forming van der Waals heterostructures (vdWHs) exhibits a wide range of interesting properties. A combined approach based on the Green's function formalism and a mean-field description of the electronic structure is used to calculate vertical electron transport in vdWHs. Tight-binding parameters obtained from Maximally Localized Wannier Functions enable us to model quantum electron transport at low computational costs. Our analysis of electron transport efficiencies provides the foundation and motivation for experimental works.

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

    NASA Astrophysics Data System (ADS)

    Sekikawa, Munehisa; Inaba, Naohiko; Yoshinaga, Tetsuya; Hikihara, Takashi

    2010-08-01

    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.

  8. Nanoscopy of Surface-Induced van der Waals-Zeeman Transitions

    SciTech Connect

    Hamamda, M.; Grucker, J.; Dutier, G.; Perales, F.; Baudon, J.; Ducloy, M.; Bocvarski, V.

    2008-10-22

    van der Waals transitions among magnetic sub-levels of a metastable rare gas atom passing near a surface immersed in a magnetic field, are described. Related transition amplitudes are calculated using both the sudden and the Landau-Zener approximations. Experimental data for Ne*({sup 3}P{sub 2}) atoms traversing a copper grating are presented. For a pair of surfaces (e.g. the opposite edges of a slit) and a sufficiently large coherence width, Fresnel's biprism interference fringes are obtained. From this interference pattern, detailed information about the transition amplitude at a sub-nanometric scale can be derived. The effect of gravity on this pattern is examined.

  9. Evidence for strong van der Waals type Rydberg-Rydberg interaction in a thermal vapor.

    PubMed

    Baluktsian, T; Huber, B; Löw, R; Pfau, T

    2013-03-22

    We present evidence for Rydberg-Rydberg interaction in a gas of rubidium atoms above room temperature. Rabi oscillations on the nanosecond time scale to different Rydberg states are investigated in a vapor cell experiment. Analyzing the atomic time evolution and comparing to a dephasing model, we find a scaling with the Rydberg quantum number n that is consistent with van der Waals interaction. Our results show that the interaction strength can be larger than the kinetic energy scale (Doppler width), which is the requirement for realization of thermal quantum devices in the GHz regime. PMID:25166800

  10. Observing the interplay between surface and bulk optical nonlinearities in thin van der Waals crystals.

    PubMed

    Deckoff-Jones, Skylar; Zhang, Jingjing; Petoukhoff, Christopher E; Man, Michael K L; Lei, Sidong; Vajtai, Robert; Ajayan, Pulickel M; Talbayev, Diyar; Madéo, Julien; Dani, Keshav M

    2016-01-01

    Van der Waals materials, existing in a range of thicknesses from monolayer to bulk, allow for interplay between surface and bulk nonlinearities, which otherwise dominate only at atomically-thin or bulk extremes, respectively. Here, we observe an unexpected peak in intensity of the generated second harmonic signal versus the thickness of Indium Selenide crystals, in contrast to the quadratic increase expected from thin crystals. We explain this by interference effects between surface and bulk nonlinearities, which offer a new handle on engineering the nonlinear optical response of 2D materials and their heterostructures. PMID:26936437

  11. Herausforderungen und Best Practices bei der Speicherung von multi-valued Attributen in LDAP-basierten Verzeichnisdiensten

    NASA Astrophysics Data System (ADS)

    Hommel, Wolfgang; Pluta, Daniel

    LDAP-basierte Verzeichnisdienste unterscheiden sich von relationalen Datenbankmanagementsystemen unter anderem stark bezüglich der Datenmodellierung. Dieser Artikel vertieft eingangs die Herausforderungen bei der LDAP-spezifischen Abbildung von Relationen zwischen mehreren multivalued Attributen. Die Diskussion erfolgt vor dem Hintergrund, dass einerseits Verzeichnisdienste generell nur bedingt zur Speicherung von Relationen geeignet sind und dass andererseits multi-valued Attribute ein mächtiges LDAP-Instrument sind, zu dem es in relationalen Datenbanksystemen keine direkte Entsprechung gibt. Anschließend werden Lösungskonzepte vorgestellt und mögliche Weiterentwicklungen des IntegraTUM-LDAP-Schemas zu deren Umsetzung skizziert, eine exemplarische Implementierung präsentiert und die Ergebnisse der bisherigen Entwicklung des IntegraTUM-Schemas gegenübergestellt.

  12. Europäisches Organ der Festkörperforschung und DDR-Devisenbringer Die Zeitschrift Physica Status Solidi im Kalten Krieg

    NASA Astrophysics Data System (ADS)

    Hoffmann, Dieter

    Mit dem Ziele, ein einheitliches internationales Organ der Festkörperphysik für den europäischen Raum zu schaffen, das eine rasche Publikation der für das Festkörpergebiet repräsentative Arbeiten ermöglicht, wird durch ein internationales Herausgebergremium eine neue wissenschaftliche Zeitschrift gegründet.

  13. Hydrogenic Rydberg States of Molecular van der Waals Complexes: Resolved Rydberg Spectroscopy of DABCO-N2

    NASA Astrophysics Data System (ADS)

    Cockett, Martin C.; Watkins, Mark J.

    2004-01-01

    The complementary threshold ionization techniques of MATI and ZEKE spectroscopy have been used to reveal well-resolved, long-lived (>10 μs) hydrogenic Rydberg series (50≤n≤98) in a van der Waals complex formed between a polyatomic molecule and a diatomic molecule for the first time. The series are observed within 50 cm-1 of the adiabatic ionization threshold as well as two core-excited thresholds corresponding to excitation of up to two quanta in the van der Waals vibra­tional mode.

  14. Epicutaneously applied Der p 2 induces a strong TH2-biased antibody response in C57BL/6 mice, independent of functional TLR4

    PubMed Central

    Stremnitzer, C; Manzano-Szalai, K; Starkl, P; Willensdorfer, A; Schrom, S; Singer, J; Reichart, U; Akira, S; Jensen-Jarolim, E

    2014-01-01

    Background The major house dust mite allergen Der p 2 is a structural and functional homologue of MD-2 within the TLR4–CD14–MD-2 complex. An asthma mouse model in TLR4-deficient mice recently suggested that the allergic immune response against Der p 2 is solely dependent on TLR4 signaling. We investigated whether similar mechanisms are important for Der p 2 sensitization via the skin. Methods In an epicutaneous sensitization model, the response to recombinant Der p 2 in combination with or without lipopolysaccharide (LPS) was compared between C57BL/6 WT and TLR4-deficient mice. We further analyzed possible adjuvant function of exogenous cysteine proteases. Results Sensitization with rDer p 2 induced similar levels of allergen-specific IgG1 and IgE antibodies in both mouse strains. LPS increased the systemic (antibody levels, cytokine release by restimulated splenocytes) and local (infiltration of immune cells into the skin) Th2 immune responses, which against our expectations were stronger in the absence of functional TLR4 expression. Barrier disruption by papain, a protease with structural homology to Der p 1, did not enhance the sensitization capacity of rDer p 2. However, the presence of LPS increased the stability of rDer p 2 against the protease. Conclusion Our data suggest that rDer p 2 alone can cause a strong TH2-biased response via the skin being enhanced in the presence of LPS. This response is not reliant on functional TLR4, but vice versa TLR4 expression rather protects against epicutaneous sensitization to house dust mite allergen Der p 2. PMID:24735481

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

    PubMed

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

    2016-07-13

    Two-dimensional layered MoS2 shows great potential for nanoelectronic and optoelectronic devices due to its high photosensitivity, which is the result of its indirect to direct band gap transition when the bulk dimension is reduced to a single monolayer. Here, we present an exhaustive study of the band alignment and relativistic properties of a van der Waals heterostructure formed between single layers of MoS2 and graphene. A sharp, high-quality MoS2-graphene interface was obtained and characterized by micro-Raman spectroscopy, high-resolution X-ray photoemission spectroscopy (HRXPS), and scanning high-resolution transmission electron microscopy (STEM/HRTEM). Moreover, direct band structure determination of the MoS2/graphene van der Waals heterostructure monolayer was carried out using angle-resolved photoemission spectroscopy (ARPES), shedding light on essential features such as doping, Fermi velocity, hybridization, and band-offset of the low energy electronic dynamics found at the interface. We show that, close to the Fermi level, graphene exhibits a robust, almost perfect, gapless, and n-doped Dirac cone and no significant charge transfer doping is detected from MoS2 to graphene. However, modification of the graphene band structure occurs at rather larger binding energies, as the opening of several miniband-gaps is observed. These miniband-gaps resulting from the overlay of MoS2 and the graphene layer lattice impose a superperiodic potential. PMID:27281693

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

    NASA Astrophysics Data System (ADS)

    Lu, Lin; Li, Xuemei

    2015-12-01

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

  17. The role of van der Waals forces in the performance of molecular diodes

    NASA Astrophysics Data System (ADS)

    Nerngchamnong, Nisachol; Yuan, Li; Qi, Dong-Chen; Li, Jiang; Thompson, Damien; Nijhuis, Christian A.

    2013-02-01

    One of the main goals of organic and molecular electronics is to relate the performance and electronic function of devices to the chemical structure and intermolecular interactions of the organic component inside them, which can take the form of an organic thin film, a self-assembled monolayer or a single molecule. This goal is difficult to achieve because organic and molecular electronic devices are complex physical-organic systems that consist of at least two electrodes, an organic component and two (different) organic/inorganic interfaces. Singling out the contribution of each of these components remains challenging. So far, strong π-π interactions have mainly been considered for the rational design and optimization of the performances of organic electronic devices, and weaker intermolecular interactions have largely been ignored. Here, we show experimentally that subtle changes in the intermolecular van der Waals interactions in the active component of a molecular diode dramatically impact the performance of the device. In particular, we observe an odd-even effect as the number of alkyl units is varied in a ferrocene-alkanethiolate self-assembled monolayer. As a result of a more favourable van der Waals interaction, junctions made from an odd number of alkyl units have a lower packing energy (by ~0.4-0.6 kcal mol-1), rectify currents 10 times more efficiently, give a 10% higher yield in working devices, and can be made two to three times more reproducibly than junctions made from an even number of alkyl units.

  18. Adsorption by design: Tuning atom-graphene van der Waals interactions via mechanical strain

    NASA Astrophysics Data System (ADS)

    Nichols, Nathan S.; Del Maestro, Adrian; Wexler, Carlos; Kotov, Valeri N.

    2016-05-01

    We aim to understand how the van der Waals force between neutral adatoms and a graphene layer is modified by uniaxial strain and electron correlation effects. A detailed analysis is presented for three atoms (He, H, and Na) and graphene strain ranging from weak to moderately strong. We show that the van der Waals potential can be significantly enhanced by strain, and present applications of our results to the problem of elastic scattering of atoms from graphene. In particular, we find that quantum reflection can be significantly suppressed by strain, meaning that dissipative inelastic effects near the surface become of increased importance. Furthermore, we introduce a method to independently estimate the Lennard-Jones parameters used in an effective model of He interacting with graphene, and determine how they depend on strain. At short distances, we find that strain tends to reduce the interaction strength by pushing the location of the adsorption potential minima to higher distances above the deformed graphene sheet. This opens up the exciting possibility of mechanically engineering an adsorption potential, with implications for the formation and observation of anisotropic low-dimensional superfluid phases.

  19. Validity and reliability of the Structured Clinical Interview for Depersonalization–Derealization Spectrum (SCI-DER)

    PubMed Central

    Mula, Marco; Pini, Stefano; Calugi, Simona; Preve, Matteo; Masini, Matteo; Giovannini, Ilaria; Conversano, Ciro; Rucci, Paola; Cassano, Giovanni B

    2008-01-01

    This study evaluates the validity and reliability of a new instrument developed to assess symptoms of depersonalization: the Structured Clinical Interview for the Depersonalization-Derealization Spectrum (SCI-DER). The instrument is based on a spectrum model that emphasizes soft-signs, sub-threshold syndromes as well as clinical and subsyndromal manifestations. Items of the interview include, in addition to DSM-IV criteria for depersonalization, a number of features derived from clinical experience and from a review of phenomenological descriptions. Study participants included 258 consecutive patients with mood and anxiety disorders, 16.7% bipolar I disorder, 18.6% bipolar II disorder, 32.9% major depression, 22.1% panic disorder, 4.7% obsessive compulsive disorder, and 1.5% generalized anxiety disorder; 2.7% patients were also diagnosed with depersonalization disorder. A comparison group of 42 unselected controls was enrolled at the same site. The SCI-DER showed excellent reliability and good concurrent validity with the Dissociative Experiences Scale. It significantly discriminated subjects with any diagnosis of mood and anxiety disorders from controls and subjects with depersonalization disorder from controls. The hypothesized structure of the instrument was confirmed empirically. PMID:19183789

  20. Paratesticular leiomyoma with a der(14)t(12;14)(q15;q24).

    PubMed

    Gorunova, Ludmila; Bjerkehagen, Bodil; Heim, Sverre

    2011-08-01

    While uterine leiomyomas are among the most common and best cytogenetically characterized solid tumors, leiomyomas at other sites are rare. Only two karyotypically abnormal leiomyomas in males have been reported to date, both of them with unspecific chromosome aberrations. We recently analyzed by G-banding a paratesticular leiomyoma, a tumor type not cytogenetically examined before, and found the pseudodiploid karyotype 46,XY,der(5)t(5;14)(q31;q24),der(14)t(12;14)(q15;q24). The leiomyoma cells demonstrated strong immunohistochemical nuclear expression of the HMGA2 protein, supporting a role of HMGA2 as the target gene in 12q14∼15 rearrangements. In uterine leiomyomas, the t(12;14)(q15;q24) is the most frequent translocation leading to overexpression of HMGA2, therefore it seems that a common pathogenetic pathway exists for benign smooth muscle tumors of both the female and male reproductive organs. The finding of this abnormality may help identify a scrotal tumor of uncertain biologic potential but with smooth muscle differentiation as benign. PMID:21962898

  1. Understanding corrosion inhibition with van der Waals DFT methods: the case of benzotriazole.

    PubMed

    Gattinoni, Chiara; Michaelides, Angelos

    2015-01-01

    The corrosion of materials is an undesirable and costly process affecting many areas of technology and everyday life. As such, considerable effort has gone into understanding and preventing it. Organic molecule based coatings can in certain circumstances act as effective corrosion inhibitors. Although they have been used to great effect for more than sixty years, how they function at the atomic-level is still a matter of debate. In this work, computer simulation approaches based on density functional theory are used to investigate benzotriazole (BTAH), one of the most widely used and studied corrosion inhibitors for copper. In particular, the structures formed by protonated and deprotonated BTAH molecules on Cu(111) have been determined and linked to their inhibiting properties. It is found that hydrogen bonding, van der Waals interactions and steric repulsions all contribute in shaping how BTAH molecules adsorb, with flat-lying structures preferred at low coverage and upright configurations preferred at high coverage. The interaction of the dehydrogenated benzotriazole molecule (BTA) with the copper surface is instead dominated by strong chemisorption via the azole moiety with the aid of copper adatoms. Structures of dimers or chains are found to be the most stable structures at all coverages, in good agreement with scanning tunnelling microscopy results. Benzotriazole thus shows a complex phase behaviour in which van der Waals forces play an important role and which depends on coverage and on its protonation state and all of these factors feasibly contribute to its effectiveness as a corrosion inhibitor. PMID:25907526

  2. Elastic properties of van der Waals epitaxy grown bismuth telluride 2D nanosheets

    NASA Astrophysics Data System (ADS)

    Guo, Lingling; Yan, Haoming; Moore, Quentarius; Buettner, Michael; Song, Jinhui; Li, Lin; Araujo, Paulo T.; Wang, Hung-Ta

    2015-07-01

    Bismuth telluride (Bi2Te3) two-dimensional (2D) nanosheets prepared by van der Waals epitaxy were successfully detached, transferred, and suspended for nano-indentation measurements to be performed on freestanding circular nanosheets. The Young's modulus acquired by fitting linear elastic behaviors of 26 samples (thickness: 5-14 nm) is only 11.7-25.7 GPa, significantly smaller than the bulk in-plane Young's modulus (50-55 GPa). Compliant and robust Bi2Te3 2D nanosheets suggest the feasibility of the elastic strain engineering of topological surface states.Bismuth telluride (Bi2Te3) two-dimensional (2D) nanosheets prepared by van der Waals epitaxy were successfully detached, transferred, and suspended for nano-indentation measurements to be performed on freestanding circular nanosheets. The Young's modulus acquired by fitting linear elastic behaviors of 26 samples (thickness: 5-14 nm) is only 11.7-25.7 GPa, significantly smaller than the bulk in-plane Young's modulus (50-55 GPa). Compliant and robust Bi2Te3 2D nanosheets suggest the feasibility of the elastic strain engineering of topological surface states. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr03282b

  3. Hermann Cohen's Das Princip der Infinitesimal-Methode: The history of an unsuccessful book.

    PubMed

    Giovanelli, Marco

    2016-08-01

    This paper offers an introduction to Hermann Cohen's Das Princip der Infinitesimal-Methode (1883), and recounts the history of its controversial reception by Cohen's early sympathizers, who would become the so-called 'Marburg school' of Neo-Kantianism, as well as the reactions it provoked outside this group. By dissecting the ambiguous attitudes of the best-known representatives of the school (Paul Natorp and Ernst Cassirer), as well as those of several minor figures (August Stadler, Kurd Lasswitz, Dimitry Gawronsky, etc.), this paper shows that Das Princip der Infinitesimal-Methode is a unicum in the history of philosophy: it represents a strange case of an unsuccessful book's enduring influence. The "puzzle of Cohen's Infinitesimalmethode," as we will call it, can be solved by looking beyond the scholarly results of the book, and instead focusing on the style of philosophy it exemplified. Moreover, the paper shows that Cohen never supported, but instead explicitly opposed, the doctrine of the centrality of the 'concept of function', with which Marburg Neo-Kantianism is usually associated. PMID:27474182

  4. Excitons in one-dimensional van der Waals materials: Sb2S3 nanoribbons

    NASA Astrophysics Data System (ADS)

    Caruso, Fabio; Filip, Marina R.; Giustino, Feliciano

    2015-09-01

    Antimony sulphide Sb2S3 has emerged as a promising material for a variety of energy applications ranging from solar cells to thermoelectrics and solid-state batteries. The most distinctive feature of Sb2S3 is its crystal structure, which consists of parallel 1-nm-wide ribbons held together by weak van der Waals forces. This structure clearly suggests that it should be possible to isolate individual Sb2S3 ribbons using micromechanical or liquid-phase exfoliation techniques. However, it is not clear yet how to identify the ribbons postexfoliation using standard optical probes. Using state-of-the-art first-principles calculations based on many-body perturbation theory, here we show that individual ribbons of Sb2S3 carry optical signatures clearly distinct from those of bulk Sb2S3 . In particular, we find a large blueshift of the optical absorption edge (from 1.38 to 2.30 eV) resulting from the interplay between a reduced screening and the formation of bound excitons. In addition, we observe a transition from an indirect band gap to a direct gap, suggesting an enhanced photoluminescence in the green. These unique fingerprints will enable extending the research on van der Waals materials to the case of one-dimensional chalchogenides.

  5. Transition metals-graphene interaction: the role of the screened van der Waals energy

    NASA Astrophysics Data System (ADS)

    Ambrosetti, Alberto; Silvestrelli, Pier Luigi

    2015-03-01

    The interaction of graphene with transition metals is of particular interest for practical applications, which include for instance the efficient production of high-quality graphene. The accurate theoretical description of transition metals-graphene interfaces, however, is a particularly challenging problem due to the complex interplay between van der Waals (vdW) and hybridization effects. Here we apply the DFT/vdW-WF2s method, which allows to augment semi-local Density Functional Theory through the introduction of screened vdW interactions. Notably, we find that a reliable modeling of the van der Waals interaction should account for complex metal screening effects, that are due to the combined contributions of the p- and s-like quasi-free electrons, and the more localized d-states. The resulting geometry and energetic properties are in good agreement with experimental data and sophisticates theoretical calculations. Moreover, the Maximally Localized Wannier Functions underlying the DFT/vdW-WF2s method allow for an intuitive understanding of the complex binding mechanism.

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

    PubMed

    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. PMID:26829055

  7. Van der Waals free energy model for solubilization of oil in micelles.

    PubMed

    Troncoso, Americo Boza; Acosta, Edgar

    2015-01-21

    This work introduces the first of a two part thermodynamic framework to estimate the solubilization of nonpolar oils in micelles conformed by nonionic surfactants with linear alkyl tails, considering their configuration and the molecular properties of the constituents. This first part introduces a formal approach to account for the lipophilic (van der Waals) contributions to the free energy of solubilization in spherical micelles. To this end, this work uses two recently developed integration methods for sphere-shell and cone-shell VDW interactions that allow the calculation of surfactant-oil and surfactant-surfactant interactions that take place within the micelles of the solubilization process studied here. The method consists in calculating the free energy of transferring a normal alkane from its continuum, and surfactants monomers from empty micelles to produce an oil swollen micelle. The lipophilic interactions are estimated using the microscopic approach of Hamaker with Lifshitz-based Hamaker constants. The influence of n-alkane and surfactant tail length on the solubilization capacity predicted by the van der Walls free energy model (VDW-FEM) are consistent with experimental trends and it is also consistent with the lipophilic terms included in the semi-empirical Hydrophilic-Lipophilic-Difference + Net-Average-Curvature's (HLD-NAC) equation that predicts the phase behavior of microemulsions. As a result, these lipophilic terms can now be defined in terms of molecular interactions and molecular properties. PMID:25415662

  8. Van der Waals pressure and its effect on trapped interlayer molecules

    PubMed Central

    Vasu, K. S.; Prestat, E.; Abraham, J.; Dix, J.; Kashtiban, R. J.; Beheshtian, J.; Sloan, J.; Carbone, P.; Neek-Amal, M.; Haigh, S. J.; Geim, A. K.; Nair, R. R.

    2016-01-01

    Van der Waals assembly of two-dimensional crystals continue attract intense interest due to the prospect of designing novel materials with on-demand properties. One of the unique features of this technology is the possibility of trapping molecules between two-dimensional crystals. The trapped molecules are predicted to experience pressures as high as 1 GPa. Here we report measurements of this interfacial pressure by capturing pressure-sensitive molecules and studying their structural and conformational changes. Pressures of 1.2±0.3 GPa are found using Raman spectrometry for molecular layers of 1-nm in thickness. We further show that this pressure can induce chemical reactions, and several trapped salts are found to react with water at room temperature, leading to two-dimensional crystals of the corresponding oxides. This pressure and its effect should be taken into account in studies of van der Waals heterostructures and can also be exploited to modify materials confined at the atomic interfaces. PMID:27385262

  9. Direct measurement of the van der Waals interaction between two Rydberg atoms

    NASA Astrophysics Data System (ADS)

    Browaeys, A.

    2013-05-01

    This talk will report on the direct measurement of the van der Waals interaction between two isolated, single Rydberg atoms separated by a controlled distance of a few micrometers. By working in a regime where the single-atom Rabi frequency of the laser used for excitation to the Rydberg state is comparable to the interaction energy, we observe a partial Rydberg blockade, whereby the time-dependent populations of the various two-atom states exhibit coherent oscillations with several frequencies. A quantitative comparison of the data with a simple model based on the optical Bloch equations allows us to extract the van der Waals energy, and to observe its characteristic C6 /R6 dependence. The magnitude of the measured C6 coefficient agrees well with ab-initio calculations, and we observe its dramatic increase with the principal quantum number n of the Rydberg state. Our results demonstrate a good degree of experimental control, which opens interesting perspectives in quantum information processing and quantum simulation using long-range interactions between atoms.

  10. Strain-Induced Electronic Structure Changes in Stacked van der Waals Heterostructures.

    PubMed

    He, Yongmin; Yang, Yang; Zhang, Zhuhua; Gong, Yongji; Zhou, Wu; Hu, Zhili; Ye, Gonglan; Zhang, Xiang; Bianco, Elisabeth; Lei, Sidong; Jin, Zehua; Zou, Xiaolong; Yang, Yingchao; Zhang, Yuan; Xie, Erqing; Lou, Jun; Yakobson, Boris; Vajtai, Robert; Li, Bo; Ajayan, Pulickel

    2016-05-11

    Vertically stacked van der Waals heterostructures composed of compositionally different two-dimensional atomic layers give rise to interesting properties due to substantial interactions between the layers. However, these interactions can be easily obscured by the twisting of atomic layers or cross-contamination introduced by transfer processes, rendering their experimental demonstration challenging. Here, we explore the electronic structure and its strain dependence of stacked MoSe2/WSe2 heterostructures directly synthesized by chemical vapor deposition, which unambiguously reveal strong electronic coupling between the atomic layers. The direct and indirect band gaps (1.48 and 1.28 eV) of the heterostructures are measured to be lower than the band gaps of individual MoSe2 (1.50 eV) and WSe2 (1.60 eV) layers. Photoluminescence measurements further show that both the direct and indirect band gaps undergo redshifts with applied tensile strain to the heterostructures, with the change of the indirect gap being particularly more sensitive to strain. This demonstration of strain engineering in van der Waals heterostructures opens a new route toward fabricating flexible electronics. PMID:27120401

  11. Van der Waals force: a dominant factor for reactivity of graphene.

    PubMed

    Lee, Jong Hak; Avsar, Ahmet; Jung, Jeil; Tan, Jun You; Watanabe, K; Taniguchi, T; Natarajan, Srinivasan; Eda, Goki; Adam, Shaffique; Castro Neto, Antonio H; Özyilmaz, Barbaros

    2015-01-14

    Reactivity control of graphene is an important issue because chemical functionalization can modulate graphene's unique mechanical, optical, and electronic properties. Using systematic optical studies, we demonstrate that van der Waals interaction is the dominant factor for the chemical reactivity of graphene on two-dimensional (2D) heterostructures. A significant enhancement in the chemical stability of graphene is achieved by replacing the common SiO2 substrate with 2D crystals such as an additional graphene layer, WS2, MoS2, or h-BN. Our theoretical and experimental results show that its origin is a strong van der Waals interaction between the graphene layer and the 2D substrate. This results in a high resistive force on graphene toward geometric lattice deformation. We also demonstrate that the chemical reactivity of graphene can be controlled by the relative lattice orientation with respect to the substrates and thus can be used for a wide range of applications including hydrogen storage. PMID:25493357

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

    PubMed Central

    Dufferwiel, S.; Schwarz, S.; Withers, F.; Trichet, A. A. P.; Li, F.; Sich, M.; Del Pozo-Zamudio, O.; Clark, C.; Nalitov, A.; Solnyshkov, D. D.; Malpuech, G.; Novoselov, K. S.; Smith, J. M.; Skolnick, M. S.; Krizhanovskii, D. N.; Tartakovskii, A. I.

    2015-01-01

    Layered materials can be assembled vertically to fabricate a new class of van der Waals heterostructures a few atomic layers thick, compatible with a wide range of substrates and optoelectronic device geometries, enabling new strategies for control of light–matter coupling. Here, we incorporate molybdenum diselenide/hexagonal boron nitride (MoSe2/hBN) quantum wells in a tunable optical microcavity. Part-light–part-matter polariton eigenstates are observed as a result of the strong coupling between MoSe2 excitons and cavity photons, evidenced from a clear anticrossing between the neutral exciton and the cavity modes with a splitting of 20 meV for a single MoSe2 monolayer, enhanced to 29 meV in MoSe2/hBN/MoSe2 double-quantum wells. The splitting at resonance provides an estimate of the exciton radiative lifetime of 0.4 ps. Our results pave the way for room-temperature polaritonic devices based on multiple-quantum-well van der Waals heterostructures, where polariton condensation and electrical polariton injection through the incorporation of graphene contacts may be realized. PMID:26446783

  13. Measuring anisotropic resistivity of single crystals using the van der Pauw technique

    NASA Astrophysics Data System (ADS)

    Borup, Kasper A.; Fischer, Karl F. F.; Brown, David R.; Snyder, G. Jeffrey; Iversen, Bo B.

    2015-07-01

    Anisotropy in properties of materials is important in materials science and solid-state physics. Measurement of the full resistivity tensor of crystals using the standard four-point method with bar shaped samples requires many measurements and may be inaccurate due to misalignment of the bars along crystallographic directions. Here an approach to extracting the resistivity tensor using van der Pauw measurements is presented. This reduces the number of required measurements. The theory of the van der Pauw method is extended to extract the tensor from parallelogram shaped samples with known geometry. Methods to extract the tensor for both known and unknown principal axis orientation are presented for broad applicability to single crystals. Numerical simulations of errors are presented to quantify error sources. Several benchmark experiments are performed on isotropic graphite samples to verify the internal consistency of the developed theory, test experimental precision, and characterize error sources. The presented methods are applied to a RuS b2 single crystal at room temperature and the results are discussed based on the error source analysis. Temperature resolved resistivities along the a and b directions are finally reported and briefly discussed.

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

    PubMed

    Vaara, Juha; Hanni, Matti; Jokisaari, Jukka

    2013-03-14

    Nuclear spin-spin coupling over van der Waals bond has recently been observed via the frequency shift of solute protons in a solution containing optically hyperpolarized (129)Xe nuclei. We carry out a first-principles computational study of the prototypic van der Waals-bonded xenon dimer, where the spin-spin coupling between two magnetically non-equivalent isotopes, J((129)Xe - (131)Xe), is observable. We use relativistic theory at the four-component Dirac-Hartree-Fock and Dirac-density-functional theory levels using novel completeness-optimized Gaussian basis sets and choosing the functional based on a comparison with correlated ab initio methods at the nonrelativistic level. J-coupling curves are provided at different levels of theory as functions of the internuclear distance in the xenon dimer, demonstrating cross-coupling effects between relativity and electron correlation for this property. Calculations on small Xe clusters are used to estimate the importance of many-atom effects on J((129)Xe - (131)Xe). Possibilities of observing J((129)Xe - (131)Xe) in liquid xenon are critically examined, based on molecular dynamics simulation. A simplistic spherical model is set up for the xenon dimer confined in a cavity, such as in microporous materials. It is shown that the on the average shorter internuclear distance enforced by the confinement increases the magnitude of the coupling as compared to the bulk liquid case, rendering J((129)Xe - (131)Xe) in a cavity a feasible target for experimental investigation. PMID:23514495

  15. Key concepts from Gibbs that empowered Van der Waals, Korteweg and Kamerlingh Onnes

    NASA Astrophysics Data System (ADS)

    Levelt Sengers, Johanna

    2003-03-01

    Gibbs founded his theory of the equilibrium of heterogeneous systems (1873-1878) on the following pillars: thermodynamic stability; phase equilibrium from tangent planes rolling across thermodynamic energy surfaces; the chemical potential; degrees of freedom; the phase rule; and criticality. These concepts inspired major interdisciplinary research on mixture phase behavior in the Netherlands.(J. Levelt Sengers, How Fluids Unmix, Edita, Amsterdam (2002)) Mathematician Korteweg and physicist Van der Waals, at the University of Amsterdam, used Gibbs's geometric approach to produce the first formulation of the Helmholtz energy of binary fluid mixtures in 1891. Physicist Kamerlingh Onnes and his students at the University of Leiden studied binary mixtures experimentally, confirming Van der Waals's model, and built many 3-D models of thermodynamic surfaces. Misconceptions about criticality abounded in Europe from 1880 to 1908, provoking attacks by Kamerlingh Onnes. Between 1907 and 1913, Amsterdam chemist Bakhuis Roozeboom and his school produced an influential book series on binary and ternary, fluid and solid phase equilibria, including reacting systems.

  16. Density-functional description of polymer crystals: A comparative study of recent van der Waals functionals

    NASA Astrophysics Data System (ADS)

    Pham, Thinh H.; Ramprasad, Rampi; Nguyen, Huy-Viet

    2016-06-01

    Due to the lack of treatment of long-range dispersion energies, density functional theory with local and semilocal approximations of exchange-correlation energy is known to fail in describing van der Waals complexes, including polymer crystals. This limitation can be overcome by using a different class of functionals, called van der Waals density functional (vdW-DF), originally developed by Dion et al. [Phys. Rev. Lett. 92, 246401 (2004)]. In this work, we performed a systematic study of structural properties of polymeric crystals using the original vdW-DF functional by Dion et al. and its variants and refinements. Our study shows that this class of functional outperforms the conventional LDA or PBE functionals and gives results with similar accuracy to that of empirical dispersion-corrected schemes such as DFT-D. This study suggests the use of vdW-DF2 functional — a revised version of vdW-DF functional — to obtain a high-fidelity prediction of structural and other properties of polymeric materials.

  17. Ab initio phonon dispersion in crystalline naphthalene using van der Waals density functionals

    NASA Astrophysics Data System (ADS)

    Brown-Altvater, Florian; Rangel, Tonatiuh; Neaton, Jeffrey B.

    2016-05-01

    Acene molecular crystals are of current interest in organic optoelectronics, both as active materials and for exploring and understanding new phenomena. Phonon scattering can be an important facilitator and dissipation mechanism in charge separation and carrier transport processes. Here, we carry out density functional theory (DFT) calculations of the structure and the full phonon dispersion of crystalline naphthalene, a well-characterized acene crystal for which detailed neutron-diffraction measurements, as well as infrared and Raman spectroscopy, are available. We evaluate the performance, relative to experiments, of DFT within the local density approximation (LDA); the generalized gradient approximation of Perdew, Burke, and Ernzerhof (PBE); and a recent van der Waals-corrected nonlocal correlation (vdW-DF-cx) functional. We find that the vdW-DF-cx functional accurately predicts lattice parameters of naphthalene within 1%. Intermolecular and intramolecular phonon frequencies across the Brillouin zone are reproduced within 7.8% and 1%, respectively. As expected, LDA (PBE) underestimates (overestimates) the lattice parameters and overestimates (underestimates) phonon frequencies, demonstrating their shortcomings for predictive calculations of weakly bound materials. If the unit cell is fixed to the experimental lattice parameters, PBE is shown to lead to improved phonon frequencies. Our study provides a detailed understanding of the phonon spectrum of naphthalene, and highlights the importance of including van der Waals dispersion interactions in predictive calculations of lattice parameters and phonon frequencies of molecular crystals and related organic materials.

  18. Atomically Sharp Interface in an h-BN-epitaxial graphene van der Waals Heterostructure

    PubMed Central

    Sediri, Haikel; Pierucci, Debora; Hajlaoui, Mahdi; Henck, Hugo; Patriarche, Gilles; Dappe, Yannick J.; Yuan, Sheng; Toury, Bérangère; Belkhou, Rachid; Silly, Mathieu G.; Sirotti, Fausto; Boutchich, Mohamed; Ouerghi, Abdelkarim

    2015-01-01

    Stacking various two-dimensional atomic crystals is a feasible approach to creating unique multilayered van der Waals heterostructures with tailored properties. Herein for the first time, we present a controlled preparation of large-area h-BN/graphene heterostructures via a simple chemical deposition of h-BN layers on epitaxial graphene/SiC(0001). Van der Waals forces, which are responsible for the cohesion of the multilayer system, give rise to an abrupt interface without interdiffusion between graphene and h-BN, as shown by X-ray Photoemission Spectroscopy (XPS) and direct observation using scanning and High-Resolution Transmission Electron Microscopy (STEM/HRTEM). The electronic properties of graphene, such as the Dirac cone, remain intact and no significant charge transfer i.e. doping, is observed. These results are supported by Density Functional Theory (DFT) calculations. We demonstrate that the h-BN capped graphene allows the fabrication of vdW heterostructures without altering the electronic properties of graphene. PMID:26585245

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

    NASA Astrophysics Data System (ADS)

    Kudryavtsev, Yaroslav V.; Gelinck, Edwin; Fischer, Hartmut R.

    2009-08-01

    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. It is demonstrated that a layer (oxide or water) at any of the surfaces influences the pressure up to distances, which are an order of magnitude larger than its own thickness. A jump on the p( D) curve is expected at contact of the adsorbed liquid layers. The retardation of van der Waals forces at 5 < D < 20 nm has the similar effect on the pressure as 1 nm oxide layers. At the far end of this range the pressure decreases by 30% due to the retardation. Nanoscale roughness plays a great role when the surfaces are close-to-contact, the crucial factor is the height distribution of asperities. However, their curvature and surface density are also important, as well as the amount of adsorbed water.

  20. Potential-energy surface and van der Waals motions of p-difluorobenzene-argon cation

    NASA Astrophysics Data System (ADS)

    Makarewicz, Jan

    2005-07-01

    The structure and dynamics of the van der Waals complex of argon with the p-difluorobenzene cation are investigated using the ab initio theory. The restricted open-shell Møller-Plesset second-order perturbation method combined with the augmented correlation-consistent polarized valence double-ζ basis set is employed to determine the electronic ground-state potential-energy surface of the cationic complex. This surface is extremely flat in a wide region of the configuration space of the Ar atom which moves almost freely over the monomer ring. However, it is bound to the monomer stronger in the cationic than in the neutral complex. Its binding energy is calculated to be 621cm-1 at a distance of 3.445Å from the monomer center. The calculated dissociation energy of 572cm-1 agrees perfectly with the experimental value of 572±6cm-1 [S. M. Belm, R. J. Moulds, and D. Lawrence, J. Chem. Phys. 115, 10709 (2001)]. The effect of a strong coupling of large-amplitude intermolecular motions on the character of van der Waals vibrational states is investigated. The vibrational structure of the spectrum of the complex is explained and its earlier assignment is partly corrected.

  1. Nonlocal van der Waals functionals: The case of rare-gas dimers and solids

    NASA Astrophysics Data System (ADS)

    Tran, Fabien; Hutter, Jürg

    2013-05-01

    Recently, the nonlocal van der Waals (vdW) density functionals [M. Dion, H. Rydberg, E. Schröder, D. C. Langreth, and B. I. Lundqvist, Phys. Rev. Lett. 92, 246401 (2004), 10.1103/PhysRevLett.92.246401] have attracted considerable attention due to their good performance for systems where weak interactions are important. Since the physics of dispersion is included in these functionals, they are usually more accurate and show less erratic behavior than the semilocal and hybrid methods. In this work, several variants of the vdW functionals have been tested on rare-gas dimers (from He2 to Kr2) and solids (Ne, Ar, and Kr) and their accuracy compared to standard semilocal approximations, supplemented or not by an atom-pairwise dispersion correction [S. Grimme, J. Antony, S. Ehrlich, and H. Krieg, J. Chem. Phys. 132, 154104 (2010), 10.1063/1.3382344]. An analysis of the results in terms of energy decomposition is also provided.

  2. Density-functional description of polymer crystals: A comparative study of recent van der Waals functionals.

    PubMed

    Pham, Thinh H; Ramprasad, Rampi; Nguyen, Huy-Viet

    2016-06-01

    Due to the lack of treatment of long-range dispersion energies, density functional theory with local and semilocal approximations of exchange-correlation energy is known to fail in describing van der Waals complexes, including polymer crystals. This limitation can be overcome by using a different class of functionals, called van der Waals density functional (vdW-DF), originally developed by Dion et al. [Phys. Rev. Lett. 92, 246401 (2004)]. In this work, we performed a systematic study of structural properties of polymeric crystals using the original vdW-DF functional by Dion et al. and its variants and refinements. Our study shows that this class of functional outperforms the conventional LDA or PBE functionals and gives results with similar accuracy to that of empirical dispersion-corrected schemes such as DFT-D. This study suggests the use of vdW-DF2 functional - a revised version of vdW-DF functional - to obtain a high-fidelity prediction of structural and other properties of polymeric materials. PMID:27276968

  3. Microwave and ab initio studies of the Xe-CH4 van der Waals complex

    NASA Astrophysics Data System (ADS)

    Wen, Qing; Jäger, Wolfgang

    2006-01-01

    An ab initio potential-energy surface of the Xe-CH4 van der Waals complex was constructed at the coupled cluster level of theory with single, double, and perturbatively included triple excitations. The recently developed small-core pseudopotential and augmented correlation-consistent polarized valence quadruple-zeta basis set was used for the xenon atom and Dunning's augmented correlation-consistent polarized valence triple-zeta basis set for the other atoms. The basis sets were supplemented with bond functions. Dipole moments were also calculated at various configurations. Rotational spectra of the Xe-CH4 van der Waals complex were recorded using a pulsed-nozzle Fourier transform microwave spectrometer. The isotopomers studied include those of CH4,CH134,CD4,CH3D, and CHD3 with the five most abundant Xe isotopes. Transitions within three internal rotor states, namely, the j =0,K=0;j=1,K=0; and j =2,K=1 states, were observed and assigned. Nuclear quadrupole hyperfine structures due to the presence of Xe131(I=3/2) were detected and analyzed. It was found that the j =1,K=0 state is perturbed by a Coriolis interaction with a nearby j =1,K=1 state. For isotopomers containing CH3D and CHD3, the j =2 states are no longer metastable and could not be observed. The spectroscopic results were used to derive structural and dynamical information of the Xe-CH4 complex.

  4. ders deformation and superplastic flow of metals extruded by KOBO method

    NASA Astrophysics Data System (ADS)

    Korbel, Andrzej; Bochniak, Włodzimierz

    2013-05-01

    The work brings the results of the study on mechanical properties of some metallic materials subjected to very large plastic deformation by KOBO extrusion. The unexpected features of the KOBO products like Lüders deformation in pure metals and superplastic flow in coarse grain materials are discussed in terms of micro- and nano-scale elements of their structure. The choice to the experiment materials having different crystallographic and phase structure (commercial purity aluminium, multiphase aluminium 7075 alloy, pure zinc and multiphase magnesium AZ91 alloy) and different history (extrusion, casting) allowed to identify the common nano-size elements of the structure generated during the KOBO deformation which seems to be responsible for the mechanical behaviour of these materials. In particular, clusters of point defects (self-interstitials) formed under the KOBO extrusion conditions (cyclic change in the deformation path, high hydrostatic pressure) were found in these materials regardless of grain size and material early history. They correlate with appearance of unstable Lüders-like or even Portevin-LeChatelier deformation at ambient and superplastic flow at elevated temperatures.

  5. Mapping van der Waals forces with frequency modulation dynamic force microscopy

    NASA Astrophysics Data System (ADS)

    Polesel-Maris, J.; Guo, H.; Zambelli, T.; Gauthier, S.

    2006-08-01

    Nanometre-size gold clusters supported on MoS2(0001) are investigated by means of ultrahigh-vacuum frequency modulation dynamic force microscopy. Topography and frequency shift images are simultaneously obtained using the average tunnelling current to regulate the tip-substrate distance. Two families of clusters are observed, giving different frequency shift images. While the topographic and frequency shift profiles have similar shapes on small clusters (size \\lesssim 1 nm), they are quite different near the top of large clusters (size \\gtrsim 4 nm): the topographic profile is rounded, but the frequency shift profile exhibits rather steep edges and a depression near the centre of the island. It is demonstrated that these differences result from the finite range of van der Waals forces. On small islands, the frequency shift is dominated by the interaction of the tip with the substrate. On large islands, it is dominated by the interaction with the island. The particular observed shape results from the geometry of the island. These interpretations are comforted by analytical and numerical calculations. In particular, the characteristic shape of the frequency shift profiles on large islands can be reproduced by introducing realistic parameters and considering only the contribution of van der Waals forces.

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

    DOE PAGESBeta

    Ganesh, P.; Kim, Jeongnim; Park, Changwon; Yoon, Mina; Reboredo, Fernando A.; Kent, Paul R. C.

    2014-11-03

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

  7. Note on Unconditional and Conditional Hypothesis Testing: A Discussion of an Issue Raised by van der Linden and Sotaridona

    ERIC Educational Resources Information Center

    Lewis, Charles

    2006-01-01

    In the context of reviewing an article for this journal (van der Linden & Sotaridona, this issue, pp. 283-304) the topic of unconditional and conditional hypothesis testing came under consideration. While this is hardly a new issue (consider, for example, arguments regarding the chi square vs. Fisher exact test of independence for a 2 x 2…

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

    NASA Astrophysics Data System (ADS)

    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

  9. Vibronic structure of the cyclopentadienyl radical and its nonrigid van der Waals cluster with nitrogen

    NASA Astrophysics Data System (ADS)

    Sun, S.; Bernstein, E. R.

    1995-09-01

    Fluorescence excitation and two color mass resolved excitation spectroscopy are employed to study the D1(2A2″)←D0(2E1″) vibronic transitions of the cyclopentadienyl radical (cpd) and its van der Waals cluster with nitrogen. The radical is created by photolysis of the cyclopentadiene dimer and cooled by expansion from a supersonic nozzle. The cpd(N2)1 cluster is generated in this cooling process. Mass resolved excitation spectra of cpd are obtained for the first 1200 cm-1 of the D1←D0 transition. The excitation spectrum of cpd(N2)1 shows a complicated structure for the origin transition. With the application of hole burning spectroscopy, we are able to assign all the cluster transitions to a single isomer. The features are assigned to a 55 cm-1 out-of-plane van der Waals mode stretch and contortional (rotational) motions of the N2 molecule with respect to the cpd radical. Empirical potential energy calculations are used to predict the properties of this cluster and yield the following results: (1) the N2 molecular axis is perpendicular to the cpd fivefold axis and parallel to the plane of the cpd ring with the two molecular centers of mass lying on the fivefold ring axis; (2) the binding energy of cpd(N2)1 is 434 cm-1; and (3) the rotational motion of the N2 molecule is essentially unhindered about the cpd fivefold axis. The molecular symmetry group D5h(MS) is applied to the nonrigid cluster, and optical selection rules exclude even↔odd transitions (Δn=0, ±2, ±4,... allowed) between the different contortional levels. Tentative assignments are given to the observed contortional features based on these considerations. The barrier to internal rotation is also small in the excited state. The results for the cpd(N2)1 van der Waals cluster are compared to those for the benzene (N2)1 and benzyl radical (N2)1 clusters.

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

    NASA Astrophysics Data System (ADS)

    Burke, John; Desroches, Mathieu; Granados, Albert; Kaper, Tasso J.; Krupa, Martin; Vo, Theodore

    2016-04-01

    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 positive forcing frequencies. In the low-frequency forcing regime, we demonstrate the existence of primary maximal canards induced by folded saddle nodes of type I and establish explicit formulas for the parameter values at which the primary maximal canards and their folds exist. Then, we turn to the intermediate- and high-frequency forcing regimes and show that the forced van der Pol possesses torus canards instead. These torus canards consist of long segments near families of attracting and repelling limit cycles of the fast system, in alternation. We also derive explicit formulas for the parameter values at which the maximal torus canards and their folds exist. Primary maximal canards and maximal torus canards correspond geometrically to the situation in which the persistent manifolds near the family of attracting limit cycles coincide to all orders with the persistent manifolds that lie near the family of repelling limit cycles. The formulas derived for the folds of maximal canards in all three frequency regimes turn out to be representations of a single formula in the appropriate parameter regimes, and this unification confirms the central numerical observation that the folds of the maximal canards created in the low-frequency regime continue directly into the folds of the maximal torus canards that exist in the intermediate- and high-frequency regimes. In addition, we study the secondary canards induced by the folded singularities in the low-frequency regime and find that the fold curves 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

  11. Die Bedeutung der Volumen- und Oberflächeneigenschaften von Biomaterialien für die Adsorption von Proteinen und nachfolgende zelluläre Reaktionen

    NASA Astrophysics Data System (ADS)

    Groth, Thomas

    2003-04-01

    Es ist schon seit längerer Zeit bekannt, dass nach Kontakt des Biomaterials mit der biologischen Umgebung bei Implantation oder extrakorporaler Wechselwirkung zunächst Proteine aus dem umgebenden Milieu adsorbiert werden, wobei die Oberflächeneigenschaften des Materials die Zusammensetzung der Proteinschicht und die Konformation der darin enthaltenden Proteine determinieren. Die nachfolgende Wechselwirkung von Zellen mit dem Material wird deshalb i.d.R. von der Adsorbatschicht vermittelt. Der Einfluss der Oberflächen auf die Zusammensetzung und Konformation der Proteine und die nachfolgende Wechselwirkung mit Zellen ist von besonderem Interesse, da einerseits eine Aussage über die Anwendbarkeit ermöglicht wird, andererseits Erkenntnisse über diese Zusammenhänge für die Entwicklung neuer Materialien mit verbesserter Biokompatibilität genutzt werden können. In der vorliegenden Habilitationsschrift wurde deshalb der Einfluss der Zusammensetzung von Polymeren bzw. von deren Oberflächeneigenschaften auf die Adsorption von Proteinen, den Aktivitätszustand der plasmatischen Gerinnung und die Adhäsion von Zellen untersucht. Dabei wurden auch Möglichkeiten zur Beeinflussung dieser Vorgänge über eine Veränderung der Volumenzusammensetzung oder durch Oberflächenmodifikationen von Biomaterialien vorgestellt. Erkenntnisse aus diesen Arbeiten konnten für die Entwicklung von Membranen für Biohybrid-Organe genutzt werden. The implantation of biomaterials or the contact of blood with extracorporal devices leads to the rapid adsorption of proteins from the surrounding biological fluids. The surface properties of materials determine the composition of the adsorption layer and the conformation of adsorbed proteins. Hence, the subsequent interaction of cells with biomaterials is dependent on the adsorption layer of proteins. The detailed knowledge on the role of surface properties in protein adsorption and cellular interactions is a useful means to learn about the

  12. The potential for distributed generation in Japanese prototype buildings: A DER-CAM analysis of policy, tariff design, building energy use, and technology development (Japanese translation)

    SciTech Connect

    Zhou, Nan; Marnay, Chris; Firestone, Ryan; Gao, Weijun; Nishida, Masaru

    2004-10-15

    The August 2003 blackout of the northeastern U.S. and CANADA caused great economic losses and inconvenience to New York City and other affected areas. The blackout was a warning to the rest of the world that the ability of conventional power systems to meet growing electricity demand is questionable. Failure of large power systems can lead to serious emergencies. Introduction of on-site generation, renewable energy such as solar and wind power and the effective utilization of exhaust heat is needed, to meet the growing energy demands of the residential and commercial sectors. Additional benefit can be achieved by integrating these distributed technologies into distributed energy resource (DER) systems. This work demonstrates a method for choosing and designing economically optimal DER systems. An additional purpose of this research is to establish a database of energy tariffs, DER technology cost and performance characteristics, and building energy consumption for Japan. This research builds on prior DER studies at the Ernest Orlando Lawrence Berkeley National Laboratory (LBNL) and with their associates in the Consortium for Electric Reliability Technology Solutions (CERTS) and operation, including the development of the microgrid concept, and the DER selection optimization program, the Distributed Energy Resources Customer Adoption Model (DER-CAM). DER-CAM is a tool designed to find the optimal combination of installed equipment and an idealized operating schedule to minimize a site's energy bills, given performance and cost data on available DER technologies, utility tariffs, and site electrical and thermal loads over a test period, usually an historic year. Since hourly electric and thermal energy data are rarely available, they are typically developed by building simulation for each of six end use loads used to model the building: electric-only loads, space heating, space cooling, refrigeration, water heating, and natural-gas-only loads. DER-CAM provides a

  13. On the van der Pauw's method applied to the measurement of low thermal conductivity materials

    NASA Astrophysics Data System (ADS)

    Morales, C.; Flores, E.; Bodega, J.; Leardini, F.; Ferrer, I. J.; Ares, J. R.; Sánchez, C.

    2016-08-01

    The electrical van der Pauw's method has recently been extended to measure the thermal conductivity of different elements and compounds. This technique provides an easy way to determine the sample in-plane thermal conductivity by avoiding the influence of the thermal contact resistances. However, the reported calculated error values appear to be underestimated when dealing with the materials with low thermal conductivity (<5 W/Km) at room temperature. The causes of this underestimation are investigated in this communication and it has been found that they are due to the drastic influence of conduction heat losses through the thermo-resistance wires as well as the resulting modification of the sample temperature map. Both phenomena lead to experimental values of the sample thermal conductivity, which are systematically higher than the tabulated ones. The magnitude of this systematic error is ˜100% dealing with the samples of macroscopic dimensions, and low thermal conductivity indicated that the obtained accurate measurements can be quite challenging.

  14. A van der Waals density functional investigation of carboranethiol self-assembled monolayers on Au(111).

    PubMed

    Mete, Ersen; Yılmaz, Ayşen; Danışman, Mehmet Fatih

    2016-05-14

    Isolated and full monolayer adsorption of various carboranethiol (C2B10H12S) isomers on the gold(111) surface has been investigated using both the standard and van der Waals density functional theory calculations. The effect of different molecular dipole moment orientations on the low energy adlayer geometries, the binding characteristics and the electronic properties of the self-assembled monolayers of these isomers has been studied. Specifically, the binding energy and work function changes associated with different molecules show a correlation with their dipole moments. The adsorption is favored for the isomers with dipole moments parallel to the surface. Of the two possible unit cell structures, (5 × 5) was found to be more stable than . PMID:27108565

  15. Self-consistent van der Waals density functional study of benzene adsorption on Si(100)

    NASA Astrophysics Data System (ADS)

    Hamamoto, Yuji; Hamada, Ikutaro; Inagaki, Kouji; Morikawa, Yoshitada

    2016-06-01

    The adsorption of benzene on the Si(100) surface is studied theoretically using the self-consistent van der Waals density functional (vdW-DF) method. The adsorption energies of two competing adsorption structures, butterfly (BF) and tight-bridge (TB) structures, are calculated with several vdW-DFs at saturation coverage. Our results show that recently proposed vdW-DFs with high accuracy all prefer TB to BF, in accord with more accurate calculations based on exact exchange and correlation within the random-phase approximation. Detailed analyses reveal the important roles played by the molecule-surface interaction and molecular deformation upon adsorption, and we suggest that their precise description is a prerequisite for accurate prediction of the most stable adsorption structure of organic molecules on semiconductor surfaces.

  16. Wavelike charge density fluctuations and van der Waals interactions at the nanoscale.

    PubMed

    Ambrosetti, Alberto; Ferri, Nicola; DiStasio, Robert A; Tkatchenko, Alexandre

    2016-03-11

    Recent experiments on noncovalent interactions at the nanoscale have challenged the basic assumptions of commonly used particle- or fragment-based models for describing van der Waals (vdW) or dispersion forces. We demonstrate that a qualitatively correct description of the vdW interactions between polarizable nanostructures over a wide range of finite distances can only be attained by accounting for the wavelike nature of charge density fluctuations. By considering a diverse set of materials and biological systems with markedly different dimensionalities, topologies, and polarizabilities, we find a visible enhancement in the nonlocality of the charge density response in the range of 10 to 20 nanometers. These collective wavelike fluctuations are responsible for the emergence of nontrivial modifications of the power laws that govern noncovalent interactions at the nanoscale. PMID:26965622

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

    PubMed Central

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

    2015-01-01

    The structural, electronic, transport and optical properties of black phosphorus/MoS2 (BP/MoS2) van der Waals (vdw) heterostructure are investigated by using first principles calculations. The band gap of BP/MoS2 bilayer decreases with the applied normal compressive strain and a semiconductor-to-metal transition is observed when the applied strain is more than 0.85 Å. BP/MoS2 bilayer also exhibits modulation of its carrier effective mass and carrier concentration by the applied compressive strain, suggesting that mobility engineering and good piezoelectric effect can be realized in BP/MoS2 heterostructure. Because the type-II band alignment can facilitate the separation of photo-excited electrons and holes, and it can benefit from the great absorption coefficient in ultra-violet region, the BP/MoS2 shows great potential to be a very efficient ultra-violet photodetector. PMID:26553370

  18. Ytterbium in quantum gases and atomic clocks: van der Waals interactions and blackbody shifts.

    PubMed

    Safronova, M S; Porsev, S G; Clark, Charles W

    2012-12-01

    We evaluated the C(6) coefficients of Yb-Yb, Yb-alkali, and Yb-group II van der Waals interactions with 2% uncertainty. The only existing experimental result for such quantities is for the Yb-Yb dimer. Our value, C(6)=1929(39) a.u., is in excellent agreement with the recent experimental determination of 1932(35) a.u. We have also developed a new approach for the calculation of the dynamic correction to the blackbody radiation shift. We have calculated this quantity for the Yb 6s(2) (1)S(0)-6s6p (3)P(0)(o) clock transition with 3.5% uncertainty. This reduces the fractional uncertainty due to the blackbody radiation shift in the Yb optical clock at 300 K to the 10(-18) level. PMID:23368178

  19. Phase diagram of van der Waals-like phase separation in a driven granular gas.

    PubMed

    Khain, Evgeniy; Meerson, Baruch; Sasorov, Pavel V

    2004-11-01

    Equations of granular hydrostatics are used to compute the phase diagram of the recently discovered van der Waals-like phase separation in a driven granular gas. The model two-dimensional system consists of smooth hard disks in a rectangular box, colliding inelastically with each other and driven by a "thermal" wall at zero gravity. The spinodal line and the critical point of the phase separation are determined. Close to the critical point, the spinodal and binodal (coexistence) lines are determined analytically. Effects of the finite size of the confining box in the direction parallel to the thermal wall are investigated. These include suppression of the phase separation by heat conduction in the lateral direction and a change from supercritical to subcritical bifurcation. PMID:15600606

  20. Light-Induced Exciton Spin Hall Effect in van der Waals Heterostructures.

    PubMed

    Li, Yun-Mei; Li, Jian; Shi, Li-Kun; Zhang, Dong; Yang, Wen; Chang, Kai

    2015-10-16

    We propose a light-induced spin Hall effect for interlayer exciton gas in monolayer MoSe2-WSe2 van der Waals heterostructure. By applying two infrared, spatially varying laser beams coupled to the exciton internal states, a spin-dependent gauge potential on the exciton center-of-mass motion is induced. This gauge potential deflects excitons in different spin states towards opposite directions, leading to a finite spin current but vanishing mass current. In the Hall bar geometry, the spin-dependent deflection gives rise to spin-dependent chiral edge states with spin-velocity locking. The spin current and chiral edge states of the excitons can be detected by spatially resolved photoluminescence spectroscopy. PMID:26550894

  1. Controlled growth of atomically thin In2Se3 flakes by van der Waals epitaxy.

    PubMed

    Lin, Min; Wu, Di; Zhou, Yu; Huang, Wei; Jiang, Wei; Zheng, Wenshan; Zhao, Shuli; Jin, Chuanhong; Guo, Yunfan; Peng, Hailin; Liu, Zhongfan

    2013-09-11

    The controlled production of high-quality atomically thin III-VI semiconductors poses a challenge for practical applications in electronics, optoelectronics, and energy science. Here, we exploit a controlled synthesis of single- and few-layer In2Se3 flakes on different substrates, such as graphene and mica, by van der Waals epitaxy. The thickness, orientation, nucleation site, and crystal phase of In2Se3 flakes were well-controlled by tuning the growth condition. The obtained In2Se3 flakes exhibit either semiconducting or metallic behavior depending on the crystal structures. Meanwhile, field-effect transistors based on the semiconducting In2Se3 flakes showed an efficient photoresponse. The controlled growth of atomically thin In2Se3 flakes with diverse conductivity and efficient photoresponsivity could lead to new applications in photodetectors and phase change memory devices. PMID:23978251

  2. Observation of Atom Wave Phase Shifts Induced by Van Der Waals Atom-Surface Interactions

    SciTech Connect

    Perreault, John D.; Cronin, Alexander D.

    2005-09-23

    The development of nanotechnology and atom optics relies on understanding how atoms behave and interact with their environment. Isolated atoms can exhibit wavelike (coherent) behavior with a corresponding de Broglie wavelength and phase which can be affected by nearby surfaces. Here an atom interferometer is used to measure the phase shift of Na atom waves induced by the walls of a 50 nm wide cavity. To our knowledge this is the first direct measurement of the de Broglie wave phase shift caused by atom-surface interactions. The magnitude of the phase shift is in agreement with that predicted by Lifshitz theory for a nonretarded van der Waals interaction. This experiment also demonstrates that atom waves can retain their coherence even when atom-surface distances are as small as 10 nm.

  3. Microstructure-dependent dynamic stability analysis of torsional NEMS scanner in van der Waals regime

    NASA Astrophysics Data System (ADS)

    Abdi, Javad; Keivani, Maryam; Abadyan, Mohamadreza

    2016-06-01

    The physico-mechanical behavior of nanoscale devices might be microstructure dependent. However, the classical continuum theory cannot correctly predict the microstructure dependency. In this paper, the strain gradient theory is employed to examine the instability characteristics of a nanoscanner with circular geometry. The governing equation of the scanner is derived incorporating the Coulomb and van der Waals (vdW) forces. The influences of applied voltage, squeeze damping and microstructure parameters on the dynamic instability of equilibrium points are studied by plotting the phase portrait and bifurcation diagrams. In the presence of the applied voltage, the phase portrait shows the saddle-node bifurcation while for freestanding scanner a subcritical pitchfork bifurcation is observed. It is concluded that the microstructure parameter enhances the torsional stability.

  4. The development of two dimensional group IV chalcogenides, blocks for van der Waals heterostructures.

    PubMed

    Sa, Baisheng; Sun, Zhimei; Wu, Bo

    2016-01-14

    In this work, we introduce a series of two dimensional (2D) group IV chalcogenides (AX)2 with the building block X-A-A-X (A = Si, Ge, Sn, and Pb, and X = Se and Te) on the basis of ab initio calculations. The analysis of energy evaluation, lattice vibration as well as the chemical bonding demonstrate the good stability of these 2D materials. Furthermore, the pictures for the chemical bonding and electronic features of the 2D (AX)2 are drawn. Their narrow gapped semiconducting nature is unraveled. Especially, strong interactions between the electrons and phonons as well as the topological insulating nature in (SiTe)2 are observed. The present results indicate that such remarkable artificial 2D (AX)2 are building blocks for van der Waals heterostructure engineering, which shows potential applications in nanoscaled electronics and optoelectronics. PMID:26667941

  5. [Citation characteristics of German authors in "Der Chirurg": hegemony of the impact factor].

    PubMed

    Hasse, W; Fischer, R J

    2010-04-01

    Characteristics of citation and language in publications of German authors from the journal "Der Chirurg" (vol 78, 2007) were analysed. Out of a total of 3,342 citations, 756 (22.62%) were from German authors with 248 (32.8) self-citations. The hegemony of the impact factor in science, research and education is critically discussed. The imbalance between the number of surgeons in the US and United Kingdom (66,032) and surgeons in the German speaking countries in Europe (25,300) is compared with respect to the counting methods used to create the impact factor of a journal. The creation of an independent impact factor in Europe and the development of an EU-based citation data bank which allows unselected access to national language scientific literature are strongly needed. PMID:19760378

  6. Quantitative bond energetics in atomic-scale junctions with significant van der Waals character

    NASA Astrophysics Data System (ADS)

    Venkataraman, Latha; Aradhya, Sriharsha; Hybertsen, Mark

    2015-03-01

    A direct measurement of the potential energy surface that characterizes individual chemical bonds in complex materials has fundamental significance for many disciplines. Here, we demonstrate that the energy profile for metallic single-atom contacts and single-molecule junctions can be mapped by fitting ambient atomic force microscope measurements carried out in the near-equilibrium regime to a physical, but simple, functional form. In particular we are able to extract bond energies for metal-molecule link bonds in cases where the interaction has significant contribution from nonspecific interactions attributed to van der Waals (vdW) interactions at short length scale in addition to specific donor-acceptor bonds. Our approach significantly expands the quantitative information extracted from these measurements, allowing direct comparisons to density functional theory (DFT) calculations instead of relying on trends in bond rupture forces alone. Currently at Cornell University.

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

    PubMed

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

    2016-09-21

    van der Waals interaction between two helium (He) atoms is studied by calculating the total energy as a function of the He-He distance within the self-consistent GW approximation, which is expected to behave correctly in the long wavelength limit. In the Born-Oppenheimer (BO) approximation, the pair potential curve has its minimum value at 2.87 Å, which is somewhat larger than the local density approximation result, 2.40 Å, and is closer to previous quantum chemistry results. The expectation value for the interatomic distance, calculated by solving the Schrödinger equation for the two nuclei problem using the BO potential energy curve, is 30 Å, which is smaller but of the same order as previous experimental and theoretical results. PMID:27538378

  8. Probing interlayer interactions in WS2 -graphene van der Waals heterostructures

    NASA Astrophysics Data System (ADS)

    Chung, Ting Fung; Yuan, Long; Huang, Libai; Chen, Yong P.

    Two-dimensional crystals based van der Waals coupled heterostructures are of interest owing to their potential applications for flexible and transparent electronics and optoelectronics. The interaction between the 2D layered crystals at the interfaces of these heterostructures is crucial in determining the overall performance and is strongly affected by contamination and interfacial strain. We have fabricated heterostructures consisting of atomically thin exfoliated WS2 and chemical-vapor-deposited (CVD) graphene, and studied the interaction and coupling between the WS2 and graphene using atomic force microscopy (AFM), Raman spectroscopy and femtosecond transient absorption measurement (TAM). Information from Raman-active phonon modes allows us to estimate charge doping in graphene and interfacial strain on the crystals. Spatial imaging probed by TAM can be correlated to the heterostructure surface morphology measured by AFM and Raman maps of graphene and WS2, showing how the interlayer coupling alters exciton decay dynamics quantitatively.

  9. Hidden scale invariance in molecular van der Waals liquids: A simulation study

    NASA Astrophysics Data System (ADS)

    Schrøder, Thomas B.; Pedersen, Ulf R.; Bailey, Nicholas P.; Toxvaerd, Søren; Dyre, Jeppe C.

    2009-10-01

    Results from molecular dynamics simulations of two viscous molecular model liquids—the Lewis-Wahnström model of orthoterphenyl and an asymmetric dumbbell model—are reported. We demonstrate that the liquids have a “hidden” approximate scale invariance: equilibrium potential energy fluctuations are accurately described by inverse power-law (IPL) potentials, the radial distribution functions are accurately reproduced by the IPL’s, and the radial distribution functions obey the IPL predicted scaling properties to a good approximation. IPL scaling of the dynamics also applies—with the scaling exponent predicted by the equilibrium fluctuations. In contrast, the equation of state does not obey the IPL scaling. We argue that our results are general for van der Waals liquids, but do not apply, e.g., for hydrogen-bonded liquids.

  10. Revisiting the adsorption of copper-phthalocyanine on Au(111) including van der Waals corrections

    SciTech Connect

    Lüder, Johann; Eriksson, Olle; Sanyal, Biplab; Brena, Barbara

    2014-03-28

    We have studied the adsorption of copper-phthalocyanine on Au(111) by means of van der Waals corrected density functional theory using the Tkatchenko-Scheffler method. We have compared the element and site resolved adsorption distances to recent experimental normal-incident X-ray standing wave measurements. The measured adsorption distances could be reproduced within a deviation of 1% for the Cu atom, 1% for the C atoms, and 2% for the N atoms. The molecule was found to have a magnetic moment of 1 μ{sub B} distributed over the Cu and the N atoms of the pyrrole ring. Simulated scanning tunnel microscopy images based on the total and on the spin-resolved differential charge densities are provided for bias voltages of −1.45 and 1.45 eV.

  11. Revisiting the adsorption of copper-phthalocyanine on Au(111) including van der Waals corrections.

    PubMed

    Lüder, Johann; Eriksson, Olle; Sanyal, Biplab; Brena, Barbara

    2014-03-28

    We have studied the adsorption of copper-phthalocyanine on Au(111) by means of van der Waals corrected density functional theory using the Tkatchenko-Scheffler method. We have compared the element and site resolved adsorption distances to recent experimental normal-incident X-ray standing wave measurements. The measured adsorption distances could be reproduced within a deviation of 1% for the Cu atom, 1% for the C atoms, and 2% for the N atoms. The molecule was found to have a magnetic moment of 1 μB distributed over the Cu and the N atoms of the pyrrole ring. Simulated scanning tunnel microscopy images based on the total and on the spin-resolved differential charge densities are provided for bias voltages of -1.45 and 1.45 eV. PMID:24697474

  12. Das Programm Oder 2006. Hochwasserschutz in Polen im Zuge der EU-Osterweiterung

    NASA Astrophysics Data System (ADS)

    Kühne, Olaf

    Hochwasser ist ein natürliches Ereignis: Seit jeher sind die Menschen mit Hochwasser und seinen Auswirkungen konfrontiert. Das Ausmaß von Hochwasser reicht dabei von Straßenüberschwemmungen bis zur Überflutung ganzer Landesteile. Auch im Oderflußsystem waren und sind Überschwemmungen keine Seltenheit, in den letzten 200 Jahren ereigneten sie sich in den Jahren 1813, 1838, 1854, 1870, 1903, 1958, 1965, 1970, 1972, 1977, 1981, 1985 und 1997. Das Hochwasser von 1997 war jedoch das schwerste im genannten Zeitraum. Als Reaktion auf das Hochwasser von 1997 wurde in der betroffenen Region das Programm 〝Oder 2006`` entwickelt. Mit seiner Hilfe sollen die Auswirkungen künftiger Hochwasserereignisse abgeschwächt werden.

  13. Communication: Multiple-property-based diabatization for open-shell van der Waals molecules

    NASA Astrophysics Data System (ADS)

    Karman, Tijs; van der Avoird, Ad; Groenenboom, Gerrit C.

    2016-03-01

    We derive a new multiple-property-based diabatization algorithm. The transformation between adiabatic and diabatic representations is determined by requiring a set of properties in both representations to be related by a similarity transformation. This set of properties is determined in the adiabatic representation by rigorous electronic structure calculations. In the diabatic representation, the same properties are determined using model diabatic states defined as products of undistorted monomer wave functions. This diabatic model is generally applicable to van der Waals molecules in arbitrary electronic states. Application to locating seams of conical intersections and collisional transfer of electronic excitation energy is demonstrated for O2 - O2 in low-lying excited states. Property-based diabatization for this test system included all components of the electric quadrupole tensor, orbital angular momentum, and spin-orbit coupling.

  14. Quantum defect theory for the van der Waals plus dipole-dipole interaction

    NASA Astrophysics Data System (ADS)

    Wang, Gao-Ren; Xie, Ting; Huang, Yin; Zhang, Wei; Cong, Shu-Lin

    2012-12-01

    We investigate the scattering dynamics governed by the long-range van der Waals plus dipole-dipole interaction potential, -C6/R6-C3/R3, which describes the long-range interaction between two polar molecules in an electric field. In the spirit of quantum defect theory, a set of parameters which are nearly constants in the threshold regime is defined to characterize the scattering process. Using appropriate boundary conditions for the scattering wave functions and relevant parameters, we explore the quantum reflection by and quantum tunneling through the long-range potential. As a sample application, the reactive collision rates of 40K87Rb + 40K87Rb are calculated.

  15. Causality, universality, and effective field theory for van der Waals interactions

    NASA Astrophysics Data System (ADS)

    Elhatisari, Serdar; König, Sebastian; Lee, Dean; Hammer, H.-W.

    2013-05-01

    We analyze low-energy scattering for arbitrary short-range interactions plus an attractive 1/r6 tail. We derive the constraints of causality and unitarity and find that the van der Waals length scale dominates over parameters characterizing the short-distance physics of the interaction. This separation of scales suggests a separate universality class for physics characterizing interactions with an attractive 1/r6 tail. We argue that a similar universality class exists for any attractive potential 1/rα for α⩾2. We also discuss the extension to multichannel systems near a magnetic Feshbach resonance. We discuss the implications for effective field theory with attractive singular power-law tails.

  16. An application of the van der Waals density functional: Hydrogen bonding and stacking interactions between nucleobases.

    PubMed

    Cooper, Valentino R; Thonhauser, T; Langreth, David C

    2008-05-28

    We apply the van der Waals density functional (vdW-DF) to study hydrogen bonding and stacking interactions between nucleobases. The excellent agreement of our results with high level quantum chemical calculations highlights the value of the vdW-DF for first-principles investigations of biologically important molecules. Our results suggest that, in the case of hydrogen-bonded nucleobase pairs, dispersion interactions reduce the cost of propeller twists while having a negligible effect on buckling. Furthermore, the efficient scaling of DFT methods allowed for the easy optimization of separation distance between nucleobase stacks, indicating enhancements in the interaction energy of up to 3 kcalmol over previous fixed distance calculations. We anticipate that these results are significant for extending the vdW-DF method to model larger vdW complexes and biological molecules. PMID:18513005

  17. Zwischen Commonsense und Wissenschaft Mathematik in der Erziehungsphilosophie A. N. Whiteheads

    NASA Astrophysics Data System (ADS)

    Sölch, Dennis

    Obwohl Whitehead heute wie selbstverständlich als Philosoph rezipiert wird, so hat er seine wissenschaftliche Laufbahn doch als Mathematiker begonnen. Lange Zeit war er gemeinsam mit Bertrand Russell als Autor der Principia Mathematica unter Mathematikern und mathematischen Logikern deutlich besser bekannt als unter Philosophen. Doch selbst von denjenigen, die sich mit Whiteheads Überlegungen zur Metaphysik, zur Wissenschaftsgeschichte und zur Theologie befassen, werden seine Schriften zur Philosophie von Erziehung und Bildung häufig kaum beachtet. So entgeht es leicht, dass Whitehead nicht nur ein auf theoretischem Gebiet brillanter Mathematiker war, sondern sein theoretisches Fachwissen im Hinblick auf pädagogische und didaktische Relevanz fortwährend reflektiert hat.

  18. The role of van der Waals interactions in surface-supported supramolecular networks.

    PubMed

    Nguyen, Manh-Thuong; Pignedoli, Carlo A; Treier, Matthias; Fasel, Roman; Passerone, Daniele

    2010-01-28

    The development of a detailed theoretical understanding of surface-supported supramolecular networks is important for designing novel organic nanodevices. By comparing with STM experiments, we show that van der Waals corrections to density functional theory (DFT) in the generalized gradient approximation (GGA) are mandatory to correctly reproduce the electronic and geometric structure of a prototypical system of this kind, the self-assembled hydrogen bonded network formed by 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) and 4,4''-diamino-p-terphenyl (DATP) deposited on Au(111). Our results reproduce both the network structure and its higher stability with respect to homomolecular networks. By successful comparison with the experiments, we demonstrate that dispersive interactions must be taken into account when rationally designing organic semiconductor nanostructures on a metallic substrate. DFT-GGA alone would fail in predicting geometric and electronic properties for weakly bounded large organic adsorbates on coinage metal surfaces. PMID:20066384

  19. Van der Waals interactions between polymers with sequence-specific polarizabilities: Stiff polymers and Gaussian coils

    NASA Astrophysics Data System (ADS)

    Lu, Bing-Sui; Naji, Ali; Podgornik, Rudolf

    2016-01-01

    We consider the van der Waals interaction between a pair of polymers with quenched heterogeneous sequences of local polarizabilities along their backbones, and study the effective pairwise interaction energy for both stiff polymers and flexible Gaussian coils. In particular, we focus on the cases where the pair of polarizability sequences are (i) distinct and (ii) identical. We find that the pairwise interaction energies of distinct and identical Gaussian coils are both isotropic and exhibit the same decay behavior for separations larger than their gyration radius, in contradistinction to the orientationally anisotropic interaction energies of distinct and identical stiff polymers. For both Gaussian coils and stiff polymers, the attractive interaction between identical polymers is enhanced if the polarizability sequence is more heterogeneous.

  20. Karl ernst von Baer's 'Uber Entwickelungsgeschichte der Thiere II' and its unpublished drawings.

    PubMed

    Tammiksaar, Erki; Brauckmann, Sabine

    2004-01-01

    In 1828 Karl Ernst von Baer (1792-1876) published his seminal Uber Entwickelungsgeschichte der Thiere. Beobachtung und Reflexion. In the preface he announced that a second volume with one copper plate would be finished 'in a few weeks'. However, it took nine years until the unfinished second volume was released, with four copperplates. In his 'Autobiography', von Baer did not clarify the reasons why he did not finish his research program of comparative embryology. The paper attempts to elucidate them, furnished by archival documents and von Baer's unpublished embryological drawings. Our sketch of a few figures will show that (1) von Baer searched for 'analogies' (homologies) as a unifying principle and (2) explained the mechanisms of embryogenesis by physiological reasoning (electromagnetism). The main objective is to show that technical problems in illustrating and conceptual difficulties impeded von Baer's ambitious research program. PMID:16302690

  1. Adsorption of polyiodobenzene molecules on the Pt(111) surface using van der Waals density functional theory

    NASA Astrophysics Data System (ADS)

    Johnston, Karen; Pekoz, Rengin; Donadio, Davide

    2016-02-01

    Adsorption of aromatic molecules on surfaces is widely studied due to applications in molecular electronics. In this work, the adsorption of iodobenzene molecules on the Pt(111) surface has been studied using density functional theory. Iodobenzene molecules, with various numbers of iodine atoms, have two non-dissociative adsorption minima. One structure exhibits chemisorption between the ring and the surface (short-range) and the other structure exhibits chemisorption between the iodine ions and the surface (long-range). Both structures have a strong van der Waals interaction with the surface. In general, the adsorption energy increases as the number of iodine atoms increases. The dissociated structure of monoiodobenzene was investigated, and the dissociation barrier and the barrier between the short- and long-range states were compared.

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

    NASA Astrophysics Data System (ADS)

    Kawanishi, Sakiko; Mizoguchi, Teruyasu

    2016-05-01

    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.

  3. Van der Waals epitaxy of functional MoO2 film on mica for flexible electronics

    NASA Astrophysics Data System (ADS)

    Ma, Chun-Hao; Lin, Jheng-Cyuan; Liu, Heng-Jui; Do, Thi Hien; Zhu, Yuan-Min; Ha, Thai Duy; Zhan, Qian; Juang, Jenh-Yih; He, Qing; Arenholz, Elke; Chiu, Po-Wen; Chu, Ying-Hao

    2016-06-01

    Flexible electronics have a great potential to impact consumer electronics and with that our daily life. Currently, no direct growth of epitaxial functional oxides on commercially available flexible substrates is possible. In this study, in order to address this challenge, muscovite, a common layered oxide, is used as a flexible substrate that is chemically similar to typical functional oxides. We fabricated epitaxial MoO2 films on muscovite via pulsed laser deposition technique. A combination of X-ray diffraction and transmission electron microscopy confirms van der Waals epitaxy of the heterostructures. The electrical transport properties of MoO2 films are similar to those of the bulk. Flexible or free-standing MoO2 thin film can be obtained and serve as a template to integrate additional functional oxide layers. Our study demonstrates a remarkable concept to create flexible electronics based on functional oxides.

  4. The influence of van der Waals forces on droplet morphological transitions and solvation forces in nanochannels.

    PubMed

    Dutka, F; Napiórkowski, M

    2014-01-22

    The morphological phase transition between sessile and lenticular shapes of a droplet placed in a nanochannel is observed upon increasing the droplet volume. The phase diagram for this system is discussed within both macroscopic and mesoscopic approaches. On the mesoscopic level, the van der Waals forces are taken into account via the effective interface potential acting between the channel walls and the droplet. We discuss the contact angle dependence on the droplet volume and the distance between the walls; this angle turns out to be smaller than the macroscopic Young's angle. The droplet's presence induces the solvation force acting between the channel walls. It can be either attractive or repulsive, depending on the width of the channel. PMID:24285307

  5. Improving the Description of Nonmagnetic and Magnetic Molecular Crystals via the van der Waals Density Functional

    NASA Astrophysics Data System (ADS)

    Obata, Masao; Nakamura, Makoto; Hamada, Ikutaro; Oda, Tatsuki

    2015-02-01

    We have derived and implemented a stress tensor formulation for the van der Waals density functional (vdW-DF) with spin-polarization-dependent gradient correction (GC) recently proposed by the authors [J. Phys. Soc. Jpn. 82, 093701 (2013)] and applied it to nonmagnetic and magnetic molecular crystals under ambient condition. We found that the cell parameters of the molecular crystals obtained with vdW-DF show an overall improvement compared with those obtained using local density and generalized gradient approximations. In particular, the original vdW-DF with GC gives the equilibrium structural parameters of solid oxygen in the α-phase, which are in good agreement with the experiment.

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

    PubMed Central

    Lin, Yu-Chuan; Ghosh, Ram Krishna; Addou, Rafik; Lu, Ning; Eichfeld, Sarah M.; Zhu, Hui; Li, Ming-Yang; Peng, Xin; Kim, Moon J.; Li, Lain-Jong; Wallace, Robert M.; Datta, Suman; Robinson, Joshua A.

    2015-01-01

    Vertical integration of two-dimensional van der Waals materials is predicted to lead to novel electronic and optical properties not found in the constituent layers. Here, we present the direct synthesis of two unique, atomically thin, multi-junction heterostructures by combining graphene with the monolayer transition-metal dichalcogenides: molybdenum disulfide (MoS2), molybdenum diselenide (MoSe2) and tungsten diselenide (WSe2). The realization of MoS2–WSe2–graphene and WSe2–MoS2–graphene heterostructures leads to resonant tunnelling in an atomically thin stack with spectrally narrow, room temperature negative differential resistance characteristics. PMID:26088295

  7. Phase diagram of Rydberg atoms with repulsive van der Waals interaction

    SciTech Connect

    Osychenko, O. N.; Astrakharchik, G. E.; Boronat, J.; Lutsyshyn, Y.; Lozovik, Yu. E.

    2011-12-15

    We report a quantum Monte Carlo calculation of the phase diagram of bosons interacting with a repulsive inverse sixth power pair potential, a model for assemblies of Rydberg atoms in the local van der Waals blockade regime. The model can be parametrized in terms of just two parameters, the reduced density and temperature. Solidification happens to the fcc phase. At zero temperature, the transition density is found with the diffusion Monte Carlo method at density {rho}=3.9 (({Dirac_h}/2{pi}){sup 2}/mC{sub 6}){sup 3/4}, where C{sub 6} is the strength of the interaction. The solidification curve at nonzero temperature is studied with the path-integral Monte Carlo approach and is compared with transitions in corresponding harmonic and classical crystals. Relaxation mechanisms are considered in relation to present experiments.

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

    SciTech Connect

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

    2009-06-15

    In this paper we investigate the influence of ultrathin water layer ({approx}1-1.5 nm) on the van der Waals/Casimir force between gold surfaces. Adsorbed water is inevitably present on gold surfaces at ambient conditions as jump-up-to contact during adhesion experiments demonstrate. Calculations based on the Lifshitz theory give very good agreement with the experiment in the absence of any water layer for surface separations d > or approx. 10 nm. However, a layer of thickness h < or approx. 1.5 nm is allowed by the error margin in force measurements. At shorter separations, d < or approx. 10 nm, the water layer can have a strong influence as calculations show for flat surfaces. Nonetheless, in reality the influence of surface roughness must also be considered, and it can overshadow any water layer influence at separations comparable to the total sphere-plate rms roughness w{sub shp}+w.

  9. 1-D Van der Waals Foams Heated by Ion Beam Energy Deposition

    SciTech Connect

    Zylstra, A. B.; Barnard, J. J.; More, R. M.

    2009-12-23

    One dimensional simulations of various initial average density aluminum foams (modeled as slabs of solid metal separated by low density regions) heated by volumetric energy deposition are conducted with a Lagrangian hydrodynamics code using a van der Waals equation of tate (EOS). The resulting behavior is studied to facilitate the design of future warm dense matter (WDM) experiments at LBNL. In the simulations the energy deposition ranges from 10 to 30 kJ/g and from 0.075 to 4.0 ns total pulse length, resulting in temperatures from approximately 1 o 4 eV. We study peak pressures and temperatures in the foams, expansion velocity, and the phase evolution. Five relevant time scales in the problem are identified. Additionally, we present a method for characterizing the level of inhomogeneity in a foam target as it is heated and the time it takes for a foam to homogenize.

  10. 1-D Van der Waals Foams Heated by Ion Beam Energy Deposition

    SciTech Connect

    Zylstra, A; Barnard, J J; More, R M

    2010-03-19

    One dimensional simulations of various initial average density aluminum foams (modeled as slabs of solid metal separated by low density regions) heated by volumetric energy deposition are conducted with a Lagrangian hydrodynamics code using a van der Waals equation of state (EOS). The resulting behavior is studied to facilitate the design of future warm dense matter (WDM) experiments at LBNL. In the simulations the energy deposition ranges from 10 to 30 kJ/g and from 0.075 to 4.0 ns total pulse length, resulting in temperatures from approximately 1 to 4 eV. We study peak pressures and temperatures in the foams, expansion velocity, and the phase evolution. Five relevant time scales in the problem are identified. Additionally, we present a method for characterizing the level of inhomogeneity in a foam target as it is heated and the time it takes for a foam to homogenize.

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

    PubMed

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

    2015-01-01

    The structural, electronic, transport and optical properties of black phosphorus/MoS2 (BP/MoS2) van der Waals (vdw) heterostructure are investigated by using first principles calculations. The band gap of BP/MoS2 bilayer decreases with the applied normal compressive strain and a semiconductor-to-metal transition is observed when the applied strain is more than 0.85 Å. BP/MoS2 bilayer also exhibits modulation of its carrier effective mass and carrier concentration by the applied compressive strain, suggesting that mobility engineering and good piezoelectric effect can be realized in BP/MoS2 heterostructure. Because the type-II band alignment can facilitate the separation of photo-excited electrons and holes, and it can benefit from the great absorption coefficient in ultra-violet region, the BP/MoS2 shows great potential to be a very efficient ultra-violet photodetector. PMID:26553370

  12. Formation of van der Waals molecules in buffer-gas-cooled magnetic traps [corrected].

    PubMed

    Brahms, N; Tscherbul, T V; Zhang, P; Kłos, J; Sadeghpour, H R; Dalgarno, A; Doyle, J M; Walker, T G

    2010-07-16

    We predict that a large class of helium-containing cold polar molecules form readily in a cryogenic buffer gas, achieving densities as high as 10(12)  cm(-3). We explore the spin relaxation of these molecules in buffer-gas-loaded magnetic traps and identify a loss mechanism based on Landau-Zener transitions arising from the anisotropic hyperfine interaction. Our results show that the recently observed strong T(-6) thermal dependence of the spin-change rate of silver (Ag) trapped in dense (3)He is accounted for by the formation and spin change of Ag(3)He van der Waals molecules, thus providing indirect evidence for molecular formation in a buffer-gas trap. PMID:20867761

  13. The effect of nonpolar solvents on Rydberg states: van der Waals complexes of azabicyclooctanes

    NASA Astrophysics Data System (ADS)

    Shang, Q. Y.; Moreno, P. O.; Dion, C.; Bernstein, E. R.

    1993-05-01

    The effect of solvation by nonpolar solvents on the (n,3s) Rydberg states of 1,4-diazabicyclo[2.2.2]octane (DABCO) and azabicyclo[2.2.2]octane (ABCO) is investigated through mass resolved excitation spectroscopy of their van der Waals complexes. The solute/solvent clusters formed in a supersonic expansion include DABCO and ABCO with Ar, n-CmH2m+2 (m=1-7), and CF4 and C2F6. The resulting spectra are analyzed with the help of empirical potential energy calculations of the cluster binding energies, minimum energy structures, van der Waals modes, and potential barriers between the various cluster minimum energy structures. Good agreement is found between the calculated and experimental results for DABCO and ABCO clustered with argon and methane. The spectra of clusters with all other hydrocarbons can be ascribed to only one major geometry for each cluster stoichiometry, despite the fact that calculations yield many stable geometries for each cluster. This apparent lack of agreement between calculations and experiments can be rationalized based on cluster binding energy, zero point energy, and the potential energy barriers between the cluster minima. The observed blue shift of the cluster 000 transition energy as a function of the n-alkane chain length can be qualitatively modeled by a Lennard-Jones potential for the solute-solvent interaction for both the ground and excited states. The model reveals a strong repulsive interaction between the Rydberg state electronic distribution and the solvent molecule. This repulsion depends on the distance between the solvent molecule and the solute molecule nitrogen atom.

  14. Freestanding van der Waals heterostructures of graphene and transition metal dichalcogenides.

    PubMed

    Azizi, Amin; Eichfeld, Sarah; Geschwind, Gayle; Zhang, Kehao; Jiang, Bin; Mukherjee, Debangshu; Hossain, Lorraine; Piasecki, Aleksander F; Kabius, Bernd; Robinson, Joshua A; Alem, Nasim

    2015-05-26

    Vertical stacking of two-dimensional (2D) crystals has recently attracted substantial interest due to unique properties and potential applications they can introduce. However, little is known about their microstructure because fabrication of the 2D heterostructures on a rigid substrate limits one's ability to directly study their atomic and chemical structures using electron microscopy. This study demonstrates a unique approach to create atomically thin freestanding van der Waals heterostructures-WSe2/graphene and MoS2/graphene-as ideal model systems to investigate the nucleation and growth mechanisms in heterostructures. In this study, we use transmission electron microscopy (TEM) imaging and diffraction to show epitaxial growth of the freestanding WSe2/graphene heterostructure, while no epitaxy is maintained in the MoS2/graphene heterostructure. Ultra-high-resolution aberration-corrected scanning transmission electron microscopy (STEM) shows growth of monolayer WSe2 and MoS2 triangles on graphene membranes and reveals their edge morphology and crystallinity. Photoluminescence measurements indicate a significant quenching of the photoluminescence response for the transition metal dichalcogenides on freestanding graphene, compared to those on a rigid substrate, such as sapphire and epitaxial graphene. Using a combination of (S)TEM imaging and electron diffraction analysis, this study also reveals the significant role of defects on the heterostructure growth. The direct growth technique applied here enables us to investigate the heterostructure nucleation and growth mechanisms at the atomic level without sample handling and transfer. Importantly, this approach can be utilized to study a wide spectrum of van der Waals heterostructures. PMID:25885122

  15. Thioarsenides: A case for long-range Lewis acid-base-directed van der Waals interactions

    SciTech Connect

    Gibbs, Gerald V.; Wallace, Adam F.; Downs, R. T.; Ross, Nancy L.; Cox, David F.; Rosso, Kevin M.

    2011-04-01

    Electron density distributions, bond paths, Laplacian and local energy density properties have been calculated for a number of As4Sn (n = 3,4,5) thioarsenide molecular crystals. On the basis of the distributions, the intramolecular As-S and As-As interactions classify as shared bonded interactions and the intermolecular As-S, As-As and S-S interactions classify as closed-shell van der Waals bonded interactions. The bulk of the intermolecular As-S bond paths link regions of locally concentrated electron density (Lewis base regions) with aligned regions of locally depleted electron density (Lewis acid regions) on adjacent molecules. The paths are comparable with intermolecular paths reported for several other molecular crystals that link aligned Lewis base and acid regions in a key-lock fashion, interactions that classified as long range Lewis acid-base directed van der Waals interactions. As the bulk of the intermolecular As-S bond paths (~70%) link Lewis acid-base regions on adjacent molecules, it appears that molecules adopt an arrangement that maximizes the number of As-S Lewis acid-base intermolecular bonded interactions. The maximization of the number of Lewis acid-base interactions appears to be connected with the close-packed array adopted by molecules: distorted cubic close-packed arrays are adopted for alacránite, pararealgar, uzonite, realgar and β-AsS and the distorted hexagonal close-packed arrays adopted by α- and β-dimorphite. A growth mechanism is proposed for thioarsenide molecular crystals from aqueous species that maximizes the number of long range Lewis acid-base vdW As-S bonded interactions with the resulting directed bond paths structuralizing the molecules as a molecular crystal.

  16. Excitons in van der Waals heterostructures: The important role of dielectric screening

    NASA Astrophysics Data System (ADS)

    Latini, S.; Olsen, T.; Thygesen, K. S.

    2015-12-01

    The existence of strongly bound excitons is one of the hallmarks of the newly discovered atomically thin semiconductors. While it is understood that the large binding energy is mainly due to the weak dielectric screening in two dimensions, a systematic investigation of the role of screening on two-dimensional (2D) excitons is still lacking. Here we provide a critical assessment of a widely used 2D hydrogenic exciton model, which assumes a dielectric function of the form ɛ (q )=1 +2 π α q , and we develop a quasi-2D model with a much broader applicability. Within the quasi-2D picture, electrons and holes are described as in-plane point charges with a finite extension in the perpendicular direction, and their interaction is screened by a dielectric function with a nonlinear q dependence which is computed ab initio. The screened interaction is used in a generalized Mott-Wannier model to calculate exciton binding energies in both isolated and supported 2D materials. For isolated 2D materials, the quasi-2D treatment yields results almost identical to those of the strict 2D model, and both are in good agreement with ab initio many-body calculations. On the other hand, for more complex structures such as supported layers or layers embedded in a van der Waals heterostructure, the size of the exciton in reciprocal space extends well beyond the linear regime of the dielectric function, and a quasi-2D description has to replace the 2D one. Our methodology has the merit of providing a seamless connection between the strict 2D limit of isolated monolayer materials and the more bulk-like screening characteristics of supported 2D materials or van der Waals heterostructures.

  17. Der p 1-pulsed myeloid and plasmacytoid dendritic cells from house dust mite-sensitized allergic patients dysregulate the T cell response.

    PubMed

    Charbonnier, Anne-Sophie; Hammad, Hamida; Gosset, Philippe; Stewart, Geoffrey A; Alkan, Sefik; Tonnel, André-Bernard; Pestel, Joël

    2003-01-01

    Although reports suggest that dendritic cells (DC) are involved in the allergic reaction characterized by a T helper cell type 2 (Th2) profile, the role of myeloid (M-DC) and plasmacytoid DC (P-DC), controlling the balance Th1/Th2, remains unknown. Here, we showed that in Dermatophagoides pteronyssinus (Dpt)-sensitized allergic patients and in healthy donors, M-DC displayed a higher capacity to capture Der p 1, a major allergen of Dpt, than did P-DC. However, Der p 1-pulsed M-DC from healthy subjects overexpressed CD80 and secreted interleukin (IL)-10, whereas M-DC from allergic patients did not. In contrast, with Der p 1-pulsed P-DC from both groups, no increase in human leukocyte antigen-DR, CD80, and CD86 and no IL-10 secretion were detected. When cocultured with allogeneic naive CD4(+) T cells from healthy donors, Der p 1-pulsed M-DC from allergic patients favored a Th1 profile [interferon (IFN)-gamma(high)/IL-4(low)] and Der p 1-pulsed P-DC, a Th2 profile (IFN-gamma(low)/IL-4(high)). In healthy donors, no T cell polarization (IFN-gamma(low)/IL-4(low)) was induced by Der p 1-pulsed M-DC or P-DC, but in response to Der p 1-pulsed M-DC, T cells secreted IL-10. The neutralization of IL-10 produced by Der p 1-pulsed M-DC from healthy donors led to an inhibition of IL-10 production by T cells and a polarization toward a type 1. Thus, IL-10 produced by M-DC might be an essential mediator controlling the balance between tolerance and allergic status. In addition, P-DC could contribute to the steady state in healthy donors or to the development of a Th2 response in allergic donors. PMID:12525566

  18. Comparative analysis of biological activities of Der p I-derived peptides on Fc epsilon receptor-bearing cells from Dermatophagoides pteronyssinus-sensitive patients.

    PubMed

    Jeannin, P; Pestel, J; Bossus, M; Lassalle, P; Tartar, A; Tonnel, A B

    1993-04-01

    The ability of four uncoupled synthetic peptides (p52-71, p117-133, p176-187, p188-199) derived from Der p I, a major allergen from the house dust mite Dermatophagoides pteronyssinus (Dpt) to stimulate Fc epsilon R+ cells from Dpt-sensitive patients was comparatively analysed. Each free peptide may specifically stimulate basophils (Fc epsilon RI+ cells) and platelets (Fc epsilon RII+ cells) from patients with significant levels of anti-Der p I IgE antibodies; p52-71 and p117-133 appear the best cell stimulation inducers. Both concentration-dependent biological activities of Der p I-peptide on Fc epsilon R+ cells are enhanced by coupling peptide to a carrier (as human serum albumin). Interestingly each Der p I-sensitive patient tested presents an individual pattern of response to peptide. Thus, from our results it appears that different Der p I sequences could be involved in the immune response to Der p I. PMID:7682161

  19. Comparative analysis of biological activities of Der p I-derived peptides on Fc epsilon receptor-bearing cells from Dermatophagoides pteronyssinus-sensitive patients.

    PubMed Central

    Jeannin, P; Pestel, J; Bossus, M; Lassalle, P; Tartar, A; Tonnel, A B

    1993-01-01

    The ability of four uncoupled synthetic peptides (p52-71, p117-133, p176-187, p188-199) derived from Der p I, a major allergen from the house dust mite Dermatophagoides pteronyssinus (Dpt) to stimulate Fc epsilon R+ cells from Dpt-sensitive patients was comparatively analysed. Each free peptide may specifically stimulate basophils (Fc epsilon RI+ cells) and platelets (Fc epsilon RII+ cells) from patients with significant levels of anti-Der p I IgE antibodies; p52-71 and p117-133 appear the best cell stimulation inducers. Both concentration-dependent biological activities of Der p I-peptide on Fc epsilon R+ cells are enhanced by coupling peptide to a carrier (as human serum albumin). Interestingly each Der p I-sensitive patient tested presents an individual pattern of response to peptide. Thus, from our results it appears that different Der p I sequences could be involved in the immune response to Der p I. PMID:7682161

  20. Distributed Energy Resources Customer Adoption Model (DER-CAM), Investment & Planing Version 3.10.5.m

    Energy Science and Technology Software Center (ESTSC)

    2014-04-01

    Version 3.10.5 is a multi-year Decision Support tool for Distributed Generation (DG). DER-CAM was initially created as an exclusively economic energy model, able to find the cost minimizing combination and operation profile of a set of DER technologies that meet heat and electric loads of a single building or microgrid for a typical test year. Now, version 3.10.5.m solves for a multiple-year horizon the technology choice question, the appropriate capacity for each selected technology asmore » well as the operational and investment schedule. Optimized investment decisions are based on techno-economic criteria, along with site information such as energy loads, economic forecast, and technology characterization. Version 3.10.5 contains: 1. a PV and battery degradation model and 2. variable performance for technologies. Efficiency, investment costs, etc. can vary over time and model technology breakthroughs and advancements.« less