Thermodynamic calculations on the catalytic growth of multiwall carbon nanotubes

We have developed a thermodynamic model of the catalytic growth of multiwall carbon nanotubes from hydrocarbon precursors at elevated temperature. Using this model we have computed the heat distribution, and carbon concentration in the catalyst. Calculations delivered a analytical formula for the growth time and growth rate. We find that the growth is mainly driven by a concentration gradient within the catalyst, rather than a temperature gradient.Comment: 9 pages, 3 figures, 1 tabl

Die Datenmodellstandardisierung und ihre Auswirkungen auf RFID-Bibliotheken

Bereits 2002, als sich die ersten Bibliotheken für den Einsatz von RFID-Systemen entschlossen, wurde auf vorhandene Standards für die Entwicklung der Selbstverbuchung und Mediensicherung zurückgegriffen. Ohne diese wäre der heutige Markt für RFID-Systeme in Bibliotheken nicht entstanden. Dabei handelte es sich, erstens, um das SIP2-Protokoll (Standard Interchange Protocol 2) für die Verbindung zwischen RFID-System und Bibliotheks-Management-System (LMS, Library Management System). Zweitens war der RFID-Standard ISO 15693 ausschlaggebend, welcher die so genannte Luftschnittstelle zwischen RFID-Etiketten und Lesegeräten beschrieb und aus dem Smartcard-Bereich stammte. Dieser Standard war die wichtigste technische Voraussetzung für die Entwicklung des Massenmarktes für RFID- Etiketten. Weitere Standards und Regelwerke existierten zur Sendeleistung und CE-Zeichen, und schliesslich gab es noch die so genannte ISIL-Nummer (International Standard Identifier for Libraries). Als eindeutige Bibliothekskennzeichnung wird sie für die Zuordnung der Medien zu einer spezifischen Bibliothek genutzt. Die jeweiligen Mediennummern einer Bibliothek zusammen mit der ISIL ermöglichen weltweit eine eindeutige Kennzeichnung der Medien. Die jüngste Entwicklung in diesem Reigen der Standards – und dies ist auch ein Novum innerhalb anderer RFID-Anwendungen ( Logistik, Lagerhaltung, Prozesskontrolle usw.) – ist die Festlegung eines Datenmodells für die RFID- Etiketten in ISO 28560, d. h. ihres Dateninhaltes und dessen Schreibweise im Speicher eines RFID-Chips. Neu ist daran, dass nicht nur die Art der Kommunikation (im übertragenen Sinne auf die Sprache: wie werden Buchstaben ausgetauscht), sondern auch deren Inhalt (Festlegung der Sprache, Wörter und Inhalte) definiert werden. Im Folgenden werden der heutige Status, die bereits sichtbaren und zukünftigen Auswirkungen der Datenmodellstandardisierung beschrieben

Raman spectroscopy and field emission measurements on catalytically grown carbon nanotubes

We used microcontact printing to pattern a silicon surface with an iron-containing catalytic solution. Multi-wall carbon nanotubes were subsequently grown on the patterned areas by chemical vapor deposition at temperatures between 650 and 1000C. We demonstrate that the diameter of the catalytically grown multi-wall nanotubes increases with the deposition temperature. Raman spectroscopy has been used to investigate the crystalline character of the obtained structures and it is found that the fraction of the nano-crystalline shell increases with the temperatures. The measurement of the field emission properties shows a correlation between the tube diameter and the emission field values.Comment: 6 pages, 6 figures, 1 tabl

Hall-effect sign-inversion in a realizable 3D metamaterial

In 2009, Briane and Milton proved mathematically the existence of three-dimensional isotropic metamaterials with a classical Hall coefficient which is negative with respect to that of all of the metamaterial constituents. Here, we significantly simplify their blueprint towards an architecture composed of only a single constituent material in vacuum/air, which can be seen as a special type of porosity. We show that the sign of the Hall voltage is determined by a separation parameter between adjacent tori. This qualitative behavior is robust even for only a small number of metamaterial unit cells. The combination of simplification and robustness brings experimental verifications of this striking sign-inversion into reach.Comment: 9 figures, 7 page

Illuminating the dark corridor in graphene: polarization dependence of angle-resolved photoemission spectroscopy on graphene

We have used s- and p-polarized synchrotron radiation to image the electronic structure of epitaxial graphene near the K-point by angular resolved photoemission spectroscopy (ARPES). Part of the experimental Fermi surface is suppressed due to the interference of photoelectrons emitted from the two equivalent carbon atoms per unit cell of graphene's honeycomb lattice. Here we show that by rotating the polarization vector, we are able to illuminate this 'dark corridor' indicating that the present theoretical understanding is oversimplified. Our measurements are supported by first-principles photoemission calculations, which reveal that the observed effect persists in the low photon energy regime.Comment: 5 pages, 4 figure

Quantum Brownian motion at strong dissipation probed by superconducting tunnel junctions

We have studied the temporal evolution of a quantum system subjected to strong dissipation at ultra-low temperatures where the system-bath interaction represents the leading energy scale. In this regime, theory predicts the time evolution of the system to follow a generalization of the classical Smoluchowski description, the quantum Smoluchowski equation, thus, exhibiting quantum Brownian motion characteristics. For this purpose, we have investigated the phase dynamics of a superconducting tunnel junction in the presence of high damping. We performed current-biased measurements on the small-capacitance Josephson junction of a scanning tunneling microscope placed in a low impedance environment at milli-Kelvin temperatures. We can describe our experimental findings by a quantum diffusion model with high accuracy in agreement with theoretical predications based on the quantum Smoluchowski equation. In this way we experimentally demonstrate that quantum systems subjected to strong dissipation follow quasi-classical dynamics with significant quantum effects as the leading corrections.Comment: 5 pages, 4 figure

The Relationship between Personality Organization and Psychiatric Classification in Chronic Pain Patients

The assessment of PO is a crucial issue for diagnosis and treatment planning in CPPs, since it represents a measure of structural impairment that is to a considerable extent independent of axis I and II diagnoses. Moreover, the STIPO dimensional rating focuses on the most salient dysfunctions at a given time. Copyright (C) 2010 S. Karger AG, BaselBackground: The present study investigated the relationship between psychiatric classification and personality organization (PO) in a secondary/tertiary clinical sample of chronic pain patients (CPPs). Sampling and Methods: Forty-three patients were administered the Structured Clinical Interview for DSM-IV (SCID I+II) and the Structured Interview of Personality Organization (STIPO). The prevalence of axis I and axis II disorders was correlated with the STIPO level of PO. The STIPO dimensional ratings of patients without personality disorder (PD) were compared to those of patients diagnosed with one or more PDs. Results: Axis I comorbidity was high (93%), and 63% of the patients met the criteria for at least one axis II diagnosis. Twenty-five patients (58%) were diagnosed as borderline PO, with high-level impairments in the dimensions `coping/rigidity', `primitive defenses' and `identity'. Higher axis I and axis II comorbidity corresponded with greater severity of PO impairment. No difference was found between the dimensional ratings of patients without PD and those of patients with one or more PDs. Conclusions