Persistence of coherent quantum dynamics at strong dissipation

The quantum dynamics of a two state system coupled to a bosonic reservoir with sub-Ohmic spectral density is investigated for strong friction. Numerically exact path integral Monte Carlo methods reveal that in contrast to conventional expectations, coherent dynamics never turns into incoherent decay for a broad class of spectral distributions. Coherences associated with substantial system-reservoir entanglement exist in non-equilibrium even when strong dissipation makes the thermodynamic state of the system to behave essentially classical. This may be of relevance for current experiments with nanoscale devices and bio-molecular aggregates.Comment: 5 pages, 5 figure

ECHO user's guide

There are no author-identified significant results in this report

Structure-function relationship of Strong Metal-Support Interaction studied on supported Pd reference catalysts

Transition metal oxide supported, nano-scaled noble metal catalysts are known to show a variety of surface modifications when they are being reduced at increasing temperatures. Such processes involve for example (surface) alloying and the formation of partially reduced oxidic support overlayers that are both induced by the so-called strong metal-support interaction (SMSI). The present work investigated a series of oxide supported Palladium powder catalysts with a loading variation between 1-5 wt.-% on their structure-function relationship after reduction in different media and at different temperatures to create a reference system and explore the nature of SMSI. Hereby surface and bulk sensitive techniques like XPS, chemisorption, TEM, DRIFTS or XRD were applied to study the influence of electronic and structural modifications on the activity in catalytic oxidation of carbon monoxide which served as the main test reaction and was conducted at ambient pressure. The catalysts were synthesized reproducibly by a controlled co-precipitation approach and by impregnation. The investigated Pd/iron oxide system shows palladium surface decoration at comparably low reduction temperatures. The surface cover was found to be volatile in oxygen containing atmosphere and formed reversibly. Dependent on the Pd particle size it increases the CO oxidation activity. Alloy formation occurs at higher reduction temperatures. In case of the Pd/zinc oxide system reversible surface alloying takes place during reduction that is also beneficial for CO oxidation, but again deactivates fast. When being reduced at even higher temperatures the additional formation of an oxidic overlayer could be observed that does not further activate the system but leads to an overall reduction of active sites. Due to alloy formation, the zinc oxide system at higher conversions shows a different selectivity behavior in acetylene hydrogenation, compared to the iron oxide system. Also in case of the Pd/titania system, reversible surface decoration by partially reduced support happens during reduction. Different to the other investigated systems the surface-cover reversibly decreases CO oxidation activity however. The Pd/alumina system was studied as a less reducible reference. As expected, it does not show SMSI-induced modifications. In the end the work clearly shows that CO oxidation is a convenient method to study activity and stability of SMSI and decouple it from other involved processes. The effects of surface modification on the catalytic activity in this test reaction however strongly depend on the specific system and pre-conditioning and can either be of activating or deactivating nature. The basic principles involved in case of SMSI seem to apply both in UHV model systems and at powder systems at ambient pressure as found by the catalytic measurements.Übergangsmetalloxid geträgerte, nano-skalige Edelmetall-Katalysatoren sind bekannt dafür, eine Reihe von Oberflächen-Veränderungen zu erfahren, wenn sie bei erhöhter Temperatur reduziert werden. Diese Prozesse beinhalten beispielsweise (Oberflächen-) Legierungsbildung und die Ausblidung von teilweise reduzierten, oxidischen Träger- Schichten, in beiden Fällen hervorgerufen durch Starke Metall-Träger Wechselwirkung (Strong Metal-Support Interaction, SMSI). Die vorliegende Arbeit untersuchte eine Reihe von oxid-geträgerten Palladium Pulverkatalysatoren mit einer Variation der Beladung von 1- 5 Gewichts-% auf ihre Struktur-Eigenschafts Beziehungen nach Reduktion in verschiedenen Medien und bei veschiedenen Temperaturen, um ein Referenzsystem zu entwickeln und der Natur von SMSI auf den Grund zu gehen. Dabei kamen oberflächen- und volumensensitive Methoden wie XPS, Chemisorption, TEM, DRIFTS oder XRD zum Einsatz, um den Einfluss von elektronischen und strukturellen Veränderungen auf die Aktivität bei katalytischer Oxidation von Kohlenmonoxid zu untersuchen, welche als wichtigste Testreaktion bei Normaldruck durchgeführt wurde. Die Katalysatoren wurden auf reproduzierbare Weise durch kontrollierte Ko-Fällung und durch Imprägnierung hergestellt. Das untersuchte Pd/Eisenoxid System zeigt Bedeckung der Pd Oberfläche nach Reduktion bei vergleichsweise niedrigen Temperaturen. Diese Bedeckung war instabil in sauerstoffhaltiger Umgebung und bildete sich reversibel aus. Abhängig von der Pd Partikelgröße erhöht sie die Aktivität bei der CO-Oxidation. Legierungsbildung findet bei höheren Reduktionstemperaturen statt. Im Falle von Pd/Zinkoxid findet reversible Legierungsbildung an der Oberfläche statt, die ebenfalls die CO-Oxidation begünstigt, aber ebenfalls schnell deaktiviert. Nach Reduktion bei noch höheren Temperaturen konnte die zusätzliche Ausbildung einer oxidischen Überschicht beobachtet werden, die das System nicht weiter aktivierte, sondern insgesamt die Zahl der aktiven Plätze reduzierte. Wegen Legierungsbildung zeigt das Zinkoxid-System bei höheren Umsätzen in der Acetylenhydrierung ein anderes Selektivitätsverhalten als das Eisenoxid-System. Im Fall von Pd/Titanoxid kommt es während der Reduktion ebenfalls zu reversibler Oberflächen- Bedeckung durch teilweise reduzierten Träger. Anders als in den beiden anderen Fällen verringert diese Schicht hier jedoch die Aktivität in der CO-Oxidation. Pd/Aluminiumoxid wurde als schwer reduzierbares Referenz-System untersucht. Wie erwartet zeigt es keine durch SMSI hervorgerufenen Veränderungen. Schlussendlich konnte in dieser Arbeit gezeigt werden, dass CO-Oxidation eine einfache und geeignete Methode ist, SMSI zu untersuchen und ihren Einfluss auf Aktivität und Stabilität von dem anderer Prozesse zu trennen. Die Effekte von Oberflächenveränderungen auf die katalytische Aktivität dieser Test-Reaktion hängen jedoch stark vom entsprechenden System und der Vorbehandlung ab und können sowohl aktivierender als auch deaktivierender Natur sein. Die Grundlegenden Prinzipien, die bei SMSI eine Rolle spielen, scheinen sowohl im Fall von Modell-Systemen unter UHV-Bedingungen als auch bei Pulver-Systemen bei Normaldruck zu gelten, wie durch die katalytischen Messungen gezeigt wurde

ECHO User\u27s Guide

Over the past several years, the ECHO classifiers have been developed to incorporate spatial as well as spectral information into the classifier decision criteria. This document contains a comprehensive description of the functional organization of the supervised and the nonsupervised ECHO processes, the manner in for individuals who intend to make use of the ECHO classifiers, although it is also of value to those wanting to understand of implement the ECHO algorithms

Thiolated chitosan nanoparticles enhance anti-inflammatory effects of intranasally delivered theophylline

BACKGROUND: Chitosan, a polymer derived from chitin, has been used for nasal drug delivery because of its biocompatibility, biodegradability and bioadhesiveness. Theophylline is a drug that reduces the inflammatory effects of allergic asthma but is difficult to administer at an appropriate dosage without causing adverse side effects. It was hypothesized that adsorption of theophylline to chitosan nanoparticles modified by the addition of thiol groups would improve theophylline absorption by the bronchial epithelium and enhance its anti-inflammatory effects. OBJECTIVES: We sought to develop an improved drug-delivery matrix for theophylline based on thiolated chitosan, and to investigate whether thiolated chitosan nanoparticles (TCNs) can enhance theophylline's capacity to alleviate allergic asthma. METHODS: A mouse model of allergic asthma was used to test the effects of theophylline in vivo. BALB/c mice were sensitized to ovalbumin (OVA) and OVA-challenged to produce an inflammatory allergic condition. They were then treated intranasally with theophylline alone, chitosan nanoparticles alone or theophylline adsorbed to TCNs. The effects of theophylline on cellular infiltration in bronchoalveolar lavage (BAL) fluid, histopathology of lung sections, and apoptosis of lung cells were investigated to determine the effectiveness of TCNs as a drug-delivery vehicle for theophylline. RESULTS: Theophylline alone exerts a moderate anti-inflammatory effect, as evidenced by the decrease in eosinophils in BAL fluid, the reduction of bronchial damage, inhibition of mucus hypersecretion and increased apoptosis of lung cells. The effects of theophylline were significantly enhanced when the drug was delivered by TCNs. CONCLUSION: Intranasal delivery of theophylline complexed with TCNs augmented the anti-inflammatory effects of the drug compared to theophylline administered alone in a mouse model of allergic asthma. The beneficial effects of theophylline in treating asthma may be enhanced through the use of this novel drug delivery system

Nature of the N-Pd interaction in nitrogen-doped carbon nanotube catalysts

In this work, the geometric and electronic structure of N species in N-doped carbon nanotubes (NCNTs) is derived by X-ray photoemission (XPS) and absorption spectroscopy (NEXAFS) of the N 1s core excitation. Substitutional N species in pyridine-like configuration and another form of N with higher thermal stability are found in NCNTs. The structural configuration of the high thermally stable N species, in the literature often referred to as graphitic N, is assessed in this work by a combined theoretical and experimental study as a 3-fold substitutional N species in an NCNT basic structural unit (BSU). Furthermore, the nature of the interaction of those N species with a Pd metal center immobilized onto NCNTs is of σ-type donation from the filled π-orbital of the N atom to the empty d-orbital of the Pd atom and a π back donation from the filled Pd atomic d-orbital to the π* antibonding orbital of the N atom. We have found that the interaction of pyridine N with Pd is characterized by a charge transfer typical of a covalent chemical bond with partial ionic character, consistent with the chemical shift observed in the Pd 3d core level of divalent Pd. Graphitic N sites interact with Pd by a covalent bond without any charge redistribution. In this case, the electronic state of the Pd corresponds to metallic Pd nanoparticles electronically modified by the interaction with the support. The catalytic reactivity of these samples in hydrogenation, CO oxidation, and oxygen reduction reaction (ORR) allowed clarifying some aspects of the metal carbon support interaction in catalysis

Finite average lengths in critical loop models

A relation between the average length of loops and their free energy is obtained for a variety of O(n)-type models on two-dimensional lattices, by extending to finite temperatures a calculation due to Kast. We show that the (number) averaged loop length L stays finite for all non-zero fugacities n, and in particular it does not diverge upon entering the critical regime n -> 2+. Fully packed loop (FPL) models with n=2 seem to obey the simple relation L = 3 L_min, where L_min is the smallest loop length allowed by the underlying lattice. We demonstrate this analytically for the FPL model on the honeycomb lattice and for the 4-state Potts model on the square lattice, and based on numerical estimates obtained from a transfer matrix method we conjecture that this is also true for the two-flavour FPL model on the square lattice. We present in addition numerical results for the average loop length on the three critical branches (compact, dense and dilute) of the O(n) model on the honeycomb lattice, and discuss the limit n -> 0. Contact is made with the predictions for the distribution of loop lengths obtained by conformal invariance methods.Comment: 20 pages of LaTeX including 3 figure

Resonance Effects in the Nonadiabatic Nonlinear Quantum Dimer

The quantum nonlinear dimer consisting of an electron shuttling between the two sites and in weak interaction with vibrations, is studied numerically under the application of a DC electric field. A field-induced resonance phenomenon between the vibrations and the electronic oscillations is found to influence the electronic transport greatly. For initially delocalization of the electron, the resonance has the effect of a dramatic increase in the transport. Nonlinear frequency mixing is identified as the main mechanism that influences transport. A characterization of the frequency spectrum is also presented.Comment: 7 pages, 6 figure