Three-dimensional effects on extended states in disordered models of polymers

We study electronic transport properties of disordered polymers in the presence of both uncorrelated and short-range correlated impurities. In our procedure, the actual physical potential acting upon the electrons is replaced by a set of nonlocal separable potentials, leading to a Schr\"odinger equation that is exactly solvable in the momentum representation. We then show that the reflection coefficient of a pair of impurities placed at neighboring sites (dimer defect) vanishes for a particular resonant energy. When there is a finite number of such defects randomly distributed over the whole lattice, we find that the transmission coefficient is almost unity for states close to the resonant energy, and that those states present a very large localization length. Multifractal analysis techniques applied to very long systems demonstrate that these states are truly extended in the thermodynamic limit. These results reinforce the possibility to verify experimentally theoretical predictions about absence of localization in quasi-one-dimensional disordered systems.Comment: 16 pages, REVTeX 3.0, 5 figures on request from FDA ([email protected]). Submitted to Phys. Rev. B. MA/UC3M/09/9

The electronic structure of amorphous silica: A numerical study

We present a computational study of the electronic properties of amorphous SiO2. The ionic configurations used are the ones generated by an earlier molecular dynamics simulations in which the system was cooled with different cooling rates from the liquid state to a glass, thus giving access to glass-like configurations with different degrees of disorder [Phys. Rev. B 54, 15808 (1996)]. The electronic structure is described by a tight-binding Hamiltonian. We study the influence of the degree of disorder on the density of states, the localization properties, the optical absorption, the nature of defects within the mobility gap, and on the fluctuations of the Madelung potential, where the disorder manifests itself most prominently. The experimentally observed mismatch between a photoconductivity threshold of 9 eV and the onset of the optical absorption around 7 eV is interpreted by the picture of eigenstates localized by potential energy fluctuations in a mobility gap of approximately 9 eV and a density of states that exhibits valence and conduction band tails which are, even in the absence of defects, deeply located within the former band gap.Comment: 21 pages of Latex, 5 eps figure

Delivering strong 1H nuclear hyperpolarization levels and long magnetic lifetimes through signal amplification by reversible exchange

Hyperpolarization turns typically weak NMR and MRI responses into strong signals so that ordinarily impractical measurements become possible. The potential to revolutionize analytical NMR and clinical diagnosis through this approach reflect this area's most compelling outcomes. Methods to optimize the low cost parahydrogen based approach signal amplification by reversible exchange (SABRE) with studies on a series of biologically relevant nicotinamides and methyl nicotinates are detailed. These procedures involve specific 2H-labelling in both the agent and catalyst and achieve polarization lifetimes of ca. 2 minutes with 50% polarization in the case of 4,6-d2-methylnicotinate. As a 1.5 T hospital scanner has an effective 1H polarization level of just 0.0005% this strategy should result in compressed detection times for chemically discerning measurements that probe disease. To demonstrate this techniques generality, we exemplify further studies on a range of pyridazine, pyrimidine, pyrazine and isonicotinamide analogues that feature as building blocks in biochemistry and many disease treating drugs

An Investigation into the Cognition Behind Spontaneous String Pulling in New Caledonian Crows

The ability of some bird species to pull up meat hung on a string is a famous example of spontaneous animal problem solving. The “insight” hypothesis claims that this complex behaviour is based on cognitive abilities such as mental scenario building and imagination. An operant conditioning account, in contrast, would claim that this spontaneity is due to each action in string pulling being reinforced by the meat moving closer and remaining closer to the bird on the perch. We presented experienced and naïve New Caledonian crows with a novel, visually restricted string-pulling problem that reduced the quality of visual feedback during string pulling. Experienced crows solved this problem with reduced efficiency and increased errors compared to their performance in standard string pulling. Naïve crows either failed or solved the problem by trial and error learning. However, when visual feedback was available via a mirror mounted next to the apparatus, two naïve crows were able to perform at the same level as the experienced group. Our results raise the possibility that spontaneous string pulling in New Caledonian crows may not be based on insight but on operant conditioning mediated by a perceptual-motor feedback cycle

Improving the hyperpolarization of (31)p nuclei by synthetic design

Traditional (31)P NMR or MRI measurements suffer from low sensitivity relative to (1)H detection and consequently require longer scan times. We show here that hyperpolarization of (31)P nuclei through reversible interactions with parahydrogen can deliver substantial signal enhancements in a range of regioisomeric phosphonate esters containing a heteroaromatic motif which were synthesized in order to identify the optimum molecular scaffold for polarization transfer. A 3588-fold (31)P signal enhancement (2.34% polarization) was returned for a partially deuterated pyridyl substituted phosphonate ester. This hyperpolarization level is sufficient to allow single scan (31)P MR images of a phantom to be recorded at a 9.4 T observation field in seconds that have signal-to-noise ratios of up to 94.4 when the analyte concentration is 10 mM. In contrast, a 12 h 2048 scan measurement under standard conditions yields a signal-to-noise ratio of just 11.4. (31)P-hyperpolarized images are also reported from a 7 T preclinical scanner

Phlebologie an deutschen Hautkliniken: eine Bestandsaufnahme im Auftrag der Deutschen Gesellschaft für Phlebologie

Reich-Schupke S, Alm J, Altmeyer P, et al. Phlebologie an deutschen Hautkliniken: Eine Bestandsaufnahme im Auftrag der Deutschen Gesellschaft für Phlebologie. Hautarzt. 2013;64(9):685-694.Phlebologic diseases have become extremely common and have major socio-economic impact. However, the percentage of dermatologists working in phlebology appears to be decreasing according to the data of the German Society of Phlebology (DGP). To investigate the reasons for this development, we-on behalf of the DGP-sent a questionnaire to 120 German Departments of Dermatology in autumn 2012. In 76 returned questionnaires, the number of physicians with additional fellowship training in phlebology averaged 1.5; the average number of those who fulfill the criteria for training fellows in phlebology was 0.9. In 71.1 % of the departments there was a phlebologist. A special phlebologic outpatient clinic existed in 73.7 % of the departments. Sonography with Doppler (89.5 %) and duplex (86.8 %) was used as the most frequent diagnostic tool. For therapy, compression (94.7 %), sclerotherapy (liquid 78.9 %, foam 63.2 %, catheter 18.4 %), endoluminal thermic procedures (radio wave 28.9 %, laser 17.1 %) and surgery (especially crossectomy and stripping 67.1 %, phlebectomy of tributaries 75 %) were used. The average number of treatments was very heterogenous in the different departments. Phlebology definitely plays an important role in dermatology. Most departments fulfill the formal criteria for the license to conduct advanced training in phlebology. A wide spectrum of phlebological diagnostic and therapeutic procedures is available.Hintergrund Venenleiden sind eine Volkskrankheit und haben eine enorme sozioökonomische Bedeutung. Dennoch scheint der Anteil der phlebologisch tätigen Dermatologen entsprechend den Zahlen der Deutschen Gesellschaft für Phlebologie (DGP) abzunehmen. Methoden Um die Ursachen dieser Entwicklung zu untersuchen, führten wir im Herbst 2012 im Auftrag der DGP eine Befragungsstudie zur Phlebologie an 120 deutschen Hautkliniken durch. Ergebnisse In 76 antwortenden Klinien gab es im Mittel 1,5 Phlebologen und 0,9 Ärzte mit Voraussetzungen zur Weiterbildungsermächtigung Phlebologie. In 71,1 % der Kliniken gab es einen Phlebologen, in 73,7 % eine phlebologische Sprechstunde. Zur Diagnostik wurden besonders die Doppler- (89,5 %) und Duplexsonographie (86,8 %) eingesetzt. In der Therapie führte die Kompressionstherapie (94,7 %), gefolgt von Sklerosierungstherapien (flüssig 78,9 %, Schaum 63,2 %, Katheter 18,4 %), den endoluminalen thermischen Verfahren (Radiowelle 28,9 %, Laser 17,1 %) und den operativen Eingriffen (vor allem Cross- und Saphenektomie 67,1 %, Seitenastexhairese 75 %). Die durchschnittlichen Behandlungszahlen waren sehr heterogen. Schlussfolgerung Die Phlebologie spielt in der Dermatologie weiterhin eine wichtige Rolle. Mehrheitlich sind in den Kliniken die Möglichkeiten zur Weiterbildung Phlebologie gegeben. Es wird ein breites Spektrum an phlebologischen Techniken zur Diagnostik und Therapie angeboten

A distributed robotic control system based on a temporal self-organizing neural network

Barreto GA, Araujo AFR, Dücker C, Ritter H. A distributed robotic control system based on a temporal self-organizing neural network. IEEE Transactions on Systems, Man, and Cybernetics. Part C, Applications and Reviews. 2002;32(4):347-357