Hole mobility in organic single crystals measured by a "flip-crystal" field-effect technique

We report on single crystal high mobility organic field-effect transistors (OFETs) prepared on prefabricated substrates using a "flip-crystal" approach. This method minimizes crystal handling and avoids direct processing of the crystal that may degrade the FET electrical characteristics. A chemical treatment process for the substrate ensures a reproducible device quality. With limited purification of the starting materials, hole mobilities of 10.7, 1.3, and 1.4 cm^2/Vs have been measured on rubrene, tetracene, and pentacene single crystals, respectively. Four-terminal measurements allow for the extraction of the "intrinsic" transistor channel resistance and the parasitic series contact resistances. The technique employed in this study shows potential as a general method for studying charge transport in field-accumulated carrier channels near the surface of organic single crystals.Comment: 26 pages, 7 figure

Skulls on the road – historical traces of anatomical connections between Erlangen and Tartu/Dorpat

The Chair for the History of Medicine at the Friedrich-Alexander-University of Erlangen-Nürnberg (FAU) is currently researching the provenance of human remains in the University Collections. Obviously, the by far largest number of those specimens is found in the Anatomical Collection, which is studied in close cooperation with the Institute of Functional and Clinical Anatomy a joint research project. Several specimens dating back to the time of Heinrich Friedrich Isenflamm (1771–1828) have been identified that went from Erlangen to Dorpat as well as others that came from Dorpat to Erlangen

Density of bulk trap states in organic semiconductor crystals: discrete levels induced by oxygen in rubrene

The density of trap states in the bandgap of semiconducting organic single crystals has been measured quantitatively and with high energy resolution by means of the experimental method of temperature-dependent space-charge-limited-current spectroscopy (TD-SCLC). This spectroscopy has been applied to study bulk rubrene single crystals, which are shown by this technique to be of high chemical and structural quality. A density of deep trap states as low as ~ 10^{15} cm^{-3} is measured in the purest crystals, and the exponentially varying shallow trap density near the band edge could be identified (1 decade in the density of states per ~25 meV). Furthermore, we have induced and spectroscopically identified an oxygen related sharp hole bulk trap state at 0.27 eV above the valence band.Comment: published in Phys. Rev. B, high quality figures: http://www.cpfs.mpg.de/~krellner

Field-induced charge transport at the surface of pentacene single crystals: a method to study charge dynamics of 2D electron systems in organic crystals

A method has been developed to inject mobile charges at the surface of organic molecular crystals, and the DC transport of field-induced holes has been measured at the surface of pentacene single crystals. To minimize damage to the soft and fragile surface, the crystals are attached to a pre-fabricated substrate which incorporates a gate dielectric (SiO_2) and four probe pads. The surface mobility of the pentacene crystals ranges from 0.1 to 0.5 cm^2/Vs and is nearly temperature-independent above ~150 K, while it becomes thermally activated at lower temperatures when the induced charges become localized. Ruling out the influence of electric contacts and crystal grain boundaries, the results contribute to the microscopic understanding of trapping and detrapping mechanisms in organic molecular crystals.Comment: 14 pages, 4 figures. Submitted to J. Appl. Phy

High prevalence of scrapie in a dairy goat herd: tissue distribution of disease-associated PrP and effect of PRNP genotype and age

Following a severe outbreak of clinical scrapie in 2006–2007, a large dairy goat herd was culled and 200 animals were selected for post-mortem examinations in order to ascertain the prevalence of infection, the effect of age, breed and PRNP genotype on the susceptibility to scrapie, the tissue distribution of diseaseassociated PrP (PrP$^{\rm d}$), and the comparative efficiency of different diagnostic methods. As determined by immunohistochemical (IHC) examinations with Bar224 PrP antibody, the prevalence of preclinical infection was very high (72/200; 36.0%), with most infected animals being positive for PrP$^{\rm d}$ in lymphoreticular system (LRS) tissues (68/72; 94.4%) compared to those that were positive in brain samples (38/72; 52.8%). The retropharyngeal lymph node and the palatine tonsil showed the highest frequency of PrP$^{\rm d}$ accumulation (87.3% and 84.5%, respectively), while the recto-anal mucosa-associated lymphoid tissue (RAMALT) was positive in only 30 (41.7%) of the infected goats. However, the efficiency of rectal and palatine tonsil biopsies taken shortly before necropsy was similar. The probability of brain and RAMALT being positive directly correlated with the spread of PrP$^{\rm d}$ within the LRS. The prevalence of infection was influenced by PRNP genetics at codon 142 and by the age of the goats: methionine carriers older than 60 months showed a much lower prevalence of infection (12/78; 15.4%) than those younger than 60 months (20/42; 47.6%); these last showed prevalence values similar to isoleucine homozygotes of any age (40/80; 50.0%). Two of seven goats with definite signs of scrapie were negative for PrP$^{\rm d}$ in brain but positive in LRS tissues, and one goat showed biochemical and IHC features of PrP$^{\rm d}$ different from all other infected goats. The results of this study have implications for surveillance and control policies for scrapie in goats

Provenienz und Anatomie einer Doppelfehlbildung

Die Erlanger Anatomische Sammlung erfuhr spätestens seit Einrichtung des „Theatrum Anatomicum“ 1754 einen steten Zuwachs unterschiedlichster Präparate historisch bislang meist ungeklärter Herkunft. Seit 1800 ist wiederholt von einer großen Anzahl von Präparaten mit Fehlbildungen in der Sammlung die Rede, die auch mehrfach durch Publikationen, Präsentationen und Vorlesungen der Öffentlichkeit vorgestellt wurden. Aufgrund der großen Zahl und Diversität der gesammelten Fehlbildungen stellten diese einen für die Erlanger Anatomie zentralen Sammlungsteil im 19. Jahrhundert dar. Sowohl die Geschichte der Serie als auch und vor allem die Provenienzen der Präparate sind noch kaum erforscht. Mein Dissertationsvorhaben nimmt sich daher dieses in mehrfacher Hinsicht sensiblen Konvoluts an. Erste Ergebnisse dieser ausgedehnten Bearbeitung, in Form der Provenienzforschung zu einem einzelnen Präparat, werden in diesem Beitrag präsentiert. Dazu werden im Speziellen zunächst das Vorgehen der morphologischen Befundung einer Doppelfehlbildung und deren Vergleich mit der historischen Literatur veranschaulicht. Ein zentraler Punkt stellt hierbei die Digitalisierung aller Ergebnisse im Inventarisierungssystem WissKI dar, mit dessen Hilfe abschließend eine standardisierte und transparente Provenienzforschung in digitaler Umgebung verwirklicht werden soll. Diese kann unter anderem Hinweise auf Leichenablieferungsregeln geben, die auf dem Papier schon seit 1769 für Fehlbildungen bestehen. Das Promotionsvorhaben will darauf aufbauen und nicht nur lokal, sondern auch überregional zur Sammlungsforschung beitragen und die bislang unklaren Beschaffungsquellen anderer Präparate offenlegen. WARNHINWEIS: In der Publikation befinden sich Bilder und Beschreibungen von menschlichen ÜberrestenPeer Reviewe

Significant differences in incubation times in sheep infected with bovine spongiform encephalopathy result from variation at codon 141 in the PRNP gene

The susceptibility of sheep to prion infection is linked to variation in the PRNP gene, which encodes the prion protein. Common polymorphisms occur at codons 136, 154 and 171. Sheep which are homozygous for the A<sub>136</sub>R<sub>154</sub>Q<sub>171</sub> allele are the most susceptible to bovine spongiform encephalopathy (BSE). The effect of other polymorphisms on BSE susceptibility is unknown. We orally infected ARQ/ARQ Cheviot sheep with equal amounts of BSE brain homogenate and a range of incubation periods was observed. When we segregated sheep according to the amino acid (L or F) encoded at codon 141 of the PRNP gene, the shortest incubation period was observed in LL141 sheep, whilst incubation periods in FF<sub>141</sub> and LF<sub>141</sub> sheep were significantly longer. No statistically significant differences existed in the expression of total prion protein or the disease-associated isoform in BSE-infected sheep within each genotype subgroup. This suggested that the amino acid encoded at codon 141 probably affects incubation times through direct effects on protein misfolding rates

Coarsening in surface growth models without slope selection

We study conserved models of crystal growth in one dimension [$\partial_t z(x,t) =-\partial_x j(x,t)$] which are linearly unstable and develop a mound structure whose typical size L increases in time ($L = t^n$). If the local slope ($m =\partial_x z$) increases indefinitely, $n$ depends on the exponent $\gamma$ characterizing the large $m$ behaviour of the surface current $j$ ($j = 1/|m|^\gamma$): $n=1/4$ for $1< \gamma <3$ and $n=(1+\gamma)/(1+5\gamma)$ for $\gamma>3$.Comment: 7 pages, 2 EPS figures. To be published in J. Phys. A (Letter to the Editor

Experimental and Numerical Investigation of Aerosol Scavenging by Sprays

In the event of a hypothetical nuclear reactor accident, the combination of plant design, operator training, and safety procedures result in low level risks to the general public; however, an additional offsite consequence mitigation system has the poten- tial to substantially decrease the amount of radioactive material that could reach a population zone in a postulated accident scenario. An experimental and numerical investigation of airborne particulate scavenging by water sprays was conducted as part of a consequence mitigation study. Previous researchers have experimentally studied the removal of aerosols by sprays, but only in a confined region. The ex- periment conducted in this research used an expansive region where sprays could significantly affect the flow fields in the spray region. Experimentation showed an expected trend of higher particle collection efficien- cies with increased residency time within the spray region, with the highest average overall collection efficiency found to be 70.6+/-3.2% at an air flow rate of 0.53 m/s and a water flow rate of 0.84 gpm. This general trend is expected because a longer resi- dency time leads to an increased probability of particle-drop interaction. Collection efficiencies were also found to increase with increased particle number density. The numerical investigation was done using a deterministic method and a Monte Carlo method. Each model shows promise based on theoretical limitations of drop size for the experimental conditions. The theory demonstrates that particle-drop relative velocity as well as the sizes significantly affect collection efficiency. An alternative study was conducted to determine the collection efficiency of non-wettable particles since the dust used in the experiment is hydrophobic. Computational Fluid Dynam- ics (CFD) models were also performed to determine the flow fields that developed within the experiment spray region and substantiate differences in the experimental and numerical models