1,996 research outputs found
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
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
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), 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 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 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 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 in brain but positive
in LRS tissues, and one goat showed
biochemical and IHC features of PrP different from all other infected
goats. The results of this study have
implications for surveillance and control policies for scrapie in goats
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 [] which are linearly unstable and develop a mound
structure whose typical size L increases in time (). If the local
slope () increases indefinitely, depends on the exponent
characterizing the large behaviour of the surface current (): for and for
.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
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