1,508 research outputs found
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
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
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
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
Atomic correlations in itinerant ferromagnets: quasi-particle bands of nickel
We measure the band structure of nickel along various high-symmetry lines of
the bulk Brillouin zone with angle-resolved photoelectron spectroscopy. The
Gutzwiller theory for a nine-band Hubbard model whose tight-binding parameters
are obtained from non-magnetic density-functional theory resolves most of the
long-standing discrepancies between experiment and theory on nickel. Thereby we
support the view of itinerant ferromagnetism as induced by atomic correlations.Comment: 4 page REVTeX 4.0, one figure, one tabl
Lifetime of d-holes at Cu surfaces: Theory and experiment
We have investigated the hole dynamics at copper surfaces by high-resolution
angle-resolved photoemission experiments and many-body quasiparticle GW
calculations. Large deviations from a free-electron-like picture are observed
both in the magnitude and the energy dependence of the lifetimes, with a clear
indication that holes exhibit longer lifetimes than electrons with the same
excitation energy. Our calculations show that the small overlap of d- and
sp-states below the Fermi level is responsible for the observed enhancement.
Although there is qualitative good agreement of our theoretical predictions and
the measured lifetimes, there still exist some discrepancies pointing to the
need of a better description of the actual band structure of the solid.Comment: 15 pages, 7 figures, 1 table, to appear in Phys. Rev.
Network analysis of synovial RNA sequencing identifies gene-gene interactions predictive of response in rheumatoid arthritis
Abstract Background To determine whether gene-gene interaction network analysis of RNA sequencing (RNA-Seq) of synovial biopsies in early rheumatoid arthritis (RA) can inform our understanding of RA pathogenesis and yield improved treatment response prediction models. Methods We utilized four well curated pathway repositories obtaining 10,537 experimentally evaluated gene-gene interactions. We extracted specific gene-gene interaction networks in synovial RNA-Seq to characterize histologically defined pathotypes in early RA and leverage these synovial specific gene-gene networks to predict response to methotrexate-based disease-modifying anti-rheumatic drug (DMARD) therapy in the Pathobiology of Early Arthritis Cohort (PEAC). Differential interactions identified within each network were statistically evaluated through robust linear regression models. Ability to predict response to DMARD treatment was evaluated by receiver operating characteristic (ROC) curve analysis. Results Analysis comparing different histological pathotypes showed a coherent molecular signature matching the histological changes and highlighting novel pathotype-specific gene interactions and mechanisms. Analysis of responders vs non-responders revealed higher expression of apoptosis regulating gene-gene interactions in patients with good response to conventional synthetic DMARD. Detailed analysis of interactions between pairs of network-linked genes identified the SOCS2/STAT2 ratio as predictive of treatment success, improving ROC area under curve (AUC) from 0.62 to 0.78. We identified a key role for angiogenesis, observing significant statistical interactions between NOS3 (eNOS) and both CAMK1 and eNOS activator AKT3 when comparing responders and non-responders. The ratio of CAMKD2/NOS3 enhanced a prediction model of response improving ROC AUC from 0.63 to 0.73. Conclusions We demonstrate a novel, powerful method which harnesses gene interaction networks for leveraging biologically relevant gene-gene interactions leading to improved models for predicting treatment response
Unraveling the spontaneous zwitterionic copolymerization mechanism of cyclic imino ethers and acrylic acid
We report a high-resolution electrospray ionization mass spectrometric (HR ESI MS) access route leading to in-depths insight into the spontaneous zwitterionic copolymerization mechanism between cyclic imino ethers (i.e. 2-methyl-2-oxazoline (MeOx), 2-ethyl-2-oxazoline (EtOx) or 2-ethyl-2-oxazine (EtOz)) with acrylic acid (AA), exploiting the characteristic species accumulating during the copolymerization as well as tandem mass spectrometry (MS/MS). We demonstrate preferences in α,ω-end group formation by screening various feed ratios of cyclic imino ethers and acrylic acid (e.g. MeOx:AA = 1:1; MeOx:AA = 2:1; MeOx:AA = 1:2). Critically, a calibration curve – based on AA-MeOx-AA dimer – was established allowing for semi-quantitative determination of the end group ratios with different feed ratios of acrylic acid. The formation of, previously suggested, alternating copolymers was confirmed by MS/MS experiments. Deviations from an ideal alternating composition were found to decrease from MeOx to EtOx to EtOz. The results of (semi-quantitative) HR ESI MS and MS/MS measurements suggest, for the first time presented in such precision, a polymerization mechanism for the spontaneous zwitterionic (alternating) copolymerization indicating optimal monomer ratios and pairings
Fluctuations and differential contraction during regeneration of Hydra vulgaris tissue toroids
We studied regenerating bilayered tissue toroids dissected from Hydra
vulgaris polyps and relate our macroscopic observations to the dynamics of
force-generating mesoscopic cytoskeletal structures. Tissue fragments undergo a
specific toroid-spheroid folding process leading to complete regeneration
towards a new organism. The time scale of folding is too fast for biochemical
signalling or morphogenetic gradients which forced us to assume purely
mechanical self-organization. The initial pattern selection dynamics was
studied by embedding toroids into hydro-gels allowing us to observe the
deformation modes over longer periods of time. We found increasing mechanical
fluctuations which break the toroidal symmetry and discuss the evolution of
their power spectra for various gel stiffnesses. Our observations are related
to single cell studies which explain the mechanical feasibility of the folding
process. In addition, we observed switching of cells from a tissue bound to a
migrating state after folding failure as well as in tissue injury.
We found a supra-cellular actin ring assembled along the toroid's inner edge.
Its contraction can lead to the observed folding dynamics as we could confirm
by finite element simulations. This actin ring in the inner cell layer is
assembled by myosin- driven length fluctuations of supra-cellular
{\alpha}-actin structures (myonemes) in the outer cell-layer.Comment: 19 pages and 8 figures, submitted to New Journal of Physic
Electron-phonon renormalization of the absorption edge of the cuprous halides
Compared to most tetrahedral semiconductors, the temperature dependence of
the absorption edges of the cuprous halides (CuCl, CuBr, CuI) is very small.
CuCl and CuBr show a small increase of the gap with increasing
temperature, with a change in the slope of vs. at around 150 K: above
this temperature, the variation of with becomes even smaller. This
unusual behavior has been clarified for CuCl by measurements of the low
temperature gap vs. the isotopic masses of both constituents, yielding an
anomalous negative shift with increasing copper mass. Here we report the
isotope effects of Cu and Br on the gap of CuBr, and that of Cu on the gap of
CuI. The measured isotope effects allow us to understand the corresponding
temperature dependences, which we also report, to our knowledge for the first
time, in the case of CuI. These results enable us to develop a more
quantitative understanding of the phenomena mentioned for the three halides,
and to interpret other anomalies reported for the temperature dependence of the
absorption gap in copper and silver chalcogenides; similarities to the behavior
observed for the copper chalcopyrites are also pointed out.Comment: 14 pages, 5 figures, submitted to Phys. Rev.
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