1,785 research outputs found
A novel, resistance-linked ovine PrP variant and its equivalent mouse variant modulate the in vitro cell-free conversion of rPrP to PrPres
Prion diseases are associated with the conversion of the normal cellular prion protein, PrPc, to the abnormal, disease-associated form, PrPSc. This conversion can be mimicked in vitro by using a cell-free conversion assay. It has recently been shown that this assay can be modified to use bacterial recombinant PrP as substrate and mimic the in vivo transmission characteristics of rodent scrapie. Here, it is demonstrated that the assay replicates the ovine polymorphism barriers of scrapie transmission. In addition, the recently identified ovine PrP variant ARL168Q, which is associated with resistance of sheep to experimental BSE, modulates the cell-free conversion of ovine recombinant PrP to PrPres by three different types of PrPSc, reducing conversion efficiencies to levels similar to those of the ovine resistance-associated ARR variant. Also, the equivalent variant in mice (L164) is resistant to conversion by 87V scrapie. Together, these results suggest a significant role for this position and/or amino acid in conversion
Natural linewidth analysis of d-band photoemission from Ag(110)
We report a high-resolution angle-resolved study of photoemission linewidths
observed for Ag(110). A careful data analysis yields kdd\tau_h \geq 22
d$-hole dynamics in Cu (I.\
Campillo et al., Phys. Rev. Lett., in press) we interpret the lifetime
enhancement by a small scattering cross-section of - and -states below
the Fermi level. With increasing distance to the -hole lifetimes get
shorter because of the rapidly increasing density of d-states and contributions
of intra--band scattering processes, but remain clearly above
free-electron-model predictions.Comment: 14 pages, 7 figure
Microscopic measurement of the linear compressibilities of two-dimensional fatty acid mesophases
The linear compressibility of two-dimensional fatty acid mesophases has
determined by grazing incidence x-ray diffraction. Surface pressure vs
molecular area isotherms were reconstructed from these measurements, and the
linear compressibility (relative distortion along a given direction for
isotropic applied stress) was determined both in the sample plane and in a
plane normal to the aliphatic chain director (transverse plane). The linear
compressibilities range over two orders of magnitude from 0.1 to 10 m/N and are
distributed depending on their magnitude in 4 different sets which we are able
to associate with different molecular mechanisms. The largest compressibilities
(10m/N) are observed in the tilted phases. They are apparently independent of
the chain length and could be related to the reorganization of the headgroup
hydrogen-bounded network, whose role should be revalued. Intermediate
compressibilities are observed in phases with quasi long-range order
(directions normal to the molecular tilt in L_2 or L_2' phases, S phase), and
could be related to the ordering of these phases. The lowest compressibilities
are observed in the solid untilted CS phase and for 1 direction of the S and
L_2'' phases. They are similar to the compressibility of crystalline polymers
and correspond to the interactions between methyl groups in the crystal.
Finally, negative compressibilities are observed in the transverse plane for
L_2' and L_2'' phases and can be traced to subtle reorganizations upon
untilting.Comment: 24 pages, 17 figure
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
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
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
Evidence of Water-related Discrete Trap State Formation in Pentacene Single Crystal Field-Effect Transistors
We report on the generation of a discrete trap state during negative gate
bias stress in pentacene single crystal "flip-crystal" field-effect transistors
with a SiO2 gate dielectric. Trap densities of up to 2*10^12 cm^-2 were created
in the experiments. Trap formation and trap relaxation are distinctly different
above and below ~280 K. In devices in which a self-assembled monolayer on top
of the SiO2 provides a hydrophobic insulator surface we do not observe trap
formation. These results indicate the microscopic cause of the trap state to be
water adsorbed on the SiO2 surface.Comment: 13 pages, 4 figures, submitted to Applied Physics Letter
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