3,095 research outputs found
Comment on "Conductance fluctuations in mesoscopic normal-metal/superconductor samples"
Recently, Hecker et al. [Phys. Rev. Lett. 79, 1547 (1997)] experimentally
studied magnetoconductance fluctuations in a mesoscopic Au wire connected to a
superconducting Nb contact. They claimed to have observed an enhancement of the
rms magnitude of these conductance fluctuations in the superconducting state
(rms(Gns)) relative to that in the normal state (rms(Gn)) by a factor of 2.8.
In this comment, we argue that the measured rms(Gns) is NOT significantly
enhanced compared to rms(Gn) when we correct for the presence of an incoherent
series resistance from the contacts, which is different when Nb is in the
superconducting or normal state.Comment: 1 pag
Cruising through molecular bound state manifolds with radio frequency
The emerging field of ultracold molecules with their rich internal structure
is currently attracting a lot of interest. Various methods have been developed
to produce ultracold molecules in pre-set quantum states. For future
experiments it will be important to efficiently transfer these molecules from
their initial quantum state to other quantum states of interest. Optical Raman
schemes are excellent tools for transfer, but can be involved in terms of
equipment, laser stabilization and finding the right transitions. Here we
demonstrate a very general and simple way for transfer of molecules from one
quantum state to a neighboring quantum state with better than 99% efficiency.
The scheme is based on Zeeman tuning the molecular state to avoided level
crossings where radio-frequency transitions can then be carried out. By
repeating this process at different crossings, molecules can be successively
transported through a large manifold of quantum states. As an important
spin-off of our experiments, we demonstrate a high-precision spectroscopy
method for investigating level crossings.Comment: 5 pages, 5 figures, submitted for publicatio
Sequence differences between histones of procyclic Trypanosoma brucei brucei and higher eukaryotes
Four histones, a, b, c, d from procyclic Trypanosoma brucei brucei, which show similarities with the amino acid composition of the core histones H3, H2A, H2B and H4, were isolated and cleaved with Endoproteinase Glu-C. The fragments were separated by FPLC reversed phase chromatography and a subset of the fragments (a5, a9, b6, c8, d3, d9, d11) was subjected to sequence analysis. A 54-71% identity was found in the sequences of the fragment c8 and the C-terminal half of H2B and of three fragments of protein d covering the N-terminal half as well as the C-terminal region of H4. The amino acid sequence of the fragment a9 showed a 57 and 54% identity with H3 sequences of Saccharomyces cerevisiae and Xenopus laevis. Neither the a5 nor the b6 sequence could be aligned with histone sequences of other eukaryotes. The significant differences of 21-48% between the T. b. brucei, histone sequences and those of calf thymus histones, which are more pronounced than the differences of Tetrahymena pyriformis and the higher eukaryote, resulted partially from replacements of amino acids with different properties and indicate specific patterns of histone-histone and/or histone-DNA contact sites in the nucleosome of T. b. brucei. These differences, together with the lack of a functional histone H1, may be sufficient to explain the lack of a salt-dependent formation of the nucleosome filament into the 30 nm fibre, which reflects alternative methods of organizing and processing the genetic information in the nucleus of the protozoan parasite and which may be of chemotherapeutic significanc
Trypanosoma brucei brucei: differences in the nuclear chromatin of bloodstream forms and procyclic culture forms
Nucleosome filaments of two stages of the life-cycle of Trypanosoma brucei brucei, namely bloodstream forms and procyclic culture forms, were investigated by electron microscopy. Chromatin of bloodstream forms showed a salt-dependent condensation. The level of condensation was higher than that shown by chromatin from procyclic culture forms, but 30 nm fibres as formed in rat liver chromatin preparations were not found. Analysis of histones provided new evidence for the existence of H1-like proteins, which comigrated in the region of the core histones in SDS-PAGE and in front of the core histones in Triton acid urea gels. Differences were found between the H1-like proteins of the two trypanosome stages as well as between the core histones in their amount, number of bands and banding pattern. It can be concluded that T. b. brucei contains a full set of histones, including H1-like proteins, and that the poor condensation of its chromatin is not due to the absence of H1, but most probably due to histone-DNA interaction being weak. It is obvious that structural and functional differences of the chromatin exist not only between T. b. brucei and higher eukaryotes, but also between various stages of the life-cycle of the parasite. It is therefore not adequate to investigate the chromatin only of the procyclic culture forms as a model for all stages of the life-cycle of T. b. bruce
Decoy oligodeoxynucleotide againstactivator protein-1 reducesneointimal proliferation after coronaryangioplasty in hypercholesterolemic minipigs
AbstractObjectivesWe sought to demonstrate, in an appropriate animal model, that co-medication with a transcription factor-blocking agent limits restenosis after percutaneous transluminal coronary angioplasty (PTCA).BackgroundEnhanced synthesis in the vessel wall of endothelin-1 (ET-1), a powerful co-mitogen for vascular smooth muscle cells, appears to be one mechanism that promotes restenosis after PTCA. Deformation-induced expression of prepro-ET-1 is governed by the transcription factor, activator protein-1 (AP-1).MethodsAn anti-AP-1 decoy oligodeoxynucleotide (dODN) strategy was devised in which the dODN-containing solution (20 nmol) was administered locally through a Dispatch catheter into the coronary arteries of hypercholesterolemic minipigs at the time of PTCA (AVE-GFX stent).ResultsTreatment with an AP-1 dODN, mimicking the consensus binding site of the transcription factor, significantly reduced neointimal formation in the coronary arteries of hypercholesterolemic minipigs (n = 10 to 12), compared with vehicle-treated coronary arteries, after four weeks of follow-up (neointimal area 2.64 ± 0.33 vs. 4.81 ± 1.04 mm2[mean ± SEM]; p < 0.05). This effect was maintained after eight weeks (neointimal area 2.04 ± 0.22 mm2; n = 3) and correlated with a reduction in both nuclear translocation of AP-1 and ET-1 synthesis in the vessel wall 48 h after PTCA (n = 4). In contrast, an AP-1 mutant dODN, to which the transcription factor does not bind, showed no effect on neointimal formation at either time point (n = 3 to 7). Moreover, a consensus dODN directed against CCAAT/enhancer binding protein (C/EBP), another deformation-sensitive transcription factor, did not significantly affect neointimal formation after four weeks (n = 3).ConclusionsThese findings demonstrate the feasibility, efficacy and specificity of the anti-AP-1 dODN approach to the treatment of restenosis, which principally but not exclusively targets deformation-induced ET-1 synthesis in the vessel wall. Provided that these findings can be extrapolated to the situation of patients with coronary artery disease, the observed extent of the inhibitory effect of the AP-1 dODN treatment suggests that this co-medication may greatly reduce the incidence of in-stent restenosis
Fractal Conductance Fluctuations in Gold--Nanowires
A detailed analysis of magneto-conductance fluctuations of quasiballistic
gold-nanowires of various lengths is presented. We find that the variance
when analyzed for much
smaller than the correlation field varies according to with indicating that the graph of
vs. is fractal. We attribute this behavior to the existence of
long-lived states arising from chaotic trajectories trapped close to regular
classical orbits. We find that decreases with increasing length of the
wires.Comment: 5 pages, Revtex with epsf, 4 Postscript figures, final version
accepted as Phys. Rev. Let
Long Distance Transport of Ultracold Atoms using a 1D optical lattice
We study the horizontal transport of ultracold atoms over macroscopic
distances of up to 20 cm with a moving 1D optical lattice. By using an optical
Bessel beam to form the optical lattice, we can achieve nearly homogeneous
trapping conditions over the full transport length, which is crucial in order
to hold the atoms against gravity for such a wide range. Fast transport
velocities of up to 6 m/s (corresponding to about 1100 photon recoils) and
accelerations of up to 2600 m/s2 are reached. Even at high velocities the
momentum of the atoms is precisely defined with an uncertainty of less than one
photon recoil. This allows for construction of an atom catapult with high
kinetic energy resolution, which might have applications in novel collision
experiments.Comment: 15 pages, 8 figure
A Closer Look on the Polyhydroxybutyrate- (PHB-) Negative Phenotype of Ralstonia eutropha PHB-4
The undefined poly(3-hydroxybutyrate)- (PHB-) negative mutant R. eutropha PHB-4
was generated in 1970 by 1-nitroso-3-nitro-1-methylguanidine (NMG)
treatment. Although being scientific relevant, its genotype remained
unknown since its isolation except a recent first investigation. In this
study, the mutation causing the PHA-negative phenotype of R. eutropha PHB-4 was confirmed independently: sequence analysis of the phaCAB operon identified a G320A mutation in phaC yielding a stop codon, leading to a massively truncated PhaC protein of 106 amino acids (AS) in R. eutropha PHB-4 instead of 589 AS in the wild type. No other mutations were observed within the phaCAB operon. As further mutations probably occurred in the genome of mutant PHB-4
potentially causing secondary effects on the cells' metabolism, the
main focus of the study was to perform a 2D PAGE-based proteome analysis
in order to identify differences in the proteomes of the wild type and
mutant PHB-4. A total of 20 differentially expressed proteins
were identified which provide valuable insights in the metabolomic
changes of mutant PHB-4. Besides excretion of pyruvate, mutant PHB-4
encounters the accumulation of intermediates such as pyruvate and
acetyl-CoA by enhanced expression of the observed protein species: (i)
ThiJ supports biosynthesis of cofactor TPP and thereby reinforces the
2-oxoacid dehydrogenase complexes as PDHC, ADHC and OGDHC in order to
convert pyruvate at a higher rate and the (ii) 3-isopropylmalate
dehydrogenase LeuB3 apparently directs pyruvate to synthesis of several
amino acids. Different (iii) acylCoA-transferases enable transfer
reactions between organic acid intermediates, and (iv) citrate lyase
CitE4 regenerates oxaloacetate from citrate for conversion with
acetyl-CoA in the TCC in an anaplerotic reaction. Substantial amounts of
reduction equivalents generated in the TCC are countered by (v)
synthesis of more ubiquinones due to enhanced synthesis of MenG2 and
MenG3, thereby improving the respiratory chain which accepts electrons
from NADH and succinate
Conductance fluctuations in mesoscopic normal-metal/superconductor samples
We study the magnetoconductance fluctuations of mesoscopic
normal-metal/superconductor (NS) samples consisting of a gold-wire in contact
with a niobium film. The magnetic field strength is varied over a wide range,
including values that are larger than the upper critical field B_c2 of niobium.
In agreement with recent theoretical predictions we find that in the NS sample
the rms of the conductance fluctuations (CF) is by a factor of 2.8 +/- 0.4
larger than in the high field regime where the entire system is driven normal
conducting. Further characteristics of the CF are discussed.Comment: 4 pages, REVTEX, 3 eps-figures included. To be published in Phys.
Rev. Lett.. Changes: one misplaced figure correcte
Repulsively bound atom pairs in an optical lattice
Throughout physics, stable composite objects are usually formed via
attractive forces, which allow the constituents to lower their energy by
binding together. Repulsive forces separate particles in free space. However,
in a structured environment such as a periodic potential and in the absence of
dissipation, stable composite objects can exist even for repulsive
interactions. Here we report on the first observation of such an exotic bound
state, comprised of a pair of ultracold atoms in an optical lattice. Consistent
with our theoretical analysis, these repulsively bound pairs exhibit long
lifetimes, even under collisions with one another. Signatures of the pairs are
also recognised in the characteristic momentum distribution and through
spectroscopic measurements. There is no analogue in traditional condensed
matter systems of such repulsively bound pairs, due to the presence of strong
decay channels. These results exemplify on a new level the strong
correspondence between the optical lattice physics of ultracold bosonic atoms
and the Bose-Hubbard model, a correspondence which is vital for future
applications of these systems to the study of strongly correlated condensed
matter systems and to quantum information.Comment: 5 pages, 4 figure
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