9,400 research outputs found
Disorder Potentials near Lithographically Fabricated Atom Chips
We show that previously observed large disorder potentials in magnetic
microtraps for neutral atoms are reduced by about two orders of magnitude when
using atom chips with lithographically fabricated high quality gold layers.
Using one dimensional Bose-Einstein condensates, we probe the remaining
magnetic field variations at surface distances down to a few microns.
Measurements on a 100 um wide wire imply that residual variations of the
current flow result from local properties of the wire.Comment: submitted on September 24th, 200
Flow and magnetic structures in a kinematic ABC-dynamo
Dynamo theory describes the magnetic field induced by the rotating, convecting and electrically conducting fluid in a celestial body. The classical ABC-flow model represents fast dynamo action, required to sustain such a magnetic field. In this letter, Lagrangian coherent structures (LCSs) in the ABC-flow are detected through Finite-time Lyapunov exponents (FTLE). The flow skeleton is identified by extracting intersections between repelling and attracting LCSs. For the case A = B = C = 1, the skeleton structures are made up from lines connecting two different types of stagnation points in the ABC-flow. The corresponding kinematic ABC-dynamo problem is solved using a spectral method, and the distribution of cigar-like magnetic structures visualized. Inherent links are found to exist between LCSs in the ABC-flow and induced magnetic structures, which provides insight into the mechanism behind the ABC-dynamo
Loss of atm sensitises p53-deficient cells to topoisomerase poisons and antimetabolites
Background: Ataxia-telangiectasia is a pleiotropic autosomal recessive disorder caused by mutations in the ATM gene. In addition to a profound cancer predisposition, another hallmark of ataxia-telangiectasia is radiosensitivity. Recently, p53-null mouse fibroblasts have been reported to be radiosensitised by the concurrent loss of ATM. Materials and methods: We compared the sensitivity of atm+/+/p53-/- and atm-/-/p53-/- mouse embryonic fibroblasts to different classes of chemotherapeutic agents using the MTT assay, Trypan Blue exclusion and fluorescence-activated cell sorting for cell cycle and apoptosis analyses. Results: Loss of ATM function in p53-deficient cells resulted in a 2- to 4-fold increase in sensitivity to the topoisomerase I poisons camptothecin and topotecan, to the topoisomerase II poisons doxorubicin, epirubicin and etoposide, and to the antimetabolites 5-fluorouracil and gemcitabine, but not to the platinum compounds cisplatin, carboplatin and oxaliplatin, the taxanes docetaxel and paclitaxel, or to busulfan. Loss of ATM function did not result in increased apoptosis, but resulted in increased Trypan Blue staining in response to epirubicin, suggesting that processes other than apoptosis may mediate cytotoxicity. ATM deficiency did not alter the extent of G1/S or G2/M cell cycle phase accumulation produced by epirubicin, suggesting that enhanced sensitivity was not due to failure of checkpoint activation. Conclusions: We provide further evidence that ATM is involved in regulating cellular defences against some cytotoxic agents in the absence of p53. Tumour-targeted functional inhibition of ATM may be a valuable strategy for increasing the efficacy of anticancer agents in the treatment of p53-mutant cancer
Aperiodic dynamical decoupling sequences in presence of pulse errors
Dynamical decoupling (DD) is a promising tool for preserving the quantum
states of qubits. However, small imperfections in the control pulses can
seriously affect the fidelity of decoupling, and qualitatively change the
evolution of the controlled system at long times. Using both analytical and
numerical tools, we theoretically investigate the effect of the pulse errors
accumulation for two aperiodic DD sequences, the Uhrig's DD UDD) protocol [G.
S. Uhrig, Phys. Rev. Lett. {\bf 98}, 100504 (2007)], and the Quadratic DD (QDD)
protocol [J. R. West, B. H. Fong and D. A. Lidar, Phys. Rev. Lett {\bf 104},
130501 (2010)]. We consider the implementation of these sequences using the
electron spins of phosphorus donors in silicon, where DD sequences are applied
to suppress dephasing of the donor spins. The dependence of the decoupling
fidelity on different initial states of the spins is the focus of our study. We
investigate in detail the initial drop in the DD fidelity, and its long-term
saturation. We also demonstrate that by applying the control pulses along
different directions, the performance of QDD protocols can be noticeably
improved, and explain the reason of such an improvement. Our results can be
useful for future implementations of the aperiodic decoupling protocols, and
for better understanding of the impact of errors on quantum control of spins.Comment: updated reference
Non-abelian plane waves and stochastic regimes for (2+1)-dimensional gauge field models with Chern-Simons term
An exact time-dependent solution of field equations for the 3-d gauge field
model with a Chern-Simons (CS) topological mass is found. Limiting cases of
constant solution and solution with vanishing topological mass are considered.
After Lorentz boost, the found solution describes a massive nonlinear
non-abelian plane wave. For the more complicate case of gauge fields with CS
mass interacting with a Higgs field, the stochastic character of motion is
demonstrated.Comment: LaTeX 2.09, 13 pages, 11 eps figure
Characteristics of improvements in balance control using vibro-tactile biofeedback of trunk sway for multiple sclerosis patients
Background and aims: Previously, we determined that training with vibrotactile feedback (VTfb) of trunk sway improves MS patients’ balance impairment. Here, we posed 5 questions: 1) How many weeks of VTfb training are required to obtain the best short-term carry over effect (CoE) with VTfb? 2) How long does the CoE last once VTfb training terminates? 3) Is the benefit similar for stance and gait? 4) Is position or velocity based VTfb more effective in reducing trunk sway? 5) Do patients’ subjective assessments of balance control improve? Methods: Balance control of 16 MS patients was measured with gyroscopes at the lower trunk. The gyroscopes drove directionally active VTfb in a head-band. Patients trained twice per week with VTfb for 4 weeks to determine when balance control with and without VTfb stopped improving. Thereafter, weekly assessments without VTfb over 4 weeks and at 6 months determined when CoEs ended. Results: A 20% improvement in balance to normal levels occurred with VTfb. Short term CoEs improved from 15 to 20% (p ≤0.001). Medium term (1–4 weeks) CoEs were constant at 19% (p ≤0.001). At 6 months improvement was not significant, 9%. Most improvement was for lateral sway. Equal improvement occurred when angle position or velocity drove VTfb. Subjectively, balance improvements peaked after 3 weeks of training (32%, p ≤0.05). Conclusions: 3–4 weeks VTfb training yields clinically relevant sway reductions and subjective improvements for MS patients during stance and gait. The CoEs lasted at least 1 month. Velocity-based VTfb was equally effective as position-based VTf
The Partition Function and Level Density for Yang-Mills-Higgs Quantum Mechanics
We calculate the partition function and the asymptotic integrated
level density for Yang-Mills-Higgs Quantum Mechanics for two and three
dimensions (). Due to the infinite volume of the phase space
on energy shell for , it is not possible to disentangle completely the
coupled oscillators (-model) from the Higgs sector. The situation is
different for for which is finite. The transition from order
to chaos in these systems is expressed by the corresponding transitions in
and , analogous to the transitions in adjacent level spacing
distribution from Poisson distribution to Wigner-Dyson distribution. We also
discuss a related system with quartic coupled oscillators and two dimensional
quartic free oscillators for which, contrary to YMHQM, both coupling constants
are dimensionless.Comment: 10 pages, LaTeX; minor changes; version accepted for publication as a
Letter in J. Phys.
Stat1 nuclear translocation by nucleolin upon monocyte differentiation
BACKGROUND: Members of the signal transducer and activator of transcription (Stat) family of transcription factors traverse the nuclear membrane through a specialized structure, called the nuclear pore complex (NPC), which represents a selective filter for the import of proteins. Karyophilic molecules can bind directly to a subset of proteins of the NPC, collectively called nucleoporins. Alternatively, the transport is mediated via a carrier molecule belonging to the importin/karyopherin superfamily, which transmits the import into the nucleus through the NPC. METHODOLOGY/PRINCIPAL FINDINGS: In this study, we provide evidence for an alternative Stat1 nuclear import mechanism, which is mediated by the shuttle protein nucleolin. We observed Stat1-nucleolin association, nuclear translocation and specific binding to the regulatory DNA element GAS. Using expression of nucleolin transgenes, we found that the nuclear localization signal (NLS) of nucleolin is responsible for Stat1 nuclear translocation. We show that this mechanism is utilized upon differentiation of myeloid cells and is specific for the differentiation step from monocytes to macrophages. CONCLUSIONS/SIGNIFICANCE: Our data add the nucleolin-Stat1 complex as a novel functional partner for the cell differentiation program, which is uniquely poised to regulate the transcription machinery via Stat1 and nuclear metabolism via nucleolin
- …