446 research outputs found
Lattice effects and current reversal in superconducting ratchets
Competition between the vortex lattice and a lattice of asymmetric artificial
defects is shown to play a crucial role in ratchet experiments in
superconducting films. We present a novel and collective mechanism for current
reversal based on a reconfiguration of the vortex lattice. In contrast to
previous models of vortex current reversal, the mechanism is based on the
global response of the vortex lattice to external forces.Comment: 12 pages, 7 figure
Flux flow resistivity and vortex viscosity of high-Tc films
The flux flow regime of high-T samples of different normal state
resistivities is studied in the temperature range where the sign of the Hall
effect is reversed. The scaling of the vortex viscosity with normal state
resistivity is consistent with the Bardeen-Stephen theory. Estimates of the
influence of possible mechanisms suggested for the sign reversal of the Hall
effect are also given.Comment: 3 pages. 4 figures upon reques
Study of the phase transition in the 3d Ising spin glass from out of equilibrium numerical simulations
Using the decay of the out equilibrium spin-spin correlation function we
compute the equilibrium Edward-Anderson order parameter in the three
dimensional binary Ising spin glass in the spin glass phase. We have checked
that the Edward-Anderson order parameter computed from out of equilibrium
numerical simulations follows with good precision the critical law as
determined in experiments and in numerical studies at equilibrium. We have also
studied the dependence of the order parameter with the lattice size. Finally we
present a large time study of the scaling of the off-equilibrium
fluctuation-dissipation relations.Comment: 14 pages, 7 Postscript figure
An action principle for the quantization of parametric theories and nonlinear quantum cosmology
By parametrizing the action integral for the standard Schrodinger equation we
present a derivation of the recently proposed method for quantizing a
parametrized theory. The reformulation suggests a natural extension from
conventional to nonlinear quantum mechanics. This generalization enables a
unitary description of the quantum evolution for a broad class of constrained
Hamiltonian systems with a nonlinear kinematic structure. In particular, the
new theory is applicable to the quantization of cosmological models where a
chosen gravitational degree of freedom acts as geometric time. This is
demonstrated explicitly using three cosmological models: the Friedmann universe
with a massless scalar field and Bianchi type I and IX models. Based on these
investigations, the prospect of further developing the proposed quantization
scheme in the context of quantum gravity is discussed.Comment: 14 page
Incorporation of a molybdenum atom in a Rubredoxin-type Centre of a de novo-designed α3DIV-L21C three-helical bundle peptide
PB would thank the PTNMRPhD (PD/00065/2013). VLP thanks the NIH for support (GM141086).The rational design and functionalization of small, simple, and stable peptides scaffolds is an attractive avenue to mimic catalytic metal-centres of complex proteins, relevant for the design of metalloenzymes with environmental, biotechnological and health impacts. The de novo designed α3DIV-L21C framework has a rubredoxin-like metal binding site and was used in this work to incorporate a Mo-atom. Thermostability studies using differential scanning calorimetry showed an increase of 4 °C in the melting temperature of the Mo-α3DIV-L21C when compared to the apo-α3DIV-L21C. Circular dichroism in the visible and far-UV regions corroborated these results showing that Mo incorporation provides stability to the peptide even though there were almost no differences observed in the secondary structure. A formal reduction potential of ∼ −408 mV vs. NHE, pH 7.6 was determined. Combining electrochemical results, EPR and UV–visible data we discuss the oxidation state of the molybdenum centre in Mo-α3DIV-L21C and propose that is mainly in a Mo (VI) oxidation state.publishersversionpublishe
Nonlinear quantum gravity on the constant mean curvature foliation
A new approach to quantum gravity is presented based on a nonlinear
quantization scheme for canonical field theories with an implicitly defined
Hamiltonian. The constant mean curvature foliation is employed to eliminate the
momentum constraints in canonical general relativity. It is, however, argued
that the Hamiltonian constraint may be advantageously retained in the reduced
classical system to be quantized. This permits the Hamiltonian constraint
equation to be consistently turned into an expectation value equation on
quantization that describes the scale factor on each spatial hypersurface
characterized by a constant mean exterior curvature. This expectation value
equation augments the dynamical quantum evolution of the unconstrained
conformal three-geometry with a transverse traceless momentum tensor density.
The resulting quantum theory is inherently nonlinear. Nonetheless, it is
unitary and free from a nonlocal and implicit description of the Hamiltonian
operator. Finally, by imposing additional homogeneity symmetries, a broad class
of Bianchi cosmological models are analyzed as nonlinear quantum
minisuperspaces in the context of the proposed theory.Comment: 14 pages. Classical and Quantum Gravity (To appear
CL100 expression is down-regulated in advanced epithelial ovarian cancer and its re-expression decreases its malignant potential
Although early stage ovarian cancer can be effectively treated with surgery and chemotherapy, the majority of cases present with advanced disease, which remains essentially incurable. Unfortunately, little is known about the genes important for the development and progression of this disease. In this study, the expression of 68 phosphatases was determined in immortalized ovarian epithelial cells (IOSE) and compared to ovarian cancer cell lines. CL100, a dual specificity phosphatase, displayed 10-25-fold higher expression in normal compared to malignant ovarian cell lines. Immunohistochemical staining of normal ovaries and 68 ovarian cancer specimens confirmed this differential expression. Re-expression of CL100 in ovarian cancer cells decreased adherent and non-adherent cell growth and induced phenotypic changes including loss of filopodia and lamellipodia with an associated decrease in cell motility. Induced expression of CL100 in ovarian cancer cells suppressed intraperitoneal tumor growth in nude mice. These results show for the first time that CL100 expression is altered in human ovarian cancer, that CL100 expression changes cell morphology and motility, and that it suppresses intraperitoneal growth of human ovarian epithelial cancer. These data suggest that down-regulation of CL100 may play a role in the progression of human ovarian cancer
Temperature dependence and mechanisms for vortex pinning by periodic arrays of Ni dots in Nb films
Pinning interactions between superconducting vortices in Nb and magnetic Ni
dots were studied as a function of current and temperature to clarify the
nature of pinning mechanisms. A strong current dependence is found for a square
array of dots, with a temperature dependent optimum current for the observation
of periodic pinning, that decreases with temperature as (1-T/Tc)3/2. This same
temperature dependence is found for the critical current at the first matching
field with a rectangular array of dots. The analysis of these results allows to
narrow the possible pinning mechanisms to a combination of two: the interaction
between the vortex and the magnetic moment of the dot and the proximity effect.
Moreover, for the rectangular dot array, the temperature dependence of the
crossover between the low field regime with a rectangular vortex lattice to the
high field regime with a square configuration has been studied. It is found
that the crossover field increases with decreasing temperature. This dependence
indicates a change in the balance between elastic and pinning energies,
associated with dynamical effects of the vortex lattice in the high field
range.Comment: 12 text pages (revtex), 6 figures (1st jpeg, 2nd-6th postscript)
accepted in Physical Review
- …