11,186 research outputs found
Magnetic remanence of Josephson junction arrays
In this work we study the magnetic remanence exhibited by Josephson junction
arrays in response to an excitation with an AC magnetic field. The effect,
predicted by numerical simulations to occur in a range of temperatures, is
clearly seen in our tridimensional disordered arrays. We also discuss the
influence of the critical current distribution on the temperature interval
within which the array develops a magnetic remanence. This effect can be used
to determine the critical current distribution of an array.Comment: 8 pages, 4 figures, Talk to be presented on 44th Annual Conference on
Magnetism & Magnetic Materials, San Jose, CA, USA Accepted to be published in
Journal of Applied Physic
Latitudinal variation of the solar photospheric intensity
We have examined images from the Precision Solar Photometric Telescope (PSPT)
at the Mauna Loa Solar Observatory (MLSO) in search of latitudinal variation in
the solar photospheric intensity. Along with the expected brightening of the
solar activity belts, we have found a weak enhancement of the mean continuum
intensity at polar latitudes (continuum intensity enhancement
corresponding to a brightness temperature enhancement of ).
This appears to be thermal in origin and not due to a polar accumulation of
weak magnetic elements, with both the continuum and CaIIK intensity
distributions shifted towards higher values with little change in shape from
their mid-latitude distributions. Since the enhancement is of low spatial
frequency and of very small amplitude it is difficult to separate from
systematic instrumental and processing errors. We provide a thorough discussion
of these and conclude that the measurement captures real solar latitudinal
intensity variations.Comment: 24 pages, 8 figs, accepted in Ap
Vortex-antivortex annihilation in mesoscopic superconductors with a central pinning center
In this work we solved the time-dependent Ginzburg-Landau equations, TDGL, to
simulate two superconducting systems with different lateral sizes and with an
antidot inserted in the center. Then, by cycling the external magnetic field,
the creation and annihilation dynamics of a vortex-antivortex pair was studied
as well as the range of temperatures for which such processes could occur. We
verified that in the annihilation process both vortex and antivortex acquire an
elongated format while an accelerated motion takes place.Comment: 4 pages, 5 figures, work presented in Vortex VII
Quantum-Mechanical Position Operator and Localization in Extended Systems
We introduce a fundamental complex quantity, , which allows us to
discriminate between a conducting and non-conducting thermodynamic phase in
extended quantum systems. Its phase can be related to the expectation value of
the position operator, while its modulus provides an appropriate definition of
a localization length. The expressions are valid for {\it any} fractional
particle filling. As an illustration we use to characterize insulator
to ``superconducting'' and Mott transitions in one-dimensional lattice models
with infinite on-site Coulomb repulsion at quarter filling.Comment: 4 pages, REVTEX, 1 ps figure
A combinatorial approach of Proteomics and Systems Biology in unravelling the mechanisms of acute kidney injury (AKI): involvement of NMDA receptor GRIN1 in murine AKI
BACKGROUND: Acute kidney injury (AKI) is a frequent condition in hospitalised patients undergoing major surgery or the critically ill and is associated with increased mortality. Based on the volume of the published literature addressing this condition, reporting both supporting as well as conflicting molecular evidence, it is apparent that a comprehensive analysis strategy is required to understand and fully delineate molecular events and pathways which can be used to describe disease induction and progression as well as lead to a more targeted approach in intervention therapies.<p></p>
RESULTS: We used a Systems Biology approach coupled with a de-novo high-resolution proteomic analysis of kidney cortex samples from a mouse model of folic acid-induced AKI (12 animals in total) and show comprehensive mapping of signalling cascades, gene activation events and metabolite interference by mapping high-resolution proteomic datasets onto a de-novo hypothesis-free dataspace. The findings support the involvement of the glutamatergic signalling system in AKI, induced by over-activation of the N-methyl-D-aspartate (NMDA)-receptor leading to apoptosis and necrosis by Ca2+-influx, calpain and caspase activation, and co-occurring reactive oxygen species (ROS) production to DNA fragmentation and NAD-rundown. The specific over-activation of the NMDA receptor may be triggered by the p53-induced protein kinase Dapk1, which is a known non-reversible cell death inducer in a neurological context. The pathway mapping is consistent with the involvement of the Renin-Angiotensin Aldosterone System (RAAS), corticoid and TNFalpha signalling, leading to ROS production and gene activation through NFkappaB, PPARgamma, SMAD and HIF1alpha trans-activation, as well as p53 signalling cascade activation. Key elements of the RAAS-glutamatergic axis were assembled as a novel hypothetical pathway and validated by immunohistochemistry.<p></p>
CONCLUSIONS: This study shows to our knowledge for the first time in a molecular signal transduction pathway map how AKI is induced, progresses through specific signalling cascades that may lead to end-effects such as apoptosis and necrosis by uncoupling of the NMDA receptor. Our results can potentially pave the way for a targeted pharmacological intervention in disease progression or induction.<p></p>
A Multiscale Approach for Modeling Crystalline Solids
In this paper we present a modeling approach to bridge the atomistic with
macroscopic scales in crystalline materials. The methodology combines
identification and modeling of the controlling unit processes at microscopic
level with the direct atomistic determination of fundamental material
properties. These properties are computed using a many body Force Field derived
from ab initio quantum-mechanical calculations. This approach is exercised to
describe the mechanical response of high-purity Tantalum single crystals,
including the effect of temperature and strain-rate on the hardening rate. The
resulting atomistically informed model is found to capture salient features of
the behavior of these crystals such as: the dependence of the initial yield
point on temperature and strain rate; the presence of a marked stage I of easy
glide, specially at low temperatures and high strain rates; the sharp onset of
stage II hardening and its tendency to shift towards lower strains, and
eventually disappear, as the temperature increases or the strain rate
decreases; the parabolic stage II hardening at low strain rates or high
temperatures; the stage II softening at high strain rates or low temperatures;
the trend towards saturation at high strains; the temperature and strain-rate
dependence of the saturation stress; and the orientation dependence of the
hardening rate.Comment: 25 pages, 15 figures, LaTe
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