7,753 research outputs found
Vortex Softening: Origin of the second peak effect in BiSrCaCuO
Transverse ac permeability measurements in BiSrCaCuO single crystals at low fields and temperatures in a vortex configuration
free of external forces show that the decrease of the critical current as
measured by magnetization loops at the second peak effect is an artifact due to
creep. On the other hand, the increase of critical current at the second peak
is due to a genuine softening of the tilting elastic properties of vortices in
the individual pinning regime that precedes the transition to a disorder state.Comment: 4 pages, 5 figures, RevTex, two column versio
Particle-vortex dynamics in noncommutative space
We study the problem of a charged particle in the presence of a uniform
magnetic field plus a vortex in noncommutative planar space considering the two
possible non-commutative extensions of the corresponding Hamiltonian, namely
the ``fundamental'' and the ``antifundamental'' representations. Using a Fock
space formalism we construct eigenfunctions and eigenvalues finding in each
case half of the states existing in the ordinary space case. In the limit of
we recover the two classes of states found in ordinary space,
relevant for the study of anyon physics.Comment: 13 pages, no figures, plain LaTeX. References adde
A monopole solution from noncommutative multi-instantons
We extend the relation between instanton and monopole solutions of the
selfduality equations in SU(2) gauge theory to noncommutative space-times.
Using this approach and starting from a noncommutative multi-instanton solution
we construct a U(2) monopole configuration which lives in 3 dimensional
ordinary space. This configuration resembles the Wu-Yang monopole and satisfies
the selfduality (Bogomol'nyi) equations for a U(2) Yang-Mills-Higgs system.Comment: 19 pages; title and abstract changed, brane interpretation corrected.
Version to appear in JHE
Remarkable magnetostructural coupling around the magnetic transition in CeCoFeSi
We report a detailed study of the magnetic properties of
CeCoFeSi under high magnetic fields (up to 16 Tesla)
measuring different physical properties such as specific heat, magnetization,
electrical resistivity, thermal expansion and magnetostriction.
CeCoFeSi becomes antiferromagnetic at 6.7 K.
However, a broad tail (onset at 13 K) in the specific heat
precedes that second order transition. This tail is also observed in the
temperature derivative of the resistivity. However, it is particularly
noticeable in the thermal expansion coefficient where it takes the form of a
large bump centered at . A high magnetic field practically washes out that
tail in the resistivity. But surprisingly, the bump in the thermal expansion
becomes a well pronounced peak fully split from the magnetic transition at
. Concurrently, the magnetoresistance also switches from negative to
positive just below . The magnetostriction is considerable and
irreversible at low temperature (
410 at 2 K) when the magnetic interactions dominate. A broad
jump in the field dependence of the magnetostriction observed at low may be
the signature of a weak ongoing metamagnetic transition. Taking altogether, the
results indicate the importance of the lattice effects in the development of
the magnetic order in these alloys.Comment: 5 pages, 6 figure
Nonlinear Supersymmetry as a Hidden Symmetry
Ver abstrac
Differential antifungal activity of human and cryptococcal melanins with structural discrepancies
Indexación: Scopus.Melanin is a pigment found in all biological kingdoms, and plays a key role in protection against ultraviolet radiation, oxidizing agents, and ionizing radiation damage. Melanin exerts an antimicrobial activity against bacteria, fungi, and parasites. We demonstrated an antifungal activity of synthetic and human melanin against Candida sp. The members of the Cryptococcus neoformans and C. gattii species complexes are capsulated yeasts, which cause cryptococcosis. For both species melanin is an important virulence factor. To evaluate if cryptococcal and human melanins have antifungal activity against Cryptococcus species they both were assayed for their antifungal properties and physico-chemical characters. Melanin extracts from human hair and different strains of C. neoformans (n = 4) and C. gattii (n = 4) were investigated. The following minimum inhibitory concentrations were found for different melanins against C. neoformans and C. gattii were (average/range): 13.7/(7.8-15.6) and 19.5/(15.6-31.2) μg/mL, respectively, for human melanin; 273.4/(125- > 500) and 367.2/(125.5- > 500) μg/mL for C. neoformans melanin and 125/(62.5-250) and 156.2/(62-250) μg/mL for C. gattii melanin. Using Scanning Electron Microscopy we observed that human melanin showed a compact conformation and cryptococcal melanins exposed an amorphous conformation. Infrared spectroscopy (FTIR) showed some differences in the signals related to C-C bonds of the aromatic ring of the melanin monomers. High Performance Liquid Chromatography established differences in the chromatograms of fungal melanins extracts in comparison with human and synthetic melanin, particularly in the retention time of the main compound of fungal melanin extracts and also in the presence of minor unknown compounds. On the other hand, MALDI-TOF-MS analysis showed slight differences in the spectra, specifically the presence of a minor intensity ion in synthetic and human melanin, as well as in some fungal melanin extracts. We conclude that human melanin is more active than the two fungal melanins against Cryptococcus. Although some physico-chemical differences were found, they do not explain the differences in the antifungal activity against Cryptococcus of human and cryptococcal melanins. More detailed studies on the structure should be considered to associate structure and antifungal activity.https://www.frontiersin.org/articles/10.3389/fmicb.2017.01292/ful
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