426 research outputs found
Deciphering solar turbulence from sunspots records
It is generally believed that sunspots are the emergent part of magnetic flux
tubes in the solar interior. These tubes are created at the base of the
convection zone and rise to the surface due to their magnetic buoyancy. The
motion of plasma in the convection zone being highly turbulent, the surface
manifestation of sunspots may retain the signature of this turbulence,
including its intermittency. From direct observations of sunspots, and indirect
observations of the concentration of cosmogenic isotopes C in tree rings
or Be in polar ice, power spectral densities in frequency are plotted.
Two different frequency scalings emerge, depending on whether the Sun is
quiescent or active. %magnetic activity is maximum or minimum. From direct
observations we can also calculate scaling exponents. These testify to a strong
intermittency, comparable with that observed in the solar wind.Comment: 5 pages, 6 figures, accepted for publication in MNRAS Letter
Transient Receptor Potential Channel M4 and M5 in Magnocellular Cells in Rat Supraoptic and Paraventricular Nuclei
The neurohypophysial hormones, vasopressin (VP) and oxytocin (OT), are synthesised by magnocellular cells in the supraoptic nucleus (SON) and the paraventricular nucleus (PVN) of the hypothalamus. The release of VP into the general circulation from the neurohypophysis increases during hyperosmolality, hypotension and hypovolaemia. VP neurones increase hormone release by increasing their firing rate as a result of adopting a phasic bursting. Depolarising after potentials (DAPs) following a series of action potentials are considered to be involved in the generation of the phasic bursts by summating to plateau potentials. We recently discovered a fast DAP (fDAP) in addition to the slower DAP characterised previously. Almost all VP neurones expressed the fDAP, whereas only 16% of OT neurones had this property, which implicates the involvement of fDAP in the generation of the firing patterns in VP neurones. Our findings obtained from electrophysiological experiments suggested that the ionic current underlying the fDAP is mediated by those of two closely-related Ca 2+-activated cation channels: the melastatin-related subfamily of transient receptor potential channels, TRPM4 and TRPM5. In the present study, double/triple immunofluorescence microscopy and reverse transcriptase-polymerase chain reaction techniques were employed to evaluate whether TRPM4 and TRPM5 are specifically located in VP neurones. Using specific antibodies against these channels, TRPM5 immunoreactivity was found almost exclusively in VP neurones, but not in OT neurones in both the SON and PVN. The most prominent TRPM5 immunoreactivity was in the dendrites of VP neurones. By contrast, most TRPM4 immunoreactivity occurred in cell bodies of both VP and OT neurones. TRPM4 and TRPM5 mRNA were both found in a cDNA library derived from SON punches. These results indictate the possible involvement of TRPM5 in the generation of the fDAP, and these channels may play an important role in determining the distinct firing properties of VP neurones in the SON. © 2011 The Authors. Journal of Neuroendocrinology © 2011 Blackwell Publishing Ltd
Optically induced magnetization dynamics and variation of damping parameter in epitaxial Co2MnSi Heusler alloy films
Copyright © 2010 The American Physical SocietyAll-optical pump-probe measurements of magnetization dynamics have been performed upon epitaxial Co2MnSi(001) Heusler alloy thin films annealed at temperatures of 300, 400, and 450 °C. An ultrafast laser-induced modification of the magnetocrystalline anisotropy triggers precession which is detected by time-resolved magneto-optical Kerr effect measurements. From the damped oscillatory Kerr rotation, the frequency and relaxation rate of the precession is determined. Using a macrospin solution of the Landau-Lifshitz-Gilbert equation the effective fields acting upon the sample magnetization are deduced. This reveals that the magnetization is virtually independent of the annealing temperature while the fourfold magnetocrystalline anisotropy decreases dramatically with increasing annealing temperature as the film structure changes between the B2 and L21 phases. From the measured relaxation rates, the value of the apparent Gilbert damping parameter is found to depend strongly upon the static field strength and in-plane static field orientation. The variation of the apparent damping parameter is generally well reproduced by an inhomogeneous broadening model in which the presence of B2 and L21 phases leads to a large dispersion of the magnetocrystalline anisotropy. However, for the sample annealed at a temperature of 300 °C, the lack of a detailed fit to the data suggests that the apparent anisotropy of the apparent damping parameter might alternatively arise due to a network of dislocations with fourfold symmetry
Self-Similar Random Processes and Infinite-Dimensional Configuration Spaces
We discuss various infinite-dimensional configuration spaces that carry
measures quasiinvariant under compactly-supported diffeomorphisms of a manifold
M corresponding to a physical space. Such measures allow the construction of
unitary representations of the diffeomorphism group, which are important to
nonrelativistic quantum statistical physics and to the quantum theory of
extended objects in d-dimensional Euclidean space. Special attention is given
to measurable structure and topology underlying measures on generalized
configuration spaces obtained from self-similar random processes (both for d =
1 and d > 1), which describe infinite point configurations having accumulation
points
Role of defects and disorder in the half-metallic full-Heusler compounds
Half-metallic ferromagnets and especially the full-Heusler alloys containing
Co are at the center of scientific research due to their potential applications
in spintronics. For realistic devices it is important to control accurately the
creation of defects in these alloys. We review some of our late results on the
role of defects and impurities in these compounds. More precisely we present
results for the following cases (i) doping and disorder in CoCr(Mn)Al(Si)
alloys, (ii) half-metallic ferrimagnetism appeared due to the creation of
Cr(Mn) antisites in these alloys, (iii) Co-doping in MnVAl(Si) alloys
leading to half-metallic antiferromagnetism, and finally (iv) the occurrence of
vacancies in the full-Heusler alloys containing Co and Mn. These results are
susceptible of encouraging further theoretical and experimental research in the
properties of these compounds.Comment: Chapter intended for a book with contributions of the invited
speakers of the International Conference on Nanoscale Magnetism 2007. Revised
version contains new figure
Treatment of Fabry Disease: Outcome of a Comparative Trial with Agalsidase Alfa or Beta at a Dose of 0.2 mg/kg
Two different enzyme preparations, agalsidase alfa (Replagal(TM), Shire) and beta (Fabrazyme(TM), Genzyme), are registered for treatment of Fabry disease. We compared the efficacy of and tolerability towards the two agalsidase preparations administered at identical protein dose in a randomized controlled open label trial.Thirty-four Fabry disease patients were treated with either agalsidase alfa or agalsidase beta at equal dose of 0.2 mg/kg biweekly. Primary endpoint was reduction in left ventricular mass after 12 and 24 months of treatment. Other endpoints included occurrence of treatment failure (defined as progression of cardiac, renal or cerebral disease), glomerular filtration rate, pain, anti-agalsidase antibodies, and globotriaosylceramide levels in plasma and urine. After 12 and 24 months of treatment no reduction in left ventricular mass was seen, which was not different between the two treatment groups. Also, no differences in glomerular filtration rate, pain and decline in globotriaosylceramide levels were found. Antibodies developed only in males (4/8 in the agalsidase alfa group and 6/8 in the agalsidase beta group). Treatment failure within 24 months of therapy was seen in 8/34 patients: 6 male patients (3 in each treatment group) and 2 female patients (both agalsidase alfa). The occurrence of treatment failures did not differ between the two treatment groups; chi(2) = 0.38 p = 0.54.Our study revealed no difference in reduction of left ventricular mass or other disease parameters after 12 and 24 months of treatment with either agalsidase alfa or beta at a dose of 0.2 mg/kg biweekly. Treatment failure occurred frequently in both groups and seems related to age and severe pre-treatment disease.International Standard Randomized Clinical Trial ISRCTN45178534 [http://www.controlled-trials.com/ISRCTN45178534]
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