3,723 research outputs found
Observations of Subarcsecond Bright Dots in the Transition Region above Sunspots with the Interface Region Imaging Spectrograph
Observations with the Interface Region Imaging Spectrograph (IRIS) have
revealed numerous sub-arcsecond bright dots in the transition region above
sunspots. These bright dots are seen in the 1400\AA{} and 1330\AA{} slit-jaw
images. They are clearly present in all sunspots we investigated, mostly in the
penumbrae, but also occasionally in some umbrae and light bridges. The bright
dots in the penumbrae typically appear slightly elongated, with the two
dimensions being 300--600 km and 250--450 km, respectively. The long sides of
these dots are often nearly parallel to the bright filamentary structures in
the penumbrae but sometimes clearly deviate from the radial direction. Their
lifetimes are mostly less than one minute, although some dots last for a few
minutes or even longer. Their intensities are often a few times stronger than
the intensities of the surrounding environment in the slit-jaw images. About
half of the bright dots show apparent movement with speeds of
10--40~km~s in the radial direction. Spectra of a few bright dots
were obtained and the Si~{\sc{iv}}~1402.77\AA{} line profiles in these dots are
significantly broadened. The line intensity can be enhanced by one to two
orders of magnitude. Some relatively bright and long-lasting dots are also
observed in several passbands of the Atmospheric Imaging Assembly onboard the
Solar Dynamics Observatory, and they appear to be located at the bases of
loop-like structures. Many of these bright dots are likely associated with
small-scale energy release events at the transition region footpoints of
magnetic loops.Comment: 5 figures, will appear in ApJ
Propagating EUV disturbances in the solar corona : two-wavelength observations
Quasi-periodic EUV disturbances simultaneously observed in 171 Ã… and 195 Ã… TRACE bandpasses propagating outwardly in a fan-like magnetic structure of a coronal active region are analysed. Time series of disturbances observed in the different bandpasses have a relatively high correlation coefficient (up to about 0.7). The correlation has a tendency to decrease with distance along the structure: this is consistent with an interpretation of the disturbances in terms of parallel-propagating slow magnetoacoustic waves. The wavelet analysis does not show a significant difference between waves observed in different bandpasses. Periodic patterns of two distinct periods: 2-3 min and 5-8 min are detected in both bandpasses, existing simultaneously and at the same distance along the loop, suggesting the nonlinear generation of the second harmonics
Effect of Concave Wall Geometry on Heat Transfer in Hypersonic Boundary Layers
Heat transfer measurements are made to investigate the effects of concave surface curvature on a high-stagnation enthalpy boundary layer in a Mach 5.1 flow. Experiments are
carried out using two curved models with 16 and 25 degree turning angles, and baseline
planar models (at plate and linear ramp) for comparative study. Streamwise and spanwise
cross-sections are obtained. Significant destabilization of the boundary layer is observed
over the adverse pressure gradient geometries. For the curved surfaces, the heat flux distribution appears to exhibit a quadratic dependence with streamwise distance, in contrast
with the linear dependence observed on the linear ramp
Local texture and percolative paths for long-range conduction in high critical current density TlBa₂Ca₂Cu₃O₈₊ₓ deposits
©1994 American Institute of Physics. The electronic version of this article is the complete one and can be found online at: http://link.aip.org/link/?APPLAB/64/106/1DOI:10.1063/1.110908A possible microstructural origin of the high critical current densities which have been obtained in c-axis-aligned, polycrystalline TlBa₂Ca₂Cu₃O₈₊ₓdeposits has been identified. The results of x-ray diffraction determinations of basal plane texture of Tl-1223 deposits prepared by spray pyrolysis are observed to depend on the size of the x-ray beam. Furthermore, most grain boundaries were found from transmission electron microscopy to have small misorientation angles. It is concluded that although overall the basal plane orientations are nearly random, there is a high degree of local texture indicative of colonies of similarly oriented grains. The spread in a-axis orientation within a colony is ~10°–15°. Intercolony conduction, it is suggested, may be enhanced by a percolative network of small-angle grain boundaries at colony interfaces
Complex carbohydrate diets are not capable of maintaining normal plasma calcium and phosphorus levels in vitamin D-deficient rats.
2-methylene-(20S,25S)-19,27-dinor-(22E)-vitamin D analogs
This invention discloses 2-methylene-(20S,25S)-19,27-dinor-(22E)-vitamin D analogs, and specifically 2-methylene-(20S,25S)-19,27-dinor-(22E)-1.alpha.,25-dihydroxyvitamin D.sub.3, and pharmaceutical uses therefor. This compound exhibits pronounced activity in arresting the proliferation of undifferentiated cells and inducing their differentiation to the monocyte thus evidencing use as an anti-cancer agent and for the treatment of skin diseases such as psoriasis as well as skin conditions such as wrinkles, slack skin, dry skin and insufficient sebum secretion. This compound also has little, if any, calcemic activity and therefore may be used to treat autoimmune disorders or inflammatory diseases in humans as well as renal osteodystrophy. This compound may also be used for the treatment or prevention of obesity
Relaxation of classical many-body hamiltonians in one dimension
The relaxation of Fourier modes of hamiltonian chains close to equilibrium is
studied in the framework of a simple mode-coupling theory. Explicit estimates
of the dependence of relevant time scales on the energy density (or
temperature) and on the wavenumber of the initial excitation are given. They
are in agreement with previous numerical findings on the approach to
equilibrium and turn out to be also useful in the qualitative interpretation of
them. The theory is compared with molecular dynamics results in the case of the
quartic Fermi-Pasta-Ulam potential.Comment: 9 pag. 6 figs. To appear in Phys.Rev.
Concerning synthesis of new biobased polycarbonates with curcumin in replacement of bisphenol a and recycled diphenyl carbonate as example of circular economy
Curcumin (CM) is a natural polyphenol well-known for its antioxidant and pharmaceutical properties, that can represent a renewable alternative to bisphenol A (BPA) for the synthesis of biobased polycarbonates (PC). In the presented strategy, preparation of the CM-based PC was coupled with chemical recycling of the fossil-based BPA polycarbonate (BPA-PC) conducting a two-steps trans-polymerization that replaces BPA monomer with CM or its tetrahydrogenated colorless product (THCM). In the first step of synthetic strategy, depolymerization of commercial BPA-PC was carried out with phenol as nucleophile, according to our previous procedure based on zinc derivatives and ionic liquids as catalysts, thus producing quantitatively diphenyl carbonate (DPC) e BPA. In the second step, DPC underwent a melt transesterification with CM or THCM monomers affording the corresponding bio-based polycarbonates, CM-PC and THCM-PC, respectively. THCM was prepared by reducing natural bis-phenol with cyclohexene as a hydrogen donor and characterized by 1H-NMR and MS techniques. Polymerization reactions were monitored by infrared spectroscopy and average molecular weights and dispersity of the two biobased polymers THCM-PC and CM-PC were determined by means of gel permeation chromatography (GPC). Optical properties of the prepared polymers were also measured
Analysis of travelling waves associated with the modelling of aerosolised skin grafts
A previous model developed by the authors investigates the growth patterns of keratinocyte cell colonies after they have been applied to a burn site using a spray technique. In this paper, we investigate a simplified one-dimensional version of the model. This model yields travelling wave solutions and we analyse the behaviour of the travelling waves. Approximations for the rate of healing and maximum values for both the active healing and the healed cell densities are obtained
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