Magnetic relaxation, flux pinning and critical currents in superconductors

A systematic study of the magnetic flux pinning properties in superconductors has been undertaken in an attempt to understand the differences between the flux creep behavior of classical superconductors and high-temperature superconductors (HTSC\u27s). In HTSC\u27s, the ratio of the effective flux pinning energy to the thermal energy, U[subscript]0/kT, is much smaller than that of conventional superconductors, often approaching unity. This results in much larger creep rates in HTSC\u27s than in conventional superconductors. It is necessary to find suitable models that describe flux creep in both classical superconductors (i.e., Nb-Ti) and HTSC\u27s (i.e., Tl[subscript]2Ba[subscript]2Ca[subscript]2Cu[subscript]3O[subscript]10). Results show that while these two classes of materials are quantitatively very different, a single pinning barrier model adequately describes both, within the proper region of the H-T plane. The model is applied to a variety of superconductors and the results are contrasted;Although the H-T plane appears to be very different for HTSC\u27s than for conventional superconductors, qualitatively the same physics describes both. In HTSC\u27s, near the upper critical field there exists a relatively wide region of superconducting fluctuations, followed successively by regions of thermodynamic reversibility, thermally assisted flux flow (TAFF), flux creep, and finally a rigid flux lattice where little, if any, motion of the flux lattice occurs. All of these regions are also present in conventional superconductors, but are often much more difficult, especially the irreversibility transition and the fluctuation region. The central finding of the flux creep analysis is that the region of flux creep is defined as a band in the H-T plane in which 2 ≤ U[subscript]0/kT ≤ 100, and that the flux creep model applies best within this band. Neither the single barrier model or a model utilizing a distribution of pinning energies is found to be adequate the entire H-T plane, which is not surprising because the physics of each region are very different

Very low latitude (L = 1.08) whistlers and correlation with lightning activity

We present analysis of more than 2000 lightning-generated whistlers recorded at a low-latitude station, located at Allahabad (geographic latitude, 25.40N; geographic longitude, 81.93E; L = 1.081), India, during December 2010 to November 2011. The main focus of this work is on the correlation between observed low-latitude whistlers and lightning activity detected by the World-Wide Lightning Location Network near the conjugate point (geography 9.87S, 83.59E) of Allahabad. Whistler occurrence is higher in the postmidnight period as compared to the premidnight period. Whistlers were observed in the daytime only on 2 days that too before 8:30 LT (morning). Seasonally, occurrence is maximum during winter months, which is due to more lightning activity in the conjugate region and favorable ionospheric conditions. About 63% of whistlers were correlated with lightning strokes in the vicinity of the conjugate point within spatial extent of 1000 km (conjugate area). Most (about 53%) whistlers were found to be associated with lightning strokes that were offset to the southeast of the conjugate point. The results indicate that an energy range of 7.5-17.5 kJ of lightning strokes generate most of whistlers at this station. The L shell calculations show that propagation paths of the observed whistlers were embedded in the topside ionosphere. Based on these results we suggest a possibility of ducted mode of propagation even for such very low latitude whistlers. ©2015. American Geophysical Union. All Rights Reserved

Exploring the differences in cloud properties observed by the Terra and Aqua MODIS Sensors

The aerosol-cloud interaction in different parts of the globe is examined here using multi-year statistics of remotely sensed data from two MODIS sensors aboard NASA's <i>Terra</i> (morning) and <i>Aqua</i> (afternoon) satellites. Simultaneous retrievals of aerosol loadings and cloud properties by the MODIS sensor allowed us to explore morning-to-afternoon variation of liquid cloud fraction (CF) and optical thickness (COT) for clean, moderately polluted and heavily polluted clouds in different seasons. Data analysis for seven-years of MODIS retrievals revealed strong temporal and spatial patterns in morning-to-afternoon variation of cloud fraction and optical thickness over different parts of the global oceans and the land. For the vast areas of stratocumulus cloud regions, the data shows that the days with elevated aerosol abundance were also associated with enhanced afternoon reduction of CF and COT pointing to the possible reduction of the indirect climate forcing. A positive correlation between aerosol optical depth and morning-to-afternoon variation of trade wind cumulus cloud cover was also found over the northern Indian Ocean, though no clear relationship between the concentration of Indo-Asian haze and morning-to-afternoon variation of COT was established. Over the Amazon region during wet conditions, aerosols are associated with an enhanced convective process in which morning shallow warm clouds are organized into afternoon deep convection with greater ice cloud coverage. Analysis presented here demonstrates that the new technique for exploring morning-to-afternoon variability in cloud properties by using the differences in data products from the two daily MODIS overpasses is capable of capturing some of the major features of diurnal variations in cloud properties and can be used for better understanding of aerosol radiative effects

Photoelectric Emission from Interstellar Dust: Grain Charging and Gas Heating

We model the photoelectric emission from and charging of interstellar dust and obtain photoelectric gas heating efficiencies as a function of grain size and the relevant ambient conditions. Using realistic grain size distributions, we evaluate the net gas heating rate for various interstellar environments, and find less heating for dense regions characterized by R_V=5.5 than for diffuse regions with R_V=3.1. We provide fitting functions which reproduce our numerical results for photoelectric heating and recombination cooling for a wide range of interstellar conditions. In a separate paper we will examine the implications of these results for the thermal structure of the interstellar medium. Finally, we investigate the potential importance of photoelectric heating in H II regions, including the warm ionized medium. We find that photoelectric heating could be comparable to or exceed heating due to photoionization of H for high ratios of the radiation intensity to the gas density. We also find that photoelectric heating by dust can account for the observed variation of temperature with distance from the galactic midplane in the warm ionized medium.Comment: 50 pages, including 18 figures; corrected title and abstract field

Razvoj i fizikokemijsko vrednovanje farmakosoma diklofenaka

Pharmacosomes are amphiphilic lipid vesicular systems that have shown their potential in improving the bioavailability of poorly water soluble as well as poorly lipophilic drugs. Diclofenac is a poorly water soluble drug and also causes gastrointestinal toxicity. To improve the water solublity of diclofenac, its pharmacosomes (phospholipid complex) have been prepared and evaluated for physicochemical analysis. Diclofenac was complexed with phosphatidylcholine (80 %) in equimolar ratio, in the presence of dichloromethane, by the conventional solvent evaporation technique. Pharmacosomes thus prepared were evaluated for drug solubility, drug content, surface morphology (by scanning electron microscopy), phase transition behaviour (by differential scanning calorimetry), crystallinity (by X-ray powder diffraction) and in vitro dissolution. Pharmacosomes of diclofenac were found to be irregular or disc shaped with rough surfaces in SEM. Drug content was found to be 96.2 1.1 %. DSC thermograms and XRPD data confirmed the formation of the phospholipid complex. Water solubility of the prepared complex was found to be 22.1 µg mL1 as compared to 10.5 µg mL1 of diclofenac. This improvement in water solubility in prepared pharmacosomes may result in improved dissolution and lower gastrointestinal toxicity. Pharmacosomes showed 87.8 % while the free diclofenac acid showed a total of only 60.4 % drug release at the end of 10 h of the dissolution study.Farmakosomi su amfifilni lipidni vezikularni sustavi sa sposobnošću poboljšanja bioraspoloživosti lijekova slabo topljivih u vodi i organskim otapalima. U svrhu povećanja topljivosti diklofenaka (ljekovite tvari koja je slabo vodotopljiva, a uzrokuje i gastrointestinalnu toksičnost) pripravljeni su i evaluirani njegovi farmakosomi (fosfolipidni kompleksi). Diklofenak je kompleksiran s fosfatidilkolinom (80 %) u ekvimolarnom omjeru, u prisutnosti diklormetana, konvencionalnom metodom evaporacije. Tako pripravljenim farmakosomima ispitivana je topljivost, sadržaj ljekovite tvari, morfologija površine (pomoću pretražne elektronske mikroskopije), ponašanje pri prijelazu faza (pomoću diferencijalne pretražne kalorimetrije), kristaliničnost (rendgenskom analizom praha) i in vitro oslobađanje. Farmakosomi diklofenaka su nepravilnog oblika ili u obliku diska te imaju neravnu površinu u SEM-u. Sadržaj ljekovite tvari je 96,2 1,1 %. DSC termogrami i XRPD podaci potvrdili su nastajanje fosfolipidnog kompleksa. Topljivost u vodi dobivenih kompleksa bila je 22,1 µg mL1, a topljivost samog diklofenaka 10,5 µg mL1. Postignuto poboljšanje topljivosti može imati za posljedicu povećano oslobađanje i manju gastrointestinalnu toksičnost. Tijekom 10 h iz farmakosoma se oslobodilo 87,8 %, a iz slobodnog diklofenaka samo 60,4 % ljekovite tvari

Coulomb Blockade and Coherent Single-Cooper-Pair Tunneling in Single Josephson Junctions

We have measured the current-voltage characteristics of small-capacitance single Josephson junctions at low temperatures (T < 0.04 K), where the strength of the coupling between the single junction and the electromagnetic environment was controlled with one-dimensional arrays of dc SQUIDs. We have clearly observed Coulomb blockade of Cooper-pair tunneling and even a region of negative differential resistance, when the zero-bias resistance of the SQUID arrays is much higher than the quantum resistance h/e^2 = 26 kohm. The negative differential resistance is evidence of coherent single-Cooper-pair tunneling in the single Josephson junction.Comment: RevTeX, 4 pages with 6 embedded figure

Monitoring Space Weather: Using Automated, Accurate Neural Network Based Whistler Segmentation for Whistler Inversion

It is challenging, yet important, to measure the - ever-changing - cold electron density in the plasmasphere. The cold electron density inside and outside of the plasmapause is a key parameter for radiation belt dynamics. One indirect measurement is through finding the velocity dispersion relation exhibited by lightning induced whistlers. The main difficulty of the method comes from low signal-to-noise ratios for most of the ground-based whistler components. To provide accurate electron density and L-shell measurements, whistler components need to be detectable in the noisy background, and their characteristics need to be reliably determined. For this reason precise segmentation is needed on a spectrogram image. Here we present a fully automated way to perform such an image segmentation by leveraging the power of convolutional neural networks, a state-of-the-art method for computer vision tasks. Testing the proposed method against a manually, and semi-manually segmented whistler dataset achieved <10% relative electron density prediction error for 80% of the segmented whistler traces, while for the L-shell, the relative error is <5% for 90% of the cases. By segmenting more than 1 million additional real whistler traces from Rothera station Antarctica, logged over 9 years, seasonal changes in the average electron density were found. The variations match previously published findings, and confirm the capabilities of the image segmentation technique

Angeitis necrotizante sistémica no supurativa

1. Se estudian 3 casos de angeítis necrotizante sistémica no supurativa: un hombre de 36 y una mujer de 58 años con granulomatosis de Wegener y un hombre de 30 años con granulomatosis alérgica del tipo descrito por Churg y Strauss. 2. Se prefiere el hombre de angeítis necrotizante sistémica no supurativa como lo ha hecho Paronetto cuando trata este capítulo desde el punto de vista inmunopatológico. 3. Consideran los autores que la lesión renal es la periglomerulitis granulomatosa parahiliar y que su presencia ya en la biopsia tiene gran valor diagnóstico. 4. Se subraya que el cuadro clínico, la marcada eosinofilia tisular y la presencia de imágenes micromultinodulares en el ganglio linfático, apoyan sólidamente un diagnóstico de granulomatosis alérgica de la forma descrita por Churg y Strauss. 5. Se hace una amplia revisión bibliográfica

The number of transmission channels through a single-molecule junction

We calculate transmission eigenvalue distributions for Pt-benzene-Pt and Pt-butadiene-Pt junctions using realistic state-of-the-art many-body techniques. An effective field theory of interacting $\pi$-electrons is used to include screening and van der Waals interactions with the metal electrodes. We find that the number of dominant transmission channels in a molecular junction is equal to the degeneracy of the molecular orbital closest to the metal Fermi level.Comment: 9 pages, 8 figure