Hotspot Temperatures Reached in Current-Driven Superconducting Niobium Filaments

In a superconducting microbridge too narrow to support vortex motion, the current-induced resistance occurs non-uniformly at definite spots designated as Phase-Slip-Centres (PSC). Further, if the core of a PSC happens to heat above the critical temperature T _c , a PSC may evolve into a normal propagating zone, or hotspot. The PSC’s time of nucleation and the HS minimum current I _h are determined, which allows deriving without ambiguity the rate of heat transfer to the substrate, the latter is compatible with a phonon blackbody radiation model at the Nb/R–sapphire interface. The computation of the HS temperature is then straightforward, while the PSC case is more involved. However, the PSC core temperature can be obtained through an independent determination of the inelastic quasi-particle diffusion length Λ _qp ～2.8 μm. The results of these computations are consistent with all the specific cases, PSCs and HSs, measured experimentally.     

Spontaneous and Light-Induced Resistive Transitions in Superconducting Thin Film Bridges

In order to study dynamically the resistive states which appear as jumps in the I–V curves of narrow bridges, we have submitted YBaCuO and Nb films to nanosecond current steps and laser pulses simultaneously. In constant current feed, the distinction between hot spots (HS) and phase-slip centers (PSCs) is unambiguous, since HS are compelled to grow or decay, at variance with the stable-in-time PSCs. Thanks to the transient method we show that, even if Joule dissipation associated to a current I is virtually sufficient to sustain the film above T_c, the zero resistance state remains metastable: a hot spot does not arise unless initiated by a PSC, which fact was not reported before. The domains of occurrence of HS and PSCs were then organized in a current–temperature plane. Finally, the theoretical problem of the HS velocity of growth is given an exact solution, in semiquantitative agreement with experiment.     

Fatty acid accumulation in the different fractions of the developing corn kernel

In the food industry, the use of the oil is determined by the composition of fatty acids, and this is highly dependent on its natural origin. The fatty acid composition of whole corn kernel was determined in three varieties of corn (Astro, GH2547, and Local). Linoleic acid was the predominant fatty acid in the oil of Astro and Local at all collection dates, whereas it was the major fatty acid in the oil of GH2547 only between 40 and 60 days after pollination (DAP). The fatty acid accumulation in the endosperm, pericarp and germ fractions of the corn kernel during maturation was determined. The accumulation pattern of oil content was different in these three kernel fractions. The highest levels of oil content in the endosperm (2.2%), germ (34.3%) and pericarp (10.8%) fractions were detected at 20, 40 and 30 (DAP), respectively. The fatty acid accumulation patterns were different amongst the analysed kernel parts, indicating a numerous differences between the three corn kernel parts. Throughout the sampling periods, the endosperm fraction was distinguished by the highest and the lowest levels of oleic and linoleic acids, respectively. At all stages of kernel development, the pericarp fraction had the highest levels of total polyunsaturated fatty acids, which has numerous healthy applications. These results may be useful in the understanding of the potential source of the beneficial unsaturated fatty acids amongst the different fractions of the corn kernel during maturation.     

Extended Domain of Existence for PSCs in Superconductors

By means of nanosecond pulse techniques, we have studied the current-induced dissipation in one-dimensional superconducting bridges, namely, metallic and high-T _c films. It is well known that narrow strips dissipate through phase-slip centers (PSC) close to T _c, or hot spots (HS) at low T, rather than by flux flow. When driven by step pulses of current, PSC give stable voltages, while HS produce a voltage linearly changing with time. By using two-step pulses of current, we have studied the decay of a HS into another HS, or a PSC, or into a zero-resistance state. It was thus found possible to reach the PSC state at arbitrary low temperatures.     

Surgical treatment by vitrectomy and autologous serum of 36 idiopathic macular holes

The release of motilin from an isolated preparation of pig duodenum has been studied. There different types of stimuli were applied: electrical nerve stimulation, intraarterially administered peptides, and instillation of test solutions into the lumen of the duodenum. Furthermore extracts of 20 different regions of the pig digestive system have been analyzed for motilin content. Analysis of the extracts only detected significant presence of motilin in the pig duodenum and jejunum (79 +/- 15 and 60 +/- 19 pmol/g). The stimulation experiments showed: (1) a significant noncholinergic depression of motilin release during electrical stimulation of the vagus nerve (nadir at 74 +/- 5% of baseline level; (2) a significant elevation of motilin release in response to intraarterially administered vasoactive intestinal peptide (VIP) (peak at 330 +/- 35% of baseline level), and (3) a significantly elevated motilin release in response to instillation of autologuous bile (peak at 170 +/- 16% of baseline level) and hydrochloric acid (peak at 196 +/- 42% of baseline level) into the duodenal lumen. In conclusion, luminal acidification and bile are important factors in stimulation of motilin release, whereas the vagally stimulated VIP release was insufficient to overcome the general inhibitory effect of vagus stimulation.     

Temporal Evolution of Normal Hot Spots in Current-Driven Superconducting Films

In addition to the critical current I_c (T), which generates Phase-Slip Centers (PSCs), thin superconducting films possess a well-defined second limiting current I_h, or current intensity able to maintain a preestablished hot spot. By pulsing step functions of the current and monitoring the voltage response on the nanosecond scale, we have determined (T I_c) and (T I_h). From a dynamic study of the two main modes of dissipation in YBCO and Nb films, it is concluded that PSCs are stable structures in current-biased bridges. In contrast, hot spots grow at a constant rate of a few tens of meters per second, determined by the thermal diffusivity of the material and by its bolometric response time. On reducing the current from I_h, the so-called healing length, or minimum normal length, was found, of the order of 0.2 m in YBCO and 2 m in Nb. In summary, the experiment provides three independent measurements (PSC nucleation time, velocity of growth, and minimum length) for only two parameters (D and ).     

Current-Temperature Diagram of Resistive States in Long Superconducting Niobium Filaments

By applying nanosecond current pulses to narrow superconducting Nb strips, we have observed the induced resistive states expected for quasi 1-D transport, namely localized phase-slip centres (PSC) and hot spots (HS). The current-controlled drive discriminates stable-in-time PSC structures near T _c from expanding HS at lower temperatures. HS-PSC exchange and return towards equilibrium are studied by using two-step current pulses. Remarkably, it appears that a hot spot never forms unless a PSC has first been nucleated. Then from a plot of the threshold currents I _c (T) and I _h (T), corresponding to PSC and HS, respectively, one can predict the response to current, temperature, or luminous excitation, as well as the effect of an applied magnetic field.     

α-Tocopherol and fatty acids contents of some Tunisian table olives (Olea europea L.): Changes in their composition during ripening and processing

An experimental investigation was carried out on Tunisian olive-fruits of Meski, Sayali and Picholine cultivars. α-Tocopherol and fatty acids (FA) contents were analyzed, during both ripening and processing, according to the Spanish style. The relationship between oil, unsaponifiable and α-tocopherol contents was determined only during ripening. A genetic effect on FA composition was observed throughout the sampling periods. The highest oleic acid content was found in Sayali cultivar at green stage (78.5% of total FA). α-Tocopherol was positively correlated with unsaturated FA content (R = 0.71, p < 0.05), and oil amount (R = 0.984; R = 0.976; R = 0.952, p < 0.05 for Picholine, Sayali and Meski, respectively), but it was not correlated with unsaponifiable matter. In processed olive-fruits, the results showed primarily, that processing according to the Spanish style is not restricted to green olive-fruits but can be successfully used in cherry olives with guaranteed quality and nutritional value of processed product (Meski and Picholine) related to FA content. Secondly, both α-tocopherol and FA amounts decreased during processing for all cultivars. This decrease was cultivar dependent. It was more pronounced in the black fruit than in the green one for the same cultivar. During fermentation, pH variation showed the same profile in all cultivars. Final pH values at the end of fermentation depend on the concentration of free FA (acidity) in the brine.     

Liquid chromatographic–mass spectrometric analysis of glycerophospholipids in corn oil

The phospholipid composition of corn oil was determined by LC/ESI-MS. The content of phospholipids in the oils varied from 5.2% to 8.7%. The major components in the phospholipids fraction were phosphatidylcholine (57.5–68.1%), phosphatidylinositol (14.5–19.8%), and phosphatidylethanolamine (10.3–13.9%). Phosphatidic acid and phosphatidylglycerol accounted for less than 10% of total phospholipid content. Various molecular species within each class were detected. The phosphatidylcholine class was mainly composed of phosphatidylcholine-C18:2/C18:1 (40–45%) and phosphatidylcholine-18:1/C18:1 (40–51%). Phosphatidylinositol-C16:0/C18:2 (50–69%) was the most abundant phosphatidylinositol. The two phosphatidylethanolamines were phosphatidylethanolamine-C16:0/C18:2 (34–42%) and phosphatidylethanolamine-C18:2/C18:2 (31–36%). Phosphatidylglycerol species were mainly phosphatidylglycerol-C16:0/C18:2 (42–48%) and phosphatidylglycerol-C16:0/C18:1 (36.7–40.3%). Identification of PC molecular species suggests the possibility that corn oil can have therapeutics effects.     

Current-Temperature Diagram of Resistive States in Long Superconducting YBa2Cu3O7 Strips

Using a sequence of stepped bias currents in the nanosecond range, we have studied the destruction of superconductivity in c-axis textured YBa₂Cu₃O₇ strips of various thickness and structure (single or multi-layers). Sufficiently far from T _c, vortex flow fades out and gradually gives way to localized dissipative structures, which can be interpreted either as Phase-Slip Centers (PSC) or normal Hot Spots (HS). A plot of the corresponding threshold currents in the current–temperature (I–T) plane indicates when each of them will occur, and how to switch over from one to the other, in a manner similar to that demonstrated for metallic materials (cf. Ladan et al., J. Low Temp. Phys. 153:103, 2008). The capability of some YBCO strips to support PSC’s at arbitrarily low temperatures escapes the common picture.