Current-induced highly dissipative domains in high Tc thin films

We have investigated the resistive response of high Tc thin films submitted to a high density of current. For this purpose, current pulses were applied into bridges made of Nd(1.15)Ba(1.85)Cu3O7 and Bi2Sr2CaCu2O8. By recording the time dependent voltage, we observe that at a certain critical current j*, a highly dissipative domain develops somewhere along the bridge. The successive formation of these domains produces stepped I-V characteristics. We present evidences that these domains are not regions with a temperature above Tc, as for hot spots. In fact this phenomenon appears to be analog to the nucleation of phase-slip centers observed in conventional superconductors near Tc, but here in contrast they appear in a wide temperature range. Under some conditions, these domains will propagate and destroy the superconductivity within the whole sample. We have measured the temperature dependence of j* and found a similar behavior in the two investigated compounds. This temperature dependence is just the one expected for the depairing current, but the amplitude is about 100 times smaller.Comment: 9 pages, 9 figures, Revtex, to appear in Phys. Rev.

Faunal responses to oxygen gradients on the Pakistan margin: A comparison of foraminiferans, macrofauna and megafauna

The Pakistan Margin is characterised by a strong mid-water oxygen minimum zone (OMZ) that intercepts the seabed at bathyal depths (150–1300 m). We investigated whether faunal abundance and diversity trends were similar among protists (foraminiferans and gromiids), metazoan macrofauna and megafauna along a transect (140–1850 m water depth) across the OMZ during the 2003 intermonsoon (March–May) and late/post-monsoon (August–October) seasons. All groups exhibited some drop in abundance in the OMZ core (250–500 m water depth; O2: 0.10–0.13 mL L−1=4.46–5.80 μM) but to differing degrees. Densities of foraminiferans >63 μm were slightly depressed at 300 m, peaked at 738 m, and were much lower at deeper stations. Foraminiferans >300 μm were the overwhelmingly dominant macrofaunal organisms in the OMZ core. Macrofaunal metazoans reached maximum densities at 140 m depth, with additional peaks at 850, 940 and 1850 m where foraminiferans were less abundant. The polychaete Linopherus sp. was responsible for a macrofaunal biomass peak at 950 m. Apart from large swimming animals (fish and natant decapods), metazoan megafauna were absent between 300 and 900 m (O2 0.2 mL L−1=8.92 μM). The progressively deeper abundance peaks for foraminiferans (>63 μm), Linopherus sp. and ophiuroids probably represent lower OMZ boundary edge effects and suggest a link between body size and tolerance of hypoxia. Macro- and megafaunal organisms collected between 800 and 1100 m were dominated by a succession of different taxa, indicating that the lower part of the OMZ is also a region of rapid faunal change. Species diversity was depressed in all groups in the OMZ core, but this was much more pronounced for macrofauna and megafauna than for foraminiferans. Oxygen levels strongly influenced the taxonomic composition of all faunal groups. Calcareous foraminiferans dominated the seasonally and permanently hypoxic sites (136–300 m); agglutinated foraminiferans were relatively more abundant at deeper stations where oxygen concentrations were >0.13 mL L−1(=5.80 μM). Polychaetes were the main macrofaunal taxon within the OMZ; calcareous macrofauna and megafauna (molluscs and echinoderms) were rare or absent where oxygen levels were lowest. The rarity of larger animals between 300 and 700 m on the Pakistan Margin, compared with the abundant macrofauna in the OMZ core off Oman, is the most notable contrast between the two sides of the Arabian Sea. This difference probably reflects the slightly higher oxygen levels and better food quality on the western side

Late imaging with [1-¹¹C]acetate improves detection of tumor fatty acid synthesis with PET

Tumors are often characterized by high levels of de novo fatty acid synthesis. The kinetics of acetate incorporation into tricarboxylic acid cycle intermediates and into lipids suggest that detection of tumors with [1-11C]acetate PET could be improved by imaging at later time points. Methods: The uptake and metabolism of [1-11C], [1-13C], and [1-14C]acetate were measured in mouse prostate and lung cancer models to investigate the time course of 11C label incorporation into tumor metabolites. Results: Radioactivity in the lipid fraction, as compared with the aqueous fraction, in extracts of C4-2B human prostate xenografts peaked at 90 min after [1-14C]acetate injection, which coincided with peak 13C label incorporation into the fatty acids palmitate and stearate. Contrast between the tumor and tissues, such as blood and muscle, increased in PET images acquired over a period of 120 min after [1-11C]acetate injection, and Patlak plots were linear from 17.5 min after injection. Similar results were obtained in a genetically engineered K-rasG12D; p53null lung cancer model, in which the mean tumor-to-lung ratio at 90 min after [1-14C]acetate injection was 4.4-fold higher than at 15 min. Conclusion: These findings suggest that when imaging de novo fatty acid synthesis with [1-11C]acetate it is preferable to measure uptake at later time points, when the effects of perfusion and 11C incorporation into tricarboxylic acid cycle intermediates and bicarbonate are declining. The data presented here suggest that future clinical PET scans of tumors should be acquired later than 30 min, when tracer accumulation due to de novo fatty acid synthesis prevails

NSC32265

13C tracer experiments were conducted at sites spanning the steep oxygen, organic matter, and biological community gradients across the Arabian Sea oxygen minimum zone, in order to quantify the role that benthic fauna play in the short-term processing of organic matter (OM) and to determine how this varies among different environments. Metazoan macrofauna and macrofauna-sized foraminiferans took up as much as 56 6 13 mg of added C m22 (685 mg C m22 added) over 2–5 d, and at some sites this uptake was similar in magnitude to bacterial uptake and/or total respiration. Bottom-water dissolved oxygen concentrations exerted a strong control over metazoan macrofaunal OM processing. At oxygen concentrations .7 mmol L21 (0.16 ml L21), metazoan macrofauna were able to take advantage of abundant OM and to dominate OM uptake, while OM processing at O2 concentrations of 5.0 mmol L21 (0.11 ml L21) was dominated instead by (macrofaunal) foraminiferans. This led us to propose the hypothesis that oxygen controls the relative dominance of metazoan macrofauna and foraminifera in a threshold manner, with the threshold lying between 5 and 7 mmol L21 (0.11 to 0.16 ml L21). Large metazoan macrofaunal biomass and high natural concentrations of OM were also associated with rapid processing of fresh OM by the benthic community. Where they were present, the polychaete Linopherus sp. and the calcareous foraminiferan Uvigerina ex gr. semiornata, dominated the uptake of OM above and below, respectively, the proposed threshold concentrations of bottom-water oxygen

Incorporating Perceptual Task Effort into the Recognition of Intention in Information Graphics

The rapidly increasing availability of electronic publications containing information graphics poses some interesting challenges in terms of information access. For example, visually impaired individuals should ideally be provided with access to the knowledge that would be gleaned from viewing the information graphic. Similarly, digital libraries must take into account the content of information graphics when constructing indices. This paper outlines our approach to recognizing the intended message of an information graphic, focusing on the concept of perceptual task effort, its role in the inference process, our rules for estimating effort, and the results of an eye tracking experiment conducted in order to evaluate and modify those rules