Magnetic breakdown in a normal-metal - superconductor proximity sandwich

We study the magnetic response of a clean normal-metal slab of finite thickness in proximity with a bulk superconductor. We determine its free energy and identify two (meta-)stable states, a diamagnetic one where the applied field is effectively screened, and a second state, where the field penetrates the normal-metal layer. We present a complete characterization of the first order transition between the two states which occurs at the breakdown field, including its spinodals, the jump in the magnetization, and the latent heat. The bistable regime terminates at a critical temperature above which the sharp transition is replaced by a continuous cross-over. We compare the theory with experiments on normal-superconducting cylinders.Comment: 7 pages Revtex, 3 Postscript figures, needs psfig.te

Transition into a low temperature superconducting phase of unconventional pinning in Sr_2RuO_4

We have found a sharp transition in the vortex creep rates at a temperature T^\ast=0.05 T_c in a single crystal of Sr_2RuO_4 (T_{c}=1.03 K) by means of magnetic relaxation measurements. For T<T^\ast, the initial creep rates drop to undetectable low levels. One explanation for this transition into a phase with such extremely low vortex creep is that the low-temperature phase of Sr_2RuO_4 breaks time reversal symmetry. In that case, degenerate domain walls separating discreetly degenerate states of a superconductor can act as very strong pinning centers.Comment: 3 pages, 2 figure

The effect of the addition of a commercial bioprotector in characteristics of "alheira" made from Alentejano pig meat

“Alheira” is a traditional fermented sausage usually produced from poultry meat. A new product was developed at a Portuguese traditional meat plant using Alentejano pig breed meat [1]. The aim of this study was to evaluate the use of a commercial bioprotector in the physicochemical, microbiological and instrumental texture parameters, as well as in the sensorial attributes of the “alheiras”. Two different treatments were compared, namely control and bioprotector and three end product “alheiras” with three days were used per treatment. One-Way ANOVA was used for statistical analyses. The pH of the “alheiras” with bioprotector (4.29) was lower than the pH of the control treatment (4.48). However, no significant differences were observed between control and bioprotector regarding water activity (aw). The “alheiras” microbiological flora showed no significant differences regarding total mesophiles, total anaerobes, lactic acid bacteria, enterobacteria, Escherichia coli and Listeria spp. The counts of psychrophiles (2×107 cfu/g) and psychrophilic anaerobes (1.7×107 cfu/g) were higher in the control treatment, whereas more yeasts and moulds (7×104 cfu/g) are present in the “alheiras” with bioprotector. No contamination with Salmonella sp. was detected, but some samples showed a minor contamination with Listeria monocytogenes. Further studies are in course to reduce microbial contamination, particularly to eradicate Listeria monocytogenes [2]. Texture Profile Analysis (TPA) results revealed that the adhesiveness of the bioprotector “alheiras” (-0.386 N s) is lower than in the control (-0.2 N s). However, no significant differences were observed for other instrumental texture parameters. Regarding sensorial analysis, although no differences were observed between control and bioprotector “alheiras”, panellists noticed some off tastes in the bioprotector treatment. Considering the results of the end product at three days shelf life, no advantage was seen in the bioprotector “alheiras”. These have lower pH, which could justify the off tastes noticed by some panellists and their higher counts of yeasts and moulds. Acknowledgements This work was supported by national funds through project PRODER (QREN/PRODER/Medida 4.1) and funded by FEDER Funds through the COMPETE and National Funds through FCT under the Strategic Project PEst-C/AGR/UI0115/2011. The authors thank PALADARES ALENTEJANOS, Lda. for their collaboration and A. Oliveira and G. Pias for their technical assistance. References: 1-Elias, M. et al. (2013) “Portuguese traditional sausage, “alheira”, made with different meat: sensory evaluation and texture.” ICoMST 2013 E-Book of Proceedings, 59th International Congress of Meat Science and Technology, Izmir, Turkey, 18-23 August 2013. 2-Felício et al. (2011) “Thermal inactivation of Listeria monocytogenes from alheiras, traditional portuguese sausage during cooking.” Food Control 22, 1960-1964

Overscreening Diamagnetism in Cylindrical Superconductor-Normal Metal-Heterostructures

We study the linear diamagnetic response of a superconducting cylinder coated by a normal-metal layer due to the proximity effect using the clean limit quasiclassical Eilenberger equations. We compare the results for the susceptibility with those for a planar geometry. Interestingly, for $R\sim d$ the cylinder exhibits a stronger overscreening of the magnetic field, i.e., at the interface to the superconductor it can be less than (-1/2) of the applied field. Even for $R\gg d$, the diamagnetism can be increased as compared to the planar case, viz. the magnetic susceptibility $4\pi\chi$ becomes smaller than -3/4. This behaviour can be explained by an intriguing spatial oscillation of the magnetic field in the normal layer

Homocysteine levels in pediatric renal transplant recipients.

Transplant Proc. 2003 May;35(3):1093-5. Homocysteine levels in pediatric renal transplant recipients. Mota C, Fonseca I, Santos MJ, Costa T, Faria MS, Henriques AC, Sarmento AM, Pereira E, Pereira M. Department of Paediatric Nephrology, Maria Pia Children's Hospital, R. da Boavista, 827, 4050-111, Porto, Portugal. [email protected] PMID: 12947872 [PubMed - indexed for MEDLIN

Bioassays against pinewood nematode: assessment of a suitable dilution agent and screening for bioactive essential oils

Acetone was investigated and found to be an appropriate alternative to Triton X-100 as a solvent of essential oils in bioassays aimed to investigate their effects on pinewood nematode (Bursaphelenchus xylophilus) mortality. Therefore it was used as dilution agent to screen the effectiveness of fifty two essential oils against this pest. Thirteen essential oils were highly effective, resulting in more than 90% pinewood nematode mortality at 2 mg/mL, with six of them resulting in 100% mortality. LC100 values ranged between 0.50 mg/mL and 0.83 mg/mL for the essential oils of Origanum vulgare and Satureja montana, respectively. Essential oils were submitted to gas chromatography and gas chromatography-mass spectrometry analysis and their chemical composition established. Data from essential oils with 100% mortality at 2 mg/mL and other essential oils previously found to have LC100 ≤ 2 mg/mL was combined, their chemical profiles investigated by correspondences analysis plus automatic classification

Dynamics of the self-interacting chameleon cosmology

In this article we study the properties of the flat FRW chameleon cosmology in which the cosmic expansion of the Universe is affected by the chameleon field and dark energy. In particular, we perform a detailed examination of the model in the light of numerical analysis. The results illustrate that the interacting chameleon filed plays an important role in late time universe acceleration and phantom crossing.Comment: 13 pages, 8 figures, to appear in Astrophysics and Space Sc

Proximity-induced screening and its magnetic breakdown in mesoscopic hybrid structures

We derive a general microscopic expression for the non-linear diamagnetic current in a clean superconductor-insulator-normal metal structure with an arbitrary interface transmission. In the absence of electron-electron interactions in the normal metal the diamagnetic response increases monotonously with decreasing temperature showing no sign of paramagnetic reentrance down to T=0. We also analyze the magnetic breakdown of proximity induced Meissner screening. We demonstrate that the magnetic breakdown field should be strongly suppressed in the limit of small interface transmissions while the linear diamagnetic current does not depend on the transmission of the insulating barrier at low enough temperatures.Comment: 7 pages, 2 figure

Rubus occidentalis – A Framboesa Preta Como progenitora de Programas de Melhoramento da Framboesa Vermelha

A framboesa preta (Rubus occidentalis L.) é uma framboesa que apresenta elevada variabilidade intraespecífica, possuindo alguns traços de interesse para o melhoramento de outras framboesas, nomeadamente para a framboesa vermelha (Rubus idaeus L.). No programa de melhoramento em curso, utilizaram-se 1081 genótipos selvagens de framboesa preta do Canadá, com o objetivo de encontrar progenitores que produzam framboesas coesas e com epiderme muito resistente, permitindo assim, por cruzamento com genótipos de framboesa vermelha, obter descendências com poder de conservação aumentado. Neste trabalho serão avaliadas nos diferentes genótipos de framboesa preta as necessidades em frio, a uniformidade do abrolhamento, a capacidade de produzir rebentos radiculares, a formação de frutos com muitas drupéolas, o tamanho e a firmeza desses frutos. A firmeza da epiderme da framboesa é uma característica de difícil avaliação, pois o seu interior é oco, encontrando-se as drupéolas agregadas em redor do receptáculo. Esta característica dificulta a avaliação da firmeza pelos métodos convencionais, tornando necessário encontrar um método adequado. As necessidades em frio foram analisadas através do abrolhamento, eliminando-se os genótipos que apresentavam um abrolhamento reduzido ou variável ao longo do lançamento, 3 semanas após o primeiro abrolhamento. Este primeiro critério de seleção eliminou cerca de 10% dos genótipos, pois tinham elevadas necessidades de frio. A avaliação da capacidade de produzir rebentos radiculares, aspecto não eliminatório mas de elevada importância nos processos de propagação vegetativa, mostrou que o número de rebentos radiculares de 40 genótipos já analisados variou entre os 0 e os 28. Mais aspetos continuarão em estudo durante este ensaio, de modo a selecionar uma framboesa preta com os hábitos vegetativos e de produção semelhantes à framboesa vermelha, mas com um fruto de firmeza elevada. De modo a complementar a seleção dos melhores genótipos para o melhoramento, serão utilizados marcadores moleculares identificando o que se encontra impresso no genoma, passível de ser transmitido à descendência. Visto que ainda não existem muitos marcadores identificados para a R. occidentalis, será necessário procurar através de ISSRs (Inter Simple Sequence Repeats) marcadores que permitam a distinção dos diferentes genótipos selecionados

Energy gap and proximity effect in MgB2MgB_2 superconducting wires

Measurements of the penetration depth $\lambda (T,H)$ in the presence of a DC magnetic field were performed in $MgB_2$ wires. In as-prepared wires $\lambda (T,H<130 Oe)$ shows a strong diamagnetic downturn below $\approx 10 K$. A DC magnetic field of $130 Oe$ completely suppressed the downturn. The data are consistent with proximity coupling to a surface $Mg$ layer left during synthesis. A theory for the proximity effect in the clean limit, together with an assumed distribution of the $Mg$ layer thickness, qualitatively explains the field and temperature dependence of the data. Removal of the $Mg$ by chemical etching results in an exponential temperature dependence for $\lambda (T)$ with an energy gap of $2 \Delta (0)/T_c\approx 1.54$ ($\Delta(0) \approx 2.61 meV$), in close agreement with recent measurements on commercial powders and single crystals. This minimum gap is only 44% of the BCS weak coupling value, implying substantial anisotropy.Comment: RevTeX 4, 4 EPS figure