Domain growth in binary mixtures at low temperatures

We have studied domain growth during spinodal decomposition at low temperatures. We have performed a numerical integration of the deterministic time-dependent Ginzburg-Landau equation with a variable, concentration-dependent diffusion coefficient. The form of the pair-correlation function and the structure function are independent of temperature but the dynamics is slower at low temperature. A crossover between interfacial diffusion and bulk diffusion mechanisms is observed in the behavior of the characteristic domain size. This effect is explained theoretically in terms of an equation of motion for the interface.

Cavitation in 3He-4He liquid mixtures at low temperatures

Bubble formation in solutions of 3He and 4He is studied within a density-functional approach. In particular, the temperature dependence of the cavitation pressure for different 3He concentrations is calculated at low temperatures and compared to that of pure 4He. The presence of Andreev states lowers the surface tension and, consequently, nucleation barriers are drastically reduced. This fact means that even at low 3He concentrations the cavitation process takes place at higher pressures than the spinodal pressure, which is not the case for pure 4He.

Optimisation of doped microcrystalline silicon films deposited at very low temperatures by Hot-Wire CVD

In this paper we present new results on doped μc-Si:H thin films deposited by hot-wire chemical vapour deposition (HWCVD) in the very low temperature range (125-275°C). The doped layers were obtained by the addition of diborane or phosphine in the gas phase during deposition. The incorporation of boron and phosphorus in the films and their influence on the crystalline fraction are studied by secondary ion mass spectrometry and Raman spectroscopy, respectively. Good electrical transport properties were obtained in this deposition regime, with best dark conductivities of 2.6 and 9.8 S cm -1 for the p- and n-doped films, respectively. The effect of the hydrogen dilution and the layer thickness on the electrical properties are also studied. Some technological conclusions referred to cross contamination could be deduced from the nominally undoped samples obtained in the same chamber after p- and n-type heavily doped layers.

Cavitation in 3He-4He liquid mixtures at low temperatures

Bubble formation in solutions of 3He and 4He is studied within a density-functional approach. In particular, the temperature dependence of the cavitation pressure for different 3He concentrations is calculated at low temperatures and compared to that of pure 4He. The presence of Andreev states lowers the surface tension and, consequently, nucleation barriers are drastically reduced. This fact means that even at low 3He concentrations the cavitation process takes place at higher pressures than the spinodal pressure, which is not the case for pure 4He.

Estratègies per a l'increment del Russeting en pera Conference

La qualitat del fruit és un concepte multidisciplinari i complex de determinar amb claredat i precisió degut a que intervenen factors lligats a la varietat, al mercat, al consumidor final o factors de seguretat agroalimentària. En el cas de poma Golden, la fruita de primera categoria està definida per criteris com calibre de més de 70 mm i sense russeting, malgrat això hi ha mercats del nord d’Espanya que aprecien més la presencia de russeting. Un altre exemple seria el cas de préssec o nectarina, es considera com a criteri de qualitat la coloració homogènia i vermella-fosca, però al mercat nacional s’aprecien els calibres grans, mentre que certs mercats europeus prefereixen els calibres més petits. En el cas de pera Conference hi ha una sèrie de criteris que la seva importància ve condicionada pel mercat o pel consumidor, com són el calibre, la forma, el color de la pell o el russeting. De tots aquests factors, probablement la presencia de russeting sigui un dels criteris que està més estès en la majoria dels mercats o consumidors que coneixen la pera Conference, la qual cosa implica la necessitat de produir Conference amb russeting. Des del punt de vista comercial el russeting presenta una altre avantatge com es una major rusticitat de la pell, la qual cosa redueix els problemes de manipulació i les pèrdues degudes a l’escaldat que apareix quan la fruita està a l’expositor dels supermercats. El russeting és una alteració de l’epidermis dels fruits, degut a la cicatrització de petites lesions que es produeixen a les primeres etapes de la formació dels fruits. L’aparició s’afavoreix per humitats altes i temperatures baixes durant les primeres setmanes posteriors a la floració. Els anys que no es donen aquestes condicions es fa necessari realitzar tractaments amb productes que afavoreixen l’aparició del russeting. L’objectiu d’aquest estudi es determinar quines son els productes i el calendari d’aplicació més eficaces per afavorir l’aparició de russeting en pera Conference, així com el seu efecte sobre els paràmetres productius.

Identificació de QTLs implicats en l'adaptació a canvis de temperatura en la planta model Arabidopsis thaliana

Estudi realitzat a partir d’una estada al Max Planck Institute for Plant Breeding Research, a Alemanya, entre 2006 i 2008. En aquest treball s´ha identificat una nove interacció epistàtica entre l'ecotip Landsberg, originari d'Europa del nord, i Kashmir-2 o Kondara, ambdós originaris d'Àsia Central. Els anàlisi de QTLs en poblacions recombinants Ler x Kas-2 i Ler x Kond indica el requeriment de 3 loci en Ler x Kas-2 i 2 loci en Ler x Kond. Els híbrids incompatibles crescuts a temperatures baixes (16°C) mostren seriosos defectes en el desenvolupament, mort cel.lular espontània i resistència a Hyaloperonospora parasitica. Aquests fenotips es suprimeixen a elevades temperatures o per mutació d'EDS1, o depleció dels nivells d'àcid sal.licílic per transformació amb salicil.lat hidroxilasa (NahG). El grau de severitat en els fenotips observats correlaciona amb els nivells d'àcid sal.licílic, indicant que aquesta molècula és essencial per a la senyalització d'incompatibilitats genètiques en Arabidopsis.

Thermal nucleation of cavities in liquid helium at negative pressures

We have investigated the nucleation rate at which cavities are formed in 4He and 3He at negative pressures due to thermal fluctuations. To this end, we have used a density functional that reproduces the He liquid-gas interface along the coexistence line. The inclusion of thermal effects in the calculation of the barrier against nucleation results in a sizable decrease of the absolute value of the tensile strength above 1.5 K.

Thermal nucleation and cavitation in 3He and 4He

Density functionals that reproduce the helium liquid-gas interface as a function of temperature have been used, within an improved homogeneous nucleation approach, to investigate thermal nucleation and cavitation in both helium isotopes. The results are compared with available experimental data on cavitation in 3He and 4He. Predictions are made for cavitation in 3He at negative pressures and for nucleation in both isotopes.

Shell structure in mixed 3He-4He droplets

Due to the immiscibility of 3He into 4He at very low temperatures, mixed helium droplets consist of a core of 4He atoms coated by a 3He layer whose thickness depends on the number of atoms of each isotope. When these numbers are such that the centrifugal kinetic energy of the 3He atoms is small and can be considered as a perturbation to the mean-field energy, a novel shell structure arises, with magic numbers different from these of pure 3He droplets. If the outermost shell is not completely filled, the valence atoms align their spins up to the maximum value allowed by the Pauli principle.

Giant heat dissipation at the low temperature reversible-irreversible transition in Gd5Ge4

The heat exchanged at the low-temperature first-order magnetostructural transition is directly measured in Gd5Ge4 . Results show that the origin and the temperature dependence of the heat exchanged varies with the reversible/irreversible character of the first-order transition. In the reversible regime, the heat exchanged by the sample is mostly due to the latent heat at the transition and decreases with decreasing temperature, while in the irreversible regime, the heat is irreversibly dissipated and increases strongly with decreasing temperature, reaching a value of 237 J/kg at 4 K.