406 research outputs found
Electron-electron interaction induced spin thermalization in quasi-low-dimensional spin valves
We study the spin thermalization, i.e., the inter-spin energy relaxation
mediated by electron-electron scattering in small spin valves. When one or two
of the dimensions of the spin valve spacer are smaller than the thermal
coherence length, the direct spin energy exchange rate diverges and needs to be
regularized by the sample dimensions. Here we consider two model systems: a
long quasi-1D wire and a thin quasi-2D sheet.Comment: Contribution to a Special Issue on Spin Caloritronic
Spin heat accumulation and its relaxation in spin valves
We study the concept of spin heat accumulation in excited spin valves, more
precisely the effective electron temperature that may become spin dependent,
both in linear response and far from equilibrium. A temperature or voltage
gradient create non-equilibrium energy distributions of the two spin ensembles
in the normal metal spacer, which approach Fermi-Dirac functions through energy
relaxation mediated by electron-electron and electron-phonon coupling. Both
mechanisms also exchange energy between the spin subsystems. This inter-spin
energy exchange may strongly affect thermoelectric properties spin valves,
leading, e.g., to violations of the Wiedemann-Franz law.Comment: 4 pages, 4 figures, close to published versio
Optimization of supercritical extraction of nimbin from neem seeds in presence of methanol as co-solvent
Mathematical modeling and optimization of the extraction of nimbin from neemseeds using supercritical carbon dioxide with methanol as co-solvent is the subject of this study. At first a correlation for Sherwood number (Sh) as a function of Reynolds number (Re) and Schmidt number (Sc) was proposed using a Genetic Algorithm (GA) technique. This correlation was compared to previous correlations and was found to give the most accurate results. Moreover, optimum conditions (temperature, pressure, solvent flow rate and particle diameter) which maximizes the extraction yield have been determined using GA. At the next step, methanol was used as a co-solvent and the dynamic equilibrium constant of solute between the solid phase and the solvent was estimated. By applying the new determined equilibrium constant, good agreement between the model and experimental data was observed
Development of chitosan, pullulan, and alginate based drug-loaded nano-emulsions as a potential malignant melanoma delivery platform
Melanoma is the most aggressive form of skin cancer and various treatments have been investigated to treat this disease, but drug resistance remains an important factor in the failure of conventional therapeutics. Here we describe the development, optimisation and characterisation of alginate, chitosan, pullulan, and their combined nano-emulsions as drug delivery platforms for potential application for melanoma. A novel nano-emulsion delivery system was designed and assessed by determining in vitro drug release, cell viability (MTT), cellular apoptosis (ELISA) and confocal microscopy. A comparative analysis of the effect of the nano-emulsions on BRAF-mutant melanoma (A375) and keratinocyte (HaCaT) cells was conducted, with the “pullulan-chitosan” nano-emulsion chosen as an approach for melanoma drug delivery. Increased apoptosis induction of melanoma cells was recorded as 90% after 72 h of treatment with doxorubicin-loaded optimal nano-emulsion. Similarly, in the same treatment, the viability of melanoma cells was decreased by 70%. More importantly, A375 cells treated with naïve doxorubicin were 100% viable compared to cells treated with doxorubicin-loaded nano-emulsion which were only 30%viable. Achieved results are indicating the importance of the drug carrier’s polymeric combination and the impact of the drug release pattern on the efficiency of the treatment. This offers potential for the abrogation of drug- efflux-related chemo-resistance
Ballistic and Diffuse Electron Transport in Nanocontacts of Magnetics
The transition from the ballistic electron transport to the diffuse one is
experimentally observed in the study of the magnetic phase transition in Ni
nanocontacts with different sizes. It is shown that the voltage needed
for Joule heating of the near-contact region to the critical temperature does
not depend on the contact size only in the diffuse mode. For the ballistic
contact it increases with decrease in the nanocontact size. The reduction of
the transport electron mean free path due to heating of NCs may result in
change of the electron transport mode from ballistic to diffusive one.Comment: 7 pages, 2 figures accepted for the publication in JETPL
(http://www.jetpletters.ac.ru). Will be published on 25 april 201
GaAs/GaP quantum dots: Ensemble of direct and indirect heterostructures with room temperature optical emission
Producción CientíficaWe describe the optical emission and the carrier dynamics of an ensemble of self-assembled GaAs quantum dots embedded in GaP(001). The QD formation is driven by the 3.6% lattice mismatch between GaAs and GaP in the Stranski-Krastanow mode after deposition of more than 1.2 monolayers of GaAs. The quantum dots have an areal density between 6 and 7.6 × 1010 per cm−2 and multimodal size distribution. The luminescence spectra show two peaks in the range of 1.7 and 2.1 eV. The samples with larger quantum dots have red emission and show less thermal quenching compared with the samples with smaller QDs. The large QDs luminescence up to room temperature. We attribute the high energy emission to indirect carrier recombination in the thin quantum wells or small strained quantum dots, whereas the low energy red emission is due to the direct electron-hole recombination in the relaxed quantum dots.Comisión Europea (project FP7-ICT-2013-613024-GRASP
Thermally driven spin injection from a ferromagnet into a non-magnetic metal
Creating, manipulating and detecting spin polarized carriers are the key
elements of spin based electronics. Most practical devices use a perpendicular
geometry in which the spin currents, describing the transport of spin angular
momentum, are accompanied by charge currents. In recent years, new sources of
pure spin currents, i.e., without charge currents, have been demonstrated and
applied. In this paper, we demonstrate a conceptually new source of pure spin
current driven by the flow of heat across a ferromagnetic/non-magnetic metal
(FM/NM) interface. This spin current is generated because the Seebeck
coefficient, which describes the generation of a voltage as a result of a
temperature gradient, is spin dependent in a ferromagnet. For a detailed study
of this new source of spins, it is measured in a non-local lateral geometry. We
developed a 3D model that describes the heat, charge and spin transport in this
geometry which allows us to quantify this process. We obtain a spin Seebeck
coefficient for Permalloy of -3.8 microvolt/Kelvin demonstrating that thermally
driven spin injection is a feasible alternative for electrical spin injection
in, for example, spin transfer torque experiments
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