Forster energy transfer signatures in optically driven quantum dot molecules

The Forster resonant energy transfer mechanism (FRET) is investigated in optically driven and electrically gated tunnel coupled quantum dot molecules. Two novel FRET induced optical signatures are found in the dressed excitonic spectrum. This is constructed from exciton level occupation as function of pump laser energy and applied bias, resembling a level anticrossing spectroscopy measurement. We observe a redistribution of spectral weight and splitting of the exciton spectral lines. FRET among single excitons induces a splitting in the spatially-direct exciton lines, away from the anticrossing due to charge tunneling in the molecule. However, near the anticrossing, a novel signature appears as a weak satellite line following an indirect exciton line. FRET signatures may also occur among indirect excitons, appearing as split indirect lines. In that case, the signatures appear also in the direct biexciton states, as the indirect satellite mixes in near the tunneling anticrossing region

Coherent control of indirect excitonic qubits in optically driven quantum dot molecules

We propose an optoelectronic scheme to define and manipulate an indirect neutral exciton qubit within a quantum dot molecule. We demonstrate coherent dynamics of indirect excitons resilient against decoherence effects, including direct exciton spontaneous recombination. For molecules with large interdot separation, the exciton dressed spectrum yields an often overlooked avoided crossing between spatially indirect exciton states. Effective two level system Hamiltonians are extracted by Feshbach projection over the multilevel exciton configurations. An adiabatic manipulation of the qubit states is devised using time dependent electric field sweeps. The exciton dynamics yields the necessary conditions for qubit initialization and near unitary rotations in the picosecond time scale, driven by the system internal dynamics. Despite the strong influence of laser excitation, charge tunneling, and interdot dipole-dipole interactions, the effective relaxation time of indirect excitons is much longer than the direct exciton spontaneous recombination time, rendering indirect excitons as potential elemental qubits in more complex schemes.Comment: Submitted to PRB, 11 pages and 6 figure

Aspectos generales de la metodología para el cálculo del Margen Bruto Estándar 2000

El objetivo de este documento de trabajo es presentar la metodología para el cálculo del Margen Bruto Estándar con periodo de referencia 1999, 2000 y 2001 (MBE 2000) y para el conjunto de categorías agrícolas definidas en el anexo de la Decisión de la Comisión 2003/369/CE. En este documento, dichas categorías vienen recogidas en el cuadro 2 del anexo. Este documento de trabajo se divide en tres secciones. En la sección 1 se presenta el marco metodológico general recogido en la legislación comunitaria, prestando especial interés a la definición de MBE. Las secciones 2 y 3 presentan, de forma resumida, la metodología seguida para el cálculo de los coeficientes MBE 2000 de las categorías de cultivos y ganados respectivamente

Serologic Evidence of West Nile Virus Infection in Horses, Coahuila State, Mexico

Serum samples were obtained from 24 horses in the State of Coahuila, Mexico, in December 2002. Antibodies to West Nile virus were detected by epitope-blocking enzyme-linked immunosorbent assay and confirmed by plaque reduction neutralization test in 15 (62.5%) horses. We report the first West Nile virus activity in northern Mexico

Planeación y estrategia de Ferris en el simulador de negocios capstone

En este documento se presenta el trabajo realizado en el simulador de negocios Capstone, en donde se dirigió una empresa de sensores llamada Ferris. Se presenta la planeación estratégica que se aplicó, su desarrollo y los resultados.ITESO, A.C

Cell surface delivery and structural re-organization by pharmacological chaperones of an oligomerization-defective α1b-adrenoceptor mutant demonstrates membrane targeting of GPCR oligomers

Many G-protein-coupled receptors, including the α1b-adrenoceptor, form homo-dimers or oligomers. Mutation of hydrophobic residues in transmembrane domains I and IV alters the organization of the α1b-adrenoceptor oligomer, with transmembrane domain IV playing a critical role. These mutations also result in endoplasmic reticulum trapping of the receptor. Following stable expression of this α1b-adrenoceptor mutant, cell surface delivery, receptor function and structural organization were recovered by treatment with a range of α1b-adrenoceptor antagonists that acted at the level of the endoplasmic reticulum. This was accompanied by maturation of the mutant receptor to a terminally N-glycosylated form, and only this mature form was trafficked to the cell surface. Co-expression of the mutant receptor with an otherwise wild-type form of the α1b-adrenoceptor that is unable to bind ligands resulted in this wild-type variant also being retained in the endoplasmic reticulum. Ligand-induced cell surface delivery of the mutant α1b-adrenoceptor now allowed co-recovery to the plasma membrane of the ligand-binding-deficient mutant. These results demonstrate that interactions between α1b-adrenoceptor monomers occur at an early stage in protein synthesis, that ligands of the α1b-adrenoceptor can act as pharmacological chaperones to allow a structurally compromised form of the receptor to pass cellular quality control, that the mutated receptor is not inherently deficient in function and that an oligomeric assembly of ligand-binding-competent and -incompetent forms of the α1b-adrenoceptor can be trafficked to the cell surface by binding of a ligand to only one component of the receptor oligomer

Self-assembled MgxZn1−xO quantum dots (0 ≤ x ≤ 1) on different substrates using spray pyrolysis methodology

By using the spray pyrolysis methodology in its classical configuration we have grown self-assembled MgxZn1−xO quantum dots (size [similar]4–6 nm) in the overall range of compositions 0 ≤ x ≤ 1 on c-sapphire, Si (100) and quartz substrates. Composition of the quantum dots was determined by means of transmission electron microscopy-energy dispersive X-ray analysis (TEM-EDAX) and X-ray photoelectron spectroscopy. Selected area electron diffraction reveals the growth of single phase hexagonal MgxZn1−xO quantum dots with composition 0 ≤ x ≤ 0.32 by using a nominal concentration of Mg in the range 0 to 45%. Onset of Mg concentration about 50% (nominal) forces the hexagonal lattice to undergo a phase transition from hexagonal to a cubic structure which resulted in the growth of hexagonal and cubic phases of MgxZn1−xO in the intermediate range of Mg concentrations 50 to 85% (0.39 ≤ x ≤ 0.77), whereas higher nominal concentration of Mg ≥ 90% (0.81 ≤ x ≤ 1) leads to the growth of single phase cubic MgxZn1−xO quantum dots. High resolution transmission electron microscopy and fast Fourier transform confirm the results and show clearly distinguishable hexagonal and cubic crystal structures of the respective quantum dots. A difference of 0.24 eV was detected between the core levels (Zn 2p and Mg 1s) measured in quantum dots with hexagonal and cubic structures by X-ray photoemission. The shift of these core levels can be explained in the frame of the different coordination of cations in the hexagonal and cubic configurations. Finally, the optical absorption measurements performed on single phase hexagonal MgxZn1−xO QDs exhibited a clear shift in optical energy gap on increasing the Mg concentration from 0 to 40%, which is explained as an effect of substitution of Zn2+ by Mg2+ in the ZnO lattice

Reduced antioxidant defense in early onset first-episode psychosis: a case-control study

Background:Our objective is to determine the activity of the antioxidant defense system at admission in patients with early onset first psychotic episodes compared with a control group. Methods: Total antioxidant status (TAS) and lipid peroxidation (LOOH) were determined in plasma. Enzyme activities and total glutathione levels were determined in erythrocytes in 102 children and adolescents with a first psychotic episode and 98 healthy controls. Results: A decrease in antioxidant defense was found in patients, measured as decreased TAS and glutathione levels. Lipid damage (LOOH) and glutathione peroxidase activity was higher in patients than controls. Our study shows a decrease in the antioxidant defense system in early onset first episode psychotic patients. Conclusions: Glutathione deficit seems to be implicated in psychosis, and may be an important indirect biomarker of oxidative stress in early-onset schizophrenia. Oxidative damage is present in these patients, and may contribute to its pathophysiology

Epigenetic Signatures Associated with Different Levels of Differentiation Potential in Human Stem Cells

BACKGROUND: The therapeutic use of multipotent stem cells depends on their differentiation potential, which has been shown to be variable for different populations. These differences are likely to be the result of key changes in their epigenetic profiles. METHODOLOGY/PRINCIPAL FINDINGS: to address this issue, we have investigated the levels of epigenetic regulation in well characterized populations of pluripotent embryonic stem cells (ESC) and multipotent adult stem cells (ASC) at the trancriptome, methylome, histone modification and microRNA levels. Differences in gene expression profiles allowed classification of stem cells into three separate populations including ESC, multipotent adult progenitor cells (MAPC) and mesenchymal stromal cells (MSC). The analysis of the PcG repressive marks, histone modifications and gene promoter methylation of differentiation and pluripotency genes demonstrated that stem cell populations with a wider differentiation potential (ESC and MAPC) showed stronger representation of epigenetic repressive marks in differentiation genes and that this epigenetic signature was progressively lost with restriction of stem cell potential. Our analysis of microRNA established specific microRNA signatures suggesting specific microRNAs involved in regulation of pluripotent and differentiation genes. CONCLUSIONS/SIGNIFICANCE: Our study leads us to propose a model where the level of epigenetic regulation, as a combination of DNA methylation and histone modification marks, at differentiation genes defines degrees of differentiation potential from progenitor and multipotent stem cells to pluripotent stem cells