Effect of the Pauli principle on photoelectron spin transport in p+p^+ GaAs

In p+ GaAs thin films, the effect of photoelectron degeneracy on spin transport is investigated theoretically and experimentally by imaging the spin polarization profile as a function of distance from a tightly-focussed light excitation spot. Under degeneracy of the electron gas (high concentration, low temperature), a dip at the center of the polarization profile appears with a polarization maximum at a distance of about $2 \; \mu m$ from the center. This counterintuitive result reveals that photoelectron diffusion depends on spin, as a direct consequence of the Pauli principle. This causes a concentration dependence of the spin stiffness while the spin dependence of the mobility is found to be weak in doped material. The various effects which can modify spin transport in a degenerate electron gas under local laser excitation are considered. A comparison of the data with a numerical solution of the coupled diffusion equations reveals that ambipolar coupling with holes increases the steady-state photo-electron density at the excitation spot and therefore the amplitude of the degeneracy-induced polarization dip. Thermoelectric currrents are predicted to depend on spin under degeneracy (spin Soret currents), but these currents are negligible except at very high excitation power where they play a relatively small role. Coulomb spin drag and bandgap renormalization are negligible due to electrostatic screening by the hole gas

Spin and recombination dynamics of excitons and free electrons in p-type GaAs : effect of carrier density

Carrier and spin recombination are investigated in p-type GaAs of acceptor concentration NA = 1.5 x 10^(17) cm^(-3) using time-resolved photoluminescence spectroscopy at 15 K. At low pho- tocarrier concentration, acceptors are mostly neutral and photoelectrons can either recombine with holes bound to acceptors (e-A0 line) or form excitons which are mostly trapped on neutral acceptors forming the (A0X) complex. It is found that the spin lifetime is shorter for electrons that recombine through the e-A0 transition due to spin relaxation generated by the exchange scattering of free electrons with either trapped or free holes, whereas spin flip processes are less likely to occur once the electron forms with a free hole an exciton bound to a neutral acceptor. An increase of exci- tation power induces a cross-over to a regime where the bimolecular band-to-band (b-b) emission becomes more favorable due to screening of the electron-hole Coulomb interaction and ionization of excitonic complexes and free excitons. Then, the formation of excitons is no longer possible, the carrier recombination lifetime increases and the spin lifetime is found to decrease dramatically with concentration due to fast spin relaxation with free photoholes. In this high density regime, both the electrons that recombine through the e-A0 transition and through the b-b transition have the same spin relaxation time.Comment: 4 pages, 5 figure

Absence of an intrinsic value for the surface recombination velocity in doped semiconductors

A self-consistent expression for the surface recombination velocity $S$ and the surface Fermi level unpinning energy as a function of light excitation power ($P$) is presented for n- and p-type semiconductors doped above the 10$^{16}$ cm$^{-3}$ range. Measurements of $S$ on p-type GaAs films using a novel polarized microluminescence technique are used to illustrate two limiting cases of the model. For a naturally oxidized surface $S$ is described by a power law in $P$ whereas for a passivated surface $S^{-1}$ varies logarithmically with $P$. Furthermore, the variation in $S$ with surface state density and bulk doping level is found to be the result of Fermi level unpinning rather than a change in the intrinsic surface recombination velocity. It is concluded that $S$ depends on $P$ throughout the experimentally accessible range of excitation powers and therefore that no instrinsic value can be determined. Previously reported values of $S$ on a range of semiconducting materials are thus only valid for a specific excitation power.Comment: 10 pages, 7 figure

El recurso de anulación en la legislación panameña

Objetivo general * Determinar si se infringe o no los principios de imparcialidad, doble instancia al acogerse el recurso de anulación y ordenarse la realización de un nuevo juicio. Objetivos específicos * Conocer el principio de imparcialidad y doble instancia. * Revisar el recurso de anulación y su vinculación con estos principios. * Determinar si se vulnera estos principios al ordenarse la realización de un nuevo juicio. * Establecer si en efecto se vulneran los derechos de los sujetos procesales. * Promover las medidas necesarias para implementar las modificaciones de la Ley 63 de 28 de agosto de 2008

Age Diversity Climate Affecting Individual‐Level Work‐Related Outcomes

The present study answers the call for more studies to investigate the age diversity climate’s effect on individual‐level outcomes. Building on the social identity approach and social exchange theory, we surveyed 110 Italian employees aged between 18 and 61 years old (M = 46.10, SD = 10.02) and investigated the role of age diversity climate in predicting intentions to quit (H1), job‐related wellbeing (H2), and work engagement (H3). Our findings confirmed the hypotheses (H1 and H2), showing the added effect of age diversity climate over and above age, job tenure, role clarity, job demands, job control, perceived support, and perceived job and organizational fit. In fact, age diversity climate accounted for a significant increase in the variance explained for two of the three hypothesized models (i.e., intentions to quit and job‐related wellbeing, but not work engagement). To conclude, this study contributes to the existing literature by showing the age diversity climate’s predictive value for turnover intentions and job‐related wellbeing, and corroborating the importance of supporting age diversity through a variety of Human Resources Management strategies

Imaging ambipolar diffusion of photocarriers in GaAs thin films

Images of the steady-state luminescence of passivated GaAs self-standing films under excitation by a tightly-focussed laser are analyzed as a function of light excitation power. While unipolar diffusion of photoelectrons is dominant at very low light excitation power, an increased power results in a decrease of the diffusion constant near the center of the image due to the onset of ambipolar diffusion. The results are in agreement with a numerical solution of the diffusion equations and with a physical analysis of the luminescence intensity at the centre of the image, which permits the determination of the ambipolar diffusion constant as a function of electron concentration.Comment: 5 figure

Characterization of a jelly of Calendula officinalis L. at 1% for stomatological use

Introducción: La Calendula officinalis L. es una de las especies vegetales más utilizadas en el tratamiento de enfermedades periodontales. Objetivo: Determinar preliminarmente los parámetros de calidad de la jalea de Calendula officinalis L. al 1% para uso estomatológico. Métodos: Se elaboraron 18 formulaciones utilizando como agente gelificante carboximetilcelulosa (CMC) e hidroxipropilmetilcelulosa (HPMC), empleando el método de incorporación. A las mismas se le determinaron los parámetros de calidad y se seleccionaron las cuatro con mejores parámetros tecnológicos para evaluar el grado de aceptación sensorial por parte de un comité de expertos. Resultados: Las formulaciones con HPMC fueron las que presentaron mejores características organolépticas y pH aceptable para su aplicación sobre la mucosa bucal; así como un área de extensibilidad óptimo, lo que permitió que fueran seleccionadas para realizar el análisis sensorial. Conclusión: Se establecieron preliminarmente los parámetros de calidad de la jalea Calendula officinalis L. al 1% siendo seleccionada la formulación codificada como HPMC 6 por presentar olor característico al extracto blando, color ámbar tenue, homogéneo y con brillo, sabor agradable, no presentar grumos ni arenosidad, área de extensibilidad de 66.96±0.91cm2, pH de 4.9 y mayor aceptabilidad sensorial.Introduction: Calendula officinalis L. is one of the plant species most used in the treatment of periodontal diseases. Objective: To determine preliminarily the quality parameters of Calendula officinalis L. jelly at 1% for stomatological use. Methods: 18 formulations were prepared using carboxymethylcellulose (CMC) and hydroxypropylmethylcellulose (HPMC) as the gelling agent, using the incorporation method. The quality parameters were determined selecting the four formulations with better technological parameters to evaluate sensory acceptance by a committee of experts. Results: The HPMC formulations presented better organoleptic characteristics and acceptable pH for its application on the buccal mucosa; as well as an area of optimal extensibility, which allowed them to be selected to carry out the sensory analysis. Conclusion: The quality parameters of the Calendula officinalis L. 1% jelly were preliminarily established the formulation encoded as HPMC 6 is selected for presenting characteristic odor to the soft extract, amber color subdued, homogeneous and glossy, pleasant taste, no lumps or grit, area of extensibility of 66.96 ± 0.91cm2, pH of 4.9 and greater sensory acceptability

Using blood cytokine measures to define high inflammatory biotype of schizophrenia and schizoaffective disorder

Background: Increases in pro-inflammatory cytokines are found in the brain and blood of people with schizophrenia. However, increased cytokines are not evident in all people with schizophrenia, but are found in a subset. The cytokine changes that best define this subset, termed the “elevated inflammatory biotype”, are still being identified. Methods: Using quantitative RT-PCR, we measured five cytokine mRNAs (IL-1β, IL-2 IL-6, IL-8 and IL-18) from peripheral blood of healthy controls and of people with schizophrenia or schizoaffective disorder (n = 165). We used a cluster analysis of the transcript levels to define those with low and those with elevated levels of cytokine expression. From the same cohort, eight cytokine proteins (IL-1β, IL-2, IL-6, IL-8, IL-10, IL-12, IFNγ and TNFα) were measured in serum and plasma using a Luminex Magpix-based assay. We compared peripheral mRNA and protein levels across diagnostic groups and between those with low and elevated levels of cytokine expression according to our transcription-based cluster analysis. Results: We found an overall decrease in the anti-inflammatory IL-2 mRNA (p = 0.006) and an increase in three serum cytokines, IL-6 (p = 0.010), IL-8 (p = 0.024) and TNFα (p < 0.001) in people with schizophrenia compared to healthy controls. A greater percentage of people with schizophrenia (48%) were categorised into the elevated inflammatory biotype compared to healthy controls (33%). The magnitude of increase in IL-1β, IL-6, IL-8 and IL-10 mRNAs in people in the elevated inflammation biotype ranged from 100 to 220% of those in the non-elevated inflammatory biotype and was comparable between control and schizophrenia groups. Blood cytokine protein levels did not correlate with cytokine mRNA levels, and plasma levels of only two cytokines distinguished the elevated and low inflammatory biotypes, with IL-1β significantly increased in the elevated cytokine control group and IL-8 significantly increased in the elevated cytokine schizophrenia group. Conclusions: Our results confirm that individuals with schizophrenia are more likely to have elevated levels of inflammation compared to controls. We suggest that efforts to define inflammatory status based on peripheral measures need to consider both mRNA and protein measures as each have distinct advantages and disadvantages and can yield different results.Danny Boerrigter, Thomas W. Weickert, Rhoshel Lenroot, Maryanne O’Donnell, Cherrie Galletly, Dennis Liu, Martin Burgess, Roxanne Cadiz, Isabella Jacomb, Vibeke S. Catts, Stu G. Fillman, and Cynthia Shannon Weicker

Dielectric disorder in two-dimensional materials

Understanding and controlling disorder is key to nanotechnology and materials science. Traditionally, disorder is attributed to local fluctuations of inherent material properties such as chemical and structural composition, doping or strain. Here, we present a fundamentally new source of disorder in nanoscale systems that is based entirely on the local changes of the Coulomb interaction due to fluctuations of the external dielectric environment. Using two-dimensional semiconductors as prototypes, we experimentally monitor dielectric disorder by probing the statistics and correlations of the exciton resonances, and theoretically analyse the influence of external screening and phonon scattering. Even moderate fluctuations of the dielectric environment are shown to induce large variations of the bandgap and exciton binding energies up to the 100 meV range, often making it a dominant source of inhomogeneities. As a consequence, dielectric disorder has strong implications for both the optical and transport properties of nanoscale materials and their heterostructures