Photovoltaic Performance of Ultrasmall PbSe Quantum Dots

We investigated the effect of PbSe quantum dot size on the performance of Schottky solar cells made in an ITO/PEDOT/PbSe/aluminum structure, varying the PbSe nanoparticle diameter from 1 to 3 nm. In this highly confined regime, we find that the larger particle bandgap can lead to higher open-circuit voltages (~0.6 V), and thus an increase in overall efficiency compared to previously reported devices of this structure. To carry out this study, we modified existing synthesis methods to obtain ultrasmall PbSe nanocrystals with diameters as small as 1 nm, where the nanocrystal size is controlled by adjusting the growth temperature. As expected, we find that photocurrent decreases with size due to reduced absorption and increased recombination, but we also find that the open-circuit voltage begins to decrease for particles with diameters smaller than 2 nm, most likely due to reduced collection efficiency. Owing to this effect, we find peak performance for devices made with PbSe dots with a first exciton energy of ~1.6 eV (2.3 nm diameter), with a typical efficiency of 3.5%, and a champion device efficiency of 4.57%. Comparing the external quantum efficiency of our devices to an optical model reveals that the photocurrent is also strongly affected by the coherent interference in the thin film due to Fabry-Pérot cavity modes within the PbSe layer. Our results demonstrate that even in this simple device architecture, fine-tuning of the nanoparticle size can lead to substantial improvements in efficiency

Promoting individual and group regulated learning in colaborative settings: an experience in Higher Education

[spa] En este trabajo presentamos una experiencia de innovación docente dirigida a promover la regulación individual y grupal del aprendizaje en estudiantes universitarios que trabajan en un entorno colaborativo mediado por ordenador. Participaron en la experiencia 127 estudiantes y tres profesores de una asignatura troncal de Psicología de la Educación de la Universitat de Barcelona (España). La experiencia se basó en el uso de una herramienta digital ¿ el 'cuaderno de bitácora'¿ en que los estudiantes debían incluir una serie de evidencias de su proceso de trabajo personal y grupal, y del progreso de su aprendizaje, que eran revisadas y comentadas sistemáticamente por los profesores. Se valoró la experiencia a partir de cuestionarios a los estudiantes y autoinformes de los profesores, así como de las calificaciones de los estudiantes. Los resultados de la experiencia fueron positivos tanto desde el punto de vista de la mejora en la organización y funcionamiento individual y grupal de los estudiantes como de la satisfacción de los estudiantes y el profesorado.[eng] We present a teaching innovation intervention aimed at promoting individual and group learning regulation in undergraduate students working in a computer supported collaborative learning environment. Participants were 127 students and three teachers of a compulsory course on Educational Psychology at the University of Barcelona (Spain). As a central point of the intervention, a digital tool --the "student’s log"-- was designed for students to include a series of evidences of their individual and group work processes, and of their learning progress, which the teachers systematically revised and marked with comments. The intervention was evaluated using student questionnaires and teachers’ self-reports, and also considered students’ final grades. The results of the intervention were positive both from the point of view of students’ learning and working processes and from the point of view of students’ and teachers’ satisfaction

Diffractive Photoproduction of Eta_c

Diffractive photoproduction of $\eta_c$ is an important process to study the effect of Odderon, whose existence is still not confirmed in experiment. A detailed interpretation of Odderon in QCD, i.e., in terms of gluons is also unclear.Taking charm quarks as heavy quarks, we can use NRQCD and take $\eta_c$ as a $c\bar c$ bound state. Hence, in the production of $\eta_c$a free $c\bar c$ pair is first produced and this pair is transformed into $\eta_c$ subsequently.In the forward region of the kinematics, the $c\bar c$ pair interacts with initial hadron through exchanges of soft gluons. This interaction can be studied with HQET, which provides a systematic expansion in the inverse of the $c$-quark mass $m_c$. We find that the calculation of the $S$-matrix element in the forward region can be formulated as the problem of solving a wave function of a $c$-quark propagating in a background field of soft gluons. At leading order we find that the differential cross-section can be expressed with four functions, which are defined with a twist-3 operator of gluons. The effect of exchanging a Odderon can be identified with this operator in our case. We discuss our results in detail and compare them with those obtained in previous studies. Our results and those from other studies show that the differential cross-section is very small in the forward region. We also show that the production through photon exchange is dominant in the extremely forward region, hence the effect of Odderon exchange can not be identified in this region.For completeness we also give results for diffractive photoproduction of $J/\Psi$.Comment: 20 pages with 3 figures. Text improve

Topical and Systemic Cannabidiol Improves Trinitrobenzene Sulfonic Acid Colitis in Mice

Background/Aims: Compounds of Cannabis sativa are known to exert anti-inflammatory properties, some of them without inducing psychotropic side effects. Cannabidiol (CBD) is such a side effect-free phytocannabinoid that improves chemically induced colitis in rodents when given intraperitoneally. Here, we tested the possibility whether rectal and oral application of CBD would also ameliorate colonic inflammation, as these routes of application may represent a more appropriate way for delivering drugs in human colitis. Methods: Colitis was induced in CD1 mice by trinitrobenzene sulfonic acid. Individual groups were either treated with CBD intraperitoneally (10 mg/kg), orally (20 mg/kg) or intrarectally (20 mg/kg). Colitis was evaluated by macroscopic scoring, histopathology and the myeloperoxidase (MPO) assay. Results: Intraperitoneal treatment of mice with CBD led to improvement of colonic inflammation. Intrarectal treatment with CBD also led to a significant improvement of disease parameters and to a decrease in MPO activity while oral treatment, using the same dose as per rectum, had no ameliorating effect on colitis. Conclusion: The data of this study indicate that in addition to intraperitoneal application, intrarectal delivery of cannabinoids may represent a useful therapeutic administration route for the treatment of colonic inflammation. Copyright (C) 2012 S. Karger AG, Base

Distributed Educational Influence and Computer-Supported Collaborative Learning

This article introduces a line of research on distributed educational influence (DEI) that has recently been developed by the research group to which the authors belong. The main hypothesis is that in computer-supported collaborative learning contexts, all participants are potential sources of educational influence (EI). According to this hypothesis, the success of collaboration and its outcomes depend on the extent to which participants take responsibility for being both providers and recipients of aid, such that EI becomes adequately distributed among the group as a whole. The paper is organized into four sections that deal respectively with: (1) the concept of DEI, its origin and its characteristics, with special attention being paid to the demands inherent to the exercising of EI in online collaborative learning; (2) an empirical approach to the study of DEI, based on case studies and a multimethod perspective that combines structural analysis of participants' activity with content analysis of their contributions; (3) a review of some interesting results obtained so far and some questions that remain open; and (4) proposals for how the study of DEI could help to enrich research on online collaborative learning

Orquestar ayudas para el aprendizaje colaborativo: herramientas, guiones y retroalimentaciones.

Los profesores constatamos reiteradamente que la forma de resolver las actividades grupales por parte de los estudiantes universitarios está muy alejada de un proceso de colaboración de alto nivel. Para ayudar a los estudiantes a desarrollar competencias de trabajo colaborativo se ha implementado una propuesta instruccional en cuatro clases (209 estudiantes), que orquesta diferentes tipos de ayuda a distintos planos. Globalmente, estudiantes y docentes valoran de forma positiva la experiencia

Migraine aura: retracting particle-like waves in weakly susceptible cortex

Cortical spreading depression (SD) has been suggested to underlie migraine aura. Despite a precise match in speed, the spatio-temporal patterns of SD and aura symptoms on the cortical surface ordinarily differ in aspects of size and shape. We show that this mismatch is reconciled by utilizing that both pattern types bifurcate from an instability point of generic reaction-diffusion models. To classify these spatio-temporal pattern we suggest a susceptibility scale having the value [sigma]=1 at the instability point. We predict that human cortex is only weakly susceptible to SD ([sigma]<1), and support this prediction by directly matching visual aura symptoms with anatomical landmarks using fMRI retinotopic mapping. We discuss the increased dynamical repertoire of cortical tissue close to [sigma]=1, in particular, the resulting implications on migraine pharmacology that is hitherto tested in the regime ([sigma]>>1), and potentially silent aura occurring below a second bifurcation point at [sigma]=0 on the susceptible scale

The Threat of Capital Drain: A Rationale for Public Banks?

This paper yields a rationale for why subsidized public banks may be desirable from a regional perspective in a financially integrated economy. We present a model with credit rationing and heterogeneous regions in which public banks prevent a capital drain from poorer to richer regions by subsidizing local depositors, for example, through a public guarantee. Under some conditions, cooperative banks can perform the same function without any subsidization; however, they may be crowded out by public banks. We also discuss the impact of the political structure on the emergence of public banks in a political-economy setting and the role of interregional mobility

Infrared and microwaves at 5.8 GHz in a catalytic reactor

An improved micro-reactor cell for IR spectroscopic studies of heterogeneous catalysis was built around a 5.8 GHz microwave cavity. The reactor can operate at 20 bars and with conventional heating up to 720 K, with reactant gas flows velocities (GHSV) from 25 000 to 50 000 h−1. The temperature of the sample under microwave irradiation was measured by time resolved IR emission spectroscopy. The first experiment performed was the IR monitoring of the desorption of carbonates induced by irradiating an alumina sample by microwaves at 5.8 GHz

Leading and following: Noise differently affects semantic and acoustic processing during naturalistic speech comprehension

Despite the distortion of speech signals caused by unavoidable noise in daily life, our ability to comprehend speech in noisy environments is relatively stable. However, the neural mechanisms underlying reliable speech-in-noise comprehension remain to be elucidated. The present study investigated the neural tracking of acoustic and semantic speech information during noisy naturalistic speech comprehension. Participants listened to narrative audio recordings mixed with spectrally matched stationary noise at three signal-to-ratio (SNR) levels (no noise, 3 dB, -3 dB), and 60-channel electroencephalography (EEG) signals were recorded. A temporal response function (TRF) method was employed to derive event-related-like responses to the continuous speech stream at both the acoustic and the semantic levels. Whereas the amplitude envelope of the naturalistic speech was taken as the acoustic feature, word entropy and word surprisal were extracted via the natural language processing method as two semantic features. Theta-band frontocentral TRF responses to the acoustic feature were observed at around 400 ms following speech fluctuation onset over all three SNR levels, and the response latencies were more delayed with increasing noise. Delta-band frontal TRF responses to the semantic feature of word entropy were observed at around 200 to 600 ms leading to speech fluctuation onset over all three SNR levels. The response latencies became more leading with increasing noise and decreasing speech comprehension and intelligibility. While the following responses to speech acoustics were consistent with previous studies, our study revealed the robustness of leading responses to speech semantics, which suggests a possible predictive mechanism at the semantic level for maintaining reliable speech comprehension in noisy environments