Heteroepitaxial InP solar cells on Si and GaAs substrates

The characteristics of InP cells processed from thin layers of InP heteroepitaxially grown on GaAs, on silicon with an intervening GaAs layer, and on GaAs with intervening Ga(x)In(1-x)As layers are described, and the factors affecting cell efficiency are discussed. Under 10 MeV proton irradiations, the radiation resistances of the heteroepitaxial cells were superior to that of homoepitaxial InP cells. The superior radiation resistance is attributed to the high dislocation densities present in the heteroepitaxial cells

Poverty Mapping Using Convolutional Neural Networks Trained on High and Medium Resolution Satellite Images, With an Application in Mexico

Mapping the spatial distribution of poverty in developing countries remains an important and costly challenge. These "poverty maps" are key inputs for poverty targeting, public goods provision, political accountability, and impact evaluation, that are all the more important given the geographic dispersion of the remaining bottom billion severely poor individuals. In this paper we train Convolutional Neural Networks (CNNs) to estimate poverty directly from high and medium resolution satellite images. We use both Planet and Digital Globe imagery with spatial resolutions of 3-5 sq. m. and 50 sq. cm. respectively, covering all 2 million sq. km. of Mexico. Benchmark poverty estimates come from the 2014 MCS-ENIGH combined with the 2015 Intercensus and are used to estimate poverty rates for 2,456 Mexican municipalities. CNNs are trained using the 896 municipalities in the 2014 MCS-ENIGH. We experiment with several architectures (GoogleNet, VGG) and use GoogleNet as a final architecture where weights are fine-tuned from ImageNet. We find that 1) the best models, which incorporate satellite-estimated land use as a predictor, explain approximately 57% of the variation in poverty in a validation sample of 10 percent of MCS-ENIGH municipalities; 2) Across all MCS-ENIGH municipalities explanatory power reduces to 44% in a CNN prediction and landcover model; 3) Predicted poverty from the CNN predictions alone explains 47% of the variation in poverty in the validation sample, and 37% over all MCS-ENIGH municipalities; 4) In urban areas we see slight improvements from using Digital Globe versus Planet imagery, which explain 61% and 54% of poverty variation respectively. We conclude that CNNs can be trained end-to-end on satellite imagery to estimate poverty, although there is much work to be done to understand how the training process influences out of sample validation.Comment: 4 pages, 2 figures, Presented at NIPS 2017 Workshop on Machine Learning for the Developing Worl

Discovery of a 3.6-hr Eclipsing Luminous X-Ray Binary in the Galaxy NGC 4214

We report the discovery of an eclipsing X-ray binary with a 3.62-hr period within 24" of the center of the dwarf starburst galaxy NGC 4214. The orbital period places interesting constraints on the nature of the binary, and allows for a few very different interpretations. The most likely possibility is that the source lies within NGC 4214 and has an X-ray luminosity of up to 7 e38 ergs/s. In this case the binary may well be comprised of a naked He-burning donor star with a neutron-star accretor, though a stellar-mass black-hole accretor cannot be completely excluded. There is no obvious evidence for a strong stellar wind in the X-ray orbital light curve that would be expected from a massive He star; thus, the mass of the He star should be <3-4 solar masses. If correct, this would represent a new class of very luminous X-ray binary -- perhaps related to Cyg X-3. Other less likely possibilities include a conventional low-mass X-ray binary that somehow manages to produce such a high X-ray luminosity and is apparently persistent over an interval of years; or a foreground AM Her binary of much lower luminosity that fortuitously lies in the direction of NGC 4214. Any model for this system must accommodate the lack of an optical counterpart down to a limiting magnitude of 22.6 in the visible.Comment: 7 pages, ApJ accepted versio

Structure and hydration of membranes embedded with voltage-sensing domains.

Despite the growing number of atomic-resolution membrane protein structures, direct structural information about proteins in their native membrane environment is scarce. This problem is particularly relevant in the case of the highly charged S1-S4 voltage-sensing domains responsible for nerve impulses, where interactions with the lipid bilayer are critical for the function of voltage-activated ion channels. Here we use neutron diffraction, solid-state nuclear magnetic resonance (NMR) spectroscopy and molecular dynamics simulations to investigate the structure and hydration of bilayer membranes containing S1-S4 voltage-sensing domains. Our results show that voltage sensors adopt transmembrane orientations and cause a modest reshaping of the surrounding lipid bilayer, and that water molecules intimately interact with the protein within the membrane. These structural findings indicate that voltage sensors have evolved to interact with the lipid membrane while keeping energetic and structural perturbations to a minimum, and that water penetrates the membrane, to hydrate charged residues and shape the transmembrane electric field

Full-Shell X-Ray Optics Development at NASA Marshall Space Flight Center

NASAs Marshall Space Flight Center (MSFC) maintains an active research program toward the development of high-resolution, lightweight, grazing-incidence x-ray optics to serve the needs of future x-ray astronomy missions such as Lynx. MSFC development efforts include both direct fabrication (diamond turning and deterministic computer-controlled polishing) of mirror shells and replication of mirror shells (from figured, polished mandrels). Both techniques produce full-circumference monolithic (primary + secondary) shells that share the advantages of inherent stability, ease of assembly, and low production cost. However, to achieve high-angular resolution, MSFC is exploring significant technology advances needed to control sources of figure error including fabrication- and coating-induced stresses and mounting-induced distortions

¡Reinventar La Rueda! Reimaginar los papeles del docente y de los estudiantes en la enseñanza del lenguaje en cursos basados en contenido predeterminado

David Swartz, Universidade Nova de LisboaRecepción: 07/07/2018 | Aceptado: 30/04/2019Correspondencia a través de ORCID: David Swartz - 0000-0001-7952-4795What if instead of providing predetermined content for language courses, and instead of framing the questions and discourse we ask students to respond to, students themselves were required to bring in their own content, initiate and respond to their own questions, and ultimately, to assess and evaluate their own work? My paper outlines an alternative approach to content-based language learning wherein students are made responsible for sharing, editing and evaluating each other´s work, as well as for providing the contents of the course´s curriculum itself. It is time to truly democratize education, to re-evaluate the teacher´s role in the classroom from the standpoint of assumed ignorance rather than presumed knowledge, and finally, to prepare for a classroom in which every student benefit from the presence and involvement of every other student. In this essay, I offer us a chance to look closer into this subject: first, to become conscious of the shortcomings of the traditional content-based language learning scenario, and secondly, to bring radical change to the classroom: to re-invent the wheel!Resumen: ¿Que pasaría si en vez de proveer contenido predeterminado para cursos de lenguaje en niveles de secundaria y nivel universitario, y en vez de proponer preguntas y discursos, le preguntamos a los estudiantes que traigan su propio contenido, que inicien y respondan a sus propias preguntas, y finalmente, que valoren y evalúen su propio trabajo? Mi ensayo delinea una alternativa al aprendizaje del lenguaje basado en contenido predeterminado, una visión en la cual los estudiantes no solo comparten su trabajo con sus compañeros, sino que son responsables de compartir, editar y evaluar, como también de proveer el contenido del curso. Es hora de democratizar educación realmente, de reevaluar el papel del maestro en la clase desde el punto de vista de ignorancia supuesta en vez de conocimiento asumido, y por ultimo, de prepararse para una clase en la cual cada estudiante se beneficie por la presencia y participación de cada otro estudiante. En este ensayo, propongo una oportunidad de explorar este tema más de cerca: primero, para concientizarnos de las falencias del escenario tradicional de la enseñanza del lenguaje basado en contenido predeterminado, y segundo, para traer un cambio radical al salón de clase: ¡para reinventar la rueda

The Love of the One for the Many and the Many for the One

UID/ELT/04097/2013 UID/ELT/04097/2019 Copyright Year 2020The philosophical “problem” of the one and the many that has occupied philosophers since Parmenides is also about love and the metaphysical foundations of authorship. In the Parmenides Plato takes up this discussion of the one and the many, leading to the most paradoxical conclusions, such as that the one is always becoming older and younger than itself at the same time. To defend Parmenides, Plato has Zeno of Elea propose the thesis that the one can be divided ad infinitum. Therefore, the one cannot be divided at all. For the poet, the paradox of the one and the many is conquered through the concept of being nothing. The authorial nothingness that the author is interested in willfully achieving involves the simultaneous unity and fragmentation of the author's authorial voice. The author seeks to represent multiplicity and unity simultaneously; which is to say, the author seeks a vision of the one through the many and the many through the one. The simultaneous love of the one for the many and the many for the one describes the self-reflective artistic act.authorsversionpublishe

Simulation of Heavily Irradiated Silicon Pixel Sensors and Comparison with Test Beam Measurements

Charge collection measurements performed on heavily irradiated p-spray DOFZ pixel sensors with a grazing angle hadron beam provide a sensitive determination of the electric field within the detectors. The data are compared with a complete charge transport simulation of the sensor which includes signal trapping and charge induction effects. A linearly varying electric field based upon the standard picture of a constant type-inverted effective doping density is inconsistent with the data. A two-trap double junction model implemented in the ISE TCAD software can be tuned to produce a doubly-peaked electric field which describes the data reasonably well. The modeled field differs somewhat from previous determinations based upon the transient current technique. The model can also account for the level of charge trapping observed in the data.Comment: 8 pages, 11 figures. Talk presented at the 2004 IEEE Nuclear Science Symposium, October 18-21, Rome, Italy. Submitted to IEEE Transactions on Nuclear Scienc

from the Song of Songs to Shakespeare’s Sonnets

UIDB/04097/2020 UIDP/04097/2020This paper discusses Shakespeare’s aesthetics of blackness as a radical interpretation and response to a disputed translation of the fifth verse from the Song of Songs, casting light on the Renaissance transition from negative theology to negative capability.publishersversionpublishe