CW and pulsed electrically detected magnetic resonance spectroscopy at 263 GHz/12 T on operating amorphous silicon solar cells

Here we describe a new high frequency/high field continuous wave and pulsed electrically detected magnetic resonance (CW EDMR and pEDMR) setup, operating at 263 GHz and resonance fields between 0 and 12 T. Spin dependent transport in illuminated hydrogenated amorphous silicon p-i-n solar cells at 5 K and 90 K was studied by in operando 263 GHz CW and pEDMR alongside with complementary X-band CW EDMR. Benefiting from the superior resolution at 263 GHz, we were able to better resolve EDMR signals originating from spin dependent hopping and recombination processes. 5 K EDMR spectra were found to be dominated by conduction and valence band tale states involved in spin dependent hopping, with additional contributions from triplet exciton states. 90 K EDMR spectra could be assigned to spin pair recombination involving conduction band tail states and dangling bonds as dominating spin dependent transport process, with additional contributions from valence band tail and triplet exciton states.Comment: 8 pages, 4 figure

Brazil: economic study of cassava

A series of studies were carried out in Brazil, on a regional basis, to determine how cassava can fit into the Brazilian agricultural economy in the future so as to assist the country in reaching policy goals (improved welfare of the rural community and increased availability of low-priced food). The recent developments in the Brazilian agricultural sector are summarized with emphasis on agricultural policies and on the balance between food production and exports. Urbanization as well as wheat subsidies have reduced the importance of cassava. Current policies, however, are found to favor food crops such as cassava that are produced by the small farmers. Trends in cassava for human food and its future potential role are also analyzed. The role of farinha as a staple food should be improved; increased per capita consumption will depend on better availability, better quality, and lower prices. To increase the consumption of fresh cassava, it is necessary to reduce marketing margins. The reduction of production costs of cassava starch is also crucial. The rapidly expanding feed industry is discussed with reference to cassava supply. Improved production technology would mean increased benefits to both producers and consumers. A dried cassava industry would reduce the need to import maize, stabilize on-farm prices of cassava, and extend the market size of the crop, particularly in NE Brazil. The cost structure of cassava production and processing is analyzed from the viewpoint of the cassava's future role as a source of rural income and its contribution to the food and feed supply. (CIAT)Se realizo una serie de estudios en Brasil, a nivel regional, para determinar el papel de la yuca en la economia agricola brasilera del futuro y ayudar a alcanzar las metas propuestas en las diferentes politicas (mayor bienestar de la comunidad rural y mayor disponibilidad de alimentos a bajo costo). Se resumen los ultimos avances en el sector agricola brasilero, con enfasis en las politicas agricolas y en el balance entre produccion de alimentos y exportaciones. La urbanizacion y los subsidios al trigo le han restado importancia a la yuca. Las politicas actuales, sin embargo, favorecen los cultivos alimenticios, como la yuca, producidos por pequenos agricultores. Tambien se analizan las tendencias del uso de la yuca en la alimentacion humana y su potencial futuro. Se debe mejorar el papel de la farinha como alimento basico; el aumento en el consumo per capita dependera de una mayor disponibilidad, una mejor calidad y precios mas bajos. Para aumentar el consumo de raices frescas es necesario reducir los margenes de mercadeo. Tambien es importante la reduccion de los costos de produccion del almidon de yuca. Se discute la creciente industria de alimentos para animales con referencia a la oferta de yuca. Un tecnologia de produccion mejorada significaria mayor beneficio tanto para los productores como para los consumidores. Una industria de yuca seca reduciria la necesidad de importar maiz, estabilizaria los precios de la yuca a nivel de finca y ampliaria el mercado del cultivo, particularmente en el nordeste del Brasil. Se analiza la estructura de los costos de produccion y procesamiento de la yuca desde el punto de vista de su futuro papel como fuente de ingresos a nivel rural y su contribucion a la oferta de alimentos para humanos y animales. (CIAT

Information requirements for guidance and control systems

Control or guidance system performance dependency on information handling by subsystem

Bayesian Markov models improve the prediction of binding motifs beyond first order

Transcription factors (TFs) regulate gene expression by binding to specific DNA motifs. Accurate models for predicting binding affinities are crucial for quantitatively understanding of transcriptional regulation. Motifs are commonly described by position weight matrices, which assume that each position contributes independently to the binding energy. Models that can learn dependencies between positions, for instance, induced by DNA structure preferences, have yielded markedly improved predictions for most TFs on in vivo data. However, they are more prone to overfit the data and to learn patterns merely correlated with rather than directly involved in TF binding. We present an improved, faster version of our Bayesian Markov model software, BaMMmotif2. We tested it with state-of-the-art motif discovery tools on a large collection of ChIP-seq and HT-SELEX datasets. BaMMmotif2 models of fifth-order achieved a median false-discovery-rate-averaged recall 13.6% and 12.2% higher than the next best tool on 427 ChIP-seq datasets and 164 HT-SELEX datasets, respectively, while being 8 to 1000 times faster. BaMMmotif2 models showed no signs of overtraining in cross-cell line and cross-platform tests, with similar improvements on the next-best tool. These results demonstrate that dependencies beyond first order clearly improve binding models for most TFs

Exploring the importance of quantum effects in nucleation: The archetypical Ne_n case

The effect of quantum mechanics (QM) on the details of the nucleation process is explored employing Ne clusters as test cases due to their semi-quantal nature. In particular, we investigate the impact of quantum mechanics on both condensation and dissociation rates in the framework of the microcanonical ensemble. Using both classical trajectories and two semi-quantal approaches (zero point averaged dynamics, ZPAD, and Gaussian-based time dependent Hartree, G-TDH) to model cluster and collision dynamics, we simulate the dissociation and monomer capture for Ne8 as a function of the cluster internal energy, impact parameter and collision speed. The results for the capture probability Ps(b) as a function of the impact parameter suggest that classical trajectories always underestimate capture probabilities with respect to ZPAD, albeit at most by 15%–20% in the cases we studied. They also do so in some important situations when using G-TDH. More interestingly, dissociation rates kdiss are grossly overestimated by classical mechanics, at least by one order of magnitude. We interpret both behaviours as mainly due to the reduced amount of kinetic energy available to a quantum cluster for a chosen total internal energy. We also find that the decrease in monomer dissociation energy due to zero point energy effects plays a key role in defining dissociation rates. In fact, semi-quantal and classical results for kdiss seem to follow a common “corresponding states” behaviour when the proper definition of internal and dissociation energies are used in a transition state model estimation of the evaporation rate constants

Knight Field Enabled Nuclear Spin Polarization in Single Quantum Dots

We demonstrate dynamical nuclear spin polarization in the absence of an external magnetic field, by resonant circularly polarized optical excitation of a single electron or hole charged quantum dot. Optical pumping of the electron spin induces an effective inhomogeneous magnetic (Knight) field that determines the direction along which nuclear spins could polarize and enables nuclear-spin cooling by suppressing depolarization induced by nuclear dipole-dipole interactions. Our observations suggest a new mechanism for spin-polarization where spin exchange with an electron reservoir plays a crucial role. These experiments constitute a first step towards quantum measurement of the Overhauser field.Comment: 5 pages, 3 figure

Second harmonic generation on incommensurate structures: The case of multiferroic MnWO4

A comprehensive analysis of optical second harmonic generation (SHG) on an incommensurate (IC) magnetically ordered state is presented using multiferroic MnWO4 as model compound. Two fundamentally different SHG contributions coupling to the primary IC magnetic order or to secondary commensurate projections of the IC state, respectively, are distinguished. Whereas the latter can be described within the formalism of the 122 commensurate magnetic point groups the former involves a breakdown of the conventional macroscopic symmetry analysis because of its sensitivity to the lower symmetry of the local environment in a crystal lattice. Our analysis thus foreshadows the fusion of the hitherto disjunct fields of nonlinear optics and IC order in condensed-matter systems

Nuclear magnetic resonance measurements reveal the origin of the Debye process in monohydroxy alcohols

Monohydroxy alcohols show a structural relaxation and at longer time scales a Debye-type dielectric peak. From spin-lattice relaxation experiments using different nuclear probes an intermediate, slower-than-structural dynamics is identified for n-butanol. Based on these findings and on diffusion measurements, a model of self-restructuring, transient chains is proposed. The model is demonstrated to explain consistently the so far puzzling observations made for this class of hydrogen-bonded glass forming liquids.Comment: 4 pages, 4 figure

Independent ferroelectric contributions and rare-earth-induced polarization reversal in multiferroic TbMn2O5

Three independent contributions to the magnetically induced spontaneous polarization of multiferroic TbMn2O5 are uniquely separated by optical second harmonic generation and an analysis in terms of Landau theory. Two of them are related to the magnetic Mn3+/4+ order and are independent of applied fields of up to 7 T. The third contribution is related to the long-range antiferromagnetic Tb3+ order. It shows a drastic decrease upon the application of a magnetic field and mediates the change of sign of the spontaneous electric polarization in TbMn2O5. The close relationship between the rare-earth long-range order and the non-linear optical properties points to isotropic Tb-Tb exchange and oxygen spin polarization as mechanism for this rare-earth induced ferroelectricity.Comment: 8 pages, 5 figure