Cosmic ray biannual variation

The study of the cosmic ray (CR) power spectrum has revealed a significant variation with a period around 2 yr that cannot be explained as a high order harmonic of the 11 yr solar cycle. Comparative study of the correlation on different time scales between CR intensity and Rz, aa, high speed streams and polar hole size has put in evidence that a high degree of coherency exists between each couple of variables at 1.58 to 1.64 yr, except between CR and Rz. On the other hand cyclic variation on a short time scale, around 26 months, has been claimed to be present in the neutrino flux. Critical tests of this hypothesis are considered and a preliminary result seems to indicate that the hypothesis of the existence of a 1.6 yr periodicity in the neutrino data during the measurement time interval, has a significance or = 99.9%. The possible origin of this variation as due to a contribution either of CR interactions in the upper atmosphere or to the solar dynamics, are discussed

A study of periodicities and recurrences in solar activity and cosmic ray modulation

The 154d periodicity was found in the cosmic ray intensity (RE) vs Flares, and some other peaks of coherency in the RC vs aa sub I, that when interpreted as aliased values, might correspond to recurring interplanetary magnetic field structures and solar wind streams. It cannot be excluded, however, that some of the correspondence with aa are of terrestrial origin. This study cannot be considered exhaustive due to the fact that other solar variables, such as polar hole size, are possibly correlated to cosmic ray intensities. However, the number of observations is small so that the interpretation of the results is very difficult

Cosmic rays 10Be biennal data and their relationship to aurorae and sunspots

The galactic cosmic ray (C.R.) variations which should give information on three dimensional aspects of the heliospheric magnetic fields and on the solar wind, which modulate their influx into the Solar System were studied. In order to decode the information from the C.R. series it is necessary to know the mechanisms through which the modulation is produced. It it clear that a balance of effects with sources at different heliospheric latitudes results in the modulated C.R. intensity. It is found that the modulation of 10Be in polar ice may be due to at least two main contributions: (1) negative and in phase with the Solar flare activity modulating the cosmic ray flux in Forbush-type decreases, and (2) positive in phase with the appearance of large wind streams situated at both polar coronal holes. It is found that the high heliolatitude activity is related to a stable periodicity of 11.1y whereas the low heliolatitude activity contributes to the wondering of the solar cycles

Cosmic ray secular variations in terrestrial records and aurorae

The rediscovery that the Sun and the solar wind can undergo important changes on historical time scales has brought into question the stability of the cyclic behavior of past time series of solar and solar-terrestrial origin. It was found by Vector Fourier analysis that the solar 11 year cycle is present in the series of 10Be, delta 180, in ice cores and of thermoluminescence (TL) in sea sediments during the last Millennia with a frequency modulation, related to the Sun behavior, as tested by comparison with the Sunspot number R sub z series. It was shown that the cyclogram of the series of yearly Aurorae from 1721 to 1979 linear-regression-corrected-for-R sub z is straight for the periodicity zeta=11,1y, which indicates that such periodicity is constant in time corresponding to the only line present in the 11y band. The maxima of this component appear at the same time together with the high speed solar wind streams taking place in coronal holes situated in high heliolatitudes. It is evidenced that the 11 year cycle has undergone frequency oscillations on a time scale of two centuries, although it is very difficult to determine the periodicities with high accuracy

Quantifying alternative splicing from paired-end RNA-sequencing data

RNA-sequencing has revolutionized biomedical research and, in particular, our ability to study gene alternative splicing. The problem has important implications for human health, as alternative splicing may be involved in malfunctions at the cellular level and multiple diseases. However, the high-dimensional nature of the data and the existence of experimental biases pose serious data analysis challenges. We find that the standard data summaries used to study alternative splicing are severely limited, as they ignore a substantial amount of valuable information. Current data analysis methods are based on such summaries and are hence suboptimal. Further, they have limited flexibility in accounting for technical biases. We propose novel data summaries and a Bayesian modeling framework that overcome these limitations and determine biases in a nonparametric, highly flexible manner. These summaries adapt naturally to the rapid improvements in sequencing technology. We provide efficient point estimates and uncertainty assessments. The approach allows to study alternative splicing patterns for individual samples and can also be the basis for downstream analyses. We found a severalfold improvement in estimation mean square error compared popular approaches in simulations, and substantially higher consistency between replicates in experimental data. Our findings indicate the need for adjusting the routine summarization and analysis of alternative splicing RNA-seq studies. We provide a software implementation in the R package casper.Comment: Published in at http://dx.doi.org/10.1214/13-AOAS687 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org). With correction

Ca II and CH+ interstellar absorption observations in the direction of resolvable binary stars

We report the initial results of a study to probe the small-scale structure in diffuse interstellar clouds by observing optical absorption lines of CH+ at 4232 °A and Ca II K at 3933 °A towards both components in resolvable binary systems. The data analysis is still in progress. To date, 70% of the Ca II spectra have been analyzed for the 19 observed systems. For half of these, a difference in the line strength or in the number of calcium components is found. The sightlines have been selected so that the observing method provides a potential probe of the small-scale structure of the interstellar medium in the range 200-4000 AU

Quantifying alternative splicing from paired-end RNA-sequencing data

RNA-sequencing has revolutionized biomedical research and, in particular, our ability to study gene alternative splicing. The problem has important implications for human health, as alternative splicing is involved in malfunctions at the cellular level and multiple diseases. However, the high-dimensional nature of the data and the existence of experimental biases pose serious data analysis challenges. We find that the standard data summaries used to study alternative splicing are severely limited, as they ignore a substantial amount of valuable information. Current data analysis methods are based on such summaries and are hence sub-optimal. Further, they have limited flexibility in accounting for technical biases. We propose novel data summaries and a Bayesian modeling framework that overcome these limitations and determine biases in a non-parametric, data-dependent manner. These summaries adapt naturally to the rapid improvements in sequencing technology. We provide efficient point estimates and uncertainty assessments. The approach allows to study alternative splicing patterns for individual samples and can also be the basis for downstream differential expression analysis. We found an over 5 fold improvement in estimation mean square error compared to a popular approach in simulations, and substantially higher correlations between replicates in experimental data. Our findings indicate the need for modifying the routine summarization and analysis of alternative splicing RNA-seq studies. We provide a software implementation in the R package casper

Epitaxial preparation of germanium cells for photovoltaic and thermophotovoltaic applications

Germanium is widely used in the advanced III-V photovoltaic technology based on arsenides and phosphides to realise triple junction (TJ) solar cells for space application and in thermophotovoltaic (TPV) devices. Nowadays, Ge cells are realised by diffusion and the cell conversion efficiency is partially limited by the broad doping profile thus obtained. Better performances could be achieved by means of homo-epitaxy of Ge on the Ge substrate, as improved thickness and doping profile control can be obtained with the epitaxial process. TJ cells, made of a InGaP/InGaAs/Ge monolithic array, have reached an efficiency value over 40% under concentration. The AM1.5 current density of the TJ cells are in the range of 15 mA/cm2 and the limiting subcell is the GaAs one: theoretical models suggest that the Ge subcell could produce a current density up to 40 mA/cm2, so that a large amount of the Ge potential is not fulfilled in the TJ cell. Epitaxial deposition of Ge would permit novel cell design (e.g. stacking 2 Ge cells) in order to obtain higher open circuit voltage. Ge cells are also employed in TPV devices to produce electricity from a heating source, thus fulfilling all the energetic content of a particular fuel and obtaining both heat and power from a single source. In this application, the advantages of Ge compared to the more common GaSb are a larger wafer size and a cheaper price. Ge epitaxial layers were deposited on both Ge and GaAs substrates by means of a home made Metal-Organic Vapor Phase (MOVPE) reactor using isobutylgermane (iBuGe). The samples were characterised by X-Ray Diffraction (XRD), Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM). Ohmic contacts were deposited on the samples in order to perform electrical characterization and to realise a simple p-n junction which showed photovoltaic effect. This work analyses the epitaxial growth of Germanium and the effect of the growth parameters (iBuGe partial pressure, temperature) on growth rate, surface morphology and material quality. In the temperature interval between 500 and 600?C a mass transport controlled regime was observed. Surface morphology showed a dependence on both the growth rate and on the substrate orientation: by using a low iBuGe partial pressure, a large density of holes were observed both by TEM and AFM. The holes almost disappeared by increasing the growth rate up to a limit of about 1mm/h, after which the surface roughness increases, degrading sample quality. XRD showed a nearly perfect crystallographic structure for the samples deposited on exaclty oriented (001) Ge substrates, while a larger diffraction peak was obtained for samples grown on (001) Ge substrated 6?off toward (110) direction. On the latter, a rougher and wave-like surface was observed by AFM while on exaclty oriented the surface was mirrorlike. n/p junctions were characterised by means of I-V and C-V techniques, and an optimal rectifying behaviour was obtained. The illuminated Ge n/p junctions reported a VOC of about 170 mV

Growth and characterization of 3C-SiC grown using CBr4 as a precursor

The growth of silicon carbide on silicon is being studied for many diverse applications and so the search for precursors that could be used to grow with improved or novel physical, structural and morphological properties is a relevant issue in this field. Here we present a study of the use of CBr4 as a precursor in the deposition of 3C-SiC in a cold walled MOVPE reactor. The growth has been studied in a range of temperatures between 1100 and 1250 ?C, on differently oriented substrates. Additionally, the effect of the C:Si ratio in the gas phase was examined by the addition of propane to the reaction mixture. At lower temperatures faceted crystals grew as islands on the substrate; faceting and 2D planar growth was obtained if higher growth temperatures were applied and at higher C:Si ratios. Atomic force and scanning microscopies revealed interesting growth habits of the island type crystals. Transmission electron microscopy in cross-section confirms that these islands are 3C-SiC and have a high crystal perfection. The crystal habit has been characterised and will be presented. Carbon tetrabromide has revealed itself to be a useful precursor for the growth of SiC and, with a judicious control of the growth conditions could be applied to the growth of thin films and nanocrystals