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We use a WISE-2MASS-Pan-STARRS1 galaxy catalog to search for a supervoid in the direction of the Cosmic Microwave Background Cold Spot. We obtain photometric redshifts using our multicolor data set to create a tomographic map of the galaxy distribution. The radial density profile centred on the Cold Spot shows a large low density region, extending over 10's of degrees. Motivated by previous Cosmic Microwave Background results, we test for underdensities within two angular radii, 5°, and 15°. Our data, combined with an earlier measurement by Granett et al. 2010, are consistent with a large Rvoid=(192 ± 15)h−1 Mpc (2σ) supervoid with δ ≃ −0.13 ± 0.03 centered at z=0.22 ± 0.01. Such a supervoid, constituting a ∼3.5 σ fluctuation in the ΛCDM model, is a plausible cause for the Cold Spot.
High-redshift quasars are unique probes of the evolution of supermassive black holes and the intergalactic medium at the end of the epoch of reionization. We present the optical spectra of eight new z ~ 6 quasars selected from the Panoramic Survey Telescope & Rapid Response System 1 (Pan-STARRS1). Details of the selection strategy can be found in Bañados et al. (2014). With this work we increase the number of known quasars at z < 5.7 by more than 10%. The quasars discovered here span a large range of luminosities (19.6 ≤ zP1 ≤ 21.2) and are remarkably heterogeneous in their spectral features: half of them show bright emission lines whereas the other half show weak or no Lyα emission line. We find a larger fraction of weak–line emission quasars than in lower redshift studies, although still based on low number statistics, this may imply that the quasar population could be more diverse than previously thought.
The IntCal09 and Marine09 radiocarbon calibration curves have been revised utilizing newly available and updated data sets from 14C measurements on tree rings, plant macrofossils, speleothems, corals, and foraminifera. The calibration curves were derived from the data using the random walk model (RWM) used to generate IntCal09 and Marine09, which has been revised to account for additional uncertainties and error structures. The new curves were ratified at the 21st International Radiocarbon conference in July 2012 and are available as Supplemental Material at www.radiocarbon.org. The database can be accessed at http://intcal.qub.ac.uk/intcal13/.
High-quality data from appropriate archives are needed for the continuing improvement of radiocarbon calibration curves. We discuss here the basic assumptions behind 14C dating that necessitate calibration and the relative strengths and weaknesses of archives from which calibration data are obtained. We also highlight the procedures, problems, and uncertainties involved in determining atmospheric and surface ocean 14C/12C in these archives, including a discussion of the various methods used to derive an independent absolute timescale and uncertainty. The types of data required for the current IntCal database and calibration curve model are tabulated with examples.
Locations of gamma dose rate sensors have often been chosen by administrative or geometrical criteria. Nowadays computational capacity allows for a more realistic basis. We use simulations of potential radioactive plumes based on weather data of one year to investigate the threats to regions without own nuclear power plants and to find good numbers and locations of sensors to detect such plumes. We optimise sensor locations by minimising a cost function that can take into account numbers of undetected plumes, their dose to the region in general, or on the population. Besides we assess the effect of administrative constraints, be it that sensors have to cover administrative units, or that optimisation is done for sub-regions separately. Finally we evaluate the robustness of the approach if less or other plumes are used. The main findings are that sensors at boundaries are often best, but also typical paths of plumes may be important, and that administrative constraints may necessitate much more sensors. The small numbers of sensors actually deployed in these regions seem sufficient. However, the latter may be an artefact of the low number of plumes we considered. Altogether, combined with other considerations, this approach can contribute to better decisions about gamma dose rate sensor locations.
The IntCal04 and Marine04 radiocarbon calibration curves have been updated from 12 cal kBP (cal kBP is here defined as thousands of calibrated years before AD 1950), and extended to 50 cal kBP, utilizing newly available data sets that meet the IntCal Working Group criteria for pristine corals and other carbonates and for quantification of uncertainty in both the 14C and calendar timescales as established in 2002. No change was made to the curves from 0–12 cal kBP. The curves were constructed using a Markov chain Monte Carlo (MCMC) implementation of the random walk model used for IntCal04 and Marine04. The new curves were ratified at the 20th International Radiocarbon Conference in June 2009 and are available in the Supplemental Material at www.radiocarbon.org.
The European Model for Inhabited Areas (ERMIN) was developed to allow a user to explore different recovery options following the contamination of an urban environment with radioactive material and to refine an appropriate strategy for the whole region affected. The input data include a description of the environment, initial deposition of radionuclides on to a reference surface and a description of countermeasures. Output information includes the average doses to members of the public from external exposure to gamma and beta radiation from deposited radionuclides and inhalation of resuspended radioactivity, the contamination on urban surfaces, the activity concentration in air from resuspension, the doses to workers undertaking the recovery work, the quantity and activity of waste generated and the cost and work required to implement the countermeasure. ERMIN has been designed to be implemented as a tool that supports the approach of decision-makers and allows the area to be broken down into smaller regions where different conditions prevail and different countermeasure packages are enacted.
La prueba de ejecución continua (CPT) se ha convertido en un componente esencial de la investigación neuropsicológica de la esquizofrenia. Además, un número considerable de estudios de imágenes cerebrales, en la mayor parte investigaciones de PET, ha empleado la CPT como estímulo cognitivo y ha establecido una hipofrontalidad relativa en los esquizofrénicos en comparación con los controles. El propósito de la presente investigación era clarificar si esta hipofrontalidad descrita antes se podía verificar también utilizando imágenes de resonancia magnética funcionales (fMRI). Se incluyó a 20 voluntarios sanos y 14 esquizofrénicos con medicación neuroléptica estable. La toma de imágenes se realizó utilizando la CPT, versión T doble, y un escáner clínico de MRI de 1,5 T con una técnica de rodaja única y una secuencia de gradiente de eco potenciado en T¡*. Los esquizofrénicos mostraron una activación disminuida en el córtex prefrontal medial derecho, el cingulado derecho y el tálamo izquierdo en comparación con los controles. Estos resultados obtenidos por fMRI se analizan con relación a los resultados publicados utilizando PET.
The relationship between the defect microstructure of SiC films grown by solid-source molecular-beam epitaxy on 4H and 6H–SiC substrates and their growth conditions, for substrate temperatures ranging between 950 and 1300 °C, has been investigated by a combination of transmission electron microscopy and atomic force microscopy. The results demonstrate that the formation of defective cubic films is generally found to occur at temperatures below 1000 °C. At temperatures above 1000 °C our investigations prove that simultaneous supply of C and Si in the step-flow growth mode on vicinal 4H and 6H substrate surfaces results in defect-free hexagonal SiC layers, and defect-free cubic SiC can be grown by the alternating deposition technique. The controlled overgrowth of hexagonal on top of cubic layers is demonstrated for thin layer thicknesses.
Bulk Y1Ba2Cu3Oy was melt-textured without the use of seed
crystals as well as by applying
top-seeding with different seeds resulting in different orientations
of the c-axis.
Samples were examined by elastic
neutron scattering and levitation force.
The levitation force of the samples strongly
depends on the orientation of the c-axis.
The local superconducting parameters were found to be
reduced with increasing distance from the seed.
In order to study this influence,
two cubes were prepared by top-seeding, but
with seeds of Nd123 that had a parallel and perpendicular
orientation of the c-axis of the Nd123-seed
with respect to the contact area of the high-Tc superconductor.
By this, different distances of the levitating surface,
which is the surface that faces directly the magnet, from
the seed were obtained. Results are presented and discussed.
The effects of substrate cleaning, nitridation time, and substrate temperature in the range 800–1000 °C on the microstructure of AlN/Si(111) films grown by simultaneous plasma-assisted molecular beam epitaxy have been investigated. It has been demonstrated, using a combination of conventional and high-resolution transmission electron microscopy, that the interface structure, the film defect structure, and the film surface roughness are strongly related. The formation of single crystal 2H–AlN films with atomically flat surfaces occurs at 800 °C for conditions of 2.5 nm/min growth rate on very pure, atomically flat Si substrates.
The ALFA mission is designed to map the entire sky at frequencies between approximately 0.3 and 30 MHz with angular resolution limited by interstellar and interplanetary scattering. Most of this region of the spectrum is inaccessible from the ground because of absorption and refraction by the Earth’s ionosphere. A wide range of astrophysical questions concerning solar system, galactic, and extragalactic objects could be answered with high resolution images at low frequencies, where absorption effects and coherent emission processes become important and the synchrotron lifetimes of electrons are comparable to the age of the universe.
DNA fingerprinting with a set of synthetic oligonucleotides
complementary to simple repetitive sequences was used to develop
molecular markers for Ascochyta rabiei, the most important
fungal pathogen of chickpea (Cicer arietinum). Two compatible
type isolates (MatI and MatII) from the U.S. Pacific Northwest
with the same low level of aggressivity were compared to highly
virulent isolates from the Mediterranean region and Pakistan to find
suitable mating partners for the production of a mapping
population. After Hinf I or Taq I restriction,
electrophoresis and in-gel hybridization with ten different simple repetitive
oligonucleotides, all tested single-spored isolates exhibited unique
fingerprint patterns. The analysis revealed that the two U.S.
mating types share a considerable amount of genetic variability. A total
of 77 polymorphic marker bands were detected. A higher
number of polymorphic bands (up to 104) was observed between these
isolates and those from different geographical regions. The
isolates from the Mediterranean region and Pakistan shared a
lower degree (between 80 and 90 bands) of detectable genetic
diversity. These data permit selection of highly virulent crossing
partners for the different mating types with a high degree of
A sexual cross was performed to prove the Mendelian segregation of
fingerprint bands for future linkage analysis. Additionally,
the fingerprint data based on 268 informative characters combined with
phenetic and phylogenetic algorithms allow determination of
the genetic identity, relatedness and diversity of the different
isolates. To confirm the phylogenetic data, two outgroupers
Ascochyta fabae and Ascochyta pisi, were included.
Results indicate that A. pisi is more closely related to
A. rabiei than A. fabae.
Scholars of Africa have long expressed dissatisfaction with theoretical models that attempt to explain the political, economic and social dynamics of the continent. According to Chazan, Mortimer, Ravenhill and Rothchild (1988, 13), this situation means that “social scientists have had little alternative but to undertake a search for new conceptual frameworks that would afford a fuller insight into the dynamic processes unfolding on the continent.” Others, such as Hyden (1983, 193), argue directly that “Africa needs a new paradigm, or set of paradigms” to explain the continent's development processes. Although there often is a call to combine or integrate various paradigms, it seldom is accompanied by specific suggestions or guidelines about how to create a new theoretical approach for the study of Africa. Moreover, theoretical discussions are not normally accompanied by a call to use appropriate and innovative methodological strategies. Failure to utilize such strategies severely limits theoretical advancement, however. We introduce a relatively new strategy in social-science methodology that is ideally suited for advancing new theoretical approaches for the study of Africa.
Before introducing this strategy, we argue that current theoretical approaches to the continent are plagued by a fundamental problem. Specifically, most previous research has failed to examine how events are shaped by the interaction between phenomena at the global, national and local levels. The majority of studies focus on one or perhaps two levels, ignoring the fact that development processes are complex and depend on interaction between factors at different levels. This situation is further complicated by the fact that each level of analysis also contains a number of different categories or sub-levels.
Picosecond time resolved photoluminescence and photoconductivity measurements are performed to investigate the influence of high intensity illumination on the properties of Fullerene crystals. A highly nonlinear dependence of both the photoluminescence characteristics and the photoconductive response of the fullerenes is seen and temperature dependent measurements indicate that the nonlinear processes are associated with an insulatormetal-like phase transition in the material, and thus that the electronic properties of the excited state are dramatically altered at high excited state densities. The observed behaviour is compared and contrasted to the changes in the optical properties upon photochemical modification of the pristine material via Raman spectroscopy. Application of a simple phenomenological model to calculate the contribution of intermolecular exchange and correlation energies in the excited state supports the proposal that the observed phenomena originate from a Mott-like phase transition. A further manifestation of this behaviour is the emergence of a broadband electroluminescent emission above a critical injection current density.
The effect of capital structure and seasonality of fresh market vegetables was examined via the Target MOTAD model. The level of capital indebtedness and the selection of either a fall or spring season resulted in significantly different levels of enterprise mixes, expected returns, risk magnitudes, rates of change of risk magnitudes, and operating capital requirements. The fall season demonstrated larger initial levels of risk and larger increases in the level of risk due to increases in indebtedness. The spring season showed larger increases in risk between the minimum risk point and the maximum expected return point (linear programming solution) on the risk-efficient frontier. Operating capital requirements were substantially higher for the fall season than for the spring season. The operating capital requirements of the spring season were significantly affected by the level of indebtedness and the magnitude of risk selected by the grower, while the larger operating capital requirements of the fall season were only marginally affected.
The radiation hydrodynamics of a 125-μm thin carbon layer illuminated by thermal radiation of Trad = 200 eV temperature is studied within a multigroup radiation model. Whereas a major part of the incident photons deposit their energy by K-shell absorption close to the surface, soft photons below the K edge and hard photons (hv > 800 eV) penetrate deeper into the material and drive a heat wave with a sharp front. A nonablated mass fraction of 20% is accelerated with a hydrodynamic efficiency of 11%. About half of the incident radiation flux is reemitted by the heated carbon plasma. The heat front trajectory can be reproduced by the analytical heating wave model when effective opacity parameters corresponding to the most penetrating components are used.
A method for the complete removal of twins from single crystals of superconducting YBa2Cu3O7−x is described. The process depends on ferroelastic behavior found to exist in the phase, and should be generally applicable to the layered perovskite-type phases containing accommodation twins resulting from a tetragonal-to-orthorhombic transformation on cooling. The twin-free, superconducting single crystals will enable investigation of a–b anisotropy of properties as well as crystal structure determination without complication by the presence of microtwins.
We have conducted structural and magnetic investigations on thermomechanically-detwinned YBa2Cu3O6+x single crystals. Single crystal x-ray diffraction studies on a fully untwinned crystal with a superconducting onset temperature of 54 K have revealed that oxygen atoms in the basal plane are offset from the crystallographic mirror plane in the a direction, leading to “zig-zag” Cu-O chains. Magnetic measurements on untwinned and twinned crystals at 77 K indicate low levels of flux pinning in both crystals, with a slightly larger amount of pinning in the twinned crystal.