bluuebunny/crossref_metadata_2025 huggingface dataset:
Assessment of the genetic diversity in cowpea (Vigna unguiculataL. Walp.) germplasm from Ghana using simple sequence repeat markers
Authors: Asare Aaron T. , Gowda Bhavani S. , Galyuon Isaac K. A. , Aboagye Lawrence L. , Takrama Jemmy F. , Timko Michael P.
Published: April 2010

Genetic diversity and phylogenetic relationships among 141 cowpea (Vigna unguiculataL. Walp.) accessions collected throughout the nine geographical regions of Ghana were evaluated using simple sequence repeat (SSR) molecular markers. Twenty-five primer combinations pre-selected by their ability to polymerase chain reaction amplify SSRs from a set of test cowpea germplasm were evaluated. Of these, 20 primer combinations gave reproducible polymorphisms among 97.2% of the cowpea accessions tested, with the remaining accessions being found to be genetically identical. The informative primer combinations revealed a total of 74 alleles at 20 loci with an average of 3.8 alleles detected per locus. Variation in heterozygosity among cowpea SSRs ranged from 0.01 to 0.84 with an average occurrence of 0.19. The polymorphism information content varied from 0.07 to 0.66 with an average of 0.38. The Ghanaian cowpea accessions clustered into five main branches, each of which was loosely associated with the geographical regions from which samples were obtained. Accession GH2288 was found to be the most divergent cowpea accession compared with all others including the outgroup IT84S-2049, a breeding line from Nigeria. Our results provide a framework for future studies aimed at the conservation and management of cultivated cowpea germplasm in Ghana, and a good starting point for the selection of parental lines for genetic improvement programmes.
Evolution of binary stars and its implications for evolutionary population synthesis
Authors: Han Z. , Chen X. , Zhang F. , Podsiadlowski Ph.
Published: April 2010

Most stars are members of binaries, and the evolution of a star in a close binary system differs from that of an ioslated star due to the proximity of its companion star. The components in a binary system interact in many ways and binary evolution leads to the formation of many peculiar stars, including blue stragglers and hot subdwarfs. We will discuss binary evolution and the formation of blue stragglers and hot subdwarfs, and show that those hot objects are important in the study of evolutionary population synthesis (EPS), and conclude that binary interactions should be included in the study of EPS. Indeed, binary interactions make a stellar population younger (hotter), and the far-ultraviolet (UV) excess in elliptical galaxies is shown to be most likely resulted from binary interactions. This has major implications for understanding the evolution of the far-UV excess and elliptical galaxies in general. In particular, it implies that the far-UV excess is not a sign of age, as had been postulated prviously and predicts that it should not be strongly dependent on the metallicity of the population, but exists universally from dwarf ellipticals to giant ellipticals.
Population Synthesis: Challenges for the Next Decade
Authors: Bruzual A. Gustavo
Published: April 2010

In this paper I present a brief summary of recent advances in the fields of stellar evolution, stellar model atmospheres, and stellar spectral libraries, which allow us to build more realistic stellar population synthesis models than those available up to now. Applications of these models to problems of current interest are discussed. Problems that need to be understood and data sets that need to be collected in order to solve issues present in these models are listed.
Stellar population study in early-type galaxies: an approach from the K band
Authors: Mármol-Queraltó Esther , Cardiel Nicolás , Sánchez-Blázquez P. , Trager S. C. , Peletier R. F. , Kuntschner H. , Silva D. R. , Cenarro A. J. , Vazdekis A. , Gorgas J.
Published: April 2010

A full understanding of the physical properties of integrated stellar systems demands a multiwavelength approach since each spectral window shows us the contribution of different types of stars. However, most of the observational effort in stellar population studies has been focused on the optical range. Now, the new generation of instruments allow us to explore the K band, where RGB and AGB stars dominate the light of the integrated spectra. Here we present a K-band spectroscopic analysis of early-type galaxies in different environments. Our sample comprises 12 field early-type galaxies observed with ISAAC at VLT with medium resolution, and they are compared with 11 Fornax cluster galaxies previously reported by Silva et al. (2008). The clear differences found in the infrared DCO and NaI indices between field and Fornax galaxies are discussed, trying to solve the puzzle formed by the near-infrared and optical measurements.
The Stellar Populations of M32: Resolving the nearest elliptical with HST ACS/HRC
Authors: Monachesi Antonela , Trager S. C. , Lauer Tod R. , Freedman Wendy , Dressler Alan , Grillmair Carl , Mighell Kenneth
Published: April 2010

We present the deepest colour-magnitude diagram (CMD) of M32 to date, obtained from deep (F435W, F555W) photometry of HST ACS/HRC images. Due to the high resolution of our images, the small photometric errors, and the completeness level of our data we obtain the most detailed resolved photometric study of M32 to date. The CMD of M32 displays a wide colour distribution of red giant branch stars, mainly due to a metallicity spread, a strong red clump and bright asymptotic giant branch stars. The detection of a “blue plume” in M32 indicates the presence of a very young stellar population. There is not a noticeable presence of blue horizontal branch stars, suggesting that an old population with [Fe/H] < −1.5 does not significantly contribute to the light or mass of M32 in our observed fields.
Stellar Populations and Kinematics in Spiral Galaxies
Authors: MacArthur Lauren A. , González J. Jesús , Courteau Stéphane , McDonald Michael
Published: April 2010

We present a detailed study of the stellar populations (SPs) and kinematics of the bulge and inner disk regions of nearby spiral galaxies (Sa-Sd) based on deep long-slit Gemini/GMOS data. We find that the SPs of spiral galaxies are not well matched by single episodes of star formation; representative SPs must involve average SP values integrated over the star formation history (SFH) of the galaxy, such as those derived from the “full population synthesis” method used here. Our spiral bulges follow the same correlations of increasing light-weighted age and metallicity with central velocity dispersion as those of elliptical galaxies and early-type bulges found in other studies, but when SFHs more complex and realistic than a single burst are invoked, the trend with age is shallower and its scatter much reduced. In a mass-weighted context, all bulges are predominantly composed of old and metal-rich SPs. Bulge formation appears to be dominated by early processes that are common to all spheroids, whether they currently reside in disks or not. While monolithic collapse cannot be ruled out in some cases, merging must be invoked to explain the SP gradients in most bulges. Further bulge growth via secular processes, or “rejuvenated” star formation, generally contributes minimally to the stellar mass budget. We also demonstrate how the combination of our full population synthesis modeling of high-quality optical spectra of integrated SPs along with optical-NIR broad-band imaging can single out potential model weaknesses and help determine the reliability of the inferred SFHs.
The influence of bars in the star formation history and chemical evolution of disk galaxies
Authors: Sánchez-Blázquez Patricia
Published: April 2010

This is a pilot study part of a larger program devoted to understand the influence of bars in the evolution of galaxy disks. Some of the goals of this observational program are to compare the stellar metallicity gradients of galaxies with and without bars, the role of bars in the redistribution of mass and angular momentum and to study the evolution of the metallicity gradients with time. Some promising results are presented as well as some words of caution.
The Evolution of Passive Galaxies since z=1: Major Mergers vs Secular Processes
Authors: López-Sanjuan Carlos , Balcells Marc , Pérez-González Pablo G. , Barro Guillermo , García-Dabó César Enrique , Gallego Jesús , Zamorano Jaime
Published: April 2010

We study the evolution of the red sequence and the blue cloud since z ~ 1 to present in GOODS-S field for MB ≤ −20 and M* ≥ 1010M⊙ selected galaxies. We segregate the galaxies in early-type galaxies (ET, E/S0/Sa), and late-type galaxies (LT, Sb-Irr) by their position in the concentration-asymmetry plane, while in passive and star-forming by their rest-frame NUV – R color and their 24μm properties.

We find that red sequence (passive early types) comoving number density rise with cosmic time in both samples, while blue cloud (star-forming late types) number density descent in luminosity-selected samples and increase in mass-selected sample. We also find a third population that comprises star-forming early-type galaxies.

Comparing the observed evolution with the disk-disk (wet) major merger rate in GOODS-S, we infer that only ~20% of M* ≥ 1010M⊙ red sequence galaxies appeared since z = 1 can be explained by this kind of mergers, suggesting that minor mergers and secular evolution are the main processes in the red sequence evolution of M* ≥ 1010M⊙ galaxies since z ~ 1.
Current status of galaxy formation modelling
Authors: Tissera Patricia B.
Published: April 2010

I summarize the main characteristics of cosmological galaxy formation models and discuss some of the main results obtained in the last years.
A Golden Decade for Stellar Populations?
Authors: Abraham Roberto G.
Published: April 2010

People working on stellar populations can look forward to an exciting decade ahead. Investigations of stellar populations lie at the heart of the science cases being used to justify the development of upcoming telescopes and emerging instrumentation technologies. Examples abound, but I will focus on three case studies: (1) Wide field astronomy with upcoming ground-based and space-based survey facilities; (2) Adaptive optics, which has the potential to revolutionize our understanding of stellar populations in both nearby and distant galaxies; (3) The James Webb Space Telescope, which may well extend the reach of stellar population work to encompass the full range of the star-forming history of the Universe. However, most of these developments will require extensive advance preparation in order to be used effectively. The time to start that preparation is now (if not yesterday). Three areas which need urgent development are highlighted in these proceedings: (1) We need a wide-field high-resolution spectroscopic capability to augment wide-area imaging surveys; (2) We need a set of AO-friendly extragalactic deep fields in order to exploit upcoming AO-fed instrumentation; and (3) Existing tools for population synthesis modeling need to be extended in order to incorporate the effects of dust. Because the physics of dust creation and destruction is so complicated and uncertain, the latter capability sounds almost impossibly hard to develop, but in this talk I will argue that some simple approaches already exist that allow dust to be injected rather naturally into population synthesis models. I will show a concrete example where incorporation of dust into spectral synthesis models allows one to detect and characterize rate of formation of circumstellar disks at high redshifts.
VISTA variable survey in the Milky Way
Authors: Hempel M. , Minniti D. , Saito R. , Pietrukowicz P. , Lucas P. W.
Published: April 2010

Over the next 5 years the VVV collaboration (Vista Variable in the Via Lactea) will conduct an extensive survey of the galactic bulge and disk in the near-IR, using the new VISTA telescope. This public survey covers a field of 520 sqr. deg, including not only regions of high star formation, but also 33 known globular clusters and ~350 open clusters. The final product will be a deep IR atlas in 5 passbands for ~109 point sources among which we expect 106 variable stars. These will be produce a 3-D map of the surveyed region using well-understood primary distance indicators such as RR Lyrae stars. The observations will be combined with data from MACHO, OGLE, EROS, VST, Spitzer, HST, Chandra, Integral, and ALMA for a complete understanding of the variable sources in the inner Milky Way. Several important implications for the history of the Milky Way, for globular cluster evolution, for the population census of the bulge and center, and for the pulsation theory will follow from this survey.
EAGLE Spectroscopy of Resolved Stellar Populations Beyond the Local Group
Authors: Evans Chris , Yang Yanbin , Puech Mathieu , Lehnert Matthew , Barker Michael , Ferguson Annette , Cuby Jean-Gabriel , Morris Simon , Rousset Gérard , Assémat François , Flores Hector
Published: April 2010

We give an overview of the science case for spectroscopy of resolved stellar populations beyond the Local Group with the European Extremely Large Telescope (E-ELT). In particular, we present science simulations undertaken as part of the EAGLE Phase A design study for a multi–integral-field-unit, near-infrared spectrograph. EAGLE will exploit the unprecedented primary aperture of the E-ELT to deliver AO-corrected spectroscopy across a large (38.5 arcmin2) field, truly revolutionising our view of stellar populations in the Local Volume.
A SAURON view of double-barred galaxies
Authors: de Lorenzo-Cáceres Adriana , Vazdekis Alexandre , Falcón-Barroso Jesús , Martínez-Valpuesta Inma
Published: April 2010

Double bars might be the key mechanisms to transport gas to the very central regions of galaxies, so double-barred galaxies are key objects to better understand the galaxy formation and evolution scenarios. In order to disentangle the role of double bars in the galaxy build up, we are performing a whole kinematical and stellar population analysis of these objects from high S/N spectroscopic data.
Synthesis of composite stellar populations models
Authors: Gomes Jean Michel , Cid Fernandes R. , Valls-Gabaud D.
Published: April 2010

Spectral synthesis is largely used in the literature to decompose stellar populations with integrated light of galaxies as if the star formation histories (SFH) could be approximated by single bursts. In the case of our method (see http://www.starlight.ufsc.br/ for the SEAGal - Semi Empirical Analysis of Galaxies - collaboration), the starlight code combines the spectra of simple stellar populations (SSP) of different ages and metallicities, computed with high spectral resolution evolutionary synthesis models of Bruzual & Charlot (2003), to reproduce the observed spectrum of a given galaxy from which we can derived a huge amount of galaxy properties such as: the population vector, stellar mass, extinction and others. We have done that for all galaxies of the SDSS database. Despite all the results of astrophysical interest, we have decided to use continuous composite stellar models (CSP) with a single metallicity and a star formation rate ∝ τ−1e−t/τ, where t stands for the time that the star formation started (1, 5 and 13 Gyr ago) and τ is the attenuation factor chosen to be 1, 5, 10 and 99 Gyr. When the attenuation with respect to the time t is very low, this mimics a single burst, and when we choose it to be very large (99 Gyr), this is almost a constant star formation rate. We have perturbed each composite model spectrum 10 times with three distinct signal/noise ratios equal to 10, 15 and 30 in λ0 = 4020 Å. These models were inserted into our code to verify how a picture of single bursts deal with continuous composite models of galaxies. Our CSP models can be easily integrated in an analytical form. Therefore, we have derived theoretically the mean ages and metallicities and compared them to the output derived by the synthesis. We can see that the synthesized mean ages weighted by light tend to be lower than the models, due to the degeneracies involved in the problem. The same thing can be found for the mean metallicities weighted by light, which tend to be higher for the output values.
Stellar metallicity distributions in local dwarf spheroidal galaxies: a comparison between model and observations
Authors: Lanfranchi Gustavo A. , Matteucci Francesca
Published: April 2010

We analyze the main populations of 6 local Dwarf Spheroidal Galaxies by comparing the observed stellar metallicity distributions with the predictions of chemical evolution models. The predicted metallicity distributions of stars generally exhibit a low range of metallicities, a peak below the one of the MW disc in the solar neighborhood (but similar to the Halo), and a sharp decrease at higher metallicities in agreement with observations. The position of the peak is related to the low star formation rates adopted whereas the sharp decrease is a consequence of the occurrence of strong galactic winds. In the low metallicity tail of the distributions we predict a low number of stars in agreement with observations.
Maximum likelihood method for fitting the Fundamental Plane of the 6dF Galaxy Survey
Authors: Magoulas C. , Colless M. , Jones D. , Springob C. , Mould J.
Published: April 2010

We have used over 10,000 early-type galaxies from the 6dF Galaxy Survey (6dFGS) to construct the Fundamental Plane across the optical and near-infrared passbands. We demonstrate that a maximum likelihood fit to a multivariate Gaussian model for the distribution of galaxies in size, surface brightness and velocity dispersion can properly account for selection effects, censoring and observational errors, leading to precise and unbiased parameters for the Fundamental Plane and its intrinsic scatter. This method allows an accurate and robust determination of the dependencies of the Fundamental Plane on variations in the stellar populations and environment of early-type galaxies.
Inverse population synthesis using a dynamical basis
Authors: Mateu Juan , Magris Gladis , Bruzual Gustavo
Published: April 2010

We introduce a new inverse population synthesis algorithm (DINBAS3D) which aims to recover the star formation and metallicity histories from galactic spectra. We investigate the use of a dynamical basis of three simple stellar population spectra that is specific for each galaxy. Our goal is to recover a robust star formation history that minimizes degeneracy effects which are very common in high resolution histories methods. In this work, we detail the method and present our findings when we apply DINBAS3D to synthetic spectra with known parameters, we compare our results with similar methods and find good agreement between them.
The expected photometrical characteristics of high redshift spiral galaxies
Authors: Mollá M. , García-Vargas M. , Martín-Manjón M.
Published: April 2010

The star formation and the subsequent metallic enrichment of spiral galaxies, occurring at the early phases of their evolution, produce emission lines whose contribution may change the colors of these objects. We have computed this contribution with consistent chemo-spectro-photometrical theoretical models in order to calculate the variations in the colors evolution.
Star Formation in the LMC: Comparative CCD Observations of Young Stellar Populations in two Giant Molecular Clouds
Authors: Ruppert Jan , Zinnecker Hans
Published: April 2010

This work deals with a CCD imaging study at optical and near-infrared wavelength of two giant molecular clouds (plus a control field) in the southern region of the Large Magellanic Cloud, one of which shows multiple signs of star formation, whereas the other does not. The observational data from VLT FORS2 (R-band) and NTT SOFI (Ks-band) have been analyzed to derive luminosity functions and color-magnitude diagrams. The young stellar content of these two giant molecular clouds is compared and confirmed to be different, in the sense that the apparently “starless” cloud has so far formed only low-luminosity, low-mass stars (fainter than mKs = 16.5 mag, not seen by 2MASS), while the other cloud has formed both faint low-mass and luminous high-mass stars. The surface density excess of low-luminosity stars (~ 2 per square arcmin) in the “starless” cloud with respect to the control field is about 20% whereas the excess is about a factor of 3 in the known star-forming cloud. The difference may be explained theoretically by the gravo-turbulent evolution of giant molecular clouds, one being younger and less centrally concentrated than the other.
What stellar populations can tell us about the evolution of the mass–metallicity relation in SDSS galaxies
Authors: Vale Asari N. , Stasińska G. , Cid Fernandes R. , Gomes J. M. , Schlickmann M. , Mateus A. , Schoenell W.
Published: April 2010

During the last three decades, many papers have reported the existence of a luminosity metallicity or mass metallicity (M–Z) relation for all kinds of galaxies: The more massive galaxies are also the ones with more metal-rich interstellar medium. We have obtained the mass-metallicity relation at different lookback times for the same set of galaxies from the Sloan Digital Sky Survey (SDSS), using the stellar metallicities estimated with our spectral synthesis code starlight. Using stellar metallicities has several advantages: We are free of the biases that affect the calibration of nebular metallicities; we can include in our study objects for which the nebular metallicity cannot be measured, such as AGN hosts and passive galaxies; we can probe metallicities at different epochs of a galaxy evolution.

We have found that the M–Z relation steepens and spans a wider range in both mass and metallicity at higher redshifts for SDSS galaxies. We also have modeled the time evolution of stellar metallicity with a closed-box chemical evolution model, for galaxies of different types and masses. Our results suggest that the M–Z relation for galaxies with present-day stellar masses down to 1010M⊙ is mainly driven by the star formation history and not by inflows or outflows.
Synthetic Stellar libraries and SSP simulations in the Gaia Era
Authors: Vallenari Antonella , Sordo Rosanna , Tantalo Rosaria , Allard France , Blomme Ronny , Bouret Jean-Claud , Brott Ines , Fremat Yves , Martayan Christophe , Damerdji Yassine , Edvardsson Bengt , Josselin Eric , Plez Bertrand , Kochukhov Oleg , Kontizas Mary , Schweitzer Andreas , Zorec Jean , Tsalmantza Paraskevi , Munari Ulisse , Saguner Tenay
Published: April 2010

The Gaia mission will obtain accurate positions, parallaxes and proper motions for 109object all over the sky. In addition, it will collect low resolution spectroscopy in the optical range for ~109objects, stars, galaxies, and QSOs. Parameters of those objects are expected to be part of the final Catalog. Complete and up-to-date libraries of synthetic stellar spectra are needed to train the algorithms to classify this huge amount of data. Here we focus on the use of the synthetic libraries of spectra calculated by the Gaia community to derive grids of Single Stellar Populations as building blocks of population synthesis models.
Binary interactions and UV photometry on photometric redshift
Authors: Zhang F. , Li L. , Han Z.
Published: April 2010

Using the Hyperz code (Bolzonella et al. 2000) we present photometric redshift estimates for a random sample of galaxies selected from the SDSS/DR7 and GALEX/DR4, for which spectroscopic redshifts are also available.

We confirm that the inclusion of ultraviolet photometry improves the accuracy of photo-zs for those galaxies with g* – r* ≤ 0.7 and zspec ≤ 0.2. We also address the problem of how binary interactions can affect photo-z estimates, and find that their effect is negligible.
Der Elternbildfragebogen für Kinder- und Jugendliche (EBF-KJ)
Authors: Titze Karl , Wiefel Andreas , Assheuer Judith , Biermann Mandy , Führer Daniel , Riezler Bernadette , Lehmkuhl Ulrike
Published: April 2010

Zusammenfassung. Der EBF-KJ ist ein klinisch ausgerichteter Fragebogen zur Erfassung der Repräsentation der Eltern-Kind-Beziehung aus der Sicht von Kindern und Jugendlichen. Er basiert auf der systemischen Familientheorie und der Familienstresstheorie. Der Fragebogen umfasst 36 Items pro Elternteil, die sich auf drei Ressourcenskalen (Kohäsion, Identifikation, Autonomie), fünf Risikoskalen (Konflikte, Ablehnung/Gleichgültigkeit, Bestrafung, emotionale Grenzüberschreitung, Ängste/Überprotektion) und die Zusatzskala Hilfe verteilen. Der vorliegende Beitrag begründet die inhaltliche Konstruktion und stellt wichtige psychometrische Eigenschaften des EBF-KJ vor. Insgesamt wurden 785 Schüler sowie 197 Patienten einer Kinder- und Jugendpsychiatrischen Klinik im Alter von 10 bis 20 Jahren (M: 14,1) untersucht. Konfirmatorische Faktorenanalysen bestätigten die faktorielle Validität. Die interne Konsistenz lag bei 12 Skalen über .80. Weiterhin belegten systematische Korrelationen zwischen dem EBF-KJ und dem FEE ( Schumacher, Eisemann & Brähler, 2000 ) die konvergente und diskriminante Validität beider Verfahren. Alle Skalen des EBF-KJ wiesen signifikante Zusammenhänge mit psychopathologischen Symptomen in Eltern- und Jugendfragebögen auf.
Impact of cloud‐radiative processes on hurricane track
Authors: Fovell Robert G. , Corbosiero Kristen L. , Seifert Axel , Liou Kuo‐Nan
Published: April 2010

Idealized simulations of tropical cyclones suggest that previously established motion sensitivity to cloud microphysical processes may emerge through cloud‐radiative feedback. When commonly employed radiation parameterizations and absorption treatments are used, microphysical schemes generate a variety of tracks, influenced by different, scheme‐dependent convective heating patterns and magnitudes. However, these variations nearly vanish when cloud‐radiative feedback is neglected, with storms becoming stronger and more compact. This study strongly motivates further research with respect to how condensation particles influence radiative processes and thus storm dynamics and thermodynamics.
Mechanisms involved in the developmental programming of adulthood disease
Authors: Warner Matthew J. , Ozanne Susan E.
Published: April 2010

There are many instances in life when the environment plays a critical role in the health outcomes of an individual, yet none more so than those experienced in fetal and neonatal life. One of the most detrimental environmental problems encountered during this critical growth period are changes in nutrition to the growing fetus and newborn. Disturbances in the supply of nutrients and oxygen to the fetus can not only lead to adverse fetal growth patterns, but they have also been associated with the development of features of metabolic syndrome in adult life. This fetal response has been termed developmental programming or the developmental origins of health and disease. The present review focuses on the epidemiological studies that identified this association and the importance that animal models have played in studying this concept. We also address the potential mechanisms that may underpin the developmental programming of future disease. It also highlights (i) how developmental plasticity, although beneficial for short-term survival, can subsequently programme glucose intolerance and insulin resistance in adult life by eliciting changes in key organ structures and the epigenome, and (ii) how aberrant mitochondrial function can potentially lead to the development of Type 2 diabetes and other features of metabolic syndrome.
The impact of film thickness and melt-quenched phase on the phase transition characteristics of Ge2Sb2Te5
Authors: Cheng Huai-Yu , Raoux Simone , Chen Yi-Chou
Published: April 2010

This study investigates the detailed phase transition behavior of Ge2Sb2Te5 (GST) thin films in the thickness range between 4–30 nm using a static laser tester. It was found that the crystallization time has a minimum for both as-deposited (around 12 nm) and melt-quenched (around 10 nm) amorphous materials. Capping the GST with a thin SiO2 layer changes this behavior and leads to a monotonic increase in crystallization time with film thickness for as-deposited amorphous samples but a decrease in time for melt-quenched, amorphous samples. The shortest crystallization time of about 7 ns was observed for the melt-quenched, amorphous 6 nm thick film. It was also found that the recrystallization time of melt-quenched, amorphous GST was shorter when the melt-quenched area was surrounded by GST in the hexagonal phase compared to GST in the rocksalt phase. The shorter recrystallization times for thinner, capped GST films indicate a promising scaling behavior of these materials for rewritable optical storage and phase change memory.
Effects of composition, strain, and atomic disorder on optical phonon frequencies in Si1−xGex
Authors: Hossain M. Z. , Johnson H. T.
Published: April 2010

Optical phonon shift coefficients are studied over the entire composition range of Si1−xGex, taking into account the effects of composition, atomistic disorder and strain. Ab initio calculations complement various experimental observations found in the literature by revealing that strain effects on the optical phonons—both hydrostatic and biaxial—vary nonlinearly with composition. Additionally, the pure mode frequencies of the highest optical phonon modes in unstrained Si1−xGex are found to shift linearly with composition, while the mixed-mode frequency shifts quadratically with composition around x=0.5. While atomic randomness affects the composition dependence of the optical phonons, the strain-shift coefficients are approximately insensitive to the local atomic configuration. Short range atomic ordering increases the linear and nonlinear effects.
Electromigration in flip chip solder joints under extra high current density
Authors: Lin Y. W. , Ke J. H. , Chuang H. Y. , Lai Y. S. , Kao C. R.
Published: April 2010

Electromigration in flip chip solder joints under extra high current density (4.5×104 A/cm2) is studied. At such a high current density level, due to Joule heating, the chip temperature is strongly coupled to the applied current density. Accordingly, it is highly desirable to have the capability to decouple the chip temperature and the current density. Two experimental setups were used in this study, one with a cooling module to keep the chip temperature constant and the other one without a cooling module. Without the cooling module, the temperature increased rapidly with the applied current. When the current density reached 4.5×104 A/cm2, a rapid failure caused by excessive Joule heating was observed only after 10 min of current stressing. With the cooling module attached, the joint exhibited a much longer life (935 h) under 4.5×104 A/cm2. It was successfully demonstrated that the cooling module was able to decouple the applied current density and the chip temperature.
Effect of the prosthetic mitral valve on vortex dynamics and turbulence of the left ventricular flow
Authors: Querzoli G. , Fortini S. , Cenedese A.
Published: April 2010

Mechanical heart valves implanted in mitral position have a great effect on the ventricular flow. Changes include alteration of the dynamics of the vortical structures generated during the diastole and the onset of turbulence, possibly affecting the efficiency of the heart pump or causing blood cell damage. Modifications to the hemodynamics in the left ventricle, when the inflow through the mitral orifice is altered, were investigated in vitro using a silicone rubber, flexible ventricle model. Velocity fields were measured in space and time by means of an image analysis technique: feature tracking. Three series of experiments were performed: one with a top hat inflow velocity profile (schematically resembling physiological conditions), and two with mechanical prosthetic valves of different design, mounted in mitral position—one monoleaflet and the other bileaflet. In each series of runs, two different cardiac outputs have been examined by changing the stroke volume. The flow was investigated in terms of phase averaged velocity field and second order moments of turbulent fluctuations. Results show that the modifications in the transmitral flow change deeply the interaction between the coherent structures generated during the first phase of the diastole and the incoming jet during the second diastolic phase. Top hat inflow gives the coherent structures which are optimal, among the compared cases, for the systolic function. The flow generated by the bileaflet valve preserves most of the beneficial features of the top hat inflow, whereas the monoleaflet valve generates a strong jet which discourages the permanence of large coherent structures at the end of the diastole. Moreover, the average shear rate magnitudes induced by the smoother flow pattern of the case of top hat inflow are nearly halved in comparison with the values measured with the mechanical valves. Finally, analysis of the turbulence statistics shows that the monoleaflet valves yield higher turbulence intensity in comparison with the bileaflet and, with top hat inflow, there is not a complete transition to turbulence.
Line-soliton dynamics and stability of Bose–Einstein condensates in (2+1) Gross–Pitaevskii equation
Authors: Radha R. , Kumar V. Ramesh , Wadati Miki
Published: April 2010

We investigate the (2+1)-dimensional Gross–Pitaevskii equation in an isotropic expulsive harmonic trap and generate bright line solitons for the condensates by employing the Hirota method. We observe that one can increase the density of the condensates (or line solitons) by suitably tuning the trap frequency even for constant scattering lengths. The two line-soliton dynamics indicate the occurrence of an instability in the condensates once the density exceeds a critical value. This instability could possibly be overcome by the addition of suitable dissipation which subsequently increases the lifespan of the condensates.
Magnetic reconnection in weakly collisional highly magnetized electron-ion plasmas
Authors: Fitzpatrick Richard
Published: April 2010

A reduced three-field model of two-dimensional magnetic reconnection in a weakly collisional, highly magnetized plasma consisting of isothermal electrons and cold ions is derived from a set of Braginskii-like fluid equations. The model is then used to calculate the linear growth rate of the reconnecting instability in collisionless and semicollisional parameter regimes.
Physicochemical study of the acetonitrile insertion into polypyrrole films
Authors: Oliveira Costa S. D. , Fernández Romero A. J. , López Cascales J. J.
Published: April 2010

A study by molecular dynamics (MD) simulation of the acetonitrile diffusion into a polypyrrole film was carried out with atomic detail in a 0.1N lithium perchlorate solution. From the simulated trajectories, the acetonitrile behavior was estimated from bulk solution to the interior of the polypyrrole film, across the polypyrrole/solution interface, for a neutral (reduced) and charged (oxidized) state of the polymer. Among other properties, the translational diffusion coefficient and rotational relaxation time of the acetonitrile were calculated, where a diminution in the translational diffusion coefficient was measured in the interior of the polypyrrole matrix compared to bulk, independently of the oxidation state of the polymer, in contrast with the behavior of the rotational relaxation time that increases from bulk to the interior of the polymer for both oxidation states. In addition, the difference of free energy ΔG associated to the acetonitrile penetration into the polymer was calculated. From the results, it was evidenced that the scarce affinity of acetonitrile to diffuse into the polymer in its reduced state is related with the positive uniform difference of free energy ΔG≈20 kJ/mol, while in the oxidized state, an important free energy barrier of ΔG≈10 kJ/mol has to pass trough for reaching stable sites inside the polymer with values of ΔG up to −10 kJ/mol.
Two-dimensional optics on silicon nitride multilayer: Refraction of Bloch surface waves
Authors: Sfez Tristan , Descrovi Emiliano , Yu Libo , Quaglio Marzia , Dominici Lorenzo , Nakagawa Wataru , Michelotti Francesco , Giorgis Fabrizio , Herzig Hans Peter
Published: April 2010

When properly designed, a dielectric multilayer can sustain Bloch surface waves (BSWs). Using a multiheterodyne scanning near-field optical microscope that resolves phase and polarization, we will show that a thin dielectric structure deposited on the multilayer deflects the BSW propagation according to Snell’s law. Moreover, the mechanism involved in this process is a transfer of energy from the BSW state in the bare multilayer to the new BSW state generated by the presence of the thin dielectric structure. No relevant radiative counterpart occurs. This characteristic validates the treatment of BSWs at the surface of dielectric multilayers as a two-dimensional phenomenon.
Elevated levels of acid and alkaline phosphatase activity in roots and rhizosphere of cowpea (Vigna unguiculata L. Walp.) genotypes grown in mixed culture and at different densities with sorghum (Sorghum bicolor L.)
Authors: Makoi Joachim H. J. R. , Chimphango Samson B. M. , Dakora Felix D.
Published: April 2010

The aim of this study was to assess P acquisition efficiency in 5 cowpea genotypes in mixed culture and at different plant densities using assays of acid and alkaline phosphatase activity and measurement of P in organs. Five cowpea genotypes (2 improved cvv. ITH98-46 and TVu1509, and 3 farmer-selected varieties, namely Bensogla, Sanzie, and Omondaw) were grown in the field at 2 planting densities (83 333 and 166 666 plants/ha) under monoculture and mixed culture with sorghum during 2005 and 2006. Fresh plant roots and rhizosphere soils were collected during the 2 years of experimentation, and assayed for acid and alkaline phosphatase activity. P concentrations in root tissue and rhizosphere soil were also determined using inductively coupled plasma-mass spectrometry. The data for 2005 and 2006 were similar, and therefore pooled for statistical analysis. Our results showed that raising cowpea density from 83 333 to 166 666 plants/ha significantly increased both acid and alkaline phosphatase activity in the rhizosphere, just as mixed culture (or intercropping) also increased the acid and alkaline phosphatase activity in cowpea rhizosphere soil. High plant density and mixed culture (or intercropping) also raised the acid phosphatase activity in fresh roots of cowpea plants. The increased enzyme activity in roots and rhizosphere soil resulted in significantly improved P nutrition in cowpea, greater plant growth, and higher grain yield in the farmer-selected varieties, especially cv. Sanzie. This suggests that field-grown legumes can be screened for high P acquisition efficiency by assaying for acid and alkaline phosphatase activities.
Prediction of seed coat proportion in narrow-leafed and yellow lupins by near-infrared reflectance spectroscopy (NIRS)
Authors: Alomar D. , Mera M. , Errandonea J. , Miranda H.
Published: April 2010

Breeding programs oriented to decrease hull percentage in lupins and consequently to improve their nutritional value could be greatly assisted by a reliable technique to predict seed coat proportion (SCP) in whole, intact seeds. The objective of this work was to evaluate the potential of near-infrared reflectance spectroscopy (NIRS) to predict the percentage of seed coat in two lupin species. Samples (n = 627) of seeds of different lines and crosses of narrow-leafed lupin (Lupinus angustifolius, n = 447) and yellow lupin (L. luteus, n = 180) were scanned in the VIS-NIR range and SCP subsequently determined by dissection and weighing of dry seed fractions (reference data). Calibrations were developed by multivariate regression (modified partial least squares (PLS)), testing different mathematical treatments. The best equation was obtained when both species were pooled in one set of samples and the best treatment of the spectral data consisted in a second subtraction order, over an interval of 8 data points (16 nm) and a smoothing segment of 8 data points. Cross validation for the selected equation showed a coefficient of determination of 88% and a standard error of 0.54%, for an average SCP of 22.63% and a standard deviation of the reference data of 1.55%. It was concluded that NIRS can be effectively applied in breeding programs as a fast, non-destructive screening tool to determine SCP in narrow-leafed and yellow lupins.
Changes in soil water content under annual, perennial, and shrub-based pastures in an intermittently dry, summer-rainfall environment
Authors: Lodge G. M. , Brennan M. A. , Harden S. , Boschma S. P.
Published: April 2010

Soil water content (SWC) was monitored in an intermittently dry environment in 2003–08, for the following pasture types: perennial ryegrass (Lolium perenne cv. Skippy), lucerne (Medicago sativa cv. Venus), phalaris (Phalaris aquatica cv. Atlas PG), a lucerne/phalaris mixture, digit grass (Digitaria eriantha ssp. eriantha cv. Premier), and old man saltbush (Atriplex nummalaria). Perennial ryegrass and phalaris pastures persisted until late winter–early spring 2005 and, after that time, were maintained as degraded annual grass pastures and bare fallows, respectively.
For all pasture types, mean SWC was generally higher for the 0–0.9 m soil depth than the 0.9–2.1 m (63 v. 51 mm of water per 0.2 m soil layer). At a soil depth of 0–0.9 m, few significant differences in SWC occurred among pasture types. However, significant differences among pasture types were recorded in SWC at depths of 0.9–2.1 m for these perennial-based pastures with low herbaceous plant densities. At this depth the SWC of lucerne/phalaris was lower (P < 0.05) than that of perennial ryegrass and phalaris pasture types in March 2005 (Day 500), and that of the degraded annual grass pasture in August 2006 (Day 1000) and December 2007 (Day 1500). Overall, maximum extractable water was highest (P < 0.05) for digit grass and old man saltbush pasture types (~180 mm) and lowest for the bare fallow (99 mm). Estimates of root depth were highest (2.0 m) for the lucerne/phalaris pasture type.
Emerging opportunities and challenges for Australian broadacre agriculture
Authors: Keating B. A. , Carberry P. S.
Published: April 2010

Agriculture globally and in Australia is at a critical juncture in its history with the current changes to input costs, commodity prices, consumption patterns and food stocks. Constraints are emerging in terms of land and water resources as well as imperatives to reduce greenhouse gas emissions. There is evidence that rates of increase in agricultural productivity are reducing, both in Australia and overseas. On top of all these drivers of change, agriculture is the sector probably most exposed to climate change, and Australian agriculture is as exposed as any in the world.
Against this turbulent background, this paper explores some of the emerging opportunities and challenges in Australian agriculture. These include new products or services from agriculture such as biofuels, forest-based carbon storage in agricultural landscapes, bio-sequestration of carbon in agricultural soils, and environmental stewardship schemes that would reward farmers for nature conservation and related non-production services from farming land. Although there are situations where all these emerging opportunities may deliver benefits to both farmers and the wider community, an overall conclusion is that none of these, on their own, will transform the nature of Australian agriculture.
Instead, the greatest emerging opportunity for Australian agriculture must be sought from productivity breakthroughs in the face of current and emerging constraints. This view is formed by looking through the lens of the global food production challenge which sees a demand for close to a doubling of food production by 2050 in the face of increasingly constrained land and water resources, soil degradation, increasing energy scarcity and limits on greenhouse gas release to the atmosphere. These same land, water, soil, energy and atmospheric constraints to agriculture apply in Australia and will shape both farming and the agricultural research agenda over coming decades.
In the face of such national and global agronomic challenges, a significant threat looms with the skills challenge facing agricultural science in Australia. The demand for the integrative skills of agronomy appears strong but the sector has suffered from disinvestment in recent decades.
Prefrontal cortex, cognitive control, and the registration of decision costs
Authors: McGuire Joseph T. , Botvinick Matthew M.
Published: April 2010

Human choice behavior takes account of internal decision costs: people show a tendency to avoid making decisions in ways that are computationally demanding and subjectively effortful. Here, we investigate neural processes underlying the registration of decision costs. We report two functional MRI experiments that implicate lateral prefrontal cortex (LPFC) in this function. In Experiment 1, LPFC activity correlated positively with a self-report measure of costs as this measure varied over blocks of simple decisions. In Experiment 2, LPFC activity also correlated with individual differences in effort-based choice, taking on higher levels in subjects with a strong tendency to avoid cognitively demanding decisions. These relationships persisted even when effects of reaction time and error were partialled out, linking LPFC activity to subjectively experienced costs and not merely to response accuracy or time on task. In contrast to LPFC, dorsomedial frontal cortex—an area widely implicated in performance monitoring—showed no relationship to decision costs independent of overt performance. Previous work has implicated LPFC in executive control. Our results thus imply that costs may be registered based on the degree to which control mechanisms are recruited during decision-making.
Dual role of protein kinase C on BK channel regulation
Authors: Zhou Xiao-Bo , Wulfsen Iris , Utku Emine , Sausbier Ulrike , Sausbier Matthias , Wieland Thomas , Ruth Peter , Korth Michael
Published: April 2010

Large conductance voltage- and Ca
2+
-activated potassium channels (BK channels) are important feedback regulators in excitable cells and are potently regulated by protein kinases. The present study reveals a dual role of protein kinase C (PKC) on BK channel regulation. Phosphorylation of S
695
by PKC, located between the two regulators of K
+
conductance (RCK1/2) domains, inhibits BK channel open-state probability. This PKC-dependent inhibition depends on a preceding phosphorylation of S
1151
in the C terminus of the channel α-subunit. Phosphorylation of only one α-subunit at S
1151
and S
695
within the tetrameric pore is sufficient to inhibit BK channel activity. We further detected that protein phosphatase 1 is associated with the channel, constantly counteracting phosphorylation of S
695
. PKC phosphorylation at S
1151
also influences stimulation of BK channel activity by protein kinase G (PKG) and protein kinase A (PKA). Though the S
1151
A mutant channel is activated by PKA only, the phosphorylation of S
1151
by PKC renders the channel responsive to activation by PKG but prevents activation by PKA. Phosphorylation of S
695
by PKC or introducing a phosphomimetic aspartate at this position (S
695
D) renders BK channels insensitive to the stimulatory effect of PKG or PKA. Therefore, our findings suggest a very dynamic regulation of the channel by the local PKC activity. It is shown that this complex regulation is not only effective in recombinant channels but also in native BK channels from tracheal smooth muscle.