bluuebunny/crossref_metadata_2025 huggingface dataset:
Abundance distribution functions for nearby late-type dwarfs
Authors: Bragança Gustavo A. , Rocha-Pinto Helio J. , de Mello Gustavo F. Porto , Rangel Rafael H. O. , Maciel Walter J.
Published: March 2010

A major role to the understanding of the chemical evolution of the Galaxy is played by studies of stellar chemical abundance distribution. In the last years, there has been an increase in the number of spectroscopic surveys of late-type stars. Classical problems on the chemical evolution of the Galaxy, such as the G dwarf problem and the age-metallicity relation, can be reinvestigated with better accuracy. We present a chemical abundance survey of 325 solar neighborhood G dwarfs stars situated within 25 pc from the Sun. We reinvestigate classical observational constraints, namely the metallicity distribution, using a number of chemical elements (Na, Si, Ca, Ni, Fe and Ba) as metallicity indicators. The abundance probability density function for each of the surveyed element was derived using a Gaussian kernel estimator. We have found mean values of −0.11, −0.14, −0.07, −0.05, −0.16 and −0.12 dex for the [Fe/H], [Na/H], [Si/H], [Ca/H], [Ni/H] and [Ba/H] pdfs, respectively. We also show that abundance distributions having higher mean values have smaller dispersion, in contradiction to the predictions of the Simple Model with Delayed Production. We discuss this result in the context and present an alternate explanation for this pattern.
Planetary nebulae in the inner Milky Way
Authors: Cavichia Oscar , Costa Roberto D. D. , Maciel Walter J.
Published: March 2010

New abundances of planetary nebulae located towards the bulge of the Galaxy are derived based on observations made at LNA (Brazil). We present accurate abundances of the elements He, N, S, O, Ar, and Ne for 56 PNe located towards the galactic bulge. The data shows a good agreement with other results in the literature, in the sense that the distribution of the abundances is similar to those works. From the statistical analysis performed, we can suggest a bulge-disk interface at 2.2 kpc for the intermediate mass population, marking therefore the outer border of the bulge and inner border of the disk.
Quantitative Spectral Analysis of hot Post-AGB Stars
Authors: Costa-Mello Daniel R. , Daflon Simone , Pereira Claudio B.
Published: March 2010

Post-AGB (PAGB) stars are luminous objects of low and intermediate mass in a final and short stage of evolution in the transition between AGB stars and planetary nebulae (PNe). In this work we present a quantitative spectral analysis of some hot PAGBs based on high resolution spectra. The stellar parameters and chemical composition were obtained from the synthesis of non-LTE spectra.
Sulfur Abundances in Orion B Stars
Authors: Daflon Simone , Cunha Katia , de la Reza Ramiro , Holtzman Jon , Chiappini Cristina
Published: March 2010

Sulfur abundances are derived for a sample of ten B MS star members of the Orion association. The analysis is based on LTE model atmospheres and non-LTE line formation theory by means of spectrum synthesis analysis of Sii and Siii lines. The abundance distribution obtained for the Orion targets is homogeneous within the errors in the analysis: A(S)=7.15±0.05. This abundance result is in agreement with the solar value and with results for the Orion nebula. The sulfur abundances for Orion combined with previous results for other OB-type stars produce a relatively shallow sulfur abundance gradient with a slope of −0.037±0.012 dex Kpc−1.
Chemical Analysis of B stars within 9–11 kpc from the Galactic Center
Authors: Herencia Maria Isela Zevallos , Daflon Simone
Published: March 2010

Radial gradients of metallicity are supported by observations of different young objects in the Galactic thin disk. The shape of the abundance distributions, however, is not completely constrained. Some works describe the abundance distributions as a function of the Galactocentric distance RG by linear fits with a single slope. On the other hand some analyses of open clusters, cepheids and OB stars suggest a discontinuity in the abundance distributions around RG=10 kpc. In this work we analyse a sample of 13 B stars members of four open clusters located within RG=9-11 kpc in order to better constrain the chemical distribution in this region of the disk.
Uncovering the Evolutionary Sequences for the C-J Stars Based on their Chemical Abundances
Authors: de Mello Ana Beatriz , Lorenz-Martins Silvia
Published: March 2010

We present chemical abundances obtained by fitting synthetic spectra to the FEROS data of 12 C-J stars, normal and silicate carbon one. The Li and 13C abundance, as well as the s-process elements abundance indicates no evidence of a diferent mechanism of formation between the two kinds of C-J stars. We also studied the α elements, and that suggests a scenario that put the carbon C-R stars as a possible progenitor of the beither C-J stars. We made also available a study of the radial velocity of some stars of the sample calculated at different epochs. That allowed us to make some discussion about the probable binary system of some silicon C-J carbon stars. Based on these abundances and radial velocities, we discuss possible evolutive sequences for the C-J.
Lithium abundances in southern associations containing young stars
Authors: da Silva Licio , Torres Carlos Alberto , de la Reza Ramiro , Quast Germano , de Melo Claudio , Sterzik Michael
Published: March 2010

In a recent paper, da Silva et al. (2009), we report results of Li abundance analysis for nine young stellar associations, defined in Torres et al. (2008), from a high-resolution optical spectroscopic survey searching for associations containing young stars (SACY), among optical counterparts of ROSAT All-Sky X-ray sources in the Southern Hemisphere. They have applied a convergence method in the (UVW) velocity space and have determined nine nearby young associations in the sample. As they are young and with different ages, those associations form an interesting laboratory to test the Li depletion theory, as a function of the star age.
Investigation of ancient substructures in the Milky Way: chemical composition study
Authors: Stonkutė Edita , Nordström Birgitta , Tautvaišienė Gražina
Published: March 2010

From high resolution spectra taken with the spectrograph FIES on the Nordic Optical Telescope, La Palma, we measure abundances of oxygen and α-elements in order to characterize stars which from their dynamical properties are suspected to have originated in disrupted satellites. We find that the chemical composition of investigated stars is homogeneous and distinct from Galactic disk dwarfs, which is providing further evidence of their extragalactic origin.
Investigation of the chemical structure of our Galaxy using radial pulsating stars as tracers
Authors: Suran Marian Doru
Published: March 2010

In this paper we try to determine the properties of different galactic components (2 < r < 12kpc) using radial pulsating stars (RPS stars) as tracers. For RPS stars in Galaxy we use a quasi-seismological inversion method (Post Theoretical Mass Method, PTM) which allows us to determine the mass M and the abundance Z for each star. Based on PTM method and using RPS stars as tracers we could determine the chemical structure and evolution of the Galaxy: abundance gradients and segregation between different evolutionary populations. This method is planned to be extended further using the RPS star observed by the KEPLER space mission.
Evolution of [O/Mg], [Na/Mg], [Al/Mg], and [K/Mg] in the Galaxy, from a NLTE analysis
Authors: Spite M. , Spite F. , Bonifacio P. , Hill V. , Andrievsky S. , Cayrel R. , François P. , Korotin S.
Published: March 2010

In the framework of he ESO Large Program “First Stars”, high resolution (R=45000) high S/N ratio spectra have been obtained for a sample of Extremely Metal Poor Stars (EMP stars), 35 giants and 18 turnoff stars. Among them 37 have a very low metallicity: [Fe/H]< −2.9.
Superbubble Hii regions: how self-enriched should they be?
Authors: Wofford Aida
Published: March 2010

I modeled the pollution of low metallicity (Z=0.001) superbubble Hii regions with the ejecta from single stellar populations of 104−106M⊙ in mass. I found that the He, C, N, and O abundance enhancements in the Hii regions, due to pollution with the enriched winds from Wolf-Rayet stars, are insignificant at 5Myr. The few localized metal enhancements observed so far in resolved extragalactic Hii regions are not associated with superbubbles and remain to be modeled in detail.
Metallicity and Planet Formation: Models
Authors: Boss Alan P.
Published: March 2010

Planets typically are considerably more metal-rich than even the most metal-rich stars, one indication that planet formation must differ greatly from star formation. There is general agreement that terrestrial planets form by the collisional accumulation of solids composed of heavy elements in the inner regions of protoplanetary disks. Two competing mechanisms exist for the formation of giant planets, core accretion and disk instability, though hybrid combinations are possible as well. In core accretion, a higher metallicity in the protoplanetary disk leads directly to larger core masses and hence to more gas giant planets. Given the strong correlation of gas giant planets detected by Doppler spectroscopy with stellar metallicity, this has often been taken as proof that core accretion is the mechanism that forms giant planets. Recent work, however, implies that the formation of gas giants by disk instability can be enhanced by higher metallicities, though not as dramatically as for core accretion. In both scenarios, the ongoing accretion of planetesimals by gas giant protoplanets leads to strong enrichments of heavy elements in their gaseous envelopes. Both scenarios also imply that gas giant planets should have significant solid cores, raising questions for gas giant interior models without cores. Exoplanets with large inferred core masses seem likely to have formed by core accretion, while gas giants at distances beyond 20 AU seem more likely to have formed by disk instability. Given the wide variety of exoplanets found to date, it appears that both mechanisms are needed to explain the formation of the known population of giant planets.
The Diversity of Extrasolar Terrestrial Planets
Authors: Bond Jade C. , Lauretta Dante S. , O'Brien David P.
Published: March 2010

Extrasolar planetary host stars are enriched in key planet-building elements. These enrichments have the potential to drastically alter the building blocks available for terrestrial planet formation. Here we report on the combination of dynamical models of late-stage terrestrial planet formation within known extrasolar planetary systems with chemical equilibrium models of the composition of solid material within the disk. This allows us to constrain the bulk elemental composition of extrasolar terrestrial planets. A wide variety of resulting planetary compositions exist, ranging from those that are essentially “Earth-like”, containing metallic Fe and Mg-silicates, to those that are dominated by graphite and SiC. This implies that a diverse range of terrestrial planets are likely to exist within extrasolar planetary systems.
Metallicity and Planet Formation – Observations
Authors: Valenti Jeff A.
Published: March 2010

Early abundance measurements established that stars known to host giant planets are metal rich compared to the Sun. More extensive abundance measurements then showed that giant planet hosts are metal rich compared to the parent sample in planet searches. Stars spanning a range of convection zone depths all show the same metallicity effect, ruling out significant abundance enhancements due to selective accretion. Most known planets migrated inwards from the snow line, but subsamples closer to and further from the star have similar iron abundances, so the stopping point of migration does not depend on metallicity. Stars recently discovered to host Neptune mass planets may be metal poor compared to the Sun, particularly if one focusses on stars that do not also host higher mass planets. This would be consistent with core-accretion models of planet formation. Before drawing physical conclusions, it will be necessary to check for metallicity bias in the subsample of stars around which Neptune mass planets could have been found. M dwarf abundances are currently too uncertain to relate planet frequency and host star metallicity, due mainly to missing or incorrect molecular line data.
A New Spin on Red Giant Rapid Rotators: Evidence for Chemical Exchange Between Planets and Evolved Stars
Authors: Carlberg Joleen K. , Majewski Steven R. , Smith Verne V. , Cunha Katia , Patterson Richard J. , Bizyaev Dmitry , Arras Phil , Rood Robert T.
Published: March 2010

Rapid rotation in red giant stars may be one signature of the past engulfment of a planetary companion. Models of the future tidal interaction of known exoplanet host stars with their planets show that many of these stars will accrete one or more of their planets, and the orbital angular momentum of these accreted planets is sometimes sufficient to spin up the host stars to a level commonly accepted as “rapid rotation” for giant stars. Planets accreted during the red giant phase should leave behind a chemical signature in the form of unusual abundance patterns in the host red giant's atmosphere. Proposed signatures of planet accretion include the enhancement of Li and 12C; both species are generally depleted in giant star atmospheres by convection but could be replenished by planet accretion. Moreover, accreted planets may preferentially enhance the stellar abundance of refractory elements assuming that the refractory nature of these elements leads to their relative enhancements in the planets themselves. Here we present preliminary results of a search for these predicted chemical signatures through high resolution spectroscopic abundance analysis of both rapidly rotating giant stars (i.e., stars with a higher probability of having experienced planet accretion) and normally rotating giant stars. We find that the rapid rotators are enhanced in Li relative to the slow rotators — a result consistent with Li replenishment through planet absorption.
Planetary populations according to the orbital angular momentum
Authors: Amarante João A. S. , Rocha-Pinto Helio J.
Published: March 2010

We investigate the angular momentum distribution of known exoplanetary systems, as a function of the planetary mass, orbital semimajor axis and metallicity of the host star. We find exoplanets seems to be classified according to at least two ‘populations’, with respect to their angular momentum properties. This classification is independent on the composition of the planet and seems to be valid for both jovian and neptunian planets, and probably can be extrapolated to the terrestrial planets of the Solar System. We analyse these ‘populations’ considering the phenomenon of planetary migration.
Lithium abundance as a boundary condition for age and mass determination of solar twin stars
Authors: Castro M. , do Nascimento J.-D. , da Costa J. S. , Meléndez J. , Bazot M. , Théado S. , de Mello G. F. Porto , De Medeiros J. R.
Published: March 2010

We explore the non-standard mixing history of five solar twins to determine as precisely as possible their mass and age. For this, we computed a grid of evolutionary models with non-standard mixing at given metallicities with the Toulouse-Geneva code for a range of stellar masses. We choose the evolutionary model that best fit the low lithium abundances observed in the solar twins. Our best model for each solar twin provides a mass and age solution constrained by their Li content and Teff determination. Li depletion due to the additional mixing in solar-twins is strongly mass dependent. An accurate lithium abundance measurement connected with non-standard models provides a more precise information about the age and mass better than that determined only by classical methods.
Distribution of refractory and volatile elements in CoRoT planet host stars
Authors: Chavero C. , de la Reza R. , Domingos R. C. , Drake N. A. , Pereira C. B. , Winter O. C.
Published: March 2010

We report on preliminary results of spectroscopic determination of the atmospheric parameters and chemical abundances of the parent stars of the recently discovered transiting planets CoRoT-2b and CoRoT-4b. We found a flat distribution of the relative abundances as a function of their condensation temperatures. Also, we introduce a new methodology to investigate a relation between the abundances of these stars and the internal migration of their planets.
Photospheric parameters and C abundances in solar-like stars with and without planets
Authors: Da Silva Ronaldo , Milone André
Published: March 2010

We have been analyzing a large sample of solar-like stars with and without planets in order to homogeneously measure their photospheric parameters and Carbon abundances. Our sample contains around 200 stars in the solar neighborhood observed with the ELODIE spectrograph, for which the observational data are publicly available. We performed spectral synthesis of prominent bands of C2 and CI lines, aiming to accurately obtain the C abundances. We intend to contribute homogeneous results to studies that compare elemental abundances in stars with and without known planets. New arguments will be brought forward to the discussion of possible chemical anomalies that have been suggested in the literature, leading us to a better understanding of the planetary formation process. In this work we focus on the C abundances in both stellar groups of our sample.
Stellar Parameters for a Sample of Stars with Planets
Authors: Ghezzi Luan , Cunha Katia , de Araújo Francisco X. , Smith Verne V. , de la Reza Ramiro , Schuler Simon
Published: March 2010

The study of chemical abundances in stars with planets is an important ingredient for the models of formation and evolution of planetary systems. In order to determine accurate abundances, it is crucial to have a reliable set of atmospheric parameters. In this work, we describe the homogeneous determination of effective temperatures, surface gravities and iron abundances for a large sample of stars with planets as well as a control sample of stars without giant planets. Our results indicate that the metallicity distribution of the stars with planets is more metal rich by ~0.13 dex than the control sample stars.
On the origin of giant planets and their hosts
Authors: Haywood Misha
Published: March 2010

The correlation between stellar metallicity and giant planets has been tentatively explained by the possible increase of planet formation probability in stellar disks with enhanced amount of metals. There are two caveats to this explanation. First, giant stars with planets do not show a metallicity distribution skewed towards metal-rich objects, as found for dwarfs. Second, the correlation with metallicity is not valid at intermediate metallicities, for which it can be shown that giant planets are preferentially found orbiting thick disk stars.

None of these two peculiarities is explained by the proposed scenarios of giant planet formation. We contend that they are galactic in nature, and probably not linked to the formation process of giant planets. It is suggested that the same dynamical effect, namely the migration of stars in the galactic disk, is at the origin of both features, with the important consequence that most metal-rich stars hosting giant planets originate from the inner disk. A planet-metallicity correlation similar to the observed one is easily obtained if stars from the inner disk have a higher percentage of giant planets than stars born at the solar radius, with no specific dependence on metallicity. We propose that the density of H2 in the inner galactic disk (the molecular ring) could play a role in setting the high percentage of giant planets that originate from this region.
Photostability of gas- and solid-phase biomolecules under astrophysical analog soft X-rays field
Authors: Pilling S. , Andrade D. P. P. , Marinho R. T. , do Nascimento E. M. , Boechat-Roberty H. M. , de Castilho R. B. , de Souza G. G. B. , Coutinho L. H. , Cavasso-Filho R. L. , Lago A. F. , de Brito A. N.
Published: March 2010

We present experimental studies on the interaction of soft X-rays on gas-phase and solid-phase amino acids and nucleobases in an attempt to verify if these molecules (supposed to be formed in molecular clouds/protostellar clouds) can survive long enough to be observed or even to be found in meteorites. Measurements have been undertaken employing 150 eV photons under high vacuum conditions at the Brazilian Synchrotron Light Laboratory (LNLS). The produced ions from the gas-phase experiments (glycine, adenine and uracil) have been mass/charge analyzed by time-of-flight spectrometer. The analysis of solid phase samples (glycine, DL-proline, DL-valine, adenine and uracil) were performed by a Fourier transform infrared spectrometer coupled to the experimental chamber. Photodissociation cross sections and halflives were determined and extrapolated to astrophysical environments. The nucleobases photostability was up to two orders of magnitude higher than for the amino acids.
Radiolysis of ammonia-containing ices by heavy cosmic rays inside dense molecular clouds
Authors: Pilling Sergio , Duarte Eduardo Seperuelo , da Silveira Enio F. , Balanzat Emmanuel , Rothard Hermann , Domaracka Alicja , Boduch Philippe
Published: March 2010

We present experimental studies on the interaction of heavy, highly charged and energetic ions (46 MeV 58Ni13+) with interstellar ammonia-containing (H2O:NH3:CO) ice analog in an attempt to simulate the physical chemistry induced by heavy ion cosmic rays inside dense astrophysical environments. The measurements were performed at the heavy ion accelerator GANIL in Caen, France. In-situ analysis have been performed by a Fourier transform infrared spectrometer. The averaged values for the dissociation cross section of water, ammonia and carbon monoxide are determined and the estimated half life for the studied species inside dense molecular clouds is 2-3 × 106 years. The IR spectra of organic residue produced by the radiolysis have revealed, at room temperature, five bands that are tentatively assigned to vibration modes of the zwitterionic glycine (NH3+CH2COO−).
Spectroscopic surveys to measure Galaxy evolution
Authors: Gilmore Gerard
Published: March 2010

Galaxies are complex non-linear systems, evolving on all time-scales. Isolating whatever set of physical processes was important at each major phase of their evolution requires artefacts which resolve the timescales of dominant physical processes. These are the chemical elements, and stellar kinematics. I consider what surveys are required to make progress in Galaxy evolution mapping, in the era of Gaia.
Dependence of pitch‐angle scattering rates and loss timescales on the magnetic field model
Authors: Orlova Ksenia G. , Shprits Yuri Y.
Published: March 2010

Radiation belt diffusion codes require, as inputs, precomputed scattering rates, which are currently bounce‐averaged in the dipole magnetic field. We present the results of computations of the bounce‐averaged quasi‐linear pitch‐angle diffusion coefficients of relativistic electrons for various distances and two MLT in the Tsyganenko 89c magnetic field model. The coefficients were computed for quiet and storm‐time conditions. We compare scattering rates bounce‐averaged in a non‐dipole field model with those in the dipole field. We demonstrate that on the day side the effects of taking into account a realistic magnetic field are negligible at distances less than six Earth radii. On the night side diffusion coefficients may significantly depend on the assumed field model. Pitch‐angle scattering rates calculated in the non‐dipole field can explain the often observed night‐side chorus induced precipitation. The physical explanation for the changes of pitch‐angle scattering rates with the field model is presented and discussed.
Electrostatic field and ion temperature drop in thin current sheets: A theory
Authors: Liu W. W. , Liang J. , Donovan E. F.
Published: March 2010

The observational evidence presented by Liang et al. (2009) showed that a neutral sheet–pointing electrostatic field frequently arises in the late growth‐phase current sheet in the magnetotail. In this paper, we elaborate on the suggestion that this electric field is associated with the thinning of the current sheet to the ion scale at which the electron and ion current sheets begin to separate. The attendant effect of a decreasing ion temperature, also interpreted in terms of a thinning current sheet, suggests that a cold plasma population is involved. We review existing theories of “charged” Harris sheet that can produce electrostatic fields and show that they cannot explain the observations for various reasons. A particular problem is the over shielding of the electrostatic field by the cold population embedding the current sheet. We argue that this problem stems from not treating the cold plasma as a separate population from the hot plasma forming the thin current sheet (TCS). We show that if the cold population is treated as external to the TCS and behaving in a largely MHD manner, the resultant solution yields an electrostatic field and ion temperature drop consistent with the observations.
Subduction initiation at passive margins: Numerical modeling
Authors: Nikolaeva K. , Gerya T. V. , Marques F. O.
Published: March 2010

Subduction is a key process for terrestrial plate tectonics, but its initiation is still not entirely understood. In particular, despite the abundance of both passive and active continental margins on Earth, no obvious cases of transition between them have been identified so far. It has been shown that at most passive margins, elastic and frictional forces exceed gravitational instability and ridge‐push forces, which precludes subduction initiation. Therefore additional factors are needed to start subduction there. We investigated numerically in two dimensions factors controlling passive margins' stability such as age of the oceanic plate, thickness of the continental lithosphere and crust, and density contrast between subcontinental and suboceanic lithospheric mantles. Our numerical experiments show that three subsequent tectonic regimes can develop at a passive margin: (1) stable margin, (2) overthrusting, and (3) subduction. Transition from stable margin to the overthrusting regime is mainly controlled by ductile strength of the lower continental crust. Further transition from overthrusting to the subduction regime is governed by the ductile strength of the subcontinental lithospheric mantle and its chemical density contrast with the suboceanic lithospheric mantle. Our experiments also demonstrate that the age of the oceanic plate is a factor of secondary importance for subduction initiation and only plays a role if other parameters are of critical values. Favorable conditions for subduction initiation thus correspond to passive margins where chemically buoyant (depleted) continental lithosphere becomes thin and hot (Moho temperature >660°C). This situation can be occasionally created by superimposed external processes such as rifting and/or thermal‐chemical plume activity.
Development of the prenatal cutaneous antigen‐presenting cell network
Authors: Elbe‐Bürger Adelheid , Schuster Christopher
Published: March 2010

The skin, and in particular the epidermis, is a physical barrier that protects the body from external threats and is critically involved in immune reactivity. Professional antigen‐presenting cells, such as epidermal Langerhans cells and dermal dendritic cells, are gaining prominence as principal players orchestrating the decision between immunity and tolerance. A focus of research interest in recent years has been the investigation of these cells in mammalian prenatal skin. In this review, we will compare the recent progress in dissecting the phenotype and functional role of antigen‐presenting cells in the developing human and mouse skin before birth and perinatally, and will discuss how this knowledge improves our understanding of the level of immunocompetence of the skin in utero.
Bacterial adaptation through distributed sensing of metabolic fluxes
Authors: Kotte Oliver , Zaugg Judith B , Heinemann Matthias
Published: March 2010

The recognition of carbon sources and the regulatory adjustments to recognized changes are of particular importance for bacterial survival in fluctuating environments. Despite a thorough knowledge base of Escherichia coli's central metabolism and its regulation, fundamental aspects of the employed sensing and regulatory adjustment mechanisms remain unclear. In this paper, using a differential equation model that couples enzymatic and transcriptional regulation of E. coli's central metabolism, we show that the interplay of known interactions explains in molecular‐level detail the system‐wide adjustments of metabolic operation between glycolytic and gluconeogenic carbon sources. We show that these adaptations are enabled by an indirect recognition of carbon sources through a mechanism we termed distributed sensing of intracellular metabolic fluxes. This mechanism uses two general motifs to establish flux‐signaling metabolites, whose bindings to transcription factors form flux sensors. As these sensors are embedded in global feedback loop architectures, closed‐loop self‐regulation can emerge within metabolism itself and therefore, metabolic operation may adapt itself autonomously (not requiring upstream sensing and signaling) to fluctuating carbon sources.
Precision and scaling in morphogen gradient read‐out
Authors: Morton de Lachapelle Aitana , Bergmann Sven
Published: March 2010

Morphogen gradients infer cell fate as a function of cellular position. Experiments in Drosophila embryos have shown that the Bicoid (Bcd) gradient is precise and exhibits some degree of scaling. We present experimental results on the precision of Bcd target genes for embryos with a single, double or quadruple dose of bicoid demonstrating that precision is highest at mid‐embryo and position dependent, rather than gene dependent. This confirms that the major contribution to precision is achieved already at the Bcd gradient formation. Modeling this dynamic process, we investigate precision for inter‐embryo fluctuations in different parameters affecting gradient formation. Within our modeling framework, the observed precision can only be achieved by a transient Bcd profile. Studying different extensions of our modeling framework reveals that scaling is generally position dependent and decreases toward the posterior pole. Our measurements confirm this trend, indicating almost perfect scaling except for anterior most expression domains, which overcompensate fluctuations in embryo length.
Relationship between depth and morphology of foraminifera in Abderaz Formation, IRAN
Authors: Shafiee Ardestani Meysam , Asgharian rostami Masoud , Balmaki Behzad , Balmaki Behnaz
Published: March 2010

Abderaz Formation at its type section with an age of Turonian-early Campanian and a thickness of 300 m contains light grey shale and marl. The study of the planktonic foraminifera in isolated form led to differentiate three morphotype groups. The first group is characterized by trochospiral tests usually indicate shallow waters, the second group contains forms with strong ornamentations and the primary keels representing mid waters and finally compact trochospiral tests with keels known as deep water indices are included in the third group. Studies on the morphotypes showed a regressive cycle for Abderaz Formation. In the present study the depth of Abderaz Formation was determined using planktonic morphotypes. As Results of the study all changes in test of planktons were observed in related to the water depth of their ecosystem. The data of the represented research are in confirmation with the Pascal Law.
Current Issues: Training To Ensure Quality Practicum Supervision of Graduate Students
Authors: Norton Jessica J.
Published: March 2010

Appropriate supervision and effective clinical instruction are essential to the education of future speech-language pathologists. Practicum supervisors assist graduate students with their integration of academic knowledge and clinical skills, which leads to their independent thinking and problem solving, and ultimately to their demonstration of clinical competencies. Despite this vital role, many supervisors do not have the education and training to be proficient mentors. Therefore, Camtasia Studio was used at the University of Virginia to create two short training programs (each 17 minutes in length) to support speech-language pathologists involved in supervisory roles at off-site facilities. Furthermore, survey results completed by these professionals following the initial trainings help to rationalize the need for additional trainings and more wide-spread instruction of speech-language pathologists who take on the role as clinical supervisor.
Business: Making Cents of Coding Systems: Billing for Professional Services
Authors: Nikjeh Dee Adams
Published: March 2010

Administrators and supervisors face daily challenges over issues such as program funding, service fees, correct coding procedures, and the ever-changing healthcare regulations. Receiving equitable reimbursement for speech-language pathology and audiology services necessitates an understanding of federal coding and reimbursement systems. This tutorial provides information pertaining to two major healthcare coding systems and explains the relationship of these systems to clinical documentation, the Medicare Physician Fee Schedule and equitable reimbursement. An explanation of coding edits and coding modifiers is provided for use in those occasional atypical situations when the standard use of procedural coding may not be appropriate. Also included in this tutorial is a brief discussion of the impact that the Medicare Improvements for Patients and Providers Act of 2008 (HR 6331 Medicare Improvements for Patients and Providers Act [MIPPA], 2008) has had on the valuation of speech-language pathology procedure codes.
Supervision: Essentials of Collaboration
Authors: Livingston Amy
Published: March 2010

This article examines collaboration in the workplace, primarily in the educational setting. The article stresses the importance of examining one's own collaborative efforts in order to effectively mentor others. By analyzing the different aspects of collaboration and realizing the importance of working together with other professionals, mentors and supervisors can teach co-laboring or collaborating more successfully to those we mentor.
Audiology: Remediating Boundary Issues: Triangulation and Self-Care
Authors: Herd Corey L. , Waide Michael P. , Cohn Tracy J.
Published: March 2010

Audiologists fill multiple roles in the lives of their clients. The audiologist is the limited-time caretaker of the client's loved one, the knowledgeable expert about speech and hearing, and sometimes, the trusted confidant. The fiduciary relationship that exists between client and clinician, however, is inherently and intentionally one-sided. Unfortunately, professionals who struggle with self-care and who lack awareness of self may find themselves faced with crossing boundaries or entangled in the complex web of relationships in their clients' lives. In this article, the authors examine relationship triangles (triangulation) and knowledge of self and self care as they relate to the audiologist's role with client management.
Current Issues: Advanced Digital Technology for Supervising Graduate Clinicians
Authors: Tellis Glenn , Cimino Lori , Alberti Jennifer
Published: March 2010

The purpose of this article is to provide clinical supervisors with information pertaining to state-of-the-art clinic observation technology. We use a novel video-capture technology, the Landro Play Analyzer, to supervise clinical sessions as well as to train students to improve their clinical skills. We can observe four clinical sessions simultaneously from a central observation center. In addition, speech samples can be analyzed in real-time; saved on a CD, DVD, or flash/jump drive; viewed in slow motion; paused; and analyzed with Microsoft Excel. Procedures for applying the technology for clinical training and supervision will be discussed.
Revealing degree distribution of bursting neuron networks
Authors: Shen Yu , Hou Zhonghuai , Xin Houwen
Published: March 2010

We present a method to infer the degree distribution of a bursting neuron network from its dynamics. Burst synchronization (BS) of coupled Morris–Lecar neurons has been studied under the weak coupling condition. In the BS state, all the neurons start and end bursting almost simultaneously, while the spikes inside the burst are incoherent among the neurons. Interestingly, we find that the spike amplitude of a given neuron shows an excellent linear relationship with its degree, which makes it possible to estimate the degree distribution of the network by simple statistics of the spike amplitudes. We demonstrate the validity of this scheme on scale-free as well as small-world networks. The underlying mechanism of such a method is also briefly discussed.
The water entry of decelerating spheres
Authors: Aristoff Jeffrey M. , Truscott Tadd T. , Techet Alexandra H. , Bush John W. M.
Published: March 2010

We present the results of a combined experimental and theoretical investigation of the vertical impact of low-density spheres on a water surface. Particular attention is given to characterizing the sphere dynamics and the influence of its deceleration on the shape of the resulting air cavity. A theoretical model is developed which yields simple expressions for the pinch-off time and depth, as well as the volume of air entrained by the sphere. Theoretical predictions compare favorably with our experimental observations, and allow us to rationalize the form of water-entry cavities resulting from the impact of buoyant and nearly buoyant spheres.
Evidence of spin-density-wave transition and enhanced thermoelectric properties in Ca3−xCexCo4O9+δ
Authors: Tang G. D. , Wang Z. H. , Xu X. N. , Qiu L. , Du Y. W.
Published: March 2010

We have investigated the effect of Ce doping on the magnetic and low-temperature thermoelectric properties of Ca3Co4O9+δ. A small shoulder occurring at about 23 K in the dχ−1/dT curve indicates an occurrence of spin-density-wave transition, which is confirmed by resistance characteristics. With partial Ce substitution, the thermopower increases while the thermal conductivity decreases. The magnetic measurements give a support to the concentration reduction in Co4+ ions, which results in the enhancement of thermopower. The dimensionless figure of merit ZT=0.016 is achieved at 335 K for Ca2.9Ce0.1Co4O9+δ, demonstrating that heavy atoms Ce doping may promise an effective way for improving thermoelectric properties of Ca3Co4O9+δ system.
Dynamic evolution of welding residual stress field under noncontact electromagnetic force
Authors: Xu Da , Liu Xuesong , Wang Ping , Yang Jianguo , Xu Wei , Fang Hongyuan
Published: March 2010

Controlling welding residual stress and distortion has still been a challenging problem due to the complexity of welding process. In this paper, a new technique with inductive electromagnetic forces has been reported for controlling welding residual stresses and distortion in welded thin plate. In order to get better understanding the associated mechanism, a hybrid three-dimensional finite element analysis, including electromagnetic force induction, welding, and electromagnetic force impact processes, has been performed to investigate the dynamic evolution of stress and strain in the welded plate under electromagnetic force impact. It is found that transient electromagnetic impact causes the mechanical response with the obvious strain rate sensitivity, and complex variation in stress and strain states in the welded plate occurs due to combination action of electromagnetic force and welding residual stress. As a result, the incompatible degree of strain field, arising from welding thermal cycle, is reduced. The residual stresses also finally fall, although the flow stress rises during electromagnetic impact. The measurement results of microhardness also indicate that the plastic strain state in local weld region is indeed changed under electromagnetic impact. Finally, continuous electromagnetic impacts experiments are conducted, and results show that this approach is very successful for reducing welding residual stresses and distortion in welded thin plates, without any impairment of appearance and performance.
Low temperature exfoliation process in hydrogen-implanted germanium layers
Authors: Ferain I. P. , Byun K. Y. , Colinge C. A. , Brightup S. , Goorsky M. S.
Published: March 2010

The feasibility of transferring hydrogen-implanted germanium to silicon with a reduced thermal budget is demonstrated. Germanium samples were implanted with a splitting dose of 5×1016 H2+ cm−2 at 180 keV and a two-step anneal was performed. Surface roughness and x-ray diffraction pattern measurements, combined with cross-sectional TEM analysis of hydrogen-implanted germanium samples were carried out in order to understand the exfoliation mechanism as a function of the thermal budget. It is shown that the first anneal performed at low temperature (≤150 °C for 22 h) enhances the nucleation of hydrogen platelets significantly. The second anneal is performed at 300 °C for 5 min and is shown to complete the exfoliation process by triggering the formation of extended platelets. Two key results are highlighted: (i) in a reduced thermal budget approach, the transfer of hydrogen-implanted germanium is found to follow a mechanism similar to the transfer of hydrogen-implanted InP and GaAs, (ii) such a low thermal budget (<300 °C) is found to be suitable for directly bonded heterogeneous substrates, such as germanium bonded to silicon, where different thermal expansion coefficients are involved.
Angular and prism coupling refractive enhancement in dye solar cells
Authors: Dominici Lorenzo , Vesce Luigi , Colonna Daniele , Michelotti Francesco , Brown Thomas M. , Reale Andrea , Di Carlo Aldo
Published: March 2010

We quantify the strong dependence of photocurrent on the angle of incidence of light in a dye solar cell (DSC). Under laser illumination the photocurrent increases for large incidence angles. The enhancements are different upon using or not a coupling prism. They are explained with a model including three different angular factors. The observed enhancements up to 25% can be useful for evaluating novel designs of an efficient photon management in DSCs. Even an effective refractive index neff≈2.0 for the mesoporous titania/electrolyte phase was retrieved from the angle dependent photocurrent.
Isotopic effects on the thermal conductivity of graphene nanoribbons: Localization mechanism
Authors: Jiang Jin-Wu , Lan Jinghua , Wang Jian-Sheng , Li Baowen
Published: March 2010

Thermal conductivity of graphene nanoribbons (GNR) with length 106 Å and width 4.92 Å after isotopic doping is investigated by molecular dynamics with quantum correction. Two interesting phenomena are found, (1) isotopic doping reduces thermal conductivity effectively in low doping region, and the reduction slows down in high doping region, (2) thermal conductivity increases with increasing temperature in both pure and doped GNR, but the increasing behavior is much more slow in the doped GNR than that in pure ones. Further studies reveal that the physics of these two phenomena is related to the localized phonon modes, whose number increases quickly (slowly) with increasing isotopic doping in low (high) isotopic doping region.
Droop in InGaN light-emitting diodes: A differential carrier lifetime analysis
Authors: David Aurélien , Grundmann Michael J.
Published: March 2010

To investigate the variation in internal quantum efficiency in InGaN structures, we measure the differential carrier lifetime of an InGaN/GaN double-heterostructure light-emitting diode under varying electroluminescence injection conditions. By coupling this measurement to an internal quantum efficiency measurement, we determine the carrier density and the radiative and nonradiative contributions to the lifetime without making any assumptions on recombination processes. We find that droop is caused by a shortening of the nonradiative lifetime with current. The observed shortening of both radiative and nonradiative lifetimes with current is found to be in excellent agreement with an ABC model including phase-space filling.
Effect of nanoscale confinement on glass transition of polystyrene domains from self-assembly of block copolymers
Authors: Robertson C. G. , Hogan T. E. , Rackaitis M. , Puskas J. E. , Wang X.
Published: March 2010

The understanding of size-dependent properties is key to the implementation of nanotechnology. One controversial and unresolved topic is the influence of characteristic size on the glass transition temperature (Tg) for ultrathin films and other nanoscale geometries. We show that Tg does depend on size for polystyrene spherical domains with diameters from 20 to 70 nm which are formed from phase separation of diblock copolymers containing a poly(styrene-co-butadiene) soft block and a polystyrene hard block. A comparison of our data with published results on other block copolymer systems indicates that the size dependence of Tg is a consequence of diffuse interfaces and does not reflect an intrinsic size effect. This is supported by our measurements on 27 nm polystyrene domains in a styrene-isobutylene-styrene triblock copolymer which indicate only a small Tg depression (3 K) compared to bulk behavior. We expect no effect of size on Tg in the limit as the solubility parameters of the hard and soft blocks diverge from each other. This strongly segregated limiting behavior agrees with published data for dry and aqueous suspensions of small polystyrene spheres but is in sharp contrast to the strong influence of film thickness on Tg noted in the literature for free standing ultrathin polystyrene films.
Proof of concept of the quantum capacitance detector
Authors: Bueno J. , Shaw M. D. , Day P. K. , Echternach P. M.
Published: March 2010

We fabricated and tested a proof-of-concept quantum capacitance detector, a superconducting radiation detector described in a recent publication [Shaw et al., Phys. Rev. B 79, 144511 (2009)]. In this concept, quasiparticle tunneling in a single Cooper-pair box is used to measure the density of quasiparticles in a superconducting absorber. We measured and characterized the response of the device to electrical quasiparticle injection obtaining its sensitivity. Moreover, we have converted the sensitivity to electrical noise-equivalent power, which is in the 10−18 W/Hz1/2 range at loading powers between 10−15–10−16 W.
Quantum dynamics of the C(D1)+HD and C(D1)+n−D2 reactions on the ã A1′ and b̃ A1″ surfaces
Authors: Defazio Paolo , Gamallo Pablo , González Miguel , Akpinar Sinan , Bussery-Honvault Béatrice , Honvault Pascal , Petrongolo Carlo
Published: March 2010

We present the Born–Oppenheimer, quantum dynamics of the reactions C(D1)+HD andC(D1)+n−D2 on the uncoupled potential energy surfaces ã A1′ and b̃ A1″, considering the Coriolis interactions and the nuclear-spin statistics. Using the real wavepacket method, we obtain initial-state-resolved probabilities, cross sections, isotopic branching ratios, and rate constants. Similarly to the C+n−H2 reaction, the probabilities present many ã A1′ or few b̃ A1″ sharp resonances, and the cross sections are very large at small collision energies and decrease at higher energies. At any initial condition, the C+HD reaction gives preferentially the CD+H products. Thermal cross sections, isotopic branching ratios, and rate constant k vary slightly with temperature and agree very well with the experimental values. At 300 K, we obtain for the various products k(CH+H)=(2.45±0.08)×10−10, k(CD+H)=(1.19±0.04)×10−10, k(CH+D)=(0.71±0.02)×10−10, k(CD+D)=(1.59±0.05)×10−10 cm3 s−1, and k(CD+H)/k(CH+D)=1.68±0.01. The b̃ A1″ contribution to cross sections and rate constants is always large, up to a maximum value of 62% for a rotationally resolved C+D2 rate constant. The upper b̃ A1″ state is thus quite important in the C(D1) collision with H2 and its deuterated isotopes, as the agreement between theory and experiment shows.