bluuebunny/crossref_metadata_2025 huggingface dataset:
Training Remembering
Authors: Nachbar Martin
Published: August 2012

I would like to start with an anecdote. When my daughter was five weeks old, she had a stiff neck, and almost couldn't turn her head at all to her left. So, my wife and I went to see an osteopath. The doctor's practice was a family business: father and son—both of them neurologists and chiropractors—work on scores of bodies day by day, manipulating and treating them. The father is also an osteopath; the son is still learning to become one. We saw the son. He treated our daughter who screamed and turned red and in turn got her back straightened, but not quite as straight as it should have been. So, the son got his father, who showed him another trick or two, explained them to his son and to us, and left again. Our daughter was now really aligned, and the son said: “Well, this is how it goes. I am still learning. While I push and pull and push and pull, my father just needs one grip and the work is done.” Our daughter sneezed. “Do we need to come back?” we asked. “No, one time is sufficient. Good-bye,” he replied and left for his next patient.
MARKET LIMITS AND THEIR LIMITS
Authors: Keat Russell
Published: August 2012

Although the market is widely regarded as the best way of organizing complex modern economies, many who take this view also believe that certain limits should be placed on its range of application. Despite its many virtues, there are some things that should not be provided through the market, or whose sale and purchase is morally problematic. But on what basis can and should such judgements be made? Debra Satz, in this important and illuminating book, provides us with a philosophical theory that specifies the relevant considerations in making these judgements, and hence in determining the proper limits of the market.
EVALUATING LIFE OR DEATH PROSPECTS
Authors: Bovens Luc , Fleurbaey Marc
Published: August 2012

We consider a special set of risky prospects in which the outcomes are either life or death (or, more generally, binary utilities). There are various alternatives to the utilitarian objective of minimizing the expected loss of lives in such prospects. We start off with the two-person case with independent risks and construct taxonomies of ex ante and ex post evaluations for such prospects. We examine the relationship between the ex ante and the ex post in this restrictive framework: There are more possibilities to respect ex ante and ex post objectives simultaneously than in the general framework, i.e. without the restriction to binary utilities (cf. Harsanyi's aggregation theorem). We extend our results to n persons and to dependent risks. We study optimal strategies for allocating risk reductions given different objectives. We place our results against the backdrop of various pro-poorly off (or prioritarian) value functions (Diamond 1967; Rabinowicz 2002; Fleurbaey 2010) for the evaluation of risky prospects.
Patterns of growth, recruitment, mortality and biomass across an altitudinal gradient in a neotropical montane forest, Dominican Republic
Authors: Sherman Ruth E. , Fahey Timothy J. , Martin Patrick H. , Battles John J.
Published: August 2012

We examined stand dynamics and biomass along an altitudinal gradient in a tropical montane forest (TMF) in the disturbance-prone Cordillera Central, Dominican Republic. We tested the general hypothesis that chronic disturbance by fire, wind, floods and landslides results in a landscape of relatively low above-ground biomass with high rates of mortality, recruitment and growth as compared with other TMFs. We also expected above-ground biomass to decrease with altitude in part due to declines in growth and increased biomass losses from mortality with increasing altitude. We resurveyed 75 0.1-ha plots distributed across the altitudinal gradient (1100–3100 m asl) 8 y after they were established. Our observations provided mixed evidence on these hypotheses. Turnover rates were high (> 2% y−1) and significantly greater on windward slopes. Above-ground biomass (mean = 306 Mg ha−1, 95% CI = 193–456 Mg ha−1) was highly variable but comparable to other TMFs. Altitudinal patterns of declining biomass and above-ground growth matched observations for other TMFs, whereas mortality and recruitment exhibited no altitudinal trends. More quantitative studies in a variety of TMF settings are needed to better understand how natural disturbance, complex environmental gradients and species dynamics interact to regulate carbon storage, sequestration and turnover across altitudinal gradients in TMFs.
Determinants of rain-forest floristic variation on an altitudinal gradient in southern Costa Rica
Authors: Chain-Guadarrama Adina , Finegan Bryan , Vilchez Sergio , Casanoves Fernando
Published: August 2012

The degree to which geographical location rather than environment affects the maintenance of high tropical forest beta diversity on altitudinal gradients is not well understood. Forest composition and its relationship to climate, soil, altitude and geographical distance were determined across an 1114-km2 landscape in south Pacific Costa Rica spanning an altitudinal gradient (0–1500 m asl). In 37 0.25-ha plots, > 200 species of dicot trees (≥ 30 cm dbh) and canopy palms (≥ 10 cm dbh) were found. Ordination analysis showed strong species composition patterns related to altitude; plot coordinates on the main axis showed negative correlations to the abundance of lowland-forest species Iriartea deltoidea (r = −0.54) and Brosimum utile (r = −0.65), and positive correlations to higher-altitude species Alchornea glandulosa (r = 0.63), Quercus sp. (r = 0.50) and Ocotea sp. 2 (r = 0.48). Mantel correlations, correlograms and variation partitioning analysis of relationships between floristic composition and spatial and environmental factors indicated that spatial location of the plots – potentially, dispersal limitation – was the single most important (R2adj = 0.149) driver of beta diversity, but that environmental heterogeneity also plays an important role. In particular, palm species turnover was strongly related to soil chemical properties. The effects of dispersal limitation on floristic assembly could determine the future distribution of plant communities as a result of climate change.
Aviation Approach Charts in an iPad®World
Authors: Tuccio William A.
Published: August 2012

The process used to create charted depictions of aviation instrument approach procedures in the United States is examined. The rapid growth of iPad®-like mobile technologies is discussed relative to the historical context of chart implementation. Notional new methods of electronic chart generation are introduced, demonstrating both the functional possibilities and concerns not directly addressed by existing regulation for private aircraft operators. These concerns suggest a ‘yin-yang’ of the stifling of innovation versus the creation of latent safety hazards. The article concludes by recommending regulatory oversight review of approach chart implementation. A glossary of terms is included at the end of this paper. The facts, analysis, and opinions offered in this article represent an independent effort of the author and do not reflect the opinions of any academic institution or government agency. The author also has a limited financial interest in certain iOS®applications.
La morphologisation dequi
Authors: FONSECA-GREBER BONNIE
Published: August 2012

Cette étude présente les résultats d'une analyse d'un corpus de français romand conversationnel et démontre, par le biais d'une série de tests de morphologisation (Schwegler, 1990) que l'ancien pronom relatif-interrogatifqui1s'est séparé en deux formes distinctes sur les plans sémantique et morphosyntaxique: (1) un pronom interrogatif autonome,qui2et (2) un préfixe relatif flexionnel,qui-qui s'ajoute au paradigme des préfixes préverbaux. La relation entrequi2etqui-est du même genre que celui déjà attesté pour la relation entre les préfixes personnels flexionnelsje,tu,il/elle, etc., et les pronoms sujets facultatifs,moi,toi,lui/elle, etc. Conformes aux processus de la grammaticalisation et propulsés par la fréquence des tournures enqui-Vdans les constructions clivées, ces résultats suggèrent en outre un changement typologique et une diglossie naissante entre l'oral spontané (préfixal) et l'écrit classique (suffixal), au moins sur le plan morphosyntaxique. Le présent article a pour but de déterminer le statut dequidans le français romand conversationnel, relatif à son stade de morphologisation par rapport aux préfixes personnels flexionnels ainsi qu'à la question d'une diglossie naissante entre l'oral et l'écrit.
Keep Up the Pace: Declines in Simple Repetitive Timing Differentiate Healthy Aging from the Earliest Stages of Alzheimer's Disease
Authors: Bangert Ashley S. , Balota David A.
Published: August 2012

The current study examined whether healthy older adults (OA) and individuals at the earliest stages of dementia of the Alzheimer's type (DAT) differ from younger adults (YA) and from each other on a simple, extended continuous tapping task using intervals (500 ms, 1000 ms, and 1500 ms) thought to differentially engage attentional control systems. OA groups sped up their tapping at the slowest target rate compared to the YA; this pattern was magnified in the early stage DAT groups. Performance variability appeared especially sensitive to DAT-related changes, as reliable differences between healthy OA and very mild DAT individuals emerged for multiple tap rates. These differences are proposed to result from breakdowns in attentional control that disrupt error-correction processes and the ability to resolve discrepancies between internally-generated temporal expectancies and the external temporal demands of the repetitive timing task. (JINS, 2012,18, 1–12)
OPTIMAL MONETARY AND FISCAL POLICIES IN A SEARCH-THEORETIC MODEL OF MONEY AND UNEMPLOYMENT
Authors: Gomis-Porqueras Pedro , Julien Benoît , Wang Chengsi
Published: August 2012

In this paper we study optimal policies in an environment where search frictions both in labor and goods markets give rise to unemployment and fiat money, as in Berentsen, Menzio, and Wright (American Economic Review, 2011). The underlying frictions that give rise to endogenous unemployment and fiat money also result in inefficient outcomes. Here we show that efficiency can be restored whenever lump sum monetary transfers are possible and a decentralized production subsidy financed by money printing and a vacancy subsidy financed by a dividend tax exist. This is the case even when the Hosios and Friedman rules do not hold.
Human Rights and Social Policy: Challenges and Opportunities for Social Research and Its Use as Evidence in the Protection and Promotion of Human Rights in Scotland
Authors: Hosie Alison , Lamb Michele
Published: August 2012

This article is the result of a joint project conducted by University of Roehampton and the Scottish Human Rights Commission, undertaken between March 2010 and April 2011. The article describes the methodological challenges encountered in the data collection phase of the project and addresses the conceptual relationship between social science and human rights research. It argues that social policy and social sciences research has an important contribution to make in the promotion and protection of human rights and demonstrates the use of the Research in Scotland's National Action Plan for Human Rights, being prepared by the Commission during 2012–13.
Early Herschel results on evolved stars and planetary nebulae
Authors: García-Lario Pedro
Published: August 2012

Herschel, an ESA space observatory equipped with science instruments provided by European-led Principal Investigator consortia with important participation from NASA, was launched on 14 May 2009. With its 3.5m diameter primary mirror, Herschel is the largest space telescope ever launched into space, and carries onboard three science instruments, whose focal plane units are cryogenically cooled inside a superfluid helium cryostat. The PACS and SPIRE instruments provide broadband imaging photometry in six bands centred at 75, 100, 160, 250, 350, and 500 microns and imaging spectroscopy over the range 55–672 microns. The HIFI instrument provides very high-resolution heterodyne spectroscopy over the ranges 157–212 and 240–625 microns. The results obtained already in the first year and a half of routine science operations demonstrate that Herschel will have strong impact on all research fields, from Solar System studies to the area of Cosmology, from the analysis of star formation to the mysteries of galaxy formation. In this talk I will review the Herschel highlights in the area of evolved stars in general and of planetary nebulae more in particular, resulting from observations performed with the three instruments onboard Herschel since launch. This will be exemplified by a few observational results, just the tip of the iceberg of what is yet to come in the remaining year and a half of science operations.
Planetary nebulae: 20 years of Hubble inquiry
Authors: Balick Bruce
Published: August 2012

The Hubble Space Telescope has served the critical roles of microscope and movie camera in the past 20 years of research on planetary nebulae (“PNe”). We have glimpsed the details of the evolving structures of neutral and ionized post-AGB objects, built ingenious heuristic models that mimic these structures, and constrained most of the relevant physical processes with careful observations and interpretation. We have searched for close physical binary stars with spatial resolution ~50 AU at 1 AU, located jets emerging from the nucleus at speeds up to 2000 km s−1 and matched newly discovered molecular and X-ray emission regions to physical substructures in order to better understand how stellar winds and ionizing radiation interact to form the lovely symmetries that are observed. Ultraviolet spectra of CNO in PNe help to uncover how stars process deep inside AGB stars with unstable nuclear burning zones. HST broadband imaging has been at the forefront of uncovering surprisingly complex wind morphologies produced at the tip of the AGB, and has led to an increasing realization of the potentially vital roles of close binary stars and emerging magnetic fields in shaping stellar winds.
Morphological classification of post-AGB stars
Authors: Manchado Arturo , García-Hernández D. Anibal , Villaver Eva , de Massas Jean Guironnet
Published: August 2012

We present a complete study of the morphology of post-Asymptotic Giant Branch (post-AGB) stars. The post-AGB stage is a very short evolutionary phase between the end of the AGB and the beginning of the Planetary Nebula (PN) stage (between 100 and 10,000 yrs). Post-AGB stars do not show variability and are not hot enough to fully ionize the hydrogen envelope. We have defined the end of the post-AGB phase and the beginning of the PN phase when the star has a temperature of 30000 K. Post-AGB stars have a circumstellar shell that is illuminated by the central stars or partially ionized. However, this circumstellar shell is too small to be resolved by ground-based observations. Thus, we have used the Hubble Space Telescope (HST) database to resolve these shells. 117 post-AGBs were found in this database. Here we present the preliminary results on their morphological classification and the correlation with the galactic latitude. Our preliminary results show that 38% of the sample are stellar-like (S), 31% bipolar (B), 12% multipolar (M) and 19% elliptical (E).
Dynamical modeling and the interactions with the ISM
Authors: Steffen Wolfgang
Published: August 2012

This paper is a review of some of the recent modeling efforts to improve our understanding of structure formation and evolution of planetary nebulae including their interaction with the interstellar medium. New propositions have been made for the formation mechanism of multi-polar PNe and PPNe. These mechanisms are based on the central engine with interacting binary stars or hole producing instabilities in expanding shock waves leading to illumination effects from the central star that change the appearance of the nebula. Furthermore, there has been a lot of progress in the observation and 3D modeling of the kinematics, which is key to the understanding of the dynamics. Extensive observational catalogs are coming online for the kinematics, as well as some very detailed proper motion measurements have been made. New techniques for morpho–kinematic 3D modeling help to make the interpretation of kinematic data more reliable and detailed. In addition to individual pointed observations, new surveys have lead to the discovery of many PNe that show clear signs of interaction with the interstellar medium. Systematic hydrodynamic models of the interaction have produced a general scheme for the observed structure that results from the interaction of an evolving planetary nebula with the ISM. Detailed modeling of the dust-gas dynamics during the interaction with the ISM have produced interesting predictions for future IR observations. Detailed models were worked out for the structure of the bowshock and tail of Mira that was recently discovered in the UV.
Galactic Bulge PNe: Carbon molecules in oxygen-rich environments
Authors: Guzmán-Ramírez Lizette , Zijlstra Albert , Níchuimín Roisin , Gesicki Krzysztof , Lagadec Eric , Millar Tom J. , Woods Paul M.
Published: August 2012

Galactic bulge planetary nebulae show evidence of mixed chemistry with emission from both silicate dust and PAHs. This mixed chemistry is unlikely to be related to carbon dredge up, as third dredge-up is not expected to occur in the low mass bulge stars. We show that the phenomenon is widespread, and is seen in 30 nebulae out of our sample of 40. A strong correlation is found between strength of the PAH bands and morphology, in particular, the presence of a dense torus. A chemical model is presented which shows that hydrocarbon chains can form within oxygen-rich gas through gas-phase chemical reactions. We conclude that the mixed chemistry phenomenon occurring in the galactic bulge planetary nebulae is best explained through hydrocarbon chemistry in an UV-irradiated, dense torus.
The impact of future space observatories on planetary nebula research
Authors: Barlow Michael J.
Published: August 2012

A comparison between the past four decades of astrophysical space missions and those expected to be launched over the next decade shows a marked decrease in numbers. However, missions such as Gaia and the JWST are expected to have a major impact on planetary nebula research. The capabilities of these and other anticipated space missions are discussed.
Trigonometric parallax of the protoplanetary nebula OH 231.8+4.2
Authors: Choi Yoon Kyung , Brunthaler Andreas , Menten Karl M. , Reid Mark J.
Published: August 2012

We report trigonometric parallx measurements for H2O masers around the protoplanetary nebula OH 231.8+4.2 carried out with the Very Long Baseline Array. Based on astrometric monitoring for 1 year, we measured a trigonometric parallax of 0.89 ± 0.04 mas, corresponding to a distance of 1.12+0.05−0.05 kpc. This is the most accurate distance to OH 231.8+4.2, and the first one based on an annual parallax measurement. The distribution and internal motions of the H2O masers are consistent with the bipolar outflow suggested in literatures.
The ionization state of the halo planetary nebula NGC 2438
Authors: Dalnodar Silvia
Published: August 2012

NGC 2438 is a classical multiple shell or halo planetary nebula (PN). Its central star and the main nebula are well studied. Also it was target of various hydrodynamic simulations (Corradi et al. 2000). This initiated a discussion whether the haloes are mainly containing recombined gas (Schönberner et al. 2002), or if they are still ionized (Armsdorfer et al. 2003). An analysis of narrow-band images and long slit spectra at multiple slit positions was done to obtain a deeper look on morphological details and the properties of the outer shell and halo. For this work there was data available from ESO (direct imaging and long slit spectroscopy) and from SAAO (spectroscopic observations using a small slit, scanning over the whole nebula). Using temperature measurements from emission lines resulted in an electron temperature which clearly indicates a fully ionized stage. Additionally measurements of the electron density suggest a variation of the filling factor.
Very deep spectroscopy of the bright Saturn nebula NGC 7009: The optical recombination spectrum and new effective recombination coefficients
Authors: Fang Xuan , Liu Xiao-Wei , Storey Peter J.
Published: August 2012

We present very deep spectroscopic observations of the rich optical recombination line (ORL) spectrum of the bright Saturn nebula NGC 7009. Detailed spectral analyses, combined with systematic emission line identifications, in the whole optical range (3040–11 000 Å) give more than 1000 emission lines, over 80% of which are ORLs. New calculations of the N ii effective recombination coefficients in intermediate coupling scheme are carried out. These N ii atomic data, together with the most recent O ii and Ne ii effective recombination coefficients, are utilized in the spectral analyses of NGC 7009. Departure from LS coupling is noticed. Agreement is found between the observed and predicted relative intensities of ORLs. The elemental abundances of C, N, O, and Ne deduced from ORLs are systematically higher than those from collisionally excited lines (CELs) by a factor of 5–7.
Polarized radiative transfer equation in some nontrivial coordinate systems
Authors: Freimanis Juris
Published: August 2012

Explicit expressions for the differential operator of stationary quasi-monochromatic polarized radiative transfer equation in Euclidean space with piecewise homogeneous real part of the effective refractive index are obtained in circular cylindrical, prolate spheroidal, elliptic conical, classic toroidal and simple toroidal coordinate system.
Newly discovered halos and outer features around southern planetary nebulae
Authors: Frew David J. , Bojičić Ivan S. , Parker Quentin A.
Published: August 2012

We have used the SuperCOSMOS Hα Survey to look for faint outer structures such as halos, ansae and jets around known planetary nebulae across 4000 square degrees of the southern Milky Way. Our search will contribute to a more accurate census of these features in the Galactic PN population. Candidate common-envelope PNe have also been identified on the basis of their microstructures. We also intend to determine more reliable distances for these PNe, which should allow a much better statistical basis for the post-AGB total mass budget. Our survey offers fresh scope to address this important issue.
A Cat's Eye view of the Eskimo from Saturn
Authors: García-Díaz Maria-Teresa , López Jose-Alberto , Steffen Wofgang , Richer Michael G. , Riesgo Hortensia
Published: August 2012

The 3-D and kinematic structure of the Eskimo nebula, NGC 2392, has been notoriously difficult to interpret given its complex morphology, multiple kinematic components and its nearly pole-on orientation along the line of sight. Here we present the most comprehensive high resolution spectroscopic mapping of the Eskimo planetary nebula to date. The data consist of 21 spatially resolved, long-slit echelle spectra tightly spaced over the Eskimo and along its bipolar jets. This data set allowed us to construct a velocity-resolved [NII] channel map of the nebula with a resolution of 10 km/s that disentagles the differente kinematic components of the nebula and reveals clearly for the first time the kinematic expansion pattern for each of the components. The spectroscopic information is combined with a HST image to construct the first detailed three dimensional model of the Eskimo with the code SHAPE. With this model we demostrate that the Eskimo is nearly a twin to the Saturn nebula, but rotated 90° to the line sight. Furthermore, we show that the main characteristics of our model apply to the general properties of the group of elliptical planetary nebulae with ansae, once the orientation is considered.
A sample of new planetary nebulae in the IPHAS and DSH catalogue
Authors: Hsia Chih-Hao , Kwok Sun
Published: August 2012

We report the optical and infrared studies of a sample of five new planetary nebulae (PNe) in the IPHAS and DSH catalogues. The PN status of these objects was confirmed by optical narrow-band imaging and low resolution spectroscopy. One object (IPHASX J195248.8+255359) is found to be a bipolar PN with faint Hα lobes and a bright core in [O iii].
On the magnetic field of OH 231.8+4.2
Authors: Leal-Ferreira Marcelo L. , Vlemmings Wouter H. T. , Diamond Philip J. , Kemball Athol , Amiri Nikta , Desmurs Jean-François
Published: August 2012

During the transition from an AGB star to a planetary nebula, a large number of low/intermediate initial mass stars loses its spherical symmetry. The process responsible for that change of morphology is, so far, not well understood. The candidates responsible for shaping these objects are (i) a companion to the star (binary/heavy planet) and its tidal forces, (ii) disk interaction and (iii) magnetic fields - or a combination of these. In particular a binary induced magnetic field is a promising option. To study this we observed the polarization of H2O masers in the known binary pre-Planetary Nebula (pPN) OH231.8+4.2. Our results show a magnetic field B|| of ~45 mG is present in the H2O maser region of this pPN.
1D radiative transfer models of 21 and 30 μm emission features in proto-planetary nebulae
Authors: Muthumariappan Chinnathambi , Reddy Bacham E.
Published: August 2012

Spectral energy distributions of six proto-planetary nebulae showing 21 and 30μ features were fit with models obtained from 1D radiative transfer code, taking FeO and MgS respectively are the carriers of the features. Atomic abundances of these carrier materials were derived and they are lower or comparable to their stellar photospheric values. This stregthens the possibility of these materials to become the carriers of their respective features.
Extending the RP survey to the outer LMC
Authors: Reid Warren , Parker Quentin A.
Published: August 2012

We are extending our search for faint PNe in the LMC to include the outer 56 deg2 area not covered in the original UKST survey of the central 25eg2 region. Candidate PNe have been selected using the Magellanic Cloud Emission Line Survey (MCELS) and the first round of observations has yielded 93 new LMC PNe while confirming the 102 previously known PNe in the outer LMC. We plan to continue our spectroscopic object identification program until we cover all our remaining candidates in the survey area. These observations, providing medium and high resolution spectra from λ3650Å to λ6900Å will additionally be used to measure fluxes for a series of research projects including luminosity functions, abundances and LMC kinematics.
Chlorine and sulfur in nearby planetary nebulae and H II regions
Authors: Rodríguez Mónica , Delgado-Inglada Gloria
Published: August 2012

We derive the chlorine abundances in a sample of nearby planetary nebulae (PNe) and H II regions that have some of the best available spectra. We use a nearly homogeneous procedure to derive the abundance in each object and find that the Cl/H abundance ratio shows similar values in H II regions and PNe. This supports our previous interpretation that the underabundance we found for oxygen in the H II regions is due to the depletion of their oxygen atoms into organic refractory dust components. For other elements, the bias introduced by ionization correction factors in their derived abundances can be very important, as we illustrate here for sulfur using photoionization models. Even for low-ionization PNe, the derived sulfur abundances can be lower than the real ones by up to 0.3 dex, and the differences found with the abundances derived for H II regions that have similar S/H can reach 0.4 dex.
NGC 7027: Probing the kinematics and excitation conditions of the warm molecular gas
Authors: Santander-García Miguel , Bujarrabal Valentín , Alcolea Javier
Published: August 2012

Tracking the mass-loss history of planetary nebulae (PNe) by means of molecular emission lines (mainly mm and sub-mm ranges) is fundamental to gain insight into the mechanism of nebular shaping. This is particularly important in cases such as NGC 7027, where most of the nebula is constituted by molecular gas (85% of a total of 1.4 M⊙, see Fong et al. 2001).

To this aim, Herschel/HIFI provides an invaluable tool to probe warm molecular gas (~50-1000 K). It produces 1-D, high resolution spectra of the whole nebula (convolved with the telescope beam) in high-excitation molecular transitions (e.g. CO J=6–5, 10–9 and 16–15). Although the morphological information is therefore lost, the kinematics and the excitation conditions can be studied with unprecedented detail (see (see Bujarrabal et al. 2011).).

We have developed a code, shapemol, which, used along the existing SHAPE software (Steffen et al. 2010), implements spatiokinematical modeling with accurate non-LTE calculations of line excitation and radiative transfer in molecular species. The high quality of the data, together with this code, have allowed us to study, for the first time, the kinematics and excitation conditions of the warm gas of a PN with such a high-excitation.
Advances in atomic data for neutron-capture elements
Authors: Sterling Nicholas C. , Witthoeft Michael C. , Esteves David A. , Stancil Phillip C. , Kilcoyne A. L. David , Bilodeau Rene C. , Aguilar Alejandro
Published: August 2012

Neutron(n)-capture elements (atomic number Z > 30), which can be produced in planetary nebula (PN) progenitor stars via s-process nucleosynthesis, have been detected in nearly 100 PNe. This demonstrates that nebular spectroscopy is a potentially powerful tool for studying the production and chemical evolution of trans-iron elements. However, significant challenges must be addressed before this goal can be achieved. One of the most substantial hurdles is the lack of atomic data for n-capture elements, particularly that needed to solve for their ionization equilibrium (and hence to convert ionic abundances to elemental abundances). To address this need, we have computed photoionization cross sections and radiative and dielectronic recombination rate coefficients for the first six ions of Se and Kr. The calculations were benchmarked against experimental photoionization cross section measurements. In addition, we computed charge transfer (CT) rate coefficients for ions of six n-capture elements. These efforts will enable the accurate determination of nebular Se and Kr abundances, allowing robust investigations of s-process enrichments in PNe.
The second release of the Toruń catalogue of Galactic post-AGB objects: New classification scheme
Authors: Szczerba Ryszard , Siódmiak Natasza , Stasińska Grazyna , Borkowski Jozef , García-Lario Pedro , Suárez Olga , Hajduk Marcin , García-Hernández D. Anibal
Published: August 2012

The investigation of post-AGB objects (proto-planetary nebulae) is very important from the standpoint of physical and chemical changes occurring during the late stages of stellar evolution. The Toruń catalogue of Galactic post-AGB and related objects is an evolutive catalogue containing astrometric, photometric and spectroscopic data as well as HST images for all known post-AGB objects and candidates in our Galaxy. This free-access catalogue can serve as an ideal tool to study different groups of post-AGB objects, especially due to the fact that all information is gathered in one place. The second release of our catalogue introduces a simple classification scheme of post-AGB objects and includes a significant number of new objects, photometric data, spectra and images. Here, using objects from the catalogue we consider the problem of the termination of the AGB phase.
Weak emission line central stars of planetary nebulae
Authors: Todt Helga , Peña Miriam , Zühlke Julia , Oskinova Lida , Hamann Wolf-Rainer , Gräfener Götz
Published: August 2012

To understand the evolution and morphology of planetary nebulae, a detailed knowledge of their central stars is required. Central stars that exhibit emission lines in their spectra, indicating stellar mass-loss allow to study the evolution of planetary nebulae in action. Emission line central stars constitute about 10 % of all central stars. Half of them are practically hydrogen-free Wolf-Rayet type central stars of the carbon sequence, [WC], that show strong emission lines of carbon and oxygen in their spectra. In this contribution we address the weak emission-lines central stars (wels). These stars are poorly analyzed and their hydrogen content is mostly unknown. We obtained optical spectra, that include the important Balmer lines of hydrogen, for four weak emission line central stars. We present the results of our analysis, provide spectral classification and discuss possible explanations for their formation and evolution.
Expansion velocities of selected PNe
Authors: Torres-Peimbert Silvia , Arrieta Anabel , Georgiev Leonid
Published: August 2012

In order to clarify the observed relation between the expansion velocity measured from lines of different ions and their ionization potential, we present kinematical data for several objects. We have measured radial velocities on ESO UVES high dispersion spectra to compare expansion velocities for a set of planetary nebulae.
Dust distribution in circumstellar shells
Authors: van Marle Allard-Jan , Meliani Zakaria , Keppens Rony , Decin Leen
Published: August 2012

We present numerical simulations of the hydrodynamical interactions that produce circumstellar shells. These simulations include several scenarios, such as wind-wind interaction and wind-ISM collisions. In our calculations we have taken into account the presence of dust in the stellar wind. Our results show that, while small dust grains tend to be strongly coupled to the gas, large dust grains are only weakly coupled. As a result, the distribution of the large dust grains is not representative of the gas distribution. Combining these results with observations may give us a new way of validating hydrodynamical models of the circumstellar medium.
Maser kinematics and infrared properties of the water fountain IRAS 18286–0959
Authors: Yung Bosco H. K. , Nakashima Jun-ichi , Imai Hiroshi , Deguchi Shuji , Diamond Philip J. , Kwok Sun
Published: August 2012

A “water fountain” is a transitional object between an AGB star and a PN. The VLBA observations of 22.2 GHz water maser emission reveal a “double-helix” outflow pattern from one of the water fountains, IRAS 18286–0959. The pattern is reasonably fit by a model consisting of two precessing jets. We propose that the two jets observed are a result of a single driving source with a significant proper motion. Using data from the AKARI catalogs, we also found that water fountains might have their own IR colors which are affected by the 9.7 μm silicate feature and the optical thickness of stellar envelopes. The colors could serve as new criteria for searching this type of rare objects.
Anomalous Diffusion of Brain Metabolites Evidenced by Diffusion-Weighted Magnetic Resonance Spectroscopy in Vivo
Authors: Marchadour Charlotte , Brouillet Emmanuel , Hantraye Philippe , Lebon Vincent , Valette Julien
Published: August 2012

Translational displacement of molecules within cells is a key process in cellular biology. Molecular motion potentially depends on many factors, including active transport, cytosol viscosity and molecular crowding, tortuosity resulting from cytoskeleton and organelles, and restriction barriers. However, the relative contribution of these factors to molecular motion in the cytoplasm remains poorly understood. In this work, we designed an original diffusion-weighted magnetic resonance spectroscopy strategy to probe molecular motion at subcellular scales in vivo. This led to the first observation of anomalous diffusion, that is, dependence of the apparent diffusion coefficient (ADC) on the diffusion time, for endogenous intracellular metabolites in the brain. The observed increase of the ADC at short diffusion time yields evidence that metabolite motion is characteristic of hindered random diffusion rather than active transport, for time scales up to the dozen milliseconds. Armed with this knowledge, data modeling based on geometrically constrained diffusion was performed. Results suggest that metabolite diffusion occurs in a low-viscosity cytosol hindered by ~2- μm structures, which is consistent with known intracellular organization.
Statins and Cerebral Hemodynamics
Authors: Giannopoulos Sotirios , Katsanos Aristeidis H , Tsivgoulis Georgios , Marshall Randolph S
Published: August 2012

HMG-CoA reductase inhibitors (statins) are associated with improved stroke outcome. This observation has been attributed in part to the palliative effect of statins on cerebral hemodynamics and cerebral auto regulation (CA), which are mediated mainly through the upregulation of endothelium nitric oxide synthase (eNOS). Several animal studies indicate that statin pretreatment enhances cerebral blood flow after ischemic stroke, although this finding is not further supported in clinical settings. Cerebral vasomotor reactivity, however, is significantly improved after long-term statin administration in most patients with severe small vessel disease, aneurysmal subarachnoid hemorrhage, or impaired baseline CA.
αCaMKII is Differentially Regulated in Brain Regions that Exhibit Differing Sensitivities to Ischemia and Excitotoxicity
Authors: Skelding Kathryn A , Spratt Neil J , Fluechter Lisa , Dickson Phillip W , Rostas John AP
Published: August 2012

Different brain regions exhibit differing sensitivities to ischemia/excitotoxicity. Whether these differences are due to perfusion or intrinsic factors has not been established. Herein, we found no apparent association between sensitivity to ischemia/excitotoxicity and the level of expression or basal phosphorylation of calcium/calmodulin-stimulated protein kinase II (αCaMKII) or glutamate receptors. However, we demonstrated significant differences in CaMKII-mediated responses after ischemia/excitotoxic stimulation in striatum and cortex. In vivo ischemia and in vitro excitotoxic stimulation produced more rapid phosphorylation of Thr253-αCaMKII in striatum compared with cortex, but equal rates of Thr286-αCaMKII phosphorylation. Phosphorylation by CaMKII of Ser831-GluA1 and Ser1303-GluN2B occurred more rapidly in striatum than in cortex after either stimulus. The differences between brain regions in CaMKII activation and its effects were not accounted for by differences in the expression of αCaMKII, glutamate receptors, or density of synapses. These results implicate intrinsic tissue differences in Thr253-αCaMKII phosphorylation in the differential sensitivities of brain regions to ischemia/excitotoxicity.
Grp1‐associated scaffold protein (GRASP) is a regulator of the ADP ribosylation factor 6 (Arf6)‐dependent membrane trafficking pathway
Authors: Venkataraman Anand , Nevrivy Daniel J. , Filtz Theresa M. , Leid Mark
Published: August 2012

GRASP interacts with Grp1 (general receptor for phosphoinositides 1; cytohesin 3), which catalyses nucleotide exchange on and activation of Arf6 (ADP‐ribosylation factor‐6). Arf6 is a low‐molecular‐mass GTPase that regulates key aspects of endocytic recycling pathways. Overexpressed GRASP accumulated in the juxtanuclear ERC (endocytic recycling compartment). GRASP co‐localized with a constitutively inactive mutant of Arf6 in the ERC such that it was reversed by expression of wild‐type Grp1. Co‐expression of GRASP and Grp1 promoted membrane ruffling, a cellular hallmark of Arf6 activation. GRASP accumulation in ERC was found to block recycling of the MHC‐I (major histocompatibility complex‐I), which is trafficked by the Arf6‐dependent pathway. In contrast, overexpression of GRASP had no effect on the recycling of transferrin receptors, which are trafficked by a clathrin‐dependent pathway. The findings suggest that GRASP regulates the non‐clathrin/Arf6‐dependent, plasma membrane recycling and signalling pathways.
An RF-powered micro-reactor for the detection of astrobiological target molecules on planetary bodies
Authors: Scott Valerie J. , Tse Margaret , Shearn Michael J. , Siegel Peter H. , Amashukeli Xenia
Published: August 2012

We describe a sample-processing micro-reactor that utilizes 60 GHz RF radiation with approximately 730 mW of output power. The instrument design and performance characterization are described and then illustrated with modeling and experimental studies. The micro-reactor's efficiency on affecting hydrolysis of chemical bonds similar to those within large complex molecules was demonstrated: a disaccharide—sucrose—was hydrolyzed completely under micro-reactor conditions. The products of the micro-reactor-facilitated hydrolysis were analyzed using mass spectroscopy and proton nuclear magnetic resonance analytical techniques.
Magneto-optical spectrum of Mn-doped ZnO nanorods
Authors: Xiong Wen
Published: August 2012

Based on the framework of the effective-mass theory, the electronic structure of ZnO nanorods doped with manganese ions in the magnetic field is calculated by the Bessel function expanding method; the conduction and valence subbands are found to be non-degenerate in ZnO nanorods doped with manganese ions. The 10 lowest possible transitions are presented and the optical circularly polarized properties of each transition are also labeled. Through the analysis, the order of the valence subbands will change when the concentration of manganese ions varies, while the optical circularly polarized properties of the lowest transitions do not change when the magnetic field and the concentration of manganese ions increase. Meanwhile, each of the radiative intensities will increase with the increase of the wave vector.
Intrinsic defect in BiNbO4: A density functional theory study
Authors: Lai Kangrong , Zhu Yingtao , Dai Ying , Huang Baibiao
Published: August 2012

Formation energies, transition energy levels, and electronic properties of various intrinsic defects in BiNbO4 systems are studied based on the first-principles density-functional theory. Our results indicate that the acceptor defects form easier than donor defects under O rich condition, while it is opposite under Bi rich condition. Under O-rich condition, Bi vacancies (Bivac) leading to p-type conductivity are the dominant intrinsic defects, whereas O vacancies (Ovac) inducing moderate n-type conductivity are the dominant intrinsic defects under Bi-rich condition. Among these intrinsic defects, Ovac is a deep donor; to the contrary, Bivac is found to be a shallow acceptor which is benefit to the separation and migration of the photogenerated carriers. Consequently, the BiNbO4 with Bivac under O-rich growth condition should be of better photocatalytic performance.
Tailoring the FeRh magnetostructural response with Au diffusion
Authors: Loving M. , de Vries M. A. , Jimenez-Villacorta F. , Le Graët C. , Liu X. , Fan R. , Langridge S. , Heiman D. , Marrows C. H. , Lewis L. H.
Published: August 2012

Factors which contribute to magnetostructural transition control have been demonstrated by study of the effects of Au incorporation on the magnetic and structural character of CsCl-structured equiatomic FeRh thin films. Sputtered films were capped with 2 nm of Au deposited at 873 K and at 323 K and subsequently characterized with magnetometry and synchrotron-based structural probes. Diffusion of Au into the FeRh film layer at 873 K is confirmed by a reduction in the Au capping layer thickness relative to the film capped at 323 K. The impact of Au diffusion on the FeRh magnetostructural character is noted by a decrease in the onset of the transition temperature, a thermally broadened first-order transition and an increased sensitivity of the transition to applied magnetic field. Additionally, magnetization data indicate that Au diffusion causes retention of the ferromagnetic phase well below the normal magnetostructural transition temperature. These results are attributed to a multiphase FeRh film layer created by thermally driven Au diffusion.
Enhanced thermal conductivity of polycrystalline aluminum nitride thin films by optimizing the interface structure
Authors: Pan T. S. , Zhang Y. , Huang J. , Zeng B. , Hong D. H. , Wang S. L. , Zeng H. Z. , Gao M. , Huang W. , Lin Y.
Published: August 2012

The growth-temperature dependency and interface structure effects on the thermal conductivity of the highly textured AlN thin films on (001) Si substrates were systematically studied by characterizing the crystal structures, surface morphologies, interface structures, chemical compositions, and thermal conductivity using x-ray diffraction analysis, atomic force microscopy, high resolution transmission electron microscopy, x-ray photoelectron spectroscopy, and 3-omega method, respectively. By optimizing the interface microstructure and the growth temperature, thermal conductivity of polycrystalline AlN thin films can be greatly enhanced from 9.9 to 26.7 W/mK, when the growth temperature increases from 330 to 560 °C. This achievement is considered to be associated with the diminishment of the amorphous and disordered layer at the AlN/Si interface.
Precise calibration of Mg concentration in MgxZn1−xO thin films grown on ZnO substrates
Authors: Kozuka Y. , Falson J. , Segawa Y. , Makino T. , Tsukazaki A. , Kawasaki M.
Published: August 2012

The growth techniques for MgxZn1−xO thin films have advanced at a rapid pace in recent years, enabling the application of this material to a wide range of optical and electrical applications. In designing structures and optimizing device performances, it is crucial that the Mg content of the alloy be controllable and precisely determined. In this study, we have established laboratory-based methods to determine the Mg content of MgxZn1−xO thin films grown on ZnO substrates, ranging from the solubility limit of x ∼ 0.4 to the dilute limit of x < 0.01. For the absolute determination of Mg content, Rutherford backscattering spectroscopy is used for the high Mg region above x = 0.14, while secondary ion mass spectroscopy is employed to quantify low Mg content. As a lab-based method to determine the Mg content, c-axis length is measured by x-ray diffraction and is well associated with Mg content. The interpolation enables the determination of Mg content to x = 0.023, where the peak from the ZnO substrate overlaps the MgxZn1−xO peak in standard laboratory equipment, and thus limits quantitative determination. At dilute Mg contents below x = 0.023, the localized exciton peak energy of the MgxZn1−xO films as measured by photoluminescence is found to show a linear Mg content dependence, which is well resolved from the free exciton peak of ZnO substrate down to x = 0.0043. Our results demonstrate that x-ray diffraction and photoluminescence in combination are appropriate methods to determine Mg content in a wide Mg range from x = 0.004 to 0.40 in a laboratory environment.
Scalar transport and perturbation dynamics in intermittent magnetohydrodynamic flow
Authors: Dey Prasanta K. , Zikanov Oleg
Published: August 2012

The phenomenon of large-scale intermittency in the magnetohydrodynamic channel flow with imposed spanwise magnetic field discovered by Boeck et al. [“Large-scale intermittency of liquid-metal channel flow in a magnetic field,” Phys. Rev. Lett. 101, 244501 (2008)]10.1103/PhysRevLett.101.244501 is further investigated. Numerical simulations are conducted to analyze features of the intermittent regime, such as transport of a passive scalar, distribution of perturbation energy between mean flow and fluctuations, and the effect of the strength of the magnetic field.