bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties of massive Population III and metal-poor stars
Authors: Schaerer Daniel
Published: December 2007

We review the properties of massive Population III and very metal-poor stars, including briefly their formation, IMF, their main sequence evolution, possible mass loss mechanisms, atmosphere modeling etc. For detailed predictions concerning the properties of these stars we refer to Schaerer (2002) and Schaerer (2002) and references therein. Extending these calculations, Schaerer (2007) present new calculations concerning the ionizing power, Ly-α strength and related properties for different metallicities as well as for a range of power-law and log-normal IMFs. For illustrations from these studies see the Figures below. New detailed calibrations for solar metallicity O-type stars have recently been presented by Martins et al. (2005).
M - L relations for rapid and slow rotators
Authors: Malkov Oleg Yu.
Published: December 2007

Comparing the radii of eclipsing binaries components and single stars we have found a noticeable difference between observational parameters of B0V - G0V components of eclipsing binaries and those of single stars of the corresponding spectral type. This difference was confirmed by re-analyzing the results of independent investigations published in the literature.
Joint Discussion 6 Neutron stars and black holes in star clusters
Authors: Rasio (ed.) F. A. , Baumgardt Holger , Corongiu Alessandro , D'Antona Francesca , Fabbiano Giuseppina , Fregeau John M. , Gebhardt Karl , Heinke Craig O. , Hut Piet , Ivanova Nataliya , Maccarone Thomas J. , Ransom Scott M. , Webb Natalie A.
Published: December 2007

This article was co-authored by all invited speakers at Joint Discussion 6 onNeutron Stars and Black Holes in Star Clusters, which took place during the IAU General Assembly in Prague, Czech Republic, on August 17 and 18, 2006. Each section presents a short summary of recent developments in a key area of research, incorporating the main ideas expressed during the corresponding panel discussion at the meeting.
Lyman break galaxies at z>6
Authors: Bouwens Rychard J. , Illingworth Garth D.
Published: December 2007

Extending the study of star-forming galaxies to z>6 is extremely difficult due to the faintness of the sources and the challenging nature of deep near-infrared observations. Nevertheless, current observations are now just good enough that we can begin drawing some conclusions about the nature of galaxies at z≳7. At present, deep near-infrared observations with NICMOS (reaching ≳27 AB mag at 5σ) cover more than 20arcmin2 of area with deep optical coverage and allow us to identify four strong z≃7–8 candidates. Comparing this sample with dropout samples at later times (z≃4–6), we are able to study evolution in the rest-frame UV LF over the range z≃8 to z≃4. We find strong evidence for significant evolution in the characteristic luminosity with time (brightening by ∼2 mag, from z≃8 to z≃4). The observed evolution appears to be the direct result of hierarchical growth in the galaxy population.
Subaru surveys for the high-redshift universe
Authors: Taniguchi Yoshiaki
Published: December 2007

We present a brief summary of Subaru observations of high-z galaxies. We discuss our future plan to probe galaxies beyond z = 10.
Galaxies in the first billion years: implications for re-ionization and the star formation history at z>6
Authors: Bunker Andrew J. , Stanway Elizabeth R. , Eyles Laurence P. , Ellis Richard S. , McMahon Richard G. , Lacy Mark , Stark Daniel P.
Published: December 2007

We discuss the selection of star-forming galaxies at z≃6 through the Lyman-break technique. Spitzer imaging implies many of these contain older stellar populations (>200Myr) which produce detectable Balmer breaks. The ages and stellar masses (∼1010M⊙) imply that the star formation rate density at earlier epochs may have been significantly higher than at z≃6, and might have played a key role in re-ionizing the universe.
High-redshift lensed galaxies
Authors: Pelló Roser , Schaerer Daniel , Richard Johan , Le Borgne Jean-Franc , Kneib Jean-Paul , Hempel Angela , Egami Eiichi , Boone Frédéric , Cuby Jean-Gabriel , Ferrara Andrea , Wise Michael W.
Published: December 2007

We present the results obtained from our deep survey of lensing clusters aimed at constraining the abundance of star-forming galaxies at z∼6–11.
UV radiative feedback on high-redshift proto-galaxies
Authors: Mesinger Andrei , Haiman Greg L. , Haiman Zoltán
Published: December 2007

We discuss the UV radiative feedback on high-redshift proto-galaxies.
Why coronal mass ejections are necessary for the dynamo
Authors: Brandenburg Axel
Published: December 2007

Large scale dynamo-generated fields are a combination of interlocked poloidal and toroidal fields. Such fields possess magnetic helicity that needs to be regenerated and destroyed during each cycle. A number of numerical experiments now suggests that stars may do this by shedding magnetic helicity. In addition to plain bulk motions, a favorite mechanism involves magnetic helicity flux along lines of constant rotation. We also know that the sun does shed the required amount of magnetic helicity mostly in the form of coronal mass ejections. Solar-like stars without cycles do not face such strong constraints imposed by magnetic helicity evolution and may not display coronal activity to that same extent. I discuss the evidence leading to this line of argument. In particular, I discuss simulations showing the generation of strong mean toroidal fields provided the outer boundary condition is left open so as to allow magnetic helicity to escape. Control experiments with closed boundaries do not produce strong mean fields.
Joint Discussion 9 Supernovae: one millennium after SN 1006
Authors: Winkler P. Frank , Hillebrandt Wolfgang
Published: December 2007

The year 2006 marks the 1000th anniversary of the supernova of 1006 C.E., the brightest supernova in all of recorded human history. This is also a time of great excitement in the supernova community: Observations from space observatories including Hubble, Chandra, XMM-Newton, and Spitzer, together with ones from powerful new ground-based telescopes and instruments, are revealing supernova remnants in the Galaxy and beyond in unprecedented detail. Fully three-dimensional computational codes and simulations running on powerful new machines are providing insight into the physics of supernovae freed from the simplifying assumptions that have restricted past understanding. Automated supernova searches are discovering hundreds of new supernovae every year, some at redshifts of 1 or beyond. And supernovae have revolutionized cosmology through the discovery of an accelerating universe, and they hold promise for deepening our understanding of the ‘dark energy’ that drives the acceleration.
SN 1006 at optical and UV wavelengths
Authors: Long Knox S.
Published: December 2007

Optical and UV emission from SN 1006 is observed on the periphery of the SNR, particularly in the NW, and arises as material from interstellar gas is ionized behind the shock front. The shapes of the emission lines have been used to infer a shock velocity of about 2900 km s−1 and to show that the electron and ion temperatures are close to that expected from standard shock theory. The combination of the shock velocity and the proper motion of the filaments in the NE accurately locates SN1006 at a distance of 2.2 kpc, some 550 pc above the Galactic plane. At UV wavelengths, ejecta from SN 1006 have also been observed as broad absorption lines from Si, Ca and Fe in spectra of the Schweitzer-Middleditch star and two quasars. The observations appear to limit the mass of Fe in SN 1006 to less than 0.16 M⊙, much less than expected from models of Type Ia supernovae. In this brief review of the UV and optical properties of SN 1006, I will summarize how these observations yield a fairly consistent description of SN 1006, and suggest what further observations might be undertaken to extend our understanding of SN 1006 in its second millennium.
Supernova remnants and their progenitors
Authors: Dickel John R.
Published: December 2007

Young supernova remnants (SNRs) show obvious differences that can be related to characteristics of the progenitors and supernova types as tabulated in Fig. 1. Questions remain.
Summary of JD 9 Supernovae: past, present, and future
Authors: Trimble Virginia L.
Published: December 2007

SN 1006 was the first (and for a very long time the only) event to be caught before peak light. A passage which, according to Stephenson, does not actually pertain to the SN, nevertheless makes clear that, even then, a hypothesis was more likely to be accepted if it made a prediction later verified, though the prediction was that something bad would happen to Emperor Sanjo In. The hypothesis was that the star was not new, but related to behavior of existing stars in Qichen Jianjun. According to the poster by P.J. Boner, Kepler made the opposite choice for ‘his’ SN, calling it a genuinely new star formed out of the ether, rather than mere change in appearance. Indeed the distinction between true novae and variable stars was not drawn correctly until Hevelius's 1662 study of Mira, after Tycho had shown that his event (and the comet of 1577) were more distant than our Moon, a point disputed by many of his contemporaries, but accepted by Galileo, who applied a very early statistical method to many different observations of SN 1572. Tycho's main advantages were better equipment and hard work, again not so different from present conditions.
Deep Impact: excavating comet Tempel 1
Authors: A'Hearn Michael F.
Published: December 2007

Results of the Deep Impact mission to impact Comet Tempel 1 are summarized.
What can pre-solar grains tell us about AGB stars?
Authors: Lugaro Maria A. , Höfner Susanne
Published: December 2007

The vast majority of pre-solar grains recovered to date show the signature of an origin in asymptotic giant branch (AGB) stars. In AGB stars, the abundances of elements lighter than silicon and heavier than iron are largely affected by proton- and neutron-capture processes, respectively, while the compositions of the elements in between also carry the signature of the initial composition of the star. Dust is produced and observed around AGB stars and the strong mass loss experienced by these stars is believed to be driven by radiation pressure on dust grains. We briefly review the main developments that have occurred in the past few years in the study of AGB stars in relation to dust and pre-solar grains. From the nucleosynthesis point of view these include: more stringent constraints on the main neutron source nucleus,13C, for theslowneutron capture process (thesprocess); the possibility of pre-solar grains coming from massive AGB stars; and the unique opportunity to infer the ‘isotopic’ evolution of the Galaxy by combining pre-solar grain data and AGB model predictions. Concerning the formation of grains in AGB stars, considerable progress has been achieved in modelling. In particular, self-consistent models for atmospheres and winds of C-stars have reached a level of sophistication which allows direct quantitative comparison with observations. In the case of stars with C/O < 1, however, recent work points to serious problems with the dust-driven wind scenario. A current trend in atmosphere and wind modelling is to investigate the possible effects of inhomogenieties (e.g., due to giant convection cells) with 2D/3D models.
New Galactic ISM results and progress towards low-frequency spectroscopy
Authors: Green Anne J. , Murphy Tara , Campbell-Wilson Duncan , Kesteven Michael , Bunton John
Published: December 2007

We dicuss new Galactic ISM results and progress towards low-frequency spectroscopy
High-redshift radio galaxies: the most massive galaxies at every epoch
Authors: De Breuck Carlos
Published: December 2007

Radio galaxies are identified with the most massive host galaxies known out to z = 5 and can put strong constraints on galaxy evolution models, provided their space density is accurately determined. Here, I present the important role low-frequency radio surveys will have in this by selecting the highest redshift radio galaxies using the steepness of their radio spectra.
A steradian of the southern sky at 151.5 MHz using the Mauritius Radio Telescope
Authors: Pandey V. N. , Shankar N. Udaya
Published: December 2007

We present a few results of a low-frequency southern sky survey carried out using the Mauritius Radio Telescope (MRT).
Modeling dense stellar systems: background
Authors: Hut Piet
Published: December 2007

I provide some background about recent efforts made in modeling dense stellar systems, within the context of the MODEST initiative. During the last four years, we have seen more than fifteen MODEST workshops, with an attendance between twenty and a hundred participants, and topics ranging from very specialized discussions to rather general overviews.
Observations of internal dynamics of globular clusters
Authors: Rolly Bedin Luigi
Published: December 2007

In preparation for the first simulation of a real globular cluster with a few 105 particles and several Gyr of evolution, which will be made possible by the advent of the new GRAPE-8, the MODEST community encharged our working group (WG-9) to provide all of the needed observational constrains. The selected clusters for this experiment were NGC 6121 (M 4) and NGC 6397. We present the status of the project.
Present status of the celestial reference system and frame
Authors: Ma Chopo
Published: December 2007

We discuss the present status of the celestial reference system and frame.
Long-term solution for the insolation quantities of the Earth
Authors: Laskar Jacques
Published: December 2007

We discuss a long-term solution for the insolation quantities of the Earth.
Relativistic aspects of Earth's rotation
Authors: Soffel Michael , Klioner Sergei A.
Published: December 2007

We discuss relativistic aspects of Earth's roration
Solar quadrupole moment from planetary ephemerides: present state of the art
Authors: Pireaux Sophie , Standish E. Myles , Pitjeva Elena V. , Rozelot Jean-Pierre
Published: December 2007

We discuss the present state of the art of the solar quadrupole moment from planetary ephemerides.
Implementation of the new nomenclature in The Astronomical Almanac
Authors: Hohenkerk Catherine Y.
Published: December 2007

This talk charts the implementation of the resolutions of the IAU XXIV General Assembly in 2000 (IAU 2000) in The Astronomical Almanac (AsA).
From atomic clocks to coordinate times
Authors: Petit Gérard
Published: December 2007

With the present level of accuracy it may be necessary to use space borne atomic clocks to directly generate TCG, and to start addressing the limitations in the coordinate time transformations.
Education in astrometry
Authors: van Altena William F. , Stavinschi Magda G.
Published: December 2007

We discuss education in astrometry.
Atacama Large Millimeter/Submillimeter Array (ALMA)
Authors: Turner Jean L. , Wootten H. Alwyn
Published: December 2007

The Atacama Large Millimeter/Submillimeter Array (ALMA) is an international effort to construct an instrument capable of matching the exquisite imaging properties of optical space telescopes at millimeter and submillimeter wavelengths. ALMA science will transform our vision of the cold, dusty, and gaseous universe, from extrasolar planets to the youngest galaxies.
Special Session 2 Innovation in teaching and learning astronomy
Authors: Ros Rosa M. , Pasachoff Jay M.
Published: December 2007

On August 17 and 18, 2006, Commission 46 on Astronomy Education and Development held a Special Session at the IAU XXVI General Assembly in Prague. The session, on Innovation in Teaching/Learning Astronomy, was organized around four themes: (i) general strategies for effective teaching, (ii) connecting astronomy with the public, (iii) effective use of instruction and information technology, and (iv) practical issues connected with the implementation of the 2003 IAU Resolution that recommended including astronomy in school curricula, assisting schoolteachers in their training and backup, and informing them about available resources. Approximately 40 papers were presented orally; in addition, 60 poster papers were displayed.
Galaxy formation and evolution using multi-wavelength, multi-resolution imaging data in the Virtual Observatory
Authors: Prema Paresh , Walton Nicholas A. , McMahon Richard G.
Published: December 2007

Observational astronomy is entering an exciting new era with large surveys delivering deep multi-wavelength data over a wide range of the electromagnetic spectrum. The last ten years has seen a growth in the study of high redshift galaxies discovered with the method pioneered by Steidel et al. (1995) used to identify galaxies above z>1. The technique is designed to take advantage of the multi-wavelength data now available for astronomers that can extend from X-rays to radio wavelength. The technique is fast becoming a useful way to study large samples of objects at these high redshifts and we are currently designing and implementing an automated technique to study these samples of objects. However, large surveys produce large data sets that have now reached terabytes (e.g. for the Sloan Digital Sky Survey, ) in size and petabytes over the next 10yr (e.g., LSST, ). The Virtual Observatory is now providing a means to deal with this issue and users are now able to access many data sets in a quicker more useful form.
NVO study of Super Star Clusters in nearby galaxies
Authors: Whitmore Bradley C.
Published: December 2007

We are using NVO tools to obtain a large (N≃100), uniform (SDSS images, cross checked with HST images; analyzed using WESIX) database of super star clusters in nearby star-forming galaxies in order to address two fundamental astronomical questions: (i) Is the initial luminosity function of star clusters universal?; and (ii) What fraction of super star clusters is ‘missing’ in optical studies (i.e., are hidden by dust)?
Large surveys and determination of interstellar extinction
Authors: Malkov Oleg Yu. , Karimov Erkin
Published: December 2007

The study of the spatial distribution of interstellar extinction, AV, is important for many investigations of galactic and extragalactic objects. Three-dimensional (3D) extinction models have been produced using spectral and photometric stellar data, open cluster data, star counts, the Galactic dust distribution model.
Criteria for spectral classification of cool stars using high-resolution spectra
Authors: Montes David , Martínez-Arnáiz Raquel M. , Maldonado Jesus , Roa-Llamazares Juan , López-Santiago Javier , Crespo-Chacón Inés , Solano Enrique
Published: December 2007

We have compiled a large number of optical spectra of cool stars taken with different high-resolution echelle spectrographs (R ≃ 40 000). Many of those are available as spectral libraries (Montes et al. 1997, 1998, 1999, .
Extracting parameters for stellar populations of SDSS galaxy spectra using evolution strategies
Authors: Gomez Juan C. , Fuentes Olac
Published: December 2007

Current surveys from modern observatories contain a huge amount of information; in particular, the Sloan Digital Sky Survey (SDSS) has reached the order of terabytes of data in images and spectra. Such amount of information needs to be exploited by sophisticated algorithms that automatically analyze the data in order to extract useful knowledge from the mega databases.
An ontology of sstronomical object types for the Virtual Observatory
Authors: Derriere Sebastian , Richard André , Preite-Martinez Andrea
Published: December 2007

The Semantic Web and ontologies are emerging technologies that enable advanced knowledge management and sharing. Their application to Astronomy can offer new ways of sharing information between astronomers, but also between machines or software components and allow inference engines to perform reasoning on an astronomical knowledge base. The first examples of astronomy-related ontologies are being developed in the european VOTech project.
The Virtual Observatory paradigm and national projects
Authors: Kembhavi Ajit K.
Published: December 2007

A Virtual Observatory (VO) seeks to provide access to very large volumes of astronomical data over the internet to every interested user, along with software for the data anlysis, and tools for data visualisation, statistics and any other applications which are necessary for mining science from the data. Handling large volumes of data requires extensive computer resources, which may not be available to the end user; transferring data from the data centre to the user needs high bandwidth, which also may not be available. A VO therefore seeks to provide computing resources as well, which could be spread over a grid. The user can locate data of interest through registries, then access the data and analyse it using the computing resources, all through simple user interfaces.
A multiwavelength study of a sample of Texas Radio Survey steep spectrum sources
Authors: Lucas Ray A. , Miller Neal , Koekemoer Anton M. , Van Duyne Jeffrey , Chambers Kenneth C.
Published: December 2007

VLA A-array snapshots were obtained of a complete sample of steep-spectrum radio sources from the Texas Radio Interferometer survey. Though similar in sensitivity to the FIRST Survey, our A-array snapshots have better resolution, and are complementary to FIRST. All initial A-array maps are made, and we are comparing them to FIRST.
Solar system bodies ‘Observations in the Past’ with the plate archive of the Main Astronomical Observatory of the Ukrainian National Academy of Sciences
Authors: Sergeeva Tetyana P. , Sergeev Aleksandre V.
Published: December 2007

The improvement of the dynamical models of solar system bodies’ motions will be very useful for the future space astrometry mission Gaia for a fast identification of objects, to discriminate between the well-known objects and the new ones. ‘Observations in the Past’ with plate archives allow realising it.
Massive physical and dynamical characterization of asteroids
Authors: Thuillot William , Berthier Jerôme , Sarkissian Armand , Mickaelian Areg M. , Sargsyan Lena A. , Iglesias Jesus , Lainey Valery , Birlan Mirel , Simon Guy
Published: December 2007

Numerous new Solar System objects, mainly asteroids, are still detected nowadays but their physical and dynamical characteristics remain not accurately determined, until dedicated observations and analysis are made. However, the Virtual Observatory is a perfect framework to search for this characterization by data mining. We are developing two studies for this goal by exploring the DENIS infrared and DFBS spectroscopic surveys. In order to scan the survey catalogues and to search for Solar System objects, we have developed a VO compliant workflow founded on the use of a recent VO tool labelled SkyBoT (Sky Bodies Tracker) (Berthier et al. 2005) and on the VizieR service provided by CDS. A public version of SkyBoT is implemented in the sky atlas Aladin since January 2006. It allows us to quickly get the precise coordinates of the asteroids, planets and natural satellites in any star field, provided we know its center, its size and the precise date of the exposure (between 1949 and 2009). Our data mining workflow performs cone search queries on SkyBoT and VizieR to extract all the known astronomical objects observed by the survey. Then the sources which are detected in the survey are correlated with the known objects to determine the matched and unmatched objects.
Future directions of the Virtual Observatory
Authors: Szalay Alexander S.
Published: December 2007

The Virtual Observatory effort has undergone a substantial evolution over the last four years. In the talk we will discuss the directions of the current effort, and consider the direction along which the Virtual Observatory might evolve along with various other large astronomy projects. We will also discuss similar efforts in other disciplines and the relation of the VO to Grid Computing.
Implementing astronomical image analysis pipelines using VO standards
Authors: Louys Mireille Y. , Bonnarel François , Schaaff André , Claudon Jean-Julien , Pestel C.
Published: December 2007

We consider here image analysis pipelines and examine how data and processes could be described in the context of the VO. The tasks chain is considered as a workflow, not only in terms of computing and resource allocation as in the Grid community, but in terms of data analysis know-how. Such pipelines may be published as coarse grain tool boxes and provide reference examples to the user.
VisIVO: an interoperable visualisation tool for Virtual Observatory data
Authors: Becciani Ugo , Comparato Marco , Costa Alessandro , Gheller Claudio , Larsson Bjorn , Pasian Fabio , Smareglia Riccardo
Published: December 2007

We present VisIVO a software for the visualisation and analysis of astrophysical data which can be retrieved from the Virtual Observatory framework and for cosmological simulations. VisIVO is VO standards compliant and supports the most important astronomical data formats such as FITS, HDF5 and VOTables. Data can be retrieved directly connecting to an available VO service (i.e., VizieR WS), loaded in the local computer memory where they can be further selected, visualised and manipulated.
Site testing at Dome C: history and present status
Authors: Vernin Jean , Agabi Abdelkrim , Aristidi Eric , Azouit Max , Chadid Merieme , Fossat Eric , Sadibekova Tatiana , Trinquet Hervé , Ziad Aziz
Published: December 2007

The idea of starting an astronomical site testing in Antarctica began during a congress organized by French Académie des Sciences, in 1992, and entitled ‘Recherches polaires-Une Stratégie pour l'an 2000’. At this time, one of us (Vernin 1994) gave a proposal for an astronomical site testing in Antarctica. This proposal was rapidly followed by a meeting between Al Harper (from ‘Center for Astrophysical Research in Antarctica’, Chicago), Peter Gillingham (from the Anglo Australian Observatory, Australia) and Jean Vernin (from Nice University) at Lake Geneva, Wisconsin, in 1993. It was decided to investigate what was the astronomical quality of South Pole station, each institute bringing its own participation: CARA, the South Pole infrastructure, University of New South Wales, a PhD student and Nice University its expertise and instruments.
Optical sky brightness at Dome C, Antarctica
Authors: Kenyon Suzanne L. , Storey John W.V.
Published: December 2007

Dome C, Antarctica is a prime site for astronomical observations in terms of climate, wind speeds, turbulence, and infrared and terahertz sky backgrounds (for example, see Aristidi et al. 2005; Storey et al. 2005). However, at present little is known about the optical sky brightness and atmospheric extinction. Using a variety of modelling techniques, together with data from the South Pole, the brightness of the night sky at Dome C is estimated in Kenyon & Storey (2006) including the contributions from scattered sunlight, moonlight,
aurorae, airglow, zodiacal light, integrated starlight, diffuse Galactic light and artificial sources. The results are compared to Mauna Kea, Hawaii. We summarise the main conclusions.
Multi-aperture interferometry at Concordia
Authors: Fossat Eric , Vakili Farrokh , Aristidi Eric , Lopez Bruno , Schmider François-Xavier , Agabi Karim , Daban Jean-Baptiste , Allouche Fatmé , Belu Adrian , Gori Pierre-Marie , Guerri Géraldine , Valat Bruno
Published: December 2007

The next generation (post-VLTI) of multi-telescope interferometric arrays operated in optical/infrared wavelengths should be kilometric, from 1 to 10 km. The Concordia station offers a unique opportunity to set such an interferometer in the best atmospheric conditions presently known on Earth.
A test for the detection of vegetation on extrasolar planets: detection of vegetation in Earthshine spectrum and its diurnal variation
Authors: Briot Danielle , Agabi Karim , Aristidi Eric , Arnold Luc , François Patrick , Riaud Pierre , Rocher Patrick , Schneider Jean
Published: December 2007

The search for life in extraterrestrial planets is to be tested first with the only planet known to shelter life. If the planet Earth is used as an example to search for a signature of life, the vegetation is one of its possible detectable signature, using the Vegetation Red Edge due to chlorophyll in the near infrared (0.725 μm). We focus on the test of the detectability of vegetation in the spectrum of Earth seen as a simple dot, using the reflection of the global Earth on the lunar surface, i.e., Earthshine. On the Antartic, the Earthshine can be seen during several hours in a day (not possible at our latitudes) and so variations due to different parts of Earth, that is to say oceans and continents facing the Moon could be detected.
Protein Binding to Amphoteric Polymer Brushes Grafted onto a Porous Hollow‐Fiber Membrane
Authors: Iwanade Akio , Umeno Daisuke , Saito Kyoichi , Sugo Takanobu
Published: December 2007

Three kinds of ampholites, i.e., 3‐aminopropionic acid (NH2C2H4COOH), (2‐aminoethyl)phosphonic acid (NH2C2H4PO3H2), and 2‐aminoethane‐1‐sulfonic acid (NH2C2H4SO3H), were introduced into an epoxy group‐containing polymer brush grafted onto a porous hollow‐fiber membrane with a porosity of 70% and pore size of 0.36 μm. The amphoteric group density of the hollow‐fiber ranged from 0.50 to 0.72 mmol/g. Three kinds of proteins, i.e., lactoferrin (Lf), cytochrome c (Cyt c), and lysozyme (Ly), were captured by the amphoteric polymer brush during the permeation of the protein solution across the ampholite‐immobilized porous hollow‐fiber membrane. Multilayer binding of the protein to the amphoteric polymer brush, with a degree of multilayer binding of 3.3, 8.6, and 15 for Lf, Cyt c, and Ly, respectively, with the (2‐aminoethyl)phosphonic acid‐immobilized porous hollow‐fiber membrane, was demonstrated with a negligible diffusional mass‐transfer resistance of the protein to the ampholite immobilized. The 2‐aminoethane‐1‐sulfonic acid‐immobilized porous hollow‐fiber membrane exhibited the lowest initial flux of the protein solution, 0.41 m/h at a transmembrane pressure of 0.1 MPa and 298 K, and the highest equilibrium binding capacity of the protein, e.g., 130 mg/g for lysozyme. Extension and shrinkage of the amphoteric polymer brushes were observed during the binding and elution of the proteins.
NOx enhancements in the middle atmosphere during 2003–2004 polar winter: Relative significance of solar proton events and the aurora as a source
Authors: Seppälä Annika , Clilverd Mark A. , Rodger Craig J.
Published: December 2007

In this study we combine odd nitrogen (NOx) observations from the GOMOS and POAM III instruments with a radio wave ionization index to provide a detailed description of the generation and descent of polar NOx into the upper stratosphere during the Northern Hemisphere winter of 2003–2004. The measurements are used to study the relative contributions of ionization due to solar proton events, energetic electron precipitation, and low‐energy (1–10 keV) electron precipitation on NOx production, and its subsequent downward transport to the upper stratosphere. We show that NOx generated from the large solar proton storm in October/November 2003 was transported into the upper stratosphere in agreement with model calculations, but that aurorally generated NOx also descended later in the winter. Both periods were highly significant and produced large long‐lived decreases in stratospheric ozone once it arrived at those altitudes. The observations made by GOMOS deep into the nighttime polar vortex are critical in differentiating between the stratospheric effects of these two events.
Future regime shift in feedbacks during Arctic winter
Authors: Miller James R. , Chen Yonghua , Russell Gary L. , Francis Jennifer A.
Published: December 2007

The Arctic is among the regions where climate is changing most rapidly today. Climate change is amplified by a variety of positive feedbacks, many of which are linked with changes in water vapor, cloud cover, and other cloud properties. We use a global climate model to examine several of these feedbacks, with a particular emphasis on determining whether there are significant temporal changes in these feedbacks that would make them stronger or weaker during the 21st century. The model results indicate that one of the significant positive feedbacks on Arctic surface air temperature in winter weakens substantially toward the end of the 21st century. The feedback loop begins with a temperature increase that produces increases in water vapor, cloud cover, and cloud optical depth which increase the downward longwave flux by 30 Wm−2 by 2060 which then increases the surface air temperature.
Temperature‐sensitive reaction intermediate of F1‐ATPase
Authors: Watanabe Rikiya , Iino Ryota , Shimabukuro Katsuya , Yoshida Masasuke , Noji Hiroyuki
Published: December 2007

F1‐ATPase is a rotary molecular motor that makes 120° stepping rotations, with each step being driven by a single‐ATP hydrolysis. In this study, a new reaction intermediate of F1‐ATPase was discovered at a temperature below 4°C, which makes a pause at the same angle in its rotation as when ATP binds. The rate constant of the intermediate reaction was strongly dependent on temperature with a Q10 factor of 19, implying that the intermediate reaction accompanies a large conformational change. Kinetic analyses showed that the intermediate state does not correspond to ATP binding or hydrolysis. The addition of ADP to the reaction mixture did not alter the angular position of the intermediate state, but specifically lengthened the time constant of this state. Conversely, the addition of inorganic phosphate caused a pause at an angle of +80° from that of the intermediate state. These observations strongly suggest that the newly found reaction intermediate is an ADP‐releasing step.
Insights into kinetochore–DNA interactions from the structure of Cep3Δ
Authors: Purvis Alan , Singleton Martin R
Published: December 2007

The CBF3 complex is an essential core component of the budding yeast kinetochore and is required for the centromeric localization of all other kinetochore proteins. We determined the crystal structure of a large section of the protein Cep3 from CBF3, which is the only component with obvious DNA‐binding motifs. The protein adopts a roughly bilobal shape, with an extended dimerization interface. The dimer has a large central channel that is sufficient to accommodate duplex B‐form DNA. The zinc‐finger domains emerge at the edges of the channel, and could bind to the DNA in a pseudo‐symmetrical manner at degenerate half‐sites in the centromeric sequence. We propose a mechanism for the modulation of DNA affinity by an acidic activator domain, which could be applicable to a wider family of transcription factors.
Effects of topology and size on statics and dynamics of complexes of hyperbranched polymers with linear polyelectrolytes
Authors: Dalakoglou G. K. , Karatasos K. , Lyulin S. V. , Lyulin A. V.
Published: December 2007

Brownian dynamics simulations with explicit hydrodynamic interactions have been employed to study generic effects of size and topology in noncovalent (Coulombic-driven) complexes formed by irregular-shaped hyperbranched polymers and linear polyelectrolytes. The behavior of the complexes was explored in detail in terms of static and dynamic properties, both in local and in the entire complex scale. The results were compared to previous studies on perfect dendrimers and other hyperbranched molecules where available. It was found that both molecular weight and structure may impart significant changes to key factors known to be associated with the ability of these systems to take part in relevant nanoscale applications.
The influence of zwitterionic lipids on the electrostatic adsorption of macroions onto mixed lipid membranes
Authors: Haugen Andrew , May Sylvio
Published: December 2007

Charged lipid membranes commonly consist of a mixture of charged and zwitterionic lipids. We suggest a model that characterizes the influence of the dipolar nature of the zwitterionic lipid species on the electrostatic adsorption of macroions onto mixed membranes in the fluid state. The model is based on Poisson-Boltzmann theory which we have modified so as to account for the dipolar character of the zwitterionic lipids. In addition the membrane lipids are allowed to adjust their lateral distribution upon macroion adsorption. We consider and compare two experimentally relevant scenarios: cationic macroions adsorbed onto anionic membranes and anionic macroions adsorbed onto cationic membranes. We show that in the former case the adsorption strength is slightly weakened by the presence of the headgroup dipoles of the zwitterionic lipids. Here, macroion-induced lipid demixing is more pronounced and the lipid headgroups tilt away from a cationic macroion upon adsorption. In contrast, for the adsorption of anionic macroions onto a cationic membrane the zwitterionic lipids strongly participate in the electrostatic interaction between membrane and macroion, thus enhancing the adsorption strength significantly (we predict up to 20%). Consistent with that we find less lateral demixing of the charged lipids and a reorientation of the dipoles of the zwitterionic headgroups towards the anionic macroions. Our results may be of importance to understand the differences in the electrostatic adsorption of proteins/peptides onto cellular membranes versus complex formation between cationic membranes and DNA.
Spin selective multiple quantum NMR for spectral simplification, determination of relative signs, and magnitudes of scalar couplings by spin state selection
Authors: Baishya Bikash , Suryaprakash N.
Published: December 2007

In the present work we demonstrate a novel method for spectral simplification and determination of the relative signs of the scalar couplings using a spin selective multiple quantum NMR experiment. A spin selective excitation of double quantum coherence of A and M spins in a weakly coupled three spin system of the type AMX, results in a doublet in the double quantum dimension whose separation corresponds to the sum of couplings of the active spins to the passive spin X. One component of the doublet has the passive spin X in ∣α⟩ state while the other component has the passive spin X in ∣β⟩ state. The spin selective conversion of double quantum coherence to single quantum coherence does not disturb the spin states of the passive spin thereby providing the spin state selection. There will be two domains of single quantum transitions in single quantum dimension at the chemical shift positions of A and M spins. The ∣α⟩ domain of A spin is a doublet because of ∣α⟩ and ∣β⟩ states of M spin only, while that of ∣β⟩ domain is another doublet in a different cross section of the spectra. The scalar coupling JAM can be extracted from any of the ∣α⟩ and ∣β⟩ domain transitions while the relative displacements of the two doublets between the two domains at the two chemical shifts provides the magnitude and sign of the scalar coupling JAX relative to the coupling JMX. Similar result is obtained for zero quantum studies on AMX spin system. The proposed technique is discussed theoretically using product operator approach. The new spin state selective double quantum J-resolved sequence has also been developed. The methodology is confirmed experimentally on a homonuclear weakly coupled three spin system and applied to two different heteronuclear five spin systems.
Vibronic dynamics of I2 trapped in amorphous ice: Coherent following of cage relaxation
Authors: Senekerimyan V. , Goldschleger I. , Apkarian V. A.
Published: December 2007

Four-wave mixing measurements are carried out on I2-doped ice, prepared by quench condensing the premixed vapor at 128K. Coherent vibrational dynamics is observed in two distinct ensembles. The first is ascribed to trapping in asymmetric polar cages in which, as in water, the valence absorption of the molecule is blueshifted by 3500cm−1, predissociation of the B state is complete upon the first extension of the molecular bond, and the vibrational frequency in the ground state (observed through coherent anti-Stokes Raman scattering) is reduced by 6.5%. The effect is ascribed to polarization of the molecule. The implied local field and the ionicity of the molecule are extracted, to conclude that the molecule is oxygen bonded to one water molecule on one side and hydrogen bonded on the other side. The second ensemble is characterized by the transient grating signal, which shows coherent vibrational dynamics on the B state. The small predissociation rate in this site suggests a symmetric cage in which the local electric field undergoes effective cancellation; and consistent with this, the extracted blueshift of the valence transition in this site (∼1500cm−1) coincides with that observed in clathrate hydrates of iodine. Remarkably, in this site, the vibrational period of the B state packet coherently stretches from an initial value of 245fsto325fs in the course of five oscillations (1.3ps), indicative of vibrationally adiabatic following of the cage expansion. The dynamics is characteristic of a molecule trapped in a tight symmetric cage, with a soft cage coordinate that relaxes without eliciting elastic response. Enclathration in low-density amorphous ice is concluded.
Diffusion-controlled reaction on a sink with two active sites
Authors: Traytak S. D. , Barzykin A. V.
Published: December 2007

We have presented an exact solution for the problem of diffusive binding to a spherical macromolecule with two axially symmetric active patches. A highly accurate approximate formula for an effective steric factor has been suggested. This model solution may serve as a benchmark for further studies of diffusive interaction in more realistic models of anisotropic reactivity.
Temperature-dependent interfacial chemical bonding states and band alignment of HfOxNy∕SiO2∕Si gate stacks
Authors: He G. , Meng G. W. , Zhang L. D. , Liu M.
Published: December 2007

Temperature-dependent interfacial chemical bonding states and band alignment of HfOxNy∕SiO2∕Si gate stacks have been investigated by X-ray photoemission spectroscopy (XPS) and spectroscopic ellipsometry (SE). By means of the chemical shifts of Hf 4f, Si 2p, O 1s, and N 1s core-level spectra, it has been found that the chemical stability of the HfOxNy∕SiO2∕Si stacks strongly depends on the annealing temperature. Analysis of temperature-dependent band alignment of HfOxNy∕SiO2∕Si stacks suggests that the valence band offset ΔEv increases slowly from 1.82eV for as-grown film to 2.55eV for annealed film at 700°C; however, the values of conduction band offset ΔEc only demonstrates a slight change in the vicinity of 1.50eV. From the band offset viewpoint, HfOxNy∕SiO2∕Si gate stack could be a promising candidate for high-k gate dielectrics.
Elucidating the contact mechanics of aluminum silicon surfaces with Green's function molecular dynamics
Authors: Campañá Carlos , Müser Martin H. , Denniston Colin , Qi Yue , Perry Thomas A.
Published: December 2007

We study the contact mechanics of a flat, elastic wall pressed against a rigid substrate with Green’s function molecular dynamics. The substrate’s height profiles are parametrized from atomic force microscope topography measurements of two different aluminum-silicon alloys. In both samples, roughness lives on disparate length scales, i.e., on relatively large scales defined by size and mean separation of load-bearing silicon particles and on much smaller scales associated with the roughness on top of individual particles. The major differences between the two alloys are their silicon content and the typical silicon particle geometry. These differences lead to quite different stress distributions on both mesoscale and microscale in our calculations. A common feature is that the stress distribution decays exponentially for large stresses σ and not like a Gaussian. Persson’s contact mechanics theory is generalized to the case where contact can only occur on silicon particles. This generalization predicts relatively accurate microscopic mean square stresses, however, it fails to predict accurate numbers for mean square stresses on the mesoscopic scales. Local overlap models are not accurate either, because they fail to describe the contact morphology.
Hydrothermal method grown large-sized zinc oxide single crystal as fast scintillator for future extreme ultraviolet lithography
Authors: Tanaka Momoko , Nishikino Masaharu , Yamatani Hiroshi , Nagashima Keisuke , Kimura Toyoaki , Furukawa Yusuke , Murakami Hidetoshi , Saito Shigeki , Sarukura Nobuhiko , Nishimura Hiroaki , Mima Kunioki , Kagamitani Yuji , Ehrentraut Dirk , Fukuda Tsuguo
Published: December 2007

The scintillation properties of a hydrothermal method grown zinc oxide (ZnO) crystal are evaluated for extreme ultraviolet (EUV) laser excitation at 13.9nm wavelength. The exciton emission lifetime at around 380nm is determined to be 1.1ns, almost identical to ultraviolet laser excitation cases. This fast response time is sufficiently short for characterizing EUV lithography light sources having a few nanoseconds duration. The availability of large size ZnO crystal up to 3in. is quite attractive for future lithography and imaging applications.
Optical studies of InN epilayers on Si substrates with different buffer layers
Authors: Yang M. D. , Shen J. L. , Chen M. C. , Chiang C. C. , Lan S. M. , Yang T. N. , Lo M. H. , Kuo H. C. , Lu T. C. , Huang P. J. , Hung S. C. , Chi G. C. , Chou W. C.
Published: December 2007

We have investigated the photoluminescence (PL) and time-resolved PL from the InN epilayers grown on Si substrates with different buffer layers. The narrowest value of the full width at half maximum of the PL peak is 52 meV with the AlN/AlGaN/GaN triple buffer layer, which is better than previous reports on similar InN epilayers on Si substrates. Based on the emission-energy dependence of the PL decays, the localization energy of carriers is also the least for the InN with a triple buffer layer. According to the x-ray diffraction measurements, we suggest that the reduced lattice mismatch between the InN epilayer and the top buffer layer is responsible for improvement of sample quality using the buffer-layer technique.
The effect of interface roughness on multilayer heterostructures
Authors: Brown Martyn Rowan , Rees Paul , Cobley Richard J. , Teng Kar Seng , Wilks Steve , Hughes Arwel
Published: December 2007

Semiconductor devices which utilize the quantum confinement of charge carriers inherently employ material layers thin enough that even monolayer interface roughness has an effect on performance. We present a method for including the effect of interface roughness on the calculation of electron energy levels and wavefunctions by solving Schrödinger’s equation across the interface between semiconductor layers. Interface roughness is approximated by considering a supplementary interface in addition to the idealized perfectly flat interface. The position of the second interface is considered to be a probabilistic distribution with a mean corresponding to the position of the perfect case. Using Green’s theorem and the appropriate reciprocity relations, we deduce a correction to the reflection and transmission probabilities of an electron incident upon a rough material interface. The procedure is presented in terms of a transfer matrix algorithm to facilitate use in existing electron reflection transmission probability models. Examples are given of the calculation of the effect of interface roughness in resonant tunneling diodes and multiquantum barriers. We also discuss how this model is applicable to a range of physical mechanisms that result in roughness at the interface of two semiconductor materials.