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Sun
Kinds of Sun Terms modified by Sun Selected AbstractsSunB, a novel Sad1 and UNC-84 domain-containing protein required for development of Dictyostelium discoideumDEVELOPMENT GROWTH & DIFFERENTIATION, Issue 7 2010Nao Shimada A gene, sunB, encoding a novel class of Sad1 and UNC-84 (SUN) domain, was isolated from a cDNA screen for suppressors of a mutation in Dd-STATa , a Dictyostelium homologue of metazoan STAT (signal transducers and activators of transcription). The SunB protein localized in the area around the nucleus in growing cells, but in the multicellular stages it was predominantly found in prespore vacuoles (PSVs). A disruptant of sunB was multinucleated in the vegetative phase; during development it formed mounds with multiple tips and failed to culminate. The mutation was cell autonomous, and showed reduced expression of the prespore marker gene pspA and elevated expression of marker genes for prestalk AB cells. Interestingly, the level of SunB was abnormally high in the prestalk cells of Dd-STATa mutants, which are defective in culmination. We conclude that SunB is essential for accurate prestalk/prespore differentiation during Dictyostelium development and that its cell-type dependent localization is regulated by a Dd-STATa-mediated signaling pathway. [source] On parameter estimation of a simple real-time flow aggregation modelINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 7 2006Huirong Fu Abstract There exists a clear need for a comprehensive framework for accurately analysing and realistically modelling the key traffic statistics that determine network performance. Recently, a novel traffic model, sinusoid with uniform noise (SUN), has been proposed, which outperforms other models in that it can simultaneously achieve tractability, parsimony, accuracy (in predicting network performance), and efficiency (in real-time capability). In this paper, we design, evaluate and compare several estimation approaches, including variance-based estimation (Var), minimum mean-square-error-based estimation (MMSE), MMSE with the constraint of variance (Var+MMSE), MMSE of autocorrelation function with the constraint of variance (Var+AutoCor+MMSE), and variance of secondary demand-based estimation (Secondary Variance), to determining the key parameters in the SUN model. Integrated with the SUN model, all the proposed methods are able to capture the basic behaviour of the aggregation reservation system and closely approximate the system performance. In addition, we find that: (1) the Var is very simple to operate and provides both upper and lower performance bounds. It can be integrated into other methods to provide very accurate approximation to the aggregation's performance and thus obtain an accurate solution; (2) Var+AutoCor+MMSE is superior to other proposed methods in the accuracy to determine system performance; and (3) Var+MMSE and Var+AutoCor+MMSE differ from the other three methods in that both adopt an experimental analysis method, which helps to improve the prediction accuracy while reducing computation complexity. Copyright © 2005 John Wiley & Sons, Ltd. [source] A software system for rigid-body modelling of solution scattering dataJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2000M.B. Kozin A computer system for rigid body modelling against solution scattering data is described. Fast algorithms to compute scattering from a complex of two arbitrary positioned subunits are implemented and coupled with the graphics program ASSA (Kozin, Volkov & Svergun, 1997, J. Appl. Cryst.30, 811-815). Mutual positions and orientations of the subunits (represented by low-resolution envelopes or by atomic models) can be determined by interactively fitting the experimental scattering curve from the complex. The system runs on the major Unix platforms (SUN, SGI and DEC workstations). [source] Comparison of Glomerular Filtration Rate between Greyhounds and Non-Greyhound DogsJOURNAL OF VETERINARY INTERNAL MEDICINE, Issue 3 2006Wm Tod Drost Greyhounds have significantly higher serum creatinine (SCr) concentration than do non-Greyhound dogs that may be attributable to differences in glomerular filtration rate (GFR). By means of plasma clearance of technetium Tc 99m diethylenetriaminepentaacetic acid, GFR was measured in 10 Greyhounds and 10 non-Greyhound dogs with normal findings of physical examination, CBC, serum biochemical analysis, and urinalysis. Dogs were fed the same diet for a minimum of 6 weeks before GFR data collection. Greyhounds had significantly higher mean ± SD GFR (3.0±0.1 vs 2.5±0.2 ml/min/kg; P= .01) and SCr concentration (1.8±0.1 vs 1.5±0.1 mg/dL; P= .03) than did non-Greyhound dogs, but the serum urea nitrogen (SUN) concentration was not significantly different (18±1 vs 18±2 mg/dL; P= .8). Therefore, the higher SCr concentration in Greyhounds is not attributable to decreased GFR, and may be associated with the high muscle mass in the breed. Healthy Greyhounds have higher GFR than do non-Greyhound dogs. [source] 1261: Pathophysiology and classification of uveitisACTA OPHTHALMOLOGICA, Issue 2010AD DICK Purpose This talk will overview the pathophysiology of non-infectious uveitis in relation to recent SUN (standardised uveitis nomenclature) disease classification. Methods The experimental and translational human evidence of autoimmunity and activation of immunity will be discussed. In addition the talk will highlight the pathways and mechanisms of tissue damage that results in sight-threatening disease. Results Traditionally, despite active immune regulatory mechanisms operative within the ocular environment, inflammation still occurs. Activated antigen and non-antigen specific T cells are generated in uveitis. The interplay with innate immunity and in particular cells of myeloid lineage both systemically and within the local environment dictate the severity and extent of pathology we observe. Conclusion The understanding of immune responses during the uveitis open many avenues to potential novel immunotherapies that not only suppress inflammation but attempt to redress immune balance, tolerance and local homeostasis within ocular tissues. [source] The primary cilium as a gravitational force transducer and a regulator of transcriptional noiseDEVELOPMENTAL DYNAMICS, Issue 8 2008Stephen J. Moorman Abstract Circumstantial evidence has suggested that the primary cilium might function as a gravity sensor. Direct evidence of its gravity-sensing function has recently been provided by studies of rohon beard neurons. These neurons showed changes in the variability of gene expression levels that are linked to the cyclic changes in the Earth's gravitational field due to the Sun and Moon. These cyclic changes also cause the tides. Rohon beard neurons, after the primary cilia have been selectively destroyed, no longer show changes in gene expression variability linked to the cyclic changes in Earth's gravitational field. After the neurons regrow their primary cilia, the link between variability in gene expression levels and the Earth's changing gravitational field returns. This suggests two new functions for the primary cilia, detecting the cyclical changes in the Earth's gravitational field and transducing those changes into changes in the variability (stochastic nature) of gene expression. Developmental Dynamics 237:1955,1959, 2008. © 2008 Wiley-Liss, Inc. [source] Something ,Paralogical' Under the Sun: Lyotard's Postmodern Condition and science educationEDUCATIONAL PHILOSOPHY AND THEORY, Issue 2 2000Michalinos ZembylasArticle first published online: 2 NOV 200 Sometimes I dream that I am an astronaut. I land my spaceship on a distant planet. When I tell me children on that planet that on earth school is compulsory and that we have homework every evening, they split their sides laughing. And so I decide to stay with them for a long, long time, Well anyway, until the summer holidays. (Cited in Lyotard, 1995, p. xix) Each state of the mind is irreducible. The mere act of giving it a name, that is of classifying it, implies a falsification of it. From all this, it would be possible to deduce that there is no science in Tlon, let alone rational thought. The paradox, however, is that sciences exist, in countless number, The metaphysicians of Tlon are not looking for truth, nor even for an approximation of it; they are after a kind of amazement. They consider metaphysics a branch of fantastic literature. They know that a system is nothing more than the subordination of all aspects of the universe to some one of them. Even the phrase ,all the aspects' can be rejected, since it presupposes the impossible inclusion of the present moment, and of past moments. (Borges, 1962, p. 10) [source] Homeostatic plasticity in a reward processing region: accumbens neurons scale too! (Commentary on Sun & Wolf)EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 4 2009Jean-Claude Béïque No abstract is available for this article. [source] Gloves Drying in the SunACADEMIC EMERGENCY MEDICINE, Issue 1 2002Mary Meyer MD No abstract is available for this article. [source] The age of Rubisco: the evolution of oxygenic photosynthesisGEOBIOLOGY, Issue 4 2007E. G. NISBET ABSTRACT The evolutionary history of oxygenesis is controversial. Form I of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) in oxygen-tolerant organisms both enables them to carry out oxygenic extraction of carbon from air and enables the competitive process of photorespiration. Carbon isotopic evidence is presented from ~2.9 Ga stromatolites from Steep Rock, Ontario, Canada, ~2.9 Ga stromatolites from Mushandike, Zimbabwe, and ~2.7 Ga stromatolites in the Belingwe belt, Zimbabwe. The data imply that in all three localities the reef-building autotrophs included organisms using Form I Rubisco. This inference, though not conclusive, is supported by other geochemical evidence that these stromatolites formed in oxic conditions. Collectively, the implication is that oxygenic photosynthesizers first appeared ~2.9 Ga ago, and were abundant 2.7,2.65 Ga ago. Rubisco specificity (its preference for CO2 over O2) and compensation constraints (the limits on carbon fixation) may explain the paradox that despite the inferred evolution of oxygenesis 2.9 Ga ago, the Late Archaean air was anoxic. The atmospheric CO2:O2 ratio, and hence greenhouse warming, may reflect Form I Rubisco's specificity for CO2 over O2. The system may be bistable under the warming Sun, with liquid oceans occurring in either anoxic (H2O with abundant CH4 plus CO2) or oxic (H2O with more abundant CO2, but little CH4) greenhouse states. Transition between the two states would involve catastrophic remaking of the biosphere. Build-up of a very high atmospheric inventory of CO2 in the 2.3 Ga glaciation may have allowed the atmosphere to move up the CO2 compensation line to reach stability in an oxygen-rich system. Since then, Form I Rubisco specificity and consequent compensation limits may have maintained the long-term atmospheric disproportion between O2 and CO2, which is now close to both CO2 and O2 compensation barriers. [source] A 2000-YEAR CONTEXT FOR MODERN CLIMATE CHANGEGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 1 2005K.A. MAASCH ABSTRACT. Although considerable attention has been paid to the record of temperature change over the last few centuries, the range and rate of change of atmospheric circulation and hydrology remain elusive. Here, eight latitudinally well-distributed (pole-equator-pole), highly resolved (annual to decadal) climate proxy records are presented that demonstrate major changes in these variables over the last 2000 years. A comparison between atmospheric 14C and these changes in climate demonstrates a first-order relationship between a variable Sun and climate. The relationship is seen on a global scale. [source] Laser Ablation (193 nm), Purification and Determination of Very Low Concentrations of Solar Wind Nitrogen Implanted in Targets from the GENESIS SpacecraftGEOSTANDARDS & GEOANALYTICAL RESEARCH, Issue 2 2009Laurent Zimmermann azote; ablation laser; purification; spectrométrie de masse; mission GENESIS The GENESIS space mission recovered ions emitted by the Sun during a 27 month period. In order to extract, purify and determine the very low quantities of solar nitrogen implanted in the GENESIS targets, a new installation was developed and constructed at the CRPG (Nancy, France). It permitted the simultaneous determination of nitrogen and noble gases extracted from the target by laser ablation. The extraction procedure used a 193 nm excimer laser that allowed for surface contamination in the outer 5 nm to be removed, followed by a step that removed 50 nm of the target material, extracting the solar nitrogen and noble gases implanted in the target. Following purification using Ti and Zr getters for noble gases and a Cu-CuO oxidation cycle for N2, the extracted gases were analysed by static mode (pumps closed) mass spectrometry using electron multiplier and Faraday cup detectors. The nitrogen blanks from the purification section and the static line (30 minutes) were only 0.46 picomole and 0.47 picomole, respectively. La mission GENESIS a récupéré des ions émis par le soleil pendant une période de 27 mois. Afin d'extraire, purifier et analyser de très faibles quantités d'azote solaire implantés dans des cibles GENESIS, une nouvelle installation a été développée et construite au CRPG. Elle a permis l'analyse simultanée de l'azote et des gaz nobles extraits de la couche d'or par ablation. La procédure d'extraction a utilisé un laser Excimer 193 nm qui a permis une étape d'extraction à 5 nm pour éliminer la pollution à la surface, suivie d'une étape qui a extrait jusqu'à une profondeur de 50 nm l'azote et les gaz rares solaires implantés dans la cible. Après une purification à l'aide de getters Ti et Zr pour les gaz rares et un cycle d'oxydation Cu-CuO pour N2, les gaz extraits ont été analysés en mode statique (pompage fermé) par spectrométrie de masse à l'aide d'un multiplicateur d'électrons et d'une cage de Faraday. Les blancs d'azote provenant de la partie purification et de la ligne en statique (30 minutes) étaient de seulement 0.46 et 0.47 picomole, respectivement. [source] Political Violence in the Republic of Rome: Nothing New under the SunGOVERNMENT AND OPPOSITION, Issue 4 2006Brenda J. Lutz At various times the Roman Republic faced outbreaks of domestic political violence, including riots and intimidation, assassinations and conspiracies to overthrow the government. Violence was particularly noticeable in the Early Republic and the Late Republic. These activities were quite similar to the terrorism and violence used by mobs and groups during the French Revolution and the tactics of fascists and leftists in Europe in the 1920s or 1930s. More accurately, the actions of mobs and others during the French Revolution and leftists and fascists in Europe were very similar to the techniques used in the Roman political system in the last five centuries BCE. [source] Korea's Place in the Sun: A Modern History By Bruce CumingsHISTORY, Issue 307 2007JAMES H. GRAYSON No abstract is available for this article. [source] A two-dimensional analytical solution for groundwater flow in a leaky confined aquifer system near open tidal waterHYDROLOGICAL PROCESSES, Issue 4 2001Zhonghua Tang Abstract Groundwater in coastal areas is commonly disturbed by tidal fluctuations. A two-dimensional analytical solution is derived to describe the groundwater fluctuation in a leaky confined aquifer system near open tidal water under the assumption that the groundwater head in the confined aquifer fluctuates in response to sea tide whereas that of the overlying unconfined aquifer remains constant. The analytical solution presented here is an extension of the solution by Sun for two-dimensional groundwater flow in a confined aquifer and the solution by Jiao and Tang for one-dimensional groundwater flow in a leaky confined aquifer. The analytical solution is compared with a two-dimensional finite difference solution. On the basis of the analytical solution, the groundwater head distribution in a leaky confined aquifer in response to tidal boundaries is examined and the influence of leakage on groundwater fluctuation is discussed. Copyright © 2001 John Wiley & Sons, Ltd. [source] Thermodynamic optimization of global circulation and climateINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 4 2005Adrian Bejan Abstract The constructal law of generation of flow structure is used to predict the main features of global circulation and climate. The flow structure is the atmospheric and oceanic circulation. This feature is modelled as convection loops, and added to the earth model as a heat engine heated by the Sun and cooled by the background. It is shown that the dissipation of the power produced by the earth engine can be maximized by selecting the proper balance between the hot and cold zones of the Earth, and by optimizing the thermal conductance of the circulation loops. The optimized features agree with the main characteristics of global circulation and climate. The robustness of these predictions, and the place of the constructal law as a self-standing principle in thermodynamics, are discussed. Copyright © 2005 John Wiley & Sons, Ltd. [source] Construction of Exact Simultaneous Confidence Bands for a Simple Linear Regression ModelINTERNATIONAL STATISTICAL REVIEW, Issue 1 2008Wei Liu Summary A simultaneous confidence band provides a variety of inferences on the unknown components of a regression model. There are several recent papers using confidence bands for various inferential purposes; see for example, Sun et al. (1999), Spurrier (1999), Al-Saidy et al. (2003), Liu et al. (2004), Bhargava & Spurrier (2004), Piegorsch et al. (2005) and Liu et al. (2007). Construction of simultaneous confidence bands for a simple linear regression model has a rich history, going back to the work of Working & Hotelling (1929). The purpose of this article is to consolidate the disparate modern literature on simultaneous confidence bands in linear regression, and to provide expressions for the construction of exact 1 ,, level simultaneous confidence bands for a simple linear regression model of either one-sided or two-sided form. We center attention on the three most recognized shapes: hyperbolic, two-segment, and three-segment (which is also referred to as a trapezoidal shape and includes a constant-width band as a special case). Some of these expressions have already appeared in the statistics literature, and some are newly derived in this article. The derivations typically involve a standard bivariate t random vector and its polar coordinate transformation. Résumé Un intervalle de confiance simultanée fournit une variété d'inférences sur les composantes inconnues d'un modéle de régression. Plusieurs articles récents utilisent des intervalles de confiance dans des buts variés; voir par exemple Sun, Raz et Faraway (1999), Spurrier (1999), Al-Saidy et al. (2003), Liu, Jamshidian et Zhang (2004), Bhargava et Spurrier (2004), Piegorsch et al. (2005), Liu et al. (2007). La construction d'intervalles de confiance simultanés pour un simple modéle de régression linéaire a une histoire riche, qui remonte aux travaux de Working et hotelling (1929). L'objet de cet article est de consolider la littérature moderne disparate sur les intervalles de confiance simultanés dans la régression linéaire, de fournir des expressions pour la construction d'intervalles de confiance simultanés de niveau exact 1 ,, pour un modéle de régression linéaire simple ou pour des formes unilatérales ou bilatérales. Nous concentrons notre attention sur les trois formes les plus reconnues: hyperbolique, à deux segments et à trois segments (qui est aussi appelée forme trapézoïdale et inclut un intervalle de largeur constante comme cas spécial). Certaines de ces expressions sont déjà apparues dans la littérature statistique, d'autres sont nouvellement introduites dans cet article. Les dérivations comprennent typiquement un vecteur aléatoire standard bivarié t et sa transformation en coordonnées polaires. [source] Variations of Water-Soluble Carbohydrate Contents in Different Age Class Modules of Leymus chinensis Populations in Sandy and Saline-Alkaline Soil on the Songnen Plains of ChinaJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 5 2007Xue-Mei Ding Abstract Leymus chinensis (Trin.) Tzvel. is a rhizomatous perennial herbage of Gramineae. Reproduction is mainly by vegetative reproduction. Tillering nodes and rhizomes of L. chinensis serve as organs for both vegetative reproduction and nutrient storage. Water-soluble carbohydrate (WSC) contents were measured in tillering nodes, nodes and internodes of rhizomes of different age classes of L. chinensis populations at three development stages, namely the dough ripe stage, the vegetative growth stage after full ripeness, and the withering stage, in two habitats: sandy soil and saline-alkaline soil. The results showed that WSC content in tillering nodes of the three age classes of L. chinensis were all markedly decreased with increasing age in both sandy soil and saline-alkaline soil. A similar trend of changes in WSC contents was observed in the nodes and internodes of rhizomes in different age classes in both habitats. The highest WSC contents were in 2-age-class nodes and internodes of rhizomes, followed by those in the 1 age class, with the lowest WSC contents found in 3-age-class nodes and internodes of rhizomes at the dough ripe and vegetative growth stages after full ripening. In turn, WSC contents decreased with increasing age at the withering stage in both habitats. The WSC content in each age class of internode was higher than that in the node of rhizome at three development stages in both habitats. (Handling editor: Jian-Xin Sun) [source] "There's Nothing Really New under the Sun": The Fallacy of the Neo-Soul GenreJOURNAL OF POPULAR MUSIC STUDIES, Issue 3 2010Phillip Lamarr Cunningham First page of article [source] Sensitivity of Stream flow and Water Table Depth to Potential Climatic Variability in a Coastal Forested Watershed,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 5 2010Zhaohua Dai Dai, Zhaohua, Carl C. Trettin, Changsheng Li, Devendra M. Amatya, Ge Sun, and Harbin Li, 2010. Sensitivity of Streamflow and Water Table Depth to Potential Climatic Variability in a Coastal Forested Watershed. Journal of the American Water Resources Association (JAWRA) 1,13. DOI: 10.1111/j.1752-1688.2010.00474.x Abstract:, A physically based distributed hydrological model, MIKE SHE, was used to evaluate the effects of altered temperature and precipitation regimes on the streamflow and water table in a forested watershed on the southeastern Atlantic coastal plain. The model calibration and validation against both streamflow and water table depth showed that the MIKE SHE was applicable for predicting the streamflow and water table dynamics for this watershed with an acceptable model efficiency (E > 0.5 for daily streamflow and >0.75 for monthly streamflow). The simulation results from changing temperature and precipitation scenarios indicate that climate change influences both streamflow and water table in the forested watershed. Compared to current climate conditions, the annual average streamflow increased or decreased by 2.4% with one percentage increase or decrease in precipitation; a quadratic polynomial relationship between changes in water table depth (cm) and precipitation (%) was found. The annual average water table depth and annual average streamflow linearly decreased with an increase in temperature within the range of temperature change scenarios (0-6°C). The simulation results from the potential climate change scenarios indicate that future climate change will substantially impact the hydrological regime of upland and wetland forests on the coastal plain with corresponding implications to altered ecosystem functions that are dependent on water. [source] Titanium isotopic compositions of well-characterized silicon carbide grains from Orgueil (CI): Implications for s-process nucleosynthesisMETEORITICS & PLANETARY SCIENCE, Issue 7-8 2007Gary R. Huss Using the 16 most-precise measurements, we estimate the relative contributions of stellar nucleosynthesis during the asymptotic giant branch (AGB) phase and the initial compositions of the parent stars to the compositions of the grains. To do this, we compare our data to the results of several published stellar models that employ different values for some important parameters. Our analysis confirms that s -process synthesis during the AGB phase only slightly modified the titanium compositions in the envelopes of the stars where mainstream silicon carbide grains formed, as it did for silicon. Our analysis suggests that the parent stars of the >1 ,m silicon carbide grains that we measured were generally somewhat more massive than the Sun (2,3 M,) and had metallicities similar to or slightly higher than solar. Here we differ slightly from results of previous studies, which indicated masses at the lower end of the range 1.5,3 M, and metallicities near solar. We also conclude that models using a standard 13C pocket, which produces a good match for the main component of s -process elements in the solar system, overestimate the contribution of the 13C pocket to s -process nucleosynthesis of titanium found in silicon carbide grains. Although previous studies have suggested that the solar system has a significantly different titanium isotopic composition than the parent stars of silicon carbide grains, we find no compelling evidence that the Sun falls off of the array defined by those stars. We also conclude that the Sun does lie on the low-metallicity end of the silicon and titanium arrays defined by mainstream silicon carbide grains. [source] Cosmic-ray exposure age and heliocentric distance of the parent bodies of enstatite chondrites ALH 85119 and MAC 88136METEORITICS & PLANETARY SCIENCE, Issue 6 2006D. Nakashima These two meteorites contain solar and cosmogenic noble gases. Based on the solar and cosmogenic noble gas compositions, we calculated heliocentric distances, parent body exposure ages, and space exposure ages of the two meteorites. The parent body exposure ages are longer than 6.7 Ma for ALH 85119 and longer than 8.7 Ma for MAC 88136. The space exposure ages are shorter than 2.2 Ma for ALH 85119 and shorter than 3.9 Ma for MAC 88136. The estimated heliocentric distances are more than 1.1 AU for ALH 85119 and 1.3 AU for MAC 88136. Derived heliocentric distances indicate the locations of parent bodies in the past when constituents of the meteorites were exposed to the Sun. From the mineralogy and chemistry of E chondrites, it is believed that E chondrites formed in regions within 1.4 AU from the Sun. The heliocentric distances of the two E chondrite parent bodies are not different from the formation regions of E chondrites. This may imply that heliocentric distances of E chondrites have been relatively constant from their formation stage to the stage of exposure to the solar wind. [source] Discovery of Earth's quasi-satelliteMETEORITICS & PLANETARY SCIENCE, Issue 8 2004Martin Connors The term quasi-satellite is used since these large orbits are not completely closed, but rather perturbed portions of the asteroid's orbit around the Sun. Due to its extremely Earth-like orbit, this asteroid is influenced by Earth's gravity to remain within 0.1 AU of the Earth for approximately 10 years (1997 to 2006). Prior to this, it had been on a horseshoe orbit closely following Earth's orbit for several hundred years. It will re-enter such an orbit, and make one final libration of 123 years, after which it will have a close interaction with the Earth and transition to a circulating orbit. Chaotic effects limit our ability to determine the origin or fate of this object. [source] The effects of nebula surface density profile and giant-planet eccentricities on planetary accretion in the inner solar systemMETEORITICS & PLANETARY SCIENCE, Issue 11 2002J. E. CHAMBERS Two surface density profiles are examined: a decaying profile with , , 1/a, where a is orbital semi-major axis, and a peaked profile in which , increases for a < 2 AU and decreases for a > 2 AU. The peaked profiles are generated by models of coagulation in an initially hot nebula. Models with initial ej,s = 0.05 (the current value) and 0.1 are considered. Simulations using the decaying profile with ej,s = 0.1 produce systems most like the observed planets in terms of mass-weighted mean a and the absence of a planet in the asteroid belt. Simulations with doubled , produce planets roughly twice as massive as the nominal case. Most initial embryos are removed in each simulation via ejection from the solar system or collision with the Sun. The asteroid belt is almost entirely cleared on a timescale of 10,100 Ma that depends sensitively on ej,s. Most initial mass with a < 2 AU survives, with the degree of mass loss increasing with a. Mass loss from the terrestrial region occurs on a timescale that is long compared to the mass loss time for the asteroid belt. Substantial radial mixing of material occurs in all simulations, but is greater in simulations with initital ej,s = 0.05. The degree of mixing is equivalent to a feeding zone of half width 1.5 and 0.9 AU for an Earth mass planet at 1 AU for the cases ej,s = 0.05 and 0.1, respectively. In simulations with ej,s = 0.05, roughly one-third and 5,10% of the mass contained in final terrestrial planets originated in the region a > 2.5 AU for the decaying and peaked profiles, respectively. In the case ej,s = 0.1, the median mass accreted from a > 2.5 AU is zero for both profiles. [source] Diurnal variation of sodium and potassium at MercuryMETEORITICS & PLANETARY SCIENCE, Issue 9 2002D. M. HUNTEN The proposed mechanism is deposition of ions and atoms on the cold night side, followed by their outward diffusion and evaporation as the Sun rises. Published criticisms of this mechanism are discussed and answered. The rate at which Na atoms can evaporate from the surfaces of the Moon and Mercury is uncertain, but, after a review of laboratory measurements, we propose that it is substantial at temperatures of 400 K and higher. Possible reasons are discussed why another group does not find the diurnal variation. There are differences in observing geometry, but the matter remains unclear. [source] The Struggle for a Place in the Sun: Rationalizing Foreign Language Study in the Twentieth CenturyMODERN LANGUAGE JOURNAL, Issue 1 2001James P. Lantolf Over the course of the past century, the MLJ was one of the sites where the vigorous, and often times passionate justification for, and defense of, foreign language (FL) study in the educational curriculum of the United States unfolded. Almost 10% of the slightly more than 4,000 articles published in the MLJ during the past century focused on the value and relevance of FL study in the educational enterprise. This article will focus on five major themes that surfaced throughout the 8 decades covered by our survey. The first theme comprises the general arguments offered by the profession in support of the value of FL study, most of which were impacted directly or indirectly by world events. The second and third themes document periods of general doubt and optimism about the place of FLs in the curriculum. In the fourth major theme, we describe the passionate and intense argumentation between the faculties of education and the defenders of FL study. The fifth, and final theme, addresses the question of which FLs should be taught in the schools and what contribution each might make to a student's education. As we enter the 21st century, it seems clear that the profession still feels compelled to justify the educational merit of its subject matter. In the end, given the twists and turns that history can take, it is difficult to predict whether FL study will eventually find an uncontested place in the sun. [source] Local kinematics and the local standard of restMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2010Ralph Schönrich ABSTRACT We re-examine the stellar kinematics of the solar neighbourhood in terms of the velocity ,, of the Sun with respect to the local standard of rest. We show that the classical determination of its component V, in the direction of Galactic rotation via Strömberg's relation is undermined by the metallicity gradient in the disc, which introduces a correlation between the colour of a group of stars and the radial gradients of its properties. Comparing the local stellar kinematics to a chemodynamical model which accounts for these effects, we obtain (U, V, W),= (11.1+0.69,0.75, 12.24+0.47,0.47, 7.25+0.37,0.36) km s,1, with additional systematic uncertainties ,(1, 2, 0.5) km s,1. In particular, V, is 7 km s,1 larger than previously estimated. The new values of (U, V, W), are extremely insensitive to the metallicity gradient within the disc. [source] Azimuthally symmetric theory of gravitation , I. On the perihelion precession of planetary orbitsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2010G. G. Nyambuya ABSTRACT From a purely non-general relativistic standpoint, we solve the empty space Poisson equation (,2,= 0) for an azimuthally symmetric setting (i.e. for a spinning gravitational system like the Sun). We seek the general solution of the form ,=,(r, ,). This general solution is constrained such that in the zeroth-order approximation it reduces to Newton's well-known inverse square law of gravitation. For this general solution, it is seen that it has implications on the orbits of test bodies in the gravitational field of this spinning body. We show that to second-order approximation, this azimuthally symmetric gravitational field is capable of explaining at least two things: (i) the observed perihelion shift of solar planets; (ii) the fact that the mean Earth,Sun distance must be increasing (this resonates with the observations of two independent groups of astronomers, who have measured that the mean Earth,Sun distance must be increasing at a rate between about 7.0 ± 0.2 m century,1 and 15.0 ± 0.3 m cy,1). In principle, we are able to explain this result as a consequence of the loss of orbital angular momentum; this loss of orbital angular momentum is a direct prediction of the theory. Further, we show that the theory is able to explain at a satisfactory level the observed secular increase in the Earth year (1.70 ± 0.05 ms yr,1). Furthermore, we show that the theory makes a significant and testable prediction to the effect that the period of the solar spin must be decreasing at a rate of at least 8.00 ± 2.00 s cy,1. [source] Heating of near-Earth objects and meteoroids due to close approaches to the SunMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2009S. Marchi ABSTRACT It is known that near-Earth objects (NEOs) during their orbital evolution may often undergo close approaches to the Sun. Indeed it is estimated that up to ,70 per cent of them end their orbital evolution colliding with the Sun. Starting from the present orbital properties, it is possible to compute the most likely past evolution for every NEO, and to trace its distance from the Sun. We find that a large fraction of the population may have experienced in the past frequent close approaches, and thus, as a consequence, a considerable Sun-driven heating, not trivially correlated to the present orbits. The detailed dynamical behaviour, the rotational and the thermal properties of NEOs determine the exact amount of the resulting heating due to the Sun. In the present paper, we discuss the general features of the process, providing estimates of the surface temperature reached by NEOs during their evolution. Moreover, we investigate the effects of this process on meteor-size bodies, analysing possible differences with the NEO population. We also discuss some possible effects of the heating which can be observed through remote sensing by ground-based surveys or space missions. [source] A new perspective on the irregular satellites of Saturn , I. Dynamical and collisional historyMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2008D. Turrini ABSTRACT The dynamical features of the irregular satellites of the giant planets argue against an in situ formation and are strongly suggestive of a capture origin. Since the last detailed investigations of their dynamics, the total number of satellites has doubled, increasing from 50 to 109, and almost tripled in the case of Saturn system. We have performed a new dynamical exploration of Saturn system to test whether the larger sample of bodies could improve our understanding of which dynamical features are primordial and which are the outcome of the secular evolution of the system. We have performed detailed N -body simulations using the best orbital data available and analysed the frequencies of motion to search for resonances and other possible perturbing effects. We took advantage of the hierarchical Jacobian symplectic algorithm to include in the dynamical model of the system also the gravitational effects of the two outermost massive satellites, Titan and Iapetus. Our results suggest that Saturn's irregular satellites have been significantly altered and shaped by the gravitational perturbations of Jupiter, Titan, Iapetus and the Sun and by the collisional sweeping effect of Phoebe. In particular, the effects on the dynamical evolution of the system of the two massive satellites appear to be non-negligible. Jupiter perturbs the satellites through its direct gravitational pull and, indirectly, via the effects of the Great Inequality, i.e. its near-resonance with Saturn. Finally, by using the hierarchical clustering method we found hints to the existence of collisional families and compared them with the available observational data. [source] | ||||||||||||||||||||||||||||||||||