Laser microprobe facility used in the elemental analysis of small feature of a sample

Laser microprobe facility is effective in the elemental analysis of small areas of heterogeneous samples. The instrument uses the focused beam of a pulsed laser to evaporate a small volume of material from a relatively massive sample

Paving the Way for Success in High School and Beyond: The Importance of Preparing Middle School Students for the Transition to Ninth Grade

P/PV's GroundWork series summarizes available evidence on a variety of social policy topics, providing a firm foundation for future work.This second brief in the series presents an overview of issues surrounding the ninth grade transition: why it is so important; why many middle school students find it so difficult; traits related to a successful transition; and what schools can do to ease difficulties in the transition. Research indicates that students unprepared to handle the transition are more likely to disengage from school, which in turn may lead to dropping out -- and a host of related problems, thus perpetuating a cycle of poverty for disadvantaged, low-income youth

The Case for School-Based Integration of Services: Changing the Ways Students, Families and Communities Engage with their Schools

P/PV's GroundWork series summarizes available evidence on a variety of social policy topics, providing a solid foundation for future work.This first issue reviews the current literature about the potential benefits of simultaneously providing three services in school -- healthcare, out-of-school-time learning and family supports -- to boost students' educational outcomes. For disadvantaged, low-income youth, research indicates that access to these supports can play a key role in helping them surmount common obstacles to educational attainment. In addition to highlighting how each affects key outcomes such as learning, school connectedness (i.e., positive feelings about school) and access to needed services, this brief summarizes the potential benefits of offering these resources through a highly integrated, school-based model

Cationic Alkylaluminum-Complexed Zirconocene Hydrides as Participants in Olefin Polymerization Catalysis

The alkylaluminum-complexed zirconocene trihydride cation [(SBI)Zr(μ-H)_3(AliBu_2)_2]^+, which is obtained by reaction of (SBI)ZrCl_2 with [Ph_3C][B(C_6F_5)_4] and excess HAl^iBu_2 in toluene solution, catalyzes the formation of isotactic polypropene when exposed to propene at -30 °C. This cation remains the sole observable species in catalyst systems free of AlMe compounds. In the presence of AlMe_3, however, exposure to propene causes the trihydride cation to be completely converted, under concurrent consumption of all hydride species by propene hydroalumination, to the doubly Me-bridged cation [(SBI)Zr(μ-Me)_2AlMe_2]^+. The latter then becomes the resting state for further propene polymerization, which produces, by chain transfer to Al, mainly AlMe_2-capped isotactic polypropene

Alkylaluminum-complexed zirconocene hydrides: identification of hydride-bridged species by NMR spectroscopy

Reactions of unbridged zirconocene dichlorides, (R_nC_5H_5−n)_2ZrCl_2 (n = 0, 1, or 2), with diisobutylaluminum hydride (HAl^iBu_2) result in the formation of tetranuclear trihydride clusters of the type (R_nC_5H_5−n)_2Zr(μ-H)_3(Al^iBu_2)_3(μ-Cl)_2, which contain three [Al^iBu_2] units. Ring-bridged ansa-zirconocene dichlorides, Me_2E(R_nC_5H_4−n)_2ZrCl_2 with E = C or Si, on the other hand, are found to form binuclear dihydride complexes of the type Me_2E(R_nC_5H_4−n)_2Zr(Cl)(μ-H)_2Al^iBu_2 with only one [Al^iBu_2] unit. The dichotomy between unbridged and bridged zirconocene derivatives with regard to tetranuclear versus binuclear product formation is proposed to be connected to different degrees of rotational freedom of their C_5-ring ligands. Alkylaluminum-complexed zirconocene dihydrides, previously observed in zirconocene-based precatalyst systems activated by methylalumoxane (MAO) upon addition of HAl^iBu_2 or Al^iBu_3, are proposed to be species of the type Me_2Si(ind)_2Zr(Me)(μ-H)_2Al^iBu_2, stabilized by interaction of their terminal Me group with a Lewis acidic site of MAO

Physical properties of 6dF dwarf galaxies

Spectral synthesis is basically the decomposition of an observed spectrum in terms of the superposition of a base of simple stellar populations of various ages and metallicities, producing as output the star formation and chemical histories of a galaxy, its extinction and velocity dispersion. The STARLIGHT code provides one of the most powerful spectral synthesis tools presently available. We have applied this code to the entire Six-Degree-Field Survey (6dF) sample of nearby star-forming galaxies, selecting dwarf galaxy candidates with the goal of: (1) deriving the age and metallicity of their stellar populations and (2) creating a database with the physical properties of our sample galaxies together with the FITS files of pure emission line spectra (i.e. the observed spectra after subtraction of the best-fitting synthetic stellar spectrum). Our results yield a good qualitative and quantitative agreement with previous studies based on the Sloan Digital Sky Survey (SDSS). However, an advantage of 6dF spectra is that they are taken within a twice as large fiber aperture, much reducing aperture effects in studies of nearby dwarf galaxies.Comment: To appear in JENAM Symposium "Dwarf Galaxies: Keys to Galaxy Formation and Evolution", P. Papaderos, S. Recchi, G. Hensler (eds.). Lisbon, September 2010, Springer Verlag, in pres

Climate-Ozone Connections

Climate change will affect the evolution of the ozone layer through changes in transport, chemical composition, and temperature. In turn, changes to the ozone layer will affect climate through radiative processes, and consequential changes in temperature gradients will affect atmospheric dynamics. Therefore, climate change and the evolution of the ozone layer are coupled. Understanding all of the processes involved is made more complex by the fact that many of the interactions are nonlinear