The association between organic matter and clay minerals in carbonaceous chondrites

There is an established relationship between organic matter content and aqueous alteration processes [1,2]. However, the relationship between meteoritic organic matter and individual aqueously generated mineral matrix phases is poorly understood. Meteoritic organic matter is primarily composed of C, H and N and therefore their bulk abundances in chondrites are strongly controlled by the organic matter content. Mössbauer Spectroscopy can characterise the ferric iron bearing matrix minerals associated with aqueous alteration, such as Fe- bearing clays and magnetite. A combination of these two parameters may indicate the presence of any organic-mineral interactions

Insight into the evolution of the Tagish Lake carbonaceous chondrite by analysis of the oxygen isotopic composition of extracted water and Mössbauer spectroscopy

Analysis of oxygen isotopes in water from Tagish Lake together with Mössbauer Spectroscopy suggest some similarities to the CI group of meteorites but also suggest differences in the extent of parent body hydrothermal alteration

Mid-infrared spectroscopy of CAI and AOA from the Allende CV3.2 chondrite

Mid-infrared spectra of bulk CAI from the CV3.2 chondrite Allende are presented and compared with astronomical spectra of cometary dust, zodiacal light,the circumstellar disk of beta Pictoris and dust around the red supergiant PR Per

Finite-size effects in amorphous Fe90Zr10/Al75Zr25 multilayers

The thickness dependence of the magnetic properties of amorphous Fe90Zr10 layers has been explored using Fe90Zr10/Al75Zr25 multilayers. The Al75Zr25 layer thickness is kept at 40 \AA, while the thickness of the Fe90Zr10 layers is varied between 5 and 20 \AA. The thickness of the Al75Zr25 layers is sufficiently large to suppress any significant interlayer coupling. Both the Curie temperature and the spontaneous magnetization decrease non-linearly with decreasing thickness of the Fe90Zr10 layers. No ferromagnetic order is observed in the multilayer with 5 {\AA} Fe90Zr10 layers. The variation of the Curie temperature $T_c$ with the Fe90Zr10 layer thickness $t$ is fitted with a finite-size scaling formula [1-\Tc(t)/\Tc(\infty)]=[(t-t')/t_0]^{-\lambda}, yielding $\lambda=1.2$, and a critical thickness $t'=6.5$ \AA, below which the Curie temperature is zero.Comment: 8 pages, 8 figure

The new generation of PowerPC VMEbus front end computers for the CERN SPS and LEP accelerators system

The CERN SPS and LEP PowerPC project is aimed at introducing a new generation of PowerPC VMEbus processor modules running the LynxOS real-time operating system. This new generation of front end computers using the state-of-the-art microprocessor technology will first replace the obsolete XENIX PC based systems (about 140 installations) successfully used since 1988 to control the LEP accelerator. The major issues addressed in the scope of this large scale project are the technical specification for the new PowerPC technology, the re-engineering aspects, the interfaces with other CERN wide projects, and the set up of a development environment. This project offers also support for other major SPS and LEP projects interested in the PowerPC microprocessor technology

Elementary transitions and magnetic correlations in two-dimensional disordered nanoparticle ensembles

The magnetic relaxation processes in disordered two-dimensional ensembles of dipole-coupled magnetic nanoparticles are theoretically investigated by performing numerical simulations. The energy landscape of the system is explored by determining saddle points, adjacent local minima, energy barriers, and the associated minimum energy paths (MEPs) as functions of the structural disorder and particle density. The changes in the magnetic order of the nanostructure along the MEPs connecting adjacent minima are analyzed from a local perspective. In particular, we determine the extension of the correlated region where the directions of the particle magnetic moments vary significantly. It is shown that with increasing degree of disorder the magnetic correlation range decreases, i.e., the elementary relaxation processes become more localized. The distribution of the energy barriers, and their relation to the changes in the magnetic configurations are quantified. Finally, some implications for the long-time magnetic relaxation dynamics of nanostructures are discussed.Comment: 19 pages, 6 figure

Correlated modal mineralogy, aqueous alteration and oxygen isotope composition of CM Chondrites

In this study we move beyond defining alteration sequences in CM chondrites towards understanding the relationship between modal mineralogy, the extent of aqueous alteration and O-isotope compositions

The Taurus Tunable Filter Field Galaxy Survey: Sample Selection and Narrowband Number-Counts

Recent evidence suggests a falling volume-averaged star-formation rate (SFR) over z ~ 1. It is not clear, however, the extent to which the selection of such samples influences the measurement of this quantity. Using the Taurus Tunable Filter (TTF) we have obtained an emission-line sample of faint star-forming galaxies over comparable lookback times: the TTF Field Galaxy Survey. By selecting through emission-lines, we are screening galaxies through a quantity that scales directly with star-formation activity for a given choice of initial mass function. The scanning narrowband technique furnishes a galaxy sample that differs from traditional broadband-selected surveys in both its volume-limited nature and selection of galaxies through emission-line flux. Three discrete wavelength intervals are covered, centered at H-alpha redshifts z = 0.08, 0.24 and 0.39. Galaxy characteristics are presented and comparisons made with existing surveys of both broadband and emission-line selection. When the number-counts of emission-line objects are compared with those expected on the basis of existing H-alpha surveys, we find an excess of ~ 3 times at the faintest limits. While these detections are yet to be independently confirmed, inspection of the stronger subsample of galaxies detected in both the line and continuum (line-on-continuum subsample; 13 %) is sufficient to support an excess population. This increase in the emission-line field population implies higher star-formation densities over z ~ 0.4. However, further study in the form of multi-object spectroscopic follow-up is necessary to quantify this and confirm the faintest detections in the sample.Comment: 48 pages, 12 figures. To appear in the Astrophysical Journal. An abridged version of the Abstract is shown her