6,894 research outputs found
Milky Way type galaxies in a LCDM cosmology
We analyse a sample of 52,000 Milky Way (MW) type galaxies drawn from the
publicly available galaxy catalogue of the Millennium Simulation with the aim
of studying statistically the differences and similarities of their properties
in comparison to our Galaxy. Model galaxies are chosen to lie in haloes with
maximum circular velocities in the range 200-250 km/seg and to have
bulge-to-disk ratios similar to that of the Milky Way. We find that model MW
galaxies formed quietly through the accretion of cold gas and small satellite
systems. Only 12 per cent of our model galaxies experienced a major merger
during their lifetime. Most of the stars formed in situ, with only about 15 per
cent of the final mass gathered through accretion. Supernovae and AGN feedback
play an important role in the evolution of these systems. At high redshifts,
when the potential wells of the MW progenitors are shallower, winds driven by
supernovae explosions blow out a large fraction of the gas and metals. As the
systems grow in mass, SN feedback effects decrease and AGN feedback takes over,
playing a more important role in the regulation of the star formation activity
at lower redshifts. Although model Milky Way galaxies have been selected to lie
in a narrow range of maximum circular velocities, they nevertheless exhibit a
significant dispersion in the final stellar masses and metallicities. Our
analysis suggests that this dispersion results from the different accretion
histories of the parent dark matter haloes. Statically, we also find evidences
to support the Milky Way as a typical Sb/Sc galaxy in the same mass range,
providing a suitable benchmark to constrain numerical models of galaxy
formationComment: 10 pages, 7 figures, mne2.cls, MNRAS, replaced with accepted versio
Image Analysis of Adventitious Root Quality in Wild Sage and Glossy Abelia Cuttings after Application of Different Indole-3-Butyric Acid Concentrations
Adventitious root (AR) formation is a key step in stem cutting propagation of economi-cally important woody ornamentals. Inadequate environmental and hormonal conditions can lead to the production of an insufficient or modest number of ARs in stem cutting, with a consequent decrease in quality. The aim of this research was to optimize wild sage and glossy abelia autumn stem cutting propagation protocols, using image analysis to assess the effects of different IBA concentrations and cultivars on AR quality. For both taxa, the treatments were: four IBA concentrations: 0, 1250, 2500 and 5000 mg L−1 and two cultivars: ‘Little Lucky’ (cv1) and ‘Yellow’ (cv2) from Lantana, and ‘Canyon Creek’ (cv1) and ‘Eduard Goucher’ (cv2) from Abelia. Results show that IBA application is not needed to enhance rooting ability; however, IBA concentration is an important factor determining the best overall AR quality in both taxa. In wild sage applying 5000 mg L−1 IBA improved AR quality in ‘Little Lucky’, increasing the root number, total length, surface area and number of forks and crossings, but decreased quality in ‘Yellow’. In glossy abelia ‘Edouard Goucher’, 5000 mg L−1 IBA increased the root number, but 1250 mg L−1 IBA improved AR quality; ‘Canyon Creek’ did not perform as well as cv2 at these concentrations. This study confirms that sensitivity to IBA dosage varies among species and their cultivars. Findings may help the commercial nursery industry produce higher quality cuttings
Halophyte common ice plants: A future solution to arable land salinization
The problems associated with the salinization of soils and water bodies and the increasing competition for scarce freshwater resources are increasing. Current attempts to adapt to these conditions through sustainable agriculture involves searching for new highly salt-tolerant crops, and wild species that have potential as saline crops are particularly suitable. The common ice plant (Mesembryanthemum crystallinum L.) is an edible halophyte member of the Aizoaceae family, which switches from C3 photosynthesis to crassulacean acid metabolism (CAM) when exposed to salinity or water stress. The aim of this review was to examine the potential of using the ice plant in both the wild and as a crop, and to describe its ecology and morphology, environmental and agronomic requirements, and physiology. The antioxidant properties and mineral composition of the ice plant are also beneficial to human health and have been extensively examined
Andreev reflection in Si-engineered Al/InGaAs hybrid junctions
Andreev-reflection dominated transport is demonstrated in Al/n-In0.38Ga0.62As
superconductor-semiconductor junctions grown by molecular beam epitaxy on
GaAs(001). High junction transparency was achieved in low-doped devices by
exploiting Si interface bilayers to suppress the native Schottky barrier. It is
argued that this technique is ideally suited for the fabrication of ballistic
transport hybrid microstructures.Comment: 9 REVTEX pages + 3 postscript figures, to be published in APL 73,
(28dec98
The VIMOS-VLT Deep Survey: Dependence of galaxy clustering on stellar mass
We have investigated the dependence of galaxy clustering on their stellar
mass at z~1, using the data from the VIMOS-VLT Deep Survey (VVDS). We have
measured the projected two-point correlation function of galaxies, wp(rp) for a
set of stellar mass selected samples at an effective redshift =0.85. We have
control and quantify all effects on galaxy clustering due to the incompleteness
of our low mass samples. We find that more massive galaxies are more clustered.
When compared to similar results at z~0.1 in the SDSS, we observed no evolution
of the projected correlation function for massive galaxies. These objects
present a stronger linear bias at z~1 with respect to low mass galaxies. As
expected, massive objects at high redshift are found in the highest pics of the
dark matter density field.Comment: 4 pages, 2 figures, 43rd Rencontres de Moriond - March 15-22, 2008 -
La Thuile (Val d'Aosta, Italy
Suspended Nanoscale Field Emitter Devices for High-Temperature Operation
In this work, we demonstrate suspended two- and four-terminal field emission devices for high-temperature operation. The planar structures were fabricated with tungsten on a 200-nm silicon nitride membrane. The insulator in the vicinity of the terminals was removed to minimize undesirable Frenkel–Poole emission and increase the resistance of leakage current pathways. The effects of temperatures up to 450 °C on Fowler–Nordheim emission characteristics and parasitic leakage resistance were studied. Turn-on voltages with magnitudes under 15 V that further decreased as a function of increasing temperature for the two-terminal device were reported. Gating at temperatures of 150 °C and 300 °C was shown for the four-terminal device, and corresponding transconductance and cutoff frequency values were computed
Suspended Nanoscale Field Emitter Devices for High-Temperature Operation
In this work, we demonstrate suspended two- and four-terminal field emission devices for high-temperature operation. The planar structures were fabricated with tungsten on a 200-nm silicon nitride membrane. The insulator in the vicinity of the terminals was removed to minimize undesirable Frenkel–Poole emission and increase the resistance of leakage current pathways. The effects of temperatures up to 450 °C on Fowler–Nordheim emission characteristics and parasitic leakage resistance were studied. Turn-on voltages with magnitudes under 15 V that further decreased as a function of increasing temperature for the two-terminal device were reported. Gating at temperatures of 150 °C and 300 °C was shown for the four-terminal device, and corresponding transconductance and cutoff frequency values were computed
Endovascular treatment of chronic cerebro spinal venous insufficiency in patients with multiple sclerosis modifies circulating markers of endothelial dysfunction and coagulation activation: a prospective study.
On Kalmbach measurability
summary:In this note we show that, for an arbitrary orthomodular lattice , when is a faithful, finite-valued outer measure on , then the Kalmbach measurable elements of form a Boolean subalgebra of the centre of
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