785 research outputs found
Spin splitting of X-related donor impurity states in an AlAs barrier
We use magnetotunneling spectroscopy to observe the spin splitting of the
ground state of an X-valley-related Si-donor impurity in an AlAs barrier. We
determine the absolute magnitude of the effective Zeeman spin splitting factors
of the impurity ground state to be g= 2.2 0.1. We also investigate
the spatial form of the electron wave function of the donor ground state, which
is anisotropic in the growth plane
Modelling of laboratory data of bi-directional reflectance of regolith surface containing Alumina
Bidirectional reflectance of a surface is defined as the ratio of the
scattered radiation at the detector to the incident irradiance as a function of
geometry. The accurate knowledge of the bidirectional reflection function (BRF)
of layers composed of discrete, randomly positioned scattering particles is
very essential for many remote sensing, engineering, biophysical applications
and in different areas of Astrophysics. The computations of BRF's for plane
parallel particulate layers are usually reduced to solve the radiative transfer
equation (RTE) by the existing techniques. In this work we present our
laboratory data on bidirectional reflectance versus phase angle for two sample
sizes of 0.3 and 1 of Alumina for the He-Ne laser at 632.8 nm (red) and
543.5nm(green) wavelength. The nature of the phase curves of the asteroids
depends on the parameters like- particle size, composition, porosity, roughness
etc. In our present work we analyse the data which are being generated using
single scattering phase function i.e. Mie theory considering particles to be
compact sphere. The well known Hapke formula will be considered along with
different particle phase function such as Mie and Henyey Greenstein etc to
model the laboratory data obtained at the asteroid laboratory of Assam
University.Comment: 5 pages, 5 figures [accepted for publication in Publications of the
Astronomical Society of Australia (PASA) on 8 June, 2011
A Giant Crater on 90 Antiope?
Mutual event observations between the two components of 90 Antiope were
carried out in 2007-2008. The pole position was refined to lambda0 =
199.5+/-0.5 eg and beta0 = 39.8+/-5 deg in J2000 ecliptic coordinates, leaving
intact the physical solution for the components, assimilated to two perfect
Roche ellipsoids, and derived after the 2005 mutual event season (Descamps et
al., 2007). Furthermore, a large-scale geological depression, located on one of
the components, was introduced to better match the observed lightcurves. This
vast geological feature of about 68 km in diameter, which could be postulated
as a bowl-shaped impact crater, is indeed responsible of the photometric
asymmetries seen on the "shoulders" of the lightcurves. The bulk density was
then recomputed to 1.28+/-0.04 gcm-3 to take into account this large-scale
non-convexity. This giant crater could be the aftermath of a tremendous
collision of a 100-km sized proto-Antiope with another Themis family member.
This statement is supported by the fact that Antiope is sufficiently porous
(~50%) to survive such an impact without being wholly destroyed. This violent
shock would have then imparted enough angular momentum for fissioning of
proto-Antiope into two equisized bodies. We calculated that the impactor must
have a diameter greater than ~17 km, for an impact velocity ranging between 1
and 4 km/s. With such a projectile, this event has a substantial 50%
probability to have occurred over the age of the Themis family.Comment: 30 pages, 3 Tables, 8 Figures. Accepted for publication in Icaru
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Trans-Di-ÎĽ-acetato-[ÎĽ-N,N-bis-(diphenyl-phosphino)aniline] bis-[chlorido-molybdenum(II)](Mo - Mo)-dichloro-methane-tetra-hydro-furan (1/0.3/1.7)
The mol-ecular structure of the title compound, [Mo2(CH 3COO)2Cl2(C30H25NP 2)]·0.3CH2Cl2·1.7C 4H8O, features an Mo - Mo dumbbell bridged by two acetate groups which are trans to each other. Perpendicular to the plane spanned by the acetate groups, the Ph2PN(Ph)PPh2 ligand bridges both Mo atoms, having a P - N - P angle of 114.09 (19)°. In a trans position to the PNP ligand are two Cl atoms, one on each molybdenum centre. The Mo - Mo bond distance is 2.1161 (9) Å, within the range known for Mo - Mo quadruple bonds. The Mo complex is located on a crystallographic twofold rotation axis which runs through the N - C bond of the ligand. The site occupation factors of the disordered solvent molecules were fixed to 0.15 for dichloromethane and 0.85 for tetrahydrofuran. © 2009
Hybridization of mouse lemurs: different patterns under different ecological conditions
<p>Abstract</p> <p>Background</p> <p>Several mechanistic models aim to explain the diversification of the multitude of endemic species on Madagascar. The island's biogeographic history probably offered numerous opportunities for secondary contact and subsequent hybridization. Existing diversification models do not consider a possible role of these processes. One key question for a better understanding of their potential importance is how they are influenced by different environmental settings. Here, we characterized a contact zone between two species of mouse lemurs, <it>Microcebus griseorufus </it>and <it>M. murinus</it>, in dry spiny bush and mesic gallery forest that border each other sharply without intermediate habitats between them. We performed population genetic analyses based on mtDNA sequences and nine nuclear microsatellites and compared the results to a known hybrid zone of the same species in a nearby wide gradient from dry spiny bush over transitional forest to humid littoral forest.</p> <p>Results</p> <p>In the spiny-gallery system, <it>Microcebus griseorufus </it>is restricted to the spiny bush; <it>Microcebus murinus </it>occurs in gallery forest and locally invades the dryer habitat of its congener. We found evidence for bidirectional introgressive hybridization, which is closely linked to increased spatial overlap within the spiny bush. Within 159 individuals, we observed 18 hybrids with mitochondrial haplotypes of both species. Analyses of simulated microsatellite data indicate that we identified hybrids with great accuracy and that we probably underestimated their true number. We discuss short-term climatic fluctuations as potential trigger for the dynamic of invasion and subsequent hybridization. In the gradient hybrid zone in turn, long-term aridification could have favored unidirectional nuclear introgression from <it>Microcebus griseorufus </it>into <it>M. murinus </it>in transitional forest.</p> <p>Conclusions</p> <p>Madagascar's southeastern transitional zone harbors two very different hybrid zones of mouse lemurs in different environmental settings. This sheds light on the multitude of opportunities for the formation of hybrid zones and indicates an important influence of environmental factors on secondary contact and hybridization. Our findings suggest that hybridization could enhance the adaptability of mouse lemurs without necessarily leading to a loss of distinctiveness. They point to a potential role of hybridization in Madagascar's diversification history that requires further investigation.</p
A test for the search for life on extrasolar planets: Looking for the terrestrial vegetation signature in the Earthshine spectrum
We report spectroscopic observations (400 to 800nm, R = approx 100) of
Earthshine in June, July and October 2001 from which normalised Earth albedo
spectra have been derived. The resulting spectra clearly show the blue colour
of the Earth due to Rayleigh diffusion in its atmosphere. They also show the
signatures of oxygen, ozone and water vapour. We tried to extract from these
spectra the signature of Earth vegetation. A variable signal (4 to 10 +/-3%)
around 700nm has been measured in the Earth albedo. It is interpreted as being
due to the vegetation red edge, expected to be between 2 to 10% of the Earth
albedo at 700nm, depending on models. We discuss the primary goal of the
present observations: their application to the detection of vegetation-like
biosignatures on extrasolar planets.Comment: 7 pages, 7 figures. A&A, accepted 6 May 200
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[N,N-Bis(diphenylÂphosphino)isopropylÂamine]dibromidonickel(II)
The title compound, [NiBr2(C27H27NP2)], was synthesized by the reaction of NiBr2(dme) (dme is 1,2-dimethoxy-ethane) with N,N-bis-(diphenyl-phosphino)isopropyl-amine in methanol/tetra-hydro-furan. The nickel(II) center is coordinated by two P atoms of the chelating PNP ligand, PH2PN(iPr)PPH2, and two bromide ions in a distorted square-planar geometry
Racial Equity Considerations In Safe To Sleep Messaging: Learning From The Community
Black infants are dying at a rate of over twice that of White infants. We know that infants in unsafe sleep positions are more likely to die from Sudden Unexpected Infant Death (SUID). Safe to Sleep® education has led to a dramatic decrease in mortality among white infants, but over 60% of Black families do not follow the Safe to Sleep® parameters. Safe to Sleep® education is given to pregnant women during the prenatal period and prior to hospital discharge, but what is the best way to share this message with Black families
Magnetic-field-induced singularities in spin dependent tunneling through InAs quantum dots
Current steps attributed to resonant tunneling through individual InAs
quantum dots embedded in a GaAs-AlAs-GaAs tunneling device are investigated
experimentally in magnetic fields up to 28 T. The steps evolve into strongly
enhanced current peaks in high fields. This can be understood as a
field-induced Fermi-edge singularity due to the Coulomb interaction between the
tunneling electron on the quantum dot and the partly spin polarized Fermi sea
in the Landau quantized three-dimensional emitter.Comment: 5 pages, 4 figure
Approach for the determination of heat transfer coefficients for filling process of pressure vessels with compressed gaseous media
Paper presented at the 6th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 30 June - 2 July, 2008.For fast and effective simulation of filling processes of
pressure vessels with compressed gaseous media the governing
equations are derived from a mass balance equation for the gas
and from energy balance equations for the gas and the wall of
the vessel. For simplicity the gas is considered as a perfectly
mixed phase and two heat transfer coefficients are introduced.
The first one is the mean heat transfer coefficient between the
gas and the inner surface of the pressure vessel and the second
one is the heat transfer coefficient between outer surface of the
vessel and the surroundings. Although the process is transient,
steady-state heat transfer coefficients for free convection are
used between outer surface of the vessel and the surroundings.
The use of available correlations for steady-state heat transfer
coefficients to describe transient processes is common practice,
e.g. in the modelling of the transient behaviour of heat
exchangers [1]. But no correlations – neither steady-state nor
transient – are available for the heat transfer coefficient
between inflowing gas and inner surface of the vessel. To solve
this problem a CFD tool is used to determine the gas velocities
at the vicinity of the inner surface of the vessel for a number of
discrete surface elements. The results of a large amount of
numerical experiments show that there exists a unique
relationship between the tangential fluid velocities at the
vicinity of the inner surface of the vessel and the gas velocity at
the inlet. Once this unique relationship is known the complete
velocity distribution at the vicinity of the inner surface can be
easily calculated from the inlet velocity of the gas. The nearwall
velocities at the outer limit of the boundary layer are
substituted into the heat transfer correlation for external flow
over flat plates. The final heat transfer coefficient is the areaweighted
mean of all local heat transfer coefficients. The
method is applied to the special case of filling a 70 MPa
composite vessel for fuel cell vehicles with hydrogen. Because
of the heat capacity of the composite wall consisting of an inner
aluminium liner wrapped with carbon fibre, heat transfer from
the compressed gas to the vessel wall strongly influences the
temperature field of the gas which is predicted by the model
and confirmed by experiments.vk201
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