52 research outputs found
Morpho-Kinematic Properties of the 21-Micron Source IRAS 07134+1005
We report the results of a Submillimeter Array (SMA) interferometric
observation of 21-micron source IRAS 07134+1005 in the CO J=3-2 line. In order
to determine the morpho-kinematic properties of the molecular envelope of the
object, we constructed a model using the Shape software to model the observed
CO map. We find that the molecular gas component of the envelopes can be
interpreted as a geometrically thick expanding torus with an expanding velocity
of 8 km/s. The inner and outer radii of the torus determined by fitting Shape
models are 1.2" and 3.0", respectively. The inner radius is consistent with the
previous values determined by radiative transfer modeling of the spectral
energy distribution and mid-infrared imaging of the dust component. The radii
and expansion velocity of the torus suggest that the central star has left the
asymptotic giant branch about 1140-1710 years ago, and that the duration of the
equatorial enhanced mass loss is about 2560-3130 years. From the absence of an
observed jet, we suggest that the formation of a bipolar outflow may lack
behind in time from the creation of the equatorial torus.Comment: 20 pages, 8 figures; accepted for publication in ApJ; Full resolution
version available at http://web.hku.hk/~junichi/paper
Ramial wood amendments (Piliostigma reticulatum) mitigate degradation of tropical soils but do not replenish nutrient exports
Restoring degraded soils to support food production is a major challenge for West African smallholders who have developed local innovations to counter further degradation. The objective of this study was to evaluate a local farmer's technique that uses ramial wood (RW) as soil amendment (Piliostigma reticulatum shrub). Three treatments were applied in an experimental plot in Burkina Faso: control (no amendment), low RW (3 Mg fresh mass·haâ1·yrâ1), and high RW (12 Mg fresh mass·haâ1·yrâ1). RW was chipped to <5âcm pieces and either buried or mulched. Topsoil carbon (C), nitrogen (N), and phosphorus (P) in control and lowâRW treatments declined after 7 years of continuous sorghum cultivation. Use of highâRW amendment stabilized soil C content while N and P declined, thus not replenishing nutrient exports. Net contribution to soil C in the layer measuring 0â15 cm was 15% of the applied C in the highâRW
amendments. Although biomass and grain yields were higher in highâRW treatments, crop productivity declined throughout the experiment for all treatments. Termite casts on RW treatments evidenced the potential role of woodâforaging termites in diluting
the impact of RW on soil fertility buildâup and soil water content. We conclude that mitigating soil degradation under semiarid conditions in Burkina Faso would require large amounts of woody amendments, particularly if the level of termite activity is high.
Additional nutrient sources would be needed to compensate for removal in exported products so that biomass and grain production can be stabilized or increased.EstaciĂłn Experimental Agropecuaria BarilocheFil: FĂ©lix, Georges F. Wageningen University. Farming Systems Ecology; HolandaFil: Clermont-Dauphin, Cathy. Montpellier SupAgro- Centre de CoopĂ©ration Internationale en Recherche Agronomique pour le DĂ©veloppement-Institut National de la Recherche Agronomique. Eco&Sols; FranciaFil: Hien, Edmond. Laboratoire Mixte International. Intensification Ecologique des Sols CultivĂ©s en Afrique de l'Ouest; Burkina FasoFil: Groot, Jeroen C.J. Wageningen University. Farming Systems Ecology; HolandaFil: Penche, Aurelien. Laboratoire Mixte International. Intensification Ecologique des Sols CultivĂ©s en Afrique de l'Ouest; Burkina FasoFil: BarthĂšs, Bernard G. Universidad Montpellier; FranciaFil: Manlay, RaphaĂ«l J. AgroParisTech; FranciaFil: Tittonell, Pablo Adrian. Instituto Nacional de TecnologĂa Agropecuaria (INTA). EstaciĂłn Experimental Agropecuaria Bariloche; ArgentinaFil: Cournac, Laurent. Montpellier SupAgro- Centre de CoopĂ©ration Internationale en Recherche Agronomique pour le DĂ©veloppement-Institut National de la Recherche Agronomique. Eco&Sols; Franci
The role of tank-treading motions in the transverse migration of a spheroidal vesicle in a shear flow
The behavior of a spheroidal vesicle, in a plane shear flow bounded from one
side by a wall, is analysed when the distance from the wall is much larger than
the spheroid radius. It is found that tank treading motions produce a
transverse drift away from the wall, proportional to the spheroid eccentricity
and the inverse square of the distance from the wall. This drift is independent
of inertia, and is completely determined by the characteristics of the vesicle
membrane. The relative strength of the contribution to drift from tank-treading
motions and from the presence of inertial corrections, is discussed.Comment: 16 pages, 1 figure, Latex. To appear on J. Phys. A (Math. Gen.
Influence of shear flow on vesicles near a wall: a numerical study
We describe the dynamics of three-dimensional fluid vesicles in steady shear
flow in the vicinity of a wall. This is analyzed numerically at low Reynolds
numbers using a boundary element method. The area-incompressible vesicle
exhibits bending elasticity. Forces due to adhesion or gravity oppose the
hydrodynamic lift force driving the vesicle away from a wall. We investigate
three cases. First, a neutrally buoyant vesicle is placed in the vicinity of a
wall which acts only as a geometrical constraint. We find that the lift
velocity is linearly proportional to shear rate and decreases with increasing
distance between the vesicle and the wall. Second, with a vesicle filled with a
denser fluid, we find a stationary hovering state. We present an estimate of
the viscous lift force which seems to agree with recent experiments of Lorz et
al. [Europhys. Lett., vol. 51, 468 (2000)]. Third, if the wall exerts an
additional adhesive force, we investigate the dynamical unbinding transition
which occurs at an adhesion strength linearly proportional to the shear rate.Comment: 17 pages (incl. 10 figures), RevTeX (figures in PostScript
Are Proto-Planetary Nebulae Shaped by a Binary? Results of a Long-Term Radial Velocity Study
The shaping of the nebula is currently one of the outstanding unsolved
problems in planetary nebula (PN) research. Several mechanisms have been
proposed, most of which require a binary companion. However, direct evidence
for a binary companion is lacking in most PNs. We have addressed this problem
by obtaining precise radial velocities of seven bright proto-planetary nebulae
(PPNs), objects in transition from the asymptotic giant branch to the PN phases
of stellar evolution. These have F-G spectral types and have the advantage over
PNs of having more and sharper spectral lines, leading to better precision. Our
observations were made in two observing intervals, 1991-1995 and 2007-2010, and
we have included in our analysis some additional published and unpublished
data. Only one of the PPNs, IRAS 22272+5435, shows a long-term variation that
might tentatively be attributed to a binary companion, with P 22 years, and
from this, limiting binary parameters are calculated. Selection effects are
also discussed. These results set significant restrictions on the range of
possible physical and orbital properties of any binary companions: they have
periods greater than 25 years or masses of brown dwarfs or super-Jupiters.
While not ruling out the binary hypothesis, it seems fair to say that these
results do not support it.Comment: 14 pages, 3 figures, to appear Astrophys J, 734 (2011 June 10
Hard X -Ray Photoelectron Spectroscopy (HAXPES) characterisation of electrochemical passivation oxide layers on Al-Cr-Fe Complex Metallic Alloys (CMA).
A Hard X-ray Photoelectron Spectroscopy (HAXPES) characterisation of the passivation layers formed by electrochemical polarisation of AlâCrâFe complex metallic alloys is presented. By employing X-ray excitation energies from 2.3 to 10.0 keV, the depth distributions of Al- and Cr-oxide and hydroxide species in the (Al,Cr)-containing passive layers could be determined. Simultaneous analyses of the shallow Al 2s and deep Al 1s core level lines (respectively, more bulk- and surface-sensitive) provided complementary information to effectively determine the depth-resolved contributions of hydroxide and oxide species within the passivation layer. A Cr threshold concentration of 18 (at.%) was found for effective passivation at pH 1
The Auger Effect
A brief histiry of the discovery of the Auger effect is given,
which is followed
by a short description of some of the fields in which this
discovery has had
a major impact
The role of chelating agents on the corrosion mechanisms of aluminium in alkaline aqueous solutions
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