1,239 research outputs found
Formation of the Flatreef deposit, northern Bushveld, by hydrodynamic and hydromagmatic processes
New lithological and whole rock compositional data show that the main platinum-group element (PGE) horizons of the Flatreef succession show strong compositional similarities to the Merensky and Bastard reefs of the western Bushveld Complex (WBC), notably in terms of many immobile and incompatible minor and trace elements such as TiO2, Zr, Y, and REE. However, Al2O3, CaO, and Na2O contents are markedly lower in the Flatreef, whereas MgO contents are higher. In view of broadly similar silicate mineral compositions in the Flatreef and the WBC reefs, we suggest that the major element compositional differences between the rocks are largely due to higher modal proportions of orthopyroxene and olivine and lower proportions of plagioclase in the Flatreef. The thickness of the mineralised interval is much greater in the Flatreef than in the WBC (several 10 s of m vs ~ 1 m) and the abundance of sulfides in the Flatreef is typically somewhat higher (on average ~ 1.5% vs ~ 1%). These data, complemented by textural observations, are interpreted to reflect enhanced hydrodynamic crystal sorting accompanied by percolation of sulfide melt through incompletely solidified cumulates. Further genetic constraints are provided by metal data: The concentration of Ni (~ 3000 ppm) in the Flatreef is broadly similar to that in the Merensky Reef of the WBC, but Cu contents are markedly higher (average ~ 1500 ppm vs 700 ppm in the WBC). The concentrations of most PGE are slightly lower (Flatreef ~ 1.5–2 ppm Pt, ~ 100–150 ppb Rh; WBC MR 3.7 ppm Pt, 240 ppb Rh), but Pd has broadly similar contents (Flatreef ~ 1.2–2 ppm; WBC MR 1.54 ppm). The relatively high Cu content of the Flatreef is interpreted as a result of assimilation of Cu sulfides from the sedimentary floor rocks. The reason for the enrichment of Pd relative to Pt, especially in the basal rocks, remains unclear. It could reflect mobilisation of Pd via a fluid phase from the country rocks or the interior of the intrusion, relatively enhanced partitioning of Pd into the sulfides, or relative Pt depletion of the earliest magma pulses in response to Pt alloy fractionation triggered by contamination with reducing country rocks
Comparing HARPS and Kepler surveys: The alignment of multiple-planet systems
Aims. We study a subset of the planetary population characterized both by
HARPS and Kepler surveys. We compare the statistical properties of planets in
systems with m.sin i >5-10 M_Earth and R>2 R_Earth. If we assume that the
underlying population has the same characteristics, the different detection
sensitivity to the orbital inclination relative to the line of sight allows us
to probe the planets' mutual inclination.
Methods. We considered the frequency of systems with one, two and three
planets as dictated by HARPS data. We used Kepler's planetary period and host
mass and radii distributions (corrected from detection bias) to model planetary
systems in a simple yet physically plausible way. We then varied the mutual
inclination between planets in a system according to different prescriptions
(completely aligned, Rayleigh distributions and isotropic) and compared the
transit frequencies with one, two or three planets with those measured by
Kepler.
Results. The results show that the two datasets are compatible, a remarkable
result especially because there are no tunable knobs other than the assumed
inclination distribution. For m.sin i cutoffs of 7-10 M_Earth, which are those
expected to correspond to the radius cutoff of 2 R_Earth, we conclude that the
results are better described by a Rayleigh distribution with mode of 1 deg or
smaller. We show that the best-fit scenario only becomes a Rayleigh
distribution with mode of 5 deg if we assume a rather extreme mass-radius
relationship for the planetary population.
Conclusions. These results have important consequences for our understanding
of the role of several proposed formation and evolution mechanisms. They
confirm that planets are likely to have been formed in a disk and show that
most planetary systems evolve quietly without strong angular momentum exchanges
(abridged).Comment: 10 pages, 6 figures, 4 tables, accepted for publication in Astronomy
& Astrophysic
Gravitational Couplings of Intrinsic Spin
The gravitational couplings of intrinsic spin are briefly reviewed. A
consequence of the Dirac equation in the exterior gravitational field of a
rotating mass is considered in detail, namely, the difference in the energy of
a spin-1/2 particle polarized vertically up and down near the surface of a
rotating body is . Here is the latitude and
, where and are, respectively, the angular
momentum and radius of the body. It seems that this relativistic quantum
gravitational effect could be measurable in the foreseeable future.Comment: LaTeX file, no figures, 16 page
Caenorhabditis elegans Maintains Highly Compartmentalized Cellular Distribution of Metals and Steep Concentration Gradients of Manganese
Bioinorganic chemistry is critical to cellular function. Homeostasis of manganese (Mn), for example, is essential for life. A lack of methods for direct in situ visualization of Mn and other biological metals within intact multicellular eukaryotes limits our understanding of management of these metals. We provide the first quantitative subcellular visualization of endogenous Mn concentrations (spanning two orders of magnitude) associated with individual cells of the nematode, Caenorhabditis elegans
A radium assay technique using hydrous titanium oxide adsorbent for the Sudbury Neutrino Observatory
As photodisintegration of deuterons mimics the disintegration of deuterons by
neutrinos, the accurate measurement of the radioactivity from thorium and
uranium decay chains in the heavy water in the Sudbury Neutrino Observatory
(SNO) is essential for the determination of the total solar neutrino flux. A
radium assay technique of the required sensitivity is described that uses
hydrous titanium oxide adsorbent on a filtration membrane together with a
beta-alpha delayed coincidence counting system. For a 200 tonne assay the
detection limit for 232Th is a concentration of 3 x 10^(-16) g Th/g water and
for 238U of 3 x 10^(-16) g U/g water. Results of assays of both the heavy and
light water carried out during the first two years of data collection of SNO
are presented.Comment: 12 pages, 4 figure
Mach's Principle and the Origin of Inertia
The current status of Mach's principle is discussed within the context of
general relativity. The inertial properties of a particle are determined by its
mass and spin, since these characterize the irreducible unitary representations
of the inhomogeneous Lorentz group. The origin of the inertia of mass and
intrinsic spin are discussed and the inertia of intrinsic spin is studied via
the coupling of intrinsic spin with rotation. The implications of spin-rotation
coupling and the possibility of history dependence and nonlocality in
relativistic physics are briefly mentioned.Comment: 14 pages. Dedicated to Carl Brans in honor of his 80th birthday. To
appear in the Brans Festschrift; v2: typo corrected, published in: At the
Frontier of Spacetime, edited by T. Asselmeyer-Maluga (Springer, 2016),
Chapter 10, pp. 177-18
Search for the exotic resonance in the NOMAD experiment
A search for exotic Theta baryon via Theta -> proton +Ks decay mode in the
NOMAD muon neutrino DIS data is reported. The special background generation
procedure was developed. The proton identification criteria are tuned to
maximize the sensitivity to the Theta signal as a function of xF which allows
to study the Theta production mechanism. We do not observe any evidence for the
Theta state in the NOMAD data. We provide an upper limit on Theta production
rate at 90% CL as 2.13 per 1000 of neutrino interactions.Comment: Accepted to European Physics Journal
Production properties of K*(892) vector mesons and their spin alignment as measured in the NOMAD experiment
First measurements of K*(892) mesons production properties and their spin
alignment in nu_mu charged current (CC) and neutral current (NC) interactions
are presented. The analysis of the full data sample of the NOMAD experiment is
performed in different kinematic regions. For K*+ and K*- mesons produced in
nu_mu CC interactions and decaying into K0 pi+/- we have found the following
yields per event: (2.6 +/- 0.2 (stat.) +/- 0.2 (syst.))% and (1.6 +/- 0.1
(stat.) +/- 0.1 (syst.))% respectively, while for the K*+ and K*- mesons
produced in nu NC interactions the corresponding yields per event are: (2.5 +/-
0.3 (stat.) +/- 0.3 (syst.))% and (1.0 +/- 0.3 (stat.) +/- 0.2 (syst.))%. The
results obtained for the rho00 parameter, 0.40 +/- 0.06 (stat) +/- 0.03 (syst)
and 0.28 +/- 0.07 (stat) +/- 0.03 (syst) for K*+ and K*- produced in nu_mu CC
interactions, are compared to theoretical predictions tuned on LEP measurements
in e+e- annihilation at the Z0 pole. For K*+ mesons produced in nu NC
interactions the measured rho00 parameter is 0.66 +/- 0.10 (stat) +/- 0.05
(syst).Comment: 20 p
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