10,466 research outputs found
Rotating dust solutions of Einstein's equations with 3-dimensional symmetry groups, Part 3: All Killing fields linearly independent of u^{\alpha} and w^{\alpha}
This is the third and last part of a series of 3 papers. Using the same
method and the same coordinates as in parts 1 and 2, rotating dust solutions of
Einstein's equations are investigated that possess 3-dimensional symmetry
groups, under the assumption that each of the Killing vectors is linearly
independent of velocity and rotation at every point
of the spacetime region under consideration. The Killing fields are found and
the Killing equations are solved for the components of the metric tensor in
every case that arises. No progress was made with the Einstein equations in any
of the cases, and no previously known solutions were identified. A brief
overview of literature on solutions with rotating sources is given.Comment: One missing piece, signaled after eq. (10.7), is added after (10.21).
List of corrections: In (3.7) wrong subscript in vorticity; In (3.10) wrong
subscript in last term of g_{23}; In (4.23) wrong formulae for g_{12} and
g_{22}; In (7.17) missing factor in velocity; In (7.18) one wrong factor in
g_{22}; In (10.9) factor in vorticity; In (10.15) - (10.20) y_0 = 0; In
(10.20) wrong second term in y. The rewriting typos did not influence result
Phytohaemagglutinin on maternal and umbilical leukocytes
Almost all the umbilical lymphocytes showed more extensive blast cell formation
than that of their mother's lymphocytes with PHA. Pathological conditions of mother in pregnancy and labor such as anemia, gestational toxicosis,
difficult labor and asphyxia of babies, inhibited the normal response of both maternal and umbilical lymphocytes to PHA.</p
Final Evolution and Delayed Explosions of Spinning White Dwarfs in Single Degenerate Models for Type Ia Supernovae
We study the occurrence of delayed SNe~Ia in the single degenerate (SD)
scenario. We assume that a massive carbon-oxygen (CO) white dwarf (WD) accretes
matter coming from a companion star, making it to spin at the critical rate. We
assume uniform rotation due to magnetic field coupling. The carbon ignition
mass for non-rotating WDs is M_{ig}^{NR} \approx 1.38 M_{\odot}; while for the
case of uniformly rotating WDs it is a few percent larger (M_{ig}^{R} \approx
1.43 M_{\odot}). When accretion rate decreases, the WD begins to lose angular
momentum, shrinks, and spins up; however, it does not overflow its critical
rotation rate, avoiding mass shedding. Thus, angular momentum losses can lead
the CO WD interior to compression and carbon ignition, which would induce an
SN~Ia. The delay, largely due to the angular momentum losses timescale, may be
large enough to allow the companion star to evolve to a He WD, becoming
undetectable at the moment of explosion. This scenario supports the occurrence
of delayed SNe~Ia if the final CO WD mass is 1.38 M_{\odot} < M < 1.43
M_{\odot}. We also find that if the delay is longer than ~3 Gyr, the WD would
become too cold to explode, rather undergoing collapse.Comment: 6 pages, 5 figures, published in the Astrophysical Journal Letters,
809, L6 (2015), added some corrections for errat
Unobserved Heterogeneity in Auctions
A common concern in the empirical study of auctions is the likely presence of auction-specific factors that are common knowledge among bidders but unobserved to the econometrician. Such unobserved heterogeneity confounds attempts to uncover the underlying structure of demand and information, typically a primary feature of interest in an auction market. Unobserved heterogeneity presents a particular challenge in first-price auctions, where identification arguments rely on the econometricianâs ability to reconstruct from observables the conditional probabilities that entered each bidderâs equilibrium optimization problem; when bidders condition on unobservables, it is not obvious that this is possible. Here we discuss several approaches to identification developed in recent work on first-price auctions with unobserved heterogeneity. Despite the special challenges of this setting, all of the approaches build on insights developed in other areas of econometrics, including those on control functions, measurement error, and mixture models. Because each strategy relies on different combinations of model restrictions, technical assumptions, and data requirements, their relative attractiveness will vary with the application. However, this varied menu of results suggests both a type of robustness of identifiability and the potential for expanding the frontier with additional work
Ion-induced nucleation in polar one-component fluids
We present a Ginzburg-Landau theory of ion-induced nucleation in a gas phase
of polar one-component fluids, where a liquid droplet grows with an ion at its
center. By calculating the density profile around an ion, we show that the
solvation free energy is larger in gas than in liquid at the same temperature
on the coexistence curve. This difference much reduces the nucleation barrier
in a metastable gas.Comment: 9 pagers, 9 figures, to be published in J. Chem. Phy
Polymerisable octahedral rhenium cluster complexes as precursors for photo/electroluminescent polymers
New polymerisable photoluminescent octahedral rhenium cluster complexes trans-[{ReâQâ}(TBP)âVB)â] (Q = S or Se; TBP â p-tert-butylpyridine; VB â vinyl benzoate) have been synthesised, characterised and used to construct rhe-nium cluster-organic polymer hybrid materials. These novel polymer systems are solution-processable and the rhenium clusters retain their photoluminescent properties within the polymer environment. Notably, when the rhenium cluster complexes are incorporated into the matrix of the electroluminescent polymer poly(N-vinylcarbazole), the resultant cluster polymer hybrid combined properties of both components and was used successfully in the construc-tion of a polymer light emitting diode (PLED). These prototype devices are the first PLEDs to incorporate octahedral rhenium clusters and provide the first direct evidence of the electroluminescent properties of rhenium clusters and indeed, to the best of our knowledge, of any member of the family of 24-electron hexanuclear cluster complexes of molybdenum, tungsten or rhenium
Research Notes : Performance of near-isogenic lines lacking seed lipoxygenases
Normal soybean seeds contain at least three lipoxygenase isozymes, called L-1, L-2, and L-3. These isozymes are responsible for the generation of objectionable grassy beany and green flavors which build a barrier against the wide utilization of soy protein products. Recently, the three types of mutants lacking L-1 (Hildebrand and Hymowitz, 1981), L-2 (Kitamura, 1984), and L-3 (Kitamura et al., 1983), respectively, were found
On the Selection of Photometric Planetary Transits
We present a new method for differentiating between planetary transits and
eclipsing binaries based on the presence of the ellipsoidal light variations.
These variations can be used to detect stellar secondaries with masses ~0.2
M_sun orbiting sun-like stars at a photometric accuracy level which has already
been achieved in transit surveys. By removing candidates exhibiting this effect
it is possible to greatly reduce the number of objects requiring spectroscopic
follow up with large telescopes. Unlike the usual candidate selection method,
which are primarily based on the estimated radius of the orbiting object, this
technique is not biased against bona-fide planets and brown dwarfs with large
radii, because the amplitude of the effect depends on the transiting object's
mass and orbital distance. In many binary systems, where a candidate planetary
transit is actually due to the partial eclipse of two normal stars, the
presence of flux variations due to the gravity darkening effect will show the
true nature of these systems. We show that many of the recent OGLE-III
photometric transit candidates exhibit the presence of significant variations
in their light curves and are likely to be due to stellar secondaries. We find
that the light curves of white dwarf transits will generally not mimic those of
small planets because of significant gravitationally induced flux variations.
We discuss the relative merits of methods used to detect transit candidates
which are due to stellar blends rather than planets. We outline how photometric
observations taken in two bands can be used to detect the presence of stellar
blends.Comment: ApJ, 11 pages, 2 figures, 1 table, replaced with accepted versio
Empirical likelihood estimation of the spatial quantile regression
The spatial quantile regression model is a useful and flexible model for analysis of empirical problems with spatial dimension. This paper introduces an alternative estimator for this model. The properties of the proposed estimator are discussed in a comparative perspective with regard to the other available estimators. Simulation evidence on the small sample properties of the proposed estimator is provided. The proposed estimator is feasible and preferable when the model contains multiple spatial weighting matrices. Furthermore, a version of the proposed estimator based on the exponentially tilted empirical likelihood could be beneficial if model misspecification is suspect
Hexaazide octahedral molybdenum cluster complexes: synthesis, properties and the evidence of hydrolysis
This article reports the synthesis, crystal structure of new molybdenum hexaazide cluster complex (âżBuâN)â[{MoâIâ}(Nâ)â] (3) and comparison of its photophysical and electrochemical properties to those of earlier reported analogues (âżBuâN)â[{MâXâ}(Nâ)â] (X = Cl, Br). Additionally, the dimerisation of 3 as a result of hydrolysis was revealed by mass spectrometry and single crystal X-Ray diffraction. Indeed, the structurally characterised compound (âżBuâN)â[{MoâIâ}(Nâ)â
)âO] represents the first example of oxo-bridged dimer of octahedral molybdenum clusters complexes
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