1,338 research outputs found
Are All Static Black Hole Solutions Spherically Symmetric?
The static black hole solutions to the Einstein-Maxwell equations are all
spherically symmetric, as are many of the recently discovered black hole
solutions in theories of gravity coupled to other forms of matter. However,
counterexamples demonstrating that static black holes need not be spherically
symmetric exist in theories, such as the standard electroweak model, with
electrically charged massive vector fields. In such theories, a magnetically
charged Reissner-Nordstrom solution with sufficiently small horizon radius is
unstable against the development of a nonzero vector field outside the horizon.
General arguments show that, for generic values of the magnetic charge, this
field cannot be spherically symmetric. Explicit construction of the solution
shows that it in fact has no rotational symmetry at all.Comment: 6 pages, plain TeX. Submitted to GRF Essay Competitio
Formation of diluted IIIāV nitride thin films by N ion implantation
iluted IIIāNāāVāĖā alloys were successfully synthesized by nitrogen implantation into GaAs,InP, and AlyGa1āyAs. In all three cases the fundamental band-gap energy for the ion beam synthesized IIIāNāāVāĖā alloys was found to decrease with increasing N implantation dose in a manner similar to that observed in epitaxially grownGaNāAs1āx and InNāPāĖāalloys. In GaNāAsāĖā the highest value of x (fraction of āactiveā substitutional N on As sublattice) achieved was 0.006. It was observed that NAs is thermally unstable at temperatures higher than 850āĀ°C. The highest value of x achieved in InNāPāĖā was higher, 0.012, and the NP was found to be stable to at least 850āĀ°C. In addition, the N activation efficiency in implantedInNāPāĖā was at least a factor of 2 higher than that in GaNāAsāĖā under similar processing conditions. AlyGa1āyNāAsāĖā had not been made previously by epitaxial techniques. N implantation was successful in producing AlyGa1āyNāAsāĖāalloys. Notably, the band gap of these alloys remains direct, even above the value of y (y>0.44) where the band gap of the host material is indirect.This work was supported by the āāPhotovoltaic Materials
Focus Areaāā in the DOE Center of Excellence for the Synthesis
and Processing of Advanced Materials, Office of Science,
Office of Basic Energy Sciences, Division of Materials
Sciences under U.S. Department of Energy Contract No. DE-ACO3-76SF00098. The work at UCSD was partially supported
by Midwest Research Institute under subcontractor
No. AAD-9-18668-7 from NREL
Identification of roots from grass swards using PCR-RFLP and FFLP of the plastid trnL (UAA) intron
BACKGROUND: The specific associations between plant roots and the soil microbial community are key to understanding nutrient cycling in grasslands, but grass roots can be difficult to identify using morphology alone. A molecular technique to identify plant species from root DNA would greatly facilitate investigations of the root rhizosphere. RESULTS: We show that trnL PCR product length heterogeneity and a maximum of two restriction digests can separate 14 common grassland species. The RFLP key was used to identify root fragments at least to genus level in a field study of upland grassland community diversity. Roots which could not be matched to known types were putatively identified by comparison of the nuclear ribosomal ITS sequence to the GenBank database. Ten taxa were identified among almost 600 root fragments. Additionally, we have employed capillary electrophoresis of fluorescent trnL PCR products (fluorescent fragment length polymorphism, FFLP) to discriminate all taxa identified at the field site. CONCLUSION: We have developed a molecular database for the identification of some common grassland species based on PCR-RFLP of the plastid transfer RNA leucine (trnL) UAA gene intron. This technique will allow fine-scale studies of the rhizosphere, where root identification by morphology is unrealistic and high throughput is desirable
Imaging the spotty surface of Betelgeuse in the H band
This paper reports on H-band interferometric observations of Betelgeuse made
at the three-telescope interferometer IOTA. We image Betelgeuse and its
asymmetries to understand the spatial variation of the photosphere, including
its diameter, limb darkening, effective temperature, surrounding brightness,
and bright (or dark) star spots. We used different theoretical simulations of
the photosphere and dusty environment to model the visibility data. We made
images with parametric modeling and two image reconstruction algorithms: MIRA
and WISARD. We measure an average limb-darkened diameter of 44.28 +/- 0.15 mas
with linear and quadratic models and a Rosseland diameter of 45.03 +/- 0.12 mas
with a MARCS model. These measurements lead us to derive an updated effective
temperature of 3600 +/- 66 K. We detect a fully-resolved environment to which
the silicate dust shell is likely to contribute. By using two imaging
reconstruction algorithms, we unveiled two bright spots on the surface of
Betelgeuse. One spot has a diameter of about 11 mas and accounts for about 8.5%
of the total flux. The second one is unresolved (diameter < 9 mas) with 4.5% of
the total flux. Resolved images of Betelgeuse in the H band are asymmetric at
the level of a few percent. The MOLsphere is not detected in this wavelength
range. The amount of measured limb-darkening is in good agreement with model
predictions. The two spots imaged at the surface of the star are potential
signatures of convective cells.Comment: 10 pages, 10 figures, accepted for publication in A&A, references
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Local structures of free-standing AlāGaāĖāN thin films studied by extended x-ray absorption fine structure
Local structural information for the first two atomic shells surrounding Ga atoms in free standing AlāGaāĖāN alloy films has been obtained by extended x-ray absorption fine structure spectroscopy. For an AlN mole fraction ranging from 0 to 0.6, we found that the first shell GaāN bond length had only a weak composition dependence, roughly one quarter of that predicted by Vegardās Law. In the second shell, the GaāGa bond length was significantly longer than that of GaāAl (Īā¼0.04ā0.065āĆ
). A bond-type specific composition dependence was observed for the second shell cationācation distances. While the composition dependence of the GaāGa bond length is ā¼70% of that predicted by Vegardās Law, the GaāAl bond length was essentially composition independent. These results suggested that local strain in AlāGaāĖāN was also accommodated by lattice distortion in the Al cation sublattice.This
work was supported by the Director, Office of Science, Of-
fice of Basic Energy Sciences, Materials Science Division of
the U.S. Department of Energy under Contract No.
DE-AC03-76SF00098. The LLO work was performed at the
UC Berkeley Integrated Materials Laboratory which was
supported in part by the National Science Foundation. C.J.G.
and M.C.R. were supported by the Australian Synchrotron
Research Program, funded by the Commonwealth of Australia
via the Major National Research Facilities Program.
SSRL was supported by the Office of Basic Energy Sciences
of the U.S. Department of Energy
Southwest Pacific Ocean Circulation and Climate Experiment (SPICE) - part I. Scientific background
Interferometry
The following recommended programs are reviewed: (1) infrared and optical interferometry (a ground-based and space programs); (2) compensation for the atmosphere with adaptive optics (a program for development and implementation of adaptive optics); and (3) gravitational waves (high frequency gravitational wave sources (LIGO), low frequency gravitational wave sources (LAGOS), a gravitational wave observatory program, laser gravitational wave observatory in space, and technology development during the 1990's). Prospects for international collaboration and related issues are also discussed
First visual orbit for the prototypical colliding-wind binary WR 140
Wolf-Rayet stars represent one of the final stages of massive stellar
evolution. Relatively little is known about this short-lived phase and we
currently lack reliable mass, distance, and binarity determinations for a
representative sample. Here we report the first visual orbit for WR
140(=HD193793), a WC7+O5 binary system known for its periodic dust production
episodes triggered by intense colliding winds near periastron passage. The IOTA
and CHARA interferometers resolved the pair of stars in each year from
2003--2009, covering most of the highly-eccentric, 7.9 year orbit. Combining
our results with the recent improved double-line spectroscopic orbit of Fahed
et al. (2011), we find the WR 140 system is located at a distance of 1.67 +/-
0.03 kpc, composed of a WR star with M_WR = 14.9 +/- 0.5 Msun and an O star
with M_O = 35.9 +/- 1.3 Msun. Our precision orbit yields key parameters with
uncertainties times 6 smaller than previous work and paves the way for detailed
modeling of the system. Our newly measured flux ratios at the near-infrared H
and Ks bands allow an SED decomposition and analysis of the component
evolutionary states.Comment: Complete OIFITS dataset included via Data Conservancy Projec
Mutual passivation of group IV donors and nitrogen in diluted GaNāAsāĖā alloys
We demonstrate the mutual passivation phenomenon of Ge donors and isovalent N in highly mismatched alloy GaNāAsāĖādoped with Ge. Layers of this alloy were formed by the sequential implantation of Ge and N ions followed by pulsed laser melting and rapid thermal annealing. The mutual passivation effect results in the electrical deactivation of GeGa donors (Ge on Ga sites) and suppression of the NAs (N on As sites) induced band gap narrowing through the formation of GeGaāNAs nearest neighbor pairs. These results in combination with the analogous effect observed in Si-doped GaNāAsāĖā provide clear evidence of the general nature of the mutual passivation phenomenon in highly mismatched semiconductor alloys.This work was supported by the Director, Office of Science,
Office of Basic Energy Sciences, Division of Materials
Sciences and Engineering, U.S. Department of Energy, under
Contract No. DE-AC03-76SF00098. One of the authors
~M.A.S.! acknowledges support by an NSF graduate research
fellowship
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