102 research outputs found
Globular Clusters as Candidates for Gravitational Lenses to Explain Quasar-Galaxy Associations
We argue that globular clusters (GCs) are good candidates for gravitational
lenses in explaining quasar-galaxy associations. The catalog of associations
(Bukhmastova 2001) compiled from the LEDA catalog of galaxies (Paturel 1997)
and from the catalog of quasars (Veron-Cetty and Veron 1998) is used. Based on
the new catalog containing 8382 pairs, we show that one might expect an
increased number of GCs around irregular galaxies of types 9 and 10 from the
hypothesis that distant compact sources are gravitationally lensed by GCs in
the halos of foreground galaxies. The King model is used to determine the
central surface densities of 135 GCs in the Milky Way. The distribution of GCs
in central surface density was found to be lognormal.Comment: 22 pages, 4 figure
Effect of pretreatment of rats with carbon tetrachloride on tolerance development
To evaluate the effect of pretreatment of rats with CCl4 on tolerance development to subsequent exposures, rats were exposed 25-7500 ppm of CCl4 vapor or given CCl4 orally, 3.25 mg/g body weight. Forty-eight hours later these rats were reexposed to a normally lethal 7500 ppm CCl4 concentration. Mortality, blood clotting time, serum bilirubin, serum and liver triglycerides, and CCl4 and CHCl3 concentrations in tissues and in the whole rat were used as a measure of the response to CCl4 exposure. Conversion of CCl4 to CHCl3 in vitro was also determined in normal and pretreated animals. It was found that animals exposed to 4000 ppm for 6 hr or given 3.25 mg/g of CCl4 orally developed tolerance to subsequent normally lethal CCl4 exposures. Serum bilirubin levels in animals protected by CCl4 pretreatment were significantly lower than in those receiving only a single exposure to CCl4. Blood clotting times in protected animals were normal, while in those not protected by pretreatment, they were greatly prolonged. Serum triglyceride levels in protected animals were normal whereas they were considerably depressed in the nonprotected animals. Liver triglycerides were elevated in both protected and nonprotected, but were not as high in the protected animals. Carbon tetrachloride conversion to CHCl3 was slower in protected than in the non-protected animals. Tolerance to CCl4 developed in animals whose ability to metabolize CCl4 had been depressed by pretreatment with the same compound. This suggests that the toxicity of CCl4 is related to its metabolic pathway or to the production of toxic intermediates.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32734/1/0000103.pd
Information storing by biomagnetites
Since the discovery of the presence of biogenic magnetites in living
organisms, there have been speculations on the role that these biomagnetites
play in cellular processes. It seems that the formation of biomagnetite
crystals is a universal phenomenon and not an exception in living cells. Many
experimental facts show that features of organic and inorganic processes could
be indistinguishable at nanoscale levels. Living cells are quantum "devices"
rather than simple electronic devices utilizing only the charge of conduction
electrons. In our opinion, due to their unusual biophysical properties, special
biomagnetites must have a biological function in living cells in general and in
the brain in particular. In this paper we advance a hypothesis that while
biomagnetites are developed jointly with organic molecules and cellular
electromagnetic fields in cells, they can record information about the Earth's
magnetic vector potential of the entire flight in migratory birds.Comment: 17 pages, 3 figure
Cluster Lenses
Clusters of galaxies are the most recently assembled, massive, bound
structures in the Universe. As predicted by General Relativity, given their
masses, clusters strongly deform space-time in their vicinity. Clusters act as
some of the most powerful gravitational lenses in the Universe. Light rays
traversing through clusters from distant sources are hence deflected, and the
resulting images of these distant objects therefore appear distorted and
magnified. Lensing by clusters occurs in two regimes, each with unique
observational signatures. The strong lensing regime is characterized by effects
readily seen by eye, namely, the production of giant arcs, multiple-images, and
arclets. The weak lensing regime is characterized by small deformations in the
shapes of background galaxies only detectable statistically. Cluster lenses
have been exploited successfully to address several important current questions
in cosmology: (i) the study of the lens(es) - understanding cluster mass
distributions and issues pertaining to cluster formation and evolution, as well
as constraining the nature of dark matter; (ii) the study of the lensed objects
- probing the properties of the background lensed galaxy population - which is
statistically at higher redshifts and of lower intrinsic luminosity thus
enabling the probing of galaxy formation at the earliest times right up to the
Dark Ages; and (iii) the study of the geometry of the Universe - as the
strength of lensing depends on the ratios of angular diameter distances between
the lens, source and observer, lens deflections are sensitive to the value of
cosmological parameters and offer a powerful geometric tool to probe Dark
Energy. In this review, we present the basics of cluster lensing and provide a
current status report of the field.Comment: About 120 pages - Published in Open Access at:
http://www.springerlink.com/content/j183018170485723/ . arXiv admin note:
text overlap with arXiv:astro-ph/0504478 and arXiv:1003.3674 by other author
Gravitational Lensing in Astronomy
Deflection of light by gravity was predicted by General Relativity and
observationaly confirmed in 1919. In the following decades various aspects of
the gravitational lens effect were explored theoretically, among them the
possibility of multiple or ring-like images of background sources, the use of
lensing as a gravitational telescope on very faint and distant objects, and the
possibility to determine Hubble's constant with lensing. Only relatively
recently gravitational lensing became an observational science after the
discovery of the first doubly imaged quasar in 1979. Today lensing is a booming
part of astrophysics.
In addition to multiply-imaged quasars, a number of other aspects of lensing
have been discovered since, e.g. giant luminous arcs, quasar microlensing,
Einstein rings, galactic microlensing events, arclets, or weak gravitational
lensing. By now literally hundreds of individual gravitational lens phenomena
are known.
Although still in its childhood, lensing has established itself as a very
useful astrophysical tool with some remarkable successes. It has contributed
significant new results in areas as different as the cosmological distance
scale, the large scale matter distribution in the universe, mass and mass
distribution of galaxy clusters, physics of quasars, dark matter in galaxy
halos, or galaxy structure.Comment: Review article for "Living Reviews in Relativity", see
http://www.livingreviews.org . 41 pages, latex, 22 figures (partly in GIF
format due to size constraints). High quality postscript files can be
obtained electronically at http://www.aip.de:8080/~jkw/review_figures.htm
Reduction of irradiation mortality through pretreatment. In m. F. Barnothy (ed.) Biological effects of magnetic fields. N.y.,
- …