7,275 research outputs found
Spontaneous and induced hyperplasia and neoplasia in the mouse lung.
,SINCE Livingood (1896) first described a spontaneous pulmonary tumour in a mouse, much has been written on the histogenesis of this common tumour, vet it is still difficult to decide whether an early lesion should be classified as hyperplastic or neoplastic. Since the introduction of line-bred strains of mice by Strong (1936) and their general use by research workers, genetic differences in susceptibility have been extensively investigated by Heston (1940) and manv others. It is accepted that the susceptibility to spontaneous development of pulmonary tumours is high in A Strain and low in C57 Black, but that there is no essential difference between the type or range of tumours seen in different strains (Stewart, 1953). As to the sites of origin and distribution of these tumours, most authors describe them as subpleural and as originating in the alveolar epithelium. As far as we know, there has been no evidence as to localising factors which cause one alveolus rather than another to develop neoplastic growth
The results of prolonged administration of isoniazid to mice, rats and hamsters.
THE demonstration that isoniazid (INH) is carcinogenic for the lungs of mice (Juhasz, Balo and Kendrey, 1957) raised a new type of cancer problem. Most known carcinogens are avoidable as human hazards and many are subject to restrictive legislation. However, INH is a valuable life-saving drug in the control of tuberculosis, and the assessment of it as a potential carcinogenic hazard for man is therefore a matter of unusual concern. Moreover, it must be noted that the induction of pulmonary alveolar adenoma or adenocarcinoma in mice by a variety of chemically dissimilar carcinogens (e.g. urethane and 4-nitro-quinoline-N-oxide) is most striking in those strains, such as A and BALB/c, which have a high spontaneous incidence of such tumours. Tumours of similar histogenesis can be induced experimentally in rats but they very rarely occur spontaneously. In terms of initiators and promoters, mice of different strains behave as though they have variable amounts of some inborn initiator which determines the response of their alveolar cells to a variety of carcinogenic promoters. Apart from known genetic factors no " initiator " a
Solar sailing - mission opportunities and innovative technology demonstration
Solar sailing is a unique and elegant form of propulsion that transcends reliance on reaction mass. Rather than carrying propellant, solar sails acquire momentum from photons, the quantum packets of energy from which sunlight is composed. In addition, since solar sails are not limited by reaction mass, they can provide continual acceleration, limited only by the lifetime of the sail film in the space environment. Therefore, solar sails can expand the envelope of possible missions, enabling new high-energy mission concepts that are essentially impossible with conventional reaction propulsion, and enhancing current mission concepts by lowering launch mass and reducing trip times
Strong lensing time delay: a new way of measuring cosmic shear
The phenomenon of cosmic shear, or distortion of images of distant sources
unaccompanied by magnification, is an effective way of probing the content and
state of the foreground Universe, because light rays do not have to pass
through mass structures in order to be sheared. It is shown that the delay in
the arrival times between two simultaneously emitted photons that appear to be
arriving from a pair of images of a strongly lensed cosmological source
contains not only information about the Hubble constant, but also the long
range gravitational effect of galactic scale mass clumps located away from the
light paths in question. This is therefore also a method of detecting shear.
Data on time delays among a sample of strongly lensed sources can provide
crucial information about whether extra dynamics beyond gravity and dark energy
are responsible for the global flatness of space. If the standard
model is correct, there should be a large dispersion in the value of as
inferred from the delay data by (the usual procedure of) ignoring the effect of
all other mass clumps except the strong lens itself. The fact that there has
not been any report of a significant deviation from the 0.7 mark during
any of the determinations by this technique may already be pointing to
the absence of the random effect discussed here.Comment: ApJ in pres
A Model for Structure Formation Seeded by Gravitationally Produced Matter
This model assumes the baryons, radiation, three families of massless
neutrinos, and cold dark matter were mutually thermalized before the baryon
number was fixed, primeval curvature fluctuations were subdominant, and
homogeneity was broken by scale-invariant fluctuations in a new dark matter
component that behaves like a relativistic ideal fluid. The fluid behavior
could follow if this new component were a single scalar field that interacts
only with gravity and with itself by a pure quartic potential. The initial
energy distribution could follow if this component were gravitationally
produced by inflation. The power spectra of the present distributions of mass
and radiation in this model are not inconsistent with the measurements but are
sufficiently different from the adiabatic cold dark matter model to allow a
sharp test in the near future.Comment: 4 pages, 2 figures submitted to ApJ Letter
Dark Matter, Modified Gravity and the Mass of the Neutrino
It has been suggested that Einstein's theory of General Relativity can be
modified to accomodate mismatches between the gravitational field and luminous
matter on a wide range of scales. Covariant theories of modified gravity
generically predict the existence of extra degrees of freedom which may be
interpreted as dark matter. We study a subclass of these theories where the
overall energy density in these extra degrees of freedom is subdominant
relative to the baryon density and show that they favour the presence of
massive neutrinos. For some specific cases (such as a flat Universes with a
cosmological constant) one finds a conservative lower bound on the neutrinos
mass of eV.Comment: 5 pages, 2 figures, 2 tables, submitted to Phys. Rev.
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