51,869 research outputs found
Laboratory measurements of the cometary photochemical phenomena
Laboratory experiments are described that provide fundamental information about photochemical processes in comets. The yield of cometary radicals such as CN, OH, etc. can be determined as a function of photolyzing wavelength. Quantum state distributions of the internal energy of the cometary radicals can also be measured as a function of wavelength permitting one to define the recoil velocity of the fragments. This type of information supplies the data needed for more elaborate models to interpret the data being obtained on comets
The Economics of Small Worlds
We examine a simple economic model of network formation where agents benefit from indirect relationships. We show that small-world featuresâshort path lengths between nodes together with highly clustered link structuresânecessarily emerge for a wide set of parameters
Improving efficiency in radio surveys for gravitational lenses
Many lens surveys have hitherto used observations of large samples of
background sources to select the small minority which are multiply imaged by
lensing galaxies along the line of sight. Recently surveys such as SLACS and
OLS have improved the efficiency of surveys by pre-selecting double-redshift
systems from SDSS. We explore other ways to improve survey efficiency by
optimum use of astrometric and morphological information in existing
large-scale optical and radio surveys. The method exploits the small position
differences between FIRST radio positions of lensed images and the SDSS lens
galaxy positions, together with the marginal resolution of some larger
gravitational lens systems by the FIRST beam. We present results of a small
pilot study with the VLA and MERLIN, and discuss the desirable criteria for
future surveys.Comment: Accepted by MNRAS. 9 pages, 5 figure
Channel-wall limitations in the magnetohydrodynamic induction generator
Discussion of magnetohydrodynamic induction generator examines the machine in detail and materials problems influencing its design. The higher upper-temperature limit of the MHD system promises to be more efficient than present turbine systems for generating electricity
Monoid varieties with extreme properties
Finite monoids that generate monoid varieties with uncountably many
subvarieties seem rare, and surprisingly, no finite monoid is known to generate
a monoid variety with countably infinitely many subvarieties. In the present
article, it is shown that there are, nevertheless, many finite monoids that
generate monoid varieties with continuum many subvarieties; these include any
finite inherently non-finitely based monoid and any monoid for which is
an isoterm. It follows that the join of two Cross monoid varieties can have a
continuum cardinality subvariety lattice that violates the ascending chain
condition.
Regarding monoid varieties with countably infinitely many subvarieties, the
first example of a finite monoid that generates such a variety is exhibited. A
complete description of the subvariety lattice of this variety is given. This
lattice has width three and contains only finitely based varieties, all except
two of which are Cross
Approaches to the synthesis of clerodane diterpenes
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