60,478 research outputs found
Spectral Pollution
We discuss the problems arising when computing eigenvalues of self-adjoint
operators which lie in a gap between two parts of the essential spectrum.
Spectral pollution, i.e. the apparent existence of eigenvalues in numerical
computations, when no such eigenvalues actually exist, is commonplace in
problems arising in applied mathematics. We describe a geometrically inspired
method which avoids this difficulty, and show that it yields the same results
as an algorithm of Zimmermann and Mertins.Comment: 23 page
Space photography and the exploration of Mars
A general exposition of the scientific potentialities and analytic framework of space photography is presented using the photography of Mars from flybys and orbiters as the principal example. Space photography is treated here as a communication process in which planetary scene information is communicated to the eye-brain receiver of earth-based interpreters. The salient parameters of this process are: (1) total information returned, (2) surface resolution, and (3) a priori knowledge regarding the planetary surface observed
Coordinates of features on the Galilean satellites
The coordinate systems of each of the Galilean satellites are defined and coordinates of features seen in the Voyager pictures of these satellites are presented. The control nets of the satellites were computed by means of single block analytical triangulations. The normal equations were solved by the conjugate iterative method which is convenient and which converges rapidly as the initial estimates of the parameters are very good
Sensitive electrochemical assays of DNA structure
Electrochemical methods have been used to study the structure and function of nucleic acids for more than 50 years. These approaches complement other experimental techniques, which we illustrate by using examples from studies of processes involved in the repair of DNA damage. The excellent sensitivity of the electrochemical approaches makes them good candidates for use as biosensors of a wide range of molecules and biological processes
The detection of FIR emission from high redshift star-forming galaxies in the ECDF-S
ABRIDGED: We have used the LABOCA Survey of the ECDF-S (LESS) to investigate
rest-frame FIR emission from typical SF systems (LBGs) at redshift 3, 4, and 5.
We initially concentrate on LBGs at z~3 and select three subsamples on stellar
mass, extinction corrected SF and rest-frame UV-magnitude. We produce composite
870micron images of the typical source in our subsamples, obtaining ~4sigma
detections and suggesting a correlation between FIR luminosity and stellar
mass. We apply a similar procedure to our full samples at z~3, 4, 4.5 and 5 and
do not obtain detections - consistent with a simple scaling between FIR
luminosity and stellar mass. In order to constrain the FIR SED of these systems
we explore their emission at multiple wavelengths spanning the peak of dust
emission at z~3 using the Herschel SPIRE observations of the field. We obtain
detections at multiple wavelengths for both our stellar mass and UV-magnitude
selected samples, and find a best-fit SED with T_dust in the ~33-41K range. We
calculate L_FIR, obscured SFRs and M_dust, and find that a significant fraction
of SF in these systems is obscured. Interestingly, our extinction corrected SFR
sample does not display the large FIR fluxes predicted from its red UV-spectral
slope. This suggests that the method of assuming an intrinsic UV-slope and
correcting for dust attenuation may be invalid for this sample - and that these
are not in fact the most actively SF systems. All of our z~3 samples fall on
the `main sequence' of SF galaxies at z~3 and our detected subsamples are
likely to represent the high obscuration end of LBGs at their epoch. We compare
the FIR properties of our subsamples with various other populations, finding
that our stellar mass selected sample shows similar FIR characteristics to SMGs
at the same epoch and therefore potentially represents the low L_FIR end of the
high redshift FIR luminosity function.Comment: 18 pages, 10 figure, MNRAS accepted, corrected typos,
acknowledgements adde
Radio Observations of GRB Host Galaxies
We present 5.5 and 9.0 GHz observations of a sample of seventeen GRB host
galaxies at 0.5<z<1.4, using the radio continuum to explore their star
formation properties in the context of the small but growing sample of galaxies
with similar observations. Four sources are detected, one of those (GRB
100418A) likely due to lingering afterglow emission. We suggest that the
previously-reported radio afterglow of GRB 100621A may instead be due to host
galaxy flux. We see no strong evidence for redshift evolution in the typical
star formation rate of GRB hosts, but note that the fraction of `dark' bursts
with detections is higher than would be expected given constraints on the more
typical long GRB population. We also determine the average radio-derived star
formation rates of core collapse supernovae at comparable redshift, and show
that these are still well below the limits obtained for GRB hosts, and show
evidence for a rise in typical star formation rate with redshift in supernova
hosts.Comment: 15 pages, MNRAS accepte
B Leptonic Decays and B- bar B Mixing with 2+1 Flavors of Dynamical Quarks
Calculations of B leptonic decays and B- bar B mixing using NRQCD heavy and
Asqtad light valence quarks on the MILC dynamical configurations are described.
Smearing has been implemented to substantially reduce the statistical errors of
the matrix elements needed for the determination of f_B. The four-fermion
matrix elements needed for the determination of f_{B_s}^2B_{B_s} have been
calculated and a preliminary result is given.Comment: 3 pages, 3 figures, talk given at Lattice2004(heavy), Batavia,
Illinois, 21-26 Jun 200
Aerosol studies in mid-latitude coastal environments in Australia
The results of the evaluation of several inversion procedures that were used to select one which provides the most accurate atmospheric extinction profiles for small aerosol extinction coefficients (that often predominate in the maritime airmass) are presented. Height profiles of atmospheric extinction calculated by a two component atmospheric solution to the LIDAR equation will be compared with corresponding in-situ extinction profiles based on the size distribution profiles obtained in Western Australia. Values of the aerosol backscatter to extinction ratio obtained from multi-angle LIDAR measurements will be used in this solution
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