10,939 research outputs found
Investigation of continental drift, phase 1 effort Progress report, 1 Apr. - 30 Sep. 1968
Feasibility of using ultrashort pulse laser ranging and independent clock radio interferometry distance measurement methods to test for existence of continental drif
Mass Profile of the Infall Region of the Abell 2199 Supercluster
Using a redshift survey of 1323 galaxies (1092 new or remeasured) in a region
of 95 square degrees centered on the nearby galaxy cluster Abell 2199, we
analyze the supercluster containing A2199, A2197, and an X-ray group. The
caustic technique accurately reproduces the true mass profiles of simulated
simple superclusters (i.e., superclusters where the virial mass of one cluster
is 2-10 times the virial mass of all other clusters in the supercluster). We
calculate the masses of the two main components of A2197 (A2197W and A2197E)
using archival X-ray observations and demonstrate that the A2199 supercluster
is simple and thus that the caustic technique should yield an accurate mass
profile. The mass profile is uncertain by ~30% within 3 Mpc/h and by a factor
of two within 8 Mpc/h and is one of only a few for a supercluster on such large
scales. Independent X-ray mass estimates agree with our results at all radii
where they overlap. The mass profile strongly disagrees with an isothermal
sphere profile but agrees with profiles suggested by simulations. We discuss
the interplay of the supercluster dynamics and the dynamics of the bound
subclusters. The agreement between the infall mass profile and other techniques
shows that the caustic technique is surprisingly robust for simple
superclusters (abridged).Comment: 49 pages, 20 figures, to appear in The Astronomical Journal, version
containing high-resolution figures available at
http://cfa-www.harvard.edu/~krines/a2199mp.p
Lamb Shift of 3P and 4P states and the determination of
The fine structure interval of P states in hydrogenlike systems can be
determined theoretically with high precision, because the energy levels of P
states are only slightly influenced by the structure of the nucleus. Therefore
a measurement of the fine structure may serve as an excellent test of QED in
bound systems or alternatively as a means of determining the fine structure
constant with very high precision. In this paper an improved analytic
calculation of higher-order binding corrections to the one-loop self energy of
3P and 4P states in hydrogen-like systems with low nuclear charge number is
presented. A comparison of the analytic results to the extrapolated numerical
data for high ions serves as an independent test of the analytic
evaluation. New theoretical values for the Lamb shift of the P states and for
the fine structure splittings are given.Comment: 33 pages, LaTeX, 4 tables, 4 figure
Coordinate-space approach to the bound-electron self-energy: Self-Energy screening calculation
The self-energy screening correction is evaluated in a model in which the
effect of the screening electron is represented as a first-order perturbation
of the self energy by an effective potential. The effective potential is the
Coulomb potential of the spherically averaged charge density of the screening
electron. We evaluate the energy shift due to a , ,
, or electron screening a , ,
, or electron, for nuclear charge Z in the range . A detailed comparison with other calculations is made.Comment: 54 pages, 10 figures, 4 table
Two-Loop Bethe Logarithms
We calculate the two-loop Bethe logarithm correction to atomic energy levels
in hydrogen-like systems. The two-loop Bethe logarithm is a low-energy quantum
electrodynamic (QED) effect involving multiple summations over virtual excited
atomic states. Although much smaller in absolute magnitude than the well-known
one-loop Bethe logarithm, the two-loop analog is quite significant when
compared to the current experimental accuracy of the 1S-2S transition: it
contributes -8.19 and -0.84 kHz for the 1S and the 2S state, respectively. The
two-loop Bethe logarithm has been the largest unknown correction to the
hydrogen Lamb shift to date. Together with the ongoing measurement of the
proton charge radius at the Paul Scherrer Institute its calculation will bring
theoretical and experimental accuracy for the Lamb shift in atomic hydrogen to
the level of 10^(-7).Comment: 4 pages, RevTe
QED self-energy contribution to highly-excited atomic states
We present numerical values for the self-energy shifts predicted by QED
(Quantum Electrodynamics) for hydrogenlike ions (nuclear charge ) with an electron in an , 4 or 5 level with high angular momentum
(). Applications include predictions of precision transition
energies and studies of the outer-shell structure of atoms and ions.Comment: 20 pages, 5 figure
Effective 3D Geometry Extraction and Reverse CAD Modeling
The goal of this work is to develop and implement a technology capability for providing cost-effective and rapid geometry evaluation of parts and processes. We were motivated by the new availability of fully three dimensional nondestructive CT scanning for a variety of manufactured parts and assemblies on a rapid and cost-effective basis, with resolutions commensurate with the tolerances required for a variety of manufacturing processes. High-speed, high-quality three dimensional scanning can be accomplished on a overnight service basis for a variety of objects, for costs ranging from a few hundreds to a few thousands of dollars. The resulting images contain quantitative information relating the local x-ray density of scanned objects at every voxel in a three dimensional raster space. There have been significant advances in methods for quantitative volumetric processing and information extraction from these images. However, for many manufacturing process verification applications, the resulting three dimensional images contain more information than can be effectively handled by many end users, particularly when the size of the 3D image data files (often larger than 1 Gbyte) is considered
Convergence Acceleration Techniques
This work describes numerical methods that are useful in many areas: examples
include statistical modelling (bioinformatics, computational biology),
theoretical physics, and even pure mathematics. The methods are primarily
useful for the acceleration of slowly convergent and the summation of divergent
series that are ubiquitous in relevant applications. The computing time is
reduced in many cases by orders of magnitude.Comment: 6 pages, LaTeX; provides an easy-to-understand introduction to the
field of convergence acceleratio
Higher-order binding corrections to the Lamb shift of 2P states
We present an improved calculation of higher-order corrections to the
one-loop self energy of 2P states in hydrogen-like systems with small nuclear
charge Z. The method is based on a division of the integration with respect to
the photon energy into a high- and a low-energy part. The high-energy part is
calculated by an expansion of the electron propagator in powers of the Coulomb
field. The low-energy part is simplified by the application of a
Foldy-Wouthuysen transformation. This transformation leads to a clear
separation of the leading contribution from the relativistic corrections and
removes higher order terms. The method is applied to the 2P_{1/2} and 2P_{3/2}
states in atomic hydrogen. The results lead to new theoretical values for the
Lamb shifts and the fine structure splitting.Comment: 18 pages, LaTeX. In comparison to the journal version, it contains an
added note (2000) which reflects the current status of Lamb shift
calculation
The X-ray Size-Temperature Relation for Intermediate Redshift Galaxy Clusters
We present the first measurements of the X-ray size-temperature (ST) relation
in intermediate redshift (z~0.30) galaxy clusters. We interpret the local ST
relation (z~0.06) in terms of underlying scaling relations in the cluster dark
matter properties, and then we use standard models for the redshift evolution
of those dark matter properties to show that the ST relation does not evolve
with redshift. We then use ROSAT HRI observations of 11 clusters to examine the
intermediate redshift ST relation; for currently favored cosmological
parameters, the intermediate redshift ST relation is consistent with that of
local clusters. Finally, we use the ST relation and our evolution model to
measure angular diameter distances; with these 11 distances we evaluate
constraints on Omega_M and Omega_L which are consistent with those derived from
studies of Type Ia supernovae. The data rule out a model with Omega_M=1 and
Omega_L=0 with 2.5 sigma confidence. When limited to models where
Omega_M+Omega_L=1, these data are inconsistent with Omega_M=1 with 3 sigma
confidence.Comment: ApJ: submitted April 7, accepted June 28, to appear Dec 1 (vol 544
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