16,962 research outputs found
Detachable caster adapter
Detachable caster adapter moves heavy welding tables when fork lift trucks are not practical. A support saddle on the adapter, connected to the caster platform by means of a hinge, fits the leg of the welding table, but can be modified to fit other leg configurations
Using the Fundamental Plane to Estimate the Total Binding Mass in A2626
We use fundamental plane (FP) distance estimates to the components of the
double cluster A2626 (cz~17,500 km/s) to constrain cluster kinematics and
estimate total binding mass. The FP coefficients for a sample of 24 early type
and S0 cluster members (alpha=1.30+/-0.36 and beta=0.31+/-0.06) are consistent
with others reported in the literature. We examine the Mg_b distributions
within both subclusters and find them to be indistinguishable. Lacking evidence
for stellar population differences, we interpret the FP zeropoint offset
(\log(D_B/D_A)=-0.037+/-0.046, where D_{cl} is distance to subcluster cl) as a
measure of the distance difference. This measurement is consistent with the
subclusters being at the same distance, and it rules out the Hubble flow
hypothesis (distances proportional to velocity) with 99% confidence; analysis
of the subcluster galaxy magnitude distributions rules out Hubble flow at 93%
confidence. Both results favor a kinematic model where the subclusters are
bound and infalling. We estimate the total cluster binding mass by modelling
the subcluster merger as radial infall. The minimum possible total binding mass
is 1.65 times higher than the sum of the standard virial masses, a difference
statistically significant at the ~3sigma level. We discuss explanations for the
inconsistency including (1) biases in the standard virial mass estimator, (2)
biases in our radial infall mass estimate, and (3) mass beyond the virialized
cluster region; if the standard virial mass is significantly in error, the
cluster has an unusually high mass to light ratio (~1000h). Because
observational signatures of departures from radial infall are absent, we
explore the implications of mass beyond the virialized, core regions.
(abridged)Comment: 14 pages and 5 figures, Latex, Accepted for publication in A
The Effects of Clumping and Substructure on ICM Mass Measurements
We examine an ensemble of 48 simulated clusters to determine the effects of
small-scale density fluctuations and large-scale substructure on X-ray
measurements of the intracluster medium (ICM) mass. We measure RMS density
fluctuations in the ICM which can be characterized by a mean mass-weighted
clumping factor C = /^2 between 1.3 and 1.4 within a density
contrast of 500 times the critical density. These fluctuations arise from the
cluster history of accretion shocks and major mergers, and their presence
enhances the cluster's luminosity relative to the smooth case. We expect,
therefore, that ICM mass measurements utilizing models which assume uniform
density at a given radius carry a bias of order sqrt(C) = 1.16. We verify this
result by performing ICM mass measurements on X-ray images of the simulations
and finding the expected level of bias.
The varied cluster morphologies in our ensemble also allow us to investigate
the effects of departures from spherical symmetry on our measurements. We find
that the presence of large-scale substructure does not further bias the
resulting gas mass unless it is pronounced enough to produce a second peak in
the image of at least 1% the maximum surface brightness. We analyze the subset
of images with no secondary peaks and find a bias of 9% and a Gaussian random
error of 4% in the derived mass.Comment: To appear in ApJ
Fundamental constants and tests of theory in Rydberg states of one-electron ions
The nature of the theory of circular Rydberg states of hydrogenlike ions
allows highly-accurate predictions to be made for energy levels. In particular,
uncertainties arising from the problematic nuclear size correction which beset
low angular-momentum states are negligibly small for the high angular-momentum
states. The largest remaining source of uncertainty can be addressed with the
help of quantum electrodynamics (QED) calculations, including a new
nonperturbative result reported here. More stringent tests of theory and an
improved determination of the Rydberg constant may be possible if predictions
can be compared with precision frequency measurements in this regime. The
diversity of information can be increased by utilizing a variety of
combinations of ions and Ryberg states to determine fundamental constants and
test theory.Comment: 10 pages; LaTe
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