1,192 research outputs found
Defining the frame of minimum nonlinear Hubble expansion variation
We characterize a cosmic rest frame in which the monopole variation of the
spherically averaged nonlinear Hubble expansion is most uniform, under
arbitrary local Lorentz boosts of the central observer. Using the COMPOSITE
sample of 4534 galaxies, we identify a degenerate set of candidate minimum
nonlinear variation frames, which includes the rest frame of the Local Group
(LG) of galaxies, but excludes the standard Cosmic Microwave Background (CMB)
frame. Candidate rest frames defined by a boost from the LG frame close to the
plane of the galaxy have a statistical likelihood similar to the LG frame. This
may result from a lack of constraining data in the Zone of Avoidance. We extend
our analysis to the Cosmicflows-2 (CF2) sample of 8162 galaxies. While the
signature of a systematic boost offset between the CMB and LG frame averages is
still detected, the spherically averaged nonlinear expansion variation in all
rest frames is significantly larger in the CF2 sample than would be reasonably
expected. We trace this to the CF2 distances being reported without a
correction for inhomogeneous distribution Malmquist bias. Systematic
differences in the inclusion of the large SFI++ subsample into the COMPOSITE
and CF2 catalogues are analysed. Our results highlight the importance of a
careful treatment of Malmquist biases for future peculiar velocities studies,
including tests of the hypothesis of Wiltshire et al [Phys. Rev. D 88 (2013)
083529; arXiv:1201.5371] that a significant fraction of the CMB temperature
dipole may be nonkinematic in origin.Comment: 25 pages, 19 figures; v4 erratum added: small corrections, no change
in conclusion
Teaching machines for teaching work study
Machines which have been used successfully for the teaching of
work measurement practices are described. Although designed to
shorten the period of instruction for beginners) they appear to be
suitable for postgraduate students and also for management - consultant
trainees
The Science of Felt: A Look at the Research Driving the Move to Eliminate Felt Soled Waders
One key to preventing new aquatic invasive species (AIS) introductions is to understand introduction pathways in order to implement prevention strategies. Significant evidence suggests that some AIS are being transported by wading anglers and many new introductions can be traced to this pathway. Research conducted in New Zealand and Montana has provided a better understanding of how AIS are likely spread by anglers and what might be required to reduce the risk of angler transport. The most significant finding is that the felt material glued to the soles of wading boots is a very problematic material and is far more likely to viably transport AIS than any other material used in waders. Based on this research, New Zealand instituted a national ban on the use of felt soles in October 2008. In the US, Alaska has announced a ban for parts of the state beginning in 2011 and New Mexico is considering a statewide ban. This presentation will provide an overview of the research into felt soles and will summarize how companies, agencies, policy makers and the public are reacting to the use of felt
Cosmic Acceleration from M Theory on Twisted Spaces
In a recent paper [I.P. Neupane and D.L. Wiltshire, Phys. Lett. B 619, 201
(2005).] we have found a new class of accelerating cosmologies arising from a
time--dependent compactification of classical supergravity on product spaces
that include one or more geometric twists along with non-trivial curved
internal spaces. With such effects, a scalar potential can have a local minimum
with positive vacuum energy. The existence of such a minimum generically
predicts a period of accelerated expansion in the four-dimensional
Einstein-conformal frame. Here we extend our knowledge of these cosmological
solutions by presenting new examples and discuss the properties of the
solutions in a more general setting. We also relate the known (asymptotic)
solutions for multi-scalar fields with exponential potentials to the
accelerating solutions arising from simple (or twisted) product spaces for
internal manifolds.Comment: 23 pages, 3 figures; added a summary Table, PRD versio
Robertson-Walker fluid sources endowed with rotation characterised by quadratic terms in angular velocity parameter
Einstein's equations for a Robertson-Walker fluid source endowed with
rotation Einstein's equations for a Robertson-Walker fluid source endowed with
rotation are presented upto and including quadratic terms in angular velocity
parameter. A family of analytic solutions are obtained for the case in which
the source angular velocity is purely time-dependent. A subclass of solutions
is presented which merge smoothly to homogeneous rotating and non-rotating
central sources. The particular solution for dust endowed with rotation is
presented. In all cases explicit expressions, depending sinusoidally on polar
angle, are given for the density and internal supporting pressure of the
rotating source. In addition to the non-zero axial velocity of the fluid
particles it is shown that there is also a radial component of velocity which
vanishes only at the poles. The velocity four-vector has a zero component
between poles
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