147,386 research outputs found
Statistics of statisticians: Critical mass of statistics and operational research groups in the UK
Using a recently developed model, inspired by mean field theory in
statistical physics, and data from the UK's Research Assessment Exercise, we
analyse the relationship between the quality of statistics and operational
research groups and the quantity researchers in them. Similar to other academic
disciplines, we provide evidence for a linear dependency of quality on quantity
up to an upper critical mass, which is interpreted as the average maximum
number of colleagues with whom a researcher can communicate meaningfully within
a research group. The model also predicts a lower critical mass, which research
groups should strive to achieve to avoid extinction. For statistics and
operational research, the lower critical mass is estimated to be 9 3. The
upper critical mass, beyond which research quality does not significantly
depend on group size, is about twice this value
Dynamic Race Prediction in Linear Time
Writing reliable concurrent software remains a huge challenge for today's
programmers. Programmers rarely reason about their code by explicitly
considering different possible inter-leavings of its execution. We consider the
problem of detecting data races from individual executions in a sound manner.
The classical approach to solving this problem has been to use Lamport's
happens-before (HB) relation. Until now HB remains the only approach that runs
in linear time. Previous efforts in improving over HB such as causally-precedes
(CP) and maximal causal models fall short due to the fact that they are not
implementable efficiently and hence have to compromise on their race detecting
ability by limiting their techniques to bounded sized fragments of the
execution. We present a new relation weak-causally-precedes (WCP) that is
provably better than CP in terms of being able to detect more races, while
still remaining sound. Moreover it admits a linear time algorithm which works
on the entire execution without having to fragment it.Comment: 22 pages, 8 figures, 1 algorithm, 1 tabl
An accurate formula for the period of a simple pendulum oscillating beyond the small-angle regime
A simple approximation formula is derived here for the dependence of the
period of a simple pendulum on amplitude that only requires a pocket calculator
and furnishes an error of less than 0.25% with respect to the exact period. It
is shown that this formula describes the increase of the pendulum period with
amplitude better than other simple formulas found in literature. A good
agreement with experimental data for a low air-resistance pendulum is also
verified and it suggests, together with the current availability/precision of
timers and detectors, that the proposed formula is useful for extending the
pendulum experiment beyond the usual small-angle oscillations.Comment: 15 pages and 4 figures. to appear in American Journal of Physic
Droplet impact on a thin fluid layer
The initial stages of high-velocity droplet impact on a shallow water layer are described, with special emphasis given to the spray jet mechanics. Four stages of impact are delineated, with appropriate scalings, and the successively more important influence of the base is analysed. In particular, there is a finite time before which part of the water in the layer remains under the droplet and after which all of the layer is ejected in the splash jet
Discrepancies in Determinations of the Ginzburg-Landau Parameter
Long-standing discrepancies within determinations of the Ginzburg-Landau
parameter from supercritical field measurements on superconducting
microspheres are reexamined. The discrepancy in tin is shown to result from
differing methods of analyses, whereas the discrepancy in indium is a
consequence of significantly differing experimental results. The reanalyses
however confirms the lower determinations to within experimental
uncertainties.Comment: submitted to Phys. Rev.
Massive molecular outflows at high spatial resolution
We present high-spatial resolution Plateau de Bure Interferometer CO(2-1) and
SiO(2-1) observations of one intermediate-mass and one high-mass star-forming
region. The intermediate-mass region IRAS20293+3952 exhibits four molecular
outflows, one being as collimated as the highly collimated jet-like outflows
observed in low-mass star formation sources. Furthermore, comparing the data
with additional infrared H2 and cm observations we see indications that the
nearby ultracompact HII region triggers a shock wave interacting with the
outflow. The high-mass region IRAS19217+1651 exhibits a bipolar outflow as well
and the region is dominated by the central driving source. Adding two more
sources from the literature, we compare position-velocity diagrams of the
intermediate- to high-mass sources with previous studies in the low-mass
regime. We find similar kinematic signatures, some sources can be explained by
jet-driven outflows whereas other are better constrained by wind-driven models.
The data also allow to estimate accretion rates varying from a few times
10^{-5}Msun/yr for the intermediate-mass sources to a few times 10^{-4}Msun/yr
for the high-mass source, consistent with models explaining star formation of
all masses via accretion processes.Comment: 14 pages text, 4 tables, 8 figures, accepted for Ap
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