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Energy, climate and water in the 21st century – Texas and Florida share a strong connection with future challenges in the Earth sciences
Bureau of Economic Geolog
Developing Mathematics Enrichment Workshops for Middle School Students: Philosophy and Sample Workshops
This paper describes our approach to organizing enrichment activities using advanced mathematics topics for diverse audiences of middle school students. We discuss our philosophy and approaches for the structure of these workshops, and then provide sample schedules and resource materials. The workshops cover activities on the following topics: Graphing Calculators; The Chaos Game; Statistical Sampling; CT Scans–the reconstruction problem; The Platonic and Archimedean solids; The Shape of Space; Symmetry; The Binary Number System and the game of NIM; Graph Theory: Proof by Counterexample
Additions to fused-fluoride lubricant coatings for reduction of low-temperature friction
Additions to fused-fluoride lubricant coatings for reduction of low temperature frictio
Direct observation of particle-hole mixing in the superconducting state by angle-resolved photoemission
Particle-hole (p-h) mixing is a fundamental consequence of the existence of a
pair condensate. We present direct experimental evidence for p-h mixing in the
angle-resolved photoemission (ARPES) spectra in the superconducting state of
Bi_2Sr_2CaCu_2O_{8+\delta}. In addition to its pedagogical importance, this
establishes unambiguously that the gap observed in ARPES is associated with
superconductivity.Comment: 3 pages, revtex, 4 postscript figure
Colloidal Dynamics on Disordered Substrates
Using Langevin simulations we examine driven colloids interacting with
quenched disorder. For weak substrates the colloids form an ordered state and
depin elastically. For increasing substrate strength we find a sharp crossover
to inhomogeneous depinning and a substantial increase in the depinning force,
analogous to the peak effect in superconductors. The velocity versus driving
force curve shows criticality at depinning, with a change in scaling exponent
occuring at the order to disorder crossover. Upon application of a sudden pulse
of driving force, pronounced transients appear in the disordered regime which
are due to the formation of long-lived colloidal flow channels.Comment: 4 pages, 4 postscript figure
Recoiling from a kick in the head-on collision of spinning black holes
Recoil ``kicks'' induced by gravitational radiation are expected in the
inspiral and merger of black holes. Recently the numerical relativity community
has begun to measure the significant kicks found when both unequal masses and
spins are considered. Because understanding the cause and magnitude of each
component of this kick may be complicated in inspiral simulations, we consider
these effects in the context of a simple test problem. We study recoils from
collisions of binaries with initially head-on trajectories, starting with the
simplest case of equal masses with no spin and then adding spin and varying the
mass ratio, both separately and jointly. We find spin-induced recoils to be
significant relative to unequal-mass recoils even in head-on configurations.
Additionally, it appears that the scaling of transverse kicks with spins is
consistent with post-Newtonian theory, even though the kick is generated in the
nonlinear merger interaction, where post-Newtonian theory should not apply.
This suggests that a simple heuristic description might be effective in the
estimation of spin-kicks.Comment: 12 pages, 10 figures. Replaced with published version, including more
discussion of convergence and properties of final hol
Formation of cosmological mass condensation within a FRW universe: exact general relativistic solutions
Within the framework of an exact general relativistic formulation of gluing
manifolds, we consider the problem of matching an inhomogeneous overdense
region to a Friedmann-Robertson-Walker background universe in the general
spherical symmetric case of pressure-free models. It is shown that, in general,
the matching is only possible through a thin shell, a fact ignored in the
literature. In addition to this, in subhorizon cases where the matching is
possible, an intermediate underdense region will necessarily arise.Comment: 6 page
ARPES Study of X-Point Band Overlaps in LaB and SmB - Contrast to SrB and EuB
In contrast to our recent finding of an X-point band gap in divalent
hexaborides, we report here that angle resolved photoemission spectroscopy
(ARPES) data shows that the gap is absent for trivalent LaB and is absent
or nearly so for mixed valent SmB. This finding demonstrates a nontrivial
evolution of the band structure from divalent to trivalent hexaborides.Comment: submitted to SCES '0
Outflows and Jets from Collapsing Magnetized Cloud Cores
Star formation is usually accompanied by outflow phenomena. There is strong
evidence that these outflows and jets are launched from the protostellar disk
by magneto-rotational processes. Here, we report on our three dimensional,
adaptive mesh, magneto-hydrodynamic simulations of collapsing, rotating,
magnetized Bonnor-Ebert-Spheres whose properties are taken directly from
observations. In contrast to the pure hydro case where no outflows are seen,
our present simulations show an outflow from the protodisk surface at ~ AU and
a jet at ~ 0.07 AU after a strong toroidal magnetic field build up. The large
scale outflow, which extends up to ~ AU at the end of our simulation, is driven
by toroidal magnetic pressure (spring), whereas the jet is powered by
magneto-centrifugal force (fling). At the final stage of our simulation these
winds are still confined within two respective shock fronts. Furthermore, we
find that the jet-wind and the disk-anchored magnetic field extracts a
considerable amount of angular momentum from the protostellar disk. The initial
spin of our cloud core was chosen high enough to produce a binary system. We
indeed find a close binary system (separation ~ 3 R_sol) which results from the
fragmentation of an earlier formed ring structure. The magnetic field strength
in these protostars reaches ~ 3 kG and becomes about 3 G at 1 AU from the
center in agreement with recent observational results.Comment: revised version, accepted for publication in ApJ, a higher resolution
version of this paper can be downloaded at
http://www.physics.mcmaster.ca/~banerjee/outflows.pd
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