1,621 research outputs found
A second row Parking Paradox
We consider two variations of the discrete car parking problem where at every
vertex of the integers a car arrives with rate one, now allowing for parking in
two lines. a) The car parks in the first line whenever the vertex and all of
its nearest neighbors are not occupied yet. It can reach the first line if it
is not obstructed by cars already parked in the second line (screening). b) The
car parks according to the same rules, but parking in the first line can not be
obstructed by parked cars in the second line (no screening). In both models, a
car that can not park in the first line will attempt to park in the second
line. If it is obstructed in the second line as well, the attempt is discarded.
We show that both models are solvable in terms of finite-dimensional ODEs. We
compare numerically the limits of first and second line densities, with time
going to infinity. While it is not surprising that model a) exhibits an
increase of the density in the second line from the first line, more remarkably
this is also true for model b), albeit in a less pronounced way.Comment: 11 pages, 4 figure
The Throat and The Voice: The Complete Text
The complete text of the 1879 volume, by J. Solis Cohen, M.D. Solis Cohen was a pioneer in laryngeal surgery and Lecturer on Laryngology and Diseases of the Chest at Jefferson Medical College from 1867-1927. 159 pages.https://jdc.jefferson.edu/throat_and_voice/1001/thumbnail.jp
Germ-Line Gene Editing and Congressional Reaction in Context: Learning From Almost 50 Years of Congressional Reactions to Biomedical Breakthroughs
On December 18, 2015, President Obama signed into law a policy rider forestalling the therapeutic modification of the human germ line. The rider, motivated by the science’s potential unethical ends, is only the most recent instance in which the legislature cut short the ongoing national conversation on the acceptability of a developing science. This essay offers historical perspective on what bills were proposed and passed surrounding four other then-developing scientific breakthroughs—Recombinant DNA, in vitro fertilization, Cloning, Stem Cells—to better analyze how Congress is, and should, regulate this exciting and promising science
Mounding Instability and Incoherent Surface Kinetics
Mounding instability in a conserved growth from vapor is analysed within the
framework of adatom kinetics on the growing surface. The analysis shows that
depending on the local structure on the surface, kinetics of adatoms may vary,
leading to disjoint regions in the sense of a continuum description. This is
manifested particularly under the conditions of instability. Mounds grow on
these disjoint regions and their lateral growth is governed by the flux of
adatoms hopping across the steps in the downward direction. Asymptotically
ln(t) dependence is expected in 1+1- dimensions. Simulation results confirm the
prediction. Growth in 2+1- dimensions is also discussed.Comment: 4 pages, 4 figure
Enhanced four-wave mixing via elimination of inhomogeneous broadening by coherent driving of quantum transition with control fields
We show that atoms from wide velocity interval can be concurrently involved
in Doppler-free two-photon resonant far from frequency degenerate four-wave
mixing with the aid of auxiliary electromagnetic field. This gives rise to
substantial enhancement of the output radiation generated in optically thick
medium. Numerical illustrations addressed to typical experimental conditions
are given.Comment: LaTeX2e, hyperref, 7 pages, 5 figures, to appear in PRA 1 august 200
On the global hydration kinetics of tricalcium silicate cement
We reconsider a number of measurements for the overall hydration kinetics of
tricalcium silicate pastes having an initial water to cement weight ratio close
to 0.5. We find that the time dependent ratio of hydrated and unhydrated silica
mole numbers can be well characterized by two power-laws in time, . For early times we find an `accelerated' hydration
() and for later times a `deaccelerated' behavior (). The crossover time is estimated as . We
interpret these results in terms of a global second order rate equation
indicating that (a) hydrates catalyse the hydration process for , (b)
they inhibit further hydration for and (c) the value of the
associated second order rate constant is of magnitude 6x10^{-7} - 7x10^{-6}
liter mol^{-1} s^{-1}. We argue, by considering the hydration process actually
being furnished as a diffusion limited precipitation that the exponents and directly indicate a preferentially `plate' like hydrate
microstructure. This is essentially in agreement with experimental observations
of cellular hydrate microstructures for this class of materials.Comment: RevTeX macros, 6 pages, 4 postscript figure
Multibeam Maser Survey of methanol and excited OH in the Magellanic clouds: new detections and maser abundance estimates
‘The definitive version is available at www.blackwell-synergy.com.’ Copyright Blackwell Publishing DOI: 10.1111/j.1365-2966.2008.12888.xPeer reviewe
Electronic structure and ferroelectricity in SrBi2Ta2O9
The electronic structure of SrBi2Ta2O9 is investigated from first-principles,
within the local density approximation, using the full-potential linearized
augmented plane wave (LAPW) method. The results show that, besides the large
Ta(5d)-O(2p) hybridization which is a common feature of the ferroelectric
perovskites, there is an important hybridization between bismuth and oxygen
states. The underlying static potential for the ferroelectric distortion and
the primary source for ferroelectricity is investigated by a lattice-dynamics
study using the Frozen Phonon approach.Comment: 17 pages, 7 figures. Phys. Rev. B, in pres
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