28,526 research outputs found
Comment on "Absence of Compressible Edge Channel Rings in Quantum Antidots"
In a recent article, Karakurt et al. [I. Karakurt et al., Phys. Rev. Lett.
89, 226803 (2002)] reported the absence of compressible regions around antidots
in the quantum Hall regime. We wish to point out a significant flaw in their
analysis, which invalidates their claim.Comment: 1 page 1 figure, to be published in Phys. Rev. Let
An Analysis of Jitter and Transit Timing Variations in the HAT-P-13 System
If the two planets in the HAT-P-13 system are coplanar, the orbital states
provide a probe of the internal planetary structure. Previous analyses of
radial velocity and transit timing data of the system suggested that the
observational constraints on the orbital states were rather small. We reanalyze
the available data, treating the jitter as an unknown MCMC parameter, and find
that a wide range of jitter values are plausible, hence the system parameters
are less well constrained than previously suggested. For slightly increased
levels of jitter () the eccentricity of the inner planet
can be in the range , the period and eccentricity of the
outer planet can be days and
respectively, while the relative pericenter alignment, , of the planets
can take essentially any value . It is
therefore difficult to determine whether and have evolved to
a fixed-point state or a limit cycle, or to use to probe the
internal planetary structure. We perform various transit timing variation (TTV)
analyses, demonstrating that current constraints merely restrict
, and rule out relative planetary inclinations within of , but that future observations could
significantly tighten the restriction on both these parameters. We demonstrate
that TTV profiles can readily distinguish the theoretically favored
inclinations of i_{rel}=0^{\circ}\,&\,45^{\circ}, provided that sufficiently
precise and frequent transit timing observations of HAT-P-13b can be made close
to the pericenter passage of HAT-P-13c. We note the relatively high probability
that HAT-P-13c transits and suggest observational dates and strategies.Comment: Published in Ap
What Brown saw and you can too
A discussion is given of Robert Brown's original observations of particles
ejected by pollen of the plant \textit{Clarkia pulchella} undergoing what is
now called Brownian motion. We consider the nature of those particles, and how
he misinterpreted the Airy disc of the smallest particles to be universal
organic building blocks. Relevant qualitative and quantitative investigations
with a modern microscope and with a "homemade" single lens microscope similar
to Brown's, are presented.Comment: 14.1 pages, 11 figures, to be published in the American Journal of
Physics. This differs from the previous version only in the web site referred
to in reference 3. Today, this Brownian motion web site was launched, and
http://physerver.hamilton.edu/Research/Brownian/index.html, is now correc
Using Transit Timing Observations to Search for Trojans of Transiting Extrasolar Planets
Theoretical studies predict that Trojans are likely a frequent byproduct of
planet formation and evolution. We examine the sensitivity of transit timing
observations for detecting Trojan companions to transiting extrasolar planets.
We demonstrate that this method offers the potential to detect terrestrial-mass
Trojans using existing ground-based observatories. We compare the transit
timing variation (TTV) method with other techniques for detecting extrasolar
Trojans and outline the future prospects for this method.Comment: submitted to ApJL, 12 pages, 2 figure
Metals plated on fluorocarbon polymers
Electroplating lead on fluorocarbon polymer parts is accomplished by etching the parts to be plated with sodium, followed by successive depositions of silver and lead from ultrasonically agitated plating solutions. Metals other than lead may be electroplated on the silvered parts
The Formation of Ice Giants in a Packed Oligarchy: Instability and Aftermath
As many as 5 ice giants--Neptune-mass planets composed of 90% ice and rock
and 10% hydrogen--are thought to form at heliocentric distances of 10-25 AU on
closely packed orbits spaced ~5 Hill radii apart. Such oligarchies are
ultimately unstable. Once the parent disk of planetesimals is sufficiently
depleted, oligarchs perturb one another onto crossing orbits. We explore both
the onset and the outcome of the instability through numerical integrations,
including dynamical friction cooling of planets by a planetesimal disk whose
properties are held fixed. To trigger instability and the ejection of the first
ice giant in systems having an original surface density in oligarchs of Sigma ~
1 g/cm^2, the disk surface density s must fall below 0.1 g/cm^2. Ejections are
predominantly by Jupiter and occur within 10 Myr. To eject more than 1 oligarch
requires s < 0.03 g/cm^2. Systems starting with up to 4 oligarchs in addition
to Jupiter and Saturn can readily yield solar-system-like outcomes in which 2
surviving ice giants lie inside 30 AU and have their orbits circularized by
dynamical friction. Our numerical simulations support the idea that planetary
systems begin in more crowded and compact configurations, like those of
shear-dominated oligarchies. In contrast to previous studies, we identify s <
0.1 Sigma as the regime relevant for understanding the evolution of the outer
solar system, and we encourage future studies to concentrate on this regime
while relaxing our assumption of a fixed planetesimal disk.Comment: Accepted to ApJ Jan 27. Incorporates comments from the referee and
community at large. 15 pages, 14 figures, including 7 colo
Bounds on negative energy densities in flat spacetime
We generalise results of Ford and Roman which place lower bounds -- known as
quantum inequalities -- on the renormalised energy density of a quantum field
averaged against a choice of sampling function. Ford and Roman derived their
results for a specific non-compactly supported sampling function; here we use a
different argument to obtain quantum inequalities for a class of smooth, even
and non-negative sampling functions which are either compactly supported or
decay rapidly at infinity. Our results hold in -dimensional Minkowski space
() for the free real scalar field of mass . We discuss various
features of our bounds in 2 and 4 dimensions. In particular, for massless field
theory in 2-dimensional Minkowski space, we show that our quantum inequality is
weaker than Flanagan's optimal bound by a factor of 3/2.Comment: REVTeX, 13 pages and 2 figures. Minor typos corrected, one reference
adde
Multi-scale Renormalisation Group Improvement of the Effective Potential
Using the renormalisation group and a conjecture concerning the perturbation
series for the effective potential, the leading logarithms in the effective
potential are exactly summed for scalar and Yukawa theories.Comment: 19 pages, DIAS STP 94-09. Expanded to check large N limit, typo's
corrected, to appear in Phys Rev
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