382 research outputs found
Kuiper Binary Object Formation
It has been observed that binary Kuiper Belt Objects (KBOs) exist contrary to
theoretical expectations. Their creation presents problems to most current
models. However, the inclusion of a third body (for example, one of the outer
planets) may provide the conditions necessary for the formation of these
objects. The presence of a third massive body not only helps to clear the
primordial Kuiper Belt but can also result in long lived binary Kuiper belt
objects. The gravitational interaction between the KBOs and the third body
causes one of four effects; scattering into the Oort cloud, collisions with the
growing protoplanets, formation of binary pairs, or creation of a single Kuiper
belt object. Additionally, the initial location of the progenitors of the
Kuiper belt objects also has a significant effect on binary formation
Imaging of Low Compressibility Strips in the Quantum Hall Liquid
Using Subsurface Charge Accumulation scanning microscopy we image strips of
low compressibility corresponding to several integer Quantum Hall filling
factors. We study in detail the strips at Landau level filling factors
2 and 4. The observed strips appear significantly wider than predicted by
theory. We present a model accounting for the discrepancy by considering a
disorder-induced nonzero density of states in the cyclotron gap.Comment: 5 pages, 3 figure
âChoicest unguentsâ: molecular evidence for the use of resinous plant exudates in late Roman mortuary rites in Britain
YesResinous substances were highly prized in the ancient world for use in ritual contexts. Details gleaned
from classical literature indicate that they played a significant role in Roman mortuary rites, in treatment
of the body and as offerings at the tomb. Outside of Egypt, however, where research has shown that a
range of plant exudates were applied as part of the mummification process, resins have rarely been
identified in the burial record. This is despite considerable speculation regarding their use across the
Roman Empire.
Focusing on one region, we investigated organic residues from forty-nine late Roman inhumations
from Britain. Using gas chromatographyemass spectrometry and the well-attested biomarker approach,
terpenic compounds were characterized in fourteen of the burials analysed. These results provided direct
chemical evidence for the presence of exudates from three different plant families: coniferous Pinaceae
resins, Mediterranean Pistacia spp. resins (mastic/terebinth) and exotic Boswellia spp. gum-resins
(frankincense/olibanum) from southern Arabia or beyond. The individuals accorded this rite had all
been interred with a package of procedures more elaborate than the norm.
These findings illuminate the multiplicity of roles played by resinous substances in Roman mortuary
practices in acting to disguise the odour of decomposition, aiding temporary soft-tissue preservation and
signifying the social status of the deceased. Nevertheless, it was their ritual function in facilitating the
transition to the next world that necessitated transportation to the most remote outpost of the late
Roman Empire, Britain.R.C.B is supported by a PhD studentship from the Art and Humanities Research Council (43019R00209)
Clock drawing performance in cognitively normal elderly
The Clock Drawing Test (CDT) is a common neuropsychological measure sensitive to cognitive changes and functional skills (e.g., driving test performance) among older adults. However, normative data have not been adequately developed. We report the distribution of CDT scores using three common scoring systems [Mendez, M. F., Ala, T., & Underwood, K. L. (1992). Development of scoring criteria for the Clock Drawing Task in Alzheimer's Disease. Journal of the American Geriatrics Society, 40, 1095-1099; Cahn, D. A., Salmon, D. P., Monsch, A. U., Butters, N., Wiederholt, W. C., & Corey-Bloom, J. (1996). Screening for dementia of the Alzheimer type in the community: The utility of the Clock Drawing Test. Archives of Clinical Neuropsychology, 11(6), 529-539], among 207 cognitively normal elderly. The systems were well correlated, took little time to use, and had high inter-rater reliability. We found statistically significant differences in CDT scores based on age and WRAT-3 Reading score, a marker of education quality. We present means, standard deviations, and t- and z-scores based on these subgroups. We found that "normal" CDT performance includes a wider distribution of scores than previously reported. Our results may serve as useful comparisons for clinicians wishing to know whether their patients perform in the general range of cognitively normal elderly. © 2007 National Academy of Neuropsychology
Electrochemical capacitance of a leaky nano-capacitor
We report a detailed theoretical investigation on electrochemical capacitance
of a nanoscale capacitor where there is a DC coupling between the two
conductors. For this ``leaky'' quantum capacitor, we have derived general
analytic expressions of the linear and second order nonlinear electrochemical
capacitance within a first principles quantum theory in the discrete potential
approximation. Linear and nonlinear capacitance coefficients are also derived
in a self-consistent manner without the latter approximation and the
self-consistent analysis is suitable for numerical calculations. At linear
order, the full quantum formula improves the semiclassical analysis in the
tunneling regime. At nonlinear order which has not been studied before for
leaky capacitors, the nonlinear capacitance and nonlinear nonequilibrium charge
show interesting behavior. Our theory allows the investigation of crossover of
capacitance from a full quantum to classical regimes as the distance between
the two conductors is changed
Density-functional theory of quantum wires and dots in a strong magnetic field
We study the competition between the exchange and the direct Coulomb
interaction near the edge of a two-dimensional electron gas in a strong
magnetic field using density-functional theory in a local approximation for the
exchange-energy functional. Exchange is shown to play a significant role in
reducing the spatial extent of the compressible edge channel regions obtained
from an electrostatic description. The transition from the incompressible edge
channels of the Hartree-Fock picture to the broad, compressible strips
predicted by electrostatics occurs within a narrow and experimentally
accessible range of confinement strengths.Comment: 24 pages latex and 10 postscript figures in self extracting fil
Low-lying meson spectrum of large strongly coupled lattice QCD
We compute the low energy mass spectrum of lattice QCD in the large
limit. Expanding around a gauge-invariant ground state, which spontaneously
breaks the discrete chiral symmetry, we derive an improved strong-coupling
expansion and evaluate, for any value of , the masses of the low-lying
states in the unflavored meson spectrum. We then take the 't Hooft limit by
rescaling ; the 't Hooft limit is smooth and no arbitrary
parameters are needed. We find, already at the fourth order of the strong
coupling perturbation theory, a very good agreement between the results of our
lattice computation and the known continuum values.Comment: 43 pages, 1 figure. Minor corrections. One reference added in section
Effective Lagrangian for strongly coupled domain wall fermions
We derive the effective Lagrangian for mesons in lattice gauge theory with
domain-wall fermions in the strong-coupling and large-N_c limits. We use the
formalism of supergroups to deal with the Pauli-Villars fields, needed to
regulate the contributions of the heavy fermions. We calculate the spectrum of
pseudo-Goldstone bosons and show that domain wall fermions are doubled and
massive in this regime. Since we take the extent and lattice spacing of the
fifth dimension to infinity and zero respectively, our conclusions apply also
to overlap fermions.Comment: 26 pp. RevTeX and 3 figures; corrected error in symmetry breaking
scheme and added comments to discussio
Broken-Symmetry States in Quantum Hall Superlattices
We argue that broken-symmetry states with either spatially diagonal or
spatially off-diagonal order are likely in the quantum Hall regime, for clean
multiple quantum well (MQW) systems with small layer separations. We find that
for MQW systems, unlike bilayers, charge order tends to be favored over
spontaneous interlayer coherence. We estimate the size of the interlayer
tunneling amplitude needed to stabilize superlattice Bloch minibands by
comparing the variational energies of interlayer-coherent superlattice miniband
states with those of states with charge order and states with no broken
symmetries. We predict that when coherent miniband ground states are stable,
strong interlayer electronic correlations will strongly enhance the
growth-direction tunneling conductance and promote the possibility of Bloch
oscillations.Comment: 9 pages LaTeX, 4 figures EPS, to be published in PR
Searching for energetic cosmic axions in a laboratory experiment: testing the PVLAS anomaly
Astrophysical sources of energetic gamma rays provide the right conditions
for maximal mixing between (pseudo)scalar (axion-like) particles and photons if
their coupling is as strong as suggested by the PVLAS claim. This is
independent of whether or not the axion interaction is standard at all energies
or becomes supressed in the extreme conditions of the stellar interior. The
flux of such particles through the Earth could be observed using a metre long,
Tesla strength superconducting solenoid thus testing the axion interpretation
of the PVLAS anomaly. The rate of events in CAST caused by axions from the Crab
pulsar is also estimated for the PVLAS-favoured parameters.Comment: 5 pages, 3 figur
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