10,702 research outputs found
Comparison of musculoskeletal networks of the primate forelimb
Anatomical network analysis is a framework for quantitatively characterizing the topological organization of anatomical structures, thus providing a way to compare structural integration and modularity among species. Here we apply this approach to study the macroevolution of the forelimb in primates, a structure whose proportions and functions vary widely within this group. We analyzed musculoskeletal network models in 22 genera, including members of all major extant primate groups and three outgroup taxa, after an extensive literature survey and dissections. The modules of the proximal limb are largely similar among taxa, but those of the distal limb show substantial variation. Some network parameters are similar within phylogenetic groups (e.g., non-primates, strepsirrhines, New World monkeys, and hominoids). Reorganization of the modules in the hominoid hand compared to other primates may relate to functional changes such as coordination of individual digit movements, increased pronation/supination, and knuckle-walking. Surprisingly, humans are one of the few taxa we studied in which the thumb musculoskeletal structures do not form an independent anatomical module. This difference may be caused by the loss in humans of some intrinsic muscles associated with the digits or the acquisition of additional muscles that integrate the thumb more closely with surrounding structures
Electron Scattering in AlGaN/GaN Structures
We present data on mobility lifetime, , quantum lifetime, ,
and cyclotron resonance lifetime, , of a sequence of high-mobility
two-dimensional electron gases in the AlGaN/GaN system, covering a density
range of cm. We observe a large discrepancy
between and (/6) and explain it as
the result of density fluctuations of only a few percent. Therefore, only
--and not -- is a reliable measure of the time between
electron scattering events in these specimens. The ratio
increases with increasing density in this series of samples, but scattering
over this density range remains predominantly in the large-angle scattering
regime
Differential freezeout and pion interferometry at RHIC from covariant transport theory
Puzzling discrepancies between recent pion interferometry data on Au+Au
reactions at s^1/2 = 130 and 200 AGeV from RHIC and predictions based on ideal
hydrodynamics are analyzed in terms of covariant parton transport theory. The
discrepancies of out and longitudinal radii are significantly reduced when the
finite opacity of the gluon plasma is taken into account.Comment: 4 pages, 3 EPS figures. Submitted to PR
Timing performance of 30-nm-wide superconducting nanowire avalanche photodetectors
We investigated the timing jitter of superconducting nanowire avalanche
photodetectors (SNAPs, also referred to as cascade switching superconducting
single photon detectors) based on 30-nm-wide nanowires. At bias currents (IB)
near the switching current, SNAPs showed sub 35 ps FWHM Gaussian jitter similar
to standard 100 nm wide superconducting nanowire single-photon detectors. At
lower values of IB, the instrument response function (IRF) of the detectors
became wider, more asymmetric, and shifted to longer time delays. We could
reproduce the experimentally observed IRF time-shift in simulations based on an
electrothermal model, and explain the effect with a simple physical picture
Non-parabolicity of the conduction band of wurtzite GaN
Using cyclotron resonance, we measure the effective mass, *, of electrons
in AlGaN/GaN heterostructures with densities, cm. From our extensive data, we extrapolate a band edge
mass of . By comparing our * data with the results of a
multi-band \textbf{k.p} calculation we infer that the effect of remote bands is
essential in explaining the observed conduction band non-parabolicity (NP). Our
calculation of polaron mass corrections -- including finite width and screening
- suggests those to be negligible. It implies that the behavior of
can be understood solely in terms of NP. Finally, using our NP and polaron
corrections, we are able to reduce the large scatter in the published band edge
mass values
Particle correlations at RHIC from parton coalescence dynamics -- first results
A new dynamical approach that combines covariant parton transport theory with
hadronization channels via parton coalescence and fragmentation is applied to
Au+Au at RHIC. Basic consequences of the simple coalescence formulas, such as
elliptic flow scaling and enhanced proton/pion ratio, turn out to be rather
sensitive to the spacetime aspects of coalescence dynamics.Comment: Contribution to Quark Matter 2004 (January 11-17, 2004, Oakland, CA).
4 pages, 2 EPS figs, IOP style fil
Rethinking the QCD collisional energy loss
It is shown that to leading order the collisional energy loss of an energetic
parton in the hot quark gluon plasma reads , where
the scale of the coupling is determined by the (parametrically soft) Debye
screening mass. Compared to previous expressions derived by Bjorken and other
authors, , the rectified result takes
into account the running of the coupling, as dictated by quantum corrections
beyond tree level. As one significant consequence, due to asymptotic freedom,
the QCD collisional energy loss becomes independent of the jet energy in the
limit . It is advocated that this resummation improved perturbative
result might be useful to (re-)estimate the collisional energy loss for
temperatures relevant in heavy ion phenomenology.Comment: contribution to "Hot Quarks 2006", Villasimius, Italy, 15-20 May 200
Acoustic phonon scattering in a low density, high mobility AlGaN/GaN field effect transistor
We report on the temperature dependence of the mobility, , of the
two-dimensional electron gas in a variable density AlGaN/GaN field effect
transistor, with carrier densities ranging from 0.4 cm to
3.0 cm and a peak mobility of 80,000 cm/Vs. Between
20 K and 50 K we observe a linear dependence T
indicating that acoustic phonon scattering dominates the temperature dependence
of the mobility, with being a monotonically increasing function of
decreasing 2D electron density. This behavior is contrary to predictions of
scattering in a degenerate electron gas, but consistent with calculations which
account for thermal broadening and the temperature dependence of the electron
screening. Our data imply a deformation potential D = 12-15 eV.Comment: 3 pages, 2 figures, RevTeX. Submitted to Appl Phys Let
Free-form lens model and mass estimation of the high redshift galaxy cluster ACT-CL J0102-4915, "El Gordo"
We examine the massive colliding cluster El Gordo, one of the most massive
clusters at high redshift. We use a free-form lensing reconstruction method
that avoids making assumptions about the mass distribution. We use data from
the RELICS program and identify new multiply lensed system candidates. The new
set of constraints and free-form method provides a new independent mass
estimate of this intriguing colliding cluster. Our results are found to be
consistent with earlier parametric models, indirectly confirming the
assumptions made in earlier work. By fitting a double gNFW profile to the lens
model, and extrapolating to the virial radius, we infer a total mass for the
cluster of M. We
estimate the uncertainty in the mass due to errors in the photometric
redshifts, and discuss the uncertainty in the inferred virial mass due to the
extrapolation from the lens model. We also find in our lens map a mass
overdensity corresponding to the large cometary tail of hot gas, reinforcing
its interpretation as a large tidal feature predicted by hydrodynamical
simulations that mimic El Gordo. Finally, we discuss the observed relation
between the plasma and the mass map, finding that the peak in the projected
mass map may be associated with a large concentration of colder gas, exhibiting
possible star formation. El Gordo is one of the first clusters that will be
observed with JWST, which is expected to unveil new high redshift lensed
galaxies around this interesting cluster, and provide a more accurate
estimation of its mass.Comment: 19 pages, 10 figures. Updated figure
- …