585 research outputs found
Development of systems and techniques for landing an aircraft using onboard television
A flight program was conducted to develop a landing technique with which a pilot could consistently and safely land a remotely piloted research vehicle (RPRV) without outside visual reference except through television. Otherwise, instrumentation was standard. Such factors as the selection of video parameters, the pilot's understanding of the television presentation, the pilot's ground cockpit environment, and the operational procedures for landing were considered. About 30 landings were necessary for a pilot to become sufficiently familiar and competent with the test aircraft to make powered approaches and landings with outside visual references only through television. When steep approaches and landings were made by remote control, the pilot's workload was extremely high. The test aircraft was used as a simulator for the F-15 RPRV, and as such was considered to be essential to the success of landing the F-15 RPRV
Ab Initio Study of Hybrid b-bar-gb Mesons
Hybrid b-bar-gb molecules in which the heavy b-bar-b pair is bound together
by the excited gluon field g are studied using the Born-Oppenheimer expansion
and numerical simulations. The consistency of results from the two approaches
reveals a simple and compelling physical picture for heavy hybrid states.Comment: 4 pages, 3 figures, uses REVTeX and epsf, final published versio
Unquenched Charmonium with NRQCD - Lattice 2000
We present results from a series of NRQCD simulations of the charmonium
system, both in the quenched approximation and with n_f = 2 dynamical quarks.
The spectra show evidence for quenching effects of ~10% in the S- and
P-hyperfine splittings. We compare this with other systematic effects.
Improving the NRQCD evolution equation altered the S-hyperfine by as much as 20
MeV, and we estimate radiative corrections may be as large as 40%.Comment: Lattice 2000 (Heavy Quark Physics
Charmonium Spectrum from Quenched Anisotropic Lattice QCD
We present a detailed study of the charmonium spectrum using anisotropic
lattice QCD. We first derive a tree-level improved clover quark action on the
anisotropic lattice for arbitrary quark mass. The heavy quark mass dependences
of the improvement coefficients, i.e. the ratio of the hopping parameters
and the clover coefficients , are examined at the tree
level. We then compute the charmonium spectrum in the quenched approximation
employing anisotropic lattices. Simulations are made with
the standard anisotropic gauge action and the anisotropic clover quark action
at four lattice spacings in the range =0.07-0.2 fm. The clover
coefficients are estimated from tree-level tadpole improvement. On
the other hand, for the ratio of the hopping parameters , we adopt both
the tree-level tadpole-improved value and a non-perturbative one. We calculate
the spectrum of S- and P-states and their excitations. The results largely
depend on the scale input even in the continuum limit, showing a quenching
effect. When the lattice spacing is determined from the splitting, the
deviation from the experimental value is estimated to be 30% for the
S-state hyperfine splitting and 20% for the P-state fine structure. Our
results are consistent with previous results at obtained by Chen when
the lattice spacing is determined from the Sommer scale . We also address
the problem with the hyperfine splitting that different choices of the clover
coefficients lead to disagreeing results in the continuum limit.Comment: 43 pages, 49 eps figures, revtex; minor changes, version to appear in
Physical Review
Genome Biol.
With genome analysis expanding from the study of genes to the study of gene regulation, 'regulatory genomics' utilizes sequence information, evolution and functional genomics measurements to unravel how regulatory information is encoded in the genome
O(a)-improved quark action on anisotropic lattices and perturbative renormalization of heavy-light currents
We investigate the Symanzik improvement of the Wilson quark action on
anisotropic lattices. Taking first a general action with nearest-neighbor and
clover interactions, we study the mass dependence of the ratio of the hopping
parameters, the clover coefficients, and an improvement coefficient for
heavy-light vector and axial vector currents. We show how tree-level
improvement can be achieved. For a particular choice of the spatial Wilson
coupling, the results simplify, and improvement is possible.
(Here is the bare quark mass and the temporal lattice spacing.)
With this choice we calculate the renormalization factors of heavy-light
bilinear operators at one-loop order of perturbation theory employing the
standard plaquette gauge action.Comment: 26 pages, 8 figure
Morphological evolution of electrochemically plated stripped lithium microstructures by synchrotron X ray phase contrast tomography
Due to its low redox potential and high theoretical specific capacity, Li metal has drawn worldwide research attention because of its potential use in next generation battery technologies such as Li S and Li O2. Unfortunately, uncontrollable growth of Li microstructures LmSs, e.g., dendrites, fibers during electrochemical Li stripping plating has prevented their practical commercialization. Despite various strategies proposed to mitigate LmS nucleation and or block its growth, a fundamental understanding of the underlying evolution mechanisms remains elusive. Herein, synchrotron in line phase contrast X ray tomography was employed to investigate the morphological evolution of electrochemically deposited dissolved LmSs nondestructively. We present a 3D characterization of electrochemically stripped Li electrodes with regard to electrochemically plated LmSs. We clarify fundamentally the origin of the porous lithium interface growing into Li electrodes. Moreover, cleavage of the separator caused by growing LmS was experimentally observed and visualized in 3D. Our systematic investigation provides fundamental insights into LmS evolution and enables us to understand the evolution mechanisms in Li electrodes more profoundl
On dynamic network entropy in cancer
The cellular phenotype is described by a complex network of molecular
interactions. Elucidating network properties that distinguish disease from the
healthy cellular state is therefore of critical importance for gaining
systems-level insights into disease mechanisms and ultimately for developing
improved therapies. By integrating gene expression data with a protein
interaction network to induce a stochastic dynamics on the network, we here
demonstrate that cancer cells are characterised by an increase in the dynamic
network entropy, compared to cells of normal physiology. Using a fundamental
relation between the macroscopic resilience of a dynamical system and the
uncertainty (entropy) in the underlying microscopic processes, we argue that
cancer cells will be more robust to random gene perturbations. In addition, we
formally demonstrate that gene expression differences between normal and cancer
tissue are anticorrelated with local dynamic entropy changes, thus providing a
systemic link between gene expression changes at the nodes and their local
network dynamics. In particular, we also find that genes which drive
cell-proliferation in cancer cells and which often encode oncogenes are
associated with reductions in the dynamic network entropy. In summary, our
results support the view that the observed increased robustness of cancer cells
to perturbation and therapy may be due to an increase in the dynamic network
entropy that allows cells to adapt to the new cellular stresses. Conversely,
genes that exhibit local flux entropy decreases in cancer may render cancer
cells more susceptible to targeted intervention and may therefore represent
promising drug targets.Comment: 10 pages, 3 figures, 4 tables. Submitte
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