1,771 research outputs found
Discretization of the Superparticle Path Integral
Requiring that the path integral has the global symmetries of the classical
action and obeys the natural composition property of path integrals, and also
that the discretized action has the correct naive continuum limit, we find a
viable discretization of the (D=3,N=2) superparticle action.Comment: 10 page
Conceptual design study of advanced acoustic-composite nacelles
Conceptual studies were conducted to assess the impact of incorporating advanced technologies in the nacelles of a current wide-bodied transport and an advanced technology transport. The improvement possible in the areas of fuel consumption, flyover noise levels, airplane weight, manufacturing costs, and airplane operating cost were evaluated for short and long-duct nacelles. Use of composite structures for acoustic duct linings in the fan inlet and exhaust ducts was considered as well as for other nacelle components. For the wide-bodied transport, the use of a long-duct nacelle with an internal mixer nozzle in the primary exhaust showed significant improvement in installed specific fuel consumption and airplane direct operating costs compared to the current short-duct nacelle. The long-duct mixed-flow nacelle is expected to achieve significant reductions in jet noise during takeoff and in turbo-machinery noise during landing approach. Recommendations were made of the technology development needed to achieve the potential fuel conservation and noise reduction benefits
Quantifying stretching and rearrangement in epithelial sheet migration
Although understanding the collective migration of cells, such as that seen
in epithelial sheets, is essential for understanding diseases such as
metastatic cancer, this motion is not yet as well characterized as individual
cell migration. Here we adapt quantitative metrics used to characterize the
flow and deformation of soft matter to contrast different types of motion
within a migrating sheet of cells. Using a Finite-Time Lyapunov Exponent (FTLE)
analysis, we find that - in spite of large fluctuations - the flow field of an
epithelial cell sheet is not chaotic. Stretching of a sheet of cells (i.e.,
positive FTLE) is localized at the leading edge of migration. By decomposing
the motion of the cells into affine and non-affine components using the metric
D, we quantify local plastic rearrangements and describe the motion
of a group of cells in a novel way. We find an increase in plastic
rearrangements with increasing cell densities, whereas inanimate systems tend
to exhibit less non-affine rearrangements with increasing density.Comment: 21 pages, 7 figures This is an author-created, un-copyedited version
of an article accepted for publication in the New Journal of Physics. IOP
Publishing Ltd is not responsible for any errors or omissions in this version
of the manuscript or any version derived from it. The Version of Record is
available online at doi:10.1088/1367-2630/15/2/02503
Revisiting and Extending Interface Penalties for Multi-Domain Summation-by-Parts Operators
General interface coupling conditions are presented for multi-domain collocation methods, which satisfy the summation-by-parts (SBP) spatial discretization convention. The combined interior/interface operators are proven to be L2 stable, pointwise stable, and conservative, while maintaining the underlying accuracy of the interior SBP operator. The new interface conditions resemble (and were motivated by) those used in the discontinuous Galerkin finite element community, and maintain many of the same properties. Extensive validation studies are presented using two classes of high-order SBP operators: 1) central finite difference, and 2) Legendre spectral collocation
Effect of Al mole fraction on carrier diffusion lengths and lifetimes in AlxGa1−xAs
The ambipolar diffusion length and carrier lifetime are measured in AlxGa1−xAs for several mole fractions in the interval 0<x<0.38. These parameters are found to have significantly higher values in the higher mole fraction samples. These increases are attributed to occupation of states in the indirect valleys, and supporting calculations are presented
Dynamical Compactification and Inflation in Einstein-Yang-Mills Theory with Higher Derivative Coupling
We study cosmology of the Einstein-Yang-Mills theory in ten dimensions with a
quartic term in the Yang-Mills field strength. We obtain analytically a class
of cosmological solutions in which the extra dimensions are static and the
scale factor of the four-dimensional Friedmann-Lemaitre-Robertson-Walker metric
is an exponential function of time. This means that the model can explain
inflation. Then we look for solutions that describe dynamical compactification
of the extra dimensions. The effective cosmological constant in the
four-dimensional universe is determined from the gravitational coupling,
ten-dimensional cosmological constant, gauge coupling and higher derivative
coupling. By numerical integration, the solution with is found to
behave as a matter-dominated universe which asymptotically approaches flat
space-time, while the solution with a non-vanishing approaches de
Sitter space-time in the asymptotic future.Comment: 30 pages, 7 figure
The Ultrasonic/Shear-Force Microscope: Integrating Ultrasonic Sensing into a Near-Field Scanning Optical Microscope
An ultrasonic transducer is incorporated into a near-field scanning optical microscope (NSOM) to augment its versatility to characterize the properties of layers adsorbed to a sample\u27s surface. Working under typical NSOM operation conditions, the ultrasonic transducer--attached underneath the sample--demonstrates sufficient sensitivity to monitor the waves generated by the tapered NSOM probe that oscillates in the proximity of, and parallel to, the sample\u27s top surface. This capability makes the newly integrated ultrasonic/shear-force microscope a valuable diagnostic tool in the study of sliding friction and surface phenomena in general. Here, it is used to concurrently and independently monitor the effects that probe-sample interactions exert on the probe (that is attached to a piezoelectric tuning fork) and on the sample (that is attached to the ultrasonic transducer). The signal from the tuning fork (TF) constitutes the so called shear-force signal, widely used in NSOM as a feedback to control the probe\u27s vertical position but whose working mechanism is not yet well understood. Tests involving repeated vertical z motion of the probe towards and away from the sample\u27s surface reveal that the TF and ultrasonic (US) signals have distinct z dependence. Additionally, where the TF signal showed abrupt changes during the approach, the US changed accordingly. A shift in the probe\u27s resonance frequency that depends on the probe-sample distance is also observed through both the TF and the US responses. Within the sensitivity of the apparatus, ultrasonic signals were detected only at probe-sample distances where the probe\u27s resonance frequency had shifted significantly. These measured signals are consistent with a probe entering and leaving a viscoelastic fluid-like film above the sample. The film acts as the medium where waves are generated and coupled to the ultrasonic sensor located beneath the sample. To our knowledge, this is the first reported use of ultrasonic detection for detailed monitoring of the distance dependence of probe-sample interactions, and provides direct evidence of sound as an energy dissipation channel in wear-free friction. This newly integrated ultrasonic/shear-force microscope, which can be implemented with any functionalized proximal probe (including aperture and apertureless NSOM), can become a valuable metrology tool in surface science and technology
The spectrum of N2O between 800 and 5200 cm(-1)
An atlas of N2O lines between 800 and 5200/cm obtained from low-pressure, long-path-length samples at 296K is presented. Many of the line centers were marked and their positions were tabulated. The peak absorptances of the weaker lines in the atlas are similar to those expected in an extreme path through the atmosphere
Quasienergy Spectroscopy of Excitons
We theoretically study nonlinear optics of excitons under intense THz
irradiation. In particular, the linear near infrared absorption and resonantly
enhanced nonlinear sideband generation are described. We predict a rich
structure in the spectra which can be interpreted in terms of the quasienergy
spectrum of the exciton, via a remarkably transparent expression for the
susceptibility, and show that the effects of strongly avoided quasienergy
crossings manifest themselves directly, both in the absorption and transmitted
sidebands.Comment: 4 pages RevTex, 3 eps figs included, as publishe
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