10,037 research outputs found
Convergence of derivative expansions of the renormalization group
We investigate the convergence of the derivative expansion of the exact
renormalization group, by using it to compute the beta function of scalar field
theory. We show that the derivative expansion of the Polchinski flow equation
converges at one loop for certain fast falling smooth cutoffs. The derivative
expansion of the Legendre flow equation trivially converges at one loop, but
also at two loops: slowly with sharp cutoff (as a momentum-scale expansion),
and rapidly in the case of a smooth exponential cutoff. Finally, we show that
the two loop contributions to certain higher derivative operators (not involved
in beta) have divergent momentum-scale expansions for sharp cutoff, but the
smooth exponential cutoff gives convergent derivative expansions for all such
operators with any number of derivatives.Comment: Latex inc axodraw. 20 page
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Turbulence and modeling in transonic flow
A review is made of the performance of a variety of turbulence models in the evaluation of a particular well documented transonic flow. This is done to supplement a previous attempt to calibrate and verify transonic airfoil codes by including many more turbulence models than used in the earlier work and applying the calculations to an experiment that did not suffer from uncertainties in angle of attack and was free of wind tunnel interference. It is found from this work, as well as in the earlier study, that the Johnson-King turbulence model is superior for transonic flows over simple aerodynamic surfaces, including moderate separation. It is also shown that some field equation models with wall function boundary conditions can be competitive with it
Broughton Archipelago Clam Terrace Survey : final report
During a 1995 aerial video survey of the coastline
of Johnstone Strait, an unusual shoreline feature
was noted and termed “clam terraces” (inset)
because of the terrace-type morphology and the
apparent association with high clam productivity
on the sandflats. Typical alongshore lengths of the
terrace ridges are 20-50m, and across-shore widths
are typically 20-40m.
An area with an especially high density of clam
terraces was noted in the Broughton Archipelago,
between Broughton and Gilford Islands of
southeastern Queen Charlotte Strait. Clam terraces
in this area were inventoried from the aerial video
imagery to quantify their distribution. The terraces accounted for over 14 km of shoreline and
365 clam terraces were documented.
A three-day field survey by a coastal geomorphologist, archeologist and marine biologist was
conducted to document the features and determine their origin. Nine clam terraces were
surveyed. The field observations confirmed that: the ridges are comprised of boulder/cobblesized
material, ridge crests are typically in the range of 1-1.5m above chart datum, sandflats are
comprised almost entirely of shell fragments (barnacles and clams) and sandflats have very high
shellfish production. There are an abundance of shell middens in the area (over 175) suggesting
that the shellfish associated with the terraces were an important food source of aboriginal
peoples.
The origin of the ridges is unknown; they appear to be a relict feature in that they are not actively
being modified by present-day processes. The ridges may be a relict sea-ice feature, although the
mechanics of ridge formation is uncertain. Sand accumulates behind the ridge because the supply
rate of the shell fragments exceeds the dispersal rate in these low energy environments.
The high density areas of clam terraces correspond to high density areas of shell middens, and it
is probable that the clam terraces were subjected to some degree of modification by aboriginal
shellfish gatherers over the thousands of years of occupation in the region. (Document contains 39 pages
Chameleon effect and the Pioneer anomaly
The possibility that the apparent anomalous acceleration of the Pioneer 10
and 11 spacecraft may be due, at least in part, to a chameleon field effect is
examined. A small spacecraft, with no thin shell, can have a more pronounced
anomalous acceleration than a large compact body, such as a planet, having a
thin shell. The chameleon effect seems to present a natural way to explain the
differences seen in deviations from pure Newtonian gravity for a spacecraft and
for a planet, and appears to be compatible with the basic features of the
Pioneer anomaly, including the appearance of a jerk term. However, estimates of
the size of the chameleon effect indicate that its contribution to the
anomalous acceleration is negligible. We conclude that any inverse-square
component in the anomalous acceleration is more likely caused by an unmodelled
reaction force from solar-radiation pressure, rather than a chameleon field
effect.Comment: 16 pages; to appear in Phys.Rev.
EXPLORING THE ABILITY TO EMPLOY VIRTUAL 3D ENTITIES OUTDOORS AT RANGES BEYOND 20 METERS
The Army is procuring the Integrated Visual Augmentation System (IVAS) system to enable enhanced night vision, planning, and training capability. One known limitation of the IVAS system is the limited ability to portray virtual entities at far ranges in the outdoors due to light wash out, accurate positioning, and dynamic occlusion. The primary goal of this research was to evaluate fixed three-dimensional (3D) visualizations to support outdoor training for fire teams through squads, requiring target visualizations for 3D non-player characters or vehicles at ranges up to 300 m. Tools employed to achieve outdoor visualizations included GPS locational data with virtual entity placement, and sensors to adjust device light levels. This study was conducted with 20 military test subjects in three scenarios at the Naval Postgraduate School using a HoloLens II. Outdoor location considerations included shadows, background clutter, cars blocking the field of view, and the sun’s positioning. Users provided feedback on identifying the type of object, and the difficulty in finding the object. The results indicate GPS only aided in identification for objects up to 100 m. Animation had a statistically insignificant effect on identification of objects. Employment of software to adjust the light levels of the virtual objects aided in identification of objects at 200 m. This research develops a clearer understanding of requirements to enable the employment of mixed reality in outdoor training.Lieutenant Colonel, United States ArmyApproved for public release. Distribution is unlimited
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