7,992 research outputs found
Applications of high power lasers
The use of computer generated, reflection holograms in conjunction with high power lasers for precision machining of metals and ceramics was investigated. The Reflection holograms which were developed and made to work at both optical wavelength (He-Ne, 6328 A) and infrared (CO2, 10.6) meet the primary practical requirement of ruggedness and are relatively economical and simple to fabricate. The technology is sufficiently advanced now so that reflection holography could indeed be used as a practical manufacturing device in certain applications requiring low power densities. However, the present holograms are energy inefficient and much of the laser power is lost in the zero order spot and higher diffraction orders. Improvements of laser machining over conventional methods are discussed and addition applications are listed. Possible uses in the electronics industry include drilling holes in printed circuit boards making soldered connections, and resistor trimming
The Food Plants and Distribution of the American Plum Borer (Lepidoptera: Pyralidae)
The North American geographical and host plant distributions for the American plnm borer, Euzophera semifuneralis, are reported. Literature and curatorial surveys found the plum borer to be present in 34 states in the U. S. as well as parts of Canada, Mexico, and South America. Pheromone surveys and direct observation found it to be present in high numbers in most cherry and plum orchards in Michigan and in 28 counties of the lower peninsula. A very wide host range representing 15 plant families was found, with most host species in the Rosaceae
Pattern Matching Analysis of Electron Backscatter Diffraction Patterns for Pattern Centre, Crystal Orientation and Absolute Elastic Strain Determination: Accuracy and Precision Assessment
Pattern matching between target electron backscatter patterns (EBSPs) and
dynamically simulated EBSPs was used to determine the pattern centre (PC) and
crystal orientation, using a global optimisation algorithm. Systematic analysis
of error and precision with this approach was carried out using dynamically
simulated target EBSPs with known PC positions and orientations. Results showed
that the error in determining the PC and orientation was < 10 of pattern
width and < 0.01{\deg} respectively for the undistorted full resolution images
(956x956 pixels). The introduction of noise, optical distortion and image
binning was shown to have some influence on the error although better angular
resolution was achieved with the pattern matching than using conventional Hough
transform-based analysis. The accuracy of PC determination for the experimental
case was explored using the High Resolution (HR-) EBSD method but using
dynamically simulated EBSP as the reference pattern. This was demonstrated
through a sample rotation experiment and strain analysis around an indent in
interstitial free steel
Direct detection of electron backscatter diffraction patterns.
We report the first use of direct detection for recording electron backscatter diffraction patterns. We demonstrate the following advantages of direct detection: the resolution in the patterns is such that higher order features are visible; patterns can be recorded at beam energies below those at which conventional detectors usefully operate; high precision in cross-correlation based pattern shift measurements needed for high resolution electron backscatter diffraction strain mapping can be obtained. We also show that the physics underlying direct detection is sufficiently well understood at low primary electron energies such that simulated patterns can be generated to verify our experimental data
Effects of introduced trout predation on non-diadromous galaxiid fish populations across invaded riverscapes
Abstract
We assessed the landscape-scale effect of predation pressure from trout on the population integrity and distributions of non-diadromous galaxiids in high-country streams of the South Island, New Zealand. The effects of trout (brown trout, Salmo trutta, and rainbow trout, Oncorhynchus mykiss) on two widespread species, the Canterbury galaxias (Galaxias vulgaris Stokell) and the alpine galaxias (G. paucispondylus Stokell) were assessed. Experiments confirmed that both species were vulnerable to trout predation and that habitat (size and disturbance regime) may be a factor in local co-occurrence. Quantitative electrofishing surveys indicated that G. paucispondylus distributions were less affected by trout than G. vulgaris distributions and that the species’ range was limited by temperature. Trout created demographic sinks for G. vulgaris across most invaded reaches, while refuge populations in streams above barriers to trout acted as demographic sources for this species. G. vulgaris was consistently absent from small, stable stream reaches far from sources, indicating that trout predation pressure and propagule pressure (driven by immigration from sources) interact to drive local G. vulgaris persistence in trout-invaded reaches. Predation pressure is likely to be highest in areas where infrequent flooding allows high densities of large trout (> 150 mm FL) to occur and where there are few refugia for galaxiids. A spatial model was developed to predict exclusion of galaxiids by trout across invaded networks. If used appropriately, the model could be used to find new refuge populations of non-diadromous galaxiids and to aid planning of active rehabilitation of trout-invaded river networks
Dual ion beam deposition of carbon films with diamondlike properties
A single and dual ion beam system was used to generate amorphous carbon films with diamond like properties. A methane/argon mixture at a molar ratio of 0.28 was ionized in the low pressure discharge chamber of a 30-cm-diameter ion source. A second ion source, 8 cm in diameter was used to direct a beam of 600 eV Argon ions on the substrates (fused silica or silicon) while the deposition from the 30-cm ion source was taking place. Nuclear reaction and combustion analysis indicate H/C ratios for the films to be 1.00. This high value of H/C, it is felt, allowed the films to have good transmittance. The films were impervious to reagents which dissolve graphitic and polymeric carbon structures. Although the measured density of the films was approximately 1.8 gm/cu cm, a value lower than diamond, the films exhibited other properties that were relatively close to diamond. These films were compared with diamondlike films generated by sputtering a graphite target
Turbulent transport measurements with a laser Doppler velocimeter
The power spectrum of phototube current from a laser Doppler velocimeter operating in the heterodyne mode has been computed. The spectrum is obtained in terms of the space time correlation function of the fluid. The spectral width and shape predicted by the theory are in agreement with experiment. For normal operating parameters the time average spectrum contains information only for times shorter than the Lagrangian integral time scale of the turbulence. To examine the long time behavior, one must use either extremely small scattering angles, much longer wavelength radiation or a different mode of signal analysis, e.g., FM detection
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