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21.
S. Gu D. G. McCartney C. N. Eastwick K. Simmons 《Journal of Thermal Spray Technology》2004,13(2):200-213
A computational fluid dynamics (CFD) model is developed to predict particle dynamic behavior in a high-velocity oxyfuel (HVOF)
thermal spray gun in which premixed oxygen and propylene are burnt in a combustion chamber linked to a long, parallel-sided
nozzle. The particle transport equations are solved in a Lagrangian manner and coupled with the two-dimensional, axisymmetric,
steady state, chemically reacting, turbulent gas flow. Within the particle transport model, the total flow of the particle
phase is modeled by tracking a small number of particles through the continuum gas flow, and each of these individual particles
is tracked independently through the continuous phase. Three different combustion chamber designs were modeled, and the in-flight
particle characteristics of Inconel were 625 studied. Results are presented to show the effect of process parameters, such
as particle injection speed and location, total gas flow rate, fuel-to-oxygen gas ratio, and particle size on the particle
dynamic behavior for a parallel-sided, 12 mm long combustion chamber. The results indicate that the momentum and heat transfer
to particles are primarily influenced by total gas flow. The 12 mm long chamber can achieve an optimum performance for Inconel
625 powder particles ranging in diameter from 20 to 40 μm. At a particular spraying distance, an optimal size of particles
is observed with respect to particle temperature. The effect of different combustion chamber dimensions on particle dynamics
was also investigated. The results obtained for both a 22 mm long chamber and also one with a conical, converging design are
compared with the baseline data for the 12 mm chamber. 相似文献
22.
Cheryl M. M. Carey Gene H. Golub Kincho H. Law 《International journal for numerical methods in engineering》1994,37(16):2857-2883
In this paper, a new solution method for the modified eigenvalue problem with specific application to structural dynamic reanalysis is presented. The method, which is based on the block Lanczos algorithm, is developed for multiple low rank modifications to a system and calculates a few selected eigenpairs. Given the solution to the original system Ax = λx, procedures are developed for the modified standard eigenvalue Problem (A + ΔA)x? = λ x?, where
- 1 ΔA = ΣjBSjBT, where Sj = S ∈ ?p × p, p ? n and B ∈ ?n × p is constant for all the perturbations Sj.
- 2 ΔA = ΣiΣj BiSjBiT, where Bi ∈ ?n × p may vary with the pertubations Sj.
23.
ED Simmons TG Burke T Haley J Medige 《Canadian Metallurgical Quarterly》1996,21(3):295-8; discussion 299
STUDY DESIGN: This study evaluates and compares the stiffness of two cervical spine fixation techniques. OBJECTIVES: This biomechanical study was carried out to compare the interspinous and Dewar cervical spine fixation techniques. SUMMARY OF BACKGROUND DATA: Interspinous wiring is a commonly used method of fixation in the cervical spine. The Dewar technique is less commonly known and practiced, and clinical experience has suggested that it may be a more stable technique. METHODS: Cervical spine specimens stabilized with the interspinous and "Dewar" techniques were biomechanically tested in flexion and in torsion. Stiffness and energy absorption under moderate loads were compared. The Dewar technique uses contoured double corticocancellous iliac grafts as internal grafts/splints fixed to the spine with threaded pins and wire. The interspinous technique is a single interspinous wire loop. Eleven fresh human cervical spines were harvested from cadavers. The spines were destabilized at C4-C5 by sectioning all tissue except the anterior longitudinal ligament. Each fixation technique was applied alternatively and tested on each spine. RESULTS: In torsion testing (n = 5), the Dewar fusion was 61% stiffer than the interspinous technique (P < 0.02). Dewar: 11.3 N/mm (s.d. 4.9 N/mm) and interspinous: 8.4 N/mm (SD 3.3 N/mm). In flexion testing (n = 6), the Dewar technique was 35% stiffer than the interspinous technique (P < 0.10). Dewar: 655.4 Nmm/degree (SD 293 Nmm/degree) and interspinous: 406.8 Nmm/degree (SD 113.0 Nmm/degree). Energy absorption with the interspinous technique was greater in flexion (P < 0.10) and in torsion (P < 0.005), indicating more deformation with the interspinous technique. There was no statistically significant difference between the means of specimens tested first and those tested second independently of the fixation technique. CONCLUSIONS: These tests indicate that the Dewar cervical spine fixation is stiffer than the single interspinous wire in both flexion and particularly torsion. This project is the only biomechanical study of the Dewar technique that we are aware of, and the results support the clinical findings regarding the effectiveness of this technique. 相似文献
24.
Smith N Sankin GN Simmons WN Nanke R Fehre J Zhong P 《The Review of scientific instruments》2012,83(1):014301
The performance of a newly developed light spot hydrophone (LSHD) in lithotripter field characterization was compared to that of the fiber optic probe hydrophone (FOPH). Pressure waveforms produced by a stable electromagnetic shock wave source were measured by the LSHD and FOPH under identical experimental conditions. In the low energy regime, focus and field acoustic parameters matched well between the two hydrophones. At clinically relevant high energy settings for shock wave lithotripsy, the measured leading compressive pressure waveforms matched closely with each other. However, the LSHD recorded slightly larger |P_| (p < 0.05) and secondary peak compressive pressures (p < 0.01) than the FOPH, leading to about 20% increase in total acoustic pulse energy calculated in a 6 mm radius around the focus (p = 0.06). Tensile pulse durations deviated ~5% (p < 0.01) due to tensile wave shortening from cavitation activity using the LSHD. Intermittent compression spikes and laser light reflection artifacts have been correlated to bubble activity based on simultaneous high-speed imaging analysis. Altogether, both hydrophones are adequate for lithotripter field characterization as specified by the international standard IEC 61846. 相似文献
25.
J. F. Holzrichter D. Eimerl E. V. George J. B. Trenholme W. W. Simmons J. T. Hunt 《Journal of Fusion Energy》1982,2(1):5-45
Pulsed high power lasers can deliver sufficient energy on inertial fusion time scales (0.1–10 ns) to heat and compress DT fuel to fusion reaction conditions. Several laser systems have been examined for application to the fusion problem. Examples are Ndglass, CO2, KrF, and I2, etc. A great deal of developmental effort has been applied to the Ndglass laser and the CO2 gas laser systems. These systems now deliver >104 kJ and >20×1012 W to inertial fusion targets. The Nova Ndglass laser is being constructed to provide >200 kJ and >200×1012 W of 1 m radiation for fusion experimentation in the mid-1980s. For inertial fusion target gain, >100 times the laser input, it is expected that the laser must deliver 3–5 MJ of energy on the 10–20 ns time scale. This paper reviews the developments in laser technology and outlines approaches to construction of a 3–5 MJ driver. 相似文献
26.
Jeffrey T RichardsAndrew C Schuerger Gene CapelleJames A Guikema 《Remote sensing of environment》2003,84(3):323-341
Fluorescence spectral characteristics associated with growth under different irradiance levels, and during rapidly changing lighting conditions, were measured on healthy bean (Phaseolus vulgaris L.) and wheat (Triticum aestivum L.) plants using a laser-induced fluorescence spectroscopy (LIFS) system. The LIFS system was designed as a prototype of a handheld field remote sensing system and used a tripled Nd:YAG laser to produce ultraviolet (UV) excitation photons at 355 nm. Dark-adapted canopies of the bean and wheat plants grown under 150, 300, or 450 μmol m−2 s−1 of photosynthetically active radiation (PAR) exhibited LIFS spectra with higher relative fluorescence intensities than emissions from light-adapted plants at all three light levels. Blue/red and blue/far-red leaf fluorescence ratios for both bean and wheat plants increased dramatically as PAR increased, but red/far-red ratios decreased as PAR increased. Light-adapted plants grown under the three light levels were then subjected to several rapidly changing lighting conditions. Plants were exposed sequentially to 150, 300, and 650 μmol m−2 s−1 PAR from metal halide lamps, followed by a fourth light treatment of 650 μmol m−2 s−1 PAR from a mixture of metal halide and tungsten-halogen lamps. The tungsten-halogen lamps added significant amounts of near-infrared (NIR) irradiation to the background light environment provided by the metal halide lamps. Results indicated that both bean and wheat canopies generally exhibited stable blue, green, red, and far-red fluorescence emissions when plants were exposed to 150, 300, and 650 μmol m−2 s−1 PAR from the metal halide lamps. In contrast, when bean and wheat plants were exposed to the NIR-enriched light supplied by the tungsten-halogen lamps, blue and green fluorescence remained stable, but red and far-red fluorescence increased dramatically immediately after exposure to the NIR photons. However, the increased levels of red and far-red fluorescence observed after exposure to NIR light decreased quickly (within 55 s) and returned to “baseline” levels observed at the start of the rapidly changing light experiments. Results indicate that handheld LIFS instruments can be used for remote sensing of plant canopies under a diversity of lighting conditions including full darkness, dawn and dusk lighting environments, and under rapidly changing light environments similar to those encountered on partly cloudy days. 相似文献
27.
Wenjun Liu Gene E. Ice Bennett C. Larson Wenge Yang Jonathan Z. Tischler J. D. Budai 《Metallurgical and Materials Transactions A》2004,35(7):1963-1967
The three-dimensional (3-D) X-ray crystal microscope is a new nondestructive tool for the 3-D characterization of the mesoscopic
and nanoscopic materials structure. A prototype microscope is installed on beamline 34-ID at the advanced photon source and
has begun initial operation. The prototype microscope has a routine spatial resolution of approximately 0.5 × 0.5 × 1 μm3 and can probe tens to hundreds of microns below a sample surface, depending on the composition of the sample. For each volume
element measured, the microscope can determine between 10 and 16 parameters. The measured parameters are the local crystallographic
phase (1 deg of freedom), the Eulerian angles of crystal orientation (3 deg of freedom), and the plastic and/or elastic strain-tensor
elements (6 to 12 deg of freedom). The time required to collect each volume element varies between 1 and 14 seconds, depending
on the precision of the parameters and the sample complexity. Much faster data acquisition and much better spatial resolution
are certain in the near future. Some initial results are presented to illustrate how the 3-D X-ray crystal microscope can
provide unprecedented information about the 3-D structure of materials.
This article is based on a presentation made at the symposium “Characterization and Representation of Material Microstructures
in 3-D” held October 8–10, 2002, in Columbus, OH, under the auspices of ASM International’s Phase Transformations committee. 相似文献
28.
David Kortenkamp Reid Simmons Tod Milam Joaquín L. Fernández 《Formal Methods in System Design》2004,24(2):157-188
This paper describes a set of tools that enables developers to log and analyze the run-time behavior of distributed control systems. A feature of the tools is that they can be applied to distributed systems. The logging tools enable developers to instrument C or C++ programs so that data indicating state changes can be logged automatically in a variety of formats. In particular, run-time data from distributed systems can be synchronized into a single relational database. Tools are also provided for visualizing the logged data. Analysis to verify correct program behavior is done using a new interval logic that is described in this paper. The logic enables system engineers to express temporal specifications for the autonomous control program that are then checked against the logged data. The data logging, visualization, and interval logic analysis tools are all fully implemented. Results are given from a NASA distributed autonomous control system application. 相似文献
29.
Gene Placzkowski 《技术计量学》2013,55(3):288-289
30.