2,572 research outputs found
Investigation of polymeric coatings by electrodeless discharge Final report
Polymeric films deposited by electrical discharge from hydrocarbon
Second constant of motion for two-dimensional positronium in a magnetic field
Recent numerical work indicates that the classical motion of positronium in a
constant magnetic field does not exhibit chaotic behavior if the system is
confined to two dimensions. One would therefore expect this system to possess a
second constant of the motion in addition to the total energy. In this paper we
construct a generalization of the Laplace-Runge-Lenz vector and show that a
component of this vector is a constant of the motion.Comment: 4 pages, no figure
Analytic perturbation theory in QCD and Schwinger's connection between the beta-function and the spectral density
We argue that a technique called analytic perturbation theory leads to a
well-defined method for analytically continuing the running coupling constant
from the spacelike to the timelike region, which allows us to give a
self-consistent definition of the running coupling constant for timelike
momentum. The corresponding -function is proportional to the spectral
density, which confirms a hypothesis due to Schwinger.Comment: 11 pages, 2 figure
Computer recommendations for an automatic approach and landing system for V/STOL aircraft. Volume 2 - Equations
Automatic approach and landing system for V/STOL aircraf
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Development and testing of an active boring bar for increased chatter immunity
Recent advances in smart materials have renewed interest in the development of improved manufacturing processes featuring sensing, processing, and active control. In particular, vibration suppression in metal cutting has received much attention because of its potential for enhancing part quality while reducing the time and cost of production. Although active tool clamps have been recently demonstrated, they are often accompanied by interfacing issues that limit their applicability to specific machines. Under the auspices of the Laboratory Directed Research and Development program, the project titled {open_quotes}Smart Cutting Tools for Precision Manufacturing{close_quotes} developed an alternative approach to active vibration control in machining. Using the boring process as a vehicle for exploration, a commercially available tool was modified to incorporate PZT stack actuators for active suppression of its bending modes. Since the modified tool requires no specialized mounting hardware, it can be readily mounted on many machines. Cutting tests conducted on a horizontal lathe fitted with a hardened steel workpiece verify that the actively damped boring bar yields significant vibration reduction and improved surface finishes as compared to an unmodified tool
Two-Loop Calculations with Vertex Corrections in the Walecka Model
Two-loop corrections with scalar and vector form factors are calculated for
nuclear matter in the Walecka model. The on-shell form factors are derived from
vertex corrections within the framework of the model and are highly damped at
large spacelike momenta. The two-loop corrections are evaluated first by using
the one-loop parameters and mean fields and then by refitting the total
energy/baryon to empirical nuclear matter saturation properties. The modified
two-loop corrections are significantly smaller than those computed with bare
vertices. Contributions from the anomalous isoscalar form factor of the nucleon
are included for the first time. The effects of the implicit density dependence
of the form factors, which arise from the shift in the baryon mass, are also
considered. Finally, necessary extensions of these calculations are discussed.Comment: 29 pages in REVTeX, 18 figures, preprint IU/NTC 94-02 //OSU--94-11
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Repeatability and comparison of clinical techniques for anterior chamber angle assessment
Purpose
To assess the repeatability of gonioscopy, van Herick method and anterior segment Optical Coherence Tomography (AS-OCT) and determine the agreement between these techniques within a community optometry setting.
Methods
Gonioscopy, van Herick method and AS-OCT imaging were performed by an optometrist on two occasions, 1 month apart, on 80 subjects aged over 40 years recruited from community optometry practices. Anterior segment images were captured with a spectral domain OCT (Topcon 3D OCT-2000; wavelength 840 nm) set to the Anterior Segment (AS) mode. Eyes were graded as open or occludable for each method. AS-OCT images from both visits were graded by a second optometrist masked to the gonioscopy and van Herick method results, and the visit on which the images were acquired. Cohen's kappa (Îş) was used to describe the intra-observer repeatability. Likelihood ratios, sensitivity and specificity of van Herick method and AS-OCT were calculated, using gonioscopy as the reference standard.
Results
Measurements were obtained from 80 eyes of 80 subjects. In four cases, AS-OCT images were un-gradable due to difficulty in locating the scleral spur. The repeatability of gonioscopy was fair Îş = 0.29, while that of the van Herick method (Îş = 0.54) and AS-OCT (Îş = 0.47) were somewhat better. The van Herick method showed good sensitivity (visit 1: 75%, visit 2: 69%) and high specificity (visit 1: 88%, visit 2: 96%). The sensitivity of AS-OCT was fair (visit 1: 46%, visit 2: 25%), but specificity was high (visit 1: 87%. visit 2: 89%).
Conclusion
Intra-observer repeatability was better for van Herick method and for AS-OCT than for gonioscopy, despite the latter being considered the gold standard method. The van Herick method appeared to be more sensitive than AS-OCT when identifying eyes at risk of angle closure. A standalone anterior segment OCT with a longer wavelength laser could afford better visualisation of the angle, and might therefore be expected to enable the examiner to make more precise classifications. These instruments are not widely used by optometrists in clinical practice in the UK at present
The role of endotoxin/lipopolysaccharide in surgically induced tumour growth in a murine model of metastatic disease
Surgical removal of a primary tumour is often followed by rapid growth of previously dormant metastases. Endotoxin or lipopolysaccharide, a cell wall constituent of Gram-negative bacteria, is ubiquitously present in air and may be introduced during surgery. BALB/c mice received a tail vein injection of 105 4T1 mouse mammary carcinoma cells. Two weeks later, animals were subjected to surgical trauma or an intraperitoneal injection of endotoxin (10 μg per animal). Five days later, animals which underwent open surgery, laparoscopy with air sufflation or received an endotoxin injection displayed increased lung metastasis compared to anaesthetic controls. These increases in metastatic tumour growth were reflected in increased tumour cell proliferation and decreased apoptosis within lung metastases. Circulating levels of the angiogenic cytokine, vascular endothelial growth factor (VEGF), were also elevated in these groups and correlated with increased plasma levels of endotoxin. Endotoxin treatment for 18 h (>10 ng ml–1) directly up-regulated VEGF production by the 4T1 tumour cells in vitro. Metastatic tumour growth in mice undergoing carbon dioxide laparoscopy, where air is excluded, was similar to anaesthetic controls. These data indicate that endotoxin introduced during surgery is associated with the enhanced growth of metastases following surgical trauma, by altering the critical balances governing cellular growth and angiogenesis. © 1999 Cancer Research Campaig
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Development and testing of an active platen for IC manufacturing
The conflicting demands for finer features and increased production rates in integrated circuit manufacturing have emphasized the need for improved wafer positioning technology. In this paper we present operational test results from a magnetically levitated platen with structurally integrated piezoelectric acctuators. The strain based actuators provide active damping of the platen`s flexible body modes, enabling increased bandwidth on the mag-lev positioning system. Test results reveal a dramatic reduction in steady state positioning error and settling time through implementation of active vibration control
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