23,140 research outputs found
A Three-Dimensional Solution of Flows over Wings with Leading-Edge Vortex Separation. Part 2: Program Description Document
For abstract, see N75-32026
Diagrammatic perturbation theory and the pseudogap
We study a model of quasiparticles on a two-dimensional square lattice
coupled to Gaussian distributed dynamical fields. The model describes
quasiparticles coupled to spin or charge fluctuations and is solved by a Monte
Carlo sampling of the molecular field distributions. The non-perturbative
solution is compared to various approximations based on diagrammatic
perturbation theory. When the molecular field correlations are sufficiently
weak, the diagrammatic calculations capture the qualitative aspects of the
quasiparticle spectrum. For a range of model parameters near the magnetic
boundary, we find that the quasiparticle spectrum is qualitatively different
from that of a Fermi liquid in that it shows a double peak structure, and that
the diagrammatic approximations we consider fail to reproduce, even
qualitatively, the results of the Monte Carlo calculations. This suggests that
the pseudogap induced by a coupling to antiferromagnetic fluctuations and the
spin-splitting of the quasiparticle peak induced by a coupling to ferromagnetic
spin-fluctuations lie beyond diagrammatic perturbation theory
Time-dependent gravitating solitons in five dimensional warped space-times
Time-dependent soliton solutions are explicitly derived in a five-dimensional
theory endowed with one (warped) extra-dimension. Some of the obtained
geometries, everywhere well defined and technically regular, smoothly
interpolate between two five-dimensional anti-de Sitter space-times for fixed
value of the conformal time coordinate. Time dependent solutions containing
both topological and non-topological sectors are also obtained. Supplementary
degrees of freedom can be also included and, in this case, the resulting
multi-soliton solutions may describe time-dependent kink-antikink systems.Comment: 19 pages, 10 figure
Impact of China's Accession to the WTO on U.S. Agricultural Exports
China's accession to the WTO has been welcomed by a broad range of U.S. agricultural interests. The WTO agreement will lower tariffs and other barriers, and increase market access, but the actual benefits to U.S. exporters will depend on the competitiveness of U.S. exports with those of other countries and on China's implementation of WTO rules. Analysis by the U.S. Department of Agriculture indicates immediate gains in export sales for U.S. agriculture, gains that will increase over time as market access expands and as Chinese economic growth boosts demand for imported agricultural products. However, some observers express less optimism, indicating that while U.S. exports to China should expand "in theory," in practice exporters will face several hurdles which must be overcome in order to reach the full potential of the Chinese market. This paper adds to USDA and other analyses of China's export potential by discussing the status of China's WTO implementation for agriculture, and provides a qualitative assessment of the potential for U.S. agricultural exports to China over the next few years.International Relations/Trade,
Universal Properties of Two-Dimensional Boson Droplets
We consider a system of N nonrelativistic bosons in two dimensions,
interacting weakly via a short-range attractive potential. We show that for N
large, but below some critical value, the properties of the N-boson bound state
are universal. In particular, the ratio of the binding energies of (N+1)- and
N-boson systems, B_{N+1}/B_N, approaches a finite limit, approximately 8.567,
at large N. We also confirm previous results that the three-body system has
exactly two bound states. We find for the ground state B_3^(0) = 16.522688(1)
B_2 and for the excited state B_3^(1) = 1.2704091(1) B_2.Comment: 4 pages, 2 figures, final versio
Design of experiments for non-manufacturing processes : benefits, challenges and some examples
Design of Experiments (DoE) is a powerful technique for process optimization that has been widely deployed in almost all types of manufacturing processes and is used extensively in product and process design and development. There have not been as many efforts to apply powerful quality improvement techniques such as DoE to improve non-manufacturing processes. Factor levels often involve changing the way people work and so have to be handled carefully. It is even more important to get everyone working as a team. This paper explores the benefits and challenges in the application of DoE in non-manufacturing contexts. The viewpoints regarding the benefits and challenges of DoE in the non-manufacturing arena are gathered from a number of leading academics and practitioners in the field. The paper also makes an attempt to demystify the fact that DoE is not just applicable to manufacturing industries; rather it is equally applicable to non-manufacturing processes within manufacturing companies. The last part of the paper illustrates some case examples showing the power of the technique in non-manufacturing environments
The automated array assembly task of the low-cost silicon solar array project, phase 2
Several specific processing steps as part of a total process sequence for manufacturing silicon solar cells were studied. Ion implantation was identified as the preferred process step for impurity doping. Unanalyzed beam ion implantation was shown to have major cost advantages over analyzed beam implantation. Further, high quality cells were fabricated using a high current unanalyzed beam. Mechanically masked plasma patterning of silicon nitride was shown to be capable of forming fine lines on silicon surfaces with spacings between mask and substrate as great as 250 micrometers. Extensive work was performed on advances in plated metallization. The need for the thick electroless palladium layer was eliminated. Further, copper was successfully utilized as a conductor layer utilizing nickel as a barrier to copper diffusion into the silicon. Plasma etching of silicon for texturing and saw damage removal was shown technically feasible but not cost effective compared to wet chemical etching techniques
Characteristics and prevalence of hardcore smokers attending UK general practitioners
BACKGROUND: Smoking remains a public health problem and although unsolicited GPs' advice against smoking causes between one and three percent of smokers to stop, a significant proportion of smokers are particularly resistant to the notion of stopping smoking. These resistant smokers have been called "hardcore smokers" and although 16% of smokers in the community are hardcore, little is known about hardcore smokers presenting to primary care physicians. Consequently, this study reports the characteristics and prevalence of hardcore smokers attending UK GPs. METHODS: A cross-sectional survey using data from two different research projects was conducted. Data for this analysis had been collected from surgery consultation sessions with 73 GPs in Leicestershire, England, (42 GPs from one project). Research assistants distributed pre-consultation questionnaires to 4147 adults attending GPs' surgery sessions. Questionnaires identified regular smokers, the proportion of hardcore smokers and their characteristics. Non-hardcore and hardcore smokers' ages, gender and nicotine addiction levels were compared. RESULTS: 1170 regular smokers attended surgery sessions and, 16.1% (95% CI, 14.1 to 18.4) were hardcore smokers. Hardcore smokers had higher levels of nicotine addiction than others (p = 0.000), measured by the Heaviness of Smoking Index and were more likely to be male [50.5% hardcore versus 35.3% non-hardcore, (OR = 1.88, 95% CI = 1.4 to 2.6)] but no age differences were observed between groups. CONCLUSION: A significant minority of the smokers who present in general practice are resistant to the notion of smoking cessation and these smokers are more heavily nicotine addicted than others. Although clinical guidelines suggest that GPs should regularly advise all smokers against smoking, it is probable that hardcore smokers do not respond positively to this and help to make up the 97%–99% of smokers who do not quit after being advised to stop smoking by GPs. General practitioners need to find approaches for raising the issue of smoking during consultations in ways that do not reinforce the negative opinions of hardcore smokers concerning smoking cessation
Gravitating multidefects from higher dimensions
Warped configurations admitting pairs of gravitating defects are analyzed.
After devising a general method for the construction of multidefects, specific
examples are presented in the case of higher-dimensional Einstein-Hilbert
gravity. The obtained profiles describe diverse physical situations such as
(topological) kink-antikink systems, pairs of non-topological solitons and
bound configurations of a kink and of a non-topological soliton. In all the
mentioned cases the geometry is always well behaved (all relevant curvature
invariants are regular) and tends to five-dimensional anti-de Sitter space-time
for large asymptotic values of the bulk coordinate. Particular classes of
solutions can be generalized to the framework where the gravity part of the
action includes, as a correction, the Euler-Gauss-Bonnet combination. After
scrutinizing the structure of the zero modes, the obtained results are compared
with conventional gravitating configurations containing a single topological
defect.Comment: 27 pages, 5 included figure
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