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61.
Conditions of equilibrium of forces are formulated for a force system in a continuous body which consists of a bulk stress
and a stress concentrated on a curve. The system of forces is interpreted as a tensor valued measure and the equilibrium of
forces is interpreted in a weak sense. The divergence theorem is proved for bulk stress fields with the corresponding singularity.
Examples of such stress fields are given.
相似文献
62.
63.
A double pulse ruby laser was used to obtained interference patterns from a laser produced plasma in helium. From patterns obtained at different times the electron density evolution was inferred by Abel inversion, with suitable approximations. There was a net evidence for electron density increase due to the action of a converging shock wave produced by reflection. 相似文献
64.
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66.
An analytical model of a tilting pad bearing was developed based on the short bearing assumption with the turbulence effect
included. In order to determine its influence on the dynamic behavior of the rotor, this model was compared against one without
the turbulence effect through a simulation of a Jeffcott/Laval rotor supported by a couple of bearings. Both models were also
used to determine the influence of geometric parameters on tilting pad bearing making use of the aforementioned system at
different rotor speeds.
When analyzing the results, the parameters which presented the largest influence were: pad preload, number of segments, radial
clearance, pad position, and pad pivoting angle. As the pad moment of inertia and the pivoting distance have changed the shaft
motion only a few microns, their effects can be neglected. The bearing model with turbulent flow effect has generated higher
hydrodynamic forces when compared to the one without this effect, which remarks the importance of considering such phenomenon
during the analysis of the high speed hydrodynamic bearings. 相似文献
67.
Lionella Palego Gino Giannaccini Giuseppe Saccomanni Alessandra Rossi Valentina Lucchesi Giovanni Mascia Laura Betti Clementina Manera Laura Bazzichi Antonio Lucacchini 《Chromatographia》2010,71(3-4):291-297
Among the techniques available for quantitative analysis of physiological amino acids, systems using optical detection are of low specificity because of possible interference at the analytical wavelength. Another disadvantage is problems of sample extraction from complex biological matrices, for example plasma. This paper describes reversed-phase LC of phenylthiocarbamyl (PTC) amino acids in plasma deproteinated by addition of acetonitrile. Specificity was monitored by photo-diode UV detection and accuracy was assessed by a plasma spiking procedure with more than one internal standard. Dual-wavelength spectrophotometry (254 and 283 nm) was also used for separate measurement of co-eluting adducts of tryptophan and ornithine. This method enables the quantification, with high reproducibility, of a total of twenty-three plasma amino acids from fasting healthy subjects. LOQ values are satisfactory for all the amino acids (average 6 μmol L?1). However, the method does not enable analysis of aspartate and overall homocystine, present at very low concentrations, in all plasma samples. This PTC–amino acid chromatographic method is inexpensive, reliable, and suitable for clinical research and therapeutic drug monitoring, but adaptation to dual on-line detection is required to improve its sensitivity. 相似文献
68.
A. Tartaglia E. C. Lorenzini D. Lucchesi G. Pucacco M. L. Ruggiero P. Valko 《General Relativity and Gravitation》2018,50(1):9
We illustrate the proposal, nicknamed LAGRANGE, to use spacecraft, located at the Sun–Earth Lagrange points, as a physical reference frame. Performing time of flight measurements of electromagnetic signals traveling on closed paths between the points, we show that it would be possible: (a) to refine gravitational time delay knowledge due both to the Sun and the Earth; (b) to detect the gravito-magnetic frame dragging of the Sun, so deducing information about the interior of the star; (c) to check the possible existence of a galactic gravitomagnetic field, which would imply a revision of the properties of a dark matter halo; (d) to set up a relativistic positioning and navigation system at the scale of the inner solar system. The paper presents estimated values for the relevant quantities and discusses the feasibility of the project analyzing the behavior of the space devices close to the Lagrange points. 相似文献
69.
Summary A masonry dam with triangular cross section is subjected to its own weight and to hydrostatic pressure in a state of plane strain. Under the constraint that the principal stresses be strictly negative in the interior, it is shown that there is a section of minimal area and, consequently, a dam of lowest weight.
Sommario Una diga in muratura di sezione triangolare è soggetta al peso proprio e alla spinta idrostatica in condizioni di deformazione piana. Si dimostra che, sotto il vincolo che le tensioni principali siano entrambe negative in tutti i punti interni, esiste una sezione di minima area e, quindi, una diga di minimo peso.相似文献
70.
Paola Stagnaro Manuela Panizza Alessandro Gandini Daniele Prevosto Mauro Lucchesi 《Journal of polymer science. Part A, Polymer chemistry》2011,49(24):5227-5238
This article reports a thorough spectroscopic characterization and the complete microstructural unravelling of a novel soluble poly(thienylene methylene) recently obtained by a straightforward process based on the methanesulfonic acid‐catalyzed self‐condensation of 2‐acetoxymethyl‐3,4‐dimethylthiophene. These macromolecules were found to generate both in situ (in the acidic reaction medium) and ex situ (by the addition of appropriate dopants) conjugated sequences consisting of alternating aromatic‐ and quinoid‐like thiophene rings, that is, conjugated thienylene methine sequences. The effect of different types of dopants on the electronic features of these polymers was assessed by the extent of bathochromic shifts they induced in the macromolecule UV–vis spectra. Doped films obtained by solution casting were characterized by dielectric spectroscopy to evaluate their electronic conductivity. The observed low values of conductivity were explained on microscopic basis evidencing the presence of polymer branching. All the structures arising from side reactions responsible for branching were determined by an exhaustive NMR study, which led to the formulation of the corresponding mechanisms. Remarkably, all these polymers, irrespective of their specific structural features and molecular weights, retained complete solubility in common solvents. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献