Gunn oscillations in thin samples with capacitive surface loading

Abstract The analysis of shells is an important subdivision of the general theory of elasticity, and its application is useful in the solution of engineering problems involving thin-walled structures. A common type of shell is one which possesses symmetry with respect to an axis of revolution. A theory for such shells has been developed by various investigators (1, 2, 3, 6) and applied to a few simple cases such as the cylindrical, spherical, and conical shapes. Boundary conditions, for the most part, have been simple static ones, and conditions of surface loading have been included in certain special cases. This paper extends the theory of axially symmetrical shells by including the body force of rotation about the axis and applies the results to the rotating conical shell. The analysis follows a pattern established by several investigators (1, 2, 3, 6) and for this reason is abbreviated to a considerable extent. Only where the inclusion of the body force makes elucidation advisable or where a slightly different method of approach is used are the steps presented in more detail.

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Elaboration and Characterization of Cu Based Nanocomposites for Electromagnetic Interferences Shielding

Defect and Diffusion Forum ◽

10.4028/www.scientific.net/ddf.412.177 ◽

2021 ◽

Vol 412 ◽

pp. 177-184

Author(s):

Farid Kara ◽

Fadhéla Otmane ◽

Samir Bellal ◽

Amira Djenet Guerfi ◽

S. Triaa

Keyword(s):

Epoxy Resin ◽

Xrd Analysis ◽

High Energy ◽

Shielding Effectiveness ◽

Emi Shielding ◽

Emi Shielding Effectiveness ◽

Cell Measurement ◽

Wave Guides ◽

Pure Cu ◽

Thin Samples

An electromagnetic interferences (EMI) shielding is a material that attenuates radiated electromagnetic energy. Polymer nanocomposites is a class of materials that combine electrical, thermal, dielectric, magnetic and/ or mechanical properties, which are useful for the suppression of electromagnetic interferences. In this work, we looked over the effectiveness of the electromagnetic interferences shielding of polymer-based nanocomposites. These are thin samples of epoxy resin strengthened with nanostructured Cu powders. Nanostructured Cu powders were obtained by mechanical milling using the high-energy RETSCH PM400 ball mill (200 rpm). A powder sampling was conducted after 3h, 6h, 12h, 24h, 33h, 46h and 58h milling for characterization requirements. XRD analysis via the Williamson-Hall method shows that the mean crystallites size decreases from 151.6 nm (pure Cu phase) to 13.8 nm (58 h milling). Simultaneously, the lattice strain increases from 0.1% (pure Cu phase) to 0.59% (58 h milling). The elaboration of thin samples was performed by mixing a vol./3 fractions of nanostructured Cu powder, epoxy resin and hardener. Thin slabs of 1 mm thickness were moulded for use in a rectangular wave-guide. The EMI shielding experimental involved a two ports S parameters cell measurement made of R120 metallic wave-guides of rectangular section (19.05x9.525 mm2) and operational over the frequency band of 9.84 to 15 GHz associated to a network analyser. Obtained results show moderate EMI shielding effectiveness for the milled Cu-based slabs.

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Surface Loading Analysis: Vehicle Load Distribution Under Timber Mats and Flexible Slab

10.1115/1.0003486v ◽

2021 ◽

Author(s):

Benjamin Zand

Keyword(s):

Load Distribution ◽

Surface Loading ◽

Vehicle Load ◽

Loading Analysis

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Tilapia rearing with high rate algal pond effluent: ammonia surface loading rates and stocking densities effects

Water Science & Technology ◽

10.2166/wst.2018.285 ◽

2018 ◽

Vol 78 (1) ◽

pp. 49-56

Author(s):

I. A. Sánchez ◽

R. K. X. Bastos ◽

E. A. T. Lana

Keyword(s):

Weight Gain ◽

Oxygen Demand ◽

Pilot Scale ◽

Ammonia Nitrogen ◽

High Rate ◽

Surface Loading ◽

Loading Rates ◽

Total Weight Gain ◽

Low Weight ◽

Total Ammonia

Abstract In two pilot-scale experiments, fingerlings and juvenile of tilapia were reared in high rate algal pond (HRAP) effluent. The combination of three different total ammonia nitrogen (TAN) surface loading rates (SLR1 = 0.6, SLR2 = 1.2; SLR3 = 2.4 kg TAN·ha−1·d−1) and two fish stocking densities (D1 = 4 and D2 = 8 fish per tank) was evaluated during two 12-week experiments. Fingerlings total weight gain varied from 4.9 to 18.9 g, with the highest value (equivalent to 0.225 g·d−1) being recorded in SLR2-D1 treatment; however, high mortality (up to 67%) was recorded, probably due to sensitivity to ammonia and wide daily temperature variations. At lower water temperatures, juvenile tilapia showed no mortality, but very low weight gain. The fish rearing tanks worked as wastewater polishing units, adding the following approximate average removal figures on top of those achieved at the HRAP: 63% of total Kjeldahl nitrogen; 54% of ammonia nitrogen; 42% of total phosphorus; 37% of chemical oxygen demand; 1.1 log units of Escherichia coli.

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