Production of high‐quality chitin and chitosan from preconditioned shrimp shells

Chitin and chitosan with improved characteristics were produced from shrimp shell waste preconditioned by limited decay or by treatment with 0.016 mol L^?1 benzoic acid. Preconditioned shrimp shells were transparent, had a clean surface and were susceptible to demineralization and deproteinization using 0.68 mol L^?1 HCl and 0.62 mol L^?1 NaOH, respectively. The ash and protein residues in the final chitosan were about 0.2% and 0.4%, respectively, the viscosity was up to 7000 cps, and the solubility and transparency nearly 100%. In comparison with treatment at ambient temperature (30 °C) without preconditioning, the chemical consumption, the duration of the treatment, ash and protein residues was reduced to 75–25%, whereas viscosity and absence of insolubles improved by a factor of 2–3. Copyright © 2006 Society of Chemical Industry     

Nonlinear Response of Imperfect Eccentrically Stiffened Ceramic-Metal-Ceramic Sigmoid Functionally Graded Material (S-FGM) Thin Circular Cylindrical Shells Surrounded on Elastic Foundations Under Uniform Radial Load

This article researches nonlinear response of imperfect eccentrically stiffened symmetric FGM thin circular cylindrical shells with ceramic-metal-ceramic layers, which are symmetric through the middle surface by Sigmoid-law distribution (S-FGM) and have stiffeners surrounded on elastic foundations under uniform radial load. The Donnell classical shell theory, stress function, and Galerkin method are used for investigation of the nonlinear stability of the S-FGM shell. The obtained results show the effects of the stiffeners, elastic foundations, mechanical load, and material parameters on the nonlinear buckling response of symmetric S-FGM circular cylindrical shells.     

Puncture of elastomer membranes by medical needles. Part II: Mechanics

Resistance to puncture by medical needles is becoming one of the most critical mechanical properties of rubber membranes, which are heavily used in protective gloves. Yet the intrinsic material parameters controlling the process of puncture by medical needles are still unknown. In a first paper presenting this two-part study, it has been shown that puncture by medical needles proceeds gradually as the needle cuts through the rubber membrane. The phenomenon of puncture by medical needles was revealed to involve contributions both from friction and fracture energy, in a similar way as for cutting. The use of a lubricant was not successful for removing the friction contribution for the determination of the material fracture energy corresponding to puncture by medical needles. This paper describes an alternative approach based on the application of a prestrain to the sample in a similar way as the work of Lake and Yeoh on cutting. A theoretical formulation for the tearing energy is derived from the theory of Rivlin and Thomas on the rupture of rubber. It is validated with a model extending expressions provided by the linear elastic fracture mechanics (LEFM) to include the non-linear stress–strain behavior displayed by rubber. For low values of the tearing energy, the total fracture energy, i.e. the sum of the puncture and tearing energies, is constant; the material fracture energy is obtained by extrapolation at zero tearing energy. This prestrain method allowed a complete removal of the friction contribution. The value obtained for the fracture energy corresponding to puncture by medical needles is found to be larger than the energy associated to cutting and smaller than that obtained for tearing. This can be related to the value of the crack tip diameter, which is, in that case, given by the needle cutting edge diameter.     

Microwave propagation at X band in cylindrical-shapedforest components: attenuation observations

Experimental results are presented for attenuation measurements performed on cylindrical-shaped forest components. Microwave propagation in simulated canopies composed of bare deciduous twigs and leafy coniferous branches was investigated at 9 GHz. In order to account for the influence of natural component parameters, the experiments were carried out under laboratory conditions where those parameters could be easily and fully controlled. The influence of the physical parameters (number density of scatterers and gravimetric water content) and the geometrical parameters (dimensions and orientation of the scatterers) on the angular and polarization attenuation behaviors is pointed out. These results supplement previous attenuation observations obtained with natural cylindrical elements     

Design and fabrication of twisted monolithic dielectric elastomer actuator

This paper presents a novel design of dielectric elastomer actuator (DEA), called single body dielectric elastomer actuator (SDEA), to improve the performance of existing DEAs. The DEA is typically configured with stacking multiple dielectric elastomer film and linearly contracted according to the applied voltage. SDEA is fabricated monolithically without external frame and has the advantages of flexibility and light weight. Thus, it is applicable to various configurations of actuators such as twisting or bending, etc. By exploiting the advantages of SDEA, we propose a new 2-ply design of SDEA. The design is configured with plying couples of monolithically fabricated SDEA. We explain how it can amplify the stroke with its basic principles of operations. In addition, its fabrication method is addressed. Finally, the results of performance evaluations are included with respect to stroke, force, speed, etc.     

Branching model for vegetation

A branching model is proposed for the remote sensing of vegetation. The frequency and angular responses of a two-scale cylinder cluster are calculated to demonstrate the significance of vegetation architecture. The results indicate that the architecture of vegetation plays an important role in determining the observed coherent effects. A two-scale branching model is implemented for soybean with its internal structure and the resulting clustering effects considered. At the scale of soybean fields, the relative location of soybean plants is described by a pair distribution function. The polarimetric backscattering coefficients are obtained in terms of the scattering properties of soybean plants and the pair distribution function. Theoretical backscattering coefficients evaluated using the hole-correction pair distribution are in good agreement with extensive data from soybean fields. The hole-correction approximation, which prevents two soybean plants from overlapping each other, is more realistic and improves the agreement between the model calculation and experimental data near normal incidence     

Polarimetric discriminators for SAR images

A method is developed for optimizing the degree of polarization of a partially polarized wave reflected by a nonstationary scattering object. The method permits, for a scattered wave and a given target characterized by its Mueller matrix, analytic computation of the maximum and minimum values of the degree of polarization, and the corresponding transmitted polarizations. A procedure for the optimization of the scattered wave intensity is also proposed. The degree of polarization and the total scattered intensity extrema are then analyzed experimentally on JPL data. It is shown that several entities such as the received intensity extrema, the coefficient of variation, the fractional polarization and the span, which are currently used for target discrimination, can be deduced from combinations of the maximum and minimum values of the degree of polarization and the scattered wave intensity. Finally, a classification of the San Francisco image, based on these indices, is conducted for a better understanding of the specific physical meaning of each index