An extension of the tearing instability theory to multiple loading parameters

The stability of a cracked, nonlinear component connected to an elastic structure and subjected to an arbitrary number of controlled loads or displacements, is discussed. First this is done with a general instability criterion expressed in terms of loads and displacements of the cracked part. Then general expressions for the tearing modulus are given for different loading situations. Finally the given equations are applied to SEN specimens under bending and tension.

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Résumé On discute de la stabilité d'un composant fissuré et non linéaire assemblé à une structure élastique et soumis à un monbre quelconque de charges ou de déplacements, appliqués dans des conditions connues. Ceci est réalisé en faisant appel, en premier lieu, à un critère général d'instabilité exprimé en termes the sollicitation et de déplacement de la portion fissurée. Ensuite, on fournit des expressions générales pour le module d'arrachement, correspondant à diverses situations de mise en charge. Enfin, les équations obtenues sont appliquées à des éprouvettes à entaille latérale simple soumises à flexion et traction.

     

Acyl exchange between oleoyl-CoA and phosphatidylcholine in microsomes of developing soya bean cotyledons and its role in fatty acid desaturation

Microsomes of developing soya bean cotyledons transfer oleate from oleoyl-CoA to phosphatidylcholine (PC) by two different mechanisms: one in which oleate transfer is accompanied by the release of free CoA and another which results in the exchange of oleate from oleoyl-CoA for unsaturated 18-carbon fatty acids of PC. The acyl exchange can be demonstrated only when bovine serum albumin is present in the incubation medium. ATP-dependent acyl-CoA synthetase is not involved in the exchange process, which apparently does not require any cofactors. In light of this exchange process, the oleate desaturase system was reinvestigated in order to determine what the actual substrate for this system is. Upon incubation of microsomes with high concentrations of [¹⁴C] oleoyl-CoA, bovine serum albumin and NADH, it could be conclusively demonstrated that most oleic acid is desaturated while part of the PC molecule. The amounts of [¹⁴C] linoleoyl-CoA formed could be explained entirely by the acyl exchange. The physiological significance of the acyl exchange system is discussed. A new method for separation of acyl-CoA from other lipids and free CoA using reversed phase column chromatography also is described.     

Quality factor of an electrically small antenna radiating close toa conducting plane

Expressions are derived for the smallest achievable radiation quality factor (Q) of an electrically small antenna in front of a conducting plane. Applying the low-frequency approximation to the source region involving an electric or a magnetic point dipole plus their images behind the plane, an expression is formed for the field in the radiation zone. The contribution of non-propagating energy in the near field is obtained explicitly using a spherical harmonics decomposition. The radiation Q is found to depend on the radius (relative to wavelength) of the smallest sphere that encloses the antenna and its image, the ratio of the vertical and horizontal dipole moments, as well as the positions of the dipoles relative to each other and to the plane. A number of simple wire structures are analysed with NEC (based on the method of moments), and the approximate Q obtained from their fractional bandwidth are compared to the corresponding theoretical minima     

Properties of the glycerol acylating enzymes in microsomal preparations from the developing seeds of safflower (Carthamus tinctorius) and turnip rape (Brassica campestris) and their ability to assemble cocoa-butter type fats

Microsomal membrane preparations from the developing seeds of safflower (Carthamus tinctorius, var. Gila) and turnip-rape (Brassica campestris, var. Bele) catalyzed the assembly of triacylglycerols (triglycerides) from sn-glycerol 3-phosphate and acyl-CoA. The membrane preparations were used to assess the acyl specificity properties of the initial acylating enzymes—glycerol 3-phosphate acyltransferase (GPAT) and 1-acylglycerol 3-phosphate acyltransferase (lysophosphatidic acid acyltransferase, LPAAT)—that are responsible for the fatty acids at positions sn-1 and sn-2 of the sn-triacylglycerol, respectively. In spectrophotometric assays it was possible to evaluate, to some extent, how these enzymes will utilize unusual and foreign fatty acids that are not normally found in these particular plant species. The acylating enzymes from both plants used, to varying extents, a comprehensive range of acyl-CoA donor species and some kinetic properties of the substrates involved are presented. The enzymes from safflower, however, were generally the more selective, whereas the turnip-rape was less particular and could utilize a range of acyl substrates. The enzymes from both plants hardly utilized erucate (C22∶1), and the significance of this is discussed in terms of mechanisms which have evolved in order to exclude certain, perhaps detrimental, fatty acids from structural membrane lipids and dedicate them to storage lipid assembly. The ability of the microsomal preparations, from the developing seeds of both plants, to synthesize cocoabutter type fats was investigated. Microsomal membranes were incubated with glycerol 3-phosphate and equimolar amounts of palmitate, oleate and stearate. Safflower preparations catalyzed the construction of sn-triacylglycerol with largely palmitate, oleate and stearate in positions sn-1, 2 and 3, respectively. The selectivity for acyl species in rape was less pronounced, however, substantial saturated-unsaturated-saturated oils were still produced. The results are discussed in terms of the acyl selectivity properties of the glycerol acylating enzymes. It is evident that given the correct composition of fatty acids, the plant can produce cocoabutter or other exotic fats.     

Electrical and gas sensing properties of <Emphasis Type="Italic">por</Emphasis>-Si/SnO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> nanocomposite layers

The electrical characteristics and chemical reactant sensitivity of layers of heterogeneous nanocomposites based on porous silicon and nonstoichiometric tin oxide por-Si/SnO _x , fabricated by the magnetron sputtering of tin with subsequent oxidation, are studied. It is shown that, in the nanocomposite layers, a system of distributed heterojunctions (Si/SnO _x nanocrystals) forms, which determine the electrical characteristics of such structures. The sensitivity of test sensor structures based on por-Si/SnO _x nanocomposites to NO₂ is determined. A mechanism for the effect of the adsorption of NO₂ molecules on the current-voltage characteristics of the por-Si(p)/SnO _x (n) heterojunctions is suggested.     

Study of scattering by a perfectly conducting wedge with finite sized faces

In this work the scattering of plane waves from a finite sized perfectly conducting wedge as a function of its opening angle and the width of its faces is studied using the combination of physical optics (po) and the physical theory of diffraction (ptd). To find out under which circumstances the ptd contribution is significant compared to the PO, the ratio of the ptd field and the po field is evaluated as a maximum and a mean value over every direction of observation in the Keller cone, as well as in the special direction of backscattering. We employ the incremental length diffraction coefficients for a wedge with finite sized faces based on equivalent edge currents derived recently for truncated wedge strips. The numerical behaviour in the limiting cases of the diffraction coefficients are discussed extensively.     

An integrated qualitative and quantitative modeling framework for computer‐assisted HAZOP studies

The article proposes a novel practical framework for computer‐assisted hazard and operability (HAZOP) that integrates qualitative reasoning about system function with quantitative dynamic simulation in order to facilitate detailed specific HAZOP analysis. The practical framework is demonstrated and validated on a case study concerning a three‐phase separation process. The multilevel flow modeling (MFM) methodology is used to represent the plant goals and functions. First, means‐end analysis is used to identify and formulate the intention of the process design in terms of components, functions, objectives, and goals on different abstraction levels. Based on this abstraction, qualitative functional models are constructed for the process. Next MFM‐specified causal rules are extended with systems specific features to enable proper reasoning. Finally, systematic HAZOP analysis is performed to identify safety critical operations, its causes and consequences. The outcome is a qualitative hazard analysis of selected process deviations from normal operations and their consequences as input to a traditional HAZOP table. The list of unacceptable high risk deviations identified by the qualitative HAZOP analysis is used as input for rigorous analysis and evaluation by the quantitative analysis part of the framework. To this end, dynamic first‐principles modeling is used to simulate the system behavior and thereby complement the results of the qualitative analysis part. The practical framework for computer‐assisted HAZOP studies introduced in this article allows the HAZOP team to devote more attention to high consequence hazards. © 2014 American Institute of Chemical Engineers AIChE J 60: 4150–4173, 2014     

Replacing fossil oil with fresh oil – with what and for what?

Industrial chemicals and materials are currently derived mainly from fossil‐based raw materials, which are declining in availability, increasing in price and are a major source of undesirable greenhouse gas emissions. Plant oils have the potential to provide functionally equivalent, renewable and environmentally friendly replacements for these finite fossil‐based raw materials, provided that their composition can be matched to end‐use requirements, and that they can be produced on sufficient scale to meet current and growing industrial demands. Replacement of 40% of the fossil oil used in the chemical industry with renewable plant oils, whilst ensuring that growing demand for food oils is also met, will require a trebling of global plant oil production from current levels of around 139 MT to over 400 MT annually. Realisation of this potential will rely on application of plant biotechnology to (i) tailor plant oils to have high purity (preferably >90%) of single desirable fatty acids, (ii) introduce unusual fatty acids that have specialty end‐use functionalities and (iii) increase plant oil production capacity by increased oil content in current oil crops, and conversion of other high biomass crops into oil accumulating crops. This review outlines recent progress and future challenges in each of these areas. Practical applications: The research reviewed in this paper aims to develop metabolic engineering technologies to radically increase the yield and alter the fatty acid composition of plant oils and enable the development of new and more productive oil crops that can serve as renewable sources of industrial feedstocks currently provided by non‐renewable and polluting fossil‐based resources. As a result of recent and anticipated research developments we can expect to see significant enhancements in quality and productivity of oil crops over the coming decades. This should generate the technologies needed to support increasing plant oil production into the future, hopefully of sufficient magnitude to provide a major supply of renewable plant oils for the industrial economy without encroaching on the higher priority demand for food oils. Achievement of this goal will make a significant contribution to moving to a sustainable carbon‐neutral industrial society with lower emissions of carbon dioxide to the atmosphere and reduced environmental impact as a result.     

Modulation of silica layer properties by varying the granulometric state of tetraethyl orthosilicate precursor aerosols during combustion chemical vapor deposition (CCVD)

Abstract

For the purpose of silica surface layer modulation, a pneumatic-controlled two-substance atomizer with inertia-based coarse droplet separation was operated at different system pressures for tetraethyl orthosilicate precursor aerosol supply during combustion chemical vapor deposition. A comprehensive testing study was performed to characterize the atomizer’s performance characteristics, initial precursor aerosols at the atomizer’s outlet, transformed aerosols before combustion, combustion aerosols and formed layers. Laser diffraction spectrometry, differential electrical mobility analyses and condensation particle counting were used for aerosol characterization with regard to particle size and particle production quantities. Layers were characterized by scanning electron microscopy, atomic force microscopy, spectral ellipsometry, water contact angle measurements and light transmission concerning geometric properties (thickness, surface structure and roughness) and physical behaviors (i.e., optical behaviors, hydrophobicity). Results show a quasi-linear relationship of the ejection mass flow of the pneumatic-controlled atomizer and geometric layer properties which again show a direct relationship to the physical properties. No correlation was found between the aerosols before combustion and the combustion aerosols since the majority of combustion aerosol particles are synthesized solely from the gas phase based on evaporated precursor material.

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