An approach to the design of composites for service at elevated and nonsteady temperatures

The language and ideas developed in the continuum mechanics area of ratcheting and shakedown can be applied to the analysis and design of composites that are subjected to both external and thermal loading. Specifically, the diagrams first proposed by Bree and previously applied to composites by Jansson and Leckie can be of value in designing composites that will remain dimensionally stable under stress and temperature cycling. Three simple cases are analyzed analytically and from these, it seems apparent that the resulting composite behavior maps (CBMs) have a characteristic shape. This shape can be conservatively estimated by the linear connection of points that correspond to initial yield and interconnected plasticity under pure mechanical and pure thermal loading. Both experimental and analytical methods of determining these points are discussed. Finally, good agreement between a CBM produced by simplified analytical procedures and a full three-dimensional (3D) finite element analysis is shown. This article is based on a presentation made in the symposium entitled “Creep and Fatigue in Metal Matrix Composites” at the 1994 TMS/ASM Spring meeting, held February 28–March 3, 1994, in San Francisco, California, under the auspices of the Joint TMS-SMD/ASM-MSD Composite Materials Committee.     

Workspace boundaries of serial manipulators using manifold stratification

Workspace boundaries of serial manipulator arms have traditionally been presented as numerical curves traced on a boundary or as analytical formulations for a specific class of manipulators. This paper presents a broadly applicable formulation to identify and visualize the workspace, based on methods adapted from differential geometry and topology. Because the position Jacobian for manipulators with more than three degrees of freedom is not square, manifold stratification of the vector function (a topological vector space) yields nonlinear analytic functions. These functions give rise to analytic and semi-analytic varieties, some of which characterize lower-dimensional manifolds (submanifolds). The process is repeated until all strata are identified. The problem of determining which stratum (or part thereof) is on the boundary is addressed by introducing an acceleration function, which yields a quadratic form whose definiteness properties delineate the exact boundary. The method yields the exact boundary of the workspace in the form of closed-form equations and is capable of identifying voids therein. A complete example is first illustrated, followed by numerous tabulated examples (some of which are compared with reported works in the literature).     

Tumour seeding following percutaneous endoscopic gastrostomy placement in head and neck cancer

We report the case of a patient with advanced squamous carcinoma of the supraglottic larynx and hypopharynx who developed metastatic gastric deposits occurring at the site of a percutaneous endoscopic gastrostomy tube, inserted 10 months previously by the pull technique. We review seven previous reports of tumour deposits occurring at the site of placement of a percutaneous endoscopic gastrostomy in patients with head and neck cancer, and consider alternative methods of enteral feeding in such patients.     

Using waste plastic bottles as additive for stone mastic asphalt

Currently, polymer modified asphalt mixture is a relatively costly mixture for paving roads. One way to reduce the cost of such constructions and rendering them more convenient is by using inexpensive polymers, i.e. waste polymers. The main purpose of this research is to determine the effect of incorporating waste plastic bottles (Polyethylene Terephthalate (PET)) on the engineering properties of stone mastic asphalt (SMA) mixture. The volumetric and mechanical properties of asphalt mixes that include various percentages of PET (0%, 2%, 4%, 6%, 8% and 10%) were calculated and assessed with laboratory tests. The appropriate amount of PET was found to be 6% by weight of bitumen. The outcomes were statistically analysed and the determination of the significance at certain confidence limits was performed with the two factor variance analysis (ANOVA). Moreover, some studies conducted on polyethylene modified asphalt mixture have also been taken into consideration in this paper. The results show that the addition of PET has a significant positive effect on the properties of SMA and it can promote the re-use of waste material in industry in an environmentally friendly and economical way.     

Some considerations of the lean flammability limits of mixtures involving hydrogen

Consistent data regarding the flammability limits of homogeneous mixtures of hydrogen gas in air at atmospheric pressure are presented for various temperatures extending down to ?130 °C. The retardation of the combustion of lean homogeneous mixtures of hydrogen and air due to the homogeneous mixing of inerts such as CO₂, N₂ and He is also considered. Moreover, the enhancement of the flammability limits of fuel mixtures involving CO, CH₄, C₃H₈ and C₂H₄ in air due to the presence of some hydrogen is also presented. Guidelines are then suggested for predicting the role of the presence of hydrogen in the fuel-air mixtures over a wide range of concentrations and temperatures.     

Empirical analysis of gross vehicle weight and free flow speed and consideration on its relation with differential speed limit

Most highly motorized countries in the world have implemented different speed limits for light weight and heavy weight vehicles. The heavy vehicle speed limit is usually chosen to be lower than that of passenger cars due to the difficulty for the drivers to safely maneuver the heavy vehicle at high speed and greater impact during a crash.However, in many cases, the speed limit for heavy vehicle is set by only considering the vehicle size or category, mostly due to simplicity in enforcement. In this study, traffic and vehicular data for all vehicle types were collected using a weigh-in-motion system installed at Federal Route 54 in Malaysia. The first finding from the data showed that the weight variation for each vehicle category is considerable. Therefore, the effect of gross vehicle weight (GVW) and category of heavy vehicle on free flow speed and their interaction were analyzed using statistical techniques.Empirical analysis results showed that statistically for each type of heavy vehicle, there was a significant relationship between free flow speed of a heavy vehicle and GVW. Specifically, the results suggest that the mean and variance of free flow speed decrease with an increase GVW by the amount unrelated to size and shape for all GVW range. Then, based on the 85th percentile principle, the study proposed a new concept for setting the speed limit for heavy vehicle by incorporating GVW where a different speed limit is imposed to the heavy vehicle, not only based on vehicle classification, but also according to its GVW.     

Nitrogen-doped reduced graphene oxide/Fe2O3 hybrid as efficient catalyst for ammonium nitrate

In this investigation, we successfully synthesized a hybrid material, N-rGO@Fe₂O₃, via a one-step hydrothermal process, comprising nitrogen-doped reduced graphene oxide and α-Fe₂O₃. Thorough characterization using diverse analytical methods validated its structure. Employing this hybrid composite as a catalyst, we studied its efficacy in the catalytic thermal decomposition of ammonium nitrate (AN). The N-rGO@Fe₂O₃/AN composite was prepared using a recurrent spray coating method with 3 % mass of the hybrid material. Thermo-gravimetric (TG) and differential scanning calorimetric (DSC) analyses were employed to investigate the catalytic effect. Computational assessment of Arrhenius parameters was conducted through isoconversional kinetic approaches. Results from the kinetic analysis allowed the determination of the critical ignition temperature. Furthermore, calorific values for pure AN and N-rGO@Fe₂O₃/AN were measured using an oxygen calorimetric bombe, revealing a 41 % reduction in activation energy barrier and a lowering of the critical ignition temperature from 292 °C to 283 °C upon incorporation of the hybrid material. Notably, the surface modification of AN with N-rGO@Fe₂O₃ resulted in an increase of 1440 J/g in the observed calorific values. These findings highlight the potential of N-rGO@Fe₂O₃ as an effective catalyst, offering promising implications for applications in enhancing ammonium nitrate thermal decomposition.     

Recovering the initial state of an infinite-dimensional system using observers

Let A be the generator of a strongly continuous semigroup T on the Hilbert space X, and let C be a linear operator from D(A) to another Hilbert space Y (possibly unbounded with respect to X, not necessarily admissible). We consider the problem of estimating the initial state z₀∈D(A) (with respect to the norm of X) from the output function y(t)=CT_tz₀, given for all t in a bounded interval [0,τ]. We introduce the concepts of estimatability and backward estimatability for (A,C) (in a more general way than currently available in the literature), we introduce forward and backward observers, and we provide an iterative algorithm for estimating z₀ from y. This algorithm generalizes various algorithms proposed recently for specific classes of systems and it is an attractive alternative to methods based on inverting the Gramian. Our results lead also to a very general formulation of Russell’s principle, i.e., estimatability and backward estimatability imply exact observability. This general formulation of the principle does not require T to be invertible. We illustrate our estimation algorithms on systems described by wave and Schrödinger equations, and we provide results from numerical simulations.     

Electroosmotic micropump for lab‐on‐a‐chip biomedical applications

Lab‐on‐a‐chip (LOC) integrated microfluidics has been a powerful tool for new developments in analytical chemistry. These microfluidic systems enable the miniaturization, integration and automation of complex biochemical assays through the reduction of reagent use and enabling portability. Electroosmotic micropumps could be employed as powerful tools to generate required flow in point of care (POC) devices. In the present study, parallel electroosmotic micropumps are investigated to improve the efficiency of simple micropumps. According to the results, parallel micropumps generate higher flow rate in comparison with conventional electroosmotic pump. In the last decade, a large variety of non‐Newtonian fluids have been utilized in biomedical application but requirements for a POC device such as high efficient driving flow, miniaturization and simple handling of POC devices remain unmet. As a consequence, in this study, power law model as non‐Newtonian fluids that flow through the parallel micropumps are investigated in order to enhance fluid pumping and decreasing voltage requirement.. It is found that as the power law index increases the mass flow rate decreases. Also, the flow rate is almost constant for the higher power law index. Obtained results, demonstrated that parallel micropump could enhance pumping of non‐Newtonian fluid (blood) up to 30%. Copyright © 2016 John Wiley & Sons, Ltd.