A new approach to predict the strength of high energy materials

This paper presents a new approach to predict the strength of energetic compounds in which there are important classes of high explosives including nitroaromatics, acyclic and cyclic nitramines, nitrate esters and nitroaliphatics. For C(a)H(b)N(c)O(d) compounds, the ratio of carbon to oxygen atoms and the predicted heat of detonation on the basis of the H(2)O-CO(2) arbitrary have been used to calculate the strength of an explosive. The new model can give good predictions for mentioned energetic compounds as determined by the Trauzl test. The novel correlation will be useful in predicting the strength or power of a new energetic compound that has significant potential in the field of explosives and propellants.     

Dietary assessment of hemodialysis patients in Tehran, Iran

Inadequate dietary intakes are a major determinant of malnutrition in hemodialysis (HD) patients. Considering the lack of information available on dietary intakes of HD patients in Iran, the present study was designed to assess the dietary intakes of HD patients in Tehran, Iran. For this cross‐sectional study, from among adult HD patients of 50 Tehran hemodialysis centers, 291 patients were randomly selected. Dietary intakes of these patients were assessed using a 4‐day dietary recall. In addition, 4 mL of blood was obtained from each patient before dialysis to measure serum urea, creatinine, albumin, phosphorus, calcium, potassium, and high sensitive C‐reactive protein levels. Dietary intakes of energy, protein and fiber were lower than recommended intakes in 88%, 84.5%, and 99% of HD patients, respectively. There were significant associations between dietary energy intake with the patient's age (p < 0.05), and HD vintage (P < 0.001). In addition, a significant association was found between dietary protein intake and sex (P < 0.05). Intakes of vitamins B1, B2, B3, B6, B12, C, E, folic acid, and of the minerals calcium and zinc (from both the diet and supplements) were lower than recommended intakes in 13.5%, 41.5%, 19%, 66%, 61%, 78%, 77%, 24%, 34%, and 98.5% of HD patients, respectively. Inadequate intakes of energy and various nutrients are prevalent in HD patients in Tehran, Iran, which may contribute to increased morbidity and mortality in these patients. Therefore, nutrition counseling and the administration of vitamin and mineral supplements are necessary in Iranian HD patients.     

Study of the synergism effect of a binary carbon system in the nanostructure of the gas diffusion electrode (GDE) of a proton exchange membrane fuel cell

We report on the use of dual carbon supports activated charcoal (AC) and Vulcan XC-72R (VC) as catalysts for the fabrication of a gas diffusion electrode. The electrocatalytic properties for the oxygen reduction reaction were evaluated in a sulfuric acid electrolyte using polarization curves and electrochemical impedance spectroscopy. The water uptake and oxygen permeability were also obtained, as were the performances of electrodes in a membrane electrode assembly. A binary support electrode exhibits better performance than the usual single support electrode, with the best performance being obtained when the mass ratio of the two carbons is 50:50.     

A Customized Particle Swarm Method to Solve Highway Alignment Optimization Problem

Abstract: Optimizing highway alignment requires a versatile set of cost functions and an efficient search method to achieve the best design. Because of numerous highway design considerations, this issue is classified as a constrained problem. Moreover, because of the infinite number of possible solutions for the problem and the continuous search space, highway alignment optimization is a complex problem. In this study, a customized particle swarm optimization algorithm was used to search for a near‐optimal highway alignment, which is a compound of several tangents, consisting of circular (for horizontal design) and parabolic (for vertical alignment) curves. The selected highway alignment should meet the constraints of highway design while minimizing total cost as the objective function. The model uses geographical information system (GIS) maps as an efficient and fast way to calculate right‐of‐way costs, earthwork costs, and any other spatial information and constraints that should be implemented in the design process. The efficiency of the algorithm was verified through a case study using an artificial map as the study region. Finally, we applied the algorithm to a real‐world example and the results were compared with the alignment found by traditional methods.     

Recent advances in understanding the reinforcing ability and mechanism of carbon nanotubes in ceramic matrix composites

Since the discovery of carbon nanotubes (CNTs), commonly referred to as ultimate reinforcement, the main purpose for fabricating CNT–ceramic matrix composites has been mainly to improve the fracture toughness and strength of the ceramic matrix materials. However, there have been many studies reporting marginal improvements or even the degradation of mechanical properties. On the other hand, those studies claiming noticeable toughening measured using indentation, which is an indirect/unreliable characterization method, have not demonstrated the responsible mechanisms applicable to the nanoscale, flexible CNTs; instead, those studies proposed those classical methods applicable to microscale fiber/whisker reinforced ceramics without showing any convincing evidence of load transfer to the CNTs. Therefore, the ability of CNTs to directly improve the macroscopic mechanical properties of structural ceramics has been strongly questioned and debated in the last ten years. In order to properly discuss the reinforcing ability (and possible mechanisms) of CNTs in a ceramic host material, there are three fundamental questions to our knowledge at both the nanoscale and macroscale levels that need to be addressed: (1) does the intrinsic load-bearing ability of CNTs change when embedded in a ceramic host matrix?; (2) when there is an intimate atomic-level interface without any chemical reaction with the matrix, could one expect any load transfer to the CNTs along with effective load bearing by them during crack propagation?; and (3) considering their nanometer-scale dimensions, flexibility and radial softness, are the CNTs able to improve the mechanical properties of the host ceramic matrix at the macroscale when individually, intimately and uniformly dispersed? If so, how? Also, what is the effect of CNT concentration in such a defect-free composite system? Here, we briefly review the recent studies addressing the above fundamental questions. In particular, we discuss the new reinforcing mechanism at the nanoscale responsible for unprecedented, simultaneous mechanical improvements and highlight the scalable processing method enabling the fabrication of defect-free CNT-concentered ceramics and CNT-graded composites with unprecedented properties. Finally, possible future directions will be briefly presented.     

Design and Optimization of Fully Digital SQUID Based on Bi-Directional RSFQ

Bi-directional RSFQ benefits from using both positive and negative SFQ pulses to manipulate and transfer digital data. This allows more flexibility in the design of simpler circuits with enhanced performance. On the other hand, using the AC bias current, one can replace on-chip resistive current distributors with inductors. This resembles RQL logic, but in contrast to RQL, it is possible to use the well-established standard RSFQ cells in bi-directional RSFQ. These two advantages (energy-efficient computation and flexibility in design) make bi-directional RSFQ a powerful tool in next-generation supercomputers and also compatible with ultra-low-temperature quantum computers. In this work, to show the power and simplicity of circuits in bi-directional RSFQ, a fully digital SQUID based on bi-directional RSFQ is designed and optimized. The circuit we show here is a delta modulating ADC with digital integrator. The circuit has fewer Josephson junctions than other reported circuits, which makes the proposed circuit more easily realizable in available LTc and HTc technologies.     

Mechanically reliable thermoelectric (TE) nanocomposites by dispersing and embedding TE-nanostructures inside a tetragonal ZrO2 matrix: the concept and experimental demonstration in graphene oxide–3YSZ system

Novel low-dimensional thermoelectric (TE) materials suffer from poor mechanical reliability, which limits their applications, especially in mechanically harsh environments. Here, we propose a new concept, in which the novel, abundant, thermally stable TE-nanostructures are dispersed and then intimately embedded inside a protective, mechanically reliable tetragonal ZrO₂ (TZP) ceramic matrix with a low thermal conductivity. We also demonstrate an experimental proof-of-principle verification of our concept in reduced-graphene oxide (GO)–3 mol% Y₂O₃–ZrO₂ (3YSZ or 3Y-TZP) nanocomposite system. TE characterizations suggest that our protective TZP matrix does not degrade the intrinsic TE property of the reduced GO network. These preliminary results are promising and encouraging to start research on similar TZP-matrix TE-nanocomposites, which contain more effective TE-nanostructures with larger intrinsic power factors. In this regard, we propose a scalable approach for fabrication of similar dense TE-nanocomposites composed of other one-dimensional and/or two-dimensional TE-nanostructures, which involves an aqueous colloidal approach and a subsequent spark plasma sintering. These new TZP-matrix TE-nanocomposites could be used for sustainable clean power generation, especially in mechanically harsh environments with thermal/mechanical shocks and vibrations, where energy availability, reliability and durability are more important than the energy efficiency. Considering the excellent biocompatibility of TZP matrix, they could even be used inside the body to power implanted medical devices.     

Augmented ε-constraint method in multiobjective staff scheduling problem: a case study

Staff scheduling is one of the most relevant issues among production planning managers. The problem is to set up an appropriate schedule for various employees to maximize the performance measurement. There are different conflicting criteria with any scheduling problem such as cost minimization, efficiency maximization, etc. The proposed model of this paper develops a new multiobjective decision-making scheduling problem, and the resulted problem is solved using two different techniques of goal programming and augmented epsilon constraint. The implementation of the new proposed model is demonstrated with a real-world case study, and they are analyzed. The preliminary results indicate that the epsilon-constraint method somewhat performs better than goal programming technique.     

CMS scheduling problem considering material handling and routing flexibility

Cell manufacturing as an application of group technology increases the flexibility and efficiency of the production. Cell scheduling problem, one of the subjects in cell manufacturing, has not been widely studied by researchers compared with other problems in cell manufacturing. In spite of great importance of material handling in cell scheduling, it has not been paid enough attention by researches. In this paper, a new mathematical model for cell scheduling problem considering material handling time and routing flexibility is proposed. The proposed model belongs to the mixed-integer nonlinear programs (MINLP). A linearization procedure is proposed to convert the MINLP to an integer program (IP) in order to develop more powerful optimization tools. Furthermore, a simulated annealing-based heuristic is developed to solve the large-size problems.     

Investigating the acoustical properties of carbon fiber‐, glass fiber‐, and hemp fiber‐reinforced polyester composites

Wood is one of the main materials used for making musical instruments due to its outstanding acoustical properties. Despite such unique properties, its inferior mechanical properties, moisture sensitivity, and time‐ and cost‐consuming procedure for making instruments in comparison with other materials (e.g., composites) are always considered as its disadvantages in making musical instruments. In this study, the acoustic parameters of three different polyester composites separately reinforced by carbon fiber, glass fiber, and hemp fiber are investigated and are also compared with those obtained for three different types of wood specimens called poplar, walnut, and beech wood, which have been extensively used in making Iranian traditional musical instruments. The acoustical properties such as acoustic coefficient, sound quality factor, and acoustic conversion factor were examined using some non‐destructive tests based on longitudinal and flexural free vibration and also forced vibration methods. Furthermore, the water absorption of these polymeric composites was compared with that of the wood samples. The results reveal that the glass fiber‐reinforced composites could be used as a suitable alternative for some types of wood in musical applications while the carbon fiber‐reinforced composites are high performance materials to be substituted with wood in making musical instruments showing exceptional acoustical properties. POLYM. COMPOS., 35:2103–2111, 2014. © 2014 Society of Plastics Engineers