Piezoelectric characterization of a single zinc oxide nanowire using a nanoelectromechanical oscillator

In this paper, we present a nanoelectromechanical oscillator with a single semiconducting zinc oxide nanowire (ZnO) doubly clamped and suspended on two metal electrodes by which the piezoelectric property on the growth of the ZnO nanowire along the c-axis, [0001], is characterized by the resonant frequency shift of the oscillator. We report that the resonance of the nanowire oscillator can be detected in ambient air and the effective piezoelectric coefficient on the growth of a ZnO nanowire along the c-axis, [0001], is significantly larger than that of bulk (0001) ZnO.     

The operating characteristics of‘ single’ and ‘ double’ non-mechanical flow line systems

Two types of ‘ series queue ’ type flow-lines are simulated. Both are balanced, mechanically unpaced systems with provision for interstage buffer stocks. The effects of buffer capacity, service-time variability and number of stations on the output efficiency of both types of line are examined and comparisons are made.     

Towards a ‘catalyst activity map’ regarding the nucleation and growth of single walled carbon nanotubes

Quantification using scanning electron microscopy (SEM) of single walled carbon nanotubes (SWNTs) grown per unit area using a Co-Fe (50:50) catalyst system, prepared by the incorporation of the appropriate metal salts into a Spin-On Glass substrate, at 900°C. The effects of substrate, as well as catalyst precursor concentration, were investigated. SWNT growth density is maximised with a catalyst precursor concentration of ≥2.5 mM, associated with the formation of catalyst nanoparticles of a critical size for SWNT nucleation. Samples were subjected to secondary growth, using a range of H₂:CH₄ ratios to determine the optimum precursor composition. It was found that nucleation and growth stages are optimal under different conditions. Optimum conditions for nucleation resulted in >10× increase in SWNT density. Optimisation is dependent on temperature and the partial pressure of reagent gas species.     

Theoretical investigation of a semiconductor ring laser driven by Chua’s oscillator

The modeling and numerical investigation of the dynamical behavior of a semiconductor ring laser (SRL) driven by Chua’s oscillator are reported. By increasing the coupling strength between the SRL and Chua’s oscillator at a fixed bias current, the SRL exhibits an intermittency route to anti-phase chaos. However, for a fixed value of the coupling strength, we report a period-doubling route to out-of-phase and anti-phase chaos when varying one of the parameters of the Chua’s oscillator are reported. We also demonstrate that a SRL driven by the chaotic output of Chua’s oscillator generates a more complex chaos compared to the one found in a SRL subject to a sinusoidally modulated current. This new way of modulation of semiconductor lasers would not only bring a general benefit in the physical equipment and reduce their cost but could have an impact for some relevant engineering applications.     

Performance of carousel systems with ‘organ-pipe’ storage

It is well known that, for carousel systems, a dedicated storage, referred to as the ‘organ-pipe’ storage in the literature, is optimal with respect to the expected travel distance for processing successive requests. What remains unanswered is how to determine its performance, which is the motivation of this study. We consider bi-directional carousels under a ‘floating’ dwell point strategy. Two important performance measures considered are system capacity (maximum throughput) and job sojourn time. We also investigate the effect of activity skew on system performance.     

Comments on ‘vendor-managed inventory with consignment stock agreement for single vendor–single buyer under the emission-trading scheme’

Zanoni, Mazzoldi, and Jaber [Zanoni, S., L. Mazzoldi, and M. Y., Jaber. 2014. Vendor-managed inventory with consignment stock agreement for single vendor–single buyer under the emission-trading scheme. International Journal of Production Research 52 (1): 20–31] consider a joint economic lot size problem under the vendor-managed inventory with consignment stock agreement and an emission-trading scheme. They show that the total cost of the system is a jointly convex function by simply showing that every element of the Hessian is positive. Noticing this mistake, we analyse the same problem in this technical note. We first provide a closed-form solution when the production rate is given. In order to avoid a complete search over all possible production rates, we then develop an efficient continuous approximation algorithm. Computational experiment shows that the approximation algorithm is effective and efficient.     

Corrigendum of ‘A deterministic model for a repairable item inventory system with a finite repair rate’

The main purpose of this corrigendum is to indicate and rectify the same mistakes made by Schrady (1967 Schrady, D. A. 1967. “A Deterministic Inventory Model for Repairable Items.” Naval Research Logistics Quarterly 14: 391–398.[Crossref] , [Google Scholar]), Nahmias and Rivera (1979 Nahmias, S., and H. Rivera. 1979. “A Deterministic Model for a Repairable Item Inventory System with a Finite Repair Rate.” International Journal of Production Research 17: 215–221.[Taylor &; Francis Online], [Web of Science ®] , [Google Scholar]), and Teunter (2004 Teunter, R. H. 2004. “Lot-Sizing for Inventory Systems with Product Recovery.” Computers and Industrial Engineering 46: 431–441.[Crossref], [Web of Science ®] , [Google Scholar]) in the course of solving their respective models in order that subsequent researchers will not follow the same. To this end, we derive the corresponding correct global-optimal formulae for the substitution-policy model (1,?n), with infinite or finite recovery (or called repair) rate, using differential calculus, as well as providing a closed-form expression to identify the optimal positive integral value of n recovery set-ups. In addition, we also rectify the formulae and solution procedure for numerically solving the constrained non-linear programme.     

Free damped vibrations of a viscoelastic oscillator based on Rabotnov’s model

Free damped vibrations of a linear viscoelastic oscillator based on Rabotnov’s model involving one fractional parameter and several relaxation (retardation) times are investigated. The analytical solution is obtained in the form of two terms, one of which governs the drift of the system’s equilibrium position and is defined by the quasi-static processes of creep occurring in the system, and the other term describes damped vibrations around the equilibrium position and is determined by the systems’s inertia and energy dissipation. The drift is governed by an improper integral taken along two sides of the cut of the complex plane. Damped vibrations are determined by two complex conjugate roots of the characteristic equation, which are located in the left half-plane of the complex plane. The behaviour of the characteristic equation roots as function of the system’s parameters is shown in the complex plane. Dedicated to the bright memory of Academician Yury N. Rabotnov.     

Experimental investigation of the stability of a clearance‐excited rotor system with optimal parameters

Abstract

The instability caused by aerodynamic forces from blade‐tip clearance is one of the most troublesome problems found in high performance tur‐bomachinery. An optimization technique has been proposed in previous work to improve the stability of a rotor‐bearing system. In this work, the validity and the practical procedure of the optimization technique are experimentally verified and demonstrated using a rotor‐bearing system. The experimental results verify the important theoretical conclusion that the threshold of stability of a rotor‐bearing system can be significantly increased by slight modification of the rotor diameters. Two examples are given to show the detailed procedure when the proposed optimization technique is used to increase the threshold of stability of an existing rotor‐bearing system.     

When a journal is both at the ‘top’ and the ‘bottom’: the illogicality of conflating citation-based metrics with quality

Scientometrics - The ‘quality’, ‘prestige’, and ‘impact’ of a scholarly journal is largely determined by the number of citations its articles receive....     

Ultimate plasticity—the universal local fracture criterion for lifetime prediction of welded structures

A method is presented of the modeling of material fatigue destruction on the basis of a ductile fracture criterion—ultimate plasticity as a function of stress 3-axity. The criterion enables one both to determine the number of cycles until the fatigue crack initiation from the stress concentrator and to predict the character of its growth. The condition of reliability of results is high accuracy of finite element modeling with geometric and physical nonlinearity taken into account. The criterion is applicable for stress concentrators of different sharpness. The local character of the criterion makes it suitable for inhomogeneous material properties, as well as for thermally loaded structures.     

‘Examples of posing’

Abstract

EXAMPLE is proverbially better than precept. ‘Things seen are mightier than things heard’. If this be generally true in relation to manners and morals, it is very specially true in matters of art. The sight of one good picture affords more instruction than many chapters on composition and chiaroscuro or the balance of lines and tones. In relation to posing the human figure, example is an imperative element of all instruction; and variety of example is necessary to suggest varied possibilities of effect, even to fertile minds. There is no piece of advice we have more frequently urged upon the photographic student than this: lose no opportunity of studying the works of great artists and note how their effects of grace, ease, beauty and dignity are secured. Sir Joshua Reynolds has pointed out the great value of this study, and told of his own mode of pursuing it, making an accurate analysis of the proportions of light and shade present, and of their mode of distribution. The aim of this mode of study is to fill the mind with a knowledge of effects, so as to afford material for suggestion in producing original work, not with a series of memoranda to guide the memory in producing imitations. In photography, fortunately, slavish imitation of paintings is scarcely possible, for few artists have painted their pictures so that the effects all come within the range of photographic possibility.     

A novel shortened electrospun nanofiber modified with a ‘concentrated’ polymer brush

Abstract

We report the fabrication of shortened electrospun polymer fibers with a well-defined concentrated polymer brush. We first prepared electrospun nanofibers from a random copolymer of styrene and 4-vinylbenzyl 2-bromopropionate, with number-average molecular weight M_n=105 200 and weight-average molecular weight M_w=296 700 (M_w/M_n=2.82). The fibers had a diameter of 593±74 nm and contained initiating sites for surface-initiated atom transfer radical polymerization (SI-ATRP). Then, SI-ATRP of hydrophilic styrene sodium sulfonate (SSNa) was carried out in the presence of a free initiator and the hydrophobic fibers. Gel permeation chromatography confirmed that M_n and M_w/M_n values were almost the same for free polymers and graft polymers. M_n agreed well with the theoretical prediction, and M_w/M_n was relatively low (<1.3) in all the examined cases, indicating that this polymerization proceeded in a living manner. Using the values of the graft amount measured by Fourier transform infrared spectroscopy, the surface area, and M_n, we calculated the graft density σ as 0.22 chains nm^?2. This value was nearly equal to the density obtained on silicon wafers (σ=0.24 chains nm^?2), which is categorized into the concentrated brush regime. Finally, we mechanically cut the fibers with a concentrated poly(SSNa) brush by a homogenizer. With increasing cutting time, the fiber length became shorter and more homogenous (11±17 μm after 3 h). The shortened fibers exhibited excellent water dispersibility owing to the hydrophilic poly(SSNa) brush layer.     

GERT analysis of a single conveyor system†

Graphical Evaluation and Review Technique (GERT) has been applied to the analysis of the discrete conveyor model for service time distributions which are general but bounded and where there is no storage at work stations and no recirculation. The model is described by states with the Markovian property. The GERT analysis gives a visual representation of the conveyor system and useful information in the conveyor system design.     

Case study of dry mixing of δ-alumina (‘Saffil’) and silicon carbide (‘Nicalon’) fibres with a rapidly solidified Al-20Si-X powder

Dry mixing of -alumina and SiC short fibres with a powder metallurgy processed aluminium alloy was performed aiming to provide a homogeneous powder material for subsequent consolidation. The major problem was to deagglomerate the clustered fibres, realizing that fibre aspect ratio should not be sacrificed to too large an extent during this first processing step. The mixing was tackled by co-processing the materials in a cylindrical tumbler operating either with or without ceramic balls. This comes down to applying two differing intensities of mechanical action. Particle size, shape, hardness and specific surface area of the materials were measured after ball milling, which was a successful deagglomeration process only for the -alumina fibre.     

Heat transfer in “oblique” flow of a fluid with Pr≪1 over a single tube

Experimental data for the heat transfer from a single tube in a flow of fluid with Pr1 at angles of attack in the range 15–80° in a convergent channel are given.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 32, No. 6, pp. 972–974, June, 1977.     

Flexible job-shop scheduling problems with ‘AND’/‘OR’ precedence constraints

The purpose of this research is to solve flexible job-shop scheduling problems with ‘AND’/‘OR’ precedence constraints in the operations. We first formulate the problem as a Mixed-Integer Linear Program (MILP). The MILP can be used to compute optimal solutions for small-sized problems. We also developed a heuristic algorithm that can obtain a good solution for the problem regardless of its size. Moreover, we have developed a representation and schedule builder that always produces a legal and feasible solution for the problem, and developed genetic and tabu search algorithms based on the proposed schedule builder. The results of the computational experiments show that the developed meta-heuristics are very effective.     

Quality costs: a critique of some ‘economic cost of quality’ models

While carrying out a study of the collection and use of quality-related costs in manufacturing industry the authors found in the literature many notional models purporting to indicate the relationships between the major categories of quality costs and a few sets of real data. Despite being based on common principles, there are wide differences between some of the models and between the models and real data. The paper categorizes and discusses the models in the light of the research experience. It is concluded that many of the models are inaccurate and misleading and serious doubts are cast on the concept of an optimum quality level corresponding to a minimum point on the total quality-cost curve.     

Comparative analysis of the performance of a novel U-shaped ‘chasing-overtaking’ production line

Fluctuations in market demands, increased mobility of workers and changing employment practices as well as companies’ increased respect for individual differences of workers have led to the phenomenon that workers with large efficiency differences work together in the same production line in manufacturing companies. In a traditional travelling production line (TrPL), low-efficiency workers can block the work of higher efficiency workers. To increase the production capacity of a travelling line composed of workers with different efficiencies, a chasing-overtaking mechanism was established and used to achieve line production capacity and efficiency improvement. A formula to calculate the production capacity of two workers with different efficiencies was derived and validated. A simulation performed to analyse the differences between the ‘chasing-overtaking’ production line (COPL), TrPL and the classic ‘bucket brigade’ production line (BBPL) with respect to production capacity, working time utilisation and equipment utilisation demonstrated that the COPL provides good production capacity and adaptability to worker differences. Finally, the statistical analysis verified that the COPL has a higher production capacity, average worker working hour utilisation rate and equipment utilisation rate than the BBPL and TrPL.