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Important statistical variations are likely to appear in the propagation of surface plasmon polariton waves atop the surface of graphene sheets, degrading the expected performance of real-life THz applications. This paper aims to introduce an efficient numerical algorithm that is able to accurately and rapidly predict the influence of material-based uncertainties for diverse graphene configurations.

Initially, the surface conductivity of graphene is described at the far infrared spectrum and the uncertainties of its main parameters, namely, the chemical potential and the relaxation time, on the propagation properties of the surface waves are investigated, unveiling a considerable impact. Furthermore, the demanding two-dimensional material is numerically modeled as a surface boundary through a frequency-dependent finite-difference time-domain scheme, while a robust stochastic realization is accordingly developed.

The mean value and standard deviation of the propagating surface waves are extracted through a single-pass simulation in contrast to the laborious Monte Carlo technique, proving the accomplished high efficiency. Moreover, numerical results, including graphene’s surface current density and electric field distribution, indicate the notable precision, stability and convergence of the new graphene-based stochastic time-domain method in terms of the mean value and the order of magnitude of the standard deviation.

The combined uncertainties of the main parameters in graphene layers are modeled through a high-performance stochastic numerical algorithm, based on the finite-difference time-domain method. The significant accuracy of the numerical results, compared to the cumbersome Monte Carlo analysis, renders the featured technique a flexible computational tool that is able to enhance the design of graphene THz devices due to the uncertainty prediction.

The purpose of this paper is to rigorously determine the tensile properties of a selective laser sintering (SLS) material. Emphasis was placed on the anisotropy and inhomogeneity of the material, the repeatability of the SLS process, and the effect of age (actually moisture absorption) on the material properties.

Two builds of 144 dogbone tensile specimens each were tested, with 18 specimens stored for 43 days in a non‐desiccated environment before testing. Specimens were distributed throughout the build volume and aligned with the apparatus' principal axes. Tensile properties were treated statistically, using the t‐test to determine the differences between various samples.

The material was transversely isotropic in Young's modulus and strain to failure, and generally orthotropic in ultimate tensile strength. The material was inhomogeneous throughout the build volume and affected by age, with a 57 per cent reduction in University of Technology after 43 days (the changes in properties were suggested to be due to moisture absorption). Properties varied by up to 25 per cent from build‐to‐build with no change in nominal process parameters.

It was not possible to confirm the “ageing” effect was caused by moisture absorption, and further work is suggested in this area. The causes of inhomogeneity and the effect of re‐coater action should also be studied further.

This is the most complete study of an SLS material's mechanical properties to date. The statistical analyses used further allow increased confidence in the conclusions drawn. This is also the only study to use cross‐fill scanning to produce specimens, and, therefore, isolate the effect of the re‐coater action.

Overview All organisations are, in one sense or another, involved in operations; an activity implying transformation or transfer. The major portion of the body of knowledge concerning operations relates to production in manufacturing industry but, increasingly, similar problems are to be found confronting managers in service industry. It is only in the last decade or so that new technology, involving, in particular, the computer, has encouraged an integrated view to be taken of the total business. This has led to greater recognition being given to the strategic potential of the operations function. In order to provide greater insight into operations a number of classifications have been proposed. One of these, which places operations into categories termed factory, job shop, mass service and professional service, is examined. The elements of operations management are introduced under the headings of product, plant, process, procedures and people.

Process capability studies are of great use to the quality practitioner, but quite often, processes with excellent capability indices have a high percentage of nonconformance. One of the major reasons for this is that the studies do not take the variation in the raw materials into account. For this study, we propose a method that allows for variations in material properties to be considered as a part of the capability study. Unlike long‐term capability studies, this method requires only a short period of time. This method has been successfully applied to an injection molding process at Cascade Engineering, Inc. in Grand Rapids, Michigan.

This paper addresses two fundamental issues with regard to the production of printed circuit boards (PCBs). First, the paper presents a statistically‐based, four‐phase strategy aimed at better organising and facilitating the characterisation of a manufacturing process. The fact that the case study addresses copper plating thickness of PCBs is secondary to the characterisation strategy. In this sense, the strategy is universal by nature. Second, the paper provides analytical insight into a new statistical methodology aimed at establishing coupon‐to‐board correlation. The general concepts surrounding these two issues are embodied within the given PCB case study. Essentially, the case analysis systematically progresses through all four phases of the parameter characterisation strategy, highlighting the key aspects of each phase. In addition, the aforementioned technique for assessing coupon‐to‐board correlation is given substantiative discussion. However, it should be pointed out that a thorough narration pertaining to many of the statistical and engineering details of the case analysis has been deliberately omitted for the sake of brevity and reading ease. As a result of such considerations, it is assumed that the reader has a working knowledge of descriptive and inferential statistics, as well as experiment design. The benefit of this approach is simple—focus is easily given to the analytical strategy and order of execution without the usual clouding imposed by mathematical explanations.

This study aims to design a femoral component with minimum volume and maximum safety coefficient. Total knee prosthesis is a well-established therapy in arthroplasty applications. And in particular, with respect to damaged or weakened cartilage, new prostheses are being manufactured from bio-materials which are compatible with the human body to replace these damages. A new universal method (design method requiring optimum volume and safety [DMROVAS]) was propounded to find the optimum design parameters of tibial component.

The design montage was analyzed via the finite element method (FEM). To ensure the stability of the prosthesis, the maximum stress angle and magnitude of the force on the knee were taken into consideration. In the analysis process, results revealed two different maximum stress areas which were supported by case reports in the literature. Variations of maximum stress, safety factor and weight were revealed by FEM analysis, and ANOVA was used to determine the F force percentage for each of the design parameters.

Optimal design parameter levels were chosen for the individual’s minimum weight. Stress maps were constructed to optimize design choices that enabled further enhancement of the design models. The safety factor variation (SFV) of 5.73 was obtained for the volume of 39,219 mL for a region which had maximum stress. At the same time, for a maximum SFV and at the same time an average weight, values of 37,308 mL and 5.8 for volume and SFV were attained, respectively, using statistical methods.

This proposed optimal design development method is new and one that can be used for many biomechanical products and universal industrial designs.

Allyn Young′s lectures, as recorded by the young Nicholas Kaldor, survey the historical roots of the subject from Aristotle through to the modern neo‐classical writers. The focus throughout is on the conditions making for economic progress, with stress on the institutional developments that extend and are extended by the size of the market. Organisational changes that promote the division of labour and specialisation within and between firms and industries, and which promote competition and mobility, are seen as the vital factors in growth. In the absence of new markets, inventions as such play only a minor role. The economic system is an inter‐related whole, or a living “organon”. It is from this perspective that micro‐economic relations are analysed, and this helps expose certain fallacies of composition associated with the marginal productivity theory of production and distribution. Factors are paid not because they are productive but because they are scarce. Likewise he shows why Marshallian supply and demand schedules, based on the “one thing at a time” approach, cannot adequately describe the dynamic growth properties of the system. Supply and demand cannot be simply integrated to arrive at a picture of the whole economy. These notes are complemented by eleven articles in the Encyclopaedia Britannica which were published shortly after Young′s sudden death in 1929.

Additive manufacturing (AM) methods such as material extrusion (ME) are becoming widely used by engineers, designers and hobbyists alike for a wide variety of applications. Successfully manufacturing objects using ME three-dimensional printers can often require numerous iterations to attain predictable performance because the exact mechanical behavior of parts fabricated via additive processes are difficult to predict. One of that factors that contributes to this difficulty is the wide variety of ME feed stock materials currently available in the marketplace. These build materials are often sold based on their base polymer material such as acrylonitrile butadiene styrene or polylactic acid (PLA), but are produced by numerous different commercial suppliers in a wide variety of colors using typically undisclosed additive feed stocks and base polymer formulations. This paper aims to present the results from an experimental study concerned with quantifying how these sources of polymer variability can affect the mechanical behavior of three-dimensional printed objects. Specifically, the set of experiments conducted in this study focused on following: several different colors of PLA filament from a single commercial supplier to explore the effect of color additives and three filaments of the same color but produced by three different suppliers to account for potential variations in polymer formulation.

A set of five common mechanical and material characterization tests were performed on 11 commercially available PLA filaments in an effort to gain insight into the variations in mechanical response that stem from variances in filament manufacturer, feed stock polymer, additives and processing. Three black PLA filaments were purchased from three different commercial suppliers to consider the variations introduced by use of different feed stock polymers and filament processing by different manufacturers. An additional eight PLA filaments in varying colors were purchased from one of the three suppliers to focus on how color additives lead to property variations. Some tests were performed on unprocessed filament samples, while others were performed on objects three-dimensional printed from the various filaments. This study looked specifically at four mechanical properties (Young’s modulus, storage modulus, yield strength and toughness) as a function of numerous material properties (e.g. additive loading, molecular weight, molecular weight dispersity, enthalpy of melting and crystallinity).

For the 11 filaments tested the following mean values and standard deviations were observed for the material properties considered: p_a = 1.3 ± 0.9% (percent additives), M_w = 98.6 ± 16.4 kDa (molecular weight), Ð = 1.33 ± 0.1 (molecular weight dispersity), H_m = 37.4 ± 7.2 J/g (enthalpy of melting) and = 19.6 ± 2.1% (crystallinity). The corresponding mean values and standard deviations for the resulting mechanical behaviors were: E = 2,790 ± 145 MPa (Young’s modulus), E’ = 1,050 ± 125 MPa (storage modulus), S_y = 49.6 ± 4.93 MPa (yield strength) and U_t = 1.87 ± 0.354 MJ/m^³ (toughness). These variations were observed in filaments that were all manufactured from the same base polymer (e.g. PLA) and are only different in terms of the additives used by the manufacturers to produce different colors or different three-dimensional printing performance. Unfortunately, while the observed variations were significant, no definitive strong correlations were found between these observed variations in the mechanical behavior of the filaments studied and the considered material properties.

These variations in mechanical behavior and material properties could not be ascribed to any specific factor, but rather show that the mechanical of three-dimensional printed parts are potentially affected by variations in base polymer properties, additive usage and filament processing choices in complex ways that can be difficult to predict.

These results emphasize the need to take processing and thereby even filament color, into account when using ME printers, they emphasize the need for designers to use AM with caution when the mechanical behavior of a printed part is critical and they highlight the need for continued research in this important area. While all filaments used were marked as PLA, the feedstock materials, additives and processing conditions created significant differences in the mechanical behavior of the printed objects evaluated, but these differences could not be accurately and reliably predicted as function of the observed material properties that were the focus of this study.

The testing methods used in the study can be used by engineers and creators alike to better analyze the material properties of their filament printed objects, to increase success in print and mechanical design. Furthermore, the results clearly show that as AM continues to evolve and grow as a manufacturing method, standardization of feedstock processing conditions and additives would enable more reliable and repeatable printed objects and would better assist designers in effectively implementing AM methods.

In class action antitrust litigation, the standards for acceptable economic analysis at class certification have continued to evolve. The most recent event in this evolution is the United States Supreme Court’s decision in Comcast Corp. v. Behrend, 133 S. Ct. 1435 (2013). The evolution of pre-Comcast law on this topic is presented, the Comcast decision is thoroughly assessed, as are the standards for developing reliable economic analysis. This article explains how economic evidence of both antitrust liability and damages ought to be developed in light of the teachings of Comcast, and how liability evidence can be used by economists to support a finding of common impact for certification purposes. In addition, the article addresses how statistical techniques such as averaging, price-dispersion analysis, and multiple regressions have and should be employed to establish common proof of damages.

That part of human behaviour which is not rigidly determined by external constraints can be considered as a sequence of more or less free choices. One can talk of a choice only if it is one of several alternatives, and of a free choice only in so far as it is not determined by conditions over which the individuals have no control. Moreover, we recognise an alternative only if it is actually elected by at least a fraction of a population. This leads to the concept of statistical freedom. Postulates are formulated which must be satisfied by any numerical measures of statistical freedom, and certain mathematical expressions are proposed which are shown to conform to these postulates. Statistical freedom has two fundamental features, which appear as factors in its numerical measure: diversity and independence. The measures of diversity and independence are derived in the first place front a certain model of society, but once they are obtained, the model is discarded, and the statistical coefficients are justified by their mathematical properties. Safeguards against arbitrary manipulation of statistical material are discussed, and the potential use of the new measures is illustrated by application to the problem of choice of profession.