Sigma Theory Research Articles

Absorbing new knowledge in small and medium-sized enterprises: A multiple case analysis of Six Sigma

The primary aim of this article is to critically analyse the development of Six Sigma theory and practice within small and medium-sized enterprises (SMEs) using a multiple case study approach. The article also explores the subsequent development of Lean Six Sigma as a means of addressing the perceived limitations of the efficacy of Six Sigma in this context. The overarching theoretical framework is that of absorptive capacity, where Six Sigma is conceptualized as new knowledge to be absorbed by smaller firms. The findings from a multiple case study involving repeat interviews and focus groups informed the development of an analytical model demonstrating the dynamic underlying routines for the absorptive capacity process and the development of a number of summative propositions relating the characteristics of SMEs to Six Sigma and Lean Six Sigma implementation.

Application of Six Sigma Method in Improving the Quality of the Spiral Bevel Gear

According to the quality problems in one gear enterprise, the DMAIC method which is the core application of the six sigma theory is used to improve the quality of the spiral bevel gear, and the quality data is analyzed by using Minitab software. Firstly, the quality problem is defined in accordance with the DMAIC procedures and the main reasons for quality problems in spiral bevel gears are determined. Secondly, measurement systems and process capability are analyzed. Then, we set a specific program for the improvements for the main causes of quality problems. Through the successful implementation of this project, the quality of spiral bevel gears is greatly improved, and the production cost is greatly reduced. The effect is very significant.

Application of Six Sigma Method in Quality Improvement of Hard Alloy Gear Circular Saw Blades

According to the quality problems in one saw blade enterprise, six Sigma theory and method are used to improve the quality o f saw blades, and establish the 6σ DMAIC improvement model. Six sigma DMIAC procedures are applied to define the problems and set at target for improvement, the main quality are investigated， and measurement systems and process capability are evaluated. Then, we set a specific program for the improvements. At last, the project is successfully implemented, result shows that failure rate reduced to 0.3%, DPMO dropped below 160, and the process capability is improved largely.

Combining a human performance model and a Six Sigma model to assess performance in a military environment

Military officials continually search for improvements in processes that focus on high-performance outcomes. This qualitative study investigated process improvements of two departments within the Naval Diving and Salvage Training Center (the Security Department and the Testing Department) by assessing performance levels of the two departments using a combinatorial model from human performance theory and Six Sigma theory. Study findings produced strong empirical evidence with specific recommendations for initiating cost-effective interventions for improvements. The Behavior Engineering Model was used to identify possible solutions to post-training performance gaps identified during the evaluation.

Sigma theory and twisted conjugacy classes

Using Sigma theory we show that for large classes of groups G there is a subgroup H of finite index in Aut.G/ such that for ’ 2 H the Reidemeister number R.’/ is infinite. This includes all finitely generated nonpolycyclic groups G that fall into one of the following classes: nilpotent-by-abelian groups of type FP1; groups G= G 00 of finite Prufer rank; groups G of type FP2 without free nonabelian subgroups and with nonpolycyclic maximal metabelian quotient; some direct products of groups; or the pure symmetric automorphism group. Using a different argument we show that the result also holds for 1-ended nonabelian nonsurface limit groups. In some cases, such as with the generalized Thompson’s groups Fn;0 and their finite direct products, H D Aut.G/.

Research on the Intelligent Quality Management System of Supply Chains Based on Six Sigma Theory

Aiming at the features of the common Supply Chain quality management, an intelligent Supply Chain quality management system based on Six Sigma theory was proposed. The Six Sigma workflow, organizational framework and system goal were adopted in the system overall design, and some traditional Six Sigma tools were integrated into the system. A sub-system for expansive intelligent Six Sigma expert model was designed, which solved the problem of knowledge acquisition in the general expert system and endowed the system with the characteristic of local intelligence.

DNA Depletion by Precipitation in the Purification of Cell Culture‐Derived Influenza Vaccines

AbstractA pilot study for the purification of cell culture‐derived human influenza virus is presented, which focuses on the early removal of DNA by precipitation. Strains of influenza virus were propagated using Madin Darby canine kidney cells as a host. A harvesting time of about 72 h postinfection was chosen to minimize the level of impurities (host cell DNA and protein). Cell culture supernatant was clarified by centrifugation and the performance of this operation was characterized on the basis of Sigma theory. An average clarification efficiency of 93 % (based on turbidity) and a product yield of 85 % (based on hemagglutination activity) were obtained at a load of 1.6 · 10–8 m s–1. Furthermore, the applicability of Sigma theory for scale‐up studies using two different laboratory centrifuges was verified. Selective precipitation of DNA was achieved by the addition of polyethyleneimine (PEI). Full factorial design was applied to optimize selectivity considering pH, ionic strength, and the concentration and molecular weight of PEI. Under optimized conditions, treatment with PEI resulted in a reduction of DNA to 15 % of the initial amount, while 86 % of virions (based on neuraminidase activity) were recovered. The subsequent concentration of virions was realized by tangential‐flow ultrafiltration. Recovery based on hemagglutination activity was determined to 63 % on average. Including the previous precipitation step, overall reduction in DNA after tangential‐flow ultrafiltration was 500‐fold. These results indicate that the suggested unit operations are suited for the early depletion of DNA in cell culture‐derived influenza vaccine production.

Normal approximation through data replication when estimating DisPMO, DePMO, left‐side and right‐side Sigma levels from non‐normal data

PurposeThis paper seeks to present a way of estimating DisPMO, DePMO, left‐side and right‐side Sigma levels (as the “mutations” of DPMO and Sigma level when applied on customer satisfaction measurements), where all critical attributes (CTQs) contain data sets that are non‐normally distributed.Design/methodology/approachThe calculation of DisPMO, DePMO, left‐side and right‐side Sigma levels is based on dynamic‐multiple CTQs without the need for assuming 1.5 Sigma shift from the mean. Using step‐wise multiple regression, CTQs are then the attributes that significantly influence overall customer satisfaction. This further developed method no longer takes normality assumption for granted, which means that, prior to calculating DisPMO, DePMO, left‐side and right‐side Sigma levels, the data should be proven as being normally distributed. To fulfil the assumption of normality, the primary data are being “replicated” by first generating random numbers that follow normal standard distribution and then adjusting (re‐calculating) these random numbers with the mean, standard deviation, and the skewness of the primary data. Simulation technique is then applied to generate a larger amount of secondary data as the basis for estimating DisPMO, DePMO, left‐side and right‐side Sigma levels.FindingsThe application of the method in a Swedish house‐building construction project suggests that: the use of multiple CTQs may reduce the risk for under‐/overestimation of Sigma levels, and DisPMO and DePMO are each other's “mirror” and both of them should be considered when calculating Sigma levels. The calculated Sigma levels suggest that the developer's performance is still quite far below Six Sigma level of performance.Originality/valueUsing the replica of the primary data as a way of approaching normality may be regarded as the main contribution of the paper in addressing one of the challenges in Six Sigma theory.

Exclusion and Discrimination as Sources of Inter-Ethnic Inequality in Peru

According to the 2003 National Household Survey, mean labour income for an indigenous worker is only 56% of that for a non-indigenous worker. Studies of ethnic discrimination in Peru’s labour markets generally find that discrimination is too low to explain inequalities of this magnitude. However, Sigma Theory (Figueroa 2003) predicts that social exclusion is a source of inter-ethnic inequality, and that has not been empirically tested. The primary aim of this paper is to fill this gap by estimating the extent to which exclusion and discrimination contribute to income inequality. Hurdle models are used to tackle down econometric endogeneity of years of schooling and truncation-at-zero of incomes. The results imply that exclusion plays a stronger role on inequality than discrimination: without exclusion, the Gini of labour income would decrease from 0.64 to 0.45, and without discrimination it would be reduced to 0.50.

An empirical investigation into Six Sigma critical success factors

This pilot research explores the critical success factors of Six Sigma to gain insight into the gaps between Six Sigma theory and execution, and to understand the primary drivers of financial improvements. The findings demonstrate the key aspects that seem to be consistent among Six Sigma organisations. Results show organisations cite Six Sigma for cost reduction, notoriety of its success and increased revenues. Chi-square analyses indicate gaps exist between theory and actual practice across the three critical success factors of team selection, project selection and project implementation. A larger percent of respondents agree on the criticality of key tasks/issues, yet fewer companies execute them in practice. Regression results demonstrate the factors of team selection and project selection significantly impact the financial improvement performance of the responding organisations. These results are beneficial for researchers investigating Six Sigma, business leaders considering its implementation and for existing companies seeking to achieve even greater improvement gains.

Using CFD To Understand How Flow Patterns Affect Retention of Cell-Sized Particles in a Tubular Bowl Centrifuge

Sigma theory is commonly used to predict the conditions that result in half of the entering particles being retained within a continuous-flow centrifuge. In this research, a 2D computational fluid dynamics (CFD) model of flow through a tubular bowl centrifuge (Sharples, 5 cm radius) was developed with Fluent software. A volume-of-fluid (VOF) approach was used for most of the simulations to track the motion of the liquid and gas phases, because the location of the gas/liquid interface depends on the centrifuge operating conditions. The CFD results indicate that the assumptions of plug flow and rigid body motion, which are fundamental assumptions of Sigma theory, were not valid for the conditions tested (700 < Rez < 3500 and 1000 < speed (rpm) < 3000). The average interfacial axial velocities (Viz) were 6−18 times greater than the plug-flow velocity (Vpf), and the average interfacial swirl velocities (Viθ) were 0.12−0.41 of that corresponding to rigid body motion (Vrbm). Despite these differences, the CFD r...

Spontaneous breaking of global and local symmetries in six-dimensional Einstein-Maxwell- sigma theory.

Higher-winding-number solutions of the nonlinear \ensuremath{\sigma} field are used to break the global as well as local symmetry of SU(2) in a six-dimensional gravity theory coupled with the U(1) Maxwell and \ensuremath{\sigma} field. The masses of three gauge bosons are split and their ratios of masses are obtained for various winding numbers. The low-lying states of this model not of Planck scale are a scalar triplet, the graviton, photon, and low-mass gauge bosons.