Signal-to-noise ratio of the MEG signal after preprocessing

Background Magnetoencephalography (MEG) provides a direct measure of brain activity with high combined spatiotemporal resolution. Preprocessing is necessary to reduce contributions from environmental interference and biological noise. New method The effect on the signal-to-noise ratio of different preprocessing techniques is evaluated. The signal-to-noise ratio (SNR) was defined as the ratio between the mean signal amplitude (evoked field) and the standard error of the mean over trials. Results Recordings from 26 subjects obtained during and event-related visual paradigm with an Elekta MEG scanner were employed. Two methods were considered as first-step noise reduction: Signal Space Separation and temporal Signal Space Separation, which decompose the signal into components with origin inside and outside the head. Both algorithm increased the SNR by approximately 100%. Epoch-based methods, aimed at identifying and rejecting epochs containing eye blinks, muscular artifacts and sensor jumps provided an SNR improvement of 5–10%. Decomposition methods evaluated were independent component analysis (ICA) and second-order blind identification (SOBI). The increase in SNR was of about 36% with ICA and 33% with SOBI. Comparison with existing methods No previous systematic evaluation of the effect of the typical preprocessing steps in the SNR of the MEG signal has been performed. Conclusions The application of either SSS or tSSS is mandatory in Elekta systems. No significant differences were found between the two. While epoch-based methods have been routinely applied the less often considered decomposition methods were clearly superior and therefore their use seems advisable.

Using interior point algorithms for the solution of linear programs with special structural features

Linear Programming (LP) is a powerful decision making tool extensively used in various economic and engineering activities. In the early stages the success of LP was mainly due to the efficiency of the simplex method. After the appearance of Karmarkar's paper, the focus of most research was shifted to the field of interior point methods. The present work is concerned with investigating and efficiently implementing the latest techniques in this field taking sparsity into account. The performance of these implementations on different classes of LP problems is reported here. The preconditional conjugate gradient method is one of the most powerful tools for the solution of the least square problem, present in every iteration of all interior point methods. The effect of using different preconditioners on a range of problems with various condition numbers is presented. Decomposition algorithms has been one of the main fields of research in linear programming over the last few years. After reviewing the latest decomposition techniques, three promising methods were chosen the implemented. Sparsity is again a consideration and suggestions have been included to allow improvements when solving problems with these methods. Finally, experimental results on randomly generated data are reported and compared with an interior point method. The efficient implementation of the decomposition methods considered in this study requires the solution of quadratic subproblems. A review of recent work on algorithms for convex quadratic was performed. The most promising algorithms are discussed and implemented taking sparsity into account. The related performance of these algorithms on randomly generated separable and non-separable problems is also reported.

Solutions of boundary element equations by a flexible elimination process

Abstract not available

A Distributed algorithm for 1-D non-linear heat conduction with an unknown point source

Abstract not available

Comparison of three algorithms for nonlinear metal cutting problems

This paper compares three alternative numerical algorithms applied to a nonlinear metal cutting problem. One algorithm is based on an explicit method and the other two are implicit. Domain decomposition (DD) is used to break the original domain into subdomains, each containing a properly connected, well-formulated and continuous subproblem. The serial version of the explicit algorithm is implemented in FORTRAN and its parallel version uses MPI (Message Passing Interface) calls. One implicit algorithm is implemented by coupling the state-of-the-art PETSc (Portable, Extensible Toolkit for Scientific Computation) software with in-house software in order to solve the subproblems. The second implicit algorithm is implemented completely within PETSc. PETSc uses MPI as the underlying communication library. Finally, a 2D example is used to test the algorithms and various comparisons are made.

A single-code software model for multiphysics analysis-engine on parallel and distributed computers with the PHYSICA toolkit

Abstract not available

Communication latency hiding in a parallel conjugate gradient method

Abstract not available

Sound generation by vortex-blade interactions

Abstract not available

The gender wage gap in the public and private sectors in Bangladesh

The gender wage gap is well studied in developed countries; however, recently it has generated much interest in developing countries. This thesis addresses three issues regarding the gender wage gap in Bangladesh. Firstly, it explores the wage determinants for formal public and private sector employees in Bangladesh and examines the gender pay gap. This is the first time different decomposition methods have been used to compare the sources of the gender wage gap as well as any potential discrimination effect in the formal sector of the Bangladeshi labour market. These decomposition methods are: the original Oaxaca (1973) and Blinder (1973) decomposition methods, the Neumark (1988), Cotton (1988), and Reimers (1983) methods, and the extended Oaxaca method including both the employment selection and the double selection correction in the wage equation. In addition to mentioned methods, to quantify the gender wage gap in monetary terms, a recently developed ‘simulated change’ approach by Olsen and Walby (2004) is also applied for the first time to the Bangladeshi data. By using the Labour Force Survey 2005-06, BBS (LFS 2005-06) data results show formal sector female employees earn about 32.1 per cent less than their male counterparts. Without considering the selection correction, a large range of human capital, demographic and labour market related variables are explained less than half of the total gender wage gap (21 to 46 per cent of the total wage gap) and the major part of the wage gap is unexplained (54 to 79 per cent of the total wage gap). This could partly be attributed to discrimination. Using the double selection correction method, the decomposition results changed where a small part of the wage gap was explained by the measured characteristics (only nine per cent of the total wage gap) and a major part is attributed to the discrimination and selection effect. The selection effect also reveals that exclusion of the double selection correction might lead to an overestimation of the gender wage gap in the formal sector of Bangladesh. In addition, results based on the Olsen and Walby (2004) simulation method show that, if the other characteristics of male and female employees were similar, ‘being female’ is sufficient, to generate significantly lower wages than males in the formal sector. If females in the workplace are treated as males, without considering any other endowment increases, females could increase their earnings by 4095.3 Taka1 per year. Results also indicate that not only endowment differences in human capital and work experience related variables were important, but discrimination appears to play a significant role in the total wage gap throughout the formal sector of the Bangladeshi labour market. Secondly, the study investigates whether public sector employees enjoyed a wage premium or not, compared to the private sector and whether the gender wage gap is greater in the public sector. In addition, the research considered whether there was an impact from the inclusion of the different selection correction terms in the wage equation. In Bangladesh, public sector employees have, on average, a 60 per cent wage premium over the private sector. Using both the original Oaxaca and the extended Oaxaca methods, where selection effect is partly captured by both explained and unexplained components, and using the public sector wage structure as the basis of the non-discriminatory wage structure, these methods revealed a considerably larger portion of explained (72 - 93 per cent of the total wage gap) and a smaller portion of unexplained part of the wage gap. However, if the selection correction is considered as another component of the decomposition outcome then the major portion of the total public and private sectors wage gap is justified (explained) by the effect of the selection correction and unexplained factors. Furthermore, a large part of the wage premium exists in favour of public sector female employees compared to males and the gender wage gap is lower in the public sector than the private sector. Finally, this study compares the gender wage gap of five different occupations. The gender wage gap is associated with labour market rigidities where one of the important factors is occupational segregation where females are disproportionately distributed in occupations resulting in lower earnings. The largest gender wage gap was found in agriculture, forestry, fisheries, production and transport labour jobs (56.4 per cent) and the lowest in the professional, technical administrative and managerial jobs (22.1 per cent). Substantial differences are found in the size of the endowment gap across occupations and larger variations occurred in the adjusted wage gap which varied from 21.4 per cent in sales and service occupations, to 100 per cent in professional and technical jobs (the highest). This too can be partly explained by discrimination. A reduction in the gender wage gap is expected not only to increase national income, but also to reduce poverty and lead to better outcomes for future generations. National policy should aim to reduce the gender wage gap and achieve gender wage equality in the formal sector; for example through a targeted program to remove the gender differences in education and to reduce the skill difference, with a better child care policy to encourage labour force retention and increased labour market experience for female employees, with anti-discriminatory policies and the enforcement of existing antidiscrimination policies, and a more equal distribution of males and females across occupations.

Applying Platform Design to Improve Product-Service Systems Collaborative Development

Part 3: Product-Service Systems

Diferencias regionales en las estructuras de ingresos laborales en Colombia

Dada la persistencia de las diferencias en ingresos laborales por regiones en Colombia, el presente artículo propone cuantificar la magnitud de este diferencial que es atribuida a la diferencia en estructuras de mercado laboral, entendiendo esta última como la diferencia en los retornos a las características de la fuerza laboral. Para ello se propone el uso de un método de descomposición del tipo Oaxaca- Blinder y se compara a Bogotá –la ciudad con mayores ingresos laborales- con otras ciudades principales. Los resultados obtenidos al conducir el ejercicio de descomposición muestran que las diferencias en estructura están a favor de Bogotá y que estas explican más de la mitad de la diferencia total, indicando que si se quieren reducir las disparidades de ingresos laborales entre ciudades no es suficiente con calificar la fuerza laboral y que es necesario indagar por las causas que hacen que los retornos a las características difieran entre ciudades.

Two complementary molecular energy decomposition schemes: the Mayer and Ziegler-Rauk methods in comparison

In the present paper we discuss and compare two different energy decomposition schemes: Mayer's Hartree-Fock energy decomposition into diatomic and monoatomic contributions [Chem. Phys. Lett. 382, 265 (2003)], and the Ziegler-Rauk dissociation energy decomposition [Inorg. Chem. 18, 1558 (1979)]. The Ziegler-Rauk scheme is based on a separation of a molecule into fragments, while Mayer's scheme can be used in the cases where a fragmentation of the system in clearly separable parts is not possible. In the Mayer scheme, the density of a free atom is deformed to give the one-atom Mulliken density that subsequently interacts to give rise to the diatomic interaction energy. We give a detailed analysis of the diatomic energy contributions in the Mayer scheme and a close look onto the one-atom Mulliken densities. The Mulliken density ρA has a single large maximum around the nuclear position of the atom A, but exhibits slightly negative values in the vicinity of neighboring atoms. The main connecting point between both analysis schemes is the electrostatic energy. Both decomposition schemes utilize the same electrostatic energy expression, but differ in how fragment densities are defined. In the Mayer scheme, the electrostatic component originates from the interaction of the Mulliken densities, while in the Ziegler-Rauk scheme, the undisturbed fragment densities interact. The values of the electrostatic energy resulting from the two schemes differ significantly but typically have the same order of magnitude. Both methods are useful and complementary since Mayer's decomposition focuses on the energy of the finally formed molecule, whereas the Ziegler-Rauk scheme describes the bond formation starting from undeformed fragment densities

Study of cyclohexanol decomposition reaction over the ferrospinels, A1−xCuxFe2O4 (A=Ni or Co and x=0, 0.3, 0.5, 0.7 and 1), prepared by ‘soft’ chemical methods

Preparation of simple and mixed ferrospinels of nickel, cobalt and copper and their sulphated analogues by the room temperature coprecipitation method yielded fine particles with high surface areas. Study of the vapour phase decomposition of cyclohexanol at 300 °C over all the ferrospinel systems showed very good conversions yielding cyclohexene by dehydration and/or cyclohexanone by dehydrogenation, as the major products. Sulphation very much enhanced the dehydration activity over all the samples. A good correlation was obtained between the dehydration activities of the simple ferrites and their weak plus medium strength acidities (usually of the Brφnsted type) determined independently by the n-butylamine adsorption and ammonia-TPD methods. Mixed ferrites containing copper showed a general decrease in acidities and a drastic decrease in dehydration activities. There was no general correlation between the basicity parameters obtained by electron donor studies and the ratio of dehydrogenation to dehydration activities. There was a leap in the dehydrogenation activities in the case of all the ferrospinel samples containing copper. Along with the basic properties, the redox properties of copper ion have been invoked to account for this added activity.