Mixed Path Research Articles

Perturbation theory for the diffusion equation by use of the moments of the generalized temporal point-spread function III Frequency-domain and time-domain results

We study the performance of a previously proposed perturbation theory for the diffusion equation in frequency and time domains as they are known in the field of near infrared spectroscopy and diffuse optical tomography. We have derived approximate formulas for calculating higher order self- and mixed path length moments, up to the fourth order, which can be used in general diffusive media regardless of geometry and initial distribution of the optical properties, for studying the effect of absorbing defects. The method of Padé approximants is used to extend the validity of the theory to a wider range of absorption contrasts between defects and background. By using Monte Carlo simulations, we have tested these formulas in the semi-infinite and slab geometries for the cases of single and multiple absorbing defects having sizes of interest (d=4-10 mm, where d is the diameter of the defect). In frequency domain, the discrepancy between the two methods of calculation (Padé approximants and Monte Carlo simulations) was within 10% for absorption contrasts Deltamu(a)<or=0.2 mm(-1) for alternating current data, and usually to within 1 degrees for Deltamu(a)<or=0.1 mm(-1) for phase data. In time domain, the average discrepancy in the temporal range of interest (a few nanoseconds) was 2%-3% for Deltamu(a)<or=0.06 mm(-1). The proposed method is an effective fast forward problem solver: all the time-domain results presented in this work were obtained with a computational time of less than about 15 s with a Pentium IV 1.66 GHz personal computer.

Dynamics and Cooperative Object Manipulation Control of Suspended Mobile Manipulators

Dynamics and control of mobile manipulators is obviously a more challenging problem compared to fixed-base robots. Including a suspension system for these mobile platforms increases their maneuverability, but considerably adds to their complexity. In this paper, a suspended wheeled mobile platform with two 6-DOF Puma-type manipulators is used to manipulate an object along a given path. To apply a model-based control algorithm, it is required to have an explicit dynamics model for such highly nonlinear system. This model should be as concise as possible to include fewer mathematical calculations for online computations. Therefore in this paper, a detailed set of dynamics equations for a multiple arm wheeled mobile platform equipped with an effective suspension system is presented. The method is based on the concept of Direct Path Method (DPM), which is extended here for such challenging type of robots. The obtained dynamics model is then verified with a dynamical analysis study using software ADAMS. Then, Natural Orthogonal Complement Method is used to include the non-holonomic constraint of the wheeled platform in a more concise dynamics model. Next, an impedance control law is applied for cooperative manipulation of an object by the two manipulators. The obtained results for a suspended wheeled platform equipped with two 6-DOF Puma-type manipulators reveal a successful performance for moving an object along a mixed circular-straight path, even in the presence of unexpected disturbing forces, system/end-effector flexibility and impacts due to contact with an obstacle.

高偏心衝撃荷重を受ける三点曲げ試験片の破壊挙動の初期き裂面接触を考慮した移動有限要素解析

Crack propagation path prediction is very important to prevent critical industrial accidents. However it is considered that the crack propagation path prediction is very difficult in occasion of High Eccentric Impact Loading. In this study, dynamic fracture path prediction under eccentric load that assumed the heavier mixed mode dynamic fracture was simulated by Moving Finite Element Method Based on Delaunay Automatic Triangulation. The generation phase and mixed phase path prediction mode simulations were carried out in these fracture simulations. The Penalty method was incorporated in order to consider the crack surface contact effects. The predicted fracture path using the Penalty method is agreed with experimental fracture path.

Stress‐suppressing model explains mediation of food insecurity in the effect of poverty reduction program on wellbeing and distress

Poverty alleviation programs for the extreme poor improve participants' economic status and may also affect other important outcomes that are seldom evaluated. A program targeted to the extreme poor by BRAC, a development organization in Bangladesh, has been successful in significantly alleviating extreme poverty and improving wellbeing, and reducing distress and food insecurity. We hypothesized that reduced food insecurity played a major role in mediating the effect of the program on wellbeing and distress. A non‐equivalent pre‐ and post‐test quasi‐experimental design was used to test the hypotheses. Linear mixed random‐intercept models and path analysis was used to test the hypothesis. Data were collected from a random sample of 209 women (110 program and 99 control) across 27 villages of 3 northern districts in 2002 and 2005‐2006. Reduced food insecurity was found to be a substantial mediator of the program's effect on other outcomes. Approximately 53% of the effect of the program on distress and 66% of the effect of the program on wellbeing was mediated through food insecurity. The results of this study are highly important as this is a large‐scale program already extended to half of the country. Findings will contribute in designing, judging the cost‐benefit and cost‐effectiveness, and in garnering support for the expansion of such programs.

Risk‐return trade‐offs to different educational paths: vocational, academic and mixed

PurposeThe purpose of this paper is to investigate the rates of return and the risks of different types of educational paths – all leading to a tertiary educational degree. The paper seeks to distinguish a purely academic educational path from a purely vocational path and a mixed path with loops through both systems.Design/methodology/approachThe paper studies the labor market outcome to compare earnings and calculate net return rates as well as risk measures to investigate whether different educational paths are characterized by different risk‐return trade‐offs. Entrepreneurs are separated from employees in order to examine whether for the same combination of education the labour market outcomes differ between the two groups.FindingsThe empirical results are based on the Swiss Labor Force Survey (SLFS) and demonstrate that mixed educational paths are well rewarded in the labor market. However, for entrepreneurs a high return is also associated with a high income variance.Research limitations/implicationsThe findings provide evidence for the existence of complementarities between vocational and academic education. Further research on mixed educational paths might provide more insight into this presumed relationship.Practical implicationsSince the results indicate that mixed educational paths are a worthwhile strategy, the permeability of a national education system is a very important educational policy issue.Originality/valueThe study is innovative in three ways: first, it focuses on complete educational paths and not just the highest educational degree. Second, an alternative measure, the Baldwin rate of return, is used to assess the profitability attached to different educational paths. Third, the income risk associated with each educational path is calculated.

Cyclists' path planning behavioral model at unsignalized mixed traffic intersections in China

Study on the cyclist's path planning behavior in mixed traffic flow intersection is very important. The paper presents a fuzzy logic based behavior model to describe cyclist path planning behaviors at unsignalized intersections in mixed traffic flow situations (with many conflicts among motorcars, non-motor vehicles and pedestrians). Field data have been collected for fuzzy logic modeling, model calibration and validation, and the simulation results are promising. The model can be used in mixed traffic flow simulation and path planning models for Personal Mobility Vehicles (PMVs).

Damage mechanisms and lifetime behavior of plasma sprayed thermal barrier coating systems for gas turbines—Part I: Experiments

Detailed damage analyses of a plasma sprayed ZrO 2/8 wt.–% Y 2O 3–MCrAlY–CMSX-4 TBC system during isothermal and cyclic oxidation tests with different dwell times at high temperature have been performed. The resulting failure mode, i.e. the particular delamination crack path, is strongly dependent on the temperature cycle applied. Isothermal exposure promotes crack propagation within the TGO, whereas thermal cycling shifts the crack path towards the TBC. Thermal cycling with dwell time at high temperature leads to a mixed delamination crack path (partly within TBC and TGO). The respective correlation between TBC lifetimes and duration of high temperature dwell time per cycle (cycle frequency) is shown and discussed.

Risk-Return Trade-Offs to Complete Educational Paths: Vocational, Academic and Mixed

This paper investigates the rates of return and the risks of different types of educational paths after compulsory education. We distinguish a purely academic educational path from a purely vocational path and a mixed path with loops through both systems. To study the labor market outcome we compare earnings and calculate net return rates as well as risk measures to investigate whether different educational paths are characterized by different risk-return trade-offs. We use Lazear's jack-of-all-trades theory on entrepreneurship to derive testable predictions about the labour market outcome of different combinations of education for entrepreneurs and employees. Our empirical results are based on the Swiss Labor Force Survey (SLFS) and demonstrate that mixed educational paths are well rewarded in the labor market. However, a high return is also associated with a high income variance which is driven by those who end up as entrepreneurs.

Callus patterns in femur lengthening using a monolateral external fixator

We studied the callus pattern seen in femoral lengthening using monolateral external fixator to determine whether callus types and shapes can predict the final outcome of the procedure. The radiographs of 41 cases of femoral lengthening (33 unilateral and 8 bilateral) in 33 patients with a mean age 11.9 years (range 4-22 years) were retrospectively analysed by four observers and classified into different shapes and types in concordance with the Ru Li classification. The classification was tested for concurrence and reproducibility by inter-observer studies. An average of 6.2 cm of lengthening (range 3-10.8) was achieved with an external fixator index of 36.5 (range 20.9-55.3). The fusiform type of callus (fixator index 32.04, maturation index 21.6) showed the best result followed by the cylinder type of callus (fixator index 35.7, maturation index 22.3) and the lateral type of callus (fixator index 33.2, maturation index 21.5). However, the concave type of callus showed poor results with a fixator index of 49.4 and a maturation index of 37.1. The homogeneous path showed the best results (fixator index 30.4, maturation index 18.6). The heterogeneous path also showed good results (fixator index 36.4, maturation index 23.9). The mixed path (fixator index 42.5, maturation index 30.8) and the lucent path (fixator index 45.1, maturation index 32.8) showed poor results. Analysis of the callus pattern helps the surgeon to predict the outcome of the procedure and guide him in planning any additional interventions if necessary.

Path-based routing provisioning with mixed shared protection in WDM mesh networks

In this paper, the authors focus on studying the problem of survivable routing provisioning to prevent single link failure in wavelength-division-multiplexing (WDM) mesh networks, and propose a novel protection scheme called mixed shared path protection (MSPP). With MSPP, the authors define three types of resources: 1) primary resources that can be used by primary paths; 2) spare resources that can be shared by backup paths; and 3) mixed resources that can be shared by both the primary and the backup paths. In the proposed protection scheme, each connection is assigned a primary path and a link disjoint backup path. Differing from pervious protection schemes, MSPP allows some primary paths and backup paths to share the common mixed resources if the corresponding constraints can be satisfied. In this paper, the authors consider three types of path-based protection schemes, i.e., dedicated path protection (DPP), shared path protection (SPP), and MSPP, and evaluate their performance for both the static and the dynamic provisioning problems. Simulation results show that MSPP outperforms DPP and SPP

Hydrogen Peroxide Electrosynthesis on Nonplatinum Materials

A combination of electrochemical and physicochemical methods is used to investigate electrocatalytic and corrosion properties of nonplatinum materials in a direct hydrogen peroxide electrosynthesis by the oxygen ionization. A modifying action of ozone and hydroquinone added in solution is established. Surface properties of the electrocatalysts are studied. Presumably, the electrosynthesis occurs via a mixed path, which includes direct oxygen electroreduction catalyzed by redox processes involving surface groups and chemical oxidation processes.

3‐D Tomography for the S‐Wave Quality Factor of the Crust and Upper Mantle Beneath the Chinese Mainland

AbstractWe select 223 pairs of Rayleigh wave from 2681 waveforms recorded at 58 stations in the Eurasia continent and west Pacific region. These data are two‐path records of the rays which pass through the Chinese mainland and meet the requirements of our study. Using the method combining phase‐matched filter and Winner filter in frequency domain, we calculate the attenuation coefficient of the mixed path between two stations. We make a mesh of 4° x 4° to the Chinese mainland and invert the attenuation coefficient of pure path for each grid element. Then we perform depth inversion for each element based on the velocity and density models to obtain the S wave quality factor (Qβ) in the depth range of about 10~350km. In this way the Qβ distribution of the whole Chinese mainland is acquired. The result shows that the lateral and vertical change of the Qβ distribution is very evident. The asthenosphere structure can be clearly identified from the image. The Qβ structure manifests remarkable variations between tectonic units. This result provides helpful information for the study on the material property, viscidity structure, and dynamic process of the Earth interior beneath the Chinese mainland.

Wavelet Analysis of Partial Discharge Acoustic Signals in a Model Transformer

The focus of acoustic partial discharge measurements is based on the discharge location. The tank wall thickness of a power transformer is usually larger than the wavelength of the signal, and therefore possesses a path for the signal, thereby complicating the triangulation procedure for the determination of the discharge location. Owing to their difference in frequency, the signals that travel faster through the mixed path of oil and tank and the slower ones that follow a direct path through oil can be differentiated. By using wavelet transform, we are able to not only discriminate between these two signals, but also to determine the exact instant at which a change in the detected signal occurs due to their interference. This is a new method of analyzing the partial discharge acoustic signal to extract the signal that travels through the direct path in oil and can lead to a more accurate discharge location.

Enhancing OODB semantics to support browsing in an OODB vocabulary representation

AbstractIn previous work, we have modeled a vocabulary given as a semantic network by an object‐oriented database (OODB). The OODB schema thus obtained provides a compact abstract view of the vocabulary. This enables the fast traversal of the vocabulary by a user. In the semantic network vocabulary, the IS‐A relationships express the specialization hierarchy. In our OODB modeling of the vocabulary, the SUBCLASS relationship expresses the specialization hierarchy of the classes and supports the inheritance of their properties. A typical IS‐A path in the vocabulary has a corresponding shorter SUBCLASS path in the OODB schema.In this paper we expose several cases where the SUBCLASS hierarchy fails to fully correspond to the IS‐A hierarchy of the vocabulary. In these cases there exist traversal paths in the semantic network for which there are no corresponding traversal paths in the OODB schema. The reason for this failure is the existence of some IS‐A relationships between concepts of two classes, which are not connected by a SUBCLASS relationship. This phenomenon weakens the accuracy of our modeling.To rectify the situation we introduce a new OODB semantic relationship IS‐A$'$ to represent the existence of IS‐A relationships between concepts of a pair of classes which are not connected via a SUBCLASS relationship. The resulting schema contains both SUBCLASS relationships and IS‐A$'$ relationships which completely model the IS‐A hierarchy of the vocabulary. We define a mixed‐class level traversal path to contain either SUBCLASS or IS‐A$'$ relationships. Consequently, each traversal path in the semantic network has a corresponding mixed traversal path in the OODB schema. Hence the introduction of the semantic OODB IS‐A$'$ relationship improves the modeling of semantic network vocabularies by OODBs. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Resource Management for Fault Tolerant PathStructures in SONET Ring Networks

There is growing interest on the part of network operators in the ability to analyze the availability of path implementations in their networks and to provide various grades of assured service availability to customers. The calculation of availability is, however, considerably more complex in today's SONET ring-based networks than in prior point-to-point systems. This is due both to the active protection nature of the rings and their dual-redundant interconnect strategies. We show that there is also more than one option for dual-ring interconnection and that a minimum cost high availability path implementation will generally involve a mixture of matched-node and explicitly dual fed treatments. We develop an economic comparison of dual feeding (df) and matched nodes (mn) in terms of the resource consumption of each scheme and show that the choice can be made on an individual ring-by-ring basis with a simple decision criterion. We then develop expressions of general use for the end-to-end unavailability of single-fed, pure df, mn and mixed df-mn path constructions. These results are a step towards on-line provisioning or path planning systems that can minimize the path implementation cost subject to an assured target level of design availability.

Propagational features of higher harmonic tweeks at low latitudes

Higher harmonic tweeks observed for the first time at the low latitude station Varanasi (geomag. lat. 14‡ 55′ N) are reported. The analysis of data shows that higher harmonic tweeks are usually not associated with whistlers and occur when the ionization in the lower ionosphere would not increases with height. The Earth-ionosphere waveguide dispersion features play an important role in the propagation of broad band lightning generated signals and their occasional observation as higher harmonic tweeks. It is shown that the conductivity of ground and sea mixed path, forming the lower surface of the waveguide, provide an estimate of the travelled distances of higher harmonic tweeks in the waveguide. The attenuation factors are computed which shows that as the harmonic number increases their probability of observation decreases. The attenuation increases as the frequencies approach the cut-off frequencies and also as the layer height falls. The tweek activity is found to increase during periods of magnetic disturbances.

A study of the distortion and propagation time-delay of Loran-C pulse wave based on a model of the propagation path

The main cause of the absolute positioning error in the Loran-C system is in the occurrence of the propagation time delay error caused by the fact that the propagation speed of the pulse signal on the actual propagation path is different from that assumed in the formation of the Loran-C maritime chart. The propagation path characteristics not only cause the propagation time delay of each received pulse signal but also generates waveform distortion in the received pulse. Hence, it is possible to estimate the propagation delay time by means of this waveform distortion. At present, a measure of the distortion of the pulse waveform distortion of the Loran-C is envelope to cycle difference (ECD). In this paper, as a new measure for the pulse-wave distortion to estimate the propagation time delay, CHACLE, or change of half-cycle length, is proposed. A method for correction of the absolute positioning error is provided based on the estimation of the propagation time delay from the measures of the wave-form distortion (CHACLE and ECD) by means of the simplified propagation path for an easy analysis and of the general propagation path. It is demonstrated that CHACLE is superior to ECD in terms of the effect of correction. Further, to confirm the validity of the correction method proposed in this paper, the present method is applied to a propagation path model resembling the mixed propagation path used in the United States to estimate the pulse time delay. It is confirmed that the absolute positioning error can be reduced to less than about 20 percent.

An evaluation of crack front effect on threshold and crack propagation

That a through-thickness crack may exhibit over the entire fatigue crack propagation (FCP) regime morphological variations such as curvature, deviation and deflection appears to be very common. This effect is hereafter referred to as the crack front effect (CFE). It includes the practical consequence that when CFE occurs, local crack length, and hence the surface and the through-thickness data derived, tend to differ. Apparently, the difference should not be significant a least for thin specimens, for which data acquisition on one face suffices, and therefore, problems resulting from CFE can be neglected in certain cases. The authors became involved in the CFE problem while studying hysteresis effects in the threshold regime, particularly when post-threshold non-propagation was observed on the surface. In brief, the specimens had a section thickness of 4mm, i.e., relatively thin (B/W = 0.066), and according to the ASIM test recommendations the surface data should have been accurate. The major questions which arose were, however, whether surface and through-thickness effects are comparable, and how reliable surface observations are. Pure copper was chosen as the material since it exhibits a mixed mode fracture path, and thus should be inherently prone to yield CFE.

Fast diffusion of Silver in single and Polycrystals of α-Alumina

Diffusion coefficients of silver into alumina were determined by the radiotracer method. For bulk, dislocations and grain boundaries, the Arrhenius equations were, respectively: D ( m 2 s −1) = 2· 10 −4 exp(−331 ( kJ mol −1)RT) ; D d· α d·a 2(m 4s −1) = 4.3·10 −16 exp(−321( kJ mol −1)/RT) ; P = D′· α′ · δ( m 3 s −1) = 9.2·10 −6 exp(−321( kJ mol −1)/RT) . In bulk, silver diffused faster than other elements; diffusion was probably accomplished through interstitial octahedral sites, and the large misfit induced by the silver atoms could be related to the low activation energy of silver compared with that of the self-interstitial. Along dislocations and grain boundaries, a rather large increase of diffusivity was observed. The high values of D'· α'/ D ratios for silver could be explained assuming a segregation coefficient α′ = 2000, in agreement with the semi-empirical models for grain-boundary segregation in alumina. The measured activation energies Q, Q d and Q' were very close. Such behaviour was difficult to explain with regard to the high values of D d/ D or D′/ D, about 10 4. This suggested the intervention of a mixed diffusion path, where jumps from structural unoccupied octahedral sites to aluminium vacancies would be highly probable, together with an increase of vacancy concentration along the grain boundaries.

Diffraction of sound above a curved surface having an impedance discontinuity

This article describes theory and experiments in the case of propagation of sound in the presence of an impedance discontinuity and a curved surface (or sound-speed gradients). The theory is based on a residue series, or creeping wave, solution developed for the propagation of sound in a stratified medium under conditions favorable to the formation of a shadow zone. The creeping wave solutions on each side of the impedance discontinuity are coupled heuristically by assuming a virtual source above discontinuity. The theory is compared to controlled measurements made indoors above a curved surface having an impedance jump (hard to soft). The measurements were made using a point source driven by frequencies in the range between 0.3 and 10 kHz. The theory is also compared to measurements made outdoors above a flat ground having a mixed path (asphalt to grass) in the presence of realistic gradients. Pure tones in the frequency range between 0.5 and 5 kHz were generated from a point source and the resulting sound-pressure levels measured on a sound level meter after suitable filtering. In all cases, there is good agreement between measurements and theory.