Comparing concurrent versus fixed parameter equating with common items: using the dichotomous and partial credit models in a mixed-item format test

There has been some discussion among researchers as to the benefits of using one calibration process over the other during equating. Although literature is rife with the pros and cons of the different methods, hardly any research has been done on anchoring (i.e., fixing item parameters to their pre-determined values on an established scale) as a method that is commonly used by psychometricians in large-scale assessments. This simulation research compares the fixed form of calibration with the concurrent method (where calibration of the different forms on the same scale is accomplished by a single run of the calibration process, treating all non-included items on the forms as missing or not reached), using the dichotomous Rasch (Rasch, 1960) and the Rasch partial credit (Masters, 1982) models, and the WINSTEPS (Linacre, 2003) computer program. Contrary to the belief and some researchers' contention that the concurrent run with larger n-counts for the common items would provide greater accuracy in the estimation of item parameters, the results of this paper indicate that the greater accuracy of one method over the other is confounded by the sample-size, the number of common items, etc., and there is no real benefit in using one method over the other in the calibration and equating of parallel tests forms.     

含预埋梁蜂窝夹层结构数值仿真与试验研究

含预埋梁蜂窝夹层结构是在纯蜂窝结构基础上改进得到的全新结构形式,综合了蜂窝结构和桁条铆接结构的优点,但该类结构的载荷分布形式以及失效模式缺乏相关研究。针对上述问题,结合国内在研尺寸最大的含预埋梁铝蜂窝夹层结构,采用层合板加筋方法进行了数值仿真,设计全尺寸物理试验对结构性能进行了试验验证。通过数值仿真和试验对比,验证了层合板加筋方法模拟含预埋梁蜂窝结构的准确性,同时研究了该类结构的载荷分布和失效模式,并为同类结构设计提供了参考依据。     

Long-term retention of a divided attention psycho-motor test combining choice reaction test and postural balance test: A preliminary study

Driving in degraded psychophysical conditions, such as under the influence of alcohol or drugs but also in a state of fatigue or drowsiness, is a growing problem. The current roadside tests used for detecting drugs from drivers suffer various limitations, while impairment is subjective and does not necessarily correlate with drug metabolite concentration found in body fluids. This work is a validation step towards the study of feasibility of a novel test conceived to assess psychophysical conditions of individuals performing at-risk activities. Motor gestures, long-term retention and learning phase related to the protocol are analysed in unimpaired subjects. The protocol is a divided attention test, which combines a critical tracking test achieved with postural movements and a visual choice reaction test. Ten healthy subjects participated in a first set of trials and in a second set after about six months. Each session required the carrying out of the test for ten times in order to investigate learning effect and performance over repetitions. In the first set the subjects showed a learning trend up to the third trial, whilst in the second set of trials they showed motor retention. Nevertheless, the overall performance did not significantly improve. Gestures are probably retained due to the type of tasks and the way in which the instructions are conveyed to the subjects. Moreover, motor retention after a short training suggests that the protocol is easy to learn and understand. Implications for roadside test usage and comparison with current tests are also discussed.     

Distractors with information in multiple choice items: a rationale based on the Rasch model

There is a substantial literature on attempts to obtain information on the proficiency of respondents from distractors in multiple choice items. Information in a distractor implies that a person who chooses that distractor has greater proficiency than if the person chose another distractor with no information. A further implication is that the distractor deserves partial credit. However, it immediately follows from the Rasch model that if a distractor deserves partial credit, then the response to that distractor and other distractors should not be pooled into a single response with a single probability of an incorrect response. Using the partial credit parameterization of the polytomous Rasch model, the paper shows how an hypothesis can be formed, and tested, regarding information in a distractor. The hypothesis is formed by studying the shape of the distractor response curves across the continuum, and the hypothesis is tested by scoring the correct response 2, the hypothesized distractor 1, and other distractors 0, and then applying the polytomous Rasch model. Multiple pieces of evidence, including fit of the responses at the two thresholds and the order of the two threshold estimates, are used in deciding if a distractor has information. An example illustrating the theory and its application is provided.     

Demand information sharing and channel choice in a dual-channel supply chain with multiple retailers

In this paper, under a dual-channel supply chain consisting of a manufacturer and multiple retailers, we investigate vertical and horizontal information sharing in different channel structures and the manufacturer’s choice on whether or not to keep a direct channel. To this end, we first study the dual-channel structure where uncertain demand is a linear function of price with a generalised-distribution base demand and show that the retailers have incentives to share information horizontally but not vertically, while the manufacturer is better off with vertical information sharing but its expected profit is not affected by horizontal information sharing. We next examine the retail-channel structure and find the basic results remain unchanged. Finally, we provide closed-form internal and external conditions under which the manufacturer can benefit from owning a dual-channel structure. Our study extends the existing literature by combining information sharing and dual-channel choice, introducing channel difference, discussing the impact of channel structure on horizontal and vertical sharing as well as providing interesting managerial insights for channel choice.     

高层钢-混凝土组合门式结构消能减震体系模拟地震振动台试验研究

对一幢复杂高层钢-混凝土组合门式结构消能减震体系的1/30缩尺模型进行了模拟地震振动台试验,深入研究了该结构的动力特性和地震反应特征,通过比较验证了粘滞阻尼器的减震效果。结果表明:结构整体空间作用显著,两座塔楼之间扭转反应较大。有、无阻尼器结构的各项反应基本满足抗震规范的要求;从平均意义上讲,阻尼器对整体结构的位移反应有一定的控制效果,对结构高空连廊的位移和两座塔楼之间的扭转反应控制效果较好。     

Rapid prototyping and flow simulation applications in design of agricultural irrigation equipment: Case study for a sample in-line drip emitter

In this study, a 3D CAD solid model of a sample agricultural irrigation emitter was created and the flow behaviour was simulated in its labyrinth channels by using a flow simulation technique. Referenced by the original design, the channel geometry was modified and the emitter was re-fabricated using rapid prototyping/additive manufacturing techniques. The flow behaviour is then re-investigated based on the re-shaped channel geometry of the labyrinth structure. The predetermined optimum pressure in the pipe was validated experimentally for both the original design and modified designs. As a result, the optimum pressure in the pipe and the flow characteristics for original both the design and modified designs of the emitter were validated. This study contributes to further research into the development of agricultural irrigation equipment aided through the utilisation of additive manufacturing and computer aided engineering tools.     

Effects of group size and learning on manual assembly performance: an experimental study

In variable manual assembly production of highly customised products, effective allocation of workers to products is required. To support decision-making here, industrial managers should be aware of the performance effects of the number of workers and learning within individual products. Evidence on such fundamental effects requires laboratory studies with products similar to those in real assembly industries. Because of the lack of such studies, this paper studies experimentally the effects of group size (one to four workers) and learning (up to four repetitions per group) on the performance of product assembly. The product, built for the purpose of the present study, consists of representative elements from real products in the mechanical engineering industry. A total of 68 undergraduate students participated in the experiments. The results from the experiments are in line with the hypotheses that the mean assembly time decreases at a decelerating rate as a function of both group size and repetitions, and that productivity per worker decreases as a function of group size. The results are explained in more detail through the experiences of the participants. Managerial implications and aspects for future research are also discussed.     

Bayesian inference in life tests based on exponential model with outliers when sample size is a random variable

Summary This paper deals with the problem of prediction of the order statistics in a future sample. Underlying model is exponential. Outlier is present in the sample drawn and the sample size is considered a random variable. Firstly, an outlier of type πδ in the exponential model, is trated. Actual predictive distribution of the order satstistics is obtained. As an extension, two sample problem is also taken up. Finally, an outlier of type π+δ is dealt and now the predictive distribution is expressed in terms of hypergeometric functions.     

Geometry and size effects on fracture trajectory in a limestone rock under mixed mode loading

The mixed mode I/II fracture initiation angle and the crack growth trajectory of a soft rock (Guiting limestone) were investigated experimentally and theoretically for two different shaped test specimens with various sizes. It was observed that for similar mode mixities in the two specimens, the fracture paths grew in two different trajectories. It is shown that the observed crack path and the fracture initiation angle can be predicted theoretically by using a generalized form of the maximum tangential stress criterion. The main difference in the fracture initiation angles was found to be related to the magnitude and sign of the T-stress.     

Noninvasive near-infrared blood glucose monitoring using a calibration model built by a numerical simulation method: Trial application to patients in an intensive care unit

We have applied a new methodology for noninvasive continuous blood glucose monitoring, proposed in our previous paper, to patients in ICU (intensive care unit), where strict controls of blood glucose levels are required. The new methodology can build calibration models essentially from numerical simulation, while the conventional methodology requires pre-experiments such as sugar tolerance tests, which are impossible to perform on ICU patients in most cases. The in vivo experiments in this study consisted of two stages, the first stage conducted on healthy subjects as preliminary experiments, and the second stage on ICU patients. The prediction performance of the first stage was obtained as a correlation coefficient (r) of 0.71 and standard error of prediction (SEP) of 28.7 mg/dL. Of the 323 total data, 71.5% were in the A zone, 28.5% were in the B zone, and none were in the C, D, and E zones for the Clarke error-grid analysis. The prediction performance of the second stage was obtained as an r of 0.97 and SEP of 27.2 mg/dL. Of the 304 total data, 80.3% were in the A zone, 19.7% were in the B zone, and none were in the C, D, and E zones. These prediction results suggest that the new methodology has the potential to realize a noninvasive blood glucose monitoring system using near-infrared spectroscopy (NIRS) in ICUs. Although the total performance of the present monitoring system has not yet reached a satisfactory level as a stand-alone system, it can be developed as a complementary system to the conventional one used in ICUs for routine blood glucose management, which checks the blood glucose levels of patients every few hours.     

Two-dimensional mixed boundary value problem in heat and mass transfer for a characteristic equation with multiple roots

A system of two differential equations of parabolic type is examined. A boundary value problem is set up and solved. A system of integrodifferential equations is obtained for determining the unknown functions. A method of reducing this to a system of ordinary Volterra integral equations is given.     

Regimes of segregation and mixing in combined size and density granular systems: an experimental study

Granular segregation in a rotating tumbler occurs due to differences in either particle size or density, which are often varied individually while the other is held constant. Both cases present theoretical challenges; even more challenging, however, is the case where density and size segregation may compete or reinforce each other. The number of studies addressing this situation is small. Here we present an experimental study of how the combination of size and density of the granular material affects mixing and segregation. Digital images are obtained of experiments performed in a half-filled quasi-2D circular tumbler using a bi-disperse mixture of equal volumes of different sizes of steel and glass beads. For particle size and density combinations where percolation and buoyancy both contribute to segregation, either radial streaks or a “classical” core can occur, depending on the particle size ratio. For particle combinations where percolation and buoyancy oppose one another, there is a transition between a core composed of denser beads to a core composed of smaller beads. Mixing can be achieved instead of segregation if the denser beads are also bigger and if the ratio of particle size is greater than the ratio of particle density. Temporal evolution of these segregated patterns is quantified in terms of a “segregation index” (based on the area of the segregated pattern) and a “shape index” (based on the area and perimeter of the segregated pattern).     

Particle screening phenomena in an oblique multi-level tumbling reservoir: a numerical study using discrete element simulation

Due to their wide usage in industrial and technological processes, granular materials have captured great interest in recent research. The related studies are often based on numerical simulations and it is challenging to investigate computational phenomena of granular systems. Particle screening is an essential technology of particle separation in many industrial fields. This paper presents a numerical model for studying the particle screening process using the discrete element method that considers the motion of each particle individually. Dynamical quantities like particle positions, velocities and orientations are tracked at each time step of the simulation. The particular problem of interest is the separation of round shape particles of different sizes using a rotating tumbling vertical cylinder while the particulate material is continuously fed into its interior. This rotating cylinder can be designed as a uniform or stepped multi level obliqued vertical vessel and is considered as a big reservoir for the mixture of particulate material. The finer particles usually fall through the sieve openings while the oversized particles are rebounded and ejected through outlets located around the machine body. Particle–particle and particle–boundary collisions will appear under the tumbling motion of the rotating structure. A penalty method, which employs spring-damper models, will be applied to calculate the normal and frictional forces. As a result of collisions, the particles will dissipate kinetic energy due to the normal and frictional contact losses. The particle distribution, sifting rate of the separated particles and the efficiency of the segregation process have been studied. It is recognized that the screening phenomenon is very sensitive to the machines geometrical parameters, i.e. plate inclinations, shaft eccentricities and aperture sizes in the sieving plates at different levels of the structure. The rotational speed of the machine and the feeding rate of the particles flow have also a great influence on the transportation and segregation rates of the particles. In an attempt to better understand the mechanism of the particle transport between the different layers of the sifting system, different computational studies for achieving optimal operation have been performed.     

Analytical and experimental study of mixed convection in tube bundles with a longitudinal flow

A solution is given to the heat problem of mixed convection in vertical tube bundles with a relative spacing s/d=1.2 and 1.4. The results have been checked out experimentally with a forced flow of liquid sodium.Translated from Ihzhenerno-Fizicheskii Zhurnal, Vol. 24, No. 1, pp. 13–18, January, 1973.     

The effect of an electrical double layer on the voltammetric performance of nanoscale interdigitated electrodes: a simulation study

Finite-element based computational simulation is performed to investigate the effect of an electrical double layer (EDL) on the electrochemical processes of nanometer-scale interdigitated electrodes (nano-IDEs). Results show that the EDL structure will alter the voltammetric current response of nano-IDEs due to the expansion of the diffuse layer into the diffusion layer at the electrode surfaces and the overlap of the electrical fields of the neighboring electrodes. The EDL induced change in the voltammetric current response is more severe for nano-IDEs with a smaller electrode size and gap spacing, and the EDL effect is influenced by the compact layer thickness, the charge valence of the redox species, the electron transfer rate, and the absence of the supporting electrolyte.     

A note on: an optimal batch size for an imperfect production system with quality assurance and rework

In [Ojha, D., Sarker, B.R., and Biswas, P., 2007. An optimal batch size for an imperfect production system with quality assurance and network. International Journal of Production Research, 45 (14), 3191–3214] three models are introduced in the context of imperfect production systems. By analysing the proposed models we identify some problems. In particular we focus on six issues of the models developed in Ojha et al. and propose some modifications. All corrections are presented in detail and the numerical example of Ojha et al. is used to show the influence of the issues addressed in this paper.     

Effects of information transparency and cooperation on supply chain performance: a simulation study

This research explores the effect of information transparency and cooperation among the front nodes of supply chains. Although published works in the supply chain (SC) domain underline the need for information transparency and cooperation for competitiveness of firms, the majority among these are conceptual or empirical. As such, the domain requires fresh effort towards analytical and simulation based research for validation. In the present work, simulation is used as the research methodology. The simulation platform is developed in ARENA®, which is based on simulation language SIMAN. It has the capability to model multi-product, multi-echelon supply chains. Cooperation is depicted in the form of demand pooling and accelerated delivery of consignments from cooperating SC nodes, when stock-out contingency occurs at a particular node. The modelling also explores the effects of full, partial and zero level of information transparency on the SC performance. The simulation results suggest that these initiatives improve SC service time performance. It is also observed that more advantages from cooperation and information transparency are obtainable when the SC is leaner. The studies also highlight that such SC initiative that motivates local optimisation at the nodes is counter-productive to SC wide performance.     

Description and evaluation of a tropospheric ozone lidar implemented on an existing lidar in the southern subtropics

Rayleigh-Mie lidar measurements of stratospheric temperature and aerosol profiles have been carried out at Reunion Island (southern tropics) since 1993. Since June 1998, an operational extension of the system is permitting additional measurements of tropospheric ozone to be made by differential absorption lidar. The emission wavelengths (289 and 316 nm) are obtained by stimulated Raman shifting of the fourth harmonic of a Nd:YAG laser in a high-pressure deuterium cell. A mosaic of four parabolic mirrors collects the backscattered signal, and the transmission is processed by the multiple fiber collector method. The altitude range of ozone profiles obtained with this system is 3?17 km. Technical details of this lidar system working in the southern tropics, comparisons of ozone lidar profiles with radiosondes, and scientific perspectives are presented. The significant lack of tropospheric ozone measurements in the tropical and equatorial regions, the particular scientific interest in these regions, and the altitude range of the ozone measurements to 16?17 km make this lidar supplement useful and its adaptation technically conceivable at many Rayleigh-Mie lidar stations.     

Workload simulation and optimisation in multi-criteria hybrid flowshop scheduling: a case study

This paper studies a real-life multiple objective flowshop scheduling problem in a cardboard company which differs from the conventional flowshop scheduling problem in several aspects, such as multi-machine stations, sequence-dependent setup times, work calendars on resources, re-entrant flows, external operations, and transfer batches between stations. A simulation-based environment is presented in which the production sequence can be interactively chosen by the user or found by a tabu-search based heuristic algorithm while a discrete-event simulation deals with the timing aspect.