Specic Model Research Articles

Computer Adaptive Testing and Cloud Computing

Computer Adaptive Testing (CAT) is an example of a Com- puter Based Test (CBT) and is one of the main trending topics in the area of knowledge testing and, more recently, in e{learning or in Intelligent Tutoring Systems scenarios. The Item Response Theory (IRT) denes the theoretical basis of a CAT implementation, which assumes the existence of a repository of properly calibrated items that is used during the testing process of a particular examinee. The calibration and adaptation are based on an Item Characteristic Curve (ICC) related to an specic model, being Rasch's models the most widely used. CAT systems require high computational cost to implement the calibration and evaluation processes and the amount of concurrent users at a time could be large enough. Thus, the platform must support high concurrency and availability to perform a desired level of functionality. Technological tendencies in computing oer each time better platforms to develop and manage big collections of data for its processing and relevant information extraction. This paper presents a perspective of using new technologies in CAT as an alternative of implementation. Particularly, the use of a cloud computing platform as current alternative for online CAT systems using the capabilities of multicore processing and big amount of RAM that oers the cloud, to resolve the proper mathematical equations related to psychometric models and the operations described in their algorithms in a real evaluation scheme.

Development high performance scientific computing application using model-driven architecture

This paper presents an approach to develop high performance scientific computing (HPSC) application for simulation fluid flow pressure in oil reservoir with use of mpiJava. The modeling and developing process adapted the modern Model-Driven Architecture (MDA) technology which was created by Object Management Group. We specially created the HPSC components to model the platform independent model (PIM) and platform specic model (PSM) of MDA. The HPSC application development was analyzed with traditional and MDA approaches.

Unitarity and real properties of the neutral meson complex

The proof of the Khaln Theorem for the neutral meson complex is analyzed. It is shown that the unitarity of the time evolution operator for the total system under considerations assures that the Khaln’s Theorem holds. The consequences of this Theorem for the neutral mesons system are discussed: it is shown that diagonal matrix elements of the exact eectiv e Hamiltonian for the neutral meson complex cannot be equal if CPT symmetry holds and CP symmetry is violated. The properties of time evolution governed by a timeindep endent eectiv e Hamiltonian acting in the neutral mesons subspace of states are considered. Using the Khaln’s Theorem it is shown that if such Hamiltonian is timeindep endent then the evolution operator for the total a system containing the neutral meson complex cannot be a unitary operator. It is shown graphically for a given specic model how the Khaln’s Theorem works. It is also shown for this model how the dierence of the mentioned diagonal matrix elements of the eectiv e Hamiltonian varies in time.

Numerical sensitivity study of irradiated nuclear fuel evolution in the RBMK reactor

The sensitivity study of the RBMKn1500 spent nuclear fuel (SNF) nuclide composition modelling was performed by investigating the essential physical reactor performance parameters (inuence of coolant density, fuel and graphite temperatures, the fuel irradiation history, axial fuel assembly power prole) and specic model parameters depending on the computational code (model geometry description, neutron ux convergence criteria, evaluated nuclear data libraries and energy intervals used, resonance self-shielding parameters, etc.). SNF nuclide composition modelling was performed by using TnDEPL sequence from the SCALE 5 code package. The study showed that some of analysed parameters can inuence the calculated SNF nuclide composition signicantly , especially for minor actinides and ssion products with high neutron capture cross-sections. It has been found that the coolant density and axial power prole have the largest inuence on irradiated fuel inventory and in order to obtain the more precise RBMKn1500 SNF nuclide composition these parameters should be modelled as close to real conditions as possible. The lattice cell pitch used for resonance self-shielding can have a signicant effect on calculated actinide activities. The correct parameter could be obtained from the experimental data that are presently unavailable.

Chronic oral administration of ginseng extract results in behavioral change but has no effects in mice models of affective and anxiety disorders

Ginseng is a popular 'tonic' herb in Chinese traditional medicine with diverse biological activity. The core of ginseng's therapeutic abilities is thought to be its neuroprotective actions in increasing cellular resilience. These actions coincide with novel theories of affective and anxiety disorders and raise the possibility that ginseng may serve as medication for these common and devastating diseases. The present study was designed to explore the possible effects of chronic ginseng extract, administered in a clinically relevant schedule (similar to antidepressants) in animal models of affective and anxiety disorders. Groups of mice received chronic oral treatment with ginseng extract (500 mg/kg/day for 3 weeks) and were tested in a large open eld, in the emergence test for anxiolytic activity, the forced swim test for antidepressant activity and the amphetamine hyperactivity test for mood stabilizing activity. Chronic ginseng had a signicant effect on reducing spontaneous locomotor activity in the open eld test but not on the distribution of activity and had no inssuence on the performance of mice in any of the specic models. Although the extract used in this study contained signicant levels of ginsenosides, detailed analysis of the brain levels of the active ingredients of ginseng may be needed to make a far reaching conclusion. However, the doses and schedule of administration of ginseng used in the present study induced some behavioral changes but did not inssuence affective- and anxiety-like measures.

A Monte Carlo Study of Structural Equation Models for Finite Mixtures

Empirical applications of structural equation modeling (SEM) typically rest on the assumption that the analysed sample is homogenous with respect to the underlying structural model or that homogenous subsamples have been formed based on a priori knowledge. However, researchers often are ignorant about the true causes of heterogeneity and thus risk to produce misleading results. Using a sequential procedure of cluster analysis in combination with multi-group SEM has been shown to be inappropriate to solve the problem of unobserved heterogeneity. Recently, two encouraging approaches have been developed in this regard: (1) Finite mixtures of structural equation models and (2) hierarchical Bayesian estimation. In this paper, we focus exclusively on the MECOSA approach to nite normal mixtures subject to conditional mean and covariance structures. Since not much is known about the performance of MECOSA, which is both a specic model and a software, we present the results of an extensive Monte Carlo simulation. It was found that MECOSA performed best where homogenous groups were present in the data in equal proportions and in conjunction with rather large differences in parameters across the groups. MECOSA performed worse when the proportions were unequal and parameters were relatively close together across groups. Of the three estimation methods available in MECOSA the two-stage minimum distance estimation (MDE) in general performed worse than the alternative EM algorithms (EM and EMG). This effect was especially pronounced under conditions of close parameters and unequal group proportions. Above that, for these conditions the modied likelihood ratio test turned out to be inappropriate in the three groups case.

A spatial similarity measure based on games: theory and practice

Model comparison games can be used not only to decide whether two specic models are equivalent or not, but also to establish a measurement of dierence among a whole class of models. We show how this is possible in the case of the spatial modal logic S4u of Bennett. The approach results in a spatial similarity measure based on topological model comparison games. After establishing the theoretical framework, we move towards practice by giving an algorithm to eectively compute the similarity measure for a class of topological models widely used in computer science applications: polygons of the real plane. In the appendix, we briefly overview an implemented system based on the theoretical framework.

New theoretical yields of intermediate mass stars

We present theoretical yields of H, 4 He, 12 C, 13 C, 14 N, and 16 O for stars with initial masses between 0.8 and 8 M and initial metallicities Z =0 :001, 0.004, 0.008, 0.02, and 0.04. We use the evolutionary tracks of the Geneva group up to the early asymptotic giant branch (AGB) in combination with a synthetic thermal-pulsing AGB evolution model to follow in detail the chemical evo- lution and mass loss up to the end of the AGB including the rst, second, and third dredge-up phases. Most of the relations used are metallicity dependent to make a realis- tic comparison with stars of dierent initial abundances. The eect of Hot Bottom Burning (HBB) is included in an approximate way. The free parameters in our calculations are the mass loss scaling parameter AGB for stars on the AGB (us- ing a Reimers law), the minimum core mass for dredge-up M min c , and the third dredge-up eciency . As derived from previous extensive modeling, AGB =4 , M min c = 0.58 M ,a nd =0 :75 including HBB are in best agree- ment with observations of AGB stars both in the Galactic disk and Magellanic Clouds. The influence of specic model assumptions and adopted parameter values on the resulting AGB yields is examined and compared with earlier theoretical work. We compare the abundances predicted during the nal stages of the AGB with those observed in planetary nebu- lae in the Galactic disk and show that the model with the aforementioned parameters is in good agreement with the observations. The metallicity dependent yields of interme- diate mass stars presented in this paper are well suited for use in galactic chemical evolution models.