Spatial pattern of a seismo-ionospheric signature using principal component analysis

This article uses principal component analysis (PCA) to determine the spatial pattern of total electron content (TEC) anomalies in the ionosphere corresponding to China's Wenchuan Earthquake of 12 May 2008 UTC (M_w?=?7.9). PCA is applied to global ionospheric maps (GIMs) with transforms conducted for the time period from 08:00 to 10:00 UT on 9 May 2008. The GIMs are subdivided into 100 smaller maps (36° longitude and 18° latitude). The smaller maps (71?×?71 pixels) form the transform matrices of corresponding dimensions (2?×?1) through image processing. The transform allows for extreme principal eigenvalues to be assigned to the seismo-ionospheric signature described by Zhao et al. [2008 Zhao, B., Yu, T., Wang, M., Wan, W., Lei, J., Liu, L. and Ning, B. 2008. Is an unusual large enhancement of ionospheric electron density linked with the 2008 great Wenchuan earthquake?. Journal of Geophysical Research, 113: A11304 doi:doi: 10.1029/2008JA013613[Crossref], [Web of Science ®] , [Google Scholar], Is an unusual large enhancement of ionospheric electron density linked with the 2008 great Wenchuan earthquake? Journal of Geophysical Research, 113, A11304, doi: 10.1029/2008JA013613.]. Results show that the range of the TEC anomaly declines with height; however, the anomaly becomes more localized and intense at higher altitudes (250–300 km), giving the anomaly the spatial pattern of a downward-facing trumpet.     

Underwater movement times with ongoing visual control

Arm movements made in a water environment take longer to perform than in an air environment due to the drag forces experienced by the arm. Movement times for ballistic underwater movements have been accurately modelled by Hoffmann and Gan (1988 Hoffmann, E.R. and Gan, K-C. 1988. Underwater ballistic movements. Ergonomics, 31(9): 1305–1316. [Taylor & Francis Online], [Web of Science ®] , [Google Scholar]). The present work models the movement time for movements that require ongoing visual control. In these movements, the ‘distance-covering’ phase is carried out at high speeds and will be affected by the fluid characteristics, while the ‘homing-in’ phase, where speeds are low, is less affected. An experiment is reported that models these effects and which indicates that a ballistic component needs to be added to the standard Fitts model in order to account for the drag forces in the distance-covering phase of the movement.

Practitioner Summary: Many tasks, such as maintenance and salvage work, require work to be done underwater. Times for performing underwater tasks are generally longer than on land. This article is one step in modelling the difference in task times for land and underwater movements.     

Yield forecasting for wheat and corn in Hungary by satellite remote sensing

We have developed an advanced version of our yield estimation method [Ferencz et al., 2004 Cs, Ferencz, Bognár, P., Lichtenberger, J., Hamar, D., Gy, Tarcsai, Timár, G., Molnár, G., Sz, Pásztor, Steinbach, P., Székely, B., Ferencz, O.E. and Ferencz-Árkos, I. 2004. Crop yield estimation by satellite remote sensing. International Journal of Remote Sensing, 25: 4113–4149.  [Google Scholar], Crop yield estimation by satellite remote sensing. International Journal of Remote Sensing, 25, pp. 4113–4149], that is able to provide reliable forecasts for corn and wheat, several weeks before the harvest. The forecasting method is based on the data of the Advanced Very High Resolution Radiometer (AVHRR) instruments of the National Oceanic and Atmospheric Administration's (NOAA) Polar Orbiting Environmental Satellites (POES). The method was applied to Hungary between the years 1996 and 2000. The forecasted yield values are all within 5% reliability with respect to the actual yield data produced by classic (non-satellite based) methods and provided by the Hungarian Statistical Office, with the exception of 1997, where the absolute error is about 8%.     

Application of the Sahebi model using ALOS/PALSAR and 66.3 cm long surface profile data

Soil moisture is important information for agricultural fields in which erosion of upper soil layers depends upon the soil moisture, and in which the yield depends on soil water content during sowing, growing and harvest periods. Although sensitivity of microwave backscatters to soil moisture is well understood, several factors, such as surface roughness and incidence angle, can interfere with the estimation of soil moisture using Synthetic Aperture Radar (SAR) data. In this letter, we evaluate the influence of these variables using Advanced Land Observing Satellite (ALOS)/Phased Array type L-Band Synthetic Aperture Radar (PALSAR) data and 66.3 cm long surface profile data using the Sahebi model (Sahebi et al. 2003 Sahebi, M. R., Bonn, F. and Gwyn, Q. H.J. 2003. Estimation of the moisture content of bare soil from RADASAT-1 SAR using simple empirical models. International Journal of Remote Sensing, 24: 2575–2583. [Taylor & Francis Online], [Web of Science ®] , [Google Scholar], Estimation of the moisture content of bare soil from RADASAT-1 SAR using simple empirical models. International Journal of Remote Sensing, 24, pp. 2575–2583). The model applied in this study has a root mean square error (RMSE) of only 1.34 dB, which suggests that 66.3 cm long surface profile data are effective for characterization of surface roughness effects on backscattering coefficients.     

Perceptual and physiological heat strain: Examination in firefighters in laboratory- and field-based studies

Firefighting demands performing heavy muscular work under adverse and potentially dangerous conditions. Although the physiological and psychological responses to simulated firefighting activities have been described, the heat strain has not been characterised using standardised indices of exercise–heat strain. The purpose of the study is to describe the physiological and perceptual strain associated with working in personal protective equipment and performing simulated firefighting activities in a hot environment using recently developed strain indices (Physiological Strain Index (PhSI); Perceptual Strain Index (PeSI)). Data from two previously published studies (Smith et al. 1995 Smith, D. L. 1995. Selected physiological and psychological responses to physical activity in different configurations of firefighting gear. Ergonomics, 38: 2065–2077. [Taylor & Francis Online], [Web of Science ®] , [Google Scholar], 2001 Smith, D. L. 2001. Effect of strenuous live-fire fire fighting drills on hematological, blood chemistry and psychological measures. Journal of Thermal Biology, 26: 375–379. [Crossref], [Web of Science ®] , [Google Scholar]) – one a laboratory-based study and one a field-based study – were re-analysed incorporating the strain indices. The laboratory study involved walking on a treadmill for 15 min while wearing three different clothing and equipment configurations. The field study involved three trials of standardised firefighting tasks in a live-fire training structure (mean trial length = 5.76 min). Heart rate, rectal temperature, thermal sensations and ratings of perceived exertion were collected in each study. PhSI and PeSI values were calculated using the formulae developed by Moran et al. (1998b Moran, D. S., Shitzer, A. and Pandolf, K. B. 1998b. A physiological strain index to evaluate heat stress. American Journal of Physiology, 275: R129–R134. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]) and Tikuisis et al. (2002 Tikuisis, P., McLellan, T. M. and Selkirk, G. 2002. Perceptual versus physiological heat strain during exercise-heat stress. Medicine & Science in Sports & Exercise, 34: 1454–1461. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]), respectively. PhSI and PeSI increased significantly over time in both studies. Even relatively brief bouts of exercise while wearing heavy impermeable clothing or simulated firefighting activity in the heat results in moderate to high levels of heat strain as assessed by PhSI and PeSI.     

A Novel High Quality High Capacity Image Hiding Scheme Based on Image Compression and an Optical Pixel Adjustment Process

ABSTRACT

Image hiding methods embed a secret image into a host image. The resultant stego-image does not attract the interceptors that would not detect the differences between the host image and the stego-image. To exploit the great developments in the area of image compression and to improve the quality of stego-image, this paper proposes a new method to embed the secret image into the host image. Basically, the secret image is compressed and then embedded into host image. The embedding method is based on the Optimal Pixel Adjustment Process (OPAP) and genetic algorithm. In the paper we addressed the important issues to build such systems. The experimental results showed that the proposed method can improve the quality from 60% to 80% when compared with the simple Least Significant Bit (LSB) replacement methods. Adding to that, the mean square error of the stego-image is much lower compared with other methods (Chan & Cheng, 2004 Chan, C.K. and Cheng, L.M. 2004. Hiding data in images by simple LSB substitution. Pattern Recognition, 37(3): 469–474. [Crossref], [Web of Science ®] , [Google Scholar]; Chang, Hsiao, & Chan, 2003 Chang, C.C., Hsiao, J.Y. and Chan, C.S. 2003. Finding optimal least-significant-bit substitution in image hiding by dynamic programming strategy. Pattern Recognition, 36(7): 1583–1595. [Crossref], [Web of Science ®] , [Google Scholar]; Thien & Lin, 2003 Thien, C.C. and Lin, J.C. 2003. A simple and high-hiding capacity method for hiding digit-by-digit data in images based on modulus function. Pattern Recognition, 36(12): 2875–2881. [Crossref], [Web of Science ®] , [Google Scholar]; Tseng, Chan, Ho, & Chu, 208; Wang, Lin, & Lin, 2001 Wang, R.Z., Lin, C.F. and Lin, J.C. 2001. Image hiding by optimal LSB substitution and genetic algorithm. Pattern Recognition, 34(3): 671–683. [Crossref], [Web of Science ®] , [Google Scholar]). Also, the proposed technique improves capacity. In other words, we can embed a secret image with size 450?×?450 inside a hosting image with size 512?×?512.     

Q 2 LEARNING AND ITS APPLICATION TO CAR MODELLING

In this paper we describe an application of Q ² learning, a recently developed approach to machine learning in numerical domains (?uc et al., 2003 ?uc , D. , D. Vladu?i? , and I. Bratko . 2003 . Qualitatively faithful quantitative prediction . Proceedings of the eighteenth International Joint Conference on Artificial Intelligence , 1052 – 1057 , Acapulco . Morgan Kaufmann . [Google Scholar] 2004 ?uc , D. , D. Vladu?i? , and I. Bratko . 2004 . Qualitatively faithful quantitative prediction . Artificial Intelligence , 158 : 189 – 214 . [CSA] [CROSSREF]  [Google Scholar]) to the automated modelling of a complex, industrially relevant mechanical system – a four wheel suspension and steering system of a car. In this experiment, first a qualitative model of this dynamic system was induced from data, and then this model was reified into a quantitative model. The induced qualitative models enable explanation of relations among the variables in the system and, when reified into quantitative models, enable accurate numerical prediction. Furthermore, the qualitative guidance of the quantitative modelling process leads to predictions that are significantly more accurate than those obtained by state-of-the-art numerical learning methods.     

Design process for developing a liquid cooling garment hood

A liquid cooling garment (LCG) protects astronauts by providing cooling effects and preventing them from overheating. The objectives of this project were to improve fit and comfort of the original LCG hood of the MACS-Delphi garment and develop a new prototype. The project was conducted by researchers with different backgrounds: apparel design and physiology and psychology. A design process framework developed by LaBat and Sokolowski (1999 LaBat, K. L. and Sokolowski, S. L. 1999. A three-stage design process applied to an industry-university textile product design project. International Textile & Apparel Association to Clothing and Textiles Research Journal, 17: 11–20. [Crossref] , [Google Scholar]) was used in order to help facilitate the process and aid in communication during the multi-disciplinary collaboration. Four crucial problems were identified: 1) the tubing layout that circulates water did not conform to the shape of the head and tubing distribution was not maximised; 2) a difficult stitching method was being used to attach tubing; 3) fabric sources were inconsistent; 4) the hood did not fit properly. Each problem was addressed, improvements implemented and a revised hood was developed. The hood was tested in an environmental chamber and demonstrated effective cooling. Revisions implemented for the LCG hood may be applied to revisions of the whole-body LCG.

Statement of Relevance:The objectives of this project were to improve fit and comfort of the original LCG hood and develop a new prototype. The new prototype will increase safety of the astronauts by providing better heat extraction quality and improved fit and increased wearer comfort.     

The classification of vigilance tasks in the real world

The ability to generalise vigilance research to operational environments has been questioned, largely due to differences between laboratory research and real-world settings. The taxonomy of vigilance tasks proposed by Parasuraman and Davies (1977 Parasuraman, R. and Davies, D. R. 1977. “A taxonomic analysis of vigilance performance”. In Vigilance: Theory, operational performance, and physiological correlates, Edited by: Mackie, R. R. 559–574. New York: Plenum. [Crossref] , [Google Scholar]) represents an attempt to classify vigilance tasks so that tasks with similar information-processing demands can be compared and the ability to generalise results enhanced. Although the taxonomy originally included complexity, the term specifically referred to multiple sources of information. Complexity has been overlooked in much of the traditional vigilance literature, although it is included in more recent studies of jobs such as air traffic control. In this paper, the taxonomy is evaluated in relation to two vigilance intensive jobs – closed circuit television surveillance operators and air traffic controllers. In its present form, the existing taxonomy of experimental settings has limited applicability to these operational settings. Therefore, recommendations for expanding the taxonomy to include more aspects of complexity are made. It is argued that the revised taxonomy be used in conjunction with situation awareness, which makes provision for the cognitive processes involved in these jobs.     

A refinement for the Rayleigh radiance computation with variation of the atmospheric pressure

The Rayleigh scattering radiance at the top of the atmosphere (TOA) depends on the surface atmospheric pressure. In processing the Coastal Zone Color Scanner (CZCS) imagery, Gordon et al. (Applied Optics, 27, 862–871, 1988 Gordon, H. R., Brown, J. W. and Evans, R. H. 1988. Exact Rayleigh scattering calculations for use with the Nimbus‐7 Coastal Zone Color Scanner.. Applied Optics, 27: pp. 862–871. [Crossref] , [Google Scholar]) developed a simple formula to account for the Rayleigh radiance changes with the variation of the surface atmospheric pressure. For the atmospheric pressure changes within ±3%, the accuracy of the Gordon et al. (1988 Gordon, H. R., Brown, J. W. and Evans, R. H. 1988. Exact Rayleigh scattering calculations for use with the Nimbus‐7 Coastal Zone Color Scanner.. Applied Optics, 27: pp. 862–871. [Crossref] , [Google Scholar]) formula in computing the Rayleigh radiance is usually within 0.4%, 0.3%, 0.15% and 0.05% for the wavelengths 412, 443, 555 and 865 nm, respectively. This could result in up to ～3% uncertainty in the derived water‐leaving radiance at the blue wavelengths for very clear atmospheres. To improve the performance, a refinement to the Gordon et al. (1988 Gordon, H. R., Brown, J. W. and Evans, R. H. 1988. Exact Rayleigh scattering calculations for use with the Nimbus‐7 Coastal Zone Color Scanner.. Applied Optics, 27: pp. 862–871. [Crossref] , [Google Scholar]) formula is developed based on the radiative transfer simulations. The refined scheme can produce Rayleigh radiance with an uncertainty within 0.1% (often within 0.05%) at the blue, while uncertainty is within 0.05% for the green to near‐infrared wavelengths. The refined algorithm has been implemented in the Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) data processing system. Results from the SeaWiFS data show the improved ocean colour products in the southern oceans where consistently low atmospheric pressures are usually observed. This could also significantly improve the performance of the Rayleigh radiance computations over the high altitude lakes. In addition, with the refined algorithm, the same Rayleigh radiance tables can be possibly used for the various ocean colour satellite sensors in which there are slightly different sensor spectral band characterizations.     

Capture of shrinking targets

‘Shrinking targets’ are targets whose size diminishes with time. The task studied is a modification of Fitts' (1954 Fitts, P. M. 1954. The information capacity of the human motor system in controlling the amplitude of movement. Journal of Experimental Psychology, 67(6): 381–391. [Crossref] , [Google Scholar]) paradigm, with the difference that, as soon as the movement is started, the target size reduces at a constant rate until it finally vanishes. Very little research has been reported on this problem apart from Johnson and Hart (1987 Johnson, W. W. and Hart, S. G. Step tracking shrinking targets. Proceedings of the Human Factors Society 31st annual meeting. October1987, New York City. pp.248–252. Santa Monica, CA: HFES.  [Google Scholar]) and Hancock and Caird (1993 Hancock, P. A. and Caird, J. K. 1993. Experimental evaluation of a model of mental workload. Human Factors, 35(3): 413–429. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]). Two experiments are reported aimed at determining the parameters that affect the movement time and the probability of capturing a target when there are different amplitudes of movement, target widths and shrink rates. A multiplicative model is required to describe movement time data, which is dependent on Fitts' Index of Difficulty, the shrink rate and the product of these two variables. An alternative model describes the critical movement time, for a specified probability of target capture, in a modified form of Fitts' Law.

Statement of Relevance: Modifications of Fitts' Law have been developed for many different movement tasks. Shrinking targets occur in circumstances such as gunnery and in computer games, where a target is moving away from the person. An expression is developed for the critical time to capture the target in terms of a modified form of Fitts' Law.     

MODELLING OF STATISTICAL LAWS FOR TEXTS USING A PEARSON SYSTEM

In this article, we have obtained a generalization of statistical laws for texts for application to natural languages, in order to determine whether this general law is applicable to model texts in accordance with the definition given in Villacampa et al. (1999a Villacampa , Y. Castro , M. A. , Usó , J. L. , and Sastre , P. 1999a. A text theory of ecological systems. Cybernetics and Systems . 30(7): 587–807.[Taylor & Francis Online], [Web of Science ®] , [Google Scholar]). The studies were carried out in the context of a system whose components generated model texts, through which we confirmed that the laws of Zipf and Mandelbrot are appropriate for explaining the texts. On the basis of a Pearson System, we also obtained a unique function for the distribution of frequencies, with said distribution being a generalization of the above-mentioned laws.

For the problem analyzed in this article, the text or text system constitutes a model of the cognitive development of individuals. We can thus infer the cognitive characteristics of different individuals by studying text systems.     

A new predicto-corrector method for pseudomonotone nonlinear complementarity problems

Based on the Logarithmic-Quadratic Proximal (LQP) method 2 Auslender, A., Teboulle, M. and Ben-Tiba, S. 1999. A logarithmic-quadratic proximal method for variational inequalities. Comput. Optim. Appl., 12: 31–40. [Crossref], [Web of Science ®] , [Google Scholar], we propose a new prediction-correction method for nonlinear complementarity problem (NCP). We obtain the predictor through a simplified inexact logarithmic-quadratic proximal method under a relaxed inexact criterion. The corrector is obtained by the improved extragradient method. Under certain conditions, the global convergence of the proposed method is proved. Preliminary numerical results indicate the efficiency of the proposed method.     

Development of an Instrument to Measure Enjoyment of Computer Game Play

This article reports on the development of an instrument designed to measure the enjoyment of computer game play. Despite the enormous technological progress in the field of computer games, enjoyment of computer game play is still not a well-defined construct. Based on Nabi and Krcmar's (2004 Nabi, R. L. and Krcmar, M. 2004. Conceptualizing media enjoyment as attitude: Implications for mass media effects research. Communication Theory, 14: 288–310. [Crossref], [Web of Science ®] , [Google Scholar]) tripartite model of media enjoyment, a survey questionnaire was developed to measure computer game players' affective, behavioral, and cognitive reactions. Expert consultation, exploratory, and confirmatory card sorting sessions were used to refine the instrument. A survey of computer game players was subsequently conducted to test the instrument. Reliabilities and construct validities were analyzed. Findings and their implications were discussed.     

Majorizing sequences for Newton's method under centred conditions for the derivative

We present semi-local and local convergence results for Newton's method in order to approximate a locally unique solution of a nonlinear equation in a Banach space setting. Our technique is more flexible than in earlier studies such that [J.A. Ezquerro, D. González, and M.A. Hernández, Majorizing sequences for Newton's method from initial value problems, J. Comput. Appl. Math. 236 (2012), pp. 2246–2258; J.A. Ezquerro, D. González, and M.A. Hernández, A general semi-local convergence result for Newton's method under centred conditions for the second derivative, ESAIM: Math. Model. Numer. Anal. 47 (2013), pp. 149–167]. The operator involved is twice Fréchet-differentiable. We also assume certain centred Lipschitz-type conditions for the derivative which are more precise than the Lipschitz conditions used in earlier works. Numerical examples are used to show that our results apply to solve equations but earlier ones do not in the semi-local case. In the local case we obtain a larger convergence ball. These advantages are obtained under the same computational cost as before [17 J.A. Ezquerro, D. González, and M.A. Hernández, Majorizing sequences for Newton's method from initial value problems, J. Comput. Appl. Math. 236 (2012), pp. 2246–2258. doi: 10.1016/j.cam.2011.11.012[Crossref], [Web of Science ®] , [Google Scholar],18 J.A. Ezquerro, D. González, and M.A. Hernández, A general semilocal convergence result for Newton's method under centered conditions for the second derivative, ESAIM: Math. Model. Numer. Anal. 47 (2013), pp. 149–167. doi: 10.1051/m2an/2012026[Crossref], [Web of Science ®] , [Google Scholar]].     

A MULTI-AGENT SYSTEM FOR THE MANAGEMENT OF ABNORMAL SITUATIONS IN AN ARTIFICIALLY GAS-LIFTED WELL

Concerning industrial automation, the management of abnormal situations becomes more important everyday. The ability to detect, isolate, and handle abnormal situations in industrial installations, could save huge amounts of money which is normally invested in reparations and/or wasted because of unjustified stoppage of processing plants. In this work, a system for the management of abnormal situations in an artificially gas-lifted well based on agents Abnormal Situations Management System (ASMS) is developed, which is part of the architecture of the industrial automation based on multi-agents systems (SADIA) proposed in Bravo, Aguilar, and Rivas (2004 Bravo , C. , J. Aguilar , and F. Rivas. 2004 . Diseño de una Arquitectura de Automatización Industrial Basada en Sistemas Multiagentes . Revista Ciencia e Ingeniería, Facultad de Ingeniería 25 ( 2 ): 77 – 88 . [Google Scholar]). This agent is based on the intelligent distributed control system based on agents (IDCSBA) reference model proposed in Aguilar, Cerrada, Mousalli, Rivas, and Hidrobo (2005 Aguilar , J. , M. Cerrada , G. Mousalli , F. Rivas , and F. Hidrobo. 2005 . A multiagent model for intelligent distributed control systems . Lecture Notes in Artificial Intelligence 3681 : 191 – 197 . [Google Scholar]). The MASINA methodology (Aguilar, Hidrobo, and Cerrada 2007 Aguilar , J. , F. Hidrobo , and M. Cerrada. 2007 . A methodology to specify multiagent systems . Lecture Notes in Artificial Intelligence 4496 : 92 – 101 . [Google Scholar]) is used in matters of analysis, design, and implementation.     

A note on ‘a replenishment policy for items with price-dependent demand,time-proportional deterioration and no shortages’

In a recent paper, Begum et al. (2012 Begum, R., Sahoo, R.R., and Sahu, S.K. (2012), ‘A Replenishment Policy for Items with Price-Dependent Demand, Time-Proportional Deterioration and no Shortages’, International Journal of Systems Science, 43, 903–910.[Taylor &; Francis Online], [Web of Science ®] , [Google Scholar], International Journal of Systems Science, 43, 903–910) established pricing and replenishment policy for an inventory system with price-sensitive demand rate, time-proportional deterioration rate which follows three parameters, Weibull distribution and no shortages. In their model formulation, it is observed that the retailer's stock level reaches zero before the deterioration occurs. Consequently, the model resulted in traditional inventory model with price sensitive demand rate and no shortages. Hence, the main purpose of this note is to modify and present complete model formulation for Begum et al. (2012) Begum, R., Sahoo, R.R., and Sahu, S.K. (2012), ‘A Replenishment Policy for Items with Price-Dependent Demand, Time-Proportional Deterioration and no Shortages’, International Journal of Systems Science, 43, 903–910.[Taylor &; Francis Online], [Web of Science ®] , [Google Scholar]. The proposed model is validated by a numerical example and the sensitivity analysis of parameters is carried out.     

A Pair-Wise Analysis of the Cognitive Demand Levels of Mathematical Tasks Used During Classroom Instruction and Those Assigned for Homework

Abstract

This research compared the cognitive demand levels of mathematical tasks engaged in during classroom instruction to paired mathematical tasks assigned for homework. The research took place in an eighth-grade classroom over the course of one school year. In total, the cognitive demand levels of 66 mathematical tasks were evaluated using the IQA Academic Rigor: Mathematics Rubric for the Potential of the Task (Boston & Smith, 2009 Boston, M. D. and Smith, M. S. 2009. Transforming secondary mathematics teaching: Increasing the cognitive demands of instructional tasks used in teachers’ classrooms. Journal for Research in Mathematics Education, 40(2): 119–156. [Web of Science ®] , [Google Scholar]). Results from this research showed that approximately two thirds of the time the mathematical tasks assigned for homework differed in levels from the tasks used during classroom instruction. Implications for student learning, classroom instruction, homework, and further research are discussed.