Wyniki wyszukiwania - BazTech

1

Piezoelectric effect on thermoelastic Lamb waves in functionally graded plates

Wang X., Ren X., Yu J., Zhou H., Zhang X., Leng J

Archives of Mechanics

|

2023

|

Vol. 75, nr 1-2

3--26

EN

Based on the Lord–Shulman thermoelectric elasticity theory, the piezoelectric effect on the thermoelastic Lamb wave propagation in the functionally graded material (FGM) plate is investigated. The coupled wave equations are solved by employing the Legendre polynomial series approach (LSPA), which poses the advantages of small scale of eigenvalues matrix and a convenient solution. It can directly obtain the complex wave number solutions without iteration. The obtained complex solutions, which represent the wave propagation and attenuation, are compared with those available data. Numerical examples show that the influence of gradient is profound. Results indicate that the piezoelectric effects on attenuation with the open and closed circuit condition are consistent for the S0 and S1 modes, but are inconsistent for the A0 and A1 modes. Although the piezoelectric effect is weak on the dispersion and attenuation of thermal waves, it is notable for their physical field distributions. In addition, the relaxation time is critical to electric displacements of a thermal wave mode, but is not essential for those of Lamb-like modes. The results can be used for the optimization of thermo-electric-elastic coupling structures.

2

A quadrature-free Legendre polynomial approach for the fast modelling guided circumferential wave in anisotropic fractional order viscoelastic hollow cylinders

Zhang X., Liang S., Shao S., Yu J.

Archives of Mechanics

|

2021

|

Vol. 73, nr 2

121--152

EN

Compared to the traditional integer order viscoelastic model, a fractional order derivative viscoelastic model is shown to be advantageous. The characteristics of guided circumferential waves in an anisotropic fractional order Kelvin–Voigt viscoelastic hollow cylinder are investigated by a quadrature-free Legendre polynomial approach combining the Weyl definition of fractional order derivatives. The presented approach can obtain dispersion solutions in a stable manner from an eigenvalue/eigenvector problem for the calculation of wavenumbers and displacement profiles of viscoelastic guided wave, which avoids a lot of numerical integration calculation in a traditional polynomial method and greatly improves the computational efficiency. Comparisons with the related studies are conducted to validate the correctness of the presented approach. The full three dimensional spectrum of an anisotropic fractional Kelvin–Voigt hollow cylinder is plotted. The influence of fractional order and material parameters on the phase velocity dispersion and attenuation curves of guided circumferential wave is discussed in detail. Moreover, the difference of the phase velocity dispersion and attenuation characteristics between the Kelvin–Voigt and hysteretic viscoelastic models is also illustrated. The presented approach along with the observed wave features should be particularly useful in non-destructive evaluations using waves in viscoelastic waveguides.

3

Effect of calcination temperature on activation behaviors of coal-series kaolin by fluidized bed calcination

Yuan S., Han Y., Li Y., Gao P., Yu J.

Physicochemical Problems of Mineral Processing

|

2018

|

Vol. 54, iss. 2

590--600

EN

This paper is aimed at investigating activation behaviors for coal-series kaolin using fluidized bed calcination as a novel method. The properties of calcined products at different temperature by fluidized bed calcination were evaluated by determination of weight loss rate, whiteness, chemical oxygen demand (COD), aluminum dissolution degree. The thermal behaviors and reaction mechanism were characterized by thermo gravimetric-differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), particle size distribution (PSD) and scanning electron microscopy (SEM). The results showed that calcination temperature was essential factor determining the properties and crystallinity of calcined products using fluidized bed calcination. Coal-series kaolin transformed into irregular and amorphous metakaolin with excellent properties as calcined at 600-900 °C, which attributed to the dehydroxylation of kaolinite and combustion of carbon/organic matter. Calcined kaolin eliminated activity ascribed to the recrystallization into mullite when calcination temperature was over 1000 °C. It was believed that fluidized bed calcination was an efficient thermal activation technology for coal-series kaolin and the calcination temperature should be controlled accurately.

4

An innovative methodology for recycling iron from magnetic preconcentrate of an iron ore tailing

Yu J., Han Y., Gao P., Li Y., Yuan S., Li W.

Physicochemical Problems of Mineral Processing

|

2018

|

Vol. 54, iss. 3

668--676

EN

Iron ore tailing is a kind of hazardous solid waste produced by iron and steel industry. In order to separate and recycle iron from the magnetic preconcentrate of an iron ore tailing, an innovative technological route of fluidized magnetization roasting followed by low-intensity magnetic separation was proposed in this paper. The effects of roasting temperature, dosages of reducing gas CO and fluidizing gas N2 on recovery rate of iron were carried out and optimized. The results showed that the hematite was almost reduced to magnetite by a gas mixture of 4 m3/h CO and 1 m3/h N2 at roasting temperature of 540 °C. Under the optimized conditions, a magnetic concentrate assaying 61.4 wt% Fe with a recovery rate of 81.8% was obtained from the magnetic preconcentrate of an iron ore tailing. The iron chemical phase, X-ray diffraction (XRD), and optical metallographic microscope analyses revealed that siderite was converted to magnetite successfully after roasting, and some coarse magnetite-hematite interlocking particles were formed due to insufficient reaction time, which could also be recovered by magnetic separation after liberating from gangue minerals.

5

Image encryption combining discrete fractional angular transform with Arnold transform in image bit planes

Zhou Z., Yu J., Liao Q., Gong L.

Optica Applicata

|

2018

|

Vol. 48, nr 2

225--236

EN

A new image encryption algorithm by using a discrete fractional angular transform and Arnold transform in image bit planes is investigated. In the image encryption algorithm, the original image is encrypted by the Arnold transform in image bit planes firstly, and then the resulting image is encrypted by the discrete fractional angular transform further. The key of the image encryption algorithm includes the parameters of the Arnold transform and the order of the discrete fractional angular transform. It is shown that the proposed image encryption algorithm is of high security and strong enough to counteract some conventional image attack manners.

6

Evaluation on gas supply reliability of urban gas pipeline network

Li J., Yan M., Yu J.

Eksploatacja i Niezawodność

|

2018

|

Vol. 20, no. 3

471--477

EN

As one of the lifeline projects, an urban gas network is a complex system, as it requires maintenance of the supply capacity when any single pipeline is isolated due to failure. For such a system, its reliability needs to be evaluated. Considering that existing structural reliability and hydraulic reliability analyses reflect different aspects of the working conditions of an urban gas network, system reliability theory is employed to explain that only the gas supply reliability can achieve a comprehensive evaluation of the work capacity of the entire urban gas network, as it takes into account the combined influence of the structural reliability and hydraulic reliability. To calculate the parameters in the gas supply reliability evaluation, such as pipeline failure rate, flow reduction in the gas network under different failure conditions, etc., some research achievements in the field of structural reliability and hydraulic reliability are fully utilized. Then, the detailed calculation procedures of these parameters are given to evaluate the gas supply reliability in terms of operational and practical considerations. Finally, using an example of a simple double-loop gas network, the detailed process of the gas supply reliability evaluation of an urban gas network is described, and the feasibility of this evaluation method is also illustrated.

PL

Miejska sieć gazowa – jeden z kluczowych elementów infrastruktury miasta – stanowi złożony system, ponieważ wymaga utrzymania zdolności przesyłowej gdy przepływ gazu w jednym z rurociągów zostaje zamknięty w wyniku awarii. W przypadku tego rodzaju systemów, konieczna jest ocena niezawodności. Biorąc pod uwagę, iż dostępne w literaturze analizy niezawodności konstrukcyjnej i niezawodności hydraulicznej odzwierciedlają różne aspekty warunków pracy miejskiej sieci gazowej, nie dają one pełnego obrazu niezawodności systemu jako całości. W artykule wykorzystano teorię niezawodności systemów, która pokazuje, że jedynie ocena niezawodności dostaw gazu stanowić może kompleksową ocenę wydajności pracy całej miejskiej sieci gazowej, ponieważ uwzględnia ona zarówno wpływ niezawodności konstrukcji jak i niezawodności hydraulicznej sieci. W pracy wykorzystano dotychczasowe obserwacje badawcze dotyczące oceny niezawodności konstrukcyjnej i niezawodności hydraulicznej sieci gazowej do obliczenia parametrów oceny niezawodności dostaw gazu, takich jak intensywność uszkodzeń rurociągu, redukcja przepływu gazu w sieci gazowej w różnych warunkach uszkodzeń, itp. Następnie, podano szczegółowe procedury obliczania tych parametrów w celu oceny niezawodności przesyłowej sieci gazowej pod kątem eksploatacyjnym i praktycznym. Na koniec, na przykładzie prostej sieci gazowej składającej się z dwóch pętli, opisano szczegółowy proces oceny niezawodności dostaw gazu w miejskiej sieci gazowej i zilustrowano możliwość wykorzystania proponowanej metody.

7

Dynamic condition-based maintenance policy for degrading systems described by a random-coefficient autoregressive model: A comparative study

Tang D., Sheng W., Yu J.

Eksploatacja i Niezawodność

|

2018

|

Vol. 20, no. 4

590--601

EN

In this paper, we optimize a dynamic condition-based maintenance policy for a slowly degrading system subject to soft failure and condition monitoring at equidistant, discrete time epochs. A random-coefficient autoregressive model with time effect is developed to describe the system degradation. The system age, previous state observations, and the item-to-item variability of the degradation are jointly combined in the proposed degradation model. Stochastic behavior for both the age-dependent and the state dependent term are considered, and a Bayesian approach for periodically updating the estimates of the stochastic coefficients is developed to combine information from a degradation database with real-time condition-monitoring information. Based on this degradation model, the dynamic maintenance policy is formulated and solved in a semi-Markov decision process framework. Incorporated with the same semi-Markov decision process framework is a novel approach for mean residual life estimation, which enables simultaneous residual life estimation with the optimization procedure. The effectiveness of using the proposed random coefficient autoregressive model with time effect rather than the existing fixed-coefficient ones to describe system degradation is demonstrated through a comparative study based on a real degradation dataset. The advantages of using a dynamic maintenance policy are also revealed.

PL

W prezentowanej pracy dokonano optymalizacji dynamicznej, uwzględniającej stan techniczny obiektu strategii utrzymania ruchu dla wolno ulegającego degradacji systemu monitorowanego w równoodległych dyskretnych chwilach czasu (epokach) pod względem uszkodzeń parametrycznych oraz stanu technicznego. Do opisu degradacji systemu opracowano model autoregresyjny z parametrami losowymi uwzględniający wpływ czasu. Proponowany model degradacji bierze pod uwagę zarówno wiek systemu jak i wcześniejsze obserwacje stanu oraz zmienność degradacji pomiędzy obiektami. Rozważano zachowanie stochastyczne zarówno składnika zależnego od wieku jak i składnika zależnego od stanu; opracowano bayesowską metodę okresowej aktualizacji oszacowań współczynników stochastycznych, która pozwala łączyć informacje z bazy danych o degradacji z informacjami z monitorowania stanu w czasie rzeczywistym. W oparciu o otrzymany model degradacji, sformułowano dynamiczną politykę utrzymania ruchu; problem optymalizacji tej polityki rozwiązywano w ramach procesu decyzyjnego semi-Markowa. Do procesu decyzyjnego włączono nowatorską metodę obliczania trwałości resztkowej, co umożliwiło ocenę trwałości resztkowej jednocześnie z przeprowadzeniem procedury optymalizacyjnej. Skuteczność wykorzystania proponowanego modelu autoregresyjnego do opisu degradacji systemu porównywano ze skutecznością dotychczasowych modeli z parametrami stałymi w badaniu opartym na rzeczywistym zbiorze danych o degradacji. Wskazano również zalety stosowania proponowanej dynamicznej strategii utrzymania ruchu.

8

Image encryption algorithm by using the logistic map and discrete fractional angular transform

Yu J., Li Y., Xie X., Zhou N., Zhou Z.

Optica Applicata

|

2017

|

Vol. 47, nr 1

141--155

EN

A new image encryption scheme based on logistic map and discrete fractional angular transform has been proposed. In the proposed scheme, the original image is encrypted with the random sequence generated by the logistic map, and the encrypted image is subsequently processed by the discrete fractional angular transform, which produces the ciphertext after double encryptions. The parameters of the logistic map and the order of the discrete fractional angular transform serve as the main keys of the image encryption algorithm. Simulation results show that the proposed image encryption algorithm can effectively resist the attacks of statistical analysis, and has acceptable encryption effect and security.

9

Introduction and overview of China’s pilot training regime

Li W., Yu J., Desrosiers R.

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

|

2016

|

Vol. 10, no. 4

543--549

EN

When operating in confined waters such as ports, channels and canals, the ship’s master may not be familiar with the specific and up-to-date navigating conditions such as wind, current and tide. In this case, the master must rely on the knowledge and experience of local experts, the seaport and river pilots, to ensure the safety of the ship, crew and environment. This paper provides an overview of the initial and periodic training required by pilots directed by the China Maritime Safety Administration in accordance with IMO’s A.960 “Recommendation on Training and Certification and Operational Procedure Maritime Pilot Other Than Deep-Sea Pilot” and China’s pilot training requirements. The paper then goes into details describing how pilot training is implemented in Dalian Maritime University (DMU), taking into account the course setting, class hour arrangement, theory and practical class distribution of different class pilots, as well as examining the equipment requirements, trainer’s qualification, and trainee’s seagoing experiences. Based on the results of the China’s pilot training regime, recommendations will be made not only for improving China’s pilot training program, but also where DMU’s best practices may be implemented at other institutions engaged in pilot professional development.

10

Behavior and mechanism of collophane and dolomite separation using alkyl hydroxamic acid as a flotation collector

Yu J., Ge Y., Hou J.

Physicochemical Problems of Mineral Processing

|

2016

|

Vol. 52, iss. 1

155--169

EN

Flotation response of collophane and dolomite using alkyl hydroxamic acid (AH) (chelating collector) was investigated in the paper. The experiments were performed using pure and artificially mixed minerals as well as a real phosphate ore. Their separation mechanisms were studied by means of zeta potential measurements, infrared analysis, adsorption measurements, thermodynamics, and quantum chemical calculations. The results indicated that AH exhibited an excellent performance in the flotation separation of collophane from dolomite in neutral medium. The P2O5 grade of the concentrate increased from 19.84% to 30.51% without any other reagents when the pH value was about 7. The zeta potential and adsorption studies showed that the adsorption of AH at the cellophane/aqueous interface was greater than that at dolomite surface, which was the essential reason that separation of collophane from dolomite. The results of Fourier Transform Infrared (FTIR) spectrum and thermodynamics calculation indicated that the adsorption of AH at collophane was attributed to the chemical bonding. Moreover, AH molecule formed O-O five-membered ring with calcium ion on the collophane surface.

11

Strengthening and toughening mechanisms for polypropylene/Glass fiber composite foams under three-phase coexistence

Gong W., Yu J., Fu H., Zhang C., He L.

Polimery

|

2015

|

T. 60, nr 7-8

457--461

EN

Composite foams were obtained through a two-step molding process in an injection molding machine. Gas phase was introduced into the mixture of molten polypropylene (PP) and solid glass fiber (GF). The interfacial behavior was investigated, and the strengthening and toughening mechanisms for PP/GF composites under three-phase coexistence were discussed. The incorporation of gas phase significantly increased the tensile strength by 112 % and impact toughness by 105 % in comparison to its unfoamed counterpart. The resulting mechanical properties of the PP/GF composite foams were found to depend considerably on the coexistence state of solid (GF) and gas (cells) phases and the cell structure of the foams.

PL

Pianki kompozytowe otrzymano w dwustopniowym procesie formowania wtryskowego. Fazę gazową wprowadzano do mieszaniny stopionego polipropylenu (PP) ze stałymi włóknami szklanymi (GF). Badano właściwości mechaniczne otrzymanych pianek PP/GF oraz omówiono mechanizmy powodujące wzmacnianie i utwardzanie tych pianek w warunkach współistnienia trzech faz. Zaobserwowano, że wprowadzenie fazy gazowej znacznie zwiększa wytrzymałość na rozciąganie (o 112 %) i udarność pianki (o 105 %) w porównaniu z wartościami otrzymanymi w przypadku jej niespienionego odpowiednika. Stwierdzono, że właściwości mechaniczne pianek kompozytowych PP/GF w znacznym stopniu zależą od stanu współistnienia fazy stałej (GF) i gazowej (pory) oraz struktury komórkowej pianki.

12

Comparison of float-sink and progressive release flotation of ground products of coal middlings

Xie W., He Y., Luo C., Zhang X., Li H., Yu J., Wang H., Shi F.

Physicochemical Problems of Mineral Processing

|

2015

|

Vol. 51, iss. 2

675--684

EN

An additional recovery of coking coal middlings can be utilized for increasing of the concentrate yield of coking coal. A combined flow sheet of comminution and flotation can realize this target. To investigate the effect of grinding process on further flotation of ground products, progressive release flotation tests were used to compare with the float-sink tests, which were regarded as a criterion. Coal middlings were ground by wet-milling with iron balls to <0.5 mm. Curves of ash vs. cumulative yields of sized products indicated that the concentrate yield of coal separated by progressive release flotation was lower than that of coal benefited by the float-sink test, with the same ash for four size fractions (0.5-0.25 mm, 0.25-0.125 mm, 0.125-0.074 mm and <0.074 mm). Distributions of elements conducted by energy disperse spectroscopy (EDX) showed that associated kaolinite was liberated and exposed on the surface. It led to the shift of local surface property from hydrophobicity to hydrophilicity. Meanwhile, analyses of chemical property performed by an X-Ray photoelectron spectrometer (XPS) depicted that the hydrophilic mineral FeOOH, which generated in the grinding process, was adsorbed on the coal surface. Flotation of the ground products were worsened due to the increase of hydrophilicity of the coal surface.

13

Polioptymalizacja procesu obróbki elektroerozyjnej z proszkami przewodzącymi w dielektryku

Dąbrowski L., Zawora J., Yu J.

Mechanik

|

2015

|

R. 88, nr 12CD1

40--44

PL

W artykule scharakteryzowano procesy obróbki EDM z użyciem proszków w dielektryku. Wykonano badania z proszkami metali; Sn, Fe, Cu i opracowano modele matematyczne tych procesów. Dokonano polioptymalizacji badanych procesów z uwagi na wydajność obróbki, czas obróbki i parametr chropowatości Ra, Przedstawiono wyniki obliczeń oraz wnioski.

EN

The EDM process described in this paper has been carried out with the electrical conductive powder in dielectric. The powders of Sb, Fe and Cu were used. The mathematical model of this process wear has been developed. The poly-optimization method has been used in view of productivity, time of machining and parameter of surface roughness Ra.

14

Incremental Computing Approximations with the Dynamic Object set in Interval-valued Ordered Information System

Yu J., Xu W.

Fundamenta Informaticae

|

2015

|

Vol. 142, nr 1-4

373--397

EN

Rough set theory has been successfully used in formation system for classification analysis and knowledge discovery. The upper and lower approximations are fundamental concepts of this theory. The new information arrives continuously and redundant information may be produced with the time in real-world application. So, then incremental learning is an efficient technique for knowledge discovery in a dynamic database, which enables acquiring additional knowledge from new data without forgetting prior knowledge, which need to be updated incrementally while the object set get varies over time in the interval-valued ordered information system. In this paper, we analyzed the updating mechanisms for computing approximations with the variation of the object set. Two incremental algorithms respectively for adding and deleting objects with updating the approximations are proposed in interval-valued ordered information system. Furthermore, extensive experiments are carried out on six UCI data sets to verify the performance of these proposed algorithms. And the experiments results indicate the incremental approaches significantly outperform non-incremental approaches with a dramatic reduction in the computational time.

15

Optimal replacement policy for a periodically inspected system subject to the competing soft and sudden failures

Tang D., Yu J.

Eksploatacja i Niezawodność

|

2015

|

Vol. 17, no. 2

228--235

EN

This paper analyzes a replacement problem for a continuously degrading system which is periodically inspected and subject to the competing risk of soft and sudden failures. The system should be correctively replaced by a new one upon failure, or it could be preventively replaced before failure due to safety and economic considerations. Dependent soft and sudden failures are considered. The degradation process of the system observed by inspections exhibits a monotone increasing pattern and is described by a gamma process. The failure rate of the sudden failure is characterized by its dependency on the system age and the degradation state. By formulating the optimization problem in a semi-Markov decision process framework, the specific form of the optimal replacement policy which minimizes the long-run expected average cost per unit time is found, considering a cost structure that includes the cost for inspections, the cost for preventive replacement, and the costs for different failure modes. The corresponding computational algorithm to obtain the optimal replacement policy is also developed. A real data set is utilized to illustrate the application of the optimal replacement policy.

PL

W artykule przeanalizowano problem wymiany dotyczący poddawanego przeglądom okresowym systemu ulegającego ciągłej degradacji i narażonego na konkurujące zagrożenie uszkodzeniami parametrycznymi i nagłymi. System taki powinien zostać wymieniony na nowy w ramach konserwacji korygującej w przypadku wystąpienia uszkodzenia lub też, ze względów bezpieczeństwa i względów ekonomicznych, można dokonać wymiany profilaktycznej jeszcze przed wystąpieniem uszkodzenia. W artykule rozważono przypadek zależnych od siebie uszkodzeń parametrycznych i nagłych. Proces degradacji systemu obserwowany podczas przeglądów ma charakter monotonicznie rosnący i można go opisać za pomocą procesu gamma. Intensywność uszkodzeń nagłych zależy od wieku systemu i jego stanu degradacji. Formułując problem optymalizacyjny w ramach semi-markowskiego procesu decyzyjnego, można określić formę optymalnej polityki wymiany, która minimalizowałaby długookresowy średni koszt na jednostkę czasu, z uwzględnieniem struktury kosztów, która obejmuje koszty przeglądów, koszty wymiany profilaktycznej oraz koszty różnych przyczyn uszkodzeń. Opracowano odpowiedni algorytm obliczeniowy umożliwiający ustalenie optymalnej polityki wymiany. Zastosowanie proponowanej optymalnej polityki wymiany zilustrowano na przykładzie zbioru rzeczywistych danych.

16

Occupational Safety and Health Status of Sanitation Workers in Urban Areas: A Pilot Study From Wuhan, China

Gong Y., Yu J., Zhang X., Liang Y.

International Journal of Occupational Safety and Ergonomics

|

2013

|

Vol. 19, No. 3

435--442

EN

Sanitation workers' workload increases quickly with rapid urbanization, but there is almost no evidence or policy recommendations for their management in developing countries. This study describes the health status and occupational protection of sanitation workers; it also explores risk factors related to their health status in Wuhan City, China. Three hundred and eighty-five sanitation workers from 54 streets of Wuhan were surveyed. Their prevalence of 2-week illness and arthritis was relatively higher than in the general population in China. Findings related to occupational protection showed that both sanitation workers (users) and their managers (providers) neglected the role of low-cost protection measures, especially masks, soap/hand sanitizer and prejob training (use rate of 7.27%, 26.75% and 43.64%, respectively). High-intensity workload was an important risk factor for 2-week illness, and prejob training was an important protective factor against arthritis.

17

Conditions for tighter focusing and higher focal depth of radially polarized vector beam

Gao X, Wang Q, Yun M, Yu J, Guo H, Zhuang S

Optica Applicata

|

2012

|

Vol. 42, nr 1

85--101

EN

The radially polarized vector beam has attracted much attention recently and was also used to obtain a smaller focal spot. In this paper, highly focusing properties of radially polarized vector beam are investigated by comparing them with those of linearly polarized beam. A condition was found for tighter focusing of radially polarized vector beam. The focal spot of radially polarized vector beam is not always smaller than that of linearly polarized beam. Even if only a longitudinal field component is considered, in fact, the condition for tighter focusing of radially polarized vector beam is very complicated. Therefore, more attention should be paid to the smaller focal spot generation by means of radially polarized vector beam in practical use. In addition, the focal depth of radially polarized beam decreases on increasing numerical aperture under condition of small radius ratio, and increases on increasing radius ratio. The focal depth difference between these two kinds of beams shrinks upon increasing radius ratio and numerical aperture.

18

Rainfall time series forecasting based on Modular RBF Neural Network model coupled with SSA and PLS

Wu Yu J., Yu J.

Journal of Theoretical and Applied Computer Science

|

2012

|

Vol. 6, nr 2

3-12

EN

Accurate forecast of rainfall has been one of the most important issues in hydrological research. Due to rainfall forecasting involves a rather complex nonlinear data pattern; there are lots of novel forecasting approaches to improve the forecasting accuracy. In this paper, a new approach using the Modular Radial Basis Function Neural Network (M–RBF–NN) technique is presented to improve rainfall forecasting performance coupled with appropriate data–preprocessing techniques by Singular Spectrum Analysis (SSA) and Partial Least Square (PLS) regression. In the process of modular modeling, SSA is applied for the time series extraction of complex trends and structure finding. In the second stage, the data set is divided into different training sets by Bagging and Boosting technology. In the third stage, the modular RBF–NN predictors are produced by a different kernel function. In the fourth stage, PLS technology is used to choose the appropriate number of neural network ensemble members. In the final stage, least squares support vector regression is used for ensemble of the M–RBF–NN to prediction purpose. The developed RBF–NN model is being applied for real time rainfall forecasting and flood management in Liuzhou, Guangxi. Aimed at providing forecasts in a near real time schedule, different network types were tested with the same input information. Additionally, forecasts by M–RBF–NN model were compared to the convenient approach. Results show that the predictions made using the M–RBF–NN approach are consistently better than those obtained using the other method presented in this study in terms of the same measurements. Sensitivity analysis indicated that the proposed M-RBF-NN technique provides a promising alternative to rainfall prediction.

19

Forward-Secure Identity-Based Public-Key Encryption without Random Oracles

Yu J., Cheng X., Hao R., Kong F., Fan J.

Fundamenta Informaticae

|

2011

|

Vol. 111, nr 2

241-256

EN

In traditional identity-based encryption schemes, security will be entirely lost once secret keys are exposed. However, with more and more use of mobile and unprotected devices, key exposure seems unavoidable. To deal with this problem, we newly propose a forward-secure identitybased public-key encryption scheme. In this primitive, the exposure of the secret key in one period doesn't affect the security of the ciphertext generated in previous periods. Any parameter in our scheme has at most log-squared complexity in terms of the total number of time periods. We also give the semantic security notions of forward-secure identity-based public-key encryption. The proposed scheme is proven semantically secure in the standard model. As far as we are concerned, it is the first forward-secure identity-based public-key encryption scheme without random oracles.

20

A Novel Multimodal Probability Model for Cluster Analysis

Yu J., Yang M-S., Hao P.

Fundamenta Informaticae

|

2011

|

Vol. 111, nr 1

81-90

EN

Cluster analysis is a tool for data analysis. It is a method for finding clusters of a data set with most similarity in the same group and most dissimilarity between different groups. In general, there are two ways, mixture distributions and classification maximum likelihood method, to use probabilitymodels for cluster analysis. However, the corresponding probability distributions to most clustering algorithms such as fuzzy c-means, possibilistic c-means, mode-seeking methods, etc., have not yet been found. In this paper, we construct a multimodal probability distribution model and then present the relationships between many clustering algorithms and the proposed model via the maximum likelihood estimation. Moreover, we also give the theoretical properties of the proposed multimodal probability distribution.