Wyniki wyszukiwania - Biblioteka Nauki

1

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

100%

Tang D. , Yu J.

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tom 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.

2

Does environmentalregulation affect the introduction of foreign direct investment in China? - Empirical research based on the spatial Durbin model

80%

Yang Y. , Niu G. , Tang D. , Zhu M.

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tom 28

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nr 1

EN

Based on the statistical data of 30 provinces in China from 2003 to 2014, this paper uses the spatial Durbin model to empirically test the influence of China’s urban environmental regulation on the introduction of foreign direct investment (FDI). The results show that there is significant spatial correlation between environmental regulation and FDI. Environmental regulation has a negative impact on the introduction of FDI, but the impact is not significant across the country, indicating that the evidence of the pollution haven hypothesis is insufficient in China. Then, the influential effect of environmental regulation on the introduction of FDI has obvious regional differences. The level of environmental regulation in the eastern region is positively correlated with the convenience in FDI introduction, while in the central and western regions, environmental regulation pose a hindrance to the introduction of FDI, which is remarkable only in the central area. In addition, labor costs and human capital levels have a direct effect on the introduction of FDI in the region. The level of regional economic development and R&D investment have a significant indirect impact on the introduction of FDI in surrounding areas, and economic openness has a significant impact on the introduction of FDI in all regions.

3

Mutual influence of energy consumption and foreign direct investment on haze pollution in China: a spatial econometric approach

80%

Tang D. , Xu H. , Yang Y.

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nr 4

EN

Based on the data of annual average values of PM₁₀ concentrations in China, this study empirically investigates the spatial autocorrelation of haze pollution in China and the mutual influence of energy consumption and foreign direct investment on haze pollution in China from 2004 to 2014 using the spatial econometric method. Moran’s I values are all above 0 during the 10 years, which indicates that haze pollution in China exists with significant spatial autocorrelation. Then the spatial econometric model estimation results show that energy consumption has a significant and positive effect on haze pollution in China while foreign direct investment has a significant and negative effect on haze pollution. Meanwhile, the regression coefficient of mutual variable of energy consumption and foreign direct investment is 0.063 at the 5% level, which suggests that foreign direct investment plays an important role in regulating the relationship between energy consumption and haze pollution, namely that the aggravation effect of energy consumption on haze pollution will increase with the increase of foreign direct investment. Finally, we provide some policy guidance for controlling haze pollution in China.

4

Optical waveform monitoring based on a free-running mode-locked femtosecond fibre laser and four-wave mixing in a highly nonlinear fibre

80%

Liu Y. , Zhang Y. G. , Tang D.

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tom Vol. 24, No. 2

62--74

EN

Optical sampling based on ultrafast optical nonlinearities is a useful technique to monitor the waveforms of ultrashort optical pulses. In this paper, we present a new implementation of optical waveform sampling systems by employing our newly constructed free-running mode-locked fibre laser with a tunable repetition rate and a low timing jitter, an all-optical waveform sampler with a highly nonlinear fibre (HNLF), and our developed computer algorithm for optical waveform display and measurement, respectively. Using a femtosecond fibre laser to generate the highly stable optical sampling pulses and exploiting the four-wave mixing effect in a 100m-long HNLF, we successfully demonstrate the all-optical waveform sampling of a 10GHz optical clock pulse sequence with a pulse width of 1.8 ps and a 80Gbit/s optical data signal, respectively. The experimental results show that waveforms of the tested optical pulse signals are accurately reproduced with a pulse width of 2.0 ps. This corresponds to a temporal resolution of 0.87 ps for optical waveform measurement. Moreover, the optical eye diagram of a 10Gbit/s optical data signal with a 1.8 ps pulse width is also accurately measured by employing our developed optical sampling system.

5

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

80%

Tang D. , Sheng W. , Yu J.

Eksploatacja i Niezawodność

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2018

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tom 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.

6

Spatial spillover effects of environmental regulations on China’s haze pollution based on static and dynamic spatial Panel data models

71%

Liu X. , Li L. , Ge J. , Tang D. , Zhao S.

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nr 4

EN

Rapid industrialization and urbanization have presented a dilemma to traditional environmental policies, and severe haze pollution has attracted particular attention in China. This paper employed the exploratory spatial data analysis technique to analyze global and local spatial auto-correlation of environmental regulations (ERS) and haze pollution. Static and dynamic spatial panel data models were further established to investigate the influence of ERS and its spatial spillover effect on haze pollution across 31 provinces of China in 2005-2015. Results showed that significant spatial autocorrelation existed for both ERS and haze pollution in China, forming different aggregation regions in terms of geographical distribution. There was strong evidence for the “inverted-U”-shaped EKC relationship between ERS and haze pollution regardless of whether it was the static or dynamic spatial econometric model. In addition, haze pollution was not only affected by economic growth, population size, and urbanization, but also by the haze pollution in the previous period. Conclusions and control strategies that would be of great significance for implementing effective management measures were synoptically discussed.

7

Thermotolerance and antioxidant response induced by heat acclimation in Freesia seedlings

71%

Yuan Y. , Qian H. , Yu Y. , Lian F. , Tang D.

Acta Physiologiae Plantarum

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2011

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tom 33

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nr 3

EN

Followed a heat acclimation pretreatment, seedlings of Freesia hybrida ‘Shangnong Jinghuanghou’ were exposed to heat stress at 38°C for 6 h treatment and then recovered at 22°C for 72 h to study the impact of heat acclimation (30°C) on thermotolerance under heat stress. The results showed that the pretreated seedlings performed better under heat stress than control. Heat acclimation could slow down the decrease of chlorophyll contents under heat stress and recover better. Higher levels of soluble sugar and proline and slight lower level of soluble protein were observed in pretreated seedlings. After recovery, similar levels of proline and soluble protein were maintained in all seedlings. However, a higher level of soluble sugar was maintained in pretreated seedlings. MDA content and EL showed a stable level in pretreated seedlings while a significant increase in control, followed by a significant decrease after recovery. Significant different responses of SOD, POD, CAT, and APX activities were observed in pretreated seedlings and control. Heat acclimation led to higher activities of these enzymes and a significant response of antioxidant enzyme activities occurred in a time-dependent manner under heat stress. Exposure to high temperature caused a significant increase in SOD and APX activity, and much higher levels in SOD and APX activity were observed in pretreated seedlings compared to control during heat stress. A slight difference in change pattern of POD and CAT activity was presented. The highest activities of POD and CAT were observed at 4 and 6 h of heat stress in pretreated seedlings and control, respectively. After 72 h recovery, the activities of all tested enzymes decreased to similar levels in all seedlings.