572 research outputs found
Multi-objective imperfect maintenance for dependent competing risk systems with multiple degradation processes
No full textMultiple competing risks are one of the important topics in reliability field, especially degradation processes and random shocks. This research aims to relax the independent assumption by considering that there exist dependent relationships not only among multiple degradation measures but also between degradation measure and random shocks. In reality, many systems have multiple components with more than one degradation measure which is dependent with each other due to their interplaying functions or common usage history. Independent assumption may underestimate system reliability estimation under many cases. Random shocks will also contribute to the system failure through two ways: (1) one is working directly on the degradation processes; (2) the other is causing immediate failure to the system. We develop a new methodology to formulate the reliability prediction model for the gradually degradating systems subject to multiple dependent competing risks of degradation processes and random shocks. Two kinds of random shocks are considered: (1) fatal shocks, which fail the system immediately; (2) non-fatal shocks, which exhibit two effects on the system degradation process, including sudden degradation increment and degradation rate acceleration. The dependency between degradation processes and random shocks are modulated by a time-scaled covariate factors while the dependency among degradation processes are fitted by copula method. Also the reliability and state probability estimation for the systems are derived under the research scope of multi-state system using both analytical and Monte Carlo simulation for the dependent competing-risk systems. Different maintenance policy models involving imperefect preventive maintenance for this dependent model are introducted and compared with each other. Multi-objective optimization is applied to consider two important targets simultaneously in maintenance issues, including long-run expected cost rate and system availability.Ph. D.Includes bibliographical referencesIncludes vitaby Yaping Wan
Zai tong yin jia xi, tong xin xi liu xi he gai tai kuang bao mo zhong jing jie chu de neng dai jie gou yi ji dui guang fu biao xian de ying xiang
No full textPh.D.Polycrystalline Cu(In, Ga)Se₂ (CIGS), Cu2ZnSn(S, Se)₄ (CZTSSe) and perovskite thin films are all well-known light absorber materials for photovoltaic solar cells. The power conversion efficiency (PCE) of CIGS, CZTSSe and perovskite solar cells has respectively achieved 22.6%, 12.6% and 22.1% in the world. In this thesis, a combination of experiment techniques including transmission electron microscopy (TEM), atomic force microscopy (AFM) and scanning tunneling microscopy (STM) has been applied to investigate the composition, structure and electronic properties of GBs in these thin films.In CIGS thin films, we have studied on two well-designed CIGS samples with different overall Cu/(Ga+In) (CGI) ratios, CGI~0.9 and CGI~0.7. For non S3 GBs in both samples, we have found that a finite GB layer with a stepwise change in composition, structure and electronic properties from the adjacent GI can provide a strong evidence to the band offset between GI and GB regions. Although the two samples have large difference in the overall CGI, neither the compositions in their GIs nor the compositions in their GBs are the same. The only difference between the two samples, the width of the GB layer, depends on the overall Cu content in the films. The type II band alignment between GI and GB regions with downward offset in both conduction and valence bands near GBs correlated well to the well-defined CGI can reveal that the GB layer has a type inversion at the probed surface and a dramatically large hole barrier. Our results can establish a comprehensive picture to understand the benign role of GBs towards carrier recombination.In CZTSSe thin films, we have investigated the composition, structure and electronic properties of three well-designed CZTS, CZTSSe and CZTSe samples with different fabrication methods. In CZTS thin film, there is downward band bending in conduction band and upward band bending in valence band at GBs which is found harmful to the PV performance. On the contrary, in CZTSe thin film, the behavior of band bending at GBs, opposite to that in CZTS thin film, is benign for the PV performance. In CZTSSe thin film, because S/(S+Se) ratio gradually increases from GB to GI, the upward band bending in conduction band and downward band bending in valence band at GBs is benign for the PV performance. In addition, the secondary phase ZnS has been found in CZTS bulk and at the Mo/CZTS interface through TEM. Therefore, many defects and secondary phases in CZTSSe thin films are the big problems for the conversion efficiency of the solar cells. Considering all the results in the three thin films, it is found that the method of preparing the CZTSSe thin films can influence the band alignment between GI and GB.In perovskite thin films, we have mainly used STM to study the band alignment between GB and GI of the perovskite thin films without illumination. By STS measurements, there is no obvious difference in band edge positions of valence and conduction bands between GI and GB regions in both samples. In the Cs₀.₁₅FA₀.₈₅PbI₂.₂Br₀.₈ thin film with light illumination, we have observed the halide segregation that is iodine-rich and bromine-rich phases accumulate in GB region and GI region respectively. This halide segregation will increase the recombination rate in the iodine-rich region to degrade the performance of perovskite solar cells.In summary, we expect that our findings can contribute to further optimizing all types of thin film solar cells.多晶銅銦鎵硒，銅鋅錫硫和鈣鈦礦薄膜都是眾所周知的製作光伏太陽能電池的光吸收材料。在世界上，銅銦鎵硒，銅鋅錫硫和鈣鈦礦太陽能電池的能量轉換效率已經分別達到了 22.6%， 12.6%和 22.1%。在本論文中，多種試驗測試手段包括透射電子顯微鏡，原子力顯微鏡和掃描隧道顯微鏡都被運用於研究這些薄膜中晶界的組分，結構和電子特性等性質。在銅銦鎵硒薄膜中，我們研究了兩個精心設計的銅銦鎵硒的樣品，它們的整體的銅與鎵和銦的組分比是不同的，分別約是 0.9 和 0.7。對於這兩個樣品中的非S3 晶界，我們發現了有一個有限邊界的晶界層，它與相鄰的晶體內部在組分，結構和電子特性方面有階梯式的變化，這就為在晶體內部與晶界中存在能帶偏移提供了有力的證據。雖然這兩個樣品在整體銅與鎵和銦的組分比上有很大區別，但是無論這兩個樣品在晶體內的組分還是在晶界處的組分都是分別相同的。這兩個樣品唯一的區別在於晶界層的寬度，它與薄膜中整體的銅含量有關。在晶體內與晶界區域形成的 II 型能帶排列表現為在晶界附近導帶和價帶都有向下的偏移，這種與邊界清晰的銅與鎵和銦的組分比相關的能帶排列可以說明晶界處存在反型和一個比較大的空穴勢壘。我們的結果在理解晶界對於載流子復合的良性作用上建立了一個全面的描述。在銅鋅錫硫硒薄膜中，我們也研究了用不同方法製備的銅鋅錫硫，銅鋅錫硫硒和銅鋅錫硒三個薄膜的組分，結構和電子特性的性質。在銅鋅錫硫薄膜中，在晶界處存在導帶向下彎曲和價帶向上彎曲，這種能帶彎曲對於電池的光伏表現有害。相反的，在銅鋅錫硒薄膜中，晶界處的能帶彎曲的表現與銅鋅錫硫相反，並且對於電池的光伏表現是良性的。在銅鋅錫硫硒薄膜中，因為 S/(S+Se)的比例從晶體內部到晶界處逐漸增大，所以晶界處的導帶向上彎曲和價帶向下彎曲對電池的光伏表現是良性的。此外，我們在銅鋅錫硫層內和鉬層與銅鋅錫硫層的界面處發現了很多的硫化鋅二次相。因此，在銅鋅錫硫硒薄膜中的缺陷和二次相對於太陽能電池的效率是很大的問題。綜合以上在三個樣品的結果，可以發現製備銅鋅錫硫薄膜的方法可以影響晶體內與晶界之間的能帶排列。在鈣鈦礦薄膜中，我們主要用掃描隧道顯微鏡研究了無光照過的薄膜中晶體內與晶界之間的能帶排列。通過掃描隧道譜的測量，在兩種不同樣品中，晶體內與晶界處的價帶和導帶的能帶邊界位置沒有明顯區別。在用光照過的Css₀.₁₅FA₀.₈₅PbI₂.₂Br₀.₈薄膜中，我們觀察到了鹵化物的分相，這種分相主要表現在富碘和富溴相分別聚集在晶界和晶體內部。這種分相會增強在富碘相內的載流子復合速率。綜上所述，我們希望我們的發現可以對進一步優化所有類型的薄膜太陽能電池做出貢獻。Ma, Yaping = 在銅銦鎵硒, 銅鋅錫硫硒和鈣鈦礦薄膜中晶界處的能帶結構以及對光伏表現的影響 / 馬亞平.2, 4 in title are subscriptThesis Ph.D. Chinese University of Hong Kong 2017.Includes bibliographical references (leaves 101-114).Abstracts also in Chinese.Title from PDF title page (viewed on …).Ma, Yaping = Zai tong yin jia xi, tong xin xi liu xi he gai tai kuang bao mo zhong jing jie chu de neng dai jie gou yi ji dui guang fu biao xian de ying xiang / Ma Yaping
Fractal dynamics analysis of the VHF radiation pulses during initial breakdown process of lightning
No full textAuthor name used in this publication: Chen, Mingli.Author name used in this publication: Du, Yaping.2009-2010 > Academic research: refereed > Publication in refereed journalVersion of RecordRGCPolyU 512908EPublishedVoR allowe
Simultaneous observations of optical and electrical signals in altitude-triggered negative lightning flashes
No full textAuthor name used in this publication: Chen, Mingli.Author name used in this publication: Du, Yaping.2002-2003 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishedVoR allowe
Spatiotemporal dynamics of carbon cycling and thermokarst in response to climate and fire-regime changes in the Arctic tundra biome
No full textAmplified climate change and fire regime shifts in the northern high latitudes are posing growing threat to key properties and functions of tundra ecosystems, including soil carbon stock, permafrost stability and vegetation types. However, it remains poorly understood how tundra ecosystems will feedback to the combined forces of changing climate and fire disturbance. In this study, I integrated paleoecology, numerical modeling and remote sensing observation to address (1) the resilience and sensitivity of tundra carbon stocks to shifting fire regimes, (2) the consequences of climate change and fire disturbance on thermokarst disturbance (e.g. collapse of ground surface after permafrost thaw), and (3) the patterns of shrub expansion in heterogenous tundra landscape in response to accelerated warming and fire disturbance. My results indicate that fire disturbance has threshold effects on tundra carbon stocks. Variation in fire return intervals from 5000 to 900 years causes minimal carbon stock loss (<5%). However, increasing fire frequency beyond every 800 years is projected to trigger sustained mobilization of ancient soil organic matter that leads to irreversible carbon stock loss from permafrost. Multi-decade remote sensing observations revealed that tundra fires resulted in pervasive thermokarst formation, and that this impact lasted more than four decades. Nevertheless, substantial spatial heterogeneity exists regarding thermokarst formation and the greatest amount of thermokarst appears in severely burned tundra ecosystems in ice-rich areas. Although fire disturbance is a strong force exacerbating permafrost degradation, widespread warming surpasses sporadic burning as the primary driver responsible for ~90% of thermokarst growth in northern Alaskan tundra over the past ~70 yrs. Permafrost thawing strongly influences shrub cover dynamics in tundra ecosystems, but the net outcome is largely contingent on topographical positions. In poorly drained tundra lowlands, thermokarst-induced water impounding resulted in massive shrub cover loss throughout three decades following fire. In contrast, shrub expansion was significantly enhanced in well-drained upland tundra after fire disturbance, especially in area burned of high severity fire. In unburned tundra, a general increase of shrub cover was detected, driven primarily by warming temperature in the lowland but by increased precipitation in the upland. Overall my research yields new insights into the complex responses of tundra ecosystems to climate and fire-regime changes, and suggests the importance of incorporating such information into earth system models for improving our understanding of land-atmosphere feedback processes.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2022-08-01The student, Yaping Chen, accepted the attached license on 2020-06-17 at 13:59.The student, Yaping Chen, submitted this Dissertation for approval on 2020-06-17 at 14:01.This Dissertation was approved for publication on 2020-06-24 at 16:07.DSpace SAF Submission Ingestion Package generated from Vireo submission #15453 on 2020-10-02 at 15:49:26Made available in DSpace on 2020-10-07T22:48:07Z (GMT). No. of bitstreams: 3
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Lysiteles subdianicus Tang, Yin, Peng, Ubick & Griswold, 2008, sp. nov.
No full textLysiteles subdianicus sp. nov. Figs 17 a–l, 22 Type material: Holotype: male, CHINA, Yunnan Province, Fugong County, Lumadeng Township, Old Shibali [N 27.07831 º, E 98.77426 º], 2305 m, 15, 21 August 2005, Guo Tang (HNU-Tang 050704). Paratypes: 2 ɗ, 2 Ψ, same data as holotype (2 ɗ, 1 Ψ: HNU; 1 Ψ: CAS). Fugong County: 3 ɗ, 5 km from Yaping to Fugong [N 27.14497 °, E 98.74463 °], 2000 m, 7 May 2004, Heng-Mei Yan (CAS-Yan04050701). Etymology. The specific name is the combination of “ sub- ” and “ dianicus ”, referring to the similarity of the new species to L. dianicus Song & Zhao, 1994. Diagnosis. This species is very similar to L. dianicus Song & Zhao, 1994 (Figs 7) in the general appearance and the genital organs, the differences are discussed in the diagnosis of L. dianicus. Description. Male (holotype): Total length 3.00. Prosoma 1.60 long, 1.30 wide; opisthosoma 1.50 long, 1.20 wide. Dorsal shield of prosoma yellow with “n”-shaped blackish brown stripes. Eye area and clypeus blackish brown. Both AER and PER strongly recurved. Eye sizes and interdistances: AME 0.09, ALE 0.20, PME 0.07, PLE 0.14, AME - AME 0.20, AME - ALE 0.20, PME - PME 0.26, PME - PLE 0.35, MOA 0.30 long, front width 0.37, back width 0.38. Sternum yellow; chelicerae and labium blackish brown; gnathocoxae brown. Legs yellow with weak spines, femora I with 3 prolateral spines, tibiae and metatarsi I, II with 2 pairs of ventral spines, tibiae and metatarsi III, IV with 1 ventral spine. Leg measurements: I: 6.30 (1.90, 2.30, 1.20, 0.90); II: 6.70 (2.00, 2.40, 1.30, 1.00); III: 4.10 (1.10, 1.50, 0.80, 0.70); IV 4.30: (1.20, 1.50, 0.90, 0.70), formula 2, 1, 4, 3. Opisthosoma oval, dorsum yellow with black markings; anteriorly with a pair of brown longitudinal stripes; medially with a pair of small white spots; posteriorly with 3 pairs of large blackish brown stripes; laterally with a black stripe; venter yellow, with a “U”-shaped faint black marking. Palp (Figs 17 e–g, j). VTA digitform, apically curved; RTA long spatulate, with a small basal apophysis, apex sharp and curved. Embolus thick, with a small helix twisted in anticlockwise. Female (one of the paratypes, Tang 050704): Total length 3.80. Markings as in male, opisthosoma dorsum markings darker than in male. Prosoma 1.60 long, 1.30 wide; opisthosoma 2.30 long, 2.20 wide. Eye sizes and interdistances: AME 0.10, ALE 0.20, PME 0.08, PLE 0.15, AME - AME 0.16, AME - ALE 0.15, PME - PME 0.25, PME - PLE 0.33, MOA 0.25 long, front width 0.35, back width 0.39. Legs grey, leg measurements: I: 4.30 (1.20, 1.60, 0.90, 0.6); II: 4.60 (1.30, 1.60, 1.00, 0.70); III: 2.80 (0.90, 1.00, 0.50, 0.40); IV: 3.20 (1.00, 1.10, 0.60, 0.50), formula 2, 1, 4, 3. Opisthosoma wider than male, dorsum with 2 pairs of small white spots. Epigyne-vulva (Figs 17 h–i, k–l). Epigyne with a large atrium, copulatory openings lateral; copulatory ducts curved in elephant’s-trunk-shape; spermathecae globular. Variation. Total length: males 3.00– 3.40 (n = 6); females 3.60–3.80 (n = 2). Abdominal markings vary in size and number among observed specimens: two females with 2 pairs of small white spots; one male only with 1 pair of white spots; one male without white spot (Figs 17. a–d); 2 specimens without ventral U-shaped black marking before spinnerets. Distribution. China (recorded from Fugong County of Yunnan Province).Published as part of Tang, Guo, Yin, Chang-Ming, Peng, Xian-Jin, Ubick, Darrell & Griswold, Charles, 2008, The crab spiders of the genus Lysiteles from Yunnan Province, China (Araneae: Thomisidae), pp. 1-41 in Zootaxa 1742 on pages 32-34, DOI: 10.5281/zenodo.18154
Amphiphilic graft copolymer based on poly(styrene-co-maleic anhydride) with low molecular weight polyethylenimine for efficient gene delivery
No full textXiaopin Duan,1,2 Jisheng Xiao,2 Qi Yin,2 Zhiwen Zhang,2 Shirui Mao,1 Yaping Li21School of Pharmacy, Shenyang Pharmaceutical University, Shenyang, 2Center of Pharmaceutics, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, ChinaBackground and methods: A new amphiphilic comb-shaped copolymer (SP) was synthesized by conjugating poly(styrene-co-maleic anhydride) with low molecular weight polyethyleneimine for gene delivery. Fourier transform infrared spectrum, 1H nuclear magnetic resonance, and gel permeation chromatography were used to characterize the graft copolymer.Results: The buffering capability of SP was similar to that of polyethyleneimine within the endosomal pH range. The copolymer could condense DNA effectively to form complexes with a positive charge (13&ndash;30 mV) and a small particle size (130&ndash;200 nm) at N/P ratios between 5 and 20, and protect DNA from degradation by DNase I. In addition, SP showed much lower cytotoxicity than polyethyleneimine 25,000. Importantly, the gene transfection activity and cellular uptake of SP-DNA complexes were all markedly higher than that of complexes of polyethyleneimine 25,000 and DNA in MCF-7 and MCF-7/ADR cell lines.Conclusion: This work highlights the promise of SP as a safe and efficient synthetic vector for DNA delivery.Keywords: poly(styrene-co-maleic anhydride), polyethylenimine, DNA, gene deliver
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