146 research outputs found
Resource allocation for relay based green communication systems
No full textThe relay based cooperative network is one of the promising techniques for next generation wireless communications, which can help extend the cell coverage and enhance the diversity. To deploy relays efficiently with limited power and bandwidth under certain performance requirements, resource allocation (RA) plays an increasingly important role in the system design. In recent years, with the fast growth of the number of mobile phone users, great portion of CO2 emission is contributed by wireless communication systems. The combination of relay techniques and RA schemes reveals the solution to green communications, which aims to provide high data rate with low power consumption. In this thesis, RA is investigated for next generation relay based green wireless systems, including the long-range cellular systems, and the short-range point-to-point (P2P) systems.
In the first contribution, an optimal asymmetric resource allocation (ARA) scheme is proposed for the decode-and-forward (DF) dual-hop multi-relay OFDMA cellular systems in the downlink. With this scheme, the time slots for the two hops via each of the relays are designed to be asymmetric, i.e., with K relays in a cell, a total of 2K time slots may be of different durations, which enhances the degree of freedom over the previous work. Also, a destination may be served by multiple relays at the same time to enhance the transmission diversity. Moreover, closed-form results for optimal resource allocation are derived, which require only limited amount of feedback information. Numerical results show that, due to the multi-time and multi-relay diversities, the proposed ARA scheme can provide a much better performance than the scheme with symmetric time allocation, as well as the scheme with asymmetric time allocation for a cell composed of independent single-relay sub-systems, especially when the relays are relatively close to the source. As a result, with the optimal relay location, the system can achieve high throughput in downlink with limited transmit power.
In the second contribution, the power consumption in relay based 60 GHz cooperative networks is studied, which is based on three-terminal diversity amplify-and-forward (DAF) and diversity DF (DDF) relaying strategies. A total power consumption model including drive power, decoding power, and power consumption of power amplifier (PA) is proposed, excluding the transmit power, as it is relatively small compared to decoding power and PA power in the indoor environment. This model is formulated as a function of drive power, which gives an easy access to the system level power allocation. To minimise the system total power consumption, the optimal drive power can be allocated to the source node by numerical searching method while satisfying the data rate requirement. The impact of relay locations on the total power consumption is also investigated. It is shown that, with the same data rate requirement, in the small source-relay separation case, DAF consumes slightly less power than DDF; while with larger source-relay separation, DAF consumes much more power than DDF.
In the future work, multiuser relay-based short-range communication systems will be considered for the 60 GHz communication in the fading channel scenario, which extends the proposed power consumption model in a more practical way. The power consumption model of other components, such as analog-to-digital converter, data buffer, modulation/demodulation could also be considered to provide more details about green P2P communications
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Model and Experiment for Water Hyacinth and Its Control
No full textMy dissertation investigates the dynamics of invasive water hyacinth (Pontederia crassipes) using a combination of modeling and empirical approaches, with support from the Greater Everglades Priority Ecosystem Science program. My dissertation has seven chapters, each addressing a critical aspect of the research, from theoretical modeling to experimental validation, and offering insights into the broader applications for invasive species control.In Chapter 1, we develop a non-spatial model to study the interaction between herbicide, invasive floating species (water hyacinth), and biocontrol. Building upon the non-spatial model from Chapter 1, Chapter 2 extends this model to spatial scales. A spatially explicit model is developed to simulate the competition between invasive floating aquatic plants (FAV) and submerged aquatic vegetation (SAV), based on the classic competition model by Scheffer et al. (2003). In Chapter 3, we introduce biological control into the spatial model that is developed in Chapter 2. The chapter introduces across the modeled landscape the concepts of traveling waves, rock-paper-scissors dynamics, and long transient patterns, which drive the exploration in the following chapters. In Chapter 4, we focus on understanding the transition between long transient spatial patterns. In Chapter 5, we investigate the mechanisms behind the transition between long transient spatial patterns in more depth. In Chapter 6, the spatial competition model is expanded to include seasonal and temperature variation, examining how these factors affect the competition between Pontederia crassipes and submerged vegetation. In Chapter 7, we shift to testing the theoretical predictions made in earlier chapters. This chapter bridges the gap between theoretical modeling and field experimentation, providing empirical support for the predictions made in earlier chapters.In the future, I plan to apply the modeling approaches developed in this dissertation to other ecosystems.</p
The Mechanisms Underlying Cognitive Impairment Induced by Chronic Intermittent Hypoxia in Rodents
No full textObstructive sleep apnea (OSA) is a common breathing and sleeping disorder, characterized by repeated episodes of airway obstruction during sleep resulting in intermittent hypoxia (IH). From clinical reports, patients with OSA are associated with behavioral and neuropsychological deficits, including impaired spatial learning memory and cognitive deficiencies. Previous studies proposed that reactive oxygen species (ROS) and apoptosis caused by intermittent hypoxia (IH) contributed to this cognitive deficits. However, the exact mechanism is still poorly understood and not settled. The endoplasmic reticulum (ER) is a cellular organelle in which all secretory and integral membrane proteins are folded and is also the site where proteins are post-translationally modified in ATP-dependent chaperone-mediated processes. In this study, we hypothesized that ER stress in the hippocampus is initiated in the OSA via elevated levels of ROS. Four groups of adult male mice were used, with two of them exposed to normoxia as control, and the other two exposed to IH treatment, each receiving either vehicle or tauroursodeoxycholic acid (TUDCA), an ER stress inhibitor. Eight-armed radial maze was used to investigate the performance of reference memory during the whole IH/normoxia treatment. After behavior test, long-term potentiation (LTP) was measured to investigate synaptic plasticity in hippocampus. Furthermore, ER stress-associated pro-apoptotic effectors were detected by Western blotting, and ultra-structure of rough ER and the morphology of hippocampal dendritic spines and synapses in the hippocampal CA1 area were observed. LTP was impaired in the hippocampus after IH treatment, which was rescued by TUDCA. Furthermore, ER stress-associated pro-apoptotic effectors, CHOP and caspase-12, were up-regulated after chronic IH treatment and was abolished by co-infusion of TUDCA. Meanwhile, increased cleaved-caspase-3 after chronic IH treatment was reduced by TUDCA via increased expression of Bcl-2. On the other hand, ultrastructural analysis of rough ER in the hippocampal CA1 revealed IH-induced ER luminal swelling, and was attenuated by TUDCA. In addition, the length of synaptic active zone was significantly reduced after chronic IH treatment and was partially rescued by the application of TUDCA. Golgi staining also showed a decrease in mature dendritic spines in IH group, and reversed by TUDCA. In behavioral analysis, the number of reference memory errors significantly increased after IH treatment and rescued by TUDCA injection. Overall, the data suggest a critical role of ER stress underlying the impairment of long-term synaptic plasticity and neurocognitive deficits in chronic IH. Targeting ER stress could be a potential therapeutic strategy for neural dysfunction in OSA. On the other hand, neuronal firing, especially robust persistent activity of neuron in hippocampus, is critical role in memory formation. Increased ROS induced by IH has been implicated in long-term potentiation of neural activity. IH could be involved in a variety of K+ channels which eventually leads to excitotoxicity by increased Ca2+-dependent glutamate release. Although the results were just shown in acute IH treatment, the chronic effect of IH on the firing frequency of hippocampus is still unknown. Therefore, to investigate the effect of chronic IH treatment on firing activities and local field potentials of hippocampal neurons, implantation of multi-channel micro-wires electrode array into hippocampus of OSA model rat was performed to monitor spontaneous discharge. The results were shown the firing frequency of pyramidal neurons (PNs) was significantly elevated after 8 hours IH in second and third days, on the other hand, interneurons (INs) seem to be more sensitive to intermittent hypoxia since the higher firing frequency was sustained from third day to seventh day after 8 hours IH, however, at the end of 14 days IH treatment, the firing frequencies of PNs and INs are all both dramatically reduced. Meanwhile, the results in this part will enable us to understand the exact change of firing pattern and local field potential during intermittent hypoxia. The percentage of complex burst spikes was decreased after 14 days IH in PNs and the power of theta rhythms was also impaired. It suggests that the disorder of neuronal pattern and the change of local field potential are associated with cognitive impairment in OSA model. After 1 week recovery, the firing frequency of PNs was rescued again, but not for that of INs. We also found that the power of theta rhythms which had an important role in memory formation was weaker after 2 weeks IH treatment, however, the precise mechanism was still unknown. From the effect of intermittent hypoxia on spontaneous discharges and LFP of hippocampal neurons in free moving rat, it may reveal some roles of IH in cognitive impairment via disorder neuronal function in CA1 region
Model and Experiment for Water Hyacinth and Its Control
No full textMy dissertation investigates the dynamics of invasive water hyacinth (Pontederia crassipes) using a combination of modeling and empirical approaches, with support from the Greater Everglades Priority Ecosystem Science program. My dissertation has seven chapters, each addressing a critical aspect of the research, from theoretical modeling to experimental validation, and offering insights into the broader applications for invasive species control.In Chapter 1, we develop a non-spatial model to study the interaction between herbicide, invasive floating species (water hyacinth), and biocontrol. Building upon the non-spatial model from Chapter 1, Chapter 2 extends this model to spatial scales. A spatially explicit model is developed to simulate the competition between invasive floating aquatic plants (FAV) and submerged aquatic vegetation (SAV), based on the classic competition model by Scheffer et al. (2003). In Chapter 3, we introduce biological control into the spatial model that is developed in Chapter 2. The chapter introduces across the modeled landscape the concepts of traveling waves, rock-paper-scissors dynamics, and long transient patterns, which drive the exploration in the following chapters. In Chapter 4, we focus on understanding the transition between long transient spatial patterns. In Chapter 5, we investigate the mechanisms behind the transition between long transient spatial patterns in more depth. In Chapter 6, the spatial competition model is expanded to include seasonal and temperature variation, examining how these factors affect the competition between Pontederia crassipes and submerged vegetation. In Chapter 7, we shift to testing the theoretical predictions made in earlier chapters. This chapter bridges the gap between theoretical modeling and field experimentation, providing empirical support for the predictions made in earlier chapters.In the future, I plan to apply the modeling approaches developed in this dissertation to other ecosystems.</p
Insights into the role of an Arabidopsis nuclear matrix binding protein AHL22 in chromatin regulation and hypocotyl growth
No full textThe nuclear matrix is a nuclear compartment with diverse functions in chromatin regulation and transcription. However, how this structure influences epigenetic modifications and gene expression in plants is largely unknown. Here we showed that a nuclear matrix binding protein, AHL22, together with two transcriptional repressors FRS7 and FRS12, regulates hypocotyl elongation by suppressing the expression of a group of SMALL AUXIN UP RNA genes (SAURs) in Arabidopsis thaliana. The repression of SAURs depended on the attachment of SAUR loci to the nuclear matrix. In addition, the AHL22 complex recruited the histone deacetylase HDA15 to SAUR loci, leading to the removal of H3ac at SAUR loci. Taken together, our results indicate that MAR-binding proteins act as a hub for chromatin and epigenetic regulators, and illustrate a novel mechanism by which nuclear matrix attachment to chromatin regulates histone modifications, transcription, and hypocotyl elongation. Die Kernmatrix ist ein Kernkompartiment mit diversen Funktionen bei der Chromatinregulierung und -transkription. Wie diese Struktur epigenetische Modifikationen und die Genexpression in Pflanzen beeinflusst, ist jedoch weitgehend unbekannt. Hier haben wir gezeigt, dass ein Kernmatrix-Bindungsprotein, AHL22, zusammen mit zwei transkriptionellen Repressoren FRS7 und FRS12 die Hypokotylverlängerung reguliert, indem es die Expression einer Gruppe von SMALL AUXIN UP RNA-Genen (SAURs) in Arabidopsis thaliana unterdrückt. Die Unterdrückung von SAURs hing von der Anheftung von SAUR-Loci an die Kernmatrix ab. Darüber hinaus rekrutierte der AHL22-Komplex die Histon-Deacetylase HDA15 an SAUR-Loci, was zur Entfernung von H3ac an SAUR-Loci führte. Zusammengenommen zeigen unsere Ergebnisse, dass MAR-bindende Proteine als Knotenpunkt für Chromatin und epigenetische Regulatoren fungieren und einen neuartigen Mechanismus veranschaulichen, durch den die Anheftung der Kernmatrix an Chromatin Histonmodifikationen, Transkription und Hypokotylverlängerung reguliert
CUHK electronic theses & dissertations collection
No full textObstructive sleep apnea (OSA) is a common breathing and sleeping disorder, characterized by repeated episodes of airway obstruction during sleep resulting in intermittent hypoxia (IH). From clinical reports, patients with OSA are associated with behavioral and neuropsychological deficits, including impaired spatial learning memory and cognitive deficiencies. Previous studies proposed that reactive oxygen species (ROS) and apoptosis caused by intermittent hypoxia (IH) contributed to this cognitive deficits. However, the exact mechanism is still poorly understood and not settled.The endoplasmic reticulum (ER) is a cellular organelle in which all secretory and integral membrane proteins are folded and is also the site where proteins are post-translationally modified in ATP-dependent chaperone-mediated processes. In this study, we hypothesized that ER stress in the hippocampus is initiated in the OSA via elevated levels of ROS. Four groups of adult male mice were used, with two of them exposed to normoxia as control, and the other two exposed to IH treatment, each receiving either vehicle or tauroursodeoxycholic acid (TUDCA), an ER stress inhibitor. Eight-armed radial maze was used to investigate the performance of reference memory during the whole IH/normoxia treatment. After behavior test, long-term potentiation (LTP) was measured to investigate synaptic plasticity in hippocampus. Furthermore, ER stress-associated pro-apoptotic effectors were detected by Western blotting, and ultra-structure of rough ER and the morphology of hippocampal dendritic spines and synapses in the hippocampal CA1 area were observed.LTP was impaired in the hippocampus after IH treatment, which was rescued by TUDCA. Furthermore, ER stress-associated pro-apoptotic effectors, CHOP and caspase-12, were up-regulated after chronic IH treatment and was abolished by co-infusion of TUDCA. Meanwhile, increased cleaved-caspase-3 after chronic IH treatment was reduced by TUDCA via increased expression of Bcl-2. On the other hand, ultrastructural analysis of rough ER in the hippocampal CA1 revealed IH-induced ER luminal swelling, and was attenuated by TUDCA. In addition, the length of synaptic active zone was significantly reduced after chronic IH treatment and was partially rescued by the application of TUDCA. Golgi staining also showed a decrease in mature dendritic spines in IH group, and reversed by TUDCA. In behavioral analysis, the number of reference memory errors significantly increased after IH treatment and rescued by TUDCA injection. Overall, the data suggest a critical role of ER stress underlying the impairment of long-term synaptic plasticity and neurocognitive deficits in chronic IH. Targeting ER stress could be a potential therapeutic strategy for neural dysfunction in OSA.On the other hand, neuronal firing, especially robust persistent activity of neuron in hippocampus, is critical role in memory formation. Increased ROS induced by IH has been implicated in long-term potentiation of neural activity. IH could be involved in a variety of K⁺ channels which eventually leads to excitotoxicity by increased Ca2⁺-dependent glutamate release. Although the results were just shown in acute IH treatment, the chronic effect of IH on the firing frequency of hippocampus is still unknown.Therefore, to investigate the effect of chronic IH treatment on firing activities and local field potentials of hippocampal neurons, implantation of multi-channel micro-wires electrode array into hippocampus of OSA model rat was performed to monitor spontaneous discharge. The results were shown the firing frequency of pyramidal neurons (PNs) was significantly elevated after 8 hours IH in second and third days, on the other hand, interneurons (INs) seem to be more sensitive to intermittent hypoxia since the higher firing frequency was sustained from third day to seventh day after 8 hours IH, however, at the end of 14 days IH treatment, the firing frequencies of PNs and INs are all both dramatically reduced. Meanwhile, the results in this part will enable us to understand the exact change of firing pattern and local field potential during intermittent hypoxia. The percentage of complex burst spikes was decreased after 14 days IH in PNs and the power of theta rhythms was also impaired. It suggests that the disorder of neuronal pattern and the change of local field potential are associated with cognitive impairment in OSA model. After 1 week recovery, the firing frequency of PNs was rescued again, but not for that of INs. We also found that the power of theta rhythms which had an important role in memory formation was weaker after 2 weeks IH treatment, however, the precise mechanism was still unknown. From the effect of intermittent hypoxia on spontaneous discharges and LFP of hippocampal neurons in free moving rat, it may reveal some roles of IH in cognitive impairment via disorder neuronal function in CA1 region.阻塞性睡眠呼吸暫停(OSA) 是一種常見的睡眠障礙疾病，這種疾病的主要特徵是在睡眠過程中反復發作的氣道阻塞，從而導致间歇性缺氧(IH)。從臨床報導中發現，OSA患者表現出行為和神經心理缺陷，包括空間學習記憶的受損和認知缺陷。通過之前的研究表明，活性氧(ROS)的增多和細胞凋亡是間歇性缺氧所引起認知功能障礙的主要機制之一，然而，其具體的機制仍不清楚。作為細胞重要的細胞器，內質網是分泌蛋白和膜蛋白折疊組裝的主要場所，同時，由ATP依賴的分子伴侶所介導的蛋白質翻譯後修飾這一過程也主要在內置網中完成。在本課題中，我們假設在OSA模型的海馬組織中，內質網應激的啟動是由於缺氧引起的與活性氧(ROS)的升高。在本課題中，我們使用了四組成年雄性小鼠，其中兩組作為正常對照組，分別接受生理鹽水和牛磺去氧膽酸（一種常用的內質網抑制劑）的腹腔注射，另外兩組接受缺氧處理，同時也分別接受照生理鹽水和牛磺去氧膽酸注射。八臂放射迷宮被用來研究參考記憶的表現。行為學結束之後，長時程增強(LTP)用來測定海馬的突觸可塑性。用免疫印跡的方法檢測內質網應激的相關凋亡蛋白的表達情況，並且觀察海馬CA1區域中，內質網超微結構和海馬樹突棘數目及突觸形態的變化。從實驗結果中，LTP在缺氧後減弱，而TUDCA能夠部分恢復由於缺氧所導致的LTP的降低。除此之外，內質網應激相關的促凋亡蛋白(CHOP和caspase-12)在缺氧組中表達升高，但是在TUDCA組中有所減低，同時，我們還發現，TUDCA也能夠減低缺氧組中cleaved-caspase-3的表達，而這一作用，可能與提高Bcl-2蛋白的表達（一個可標記的抗凋亡蛋白）有關。在間歇性缺氧組的海馬CA1區域中，粗面內質網出現管腔的腫脹，這一超微結構的變化表明在內質網出現官腔中有的許多未折疊蛋白聚集，並通過TUDCA的注射能夠降解未折疊蛋白來緩解這一現象的發生。同時，在IH處理後，突觸超微結構也發生了形態上的變化。突觸活性區的長度在IH處理組中顯著減少，但是在TUDCA組中有一定程度的恢復。高爾基染色顯示，成熟樹突棘（海馬突觸可塑性的結構基礎）的數目在間歇性缺氧組中有所下降，而在TUDCA治療後，成熟樹突棘的數目有所上升。我們發現參考記憶錯誤次數在缺氧後都有明顯的升高，而在注射TUDCA後，參考記憶錯誤次數都有所降低。總之，這些結果證明，內質網應激在間歇性缺氧的所引起的長時程突觸可塑性減弱和神經認知功能的損傷起到關鍵的作用，而抑制內質網應激對OSA中的出現神經功能紊亂起到一定的預防和治療效果。而另一方面，神經元的放電，特別是海馬中神經元穩定持久的放電形式，對記憶的形成起到關鍵的作用。間歇性缺氧所引起的ROS的升高對於長時程增強的神經活動存在一定的關係，因為，通過以往的研究發現，間歇性缺氧可以通過多種鉀離子通道的啟動，最終由於鈣離子依賴的谷氨酸釋放的增多从而導致興奮性毒性的神經遞質的釋放。而這些結果只在急性缺氧模型中發現，慢性的間歇性缺氧對海馬的放電頻率的影響仍是未知之數。因此，為了探討長時程的間歇性缺氧對海馬神經元的放電頻率和局部場電位的影響，多管道微絲電極陣列植入OSA大鼠的海馬中來監控自發放電的影響。結果表明，錐體細胞的放電頻率在第二天和第三天的8小時的間歇性低氧後明顯的升高了。另一方面，我們觀察到中間神經元似乎對間歇性缺氧更敏感，因為，從第三天到第七天缺氧8小時後，神經元的放電頻率都明顯的增高。但是在間歇性缺氧14天后，錐體細胞和中間神經元的放電頻率都所有顯著性的減少。同時，這一部分結果準確表明了海馬神經元的放電模式和局部場電位在間歇性缺氧的模型的是如何變化的。我們發現錐體細胞所具有的複合簇狀放電的比例減少，同時，theta波(與記憶的形成有關)的能量也有所減低。而這種神經元活動和局部的場電位的異常變化可能與OSA模型中出現的總認知功能障礙有關。在恢復一周後，錐體細胞的放電頻率有所增加，基本上可以恢復到缺氧前的狀態，但是中間神經元的頻率卻沒有多大的改變, 但是，其具體機制仍不清楚。從間歇性缺氧對大鼠海馬神經元自發放電和場電位影響的結果，它揭示了間歇性缺氧通過擾亂海馬CA1區域神經元的功能從而導致認知功能損傷。Xu, Linhao.Thesis (Ph.D.)--Chinese University of Hong Kong, 2014.Includes bibliographical references (leaves 167-199).Abstracts also in Chinese.Title from PDF title page (viewed on 03, October, 2016).Detailed summary in vernacular field only.Detailed summary in vernacular field only.Detailed summary in vernacular field only.Detailed summary in vernacular field only.Detailed summary in vernacular field only
iSky:Efficient and Progressive Skyline Computing in a Structured P2P Network
No full textAn interesting problem in peer-based data management is efficient support for skyline queries within a multiattribute space. A skyline query retrieves from a set of multidimensional data points a subset of interesting points, compared to which no other points are better. Skyline queries play an important role in multi-criteria decision making and user preference applications. In this paper, we address the skyline computing problem in a structured P2P network. We exploit the iMinMax(θ) transformation to map high-dimensional data points to 1-dimensional values. All transformed data points are then distributed on a structured P2P network called BATON, where all peers are virtually organized as a balanced binary search tree. Subsequently, a progressive algorithm is proposed to compute skyline in the distributed P2P network. Further, we propose an adaptive skyline filtering technique to reduce both processing cost and communication cost during distributed skyline computing. Our performance study, with both synthetic and real datasets, shows that the proposed approach can dramatically reduce transferred data volume and gain quick response time
Modeling the Effects of Temperature and Limiting Nutrients on the Competition of an Invasive Floating Plant, Pontederia crassipes, with Submersed Vegetation in a Shallow Lake
No full textThe potential for a non-native plant species to invade a new habitat depends on broadscale factors such as climate, local factors such as nutrient availability, and the biotic community of the habitat into which the plant species is introduced. We developed a spatially explicit model to assess the risk of expansion of a floating invasive aquatic plant species (FAV), the water hyacinth (Pontederia crassipes), an invader in the United States, beyond its present range. Our model used known data on growth rates and competition with a native submersed aquatic macrophyte (SAV). In particular, the model simulated an invasion into a habitat with a mean annual temperature different from its own growth optimum, in which we also simulated seasonal fluctuations in temperature. Twenty different nutrient concentrations and eight different temperature scenarios, with different mean annual amplitudes of seasonal temperature variation around the mean of the invaded habitat, were simulated. In each case, the ability of the water hyacinth to invade and either exclude or coexist with the native vegetation was determined. As the temperature pattern was changed from tropical towards increasingly cooler temperate levels, the competitive advantage shifted from the tropical FAV to the more temperate SAV, with a wide range in which coexistence occurred. High nutrient concentrations allowed the coexistence of FAV, even at cooler annual temperatures. But even at the highest nutrient concentrations in the model, the FAV was unlikely to persist under the current climates of latitudes in the Southeastern United States above that of Northern Alabama. This result may have some implications for where control efforts need to be concentrated
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