Resource Allocation in Ad Hoc Networks

Unlike the centralized network, the ad hoc network does not have any central administrations and energy is constrained, e.g. battery, so the resource allocation plays a very important role in efficiently managing the limited energy in ad hoc networks. This thesis focuses on the resource allocation in ad hoc networks and aims to develop novel techniques that will improve the network performance from different network layers, such as the physical layer, Medium Access Control (MAC) layer and network layer. This thesis examines the energy utilization in High Speed Downlink Packet Access (HSDPA) systems at the physical layer. Two resource allocation techniques, known as channel adaptive HSDPA and two-group HSDPA, are developed to improve the performance of an ad hoc radio system through reducing the residual energy, which in turn, should improve the data rate in HSDPA systems. The channel adaptive HSDPA removes the constraint on the number of channels used for transmissions. The two-group allocation minimizes the residual energy in HSDPA systems and therefore enhances the physical data rates in transmissions due to adaptive modulations. These proposed approaches provide better data rate than rates achieved with the current HSDPA type of algorithm. By considering both physical transmission power and data rates for defining the cost function of the routing scheme, an energy-aware routing scheme is proposed in order to find the routing path with the least energy consumption. By focusing on the routing paths with low energy consumption, computational complexity is significantly reduced. The data rate enhancement achieved by two-group resource allocation further reduces the required amount of energy per bit for each path. With a novel load balancing technique, the information bits can be allocated to each path in such that a way the overall amount of energy consumed is minimized. After loading bits to multiple routing paths, an end-to-end delay minimization solution along a routing path is developed through studying MAC distributed coordination function (DCF) service time. Furthermore, the overhead effect and the related throughput reduction are studied. In order to enhance the network throughput at the MAC layer, two MAC DCF-based adaptive payload allocation approaches are developed through introducing Lagrange optimization and studying equal data transmission period

Resource allocation in ad hoc networks

Unlike the centralized network, the ad hoc network does not have any central administrations and energy is constrained, e.g. battery, so the resource allocation plays a very important role in efficiently managing the limited energy in ad hoc networks. This thesis focuses on the resource allocation in ad hoc networks and aims to develop novel techniques that will improve the network performance from different network layers, such as the physical layer, Medium Access Control (MAC) layer and network layer. This thesis examines the energy utilization in High Speed Downlink Packet Access (HSDPA) systems at the physical layer. Two resource allocation techniques, known as channel adaptive HSDPA and two-group HSDPA, are developed to improve the performance of an ad hoc radio system through reducing the residual energy, which in turn, should improve the data rate in HSDPA systems. The channel adaptive HSDPA removes the constraint on the number of channels used for transmissions. The two-group allocation minimizes the residual energy in HSDPA systems and therefore enhances the physical data rates in transmissions due to adaptive modulations. These proposed approaches provide better data rate than rates achieved with the current HSDPA type of algorithm. By considering both physical transmission power and data rates for defining the cost function of the routing scheme, an energy-aware routing scheme is proposed in order to find the routing path with the least energy consumption. By focusing on the routing paths with low energy consumption, computational complexity is significantly reduced. The data rate enhancement achieved by two-group resource allocation further reduces the required amount of energy per bit for each path. With a novel load balancing technique, the information bits can be allocated to each path in such that a way the overall amount of energy consumed is minimized. After loading bits to multiple routing paths, an end-to-end delay minimization solution along a routing path is developed through studying MAC distributed coordination function (DCF) service time. Furthermore, the overhead effect and the related throughput reduction are studied. In order to enhance the network throughput at the MAC layer, two MAC DCF-based adaptive payload allocation approaches are developed through introducing Lagrange optimization and studying equal data transmission period.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Selective Metallization Induced by Laser Activation: Fabricating Metallized Patterns on Polymer via Metal Oxide Composite

Recently, metallization on polymer substrates has been given more attention due to its outstanding properties of both plastics and metals. In this study, the metal oxide composite of copper–chromium oxide (CuO·Cr₂O₃) was incorporated into the polymer matrix to design a good laser direct structuring (LDS) material, and the well-defined copper pattern (thickness =10 μm) was successfully fabricated through selective metallization based on 1064 nm near-infrared pulsed laser activation and electroless copper plating. We also prepared polymer composites incorporated with CuO and Cr₂O₃; however, these two polymer composites both had very poor capacity of selective metallization, which has no practical value for LDS technology. In our work, the key reasons causing the above results were systematically studied and elucidated using XPS, UV–vis–IR, optical microscopy, SEM, contact angle, ATR FTIR, and so on. The results showed that 54.0% Cu²⁺ in the polymer composite of CuO·Cr₂O₃ (the amount =5 wt %) is reduced to Cu⁰ (elemental copper) after laser activation (irradiation); however, this value is only 26.8% for the polymer composite of CuO (the amount =5 wt %). It was confirmed that to achieve a successful selective metallization after laser activation, not only was the new formed Cu⁰ (the catalytic seeds) the crucial factor, but the number of generated Cu⁰ catalytic seeds was also important. These two factors codetermined the final results of the selective metallization. The CuO·Cr₂O₃ is very suitable for applications of fabricating metallic patterns (e.g., metal decoration, circuit) on the inherent pure black or bright black polymer materials via LDS technology, which has a prospect of large-scale industrial applications

Effects of Different Ages of Robinia pseudoacacia Plantations on Soil Physiochemical Properties and Microbial Communities

Robinia pseudoacacia is widely planted on the Loess Plateau as a strong drought-tolerant and salt-tolerant species for vegetation restoration. However, this mode of pure plantation has triggered great concern over the soil ecosystem. The aim of this study was to explore the effects of the plantation on soil physiochemical properties, soil microorganisms, and the relationship between them in Robinia pseudoacacia plantations of different ages. Four different ages of Robinia pseudoacacia stands, including 10-year-old, 15-year-old, 25-year-old, and 40-year-old (abbreviated as Y10, Y15, Y25, and Y40, respectively) were selected, and 20 soil physicochemical and biological indicators were determined. The variation in soil microbial biomass was influenced by sampling depth, and consistent with the variations in TN (soil total nitrogen) and SOC (soil organic carbon) during 25 years’ artificial forestation. Soil moisture increased significantly at Y15 and then decreased at Y40 but other soil properties remained relatively stable. The contents of phosphor lipid fatty acid (PLFA) of different microbial groups followed the order of B (Bacteria) > G− (Gram-negative) > G+ (Gram-positive) > A (Actinomycetes) > F (Fungi). The ratios of F/B (Fungi to Bacteria) and Sat/Mono (Saturated PLFAs to Monosaturated PLFAs) of different ages of plantations showed a similar trend, i.e., declined first, then rose, and declined again. The ratios of Cy/Pre (Cyclopropyl PLFAs to Precursor PLFAs) and G+/G− (Gram-positive to Gram-negative) of the soil of all ages of plantations showed a trend of slow growth and a trend of rapid growth, respectively. Redundancy analysis showed that the contents of individual PLFAs and total PLFA were positively correlated with SOC and TN, but variations of soil PLFA ratios mostly depended on other soil properties. After artificial forestation, the ratios of F/B and Sat/Mono were lower than before forestation, while the ratio of Cy/Pre varied with different soil layers. The ratio of G+/G− increased with the increase in afforestation time, peaking at the 25th year. The contents of individual PLFAs and total PLFA may be sensitive indicators of SOC and TN within 25 years’ plantation. Lower ratio of F/B and higher G+/G− suggest that the sustainability of the ecosystem is weaker and the fertility of the soil is lower after plantation of Robinia pseudoacacia

Fabricating Metallic Circuit Patterns on Polymer Substrates through Laser and Selective Metallization

Nowadays, with the rapid development of portable electronics, wearable electronics, LEDs, microelectronics, and bioelectronics, the fabrication of metallic circuits onto polymer substrates with strong adhesion property is an ever-increasing challenge. In this study, the high-resolution and well-defined metallic circuits were successfully prepared on the polymer surface via laser direct structuring (LDS) based on copper hydroxyl phosphate [Cu₂(OH)­PO₄], and the key mechanism of the selective metallization was systematically investigated. XPS confirmed that Cu⁰ (elemental copper) was formed through photochemical reduction reaction of Cu₂(OH)­PO₄, after 1064 nm NIR pulsed laser irradiation. During the electroless plating, because it is the important active catalytic center, this newly formed Cu⁰ was the key factor to achieve the successful selective metallization. SEM revealed that after the electroless plating, the copper layer actually physically anchored into the polymer substrate, giving an excellent mechanical adhesion property of the obtained metallic patterns. In addition, the micro-Raman surface imaging approved the generation of the amorphous carbon on the polymer composites’ surface after NIR laser irradiation, and the chemical reaction region caused by the pulsed laser spot was found at approximately 40 μm. This environmentally friendly and effective strategy for fabricating circuit patterns on the polymer surface has a possible application in the printed circuit plate (PCB) industry

Effects of hydrogen sulfide on the growth and physiological characteristics of Miscanthus sacchariflorus seedlings under cadmium stress

As a gas signal molecule, hydrogen sulfide (H2S) can participate in many physiological and biochemical processes such as seed germination and photosynthesis regulation. In order to explore the regulatory effect of H2S on the growth of Miscanthus sacchariflorus under Cd stress and to provide sufficient theoretical basis for the complex action of H2S and energy plants to remediate soil pollution. In this experiment, the effects of different concentrations of H2S (10, 25, 50, 100, 300, 400, 500 μmol·L−1 (μM)) pretreatment on the growth index, lipid peroxidation degree, chlorophyll (Chl) content, osmoregulation substance content, antioxidant enzyme activity and non-enzymatic antioxidant content of M. sacchariflorus under Cd stress (50 μM) were studied. The results showed that under Cd stress, the reactive oxygen species (ROS) content in the body of M. sacchariflorus was unbalanced, and the growth were severely inhibited, the activities of antioxidant enzymes, such as catalase (CAT) and superoxide dismutase (SOD) significantly decreased, and the content of osmoregulation substance, ascorbic acid (AsA) and glutathione (GSH) significantly increased. With the increase of H2S concentration, its effect on resisting Cd stress can be shown as ''low concentration promotes, high concentration inhibits''. When the concentration of H2S ≤ 300 μM, although there was no significant difference in Cd content compared with Cd treatment alone, it can regulate the activities of peroxidase (POD), SOD, glutathione reductase (GR) and monodehydroascorbate reductase (MDHAR), increase the content of osmoregulation substances, oxidized glutathione (GSSG), and the transformation rate of AsA and dehydroascorbic acid (DHA) to reduce the oxidative damage and improve the growth and photosynthetic indicators of plants; when the concentration of H2S ≥ 400 μM, Cd content in the ground and root decreased significantly, but the transport factor increased significantly, the growth status of M. sacchariflorus were more severely inhibited by the combined stress of H2S and Cd. In this experiment, it was found that the concentration of H2S pretreatment ≤ 300 μM could regulate the growth of M. sacchariflorus under Cd stress to normal level, and when the treatment concentration was 50 μM, the effect was the best. It will provide a new idea for the treatment of contaminated soil by energy plants

Local Controllable Laser Patterning of Polymers Induced by Graphene Material

Graphene has been successfully applied to the field of polymer laser patterning. As an efficient 1064 nm near-infrared (NIR) pulsed laser absorber, only 0.005 wt % (50 ppm) of graphene prepared by mechanical exfoliation endowed polymer materials with very good NIR pulsed laser patterning. Optical microscopy observed that the generated black patterns came from the local discoloration of the polymer surface subjected to the laser irradiation, and the depth of the discolored layer was determined to be within 221–348 μm. The X-ray photoelectron spectroscopy confirmed that the polymer surface discoloration was contributed by the local carbonization of polymers caused by graphene due to its high photothermal conversion capacity. Raman depth imaging successfully detected that the generated carbon in the discolored layer was composed of amorphous carbon and complex sp/sp²-carbon compounds containing CC or conjugated CC/CC structures. This study also provides a simple guideline to fabricate laser-patterning polymer materials based on graphene. We believe that graphene has broad application prospects in the field of polymer laser patterning. Importantly, this work opens up a valuable, feasible direction for the practical application of this new carbon material