With the development of wireless communication systems, the demand for providing tunability in the wireless communication circuits becomes more and more intense. Among the technologies, semiconductor varactor is the critical component that is capable of implementing tunable and adaptive characteristics, particularly for the frond- end components of the wireless communication systems. For base station applications, high voltage handling capability, typically of 100 V or greater, high quality factor (Q), typically of above 100 at operation frequency, and high linearity, OIP3 > 65 dBm, are required. This work will mainly discuss in detail the design, fabrication and characterization to achieve the high-voltage high-Q and high-linearity microwave power varactors for wireless base station applications. Some preliminary varactor applications in the test tunable circuits will be demonstrated too. In this dissertation, we first introduce the physics of the semiconductor varactors and the motivation for choosing GaN as the candidate material for this microwave power varactor. Then we elucidate the critical design considerations for achieving high breakdown voltage, high quality factor and high linearity. The novel Schottky barrier engineered design using a thin InGaN surface layer on top of GaN to enhance the breakdown voltage of GaN-based Schottky diodes is therefore introduced. We then show the theoretical and experimental studies on the suppression mechanisms for electron tunneling in the InGaN/GaN Schottky barriers. The detailed material characterization for the InGaN/GaN material system and its application for the enhancement-mode HEMTs are also presented. Next, we discuss the initial device fabrication procedure and the improving methods based on the initial DC and RF measurement results. Thereafter, we report the detailed characterizations of the fabricated devices including the high-voltage I-V and C-V, S- parameters for 1-port and 2-port devices, linearity and application in the tunable resonant circuits. Finally, we summarize the dissertation and outline the future work. In this work, we achieved a high-performance GaN-based microwave power varactors with breakdown voltage > 100 V, quality factor > 100 and OIP3 > 71 dBm. It meets the initial goal of this project as well as the specifications in some practical applications. To the best of our knowledge, this combination of breakdown voltage, Q and OIP3 represents remarkable advancement from any other reported varactors

As bulk CMOS is approaching its scaling limit, SOI CMOS is gaining more and more attentions and is considered as a potential candidate for achieving 10-nm CMOS. Fully- depleted SOI MOSFETs have several inherent advantages over bulk MOSFETs-low junction capacitance, no body effect and no need for body doping to confine gate depletion. This dissertation presents a comprehensive, 2-D simulation- based design study on the scaling limit of ultra-thin silicon-on-insulator MOSFETs. Starting with the lateral- field analysis of fully-depleted (FD) SOI MOSFETs, it is shown that the general scale-length model is inapplicable for predicting the minimum scalable channel length when the buried-oxide is very thick. The scaling of FDSOI MOSFETs is independent of the buried-oxide thickness. An empirical prediction equation is developed by approximating the constant contours in a design plane of silicon-film and gate-dielectric thickness. Ultimately, ̃5tSi with a high-k gate dielectric. Other factors such as body doping, substrate biasing, and buried-insulator permittivity and bandgap affecting short-channel scaling of FDSOI are also investigated. Empirical prediction equations are developed for FDSOI devices with body doping and low-k buried-insulators. In principle, the can be improved from ̃5tSi to ̃2tSi by body doping. The can also be reduced 15% shorter from k=3.9 to k=1. Finally, the scaling limit of FDSOI MOSFETs is discussed. From the electrostatic perspective 10-nm FDSOI CMOS requires scaling both high-k gate-dielectric and silicon-film thickness to their limits of ̃2 nm. However, silicon-film thickness cannot below ̃3 nm to avoid severe mobility degradation. The scaling limit of FDSOI MOSFETs with a feasible HfO2 gate dielectric is then projected to be ̃17 nm. 10-nm FDSOI CMOS can be achieved only if there is a breakthrough on thin silicon-film mobility

The strychnine-sensitive glycine receptor (GlyR) mediates inhibitory synaptic transmission in the spinal cord and brainstem and is linked to neurological disorders, including autism and hyperekplexia. Understanding of molecular mechanisms and pharmacology of glycine receptors has been hindered by a lack of high-resolution structures. Here we report electron cryo-microscopy structures of the zebrafish α1 GlyR with strychnine, glycine, or glycine and ivermectin (glycine/ivermectin). Strychnine arrests the receptor in an antagonist-bound closed ion channel state, glycine stabilizes the receptor in an agonist-bound open channel state, and the glycine/ivermectin complex adopts a potentially desensitized or partially open state. Relative to the glycine-bound state, strychnine expands the agonist-binding pocket via outward movement of the C loop, promotes rearrangement of the extracellular and transmembrane domain 'wrist' interface, and leads to rotation of the transmembrane domain towards the pore axis, occluding the ion conduction pathway. These structures illuminate the GlyR mechanism and define a rubric to interpret structures of Cys-loop receptors.

The effects of hyperopia and frugality on spending have not been directly compared. Moreover, previous research on hyperopia has focused on the avoidance of luxury spending, rather than spending on routine consumer goods. We address these gaps in the literature by comparing how hyperopia and frugality affect monthly spending, and spending on ordinary consumer goods. Our survey indicates that both tendencies relate to lower monthly spending. Our shopping experiment extends these findings by showing that both hyperopic and frugal consumers avoid purchasing higher priced consumer goods when lower priced substitutes are available. Our findings contribute to the literature, which suggests that hyperopic consumers avoid indulgent luxuries, by showing that they also avoid higher priced routine consumer goods and exhibit lower monthly spending, similar to frugal consumers, but for fundamentally different reasons. Hyperopia inhibits spending by lowering the motivation to spend, while frugality inhibits spending by increasing the motivation to save.

The cell-autonomous role of synaptic transmission in the regulation of neuronal structural and electrical properties is unclear. We have now employed a genetic approach to eliminate glutamatergic synaptic transmission onto individual CA1 pyramidal neurons in a mosaic fashion in vivo. Surprisingly, while electrical properties are profoundly affected in these neurons, as well as inhibitory synaptic transmission, we found little perturbation of neuronal morphology, demonstrating a functional segregation of excitatory synaptic transmission from neuronal morphological development.

Finite element analysis (FEA)-based biomechanical modeling can be used to predict lung respiratory motion. In this technique, elastic models and biomechanical parameters are two important factors that determine modeling accuracy. We systematically evaluated the effects of lung and lung tumor biomechanical modeling approaches and related parameters to improve the accuracy of motion simulation of lung tumor center of mass (TCM) displacements. Experiments were conducted with four-dimensional computed tomography (4D-CT). A Quasi-Newton FEA was performed to simulate lung and related tumor displacements between end-expiration (phase 50%) and other respiration phases (0%, 10%, 20%, 30%, and 40%). Both linear isotropic and non-linear hyperelastic materials, including the neo-Hookean compressible and uncoupled Mooney-Rivlin models, were used to create a finite element model (FEM) of lung and tumors. Lung surface displacement vector fields (SDVFs) were obtained by registering the 50% phase CT to other respiration phases, using the non-rigid demons registration algorithm. The obtained SDVFs were used as lung surface displacement boundary conditions in FEM. The sensitivity of TCM displacement to lung and tumor biomechanical parameters was assessed in eight patients for all three models. Patient-specific optimal parameters were estimated by minimizing the TCM motion simulation errors between phase 50% and phase 0%. The uncoupled Mooney-Rivlin material model showed the highest TCM motion simulation accuracy. The average TCM motion simulation absolute errors for the Mooney-Rivlin material model along left-right, anterior-posterior, and superior-inferior directions were 0.80 mm, 0.86 mm, and 1.51 mm, respectively. The proposed strategy provides a reliable method to estimate patient-specific biomechanical parameters in FEM for lung tumor motion simulation.

Nowadays, large open spaces are popular in office buildings. However, occupants often complain about too cold and/or too warm in large open spaces. It remains a challenge to control the operation of air-conditioning systems to provide occupant comfort due to the ununiform distribution of airflow, internal heat gains and occupancy. Previous studies using CFD tools or building energy modelling tools alone did not solve the combined problem of the distributive temperature field in the space and the cooling demand from multiple terminal units. This study proposed to divide the large space into multiple subzone areas based on the layout of the terminal cooling equipment and the distribution of internal heat gains and occupancy. Regarding the uneven thermal environment among subzones, a coupling of FLUENT with EnergyPlus is used to compute the optimal thermostat setpoint for each subzone to ensure uniform occupant comfort in the large space. EnergyPlus computes the interior wall surface temperatures and terminal unit supply air flowrate of each subzone, which are passed to the CFD simulations as boundary conditions; while FLUENT simulates the temperature and PMV field with user defined function (UDF), as well as airflow rates across the virtual partition walls between two adjacent subzones, which are passed to EnergyPlus for consideration as inter-zone airflow. A case study using open office space in Hong Kong is conducted to demonstrate the validity of the methodology. Different temperature setpoints were estimated for the subzones, and the results indicated the subzone-based temperature setpoint could achieve uniform occupant thermal comfort and avoid overcooling. In addition, the coupling method improves the prediction accuracy of cooling energy than the standalone EnergyPlus program. Therefore, the coupling method can effectively provide a thermally comfortable environment with less energy use in large open office served by multiple terminal units.

Background

Low-tar cigarette smoking is gaining popularity in China. The China National Tobacco Corporation (CNTC) promotes low-tar cigarettes as safer than regular cigarettes.

Methods

A total of 543 male smokers smoking cigarettes with different tar yields (15 mg, regular cigarettes, 10-13 mg low-tar cigarettes and < 10 mg low-tar cigarettes) were recruited in Shanghai, China, who then completed a questionnaire on smoking behaviour and provided a urine sample for analysis of the nicotine metabolites cotinine and trans-3'-hydroxycotinine. A total of 177 urine samples were selected at random for the analysis of the carcinogens polycyclic aromatic hydrocarbon metabolites (PAHs) (1-hydroxypyrene, naphthols, hydroxyfluorenes and hydroxyphenanthrenes) and the tobacco specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-butanone (NNK) metabolites, 4-(methylnitrosamino)-1-(3-pyridyl)-butanol (NNAL) and NNAL-glucuronide. Values were normalised by creatinine to correct for possible distortions introduced by dilution or concentration of the urine.

Results

Smokers of low-tar cigarettes smoked fewer cigarettes per day (p=0.001) compared to smokers of regular cigarettes. Despite this lower reported consumption, levels of cotinine, trans-3'-hydroxycotinine and PAHs in urine of people smoking low-tar cigarettes were not correlated with nominal tar delivery of the cigarettes they smoked. Urine concentrations of NNAL were higher in smokers of lower tar than higher tar cigarettes.

Conclusions

Chinese low-tar cigarettes do not deliver lower doses of nicotine and carcinogens than regular cigarettes, therefore it is unlikely that there would be any reduction in harm. CNTC's promotion of low-tar cigarettes as 'less harmful' is a violation of the World Health Organization Framework Convention on Tobacco Control, which China ratified in 2005.

Background

Differences in carcinogen exposure from different cigarette products could contribute to differences in smoking-associated cancer incidence among Chinese compared with US smokers.

Methods

Urine concentrations of metabolites of nicotine, the tobacco-specific nitrosamine (TSNA) 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), and polycyclic aromatic hydrocarbon metabolites (PAHs) were compared in 238 Chinese and 203 US daily smokers.

Results

Comparing Chinese versus US smokers, daily nicotine intake and nicotine intake per cigarette smoked were found to be similar. When normalised for cigarettes per day, urine NNAL excretion was fourfold higher in US smokers, while the excretion of urine metabolites of the PAHs fluorene, phenanthrene and pyrene metabolites was 50% to fourfold higher in Chinese smokers (all, p<0.0001). Similar results were seen when NNAL and PAHs excretion was normalised for daily nicotine intake.

Conclusions

Patterns of carcinogen exposure differ, with lower exposure to TSNA and higher exposure to PAHs in Chinese compared with US smokers. These results most likely reflect country differences in cigarette tobacco blends and manufacturing processes, as well as different environmental exposures.

Trial registration number

NCT00264342.

The synthesis of metal frameworks perforated with nanotunnels is a challenge because metals have high surface energies that favor low surface area structures; traditional liquid-crystal templating techniques cannot achieve the synthetic control required. We report a synthetic strategy to fabricate metal nanomaterials with highly ordered, tunable mesostructures in confined systems based on a new quasi-hard-templating liquid-crystals mechanism. The resulting platinum nanowires exhibit long range two-dimensional hexagonally ordered mesopore structures. In addition, single crystalline hexagonal mesoporous platinum nanowires with dominant {110} facets have been synthesized. Finally, we demonstrate that the mesostructures of metal nanomaterials can be tuned from hexagonal to lamellar mesostructures.