细粒沉积物多组分粒度特征及其成因机制研究

By using high-resolution laser grain size instrument Mastersizer 2000, the grain size distribution of windblown depositions (loess and sandy dunes), aqueous sediments (lake, river, riverside and foreshore sand), weathering crust, sloping materials and other fine-grain sediments are systemically measured. The multimodal characteristics of grain size distribution of these sediments are carefully studied. The standard patterns and their grain size characteristics of various sediments are systemically summarized. The discrepancies of multimodal distribution among windblown depositions, aqueous sediments and other sediments are concluded and the physical mechanisms of grain size multimodal distribution of various sediments are also discussed in this paper. The major conclusions are followed: 1. The multimodal characteristic of grain size distribution is a common feature in all sediments and results from properties of transportation medium, dynamic intensity, transportation manner and other factors. 2. The windblown depositions are controlled by aerodynamic forcing, resulting in that the median size of the predominant mode gradually decreases form sandy dunes to loess. Similarly, the aqueous sediments are impacted by dynamic forces of water currents and the median grain size of the predominant mode decreases gradually from river to lake sediments. Because the kinetic viscidity of air is lower than of water, the grain size of modes of windblown depositions is usually finer than that of corresponding modes of aqueous sediments. Typical characteristics of sediments grain size distribution of various sediments have been summarized in the paper: (1) Suspended particles which diameters are less than 75μm are dominant in loess and dust. There are three modes in loess’ grain size distribution: fine, median and coarse (the median size is <1μm、1-10μm、10-75μm, respectively). The coarse mode which percentage is larger than that of others is controlled by source distance and aerodynamic intensity of dust source areas. Some samples also have a saltation mode which median size is about 300-500μm. Our analysis demonstrates that the interaction of wind, atmospheric turbulence, and dust grain gravity along the dust transportation path results in a multimodal grain size distribution for suspended dust. Changes in the median sizes of the coarse and medium modes are related to variation in aerodynamic forcing (lift force related to vertical wind and turbulence) during dust entrainment in the source area and turbulence intensity in the depositional area. (2) There is a predominant coarse saltation mode in grain size distribution of sandy dunes, which median size is about 100-300μm and the content is larger than that of other modes. The grain size distribution curve is near axis symmetric as a standard logarithm normal function. There are some suspended particles in some samples of sandy dunes, which distribution of the fine part is similar to that of loess. Comparing with sandy samples of river sediments, the sorting property of sandy dunes is better than of river samples although both they are the saltation mode. Thus, the sorting property is a criterion to distinguish dune sands and river sands. (3) There are 5~6 modes (median size are <1μm, 1-10μm, 10-70μm, 70-150μm, 150-400μm, >400μm respectively) in grain size distribution of lacustrine sediments. The former 4 modes are suspensive and others are saltated. Lacustrine sediments can be divided into three types: lake shore facies, transitional facies and central lake facies. The grain size distributions of the three facies are distinctly different and, at the same time, the transition among three modes is also clear. In all these modes, the third mode is a criteria to identify the windblown deposition in the watershed. In lake shore sediments, suspended particles are dominant, a saltation mode sometimes occurs and the fourth mode is the most important mode. In the transitional facies, the percentage of the fourth mode decreases and that of the second mode increases from lake shore to central lake. In the central lake facies, the second mode is dominant. A higher content of the second mode indicates its position more close to the central lake. (4) The grain size distribution of river sediments is the most complex. It consist of suspension, saltation and rolling modes. In most situations, the percentage of the saltation mode is larger than that of other modes. The percentage of suspension modes of river sediments is more than of sandy dunes. The grain size distribution of river sediments indicates dynamic strength of river currents. If the fourth mode is dominant, the dynamic forcing of river is weaker, such as in river floodplain. If the five or sixth mode is dominant, the water dynamic forcing of rivers is strong. (5) Sediments can be changed by later forcing in different degree to form some complicated deposition types. In the paper, the grain size distribution of aqueous sediments of windblown deposition, windblown sediments of aqueous deposition, weathering crust and slope materials are discussed and analyzed. 3. The grain size distribution characteristics of different sediments are concluded: (1) Modal difference: Usually there are suspended and saltation modes in the windblown deposition. The third mode is dominant in loess dust and the fifth mode is predominant in sandy dunes. There are suspended, saltation and rolling particles in aqueous sediments. In lacustrine sediments, the second and fourth mode are predominant for central lake facies or lake shore facies, respectively. In river sediments, the fourth, or fifth, or sixth mode is predominant. Suspended modes: the grain size of suspended particles of windblown depositions usually is less than 75μm. The content of suspended particles is lower or none in sandy dunes. However, suspended particles of aqueous sediments may reach 150μm. Difference in grain size of suspended modes represents difference between transitional mediums and the strength of dynamic forcing. Saltation modes: the median size of saltation mode of sandy dunes fluctuates less than that of river sediments. (2) Loess dust and lacustrine sediment: Their suspended particles are clearly different. There is an obvious pit between the second and the third modes in grain size distribution of lacustrine sediments. The phenomenon doesn’t occur in loess dust. In lacustrine sediments, the second mode can be a dominant mode, such as central lake facies, and contents of the second and the third modes change reversely. However, the percentage of the third mode is always the highest in loess dust. (3) Dune Sand and fluvial sand: In these two depositions, the saltation particles are dominant and the median sizes of their saltation modes overlay in distribution range. The fifth mode of dune sand fluctuates is sorted better than that of fluvial sand. (4) Lacustrine and fluvial sediments: In lacustrine sediments, there are 5-6 modes and suspended particles can be predominant. The second mode is dominant in central lake facies and the third mode is dominant in lake shore facies. Saltation or roll modes occurred in central lake facies may indicate strong precipitation events. In fluvial sediments, saltation particles (or rolling particles) usually dominant. 4. A estimation model of lake depth is firstly established by using contents of the second, the third and the fourth modes. 5. The paleoenvironmental history of the eastern part of SongLiao basin is also discussed by analyzing the grain size distribution of Yushu loess-like sediments in Jilin. It was found that there is a tectonic movement before 40ka B.P. in SongLiao basin. After the movement, loess dust deposited in Yushu area as keerqin desert developed. In recent 2000 years, the climate became drier and more deserts activated in the eastern part of Song-Liao basin.

Laserterapia em Implantologia

Projeto de Pós-Graduação/Dissertação apresentado à Universidade Fernando Pessoa como parte dos requisitos para obtenção do grau de Mestre em Medicina Dentária

Energy storage systems for wave energy converters and microgrids

The thesis initially gives an overview of the wave industry and the current state of some of the leading technologies as well as the energy storage systems that are inherently part of the power take-off mechanism. The benefits of electrical energy storage systems for wave energy converters are then outlined as well as the key parameters required from them. The options for storage systems are investigated and the reasons for examining supercapacitors and lithium-ion batteries in more detail are shown. The thesis then focusses on a particular type of offshore wave energy converter in its analysis, the backward bent duct buoy employing a Wells turbine. Variable speed strategies from the research literature which make use of the energy stored in the turbine inertia are examined for this system, and based on this analysis an appropriate scheme is selected. A supercapacitor power smoothing approach is presented in conjunction with the variable speed strategy. As long component lifetime is a requirement for offshore wave energy converters, a computer-controlled test rig has been built to validate supercapacitor lifetimes to manufacturer’s specifications. The test rig is also utilised to determine the effect of temperature on supercapacitors, and determine application lifetime. Cycle testing is carried out on individual supercapacitors at room temperature, and also at rated temperature utilising a thermal chamber and equipment programmed through the general purpose interface bus by Matlab. Application testing is carried out using time-compressed scaled-power profiles from the model to allow a comparison of lifetime degradation. Further applications of supercapacitors in offshore wave energy converters are then explored. These include start-up of the non-self-starting Wells turbine, and low-voltage ride-through examined to the limits specified in the Irish grid code for wind turbines. These applications are investigated with a more complete model of the system that includes a detailed back-to-back converter coupling a permanent magnet synchronous generator to the grid. Supercapacitors have been utilised in combination with battery systems for many applications to aid with peak power requirements and have been shown to improve the performance of these energy storage systems. The design, implementation, and construction of coupling a 5 kW h lithium-ion battery to a microgrid are described. The high voltage battery employed a continuous power rating of 10 kW and was designed for the future EV market with a controller area network interface. This build gives a general insight to some of the engineering, planning, safety, and cost requirements of implementing a high power energy storage system near or on an offshore device for interface to a microgrid or grid.

Multi-scale modelling of atomic layer deposition

High-permittivity ("high-k") dielectric materials are used in the transistor gate stack in integrated circuits. As the thickness of silicon oxide dielectric reduces below 2 nm with continued downscaling, the leakage current because of tunnelling increases, leading to high power consumption and reduced device reliability. Hence, research concentrates on finding materials with high dielectric constant that can be easily integrated into a manufacturing process and show the desired properties as a thin film. Atomic layer deposition (ALD) is used practically to deposit high-k materials like HfO2, ZrO2, and Al2O3 as gate oxides. ALD is a technique for producing conformal layers of material with nanometer-scale thickness, used commercially in non-planar electronics and increasingly in other areas of science and technology. ALD is a type of chemical vapor deposition that depends on self-limiting surface chemistry. In ALD, gaseous precursors are allowed individually into the reactor chamber in alternating pulses. Between each pulse, inert gas is admitted to prevent gas phase reactions. This thesis provides a profound understanding of the ALD of oxides such as HfO2, showing how the chemistry affects the properties of the deposited film. Using multi-scale modelling of ALD, the kinetics of reactions at the growing surface is connected to experimental data. In this thesis, we use density functional theory (DFT) method to simulate more realistic models for the growth of HfO2 from Hf(N(CH3)2)4/H2O and HfCl4/H2O and for Al2O3 from Al(CH3)3/H2O.Three major breakthroughs are discovered. First, a new reaction pathway, ’multiple proton diffusion’, is proposed for the growth of HfO2 from Hf(N(CH3)2)4/H2O.1 As a second major breakthrough, a ’cooperative’ action between adsorbed precursors is shown to play an important role in ALD. By this we mean that previously-inert fragments can become reactive once sufficient molecules adsorb in their neighbourhood during either precursor pulse. As a third breakthrough, the ALD of HfO2 from Hf(N(CH3)2)4 and H2O is implemented for the first time into 3D on-lattice kinetic Monte-Carlo (KMC).2 In this integrated approach (DFT+KMC), retaining the accuracy of the atomistic model in the higher-scale model leads to remarkable breakthroughs in our understanding. The resulting atomistic model allows direct comparison with experimental techniques such as X-ray photoelectron spectroscopy and quartz crystal microbalance.

Electrical machine characterisation and analysis for renewable energy applications

There has been an increased use of the Doubly-Fed Induction Machine (DFIM) in ac drive applications in recent times, particularly in the field of renewable energy systems and other high power variable-speed drives. The DFIM is widely regarded as the optimal generation system for both onshore and offshore wind turbines and has also been considered in wave power applications. Wind power generation is the most mature renewable technology. However, wave energy has attracted a large interest recently as the potential for power extraction is very significant. Various wave energy converter (WEC) technologies currently exist with the oscillating water column (OWC) type converter being one of the most advanced. There are fundemental differences in the power profile of the pneumatic power supplied by the OWC WEC and that of a wind turbine and this causes significant challenges in the selection and rating of electrical generators for the OWC devises. The thesis initially aims to provide an accurate per-phase equivalent circuit model of the DFIM by investigating various characterisation testing procedures. Novel testing methodologies based on the series-coupling tests is employed and is found to provide a more accurate representation of the DFIM than the standard IEEE testing methods because the series-coupling tests provide a direct method of determining the equivalent-circuit resistances and inductances of the machine. A second novel method known as the extended short-circuit test is also presented and investigated as an alternative characterisation method. Experimental results on a 1.1 kW DFIM and a 30 kW DFIM utilising the various characterisation procedures are presented in the thesis. The various test methods are analysed and validated through comparison of model predictions and torque-versus-speed curves for each induction machine. Sensitivity analysis is also used as a means of quantifying the effect of experimental error on the results taken from each of the testing procedures and is used to determine the suitability of the test procedures for characterising each of the devices. The series-coupling differential test is demonstrated to be the optimum test. The research then focuses on the OWC WEC and the modelling of this device. A software model is implemented based on data obtained from a scaled prototype device situated at the Irish test site. Test data from the electrical system of the device is analysed and this data is used to develop a performance curve for the air turbine utilised in the WEC. This performance curve was applied in a software model to represent the turbine in the electro-mechanical system and the software results are validated by the measured electrical output data from the prototype test device. Finally, once both the DFIM and OWC WEC power take-off system have been modeled succesfully, an investigation of the application of the DFIM to the OWC WEC model is carried out to determine the electrical machine rating required for the pulsating power derived from OWC WEC device. Thermal analysis of a 30 kW induction machine is carried out using a first-order thermal model. The simulations quantify the limits of operation of the machine and enable thedevelopment of rating requirements for the electrical generation system of the OWC WEC. The thesis can be considered to have three sections. The first section of the thesis contains Chapters 2 and 3 and focuses on the accurate characterisation of the doubly-fed induction machine using various testing procedures. The second section, containing Chapter 4, concentrates on the modelling of the OWC WEC power-takeoff with particular focus on the Wells turbine. Validation of this model is carried out through comparision of simulations and experimental measurements. The third section of the thesis utilises the OWC WEC model from Chapter 4 with a 30 kW induction machine model to determine the optimum device rating for the specified machine. Simulations are carried out to perform thermal analysis of the machine to give a general insight into electrical machine rating for an OWC WEC device.

Midlatitude daytime D region ionosphere variations measured from radio atmospherics

We measured the midlatitude daytime ionospheric D region electron density profile height variations in July and August 2005 near Duke University by using radio atmospherics (or sferics for short), which are the high-power, broadband very low frequency (VLF) signals launched by lightning discharges. As expected, the measured daytime D region electron density profile heights showed temporal variations quantitatively correlated with solar zenith angle changes. In the midlatitude geographical regions near Duke University, the observed quiet time heights decreased from ∼80 km near sunrise to ∼71 km near noon when the solar zenith angle was minimum. The measured height quantitative dependence on the solar zenith angle was slightly different from the low-latitude measurement given in a previous work. We also observed unexpected spatial variations not linked to the solar zenith angle on some days, with 15% of days exhibiting regional differences larger than 0.5 km. In these 2 months, 14 days had sudden height drops caused by solar flare X-rays, with a minimum height of 63.4 km observed. The induced height change during a solar flare event was approximately proportional to the logarithm of the X-ray flux. In the long waveband (wavelength, 1-8 Å), an increase in flux by a factor of 10 resulted in 6.3 km decrease of the height at the flux peak time, nearly a perfect agreement with the previous measurement. During the rising and decaying phases of the solar flare, the height changes correlated more consistently with the short, rather than the long, wavelength X-ray flux changes. © 2010 by the American Geophysical Union.

Comparative analyses of seven algorithms for copy number variant identification from single nucleotide polymorphism arrays.

Determination of copy number variants (CNVs) inferred in genome wide single nucleotide polymorphism arrays has shown increasing utility in genetic variant disease associations. Several CNV detection methods are available, but differences in CNV call thresholds and characteristics exist. We evaluated the relative performance of seven methods: circular binary segmentation, CNVFinder, cnvPartition, gain and loss of DNA, Nexus algorithms, PennCNV and QuantiSNP. Tested data included real and simulated Illumina HumHap 550 data from the Singapore cohort study of the risk factors for Myopia (SCORM) and simulated data from Affymetrix 6.0 and platform-independent distributions. The normalized singleton ratio (NSR) is proposed as a metric for parameter optimization before enacting full analysis. We used 10 SCORM samples for optimizing parameter settings for each method and then evaluated method performance at optimal parameters using 100 SCORM samples. The statistical power, false positive rates, and receiver operating characteristic (ROC) curve residuals were evaluated by simulation studies. Optimal parameters, as determined by NSR and ROC curve residuals, were consistent across datasets. QuantiSNP outperformed other methods based on ROC curve residuals over most datasets. Nexus Rank and SNPRank have low specificity and high power. Nexus Rank calls oversized CNVs. PennCNV detects one of the fewest numbers of CNVs.

Modeling X-ray photoionized plasmas produced at the Sandia Z-facility

In experiments at the high-power Z-facility at Sandia National Laboratory in Albuquerque, New Mexico, we have been able to produce a low density photoionized laboratory plasma of Fe mixed with NaF. The conditions in the experiment allow a meaningful comparison with X-ray emission from astrophysical sources. The charge state distributions of Fe, Na and F are determined in this plasma using high resolution X-ray spectroscopy. Independent measurements of the density and radiation flux indicate unprecedented values for the ionization parameter xi = 20-25 erg cm s(-1) under nearly steady-state conditions. First comparisons of the measured charge state distributions with X-ray photoionization models show reasonable agreement, although many questions remain.

Packet classification by multi-level cutting of the classification space: An algorithmic-architectural solution for IP packet classification in next generation networks

Traditionally, the Internet provides only a “best-effort” service, treating all packets going to the same destination equally. However, providing differentiated services for different users based on their quality requirements is increasingly becoming a demanding issue. For this, routers need to have the capability to distinguish and isolate traffic belonging to different flows. This ability to determine the flow each packet belongs to is called packet classification. Technology vendors are reluctant to support algorithmic solutions for classification due to their non-deterministic performance. Although CAMs are favoured by technology vendors due to their deterministic high lookup rates, they suffer from the problems of high power dissipation and high silicon cost. This paper provides a new algorithmic-architectural solution for packet classification that mixes CAMs with algorithms based on multi-level cutting the classification space into smaller spaces. The provided solution utilizes the geometrical distribution of rules in the classification space. It provides the deterministic performance of CAMs, support for dynamic updates, and added flexibility for system designers.

Analysis of Latent Tracks for MeV protons in CR-39

For protons of energy up to a few MeV, the temporal evolution of etched latent tracks in CR-39 nuclear track detector has been numerically modeled by assuming that the electronic energy loss of the protons governs the latent track formation. The technique is applied in order to obtain the energy spectrum of high intensity laser driven proton beams, with high accuracy. The precise measurement of the track length and areal track density have been achieved by scanning short etched, highly populated CR-39 employing atomic force microscope.

Packet classification by multi-level cutting of the classification space

Traditionally, the Internet provides only a “best-effort” service, treating all packets going to the same destination equally. However, providing differentiated services for different users based on their quality requirements is increasingly becoming a demanding issue. For this, routers need to have the capability to distinguish and isolate traffic belonging to different flows. This ability to determine the flow each packet belongs to is called packet classification. Technology vendors are reluctant to support algorithmic solutions for classification due to their nondeterministic performance. Although content addressable memories (CAMs) are favoured by technology vendors due to their deterministic high-lookup rates, they suffer from the problems of high-power consumption and high-silicon cost. This paper provides a new algorithmic-architectural solution for packet classification that mixes CAMs with algorithms based on multilevel cutting of the classification space into smaller spaces. The provided solution utilizes the geometrical distribution of rules in the classification space. It provides the deterministic performance of CAMs, support for dynamic updates, and added flexibility for system designers.

Nonlinear frequency coupling in dual radio-frequency driven atmospheric pressure plasmas

Plasma ionization, and associated mode transitions, in dual radio-frequency driven atmospheric pressure plasmas are governed through nonlinear frequency coupling in the dynamics of the plasma boundary sheath. Ionization in low-power mode is determined by the nonlinear coupling of electron heating and the momentary local plasma density. Ionization in high-power mode is driven by electron avalanches during phases of transient high electric fields within the boundary sheath. The transition between these distinctly different modes is controlled by the total voltage of both frequency components.

Proton radiography of a shock-compressed target

In this paper we report on the radiography of a shock-compressed target using laser produced proton beams. A low-density carbon foam target was shock compressed by long pulse high-energy laser beams. The shock front was transversally probed with a proton beam produced in the interaction of a high intensity laser beam with a gold foil. We show that from radiography data, the density profile in the shocked target can be deduced using Monte Carlo simulations. By changing the delay between long and short pulse beams, we could probe different plasma conditions and structures, demonstrating that the details of the steep density gradient can be resolved. This technique is validated as a diagnostic for the investigation of warm dense plasmas, allowing an in situ characterization of high-density contrasted plasmas.

HTS Machines as Enabling Technology for All-Electric Airborne Vehicles

Environmental protection has now become paramount as evidence mounts to support the thesis of human activity-driven global warming. A global reduction of the emissions of pollutants into the atmosphere is therefore needed and new technologies have to be considered. A large part of the emissions come from transportation vehicles, including cars, trucks and airplanes, due to the nature of their combustion-based propulsion systems. Our team has been working for several years on the development of high power density superconducting motors for aircraft propulsion and fuel cell based power systems for aircraft. This paper investigates the feasibility of all-electric aircraft based on currently available technology. Electric propulsion would require the development of high power density electric propulsion motors, generators, power management and distribution systems. The requirements in terms of weight and volume of these components cannot be achieved with conventional technologies; however, the use of superconductors associated with hydrogen-based power plants makes possible the design of a reasonably light power system and would therefore enable the development of all-electric aero-vehicles. A system sizing has been performed both for actuators and for primary propulsion. Many advantages would come from electrical propulsion such as better controllability of the propulsion, higher efficiency, higher availability and less maintenance needs. Superconducting machines may very well be the enabling technology for all-electric aircraft development.

HTS Motors in Aircraft Propulsion: Design Considerations

Current high temperature superconducting (HTS) wires exhibit high current densities enabling their use in electrical rotating machinery. The possibility of designing high power density superconducting motors operating at reasonable temperatures allows for new applications in mobile systems in which size and weight represent key design parameters. Thus, all-electric aircrafts represent a promising application for HTS motors. The design of such a complex system as an aircraft consists of a multi-variable optimization that requires computer models and advanced design procedures. This paper presents a specific sizing model of superconducting propulsion motors to be used in aircraft design. The model also takes into account the cooling system. The requirements for this application are presented in terms of power and dynamics as well as a load profile corresponding to a typical mission. We discuss the design implications of using a superconducting motor on an aircraft as well as the integration of the electrical propulsion in the aircraft, and the scaling laws derived from physics-based modeling of HTS motors.