EXPERIMENTAL AND COMPUTATIONAL STUDIES OF ELECTROMAGNETIC CLOAKING AT MICROWAVES

An invisibility cloak is a device that can hide the target by enclosing it from the incident radiation. This intriguing device has attracted a lot of attention since it was first implemented at a microwave frequency in 2006. However, the problems of existing cloak designs prevent them from being widely applied in practice. In this dissertation, we try to remove or alleviate the three constraints for practical applications imposed by loosy cloaking media, high implementation complexity, and small size of hidden objects compared to the incident wavelength. To facilitate cloaking design and experimental characterization, several devices and relevant techniques for measuring the complex permittivity of dielectric materials at microwave frequencies are developed. In particular, a unique parallel plate waveguide chamber has been set up to automatically map the electromagnetic (EM) field distribution for wave propagation through the resonator arrays and cloaking structures. The total scattering cross section of the cloaking structures was derived based on the measured scattering field by using this apparatus. To overcome the adverse effects of lossy cloaking media, microwave cloaks composed of identical dielectric resonators made of low loss ceramic materials are designed and implemented. The effective permeability dispersion was provided by tailoring dielectric resonator filling fractions. The cloak performances had been verified by full-wave simulation of true multi-resonator structures and experimental measurements of the fabricated prototypes. With the aim to reduce the implementation complexity caused by metamaterials employment for cloaking, we proposed to design 2-D cylindrical cloaks and 3-D spherical cloaks by using multi-layer ordinary dielectric material (εr>1) coating. Genetic algorithm was employed to optimize the dielectric profiles of the cloaking shells to provide the minimum scattering cross sections of the cloaked targets. The designed cloaks can be easily scaled to various operating frequencies. The simulation results show that the multi-layer cylindrical cloak essentially outperforms the similarly sized metamaterials-based cloak designed by using the transformation optics-based reduced parameters. For the designed spherical cloak, the simulated scattering pattern shows that the total scattering cross section is greatly reduced. In addition, the scattering in specific directions could be significantly reduced. It is shown that the cloaking efficiency for larger targets could be improved by employing lossy materials in the shell. At last, we propose to hide a target inside a waveguide structure filled with only epsilon near zero materials, which are easy to implement in practice. The cloaking efficiency of this method, which was found to increase for large targets, has been confirmed both theoretically and by simulations.

Melting of metasomatized peridotite at 4–6 GPa and up to 1200 °C: an experimental approach

The phase assemblages and compositions in a K-bearing lherzolite + H2O system are determined between 4 and 6 GPa and 850–1200 °C, and the melting reactions occurring at subarc depth in subduction zones are constrained. Experiments were performed on a rocking multi-anvil apparatus. The experiments had around 16 wt% water content, and hydrous melt or aqueous fluid was segregated and trapped in a diamond aggregate layer. The compositions of the aqueous fluid and hydrous melt phases were measured using the cryogenic LA-ICP-MS technique. The residual lherzolite consists of olivine, orthopyroxene, clinopyroxene, and garnet, while diamond (C) is assumed to be inert. Hydrous and alkali-rich minerals were absent from the run products due to preferred dissolution of K2O (and Na2O) to the aqueous fluid/hydrous melt phases. The role of phlogopite in melting relations is, thus, controlled by the water content in the system: at the water content of around 16 wt% used here, phlogopite is unstable and thus does not participate in melting reactions. The water-saturated solidus, i.e., the first appearance of hydrous melt in the K–lherzolite composition, is located between 900 and 1000 °C at 4 GPa and between 1000 and 1100 °C at 5 and 6 GPa. Compositional jumps between hydrous melt and aqueous fluid at the solidus include a significant increase in the total dissolved solids load. All melts/fluids are peralkaline and calcium-rich. The melting reactions at the solidus are peritectic, as olivine, clinopyroxene, garnet, and H2O are consumed to generate hydrous melt plus orthopyroxene. Our fluid/melt compositional data demonstrate that the water-saturated hybrid peridotite solidus lies above 1000 °C at depths greater than 150 km and that the second critical endpoint is not reached at 6 GPa for a K2O–Na2O–CaO–FeO–MgO–Al2O3–SiO2–H2O–Cr2O3(–TiO2) peridotite composition.

(Table 1) Experimental results of Kd at various conditions from ODP Hole 131-808C

A comprehensive experimental study, utilizing a rocking autoclave hydrothermal apparatus with isotope tracers, was applied to evaluate the temperature of squeezing artifacts on B contents and isotopic compositions in pore waters. The partition coefficient (KD) was determined at temperatures from 25 ° to 350 °C, at 800 bars, and this information was applied to reconstruct pore water B and d11B in ODP drill sites, where pH, T, and porosity are known. The partition coefficient of B is a function of temperature, pH, and sediment mineralogy. The solution pH exerts a dominant control at low temperatures; however, KD decreases to a value of essentially zero (compared to that of KD = ~3.5 at 25 °C) at high temperatures indicating no adsorption. Two empirical equations were derived to represent most of the available experimental results. For pelagic clay rich sediments, a KD = -3.84-0.020T + 0.88pH (R = 0.84; 1sigma = 0.25) is established. For sediments that have experienced progressive metamorphism, a KD = -1.38-0.008T + 0.59pH (R = 0.81; 1sigma = 0.37) can be applied. Similarly the effect on pore water d11B can be corrected if the fractionation factors at different temperatures are assumed. The corrected B and d11B in ODP Sites 671, 672, and 808 indicate significant mobilization of bulk B in sediment (exchangeable + lattice bound) at depth, especially near the décollement zone or other potential flow conduits. Tectonically expelled fluids from mud diapirs of Barbados Ridge Complex, hot springs of Rumsey Hills, California, and mud pot waters of the Salton Sea geothermal field, are enriched in B (up to 20 mM) with lower d11B, supporting the argument of B mobilization as a result of fluid expulsion in accretionary prisms.

Analysis of spatial microbial properties from experimental plots of the Jena experiment (September 2010)

The study was carried out on the main plots (Main Experiment) of a large grassland biodiversity experiment, the Jena Experiment. In the main experiment, 82 grassland plots of 20 x 20 m were established from a pool of 60 species belonging to four functional groups (grasses, legumes, tall and small herbs). In May 2002, varying numbers of plant species from this species pool were sown into the plots to create a gradient of plant species richness (1, 2, 4, 8, 16 and 60 species) and functional richness (1, 2, 3, 4 functional groups). Plots were maintained by bi-annual weeding and mowing. This data set consists of standard deviation (SD), mean and stability (stab) of soil microbial basal respiration (µl O2/h/g dry soil) and microbial biomass carbon (µg C/g dry soil). Data were derived by taking soil samples and measuring basal and substrate-induced microbial respiration with an oxygen-consumption apparatus. Samples for calculating the spatial stability of soil microbial properties were taken on the 20th of September in 2010. Oxygen consumption of soil microorganisms in fresh soil equivalent to 3.5 g dry weight was measured at 22°C over a period of 24 h. Basal respiration (µlO2/g dry soil/h) was calculated as mean of the oxygen consumption rates of hours 14 to 24 after the start of measurements. Substrate- induced respiration was determined by adding D-glucose to saturate catabolic enzymes of microorganisms according to preliminary studies (4 mg g-1 dry soil solved in 400 µl deionized water). Maximum initial respiratory response (µl O2/g dry soil/ h) was calculated as mean of the lowest three oxygen consumption values within the first 10 h after glucose addition. Microbial biomass carbon (µg C/g dry soil) was calculated as 38 × Maximum initial respiratory response according to prelimiray studies.

Analysis of temporal microbial properties from experimental plots of the Jena experiment (2003-2014)

The study was carried out on the main plots (Main Experiment) of a large grassland biodiversity experiment, the Jena Experiment. In the main experiment, 82 grassland plots of 20 x 20 m were established from a pool of 60 species belonging to four functional groups (grasses, legumes, tall and small herbs). In May 2002, varying numbers of plant species from this species pool were sown into the plots to create a gradient of plant species richness (1, 2, 4, 8, 16 and 60 species) and functional richness (1, 2, 3, 4 functional groups). Plots were maintained by bi-annual weeding and mowing. This data set consists of standard deviation (SD), mean and stability (stab) of soil microbial basal respiration (µl O2/h/g dry soil) and microbial biomass carbon (µg C/g dry soil). Data were derived by taking soil samples and measuring basal and substrate-induced microbial respiration with an oxygen-consumption apparatus. Samples for calculating the temporal stability were taken every year in May/June from 2003 to 2014, except in 2005. Oxygen consumption of soil microorganisms in fresh soil equivalent to 3.5 g dry weight was measured at 22°C over a period of 24 h. Basal respiration (µlO2/g dry soil/h) was calculated as mean of the oxygen consumption rates of hours 14 to 24 after the start of measurements. Substrate- induced respiration was determined by adding D-glucose to saturate catabolic enzymes of microorganisms according to preliminary studies (4 mg g-1 dry soil solved in 400 µl deionized water). Maximum initial respiratory response (µl O2/g dry soil/h) was calculated as mean of the lowest three oxygen consumption values within the first 10 h after glucose addition. Microbial biomass carbon (µg C/g dry soil) was calculated as 38 × Maximum initial respiratory response according to prelimiray studies.

Experimental science : elementary practical and experimental physics.

Mode of access: Internet.

An experimental and modelling study of the capture of CO2 from gas mixtures with different techniques, with focus on multicomponent effects.

In the present work, the deviations in the solubility of CO2, CH4, and N2 at 30 °c in the mixed gases (CO2/CH4) and (CO2/N2) from the pure gas behavior were studied using the dual-mode model over a wide range of equilibrium composition and pressure values in two glassy polymers. The first of which was PI-DAR which is the polyimide formed by the reaction between 4, 6-diaminoresorcinol dihydrochloride (DAR-Cl) and 2, 2’-bis-(3, 4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA). The other glassy polymer was TR-DAR which is the corresponding thermally rearranged polymer of PI-DAR. Also, mixed gas sorption experiments for the gas mixture (CO2/CH4) in TR-DAR at 30°c took place in order to assess the degree of accuracy of the dual-mode model in predicting the true mixed gas behavior. The experiments were conducted on a pressure decay apparatus coupled with a gas chromatography column. On the other hand, the solubility of CO2 and CH4 in two rubbery polymers at 30⁰c in the mixed gas (CO2/CH4) was modelled using the Lacombe and Sanchez equation of state at various values of equilibrium composition and pressure. These two rubbery polymers were cross-linked poly (ethylene oxide) (XLPEO) and poly (dimethylsiloxane) (PDMS). Moreover, data about the sorption of CO2 and CH4 in liquid methyl dietahnolamine MDEA that was collected from literature65-67 was used to determine the deviations in the sorption behavior in the mixed gas from that in the pure gases. It was observed that the competition effects between the penetrants were prevailing in the glassy polymers while swelling effects were predominant in the rubbery polymers above a certain value of the fugacity of CO2. Also, it was found that the dual-mode model showed a good prediction of the sorption of CH4 in the mixed gas for small pressure values but in general, it failed to predict the actual sorption of the penetrants in the mixed gas.

(Table 1) Experimental details and results

Factor-of-safety analyses of submarine slope failure depend critically on the shear strength of the slope material, which is often evaluated with residual strength values and for normally consolidated sediments. Here, we report on direct measurements of both shear strength and cohesion for a quartz-clay mixture over a wide range of overconsolidation ratios (OCRs). For normally consolidated sediment at low stresses, cohesion is the dominant source of shear strength compared to friction. Significant increases in peak shear strength occur for OCR > 4, and the primary source of this strength increase is due to increased cohesion, rather than friction. The proportion of added shear strength due to cohesion depends log-linearly on the OCR. We show that at shallow depths where OCR values can be high, overconsolidated clays can be stronger than pure or nearly pure quartz sediments, which are cohesionless under near-surface conditions. Our data also suggest that areas which have experienced significant unroofing due to previous mass movements are less likely to experience subsequent failure at shallow depths due to increased peak strength, and if failure occurs it is expected to be deeper where the OCR is lower. In seismically active areas, this is one potential explanation for the general observation of lower slope failure recurrence compared to rates expected from triggering due to local earthquakes.

Design and Experimental Investigation of a Hydroxyl Ammonium Nitrate Based Workhorse Microthruster

Thesis (Master's)--University of Washington, 2016-08

Foil rolling : a new interpretation of experimental results

This paper explores a new interpretation of experiments on foil rolling. The assumption that the roll remains convex is relaxed so that the strip profile may become concave, or thicken in the roll gap. However, we conjecture that the concave profile is associated with phenomena which occur after the rolls have stopped. We argue that the yield criterion must be satisfied in a nonconventional manner if such a phenomenon is caused plastically. Finite element analysis on an extrusion problem appears to confirm this conjecture.