The Use of Bioelectrochemical System (BES) to Upgrade Biogas into Biomethane under Thermophilic Conditions

Anaerobic digestion (AD) is used increasingly worldwide to convert organic waste materials into the renewable energy of methane gas. However, the produced biogas consists of a mixture of typically 50% methane CO2, respectively. The presence of CO2 in biogas affects engine performance; therefore, removing CO2 content will significantly improve the usability of biogas. Recently, integrating bioelectrochemical systems (BESs) with AD processes have been considered as a way to increase methane content. The principle of the BES in enriching biogas in methane content is thought to be in the transfer of electrons from an active cathode either directly to methanogens or via reduction of protons to H2 and subsequent H2 transfer to hydrogenotrophic methanogens that reduce CO2 to CH4. Two different types of BES have been described in this thesis: one is membrane-free single-chamber reactor which contains both anode and cathode; the other reactor consists of two-chambers separated by an ion-exchange membrane in order to avoid interference of the anodic reaction with the cathode. This study combined BES with AD (thermophilic anaerobic sludge used as an inoculum) and investigated the capability of upgrading biogas to methane under thermophilic conditions. For the first time, we showed a direct comparison between single and two-chamber systems. Based on the results, the following observations were made: 1. The application of the BES to a glucose fed AD resulted in an immediate increase in biogas production (approximately from 1 L/L/d to 1.5 L/L/d) and methane content (approximately from 50% to about 65%). This applied for both reactor configurations (single- and two-chamber for the first 4 days. However, after one week the methane content of the single chamber decreased to that of the control AD without BES, while the two-chamber reactor increased its methane level to > 90%. The reason for the diminished longer term performance of the single chamber reactor is presumably the production of oxygen by the anode as indicated by increased redox potential. 2. pH adjustment was needed during the operation of the two-chamber reactor as its cathodic chamber tended to be alkaline (>9); while the pH of the single-chamber reactor was in the range of 6-7. 3. After 3 weeks experiment, both single- and two-chamber reactor showed signs of failure by an accumulation of VFA and diminished methane production. The build-up of VFA was attributed to the H2 produced by the BES inside the AD which was known to result in VFA accumulation. To avoid the volatile fatty acids (VFAs) accumulation, the BES was removed from the AD and placed in-line with the AD, receiving the biogas by functioning as a biogas-filter. This novel concept of using a BES as a biogas-filter was evaluated as an alternative way of upgrading biogas to methane. And the microbial community of a mixed-culture methane producing biocathode was investigated to illuminate the possible role of microbial in methane production. Results revealed that: 1. When applying a WE potential at -1.1 V vs. Ag/AgCl the biofilter increased the methane content of inflowing biogas from 50% to 85%. 2. The microbial community at the start of the experiment was dominated by two phylotypes of Archea- Methanosarcina and Methanobacteria. However, at the end of experiment hydrogenotrophic Methanothermobacter was the majority population of Archea (95.4%). 3. Based on the analysis of energy efficiency, it was showed that final energy output as extra methane was 57.1 kJ and the overall energy efficiency was 56%. 4. The use of BES as an inline biofilter to remove CO2 from biogas represents an alternative, not yet published approach that is not likely to cause digester failure as observed by BES imbedded in the AD but showing similar performance. Overall, this thesis showed the capacity of BES on biogas upgrading and the selection of electromethanogens on the biocathode during the BES operation in the two-chamber reactor. Thus, further studies on the optimisation of BES process and the mechanisms of catalysis of biocathode will provide essential knowledge for improving BES performance for the practical application

Fiscal Decentralization and Government Size: The Role of Democracy

This paper examines how the level of democracy in a country affects the relationship between fiscal decentralization and government size. We argue that political regimes, proxied by their democracy levels, are important for different decentralization theories to predict the impact of fiscal decentralization on government size. We test this argument using cross-country data from 76 developed and developing countries during 1972–2013. We find strong and robust evidence that fiscal decentralization is negatively associated with government size and that a higher level of democracy tends to mitigate the negative impact of fiscal decentralization. Therefore, our study contributes to the literature by offering a novel insight on mixed results regarding the relationship between fiscal decentralization and government size in the literature

Thermal Performance Analysis of Lithium Battery Thermal Management System for New Energy Vehicles

The battery of new energy vehicle is the core part of the whole vehicle.By analyzing the thermal management system of lithium battery,the service life, safety and performance of lithium battery can be effectively improved. The thermal management of lithium battery is related to its temperature, which also determines the battery capacity, heat consumption rate, battery state working voltage and other impor_x005ftant parameters of lithium battery. Therefore, the thermal management of battery is particularly important for the performance of sexual energy vehicles.This paper will introduce the composition of the battery system,analyze the current research situation of the thermal management system of lithium battery packs in new energy vehicles for civil use, and look forward to the future development direction of the thermal management system of lithium battery packs in new energy vehicles

Physically based geometry and reflectance recovery from images

An image is a projection of the three-dimensional world taken at an instance in space and time. Its formation involves a complex interplay between geometry, illumination and material properties of objects in the scene. Given image data and knowledge of some scene properties, the recovery of the remaining components can be cast as a set of physically based inverse problems. This thesis investigates three inverse problems on the recovery of scene properties and discusses how we can develop appropriate physical constraints and build them into effective algorithms. Firstly, we study the problem of geometry recovery from a single image with repeated texture. Our technique leverages the PatchMatch algorithm to detect and match repeated patterns undergoing geometric transformations. This allows effective enforcement of translational symmetry constraint in the recovery of texture lattice. Secondly, we study the problem of computational relighting using RGB-D data, where the depth data is acquired through a Kinect sensor and is often noisy. We show how the inclusion of noisy depth input helps to resolve ambiguities in the recovery of shape and reflectance in the inverse rendering problem. Our results show that the complementary nature of RGB and depth is highly beneficial for a practical relighting system. Lastly, in the third problem, we exploit the use of geometric constraints relating two views, to address a challenging problem in Internet image matching. Our solution is robust to geometric and photometric distortions over wide baselines. It also accommodates repeated structures that are commonly found in our modern environment. Building on the image correspondence, we also investigate the use of color transfer as an additional global constraint in relating Internet images. It shows promising results in obtaining more accurate and denser correspondence

Quantitative Prediction of Segregation at Process Scale

Segregation, or the separation/stratification of particles with differing properties, can lead to significant handling problems, product non-uniformity, and even complete batches being discarded at huge financial loss in multiple industries. Thus, one could argue that segregation is one of the most important factors in industrial processing of granular materials. There has been a tremendous focus in recent years on granular segregation problems and much has been learned about the mechanisms driving those phenomena. Segregation model development holds promise for translation of academic research into industrial practice; however, experimental validation of dynamic models is extremely difficult and typical segregation models are not inherently built with scale-up in mind. One unique aspect of our work is that we overcome these experimental limitations by exploiting a novel framework for segregation testing based on establishing an “equilibrium” between mixing and segregation in free surface granular flows in order to alter the steady-state distribution of particles. By achieving this balance between the rate of segregation and the perturbation rate, we combine the model expressions that we are interested in testing with dramatically simplified experiments to ultimately deduce the segregation rate and validate the expressions. Moreover, by exploring a novel view of the interplay between granular rheology and segregation, we have introduced a new way of structuring segregation rate models that make them inherently more scalable and accurate for industrial use than any models previously reported. Types of segregation properties studied in this research include density, size, wet and shape. Our results suggest that one can prescribe (or design) industrial operating conditions that will lead to dramatically lower segregation extents

Video segmentation: Temporally-constrained graph-based optimization

Master'sMASTER OF ENGINEERIN

Essays on Health and Labor Policies

This dissertation consists of three papers on health economics and labor economics. The first chapter investigates how workplace breastfeeding laws that require firms to provide a lactation room in the workplace affect the labor market outcomes of mothers of infants. Summers (1989) predicts that such mandated benefits depress the demand for mothers of infants and increase their supply and, thus, depress wages. However, I argue that such mandated benefits can increase both the demand for and the wages of mothers of infants who have a strong propensity to increase their work attachment. I exploit the plausibly exogenous variation in the timing of state mandates on workplace lactation support, analyzing data in the National Immunization Survey and the Current Population Survey. The second chapter investigates changes in the usage or preventive services among the Medicare beneficiaries following the Affordable Care Act's "Medicare Preventive Benefits" reform, which eliminates cost-sharing for Medicare-covered preventive services that are recommended (rated A or B) by the U.S. Preventive Services Task Force. Following intuition in Chetty et al. (2013) that individuals with no knowledge of certain policies behave as they would in the absence of the policy, I identify the impact of the reform by comparing the usage of all Medicare-covered preventive services across regions with different levels of knowledge of the reform. Exploiting the sample of beneficiaries that move across HRRs, I find that the knowledge of the reform is driven by the demand side factors rather than the supply side factors. The third chapter investigates the causal impact of physician counseling on obesity, exploiting the eligibility criterion of the Medicare's Intensive Behavioral Therapy (IBT) for Obesity program, using a fuzzy Regression Discontinuity (RD) approach. I using the 5% random sample of the Medicare historical claim data and I inventively collect the BMI information using the ICD-9 diagnosis codes. I find that the intensive behavioral therapy is not effective in reducing obesity, and we are able to rule out confounding factors such as the use of bariatric procedures, massages, psychological therapy, smoking counseling, and the diagnoses of chronic conditions

Stabilization and current-induced motion of antiskyrmion in the presence of anisotropic Dzyaloshinskii-Moriya interaction

Topological defects in magnetism have attracted great attention due to fundamental research interests and potential novel spintronics applications. Rich examples of topological defects can be found in nanoscale non-uniform spin textures, such as monopoles, domain walls, vortices, and skyrmions. Recently, skyrmions stabilized by the Dzyaloshinskii-Moriya interaction have been studied extensively. However, the stabilization of antiskyrmions is less straightforward. Here, using numerical simulations we demonstrate that antiskyrmions can be a stable spin configuration in the presence of anisotropic Dzyaloshinskii-Moriya interaction. We find current-driven antiskyrmion motion that has a transverse component, namely antiskyrmion Hall effect. The antiskyrmion gyroconstant is opposite to that for skyrmion, which allows the current-driven propagation of coupled skyrmion-antiskyrmion pairs without apparent skyrmion Hall effect. The antiskyrmion Hall angle strongly depends on the current direction, and a zero antiskyrmion Hall angle can be achieved at a critic current direction. These results open up possibilities to tailor the spin topology in nanoscale magnetism, which may be useful in the emerging field of skyrmionics.Comment: 31 pages, 6 figures, to appear in Physical Review

Rigid-foldable cylindrical origami with tunable mechanical behaviors

Rigid-foldable origami shows significant promise in advanced engineering applications including deployable structures, aerospace engineering, and robotics. It undergoes deformation solely at the creases during the folding process while maintaining rigidity throughout all facets. However, most types of cylindrical origami, such as Kresling origami, water-bomb origami, and twisted tower origami, lack rigid-foldability. Although shape transformation can be achieved through elastic folding, their limited rigid foldability constrains their engineering applications. To address this limitation, we proposed a type of cylindrical origami inspired by Kresling origami, named foldable prism origami (FP-ori), in this paper. FP-ori possesses not only rigid-foldability but also several tunable properties, including flat-foldability, self-locking, and bistability. The geometric properties of FP-ori were analyzed and the relationship between different parameters and tunable mechanical behaviors were verified through finite element method simulations, as well as experiments using paper models. Furthermore, we proposed stacked structures composed of multiple cubic FP-ori units, the rotation directions of which could be controlled through the combination arrangement. And drawing inspiration from kirigami, a negative Poisson’s ratio tessellation structure was created. These results indicated that FP-ori has substantial potential for broad application in engineering fields