Dependency of the impacts of geoengineering on the stratospheric sulfur injection strategy – Part 1: Intercomparison of modal and sectional aerosol modules

Injecting sulfur dioxide into the stratosphere with the intent to create an artificial reflective aerosol layer is one of the most studied options for solar radiation management. Previous modelling studies have shown that stratospheric sulfur injections have the potential to compensate for the greenhouse-gas-induced warming at the global scale. However, there is significant diversity in the modelled radiative forcing from stratospheric aerosols depending on the model and on which strategy is used to inject sulfur into the stratosphere. Until now, it has not been clear how the evolution of the aerosols and their resulting radiative forcing depends on the aerosol microphysical scheme used – that is, if aerosols are represented by a modal or sectional distribution. Here, we have studied different spatio-temporal injection strategies with different injection magnitudes using the aerosol–climate model ECHAM-HAMMOZ with two aerosol microphysical modules: the sectional module SALSA (Sectional Aerosol module for Large Scale Applications) and the modal module M7. We found significant differences in the model responses depending on the aerosol microphysical module used. In a case where SO2 was injected continuously in the equatorial stratosphere, simulations with SALSA produced an 88 %–154 % higher all-sky net radiative forcing than simulations with M7 for injection rates from 1 to 100 Tg (S) yr−1. These large differences are identified to be caused by two main factors. First, the competition between nucleation and condensation: while injected sulfur tends to produce new particles at the expense of gaseous sulfuric acid condensing on pre-existing particles in the SALSA module, most of the gaseous sulfuric acid partitions to particles via condensation at the expense of new particle formation in the M7 module. Thus, the effective radii of stratospheric aerosols were 10 %–52 % larger in M7 than in SALSA, depending on the injection rate and strategy. Second, the treatment of the modal size distribution in M7 limits the growth of the accumulation mode which results in a local minimum in the aerosol number size distribution between the accumulation and coarse modes. This local minimum is in the size range where the scattering of solar radiation is most efficient. We also found that different spatial-temporal injection strategies have a significant impact on the magnitude and zonal distribution of radiative forcing. Based on simulations with various injection rates using SALSA, the most efficient studied injection strategy produced a 33 %–42 % radiative forcing compared with the least efficient strategy, whereas simulations with M7 showed an even larger difference of 48 %–116 %. Differences in zonal mean radiative forcing were even larger than that. We also show that a consequent stratospheric heating and its impact on the quasi-biennial oscillation depend on both the injection strategy and the aerosol microphysical model. Overall, these results highlight the crucial impact of aerosol microphysics on the physical properties of stratospheric aerosol which, in turn, causes significant uncertainties in estimating the climate impacts of stratospheric sulfur injections.

Online Relaxation Refinement for Satisficing Planning: On Partial Delete Relaxation, Complete Hill-Climbing, and Novelty Pruning

In classical AI planning, heuristic functions typically base their estimates on a relaxation of the input task. Such relaxations can be more or less precise, and many heuristic functions have a refinement procedure that can be iteratively applied until the desired degree of precision is reached. Traditionally, such refinement is performed offline to instantiate the heuristic for the search. However, a natural idea is to perform such refinement online instead, in situations where the heuristic is not sufficiently accurate. We introduce several online-refinement search algorithms, based on hill-climbing and greedy best-first search. Our hill-climbing algorithms perform a bounded lookahead, proceeding to a state with lower heuristic value than the root state of the lookahead if such a state exists, or refining the heuristic otherwise to remove such a local minimum from the search space surface. These algorithms are complete if the refinement procedure satisfies a suitable convergence property. We transfer the idea of bounded lookaheads to greedy best-first search with a lightweight lookahead after each expansion, serving both as a method to boost search progress and to detect when the heuristic is inaccurate, identifying an opportunity for online refinement. We evaluate our algorithms with the partial delete relaxation heuristic hCFF, which can be refined by treating additional conjunctions of facts as atomic, and whose refinement operation satisfies the convergence property required for completeness. On both the IPC domains as well as on the recently published Autoscale benchmarks, our online-refinement search algorithms significantly beat state-of-the-art satisficing planners, and are competitive even with complex portfolios.

Classification and properties of coastal wind profiles with negative gradients – an observational study

Wind profiles with a negative gradient are frequently occurring over the Baltic Sea and are important to take into consideration for offshore wind power as they affect not only the power production, but also the loads on the structure and the behavior of the wake behind the turbine. In this study, we classified non-normal profiles as wind profiles having negative shear in at least one part of the profile between 28 and 300 m: low-level jets (with a local wind maximum in the profile), profiles with a local minimum, and negative profiles. Using observations spanning over 3 years, we show that the non-normal wind profiles are common over the Baltic Sea in late spring and summer, with a peak of 40 % relative occurrence in May. Negative profiles (in the 28–300 m layer) were mostly occurring during unstable conditions, in contrast to low-level jets that primarily occurred in stable stratification. There were indications that the the zone with strong shear during low-level jets could cause a relative suppression of the variance for large turbulent eddies compared to the peak of the velocity spectra, in the layer below the jet core. Swell conditions were found to be favourable for the occurrence of negative profiles and profiles with a local minimum, as the waves fed energy into the surface layer, resulting in an increase of the wind speed from below.

On Surface-Plasmon-Polariton Waves Excited in the Turbadar–Otto Configuration

A local minimum in the plot of linear reflectance versus angle of incidence, on its own, is insufficient to identify a surface-plasmon-polariton wave (SPPW). Further checks are required in order to confirm the identity of a SPPW. The wavenumber should be compared with that extracted from the dispersion relation for the corresponding canonical boundary-value problem. Also, for prism-coupled configurations such as the Turbadar–Otto configuration which are based on SPPW-excitation via evanescent waves, the angle of incidence should be greater than the critical angle needed for total internal reflection.

Essays in Labour Economics: Evidence from Voluntary and Mandatory Wage Floors in the United States and New Zealand

<p>This thesis expands the literature on minimum and living wages by investigating local minimum wage ordinances and voluntary living wage programs. This thesis is presented as three distinct papers; the first explores a county-wide minimum wage ordinance in New Mexico, USA, while papers 2 and 3 explore New Zealand’s voluntary living wage program. In the United States, local minimum wage ordinances are growing in popularity, and research is emerging on their effects. Setting minimum wages at the local level is politically easier than enacting Federal legislation, and local minimum wages may be better targeted to local economic conditions. In my first chapter, “Local Minimum Wage Laws and Labour Market Outcomes: Evidence from New Mexico,” I use fixed effects and synthetic control analysis to uncover the effects of a local minimum wage law on the Albuquerque/Bernalillo region of New Mexico, with a focus on how provisions exempting tipped workers affect gains in earnings. My findings reveal that these provisions can lead to reductions in hourly wages for workers exempted from the minimum wage even when the labour market is not harmed overall. I find that the minimum wage ordinance did not reduce teen employment but that it served to increase the supply of teen labour leading to an increase in the teen unemployment rate. The second and third papers in this thesis address the voluntary living wage program in New Zealand. In the first quantitative work on New Zealand’s living wage, I utilize data from Statistics New Zealand’s Integrated Data Infrastructure (IDI) to explore several facets of the living wage experience for employers and employees. In the second paper, “The New Zealand Living Wage: Earnings, Labour Costs and Turnover,” I investigate the characteristics of New Zealand living wage firms and use fixed effects to examine the impact of living wage certification on employment, worker earnings and turnover. My results provide some evidence for increases in labour costs and worker earnings following certification but find that this change is driven by changes in small firms that employ few workers. I find no evidence of a reduction in turnover. In my final chapter, “Who Benefits from Living Wage Certification?” I investigate the distribution of benefits from the living wage based on an employees’ pre-treatment earnings, time of hire and whether or not they remained employed with the living wage firm. To do this, I utilize a worker-level panel dataset containing the full earnings history of all workers that were employed for a living wage or matched control firm between January 2014 and December 2015. I use fixed effects models containing fixed effects for worker, firm and month to compare patterns of earnings growth for workers hired before certification (‘pre-hires’) with those hired after certification (‘joiners’) and those who left their living wage job but remained in the workforce (‘leavers’). I also estimate the impact of living wage employment on the earnings of low-income workers. I find that the financial benefit of the living wage accrues almost exclusively to workers hired after certification and to low income workers. In addition, my analysis on the worker-level panel suggests that overall earnings growth in living wage firms lagged that in control firms over the observation period. This result is driven by relative declines in earnings for living wage workers in large firms and is attributed to increases in the published living wage rate that lags behind wage growth in the relevant segments of the job market.</p>

Essays in Labour Economics: Evidence from Voluntary and Mandatory Wage Floors in the United States and New Zealand

<p>This thesis expands the literature on minimum and living wages by investigating local minimum wage ordinances and voluntary living wage programs. This thesis is presented as three distinct papers; the first explores a county-wide minimum wage ordinance in New Mexico, USA, while papers 2 and 3 explore New Zealand’s voluntary living wage program. In the United States, local minimum wage ordinances are growing in popularity, and research is emerging on their effects. Setting minimum wages at the local level is politically easier than enacting Federal legislation, and local minimum wages may be better targeted to local economic conditions. In my first chapter, “Local Minimum Wage Laws and Labour Market Outcomes: Evidence from New Mexico,” I use fixed effects and synthetic control analysis to uncover the effects of a local minimum wage law on the Albuquerque/Bernalillo region of New Mexico, with a focus on how provisions exempting tipped workers affect gains in earnings. My findings reveal that these provisions can lead to reductions in hourly wages for workers exempted from the minimum wage even when the labour market is not harmed overall. I find that the minimum wage ordinance did not reduce teen employment but that it served to increase the supply of teen labour leading to an increase in the teen unemployment rate. The second and third papers in this thesis address the voluntary living wage program in New Zealand. In the first quantitative work on New Zealand’s living wage, I utilize data from Statistics New Zealand’s Integrated Data Infrastructure (IDI) to explore several facets of the living wage experience for employers and employees. In the second paper, “The New Zealand Living Wage: Earnings, Labour Costs and Turnover,” I investigate the characteristics of New Zealand living wage firms and use fixed effects to examine the impact of living wage certification on employment, worker earnings and turnover. My results provide some evidence for increases in labour costs and worker earnings following certification but find that this change is driven by changes in small firms that employ few workers. I find no evidence of a reduction in turnover. In my final chapter, “Who Benefits from Living Wage Certification?” I investigate the distribution of benefits from the living wage based on an employees’ pre-treatment earnings, time of hire and whether or not they remained employed with the living wage firm. To do this, I utilize a worker-level panel dataset containing the full earnings history of all workers that were employed for a living wage or matched control firm between January 2014 and December 2015. I use fixed effects models containing fixed effects for worker, firm and month to compare patterns of earnings growth for workers hired before certification (‘pre-hires’) with those hired after certification (‘joiners’) and those who left their living wage job but remained in the workforce (‘leavers’). I also estimate the impact of living wage employment on the earnings of low-income workers. I find that the financial benefit of the living wage accrues almost exclusively to workers hired after certification and to low income workers. In addition, my analysis on the worker-level panel suggests that overall earnings growth in living wage firms lagged that in control firms over the observation period. This result is driven by relative declines in earnings for living wage workers in large firms and is attributed to increases in the published living wage rate that lags behind wage growth in the relevant segments of the job market.</p>

Selective Hole Filling of Red Blood Cells for Improved Marker-Controlled Watershed Segmentation

Manual counting and evaluation of red blood cells with the presence of malaria parasites is a tiresome, time-consuming process that can be altered by environmental conditions and human error. Many algorithms were presented to segment red blood cells for subsequent parasitemia evaluation by machine learning algorithms. However, the segmentation of overlapping red blood cells always has been a challenge. Marker-controlled watershed segmentation is one of the methods that was implemented to separate overlapping red blood cells. However, a high number of overlapped red blood cells were still an issue. We propose a novel approach to improve the segmentation efficiency of marker-controlled watershed segmentation. Local minimum histogram background segmentation with a selective hole filling algorithm was introduced to improve segmentation efficiency of marker-controlled watershed segmentation on a high number of overlapping red blood cells. The local minimum was selected on the smoothed histogram for background segmentation. The combination of selective filling, convex hull, and Hough circle detection algorithms was utilized for the intact segmentation of red blood cells. The markers were computed from the resulted mask, and finally, marker-controlled watershed segmentation was applied to separate overlapping red blood cells. As a result, the proposed algorithm achieved higher background segmentation accuracy compared to popular background segmentation algorithms, and the inclusion of corner details improved watershed segmentation efficiency.

Analyzing Oxygen Ionization in the Circumgalactic Medium

Galaxies are surrounded by low-density, highly-ionized clouds of gas, called the Circumgalactic Medium (CGM), which provides insight into galaxy evolution. CGM observations are sensitive to ionization levels, which requires studying ionization types: photoionization (PI), more density-dependent and associated with cooler gas, and collisional ionization (CI), more temperature-dependent and associated with hotter gas. We analyzed PI and CI components for oxygen ionization states using cosmological galaxy simulations. For each ion, we plotted mass distributions into PI and CI phases and created 2D covering-fraction projections of column density at different thresholds. We analyzed changes for different mass-bin galaxies. Our results are: O vii and O ix are the only predominantly-CI ion states. O vi is a local minimum in both PI and CI gas. Column density distributions greatly emphasize higher ion states. Shapes of covering-fraction plots at higher thresholds resemble the 3D-plots. CI gas dominates more in higher mass galaxy simulations.

A progressive online external parameter calibration and initialization method for stereo-IMU system

Purpose This paper aims to present a pipeline to progressively deal with the online external parameter calibration and estimator initialization of the Stereo-inertial measurement unit (IMU) system, which does not require any prior information and is suitable for system initialization in a variety of environments. Design/methodology/approach Before calibration and initialization, a modified stereo tracking method is adopted to obtain a motion pose, which provides prerequisites for the next three steps. Firstly, the authors align the pose obtained with the IMU measurements and linearly calculate the rough external parameters and gravity vector to provide initial values for the next optimization. Secondly, the authors fix the pose obtained by the vision and restore the external and inertial parameters of the system by optimizing the pre-integration of the IMU. Thirdly, the result of the previous step is used to perform visual-inertial joint optimization to further refine the external and inertial parameters. Findings The results of public data set experiments and actual experiments show that this method has better accuracy and robustness compared with the state of-the-art. Originality/value This method improves the accuracy of external parameters calibration and initialization and prevents the system from falling into a local minimum. Different from the traditional method of solving inertial navigation parameters separately, in this paper, all inertial navigation parameters are solved at one time, and the results of the previous step are used as the seed for the next optimization, and gradually solve the external inertial navigation parameters from coarse to fine, which avoids falling into a local minimum, reduces the number of iterations during optimization and improves the efficiency of the system.