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1. Life cycle assessment of aquaculture systems: Does burden shifting occur with an increase in production intensity?

   https://doi.org/10.1016/j.aquaeng.2020.102130  

   Ghamkhar, Ramin; Boxman, Suzanne; Main, Kevan; Zhang, Qiong; Trotz, Maya; Hicks, Andrea (January 2021, Aquacultural engineering)

   null (Ed.)

   Life cycle assessment (LCA), a tool used to assess the environmental impacts of products and processes, has been used to evaluate a range of aquaculture systems. Eighteen LCA studies were reviewed which included assess- ments of recirculating aquaculture systems (RAS), flow-through systems, net cages, and pond systems. This re- view considered the potential to mitigate environmental burdens with a movement from extensive to intensive aquaculture systems. Due to the diversity in study results, specific processes (feed, energy, and infrastructure) and specific impact categories (land use, water use, and eutrophication potential) were analyzed in-depth. The comparative analysis indicated there was a possible shift from local to global impacts with a progression from extensive to intensive systems, if mitigation strategies were not performed. The shift was partially due to increased electricity requirements but also varied with electricity source. The impacts from infrastructure were less than 13 % of the environmental impact and considered negligible. For feed, the environmental impacts were typically more dependent on feed conversion ratio (FCR) than the type of system. Feed also contributed to over 50 % of the impacts on land use, second only to energy carriers. The analysis of water use indicated intensive recirculating systems efficiently reduce water use as compared to extensive systems; however, at present, studies have only considered direct water use and future work is required that incorporates indirect and consumptive water use. Alternative aquaculture systems that can improve the total nutrient uptake and production yield per material and energy based input, thereby reducing the overall emissions per unit of feed, should be further investigated to optimize the overall of aquaculture systems, considering both global and local environmental impacts. While LCA can be a valuable tool to evaluate trade-offs in system designs, the results are often location and species specific. Therefore, it is critical to consider both of these criteria in conjunction with LCA results when developing aquaculture systems. 

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2. Quantifying baseline costs and cataloging potential optimization strategies for kelp aquaculture carbon dioxide removal

   https://doi.org/10.3389/fmars.2022.966304  

   Coleman, Struan; Dewhurst, Tobias; Fredriksson, David W.; St. Gelais, Adam T.; Cole, Kelly L.; MacNicoll, Michael; Laufer, Eric; Brady, Damian C. (August 2022, Frontiers in Marine Science)

   To keep global surface warming below 1.5°C by 2100, the portfolio of cost-effective CDR technologies must expand. To evaluate the potential of macroalgae CDR, we developed a kelp aquaculture bio-techno-economic model in which large quantities of kelp would be farmed at an offshore site, transported to a deep water “sink site”, and then deposited below the sequestration horizon (1,000 m). We estimated the costs and associated emissions of nursery production, permitting, farm construction, ocean cultivation, biomass transport, and Monitoring, Reporting, and Verification (MRV) for a 1,000 acre (405 ha) “baseline” project located in the Gulf of Maine, USA. The baseline kelp CDR model applies current systems of kelp cultivation to deep water (100 m) exposed sites using best available modeling methods. We calculated the levelized unit costs of CO 2 eq sequestration (LCOC; $ tCO 2 eq -1 ). Under baseline assumptions, LCOC was $17,048 tCO 2 eq -1 . Despite annually sequestering 628 tCO 2 eq within kelp biomass at the sink site, the project was only able to net 244 C credits (tCO 2 eq) each year, a true sequestration “additionality” rate (AR) of 39% (i.e., the ratio of net C credits produced to gross C sequestered within kelp biomass). As a result of optimizing 18 key parameters for which we identified a range within the literature, LCOC fell to $1,257 tCO 2 eq -1 and AR increased to 91%, demonstrating that substantial cost reductions could be achieved through process improvement and decarbonization of production supply chains. Kelp CDR may be limited by high production costs and energy intensive operations, as well as MRV uncertainty. To resolve these challenges, R&D must (1) de-risk farm designs that maximize lease space, (2) automate the seeding and harvest processes, (3) leverage selective breeding to increase yields, (4) assess the cost-benefit of gametophyte nursery culture as both a platform for selective breeding and driver of operating cost reductions, (5) decarbonize equipment supply chains, energy usage, and ocean cultivation by sourcing electricity from renewables and employing low GHG impact materials with long lifespans, and (6) develop low-cost and accurate MRV techniques for ocean-based CDR. 

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3. Asymptotic analysis for sound-hard acoustic scattering by two closely-situated spheres

   Camille Carvalho, Arnold Kim (January 2022, WAVES 2022)

   We consider acoustic binding of particles resulting from radiation forces created through multiple scattering. This problem has potential for developing methods for assembling novel meta-materials. A key consideration in acoustic binding is when two or more particles are closely situated to one another and form a cluster. For that case, the near-field scattering by the particles becomes important. Here, we study multiple scattering by two closely-situated sound-hard spheres. Using boundary integral equation (BIE) methods, we find that a close evaluation problem arises leading to a nearly singular system of BIEs governing the surface fields. An asymptotic analysis of the problem reveals that this nearly singular behavior will lead to large error in the numerical solution unless it is explicitly addressed. 

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4. Shearing-box simulations of MRI-driven turbulence in weakly collisional accretion discs

   https://doi.org/10.1093/mnras/stz1111  

   Kempski, Philipp; Quataert, Eliot; Squire, Jonathan; Kunz, Matthew W (July 2019, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT We present a systematic shearing-box investigation of magnetorotational instability (MRI)-driven turbulence in a weakly collisional plasma by including the effects of an anisotropic pressure stress, i.e. anisotropic (Braginskii) viscosity. We constrain the pressure anisotropy (Δp) to lie within the stability bounds that would be otherwise imposed by kinetic microinstabilities. We explore a broad region of parameter space by considering different Reynolds numbers and magnetic-field configurations, including net vertical flux, net toroidal-vertical flux, and zero net flux. Remarkably, we find that the level of turbulence and angular-momentum transport are not greatly affected by large anisotropic viscosities: the Maxwell and Reynolds stresses do not differ much from the MHD result. Angular-momentum transport in Braginskii MHD still depends strongly on isotropic dissipation, e.g. the isotropic magnetic Prandtl number, even when the anisotropic viscosity is orders of magnitude larger than the isotropic diffusivities. Braginskii viscosity nevertheless changes the flow structure, rearranging the turbulence to largely counter the parallel rate of strain from the background shear. We also show that the volume-averaged pressure anisotropy and anisotropic viscous transport decrease with increasing isotropic Reynolds number (Re); e.g. in simulations with net vertical field, the ratio of anisotropic to Maxwell stress (αA/αM) decreases from ∼0.5 to ∼0.1 as we move from Re ∼ 103 to Re ∼ 104, while 〈4$$\pi$$Δp/B2〉 → 0. Anisotropic transport may thus become negligible at high Re. Anisotropic viscosity nevertheless becomes the dominant source of heating at large Re, accounting for $${\gtrsim } 50 {{\ \rm per\ cent}}$$ of the plasma heating. We conclude by briefly discussing the implications of our results for radiatively inefficient accretion flows on to black holes. 

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5. Bridge inspection component registration for damage evolution

   https://doi.org/10.1177/14759217221083647  

   Bianchi, Eric_L; Sakib, Nazmus; Woolsey, Craig; Hebdon, Matthew (May 2022, Structural Health Monitoring)

   There have been great advances in bridge inspection damage detection involving the use of deep learning models. However, automated detection models currently fall short of giving an inspector an understanding of how the damage has progressed from one inspection to the next. The rate-of-change of the damage is a critical piece of information used by engineers to determine appropriate maintenance and rehabilitation actions to prevent structural failures. We propose a simple methodology for registering two bridge inspection videos or still images, collected at different stages of deterioration, so that trained model predictions may be directly measured and damage progression compared. The changes may be documented and presented to the inspector so that they may quickly evaluate key interest regions in the inspection video or image. Three approaches referred to as rigid, deformable, and hybrid image registration methods were experimentally tested and evaluated based on their ability to preserve the geometric characteristics of the referenced image. It was found in all experiments that the rigid, homography-based transformations performed the best for this application over a state-of-the-art deformable registration method, RANSAC-Flow. 

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