Grid-stretching capability for the GEOS-Chem 13.0.0 atmospheric chemistry model

Modeling atmospheric chemistry at fine resolution globally is computationally expensive; the capability to focus on specific geographic regions using a multiscale grid is desirable. Here, we develop, validate, and demonstrate stretched grids in the GEOS-Chem atmospheric chemistry model in its high-performance implementation (GCHP). These multiscale grids are specified at runtime by four parameters that offer users nimble control of the region that is refined and the resolution of the refinement. We validate the stretched-grid simulation versus global cubed-sphere simulations. We demonstrate the operation and flexibility of stretched-grid simulations with two case studies that compare simulated tropospheric NO2 column densities from stretched-grid and cubed-sphere simulations to retrieved column densities from the TROPOspheric Monitoring Instrument (TROPOMI). The first case study uses a stretched grid with a broad refinement covering the contiguous US to produce simulated columns that perform similarly to a C180 (∼ 50 km) cubed-sphere simulation at less than one-ninth the computational expense. The second case study experiments with a large stretch factor for a global stretched-grid simulation with a highly localized refinement with ∼10 km resolution for California. We find that the refinement improves spatial agreement with TROPOMI columns compared to a C90 cubed-sphere simulation of comparable computational demands. Overall, we find that stretched grids in GEOS-Chem are a practical tool for fine-resolution regional- or continental-scale simulations of atmospheric chemistry. Stretched grids are available in GEOS-Chem version 13.0.0.

Grid-Stretching Capability for the GEOS-Chem 13.0.0 Atmospheric Chemistry Model

Modeling atmospheric chemistry at fine resolution globally is computationally expensive; the capability to focus on specific geographic regions using a multiscale grid is desirable. Here, we develop, validate, and demonstrate stretched-grids in the GEOS-Chem atmospheric chemistry model in its high performance implementation (GCHP). These multiscale grids are specified at runtime by four parameters that offer users nimble control of the region that is refined and the resolution of the refinement. We validate the stretched-grid simulation versus global cubed-sphere simulations. We demonstrate the operation and flexibility of stretched-grid simulations with two case studies that compare simulated tropospheric NO2 column densities from stretched-grid and cubed-sphere simulations to retrieved column densities from the TROPOspheric Monitoring Instrument (TROPOMI). The first case study uses a stretched-grid with a broad refinement covering the contiguous US to produce simulated columns that perform similarly to a C180 (~50 km) cubed-sphere simulation at less than one-ninth the computational expense. The second case study experiments with a large stretch-factor for a global stretched-grid simulation with a highly localized refinement with ~10 km resolution for California. We find that the refinement improves spatial agreement with TROPOMI columns compared to a C90 cubed-sphere simulation of comparable computational demands, despite conducting the simulation at a finer resolution than parent meteorological fields. Overall we find that stretched-grids in GEOS-Chem are a practical tool for fine resolution regional- or continental-scale simulations of atmospheric chemistry. Stretched-grids are available in GEOS-Chem version 13.0.0.

Non-Linear Vibration of Thick Dielectric Membrane Disks With Radial Loads

This study analyzes the large-amplitude, non-linear vibration of dielectric elastomer membrane disks with applied voltages through their thickness and mechanical loads applied radially around their outer circumferential surface. The material is modeled as an isotropic ideal dielectric, with the large-stretch mechanical stiffening captured using the Gent hyperelastic constitutive model. The fully non-linear equation of motion for the coupled electromechanical system is derived using Hamilton’s principle. The disk comes to a steady equilibrium where the compressive stresses due to the applied voltage balance the tensile stresses from the applied radial loads. The equilibria are calculated numerically for a wide range of radial loads, applied voltages, and limiting stretches. It is possible for the disk to have two stable steady equilibria at given radial load and applied voltage, which gives rise to an instability where extreme stretches occur for infinitesimal changes in applied voltage. The equation of motion is determined for small vibrations of the system about equilibrium. Unlike for thin membrane disks, the vibrating mass of thick membrane disks depends on the steady equilibrium stretch. The natural frequency for membrane disks meaningfully decreases with increasing thickness due to the inertia associated with dynamic changes in the membrane thickness. The amount of axial inertia depends on the ratio of the nominal disk thickness to its radius and the steady equilibrium stretch. Large amplitude vibrations are numerically investigated for a wide range of system parameters. The frequency response characteristics of circular membranes due to sinusoidal voltage fluctuations are analyzed about small and large equilibrium stretches. Whereas axial inertia meaningfully alters the frequency response about small equilibrium stretches, it has negligible effects on the frequency response about large equilibrium stretches.

The Adaptive Potential of the Middle Domain of Yeast Hsp90

The distribution of fitness effects (DFEs) of new mutations across different environments quantifies the potential for adaptation in a given environment and its cost in others. So far, results regarding the cost of adaptation across environments have been mixed, and most studies have sampled random mutations across different genes. Here, we quantify systematically how costs of adaptation vary along a large stretch of protein sequence by studying the distribution of fitness effects of the same ≈2,300 amino-acid changing mutations obtained from deep mutational scanning of 119 amino acids in the middle domain of the heat shock protein Hsp90 in five environments. This region is known to be important for client binding, stabilization of the Hsp90 dimer, stabilization of the N-terminal-Middle and Middle-C-terminal interdomains, and regulation of ATPase–chaperone activity. Interestingly, we find that fitness correlates well across diverse stressful environments, with the exception of one environment, diamide. Consistent with this result, we find little cost of adaptation; on average only one in seven beneficial mutations is deleterious in another environment. We identify a hotspot of beneficial mutations in a region of the protein that is located within an allosteric center. The identified protein regions that are enriched in beneficial, deleterious, and costly mutations coincide with residues that are involved in the stabilization of Hsp90 interdomains and stabilization of client-binding interfaces, or residues that are involved in ATPase–chaperone activity of Hsp90. Thus, our study yields information regarding the role and adaptive potential of a protein sequence that complements and extends known structural information.

The adaptive potential of the middle domain of yeast Hsp90

The distribution of fitness effects (DFE) of new mutations across different environments quantifies the potential for adaptation in a given environment and its cost in others. So far, results regarding the cost of adaptation across environments have been mixed, and most studies have sampled random mutations across different genes. Here, we quantify systematically how costs of adaptation vary along a large stretch of protein sequence by studying the DFEs of the same ≈2300 amino-acid changing mutations obtained from deep mutational scanning of 119 amino acids in the middle domain of the heat-shock protein Hsp90 in five environments. This region is known to be important for client binding, stabilization of the Hsp90 dimer, stabilization of the N-terminal-Middle and Middle-C-terminal interdomains, and regulation of ATPase-chaperone activity. Interestingly, we find that fitness correlates well across diverse stressful environments, with the exception of one environment, diamide. Consistent with this result, we find little cost of adaptation; on average only one in seven beneficial mutations is deleterious in another environment. We identify a hotspot of beneficial mutations in a region of the protein that is located within an allosteric center. The identified protein regions that are enriched in beneficial, deleterious, and costly mutations coincide with residues that are involved in the stabilization of Hsp90 interdomains and stabilization of client binding interfaces, or residues that are involved in ATPase chaperone activity of Hsp90. Thus, our study yields information regarding the role and adaptive potential of a protein sequence that complements and extends known structural information.

The Development of Highly Flexible Stretch Sensors for a Robotic Hand

Demand for highly compliant mechanical sensors for use in the fields of robotics and wearable electronics has been constantly rising in recent times. Carbon based materials, and especially, carbon nanotubes, have been widely studied as a candidate piezoresistive sensing medium in these devices due to their favorable structural morphology. In this paper three different carbon based materials, namely carbon black, graphene nano-platelets, and multi-walled carbon nanotubes, were utilized as large stretch sensors capable of measuring stretches over 250%. These stretch sensors can be used in robotic hands/arms to determine the angular position of joints. Analysis was also carried out to understand the effect of the morphologies of the carbon particles on the electromechanical response of the sensors. Sensors with gauge factors ranging from one to 1.75 for strain up to 200% were obtained. Among these sensors, the stretch sensors with carbon black/silicone composite were found to have the highest gauge factor while demonstrating acceptable hysteresis in most robotic hand applications. The highly flexible stretch sensors demonstrated in this work show high levels of compliance and conformance making them ideal candidates as sensors for soft robotics.

Renewable Energy in Africa; Potential, Impact and The Way Forward

Renewable energy sources are abundantly available in Africa due to the continent’s geographical location. For example, it is the sunniest continent on earth with about 85% of the landscape having solar insolation of approximately 2000 kWh/m2 in a year and also with a large stretch of coastline where both wind and wave energy resources are abundant. The available renewable energy sources are underutilised due to many challenges such as inadequate funds, bad or nonexistent policies, and unavailability of skilled labour. This paper, therefore, aims to investigate the impact of renewable energy on Africa and the world as a whole if these renewables are utilised efficiently. The paper again will look into the reasons why renewable energies in Africa are underutilised and recommend possible solutions to these problems as well. Moreover, the paper will discuss the social, economic and environmental impacts of utilising renewable energy in Africa regarding jobs creation, infrastructure development, revenue creation, and reduction of carbon emissions into the atmosphere. The efficient utilization of these renewable energy resources will make Africa a powerhouse of clean energy production for its use and export.

Modeling the impairment of airway smooth muscle force by stretch

Imposed length changes of only a small percent produce transient reductions in active force in strips of airway smooth muscle (ASM) due to the temporary detachment of bound cross-bridges caused by the relative motion of the actin and myosin fibers. More dramatic and sustained reductions in active force occur following large changes in length. The Huxley two-state model of skeletal muscle originally proposed in 1957 and later adapted to include a four-state description of cross-bridge kinetics has been widely used to model the former phenomenon, but is unable to account for the latter unless modified to include mechanisms by which the contractile machinery in the ASM cell becomes appropriately rearranged. Even so, the Huxley model itself is based on the assumption that the contractile proteins are all aligned precisely in the direction of bulk force generation, which is not true for ASM. The present study derives a coarse-grained version of the Huxley model that is free of inherent assumptions about cross-bridge orientation. This simplified model recapitulates the key features observed in the force-length behavior of activated strips of ASM and, in addition, provides a mechanistically based way of accounting for the sustained force reductions that occur following large stretch.

Implementation of a Visco-Elastic Model Into Slender Rod Theory for Deepwater Polyester Mooring Line

Polyester mooring line is gradually becoming popular in deepwater engineering because of its lightweight property. In catenary mooring system, the horizontal restoring force comes from the gravity effect of the catenary mooring line which occupies the payload of the platform. Thus, the synthetic mooring line overcomes the drawback together with the taut mooring system which utilizes the axial elasticity to offer restoring force. The synthetic mooring line may only be one seventh weight of the steel mooring line and has low tensile stiffness which leads to a large stretch, and nonlinear material characteristics such as visco-elasticity. These two terms need to improve the slender rod theory which is proposed by Garrett for no stretched lines and improved by Paulling and Webster for small stretched lines. In this topic, a method for large stretched slender rod theory is introduced with the finite element method to deal with the problems of the large rotation and the large deformation. And then a linear visco-elastic model in the stretch-tension relation is utilized to simulate the properties of polyester line such as creep, strain-stress hysteresis and excitation period-dependent stiffness. Finally, an implementation method for integrating the visco-elastic model into slender rod theory is proposed with the numerical method and corroborated by a specified case which has the analytical results.