Elastocaloric response of PbTiO3 predicted from a first-principles effective Hamiltonian

A first-principles based effective Hamiltonian is used within a molecular dynamics simulation to study the elastocaloric effect in PbTiO3. It is found that the transition temperature is a linear function of uniaxial tensile stress. Negative temperature change is calculated, when the uniaxial tensile stress is switched off, as a function of initial temperature Delta-T(T_initial). It is predicted that the formation of domain structures under uniaxial tensile stress degrades the effectiveness of the elastocaloric effect.Comment: 6 pages, 7 figures, published in JPS

Modeling Light Use Efficiency in a Subtropical Mangrove Forest Equipped with CO2 Eddy Covariance °C

Despite the importance of mangrove ecosystems in the global carbon budget, the relationships between environmental drivers and carbon dynamics in these forests remain poorly understood. This limited understanding is partly a result of the challenges associated with in situ flux studies. Tower-based CO2 eddy covariance (EC) systems are installed in only a few mangrove forests worldwide, and the longest EC record from the Florida Everglades contains less than 9 years of observations. A primary goal of the present study was to develop a methodology to estimate canopy-scale photosynthetic light use efficiency in this forest. These tower-based observations represent a basis for associating CO2 fluxes with canopy light use properties, and thus provide the means for utilizing satellite-based reflectance data for larger scale investigations. We present a model for mangrove canopy light use efficiency utilizing the enhanced green vegetation index (EVI) derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) that is capable of predicting changes in mangrove forest CO2 fluxes caused by a hurricane disturbance and changes in regional environmental conditions, including temperature and salinity. Model parameters are solved for in a Bayesian framework. The model structure requires estimates of ecosystem respiration (RE), and we present the first ever tower-based estimates of mangrove forest RE derived from nighttime CO2 fluxes. Our investigation is also the first to show the effects of salinity on mangrove forest CO2 uptake, which declines 5% per each 10 parts per thousand (ppt) increase in salinity. Light use efficiency in this forest declines with increasing daily photosynthetic active radiation, which is an important departure from the assumption of constant light use efficiency typically applied in satellite-driven models. The model developed here provides a framework for estimating CO2 uptake by these forests from reflectance data and information about environmental conditions

A Discussion of Thirteen Financial Accounting Topics

The purpose of this paper is to investigate thirteen different financial reporting topics and principles using specific scenarios that have been presented in a case study. These topics include the effects of different U.S. GAAP reporting options, the calculation of return on net operating assets, the statement of cash flows, the treatment of accounts receivable, U.S. GAAP policies, the effects of depreciation expense, contingencies, long-term debt, common stock, the treatment of investments, revenue recognition, the effects of deferred income taxes, and retirement obligations. Each case study introduces a company (or multiple companies) that exemplifies the topic for analysis. Then, several questions guide the analysis of the issue. Analysis of the issue in each case study leads to a better understanding of the U.S. generally accepted accounting principles surrounding the issue and often sheds light on the effects the issue has on the financial statements or company’s performance overall. These case studies help to develop an understanding of the accounting issues that goes beyond a simple understanding of the journal entries

Direct Generation of Oxygen via Electrocatalytic Carbon Dioxide Reduction with an Ionic Liquid

The feasibility of long duration crewed space exploration missions will depend on the supply of consumables, such as oxygen, to keep the crew alive. Air revitalization is a function of environmental control and life support systems (ECLSS) employed on any crewed spacecraft. On longer duration missions, such as on the International Space Station (ISS), resource regeneration reduces the amount of consumables that must be provided for the mission. Systems on the ISS recover O2&nbsp;from metabolically produced CO2, which itself is collected from the ISS cabin where astronauts live and work. The current state-of-the-art for O2&nbsp;recovery onboard the ISS can only recover up to 54% of the O2&nbsp;available in respired CO2&nbsp;and relies on the resupplied H2O to the ISS. An alternative O2&nbsp;generation process is solvated electrochemical CO2&nbsp;reduction, enabled in spacecraft environments by using a non-volatile ionic liquid (IL) solvent, electrolyte, and catalysis promoter. An electrochemical CO2&nbsp;reduction system (ECRS) could improve O2&nbsp;recovery from CO2&nbsp;by up to 70%, or it could function to recover 50% O2&nbsp;from CO2&nbsp;without a net water loss, which can be advantageous in missions where in-situ resource utilization (ISRU) of Martian atmospheric CO2&nbsp;is desired. Ionic liquid supported electrochemical CO2&nbsp;reduction is evaluated to determine its feasibility for space applications. The requirements, sizing, and challenges of including an ECRS are considered for various possible ECLSS or ISRU architectures. The current state-of-the-art for IL supported CO2&nbsp;electrolysis is reviewed, and selections of ILs studied experimentally in this work are presented and justified. Thermophysical properties of the ILs as neat and aqueous solutions are measured to aid in understanding and design of the ILs themselves and in systems using them. Aqueous IL solutions are studied using cyclic voltammetry and constant potential electrolysis with gaseous product analysis to determine if and how the selected ILs promote electrochemical CO2&nbsp;reduction. A concept for a vacuum-assisted product removal (VAPR) CO2&nbsp;electrolyzer is presented as a possible solution to space application environmental conditions and requirements, and the concept is demonstrated through the design and testing of a prototype electrolyzer.</p

Seasonal Evapotranspiration Patterns in Mangrove Forests

Diurnal and seasonal controls on water vapor fluxes were investigated in a subtropical mangrove forest in Everglades National Park, Florida. Energy partitioning between sensible and latent heat fluxes was highly variable during the 2004–2005 study period. During the dry season, the mangrove forest behaved akin to a semiarid ecosystem as most of the available energy was partitioned into sensible heat, which gave Bowen ratio values exceeding 1.0 and minimum latent heat fluxes of 5 MJ d1. In contrast, during the wet season the mangrove forest acted as a well-watered, broadleaved deciduous forest, with Bowen ratio values of 0.25 and latent heat fluxes reaching 18 MJ d1. During the dry season, high salinity levels (\u3e30 parts per thousand, ppt) caused evapotranspiration to decline and correspondingly resulted in reduced canopy conductance. From multiple linear regression, daily average canopy conductance to water vapor declined with increasing salinity,vapor pressure deficit, and daily sums of solar irradiance but increased with air temperature and friction velocity. Using these relationships, appropriately modified Penman-Monteith and Priestley-Taylor models reliably reproduced seasonal trends in daily evapotranspiration. Such numerical models, using site-specific parameters, are crucial for constructing seasonal water budgets, constraining hydrological models, and driving regional climate models over mangrove forests

Understanding Coastal Carbon Cycling by Linking Top- Down and Bottom-Up Approaches

The coastal zone, despite occupying a small fraction of the Earth\u27s surface area, is an important component of the global carbon (C) cycle. Coastal wetlands, including mangrove forests, tidal marshes, and seagrass meadows, compose a domain of large reservoirs of biomass and soil C [Fourqurean et al., 2012; Donato et al., 2011; Pendleton et al., 2012; Regnier et al., 2013; Bauer et al.,2013]. These wetlands and their associated C reservoirs (2 to 25 petagrams C; best estimate of 7 petagrams C [Pendleton et al., 2012]) provide numerous ecosystem services and serve as key links between land and ocean

Controls on mangrove forest-atmosphere carbon dioxide exchanges in western Everglades National Park

We report on net ecosystem production (NEP) and key environmental controls on net ecosystem exchange (NEE) of carbon dioxide (CO2) between a mangrove forest and the atmosphere in the coastal Florida Everglades. An eddy covariance system deployed above the canopy was used to determine NEE during January 2004 through August 2005. Maximum daytime NEE ranged from −20 to −25 mmol (CO2) m−2 s−1 between March and May. Respiration (Rd) was highly variable (2.81 ± 2.41 mmol (CO2) m−2 s−1), reaching peak values during the summer wet season. During the winter dry season, forest CO2 assimilation increased with the proportion of diffuse solar irradiance in response to greater radiative transfer in the forest canopy. Surface water salinity and tidal activity were also important controls on NEE. Daily light use efficiency was reduced at high (\u3e34 parts per thousand (ppt)) compared to low (ppt) salinity by 46%. Tidal inundation lowered daytime Rd by ∼0.9 mmol (CO2) m−2 s−1 and nighttime Rd by ∼0.5 mmol (CO2) m−2 s−1. The forest was a sink for atmospheric CO2, with an annual NEP of 1170 ± 127 g C m−2 during 2004. This unusually high NEP was attributed to year‐round productivity and low ecosystem respiration which reached a maximum of only 3 g C m−2 d−1. Tidal export of dissolved inorganic carbon derived from belowground respiration likely lowered the estimates of mangrove forest respiration. These results suggest that carbon balance in mangrove coastal systems will change in response to variable salinity and inundation patterns, possibly resulting from secular sea level rise and climate change. Citation: Barr, J. G., V. Engel, J. D. Fuentes