Nuclear quantum effects in water exchange around lithium and fluoride ions

We employ classical and ring polymer molecular dynamics simulations to study the effect of nuclear quantum fluctuations on the structure and the water exchange dynamics of aqueous solutions of lithium and fluoride ions. While we obtain reasonably good agreement with experimental data for solutions of lithium by augmenting the Coulombic interactions between the ion and the water molecules with a standard Lennard-Jones ion-oxygen potential, the same is not true for solutions of fluoride, for which we find that a potential with a softer repulsive wall gives much better agreement. A small degree of destabilization of the first hydration shell is found in quantum simulations of both ions when compared with classical simulations, with the shell becoming less sharply defined and the mean residence time of the water molecules in the shell decreasing. In line with these modest differences, we find that the mechanisms of the exchange processes are unaffected by quantization, so a classical description of these reactions gives qualitatively correct and quantitatively reasonable results. We also find that the quantum effects in solutions of lithium are larger than in solutions of fluoride. This is partly due to the stronger interaction of lithium with water molecules, partly due to the lighter mass of lithium, and partly due to competing quantum effects in the hydration of fluoride, which are absent in the hydration of lithium.Comment: 12 pages, 8 figure

Outage Performance Analysis of Multicarrier Relay Selection for Cooperative Networks

In this paper, we analyze the outage performance of two multicarrier relay selection schemes, i.e. bulk and per-subcarrier selections, for two-hop orthogonal frequency-division multiplexing (OFDM) systems. To provide a comprehensive analysis, three forwarding protocols: decode-and-forward (DF), fixed-gain (FG) amplify-and-forward (AF) and variable-gain (VG) AF relay systems are considered. We obtain closed-form approximations for the outage probability and closed-form expressions for the asymptotic outage probability in the high signal-to-noise ratio (SNR) region for all cases. Our analysis is verified by Monte Carlo simulations, and provides an analytical framework for multicarrier systems with relay selection

Role of Mitochondria in Postmortem Proteolysis and Meat Tenderness

Among all eating quality characteristics in beef, tenderness is regarded as one of the most important traits. Previous research indicates that consumers are willing to pay a premium for beef guaranteed to be tender. Yet, tenderness is difficult to control and predict as it is influenced by a multitude of factors. Among these factors, meat aging has been shown to be a strong determinant of tenderness. Meat aging describes a process in which muscle tissue is broken down by other proteins within the muscle, resulting in a more tender product after cooking. Two well-recognized proteins that participate in the breakdown of muscle tissue are known as calpains and caspases. The process of breaking down muscle tissue is necessary to achieve the desirable palatability that consumers seek in beef and is an essential phenomenon for converting muscle tissue into edible meat. However, even knowing this, issues with producing meat products that are consistently tender still exist. This suggests that there are other factors that are influencing the aging process that we do not quite understand. Known as the “power house” of a cell, mitochondria are responsible for generating a large portion of the necessary energy that is required for organisms to live. Mitochondria are often ignored for their role in the conversion of muscle to meat due to requiring oxygen to function. However, these organelles can participate in other functions that do not require oxygen, such as sequestering calcium and signaling for cell death in the muscle. Interestingly, these two events are associated with calpain and caspase activities, and hence, could potentially partially explain the variation observed with meat tenderness. Therefore, we hypothesize that mitochondria influence the aging process by limiting available calcium for calpains momentarily but later enhancing tenderness by participating in cell death. To test this hypothesis, we evaluated the effects of calcium uptake by the mitochondria on tenderness, different muscle characteristics and proteins of steaks that vary in tenderness, and the ability of the mitochondria to initiate cell death in meat. Our results showed that mitochondria could influence meat tenderness by controlling cellular calcium levels, and subsequently, calpain activity. Furthermore, muscles that possess less mitochondria appear to positively impact meat tenderness. Although the results suggest that more mitochondria negatively impact tenderness, our results also indicated that mitochondria could improve tenderness by participating in cell death by activating the caspase system. In conclusion, this project demonstrates that the improvement in meat tenderness may be partly regulated by the presence of mitochondria in the muscle, yet it is important to consider that the observed effects may be species, breed, and muscle dependent

Using repeated cross-sections to explore movements in and out of poverty

Movements in and out of poverty are of core interest to both policymakers and economists. Yet the panel data needed to analyze such movements are rare. In this paper, the authors build on the methodology used to construct poverty maps to show how repeated cross-sections of household survey data can allow inferences to be made about movements in and out of poverty. They illustrate that the method permits the estimation of bounds on mobility, and provide non-parametric and parametric approaches to obtaining these bounds. They test how well the method works on data sets for Vietnam and Indonesia where we are able to compare our method to true panel estimates. The results are sufficiently encouraging to offer the prospect of some limited, basic, insights into mobility and poverty duration in settings where historically it was judged that the data necessary for such analysis were unavailable.Rural Poverty Reduction,Regional Economic Development,Statistical&Mathematical Sciences,Achieving Shared Growth

Combining tower mixing ratio and community model data to estimate regional-scale net ecosystem carbon exchange by boundary layer inversion over 4 flux towers in the U.S.A.

We evaluated an idealized boundary layer (BL) model with simple parameterizations using vertical transport information from community model outputs (NCAR/NCEP Reanalysis and ECMWF Interim Analysis) to estimate regional-scale net CO2 fluxes from 2002 to 2007 at three forest and one grassland flux sites in the United States. The BL modeling approach builds on a mixed-layer model to infer monthly average net CO2 fluxes using high-precision mixing ratio measurements taken on flux towers. We compared BL model net ecosystem exchange (NEE) with estimates from two independent approaches. First, we compared modeled NEE with tower eddy covariance measurements. The second approach (EC-MOD) was a data-driven method that upscaled EC fluxes from towers to regions using MODIS data streams. Comparisons between modeled CO2 and tower NEE fluxes showed that modeled regional CO2 fluxes displayed interannual and intra-annual variations similar to the tower NEE fluxes at the Rannells Prairie and Wind River Forest sites, but model predictions were frequently different from NEE observations at the Harvard Forest and Howland Forest sites. At the Howland Forest site, modeled CO2 fluxes showed a lag in the onset of growing season uptake by 2 months behind that of tower measurements. At the Harvard Forest site, modeled CO2 fluxes agreed with the timing of growing season uptake but underestimated the magnitude of observed NEE seasonal fluctuation. This modeling inconsistency among sites can be partially attributed to the likely misrepresentation of atmospheric transport and/or CO2gradients between ABL and the free troposphere in the idealized BL model. EC-MOD fluxes showed that spatial heterogeneity in land use and cover very likely explained the majority of the data-model inconsistency. We show a site-dependent atmospheric rectifier effect that appears to have had the largest impact on ABL CO2 inversion in the North American Great Plains. We conclude that a systematic BL modeling approach provided new insights when employed in multiyear, cross-site synthesis studies. These results can be used to develop diagnostic upscaling tools, improving our understanding of the seasonal and interannual variability of surface CO2 fluxes