Tight coupling in thermal Brownian motors

We study analytically a thermal Brownian motor model and calculate exactly the Onsager coefficients. We show how the reciprocity relation holds and that the determinant of the Onsager matrix vanishes. Such condition implies that the device is built with tight coupling. This explains why Carnot's efficiency can be achieved in the limit of infinitely slow velocities. We also prove that the efficiency at maximum power has the maximum possible value, which corresponds to the Curzon-Alhborn bound. Finally, we discuss the model acting as a Brownian refrigerator

Total polyphenol content of green, roasted and cooked Harar and Yirgacheffee Coffee, Ethiopia

The effect of solvent composition on the total polyphenols content of green, roasted coffee and traditional coffee beverage preparation stages (Abol, Tona and Bereka) were studied by UV-Vis spectroscopy. The maximum extracted polyphenol of 640.3 mg GAE/100 g and 641.9 mg GAE/100 g were obtained at Harar and Yirgacheffee green coffee extracts with at 85% methanol, respectively. The results showed that total phenolic contents of extracts were found to be in the order of green> roasted >cooked (Abol>Tona>Bereka) in both coffee samples. Application of ANOVA revealed that a significant variation (p <0.05) was noted between the green, roasted, Abol, Tona and Breka coffee processing procedures. In general, this study revealed that there was a loss of substantial amount of total polyphenols through the traditional way of coffee brewing, probably ascribed to continuous provision of heating leads to degradation of existing polyphenols and formation of less stable and volatile products.Keywords: Coffee, Green, Roasted, Cooked, Polypheno

Pattern of functional diversity along the elevation gradient in the dry evergreen Afromontane forest of Hararghe Highland, Southeast Ethiopia

Understanding plant species distribution patterns along environmental gradients is fundamental to managing ecosystems, particularly when habitats are fragmented due to intensive human land use pressure. The variation pattern of functional diversity of plant communities along the elevation gradient in the Dindin dry evergreen Afromontane forest was tested. Fifty four plots of 20 x 20 m (400 m2) were established at 200 m intervals starting 2,300–2,900 m a. s. l. and woody species composition, and environmental variables were recorded. Nine functional diversity indices based on functional distances were employed to esimate functional diversity. The mixed effect model was used to determine the effect of elevation, aspect and slope on functional diversity indices. The results showed that functional diversity in communities varied greatly; functional diversity revealed a decrease with increasing elevation and a‘‘humped’’ pattern, with peak diversity appearing at middle elevation. Functional diversity was significantly correlated with elevation, slope, and aspect. Functional diversity was significantly correlated with species richness and evenness. Environmental filtering was important to the functional diversity pattern; the nine indices were all successful in the analysis of functional diversity in the plant community with different effectiveness, and modified functional attribute diversity, plot-based functional diversity, community based functional diversity, functional richness, and community weight mean of woody density performed better than the other four indices in this study

Stochastic Resonance of a Flexible Chain Crossing over a Barrier

We study the stochastic resonance (SR) of a flexible polymer surmounting a bistable-potential barrier. Due to the flexibility that can enhance crossing rate and change chain conformations at the barrier, the SR behaviors manifest many features of an entropic SR of a new kind, such as the power amplification peaks at optimal chain lengths and elastic constants as well as the optimal noise strengths. The pronounced peaks that emerge depending on the chain lengths and conformation states suggest novel means of manipulating biopolymers, such as efficient separation methods, within undulating channels.Comment: 13 pages, 9 figure

Brownian motors: current fluctuations and rectification efficiency

With this work we investigate an often neglected aspect of Brownian motor transport: The r\^{o}le of fluctuations of the noise-induced current and its consequences for the efficiency of rectifying noise. In doing so, we consider a Brownian inertial motor that is driven by an unbiased monochromatic, time-periodic force and thermal noise. Typically, we find that the asymptotic, time- and noise-averaged transport velocities are small, possessing rather broad velocity fluctuations. This implies a corresponding poor performance for the rectification power. However, for tailored profiles of the ratchet potential and appropriate drive parameters, we can identify a drastic enhancement of the rectification efficiency. This regime is marked by persistent, uni-directional motion of the Brownian motor with few back-turns, only. The corresponding asymmetric velocity distribution is then rather narrow, with a support that predominantly favors only one sign for the velocity.Comment: 9 pages, 4 figure

The Existing Forest Coffee Market Channel of Essara Woreda and Actors Involved in the Chain the Cause of Dawuro Zone, Southern Nation Natonalits and Peoples Region, Ethiopia

Forest coffee originates in Southwestern and Southeastern Ethiopia where 30% of production and 10 % to 20% of the country’s total export originates from. The general objective of the study was to analyze the factors that affect the existing forest coffee value chain of Essara woreda with specific focus of identify the existing coffee market channel and actors involved in the chain, the structure and performance of coffee chain determinants of market surplus production, price received by coffee farm households and the role of gender in coffee value chain. To these end 235 sample producers, local coffee collector, local traders, wholesalers and consumers were identified from 9 kebele, Balle and Tarcha town for the study. Based on the findings of the study the volume of production and marketing were found to be affected by age, family size, market Center and all-weather road distance, the level of deforestation and factors that aggravated deforestation, selling price, experience of producer households and mixing forest coffee to garden coffee to increase the volume. About 2%  of market surplus coffee is transacted in through formal market while, 98 % is through conventional market, as a result of which producer obtain less income and 98 % forest coffee producer’s income source is depending on natural forest coffee production and marketing while, the level of deforestation is too high it needs appropriate intervention and awareness creation. Market margin of the area indicated that the large share of benefit is concentrated at roadside, café and hotel coffee brewers and venders. Hence, in order to improve the profit margin and level of producers’ benefit value addition and increase in sale price for their produce at farm get level is recommended Keywords: Essara Woreda, value chain, actor’s, market channe

Segregation of receptor-ligand complexes in cell adhesion zones: Phase diagrams and role of thermal membrane roughness

The adhesion zone of immune cells, the 'immunological synapse', exhibits characteristic domains of receptor-ligand complexes. The domain formation is likely caused by a length difference of the receptor-ligand complexes, and has been investigated in experiments in which T cells adhere to supported membranes with anchored ligands. For supported membranes with two types of anchored ligands, MHCp and ICAM1, that bind to the receptors TCR and LFA1 in the cell membrane, the coexistence of domains of TCR-MHCp and LFA1-ICAM1 complexes in the cell adhesion zone has been observed for a wide range of ligand concentrations and affinities. For supported membranes with long and short ligands that bind to the same cell receptor CD2, in contrast, domain coexistence has been observed for a rather narrow ratio of ligand concentrations. In this article, we determine detailed phase diagrams for cells adhering to supported membranes with a statistical-physical model of cell adhesion. We find a characteristic difference between the adhesion scenarios in which two types of ligands in a supported membrane bind (i) to the same cell receptor or (ii) to two different cell receptors, which helps to explain the experimental observations. Our phase diagrams fully include thermal shape fluctuations of the cell membranes on nanometer scales, which lead to a critical point for the domain formation and to a cooperative binding of the receptors and ligands.Comment: 23 pages, 6 figure