149 research outputs found
Free energy of colloidal particles at the surface of sessile drops
The influence of finite system size on the free energy of a spherical
particle floating at the surface of a sessile droplet is studied both
analytically and numerically. In the special case that the contact angle at the
substrate equals a capillary analogue of the method of images is
applied in order to calculate small deformations of the droplet shape if an
external force is applied to the particle. The type of boundary conditions for
the droplet shape at the substrate determines the sign of the capillary
monopole associated with the image particle. Therefore, the free energy of the
particle, which is proportional to the interaction energy of the original
particle with its image, can be of either sign, too. The analytic solutions,
given by the Green's function of the capillary equation, are constructed such
that the condition of the forces acting on the droplet being balanced and of
the volume constraint are fulfilled. Besides the known phenomena of attraction
of a particle to a free contact line and repulsion from a pinned one, we
observe a local free energy minimum for the particle being located at the drop
apex or at an intermediate angle, respectively. This peculiarity can be traced
back to a non-monotonic behavior of the Green's function, which reflects the
interplay between the deformations of the droplet shape and the volume
constraint.Comment: 24 pages, 19 figure
Electron-Electron Interaction in Disordered Mesoscopic Systems: Weak Localization and Mesoscopic Fluctuations of Polarizability and Capacitance
The weak localization correction and the mesoscopic fluctuations of the
polarizability and the capacitance of a small disordered sample are studied
systematically in 2D and 3D geometries. While the grand canonical ensemble
calculation gives the positive magnetopolarizability, in the canonical ensemble
(appropriate for isolated samples) the sign of the effect is reversed. The
magnitude of mesoscopic fluctuations for a single sample exceeds considerably
the value of the weak localization correction.Comment: 13 pages Latex, 3 .eps figures included. To appear in Phys. Rev. B.
Minor corrections, in particular in formulae; new references adde
Zoonosis emergence linked to agricultural intensification and environmental change
A systematic review was conducted by a multidisciplinary team to analyze qualitatively best available scientific evidence on the effect of agricultural intensification and environmental changes on the risk of zoonoses for which there are epidemiological interactions between wildlife and livestock. The study found several examples in which agricultural intensification and/or environmental change were associated with an increased risk of zoonotic disease emergence, driven by the impact of an expanding human population and changing human behavior on the environment. We conclude that the rate of future zoonotic disease emergence or reemergence will be closely linked to the evolution of the agriculture–environment nexus. However, available research inadequately addresses the complexity and interrelatedness of environmental, biological, economic, and social dimensions of zoonotic pathogen emergence, which significantly limits our ability to predict, prevent, and respond to zoonotic disease emergence
Membrane-mediated interactions
Interactions mediated by the cell membrane between inclusions, such as
membrane proteins or antimicrobial peptides, play important roles in their
biological activity. They also constitute a fascinating challenge for
physicists, since they test the boundaries of our understanding of
self-assembled lipid membranes, which are remarkable examples of
two-dimensional complex fluids. Inclusions can couple to various degrees of
freedom of the membrane, resulting in different types of interactions. In this
chapter, we review the membrane-mediated interactions that arise from direct
constraints imposed by inclusions on the shape of the membrane. These effects
are generic and do not depend on specific chemical interactions. Hence, they
can be studied using coarse-grained soft matter descriptions. We deal with
long-range membrane-mediated interactions due to the constraints imposed by
inclusions on membrane curvature and on its fluctuations. We also discuss the
shorter-range interactions that arise from the constraints on membrane
thickness imposed by inclusions presenting a hydrophobic mismatch with the
membrane.Comment: 38 pages, 10 figures, pre-submission version. In: Bassereau P., Sens
P. (eds) Physics of Biological Membranes. Springer, Cha
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Effect of NaCl on the Growth of Germinating Upland Cotton (Gossypium hirsutum L.) Seeds
Responses to environmental stresses such as excess salinity are difficult to understand if not studied under defined conditions. The objective of this study was to determine if cottonseed radicle and cotyledon growth during germination was affected by exogenous NaCl. Cottonseeds were imbibed in moistened paper toweling for 24 h at 32°C before transfer to an agar media containing selected concentrations of NaCl for an additional 24 h. Radicle linear growth extension was stimulated at low NaC1 concentrations (80 mM), but increasingly inhibited as NaCl concentrations increased from 160 to 400 mM. Radicle and cotyledon fresh weights were increasingly inhibited by NaCl concentrations between 0 and 400 mM. NaCl inhibition of radicle fresh weights was more pronounced than that of cotyledons. We conclude that the inhibitory effects of NaCl can be quantified as reductions in cottonseed radicle and cotyledon growth
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Exogenous L- and D-Proline Does Not Reduce NaCl Inhibition of Radidle Growth of Germinating Cotton (Gossypium hirsutum L.) Seeds
The adaptive significance of proline (Pm) accumulation in cotton seeds can be assessed by determining if NaCl tolerance is influenced by changes in the Pm level of the seed. The objective of this study was to determine if exogenous L-Pro and D-Pro reduce NaCl inhibition of radicle growth of germinating cotton seeds. Seeds were imbibed for 24 h at 32°C before transfer to agar medium containing either Pro, NaCl or mixtures of both. Results indicate that exogenous Pro increases the Pro contents of cotton seed radicles and cotyledons to a similar extent. Such increases are independent of whether L- or D-Pro is fed exogenously. Results also show that exogenous Pro does not significantly reduce NaCl inhibition of radicle growth in germinating cotton seeds.
Accumulation of Proline in Germinating Cotton (Gossypium hisutum L.) Seeds During NaCl Stress
The accumulation of proline (Pro) in plants during NaCl stress may have adaptive significance and the study of this response could reveal a genetic strategy for enhancing NaCl tolerance. Our objective was to determine if the Pro content of germinating cotton seeds is altered by exposure to exogenous NaCl. Seeds were imbibed for 24 h at 32°C before transfer to agar media containing NaCl. After 24 h of NaCl exposure, the Pro contents of radicles and cotyledons were measured using a colorimetric assay. Results showed that Pro contents of both radicles and cotyledons increased as the level of NaCl increased. The bulk of Pro content increases were restricted to the radicle and occurred in the range of NaC1 concentrations from 200 to 400 mM NaCl
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Can Cotton (Cossypium hirsutum) Seed Vigor Be Assessed in the Absence of Growth?
Although seed vigor is ultimately expressed in terms of growth, it is not clear if metabolic processes unlinked to growth can also estimate vigor. The objective of this study was to determine if the relationship between seed vigor and ethanol metabolism differed depending on whether seed growth was presence or absence. For individua1 imbibed cotton seed, ethanol assimilation in air and ethanol biosynthesis in N₂ gas was correlated to seed vigor as measured by cool test performance. Seed growth in N₂ gas was prevented by the addition of polyethylene glycol. Results were inconclusive, because seed performance (radicle growth) during cool testing was not significantly correlated to either ethanol biosynthesis or ethanol assimilation. It was concluded that ethanol metabolism both in the absence and presence of seed growth has limited usefulness as a metabolic marker of cotton seed vigor
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