1,905 research outputs found
Bending Resistance and Chemically Induced Moments in Membrane Bilayers
Pure bending of a membrane bilayer is developed including different properties for each membrane half. Both connected and unconnected bilayer surfaces are treated. The bilayer bending resistance is the resultant of parallel surface compression “resistances.” The neutral surface is a function of the upper and lower surface compressibility moduli and does not necessarily coincide with the mid-surface. Alterations in the interfacial chemical free energy density (surface tension) on either face can create induced bending moments and produce curvature; even small changes can have a pronounced curvature effect. Chemically induced moments are considered as a possible mechanism for crenation of red blood cells
An analytical analysis of vesicle tumbling under a shear flow
Vesicles under a shear flow exhibit a tank-treading motion of their membrane,
while their long axis points with an angle < 45 degrees with respect to the
shear stress if the viscosity contrast between the interior and the exterior is
not large enough. Above a certain viscosity contrast, the vesicle undergoes a
tumbling bifurcation, a bifurcation which is known for red blood cells. We have
recently presented the full numerical analysis of this transition. In this
paper, we introduce an analytical model that has the advantage of being both
simple enough and capturing the essential features found numerically. The model
is based on general considerations and does not resort to the explicit
computation of the full hydrodynamic field inside and outside the vesicle.Comment: 19 pages, 9 figures, to be published in Phys. Rev.
The global spread of crop pests and pathogens
AimTo describe the patterns and trends in the spread of crop pests and pathogens around the world, and determine the socioeconomic, environmental and biological factors underlying the rate and degree of redistribution of crop-destroying organisms. LocationGlobal. MethodsCurrent country- and state-level distributions of 1901 pests and pathogens and historical observation dates for 424 species were compared with potential distributions based upon distributions of host crops. The degree of saturation', i.e. the fraction of the potential distribution occupied, was related to pest type, host range, crop production, climate and socioeconomic variables using linear models. ResultsMore than one-tenth of all pests have reached more than half the countries that grow their hosts. If current trends continue, many important crop-producing countries will be fully saturated with pests by the middle of the century. While dispersal increases with host range overall, fungi have the narrowest host range but are the most widely dispersed group. The global dispersal of some pests has been rapid, but pest assemblages remain strongly regionalized and follow the distributions of their hosts. Pest assemblages are significantly correlated with socioeconomics, climate and latitude. Tropical staple crops, with restricted latitudinal ranges, tend to be more saturated with pests and pathogens than temperate staples with broad latitudinal ranges. We list the pests likely to be the most invasive in coming years. Main conclusionsDespite ongoing dispersal of crop pests and pathogens, the degree of biotic homogenization of the globe remains moderate and regionally constrained, but is growing. Fungal pathogens lead the global invasion of agriculture, despite their more restricted host range. Climate change is likely to influence future distributions. Improved surveillance would reveal greater levels of invasion, particularly in developing countries
Fluid-membrane tethers: minimal surfaces and elastic boundary layers
Thin cylindrical tethers are common lipid bilayer membrane structures,
arising in situations ranging from micromanipulation experiments on artificial
vesicles to the dynamic structure of the Golgi apparatus. We study the shape
and formation of a tether in terms of the classical soap-film problem, which is
applied to the case of a membrane disk under tension subject to a point force.
A tether forms from the elastic boundary layer near the point of application of
the force, for sufficiently large displacement. Analytic results for various
aspects of the membrane shape are given.Comment: 12 page
Biomarker analyses of clinical outcomes in patients with advanced hepatocellular carcinoma treated with Sorafenib with or without Erlotinib in the SEARCH Trial
Purpose: Sorafenib is the current standard therapy for advanced HCC, but validated
biomarkers predicting clinical outcomes are lacking. This study aimed to identify biomarkers
predicting prognosis and/or response to sorafenib, with or without erlotinib, in HCC patients from
the phase 3 SEARCH trial.
Experimental Design: 720 patients were randomized to receive oral sorafenib 400 mg BID plus
erlotinib 150 mg QD or placebo. Fifteen growth factors relevant to the treatment regimen and/or
to HCC were measured in baseline plasma samples.
Results: Baseline plasma biomarkers were measured in 494 (69%) patients (sorafenib plus
erlotinib, n=243; sorafenib plus placebo, n=251). Treatment arm–independent analyses showed
that elevated HGF (HR, 1.687 [high vs low expression]; endpoint multiplicity adjusted [e-adj]
P=0.0001) and elevated plasma VEGF-A (HR, 1.386; e-adj P=0..0377) were significantly
associated with poor OS in multivariate analyses, and low plasma KIT (HR, 0.75 [high vs low];
P=0.0233; e-adj P=0.2793) tended to correlate with poorer OS. High plasma VEGF-C
independently correlated with longer TTP (HR, 0.633; e-adj P=0.0010) and trended toward
associating with improved disease control rate (univariate:OR, 2.047; P=0.030; e-adj P=0.420).
In 67% of evaluable patients (339/494), a multimarker signature of HGF, VEGF-A, KIT, epigen,
and VEGF-C correlated with improved median OS in multivariate analysis (HR, 0.150;
P<0.00001). No biomarker predicted efficacy from erlotinib.
Conclusions: Baseline plasma HGF, VEGF-A, KIT, and VEGF-C correlated with clinical
outcomes in HCC patients treated with sorafenib with or without erlotinib. These biomarkers
plus epigen constituted a multimarker signature for improved OS
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SPECIFICATIONS FOR FUEL ASSEMBLIES FOR CORE I OF THE EXPERIMENTAL GAS- COOLED REACTOR
Specifications for the fuel assemblies Experimental Gas Cooled Reactor (EGCR) Core-I were developed for use in procuring the first core loading. A fuel assembly for the EGCR consists of a cluster of seven cylindrical fuel elements spaced and supported within a graphite sleeve. Each fuel element consists of a stainless-steel tube containing a column of hollow UO/sub 2/ pellets and having a spacer brazed at the midsection to control the spacing between fuel elements in a cluster. A master specification for the fuel assembly, a supplementary specification for each of the components, and a specification on record keeping daring manufacture are included. (auth
Percolation and jamming in random sequential adsorption of linear segments on square lattice
We present the results of study of random sequential adsorption of linear
segments (needles) on sites of a square lattice. We show that the percolation
threshold is a nonmonotonic function of the length of the adsorbed needle,
showing a minimum for a certain length of the needles, while the jamming
threshold decreases to a constant with a power law. The ratio of the two
thresholds is also nonmonotonic and it remains constant only in a restricted
range of the needles length. We determine the values of the correlation length
exponent for percolation, jamming and their ratio
A lattice model for the kinetics of rupture of fluid bilayer membranes
We have constructed a model for the kinetics of rupture of membranes under
tension, applying physical principles relevant to lipid bilayers held together
by hydrophobic interactions. The membrane is characterized by the bulk
compressibility (for expansion), the thickness of the hydrophobic part of the
bilayer, the hydrophobicity and a parameter characterizing the tail rigidity of
the lipids. The model is a lattice model which incorporates strain relaxation,
and considers the nucleation of pores at constant area, constant temperature,
and constant particle number. The particle number is conserved by allowing
multiple occupancy of the sites. An equilibrium ``phase diagram'' is
constructed as a function of temperature and strain with the total pore surface
and distribution as the order parameters. A first order rupture line is found
with increasing tension, and a continuous increase in proto-pore concentration
with rising temperature till instability. The model explains current results on
saturated and unsaturated PC lipid bilayers and thicker artificial bilayers
made of diblock copolymers. Pore size distributions are presented for various
values of area expansion and temperature, and the fractal dimension of the pore
edge is evaluated.Comment: 15 pages, 8 figure
Proteomic characterization of a lutein-hyperaccumulating Chlamydomonas reinhardtii mutant reveals photoprotection-related factors as targets for increasing cellular carotenoid content
Background
Microalgae are emerging hosts for the sustainable production of lutein, a high-value carotenoid; however, to be commercially competitive with existing systems, their capacity for lutein sequestration must be augmented. Previous attempts to boost microalgal lutein production have focussed on upregulating carotenoid biosynthetic enzymes, in part due to a lack of metabolic engineering targets for expanding lutein storage.
Results
Here, we isolated a lutein hyper-producing mutant of the model green microalga Chlamydomonas reinhardtii and characterized the metabolic mechanisms driving its enhanced lutein accumulation using label-free quantitative proteomics. Norflurazon- and high light-resistant C. reinhardtii mutants were screened to yield four mutant lines that produced significantly more lutein per cell compared to the CC-125 parental strain. Mutant 5 (Mut-5) exhibited a 5.4-fold increase in lutein content per cell, which to our knowledge is the highest fold increase of lutein in C. reinhardtii resulting from mutagenesis or metabolic engineering so far. Comparative proteomics of Mut-5 against its parental strain CC-125 revealed an increased abundance of light-harvesting complex-like proteins involved in photoprotection, among differences in pigment biosynthesis, central carbon metabolism, and translation. Further characterization of Mut-5 under varying light conditions revealed constitutive overexpression of the photoprotective proteins light-harvesting complex stress-related 1 (LHCSR1) and LHCSR3 and PSII subunit S regardless of light intensity, and increased accrual of total chlorophyll and carotenoids as light intensity increased. Although the photosynthetic efficiency of Mut-5 was comparatively lower than CC-125, the amplitude of non-photochemical quenching responses of Mut-5 was 4.5-fold higher than in CC-125 at low irradiance.
Conclusions
We used C. reinhardtii as a model green alga and identified light-harvesting complex-like proteins (among others) as potential metabolic engineering targets to enhance lutein accumulation in microalgae. These have the added value of imparting resistance to high light, although partially compromising photosynthetic efficiency. Further genetic characterization and engineering of Mut-5 could lead to the discovery of unknown players in photoprotective mechanisms and the development of a potent microalgal lutein production system
Diffuse inverse Compton and synchrotron emission from dark matter annihilations in galactic satellites
Annihilating dark matter particles produce roughly as much power in electrons
and positrons as in gamma ray photons. The charged particles lose essentially
all of their energy to inverse Compton and synchrotron processes in the
galactic environment. We discuss the diffuse signature of dark matter
annihilations in satellites of the Milky Way (which may be optically dark with
few or no stars), providing a tail of emission trailing the satellite in its
orbit. Inverse Compton processes provide X-rays and gamma rays, and synchrotron
emission at radio wavelengths might be seen. We discuss the possibility of
detecting these signals with current and future observations, in particular
EGRET and GLAST for the gamma rays.Comment: 13 pages, 5 figure
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