154 research outputs found
Steric Effects in Electrolytes: A Modified Poisson-Boltzmann Equation
The adsorption of large ions from solution to a charged surface is
investigated theoretically. A generalized Poisson--Boltzmann equation, which
takes into account the finite size of the ions is presented. We obtain
analytical expressions for the electrostatic potential and ion concentrations
at the surface, leading to a modified Grahame equation. At high surface charge
densities the ionic concentration saturates to its maximum value. Our results
are in agreement with recent experiments.Comment: 4 pages, 2 figure
Mean field and corrections for the Euclidean Minimum Matching problem
Consider the length of the minimum matching of N points in
d-dimensional Euclidean space. Using numerical simulations and the finite size
scaling law , we obtain
precise estimates of for . We then consider
the approximation where distance correlations are neglected. This model is
solvable and gives at an excellent ``random link'' approximation to
. Incorporation of three-link correlations further improves
the accuracy, leading to a relative error of 0.4% at d=2 and 3. Finally, the
large d behavior of this expansion in link correlations is discussed.Comment: source and one figure. Submitted to PR
Characterization of growth and metabolism of the haloalkaliphile Natronomonas pharaonis
Natronomonas pharaonis is an archaeon adapted to two extreme conditions: high salt concentration and alkaline pH. It has become one of the model organisms for the study of extremophilic life. Here, we present a genome-scale, manually curated metabolic reconstruction for the microorganism. The reconstruction itself represents a knowledge base of the haloalkaliphile's metabolism and, as such, would greatly assist further investigations on archaeal pathways. In addition, we experimentally determined several parameters relevant to growth, including a characterization of the biomass composition and a quantification of carbon and oxygen consumption. Using the metabolic reconstruction and the experimental data, we formulated a constraints-based model which we used to analyze the behavior of the archaeon when grown on a single carbon source. Results of the analysis include the finding that Natronomonas pharaonis, when grown aerobically on acetate, uses a carbon to oxygen consumption ratio that is theoretically near-optimal with respect to growth and energy production. This supports the hypothesis that, under simple conditions, the microorganism optimizes its metabolism with respect to the two objectives. We also found that the archaeon has a very low carbon efficiency of only about 35%. This inefficiency is probably due to a very low P/O ratio as well as to the other difficulties posed by its extreme environment
Systems analysis of bioenergetics and growth of the extreme halophile Halobacterium salinarum
Halobacterium salinarum is a bioenergetically flexible, halophilic microorganism that can generate energy by respiration, photosynthesis, and the fermentation of arginine. In a previous study, using a genome-scale metabolic model, we have shown that the archaeon unexpectedly degrades essential amino acids under aerobic conditions, a behavior that can lead to the termination of growth earlier than necessary. Here, we further integratively investigate energy generation, nutrient utilization, and biomass production using an extended methodology that accounts for dynamically changing transport patterns, including those that arise from interactions among the supplied metabolites. Moreover, we widen the scope of our analysis to include phototrophic conditions to explore the interplay between different bioenergetic modes. Surprisingly, we found that cells also degrade essential amino acids even during phototropy, when energy should already be abundant. We also found that under both conditions considerable amounts of nutrients that were taken up were neither incorporated into the biomass nor used as respiratory substrates, implying the considerable production and accumulation of several metabolites in the medium. Some of these are likely the products of forms of overflow metabolism. In addition, our results also show that arginine fermentation, contrary to what is typically assumed, occurs simultaneously with respiration and photosynthesis and can contribute energy in levels that are comparable to the primary bioenergetic modes, if not more. These findings portray a picture that the organism takes an approach toward growth that favors the here and now, even at the cost of longer-term concerns. We believe that the seemingly "greedy" behavior exhibited actually consists of adaptations by the organism to its natural environments, where nutrients are not only irregularly available but may altogether be absent for extended periods that may span several years. Such a setting probably predisposed the cells to grow as much as possible when the conditions become favorable
Self-Consistent Field study of Polyelectrolyte Brushes
We formulate a self-consistent field theory for polyelectrolyte brushes in
the presence of counterions. We numerically solve the self-consistent field
equations and study the monomer density profile, the distribution of
counterions, and the total charge distribution. We study the scaling relations
for the brush height and compare them to the prediction of other theories. We
find a weak dependence of the brush height on the grafting density.We fit the
counterion distribution outside the brush by the Gouy-Chapman solution for a
virtual charged wall. We calculate the amount of counterions outside the brush
and find that it saturates as the charge of the polyelectrolytes increases
Polyakov loop correlators from D0-brane interactions in bosonic string theory
In this paper we re-derive the effective Nambu-Goto theory result for the
Polyakov loop correlator, starting from the free bosonic string and using a
covariant quantization. The boundary conditions are those of an open string
attached to two D0-branes at spatial distance R, in a target space with compact
euclidean time. The one-loop free energy contains topologically distinct
sectors corresponding to multiple covers of the cylinder in target space
bordered by the Polyakov loops. The sector that winds once reproduces exactly
the Nambu-Goto partition function. In our approach, the world-sheet duality
between the open and closed channel is most evident and allows for an explicit
interpretation of the free energy in terms of tree level exchange of closed
strings between boundary states. Our treatment is fully consistent only in
d=26; extension to generic d may be justified for large R, and is supported by
Montecarlo data. At shorter scales, consistency and Montecarlo data seem to
suggest the necessity of taking into account the Liouville mode of Polyakov's
formulation.Comment: 17 pages, 4 figures, minor corrections, a few references added,
version accepted for publication in JHE
Flux-Tube Ring and Glueball Properties in the Dual Ginzburg-Landau Theory
An intuitive approach to the glueball using the flux-tube ring solution in
the dual Ginzburg-Landau theory is presented. The description of the flux-tube
ring as the relativistic closed string with the effective string tension
enables us to write the hamiltonian of the flux-tube ring using the Nambu-Goto
action. Analyzing the Schr\"odinger equation, we discuss the mass spectrum and
the wave function of the glueball. The lowest glueball state is found to have
the mass and the size .Comment: 24 pages, 6 figures, revte
The interaction between the proliferating macroalga Asparagopsis taxiformis and the coral Astroides calycularis induces changes in microbiome and metabolomic fingerprints
Mediterranean Sea ecosystems are considered as hotspots of biological introductions, exposed to possible negative effects of non-indigenous species. In such temperate marine ecosystems, macroalgae may be dominant, with a great percentage of their diversity represented by introduced species. Their interaction with temperate indigenous benthic organisms have been poorly investigated. To provide new insights, we performed an experimental study on the interaction between the introduced proliferative red alga Asparagopsis taxiformis and the indigenous Mediterranean coral Astroides calycularis. The biological response measurements included meta-barcoding of the associated microbial communities and metabolomic fingerprinting of both species. Significant changes were detected among both associated microbial communities, the interspecific differences decreasing with stronger host interaction. No short term effects of the macroalga on the coral health, neither on its polyp activity or its metabolism, were detected. In contrast, the contact interaction with the coral induced a change in the macroalgal metabolomic fingerprint with a significant increase of its bioactivity against the marine bacteria Aliivibrio fischeri. This induction was related to the expression of bioactive metabolites located on the macroalgal surface, a phenomenon which might represent an immediate defensive response of the macroalga or an allelopathic offense against coral.ERA-NET Biome project "SEAPROLIF"; CNRS; Provence Alpes Cote d'Azur Region; TOTAL Fundation; Fundacao para a Ciencia e a Tecnologia (FCT) [Netbiome/0002/2011]; FCT fellowships [SFRH/BPD/63703/2009, SFRH/BPD/107878/2015]info:eu-repo/semantics/publishedVersio
C1-Ten Is a Protein Tyrosine Phosphatase of Insulin Receptor Substrate 1 (IRS-1), Regulating IRS-1 Stability and Muscle Atrophy
Muscle atrophy occurs under various catabolic conditions, including insulin deficiency, insulin resistance, or increased levels of glucocorticoids. This results from reduced levels of insulin receptor substrate 1 (IRS-1), leading to decreased phosphatidylinositol 3-kinase activity and thereby activation of FoxO transcription factors. However, the precise mechanism of reduced IRS-1 under a catabolic condition is unknown. Here, we report that C1-Ten is a novel protein tyrosine phosphatase (PTPase) of IRS-1 that acts as a mediator to reduce IRS-1 under a catabolic condition, resulting in muscle atrophy. C1-Ten preferentially dephosphorylated Y612 of IRS-1, which accelerated IRS-1 degradation. These findings suggest a novel type of IRS-1 degradation mechanism which is dependent on C1-Ten and extends our understanding of the molecular mechanism of muscle atrophy under catabolic conditions. C1-Ten expression is increased by catabolic glucocorticoid and decreased by anabolic insulin. Reflecting these hormonal regulations, the muscle C1-Ten is upregulated in atrophy but downregulated in hypertrophy. This reveals a previously unidentified role of C1-Ten as a relevant PTPase contributing to skeletal muscle atrophy.open2
- …