377 research outputs found
Assessment of microbial plankton diversity as an ecological indicator in the NW Mediterranean coast
High-throughput sequencing of microbial assemblages has been proposed as an alternative methodology to the traditional ones used in marine monitoring and environmental assessment. Here, we evaluated pico- and nanoplankton diversity as ecological indicators in NW Mediterranean coastal waters by comparing their diversity in samples subjected to varying degrees of continental pressures. Using metabarcoding of the 16S and 18S rRNA genes, we explored whether alphadiversity indices, abundance of Operational Taxonomic Units and taxonomic groups (and their ratios) provide information on the ecological quality of coastal waters. Our results revealed that only eukaryotic diversity metrics and a limited number of prokaryotic and eukaryotic taxa displayed potential in assessing continental influences in our surveyed area, resulting thus in a restrained potential of microbial plankton diversity as an ecological indicator. Therefore, incorporating microbial plankton diversity in environmental assessment could not always result in a significant improvement of current marine monitoring strategies.Preprint2,35
Criticality in confined ionic fluids
A theory of a confined two dimensional electrolyte is presented. The positive
and negative ions, interacting by a potential, are constrained to move on
an interface separating two solvents with dielectric constants and
. It is shown that the Debye-H\"uckel type of theory predicts that
the this 2d Coulomb fluid should undergo a phase separation into a coexisting
liquid (high density) and gas (low density) phases. We argue, however, that the
formation of polymer-like chains of alternating positive and negative ions can
prevent this phase transition from taking place.Comment: RevTex, no figures, in press Phys. Rev.
Clustering transitions in vibro-fluidized magnetized granular materials
We study the effects of long range interactions on the phases observed in
cohesive granular materials. At high vibration amplitudes, a gas of magnetized
particles is observed with velocity distributions similar to non-magnetized
particles. Below a transition temperature compact clusters are observed to form
and coexist with single particles. The cluster growth rate is consistent with a
classical nucleation process. However, the temperature of the particles in the
clusters is significantly lower than the surrounding gas, indicating a
breakdown of equipartition. If the system is quenched to low temperatures, a
meta-stable network of connected chains self-assemble due to the anisotropic
nature of magnetic interactions between particles.Comment: 4 pages, 5 figure
Thermodynamics of Electrolytes on Anisotropic Lattices
The phase behavior of ionic fluids on simple cubic and tetragonal
(anisotropic) lattices has been studied by grand canonical Monte Carlo
simulations. Systems with both the true lattice Coulombic potential and
continuous-space electrostatic interactions have been investigated. At
all degrees of anisotropy, only coexistence between a disordered low-density
phase and an ordered high-density phase with the structure similar to ionic
crystal was found, in contrast to recent theoretical predictions. Tricritical
parameters were determined to be monotonously increasing functions of
anisotropy parameters which is consistent with theoretical calculations based
on the Debye-H\"uckel approach. At large anisotropies a two-dimensional-like
behavior is observed, from which we estimated the dimensionless tricritical
temperature and density for the two-dimensional square lattice electrolyte to
be and .Comment: submitted to PR
The thermoacidophilic methanotroph Methylacidiphilum fumariolicum SolV oxidizes subatmospheric H<sub>2</sub> with a high-affinity, membrane-associated [NiFe] hydrogenase
The trace amounts (0.53 ppmv) of atmospheric hydrogen gas (H2) can be utilized by microorganisms to persist during dormancy. This process is catalyzed by certain Actinobacteria, Acidobacteria, and Chloroflexi, and is estimated to convert 75 × 1012 g H2 annually, which is half of the total atmospheric H2. This rapid atmospheric H2 turnover is hypothesized to be catalyzed by high-affinity [NiFe] hydrogenases. However, apparent high-affinity H2 oxidation has only been shown in whole cells, rather than for the purified enzyme. Here, we show that the membrane-associated hydrogenase from the thermoacidophilic methanotroph Methylacidiphilum fumariolicum SolV possesses a high apparent affinity (Km(app) = 140 nM) for H2 and that methanotrophs can oxidize subatmospheric H2. Our findings add to the evidence that the group 1h [NiFe] hydrogenase is accountable for atmospheric H2 oxidation and that it therefore could be a strong controlling factor in the global H2 cycle. We show that the isolated enzyme possesses a lower affinity (Km = 300 nM) for H2 than the membrane-associated enzyme. Hence, the membrane association seems essential for a high affinity for H2. The enzyme is extremely thermostable and remains folded up to 95 °C. Strain SolV is the only known organism in which the group 1h [NiFe] hydrogenase is responsible for rapid growth on H2 as sole energy source as well as oxidation of subatmospheric H2. The ability to conserve energy from H2 could increase fitness of verrucomicrobial methanotrophs in geothermal ecosystems with varying CH4 fluxes. We propose that H2 oxidation can enhance growth of methanotrophs in aerated methane-driven ecosystems. Group 1h [NiFe] hydrogenases could therefore contribute to mitigation of global warming, since CH4 is an important and extremely potent greenhouse gas.</p
A molecular dynamics study on the equilibrium magnetization properties and structure of ferrofluids
We investigate in detail the initial susceptibility, magnetization curves,
and microstructure of ferrofluids in various concentration and particle dipole
moment ranges by means of molecular dynamics simulations. We use the Ewald
summation for the long-range dipolar interactions, take explicitly into account
the translational and rotational degrees of freedom, coupled to a Langevin
thermostat. When the dipolar interaction energy is comparable with the thermal
energy, the simulation results on the magnetization properties agree with the
theoretical predictions very well. For stronger dipolar couplings, however, we
find systematic deviations from the theoretical curves. We analyze in detail
the observed microstructure of the fluids under different conditions. The
formation of clusters is found to enhance the magnetization at weak fields and
thus leads to a larger initial susceptibility. The influence of the particle
aggregation is isolated by studying ferro-solids, which consist of magnetic
dipoles frozen in at random locations but which are free to rotate. Due to the
artificial suppression of clusters in ferro-solids the observed susceptibility
is considerably lowered when compared to ferrofluids.Comment: 33 pages including 12 figures, requires RevTex
Microbial Transformations of Nitrogen, Sulfur, and Iron Dictate Vegetation Composition in Wetlands: A Review
The majority of studies on rhizospheric interactions focus on pathogens, mycorrhizal symbiosis, or carbon transformations. Although the biogeochemical transformations of N, S, and Fe have profound effects on vegetation, these effects have received far less attention. This review, meant for microbiologists, biogeochemists, and plant scientists includes a call for interdisciplinary research by providing a number of challenging topics for future ecosystem research. Firstly, all three elements are plant nutrients, and microbial activity significantly changes their availability. Secondly, microbial oxidation with oxygen supplied by radial oxygen loss from roots in wetlands causes acidification, while reduction using alternative electron acceptors leads to generation of alkalinity, affecting pH in the rhizosphere, and hence plant composition. Thirdly, reduced species of all three elements may become phytotoxic. In addition, Fe cycling is tightly linked to that of S and P. As water level fluctuations are very common in wetlands, rapid changes in the availability of oxygen and alternative terminal electron acceptors will result in strong changes in the prevalent microbial redox reactions, with significant effects on plant growth. Depending on geological and hydrological settings, these interacting microbial transformations change the conditions and resource availability for plants, which are both strong drivers of vegetation development and composition by changing relative competitive strengths. Conversely, microbial composition is strongly driven by vegetation composition. Therefore, the combination of microbiological and plant ecological knowledge is essential to understand the biogeochemical and biological key factors driving heterogeneity and total (i.e., microorganisms and vegetation) community composition at different spatial and temporal scales
Microfluidic analysis techniques for safety assessment of pharmaceutical nano- and microsystems
This chapter reviews the evolution of microfabrication methods and materials, applicable to manufacturing of micro total analysis systems (or lab‐on‐a‐chip), from a general perspective. It discusses the possibilities and limitations associated with microfluidic cell culturing, or so called organ‐on‐a‐chip technology, together with selected examples of their exploitation to characterization of pharmaceutical nano‐ and microsystems. Materials selection plays a pivotal role in terms of ensuring the cell adhesion and viability as well as defining the prevailing culture conditions inside the microfluidic channels. The chapter focuses on the hepatic safety assessment of nanoparticles and gives an overview of the development of microfluidic immobilized enzyme reactors that could facilitate examination of the hepatic effects of nanomedicines under physiologically relevant conditions. It also provides an overview of the future prospects regarding system‐level integration possibilities facilitated by microfabrication of miniaturized separation and sample preparation systems as integral parts of microfluidic in vitro models.Non peer reviewe
Scaling and universality in the phase diagram of the 2D Blume-Capel model
We review the pertinent features of the phase diagram of the zero-field
Blume-Capel model, focusing on the aspects of transition order, finite-size
scaling and universality. In particular, we employ a range of Monte Carlo
simulation methods to study the 2D spin-1 Blume-Capel model on the square
lattice to investigate the behavior in the vicinity of the first-order and
second-order regimes of the ferromagnet-paramagnet phase boundary,
respectively. To achieve high-precision results, we utilize a combination of
(i) a parallel version of the multicanonical algorithm and (ii) a hybrid
updating scheme combining Metropolis and generalized Wolff cluster moves. These
techniques are combined to study for the first time the correlation length of
the model, using its scaling in the regime of second-order transitions to
illustrate universality through the observed identity of the limiting value of
with the exactly known result for the Ising universality class.Comment: 16 pages, 7 figures, 1 table, submitted to Eur. Phys. J. Special
Topic
A Meta-analysis of Multiple Myeloma Risk Regions in African and European Ancestry Populations Identifies Putatively Functional Loci
Genome-wide association studies (GWAS) in European populations have identified genetic risk variants associated with multiple myeloma (MM)
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