15 research outputs found
Correlation between flexibility of chain-like polyelectrolyte and thermodynamic properties of its solution
Structural and thermodynamic properties of the model solution containing
charged oligomers and the equivalent number of counterions were studied by
means of the canonical Monte Carlo simulation technique. The oligomers are
represented as (flexible) freely jointed chains or as a linear (rigid) array of
charged hard spheres. In accordance with the primitive model of electrolyte
solutions, the counterions are modeled as charged hard spheres and the solvent
as dielectric continuum. Significant differences in the pair distribution
functions, obtained for the rigid (rod-like) and flexible model are found but
the differences in thermodynamic properties, such as, enthalpy of dilution and
excess chemical potential, are less significant. The results are discussed in
light of the experimental data an aqueous polyelectrolyte solutions. The
simulations suggest that deviations from the fully extended (rod-like)
conformation yield slightly stronger binding of counterions. On the other hand,
the flexibility of polyions, even when coupled with the ion-size effects,
cannot be blamed for qualitative differences between the theoretical results
and experimental data for enthalpy of dilution.Comment: 14 pages, 10 figure
Influence of solvent granularity on the effective interaction between charged colloidal suspensions
We study the effect of solvent granularity on the effective force between two
charged colloidal particles by computer simulations of the primitive model of
strongly asymmetric electrolytes with an explicitly added hard sphere solvent.
Apart from molecular oscillating forces for nearly touching colloids which
arise from solvent and counterion layering, the counterions are attracted
towards the colloidal surfaces by solvent depletion providing a simple
statistical description of hydration. This, in turn, has an important influence
on the effective forces for larger distances which are considerably reduced as
compared to the prediction based on the primitive model. When these forces are
repulsive, the long-distance behaviour can be described by an effective Yukawa
pair potential with a solvent-renormalized charge. As a function of colloidal
volume fraction and added salt concentration, this solvent-renormalized charge
behaves qualitatively similar to that obtained via the Poisson-Boltzmann cell
model but there are quantitative differences. For divalent counterions and
nano-sized colloids, on the other hand, the hydration may lead to overscreened
colloids with mutual attraction while the primitive model yields repulsive
forces. All these new effects can be accounted for through a solvent-averaged
primitive model (SPM) which is obtained from the full model by integrating out
the solvent degrees of freedom. The SPM was used to access larger colloidal
particles without simulating the solvent explicitly.Comment: 14 pages, 16 craphic
White Paper and Roadmap for Quantum Gravity Phenomenology in the Multi-Messenger Era
The unification of quantum mechanics and general relativity has long been
elusive. Only recently have empirical predictions of various possible theories
of quantum gravity been put to test. The dawn of multi-messenger high-energy
astrophysics has been tremendously beneficial, as it allows us to study
particles with much higher energies and travelling much longer distances than
possible in terrestrial experiments, but more progress is needed on several
fronts.
A thorough appraisal of current strategies and experimental frameworks,
regarding quantum gravity phenomenology, is provided here. Our aim is twofold:
a description of tentative multimessenger explorations, plus a focus on future
detection experiments.
As the outlook of the network of researchers that formed through the COST
Action CA18108 "Quantum gravity phenomenology in the multi-messenger approach
(QG-MM)", in this work we give an overview of the desiderata that future
theoretical frameworks, observational facilities, and data-sharing policies
should satisfy in order to advance the cause of quantum gravity phenomenology.Comment: Submitted to CQG for the Focus Issue on "Quantum Gravity
Phenomenology in the Multi-Messenger Era: Challenges and Perspectives".
Please contact us to express interesst of endorsement of this white pape
Attraction between like-charged surfaces induced byorientational ordering of divalent rigid rod-likecounterions: theory and simulations
Attraction between like-charged surfaces induced by orientational ordering of divalent rigid
rod-like counterions: theory and simulations
Computer simulation of molecular exchange in colloidal systems
In this paper, we introduce two computer simulation models to study molecular exchange between aggregates in a colloidal dispersion. The Brownian motion of the colloidal aggregates is simulated as a random walk with a Gaussian distributed step length. In model I, the exchanging molecules are simulated as discrete particles with the exchange process characterized by desorption, molecular diffusion, and adsorption. A molecule desorbed from an aggregate is registered in the simulation and allowed to undergo individual Brownian motion until it adsorbs onto another colloidal aggregate or returns to the same aggregate from which it originated. In this detailed simulation, random size fluctuations are obtained in addition to a net variation in a relaxing, nonequilibrium size distribution. For many processes, net variations are very slow compared to the random fluctuations, making this detailed method very time consuming for studying a relaxing size distribution. For this reason, we also consider, in model II, a more approximate method where only the net flow of molecules between aggregates is considered. Here, the flow of molecules is for each time step calculated assuming steady state conditions and pair wise additivity. The flow between an isolated pair of aggregates can be solved exactly. Although the pair flow is a good approximation at short separations, it becomes significantly reduced at larger separations because of the presence of other aggregates. This screening of the flow at larger separations is accounted for by introducing an exponential damping function. With these models, we have simulated the solubilization of larger oil drops by smaller micelles which has previously been experimentally studied in a nonionic surfactant-water-oil system. Besides comparing with experiments, the simulations provides a test of a previous mean-field cell model analysis of the solubilization process
Bridging like-charged macroions through longdivalent rod-like ions
Bridging like-charged macroions through longdivalent rod-like ion
Influence of added salt on the surface induced ordering of nanoparticles with discretely distributed charges
The formation of an electric double layer composed of spherical nanoparticles is analyzed by means of a generalized Poisson-Boltzmann model and Monte Carlo simulations. We study a solution of symmetric and asymmetric mixtures of spherical particles that reside between two planar like-charged surfaces. Each spherical particle carries two elementary charges that are attached at its poles. The electrolyte solution also contains monovalent point-like salt ions. Our theoretical model properly accounts for intra-particle correlations - that is correlations between the spatially separated charges belonging to a single multivalent spherical particle. Correlations between different spherical particles are neglected. It is shown that added salt decreases the number density close to the charged surface and influences the orientation of spherical particles. Increasing salt concentration decreases the order parameter of the spherical particles. Generalized Poisson-Boltzmann results, obtained by solving an integral differential equation, and predictions from Monte Carlo (MC) simulations are in excellent agreement
High spatial heterogeneity of water stress levels in Refošk grapevines cultivated in Classical Karst
Grapevines are being challenged by climate changes, forcing winemakers to implement irrigation systems to cope with excessive water stress. Previous studies focused on a small set of international varieties, and only few data are available for terroirs hosting cultivars with possibly different responses to drought stress. In this light, we monitored grapevine water status and grape's physical and chemical composition, as well as concentration and structural characteristics of grape extractable polyphenols, in ten different Refošk vineyards located in the Classical Karst terroir during 2018 and 2019. Grapevines did not suffer severe stress during the two years, but their response to water shortage periods was highly heterogeneous, as pre-dawn (Ψpd) and minimum (Ψmin) leaf water potential significantly differed between vineyards, especially during the drier part of the season. Moreover, the timing of maximum water stress differed in the two years, as in 2019 longer water shortage periods and higher temperature occurred at flowering stage and before veraison, while in 2018 they were higher after veraison. These differences influenced berry's quality, as titratable and malic acid concentration in juice, as well as total anthocyanin, total polyphenols and higher high molecular weight proanthocyanidins (HMWP) concentration in skins, were higher in 2019 than in 2018. Regarding seed proanthocyanidins, HMWP concentration, mean degree of polymerisation (mDP) and percentage of galloylation (G) in seeds were higher in 2018 than in 2019. The differences in water status measured in spatially close-related vineyards strongly support the importance of monitoring grapevines’ water status dynamics to design adequate and effective water management activities rather than relying on climate data solely. Moreover, the timing of water shortage periods also played a role in determining Refošk grape quality. Our analyses showed that the higher (but still moderate, with Ψpd and Ψmin mean values around −0.50 and −1.25 MPa, respectively) water stress between veraison and harvest occurred in 2018 might reduce Refošk grape acidity and increase concentration, polymerisation and galloylation of seed extractable proanthocyanidins