Fraction Of Charge Research Articles

Simultaneous uptake of NOM and Microcystin-LR by anion exchange resins: Effect of inorganic ions and resin regeneration

This study investigated the efficiency of a strongly basic macroporous anion exchange resin for the co-removal of Microcystin-LR (MCLR) and natural organic matter (NOM) in waters affected by toxic algal blooms. Environmental factors influencing the uptake behavior included MCLR and resin concentrations, NOM and anionic species, specifically nitrate, sulphate and bicarbonate. A860 resin exhibited an excellent adsorption capacity of 3800 μg/g; more than 60% of the MCLR removal was achieved within 10 min with a resin dosage of 200 mg/L (∼1 mL/L). Further, kinetic studies revealed that the overall removal of MCLR is influenced by both external diffusion and intra-particle diffusion. Increasing NOM concentration resulted in a significant reduction of MCLR uptake, especially at lower resin dosages, where a competitive uptake between the charged NOM fractions and MCLR was observed due to limited active sites. In addition, MCLR uptake was significantly reduced in the presence of sulphate and nitrate in the water matrix. Moreover, performance of the resin proved to be stable from one regeneration cycle to another. Approximately 80% of MCLR and 50% of dissolved organic carbon (DOC) were recovered in the regenerated brine. Evidences of resin saturation and site reduction were also observed after 2000 bed volumes (BV) of operation. For all the investigated water matrices, a resin dosage of 1000 mg/L (∼4.5 mL/L) was sufficient to lower MCLR concentration from 100 μg/L to below the World Health Organization guideline of 1 μg/L, while simultaneously providing more than 80% NOM removal.

Compressed H3S: inter-sublattice Coulomb coupling in a high-TC superconductor

Upon thermal annealing at or above room temperature (RT) and at high hydrostatic pressure P ~ 155 GPa, sulfur trihydride H3S exhibits a measured maximum superconducting transition temperature TC ~ 200 K. Various theoretical frameworks incorporating strong electron–phonon coupling and Coulomb repulsion have reproduced this record-level TC. Of particular relevance is that experimentally observed H–D isotopic correlations among TC, P, and annealed order indicate an H–D isotope effect exponent α limited to values ⩽ 0.183, leaving open for consideration unconventional high-TC superconductivity with electronic-based enhancements. The work presented herein examines Coulombic pairing arising from interactions between neighboring S and H species on separate interlaced sublattices constituting H3S in the Imm structure. The optimal value of the transition temperature is calculated from TC0 = Λe2/ζ, with Λ = 0.007465 Å, inter-sublattice S–H separation spacing ζ = a0/, interaction charge linear spacing = a0 (3/σ)1/2, average participating charge fraction σ = 3.43 ± 0.10 estimated from calculated H-projected electron states, and lattice parameter a0 = 3.0823 Å at P = 155 GPa. The resulting value of TC0 = 198.5 ± 3.0 K is in excellent agreement with transition temperatures determined from resistivity (196–200 K onsets, 190–197 K midpoints), susceptibility (200 K onset), and critical magnetic fields (203.5 K by extrapolation). Analysis of mid-infrared reflectivity data confirms the expected correlation between boson energy and ζ−1. Suppression of TC below TC0, correlating with increasing residual resistance for < RT annealing, is treated in terms of scattering-induced pair breaking. Correspondences between H3S and layered high-TC superconductor structures are also discussed, and a model considering Compton scattering of virtual photons of energies ⩽ e2/ζ by inter-sublattice electrons is introduced, illustrating that Λ ∝ ƛC, where ƛC is the reduced electron Compton wavelength.

Experimental investigation of an ejector-enhanced auto-cascade refrigeration system

This study presents the experimental investigation of an ejector-enhanced auto-cascade refrigeration cycle (EARC) with zeotropic refrigerant R134a/R23. Performance comparisons among the EARC and two conventional cycles were conducted at selected operating conditions. The effects of ambient temperature, charged mass fraction ratio of the mixture, throttle valve opening, and heat load on the performance characteristics of the EARC were investigated. The results indicated that the EARC had more advantages in terms of lower refrigeration temperature and higher energy utilization efficiency over the conventional cycles, and the coefficient of performance (COP) and exergy efficiency improvements of the EARC reached up to 9.6% and 25.1%, respectively. The throttle valve opening was optimal with respect to the maximum system exergy efficiency determination. The refrigerant R134a/R23 with the optimal mass fraction ratio of 0.70/0.30 was proposed.

Charge and hydrophobicity of casein peptides influence transepithelial transport and bioavailability

Antioxidant casein peptides were separated by SP-Sephadex C-25 and C 18 columns. The transepithelial transport and bioavailability including the transport ratio and the remaining ratios of antioxidant activity (RRAA) of these peptide absorbates, were then investigated using a Caco-2 cell monolayer. The results indicate that both the negatively charged peptide fractions (CF1, CF2 and CF3) and the more hydrophilic fraction (HF1) were mainly transported via PepT1 and paracellular routes. The positively charged fractions (CF4 and CF5) and hydrophobic fractions (HF2, HF3 and HF4) were transported via PepT1 and transcytosis. The strongly negatively charged and more hydrophobic fractions showed a higher transport ratio, which ranged from 9.5 to 12.5%; however, the transport ratio of positively charged and hydrophilic fractions ranged from 4.0 to 8.5%. The positively charged and hydrophilic fractions showed a higher RRAA.

Multiple periodicity in a nanoparticle-based single-electron transistor

A single-electron transistor is a nano-device with large potential for low-power applications that can be used as logic elements in integrated circuits. In this device, the conductance oscillates with a well-defined period due to the Coulomb blockade effect. By using a unique technique, we explore single-electron transistors based on a single metallic nanoparticle with tunable coupling to electric leads. We demonstrate a unique regime in which the transistor is characterized by multi-periodic oscillations of the conductance with gate voltage where the additional periods are harmonics of the basic periodicity of the Coulomb blockade and their relative strength can be controllably tuned. These harmonics correspond to a charge change on the dot by a fraction of the electron charge. The presence of multiple harmonics makes these transistors potential elements in future miniaturization of nano-sized circuit elements.

Measurement of the charging state of 4–70 nm aerosols

The charging state of aerosols in an 8m3 reaction chamber was measured using an electrostatic classifier with a condensation particle counter at different levels of ionization in the chamber. By replacing the Kr-85 neutralizer in the classifier with a radioactively neutral dummy we were able to measure only the aerosols that were charged inside our reaction chamber. These measurements were then compared with measurements using the neutralizer to get the charging state of the aerosols, which refers to the charged fraction of the aerosols compared to an equilibrium charge distribution. Charging states were measured for both positively and negatively charged aerosols while the ionization in the chamber was varied using external gamma sources. We find that the negatively charged aerosols were overcharged (relative to the equilibrium) by up to about a factor of 10 below 10nm and at 16±2% from 10 to 70nm. At higher levels of radiation on the chamber the smaller aerosols were less overcharged while the large aerosols were more overcharged (23±2%). For the positively charged aerosols only the smallest aerosols were overcharged while those over 10nm were undercharged (relative to the equilibrium) by 21±3%. Increasing the radiation on the chamber increased the undercharge above 10nm to 25±2% while the overcharge below 10nm disappeared. The split between positive and negative charges above 10nm can be explained by differences in mobility of small negative and positive ions. The overcharge below 10nm can be explained by ions participating in the formation of aerosols of both signs, while the reduction in this overcharge at higher levels of ionization may be explained by faster recombination.

Cylindrical freak waves in a non-Maxwellian dusty bulk-sheath plasma: An approximate solution for the cylindrical nonlinear Schrödinger equation

The properties of cylindrical dust ion-acoustic freak waves (FWs) are investigated in an unmagnetized collisionless dusty plasma in the presence of the sheath bulk model, which contain stationary negatively charged dust grains, nonthermal electrons, and inertial warm ions. For this purpose, the reductive perturbation method is used to reduce the fluid equations to a cylindrical Gardner/extended Korteweg–de Vries (CEKdV) equation. After that a cylindrical nonlinear Schrödinger equation (CNLSE) is obtained from the cylindrical EKdV using the derivative expansion method. The variation of the structural properties of the planar (one-dimensional) FWs with relevant plasma parameters is examined, in particular focusing on the temperature ratio of the ions-to-electrons, the fraction of negative charge residing on the dust and the nonthermal parameter. Moreover, the nonlinear dynamic of the sheath is obtain which may explain the solution of the exact analytical freak wave of the CNLSE using a suitable transformation.

Do fractionally incremented nuclear charges improve time-dependent density functional theory excitation energies as reliably as fractional orbital populations?

Gaiduk et al. (Phys Rev Lett 108:253005, 2012) showed that one can improve local, semilocal, and hybrid approximations to the Kohn–Sham effective potentials of atoms and molecules by removing a system-independent fraction of electron charge from the highest occupied molecular orbital (HOMO); if the corrected Kohn–Sham potential is used for adiabatic linear-response time-dependent density functional theory (TDDFT) calculations, accurate Rydberg excitation energies are obtained. One may ask whether the same effect could also be achieved by fractionally increasing the positive charges of the nuclei. We investigate this question and find that a small increase in nuclear charges can indeed substantially reduce errors in TDDFT Rydberg excitation energies. However, the optimal magnitude of the charge increase is system-dependent. In addition, the procedure is ambiguous for molecules, where one has to decide how to distribute the additional charge among individual nuclei. These two drawbacks of the fractional nuclear charge method make it disadvantageous compared to the HOMO depopulation technique.

Scaling Theory of Polyelectrolyte Nanogels* *Supported by China Earthquake Administration under Grant No. 20150112 and National Natural Science Foundation of China under Grant No. 21504014

The present paper develops the scaling theory of polyelectrolyte nanogels in dilute and semidilute solutions. The dependencies of the nanogel dimension on branching topology, charge fraction, subchain length, segment number, solution concentration are obtained. For a single polyelectrolyte nanogel in salt free solution, the nanogel may be swelled by the Coulombic repulsion (the so-called polyelectrolyte regime) or the osmotic counterion pressure (the so-called osmotic regime). Characteristics and boundaries between different regimes of a single polyelectrolyte nanogel are summarized. In dilute solution, the nanogels in polyelectrolyte regime will distribute orderly with the increase of concentration. While the nanogels in osmotic regime will always distribute randomly. Different concentration dependencies of the size of a nanogel in polyelectrolyte regime and in osmotic regime are also explored.

Structure and reentrant percolation in an inverse patchy colloidal system.

Two-dimensional systems of inverse patchy colloids modeled as disks with a central charge and having their surface decorated with oppositely pointlike charged patches are investigated using molecular dynamics simulations. The self-assembly of the patchy colloids leads to diverse ground state configurations ranging from crystalline arrangements of monomers to linear clusters, ramified linear clusters and to percolated configurations. Two structural phase diagrams are constructed: (1) as a function of the net charge and area fraction, and (2) as a function of the net charge and the range of the pair interaction potential. An interesting reentrant percolation transition is obtained as a function of the net charge of the colloids. We identify distinct mechanisms that lead to the percolation transition.

The Vibronic Theory of Size Effects in CO Oxidation by Gold Nanocatalysts

A theoretical model, based on the vibronic theory of catalysis, has been developed for the CO oxidation reaction catalyzed by gold nanoparticles. The charge fraction transferred between the catalyst and the adsorbed CO molecule depends upon the relative positions of the size-dependent Fermi level of the cluster and the energy levels of the molecular orbitals of CO adsorbed onto the cluster. The charge transferred from the nanocluster to the adsorbed CO molecule increases the absolute values of forces deforming the molecule chemical bond and force constants defining the curvature of potential for nuclear oscillation leading to the decrease in activation energy for CO oxidation. The application of vibronic and jellium theories to CO oxidation provides an explanation of the observed cluster size effects. The relative locations of electronic energy levels of a gold cluster and a CO molecule before and after the adsorption onto the cluster surface

Statistical–mechanical theory of self-diffusion in dilute suspensions of macroions

Self-diffusion in dilute suspensions of macroions is studied theoretically based on the nonlinear non-Markov Langevin equations for macroions recently derived by one of the present authors (M.T.). Not only the short-time self-diffusion coefficient of macroion but also its long-time self-diffusion coefficient are then found analytically as a function of charge and volume fraction. The theoretical results, including a crossover map in charge–volume fraction plane, are then tested by the Brownian-dynamics simulations on macroions and small ions. Thus, they are shown to agree with the simulation results well within error.

Determination of tRNA aminoacylation levels by high-throughput sequencing.

Transfer RNA (tRNA) decodes mRNA codons when aminoacylated (charged) with an amino acid at its 3′ end. Charged tRNAs turn over rapidly in cells, and variations in charged tRNA fractions are known to be a useful parameter in cellular responses to stress. tRNA charging fractions can be measured for individual tRNA species using acid denaturing gels, or comparatively at the genome level using microarrays. These hybridization-based approaches cannot be used for high resolution analysis of mammalian tRNAs due to their large sequence diversity. Here we develop a high-throughput sequencing method that enables accurate determination of charged tRNA fractions at single-base resolution (Charged DM-tRNA-seq). Our method takes advantage of the recently developed DM-tRNA-seq method, but includes additional chemical steps that specifically remove the 3′A residue in uncharged tRNA. Charging fraction is obtained by counting the fraction of A-ending reads versus A+C-ending reads for each tRNA species in the same sequencing reaction. In HEK293T cells, most cytosolic tRNAs are charged at >80% levels, whereas tRNASer and tRNAThr are charged at lower levels. These low charging levels were validated using acid denaturing gels. Our method should be widely applicable for investigations of tRNA charging as a parameter in biological regulation.

Mobility and Bipolar Diffusion Charging Characteristics of Crumpled Reduced Graphene Oxide Nanoparticles Synthesized in a Furnace Aerosol Reactor

Crumpled graphene oxide (CGO) nanoparticles were synthesized by atomizing a solution of graphene oxide sheets (GO) into a furnace aerosol reactor, in which GO was thermally reduced. By using a differential mobility analyzer (DMA), CGO nanoparticles of uniform mobility sizes were classified and collected. The morphology and sizes of these CGO nanoparticles were characterized by transmission electron microscope. The projected area equivalent size of CGO calculated from TEM images (offline measurements) was correlated to the electrical mobility size of CGO measured by a scanned mobility particle sizer system, which consisted of a DMA and a condensation particle counter (online measurements), and a reasonable match between the two sizes was observed. Further, the bipolar diffusion charging characteristics of CGO synthesized at different temperatures were studied with a tandem differential mobility analyzer system, from which the charge fractions of CGO were determined. The synthesis temperature affected the charge fractions of CGO with the same electrical mobility size, which was attributed to the different conductivities of CGO thermally reduced at different temperatures. CGO nanoparticles synthesized at 400 °C had the highest conductivity and the largest fraction of charged particles.

Factors responsible for the aggregation behavior of hydrophobic polyelectrolyte PEA in aqueous solution studied by molecular dynamics simulations

Self-association (i.e. interchain aggregation) behavior of atactic poly(ethacrylic acid) PEA in dilute aqueous solution as function of degree-of-neutralization by Na+ counter-ions (i.e. charge fraction f) was investigated by molecular dynamics simulations. Aggregation is found to occur in the range 0≤f≤0.7 in agreement with experimental results compared at specified polymer concentration Cp=0.36mol/l in dilute solution. The macromolecular solution was characterized and analysed for radius-of-gyration, torsion angle distribution, inter and intra-molecular hydrogen bonds, radial distribution functions of intermolecular and inter-atomic pairs, inter-chain contacts and solvation enthalpy. The PEA chains form aggregate through attractive inter-chain interaction via hydrogen bonding, in the range f<0.7, in agreement with experimental observation. The numbers of inter-chain contacts decreases with f. A critical structural transition occurs at f=0.7, observed via simulations for the first time, in Rg as well as inter-chain H-bonds. The inter-chain distance increases with f due to repulsive interactions between COO− groups on the chains. PEA-PEA electrostatic interactions dominant solvation enthalpy. The PEA solvation enthalpy becomes increasingly favorable with increase in f. The transition enthalpy change, in going from uncharged (acid) state to fully charged state (f=1) is unfavorable towards aggregate formation.

Coulomb fission in multiply charged molecular clusters: Experiment and theory.

A series of three multiply charged molecular clusters, (C6H6)nz+ (benzene), (CH3CN)nz+ (acetonitrile), and (C4H8O)nz+ (tetrahydrofuran), where the charge z is either 3 or 4, have been studied for the purpose of identifying the patterns of behaviour close to the charge instability limit. Experiments show that on a time scale of ∼10-4 s, ions close to the limit undergo Coulomb fission where the observed pathways exhibit considerable asymmetry in the sizes of the charged fragments and are all associated with kinetic (ejection) energies of between 1.4 and 2.2 eV. Accurate kinetic energies have been determined through a computer simulation of peak profiles recorded in the experiments and the results modelled using a theory formulated to describe how charged particles of dielectric materials interact with one another [E. Bichoutskaia et al., J. Chem. Phys. 133, 024105 (2010)]. The calculated electrostatic interaction energy between separating fragments gives an accurate account for the measured kinetic energies and also supports the conclusion that +4 ions fragment into +3 and +1 products as opposed to the alternative of two +2 fragments. This close match between the theory and experiment reinforces the assumption that a significant fraction of excess charge resides on the surfaces of the fragment ions. It is proposed that the high degree of asymmetry seen in the fragmentation patterns of the multiply charged clusters is due, in part, to limits imposed by the time window during which observations are made.

Theoretical Study of the Self-Assembly and Optical Properties of 1D Chains of Magnetic–Plasmonic Nanoparticles

A study is presented of the self-assembly and optical behavior of one-dimensional (1D) chains of colloidal magnetic–plasmonic core–shell Fe3O4@Au nanoparticles. The superparamagnetic core enables adaptive magnetophoretic control of the particles and provides interparticle coupling that drives the assembly process. The plasmonic shell provides unique optical and photothermal properties of assembled structures. Monte Carlo analysis and full-wave field theory are combined to investigate the self-assembly and optical properties of 1D chains, respectfully. The Monte Carlo simulations demonstrate that the particle volume fraction and surface charge can be tailored to control the formation, aggregation, and spacing of chains. The optical analysis shows that as a chain forms its absorption spectrum red shifts and asymptotically converges to that of an infinite chain. In addition, strong field enhancement occurs in the gaps between neighboring particles at plasmon resonance, while photothermal transduction is focused and enhanced within the center of the chain. The ability to adaptively control the magnetic and optical behavior of colloidal plasmonic particles using an external field opens up a host of opportunities for novel imaging, sensing, theranostic, and optofluidic applications. Moreover, while the theory is demonstrated for the analysis of 1D particle chains, the numerical methods readily extend to 2D and 3D assemblies of multilayered core–shell nanoparticles that have magnetic and plasmonic layers. As such, this approach is useful for the rational design of optically functional colloids and the bottom-up fabrication of nanostructured interfaces and media with novel magnetic and photonic functionality.

On the efficiency of a hydrogel-based desalination cycle

Polyelectrolyte based hydrogels swollen in seawater can release partially desalinated water under compression, and hence can be used as desalination agents. We use a previously developed model for the swelling of a hydrogel based on earlier work by Katchalsky and Michaeli to analyse the thermodynamic costs of a full desalination cycle. We investigate salt concentrations from 0.6mol/l down to 10−3mol/l, thereby covering the full range from sea water to potable water, and investigate gels with varying crosslinking degree N and charge fraction α. Our results demonstrate that most efficient are either strongly charged gels with high degree of crosslinking, or gels with intermediate charge fraction and low crosslinking degree. Our analytical model allows us to extract the mechanical work needed to compress the gel, and ultimately to calculate the energy cost to desalinate water by using a hydrogel as a desalination agent. Our theoretical results suggest that hydrogels can compete in energy costs with other standard desalination methods.

Quenched polyelectrolytes with hydrophobicity independent from chemical charge fraction: A SANS and SAXS study

We investigate by SANS and SAXS the structure of semidilute aqueous hydrophobic quenched polyelectrolyte solutions, in which we can vary independently the hydrophobicity and the chemical/electrostatic charge fraction (above the Manning condensation threshold 36%). Such a de-correlation is the original point of the work, reached using statistical tri-copolymers poly(acrylamide-co-styrene-co-2-acrylamido-2-methylpropane-sodium sulfonate), poly(AMx-co-STy-co-AMPSz). The hydrophobicity is brought by ST, the chemical electrostatic charge by AMPS and solubility without charge by AM. We consider that although these copolymers have chemical structure different from partially sulfonated polystyrene sulfonate, PS-co-SSNa, made of two monomers, one charged, one hydrophobic, they have however vicinal behavior. The variation of chemical charge, has no strong consequence on the structure properties which is in agreement with the fact that it is always larger than the Manning threshold. The dependence of q∗ with AM content shows that AM reduces hydrophobicity. The similarity with PS-co-SSNa, for which pearl necklace-like conformations were directly measured by SANS (form factor using ZAC method), suggests that pearl necklace conformations are also adopted by these tri-copolymers and that this behavior could be so generalized to a much larger range of synthetic hydrophobic polyelectrolytes using simple copolymerization.

Влияние атомных процессов на зарядовые состояния и фракции быстрых тяжёлых ионов при прохождении через газовые, твердотельные и плазменные мишени

Влияние атомных процессов на зарядовые состояния и фракции быстрых тяжёлых ионов при прохождении через газовые, твердотельные и плазменные мишени