Sign Of Charge Research Articles

Enantioselective optical trapping of chiral nanoparticles by tightly focused vector beams

Two enantiomers (mirror images) can show drastically different behaviors, resulting in the enantiomers’ identification and separation being in high demand in biomedical research and industry. Here, we introduce an optical approach in which, by using a tightly focused vector beam with radially varied polarizations, we realize the selective trapping of both enantiomeric forms. Numerical results show that such a focused field exhibits bifocal spot intensity distribution and can simultaneously stably trap one enantiomer in one focal spot and the other enantiomer in the other spot in three dimensions, achieving an effective separation of the chiral entities. The trapping distance and position of the enantiomeric pairs can be changed by separately varying the magnitude and sign of the polarization topological charge of the vector beam. And the difference in trapping potentials of the particles with different chirality provides a further identification of the chirality. Our theory indicates that the enantiomers’ identification and separation can be mediated by the same incident beam, providing a possible route to detect, separate, and manipulate chiral objects at nanometer scales.

On neutralization of charged black holes

Abstract For non-spinning, charged (Reissner–Nordström) black holes, the particles with an opposite sign of charge with respect to that of the black hole will be pulled into the black hole by the extra electromagnetic force. Such a hole will be quickly neutralized so that there should not exist significantly charged, non-spinning black holes in the universe. The case of spinning, charged (Kerr–Newmann, KN) black holes is more complicated. For a given initial position and initial velocity of the particle, an oppositely charged particle does not always more easily fall into the black hole than a neutral particle. The possible existence of a magnetosphere further complicate the picture. One therefore cannot straightforwardly conclude that a charged spinning black hole will be neutralized. In this paper, we make the first step to investigate the neutralization of KN black holes without introducing a magnetosphere. We track the particle trajectories under the influence of the curved space–time and the electromagnetic field carried by the spinning, charged black hole. A statistical method is used to investigate the neutralization problem. We find a universal dependence of the falling probability into the black hole on the charge of the test particle, with the oppositely charged particles having a higher probability of falling. We therefore conclude that charged, spinning black holes without a magnetosphere should be quickly neutralized, consistent with people’s intuition. The neutralization problem of KN black holes with a corotating force-free magnetosphere is subject to further studies.

Vortex chirality-dependent filtering in helically twisted single-ring photonic crystal fibers.

Helically twisted microstructured optical fibers have a wide application prospect in the field of optical vortex communications. In this paper, a helically twisted single-ring photonic crystal fiber (HS-PCF) is proposed for orbital angular momentum (OAM) vortex modes selective filtering. And the theoretical framework of OAMs filtering is also constructed. Positive and negative OAM vortexes have different transmission losses in HS-PCF, and the loss difference between them increases significantly after the twist rate reaches a certain value. Such fibers can filter out OAMs with a certain sign of the topological charge (depending on the handedness of the thread), while dissipating oppositely charged OAMs. In addition to the general OAMs, i.e., zero-order radial vortex modes, the helically twisted fiber also performs a good selective filtering for the first-order radial vortex modes. Remarkably, the filtering bandwidth of HS-PCF is very broad, covering four communication bands from O- to C-band. This kind of fiber can be used as a broadband OAMs filter.

Like-Charge Attraction between Metal Nanoparticles in a 1∶1 Electrolyte Solution.

We calculate the force between two spherical metal nanoparticles of charge Q_{1} and Q_{2} in a dilute 1∶1 electrolyte solution. Numerically solving the nonlinear Poisson-Boltzmann equation, we find that metal nanoparticles with the same sign of charge can attract one another. This is fundamentally different from what is found for like-charged, nonpolarizable, colloidal particles, the two-body interaction potential for which is always repulsive inside a dilute 1∶1 electrolyte. Furthermore, the existence of like-charge attraction between spherical metal nanoparticles is even more surprising in view of the result that such attraction is impossible between parallel metal slabs, showing the fundamental importance of curvature. To overcome a slow convergence of the numerical solution of the full nonlinear Poisson-Boltzmann equation, we developed a modified Derjaguin approximation which allows us to accurately and rapidly calculate the interaction potential between two metal nanoparticles or between a metal nanoparticle and a phospholipid membrane.

Erythromycin, Cethromycin and Solithromycin display similar binding affinities to the E. coli's ribosome: A molecular simulation study

Macrolide antibiotics bind to the exit tunnel of the ribosome and inhibit protein synthesis blocking its translocation. Thus, antibiotics including the known macrolide Erythromycin (ERY) are active against bacteria. However, at present, some bacteria show resistance to drugs, which requires the development of new powerful antibacterial agents. One possible way is to use the ERY structure, but change its side chains, while the size of the lactone ring can remain unchanged or change. In this work we consider Cethromycin (CET) and Solithromycin (SOL), which are ketolides with quinolylallyl group at C6 and aminophenyl at C11, respectively (both of them have the same lactone ring as ERY). Experiments have shown that these ketolides have improved efficacy against pathogens, but their binding affinity to the E. coli's ribosome is almost identical. To clarify this issue, we have studied in detail the binding mechanisms of ERY, CET and SOL using the docking and molecular dynamic simulations. In agreement with the experiments, we showed that these compounds have similar binding affinities. Desosamine and lactone ring groups play a critical role in the binding of ERY to the ribosome. In CET and SOL, the contribution of keto and alkylaryl groups is balanced by cyclic carbamate. We have demonstrated that increased fluctuations in the ribosomal residues at the binding site led to an increase in the entropic term in the free binding energy of ERY compared to SOL and CET. The alkyl-aryl arm of both ketolides strongly interacts with A752 and U2609. In addition, the presence of macrolides in the exit tunnel can alter the conformation of U2585, which is located in the peptidyl transferase center, through non-bonded interaction. Therefore, the side chain of ketolides affects not only the binding site but also other residues possibly leading to a strong effect on the protein synthesis process. We predict that to combat bacterial mutations, it is necessary either to design a bulk and charged group as a cladinose, or to use several groups with different signs of charges. This prediction can be used for the development of new efficient antibiotics.

The pH-dependent electrostatic interaction of a metal nanoparticle with the MS2 virus-like particles

The electrostatic interaction of metal nanoparticles with viruses is attracting great interest due to their antiviral activity and their role in enhancing the detection of viruses at ultra-low concentrations. We model the MS2 virus devoid of its single strand RNA core using a core-shell model. The dependence of the inner and outer surface charge density on the pH is taken into account in our model of the interaction. Varying the pH causes a change in the sign of the outer surface charge leading to the attractive-repulsive transition in the electrostatic interaction between the MS2 virus and metal nanoparticle at pH = 4.

Phase detection of coherence singularities and determination of the topological charge of a partially coherent vortex beam

In the theory of partial coherence, coherence singularities can occur in the spectral degree of coherence (SDOC): in case the fields at two different points are completely uncorrelated, the phase of the SDOC is undefined. For a partially coherent vortex beam, the detection of coherence singularities is linked to the measurement of topological charge, whose magnitude equals the number of ring dislocations in its far field amplitude. However, the phase distribution of coherence singularities is rarely mentioned in the literature and the amplitude distribution can hardly reflect the sign of topological charge. In this letter, we present a phase-analysis method for measuring the coherence singularities by introducing a movable perturbation at a certain point in an illumination window of a finite size. Using the proposed method, we measure experimentally the coherence singularities of a partially coherent vortex beam in the focal plane. From the results, the magnitude and sign of the topological charge can be determined simultaneously from the phase distribution of the coherence singularities. Our results can find application in information transmission.

Mechanisms of ferritin assembly studied by time-resolved small-angle X-ray scattering.

The assembly reaction of Escherichia coli ferritin A (EcFtnA) was studied using time-resolved small-angle X-ray scattering (SAXS). EcFtnA forms a cage-like structure that consists of 24 identical subunits and dissociates into dimers at acidic pH. The dimer maintains native-like secondary and tertiary structures and can reassemble into a 24-mer when the pH is increased. The time-dependent changes in the SAXS profiles of ferritin during its assembly were roughly explained by a simple model in which only tetramers, hexamers, and dodecamers were considered intermediates. The rate of assembly increased with increasing ionic strength and decreased with increasing pH (from pH6 to pH8). These tendencies might originate from repulsion between assembly units (dimers) with the same net charge sign. To test this hypothesis, ferritin mutants with different net charges (net-charge mutants) were prepared. In buffers with low ionic strength, the rate of assembly increased with decreasing net charge. Thus, repulsion between the assembly unit net charges was an important factor influencing the assembly rate. Although the differences in the assembly rate among net-charge mutants were not significant in buffers with an ionic strength higher than 0.1, the assembly rates increased with increasing ionic strength, suggesting that local electrostatic interactions are also responsible for the ionic-strength dependence of the assembly rate and are, on average, repulsive.

Influence of the projectile charge sign in light particle single ionization of H2O

Positron- and electron-impact ionization of the 1b1 and 3a1 orbitals of H2O is studied by means of the CDW-EIS model at an impact energy of 81 eV. Fully differential cross sections are calculated and contrasted after a proper average procedure over molecular orientations. Double binary peaks are observed for positron-impact and coplanar geometries, while only single binary peaks are exhibited for electron-impact ionization. For the denominated perpendicular planes, similar structures are observed, with an enhancement or decrease of the binary and recoil lobes. Forward electron emission is analysed identifying the electron capture to the continuum structure for positron-impact. A high narrow peak and a huge dip for positron- and electron-impact are respectively observed, structures already seen in previous ionization studies involving both light and heavy projectiles.

The role of nonlinear body force in production of electric wind in an asymmetric surface dielectric barrier discharge

The electrohydrodynamic body force produced in an asymmetric surface dielectric barrier discharge is widely utilized in flow control applications. The mechanism of body force production has a key role in the performance of plasma actuators. In this paper, a novel supplementary theory of body force production, named ‘nonlinear force’, is described as a new interesting component of total body force. This force is distinct from the well-known body force with a Coulomb origin, and also acts through a different mechanism. The theory of nonlinear force shows that it is unidirectional and pushes all particles towards the lower electrode irrespective of the charge sign and variations in electric field polarity.

Determining topological charge based on an improved Fizeau interferometer.

We propose a new method to determine topological charge by using an improved Fizeau interferometer. This interferometer is very easy to realize, as well as interference fringes are very distinct. Phases of vortex, Hermite-Gaussian, and elliptical vortex beams are experimentally verified using this method. It provides a convenient way to determine the sign and magnitude of topological charge. This method may have some potential applications in space optical communication.

Investigation of the interfacial properties of platinum stepped surfaces using peroxodisulfate reduction as a local probe

Peroxodisulfate (PDS) reduction has been investigated by electrochemical and FTIR techniques in a wide pH range, on platinum stepped single crystals electrodes vicinal to the (111) pole. PDS reduction is a structure-sensitive reaction and proceeds on well differentiated potential regions for terrace and step sites. This fact allows gaining local information about the individual behavior of those sites. The reaction proceeds at appreciable rate in a narrow potential range, being inhibited in the low and high potential regions of the voltammogram. The inhibition of the reaction at low potentials is most likely associated with a change in the sign of the charge on the electrode, from positive to negative. Therefore, PDS reduction gives an approximate indication of the position of the potential of zero free charge (pzfc). In this way, two local values of pzfc, associated with terrace and steps sites, can be determined. Such values of local pzfc are compared with the local values of potential of maximum entropy (pme) of double layer formation deduced from laser induced T-jump experiment. Good agreement between both magnitudes is found, especially for terraces. The local pzfc on terraces shifts to more positive potentials as the terrace length diminishes, while the local pzfc for steps remains constant. The inhibition of PDS reduction at high potentials can also be related with a second inversion in the sign of the electrode charge. Therefore, PDS reduction can be used to determine a second pzfc on the (111) terraces at high potentials, revealing a non-monotonic charge – potential relationship. Spectroscopic experiments allow the identification of the species involved in PDS reduction.

Regulation of the Stability of Titania Nanosheet Dispersions with Oppositely and Like-Charged Polyelectrolytes.

Charging and aggregation processes of titania nanosheets (TNS) were extensively studied in the presence of oppositely charged or like-charged polyelectrolytes in aqueous dispersions. The surface charge of the TNS was systematically varied by the pH; therefore, positive nanosheets were obtained at pH 4 and negative ones at pH 10. Strong adsorption of poly(styrene sulfonate) (PSS) of high negative line charge density on the TNS was observed at pH 4, leading to charge neutralization and reversal of the original sign of charge of the nanosheets. The adsorption of like-charged poly(diallyldimethylammonium chloride) (PDADMAC) was also feasible through a hydrophobic interaction. The predominating interparticle forces were mainly of the DLVO-type, but additional patch-charge attraction also took place in the case of PSS at low surface coverage. The TNS was found to be hydrophilic at pH 10 and no adsorption of like-charged PSS was possible because of strong electrostatic repulsion between the polyelectrolyte and the surface. The PDADMAC showed high affinity to the oppositely charged TNS surface in alkaline dispersions, giving rise to neutral and positively charged nanosheets at appropriate polyelectrolyte doses. Formation of a saturated PDADMAC layer on the TNS led to high resistance against salt-induced aggregation through the electrosteric stabilization mechanism. These results shed light on the importance of polyelectrolyte concentration, ionic strength, and charge balance on the colloidal stability of TNS, which is especially important in applications, where the nanosheets are dispersed in complex solution containing polymeric compounds and electrolytes.

Measuring the topological charge of an x-ray vortex using a triangular aperture

In this paper, for the first time, we demonstrate that the topological charge of a hard x-ray vortex can be measured by a single diffraction pattern from a triangular aperture. The x-ray vortex was produced by a spiral Fresnel zone plate (SFZP) with topological charges of ±1. The triangular aperture was placed in the proximity of the focal plane of the SFZP. Explicit diffraction patterns, which agreed well with the calculated results, were observed and they were rotated by 180° by inverting the sign of the topological charge.

Detecting the topological charge of partially coherent electromagnetic vortex beams through the orientation angle of polarization

By analysis of the orientation angle of polarization (OAoP) of a partially coherent electromagnetic Gaussian Schell-model vortex (EGSMV) beam, we find that the OAoP distribution is the shape of petal and demonstrate an implicit rule that the number of petals is equal to twice the magnitude of the topological charge of the partially coherent EGSMV beam. The sign of the topological charge is related to the rotation direction of the petals. This novel rule provides an effective method for detecting the orbital angular momentum of a partially coherent electromagnetic vortex beam in applications such as free space optical communication and quantum information.

Nonequilibrium Uptake Kinetics of Molecular Cargo into Hollow Hydrogels Tuned by Electrosteric Interactions.

Hollow hydrogels represent excellent nano- and microcarriers due to their ability to encapsulate and release large amounts of cargo molecules (cosolutes) such as reactants, drugs, and proteins. In this work, we use a combination of a phenomenological effective cosolute-hydrogel interaction potential and dynamic density functional theory to investigate the full nonequilibrium encapsulation kinetics of charged and dipolar cosolutes by an isolated charged hollow hydrogel immersed in a 1:1 electrolyte aqueous solution. Our analysis covers a broad spectrum of cosolute valences ( zc) and electric dipole moments (μc), as well as hydrogel swelling states and hydrogel charge densities. Our calculations show that, close to the collapsed state, the polar cosolutes are predominantly precluded and the encapsulation process is strongly hindered by the excluded-volume interaction exerted by the polymer network. Different equilibrium and kinetic sorption regimes (interface versus interior) are found depending on the value and sign of zc and the value of μc. For cosolutes of the same sign of charge as the gel, the superposition of steric and electrostatic repulsion leads to an "interaction-controlled" encapsulation process, in which the characteristic time to fill the empty core of the hydrogel grows exponentially with zc. On the other hand, for cosolutes oppositely charged to the gel, we find a "diffusion-controlled" kinetic regime, where cosolutes tend to rapidly absorb into the hydrogel membrane and the encapsulation rate depends only on the cosolute diffusion time across the membrane. Finally, we find that increasing μc promotes the appearance of metastable and stable surface adsorption states. For large enough μc, the kinetics enters an "adsorption-hindered diffusion", where the enhanced surface adsorption imposes a barrier and slows down the uptake. Our study represents the first attempt to systematically describe how the swelling state of the hydrogel and other leading physical interaction parameters determine the encapsulation kinetics and the final equilibrium distribution of polar molecular cargo.

Electrochemical Properties of Homogeneous and Heterogeneous Anion Exchange Membranes Coated with Cation Exchange Polyelectrolyte.

Coating ion exchange membranes with polyelectrolyte has been proven to be a cheap way to reduce concentration polarization and increase limiting current (for polyelectrolytes carrying fixed groups of the same sign of charge with respect to the membrane bulk), to create high monovalent selectivity, and to add the function of H+/OH− ions generation (for polyelectrolytes bearing fixed groups of the opposite sign of charge with respect to the membrane bulk). In the latter case, the balance between the counterion transport and the H+/OH− ions generation is affected by parameters of the substrate and the modifying layer. In this study we investigated the electrochemical characteristics of homogeneous Neosepta AMX-Sb and heterogeneous MA-41P membranes coated with one, two, or three layers of oppositely charged polyelectrolyte (the maximum thickness of each layer was 5 µm). It was found that the limiting current decreased earlier and the generation of H+/OH− ions was stronger in the case of the heterogeneous membrane. The shift in the pH of the solution depended more on the generation of H+/OH− ions at the modifying layer/solution interface than on the generation at the membrane/modifying layer interface, and in all cases water splitting started in the same range of potential drops over the membrane.

Strongly Intensive Observables in the Model with String Fusion

We calculate the strongly intensive observables for multiplicities in two rapidity windows in the model with independent identical strings taking into account the charge sign of particles. We express the observables through the string pair correlation functions describing the correlations between the same and opposite sign particles produced in a string decay. We extract these charge-wise string two-particle correlation functions from the ALICE data on the forward-backward correlations and the balance function. Using them we predict the behavior of the charge-wise strongly intensive observables in the model with independent identical strings. We also show that the observable between multiplicities in two acceptance windows separated in rapidity, which is a strongly intensive in the case with independent identical strings, loses this property, when we take into account string fusion effects and a formation of strings of a few different types takes place in a collision. We predict the changes in the behaviour of this observable with energy and collision centrality, arising due to the string fusion phenomena.

The Position of Solid Carbon Dioxide in the Triboelectric Series

The process of releasing liquid carbon dioxide from a fire extinguisher is accompanied by a strong static charging of the plastic material making up the extinguisher discharge horn. Firefighters often report an electric shock when operating CO2 extinguishers, but the origin of this electrostatic hazard is largely unknown. Here, we begin to investigate this phenomenon, and test the hypothesis of plastic samples being tribocharged on contact with rapidly flowing solid CO2. Using Faraday pail measurements, we show that non-conductive polymers gain a net static charge when brought in and out of contact with dry ice (solid CO2). These measurements of charge sign and magnitude give indirect evidence helping to place solid CO2 for the first time on the triboelectric series. Polydimethylsiloxane (PDMS), polytetrafluoroethylene (PTFE), and polyvinyl chloride (PVC) samples acquire a negative charge when rubbed against dry ice, whereas poly(methyl methacrylate) (PMMA), glass, and nylon surfaces become positively charged. Therefore, we suggest the position of dry ice in the triboelectric series to be close to that of materials with stable cations and unstable anions, possibly locating it between PMMA and PVC.

String model calculation of the strongly intensive observables for multiplicities in two windows

We calculate the strongly intensive observables for multiplicities in two rapidity windows in the model with independent identical strings taking into account the charge sign of particles. We express the observables through the string pair correlation functions describing the correlations between the same and opposite sign particles produced in a string decay. We extract these charge-wise string two-particle correlation functions from the ALICE data on the forward-backward correlations and the balance function. Using them we predict the behavior of the charge-wise strongly intensive observables in the model with independent identical strings.