Unit Charge Research Articles

A novel cationic β-cyclodextrin decorated with a choline-like pendant exhibits Iodophor, Mucoadhesive and bactericidal properties

Iodine is a vital microelement and a powerful antiseptic with a rapid and broad spectrum of action. The development of iodophor compounds to improve the solubility and stability of iodine is still challenging. Here, we report the synthesis of a novel cationic β-cyclodextrin bearing a choline-like pendant (β-CD-Chol) designed to complex and deliver iodine to bacterial cells. The characterization of β-CD-Chol and the investigation of the inclusion complex with iodine were performed by NMR spectroscopy, mass spectrometry, UV–vis spectrophotometry, isothermal titration calorimetry, and dynamic light scattering. The functionalization with the positively charged unit conferred improved water-solubility, mucoadhesivity, and iodine complexation efficiency to the β-CD scaffold. The water-soluble β-CD-Chol/iodine complex efficiently formed both in solution and by solid-vapor reaction. The solid complex exhibited a significant stability for months. Iodine release from the inclusion complex was satisfactory and the bactericidal activity was proved against a Staphylococcus epidermidis strain. The absence of cytotoxicity tested on human keratinocytes and the improved mucoadhesivity make β-CD-Chol a promising drug delivery system and an appealing iodophor candidate for iodine-based antisepsis including mucosa disinfection.

Scheduling of mobile charging stations with local renewable energy sources

Due to the depletion of fossil resources and increasing environmental concerns, electric vehicles (EVs) have been attracting more attention at the last decade. Their extensive integration into the energy systems, however, has led to numerous operational and technological challenges, especially during their bulk charging. In this study, an optimization algorithm based on mixed integer linear programming is proposed to dispatch mobile charging stations (MCSs), which have emerged as both an alternative and supplement to permanent charging stations (PCSs). It is aimed to mitigate the number of EVs that cannot be charged in PCSs, due mostly to the limited charging unit capacity and prolonged waiting times, by using an MCS. Five determinative cases involving a combination of different operating and pricing mechanisms are evaluated. The results reveal that the use of the MCS provides both economic and operational benefits. In the best case determined according to the result of the comparisons with various pricing mechanisms, the MCS provides an operational improvement of 64.3 % compared to the case without the MCS. The quantity of EVs requesting service is 1074 in all cases, while 986 EVs are served in the case with the best results. Besides, a profit increase of 46 % is achieved for the cases in which dynamic pricing is applied. An important point to note is that with the incentive mechanism applied, there is a significant increase in the profit in Case 5, while the number of EVs served is 967. In case 4, without incentive mechanism, the number of EVs served is 968.

The value of charge of Fe single to multiple atoms doped in Ge: Combined experimental and density functional theory study

With the aim to find out the value of an electronic charge that the Fe atoms acquire when they are doped in Ge bulk, a set of experimental and density functional theory (DFT) studies have been carried out of the model systems consisting of intermixed Fe–Ge films. Such films were prepared by electron and thermal evaporation in ultra-high vacuum (UHV) on the surface of Mo(110) substrate by initial formation of the Ge film of a mean thickness of 7.5 nm, onto which the Fe films were subsequently deposited, maintaining certain Fe to Ge concentration ratio, namely, 0.2, 0.4, 0.7 and 1.0. Annealing of such double Fe–Ge films results in notable interdiffusion of the components with quite uniform distribution of the elements throughout the intermixed layer. The details of formation of such layers were in-situ controlled by Auger electron spectroscopy (AES), low-energy ion scattering spectroscopy (LEIS), low-energy electron diffraction (LEED) and work function measurements, in combination with Ar ion depth profiling. By analyzing the Fe Auger LMM-triplet, the absolute values of the charge that Fe atoms acquire when doped in Ge, were estimated for four different Fe–Ge intermixed layers with above-mentioned different Fe to Ge concentration ratio. The corresponding plot of the charge versus Fe to Ge concentration allows to estimate the charge of a single doped Fe atom, which equals to +0.34e (electron charge units) and gradually decreases to 0.07e for high Fe concentration. To verify the experimental values of the Fe charge the calculations were done by periodic DFT as implemented in full-potential FHI-aims code. Among the used algorithms of Mulliken, Hirshfeld, and Bader's atoms-in-molecules, the latter gives good correlation between charges of Fe dopant and its concentration.

EMF revisited

This paper was inspired by a recent publication by Redžíc (2018 Eur. J. Phys. 39 025205) which threw into bold relief the differences between the way Maxwell viewed the current and the way Lorentz visualized it. We make the assumption that for a circuit of laboratory dimensions current (and charge perturbation effects in general) can be assumed to propagate instantaneously around the loop. Our second fundamental assumption is the commonly accepted one that E is the force per unit charge on a stationary charge. We use these facts to make the usual definition of electromotive force more rigorous and to derive the Lorentz force formula.

Rearrangement of the Conformations of Polyampholitic Macromolecules on the Surface of a Charged Spherical Metal Nanoparticle in an Alternating Electric Field: Molecular Dynamic Simulation

The rearrangement of the conformational structure of polyampholytic polypeptides on the surface of a charged spherical gold nanoparticle with its polarity intermittently changing over time was studied using molecular dynamics modeling. The angular distributions of the polypeptide atoms, as well as the radial distributions of the macrochain atomic density in the equatorial region of the nanoparticle with differentiation according to the types of links, were calculated. The polyampholyte shell acquired an annular shape, and the resulting macromolecular ring was located around the charged nanoparticle perpendicularly to the vector of the external electric field strength. With an increase in the charge of the nanoparticle, the ring belt was ordered according to the types of macrochain links, forming concentric annular layers. The diameter of the macromolecular ring depended on the law of distribution of charged units in the macrochain. At elevated temperatures the annular macromolecular ring was deformed at the moments of the highest polarization of the nanoparticle.

Theoretical quantification of pH-responsiveness of blend membrane

In this work, a simple predictive mathematical model has been presented that quantifies the membrane parameters, e.g., permeability, effective pore diameter and number of charged units in a polymer chain in a pH-varying environment devoid of added salt. This has been validated experimentally for the case of poly(vinylidene fluoride) (PVDF) membranes blended with poly(methyl methacrylate)-co-poly(acrylic acid) (PMMA-co-PAA) additive copolymer. The effect of Donnan potential was incorporated into the model and estimated using electrokinetic characterizations. It varied considerably from 0.25 to −1.93 units (dimensionless) from pH 2 to 11. Variations of surface morphology and the electronic structure of the blend membrane with pH were studied in detail. Molecular simulations were performed to estimate the effective distance between the neighboring units in the charged/uncharged states and for confirming the copolymer chain behavior in different pH environments. Adsorption experiments were conducted to compare the variation of the number of uncharged units with pH with those estimated using the model. A pH-dependent permeability hysteresis behavior was observed which was explained using an intermolecular hydrogen bonding mechanism. About 80 % variation in the permeability of the blend membrane was observed between the pH limits which was in close agreement with the model results.

Cationic amino-acid functionalized polymethacrylamide vectors for siRNA transfection based on modification of poly(2-isopropenyl-2-oxazoline)

Poly(2-isopropenyl-2-oxazoline) (PiPOx) is a functional polymer showing great potential for the development of smart biomaterials. The straightforward synthesis and post-polymerization functionalization of PiPOx offers many opportunities for tailoring the properties of the polymer towards biomaterials. In this study we report for the first time PiPOx-based cationic charged polymethacrylamides with amino acid side chains that can complex siRNA and promote transfection in vitro. Therefore, PiPOx was fully modified via ring opening addition reactions with the carboxylic acid groups of a series of N-Boc-L-amino acids and their reaction kinetics were investigated. Based on the determined kinetic constants, another series of PiPOx-based copolymers with balanced hydrophilic/hydrophobic content of N-Boc-L-amino acids were obtained via one-pot modification reaction with two different N-Boc-L-amino acids. The N-Boc protected homopolymers and related copolymers were deprotected to obtain (co)polymers with the targeted side chain cationic charged units. The (co)polymers' structures were fully investigated via FT-IR and 1H NMR spectroscopy, size exclusion chromatography (SEC), and TGA–DSC–MS analysis. The polarimetry measurements revealed that the homopolymers retain their chiroptical properties after post-modification, and a sign inversion is noticed from (L) N-Boc-protected analogues to (D) for the TFA cationic charged homopolymers. Generally, cationically charged homopolymers with hydrophilic amino acids on the side chain showed efficient complexation of siRNA, but poor transfection while cationic copolymers having both tryptophan and valine or proline side chains revealed moderate siRNA binding, high transfection efficiency (> 90% of the cells) and potent gene silencing with IC50 values down to 5.5 nM. Particularly, these cationic copolymers showed higher gene silencing potency as compared to the commercial JetPRIME® reference, without reducing cell viability in the concentration range used for transfection, making this a very interesting system for in vitro siRNA transfection.

Low-dimensional lead chromate-based hybrid system for capacitance and polarization performances: a flexible device for pressure-induced voltage generator

AbstractOrganic molecule–functionalized lead chromate nanoparticle was synthesized using a complexation strategy route. The structural characterization revealed the single-phase lead chromate system belongs to monazite-type monoclinic structure with the space group of P21/n. The unit cell consists of an alternating chain of polyhedra (PbO9) and tetrahedra (CrO4) units, connected via edge and corner-sharing arrangement. A flexible device of lead chromate was fabricated and investigated dielectric capacitance, electrical impedance, conductivity, and field dependent polarization performances under different frequency and temperature environments. The device displayed a maximum dielectric constant (εʹ) value ~ 2400 at 120°C under 100 Hz frequency condition. High dielectric constant value is originated from the orientation polarization of CrO4 unit and space charge contribution in the system. AC conductivity of the device suggested the polaronic charge carriers control the overall conduction process via localized hopping mechanism. A fatigue-free polarization behavior was observed in the device under the applied field of 4.0 kV/mm, for 103 cycles and retained the polarization value ~ 0.26 μC/cm2 over the switching cycles. Lead chromate–based device also showed pressure-induced voltage generation under different pressure conditions and could have the potential application as a voltage generator.

Applying a 2 kW Polymer Membrane Fuel-Cell Stack to Building Hybrid Power Sources for Unmanned Ground Vehicles

The novel constructions of hybrid energy sources using polymer electrolyte fuel cells (PEMFCs), and supercapacitors are developed. Studies on the energy demand and peak electrical power of unmanned ground vehicles (UGVs) weighing up to 100 kg were conducted under various conditions. It was found that the average electrical power required does not exceed ~2 kW under all conditions studied. However, under the dynamic electrical load of the electric drive of mobile robots, the short peak power exceeded 2 kW, and the highest current load was in the range of 80–90 A. The electrical performance of a family of PEMFC stacks built in open-cathode mode was determined. A hydrogen-usage control strategy for power generation, cleaning processes, and humidification was analysed. The integration of a PEMFC stack with a bank of supercapacitors makes it possible to mitigate the voltage dips. These occur periodically at short time intervals as a result of short-circuit operation. In the second construction, the recovery of electrical energy dissipated by a short-circuit unit (SCU) was also demonstrated in the integrated PEMFC stack and supercapacitor bank system. The concept of an energy-efficient, mobile, and environmentally friendly hydrogen charging unit has been proposed. It comprises (i) a hydrogen anion exchange membrane electrolyser, (ii) a photovoltaic installation, (iii) a battery storage, (iv) a hydrogen buffer storage in a buffer tank, (v) a hydrogen compression unit, and (vi) composite tanks.

Conformational Rearrangements of Adsorbed Polyampholytes under Periodic Changes in Polarity of a Charged Prolate Gold Nanospheroid

Conformational rearrangements of polyampholytic polypeptides adsorbed on the surface of a charged prolate gold nanospheroid with a periodic change in time of its polarity along the rotation axis have been studied using molecular dynamics simulation. The radial distributions of the density of polypeptide atoms in the equatorial region of the nanospheroid have been calculated, as well as the distributions of the linear density of polypeptide atoms along the major axis of the nanospheroid. At a low simulation temperature, a girdle polyampholytic fringe was formed in the central region of the nanospheroid and its ordering by layers, depending on the type of units, occurred with an increase in the charge of the nanospheroid with a simultaneous increase in the width of the macromolecular fringe along the rotation axis. The thickness of such a fringe along the cross section depends on the distance between the oppositely charged units in thepolyampholyte. At high temperatures and high absolute values of the total charge of the spheroidal nanoparticle, there were periodic displacements of the polyampholytic fringe toward the poles of the nanospheroid, being in antiphase for oppositely charged metallic nanospheroids. A mathematical model is presented for describing the conformational structure of a polyampholyte macromolecule on a prolate nanospheroid in an alternating electric field with the approximation of a prolate spheroid by a spherical cylinder

Possible zero-magnetic field fractional quantization in In0.75Ga0.25As heterostructures

In this Letter, we report a systematic study of a structure found in zero magnetic field at or near 0.2 ×(e2/h) in In0.75Ga0.25As heterostructures, where e is the fundamental unit of charge and h is Planck's constant. This structure has been observed in many samples and stays at near constant conductance despite a large range of external potential changes, the stability indicating a quantum state. We have also studied the structure in the presence of high in-plane magnetic fields and find an anisotropy which can be related to the Rashba spin–orbit interaction and agrees with a recent theory based on the formation of coherent back-scattering. A possible state with conductance at 0.25 ×(e2/h) has also been found. The quantum states described here will help with the fundamental understanding of low-dimensional electronic systems with strong spin–orbit coupling and may offer new perspectives for future applications in quantum information schemes.

Pressure and isothermal compressibility of complex plasmas in the average Wigner–Seitz cell model with regard to nonlinear screening effect

AbstractWe consider a two‐component electroneutral equilibrium complex plasma of finite‐sized macroions (each with a charge , ) and point oppositely charged microions with unit charges. We take into account a macroions nonlinear screening effect and obtain system pressure in the Wigner–Seitz average cell model within the framework of the Poisson–Boltzmann approximation. It is shown that the obtained pressure and isothermal compressibility are positive over the entire range of macroions concentrations.

Design Considerations with Different Shielding Barriers and HTS Resonance Coils for Wireless Power Charging Unit in High-Speed Magnetic Levitation Train

Design Considerations with Different Shielding Barriers and HTS Resonance Coils for Wireless Power Charging Unit in High-Speed Magnetic Levitation Train

Comparative Analysis of Different Control Strategies for Relift Luo Converter

Dual-output DC to DC converters have drawn attention in the domestic, automobile, and industrial domains. A dual-output converter usually provides a voltage step-down channel and a voltage step-up channel. Typically, an automobile needs a battery charging unit, a traction motor drive, and several other applications. A typical application may require two channels of DC output with a low-voltage (LV) channel and a high-voltage (HV) channel. While the generic boost-derived and quadratic boost-derived dual-output converters are available in the literature, this article focuses on the control aspects of a relift type Luo converter-derived dual-output converter (LDDOC). A solar photovoltaic (SPV) source is the main power, and it charges a battery. The LV loads may be connected across the battery, and the relift stage delivers a regulated 48 V output. The regulation of the 48 V output using a PI controller, a fuzzy logic controller, an ANN-based controller, and a sliding mode controller (SMC) has been studied using simulations. The simulations reveal that the sliding mode controller is advantageous because of meeting out the required performance, easy implementation, and low cost. An experimental setup has also been developed to verify the performance of the sliding mode controller for the regulation of the HV channel output voltage at 48 V.

The cosmological constant is probably still zero

We consider a wide class of four-dimensional effective field theories in which gravity is coupled to multiple four-forms and their dual scalar fields, with membrane sources charged under the corresponding three-form potentials. Four-form flux, quantised in units of the membrane charges, generically generates a landscape of vacua with a range of values for the cosmological constant that is scanned through membrane nucleation. We list various ways in which the landscape can be made sufficiently dense to be compatible with observations of the current vacuum without running into the empty universe problem. Further, we establish the general criteria required to ensure the absolute stability of the Minkowski vacuum under membrane nucleation and the longevity of those vacua that are parametrically close by. This selects the current vacuum on probabilistic grounds and can even be applied in the classic model of Bousso and Polchinski, albeit with some mild violation of the membrane weak gravity conjecture. We present other models where the membrane weak gravity conjecture is not violated but where the same probabilistic methods can be used to tackle the cosmological constant problem.

Single Elementary Charge Fluctuations on Nanoparticles in Aqueous Solution.

100 years ago, in 1923, the Nobel prize in physics was awarded for measurement of the unit charge. In addition to a profound impact on contemporary physics, this discovery has reshaped our understanding of charge-based interactions in chemistry and biology, ranging from oxidation and ionization to protein folding and metabolism. In a liquid, the discrete nature of the electric charge becomes prominent at the nanoscale when a charge carrier is exchanged between a molecule or a nanoparticle and the surrounding medium. However, our ability to observe the dynamics of such interactions at the level of a single elementary charge is limited due to the abundance of ions in water. Here, we report on the observation of single binding-unbinding events with elementary charge resolution at the surface of a nanoparticle suspended in water. Discrete steps in the electrical charge are revealed by analyzing the motion of optically trapped nanoparticles under the influence of an applied sinusoidal electric field. The measurements are sufficiently fast and long to observe individual (dis)charging events that occur on average every 3 s. Our results offer prospective routes for studying the dynamics of diverse chemical and biological phenomena on the nanoscale with elementary charge resolution.

Pseudocatalytic acceleration of hydrothermal leaching of amylose from starch in acidic media

Kinetic studies were conducted at 60–700C using buffer solutions with pH 3–5 to establish the effect of solution acidity on the efficiency of amylose leaching from starch. It was shown that the kinetic data are well described by the Kruger-Ziegler model. It was established that as the pH of the solutions decreases from 5.0 to 3.0, the activation energy of amylose leaching process decreases from 185 to 22 kJ/mol, and its dependence on hydrogen ion concentration is described by two linear segments within the pH ranges of 3.0–3.3 and 3.6–5.0. The effect of reducing the hydrogen bond energy upon addition of an additional proton to the water molecule was demonstrated through quantum-chemical modeling using the Gaussian 09 software. It was shown that protonation of the water molecule leads to a decrease in the effective charge on the oxygen atom from –0.626 to –0.142 unit of electron charge. At the same time, the linearity of the hydrogen bond along the –ОН–О– atoms is violated, the length of the hydrogen bond increases from 1.856 to 2.370 Å, and the binding energy decreases by 4.6 times. Thus, hydrogen ions can be considered as a kind of pseudo-catalyst for the process of amylose leaching from starch grains, since in their presence the activation energy of the process decreases and its rate increases. It was concluded that the process of hydrothermal leaching of amylose from starch can be intensified by carrying it out in acidic media without additional heating of starch suspensions.

CONFORMATIONAL STRUCTURE OF AN ADSORBED POLYELECTROLYTE ON A NANOPARTICLE WITH LOW CONDUCTIVITY IN AN ALTERNATING ELECTRIC FIELD

An analytical form of the model of the quasi-equilibrium conformational structure of the units of the Gaussian chain of a polyelectrolyte adsorbed on a nanospheroid witha relatively low electrical conductivity (undoped semiconductor) polarized in an external harmonically varying quasi-static electric field with a frequency significantly lower than the plasma frequency of the nanoparticle material is proposed. Variants ofthe model are discussed that go beyond the scope of the quasi-static approximation, i.e., take into account the effects of delay, the manifestation of which will be noticeable in the case of sufficiently extended nanostructures. Electrically induced conformational changes of generally neutral polyampholytic polypeptides on the surface of a spherical germanium nanoparticle in a static or alternating external electric field have been studied by molecular dynamics. In a static electric field, in the case of asmall distance between the charged units in the polyampholyte, a large number of macrochain loops were formed, elongated in the direction of the polarization axis of the nanoparticle. If the distance between the oppositely charged amino acid residues of the polypeptide exceeded the diameter of the nanoparticle, the charged units were mainly localized in the oppositely charged subpolar regions of the polarized germanium nanoparticle. In an alternating electric field, a girdle polyampholyte edge was formed in the equatorial region of the nanoparticle, the macrochain links of which were desorbed from the surface with an increase in the amplitude of the polarizing alternating electric field.

Energy storage steady-state PCS power allocation algorithm based on SOC dynamic sequencing

A power allocation algorithm for energy storage PCS based on SOC sequencing is proposed, aiming at the problem that the energy management system (EMS) can allocate the power of the energy storage unit power converter (PCS) in the existing centralized electrochemical energy storage station steady-state power control, and cannot take into account the equalization of the state of charge (SOC) of the energy storage unit and the power control accuracy of the whole station. Based on the analysis of the characteristics of PCS power allocation algorithms commonly used in engineering, this paper proposes an algorithm to determine the PCS control priority based on the SOC ranking results, and then realize PCS power allocation. The simulation results show that compared with other steady-state PCS power allocation algorithms, the algorithm proposed in this paper can enable the whole station to achieve a better balance of the SOC of the energy storage unit under the premise of satisfying the power control accuracy, so that the energy storage station can provide better steady-state power support for the power grid.

Feasibility study of using OWC wave converter to supply the required electric charge of a refinery unit (Case study)

Feasibility study of using OWC wave converter to supply the required electric charge of a refinery unit (Case study)