Charge carriers drift induced THz amplification in dual-layer graphene structure

The terahertz plasmon amplification in structure based on graphene with spatial dispersion of its hydrodynamic conductivity is investigated theoretically. The spatial dispersion of graphene conductivity is related to accounting of charge carriers pressure forces and direct current in graphene. It was shown that the real part of graphene conductivity becomes negative at THz frequency range due to direct electric current in graphene.

The impact of titanium oxide nanoparticles and low direct electric current on biofilm dispersal of $Bacillus~cereus$ and $Pseudomonas~aeruginosa$: A comparative study

Bacteria growing in biofilms cause a wide range of environmental, industrial and public health risks. Because biofilm bacteria are very resistant to antibiotics, there is an urgent need in medicine and industry to develop new approaches to eliminating bacterial biofilms. One strategy for controlling these biofilms is to generate an antibiofilm substance locally at the attachment surface. Direct electric current (DC) and nanoparticles (NPs) of metal oxides have outstanding antimicrobial properties. In this study we evaluated the effect of titanium oxide nanoparticle (TiO$_2$-NP) concentrations from 5 to 160 $\mu$g/mL on Bacillus cereus and Pseudomonas aeruginosa biofilms, and compared this with the effect of a 9 V, 6 mA DC electric field for 5, 10 and 15 min. TiO$_2$-NPs were characterized using transmission and scanning electron microscopes, X-ray diffraction and FTIR. They exhibited an average size of 22-34 nm. The TiO$_2$-NP concentrations that attained LD50 were $104 \pm 4$ $\mu$g/mL and $63 \pm 3$ $\mu$g/mL for B. cereus and P. aeruginosa, respectively. The eradication percentages obtained by DC at 5, 10, and 15 min exposure were 21%, 29%, and 33% respectively for B. cereus and 30%, 39%, and 44% respectively for P. aeruginosa. Biofilm disintegration was verified by exopolysaccharide, protein content and cell surface hydrophobicity assessment, as well as scanning electron microscopy. These data were correlated with the reactive oxygen species produced. The results indicated that both DC and TiO$_2$-NPs have a lethal effect on these bacterial biofilms, and that the DC conditions used affect the biofilms in a similar way to TiO$_2$-NPs at concentrations of 20-40 $\mu$g/mL.

Efficient Use of Carbon Fibers as Heating Elements for Curing of Epoxy Matrix Composites

The aim of this study is to achieve a fully cured thermoset matrix that is heated by a direct electric current passing through the reinforcement fibers i.e., the Joule heating effect. Two types of fibers were used as heating elements for curing the epoxy resins. Kanthal resistance fibers were used as reference heating elements and subsequently, they were replaced by a Torayca Carbon Tow of the same radius. The specimens were cured by the heat produced by a direct electric current passing through the fibers and achieving temperatures of 50 °C and 70 °C. Specimens cured in a conventional oven were also manufactured, to compare the resistance heating method to the conventional one. Next, all specimens were mechanically characterized in a quasi-static three-point bending mode of loading and experimental results were compared to derive useful conclusions concerning the applicability of the technique to polymer/composite materials mass production. Finally, a preliminary economical study concerning power consumption needed for the application of both the traditional oven curing and the carbon fibers heating elements use for the manufacturing of the same amounts of materials is presented, showing a maximum financial benefit that can be achieved, on the order of 68%.

Bioelectric Effect of a Microcurrent Toothbrush on Plaque Removal

This study evaluated the effectiveness of a microcurrent toothbrush (approved by the US Food and Drug Administration [FDA]), which employs a superimposed alternating and direct electric current, named as a Proxywave® technology, similar to the intensity of the biocurrent, in plaque removal and reducing gingivitis by biofilm removal through the bioelectric effect. This study enrolled 40 volunteers with gingivitis. Dental observations were made every two weeks, before and after the use of each toothbrush. We randomly assigned participants into two groups: one group used the Proxywave® toothbrush (PB) for two weeks followed by the control toothbrush (CB) for two weeks, while the other group used the CB for two weeks followed by the PB. The participants had a two-week washout period. If the toothbrush used earlier has had an effect on the bacterial flora in the oral cavity, this is to remove this effect and return it to its previous state. During each dental visit, we recorded plaque index (PI) and gingival index (GI) scores. The PI and GI scores were significantly lower in both the PB and the CB (p < 0.05). Considering the PI, there was no significant difference between the toothbrushes on all the surfaces. Considering the GI, the PB showed a significant decrease in the interproximal surface, compared to the CB (p < 0.05). The PB showed a significant decrease in the interproximal GI and had a beneficial effect in the interproximal area where the bristles could not reach. No adverse events were observed in the participants during the clinical trial. The microcurrent toothbrush is a device that can be safely used for plaque removal.

Effects of Preharvest Methyl Jasmonate Elicitation and Electrical Stimulation on Camptothecin Production by In Vitro Plants of Ophiorrhiza ridleyana Craib

To enhance plant camptothecin (CPT) production in vitro, 5-month-old Ophiorrhiza ridleyana Craib plant cultures were treated with solutions of methyl jasmonate (MeJA) dissolved in ethanol, which were applied to the surface of the solid culture medium. It was demonstrated that the maximum CPT content in the tissue-cultured plants was achieved after 12 h elicitation with 50 µM MeJA. The mean CPT contents in roots and stems were 50.8 and 67.0 µg/g DW, respectively, which were approximately 1.8- and 2.6-fold higher, respectively, than those of the control. However, MeJA elicitation showed no significant effect on CPT accumulation in O. ridleyana leaves. Moreover, it was found that direct electric current (DC) stimulation also significantly increased CPT accumulation in O. ridleyana. The treatment with DC at 20 mA for 3 min of stimulation enhanced 3-fold the CPT content in roots, stems, and leaves to 41.9, 36.0 and 19.6 µg/g DW, respectively, which were approximately 1.5-, 1.7- and 1.4-fold higher, respectively, as compared to those of the control. The results demonstrate that preharvest treatment by MeJA elicitation and electrical stimulation can be beneficial for secondary metabolite production of CPT in tissue-culture plants of O. ridleyana.

Development of ideas about "bias current"

Purpose. In electrical engineering, radio engineering, such concepts as charge, electric field, magnetic field, electromagnetic field, direct electric current, alternating current are used. These abstract concepts reflect certain real physical phenomena. For example, current is understood as the directed movement of electric charges. However, there is also a conditionally abstract concept of "bias current", which was introduced by Maxwell to explain the passage of current through a section of capacitor where there are no charges. The purpose of the article is to reveal the substantive meaning of this term and to explain the real mechanism of current flow in an electric circuit. Methodology. Analysis of the phenomenon is performed on the basis of such traditional concepts as charge, electric field, magnetic field, electromagnetic field, direct electric current, alternating current. Analysis of the contradiction between the concept of current as a directed movement of charges and the concept of "bias current" as a current without charges is presented. Theoretical coordination of the "bias current "concepts and current as a directed motion of charges is done. Findings. It is shown that for all sections of a closed electric circuit, the definition of current as a directed movement of charges is valid only for direct current, when the charges are actually moving in all sections of the circuit. In the circuit with the capacitor, direct current does not flow, because there are no charges in the gap between the plates of the capacitor. However, alternating current occurs, at the moment when the circuit is closed. In the area of the conductor there is a directed movement of charges and the cause of the movement is an electric field, which is variable and occurs together with the alternating magnetic field in all parts of the circuit, including the part of the capacitor where there are no charges. It is shown that in general the concept of current as a directed motion of charges is correct, but conditionally abstract, because in fact the root cause is what is called an electromagnetic field. The concept of bias current is a conditionally abstract expression of the electromagnetic field. Originality. The novelty is that it is possible to understand adequately and non-abstractly the processes that occur in an electric circuit during the passage of current, that no current creates an electric field around the conductor on which charges move, and vice versa, alternating electric field leads to charges ,which are in the conductor areas. Practical value. Understanding the real essence of the term makes it possible to assess correctly the processes occurring in the electrical circuit; gives the answer whether the movement of charges occurs gradually or immediately around the circle when connecting an e.r.s. and closing the circuit. This understanding gives you an idea of what happens when the capacitor electrodes are connected to an e.r.s. and why do the electrons in a conductor come in a directed motion, what is the nature of the force acting on the electrons.

Influence of direct electric field on PMCG-alginate-based microcapsule

In this study, the influence of direct electric current on a microcapsule was investigated. The microcapsule consisted of a core from a calcium ion and sodium alginate (SA) complex and the microcapsule membrane was formed by the polyionic complexation of poly(methylene-co-guanidine) (PMCG) and cellulose sulfate (CS). Microcapsules showed swelling and decreasing mechanical properties under the applied electric current, and the microcapsule membrane showed anisotropic swelling on the electrode side. The effect is attributed to an electrokinetic phenomenon, predominant formation of hydroxyl ions, and the diffusion of hydrated ions. The swelling degree of the microcapsule and microcapsule membrane at different pH and the applied electric current under alkali and acidic conditions was investigated. The swelling degree was influenced by the dissociation of the membrane, which was observed after applying the electric field, which was caused by the electrokinetic effect and the neutralization of the polycation (under alkali conditions) or polyanionic (under acidic conditions) segment during membrane formation.

Усиление терагерцовых электромагнитных волн в структуре с двумя слоями графена при протекании постоянного электрического тока: гидродинамическое приближение

The amplification of electromagnetic terahertz radiation in a structure with two layers of hydrodynamic graphene with a direct electric current is studied theoretically. The hydrodynamic conductivity of graphene is investigated. It is shown that the real part of the graphene conductivity can be negative in the terahertz frequency range at the drift velocities of charge carriers in graphene that are lower than the phase velocity of the electromagnetic wave. For small wavevectors of a terahertz wave incident on a graphene structure, the spatial dispersion insignificantly contributes to the hydrodynamic graphene conductivity. Because of this, the amplification efficiency does not depend on the direction of currents in each of the graphene layers. It is shown that graphene with direct electric current can be used to create THz amplifiers operating at room temperature.