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Concept: Charge density


The new three-dimensional structure that the graphene connected with SWCNTs (G-CNTs, Graphene Single-Walled Carbon Nanotubes) can solve graphene and CNTs' problems. A comprehensive study of the mechanical and electrical performance of the junctions was performed by first-principles theory. There were eight types of junctions that were constituted by armchair and zigzag graphene and (3,3), (4,0), (4,4), and (6,0) CNTs. First, the junction strength was investigated. Generally, the binding energy of armchair G-CNTs was stronger than that of zigzag G-CNTs, and it was the biggest in the armchair G-CNTs (6,0). Likewise, the electrical performance of armchair G-CNTs was better than that of zigzag G-CNTs. Charge density distribution of G-CNTs (6,0) was the most homogeneous. Next, the impact factors of the electronic properties of armchair G-CNTs were investigated. We suggest that the band gap is increased with the length of CNTs, and its value should be dependent on the combined effect of both the graphene’s width and the CNTs' length. Last, the relationship between voltage and current (U/I) were studied. The U/I curve of armchair G-CNTs (6,0) possessed a good linearity and symmetry. These discoveries will contribute to the design and production of G-CNT-based devices.

Concepts: Electric charge, Carbon, Carbon nanotube, Allotropes of carbon, Graphite, Graphene, Tensile strength, Charge density


We previously reported that nanoparticles (NPs) coated with 10 kDa PEG were mucoadhesive. Here, we demonstrate that by increasing the surface density, PEG with molecular weight (MW) as high as 40 kDa can be used as a mucoinert NP surface coating.

Concepts: Molecule, Mass, In vivo, Coating, Atomic mass unit, Molecular mass, Charge density


Triboelectric nanogenerators have been invented as a highly efficient, cost-effective and easy scalable energy-harvesting technology for converting ambient mechanical energy into electricity. Four basic working modes have been demonstrated, each of which has different designs to accommodate the corresponding mechanical triggering conditions. A common standard is thus required to quantify the performance of the triboelectric nanogenerators so that their outputs can be compared and evaluated. Here we report figure-of-merits for defining the performance of a triboelectric nanogenerator, which is composed of a structural figure-of-merit related to the structure and a material figure of merit that is the square of the surface charge density. The structural figure-of-merit is derived and simulated to compare the triboelectric nanogenerators with different configurations. A standard method is introduced to quantify the material figure-of-merit for a general surface. This study is likely to establish the standards for developing TENGs towards practical applications and industrialization.

Concepts: Electric charge, Fundamental physics concepts, Density, Electrostatics, Engineering, Introductory physics, Standard, Charge density


Size fractionation, amplified by the surface charge density of graphene oxide (GO) sheets, broadens the pH dependent isotropic (I) to nematic (N) phase transition in aqueous dispersions of graphene oxide (GO). In this biphasic region, a highly organized droplet nematic phase of uniform size (20 ± 2.8 μm diameter) with an isotropic interior is observed.

Concepts: Iron, Fundamental physics concepts, Density, Big Bang, Phase transition, Liquid crystal, Charge density


This review updates and consolidates evidence on the safety of transcranial Direct Current Stimulation (tDCS). Safety is here operationally defined by, and limited to, the absence of evidence for a Serious Adverse Effect, the criteria for which are rigorously defined. This review adopts an evidence-based approach, based on an aggregation of experience from human trials, taking care not to confuse speculation on potential hazards or lack of data to refute such speculation with evidence for risk. Safety data from animal tests for tissue damage are reviewed with systematic consideration of translation to humans. Arbitrary safety considerations are avoided. Computational models are used to relate dose to brain exposure in humans and animals. We review relevant dose-response curves and dose metrics (e.g. current, duration, current density, charge, charge density) for meaningful safety standards. Special consideration is given to theoretically vulnerable populations including children and the elderly, subjects with mood disorders, epilepsy, stroke, implants, and home users. Evidence from relevant animal models indicates that brain injury by Direct Current Stimulation (DCS) occurs at predicted brain current densities (6.3-13 A/m(2)) that are over an order of magnitude above those produced by conventional tDCS. To date, the use of conventional tDCS protocols in human trials (≤40 min, ≤4 milliamperes, ≤7.2 Coulombs) has not produced any reports of a Serious Adverse Effect or irreversible injury across over 33,200 sessions and 1000 subjects with repeated sessions. This includes a wide variety of subjects, including persons from potentially vulnerable populations.

Concepts: Electric charge, Fundamental physics concepts, Density, Evidence-based medicine, Alternative medicine, Transcranial direct current stimulation, Charge density, Current density


In this paper, we characterized the interactions between two-component liposomal membranes and monovalent electrolyte ions. Liposomes were formed from neutral (phosphatidylcholine) and anionic (phosphatidylglycerol) lipids mixed in various ratios. Microelectrophoresis was used to determine the dependence of the membrane surface charge density on the p H of the electrolyte solution. Changes in the membrane electric charge caused by the adsorption of Na(+) , Cl(-) , H(+) , and OH(-) ions were observed, and the equilibria among these ions and the phosphatidylcholine-phosphatidylglycerol membrane surface were quantified. We proposed a mathematical model for characterizing these equilibria. Using this model, together with experimental data of the membrane surface charge density, we determined association constants characterizing the equilibria. Knowledge of these parameters was necessary to calculate the theoretical curves of the model. We validated the model by curve-fitting the experimental data points to simulated data generated by the model.

Concepts: Electron, Electric charge, Mathematics, Fundamental physics concepts, Electrostatics, Membrane biology, Electrolyte, Charge density


Magnesium silicate as a high-performance adsorption material has attracted increasing attention for the removal of organic dye pollution. Here, we prepared a series of magnesium silicate hydrates (MSH) in a hydrothermal route, and carefully investigated the corresponding adsorption behavior towards methylene blue (MB) as well as the effect of surface charge on adsorption capacity. The results show that surface charge plays a key role in the adsorption performance of MSH for MB, a negative surface charge density follows the increase of Si/Mg feeding ratio from 1.00 to 1.75, and furthermore the higher negative charge favors the improvement of the adsorption capacity. Among four investigated samples (MSH = 1.00, 1.25, 1.50, and 1.75), MSH-1.75 has the highest negative surface charge and shows the largest adsorption capacity for MB. For example, the equilibrium adsorption quantity is 307 mg·g−1 for MSH-1.75, which is 35% higher than that of 227 mg·g−1 for MSH-1.00. Besides, for MSH-1.75, the as-prepared sample with negative charge exhibits ca. 36% higher adsorption quantity compared to the sample at the zero point of charge (pHZPC). Furthermore, magnesium silicate hydrate material with Si/Mg feeding ratio = 1.75 demonstrates the promising removal efficiency of beyond 98% for methylene blue in 10 min, and the maximum adsorption capacity of 374 mg·g−1 calculated from the Langmuir isotherm model.

Concepts: Electric charge, Fundamental physics concepts, Density, Electrostatics, Adsorption, Surface chemistry, Charge density, Current density


Tick-borne Babesia parasites are responsible for costly diseases worldwide. Improved control and prevention tools are urgently needed, but development of such tools is limited by numerous gaps in knowledge of the parasite-host relationships. We hereby used atomic force microscopy (AFM) and frequency-modulated Kelvin probe potential microscopy (FM-KPFM) techniques to compare size, texture, roughness and surface potential of normal and infected Babesia bovis, B. bigemina and B. caballi erythrocytes to better understand the physical properties of these parasites. In addition, AFM and FM-KPFM allowed a detailed view of extraerythrocytic merozoites revealing shape, topography and surface potential of paired and single parasites. B. bovis-infected erythrocytes display distinct surface texture and overall roughness compared to noninfected erythrocytes. Interestingly, B. caballi-infected erythrocytes do not display the surface ridges typical in B. bovis parasites. Observations of extraerythrocytic B. bovis, B. bigemina and B. caballi merozoites using AFM revealed differences in size and shape between these three parasites. Finally, similar to what was previously observed for Plasmodium-infected erythrocytes, FM-KPFM images reveal an unequal electric charge distribution, with higher surface potential above the erythrocyte regions that are likely associated with Babesia parasites than over its remainder regions. In addition, the surface potential of paired extraerythrocytic B. bovis Mo7 merozoites revealed an asymmetric potential distribution. These observations may be important to better understand the unique cytoadhesive properties of B. bovis-infected erythrocytes, and to speculate on the role of differences in the distribution of surface charges in the biology of the parasites.

Concepts: Electric charge, Electricity, Electrostatics, Atom, Force, Scanning probe microscopy, Babesia, Charge density


Electrocatalytic hydrogen evolution reaction (HER) in alkaline solution is hindered by its sluggish kinetics toward water dissociation. Nickel-based catalysts, as low-cost and effective candidates, show great potentials to replace platinum (Pt)-based materials in the alkaline media. The main challenge regarding this type of catalysts is their relatively poor durability. In this work, we conceive and construct a charge-polarized carbon layer derived from carbon quantum dots (CQDs) on Ni3N nanostructure (Ni3N@CQDs) surfaces, which simultaneously exhibit durable and enhanced catalytic activity. The Ni3N@CQDs shows an overpotential of 69 mV at a current density of 10 mA cm-2in a 1 M KOH aqueous solution, lower than that of Pt electrode (116 mV) at the same conditions. Density functional theory (DFT) simulations reveal that Ni3N and interfacial oxygen polarize charge distributions between originally equal C-C bonds in CQDs. The partially negatively charged C sites become effective catalytic centers for the key water dissociation step via the formation of new C-H bond (Volmer step) and thus boost the HER activity. Furthermore, the coated carbon is also found to protect interior Ni3N from oxidization/hydroxylation and therefore guarantees its durability. This work provides a practical design of robust and durable HER electrocatalysts based on nonprecious metals.

Concepts: Electric charge, Chemical reaction, Water, Hydrogen, Catalysis, Chemistry, Haber process, Charge density


Chitosan (CS) is an abundant and renewable polysaccharide that is reported to exhibit a great variety of beneficial properties. However, the poor solubility of chitosan in water limits its applications. In this paper, we successfully synthesized singleN-quaternized (QCS) and doubleN-diquaternized (DQCS) chitosan derivatives, and the resulting quaternized materials were water-soluble. The degree of quaternization (DQ) of QCS and DQCS was 0.8 and 1.3, respectively. These derivatives were characterized by FTIR, ¹H NMR,13C NMR, TGA, and SEM. Moreover, the antioxidant activity of the chitosan was evaluated by free radical scavenging ability (against DPPH-radical, hydroxyl-radical, and superoxide-radical) and ferric reducing power. Our results suggested that the antioxidant abilities were in the order of DQCS > QCS > CS, which was consistent with the number of quaternized groups. These data demonstrate that the number of quaternized groups of chitosan derivatives contributes to their antioxidant activity. Therefore, DQCS, with a higher number of quaternized groups and higher positive charge density, is endowed with high antioxidant activity, and can be used as a candidate material in food and pharmaceutical industries.

Concepts: Electric charge, Fundamental physics concepts, Density, Radical, Vitamin C, Materials science, Charge density, Chitosan