Temperature Dependence of the Electrical Properties of Na2Ti3O7/Na2Ti6O13/POMA Composites

The temperature dependence of the electrical properties of composites formed by biphasic sodium titanate and poly(o-methoxyaniline) (Na₂Ti₃O₇/Na₂Ti₆O₁₃/POMA) with different concentrations of POMA (0%, 1%, 10%, 15%, 35% and 50%) in the ceramic matrix was determined from measurements of complex impedance. The structural details were studied by means of X-ray diffraction, confirming the formation of the Na₂Ti₃O₇/Na₂Ti₆O₁₃/POMA composites. The displacement of the (200) reflection from 2θ = 10.45° to 11.15° in the composites with 10 and 15% of POMA suggested the partial replacement of H⁺ for Na⁺ in the Na₂Ti₃O₇ structure. The thermal properties were investigated by Thermogravimetry and Differential Thermal Analysis. The Thermogravimetry curves of the composites with POMA content of 1, 10 and 15% presented profiles similar to that of pure sodium titanate sample. The composites with 35 and 50% of POMA showed a process at temperatures around 60–70 °C, which was associated with water absorbed by the polymer. The analysis of the complex impedance spectroscopy measurements revealed that the electrical resistivity of the composites in the range from 0 to 35% increased by two orders of magnitude, with different values for each concentration. This positive temperature coefficient of resistivity was less noticeable in the composite with highest POMA mass content (50%). The rapid increase in resistivity caused an increase in the relaxation time calculated from the time domain. The electrical response of the 50% of POMA compound changes in relation to what was observed in the other compounds, which suggests that there is a saturation limit in the increase in resistivity with POMA content.     

An appraisal of experimental designs: Application to enantioselective capillary electromigration techniques

Enantioresolution processes are vital tools for investigating the enantioselectivities of chiral compounds. An analyst resolves to optimize enantioresolution conditions once they are determined. Generally, optimization is conducted by a one-factor-at-a-time (OFAT) approach. Although this approach may determine an adequate condition for the method, it does not often allow the estimation of the real optimum condition. Experimental designs are conducive for the optimization of enantioresolution methods via capillary electromigration techniques (CETs). They can efficiently extract information from the behavior of a method and enable the estimation of the real optimum condition. Furthermore, the application of the analytical quality by design (AQbD) approach to the development of CET-based enantioselective methods is a trend. This article (i) offers an overview of the application of experimental designs to the development of enantioselective methods from 2015 to mid-2020, (ii) reveals the experimental designs that are presently employed in CET-based enantioresolutions, and (iii) offers a critical point of view on how the different experimental designs can aid the optimization of enantioresolution processes by considering the method parameters.     

Carbon black-chitosan film-based electrochemical sensor for losartan

Journal of Solid State Electrochemistry - A novel electrochemical method for determination of losartan using a glassy carbon electrode modified with carbon black nanoparticles immobilized within a...     

A mathematical study of the tethered slingshot maneuver using the elliptic restricted problem

Nonlinear Dynamics - The main objective of the present paper is to find the modifications that a tethered slingshot maneuver (TSSM) can make in the orbit of a spacecraft, both in terms of energy...     

Ion‐Conductive,Viscosity‐Tunable Hexagonal Boron Nitride Nanosheet Inks

Liquid‐phase exfoliation of layered solids holds promise for the scalable production of 2D nanosheets. When combined with suitable solvents and stabilizing polymers, the rheology of the resulting nanosheet dispersions can be tuned for a variety of additive manufacturing methods. While significant progress is made in the development of electrically conductive nanosheet inks, minimal effort is applied to ion‐conductive nanosheet inks despite their central role in energy storage applications. Here, the formulation of viscosity‐tunable hexagonal boron nitride (hBN) inks compatible with a wide range of printing methods that span the spectrum from low‐viscosity inkjet printing to high‐viscosity blade coating is demonstrated. The inks are prepared by liquid‐phase exfoliation with ethyl cellulose as the polymer dispersant and stabilizer. Thermal annealing of the printed structures volatilizes the polymer, resulting in a porous microstructure and the formation of a nanoscale carbonaceous coating on the hBN nanosheets, which promotes high wettability to battery electrolytes. The final result is a printed hBN nanosheet film that possesses high ionic conductivity, chemical and thermal stability, and electrically insulating character, which are ideal characteristics for printable battery components such as separators. Indeed, lithium‐ion battery cells based on printed hBN separators reveal enhanced electrochemical performance that exceeds commercial polymer separators.     

Photoelectrochemical biosensing platform for the SARS-CoV-2 spike and nucleocapsid proteins

The COVID-19 pandemic is still a continuing worldwide challenge for public health systems. Early and ultrasensitive identification of the infection is essential for preventing the spread of COVID-19 by pre-symptomatic or asymptomatic individuals, particularly in the community and in-home settings. This work presents a versatile photoelectrochemical (PEC) immunosensor for SARS-CoV-2 detection based on a composite material formed by bismuth vanadate (BiVO₄) and strontium titanate (SrTiO₃). The PEC platform was denoted as BiVO₄/SrTiO₃/FTO, and it can be tuned for the detection of either Spike (S) or Nucleocapsid (N) protein by simply altering the antibody immobilized on the platform's surface. Chemical, morphological, and electrochemical characterizations were performed by X-Ray Diffraction, Scanning Electron microscopy, Energy-dispersive X-ray spectroscopy, Electrochemical Impedance Spectroscopy, and Amperometry. With a simple sensing architecture of the PEC platform, it was possible to achieve a linear response range of 0.1 pg mL⁻¹ to 1000 ng mL⁻¹ for S protein and 0.01 pg mL⁻¹ to 1000 ng mL⁻¹ for N protein. The PEC immunosensors presented recovery values for the two SARS-CoV-2 proteins in artificial saliva samples between 97 % and 107.20 % suggesting a good accuracy for the proposed immunosensors.     

Electron spin echo modulation and relaxation in polythiophene

Electron spin echo measurements on neutral poly (thiophene) show a clear modulation of the spin-echo decay. Analysis of the modulation and its Fourier transformed (ω) power spectrum indicates that the wave function of the spin defect is extended over ～ 25 proton nuclei. The functional behavior of the longitudinal relaxation, T₁, versus temperature is very similar to that observed previously for (CH)_x, although T₁ values for poly (thiophene) are significantly longer.     

Histochemical and ultrastructural study of collagen fibers in mouse pubic symphysis during late pregnancy

Reference is usually made to the parallel orientation towards the main line of exerted tension at the pubic joint in mice, for supporting forces applied to the joint. Despite the wealth of morphological information about the extracellular matrix in this joint, little is known regarding the involvement of the crimp of collagen fibers in the dramatic transformations occurring in this region during the last 3 days of pregnancy. Examination of the collagenous architecture suggests that the biomechanical properties are directly related to fibril diameters, composition of ground substance and changes in the bundle morphology, particularly in the crimp structure. The purpose of this study was to further describe the transformation of the collagen fibers of the pubic symphysis during late mouse pregnancy. We examined the architecture of collagen fibers in the symphysis and pubic ligament through the Picrosirius-polarization method and also through scanning electron microscopy to directly visualize and measure the crimping from pregnant and virgin mice. The crimp angle and the length of five consecutive crimps were measured according to Patterson-Kane et al. [Connect. Tissue Res. 36 (1997) 253]. It could be demonstrated that the angles progressively decreased and the crimp length increased, denoting that the fibers have untwisted during the relaxation process. Our findings suggest that a disruption of the helical arrangement of the collagen containing fibers may contribute to explaining the rapid remodeling that occurs at the end of pregnancy and that is responsible for an increase in pliancy and length of the pubic ligament in mice.     

Three-dimensional sand ripples as the product of vortex instability

Three-dimensional sand ripples can be observed under steady liquid flows in both nature and industry. Some examples are the ripples observed on the bed of rivers and in petroleum pipelines conveying sand. Although of importance, the formation of these patterns is not completely understood. There are theoretical and experimental evidence that aquatic ripples grow from two-dimensional bed instabilities, so that a straight vortex is formed just downstream of their crests. The proposition of Raudkivi (2006) [18], that three-dimensionality has its origin in a vortex instability, is employed here. This paper presents a linear stability analysis of the downstream vortex in order to obtain the transverse scales of three-dimensional ripples. The obtained wavelength is compared with experimentally observed ripples.     

Immobilization of Cyclodextringlycosyltransferase (CGTase) from Bacillus firmus in Commercial Chitosan

The enzyme cyclodextringlycosyltransferase (CGTase) was immobilized in commercial chitosan with different methods of immobilization at different temperatures, with the aim of obtaining a product with improved activity and higher recovery of the free enzyme activity. Three immobilization methods were tested: adsorption, covalent bonding with -aminopropyltriethoxysilane (CB-APTS), and covalent bonding with hexamethylenediamine (BC-HEMDA). Two test conditions were used, 7 °C without agitation and 26 °C with stirring. The best results were obtained with the method that uses HEMDA as the bifunctional covalent binding agent, giving the highest immobilized enzyme specific activity, 0.263 mol -CD/min mg of protein, and highest enzyme activity recovery, 5.2%, when immobilization was carried out at 7 °C.