Search Results (10)

Estrogens in aquatic environments pose significant ecological and health risks due to their cumulative effects rather than individual impacts. This study investigates the voltammetric behavior of estrone (E1), 17β-estradiol (E2), estriol (E3), and 17α-ethinylestradiol (EE2), presenting a cost-effective and straightforward method for their simultaneous determination. Using differential pulse voltammetry (DPV) with a boron-doped diamond electrode, the method demonstrates high precision (deviations under 4%) and a linear dynamic range of 15.35–134.55 µmol·L⁻¹. Integration of a vacuum evaporation step reduced detection limits to 10⁻⁸ mol·L⁻¹, enabling effective analysis of real water samples. This optimized approach ensures practical applicability for monitoring total estrogen content in aquatic systems, providing an accessible and reliable alternative to conventional methods. Full article

The surface cold working (SCW) of austenitic stainless steel (SS) causes martensitic transformation in the surface layers, and the percentage fraction of the strain-induced martensite depends on the degree of SCW. Higher content of α′−martensite increases the surface micro-hardness and fatigue strength, but deterioration of the corrosion resistance is possible. Therefore, the desired operational behaviour of austenitic SS can be ensured by the corresponding degree of SCW and heat treatment. This article evaluates the effects of SCW performed by diamond burnishing (DB) and heat treatment on the surface integrity (SI), rotating fatigue strength, and corrosion resistance of AISI 304 austenitic SS for two initial states: as-received hot-rolled bar and initially heat-treated at 1100 °C for one hour followed by quenching in water. Then, DB was implemented as a smoothing and hardening process, both alone and in combination with heat treatment at 350 °C for three hours after DB. The electrochemical performance was examined by open circuit potential measurements, followed by potentiodynamic tests. For both initial states, smoothing DB provided the lowest roughness, whereas an improvement in the maximum surface micro-hardness was obtained after hardening DB and subsequent heat treatment. The maximum fatigue strength was obtained by hardening multi-pass DB without subsequent heat treatment for the as-received initial state. Smoothing DB and subsequent heat treatment maximised the surface corrosion resistance for the two initial states, whereas a minimum corrosion rate was obtained for the initially heat-treated state. For the as-received state, smoothing DB and subsequent heat treatment simultaneously lead to a high fatigue limit (equal to that obtained by hardening single-pass DB) and a low corrosion rate. Full article

Fe-Cu-Co prealloyed powder is used for bonding metal of diamond tools. In order to obtain diamond tools with good mechanical properties by pressureless sintering, it is necessary to add Cu-Sn sintering aids. The substrate also has high corrosion resistance requirements, which is conducive to the chemical erosion of diamond tools. This paper mainly studies the effects of Cu-Sn on the corrosion behavior of pressureless sintered Fe-Cu-Co substrate. The results show that the linear contraction rate and relative density of pressureless sintered Fe-Cu-Co alloy at 875 °C reach their peak when the Cu-Sn content is 8 wt.%, 15.13% and 97.5%, respectively. The substrate is mainly composed of α-Fe and Cu-rich phases, and selective corrosion occurs during electrochemical corrosion; namely, α-Fe grains are more prone to corrosion than Cu-rich grains to form porous corrosion surfaces. With the increase in Cu-Sn addition, the volume fraction of the Cu-rich phase increases, the corrosion current density and the passive current density gradually decrease, and the corrosion resistance of the alloy is improved. The amount and integrity of anodic passive film on the Fe-Cu-Co surface increases with the increase in Cu-Sn addition. The oxygen content of the anodic passivation film is lower than that of the active corrosion products of the α-Fe phase, thus reducing the oxygen concentration gradient and slowing down the corrosion. The addition of Cu-Sn is conducive to improving the corrosion resistance of Fe-Cu-Co alloy as the substrate of diamond tools. Full article

In the present article, we prove some new generalizations of dynamic inequalities of Hardy-type by utilizing diamond-$\alpha$ dynamic integrals on time scales. Furthermore, new generalizations of dynamic inequalities of Hardy-type in two variables on time scales are proved. Moreover, we present Hardy inequalities for several functions by using the diamond-$\alpha$ dynamic integrals on time scales. The results are proved by using the dynamic Jensen inequality and the Fubini theorem on time scales. Our main results extend existing results of the integral and discrete Hardy-type inequalities. Symmetry plays an essential role in determining the correct methods to solve dynamic inequalities. Full article

In this paper, we extend some Steffensen-type inequalities to time scales by using the diamond-$\alpha$-dynamic integral. Further, we prove some new Steffensen-type inequalities for convex functions utilizing positive $\sigma$-finite measures in time scale calculus. Moreover, as a special case, we obtain these inequalities for the delta and the nabla integral. By using the relation between calculus on time scales $\mathbb{T}$ and differential calculus on $\mathbb{R}$, we obtain already-known Steffensen-type inequalities. Full article

The motivation of this paper is to explore some new inequalities of Steffensen-type which were demonstrated by Pečarić and Kalamir in 2014. The main idea is to investigate a class of certain inequalities by employing diamond-$\alpha$ dynamic integral on time scales. In addition, to obtain some new inequalities as special cases, we also extend our results to continuous and discrete calculations. Full article

This work is motivated by the work of Josip Pečarić in 2013 and 1982 and the work of Srivastava in 2017. By the utilization of the diamond-$\alpha$ dynamic inequalities, which are defined as a linear mixture of the delta and nabla integrals, we present and prove very important generalized results of diamond-$\alpha$ Steffensen-type inequalities on a general time scale. Symmetry plays an essential role in determining the correct methods to solve dynamic inequalities. Full article

Integral equations and inequalities have an important place in time scales and harmonic analysis. The norm of integral operators is one of the important study topics in harmonic analysis. Using the norms in different variable exponent spaces, the boundedness or compactness of the integral operators are examined. However, the norm of integral operators on time scales has been a matter of curiosity to us. In this study, we prove the equivalence of the norm of the restricted centered fractional maximal diamond-$\alpha$ integral operator ${\mathrm{M}}_{\mathrm{a},\mathsf{\delta }}^{\mathrm{c}}$ to the norm of the centered fractional maximal diamond-$\alpha$ integral operator ${\mathrm{M}}_{\mathrm{a}}^{\mathrm{c}}$ on time scales with variable exponent Lebesgue spaces. This study will lead to the study of problems such as the boundedness and compactness of integral operators on time scales. Full article

In this paper, we investigate some new generalizations and refinements for Hölder’s inequality and it’s reverse on time scales through the diamond-$\alpha$ dynamic integral, which is defined as a linear combination of the delta and nabla integrals, which are used in various problems involving symmetry. We develop a number of those symmetric inequalities to a general time scale. Our results as special cases extend some integral dynamic inequalities and Qi’s inequalities achieved on time scales and also include some integral disparities as particular cases when $\mathbb{T}=\mathbb{R}$. Full article