Copper-doped silica cuprous sulfate (CDSCS) as a highly efficient and new heterogeneous nano catalyst for [3+2] Huisgen cycloaddition

The synthesis and characterization of copper-doped silica cuprous sulfate (CDSCS) as a new and efficient heterogeneous nano catalyst are described. CDSCS has been fully characterized by different microscopic, spectroscopic and physical techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic forced microscopy (AFM), X-ray diffraction (XRD), inductively coupled plasma (ICP) analysis, thermogravimetric analysis (TGA) and FT-IR. CDSCS is proved to be a useful heterogeneous nano catalyst in Cu(I)-catalyzed ‘Click’ cycloaddition of organic azides with terminal alkynes. CDSCS catalyzes the 1,3-dipolar cycloaddition reactions of β-azido alcohols and alkynes at room temperature, in THF/H₂O (1:1, v/v) solution. Using CDSCS, 1,4-disubstituted 1,2,3-triazole adducts are mainly obtained, in good to excellent yields and in short reaction times. These compounds have featural resemblance to β-adrenoceptor blocking agents. CDSCS was approved as a chemically and thermally stable nano catalyst that can be reused for many consecutive trials without a significant decline in its reactivity.     

Adaptive fuzzy sliding mode control scheme for uncertain systems

Most physical systems inherently contain nonlinearities which are commonly unknown to the system designer. Therefore, in modeling and analysis of such dynamic systems, one needs to handle unknown nonlinearities and/or uncertain parameters. This paper proposes a new adaptive tracking fuzzy sliding mode controller for a class of nonlinear systems in the presence of uncertainties and external disturbances. The main contribution of the proposed method is that the structure of the controlled system is partially unknown and does not require the bounds of uncertainty and disturbance of the system to be known; meanwhile, the chattering phenomenon that frequently appears in the conventional variable structure systems is also eliminated without deteriorating the system robustness. The performance of the proposed approach is evaluated for two well-known benchmark problems. The simulation results illustrate the effectiveness of our proposed controller.     

Systematically engineered electrospun conduit based on PGA/collagen/bioglass nanocomposites: The evaluation of morphological,mechanical, and bio‐properties

Peripheral nerve injury can considerably affect the daily life of affected people through reduced function and permanent deformation of the nerve. One of the conventional treatments used for the management of the disease is the application of autograft, which is recognized as a golden standard method; however, the process of gaining access to autograft has posed a significant challenge to its use. Nerve guidance channels (conduits), which are made in different methods, can act as an alternative therapy for patients that have undergone nerve injury; but, achieving these conduits has always been a major dilemma to be applied for patients with nerve injury. In this study, a novel conduit based on polymer blend nanocomposites of polyglycolic acid (PGA), collagen, and nanobioglass (NBG) were prepared by electrospinning technique and then compared with PGA/collagen and PGA conduits that were made in previous studies. Additionally, their various properties were characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD), contact angle, dynamic mechanical thermal analysis (DMTA), tensile strength, Fourier‐transform infrared (FTIR), and the porosity and degradation. The results showed that the mechanical, chemical, biocompatibility, and biodegradability properties of PGA/collagen/NBG conduits were more favorable in comparison with other materials. According to 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) assay and 4′,6‐diamidino‐2‐phenylindole (DAPI) staining technique, nanofibrous electrospun PGA/collagen/NBG conduits are more suitable for cell adhesion and proliferation in comparison with either PGA or PGA/collagen conduits and can have potential for nerve regeneration.     

Crystal structure and physical properties of a new CuTi2S4 modification in comparison to the thiospinel

A new modification of CuTi(2)S(4) was prepared from the elements at 425 degrees C. It crystallizes in the rhombohedral space group Rm, with lattice parameters of a = 7.0242(4) A, c = 34.834(4) A, and V = 1488.4(2) A(3) (Z = 12). Two topologically different interlayer regions exist between the close-packed S layers that alternate along the c axis: one comprises both Cu (in tetrahedral voids) and Ti atoms (in octahedral voids), and the second exclusively Ti atoms (again in octahedral voids). In contrast to the known modification, the spinel, Cu-Ti interactions of 2.88 A occur that have bonding character according to the electronic structure calculations. Both CuTi(2)S(4) modifications are metallic Pauli paramagnets due to Ti d contributions. The Pauli susceptibility of the Rm form is larger than that of the thiospinel in quantitative agreement with the LMTO-ASA band structure calculations. The irreversible transformation to the spinel takes place at temperatures above 450 degrees C.     

Speciation analysis of mercury in water samples by cold vapor atomic absorption spectrometry after preconcentration with dithizone immobilized on microcrystalline naphthalene

Trace amounts of inorganic mercury (Hg²⁺) and methylmercury cations (MeHg²⁺) were adsorbed quantitatively from acidic aqueous solution onto a column packed with immobilized dithizone on microcrystalline naphthalene. The trapped mercury was eluted with 10 ml of 7 mol L^–1 hydrochloric acid solution. The Hg²⁺ was then directly reduced with tin (II) chloride, and volatilized mercury was determined by cold vapor atomic absorption spectrometry (CVAAS). Total mercury (Hgt) was determined after decomposition of MeHg⁺ into Hg²⁺. Hg²⁺ and MeHg⁺ cations were completely recovered from the water with a preconcentration factor of 200. The relative standard deviation obtained for eight replicate determinations at a concentration of 0.3 g L^–1 was 1.8%. The procedure was applied to analysis of water samples, and the accuracy was assessed via recovery experiment.     

Preparation of protein gradients through the controlled deposition of protein-nanoparticle conjugates onto functionalized surfaces

This paper describes a simple method for the preparation and characterization of protein density gradients on solid supports. The method employs colloidal metal nanoparticles as protein carriers and optical tags and is capable of forming linear, exponential, 1D, 2D, and multiprotein gradients of varying slope without expensive or sophisticated surface patterning techniques. Surfaces patterned with proteins using the procedures described within are shown to support cell growth and are thus suitable for studies of protein-cell interactions.     

‘Click Synthesis’ of Some Novel Benzimidazol Oxime Ethers Containing Heterocycle Residues as Potential ß‐Adrenergic Blocking Agents

The ‘click synthesis’ of some novel O‐substituted oximes, 5a – 5j , which contain heterocycle residues, as new analogs of ß‐adrenoceptor antagonists is described (Scheme 1). The synthesis of these compounds was achieved in four steps. The formation of (E)‐2‐(1H‐benzo[d]imidazol‐1‐yl)‐1‐phenylethanone oxime, followed by their reaction with 2‐(chloromethyl)oxirane, afforded mixture of oil compounds 3 and 4 , which by a subsequent tetra‐n‐butylammonium bromide (TBAB)‐catalyzed reaction with N H heterocycle compounds (Scheme 1), led to the target compounds 5a – 5j in good yields.     

A fractional-order model for the novel coronavirus (COVID-19) outbreak

Nonlinear Dynamics - The outbreak of the novel coronavirus (COVID-19), which was firstly reported in China, has affected many countries worldwide. To understand and predict the transmission...     

Curing Kinetics Modeling of Epoxy Modified by Fully Vulcanized Elastomer Nanoparticles Using Rheometry Method

In this study, the curing kinetics of epoxy nanocomposites containing ultra-fine full-vulcanized acrylonitrile butadiene rubber nanoparticles (UFNBRP) at different concentrations of 0, 0.5, 1 and 1.5 wt.% was investigated. In addition, the effect of curing temperatures was studied based on the rheological method under isothermal conditions. The epoxy resin/UFNBRP nanocomposites were characterized via Fourier transform infrared spectroscopy (FTIR). FTIR analysis exhibited the successful preparation of epoxy resin/UFNBRP, due to the existence of the UFNBRP characteristic peaks in the final product spectrum. The morphological structure of the epoxy resin/UFNBRP nanocomposites was investigated by both field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) studies. The FESEM and TEM studies showed UFNBRP had a spherical structure and was well dispersed in epoxy resin. The chemorheological analysis showed that due to the interactions between UFNBRP and epoxy resin, by increasing UFNBRP concentration at a constant temperature (65, 70 and 75 °C), the curing rate decreases at the gel point. Furthermore, both the curing kinetics modeling and chemorheological analysis demonstrated that the incorporation of 0.5% UFNBRP in epoxy resin matrix reduces the activation energy. The curing kinetic of epoxy resin/UFNBRP nanocomposite was best fitted with the Sestak–Berggren autocatalytic model.     

The 2 × 1 reconstruction of the rutile TiO2(0 1 1) surface: A combined density functional theory, X-ray diffraction, and scanning tunneling microscopy study

An extensive search for possible structural models of the (2 × 1)-reconstructed rutile TiO₂(0 1 1) surface was carried out by means of density functional theory (DFT) calculations. A number of models were identified that have much lower surface energies than the previously-proposed ‘titanyl’ and ‘microfaceting’ models. These new structures were tested with surface X-ray diffraction (SXRD) and voltage-dependent STM measurements. The model that is (by far) energetically most stable shows also the best agreement with SXRD data. Calculated STM images agree with the experimental ones for appropriate tunneling conditions. In contrast to previously-proposed models, this structure is not of missing-row type; because of its similarity to the fully optimized brookite TiO₂(0 0 1) surface, we call it the ‘brookite (0 0 1)-like’ model. The new surface structure exhibits two different types of undercoordinated oxygen and titanium atoms, and is, in its stoichiometric form, predicted to be rather inert towards the adsorption of probe molecules.