This study investigates the chemical and mineralogical composition, particle size distribution, and physical and chemical properties of raw dune sands from the Kushkupyr district of Uzbekistan. The particle size distribution indicates a predominance of particles larger than 0.007 mm, with a fineness modulus of less than one, which classifies these sands as fine-grained. Scanning electron microscopy (SEM) reveals that the sand particles consist primarily of irregularly shaped quartz grains. This work proposes compositions for producing sodium silicate based on a microsilica – dune sand – caustic soda system.
Exploring Pt-free electrocatalysts for hydrogen evolution reaction (HER) is crucial for achieving low-cost hydrogen production. Herein, we present a facile one-pot approach for coconut-driven hierarchical porous carbon nanofibers (h-CNFs) encapsulated metal nanocrystals (M/h-CNFs) (M = Co, Cu, W, Mo, and Bi) by direct impregnation of coconut fibers in metal precursors solution followed by carbonization under argon. Coconut fiber with its rich built-in ether (C-O-C) and hydroxyl (OH) groups, can act as a source for carbon and as a rector to drive the scalable production (several grams) of ultra-long (similar to 100-500 mu m) hierarchical porous nanofibers (multimodal pores), well-distribution of tiny metal nanocrystals (10-20 nm) active sites, and high surface area (275.8 m(2)/g). These merits endowed the electrocatalytic HER performance of M/h-CNFs significantly higher than metal-free h-CNFs, but Co/h-CNFs and Cu/h-CNFs revealed activities close to the commercial Pt/C (10 wt % Pt) catalyst with a current density (similar to 300 mA/cm(2)), low overpotential of (154 mV), and H-2 production rate of (19.5 mol g(-1)& centerdot;h(-1)), although low metal content (i.e., similar to 10 wt %). This study is evidence for paving the way for the conversion of coconut fiber wastes to a cost-effective catalyst for HER.
Searching by numerical simulation for structures with optimal damping properties among viscoelastic hollow cylindrical bodies with a filler is usually associated with a large amount of computation. Formulating the mechanical problem as one of natural vibrations and natural wave propagation makes it possible to evaluate the dissipative properties of such a structure independently of external force and kinematic actions, and thereby to reduce the computational cost substantially. The solution of the natural vibration problem for a piecewise homogeneous viscoelastic hollow cylindrical body with a filler yields complex natural frequencies, the real part of which represents the vibration frequency and the imaginary part the damping factor (attenuation rate). The mechanical behavior of the viscoelastic material is described by the linear Boltzmann–Volterra hereditary theory with a three-parameter Koltunov–Rzhanitsyn relaxation kernel, within which the material characteristics are represented by complex dynamic moduli—the shear modulus and the bulk modulus—that, as a rule, depend on frequency. In the natural vibration problem these moduli become functions of the real part of the sought complex natural frequency alone, which makes the standard eigenvalue procedures of commercial finite-element codes inapplicable. The paper presents an algorithm that removes this difficulty. The dispersion relation of the piecewise homogeneous cylinder is obtained analytically in the form of a complex determinant of order 12 for a two-layer and 18 for a three-layer configuration, the elements of which are Bessel and Neumann functions of complex argument; the global stiffness and mass matrices needed for the general configuration can be assembled automatically in a general-purpose finite-element code such as ABAQUS; the resulting complex characteristic equation is solved by Muller’s method—every iteration of which evaluates the determinant by Gaussian elimination with partial pivoting, so that no expansion of the determinant is required. The efficiency of the algorithm is demonstrated for a two-layer viscoelastic hollow cylindrical body with a filler, the outer load-carrying layer being made of Kh12 steel and the inner layer (the filler) of 30 L steel. The real and imaginary parts of the complex natural frequencies, of the phase velocities and of the attenuation are obtained as functions of the dimensionless wave number, of Poisson’s ratio, of the ratio of the layer radii and of the ratio of the instantaneous elastic moduli of the layers.
Ushbu ishda rektifikatsion kolonnani boshqarishda PID rostlagich va noqat’iy mantiqni birgalikda qo'llash imkoniyati o'rganildi. Tadqiqotdan ko'zlangan maqsad xatolik hamda uning o'zgarishiga qarab boshqaruv signalini tuzatadigan noqat’iy modelni ishlab chiqish va uni oddiy PID rostlagich bilan taqqoslashdan iborat. Obyekt ikkinchi tartibli uzatish funksiyasi ko'rinishida olindi, modellashtirish esa MATLAB/Simulink muhitida 300s davomida bajarildi. Tizimlar o'rnatilish vaqti, maksimal oshib ketish, statik xatolik va barqarorlashish vaqti bo'yicha baholandi. Hisoblash natijalarida noqat’iy-PID boshqaruv o'rnatilish vaqtini 45s dan 28s gacha, maksimal oshib ketishni 14 % dan 4 % gacha, statik xatolikni 1,8 % dan 0,3 % gacha va barqarorlashish vaqtini 52s dan 31s gacha kamaytirdi. Demak, tanlangan model sharoitida noqatiy tuzatish PID rostlagichning o'tish jarayonini sezilarli yaxshilaydi.
The potential of insect-derived chitosan, particularly from the black soldier fly (Hermetia illucens L.), as a sustainable resource for food packaging is attracting growing interest within the food industry. In this study, we have developed a biodegradable, antibacterial food packaging material, incorporating black soldier fly chitosan (BSCS), glycerol (GC), and glacial acetic acid (AA) as key components. The resulting film exhibits excellent uniformity and compatibility, which is confirmed by SEM (uniform microstructure), FTIR (strong intermolecular hydrogen bonding) and XRD (amorphous network structure), with strong inter-molecular hydrogen bonding interactions between BSCS, GC, and AA, which facilitate the formation of an amorphous network structure. When compared to commercial chitosan-based films, the BSCS-based composite with a deacetylation degree of 97.6% similar to 98.4% demonstrates notable improvements in thermal stability (15.2% higher) and biodegradability (13.7% higher). The composite films further display robust antioxidant and antibacterial properties, with the film prepared showing the most superior performance. Additionally, the composite film effectively retards the spoilage of cherry tomatoes, reducing the weight loss rate by 11.35% during 10 days of storage and extending their shelf life by 4 similar to 6 days. This biodegradable, active packaging material derived from black soldier fly chitosan presents a promising alternative to petroleum-based packaging and holds considerable potential for applications in fruit preservation.
