Abstract FDM 3D printing process is subject to a variety of adjustable parameters that significantly influence the structure and quality of the printed samples. In this study, we undertook a thorough examination of how different nozzle types, in conjunction with specific software settings, affect the structural uniformity of the printed samples. Our evaluation criterion focused on achieving and analyzing extruded filament fibers (f-fibers) with minimal width. To accomplish this, we systematically modified various printing parameters and evaluated the quality of the f-fiber structure at each stage. Key parameters tested included print temperature, nozzle-to-bed distance, programmed line width, nozzle design and its construction material composition. For each parameter examined, a distinct hypothesis was formulated, followed by results that encompassed both visual macro photographs and analytical conclusions elucidating our observations. This research empowers 3D printing professionals to assess how individual print settings or the morphology of specific nozzles can impact the final output.
Numerical method for solving the problems of nonstationary vibrations for structural members made of electroelastic functionally graded material is presented taking into account electromechanical losses and interaction with the acoustic medium. Universal numerical approach is used for studying the vibrations of plane layers, cylinders, and spheres. It is based on finite-difference expressions. To take into account the dissipative characteristics of the material, the Kelvin–Voigt viscoelasticity model is used for the case of electroelasticity. Similar to complex moduli, the mechanical, dielectric, and piezoelectric damping coefficients are introduced to account for mechanical and electrical losses. Numerical studies of the behavior of functionally inhomogeneous cylinders and spheres under the action of nonstationary electrical load have shown that mechanical losses have the greatest effect on the damping of vibrations. It is concluded that taking into account energy dissipation according to the viscoelastic Kelvin–Voigt model with experimentally substantiated damping coefficients allows modeling the vibrations of piezoelectric elements with sufficient accuracy. The dependence of the logarithmic decrements of vibrations on the polymer fraction and the geometric dimensions of the cylinder is studied. The damping of vibrations of a piezoelectric sphere immersed in the fluid under electrical load of a step-like profile is analyzed. It is established that the damping of vibrations occurs in this case more than ten times faster than when accounting for internal mechanical losses without the acoustic medium.
We consider an extended variant of the classical coupon collector's problem with infinite number of collections. An arriving coupon is placed in the $r^{th}$ collection, $r\ge0$, if $r$ is the smallest index such that the corresponding collection still does not have a coupon of this type. We derive distributional limit theorems for the number of empty spots in different collections at the time when the $0^{th}$ collection was completed, as well as after some delay. We also obtain limiting distributions for completion times of different collections. All main results are given in an ultimate infinite-dimensional form in the sense of distributional convergence in $\mathbb R^\infty$. The main tool in the proofs is convergence of specially constructed point processes.
Ceramic membranes based on natural clays are attractive for water treatment, yet their fabrication by selective laser sintering (SLS) remains largely unexplored. In this work, bentonite-based porous ceramic supports were produced by SLS of 65 vol% bentonite / 35 vol% polyamide-12 (PA12) powder mixture followed by thermal removal of the polymer. The SLS parameters were adjusted to obtain defect-free green bodies with anisotropic expansion relative to the CAD model (-4.6% to-8% in length, width and +33.3% in thickness), whereas subsequent sintering at 950 degrees C yielded porous supports with net linear shrinkage of about 6-8.5% in-plane and almost no change in thickness. XRD and FTIR show that the layered montmorillonite structure is destroyed during firing and transformed into an amorphous aluminosilicate matrix with quartz as the main crystalline phase, while the disappearance of PA12 bands confirms complete binder removal. SEM/EDS reveal a transition from a plate-like aluminosilicate-polymer composite with intergranular macroporosity to a chemically homogeneous aluminosilicate ceramic with an open, interconnected macropore network (10-50 mu m). TG/DSC analysis locates the main PA12 degradation between 400 and 600 degrees C, defining the critical window for controlled binder burnout. Nitrogen adsorption-desorption demonstrates the evolution from a predominantly mesoporous green body with low pore volume to a mainly macroporous support with more than a twofold increase in total pore volume. These results demonstrate the feasibility of SLS for fabricating bentonite-based porous ceramic supports as precursors for functional ceramic membranes and provide a basis for further optimisation of composition, printing and sintering parameters.
Nuclear Power Plants (NPPs) equipped with Light- and Heavy-Water-cooled nuclear-power Reactors (LWRs and HWRs) (95% of 442 reactors) have thermal efficiencies within 26-38%, which are significantly lower than those achieved at Thermal Power Plants (ThPPs), i.e., up to 55% for SuperCritical Pressure (SCP) coal-fired PPs and up to 62.5% for combined-cycle PPs. Enhancing the efficiency of next-generation - Generation-IV nuclear-powerreactors NPPs is crucial for the modern nuclear-power industry. The conventional approach to increasing thermal efficiency of NPPs with LWRs and HWRs involves transitioning from SubCPs to SCPs, a strategy employed in the thermal-power industry over 60 years ago. Largecapacity SuperCritical Water-cooled Reactors (SCWRs) and SCP Small Modular Reactors (SMRs) are currently under development, necessitating a comprehensive understanding of heat transfer at SCPs. Therefore, as the first step towards our knowledge of the SC-Heat-Transfer (HT) specifics of the experimental data obtained in vertical short 1-, 3-, and 7-rod bundles (all heated rods are equipped with 4 helical ribs) cooled with SCW upward flow have been used. This dataset was obtained by Dr. V. Razumovskiy1 and his co-workers at the National Technical University of Ukraine, at several SCW pressures: 22.6; 24.5; and 27.5 MPa, mass flux within the range of 800-2700 kg/m2s, heat flux within 720-3200 kW/m2 and with upward flow in short vertical bundles (heated length 0.485 m). The current paper is dedicated to the analysis of these data.
