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Laser beam melting process based on complete-melting energy density for commercially pure titanium
摘要： Laser beam melting (LBM) based on the complete-melting energy density for commercially pure titanium (CP-Ti) was investigated. Process parameters were set corresponding to the thermodynamically calculated energy density for full melting of CP-Ti. From the calculated energy density, power of 50–250 W and scan speed of 371–1855 mm/s were derived with the fixed other conditions. Microstructural study on formation of pores was conducted to understand the change in part’s density. Fundamental study with wide range of LBM process parameters, particularly based on the complete-melting energy density, could confirm the effects like high density and porous structure.
关键词： Laser beam melting,Complete-melting,Pure Ti,Energy density,Additive manufacturing
更新于2025-09-12 10:27:22
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Correlations between Process Parameters and Outcome Properties of Laser-Sintered Polyamide
摘要： As additive manufacturing (AM) becomes more accessible, correlating process parameters with geometric and mechanical properties is an important topic. Because the number of process variables in AM is large, extensive studies must be conducted in order to underline every particular influence. The study focuses on two variables—part orientation in the orthogonal horizontal plane and energy density—and targets two outcomes—geometric and tensile properties of the parts. The AM process was conducted on selective laser sintering (SLS) machine EOS Formiga P100 using EOS white powder polyamide (PA2200). After finishing the sinterization process, the parts were postprocessed, measured, weighted, and mechanically tested. The geometric evaluation and mass measurements of every sample allowed us to compute the density of all parts according to the sinterization energy and orientation, and to determine the relative error of every dimension. By conducting the tensile testing, the elastic and strength properties were determined according to process variables. A linear trend regarding sample density and energy density was identified. Also, large relative dimensional errors were recorded for the lowest energy density. Mechanical properties encountered the highest value for the highest energy density at a 45° orientation angle.
关键词： additive manufacturing,sample orientation,laser sintering,energy density,mechanical properties,polymer processing
更新于2025-09-11 14:15:04
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Transmission Spectra of a Symmetric Photonic Crystal Structure with a High-Permittivity Interstitial Layer
摘要： Transmission spectra are recorded for a one-dimensional photonic crystal structure with the permittivity of the interstitial (or cavity) layer exceeding the permittivity of layers in Bragg mirrors by many times. It is shown that the transmission can be suppressed almost completely both in the photonic band gap (except for a narrow defect-mode region) and beyond it. Specific features of the energy density distribution of the wave field over the structure are revealed.
关键词： photonic crystal,transmission spectra,defect mode,high-permittivity interstitial layer,energy density distribution
更新于2025-09-10 09:29:36
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Redox-Mediated Shape-transformation of Fe3O4 Nanoflake to Chemically Stable Au-Fe2O3 Composite Nanorod for High-Performance Asymmetric Solid-State Supercapacitor Device
摘要： Development of a stable and highly active metal oxide based electrochemical supercapacitor is a major challenge. Herein, we report Au-Fe2O3 nanocomposite having tiny amount of gold (3 atomic % Au) by employing a simple redox-mediated synthetic methodology using modified hydrothermal system. Structural and morphological studies of the synthesized Au-Fe2O3 nanocomposite have been performed both experimentally (XRD, IR, Raman, XPS, TEM and FESEM analyses) and theoretically (WIEN2K). A probable dissolution-nucleation-recrystallization growth mechanism has been suggested to explain the morphological transformation from Fe3O4 nanoflake to Au-Fe2O3nanorod. We have observed the superior chemical stability of Au-Fe2O3 nanocomposite in acidic medium due to composite formation. The electrochemical measurement of the synthesized Au-Fe2O3 nanocomposite exhibits specific capacitance of ~570 F g-1 at the current density of 1 A g-1 in 0.5 M H2SO4 electrolyte. The result is superior compared to the mother component i.e., Fe2O3 (138 F g-1) under identical condition. It is credited to its higher specific surface area and composite effect. Theoretically, decrease in band gap associated with increase in conductivity support the superiority of Au-Fe2O3 nanocomposite compared to the mother compound i.e., Fe2O3. In addition, electrochemical kinetic analysis showed that the charge-storage mechanism is mostly from a dominant capacitive process (78 % at 1.5 mV s-1). Solid-state asymmetric supercapacitor device has been fabricated using synthesized Au-Fe2O3 composite nanorod as positive and activated carbon as negative electrodes. The asymmetric solid-state device exhibits maximum energy density of 34.2 Wh kg-1 and power density of 2.73 kW kg-1 at current densities 1 A g-1 and 10 A g-1, respectively. Thus, the synthesized nanocomposite shows excellent activity as a supercapacitor with long term durability (91% capacitance retention) up to 5000 cycles even in acidic medium.
关键词： Shape-transformation,Redox mediated synthesis,Chemical stability,High power density/energy density,Au-Fe2O3 composite nanorod,Asymmetric supercapacitor
更新于2025-09-09 09:28:46
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Heterogeneity governs diameter-dependent toughness and strength in SiC nanowires
摘要： Using a combination of density functional theory and molecular dynamics simulations, this paper reveals the atomistic origin of diameter-dependent extreme mechanical behavior of [111] 3C-SiC nanowires obtained from an energy-based framework. Our results suggest that heterogeneity in atomic stress and variations in diameter-dependent potential-energy density have a profound impact on extreme mechanical properties in the nanowires. The heterogeneity in stress evolves from the nonuniform bond lengths mediated by low coordinated surface atoms—and it penetrates the entire cross section in thinner nanowires and constitutes the atomistic basis for their large reduction in fracture strain, toughness, and strength. Although stress heterogeneity is substantially higher in ultrathin nanowires, its intensity drops and saturates rapidly in larger nanowires following a nonlinear dependence on diameter. The maximum stress heterogeneity in a cross section localizes crack nucleation at the core in ultrathin nanowires but near the surface in larger nanowires. Moreover results show that stiffness, toughness, strength, and fracture strain of the nanowires increase nonlinearly with increasing diameter and saturate at a lower value compared to bulk SiC. In addition to resolving wide discrepancies in the reported values of the ?rst-order elastic modulus in SiC nanowires, the ?ndings highlight heterogeneity as a critical factor for inducing diameter-dependent extreme mechanical behavior in brittle nanowires.
关键词： heterogeneity,atomic stress,strength,toughness,potential-energy density,fracture strain,SiC nanowires,diameter-dependent,mechanical properties
更新于2025-09-09 09:28:46
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ELECTROMAGNETIC FIELD THEORY FOR INVARIANT BEAMS USING SCALAR POTENTIALS
摘要： We present a description of the electromagnetic ?eld for propagation invariant beams using scalar potentials. Fundamental dynamical quantities are obtained: energy density, Poynting vector and Maxwell stress tensor. As an example, all these quantities are explicitly calculated for the Bessel beams, which are invariant beams with circular cylindrical symmetry.
关键词： Poynting vector,scalar potentials,Maxwell stress tensor,propagation invariant beams,Bessel beams,electromagnetic field,energy density
更新于2025-09-09 09:28:46
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Direct comparison of pulsed spark discharges in air and water by synchronized electrical and optical diagnostics
摘要： In this study, a direct comparison was made between pulsed spark discharges in air and water in sub-mm gaps. The discharges were ignited at atmospheric pressure in the same discharge arrangement for air and water, using a solid-state microsecond pulse source with ≈1 μs voltage rise time (Umax up to 37 kV). Fast voltage and current measurements were synchronized with iCCD imaging with high spatial resolution on symmetrical half-sphere tungsten electrodes (electrode gaps of up to 0.7 mm for air and 0.3 mm for water). The breakdown voltage and electrical ?eld strength, maximal current, transferred charge, consumed electrical energy and discharge emission structure (e.g. discharge channel diameters) was obtained for all cases. Using the synchronization of the electrical data and the iCCD imaging, current and energy densities were estimated for the sparks in air and water. It was found that the breakdown voltage, the discharge current, the transferred charge, and the consumed electrical energy increase with the gap distance, and that this dependency is much stronger for discharges in water (compared to air). Due to the use of the same discharge arrangement and the same applied voltage, the di?erence in the discharge characteristics was directly quanti?ed.
关键词： energy density,spark discharges,water,optical diagnostics,breakdown voltage,electrical diagnostics,air,discharge current
更新于2025-09-04 15:30:14
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Enhanced dielectric properties and energy density of flexible KTa0.2Nb0.8O3-BaTiO3/P(VDF-TrFE-CTFE) nanocomposite
摘要： In this work, KTa0.2Nb0.8O3–BaTiO3 (KTN–BT) hybrid nanoparticles were synthesized via a facile one-pot hydrothermal method. Flexible nanocomposite films comprised of poly (vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) P(VDF-TrFE-CTFE) matrix and KTN–BT hybrid fillers of different molar ratio were prepared by solution-casting. It is revealed that the introduction of BT to the KTN causes decreased grain size and homogenous morphology, improving the dielectric constant, breakdown strengthen and energy density of nanocomposite films. Typically, the nanocomposite film containing 40 vol% KTN–BT possesses a dielectric constant of 322 at 100 Hz, which is 8.7 times than that of pure polymer. Also, nanocomposite film with < 10 vol% of filler could achieve high breakdown strength of over 300 MV m?1. The energy density of the film containing 2 vol% KTN–BT filler is 61.4% higher than that of pure P(VDF-TrFE-CTFE) polymer. (7.1 J cm?3 compared to 4.4 J cm?3.) In addition, the nanocomposites also displayed good flexibility and kept excellent dielectric properties after bending and folding. All the improved performance enables these composites to meet the requirements of many flexible electronic devices and energy storage devices.
关键词： KTN–BT,dielectric properties,P(VDF-TrFE-CTFE),nanocomposite,energy density
更新于2025-09-04 15:30:14
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Optimization and Characterization of High-Harmonic Generation for Probing Solid Density Plasmas
摘要： The creation of high energy density plasma states produced during laser–solid interaction on a sub-picosecond timescale opens a way to create astrophysical plasmas in the lab to investigate their properties, such as the frequency-dependent refractive index. Available probes to measure absorption and phase-changes given by the complex refractive index of the plasma state are extreme-UV (EUV) and soft X-ray (XUV) ultra-short pulses from high harmonic generation (HHG). For demanding imaging applications such as single-shot measurements of solid density plasmas, the HHG probe has to be optimized in photon number and characterized in intensity and wavefront stability from shot-to-shot. In an experiment, a coherent EUV source based on HHG driven by a compact diode-pumped laser is optimized in photons per pulse for argon and xenon, and the shot-to-shot intensity stability and wavefront changes are characterized. The experimental results are compared to an analytical model estimating the HHG yield, showing good agreement. The obtained values are compared to available data for solid density plasmas to con?rm the feasibility of HHG as a probe.
关键词： pump-probe,XUV,diode-pumped lasers,high energy density physics,high-harmonic generation
更新于2025-09-04 15:30:14