Density Law Research Articles

Laser waterless cleaning of residual organic solvents on the surface of polyurethane coatings.

Residual organic solvents have a great impact on the physical and mental health of equipment operators in industry and agriculture. Laser waterless cleaning technology of residual organic solvents on the surface of polyurethane coatings has great application prospects and is a good way to tackle the pollution problem. In this paper, the evolutionary behavior of a laser waterless cleaning mechanism and substrate surface state is analyzed. The influence law of laser energy density and scanning speed on the residual solvent cleaning effect was investigated. The optimal laser cleaning parameters were obtained by comprehensive evaluation of the substrate surface cleaning effect and microscopic morphology. The peak of solvent characteristics before and after laser cleaning was detected by Raman spectroscopy. The results demonstrated that the laser cleaning effect was better with the increase of energy density or the decrease of scanning speed in the substrate damage range, and the best laser cleaning parameters were laser energy density of 0.24J/c m 2 and scanning speed of 500mm/s. A significant reduction of the peak of Raman spectroscopy was found, reflecting the excellent effect of laser waterless cleaning of residual organic solvents.

NUMERICAL INVESTIGATION OF PLATE COOLING USING MULTIPLE IMPINGING JETS IN DIFFERENT ALIGNMENTS

In this study, convective heat transfer by multiple impinging jet arrays in different arrangements is numerically investigated using Computational Fluid Dynamics (CFD). Computational domain consists of multiple jet array either in inline or staggered alignment and a target plate to be cooled by impinging jets. Distance between the jet array and the target plate is kept constant at H=28 mm. Diameter of circular jet nozzles is fixed at D=5 mm for all configurations. Effects of jet Reynolds number (Rej), spacing between circular jets and the alignment of the jet nozzles on aerothermal performance are parametrically investigated in the scope of this study. For staggered and inline alignments of the jet nozzles, Rej ranges from 5000 to 20000 and the ratio of the spacing to the jet diameter (s/D) changes between 2 and 6. CFD calculations are performed using finite volume based ANSYS-Fluent flow solver. Simulations are conducted for incompressible, steady and turbulent flow using k-ω SST turbulence model with ideal gas assumption for density and Sutherland law for viscosity. After intensive mesh convergence and validation tests, appropriate mesh resolution is determined and parametric investigations are performed. The study reveals that most dominant parameter for plate cooling is Rej followed by spacing between jets and finally jet alignment. For all Rej, inline jet nozzle alignment provides 15% higher average heat transfer rate than staggered alignment when s/D is close to the lower limit. However, it is shown that jet alignment does not affect thermal performance when s/D is higher.

Temporal-spatial dynamics of electronic plasma in a femtosecond laser-induced sapphire microstructure.

In this study, the time-spatial evolution of single-pulse femtosecond laser-induced plasma in sapphire is studied by using femtosecond time-resolved pump-probe shadowgraphy. Laser-induced sapphire damage occurred when the pump light energy was increased to 20µJ. Based on its shadowgraphy image, the threshold electron density can be estimated to be about 2.48×1020 c m -3. The evolution law of the transient peak electron density and its spatial position as femtosecond laser propagation in sapphire were researched. The transitions from single-focus to multi-focus as the laser focus shifted from the surface to a deeper part were observed from the transient shadowgraphy images. The focal point distance in multi-focus increased as the focal depth increased. The distributions of femtosecond laser-induced free electron plasma and the final microstructure were consistent with each other.

A shockwave calculation method for aluminized explosive of deep water explosion based on the Kirkwood‐Bethe model

AbstractTo calculate the shockwave propagation of deep water explosions for different explosives quickly and accurately, a calculation method, based on the Kirkwood‐Bethe theory, was proposed. At the same time, an underwater explosion experiment of the aluminized explosive was carried out in the pressure vessel under high hydrostatic pressure. Then, the calculated results and experimental results were compared for peak pressure, impulse and energy flux density. The results indicated that the proposed method can quickly and accurately determine the shockwave propagation of deep water explosions for the aluminized explosives, with satisfactory agreement with experimental data. Using the proposed method, the shockwave of aluminized explosive under the conditions of different charge weight, different depth and different distance were calculated, the propagation laws of peak pressure, impulse and energy flux density with depth and distance were obtained. The calculation method proposed could be used to calculate shockwave propagation for any kind of explosive, if only knows the parameters of detonation and JWL equation of state.

Effect of Scanning Strategies on the Microstructure and Mechanical Properties of Ti-22Al-25Nb Alloy Fabricated through Selective Laser Melting

In this study, Ti-22Al-25Nb intermetallic compound alloys are fabricated through selective laser melting (SLM) at four scanning speeds (600, 700, 800, and 900 mm/s). The microstructure and mechanical properties of the selective laser melting fabricated alloys are systematically evaluated. The results indicate that scanning speed significantly affects microstructure characteristics (e.g., relative density, grain size, texture density, and the precipitation of secondary phases). The variation laws of the relative density, grain size, and texture density are likewise affected by scanning speed. The relative density, grain size, and texture density increase and then decrease with the increase in scanning speed. The alloy fabricated with the lowest scanning speed (600 mm/s) exhibits the maximum relative density, grain size, and texture density. By contrast, the alloy with the highest scanning speed (900 mm/s) exhibits the minimum relative density, grain size, and texture density. Furthermore, the precipitations of the O phase and Ti3Al phase are primarily distributed in regions with a high strain concentration near the pool boundary. The alloy fabricated with a 600 mm/s scanning speed simultaneously achieves the highest strength and elongation, which is closely correlated with the uniform distribution of secondary phases.

Phonons, magnons and lattice thermal transport in 2H-NbSe2: A first principles study

The vibrational and electrical properties as well as phonon–magnon scattering contribution to the thermal transportation of Niobium di-selenide using the first principles calculation method. The DFT plus spin–orbit coupling was applied to comprehend the lattice spin effect on the thermal conductivity in two-dimensional materials in general. At room temperature, in-plane thermal conductivity is 100.2 Wm−1K−1 and out-of-plane thermal conductivity is 6.21 Wm−1K−1 as found in this study. From self-energy analysis, phonon–magnon scattering rate at high frequency is maximum two orders of magnitude higher than at low frequency because of the Noether’s law of energy conservation and higher density of state at high frequency region. Higher temperatures make this phenomenon even more pronounced. Additionally, carrier density and mobility for NbSe2 is calculated at various temperatures. At room temperature, the carrier mobility is around 1000 cm2V−1s−1 in this study.

Distribution optimization of thermal through-silicon via for 3D chip based on thermal-mechanic coupling

This study establishes a unit cell model of thermal-mechanical coupling of 3D chip thermal through-silicon via (TTSV), and conducts optimization study under the constraints of the given ratio of total unit cell volume to TTSV volume. A single-degree-of-freedom optimization study with TTSV spacing as the design variable was first carried out to analyze the impact laws of heat flow density in the hot spot region, TTSV filling material and volume share on the optimal structure and maximum temperature. The results of the two-degree-of-freedom optimization with TTSV spacing and TTSV array rotation angle as design variables were further investigated to determine the distribution of thermal stresses. The maximum temperature of the cell decreases and then increases with the increase in the TTSV pitch, regardless of the rotation angle of the TTSV array, and there exists a minimum value. The higher the temperature, the higher the thermal stress. Thermal stress is always concentrated in the inner and edge regions of the TTSV.

Aging in binary-state models: The Threshold model for complex contagion.

We study the non-Markovian effects associated with aging for binary-state dynamics in complex networks. Aging is considered as the property of the agents to be less prone to change their state the longer they have been in the current state, which gives rise to heterogeneous activity patterns. In particular, we analyze aging in the Threshold model, which has been proposed to explain the process of adoption of new technologies. Our analytical approximations give a good description of extensive Monte Carlo simulations in Erdős-Rényi, random-regular and Barabási-Albert networks. While aging does not modify the cascade condition, it slows down the cascade dynamics towards the full-adoption state: the exponential increase of adopters in time from the original model is replaced by a stretched exponential or power law, depending on the aging mechanism. Under several approximations, we give analytical expressions for the cascade condition and for the exponents of the adopters' density growth laws. Beyond random networks, we also describe by Monte Carlo simulations the effects of aging for the Threshold model in a two-dimensional lattice.

ИССЛЕДОВАНИЕ ВЛИЯНИЯ ФАЗОВЫХ ШУМОВ МОДУЛЯТОРОВ ЦИФРОВЫХ СИГНАЛОВ НА ВЕРОЯТНОСТНЫЕ ХАРАКТЕРИСТИК ПРИ ИХ ПРИЕМЕ

The results of studies of the distorting effect for phase noise of digital signal modulators, generated by short-term instability of clock generators, on the degradation of probabilistic characteristics (bit error probability) when receiving digital signals with two-dimensional "constellations" (signals with multi-position phase shift keying and signals with amplitude-phase shift keying) are presented. Research is carried out for two models of phase noises with parameters of their power with uniform and normal laws of phase density distribution. Numerical estimates of energy losses are given, obtained by theoretical calculation and computer simulation of the algorithm for receiving digital signals using the considered models of phase noise with respect to additive white Gaussian channel noise. It is shown that the energy losses calculated using the analytical relation for these signals are fairly approximate estimates in relation to the simulation results. It is also shown that for signals with 2-position phase shift keying and for amplitude-phase keying with a keying order equal to 8, in the presence of phase noise with specified powers and distribution density laws, the bit error probabilities are practically equivalent to the theoretical values of the bit error probabilities for channel with additive white Gaussian noise - in this case, the energy loss is almost equal to 0. Signals with 8-position phase-shift keying are most susceptible to the distorting effect of phase noise - for the considered phase noise power parameter, the energy loss exceeds 1.5 dB. The method of reducing energy losses when receiving the considered series of digital signals is based on the use of clock generators with a decrease in the power of phase noise

Theoretical and experimental study on performance of compound-driven MR valve-controlled damper

A compound-driven magnetorheological (MR) valve is designed to cope with the low reliability and high energy consumption of traditional MR valves. The operating magnetic field of the valve is applied by both the excitation coil and ring magnet, maintaining excellent pressure drop performance even at zero current. To analyze the performance and obtain the variation law of the magnetic flux density and pressure drop, a pressure drop mathematical model and a magnetic field simulation model are established. The key parameters of the MR valve are also optimized using non-dominated sorting genetic algorithms-II. A dynamic performance test system is built, and the influence of the load on the pressure drop and hysteresis characteristics of the MR valve is studied. The results show that the optimized pressure drop and adjustable coefficient are improved by 4.7% and 8.6% respectively. The pressure drop grows nonlinearly with the electric current and reaches saturation at a current of 1.5 A, and a pressure drop of 1485 kPa is still generated at zero current. The output damping force of the compound-driven MR valve-controlled damper can be continuously adjustable, indicating that the dynamic performance of the damper can be controlled by adjusting the input current.

Experimental Study on Mechanical Behavior and Energy Evolution Characteristics of Gas-Filled Deep Coal under Cyclic Loading

To study the mechanical behavior and energy evolution law of gas-filled deep coal, conventional triaxial compression experiments under different confining pressure and gas pressure conditions and cyclic loading and unloading experiments under different gas pressures were carried out. The failure characteristics and mechanical parameters evolution of two loading modes were analyzed. In addition, the energy density and ratio evolution law under cyclic loading was revealed, and based on these findings, an attempt was made to depict the relation of cumulative dissipated energy density and volumetric strain by fitting the experimental data. The results indicated that failure of coal is expressed as a single shear surface under conventional compression, while under cyclic loading mode, coal behaves with multi-fracture crushing failure. Mechanical parameters showed a trend of decay with increasing gas pressure, and that cyclic loading and unloading increases the bearing capacity of coal by 8–38%. The dissipated energy density and ratio grew significantly when coal entered the yield stage. In the compaction stage, the cumulative dissipated energy density rose with volumetric strain in the form of an exponential function, and it increased with relative volumetric strain as a power function.

Maximum density perspectives on the stability of Brinkman porous convection in a vertical channel

The stability of parallel buoyant flow is studied in a vertical layer of Brinkman porous medium possessing a density maximum in its interior with quadratic density law. The vertical boundaries are considered to be rigid and maintained at different uniform temperatures. The similarities and differences between the linear and quadratic density-temperature relationships on the base flow, stability features of fluid flow, and the mode of instability are underlined. If the flow is governed by classical Darcy's law, then it is proved analytically that the base flow remains unconditionally stable irrespective of how the density varies with temperature. On the contrary, the change in the density-temperature relationship affects the stability of base flow when the flow is governed by either unsteady Darcy's law or the Brinkman-extended Darcy law and for these cases, the eigenvalue problem is solved numerically. For the unsteady Darcy flow model, instability occurs through the traveling-wave mode in a certain range of Darcy–Prandtl number for the quadratic density law yet the base flow is always stable if the density law is linear. The nature of the density-temperature relationship and the magnitude of governing parameters combine together in influencing the instability of fluid flow in the Brinkman regime. The possibility of otherwise stabilization of the base flow becoming unstable with the change in the density-temperature relationship from linear to quadratic for the same values of governing parameters is identified. These intricacies are discussed in detail by computing the critical stability parameters for different values of the Darcy–Prandtl number and the Darcy number.

High power laser powder bed fusion of Inconel 718 alloy: Effect of laser focus shift on formability, microstructure and mechanical properties

In this study, a 1 kW high-power laser powder bed fusion (HP-LPBF) equipment was employed for the additive manufacturing of Inconel 718 (IN718) alloy, and the effects of laser focus shift (F s 0, +5, +10, +15, +20 mm) on the formability, microstructure and mechanical properties of the HP-LPBF samples were investigated. Results suggest that HP-LPBF is able to produce near full-dense samples with high build rates by applying larger scanning speeds and hatch spacings. The process limit can be further expanded when a suitable F s is adopted through its impact on the energy density, laser spot size and laser intensity distribution. As the increase of F s , the surface roughness of HP-LPBF sample decreases initially but increases subsequently. The corresponding melting mode transforms from keyhole to transition and then to conduction. Besides, the F s is found to be influential in the mechanical properties by changing the primary dendritic arm spacing, the fraction of Laves phase and the grain size. The optimal performance at the F s of +10 mm is comparable to the low-power laser powder bed fusion (LP-LPBF), whereas its maximal build rate (16 mm 3 /s) rises to around 3-12 times that of the latter. Moreover, the scaling law of energy density for LP-LPBF remains applicable for HP-LPBF when the focal plane is located at the build surface, but not if the focal plane is shifted away. Based on those findings, the potential efficiency and limitations of HP-LPBF with higher laser powers (≥2 kW) were briefly prospected.

State-level legal and sociodemographic correlates of child marriage rates in the United States

The United States and 193 other nations have pledged to end child marriage, which is widely considered a violation of basic human rights, by 2030 under the United Nations Sustainable Development Goals (SDG 5.3). Although there is a breadth of knowledge on child marriage in many low- and middle-income countries, little research and policy discussion exists surrounding child marriage within the United States. Using administrative data from several sources, this study examines how a range of different state-level variables, including political lean, academic performance, median household income, religiosity, population density, and median distance to an abortion clinic are related to variation in child marriage rates across states. Additionally, the study examines how minimum age requirements and other state laws, such as parental and judicial consent, are related to child marriage rates. Significant correlates of higher state-level child marriage rates in the United States included lower median state income, higher religiosity, lower academic performance, and more Republican political lean, whereas state minimum marriage age laws, median distance to an abortion clinic, population density, and state law loopholes were not significantly correlated with child marriage rates. Setting a federal minimum marriage age of 18 years would be necessary to eliminate child marriage in the United States.

A review of underwater acoustic metamaterials for underwater acoustic equipment

Researchers use underwater acoustic equipment to explore the unknown ocean environment, which is one of the important means to understand and utilize the ocean. For underwater acoustic equipment, the application of underwater acoustic metamaterials is the premise to ensure and improve the performance of underwater acoustic communication, acoustic stealth, and sonar detection. Due to the limitations of mass density law and high hydrostatic pressure, traditional underwater acoustic materials cannot effectively absorb low-frequency sound waves and have low efficiency of elastic energy conversion. The sound absorption effect is poor under low frequency and high hydrostatic pressure. In recent years, with the development of acoustic metamaterials technology, all kinds of underwater acoustic metamaterials have also been proposed. Compared with sound waves propagating in the air, underwater sound is more difficult to control than air sound with the same frequency, so the design of underwater acoustic metamaterials is more complicated. This paper reviews the basic characteristics, development history of sound absorption, sound insulation decoupling, and underwater acoustic guided metamaterials, then the existing problems and the future development direction of underwater acoustic metamaterials are discussed.

Experimental Study on the Thermodynamic Damage Power of Ammunition Deflagration in a Closed Explosive Device

The high temperature and high pressure gas produced by propellant deburning has strong thermal effect,which will produce strong thermal damage effect on the target. In this study, an improved closed explosive device was used to simulate the thermal shock loading of 5/7 single base propellant with a charge mass of 17.4 g, and the change law of heat flow density of propellant in the process of deflagration in a closed environment was tested. The experimental results show that the temperature rises rapidly during the deflagration of the 5/7 single-base propellant, and the maximum heat flow density can reach 17.68 MW/ m2 . The curves obtained from the three tests have good consistency in the change trend, which proves the engineering practicability of the improved closed explosive device in the study.

Study on electrical conductivity of detonation products of aluminized explosives

Using the thermodynamic equilibrium constant method and JWL-Miller equation of state, based on the calculation of the thermodynamic parameters such as the composition, pressure, and explosion temperature of the detonation products of aluminized explosives in the Magnetocumulative generator, the Saha ionization equation, and gas conductivity calculation model are used to write Matlab code to calculate the electron density and conductivity of the detonation products of the magnetic flux compression generator. The temporal and spatial variation law of electron density and conductivity is revealed. The simulation shows that the thickness of the maximum conductivity layer in the detonation process is about 1 mm and moves at a uniform speed following the CJ surface. The maximum conductivity of HMX/Al (70/30) is 1.88e5 Ω−1·m−1, with an error of 6%, and the maximum conductivity of RA1 (HMX / DNAN / Al) is 2.7e4 Ω−1·m−1

Ti6554 titanium alloy electrically assisted compression: modelling and simulation based on dislocation density theory

Electrically assisted compression experiments were conducted on Ti6554 titanium alloy to investigate the electroplasticity behavior under different process parameters (current density, duty cycle) and to analyze the effect of pulsed current on flow stress and temperature. An electroplasticity constitutive model based on dislocation density theory was developed and using ABAQUS subroutine secondary development for electrically assisted compression simulation. The results show that the established electroplasticity constitutive model can better predict the true stress-strain curves under different process parameters, and the average error is controlled at 6%. The evolution law of dislocation density reveals that α, which characterizes the dislocation strength, is smaller with the increase of current density, n and K2, which characterize the dynamic recovery mechanism of the material, increase with the increase of current density, and the dislocation density ρ decreases with the increase of deformation temperature.

A dynamically bi‐orthogonal solution method for a stochastic Lighthill‐Whitham‐Richards traffic flow model

AbstractMacroscopic traffic flow modeling is essential for describing and forecasting the characteristics of traffic flow. However, the classic Lighthill–Whitham–Richards (LWR) model only provides equilibrium values for steady‐state conditions and fails to capture common stochastic variabilities, which are a necessary component of accurate modeling of real‐time traffic management and control. In this paper, a stochastic LWR (SLWR) model that randomizes free‐flow speed is developed to account for the stochasticity incurred by the heterogeneity of drivers, while holding individual drivers’ behavior constant. The SLWR model follows a conservation law of stochastic traffic density and flow and is formulated as a time‐dependent stochastic partial differential equation. The model is solved using a dynamically bi‐orthogonal (DyBO) method based on a spatial basis and stochastic basis. Various scenarios are simulated and compared with the Monte Carlo (MC) method, and the results show that the SLWR model can effectively describe dynamic traffic evolutions and reproduce some commonly observed traffic phenomena. Furthermore, the DyBO method shows significant computational advantages over the MC method.

A self-consistent dynamical model of the Milky Way disc adjusted to Gaia data

Context. Accurate astrometry achieved by Gaia for many stars in the Milky Way provides an opportunity to reanalyse the Galactic stellar populations from a large and homogeneous sample and to revisit the Galaxy gravitational potential. Aims. This paper shows how a self-consistent dynamical model can be obtained by fitting the gravitational potential of the Milky Way to the stellar kinematics and densities from Gaia data. Methods. We derived a gravitational potential using the Besancon Galaxy Model, and computed the disc stellar distribution functions based on three integrals of motion (E, Lz, I3) to model stationary stellar discs. The gravitational potential and the stellar distribution functions are built self-consistently, and are then adjusted to be in agreement with the kinematics and the density distributions obtained from Gaia observations. A Markov chain Monte Carlo (MCMC) is used to fit the free parameters of the dynamical model to Gaia parallax and proper motion distributions. The fit is done on several sets of Gaia data, mainly a subsample of the GCNS (Gaia catalogue of nearby stars to 100 pc) with G < 17, together with 26 deep fields selected from eDR3, widely spread in longitudes and latitudes. Results. We are able to determine the velocity dispersion ellipsoid and its tilt for subcomponents of different ages, both varying with R and z. The density laws and their radial scale lengths for the thin and thick disc populations are also obtained self-consistently. This new model has some interesting characteristics that come naturally from the process, such as a flaring thin disc. The thick disc is found to present very distinctive characteristics from the old thin disc, both in density and kinematics. This lends significant support to the idea that thin and thick discs were formed in distinct scenarios, as the density and kinematics transition between them is found to be abrupt. The dark matter halo is shown to be nearly spherical. We also derive the solar motion with regards to the Local Standard of Rest (LSR), finding U⊙ = 10.79 ± 0.56 km s−1, V⊙ = 11.06 ± 0.94 km s−1, and W⊙ = 7.66 ± 0.43 km s−1, in close agreement with recent studies. Conclusions. The resulting fully self-consistent gravitational potential, still axisymmetric, is a good approximation of a smooth mass distribution in the Milky Way and can be used for further studies, including finding streams, substructures, and to compute orbits for real stars in our Galaxy.