Particles In Space Research Articles

Microstructure Evolution and Mechanical Properties of As-Cast and As-Compressed ZM6 Magnesium Alloys during the Two-Stage Aging Treatment Process.

In the present study, different solid solution and aging processes of as-cast and as-compressed ZM6 (Mg2.6Nd0.4Zn0.4Zr) alloy were designed, and the microstructure and precipitation strengthening mechanisms were discussed. After the pre-aging treatment, a large amount of G.P. zones formed in the α-Mg matrix over the course of the subsequent secondary G.P. prescription, where the fine and dispersed Mg12(Nd,Zn) phases were precipitated at the grain boundaries. The pre-aging and secondary aging processes resulted in the Mg12(Nd,Zn) phase becoming globular, preventing grain boundary sliding and decreasing grain boundary diffusion. Meanwhile, precipitation phase â″(Mg3Nd) demonstrated a coherent relationship with the α-Mg matrix after the pre-aging process, and after the secondary aging phase, Mg12Nd increases and became semi-coherent in the matrix. Compared to an as-cast ZM6 alloy, the yield strength of the as-compressed ZM6 alloy increased sharply due to an increase in the yield strength that was proportional to the particle spacing, where the dislocation bypassed the second phase particle. Compared to the single-stage aging process, the two-stage aging process greatly improved the mechanical properties of both the as-cast and as-compressed ZM6 alloys. The difference between the as-cast and as-compressed states is that an as-compressed ZM6 alloy with more dislocations and twins has more dispersed precipitates in the G.P. zones after secondary aging, meaning that it is greatly strengthened after the two-stage aging treatment process.

Levofloxacin molecularly imprinted two dimensional photonic crystal hydrogel sensor

A novel levofloxacin (LVFX) molecularly imprinted two dimensional (2D) photonic crystal hydrogels (LVFX-MIPCH) sensor has been developed, which could be used for the visual monitoring of LVFX. The response performance of the MIPCH sensor would be explored by measuring the diameter of the Debye diffraction ring. In the presence of LVFX, the hydrogel volume shrinks, leads to the particle spacing of photonic crystal in the gel decreases, thus causes the diameter of the Debye diffraction ring increases. As the concentration of LVFX in the solution increases from 0 to 10−12 M, the diameter of the Debye diffraction ring increases by 2.5 mm, and the corresponding particle spacing of photonic crystal decreases by 3.16 nm. Then, with the concentration continues to increase to 10−3 M, the diameter of the Debye diffraction ring increases by 10.0 mm, and the corresponding particle spacing decreases by 32 nm. A linear relationship between the change of particle spacing of photonic crystal (Δd) and the logarithm value of the LVFX concentration (lg c) in the range from 10−10 to 10−4 M. Besides, the diffraction peak wavelength of the sensor gradually blue-shifted, consistent with the sensor color change(from orange to blue) by naked eye. Besides, The LVFX-MIPCH sensor showed high sensitivity(as low as 10−12 M), excellent specific recognition and stable reusability.

Colorimetric two-dimensional photonic crystal biosensors for label-free detection of hydrogen peroxide

Hydrogen peroxide (H2O2) detection is highly desirable for both environment and health concerns and a number of methods have been developed to monitor H2O2. However, most methods are limited due to the need of sophisticated instrument and high cost. Here we report a label-free two-dimensional (2-D) photonic crystal (PhC) horseradish peroxidase/bovine serum albumin (HRP/BSA) protein composite hydrogel sensor to monitor H2O2. Our 2-D PhC HRP/BSA protein composite hydrogel sensor is fabricated by mild protein cross-linking of BSA and HRP with glutaraldehyde, where BSA acts as a scaffold of HRP while HRP acts as the recognition molecule. The 2-D PhC HRP/BSA protein composite hydrogel sensor selectively detects H2O2 since HRP can specifically decompose H2O2 accompanying with heme inactivation. This protein hydrogel undergoes a volume phase transition as a result of peroxidase inactivation. The inactivation-induced conformational change of HRP gives rise to a decreased cross-linking density, which enlarges the particle spacing and decreases the Debye ring of the 2-D photonic crystals (PhCs). Our optimized 2-D PhC HRP/BSA-75 protein composite hydrogel sensors show a good linear range from 8.8 × 10-6 M to 60.6 × 10-6 M and an excellent sensitivity with a limit of detection of 8.8 × 10-6 M. This sensor fabrication method demonstrates the proof-of-concept for utilizing proteins with few lysine groups to develop smart PhC protein composite hydrogel sensors to determine H2O2 concentration in solution, which makes it possible for developing protein organogel sensors to detect gaseous H2O2 in the future.

Particle energization in space plasmas: towards a multi-point, multi-scale plasma observatory

This White Paper outlines the importance of addressing the fundamental science theme “How are charged particles energized in space plasmas” through a future ESA mission. The White Paper presents five compelling science questions related to particle energization by shocks, reconnection, waves and turbulence, jets and their combinations. Answering these questions requires resolving scale coupling, nonlinearity, and nonstationarity, which cannot be done with existing multi-point observations. In situ measurements from a multi-point, multi-scale L-class Plasma Observatory consisting of at least seven spacecraft covering fluid, ion, and electron scales are needed. The Plasma Observatory will enable a paradigm shift in our comprehension of particle energization and space plasma physics in general, with a very important impact on solar and astrophysical plasmas. It will be the next logical step following Cluster, THEMIS, and MMS for the very large and active European space plasmas community. Being one of the cornerstone missions of the future ESA Voyage 2050 science programme, it would further strengthen the European scientific and technical leadership in this important field.

Investigation on thermo-mechanical performance of fully ceramic microencapsulated fuel

• A finite element method (FEM) model for FCM fuel thermo-mechanical performances analysis was presented. • The thermo-mechanical behaviors, coupled with irradiation behaviors were developed. • A 3D modeling of FCM fuel pellet with typical packing fractions was realized by an optimized stochastic strategy. • Effects of thermal boundaries, burnup, particle spacing, no fuel zone width and other key parameters were well investigated. Fully ceramic microencapsulated (FCM) fuel is a promising ATF concept with extraordinary fission product inclusion capacity, excellent oxidation and corrosion resistance, and high thermal conductivity. The thermo-mechanical performances are of great significance when evaluating the safety and applicability of a nuclear fuel. In this study, a finite element method (FEM) model for FCM thermo-mechanical performances analysis was presented. The thermo-mechanical behaviors, coupled with irradiation behaviors (including irradiation-induced dimensional change (IIDC), heat generation, conduction, thermal expansion, creep, burnup, and gap/plenum pressure, etc.), were developed to investigate the thermal and mechanical characteristics of TRISO-based FCM Fuel. A simplified model of TRISO fuel particles was established and validated. After that, a full 3D modeling of FCM fuel pellet with typical packing fractions was realized by an optimized stochastic strategy. A numerical method was validated and successfully applied to realize the simulations of a FCM fuel pellet. Two different thermal boundaries, namely fixed particle power and fixed pellet power, were performed to investigate the irradiation behavior of FCM fuel. Moreover, the effects of burnup, particle spacing, no fuel zone width and other key parameters were well studied and investigated. The performed calculation showed that temperature and stress in matrix and TRISO are both positively correlated with the packing fraction. It's worth noting that compared with the cases of fixed particle power, cases of fixed pellet power may lead to higher fuel temperature and higher stress. The results also implied that from the perspective of probability evaluation, most of the TRISO particles in FCM fuel can maintain the structural integrity under different packing fractions, but some of the particles with higher stress may crack or damage, especially in the cases of high burnup and high packing fraction.

Al-Cu-Ce(-Zr) alloys with an exceptional combination of additive processability and mechanical properties

High-temperature Al-9Cu-6Ce and Al-9Cu-6Ce-1Zr (wt%) alloys were designed for fabrication with laser powder bed fusion additive manufacturing (AM). An ultra-fine eutectic structure comprising FCC-Al and particles of a previously unidentified Al8Cu3Ce intermetallic phase was obtained with an inter-particle spacing of approximately 280 nm. The inherent hot-tearing resistance of the eutectic alloys resulted in > 99.5% relative density. A thermodynamic model suggested improved hot-tearing resistance of the present alloys relative to the benchmark AM AlSi10Mg alloy. The Al-Cu-Ce alloy exhibited superior thermal stability with approximately 75% of the as-fabricated hardness retained after 200 h exposure at 400 °C, owed to the coarsening resistance of the intermetallic particles. The Al-Cu-Ce-Zr alloy age-hardened through precipitation of nanoscale Al3Zr precipitates. The aged microstructure was stable at 350 °C with a 13% higher hardness after 200 h exposure compared to the as-fabricated condition. The combined influence of ultra-fine spacing and coarsening resistance of the intermetallic particles resulted in the higher yield strength of the Al-Cu-Ce and Al-Cu-Ce-Zr alloys compared to AM AlSi10Mg and Scalmalloy at temperatures greater than 200 °C. This work essentially demonstrates that thermally stable Al alloys with exceptional mechanical properties can be produced by additive manufacturing.

Evaporation of Primordial Black Holes into Light Dark Particles

We propose a novel way of investigating primordial black holes via the direct detection of light species, and viceversa. In particular, we examine the scenario, dubbed as ePBH-DM, where primordial black holes with masses from 1014 to 1016 g evaporate at present times into light dark species with masses smaller than 1 GeV. Such particles are typically emitted with relativistic velocities, thus allowing for their observations in direct detection experiments devoted to dark matter searches. Thus, we show that the latest data of the XENON1T experiment place very stringent constraints on the combined parameter space of primordial black holes and light dark particles.

A study of maximum pseudorapidity gap distributions in 16O-nucleus interactions at 3.7, 60 and 200A GeV/c

The main aim of this paper is to present some interesting results on event-by-event maximum 2-particle gap ([Formula: see text]) in the pseudorapidity space of the relativistic charged particles [Formula: see text] produced in the [Formula: see text]O-AgBr interactions at 3.7, 60 and 200[Formula: see text]A GeV/c. The distribution of [Formula: see text] has been obtained for the experimental and AMPT simulated data. Distinct peaks are obtained in the [Formula: see text]-distributions of the relativistic charged particles in low [Formula: see text]-region. Further, the position of the peak is found to depend on the incident energy. The experimental results are not well supported by the results obtained for the AMPT simulated data. The findings presented here may be found useful in understanding the mechanism of the multiparticle production in relativistic nuclear interactions.

Dynamic cutting force model for cutting SiCp/Al composites considering particle characteristics stochastic models

Because the particle shape, size, and spacing in SiCp/Al composites are not constant, the stochastic fluctuation phenomenon of their cutting force is more remarkable than those of continuous materials. This study aims to develop an analytical model of the dynamic cutting force in the orthogonal cutting of SiCp/Al composites. The stochastic models of the particle volume fraction, particle size, and aspect ratio are established. Based on analysing the mechanical mechanisms in different zones and the heat generation mechanisms in the shear and rubbing sources in the cutting process, a dynamic cutting force model is developed for SiCp/Al composites. This model considers the stochasticity of the particle characteristics and the dynamic change characteristic of heat generation. The predicted results yielded the average and maximum relative errors for the tangential force as 7.29% and 9.86%, respectively, and those for the radial force as 7.36% and 10.33%, respectively. Comparison of the analytical and experimental results presents a good agreement. The effects of the cutting parameters and the tool wear on the average cutting force in the orthogonal cutting of SiCp/Al composites are discussed. Moreover, the effects of the particle characteristics on each component of the cutting force are also analysed. In particular, the dynamic cutting force model can accurately present the dynamic fluctuation characteristics of the cutting process of SiCp/Al composites and study the variation tendency of average cutting force. This work provokes more in-depth thoughts of dynamic fluctuation details in the cutting process and provides the guiding significance for industrial SiCp/Al composites machining.

Microscale magnetoelectricity: Effect of particles geometry, distribution, and volume fraction

Achieving efficient magnetoelectric coupling of core-shell and particulate multiferroic composites has been a challenging hurdle; however, research has shown unwavering interest to overcome this barrier in pursuit of their implementation into promising potential applications. Herein, a fully coupled computational model of core-shell and particulate composites is developed and verified to investigate the magnetoelectric interactions of the particle and matrix on the microscale. The effects of particle geometry, settling, and agglomeration were exhaustively studied by investigating seven different shapes and a wide range of vertical and lateral particle spacing. Overall, it was found that utilizing particle geometries and positioning that closely resemble a laminate configuration, such as a prolate ellipsoid and horizontal particle alignment, enhances the magnetoelectric coupling of the composite structure. The results coincided with the experimental results concerning settling and agglomeration.

A theoretical thermal conductivity model for soils treated with microbially induced calcite precipitation (MICP)

Soil thermal conductivity is a predominant factor affecting the efficiency of exploitation of geothermal energy. Microbially induced calcite precipitation (MICP) technology has been proved to be effective in improving soil thermal conductivity. However, there is still a lack of a thermal conductivity prediction model for MICP treated soils. In this study, a theoretical thermal conductivity prediction model was developed based on the heat conduction theory and a simplified 2D geometric soil unit. The performance of this model was evaluated using the measured thermal conductivity in published literature. The results show that the predicted soil thermal conductivity agrees with the measured values well, especially, when the soil saturation (water content of the soil) is greater than 0.1. We analyze the influencing factors of soil thermal conductivity after MICP treatment on micro-scale. The results show that the soil thermal conductivity increases nonlinearly with the ratio of cement radius to soil particle radius, β. For example, the thermal conductivity can be increased by more than 16 times from 0.25 W/(m K) to 4.14 W/(m K) when β increases from 0 is 0.8, if the ratio of soil particle spacing to soil particle radius ξ is zero. ξ is also found to have a significant influence on soil thermal conductivity. For example, the soil thermal conductivity increases by 0.19 W/(m K) and 1.08 W/(m K) in dry and saturated states, respectively, when ξ increases from 0 to 0.33. This theoretical thermal conductivity model will provide a great calculation method for the soil thermal conductivity after MICP treatment.

Approximate projection method for the construction of multi- α -cluster spaces

An approximate but straight forward projection method to molecular many alpha-particle states is proposed and the overlap to the shell model space is determined. The resulting space is in accordance with the shell model, but still contains states which are not completely symmetric under permutations of the alpha-particles, which is one reason to call the construction semi-microscopic. A new contribution is the construction of the 6- and 7-$\alpha$-particle spaces. The errors of the method propagate toward larger number of alpha-particles and larger shell excitations. In order to show the effectiveness of the construction proposed, the so obtained spaces are applied, within an algebraic cluster model, to $^{20}$Ne, $^{24}$Mg and $^{28}$Si, each treated as a many-alpha-particle system. Former results on $^{12}$C and $^{16}$O are resumed.

Solving 2-D Slamming Problems by an Improved Higher-Order Moving Particle Semi-Implicit Method

Abstract A higher-order moving particle semi-implicit (MPS) method was further developed to solve 2-D water entry problems. To overcome the inconsistency in the original MPS methods, a pressure gradient correction was implemented to guarantee the first-order consistency of the gradient. The corrective matrix was modified by using the derivative of the kernel function. A particle shifting technique was also applied to improve the numerical stability. Validation studies were carried out for water entry of a rigid wedge with the tilting angles of 0, 10, and 20, and two rigid ship sections. Convergence studies were conducted on domain size, particle spacing, and time step. A particle convergence index method was proposed to evaluate numerical uncertainties in the improved MPS method. Uncertainties in numerical solutions due to spatial discretization were calculated. The predicted impact pressures and forces by the present method are in good agreement with experimental data. Introduction Slamming can cause local structural deformation and damages. It is important to solve highly nonlinear water-entry problems involving breaking free surfaces. Many studies on the impact of pressures/ loads during water entry or slamming have been performed using experiments, analytical solutions, and numerical simulations. Extensive drop tests have been conducted. For example, Bisplinghoff and Doherty (1952) carried out a series of experiments for free-fall wedges. Because ship motions in waves can lead to asymmetric water entry, wedges with different tilt angles were tested by Barjasteh et al. (2016). A more detailed review of studies based on theoretical, potential-flow, and computational fluid dynamics (CFD) methods is presented in the work of Peng and Qiu (2018).

Research on the Inertial Migration Characteristics of Bi-Disperse Particles in Channel Flow

The inertial focusing effect of particles in microchannels shows application potential in engineering practice. In order to study the mechanism of inertial migration of particles with different scales, the motion and distribution of two particles in Poiseuille flow are studied by the lattice Boltzmann method. The effects of particle size ratio, Reynolds number, and blocking rate on particle inertial migration are analyzed. The results show that, at a high blocking rate, after the same scale particles are released at the same height of the channel, the spacing between the two particles increases monotonically, and the change in the initial spacing has little effect on the final spacing of inertial migration. For two different size particles, when the smaller particle is downstream, the particle spacing will always increase and cannot remain stable. When the larger particle is downstream, the particle spacing increases firstly and then decreases, and finally tends to be stable.

Supercooling suppression and mechanical property improvement of phase change nanofibers by optimizing core distribution

Phase change fibers (PCFs) as a kind of composite material, the composition and spatial distribution of each phase have a great influence on its thermal and mechanical properties. In this article, PCFs with polyvinylpyrrolidone (PVP), polyvinyl butyral (PVB), and polyacrylonitrile (PAN) as sheath and 30% octadecane kerosene as core were prepared by coaxial electrospinning. It was found that octadecane had the highest supercooling degree when it was encapsulated in PVB. Thus, we used pure octadecane, 30% octadecane of isopropanol, chloroform, and kerosene solutions as core solutions, adjusted the fine structure of octadecane in PVB sheath, and four kinds of PCFs with different octadecane particle size and spacing were prepared. Successfully reduced the supercooling degree of octadecane. To compare the mechanical properties of the four fibers. It was found that the composite fiber obtained by using isopropanol as octadecane solvent had the most comprehensive mechanical performance. To find a universal method to control the distribution structure of phase change materials (PCMs) in fibers by coaxial electrospinning, we used PAN and PVDF as the sheath solution, pure octadecane, 30% octadecane in isopropanol, chloroform, petroleum ether, and kerosene solutions as a core solution to prepare the PCFs. Characterization results and analysis of the properties of solutions showed that only when the viscosity of the core and sheath solution was relatively low, it could obtain the bamboo-like structured fibers. And continuous core-sheath structured fibers could be obtained in two situations. First, the low viscosity of sheath solution and high viscosity of core solution; second, the high viscosity of sheath solution.

Factors affecting stress in anode particles during charging process of lithium ion battery

During charging and discharging, the insertion and extraction of lithium ions into and from the active materials can cause stress in a lithium ion battery (LIB). Excessive stress will lead to cracking, breaking and pulverization of active particles, which can result in multiple failure modes such as capacity decay and life reduction of the battery. In this research, an electrochemical and mechanical coupling model of a LIB with the NCM cathode and graphite anode is built at mesoscopic scale. The electrochemical and mechanical characteristics of the model during the charging process are analyzed. By changing the charging rates and design parameters of the anode electrode such as the particle radius, spacing coefficient, electrode thickness and diffusion coefficient, the effects of them on the lithium concentration, strain and stress in the anode particles during the charging process are investigated. The results show that lower charging rate, greater spacing coefficient, smaller electrode thickness and greater diffusion coefficient could help to decrease the stress in anode particles during charging.

Numerical study of particle separation with standing surface acoustic waves (SSAW)

The particle manipulation technology based on standing surface acoustic waves (SSAW) has been widely used with high efficiency and low consumption. However, it is difficult to study particle motion at the microscopic scale with experimental methods and conventional continuous methods. In this paper, computational fluid dynamics (CFD) and the discrete element method (DEM) are used to describe the fluid-particle flow, and the effect of the acoustic field is calculated according to Gorkov's theory. The established model is validated by the particle separation in micro-channel under SSAWs as the simulation results are in good agreement with experiments in publication. The consistency between the numerical simulation results and the experimental results in separation time and separation distance confirms the merits of model. The particle motion, space distribution, velocity field, force analysis and particle collision have been conducted thoroughly to reveal the mechanism of the separation.

Applicability of Beer's law in particulate system from random to regular arrangement: A numerical evaluation

Beer's law is the foundation of the classic radiative transfer theory. Recently, many studies have pointed out the existence of non-Beerian transport behavior in spatially correlated and statistically non-homogeneous and anisotropic particulate systems. However, there still lacks a comprehensive quantitative evalution of the applicability of Beer's law in particulate medium from random to regular arrangement. In this work, a numerical approach is proposed to quantitatively analyze and determine the applicability of Beer's law in particulate systems from regular arrangement to random arrangement. A simple approach for characterizing structural randomness of particulate system is presented. The results show that the non-Beerian behaviors exist in statistically isotropic and homogeneous particulate media. The structural randomness has a significant influence on the transmission distribution and hence the applicability of Beer's law in particulate systems. Quantitative dependent relation of validity of Beer's law on structural randomness in particulate system is obtained. Both particle spacing and structural randomness have significant impact on the applicability of Beer's law. This work is helpful for the understanding of non-Beerian radiative transfer in particulate media and guiding related engineering applications of radiative transfer theory.

Chemo-mechanical analysis of ratcheting deformation in silicon particle electrode under cyclic charging and discharging

Evidences have accumulated that high capacity silicon electrode will expand/shrink dramatically during cyclic charging/discharging operation. In this process, the electrode may undergo elastic-inelastic deformation, and cyclic asymmetric behavior of tension and compression can naturally result in the electrode ratcheting deformation. In this paper, a chemo-mechanical semi-analytical model is established to describe the ratcheting behavior of the silicon particle electrode based on concentration-dependent material properties. The results show that inelastic deformation can reduce the rapid increase of the stresses and further reduce the possibility of surface crack. However, the accumulated irreversible inelastic strain may become one of the important factors for mechanical degradation and even electrode failure. The influence of hydrostatic stress on electrode ratcheting behavior is discussed in detail. It can decrease the concentration gradient and stress level, thereby reducing the inelastic region and ratcheting deformation, which will prolong the predicted lifetime of the electrode. The diffusion coefficient, particle size and the charging rate have also been investigated. The results reveal that ratcheting deformation may be decreased by the high diffusivity, the small particle size and slow charging strategy, which will improve the mechanical stability and capacity of the electrode. Meanwhile, interparticle contact may worsen the ratcheting deformation. Increasing the electrode porosity appropriately can provide space for silicon particles to expand, which may reduce the ratcheting deformation. The present work gives a new explanation for ratcheting deformation in silicon particle electrode and provides a theoretical basis for guiding one in designing next-generation high capacity lithium-ion batteries.

Versatile Silver Nanoparticles-Based SERS Substrate with High Sensitivity and Stability

Surface-enhanced Raman scattering has developed into a mature analytical technique useful in various applications; however, the reproducible fabrication of a portable SERS substrate with high sensitivity and good uniformity is still an ongoing pursuit. Reported herein is a rapid fabrication method of an inexpensive SERS substrate that enables sub-nanomolar detection of molecular analytes. The SERS substrate is obtained by application of silver nanoparticles (Ag NPs)-based ink in precisely design patterns with the aid of an in-house assembled printer equipped with a user-fillable pen. Finite-difference time-domain (FDTD) simulations show a 155-times Ag NP electric field enhancement for Ag nanoparticle pairs with particle spacing of 2 nm. By comparing the SERS performance of SERS substrate made with different support matrices and fabrication methods, the PET-printed substrate shows optimal performance, with an estimated sensitivity enhancement factor of 107. The quantitative analysis of rhodamine 6G absorbed on optimized SERS substrate exhibits a good linear relationship, with a correlation coefficient (R2) of 0.9998, between the SERS intensity at 610 cm−1 and the concentration in the range of 0.1 nM—1μM. The practical low limit detection of R6G is 10 pM. The optimized SERS substrates show good stability (at least one month) and have been effectively tested in the detection of cancer drugs, including doxorubicin and metvan.