Academic Journals

Manufacturing process of AA5083/nano-γAl 2 O 3 localized composite metal foam fabricated by friction stir processing route (FSP) and microstructural characterization

The Behavior Analyst - Thu, 03/01/2018 - 00:00
Abstract

The aluminum alloy AA5083 is a technologically important structural alloy as it is lightweight, with outstanding weldability and formability, moderate corrosion resistance and strength, making it suitable for a wide range of marine and transportation applications. In the present study, AA5083/nano-γAl2O3 composite metal foam was fabricated using a friction stir processing route (FSP). More precisely, the paper presents a first attempt to use grooves for the integration of the foaming and stabilizing agent on the metal foam precursor by FSP. The implementation of grooves allows to control the amount of foaming, integrates the stabilizing particles within the precursor and permits the production of localized metal foams. Unlike the commonly used manufacturing processes, only one plate is required for the production of the precursor sample in the proposed process. Therefore, this process can be easily implemented in the industrial sector. Furthermore, γ-Al2O3 nanostructured reinforcement, which is characterized by increased interfacial energy, was utilized as a stabilizing agent. The precursor specimens were manufactured by mixing blowing agent powder (0.4% w/w TiH2) and stabilization agent nanopowder (2% w/w γ-Al2O3) into the 5083 aluminum alloy matrix using FSP. The effects of the number of FSP passes and the foaming conditions (holding temperature and time) on the pore density, morphology and distribution were investigated. The microstructure and porosity evolution of the so-obtained metal foam was also examined and analyzed. Results indicate that, following the foaming procedure, a porosity of 60% and an equivalent pore diameter ranging from 0.2 to 3.3 mm can be achieved. Moreover, the microstructure was found to be closely related to microhardness distribution perpendicular to the traversing direction of the FSP tool for both precursor and foamed specimens.

Categories: Academic Journals

Fabrication of periodically micropatterned magnetite nanoparticles by laser-interference-controlled electrodeposition

The Behavior Analyst - Thu, 03/01/2018 - 00:00
Abstract

This paper introduces a laser-interference-controlled electrochemical deposition method for direct fabrication of periodically micropatterned magnetite (Fe3O4) nanoparticles (NPs). In this work, Fe3O4 NPs were controllably synthesized on the areas where the photoconductive electrode was exposed to the periodically patterned interferometric laser irradiation during the electrodeposition. Thus, the micropattern of Fe3O4 NPs was controlled by interferometric laser pattern, and the crystallization of the particles was controlled by laser interference intensity and electrochemical deposition conditions. The bottom-up electrochemical approach was combined with a top-down laser interference methodology. This maskless method allows for in situ fabrication of periodically patterned magnetite NPs on the microscale by electrodeposition under room temperature and atmospheric pressure conditions. In the experiment, Fe3O4 NPs with the mean grain size below 100 nm in the pattern of 5-μm line array were achieved within the deposition time of 100 s. The experiment results have shown that the proposed method is a one-step approach in fabricating large areas of periodically micropatterned magnetite NPs.

Categories: Academic Journals

Ion imprinting approach for the fabrication of an electrochemical sensor and sorbent for lead ions in real samples using modified multiwalled carbon nanotubes

The Behavior Analyst - Thu, 03/01/2018 - 00:00
Abstract

A highly selective electrochemical sensor for lead ions was fabricated using mutiwalled carbon nanotube as the backbone. The binding sites for lead ions were sculpted with lead ion as template and NNMBA-crosslinked polyacrylamide as the solid matrix on MWCNTs (MWCNT-IIP) on lead ion sensing and selectivity. System without lead ions was also synthesized (MWCNT-NIP). To check the role of the MWCNT, ion-imprinted polymer (IIP) and non-imprinted polymer (NIP) without MWCNT were also synthesized. In both systems, the ion-imprinted polymer showed high specificity towards lead ion. The developed materials were characterized using various analytical techniques. The sites left by the lead ions in MWCNT-IIP are highly selective to lead ions and resulted in electrochemical response when a platinum electrode was modified with this nanostructure. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were employed to explore the features of the developed electrochemical sensor towards lead ions. The developed material could sense Pb(II) ions in the presence of other metal ions, and the limit of detection was found to be 2 × 10−2 μM. The sensing system could successfully discriminate Pb(II) ions from different real samples which includes environmental sample such as lake water, mining effluent, food sample and cosmetics. Also the same was exploited for the extraction of Pb(II) ions. The recoveries from various samples using MWCNT-IIP were > 99%. But those of MWCNT-NIP were in the range 62–68%.

Categories: Academic Journals

Microwave absorption performance of iron oxide/multiwalled carbon nanotubes nanohybrids prepared by electrostatic attraction

The Behavior Analyst - Thu, 03/01/2018 - 00:00
Abstract

Designing the structure with dielectric loss and magnetic loss integrated contributes to expansion of microwave absorption bandwidth. Nanohybrid materials composed of iron oxide (Fe3O4) and multiwalled carbon nanotubes (MWCNTs) were prepared through a newly electrostatic attraction method as high-performance microwave absorbers in the 2–18 GHz band. The nanohybrids are characterized by transmission electron microscopy, X-ray diffraction, and vector network analysis. Microstructural analysis showed that Fe3O4 and MWCNTs were well-connected through electrostatic interaction in the nanohybrids. The experimental results indicated that MWCNTs/PEDOT: PSS/Fe3O4 possessed higher reflection loss and broader absorption bandwidth than MWCNTs. MWCNTs/SDBS/Fe3O4 had better matching of dielectric loss and magnetic loss, the absorption bandwidth below − 10 dB was up to 8 GHz. This work further reveals that the novel electrostatic attraction method could be efficiently enlarged electromagnetic wave attenuation performance in absorb materials.

Categories: Academic Journals

Efficient and selective separation of U(VI) and Th(IV) from rare earths using functionalized hierarchically mesoporous silica

The Behavior Analyst - Thu, 03/01/2018 - 00:00
Abstract

The separation and recovery of U(VI) and Th(IV) from rare earths are very important to avoid environmental pollution. A functional fibrous hierarchically bimodal mesoporous silica (F-SiO2-DP) as an high efficient adsorbent for selective adsorption of uranium and thorium, which had hierarchically bimodal mesoporous structure and specific surface area of ca. 474.1 m2 g−1, was prepared by post-modification method using 2,9-diamide-1,10-phenanthroline. The synthesized adsorbent was characterized by HR-TEM, SEM, FT-IR, N2 adsorption–desorption, TGA techniques, XRD and NMR spectroscopy. The effects of pH, contact time, initial U(VI) and Th(IV) concentration, temperature and the presence of competitive metal ions on U(VI) and Th(IV) adsorption behavior were studied in detail. The hierarchically bimodal mesoporous structure endows F-SiO2-DP with faster adsorption rate, which can reach equilibrium within 10 min, as well as higher adsorption capacities for U(VI) and Th(IV) compared with unimodal mesoporous silica like MCM-41 functionalized with 2,9-diamide-1,10-phenanthroline. The maximum adsorption capacities reach 416 mg g−1 for U(VI) at pH 5.0 and 277 mg g−1 for Th(IV) at pH 3.8, which are much higher than most of previously reported mesoporous silica-based adsorbents. The selectivity coefficient of U(VI) and Th(IV) over Ce(III), Nd(III), Sm(III), Eu(III), Gd(III), Y(III) and Yb(III) is all larger than 9 at pH 3.8, indicating that F-SiO2-DP possesses a good simultaneously selective adsorption performance for U(VI) and Th(IV). This work demonstrates that F-SiO2-DP with hierarchically bimodal mesoporous structure has promising application in adsorption and separation of actinides from lanthanides, which is crucial to the environmental protection.

Categories: Academic Journals

Characterization of hollow silica–polyelectrolyte composite nanoparticles by small-angle X-ray scattering

The Behavior Analyst - Thu, 03/01/2018 - 00:00
Abstract

Hollow silica–polyelectrolyte composite nanoparticles were prepared using templates of spherical polyelectrolyte brushes which consist of a polystyrene (PS) core and a densely grafted linear poly(acrylic acid) shell. The obtained hollow particles were systematically studied by small-angle X-ray scattering (SAXS) in combination with other characterization methods such as transmission electron microscopy and dynamic light scattering. The hollow structure formed by dissolving the PS core was confirmed by the reduction of electron density to zero in the cavity through fitting SAXS data. SAXS revealed both the inward and outward expansions of the hollow silica–polyelectrolyte composite particles upon increasing pH from 3 to 9, while further increasing pH led to the partial dissolution of silica layer and even destruction of the hollow structure. SAXS was confirmed to be a unique and powerful characterization method to observe hollow silica nanoparticles, which should be ideal candidates for controlled drug delivery.

Categories: Academic Journals

Toughening mechanisms of low transformation temperature deposited metals with martensite–austenite dual phases

The Behavior Analyst - Thu, 03/01/2018 - 00:00
Abstract

Four groups of low transformation temperature (LTT) deposited metals with different Ni contents were prepared, and their microstructures were characterized by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and electron backscattered diffraction techniques. The relationship between the microstructures of the mixed martensite–retained austenite (RA) phases and their impact toughness were investigated; it was found that the impact toughness of the LTT deposited metals increased with increasing volume fraction of RA. In particular, its magnitude was higher for the specimens containing the lath martensite, interlath RA, and intercellular RA phases than for those composed of the lath martensite and interlath RA. The toughness of the lath martensite–RA mixed microstructure was primarily determined by the presence of the soft RA phase (containing film interlath RA and stringer intercellular RA), while lath martensite phase characterized by a high density of tangled dislocations and relatively small amount of twinned substructures resulted in the embrittlement of the LTT deposited metals. The dislocation absorption by the retained austenite and transformation-induced plasticity (TRIP) effects of RA were found to be main reasons for the improvement in materials toughness during crack initiation stage. The subsequent crack propagation proceeds via the TRIP and the transformation-induced crack termination mechanisms; it is also significantly affected by the increased fraction of martensite/RA boundaries. The optimization of the RA fraction in the martensite–RA dual structure is a potentially effective method for the toughness enhancement of the LTT deposited metals containing martensite–RA dual phases.

Categories: Academic Journals

Improving the high-frequency magnetic properties of as-deposited CoFe films by ultra-low gas pressure

The Behavior Analyst - Thu, 03/01/2018 - 00:00
Abstract

CoFe films without buffer layers were deposited at different ultra-low argon pressures ranging from 0.085 to 0.847 mTorr. This pressure range was one to two orders lower than the normal sputtering pressure. As a consequence, the static magnetic properties, including coercivity and magnetic anisotropy field, were improved with decrease argon pressure. The high-frequency permeability spectra showed that the resonance frequency and the damping factor of the films also reached optimal values at ultra-low pressure. Basing on atomic force microscopy observations, we attributed the excellent properties to the improved morphologies of the films and released internal stress.

Categories: Academic Journals

Stable periodic orbits for spacecraft around minor celestial bodies

The Psychological Record - Thu, 03/01/2018 - 00:00
Abstract

We are interested in stable periodic orbits for spacecraft in the gravitational field of minor celestial bodies. The stable periodic orbits around minor celestial bodies are useful not only for the mission design of the deep space exploration, but also for studying the long-time stability of small satellites in the large-size-ratio binary asteroids. The irregular shapes and gravitational fields of the minor celestial bodies are modeled by the polyhedral model. Using the topological classifications of periodic orbits and the grid search method, the stable periodic orbits can be calculated and the topological cases can be determined. Furthermore, we find five different types of stable periodic orbits around minor celestial bodies: (1) stable periodic orbits generated from the stable equilibrium points outside the minor celestial body; (2) stable periodic orbits continued from the unstable periodic orbits around the unstable equilibrium points; (3) retrograde and nearly circular periodic orbits with zero-inclination around minor celestial bodies; (4) resonance periodic orbits; (5) near-surface inclined periodic orbits. We take asteroids 243 Ida, 433 Eros, 6489 Golevka, 101955 Bennu, and the comet 1P/Halley for examples.

Categories: Academic Journals

Calibration of atmospheric density model using two-line element data

The Psychological Record - Thu, 03/01/2018 - 00:00
Abstract

For satellites in orbits, most perturbations can be well modeled, however the inaccuracy of the atmospheric density model remains the biggest error source in orbit determination and prediction. The commonly used empirical atmospheric density models, such as Jacchia, NRLMSISE, DTM, and Russian GOST, still have a relative error of about 10%–30%. Because of the uncertainty in the atmospheric density distribution, high accuracy estimation of the atmospheric density cannot be achieved using a deterministic model. A better way to improve the accuracy is to calibrate the model with updated measurements. Twoline element (TLE) sets provide accessible orbital data, which can be used in the model calibration. In this paper, an algorithm for calibrating the atmospheric density model is developed. First, the density distribution of the atmosphere is represented by a power series expansion whose coefficients are denoted by the spherical harmonic expansions. Then, the useful historical TLE data are selected. The ballistic coefficients of the objects are estimated using the BSTAR data in TLEs, and the parameterized model is calibrated by solving a nonlinear least squares problem. Simulation results show that the prediction error is reduced using the proposed calibration algorithm.

Categories: Academic Journals

A note on the full two-body problem and related restricted full three-body problem

The Psychological Record - Thu, 03/01/2018 - 00:00
Abstract

Truncating at the second order of the mutual potential between two rigid bodies, time-explicit first order solutions to the rotations and the orbital motion of the two bodies in the planar full two-body problem (F2BP) are constructed. Based on this analytical solution, equations of motion (EOMs) for the related restricted full three-body problem are given. In the case of the synchronous or double synchronous states for the full two-body problem, EOMs for the related restricted full three-body problem (RF3BP) are also given. At last, one example—the “collinear libration point” in the binary asteroid system—is given.

Categories: Academic Journals

Stabilization of coupled orbit–attitude dynamics about an asteroid utilizing Hamiltonian structure

The Psychological Record - Thu, 03/01/2018 - 00:00
Abstract

The gravitationally coupled orbit–attitude dynamics, also called the full dynamics, in which the spacecraft is modeled as a rigid body, is a high-precision model for the motion in the close proximity of an asteroid. A feedback control law is proposed to stabilize relative equilibria of the coupled orbit–attitude motion in a uniformly rotating second degree and order gravity field by utilizing the Hamiltonian structure. The feedback control law is consisted of potential shaping and energy dissipation. The potential shaping makes the relative equilibrium a minimum of the modified Hamiltonian by modifying the potential artificially. With the energy-Casimir method, it is theoretically proved that an unstable relative equilibrium can always be stabilized in the Lyapunov sense by the potential shaping with sufficiently large feedback gains. Then, the energy dissipation leads the motion to converge to the relative equilibrium. The proposed stabilization control law has a simple form and is easy to implement autonomously, which can be attributed to the utilization of natural dynamical behaviors in the controller design.

Categories: Academic Journals

Optimization of observing sequence based on nominal trajectories of symmetric observing configuration

The Psychological Record - Thu, 03/01/2018 - 00:00
Abstract

This paper presents the crucial method for obtaining our team’s results in the 8th Global Trajectory Optimization Competition (GTOC8). Because the positions and velocities of spacecraft cannot be completely determined by one observation on one radio source, the branch and bound method for sequence optimization of multi-asteroid exploration cannot be directly applied here. To overcome this difficulty, an optimization method for searching the observing sequence based on nominal low-thrust trajectories of the symmetric observing configuration is proposed. With the symmetric observing configuration, the normal vector of the triangle plane formed by the three spacecraft rotates in the ecliptic plane periodically and approximately points to the radio sources which are close to the ecliptic plane. All possible observing opportunities are selected and ranked according to the nominal trajectories designed by the symmetric observing configuration. First, the branch and bound method is employed to find the optimal sequence of the radio source with thrice observations. Second, this method is also used to find the optimal sequence of the left radio sources. The nominal trajectories are then corrected for accurate observations. The performance index of our result is 128,286,317.0 km which ranks the second place in GTOC8.

Categories: Academic Journals

Overview of China’s 2020 Mars mission design and navigation

The Psychological Record - Thu, 03/01/2018 - 00:00
Abstract

Scheduled for an Earth-to-Mars launch opportunity in 2020, the China’s Mars probe will arrive on Mars in 2021 with the primary objective of injecting an orbiter and placing a lander and a rover on the surface of the Red Planet. For China’s 2020 Mars exploration mission to achieve success, many key technologies must be realized. In this paper, China’s 2020 Mars mission and the spacecraft architecture are first introduced. Then, the preliminary launch opportunity, Earth–Mars transfer, Mars capture, and mission orbits are described. Finally, the main navigation schemes are summarized.

Categories: Academic Journals

Stable periodic orbits for spacecraft around minor celestial bodies

The Behavior Analyst - Thu, 03/01/2018 - 00:00
Abstract

We are interested in stable periodic orbits for spacecraft in the gravitational field of minor celestial bodies. The stable periodic orbits around minor celestial bodies are useful not only for the mission design of the deep space exploration, but also for studying the long-time stability of small satellites in the large-size-ratio binary asteroids. The irregular shapes and gravitational fields of the minor celestial bodies are modeled by the polyhedral model. Using the topological classifications of periodic orbits and the grid search method, the stable periodic orbits can be calculated and the topological cases can be determined. Furthermore, we find five different types of stable periodic orbits around minor celestial bodies: (1) stable periodic orbits generated from the stable equilibrium points outside the minor celestial body; (2) stable periodic orbits continued from the unstable periodic orbits around the unstable equilibrium points; (3) retrograde and nearly circular periodic orbits with zero-inclination around minor celestial bodies; (4) resonance periodic orbits; (5) near-surface inclined periodic orbits. We take asteroids 243 Ida, 433 Eros, 6489 Golevka, 101955 Bennu, and the comet 1P/Halley for examples.

Categories: Academic Journals

Calibration of atmospheric density model using two-line element data

The Behavior Analyst - Thu, 03/01/2018 - 00:00
Abstract

For satellites in orbits, most perturbations can be well modeled, however the inaccuracy of the atmospheric density model remains the biggest error source in orbit determination and prediction. The commonly used empirical atmospheric density models, such as Jacchia, NRLMSISE, DTM, and Russian GOST, still have a relative error of about 10%–30%. Because of the uncertainty in the atmospheric density distribution, high accuracy estimation of the atmospheric density cannot be achieved using a deterministic model. A better way to improve the accuracy is to calibrate the model with updated measurements. Twoline element (TLE) sets provide accessible orbital data, which can be used in the model calibration. In this paper, an algorithm for calibrating the atmospheric density model is developed. First, the density distribution of the atmosphere is represented by a power series expansion whose coefficients are denoted by the spherical harmonic expansions. Then, the useful historical TLE data are selected. The ballistic coefficients of the objects are estimated using the BSTAR data in TLEs, and the parameterized model is calibrated by solving a nonlinear least squares problem. Simulation results show that the prediction error is reduced using the proposed calibration algorithm.

Categories: Academic Journals

A note on the full two-body problem and related restricted full three-body problem

The Behavior Analyst - Thu, 03/01/2018 - 00:00
Abstract

Truncating at the second order of the mutual potential between two rigid bodies, time-explicit first order solutions to the rotations and the orbital motion of the two bodies in the planar full two-body problem (F2BP) are constructed. Based on this analytical solution, equations of motion (EOMs) for the related restricted full three-body problem are given. In the case of the synchronous or double synchronous states for the full two-body problem, EOMs for the related restricted full three-body problem (RF3BP) are also given. At last, one example—the “collinear libration point” in the binary asteroid system—is given.

Categories: Academic Journals

Stabilization of coupled orbit–attitude dynamics about an asteroid utilizing Hamiltonian structure

The Behavior Analyst - Thu, 03/01/2018 - 00:00
Abstract

The gravitationally coupled orbit–attitude dynamics, also called the full dynamics, in which the spacecraft is modeled as a rigid body, is a high-precision model for the motion in the close proximity of an asteroid. A feedback control law is proposed to stabilize relative equilibria of the coupled orbit–attitude motion in a uniformly rotating second degree and order gravity field by utilizing the Hamiltonian structure. The feedback control law is consisted of potential shaping and energy dissipation. The potential shaping makes the relative equilibrium a minimum of the modified Hamiltonian by modifying the potential artificially. With the energy-Casimir method, it is theoretically proved that an unstable relative equilibrium can always be stabilized in the Lyapunov sense by the potential shaping with sufficiently large feedback gains. Then, the energy dissipation leads the motion to converge to the relative equilibrium. The proposed stabilization control law has a simple form and is easy to implement autonomously, which can be attributed to the utilization of natural dynamical behaviors in the controller design.

Categories: Academic Journals

Optimization of observing sequence based on nominal trajectories of symmetric observing configuration

The Behavior Analyst - Thu, 03/01/2018 - 00:00
Abstract

This paper presents the crucial method for obtaining our team’s results in the 8th Global Trajectory Optimization Competition (GTOC8). Because the positions and velocities of spacecraft cannot be completely determined by one observation on one radio source, the branch and bound method for sequence optimization of multi-asteroid exploration cannot be directly applied here. To overcome this difficulty, an optimization method for searching the observing sequence based on nominal low-thrust trajectories of the symmetric observing configuration is proposed. With the symmetric observing configuration, the normal vector of the triangle plane formed by the three spacecraft rotates in the ecliptic plane periodically and approximately points to the radio sources which are close to the ecliptic plane. All possible observing opportunities are selected and ranked according to the nominal trajectories designed by the symmetric observing configuration. First, the branch and bound method is employed to find the optimal sequence of the radio source with thrice observations. Second, this method is also used to find the optimal sequence of the left radio sources. The nominal trajectories are then corrected for accurate observations. The performance index of our result is 128,286,317.0 km which ranks the second place in GTOC8.

Categories: Academic Journals

Overview of China’s 2020 Mars mission design and navigation

The Behavior Analyst - Thu, 03/01/2018 - 00:00
Abstract

Scheduled for an Earth-to-Mars launch opportunity in 2020, the China’s Mars probe will arrive on Mars in 2021 with the primary objective of injecting an orbiter and placing a lander and a rover on the surface of the Red Planet. For China’s 2020 Mars exploration mission to achieve success, many key technologies must be realized. In this paper, China’s 2020 Mars mission and the spacecraft architecture are first introduced. Then, the preliminary launch opportunity, Earth–Mars transfer, Mars capture, and mission orbits are described. Finally, the main navigation schemes are summarized.

Categories: Academic Journals

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