Skeleton Matrix Research Articles

Highly efficient and reusable polyacrylonitrile-based nanocomposite sorbents for oil spill removal

Nanostructured porous materials are desirable sorbents for separating and removing oil spills from water. This work examines the performance of the prepared efficient sorbents in the oil sorption process. Polyacrylonitrile (PAN) fibers served as the skeleton matrix, while glutaraldehyde and poly(vinyl alcohol) (PVA) served as cross-linking agents. The prepared polymer sorbents showed high adsorption capacity (12.47 g/g), porosity (95.41%) and low density (0.069 g/cm3). The incorporation of carbon nanostructures (nanotubes or graphene oxide) in the sorbent increased the adsorption capacity to 14.85 g/g. The hydrophobic nature of carbon nanotubes significantly increases the contact angle of water with the surface of the nanocomposite absorber and reaches 137.5 degrees. The obtained sorbents showed good reusability in the adsorption process and maintained an adsorption capacity of about 10 g/g after 5 cycles. The optimal temperature range for using nanocomposite sorbents was 25°C to 35°C. The combination of high sorption capacity, low porosity and density in modified polyacrylonitrile, along with its reusability, makes this designed sorbent highly suitable for efficient removal of oil spills.

Kinetic investigation and numerical simulation of reactor with prepared diatomite/CaCO3 for high-temperature thermal energy storage application

Calcium looping (CaL) thermochemical energy storage (TCES) gradually appears in high temperature concentrating solar power (CSP) plants. However, the CSP-Cal integrated system has encountered challenges related to the high temperature stability of calcium-based materials and reactor design. Firstly, the wet ball milling-impregnation method was used to experimentally prepare the diatomite calcium-based thermal storage materials, and a natural diatomite skeleton matrix was obtained. A modified diatomite/CaCO3 composite thermochemical energy storage material was synthesized. The material can keep maintaining an effective conversion rate of up to 85 % by repeating charging and discharging heat storage processes for 20 times. At the same time, the 3-dimensional diffusion model was applied to investigate the reaction kinetics during the heat storage process. Secondly, numerical studies were carried out to simulate the decarbonization process of the packed bed reactor used in CSP, illustrating the complex coupling mechanism of the multiple physical processes. The results reveal that increasing the temperature and velocity of heat transfer fluid (HTF) can accelerate the heat storage process and changing porosity can modify the reaction pattern. Finally, in order to enhance the heat transfer and flow rate of HTF inside the reactor, spiral metal porous channels of large permeability with high thermal conductivity are embedded in the reactor, which promotes CO2 emission and reduces the completion time during a decarbonization reaction. This study not only proposes a novel approach to prepare the calcium-based heat storage materials but optimizes the energy storage performance of packed bed reactors.

Phase change materials encapsulated in a novel hybrid carbon skeleton for high-efficiency solar-thermal conversion and energy storage

Phase change materials (PCMs) with high energy density and stationary transition temperature are now considered promising solar energy storage mediums. However, their intrinsic poor light absorption, thermal conductivity and stability severely impede their potential applications. In this study, a novel carbonized hybrid aerogel (CHA) structure was firstly constructed by incorporating MXene and carbon nanofibers (CNFs) into a continuous phase polyamic acid salt (PAAS) aqueous solution, followed by directional freezing, vacuum drying, imidization, and carbonization processes. Finally, the composite PCMs (CPCMs) were fabricated by vacuum impregnation of PCMs into the CHAs. The CPCM, of which CHA consists of 20 wt% MXene and 10 wt% CNF@PDA, demonstrates high solar-thermal conversion efficiency (>91 %), improved thermal conductivity of 0.40 W·m−1·K−1, great thermal stability (enthalpy loss < 0.19 % after 100 cycling tests with no obvious leakage). The introduction of MXene and CNFs endows PCM with broader light absorption spectrum range. The skeleton matrix embedded with bonded MXene sheets and CNFs provides more thermal pathways, light absorption sites and carrying capacity, improves the thermal conductivity, solar-thermal conversion property and stability of PCM. In addition, CPCM also exhibits outstanding EMI SE (95 dB). The multifunctional and high-performance CPCMs shows potential to realize the effective capture and utilization of solar energy. This work provides a new strategy to construct stable and multifunctional hybrid carbon skeleton for high-efficiency solar-thermal conversion and energy storage.

Bisimulations for delayed switched Boolean control networks and its application in controllability

AbstractThis paper investigates bisimulation relations of delayed switched Boolean control networks (DSBCNs), using the semi‐tensor product (STP) approach. Firstly, the notion of bisimulation in DSBCNs is formalized. Subsequently, based on the skeleton matrix of DSBCN, two necessary and sufficient conditions are derived for checking this notion. Moreover, as an application of bisimulation relations, this paper explores the propagation of controllability for DSBCNs through a bisimulation relation. It shows the possibility that the controllability of a DSBCN can be inferred by studying a potentially simpler DSBCN. At last, two examples are proposed to illustrate the efficiency of the obtained results.

A laboratory evaluation of factors affecting rutting resistance of asphalt mixtures using wheel tracking test

Rutting is one of the most common distresses in early damage to asphalt pavements. It can raise the risk of ride safety issues, accelerate pavement deterioration, and increase maintenance costs. To investigate the factors that affect the rutting resistance of asphalt mixtures, internal factors (such as aggregate gradation, asphalt content, and layer thickness), external factors (including temperature and traffic loading), and human factors (such as compaction degree) were tested using wheel tracking tests. The test results showed that the rutting resistance of asphalt mixtures can be improved by designing a tightly interlocked aggregate skeleton using the Bailey method's primary control sieve, using an optimal asphalt content, achieving sufficient compaction, maintaining a layer thickness of 2.5–3 times its nominal maximum aggregate size, using an asphalt softening point higher than the pavement temperature, and avoiding overloaded vehicles. In highly rutted areas, it is recommended to use a stone mastic asphalt with a stable aggregate skeleton matrix and styrene-butadiene-styrene modified asphalt with a softening point higher than the highest pavement temperature.

Effect of Multiwalled Carbon Nanotubes (MWCNTs) on Mechanical Properties of Gypsum-Treated Soil

The introduction of nanomaterial into structural engineering has resulted in improved compressive and flexural strengths of concrete. Whereas, very little research has been carried out in exploring its benefits in the field of geotechnical engineering. In this study, the effects of Multiwalled Carbon Nanotubes (MWCNTs) on the properties of gypsum (cementitious agent) treated low plastic clays were investigated. Unconfined compressive strength (UCS) and direct shear tests were conducted on untreated and treated samples with varying gypsum contents (9–18% by weight) and MWCNTs, (0.001–0.1% by weight of gypsum). The durability study of optimum treated sample was conducted by curing them for 2–28 days in unsoaked and soaked conditions. Results revealed that UCS, cohesion, and angle of internal friction of the treated samples improved up to 414, 232, and 78%, respectively, compared to untreated samples. Moreover, scanning electron microscopy (SEM) analysis of the treated samples also carried out. SEM results revealed that MWCNTs act as nano-fillers and nano-reinforcements, reducing the inter-particle spacing, resulting in a denser, stiffer, and stronger soil skeleton matrix, and ultimately improving the mechanical properties of soil. Therefore, nanomaterials can be used as potential contenders in soil stabilization for enhancing the mechanical properties of the soils.

Synergies of Adjacent Sites in Atomically Dispersed Ruthenium toward Achieving Stable Hydrogen Evolution.

It is a challenge to fabricate atomically dispersed metal clusters in polymeric carbon nitride (PCN) for durable photocatalytic reactions owing to the thermodynamic stability limitation. Herein, atomically dispersed Ru clusters are implanted into the PCN skeleton matrix based on an ionic diffusion and coordination (IDC) strategy, the stability of which is improved owing to the robust Ru-N bonds in the formed RuN4 and RuN3 configurations. Additionally, RuN4 and RuN3 as charge transport bridges between two adjacent melon strands efficaciously conquer hydrogen bond restriction in the skeleton to facilitate the in-plane mobility and separation of charge carriers. Moreover, the synergistic effect of adjacent Ru atoms is triggered on the assembled RuN3-RuN4 and RuN3-RuN3 in the atomically dispersed Ru clusters to significantly decrease hydrogen adsorption energy. As a result, the optimal PCN-Ru photocatalyst achieves nearly 6 times higher than the photocatalytic hydrogen evolution (PHE) rate of the Pt/PCN benchmark and maintains the long-term stable running for 104 h of 26 cycles; its overall PHE performance is far superior to the most of single atoms supported on g-C3N4 photocatalysts reported. The findings here gain new insight into the preparation strategy, structure configuration, and reaction mechanism for atomically dispersed metal clusters supported on PCN, which further stimulates the intensive investigations toward developing more efficient and stable PCN-like photocatalytic materials.

Sphere-in-fiber hybrid of N-doped carbon/cerium dioxide as an interlayer material with superior electrocatalytic performance for lithium sulfide precipitation and conversion

The inferior conductivity and infamous “shuttle effect” of lithium-sulfur (Li-S) batteries lead to low sulfur utilization and undesired cycle stability, which both seriously affect their practical application. Here, a multifunctional nanofiber material based on cerium dioxide spheres embedded inside nitrogen-doped carbon fibers (denoted as NCF@CeO2) fabricated by electrospinning technology is used as an interlayer for high-performance Li-S batteries. The nitrogen-doped carbon fiber skeleton matrix provides a through-conducting grid to accelerate electron transfer at the interface of the nitrogen-doped carbon and the CeO2, and the large specific surface area guarantees a sufficient interfacial fast-redox reaction for sulfur species. CeO2 with a hollow structure provides strong physicochemical adsorption of lithium polysulfides (LiPSs) to weaken the migration behavior, and abundant oxygen defects as catalytic active sites are conducive to lithium sulfide conversion. The “sphere in fiber” construction minimizes the direct contact between the catalyst and electrolyte, effectively avoiding side reactions. Based on the multiple functions of nitrogen-doped carbon fibers and CeO2, Li-S batteries with NCF@CeO2 interlayers exhibit superior electrochemical performances, including a high discharge specific capacity of 1072.9 mAh g−1 at 0.2 C and a low capacity decay rate of only 0.063% per cycle after 1000 cycles. Moreover, the mechanisms of LiPSs adsorption-conversion and the quantification of the catalytic ability are elaborately clarified.

Ultrahigh-Strength Porous Ceramic Composites via a Simple Directional Solidification Process.

Porous ceramics possess great application potential in various fields. However, the contradiction between their pores and their strength have significantly hampered their applications. In this study, we present a simple directional solidification process that relies on its in situ pore forming mechanism to fabricate Al2O3/Y3Al5O12/ZrO2 porous eutectic ceramic composites with a highly dense and nanostructured eutectic skeleton matrix and a lotus-type porous structure. The flexural strength of this porous ceramic composite with a porosity of 34% is 497 MPa at ambient temperature, which is a new record of the strength of all current porous ceramics. This strength can remain at 324 MPa when the temperature increases up to 1773 K because of its refined lamellar structure and strong bonding interface. We demonstrate an interesting application of the directional solidification in efficiently preparing the ultrahigh-strength porous ceramic with high purity. The findings will open a window to the strength of porous ceramics.

Influence of the aggregate skeleton matrix and volumetric composition on the resistance of stone mastic asphalt to permanent deformation

The influence of different aggregate skeleton matrices, as well volumetric composition and mixture stiffness, on the resistance of SMA to permanent deformation was assessed. Nine SMA with different optimised aggregate skeleton matrices, studied elsewhere, were now evaluated to permanent deformation with wheel tracking. The results were statistically analysed concerning relationship with specimens’ volumetric characteristics, Marshall properties and mixture stiffness. Aggregate skeleton optimised with the dry rodded compaction tend to produce asphalt mixtures similar to SMA designed with pre-established grading envelopes. SMA with aggregate skeleton optimised with Proctor and steel roller compaction showed higher coarse aggregates and binder contents, and thus, it is expected a better cracking resistance and durability for the same level of resistance to permanent deformation. Statistical analysis shows that the new proposed property (ratio between binder film thickness and porosity) and, ratio between Marshall stability and flow had the best correlations with permanent deformation properties.

Delignified bamboo as skeleton matrix for shape-stable phase change heat storage material with excellent reversible thermochromic response property

Abstract In this study, the porous bamboo material (DB) was obtained by removing the intercalated substance between the fibers through a simple delignification process, and was used as support matrix by impregnating a reversible thermochromic compound (BP: BPA: TD) to prepare a shape-stable bamboo-based composite reversible thermochromic phase change material (TBB-DB). Fourier Transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analysis of bamboo and DB showed that lignin was removed from bamboo by the delignification process. The open porous structure founded in scanning electron microscopy micrographs allows the rapid impregnation of TBB to achieve reversible thermochromic and phase change storage properties. The reduction in surface roughness and contact angle leads to an increase in the hydrophilicity of the DB for the subsequent impregnation of the TBB into the porous structure of DB. DB also showed good mechanical properties and thermodynamic stability. The effects of different proportions of the color developer and the solvent in the compound TBB on the reversible thermochromic and phase change energy storage properties of TBB-DB were investigated. TBB-DB1:4:50 showed a better reversible thermochromic properties and energy storage properties (the highest latent heat, favorable melting and crystallization temperatures). As for TBB-DB1:4:50, the FTIR, XRD, thermal stability analysis showed that there is no chemical reaction occurred during the entire impregnation process, which is conductive to the reversible thermochromic phase change energy storage characteristics of TBB-DB1:4:50. The color of TBB-DB1:4:50 changed from rose red to white as the temperature increased. Compared with DB, TBB-DB1:4:50 showed endothermic and exothermic peaks, and its ΔHm and ΔHL+S were 113.5 J g−1 and 109.8 J g−1, respectively, indicating that TBB1:4:50 was well impregnated into DB to form a composite phase change material. TBB-DB1:4:50 also has good durability, making it able to withstand long-term recycling and maintain the original excellent performance.

SnO2 nano-crystals anchored on N-doped porous carbon with enhanced lithium storage properties

Sn-based oxides have been considered as promising anode candidates for lithium-ion batteries (LIBs), but their commercialization is always impeded by severe volume expansion and unsatisfactory electron conductivity. In order to overcome these disadvantages, a novel SnO2/C nanocomposites are devised and fabricated via a 3D-network composite-gel precursors derived from macromolecule polyacrylamide, in which ultrasmall SnO2 nanocrystals (<10 nm) are uniformly confined in the N-doped porous carbon skeleton matrix. To generate suitable carbon coating and inherit the N-doped porous framework, mild heat treatment at 300℃ is used to make the carbonization process moderate, which isconduciveto the formation of ultrafine SnO2 and further strengthen skeleton structure. Such a stable N-doped porous matrix allows the strengths, not only can the integrity of electrode and SnO2 nanoparticles be well maintained, but also the electronic conductivity and the quantity of active sites can be effectively promoted. As a result, this novel microstructure availably gives a reversible capability of 1011.2 mAh/g at 0.2A/g after 160 cycles and delivers a remarkable high-rate lithium storage of 357.8 mAh/g even at 12.8 A/g. Presumably, these findings may present a tactic to provide reasonable guidance for the design of metal oxide-based energy storage functional materials with huge volume variation.

Skeletonization-Scheme-Based Adaptive Near Field Sampling for Radio Frequency Source Reconstruction

Radio frequency (RF) source reconstruction is useful for RF radiation analysis and interference diagnosis in Internet of Things. Near field (NF) sampling is a critical step of RF source reconstruction. Accurate RF source reconstruction usually requires a large number of NF samples, which results in tremendous effort of NF sampling. This article presents an adaptive NF sampling method based on the skeletonization scheme. First, sources to be reconstructed are related to NF samples through integral equation (IE). Second, the IE is discretized with the method of moments, and thus the interaction matrix between source and field points is found. Third, strong rank-revealing QR factorization is applied to the interaction matrix, which results in a permutation matrix, a row skeleton matrix, and a transformation matrix. Finally, a small number of skeleton sampling points are selected by analyzing the permutation matrix. The fields at skeleton sampling points can be used to calculate the fields at other sampling points through the transformation matrix. Hence, one only needs to perform NF sampling at a small number of skeleton sampling points, which significantly reduces the expenditure of NF sampling. Simulations using synthetic and measurement data are presented to show the effectiveness and advantages of the proposed sampling method.

An Iteration-Free Domain Decomposition Method for the Fast Finite Element Analysis of Electromagnetic Problems

An iteration-free finite element domain decomposition method (DDM) is proposed for the simulation of 3-D electromagnetic problems. The finite element tearing and interconnecting (FETI) with Robin-type transmission condition is introduced to construct a domain decomposition framework. Based on hierarchical ( $\mathcal {H}$ -) matrix algorithm, the numerical Green’s function of each subdomain can be represented by a data-sparse matrix form. Subsequently, the original 3-D problem is reduced to a 2-D problem on the skeleton. Derived from the finite element discretization of pseudo-differential operator, the skeleton matrix can also be efficiently approximated with an $\mathcal {H}$ -matrix by assembling all the numerical Green’s functions of subdomains. Based on $\mathcal {H}$ -LU factorization algorithm, the computational complexity and memory requirement for the direct solution of the skeleton equation can be reduced to be logarithmic linear. The resulting direct FETI (D-FETI) method completely depends on direct method without any iterative process. Hence, it does not suffer from the issue of convergence rate, and avoids redundant computations for multiple right-hand side problems. Numerical examples demonstrate the effectiveness of the proposed method.

Effects of magnesium deprivation on development and biomineralization in the sea urchin Arbacia lixula

ABSTRACTEchinoderms have an extensive endoskeleton composed of magnesian calcite and occluded matrix proteins. As biomineralization in sea urchin larvae is sensitive to the Magnesium:Calcium ratio of seawater, we investigated the effects of magnesium deprivation on development and skeletogenesis in the sea urchin Arbacia lixula. We focused on the localization of the skeletogenic cells (primary mesenchyme cells) and the spatial expression of associated genes. Embryos reared in Mg-free seawater exhibited developmental delay from 6-h post-fertilization and at 24 h embryos showed complete lack of biomineral formation. Larvae (48–72 h) exhibited severe skeleton malformations. Fluorescent labelling revealed that the primary mesenchyme cells and the developing skeleton of treated embryos were in an abnormal ectopic location. Expression of the skeleton matrix protein gene (msp130) in the primary mesenchyme cells as seen using in situ hybridization was normal at 24 h. At 48 h this gene was down-regulated in control larvae, but not in treated larvae. Development of the pigment cells, immune cells that, like the skeleton, are mesodermal derivatives, was also impaired. Our results highlight the essential role of Mg in skeleton formation in sea urchin embryos with an indication that this element is also generally important for the development of mesoderm.Abbreviations: hpf: hours post fertilization; PMCs: primary mesenchyme cells; ACC: amorphous calcium carbonate; MgFSW: magnesium-free seawater; FSW: filtered seawaterImpact statementEchinoderms have an extensive endoskeleton composed of magnesian calciteWe investigated the effects of magnesium deprivation on development and skeletogenesis in the sea urchin Arbacia lixulaMagnesium deprivation caused developmental delay and skeleton malformationsPrimary mesenchyme cells of treated embryos were in an abnormal ectopic locationThe spatial and temporal expression profile of the skeleton matrix protein gene (msp130) was found to be different from controlsOur results highlight the essential role of Mg across developmental processes in sea urchin embryos.

Calculating skeleton matrix of asynchronous sequential machines based on the semi‐tensor product of matrices

In this study, the problem of calculating the skeleton matrix for asynchronous sequential machine (ASMs) is addressed in the framework of the semi-tensor product (STP) of matrices. By applying the STP of matrices and Boolean algebra, a new algebraic expression of ASMs is deduced. By utilising the algebraic expression, the skeleton matrix of ASMs can be easily derived, then the notion of generalised skeleton matrix is further defined for the ASMs with infinite cycles or critical races, and an algorithm of calculating the generalised skeleton matrix is also proposed. For the model matching problem of input/output ASMs, a novel approach is proposed to calculate reachability indictor and generalised fused skeleton matrix. Two examples are presented to illustrate the effectiveness of the proposed results.

Nanotechnology Applied to Chemical Soil Stabilization

The chemical stabilization of a soil is dependent on a wide range of parameters, being the most important ones associated to the soil properties and cementitious materials. The mechanical behavior of a soil can be improved with addition of nanoparticles, which are not a cementitious material but once introduced in a soil they are expected to reduce the interparticles’ spacing and nanoreinforce it. This will promote the construction of a stronger and stiffer soil skeleton matrix together with the cementitious materials. However, to maximize the benefits of the nanoparticles added to a stabilized soil it is crucial to overcome the problems related with particle agglomeration. Thus, it was defined a screening strategy which comprises the characterization of the nanoparticles, the definition of the aqueous medium with surfactant addition, the characterization of the surfactant and the application of energy to promote the particles’ dispersion. The quality of the suspension, in terms of particles’ dispersion, was evaluated trough the analysis of the particle size distribution given by dynamic light scattering (DLS). After, a series of performance tests with cement Portland and nanoparticles were conducted. The results from the unconfined compressive strength (UCS) tests have shown the high potential of adding multiwall carbon nanotubes to a chemically stabilized soil. The results have also pointed out the importance of the nanoparticles dispersion process.

스위칭 비동기 순차 머신을 위한 모델 정합 교정 제어기 설계

Abstract This paper presents the solution to model matching of switched asynchronous sequential machines by correctivecontrol. We propose a model of switched asynchronous sequential machines, in which the system can have dif-ferent dynamics of asynchronous machines governed by a pre-dete rmined sequence of switching. The control ob-jective is to derive a corrective control law so that the stable state behavior of the closed-loop system can matchthat of a prescribed model. A new skeleton matrix is defined to represent the reachability of the switched asyn-chronous machine, and a novel control scheme is presented that interweaves the switching signal and the correc-tive control procedure. A design algorithm for the proposed con troller is illustrated in a case study. Key Words : Switched Asynchronous Sequential Machines, Model Matching, C orrective Control, Switching Sequence.Received: Aug. 1, 2014Revised : Feb. 11, 2015Accepted: Feb. 17, 2015 † Corresponding author(jmyang@ee.knu.ac.kr)

Applying Multiwall Carbon Nanotubes for Soil Stabilization

The chemical stabilization of a soil is a technique where the soil is mixed with cementitious material in order to improve its mechanical behavior. The chemical stabilization is dependent on a wide range of parameters, being the most important ones associated to the soil properties and cementitious material characteristics. The nanoparticles are not a cementitious material but once introduced in a soil they are expected to reduce the interparticles’ spacing, which will promote the construction of a stronger and stiffer soil skeleton matrix together with the cementitious material, therefore improving the mechanical properties of the soil. Thus, optimization of nanoparticles distribution is required to obtain a final material with the best characteristics at a competitive cost. In order to maximize the benefits of the nanoparticles (multiwall carbon nanotubes, MWCNT) added to a stabilized soil it is crucial to overcome the problems related with particle agglomeration. Thus, it was defined a strategy which comprises the characterization of the MWCNT (zeta potential and size), the definition of the aqueous medium with surfactant addition (a plycarboxylate-based surfactant was tested), the characterization of the surfactant (viscosity, molecular weight, zeta potential and molecule size) and the application of energy (with a particular power and during a specific time) to promote the particles’ dispersion. The quality of the suspension, in terms of particles’ dispersion, was evaluated trough the analysis of the particle size distribution given by dynamic light scattering (DLS). After, a series of performance tests (unconfined compression strength, UCS) test with the soil were conducted over samples with 7 of curing time. The preliminary results of the performance tests have shown the high potential of adding multiwall carbon nanotubes to a chemically stabilized soil. The results have also pointed out the importance of the nanoparticle homogenization process where the presence of the surfactant has a major role.

Modeling Dynamic Behaviors of Reticulated Ceramic/Metal Composites (RCMC)

Reticulated ceramic/metal composites (RCMC) are characterized by the ceramic skeleton and metallic matrix both continuous in three-dimensional space, and this special structure makes full use of the ceramic phase’s high strength and the metal phase’s toughness. Correspondingly, the deformation and damages mechanisms of RCMC under dynamic load conditions are very complicated and the related studies are quite important. In the current study, the dynamic properties of RCMC are investigated by using finite element methods based on the factitious microstructures of SiC/Al composites. The ceramic/metal interface is induced by employing a “constrained-tie-break” method, so as to study the effects of interface when suffering from a dynamic impact loads. Effects of the phase distribution, shape, ratio, as well as the size are systematically analyzed. The methods proposed in this paper would be helpful for predicting the dynamic behaviors of RCMC, and developing new ceramic/metal composites.