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This study reports treatment of low-zinc EAF dust for obtaining high-grade metallized product with a focus on multiple valuable elements via microwave reduction followed by magnetic separation. In reduction, the conversions of components of iron, zinc, lead, manganese and chromium, mainly in the form of spinel phases, to Fe, Zn, PbCl2, MnO and Cr2O3, respectively, were partially restrained by the formation of complex silicates, e.g., Ca3Al0.84Fe1.16Si3O12. After microwave reduction under the conditions of C/Fe mass ratio of 0.25, temperature of 1323 K, dwell time of 15 min, heating rate of 25 K/min and microwave power of 2200 W, the reduced briquette had the iron metallization degree of 96.20%, with volatilization of 98.38% of Zn and 80.22% of Pb. By magnetic separation, a high-grade metallized product containing 81.77 wt% Fe (79.97 wt% metallic iron) and 0.04 wt% Zn, satisfying the Chinese standard (YB/T 4272–2012) of the first-grade metallized product from dust, was obtained.

To dispose the problem of ferronickel slag for its value-added application, it was used for preparing thermal insulation materials by sintering of the slag in the presence of another waste, fly ash cenosphere (FAC), as pore former. The thermodynamic and experimental analyses revealed that the original phase of the slag, olivine, could be transformed to thermal insulation phases, including enstatite and cordierite, by optimizing sintering temperature in the range 1100–1300 °C. Specifically, after initial decomposition of ferronickel slag, there existed a low-iron olivine phase and cordierite and enstatite became the dominant phases when the sintering temperature increased from 1100 °C to 1300 °C. Except for the phase transformation, the microstructural evolution with proper pore features (porosity and size) contributed to a resulting material with desirable thermal and mechanical properties. It was shown that the ferronickel slag sintered at 1200 °C for 2 h with the addition of 25 wt % FAC exhibited the optimal thermal and mechanical performance. Additionally, it possessed good acid and alkali resistances. The results confirmed the feasibility of co-utilization of ferronickel slag and FAC for producing superior thermal insulation materials at a proper temperature, making efficient utilization of both wastes.

A novel strategy for selective recovery of chromium from ferronickel slag via microwave assisted sodium peroxide roasting followed by water leaching was proposed in this study. The experimental results showed that 94.21% of chromium was leached with 64.43% of sodium and 6.13% of silicon, while only 0.06 wt% chromium remained in the leaching residue when the mixture of ferronickel slag and sodium peroxide with the mass ratio of 1 was roasted at 600 °C for 20 min before leaching at 50 °C for 1 h with the liquid-to-solid ratio of 10 mL/g. In comparison with conventional roasting, the microwave roasting showed a much higher efficiency for recovering chromium from ferronickel slag with the recovery of chromium increased by 12.92%, resulting from the enhanced conversion of Cr2O3 in the slag to NaCrO2 and from the looser and more porous structure during the roasting process which was beneficial for subsequent water leaching.

A series of Fe/h-BN catalysts promoted with Cu or Mn were prepared for Fischer-Tropsch synthesis (FTS). The physicochemical properties, crystal structures and morphologies of the catalysts were characterized by N2 physisorption, FT-IR, TPR, XPS, XRD, MES and TEM. It is found that iron oxide nanoparticles are highly dispersed on h-BN matrix due to the anchoring effect of surface defects and the accommodation of porous structures of h-BN. The characterization results indicate that strong interaction between iron oxide and h-BN is present on un-promoted catalyst, which endows the h-BN supported iron catalyst with stable properties under FTS conditions but severely retards reduction of the catalyst. The addition of Cu to Fe/h-BN can to some extent overcome the strong interaction by introducing more sites for dissociating H2. It is observed that Cu promoter can increase the reduction or carburization degree and thus enhance the FTS activity. The addition of Mn to Fe/h-BN can weaken the strong interaction by altering the electron structure of iron species. And the electron-rich Fe species are responsible for easy reduction and the enhanced FTS performance. Besides, a higher activity can be realized by co-adding Cu and Mn to the Fe/h-BN catalyst. These results suggest that the synergistic effect of Mn and Cu can largely improve the performance of Fe/h-BN catalyst without impairing the stability of the catalyst. The present study paves a way to tailor the performances of FTS catalysts with h-BN as support.

The surface chemistry of catalyst plays a vital role in the catalytic process. And the effects of surface groups of porous boron nitride (p-BN) on the hydrogenation reaction have not been studied in detailed. In this work, two main surface species of Co/p-BN catalyst were tuned thermally and their roles on the hydrogenation reaction were discriminated by α, β-unsaturated aldehyde hydrogenation reaction. The surface B O content decreased at higher reduction temperature and the cobalt phase changed from CoO to the mixture of CoO and Co0. The Co/p-BN-500 exhibited the highest selectivity to C O hydrogenation. And its turnover frequency (TOF) of 13.2 h−1 is close to the optimal value of reported cobalt catalysts. When the reaction proceeds, hydrogenation rate of C O increases but that of C C decreases gradually, thus a surface groups variation was expected at the initial period. Further in-situ FTIR spectra showed the band intensity of edge N H increases as the adsorption proceeds at 50°С but it decreases as the temperature rise to 200°С, in combined with the shift of C O adsorption peak, a intermolecular hydrogen bond between edge N H and the terminal C O group was suggested, which account for the better selectivity to C O than C C.

Coating actives with carbon is an effective way to improve the performance of Ni Fe battery, and relevant study has focused on the nanoFe/FeOx, while the micron particles used in the industry have been usually ignored. Herein, we achieve the uniform and thickness-controllable carbon coating for the micron-sized dodecahedral Fe3O4, and study the influence of the carbon thickness on the performance of the Fe anode in details. As a result, capacity, rate performance and stability are improved with the increase of carbon coating because of lower charge-transfer resistance and more complete structure. However, for the first plateau (Fe0→Fe2+) which is typically applied in the industry, the improvement of the carbon coating is limited with the thickness of the carbon, owing to insufficient impact of mitigating passivation. For the second and third plateaus (Fe2+→Fe3+), with the increase of the carbon coating, the capacity and rate performance are both markedly improved because a more completed structure can better promise the conductivity. As the thickness of the carbon coating is 20 nm, the electrode exhibits 141 mAh g−1 at a high current density of 36 A g−1. These results are of great significance to the development of industrial Ni-Fe battery.

Nitrogen doping is an efficient strategy to improve the catalytic activity of carbocatalysts in direct dehydrogenation reactions. The interpretation of enhanced activity is now mainly attributed to the strengthened basicity. On the other side of doping, electronic properties that differed in various nitrogen doping configurations, however, were barely considered. Herein, to elucidate the role of graphitic N, pyridinic N and pyrrolic N, N-doped porous carbon balls with tunable contents of these nitrogen species were used as moulded carbocatalysts for steam-free direct dehydrogenation of ethylbenzene to styrene. Along with C O groups that were commonly certified as active sites on carbocatalysts, graphitic N contributes to the styrene yield. The former serves as active site that directly activates and dissociates C–H bond, while the latter one provides additional electrons into the delocalized π-system and leads to improved chemical reactivity of C O. The loss of C O active sites is not only attributed to the carbon deposition as illustrated by the elevated area ratio of D3 to G band in Raman spectra, but also its failed regeneration from intermediate hydroxyl groups (C–OH), which was proved by the tiny thermal decomposed products of CO and H2O as detected by the on-line mass spectrometry and gas chromatography.

This paper investigated the combustion behavior of coke breeze granulated with other raw materials for iron ore sintering in a broad temperature range up to 1350 °C in air and sintering flue gas atmosphere, based on the exploration of the physiochemical characteristics of the coke breeze granules in industry. It was shown that after granulation the −0.25 mm coke breeze particles adhered to nuclei constituted by other sintering raw materials or served as a component of granules composed of mixed fine particles with homogeneous composition. Conversely, +0.5 mm coke breeze particles acted as nuclei to which fine particles of other materials adhered. The coke breeze particles with size of 0.25–0.5 mm, on the other hand, had dual roles as either adhering fines or nuclei. According to the combustion tests of typical granules consisted of −0.25 or 2–3 mm coke breeze particles, the structure and size of the granules as well as atmosphere strongly affected the combustion behavior of coke breeze. The adhering fines on the surface of coke breeze caused a decrease in its combustion rate in air (e.g., up to 26% at 950 °C and 1050 °C). Compared with the adhering fines, the sintering flue gas atmosphere played a more pronounced role in reducing the combustion rate. In this atmosphere, the combustion rate was in close association with the reaction between coke breeze and iron oxide in adjacent iron ore particles. The granules composed of −0.25 mm mixed particles could exhibit lower reduction reaction temperature (approximately a 100 °C difference) and stronger reduction reaction intensity than those consisted of coarse coke breeze in the size of 2–3 mm, leading to a higher heat loss. Minimizing the addition of −0.25 mm coke breeze, maintaining the highest combustion temperature at around 1300 °C, and keeping relatively high oxygen content in atmosphere are expected to promote combustion efficiency of coke breeze and thus energy utilization in iron ore sintering.

Due to its high carbon and low impurities contents, as well as good reactivity, biochar can partly or totally replace coal or coke as a promising reducing agent in metallurgy. This study offers a new method to produce qualified metallized pellets for steelmaking after microwave-assisted self-reduction of iron ore-biochar composite pellets. The key point was to prepare green composite pellets with good quality indexes which also allowed sufficient self-reduction under microwave irradiation. For this purpose, core-shell iron ore-biochar composite pellets were prepared with inhomogeneous biochar distribution. It was found that high grade iron concentrates A and B could be used together for improving pelletizing. Controlling the distributions and proportions of iron concentrate B (different additions in the core and shell) and biochar (all located in the core of the pellets) would contribute to high-quality iron ore-biochar green composite pellets with the drop number of 3.6 times/0.5 m, compressive strength of 11.1 N/p, and decrepitation temperature of 410 °C under the pelletizing conditions of total proportion of iron concentrate B of 30%, pelletizing time of 16 min, rotation speed of 25 r/min, bentonite dosage of 2.3%, C/Fe mass ratio of 0.225, pellet moisture content of 13.0%, and proportions of iron concentrates A and B in the shell of 10% and 0%, respectively. The subsequent microwave reduction tests showed that the core-shell metallized pellets with the total iron content and metallization degree of 89.15% and 95.52%, respectively, could be obtained after microwave reduction at 1050 °C for 30 min under N2 atmosphere. They had better reduction indexes than those produced from the pellets with homogeneous structure, serving as a good burden for steelmaking directly.

The development of efficient and low-cost hydrogen evolution reaction (HER) catalysts is critical for energy storage and conversion devices. Herein, we develop a facile method to fabricate a novel hybrid by in situ growing CoP porous nanoplates on reduced graphene oxide (RGO). The hybrid shows excellent HER performance in acid media with a low Tafel slope of 57 mV dec−1, small onset overpotential of 76 mV and long-term durability with 86.3% current density retention after 10 h electrocatalysis. The superb HER activity can be ascribed to the unique structure of porous hexagonal nanoplates. On the one hand, the porous structure provides abundant active sites for HER. On the other hand, hexagonal nanoplates provide large contact with RGO, enhancing the charge transfer ability. In addition, the hybrid with such structure shows good stability under ambient atmosphere and can maintain the initial HER activity even after six months of storage. This work demonstrates that large contact between active component and conductive support is not only beneficial to the HER activity and durability, but also beneficial to the stability of material itself.

Rational design and optimization of metal-free electrocatalysts for the oxygen reduction reaction (ORR) is crucial for fuel cells and metal-air batteries. However, identifying design principle that links the active sites and their synergistic effects is far from satisfactory, especially for B,N-codoped graphene. Herein, we provide four B,N-codoped porous graphenes with tunable contents of pyridinic N, graphitic N, BC3 and C-B(N)O. BC3 shows multiple-fold specific activity compared with graphitic N and pyridinic N, while C-B(N)O offers no positive contribution. Density functional theory calculations indicate that the synergistic effect between graphitic N and BC3 can effectively facilitate the reduction of O2. These pinpoint that graphitic N and BC3 are the main active sites among various nitrogen or/and boron doping configurations. The most active catalyst exhibits superior activity than the commercial Pt/C catalyst using the RDE method in alkaline media, and displays comparable power density to Pt/C catalyst in Zn-air battery.

For most of WO 3 , a visible-light-driven photocatalyst, its barrier in photocatalytic degradation is the low conduction band (CB) potential that can not reduce O 2 to O 2 − and HO 2 radicals and thus results in fast recombination of electron/hole. With this in mind, a new active FeWO 4 /Fe 2 O 3 di-modified WO 3 was designed and prepared via by a straightforward but effective strategy by introducing of FeWO 4 and Fe 2 O 3 clusters (or nanoparticles) on WO 3 . The performance of di-modified WO 3 showed super high photocatalytic activity in degrading quasi-phenothiazine dyes of Methylene blue (MB), Toluidine blue (TB), Azure I (AI) and Acridine orange (AO) under visible light irradiation, and the corresponding k values are 5.3, 4.4, 3.8 and 5.8 times larger than that of pure WO 3 , respectively. This improvement was mainly due to the fact that photoexcited electrons can migrate to the matching CB of firmly and highly dispersed FeWO 4 and Fe 2 O 3 , then be consumed rapidly by a valence decrease from Fe 3+ to Fe 2+ and Fenton reaction between Fe 2+ and H 2 O 2 . And the strong adsorption of Fe species toward N and S (or N) elements in quasi-phenothiazine dyes, also positively promoted the efficiency of degradation.

Hexagonal boron nitride nanosheets (BNNSs), which show outstanding thermal conductivity and chemical stability, have drawn more and more attention in recent years. However, the limited yield, dispersivity and the polydispersed size of the exfoliated ones hinder their further application. Here, we present a method of effective and scalable synthesis of quasi-monodispersed BN colloidal nanocrystals by “solid-state synthesis” combined with “solvent cutting” technique. The key of the technique is the imperfect nitridation of the BO species, which yield the boron oxides and amorphous BN that coexist with the well crystallized BN domains. As the impurities that separate the well crystallized BN domains are removed, the BN skeleton with better crystallinity is remained. The BN colloidal nanocrystals are obtained when the solvents cut the weak grain boundary in BN skeleton. The lateral size of as-prepared BN colloidal nanocrystals could be well controlled for 3 nm, 10 nm and 20 nm. The zeta potentials of colloid are below −30 mV in a pH range of 5–12. That means the BN colloid can keep high colloidal stability over a wide pH range. As an exemplary application of colloidal BN nanocrystals, the BN film is coated on the copper foil by a simple dip-coating method. The coated copper foil shows remarkable anti-electrochemical corrosion property. This study not only paves a way for the synthesis of colloidal BN nanocrystals, but also gives an alternative choice for a facile and low cost protective BN coating.

The influence of growth parameters such as N2/Ar mixture, sputtering pressure and growth time on InxAl1−xN films is investigated. We find that with an increase in N2 flow rate from 6 to 12 and 18sccm, the RMS has substantially improved from 5.4 to 2.5 and 2.35 nm. The full width at half maximum (FWHM) is decreased as the N2 flow rate increases. The grain size and thickness shows an almost linear relationship with N2 flow rate variation. The granular structure grown at 1 Pa seems to be more compact than the sample at 1.5 Pa and 1.2 Pa. As the growth time is increased to 60, 90 and 120 min, the crystallite size is 7, 9 and 14 nm and the RMS is measured to 2.35, 3.57 and 4.14 nm, respectively. The thickness of the samples has a certain positive relationship with the pressure and growth time. In addition, we find the optimizing growth parameter is 18sccm N2 flow rate, 1 Pa pressure and 60 min growth time. The In content (x) is calculated to be 0.6. The band gap of the film is calculated to be 1.97 eV. The sheet resistance of the optimizing growth parameter is 1076 (Ω/□). We further fabricate In0.6Al0.4N photoelectric device, which is revealed to have significant photo-respond with stable photocurrent. The saturation time of the current is 0.5–0.8 s. Our work is meaningful for InxAl1−xN film layer improvement and application in the future.

The feasibility of a facile route to recover platinum-group metals (PGMs) from spent catalyst by microwave smelting of spent catalyst with the additions of nickel matte as metal collector and sodium salts as fluxes was verified, based on the thermodynamic and experimental analyses which evaluated the dielectric properties, conductivities/resistances and viscosities of the materials involved in the smelting process. The results showed that the combined use of sodium salts reduced the viscosity and smelting temperature effectively by breaking the silicon-oxygen tetrahedron structure which facilitated the collection of PGMs and the separation of PGMs-enriched nickel matte from smelting slag. In association with the eddy current loss and swirling sedimentation effect produced by microwave heating, 98.59% of Pt, 97.91% of Pd and 97.16% of Rh were collected under the optimal smelting conditions of the mass ratios of nickel matte, Na2B4O7 and Na2CO3 to spent catalyst of 1.25, 0.575 and 0.125, respectively, temperature of 1250 °C, time of 2 h, and N2 atmosphere. This new strategy enabled rapid collection of PGMs from spent catalyst at the low temperature within a short time, contributing to energy conservation and environmental protection.

This study addresses the difficulty of obtaining relatively low-cost semi-polar (11–22) AlN films epitaxially grown on m-plane sapphire substrates with high crystalline quality by applying a cost-effective high-temperature annealing process conducted at 1700 °C to films grown via standard-temperature metal organic chemical vapor deposition. The X-ray diffraction rocking curves of the annealed films along the [11–23] and [10–10] directions obtain full width at half maximum values of 0.152° and 0.193°, respectively. Atomic force microscopy results demonstrate the occurrence of a significant recrystallization process in the columnar formations of AlN films during annealing, resulting in increased AlN crystal grain size. Raman spectroscopy measurements reveal that the semi-polar (11–22) AlN films are subject to increased compressive stress after the annealing process. Transmission electron microscopy analyses confirm that our semi-polar AlN films provide appropriately low dislocation and basal stacking fault densities of 5.6 × 109 cm−2 and 1.05 × 105 cm−1, respectively. The proposed approach therefore obtains low-cost AlN films that are suitable for the mass manufacture of efficient optoelectronic devices.

Compared with mushroomed progress in metal-free C-rich BCN catalysts, little is known about the BN-rich BCN or even BN ones. Its related study has drawn great interest recently but still in its infancy stage. In this study, three kinds of BCN nanosheets (NSs) with tuned surface carbon contents (5.5–14.3%), specific surface area (SSA, 82–290 m2/g) and morphologies (ultrathin nanosheets, triangular plates) were fabricated through a solid state reaction by simply adjusting the reaction temperature, and those effects on the ethylbenzene dehydrogenation performances were studied in CO2 atmosphere. The morphology evolution of BCN NSs from ultrathin nanosheets to the triangular plates was observed and control experiments were carried out. The BCN nanosheets show relatively strong interaction with CO2 and distinct CO2 absorption properties. The CO2 temperature programmed desorption also indicates that the desorption peaks of CO2 are above 400 °C, enabling them potential CO2 utilization catalysts. A weak association was found between the surface C contents and the catalytic performance as it normalized with SSA, and the B-O species could be taken as an active site in CO2 atmosphere. Though much progress still needed, it is convincing that the BCN catalyst could be a promising metal-free catalyst in dehydrogenation beyond carbocatalyst.

The correlation between the catalytic activities and electrochemical features of MoSx material is important to study the work process of structure on catalytic performance. In this work, adopting the centimeter-scale ultra-thin MoSx film as a research model, we try to establish a persuasive electrochemical features–catalysis correlation in two different ultra-thin MoSx structures, of which one is O contaminated and another is O free. The results indicate that whatever the structure of MoSx is, high turnover frequency (TOF) and large cathodic current density (J) require low charge-transfer resistance (Rct); low over-potential (η) requires low charge-transfer resistance (Rct) and rich active sites; low Tafel slope requires the high activity of the active sites; and high exchange current densities (Jo) requires a match between the activity of the active sites and Rct. These results provide useful information for the further improvement of MoSx material. From the catalytic activities we can infer which parameters of the electrochemical features need to be improved, and then selectively adjust its physical structure.

In this manuscript, we provide a framework for zero-Hopf singularity for a general two dimensional system with two delays. The distribution of the eigenvalues for the linearized system at an equilibrium point is studied in detail. Explicit conditions for the system to undergo a zero-Hopf bifurcation are established and the corresponding normal form up to the third order terms is derived. Our theoretical results are applied to a Kaldor–Kalecki model of business cycles.

The replacement of superheated steam with CO 2 for ethylbenzene (EB) dehydrogenation to produce styrene (ST) is of great importance from both scientific and practical perspectives, while it is still a big challenge to design and synthesize catalysts for dehydrogenation in the presence of CO 2 . Research into shape-controlled nanocrystals has proved that well-defined facets are of great importance for understanding the catalytic phenomena due to their definite surface structure. In the present work, α-Fe 2 O 3 nanocrystals enclosed by various crystal facets provide us the clue to understand the role of CO 2 in dehydrogenation. O(III) (the triply coordinated surface oxygen atom) is found to play an important role in activating CO 2 under reaction conditions, which is supported by both experimental and theoretical results. These results have deepened knowledge about the role of CO 2 in dehydrogenation over pure α-Fe 2 O 3 catalysts, which is significant in designing relative catalysts rationally.

The reduction of ferromanganese spinel (MnFe2O4) in microwave field using biochar as reducing agent was investigated in this study. It was found that the MnFe2O4-biochar composite briquette possessed good microwave absorption capability with microwave penetration depth less than 20 mm at 2.45 GHz, enabling its efficient self-reduction under microwave irradiation. The MnFe2O4 was initially reduced to monoxide and then transformed to metallic iron and MnO. The iron metallization degree of reduced briquette reached 90.19% under the conditions of the C/MnFe2O4 molar ratio (n(C)/n(MnFe2O4)) of 3, reduction temperature of 1050 °C, and dwell time of 15 min. The selective heating effect of microwave induced the transformation of MnFe2O4 and promoted the breaking of chemical bond between Mn and Fe based on the density functional theory analysis. The microwave heating mechanism was associated with the phase transformation in the reduction process. At low temperatures, the dielectric loss due to interfacial polarization and dipolar polarization and the magnetic loss originated primarily from natural resonance controlled the heating process. As the temperature exceeded 572.9 °C, the composite briquette had a sharp decrease of magnetic response. The formation of (FeO)x(MnO)1-x led to slight fluctuations of permittivity with increasing temperature. When the temperature was higher than 903.5 °C, the conductive loss increased dramatically because of the formation of metallic iron, which could speed up the reduction process due to the “lens effect” of microwave. Based on the combined use of microwave energy and sustainable reducing agent with a focus on the correlation between phase transformation and microwave heating mechanism, this study has validated the feasibility of the route for comprehensive utilization of spinel-structured metallurgical solid wastes, showing the bright prospect of its industrial applications.

A better understanding of the gravity flow mechanism of caved material is required to increase ore recovery in caving mining. This study presents a novel computational framework PRF3D (3D particle random flow) capable of simulating the flow behavior of caved ore and rock in sublevel caving mining. The PRF3D framework combines the advantages of the discrete element method and stochastic medium theory and uses the billboard technique of OpenGL to render and visualize particles. The new framework can automatically record the ore recovery indicators, display the shape of the draw zone in real time and capture the fines percolation. An isolated physical draw experiment is conducted to validate the accuracy and efficiency of the PRF3D from both qualitative and quantitative perspectives. After validation, various numerical tests are conducted to investigate the influence of the sublevel height, drawpoint spacing, drawpoint size and particle size of overlaying rock on the multidraw behavior of caved ore and rock in sublevel caving mining. The performance of PRF3D is also demonstrated by benchmarking with the reported simulations.

Ni modified MoO3 (Ni-MoO3) had been synthesized by a facile one-step hydrothermal technique and was used for oxidative desulfurization (ODS) of dibenzothiophene (DBT) in the decalin/acetonitrile biphasic system with H2O2 as oxidant, the effect of different operating conditions was investigated. Under the optimal reaction condition, Ni-MoO3 catalyst showed excellent ODS performance toward DBT, the highest sulfur removal efficiency can be up to 99.8% and sulfur content was wiped out from 5000 to 10 ppm, which is more effective than the recent reported MoO3-based catalysts. The reaction kinetics obeyed the pseudo-first-order equation with an apparent rate constant of 0.076 min−1, which is twice that of pure MoO3 (0.035 min−1). The ODS mechanism of DBT with Ni-MoO3 was explored by combining radical scavenger, FT-IR experiments and theoretical analysis, proving that surface oxygen vacancies and Lewis acid sites play important roles in the high-efficiency ODS reaction with Ni-MoO3 catalyst.

Since electromagnetic pollution is becoming more and more serious, novel composite microwave absorbents are gaining much attention. Here, Co3Fe7/C core–shell microspheres for microwave absorption were synthesized for the first time. At first, hollow CoFe2O4 microspheres were prepared via a solvothermal method at 200 °C for 15 h. Then CoFe2O4-hydrochar microspheres were synthesized by hydrothermal method in an aqueous glucose solution containing hollow CoFe2O4 microspheres. After annealed under Ar atmosphere at 500 °C, the CoFe2O4-hydrochar microspheres were converted into CoFe2O4–Co3Fe7/C microspheres. Co3Fe7/C core–shell microspheres came into being after annealed at 600 °C. Both the CoFe2O4–Co3Fe7 nanoparticles and Co3Fe7 nanoparticles were encapsulated in the carbon shells, and the microsphere morphology could be retained during the carbothermal process. Especially, the core–shell structure caused that the density of the Co3Fe7/C microspheres was below 2 g/cm3. Resulting from the synergistic effect of Co3Fe7 nanoparticles and partially graphitized carbon, the minimum reflection loss (RL) of Co3Fe7/C microspheres was as low as −44.4 dB obtained with 1.6 mm thickness. Owing to the characteristics of low density and good microwave absorption, the Co3Fe7/C core–shell microspheres could be used as a lightweight and highly efficient microwave absorbent.

Mesoporous Fe/C and core–shell Fe–Fe3C@C composites were successfully prepared through the in-situ polymerization of Fe3+/phenolic resin coupled with F127 and the subsequent high-temperature carbonization. The experiments involved the preparation of an iron-containing carbon precursor and the heat-treatment process. Two composites with different morphology and structure could be obtained by changing the content of Fe(NO3)3·9H2O in the precursor. The crystalline phase, structure and microwave absorption of the two composites were investigated. Fe particles were uniformly embedded into the mesoporous networks to form mesoporous Fe/C composite with high surface area of 467.3 m2/g and low density of 1.92 g/cm3. The Fe–Fe3C particles encapsulated by graphitized carbon layers formed the core–shell structure with surface area and density of 259.5 m2/g and 2.67 g/cm3. Fe/C and Fe–Fe3C@C composites exhibited excellent electromagnetic absorbing ability, the effective absorption bandwidth reached 3.36 and 5.04 GHz with the matching thicknesses of 2 and 1.5 mm correspondingly. This originated mainly from the effective impedance match and multiple interfacial polarizations. Furthermore, the increase of Fe3+ not only promoted the graphitization degree of carbon shell, but also increased the complex permittivity and permeability of core–shell structure, thus improved the impedance matching. Owing to high surface area, low density and excellent microwave absorbability, the mesoporous Fe/C and core–shell Fe–Fe3C@C composites are promising candidates as lightweight and high-efficiency microwave absorbents.

Since electromagnetic pollution is becoming more and more serious, the lightweight and highly efficient microwave absorbents are urgently needed to absorb unwanted electromagnetic microwaves. In this work, single-crystal octahedral CoFe 2 O 4 nanoparticles with the diameter of about 20–25 nm were successfully incorporated into the porous carbon balls (CB) via a one-step hydrothermal method. The incorporation of the CoFe 2 O 4 nanoparticles into CB reduced the dielectric loss and increased the magnetic loss, resulting in better impedance matching. When the CoFe 2 O 4 content in CoFe 2 O 4 /CB composites was 10 wt.%, the minimum reflection loss (RL) was as low as −37.2 dB, and the frequency band of RL below −10 dB was 12.9–17.1 GHz obtained with 1.5 mm thickness. This excellent microwave absorption performance was much better than that of the pure octahedral CoFe 2 O 4 nanoparticles, CB, and CoFe 2 O 4 /CB composites with CoFe 2 O 4 content of 8.5 wt.%. Owing to the low density of 1.1–1.2 g/cm 3 and good microwave absorption, the CoFe 2 O 4 /CB composite can meet the multiple requirements of microwave absorbent.

In this work, monodisperse hollow cobalt ferrite (CoFe 2 O 4 ) microspheres with mean diameter of 150 nm and shell thickness of 50 nm have been successfully prepared via a one-pot solvothermal method. In order to improve the microwave absorption, a thermal reduction process was designed to synthesize hollow CoFe 2 O 4 –Co 3 Fe 7 microspheres. Scanning electron microscopy and transmission electron microscopy images showed that the CoFe 2 O 4 –Co 3 Fe 7 microspheres retained hollow structure. Microwave absorption results revealed that hollow CoFe 2 O 4 –Co 3 Fe 7 microspheres exhibited much stronger electromagnetic absorption than the original hollow CoFe 2 O 4 microspheres. Most importantly, when the sample thickness was 1.3 mm, the reflection loss (RL) less than −10 dB was obtained in the frequency range of 12.5–17.7 GHz, which nearly covered the entire Ku-band. When the sample thickness increased to 2 mm, the minimum RL was as high as −41.6 dB with the effective bandwidth (the bandwidth of RL at −10 dB) of 3 GHz. The enhanced microwave absorption was attributed to efficient complement between dielectric loss and magnetic loss. These results indicated that the hollow CoFe 2 O 4 –Co 3 Fe 7 microspheres could be used as a new candidate for microwave absorbents, especially in Ku-band.

Anti-retroviral treatments (ART) such as HAART have been used to control the replication of HIV virus in HIV-positive patients. In this paper, we study an in-host model of HIV infection with ART and carry out mathematical analysis of the global dynamics and bifurcations of the model in different parameter regimes. Among our discoveries is a parameter region for which backward bifurcation can occur. Biologically, the catastrophic behaviors associated with backward bifurcations may explain the sudden rebound of HIV viral load when ART is stopped, and possibly provide an explanation for the viral blips during ART suppression of HIV.

This manuscript is to study codimension-2 bifurcations for coupled nonlinear BVP oscillators with hard characteristics. Sufficient conditions are given for the model to demonstrate Hopf, Bogdanov-Takens (BT), double Hopf, and fold-Hopf bifurcations. By computing normal forms of those bifurcations, bifurcation diagrams such as Hopf, homoclinic, double limit cycle, and torus bifurcations are obtained. Some examples are given to confirm the theoretical results.

In this study, corrosion synthesis of boron carbide particles with pore size ranging from hundreds of nanometers to several micrometers was reported. Firstly, the pristine boron carbide powders which contain free carbon have been synthesized at 350 °C in a steel autoclave. As the pristine boron carbide was refluxed by HClO 4 at 170 °C for 1–2 h, the boron carbide particles with macropores were produced. Similarly, the boron carbide nanocages can also be obtained. The corrosion of the embedded amorphous and/or low crystallinity carbon/boron carbide using HClO 4 was considered for the formation of boron carbide with macropores and hollow nanocages.

Honeycomb-like graphitic macroporous carbon (HGMC) was synthesized by means of pyrolysis of NH4HCO3 using Mg powder as reductant in an autoclave at 550 °C. The characterization of structure and morphology was carried out by X-ray diffraction (XRD), Raman spectrum, field-emission scanning electron microscopy (FESEM), and (High-resolution) transmission electron microscope [(HR)TEM]. The results of nitrogen adsorption–desorption indicate that the products are macropore materials with the pore size of 1–3 μm, and the Brunauer–Emett–Teller (BET) surface area was 14 m2/g. As a typical morphology, the possible growth process of HGMC was also investigated and discussed. The experimental results show that the in situ formed MgO microparticles play a template role during the HGMC formation.

A system of three coupled van der Pol oscillators with delay is considered. Hopf bifurcations at the zero equilibrium as the delay increases are exhibited. The existence and stability of multiple periodic solutions are established using a symmetric Hopf bifurcation result of Wu (Trans. Amer. Math. Soc. 350 (1998) 4799–4838).

In this paper, we study the dynamical behaviors of the following van der Pol oscillator with delay x@?+@e(x^2-1)x@?+x=@eg(x(t-@t)). In the case that its associated characteristic equation has a simple zero root and a pair of purely imaginary roots (zero-Hopf singularity), the normal form is obtained by performing a center manifold reduction and by using the normal form theory developed by Faria and Magalhaes. A critical value @e"0 of @e in (0,2) is obtained to predict the bifurcation diagrams from which saddle-node bifurcation, pitchfork bifurcation, Hopf bifurcation (the existence and stability of the periodic solutions), and heteroclinic bifurcation are determined. Some examples are given to confirm the theoretical results.

Leaf-like carbon sheets have been obtained by the pyrolysis of dichloromethane and ferrocene in an autoclave in 300–600 °C on Cu ribbons for 90 min. The thickness of the sheets could be controlled from 50 to 200 nm by adjusting the experimental parameters. The formation process was studied by observing product-evolution utilizing the real-time imaging capabilities of emission scanning electron microscope, and it is considered that Diffusion-Limited Aggregation mechanism could be responsible for their growth. Thermo-gravimetric analysis curves show that the initial thermal decomposition temperature of the carbon sheets increases from 300 to 420 °C with the increasing preparation temperature. The Brunauer–Emmett–Teller specific surface area was 398 m 2 /g and with a narrow pore distribution in the range of 2–5 nm. By changing the carbon sources, solid carbon spheres as well as chain-like solid carbon spheres (3–5 μm) could be selectively prepared using one-pot reactions.

In this paper, we study the following Kaldor–Kalecki model of business cycles describing the interaction of the gross product Y and the capital product K : { d Y ( t ) d t = α [ I ( Y ( t ) ) − β K ( t ) − γ Y ( t ) ] , d K ( t ) d t = I ( Y ( t − τ ) ) − ( β + q ) K ( t ) . Single and multi-parameter bifurcation analysis of the system is carried out to perform center manifold reduction. We show that this system can exhibit codimension-1 singularity (transcritical and pitchfork bifurcations) and codimenion-2 singularity (nontransversal and symmetric BT bifurcations) under certain conditions on the time delay τ and the nonlinearity of I ( Y ) by using the normal form method for DDEs due to Faria and Magalhaes. In addition, we use the normal forms of the system to predict bifurcation diagrams such as pitchfork bifurcations, homoclinic bifurcations and double limit cycle bifurcations, which are confirmed by numerical simulations.

Silicon carbide (3C-SiC) nanocrystals were prepared starting from SiO2, C2H5OH, and metallic Mg in an autoclave at 200 °C. X-ray diffraction patterns of the sample can be indexed as the cubic phase of SiC with the lattice constant a = 4.357 A, in good agreement with the reported value (JCPDS card no. 29-1129; a = 4.359 A). Transmission electron microscopy images show that the product mainly composed of nanowires with diameters in the range of 10–30 nm and lengths up to tens of micrometers; High-resolution transmission electron microscopy images reveal that these 3C-SiC nanowires grow along [1 1 1] direction; As polyvinylpyrrolidine was added into the above reactant system, the final products obtained at 180 °C were mixed 3C and 2H-SiC flakes. Thermal gravimetric analysis curves reveal that these two samples have thermal stability below 800 °C, and room-temperature photoluminescence spectrum of the 3C-SiC sample show a strong emission peak centered at 403 nm.

A symmetric BAM neural network model with delay is considered. Some results of Hopf bifurcations occurring at the zero equilibrium as the delay increases are exhibited. The existence of multiple periodic solutions is established using a symmetric Hopf bifurcation result of Wu [J. Wu, Symmetric functional differential equations and neural networks with memory, Transactions of the American Mathematical Society 350 (12) (1998) 4799–4838].

Let M n ( R ) be the linear space of all n × n matrices over the real field R. For any A ∈ M n ( R ) , let ρ ( A ) and ‖ A ‖ ∞ denote the spectral radius and the infinity norm of A, respectively. By introducing a class of transformations φ a on M n ( R ) , we show that, for any A ∈ M n ( R ) , ρ ( A ) ‖ A ‖ ∞ if φ ‖ A ‖ ∞ n ( A ) = 0 . If A ∈ M n ( R ) is nonnegative, we prove that ρ ( A ) ‖ A ‖ ∞ if and only if φ ‖ A ‖ ∞ n ( A ) = 0 , and ρ ( A ) = ‖ A ‖ ∞ if and only if the transformation φ ‖ A ‖ ∞ preserves the spectral radius and the infinity norm of A. As an application, we investigate a class of linear discrete dynamic systems in the form of X ( k + 1 ) = A X ( k ) . The asymptotical stability of the zero solution of the system is established by a simple algebraic method.

The near-edge X-ray absorption fine structure (NEXAFS) spectra and crystal structures of the e - O 8 phase and the metallic ζ - O 2 phase have been investigated using full-potential linearized augmented plane-wave (FLAPW) and pseudopotential plane-wave methods. The change in NEXAFS spectra for the k -edge of the oxygen atom suggests a means for identifying the phase transition from e - O 8 to ζ - O 2 experimentally. The abrupt change of the bond length L (O1–O1) induced by pressure is believed to be responsible for the phase transition. There is no pressure-induced softening behavior in our calculated phonon dispersion curves near the phase transition pressure.

A mathematical model that describes HIV infection of CD4(+) T cells is analyzed. Global dynamics of the model is rigorously established. We prove that, if the basic reproduction number R(0)or = 1, the HIV infection is cleared from the T-cell population; if R(0)1, the HIV infection persists. For an open set of parameter values, the chronic-infection equilibrium P* can be unstable and periodic solutions may exist. We establish parameter regions for which P* is globally stable.

Urchin-like Fe 3 BO 5 @carbon core–shell structures (defined as “FBOC”) have been fabricated by a one-step co-pyrolysis method using boric acid and ferrocene as raw materials. This complex architecture is composed of high-density Fe 3 BO 5 @carbon nanocables that stand on Fe 3 BO 5 @carbon structure. After removing the Fe 3 BO 5 , hollow urchin-like carbon material was obtained. In the reaction process, B 2 O 3 and H 2 O that decomposed from H 3 BO 3 have synergistic effect on the formation of urchin-like structures. It is found that urchin-like structures can also be obtained when other materials that can release H 2 O and B 2 O 3 react with ferrocene. The influences of the reaction conditions on the preparation of FBOC have been discussed in detail.

For a stable matrix A with real entries, sufficient and necessary conditions for A − D to be stable for all non-negative diagonal matrices D are obtained. Implications of these conditions for the stability and instability of constant steady-state solutions to reaction–diffusion systems are discussed and an example is given to show applications.

A SEIR model for the transmission of an infectious disease that spreads in a population through direct contact of the hosts is studied. The force of infection is of proportionate mixing type. A threshold sigma is identified which determines the outcome of the disease; if sigmaor = 1, the infected fraction of the population disappears so the disease dies out, while of sigma1, the infected fraction persists and a unique endemic equilibrium state is shown, under a mild restriction on the parameters, to be globally asymptotically stable in the interior of the feasible region. Two other threshold parameters sigma' and sigma are also identified; they determine the dynamics of the population sizes in the cases when the disease dies out and when it is endemic, respectively.

A necessary and sufficient condition for the stability ofn×nmatrices with real entries is proved. Applications to asymptotic stability of equilibria for vector fields are considered. The results offer an alternative to the well-known Routh–Hurwitz conditions.

The preparation and tests of the self-cleaning membranes are described in the paper. Satisfactory improvements of permeate flux are obtained, and some information on the change of structure of the enzyme layer is given indirectly. The experiments illustrate that it is possible to maintain the relatively high flux while the amount of enzyme may be decreased by optimizing the structure of the enzyme layer. The strength of immobilized enzyme, the loss of protein and effect of immobilized enzyme on protein molecules are also discussed.