Showing papers by "Yanshan University published in 2013"
TL;DR: It is shown that hardening of cBN is continuous with decreasing twin thickness down to the smallest sizes investigated, contrasting with the expected reverse Hall–Petch effect below a critical grain size or the twin thickness of ∼10–15 nm found in metals and alloys.
Abstract: The hardness, toughness and chemical stability of the well-known superhard material cubic boron nitride have been improved by using a synthesis technique based on specially prepared ‘onion-like’ precursor materials. Superhard polycrystalline cubic boron nitride, second only to diamond in hardness, is superior to diamond in terms of thermal and chemical stability and is used widely as an abrasive. The hardness of many materials can be improved by decreasing the grain size, and here Yongjun Tian and colleagues use this principle in a new synthesis technique — based on specially prepared 'onion-like' precursor materials — capable of increasing the hardness of cubic boron nitride. The structure of the resulting polycrystalline material is dominated by nanometre-scale twin domains, yielding a solid combining ultrahigh hardness (exceeding that of a synthetic diamond single crystal) with a high oxidization temperature and extreme fracture toughness. If nanotwins at similar scales can be reproduced in polycrystalline diamond, it may be possible to raise diamond itself to new levels of hardness and stability. Cubic boron nitride (cBN) is a well known superhard material that has a wide range of industrial applications. Nanostructuring of cBN is an effective way to improve its hardness by virtue of the Hall–Petch effect—the tendency for hardness to increase with decreasing grain size1,2. Polycrystalline cBN materials are often synthesized by using the martensitic transformation of a graphite-like BN precursor, in which high pressures and temperatures lead to puckering of the BN layers3. Such approaches have led to synthetic polycrystalline cBN having grain sizes as small as ∼14 nm (refs 1, 2, 4, 5). Here we report the formation of cBN with a nanostructure dominated by fine twin domains of average thickness ∼3.8 nm. This nanotwinned cBN was synthesized from specially prepared BN precursor nanoparticles possessing onion-like nested structures with intrinsically puckered BN layers and numerous stacking faults. The resulting nanotwinned cBN bulk samples are optically transparent with a striking combination of physical properties: an extremely high Vickers hardness (exceeding 100 GPa, the optimal hardness of synthetic diamond), a high oxidization temperature (∼1,294 °C) and a large fracture toughness (>12 MPa m1/2, well beyond the toughness of commercial cemented tungsten carbide, ∼10 MPa m1/2). We show that hardening of cBN is continuous with decreasing twin thickness down to the smallest sizes investigated, contrasting with the expected reverse Hall–Petch effect below a critical grain size or the twin thickness of ∼10–15 nm found in metals and alloys.
614 citations
TL;DR: Using density functional calculations, this work systematically investigated the hydrogen storage properties of the two-dimensional Ti2C phase, which is a representative of the recently synthesized MXene materials and confirmed the hydrogen molecules bound by Kubas-type interaction can be adsorbed and released reversibly under ambient conditions.
Abstract: Searching for reversible hydrogen storage materials operated under ambient conditions is a big challenge for material scientists and chemists. In this work, using density functional calculations, we systematically investigated the hydrogen storage properties of the two-dimensional (2D) Ti2C phase, which is a representative of the recently synthesized MXene materials ( ACS Nano 2012 , 6 , 1322 ). As a constituent element of 2D Ti2C phase, the Ti atoms are fastened tightly by the strong Ti-C covalent bonds, and thus the long-standing clustering problem of transition metal does not exist. Combining with the calculated binding energy of 0.272 eV, ab initio molecular dynamic simulations confirmed the hydrogen molecules (3.4 wt % hydrogen storage capacity) bound by Kubas-type interaction can be adsorbed and released reversibly under ambient conditions. Meanwhile, the hydrogen storage properties of the other two MXene phases (Sc2C and V2C) were also evaluated, and the results were similar to those of Ti2C. Therefore, the MXene family including more than 20 members was expected to be a good candidate for reversible hydrogen storage materials under ambient conditions.
365 citations
TL;DR: This paper studies the smart control issue for an autonomous microgrid in order to maintain the secure voltages as well as maximize economic and environmental benefits.
Abstract: This paper studies the smart control issue for an autonomous microgrid in order to maintain the secure voltages as well as maximize economic and environmental benefits. A control scheme called as multi-agent based hierarchical hybrid control is proposed versus the hierarchical control requirements and hybrid dynamic behaviors of the microgrid. The control scheme is composed of an upper level energy management agent, several middle level coordinated control agents and many lower level unit control agents. The goals of smart control are achieved by designed control strategies. The simulations are given to demonstrate the effectiveness of proposed smart control for an autonomous microgrid.
219 citations
TL;DR: Control of the specific composition and the NTE properties of La(Fe, Si)13-based compounds suggests their potential application as NTE materials.
Abstract: La(Fe, Si)13-based compounds are well-known magnetocaloric materials, which show a pronounced negative thermal expansion (NTE) around the Curie temperature but have not been considered as NTE materials for industrial applications. The NaZn13-type LaFe13–xSix and LaFe11.5–xCoxSi1.5 compounds were synthesized, and their linear NTE properties were investigated. By optimizing the chemical composition, the sharp volume change in La(Fe, Si)13-based compounds was successfully modified into continuous expansion. By increasing the amount of Co dopant in LaFe11.5–xCoxSi1.5, the NTE shifts toward a higher temperature region, and also the NTE operation-temperature window becomes broader. Typically, the linear NTE coefficient identified in the LaFe10.5Co1.0Si1.5 compound reaches as much as −26.1 × 10–6 K–1, with an operation-temperature window of 110 K from 240 to 350 K, which includes room temperature. Such control of the specific composition and the NTE properties of La(Fe, Si)13-based compounds suggests their poten...
215 citations
TL;DR: In this paper, the upconversion quantum efficiency of Ho3+/Yb3+ codoped CaWO4 phosphor was evaluated under 980-nm diode laser excitation.
Abstract: Under 980 nm diode laser excitation, efficient upconversion emissions from the Ho3+/Yb3+ codoped CaWO4 phosphor were obtained. The upconversion quantum efficiency was evaluated to be about 3.3% when the power density of the excitation laser was 47 W/cm2. Additionally, temperature dependent blue emissions from the 5F2,3/3K8 and 5G6/5F1 states of Ho3+ ions were studied in the range of 303–923 K. The result demonstrated that using the ratio between the blue luminescence intensities of Ho3+ ions, the sensitivity and the accuracy for optical thermometry achieved here are superior to the previously reported Er3+ green fluorescence based optical temperature sensors.
215 citations
TL;DR: An early warning system for geohazards in reservoir region is described, which relies on the WSN technology inspired by the existing work and incorporates data fusion and reconstruction approaches to bring together all data into a single view of the geohazard under monitoring.
Abstract: The wireless sensor network (WSN) technology has applied in monitoring natural disasters for more than one decade. Disasters can be closely monitored by augmenting a variety of sensors, and WSN has merits in (1) low cost, (2) quick response, and (3) salability and flexibility. Natural disaster monitoring with WSN is a well-known data intensive application for the high bandwidth requirements and stringent delay constraints. It manifests a typical paradigm of data-intensive application upon low-cost scalable system. In this study, we first assessed representative works in this area by classifying those in the domains of application of WSNs for disasters and optimization technologies significantly distinguishing these from general-purpose WSNs. We then described the design of an early warning system for geohazards in reservoir region, which relies on the WSN technology inspired by the existing work with focuses on issues of (1) supporting reliable data transmission, (2) handling huge data of heterogeneous sources and types, and (3) minimizing energy consumption. This study proposes a dynamic routing protocol, a method for network recovery, and a method for managing mobile nodes to enable real-time and reliable data transmission. The system incorporates data fusion and reconstruction approaches to bring together all data into a single view of the geohazard under monitoring. A distributed algorithm for joint optimal control of power and rate has been developed, which can improve utility of network (> 95 %) and to minimize the energy consumption (reduction by > 20 % in comparison with LEACH). Experimental results indicate the potentials of the proposed approaches in terms of adapting to the needs of early warning on geohazards.
174 citations
TL;DR: It is shown that initial silanization takes place very fast but the progress toward saturation is very slow, and the mechanism may involve adsorption, chemical sorption, and chemical diffusion processes.
Abstract: Silanization of magnetic ironoxide nanoparticles with (3-aminopropyl)triethoxylsilane (APTES) is reported The kinetics of silanization toward saturation was investigated using different solvents including water, water/ethanol (1/1), and toluene/methanol (1/1) at different reaction temperature with different APTES loading The nanoparticles were characterized by Fourier transform infrared spectroscopy, vibrating sample magnetometry, transmission electron microscopy, and thermal gravimetric analysis (TGA) Grafting density data based on TGA were used for the kinetic modeling It is shown that initial silanization takes place very fast but the progress toward saturation is very slow, and the mechanism may involve adsorption, chemical sorption, and chemical diffusion processes The highest equilibrium grafting density of 301 mg/g was yielded when using toluene/methanol mixture as the solvent at a reaction temperature of 70 °C
163 citations
TL;DR: It is suggested that charged groups in the host resins improve the dispersion of embedded nanoparticles and enhance the reactivity and capacity for sorption of metal ions.
Abstract: A novel hybrid nanomaterial was fabricated by encapsulating ZrO2 nanoparticles into spherical polystyrene beads (MPS) covalently bound with charged sulfonate groups (−SO3–). The resultant adsorbent, Zr–MPS, exhibited more preferential sorption toward Pb(II) than the simple equivalent mixture of MPS and ZrO2. Such observation might be ascribed to the presence of sulfonate groups of the polymeric host, which could enhance nano-ZrO2 dispersion and Pb(II) diffusion kinetics. To further elucidate the role of surface functional groups, we encapsulated nano-ZrO2 onto another two macroporous polystyrene with different surface groups (i.e., −N(CH3)3+/–CH2Cl, respectively) and a conventional activated carbon. The three obtained nanocomposites were denoted as Zr–MPN, Zr–MPC, and Zr–GAC. The presence of −SO3– and −N(CH3)3+ was more favorable for nano-ZrO2 dispersion than the neutral −CH2Cl, resulting in the sequence of sorption capacities as Zr–MPS > Zr–MPN > Zr–GAC > Zr–MPC. Column Pb(II) sorption by the four nanoco...
161 citations
TL;DR: A liquid filled PCF of the small hole in the fiber core is designed and it is found that filling liquid increases the resonance strength peak by thirty eight percent for the y-polarized resonance point.
Abstract: The polarization filter characters of a gold-coated and liquid-filled photonic crystal fiber are studied using the finite element method. Results show that the resonance strength and wavelengths are different in two polarized directions. Filling liquid of refractive index n=1.33 (purified water) in holes in longitudinal direction can increase the loss of core mode polarized in the y-direction around the resonance peak. The resonance strength is much stronger in y-polarized direction than in x-polarized direction. The resonance strength can achieve 508dB/cm in y-polarized direction at the communication wavelength of 1311nm in one of our structures. Moreover, the full width half maximum is only 20nm. Such a small number makes such photonic crystal fibers promising candidate to filter devices. A liquid filled PCF of the small hole in the fiber core is designed and we find that filling liquid increases the resonance strength peak by thirty eight percent for the y-polarized resonance point.
130 citations
20 Aug 2013-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the tensile and impact properties of two low-carbon bainitic transformation-induced plasticity (TRIP) steels, one being Al-free and the other being Alcontaining, have been investigated.
Abstract: The tensile and impact properties of two low-carbon bainitic transformation-induced plasticity (TRIP) steels, one being Al-free and the other being Al-containing, have been investigated. The two steels are featured by the existence of different sizes and shapes of retained austenite showing different mechanical stabilities. Compared with the Al-containing steel, the Al-free steel shows significantly improved tensile strength, uniform strain and total elongation, but exhibits much decreased impact toughness. These results demonstrate conflicting effects of strain-induced martensitic transformation of retained austenite on tensile ductility and impact toughness of TRIP steels. It is indicated that a wide distribution of size and shape of retained austenite is favorable for sustained high strain hardening rate and increased uniform tensile strain; however, thin films of retained austenite, which is mechanically more stable, tends to enhance impact toughness.
125 citations
TL;DR: The particles with extremely lower density than common magnetic particles exhibited solid-like magnetorheological phase characteristics, and the flow curves were fitted to the Cho-Choi-Jhon model of the rheological equation of state.
Abstract: Core–shell-structured magnetic polystyrene (PS)/inorganic particles were fabricated by Pickering emulsion polymerization using nanosized Fe2O3 particles as a solid stabilizer. Scanning electron microscopy and transmission electron microscopy confirmed the synthesized PS/Fe2O3 particles to be comprised of a PS surface coated with Fe2O3 nanoparticles. The chemical structure of the composite nanospheres was characterized by Fourier transform infrared spectroscopy and X-ray diffraction. The thermal properties of composite nanospheres and corresponding pure polymer were examined by thermogravimetric analysis. The rheological properties of the core–shell-structured magnetic PS/inorganic particles dispersed in silicone oil were investigated under an external magnetic field strength using a rotational rheometer. The particles with extremely lower density than common magnetic particles exhibited solid-like magnetorheological phase characteristics, and the flow curves were fitted to the Cho–Choi–Jhon model of the r...
TL;DR: A novel robust controller named fractional order sliding mode controller (FOSMC) is proposed for ABS to regulate the slip to a desired value and can not only deal with the uncertainties in ABS system but also track the desired slip faster than conventional integer order SMC with proportional or proportional-derivative sliding surface.
TL;DR: Analysis of the SdH data manifests that the high-mobility bulk electron carriers dominate the magnetotransport and are responsible for the observed large linear MR in YPdBi crystals, implying that the Heusler-based topological insulators have superiorities for investigating the novel quantum transport properties and developing the potential applications.
Abstract: We report the observation of a large linear magnetoresistance (MR) and Shubnikov-de Hass (SdH) quantum oscillations in single crystals of YPdBi Heusler topological insulators. Owning to the successfully obtained the high-quality YPdBi single crystals, large non-saturating linear MR of as high as 350% at 5K and over 120% at 300 K under a moderate magnetic field of 7 T is observed. In addition to the large, field-linear MR, the samples exhibit pronounced SdH quantum oscillations at low temperature. Analysis of the SdH data manifests that the high-mobility bulk electron carriers dominate the magnetotransport and are responsible for the observed large linear MR in YPdBi crystals. These findings imply that the Heusler-based topological insulators have superiorities for investigating the novel quantum transport properties and developing the potential applications.
TL;DR: It is indicated that the dynamical characteristics of EEG data with MPE can identify the differences among seizure-free, pre-seizure and seizure states, and this supports the view that EEG has a detectable change prior to an absence seizure.
TL;DR: In this paper, Ni-promoted MoS2 microspheres consisting of nanosheets have been prepared via a facile one-pot hydrothermal synthesis for the first time.
Abstract: Ni-promoted MoS2 microspheres consisting of nanosheets have been prepared via a facile one-pot hydrothermal synthesis for the first time. The electrochemical hydrogen evolution reaction (HER) results demonstrated that the Ni-promoted MoS2 catalysts showed superior catalytic activity in the HER compared to pure MoS2 catalysts.
TL;DR: The gravitational search algorithm (GSA) is used to optimize the regularization parameter @c and the kernel parameter @s^2 of the online LS-SVM modeling to avoid blindness and inaccuracy in parameter selection.
Abstract: Accurate heat rate forecasting is very important in ensuring the economic, efficient, and safe operation of a steam turbine unit. The support vector machine (SVM) is a novel tool from the artificial intelligence field that has been successfully applied to heat rate forecasting. The least squares SVM (LS-SVM) is an improved algorithm based on the SVM. LS-SVM has minimal computational complexity and fast calculation. However, traditional LS-SVM, which was established by using offline data samples, can no longer accurately describe the actual system working condition, thereby resulting in problems when directly used in heat rate prediction. In this paper, a heat rate forecasting method based on online LS-SVM, which possesses dynamic prediction functions, is proposed. To avoid blindness and inaccuracy in parameter selection, the gravitational search algorithm (GSA) is used to optimize the regularization parameter @c and the kernel parameter @s^2 of the online LS-SVM modeling. The results confirm the efficiency of the proposed method.
TL;DR: In this article, the mechanical properties of various vanadium carbides were investigated by means of nano-indentation and first-principles techniques, and the results showed that cubic VC in Ni-Cr cast iron possesses a relatively high Vickers hardness (33.3± 0.5 GPa) and Young's modulus (436± 8 GPa).
TL;DR: In this article, the catalytic effect of MoS2 and MoO2 on the hydrogen absorption/desorption kinetics of MgH2 has been investigated and it is shown that MoS 2 has a superior catalytic ability over MoO 2 on improving the hydrogen kinetic properties of MGH2.
TL;DR: In this paper, the performance of ZrP and ZrO2 was investigated and the enhanced sorption properties towards anion-phosphate were explored and the uptake of phosphate onto ZrPs was examined and common used anion exchange resin (D201) and zirconium dioxide particles were introduced for references with coexistence of common anions (SO 4 2 -, NO 3 - and Cl− ions).
TL;DR: The data indicate that carbonylation modification of the Na/K-ATPase α1 subunit is involved in a feed-forward mechanism of regulation of ouabain-mediated renal proximal tubule Na/k-atPase signal transduction and subsequent sodium transport.
TL;DR: In this paper, aluminum metal matrix composites (AMMCs) reinforced with tungsten carbide (WC) particles are manufactured through warm accumulative roll bonding (ARB), and the tensile, hardness, and wear properties of the Al/WC composites are determined.
TL;DR: The in vitro study showed that these Tween 20-UCNPs@HA complexes could efficiently produce (1)O2 to kill cancer cells under 980 nm NIR excitation, making them become a multifunctional platform for simultaneous PDT and bio-imaging.
Abstract: The utilization of up-conversion nanoparticles (UCNPs) for photodynamic therapy (PDT) has gained significant interest due to their unique ability to convert near infrared light to UV/visible light. Previous work mainly focused on the fabrication of green and red emitting UCNPs to load photosensitizers (PSs) for PDT. In this work, we firstly developed a new multifunctional nanoplatform combining blue-emitting UCNPs with blue-light excited PS (hypocrellin A, HA) as a NIR photosensitizing nanoplatform for PDT of cancer cells. Tween 20 coated NaYbF4:Tm, Gd@NaGdF4 UCNPs (Tween 20-UCNPs) with strong blue up-conversion luminescence and good water dispersibility were prepared for use as PS carriers. The blue emission band matched well with the efficient absorption band of HA, thereby facilitating the resonance energy transfer from UCNPs to HA and then activating HA to produce singlet oxygen (1O2). The in vitro study showed that these Tween 20-UCNPs@HA complexes could efficiently produce 1O2 to kill cancer cells under 980 nm NIR excitation. Moreover, these Gd3+ and Yb3+ containing nanoparticles also exhibited positive contrast effects in both T1 weighted magnetic resonance imaging (MRI) and computed tomography (CT) imaging, making them become a multifunctional platform for simultaneous PDT and bio-imaging.
TL;DR: Simulations demonstrating metastable carbon phases as the result of pressure induced carbon nanotube polymerization show versatile and superior physical properties, such as superhardness, high tensile strength and ductility, and tunable electronic properties (semiconducting or metallic).
Abstract: The exploration of novel functional carbon polymorphs is an enduring topic of scientific investigations. In this paper, we present simulations demonstrating metastable carbon phases as the result of pressure induced carbon nanotube polymerization. The configuration, bonding, electronic, and mechanical characteristics of carbon polymers strongly depend on the imposed hydrostatic/non-hydrostatic pressure, as well as on the geometry of the raw carbon nanotubes including diameter, chirality, stacking manner, and wall number. Especially, transition processes under hydrostatic/non-hydrostatic pressure are investigated, revealing unexpectedly low transition barriers and demonstrating sp(2)→sp(3) bonding changes as well as peculiar oscillations of electronic property (e.g., semiconducting→metallic→semiconducting transitions). These polymerized nanotubes show versatile and superior physical properties, such as superhardness, high tensile strength and ductility, and tunable electronic properties (semiconducting or metallic).
TL;DR: In this paper, a single-carrier modulation strategy is proposed for three-level neutral-point-clamped inverters in three-phase transformerless photovoltaic systems.
Abstract: Modulation strategy is one of the most important issues for three-level neutral-point-clamped inverters in three-phase transformerless photovoltaic systems. A challenge for modulation is how to keep the common-mode voltages constant to reduce the leakage currents. A single-carrier modulation strategy is proposed. It has a very simple structure, and the common-mode voltages can be kept constant with no need of complex space-vector modulation or multicarrier pulsewidth modulation. Experimental results verify the theoretical analysis and the effectiveness of the presented method.
TL;DR: An extended technique— a variable-cell NEB (VC-NEB) technique combined with the ab initio method, implemented in the USPEX code, which is applied to reconstructive solid-solid phase transitions of GaN and studies the mechanism of the recently predicted insulator-metal phase transition of BH.
01 Jan 2013-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the effects of heat treatment on the structural evolution and mechanical properties of the Ti-20Zr-6.5Al-4V (wt%) alloy were evaluated.
Abstract: This study aims to evaluate the effects of heat treatment on the structural evolution and mechanical properties of the Ti–20Zr–6.5Al–4V (wt%) alloy. The alloy was melted via electromagnetic induction, homogenized, transus-processed, solid-solubilized, and then aged at different temperatures (from 450 °C to 700 °C) for 120 min. X-ray diffraction was used to characterize the phase compositions in the alloy under different conditions. During the solution treatment process, the alloy underwent the following phase transformation: β→α+β (retained)+α″+fcc phase. Martensite α″ and β phases transformed into the α phase after the aging treatment. The fcc phase became completely dissolved when the aging temperature increased to 700 °C. At this temperature, the mechanical properties of the alloy reached their optimum combination at σb=1437 MPa, σ0.2=1294 MPa, and e=6.69%.
TL;DR: In this paper, band structure and magneto-transport investigations of the inverse Heusler compound Fe2CoSi have been conducted and it has been shown that the dominant spin carriers change from the gapless minority spin channel to the majority spin channel at the Fermi level.
Abstract: This work reports on band structure and magneto-transport investigations of the inverse Heusler compound Fe2CoSi. First-principles calculations show that Fe2CoSi has a very peculiar band structure with a conducting property of the majority spin channel and a nearly zero bandgap in the minority spin channel. The prepared Fe2CoSi sample possesses a highly ordered inverse Heusler structure with a magnetic moment of at 5 K and a high Curie temperature of 1038 K. With increasing temperature, a crossover from positive to negative magnetoresistance (MR) is observed. Combining this with the Hall effect measurements, we suggest that the intriguing crossover of the MR can be ascribed to the dominant spin carriers that change from the gapless minority spin channel to the majority spin channel at the Fermi level.
TL;DR: In this paper, an amplitude adaptive notch filtering (AANF) is proposed for grid signal processing and synchronization of distributed generation systems that provide improvement solutions for both grid-connected and stand-alone mode of microgrids.
Abstract: This letter presents an amplitude adaptive notch filtering (AANF) as a tool for grid signal processing and synchronization of distributed generation systems that provide improvement solutions for both grid-connected and stand-alone mode of microgrids. The proposed technique is simple and offers a high degree of immunity and insensitivity to power disturbances, especially when the signal amplitude varies. Since the powerful technique can reduce impact of the amplitude variation of signal, it has a wider range of application and can take the place of the traditional ANF in the microgrids. This technique can also be used in the detection of symmetrical components, harmonics, active power, and reactive power. Theoretical analysis is presented and the performance of the method is evaluated by simulation.
TL;DR: Li et al. as mentioned in this paper analyzed the effects of climate change on the ecosystems in Xinjiang, using the 1-km annual GPP and NPP datasets from the MODIS products from 2000 to 2010 and the AVHRR BU LAI products from 1981 to 2011.
TL;DR: In this article, the minimum reflection loss (RL ) is less than −20dB at 2.72-18.0 GHz with a thickness between 1.21 and 6.00mm for 40% MWCNT/FeNi composites, and a minimum RL value of −47.6dB at 12.09-14.5 GHz on a specimen with a matching thickness of 1.79mm.