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The hydrogen recirculation in proton exchange membrane fuel cell (PEMFC) is recommended for the hydrogen supply of PEMFC, and hydrogen ejectors are gradually being used in fuel cell vehicles due to low noise and low energy consumption. However, there is a lack of discussion about the influence of recirculation rate on the stack. Due to passive regulating mechanism of the ejectors, a miniature speed-adjustable peristaltic pump is used to simulate the hydrogen ejector in this study to investigate the effect of hydrogen recirculation on the performance of PEMFC stack. Experiments are conducted under different pump flow rates. The stack with hydrogen recirculation is proven to have better performance, but over high pump flow rate can lead to hydrogen shortage. It is interesting to find that the flow rate fluctuation of hydrogen inlet affects the stability of stack performance, and pressure drop and recovery time during purge process are proposed as effective indicators for performance analysis. Finally, pump flow rates between 60 ml/min and 105 ml/min are defined as “effective area”. Based on the analysis of effective indicators, keeping at “effective area” is further proved to improve the performance of the stack, which is also useful to design hydrogen recirculation.

Performance enhancement of vibration isolation of a circular ring by means of a shape memory alloy (SMA) wire rope is investigated. The restoring and the damping force of the SMA are approximated by two cubic polynomials. The ring with the SMA wire along the horizontal diametral line is mathematically modeled by two coupled nonlinear partial differential equations with the boundary conditions. The nonlinear partial differential equations are discretized via the Galerkin method. The method of harmonic balance is applied to derive the expressions for frequency response and the force transmissibility of the circular ring design. The developed vibration isolation approach is successfully implemented to change the path of vibration transmission to attenuate the transmitted motion. The effects of the introduced horizontal SMA stiffness and damping on vibration isolation are examined. The resultant SMA stiffness is shown to extend the isolation range to lower frequencies, while the horizontal SMA damping has the ability to reduce the resonance response. The numerical simulations support the analytical results. Then, the isolation performances obtained employing different types of NiTiNOL (i.e., NiTi7, NiTi19/NiTi1, ST49/NiTi7, ST49/NiTi1) are compared. The results demonstrate that the SMA composed of NiTi19/NiTi1 is optimum for the ring isolation design. The developed ring beam vibration isolator reduces the transmissibility around the resonance frequency and performs better at high frequencies for appropriate types of SMA.

The proton exchange membrane fuel cell (PEMFC) stack consists of individual cells in series. Its operating life is subjected to performance of the weakest cell because of the short-board effect, thus voltage uniformity during dynamic long-running process is significant to its durability. In this work, based on a 1044 h aging experiment on a 6.55 kW PEMFC stack under dynamic driving cycle, voltage uniformity is analyzed. In a single cycle, voltage uniformity becomes worse with the increase of loading current and there are some local maxima of voltage coefficient variation (Cv) at the moment of loading or unloading step. Cv value at higher current is greater and increases faster with cycles. At the end of experiment, Cv at 135 A is more than 6%. Besides, skewness (Sk) is used to evaluate the skew direction and degree of cell voltage data in a cycle. In most cycles, Sk values at 34.22 A are above 0 and Sk values at 59.70 A and 135 A are below 0. After the Box-Cox transformation, which is used to improve symmetry of data and reduce Sk, the cell voltage data have passed the verifications of normal fitting, probability-probability plot and quantile-quantile plot. Therefore, it is found that cell voltage data tend to obey skewed normal distribution, which is of positive significance for improving voltage uniformity and durability of PEMFC stack.

Gear rolling process is a continuous rolling process by rotating and radial feeding motion of rolling wheel. It has advantages of low manufacturing cost, high gear strength and low forming load. The rolling processes of extrusion forming, gear splitting, continuous rolling and reshaping were analyzed by finite element method. The kinematic relationship between the rolling wheel and the forming gear during rolling deformation was studied. The results showed that the meshing motion between the rolling wheel and the billet could be guaranteed when the initial extrusion of the billet was not less than 1 mm. At the rolling gear splitting stage, the equivalent strain of the billet was shown to be related to the deformation of the material, which attained the largest at the root of the tooth. However, the equivalent stress of the billet was found to be dependent on the contact position of the rolling wheel, which has the maximum value at the root of the tooth in the contact area. During the continuous rolling forming stage, the forming load varied regularly and increased continuously with the rolling feed. The tooth profile of the gear was complete after the rolling reshaping process. According to the analysis and calculation results, the structure of rolling forming device was designed. Experiments showed that spiral bevel gears were able to be formed by rolling, and the billet size had an effect on the rolling process. When the size of billet was about 2 mm larger than the dividing circle radius of target gear, the quality of rolled gear was better. The results have important guiding significance for further research rules of rolling forming processes.

Lightweight composite armour systems composed of a B4C ceramic panel and composite back panel have excellent bulletproof performance and are used to resist attacks from armour-piercing incendiary projectiles. Numerical simulations can be used to simulate the process of projectiles impacting armour; thus, this method is widely used in armour ballistic performance analyses. To verify the accuracy of the B4C material model, a finite element method based on two-dimensional smoothed particle hydrodynamics is used to simulate the penetration process of steel projectiles into B4C/Al composite armour. To verify the accuracy of the ultra-high molecular weight polyethylene (UHMW-PE) model, a three-dimensional Lagrange method was used to simulate the penetration of a fragment simulating projectile into the UHMW-PE. The influence of geometric strain in the erosion algorithm on the ballistic performance of the UHMW-PE was investigated, and the erosion geometric strain suitable for the UHMW-PE was identified. The impact of a 12.7 mm armour-piercing incendiary projectile on the B4C/UHMW-PE and B4C/C/UHMW-PE armours was then simulated and tested experimentally. The results showed that the B4C/UHMW-PE armour was penetrated by the projectile, while the B4C/C/UHMW-PE armour was not penetrated. The ballistic performance of the B4C composite armour, damage state of the B4C ceramic, and bulge deformation of the UHMW-PE were accurately obtained in the simulations. A comparison with the experimental results showed that the proposed method could accurately simulate the penetration process of the B4C/UHMW-PE armour, reveal the penetration mechanism of composite armour, reduce the number of projectile tests, and provide a basis and technical means for the design and optimisation of lightweight composite armour.

We investigate the orientation switching of individual azobenzene molecules adsorbed on a Au(111) surface using a laser-assisted scanning tunneling microscope (STM). It is found that the rotational motion of the molecule can be regulated by both sample bias and laser wavelength. By measuring the switching rate and state occupation as a function of both bias voltage and photon energy, the threshold in sample bias and the minimal photon energy are derived. It has been revealed that the tip-induced local electrostatic potential remarkably contributes to the reduction in hopping barrier. We also find that the tunneling electrons and photons play distinct roles in controlling rotational dynamics of single azobenzene molecules on the surface, which are useful for understanding dynamic behaviors in similar molecular systems.

High temperature proton exchange membrane fuel cell (HT-PEMFC) with phosphoric acid doped polybenzimidazole (PBI) electrolyte shows multiple advantages over conventional PEMFC working at below 373 K, such as faster electrochemical kinetics, simpler water management, higher carbon monoxide tolerance. However, starting HT-PEMFC from room temperature to the optimal operating temperature range (433.15 K–453.15 K) is still a serious challenge. In present work, the start-up strategy is proposed and evaluated and a three-dimensional non-isothermal dynamic model is developed to investigate start-up time and temperature distribution during the start-up process. The HT-PEMFC is preheated by gas to 393.15 K, followed by discharging a current from the cell for electrochemical heat generation. Firstly, different current loads are applied when the average temperature of membrane reaches 393.15 K. Then, the start-up time and temperature distribution of co-flow and counter-flow are compared at different current loads. Finally, the effect of inlet velocity and temperature on the start-up process are explored in the case of counter-flow. Numerical results clearly show that applied current load is necessary to reduce start-up time and just 0.1 A/cm2 current load can reduce startup time by 45%. It is also found that co-flow takes 18.8% less time than counter-flow to heat membrane temperature to 393.15 K, but the maximum temperature difference of membrane is 39% higher than the counter-flow. Increasing the inlet gas flow velocity and temperature can shorten the start-up time but increases the temperature difference of the membrane.

To assess the effect of the mass-stiffness distribution of the cab and vibratory roller on the ride quality, the acceleration-frequency characteristics of the isolation systems are researched based on the nonlinear dynamic model of the vehicle. The complex domain is used to solve the vibration equations in the frequency region. The effect of the mass and stiffness parameters of the cab and vehicle is then analyzed via MATLAB software. The research results show that the resonant frequency of the cab's isolations and their acceleration-frequency is insignificantly affected by the mass-stiffness distributions in the case of without the excitation of the vibrator drum. Conversely, under an excitation 28 Hz of the vibrator drum, the mass-stiffness distributions strongly affect on the acceleration-frequency of the cab isolations, especially, when increasing the stiffness coefficient and reducing the cab mass with α= 1.5, the vehicle’s ride quality and structural durability of the vibratory rollers are greatly improved.

The near-infrared window of fluorescent heptamethine cyanine dyes greatly facilitates biological imaging because there is deep penetration of the light and negligible background fluorescence. However, dye instability, aggregation, and poor pharmacokinetics are current drawbacks that limit performance and the scope of possible applications. All these limitations are simultaneously overcome with a new molecular design strategy that produces a charge balanced and sterically shielded fluorochrome. The key design feature is a meso-aryl group that simultaneously projects two shielding arms directly over each face of a linear heptamethine polyene. Cell and mouse imaging experiments compared a shielded heptamethine cyanine dye (and several peptide and antibody bioconjugates) to benchmark heptamethine dyes and found that the shielded systems possess an unsurpassed combination of photophysical, physiochemical, and biodistribution properties that greatly enhance bioimaging performance.

Density functional theory was used to investigate the anticorrosion mechanism of Cr-doped nickel-base alloy in Br/O environment. The adsorption properties including adsorption energy, bond length a...

The uniformity of substrate temperature is an important factor to be considered in the design of microchannel heat sink which has been widely used in the micro-channel reactors, electric chip cooling and various type fuel cells. Therefore, two novel annular microchannel heat sink designs are proposed to improve the flow distribution and substrate temperature uniformity of the microchannel heat sink. One is the MRNH design which is the plain configuration; another is the MRSH design which is the enhanced configuration of the MRNH design. Firstly, the values of Nusselt number and pressure drop of the MRNH with the interleaved inlets and outlets are numerically and experimentally examined. It shows that the simulated results are consistent with the experimental results. Then, the influences of two different arrangements of the inlets and outlets on the performance of the MRNH are numerically compared. The result shows that temperature uniformity of the interleaved arrangement is better than that of the sequential arrangement. Finally, the comparison of the performance of MRSH and MRNH designs, and the effects of the geometric parameters of MRSH are numerically investigated. The MRSH design has better temperature substrate temperature uniformity compared to MRNH design. Thermal resistances in the MRSH design are smaller than those in MRNH. The total thermal resistances increase with the increase of slant angle for MRSH design. The maximum total thermal resistances are reduced by 9.5% when the slant angle decreases from 40° to 20°. The Nusselt number increases with increasing the dimensionless width of the oblique channel.

Molecular dynamics simulations are used to investigate the effects of temperature, strain rate and molecule length on the deformation of graphene/polyethylene composites. At higher temperature, the host molecules move easily to fit the strain during the deformation. When the strain rate is lower, atoms in the composite model are more relaxed to fit the strain, thus the yield stress of the composite model is smaller than that at a higher strain rate. Due to the longer the length of molecules, the relative movement between molecules is more difficult with the increase of the strain, resulting in a larger yield stress.

Two low-energy excitations of a single water molecule are observed via inelastic electron tunneling spectroscopy, where a significant enhancement is achieved by attaching the molecule to the tip apex in a scanning tunneling microscope. Density functional theory simulations and quantum mechanical calculations of an asymmetric top are carried out to reveal the origin of both excitations. Variations in tunneling junction separation give rise to the quantum confinement effect on the quantum state of a water molecule in the tunneling junction. Our results demonstrate a potential method for measuring the dynamic behavior of a single molecule confined in a tunneling junction, where the molecule–substrate interaction can be purposely tuned.

Nano-size EVONIK AEROXIDE® P25 titanium dioxide, TiO2, powder was heat-treated at temperatures, 700–900°C, in air. An X-ray diffraction study showed that the P25 powder is composed of approximately 20 and approximately 80 mass% of rutile and anatase phases, respectively. It was also shown that the transformation from anatase to rutile induced by hightemperature heat treatment was almost completed at 750°C, whereas a small amount (less than 3 mass%) of anatase phase was still left even in the powder heat-treated at 900°C. The transformation behaviour was consistent with results obtained by Raman scattering spectroscopy. Raman experiments also indicated that high-temperature heating induced the formation of oxide ion vacancies. Powders were dispersed in methyl orange (MO) aqueous solution, and the bleach rate of MO was measured to evaluate photocatalytic activity under ultraviolet (UV)- and visible-light irradiation. After the heat treatment, the UV-light photocatalytic performance sharply deteriorated. Interestingly, visible-light photocatalytic activity was enhanced by high-temperature heating and reached the highest performance for an 800°C-heated sample, indicating that the P25 powder obtained high visible-light photocatalytic performance after heat treatment. Even after 900°C heat treatment, the photocatalytic performance was higher than that of as-received powder. Enhancement of photocatalytic activities was discussed in relation to visible light absorption and charge carrier transfer., T.I., H.O. and D.H. were supported by a programme, the Strategic Research Foundation at Private Universities, grant no. S1311023, from Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.

In order to study the damage characteristics of the yellow sandstone containing pores under the freeze-thaw cycle, the uniaxial compression test of saturated water-stained yellow sandstones with different freeze-thaw cycles was carried out by rock servo press, the microstructure was qualitatively analyzed by Zeiss 508 stereo microscope, and the microdamage mechanism was quantitatively studied by using specific surface area and pore size analyzer. The mechanism of weakening mechanical properties of single-hole yellow sandstone was expounded from the perspective of microstructure. The results show the following. (1) The number of freeze-thaw cycles and single-pore diameter have significant effects on the strength and elastic modulus of the yellow sandstone; the more the freeze-thaw cycles and the larger the pore size, the lower the strength of the yellow sandstone. (2) The damage modes of the yellow sandstone containing pores under the freeze-thaw cycle are divided into five types, and the yellow sandstone with pores is divided into two areas: the periphery of the hole and the distance from the hole; as the number of freeze-thaw cycles increases, different regions show different microscopic damage patterns. (3) The damage degree of yellow sandstone is different with freeze-thaw cycle and pore size. Freeze-thaw not only affects the mechanical properties of yellow sandstone but also accelerates the damage process of pores. (4) The damage of the yellow sandstone by freeze-thaw is logarithmic function, and the damage of the yellow sandstone is a power function. The damage equation of the yellow sandstone with pores under the freezing and thawing is a log-power function nonlinear change law and presents a good correlation.

A novel nonlinear vibration isolator in the shape of a circular ring is investigated in this study. When the ring is compressed along a diametral line, it exhibits highly nonlinear geometric stiffness due to the effects of stretching-induced tension coupled with the curvature changes. The use of stiffness nonlinearity improves vibration isolation efficiency. A mechanical model of the ring under compression is derived from beam theory. Methods of direct separation of motions and harmonic balance are employed to determine the frequency response and displacement transmissibility of the device under base excitations for different geometric configurations. The analytical results are numerically validated via direct time integration of the equation of motion and via experimental data. It is shown that an increase in the pre-deformation of the ring enhances the vibration isolation performance.

Hexagonal boron nitride (h-BN) is an attractive wide-bandgap material for application to emitters and detectors operating in the deep ultraviolet (DUV) spectral region. The optical transmittance of h-BN in the DUV region is particularly important for these devices. We report on the deposition of thick h-BN films (&gt, 200 nm) on Al0.7Ga0.3N templates via radio-frequency sputtering, along with the realization of ultrahigh transmittance in the DUV region. The fraction of the gas mixture (Ar/N2) was varied to investigate its effects on the optical transmittance of BN. DUV light transmittance of as high as 94% was achieved at 265 nm. This value could be further enhanced to exceed 98% by a post-annealing treatment at 800 &deg, C in a N2 ambient for 20 min. The phase of the highly DUV&ndash, transparent BN film was determined to be a purely hexagonal structure via Raman spectra measurements. More importantly, these deposition processes were performed at a low temperature (300 &deg, C), which can provide protection from device performance degradation when applied to actual devices.

To investigate the effect of aggregate contact condition on the deformation stability of asphalt mixture (DSAM), computed tomography system was used to acquire a contact parameter of aggregates – t...

Ag/Bi2WO6/graphene oxide composite with excellent photocatalytic properties was successfully prepared by hydrothermal-photoreduction synergistic method and is applied in antibiotics degradation. The structure and properties of as-prepared photocatalysts were characterized by Fourier infrared spectrum (FTIR), X-ray photoelectron spectroscopy (XPS), specific surface area analyzer (BET), scanning electron microscopy (SEM), X-ray diffraction (XRD), and atomic force microscope (AFM). The results indicated that Ag and Bi2WO6 were uniformly loaded on the surface of graphene oxide. In addition, graphene oxide with conjugated carbon network structures has been applied as a photocatalyst supporter for the high electronic conductivity and the large reactive sites. Compared with the pure graphene oxide, the as-prepared Ag/Bi2WO6/graphene oxide catalyst exhibited excellent degradation efficiency and stability for degrading tylosin under Xe lamp irradiation. Under simulated sunlight irradiation, the photodegradation efficiency of tylosin by Ag/Bi2WO6/graphene oxide achieved at 98% within 2 h, compared to 50% by pure graphene oxide. The excellent photodegradation ability is caused by the synergetic effect of Ag, Bi2WO6, and graphene oxide nanoparticles.

The orientation switching of a single azobenzene molecule on Au(111) surface excited by tunneling electrons and/or photons has been demonstrated in recent experiments. Here we investigate the rotation behavior of this molecular rotor by first-principles density functional theory (DFT) calculation. The anchor phenyl ring prefers adsorption on top of the fcc hollow site, simulated by a benzene molecule on close packed atomic surface. The adsorption energy for an azobenzene molecule on Au(111) surface is calculated to be about 1.76 eV. The rotational energy profile has been mapped with one of the phenyl rings pivots around the fcc hollow site, illustrating a potential barrier about 50 meV. The results are consistent with experimental observations and valuable for exploring a broad spectrum of molecules on this noble metal surface.

Functionalized α-GDY with – H, – F, and – N for different displacement distance were designed as promising membranes for separation CO2 from CH4 by using molecular dynamics simulations. The α-GDY were regulated to form suitable pore sizes by functionalization and displacement for separation CO2 from CH4. F-GDY membranes and displacement distance with 1/3 have ultralow CO2 selectivity over N2 of ~0, which indicate that no CO2 pass through F-GDY membranes and CO2 and CH4 were separated efficiently. Among these membranes, N-GDY with 1/3 displacement distance has highest permeance of 5.97 × 10-5 mol m-2 s-1 Pa-1 at 300 K. Relative concentrations distribution confirmed that almost CO2 molecules adsorbed the pore wall of membrane, CH4 distributed in the gas box and vacuum. The interaction energy between gas molecules and membrane was analyzed to elucidate the significant impact of functionalization on the selectivity of CO2 over CH4 and CH4 permeances passing through porous BN membranes.

We have carried out first-principles calculations on structural, electronic, carrier mobility and thermal transport properties of monolayer SrFBr. The dynamic, energetic, mechanical and thermodynamic stability of monolayer SrFBr is all confirmed. It is found that the monolayer SrFBr processes a direct bandgap of 5.23 eV (6.41 eV) obtained by PBE (HSE06), larger than many other 2D materials, and the wide bandgap of monolayer SrFBr can be regulated effectively by strain conditions. Along x and y directions, carrier mobility exhibited a maximum of 471 cm2 V−1· s−1. The lattice thermal conductivity obtained is 1.20 W m−1 K−1 at room temperature, which is lower than many other 2D materials. Additionally, we also obtain the related thermal properties, including group velocity, scattering rates, Gruneisen parameter and the volume of phase space, to explore the reason of the low thermal conductivity.

A novel photoelectrode of three-dimensional (3D) lupinus-like TiO2 nanorod@Sn3O4 nanosheet hierarchical heterostructured arrays (TiO2@Sn3O4 HHAs) on a transparent F-doped SnO2 glass substrate was designed and fabricated by a two-step solvothermal growth process. Photoelectrochemical (PEC) measurements showed that the 3D lupinus-like TiO2@Sn3O4 HHAs photoelectrode displayed enhanced photocurrent density (3-fold increase with respect to that of pure TiO2), improved conversion efficiency, more negative onset potential (from −0.13 to −0.33 V vs normal hydrogen electrode), and higher light on/off cycle stability. The improved PEC properties may be ascribable to the enhancement of light harvesting and large contact area with the electrolyte by increased surface area as well as improvement of charge transfer and collection through the synergistic effects between band structures and morphology.

While good ohmic contact formation has been achieved on both p-GaN and n-AlGaN surfaces, the turn-on and operating voltages of AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs) remain very high. We find that this critical problem is mainly caused by the large difference between the annealing temperatures required for ohmic contact formation on the p-GaN and high Al-fraction n-AlGaN surfaces. We studied the effects of the high-temperature annealing treatments required for n-ohmic contact formation on the subsequent p-ohmic contact formation process in DUV-LEDs. The results show that post-annealing treatment at high temperature is necessary to form an ohmic contact on n-Al0.7Ga0.3N, but a treatment temperature of 900°C or more could cause severe degradation of the specific contact resistivity and the bulk resistivity of p-GaN. We conclude that 900°C is the optimum temperature to form an ohmic contact on n-Al0.7Ga0.3N in DUV-LEDs, where p-GaN and n-Al0.7Ga0.3N act as the p- and n-ohmic contact layers, respectively. We also found that the specific contact resistivity of p-GaN can be reduced by an additional low-temperature annealing treatment after the high-temperature annealing step; this effect can be attributed to the enhancement of the hole concentration in the p-GaN surface contact region. Finally, DUV-LEDs that emit at 280 nm were fabricated using four different annealing treatments during processing. A considerable reduction in the series resistance and thereby in the operating voltage was confirmed using the annealing process proposed above, consisting of a high-temperature anneal at 900°C followed by a low-temperature anneal at 500°C for 3 min.

The hybrid composite materials are a new type of composite material. Due to their complex microscopic structures, it is very challenging to predict the equivalent thermal conductivities of hybrid composites. In this paper, an innovative hybrid wavelet-based learning method assisted multiscale analysis is developed to predict the effective thermal conductivities of hybrid composite materials with heterogeneous conductivity by the asymptotic homogenization method, wavelet transform method, and machine learning method. This innovative approach mainly includes two parts: off-line multi-scale modeling and on-line machine learning. Firstly, the material database about thermal transfer performance of hybrid composites is established by the asymptotic homogenization method and off-line multi-scale modeling, and then the off-line material database is preprocessed by the wavelet transform method. Secondly, the artificial neural network and support vector regression method are employed to establish the on-line machine learning model for predicting the equivalent heat conduction properties of hybrid composites. Finally, the effectiveness of the proposed hybrid wavelet-based learning method is verified by numerical experiments on the periodic and random hybrid composites. The numerical results show that the hybrid wavelet-based artificial neural network method owns the optimal capability of parameter prediction and anti-noise. Furthermore, it should be emphasized that the hybrid wavelet-based learning method can not only extract the important features of off-line material database for random hybrid composites with high-dimensional large-scale data features, but also significantly reduce the quantity of input data for ensuring the successful on-line supervised learning and improve the training efficiency and anti-noise performance of the machine learning model. The established hybrid wavelet-based learning method in this paper can not only be used to evaluate the equivalent thermal conductivities of hybrid composite materials, but also further extend to the predicting of the equivalent physical and mechanical properties of composite materials.

The quasiparticle band structures of monolayer α-ZrNX (X = Cl, Br, I) and β-ZrNX (X = Cl, Br, I) are researched by using an exact quasiparticle approximation GW theory. Our results show that both monolayer α-ZrNX (X = Cl, Br, I) and β-ZrNX (X = Cl, Br, I) are two-dimensional semiconductors with wide band gaps (larger than 3.5 eV). We have considered the effect of exciton, calculated their optical properties by GW0+BSE method, and obtained the accurate dielectric function spectrum. We find that monolayer α-ZrNI has excellent light absorption in the ultraviolet region. By studying the exciton binding energy of monolayer α-ZrNX (X = Cl, Br, I), it is found that monolayer α-ZrNCl and α-ZrNBr have relatively large exciton binding energies (0.74 eV, 0.67 eV). The relationship between the band gaps and the exciton binding energies in two-dimensional semiconductors has also been discussed. Our present work gives more accurate information on the energy band structures and optical properties of monolayer ZrNX (X = Cl, Br, I), which is of guiding significance for the future investigation on monolayer ZrNX (X = Cl, Br, I). And the investigation of the exciton binding energy has a reference value for the study of the exciton effect in two-dimensional semiconductors.

Compound ceramic coatings with the main crystalline of Al2TiO5 (in the as-prepared coating without treatment) were prepared in situ on the surface Ti–6Al–4V alloy by means of pulsed bipolar micro-arc oxidation in NaAlO2 solution. For the purpose of studying the anti-oxidation properties of the samples, the coated samples treated in argon and the as-coated samples were calcined in air at 1000 °C. And the related characteristics were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray fluorescence (XRF) spectroscopy, respectively. The results show that, when it was calcined in air for 1 h, Al2TiO5 in the as-prepared coating decomposed and transformed into α-Al2O3 and rutile TiO2. However, after almost 4 h in argon, Al2TiO5 in the as-prepared coating decomposed and the final coating surface contents are completely α-Al2O3, and those of the middle interface are mainly Al2O3 and Ti2O3. The morphologies of the coatings after calcination in argon and air are different. High-temperature oxidation occurred violently in the alloy substrate without coatings. Furthermore, the weight gain curves of the as-prepared samples and the coated samples treated in argon both show a parabolic shape.

Graphitic carbon nitride (g-C3N4) has recently emerged as an attractive photocatalyst for solar energy conversion. However, the photocatalytic activities of g-C3N4 remain moderate because of the insufficient solar-light absorption and the fast electron–hole recombination. Here, defect-modified g-C3N4 (DCN) photocatalysts, which are easily prepared under mild conditions and show much extended light absorption with band gaps decreased from 2.75 to 2.00 eV, are reported. More importantly, cyano terminal CN groups, acting as electron acceptors, are introduced into the DCN sheet edge, which endows the DCN with both n- and p-type conductivities, consequently giving rise to the generation of p–n homojunctions. This homojunction structure is demonstrated to be highly efficient in charge transfer and separation, and results in a fivefold enhanced photocatalytic H2 evolution activity. The findings deepen the understanding on the defect-related issues of g-C3N4-based materials. Additionally, the ability to build homojunction structures by the defect-induced self-functionalization presents a promising strategy to realize precise band engineering of g-C3N4 and related polymer semiconductors for more efficient solar energy conversion applications.

Functional poly(o-methoxyaniline) (POMA) microsheets are successfully synthesized in the presence of (NH4)3[CoMo6O24H6]·7H2O (CoMo6) under acidic conditions. It is proposed that the light-green CoMo6 precipitates formed in the initial reaction systerm serve as a polymerization reaction template for the formation of POMA microsheets. Moreover, POMA microsheets show pH-dependent fluorescence and exhibit enhanced fluorescence properties in comparision with POMA synthesized by conventional method in the absence of CoMo6.

The vehicular fuel cell stack is unavoidably impacted by the vibration and shock in the real-world due to the road unevenness. However, influences of vibration on fuel cell stack have yet to be investigated completely. In this paper, the performance of a fuel cell stack is experimentally studied in terms of gas-tightness, voltage degradation, AC impedance spectra, polarization curve and characteristic parameters in polarization curve through long-term strengthened road vibration tests, in order to investigate the influences of road-induced vibration on performance degradation of fuel cell stack. The vibration tests are carried out on a six-channel multi axial simulation table with the vibration excitation spectra originally derived from the strengthened road of the ground prove. During the vibration test, several kinds of performance test including gas-tightness test, AC impedance diagnosis and polarization curve test are conducted at regular intervals. After the vibration test, the gas leakage rate of anode reaches 1.73 times of the initial value. The open circuit voltage and rated voltage decreases by 0.90% and 3.58%, respectively. Meanwhile, the performance of individual cell voltage uniformity becomes worse distinctly. With the increase of vibration duration, the ohmic resistance obtained from AC impedance diagnosis ascends approximately linearly and presents a growth of 5.36% ultimately. An improved empirical fuel cell polarization curve model is adopted to fit the current–voltage data and estimate the characteristic parameters which decide the shape of polarization curve. It is noted that the limiting current density declines distinctly and the mass transfer loss increases mainly at the range of high current densities. The results indicate that the long-term strengthened road vibration condition exerts a significant influence on the durability of fuel cell stack.

The external quantum efficiency (EQE) in electrically injected AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs) is severely limited by their poor current injection efficiency (CIE). We report improvement in the CIE via controlling the relaxation of strains in the p-AlGaN hole injection layer (HIL) and the electron blocking layer (EBL). Simulation results show that an unrelaxed strain in the HIL associated with a relaxed strain in EBL can significantly enhance CIE. Deeper analysis indicates that high hole concentrations can be generated at HIL/EBL interface by strain-induced piezoelectric fields, which can then provide abundant numbers of holes for injection into quantum wells. Two sub-280 nm DUV-LEDs were fabricated with specific designs for different strain relaxations in the p-AlGaN HIL by changing the HIL thickness from 200 to 20 nm. The strain difference was identified using Raman spectroscopy. Electroluminescence measurements demonstrated much higher EQE in the strained-HIL DUV-LEDs. By separating the EQE contributions of three efficiencies, i.e. the CIE, the radiative recombination efficiency and the light extraction efficiency, we found that the EQE enhancement could mainly be attributed to the improved CIE, which agreed well with the simulation results.

A novel lanthanide germanate, namely RbNdGe2O6, has been successfully synthesized by high-temperature solid-state reaction in open air atmosphere for the first time. Single crystal X-ray diffraction indicates a 3D framework composed of 1D neodymium oxygen chains connected with cyclogermanate Ge3O9 units with Rb+ located in the internal space. X-ray powder diffraction coupled with Rietveld refinement reveals the sample’s phase purity we have prepared. Thermal behavior analysis shows RbNdGe2O6 is very stable, it doesn’t decomposition until heated up to 998 ​°C. UV–visible absorption and diffuse reflection spectrum feature characteristic absorption bands of f-electron transition and an optical bandgap value of 4.65 ​eV. Magnetic susceptibilities measurement gives significant antiferromagnetic interactions between magnetic centers. The photodegradation experiments were performed to evaluate photocatalytic activities of RbNdGe2O6. By using P25 as a reference, RbNdGe2O6 features to be an effective visible-light-driven catalyst in photodegrading methylene blue. Although the BET value of RbNdGe2O6 is only 3% that of P25, the photocatalytic activity reaches 0.55 times that of P25. Furthermore, the proposed photocatalytic mechanism which dominated by holes was further verified by adding ammonium oxalate as a quencher.

In order to study the effect of dip angle on the tensile strength and failure characteristics of red sandstone, based on the results of the Brazilian splitting test for indoor double-hole red sandstone samples, using the PFC2D particle flow numerical simulation technique to simulate the Brazilian splitting test of precast double-hole red sandstone samples, the effect of dip angle on the tensile strength and failure characteristics of red sandstone samples is studied, further, the evolution characteristics of the surface stress field of the double-hole red sandstone specimen during the tension process are analyzed, and the failure mechanism of the red sandstone in the double-hole red sandstone is revealed. The results show: (1) Increasing the inclination angle of the double hole from 0°to 60°the tensile strength of the sample is stepped down, the maximum drop is when the double hole is inclined at 45°;(2)When the double hole inclination angle is 0°-30°, the crack extends through a single hole; when the double hole inclination angle is 45°-60°, the crack propagates through the double hole.(3)The tensile stress concentration zone near the double hole is the main factor affecting the tensile strength and crack propagation of the sample: ① When the tensile stress concentration region at the edge of the hole A and the hole B is not penetrated (0°, 15°, 30°), the tensile strength of the sample is large, when the crack propagates, only a single hole is penetrated; ② When the tensile stress concentration region at the edge of the hole A and the hole B is penetrated (45°, 60°), the tensile strength of the sample is greatly reduced, the double hole is penetrated when the crack propagates.

Probing the optical Stark effect at the single-molecule or atomic scale is crucial for understanding many photoinduced chemical and physical processes on surfaces. Here, we report a study about the optical Stark effect of single atomic defects on a TiO2(110) surface with photoassisted scanning tunneling spectroscopy. When a laser is coupled into the tunneling junction, the midgap state of the OH-O-2 defects changes remarkably in differential conductance spectra. As the laser power gradually increases, the energy of the midgap state shifts away from the Fermi level with an increase in intensity and a broadening of the peak width. The observation can be explained as an optical Stark effect with the Autler-Townes formula. This large optical Stark effect is due to a tip enhancement and a strong dipole moment in the transient charged state during electron tunneling. Our study provides different aspects in exploring electron-photon interactions at the microscopic scale.

An ultra-wideband terahertz filter was investigated based on the frequency selective surface (FSS) designed by the Jerusalem cross slot structure. Through careful modeling and systematic analyzing, good stopband filtering characteristics in the range of 0.35 –0.55 THz are achieved with the transmittance < 0.1. When the filter’s bandwidth increases, our results show the FSS filter is still able to provide sound angular stability, polarization stability, and sufficient robustness.

An accurate dynamic mechanical model plays a vital role in the engineering application of rubber-like materials. Though many researchers have done work on these models, it is still difficult to fit the model's parameters via dynamic mechanical thermal analysis (DMTA) data, especially for Havriliak–Negami (HN) model. A methodology is proposed to determine the parameters in HN model. The DMTA data of carbon black filled rubber (CBFR) NR100N550 is utilized to verify the methodology in this paper. The time–temperature superposition principle (TTSP) is applied to investigating the viscoelastic properties of CBFR NR100N550 at wide frequency range. The experimental results show that the proposed methodology could be applied to obtaining parameters in HN model. HN model is able to model the dynamic mechanical properties of carbon black filled rubbers at wide frequency range, which are correlated with the chemical structure of the polymers.

In this work, fiber optic sensors were developed and utilized in concrete structure freeze–thaw cycle monitoring due to their exclusive properties compared with conventional sensing technologies, which can realize more accurate, effective, long-term and real-time monitoring. Fiber Bragg grating (FBG) sensing technique and white light interferometer (WLI) sensing technique were introduced and used to test the residual expansion strain in a number of cylindrical concrete samples. Embedded FBG and WLI sensors were designed and their performances were evaluated in real-time when the concrete samples were saturated with water and subjected to repeated freezing and thawing cycles. This work was intended to show the feasibility of the developed sensors on monitoring the concrete freeze–thaw damage based on residual strain, and a new evaluation index compared with the traditional methods (mass loss rate and relative dynamic elastic modulus). The residual strain sensitively measured by fiber sensors was basically fitted with the phenomenon that the residual strain increased along with the number of freeze–thaw cycles, indicating that two fiber sensing techniques were able to monitor the concrete freeze–thaw damage. Meanwhile, comparing the two techniques from four aspects, WLI was more suitable for residual strain monitoring in concrete freeze–thaw damage.

To improve the preparation technology and mechanical properties of carbon/carbon composites, a kind of Zirconium dioxide modified Carbon/carbon (C/C–ZrO2) composites were prepared by Sol-Gel Process combined with isothermal chemical vapor infiltration (ICVI) method. This method could shorten preparation cycle greatly to reduce the cost. The microstructures and mechanical properties of the C/C–ZrO2 composites were investigated. The results indicate that the ZrO2 modified phase is uniformly distributed in the carbon matrix, the bending strength and modulus of C/C–ZrO2 composites are much higher than unmodified C/C composites due to its particle toughening and fiber toughening.

Functional Polyaniline (PANI) nanotubes are easily synthesized in high yield by an in situ polymerization using a fibrillar complex of acid orange II (AO II) and FeCl3as a template. During the process, the complex templates help direct the growth of fibrillar PANI on their surfaces, resulting in the formation of composite micro/nanofibers of PANI. After polymerization, by the post-treatment of removing templates in 1.0 M hydrochloric acid solution, PANI nanotubes with azo function and high electric conductivity of PANI are readily fabricated. The PANI nanotubes have about 150nm-300nm in diameter and several microns in length. At room temperature, the electric conductivity of PANI nanotubes is up to 10-1S/cm order of magnitude. The characterizations, including FTIR, UV-visible, XRD and TG, are presented.

In a redox system containing ascorbic acid(AA) and ammonium persulfate(APS), Poly(o-chloroaniline)(POC) micro/nanostructures including nanoparticles, nanofibers, and microspheres were successfully prepared through a self-assembly process in absence of additional template. The results indicated that POC morphologies were strongly affected by the molar ratio of o-chloroaniline(OC) to ascorbic acid([OC]/[AA]) and the reaction temperature. The fibrillar or spherical POC micro/nanostructures could be dynamically controlled in the AA/APS redox system by changing the polymerization rate of OC monomers. Thermogravimetric analysis showed that the POC nanofibers had a better thermal stability than POC microspheres. The conductivity of POC nanofibers could reach 5.5×10-3S/cm, while the microspheres were almost insulators.

Filled rubber-like materials show a significant dependence on predeformation, frequency and amplitude when they are loaded with static predeformations superimposed by harmonic deformations. In order to investigate this predeformation-, frequency- and amplitude-dependent material behavior, a recently developed constitutive model of finite viscoelasticity is proposed based on the models of Lion and Kardelky (2004) and Hofer and Lion (2009). The constitutive equations are geometrically linearized in the neighborhood of predeformation and then formulated for incompressible materials. Finally, the process of parameter identification and some numerical aspects are shown. Additionally, the experimental verification and some numerical simulations will also be supplied. The results show that our model cannot only be used for loading cases with small strains but also with large strains. It may have some meanings for practical engineering applications.

A novel P–N containing intumescent flame retardant, 2-cyclic pentaerythritoloctahydrogen tetraphosphate-4,6-benzene sulfonic acid sodium ammion-triazine (CTOB) was synthesized and used as an additive in intumescent flame retardant composites containing organic montmorillonite (OMMT) and Nylon 6. The thermal stability and flammability properties of Nylon 6, CTOB, OMMT and their composites were investigated by TGA, limiting oxygen index (LOI) and cone calorimeter tests. Synergistic effects between CTOB and OMMT in the Nylon 6/CTOB/OMM composite were observed. A combination of CTOB and OMMT improved the thermal stability and the flammability properties of Nylon 6 and increased the LOI value to 28.0%. The average and peak heat release rates of the ternary composite were reduced by about 65.7% and 49.3%, respectively, compared with those of Nylon 6. The residue generated after the cone calorimeter tests upon combustion of the ternary composite was a compact and dense char as revealed by SEM, which is critically important for an excellent flame retardant. [New Carbon Materials 2015, 30(2): 186–192]

In this paper, we introduce the 3D design of a vector light sensor for angular proximity detection applications. The sensor structure is based on creating photo sensors on side walls of micro-sized (micron scale) mesa pyramids etched in silicon. On each facet of the mesa pyramid, p-n junctions are formed and used as photodiodes. Unlike planar pixels, this 3D pixel design allows for estimation of the direction of the light incident on the sensor. We present the operating principle, fabrication details and the experimental verification of the device's performance. The sensor's unique design, simple fabrication process, and readout integrated circuit's compatibility adds merits to the current planar designs and could be utilized in angular proximity applications such as multi-focus level imaging or environment mapping for real-time dynamic virtual and augmented visualizations.

In this study, shrinkage-compensating concrete mixtures were prepared with various amount of CaO-based expansion agent to investigate their workability, mechanical property and durability. The experimental results indicate that CaO-based Expansive Agent has little effect on the performance of the fresh concrete workability. The mechanical properties and durability have been affected by the boundary limitation conditions. Adding 20-25kg CaO-based expansive agent per cubic meter concrete in replacement of equal amount of cementitious materials or sand would effectively compensate the deformation induced by chemical shrinkage and drying shrinkage.