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Solvothermal synthesis technique is an effective method to create composite materials. In this paper, a series of TiO2@MIL-101(Cr) were prepared by the solvothermal method for photocatalytic denitrification of pyridine in fuel under visible light irradiation. The products were characterized by XRD, FT-IR, SEM, TEM, BET, DRS, and ESR. The result shows that 20%TiO2@MIL-101(Cr) has high catalytic activity, the pyridine removal efficiency reaches values as high as 70% after irradiation for 240 min. Finally, we obtained the possible mechanism of photocatalytic denitrification according to the HPLC-MS spectrometry results analysis.

The fabrication of solid-state single-molecule switches with high on-off conductance ratios has been proposed to advance conventional technology in areas such as molecular electronics. Herein, we employed the scanning tunneling microscope break junction (STM-BJ) technique to modulate conductance in single-molecule junctions using mechanically induced stretching. Compound 1a possesses two dihydrobenzothiophene (DHBT) anchoring groups at the opposite ends linked with rigid alkyne side arms to form a gold-molecule-gold junction, while 1b contains 4-pyridine-anchoring groups. The incorporation of ferrocene into the backbone of each compound allows rotational freedom to the cyclopentadienyl (Cp) rings to give two distinct conductance states (high and low) for each. Various control experiments and suspended junction compression/retraction measurements indicate that these high- and low-conductance plateaus are the results of conformational changes within the junctions (extended and folded states) brought about by mechanically induced stretching. A high-low switching factor of 42 was achieved for 1a, whereas an exceptional conductance ratio in excess of 2 orders of magnitude (205) was observed for 1b. To the best of our knowledge, this is the highest experimental on-off conductance switching ratio for a single-molecule junction exploiting the mechanically induced STM-BJ method. Computational studies indicated that the two disparate conductance states observed for 1a and 1b result from mechanically induced conformational changes due to an interplay between conductance and the dihedral angles associated with the electrode-molecule interfaces. Our study reveals the structure-function relationship that determines conductance in such flexible and dynamic systems and promotes the development of a single-molecule variable resistor with high on-off switching factors.

To estimate the multiaxial notch local elastic–plastic strains real timely, an online notch elastic–plastic analytical method is proposed coupling with the modified pseudo stress criterion and Chaboche constitutive model. Moreover, for the Ramberg–Osgood material, the non-proportional cyclic strain hardening can be well considered by the proposed unified online accumulation method of equivalent plastic strain increment. Meanwhile, a rapid and effective simulating algorithm for the proposed online method is provided and verified by the experimental data of TC21 titanium alloy and SAE1070 steel notched specimens. Comparisons show that the simulated results can agree with the measured data quite well under multiaxial irregular loading.

Soft rice is a kind of high-quality rice between glutinous rice and sticky rice. It has low amylose content, crystal clear grains, sweet taste, soft glutinous, and is suitable for cooking and porridge. Chalkiness in soft rice is a white opaque part formed by loose endosperm. It is an important character that affects the appearance quality, processing, and cooking quality of rice, and also an important limiting factor that restricts the standard rate of high-quality rice in China. The combination of scanning electron microscope and energy dispersive spectrometer (SEM-EDS) can be used for in-depth analysis of rice, visualization, and quantitative analysis of element distribution in rice. The results showed that there were many kinds of mineral elements in soft rice seeds, among which C and O were the most abundant, followed by N and P, and Mg, Al, P, S, K, Ca, Mn, and Zn were less. The contents of C, N, P, and S in the non-chalky area were significantly higher than those in the chalky area. Especially N and S were the best indicators of protein, and the contents in the chalky area were higher than those in the non-chalky area. It means that the protein content in the chalky part of soft rice seed is less than that in the non-chalky part, which affects the nutritional quality of soft rice. Therefore, the results of this study laid a solid foundation for the in-depth analysis of the distribution of mineral elements and protein in soft rice and their effects on the quality of soft rice, which also provided important information for the cultivation of new high-quality rice varieties in the future.

The three isomeric tetraarylethylene derivatives DPDT-o-CHO, DPDT-m-CHO and DPDT-p-CHO have been designed and synthesized, based on a 1,1-diphenyl-2,2-(2-dithiophen) ethylene (DPDT) core doubly bonded to the phenyl group with an ortho-/meta-/para-aldehyde substituent for unique aggregation-induced emission (AIE)-active luminescences. They exhibited remarkable photochromic behaviors based on the UV-light induced photocyclization reaction, including fluorescence enhancement in solution and emission quenching in the solid state. Moreover, the positions of the substituent aldehyde group exert distinct influence on their molecular conformation and spatial arrangement, resulting in distinct photoresponse. Interestingly, the solid-state of meta-substituted isomer DPDT-m-CHO undergoes a fast reversible photo-switch with a high colorimetric contrast and exhibited a rewritable process on filter paper, which highlight the advantage of these AIE-active photochromic molecules in various practical applications. In addition, owing to the reaction of the aldehyde group with hydrogen sulfite (HSO3−) to generate ionic adducts triggering the disaggregation process, the three AIE-active luminogens were capable of exhibiting a “turn-off” fluorescence response to hydrogen sulfite in high water content. Our work provides a general method to design aldehyde group functionalized regioisomeric AIE luminogens with photochromic features by the controllable UV-light induced photocyclization reaction and fluorescence quenching by reverse chemical reaction-based disaggregation, indicating the prospective applications of these luminogens in information security and specific fluorescence sensing.

Achieving ultrathin two-dimensional (2D) metal–organic framework (MOF) nanosheets is an extremely meaningful topic and still remains a great challenge. Herein, for the first time, a single-layer 2D Zn-MOF nanosheet was obtained by a facile top-down strategy based on 3D layered Zn-MOF crystals. It involves two steps: firstly, weakening the van de Waals interactions between layers by the protonation of the Zn-MOF under acidic conditions; secondly, further destroying the weakened van der Waals interactions through electrostatic interactions using negatively charged tape molecules, congo red (CR) or methyl orange (MO). Transmission electron microscopy and atomic force microscopy studies demonstrated that ultrathin single-layer (3.4 nm) 2D Zn-MOF nanosheets were obtained, with an ultra-large lateral size (ca. 6 μm), and showed unprecedented adsorption performance toward CR. For CR, the 2D Zn-MOF nanosheets could not only achieve record high uptake capacity (6639.55 mg g−1), but also present efficient and rapid removal. It is worth noting that the adsorption of CR could prevent restacking of the exfoliated 2D Zn-MOF nanosheets and facilitate further exfoliation, which in turn provided more 2D Zn-MOF nanosheets for CR adsorption. Moreover, CR can be selectively and efficiently removed even from the mixed dye solution with different charges. It is anticipated that this methodology could provide a concept to integrate exfoliation and pollutant removal into one process, fulfilling the facile synthesis of ultrathin functionalized 2D nanosheets, with high performance for pollutant removal.

International audience; Water-soluble thermoresponsive polymers present either upper critical solution temperature (UCST) or lower critical solution temperature (LCST) depending on the location of their miscibility range with water at high temperatures or at low temperatures. Compared with LCST polymers, the water-soluble UCST polymers are still less explored until now. In this work three copolymers of P(AAm-co-GAA) were synthesized by copolymerizing two acrylamide monomers, acrylamide (AAm) and acrylamide functionalized with natural glycyrrhetinic acid (GAA), using reversible addition-fragmentation chain transfer (RAFT) polymerization. These copolymers exhibited the typical UCST thermoresponsive behavior, and their phase transition temperatures could be easily tuned to around 37 C for potential biological applications. Moreover, the UCST of P(AAm-co-GAA) can be adjusted not only by the content of glycyrrhetinic acid (GA) and polymer concentrations, but also by the host-guest interactions between GA and cyclodextrins (β-and g-CD). The suitable value of UCST and the biocompatible nature of GA and CDs may endow these copolymers with practical applications in biomedical chemistry

International audience; Polydiacetylenes (PDA) can undergo a blue-to-red color transition in response to external stimuli because of the extensive delocalized p-electron networks and intrinsic conformational restrictions, which make PDA particularly attractive building blocks for stimuli-responsive materials. In this work, a blue chiral C4-MOP/PDA gel was fabricated successfully by UV irradiating a white supramolecular gel that was assembled from a triterpenoid-derived gelator (C4-MOP) and a diacetylene monomer (PCDA). This photopolymerization was completed within 5 min with the generation of the new negative Cotton effect at 657 nm in the visible blue light region, which strongly revealed the transmission, amplification and visualization of molecular chirality during this gelation and the photopolymerization process. Notably, the nanotubular microstructures of the white gel C4-MOP/PCDA that curled from twisted ribbons barely changed after polymerization into C4-MOP/PDA. In addition, because C4-MOP/PDA contained an alternating ene-acetylene conjugated structure, it exhibited multiple color transitions to external stimuli including temperature, organic solvent, and mechanical force. This work provides chiral polydiacetylene assemblies by using natural triterpenoid gelators, and may open new developments in the design of smart responsive chiral PDA materials.

Two-dimensional materials with intrinsic long-range ordered magnetic moments have drawn a lot of attention. However, for practical applications, whether or not the magnetism is stable in their nanostructures has not been revealed. Here, based on the recently proposed magnetic penta-hexa-graphene, we study the electronic and magnetic properties of its nanoribbons (named PHGNRs). The results show that the PHGNRs have intrinsic robust magnetic moments that are different from zigzag graphene nanoribbons, where the magnetic moments caused by the edge effect are vulnerable. Moreover, the magnetic ground states, namely, ferromagnetic (FM) or antiferromagnetic (AFM), can be transformed by changing the width of PHGNRs. Most interestingly, under the FM ground state, the spin-polarized electronic properties reveal that the zigzag PHGNRs transform from spin-gapless semiconductors (SGSs) to half-metals, as the width of nanoribbons increases, while all the armchair PHGNRs are magnetic semiconductors. Furthermore, by considering different edge effects caused by the residual carbon atoms on the edges, the PHGNRs can further derive different types of SGSs, as well as half-metals. Our work suggests that the PHGNRs possessing intrinsic robust magnetic moments have potential applications in the field of spintronic devices.

Fano resonance is realized theoretically in a photonic crystal. The structure is composed of a cavity side coupled to a partially transmitting waveguide. By optimizing the structure parameters, asymmetric sharp Fano resonance transmit-tance spectrum is achieved with quality factor of 2 213, extinction ratio of 57 dB and peak loss of 0.2 dB. The sharp spectrum can be used in sensor applications. Such as pressure sensor, the pressure sensitivity is about 9.15 nm/GPa. and for refractive index sensing application, the sensitivity is about 800 nm/RIU, and the maximum of figure of merit can reach 1 000. Besides, this sharp Fano resonance based on photonic crystal has potential applications in optical switches, filters etc. And it can be integrated into optical communications and optical integration circuits.

Triazole heterocyclic compounds have a wide range of applications in the fields of medicine, pesticide, energetic materials, etc. Introducing halogen atoms and amino groups into the triazole ring can obtain a series of important intermediates that can be further modified. 4,5-Dibromo-1-H-1,2,3-triazole (5), 3,5-dibromo-1-H-1,2,4-triazole (6), 3,5-dibromo-4-H-1,2,4-triazole (7) and 1-amino-4,5-dibromo-1,2,3-triazole (8), 2-amino-4,5-dibromo-1,2,3-triazole (9) and 1-amino-3,5-dibromo-1,2,4-triazole (10) were synthesized through the bromination and amination of 1,2,3-triazole (1), 1-amino-1,2,3-triazole (2), 1,2,4-triazole (3) and 4-amino-1,2,4-triazole (4). Their structures were characterized by IR, EI-MS, ESI-MS, 1H and13C-NMR techniques. Single crystals of these compounds were grown by evaporation solution growth technique. The cell parameters and crystal structures were determined by X-ray single crystal diffraction studies. Among these compounds, 6 and 7, 8 and 9 were isomers, respectively. Through intermolecular hydrogen bonding, 1 forms zigzag chain structure, while 4 and 5 form cyclic trimers.

In this paper, acrylate-terminated polysiloxane was synthesised and used as raw materials for the synthesis of cationic core/shell polysiloxane acrylate emulsion, which was applied as binders in the pigment dyeing of cotton fabrics. The experimental results showed that: the cationic core/shell poly siloxane acrylate emulsion in this article is in nano size of 100nm. During the film formation of the emulsion, there are core-core and shell-shell fusion phenomena between the latex particles, and same poly siloxane chain aggregates on the surface of the film. When the emulsion is used in the pigment dyeing of cotton fabrics, the dyed cotton fabrics feel soft, and the soaping fastness and dry/wet rubbing fastness meet the national quality requirements, as soaping fastness can reach grade 4 ~ 5, dry rubbing fastness can reach grade 4 ~ 5, and wet rubbing fastness can reach grade 4.

With global resource shortage and deterioration of ecological environment, the research and development of clean and renewable energy is of vital importance. Using first-principles calculations, we firstly study water splitting catalyzed by metal based biomolecule porphyrin (MPP) (M = Mg, Ba, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn). Among all the systems, after releasing electron, TiPP is the most effective catalyst for H 2 O splitting. TiPP and the remainder O atom form the very stable structure OTiPP. The H 2 O + OTiPP can release electron with the 6.76 eV potential barrier. The releasing electron process of porphyrin can be easily realized under the effect of solar energy by experiment study. After releasing electron, OTiPP can effectively catalyze the dissociation of H + from H 2 O in an exothermic process. The desorption of O atom is an endothermic process with 0.72 eV barrier. The H 2 O + OTiPP system can readily return to its original state OTiPP, in other word, the OTiPP can be a sustainable cycling catalyst for water splitting under the effect of potential barrier transfer. The whole catalytic process is remarkable clean without any pollution. This method may open up new avenues for the development of future clean energy and extraordinary biomimetic photosynthesizers.

A series of biruthenium complexes linked by oligothiophene bridges of variable lengths (4a–4d) have been prepared to probe intramolecular electronic delocalization as a function of the chain length...

Carbon fiber reinforced plastics (CFRP) are promising lightweight materials for vehicle applications. 316L is one of the most widely used types of austenite stainless steels and applied in lots of automotive applications. The existence of crevices will result in galvanic corrosion and crevice corrosion when CFRPs and 316L are directly connected. A crevice former for the galvanic system was therefore designed and applied to evaluate the crevice corrosion behaviors and study the mechanism of galvanic crevice corrosion through several electrochemical techniques in this research. The results showed that the crevice corrosion of galvanic systems grew from crevice mouth to the inside crevice and could be divided into four steps, metastable pitting corrosion at the crevice mouth, initiating step of crevice corrosion, propagating step and ending step of crevice corrosion. Because of the influences of the galvanic system, electrode reaction rates were speeded up and the passivation region was shortened at the initiating stage of crevice corrosion. Corrosion rate was observed to be higher in the galvanic system than that in normal crevice systems.

Fluorescent carbon nanodots (CNDs) capable of dual emission blue and red light (B-R-CNDs) (460 and 610 nm) have been synthesized by a simple and low cost electrochemical method of discharging indol...

As the applications of supramolecular assemblies are ultimately inscribed in their nanostructures, strategies that can precisely fabricate and regulate supramolecular architectures from small molecules are of great importance. Herein, in this research multiple modulations of supramolecular assembled structures of a natural triterpenoid-tailored bipyridinium amphiphile, 1-[2-(methyl glycyrrhetate)-2-oxoethyl]-[4,4']bipyridinium bromide (MGBP), have been achieved by adjusting solvents or counterions. Depending on the polarity of solvents, MGBP assembled into nanofibers, helices, pentagon and hexagon microsheets, respectively. Moreover, the nanofibers in methanol/water can transform into ribbons, robust fibers and fiber bundles by addition of counterions with different ionic sizes and valences. This work presents a simple and feasible methodology to modulate assembly structures of a natural triterpenoid-based amphiphile, which may expand the application of natural products in supramolecular materials.

Capsules with holes in the walls exist in natural systems like virus capsids, and in biomimetic systems like immune-stimulating complexes vaccines and liposomes of phospholipids/surfactants mixtures. Structuring pores into stable membrane and controlling their opening are extremely useful for applications that require nano-pores as channels for material exchange and transportation. Polymersomes, which are stable and robust vesicles made of amphiphilic block copolymer, are good candidates for drug carriers or micro/nanoreactors. Engineering structure-inherent and light-gated nano-porous polymersomes is especially appealing, but still unexplored. Here we present these polymersomes made from a polymer including a tetraphenylethene (TPE) in its center. TPE is an emblematic fluorogen with aggregation-induced emission, which possesses two stereoisomers sensitive to photoisomerization. Trans-isomer of the polymer forms classical vesicles, cis-isomer forms cylindrical micelles, while trans/cis mixtures construct perforated vesicles with nano-pores. Under UV light, the classical polymersomes of trans-isomer can be perforated by its cis-counterpart generated from the photoisomerization.

International audience; Vitrimers are covalent polymer networks that can change their topology through thermally activated bond exchange reactions. In this work, fully biobased and recyclable vitrimers were developed from epoxidized soybean oil (ESO) and natural glycyrrhizic acid (GL) as it was without additional chemical modification, which avoided the use of nonrenewable petroleum resources and resolved the disposal problems of materials. Because of the unique rigid skeleton of GL, ESO/GL vitrimers showed good thermal stability and mechanical properties. Driven by the transesterification-induced topological network rearrangements, these ESO/GL vitrimers exhibited high performance of welding, repairing, and shape memory. They were also recyclable and chemically degradable by ethylene glycol. More importantly, these vitrimers could be used as repairable and recyclable adhesives.

To date, flexible sensors derived from hydrogel materials have been popularly adopted in the field of wearable electronic devices. It is urgent and prospective to create a high-performance and multi-functional hydrogel by simple and green methods to satisfy the various demands for long-term direct human contact. Herein, a sustainable physical double network hydrogel is prepared by natural glycyrrhizic acid (GL) and biocompatible polyvinyl alcohol (PVA) in water/glycerol solvent, which exhibits high mechanical properties, good biocompatible, anti-freezing and anti-drying ability. Inspired by the reducing abilities of GL, a gradient silver nanoparticles layer can be constructed in situ on the hydrogel surface without additional reducing agents. It not only affords the UV-light shielding and antibacterial effect for the hydrogel, but also effectively improves the sensing performance. The simultaneous realization of desired properties enables the hydrogel to be assembled into a sensor to detect all-dimensional human motion with high sensitivity, stability and durability. Benefiting from the renewable raw material, non-toxic reagent and facile preparation process, this work provides new insight and inspiration for the design of flexible sensors with high performance, multi-functionality and sustainability.

Intense, polarization controllable, and single-cycle terahertz pulses as light source are important tools to investigate physical and biological properties of materials. In this paper, we have detected efficient terahertz emission from layered transition-metal pentatelluride ZrTe5 excited by femtosecond laser pulse due to its strong anisotropy and high mobility of electrons. The physical mechanism of terahertz generation from this material is studied and the absolute predominance of diffusion current induced by photo-Dember effect is proved. In addition, we have achieved the modulation of terahertz polarization by adjusting the polarization states of the pump pulse. The generated elliptically polarized THz pulse is crucial for the investigation of vibration modes of chiral biological molecules, such as proteins and DNAs. Our findings indicate that strong and polarization-controllable THz emission can be generated by ZrTe5.

The transmission properties have been investigated for the anisotropic plasma photonic crystal (APPC) with defect layer. Based on the transfer matrix method (TMM), the total transmission coefficient for the symmetry APPC with defect layer has been deduced. The numerical simulations shows that transmittance spectrums are the same as those of the general plasma crystal when the thickness of the defect layer is small. With the increasing of the thickness of the defect layer, the transmittance peak is split into more transmittance peaks called as the defect modes, which is different from the general plasma crystal. The defect modes caused by the defect layer in the APPC open up another choices of multichannel filters for EM waves in practice.

Hybrid organic-inorganic perovskites, especially methylammonium lead triiodide (MAPbI(3)), are intensely studied for their optoelectronic properties. The organic MA(+) cation is held responsible for the superior performance of MAPbI(3) but also its instability toward moisture and heat. To explore compositions beyond MAPbI(3), we performed experiments and calculations on two isomorphous perovskites CsSnBr3 and MASnBr(3). CsSnBr3 is slightly smaller than MASnBr(3) in cell dimension, but outperforms MASnBr(3) in band gap energy, charge-carrier reduced effective mass, and optical dielectric constant all by approximate to 19%. These merits accumulate to drastically cut the exciton binding energy from 33 meV for MASnBr(3) to 19.6 meV for CsSnBr3, making CsSnBr3 a black, free-carrier semiconductor. CsSnBr3 also exhibits distinctly higher stability toward moisture and heat than its organic counterparts. These advantages suggest ecofriendly applications for CsSnBr3, such as tandem solar cells and direct X-ray detectors.

The damage and tensile mechanical behavior of C/SiC composites plate after hypervelocity penetration are studied in this paper. Hypervelocity penetration is applied along the out-of-plane direction by an electrical gun at 3.5 km s - 1 , and the target is recovered for damage observation and tension test. Quasi-static tensions on the recovered targets and the slices cut from damage zone are examined along with high-speed photography. Moreover, corresponding numerical simulations are carried out. The damage zone in the vicinity of the penetration hole is small ( ∼ 10 mm), and the damage mode involves SiC matrix fracture, delamination, fiber bundle splitting and fiber breaking. The simulation results suggest that the degree of damage decreases exponentially with the increasing distance from the penetration hole center of the target plate. As the degree of damage increases, the tensile strength of C/SiC composites decreases and the corresponding fracture mode changes from shear failure to tensile breakage. Additionally the fracture surface becomes smoother, the quantity and length of fiber pullout also increases. Since the decrease of elastic modulus induced by damage weakens the stress concentration effect of the penetration hole, the residual strength of recovered target plate is only reduced from 241 MPa to 175 MPa.

Energy transfer and interchange are central for fabricating white light-emitting organic materials. However, increasing the efficiency of light energy transfer remains a considerable challenge because of the occurrence of "cross talk". In this work, by exploiting the unique photophysical properties of cucurbituril-triggered host-guest interactions, the two complementary luminescent colors blue and yellow for white light emission were independently obtained from a single fluorophore dye rather than energy transfer. Further study suggested that the rigid cavity of cucurbiturils efficiently prevented the aggregation of the dye and improved its thermal stability in the solid state by providing a regular nanosized fence for each encapsulated dye molecule. As a result, a novel macrocycle-assisted supramolecular approach for obtaining solid, white light-emitting organic materials with low cost, high efficiency, and easy scale-up was successfully demonstrated.

We report a compact ultrafast thulium-doped all-fiber laser delivering 65-fs pulses through nonlinear compression in a dispersion and nonlinearity managed fiber chain. The laser outputs 560-mW, 3.2-nJ pulses with a very broad bandwidth >160 nm at the central wavelength of 1980 nm. Numerical simulation investigates and verifies the formation and evolution of the ultrafast pulse. ASTAR (Agency for Sci., Tech. and Research, S’pore)

The average size and density evolution of dislocation loops in AL-6XN austenitic stainless steel, a candidate fuel cladding material for supercritical water-cooled reactor, under proton irradiation were simulated through a rate theory model. The simulation results exhibit relatively good agreement with the experimental results at 563 K. The size and density of defect clusters are calculated under irradiation temperature between 550 K and 900 K and irradiation doses up to 15 dpa which satisfies the working condition in supercritical water-cooled reactor. The fast nucleation between self-interstitials happens at the initial stage of irradiation. The average size of dislocation loops increases while the average density of these loops reduces with the increasing temperature, and the average density approaches to a constant when irradiated at higher irradiation doses. The mechanism is discussed based on the variation of rate constants of defect reactions and the variation of the diffusion coefficients of interstitials and dislocation loops with dose and temperature.

Fracture behavior of C/SiC composites under compressive loading is investigated both experimentally and numerically. Dynamic experiments are carried out using a modified split Hopkinson pressure bar (SHPB), along with high-speed photography. A microstructure based approach is employed to model the C/SiC composites, including SiC matrix, voids, warp and weft fiber bundles. Dynamic microstructure response and microdamage evolution are captured accurately by numerical simulations. The fracture plane of the C/SiC composites under quasi-static loading is rough, with fiber bundle splitting and fiber pullout. However, the fracture plane becomes much smoother under dynamic loading, with a negligible fiber bundle splitting or fiber pullout. Two dynamic fracture modes are observed in the high-speed images, and proved to be induced by the inhomogeneous microstructure according to the numerical simulation results. One of the fracture modes improves the toughness of the C/SiC composites significantly (an increase of 35%), mostly without strength decrease. Moreover, the low-temperature heat treatment significantly influences the mechanical properties (e.g. elastic modulus, strength, and fracture strain) of the C/SiC composites, owing to the increase in the number of microcracks and the decrease in the strength of fiber-matrix interfaces.

In this work, Mode I dynamic fracture experiments are conducted on pre-cracked three point bending specimens by using modified Split-Hopkinson pressure bar. The microstructure of magnesium alloy AZ31B is modified through equal channel angular pressing (ECAP). The two sets of specimens with different initial textures are considered here: one set of the specimens are machined from a hot rolled AZ31B Mg alloy plate with a bigger grain size; the other set are machined from the billet with material treated by four pass of ECAP after they are cut from the hot rolled plate and they are with the finer grain size. Critical crack tip opening displacement (CTOD) is invocated to determine the dynamic fracture property. Digital image correlation (DIC) technique is used to determine the strain contours around the crack tip and electron back scatter diffraction (EBSD) is employed to analyze the texture evolution after tests. It is found that the dynamic fracture property of fine grain specimen is better than that of coarse grain specimen. The fracture property of both sets of specimens is enhanced by increasing the loading rates. Texture analysis shows the formation of tensile twinning in the ligament ahead of the crack tip in the coarse grain specimen but no sign in fine grain specimen. The brittle features e. g. cleavage planes and twinning lamellas are observed on the fracture surface of coarse grain specimen by scanning electron microscope (SEM). However, the relative ductile features such as micro-voids surrounding by tear ridges present on the fracture surface of fine grain specimen. The improvement on dynamic fracture properties of magnesium alloy through ECAP has important significance in the aerospace and automobile industry.

One-dimensional hollow nanostructures have potential applications in many fields and can be fabricated using various methods. Herein, a selective-oxidation route for the synthesis of unique Te x Se y nanotubes (STNTs) with a controlled morphology using Te x Se y @Se core–shell nanowires (TSSNWs) as a template is reported. Because of the lower redox potential of TeO2/Te compared to that of H2SeO3/Se, the Te in TSSNWs can be preferentially oxidized by an appropriate oxidant of HNO2 to form STNTs. The inner diameters and wall thicknesses of the STNTs can be tuned by modulating the core diameters and shell thicknesses of the TSSNWs, respectively. The STNTs can be assembled into a monolayer composed of well-arranged nanotubes using the Langmuir–Blodgett technique. A device based on films stacked with 10 STNT monolayers was fabricated to investigate the photocoductivity of the STNTs. The STNTs exhibited a good photoresponse over the whole ultraviolet–visible spectrum, revealing their potential for application in optoelectronic devices.

Using first-principles calculations, we predict the existence of two dimensional (2D) pentagonal ZnO 2 (penta-ZnO 2 ) sheet and confirm that penta-ZnO 2 is dynamically and mechanically stable. Due to its unique atomic configuration, penta-ZnO 2 has intrinsic negative Possion's ratio, contrary to the most existing materials. Furthermore, Penta-ZnO 2 is much more flexible than graphene-like ZnO and penta-graphene in elasticity. Using the Heyd-Scuseria-Ernzerhof (HSE06) functional, the calculated indirect energy band gap is 4.53 eV, which is corresponding with optical gap (4.54 eV). More interesting, in the visible range of light, we find that penta-ZnO 2 has very low reflectance (0.0035%). Together with the expected zero absorption below the band gap, the light transmittance of penta-ZnO 2 is almost 100% in a broad spectral range. Our study demonstrates that penta-ZnO 2 possesses unique stable structure and promising mechanical, electronic and optical properties, which offers great potential in a wide range of applications in optoelectronics. Especially, the high flexibility and high light transmission make the penta-ZnO 2 to be a promising candidate for transparent electrodes.

In this work, flyer plate impact experiments are conducted on a commercially available magnesium alloy, AZ31B. Equal channel angular pressing (ECAP) process is an established procedure for fabrication of ultra-refined grain structures in metals and alloys. The microstructure of commercially available AZ31B is refined through ECAP process and two sets of specimens with different initial textures and microstructure are considered here. One set of the specimens is machined from a hot rolled AZ31B Mg alloy plate and the others are processed by ECAP of four pass after samples are cut from the initial material. The Hugoniot elastic limit (HEL) and spall strength are determined by analyzing the measured free surface velocity profiles of the specimens. Scanning electron microscope (SEM) is used to observe the microvoids produced along the spall plane and electron back scatter diffraction (EBSD) is employed to examine the twinning distribution on the cross-section of the recovered specimens cutting along the thickness direction. It is found that elastic precursor decay appears in the as-received (without ECAP process) specimens but it is absent in ECAPed specimens. The HEL of the as-received specimens is higher than that of ECAPed specimens over various impact velocities and showed strain rate sensitivity. The spall strength of both sets of specimens is almost identical and enhanced by increasing the impact velocity. The SEM results showed that in the as-received specimens the spall is dominated by coalescence of microvoids emerged along the grain boundaries in a brittle manner. However, in the ECAPed specimens spall was dominated by coalescence of microvoids characterized by inner dimples formation by the pull out of grains in a ductile mode.

Dynamic response and fracture mechanisms of Carbon Fiber Reinforced Silicon Carbide Composites (C/SiC) especially during low-velocity ballistic penetration are studied both experimentally and numerically. The gas-gun facility is used to fire spherical metallic projectile for striking velocity of 150 m s −1 on the target panels, and the impact phenomenon is captured through high-speed photography. A micro-structure based approach is employed to model C/SiC target in this paper. This proposed numerical technique captured the mechanical response (residual energy, expansion process and velocity of debris cloud, fracture morphology and mode) of target, with adequate accuracy. The fracture modes involve void collapse, delamination, fiber bundle splitting and breakage. The debris cloud possesses two types of constituents, classified by fragments' volume and high-energy powdering column at the front. The experimental and calculated results emphasize that the impact velocity, projectile shape and hardness have significant influence on the mechanical behavior of C/SiC composites, including fragment size, fracture surface morphology, fracture mode and mechanism.

This paper studies the mechanical behavior of Alumina ceramic-Kovar joint under quasi-static and dynamic four-point bending (FPB). The joint is fabricated by molybdenum-manganese (Mo-Mn) metallization method with extra additions. The bend strength of the joint is improved by glass phase migration. Electronic universal testing machine and modified split Hopkinson pressure bar (SHPB) are employed to realize the loading process. The microstructure of the joint is investigated by scanning electron microscope (SEM) and the chemical composition is determined by energy dispersive spectrometer (EDS). Digital image correlation (DIC) technique is used to determine the displacement contours and ultra-high speed camera is used to monitor the deformation and crack evolution around the joint. It is found that the specimen will slip due to the different Young's modulus of base material. The dynamic bend strength of the joint is lower than the quasi-static bend strength. The failure mechanism of the ceramic-metal joint is mainly intergranular failure for the dynamic bend but mixed transgranular/intergranular failure for the quasi-static case. The crack starts from the inherent voids inside the ceramic and then expands along the metallization band between solder and ceramic.

This letter presents a novel two-dimensional planar-phased array with wide-angle scanning performance. A parasitic pixel layer-based antenna is used as the array element. The antenna optimized with a multiobjective genetic algorithm has wide beamwidth in both xoz- and yoz-planes. A 64-element planar (8 × 8) array is fabricated and measured to validate its scanning performance. With the uniform and optimized inputs, respectively, applied to the high- and low-elevation areas, the measured results show that the phased array is able to scan its main beam from -75° to +75° in both xoz- and yoz-planes, and it supports 3-dB beam coverages from -85° to +85° in the xoz-plane and from -85° to +80° in the yoz-plane.

173 p. Photonic crystal fiber (PCF) has been studied intensively in the past decade owing to its potential device applications in optical communication systems. PCFs have many advantages compared with the conventional fibers. Firstly, they have flexibly-tailored optical properties. Due to the microstructure dependence of their modal properties, the degree of freedom is increased dramatically in the design. Many properties such as the cutoff conditions, birefringence, dispersion and nonlinearity can be tailored beyond the possibilities in conventional fibers. Moreover, because of the single material in most PCFs, their improved temperature stability makes such novel fiber a suitable transmission medium. Secondly, the unique holey structure makes many applications possible. Due to the special stack-and-draw fabrication technique, the arrangement of air-holes in the microstructure can be customized. Multiple layers of claddings can be easily obtained by controlling the air-hole dimensions of capillary tubes in different layers. Multi-core structures are achieved by simply introducing multiple solid rods during the stacking process. The existence of air-holes enables the possibilities of injecting gases/liquids, so that PCF can be used as sensors. DOCTOR OF PHILOSOPHY (EEE)

A modified formula to calculate the axial conductivity of nanowires was proposed based on the one-dimensional quantum state density distribution and Boltzmann transport theory. Numerical simulations of the ZnO nanowires (ZnONWs) and Nitrogen-doped ZnO nanowires (N-ZnONWs) were implemented using data from the first principles calculation. The results indicate that ZnONWs are low-conductivity wide band-gap semiconductors owing to their low carrier concentrations at room temperature, with N-doping increasing the conductivity. The N-ZnONWs carrier concentrations increased with increasing temperature, and possessed significantly higher carrier concentrations than ZnONWs. With an increase in diameter, the ZnONWs conductivities increased, whereas the N-ZnONWs conductivities decreased.

The 2 μm spectral region is useful for applications in processing of semiconductors and clear polymers, and also interactions with water-rich biological tissues and biomaterials [1]. Fiber laser sources are attractive as 2 μm sources as they offer excellent beam quality, and the ability to dissipate heat along long fiber lengths enabling high output power. However, amplification of pulses with high peak power is limited by nonlinear effects due to the small mode area. Chirped pulse amplification (CPA) technique allows amplification of high energy pulses by first stretching the pulse — chirping — to minimize nonlinear effects [2]. The amplified pulse is then compressed using dispersion compensation elements such as diffraction gratings. However, when the pulse is chirped to long durations in the scale of hundreds of picoseconds or longer, diffraction gratings require distances of a few meters which negates the compactness of fiber laser systems.

Infrared vision system uses infrared lens to collect radiation and focus the object onto the detector. Information such as pixel and temperature distribution could be captured and displayed as images. Infrared optics are the “eyes” of the vision system. The need of broadband, compact, low cost are driven by increasing commercial applications such as UAV, autonomous driving and smart phone. This paper presents our latest development in infrared optics design for broadband application and optics manufacturing based on Chalcogenide glasses for potential mass production. New optics design makes a single lens to achieve dual wavelength band (MWIR and LWIR) switchable. The aspheric lens and diffractive optical element (DOE) configuration are investigated to realize the broadband and compact lens design. In LWIR regime, several detector manufacturers have demonstrated both cooled and uncooled technologies with pixel size down to 12μm. It sets new standard for size, weight, power and performance in terms of resolution. Chalcogenide material is gradually taking over Germanium in broad IR regime. It performs especially well in the 8 to 12μm range, because of its lowest absorption and dispersion in LWIR. The low dn/dT of the Chalcogenide makes lens athermalization much simpler by removing required mechanical compensation complexity. The Chalcogenide series of glasses can be processed by molding. As compare to the polished/machined glass lens which take more than 1 hour for each piece, the molding process time will be reduced to 5 mins.

Alkaline ionic liquid aqueous solutions were used to extract biphenyl cyclooctene lignans derivatives, and hydrolyze to the free-state biphenyl cyclooctene lignans simultaneously from Schisandra chinensis by microwave-assisted heating. The hydrogen bonds formatted between ionic liquid and water molecular attacks the amorphous region of cellulose. Selective heating by microwave produce the more polar regions, which results in swelling and fragmentation of raw materials near the hot spots. Therefore, ionic liquid-microwave-assisted extraction method of free-state biphenyl cyclooctene lignans was set up. The solid residue after treatment was characterized by infrared spectroscopy and scanning electron microscopy, which showed that cellulose, hemicellulose, and lignin were removed partially. The water content of ionic liquid solution affected its viscosity and diffusivity, and in turns the extraction efficiency of lignans. The IL solutions with different mole fractions of IL were detected by FTIR and Raman spectroscopy, the result shows that IL solutions with higher water contents (>0.6) won't form clusters. The optimum hydrolysis conditions were 0.2 g of ionic liquid catalyst per 5.0 g of S. chinensis fruits, a microwave irradiation power of 600 W, and heating time of 12 min, which gave a yield of free-state biphenyl cyclooctene lignans of 4.12±0.37 mg g-1. Besides, a hydrolysis mechanism of ester-bond biphenyl cyclooctene lignans and decreasing "biomass recalcitrance effect" by ionic liquid microwave-assisted method was proposed.

Metal oxide (MO) semiconductor thin films prepared from solution typically require multiple hours of thermal annealing to achieve optimal lattice densification, efficient charge transport, and stable device operation, presenting a major barrier to roll-to-roll manufacturing. Here, we report a highly efficient, cofuel-assisted scalable combustion blade-coating (CBC) process for MO film growth, which involves introducing both a fluorinated fuel and a preannealing step to remove deleterious organic contaminants and promote complete combustion. Ultrafast reaction and metal–oxygen–metal (M-O-M) lattice condensation then occur within 10–60 s at 200–350 °C for representative MO semiconductor [indium oxide (In(2)O(3)), indium-zinc oxide (IZO), indium-gallium-zinc oxide (IGZO)] and dielectric [aluminum oxide (Al(2)O(3))] films. Thus, wafer-scale CBC fabrication of IGZO-Al(2)O(3) thin-film transistors (TFTs) (60-s annealing) with field-effect mobilities as high as ∼25 cm(2) V(−1) s(−1) and negligible threshold voltage deterioration in a demanding 4,000-s bias stress test are realized. Combined with polymer dielectrics, the CBC-derived IGZO TFTs on polyimide substrates exhibit high flexibility when bent to a 3-mm radius, with performance bending stability over 1,000 cycles.

This paper studies the effect of fly ash on rheological properties of magnesium oxychloride cement (MOC) paste. Six different dosages of fly ash (0%, 15%, 20%, 25%, 30%, and 35% by weight o...