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ABSTRACTMany critical concreting activities require the determination of the in-place concrete strength. It can be costly to wait too long to execute these activities, but acting too early can have a negative impact on structural performance. Conventional moulded concrete cylinders and alternative strength assessment methods such as the maturity method are commonly used to assess concrete’s in-place strength. This study is focused on a special case when the maturity method is applied for evaluating concrete strength in cold weather at an early age. Specifically, the study proposes an alternative method for calibrating the activation energy, an input for the maturity method. Concretes cured at two different temperatures are used to calibrate the activation energy. The maturity method based on this activation energy predicted the cold weather concrete’s compressive strength satisfactorily. It was also found that for a successful application of the proposed activation energy calibration, the two temperatures should represent the expected minimum and maximum temperature at the site. Furthermore, the results showed that the maturity method based on the proposed activation energy calibration method performed better than the conventional cylinder method.

Fused Filament Fabrication (FFF), also known as Fused Deposition Modelling (FDM), is one of the innovative 3D printing technologies for fabricating complex components and products. Mechanical properties of 3D-printed components mostly depend on intricate process parameters of 3D printing. This study experimentally investigates the effects of four key process parameters, including layer thickness, raster angle, feed rate, and nozzle temperature, on the tensile properties and interfacial bonding behaviours of FFF printed Polylactic Acid (PLA), and their failure mechanisms. The effect of the key parameters on surface roughness is also evaluated, which is critical for enhancing manufacturing and material performance, expecting to provide a potential guide for optimisation of the FFF printing process for improving product quality. The experimental results demonstrate that tensile strength improves up to 10 and 7% with increasing nozzle temperature (200 °C to 220 °C) and low feed rate (60 mm/sec to 40 mm/sec) during the 3D printing process. The tensile strength increases up to 12% with decreasing layer thickness (0.4 mm to 0.2 mm) and 40% with decreasing raster angle (90° to 0°). The experimental findings on surface roughness indicate that FFF-printed PLA samples were significantly influenced by the layer thickness and raster angle, and an improvement in surface roughness is observed with the increase of nozzle temperature and reduction in feed rate. Microstructural SEM analysis was conducted to investigate the ruptured surfaces of the FFF printed PLA samples, focusing on the interlayer bonding quality and morphological characteristics including the effect of void formation, poor adhesion, and insufficient fusion between adjacent surface contact area with the effect of printing parameters. The feed rate and nozzle temperature were found to substantially influence the interlayer bonding between two adjacent surfaces.

Fused Filament Fabrication (FFF), a process parameters-dependent manufacturing method, currently dominates the additive manufacturing (AM) sector because of its prominent ability to produce parts with intricate profiles, customise products, and minimise waste. Though the effects of FFF process parameters were investigated experimentally, recent research highlighted the importance of developing numerical modelling and computational methods on optimising the FFF printing process and FFF-printed materials. This study aims to investigate the tensile strength (TS) of FFF-printed high-impact polystyrene (HIPS) via devising a systematic testing and analysis framework, which combines experimental testing, representative volume element (RVE)-finite element method (FEM), rule of mixture (ROM), and artificial neural networks (ANN). HIPS samples are fabricated using FFF considering the variations of infill density, layer thickness, nozzle temperature, raster angle, and build orientation, and tested with standard tensile testing. The rule of mixtures (ROM) and its modified version (MROM) are employed to calculate the TS of longitudinally and transversely built samples at various infill densities, respectively, while an ANN model is constructed to investigate the effect of material anisotropy precisely. The optimal ANN architecture is built with five hidden layers with the number of neurons in each layer as 44, 82, 169, 362, and 50. Although both MROM and ANN perform well on the validation set, ANN exhibits superior accuracy with only a maximum error of 0.13% for training set and 11% for validation set. The combination of the RVE-FEM, MROM, and ANN approaches can significantly improve the FFF printing process of polymers for optimisation.

The Zr55Cu30Al10Ni5amorphous alloy with thickness 0.5 mm and width of 75 mm was fabricated by twin-roll casting. Due to high rolling force, the alloy exhibited high energy state, high free volume and microstructure inhomogeneity. However, the friction property is not clear because of excellent plasticity and high free volume. The present study tested the friction property of the alloy by rotating pin-on-disk method and investigated the friction behavior and wear mechanism. Besides, the abrasive resistance was improved by subsequent annealing treatment. The results show that the wear mechanisms are mainly abrasive wear, adhesion wear, delamination wear and fatigue wear. The wear law is in accordance with the Archard's empirical wear law. The structural stability and uniformity of that cast strip can be increased by annealing the cast strip at the glass transition temperature. Meanwhile, the wear resistance of the amorphous alloy is improved, and the wear rate in the annealed state is reduced to 88.7 percent of that in the as-cast state, so that abrasive resistance is improved. This study provides a little theoretical basis for amorphous alloy as wear-resistant material and expands the application of amorphous alloy in engineering materials.

This study provides detailed insights into the effect of specimen size on the residual compressive strength of hybrid polyethylene-steel fibre reinforced high strength engineered cementitious composite after exposure to elevated temperatures. A mix design with high residual performance was selected and a total of 120 specimens with different cross-section shape (square and circular), aspect ratio (1 and 2) and sizes (cylinders of 40 mm, 75 mm, 100 mm, 150 mm diameter with height to diameter ratio of 2:1, cubes of 50 mm, 75 mm, 100 mm side and prism of size 75 × 75 × 150 mm) were cast. These specimens were subjected to temperatures ranging from 200 to 800 °C and the residual compressive strength and change in microstructure was then analysed after air cooling. Experimental results indicated that cubic specimens experienced less strength loss compared to prism specimens with the same cross-sectional area and the damage was found to decrease with increase in the volume to surface area ratio of the specimens. Furthermore, no spalling occurred in any of the specimens despite the change in specimen size or cross-section. Unlike previous studies that did not present any clear influence of specimen size, the present work established that the residual strength is dependent on aspect ratio and volume to surface area ratio of the specimen. As a result, these findings are valuable for selecting appropriate specimen size in elevated temperature studies and for the development of suitable guidelines to facilitate meaningful comparisons with the existing data.

Based on the millisecond-nanosecond combined laser mode, the irradiated morphology of monocrystalline silicon is studied experimentally. During the experiment, a high-precision point thermometer is used for monitoring. A shadow method to measure plasma evolution and a metallographic microscope for analysis after the experiment are used. The cleavage and ablation law and the mechanism of monocrystalline silicon are studied under different laser energy densities and delay time conditions. The analysis shows that when the combined laser acts on silicon, the millisecond laser has the effect of preheating. The preheating effect will change the thermal physical properties of monocrystalline silicon, such as the absorption coefficient. Controlling the delay time can improve the energy coupling between the silicon and the nanosecond laser. Changing the delay time also changes the effect of the damage.

ABSTRACTWith the advancement of material technology, the use of high-strength and high-performance materials in the construction industry is gaining popularity. Steel–polyvinyl alcohol (steel–PVA) hybrid fibre engineered cementitious composites (ECC) is one of such high-performance class of construction materials whose mechanical properties are not well studied in the literature especially in high-strength matrix. Therefore, in this paper, the mechanical properties of four different grades of high-strength steel–PVA ECC are experimentally investigated. ECC with nominal compressive strengths from 60 to 100 MPa are developed. Their mechanical properties including compressive and tensile stress–strain behaviour, elastic modulus and toughness are studied with particular focus on high-strength matrix. Test results show that the developed steel–PVA ECC could achieve good tensile (~0.8%) and compressive (~0.5%) ductility for general structural applications. Simple empirical relationships to predict the elastic modulus and tensile strength of the developed steel–PVA ECC as a function of their compressive strength are suggested. Moreover, an analytical model to generate a complete compressive stress–strain curve of the high-strength steel–PVA ECC is proposed and verified against the experimental results. The proposed stress–strain model would present a useful reference for non-linear analysis of structural elements utilising steel–PVA ECC.

ABSTRACTIn order to improve the wear resistance of carburised M50NiL steel, the surface layer was deposited with Ti coating by magnetron sputtering and then plasma nitrided for 2 h with hollow cathode equipment. The influence of nitriding temperature (750, 800 and 850°C) on microstructure and mechanical properties of the coating were investigated. Results show that the coating of specimen 750 containing Ti-based-nitrides possesses higher nanohardness (13.769 ± 0.738 GPa) than the carburised layer (7.695 ± 0.338 GPa) and the load bearing capacity reaches 18 N due to the supporting carburised layer. The friction coefficient and wear rate of the specimen 750 decrease 23.1 and 72.2%, respectively, compared with the carburised specimen. The hardness and wear performance of the specimen 800 and 850 were underestimated by traditional test criterion because a loose and porous a′C(N)layer was formed on the surface due to sputtering effect of steel hollow cathode.

Nano-hydroxyapatite (nHAP) has high immobilization efficiency for reducing the lead (Pb) absorption of crops in Pb-contaminated soils. However, little information is available on the special and possible processes where nHAP in plant roots acts as a barrier, capturing Pb ions and decreasing Pb mobility in root cells. The internalization of nHAP in root cells with special attention given to the potential for reducing the toxicity and mobility of Pb in rice was investigated in hydroponic experiments using ICP, SEM-EDS and TEM-EDS techniques after exposure to Pb for 14 d. The results showed that nHAP existing in root cells was beneficial for alleviating Pb stress and restraining the translocation of Pb from roots to shoots. The primary mechanisms identified were: (a) the binding of Pb to the nHAP existing in root cells, reducing the interference of Pb ions with critical cell functions, and (b) the transformation of Pb ions into Pb-deposits in root cells, reducing the movement of Pb to the aerial parts. The result is useful for understanding the immobilization mechanisms of Pb in plant root cells by the application of environmental nanomaterials.

Resistance to cytotoxic chemotherapy drugs remains as the major cause of treatment failure in acute myeloid leukemia. Histone deacetylases (HDAC) are important regulators to maintain chromatin structure and control DNA damage; nevertheless, how each HDAC regulates genome stability remains unclear, especially under genome stress conditions. Here, we identified a mechanism by which HDAC3 regulates DNA damage repair and mediates resistance to chemotherapy drugs. In addition to inducing DNA damage, chemotherapy drugs trigger upregulation of HDAC3 expression in leukemia cells. Using genetic and pharmacological approaches, we show that HDAC3 contributes to chemotherapy resistance by regulating the activation of AKT, a well-documented factor in drug resistance development. HDAC3 binds to AKT and deacetylates it at the site Lys20, thereby promoting the phosphorylation of AKT. Chemotherapy drug exposure enhances the interaction between HDAC3 and AKT, resulting in decrease in AKT acetylation and increase in AKT phosphorylation. Whereas HDAC3 depletion or inhibition abrogates these responses and meanwhile sensitizes leukemia cells to chemotoxicity-induced apoptosis. Importantly, in vivoHDAC3 suppression reduces leukemia progression and sensitizes MLL-AF9+leukemia to chemotherapy. Our findings suggest that combination therapy with HDAC3 inhibitor and genotoxic agents may constitute a successful strategy for overcoming chemotherapy resistance.

Ocular toxoplasmosis (OT) caused by Toxoplasma gondii is a major cause of infectious uveitis, however little is known about its immunopathological mechanism. Susceptible C57BL/6 (B6) and resistant BALB/c mice were intravitreally infected with 500 tachyzoites of the RH strain of T. gondii. B6 mice showed more severe ocular pathology and higher parasite loads in the eyes. The levels of galectin (Gal)-9 and its receptors (Tim-3 and CD137), interferon (IFN)-γ, IL-6 and IL-10 were significantly higher in the eyes of B6 mice than those of BALB/c mice; however, the levels of IFN-α and -β were significantly decreased in the eyes and CLNs of B6 mice but significantly increased in BALB/c mice after infection. After blockage of galectin--receptor interactions by α-lactose, neither ocular immunopathology nor parasite loads were different from those of infected BALB/c mice without α-lactose treatment. Although the expressions of Gal-9/receptor were significantly increased in B6 mice and Gal-1 and -3 were upregulated in both strains of mice upon ocular T. gondii infection, blockage of galectins did not change the ocular pathogenesis of genetic resistant BALB/c mice.However, IFN-α and -β were differently expressed in B6 and BALB/c mice, suggesting that type I IFNs may play a protective role in experimental OT. [ABSTRACT FROM AUTHOR]

AbstractThe structural responses of fibre-reinforced polymer (FRP)-strengthened steel-reinforced concrete (RC) slabs under moving-wheel cyclic loads are investigated numerically in this paper. A finite element model considering the deterioration of material properties of concrete, steel and FRP under moving-wheel cyclic loading is developed and employed for the numerical analysis. The finite element model is firstly employed to model the structural response of a RC-reinforced slab under moving-wheel cyclic load for validation of the loading procedures. Then the model is extended for numerical analysis of FRP-strengthened RC slabs under moving-wheel cyclic loads. The structural behaviour of FRP-strengthened RC slabs under static, fixed-point cyclic and moving-wheel cyclic loads is compared in this paper to examine the effect of the loading conditions.

The quenched M50NiL steel was plasma nitrided at 460°C for different time to investigate the effects of the duration time on the microstructure, microhardness and wear resistance of the nitrided layers. The results show that the plasma nitrided layer depth increases with increasing nitriding time. The plasma nitrided layer includes only the diffusion layer without compound layer. The main phases in the nitrided surface layer are nitrogen expended α′-Fe and γ′-Fe4N. The microstructure of the nitrided layer is refined. The wear resistance of the nitrided samples can be improved significantly by plasma nitriding. The sample nitrided for 4 h possesses the highest wear resistance, due to its relatively smooth surface and ultra-fine grains in the nitrided layer.

Remote sensing provides aerosol loading information, but to address climate and air quality model validation, there are additional needs to acquire aerosol composition information. In this study, a comprehensive aerosol composition model is established to quantify black carbon (BC), brown carbon (BrC), mineral dust (DU), particulate organic matters, ammonium sulfate like (AS), sea salt, and aerosol water uptake. We develop forward modeling of aerosol components, including microphysical parameters (real and imaginary refractive indices, volume fraction ratio of fine to coarse mode, and sphericity) and hygroscopic growth models, and propose an optimization scheme to estimate the components. The uncertainties caused by input parameters are also assessed. Sun‐sky radiometer measurements and meteorological data obtained during a campaign in Huairou, Beijing, are processed to estimate aerosol components, which are further compared with synchronous in situ chemical measurements. The results show generally good consistencies between remotely estimated and measured components (e.g., correlation coefficients for BC, BrC, AS, and PM2.5lie in about 0.8–0.9). The comparisons between modeled and observed microphysical parameters also show good agreements, with the exception of sphericity, which is likely caused by high uncertainties of this parameter. Sensitivity studies show that BC and BrC are highly sensitive to imaginary refractive index, while DU is strongly correlated to both volume size and sphericity. The performance of composition retrieval is expected to be improved when the sphericity uncertainty is significantly reduced. Aerosol main components including BC, BrC, DU, POM, AS, SS, and AW are quantitatively estimated by remote sensing measurementsThe estimated BC, BrC, AS, and fine components are preliminarily validated by synchronous in situ observationAerosol imaginary refractive index is sensitive to BC and BrC, while volume size and sphericity parameter have strong correlations with DU

The immune effect and safety evaluation of rAAV (recombinant adeno-associated virus)-containing Bcsg1(breast cancer-specific gene 1)(rAAV/Bcsg1)-transfected DC (dendritic cell) (rAAV/Bcsg1-DC) vaccine in immunotherapy for (BCSG1) (+) BC was assessed. Immune effect of cytotoxic T lymphocytes (CTLs) on Bcsg1 (+) BC cells, and rAAV gene residuals in mature CTL cells and culture medium were determined. Nude mouse xenograft tumor model was established to assess the inhibition effects of DC-activated CTLs on tumor growth. DC cell surface markers were highly expressed in rAAV/Bcsg1 group and lysate-DC group, and rAAV/Bcsg1-DC-CTL showed stronger cytotoxic activity targeting Bcsg1 (+) BC cells. The rAAV/Bcsg1-DC vaccine-treated groups showed lower mean tumor weight, higher tumor inhibition rates and slower tumor growth. rAAV/Bcsg1-DC can induce highly efficient CTL-targeting Bcsg1 antigen without rAAV gene residuals.

The 6061 aluminum alloy wires with diameters of 0.15 mm and 0.20 mm were cut into different structural sizes of 5 × 10 mm and 10 × 15 mm by a spring machine to bend the aluminum alloy fibers, one is 5 mm short side, 10 mm long side, and 1 mm arc radius, and the other is 10 mm short side, 15 mm long side, and 1 mm arc radius. Special cylindrical molds are used to prepare folding sheets with different porosities using vacuum hot pressing sintering technology. Bent aluminum fiber porous material. The gas displacement method was used to detect the pore size and pore size distribution, and the Plastic Deformation Behavior were analyzed by quasi-static uniaxial compression test. Research shows that the material presents a three-stage stress-strain curve, from the initial nonlinear elastic deformation stage to the pseudo-platform stage and the densification stage, the wire diameter and structure of the material The smaller the size, the more conducive to the densification of the silk skeleton, and the smaller the average pore size formed, the higher the compressive strength.

Annealed and quenched M50NiL steel specimens were plasma nitrided at 460°C for 4 h under a mixture gaseous supply of 0.05N2+0.4H2 L min-1 to investigate the effects of the substrate microstructure on the features of nitrided layer, such as microstructure, microhardness and wear resistance. The results show that the nitrided layer is mainly consisted of α-Fe, γ'-Fe4N and α'N (nitrogen expanded martensite) phases. The surface hardness is significantly enhanced. For the quenched specimens, the nitrided depth decreases with increasing quenched temperature. Compared to the quenched specimens, the nitrided depth of the annealed specimen is thicker under the same nitriding condition. The mechanism may be the variation in the amounts of interstitial carbon atoms and substitution alloying elements in the lattice, and the compressive residual stresses in the substrate. It is also demonstrated that the wear resistance for both the annealed and the quenched specimens can be significantly improved by plasma nitriding treatment. [ABSTRACT FROM AUTHOR]

Controllable ZnO architectures have been achieved on zinc substrates via a versatile one-pot hydrothermal method without assistance of any surfactants or organic solvent. The morphologies of ZnO architectures have been successfully manipulated by adjusting the concentration of NaOH and temperature of the reaction system. Among the as prepared ZnO architectures, the sheet flower-like ones exhibited highest photocatalytic activity in the degradation of methyl orange (MO) under ultraviolet (UV) illumination for their nanosheets assembled structural feature.

The quenched M50NiL steel specimens have been plasma nitrided at temperatures from 460 to 590°C for 4 h under a constant mixture gaseous supply of 0·05N2–0·4H2L min-1. The effects of the treatment temperature on the microstructure, microhardness and wear resistance of the surface nitrided layers are studied. The results show that the plasma nitrided layer includes only the diffusion layer without conventional compound layer. The surface hardness is significantly enhanced. a'-Fe and ?'-Fe4N phases in surface layer are formed at relatively low nitriding temperatures (460–560°C), while a low nitrogen phase FeN0·076forms when the nitriding temperature exceeds 575°C. With the increase in nitriding temperature, the nitrided layer thickness increases, whereas both the surface and core microhardness of the nitrided specimens decreases. The wear resistance of specimens can also be improved significantly by plasma nitriding.

Two hundred and ninety F9recombinant inbred lines (RILs) derived from the bread wheat cultivar Gaocheng 8901 and the waxy wheat cultivar Nuomai 1 were used in determining the high-molecular-weight glutenin subunit (HMW-GS) and waxy protein subunit combinations and their effects on the dough quality and texture profile analysis (TPA) of cooked Chinese noodles. Seven alleles were detected at Glu-1 loci. There were two alleles found at each of the Wx-A1, Wx-B1 and Wx-D1 loci. Eight allelic combinations were observed for HMW-GS, LMW-GS and waxy proteins, respectively. Both the 1/7+8/5+10 and 1/7+8/5+12 combinations contributed to dough elasticity, and the 1/7+8/5+10 combination also provided better TPA characteristics. Compared to Wx protein, HMW-GS was more important on dough alveogram properties. LMW-GS significantly affected springiness and cohesiveness; HMW-GS mainly affected the hardness; Wx×LMW-GS significantly affected the springiness, cohesiveness and chewiness; HMW-GS×Wx×LMW-GS mainly influenced the springiness and chewiness. But HMW-GS×LMW-GS only affected the spinginess. These indicated the TPA of noodles was significantly affected by the interactions between glutenin and Wx proteins.

Rice stripe is a serious viral disease of japonicarice (Oryza sativaL.) cultivars in Asia. Resistance to this disease can be divided into that to rice stripe virus (RSV) and to the pest (small brown planthopper, SBPH). Here we have used a doubled‐haploid (DH) population bred from the cross Zhaiyeqing8 (ZYQ8) × Jingxi17 (JX17) and four separate inoculation methods to genetically dissect the rice stripe resistance present in ZYQ8. Two linked RSV resistance quantitative trait loci (QTLs) were located on chromosome 1, and one on chromosome 11, jointly explaining 30 to 44% of the trait variance. The main‐effect qSTV11was mapped close to the established RSV resistance gene Stvb‐iFor resistance to SBPH, three QTLs were located, mapping to chromosomes 1, 2, and 11, and jointly explaining 44 to 51% of the trait variance. The large‐effect qSBPH1appears to be a novel QTL conferring a degree of tolerance and antibiosis against SBPH. The positive alleles at all six QTLs were present in ZYQ8. Analysis of a set of chromosome segment substitution lines (CSSLs) in which chromosomal segments of various indicavarieties were present in a japonicabackground showed that rice stripe resistance genes/QTLs are common on the long arm of chromosome 1.

The dwarf-male-sterilewheat is unique to China and has been improved by introducing good germplasm. In order to clear the subunits background of Dwarf-Male-Sterilewheat, sodium dodecyl sulphate polyacrylamide-gel electrophoresis (SDS-PAGE) was used to detect the high and low molecular weight glutenin subunits (HMW-GS and LMW-GS) compositions in BC1F1, F2 and F3 generations from Dwarf-Male-Sterilewheat. Twenty-five alleles and 49 HMW-GS compositions at the Glu-1loci were detected in different generations. Null and subunit 1 were mainly existed at Glu-A1, and 7 + 8 and 7 + 9 were primarily detected at Glu-B1in different generations. Subunit combination 5 + 10 mainly appeared in BC1F1, while 2 + 12 major presented in F2 and F3 generations. HMW-GS compositions null, 7 + 8, 5 + 10 and null, 7 + 9, 5 + 10 showed higher frequencies than other banding patterns, followed by null, 14 + 15, 5 + 10 and null, 7 + 9, 2 + 12 combinations. In addition, some rare subunit combinations such as 14 + 15, 13 + 16, 17 + 18, 4 + 12, 2 + 10 and 5 + 12 were found in different generations. Eighteen alleles and 51 LMW-GS compositions at Glu-3loci were found in different generations. Glu-A3a and Glu-B3d showed higher frequencies than others among three generations. There were mainly a, b, c alleles at Glu-D3. Thirty, 31 and 14 different combinations were detected in BC1F1, F2 and F3 populations, respectively. There were some good combinations such as A3d/ B3h, A3d/ B3d/ D3a, A3b/ B3b/ D3a, A3a/ B3d/ D3a for different quality characteristics. So some desirable subunit combinations could be selected from different generations and new cultivars with good quality under distinct subunits background should be bred from Dwarf-Male-Sterilewheat in future.

The linear and volumetric thermal expansion coefficients of bismuth nanowire and nanoflower have been measured from 298 to 478 K by high-temperature X-ray diffraction methods. The bismuth nanowire and nanoflower were prepared by a simple solvothermal technique. It was found that the linear and volumetric thermal expansion coefficient of the nanowire decreases initially, then increases, and decreases finally with increasing temperature. The nanowire and nanoflower possess smaller linear thermal expansion coefficient in the a-axis direction in the whole measured temperature range and in the c-axis direction at high temperature as compared to the conventional bulk bismuth. The volumetric expansion coefficients of the nanowire and nanoflower are always smaller than those of the corresponding bulk materials. The results were discussed on the basis of the contributions from point defects, stress, and valence electrons. Our results demonstrated that the anisotropic thermal expansion behavior of bismuth nanowires is an intrinsic property.

The longitudinal deformations of the pipe roof in the entrance of a shallow multiarch tunnel of Tujiangchong were monitored by a series of strain gauges, and the working mechanism of the pipe roof was analyzed according to the field test results. A three-dimensional finite difference code, FLAC3D, was adopted to simulate the deformation of the pipe roof and to evaluate its effect on ground surface settlement. Both the calculated and numerical results fit the field observations quite well. The numerical results indicated that a double-layer pipe roof provided a restraining effect on ground movement and helped to reduce the tunnel deformation and corresponding ground surface settlement. Ground settlement directly above the crown could be reduced by 40% to 50% compared with the settlement induced by tunneling without any pipe roof reinforcement. This project provided a successful case history of using double-layer pipe roof reinforcement in a shallow multiarch tunnel construction.

A nonlinear theory is developed in this paper to investigate the elastic in-plane buckling of shallow tied circular arches under uniformly distributed radial loading, in which the effects of the prebuckling deformation and geometric nonlinearity are included. Prescriptive formulae for the elastic buckling loads of tied arches are derived, as well as the critical stiffness that delineates between the possibility that the arch will buckle, or that it will not buckle, in its plane of loading. The relationship between the buckling load and a modified slenderness parameter of the arch is also discussed. The paper also includes the results of two short-term tests undertaken on shallow reinforced concrete tied arches, and the solutions are also analysed using the well-known ABAQUS software. The consistency of the critical loads and the load versus deflection responses demonstrates the accuracy and practicability of the analytical results derived in the paper.

A mechanochemical intercalation approach which applies a simple mechanical milling to induce intercalation reaction was applied to introduce controlled amount of tetraethoxylsilane (TEOS) into surfactant-preexpanded graphite oxide, and the relationships between the intercalation structure, the porosities of the calcined products, and the Si addition were examined. It was found that a small added amount of TEOS produced a more expanded ordered layer structure with the interlayer distance and silicon content increasing with the amount of TEOS added, although a large amount of added TEOS easily induces layer delamination, resulting in a less ordered structure. The silica structure in the composite is changed from a disordered structure having enhanced bond strain to a condensed silica network when the amount of TEOS added increases. The porosities of the final calcined samples increase with the increase of silicon content but then decrease slightly after reaching a maximum where silicon content starts to become constant, indicating that both silicon content and the composition state of silica particles and carbon layers play important roles in porosity formation.

AbstractObjective:To investigate the effects of resuscitation with three different oxygen concentrations on cerebral intra- and extra-cellular calcium, sodium and potassium changes in asphyxiated rat fetuses.Methods: Fifty-six fetal rats of gestational age of 20 days were randomly assigned into five study groups: sham operation group (control, n=11), room-air resuscitation group (n=10), and 3 oxygen-resuscitated groups (n=14, 11, and 10 respectively). Different inhaled oxygen concentrations and different timings of oxygen delivery were assigned. Except for control all fetal rats were rendered ischemic and hypoxic in uteroby interrupting the placental circulation. After re-circulation, intra- and extra- cellular concentrations of calcium, sodium, and potassium in the brains were measured for each individual group.Results:The mean intracellular free calcium concentration of fetal rat brains was similar for the room-air resuscitation group (552.1±93.5 nmol/L) and the group resuscitated with 92.8% oxygen (520.6±79.1 nmol/L), and both were significantly higher than in the control (315.3±86.9 nmol/L) (P<0.001). After resuscitation with 65% oxygen, be it instituted before or immediately after hypoxia, their mean intracellular free calcium concentrations in the brain cells (441.5±47.9 and 452.9±36.4 nmol/L respectively) were significantly lower than those in the room-air resuscitation (P<0.01) and 92.8% oxygen group (P<0.05), though still higher than in the control (P>0.05). There was no difference in the total concentrations of calcium, sodium, or potassium among all groups.Conclusion:Resuscitation with 92.8% oxygen or room air exerted a similar effect on the parameters measured, indicating that resuscitation of asphyxiated neonates using 100% oxygen might not be superior to using room air. Resuscitation with 65% oxygen resulted in lower cerebral intracellular calcium concentrations and might produce a better outcome than using 100% oxygen or room air.

Two refined quadrilateral flat shell elements named RSQ20 and RSQ24 are constructed in this paper based on the refined non-conforming element method, and the elements can satisfy the displacement compatibility requirement at the interelement of the non-planar elements by introducing the common displacements suggested by Chen and Cheung. A refined quadrilateral plate element RPQ4 and a plane quadrilateral isoparametric element are combined to obtain the refined quadrilateral flat shell element RSQ20, and a refined quadrilateral flat shell element RSQ24 is constructed on the basis of a RPQ4 element and a quadrilateral isoparametric element with drilling degrees of freedom. The numerical examples show that the present method can improve the accuracy of shell analysis and that the two new refined quadrilateral flat shell elements are efficient and accurate in the linear analysis of some shell structures. Copyright © 2000 John Wiley & Sons, Ltd.

The heats of formation of TNAZ(1,3,3-trinitroazetidine) and related compounds have been calculated with the B3LYP/6-31G(d,p) model to give a mean absolute deviation of 3.1kcal/mol for 18 singlet species and 5.1kcal/mol for 12 free radical intermediates. A minimal seven-parameter atom/group additivity scheme was developed that reduces these errors to 1.1 and 1.3kcal/mol, respectively. Based on these calculations a set of structural enthalpy increments was compiled that allows the precise estimation of heats of formation of highly nitrated species from simpler ones via isodesmic reactions that are independent of atom/group additivity parameters. In a parallel analysis, an augmented Benson group-additivity scheme was developed that allows facile estimation of the heats of formation of the several nitroazetidines as well as related radical species with a precision that is comparable to that obtained via quantum mechanical calculations. In the final section measured activation energies for the initial fragmentation steps, for eight species, are compared with the computed enthalpies for dissociation. The computed lowest energy structures for eleven species are summarized in an appendix.

The thermal decomposition of 2,2-dinitropropane (DNP) was investigated in a shock tube over the temperature range 970−1200 K, under high dilution in argon at total pressures 4.5−5.5 atm. The decay of DNP and the production of NO2 were followed spectrophotometrically at 280 and 405 nm, respectively. The derived unimolecular rate constant for dissociation is kuni = 10^13.1 exp(−23 000/T) s^-1. The products of pyrolysis were identified and quantitated using FTIR, GC, and GC/MS. The principal products are CO, NO, acetone, CH3C&tbd1;H, CH2&dbd;C&dbd;CH2, CH3CN, CO2, CH3OH, CH4, H2O, and CH2O. The first step in the decomposition appears to be C−NO2 bond fission. However, the temporal profiles of NO2 during the decomposition are distinctively different from those recorded during the decompositions of CH3NO2 or 2-nitropropane, thus pointing to distinctive features in the mechanism. A compilation of 90 elementary steps is proposed. Numerical simulations based on this mechanism reproduce quantitatively the experimentally determined [NO2] vs time profiles for a range of conditions, as well as the distributions of major products. Sensitivity analysis of the mechanism reveals that only 57 steps are essential for describing the overall pyrolysis under the current experimental conditions. The following intermediates play critical roles in the decomposition:  H, OH, NO2, HCO, and HNO.

The kinetics of the thermal decomposition of 2-nitropropane was investigated in a shock tube over the temperature range 970−1150 K under high dilution in argon at total pressures 4.5−6 atm. The decay of 2-nitropropane and the production of NO2 were followed spectrophotometrically at 276 and 405 nm, respectively. The unimolecular rate constant deduced from the loss of 2-nitropropane at the high-pressure limit is:  k∞ = 10^14.55±0.13 exp{(−54.2 ± 3.8 kcal/mol)/RT} s^-1. The products of pyrolysis were identified and quantified with FTIR and GC. The major products are NO, CH3CH&dbd;CH2, CO, CH3CHO, C2H4, and (CH3)2CO. The decomposition proceeds primarily through C−N bond fission, while the contribution from the five center elimination of HONO accounts for less than 20% of the total loss of 2-nitropropane. A reaction mechanism that consists of 81 elementary steps is proposed; it accounts quantitatively for the overall pyrolysis. Numerical simulations with the mechanism reproduce reasonably well the NO2 vs time profiles at different temperatures and the distributions of major reaction products over the temperature range studied. When the mechanism was subjected to a sensitivity and principal component analysis, it was found that only 58 reactions in the mechanism are needed to faithfully reproduce the observed product distributions. The fragmentation and reaction sequence in the pyrolysis is graphically presented so that the fundamental chemistry of the overall reaction can be readily visualized. The initial stage of the decomposition of 2-nitropropanol was also investigated following the above experimental protocol. The rate of the pyrolysis appears to be similar to that of the 2-nitropropane over the temperature range studied, but it has a much lower activation energy. The unimolecular rate constant can be expressed as 10^11.29±0.78 exp{(−37.5 ± 3.6 kcal/mol)/RT} s^-1. No pressure dependence was observed over the pressure range investigated (4−5.3 atm), and therefore it is presumed that the rate constant represents the high-pressure limit. Both the low A factor and the low activation energy suggest the involvement of the OH group in the first step of the reaction. NO2 production and subsequent consumption during the decomposition was also observed. The reaction products from this species are similar to those of 2-nitropropane.

Pycnogenol (procyanidin extracted from Pinus maritima) has been shown to be a potent free radical scavenger and an antioxidant phytochemical. The effects of pycnogenol on immune and haemopoietic dysfunction in senescence-accelerated mice (SAM), as a murine model of accelerated ageing, were determined. SAMP8, a strain of senile-prone mice, exhibit learning and memory deficits, immunodeficiency and dysfunction of the haemopoietic system. Oral feeding with pycnogenol for 2 months significantly improved their T- and B-cell function. Pycnogenol also augmented the proliferative capacity of haemopoietic progenitors of bone marrow in SAMP8. These data suggest that pycnogenol may be useful for either retardation or restoration of parameters associated with ageing.

The kinetics of decomposition of azetidine {(CH2)3N(SINGLEBOND)H)} was measured using single-pulse shock-tube techniques, over the temperature range 855–1100 K, in high argon dilution. These data confirm and extend an earlier investigation that utilized the very low-pressure pyrolysis method. A brief survey of many reports regarding the interesting features of azetidine is presented. In two appendices the thermodynamic and kinetic data on trimethylene sulfide, oxide, and immine are intercompared. New ab-initio calculations are cited for the parent species and their fragmentation products. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 185–191, 1998.

Fluorocarbon-modified polyacrylamide chains can form large multichain aggregates. The aggregation behavior of a series of fluorocarbon-modified polyacrylamides in water has been investigated by a combination of static and dynamic laser light scattering (LLS). The critical aggregation concentration (CAC) was estimated from the emergence of a second peak in the line-width distribution measured in dynamic LLS. Our results showed that CAC strongly depends on the amount of 2-(N-ethylperfluorooctanesulfonamido)ethyl acrylate (FX-13) copolymerized with polyacrylamide and also on the polymer concentration. When the FX-13 content is 0.227 mol %, CAC is as low as 1.34 × 10^-4 g/mL, while when the FX-13 content is less than 0.028 mol %, no aggregation has been observed over the entire concentration range studied. A combination of the weight-average molecular weight from static LLS and the area ratio of the two peaks in the line-width distribution from dynamic LLS leads us to the estimation that on average each aggregate consists of ~5−9 individual polymer chains for the acrylamide copolymer with 0.227 mol % FX-13. The solution contained 40 wt % of the multichain aggregates when the polymer concentration was higher than the CAC. On the other hand, the intensity ratio of the light scattered from the multichain aggregates over that from individual chains increased linearly with increasing polymer concentration.