Tailoring the electrical properties of tellurium nanowires via surface charge transfer doping

Recent evidence suggests that some nanomaterials, which are widely used in many fields, have health effects. In order to investigate the cytotoxicity induced by nanosized copper particles (nano-Cu), PC12 cells, which were widely used as an in vitro model for the neuron research, were treated with different concentrations (0, 1, 10, 30, and 100???g/mL) of nano-Cu. The cell viability was determined by measurement of the reduction product of 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT). The oxidative stress induced by nano-Cu and its possible mechanism were studied in relation to the generation of reactive oxygen species (ROS) and the cellular activity of superoxide dismutase (SOD). Results showed that incubation of PC12 cells with increasing concentrations of nano-Cu induced a decrease of cell viability in a concentration- and time-dependent manner. In addition, flow cytometry assay using Annexin V-FITC/PI staining was used to investigate the mode of nano-Cu-induced cell death and quantified the percentage of apoptotic cells. Results showed that nano-Cu induced the significant apoptosis in PC12 cells. Meanwhile, intracellular accumulation of ROS was increased with the increased concentrations of nano-Cu and it was associated with decreased SOD activity, which was probably due to protect effects against the oxidative stress in PC12 cells. Results suggested that both excessive intracellular ROS and decreased SOD contributed to nano-Cu-induced cytotoxicity. In other words, the increasing of oxidative stress was a key mechanism in PC12 apoptosis induced by nano-Cu.     

XRF spectrometer calibration for copper determination in wood

Method of X‐ray fluorescence (XRF) spectrometer calibration for copper analysis in wood was elaborated. Copper salt standard solutions for XRF measurements of liquid samples were prepared, and calibration curve of copper content dependence on impulse counts was determined. Specimens of pine wood (Pinus sylvestris L.) were treated with different solutions of copper‐based preservative (alkaline copper quarternary ammonium compound type) applying model low‐pressure preservation process. After treatment, wood specimens were sliced into six pieces, and exposed surfaces were analyzed using mapping option of XRF spectrometer. Then, wood from each analyzed surface was peeled with abrasive paper and dissolved in 65% nitric (V) acid. Copper content in solutions was determined using obtained calibration curve, and calibration dependence of copper content in wood on the average impulse counts on particular surfaces was calculated. Obtained results of copper content were consistent with values calculated on the basis of differences of samples weight before and after treatment. It confirms that proposed procedure is correct, and obtained equation may be used for unknown samples examination. Copyright © 2012 John Wiley & Sons, Ltd.     

Behavior of Ultrafine Particles generated from organic vapors by corona ionizers

This paper reports an experimental study on the stability, coagulation and diffusion of molecular clusters and ultrafine particles generated from organic vapors by corona ionizers. Upon leaving the ionizer, particles are made to flow within several types of vessels: depending on the specific geometry of the flow system, clusters either coagulate into large particles or are deposited on the walls. Particles larger than 4nm and molecular clusters penetrate through a wire-screen type diffusion battery, but particles in the size range between 2 and 4nm are collected. Among the organic compounds tested (aromatics, alcohols, ketones and others), only aromatic compounds appear to yield unstable clusters which grow into detectable particles (>2nm) through Brownian coagulation. The other compounds either do not undergo the gas-to-particle conversion process or are too small to be detected. Furthermore, the presence of moisture seems to be of fundamental importance in the particle generation phenomenon. The addition of alcohols to the vapor mixture inhibits particle formation.     

Visualising impregnated chitosan in Pinus radiata early wood cells using light and scanning electron microscopy

Chitosan, a deacetylated product of an abundant naturally occurring biopolymer chitin, has been used in a range of applications, particularly in food and health areas, as an antimicrobial agent. In the work reported here Pinus radiata wood was impregnated with chitosan as an environmentally compatible organic biocide (Eikenes et al., 2005a, Eikenes et al., 2005b) to protect wood against wood deteriorating microorganisms and to thus prolong the service life of wooden products. We developed sample preparation techniques targeted to visualise impregnated chitosan within wood tissues using light microscope and field-emission scanning electron microscope (FE-SEM). Sections were viewed with the light microscope without staining with a dye as well as after staining with the dye toluidine blue. Light microscopy was also undertaken on sections that had been stained with 1% aqueous osmium tetroxide (OsO₄). For SEM observations, the sections were treated with OsO₄ and then examined with the FE-SEM, first in the secondary electron imaging mode (SEI) and then in the backscattered electron imaging (BEI) mode, imaging the same areas of a section in both SEI and BEI modes. The preparation techniques employed and the combined use of light and scanning electron microscopy provided valuable complementary information, revealing that chitosan had penetrated into the cavities (cell lumens, intercellular spaces) of all sizes present within wood tissues and had also impregnated early wood cell walls. The information obtained is discussed in relation to its importance in further development of chitosan formulations and refinement of impregnation technologies to optimise chitosan impregnation into and distribution within wood tissues as well as in assessing chitosan efficacy.     

低分子量酚醛树脂处理对杉木细胞壁的改性机理研究

木材细胞壁的改性机理研究是改良木材处理试剂,优化木材处理工艺,提高木材密度、力学、尺寸稳定性等各项性能的关键。以人工林杉木为研究对象,采用合成的水溶性低分子量酚醛树脂(PF)对杉木试材进行逐步的真空加压浸渍处理,通过高精度、高分辨的X射线衍射仪(XRD)、傅里叶变换红外光谱仪(FTIR)和核磁共振仪(NMR)(采用交叉极化/魔角旋转法进行连续测试)对处理和对照试样的相关物理和化学性能进行了对比分析,研究结果表明：水溶性低分子量PF处理后,试样的结晶度与未处理的对照样相比,数值降低明显,平均降低率分别为12.67%,11.91%和6.26%。结合FTIR和NMR 13C的检测谱图发现,水溶性低分子量PF改性后的杉木与对照杉木相比,没有增加新的酯类、醚类等官能团特征峰和化学位移,认为水溶性低分子量PF不能与杉木发生明显的化学反应,但会进入到结构较松散、空隙尺寸较大、相对面积较多的管胞细胞壁中的非结晶区,形成物理性的充填,最终引起杉木相对结晶度的降低。本研究对于研发新型木材改性试剂、优化木材改性处理工艺具有重要的参考价值,研究结果还将为进一步探明木材细胞壁的改性机制、丰富木材细胞壁的改性理论提供重要的依据。     

Nanoindentation mapping of a wood-adhesive bond

A mapping experiment of a wood phenol–resorcinol–formaldehyde adhesive bond was performed by means of grid nanoindentation. The variability of the modulus of elasticity and the hardness was evaluated for an area of 17 μm by 90 μm. Overall, the modulus of elasticity of the adhesive was clearly lower than the modulus of wood cell walls, whereas the hardness of the adhesive was slightly higher compared to cell walls. A very slight trend of decreasing modulus of elasticity was found with increasing distance from the immediate bond line. However, the trend was superimposed by a high variability of the modulus of elasticity in dependence on the position in the wood cell wall. The unexpectedly high variation of the modulus between 12 and 24 GPa may be explained by the interaction between the helical orientation of the cellulose microfibrils in the S2 layer of the wood cell wall and the geometry of the three-sided Berkovich type indenter pyramid used. Corresponding to the very slight decrease in modulus with increasing distance from the bond line, a similar but clearer trend was found for hardness. Both trends of changing mechanical properties of wood cell walls with varying distance from the bond line are attributed to effects of adhesive penetration into the wood cell wall. PACS 81.70.-q     

Characterization of the structural and dynamic changes of cell wall obtained by ultrasound-water and ultrasound-alkali treatments

It is well-known that ultrasound has been studied for its cavitation, mechanical and thermal effects. As a pretreatment technology, ultrasonic alkali treatment has attracted much attention in the field of biomass biochemical transformation. In this study, the structural and dynamic changes of wood cell walls during ultrasound-water, alkali, and ultrasound-alkali treatments were investigated by stereoscopic microscopy, confocal Raman microscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction. The results indicated that the ultrasound-water, alkali, and ultrasound-alkali treatments had the effect of removing extractives from conduits. The uniform self-shrinking samples with shrinkage conduits were obtained by the alkali and ultrasound-alkali treatments. All of the treatments affected the relative content, structure and distribution of the chemical components in the wood cell walls. Compared with water-immersion samples, the relative content of hemicellulose of the treated samples reduced from 32.31% to 7.02% for ultrasound-8% NaOH treated samples. For the signal intensity of lignin, ultrasound-water treated and ultrasound-alkali treated samples displayed a more significant reductions than the alkali treated samples in the cell wall region. The crystal zone and amorphous zone of cellulose coexisted before and after the treatment, for all of the treated samples, and particularly for the ultrasound-assisted treated samples, the crystallinity increased from 38.15% for water-immersion samples to 57.42% for ultrasound-8% NaOH treated samples.     

紫外显微分光光度法测定杉木枝条木质素微区分布

在采用光学显微镜及共聚焦激光显微镜对杉木春季枝条的显微结构及其细胞壁木质素定性测量的基础上,首次在国内应用紫外显微分光光度计对其细胞壁木质素微区含量分布进行了原位测定。结果表明:杉木枝条木材管胞细胞壁木质素在不同微区部位含量分布呈不均一性,其浓度大小依次为细胞角隅胞间层、复合胞间层和次生壁,吸光度均值分别为0.489,0.307和0.278。杉木枝条其木质素定量测定与其定性观察结果是相一致的。为国内测量木材细胞壁木质素微区含量分布提供了新的测量方法。     

Microscopic characterization of tension wood cell walls of Japanese beech (Fagus crenata) treated with ionic liquids

Tension wood that is an abnormal part formed in angiosperms has been barely used for wood industry. In this study, to utilize the tension wood effectively by means of liquefaction using ionic liquid, we performed morphological and topochemical determination of the changes in tension wood of Japanese beech (Fagus crenata) during ionic liquid treatment at the cellular level using light microscopy, scanning electron microscopy and confocal Raman microscopy. Ionic liquid treatment induced cell wall swelling in tension wood. Changes in the tissue morphology treated with ionic liquids were different between normal wood and tension wood, moreover the types of ionic liquids. The ionic liquid 1-ethyl-3-methylimidazolium chloride liquefied gelatinous layers rapidly, whereas 1-ethylpyridinium bromide liquefied slowly but delignified selectively. These novel insights into the deconstruction behavior of tension wood cell walls during ionic liquid treatment provide better understanding of the liquefaction mechanism. The obtained knowledge will contribute to development of an effective chemical processing of tension wood using ionic liquids and lead to efficient use of wood resources.     

化学镀铜天然高分子材料表面特征的近红外光谱分析

通过对天然高分子材料木材进行化学镀的方法制成的木质电磁屏蔽材料既可以保留木材的一些优良特性,又能有效改善木材导电、 导热和电磁屏蔽性,不仅为木材的增值利用开辟了新道路,还为电磁屏蔽材料的加工利用拓宽了领域。本研究利用近红外光谱结合主成分分析法对化学镀铜处理前后样品进行了分析研究,旨在探讨利用近红外光谱技术研究该材料表面特性的可行性。结果表明：(1)化学镀铜前后样品表面的近红外光谱在形状和吸收强度上存在显著差异,而不同镀铜时间的样品之间也存在差异,尤其是反应未充分的样品。(2)经过主成分分析后,镀铜前后样品沿PC1轴、 PC2轴大致分成了6类,其中未处理样品、 活化处理样品性质较接近,镀铜时间25和40 min样品因反应充分,性质也比较类似,说明近红外光谱中包含反映材料处理前后的重要特征信息。(3)比较近红外区域和可见光区域光谱的主成分分析效果,发现近红外光谱区比可见光光谱区对镀铜处理前后样品的分类效果好,可见光光谱在突出样品的表面颜色特征信息方面表现更好,这说明两者结合运用更有利于样品表面特征信息的表征。     

Relaxation of ideal classical particles in a one‐dimensional box

We study the deterministic dynamics of non‐interacting classical gas particles confined to a one‐dimensional box as a pedagogical toy model for the relaxation of the Boltzmann distribution towards equilibrium. Hard container walls alone induce a uniform distribution of the gas particles at large times. For the relaxation of the velocity distribution we model the dynamical walls by independent scatterers. The Markov property guarantees a stationary but not necessarily thermal velocity distribution for the gas particles at large times. We identify the conditions for physical walls where the stationary velocity distribution is the Maxwell distribution. For our numerical simulation we represent the wall particles by independent harmonic oscillators. The corresponding dynamical map for oscillators with a fixed phase (Fermi–Ulam accelerator) is chaotic for mesoscopic box dimensions.     

Cobalt redistribution over the surface of inhomogeneous cobalt-copper alloy films

The surfaces of electrodeposited 1-μm-thick Co_xCu_100−x (x=8, 11, and 20 at. %) films and also of 0.2-μm-thick films obtained by sputtering targets made of the electrodeposited films with an argon ion beam are analyzed by atomic force microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy (XPS). XPS data indicate that cobalt is absent on the surface of the electrodeposited films but is present in the bulk and on the surface of the sputtered films. The difference in the XPS spectra of copper in the electrodeposited and sputtered films of the same composition is less significant. The data obtained are explained within the framework of a qualitative model according to which subgrains of the basic (copper) component coalesce into large clusters, which subsequently take on a regular oval shape on the free surface. This process favors cobalt atom migration from the free surface to near-surface voids. High-energy particles existing in the flux of the target sputtering products bombard the growth front of the ion-sputtered films, causing the fastest sputtered cobalt atoms to penetrate into the copper matrix as point defects.     

In situ observations of compressive behaviour of aluminium foams by local tomography using high-resolution X-rays

We have investigated the compressive behaviour of closed-cell aluminium foams using a high-resolution X-ray CT. The microstructures of cell walls or Plateau borders in the foams were visualized in 3D using the local tomography technique which is a high-resolution CT method to reconstruct a region of interest within a large sample. The shapes and the 3D distribution of micropores, particles, and regions of solute segregation in the foams are evaluated, comparing the cell walls with the Plateau borders. Under compressive loads, the damage behaviour of such microstructures has been observed using an in situ test rig. It is found that the microcracks were mainly initiated from the cell walls and the micropores with large diameters were also damaged. The crack initiation sites are classified from the results. In addition, a method for non-destructive characterization of elastic and plastic deformation in the foams, which is called a 3D microstructure gauge (MG) method, is presented. Thousands of micropores as markers on each load were automatically matched by the information of those volumes and surface areas. The local strain mapping by the MG indicates that the edges of the micropores with large diameters have large strain under compression and this is consistent with the crack analyses.     

Stationary nonequilibrium states in boundary-driven Hamiltonian systems: Shear flow

We investigate stationary nonequilibrium states of systems of particles moving according to Hamiltonian dynamics with specified potentials. The systems are driven away from equilibrium by Maxwell-demon reflection rules at the walls. These deterministic rules conserve energy but not phase space volume, and the resulting global dynamics may or may not be time reversible (or even invertible). Using rules designed to simulate moving walls, we can obtain a stationary shear flow. Assuming that for macroscopic systems this flow satisfies the Navier-Stokes equations, we compare the hydrodynamic entropy production with the average rate of phase-space volume compression. We find that they are equalwhen the velocity distribution of particles incident on the walls is a local Maxwellian. An argument for a general equality of this kind, based on the assumption of local thermodynamic equilibrium, is given. Molecular dynamic simulations of hard disks in a channel produce a steady shear flow with the predicted behavior.     

Growth of carbon nanotubes on metal nanoparticles: a microscopic mechanism from ab initio molecular dynamics simulations

We report on ab initio molecular dynamics simulations of the early stages of single-walled carbon nanotube (SWCNT) growth on metal nanoparticles. Our results show that a sp2 bonded cap is formed on an iron catalyst, following the diffusion of C atoms from hydrocarbon precursors on the nanoparticle surface. The weak adhesion between the cap and iron enables the graphene sheet to "float" on the curved surface, as additional C atoms covalently bonded to the catalyst "hold" the tube walls. Hence the SWCNT grows capped. At the nanoscale, we did not observe any tendency of C atoms to penetrate inside the catalyst, consistent with total energy calculations showing that alloying of Fe and C is very unlikely for 1 nm particles. Root growth was observed on Fe but not on Au, consistent with experiment.     

Improving mixture of grains by using bi-dimensional Galton boards

This paper presents an experimental and numerical study that deals with the problem of mixing grains falling down through a bi-dimensional Galton board (BGB). The special issue addressed here is the influence of the presence of lateral walls in the BGB. Disks of equal diameters but different species are launched from the top of the device. During the fall, disks collide with obstacles (arranged to form a triangular lattice) and with the lateral walls. The exit distribution of particles at the bottom of the board is determined and the incidence of the presence of walls in the mixing quality is studied as a function of W the relative separation between lateral walls. Two types of indexes are evaluated to characterize the efficiency in the obtained mixture. The presence of walls has proven to be crucial to enhance the quality of the mixture of particles.     

Damage Mechanisms of Hierarchical Composites: Computational Modelling

Computational studies of damage mechanisms in hierarchical composites, including biocomposites, nanoparticle reinforced polymer composites and other materials are discussed. Different methods of the analysis of hierarchical effects in the multiscale composites are demonstrated, among them, hierarchical fiber bundle model, 3D multiscale finite element models, analytical studies. Considering wood as a gradient, cellular material with layered composite cell walls, one analyzed the effect of wood structure on damage resistance of wood. The influence of nanoparticles distribution in unidirectional polymer matrix composites with secondary nanoreinforcement on the strength and damage resistance of the composites is demonstrated. The concept of nanostructuring of interfaces and grain boundaries as an important reserve of the improvement of the materials properties is formulated.     

Iron nanoparticle growth induced by Kr–F excimer laser photolysis of Fe(CO)5

We report the uptake by wheat, lupin and Arabidopsis of mesoporous silica nanoparticles functionalised with amine cross-linked fluorescein isothiocyanate (MSN-APTES-FITC). The preparation of these particles at room temperature enabled the synthesis of 20 nm particles that contained a network of interconnected pores around 2 nm in diameter. The uptake and distribution of these nanoparticles were examined during seed germination, in roots of plants grown in a hydroponic system and in whole leaves and roots of plants via vacuum infiltration. The nanoparticles did not affect seed germination in lupin and there was no phytotoxicity. Following germination of wheat and lupin grown in a nutrient solution containing nanoparticles, they were found within cells and cell walls of the emerging root and in the vascular transport elements, the xylem, and in other associated cells. In leaves and roots of Arabidopsis the nanoparticles were found, following vacuum infiltration of whole seedlings, to be taken up by the entire leaf and they were principally found in the intercellular spaces of the mesophyll but also throughout much of the root system. We propose that MSNs could be used as a novel delivery system for small molecules in plants.     

Mechanical properties of pyrolysed wood: a nanoindentation study

The present work focuses on changes of mechanical properties in pyrolysed spruce wood as a function of temperature up to 2400°C. Nanoindentation tests are used for the determination of mechanical properties at the scale of single wood cell walls. Hardness, indentation modulus and elasto-plastic/brittle behaviour of the carbonaceous residues are derived as function of pyrolysis temperature. Hardness values increase continuously by more than one order of magnitude to 4.5?GPa at 700°C. The indentation modulus shows complex changes with a minimum of 5?GPa around 400°C and a maximum of 40?GPa around 1000°C. The deformation induced by the indenter is largely visco-plastic in native wood, but it is almost purely elastic in the carbonaceous residue, with particular low values of the indentation ductility index around 700°C. A low density and a strongly cross-linked carbon structure may explain the mechanical behaviour at these intermediate temperatures. A final decrease of the modulus and a slight decrease of ductility for temperatures above 2000°C can be attributed to a continuous structural transition of the material towards graphite-like stacking of carbon sheets and to preferred carbon orientation along the wood cell axis.     

Convective heat transfer flow of nanofluid in a porous medium over wavy surface

In this letter, water base nanofluid flow over wavy surface in a porous medium of spherical packing beds is investigated. The copper oxides particles are taken into account. These properties are rehabilitated when fluid interacts with porous walls. For porous medium, Dupuit–Forchheimer model; an extension of Darcy's law model is utilized. The natures of velocity and temperature profiles of nanofluid are discussed graphically whereas the values of convection heat transfer coefficient in the presence of different nanoparticles concentrations in porous medium is presented in tabular form. The obtained results illustrate that convection heat transfer is improved by nanoparticles concentration but reduces when fluid attract to pores structured medium. On the other hand, when particles are added in fluid, convection heat transfer rate is improved but flow velocity is declined.