Actual versus apparent within cell wall variability of nanoindentation results from wood cell walls related to cellulose microfibril angle

Hardness and elastic modulus of spruce wood cell walls parallel to their axial direction were investigated by means of nanoindentation. In the secondary cell wall layer S2 of individual earlywood and compression wood tracheids, a systematic pattern variability was found. Several factors potentially affecting nanoindentation results were investigated, i.e. specimen orientation related to the indenter tip, cutting direction during specimen preparation, tip geometry, specimen and fibre inclination, respectively, and finally micro fibril orientation. Mechanical property measurements were correlated with structural features measured by confocal Raman spectroscopy. It was demonstrated that very high variability in the measurement of micromechanical cell wall properties can be caused by unintentional small fibre misalignment by few degrees with regard to the indentation direction caused by sub-optimal specimen preparation.     

The derivation of the microfibril angle in softwood using wide-angle synchrotron X-ray diffraction on structurally characterised specimens

The micro-fibril angle of specimens of Pinus radiata was measured by preparing a microsection of 1000 wood cell walls and irradiating with an X-ray beam from a synchrotron source. The (002) X-ray intensity scattered by the cellulose fibres in each wall was calculated, and the total azimuthal distribution was determined by summing the individual intensities. This is compared to the predicted intensity distributions obtained from geometrical measurements on images of real wood cell walls. The length and orientation of each of the wood cells was prepared, and based on these measurements the predicted intensity distribution was determined. It is shown that an analysis derived for square wood cells is sufficient for the accurate determination of microfibril angle, which an assumption that has not been previously verified.     

The importance of dehydration in determining ion transport in narrow pores

The transport of hydrated ions through narrow pores is important for a number of processes such as the desalination and filtration of water and the conductance of ions through biological channels. Here, molecular dynamics simulations are used to systematically examine the transport of anionic drinking water contaminants (fluoride, chloride, nitrate, and nitrite) through pores ranging in effective radius from 2.8 to 6.5 Å to elucidate the role of hydration in excluding these species during nanofiltration. Bulk hydration properties (hydrated size and coordination number) are determined for comparison with the situations inside the pores. Free energy profiles for ion transport through the pores show energy barriers depend on pore size, ion type, and membrane surface charge and that the selectivity sequence can change depending on the pore size. Ion coordination numbers along the trajectory showed that partial dehydration of the transported ion is the main contribution to the energy barriers. Ion transport is greatly hindered when the effective pore radius is smaller than the hydrated radius, as the ion has to lose some associated water molecules to enter the pore. Small energy barriers are still observed when pore sizes are larger than the hydrated radius due to re‐orientation of the hydration shell or the loss of more distant water. These results demonstrate the importance of ion dehydration in transport through narrow pores, which increases the current level of mechanistic understanding of membrane‐based desalination and transport in biological channels.     

The power flow angle of acoustic waves in thin piezoelectric plates

The curves of slowness and power flow angle (PFA) of quasi-antisymmetric (A0) and quasi-symmetric (S0) Lamb waves as well as quasi-shear-horizontal (SH0) acoustic waves in thin plates of lithium niobate and potassium niobate of X-,Y-, and Z-cuts for various propagation directions and the influence of electrical shorting of one plate surface on these curves and PFA have been theoretically investigated. It has been found that the group velocity of such waves does not coincide with the phase velocity for the most directions of propagation. It has been also shown that S0 and SH0 wave are characterized by record high values of PFA and its change due to electrical shorting of the plate surface in comparison with surface and bulk acoustic waves in the same material. The most interesting results have been verified by experiment. As a whole, the results obtained may be useful for development of various devices for signal processing, for example, electrically controlled acoustic switchers.     

The acoustic properties of TiNiMoFe-based alloys

A study is made of the laws of variation of the acoustic properties of TiNi-based alloys depending on the alloy composition and the temperature. It is demonstrated that, in the temperature range of existence of the B2 phase and the possible strain-induced martensite formation, the vibrations of TiNiMoFe differ from those of conventional materials. Upon excitation of spontaneous vibrations in the M _f≤T≤M _d range, there appears a region of long-term, small-amplitude low-frequency sound vibrations. It is found that free low-frequency vibrations of a sample of TN-10 alloy [1] are characterized by a low level of decrement in the above-indicated temperature range.     

The mechano-sorptive creep susceptibility of two softwoods and its relation to some other materials properties

This paper describes a new design of bending creep machine for accurate measurements of mechano-sorptive creep. Tests on two species of pine showed that at low stresses bending and tension gave similar results. It is shown that the mechano-sorptive creep susceptibility correlates with the mean microfibrillar angle of the S2 layer in a continuous relation that includes two species of pine, including one which showed evidence of compression wood; thus giving further evidence of the importance of inter-microfibril stresses in the S2 layer in mechano-sorptive creep. Accordingly, mechano-sorptive creep susceptibility also correlated continuously with elastic compliance; thus encouraging the possibility of the selection of non-susceptible material by machine stress grading. These two correlations also diminish the main obstacle to research on mechano-sorptive creep, the excessive variability of the material and the consequent difficulty of matching of samples.     

Effect of the beam-vessel angle on the received acoustic signalfrom blood

In order to explore the feasibility of algorithms to determine the three dimensional (3D) velocity magnitude from the received ultrasonic blood echo from a single line of sight, the signal from small sample volumes is studied as a function of beam-vessel angle. As opposed to previous treatments of the effect of the beam-vessel angle on the received acoustic signal, a wideband signal is transmitted and the returned signal in each sample volume is analyzed. High-resolution experimental M-mode images of radio-frequency (rf) echo signals are used to visualize the flow in individual regions of interest. These experiments confirm the predictions of a theoretical model for the signal and its second moment. It is shown that the two major effects limiting the correlated signal interval are the spread of axial velocities within the sample volume and the transit time across the lateral beam width. Particularly for small beam-vessel angles, the spread of velocities limits the correlated signal interval. In addition, the experimental results demonstrate that accurate velocity estimation for low volume flow rates and particularly for large beam-vessel angles may involve detection of changes in the correlation magnitude. For low volume flow rates, the shape of the correlation surface can be affected by small regions of blood with a strong scattering intensity located near the initial region of interest     

Mechanical response of longleaf pine to variation in microfibril angle,chemistry associated wavelengths,density, and radial position

The composite structure of the S₂ layer in the wood cell wall is defined by the angle of the cellulose microfibrils and concentration of polymers and this structure impacts strength and stiffness. The objective of this study was to use near infrared spectroscopy and X-ray diffraction to determine the effect of lignin and cellulose associated wavelengths, microfibril angle, density, and radial position within the tree on strength and stiffness. The aromatic portion of lignin provided a good predictive role on strength and stiffness at high microfibril angles. However, in mature wood where microfibril angle and lignin content was low, cellulose associated wavelengths became increasingly important. The increased importance of the aromatic portion of lignin (1665 nm) on the strength as microfibril angle increased was attributable to the plastic deformation of lignin that occurred beyond the yield point. Finally, a fourfold increase in stiffness was observed when the microfibril angle dropped from 40 to 5°.     

An approximate method of determining the vibration angle of turboblading with lashing wire

Zusammenfassung Es wird ein Verfahren zum Berechnen der Schwingungsrichtung von Schaufeln entwickelt, die durch einen Bindedraht miteinander verbunden und in ihrer Grundeigenschwingung angeregt sind. Die Theorie beruhl auf dem Variationsproblem der Form?nderungsarbeit des betrachteten Systems und stützt sich auf einfache Voraussetzungen, die die Natur des gekoppelten Schwingungssystems kennzeichnen. Dabei wird angenommen, da? sich die verbundenen Schaufeln nicht verjüngen (also ihr Querschnitt über die gesamte Schaufelh?he konstant ist) und ein System schlanker K?rper bilden. Einflüsse durch die Werkstoffd?mpfung und die Zentrifugalkr?fte bleiben unberücksichtigt. Die Auswertung erstreckt sich über ein Schaufelsystem mit nur einem Bindedraht, doch steht einer übertragung auf systeme mit mehreren Verbindungen nichts im Wege. Es ergibt sich für den Fall mit einem Draht, da? die Schwingungsrichtung nur wenig von der Achse des maximalen Tr?gheitsmoments abweicht. M?glichkeiten zur Verfeinerung der Theorie werden aufgezeigt.

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Presented at X. International Congress for Theoretical and Applied Mechanics, September 1956, University of Bruxelles, Belgium.     

含硫纤维素衍生物的性能研究

研究了含硫纤维素衍生物:巯基纤维素(SC)和纤维素磺原酸酯(CCX)这两种材料的性能及它们对重金属离子的吸附性能和吸附机理。实验表明,含硫纤维素衍生物作为一种固体吸附材料其化学性质比无机硫化物稳定,暴露于空气中放置一个月后,SC和CCX含硫量下降率<10%,在室温下,中性水溶液中浸泡10天,其水解率<3%;SC饱和吸附容量(mg/g)为:Hg2 58、Cu2 17、Pb2 55、Cd2 29,CCX饱和吸附容量(mg/g)为:Hg2 82、Cu2 26、Pb2 77、Cd2 49;SC和CCX都易于再生,再生10次后其对重金属离子的饱和吸附容量不变。     

Gradient of nanomechanical properties in the interphase of cellulose nanocrystal composites

The nanoscale transitional zone between a nanofiber and surrounding matrix (interphase) defines the ultimate mechanical characteristics in nanocomposite systems. In spite of this importance, one can hardly find quantitative data on the mechanical properties of this transitional zone in the cellulose–nanofiber composites. In addition, most of the theoretical models to predict the mechanical properties of interphase are developed with the assumption that this transitional zone is independent of the nanofiber size. In the current study, we show that the mechanical properties of interphase in cellulose nanocrystal (CNC) composites can be quantitatively characterized and the correlation with the size of CNCs can be mapped. The peak force tapping mode in atomic force microscope (AFM) was used to characterize deformation, adhesion, and modulus gradient of the interphase region in poly(vinyl alcohol) (PVA)–poly(acrylic acid) (PAA)–cellulose nanocrystal (CNC) composites. In comparison to the polymer matrix, the adhesion force of CNC was lower. The average elastic modulus in the interphase varied from 12.8 GPa at the interface of CNC to 9.9 GPa in PVA–PAA matrix. It was observed that the existence of PAA increased the gradient of mechanical and adhesion properties of the interphase zone. This occurs due to the variation in the ester linkage density from the CNC interface to the polymer matrix. Finally, it is shown that interphase thickness is higher for CNCs with larger diameter.     

蓝宝石衬底的斜切角对GaN薄膜特性的影响

利用金属有机物化学气相沉积技术在具有斜切角度的蓝宝石衬底(0～0.3°)上生长了非故意掺杂GaN薄膜,并采用显微镜、X射线双晶衍射、光荧光及霍尔技术对外延薄膜的表面形貌、晶体质量、光学及电学特性进行了分析.结果表明,采用具有斜切角度的衬底,可以有效改善GaN外延薄膜的表面形貌、降低位错密度、提高GaN的晶体质量及其光电特性,并且存在一个衬底最优斜切角度0.2°,此时外延生长出的GaN薄膜的表面形貌和晶体质量最好.     

The role of basal-plane oxygen atoms in determining the ferroelastic and microstructural properties of Y-Ba-Cu-O

The basal-plane oxygen atoms in YBa₂Cu₃O_7−x behave like a lattice gas, with very high diffusivity, especially for oxygen-deficient specimens. Implicit in this behaviour is the property that even a small amount of stress applied along theb-axis (b >a) can make these oxygen atoms hop from the (0,1/2,0) sites to the (1/2,0,0) sites. This is suggested as the primary mechanism responsible for the ferroelastic switching observed in this crystal. Since the material is an oxide of a mixed-valence element (Cu), the common occurrence of overall nonstoichiometry is only to be expected. Also, as discussed by Khachaturyan and others, except at very high temperature, the oxygen atoms and the vacancies will always have a tendency for ordering and/or precipitation into configurations which approach near-perfect stoichiometry locally. However, not all evidence for ordering is in conformity with the predictions of Khachaturyan’s concentration-wave model. The experimental data are examined critically. Further experiments to resolve the discrepancies are suggested.     

The structure and mechanical properties of sheets prepared from bacterial cellulose

A preliminary experiment has shown that a sheet-shaped material prepared from bacterial cellulose has remarkable mechanical properties, the Young's modulus being as high as >15 GPa across the plane of the sheet. The mechanical properties were little affected by the fermentation conditions of pellicles and the preparation conditions of the sheets, i.e. the pressing and drying of pellicles. From structural investigations, the high Young's modulus has been ascribed to the unique super-molecular structure in which fibrils of biological origin are preserved and bound tightly by hydrogen bonds. It has also been found that a pulp obtained from bacterial cellulose gives a strong paper and is useful for reinforcing conventional pulp papers and enabling paper-making from some fibrous materials.     

The structure and mechanical properties of sheets prepared from bacterial cellulose

A sheet obtained from bacterial cellulose had a remarkably high modulus of elasticity as reported in Part 1 of this series. The Young's modulus of a sheet prepared by squeezing and drying a gel-like pellicle of bacterial cellulose was found to be > 15 G Pa. In addition, it has been found that treatment of the gel-like pellicles or dried sheets of bacterial cellulose with alkaline and/or oxidative solutions improves the mechanical properties significantly, and the Young's modulus of the resulting sheets approaches 30 G Pa. In this paper, improvement of the mechanical properties of bacterial cellulose sheets by the removal of impurities is investigated and the applicability of bacterial cellulose to diaphragms of electroacoustic transducers is discussed.     

The importance of grain boundary complexions in affecting physical properties of polycrystals

In recent decades researchers have revealed a rich variety of grain boundary segregation phenomena, including interfacial phase, or complexion, transitions. Grain boundary complexion transitions have been shown to induce discontinuous changes in materials properties as a function of temperature and chemical potential, and have been used to explain phenomena that had previously evaded satisfactory explanation. This review article discusses how grain boundary complexions relate to mass transport and mechanical properties, by highlighting both what is understood and emphasizing topics requiring additional study.     

Set of high-frequency permeameters for determining the permeability and loss angle of ferromagnetic materials

Conclusions It is possible, by means of the high-frequency permeameter method, to determine the permeability and loss angle of magnetic materials at fixed frequencies whose number can be very large. Owing to its advantages, this method can be recommended for wide use in laboratories and under workshop conditions.     

Experimental study of acoustic devices for determining the levels and states of liquid media

The article is based on a paper read at the International Scientific-Practical Conference Piezoelectric Devices and Sensors, held at Obninsk on January 14–15, 1993.Translated from Izmeritel'naya Tekhnika, No. 2, pp. 28–32, February, 1994.