Mechanical performance and cellulose microfibrils in wood with high S2 microfibril angles

Corewood and compression wood, both with high S2 microfibril angles, are the worst parts of the tree most in need of improvement in wood quality. This study focuses on the characteristics of cellulosic reinforcement in wood with high S2 microfibril angles lying between 35° and 60°, as well as the probable influence of these characteristics on wood longitudinal mechanical properties. Stiffness and tensile strength were measured on 221 thin radiata pine wood strips. The results indicate that at high angles, the average values of wood stiffness and tensile strength are low with relatively large variations. The variations of stiffness and strength are weakly correlated with the variation of S2 microfibril angles, regardless of wood type. Further study involved examining the characteristics of cellulose microfibrils within the S2 layer using dual axis electron tomography for samples with the same microfibril angle but differing mechanical performance. From the fact that the severe compression wood possessed fewer cellulose microfibrils and had abundant dislocations, and that at many kinking points these cellulose microfibrils were broken down into shorter dislocation segments, it was concluded that the characteristics of cellulose microfibril reinforcement are responsible for the inferior stiffness and tensile strength in the severe compression wood compared with normal corewood with the same high S2 microfibril angle.     

Compliance of a microfibril subjected to shear and normal loads.

Many synthetic bio-inspired adhesives consist of an array of microfibrils attached to an elastic backing layer, resulting in a tough and compliant structure. The surface region is usually subjected to large and nonlinear deformations during contact with an indenter, leading to a strongly nonlinear response. In order to understand the compliance of the fibrillar regions, we examine the nonlinear deformation of a single fibril subjected to a combination of shear and normal loads. An exact closed-form solution is obtained using elliptic functions. The prediction of our model compares well with the results of an indentation experiment.     

Hydrolysis of Cellulose Acetate and Cellulose Acetate Butyrate Pseudolatexes Prepared by a Solvent Evaporation-Microfluidization Method

Aqueous colloidal Cellulose acetate dispersions have recently been introduced as an alternative to organic polymer solutions for the coating of osmotically active cores with a semipermeable membrane. Cellulose esters are known to hydrolytically degrade in an aqueous environment. This study followed the chemical degradation of pseudolatexes of the cellulose esters, cellulose acetate and cellulose acetate butyrate, over time and as a function of temperature. The pseudolatexes were prepared by a microfluidization-solvent evaporation method. The hydrolysis of the cellulose esters was followed by determining the pH and the amount of the acidic degradation products, acetic and butyric acid, in the aqueous phase of the polymer dispersions with an HPLC assay. The degradation followed a pseudo first-order equation and rate constants and activation energies were calculated. In addition to chemical instability, agglomeration and gelling of the colloidal particles occurred. The pseudolatexes were stable at 4°C, however, if stored at higher temperatures, the preparation of a redispersible polymer powder is recommended.     

The calculation of branch flows in a directed network

This paper describes a procedure for the calculation of branch flows in a directed network in which the node-to-node flows are prescribed. The node-to-node paths of the network are enumerated using a combinatorial process. Procedures based on the path list are used to allocate the node-to-node flows to the alternative paths of the network according to Wardrop's first principle. The calculation, although necessarily iterative, is rapidly convergent. The method has been implemented as a computer program and the results obtained for a typical network are discussed. A linear relationship between branch potential and branch flow has been used, but the method can be extended to piece-wise linear and non-linear relationships.     

Initial water impact of a wedge at vertical and oblique angles

This paper examines initial asymmetric wedge-impact flows with horizontal as well as vertical impact velocity. The method of two-dimensional vortex distributions is employed to model the initial-boundary-value problem. The numerical analysis involves discretization of the body surface and an iterative solution technique. Experimental drop tests of a prismatic wedge were performed to gain understanding and provide data for comparison of initial water impact when asymmetry and horizontal impact velocity are present. The experimental investigation of initial flow separation off the wedge vertex (i.e., keel) during impact is described. Initial separation-ventilation of the flow from the vertex due to asymmetric impact or horizontal-vertical impact velocity is examined in relation to the present theory. Agreement between the data and the numerical predictions was demonstrated for small degrees of asymmetry and small ratios of horizontal to vertical impact velocity. The initial flow detachment from the vertex also revealed interesting hydrodynamic characteristics.     

细菌纤维素在模拟体液中的降解研究

研究了不同性质的纤维素酶对细菌纤维素(BC)的降解活性,着重探讨了在纤维素酶作用下,影响BC在模拟人体环境中降解行为的因素。研究表明中性纤维素酶在模拟人体环境的条件下对BC具有较高的降解活性。纤维素酶在模拟体液中的活性会随着时间延长而降低,但并未丧失活性,纤维素酶在模拟人体的环境下依然具有长期降解BC的作用。β-葡糖苷酶对BC的降解有很大的促进作用,当β-葡萄糖苷酶在复合酶中质量分数为60%时,复合酶降解BC膜的速率达到最大。     

Flow of a Casson fluid in a narrow tube with a side branch

Development of a mathematical model suitable for studying the mass-flux and hematocrit reduction due to plasma skimming in a capillary emerging from an artery making an angle with the parent artery is of primary concern in the paper. The flow is considered to have three phases – the peripheral plasma layer, the cell depleted middle layer and the core region where the concentration of erythrocytes is highest. Both steady and pulsatile flow situation are studied. The analysis for pulsatile flow has been carried out by considering the pressure gradient as a periodic function of time and the inertial effects as negligibly small. A perturbation technique is employed to solve the resulting quasi-steady non-linear system of equations that are considered to govern the flow. Basing upon relevant experimental data available for coronary arteries as well as very small vessels of the circulatory system, the study has been performed by considering Womeresely parameter to be small (less than unity). The theoretical estimates computed under the purview of the present mathematical analysis reveal that hematocrit in the branch capillary decreases with an increase in the yield stress of blood, both in steady and pulsatile flows for any branching angle. Further, erythrocytes entrainment from the parent artery to the branch capillary is least when the branch is perpendicular to the parent artery.     

Machinability characteristics evolution of CFRP in a continuum of fiber orientation angles

Circular orthogonal milling tests on unidirectional carbon fiber reinforced polymer (UD-CFRP) laminate disks were conducted to investigate the machinability characteristics evolution in a continuum of fiber orientation angles (β). Experimental results show that surface cavities are the main machined surface damages, which elevate the surface roughness Ra. The surface cavities systematically appear between angles β?=?25° and β?=?75° for down-milling and β?=?20° and β?=?50° for up-milling and their occurrence may not be influenced by the cutting velocity and the feed rate. In the surface cavity region, low-level cutting forces are generated, which is highly correlated with the occurrence of fiber–matrix debonding for both down-milling and up-milling. SEM micrographs show that the formation of the surface cavities is mainly caused by the occurrence and propagation of fiber–matrix debonding, followed by bending-induced fiber fractures and compression-induced fiber fractures. Based on those observations, a novel milling strategy taking the fiber orientation angle into consideration is proposed to avoid the surface cavities; this unique approach provides a new way to milling typical aerospace CFRP laminates with high machined surface quality.     

Radiation transfer in a real spectrum. Integration with respect to the frequency and angles

The method of integration with respect to the frequency of the radiation field in systems with complex spectrum is generalized in order to obtain heat-exchange characteristics integrated with respect to the angles.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 38, No. 2, pp. 278–285, February, 1980.     

Changes in contact angles as a function of time on some pre-oxidized biomaterials

Interfaces between biomaterials, tissue and body fluids such as blood play a key role in determining the nature of the interaction between biomaterials and the living organism. The wettability of these biomaterials in relationship to their microenvironment is an important factor to consider when characterizing surface behaviour. The measure of the contact angle between a fluid and material surface can be used to define wettability for that particular microenvironment.In this study, pure Ti, Ti6AI4V alloy, austenitic and martensitic Ni-Ti alloys, pure Ni, AISI Type 316L stainless steel, Co-Cr alloy, and -alumina were investigated. All metallic materials were mechanically polished and oxidized at 300 °C for 30 min in pure oxygen. Oxide films formed on the surfaces of these materials were examined under the electron microscope and their crystalline structures were identified by the electron diffraction method. The initial contact angle (_o) and its changes (/t) as a function of time in 1% NaCl solution drop were measured.The results of this study indicated that (i) Ti and its alloys were covered with mainly TiO₂ (tetragonal structure), (ii) NiO (cubic structure) was found on pure Ni, (iii) the spinel type oxide (cubic structure) was formed on both 316L stainless steel and Co-Cr alloy, (iv) TiO₂ (except for oxides formed on Ti6AI4V alloy) showed a rapid spreading characteristic in 1% NaCl solution; while (v) a relatively slow spreading behaviour was observed on the cubic structure oxides.     

Relations between the critical angles and the optical tensor of a biaxial material

The behavior of the critical angles between a high-index isotropic medium and a biaxial crystal with arbitrary orientation of the optical tensor has been theoretically analyzed and numerically modeled. The results indicate that, as the biaxial crystal is rotated around an axis perpendicular to the interface, two critical angles appear, corresponding to the excitation of two eigen modes, which periodically vary with a period of pi. An optical procedure for fully characterizing the optical tensor of a biaxial crystal is suggested on the basis of the twist-angle dependence of these critical angle. This procedure simply requires the measurement of the p- to s-conversion reflectivity against the sample rotation angle, with just one polished surface of a biaxial crystal.     

Measurement of lengths and angles by means of a photoelectric direct reading-off microscope

We consider the measurement of lengths and angles over a broad range with error amounting to fractions of a micrometer or angular second using a newly designed mockup of a photoelectric direct reading-off microscope. The microscope implements a pulse-position method of transforming information through application of a scanner in the form of a rotating polyhedral mirror.Translated from Izmeritel'naya Tekhnika, No. 6, pp. 15–18, June, 1995.The present study was completed with the financial support of the Russian Foundation for Applied Research (project RTK).     

Generation and damping of flow oscillations in the region of a joint between a pipeline and a blind branch

We consider the problem of self-excitation of oscillations in the pipes of main gas-compressor stations. We present results of model investigations of intense narrow-band oscillations of pressure and velocity in a gas flow, which are due to the occurrence of instability and the formation of a self-oscillating system in the zone of a joint between a pipeline and a blind branch-resonator. The possibility of prevention or attenuation of self-oscillations is indicated. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 6, pp. 1099–1106, November–December, 1998.