Longitudinal Direction Parallel Research Articles

Directional effect of a magnetic field on oscillatory low-Prandtl-number convection

The directional effect of a magnetic field on the onset of oscillatory convection is studied numerically in a confined three-dimensional cavity of relative dimensions 4:2:1 (length:width:height) filled with mercury and subject to a horizontal temperature gradient. The magnetic field suppresses the oscillations most effectively when it is applied in the vertical direction, and is the least efficient when applied in the longitudinal direction (parallel to the temperature gradient). In all cases, however, exponential growths of the critical Grashof number, Grc (Gr, ratio of buoyancy to viscous dissipation forces) with the Hartmann number (Ha, ratio of magnetic to viscous dissipation forces) are obtained. Insight into the damping mechanism is gained from the fluctuating kinetic energy budget associated with the time-periodic disturbances at threshold. The kinetic energy produced by the vertical shear of the longitudinal basic flow dominates the oscillatory transition, and when a magnetic field is applied, it increases in order to balance the stabilizing magnetic energy. Moreover, subtle changes in the spatial distribution of this shear energy are at the origin of the exponential growth of Grc. The destabilizing effect of the velocity fluctuations strongly decreases when Ha is increased (due to the decay of the velocity fluctuations in the bulk accompanied by the appearance of steep gradients localized in the Hartmann layers), so that an increase of the shear of the basic flow at Grc is required in order to sustain the instability. This yields an increase in Grc, which is reinforced by the fact that the shear of the basic flow naturally decreases at constant Gr with the increase of Ha, particularly when the magnetic field is applied in the vertical direction. For transverse and longitudinal fields, the decay of the velocity fluctuations is combined with an increase of the shear energy term due to a sustained growth in stabilizing magnetic energy with Ha.

Structural investigations into the interaction of hemoglobin and part structures with bacterial endotoxins

An understanding of details of the interaction mechanisms of bacterial endotoxins (lipopolysaccharide, LPS) with the oxygen transport protein hemoglobin is still lacking, despite its high biological relevance. Here, a biophysical investigation into the endotoxin:hemoglobin interaction is presented which comprises the use of various rough mutant LPS as well as free lipid A; in addition to the complete hemoglobin molecule from fetal sheep extract, also the partial structure alpha-chain and the heme-free sample are studied. The investigations comprise the determination of the gel-to-liquid crystalline phase behaviour of the acyl chains of LPS, the ultrastructure (type of aggregate structure and morphology) of the endotoxins, and the incorporation of the hemoglobins into artificial immune cell membranes and into LPS. Our data suggest a model for the interaction between Hb and LPS in which hemoglobins do not react strongly with the hydrophilic or with the hydrophobic moiety of LPS, but with the complete endotoxin aggregate. Hb is able to incorporate into LPS with the longitudinal direction parallel to the lipid A double-layer. Although this does not lead to a strong disturbance of the LPS acyl chain packing, the change of the curvature leads to a slightly conical molecular shape with a change of the three-dimensional arrangement from unilamellar into cubic LPS aggregates. Our previous results show that cubic LPS structures exhibit strong endotoxic activity. The property of Hb on the physical state of LPS described here may explain the observation of an increase in LPS-mediating endotoxicity due to the action of Hb.

Anisotropic resistivity of (100)-oriented mesoporous silicon

The resistivity of (100)-oriented mesoporous silicon has been studied using two different electrode configurations. The authors observed that the electronic transport along the longitudinal direction (parallel to the sample surface) is strongly inhibited at room temperature but not along the perpendicular direction. They show that such electrical anisotropy can be removed by heating the material, reporting an increase of six orders of magnitude of the longitudinal conductivity when the temperature rises from 20to100°C. These experimental findings are interpreted on the basis of the material morphology and nanostructuration, which determine the availability of percolative pathways for free charge carriers.

Thermal expansion anisotropy in extruded SiC particle reinforced 2080 aluminum alloy matrix composites

Thermal expansion behavior is an important physical property of metal matrix composites (MMCs). For extruded Al/SiC p composites, both the particle volume percent and the orientation relative to the extrusion direction have significant effects on the coefficient of thermal expansion (CTE) of a composite. In this study, the coefficient of thermal expansion of extruded, SiC particle reinforced 2080 Al composites were measured using a thermal mechanical analyzer (TMA). It was found that the anisotropic distribution of SiC particles determines the anisotropic thermal behavior of Al/SiC p composites. For the same SiC content, the CTE in the short transverse direction (normal to the extrusion axis) is higher than that in the transverse direction, with the longitudinal direction (parallel to the extrusion axis) having the lowest CTE. Finite element modeling (FEM), based on the actual microstructure of Al/SiC p composites, was employed to simulate the thermal behavior. The experimental results for the CTE of the composite correlated very well with those predicted by two-dimensional (2D) numerical models. The FEM results showed that orientation of SiC particles changes the internal stress in the composite, which yields anisotropic thermal behavior. A comparison was made between the experimental results and the FEM model, and these were related to several analytical models.

Fatigue strength in laser welding of the lap joint

Finite element analysis and fatigue test are performed to estimate the fatigue strength for the laser-welded lap joint. Concentrating on the application of design and manufacturing technology using the laser-welded lap joints, the residual stress and welding direction of the laser-welded lap joint have to be considered in relation to its fatigue strength. After three-dimensional modeling for the longitudinal direction parallel to fatigue load and transverse direction perpendicular to that, residual stress fields in laser-welded lap joint are calculated using thermo-elastic-plastic finite element analysis. Then the equivalent fatigue stress with residual stress effect is obtained. In order to ensure reliability of calculated fatigue strength, fatigue test is performed. The calculated and experimental results showed good agreement. The fatigue strength in the transverse direction welding is higher than that of longitudinal direction welding.

Effect of reinforcement-particle-orientation anisotropy on the tensile and fatigue behavior of metal-matrix composites

The effect of extrusion-induced particle-orientation anisotropy on the mechanical behavior of metal-matrix composites (MMCs) was examined. In this study, we have shown that this anisotropy has a significant influence on the tensile and fatigue behavior SiC particle-reinforced Al alloy composites. The preferred orientation of SiC particles was observed parallel to the extrusion axis, with the extent of orientation being highest for the lowest-volume-fraction composites. The composites exhibited higher Young’s modulus and tensile strength along the longitudinal direction (parallel to the extrusion axis) than in the transverse direction. The extent of anisotropic behavior increased with increasing volume fraction, because of the increasing influence of the SiC reinforcement on the Young’s modulus and tensile properties. The preferred orientation also resulted in anisotropy in the fatigue behavior of the composite material. The trends mirrored those observed in tension, with higher overall fatigue strengths for both orientations and a higher anisotropy with increasing volume fraction of particles. The influence of particle-orientation anisotropy and the resulting tensile and fatigue damage mechanisms is discussed.

A tunneling magnetoresistance sensor overlaid with a longitudinal bias stack

In this study, a tunneling magnetoresistance (TMR) sensor overlaid with a longitudinal bias (LB) stack is fabricated, its magnetic and TMR properties are characterized, and its read performance is tested. The TMR sensor comprises Ta/Ni–Fe/Pt–Mn/Co–Fe/Ru/Co–Fe/Al–O/Co–Fe/Ni–Fe/Cu films, and the LB stack comprises Ru/Co–Fe/Pt–Mn/Ta films. A transverse-field anneal is applied to the TMR sensor to develop strong antiferromagnetic/ferromagnetic coupling within the Pt–Mn/Co–Fe films in a transverse direction perpendicular to an air bearing surface (ABS), thereby forming a transverse flux closure within the Co–Fe/Ru/Co–Fe films for operating the TMR sensor properly. A longitudinal-field anneal is applied to the LB stack to develop strong ferromagnetic/antiferromagnetic coupling within the Co–Fe/Pt–Mn films in a longitudinal direction parallel to the ABS, thereby forming a longitudinal flux closure within the Co–Fe/Ni–Fe/Cu/Ru/Co–Fe films for attaining stable TMR responses. The TMR sensor exhibits good magnetic and TMR properties, including low ferromagnetic coupling fields, high pinning fields, low junction resistance-area products, and high TMR coefficients. The TMR sensor overlaid with the LB stack shows stable, highly sensitive TMR responses.

割裂引張強度試験下におけるコンクリートのガス透過性に関する実験的考察

A gas pressure difference of 0.2N/mm2 was maintained between the cross sections of concrete with simultaneous increase of loading in the split tensile strength test configuration. A single crack that formed in the longitudinal direction parallel to the loading increased the gas permeability of the concrete. It was found that gas permeability was gradually increased at a crack opening of about 0.02mm and then rapidly increased until the crack opening reached 0.08mm. The degree of water saturation of concrete had significant effect on the formation of the crack and hence failure of the concrete under investigation. Oven dried concrete exhibited gradual increase of the gas permeability while water saturated concrete showed rapid increase of the gas permeability at the crack opening of 0.02mm. In this way the gas permeability of concrete subjected to the split tensile strength test was controlled by the failure mechanism.

The importance of longitudinal stress effects on the static conditions of the final lining of a tunnel

The effects of stresses acting in the longitudinal direction (parallel to the tunnel axis) in certain cases take on an important role in the definition of the static conditions of the final lining, and if they are not foreseen, can lead to instabilities that often require difficult and expensive repair interventions. The case in which the final lining shows a marked irregularity of thickness along the tunnel axis is typical, for example, when the preliminary supports are of a truncated-cone type placed in advancement ahead of the excavation face. The produced anomalous stresses are basically due to the difference in transverse stiffness (and, therefore, in the radial displacements) between the adjoining lining sections. A simple calculation procedure has been set up in this work which permits the estimation of the three-dimensional stress state inside the concrete in the presence of a thickness anomaly and of a homogeneous and uniform radial load at the lining extrados. The approach followed is able to furnish the trend of the safety factor regarding the rupture of concrete, in function of the distance from the thickness anomaly, in such a way as to be able to design the lining thickness and any necessary steel reinforcements.

Crystal structure of the β′′ phase in an Al–l.0mass%Mg2Si–0.4mass%Si alloy

Abstract The crystal structure of the β′′ phase in an Al–1.0mass%Mg2Si–0.4mass%Si alloy aged at 423 K for 2400 ks has been investigated by high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and micro beam diffraction (MBD) techniques and energy dispersive X-ray spectroscopic (EDX) analysis. The aging treatment at 423 K for 2400 ks was a specific aging condition such that the β′′ phase predominantly precipitates. The β″ phase has a monoclinic lattice with the lattice parameters a=0.77±0.02 nm, b=0.67±0.01 nm, c=0.203 nm, and γ=75±0.5°. Its space group is P2/m. The crystallographic orientation relationship is found as follows: (001)β′′//(001)m and 100β′′// [310]m. The β′′ phase has a needle shape with its longitudinal direction parallel to the direction of [001]β′′. The chemical composition of the β′′ phase is Si:Al:Mg=6:3:1.

3-D x-ray mirror metrology with a vertical scanning long trace profiler (abstract)

The long trace profiler (LTP) was originally developed at Brookhaven National Laboratory for the specific purpose of measuring the surface figure of large cylindrical mirrors used at grazing incidence in synchrotron radiation (SR) beamlines. In its original configuration, it could measure only along one line down the center of the cylinder. A single linear profile is often sufficient to gauge the quality of the optical surface on these kinds of mirrors. For some applications it is necessary to measure the topography of the entire surface, not just along one line but over a grid that covers the entire surface area. We have modified a standard LTP to enable measurement of the complete surface of Wolter telescope optics in a vertical configuration. The vertical scanning LTP (VSLTP) is capable of producing a complete 3-D map of the surface topography errors relative to the ideal desired surface on complete segments of paraboloids and hyperboloids. The instrument uses a penta prism assembly to scan the probe beam in the longitudinal direction parallel to the mirror symmetry axis and uses a precision rotary stage to provide scans in the azimuthal direction. A Risley prism pair and a dove prism are used to orient the probe beam in the proper direction for the azimuthal scans. The repeatability of the prototype instrument is better than 20 nm over trace lengths of 35 mm with a slope measurement accuracy of about 1 microradian.

Corrosion and mechanical properties of aluminum alloy panels

Thin tensile specimens with a gauge length of 30  6  0.3 mm were cut from the panel assembly in the longitudinal direction parallel to the plane of the assembly layer by layer under electroerosion conditions avoiding overheating and structural changes in the material. Specimens were tested in3% NaC1 + 0.1% H202 solution under constant load for 60 days with the aim of determining the maximum safe stress with corrosion cracking of different layers of the initial material through the thickness of the panel assembly. It follows from Fig. 1 that the sharpest increase in the level of safe maximum stress is observed in the section at a depth of 1.5 mm from the ribbed surface. The difference in sensitivity to corrosion cracking of panels with and without ribbed surfaces could affect their corrosion-fatigu e behavior. In order to check this possibility, corrosion-fatigu e tests were carried out in natural Black Sea water on flat specimens cut from areas of the panel assembly between the ribs and having a thickness equal to that of the assembly. Tests were performed under pure bending low-cycle asymmetric loading conditions with a cycle starting from zero at different frequencies v and with overall strain amplitude in an IPPU unit [2] in such a way that the maximum tensile stress was formed either at the ribbed or the plain side of the assembly. At a frequency of 1.7.10 -3 Hz or more, loading was accomplished with a sinusoidal cycle, and at frequencies below 1.7.10 -3 Hz the cycle was trapezoidal. Loading and unloading time was 5 min. Tests showed that at a frequency of 0.83 Hz the dependence of endurance on cyclic strain on semilogarithmic coordinates has a break characteristic for corrosion fatigue curves in the region of amplitude e = 0.4%. Crack initiation at the ribbed side of the panel occurs five to six times more quickly than at the flat side, and even in cases when the maximum tensile bending stress is applied to the plain side, crack initiation occurred at the ribbed side. Subsequently, the crack initiated at the surface developed in a direction perpendicular to the normal stress. At lower frequencies crack propagation direction varied by 90 ~ the crack branched, its propagation into the body of the specimen was slowed down, and the material delaminated. It was noted that a decrease in loading frequency starting from 1.7- 10 -2 Hz leads to a smooth decrease in the number of cycles before the appearance of a visible crack, and this agrees with the known character of the effect of frequency on endurance. In Caking specimens to complete failure this frequency relationship is not observed since delamination hinders crack development. In view of this, it was thought desirable to carry out tests to the point when a visible crack developed with subsequent plotting of the damage curves (Fig. 2). As can be seen, the corrosion-fatigu e properties of a panel assembly vary with tension at the ribbed and plain sides. In order to establish the reasons for variation in corrosion-mechan ical properties through the thickness of the panel assembly a layer-layer analysis was carried out on thin (0.3 mm) specimens prepared in the same way as specimens for corrosion cracking tests. The strength properties through the thickness of the assembly are practically unchanged, whereas ductility varies uniformly from the greatest value at the ribbed surface to the least at the plain surface.

Intra- and extracytoplasmic microtubules in coleoptiles of Avena

A study is made of microtubules in normal young elongating cells of coleoptiles of Avena . In the cytoplasm are found large masses consisting entirely of microtubules. There are many strong indications that the microtubules can pass directly through the cell membranes. Extracytoplasmic microtubules are universally present in the outer, hyaline layer of the young cell wall. They show some degree of preferred orientation perpendicular to the surface of the wall, and in other cases in transverse and longitudinal direction parallel to the wall surface. Extracytoplasmic microtubules are also found sometimes in the vacuole, where they rapidly disintegrate. The implications of these findings with regard to problems of cell wall growth and cell elongation are discussed.

Radiation effects on strengths of boron-epoxy composites in various environments

Light weight, high strength boron-epoxy composites were irradiated in a nuclear reactor and then mechanically tested for strength. These boron-epoxy laminates, made by reinforcing an epoxy matrix with 15 plies of unidirectional boron filaments, were irradiated and tested under three different combinations of temperature which could occur in a nuclear-powered spacecraft using a cryogenic propellant. Specimens of group 1 were irradiated in air or water at ambient temperatures below 80 °C and were tested at room temperature, as were specimens of group 2 which were irradiated in liquid hydrogen at −253 °C. Specimens of group 3 were irradiated and tested in liquid nitrogen at −196 °C without an intermediate warmup. Mechanical strengths of all specimen groups were degraded primarily by thermal neutrons. For equivalent thermal-neutron fluences, flexural strengths in the longitudinal direction (parallel to boron filaments) were best for specimens of group 1, next best for those of group 2, and poorest for those of group 3. This order of degradation seems to be dictated by the more radiation-sensitive interlaminar shear strength, which measures epoxy-to-filament bonding. The order of damage above was reversed for transverse flexural strengths.

Carrying Capacity and Fracture of Notched Glass Fiber Composite Columns

A study was made of the carrying capacity and fracture of glass fiber composite notched columns having pinned-ends and loaded in compression. Apparently the cracks had a detrimental effect by lowering the maximum carrying capacity of the columns. However, these cracks, which were initially machined in the transverse direction at the center of the column, changed their direction of propagation with increasing load and continued their propagation in the longitudinal direction parallel to the glass fibers. A compari son of these tests results with those obtained previously on aluminum columns [1-3] is also given.