Short Bar Research Articles

The structure of tight junctions in the ciliary epithelium.

The tight junctions of the ciliary epithelium act as a barrier preventing the passage of blood borne macromolecules into the posterior chamber. The use of the freeze-fracture technique has led to a good knowledge of their morphological pattern in various species. However, in order to attempt a correlation of the morphology of the tight junctions with their physiological properties, their intimate substructure must be considered. As in other glutaraldehyde-fixed epithelia, the tight junctions appear as networks (variable in their apico-basal thickness) of more or less discontinuous P-face ridges and as complementary E-face furrows in which some particles or short bars are found. The significance of the discontinuities of ridges has been analysed. The continuity of the junctional fibrils was evident as assessed both by quantitative measurements as well as morphological examination of complementary fracture faces. In addition, the absence of loss of junctional material showed that the integrity of the junction was preserved during the freeze-fracture process, even in conditions where an increase in "transfer" of junctional elements was experimentally induced. Most of all, a "pore system" due to visualizable gaps in the fibrils is not tenable for the ciliary epithelium. Furthermore, the analysis of transition steps at the level of membrane "fusion" showed that the tight junctions of the ciliary epithelium must now be considered as formed by two slightly offset fibrils, one per adjacent plasma membrane.

Elevated temperature compressive steady state deformation and failure in the oxide dispersion strengthened alloy MA 6000E

A study of the compressive flow strength-strain rate behavior of the oxide dispersion strengthened (ODS) alloy MA 6000E has been conducted between 1144 and 1366 K. Specimens taken in the longitudinal, long transverse, and short transverse bar directions were tested at strain rates ranging from 2.1 × 10−5 s−1 to 2.1 × 10−7 s−1. The inherent compressive strength of MA 6000E was essentially independent of orientation. Testing at the higher temperatures and slower strain rates produced large scale cracking. Such cracks formed and propagated in bands in which slip had dissolved and redistributed the γ’ precipitates. Steady state deformation could be described through use of a threshold stress model of creep where threshold stresses were calculated as functions of temperature and orientation from the relatively fast flow stress-strain rate data and the assumption that the effective stress exponent was 3.5.

Torsion of a long cylindrical elastic bar partially embedded in a layered elastic half space

This is a study of the axially symmetric torsion of a long elastic cylindrical bar which is embedded in a layered elastic half space. The stress singularity factor at the embedded end of the bar is estimated by an existing method, and its effects on the solution are investigated. Such effects are found to be not so significant, especially for long bars and when the main concern is only on the torque-twist angle relationship. Even for rather short bars, the results given by this study agree well with those by an existing method, which is more rigorous but restrictive only to the case of an infinitely rigid bar.

A Two-Dimensional Numerical Analysis for Elastic Wave Propagation in Short Cylindrical Bars to a Longitudinal Impact

ホプキンソン圧縮棒(SHPB)法に対する一次元波動理論の適用限界を検討するために,短い円柱の一端の全面および同心円領域が縦衝撃を受ける場合の軸対称波動伝ぱ問題を従特性曲線法により解析した。特に同心円領域が衝撃を受ける場合について,円柱の直径に対する衝撃を受ける同心円の直径の比が衝撃応答に与える影響を調べ,SHPB法における試片と出力棒の直径比の適正値を求めた。また,実験を行い,本解析法の妥当性を確かめた。

Failure of graphite short bars with hemispherical seats

A very high-temperature gas-cooled reactor (VHTR) has been developed by Japan Atomic Energy Research Institute and its core consists of so-called fuel blocks, removable reflector blocks and so on. These graphite blocks are supported by thin cylindrical graphite bars called support posts. These posts are in contact with the blocks through hemispherical seats to absorb the relative displacement of blocks by small inclination or rotation of the posts. The reliability of support post structure of this kind is still uncertain, but it is considered to be important because they are unreplaceable through a reactor lifetime. Failure mechanism of support post under compressave load was studied by using 1/6-scale models made of homogeneous graphite. The Weibull distribution was assumed as a probability density function of fracture strength of support post. The followings are the main conclusions. 1. (1) The compressive fracture strength decreases with increasing of slenderness ratio. 2. (2) The compressive fracture strength was independent of a parameter ( 1 r p − 1/r s ): the difference of reciprocal radii of curvature at the post-end and the post seat. 3. (3) The compressive fracture strength remains almost constant within 0–2° of the inclined angle of support post. 4. (4) The failure of support post mostly occurred near the post-end. The volume effect of graphite material and the apparent change of slenderness ratio by oxidation were also discussed.

Effect of acid attack on concrete with different admixtures or protective coatings

Different admixtures and coatings were used in an attempt to improve the chemical resistance of a standard concrete mix. The admixtures included pulverised fuel ash, styrene butadiene latex, water reducing, super plasticising, retarding and water-proofing agents. Coatings, including PMMA and polymer emulsions, were brushed onto hardened concrete cubes. Forty 102 mm cubes containing the different admixtures or coatings were immersed in a channel with a 1% solution of continuously flowing sulphuric acid. Twenty cubes contained centrally positioned short mild steel bars. The changes in weight with time for each cube were determined continuously up to 172 days exposure, and the condition of the reinforcement was visually examined at termination. The effects of admixture aadditions on the workability and compressive strength of the concrete were also investigated.

Numerical Fracture Analysis of Chevron‐Notched Specimens: I, Shear Correction Factor, k

Numerical analyses are developed in both short bar and 4‐point bend bar cases to estimate the interlaminar shear correction factor k of chevron‐notched specimens with various kinds of geometry. The values of k were calculated by comparing the specimen compliances of Bluhm's slice models with those of finite element models. We elucidated the effect of surface boundary on k and modified the Bluhm's assumption. The modification has a slight influence on compliance, but is substantial when considering the stress intensity factor and elastic stored energy at fracture load. The present results give a basis for further consideration of the fracture behavior of chevron‐notched specimens. Part II is a discussion of the stability condition for crack growth of chevron‐notched specimens using the present results.

Compliance calibration of a family of short rod and short bar fracture toughness specimens

A family of short rod and short bar specimen geometries is defined for which the calibrations of all members of the family are equivalent. The family includes most of the short rod and short bar specimens now being used to test metallic materials. Experimental compliance vs crack length measurements were made for calibration purposes on members of the family and on specimens which purposely differed from the family in certain respects. The resulting calibrations are presented in a form which is readily usable in analyzing short rod/short bar fracture toughness tests. The calibrations of this study are used to correlate with previously published short rod calibrations. Very good agreement among compliance-derived calibrations was found, but the currently-used calibration based on comparison testing against ASTM E399 K Ic tests was found to be several percent lower than the compliance-based calibrations. Probable reasons for such a discrepancy are discussed, and recommendations are made concerning which calibration to use.

Torsion of an Infinite Solid Having a Rigid Cylindrical Inclusion of Finite Length

Axisymmetric torsion problem of an infinite solid having a rigid cylindrical inclusion of finite length is considered within the limits of the three dimensional elasticity theory. This problem relates to the torsional stress states in fiber reinforced composite materials containing discontinuous or broken fibers, and that of a short bar inserted in a hole. Harmonic stress function and the method of Fourier transforms are employed and the solution of the resultant dual integral equations is derived through a series expansion method. Numerical calculations are carried out for the stress distributions of practical importance. The effects of the presence of the inclusion on the uniform torsional stress field are also examined.

Comparison of fracture toughness of aluminium alloys from short bar and compact specimens

Comparison of fracture toughness of aluminium alloys from short bar and compact specimens

Extended range stress intensity factor expressions for chevron-notched short bar and short rod fracture toughness specimens

Extended range stress intensity factor expressions for chevron-notched short bar and short rod fracture toughness specimens

Probability summation and regional variation in contrast sensitivity across the visual field

Contrast sensitivity at different positions in the visual field has been measured at various spatial frequencies using a patch of grating suitably vignetted to give a stimulus localized in both space and spatial frequency. While contrast sensitivity along a vertical line through the fixation point falls off steadily from a maximum at the centre, sensitivity along a horizontal line displaced 42 periods of the grating above the fixation point is approximately constant, at least out to 32 periods from the mid-line. The way in which detectability increases with increasing number of cycles (2 up to 64) has been measured for gratings with short horizontal bars centred on the fixation point and for gratings with short vertical bars centred on the mid-line 42 periods above it. The relation between sensitivity and number of cycles can in each case be explained exactly assuming probability summation across space as long as the variation in sensitivity across the visual field is taken into account.

Determination of fracture toughness of high strength aluminum alloys with chevron notched short rod and short bar specimens

Fracture toughness of high strength aluminum alloys, determined with chevron-notched short bar and short rod specimens is in agreement with results from compact specimens only for K Ic < 30 MNm −3 2 . For higher K ic -values the short rod/short bar specimens exceed the K Ic -values up to 60%. The reason for the high short bar/short rod values is a rising crack growth resistance curve.

Displacements and normal stresses taking account of the shear of short thin-walled cylindrical shells and bars

Displacements and normal stresses taking account of the shear of short thin-walled cylindrical shells and bars

Compliance and stress intensity coefficients for short bar specimens with chevron notches

For the determination of fracture toughness especially with brittle materials, a short bar specimen with rectangular cross section and chevron notch can be used. As the crack propagates from the tip of the triangular notch, the load increases to a maximum then decreases. To obtain the relation between the fracture toughness Kic and maximum load Pmax, calculations of Srawley and Gross for specimens with a straight-through crack were applied to the specimens with chevron notches. For the specimens with a straight-through crack, an analytical expression was obtained. This expression was used for the calculation of the Kic−Pmax relation under the assumption that the change of the compliance with crack length for the specimen with a chevron notch is the same as for a specimen with a straight-through crack.

Performance of Chevron-Notch Short Bar Specimen in Determining the Fracture Toughness of Silicon Nitride and Aluminum Oxide

Abstract Ease of preparation and testing are advantages unique to the chevron-notch specimen used for the determination of the plane strain fracture toughness of extremely brittle materials. During testing, a crack develops at the notch tip and extends stably as the load is increased. For a given specimen and notch configuration, maximum load always occurs at the same relative crack length independent of the material. Fracture toughness is determined from the maximum load with no need for crack length measurement. Chevron notch acuity is relatively unimportant since a crack is produced during specimen loading. In this paper, the authors use their previously determined stress intensity factor relationship for the chevron-notch short bar specimen to examine the performance of that specimen in determining the plane strain fracture toughness of silicon nitride and aluminum oxide.

Impact Bending Test on Steel at Low Temperatures Using a Split Hopkinson Bar

By using a split Hopkinson bar type apparatus, impact bending tests of 0.45% carbon steel were carried out on U-notched annealed specimens and quenched-and-tempered ones. The load-deflection curves were determine easily by the tests. The temperature dependences of the yield load, the maximum load, the fracture load and the absorbed energy were determined within the temperature range from room temperature to -195°C. The absorbed energies agree fairly well with the ordinary Charpy values at these temperatures for both specimens. Repeated impact bending tests with a short striker bar were also carried out and it has become clear that the crack initiates at or slightly beyond the maximum load.

The tight junctions of rabbit choroid plexus and ciliary body epithelia. A comparative study using the double replica freeze-fracture technique

The spatial arrangement of tight junctions in choroid plexus and ciliary body rabbit epithelia has been determined by studying freeze-fracture complementary replicas. In the choroid plexus epithelium, the interruptions of the junctional P-face fibrils were measured to be 14% of their total length. In the ciliary body epithelium, where the fibrils were found to be more fragmented than in the choroid plexus, the P-face fibril interruptions accounted for 12 % of the total length of the zonulae occludentes sealing the non-pigmented cells and 30% in the focal linear tight junctions connecting the non-pigmented and pigmented cells at their apices. In both epithelia, the interruptions of the ridges are precisely complemented by particles or short bars of similar length found in the E-face furrows. Consequently, it is possible to conclude that the junctional fibrils are continuous in these two epithelia. For the zonulae occludentes, this continuity appears to be inconsistent with the ‘leaky’ properties of these epithelia shown by some physiological investigations.

A length aftereffect from grating adaptation: now you see it ... now you don't.

Adaptation to a grating of short bars has the effect of increasing the apparent length of a subsequently viewed test bar, and adaptation to a grating of long bars has the effect of decreasing the apparent length of a subsequently viewed test bar. However, decreasing the interspace between the long adaptation bars has the effect of (1) negating the length aftereffect and (2) reducing the apparent width of the test bar viewed by the retina previously adapted to the grating of long bars.

Cell junctions in the endothelia and connective tissue of the rat choroid plexus.

AbstractCell junctions between endothelial cells and between connective tissue cells (leptomeninges) of the rat choroid plexus were studied by freeze‐fracture. Special attention was paid to the problems of identifying fractured cell membranes and fracture faces. Tight junctions in arterioles are comprised of continuous small‐meshed networks of strands appearing as shallow grooves with aligned particles on E‐faces, and low ridges with some particles on P‐faces. In the fenestrated capillaries the tight junctions are represented by discontinuous, isolated slightly elevated ridges with some particles on P‐faces, and corresponding shallow grooves devoid of particles on E‐faces. Junctions in venules appeared as a less developed version of the junctions in the fenestrated capillaries. Extended areas of the meningeal cell membranes exhibit cell junctions. Tight junctions in this tissue are comprised of a loose discontinuous arrangement of isolated, often branched junctional elements. On P‐faces the elements appear as elongated crests with a distinct furrow running along the edge of the crest, occupied by a few particles. On E‐faces corresponding elongated impressions are present and occupied by aligned particles and a few short bars. The arrangement of these tight junction elements are not supportive of any significant barrier function. Small gap junctions occur “freely” in the membrane, or they are sometimes surrounded by tight junction elements. Very large gap junctions (up to about 10,000 particles) are mostly surrounded and interconnected by tight junctional elements. The possible significance of the variability of gap junction size, and the relation to tight junction elements is discussed.