Original Cross-sectional Area Research Articles

Flexural behavior of RC beams reinforced by ECC layer and steel plate: numerical simulation

PurposeThe combination of an Engineered Cementitious Composite (ECC) layer and steel plate to reinforce RC beams (ESRB) is a new strengthening method. The ESRB was proposed based on the steel plate at the bottom of RC beams, aiming to solve the problem of over-reinforced RC beams and improve the bearing capacity of RC beams without affecting their ductility.Design/methodology/approachIn this paper, the finite element model of ESRB was established by ABAQUS. The results were compared with the experimental results of ESRB in previous studies and the reliability of the finite element model was verified. On this basis, parameters such as the width of the steel plate, thickness of the ECC layer, damage degree of the original beam and cross-sectional area of longitudinal tensile rebar were analyzed by the verified finite element model. Based on the load–deflection curve of ESRB, ESRB was discussed in terms of ultimate bearing capacity and ductility.FindingsThe results demonstrate that when the width of the steel plate increases, the ultimate load of ESRB increases to 133.22 kN by 11.58% as well as the ductility index increases to 2.39. With the increase of the damage degree of the original beam, the ultimate load of ESRB decreases by 23.7%–91.09 kN and the ductility index decreases to 1.90. With the enhancement of the cross-sectional area of longitudinal tensile rebar, the ultimate bearing capacity of ESRB increases to 126.75 kN by 6.2% and the ductility index elevates to 2.30. Finally, a calculation model for predicting the flexural capacity of ESRB is proposed. The calculated results of the model are in line with the experimental results.Originality/valueBased on the comparative analysis of the test results and numerical simulation results of 11 test beams, this investigation verified the accuracy and reliability of the finite element simulation from the aspects of load–deflection curve, characteristic load and failure mode. Furthermore, based on load–deflection curve, the effects of steel plate width, ECC layer thickness, damage degree of the original beam and cross-sectional area of longitudinal tensile rebar on the ultimate bearing capacity and ductility of ESRB were discussed. Finally, a simplified method was put forward to further verify the effectiveness of ESRB through analytical calculation.

Generating waist area-dependent ground reaction forces for long-duration spaceflight

Prolonged microgravity exposure greatly weakens the bones and muscles of astronauts. This is a critical biomechanical issue for astronauts as they may be more prone to bone fractures. To combat this issue, lower body negative pressure (LBNP) is a concept that generates artificial gravitational forces that may help strengthen bones and muscles during long-term spaceflight. Negative pressure, defined as below ambient pressure, is applied within a chamber that encompasses the lower half of the body. By increasing the negative pressure, more ground reaction forces (GRFs) are generated beneath the subject’s feet. We hypothesize that increasing the cross-sectional area (CSA) of the subject’s waist will generate greater GRFs beneath the subject’s feet. Six healthy subjects volunteered to participate under two different experimental conditions: 1) original CSA of their waist and 2) larger CSA of their waist. In both conditions the subjects were suspended in a supine position (simulated microgravity) along with a weight scale beneath their feet. Negative pressures ranged from zero to 50 mmHg, increasing in increments of 5 mmHg. At −50 mmHg, original CSAs generated 1.18 ± 0.31 (mean ± SD) of their normal bodyweight. Subjects generated about one bodyweight at −45 mmHg using their original waist CSA. At −50 mmHg, larger CSAs generated 1.46 ± 0.31 of their normal bodyweight. Subjects generated about one bodyweight at −35 mmHg using their larger waist CSA. These data support our hypothesis. This novel technique may apply less stress to the cardiovascular system and conserve power for exercise in the spacecraft.

A Parylene Neural Probe Array for Multi-Region Deep Brain Recordings.

A Parylene C polymer neural probe array with 64 electrodes purposefully positioned across 8 individual shanks to anatomically match specific regions of the hippocampus was designed, fabricated, characterized, and implemented in vivo for enabling recording in deep brain regions in freely moving rats. Thin film polymer arrays were fabricated using surface micromachining techniques and mechanically braced to prevent buckling during surgical implantation. Importantly, the mechanical bracing technique developed in this work involves a novel biodegradable polymer brace that temporarily reduces shank length and consequently, increases its stiffness during implantation, therefore enabling access to deeper brain regions while preserving a low original cross-sectional area of the shanks. The resulting mechanical properties of braced shanks were evaluated at the benchtop. Arrays were then implemented in vivo in freely moving rats, achieving both acute and chronic recordings from the pyramidal cells in the cornu ammonis (CA) 1 and CA3 regions of the hippocampus which are responsible for memory encoding. This work demonstrated the potential for minimally invasive polymer-based neural probe arrays for multi-region recording in deep brain structures.

Ground Reaction Forces generated by a Lower Body Negative Pressure Exercise Device for Space Flight

Loss of bone and muscle are leading concerns among astronauts during prolonged space flight. Lower body negative pressure (LBNP) chambers generate gravitational and cardiovascular stresses to maintain musculoskeletal strength and fitness by means of suction pressure. Ground reaction forces (GRFs) generated underneath the user’s feet are directly proportional to the level of negative pressure applied. However, the exact mechanism of GRF generation remains unresolved. We hypothesize that increasing the cross‐sectional area (CSA) of the user’s waist in contact with a flexible waist seal will increase the GRFs generated at a given vacuum pressure. To test our hypothesis, we collected GRFs generated by 6 healthy subjects under two conditions: original (unchanged) CSA of their waist and a greater waist CSA using expanded cushioning around waist of the same subjects. GRFs were measured with LBNP levels ranging from 0 (ambient pressure) to 50 mmHg with subjects lying in supine position to simulate microgravity. The original CSA of 467.7 cm2 ± 69.0 cm2 generated 118 % ± 31 % body weight at −50 mmHg. However, the larger CSA of 1,451.0 cm2 ± 331.0 cm2 generated a mean GRF of 146 % ± 31% body weight at −50 mmHg. A one‐way ANOVA test resulted in p‐values < 0.05 for all pressures, denoting statistically significant increases in larger compared with original CSA GRF. The GRF generated with larger CSA followed this equation GRF = −1.8211 (LBNP) + 0.7899 while the GRF generated with original CSA followed the equation: GRF = −1.5079 (LBNP) + 0.3995. These data support our hypothesis that GRFs generated by LBNP are directly proportional to the waist CSA. Using this new concept, astronauts may generate GRFs at lower LBNP levels to prevent pre‐syncopal symptoms during exercise in space.Support or Funding InformationSupported by NASA grants NNX13AJ12G and NSSC19K0409.Average weight measurements with varying pressures for six volunteers; red is original CSA of subject's waist and blue is larger CSA.Figure 1

A revision of the conductive hearing loss in Cranium 4 from the Middle Pleistocene site of Sima de los Huesos (Burgos, Spain)

Pathological conditions have been previously documented in the Middle Pleistocene Sima de los Huesos hominins from northern Spain, and several of these have clear behavioral implications. Within this fossil assemblage, Cranium 4 shows bilateral external auditory exostoses which have been preliminarily interpreted as causing a significant hearing loss in this individual. If confirmed, this would be the oldest recorded case of deafness in human history and could have important implications for the antiquity of this condition, as well as social interactions. To further investigate this case, the current study presents 3D reconstructions of the entire outer and middle ear, based on computed tomography scans of both temporal bones in Cranium 4. We established the degree of stenosis in both external auditory canals, showing that in both cases the degree of stenosis is less than 52% of the original cross-sectional area of each canal. Based on clinical studies in living humans, the buildup of wax due to the degree of stenosis in Cranium 4 is unlikely to have caused frequent external ear infections. In addition, we estimated the pattern of sound power transmission up to 5 kHz in both ears relying on a comprehensive model developed in the bioengineering literature and which has been applied previously to the Sima de los Huesos hominins. The model was modified to account for the peculiar shape of the pathological external ear canals in Cranium 4. The results show that this pathology had little to no influence on the sound power transmission in this individual. Thus, we conclude that the exostoses present in both ears of Cranium 4 did not significantly affect their hearing.

Case Study of Concrete Repairs on Jetty in Port Nolloth, Northern Cape

This paper describes the rehabilitation of the jetty in Port Nolloth, Northern Cape. The history of the jetty is not 100% certain, but it is believed that the previous wooden jetty was replaced by the current concrete structure towards the late 1940’s. There were no as-built drawings of the jetty structure available. The jetty was in a deteriorated state and required a very thorough forensic investigation to determine the state of deterioration and to develop a design for the rehabilitation thereof. The forensic study, conducted by a specialist sub-contractor, included ferro-scanning (steel reinforcement number and spacing), core samples, non-destructive testing on the structure and visual inspections. From the investigation it was found that the concrete used for the jetty is generally of good quality (high strength, good compaction, and good aggregate distribution) and cover depths are in most locations in excess of 40 mm. However, after 60 years of marine exposure the structure suffers from very high chloride contamination and severe rebar corrosion damage. Previous repairs were found to generally have failed to offer any noteworthy protection to the structure. Large cracks, spalled concrete and exposed corroded steel reinforcement were evidence of the chloride contamination. A structural analysis to verify the jetty capacity was also completed and it was found that it is imperative that the original cross-sectional area of the piles is restored. The methods proposed and employed to rehabilitate the jetty were patch repair (trowel applied concrete and sprayed concrete), sectional casting of concrete (with formwork), and replacement of reinforcement. The work commenced mid-2016 and was substantially completed end of 2017.

Effect of heat treatment on the tensile strength of ‘Elgiloy’ orthodontic wire

ObjectiveElgiloy is the trade name of a cobalt–chromium–nickel superalloy that is offered for orthodontic use as wire. Despite some years of use, there is very little information in the dental literature on its mechanical properties, and especially on the effect of the hardening heat treatment (HT), that may be used after forming, on the tensile strength (TS) in relation to the four ‘tempers’ that are available. MethodsStraight lengths of round wire of the four available tempers, Blue, Yellow, Green and Red, were tested in direct tension at 5mm/min in air at 23°C to fracture, both as-supplied (AS) and with HT at 500°C for 5h, in air. HT was done in a high-uniformity, three-zone tube furnace in an alumina boat. The wires were then allowed to cool to room temperature in the boat, outside the furnace. The nominal (original cross-sectional area) peak stress was calculated. ResultsTS varied from 1.4 to 2.1GPa, AS, and 1.6 to 2.8GPa HT, according to temper, but with appreciable variation within tempers. Even so, the TS plot of HT vs. AS was very straight and of narrow distribution (intercept: −0.638±0.064GPa, slope: 1.575±0.036, r2: 0.994918, n=12, F=1957.7, p∼8×10−13). SignificanceThe strengthening due to HT was highly regular and TS can be reliably predicted on the basis of the AS value, but this of course cannot be known without specific batch testing. However, the unexpectedly large variation in the AS values within tempers renders such a prediction of lower reliability and usefulness in practice. Indeed, the distinction between tempers can be negligible, making selection according to application demands problematic, and differential property expectation less than certain. No such product data are provided commercially. Quality control is not as tight as might be expected. The implications for treatment need to be explored.

Determination of Constant Parameters of Copper as Power-Law Hardening Material at Different Test Conditions

Abstract In this paper a technique has been developed to determine constant parameters of copper as a power-law hardening material by tensile test approach. A work-hardening process is used to describe the increase of the stress level necessary to continue plastic deformation. A computer program is used to show the variation of the stress-strain relation for different values of stress hardening exponent, n and power-law hardening constant, α . Due to its close tolerances, excellent corrosion resistance and high material strength, in this analysis copper (Cu) has been selected as the material. As a power-law hardening material, Cu has been used to compute stress hardening exponent, n and power-law hardening constant, α from tensile test experiment without heat treatment and after heat treatment. A wealth of information about mechanical behavior of a material can be determined by conducting a simple tensile test in which a cylindrical specimen of a uniform cross-section is pulled until it ruptures or fractures into separate pieces. The original cross sectional area and gauge length are measured prior to conducting the test and the applied load and gauge deformation are continuously measured throughout the test. Based on the initial geometry of the sample, the engineering stress-strain behavior (stress-strain curve) can be easily generated from which numerous mechanical properties, such as the yield strength and elastic modulus, can be determined. A universal testing machine is utilized to apply the load in a continuously increasing (ramp) manner according to ASTM specifications. Finally, theoretical results are compared with these obtained from experiments where the nature of curves is found similar to each other. It is observed that there is a significant change of the value of n obtained with and without heat treatment it means the value of n should be determined for the heat treated condition of copper material for their applications in engineering fields.

Use of High-definition Computed Tomography to Assess Endotracheal Tube Luminal Narrowing after Mechanical Ventilation

202 July 2013 P and clearance of mucus are key mechanisms in the physiology of the respiratory system. Their regulation is often impaired in intubated patients who show superabundant production and inefficient clearance. As a result, a variably thick layer of mucus ultimately adheres to the inner surface of the endotracheal tube (ETT), reducing its original cross-sectional area. This luminal narrowing significantly impacts airflow resistance that varies inversely to the fourth power of the conduit’s radius according to the Poiseuille’s equation (ΔP = 8 μLQ(πr4)−1). Patient’s work of breathing may consequently increase.1 However, the importance of ETT progressive luminal narrowing during mechanical ventilation is still widely unrecognized, and currently used suctioning systems are unable to maintain the ETT function.2 To study the magnitude of this adverse event, we developed an innovative approach to visualize the accretion of mucus in extubated ETTs with high-definition computed tomography. The ETT is collected on extubation and sealed. Scanning is performed on a positron emission tomography-computed tomography scanner (Siemens, Malvern, PA), with resolution down to 15 μm. Multiplanar images of the ETT, particularly its lung end (terminal 10 cm), show the reduced inner diameter on coronal (fig. A) and transverse (fig. B) sections. 3D-volume rendering reconstructions of the lumen can also be obtained (fig. C). This technique precisely visualizes the morphology of the lumen and quantifies the existing amount of mucus. Measurements such as volume of secretions/air or minimum cross-sectional area can be collected, all of which may have exerted significant effects in vivo. High-definition computed tomography may also be useful to study the efficacy of devices for the maintenance of the ETT function.3

Influence of material transition and interfacial area changes on flow and concentration in electro-osmotic flows

This paper presents a numerical study to investigate the effect of geometrical and material transition on the flow and progression of a sample plug in electrokinetic flows. Three cases were investigated: (a) effect of sudden cross-sectional area change (geometrical transition or mismatch) at the interface, (b) effect of only material transition (i.e. varying ζ-potential), and (c) effect of combined material transition and cross-sectional area change at the interface. The geometric transition was quantified based on the ratio of reduced flow area A2 at the mismatch plane to the original cross-sectional area A1. Multiple simulations were performed for varying degrees of area reduction i.e. 0–75% reduction in the available flow area, and the effect of dispersion on the sample plug was quantified by standard metrics. Simulations showed that a 13% combined material and geometrical transition can be tolerated without significant loss of sample resolution. A 6.54% reduction in the flow rates was found between 0% and 75% combined material and geometrical transition.

Local small airway epithelial injury induces global smooth muscle contraction and airway constriction

Small airway epithelial cells form a continuous sheet lining the conducting airways, which serves many functions including a physical barrier to protect the underlying tissue. In asthma, injury to epithelial cells can occur during bronchoconstriction, which may exacerbate airway hyperreactivity. To investigate the role of epithelial cell rupture in airway constriction, laser ablation was used to precisely rupture individual airway epithelial cells of small airways (<300-μm diameter) in rat lung slices (∼250-μm thick). Laser ablation of single epithelial cells using a femtosecond laser reproducibly induced airway contraction to ∼70% of the original cross-sectional area within several seconds, and the contraction lasted for up to 40 s. The airway constriction could be mimicked by mechanical rupture of a single epithelial cell using a sharp glass micropipette but not with a blunt glass pipette. These results suggest that soluble mediators released from the wounded epithelial cell induce global airway contraction. To confirm this hypothesis, the lysate of primary human small airway epithelial cells stimulated a similar airway contraction. Laser ablation of single epithelial cells triggered a single instantaneous Ca(2+) wave in the epithelium, and multiple Ca(2+) waves in smooth muscle cells, which were delayed by several seconds. Removal of extracellular Ca(2+) or decreasing intracellular Ca(2+) both blocked laser-induced airway contraction. We conclude that local epithelial cell rupture induces rapid and global airway constriction through release of soluble mediators and subsequent Ca(2+)-dependent smooth muscle shortening.

Numerical Simulations of Misalignment Effects in Microfluidic Interconnects

AbstractNumerical simulations were performed to see the effect of geometrical misalignment in pressure driven flows. Geometric misalignment effects on flow characteristics arising in three types of interconnection methods a) end-to-end interconnection, b) channel overlap when chips are stacked on top of each other, and c) the misalignment occurring due to the offset between the external tubing and the reservoir were investigated. For the case of end-to-end interconnection, the effect of misalignment was investigated for 0, 13, 50, 58, and 75% reduction in the available flow area at the location of geometrical misalignment. In the interconnection through channel overlap, various possible misalignment configurations were simulated by maintaining the same amount of misalignment (75% flow area reduction) for all the configurations. The effect of misalignment in a Tube-in-Reservoir interconnection was investigated by positioning the tube at an offset of 164μm from the reservoir center. All the results were evaluated in terms of the equivalent length of a straight pipe. The effect of reynolds number (Re) was also taken into account by performing additional simulations of aforementioned cases at reynolds numbers ranging from 0.075 to 75. The results are interpreted in terms of equivalent length (Le) as a function of Re and misalignment area ratio (A1:A2), where A1 is the original cross-sectional area of the channel and A2 is the available flow area at mismatch location. Equivalent length calculations revealed that the effect of misalignment in tube-in-reservoir interconnection method was the most insignificant when compared to the other two methods of interconnection

Americans should be proud of their accomplishments in soil conservation: A tale of two regions

Over the past 30 or so years, Americans have been subjected to dire assessments of current soil erosion (Trimble and Crosson 2000). Dirt, an interesting new book by David Montgomery, is more objective and moderate, but it still leaves a somewhat negative slant in that one would not know just how much improvements have occurred in the United States. For example, the book includes a map of the Southern Piedmont showing that it lost an average of 18 cm (7 in) of soil to historical erosion. While that's true, what he doesn't tell us is that most of that soil had eroded by the early 20th century and that erosion there has been arrested relative to the 19th century. Another region barely mentioned in passing by Montgomery is the Northern Mississippi Valley Loess Hills (Driftless Area). Settled in the1850s, erosion there was so rampant in the early 20th century that some stream valleys were being buried at rates averaging 15 cm (6 in) per year. Roads, bridges, mills, houses, farms, even villages, were sometimes buried or made unusable within a few years. Tributary stream channels were often eroded to several times their original cross-sectional area, furnishing even more sediment to …

Americans should be proud of their accomplishments in soil conservation: A tale of two regions

Over the past 30 or so years, Americans have been subjected to dire assessments of current soil erosion (Trimble and Crosson 2000). Dirt, an interesting new book by David Montgomery, is more objective and moderate, but it still leaves a somewhat negative slant in that one would not know just how much improvements have occurred in the United States. For example, the book includes a map of the Southern Piedmont showing that it lost an average of 18 cm (7 in) of soil to historical erosion. While that's true, what he doesn't tell us is that most of that soil had eroded by the early 20th century and that erosion there has been arrested relative to the 19th century. Another region barely mentioned in passing by Montgomery is the Northern Mississippi Valley Loess Hills (Driftless Area). Settled in the1850s, erosion there was so rampant in the early 20th century that some stream valleys were being buried at rates averaging 15 cm (6 in) per year. Roads, bridges, mills, houses, farms, even villages, were sometimes buried or made unusable within a few years. Tributary stream channels were often eroded to several times their original cross-sectional area, furnishing even more sediment to …

Conversion of Elongation Values for Cold-Rolled Low Carbon Steel Sheets

Abstract It is often difficult or impossible to prepare tension test pieces from flat steel products to specified standard size due to inadequate sample piece size. Hence several sizes of test pieces yielding different gage lengths are envisaged. However, the value of the total elongation beyond maximum stress in tension testing depends on the gage length due to the effect of necking. Acceptance values of elongation at fracture for flat steel products are therefore specified together with corresponding gage lengths, e.g., 50 or 80 mm (fixed gage lengths) and k So (proportional gage lengths) where k takes the value of 4.00, 5.65, 8.16, or 11.30 and k √SO is the original cross-sectional area of the test piece in mm2. Methods for converting room temperature percentage elongation at fracture obtained on various proportional and nonproportional gage lengths to other gage lengths exist for austenitic, carbon, and low alloy steels as hot-rolled, normalized, annealed, etc., but not as cold-reduced. These methods are also not valid where the gage length is greater than 25 times √SO or where the width-to-thickness ratio of the test piece is greater than twenty. This paper proposes a possible solution for cold-rolled low carbon steel sheets of thickness less than 2.0 mm, which continue to be, if not the major, one of the major raw materials in the automotive industry. The solution lies in the modification of the exponent in the Oliver formula used for flat steel products other than cold-rolled low carbon steel sheets.

Equilibrium and cross-sectional stability of tidal inlets: application to the Frisian Inlet before and after basin reduction

The focus of this paper is on the adaptation of the inlet cross-sectional area after basin reduction. To calculate the new equilibrium and degree of stability, use is made of a method first proposed by Escoffier. As part of this study his largely empirical approach is expanded and given a physical basis. The inlet channel is divided in an entrance and interior section. Sand enters the entrance section on the flood and is removed by the ebb tidal current. On annually average basis, the volume of sand entering the inlet is assumed to be a constant fraction of the littoral drift. A theoretical expression for the ebb tidal sand transport as a function of the tidal velocity amplitude and a length dimension of the cross-section is derived. An important ingredient in the stability analysis is the empirical cross-sectional area versus tidal prism relationship for inlets in equilibrium and the related equilibrium velocity. A physical justification for this relationship is presented. As a measure for cross-sectional stability, a stability index, S, is introduced. For S≥1, the inlet is very stable. Stability increases with increasing values of S. For inlets that are very stable, the value of S can be related to P/ V, i.e. the ratio of tidal prism and volume of littoral drift. A method to determine the time scale for the entrance section to return to a new equilibrium after a change in basin surface area is presented. To illustrate its practical use, the Escoffier method is applied to the Frisian Inlet before and after basin reduction. In 1969, the basin area and tidal prism were reduced by approximately 30%. Based on the Escoffier method, the original equilibrium cross-sectional area of 22,000 m 2 is expected to reduce to 15,500 m 2. The adaptation time scale is estimated to be 30 years. Even after basin reduction, the inlet remains very stable with S=31 and P/ V=585.

Correction factor suggestion for ACI development length provisions based on flexural testing of RC slabs with various levels of corroded reinforcing bars

Reinforcement corrosion is a major influencing factor in deterioration of reinforced- and prestressed-concrete structures. Concrete structures exposed to chlorides from seawater, deicing chemicals, salt, salt water, brackish water, or spray from these sources are more vulnerable to corrosion. The corrosion characteristics of corroded reinforcing bars are a very important topic in the durability and strength of concrete structures. Both experimental and analytical studies on this topic, however, are scarce to the point of nonexistence. In order to qualitatively and quantitatively understand the effect of corrosion level on the bond strength and development length in RC slab members, a series of tests are carried out. The reinforcing bar of the specimen is corroded after concrete casting. One type of reinforcing bar HD10 is corroded to 1%, 2%, 3%, 5%, 7%, 10%, and 15% of its original cross-sectional area of the reinforcement using current-induced accelerated corrosion technique. After the effective corrosion is applied, flexural tests are performed. The analysis results show that the effect of corrosion level on bond strength and development length was apparent. In addition, after 2% corrosion level, the current design code for development length should be reviewed and more studies are needed in the future for verification.

Correction factor suggestion for ACI development length provisions based on flexural testing of RC slabs with various levels of corroded reinforcing bars

Reinforcement corrosion is a major influencing factor in deterioration of reinforced- and prestressed-concrete structures. Concrete structures exposed to chlorides from seawater, deicing chemicals, salt, salt water, brackish water, or spray from these sources are more vulnerable to corrosion. The corrosion characteristics of corroded reinforcing bars are a very important topic in the durability and strength of concrete structures. Both experimental and analytical studies on this topic, however, are scarce to the point of nonexistence. In order to qualitatively and quantitatively understand the effect of corrosion level on the bond strength and development length in RC slab members, a series of tests are carried out. The reinforcing bar of the specimen is corroded after concrete casting. One type of reinforcing bar HD10 is corroded to 1%, 2%, 3%, 5%, 7%, 10%, and 15% of its original cross-sectional area of the reinforcement using current-induced accelerated corrosion technique. After the effective corrosion is applied, flexural tests are performed. The analysis results show that the effect of corrosion level on bond strength and development length was apparent. In addition, after 2% corrosion level, the current design code for development length should be reviewed and more studies are needed in the future for verification.

Elastic behaviour of sport surface materials

During locomotion, the contact forces between the foot and ground are three-dimensional. However, previous studies quantifying the force-deformation behaviour of shoe and/or surface materials have involved single, uniaxial tests. Many of these studies have also been subject to errors due to boundary conditions. Elastomeric foams used in sport shoes and surfaces are highly compressible and nonlinear, and behave differently under tension and compression. Therefore, the purposes of this paper were to develop an objective set of measures to determine the three-dimensional elastic behaviour of these materials, and to use the method to quantify the behaviour of three materials used in a specific synthetic running track. Unconfined compression and tension, and confined compression loading tests were performed on standard-sized samples. Longitudinal and transverse stretch were determined from the loading apparatus and/or from analysis of images taken during the test. Nominal stress was calculated from original cross-sectional area and loading force. A method to determine the bimodal, nonlinear and compressible behaviour of the materials used in sport shoes and surfaces has not been presented before. This study is the first to quantify the complete elastic behaviour for materials used in running surfaces.

Prevention of chronic cerebral vasospasm in dogs with milrinone.

Delayed cerebral ischemia resulting from vasospasm is a major cause of morbidity and death in patients with aneurysmal subarachnoid hemorrhage. Milrinone, because it inhibits Type IV cyclic adenosine monophosphate-specific phosphodiesterase enzyme in both cardiac and vascular smooth muscle, is a powerful inotrope and vasodilator, but it has little effect on heart rate or blood pressure. Because of these properties, milrinone is an attractive potential therapy after subarachnoid hemorrhage. The purpose of the present study was to investigate the effect of milrinone on chronic experimental cerebral vasospasm. A double-hemorrhage canine model of vasospasm was used to study the efficacy of milrinone. Angiographic vasospasm and systemic hemodynamics were compared in a treatment group of animals that received a loading dose of milrinone (0.05 mg/kg, intravenously) and then slow-release (0.05 microgram/kg/min) milrinone pellets (n = 10) and a control group that received placebo pellets (n = 9), over an 8-day period after the initial subarachnoid hemorrhage. The hemorrhage was created by injection of 4 ml of autologous, nonheparinized, arterial blood into the cisterna magna on Days 1 and 3. Hemodynamic measurements, including cardiac output determinations, were made on Days 0, 1, 3, 6, and 8 with a pulmonary artery catheter, and angiographic vasospasm was assessed on Day 8 by comparison with baseline angiograms. Treatment with milrinone caused no significant changes in systemic hemodynamics. Angiographic vasospasm, however, was significantly reduced in the Day 8 angiograms for the treated group, compared with the control group (98.28 +/- 14.06 and 67.89 +/- 13.06% of original vessel cross-sectional area, respectively; P < 0.001). Milrinone is effective in preventing chronic cerebral vasospasm in a canine model of experimental chronic cerebral vasospasm. This effect is independent of changes in systemic hemodynamics. Milrinone and related drugs warrant further investigation for the treatment of cerebral vasospasm.