Second Series Of Tests Research Articles

Saturation and Preloading Effects on the Cyclic Behavior of Sand

In order to study pore water pressure response and liquefaction characteristics of sand, which has previously experienced liquefaction, two series of cyclic triaxial tests were run on medium dense sand specimens. In the first test series the influence of the soil saturation under undrained cyclic loading has been studied. It summarizes results of cyclic triaxial tests performed on Hostun-RF sand at various values of the Skempton’s pore-pressure coefficient. Analysis of experimental results gives valuable insights on the effect of soil saturation on sand response to undrained cyclic paths. In the second series of tests, the preloading influence on the resistance to the sands liquefaction has been realized on samples at various histories of loading. It was found that a large preloading induces a reduction of the resistance of sands to liquefaction.

Influence of grouting condition on crack and load-carrying capacity of post-tensioned concrete beam due to chloride-induced corrosion

Chloride-induced corrosions of a sheath and a prestressing tendon in post-tensioned concrete (PC) beams are investigated under different grouting conditions. Two series PC beams were tested by the electrically accelerated corrosion. The first series of accelerated corrosion tests were performed to determine the influence of grouted ratios in a straight sheath on the corrosion of the sheath and the prestressing tendon. In the second series of tests, the influence of the length of grout filling was investigated in a curved sheath on the corrosion process. After the accelerated corrosion tests, the mechanical behavior of the deteriorated PC beams was investigated under flexural loading. The results of the experiments show that corrosion of the sheath and the prestressing tendon significantly decreases the load-carrying capacity of PC beams. As the grouted ratios in the straight sheath and the length of grout filling in the curved sheath increase, the cracks due to corrosion of the sheath propagate earlier along the prestressing tendon and the width of the cracks increases. From the view point of load-carrying capacity, it is verified that proper grouting can protect a prestressing tendon from corrosion despite the wider cracks due to corrosion of the sheath. The presence of water inside the sheath leads to increased corrosion of both the sheath and the prestressing tendon, resulting in the decrease in the load-carrying capacity of the PC beam.

Operation of Membrane Bioreactor with Powdered Activated Carbon Addition

The effect of powdered activated carbon (PAC) addition to the activated sludge (AS) in a membrane bioreactor (MBR) has been investigated. The long term nature of the tests allowed the PAC to gradually incorporate into the biofloc forming biologically activated carbon (BAC). One series of tests involved 4 bench scale (2 L) MBRs operated at sludge retention times (SRTs) of 30 days with PAC inventories of 0, 1, 3 and 5 g/L and steady state biomass concentrations of 12.0±1.0 g/L. The characteristics of the mixed liquors (MLSS) from the 4 reactors were compared. Short term filtration tests, including measurement of specific cake resistance (SCR), flux decline profile, and irreversible fouling resistance in an unstirred cell and “sustainable” flux (by monitoring transmembrane pressure (TMP) rise) in a crossflow cell all showed better filtration performance for the MLSS with BAC compared with the AS alone. In terms of SCR and flux decline profile the 1 g/L PAC addition performed best, but in terms of minimizing irreversible membrane fouling and maximizing “sustainable” flux the 5 g/L PAC was best. All 4 systems showed lower total organic carbon (TOC) in the permeate compared to the bioreactors, but the lowest permeate TOC (and the best removal) was for the highest PAC loading. The benefit of PAC addition was confirmed in a second series of tests with two 20 L MBRs with submerged hollow fibers, one operated without PAC, the MBR(AS), and the other with 5 g/L PAC, the MBR(BAC). For an SRT of 30 days (which involved 3.3% sludge wastage per day and 3.3% new PAC addition per day) and a fixed flux of 21 L/m2hr the MBR(AS) showed a TMP rise of about 2.4 kPa/day whereas the MBR(BAC) showed a rise of only 0.8 kPa/day. However when the MBRs were operated without wastage the performance of the MBR(BAC) was worse than the MBR(AS). Thus the improved performance of the MBR(BAC) requires regular replenishment of aged BAC with fresh PAC.

Air ingress benchmarking with computational fluid dynamics analysis

The air ingress accident is a complicated accident scenario that may limit the deployment of high-temperature gas reactors. The complexity of this accident scenario is compounded by multiple physical phenomena that are involved in the air ingress event. These include diffusion, natural circulation, and complex chemical reactions with graphite and oxygen. In an attempt to better understand the phenomenon, the FLUENT-6 computational fluid dynamics code was used to assess two air ingress experiments. The first was the Japanese series of tests performed in the early 1990s by Takeda and Hishida. These separate effects tests were conducted to understand and model a multi-component experiment in which all three processes were included with the introduction of air in a heated graphite column. MIT used the FLUENT code to benchmark these series of tests with quite good results. These tests are generically applicable to prismatic reactors and the lower reflector regions of pebble-bed reactors. The second series of tests were performed at the NACOK facility for pebble bed reactors as reported by Kuhlmann [Kuhlmann, M.B., 1999. Experiments to investigate flow transfer and graphite corrosion in case of air ingress accidents in a high-temperature reactor]. These tests were aimed at understanding natural circulation of pebble bed reactors by simulating hot and cold legs of these reactors. The FLUENT code was also successfully used to simulate these tests. The results of these benchmarks and the findings will be presented.

The role of SAPL as a boundary lubricant in prosthetic joints

The purpose of this study was to test the potential of the body's natural lubricant, surface-active phospholipids (SAPL), to decrease friction in prosthetic joints by acting as a boundary lubricant, and to test the interaction of SAPL with Pyrolytic Carbon (PyC), a new material used in artificial heart valves and joint replacements of the upper limb. Initial testing [Coller R, Hargreaves DJ, Hills BA, Crawford RW. Is SAPL the boundary lubricant in prosthetic joints: friction testing and surface rinsing. Australian Journal of Mechanical Engineering 2004;1:63–71] slid ultra-high molecular weight polyethylene (UHMWPE) pins against highly polished stainless steel plates (surface roughness of 0.01 μm). This second series of tests was a continuation of previous research, validating the results and expanding the experiments to investigate the interaction of SAPL with PyC. In both cases, a Hounsfield test rig was used to perform the tests at ambient room conditions and at 37 °C. In both series of tests, comparative friction measurements were made using a synthetic SAPL, dipalmitoyl phosphatidylcholine (DPPC) with saline and saline only as the lubricants. When DPPC was used, the friction was reduced by 50% for the UHMWPE/SS combination, and was reduced by more than 75% for the UHMWPE/PyC combination, suggesting that DPPC acts as an effective boundary lubricant. This recent study, along with previous testing [Coller R, Hargreaves DJ, Hills BA, Crawford RW. Is SAPL the boundary lubricant in prosthetic joints: friction testing and surface rinsing. Australian Journal of Mechanical Engineering 2004;1:63–71], strongly suggests that SAPL has the ability to decrease friction in prosthetic joints by acting as a boundary lubricant, and that SAPL interacts favourably with PyC.

Estimation of the Transmissibility of Anti-Vibration Gloves when Used with Specific Tools

Anti-vibration gloves are increasingly being used as personal protective equipment to help reduce the hazards of hand-transmitted vibration. A vibration transfer function method for estimating the tool-specific performance of anti-vibration gloves has been proposed to help select appropriate gloves for particular tools and to assess the potential risks posed by tool vibration. This study evaluates the validity of the method by comparing the predicted vibration transmissibility with the measured value. Two typical vibration-attenuating gloves (air-bladder and visco-elastic material gloves) were used in the study. Two series of experiments were performed for the evaluation. In the first series, the isolation efficiency of selected anti-vibration gloves was evaluated in the laboratory under synthesized handle vibration spectra of six different tools. The second series of tests involved the measurement of the glove transmissibility, while operating two different pneumatic chipping hammers. The results of the study show reasonably good agreements between the predicted and measured acceleration transmissibility values of the candidate gloves. It is thus concluded that the transfer function method provides a reasonably good estimate of vibration attenuation performance of gloves for specific tools.

Influence of the coating material on the loosing of dental implant abutment screw joints

Dental implant abutment screw joints tend to loosen and prosthesis rotation has been observed under clinical conditions. Some dental implant manufacturers suggest coated abutment screw to prevent the displacement of dental prosthesis. In the present work, the opening torque (N cm) was measured as a function of tightening torque (N cm) for dental implant abutment screws coated with four different materials (TiC, TiCN, Teflon and Parylene) to clarify the influence of the coating material on abutment screw stability and to analyze the relationship between preload and opening torque. On a first series of tests, closing and opening torque (N cm) of abutment screws without coating and with coating tightened to 20, 30, 32, 35 and 40 N cm was recorded. In a second series of tests, changes in opening torque values were analyzed after successive closures that were tightened at constant values of 30, 32 and 35 N cm. On a third series of tests, abutment screws without coating and with Teflon coating were tightened to 32 N cm and submitted to cyclic loading. The results showed that for all abutment screws the opening torque was less than the tightening torque. For a given applied tightening torque (35 N cm), the screws without a coating had the highest opening torque (31.6 ± 0.9 N cm [mean ± S.D.]). The screw coated with TiN had the smallest average opening torque (12.2 ± 0.6 N cm) after tightening at 20 N cm. A progressive decrease in opening torque values was measured in all screw groups after repeated closures. After six retightenings (35 N cm) a statistically significant difference ( P < .05) was observed in opening torque among uncoated Ti screw group (31.5 ± 0.6 N cm) and coated screw tested groups (Parylene = 29.6 ± 0.4, Teflon = 29.1 ± 0.7). Under cyclic loading Ti screws without coating are more stable than Teflon coated screws. The present work suggests that one must be aware of the magnitude of the opening torque when specifying a certain coating/preload combination. The present methodology shows how to calculate the relevant quantities.

Experimental result on rewetting of hot surfaces by droplet impingement

The paper is dealing with a research carried out at the Institute of Thermal-Fluid Dynamics of ENEA (Casaccia Center) to investigate the rewetting of a hot surface cooled with droplet impingement. After the droplet impingement, the liquid film falls along the surface. The reference situation is the external surface of a tank which, after a fire, is subjected to flames or high temperature anyway, and is cooled with water or an extinguishing liquid. The experiment is characterized by a one-dimensional liquid spray, i.e., droplets having a uniform, constant diameter, impinging on the heated surface. The cooling rate of the hot surface has been detected as a function of wall temperature, droplet diameter and velocity, and point of impact of the spray on the heated surface. The working principle of such a spray is based on the varicose rupture of a liquid jet (Rayleigh–Weber instability): imposing a periodic perturbation of appropriate amplitude and frequency on the jet surface, the flow is “constrained” to break soon after leaving the nozzle, eventually obtaining constant diameter drops, depending, for a given liquid, on the nozzle diameter and liquid velocity. Dimensions of droplets used in the present work range from about 0.3 to 1.5 mm. A digital image system allows to know, for each nozzle, droplet diameter and aspect ratio. Each nozzle disk is manufactured in order to have the same cross flow area independent of the number of nozzles in the disk. The rewetting velocity has been calculated from the response of the thermocouples placed on the heated wall and from a digital image system based on the video image registered during the runs. A comparison of the two methods is provided. Two different locations of the jet impingement on the heated surface are tested. The spray is impinging outside the heated length, just upstream the copper clamp in one series of tests, while in a second series of tests the spray impinges directly on the first wall thermocouple, 25 mm below the beginning of the heated length. Prediction of the rewetting velocity obtained using available correlations has shown a good agreement with experimental data.

Taste and odour testing: how valuable is training?

Correct identification of specific tastes and odours in a water supply can be a powerful tool in identifying the cause of the problem and facilitating rapid remediation. While taste and odour identification can be achieved by laboratory testing, consumer involvement is not only worthwhile as a public education exercise but can also indicate tastes and odours to which the public do not object. Interpretation of taste and odour results is a complex process. The Australian Water Quality Centre (AWQC), based in Adelaide, South Australia, has established a flavour profile panel, trained in Flavour Profile Analysis (FPA). This group was chosen to carry out a survey of tastes and odours present in selected Australian water supplies and laboratory treated water and bottled water. The waters were also assessed by a group of untrained volunteers to simulate the responses of consumers. In two series of tests there were significant differences in responses between the groups with respect to the intensity of the tastes and odours detected. In both instances the responses by the trained group were more consistent, making interpretation of results more straightforward. In the second series of tests the panellists were also asked their personal preferences. The results showed in general the preferred waters were those with minimal taste and odour and this was generally irrespective of the type of taste and odour present.

Un nouvel implant pour les fractures de l’humérus proximal : la plaque à corbeille: Étude expérimentale

Purpose of the study We conducted a comparative study of three ostheosynthesis systems for proximal humeral fractures. The conclusions led to the elaboration of a rigid extramedullary osteosynthesis implant. This novel implant allows specific fixation of the tuberosities via six adjustable and removable hooks organized like a basket. There are two versions, with and without a central cephalic locking screw. We report two static biomechanical studies conducted to analyze this material. Material and methods The two studies were performed on fresh frozen cadaver specimens with known bone density and with an experimental model of a four-fragment fracture of the proximal humerus. The first tests were designed to measure axial pressure reproducing the physiological movement applying the most stress on the head of the humerus. This allowed a global analysis of the mechanical behavior of the implant and an assessment of the contribution of the central cephalic locking screw. The second series of tests were traction tests used to analyze the behavior of the tuberosities fixed with the hooks. We assess the assemblies by measuring the mechanical resistance: rigidity of the fixation was recorded in mm/100N. Pre- and post-procedure x-rays and photographs were obtained to allow a subjective assessment of fragment displacement. Results The first series of tests demonstrated that the implant, with the central cephalic locking screw, presented good overall mechanical properties. The notion of better stability of the tuberosities obtained with the hooks, as seen during the first tests, was reinforced by the data from the second tests, although no statistically significant difference was demonstrated. We also noted that there was no statistically significant correlation between bone density and the slopes of the force-resistance curves. Discussion This prototype implant has an overall mechanical resistance equivalent to the reference implant, with at least equivalent performance. Proof of the usefulness of the central locking screw was not established, even though improved tolerance to loading by better force distribution seemed apparent. The contribution of the hook basket was not demonstrated. Data from the observations do however suggest the expectations of the implant will be fulfilled. Tests conducted on a larger scale would probably demonstrate a difference. It is clear that the small number of implants used here limited the study. Comparison with data in the literature show that this new prototype is adapted to the mechanics of the proximal humerus. Resistant to physiological stress, the implant allows pendular movement and passive physical therapy during the early post-operative period.

Compressive behavior of pultruded composite plates with circular holes

Compressive behavior of E-glass fiber/isophthalic polyester resin matrix pultruded composite sheet material is reported for two thicknesses. The effect of circular holes on compressive strength and failure strain was also investigated. In the first series of tests, compression tests were performed with plate specimens without any hole. These specimens were instrumented with several pairs of back-to-back axial strain gages at different locations on the surface of the specimen to capture global buckling (if any) during compression. In the second series of tests, plate specimens with circular holes were prepared. A wide range of diameter to width ratio of D/ W=0.075–0.75 was chosen. The open-hole specimens were also instrumented with several strain gages (combination of single and strip gages) in and around the surface of the hole to determine the strain distribution, strain concentration factor, transverse and through-the-thickness normal strain, etc. A relationship between the compressive strength and hole-diameter was established, and compared with the base line material properties. Finally, an attempt was made to determine the compressive failure initiation mechanisms and failure progression mechanisms in the presence of holes through sectioning and examining under a stereo microscope.

Susceptibility of stored-product beetles on wheat and maize treated with thiamethoxam: effects of concentration, exposure interval, and temperature

Sitophilus zeamais Motschulsky, the maize weevil, Oryzaephilus surinamensis (L.), the saw-toothed grain beetle, and Tribolium castaneum (Herbst), the red flour beetle, were exposed for 1, 2, 3, and 6 d at 22°C, 27°C, and 32°C on maize treated with 0, 0.5, 1.0, 2.0, or 4.0 ppm thiamethoxam, a new-generation neonicotenoid insecticide. A second series of tests was conducted on hard winter wheat using S. oryzae (L.), the rice weevil, Rhyzopertha dominica (F.), the lesser grain borer, and T. castaneum. Mortality of all species on both commodities generally increased with insecticide concentration, exposure interval, and temperature, and data were described by linear and non-linear regressions with concentration as the independent variable. Mortality of S. zeamais ranged from 58% to 90% on maize treated with 0.5 ppm thiamethoxam, and approached 95–100% as concentration increased to 4 ppm. Oryzaephilus surinamensis appeared to be slightly less susceptible than S. zeamais; mortality ranged from about 18% to 80% at 5 ppm and there was a more gradual increase in mortality as concentration increased. Mortality of T. castaneum generally did not exceed 40% at any concentration unless the beetles were exposed for 6 d. Mortality of R. dominica and S. oryzae was less than 60% when exposed on treated wheat for 1 and 2 d, but increased to nearly 100% when exposed for 6 d at 27°C and 32°C. Mortality of T. castaneum did not exceed 20% at the 1- and 2-d exposures, and approached 100% only when beetles were exposed for 6 d at 32°C. Few F 1 adults of any species were found in treated maize or in treated wheat but the number of F 1 T. castaneum in untreated maize and untreated wheat was very low compared with the other species. Results show that thiamethoxam would be an effective protectant of stored maize seed and stored wheat seed.

Experimental Study of Mechanical Behaviour of Rock Joints Under Cyclic Loading

Evaluation of the effects of small repetitive earthquakes on the strength parameters of rock joints in active seismic zones is of interest of the designers of underground constructions. In order to evaluate these effects, it is necessary to study the behaviour of rock joints under dynamic and cyclic loadings. This paper presents the results of a systematic study on the behaviour of artificial rock joints subjected to cyclic shearing. More than 30 identical replicas have been tested using triaxial compression devices under different conditions of monotonic and cyclic loading. At the first stage a few samples have been tested in monotonic loading modes under various confining pressures and rate of displacement. In the second series of tests, small cyclic loads were applied on the samples for increasing number of cycles, frequency levels and stress amplitudes. These were then followed by monotonic loading again. The variations of maximum and residual shear strengths for each test have been studied. The results show increase of shear strength as a result of the increase in confining pressure and they display decrease of shear strength due to the increase of rate of loading, number of cycles, frequency levels and stress amplitudes.

Bond between Carbon Fiber Reinforced Polymer Bars and Concrete. I: Experimental Study

The bond characteristics of four different types of carbon fiber reinforced polymer (CFRP) rebars (or tendons) with different surface deformations embedded in lightweight concrete were analyzed experimentally. In a first series of tests, local bond stress-slip data, as well as bond stress-radial deformation data, needed for interface modeling of the bond mechanics, were obtained for varying levels of confining pressure. In addition to bond stress and slip, radial stress and radial deformation were considered fundamental variables needed to provide for configuration-independent relationships. Each test specimen consisted of a CFRP rebar embedded in a 76-mm-(3 in.)-diam, 102-mm-(4 in.)-long, precracked lightweight concrete cylinder subjected to a constant level of pressure on the outer surface. Only 76 mm (3 in.) of contact were allowed between the rebar and the concrete. For each rebar type, bond stress-slip and bond stress-radial deformation relationships were obtained for four levels of confining axisymmetric radial pressure. It was found that small surface indentations were sufficient to yield bond strengths comparable to that of steel bars. It was also shown that radial pressure is an important parameter that can increase the bond strength almost threefold for the range studied. In a second series of tests, the rebars were pulled out from 152-mm-(6 in.)-diam, 610-mm-(24 in.)-long lightweight concrete specimens. These tests were conduced to provide preliminary data for development length assessment and model validation (Part II).

Decanting Tests at Ohmsett with and Without Emulsion Breakers1

ABSTRACT This paper summarizes a multi-year research program to address the decanting of water from oil spill fluids recovered by skimmers. The first series of tests, with two weir-type skimmers at Ohmsett, was conducted to study the rate and amount of free water separation that can be expected in temporary storage containers. The goal of this study was to predict the best time to decant water back into the boomed area and optimize the available onsite storage space. The results indicated that “primary break” (the initial separation of the recovered liquids) occurred within a few minutes to one hour, depending on the physical characteristics of the oil. Rapidly decanting this free water layer may offer immediate increases of 200 to 300% in available temporary storage volume. Initial oil concentrations in the decanted water also depended on the physical properties of the oil; they ranged from 100 to 3000 mg/L These declined by a factor of approximately 3 after one hour of settling, and by a factor of approximately 5 after one day. The second series of tests was undertaken to develop a more complete understanding of the use of emulsion breakers injected into an oil spill recovery system at both lab-scale (at SL Ross) and mid-scale (at Ohmsett). The experiments were designed to assess the injection/mixing/settling regimes required for optimum water-removal from a meso-stable water-in-oil emulsion with an oil spill demulsifier. The use of a demulsifier injected into a recovery system, combined with decanting, did substantially reduce the volume of water in temporary storage tanks and the water content of emulsions for disposal/recycling.

FOUR-DIMENSIONAL LOCAL BOUNDARY SURFACES OF AN ISOTROPICALLY CONSOLIDATED LOOSE SAND

ABSTRACT Undrained anisotropy, together with the undrained response to monotonic as well as cyclic rotation of principal stress directions, of an isotropically consolidated loose Ham River sand has been investigated by performing three series of hollow cylinder tests. The initial anisotropy of the sand when subjected to a single consolidation pressure was successfully established in the first series of tests, each using different, but fixed in each test, values of α (i.e., the direction of major principal stress relative to the vertical deposition direction) at different b values (i.e., the relative magnitude of intermediate principal stress). The response against monotonic principal stress rotation was also examined in the second series of tests, in which the total stress path defined using the shear stress, t, and α was varied in various manner with b fixed at 0.5. In the third series of tests, the response to cyclic changes of both α and b was examined, and the results were interpreted with the comparative behaviour of the monotonic loading tests with different combinations of α and b. It was found that the sand’s undrained anisotropy and cyclic response could be interpreted by invoking the concept of undrained local boundary surface (LBS). The four-dimensional LBS could be visualized in (t, p′, α) space as a family of superimposed three-dimensional shapes with different b values.

Measurement of Dissolution Rates of UO2 Matrix with the Isotope Dilution Method

ABSTRACTThe objective of this work was to measure the actual rates of matrix dissolution of UO2 in synthetic groundwater by using an isotope dilution method to provide a quantitative estimate of precipitation effects. A preliminary series of tests was performed under oxidising conditions, in contact with air. The second series of tests was under reducing conditions produced by actively corroding iron. The solid phases were fragments of unirradiated fuel pellets and intact pellets. The aqueous phase was a dilute, synthetic groundwater - so-called modified Allard water that is buffered by sodium bicarbonate/carbonate. This paper gives results for the experiments under oxidising conditions and preliminary tests under reducing conditions. In contact with air, the U concentrations reached higher levels than measured in previous experiments with spent fuel or with UO2 pellets. The comparison of the U concentrations calculated from isotopicratios with the experimental results suggests precipitation has begun at later stages of restarted tests. The measurements in the presence of actively corroding iron gave very low concentrations in the aqueous phase. At contact times longer than one week, all U seemed to disappear from solution and sorb or precipitate on UO2 or Fe surfaces in the test vessel.

A comparison of two methods for the calculation of accumulated oxygen deficit

The aim of this study was to compare accumulated oxygen deficit data derived using two different exercise protocols with the aim of producing a less time-consuming test specifically for use with athletes. Six road and four track male endurance cyclists performed two series of cycle ergometer tests. The first series involved five 10 min sub-maximal cycle exercise bouts, a VO2peak test and a 115% VO2peak test. Data from these tests were used to estimate the accumulated oxygen deficit according to the calculations of Medbø et al. (1988). In the second series of tests, participants performed a 15 min incremental cycle ergometer test followed, 2 min later, by a 2 min variable resistance test in which they completed as much work as possible while pedalling at a constant rate. Analysis revealed that the accumulated oxygen deficit calculated from the first series of tests was higher (P<0.02) than that calculated from the second series: 52.3±11.7 and 43.9±6.4 ml·kg−1, respectively (mean±s). Other significant differences between the two protocols were observed for VO2peak, total work and maximal heart rate; all were higher during the modified protocol (P<0.01 and P<0.02, respectively). Oxygen kinetics were also significantly faster during the modified 2 min maximal test. We conclude that the difference in accumulated oxygen deficit between protocols was probably due to a reduced oxygen uptake, possibly caused by a slower oxygen on-response during the 115% VO2peak test in the first series, and VO2—power output regression differences caused by an elevated VO 2 during the early stages of the second series.

Effects of hindlimb unweighting on the mechanical and structure properties of the rat abdominal aorta.

Previous studies have shown that hindlimb unweighting of rats, a model of microgravity, reduces evoked contractile tension of peripheral conduit arteries. It has been hypothesized that this diminished contractile tension is the result of alterations in the mechanical properties of these arteries (e.g., active and passive mechanics). Therefore, the purpose of this study was to determine whether the reduced contractile force of the abdominal aorta from 2-wk hindlimb-unweighted (HU) rats results from a mechanical function deficit resulting from structural vascular alterations or material property changes. Aortas were isolated from control (C) and HU rats, and vasoconstrictor responses to norepinephrine (10(-9)-10(-4) M) and AVP (10(-9)-10(-5) M) were tested in vitro. In a second series of tests, the active and passive Cauchy stress-stretch relations were determined by incrementally increasing the uniaxial displacement of the aortic rings. Maximal Cauchy stress in response to norepinephrine and AVP were less in aortic rings from HU rats. The active Cauchy stress-stretch response indicated that, although maximum stress was lower in aortas from HU rats (C, 8.1 +/- 0.2 kPa; HU, 7.0 +/- 0.4 kPa), it was achieved at a similar hoop stretch. There were also no differences in the passive Cauchy stress-stretch response or the gross vascular morphology (e.g., medial cross-sectional area: C, 0.30 +/- 0.02 mm(2); HU, 0.32 +/- 0.01 mm(2)) between groups and no differences in resting or basal vascular tone at the displacement that elicits peak developed tension between groups (resting tension: C, 1.71 +/- 0.06 g; HU, 1.78 +/- 0.14 g). These results indicate that HU does not alter the functional mechanical properties of conduit arteries. However, the significantly lower active Cauchy stress of aortas from HU rats demonstrates a true contractile deficit in these arteries.

Heat Transfer Characteristics of Ice Melting in Water and Salt Solutions

Ice cubes were placed in identical beakers, one containing tap water and the other containing a sodium chloride salt solution. Both beakers and their original contents were at 20°C. As expected, the ice cubes floated and slowly melted, however, it was found that the ice cube in the water melted 25% faster than in the brine, contrary to expectation. A second series of tests were undertaken in which the ice cubes were made to sink to the bottom by placing them in a coarse string bag with weights attached. It was found that the submerged ice cube in the brine solution melted four times faster than that submerged in tap water. Computational Fluid Dynamics, has shown that the paradoxical experimental findings can all be explained by considering the strength and direction of buoyancy driven currents.