Attenuation coefficient and propagation speed estimates of intercostal tissue as a function of pig age

Attention coefficient and propagation speed of intercostal tissues were estimated from chest walls removed postmortem (pm) from 15 5.3 /spl plusmn/ 2.3-day-old, 19 31 /spl plusmn/ 6-day-old, and 15 61 /spl plusmn/ 3-day-old crossbred pigs. These ultrasonic propagation properties were determined from measurements through the intercostal tissues, from the surface of the skin to the parietal pleura. The chest walls were placed in a 0.9% sodium chloride solution, sealed in freezer bags, and stored at -15/spl deg/C prior to measurements. When evaluated, chest-wall storage time ranged between 1 and 477 days pm. All chest walls were allowed to equilibrate to 22/spl deg/C in a water bath prior to evaluation. There was an age dependency of the intercostal tissue propagation speed, with the speed increasing with increasing age. The attenuation coefficient of intercostal tissue was shown to be independent of the age of the pig at the discrete frequencies of 3.1 and 6.2 MHz. For pig intercostal tissues, the estimated attenuation coefficient over the 3.1-9.2 MHz frequency range was A = 1.94f/sup 0.90/ where A is in decibels per centimeter (dB/cm) and f is the ultrasonic frequency in megahertz. In order to determine if there was an effect of storage time pm on estimates of attenuation coefficient, a second experiment was conducted. Five of the youngest pig chest walls measured on day 1 pm in the first experiment were stored at 4/spl deg/C prior to the first evaluation then stored at -15/spl deg/C before being measured again at 108 days pm. There was no difference in the estimated intercostal tissue attenuation coefficient as a function of storage time pm.     

Attenuation coefficient estimates of mouse and rat chest wall

Attenuation coefficients of intercostal tissues were estimated from chest walls removed postmortem (pm) from 41 6-to-7-week-old female ICR mice and 27 10-to-11-week-old female Sprague-Dawley rats. These values were determined from measurements through the intercostal tissues, from the surface of the skin to the parietal pleura. Mouse chest walls were sealed in plastic wrap and stored at 4 degrees C until evaluated, and rat chest walls were sealed in Glad-Lock Zipper sandwich bags, and stored at -15 degrees C. When evaluated, chest wall storage time ranged between 1 and 2 days pm for mice and between 41 and 110 days pm for rats. All chest walls were allowed to equilibrate to 22 degrees C in a water bath prior to evaluation. For both mouse and rat intercostal tissues, the estimated frequency normalized attenuation coefficient was 1.1 dB/cm-MHz. In order to determine if there was an effect of storage time on estimates of attenuation coefficient, an independent experiment was conducted. The intercostal tissues from six mouse chest walls were evaluated at three time points (1, 22, and 144 days pm), and from six rat chest walls were evaluated at four time points (1, 22, 50, and 125 days pm). There was no difference in the estimated intercostal tissue attenuation coefficient as a function of time postmortem.     

Effects of the scattering coefficient on width estimates in a two-layer tissue

Abstract

We pose the problem of estimating the width of the upper layer of a two-stratum medium using data from reflectance measurements made at the interface separating the medium from its surroundings. The lower stratum is assumed to be infinite. In this analysis both the scattering and the absorption coefficients are allowed to differ, but are assumed to be known. We also suggest a simple way to include effects of noise into the analysis.     

Study of the fatigue lifetimes and crack propagation behaviour of a high speed steel as a function of the R value

High speed steels, such as the alloy H‐13, when used as forging dies are subjected to both wear and cyclic loading, and both of these factors can affect the useful life of such dies. It follows that it is of some importance to determine the fatigue characteristics of such steels. However, fatigue studies of such alloys are limited, especially with respect to fatigue crack propagation (FCP) behaviour as a function of mean stress, and therefore more detailed studies are necessary. In the present study, the fatigue lifetimes and the crack propagation behaviour of a high speed steel were experimentally investigated in laboratory air under different stress ratios, R. A modified linear‐elastic fracture mechanics (LEFM) approach was applied to analyze the experimentally‐obtained FCP behaviour. The predicted S–N curves and crack growth behaviour for a wide range of R ratios agree well with the experimental data, and the modified LEFM approach is therefore considered to be useful for evaluation of the fatigue behaviour of this class of high strength steels.     

Pedestrian fatality risk as a function of car impact speed

Knowledge of the amount of violence tolerated by the human body is essential when developing and implementing pedestrian safety strategies. When estimating the potential benefits of new countermeasures, the pedestrian fatality risk as a function of impact speed is of particular importance. Although this function has been analysed previously, we state that a proper understanding does not exist. Based on the largest in-depth, pedestrian accident study undertaken to date, we derive an improved risk function for adult pedestrians hit by the front of passenger cars. Our results show far lower fatality risks than generally reported in the traffic safety literature. This discrepancy is primarily explained by sample bias towards severe injury accidents in earlier studies. Nevertheless, a strong dependence on impact speed is found, with the fatality risk at 50 km/h being more than twice as high as the risk at 40 km/h and more than five times higher than the risk at 30 km/h. Our findings should have important implications for the development of pedestrian accident countermeasures worldwide. In particular, the scope of future pedestrian safety policies and research should be broadened to include accidents with impact speeds exceeding 50 km/h.     

Measurement of critical temperature as a function of field

The critical temperature has been measured for various magnet conductors as a function of the perpendicular applied magnetic field. The isothermal environment was provided by a variable temperature cryostat which fits into the bore of a 10 telsa solenoid. The temperature gradient across the sample volume was measured to be less than 25 millikelvins. The superconducting to normal state transition was measured resistively, using sample current densities from 0.01 to 2 A cm^?2. The maximum applied magnetic field was 10 T and varied less than 0.5% in the sample volume. The critical transport current range of the samples measured from tens to thousands of amperes in the presence of a 10 T perpendicular magnetic field at 4.2 K.     

Elastic constants of silver as a function of temperature

The temperature dependence of the elastic constants of silver single crystals has been determined over the range 300–1173 K with the piezoelectric ultrasonic composite oscillator technique (PUCOT). From a comparison of the present results with those available from the literature, it is deduced that the PUCOT and hence other standing-wave techniques are adequate for measuring compliances, but these techniques may have complications for computations of stiffnesses.     

Conduction mechanism in anthracene as a function of temperature

Conduction mechanism in anthracene single crystal grown by Bridgman method was carried out. The investigations consisted of dark- and photo-current variation with respect to (i) applied electric field and (ii) temperature. The applied electric field ranged from 0·5 to 2·5 kV/cm and the temperature range was between 300 K and 450 K. Photo and dark current variations with temperature indicate, based on activation energy determination, that a band model can be applied to the conduction process. The band gap is calculated to be 1·6 eV. The band model consists of a recombination centre 0·37 eV above the valence band edge and a trap level 0·55 eV below the conduction band edge to which electrons are first thermo-optically excited and then they are thermally excited into the conduction band.     

Thermal conductivity of ketones as a function of temperature and pressure

Results are presented from an experimental study of thermal conductivity of ketones in the liquid and gaseous states at various temperatures and pressures, including the range of critical and supercritical state parameters.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 47, No. 2, pp. 256–262, August, 1984.     

Understanding doped V2O3 as a functional positive temperature coefficient material

Doped V₂O₃ is examined to understand its useful properties as a positive temperature coefficient (PTC) material. The effects of different dopant species and combinations of dopant species and the effects of microstructure are examined in terms of the properties of transition temperature, transition width, resistivity ratio, and transition hysteresis size. In addition to the previously used dopants of Cr and Al, the dopants In, Al+Cr, Al+In, and Al+Ga are also found to be effective at producing a PTC phase transition. The combination of Al+In produced the best resistivity ratio for its transition temperature. Higher sintering temperatures are found to produce larger grains and a sharper transition. The sharper transition is interpreted as the combined effect of heterogeneous nucleation and self-catalysation within a single grain. The hysteresis decreases from over 100 K between the first cooling and the following heating to around 50 K for subsequent thermal cycles. This is most likely a result of the formation of microcracks which are observed in the ceramic. An additional five cycles, though, shows no measurable decrease in the hysteresis size indicating no further growth of the microcracks.     

Electrical transport as a function of temperature in hexacyanoferrate complexes

The electrical conductivity as a function of temperature and the current–voltage dependences of potassium and nickel hexacyanoferro and ferri complexes, have been determined. Charge transfer via the electron delocalization along overlapping d_z ² orbitals of the iron to * orbitals of the ligands (–CN) as well as the ionic conduction via Fe²⁺, Fe³⁺, K⁺, and Ni²⁺ cations are considered as the main sources participating in the conduction processes. The energy gaps, as calculated from the observed maximal absorption wavelengths of ultraviolet and visible spectra, and the activation energies for the free carriers, from the temperature dependence of the electrical conductivity measurements, are consistent with those of semiconductor materials.     

Literature review of pedestrian fatality risk as a function of car impact speed

The aim of this review was to evaluate all studies of pedestrian fatality risk as a function of car impact speed. Relevant papers were primarily investigated with respect to data sampling procedures and methods for statistical analysis. It was uniformly reported that fatality risk increased monotonically with car impact speed. However, the absolute risk estimates varied considerably. Without exceptions, papers written before 2000 were based on direct analyses of data that had a large bias towards severe and fatal injuries. The consequence was to overestimate the fatality risks. We also found more recent research based on less biased data or adjusted for bias. While still showing a steep increase of risk with impact speed, these later papers provided substantially lower risk estimates than had been previously reported.     

The thermal conductivity of talc as a function of pressure and temperature

Talc is a commonly used pressure-transmitting and gasket material for high-temperature and -pressure applications. The thermal conductivity of talc at high pressures and temperatures is therefore valuable in the design of high-pressure experiments and apparatus. In this paper measurements of the thermal conductivity of fired and unfired talc are presented. Measurements were made at pressures ranging from 0 to 2.5 GPa and temperatures from 150 to 900 K. The thermal conductivity was measured with the hotwire technique. The thermal conductivity results for both the fired and the unfired talc show a slight increase with increasing pressure. The absolute value of the thermal conductivity of talc is lower in the fired material than in the unfired material. In both cases, the thermal conductivity varied less than 15% over the temperature range studied. X-Ray diffraction studies have shown talc to be highly disordered. The results are shown to be consistent with those expected for a disordered crystal.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Intrinsic ductility for structural materials as a function of stress and temperature

Abstract

In recent years, a method has been developed to measure current creep strength at nearly constant structure in a high precision stress relaxation test (SRT), covering at least five decades in creep rate in a one day test. Results have been reported on a wide range of metallic alloys, polymers, composites and ceramics. In the present paper it is shown that these same data can be used to determine a measure of intrinsic ductility over the same range of stress, using results on a low alloy Cr–Mo–V steel. This is based on an experimental and theoretical correlation between elongation at failure and strain rate sensitivity, m. This refined SRT test can now be used to evaluate both the intrinsic creep strength and the intrinsic ductility as a function of stress in a single short-time test. The test can detect embrittling phenomena at very low creep rates as a function of temperature. This measure of ductility may be used directly in engineering design and remaining life assessment.     

Creep behavior of nanocrystalline Au films as a function of temperature

Freestanding nanocrystalline Au films, subjected to nominally elastic loads at 25–110 °C, demonstrated high primary (10^?7–10^?4 s^?1) and steady-state creep rates (10^?8–10^?5 s^?1). The deformation mechanisms for creep were strongly temperature dependent: grain boundary sliding-based creep dominated at room temperature and 50 °C, while the contribution of dislocation-mediated creep increased at 80 and 110 °C. The effect of applied stress on primary and steady-state creep strain at different temperatures was captured well by a non-linear model that was based on the kinetics of thermal activation. Multi-cycle creep experiments showed that at room temperature virtually all the primary strain accumulated during each forward creep cycle was recovered upon complete unloading. As the contribution of dislocation-mediated creep increased with temperature, the ratio of strain recovery to primary strain accumulated during each cycle was reduced due to the accumulation of plastic strain at higher temperatures. Notably, at all temperatures, the steady-state creep rate decreased after the first creep cycle. Moreover, the entire creep response remained virtually unchanged in all subsequent cycles, which implies that the first creep cycle resulted in mechanical annealing. This conclusion was further supported by calculations of the activation entropy: A reduction in its magnitude between the first and all subsequent creep cycles at all temperatures pointed out to mechanical annealing of initial material defects during the first loading cycle. The negative values of the calculated activation entropy indicated that entropy changes due to annihilation of defects-dominated entropy changes associated with the generation of new defects. Finally, the activation entropy for steady-state creep was temperature insensitive, but increased with stress, which is consistent with an increase in defect generation at higher stresses.     

Room temperature hardness of gadolinia-doped ceria as a function of porosity

Porous gadolina-doped ceria (Ce_0.9Gd_0.1O_1.95, GDC10) is commonly used as a functional electrode support in solid oxide fuel cells, gas sensors, and gas separators. In addition, dense GDC10 is commonly used as a solid oxide fuel cell electrolyte and a gas separation membrane. Although, porosity affects a wide range of electrical, thermal, and mechanical properties of solids, this study focuses on (i) the Vickers indentation hardness, H, as a function of volume fraction porosity, P, ranging from 0.08 to 0.60 and (ii) the load dependence of H for Vickers indentation loads of 0.98–9.8 N. For the 13 GDC10 included in this study, the decrease in H with increasing P is approximated by the empirical relationship H = H ₀ exp(?b _H P), where H ₀ = 5.844 GPa and b _H  = 6.68. In addition, the H values were roughly independent of the applied load.