bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanical properties of rat soleus aponeurosis and tendon during variable recruitmentin situ
Authors: Monti Ryan J. , Roy Roland R. , Zhong Hui , Edgerton V. R. 
Published: August 2003

SUMMARYThe in vitro mechanical properties of tendons are well described,whereas little data exist for conditions mimicking those found in vivo. Descriptions of the in situ mechanical properties of aponeuroses are more common, but the results are variable. Our goal was to examine the mechanical properties of these tissues under conditions mimicking the in vivo state. Tissue strains were measured in the rat(Rattus norvegicus) soleus muscle directly from the spacing of metal markers implanted within the tissues of interest using an X-ray video microscope. Strains were measured for the tendon and three regions (proximal,middle and distal) of the aponeurosis. Muscle stimulation was accomplished through isolated ventral rootlets, allowing force to be graded in seven repeatable increments independent of muscle-tendon unit length. Peak strains(during maximal tetanic contraction at optimum length; Po)were ∼5% in tendon and ∼12% in all regions of the aponeurosis. At forces above 50% of Po, tissue stiffness was nearly constant in all regions, and a pronounced toe region was observed only at forces below ∼25% of Po. Stiffness increased in all regions as the muscle-tendon unit was lengthened. These results suggest that using mechanical properties measured ex vivo or during single contractile events in situ to estimate the in vivo behavior of tendon and aponeurosis may lead to errors in estimating the distribution of strain among the contractile and series elastic elements of the muscle.
Lung ventilation during treadmill locomotion in a terrestrial turtle,Terrapene carolina
Authors: Landberg Tobias , Mailhot Jeffrey D. , Brainerd Elizabeth L. 
Published: August 2003

SUMMARYThe limb girdles and lungs of turtles are both located within the bony shell, and therefore limb movements during locomotion could affect breathing performance. A mechanical conflict between locomotion and lung ventilation has been reported in adult green sea turtles, Chelonia mydas, in which breathing stops during terrestrial locomotion and resumes during pauses between bouts of locomotion. We measured lung ventilation during treadmill locomotion using pneumotach masks in three individual Terrapene carolina (mass 304-416 g) and found no consistent mechanical effects of locomotion on breathing performance. Relatively small tidal volumes(2.2±1.4 ml breath-1; mean ± s.d., N=3 individuals) coupled with high breath frequencies(36.6±26.4 breaths min-1; mean ± s.d., N=3 individuals) during locomotion yield mass-specific minute volumes that are higher than any previously reported for turtles (264±64 ml min kg-1; mean ± s.d., N=3 individuals). Minute volume was higher during locomotion than during recovery from exercise(P&lt;0.01; paired t-test), and tidal volumes measured during locomotion were not significantly different from values measured during brief pauses between locomotor bouts or during recovery from exercise(P&gt;0.05; two-way ANOVA). Since locomotion does not appear to conflict with breathing performance, the mechanism of lung ventilation must be either independent of, or coupled to, the stride cycle. The timing of peak airflow from breaths occurring during locomotion does not show any fixed phase relationship with the stride cycle. Additionally, the peak values of inhalatory and exhalatory airflow rates do not differ consistently with respect to the stride cycle. Together, these data indicate that T. carolina is not using respiratory-locomotor coupling and limb and girdle movements do not contribute to lung ventilation during locomotion. X-ray video recordings indicate that lung ventilation is achieved via bilateral activity of the transverse (exhalatory) and oblique (inhalatory) abdominal muscles. This specialized abdominal ventilation mechanism may have originally circumvented a mechanical conflict between breathing and locomotion in the ancestor of turtles and subsequently allowed the ribs to abandon their role in lung ventilation and to fuse to form the shell.
Nitric oxide mediates seasonal muscle potentiation in clam gills
Authors: Gainey Louis F. , Greenberg Michael J. 
Published: August 2003

SUMMARY
The physiology and timing of gill muscle potentiation were explored in the clam Mercenaria mercenaria. When isolated demibranchs were exposed twice (with an intervening wash) to the same concentration of 5-hydroxytryptamine, the second contraction was larger than the first. This potentiation was seasonal: it was present from November through June, and absent from July through October. Potentiation was not affected by the geographic origin of the clams, nor by their acclimation temperature. Potentiation was inhibited by the nitric oxide synthase (NOS) inhibitor l-NAME and mimicked by the nitric oxide (NO) donor DEANO. During the season of potentiation, immunoreactive NOS appeared in the gill muscles and the gill filament epithelium, but during the off-season, the enzyme occurred at the base of the gill filaments. Potentiation was inhibited by ODQ,which inhibits soluble guanylate cyclase (sGC), and it was mimicked by dibutyryl-cGMP, an analog of cyclic GMP (cGMP). Moreover, potentiation was inhibited by the protein kinase G (PKG) inhibitor Rp-8-CPT-cGMPS. During the season of potentiation, immunoreactive sGC was concentrated in the gill muscles and the gill filament epithelium; but during the off-season,immunoreactive sGC was found in the gill filament epithelium. These data suggest that the potentiation of gill muscle is mediated by a NO/cGMP/PKG signaling pathway.
Sex differences in the thermoregulation and evaporative water loss of a heterothermic bat,Lasiurus cinereus,during its spring migration
Authors: Cryan Paul M. , Wolf Blair O. 
Published: August 2003

SUMMARYThis study quantifies sex differences in thermoregulation and water loss of a small (20-35 g) insectivorous heterothermic mammal, the hoary bat Lasiurus cinereus, during its spring migration. We measured body temperature, metabolic rate and evaporative water loss, and calculated wet thermal conductance, for bats exposed to air temperatures ranging from 0 to 40°C for periods of 2-5 h. Pregnant females maintained normothermic body temperatures (35.7±0.7°C; mean ± s.e.m.)independent of air temperature. In contrast, males became torpid during the majority (68%) of exposures to air temperatures &lt;25°C. The thermal neutral zone (TNZ) ranged between approximately 30°C and 34°C in both sexes and, within the TNZ, females had lower mass-specific metabolic rates(6.1±0.2 mW g-1) than males (9.0±0.9 mW g-1). Wet thermal conductance values in torpid bats (0.7±0.5 mW g-1 deg.-1) were lower than those of normothermic individuals (1.1±0.3 mW g-1 deg.-1). Mass-specific rates of evaporative water loss in males were consistently higher than in females at most air temperatures and rates of water loss in torpid bats were 63±6% of normothermic values. These results suggest that male and pregnant female L. cinereus employ different thermoregulatory strategies during their spring migration. Females defend normothermic body temperatures, presumably to expedite embryonic growth, while males use torpor, presumably to minimize energy and water deficits. These variable thermoregulatory strategies may reflect continental differences in the summer distribution of the sexes.
Form and function of the bulbus arteriosus in yellowfin tuna (Thunnus albacares), bigeye tuna (Thunnus obesus) and blue marlin(Makaira nigricans): static properties
Authors: Braun Marvin H. , Brill Richard W. , Gosline John M. , Jones David R. 
Published: August 2003

SUMMARY
The juxtaposition of heart and gills in teleost fish means that the Windkessel function characteristic of the whole mammalian arterial tree has to be subserved by the extremely short ventral aorta and bulbus arteriosus. Over the functional pressure range, arteries from blue marlin (Makaira nigricans) and yellowfin tuna (Thunnus albacares) have J-shaped pressure-volume (P-V) loops, while bulbi from the same species have r-shaped P-V loops, with a steep initial rise followed by a compliant plateau phase. The steep initial rise in pressure is due to the geometry of the lumen. The interactions between radius, pressure and tension require a large initial pressure to open the bulbar lumen for flow. The plateau is due to the unique organization of the bulbar wall. The large elastin:collagen ratio, limited amount of collagen arranged cirumferentially, lack of elastin lamellae and low hydrophobicity of the elastin itself all combine to lower stiffness, increase extensibility and allow efficient recoil. Even though the modulus of bulbus material is much lower than that of an artery, at large volumes the overall stiffness of the bulbus increases rapidly. The morphological features that give rise to the special inflation characteristics of the bulbus help to extend flow and maintain pressure during diastole.
Blubber and buoyancy: monitoring the body condition of free-ranging seals using simple dive characteristics
Authors: Biuw Martin , McConnell Bernie , Bradshaw Corey J. A. , Burton Harry , Fedak Mike 
Published: August 2003

SUMMARYElephant seals regularly perform dives during which they spend a large proportion of time drifting passively through the water column. The rate of vertical change in depth during these `drift' dives is largely a result of the proportion of lipid tissue in the body, with fatter seals having higher (more positive or less negative) drift rates compared with leaner seals. We examined the temporal changes in drift rates of 24 newly weaned southern elephant seal(Mirounga leonina) pups during their first trip to sea to determine if this easily recorded dive characteristic can be used to continuously monitor changes in body composition of seals throughout their foraging trips. All seals demonstrated a similar trend over time: drift rates were initially positive but decreased steadily over the first 30-50 days after departure(Phase 1), corresponding to seals becoming gradually less buoyant. Over the following ∼100 days (Phase 2), drift rates again increased gradually,while during the last ∼20-45 days (Phase 3) drift rates either remained constant or decreased slightly. The daily rate of change in drift rate was negatively related to the daily rate of horizontal displacement (daily travel rate), and daily travel rates of more than ∼80 km were almost exclusively associated with negative changes in drift rate. We developed a mechanistic model based on body compositions and morphometrics measured in the field,published values for the density of seawater and various body components, and values of drag coefficients for objects of different shapes. We used this model to examine the theoretical relationships between drift rate and body composition and carried out a sensitivity analysis to quantify errors and biases caused by varying model parameters. While variations in seawater density and uncertainties in estimated body surface area and volume are unlikely to result in errors in estimated lipid content of more than±2.5%, variations in drag coefficient can lead to errors of ≥10%. Finally, we compared the lipid contents predicted by our model with the lipid contents measured using isotopically labelled water and found a strong positive correlation. The best-fitting model suggests that the drag coefficient of seals while drifting passively is between ∼0.49 (roughly corresponding to a sphere-shaped object) and 0.69 (a prolate spheroid), and we were able to estimate relative lipid content to within approximately±2% lipid. Our results suggest that this simple method can be used to estimate the changes in lipid content of free-ranging seals while at sea and may help improve our understanding of the foraging strategies of these important marine predators.
Finite element analysis in spine research
Authors: Fagan M J , Julian S , Mohsen A M 
Published: August 2003

Finite element analysis is a widely accepted tool used in many industries and research activities. It allows new designs to be thoroughly ‘tested’ before a prototype is even manufactured, components and systems which cannot readily be experimented upon to be examined, and ‘diagnostic’ investigations to be undertaken. Finite element models are already making an important contribution to our understanding of the spine and its components. Models are being used to reveal the biomechanical function of the spine and its behaviour when healthy, diseased or damaged. They are also providing support in the design and application of spinal instrumentation. The spine is a very complex structure, and many of the models are simplified and idealized because of the complexity and uncertainty in the geometry, material properties and boundary conditions of these problems. This type of modelling simplification is not peculiar to spinal modelling problems. Indeed, the idealization is often a strength when there is such uncertainty and variation between one individual and another, allowing cause-effect relationships to be isolated and fully explored, and the inherent variability of experimental tests to be eliminated. This paper reviews the development of finite element analysis in spinal modelling. It shows how modelling provides a wealth of information on our physiological performance, reduces our dependence on animal and cadaveric experiments and is an invaluable complement to clinical studies. It also leads to the conclusion that, as computing power and software capabilities increase, it is quite conceivable that in the future it will be possible to generate patient-specific models that could be used for patient assessment and even pre- and inter-operative planning.
Patient-specific spine models. Part 1: Finite element analysis of the lumbar intervertebral disc—a material sensitivity study
Authors: Fagan M J , Julian S , Siddall D J , Mohsen A M 
Published: August 2003

If patient-specific finite element models of the spine could be developed, they would offer enormous opportunities in the diagnosis and management of back problems. Several generic models have been developed in the past, but there has been very little detailed examination of the sensitivity of these models' characteristics to the input parameters. This relationship must be thoroughly understood if representative patient-specific models are to be realized and used with confidence. In particular, the performance of the intervertebral discs are central to any spine model and need detailed investigation first. A generic non-linear model of an intervertebral disc was developed and subjected to compressive, flexion and torsional loading regimes. The effects of both material and geometric non-linearities were investigated for the three loading schemes and the results compared with experimental data. The basic material properties of the fibres, annulus and nucleus were then varied and the effects on the stiffness, annulus bulge and annulus stresses analysed. The results showed that the non-linear geometry assumption had a significant effect on the compression characteristics, whereas the non-linear material option did not. In contrast, the material non-linearity was more important for the flexural and torsional loading schemes. Thus, the inclusion of non-linear material and geometry analysis options in finite element models of intervertebral discs is necessary to predict in vivo load-deflection characteristics accurately. When the influence of the material properties was examined in detail, it was found that the fibre properties did not have a significant effect on the compressive stiffness of the disc but did affect the flexural and torsional stiffnesses by up to ±20 per cent. All loading modes were sensitive to the annulus properties with stiffnesses varying by up to ±16 per cent. The model also revealed that for a particular compressive deformation or flexural or torsional rotation, the disc bulge was not sensitive to any of the material properties over the range of properties considered. The annulus stresses did differ significantly as the material properties were varied (up to 70 per cent under a compressive load and 60 per cent during disc flexion).
Influence of fuel volatility on combustion and emission characteristics in a gas turbine combustor at different inlet pressures and swirl conditions
Authors: Sharma N. Y. , Som S. K. 
Published: August 2003

The practical challenges in research in the field of gas turbine combustion mainly centre around a clean emission, a low liner wall temperature and a desirable exit temperature distribution for turboma-chinery applications, along with fuel economy of the combustion process. An attempt has been made in the present paper to develop a computational model based on stochastic separated flow analysis of typical diffusion-controlled spray combustion of liquid fuel in a gas turbine combustor to study the influence of fuel volatility at different combustor pressures and inlet swirls on combustion and emission characteristics. A κ-ɛ model with wall function treatment for the near-wall region has been adopted for the solution of conservation equations in gas phase. The initial spray parameters are specified by a suitable probability distribution function (PDF) size distribution and a given spray cone angle. A radiation model for the gas phase, based on the first-order moment method, has been adopted in consideration of the gas phase as a grey absorbing-emitting medium. The formation of thermal NO x as a post-combustion reaction process is determined from the Zeldovich mechanism. It has been recognized from the present work that an increase in fuel volatility increases combustion efficiency only at higher pressures. For a given fuel, an increase in combustor pressure, at a constant inlet temperature, always reduces the combustion efficiency, while the influence of inlet swirl is found to decrease the combustion efficiency only at higher pressure. The influence of inlet pressure on pattern factor is contrasting in nature for fuels with lower and higher volatilities. For a higher-volatility fuel, a reduction in inlet pressure decreases the value of the pattern factor, while the trend is exactly the opposite in the case of fuels with lower volatilities. The NOx emission level increases with decrease in fuel volatility at all combustor pressures and inlet swirls. For a given fuel, the NOx emission level decreases with a reduction in combustor pressure and an increase in inlet swirl number.
Study on the natural air cooling of electronic equipment casings: Effects of the outlet vent and the power heater locations on the cooling capability
Authors: Ishizuka M , Peng G , Kitamura Y 
Published: August 2003

This paper is concerned with the natural cooling of electronic equipment casings. Effects of the size and the location of the outlet vent as well as the relative distance from the outlet vent location to the power heater position on the flow resistance have been investigated experimentally by using a simple model casing simulated for practical natural air cooled electronic equipment casings. The result shows that the mean temperature rise inside the casing increases with increase in the heater input power, but decreases linearly with increase in the vent porosity coefficient in logarithmic coordinates. As the heater approaches the outlet vent, the temperature rise increases linearly in the logarithmic scale. By defining a new dimensionless parameter called the equivalent Reynolds number, involving the Reynolds number and the porosity coefficient, the flow resistance coefficient is found to have a close logarithmic linear correlation, K = kxχ−1.5, with the equivalent Reynolds number. Its validation has been proved by the good agreement with experimental results. The result indicates that the relative distance from the outlet vent to the heat dissipation unit can be considered as a chimney height in the practical engineering design. Although further more detailed validations are needed, a useful correlation between the flow resistance coefficient, the Reynolds number and the porosity coefficient has been presented for the design application of natural cooling electronic casings.
Integration of solid oxide fuel cells into gas turbine power generation cycles. Part 1: Fuel cell thermodynamic modelling
Authors: Pangalis M. G. , Martinez-Botas R. F. , Brandon N. P. 
Published: August 2003

The development of a detailed thermodynamic model of a fuel cell is presented. This model predicts the performance of a gas turbine and fuel cell systems integrated together in hybrid power generation cycles. The achievement of this goal involved the independent modelling of each component (prereformer, internal reformer, active area, combustion zone and fuel preheating) using numerical methods in the form normally required by cycle calculations used in gas turbine design. The fuel cell model was based on the principle of operation of the Westinghouse tubular solid oxide fuel cell (SOFC) design, involving internal reforming and prereforming of methane. Its performance was examined under a wide range of operating conditions leading to exhaust temperatures in the range 370–935°C. Fuel cell system efficiencies as high as 56 per cent were predicted at low current densities (150mA/cm2), while the efficiency dropped to 38.7 per cent at high current densities (600mA/cm2) owing to the irreversibilities developed. Pressurized operation of the fuel cell was assessed in the range 1–25 atm; high-pressure operation leads to an increased power output, particularly at high current densities, but it also produces a significant decrease in electrical efficiency (from 55 to 37 per cent). Pressurized operation should only be contemplated when the fuel cell is integrated with a gas turbine, as shown in Part 2 of this paper, where the hybrid configuration will be shown to give an impressive 76.4 per cent maximum electrical efficiency.
Integration of solid oxide fuel cells into gas turbine power generation cycles. Part 2: Hybrid model for various integration schemes
Authors: Cunnel C , Pangalis M. G. , Martinez-Botas R. F. 
Published: August 2003

The second part of this paper deals with modelling gas turbine cycles integrated with a fuel cell model to produce hybrid cycles. The main objectives were to develop an understanding of the integration options and to determine the theoretical optimum configuration. Six different realistic cycles are analysed and discussed. The fuel cell model is detailed in Part 1 of this paper. The gas turbine cycles considered included intercooling, reheat and recuperation. The choice of hybrid configuration will depend on the application, but from this analysis it is shown that a recuperated gas turbine cycle with a fuel cell ahead of the combustor is a good choice for power generation at small/medium scale. This cycle achieved a thermal efficiency of 64.1 per cent at a relatively low pressure ratio of 14; the specific power, although lower than that of other configurations explored, was found to be reasonable at 520 kW/kgs. The addition of an intercooler to this cycle indicated a further increase in efficiency at 69.6 per cent and a considerable increase in specific power; the corresponding pressure ratio was 30, which would lead to a significantly different gas turbine. The maximum efficiency of all cases was found for a cycle containing a primary fuel cell (ahead of the combustor) and a reheat fuel cell (in-between the high-pressure and low-pressure turbine) with a numerical value of 76.4 per cent at a low pressure ratio but leading to a much reduced power (200 kW/kgs); a peak specific power of 489 kW/kgs was found but at much higher pressure ratios.