bluuebunny/crossref_metadata_2025_split huggingface dataset:
Daily Changes in the Curved Crown‐Rump Length of Individual Sheep Fetuses During the Last 60 Days of Pregnancy and Effects of Different Levels of Maternal Nutrition
Authors: Mellor D. J. , Matheson I. C. 
Published: December 2014

A method is described by which daily changes in the curved crown‐rump length (CRL) of individual sheep fetuses were observed during the last 50 to 60 days of pregnancy. The mean discrepancy between the derived value for CRL and the CRL measured directly in eight fetuses aged between 100 and 135 days and in 12 lambs born at 143 to 150 days was 1·5±0·2 per cent (mean ± s.e.).In adequately nourished ewes between 100 and 115 days of gestation growth rate showed a between‐fetus range of 4·2 to 7·5 mm.day‐1 (n = 16), remained constant within each fetus until about 132 days and then decreased by about 27 per cent (n = 4). Decreases in growth rate of about 30 to 44 per cent occurred within three days of the introduction of maternal undernutrition at 115 or 120 days of gestation (n = 6) and in two other fetuses maternal undernutrition effected an almost complete cessation of growth. The relationship between fetal CRL and weight is described and some physiological implications of the results are discussed.
Lactation in the Rabbit: Mammary Blood Flow and Cardiac Output
Authors: Ôta K. , Peaker M. 
Published: December 2014

In anaesthetized rabbits, cardiac output (c.o.) and its distribution to the mammary glands, heart, liver and kidneys have been determined in established lactation (11—13 days), late lactation (26—27 days) and in virgins. During lactation, the volume of circulating blood, c.o., mammary blood flow and mammary weight were significantly greater than in virgins. There were no significant differences in c.o. and % c.o. received by the mammary glands between established and late lactation, and no significant decrease in mammary blood flow in late lactation. The weights of the liver and kidneys were significantly increased in lactation but there were no significant differences in liver, heart (coronary) and kidney blood flow. The rate of growth of the young was positively and significantly correlated with % c.o. received by the mammary glands and mammary weight, but not with c.o. Strong correlation was also observed between the % c.o. received by the mammary glands and mammary weight.There were no significant differences in c.o., mammary % c.o. and mammary blood flow in animals in established lactation 2—3 h and 24 h after suckling (i.e. shortly after and just before suckling). By 48 h after the last suckling mammary blood flow and % c.o., but not c.o., were significantly decreased. Possible factors causing these changes are discussed.The results are discussed in relation to the change in milk composition that occurs in late lactation in this species and to the role and effects of prolactin. It is suggested that events occurring during lactation have different sensitivities to prolactin.
A Comparative Study of the Portal Vessels Connecting the Endocrine and Exocrine Pancreas, with a Discussion of Some Functional Implications
Authors: Henderson J. R. , Daniel P. M. 
Published: December 2014

We have examined the pattern of the capillaries of the pancreas in rabbits, rats, mice, guinea‐pigs, cats and baboons, using arterial and venous injections of Berlin blue. In all these species we found extensive, direct connexions between the capillary beds of the islets and the exocrine tissue of the gland, forming a highly developed portal system.Some of the functional implications of these vascular connexions are discussed, particularly the influence of the islet hormones insulin, glucagon and somatostatin upon the exocrine cells.
The Effect of Exogenous Adenosine Triphosphate on Potassium Movements in HeLa Cells
Authors: Aiton J. F. , Lamb J. F. 
Published: December 2014

The effect of exogenous adenosine triphosphate (ATP) on the potassium movements of cultured HeLa cells has been studied. The results obtained were consistent with the hypothesis that, in these cells, externally applied ATP activates a tightly coupled potassium‐potassium (K‐K) exchange mechanism. The response to ATP was characterized by a transient, 20‐fold increase in both the potassium influx and potassium efflux. The tight coupling of the K‐K exchange mechanism was confirmed by the results of several different types of experiment, all of which demonstrated the consistent matching of the ATP‐stimulated fluxes.Two different strains of HeLa cells gave quantitatively different responses under similar experimental conditions. The reason for this difference was investigated and evidence was obtained which was consistent with the view that the membrane potential also influenced the HeLa cell K‐K exchange mechanism.
Effects of Starvation on Cardiovascular Function (including the Mammary Circulation) and Water Balance in Pregnant Goats
Authors: Chaiyabutr N. , Faulkner Anne , Peaker M. 
Published: December 2014

In conscious goats, starved for 48 hr, in mid‐pregnancy (70 days) cardiac output and blood volume decreased; total peripheral resistance increased; heart rate, stroke volume, blood pressure, mammary blood flow and mammary resistance were not significantly affected. In late pregancy (132 days) cardiac output, heart rate, blood volume and mammary blood flow fell; peripheral resistance increased; stroke volume and blood pressure were not significantly affected. In mid‐pregnancy, water consumption fell and the animals entered a stage of negative sensible water balance which persisted for both days of starvation. A similar change was obtained on the first day in late‐pregnant goats, but on the second day water consumption increased and positive water balance was restored.Cardiac output, heart rate, blood volume and mammary blood flow were higher in fed late‐pregnant than in fed mid‐pregnant goats, total peripheral resistance was lower while there were no significant changes in stroke volume or blood pressure. Indications of correlations between litter size and cardiac function were obtained.The results are compared with previous studies on the effects of starvation in lactating animals and are discussed in relation to the control of cardiac function and mammary blood flow in pregancy and lactation.
An Electrophysiological Study of the Effects of Ionophore A23187 on Nauphoeta Salivary Glands
Authors: Mitchell Mary R. , Martin A. R. 
Published: December 2014

The ionophore A23187 produces a hyperpolarization of cockroaclch salivary gland cells in the presence or absence of added calcium ions. The effect is greater and more prolonged in the presence of calcium and is dependent on the external potassium ion concentration.It is proposed that the ionophore can increase the intracellular calcium ion concentration by an increase in influx from the external medium or by mobilization of intracellular calcium stores and that this results in an increase in the potassium permeability, thus producing a hyperpolarization.
QUANTITATIVE ASPECTS OF PREOPTIC THERMOSENSITIVITY IN THE CONSCIOUS OX
Authors: Calvert D. T. , Findlay J. D. , McLean J. A. 
Published: December 2014

An attempt has been made to study the quantitative relationship between the temperature of the anterior hypothalamic/preoptic (AH/PO) region and heat balance in the conscious ox (Bos taurus) at a thermoneutral air temperature of 20 °C. Heat balance was measured by combined gradient‐layer and open‐circuit calorimetry and AH/PO temperature was controlled using a water‐perfused thermode.Continuous warming or cooling of the AH/PO region caused a transient heat imbalance which shifted core temperature to a new stable level dependent upon the level of stimulation. The heat balance responses to continuous AH/PO warming included peripheral vasodilation and increased respiratory and cutaneous evaporative heat loss; those to AH/PO cooling consisted mainly of decreased heat loss. Heat production was largely unaffected by both AH/PO warming and cooling. The heat balance responses developed only slowly, reaching a peak up to 50 min after the start of stimulation and taking several hours to complete.The change to stability in core temperature during continuous AH/PO stimulation and the additional heat loss prior to that stability were the most sensitive indicators of response of all the variables measured. A significant response was observed in these parameters even at the smallest stimulus level (less than 0·33 °C) and correlation of response with stimulus level was precise with a zero threshold for response. This suggests a continuity of operation of the AH/PO mechanism about zero.Several responses showed a curved relationship between slope of response and stimulus level, such that the increment in response per unit increase in stimulus level became greater as stimulus level increased. The results suggest a two‐tier form of thermoregulation in the ox with AH/PO sensitivity to warming greater than its sensitivity to cooling. It appears also that AH/PO temperature is at least as dominant in the thermoregulatory mechanisms in the ox as it is in smaller animals.
USE OF HIGH PERFORMANCE LIQUID CHROMATOGRAPHY TO STUDY ABSORPTION AND METABOLISM OF PURINES BY RAT JEJUNUM IN VITRO
Authors: Parsons D. S. , Shaw M. I. 
Published: December 2014

A simple and specific analytical method incorporating high performance (anion‐exchange) liquid chromatography has been used to study the absorption and metabolism of some purine derivatives in an in vitro preparation of adult rat jejunum. When present in the lumen the purine bases guanine (4 x 10−5 M), hypoxanthine or xanthine (10−4−3 x 10−4 M) do not appear in the serosal secretions but the uric acid (UA) content of these secretions is increased. With UA in the intestinal lumen (10−4−3 x 10−4 M) the serosal UA is increased, in some cases to a higher concentration than that in the lumen. With adenine in the lumen (10−4−10−3 M) there is an increased appearance of UA and adenine also appears in the serosal secretions, but the concentration of adenine never exceeds that in the lumen.It is concluded that purines absorbed from the lumen are significantly metabolized to UA during translocation across rat jejunum. Negligible amounts of metabolites are found in the luminal solutions except for guanine which appears to be degraded in the lumen.
PROTEIN TURNOVER WITH SPECIAL REFERENCE TO MAN
Authors: Waterlow J. C. 
Published: December 2014

This review is concerned with rates of N flux in the living animal rather than with mechanisms of protein synthesis and breakdown at the cellular level. Methods of measuring protein turnover in the whole body are discussed, with special emphasis on studies in man, and results obtained by different methods have been compared.Aspects of whole body protein turnover which are of physiological interest include its relation to body size, growth and development, energy metabolism and food intake. There are substantial increases in protein turnover in injury, and changes that occur in exercise are beginning to be explored.From the physiological point of view these results point the need for future research along two main lines. The first is that of regulation: a wide variety of hormones stimulate or repress protein synthesis and breakdown, with varying actions in different tissues. These effects, however, do not in themselves explain the mechanism by which a balance between synthesis and breakdown is maintained. Secondly, the fact that all cellular proteins are in a dynamic state poses questions about the relation between structure and function in tissues such as muscle and brain, which physiologists have hardly begun to tackle.
THE EFFECT OF VARIATION IN PHOSPHORUS INTAKE ON NET INTESTINAL PHOSPHORUS ABSORPTION, SALIVARY PHOSPHORUS SECRETION AND PATHWAY OF EXCRETION IN SHEEP FED ROUGHAGE DIETS
Authors: Scott D. , McLean A. F. , Buchan W. 
Published: December 2014

Quarterly Journal of Experimental Physiology 69–3 (1984)On page 448 the sentence 3 lines from the bottom should readThe sheep were fitted with a re‐entrant cannula in the duodenum close to the pylorus and digesta was collected through this cannula for 30 h after dosing, unlabelled donor material being used to replace that removed.
THE ONTOGENY OF VASOACTIVE INTESTINAL POLYPEPTIDE‐LIKE AND SUBSTANCE P‐LIKE IMMUNOREACTIVITY IN THE DIGESTIVE TRACT OF THE SHEEP
Authors: Harrison F. A. , Wathuta E. M. 
Published: December 2014

Using the technique of indirect immunofluorescence cytochemistry, the development of structures showing vasoactive intestinal polypeptide‐like (VIP‐l.i.) and substance P‐like (SP‐l.i.) immunoreactivity was studied in the gut of the fetal sheep and of new‐born lambs. The fetuses were obtained by hysterotomy at known stages of gestation. VIP‐l.i. immunoreactivity was first detected at mid‐gestation (70 d) in neuronal structures in the myenteric plexus of the oesophagus and the forestomachs. SP‐l.i. immunoreactivity was detectable at 50 d of gestation in neuronal structures in the myenteric and submucous plexuses of the forestomachs and abomasum and in the myenteric plexus of the rectum. SP‐l.i. immunoreactivity was also seen in open‐type endocrine cells in the abomasal epithelium.Subsequently, VIP‐l.i. staining progressively appeared caudally from the oesophagus and later cranially from the rectum. By birth the full adult staining pattern had developed in all regions except the colon. SP‐l.i. was found to progress cranially and caudally from the forestomachs and abomasum and also cranially from the rectum and by birth the gut showed staining fully representative of the adult distribution. The SP‐reactive endocrine cells appeared progressively along the intestine as the fetus developed and by birth were found predominantly in the small and large intestine with only a few in the abomasum.
Cardiovascular and respiratory responses to chronic intermittent hypoxia in adult female rats
Authors: Souza George Miguel P. R. , Bonagamba Leni G. H. , Amorim Mateus R. , Moraes Davi J. A. , Machado Benedito H. 
Published: December 2014

New Findings
What is the central question of this study?
Chronic intermittent hypoxia (CIH) induces hypertension in male rats. There is evidence that the development of high blood pressure in females is attenuated in other models of hypertension. Due to the lack of information about the cardiovascular effect of CIH in female rats, we set out to determine whether female rats develop hypertension after CIH.
What is the main finding and its importance?
Different from other experimental models of hypertension, adult female rats develop high blood pressure after CIH. These findings provide new perspectives for a better understanding of the neural mechanisms underlying the development of hypertension in females.
Adult male rats develop hypertension in response to chronic intermittent hypoxia (CIH). Female rats are known to be protected against the development of hypertension in several experimental models. In this study, we aimed to verify whether the development of hypertension was also prevented in female rats exposed to CIH. Adult female rats were submitted to 35 days of CIH, 8 h per day. At the end of the CIH protocol, the rats were anaesthetized for the implantation of an arterial catheter and the next day the mean arterial pressure and heart rate were recorded in conscious rats. Considering that changes in the respiratory pattern have been associated with the development of hypertension in the CIH model, the respiratory pattern of adult female rats was also evaluated after CIH exposure using whole‐body plethysmography. Adult female rats submitted to CIH (n = 27) presented a significant increase in mean arterial pressure when compared with the control group (n = 26). Moreover, CIH‐exposed female rats presented an increase in the frequency and duration of apnoeas when compared with control rats. These data show that adult female rats develop changes in the respiratory pattern and high blood pressure in response to CIH.
Technical and Economic Analysis of Repowering a Coal-Fired Power Plant
Authors: Roy-Aikins Joseph , Rampershad Reshleu J. 
Published: December 2014

Owing to an abundance of coal reserves, about 92 percent of the electrical power produced in South Africa is generated in central power stations fired on cheaply priced coal. With a few power stations approaching the end of their design life, the question arises as to what to do with these outdated and inefficient plants. Retrofitting or repowering a station with gas turbines is one option being considered. As a case study, this paper investigates the technical and economic feasibility of repowering the Arnot power station to convert it to a combined cycle plant with increased capacity. This power station has six generating units, each of nominal capacity 350 MW and of average age 25 years. Four are in service, and the others are in reserve storage. Several repowering options were considered and the proposed re-design is parallel repowering, where additional steam for a steam turbine is generated in a gas turbine heat recovery steam generator to supplement the steam generated in a coal-fired boiler. Since natural gas, the preferred fuel for gas turbines, is not readily available in the country, kerosene was used as gas turbine fuel. Consequently, the performance of the chosen gas turbine had to be re-evaluated.
The output of each unit increased by 77 MW and the efficiency by 8 percentage points to 43 percent, after repowering. Repowering was feasible, technically. An economic analysis was required to determine the magnitude of the economic benefits of repowering, if any, and it turned out that the cost of electricity generated by the new technology was higher than that produced by the outgoing one. It was concluded, therefore, that repowering the steam turbine units with gas turbines fired on kerosene was uneconomical, for the performance level achieved.
Effective Decision Making in Simple and Combined Cycle Schemes at the Turn of the Millennium
Authors: Gayraud Stéphane , Singh Riti 
Published: December 2014

The electricity supply industry is being restructured all over the world. Privatisation, with the emergence of Independent Power Projects (IPPs), especially in developing countries, and liberalisation of the power generation market are changing decision-making processes in a radical way. New challenges of deregulation and customer demands, and economic instabilities in south-east Asia, oblige electric utilities to face a double jeopardy: least-cost planning and least-risk investments.
Consumers are encouraged to save energy and emission reduction policies are implemented to promote utilisation of high efficiency, clean power production technologies.
The aim of this paper is to introduce the concept of life cycle risk management and Decision Support System (DSS) for open and combined cycle schemes, highlighting the market potential for Flexible Mid-size Gas Turbines (FMGT) in mid-merit applications.
The DSS that has been developed at Cranfield University includes: plant simulation program, providing design and off-design performance, maintenance planning, component degradation, and load-following models. In addition several economic techniques based upon engineering finance and project accounting make power plant economic appraisals possible.
The DSS also provides a Monte Carlo risk analysis in order to deal with technical and economic uncertainties in a very effective way.
Case studies will stress several parameters that planners have to carefully assess when making decision in the context of the coming millennium, bringing all sorts of new challenges and areas of uncertainty that will be discussed in the paper.
Hybrid Brush Pocket Damper Seals for Turbomachinery
Authors: Laos Hector E. , Vance John M. , Buchanan Steven E. 
Published: December 2014

Pocket damper seals perform a dual function: both sealing the pressurized gas around a rotating shaft and providing large amounts of vibration damping. The annular cavity between the labyrinth seal teeth is subdivided into separate annular cavities around the circumference of the rotor by partitioning walls. Also, the upstream and downstream teeth have different radial clearances to the rotor. These seals have been shown to provide a remarkable amount of direct damping to attenuate vibration in turbomachinery, but they generally leak more than conventional labyrinth seals if both seals have the same minimum clearance. Conversely, brush seals allow less than half the leakage of labyrinth seals, but published test results show no significant amount of damping. They are considered to be a primary choice for the seals in new aircraft engine designs because of their low leakage. This paper will describe a recently invented hybrid brush/pocket damper seal that combines high damping with low leakage. Previous brush seal results were studied and calculations were made to select a brush seal to combine with the pocket damper design. The result is a hybrid seal with high damping and low leakage. A special design feature can also allow active vibration control as a bonus benefit.
A computer code written for the original pocket damper seal was modified to include the brush element at the exit blade. Results from the computer code indicate that the hybrid seal can have less leakage than a six bladed (or 6 knives) labyrinth seal along with orders of magnitude more damping.
Experimental evaluations of the damping and leakage performance of the hybrid seal are being conducted by the authors. The experimental work reported here tested the damping capability of the new hybrid brush seal by exciting the seal journal through an impedance head. A conventional six-bladed labyrinth seal of the same working dimensions was also tested. The brush hybrid pocket damper seal is found to leak less than the labyrinth seal while producing two to three times more damping than the original pocket damper seal, (orders of magnitude more than the conventional labyrinth).
One Step Ahead Adaptive Control for Gas Turbine Power Plants
Authors: Camporeale S. M. , Dambrosio L. , Fortunato B. 
Published: December 2014

The feasibility of the application of One Step Ahead Adaptive (OSAA) Control technique to a gas turbine power plant is investigated. The OSAA technique is a control algorithm especially suitable for non-linear and time-varying systems. This technique uses the Least Square algorithm to estimate in real-time a linear model of the controlled system, and, uses the estimated linear model to evaluate the feedback control variables.
The proposed technique allows to control the Gas Turbine power plant in a wide range of electric loads due to its intrinsic adaptive capabilities. Moreover, the OSAA control does not require the knowledge of the dynamic characteristics (e.g. state space systems or transfer functions) in order to design the control system.
The OSAA control system has been applied to a single shaft Gas Turbine power plant, which is numerically simulated. The proposed control technique has been tested both in Single-Input Single Output (SISO) mode and in Multi-Input Multi-Output (MIMO) mode. Starting from a steady-state condition, the power plant has been supposed to undergo a step reduction of the electric load. The results show that the OSAA control technique effectively counteracts the load reduction with limited overshoots in the controlled variables and, introducing a integral correction, a negligible static error.