Minimum Average Value Research Articles

Field Studies on Circadian Rhythms of Core Temperature in Tropical Inhabitants Compared with Those in European Inhabitants

In order to know the characteristics of circadian rhythms in core temperature in tropical inhabitants, we measured rectal temperatures every 10 min for 50 h in 6 Vietnamese, 20–22 years old (5 males and 1 female) under natural conditions. Ambient temperatures ranged from 33 to 36°C. These data obtained in tropical inhabitants were compared with those in Polish inhabitants. The participants in both groups were usually sitting during wakefulness and lying in bed during sleep. The results obtained are summarized as follows: (1) The average maximum value was 37.7°C, which was significantly higher than in the Europeans; (2) The average minimum value was 36.2°C, which was lower; (3) A range of oscillation was 1.5°C, which was clearly greater than in the Europeans. The higher maximum value of core temperature, which was actively regulated under warm temperature, seemed of adaptive significance in order to reduce water consumption. A greater rage of oscillation in tropical Vietnamese people might have ecological significance for efficient acclimatization in the warm environment, suggesting that the setpoint of core temperature could show a greater range of oscillation.

The effect of rider weight on rider-induced loads during common cycling situations

Motivated by the desire to provide information useful in the design analysis of bicycle frames, the hypothesis tested was that a simple linear model would relate the maximum magnitudes of rider-induced loads to rider weight. Rider-induced loads are loads developed as a result of weight and muscular actions during pedalling. To test this hypothesis, five riders spanning a wide weight range rode a bicycle unrestrained on a treadmill. Dynamometers measured six components of pedal loads and five components of both seat and handlebar loads while riders rode three common cycling situations — seated cruising, seated climbing, and standing climbing. Average, average maximum, and average minimum values were computed for all load components and each was analyzed statistically. For all three test cases, the regression slope was significant for the force component normal to the pedal surface. Because the normal pedal force component has been shown previously to dominate frame stress at the point most likely to fatigue (Hull and Bolourchi, 1988, J. Strain. Anal. 23, 105–114), the results of this study should be useful in designing frames optimized for minimum weight and acceptable structural reliability.

Average Performance of Heuristics for Satisfiability

Distribution-free tight lower bounds on the average performance ratio for random search, for a greedy heuristic and for a probabilistic greedy heuristic are derived for an optimization version of satisfiability. On average, the random solution is neverworse than ofthe optimal, regardless ofthe data-generating distribution. The lower bound on the average greedy solution is at least of the optimal, and this bound increases with the probability ofthe greedy heuristic selecting the optimal at each step. In the probabilistic greedy heuristic, prob- abilities are introduced into the search strategy so that a decrease in the probability of finding the optimal solution occurs only if the nonoptimal solution becomes closer to the optimal. Across problem instances, and regardless of the distribution giving rise to data, the minimum average value of the solutions identified by the probabilistic greedy heuristic is no less than of the optimal. AMS(MOS) subject classification. 68Q25 1. Introduction. This paper examines the average performance ofrandom search, ofa greedy heuristic and ofa probabilistic version ofa greedy heuristic for an optimization version of satisfiability. We derive tight lower bounds on the average performance of each heuristic. The analysis assumes no specific data-generating distributions and therefore is valid for all distributions.

Acute postburn edema: Role of strongly negative interstitial fluid pressure

Interstitial fluid hydrostatic pressure (Pif) was measured with micropipettes during the acute edema generation that followed thermal skin injury in rats. Intradermal Pif was reduced from normal level of -1 mmHg to very negative values after thermal injury. The strongly negative Pif reflects a tissue imbibition pressure created by the thermal injury. The magnitude and duration of this pressure was dependent on the extent of the injury and the availability of fluid. After in vivo injury to 10 and 40% of the total body surface area (TBSA), mean intradermal Pif was temporarily reduced to -20 and -31 mmHg, respectively. Intravenous fluid infusion resulted in a rapid return of Pif to slightly positive values. Fluid available for transfer from the circulation was reduced by inducing the injury after killing the animal (postmortem injury) and even more by the subcutaneous insertion of a plastic barrier: this led to more pronounced reductions in Pif to average minimum values of -95 and -135 mmHg, respectively. Our data show that increased tissue imbibition pressure and increased net filtration pressure (tissue mechanisms) are responsible for a major part of the acute fluid shifts into thermally injured skin. Vascular mechanisms (permeability changes and intravascular pressure) are involved in the postburn edema development but are clearly less important than hitherto believed.

Acute postburn edema: role of strongly negative interstitial fluid pressure.

Interstitial fluid hydrostatic pressure (Pif) was measured with micropipettes during the acute edema generation that followed thermal skin injury in rats. Intradermal Pif was reduced from normal level of -1 mmHg to very negative values after thermal injury. The strongly negative Pif reflects a tissue imbibition pressure created by the thermal injury. The magnitude and duration of this pressure was dependent on the extent of the injury and the availability of fluid. After in vivo injury to 10 and 40% of the total body surface area (TBSA), mean intradermal Pif was temporarily reduced to -20 and -31 mmHg, respectively. Intravenous fluid infusion resulted in a rapid return of Pif to slightly positive values. Fluid available for transfer from the circulation was reduced by inducing the injury after killing the animal (postmortem injury) and even more by the subcutaneous insertion of a plastic barrier: this led to more pronounced reductions in Pif to average minimum values of -95 and -135 mmHg, respectively. Our data show that increased tissue imbibition pressure and increased net filtration pressure (tissue mechanisms) are responsible for a major part of the acute fluid shifts into thermally injured skin. Vascular mechanisms (permeability changes and intravascular pressure) are involved in the postburn edema development but are clearly less important than hitherto believed.

Nasal heat and water exchange in gray seals.

Metabolic rate (MR), expired air temperature (Tex), respiratory frequency (f), respiratory minute volume (V), and skin (Ts) and body (Tb) temperatures were recorded in three gray seals (Halichoerus grypus) at ambient air temperatures (Ta) between -40 and +20 degrees C. At Ta within the thermoneutral zone, MR averaged 3.7 W.kg-0.75, while mean V was 0.26 1.min-1.kg-0.75. At Ta below -11 degrees C [apparent lower critical temperature (Tlc)], both MR and V increased linearly with decreasing Ta. Average maximum MR (9.6 W.kg-0.75) and V (0.57 1.min-1.kg-0.75) were both recorded at Ta of -40 degrees C. Tex decreased with decreasing Ta to an average minimum value of 8 degrees C at Ta of -30 degrees C. The highest Tex recorded was 32 degrees C at Ta of +20 degrees C. At Ta of -20 degrees C, both total respiratory heat loss, with one exception, and respiratory evaporative water loss reached their lowest values. At this Ta, 66% of the heat and 80% of the water added to the inspired air were regained on expiration. We suggest that nasal heat exchange may be of considerable importance for thermal and water balance in many pinnipeds.

The Zambezi River in Moçambique

SUMMARY. Surveys of the physico‐chemical status of the River Zambezi in Moçambique were conducted between April 1973 and May 1974, to characterize the river prior to the closure of the Cabora Bassa Dam and to provide baseline data from which future changes in the river ecosystem can be followed.The temperature of the river water increases by about 3°C from Lake Kariba to the sea, and with an average pH of 7.8 the water is slightly more alkaline than Kariba Dam water. The river is well oxygenated with no sign of hydrogen sulphide. Transparency is generally very low and changes are mainly determined by the floods of local tributaries. The overall average total alkalinity is 55 mg 1−1 CaCO3, with no regular seasonal variation, average concentrations of chloride and sulphate are respectively, 5.4 mg 1−1 Cl− and 5.3 mg 1−1 SO2‐4. They increase under both the influence of the ionically rich Shire River and the sea; the latter due to vertical mixing. Total hardness and calcium hardness behave in a similar way, while conductivity and silica concentrations increase slightly until the Zambezi—Shire confluence, at which point, conductivity increases by 25% to an average peak value of 153 μS cm−1, and silica decreases by 15% to a minimum average value of 15.5 mg 1−1 SiO2. Ammonia and nitrate concentrations show a clear seasonal variation, with respectively, minimum dry season and maximum wet season average values of about 0.05 mg 1−1 and 0.3 mg 1−1. The overall average concentration of nitrite is 0.004 mg 1−1. Orthophosphate in the river is mostly affected by Lake Kariba, though other sources are also of some importance. Maximum average concentrations of about 0.4 mg 1−1 PO3‐4 were recorded during the dry season after the overturn of Lake Kariba. The concentration of dissolved metals is mainly determined by the outflow of Kariba and by the Shire River, with only K and Mg apparently affected by the outflow from Lake Kafue.It is concluded that the water quality of the Middle Zambezi is mainly determined by the Kariba Dam, with the Kafue Dam playing a minor role. At the time of the pre‐impoundment survey, the main impact on water quality of the Lower Zambezi came from the Shire River. With the addition of yet another large reservoir on the Zambezi, in the form of Cabora Bassa, together with the appreciable effect of tributary rivers on the lake, and the likely increased impact of the Shire River on the now more regulated river, the quality of the Lower Zambezi is expected to alter considerably, with concomitant ecological changes.

Exhalation time characterizing exhaustion while wearing respiratory protective masks.

Exhalation time has been determined to be a rapid and reliable measure of the state of respiratory exhaustion of a working individual. Values of exhalation time obtained for healthy, young men during exercise decreased in value until a minimum was reached at the limit of their endurance. Although the average values varied somewhat among subjects, exhalation times at exhaustion for a particular individual were found to be very consistent, the standard deviation being approximately 10% of the mean. The average minimum value of 0.66 sec for 18 subjects appeared to be independent of inhalation resistance over the range of.11—.66 mm H2O—min/liter at 0.22 mm H2O—min/liter exhalation resistance. Exhalation time at exhaustion also appears to be independent of exhalation resistance over the range 0—0.6 mm H2O—min/liter.

An Investigation into the possible Control of the Mealybug Vectors of Cacao Swollen-shoot Virus by Trunk Implantation with Dimefox

SummaryPreliminary experiments having shown that dimefox (bis(dimethylamino) fluorophosphine oxide) placed in holes drilled at ground-level in cacao trees gave encouraging results in controlling the most important of the mealybugs that transmit swollen-shoot virus (Pseudococcus njalensis (Laing), Planococcus citri (Risso) and Ferrisiana virgata (Ckll.)), two further experiments to investigate the technique and determine the optimum dosage were performed in Ghana in April-June and September-November 1953, respectively. A randomised-block layout was used, with four replicates (each comprising a plot of seven trees) of each treatment at Tafo and, in the first experiment, another two at Bunso. The first experiment disclosed no significant difference in effect when the implantation holes were spaced four inches as against two inches between centres and the former spacing alone was used in the second experiment. The dosage levels of dimefox, based on the weight of the aerial part of the tree estimated from the girth—weight ratio, were 75, 150, 225 and 300 parts per million w/w in each experiment, the lowest representing about one-twelfth of the soil-application rate, and also 375 p.p.m. in the second experiment. The results were assessed in terms of the total number of mealybugs, of all three species, counted on the various parts of the trees, which were felled and examined six weeks after treatment; counts made on a duplicate set of trees in the second experiment that were felled at nine weeks were significantly greater.Statistical analyses of the logarithmic transformations of the population figures obtained at six weeks showed the regression of population on dosage to be a curve of quadratic form. There was thus a limit to the response obtained, the minimum populations of total mealybugs (adults + nymphs) being achieved at a dose rate of 281 p.p.m. in the first experiment and 317 p.p.m. in the second. In the former, the minimum value of the average population of total mealybugs per tree was below that required for efficient control (one per tree), but the variability of the response was such that the population on 35 per cent, of trees so treated would have been above that level; in the latter, the minimum average value attainable was only slightly less than one, and consequently the population on nearly half the trees would have exceeded the level for effective control. Analysis of the combined results from those replications of each experiment that were sited at Tafo showed that a given dosage rate appeared only about half as effective, in terms of the residual population (expressed logarithmically), in October-November as in April-May, but concurrent records from untreated control trees suggest that this may partly have been because populations were falling naturally at the earlier date. Slight leaf-shedding occurred in some of the treated trees.

Acoustic Irritation Threshold of Ringbilled Gulls

When exposed to high-intensity sound, ringbilled gulls do not, to any extent, show the head-shaking reaction that was previously observed for ducks. They do, however, show a great tendency to cringe or crouch and are also subject to a temporary change in the rate of heart beat. These reactions are used to define and measure an acoustic “irritation threshold” at different frequencies between 100 and 3000 cps. The threshold determined with reference to the cringing reaction is remarkably reproducible over a period of weeks (having an average minimum value of about 85 db at 400 to 500 cps) but rises considerably during the first eleven months of the bird's life.

Seasonal Changes in the Phosphate Content of Sea Water in relation to the Growth of the Algal Plankton during 1923 and 1924

1. The seasonal changes in the sea water of the English Channel and. of Plymouth Sound have now been followed for almost two years, and the second year's results closely resemble those of the first, and again confirm the earlier surface results obtained by Matthews. For 1923 the average consumption at Station El, surface to bottom, 70 metres, was 29·6 mg. of P2O5 per cubic metre, leaving a balance of 7·4 mg. out of the original 37 mg. For 1924 the corresponding figures were, used up 28·3 mg., balance 8·7 mg., winter concentration 37 mg. The minimum average value was obtained in June and July in 1924, in July only in 1923. During June, July, and August, 1924, the surface water was almost entirely denuded of phosphate, values from 1·5 to 2·5 mg. per cubic metre being obtained. These figures would be milligrams per metric ton if fresh water were being considered, as it is they are milligrams per 1027 kg. for. water of S35·3% at 11°C, so it may be appreciated that very little phosphate remains unutilized by the phytoplankton.2. Owing probably to the high sunshine record for March the year 1924 was over a month ahead of 1923 in the spring as regards phosphate consumption, and, therefore, it may be presumed in the multiplication of the phytoplankton. At the same time, in the attainment of definite temperatures 1924 lagged about a month behind. 1923 in spring. Since temperature has such a marked effect upon the rate of development of the plankton as a whole it appears that the zooplankton must have been retarded in 1924 as compared with 1923.3. Samples obtained from the tropics show that even in winter phosphate may be much diminished, for the light is bright. The periodic alterations in phosphate content are, therefore, suppressed or much reduced as compared with the temperature zones. It is indicated that in arctic latitudes the sea becomes even richer in phosphate during winter than it does here, accordingly the summer development of phytoplankton is all the. more abundant.