Low Ambient Temperature Conditions Research Articles

Effects of Dominance on Vigilance in Avian Social Groups

During winter, many temperate-zone animals must survive harsh environmental conditions of low ambient temperatures, long nights, and unpredictable food supplies. Two evolutionary forces are thought to affect an individual's survivorship during winter: risk of starvation and risk of predation (Lima 1986, McNamara and Houston 1990, Grubb and Pravosudov 1994a, Pravosudov and Grubb 1997). Foraging and vigilance for predators appear to be mutually exclusive forms of behavior that an animal must trade off (Lima 1986). To reduce the risk of starvation, an animal must maximize the rate of foraging and energy intake, but to reduce the risk of predation, it must maximize its vigilance. Social foraging has been thought to benefit all members of a group by allowing each member to increase its foraging efficiency while sharing vigilance with the rest of the group (Elgar 1989). Vigilance in social groups of birds may be directed at predators or dominant group members (Waite 1987a, b; Elgar 1989). Recent studies have suggested that vigilance toward dominant individuals could be directed at both conspecifics and heterospecifics in multispecies groups (Popp 1988, Carrascal and Moreno 1992, Sasvari 1992). Ekman (1987) reported that subordinate Willow Tits (Parus montanus) were more vigilant than dominant individuals. Hogstad (1988a), on the other hand, reported the opposite trend, with dominant Willow Tits being more vigilant than subordinates. The latter report, however, was equivocal because in some instances juvenile females, which always have the lowest dominance rank, had the highest vigilance rates (Hogstad 1988a). However, the absolute rate of vigilance might not be the best measure of benefits for group members. Both studies of Willow Tits examined vigilance of group members within groups but did not provide comparative records for solitary individuals. Because parids seldom (if ever) are solitary in nature, only a manipulative study can provide records for solitary birds under controlled circumstances. Although dominance-related vigilance within the same species occasionally has been studied in controlled experiments (Waite 1987a, b), the effect of heterospecific group members on vigilance has been

Psychrophilic anaerobic treatment of low strength wastewaters

Psychrophilic (2 to 20°C) anaerobic treatment of low strength synthetic and malting wastewater was investigated using a single and hvo module expanded granular sludge bed (EGSB) reactor system. The chemical oxygen demand (COD) removal efftciencies found in the experiments exceeded 90% in the single module reactor at an organic loading rate up to 12 g COD dm −3’ day −1 and a HRT of 1.6 h at 10–12°C ambient temperature using influent concentrations ranging from 500 to 800 mg COD dm −3 When a two module EGSB system was used at the temperature range l0–15°C, soluble COD removal and volatile fatty acids removal of 67–78% and 90–96% were achieved, respectively, and an OLR between 2.8–12.3 kg COD m -3 day −1 and a HRT of 3.5 h. The second module serves mainly as a scavenger of non-degraded volatile fatty acids (VFA) horn the fust module. The optimal temperatures for substrate conversion of reactor sludge, after it has heen exposed to long term psychrophilic conditions, were similar to those of the original mesophilic inoculum. The specific activities of the sludge in the reactor increased in time by a factor 3, indicating enrichment of methanogens and acetogens even at low temperatures. By adapting the process design to the expected prevailing conditions inside the reactor, the loading potentials and overall stability of the anaerobic high-rate process may be distinctly improved under psychrophilic conditious. The results obtained clearly reveal the big potentials of anaerobic wastewater treatment under low ambient (l0–12°C) temperature conditions for low strength wastewaters, very likely including domestic sewage.

Radiotelemetric measurement of body temperature in feedlot steers during winter.

Little is known concerning body temperature regulation in cattle under conditions of low ambient temperature. To investigate the influence of cold on body temperature regulation, core body temperatures of feedlot steers (crossbred Bos taurus) were monitored for two winters in Nebraska, from late December to mid-March in yr 1 and from late December through June in yr 2. In yr 1, radiotransmitters to monitor temperature were implanted in the peritoneum of five steers (360 kg); in yr 2, four steers (320 kg) were used. Body temperatures and ambient temperatures were recorded at 3-min intervals and were mathematically filtered to produce 120 readings/d. For yr 1 and 2, daily maximum (40.09 and 39.66 degrees C), minimum (38.78 and 38.64 degrees C), and average (39.29 and 39.06 degrees C) body temperatures were not affected by ambient temperatures. Body temperatures exhibited circadian rhythms with the minima at approximately 0800 and the maxima at approximately 1900. For both years, sharp peaks in body temperature were often seen in the evening and, for yr 2, to a lesser extent in the morning. The occurrence of peaks was normally congruent, within a 1.5-h window, across steers. Congruent peaks in the evening with peak heights of 1.05 and .77 degrees C occurred on 65 and 56% of the days in yr 1 and 2, respectively. Occurrence of congruent peaks was correlated with dusk; peaks followed dusk by 30 to 60 min. Ambient temperature also influenced the occurrence of peaks; few peaks were observed when average daily ambient temperatures were below -7.5 degrees C. The dynamic changes in body temperature throughout the day, including the peaks in body temperature after dusk, strongly suggest that thermoregulatory systems in steers respond not only to current ambient conditions, but also to more integrative measures such as day length and daily heat load.

Low Ambient Temperature and Neuroendocrine Response to Hypoglycemia in Men

Nutritional factors, such as an excess or a deficiency of glucose, play an important role in neuroendocrine regulations. Hormonal and metabolic responses to hypoglycemia were examined in healthy non-obese volunteers under conditions of low ambient temperature. Hypoglycemia was induced by intravenous injection of insulin in two randomized trials performed at room temperature and at 4 degrees C. At room temperature, the typical neuroendocrine response to hypoglycemia was established. The increases of ACTH, beta-endorphin, growth hormone and cortisol in response to insulin hypoglycemia failed to be modified by low ambient temperature. Acute cold exposure significantly reduced epinephrine and totally inhibited prolactin response to insulin-induced hypoglycemia. In spite of significant changes in epinephrine response to hypoglycemia at low ambient temperature, no striking differences in plasma glucose levels compared to those measured at room temperature were observed. However, under conditions of low temperature the reestablishment of normoglycemia was delayed. No changes in free fatty acids were found under our experimental conditions. The presented data show that low ambient temperature exerts selective effects on some neuroendocrine and metabolic parameters.

Ambient temperature effect on automotive exhaust emissions: FTP and ECE test cycle responses

Over the past decades, the automotive industry has managed to successfully meet the demands set by the continuous and worldwide progress in exhaust emission legislation. This has, to a great extent, been possible by employing catalytic exhaust after-treatment. The growing use of advanced emission control has now brought an increasing number of vehicles using such technology to the areas of cold climate like the Nordic countries. However, low ambient temperature and cold operating conditions have been found to increase emissions and to diminish the performance of a catalyst system. This has been the case, because the design guidelines are mainly set by the legislation, in which low ambient temperature conditions have not been considered in test procedures so far. This paper discusses the emissions performance of current technology vehicles under low ambient temperature conditions. Both the US FTP75 as well as the ECE test procedure, now comprising the ECE15 and the EUDC driving schedules, have been used to assess the response of vehicles and their emission control systems. Altogether, 10 current-technology vehicles have been tested at subzero temperatures. The results show clearly the negative effect of low ambient temperature. Furthermore, they illustrate how dependent the emission output is on the test procedure and driving schedule applied.

The effects of supercooling and freezing on natural convection in seawater

Results of an experimental study of the convective heat and mass transfer processes for downward freezing from a horizontal surface into seawater at 35‰, i.e. at oceanic salinity, are presented here. Liquid supercooling of about 5.0°C was detected at the cooling surface before freezing began. Supercooled water was also detected far from the cooling surface, under some conditions. This supercooling, before freezing, allowed the possibility for density extremum effects to arise under some conditions of low ambient water temperature and large extracted heat flux. After freezing, however, flow visualization revealed that the flow was downward, below the freezing surface. At the high cooling and freezing rate used in these experiments the ice layer and water-ice interface salinities were found to be only weakly dependent on the ice growth rate. Convective heat transfer rates were found to be strongly affected by solute rejection upon freezing.

Thermoregulation in the female hedgehog, Erinaceus europaeus, during the breeding season.

The body temperatures of 3 breeding and 7 non-breeding female hedgehogs were monitored during 3 years. Lactating females had significantly higher and less variable body temperatures than did pregnant and non-breeding hedgehogs. Breeding females had circadian body temperature cycles that were more biphasic than those of non-breeders. Females maintaining higher mean daily body temperatures showed less variability about the mean than those exhibiting lower mean daily body temperatures. The rate at which body temperatures became more variable as mean daily body temperatures fell was 4.6 times more rapid in non-breeding females than in pregnant and lactating hedgehogs. With the exception of a single female in late gestation, hedgehogs readily became torpid under conditions of low ambient temperature and short photoperiod during summer, particularly when their food intake was restricted.

Experimental study of evaporation of a volatile pendant drop under high mass flux conditions.

Experimental studies on the rate of evaporation of a volatile, pendant liquid drop under high ambient temperature conditions (high mass flux) were carried out for the evaporation of water, methanol, n-hexane, n-pentane and carbon tetrachloride drops into dry air. Measurements were made for Rep = 32-328, Sc = 0.60-1.66 and dimensionless driving force B=0.02-1.36. Experimental results for the rate of evaporation of a liquid drop under low ambient temperature conditions showed good agreement with the low-flux equation by Ranz and Marshall and also with previous numerical solutions. Experimental results for rate of evaporation under high ambient temperature conditions showed a systematic deviation from the Ranz-Marshall correlation. Taking into account the effect of high mass flux together with the effect of variable properties, a new correlation equation was proposed which correlated all the experimental data very well.

Basking Behaviour in Larvae of the Butterfly Euphydryas Aurinia

The body temperatures of basking Euphydryas aurinia Rott. (Nymphalidae) larvae were measured using thermistor probes under field conditions. These showed that basking larvae could elevate their body temperatures to well above ambient. Under conditions of low ambient temperature but high solar radiation intensity, the temperature excess (i.e. observed body temperature minus ambient) of basking larvae can attain 30'C. Increases in body temperature were positively correlated with periods of high solar radiation intensity. The contribution of larval colour and behaviour is discussed.

Instruments for developing countries and for operation in difficult circumstances

Abstract

Evaluation of fatigue lifetime and elucidation of fatigue mechanism in plasticized poly(vinyl chloride) in terms of dynamic viscoelasticity

The fatigue behavior of plasticized poly(vinyl chloride) was investigated by means of a tension–compression-type fatigue apparatus. Complex elastic modulus and mechanical loss tangent were obtained continuously with time under the conditions of constant ambient temperature as a function of imposed strain amplitude. Brittle failure was observed under the conditions of low ambient temperatures and small strain amplitudes, or forced convection of air, whereas thermal failure was observed under the conditions of high ambient temperatures, or large strain amplitudes and natural convection of air. In the case of brittle failure, the dynamic storage modulus E′ exhibited a maximum and the loss tangent tanδ exhibited a minimum on approaching the point of failure. In the case of thermal failure, E′ decreased and tanδ increased monotonously until the onset of thermal failure. It was found that failure occurs when the effective energy loss reaches a certain magnitude depending on an ambient temperature. The fatigue criterion was represented schematically from a standpoint of self-heating. When the heat generation rate of the specimen under cyclic staining is larger than that of the heat transfer to the surroundings, thermal failure takes place. In this case, the specimen temperature increases up to a limiting constant temperature corresponding to the α-absorption temperature. When the heat generation rate is nearly equal to that of the heat transfer to the surroundings, the specimen temperature does not change appreciably and brittle failure takes place.

Thermoregulatory adjustments of skin blood flow in chronically spinalized dogs.

In awake dogs chronically spinalized at the level of Th3-Th6, the isolated section of the spinal cord was selectively cooled or heated at low, constant ambient air temperatures. A decrease of the skin temperatures at one or both hindpaws indicating cutaneous vasoconstriction was induced in 5 out of 7 animals by the spinal cold stimulus. These observations were confirmed by measuring cutaneous heat conductivity of the hindpaws. Selective heating of the spinal cord only occasionally induced a cutaneous vasodilatation. At the low ambient temperature conditions, the vasoconstriction induced by the spinal cold stimulus sometimes did persist after the end of spinal cord cooling. This indicated that peripheral cold stimuli also could induce reflex vasoconstrictor activity in the isolated spinal cord. The observations made on the influence of central cold stimuli on cutaneous blood flow in the spinalized animal contribute further support to the hypothesis that basic properties for thermoregulatory performance are established in spinal neuronal networks.