Hyper-resistive modeling in the spheromak

Current drive by coaxial helicity injection in the Sustained Spheromak Physics Experiment (SSPX) is modeled by a hyper-resistive term in Ohm's law for discharges in which magnetic fluctuations are small (1–3%). The current on the open magnetic field lines from the applied vacuum bias flux is assumed completely relaxed; interior to the spheromak, the helicity flux balances the ohmic losses. The poloidal area of the spheromak is found to depend on the strength of the hyper-resistive diffusion coefficient, allowing potentially large amplifications of the vacuum flux and discharge current. One discharge is examined in detail; the best fit to the experimental data finds that a limited fraction of the helicity injected into the flux conserver is effectively applied to current drive interior to the spheromak.     

Interactions of temperature and dietary protein concentration in growth and feeding of Manduca sexta caterpillars

Abstract .Temperature and the protein content of food affect rates of consumption and growth in herbivorous insects in different ways: reduced temperature typically reduces both consumption and growth rates, whereas reduced dietary protein typically increases consumption rate but either reduces or has no effect on growth rate. The interactions between temperature and dietary protein concentration in affecting consumption, growth and efficiency in fifth-instar caterpillars of Manduca sexta were studied, using both short-term (4 h) and long-term (duration of fifth stadium) experiments. The short-term experiments examined constant temperatures between 14 and 42°C, whereas the long-term experiments examined constant temperatures between 18 and 34°C; both experiments considered two levels of dietary protein. In both experiments, caterpillars had significantly higher consumption and frass production rates on low-protein compared with high-protein diets at each test temperature between 18 and 34°C, thereby compensating for the lower diet quality. In contrast, at more extreme temperatures (14 and 42°C) in the short-term studies, consumption and frass production rates were lower on low-protein compared with high-protein diets. As a result, there were substantial interactions between temperature and dietary protein for consumption and frass production rates in the short-term experiments, but not in the long-term experiments. These results suggest that interactions between temperature and dietary protein may emerge because of the failure of compensatory feeding responses at low and high temperatures. It is hypothesized that the failure of compensatory responses is more likely to occur under diurnally fluctuating temperatures than under a constant temperature with the same mean, and it is proposed that interactions between temperature and dietary protein for consumption are relevant to M. sexta and other caterpillars that experience wide diurnal fluctuations in temperature in the field.     

Variations of opisthaptoral hard parts of Gyrodactylus salaris Malmberg, 1957 (Monogenea: Gyrodactylidae) on parr of Atlantic Salmon Salmo salar L. in laboratory experiments

On parr of Atlantic salmon Salmo salar L. in laboratory experiments at different water temperatures, opisthaptoral hard parts of Gyrodactylus salaris Malmberg, 1957 differed in size. Their shape, on the other hand, varied only slightly. The opisthaptoral hard parts were largest at the lowest water temperatures and decreased in size with increasing water temperatures (1.5°C to 20.0°C). At both 18.0°C and 20.0°C the opisthaptoral hard parts of G. salaris were smaller than has been found under natural conditions. In the experiments, the mean size of the opisthaptor in the G. salaris micropopulation at each water temperature gradually increased or decreased compared to the mean size at the start of the experiments. At the end of the experiments the mean size of the opisthaptoral hard parts in the G. salaris micropopulations showed a significant regression to the different water temperatures.     

Experimental and Natural Warming Elevates Mercury Concentrations in Estuarine Fish

Marine food webs are the most important link between the global contaminant, methylmercury (MeHg), and human exposure through consumption of seafood. Warming temperatures may increase human exposure to MeHg, a potent neurotoxin, by increasing MeHg production as well as bioaccumulation and trophic transfer through marine food webs. Studies of the effects of temperature on MeHg bioaccumulation are rare and no study has specifically related temperature to MeHg fate by linking laboratory experiments with natural field manipulations in coastal ecosystems. We performed laboratory and field experiments on MeHg accumulation under varying temperature regimes using the killifish, Fundulus heteroclitus. Temperature treatments were established in salt pools on a coastal salt marsh using a natural temperature gradient where killifish fed on natural food sources. Temperatures were manipulated across a wider range in laboratory experiments with killifish exposed to MeHg enriched food. In both laboratory microcosms and field mesocosms, MeHg concentrations in killifish significantly increased at elevated temperatures. Moreover, in field experiments, other ancillary variables (salinity, MeHg in sediment, etc.) did not relate to MeHg bioaccumulation. Modeling of laboratory experimental results suggested increases in metabolic rate as a driving factor. The elevated temperatures we tested are consistent with predicted trends in climate warming, and indicate that in the absence of confounding factors, warmer sea surface temperatures could result in greater in bioaccumulation of MeHg in fish, and consequently, increased human exposure.     

The vulnerability to freezing-induced xylem cavitation of Larrea tridentata (Zygophyllaceae) in the Chihuahuan desert

The temperature dependence of freezing-induced xylem cavitation was studied in a Chihuahuan desert population of Larrea tridentata (Zygophyllaceae). Field measurements of wood temperature and xylem embolism were combined with anatomical studies and laboratory measurements of embolism in stem and root samples frozen under controlled conditions. Our laboratory experiments corroborated the previously observed relationship between minimum freezing temperature and embolism. The area of the low-temperature exotherms produced during the freezing treatments was correlated with the resulting embolism, suggesting that the freezing of water inside parenchyma cells is associated with the occurrence of xylem embolism. In the laboratory experiments, embolism in stems increased only at temperatures below -14°C. Although this meant that the studied population was more resistant to freezing-induced xylem embolism than a previously studied population from the Sonoran desert, the impact of freezing was nevertheless greater because of much lower environmental temperatures. This result suggests that dieback associated with periodic extreme freezes may contribute to limiting the present distribution of L. tridentata in central New Mexico. Although laboratory experiments showed that root xylem embolism increased after freezing to less negative minimum temperatures than stems (significant effects at T = -7°C), root embolism in the field was lower than shoot embolism in accordance with measured soil temperatures throughout the study.     

连续温度梯度下昆虫趋温性的研究现状与展望

昆虫作为一种能够自由活动的生物,可以通过运动主动选择对其有利的环境温度。大多数研究中昆虫被迫接受人为设定的恒温或变温,并未体现出昆虫本身对适宜温度的主动选择性。连续温度梯度是在某一介质的两端产生由高到低连续变化的温度范围。在一定温度梯度中昆虫趋温行为的研究揭示了其主动选择的适宜温度,这对了解昆虫的空间动态、提高测报准确性和开发防治新方法有重要意义。总结了产生连续温度梯度的各种装置,致冷、加热和温度测量方法以及昆虫趋温行为的观察装置和方法,包括在植物体上(内)及空气、下垫面、粮食和土壤等介质中产生温度梯度的方法及装置。各装置以水浴或电器设备制冷或加热,肉眼观察手工记录或以摄像机、声音信号采集系统等方法记录昆虫的行为。综述了多种昆虫生长发育、栖息、产卵或取食的偏好温度,总结了性别、发育阶段和生态型等生理因素及光照、湿度和预适应温度等环境因子对昆虫偏好温度变化的影响。昆虫的趋温性因种而异,同种昆虫不同发育阶段或不同生命活动所趋温度不同。多数种类昆虫雄性成虫的偏好温度比雌性略高。某些昆虫的多型现象可能导致其种内不同生态型的偏好温度存在差异。光照和湿度的变化会影响某些昆虫对温度的反应。有些昆虫经预适应温度训练后,其偏好温度发生改变。某些昆虫对温度的偏好呈现出一定的日变化和季节变化规律。饥饿条件下昆虫的偏好温度降低。温度梯度的有无及其方向、温度的高低、温差的大小等因素都会影响昆虫的活动性。最后分析了本类研究中存在的问题和不足,并展望了未来的研究方向,指出开展对重要农林作物害虫和天敌趋温行为及其生理学机制,外界环境因素影响昆虫趋温性等方面的探索将是未来该领域研究的重点内容。     

动物舌温与血液灌注率的关系特性研究

结合中医舌诊机理而进行的生物传热研究具有重要的意义。采用多种先进仪器和手段,在大量动物实验的基础上,通过对动物造模改变猪舌的血液灌注率,测试相应条件下的舌面温度,得到舌表面不同位置处的温度与血液灌注率之间的关系。结果表明,舌表面温度随血液灌注率的增加而升高,但血液灌注率增大到一定值后,舌面温度将维持不变,血液灌注率值也不再增长。通过实验得到的温度与血液灌注率间的变化规律,将为建立适合于舌体传热特性的生物传热模型提供客观依据。     

Probing the kinetics of single molecule protein folding

We propose an approach to integrate the theory, simulations, and experiments in protein-folding kinetics. This is realized by measuring the mean and high-order moments of the first-passage time and its associated distribution. The full kinetics is revealed in the current theoretical framework through these measurements. In the experiments, information about the statistical properties of first-passage times can be obtained from the kinetic folding trajectories of single molecule experiments (for example, fluorescence). Theoretical/simulation and experimental approaches can be directly related. We study in particular the temperature-varying kinetics to probe the underlying structure of the folding energy landscape. At high temperatures, exponential kinetics is observed; there are multiple parallel kinetic paths leading to the native state. At intermediate temperatures, nonexponential kinetics appears, revealing the nature of the distribution of local traps on the landscape and, as a result, discrete kinetic paths emerge. At very low temperatures, exponential kinetics is again observed; the dynamics on the underlying landscape is dominated by a single barrier. The ratio between first-passage-time moments is proposed to be a good variable to quantitatively probe these kinetic changes. The temperature-dependent kinetics is consistent with the strange kinetics found in folding dynamics experiments. The potential applications of the current results to single-molecule protein folding are discussed.     

Some comments on interpretations of Viking biological experiments.

Data from Viking experiments are analyzed from a biological viewpoint. The lack of organic matter in Martian soil could be due to the specificity of regions with optimal landing conditions. All data of labeled release experiments may be explained by assuming the existence of psychrophilic organisms, cultivated at temperatures above optimal ones, and other factors of a biological origin. The biological interpretation does not contradict the results of other life search experiments.     

Some comments on interpretations of Viking biological experiments

Data from Viking experiments are analyzed from a biological viewpoint. The lack of organic matter in Martian soil could be due to the specificity of regions with optimal landing conditions. All data of labeled release experiments may be explained by assuming the existence of psychrophilic organisms, cultivated at temperatures above optimal ones, and other factors of a biological orgin. The biological interpretation does not contradict the results of other life search experiments.     

Base Composition and Hybridization Studies of the Three Double-Stranded RNA Segments of Bacteriophage φ6

The three double-stranded ribonucleic acid (dsRNA) segments of the bacteriophage phi6 were isolated and shown to have similar melting temperatures and base compositions. RNA:RNA hybridization experiments with the isolated segments eliminate the possibility that the two smaller dsRNA segments arise from a cleavage of the large dsRNA segment. The two smaller RNA segments reanneal rapidly even at low temperatures; in contrast, the large dsRNA reannealed only at higher temperatures. Evidence is also presented which suggests that the dsRNAs may contain a short single-stranded RNA tail.     

Effects of temperature abuse on survival of Vibrio vulnificus in oysters.

Opaque and translucent morphotypes of a TnphoA-containing strain of Vibrio vulnificus were fed to oysters, which were subsequently stored at temperatures ranging from 0.5 to 22 degrees C for 10 days. Samples of oysters were homogenized and plated at intervals to determine the cell density of V. vulnificus and total aerobic population of bacteria present. At all temperatures, the numbers of V. vulnificus (both morphotypes) declined over the 10-day study period. The same observation was made with a lower inoculum of V. vulnificus. Identical experiments with shucked oysters showed a more rapid decrease in V. vulnificus. Identical experiments with shucked oysters showed a more rapid decrease in V. vulnificus to levels below limits of detection. Little change in the total bacterial counts was observed in shellstock oysters at any of the test temperatures, whereas incubation at the higher temperatures (17 and 22 degrees C) resulted in large increases in total counts in shucked oysters. These data suggest that temperature abuse of oysters may not be a factor in increasing the public health risk of V. vulnificus through raw oyster consumption. However, the data also suggest that even with proper storage, indigenous levels of V. vulnificus may remain sufficiently higher in shellstock oysters to produce infection in compromised hosts.     

Temperature Effects on Day Old Drosophila Pupae

Day old Drosophila pupae were subjected to a variety of closely controlled temperature shocks. Twenty-five hours after puparium formation (at 23°), temperatures from 39.5–41.5° (Q₁ = 2.3) differentially disturb the formation of the posterior crossvein. Three other separate treatments disturb posterior crossvein formation: treatments in the range 36.0–37.0° at 25 hours; 37.3–37.8° at 25 hours; and 39.5–41.5° at 19 hours. Certain qualitative effects are associated with certain temperatures: elliptical holes are seen in wings of flies exposed 25 hours after puparium formation to temperatures from 37.3–37.8°. Anterior crossvein defects ensue if animals are similarly exposed to temperatures from 37.9–38.2°. Within the physiological range, animals raised at higher temperatures are more resistant to the effects of temperatures at 39.5–41.5°. An extremely rapid temperature adaptation by exposures to temperatures in the range 31–38° results in markedly greater resistance to heat shock; here resistance to production of crossvein defects increases faster than to death. The association between qualitative effects and treatment temperatures is modified by changing the temperature at which the animals spend their first day of pupal life. Summation experiments support conclusions drawn from the simpler experiments. Genetic variation and interspecific variation are discussed in the present context, as well as implications of the role of protein denaturation in the biological effects of high temperatures and further, more general experiments.     

Rapid divergence in physiological and life-history traits between northern and southern populations of the British introduced neo-species, Senecio squalidus

Alien plants provide a unique opportunity to study evolution in novel environments, but relatively little is known about the extent to which they become locally adapted to different environments across their new range. Here, we compare northern and southern populations of the introduced species Senecio squalidus in Britain; S. squalidus has been in southern Britain for approximately 200  years and reached Scotland only about 50  years ago. We conducted common garden experiments at sites in the north and south of the species' range in Britain. We also conducted glasshouse and growth chamber experiments to test the hypothesis that southern genotypes flower later, are more drought-tolerant, germinate and establish better at warmer temperatures, and are less sensitive to cold stress than their more northern counterparts. Results from the common garden experiments are largely consistent with the hypothesis of rapid adaptive divergence of populations of the species within the introduced range, with genotypes typically showing a home-site advantage. Results from the glasshouse and growth chamber experiments demonstrate adaptive divergence in ability to tolerate drought stress and high temperatures, as well as in phenology. In particular, southern genotypes were more tolerant of dry conditions and high temperatures and they flowered later than northern genotypes. Our results show that rapid local adaptation can occur in alien species, and they have implications for our understanding of the ecological genetics of range expansion of introduced weeds.     

Temperature effects on bioconcentration of DDE by Daphnia

1. Lake temperatures vary with season, latitude, elevation and as a result of thermal pollution. In addition, lake temperatures may increase with global warming. Radiotracer experiments were conducted to determine the effects of temperature on the bioaccumulation of lipophilic organic contaminants by zooplankton. Daphnia pulex were exposed to ¹⁴C-labelled DDE, a stable metabolite of the organochlorine pesticide DDT, in particle-free water for 24 h. An increase in temperature from 5 to 25 °C resulted in a 314% increase in bioconcentration factor (the ratio of contaminant concentration in the organism to contaminant concentration in the water).
2. To mimic the fluctuating temperatures experienced by zooplankton during diel vertical migration, we conducted experiments in which animals were exposed to 25 °C for 12 h in the light, then 15 °C for 12 h in the dark. Exposure to this fluctuating temperature regime for 48 h resulted in a 27–33% increase in bioconcentration factor relative to a constant 20 °C control.
3. Live animals accumulated more than twice the amount of DDE than freshly killed animals, indicating that the activity of the organism is important in bioconcentration. This finding sheds light on the possible mechanisms for the increase in bioconcentration at higher constant temperatures. Daphnia pump more water through their branchial chambers at higher temperatures. Thus, if the thoracic limbs are an important site of contaminant uptake, then animals are exposed to more contaminant molecules at higher temperatures. Other possible mechanisms include changes in the thickness of the diffusive boundary layer and changes in cell membrane permeability.     

THE INFLUENCE OF CERTAIN MANUFACTURING PROCESSES ON THE STAPHYLOCOCCUS AUREUS CONTENT OF SPRAY-DRIED MILK

SUMMARY: Dried milk was prepared from milks inoculated with pure cultures of Staph. aureus , using a small pilot-type batch vacuum evaporator and spray drier. Vacuum evaporation reduced the numbers of Staph. aureus in most experiments but one strain was capable of multiplication at evaporating temperatures up to about 43°. Above 49° the organisms declined rapidly and at 56° they were eliminated. Residual staphylococci present in the warm concentrated milk feeding the drier increased in some experiments but declined markedly in others. Staphylococci added directly to warm concentrated milk always proliferated. A small proportion of staphylococci survived spray drying, even with high hot air temperatures. Different strains varied in their susceptibility to different stages of the whole process.     

Seed germination of a tropical rain forest pioneer tree (Heliocarpus donnell-smithii) in response to diurnal fluctuation of temperature

The tropical rain forest pioneer tree Heliocarpus donnell-smithii Rose establishes itself only in light gaps of the forest canopy. A series of experiments with fluctuating temperatures have shown that the germination is increased if the temperature rises above 31°C during a few hours each day. The laboratory experiments were complemented with determinations of the seed viability in the soil each month during one year, and with determinations of germination under the natural diurnal fluctuation of temperature in a forest gap. Germination increases under fluctuating temperatures, and the seeds can remain dormant when buried in the soil during several months. The diurnal heating of the soil of light gaps as contrasted with the almost constant temperature under undisturbed canopies may be a precise environmental indicator of appropriate conditions for germination and establishment of the pioneer heliophytes of the rain forest.     

Effects of intermittent flow and irradiance level on back reef Porites corals at elevated seawater temperatures

Corals inhabiting shallow back reef habitats are often simultaneously exposed to elevated seawater temperatures and high irradiance levels, conditions known to cause coral bleaching. Water flow in many tropical back reef systems is tidally influenced, resulting in semi-diurnal or diurnal flow patterns. Controlled experiments were conducted to test effects of semi-diurnally intermittent water flow on photoinhibition and bleaching of the corals Porites lobata and P. cylindrica kept at elevated seawater temperatures and different irradiance levels. All coral colonies were collected from a shallow back reef pool on Ofu Island, American Samoa. In the high irradiance experiments, photoinhibition and bleaching were less for both species in the intermittent high-low flow treatment than in the constant low flow treatment. In the low irradiance experiments, there were no differences in photoinhibition or bleaching for either species between the flow treatments, despite continuously elevated seawater temperatures. These results suggest that intermittent flow associated with semi-diurnal tides, and low irradiances caused by turbidity or shading, may reduce photoinhibition and bleaching of back reef corals during warming events.     

Sea ice bacterial growth rate, growth efficiency and preference for inorganic nitrogen sources in the Baltic Sea

Seasonal Baltic Sea ice is structurally similar to polar sea ice and provides habitats for diverse ice organism assemblages that are integral to the biogeochemistry and ecology of the sea during winter. Temperature and inorganic nitrogen sources have been suggested to control bacterial growth, with increasing dependence on ammonium at low temperatures. To study the bacterial growth and preference for the nitrogen source, we conducted experiments at 0 and 4°C, using ammonium and nitrate as nitrogen sources at two coastal fast-ice stations in the Gulf of Finland and in the Gulf of Bothnia during three successive winters. The two study sites differ markedly in relation to the allochthonous dissolved organic matter supply from the catchment area. High levels of bacterial growth were recorded at both study sites, with community generation times of 15–37 h. The measured bacterial growth efficiencies of 20–58% suggest that the Baltic sea ice brines provide a rich medium for bacterial growth and efficient functioning of bacteria-based food webs. Our experiments with sea ice samples showed a preference for ammonium at both temperatures and high potential growth in both types of nitrogen supplies. No major differences in phosphorus depletion rates were found at the two temperatures, but rates were always highest when ammonium was added to the experiments. These experiments point out that ice maturity, presumably through changes in bacterial community structure, impacts nitrogen processes and that these processes are pronounced prior to melting of the ice.