Constant Low Temperature Research Articles

Fluctuating thermal regimes extend longevity and maintain fecundity to increase shelf‐life of Drosophila melanogaster cultures

AbstractReduced temperatures increase longevity in cold‐tolerant insects, but insects that are not cold‐tolerant experience elevated mortality at constant low temperatures. Fluctuating thermal regimes (FTRs) increase longevity in many insect species while slowing or delaying development and senescence. Under FTR insects are held at low temperature with a daily warm pulse of increased temperature. The model organism Drosophila melanogaster is widely used for diverse research activities and numerous transgenic strains have been developed and must be maintained in continuous culture at stock centres. We measured the effect of FTR that oscillates between 6 and 22 °C on the longevity and fertility of adult D. melanogaster versus a constant temperature of 6 and 22 °C. We demonstrate that FTR increases mean longevity by 8.8‐fold compared to a constant 6 °C and by 5.9‐fold to a constant 22 °C. We assessed male and female fertility of FTR treated adults from 20 to 100 days at 20 day intervals and constant temperature treated adults after 7 days. Under FTR males exhibited increased fertility peaking at 80 days before dropping significantly at 100 days. Mean female fertility declined steadily under FTR but remained at 53% of constant temperature‐treated flies after 60 days. The increased male fertility remains unexplained. Fertility of the offspring of FTR‐treated adults did not differ from flies reared at constant 22 °C. FTR extends generations and cultures incubated under this protocol can establish new cultures. FTR can be used to further investigate the accumulation and mitigation of chill injury and is suitable for reducing maintenance in stock centres.

Beneficial effects of exposure to fluctuating temperatures during interrupted development in insects

Many insects overwinter in diapause, a state that protects them from chill injuries due to exposure to low temperatures. Those insects resume development in the spring, leaving behind the protection of the diapause state. Spring cold snaps and variable weather, which are expected to increase with climate change, make spring development risky for some insects. Insects exposed to constant low temperature stress while they are undergoing pupation have been shown to have increased mortality, wing deformities, and flight defects. Interrupting pupal development with recurring pulses of heat instead of a constant low temperature abrogates these effects. However, the mechanisms underlying the beneficial effects of fluctuating temperatures are largely unknown. Most evidence points to the warm period as a time of repair, but the specific systems that are being repaired remain unknown. To broadly explore what systems are involved, we used the alfalfa leafcutting bee, Megachile rotundata. This species is used in agriculture, commercially reared, and has been shown to exhibit benefits of exposure to fluctuating temperatures during development. Bees undergoing metamorphosis were exposed to constant (6C) or fluctuating (1 hour a day at 20C) low temperature stress. After one week in the temperature treatment, bees were flash frozen and assayed for macromolecule concentrations. We measured total lipid, sugar, and stored glycogen and trehalose concentrations. We predicted that total lipid content and glycogen would be higher in bees interrupted with fluctuating low temperature stress. Bees exposed to constant low temperature stress had 40% lower total lipid concentration compared to bees exposed to fluctuating stress, suggesting that not only lipid stores and possibly cell membranes may be compromised in those bees. Understanding the mechanisms underlying beneficial effects of fluctuating temperatures is important for several reasons. In M. rotundata, farmers routinely interrupt development with constant low temperature stress, resulting in bee loss and subsequent decreases in pollination services. Furthermore, many studies are carried out at constant temperatures, and insects are frequently reared at constant temperatures, possibly creating stressful conditions that could negatively affect an insect's physiology

Flow Field and Temperature Field in a Four-Strand Tundish Heated by Plasma

Tundish plasma heating is an effective method for achieving steady casting with low superheat and constant temperature. In order to study the flow field, temperature field in tundish heated by plasma, a three-dimensional transient mathematical model was established in the present work. A four-strand T-type tundish in a steelmaking plant was used to explore the changes in the flow field and temperature field of molten steel in the tundish under different plasma heating powers. The results showed that plasma heating affected the flow state of molten steel. It could eliminate the short-circuit flow at outlet. When the plasma heating was 500 kW, the molten steel had an obvious upward flow. The turbulence intensity was improved and distributed evenly with an increase in plasma heating power. In the prototype tundish, the temperature of the outlet was dropped by nearly 2–3 K within 300 s. With the increase of plasma heating power, the low temperature area in the tundish gradually was decreased. When the heating power was 1000 kW, the temperature difference of two outlets was 0.5 K and the overall temperature distribution was more uniform. The research results have a certain guiding significance for the selection of the actual plasma heating power on site.

Computational Fluid Dynamics Investigation on Catalytic Hydrodeoxygenation of a Bio-Oil Model Compound in a Fluidized Bed Reactor

Abstract Bio-oil produced from waste biomass by various thermochemical approaches possess several drawbacks primarily due to the presence of oxygenated compounds. These compounds render bio-oil difficult to be used as normal fuel for combustion. Thus, bio-oil must be processed to remove oxygenated compounds from it. One important process found suitable to deoxygenate bio-oil is the catalytic hydrodeoxygenation (HDO) using an appropriate catalyst. In literature, limited studies exist on the application of computational fluid dynamics (CFD) on hydrodeoxygenation of bio-oil model compounds. Therefore, authors utilized the computational fluid dynamics framework to delineate effect of process variables on the catalytic hydrodeoxygenation of 2-hydroxybenzaldehyde (2-HB) which is a bio-oil model compound in this study. The range of conditions considered herein are weight hourly space velocity (WHSV) = 1 h−1, 3 h−1, and 5 h−1; superficial hydrogen gas velocity, u = 0.075 m/s, 0.15 m/s, and 0.25 m/s; Pd/Al2O3 catalyst load = 0.06 kg and temperature, T = 498 K, 598 K, and 698 K. The present solution approach has also been applied to reproduce literature results on hydrodynamics of multiphase fluidized bed systems for comparison purpose. The hydrodynamics inside the fluidized bed reactor have been compared with and without HDO of 2-HB. The HDO of 2-HB yield phenol as the most dominant constitute of the products. Other products include benzene and benzaldehyde but in less fractions. Disclosing a few important results one can find that at constant low temperature (498 K), by increasing the values of WHSV the phenol fraction decreases, whereas those of benzene and benzaldehyde increases when u = 0.25 m/s. This effect becomes more rigorous at high constant temperature (698 K) especially in the case of phenol and benzene fractions. Moreover, most of the conversion of 2-HB and formation of products (phenol, benzene, and benzaldehyde) occurs within 2 s of fluidization time.

Exploring Microbial Biosignatures in Mn-Deposits of Deep Biosphere: A Preliminary Cross-Disciplinary Approach to Investigate Geomicrobiological Interactions in a Cave in Central Italy

The terrestrial subsurface offers privileged sites both to search for microbial life and to observe still mostly unknown characteristic lithologies. In particular, caves represent natural laboratories to investigate unique minerogenetic processes and biotic interactions, connected to these phenomena. Manganese mineralization in cave environments provides a window to understand the complex Mn cycle and the development of microbial communities in special conditions, such as low constant temperature, absence of light and, in particular, low-energy environments. In the current study, we isolated and characterized Mn-samples taken from the cave “Grotta Grande dei Cervi,” L’Aquila, Central Italy, and we used a multidisciplinary approach to characterize them, with the purpose of understanding the biogeochemical processes in extreme environments. A chemical characterization of the samples was done by EDS; further investigations are underway with other multidisciplinary methodologies to understand whether the Mn laminae are related to biological processes. SEM investigations revealed microbial imprints, showing cell-like structures and suggesting that the cell-like shapes occur within internal laminae. A culture-independent approach was used to assess the possibility that biotic factors may be involved in the production of these mineralizations and to investigate the nature of the microbial community in these materials. A molecular approach was the first step to investigate the role of microorganisms in forming manganese oxides associated with water bearing rocks. DNA from the black deposits was extracted and sequence analyses of specimens were performed. Our data support the hypothesis that microorganisms may contribute to the mineralizations of manganese in this environment, providing new encouraging insight into the role of microorganisms in the Mn cycle and the processes of energy acquisition in unfavorable conditions, with relevant implications for astrobiology.

Influence of temperature on germination of new buffelgrass (Cenchrus ciliaris) genotypes

Buffelgrass (Cenchrus ciliaris) is widely grown in tropical and sub-tropical arid rangelands around the globe because of its high tolerance to drought and high level of nutrients. In the present study, the seed germination response of 12 buffelgrass genotypes (nine collected accessions and three introduced varieties) was tested to record the various effects of storage duration and temperature treatments on germination. Five constant temperature treatments (15, 20, 25, 30 and 35°C) and two storage durations (12 and 24 months) were used. The studied buffelgrass genotypes responded differently to the different storage durations and temperature regimes, suggesting the importance of genotype assessment under different environments. The highest germination percentages were recorded for genotype BUR-1 at 20°C (45%) after 12 months. No germination occurred after 12 months at low constant temperatures (15°C) for all genotypes except BUR-1, BUR-2 and UIA. Therefore, there is a large genetic variability among buffelgrass genotypes for seed germination, which could permit improvement by selection and breeding.

Periodic Cooling during Incubation Alters the Adrenocortical Response and Posthatch Growth in Zebra Finches.

AbstractIn birds, incubation temperature is critically deterministic for a range of traits. When parents leave the nest to forage, developing embryos can be exposed to cooling events that represent thermal stress. To investigate the consequences of periodic cooling on offspring development and physiology, we exposed zebra finch embryos to cooling events throughout the incubation period. We then compared embryonic survival, egg mass change, incubation duration, posthatch growth, and adrenocortical response of these individuals with embryos reared at a constant optimal temperature of 37.4°C and embryos reared at a constant suboptimal temperature of 36.4°C, the mean incubation temperature of periodically cooled embryos. There were no differences in embryonic survival or egg mass change during incubation, but individuals exposed to periodic cooling had longer incubation periods than those from the 37.4°C treatment and shorter incubation periods than those from the 36.4°C treatment. Periodically cooled individuals showed slower posthatch growth in comparison with both constant-temperature treatments, but this did not impact adult body size. Treatment groups did not differ in their adrenocortical response, but embryos exposed to periodic cooling and a constant temperature of 37.4°C were able to habituate to repeated capture and restraint stress, while individuals exposed to the constant temperature of 36.4°C were not. These results point to the differential impacts of cooling events versus constant low temperatures during incubation on posthatch growth and physiology and may represent a way for parents to devote less energy toward incubation while still ensuring offspring success.

MIXED CONVECTION IN A SINGLE-WALLED CARBON NANOTUBE-WATER NANOFLUID FILLED PARTIALLY HEATED TRIANGULAR LID-DRIVEN CAVITY HAVING AN ELASTIC BOTTOM WALL

In this study, mixed convection of nanofluid filled triangular cavity with a partial heater and having an elastic bottom wall is analyzed with finite element method. Left vertical wall is partially heated while the inclined wall is kept at constant lower temperature. The bottom wall is flexible and inclined wall is moving at constant speed. Influences of Richardson number, elastic modulus of flexible wall, solid nanoparticle volume fraction on the convective heat transfer characteristics are analyzed. It was observed that, lower values of Richardson number, elastic modulus of the flexible wall and higher values of nano-particle volume fraction resulted in higher local and average heat transfer enhancements. Average heat transfer enhanced significantly when solid particle volume fraction of nanoparticle was increased. Enhancements up to 121% were obtained at solid volume fraction of 0.04 as compared to pure water at Richardson number of 1. Effects of elastic modulus of the bottom wall were found to be marginal and at Ri=1, enhancements up to 2% were achieved by using a more flexible wall.

Application of temperature-controlled ultrasound treatment and its potential to reduce phosphate content in frankfurter-type sausages by 50%

The objective of this study was to evaluate the effect of ultrasound treatments with different durations (15, 20, 25, 30, and 35 min) at a low static temperature (12 °C) controlled by an intelligent temperature control and monitoring system on the quality of 50% reduced-phosphate frankfurters. The results show that without ultrasound treatment, phosphate reduction caused some obvious deficits in the textural properties, sensorial parameters, and oxidative stability of frankfurters. Moreover, 25-min ultrasound treatment could significantly lower the cooking loss and enhance emulsion stability, textural properties, and sensorial parameters of reduced phosphate frankfurters, which was also verified by dynamic water distribution analysis and microstructural observation. Additionally, low constant temperature during ultrasound treatment was another crucial factor in retarding lipid oxidation during storage. Therefore, ultrasound treatment with moderate duration and stable low temperature could be considered a successful approach to obtain healthier reduced-phosphate frankfurters under the “clean label” concept.

Impact of Partial Slip and Heat Source on MHD Mixed Convection Flow of Nanofluid in a Double Lid-Driven Cavity Containing Insulated Obstacle

The current investigation analyzes the effects of partial slip and heat generation on the mixed convection flow with heat transfer in an inclined double lid-driven square cavity containing centered square adiabatic obstacle in the presence of magnetic field. The used cavity is subjected to constant heat flux and filled with Cu-water nanofluid. The top and bottom horizontal walls are thermally insulated and move with uniform velocity while the right vertical wall is maintained at a constant low temperature. A uniform heat flux is located in a part of th left wall of the cavity while the remaining part of this wall is thermally insulated. Finite volume technique is utilized to solve dimensionless governing equations of the problem. The proposed method is validated with the previous published numerical studies which distinctly offer a good agreement. The obtained results show that changing in the heat source length affects much the flow and thermal fields than the position of heat source. The averag Nusselt number decreases when the aspect ratio of the obstacle and heat source length increases. The heat transfer rate behaves nonlinearly with inclination of the cavity.

Flexible Reduced Graphene Oxide/Polyacrylonitrile Dielectric Nanocomposite Films for High-Temperature Electronics Applications

Polymer dielectrics possess excellent flexibility compared with inorganic ceramic materials. However, the relatively low dielectric constant and working temperature significantly constrain their wi...

Numerical study on the influence of RHCM on the basic parameters of filling the cavity

Injection molding is a very popular processing technology of polymeric materials. In the conventional injection molding, the low constant temperature of the mold is used for efficient heat removal. However, low mold temperature is not feasible for thin-walled and micro-featured parts. For these kinds of parts the RHCM (rapid heat cycle molding) technologies were developed, where the temperature of the mold is increased to above transition temperature of the polymer before the filling phase starts.In this paper, the influence of processing parameters and part thickness on maximum flow length was investigated with numerical simulations for thin-walled geometry manufactured with RHCM technology. Obtained results showed strongly nonlinear relations between maximum flow length, part thickness, and volumetric flow rate, whereas the relation between flow length, injection pressure, and cavity surface temperature was linear. Surprisingly, the cavity surface temperature had the smallest influence on maximum flow length, which may result from the velocity flow rate high enough to prevent the part from excessive solidification befor the maximum injection pressure is reached.

The effect of pressure on the characteristics of supercritical carbon dioxide extracts from Calamintha nepeta subsp. nepeta.

Chemists and industrialists are continuously attempting to develop greener and more environmentally benign chemical processes to extract essential oils and bioactive metabolites of high purity, finding various applications in cosmetics, detergents, nutraceuticals and pharmaceuticals. An increase preferenced for natural products over synthetic ones has made supercritical fluid technology a primary alternative for the generation of high-value bioactive ingredients. This effective technique requires only moderate temperatures, eliminates clean-up steps and avoids the use of harmful organic solvents. In this context, our study was focused on the chemical analysis of Calamintha nepeta subsp. nepeta aromatic extracts obtained with supercritical carbon dioxide. The effect of different operating conditions on the capacity of the lipophilic solvent to extract the targeted volatile components was also studied. The process was carried out at a fairly low constant temperature of 40°C, and with varying the pressure from 90 to 300 bar. The chemical composition of the extracts was analyzed by gas chromatography-mass spectroscopy. The results showed that the composition pattern, the concentrations of individual components and the quality of the extractable analytes were affected by pressure increase. The extraction yields varied from 0.73 to 1.21 wt% at 90 and 300 bar, respectively.

Silicon emissivity as a function of temperature

In this paper we present the temperature-dependent emissivity of a silicon sample, estimated from its cool-down curve in a constant low temperature environment ( ~ 82K). The emissivity value follow a linear dependency in the 120–260 K temperature range. This result is of great interest to the LIGO Voyager gravitational wave interferometer project since it would mean that no extra high thermal emissivity coating on the test masses would be required in order to cool them down to 123 K. The results presented here indicate that bulk silicon itself can have sufficient thermal emissivity in order to cool the 200 kg LIGO Voyager test masses only by radiation in a reasonable short amount of time (less than a week). However, it is still not clear if the natural emissivity of silicon will be sufficient to maintain the LIGO Voyager test masses at the desired temperature (123 K) while removing power absorbed by the test masses. With the present results, a black coating on the barrel surface of the test masses would be necessary if power in excess of 6 W is delivered. However, the agreement we found between the hemispherical emissivity obtained by a theory of semi-transparent Silicon and the obtained experimental results makes us believe that the LIGO Voyager test masses, because of their dimensions, will have effective emissivities around 0.7, which would be enough to remove about 8.6 W (7.5 W) for a shield at 60 K (80 K). This hypothesis may be confirmed in the near future with new measurements.

Phospholipid fatty acids are correlated with critical thermal tolerance but not with critical pressure tolerance in the shallow-water shrimp Palaemon varians during sustained exposure to low temperature

Some extant deep-sea shrimp are known to be descended from shallow-water ancestors that adapted to environmental conditions (constant low temperature and high hydrostatic pressure) in the deep sea. During acclimation to low temperature and high hydrostatic pressure representative of the deep-sea, critical thermal tolerance decreases and critical pressure tolerance increases in the shallow-water shrimp Palaemon varians. It has been suggested that these shifts may depend in part on adjustments to phospholipid fatty acid composition and/or metabolic adjustments. Here, we present evidence that metabolic rate does not change during sustained exposure to low temperature (5 °C) in the shallow-water shrimp Palaemon varians, and that metabolic rate and acute environmental tolerances are not correlated during sustained exposure to low temperature, suggesting that standard metabolic rate does not affect acute environmental tolerances. In contrast, we present evidence that phospholipid fatty acid composition does shift during sustained exposure to low temperature. Desaturation of fatty acids during sustained exposure to low temperature supports the suggestion that cell lipid bilayer homeoviscous modifications are important in low temperature acclimation. Shifts in several individual phospholipid fatty acids during sustained low temperature exposure are correlated with critical thermal tolerance. Exploring the greater complexity apparent in the responses of these phospholipid fatty acids to sustained low temperature exposures suggests a potential homeostatic impact moderating adverse impacts on nervous system function. However, shifts in phospholipid fatty acids are not correlated with critical pressure tolerance during exposure to low temperature, suggesting that shifts in critical pressure tolerance are related to modifications other than cell lipid bilayer composition.

Effect of Porous Medium and Copper Heat Sink on Cooling of Heat-Generating Element

Cooling of heat-generating elements is a challenging problem in engineering. In this article, the transient free convection of a temperature-dependent viscosity liquid inside the porous cavity with copper radiator and the heat-generating element is studied using mathematical modeling techniques. The vertical and top walls of the chamber are kept at low constant temperature, while the bottom wall is kept adiabatic. The working fluid is a heat-conducting liquid with temperature-dependent viscosity. A mathematical model is developed based on dimensionless stream function, vorticity, and temperature variables. The governing properties are the variable viscosity, geometric parameters of the radiator, and size of thermally insulated strip on vertical surfaces of the cavity. The effect of these parameters on the energy transport and circulation patterns are analyzed numerically. Based on the numerical results obtained, recommendations are given on the optimal values of the governing parameters for the effective operation of the cooling system. It is shown that the optimal number of radiator fins for the cooling system configuration under consideration is 3. In addition, the thermal insulation of the vertical walls and the increased thickness of the radiator fins have a negative effect on the operation of the cooling system.

Compressive Strength Gain Behavior and Prediction of Cement-Stabilized Macadam at Low Temperature Curing

For cement-based materials, the curing temperature determines the strength gain rate and the value of compressive strength. In this paper, the 5% cement-stabilized macadam mixture is used. Three indoor controlled temperature curing and one outdoor natural curing scenarios are designed and implemented to study the strength development scenario law of compressive strength, and they are standard temperature curing (20°C), constant low temperature curing (10°C), day interaction temperature curing (varying from 6°C to 16°C), and one outdoor natural temperature curing (in which the air temperature ranges from 4°C to 20°C). Finally, based on the maturity method, the maturity-strength estimation model is obtained by using and analyzing the data collected from the indoor tests. The model is proved with high accuracy based on the validated results obtained from the data of outdoor tests. This research provides technical support for the construction of cement-stabilized macadam in regions with low temperature, which is beneficial in the construction process and quality control.

Body mass of honey bee drones developing in constant and in changing temperatures

The body mass of honey bee (Apis mellifera) drones was investigated during a post-capping development under four temperature regimes: constant low temperature (32 °C), constant high temperature (35 °C), low temperature in the early stage followed by high temperature in the later stage, and high temperature in the early stage followed by low temperature in the later stage. The temperature regimes had significant influence on the drones’ body mass. The heaviest drones were obtained when the temperature was high at the early stage and low at the later stage of the post-capping period. The most lightweight drones occurred at constant high temperature. The body mass of drones was changing significantly over their adult life and was highest at the age of five days. After this age, the body mass tended to decrease until the end of life. These results suggest that the highest body mass of drones can be obtained by keeping them during the post-capping development in changing and not constant temperatures.

Comparison of Local Heat Transfer Distribution in Between Three-Dimensional Inclined Closed and Open Cavities

Abstract The phenomenon of natural convection is investigated in three-dimensional (3D) cavities with four adiabatic walls and one hot wall. The surface opposite to the hot wall is either a wall (closed cavity) at a lower constant temperature or is open to ambient at a lower temperature (open cavity). It is pointed out here that not only overall heat transfer is important, the distribution of local heat transfer is also important. To quantify the uniformity of heat transfer distribution, the ratio of maximum to average heat transfer is calculated for various Rayleigh numbers as well as inclination angles for open and closed cavities. A significant difference in the local heat transfer profile along the hot surface of the closed cavity in comparison to that in open cavity for small inclination angle (especially at higher values of Rayleigh number) is noted. However, the profile is remarkably similar in the case of vertical cavities. For inclined closed cavities, there is a buoyancy component of the flow acceleration normal to the hot and cold wall, which is absent in the case of vertical cavities. For lower inclinations, this component brings the three-dimensionality in the flow field and leads to the differences in the flow patterns. The fluid striking the cold wall in the case of the closed cavity causes significantly different flow patterns that, in turn, lead to nonuniform local heat transfer. To explain the flow behavior, iso-surfaces, stream ribbons, and the Y-components of the flow velocity are plotted at different surfaces of the closed cavity.

Avalanche photodiode single-photon detector with high time stability

Avalanche photodiode single-photon detector is one of the ultra-sensitivity photoelectric detector, which has important applications in the fields of long-distance laser ranging, laser imaging, and quantum communication. However, due to the high temperature sensitivity of the avalanche voltage, the avalanche photodiode single-photon detector is prone to fluctuation of the avalanche gain when it works in the field environment, which leads to the delay drift and seriously reduces the time stability. In this paper, we proposed a method of stabilizing the delay of the single-photon detector. An embedded system was used to control avalanche photodiode at constant low temperature and compensate the delay drift of the detection circuit caused by the change of environment temperature in real time. A high time stability avalanche photodiode single-photon detector was realized by this method. In the experiment, the environment temperature changed from 16 ℃ to 36 ℃, and the avalanche photodiode was controlled at 15 ℃. After compensation, the delay drift of the avalanche photodiode single-photon detector was within ±1 ps, and the time deviation was 0.15 ps@100 s. This work is expected to provide an effective solution for the application of high-stability single-photon detector in the field and space environment.