Environmental Variables Temperature Research Articles

Adaptive activity patterns of a blue wildebeest population to environmental variability in fragmented, semi-arid Kalahari, Botswana

The blue wildebeest (Connochaetes taurinus) population in semi-arid savannah regions face intense spatial and temporal environmental variability over the annual cycle. The population in the Kalahari has lost critical seasonal ranges outside the protected areas due to human induced landscape changes. The population is faced with sparse and patchy forage availability, seasonally very high day temperatures, high predation pressure and limited availability and variable quality of water. We investigated the adaptive strategies of wildebeest in the Central Kalahari Game Reserve with a focus on how daily activity patterns respond to environmental variability in semi-arid Kalahari. The population coped with heat stress by maximising their activity in the cool hours of the day. They avoided predation pressure and loss of body condition by minimising activity at night and in dry seasons, respectively. We conclude that seasonal variations in temperature and light play a critical role in the timing of foraging activity.

Habitat- and season-specific temperatures affect phenotypic development of hatchling lizards

Embryonic environments influence phenotypic development, but relatively few experiments have explored the effects of natural environmental variation. We incubated eggs of the lizard Anolis sagrei under conditions that mimicked natural spatial and temporal thermal variation to determine their effects on offspring morphology and performance. Incubation temperatures mimicked two microhabitats (open, shade) at two different times of the incubation season (April, July). Egg survival, incubation duration and offspring size were influenced by interactions between habitat- and season-specific nest temperatures, and locomotor performance was influenced primarily by temporal factors. These findings highlight the importance of spatial and temporal environmental variation in generating variation in fitness-related phenotypes.

Mission and Motion Planning for Autonomous Underwater Vehicles Operating in Spatially and Temporally Complex Environments

This paper seeks to enhance the autonomy of underwater vehicles. The proposed approach takes as input a mission specified via a regular language and automatically plans a collision-free, dynamically feasible, and low-cost trajectory which enables the vehicle to accomplish the mission. Regular languages provide a convenient mathematical model that frees users from the burden of unnatural low-level commands and instead allows them to describe missions at a high level in terms of desired objectives. To account for the constraints imposed by the mission, vehicle dynamics, collision avoidance, and the complex spatial and temporal variability of the ocean environment, the approach tightly couples mission planning with sampling-based motion planning. A key aspect is a discrete abstraction obtained by combining the finite automaton representing the regular language with a navigation roadmap constructed by probabilistic sampling. The approach searches the discrete abstraction to compute low-cost and collision-free navigation routes that are compatible with the mission. Sampling-based motion planning is then used to expand a tree of dynamically feasible trajectories along the navigation routes. The approach is validated both in simulation and field experiments. Results demonstrate the efficiency and the scalability of the approach and show significant improvements over related work.

Estimating effective boundaries of population growth in a variable environment

We study the impact of age-structure and temporal environmental variability on the persistence of populations. We use a linear age-structured model with time-dependent vital rates. It is the same as the one presented by Chipot in (Arch. Ration. Mech. Anal. 82(1):13-25, 1983), but the assumptions on the vital rates are slightly different. Our main interest is in describing the large-time behavior of a population provided that we know its initial distribution and transient vital rates. Using upper and lower solutions for the characteristic equation, we define time-dependent upper and lower boundaries for a solution in a constant environment. Moreover, we estimate solutions for the general time-dependent case and also for a special case when the environment is changing periodically.

Niche Conservatism for Ecological Preference in the Louisiana iris species complex.

Spatial and temporal environmental variation influences evolutionary processes such as divergence among populations and species. Here, we investigate the patterns of niche evolution for the Louisiana irises as well as understanding the phylogenetic relationship between these species. Using BEAST, a species phylogeny was generated for the Louisiana irises in order to test the hypothesis of whether niche conservatism has played an important role for this species complex. Species Distribution Models were constructed for present day distributions to determine the environmental factors, which contribute to species ranges. Tests of niche similarity were performed in order to evaluate if niche conservatism is apparent within this species complex. We demonstrate that the Louisiana iris species complex is a monophyletic clade with I. brevicaulis and I. fulva as being sister to each other. The differences observed among the iris species, in regard to associated environmental factors suggest an effect from these components on the distributions and habitats occupied. Furthermore, tests of niche similarity indicate niche conservatism for all species comparisons. Working at the species level and assessing various factors that can influence differentiation, this study assessed a more complete picture of the ecological and evolutionary history of this species complex across their geographic and ecological range.

Thermal error characteristic analysis and modeling for machine tools due to time-varying environmental temperature

The accuracy of machine tools is affected by both internal heat sources and time-varying environmental temperature. Therefore, the thermal deformation caused by environmental temperature variation is an important factor, which requires attention during thermal error modeling. In order to analyze the influence of time-varying environmental temperature on the thermal error of the machine tool, this paper proposed a thermal error modeling approach by using the thermal error transfer function of the machine tool. The approach was implemented in the following three steps. First, the thermal time constant of major components was calculated, according to structural parameters. Then, the thermal error transfer function of the components was derived. Finally, the thermal error transfer function of the whole machine was built based on the construction relationship. The analytical approaches of time domain and frequency domain were applied to obtain the thermal characteristics of machine tools based on the thermal error transfer function. Numerical simulations and the Z-axis operating experiment of three-axis milling machine were performed to verify the accuracy and effectiveness of the thermal error predicted model. The result shows that the proposed model is versatile and general with a clear modeling mechanism, which would provide a useful tool for the analysis and optimization design of machine tools with good thermal robustness.

One-side non-covalent modification of CVD graphene sheet using pyrene-terminated PNIPAAm generated via RAFT polymerization for the fabrication of thermo-responsive actuators

Thermo-responsive graphene-polymer films have been obtained by the modification of large CVD graphene films with pyrene-terminated poly(N-isopropylacrylamide) (PNIPAAm) via non-covalent π-π stacking interactions. Pyrene-terminated PNIPAAm was prepared by reversible addition fragmentation chain transfer (RAFT) polymerization using a pyrene-functionalized RAFT agent. Since PNIPAAm possesses a lower critical solution temperature (LCST) of 32°C, the as-prepared graphene-PNIPAAm films could be reversibly deformed as a result of the morphology response of PNIPAAm to the environmental temperature variation. In addition, the thermo-triggered deformation of the graphene-PNIPAAm films was observed to be reversible and controllable by manipulation of the environmental temperature. Atomic force microscopy (AFM) and high-resolution SEM analysis evidenced the successful attachment of the PNIPAAm on the graphene surface. The thickness of the polymer was revealed by high-resolution scanning electron microscopy (SEM). The successful stepwise fabrication of the CVD graphene-polymer composite films was also characterized using Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). These thermo-responsive composite films would be highly desirable for a wide range of applications, such as thermo-responsive actuators, a thermo-responsive intelligent switch was fabricated using these thermo-responsive graphene composite films.

Energetic costs of activity in wild lake trout: a calibration study using acceleration transmitters and positional telemetry

Acceleration telemetry transmitters offer the opportunity to estimate the cost of behaviours in free-ranging fishes, but a methodology to translate acceleration data into metabolic equivalents is still needed. This study extends previous calibration studies, explores how well tail-beat frequency transmitters fulfill their role, and presents a procedure to convert acceleration data into metabolic cost within a framework consistent with traditional fish bioenergetics models and thus facilitates comparisons of energetic costs between natural fish populations. These objectives were achieved by comparing data from lake trout (Salvelinus namaycush) in a laboratory setting with data from three natural populations. In the laboratory, tail-beat frequency, acceleration values, and oxygen consumption increased progressively with swimming speed. In the wild, individual swimming speeds estimated from positional telemetry were consistently underestimated by, but positively related to, transmitter-based acceleration values. The proposed rationale to estimate metabolic rate from acceleration data accounts for variation in fish mass and environmental temperature. We demonstrated how this novel method permits comparison of metabolic costs associated with the levels of activity typical of lake trout living in two different lakes.

Compensation for spindle’s axial thermal growth based on temperature variation on vertical machine tools

A new spindle’s axial thermal growth model based on temperature variation is proposed considering the limitations of spindle’s axial thermal growth model based on rotating speed. The model based on temperature variation is thereafter derived, and its mechanism is analyzed. It is found that model based on temperature variation is more robust. In the proposed model, a filtering method for calculating error and the identification process for parameters are also presented. The environmental temperature variation error and the repeatability of thermal growth at a constant rotating speed were investigated using a drilling center. Thereafter, the thermal growths at different rotating speeds were investigated using the same drilling center. Furthermore, the thermal growth with the disturbance of cooler was investigated using a milling center. The comparison of model based on rotating speed and model based on temperature variation is simulated, and the results indicate that the robustness of model based on temperature variation for rotating speeds and disturbance of cooler is stronger than model based on rotating speed. Finally, the experimental verification is carried out.

Seasonal metabolic acclimatization in the herbivorous desert lizard Uromastyx philbyi (Reptilia: Agamidea) from western Saudi Arabia

Many ectotherms adjust their metabolic rate seasonally in association with variations in environmental temperatures. The range and direction of these seasonal changes in reptilian metabolic rates are thought to be linked to the seasonality of activity and energy requirements. The present study was conducted to measure the standard metabolic rate (SMR) of seasonally-acclimatized Uromastyx philbyi with different body masses at 20, 25, 30, 35 and 40°C using open-flow respirometry during the four seasons. SMR was mass-dependent. The mean exponent of mass, “b”, in the metabolism-body mass relation was 0.76 (variance=0.0007). Likewise, SMR increased as temperature increased with low Q10 values at high temperatures and high Q10 values at low temperatures. The lowest and highest Q10 values were achieved for temperature ranges of 30–35°C for summer-acclimatized dhabbs (Q10=1.6) and 20–25°C for winter-acclimatized dhabbs (Q10=3.9). Seasonal acclimatization effects were obvious at all temperatures (20–40°C). Winter-acclimatized dhabbs had the lowest metabolic rates at all temperatures. The seasonal acclimatization patterns displayed by U. philbyi may represent a valuable adaptation for herbivorous desert lizards that inhabit subtropical deserts to facilitate activity during their active seasons and to conserve energy during inactivity at low temperatures.

Online decorrelation of humidity and temperature in chemical sensors for continuous monitoring

A method for online decorrelation of chemical sensor signals from the effects of environmental humidity and temperature variations is proposed. The goal is to improve the accuracy of electronic nose measurements for continuous monitoring by processing data from simultaneous readings of environmental humidity and temperature. The electronic nose setup built for this study included eight metal-oxide sensors, temperature and humidity sensors with a wireless communication link to external computer. This wireless electronic nose was used to monitor the air for two years in the residence of one of the authors and it collected data continuously during 537days with a sampling rate of 1 sample per second. To estimate the effects of variations in air humidity and temperature on the chemical sensors' signals, we used a standard energy band model for an n-type metal-oxide (MOX) gas sensor. The main assumption of the model is that variations in sensor conductivity can be expressed as a nonlinear function of changes in the semiconductor energy bands in the presence of external humidity and temperature variations. Fitting this model to the collected data, we confirmed that the most statistically significant factors are humidity changes and correlated changes of temperature and humidity. This simple model achieves excellent accuracy with a coefficient of determination R2 close to 1. To show how the humidity–temperature correction model works for gas discrimination, we constructed a model for online discrimination among banana, wine and baseline response. This shows that pattern recognition algorithms improve performance and reliability by including the filtered signal of the chemical sensors.

I’m not like everybody else: urbanization factors shaping spatial distribution of native and invasive ants are species-specific

Urbanization is a major global change inducing complex and multiple modifications of landscapes and ecosystems. The spatial distributions of organisms experiencing these modifications will likely shift specifically, depending on each species’ response to each environmental modification induced by urbanization. We sampled two ant genera (Lasius and Tetramorium) at 1248 locations along an urbanization gradient in Lyon, France and used high resolution spatial layers for 18 spatial (e.g., open habitat fragmentation, bioclimatic data and surface temperatures) and temporal (e.g., comparison of Normalized Difference Vegetation Index between 1986 and 2015) environmental variables associated with urbanization. Coupling two different analytical methods (Outlying Mean Index and Boosted Regression Trees), we showed that each species’ distribution was influenced by its own combination of environmental factors. Two morphologically cryptic Tetramorium species (T. sp.E and T. sp.U2) were both highly abundant but with opposite responses to urbanization: while T. sp.E was favored by urbanized habitat, T. sp.U2 avoided urbanized areas. Among Lasius species, we detected 63 occurrences of the invasive ant Lasius neglectus, the distribution of which was favored only by embankments along roads. We found that, even at this reduced spatial scale, climatic effects influenced most species and interacted with urbanization factors.

Temperature mediates continental-scale diversity of microbes in forest soils.

Climate warming is increasingly leading to marked changes in plant and animal biodiversity, but it remains unclear how temperatures affect microbial biodiversity, particularly in terrestrial soils. Here we show that, in accordance with metabolic theory of ecology, taxonomic and phylogenetic diversity of soil bacteria, fungi and nitrogen fixers are all better predicted by variation in environmental temperature than pH. However, the rates of diversity turnover across the global temperature gradients are substantially lower than those recorded for trees and animals, suggesting that the diversity of plant, animal and soil microbial communities show differential responses to climate change. To the best of our knowledge, this is the first study demonstrating that the diversity of different microbial groups has significantly lower rates of turnover across temperature gradients than other major taxa, which has important implications for assessing the effects of human-caused changes in climate, land use and other factors.

Time-resolved single-photon detection module based on silicon photomultiplier: A novel building block for time-correlated measurement systems

We present the design and preliminary characterization of the first detection module based on Silicon Photomultiplier (SiPM) tailored for single-photon timing applications. The aim of this work is to demonstrate, thanks to the design of a suitable module, the possibility to easily exploit SiPM in many applications as an interesting detector featuring large active area, similarly to photomultipliers tubes, but keeping the advantages of solid state detectors (high quantum efficiency, low cost, compactness, robustness, low bias voltage, and insensitiveness to magnetic field). The module integrates a cooled SiPM with a total photosensitive area of 1 mm(2) together with the suitable avalanche signal read-out circuit, the signal conditioning, the biasing electronics, and a Peltier cooler driver for thermal stabilization. It is able to extract the single-photon timing information with resolution better than 100 ps full-width at half maximum. We verified the effective stabilization in response to external thermal perturbations, thus proving the complete insensitivity of the module to environment temperature variations, which represents a fundamental parameter to profitably use the instrument for real-field applications. We also characterized the single-photon timing resolution, the background noise due to both primary dark count generation and afterpulsing, the single-photon detection efficiency, and the instrument response function shape. The proposed module can become a reliable and cost-effective building block for time-correlated single-photon counting instruments in applications requiring high collection capability of isotropic light and detection efficiency (e.g., fluorescence decay measurements or time-domain diffuse optics systems).

A drift line bias estimator: ARMA-based filter or calibration method, and its application in BDS/GPS-based attitude determination

The multi-antenna synchronized receiver (using a common clock) is widely applied in GNSS-based attitude determination (AD) or terrain deformations monitoring, and many other applications, since the high-accuracy single-differenced carrier phase can be used to improve the positioning or AD accuracy. Thus, the line bias (LB) parameter (fractional bias isolating) should be calibrated in the single-differenced phase equations. In the past decades, all researchers estimated the LB as a constant parameter in advance and compensated it in real time. However, the constant LB assumption is inappropriate in practical applications because of the physical length and permittivity changes of the cables, caused by the environmental temperature variation and the instability of receiver-self inner circuit transmitting delay. Considering the LB drift (or colored LB) in practical circumstances, this paper initiates a real-time estimator using auto regressive moving average-based (ARMA) prediction/whitening filter model or Moving average-based (MA) constant calibration model. In the ARMA-based filter model, four cases namely AR(1), ARMA(1, 1), AR(2) and ARMA(2, 1) are applied for the LB prediction. The real-time relative positioning model using the ARMA-based predicting LB is derived and it is theoretically proved that the positioning accuracy is better than the traditional double difference carrier phase (DDCP) model. The drifting LB is defined with a phase temperature changing rate integral function, which is a random walk process if the phase temperature changing rate is white noise, and is validated by the analysis of the AR model coefficient. The auto covariance function shows that the LB is indeed varying in time and estimating it as a constant is not safe, which is also demonstrated by the analysis on LB variation of each visible satellite during a zero and short baseline BDS/GPS experiment. Compared to the DDCP approach, in the zero-baseline experiment, the LB constant calibration (LBCC) and MA approaches improved the positioning accuracy of the vertical component, while slightly degrading the accuracy of the horizontal components. The ARMA(1, 0) model, however, improved the positioning accuracy of all three components, with 40 and 50 % improvement of the vertical component for BDS and GPS, respectively. In the short baseline experiment, compared to the DDCP approach, the LBCC approach yielded bad positioning solutions and degraded the AD accuracy; both MA and ARMA-based filter approaches improved the AD accuracy. Moreover, the ARMA(1, 0) and ARMA(1, 1) models have relatively better performance, improving to 55 % and 48 % the elevation angle in ARMA(1, 1) and MA model for GPS, respectively. Furthermore, the drifting LB variation is found to be continuous and slowly cumulative; the variation magnitudes in the unit of length are almost identical on different frequency carrier phases, so the LB variation does not show obvious correlation between different frequencies. Consequently, the wide-lane LB in the unit of cycle is very stable, while the narrow-lane LB varies largely in time. This reasoning probably also explains the phenomenon that the wide-lane LB originating in the satellites is stable, while the narrow-lane LB varies. The results of ARMA-based filters are better than the MA model, which probably implies that the modeling for drifting LB can further improve the precise point positioning accuracy.

Limiting sensitivity of location probing of power transmission lines while detecting ice coatings

Ice coatings on power transmission lines (PTSs) are detected during location probing from the amplitude reduction and the increase of propagation (delay) time of the reflected signals. The stability of the amplitude and delay of the reflected signals in the normal conditions in the absence of glaze ice and the limiting sensitivity of the method of location are studied in the article. As a result of long-term measurements on operating power transmission lines, the daily–annual variation of amplitude U and delay Δτ of the reflected signals were detected due to the high sensitivity of the method of location, which is mainly due to variations in environmental temperature. It was shown that these variations, combined with the random fluctuations,in normal conditions are much smaller than the changes of the amplitude and delay of signals upon early appearance of ice coatings. The recommendations on selection of the values of settings (operating threshold) are given by the amplitude and delay upon detection of the glaze ice and damage to the power transmission lines by the method of location.

Population genetic analysis and bioclimatic modeling in Agave striata in the Chihuahuan Desert indicate higher genetic variation and lower differentiation in drier and more variable environments

Is there an association between bioclimatic variables and genetic variation within species? This question can be approached by a detailed analysis of population genetics parameters along environmental gradients in recently originated species (so genetic drift does not further obscure the patterns). The genus Agave, with more than 200 recent species encompassing a diversity of morphologies and distributional patterns, is an adequate system for such analyses. We studied Agave striata, a widely distributed species from the Chihuahuan Desert, with a distinctive iteroparous reproductive ecology and two recognized subspecies with clear morphological differences. We used population genetic analyses along with bioclimatic studies to understand the effect of environment on the genetic variation and differentiation of this species. We analyzed six populations of the subspecies A. striata subsp. striata, with a southern distribution, and six populations of A. striata subsp. falcata, with a northern distribution, using 48 ISSR loci and a total of 541 individuals (averaging 45 individuals per population). We assessed correlations between population genetics parameters (the levels of genetic variation and differentiation) and the bioclimatic variables of each population. We modeled each subspecies distribution and used linear correlations and multifactorial analysis of variance. Genetic variation (measured as expected heterozygosity) increased at higher latitudes. Higher levels of genetic variation in populations were associated with a higher variation in environmental temperature and lower precipitation. Stronger population differentiation was associated with wetter and more variable precipitation in the southern distribution of the species. The two subspecies have genetic differences, which coincide with their climatic differences and potential distributions. Differences in genetic variation among populations and the genetic differentiation between A. striata subsp. striata and A. striata subsp. falcata is correlated with differences in environmental climatic variables along their distribution. We found two distinct gene pools that suggest active differentiation and perhaps incipient speciation. The detected association between genetic variation and environment variables indicates that climatic variables are playing an important role in the differentiation of A. striata.

Tracking performance of optical phase locking loop with frequency discrimination and control subloop

Optical phase locking is a key technique in homodyne coherent optical communication, coherent optical detection, and active coherent laser beam combination. In these applications, environmental temperature variation and mechanical vibration would affect the accuracy of phase locking, or even cause losing lock. These disturbances are generally equivalent to introducing phase jitter, phase step, frequency ramp, and frequency step in the loop. A frequency discrimination and control subloop is introduced to improve the frequency acquisition, and the tracking performance is studied experimentally. The loop can track phase step in 0.2 ms, and precisely track ±π/2 sine phase jitter for jittering frequency lower than 1 kHz. For frequency ramp, the residual phase error is unaffected for ramping rates slower than 40 MHz/s. The frequency discrimination and control subloop makes the loop lock quickly under a frequency step larger than the pull-in frequency. The mean tracking time is 31 ms for a 1 MHz frequency step. The maximum trackable frequency step is around 160 MHz. Continuous or step variation of phase and frequency could be tracked by the loop with the frequency discrimination and control subloop.

High temperature and temperature variation undermine future disease susceptibility in a population of the invasive garden ant Lasius neglectus.

Environmental temperature and temperature variation can have strong effects on the outcome of host-parasite interactions. Whilst such effects have been reported for different host systems, long-term consequences of pre-infection temperatures on host susceptibility and immunity remain understudied. Here, we show that experiencing both a biologically relevant increase in temperature and temperature variation undermines future disease susceptibility of the invasive garden ant Lasius neglectus when challenged with a pathogen under a constant temperature regime. In light of the economic and ecological importance of many social insects, our results emphasise the necessity to take the hosts' temperature history into account when studying host-parasite interactions under both natural and laboratory conditions, especially in the face of global change.

Comparative transcriptomics across populations offers new insights into the evolution of thermal resistance in marine snails

Adaptation to thermal conditions in intertidal ectotherms involves tolerating and surviving frequent and often extreme variations in environmental temperatures. Modulation of gene expression plays an important role in the adaptive evolution of thermal tolerance. To understand such patterns, we investigated the thermal tolerance among three Asian populations (from Xiamen, Hong Kong, and Singapore) of the marine littorinid snail Echinolittorina malaccana and examined gene expression profiles in these populations before, during, and after heat stress using an Illumina RNA-sequencing platform. Analysis of transcriptomic changes between different conditions revealed that a proportion of the differentially expressed genes showed similar expression profiles across all three populations, including many classic molecular chaperones such as HSP70 and HSP90 that may constitute the core of the thermal stress response machinery in marine snails. Meanwhile, population-specific transcriptomic responses to heat stress were also detected. A few genes in particular showed more analogous expression profiles in the more thermally tolerant Hong Kong and Singapore populations, and these genes are likely to contribute, at least in part, to the enhanced thermal tolerance of these populations. We argue that repression of a subset of metabolic genes including several cytochrome P450 gene family members, to minimize energy expenditure and control reactive oxygen species turnover, may underpin the enhanced thermal resistance in these two populations. As such, these findings offer new insights into how marine snails cope with thermal stress and their potential evolutionary trajectory toward adapting to a warming climate.