Dynamics Of Energy Flow Research Articles

Habitat heterogeneity shapes and shifts scorpion assemblages in a Brazilian seasonal dry tropical forest

Previous observations support predictions that habitat structure plays a major role in the distribution of species in several tropical regions. In such environments, arthropods are a key component of ecosystems because they are predators that may directly influence the energy flow dynamics in the ecosystem. As such, we investigated the effects of environmental structure on scorpion diversity in the Caatinga ecoregion - a seasonally dry tropical forest mainly distributed in northeastern Brazil. Scorpions were sampled in 12 locations in different Caatinga sites. At each location, we recorded a set of environmental predictors, including litter depth, and the densities of trees, shrubs, stones, and fallen logs. A total of 782 scorpions were collected, including eight species in the family Buthidae and two species in the family Bothriuridae. Scorpion composition and abundance were positively correlated with shrub and tree densities, illustrating the importance of landscape features for the maintenance of scorpion assemblages in Caatinga environments. Furthermore, based on new substantial insights, habitat degradation caused by human activities negatively affects the assemblage of Caatinga scorpions.

Quantum dynamics of vibrational energy flow in oscillator chains driven by anharmonic interactions

A new model of vibrational energy transfer in molecular systems taking into account anharmonic (third order) interactions of localized vibrations with a chain of harmonic oscillators is developed. The role of the energy spectrum of the chain and of the magnitude of the non-linear coupling is discussed in detail by an exact numerical solution of the quantum dynamical problem based on the tensor-train (matrix product state) representation of the vibrational wave function. Results show that the type of wave packet motion is determined by the eigen-spectrum of the chain and by its excitation time. It is found that when the excitation of the chain takes place on a much shorter timescale than the energy transfer along the chain the vibrational wave packet moves in a ballistic way independently of the length of the chain. On the other hand when the excitation of the chain takes place on the timescale of the energy transfer along the chain the overall motion becomes superballistic. These findings shed new light on recent observations of ballistic energy transfer along polymethylene chains.

Intraspecific variation and energy channel coupling within a Chilean kelp forest.

The widespread importance of variable types of primary production, or energy channels, to consumer communities has become increasingly apparent. However, the mechanisms underlying this "multichannel" feeding remain poorly understood, especially for aquatic ecosystems that pose unique logistical constraints given the diversity of potential energy channels. Here, we use bulk tissue isotopic analysis along with carbon isotope (δ13 C) analysis of individual amino acids to characterize the relative contribution of pelagic and benthic energy sources to a kelp forest consumer community in northern Chile. We measured bulk tissue δ13 C and δ15 N for >120 samples; of these we analyzed δ13 C values of six essential amino acids (EAA) from nine primary producer groups (n=41) and 11 representative nearshore consumer taxa (n=56). Using EAA δ13 C data, we employed linear discriminant analysis (LDA) to assess how distinct EAA δ13 C values were between local pelagic (phytoplankton/particulate organic matter), and benthic (kelps, red algae, and green algae) endmembers. With this model, we were able to correctly classify nearly 90% of producer samples to their original groupings, a significant improvement on traditional bulk isotopic analysis. With this EAA isotopic library, we then generated probability distributions for the most important sources of production for each individual consumer and species using a bootstrap-resampling LDA approach. We found evidence for multichannel feeding within the community at the species level. Invertebrates tended to focus on either pelagic or benthic energy, deriving 13-67% of their EAA from pelagic sources. In contrast, mobile (fish) taxa at higher trophic levels used more equal proportions of each channel, ranging from 19% to 47% pelagically derived energy. Within a taxon, multichannel feeding was a result of specialization among individuals in energy channel usage, with 37 of 56 individual consumers estimated to derive >80% of their EAA from a single channel. Our study reveals how a cutting-edge isotopic technique can characterize the dynamics of energy flow in coastal food webs, a topic that has historically been difficult to address. More broadly, our work provides a mechanism as to how multichannel feeding may occur in nearshore communities, and we suggest this pattern be investigated in additional ecosystems.

Interfacial Vibrational Dynamics of Ice Ih and Liquid Water.

Insights into energy flow dynamics at ice surfaces are essential for understanding chemical dynamics relevant to atmospheric and geographical sciences. Here, employing ultrafast surface-specific spectroscopy, we report the interfacial vibrational dynamics of ice Ih. A comparison to liquid water surfaces reveals accelerated vibrational energy relaxation and dissipation at the ice surface for hydrogen-bonded OH groups. In contrast, free-OH groups sticking into the vapor phase exhibit substantially slower vibrational dynamics on ice. The acceleration and deceleration of vibrational dynamics of these different OH groups at the ice surface are attributed to enhanced intermolecular coupling and reduced rotational mobility, respectively. Our results highlight the unique properties of free-OH groups on ice, putatively linked to the high catalytic activities of ice surfaces.

Ultrafast Energy Flow Dynamics in a Conjugated Polymer-Based Host–Guest Light-Harvesting System

Conjugated polymer-based light-harvesting systems have been the subject of research because of their multichromophoric property. Here, we mainly emphasize on the ultrafast relaxation dynamics of po...

Contribution of energy transfer processes to excitation and relaxation of Yb3+ ions in Gd3(Al,Ga)5O12:RE3+, Yb3+ (RE3+ = Tm3+, Er3+, Ho3+, Pr3+)

Abstract Gd3(Al,Ga)5O12:RE3+, Yb3+ single crystals (RE3+ = Tm3+, Er3+, Ho3+, Pr3+) were fabricated by the Czochralski technique. Effect of Yb3+ concentration on spectral distribution of luminescence emitted by interacting RE3+-Yb3+ ion pairs and on the dynamics of excitation energy flow in systems under study was investigated and interpreted referring to previously reported spectroscopic features of Gd3(Al,Ga)5O12:RE3+ systems. It was concluded that observed quenching of the Yb3+ emission by co-doped rare earth ions results from an interplay between phenomena of quantum cutting, down shifting and energy dissipation by multiphonon emission.

Foundations and Frontiers of Ecosystem Science: Legacy of a Classic Paper (Odum 1969)

Ecosystem ecology, like all scientific disciplines, is often propelled forward by “classic” papers that identify key concepts within the field and define the core questions for generations of scientists. Here, we examine the legacy and sustained impact of a paper long considered a classic in ecology, E.P. (Gene) Odum’s 1969 “The strategy of ecosystem development.” Odum’s paper presented testable predictions about species diversity, energy flow, and biogeochemical dynamics during ecosystem succession and provided guiding principles for environmental conservation and management. Odum’s 24 predictions on “ecosystem development” were a key component of this paper’s legacy: The framework was referenced in 62.0% and tested in 28.7% of 1598 citing papers we examined. Although we found that support for Odum’s framework grew over time, support for any particular prediction was inconsistent, highlighting the unresolved nature of some of the framework’s principles. Odum’s conceptual framework for ecosystem studies—as well as his forward-thinking attempts to connect ecosystem ecology with humans and society—continues to be pertinent to current and future research frontiers. Simplicity of the framework was its strength, and major limitation, painting ecosystem functioning in broad strokes, with no acknowledgement about interactions among the predictions. Newer generations have their work cut out for them by bridging evolutionary biology and ecosystem science or metabolic theory and ecological stoichiometry. Similarly, newer generations are using Odum’s multidisciplinary approach to address the most pressing global change issues and designing solutions that make the Earth life sustaining system compatible with growing human demands.

Time-resolved fluorescence measurements on leaves: principles and recent developments

Photosynthesis starts when a pigment in the photosynthetic antennae absorbs a photon. The electronic excitation energy is then transferred through the network of light-harvesting pigments to special chlorophyll (Chl) molecules in the reaction centres, where electron transfer is initiated. Energy transfer and primary electron transfer processes take place on timescales ranging from femtoseconds to nanoseconds, and can be monitored in real time via time-resolved fluorescence spectroscopy. This method is widely used for measurements on unicellular photosynthetic organisms, isolated photosynthetic membranes, and individual complexes. Measurements on intact leaves remain a challenge due to their high structural heterogeneity, high scattering, and high optical density, which can lead to optical artefacts. However, detailed information on the dynamics of these early steps, and the underlying structure–function relationships, is highly informative and urgently required in order to get deeper insights into the physiological regulation mechanisms of primary photosynthesis. Here, we describe a current methodology of time-resolved fluorescence measurements on intact leaves in the picosecond to nanosecond time range. Principles of fluorescence measurements on intact leaves, possible sources of alterations of fluorescence kinetics and the ways to overcome them are addressed. We also describe how our understanding of the organisation and function of photosynthetic proteins and energy flow dynamics in intact leaves can be enriched through the application of time-resolved fluorescence spectroscopy on leaves. For that, an example of a measurement on Zea mays leaves is presented.

Long‐term ecological studies in northern lakes—challenges, experiences, and accomplishments

AbstractWe review three long‐term research programs performed over the last four decades on the ecology and management of oligotrophic lake systems with different fish communities at 69° N in Norway. Through whole‐lake perturbation experiments, intensive culling of stunted fish removed 35 tons (1984–1991) of Arctic charr Salvelinus alpinus in Takvatn (15 km2) and 153 tons (1981–1983, 2002–2004) of European whitefish Coregonus lavaretus in Stuorajavri (25 km2). In Takvatn, the overcrowded charr population decreased to 20% of the initial abundance, whereas brown trout Salmo trutta abundance increased. Somatic growth improved strongly in both species. In charr, ontogenetic habitat shifts broke down, the diet changed to more benthos, and plankton‐borne parasites decreased. High abundance of juvenile, littoral charr provided new prey for trout, creating an alternative, predator‐regulated stable state. Similar density reductions, positive effects on growth and reduced parasite loads occurred in whitefish in Stuorajavri. Despite the heavy culling, however, a new stable state did not occur and the fish community returned to the pre‐culling situation. In the Pasvik watercourse, vendace Coregonus albula invaded around 1990 after an upstream introduction. The population of this non‐native, highly specialized planktivore increased rapidly, resulting in steep density declines in zooplankton and the native planktivorous whitefish morph, and large changes in energy flow and structure and dynamics of the lacustrine food web. These programs show that long‐term research is essential for understanding the ecology of manmade disturbances and providing a scientific basis for management efforts.

Trophic network of aquatic macroinvertebrates along an altitudinal gradient in a Neotropical mountain river

Studies of trophic networks and the evaluation of processes that occur along altitudinal gradients in river systems are of great importance because they allow an understanding of energy flow dynamics and provide scientific tools for the planning and management of river ecosystems. This research describes the trophic network of aquatic macroinvertebrates along an altitudinal gradient of the Gaira River, a mountain Neotropical watercourse located in the Sierra Nevada de Santa Marta in northern Colombia. The organisms were collected in the upper, middle and lower reaches of the river during the rainy and dry seasons (between 2010 and 2013). Trophic relationships were evaluated through gut content analysis. The contents were determined and quantified using photographs and expert review, and a binary consumption matrix was used to determine the characteristics of the trophic network. We characterized the diet composition at each site for each season using discriminant analysis. Trophic networks during the dry seasons showed higher trophic species richness and linkage density, and the predominance of coarse particulate organic matter (CPOM) and fine particulate organic matter (FPOM) in the high and medium sections of the river. During the dry seasons the diets had a lower number of basal species, but in the low river section there was a high percentage of fungi and microalgae. During the rainy seasons, no patterns were observed for the percentage of resources. Results indicated a direct relation between periods of hydrologic stability and an increase of CPOM during dry seasons and an increase of resource diversity consumed by macroinvertebrates at all sites during the rainy season, showing that changes in trophic networks of the Gaira River were more important during seasonal periods than along the altitudinal gradient.

Real-Time Atomistic Dynamics of Energy Flow in an STM Setup: Revealing the Mechanism of Current-Induced Molecular Emission.

Detailed understanding of the current-induced fluorescence mechanism constitutes an exciting challenge as it can open the way to efficient coupling between an electric field and light at the nanoscale. At the same time, a number of published experimental studies give an unclear, contradictory picture of this phenomenon working principle. Here, for a system consisting of a silver tip and a porphyrin molecule, we perform for the first time fully atomistic, real-time nonadiabatic dynamics simulations to study the process of energy transfer and relaxation in an STM setup. We calculate time scales of all crucial processes and explain their atomic details. On this basis, we confirm and characterize the dual mechanism of the observed emission based on competing elastic and inelastic electron transfer between the metal tip and the molecule.

Optimal Sensor Collaboration for Parameter Tracking Using Energy Harvesting Sensors

In this paper, we design an optimal sensor collaboration strategy among neighboring nodes while tracking a time-varying parameter using wireless sensor networks in the presence of imperfect communication channels. The sensor network is assumed to be self-powered, where sensors are equipped with energy harvesters that replenish energy from the environment. In order to minimize the mean square estimation error of parameter tracking, we propose an online sensor collaboration policy subject to real-time energy harvesting constraints. The proposed energy allocation strategy is computationally light and only relies on the second-order statistics of the system parameters. For this, we first consider an offline non-convex optimization problem, which is solved exactly using semidefinite programming. Based on the offline solution, we design an online power allocation policy that requires minimal online computation and satisfies the dynamics of energy flow at each sensor. We prove that the proposed online policy is asymptotically equivalent to the optimal offline solution and show its convergence rate and robustness. We empirically show that the estimation performance of the proposed online scheme is better than that of the online scheme when channel state information about the dynamical system is available in the low SNR regime. Numerical results are conducted to demonstrate the effectiveness of our approach.

Control of Energy Flow Dynamics between Tetracene Ligands and PbS Quantum Dots by Size Tuning and Ligand Coverage.

We have prepared a series of samples with the ligand 6,13-bistri(iso-propyl)silylethynyl tetracene 2-carboxylic acid (TIPS-Tc-COOH) attached to PbS quantum dot (QD) samples of three different sizes in order to monitor and control the extent and time scales of energy flow after photoexcitation. Fast energy transfer (∼1 ps) to the PbS QD occurs upon direct excitation of the ligand for all samples. The largest size QD maintains the microsecond exciton lifetime characteristic of the as-prepared oleate terminated PbS QDs. However, two smaller QD sizes with lowest exciton energies similar to or larger than the TIPS-Tc-COO- triplet energy undergo energy transfer between QD core and ligand triplet on nanosecond to microsecond timescales. For the intermediate size QDs in particular, energy can be recycled many times between ligand and core, but the triplet remains the dominant excited species at long times, living for ∼3 μs for fully exchanged QDs and up to 30 μs for partial ligand exchange, which is revealed as a method for controlling the triplet lifetime. A unique upconverted luminescence spectrum is observed that results from annihilation of triplets after exclusive excitation of the QD core.

Mathematical model for integrated coal fired thermal boiler using physical laws

The boiler of coal-fired thermal power plant consists of integrating process units such as the furnace, economizer, drum, and superheater. There is a lack of proper dynamic model derived from mass and energy balances of individual units integrated together where dynamics of material and energy flow are not understood properly supporting the larger footprints and environmental impact of the specific industry. This paper considers formulation of simple mathematical models for integrated boiler units based on first principle laws (excluding furnace). The derived equations are validated with the real-time plant data from 210 MW coal-fired thermal power plant. Though temperature and pressures are convertible at equilibrium through Clausius-Clapeyron equation, the model supports for level, temperature and pressure measurements and predictions. The effects of change in parameters of the boiler are studied and discussed in detail. The model can be used for further process control studies.

Merit of non-uniform over uniform heating in a porous cavity

Energy transport in a bottom-heated porous cavity utilizing uniform and non-uniform heating is important as a fundamental study as well as from the perspective of various industrial and technological applications. The present work reports enhanced thermal energy transport using sinusoidally non-uniform heating over uniform heating from bottom of a square cavity which is filled with fluid-saturated porous medium and cooled from sidewalls that translate. Comparative assessments of thermal performance under various parametric variations are performed on the basis of mean temperature of heating, which is maintained fixed for both types of heating. Flow physics of this problem is described by a set of nonlinear and coupled equations, which are solved numerically by an in-house CFD code. The results obtained from the present simulation reveal that, because of same mean temperature of bottom heating, the sinusoidally non-uniform heating significantly contributes towards higher heat transfer. The dynamics of thermal energy flow from the source to the sink is also addressed comprehensively using heatfunction and heatlines.

Enhanced thermal energy transport using adiabatic block inside lid-driven cavity

Most of the energy related applications are involved with heat transfer and fluid flow, and the efficient utilization of energy system is always a matter of great importance. With a simple flow geometry, the present work is devoted to report a better thermal energy transfer utilizing an adiabatic block in a sidewalls moving, differentially-heated cavity. The study demonstrates the effective role of the adiabatic block on energy transport from source to sink. The adiabatic block, depending on the situations, both favors and hinders overall heat transfer of the system. The size of the block decides the modality of thermal energy transfer. In this work, different speeds and configurations of wall motion are investigated exhaustively to assess the extent of heat transfer augmentation and the optimal block sizes. The results indicate that, up to a certain block size, the thermal energy transport of this cavity enhances. Heat transfer augmentation is remarkably high for opposing flow situation. The dynamics of energy flow from the source to the sink is presented using heatfunction that reveals the evolution of energy recirculation cells in the cavity. The presence of an adiabatic block potentially suppresses this energy recirculation. The evolved vortical flow structure in the cavity is explained using elliptical and hyperbolic points. The study is further extended to include the impact of cavity inclination on the thermal performance.

Assessing the impact of acute disturbances on the structure and composition of a coral community using innovative 3D reconstruction techniques

Loss of live coral and declines in the structural complexity of reef habitats affects ecosystem-level processes such as energy flow, nutrient cycling, and community dynamics. Scleractinian corals are the primary contributor to the biological and physical three-dimensional (3D) structure of coral reef ecosystems. Disturbance events that induce coral mortality can alter the 3D structure of reefs habitats and lead to disruptions in trophic structure and organismal relationships that drive ecological processes. The coral reef ecosystem at Wai‘ōpae, southeast Hawai‘i Island, experienced several acute disturbance events in 2014, including a hurricane, tropical storms, and a severe coral bleaching event. This study utilized innovative 3D reconstruction techniques to create high-resolution models of the coral reef habitat and quantify structural metrics known to affect the biodiversity and abundance of associated reef organisms. A volumetric analysis was applied to the reconstructed 3D point clouds to determine the precise loss of habitat that occurred throughout the surveyed reef area. Conducting a temporal analysis using 3D reconstructions enabled us to test the hypothesis that volume and 3D architectural complexity of the coral community at Wai‘ōpae was significantly impacted by the acute disturbance events.

Pronounced species turnover, but no functional equivalence in leaf consumption of invasive amphipods in the river Rhine

A growing body of literature focuses on the adverse effects of biological invasions, e.g., on the decline of indigenous biodiversity, while studies on the consequences of invasions on components of ecosystem functioning are comparatively rare. Owing to their leaf shredding activity, amphipods play a fundamental role in determining energy flow dynamics in Central European freshwater ecosystems, but whether the dramatic change in species composition after the invasion of Ponto–Caspian taxa affects this process has not been addressed in a comprehensive study. In a laboratory experiment we determined consumption rates of three leaf types (Alnus glutinosa, Betula pendula, Quercus robur) from common riparian arboreal vegetation in the Rhine drainage—one of the most heavily invaded river systems worldwide—by the most common native (Gammarus fossarum, G. pulex, G. roeselii) and invasive amphipods (Dikerogammarus villosus, Echinogammarus ischnus). Leaf-shredding activity was significantly lower in invasive than in native amphipods across leaf types, and a subsequent analysis ruled out an effect of different metabolic rates as an explanation. Another experiment was motivated by the observation that native amphipods are nowadays restricted to smaller tributaries to the Rhine, while invasive taxa are dominant in the main channel. As leaf litter shredding may be more important in headwaters than in lower parts of streams, we sought for a signature of within-species variation in the feeding ecology of amphipods and thus compared two different populations of G. pulex, but found very similar leaf consumption rates in upstream and downstream populations, suggesting that food preferences in amphipods could be species-specific with little potential for microevolution or environmentally induced plasticity. In conclusion, the rapid replacement of native amphipod species in the Rhine drainage likely affects vital ecosystem services, with the potential to change the aquatic food web (e.g., through reduced shredding activity and hence, reduced resource availability for particle-feeding detritivores), unless other taxonomic groups compensate for those functional alterations.

Energy flow and functional compensation in Great Basin small mammals under natural and anthropogenic environmental change

Research on the ecological impacts of environmental change has primarily focused at the species level, leaving the responses of ecosystem-level properties like energy flow poorly understood. This is especially so over millennial timescales inaccessible to direct observation. Here we examine how energy flow within a Great Basin small mammal community responded to climate-driven environmental change during the past 12,800 y, and use this baseline to evaluate responses observed during the past century. Our analyses reveal marked stability in energy flow during rapid climatic warming at the terminal Pleistocene despite dramatic turnover in the distribution of mammalian body sizes and habitat-associated functional groups. Functional group turnover was strongly correlated with climate-driven changes in regional vegetation, with climate and vegetation change preceding energetic shifts in the small mammal community. In contrast, the past century has witnessed a substantial reduction in energy flow caused by an increase in energetic dominance of small-bodied species with an affinity for closed grass habitats. This suggests that modern changes in land cover caused by anthropogenic activities--particularly the spread of nonnative annual grasslands--has led to a breakdown in the compensatory dynamics of energy flow. Human activities are thus modifying the small mammal community in ways that differ from climate-driven expectations, resulting in an energetically novel ecosystem. Our study illustrates the need to integrate across ecological and temporal scales to provide robust insights for long-term conservation and management.

Directionality Theory and the Entropic Principle of Natural Selection

Darwinian fitness describes the capacity of an organism to appropriate resources from the environment and to convert these resources into net-offspring production. Studies of competition between related types indicate that fitness is analytically described by entropy, a statistical measure which is positively correlated with population stability, and describes the number of accessible pathways of energy flow between the individuals in the population. Directionality theory is a mathematical model of the evolutionary process based on the concept evolutionary entropy as the measure of fitness. The theory predicts that the changes which occur as a population evolves from one non-equilibrium steady state to another are described by the following directionality principle–fundamental theorem of evolution: (a) an increase in evolutionary entropy when resource composition is diverse, and resource abundance constant; (b) a decrease in evolutionary entropy when resource composition is singular, and resource abundance variable. Evolutionary entropy characterizes the dynamics of energy flow between the individual elements in various classes of biological networks: (a) where the units are individuals parameterized by age, and their age-specific fecundity and mortality; where the units are metabolites, and the transitions are the biochemical reactions that convert substrates to products; (c) where the units are social groups, and the forces are the cooperative and competitive interactions between the individual groups. % This article reviews the analytical basis of the evolutionary entropic principle, and describes applications of directionality theory to the study of evolutionary dynamics in two biological systems; (i) social networks–the evolution of cooperation; (ii) metabolic networks–the evolution of body size. Statistical thermodynamics is a mathematical model of macroscopic behavior in inanimate matter based on entropy, a statistical measure which describes the number of ways the molecules that compose the a material aggregate can be arranged to attain the same total energy. This theory predicts an increase in thermodynamic entropy as the system evolves towards its equilibrium state. We will delineate the relation between directionality theory and statistical thermodynamics, and review the claim that the entropic principle for thermodynamic systems is the limit, as the resource production rate tends to zero, and population size tends to infinity, of the entropic principle for evolutionary systems.