We present a novel conceptual framework and methodology for studying virtual water trade. We utilize complex network theory to analyze the structure of the global virtual water trade associated with ...the international food trade. In the global virtual water trade network, the nations that participate in the international food trade correspond to the nodes, and the links represent the flows of virtual water associated with the trade of food from the country of export to the country of import. We find that the number of trade connections follows an exponential distribution, except for the case of import trade relationships, while the volume of water that each nation trades compares well with a stretched exponential distribution, indicating high heterogeneity of flows between nations. There is a power law relationship between the volume of virtual water traded and the number of trade connections of each nation. Highly connected nations are preferentially linked to poorly connected nations and exhibit low levels of clustering. However, when the volume of virtual water traded is taken into account, this structure breaks down. This indicates a global hierarchy, in which nations that trade large volumes of water are more likely to link to and cluster with other nations that trade large volumes of water, particularly when the direction of trade is considered. Nations that play a critical role in maintaining the global network architecture are highlighted. Our analysis provides the necessary framework for the development of a model of global virtual water trade aimed at applications ranging from network optimization to climate change impact evaluations.
Key Points
The network approach is a novel way to analyze virtual water trade
Key features of the global structure are highlighted
Roles of countries and continents in virtual water trade are quantified
Does a dynamic drainage density have a role on species persistence in the river basin? The general viability of a focus species under time‐varying hydrologic connectivity and habitat quality is a ...topic gaining traction in view of recent advances in our understanding of flowing fluvial network dynamics and of ecological interactions occurring on directed trees. Here, we combine metapopulation dynamics and scaling theory to investigate how the structure of river networks and time‐changing hydrological and geomorphological attributes control local metapopulation survival. This is done by introducing seasonal fluctuations of the drainage density subsuming overall time‐changing connectivity and distributed changes in habitat quality of the fluvial domain. Suitable replicas of channel networks within an assigned domain are used to compute the statistics of evolving metapopulation capacities, properties of a landscape matrix measuring the viability of the focus species. To obtain consistent replicas of the substrate for ecological interactions, we employ constructs whose suitability for the task has long been established. We find that the river network structure blends the fluctuations into a nontrivial scaling of the metapopulation capacity with the sum of total active contributing sites at any point of the flowing network. The latter is proportional to the mean distance to the outlet of the flowing dendrite and to the tree diameter—a measure of the overall connectivity of the active stream links. Scaling emerges as a robust ensemble property that enables the linkage of ecological patterns across a river network to clearly identified hydrological and geomorphological factors.
Plain Language Summary
Contractions and expansions of the active flowing river networks matter for the persistence of ecological species owing to the related changes on local habitat suitability. The general viability of a focus species is determined here by the value of the so‐called metapopulation capacity, the maximum eigenvalue of a suitable landscape matrix, which depends on the extent of the active network. The range of metapopulation capacities experienced by a dynamically changing flowing river network is shown to scale with total contributing area, a result that bears implications on our ability to predict the connection of hydrology and ecology.
Key Points
Fluctuations of drainage density matter for a species' metapopulation dynamics owing to related changes on local habitat size and network connectivity
Viability of the focus species is determined by the value of the maximum eigenvalue of a suitable landscape matrix depending on drainage density
The range of metapopulation capacities of flowing river network scales with mean total active contributing area measuring time‐changing connectivity
The Lasso is a popular model selection and estimation procedure for linear models that enjoys nice theoretical properties. In this paper, we study the Lasso estimator for fitting autoregressive time ...series models. We adopt a double asymptotic framework where the maximal lag may increase with the sample size. We derive theoretical results establishing various types of consistency. In particular, we derive conditions under which the Lasso estimator for the autoregressive coefficients is model selection consistent, estimation consistent and prediction consistent. Simulation study results are reported.
Many details about the flow of water in soils in a hillslope are unknowable given current technologies. One way of learning about the bulk effects of water velocity distributions on hillslopes is ...through the use of tracers. However, this paper will demonstrate that the interpretation of tracer information needs to become more sophisticated. The paper reviews, and complements with mathematical arguments and specific examples, theory and practice of the distribution(s) of the times water particles injected through rainfall spend traveling through a catchment up to a control section (i.e., “catchment” travel times). The relevance of the work is perceived to lie in the importance of the characterization of travel time distributions as fundamental descriptors of catchment water storage, flow pathway heterogeneity, sources of water in a catchment, and the chemistry of water flows through the control section. The paper aims to correct some common misconceptions used in analyses of travel time distributions. In particular, it stresses the conceptual and practical differences between the travel time distribution conditional on a given injection time (needed for rainfall‐runoff transformations) and that conditional on a given sampling time at the outlet (as provided by isotopic dating techniques or tracer measurements), jointly with the differences of both with the residence time distributions of water particles in storage within the catchment at any time. These differences are defined precisely here, either through the results of different models or theoretically by using an extension of a classic theorem of dynamic controls. Specifically, we address different model results to highlight the features of travel times seen from different assumptions, in this case, exact solutions to a lumped model and numerical solutions of the 3‐D flow and transport equations in variably saturated, physically heterogeneous catchment domains. Our results stress the individual characters of the relevant distributions and their general nonstationarity yielding their legitimate interchange only in very particular conditions rarely achieved in the field. We also briefly discuss the impact of oversimple assumptions commonly used in analyses of tracer data.
Key Points
Define properly the kinematics of catchment travel time distributions
Correct common misconceptions with notable implications, e.g., for tracer studies
Distinguish travel from residence time distributions
Sinuous channels wandering through coastal wetlands have been thought to lack lateral‐migration features like meander cutoffs and oxbows, spurring the broad interpretation that tidal and fluvial ...meanders differ morphodynamically. Motivated by recent work showing similarities in planform dynamics between tidal and fluvial meandering channels, we analyzed meander neck cutoffs from diverse tidal and fluvial environments worldwide, and show that tidal cutoffs are widespread. Their perceived paucity stems from pronounced channel density and hydrological connectivity in coastal wetlands, comparatively small size of most tidal channels, and typically dense vegetation cover. Although these factors do not efface tidal meander cutoffs, they collectively inhibit oxbow formation and make tidal cutoffs ephemeral features that can escape detection. We argue that similar morphodynamic processes drive cutoff formation in tidal and fluvial landscapes, with differences arising only during post‐cutoff evolution. Such process similarity has important implications for understanding coastal wetland ecomorphodynamics and predicting their long‐term evolution.
Plain Language Summary
The sinuous channels that wander through tidal coastal wetlands look like meandering rivers. However, features of alluvial floodplains that indicate active river meandering over time, such as oxbow lakes and meander cutoffs, are difficult to find in tidal settings. Their apparent absence has led researchers to infer that tidal and fluvial meanders evolve differently. We re‐examined this inference by identifying, measuring, and compiling examples of meander cutoffs from a variety of tidal coastal wetlands and fluvial floodplains worldwide. Our analysis suggests that the shapes and geometric properties of tidal and fluvial cutoffs are indeed remarkably similar. This indicates that while tidal and fluvial environments differ in many ways, they nevertheless share the same physical mechanism affecting meander morphodynamical evolution. Differences between tidal and fluvial meanders do arise after a meander is cut off. We observe that tidal meanders remain preferentially connected to the parent channel, preventing the formation of crescent‐shaped oxbow lakes and thus making tidal cutoffs more difficult to detect. Our results indicate a close similarity in meandering channel behavior across tidal and fluvial systems, which opens new opportunities for how researchers model tidal wetlands, with important implications for the effective conservation and restoration of these critical ecosystems.
Key Points
Tidal meander cutoffs are far more common than typically thought and share remarkable morphometric similarities with fluvial counterparts
Similar mechanisms trigger cutoffs in both tidal and fluvial landscapes, with differences arising only during post‐cutoff evolution
Tidal cutoffs seldom disconnect from parent channels and rarely form oxbows due to the high hydrological connectivity of tidal wetlands
We generalize a recently proposed model for cholera epidemics that accounts for local communities of susceptibles and infectives in a spatially explicit arrangement of nodes linked by networks having ...different topologies. The vehicle of infection (Vibrio cholerae) is transported through the network links that are thought of as hydrological connections among susceptible communities. The mathematical tools used are borrowed from general schemes of reactive transport on river networks acting as the environmental matrix for the circulation and mixing of waterborne pathogens. Using the diffusion approximation, we analytically derive the speed of propagation for travelling fronts of epidemics on regular lattices (either one-dimensional or two-dimensional) endowed with uniform population density. Power laws are found that relate the propagation speed to the diffusion coefficient and the basic reproduction number. We numerically obtain the related, slower speed of epidemic spreading for more complex, yet realistic river structures such as Peano networks and optimal channel networks. The analysis of the limit case of uniformly distributed population sizes proves instrumental in establishing the overall conditions for the relevance of spatially explicit models. To that extent, the ratio between spreading and disease outbreak time scales proves the crucial parameter. The relevance of our results lies in the major differences potentially arising between the predictions of spatially explicit models and traditional compartmental models of the susceptible-infected-recovered (SIR)-like type. Our results suggest that in many cases of real-life epidemiological interest, time scales of disease dynamics may trigger outbreaks that significantly depart from the predictions of compartmental models.
•The HIIT-B promote increase on heart rate and lactate concentration independently of music on session, however the presence of preference music promote improve on positive feeling response ...differently of non-preference music promote negative feeling.•The presence of preference music on session promoted greater number of movements compared to the without music and non-preference music conditions.•The music on session does not influence heart rate, rating of perceived -exertion and -recovery response around sets.•The preference music promote reduction on tension, however, non-preference music induced alterations on mental confusion and total mood disturbance after exercise session.
The use of music in exercise sessions is considered an interesting strategy as it facilitates, through motivation, an improvement in physical performance, as well as a reduction in the subjective perception of effort and an improvement in mood. Such factors are important for the maintenance of physical exercise programs, however, considering high intensity interval training, the effects of music remain inconclusive. Thus, the objective of this study was to evaluate the influence of music during high intensity interval training sessions using body weight (HIIT-B) on the physiological parameters and mood state of adults. Methods: 11 CrossFit male practitioners were randomly submitted to three sessions of HIIT-B under the following experimental conditions: preference music (PM), non-preference music (nPM) and without music (WM). The HIIT-B protocol consisted of 20 sets of 30 s of stimulus using maximal intensities followed by 30 s of passive recovery. The following exercises were used: jumping jacks, burpee, mountain climber and squat jumping. The following parameters were analyzed: heart rate (HR), lactate (La), total amount of movements (TAM), affective response (AR), rating of perceived exertion (RPE), recovery (RPR) and mood states. Results: although an increase (p< 0.05) of HR, RPE and La, reduction of RPR was found after performing the HIIT session, no differences were found between the three conditions to these parameters. The nPM condition promoted lower (p< 0.001) TAM compared to the WM and PM conditions, which also differed from each other. However, for AR, a music effect was found among the protocols (p< 0.0001), indicating that the PM session promoted an increase in pleasure, unlike WM and nPM session which provided pleasure reduction and displeasure respectively. The WM session did not promote any changes. There were no main effects on time for depression and anger, which were different for vigor, fatigue, mental confusion, tension and mood disturbance. Additionally, differences were found after session to tension (p = 0.0229), vigor (p = 0.0424) and fatigue (p = 0.0400) for PM condition, vigor (p = 0.0424), fatigue (p = 0.0400) mental confusion (p = 0.0302) and mood disturbance (p = 0.0129) for nPM and vigor (p = 0.0363) and fatigue (p = 0.0468) to WM conditions. Conclusion: Listening to preferred music during an 'all out' HIIT-B session increases exercise performance and elicits more positive affective responses in recreationally active adult males, despite similar HR, blood lactate, RPE and fatigue compared to nonpreferred music or no-music.
Presynaptic inhibition of transmission between Ia afferent terminals and alpha motoneurons (Ia PSI) is a major control mechanism associated with soleus H-reflex modulation during human locomotion. ...Rhythmic arm cycling suppresses soleus H-reflex amplitude by increasing segmental Ia PSI. There is a reciprocal organization in the human nervous system such that arm cycling modulates H-reflexes in leg muscles and leg cycling modulates H-reflexes in forearm muscles. However, comparatively little is known about mechanisms subserving the effects from leg to arm. Using a conditioning-test (C-T) stimulation paradigm, the purpose of this study was to test the hypothesis that changes in Ia PSI underlie the modulation of H-reflexes in forearm flexor muscles during leg cycling. Subjects performed leg cycling and static activation while H-reflexes were evoked in forearm flexor muscles. H-reflexes were conditioned with either electrical stimuli to the radial nerve (to increase Ia PSI; C-T interval = 20 ms) or to the superficial radial (SR) nerve (to reduce Ia PSI; C-T interval = 37-47 ms). While stationary, H-reflex amplitudes were significantly suppressed by radial nerve conditioning and facilitated by SR nerve conditioning. Leg cycling suppressed H-reflex amplitudes and the amount of this suppression was increased with radial nerve conditioning. SR conditioning stimulation removed the suppression of H-reflex amplitude resulting from leg cycling. Interestingly, these effects and interactions on H-reflex amplitudes were observed with subthreshold conditioning stimulus intensities (radial n., ∼0.6×MT; SR n., ∼ perceptual threshold) that did not have clear post synaptic effects. That is, did not evoke reflexes in the surface EMG of forearm flexor muscles. We conclude that the interaction between leg cycling and somatosensory conditioning of forearm H-reflex amplitudes is mediated by modulation of Ia PSI pathways. Overall our results support a conservation of neural control mechanisms between the arms and legs during locomotor behaviors in humans.
Global food security increasingly relies on the trade of food commodities. Freshwater resources are essential to agricultural production and are thus embodied in the trade of food commodities, ...referred to as “virtual water trade.” Agricultural production predominantly relies on rainwater (i.e., “green water”), though irrigation (i.e., “blue water”) does play an important role. These different sources of water have distinctly different opportunity costs, which may be reflected in the way these resources are traded. Thus, the temporal dynamics of the virtual water trade networks from these distinct water sources require characterization. We find that 42 × 109 m3 blue and 310 × 109 m3 green water was traded in 1986, growing to 78 × 109 m3 blue and 594 × 109 m3 green water traded in 2008. Three nations dominate the export of green water resources: the USA, Argentina, and Brazil. As a country increases its export trade partners it tends to export relatively more blue water. However, as a country increases its import trade partners it does not preferentially import water from a specific source. The amount of virtual water that a country imports by increasing its import trade partners has been decreasing over time, with the exception of the soy trade. Both blue and green virtual water networks are efficient: 119 × 109 m3 blue and 105 × 109 m3 green water were saved in 2008. Importantly, trade has been increasingly saving water over time, due to the intensification of crop trade on more water‐efficient links.
Key Points
Blue and green water are traded differently due to distinct opportunity costs
Green water exports oscillate over time, while imports steadily increase
Both blue and green networks have been increasingly saving water over time
Neural output from the locomotor system for each arm and leg influences the spinal motoneuronal pools directly and indirectly through interneuronal (IN) reflex networks. While well documented in ...other species, less is known about the functions and features of convergence in common IN reflex system from cutaneous afferents innervating different foot regions during remote arm and leg movement in humans. The purpose of the present study was to use spatial facilitation to examine possible convergence in common reflex pathways during rhythmic locomotor limb movements. Cutaneous reflexes were evoked in ipsilateral tibialis anterior muscle by stimulating (in random order) the sural nerve (SUR), the distal tibial nerve (TIB), and combined simultaneous stimulation of both nerves (TIB&SUR). Reflexes were evoked while participants performed rhythmic stepping and arm swinging movement with both arms and the leg contralateral to stimulation (ARM&LEG), with just arm movement (ARM) and with just contralateral leg movement (LEG). Stimulation intensities were just below threshold for evoking early latency (<80 ms to peak) reflexes. For each stimulus condition, rectified EMG signals were averaged while participants held static contractions in the stationary (stimulated) leg. During ARM&LEG movement, amplitudes of cutaneous reflexes evoked by combined TIB&SUR stimulation were significantly larger than simple mathematical summation of the amplitudes evoked by SUR or TIB alone. Interestingly, this extra facilitation seen during combined nerve stimulation was significantly reduced when performing ARM or LEG compared to ARM&LEG. We conclude that locomotor rhythmic limb movement induces excitation of common IN reflex pathways from cutaneous afferents innervating different foot regions. Importantly, activity in this pathway is most facilitated during ARM&LEG movement. These results suggest that transmission in IN reflex pathways is weighted according to the number of limbs directly engaged in human locomotor activity and underscores the importance of arm swing to support neuronal excitability in leg muscles.
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