Continuous Disturbance Research Articles

Finite-time output feedback attitude synchronization for multiple spacecraft

Distributed attitude control for spacecraft formation without angular velocity measurement is complicated and challenging. Based on nonsingular terminal sliding mode, this paper designs two kinds of finite-time attitude synchronization controllers with inertia uncertainties and external disturbances. Aiming at calculating angular velocity in finite time, a nonlinear state observer and an angular velocity calculation algorithm are firstly developed. Then, two strategies for estimating reference signals and two distributed output feedback controllers, based on continuous adaptive technology and adaptive disturbance observer, are designed respectively. Different from existing results, the controllers are inherently continuous and the control chattering is greatly reduced. Also, the designed nonlinear observers need no prior knowledge on the upper bound of uncertain state and are proved finite-time convergent via Lyapunov theory. Finally, simulations and comparisons demonstrate the effectiveness of the proposed schemes.

Effect of extreme oceanic events in the coral formations of Islas del Rosario, Colombian Caribbean

The increase in frequency and intensity of extreme oceanic events limits the capacity of recoveryof ecosystems, threatening their subsistence. Thus, in order to understand the relationship between coral healthand extreme environmental events, data on sea temperature, runoff and / or salinity, turbidity were analyzed in theIslas del Rosario in comparison with coral cover, and coral signs of deterioration (e.g., bleaching, coral diseases).In the time series of environmental variables, oceanic events that exceeded a statistical threshold were calculated,establishing their intensity, duration and frequency. The attributes of the community were studied through observations in two stations of the National Coral Reef Monitoring System in Colombia (SIMAC), assessed in two timewindows (long term, 1998-2013 and short term, 2013-2014). The extreme events of sea surface temperature, riverdischarge and associated turbidity, were the main variables related to the reduction of coral cover. The massivecoral bleaching of 2005 and other subsequent events resulted in a reduction in coral coverage between 2004 and2010. During the short-term observations there were no strong extreme events or changes in coral formations,although thermal stress and reductions in salinity in the rainy season were associated with a slight bleaching inNovember 2014. Although the signs of deterioration are low, it is important to consider them, since the synergybetween continuous disturbances can lead to a loss of coral cover.

Study of the Noise Immunity of Modern Standards of Satellite Communications to the Impact of Non-Stationary Interference

This article considers the model of impact of non-stationary interference on the satellite communications channels of standard DVB-S and DVB-RCS, and also on the channels with frequency-hopping spread spectrum. The results of the impact of unintentional non-stationary interference on the satellite communications channels, which occurs from stationary and mobile sources of interference with the same average power, were compared. The bit error probability is used as a measure of noise immunity of satellite communications channels. In the article the term time coefficient of the disturbance noise existence was introduced. Its essence is to substantiate the degree of noise energy concentration in some time area of the desired signal. As an indication, characterizing noise immunity of data lines to the influence of unsteady noises the bit-error probability was chosen. It depends on the time coefficient of the disturbance noise existence. In the definite period of time coefficient of the unsteady noise existence for low signal-to-noise ratio they can have a more dangerous effect on data lines with FHSS than the continuous disturbance noise increasing the bit-error possibility.

Vegetation spatial and temporal dynamic characteristics based on NDVI time series trajectories in grassland opencast coal mining

The spatiotemporal dynamic patterns of vegetation in mining area are still unclear. This study utilized time series trajectory segmentation algorithm to fit Landsat NDVI time series which generated from fusion images at the most prosperous period of growth based on ESTARFM algorithm. Combining with the shape features of the fitted trajectory, this paper extracted five vegetation dynamic patterns including pre-disturbance type, continuous disturbance type, stabilization after disturbance type, stabilization between disturbance and recovery type, and recovery after disturbance type. The result indicated that recovery after disturbance type was the dominant vegetation change pattern among the five types of vegetation dynamic pattern, which accounted for 55.2% of the total number of pixels. The follows were stabilization after disturbance type and continuous disturbance type, accounting for 25.6% and 11.0%, respectively. The pre-disturbance type and stabilization between disturbance and recovery type accounted for 3.5% and 4.7%, respectively. Vegetation disturbance mainly occurred from 2004 to 2009 in Shengli mining area. The onset time of stable state was 2008 and the spatial locations mainlydistributed in open-pit stope and waste dump. The reco-very state mainly started since the year of 2008 and 2010, while the areas were small and mainly distributed at the periphery of open-pit stope and waste dump. Duration of disturbance was mainly 1 year. The duration of stable period usually sustained 7 years. The duration of recovery state of the type of stabilization between disturbances continued 2 to 5 years, while the type of recovery after disturbance often sustained 8 years.

Method of determination the level of the state critical infrastructure importance in the civil aviation

The process of rapid development of information and communication technologies caused considerable and sometimes revolutionary changes in all life spheres of most countries. It significantly increased the vulnerability of different networks, systems and facilities and was much complicated the ensuring of their reliable protection and security. All these factors led the fact that leading countries began to devote great attention to the protection of the most important means for the security of its citizens, society and the state; objects, systems and resources, and processes of critical objects identification, calculation of their criticality level and the assessment of the effects of possible interruptions. In this paper the formalize method of determination the level of the state critical infrastructure importance in the field of civil aviation is proposed that by introducing a basic set of system and sets of subsystems, components, functions, continuity disturbances (interruptions, functional loss), their characteristics and effects, and constructing a three-dimensional matrix of criticality and calculation of the additional weight criticality factors, makes it possible to assess (determine) the importance level and rank critical aviation information systems both by both quantitative and qualitative parameters. In further research study based on this method special software will allow for experimental research and confirm the possibility of determining the importance level of different categories of critical aviation information systems.

Characterising Bedrock Aquifer Systems in Korea Using Paired Water-Level Monitoring Data

This study focused on characterising aquifer systems based on water-level changes observed systematically at 159 paired groundwater monitoring wells throughout Korea. Using spectral analysis, principal component analysis (PCA), and cross-correlation analysis with linear regression, aquifer conditions were identified from the comparison of water-level changes in shallow alluvial and deep bedrock monitoring wells. The spectral analysis could identify the aquifer conditions (i.e., unconfined, semi-confined and confined) of 58.5% of bedrock wells and 42.8% of alluvial wells: 93 and 68 wells out of 159 wells, respectively. Even among the bedrock wells, 50 wells (53.7%) exhibited characteristics of the unconfined condition, implying significant vulnerability of the aquifer to contaminants from the land surface and shallow depths. It appears to be better approach for deep bedrock aquifers than shallow alluvial aquifers. However, significant portions of the water-level changes remained unclear for categorising aquifer conditions due to disturbances in data continuity. For different aquifer conditions, PCA could show typical pattern and factor scores of principal components. Principal component 1 due to wet-and-dry seasonal changes and water-level response time was dominant covering about 55% of total variances of each aquifer conditions, implying the usefulness of supplementary method of aquifer characterisation. Cross-correlation and time-lag analysis in the water-level responses to precipitations clearly show how the water levels in shallow and deep wells correspond in time scale. No significant differences in time-lags was found between shallow and deep wells. However, clear time-lags were found to be increasing from unconfined to confined conditions: from 1.47 to 2.75 days and from 1.78 to 2.75 days for both shallow alluvial and deep bedrock wells, respectively. In combination of various statistical methods, three types of water-level fluctuation patterns were identified from the water-level pairs: Type I of identical aquifer systems (77.8%), Type II of the different aquifer systems with different recharge flow paths (9.5%), and Type III of unmatched aquifer system pairs and correlations (12.7%). Type I and II could be used as verification of aquifer condition in the paired monitoring system. However, Type III shows the complexity of water-level fluctuation in different aquifer conditions. This study showed that confined or not-confined conditions are not directly related to the depth of wells in the aquifer. Therefore, the utilisation of groundwater as a water-supply source should be carefully designed, tested for its hydrogeologic conditions, and managed to ensure sustainable quantity and quality.

Quantification of task-dependent cortical activation evoked by robotic continuous wrist joint manipulation in chronic hemiparetic stroke

BackgroundCortical damage after stroke can drastically impair sensory and motor function of the upper limb, affecting the execution of activities of daily living and quality of life. Motor impairment after stroke has been thoroughly studied, however sensory impairment and its relation to movement control has received less attention. Integrity of the somatosensory system is essential for feedback control of human movement, and compromised integrity due to stroke has been linked to sensory impairment.MethodsThe goal of this study is to assess the integrity of the somatosensory system in individuals with chronic hemiparetic stroke with different levels of sensory impairment, through a combination of robotic joint manipulation and high-density electroencephalogram (EEG). A robotic wrist manipulator applied continuous periodic disturbances to the affected limb, providing somatosensory (proprioceptive and tactile) stimulation while challenging task execution. The integrity of the somatosensory system was evaluated during passive and active tasks, defined as ‘relaxed wrist’ and ‘maintaining 20% maximum wrist flexion’, respectively. The evoked cortical responses in the EEG were quantified using the power in the averaged responses and their signal-to-noise ratio.ResultsThirty individuals with chronic hemiparetic stroke and ten unimpaired individuals without stroke participated in this study. Participants with stroke were classified as having severe, mild, or no sensory impairment, based on the Erasmus modification of the Nottingham Sensory Assessment. Under passive conditions, wrist manipulation resulted in contralateral cortical responses in unimpaired and chronic stroke participants with mild and no sensory impairment. In participants with severe sensory impairment the cortical responses were strongly reduced in amplitude, which related to anatomical damage. Under active conditions, participants with mild sensory impairment showed reduced responses compared to the passive condition, whereas unimpaired and chronic stroke participants without sensory impairment did not show this reduction.ConclusionsRobotic continuous joint manipulation allows studying somatosensory cortical evoked responses during the execution of meaningful upper limb control tasks. Using such an approach it is possible to quantitatively assess the integrity of sensory pathways; in the context of movement control this provides additional information required to develop more effective neurorehabilitation therapies.

Epiphytic Mosses in the Humid Mountain Forests of the Sierra Madre Oriental, Mexico — Species Richness, Rarity and Composition

Abstract The Humid Mountain Forests of Mexico (HMFs) harbor high species diversity and are subject to continuous fragmentation and disturbance. We inventoried the epiphytic mosses in forest fragments and on isolated trees located in the Eastern Sierra Madre (Sierra Madre Oriental). We determined the size and canopy openness of 60 trees and recorded the occurrence of epiphytic mosses on trunks. Ninety-three species and five varieties of mosses were detected, distributed among 61 genera and 26 families. Thirty-two moss taxa were strictly epiphytic and 61 were facultative. Eighteen percent (17 species) of all recorded species were rare and only 3% (3 species) were common. Nineteen genera of phorophytes were sampled. Quercus had the highest epiphytic richness. Species richness and epiphytic mosses assemblages differ between forest fragments and isolated trees. Canopy openness and mean host tree height determine the epiphytic moss richness and species assemblages. Our study further underlines the importance of...

Soil microbial communities are shaped by vegetation type and park age in cities under cold climate.

Soil microbes play a key role in controlling ecosystem functions and providing ecosystem services. Yet, microbial communities in urban green space soils remain poorly characterized. Here we compared soil microbial communities in 41 urban parks of (i) divergent plant functional types (evergreen trees, deciduous trees and lawn) and (ii) different ages (constructed 10, ∼50 and >100 years ago). These microbial communities were also compared to those in 5 control forests in southern Finland. Our results indicate that, despite frequent disturbances in urban parks, urban soil microbes still followed the classic patterns typical of plant-microbe associations in natural environments: both bacterial and fungal communities in urban parks responded to plant functional groups, but fungi were under tighter control of plants than bacteria. We show that park age shaped the composition of microbial communities, possibly because vegetation in old parks have had a longer time to modify soil properties and microbial communities than in young parks. Furthermore, control forests harboured distinct but less diverse soil microbial communities than urban parks that are under continuous anthropogenic disturbance. Our results highlight the importance of maintaining a diverse portfolio of urban green spaces and plant communities therein to facilitate complex microbial communities and functions in urban systems.

Edge responses are different in edges under natural versus anthropogenic influence: a meta-analysis using ground beetles.

Most edges are anthropogenic in origin, but are distinguishable by their maintaining processes (natural vs. continued anthropogenic interventions: forestry, agriculture, urbanization). We hypothesized that the dissimilar edge histories will be reflected in the diversity and assemblage composition of inhabitants. Testing this “history‐based edge effect” hypothesis, we evaluated published information on a common insect group, ground beetles (Coleoptera: Carabidae) in forest edges. A meta‐analysis showed that the diversity‐enhancing properties of edges significantly differed according to their history. Forest edges maintained by natural processes had significantly higher species richness than their interiors, while edges with continued anthropogenic influence did not. The filter function of edges was also essentially different depending on their history. For forest specialist species, edges maintained by natural processes were penetrable, allowing these species to move right through the edges, while edges still under anthropogenic interventions were impenetrable, preventing the dispersal of forest specialists out of the forest. For species inhabiting the surrounding matrix (open‐habitat and generalist species), edges created by forestry activities were penetrable, and such species also invaded the forest interior. However, natural forest edges constituted a barrier and prevented the invasion of matrix species into the forest interior. Preserving and protecting all edges maintained by natural processes, and preventing anthropogenic changes to their structure, composition, and characteristics are key factors to sustain biodiversity in forests. Moreover, the increasing presence of anthropogenic edges in a landscape is to be avoided, as they contribute to the loss of biodiversity. Simultaneously, edges under continued anthropogenic disturbance should be restored by increasing habitat heterogeneity.

Finite-Time Stabilization for a Class of Nonlinear Differential-Algebraic Systems Subject to Disturbance

In this paper, finite-time stabilization problem for a class of nonlinear differential-algebraic systems (NDASs) subject to external disturbance is investigated via a composite control manner. A composite finite-time controller (CFTC) is proposed with a three-stage design procedure. Firstly, based on the adding a power integrator technique, a finite-time control (FTC) law is explicitly designed for the nominal NDAS by only using differential variables. Then, by using homogeneous system theory, a continuous finite-time disturbance observer (CFTDO) is constructed to estimate the disturbance generated by an exogenous system. Finally, a composite controller which consists of a feedforward compensation part based on CFTDO and the obtained FTC law is proposed. Rigorous analysis demonstrates that not only the proposed composite controller can stabilize the NDAS in finite time, but also the proposed control scheme exhibits nominal performance recovery property. Simulation examples are provided to illustrate the effectiveness of the proposed control approach.

Hybrid Strategy for Nonlinear Control of (6 DOF) Under Actuated Tricolor UAV

This paper, proposed a hybrid strategy for nonlinear control of six degree of freedom (6 DOF) underactuated trirotor Unmanned Aerial Vehicle (UAV). The hybrid control strategy consists of Nonlinear Disturbance Observer (NDO) along with Proportional, Integral and Derivative (PID) controller to control the model of nonlinear (6 DOF) underactuated trirotor UAV. The control model of the UAV is divided in to two sub-models, altitude control and the attitude control such that, the PD controller is used to control the altitude of the UAV and (NDO)with the PID controller is used to control the attitude of UAV. However, the stability of the aircraft is proved by using Lyapunov stability criteria. The robustness of the proposed control strategy is compared with the nonlinear observer design with backstepping control of UAV. It shows that the proposed hybrid strategy have better response less steady state error and good robustness in the presence of continuous disturbance in the model of UAV.

Effects of nitrogen and phosphorus additions on soil methane uptake in disturbed forests

AbstractAtmospheric nitrogen (N) deposition is generally thought to suppress soil methane (CH4) uptake in natural forests, and phosphorus (P) input may alleviate this negative effect. However, it remains unclear how N and P inputs control soil CH4 uptake in disturbed forests. In this study, soil CH4 uptake rates were measured in two disturbed forests, including a secondary forest (with previous, but not recent, disturbance) and a plantation forest (with recent continuous disturbance), in southern China for 34 months of N and/or P additions: control, N addition (150 kg N ha−1 yr−1), P addition (150 kg P ha−1 yr−1), and NP addition (150 kg N ha−1 yr−1 plus 150 kg P ha−1 yr−1). Mean CH4 uptake rate in control plots was significantly higher in the secondary forest (24.40 ± 0.81 µg CH4‐C m−2 h−1) than in the plantation forest (17.07 ± 0.70 µg CH4‐C m−2 h−1). CH4 uptake rate had negative relationships with soil water‐filled pore space in both forests. In the secondary forest, N, P, and NP additions significantly decreased CH4 uptake by 39.7%, 27.8%, and 37.6%, respectively, but had no significant effects in the plantation forest, indicating that P input does not alleviate the suppression of CH4 uptake by N deposition. Taken together, our findings suggest that reducing anthropogenic disturbance, including harvesting of forest floor, and anthropogenic N and P inputs will increase soil CH4 uptake in disturbed forests, which is important in view of the increased trends in global warming during recent decades.

Sleep complaints are associated with reduced left prefrontal activation during a verbal fluency task in patients with major depression: A multi-channel near-infrared spectroscopy study

BackgroundRecent studies have indicated the potential clinical use of near-infrared spectroscopy (NIRS) as a tool for assisting in the diagnosis of major depressive disorder (MDD). Although sleep complaints are often manifested in MDD, no study has elucidated the possible association between the objective evaluation of sleep and NIRS signals in MDD. MethodsFourteen patients with MDD and 15 healthy controls wore waist actigraphy equipment before the NIRS scan to investigate sleep parameters. We performed a 52-channel NIRS scan and measured changes in oxygenated hemoglobin ([oxy-Hb]) during a verbal fluency task. ResultsIn patients with MDD, a significant negative correlation was observed between the 17-item Hamilton Depressive Rating Scale score and cerebral reactivity of the right temporal region (ps:=−0.804 to −0.762; FDR-corrected; p=0.008–0.012). The Pittsburgh Sleep Questionnaire Index, which enables assessment of continuous sleep quality and disturbances, was negatively correlated with [oxy-Hb] changes in the left prefrontal cortex (ps=−0.630 to −0.551; FDR-corrected; p=0.043–0.048). Actigraphic sleep variables prior to the NIRS measurement showed no significant correlation with [oxy-Hb] changes. LimitationsThe limitations were small sample size with the low severity of depression and the use of actigraphy for only one night. ConclusionSelf-rated sleep disturbance were associated with decreased left prefrontal reactivity during a verbal fluency task in patients with MDD. Our result indicates that the reactivity of the prefrontal region is susceptible to sleep complaints, providing further evidence to support potential clinical application of NIRS.

Neural Network-Based Self-Tuning PID Control for Underwater Vehicles.

For decades, PID (Proportional + Integral + Derivative)-like controllers have been successfully used in academia and industry for many kinds of plants. This is thanks to its simplicity and suitable performance in linear or linearized plants, and under certain conditions, in nonlinear ones. A number of PID controller gains tuning approaches have been proposed in the literature in the last decades; most of them off-line techniques. However, in those cases wherein plants are subject to continuous parametric changes or external disturbances, online gains tuning is a desirable choice. This is the case of modular underwater ROVs (Remotely Operated Vehicles) where parameters (weight, buoyancy, added mass, among others) change according to the tool it is fitted with. In practice, some amount of time is dedicated to tune the PID gains of a ROV. Once the best set of gains has been achieved the ROV is ready to work. However, when the vehicle changes its tool or it is subject to ocean currents, its performance deteriorates since the fixed set of gains is no longer valid for the new conditions. Thus, an online PID gains tuning algorithm should be implemented to overcome this problem. In this paper, an auto-tune PID-like controller based on Neural Networks (NN) is proposed. The NN plays the role of automatically estimating the suitable set of PID gains that achieves stability of the system. The NN adjusts online the controller gains that attain the smaller position tracking error. Simulation results are given considering an underactuated 6 DOF (degrees of freedom) underwater ROV. Real time experiments on an underactuated mini ROV are conducted to show the effectiveness of the proposed scheme.

The immunity of the KNX model to continuous electromagnetic disturbances

The immunity of the KNX model to continuous electromagnetic disturbances

PQ state space representation and its application to electromagnetic compatibility/incompatibility degree, influence degree, and PQ performance assessment

This study introduces power quality (PQ) state space representation to describe continuous PQ disturbances. A tolerance boundary is designed to represent the integrated disturbance tolerance of all equipment connected to electric power network, and the uncertainty of integrated disturbance tolerance is described with the cloud model. Electromagnetic compatibility and incompatibility degree indices are proposed to reflect the severity of PQ disturbances affecting the equipment. The influence degree index is defined to quantify the severity and impact scope of PQ disturbances. The uncertainty of equipment fault state is expressed by a fuzzy membership function. Subsequently, PQ performance is assessed according to equipment compatibility/incompatibility degree to PQ disturbances. Case studies on a 14-bus distribution system are performed and analysed. Results reveal the effectiveness and reasonableness of the proposed indices in assessing equipment compatibility/incompatibility degree to PQ disturbances, influence of PQ disturbances on the equipment, and PQ performance.

Reducing the gap between seismic imaging and geology: Horizon consistent velocity analysis and modelling for pre-stack time and depth migrations

S eismic velocities and migration techniques have great impact in the reservoir imaging at any stage of the exploration for hydrocarbons. The effectiveness of a migration algorithm is commonly measured by the ability to boost the signal continuity, against noise and other disturbances such as diffractions from out-of-plane events (Jones, 2010). By contrast, migration is a process applied to reposition the energy from where it originated, to resolve the geometry and positioning of the events. The success of the process is heavily reliant on the velocity field used. The consistency between the velocity field and events is a quality indicator in seismic inversion exercises, for both the low frequency background and the high frequency intervals identified in velocity logs. The migration itself can be seen as an inversion procedure, with the velocity gradients required to be consistent with vertical trends and amplitude events (Guillaume et al., 2011; Benson et al., 2015). The understanding of geological velocities progresses with exploration and the increasing number of wells and geophysical data available, which gradually establish lithological and rock physics properties, together with tectonic and burial history. Several pre-stack algorithms are available for time migration (PSTM) as well as for depth migration (PSDM), which allow the velocity analysis and modelling sequence to more closely integrate geophysical and geological data. Nowadays, pre-conditioned migration velocities are common in the depth imaging, during the processing of PSDM. The approach is applied for complex geology and relies on seismic and non-seismic data, also combined through different joint inversion techniques (Droujinine et al., 2008; Foss et al., 2008; Houghton et al., 2014). We present a migration workflow, originally designed for regional 2D seismic and applicable to 3D, which links the velocity modelling for PSTM with PSDM, and allows geological constraints to be applied at the PSTM stage (Figure 1).

Sleep and mental disorders: A meta-analysis of polysomnographic research.

Investigating sleep in mental disorders has the potential to reveal both disorder-specific and transdiagnostic psychophysiological mechanisms. This meta-analysis aimed at determining the polysomnographic (PSG) characteristics of several mental disorders. Relevant studies were searched through standard strategies. Controlled PSG studies evaluating sleep in affective, anxiety, eating, pervasive developmental, borderline and antisocial personality disorders, attention-deficit-hyperactivity disorder (ADHD), and schizophrenia were included. PSG variables of sleep continuity, depth, and architecture, as well as rapid-eye movement (REM) sleep were considered. Calculations were performed with the "Comprehensive Meta-Analysis" and "R" software. Using random effects modeling, for each disorder and each variable, a separate meta-analysis was conducted if at least 3 studies were available for calculation of effect sizes as standardized means (Hedges' g). Sources of variability, that is, sex, age, and mental disorders comorbidity, were evaluated in subgroup analyses. Sleep alterations were evidenced in all disorders, with the exception of ADHD and seasonal affective disorders. Sleep continuity problems were observed in most mental disorders. Sleep depth and REM pressure alterations were associated with affective, anxiety, autism and schizophrenia disorders. Comorbidity was associated with enhanced REM sleep pressure and more inhibition of sleep depth. No sleep parameter was exclusively altered in 1 condition; however, no 2 conditions shared the same PSG profile. Sleep continuity disturbances imply a transdiagnostic imbalance in the arousal system likely representing a basic dimension of mental health. Sleep depth and REM variables might play a key role in psychiatric comorbidity processes. Constellations of sleep alterations may define distinct disorders better than alterations in 1 single variable. (PsycINFO Database Record

Paleoecology and Geoarchaeology at El Palmar and the El Zotz Region, Guatemala

A new paleoecology record from the El PalmarCivaladds to the emerging geoarchaeological record of El Zotz, Guatemala. El Palmar's 3 m stratigraphic record began in the Archaic period before 1500 B.C. at or just before initial Maya impacts. From the lowest level, Late Archaic organic deposition, with evidence for diverse tropical forest and a steady water table, transitioned to Early Preclassic clay deposition, decreased forest taxa, three known food taxa, and more economic species. Clay deposition continued through the Preclassic, with occasional organic and high charcoal deposition, increasing maize, and other possible economic pollen. Classic El Palmar saw a new land use type with continued disturbance evidence but diverse and greater forest cover. Human impacts continued, leaving high amounts of disturbance taxa, charcoal, and the highest maize pollen level, concomitant with lower deposition rates, δ13C evidence of increased, diverse tropical forest taxa and organic sediments. El Zotz Aguada's Early Classic to Postclassic sediment record overlaps this, with maize and squash pollen evidence changing to Classic period copal tree pollen dominance. Both records indicate the maximum quantity of C4taxa derived organic matter was about 40%, leaving at least half from C3taxa such as tropical forest species.