Temporal Time Scales Research Articles

Temporal blindspots in Occupy Philadelphia

ABSTRACT This paper analyzes the disjunctive temporalities of Occupy Philadelphia’s political constituencies. Drawing on both an ethnographic participant observation study of the Occupy Philadelphia movement and Philadelphia’s neoanarchist political communities, and on recent social scientific theorization of events, the paper argues that contradictory ideas about temporal timescales, momentum, duration, sequences, and rhythms of tactical and strategic action problematized interaction and coordination among movement participants. These points of coordinative disjuncture can be traced back to differences in participants’ ideas about prefigurative politics and strategic temporalities. Limning the temporal expectations and experiences of social movement participants, this paper contributes to the examination of both linkages and disjunctures between eventful temporalities experienced in moments of protest and in social movements with diverse timescales.

An improved coupled framework for Glacier classification: an integration of optical and thermal infrared remote-sensing bands

ABSTRACTThis study evaluates the applicability of optical and thermal infrared (TIR) bands by the applications of two different satellite sensors for characterizing debris covers of Zemu glacier situated in the North Sikkim Himalayas India. Differentiating supraglacial debris (SGD), clean ice, and ice-covered glaciers from periglacial debris (PGD) cover is a challenging task due to similarities between their spectra. Previous studies suggest that the difference between thermal and optical properties can be used in the separation of SGD (part of the glacier boundary) and PGD (outside the glacier boundary) accurately. Thus a novel multi-criteria approach has been constructed to characterize the glacier cover utilizing Maximum Likelihood Classifier (MLC) and hybrid classification (HC) methods. Based on the integration of optical and TIR bands from two satellite systems such as Landsat and Indian Remote Sensing Satellite Linear Imaging Spectral Scanner 3, total six different image combinations were prepared to explore glacier features under various mathematical and image processing operations. Each image band combination represents a distinctive characterization of the debris cover of Zemu glacier. The spatial-spectral profiles of glacial features (spectral signatures) were drawn to distinguish SGD and PGD. The accuracy assessment was performed to test the correctness of classified maps resulted from MLC and HC methods. The HC maps show a larger efficiency (near to 90%) than MLC maps (near to 85%). The outcomes offered better understandings in the classification of SGD and PGD by using the combined products of optical and TIR remote-sensing sensors. The ground-based observations such as GPS points, field photographs of the Zemu glacier topography, and high-resolution Google Earth images helped to reduce the misclassification and improved the classification accuracy. Furthermore, a cloud removal method was applied for TIR bands to improve the accuracy of the glacier classification. The glacier features and their area statistics have been compared to temporal time scales, illustrating annual fluctuations in glacial characteristics.

A Framework for Validation of Remotely Sensed Precipitation and Evapotranspiration Based on the Budyko Hypothesis

AbstractDespite offering spatially and temporally continuous measurements, the use of remotely sensed P and E in data‐scarce catchments is hindered by the lack of ground‐based measurements that enable comprehensive validation. This study proposes a novel validation framework that characterizes the combined error in the long‐term average estimates of remotely sensed P and E by making use of the Budyko hypothesis, specifically Fu's equation. A Root Mean Square Error (RMSE)‐based error metric that is capable of translating individual biases in P and E estimates onto the Budyko space is developed. A controlled sensitivity experiment using data from Model Parameter Estimation Experiment (MOPEX) catchments in the United States showed that the developed error metric is more sensitive to biases in P compared to biases in estimates of E. Validating the framework using combinations of different satellite‐based estimates of P and E revealed that the framework succeeds in arriving at the same conclusions as a traditional validation method with regards to the quality of P and E data sets. The framework offers a physically consistent, parametrically efficient basis for the selection of remotely sensed P and E data sets for hydrologic studies. Due to lack of consideration for catchment storage in the formulation of Fu's equation, the developed error metric is limited to long temporal time scales. As a result, the error metric is capable of characterizing the bias in P and E data sets and not the variance.

Impacts of hydraulic redistribution on grass-tree competition vs facilitation in a semi-arid savanna.

A long-standing ambition in ecosystem science has been to understand the relationship between ecosystem community composition, structure and function. Differential water use and hydraulic redistribution have been proposed as one mechanism that might allow for the coexistence of overstory woody plants and understory grasses. Here, we investigated how patterns of hydraulic redistribution influence overstory and understory ecophysiological function and how patterns vary across timescales of an individual precipitation event to an entire growing season. To this end, we linked measures of sap flux within lateral and tap roots, leaf-level photosynthesis, ecosystem-level carbon exchange and soil carbon dioxide efflux with local meteorology data. The hydraulic redistribution regime was characterized predominantly by hydraulic descent relative to hydraulic lift. We found only a competitive interaction between the overstory and understory, regardless of temporal time scale. Overstory trees used nearly all water lifted by the taproot to meet their own transpirational needs. Our work suggests that alleviating water stress is not the reason we find grasses growing in the understory of woody plants; rather, other stresses, such as excessive light and temperature, are being ameliorated. As such, both the two-layer model and stress gradient hypothesis need to be refined to account for this coexistence in drylands.

Tracing the accretion history of supermassive black holes through X-ray variability: results from the ChandraDeep Field-South

We study the X-ray variability properties of distant AGNs in the Chandra Deep Field-South region over 17 years, up to $z\sim 4$, and compare them with those predicted by models based on local samples. We use the results of Monte Carlo simulations to account for the biases introduced by the discontinuous sampling and the low-count regime. We confirm that variability is an ubiquitous property of AGNs, with no clear dependence on the density of the environment. The variability properties of high-z AGNs, over different temporal timescales, are most consistent with a Power Spectral Density (PSD) described by a broken (or bending) power-law, similar to nearby AGNs. We confirm the presence of an anti-correlation between luminosity and variability, resulting from the dependence of variability on BH mass and accretion rate. We explore different models, finding that our acceptable solutions predict that BH mass influences the value of the PSD break frequency, while the Eddington ratio $\lambda_{Edd}$ affects the PSD break frequency and, possibly, the PSD amplitude as well. We derive the evolution of the average $\lambda_{Edd}$ as a function of redshift, finding results in agreement with measurements based on different estimators. The large statistical uncertainties make our results consistent with a constant Eddington ratio, although one of our models suggest a possible increase of $\lambda_{Edd}$ with lookback time up to $z\sim 2-3$. We conclude that variability is a viable mean to trace the accretion history of supermassive BHs, whose usefulness will increase with future, wide-field/large effective area X-ray missions.

Reminiscence Therapy Improved Recall of Autobiographical Memory

Reminiscence Therapy Improved Recall of Autobiographical Memory

Coherent modes in multi‐scale variability of precipitation over the headwater catchments in the Pearl River basin, South China

This paper studies the coherent modes of multi-scale variability of precipitation over the headwater catchments in the Pearl River basin in South China. Long-term (1952–2000) daily precipitation data spatially averaged for 16 catchments in the basin are studied. Wavelet transform analysis is performed to capture the fluctuation embedded in the time series at different temporal timescales ranging from 6 days to 8.4 years. The catchment clusters of the coherent modes are delineated using the principal component analysis on the wavelet spectra of precipitation. The results suggest that as much as 98% of the precipitation variability is explained by only two coherent modes: high small-scale mode and high seasonal mode. The results also indicate that a large majority of the catchments (i.e., 15 out of 16) exhibit consistent mode feature on multi-scale variability throughout three sub-periods studied (1952–1968, 1969–1984, and 1985–2000). The underlying effects of the coherent modes on the regional flood and drought tendency are also discussed.

Venus cloud-tracked and doppler velocimetry winds from CFHT/ESPaDOnS and Venus Express/VIRTIS in April 2014

We present new coordinated observations and measurements of the wind amplitude and its variability at Venus cloud-tops based on the two complementary techniques of Ground-based Doppler velocimetry (Widemann et al., 2007, 2008; Machado et al., 2012, 2014) and cloud-tracked winds using ESA Venus Express/ VIRTIS-M imaging at 0.38 µm (Drossart et al., 2007; Sanchez-Lavega et al., 2008; Hueso et al., 2012; Machado et al., 2014). Cloud-tracked winds trace the true atmospheric motion also responsible for the Doppler-Fizeau shift of the solar radiation on the dayside by super-rotating moving cloud-tops with respect to both the Sun and the observer (Machado et al., 2014), and based on this complementarity, we performed a new coordinated campaign in April 2014 combining both Venus Express observations and ground-based Doppler wind measurements on the dayside of Venus’ cloud tops at Canada-France-Hawaii telescope at a phase angle Φ=(76±0.3)∘. The analysis and results show (1) additional confirmation of the coherence, and complementarity, in the results provided by these techniques, on both spatial and temporal time scales of the two methods; (2) first-time estimation of the meridional component of the wind in another planet using the Doppler velocimetry technique, with evidence of a symmetrical, poleward meridional Hadley flow in both hemispheres of v¯m = 22± 15.5 ms−1; (3) spatial and temporal variability of the zonal flow with latitude and local time, with a significant increase of wind amplitude near the morning terminator previously reported in Feb. 2011 observations.

Some Perspectives on Avalanche Climatology

Avalanche climatology is defined as the study of the relationships between climate and snow avalanches, and it contributes in aiding avalanche hazard mitigation efforts. The field has evolved over the past six decades concerning methodology, data monitoring and field collection, and interdisciplinary linkages. Avalanche climate research directions are also expanding concerning treatment in both spatial scale and temporal timescales. This article provides an overview of the main themes of avalanche climate research in issues of scale from local to global, its expanding interdisciplinary nature, as well as its future challenges and directions. The growth of avalanche climatology includes themes such as its transformation from being mostly descriptive to innovative statistical methods and modeling techniques, new challenges in microscale efforts that include depth hoar aspects and increased field studies, expanding synoptic climatology applications on studying avalanche variations, efforts to reconstruct past avalanches and relate them to climatic change, and research on potential avalanche responses to recent twentieth-century and future global warming. Some suggestions on future avalanche climatology research directions include the expansion of data networks and studies that include lesser developed countries, stronger linkages of avalanche climate studies with GIScience and remote sensing applications, more innovative linkages of avalanches with climate and societal applications, and increased emphases on modeling and process-oriented approaches.

Interannual variability of winter‐spring temperature in the Middle Atlantic Bight: Relative contributions of atmospheric and oceanic processes

AbstractRelative contributions between the local atmospheric and oceanic processes on the interannual variability of winter‐spring shelf temperature in the Middle Atlantic Bight (MAB) are investigated based on a regional ocean model. The model demonstrates sufficient capability to realistically simulate the interannual temperature changes during 2003–2014. On interannual time scales, the mean winter/spring temperature in the MAB is determined by the combination of the initial temperature at the beginning of the season and the mean cumulative air‐sea flux, while the mean cumulative ocean advective flux plays a secondary role. In spite of the overall importance of air‐sea flux in determining the winter and spring temperature, the relative contributions between air‐sea flux and ocean advective flux on the evolution of the temperature anomaly in each individual year varies. The predictability of spring (April–June) temperature based on winter (January–March) temperature is weak because the temporal decorrelation time scale changes significantly from year to year. Both the highly variable shelf temperature and its decorrelation time scale are affected by the changes in the relative contributions between the air‐sea flux and ocean advective flux.

Ultrafast pulse compression, stretching-and-recompression using cholesteric liquid crystals

We have experimentally demonstrated the feasibility of direct compression, or stretching and recompression of laser pulses in a very wide temporal time scale spanning 10's fs to ~1 ps time with sub-mm thick cholesteric liquid crystal (CLC) cells. The mechanisms at work here are the strong dispersion at the photonic band-edges and nonlinear phase modulation associated with the non-resonant ultrafast molecular electronic optical nonlinearity. The observed pulse compression limit, spectral characteristics and intensity dependence of the compression are in good agreement with theoretical expectations and simulations based on a coupled-mode propagation model. Owing to the large degree of freedom to engineer the wavelength locations of CLC photonic bandgap and band-edges, these self-action all-optical processes can be realized with ultrafast lasers pulses in a very wide spectral region from the visible to near infrared, with potential applications in compact ultrafast photonic modulation devices/platforms.

Different correlations between NDVI and meteorological factors at temporal-time scales

Different correlations between NDVI and meteorological factors at temporal-time scales

Director reorientation in a nematic liquid crystal with a photosensitive layer.

We use a molecular-motor model previously proposed for a nematic cell with an azo-dye monolayer to calculate the director orientation when light is normally impinged on the cell. We consider an initial planar configuration for which one of the surrounding plates, which we call the reference plate, is submitted to a hard-anchoring boundary condition. The other confining plate has a coating monolayer of azo-dye molecules such that the change of the orientation of azo-dye isomers, due to light, causes changes in the nematic director. The boundary conditions on both plates along with the optical field determine the director configuration in the bulk. The existence of periodic solutions for the density of isomers in trans and cis states, corresponding to weak optical fields, has been discussed in the literature. Using a similar approach, we find an approximate expression for the density of isomers, written in terms of the director angle, which allows us to close the equation for the director configuration on the boundary having a photosensitive plate. We decouple the director's angle and the isomer densities by assuming extremely different temporal time scales between them. We show for a given sample that switching times inversely depend on the trans-cis transition rate of photoexcitation whereas relaxation times do not depend on it. On the other hand, switching and relaxation times linearly depend on effective surface viscosity values. Our model allows us to estimate surface viscosity values.

Characterizing Motif Dynamics of Electric Brain Activity Using Symbolic Analysis

Motifs are small recurring circuits of interactions which constitute the backbone of networked systems. Characterizing motif dynamics is therefore key to understanding the functioning of such systems. Here we propose a method to define and quantify the temporal variability and time scales of electroencephalogram (EEG) motifs of resting brain activity. Given a triplet of EEG sensors, links between them are calculated by means of linear correlation; each pattern of links (i.e., each motif) is then associated to a symbol, and its appearance frequency is analyzed by means of Shannon entropy. Our results show that each motif becomes observable with different coupling thresholds and evolves at its own time scale, with fronto-temporal sensors emerging at high thresholds and changing at fast time scales, and parietal ones at low thresholds and changing at slower rates. Finally, while motif dynamics differed across individuals, for each subject, it showed robustness across experimental conditions, indicating that it could represent an individual dynamical signature.

Measurement of flood peak effects as a result of soil and land management, with focus on experimental issues and scale

As a result of several serious flood events which have occurred since 2000, flooding across Europe is now receiving considerable public and media attention. The impact of land use on hydrology and flood response is significantly under-researched, and the links between land use change and flooding are still unclear. This study considers runoff data available from studies of arable in-field land use management options, applied with the aim of reducing diffuse pollution from arable land, in order to investigate whether these treatments also have potential to reduce downstream flooding. Intensive monitoring of 17 hillslope treatment areas produced a record of flood peak data covering different mitigation treatments for runoff which occurred in the winter of 2007–2008. We investigated event total runoff responses to rainfall, peak runoff, and timing of the runoff peaks from replicates of different treatments, in order to assess whether there is a significant difference in flood peak response between different mitigation options which could be used to mitigate downstream flood risk. A mixed-modelling approach was adopted in order to determine whether differences observed in runoff response were significant. The results of this study suggest that changes in land use management using arable in-field mitigation treatments can affect local-scale runoff generation, with differences observed in the size, duration and timing of flood peaks as a result of different management practices, but the study was unable to allow significant treatment effects to be determined. We suggest that further field studies of the effects of changes in land use and land use management need to upscale towards farm and catchment scale experiments which consider high quality before-and-after data over longer temporal timescales. This type of data collection is essential in order to allow appropriate land use management decisions to be made.

ON REYNOLDS' DILATANCY AND SHEAR BAND EVOLUTION: A NEW PERSPECTIVE

Dense granular media exhibit rich phenomenology when subject to imposed stresses and strains. This is a result of the many degrees of freedom present in an assembly of grains and the nonlinear interactions between the grains. Their complex behavior include the self-organization of load-bearing columnar structures known as force chains across a wide range of spatial scales. Behavior akin to phase transitions from a strong solid-like to a weak liquid-like response can also be observed with shear bands, i.e. regions where force chains collectively buckle, being the signature microstructure in this transition from the stable to the failure regime. An inherent aspect of shear bands and dense granular failure is the phenomenon of dilatancy, i.e. expansion in volume, when the material is subjected to a combined compression and shear. To understand the origins of dilatancy, it is useful to consider the granular material as a mixture of two components: grains and the interstitial material filling the voids or pores between the grains. The grains within a dense granular material respond to applied loads by rearranging to create local zones which contract and dilate. Extant studies of this mechanical response are typically focused on the solid skeleton, in particular, the topology of the network representing the physical contacts between grains. Here, we propose an alternative perspective which is to consider network representations of the evolving anisotropic pore space. We demonstrate how to construct pore space networks that express the local size of voids about a grain through network edge weights. We investigate sectors of the loading history when a percolating giant component of the pore space network exists. By defining two weight functions for edge properties, we: (i) discover via a recurrence plot-based analysis a temporal time scale for jamming–unjamming (contractant-dilatant) dynamics in shear bands; and show that (ii) the formation of a persistent shear band in response to the deformation places grains in a configuration predisposed to the efficient transport of interstitial material as evidenced by the location of percolating shortest path routes through the most dilatant sites. A proper understanding of the micromechanics of pore evolution with respect to shear bands and dilatancy is key to a range of applications such as modeling ground water flow, dewatering systems, carbon capture and sequestration.

Phase difference analysis of temperature and vegetation phenology for beech forest: a wavelet approach

Temporal shifts in phenology or vegetation period of plants are seen as indicators of global warming with potentially severe impacts on ecosystem functioning. In spite of increasing knowledge on drivers, it is of utmost importance to disentangle the relationship between air temperatures, phenological events, potential temporal lags (phase shifts) and time scale for certain plant species. Assessing the phase shifts as well as the scale-dependent relationship between temperature and vegetation phenology requires the development of a nonlinear temporal model. Therefore, we use wavelet analysis and present a framework for identifying scale-dependent cross-phase coupling of bivariate time series. It allows the calculation of (a) scale-dependent decompositions of time series, (b) phase shifts of seasonal components in relation to the annual cycle, and (c) inter-annual phase differences between seasonal phases of different time series. The model is applied to air temperature data and remote sensing phenology data of a beech forest in Germany. Our study reveals that certain seasonal changes in amplitude and phase with respect to the normal annual rhythm of temperature and beech phenology are coupled time-delayed components, which are characterized by a time shift of about one year.

Temporal and diel cycling of nutrients in a barrier–lagoon complex: Implications for phytoplankton abundance and composition

The cycling of nutrients (silicate, nitrate, ammonium and phosphate) in a quasi-pristine barrier–lagoon complex (Louro Lagoon, NW Iberian Peninsula) was studied both in a diel and temporal timescale covering different seasonal conditions. Hydrographical and meteorological conditions exert a major control on the nutrient cycling in the lagoon. From late autumn to early spring the lagoon is characterized by oxic conditions due to significant freshwater inputs and sporadic communication with the sea. In summer, elevated primary production coupled with water stagnancy leads to bottom waters hypoxia and marked diel variation of pH, oxygen and redox potentials. Diel variation of nutrients was only evident when mixing of surface and bottom waters during the night was observed.Temporal changes in nutrients concentrations and their relative abundance were found to induce a clear shift in the phytoplankton composition. In winter, during silicate and nitrate abundance and low phosphate, diatoms predominate. In summer, under hypoxic conditions, sediments take control on the supply of nutrients leading to increased phosphate availability relative to nitrate/ammonium or silicate. Diatoms are then replaced during the summer blooms – linked to low atomic N:P ratios (typically <2) – by flagellates and green algae with minor contributions of cyanophytes and dinoflagellates.

Morphogengineering roots: comparing mechanisms of morphogen gradient formation

BackgroundIn developmental biology, there has been a recent focus on the robustness of morphogen gradients as possible providers of positional information. It was shown that functional morphogen gradients present strong biophysical constraints and lack of robustness to noise. Here we explore how the details of the mechanism which underlies the generation of a morphogen gradient can influence those properties.ResultsWe contrast three gradient-generating mechanisms, (i) a source-decay mechanism; and (ii) a unidirectional transport mechanism; and (iii) a so-called reflux-loop mechanism. Focusing on the dynamics of the phytohormone auxin in the root, we show that only the reflux-loop mechanism can generate a gradient that would be adequate to supply functional positional information for the Arabidopsis root, for biophysically reasonable kinetic parameters.ConclusionsWe argue that traits that differ in spatial and temporal time-scales can impose complex selective pressures on the mechanism of morphogen gradient formation used for the development of the particular organism.

Estimativa da variação da produtividade do arroz em diferentes escalas temporais do índice SPI

O objetivo deste trabalho foi avaliar a acurácia do índice de seca SPI (índice padronizado de precipitação), em diferentes escalas temporais, na determinação da ocorrência de eventos de seca e na estimativa de seus efeitos na produtividade do arroz de terras altas, em seis diferentes microrregiões do Estado de Goiás. Foram utilizados dados diários de precipitação, provenientes de estações pluviométricas localizadas nos municípios de Uruaçu, Aruanã, Alexânia, Mineiros, Catalão e Itumbiara, no Estado de Goiás, como também a série histórica de produtividade do arroz de terras altas para as microrregiões goianas de Porangatu, Rio Vermelho, Entorno de Brasília, Sudoeste de Goiás, Catalão e Meia-Ponte. As escalas temporais utilizadas foram: mensal, trimestral, semestral e anual. As diferenças entre as escalas temporais do SPI foram avaliadas quanto ao número e frequência dos eventos de seca, ao percentual de acerto na estimativa da variação da produtividade ajustada de arroz, e quanto aos desvios entre essas estimativas e a produtividade observada. O aumento na escala temporal do SPI possibilita a identificação de eventos de seca de maior duração, e a escala anual (SPI-12) apresentou o melhor desempenho na estimativa da variação da produtividade ajustada de arroz de terras altas.