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The present study examined three key aspects of the sunshine duration -global solar radiation model over North India: calibration of Angstrom coefficients for both daily and monthly time scales, stability analysis of the Angstrom coefficients, and lastly, implying the data-driven artificial and convolutional neural network (ANN and CNN) regressions for higher accuracy and identification of non-linear relationship between the two variables. The average values of the Angstrom coefficients for the region were determined to be a = 0.26, b = 0.45 with coefficient of variation (R2) = 0.80 for monthly and a = 0.29, b = 0.43 with R2 = 0.79 for daily sunshine-radiation data, respectively. A significant (p < 0.01) linear relationship exists between sunshine duration and global radiation, with interchangeable Angstrom coefficients at two time scales. The daily Angstrom coefficients were steadier than those calibrated with monthly data with different data lengths. Also, the time-variation of Angstrom coefficients was insignificant. ANN and CNN regression models showed better performance, improving R2 from 1–6%. Further, ANN regression plots for monthly data values also exhibited pronounced non-linear behaviour for Lucknow and Varanasi, and exhibited the usual non-linear relationship for daily values. However, for most stations, the improvement of the ANN model over the conventional A-P model was insignificant. Therefore, for practical applications, the linear A-P model should be considered due to its simplicity and reasonable accuracy. [ABSTRACT FROM AUTHOR]

Although the entropy algorithm is widely applied in signal complexity analysis, its stability and reliability are limited due to the existence of abnormal signal points. In order to explore the influence of aging and stroke on the human neuromuscular system, refined fuzzy entropy and refined composed multiscale fuzzy entropy were proposed and applied in this study. The simulation results verified that the proposed algorithm improves the stability and the accuracy of entropy estimation. In the experiment, 11 patients after stroke, 10 young controls and 10 aged controls were recruited to perform grasping tasks under different grip strength levels. The grip force signals and surface EMG signals of four muscles on the forearm of the subject’s hemiplegic side (patient) or dominant side (healthy control) were recorded. The results showed that as the time scale increases from 1 to 10, the EMG entropy value: 1) increases at first and then decreases across populations; 2) is larger for the older control subjects than for the younger control subjects originally but then becomes greater for the younger subjects as time increases; 3) is larger for the group of older control subjects than for the stroke survivors in the beginning but then becomes larger in the control subjects. The possible mechanism underlying the changes might be the aging-induced increase in the internal noise of the neuromuscular system and the transfer of effective information on the time scale of EMG signals after stroke. Meanwhile, the influence of aging and stroke on the human neuromuscular system is comprehensively studied by a stable and reliable entropy algorithm, and it contributes to the rehabilitation clinical evaluation of stroke patients.

The pollutant transport equilibrium in a watershed can be analyzed on a large time scale, and land‐use export coefficients can be calculated directly under certain hydrologic and transport conditions, by ignoring hydrologic and transport processes at small space and time scales on hydrologic response units. In this study, the water environment system of a watershed was deconstructed into three parts (source, source‐sink, and runoff transport) to construct a pollutant transportation equilibrium model on a large time scale. A watershed with an annual source‐sink accumulation of zero was defined as a completely transported watershed; therefore, we derived a completely transported equilibrium equation. The problem of seeking the land export coefficient was converted into a problem of seeking the optimal solution of linear programming, which can be estimated according to the variation in pollutant output processes. The feasibility of the solution can be analyzed using multi‐year stochastic rainfall processes. The model was used to analyze the transport equilibrium of chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) upstream of the monitored cross‐sections in a watershed, which covered 3145.66 km2. The land export coefficients were calculated according to the model. The model calculations indicated that the watershed was completely transported during perennial years. The calculated export coefficients of COD, TN, and TP for farmland, primary vegetation, and urban land were within the range of general empirical values. The calculated maximum accumulations of COD, TN, and TP were 0.19 × 107, 0.063 × 107, and 0.049 × 106 kg, respectively, for perennial rainfall. Practitioner Points: A completely transported watershed was defined, and a model of pollutant transportation equilibrium with large time‐scale was constructed.A problem of seeking the optimal solution of a linear programming was designed to estimate the land export coefficient of COD, TN, and TP.The runoff transport and accumulation processes of COD, TN, and TP in a watershed was analyzed. [ABSTRACT FROM AUTHOR]

Parasite can alter the dynamics and diversity of competitive communities indirectly. Here, we firstly constructed a cyclic competition system with three species mediated by a free-living parasite. Subsequently, we explored the effects of parasite traits on the transient dynamics of three host species, as well as the stability and species richness of the competitive community at different time-scales. Simulation results reveal that the invasion of parasite is a key factor in inducing the community unstability. Parasite traits and interspecific competition are likely crucial in structuring communities and disease dynamics. In particularly, parasite invasion can transform the classically periodic oscillation of cyclic community into more complex dynamics, such as periodic oscillation of the community at a large time scale, and periodic oscillation of a single species at a small time scale. Additionally, analysis of the autocorrelation function and partial autocorrelation function analysis for time series of species’ biomass in the cyclic competition system indicate that the time series of species’ biomass at both large and small time scales are stationary. Furthermore, as parasites invade the initial stage equilibrium dynamics of cyclic competition system, pathogenic infection can induce to the extinction of two species, leaving only one species to persist and undergo periodic oscillation. In cases of initial local stability, pathogenic infection can cause all three species to undergo periodic oscillation coincidently. Moreover, the observed transient dynamics of cyclic communities, including the timing of sudden switches in dynamics and other characteristics of transients, occur during the process of parasite invasion. Finally, three parasite traits (transmission rate, shedding rate and virulence) can alter the periodicity and corresponding species richness of cyclic competition. In short, parasite invasion can dramatically change community stability and species diversity. [ABSTRACT FROM AUTHOR]

The Standardized Precipitation Index (SPI) is a standardized measure of the variability of precipitation and is widely used for drought assessment around the world. In general, the probability distribution used to calculate the SPI in many studies is Gamma. In addition, a monthly time-scale is applied to calculate the SPI to assess drought based on atmospheric moisture supply over the medium-to-long term. However, probability distributions other than Gamma are applied in various regions, and the need for a daily time-scale is emerging as concerns about fresh drought increase. There are two main innovations of our work. The first is that we investigate the optimal probability distribution of daily SPIs rather than monthly SPIs, and the second is that we address the issue of determining the minimum time-scale that can be applied when applying a daily time-scale. In this study, we investigate the optimal probability distribution and the minimum-applicable time-scale for calculating the daily SPI using daily precipitation time series observed over 42 years at 56 sites in South Korea. Six candidate probability distributions (Gumbel, Gamma, GEV, Log-logistic, Log-normal, and Weibull) and ten time-scales (5 day, 10 day, 15 day, 21 day, 30 day, 60 day, 90 day, 180 day, 270 day, and 365 day) were applied to calculate the daily SPI. A chi-square test and AIC were applied to investigate the appropriate probability distribution for each time-scale, and the normality of the daily SPI time series derived from each probability distribution were compared. The Weibull distribution was suitable for calculating the daily SPI for short time-scales of 30 days or less, while the GEV distribution was suitable for longer time-scales of 270 days or more. However, overall, Gamma was found to be the best probability distribution. While there were some regional variations, the minimum time-scales that could be applied per season were as follows: 15 days for spring and summer, 21 days for fall, and 30 days for winter. It is shown that the minimum time-scale depends on how many zero values are included in the moving cumulative-precipitation time series, and it is shown that it is appropriate to have less than about 2.5%. Finally, the applicability of the GEV distribution is investigated. [ABSTRACT FROM AUTHOR]

A new species of the genus Niphargus Schiödte, 1849 (Crustacea: Amphipoda: Niphargidae), co-existing with other stygobiotic amphipods, Diasynurella kiwi Marin and Palatov, 2023 and Pontonyx donensis (Martynov, 1919) (Crangonyctidae), is described from a small spring on a shore of Kiziterinka River in Rostov-on-Don City in the mouth of the Don River. Two of the three species in the studied spring, D. kiwi and the discovered Niphargus, belong to microcrustaceans not exceeding the total body size of 3 mm. The new species, Niphargus rostovi sp. nov., represents one of the smallest species within the genus and is mostly related to the Greek Niphargus karkabounasi Ntakis, Anastasiadou, Zakšek and Fišer, 2015, which is also not reaching the body size of 3 mm. One more related undescribed species is found on the Crete Island by the molecular genetic data. These species represent a separate phylogenetic lineage within the "carpathicus" species complex, which diverged from the congeners in the Late Miocene for more than 10 Mya. At the same time, the speciation within the ingroup started about 5–6 Mya, obviously correlating with the drainage of the Euxinian basin of the Eastern Paratethys, connecting the lower Don and southern Greece areas. Niphargus potamophilus Birštein, 1954 is also first recorded from the mouth of the Belbek River in the Crimean Peninsula, closing the known area from the Kuban River delta to Rostov-on-Don area and further along the western coast of the Black Sea to Bulgaria. Analysis of the recent records of long-time lineages of endemic/subterranean/stygobiotic animals unable to disperse for long distances assumed that glacial refugium existed at the mouth of the Don River, along with the South Caucasus (Colchis) and the southern Caspian (Hyrcania), where many species have survived several periods of glaciation since the late Miocene. [ABSTRACT FROM AUTHOR]

Transient response performance and steady-state operation performance are the two most important performance indicators of a motor drive system. In order to solve these two problems, this study proposes a new induction motor (IM) model, and then designs a new simplified linearization controller method. First, the tangential force that determines the transient process of the motor is represented by electromagnetic torque, and the radial force is represented by reactive torque. Then, the dual-torque model of IM is derived, which not only accurately shows the rotating air-gap magnetic field through the amplitude and rotating angular frequency, but also visually demonstrates the physical essence of the transient process of IM. Then, this study proposes a simplified feedback linearization method without the analysis of zero dynamic. In addition, a time-scale hierarchical control system is designed to reduce the ripple caused by the coupling of different time-scale variables. The experimental results show that the steady-state torque ripple of the proposed method is 65% lower than that of RFOC, and the torque response speed is 10% higher than that of DTC. [ABSTRACT FROM AUTHOR]

We consider a finite-horizon LQ optimal control problem governed by a time-varying discrete system with two time-scales. Both fixed and free final state approaches for the asymptotic analysis and solution of this problem are proposed. In the first approach, an iterative algorithm converging to the solution of the corresponding two-point boundary value problem, which is not exactly solvable, is constructed, thereby finding an approximate optimal control value. We propose a simplified and lower-cost feedback controller in order to find the approximate optimal index in the second approach. Two examples are given to illustrate the proposed method. [ABSTRACT FROM AUTHOR]

Transient response performance and steady-state operation performance are the two most important performance indicators of a motor drive system. In order to solve these two problems, this study proposes a new induction motor (IM) model, and then designs a new simplified linearization controller method. First, the tangential force that determines the transient process of the motor is represented by electromagnetic torque, and the radial force is represented by reactive torque. Then, the dual-torque model of IM is derived, which not only accurately shows the rotating air-gap magnetic field through the amplitude and rotating angular frequency, but also visually demonstrates the physical essence of the transient process of IM. Then, this study proposes a simplified feedback linearization method without the analysis of zero dynamic. In addition, a time-scale hierarchical control system is designed to reduce the ripple caused by the coupling of different time-scale variables. The experimental results show that the steady-state torque ripple of the proposed method is 65% lower than that of RFOC, and the torque response speed is 10% higher than that of DTC.

Drought is a natural hazard that affects almost all regions. In recent years, it has become more intense and frequentcausing adverse impacts on the socio-economic conditions of the country. The primary cause of drought developmentis the deficiency in precipitation impacting crop production during kharif with a follow-up effect also in crops grownduring rabi. The present study was carried out over one of the most drought-prone regions of India, i.e. Marathwadaregion, Maharashtra to characterize meteorological drought through the Standardized Precipitation Index (SPI) duringboth kharif and rabi crop growing seasons. SPI was computed at different time scales (1, 3, 6, 9 and 12-month) usingin-situ precipitation data for 35 years (1980-2014). Drought area observed by multi-time-scale SPI was correlated withdrought declared by the Government and foodgrain production for 15 years (2000–14). It was observed that none ofthe time scales of SPI had a significant correlation with declared drought. However, correlation analysis of multiscaleSPI with foodgrain production showed that 3-month SPI had a significant correlation (r= -0.72) during kharif, while alow correlation was observed between multiscale SPI and foodgrain production for rabi season. Therefore, informationobserved by SPI would be useful if it could be combined with other biophysical conditions and drought indices toincrease its accuracy and reliability for effective drought characterization and monitoring.

Purpose: To compare hazard ratios obtained by using time on study (conventional) versus biological age as the time-scale in survival analyses for a known age-dependent association between an exposure and outcome.Methods: We conducted a retrospective cohort study of 9 million people in Ontario, Canada who were followed from 2003 to 2018 to identify incident ischemic stroke using linked administrative health data. Using cause-specific hazards models, we calculated hazard ratios (HR) of ischemic stroke in women compared to men using the two different time scales. By using piecewise estimates and interaction terms, we evaluate the effect of sex on stroke incidence across age groups.Results: In unadjusted analyses, the reduction in the hazard of ischemic stroke in women compared to men was greater with age as time-scale (HR 0.77; 0.76-0.78) compared to conventional time-scale (HR 0.93; 0.92-0.93); however, the estimates were similar (HR 0.78 with age vs. 0.77 with conventional) in multivariable adjusted analyses. The estimates obtained by two methods across different age groups varied modestly, except in those under 30 years (HR 1.47; 1.19-1.83 with age vs. 1.08; 0.99-1.17 with conventional).Conclusions: When evaluating age-dependent association between an exposure and outcome, estimates of association vary based on the time-scale used in survival analysis, requiring thoughtful consideration. [ABSTRACT FROM AUTHOR]

This study investigates the impact of both social and news sentiments indices on the dynamic stock–bond correlation across wavelet-based time-scales over the period 1998–2016. Our results show that the news sentiments namely unemployment, tsunami and sanctions exhibit significant effects during expansion at the shortest time-scale of [2–4] days. These predictors remain significant with reverse signs during recession on the long investment horizon. Yet, the predictability of social media sentiments differs from that of news sentiments with the pattern of reversal in sign also presents for some proxies including windstorm and investment flows. Statistically, our further analysis confirmed the predictability of the sentiments out-of-sample. Excluding the news and social media sentiment effects has also resulted in minimizing the value-at-risk of the (40/60) stock/bond portfolios the most at the investment horizon of [32–64] days during recessions. Our results remain the same after performing some robustness checks. [ABSTRACT FROM AUTHOR]

This article presents behavior and EEG dataset collected from 19 healthy human volunteers (10 females) in the age group of 21–29 (mean = 26.9, SD = ±2.15) years at National Brain Research Centre, India during a psychophysical paradigm customized to characterize the brain network interactions during saliency processing. We provide all the raw stimulus files used in developing the experimental paradigm of the linked research article “Organization of directed functional connectivity among nodes of ventral attention network reveals the common network mechanisms underlying saliency processing across distinct spatial and spatio-temporal scales” [1] for replication and use by researchers across various cohorts of the population. Pre-processed EEG time-series segmented into epochs corresponding to three experimental trial conditions, across two visual attention tasks testing the effect of salient distractors on goal-driven tasks are provided. The dataset also includes reaction times corresponding to individual trials. Additionally, structural MRI files corresponding to each individual and 3D EEG sensor locations of all volunteers are provided to assist in accurate source localization. Therefore, the presented dataset will not only facilitate the conventional time resolved EEG analysis like evoked activity and time-frequency analysis at the sensor level but will also facilitate the investigation of source level analysis like global coherence or phase-amplitude coupling within selected regions of the brain.

The short-time Fourier transform (STFT) is extensively used to convert signals from the time-domain into the time–frequency domain. However, the standard STFT has the drawback of having a fixed window size. Recently, we proposed a variant of that transform which fixes the window size in the frequency domain (STFT-FD). In this paper, we revisit that formulation, showing its similarity to existing techniques. Firstly, the formulation is revisited from the point of view of the STFT and some improvements are proposed. Secondly, the continuous wavelet transform (CWT) equation is used to formulate the transform in the continuous time using wavelet theory and to discretize it. Thirdly, the constant-Q transform (CQT) is analyzed showing the similarities in the equations of both transforms, and the differences in terms of how the sweep is carried out are discussed. Fourthly, the analogies with multi-resolution STFT are analyzed. Finally, the representations of a period chirp and an electrocardiogram signal in the time–frequency domain and the time-scale domain are obtained and used to compare the different techniques. The analysis in this paper shows that the proposed transform can be expressed as a variant of STFT, and as an alternative discretization of the CWT. It could also be considered a variant of the CQT and a special case of multi-resolution STFT. [ABSTRACT FROM AUTHOR]

The time-scales theory provides a powerful theoretical tool for studying differential and difference equations simultaneously. With regard to Herglotz type variational principle, this generalized variational principle can deal with non-conservative or dissipative problems. Combining the two tools, this paper aims to study time-scales Herglotz type Noether theorem for delta derivatives of Birkhoffian systems. We introduce the time-scales Herglotz type variational problem of Birkhoffian systems firstly and give the form of time-scales Pfaff–Herglotz action for delta derivatives. Then, time-scales Herglotz type Birkhoff’s equations for delta derivatives are derived by calculating the variation of the action. Furthermore, time-scales Herglotz type Noether symmetry for delta derivatives of Birkhoffian systems are defined. According to this definition, time-scales Herglotz type Noether identity and Noether theorem for delta derivatives of Birkhoffian systems are proposed and proved, which can become the ones for delta derivatives of Hamiltonian systems or Lagrangian systems in some special cases. Therefore, it is shown that the results of Birkhoffian formalism are more universal than Hamiltonian or Lagrangian formalism. Finally, the time-scales damped oscillator and a non-Hamiltonian Birkhoffian system are given to exemplify the superiority of the results.

Aim: Climate change is expected to have important effects on plant phenology and carbon storage, with further shifts predicted in the future. Therefore, we proposed the community carbon accumulation rate (CAR) from the start of the growing season (SOS) to the peak of the growing season (POS) to fill the gap that the dynamic interactions between plant phenology and plant carbon research. Location: Tibetan Plateau. Major taxa: Alpine grassland plants. Time period: 2015. Methods: We conducted a transect survey across grasslands to measure community aboveground net primary production and carbon concentration. Additionally, phenology indicator data (SOS and POS) were extracted from the Global Inventory Modeling and Mapping Studies (GIMMS) normalized difference vegetation index version 3 database. Next, we used 'changepoint' analysis to detect the patterns of CARs, and performed linear regression and one‐way ANOVA to explore the variability of CARs in response to the environmental factors. Ultimately, the total effects of environmental factors on CARs were illustrated by a structural equation model. Results: Our results indicated that three CAR patterns were detected, which are low‐CAR (0.15 g/m2/day), medium‐CAR (0.31 g/m2/day) and high‐CAR (0.84 g/m2/day) patterns. We found that the availabilities of water and heat mediated CARs by regulating soil nutrition variability, and that drought climate and insufficient soil resources co‐constrained the community CAR at long time‐scales. In contrast, high CAR could be explained by more water and heat availability via either direct or indirect effects on soil moisture and soil nutrients. Main conclusions: Our findings highlight that water and heat availability are critical driving factors in ecological carbon accumulation processes undergoing climate change. Meanwhile, the vegetative phenology also has important effect on carbon accumulation. Consequently, we propose incorporating the dynamic interactions between plant phenology and plant carbon into the ecological carbon cycle model to improve our understanding of resource utilization and survival strategies of plants under environmental change. [ABSTRACT FROM AUTHOR]

Abstract The Random Resistor cum Tunnelling Network (RRTN) model was proposed from our group by considering an extra phenomenological (semi-classical) tunnelling process into a classical RRN bond percolation model. We earlier reported about early-stage two inverse power-laws, followed by large time purely exponential tail in some of the RRTN macroscopic current relaxations. In this paper, we investigate on the broader perspective of current relaxation. We present here an analytical argument behind the strong convergence (irrespective of initial voltage configuration) of the bulk current towards its steady-state, mapping the problem into a special kind of Gauss–Seidel method. We find two phenomenological time-scales (referred as τ t and τ s), those emerge from the variation of macroscopic quantities during current dynamics. We show that not both, only one of them is independent. Thus there exists a single scale in time which controls the entire dynamics. Highlights • o-bond and t-bond behave differently during RRTN current relaxation. • Their behaviours are associated with two separate time-scales. • Their ratio converges for large sample. There exists only one independent time-scale. • The steady-state convergence of current comes as consequence of Gauss–Seidel method. [ABSTRACT FROM AUTHOR]

Dynamic Traffic Assignment (DTA) is a mathematical framework that with a System Optimal (SO) objective is often used for long-term transport planning, design, and traffic management. However, the conventional SO-DTA formulation gives optimal solutions having an unrealistic vehicle Holding-Back (HB) property. Existing approaches in the literature aiming to resolve the HB problem are either computationally intractable or suffer from recursive parameter selection problem. In addition, most of the existing Signal Control (SC) models considered in the DTA formulation are mixed-integer or nonlinear in nature that are not scalable for large networks. With an exception, there exists a linear signal control model that can only set signal control cycle-length equal to DTA time-slot duration, and thus trades the accuracy of the SO-DTA solution for a more realistic cycle-length. In this article, we address the above issues by proposing a linear Non-Holding-Back SO-DTA with SC (NHB DTA-SC) formulation for single destination networks. The embedded signal control in the proposed framework enables us to set realistic cycle-length using any DTA time-slot (i.e., flexible time-scale). We find that the time-scale has a significant impact on traffic density which affects vehicle-discharged emissions. To this end, we develop a novel linear Emission-Based DTA with SC (EB DTA-SC) formulation that obtains NHB flows as well as lowest possible emission. Our results show that there is a 32% difference between emission estimated by 60-second and 5-second time-scales. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the de Groot dual topology of time scales. The de Groot dual topology is related to the concept of potential infinity instead of actual infinity. Whenever the real number line ℝ denotes time then its dual space * is compact and this provides insight that time is unbounded but finite in the sense of compact. On the other hand time scales are arbitrary non-empty closed subsets of (not only the real intervals or discrete sets) and include the real numbers. * has the usual topology on every bounded time scales but its topological structure differs when time scales are unbounded. Therefore, we state the topological properties of a time scale with respect the de Groot dual topology and determine the connectedness conditions of it. Moreover, we illustrate our results with known examples of discrete and continuous time scales. [ABSTRACT FROM AUTHOR]

We have compiled historical observations, spanning ∼100 years, for a dozen of the best-studied LBVs in the Local Group. We described how we prepared structure functions for their light-curves and calculated two parameters (the structure function slope and the characteristic time-scale) to describe the behaviour of the LBVs. The sensitivity of those parameters to the variability behaviour of the stars was tested with a number of photometric data sets. The slope of the structure function may anticorrelate with the time-scale. These types of variable stellar objects are crucial to studies of stellar variability and the final stages of stellar evolution. [ABSTRACT FROM AUTHOR]

Background Measures of spike train synchrony are widely used in both experimental and computational neuroscience. Time-scale independent and parameter-free measures, such as the ISI-distance, the SPIKE-distance and SPIKE-synchronization, are preferable to time scale parametric measures, since by adapting to the local firing rate they take into account all the time scales of a given dataset. New method In data containing multiple time scales (e.g. regular spiking and bursts) one is typically less interested in the smallest time scales and a more adaptive approach is needed. Here we propose the A-ISI-distance, the A-SPIKE-distance and A-SPIKE-synchronization, which generalize the original measures by considering the local relative to the global time scales. For the A-SPIKE-distance we also introduce a rate-independent extension called the RIA-SPIKE-distance, which focuses specifically on spike timing. Results The adaptive generalizations A-ISI-distance and A-SPIKE-distance allow to disregard spike time differences that are not relevant on a more global scale. A-SPIKE-synchronization does not any longer demand an unreasonably high accuracy for spike doublets and coinciding bursts. Finally, the RIA-SPIKE-distance proves to be independent of rate ratios between spike trains. Comparison with existing methods We find that compared to the original versions the A-ISI-distance and the A-SPIKE-distance yield improvements for spike trains containing different time scales without exhibiting any unwanted side effects in other examples. A-SPIKE-synchronization matches spikes more efficiently than SPIKE-synchronization. Conclusions With these proposals we have completed the picture, since we now provide adaptive generalized measures that are sensitive to firing rate only (A-ISI-distance), to timing only (ARI-SPIKE-distance), and to both at the same time (A-SPIKE-distance). [ABSTRACT FROM AUTHOR]

A class of random non-stationary signals termed timbre × dynamics is introduced and studied. These signals are obtained by non-linear transformations of stationary random Gaussian signals, in such a way that the transformation can be approximated by translations in an appropriate representation domain. In such situations, approximate maximum likelihood estimation techniques can be derived, which yield simultaneous estimation of the transformation and the power spectrum of the underlying stationary signal. This paper focuses on the case of modulation and time warping of stationary signals, and proposes and studies estimation algorithms (based on time-frequency and time-scale representations respectively) for these quantities of interest. The proposed approach is validated on numerical simulations on synthetic signals, and examples on real life car engine sounds. [ABSTRACT FROM AUTHOR]

The time-scale domain geometrical-based method for the characterization of the time varying ultrawideband (UWB) channel typical of an infostation channel is presented. Compared to methods that use Doppler shift as a measure of time-variation in the channel this model provides a more reliable measure of frequency dispersion caused by terminal mobility in the UWB infostation channel. Particularly, it offers carrier frequency independent method of computing wideband channel responses and parameters which are important for ultrawideband systems. Results show that the frequency dispersion of the channel depends on the frequency and not on the choice of bandwidth. And time dispersion depends on bandwidth and not on the frequency. It is also shown that for time-varying UWB, frame length defined over the coherence time obtained with reference to the carrier frequency results in an error margin which can be reduced by using the coherence time defined with respect to the maximum frequency in a given frequency band. And the estimation of the frequency offset using the time-scale domain (wideband) model presented here (especially in the case of multiband UWB frequency synchronization) is more accurate than using frequency offset estimate obtained from narrowband models.

Age replacement is one of the most used maintenance policies based on preventive action in order to prevent the failure of a system. Age replacement means that a system is replaced at failure or at a specified replacement age, whichever occurs first. In current age replacement policies, the replacement age is identified without consideration of the effects from operating conditions. However, the lifetime of a system may be affected by various operating conditions, such as the surrounding environment and the operators. In such cases, the replacement age of the system should differ for different situations. Thanks to the improvement of information communication technology, various information about the systems operating conditions can be obtained via the on-line monitoring. This research proposed an adaptive age replacement policy for systems under variable operating conditions using a cumulative exposure model. Based on the on-line information, we proposed a new time-scale instead of the age with consideration of operating conditions. Next, the new time-scale is used to determine the optimal replacement interval which will minimize the average maintenance cost per unit time (also known as cost rate). Some numerical examples are carried out in order to illustrate the proposed adaptive age replacement policy. The optimal age replacement policy considering the operating conditions reduces the total maintenance costs and enhances the effective maintenance plan for systems operating under various conditions. [ABSTRACT FROM AUTHOR]

It is well known that turbulence energy is overpredicted by the linear k – ε model at the stagnation point. This problem causes inadequate predictions of the flow field. In this paper, to evaluate the performance of a low-Reynolds-number (LRN) type turbulence model for flows on a complex wall shape, we carried out simulations of flows around various wall shapes. Based on this evaluation, we improved the model by introducing a time scale based on the velocity gradient parameter. The proposed model is evaluated in four complex turbulent flows, i.e., forward-facing step, two-dimensional block, two-dimensional hill and three-dimensional block flows. The results, together with the proposed model, are in good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

Over the past twelve years the number of papers that explore the impacts of climate change on biodiversity in the conservation literature has grown on average by 20% annually. By categorising these papers on their primary research questions, we show that the vast majority of these articles (88.6%) focus only on those impacts that arise directly as a result of climate change, ignoring the potentially significant indirect threats that arise from human adaptation responses. This pattern has remained fairly consistent throughout the review period (2000-2012), with a trend towards more articles considering both direct and indirect impacts towards the end of the period. We also find a bias in the time-frames considered by published articles that project future impacts of climate change on biodiversity, with more than three-quarters (77.9%) of papers only considering impacts after 2031, and almost half (49.1%) only considering impacts after 2051. This focus on long-term, direct impacts creates a mismatch, not only with the life-cycles of species and timescales of many ecological processes, but also with most management and policy timelines and the short-term nature of human decision making processes. The focus on studying the long-term, direct impacts of climate change on biodiversity is likely a function of the lack of availability of climate projections on shorter temporal scales; a perception that short-term impacts will be minor; and, insufficient integration with the social and political sciences. While the direct impact of changes in mean climatic conditions will significantly change the biosphere by the end of the century, near term changes in seasonality and extreme events coupled with human adaptation responses are likely to have substantial impacts much sooner, threatening the survival of species and ecosystems. It is therefore essential that we balance our research efforts to facilitate a better understanding of these more imminent threats. [ABSTRACT FROM AUTHOR]

The theory of large orebodies hosted in small intrusion emphasizes the relation between the geometrical scale of a magmatic intrusion and the efficiency of endogenic metallic mineralization. However, the essence of this relation is poorly understood till now. The basic problems related to the magma metallogenic system were briefly analyzed, and the intrinsic relations between the geometrical scale of an intrusion and several key factors controlling mineralization were focused. The published functional relation between the cooling duration and the migrating distance of solidus front in a magmatic intrusion was used to estimate the solidification time-scale of a magmatic intrusion. It is found that the living time-scale of the small intrusion is consistent with the time-scale required for forming a super-giant deposit. Based on Stock's Law, the simulation suggests that the small intrusions containing melano-microgranular enclaves are characterized by rapid ascending of magma, which is consistent with the experimental observations showing positive relation of the fluid solubility of ore-forming metal to its pressure (P) and temperature (T). The relations of the magma production to the source decompression rate and the volatile concentration in the produced magma were analyzed. Accordingly, it is proposed that the magma production followed a huge volume of magmatism must decrease, and hence the ratio of fluid and melt increases gradually. Therefore, it is helieved that a super-giant deposit can form immediately behind the extensive magmatism, and such a metallogenic process can be called as the post-batholith metallogenesis, taking the felsic magma metallogenic system as an example. In general, it is concluded that the scale effect of the magma metallogenic system is an important geological effect, and the analysis of scale effect supports the theory of giant deposit mineralized by the small intrusion. [ABSTRACT FROM AUTHOR]

Abstract: Dimensionless time is a universal parameter that may be used to predict real field behavior from scaled laboratory experiments in relation to imbibition processes in porous media. Researchers work to nondimensionalize the time has been through the use of parameters that are inherited to the properties of the moving fluids and the porous matrix, which may be applicable to spontaneous imbibition. However, in forced imbibition, the dynamics of the process depends, in addition, on injection velocity. Therefore, we propose the use of scaling velocity in the form of a combination of two velocities, the first of which (the characteristic velocity) is defined by the fluid and the porous medium parameters and the second is the injection velocity, which is a characteristic of the process. A power-law formula is suggested for the scaling velocity such that it may be used as a parameter to nondimensionalize time. This may reduce the complexities in characterizing two-phase imbibition through porous media and works well in both the cases of spontaneous and forced imbibition. The proposed scaling-law is tested against some oil recovery experimental data from the literature. In addition, the governing partial differential equations are nondimensionalized so that the governing dimensionless groups are manifested. An example of a one-dimensional countercurrent imbibition is considered numerically. The calculations are carried out for a wide range of Ca and Da to illustrate their influences on water saturation as well as relative water/oil permeabilities. [Copyright &y& Elsevier]

We present some new criteria for the oscillation of even order dynamic equation on an unbounded above time scale $${\mathbb{T}}$$, where α and λ are the ratios of positive odd integers, a and q is a real valued positive rd-continuous functions defined on $${\mathbb{T}}$$. [ABSTRACT FROM AUTHOR]

1. Network analysis is widely used in diverse fields and can be a powerful framework for studying the structure of biological systems. Temporal dynamics are a key issue for many ecological and evolutionary questions. These dynamics include both changes in network topology and flow on the network. Network analyses that ignore or do not adequately account for the temporal dynamics can result in inappropriate inferences. 2. We suggest that existing methods are currently under-utilized in many ecological and evolutionary network analyses and that the broader incorporation of these methods will considerably advance the current field. Our goal is to introduce ecologists and evolutionary biologists interested in studying network dynamics to extant ideas and methodological approaches, at a level appropriate for those new to the field. 3. We present an overview of time-ordered networks, which provide a framework for analysing network dynamics that addresses multiple inferential issues and permits novel types of temporally informed network analyses. We review available methods and software, discuss the utility and considerations of different approaches, provide a worked example analysis and highlight new research opportunities in ecology and evolutionary biology. [ABSTRACT FROM AUTHOR]

The time-scale domain geometrical-based method for the characterization of the time varying ultrawideband (UWB) channel typical of an infostation channel is presented. Compared to methods that use Doppler shift as a measure of time-variation in the channel this model provides a more reliable measure of frequency dispersion caused by terminal mobility in the UWB infostation channel. Particularly, it offers carrier frequency independent method of computing wideband channel responses and parameters which are important for ultrawideband systems. Results show that the frequency dispersion of the channel depends on the frequency and not on the choice of bandwidth. And time dispersion depends on bandwidth and not on the frequency. It is also shown that for time-varying UWB, frame length defined over the coherence time obtained with reference to the carrier frequency results in an error margin which can be reduced by using the coherence time defined with respect to the maximum frequency in a given frequency band. And the estimation of the frequency offset using the time-scale domain (wideband) model presented here (especially in the case of multiband UWB frequency synchronization) is more accurate than using frequency offset estimate obtained from narrowband models. [ABSTRACT FROM AUTHOR]

Abstract: Collagen is the prime construction material in vertebrate biology, determining the mechanical behavior of connective tissues such as tendon, bone and skin. Despite extensive efforts in the investigation of the origin of collagen unique mechanical properties, a deep understanding of the relationship between molecular structure and mechanical properties remains elusive, hindered by the complex hierarchical structure of collagen-based tissues. In particular, although extensive studies of viscoelastic properties have been pursued at the macroscopic (fiber/tissue) level, fewer investigations have been performed at the smaller scales, including in particular collagen molecules and fibrils. These scales are, however, important for a complete understanding of the role of collagen as an important constituent in the extracellular matrix. Here, using an atomistic modeling approach, we perform in silico creep tests of a collagen-like peptide, monitoring the strain-time response for different values of applied external load. The results show that individual collagen molecules exhibit a nonlinear viscoelastic behavior, with a Young''s modulus increasing from 6 to 16GPa (for strains up to 20%), a viscosity of 3.84.±0.38Pa·s, and a relaxation time in the range of 0.24–0.64ns. The single molecule viscosity, for the first time reported here, is several orders of magnitude lower than the viscosity found for larger-scale single collagen fibrils, suggesting that the viscous behavior of collagen fibrils and fibers involves additional mechanisms, such as molecular sliding between collagen molecules within the fibril or the effect of relaxation of larger volumes of solvent. Based on our molecular modeling results we propose a simple structural model that describes collagen tissue as a hierarchical structure, providing a bottom-up description of elastic and viscous properties form the properties of the tissue basic building blocks. [Copyright &y& Elsevier]

This paper improves and presents an advanced method of the voice conversion system based on Gaussian Mixture Models (GMM) models by changing the time-scale of speech. The Speech Transformation and Representation using Adaptive Interpolation of weiGHTed spectrum (STRAIGHT) model is adopted to extract the spectrum features, and the GMM models are trained to generate the conversion function. The spectrum features of a source speech will be converted by the conversion function. The time-scale of speech is changed by extracting the converted features and adding to the spectrum. The conversion voice was evaluated by subjective and objective measurements. The results confirm that the transformed speech not only approximates the characteristics of the target speaker, but also more natural and more intelligible. [ABSTRACT FROM AUTHOR]

This article proposes a novel approach for measuring similarity in discrete signals/time series. The proposed approach is based on a linear regression analysis which considers the relations of the sequences in time domain. Linear regression is an efficient measure to compare signals when translations such as amplitude-scale and amplitude-shift are involved in the signal. However, it fails to measure similarity of sequences when they are similar in shape but different in time-shifting or phase delay. These deficiencies are resolved when the sequences are analysed using the proposed optimised regression algorithm. In this approach, a re-sampling technique may be used to modify the shorter sequence to have the same length as the other sequence. Then, one sequence is circularly shifted along the time axis, sample by sample, using the proposed optimised regression algorithm to obtain the highest similarity between the two sequences. Similarity of the two modified sequences is computed using a modified block distance measure. Comparative simulation results are carried out, which indicate a better accuracy for the proposed method in classification problems. [ABSTRACT FROM AUTHOR]

Abstract: Brain oscillations constitute a prominent feature of electroencephalography (EEG), in both physiological and pathological states. An efficient separation of oscillation from transient signals in EEG is important not only for detection of oscillations, but also for advanced signal processing such as source localization. A major difficulty lies in the fact that filtering transient phenomena can lead to spurious oscillatory activity. Therefore, in the presence of a mixture of transient and oscillatory events, it is not clear to which extent filtering methods are able to separate them efficiently. The objective of this study was to evaluate methods for separating oscillations from transients. We compared three methods: finite impulse response (FIR) filtering, wavelet analysis with stationary wavelet transform (SWT), time–frequency sparse decomposition with Matching Pursuit (MP). We evaluated the quality of reconstruction and the results of automatic detection of oscillations intermingled with transients. The emphasis of our study was on epileptic signals and single channel processing. In both simulations and on real data, FIR performed generally worse than the time–frequency methods. Both SWT and MP showed good results in separation and detection, each method having its advantages and its limitations. The SWT had good results in separation and detection of transients due to the time invariance property, but still did not completely resolve the frequency overlap for the oscillation during the time–frequency thresholding. The MP provides a sparse representation, and gave good results for simulated data. However, in the real data, we observed distortions introduced by the subtractive approach, and departure from dictionary waveforms. Future directions are proposed for overcoming these limitations. [Copyright &y& Elsevier]

The simplistic approach to mechanical testing routinely employed in dental research does not recognize the many factors that influence the outcome, not least the non-existence of strength as a true material property. The roles of test time-scale, environmental interaction, and internal changes need evaluation. However, service conditions also involve multiple loading cycles which interact with other processes, while 'episodic' challenges are altogether outside the normal frame of testing. The case is made for testing that allows for dynamic damage-accumulation through a survival-curve approach. [ABSTRACT FROM AUTHOR]

Carrying out information about the microstructure and stress behaviour of ferromagnetic steels, magnetic Barkhausen noise (MBN) has been used as a basis for effective non-destructive testing methods, opening new areas in industrial applications. One of the factors that determines the quality and reliability of the MBN analysis is the way information is extracted from the signal. Commonly, simple scalar parameters are used to characterize the information content, such as amplitude maxima and signal root mean square. This paper presents a new approach based on the time-frequency analysis. The experimental test case relates the use of MBNsignals to characterize hardness gradients in a AISI4140 steel. To that purpose different time-frequency (TFR) and time-scale (TSR) representations such as the spectrogram, the Wigner-Ville distribution, the Capongram, the AR gram obtained from an Auto Regressive model, the scalogram, and the Mellingram obtained from a Mellin transform are assessed. It is shown that, due to nonstationary characteristics of the MBN, TFRs can provide a rich and new panorama of these signals. Extraction techniques of some time-frequency parameters are used to allow a diagnostic process. Comparison with results obtained by the classical method highlights the improvement on the diagnosis provided by the method proposed. [ABSTRACT FROM AUTHOR]

The article presents a study regarding the scaling properties of streamflow using statistical methods. It mentions that the study aims to compare and evaluate the effectiveness of different techniques in data gathering such as shape analysis of flood hydrographs, multifractal framework using spectral and moment analysis, and analysis of flood frequency. The researchers say that they want to find out the relation of scaling properties and flow dynamics. Furthermore, they learn that timescale parameters and flow dynamics are indeed interconnected.

Abstract: In order to define time-scales of erosion and sedimentary transfer in the Himalaya, 238U–234U–230Th disequilibria have been analysed in river bank sediments and in bedloads collected along the Kali Gandaki river, one of the main Nepalese rivers, and in the Ghaghara and Gandak rivers, two major plain tributaries of the Ganges. The Th activity ratios and U/Th ratios in river sediments of the two Ganges tributaries constantly decrease from upstream to downstream. This is related to the maturation of sediments by weathering during their transfer to the plain. The U-series data allow to calculate a transfer time for the sediments in the alluvial Gangetic plain from the chain front to the confluence with the Ganges of about 100 kyr for both rivers. The Kali Gandaki river sediment data highlight a decrease of both the Th isotopic and U/Th ratios which is explained by a mixing between two sources with similar U/Th ratios but having suffered a different U–Th fractionation history. Interpretation of the U-series data in the frame of this scenario gives long time-scales of weathering of several 100''s kyr for the Himalayan terranes. The results imply that Himalayan bedrocks are submitted to a long in situ stage of weathering before their erosion and transfer into the rivers. In addition, occurrence of similar U–Sr signatures in dissolved (i.e. <0.1–0.2 μm) and sediment phases of the Kali Gandaki river suggests that “dissolved” uranium could be carried by colloids constituted by sedimentary microparticles. This precludes the use of U-series disequilibria in this river to calculate weathering budgets and to assess whether the erosion is working at steady-state or not. [Copyright &y& Elsevier]

This paper proposes a module-based and unified approach to chaotic circuit design, where the description is based on the state equations without physical dimensions for simplicity of a general discussion. The main design process consists of transformation of state variables, transformation from differential to integral operations, and transformation of the time-scale. The designed circuit consists of anti-adder module integrator module, and inverter module. A novel 3-scroll Chua's circuit and a generalized Lorenz-like circuit are designed and implemented for verifying the effectiveness of this systematic circuit design methodology. Experimental observations are provided for confirmation. Comparing with the traditional circuit design methods, this new design approach has the following typical characteristics: (i) module-based and unified design; (ii) independent adjustment of system parameters; (iii) adjustment of distribution regions for the frequency spectra of chaotic signals; (iv) prominent observability. [ABSTRACT FROM AUTHOR]

Inspired by the work on image processing by Perona and Malik, diffusion-based models were first investigated by Gonçalvès and Payot to improve the readability of Cohen class time-frequency representations. They rely on signal-dependent partial differential equations that yield adaptive smoothed representations with sharpened time-frequency components. Here, we demonstrate the versatility and utility of this family of methods, and we propose new adaptive diffusion processes to locally control both the orientation and the strength of smoothing. Our approach is an improvement on previous works as it provides a unified framework not only for the Cohen class but for the affine class as well. The latter is of particular interest because, except for some special techniques such as the reassignment method, no signal-dependent smoothing technique exists to process bilinear time-scale distributions, nor even a transposition of the adaptive optimal-kernel method proposed by Baraniuk and Jones. [ABSTRACT FROM AUTHOR]