Time Diversity Research Articles

Performance assessment of hybrid PPM–BPSK–SIM based FSO communication system using time and wavelength diversity under variant atmospheric turbulence

In this paper, free space optical communication system employing a hybrid modulation technique called pulse position modulation–binary phase shift keying–subcarrier intensity modulation technique, is investigated using wavelength and time diversity, by considering log-normal and gamma–gamma probability density function as the channel-fading statistics under weak, moderate and strong turbulence. The analytical average bit error rate and closed form of expression of the proposed hybrid modulation scheme are derived. The outcomes of the simulation demonstrate the outstanding consistency of the derived closed form expression with those achieved by the Gauss–Hermite approximation and the Monte Carlo simulations.

A shared local oscillator spatial diversity PM-CO-OFDM systems based on group timing synchronization and diversity branch phase correction in satellite-to-ground optical communications

Due to the complexity and strong fluctuations of atmosphere turbulence, it is always a challenging task to mitigate atmospheric turbulence effects in space optical communications. In this paper, we demonstrate a shared local oscillator (LO) spatial diversity polarization multiplexing coherent optical orthogonal frequency division multiplexing (PM-CO-OFDM) system based on group timing synchronization and diversity branch phase correction in downstream low earth orbit satellite-to-ground (LEO-StG) optical communications. For the shared LO coherent receiver system, the maximal ratio combining (MRC) technique is used at the receiver to improve the system performance, and the diversity gain is found to depend on the relative phase offset (RPO) among the different branches. Simulation results under different turbulence channels not only demonstrate that the RPO can be effectively compensated by group timing synchronization and diversity branch phase correction, but also show the improvement in receiver sensitivity. Furthermore, the number of optimal branches is also investigated. The superiorities of such spatial diversity scheme make it highly desirable for potential application in LEO-StG optical communications.

Linear stability analysis of heterogeneous traffic flow considering degradations of connected automated vehicles and reaction time

With the development of connected automated vehicles (CAVs) technologies, traffic flow on the road is converting into the heterogeneous traffic flow, which consists of CAVs and human-driven vehicles (HDVs). Considering the function of CAVs would degrade when following HDVs in heterogeneous traffic flow. Moreover, the reaction time of degraded CAVs would be different with CAVs or HDVs. This paper deduces and analyzes the linear stability of such heterogeneous traffic flow based on CAVs degradations and reaction time diversity. Firstly, considering the degradations of CAVs, the vehicle types and their ratios in heterogeneous traffic flow are analyzed. Secondly, the car-following model and the reaction time of three types of vehicles are discussed. Then, the linear stability condition of heterogeneous traffic flow is proposed. Finally, the impact factors on the stability condition are illustrated through numerical analysis. The results show that the high penetration rate of CAVs and the short reaction time can improve the linear stability of heterogeneous traffic flow. Besides, when the penetration rate of CAVs increases to 65%, the stability of heterogeneous traffic flow is not affected by speed. Furthermore, the analysis shows that CAVs degradations also has a negative effect on linear stability.

A Fast and efficient stochastic opposition-based learning for differential evolution in numerical optimization

Abstract A fast and efficient stochastic opposition-based learning (OBL) variant is proposed in this paper. OBL is a machine learning concept to accelerate the convergence of soft computing algorithms, which consists of simultaneously calculating an original solution and its opposite. Recently, a stochastic OBL variant called BetaCOBL was proposed, which is capable of controlling the degree of opposite solutions, preserving useful information held by original solutions, and preventing the waste of fitness evaluations. While it has shown outstanding performance compared to several state-of-the-art OBL variants, the high computational cost of BetaCOBL may hinder it from cost-sensitive optimization problems. Also, as it assumes that the decision variables of a given problem are independent, BetaCOBL may be ineffective for optimizing inseparable problems. In this paper, we propose an improved BetaCOBL that mitigates all the limitations. The proposed algorithm called iBetaCOBL reduces the computational cost from O(NP2 · D) to O(NP · D) (NP and D stand for population size and a dimension, respectively) using a linear time diversity measure. Also, the proposed algorithm preserves strongly dependent variables that are adjacent to each other using multiple exponential crossover. We used differential evolution (DE) variants to evaluate the performance of the proposed algorithm. The results of the performance evaluations on a set of 58 test functions show the excellent performance of iBetaCOBL compared to ten state-of-the-art OBL variants, including BetaCOBL.

LA PNEUMATOLOGIE DE VATICAN II

La pneumatologie du Concile Vatican II figurait parmi les Questiones disputatae entre théologiens orthodoxes, protestants et catholiques après le Concile. Cette génération ayant disparu, il est important de dresser un nouveau bilan. Pour ce faire, il ne suffit pas de compter le nombre d’occurrences du terme Saint-Esprit dans le texte conciliaire, mais il importe de voir si le recours au Saint-Esprit déter­mine la perspective théologique adoptée par le Concile et intervient à des points stratégiques de l’argumentation. Un nouvel examen de la question conduit à l’iden­tification de trois domaines où la pneumatologie conciliaire joue un rôle important en ecclésiologie : l’Esprit Saint est co-instituant de l’Église. Il est en même temps source de la diversité et de l’unité, si bien qu’on ne peut la concevoir que comme unité catholique; enfin, le fait qu’il dispense ses dons à tous les fidèles fonde la participation de tous à la vie de l’Église. De plus, non seulement l’Esprit habite dans l’Église comme en un temple, mais il remplit aussi l’univers, précédant l’action de l’Église et en dépassant les frontières. En conclusion, l’essai souligne le fait que les développements postconciliaires sur des questions cruciales, telles que la théologie des ministères, la réflexion sur le sensus fidei et la synodalité, dépendent des fondements posés par Vatican II. De plus, la théologie de la mission et la théologie des religions n’auraient pas connu de tels développements sans la réflexion conciliaire sur le rôle du Saint-Esprit dans le monde et au-delà des frontières de l’Église.

A Robust Mixed-Integer Linear Programming Model for Mitigating Rail Transit Disruptions Under Uncertainty

In this paper, we propose a two-stage robust optimization framework to evaluate widely controllable commuter flow strategies that can help mitigate uncertain disruption impacts on rail transit commuter flows. In the operation-as-usual stage, preemptive control strategies including timetable adjustment, commuter path choice diversion, and commuter trip starting time diversion are planned within budget and other requirement constraints. In the disruption stage, optimal contingency routing is derived to minimize disruption impacts. To this end, a linear programming model that simulates the commuter movement logic under train service and platform disruption events is developed, which is then integrated in a mixed-integer max-min optimization model to evaluate the worst-case impacts on commuter flows arising from a set of uncertain disruption scenarios. We show that the two-stage robust optimization framework can be solved by a cutting plane algorithm efficiently using high performance and parallel computing platforms. Finally, we demonstrate the application of the model in mitigating disruption impacts through computational studies based on an actual rail transit network.

Transdermal subcarrier L-PSK or DBPSK optical wireless links with time diversity, skin attenuation and spatial jitter

Recent advances in both optical wireless communication systems and implantable medical devices have paved the way for the establishment of high-speed transdermal optical wireless (TOW) communication links for telemetry with medical implants. However, the performance of such wireless links is primary degraded by skin-induced attenuation effect along with spatial jitter. In order to deal with these limitations, in this work, we propose, for the first time in the TOW communication field, the subcarrier intensity modulation technique. On top of that, the stochastic nature of pointing errors which little has been reported in the open TOW technical literature, is considered. Under these circumstances, an average symbol error propability (ASEP) analysis for typical subcarrier L-PSK or DBPSK TOW link configurations with time diversity technique is performed. In this context, novel analytical ASEP expressions are derived, while appropriate analytical results are depicted and validated by Monte Carlo simulations over a wide signal-to-noise ratio range.

Endogenous phytohormones and the expression of flowering genes synergistically induce flowering in loquat

Flowering is an important process for the reproduction of higher plants. Up to this point, the studies on flowering have mostly focused on the model plant Arabidopsis thaliana, and the flowering mechanism of fruit trees remains mostly unknown. The diversity of the flowering time of loquat (Eriobotrya japonica Lindl.) makes it an ideal material to study the regulation of flowering. In this study, we first observed the inflorescence bud differentiation in two varieties of loquat that had different blooming times (cv. Dawuxing (E. japonica), that blooms in the fall and cv. Chunhua (E. japonica×Eriobotrya bengalensis Hook. f.) that blooms in the spring) and found that the starting time of inflorescence bud differentiation and the speed of inflorescence development were responsible for the difference in blooming times. The determination of endogenous phytohormones by high performance liquid chromatography (HPLC) indicated that abscisic acid (ABA), zeatin (ZT), and gibberellin (GA3) promoted flowering in loquat, while indole-3-acetic acid (IAA) was mainly involved in inflorescence bud differentiation in Chunhua. A transcription level analysis illustrated that multiple flowering-related genes could respond to different signals, integrate to the TFL1, AP1 and FT genes, and then synergistically regulate flowering in loquat. Thus, this study provides a new insight into flowering regulation mechanisms in loquat.

Educação social em discussão:

In this issue we will identify the heritage and history of the development of Social Education in Portugal, as a theoretical conceptualization and consequently as a profession, but similarly the processes of professionalization and professionality. We will present the knowledge and competencies essential to professional performance, from the perspective of the various invited authors. This discussion will be based on the theoretical and practical recognition of Social Education as a professional field and also underlines the relevance of teaching-learning, mediation, ethics and deontology and diversity in different and peculiar times.

Good things take time—Diversity effects on tree growth shift from negative to positive during stand development in boreal forests

Abstract Long‐term grassland biodiversity experiments have shown that diversity effects on productivity tend to strengthen through time, as complementarity among coexisting species increases. But it remains less clear whether this pattern also holds for other ecosystems such as forests, and if so why. Here we explore whether diversity effects on tree growth change predictably during stand development in Finland's boreal forests. Using tree ring records from mature forests, we tested whether diameter growth trajectories of dominant tree species growing in mixture differed from those in monoculture. We then compared these results with data from the world's longest running tree diversity experiment, where the same combinations of species sampled in mature forests were planted in 1999. We found that diversity effects on tree growth strengthened progressively through time, only becoming significantly positive around 20 years after seedling establishment. This shift coincided with the period in which canopy closure occurs in these forests, at which time trees begin to interact and compete above‐ground. These temporal trends were remarkably consistent across different tree species sampled in mature forests, and broadly matched growth responses observed in the much younger experimental plots. Synthesis. Our results mirror those from grassland ecosystems and suggest that canopy closure is a key phase for promoting niche complementarity in diverse tree communities. They also provide a series of testable hypotheses for the growing number of tree diversity experiments that have been established in recent years.

Advance in study on 16S rRNA gene sequencing technology in oral microbial diversity.

The 16S rRNA gene is the most commonly used molecular marker for identifying microorganisms. It is used in sequencing technology, including the first-generation, the second-generation, and the third-generation sequencing technology. A large number of studies on the 16S rRNA gene have contributed to a deeper understanding of oral microbial diversity. In the healthy oral cavity, there is microbial diversity in time and space. With the occurrence or development of oral diseases such as caries, periodontal disease, or halitosis, the microbial diversity will be changed.

Integrated crop–livestock systems in lowlands increase the availability of nutrients to irrigated rice

AbstractIntegrated crop–livestock systems (ICLS) associated with crop rotation and soil conservation management cause numerous changes in nutrient fluxes and soil biochemical dynamics. In this sense, there is a gap in the impact of integrated production systems on nutrient dynamics and soil microbial activity in lowlands. In this context, this work had the objective of evaluating the nutrient availability and the activity of extracellular enzymes in a Gleyic Luvic Planosol under ICLS. The experiment has five paddy‐farming systems with a range of crop diversity (both in time and space) and grazing occurring mainly in the winter season. Soil solution samples were taken in cropping seasons (2014/2015, 2015/2016, and 2016/2017), from the first day after flooding (DAF) to approximately 70 DAF. The integration of rice with livestock increased urease activity (+84%), β‐glucosidase (+49%), and fluorescein diacetate (+105%), especially as the level of diversification and use intensification of pastures. In general, there was an increase in the availability of ammonium (+70%), phosphorus (+177%), potassium (+62%), and calcium (+20%) in the soil solution with the adoption of ICLS and soil conservation management, compared with the traditional rice system. Thus, the adoption of ICLS contributes to increase the process of biochemical functioning of the soil with consequent intensification of nutrient cycling and availability. Thus, the ICLS can sustainably increase nutrient availability in the soil and reduce the need to feed large amounts of fertilizer into irrigated rice production systems.

Mid and long-term ecological impacts of ski run construction on alpine ecosystems

The proliferation of ski run construction is a worldwide trend. The machine-grading of slopes involved during ski run construction changes the physical, chemical and biological properties of the soil, having significant long-term ecological impact on the environment. Establishing and developing plant communities in these affected areas is crucial in rehabilitating the biotic and abiotic soil environment, while also improving slope stability and reducing the risk of natural hazards. This study evaluates changes in plant-soil properties and the long-term effects of machine-grading and subsequent restoration of ski runs so as to contribute to formulating the best practices in future ski run constructions. Study plots were established in 2000 and re-surveyed in 2017 on ski runs, which had been machine-graded and hydroseeded in the 1990s. Vegetation, root trait and soil surveys were carried out on ski run plots and compared to paired, undisturbed control sites off the ski runs. Plant cover remained unchanged on the ski-runs over time but plant richness and diversity considerably increased, reaching similar levels to undisturbed vegetation. Plant composition moved towards more semi-natural stages, showing a reduction in seeded plants with a comparable increase in the cover of colonizing native species. Root trait results were site-specific showing great variations between the mid and long-term after-effects of machine-grading and revegetation when compared to undisturbed sites. Under long-term management, the soil pH was still higher and the organic C content still lower in the ski runs than in the undisturbed sites, as the aggregate stability. The standard actions applied (machine-grading, storage and re-use of topsoil, hydroseeding of commercial seed mixtures, application of manure soon after seeding and low-intensity grazing) allowed the ecosystem to partially recover in three decades, and even if the soil has still a lower chemical and physical fertility than the undisturbed sites, the plant species composition reveals a satisfactory degree of renaturalization.

Modeling occupancy-driven building loads for large and diversified building stocks through the use of parametric schedules

Building energy modeling provides a fundamental tool to evaluate the potential for energy efficiency to contribute to reducing world energy consumption and global emissions. Occupancy-related operations are a key source of uncertainty for building energy analysis, particularly for aggregated building stocks. At a district or city level, it is critical to estimate aggregated power load profiles for sizing power grid infrastructure, power plant capacity allocation, and energy efficiency measures. The stochastic nature of behavior-related operations complicates the creation of models that accurately capture building load profiles for entire building stocks. This research introduces a new methodology called parametric schedules to model occupancy-driven schedules for large and diverse building stocks. In contrast to computationally expensive methodologies proposed in the literature, our work does not use a recursive time-consuming step. Occupancy is estimated by the extrapolation of operation times directly from metered electric consumption data; occupancy-related schedules are stochastically assigned to each building model, guaranteeing diversity of operation times in the stock. Our procedure has been tested on a large, diversified data-set of ∼25,000 commercial buildings in Los Angeles, California. It proved to be able to adequately represent the stochastic schedules diversity of the stock and to refine the stock calibration process by 1%. This innovative approach represents a useful asset for utility companies, grid operators, urban planners, and balancing authorities, seeking to improve building stock modeling and better estimate the impact of energy conservation measures. – This work is part of a larger stock modeling tool called ComStock, which is under development by NREL.

Allele combinations of maturity genes E1-E4 affect adaptation of soybean to diverse geographic regions and farming systems in China

Appropriate flowering and maturity time are important for soybean production. Four maturity genes E1, E2, E3 and E4 have been molecularly identified and found to play major roles in the control of flowering and maturity of soybean. Here, to further investigate the effect of different allele combinations of E1-E4, we performed Kompetitive Allele Specific PCR (KASP) assays based on single nucleotide polymorphisms (SNPs) at these four E loci, and genotyped E1-E4 genes across 308 Chinese cultivars with a wide range of maturity groups. In total, twenty-one allele combinations for E1-E4 genes were identified across these Chinese cultivars. Various combinations of mutations at four E loci gave rise to the diversity of flowering and maturity time, which were associated with the adaptation of soybean cultivars to diverse geographic regions and farming systems. In particular, the cultivars with mutations at all four E loci reached flowering and maturity very early, and adapted to high-latitude cold regions. The allele combinations e1-as/e2-ns/e3-tr/E4, E1/e2-ns/E3/E4 and E1/E2/E3/E4 played important roles in the Northeast China, Huang-Huai-Hai (HHH) Rivers Valley and South China regions, respectively. Notably, E1 and E2, especially E2, affected flowering and maturity time of soybean significantly. Our study will be beneficial for germplasm evaluation, cultivar improvement and regionalization of cultivation in soybean production.

Dual frame OFDM with optical phase conjugation for MIMO system in multimode fiber

For nonlinearity and dispersion mitigation in optical fiber, the authors propose a dual frame OFDM transmission, based on optical phase conjugation. The proposed dual frame OFDM is modification of asymmetrically clipped OFDM (ACO-OFDM) frame. The proposed OFDM frame consist of two positive frames, first one is time compressed ACO-OFDM frame and second one is optical phase conjugated version of first frame. This increases the bandwidth efficiency and total transmitted power for the system. For electronic dispersion compensation (EDC) in conventional OFDM, signal pre-processing is applied at transmitter side where it requires channel information. In case of OFDM and multiple input multiple output (MIMO) system setup for multi mode fiber, channel becomes almost unpredictable. The proposed dual frame OFDM does not require EDC at transmitter side. For received optical power $$-12$$ dbm conventional ACO-OFDM records bit error rate (BER) $$4.48*10^{-1}$$ and proposed dual frame ACO-OFDM with OPC records BER $$2.58*10^{-4}$$ . Simulation results for variable fiber length show BER $$2.20*10^{-1}$$ for phase conjugated subcarrier coding and $$2.24*10^{-3}$$ for proposed ACO-OFDM with OPC for multi-mode fiber length 500 m. It also allows different multiframe transmission based on time and wavelength diversity.

Spatio-temporal modelling of economic phenomena in the context of reducing the dimensions of the random field

Motivation: Clear spatial diversity and high variability in time of economic phenomena and the fact that they show dependencies in space and time dimensions, as well as the spatio-temporal dependencies, lead to the consideration of the phenomena in terms of random fields. On the other hand, applying methods and tools from the field of multidimensional stochastic processes called random fields is difficult due to the specificity of the economic data, in particular to a low number of the observations in space. Hence, there arises the problem of the reduction of the dimensions (especially the space dimension) of the random fields which define economic phenomena. Aim: The aim of the paper is to discuss a model that will reflect the structure of spatial connections and dependence in the spatio-temporal process, while reducing the dimension of space as a non-random argument of the random field. As a result, the set of N time series will be analysed. Therefore, we build a multiple-equation model of autoregressive character with a spatial structure of dependence. In the paper we discuss the advantages and cognitive values of such an approach to the study of economic phenomena in spatio-temporal terms. Results: The empirical example concerns the unemployment rate in Poland across provinces (NUTS2) in the period from January 2011 to April 2019. The data create spatio-temporal series which is the realisation of the two-dimensional random field. The model building strategy is based on a vector autoregressive (VAR) specification, where there are as many time series as the provinces. The study shows that the use of the concept of the conditional, with regard to space dimension, random field simplifies the econometric analysis of the spatio-temporal process under consideration without losing the accuracy of the description of his basic properties.

Reproducibly sampling SARS-CoV-2 genomes across time, geography, and viral diversity.

The COVID-19 pandemic has led to a rapid accumulation of SARS-CoV-2 genomes, enabling genomic epidemiology on local and global scales. Collections of genomes from resources such as GISAID must be subsampled to enable computationally feasible phylogenetic and other analyses. We present genome-sampler, a software package that supports sampling collections of viral genomes across multiple axes including time of genome isolation, location of genome isolation, and viral diversity. The software is modular in design so that these or future sampling approaches can be applied independently and combined (or replaced with a random sampling approach) to facilitate custom workflows and benchmarking. genome-sampler is written as a QIIME 2 plugin, ensuring that its application is fully reproducible through QIIME 2's unique retrospective data provenance tracking system. genome-sampler can be installed in a conda environment on macOS or Linux systems. A complete default pipeline is available through a Snakemake workflow, so subsampling can be achieved using a single command. genome-sampler is open source, free for all to use, and available at https://caporasolab.us/genome-sampler. We hope that this will facilitate SARS-CoV-2 research and support evaluation of viral genome sampling approaches for genomic epidemiology.

Formation binning: a new method for increased temporal resolution in regional studies, applied to the Late Cretaceous dinosaur fossil record of North America

AbstractThe advent of palaeontological occurrence databases has allowed for detailed reconstruction and analyses of species richness through deep time. While a substantial literature has evolved ensuring that taxa are fairly counted within and between different time periods, how time itself is divided has received less attention. Stage‐level or equal‐interval age bins have frequently been used for regional and global studies in vertebrate palaeontology. However, when assessing diversity at a regional scale, these resolutions can prove inappropriate with the available data. Herein, we propose a new method of binning geological time for regional studies that intrinsically incorporates the chronostratigraphic heterogeneity of different rock formations to generate unique stratigraphic bins. We use this method to investigate the diversity dynamics of dinosaurs from the Late Cretaceous of the Western Interior of North America prior to the Cretaceous–Palaeogene mass extinction. Increased resolution through formation binning pinpoints the Maastrichtian diversity decline to between 68 and 66 Ma, coinciding with the retreat of the Western Interior Seaway. Diversity curves are shown to exhibit volatile patterns using different binning methods, supporting claims that heterogeneous biases in this time‐frame affect the pre‐extinction palaeobiological record. We also show that the apparent high endemicity of dinosaurs in the Campanian is a result of non‐contemporaneous geological units within large time bins. This study helps to illustrate the utility of high‐resolution, regional studies to supplement our understanding of factors governing global diversity in deep time and ultimately how geology is inherently tied to our understanding of past changes in species richness.

Evaluating and Modeling IEEE 802.15.4 TSCH Resilience against Wi-Fi Interference in New-Generation Highly-Dependable Wireless Sensor Networks

Thanks to its ability to effectively counteract disturbance and interference, including the traffic generated by co-located Wi-Fi networks, Time Slotted Channel Hopping (TSCH) is currently gaining momentum in many application fields characterized by demanding reliability and determinism requirements. In particular, the ability of TSCH to change transmission frequency on every attempt sensibly mitigates packet losses and latencies, improving the overall behavior in a tangible way.In this paper, the communication quality achieved by TSCH in a setup that includes real motes exposed to a realistic interfering traffic is evaluated experimentally. A theoretical model is also developed, based on quite simple assumptions about the effectiveness of time and frequency diversity, which satisfactorily matches the real behavior. The model permits to determine how much network parameters like, e.g., the retry limit, actually affect communication, and can be exploited to find proper settings for them. Finally, the ability of channel hopping to prevent narrowband interference from disrupting communication is assessed. As results show, this mechanism makes motes suffer from an equivalent interference that roughly corresponds to the mean interference evaluated over all physical channels.