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Sequence time-domain reflectometry (STDR) and spread spectrum time-domain reflectometry (SSTDR) detect, locate, and diagnose faults in live (energized) electrical systems. In this paper, we survey the present SSTDR literature for discussions on theory, algorithms used in its analysis, and its more prominent implementations and applications. Our review includes both scientific litera-ture and selected patents. We also discuss future applications of SSTDR.

In this paper, we present a method for estimating complex impedances using reflectometry and a modified steepest descent inversion algorithm. We simulate spread spectrum time domain reflectometry (SSTDR), which can measure complex impedances on energized systems for an experimental setup with resistive and capacitive loads. A parametric function, which includes both a misfit function and stabilizer function, is created. The misfit function is a least squares estimate of how close the model data matches observed data. The stabilizer function prevents the steepest descent algorithm from becoming unstable and diverging. Steepest descent iteratively identifies the model parameters that minimize the parametric function. We validate the algorithm by correctly identifying the model parameters (capacitance and resistance) associated with simulated SSTDR data, with added 3 dB white Gaussian noise. With the stabilizer function, the steepest descent algorithm estimates of the model parameters are bounded within a specified range. The errors for capacitance (220pF to 820pF) and resistance (50 Ω to 270 Ω) are < 10%, corresponding to a complex impedance magnitude |R +1/jωC| of 53 Ω to 510 Ω.

Electrical impedance measurements provide insight into electrical device behavior and allow for improvements in troubleshooting efforts, simulation environments, and an overall understanding of device capabilities. The contributions of this dissertation include an assessment of spread spectrum time domain reflectometry (SSTDR) measurement variability focused on minimum detectable changes in SSTDR measurement response, including compelling results on its ability to conduct multiple consecutive measurements with minimal variation between measurements. It also includes an exploration into SSTDR impedance measurement potential with simulations of real-world scenarios known to obscure current methods of measuring impedance such as high noise and multiple signal environments, as well as potential device improvements to increase its measurement abilities. Additionally, validation of SSTDR as a viable method for measuring electrical impedance over a wide band of frequencies with a detailed assessment of measurement error, including recommendations for improving SSTDR impedance measurement capabilities, is also included. SSTDR is shown to provide low variation between measurements, high noise immunity, and promising impedance measurement capabilities, allowing the capacity of SSTDR to be extended beyond detecting and locating impedance changes to measuring impedance. With the potential of SSTDR to test on energized systems or electrically noisy environments and its ability to enable parallel testing of multiple ports with non-interfering signals, SSTDR may one day replace the VNA and switching matrices.

In this paper, we present a method for estimating complex impedances using reflectometry and a modified steepest descent inversion algorithm. We simulate spread spectrum time domain reflectometry (SSTDR), which can measure complex impedances on energized systems for an experimental setup with resistive and capacitive loads. A parametric function, which includes both a misfit function and stabilizer function, is created. The misfit function is a least squares estimate of how close the model data matches observed data. The stabilizer function prevents the steepest descent algorithm from becoming unstable and diverging. Steepest descent iteratively identifies the model parameters that minimize the parametric function. We validate the algorithm by correctly identifying the model parameters (capacitance and resistance) associated with simulated SSTDR data, with added 3 dB white Gaussian noise. With the stabilizer function, the steepest descent algorithm estimates of the model parameters are bounded within a specified range. Furthermore, the errors for capacitance (220pF to 820pF) and resistance (50 Ω to 270 Ω) are < 10%, corresponding to a complex impedance magnitude |R +1/jωC| of 53 Ω to 510 Ω.

The latitudinal diversity gradient—the tendency for more species to occur toward the equator—is the dominant pattern of life on Earth, yet the mechanisms responsible for it remain largely unexplained. Recently, the analysis of global data has led to advances in understanding, but these advances have been mostly limited to vertebrates and trees and have not provided consensus answers. Here we synthesize large-scale geographic, phylogenetic, and fossil data for an exemplar invertebrate group—ants—and investigate whether the latitudinal diversity gradient arose due to higher rates of net diversification in the tropics, or due to a longer time period to accumulate diversity due to Earth’s climatic history. We find that latitudinal affinity is highly conserved, temperate clades are young and clustered within tropical clades, and diversification rate shows no systematic variation with latitude. These results indicate that diversification time—and not rate—is the main driver of the diversity gradient in ants. Multiple hypotheses have been proposed for the declining biodiversity gradient between the tropics and poles. Here, the authors compile and analyze geographic data for all ant species and large-scale phylogenies, suggesting that diversification time drives the latitudinal diversity gradient in ants.

While the regional distribution of non-native species is increasingly well documented for some taxa, global analyses of non-native species in local assemblages are still missing. Here, we use a worldwide collection of assemblages from five taxa - ants, birds, mammals, spiders and vascular plants - to assess whether the incidence, frequency and proportions of naturalised non-native species depend on type and intensity of land use. In plants, assemblages of primary vegetation are least invaded. In the other taxa, primary vegetation is among the least invaded land-use types, but one or several other types have equally low levels of occurrence, frequency and proportions of non-native species. High land use intensity is associated with higher non-native incidence and frequency in primary vegetation, while intensity effects are inconsistent for other land-use types. These findings highlight the potential dual role of unused primary vegetation in preserving native biodiversity and in conferring resistance against biological invasions. Anthropogenic habitat modification is considered a driver of non-native species establishment. Here, the authors quantify the occurrence of non-native species in local assemblages of vascular plants, ants, spiders, birds and mammals, finding generally greater presence and frequency under disturbed land-use types.

The tropics contain the overwhelming majority of Earth’s biodiversity: their terrestrial, freshwater and marine ecosystems hold more than three-quarters of all species, including almost all shallow-water corals and over 90% of terrestrial birds. However, tropical ecosystems are also subject to pervasive and interacting stressors, such as deforestation, overfishing and climate change, and they are set within a socio-economic context that includes growing pressure from an increasingly globalized world, larger and more affluent tropical populations, and weak governance and response capacities. Concerted local, national and international actions are urgently required to prevent a collapse of tropical biodiversity. The immense biodiversity of tropical ecosystems is threatened by multiple interacting local and global stressors that can only be addressed by the concerted efforts of grassroots organizations, researchers, national governments and the international community.

Island systems are known to harbor disproportionate amounts of geographically restricted biodiversity and to experience high rates of species loss, and they ultimately represent critical systems with significant conservation values. However, knowledge of the biodiversity value of insular systems remains highly fragmented and incomplete for many groups of organisms, especially insects. This gap limits our understanding of their global significance for biodiversity and inhibits prioritization for future exploration and conservation efforts. Here, we developed a new database to present current knowledge on ants on 2678 islands globally, based on nominal species, and provide information on their native or exotic status. In total, this database contains 7010 ant species (44.6% of the known global ant fauna) that have been recorded on islands globally from 449,232 records. In addition, this database identifies 108 large islands (area > 200 km²) that have received no ant sampling efforts globally. This new data set provides the most comprehensive understanding of ant diversity and composition on islands globally, opening up new opportunities to address questions on a multitude of research questions and fields related to biogeography, ecology, and evolution. This data set also provides a roadmap for future exploration and conservation actions in connection with ants on islands as well as overall ant diversity, with updates available as new records and taxonomic updates are published. There are no copyright restrictions on this database and users should cite this data paper in publications when using the data.

On a global scale, biodiversity is geographically structured into regions of biotic similarity. Delineating these regions has been mostly targeted for tetrapods and plants, but those for hyperdiverse groups such as insects are relatively unknown. Insects may have higher biogeographic congruence with plants than tetrapods due to their tight ecological and evolutionary links with the former, but it remains untested. Here, we develop a global regionalization for a major and widespread insect group, ants, based on the most comprehensive distributional and phylogenetic information to date, and examine its similarity to regionalizations for tetrapods and vascular plants. Our ant regionalization supports the newly proposed Madagascan and Sino-Japanese realms based on tetrapod delineations, and it recovers clusters observed in plants but not in tetrapods, such as the Holarctic and Indo-Pacific realms. Quantitative comparison suggests strong associations among different groups—plants showed a higher congruence with ants than with tetrapods. These results underscore the wide congruence of diverse distribution patterns across the tree of life and the similarities shared by insects and plants that are not captured by tetrapod groups. Our analysis highlights the importance of developing global biogeographic maps for insect groups to obtain a more comprehensive geographic picture of life on Earth. In this study, the authors delineate a global biogeographic map for ants based on their distributions and phylogenetic relationships. They show that current biogeographic maps based on tetrapod groups fail to capture important regions for biodiversity shared by insects and plants, which are both known to possess strong ecological and evolutionary ties.

One of the best-known general patterns in island biogeography is the species–isolation relationship (SIR), a decrease in the number of native species with increasing island isolation that is linked to lower rates of natural dispersal and colonization on remote oceanic islands. However, during recent centuries, the anthropogenic introduction of alien species has increasingly gained importance and altered the composition and richness of island species pools. We analyzed a large dataset for alien and native plants, ants, reptiles, mammals, and birds on 257 (sub) tropical islands, and showed that, except for birds, the number of naturalized alien species increases with isolation for all taxa, a pattern that is opposite to the negative SIR of native species. We argue that the reversal of the SIR for alien species is driven by an increase in island invasibility due to reduced diversity and increased ecological naiveté of native biota on the more remote islands.