Large Threshold Research Articles

Near infrared spectroscopy discriminates glutinous and non-glutinous sorghum using an approach based on typical samples and direct calibration

Sorghum has a long history of cultivation and is an important food and economic crop. It can be divided into glutinous and non-glutinous varieties according to the starch structure and content. Rapid discrimination between the two would help the winemaking, feed, and food industries complete purchase pricing, ingredients, and quality control. In this study, 38 different samples were acquired, including 14 glutinous and 24 non-glutinous sorghum samples. Near infrared (NIR) spectra of glutinous and non-glutinous sorghum, pre-treated using the standard normal variable (SNV) transformation were found to have slightly different absorbances in the combination and first overtone bands. Based on the distribution of the starch-related and hydrogen-containing groups in the NIR region, it was concluded that glutinous sorghum has more C-O and C-C groups than non-glutinous sorghum. This study proposes an approach based on typical samples and direct calibration (TSDC) for binary discrimination. The TSDC approach consists of three functions. First, typical samples of two types of samples were selected. Second, typical type samples are used as dependent variables, predicted samples are used as independent variables, and formula regression is used to obtain fitted coefficients. Finally, if the formula regression model has no solution or the fitted coefficient is 1, typical type samples are reselected. Using the TSDC approach, discrimination accuracy can achieve 100% accuracy at 0.5 threshold. A larger threshold can be set to select better type characteristic predicted samples for discrimination. The TSDC approach can build excellent model through real relevance between the NIR spectra and the properties of interest, and the use of typical type samples greatly reduces modeling work compared with complex pattern recognition methods, especially for highly varied agricultural products. Therefore, it can efficiently propel the application and development of NIR detection technology. More research is required to apply the TSDC approach to three types of samples.

Conditional Dichotomy of Boolean Ordered Promise CSPs

Promise Constraint Satisfaction Problems (PCSPs) are a generalization of Constraint Satisfaction Problems (CSPs) where each predicate has a strong and a weak form and given a CSP instance, the objective is to distinguish if the strong form can be satisfied vs. even the weak form cannot be satisfied. Since their formal introduction by Austrin, Guruswami, and H\aa stad, there has been a flurry of works on PCSPs [BBKO19,KO19,WZ20]. The key tool in studying PCSPs is the algebraic framework developed in the context of CSPs where the closure properties of the satisfying solutions known as the polymorphisms are analyzed. The polymorphisms of PCSPs are much richer than CSPs. In the Boolean case, we still do not know if dichotomy for PCSPs exists analogous to Schaefer's dichotomy result for CSPs. In this paper, we study a special case of Boolean PCSPs, namely Boolean Ordered PCSPs where the Boolean PCSPs have the predicate $x \leq y$. In the algebraic framework, this is the special case of Boolean PCSPs when the polymorphisms are monotone functions. We prove that Boolean Ordered PCSPs exhibit a computational dichotomy assuming the Rich 2-to-1 Conjecture [BKM21] which is a perfect completeness surrogate of the Unique Games Conjecture. Assuming the Rich 2-to-1 Conjecture, we prove that a Boolean Ordered PCSP can be solved in polynomial time if for every $\epsilon>0$, it has polymorphisms where each coordinate has Shapley value at most $\epsilon$, else it is NP-hard. The algorithmic part of our dichotomy is based on a structural lemma that Boolean monotone functions with each coordinate having low Shapley value have arbitrarily large threshold functions as minors. The hardness part proceeds by showing that the Shapley value is consistent under a uniformly random 2-to-1 minor. Of independent interest, we show that the Shapley value can be inconsistent under an adversarial 2-to-1 minor.

Observation of Large Threshold Voltage Shift Induced by Pre-applied Voltage to SiO2 Gate Dielectric in Organic Field-Effect Transistors

Field-effect transistors based on organic semiconducting materials (OFETs) have unique advantages of intrinsically mechanical flexibility, simple preparation process, low manufacturing cost, and large-area preparation. Through the innovation of new material design and device structures, the performance of device parameters such as mobility, on–off current ratio, and the threshold voltage (VTH) of OFETs continues to improve. However, the VTH shift of OFETs has always been an important problem restricting their practical applications. In this work, we observe that the VTH of polymer OFETs with the widely investigated device structure of a SiO2 bottom-gate dielectric is noticeably shifted by pre-applying a large gate voltage. Such a shift in VTH remains to a large extent, even after modifying the surface of the SiO2 dielectric using a hexamethyldisilazane (HMDS) self-assembled monolayer. This behavior of VTH can be ascribed to the charge trappings at the bulk of the SiO2. In addition, the generality of this observation is further proven by using two other conjugated polymers including p-type PDPP3T and n-type PTzNDI-2FT, and a similar trend is obtained.

Assessing the importance of the choice threshold in quantifying market risk under the POT approach (EVT)

From a theoretical point of view, the selection of thresholds is a critical issue in the framework of the Peaks Over Threshold (POT) approach, which is why in the last decade numerous methodologies have been proposed for its selection. In this paper, we address this subject from an empirical point of view by assessing to what extent the selection of the threshold is decisive in quantifying the market risk. For measuring market risk, we use the Value at Risk (VaR) and the Expected Shortfall (ES) measures. The results obtained indicate that there is a large set of thresholds that provide similar Generalized Pareto Distribution (GPD) quantiles estimators and as a consequence similar market risk measures. Just only, for large thresholds, those corresponding to the 98th and 99th percentile of the GPD some differences are found. It means that the choice of threshold in the framework of the POT method may not be relevant in quantifying market risk when we use the VaR and ES measures for this task.

Design of DWDM optical communication systems with different modulation formats using DCF and a repeater.

The dense wavelength division multiplexing (DWDM) technique has been used to provide a large capacity and low bandwidth loss for optical communication systems. In this paper, simulation designs by Optisystem15.0 of carrier-suppressed return to zero (CSRZ), differential phase shift keying (DPSK), and intensity modulation is proposed to determine which modulation format is more compatible with four and eight DWDM channels for transmitting an optical signal over 400km distance. For a long optical path, the dispersion compensation fiber (DCF) technique is proposed to eliminate dispersion effects and increase the possibility of transmitting multiple optical wavelengths over long single-mode fiber. Optical amplifiers are used to amplify the optical signal with a distorted signal and process the attenuation caused by the long transmission distance. In DCF network design, CSRZ offers the best performance because of the large quality factor (24.560) and high threshold power (15dBm), which make the system compatible with increased distance between the transmitter and receiver; next is intensity modulation with a 24.5604 quality factor and 13dBm threshold power value; DPSK comes in last with the worst performance, with a quality factor of 10 at 13dBm power due to non-linear effects, especially non-linear phase noise. In the repeater design, the DPSK modulation format has the best performance with a large quality factor of 20.7913 at a high threshold power of 14dBm for 150GHz spacing; this is because the repeater technique is compatible with reducing the non-linear effects of the DPSK format. CSRZ and intensity modulation have the same performance with a 12 quality factor at 4dBm power for intensity modulation and 3dBm power for CSRZ modulation.

IrSi3As3: a first transition metal arsenide non-linear optical material

Transition metal silicon arsenide with Ir–Si and Ir–As covalent bonding exhibits remarkable non-linear optical properties: high second harmonic generation activity and a large laser damage threshold.

Flexible optical limiters based on Cu3VSe4 nanocrystals.

Optical limiters are greatly needed to protect eyes and sensitive optoelectronic devices such as photodetectors and sensors from laser damage, but they are currently plagued by low efficiency. In this work, we utilized Cu3VSe4 nanocrystals (NCs) to enhance laser protection performance, and they exhibit higher saturation intensity and broader nonlinear spectral response extending into the near IR region than the C60 benchmark. A flexible optical limiter goggle prototype based on the NCs significantly attenuated the incident laser beam, with Z scan and I scan measurements demonstrating a giant nonlinear absorption coefficient β value of 1.0 × 10-7 m W-1, a large optical damage threshold of 3.5 J cm-2, and a small starting threshold of 0.22 J cm-2. Transient absorption spectroscopy disclosed that the origin of the excellent nonlinearity was associated with quasi-static dielectric resonance behavior and a large TPA cross-section of 3.3 × 106 GM was measured for Cu3VSe4 NCs, suggesting the potential of intermediate bandgap (IB) semiconductors as alternatives to plasmonic noble metals for ultrafast photonics. Hence, optical limiters based on such semiconductors offer new avenues for laser protection in optoelectronic and defense fields.

CNT/Cu composite cathode: A new approach to long lifetime for explosive emission cathode

Carbon nanotube (CNT) cathodes have attracted much attention in recent years due to the advantages of large field enhancement factor and low emission threshold. However, the severe ablation under intense emission makes the lifetime short and therefore limits the application in the field such as high power microwave generation. To resolve this problem, this paper proposes to mix CNTs with metals, and a novel CNT/Cu composite cathode is manufactured. The lifetime experiments under voltage of 940 kV and repetition frequency of 20 Hz demonstrate that the lifetime of the CNT/Cu composite cathode is over 3 × 105 pulses, which is much longer than that of the normal copper cathode by at least one order of magnitude. The microscopic morphology analysis reveals that the CNT micro-protrusions and whiskers should be vital for the good emission property of the new cathode.

Regional variability of the mean and extreme characteristics of the present meteorological regime of the eastern part of the Baltic Sea catchment

The features of the regional heterogeneity of the modern meteorological regime are assessed, as a refinement of existing estimates of large-scale climate changes – for the eastern part of the Baltic Sea catchment on the example of the Leningrad Region and nearby territories of neighbouring subjects of the Russian Federation (northern part of the region), as well as the Zapadnaya Dvina catchment within the Republic of Belarus (southern part of the region). Significant differences in surface air temperature and snow water equivalent (hereinafter referred to as snow storage) were revealed for the winter period, with similar precipitation, more intense interannual and long-term changes in the southern part of the region. The common feature for the region is the presence of a significant correlation of the long-term January – March atmospheric circulation indices variability only with the variability of surface air temperature, as well as minor differences in the number of anomalous years with similar anomaly amplitudes. Surface air temperature has the greatest contribution to the long-term variability of snow storage everywhere, which is most pronounced in the south of the region. The turning points in the long-term variability of surface air temperature coincide in the north and south of the region, the turning points in the course of total precipitation do not coincide. The number of anomalies (exceeding the standard deviation) in the long-term series of characteristics in the northern and southern parts of the region differ little (9–12 cases in the positive and negative ranges of values) in the absence of coincidences and the similarity of the amplitude of the anomalies. The range of values of extreme threshold values (extreme percentiles) of surface air temperature in the north of the region is lower than the range of values in the south, the variability of small percentiles exceeds the variability of large ones; the rate of long-term increase in average temperatures is accompanied by a significant increase in small percentiles in the north and large percentiles in the south of the region. The values of extreme threshold values of precipitation and their standard deviation vary little across the territory; positive trends in maximums and negative trends in minimum thresholds are small, consistent with a slight increase in mean total precipitation. According to the spatial distribution of average values of snow storage, the values of their extremely small and large threshold values in the north of the region are higher than in the south; in the north of the region, the values of percentiles in the interval 1985–2002 stand out as the lowest.

Influence of neutron/gamma irradiation on damage and scintillation of Ga-doped ZnO thin films

As a new type of inorganic scintillator, ZnO crystal doped with Ga has been used for Ultra-fast scintillating detectors with fast response to detect X-ray, gamma, neutron, and charged particles. Moreover, due to the large bandgap energy and high threshold displacement energy, ZnO: Ga has a strong radiation resistance in theory. However, there is a lack of experimental studies on the change of scintillation properties of ZnO: Ga under an intense irradiation environment. This study deposited thin Ga-doped ZnO films on α-Al2O3(0001) substrate by dual-target reactive magnetron sputtering. The ZnO: Ga samples were irradiated by neutrons from 1010 to 7.1 × 1014 neutrons/cm2 (1 MeV neutron equivalent fluence) and γ rays from 500 to 10,000 Gy, respectively. The structural and optical properties of all irradiated samples were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), optical transmittance (TS), and effective light output at room temperature. The results indicated that all the irradiated samples are still in both hexagonal wurtzite structure and c-axis orientation. Compared with unirradiated samples, it is found that the samples' optical transmittance, energy resolution, and effective light output have little change due to irradiation, which has fully proved that the ZnO: Ga scintillation films have good radiation resistance under neutron and gamma irradiation. Hence, ZnO: Ga is an attractive candidate for radiation detectors with ultra-fast responses under extreme radiation environments.

Normally-OFF AlGaN/GaN-based HEMTs with decreasingly graded AlGaN cap layer

In this work, an enhancement-mode (E-mode) AlGaN/GaN-based high-electron-mobility transistor (HEMT) with a graded AlGaN cap layer (GACL) is proposed and numerically studied by Silvaco technology computer-aided design. The GACL is designed with a decreasingly graded Al composition x along [0001] direction and the initial x is smaller than the Al composition of the Al0.2Ga0.8N barrier layer (BL). This GACL scheme can simultaneously produce high-concentration polarization-induced holes and negative net polarization charges at the GACL/BL interface. This can facilitate the separation of the conduction band (E C) and Fermi level (E F) at the 2DEG channel and therefore benefit the normally-OFF operation of the device. The optimized graded-AlGaN-gated metal-semiconductor HEMT can achieve a large threshold voltage of 4 V. Furthermore, we demonstrated that shortening the gate length on the GACL and inserting an oxide layer between the gate and GACL can be both effective to suppress gate leakage current, enhance gate voltage swing, and improve on-state drain current of the device. These numerical investigations can provide insights into the physical mechanisms and structural innovations of the E-mode GaN-based HEMTs in the future.

Impact of assimilating atmospheric motion vectors from Himawari-8 and clear-sky radiance from FY-4A GIIRS on binary typhoons

Binary typhoons (Maysak and Haishen) uncommonly hit northeastern China in 2020, which brought historical extreme precipitation to this region within less than a week. The impact of high-frequency (15-min) assimilating atmospheric motion vectors (AMVs) from Himawari-8 and clear-sky radiance from Fengyun-4A (FY-4A) Geostationary Interferometric Infrared Sounder (GIIRS) on this rare case has been investigated based on the Weather Research and Forecasting Model (WRF) and three-dimensional variational (3D-Var) data assimilation system. The study indicates that the dynamic adjustment is obvious from assimilated hourly AMVs information, but it still needs to be combined with the 15-min FY-4A thermal field adjustment, which is essential for better forecast simulations of minimum sea level pressure (MSLP) and landfall precipitation. A detailed typhoon structure is accurately reproduced for Maysak (Haishen) with fewer (more) anomalies of upper-level warm temperatures and lower-level negative geopotential heights in the decay (intensification) phase. Meanwhile, the performance of three hourly landfall precipitation by Maysak is evaluated with better spatial distribution and higher equitable threat scores (ETS) for the large threshold (20 mm), resulting from wet bias reduction by much drier water vapor conditions in the analysis and more precise forecasts of relative humidity, water vapor transportation, and its divergence. However, it achieves neutral to negative impacts on track forecasts for Maysak and wind simulations at different levels. This research may provide guidance for monitoring and forecasting typhoons of assimilation from different satellite information in mid-to-high latitude regions in East Asia.

Organic Phase-Change Memory Transistor Based on an Organic Semiconductor with Reversible Molecular Conformation Transition.

Phase-change semiconductor is one of the best candidates for designing nonvolatile memory, but it has never been realized in organic semiconductors until now. Here, a phase-changeable and high-mobility organic semiconductor (3,6-DATT) is first synthesized. Benefiting from the introduction of electrostatic hydrogen bond (S···H), the molecular conformation of 3,6-DATT crystals can be reversibly modulated by the electric field and ultraviolet irradiation. Through experimental and theoretical verification, the tiny difference in molecular conformation leads to crystalline polymorphisms and dramatically distinct charge transport properties, based on which a high-performance organic phase-change memory transistor (OPCMT) is constructed. The OPCMT exhibits a quick programming/erasing rate (about 3 s), long retention time (more than 2h), and large memory window (i.e., large threshold voltage shift over 30V). This work presents a new molecule design concept for organic semiconductors with reversible molecular conformation transition and opens a novel avenue for memory devices and other functional applications.

Colour‐related, binocular interactions in patients with dyschromatopsia

AbstractWe report findings of monocular and binocular assessments of colour vision and thresholds for rod‐ and cone‐mediated sensitivity in two young patients (P1 and P2) diagnosed with monocular dyschromatopsia. Altered, monocular, colour perception with no clear diagnosis was reported in each patient based on results from a number of clinical visual assessment tests carried out over several years. Electrodiagnostic tests also revealed reduced Yellow / Blue (YB) chromatic sensitivity in P1. Both patients exhibited unexpected binocular interactions of colour signals. This abstract focuses mostly on the results obtained in P1, but similar results using the same visual assessment tests will also be presented for P2.P1 experienced visual discomfort, often manifested as differences between monocular and binocular viewing, noise‐like appearance of uniform fields and colours over the field, when viewed monocularly with either eye. As a result of these reports, we re‐examined P1's visual deficits using the Colour Assessment and Diagnosis (CAD) and the Flicker‐Plus (FP) tests (http://www.city-occupational.co.uk/). The FP test measures rod‐ and cone‐mediated rapid flicker sensitivity centrally (along the direction of gaze) and at 6 deg eccentricity in each of the four quadrants.Colour Vision. P1 shows significant loss of YB colour vision when tested monocularly in the right eye, but normal red‐green (RG) and YB colour vision in the left eye. When tested binocularly, P1 continues to show the same loss of YB colour vision observed when using only the right eye. These results were unexpected since P1 shows ‘normal’ binocular summation for both colour and flicker sensitivity, even when the thresholds are above the normal range.Rod‐ / Cone‐sensitivity. The patient's cone‐mediated, flicker sensitivity at all five locations investigated (under binocular viewing) was normal (with flicker detection thresholds, often under 2%), but only for the cone‐enhanced condition. When tested with rod‐enhanced stimuli, P1 shows much reduced sensitivity with larger thresholds in the periphery, but only in binocular viewing. Such responses have not been observed previously.In conclusion, P1 shows loss of YB colour vision in the right eye and also significant loss of rod‐mediated sensitivity at each of the five locations investigated. The patient's cone mediated thresholds, at every location tested, were consistently below the mean expected for normal trichromats, both binocularly and with each eye. The YB colour vision measured binocularly remained severely abnormal with thresholds similar to the right eye, in spite of normal colour vision in the left eye. Preliminary observations also suggest that the patient's colour and rapid flicker sensitivity can be affected by fatigue and other factors.Although patient, P2, varied significantly to P1 in monocular thresholds, a similar binocular, inhibitory interaction between the two eyes was observed when processing colour signals. These observations and the unusual interactions between signals derived from the two eyes point towards abnormal central processing of colour signals.

A DNA barcoding and photo-documentation resource of water mites (Acariformes, Hydrachnidia) of Siberia: Accurate species identification for global climate change monitoring programs

Water mites (Hydrachnidia) are good model organisms for the assessment and long-term monitoring of the biological impacts of natural and human-induced environmental changes in freshwater ecosystems, including those related to global climate change. However, monitoring programs using water mites as bioindicators may be impeded by difficulties associated with species identification. Here we integrate conventional morphology, DNA sequence data (using the COX1 barcoding locus) and extensive voucher photo documentation to create and validate a tool for accurate species identification of water mites in Western Siberia (including a dedicated reference climate monitoring and research site). Using this approach, we detected a total of 95 species, of which, one was a conventional new species; 14 taxa were cryptic species having large among-species COX1 K2P distances but lacking any apparent morphological differences. Our a priori species delimitation was successfully validated a posteriori. An automatic species delimitation algorithm (ASAP) identified exactly the same set of 95 species, with a species delimitation threshold of 6.1%. This result agrees with previous works suggesting a large threshold of 5.6–6.0% for water mites, but contrasts with the BOLD approach which uses a much lower threshold to identify BINs (1%). Furthermore, by comparing our identified sequences with GenBank data, we expanded known geographic ranges of several water mite species. Using extensive GenBank data on mites in Canadian waters, four species were detected to be Holarctic rather than Palaearctic as thought previously (Lebertia obscura, Limnesia undulatoides, Oxus nodigerus and Arrenurus papillator). Four species, Lebertia obscura, Torrenticola brevirostris, Hygrobates limnocrenicus and Unionicola parvipora, were recorded for the first time in Russia. We provide an annotated species checklist reporting the distribution, ecology, bioindiocation potential, and COX1 barcode sequence data along with high-resolution photographs of each DNA voucher. Future ecological and biodiversity studies will benefit from using molecular tools for accurate identification of useful mesofaunal bioindicator organisms, such as water mites.

Efficient computation of temporal exceeding probability of ship responses in a random wave field

In this work, we develop a computational framework to efficiently quantify the temporal exceeding probability of ship responses in a random wave field generated by a narrow-band spectrum, i.e., the fraction of time that ship responses exceed a given threshold. In particular, we consider large thresholds so that the response exceedance needs to be treated as rare events. Our computational framework builds on the parameterization of wave field into wave groups and efficient sampling in the group parameter space through Bayesian experimental design (BED). Previous works following this framework exclusively studied extreme statistics of group-maximum response, i.e., the maximum response within a wave group, which is however not straightforward to interpret in practice (e.g., its value depends on the subjective definition of the wave group). In order to adapt the framework to the more robust measure by the temporal exceeding probability, novel developments need to be introduced to the two components of BED (on surrogate model and acquisition function), which are detailed in the paper. We validate our framework for a case of ship roll motion (without capsizing) calculated by a nonlinear roll equation, in terms of the agreement of our results to the true solution and the independence of our results to the criterion of defining groups. Finally, we demonstrate the coupling of the framework with CFD models to handle more realistic and general ship response problems.

Extremal Binary PFAs with Small Number of States

The largest known reset thresholds for DFAs are equal to [Formula: see text], where [Formula: see text] is the number of states. This is conjectured to be the maximum possible. PFAs (with partial transition function) can have exponentially large reset thresholds. This is still true if we restrict to binary PFAs. However, asymptotics do not give conclusions for fixed [Formula: see text]. We prove that the maximal reset threshold for binary PFAs is strictly greater than [Formula: see text] if and only if [Formula: see text]. These results are mostly based on the analysis of synchronizing word lengths for a certain family of binary PFAs. This family has the following properties: it contains the well-known Černý automata; for [Formula: see text] it contains a binary PFA with maximal possible reset threshold; for all [Formula: see text] it contains a PFA with reset threshold larger than the maximum known for DFAs. Analysis of this family reveals remarkable patterns involving the Fibonacci numbers and related sequences such as the Padovan sequence. We derive explicit formulas for the reset thresholds in terms of these recurrent sequences. Asymptotically the Černý family gives reset thresholds of polynomial order. We prove that PFAs in the family are not extremal for [Formula: see text]. For that purpose, we present an improvement of Martyugin’s prime number construction of binary PFAs.

Functional network characteristics based on EEG of patients in acute ischemic stroke: A pilot study.

Ischemic stroke is a common type of stroke associated with reorganization of functional network of the brain. This pilot study aimed to investigate the characteristics of functional brain networks based on EEG in patients with acute ischemic stroke. Seven patients with ischemic stroke within 72 hours of onset and seven healthy controls were enrolled in the study. Dynamic EEG monitoring and clinical information were repeatedly collected within 72 hours (T1), on the 5th day (T2), and on the 7th day (T3) of stroke onset. A directed transfer function was employed to construct functional brain connection patterns. Graph theoretical analysis was performed to evaluate the characteristics of functional brain networks. First, we found that the brain networks of ischemic stroke patients were quite different from the healthy controls. The clustering coefficient (0.001 < Threshold < 0.2) in Delta, Theta, and Alpha bands for the patients were significantly lower (P < 0.01) and the shortest path length in all bands (0.001 < Threshold < 0.2) for the patients were significantly longer (P < 0.01). Moreover, the peaks of the shortest path length for the patients seemed to be higher in all bands with larger thresholds. Secondly, the brain networks for the patients showed a characterized time-variation pattern. The clustering coefficient (0.001 < Threshold < 0.2) of T1 was higher than that of T2 in alpha band (P < 0.01). The shortest path length (0.001 < Threshold < 0.2) of T3 was shorter than that of T2 (P < 0.01) in all bands, and the peak of T3 was numerically higher than that of T2 in all bands with narrower thresholds. Functional brain networks in patients with acute ischemic stroke showed impaired global functional integration and decreased efficiency of information transmission compared with healthy subjects. The shortening of the shortest path length during the recovery indicates neural plasticity and reorganization.

Freshwater microcrustaceans (Copepoda: Cyclopidae) on islands: a review

Little is known about the insular diversity and its determinants in the freshwater invertebrates in comparison to land animals. Our goal is to obtain global-scale information on the insular diversity in Cyclopidae, test its relationships with the geographical variables in different types of islands, and compare the patterns to those observed in other organisms. In total 291 species and subspecies were reported in the 35 islands included in our analyses. The total and endemic species richness have strong positive correlations with surface area and maximum elevation of the islands; regression slopes are larger in the oceanic than in continental islands. Small-island effects occur in the relationships between the endemic species richness and area and elevation. Distance from mainland has negative correlations with the total and endemic species richness in the oceanic islands. Compositional similarity (in contrast to species richness) is determined by the geographic variables to only a minor extent, while space has stronger impact. The relationships found in Cyclopidae generally fit those observed in other predominantly terrestrial organisms, yet some characteristics (negative intercepts in the area–species and elevation–species relationships; large area and high elevation thresholds below which no endemic species occurs) are suggested to be specific to fresh waters.

Bayesian time-varying quantile regression on exceedance

ABSTRACT Exceedance analysis aims to model extreme data that are in the tail of the distribution, with these values being greater than a threshold. In this type of modelling, the tail can usually have different types of shapes. For exceedance, the extreme value theory shows that generalized Pareto distribution (GPD) is the limit distribution of sufficiently large thresholds. The studies on extreme analysis primarily focus on estimating the probability of the occurrence of extreme events, which are the values that are in the highest quantiles of the distribution. Based on this, this work proposed a quantile regression model for the GPD distribution, where the high quantiles of the distribution are written as a function of covariates. The proposed model also allows the regression parameters to vary over time. The parameter estimation of these new models is conducted under the Bayesian paradigm. Simulations are conducted to analyze the performance of our proposed models. Results of temperature applications in the USA and Brazil (environmental data) and consumer price index in Brazil (financial data) have efficiently explained how covariates influence the quantile behaviour over time.