Dense Class Research Articles

Fitting phase\u2013type scale mixtures to heavy\u2013tailed data and distributions

We consider the fitting of heavy tailed data and distributions with a special attention to distributions with a non–standard shape in the “body” of the distribution. To this end we consider a dense class of heavy tailed distributions introduced in Bladt et al. (Scand. Actuar. J., 573–591 2015), employing an EM algorithm for the maximum likelihood estimation of its parameters. We present methods for fitting to observed data, histograms, censored data, as well as to theoretical distributions. Numerical examples are provided with simulated data and a benchmark reinsurance dataset. Empirical examples show that the methods will in most cases adequately fit both body and tail simultaneously.

Kajian Awal Penentuan Daerah Prospek Panas Bumi di Gunung Bur Ni Telong berdasarkan Analisis Data DEM SRTM dan Citra Landsat 8

Research for a preliminary study of Bur Ni Telong, geothermal area, Bener Meriah district using remote sensing techniques has been done. The aims of the research were to determine the morphological condition based on the fault and fracture (FFD) map from the interpreted digital elevation model (DEM) shuttle radar topography mission (SRTM) and to know the vegetation density and surface temperature distribution using Landsat 8 image. The DEM SRTM data were analyzed using the lineament pattern which related to faults and fractures. The vegetation density was calculated using normalized difference vegetation index (NDVI) transformation. The estimated surface temperature was used to locate temperature anomaly. Referring to the geographical map, the dense class area include Silih Nara-Ketol-Peulimbang to Peudada, Juli to Sawang, and Bandar area. The fault and fracture dominantly have directions in East-West and Northwest-Southeast. While based on NDVI map we conclude that the area is covered by dense vegetation, dominated by intermediate to dense of vegetation. The LST map shows the location of maximum surface temperature values are in agreement with residential areas and uncovered areas, as in the areas of Simpang Tiga Redelong and Takengon. Some geothermal manifestations are located in sparse to intermediate vegetation areas with high temperature.

Longterm temporal analysis of vegetation cover and soil use on Ilha de Mosqueiro, Belém, Pará, Amazonian Brazil

Assessing the dynamics of land use is important in providing quantified estimates of the extent of ecosystem change, and so and structured planning to reduce its environmental and social impacts. The objective of the current study was to analyze the dynamics of vegetation and soil use on Ilha de Mosqueiro,
 Belém, Pará State, northern Brazil, between 1984 and 2014, via digital image processing. For this purpose, satellite images of Ilha de Mosqueiro (orbit/point 224/62) were used. These comprised of Landsat 5 Satellite, Sensor TM, images for the years 1984, 1996 and 2008, and 2014 images from the Landsat Satellite 8, OLI
 sensor. These images were processed so as to classify and determine the area occupied by the following classes: dense vegetation, secondary vegetation, low growth, exposed soil, urban area and other. There was a continuous reduction of the dense vegetation class between 1984 and 2008; this accounted for 67.8% of the total area the Ilha de Mosqueiro in 1984, and 31% in 2008. At the same time the class open soil showed continuous growth across all evaluated periods, representing 2.25% of land cover in 1984, increasing to 2.33% and 4.20%, in 1996 and 2014, respectively. Between 1984 and 2014, there was a great increase in the class urban area, generally associated with the generation of environmental problems, due to irregular occupation and lack of environmental and urban management of the island.

Approximation of ruin probabilities via Erlangized scale mixtures

In this paper, we extend an existing scheme for numerically calculating the probability of ruin of a classical Cramér–Lundbergreserve process having absolutely continuous but otherwise general claim size distributions. We employ a dense class of distributions that we denominate Erlangized scale mixtures (ESM) that correspond to nonnegative and absolutely continuous distributions which can be written as a Mellin–Stieltjes convolution Π⋆G of a nonnegative distribution Π with an Erlang distribution G. A distinctive feature of such a class is that it contains heavy-tailed distributions.We suggest a simple methodology for constructing a sequence of distributions having the form Π⋆G with the purpose of approximating the integrated tail distribution of the claim sizes. Then we adapt a recent result which delivers an explicit expression for the probability of ruin in the case that the claim size distribution is modeled as an Erlangized scale mixture. We provide simplified expressions for the approximation of the probability of ruin and construct explicit bounds for the error of approximation. We complement our results with a classical example where the claim sizes are heavy-tailed.

Tracking Labrador Sea Water property signals along the Deep Western Boundary Current

AbstractObservations of the Deep Western Boundary Current (DWBC) at Line W on the western North Atlantic continental slope southeast of Cape Cod from 1995 to 2014 reveal water mass changes that are consistent with changes in source water properties upstream in the Labrador Sea. This is most evident in the cold, dense, and deep class of Labrador Sea Water (dLSW) that was created and progressively replenished and deepened by recurring winter convection during the severe winters of 1987–1994. The arrival of this record cold, fresh, and low potential vorticity anomaly at Line W lags its formation in the Labrador Sea by 3–7 years. Complementary observations along the path of the DWBC provide further evidence that this anomaly is advected along the boundary and indicate that stirring between the boundary and the interior intensifies south of the Flemish Cap. Finally, the consistency of the data with realistic advective and mixing time scales is assessed using the Waugh and Hall (2005) model framework. The data are found to be best represented by a mean transit time of 5 years from the Labrador Sea to Line W, with a leading order role for both advection by the DWBC and mixing between the boundary flow and interior waters.

Assessing post-industrial land cover change at the Pine Point Mine, NWT, Canada using multi-temporal Landsat analysis and landscape metrics

This study investigates land cover change near the abandoned Pine Point Mine in Canada's Northwest Territories. Industrial mineral development transforms local environments, and the effects of such disturbances are often long-lasting, particularly in subarctic, boreal environments where vegetation conversion can take decades. Located in the Boreal Plains Ecozone, the Pine Point Mine was an extensive open pit operation that underwent little reclamation when it shut down in 1988. We apply remote sensing and landscape ecology methods to quantify land cover change in the 20years following the mine's closure. Using a time series of near-anniversary Landsat images, we performed a supervised classification to differentiate seven land cover classes. We used raster algebra and landscape metrics to track changes in land cover composition and configuration in the 20years since the mine shut down. We compared our results with a site in Wood Buffalo National Park that was never subjected to extensive anthropogenic disturbance. This space-for-time substitution provided an analog for how the ecosystem in the Pine Point region might have developed in the absence of industrial mineral development. We found that the dense conifer class was dominant in the park and exhibited larger and more contiguous patches than at the mine site. Bare land at the mine site showed little conversion through time. While the combination of raster algebra and landscape metrics allowed us to track broad changes in land cover composition and configuration, improved access to affordable, high-resolution imagery is necessary to effectively monitor land cover dynamics at abandoned mines.

A hybrid hierarchical framework for classification of breast density using digitized film screen mammograms

In the present work, a hybrid hierarchical framework for classification of breast density using digitized film screen mammograms has been proposed. For designing of an efficient classification framework 480 MLO view digitized screen film mammographic images are taken from DDSM dataset. The ROIs of fixed size i.e. 128 × 128 pixels are cropped from the center area of the breast (i.e. the area where glandular ducts are prominent). A total of 292 texture features based on statistical methods, signal processing based methods and transform domain based methods are computed for each ROI. The computed feature vector is subjected to PCA for dimensionality reduction. The reduced feature space is fed to the classification module. In this work 4-class breast density classification has been conducted using hierarchical framework where the first classifier is used to classify an unknown test ROI into B-I/other class. If the test ROI is predicted as other class, it is inputted to second classifier for the classification into B-II/dense class. If the test ROI is predicted as belonging to dense class, it is inputted to classifier for the classification into B-III/B-IV class. In this work five hierarchical classifiers designs consisting of 3 PCA-kNN, 3 PCA-PNN, 3 PCA-ANN, 3 PCA-NFC and 3 PCA-SVM classifiers has been proposed. The obtained maximum OCA value is 80.4% using PCA-NFC in hierarchical approach. Further, the best performing individual classifiers are clubbed together in a hierarchical framework to design hybrid hierarchical framework for classification of breast density using digitized screen film mammograms. The proposed hybrid hierarchical framework yields the OCA value of 84.1%. The result achieved by the proposed hybrid hierarchical framework is quite promising and can be used in clinical environment for differentiation between different breast density patterns.

Tingkat Kenyamanan Di Hutan Kota Patriot Bina Bangsa Kota Bekasi

The development of urban area was accured quickly and lead to many environmentalproblems such as the rising of temperatures and decreasing of environmental quality. Greenopen space (RTH)was needed to overcome those problems. The objectives of the researchwere to figure out the characteristics of vegetation in Patriot Bina Bangsa Urban Forest(including the species, density, broad canopy coverage), to figure out comfort index ofPatriot Bina Bangsa Urban Forest and to find out the visitor’s perception about comfortsvalue of facilities. The analysis of vegetation was employed as the method of data collectionsensus method was used as the sampling method, and temperature humidity index (THI) wasused to determine the comfort level. Interview techniques with random sampling method wasused to determine the visitors perception. The result showed that the vegetationcharacteristics of Patriot Bina Bangsa Urban Forest took effects to temperature andhumidity. High density of tree could decrease the air temperature and increase the humidity, where dense canopy class had air temperature at 27.6 ºC and humidity at 80.1%; moderatecanopy class had air temperature at 29.1 ºC and humidity at 73.2%; sparse canopy class hadair temperature at 30.1 ºC and humidity at 70.5%. Based on the temperature humidity index(THI), Patriot Bina Bangsa Urban Forest was categorized as uncomfortable, with THI values>26. Most of visitors (77.72%) believed that the facilities wich exist in Patriot Bina BangsaUrban Forest ware categorized good.Key words :Patriot Bina Bangsa Urban Forest, urban forest comfort, city

Assessment the Effect of Drought on Vegetation in Desert Area using Landsat Data

Drought phenomenon is one kind of a disaster that can significantly affect the density of vegetation in any area especially dry regions. This study tries to express the effect of drought on vegetation cover in Yazd-Ardakan plain, central Iran. At first, annual average for SPI index was calculated from 1996 to 2015, and then NDVI was calculated for May in 1998, 2000, 2009, 2010, 2011 and 2015. Afterwards, NDVI maps were classified into three groups including no vegetation, poor vegetation (pastures), and dense vegetation (farmlands and gardens). Based on the results the worst value of drought was −1.92 in year 1999. Besides, the annual SPI of 1996 with value of 2.4 was considered as the wettest year during study period (1996–2015). The highest percentage of dense vegetation and poor vegetation were related to 2010 and 1998 respectively, and the lowest percentage for both classes was related to 2000. There was correlation among the area of poor vegetation class in middle of spring and previous annual SPI at the significant level of 95%. In contract, no correlation was found between dense vegetation class areas in middle spring and previous amount of annual SPI. The study of the correlation between the SPI average and the percentage of vegetation classes indicated that pastures were highly sensitive to SPI changes; however, farming lands showed less sensitivity in short term due to using deep wells.

Enlarging learnable classes

We study which classes of recursive functions satisfy that their union with any other explanatorily learnable class of recursive functions is again explanatorily learnable. We provide sufficient criteria for classes of recursive functions to satisfy this property and also investigate its effective variants. Furthermore, we study the question which learners can be effectively extended to learn a larger class of functions. We solve an open problem by showing that there is no effective procedure which does this task on all learners which do not learn a dense class of recursive functions. However, we show that there are two effective extension procedures such that each learner is extended by one of them.

More Polish full groups

We associate to every action of a Polish group on a standard probability space a Polish group that we call the orbit full group. For discrete groups, we recover the well-known full groups of pmp equivalence relations equipped with the uniform topology. However, there are many new examples, such as orbit full groups associated to measure-preserving actions of locally compact groups. We also show that such full groups are complete invariants of orbit equivalence.We give various characterizations of the existence of a dense conjugacy class for orbit full groups, and we show that the ergodic ones actually have a unique Polish group topology. Furthermore, we characterize ergodic full groups of countable pmp equivalence relations as those admitting non-trivial continuous character representations.

Monitoring Forest Cover Change and Fragmentation Using Remote Sensing and Landscape Metrics in Nyungwe-Kibira Park

The objective of this study was to evaluate forest cover change and forest degradation in Nyungwe-Kibira Park, a natural reserve straddling Rwanda and Burundi from 1986 to 2015. Landsat TM, ETM+ and 8OLI images of 30 m spatial resolution were used as primary datasets. Geographic Information System (GIS) techniques were used for forest cover mapping and landscape metrics were calculated by using FRAGSTATS software. Classification and change analysis of forest cover type and landscape patterns analysis were carried out. In addition, to analyze the correlated external disturbances, the buffer zone of 5 Km was delineated outside the boundary of Nyungwe-Kibira Park. The results revealed that in among 5 land cover classes considered within the Park, the dominant one was dense forest class covering over 70% of the entire Park area while in the buffer zone cultivated and open land dominated at over 90% between the years 1986 and 2015. Change detection highlighted that within Nyungwe-Kibira forest, approximately 0.27% (4.97 Km2) of forest cover was cleared while 0.07% (1.22 Km2) was regenerated annually. In the buffer zone, the annual cleared forest cover was about 0.76% (13.02 Km2). The five landscape indices chosen at class level indicated a considerable fragmentation of forest inside the Park and the highest fragmentation in the buffer zone. Indeed, these results shed a bleak image over the future of the Nyungwe-Kibira forest that should be helpful for the policy-makers and managers of these natural parks to establish adequate policies to mitigate the forest loss and degradation by implementing quick and effective solutions.

Effects of management activities on vegetation diversity, dispersion pattern and stand structure of community-managed forest (Shorea robusta) in Nepal

Analyzing spatial patterns of population distribution in forests may assist to infer the underlying ecological processes and the factors responsible for pattern formation. This study aimed at analyzing the effects of management activities on species richness, diversity, distribution pattern, and forest stand structure in Chisapani Community Forest of Tanahun District, Nepal. The forest was stratified on the basis of crown cover and nested quadrat plots of 20 × 25 m were laid randomly. Trees having ≥5 cm diameter at breast height (dbh) were identified, and their diameter and height were recorded. Altogether, 44 species were recorded representing 39 genera and 27 families. The mean species density of the forest was 192 trees ha−1 and the average basal area was 16.2 m2 ha−1. Tukey’s post-hoc test showed the significant difference in species richness between open and dense crown class. Except Woodfordia fruticosa, all other species were found with patchy distribution. This study showed that unrestricted access does not necessarily maintain species diversity or regulate the forest stand structure, because people preferred species with high economic potential. Hence, a strategy for maintaining species diversity, regulating stand structure, and finding synergy between biodiversity conservation and conservation outcome is needed.

Lévy Processes, Phase-Type Distributions, and Martingales

Lévy processes are defined as processes with stationary independent increments and have become increasingly popular as models in queueing, finance, etc.; apart from Brownian motion and compound Poisson processes, some popular examples are stable processes, variance gamma processes, CGMY Lévy processes (tempered stable processes), NIG (normal inverse Gaussian) Lévy processes, and hyperbolic Lévy processes. We consider here a dense class of Lévy processes, compound Poisson processes with phase-type jumps in both directions and an added Brownian component. Within this class, we survey how to explicitly compute a number of quantities that are traditionally studied in the area of Lévy processes, in particular two-sided exit probabilities and associated Laplace transforms, the closely related scale function, one-sided exit probabilities and associated Laplace transforms coming up in queueing problems, and similar quantities for a Lévy process with reflection in 0. The solutions are in terms of roots to polynomials, and the basic equations are derived by purely probabilistic arguments using martingale optional stopping; a particularly useful martingale is the so-called Kella-Whitt martingale. Also, the relation to fluid models with a Brownian component is discussed.

Wigner-von Neumann type perturbations of periodic Schrödinger operators

We study decaying oscillatory perturbations of periodic Schrödinger operators on the half line. More precisely, the perturbations we consider satisfy a generalized bounded variation condition at infinity and an L p L^p decay condition. We show that the absolutely continuous spectrum is preserved, and give bounds on the Hausdorff dimension of the singular part of the resulting perturbed measure. Under additional assumptions, we instead show that the singular part embedded in the essential spectrum is contained in an explicit countable set. Finally, we demonstrate that this explicit countable set is optimal. That is, for every point in this set there is an open and dense class of periodic Schrödinger operators for which an appropriate perturbation will result in the spectrum having an embedded eigenvalue at that point.

Calculation of ruin probabilities for a dense class of heavy tailed distributions

In this paper, we propose a class of infinite-dimensional phase-type distributions with finitely many parameters as models for heavy tailed distributions. The class of finite-dimensional phase-type distributions is dense in the class of distributions on the positive reals and may hence approximate any such distribution. We prove that formulas from renewal theory, and with a particular attention to ruin probabilities, which are true for common phase-type distributions also hold true for the infinite-dimensional case. We provide algorithms for calculating functionals of interest such as the renewal density and the ruin probability. It might be of interest to approximate a given heavy tailed distribution of some other type by a distribution from the class of infinite-dimensional phase-type distributions and to this end we provide a calibration procedure which works for the approximation of distributions with a slowly varying tail. An example from risk theory, comparing ruin probabilities for a classical risk process with Pareto distributed claim sizes, is presented and exact known ruin probabilities for the Pareto case are compared to the ones obtained by approximating by an infinite-dimensional hyper-exponential distribution.

Special homeomorphisms and approximation for Cantor systems

E. Akin, E. Glasner, and B. Weiss had constructed the special homeomorphism that has a dense Gδ conjugacy class in the space of all Cantor homeomorphisms. M. Hochman showed that the universal odometer is the special homeomorphism in the space of all topologically transitive Cantor homeomorphism. Following the approach of E. Akin, E. Glasner, and B. Weiss, we show that the universal odometer is the special homeomorphism in the space of all chain transitive Cantor systems. We extend this result to the space of chain transitive systems that are restricted by a periodic spectrum. Further, we construct the special homeomorphism in the space of all chain recurrent systems. In doing so, every 0-dimensional system is described as the inverse limit of a sequence of finite directed graphs and graph homomorphisms. In the previous paper, we had shown that a certain periodic condition determines whether a Cantor system approximates a chain mixing Cantor system by topological conjugacies. We shall extend this result to the chain transitive case. These conditions are described in terms of sequences of finite directed graphs and graph homomorphisms.

Large conjugacy classes, projective Fraïssé limits and the pseudo-arc

We show that the automorphism group, Aut(ℙ), of a projective Fraisse limit ℙ, whose natural quotient is the pseudo-arc, has a comeager conjugacy class. This generalizes an unpublished result of Izhar Oppenheim that Aut(ℙ) (and consequently, the group of all homeomorphisms of the pseudo-arc) has a dense conjugacy class. We also present a simple proof of the result of Oppenheim.

Minimal external representations of tropical polyhedra

Tropical polyhedra are known to be representable externally, as intersections of finitely many tropical half-spaces. However, unlike in the classical case, the extreme rays of their polar cones provide external representations containing in general superfluous half-spaces. In this paper, we prove that any tropical polyhedral cone in Rn (also known as “tropical polytope” in the literature) admits an essentially unique minimal external representation. The result is obtained by establishing a (partial) anti-exchange property of half-spaces. Moreover, we show that the apices of the half-spaces appearing in such non-redundant external representations are vertices of the cell complex associated with the polyhedral cone. We also establish a necessary condition for a vertex of this cell complex to be the apex of a non-redundant half-space. It is shown that this condition is sufficient for a dense class of polyhedral cones having “generic extremities”.

Solution of the Dirichlet problem for G-minimal graphs with a continuity and approximation method

We consider the Dirichlet problem for so-called G-minimal graphs in two dimensions. These are immersions of minimal surface type which can be presented as graphs over a planar domain. With the aid of a weight matrix G we derive a quasilinear elliptic and homogeneous differential equation for this height function. Then we solve the Dirichlet problem over convex domains Ω without differentiability assumptions and continuous boundary data with a constructive continuity and approximation method. We firstly establish an a priori C 1+α -estimate up to the boundary of the solution as we take the dense problem class of strictly convex C 2+α -domains and C 2+α -boundary data. By proving theorems on stability and compactness of graphs we solve this boundary value problem with a nonlinear continuity method. Then we introduce weighted conformal parameters in the graph and consider the parametric problem on the unit disc. Finally, we solve the original Dirichlet problem by using an approximation argument and the important parametric compactness theorem.