Superstatistical generalisations of Wishart-Laguerre ensembles of random matrices

Using Beck and Cohen's superstatistics, we introduce in a systematic way a family of generalized Wishart–Laguerre ensembles of random matrices with Dyson index β = 1, 2 and 4. The entries of the data matrix are Gaussian random variables whose variances η fluctuate from one sample to another according to a certain probability density f(η) and a single deformation parameter γ. Three superstatistical classes for f(η) are usually considered: χ2-, inverse χ2- and log-normal distributions. While the first class, already considered by two of the authors, leads to a power-law decay of the spectral density, we here introduce and solve exactly a superposition of Wishart–Laguerre ensembles with inverse χ2-distribution. The corresponding macroscopic spectral density is given by a γ-deformation of the semi-circle and Marčenko–Pastur laws, on a non-compact support with exponential tails. After discussing in detail the validity of Wigner's surmise in the Wishart–Laguerre class, we introduce a generalized γ-dependent surmise with stretched-exponential tails, which well approximates the individual level spacing distribution in the bulk. The analytical results are in excellent agreement with numerical simulations. To illustrate our findings we compare the χ2- and inverse χ2-classes to empirical data from financial covariance matrices

Characterisation of stability behaviour of ultra fine alumina powder in view its colloidal processing by gel-casting

The paper reports on results study aimed at assessing of the influence of dispersant type on the electrochemical properties of highly concentrated alumina suspension. The relationship between the type of dispersant and the stabilization ability towards ultrafine alumina powder CT3000 has been studied. The effectiveness was determined mainly by the zeta potential value, specific surface charge, the shift in the pH(iep) and by visual controlling the fluidity of the slurry at constant solid loading. A good agreement between the zeta potential and the specific surface charge as a way to determine the optimal dose of dispersant has been documented. Gel-casting experiments showed that the Dolapix CE64, an ammonium polyacrylate dispersant was the best dispersant for the studied powder.Peer reviewe

Reliable low-cost fabrication of low-loss Al2O3:Er3+Al_2O_3:Er^{3+} waveguides with 5.4-dB optical gain

A reliable and reproducible deposition process for the fabrication of $Al_2O_3$ waveguides with losses as low as 0.1 dB/cm has been developed. The thin films are grown at ~ 5 nm/min deposition rate and exhibit excellent thickness uniformity within 1% over 50times50 mm2 area and no detectable $OH^{-}$ incorporation. For applications of the $Al_2O_3$ films in compact, integrated optical devices, a high-quality channel waveguide fabrication process is utilized. Planar and channel propagation losses as low as 0.1 and 0.2 dB/cm, respectively, are demonstrated. For the development of active integrated optical functions, the implementation of rare-earth-ion doping is investigated by cosputtering of erbium during the $Al_2O_3$ layer growth. Dopant levels between 0.2-5times $1020 cm^{-3}$ are studied. At $Er^{3+}$ concentrations of interest for optical amplification, a lifetime of the 4I13/2 level as long as 7 ms is measured. Gain measurements over 6.4-cm propagation length in a 700-nm-thick $Al_2O_3:Er^{3+}$ channel waveguide result in net optical gain over a 41-nm-wide wavelength range between 1526-1567 nm with a maximum of 5.4 dB at 1533 n

Current and Future Therapeutic Approaches for Thymic Stromal Cell Defects

Inborn errors of thymic stromal cell development and function lead to impaired T-cell development resulting in a susceptibility to opportunistic infections and autoimmunity. In their most severe form, congenital athymia, these disorders are life-threatening if left untreated. Athymia is rare and is typically associated with complete DiGeorge syndrome, which has multiple genetic and environmental etiologies. It is also found in rare cases of T-cell lymphopenia due to Nude SCID and Otofaciocervical Syndrome type 2, or in the context of genetically undefined defects. This group of disorders cannot be corrected by hematopoietic stem cell transplantation, but upon timely recognition as thymic defects, can successfully be treated by thymus transplantation using cultured postnatal thymic tissue with the generation of naïve T-cells showing a diverse repertoire. Mortality after this treatment usually occurs before immune reconstitution and is mainly associated with infections most often acquired pre-transplantation. In this review, we will discuss the current approaches to the diagnosis and management of thymic stromal cell defects, in particular those resulting in athymia. We will discuss the impact of the expanding implementation of newborn screening for T-cell lymphopenia, in combination with next generation sequencing, as well as the role of novel diagnostic tools distinguishing between hematopoietic and thymic stromal cell defects in facilitating the early consideration for thymus transplantation of an increasing number of patients and disorders. Immune reconstitution after the current treatment is usually incomplete with relatively common inflammatory and autoimmune complications, emphasizing the importance for improving strategies for thymus replacement therapy by optimizing the current use of postnatal thymus tissue and developing new approaches using engineered thymus tissue

The Radius of Metric Subregularity

There is a basic paradigm, called here the radius of well-posedness, which quantifies the "distance" from a given well-posed problem to the set of ill-posed problems of the same kind. In variational analysis, well-posedness is often understood as a regularity property, which is usually employed to measure the effect of perturbations and approximations of a problem on its solutions. In this paper we focus on evaluating the radius of the property of metric subregularity which, in contrast to its siblings, metric regularity, strong regularity and strong subregularity, exhibits a more complicated behavior under various perturbations. We consider three kinds of perturbations: by Lipschitz continuous functions, by semismooth functions, and by smooth functions, obtaining different expressions/bounds for the radius of subregularity, which involve generalized derivatives of set-valued mappings. We also obtain different expressions when using either Frobenius or Euclidean norm to measure the radius. As an application, we evaluate the radius of subregularity of a general constraint system. Examples illustrate the theoretical findings.Comment: 20 page

Ro-vibrational averaging of the isotropic hyperfine coupling constant for the methyl radical

© 2015 AIP Publishing LLC. We present the first variational calculation of the isotropic hyperfine coupling constant of the carbon-13 atom in the CH3 radical for temperatures T = 0, 96, and 300 K. It is based on a newly calculated high level ab initio potential energy surface and hyperfine coupling constant surface of CH3 in the ground electronic state. The ro-vibrational energy levels, expectation values for the coupling constant, and its temperature dependence were calculated variationally by using the methods implemented in the computer program TROVE. Vibrational energies and vibrational and temperature effects for coupling constant are found to be in very good agreement with the available experimental data. We found, in agreement with previous studies, that the vibrational effects constitute about 44% of the constant's equilibrium value, originating mainly from the large amplitude out-of-plane bending motion and that the temperature effects play a minor role

Carbothermal Upgrading of the Awaso Bauxite Ore using Waste Pure Water Sachets as Reductant*

Waste Pure Water Sachets (PWS) are currently among the fastest growing solid wastes generated in Ghana. Government’s attempt at banning its production and usage has been thwarted by the realisation that such a measure will increase the unemployment rate since the sachet water business employs a significant proportion of people. Meanwhile, the country currently exports its bauxite raw, without any value addition. Gradual depletion of high grade bauxite (with high alumina content) and the emergence of low grade bauxite with high iron oxide content calls for novel and inexpensive ways to upgrade these low ores. This project investigates a simple way of generating carbonaceous materials from PWS and their subsequent utilisation as reductants in the carbothermal upgrading of the Ghana Awaso bauxite. Samples of PWS were heat-treated in the temperature range 130-180 °C and the resulting molten material was cooled to render it brittle. The brittle mass was then pulverised and characterised by XRD and SEM. Composite pellets of bauxite sample and pulverised PWS were then formed, oven dried, placed in a fireclay crucible and heated in a gas-fired furnace. The magnetic fraction after reduction was separated by a Low Intensity Magnet and weighed. XRD analyses of the pulverised PWS showed peaks identical to those of high density polyethylene (HDPE). It was further observed that after about 30 min of firing, a large portion of the sample could be attracted by the magnet, indicating the suitability of the waste polymer as an important carbonaceous material for bauxite upgrading. The use of PWS as reductant prevented the formation of hercynite (FeAl2O4).Keywords: Pure water sachets, Bauxite, Gas-fired furnace, Magnetic fraction, High density polyethylen

Melatonin prevents cytosolic calcium overload, mitochondrial damage and cell death due to toxically high doses of dexamethasone-induced oxidative stress in human neuroblastoma SH-SY5Y cells

Stressor exposure activates the hypothalamic-pituitary-adrenal (HPA) axis and causes elevations in the levels of glucocorticoids (GC) from the adrenal glands. Increasing evidence has demonstrated that prolonged exposure to high GC levels can lead to oxidative stress, calcium deregulation, mitochondrial dysfunction and apoptosis in a number of cell types. However, melatonin, via its antioxidant activity, exhibits a neuroprotective effect against oxidative stress-induced cell death. Therefore, in the present study, we explored the protective effect of melatonin in GC-induced toxicity in human neuroblastoma SH-SY5Y cells. Cellular treatment with the toxically high doses of the synthetic GC receptor agonist, dexamethasone (DEX) elicited marked decreases in the levels of glutathione and increases in ROS production, lipid peroxidation and cell death. DEX toxicity also induced increases in the levels of cytosolic calcium and mitochondrial fusion proteins (Mfn1 and Opa1) but decreases in the levels of mitochondrial fission proteins (Fis1 and Drp1). Mitochondrial damage was observed in large proportions of the DEX-treated cells. Pretreatment of the cells with melatonin substantially prevented the DEX-induced toxicity. These results suggest that melatonin might exert protective effects against oxidative stress, cytosolic calcium overload and mitochondrial damage in DEX-induced neurotoxicity

Correlated decay of triplet excitations in the Shastry-Sutherland compound SrCu2_2(BO3_3)2_2

The temperature dependence of the gapped triplet excitations (triplons) in the 2D Shastry-Sutherland quantum magnet SrCu$_2$(BO$_3$)$_2$ is studied by means of inelastic neutron scattering. The excitation amplitude rapidly decreases as a function of temperature while the integrated spectral weight can be explained by an isolated dimer model up to 10~K. Analyzing this anomalous spectral line-shape in terms of damped harmonic oscillators shows that the observed damping is due to a two-component process: one component remains sharp and resolution limited while the second broadens. We explain the underlying mechanism through a simple yet quantitatively accurate model of correlated decay of triplons: an excited triplon is long-lived if no thermally populated triplons are near-by but decays quickly if there are. The phenomenon is a direct consequence of frustration induced triplon localization in the Shastry--Sutherland lattice.Comment: 5 pages, 4 figure

A density-based statistical analysis of graph clustering algorithm performance

This is a pre-copyedited, author-produced version of an article accepted for publication in Journal of Complex Networks following peer review. The version of record: Pierre Miasnikof, Alexander Y Shestopaloff, Anthony J Bonner, Yuri Lawryshyn, Panos M Pardalos, A density-based statistical analysis of graph clustering algorithm performance, Journal of Complex Networks, Volume 8, Issue 3, June 2020, cnaa012, https://doi.org/10.1093/comnet/cnaa012 is available online at: https://doi.org/10.1093/comnet/cnaa012© 2020 The authors. Published by Oxford University Press. All rights reserved. We introduce graph clustering quality measures based on comparisons of global, intra- A nd inter-cluster densities, an accompanying statistical significance test and a step-by-step routine for clustering quality assessment. Our work is centred on the idea that well-clustered graphs will display a mean intra-cluster density that is higher than global density and mean inter-cluster density. We do not rely on any generative model for the null model graph. Our measures are shown to meet the axioms of a good clustering quality function. They have an intuitive graph-theoretic interpretation, a formal statistical interpretation and can be tested for significance. Empirical tests also show they are more responsive to graph structure, less likely to breakdown during numerical implementation and less sensitive to uncertainty in connectivity than the commonly used measures