Correction on Moments of minors of Wishart matrices

Correction on Moments of minors of Wishart matrices by M. Drton and A. Goia (Ann. Statist. 36 (2008) 2261-2283), arXiv:math/0604488Comment: Published in at http://dx.doi.org/10.1214/12-AOS988 the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org

Classification methods for Hilbert data based on surrogate density

An unsupervised and a supervised classification approaches for Hilbert random curves are studied. Both rest on the use of a surrogate of the probability density which is defined, in a distribution-free mixture context, from an asymptotic factorization of the small-ball probability. That surrogate density is estimated by a kernel approach from the principal components of the data. The focus is on the illustration of the classification algorithms and the computational implications, with particular attention to the tuning of the parameters involved. Some asymptotic results are sketched. Applications on simulated and real datasets show how the proposed methods work.Comment: 33 pages, 11 figures, 6 table

Thermo-physical behaviour and energy performance assessment of PCM glazing system configurations: A numerical analysis

The adoption of Phase Change Materials (PCMs) in glazing systems was proposed to increase the heat capacity of the fenestration, being some PCMs partially transparent to visible radiation. The aim of the PCM glazing concept was to let (part) of the visible spectrum of the solar radiation enter the indoor environment, providing daylighting, while absorbing (the largest part of) the infrared radiation. In this paper, the influence of the PCM glazing configuration is investigated by means of numerical simulations carried out with a validated numerical model. Various triple glazing configurations, where one of the two cavities is filled with a PCM, are simulated, and PCM melting temperatures are investigated. The investigation is carried out in a humid subtropical climate (Cfa according to Köppen climate classifi-cation), and "typical days" for each season are used. The results show that the position of the PCM layer (inside the outer or the inner cavity) has a relevant influence on the thermo-physical behaviour of the PCM glazing system. PCM glazing systems (especially those with the PCM layer inside the outermost cavity) can be beneficial in terms of thermal comfort. The assessment of the energy performance and efficiency is instead more complex and sometimes controversial. All the configurations are able to reduce the solar gain during the daytime, but sometimes the behaviour of the PCM glazing is less efficient than the reference one. ©2012. Higher Education Press Limited Company. Production and hosting by Elsevier B.V. Open access underCC BY-NC-ND license

Effects of “classical” vs. “dynamic” silviculture of sessile oak-dominated stands in terms of height, diameter increments and natural mortality

Traditional oak silviculture in Romania is associated with high labor costs and long rotation cycles which are imposed by current norms and regulations. A small-scale R&D project, consisting of a block with four plots of 200 m2, was established in 2001 in a 15-year old sessile oak-dominated stand. The stand was regenerated naturally through the application of group shelterwood cutting. In each plot, ”potential” final crop trees were selected based on vigor-quality-distribution criteria and marked with paint. Silvicultural interventions like cleaning-respacing and thinning of different intensities were performed in three plots (the fourth one was kept as control) in 2001, 2004 and 2009. The effect of stand density on diameter increment was more obvious when considering only the “potential” final crop trees than when all trees were considered. Their quadratic mean diameter (QMD) had reached values close to 20 cm at 35 (30-40) years in the plots with the lowest stand density (STT) and about 15-16 cm for other plots. STT stand with the lowest stand density shows low HDR values having slander trees. The mortality intensity between 2001 and 2019 was highest in the control plot and lowest in STT. Sessile oak showed the highest mortality, followed by Hungarian oak and Turkey oak. In all plots, trees had reached heights corresponding to the hg of ca. 15 m, which is normal for a sessile oak stand of high productivity. The obtained results indicate the ”dynamic”, crop tree silviculture with the active selection of the most valuable individuals as ”potential” final crop trees at the end of thicket stage as being a possible solution for managing sessile oak young and medium-aged stands. Nonetheless, these trees should be managed by subsequent crown thinning, in order to produce timber with as uniform as possible radial increments of 2-3 mm, as is requested by veneer and high-quality saw log buyers

Exploring the total positivity of yields correlations

We test the plausibility of the total positivity assumption of interest rates changes recently introduced in order to justify the presence of shift, slope and curvature for yield curves. To this aim, we introduce and discuss a test of total positivity of order for covariance and correlation matrices. The explicit expressions of the test statistics are given for Gaussian samples and an extension to a distribution-free framework is made via a bootstrap method. After exploring with simulation the robustness of such tests, we show using real data how it is realistic to assume that correlation matrices of interest rates changes are totally positive of order two. Conclusions on total positivity of order three are more controversial

The impact of an ideal dynamic building envelope on the energy performance of low energy office buildings

This paper shows the results of a research activity aimed at assessing the advantages of an ideal adaptive building skin over conventional building envelope systems. The basic idea underlying the research consists in imagining an ideal building envelope system characterised by the capability of continuously changing (within a certain range) some of its thermo-physical and optical properties. The reason for the continuous tuning of thermo-physical and optical properties lies in the assumption that an optimised (fixed) configuration, where the properties do not change over time, is not able to minimise the total energy demand of the building at each moment. For the sake of this purpose, an ideal dynamic WWR (Window-to-Wall Ratio) building envelope system for low energy office buildings was modelled and simulated. An integrated thermal-lighting building simulation tool was used. The energy performance of such a system was then analysed and compared against the performance of a conventional façade realised with best-available technologies. The results of the investigation demonstrated the advantages of a dynamic WWR configuration over a static one. However, the improvements achieved in energy demand were lower than expected. This behaviour is strictly related to the configuration of the building used as a reference, which already showed a very high energy performance. Limitations presented by the research method are also briefly pointed out and discussed