Applying data mining techniques for spatial distribution analysis of plant species co-occurrences

The continuous growth of biodiversity databases has led to a search for techniques that can assist researchers. This paper presents a method for the analysis of occurrences of pairs and groups of species that aims to identify patterns in co-occurrences through the application of association rules of data mining. We propose, implement and evaluate a tool to help ecologists formulate and validate hypotheses regarding co-occurrence between two or more species. To validate our approach, we analyzed the occurrence of species with a dataset from the 50-ha Forest Dynamics Project on Barro Colorado Island (BCI). Three case studies were developed based on this tropical forest to evaluate patterns of positive and negative correlation. Our tool can be used to point co-occurrence in a multi-scale form and for multi-species, simultaneously, accelerating the identification process for the Spatial Point Pattern Analysis. This paper demonstrates that data mining, which has been used successfully in applications such as business and consumer profile analysis, can be a useful resource in ecology.     

BNCT project at Tehran Research Reactor: Current and prospective plans

Boron Neutron Capture Therapy (BNCT) for brain tumor treatment is under development at the Tehran Research Reactor (TRR). This paper presents all current research activities that were performed during recent years as well as the prospective of BNCT research at TRR. The theoretical and experimental investigations show that TRR has a very good potential to consider it as a pilot facility for BNCT research in the Middle East and could be facilitated for clinical applications. In this way, there are some steps and also some challenges which are described in the paper.     

Exact formulations and algorithm for the train timetabling problem with dynamic demand

In this paper we study the design and optimization of train timetabling adapted to a dynamic demand environment. This problem arises in rapid train services which are common in most important cities. We present three formulations for the problem, with the aim of minimizing passenger average waiting time. The most intuitive model would consider binary variables representing train departure times but it yields to non-linear objective function. Instead, we introduce flow variables, which allow a linear representation of the objective function. We provide incremental improvements on these formulations, which allows us to evaluate and compare the benefits and disadvantages of each modification. We present a branch-and-cut algorithm applicable to all formulations. Through extensive computational experiments on several instances derived from real data provided by the Madrid Metropolitan Railway, we show the advantages of designing a timetable adapted to the demand pattern, as opposed to a regular timetable. We also perform an extensive computational comparison of all linear formulations in terms of size, solution quality and running time.     

Shear effects on expanded graphite under uniaxial pressure: An in situ small angle neutron scattering study

In a previous work [1] we elucidated the in situ evolution of the porosity of out-of-plane compressed flexible graphite under uniaxial pressure up to 1000 bar using small-angle neutron scattering (SANS) technique. In order to understand the influence of shear effect on the properties of flexible graphite we study, in the present paper, the in situ behaviour of in-plane compressed flexible graphite under a uniaxial pressure. The sample had a pleated layered structure in which anisotropic SANS patterns revealed a distribution of differently oriented ellipsoid pores. Uniaxial compression generates important shear effects in this kind of sample.We have determined the evolution of the system fractal dimension, pore size distribution and apparent specific surface area with applied pressure which together allow us to describe the meso and macro pore structure evolution. Under pressure, the irreversible collapse and splitting of larger pores into smaller size ones which is characteristic of out-of-plane uniaxial compression [1], is accompanied, in the presence of shear stress components, by an in-plane slipping mechanism giving rise to cracks and consequently to interface formation.     

汶川地震公路隧道洞口结构震害分析及震害机理研究

通过对汶川地震公路隧道震害调查资料的统计分析,对隧道洞口结构进行了震害分析,结果表明：洞外结构受次生灾害影响较大,地震惯性力影响明显;硬岩洞口段隧道结构基本无破坏,软岩洞口段隧道结构震害较严重。通过三维有限差分数值模拟计算和现场典型震害分析,研究了公路隧道洞口结构的震害机理。探明了洞外结构震害机理,即洞外结构受次生灾害影响较大,震害的主要原因是地震惯性力,洞门墙结构和基础设计不合理以及隧道洞口所处位置也是影响洞外结构震害的重要因素。探明了洞口段隧道结构震害机理,即正穿坡面洞口段隧道结构存在软硬围岩交界面时,其附近软岩内隧道结构受较大强制位移作用;正穿坡面洞口段隧道结构覆盖层为软岩时,震害的主要因素是地震惯性力。研究成果对公路隧道洞口结构的抗减震技术有着重要的意义。     

Preparation of the anatase/TiO2(B) TiO2 by self-assembly process and the high photodegradable performance on RhB

The TiO₂ samples, synthesized with different addition amount of titanium source, have been prepared by a bottom-up method employing inverse lamellar micelles as the template in a surfactant molecular self-assembly process. The products were characterized by X-ray diffraction (XRD), Raman, Field-emission scanning electron microscope (FESEM), Transmission scanning electron microscopy (TEM), X-ray photoelectron Spectroscopy (XPS), Nitrogen adsorption-desorption isotherms, Photoluminescence spectra (PL), UV–vis diffuse reflectance (DRS) and photodegradable tests. The results show that all samples are biphases TiO₂ (anatase and TiO₂(B)). In addition, with the increment of titanium source, the microstructure of three samples have changed from small 3D aggregates to big 3D aggregates composed of 2D nanosheets, and the proportion of the anatase phase in three products and the specific surface area (BET) of the samples gradually increased, which not only can suppress the recombination of photogenerated electrons and holes, and can also enhance the photodegradable performance and the adsorption performance of three products on organic pollutants RhB. The 2.5-TiO₂ Ss exhibited the best photodegradable performance among three samples. Meanwhile, the 2.5-TiO₂ Ss also had a good cycle stability and low performance loss (8%).     

Reliable high strength alumina fabricated by DCC-HVCI using submicron calcium citrate complex

Ceramics with high strength and reliability are highly demanded in engineering applications. In this paper, a modified direct coagulation casting via high valence counter ions (DCC-HVCI) method for alumina using calcium citrate complex assisted by glycerol diacetate was investigated. Calcium citrate complex suspensions were prepared by mixing tri-ammonium citrate and calcium chloride in water. Effect of reaction time on the chelating properties of the prepared suspensions was investigated. Concentrated alumina suspensions with a solid loading of 50 vol% were prepared by mixing the calcium citrate complex suspensions and alumina powder at pH of 10.5. Then the suspensions were coagulated by adding 3–6 vol% glycerol diacetate at temperatures of 40–70 °C for 2–6 h. The compressive strength of the coagulated wet samples is in the range 1.1–2.4 MPa. Alumina ceramics sintered at 1550 °C shows homogeneous microstructures with flexural strength and Weibull modulus of 455±17 MPa and 30, respectively.     

Phase evolution and thermal stability of novel high-entropy (Mo0.2Nb0.2Ta0.2V0.2W0.2)Si2 ceramics

Owing to the high melting points and high-temperature stability, transition-metal disilicides are potential components for aerospace, automotive, and industrial engineering applications. However, unwanted oxidation known as PEST oxidation severely limits their application owing to the formation of volatile transition metal oxides, especially in the temperature range of 500–1000 °C. To overcome this problem, a new class of high-entropy disilicides, (Mo_0.2Nb_0.2Ta_0.2V_0.2W_0.2)Si₂, was selected by first-principles calculations and then successfully fabricated using a hot-pressing sintering technique. Furthermore, the phase evolution, thermal expansion behavior, thermal conductivity, and oxidation behavior were systematically investigated. Compared with MoSi₂, (Mo_0.2Nb_0.2Ta_0.2V_0.2W_0.2)Si₂ possessed a lower thermal conductivity (10.9–14.7 W·m^?1·K^?1) at 25–1000 °C, higher thermal expansion coefficients (8.6 ± 1.3^–6 K^–1) at 50–1200 °C, and especially an excellent thermal stability at 500–1000 °C owing to slow diffusion and selective oxidation. This work provides a strong foundation for the synthesis and application of high-entropy disilicides.     

Electrically conductive aluminosilicate/graphene nanocomposite

Highly electrically conductive ceramic material based on aluminosilicate/graphene nanocomposite has been prepared by high pressure (400 MPa) compaction of montmorillonite intercalated with polyaniline followed with the high temperature (1400 °C) treatment in argon atmosphere. Tablets pressed from polyaniline/montmorillonite intercalate exhibits strong texture due to the disk-shaped montmorillonite particles and, consequently, the high anisotropy in conductivity. The high temperature induced phase transformation of montmorillonite into cristobalite and mullite preserved the aluminosilicate layered structure and created good conditions for formation of graphene sheets from polyaniline layers intercalated in montmorillonite. Therefore, the texture and anisotropy in conductivity remain preserved in resulting aluminosilicate/graphene tablets, while the in-plane conductivity in aluminosilicate/graphene tablets is 23,000× higher than the conductivity of uncalcined polyaniline/montmorillonite tablets. Simple fabrication method of aluminosilicate/graphene tablets is very promising for the manufacturing of the electrically conductive and tough ceramic material, which can be exposed to corrosive environment as well as to high temperatures.     

Real-time control of power systems using nodal prices

This article presents a novel control scheme for achieving optimal power balancing and congestion management in electrical power systems via nodal prices. We develop a dynamic controller that guarantees economically optimal steady-state operation while respecting all line flow constraints in steady-state. A benchmark example illustrates the effectiveness of the proposed control scheme.