Search results for "TFA"

Urban water quality modelling: a parsimonious holistic approach for a complex real case study

2010

In the past three decades, scientific research has focused on the preservation of water resources, and in particular, on the polluting impact of urban areas on natural water bodies. One approach to this research has involved the development of tools to describe the phenomena that take place on the urban catchment during both wet and dry periods. Research has demonstrated the importance of the integrated analysis of all the transformation phases that characterise the delivery and treatment of urban water pollutants from source to outfall. With this aim, numerous integrated urban drainage models have been developed to analyse the fate of pollution from urban catchments to the final receiving …

Dades massives i estadística: La perspectiva d'un estadístic

2014

Les dades massives (big data) representen un recurs sense precedents per a afrontar reptes científics, econòmics i socials, però també incrementen la possibilitat de traure conclusions enganyoses. Per exemple, l’ús d’enfocaments basats exclusivament en dades i que es despreocupen de comprendre el fenomen en estudi, que s’orienten a un objectiu esmunyedís i canviant, que no tenen en compte problemes determinants en la recopilació de dades, que resumeixen o «cuinen» inadequadament les dades i que confonen el soroll amb el senyal. Repassarem alguns casos reeixits i il·lustrarem com poden ajudar els principis de l’estadística a obtenir una informació més fiable de les dades. També abordarem els…

Portfolio diversification in the sovereign credit swap markets

2018

We develop models for portfolio diversification in the sovereign credit default swaps (CDS) markets and show that, despite literature findings that sovereign CDS spreads are affected by global factors, there is sufficient idiosyncratic risk to be diversified. However, we identify regime switching in the times series of CDS spreads and spread returns, and the optimal diversified strategies can be regime dependent. The developed models trade off the CVaR risk measure against expected return, consistently with the statistical properties of spreads. We consider three investment strategies suited for different CDS market participants: for investors with long positions, speculators that hold unco…

Nemastoma bidentatum (Arachnida: Opiliones: Nemastomatidae): neu für Deutschland und die Tschechische Republik

2007

Nemastoma bidentatum (Arachnida: Opiliones: Nemastomatidae): first records for Germany and the Czech Republic. N. bidentatum Roewer, 1914 was found at two places in Germany: first on the island "Harriersand" in the Weser river (Lower Saxony), second on the banks of the river Elbe in the Elbsandsteingebirge (Saxony). Adjacent to the latter locality an occurrence in the Czech Republic could be located close to the German/Czech border in the floodplain of the river Elbe as well. These records are the first for Germany and the Czech Republic. They enlarge the distribution area of N. bidentatum remarkably in both a northern and a western direction. The two populations show conspicuous difference…

Incorporating stand level risk management options into forest decision support systems

2018

Aim of study:  To examine methods of incorporating risk and uncertainty to stand level forest decisions. Area of study: A case study examines a small forest holding from Jonkoping, Sweden. Material and methods: We incorporate empirically estimated uncertainty into the simulation through a Monte Carlo approach when simulating the forest stands for the next 100 years. For the iterations of the Monte Carlo approach, errors were incorporated into the input data which was simulated according to the Heureka decision support system. Both the Value at Risk and the Conditional Value at Risk of the net present value are evaluated for each simulated stand. Main results: Visual representation of the er…

Determination of hydroxylated benzophenone UV filters in sea water samples by dispersive liquid-liquid microextraction followed by gas chromatography…

2010

A new analytical method for the determination of four hydroxylated benzophenone UV filters (i.e. 2-hydroxy-4-methoxybenzophenone (HMB), 2,4-dihydroxybenzophenone (DHB), 2,2'-dihydroxy-4-methoxybenzophenone (DHMB) and 2,3,4-trihydroxybenzophenone (THB)) in sea water samples is presented. The method is based on dispersive liquid-liquid microextraction (DLLME) followed by gas chromatography-mass spectrometry (GC-MS) determination. The variables involved in the DLLME process were studied. Under optimized conditions, 1000 microL of acetone (disperser solvent) containing 60 microL of chloroform (extraction solvent) were injected into 5 mL of aqueous sample adjusted to pH 4 and containing 10% NaCl…

On the Consistent Use of VaR in Portfolio Performance Evaluation: A Cautionary Note

2010

The portfolio performance measures based on the Value-at-Risk (VaR) concept have gained widespread popularity and are often used in empirical studies. Unfortunately, we have noticed that in majority of empirical studies a VaR-based performance measure is used inconsistently. The goal of this paper is, therefore, to emphasize how to consistently use VaR in portfolio performance evaluation. We also elaborate on a simple framework that allows to derive a general formula for a portfolio performance measure which is not limited to the use of VaR-based reward and risk measures, but is valid for all reward and risk measures that satisfy a few plausible properties.

Cryptic diversity, niche displacement and our poor understanding of taxonomy and ecology of aquatic microorganisms

2022

AbstractThe analysis of ecological niche is an important task to correctly identify the role exerted by species within ecosystems, to assess their vulnerability, to plan effective measures addressed at fulfilling the postulates of biological conservation, and ultimately to prevent biodiversity loss. However, for the majority of organisms our knowledge about the actual extent of their ecological niche is quite limited. This is especially true for microscopic organisms. Evidence exists that in different geographical areas allegedly conspecific populations can show different, if not antithetical, ecological requirements and not-overlapping ecological niches. This opinion paper discusses whethe…

2014

This paper presents a mathematical model for robust production planning. The model helps fashion apparel suppliers in making decisions concerning allocation of production orders to different production plants characterized by different lead times and production costs, and in proper time scheduling and sequencing of these production orders. The model aims at optimizing these decisions concerning objectives of minimal production costs and minimal tardiness. It considers several factors such as the stochastic nature of customer demand, differences in production and transport costs and transport times between production plants in different regions. Finally, the model is applied to a case study.…

Studying the stability of Solvent Red 19 and 23 as excise duty components under the influence of controlled factors

2020

Abstract In this study, we examine the chemical stability of two disazo dyes, namely Solvent Red 19 and 23 (SR 19 and SR 23), under simulated conditions. Both dyes are considered to be chemically stable under normal exploitation conditions and therefore, are used extensively as excise duty components that enable a rapid visual verification of the tax levels that were imposed on fuel products as well as identifying fuel usage. However, the results from this study confirmed that the colour of the samples that had been fortified with either SR 19 or SR 23 fades under the influence of external conditions such as UV-A irradiation and temperature over time. The UV-A irradiation was the dominant f…