Search results for "Variable"
showing 10 items of 1674 documents
A comparison of two different formulations for Arc Routing Problems on Mixed graphs
2006
[EN] Arc routing problems on mixed graphs have been modelled in the literature either using just one variable per edge or associating to each edge two variables, each one representing its traversal in the corresponding direction. In this paper, and using the mixed general routing problem as an example, we compare theoretical and computationally both formulations as well as the lower bounds obtained from them using Linear Programming based methods. Extensive computational experiments, including some big and newly generated random instances, are presented.
A versatile mechanized setup for controlled experiments in archeology
2020
Experimentation has always played an important role in archeology, in particular to create reference collections for use-wear studies. Different types of experiments can answer different questions; all types should therefore be combined to obtain a holistic view. In controlled experiments, some factors are tested, while the other factors are kept constant to improve the signal-to-noise ratio. Yet, controlled experiments have been conducted with variable degrees of control. Although they seem decoupled from archeological applications, mechanized experiments and the robust causal relationships they measure are critical to answer archeological questions like understanding the processes of use-…
Semi-Supervised Support Vector Biophysical Parameter Estimation
2008
Two kernel-based methods for semi-supervised regression are presented. The methods rely on building a graph or hypergraph Laplacian with both the labeled and unlabeled data, which is further used to deform the training kernel matrix. The deformed kernel is then used for support vector regression (SVR). The semi-supervised SVR methods are sucessfully tested in LAI estimation and ocean chlorophyll concentration prediction from remotely sensed images.
Determinants and efficiency of Pakistan's chemical products' exports: An application of stochastic frontier gravity model.
2019
The estimation of efficiency of industry-specific exports is very important to find exports' gap and to frame exports promotion policy for targeted industry. This study attempts to investigate the main determinants of chemical products' exports of Pakistan with 62 trading partners by applying Stochastic Frontier Analysis (SFA) on an augmented gravity model for a period 1995-2015. The results corroborate that chemical products' exports follow gravity patterns. This study finds a negative and significant impact of import tariff on exports of chemical products while the positive impact of devaluation has been observed. Further, the estimations also take into account the impact of Preferential …
The Close T Tauri Binary System V4046 Sgr: Rotationally Modulated X-Ray Emission from Accretion Shocks
2012
We report initial results from a quasi-simultaneous X-ray/optical observing campaign targeting V4046 Sgr, a close, synchronous-rotating classical T Tauri star (CTTS) binary in which both components are actively accreting. V4046 Sgr is a strong X-ray source, with the X-rays mainly arising from high-density (n_e ~ 10^(11-12) cm^(-3)) plasma at temperatures of 3-4 MK. Our multiwavelength campaign aims to simultaneously constrain the properties of this X-ray emitting plasma, the large scale magnetic field, and the accretion geometry. In this paper, we present key results obtained via time-resolved X-ray grating spectra, gathered in a 360 ks XMM-Newton observation that covered 2.2 system rotatio…
Effects of radiation in accretion regions of classical T Tauri stars
2019
Models and observations indicate that the impact of matter accreting onto the surface of young stars produces regions at the base of accretion columns, in which optically thin and thick plasma components coexist. Thus an accurate description of these impacts requires to account for the effects of absorption and emission of radiation. We study the effects of radiation emerging from shock-heated plasma in impact regions on the structure of the pre-shock downfalling material. We investigate if a significant absorption of radiation occurs and if it leads to a pre-shock heating of the accreting gas. We developed a radiation hydrodynamics model describing an accretion column impacting onto the su…
CSI 2264: Simultaneous optical and X-ray variability in pre-main sequence stars. I. Time resolved X-ray spectral analysis during optical dips and acc…
2017
Pre-main sequence stars are variable sources. In stars with disks, this variability is related to the morphology of the inner circumstellar region (<0.1 AU) and that of the photosphere and corona, all impossible to be spatially resolved with present day techniques. This has been the main motivation for the Coordinated Synoptic Investigation of NGC 2264. In this paper, we focus on the stars with disks. We analyze the X-ray spectral properties extracted during optical bursts and dips in order to unveil the nature of these phenomena. We analyze simultaneous CoRoT and Chandra/ACIS-I observations to search for coherent optical and X-ray flux variability in stars with disks. Then, stars are an…
Air pollution in European countries and life expectancy—modelling with the use of neural network
2019
Abstract The present paper discusses a novel methodology based on neural network to determine air pollutants’ correlation with life expectancy in European countries. The models were developed using historical data from the period 1992–2016, for a set of 20 European countries. The subject of the analysis included the input variables of the following air pollutants: sulphur oxides, nitrogen oxides, carbon monoxide, particulate matters, polycyclic aromatic hydrocarbons and non-methane volatile organic compounds. Our main findings indicate that all the variables significantly affect life expectancy. Sensitivity of constructed neural networks to pollutants proved to be particularly important in …
Wind speed and temperature trends impacts on reference evapotranspiration in Southern Italy
2014
In this study, the impacts of both temperature and wind speed trends on reference evapotranspiration have been assessed using as a case study the Southern Italy, which present a wide variety of combination of such climatic variables trends in terms of direction and magnitude. The existence of statistically significant trends in wind speed and temperature from observational datasets, measured in ten stations over Southern Italy during the period 1968–2004, has been investigated. Time series have been examined using the Mann–Kendall nonparametric statistical test in order to detect possible evidences of wind speed and temperature trends at different temporal resolution and significance level.…
Implementation of pressure reduction valves in a dynamic water distribution numerical model to control the inequality in water supply
2013
The analysis of water distribution networks has to take into account the variability of users' water demand and the variability of network boundary conditions. In complex systems, e.g. those characterized by the presence of local private tanks and intermittent distribution, this variability suggests the use of dynamic models that are able to evaluate the rapid variability of pressures and flows in the network. The dynamic behavior of the network also affects the performance of valves that are used for controlling the network. Pressure reduction valves (PRVs) are used for controlling pressure and reducing leakages. Highly variable demands can produce significant fluctuation of the PRV set po…