Robust estimation in linear regression models with fixed effects

In this work we extend the procedure proposed by Peña and Yohai (1999) for computing robust regression estimates in linear models with fixed effects. We propose to calculate the principal sensitivity components associated to each cluster and delete the set of possible outliers based on an appropriate robust scale of the residuals. Some advantage of our robust procedure are: (a) it is computationally low demanding, (b) it is able to avoid the swamping effect often present in similar methods, (c) it is appropriate for contamination in the error term (vertical outliers) and possibly masked high leverage points (horizontal outliers). The performance of the robust procedure is investigated through several simulation studies.Fixed effects models, Outlier detection, Principal sensitivity vector

Temporary Employment in Tourism Activities: Regional differences in Spain

The great capacity of tourism to provide employment, especially between groups of workers with a more difficult insertion in the labour market, is one of its most well-known positive aspects. However Tourism employment is often described as low skilled, which is associated with average lower wages, higher percentage of fixed-term contracts, and longer working day than other industries. Nevertheless, this is not true for all tourism activities. Although this description could be close for hotels and restaurants labour market, it is completely different for land transport, travel agencies and tour operators activities. This could be related with the fact that each characteristic tourism industry provides a different percentage of his output to tourists, as it is shown in the Spanish Tourism Satellite Account. Given that, the aim of this paper is to analyse what factors can determine the incidence of temporary employment in Tourism activities in Spain and to discuss regional differences. As result, our first step is to identify the labour market characteristics of the different tourism activities. These results are clear influenced by the particularities of the different activities (labour market of transport activities is very different from hotels and restaurants activities) and not by a tourism characteristic. Thus, the second step is to analyse how tourism influence in the labour-market conditions after controlling for the particularities of the different tourism activities. In this case, we focus in just one characteristic of the labour market very associated with low-quality jobs; the share of workers with fixed-term jobs. Although Spain is one of the countries with the highest arrivals of tourists, those are not equally distributed by regions. This allows us to identify the degree of specialization of each region in tourism, and to analyse its impact in the share of workers with fixed-term contracts. Results show that the highest tourism specialization of the region decreases the share of workers with fixed-term contracts, after isolating the particularities of the different tourism activities. It seems that this low-quality characteristic disappear with the development of the sector in some regions.

Smart navigation system for electric vehicles charging

In the present time, there is still a lack of popularity in the use of electric vehicles, because of the actual disadvantages that they have. For this work presents the process of research and development of a web based application with the main purpose of helping Electric Vehicle owners decide the Charging Station that, by selecting it to go and charge their vehicles, represents the lowest cost in time or money (depending on their priorities) when they need to go to charge their electric vehicles and to give them less time or energy consuming route to follow in order to arrive to the charging station selected. This, to reduce the concern of the users about if the can or not arrive to a charging station. To do this, the application has been developed with several features to help the users. First, the application has the feature of being accessed from multiple type of devices. Second, the application has the feature of detecting the users locations using Global Positioning System. Third, the application has the ability to find the charging stations and their coordinates that are near to the users. Fourth, the application has the ability to formulate the route with the lowest time or energy cost between the users locations and the charging stations. Fifth, after creating all the routes, the application shows the users the parameters of every route and charging station. Sixth, the application has the ability to let the users decide the priority to select the charging station. Seventh, the application let the users decide the battery percentage that they want their vehicles to have after charging them. This application was created using mostly Javascript language, Expressjs as the framework and for the user interface jQuery. Moreover, MongoDB and PosgreSQL were used as databases. Furthermore, some web services like Amazon Web Services were used for server hosting, OpenStreetMap for obtaining GeoSpatial data, Open Charging Map for obtaining charging stations coordinates and data and Fuel Economy for obtaining vehicles data were used to complement the application. For the route formulation, Dijkstra's algorithm and pgRouting was used. Results indicated that the application can successfully recommend routes and charging stations to the users with a reduction of 90\% of time needed against the less time consuming cheapest option when time is the priority and a reduction of 27 times the money needed for the fastest option when price is the priority. Meaning that the navigation system can successfully reduce the time or costs to adjust to the users necessities

The Effect of Rock Properties on Fracture Conductivity in the Marcellus Shale

Hydraulic fracturing is a stimulation technique that has made production from unconventional reservoirs such as shale formations economically feasible. This technique creates high conductivity paths that improve the communication between the reservoir and the wellbore. The success of this technique depends on the ability to fracture the rock and to maintain fracture conductivity. Therefore, in order to have a successful treatment, the effect of parameters such as formation properties, type of proppant and proppant concentration on fracture conductivity and fracture creation should be considered. This work investigates the relationship between fracture conductivity and formation properties for two different locations in the Marcellus shale. Multiple cores from the locations were collected to ensure repeatability in the results. The core samples were fractured parallel and perpendicular to the bedding planes in order to analyze the effect of anisotropy in fracture conductivity. Additionally, compressive triaxial tests were performed to obtain the rock mechanical properties in the elastic region until permanent deformation was reached, and X-ray Diffraction analysis was used to obtain mineralogy composition. The laboratory results were compared with previous fracture conductivity data and surface roughness data from the same Marcellus shale locations. The findings showed that the anisotropy effect is present for this formation and reflected in the fracture conductivity values, where samples parallel to the bedding plane seem to have higher Young’s Modulus. At proppant monolayer concentration the main mechanism for conductivity loss is proppant embedment, where due to the high localized stress, the rock-proppant interaction goes directly to permanent deformation of the rock. It was also observed that a higher Young’s Modulus helps to maintain the fracture width which translates in lower rate of conductivity loss with increasing closure stress. Rock mechanical properties have impact on fracture conductivity. This effect is less pronounced if a multilayer proppant concentration is used, where the proppant pack characteristics become an important parameter in fracture conductivity

Recent results on self-dual configurations on the torus

We review the recent progress on our understanding of self-dual SU(N) Yang-Mills configurations on the torus.Comment: Latex 3 pages, 1 figure. Contribution to the Lat99 Proceeding

Perturbative construction of self-dual configurations on the torus

We develop a perturbative expansion which allows the construction of non-abelian self-dual SU(2) Yang-Mills field configurations on the four-dimensional torus with topological charge 1/2. The expansion is performed around the constant field strength abelian solutions found by 't Hooft. Next to leading order calculations are compared with numerical results obtained with lattice gauge theory techniques.Comment: latex file. 32 pages and 4 figures(24 eps files

Capacity pricing schemes to implement open-access rail in Tanzania

We analyze alternative capacity pricing schemes (access charges) to implement an open-access railway system in Tanzania. We show that the implementation of variable access charges widely used in the railway industry may result in levels of traffic lower than the traffic operated by an integrated railway company. We propose the use of fixed access charges to avoid this problem and discuss the main advantages and disadvantages to implement them in the context of multiple freight train services in Tanzania

Atmospheric implications of untested carbonyl photochemistry: an evaluation using chemically explicit and global 3D modelling

From the millions of gaseous species present on Earth’s atmosphere, those containing the carbonyl group (C=O) are some of the most atmospherically important. While all organic species react with OH and other radicals, the C=O bond in carbonyls provides a chromophore for photolysis reactions. Consequently, carbonyls react quickly and are an important source of atmospheric radicals. Recent laboratory findings on the photochemistry of several aldehydes have yielded new photochemical and photophysical mechanisms that are of unknown importance in atmospheric chemistry, which paves the way for this thesis. Here, two atmospheric models, GEOS-Chem and AtChem2, were used to understand the implications and relevance of these untested and new carbonyl photochemistry findings on atmospheric sources and composition. The results of implementing the two models to explore carbonyl photochemistry are described in this thesis in five chapters. Two chapters explore the previously untested primary production of molecular hydrogen (H2) from a range of aldehydes. Both in AtChem2 and in GEOS-Chem, a 1% quantum yield for H2 was tested, based on experimental data for acetaldehyde photolysis. Globally, and under three different atmospheric settings (urban, pristine oceanic and pristine forested), both models showed that biogenic-related aldehydes (e.g., methylgyoxal and glycolaldehyde) make an important contribution to the chemical H2 production; GEOS-Chem showed that it is up to 10% throughout the troposphere (most influential in tropical regions). Results showed that including the previously unaccounted photolytic sources of H2 does not improve model biases but calls for more experimental research into the true H2channel quantum yields for the most important aldehydes. Following, in a collaborative project with the New South Wales state government framed within Australia’s potential migration to a H2 economy, we implemented the AtChem2 model to test the sensitivity of radicals (OH and HO2) to changes in H2 levels. Radicals and other gases (e.g., CH4, CH3OH) displayed sensitivity to increases in H2 levels, highlighting the necessity of careful consideration of a potential new source of H2 to the Australian atmosphere. In the next chapter, the atmospheric fate of trifluoroacetaldehyde (CF3CHO), a fluorinated carbonyl produced from the oxidation of a fourth-generation refrigerant (HFO-1234ze, CF3CF=CF2), was modelled. CF3CHO photolysis has been shown to be a source of fluoroform (HFC-23) in small yields. The degradation and deposition pathways of CF3CHO were modelled using AtChem2 to provide a range of values on the production of HFC-23. The modelling estimates show that CF3CHO could contribute up to 14.7% to the current HFC-23 global growth rate. Finally, a new mechanism called photophysical oxidation (PPO) in carbonyls was also studied using acetaldehyde as a benchmark compound. In acetaldehyde, PPO forms the peroxyacetyl radical, which affects peroxyacetylnintrate (PAN) formation. Results using GEOS-Chem showed that PPO in acetaldehyde could be responsible for 3% of the global chemical production of PAN. However, PPO is unlikely to be important when photolysis is not the dominant carbonyl degradation pathway. This thesis provides new insight into carbonyl photochemistry through modelling applications: A new H2 simulation in GEOS-Chem was developed; in which further research related to H2 can be performed, the possible generation of HFC-23 from a new secondary source was explored, and a new photophysical mechanism for carbonyls was assessed. Ultimately, the results from exploring carbonyl photochemistry throughout this PhD are intended to be used as guide for new laboratory research