624 research outputs found
The Impact of Airline Differentiation on Marginal Cost Pricing at UK Airports
No full textAirport pricing is a central issue in international transport policies, which tend to support pricing schemes based on marginal operating costs. This paper aims to provide empirical evidence in support of increased differentiation in airport charges on the basis of marginal passenger costs being sensitive to the type of airline, i.e. full-service, low-cost, and charter. To that end, both long- and short-run multi-output cost functions are estimated over an unbalanced pool database of 29 UK airports observed between 1995 and 2009. The passenger output is hedonically-adjusted in order to introduce the desired level of disaggregation while also keeping a parsimonious specification. Results show that low-cost passengers impose significantly lower costs to airport infrastructure than those from either full-service or charter airlines. A full schedule of marginal and average incremental cost estimates for the combined passenger categories is provided for all sample airports. Taking into account the existence of returns to scale and economies of capacity, this provides a useful guide for optimal pricing of aeronautical infrastructure under either single- or dual-till regulations
Dimensions of the author citation potential
No full textThe citation potential is a measure of the probability of being cited. Obviously, it is different among fields of science because of systematic differences in publication and citation behaviour across disciplines. In the past, the citation potential was studied at journal level considering the average number of references in established groups of journals. In this paper, some characterizations of the author’s scientific research through three different research dimensions are proposed: production (journal papers), impact (journal citations), and reference (bibliographical sources). An empirical application, in a set of 120 randomly selected authors in four subject areas, shows that the ratio between production and impact dimensions is a normalized measure of the citation potential at the level of individual authors.41040
Interferometric inverse synthetic aperture radar experiment using an interferometric linear frequency modulated continuous wave millimetre-wave radar
No full textD. Felguera-Martín,1 J.-T. González-Partida,1 P. Almorox-González,1 M. Burgos-García,1 and B.-P. Dorta-Naranjo2 1Universidad Politécnica de Madrid, Ciudad Universitaria s/n, Grupo de Microondas y Radar. Departamento de Señales, Sistemas y Radiocomunicaciones, Madrid, Spain 2Universidad de Las Palmas de Gran Canaria, Departamento de Señales y Comunicaciones, Las Palmas de Gran Canaria, Spain An interferometric linear frequency modulated continuous wave (LFMCW) millimetre-wave radar is presented, along with the results of an experiment conducted to study the feasibility of using it in a future millimetre-wave interferometric inverse synthetic aperture radar (InISAR) system. First, a description of the radar is given. Then, the signal processing chain is described, with special attention to the phase unwrapping technique. The interferometric phase is obtained by unwrapping the prominent target's phase in each antenna using a sliding frame processing technique. Cell migration issues in this method are also addressed. Simulations were carried out to illustrate and assess the processing chain and to show the effects of multipath echoes on the height measurement. In the real experiment, the range, speed and height of a moving target were tracked over consecutive inverse synthetic aperture radar (ISAR) image frames, verifying the performance of the whole system
Hábitos de publicación y citación según campos científicos: Principales diferencias a partir de las revistas JCR
No full textJournals’ impact indicators are not comparable among scientific fields because of systematic differences in publication and citation habits. In this work, the impact factor was decomposed into five independent variables, as applied to journal category, fields, and areas considered in the databases of the leading provider of science indicators, Thomson Reuters. A Principal Component Analysis was employed to find the sources of the variance and a Cluster Analysis was used to detect similarities. In spite of systematic differences between disciplines, the principal components explain 78% of the total variance. From the statistical point of view, some categories of Science are closer to the Social Sciences than to Science and vice versa.Los indicadores de impacto de revistas no son comparables entre campos científicos debido a las diferencias significativas en los hábitos de publicación y citación. En este trabajo se presenta una descomposición del factor de impacto en cinco variables independientes. Esta descomposición se aplica a las categorías de revista, campos y áreas considerados en las bases de datos del principal proveedor de indicadores científicos, Thomson Reuters. Para localizar las fuentes de la varianza se emplea un Análisis de Componentes Principales y para detectar las semejanzas se utiliza un Análisis Cluster. A pesar de las diferencias sistemáticas entre disciplinas, las componentes principales explican el 78% de la varianza total. Existen categorías de Ciencias que están más próximas, desde el punto de vista estadístico, de algunas Ciencias Sociales que del resto de Ciencias y viceversa
An approach to the author citation potential: measures of scientific performance which are invariant across scientific fields
No full textThe citation potential is a measure of the probability of being cited. Obviously, it is different among fields of science, social science, and humanities because of systematic differences in publication and citation behaviour across disciplines. In the past, the citation potential was studied at journal level considering the average number of references in established groups of journals (for example, the crown indicator is based on the journal subject categories in the Web of Science database). In this paper, some characterizations of the author's scientific research through three different research dimensions are proposed: production (journal papers), impact (journal citations), and reference (bibliographical sources). Then, we propose different measures of the citation potential for authors based on a proportion of these dimensions. An empirical application, in a set of 120 randomly selected highly productive authors from the CSIC Research Centre (Spain) in four subject areas, shows that the ratio between production and impact dimensions is a normalized measure of the citation potential at the level of individual authors. Moreover, this ratio reduces the between-group variance in relation to the within-group variance in a higher proportion than the rest of the indicators analysed. Furthermore, it is consistent with the type of journal impact indicator used. A possible application of this result is in the selection and promotion process within interdisciplinary institutions, since it allows comparisons of authors based on their particular scientific research.149614671,2052,084Q1Q1SCIESSC
Indicador bibliométrico basado en el índice h
No full textEn este trabajo se proponen
soluciones que consideran las citas de aquellos artículos que pueden contribuir, con
una alta probabilidad, a incrementar el valor del índice h en el futuro
Estudio de la intensidad en el marco de la prosodia de Canarias1
No full textThis work aims at determining the importance of intensity within the research framework of Canarian prosody, by taking into account an acoustic and statistical study from a corpus of 648 sentences uttered in a formal speech style by Canarian informants from two diatopically opposed islands: El Hierro, which belongs to the western region of the Canarian Archipelago, and Fuerteventura, which belongs to the eastern region. With the obtained acoustic results, we have labelled the tonic vowels according to their intensity, by taking into account a differential threshold of 4 dB, which has been recently determined in a perceptive-type study (Dorta, Martín Gómez and Jorge Trujillo, in press). Furthermore, a statistical analysis has been carried out in R (R Core Team, 2015) and ULLRToolbox (Hernández-Cabrera, 2012). From the acoustic results obtained, the amplitude of the accentuated is found to be higher in the following circumstances: in the nuclear accent, the acute accent and the plain accent, the contrast tonic/ post-tonic, the declarative modality and pertaining to Fuerteventura. From the statistical results we highlight the importance of the contrast tonic/ post-tonic in the SPrep, which reflects the acoustically registered final descent in intensityEste trabajo tiene como objetivo determinar la importancia de la intensidad en el marco de investigación de la prosodia canaria, a partir del estudio acústico y estadístico de un corpus de 648 oraciones emitidas en un estilo formal de habla por informantes canarios procedentes de dos islas diatópicamente opuestas: una pertenece a la zona occidental del archipiélago canario (El Hierro) y la otra a la zona oriental (Fuerteventura). Con los resultados acústicos obtenidos, hemos etiquetado las vocales tónicas por su intensidad, teniendo en cuenta un umbral diferencial de 4 dB, determinado recientemente en un estudio de tipo perceptivo (Dorta, Martín Gómez y Jorge Trujillo, en prensa). El análisis estadístico de los datos se ha realizado con los programas R (R Core Team, 2015) y ULLRToolbox (Hernández-Cabrera, 2012). Según los resultados acústicos, la amplitud de la acentuada se ve favorecida en los contextos siguientes: núcleo entonativo, acento agudo y llano, contraste tónica-postónica, modalidad declarativa y pertenencia a Fuerteventura. Los resultados estadísticos destacan la relevancia del contraste entre tónica y postónica en el SPrep, reflejo del descenso final de intensidad registrado acústicamente
Porcentaje de artículos altamente citados: una medida comparable del impacto de revistas entre campos científicos
No full textCurrently the two most used bibliometric indicators for evaluating scholarly journals are the impact factor and the h-index. However, both indicators vary heavily depending on the scientific field, restricting comparability. In addition, the impact factor is not robust in dealing with articles with a large number of citations, while the h-index is dependent on the size of the journal. These limitations, when comparing journals of different sizes and fields, make it necessary to look to other journal impact factors that can be comparable between scientific fields, that are independent of the journal size, and that are also robust in the presence of items with a high number of citations. An alternative index is based on the percentage of highly cited articles in a journal. This paper empirically compares such an index with the impact factor and the h-index by using different time windows and levels of citation that can determine when a document can be considered as highly cited compared to others of the same year and discipline. The main outcome of this comparison suggests that the best index for obtaining data distributions that are comparable between scientific fields is by taking the 20% citation percentile over a three-year time frame for considering citations.Actualmente, los dos indicadores bibliométricos más empleados en la evaluación de revistas científicas son el índice de impacto y el índice h. Sin embargo, ambos indicadores dependen fuertemente del campo científico, lo que los hace no comparables entre campos. Además, el índice de impacto no es robusto a la presencia de artículos con un gran número de citas, mientras que el índice h depende del tamaño de la revista. Estas limitaciones a la hora de comparar revistas de diferentes tamaños y campos hace necesario considerar al mismo tiempo otros indicadores de impacto para revistas que sí puedan ser comparables entre campos, no dependan del tamaño de la revista y sean además robustos a la presencia de artículos con un elevado número de citas. Una alternativa es el porcentaje de artículos altamente citados en cada revista. En este trabajo se compara empíricamente este indicador con el índice de impacto y el índice h, y se analizan diferentes arcos temporales y cotas para que un documento pueda ser considerado altamente citado en comparación con otros del mismo año y campo. Como principal resultado se obtiene que un percentil del 20% y una ventana de citación de tres años producen distribuciones de datos más comparables entre campos científicos
Early detection of ectopic pregnancy : use of a sensitive urine pregnancy test and transvaginal ultrasonography
No full textWe performed a prospective study to evaluate the reliability of a rapid monoclonal antibody urine pregnancy test with a sensitivity limit of 20 mIU/mL combined with transvaginal ultrasonography in the early diagnosis of ectopic pregnancy in 116 women with subacute pelvic pain and a stable general condition. The diagnosis of tubal pregnancy was confirmed with laparoscopy in 100 of the 103 women with positive sensitive urine pregnancy tests and no intrauterine gestational sac at transvaginal ultrasonography. Laparoscopy revealed a hemorrhagic corpus luteum in four of the eight subjects with negative monoclonal antibody pregnancy tests and no intrauterine gestational sac, an ovarian cyst in three and a normal pelvis in one. Of the five women with a positive pregnancy test and an intrauterine gestational sac, two had a hemorrhagic corpus luteum, two a normal pelvis and one a tubal pregnancy at laparoscopy. The sensitivity of a monoclonal antibody urine pregnancy test and transvaginal ultrasonography combined for the diagnosis of ectopic pregnancy was 99%, and the specificity was 80%, with positive and negative predictive values of 97% and 92%, respectively
GIS-assisted modelling for debris flow hazard assessment based on the events of May 1998 in the area of Sarno, Southern Italy. Part I: Maximum run-out
No full textBased on the debris flow events that occurred in May 1998 in the area of Sarno, Southern
Italy, this paper presents an approach to simulate debris flow maximum run-out. On the
basis of the flow source areas and an average thickness of 1·2 m of the scarps, we estimated
debris flow volumes of the order of 104 and 105 m3. Flow mobility ratios (ΔH/L) derived from
the x, y, z coordinates of the lower-most limit of the source areas (i.e. apex of the alluvial fan)
and the distal limit of the flows ranged between 0·27 and 0·09. We performed regression
analyses that showed a good correlation between the estimated flow volumes and mobility
ratios. This paper presents a methodology for predicting maximum run-out of future debris
flow events, based on the developed empirical relationship. We implemented the equation
that resulted from the calibration as a set of GIS macros written in Visual Basic for Applications
(VBA) and running within ArcGIS. We carried out sensitivity analyses and observed
that hazard mapping with this methodology should attempt to delineate hazard zones with a
minimum horizontal resolution of 0·4 km. The developed procedure enables the rapid delineation
of debris flow maximum extent within reasonable levels of uncertainty, it incorporates
sensitivities and it facilitates hazard assessments via graphic user interfaces and with
modest computing resource
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