• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 348
  • 208
  • 135
  • 114
  • 78
  • 45
  • 44
  • 23
  • 12
  • 12
  • 12
  • 10
  • 9
  • 7
  • 2
  • Tagged with
  • 1130
  • 175
  • 153
  • 131
  • 119
  • 119
  • 119
  • 93
  • 76
  • 73
  • 68
  • 58
  • 57
  • 56
  • 53
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
201

Cold cloud climatology over Europe and the Mediterranean during the warm season from Meteosat IR imagery

Pinelli, Francesca <1980> 14 June 2010 (has links)
Thermal infrared (IR, 10.5 – 12.5 m) images from the Meteosat Visible and Infrared Imager (MVIRI) of cold cloud episodes (cloud top brightness temperature < 241 K) are used as a proxy of precipitating clouds to derive a warm season (May-August) climatology of their coherency, duration, span, and speed over Europe and the Mediterranean. The analysis focuses over the 30°-54°N, 15°W-40°E domain in May-August 1996-2005. Harmonic analysis using discrete Fourier transforms is applied together with a statistical analysis and an investigation of the diurnal cycle. This study has the objective to make available a set of results on the propagation dynamics of the cloud systems with the aim of assist numerical modellers in improving summer convection parameterization. The zonal propagation of cold cloud systems is accompanied by a weak meridional component confined to narrow latitude belts. The persistence of cold clouds over the area evidences the role of orography, the Pyrenees, the Alps, the Balkans and Anatolia. A diurnal oscillation is found with a maximum marking the initiation of convection in the lee of the mountains and shifting from about 1400 UTC at 40°E to 1800 UTC at 0°. A moderate eastward propagation of the frequency maximum from all mountain chains across the domain exists and the diurnal maxima are completely suppressed west of 5°W. The mean power spectrum of the cold cloud frequency distribution evidences a period of one day all over Europe disappearing over the ocean (west of 10°W). Other maxima are found in correspondence of 6 to 10 days in the longitudes from 15° W to 0° and indicate the activity of the westerlies with frontal passage over the continent. Longer periods activities (from 15 up to 30 days) were stronger around 10° W and from 5° W to 15° E and are likely related to the Madden Julian Oscillation influence. The maxima of the diurnal signal are in phase with the presence of elevated terrain and with land masses. A median zonal phase speed of 16.1 ms-1 is found for all events ≥ 1000 km and ≥ 20 h and a full set of results divided by years and recurrence categories is also presented.
202

The polarization of horizontal ground motion: an analysis of possible causes

Pischiutta, Marta <1980> 28 May 2010 (has links)
No description available.
203

Probabilistic tomography of atmospheric parameters from GNSS data

Ortolani, Alberto <1969> 16 May 2011 (has links)
The objective of the work is the evaluation of the potential capabilities of navigation satellite signals to retrieve basic atmospheric parameters. A capillary study have been performed on the assumptions more or less explicitly contained in the common processing steps of navigation signals. A probabilistic procedure has been designed for measuring vertical discretised profiles of pressure, temperature and water vapour and their associated errors. Numerical experiments on a synthetic dataset have been performed with the main objective of quantifying the information that could be gained from such approach, using entropy and relative entropy as testing parameters. A simulator of phase delay and bending of a GNSS signal travelling across the atmosphere has been developed to this aim.
204

Development of SuperEnsemble Techniques for the Mediterranean Ocean Forecasting System

Pistoia, Jenny <1983> 28 March 2012 (has links)
This research activity studied how the uncertainties are concerned and interrelated through the multi-model approach, since it seems to be the bigger challenge of ocean and weather forecasting. Moreover, we tried to reduce model error throughout the superensemble approach. In order to provide this aim, we created different dataset and by means of proper algorithms we obtained the superensamble estimate. We studied the sensitivity of this algorithm in function of its characteristics parameters. Clearly, it is not possible to evaluate a reasonable estimation of the error neglecting the importance of the grid size of ocean model, for the large amount of all the sub grid-phenomena embedded in space discretizations that can be only roughly parametrized instead of an explicit evaluation. For this reason we also developed a high resolution model, in order to calculate for the first time the impact of grid resolution on model error.
205

The role of the West African Monsoon in the tropical to mid-latitudes climate

Pasqui, Massimiliano <1971> 11 May 2012 (has links)
The interaction between atmosphere–land–ocean–biosphere systems plays a prominent role on the atmospheric dynamics and on the convective rainfall distribution over the West Africa monsoon area during the boreal summer. In particular, the initialization of convective systems in the Sub – Sahelian region has been directly linked to soil moisture heterogeneities identified as the major triggering, development and propagation of convective systems. The present study aims at investigating African monsoon large scale convective dynamics and rainfall diurnal cycle through an exploration of the hypothesis behind the mechanisms of a monsoon phenomenon as an emergence of a collective dynamics of many propagating convective systems. Such hypothesis is based on the existence of an internal self – regulation mechanism among the various components. To achieve these results a multiple analysis was performed based on remote sensed rainfall dataset, and global and regional modelling data for a period of 5 seasons: 2004 - 2008. Satellite rainfall data and convective occurrence variability were studied for assessing typical spatio – temporal signatures and characteristics with an emphasis to the diurnal cycle footprint. A global model and regional model simulation datasets, specifically developed for this analysis and based on Regional Atmospheric Modelling System – RAMS, have been analysed. Results from numerical model datasets highlight the evidence of a synchronization between the destabilization of the convective boundary layer and rainfall occurrence due to the solar radiation forcing through the latent heat release. This supports the conclusion that the studied interacting systems are associated with a process of mutual adjustment of rhythms. Furthermore, this rainfall internal coherence was studied in relation to the West African Heat Low pressure system, which has a prominent role in the large scale summer variability over the Mediterranean area since it is acting as one of dynamic link between sub tropical and midlatitudes variability.
206

Genome characterization through a mathematical model of the genetic code: an analysis of the whole chromosome 1 of A. thaliana

Properzi, Enrico <1976> 18 February 2013 (has links)
The objective of this work is to characterize the genome of the chromosome 1 of A.thaliana, a small flowering plants used as a model organism in studies of biology and genetics, on the basis of a recent mathematical model of the genetic code. I analyze and compare different portions of the genome: genes, exons, coding sequences (CDS), introns, long introns, intergenes, untranslated regions (UTR) and regulatory sequences. In order to accomplish the task, I transformed nucleotide sequences into binary sequences based on the definition of the three different dichotomic classes. The descriptive analysis of binary strings indicate the presence of regularities in each portion of the genome considered. In particular, there are remarkable differences between coding sequences (CDS and exons) and non-coding sequences, suggesting that the frame is important only for coding sequences and that dichotomic classes can be useful to recognize them. Then, I assessed the existence of short-range dependence between binary sequences computed on the basis of the different dichotomic classes. I used three different measures of dependence: the well-known chi-squared test and two indices derived from the concept of entropy i.e. Mutual Information (MI) and Sρ, a normalized version of the “Bhattacharya Hellinger Matusita distance”. The results show that there is a significant short-range dependence structure only for the coding sequences whose existence is a clue of an underlying error detection and correction mechanism. No doubt, further studies are needed in order to assess how the information carried by dichotomic classes could discriminate between coding and noncoding sequence and, therefore, contribute to unveil the role of the mathematical structure in error detection and correction mechanisms. Still, I have shown the potential of the approach presented for understanding the management of genetic information.
207

Radar based improvements and diagnosis of the convective capabilities of the cosmo-2 model

Laudanna Del Guerra, Franco <1977> 16 April 2013 (has links)
In the last few years the resolution of numerical weather prediction (nwp) became higher and higher with the progresses of technology and knowledge. As a consequence, a great number of initial data became fundamental for a correct initialization of the models. The potential of radar observations has long been recognized for improving the initial conditions of high-resolution nwp models, while operational application becomes more frequent. The fact that many nwp centres have recently taken into operations convection-permitting forecast models, many of which assimilate radar data, emphasizes the need for an approach to providing quality information which is needed in order to avoid that radar errors degrade the model's initial conditions and, therefore, its forecasts. Environmental risks can can be related with various causes: meteorological, seismical, hydrological/hydraulic. Flash floods have horizontal dimension of 1-20 Km and can be inserted in mesoscale gamma subscale, this scale can be modeled only with nwp model with the highest resolution as the COSMO-2 model. One of the problems of modeling extreme convective events is related with the atmospheric initial conditions, in fact the scale dimension for the assimilation of atmospheric condition in an high resolution model is about 10 Km, a value too high for a correct representation of convection initial conditions. Assimilation of radar data with his resolution of about of Km every 5 or 10 minutes can be a solution for this problem. In this contribution a pragmatic and empirical approach to deriving a radar data quality description is proposed to be used in radar data assimilation and more specifically for the latent heat nudging (lhn) scheme. Later the the nvective capabilities of the cosmo-2 model are investigated through some case studies. Finally, this work shows some preliminary experiments of coupling of a high resolution meteorological model with an Hydrological one.
208

Global scale investigation of cirrus clouds properties using active and passive sensors

Veglio, Paolo <1982> 16 April 2013 (has links)
A year of satellite-borne lidar CALIOP data is analyzed and statistics on occurrence and distribution of bulk properties of cirri are provided. The relationship between environmental and cloud physical parameters and the shape of the backscatter profile (BSP) is investigated. It is found that CALIOP BSP is mainly affected by cloud geometrical thickness while only minor impacts can be attributed to other quantities such as optical depth or temperature. To fit mean BSPs as functions of geometrical thickness and position within the cloud layer, polynomial functions are provided. It is demonstrated that, under realistic hypotheses, the mean BSP is linearly proportional to the IWC profile. The IWC parameterization is included into the RT-RET retrieval algorithm, that is exploited to analyze infrared radiance measurements in presence of cirrus clouds during the ECOWAR field campaign. Retrieved microphysical and optical properties of the observed cloud are used as input parameters in a forward RT simulation run over the 100-1100 cm-1 spectral interval and compared with interferometric data to test the ability of the current single scattering properties database of ice crystal to reproduce realistic optical features. Finally a global scale investigation of cirrus clouds is performed by developing a collocation algorithm that exploits satellite data from multiple sensors (AIRS, CALIOP, MODIS). The resulting data set is utilized to test a new infrared hyperspectral retrieval algorithm. Retrieval products are compared to data and in particular the cloud top height (CTH) product is considered for this purpose. A better agreement of the retrieval with the CALIOP CTH than MODIS is found, even if some cases of underestimation and overestimation are observed.
209

Lietuvos bendrojo pobūdžio stacionarinių asmens sveikatos priežiūros įstaigų veiklos efektyvumo įvertinimas / Evaluation of performance efficiency of acute hospitals in Lithuania

Kalibatas, Vytenis 30 January 2006 (has links)
1. Introduction Pastaraisiais metais, ypač reformuojant stacionarinę sveikatos priežiūrą, vis didesnis dėmesys skiriamas ligoninių veiklos vertinimui daugelyje šalių, nes stacionarinei sveikatos priežiūrai skiriama 45-75% visų sveikatos priežiūrai skirtų lėšų (1). Vertinant ligoninės veiklos rodiklius, dažniausiai apsiribojama pagrindine jos funkcija - paslaugų teikimu (2-4). Tradiciškai sveikatos priežiūros organizacijų veikla yra vertinama pagal paslaugų apimtis (5), o gydytų pacientų skaičius yra labiausiai paplitęs stacionarinių sveikatos priežiūros įstaigų veiklos rodiklis. Nepaisant to, kad šiuolaikiniai sveikatos priežiūros organizacijų veiklos vertinimo modeliai apima daug įvairių aspektų ir dimensijų (tokių kaip paslaugų kokybė, pajėgumas gauti reikiamus išteklius, pajėgumas reaguoti į visuomenės poreikius, veiklos efektyvumas, veiksmingumas, produktyvumas, našumas, organizacijos kultūra ir pan.), sveikatos priežiūros įstaigų veiklos vertinimas pagal pacientų (paslaugų atvejų) skaičių išlieka kaip vienas pagrindinių rodiklių jau vien dėl to, kad daugumoje sveikatos sistemų apmokėjimas sveikatos priežiūros organizacijoms yra pagrįstas gydytų pacientų ar suteiktų paslaugų apimtimis (6,7). Tačiau analizuojant vien tik stacionarinėje asmens sveikatos priežiūros įstaigoje (ASPĮ) gydytų pacientų (atvejų) skaičių per tam tikrą laiko periodą, daryti išvadas apie ligoninės veiklą ir ypač lyginti su kitomis ligoninėmis yra pakankamai sudėtinga ir net nevisiškai objektyvu... [to full text]
210

Comparing Obesity Trends in Rural Versus Urban Peru from 1991 to 2005

Timar, Dana 06 November 2009 (has links)
Background: The changes in diet and physical activity in populations over time has been described as the nutrition transition. It is currently thought that many developing nations are in a transition from the receding famine to the degenerative disease profile as these nations adopt “western diets” and the people become more sedentary. The literature has shown a unique relationship between Gross National Income (GNI) per capita and obesity. At or above a GNI per capita of $2500 (US), prevalence of obesity increase among lower socioeconomic status (SES) groups and falls in upper SES groups. Methods: To examine this transition in one country, data were analyzed from Peru. The data were obtained from the United States Agency for International Development’s Demographic Health Surveys administered from 1991 to 2008. During this time Peru’s GNI per capita increased from $1090 to $3990. For the analysis, all non pregnant women aged 15 to 49 who had body mass index (BMI) measurements taken during the survey were included. Prevalence ratios of underweight, normal weight, overweight, and obesity were compared for place of residence (urban or rural) and educational attainment for all four surveys completed during those years (1991-2, 1996, 2000, and 2004-5). Food consumption patterns in children from the same household were examined for surveys completed in 2000 and 2004. Results and Discussion: Over the survey period (1991-2005), average BMI measurements and obesity prevalence increased in all women in Peru from 8-12%. However, both average BMI and prevalence of obesity increased more rapidly in rural women. In terms of educational attainment, a proxy for SES, obesity was highest among urban women with higher educational attainment initially. However, it increased among other educational attainment groups over time. For rural women, obesity was highest among those with lower educational attainment over time. The consumption of oils, fats, and butters increased from 2000 to 2004 in both urban and rural children with the greatest increase among rural children. Based on the results, it appears that there is evidence of increased prevalence of obesity in rural compared to urban women in Peru from 1991-2005 suggestive of the nutrition transition from receding famine to degenerative disease. The more rapid increase in both BMI and obesity in rural women may be the result of increased access to different food products such as oils, fats and butters and increased consumption in rural areas. More research should be done to further clarify factors affecting this transition and the public health community and the government should examine and attempt to prevent further increase in obesity in Peru.

Page generated in 0.045 seconds