Search results for "Statistica"
showing 10 items of 5969 documents
GDP Density Disparities in Old Europe: Theil Decomposition in Cross-Country Historical Perspective
2011
The political, social and economic aspects of Old Europe have experienced profound changes over the last century. The levels and variations of GDP provide a good, though partial, representation of these changes with specific reference to the economic development. According to historical data, GDP shows strong increases in Europe; among these countries also Italy. But, what can we say about the cross-country income inequality? In this paper, we analyze cross-country disparities of GDP density from 1870 to 2008 in fourteen western European countries. In particular, we use a Duro-Esteban decomposition of the Theil index to identify the separate contribution of GDP per capita and population den…
Regression imputation for Space-Time datasets with missing values
2009
Data consisting in repeated observations on a series of fixed units are very common in different context like biological, environmental and social sciences, and different terminology is often used to indicate this kind of data: panel data, longitudinal data, time series-cross section data (TSCS), spatio-temporal data. Missing information are inevitable in longitudinal studies, and can produce biased estimates and loss of powers. The aim of this paper is to propose a new regression (single) imputation method that, considering the particular structure and characteristics of the data set, creates a “complete” data set that can be analyzed by any researcher on different occasions and using diff…
Herding in the cryptocurrency market: CSSD and CSAD approaches
2018
Abstract We analyse the existence of herding in the cryptocurrency market through the cross-sectional standard (absolute) deviation of returns. Our results show that extreme dispersion of returns is explained by rational asset pricing models although it is possible to observe herding during down markets, which highlights the inefficiency and risk of cryptocurrencies. We also observe that the smallest digital currencies are herding with the largest ones, thus traders base their decisions on the performance of the main cryptocurrencies. However, the herding phenomenon cannot be solely attributed to Bitcoin, since the rest of the market is not herding with the main cryptocurrency.
Ab initio calculations of SrTiO3, BaTiO3, PbTiO3, CaTiO3, SrZrO3, PbZrO3 and BaZrO3 (001), (011) and (111) surfaces as well as F centers, polarons, K…
2014
In this paper, the review of recent results of calculations of surface relaxations, energetics, and bonding properties for ABO 3 perovskite (001), (011) and (111) surfaces using mostly a hybrid description of exchange and correlation is presented. Both AO and BO 2-terminations of the nonpolar (001) surface and A , BO , and O terminations of the polar (011) surface, as well as B and AO 3-terminations of the polar (111) surface were considered. On the AO -terminated (001) surface, all upper-layer A atoms relax inwards, while all second layer atoms relax outwards. For the BO 2-terminated (001) surface, in most cases, the largest relaxations are on the second-layer metal atoms. For almost all …
Emission of real phonons due to electron’s self-dressing in a covalent crystal
2011
A slow monoelectronic excitation in a covalent crystal at the temperature T=0 is analyzed. The interaction with zero-point longitudinal acoustic phonons leads to the formation of a dressed electronic state at an energy level lower than that of the initial bare state. This aspect of the dressing process is described here by hypothesizing that the excess of energy is released with the emission of real phonons. Specifically, this paper considers the transition probability from the bare monoelectronic state to a dressed state of the electron accompanied by real phonons and a deformation field. The spectrum of the real phonons emitted during the electronic self-dressing is calculated by applying…
Average Structure vs. Real Structure: Molecular Dynamics Studies of Silica
2003
The microscopic structure of a crystal and thermal fluctuations of the atoms constituting the crystal are intimately connected with the macroscopic elastic properties including mechanical stability. In some cases, however, the picture is more complex than that which is drawn in text books on solid state physics. (i) The instantaneous microscopic structure can deviate in a non-Gaussian way from the average structure even when domain disorder and/or crystal defects are absent. Quasi harmonic approximations may then turn out to be meaningless. (ii) The crystal is subject to external pressures that are sufficiently large in order to render the definition of elastic constants non unique. These t…
Multidimensional scaling and stock location assignment in a warehouse: an application
1999
By means of an application, in the present paper, the suitability of a multivariate statistical methodology, as multidimensional scaling (MDS), to solve an optimization problem is shown. In particular, considering the stock location assignment problem in the warehouse of a supermarket chain, the solution gained by applying MDS to a set of seven variables is compared with the one obtainable by considering the usual techniques applied in this context. A wide discussion of results is reported.
Machine learning risk prediction of mortality for patients undergoing surgery with perioperative SARS-CoV-2: the COVIDSurg mortality score
2021
The British journal of surgery 108(11), 1274-1292 (2021). doi:10.1093/bjs/znab183
Theresa May’s Representation of Reality in her Brexit Speeches
2020
This study analyses Theresa May’s three seminal Brexit speeches. These describe the kind of desirable post-Brexit EU-UK relationship that she envisioned, and together constitute a corpus of 18,532 words. The speeches can be considered as landmarks on a timeline that was initially meant to lead to the delivery of Brexit. It is hypothesized that there may be meaningful differences between the speeches, and that these affect the representation of reality. These in turn would have a bearing on May’s discursive self-representation as either an individualized or a collectivized social actor. To account for such representational values, the study draws on Halliday’s Transitivity System (1994), sta…
Phase Behavior of Active Swimmers in Depletants: Molecular Dynamics and Integral Equation Theory
2013
We study the structure and phase behavior of a binary mixture where one of the components is self-propelling in nature. The inter-particle interactions in the system were taken from the Asakura-Oosawa model, for colloid-polymer mixtures, for which the phase diagram is known. In the current model version the colloid particles were made active using the Vicsek model for self-propelling particles. The resultant active system was studied by molecular dynamics methods and integral equation theory. Both methods produce results consistent with each other and demonstrate that the Vicsek model based activity facilitates phase separation, thus broadening the coexistence region.