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Search Results: 1 - 10 of 117881 matches for " T.; Petrakis "
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Elliptical Anisotropy Statistics of Two-Dimensional Differentiable Gaussian Random Fields: Joint Probability Density Function and Confidence Regions
Manolis P. Petrakis,Dionissios T. Hristopulos
Statistics , 2012,
Abstract: Two-dimensional data often have autocovariance functions with elliptical equipotential contours, a property known as statistical anisotropy. The anisotropy parameters include the tilt of the ellipse (orientation angle) $\theta$ with respect to the coordinate system and the ratio $R$ of the principal correlation lengths. Sample estimates of anisotropy parameters are needed for defining suitable spatial models and for interpolation of incomplete data. The sampling joint probability density function characterizes the distribution of anisotropy statistics $(\hat{R}, \hat{\theta})$. By means of analytical calculations, we derive an explicit expression for the joint probability density function, which is valid for Gaussian, stationary and differentiable random fields. Based on it, we derive an approximation of the joint probability density function that is independent of the autocovariance function and provides conservative confidence regions for the sample-based estimates $(\hat{R},\hat{\theta})$. We also formulate a statistical test for isotropy based on the approximation of the joint probability density function. The latter provides (i) a stand-alone approximate estimate of the $(\hR, \htheta)$ distribution (ii) computationally efficient initial values for maximum likelihood estimation, and (iii) a useful prior for Bayesian anisotropy inference. We validate the theoretical analysis by means of simulations, and we illustrate the use of confidence regions with a real-data case study.
Informal Financing of Small – Medium Enterprise Sector: The Case of Greece  [PDF]
Panagiotis Petrakis, Konstantinos Eleftheriou
Journal of Service Science and Management (JSSM) , 2009, DOI: 10.4236/jssm.2009.24045
Abstract: In this paper, we attempt to find a “channel” through which Greek economy can exhibit a relative “resistance” in a credit crunch. For this purpose, we specify an error correction model so as to test the relationship between corporate bank loans and commercial papers comprised of post-dated cheques and bills of exchange. The results show that corporate bank loans and cheques - bills of exchange are substitutes. This finding combined with the fact that in Greece, the issuance of these papers is positively connected with the informal economic activity which in turn rises during economic downturns, has a strong economic implication regarding the ability of Greek economy to partly “amortize” the shocks connected with the current financial crisis.
Time and Risk Entrepreneurial Characteristics of Growth: The Case of Persisted Light Industrial Prototypes  [PDF]
P. E. Petrakis
iBusiness (IB) , 2010, DOI: 10.4236/ib.2010.21002
Abstract: This article is about the role of entrepreneurial perception of time and risk vis à vis structural change and growth. Entrepreneurship is a basic constituent element of social capital which in turn is a productive lubricant of the growth process. Different structural entrepreneurial prototypes with respect to time and risk have different structural change effects. Those structural changes (and any structural changes) are not neutral as far as the implications of growth rate changes are concerned. Therefore the time and risk characteristics of active entrepreneurship are reflected in the growth process either in the form of structural change and/or in the form of growth rate change.
On the Ideal Duration of Entrepreneurial Resources Commitment  [PDF]
Panagiotis E. Petrakis
Technology and Investment (TI) , 2010, DOI: 10.4236/ti.2010.11006
Abstract: The paper proposes that the entrepreneur’s perception of time in the form of average ideal duration of entre-preneurial resources commitment is an important personal trait. The entrepreneur develops a particular checking filter for the entrepreneurial involvement on which the evaluation of entrepreneurial opportunities is based. The concept of ideal time dimension of entrepreneurial engagement is crucially related to the de-velopment of structural prototype prevailing in space and time. Three main influences have been located with respect to the formation of duration on entrepreneurial commitment: microeconomic influences, long-term macro-environmental influences and short-term macro-environmental influences.
Cultural Background and Economic Development Indicators: European South Vs European North  [PDF]
P.E. Petrakis
Modern Economy (ME) , 2011, DOI: 10.4236/me.2011.23035
Abstract: This paper examines the relationship between cultural background and economic development. We focus on the example of Greece in order to analyze the cultural disparities between the Mediterranean and the North-ern European countries. We find that there is a common cultural model characterizing the Southern European nations, which spans the Mediterranean coast, from Portugal to Turkey. These countries are characterized by high uncertainty and absence of future orientation. On the other hand the cultural background in Northern European countries is found on individualism. The paper shows that the cultural values model is mirrored in the basic traits characterizing the economic and business environment of the areas (North-South) under examination. The differential cultural background is reflected in the basic economic and social developmental indicators in a consistent way.
Uso de vitamina C en la solución tumescente de liposucción como inductor de lipolisis y fibrosis: Trabajo experimental
Antoniadis Petrakis,N.; González Romero,T.C.;
Cirugía Plástica Ibero-Latinoamericana , 2007, DOI: 10.4321/S0376-78922007000200004
Abstract: liposuction does not always let to remove all the amount of adipose tissue which causes lipodistrophy, for that reason, it is recommended the necessity to improve that technique. we try to demonstrate that the use of vitamin c in the tumescence solution induces lipolysis and raises fibrosis. this article is a descriptive, prospective, experimental and comparative research of a sample of 30 mice of sprague- dawley type of both sexes, which were infiltrated with a tumescence solution in the subdermic inguinal region with vitamin c to the experimental group and with tumescence solution without vitamin c to the control group, for a further histological macroscopic as well as microscopic study. the results showed that 100% of the samples with vitamin c presented changes in the adipose tissue which suggested lipolysis, whereas 82% were evidence for the formation of young collagen. as a conclusion, vitamin c helps lipolysis and promotes synthesis of collagen when it is used as a part of the tumescence solution in experimental animals.
Uso de vitamina C en la solución tumescente de liposucción como inductor de lipolisis y fibrosis: Trabajo experimental Use of vitamine C in liposuction tumescent solution as lipolisis and fibrosis inductor: Experimental study
N. Antoniadis Petrakis,T.C. González Romero
Cirugía Plástica Ibero-Latinoamericana , 2007,
Abstract: La Liposucción no permite siempre extraer todo el tejido adiposo causante de la lipodistrofia, por lo cual se plantea la necesidad de perfeccionar esta técnica. Nuestro objetivo es el demostrar que el uso de la vitamina C en la solución tumescente induce lipólisis y aumenta la fibrosis. El presente es un estudio descriptivo, prospectivo, experimental y comparativo de una muestra de 30 ratas Sprague-Dawley de ambos sexos, a las cuales se les infiltró solución tumescente en el tejido subdérmico de la región inguinal, con vitamina C al grupo experimental y con solución tumescente sin vitamina C al grupo control, para su posterior estudio histológico macroscópico y microscópico. El 100% de las muestras con vitamina C evidenciaron cambios a nivel del tejido adiposo sugerentes de lipólisis y en el 82% se evidenciaron cambios en el tejido conectivo sugerentes de formación de colágeno joven. Concluimos que la vitamina C favorece la lipolisis y promueve la síntesis de colágeno cuando se utiliza como parte de la solución tumescente en animales de experimentación Liposuction does not always let to remove all the amount of adipose tissue which causes lipodistrophy, for that reason, it is recommended the necessity to improve that technique. We try to demonstrate that the use of vitamin C in the tumescence solution induces lipolysis and raises fibrosis. This article is a descriptive, prospective, experimental and comparative research of a sample of 30 mice of Sprague- Dawley type of both sexes, which were infiltrated with a tumescence solution in the subdermic inguinal region with vitamin C to the experimental group and with tumescence solution without vitamin C to the control group, for a further histological macroscopic as well as microscopic study. The results showed that 100% of the samples with vitamin C presented changes in the adipose tissue which suggested lipolysis, whereas 82% were evidence for the formation of young collagen. As a conclusion, vitamin C helps lipolysis and promotes synthesis of collagen when it is used as a part of the tumescence solution in experimental animals.
Finite-Size Effects on Return Interval Distributions for Weakest-Link-Scaling Systems
Dionissios T. Hristopulos,Manolis P. Petrakis,Giorgio Kaniadakis
Physics , 2013, DOI: 10.1103/PhysRevE.89.052142
Abstract: The Weibull distribution is a commonly used model for the strength of brittle materials and earthquake return intervals. Deviations from Weibull scaling, however, have been observed in earthquake return intervals and in the fracture strength of quasi-brittle materials. We investigate weakest-link scaling in finite-size systems and deviations of empirical return interval distributions from the Weibull distribution function. We use the ansatz that the survival probability function of a system with complex interactions among its units can be expressed as the product of the survival probability functions for an ensemble of representative volume elements (RVEs). We show that if the system comprises a finite number of RVEs, it obeys the $\kappa$-Weibull distribution. We conduct statistical analysis of experimental data and simulations that show good agreement with the $\kappa$-Weibull distribution. We show the following: (1) The weakest-link theory for finite-size systems involves the $\kappa$-Weibull distribution. (2) The power-law decline of the $\kappa$-Weibull upper tail can explain deviations from the Weibull scaling observed in return interval data. (3) The hazard rate function of the $\kappa$-Weibull distribution decreases linearly after a waiting time $\tau_c \propto n^{1/m}$, where $m$ is the Weibull modulus and $n$ is the system size in terms of representative volume elements. (4) The $\kappa$-Weibull provides competitive fits to the return interval distributions of seismic data and of avalanches in a fiber bundle model. In conclusion, using theoretical and statistical analysis of real and simulated data, we show that the $\kappa$-Weibull distribution is a useful model for extreme-event return intervals in finite-size systems.
A Nonlinear Control Model of Growth, Risk and Structural Change  [PDF]
P. E. Petrakis, S. Kotsios
Intelligent Information Management (IIM) , 2010, DOI: 10.4236/iim.2010.22010
Abstract: Uncertainty is perceived as the means of removing the obstacles to growth through the activation of Knig- htian entrepreneurship. A dynamic stochastic model of continuous-time growth is proposed and empirically tested, including equilibrating and creative entrepreneurial activity. We find that uncertainty affects economic growth and the rate of return, and causes structural changes in portfolio shares for the two types of entrepreneurial events. Structural change depends mainly on the intertemporal rate of substitution, productiv-ity ratios, and finally intersectoral difference in return and risk.
Good Manufacturing Practice (GMP) guidelines for virgin olive oil production
Petrakis, Christos
Grasas y Aceites , 1994,
Abstract: This paper presents GMP guidelines for the production of virgin olive oil. Standard procedures and conditions are indicated for olive production, harvesting, transportation and storage, for oil manufacture, storage and packaging, for buildings, process logistics and the materials used throughout the production chain.
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