Papers by Alina Barbulescu
In this paper we present a simple nesting optimization method for a single dimension direction. T... more In this paper we present a simple nesting optimization method for a single dimension direction. The method consists in sequential generations of certain combinations searching for fine results using reasonable computation resources. The algorithm has been transposed in Visual Basic for checks and exemplifications. The results consist in the exact sequence of the given pieces along the row material bar and indications regarding computation volume for the initial optimization conditions.
Fractal dimensions are the most important attributes of fractals and the Box counting dimension i... more Fractal dimensions are the most important attributes of fractals and the Box counting dimension is widely used. Usually it is not so easy to determine dimensions. In some papers we have considered a class of functions and we have studied the finitude of the Hausdorff h-measures of the graph, Ã, of an element of this class. In this paper we determine the Box dimension of Ã.
In this article we charaterize the primes Fibonacci numbers of the form $x^2 +ry^2$, where $r = 1... more In this article we charaterize the primes Fibonacci numbers of the form $x^2 +ry^2$, where $r = 1,$ $r$ is a prime positive integer number or r is a power of a prime positive integer, using techniques of combinatorics and numbers theory. We also evaluate some distances related to the Fibonacci numbers and function.
Acta Physica Polonica B, 2006
When an ultrasonic wave passes through a liquid medium, containing microscopic gas inclusion, it ... more When an ultrasonic wave passes through a liquid medium, containing microscopic gas inclusion, it can produce cavitation. At the boundary of a cavitating zone, a voltage appears as a effect of the collapse/rebound cycle of the cavitation bubbles. In this paper we establish a mathematical model of the voltage induced at the boundary of an acoustic cavitation zone, when the liquid was the crude oil. It is compared to that obtained for diesel, in order to prove that the ARIMA process can appropriately describe the fluctuations of generated voltage in different liquids. We also discuss the hypothesis of the relation between the ARIMA parameters and the liquid nature.
In this study, the temporal characteristics of precipitations evolutions are investigated for the... more In this study, the temporal characteristics of precipitations evolutions are investigated for the region of Dobroudja, Romania. The current work presents the results for the forecasting the rainfalls in some of the Dobroudja cities, using the wavelet analysis, which have recently attracted great interest. Since rainfall time series present high non-linearity and non-stationarity, using only some neural networks models, one can not cope with these aspects. Our model is based on wavelets decompositions for the entire series, or for the subseries in which the initial series are split after the break points determination. A comparison between our model, the one based on the neural network, and the multiplicative one is provided.
An ultrasonic field that goes over a liquid can produce or move cavitation bubbles and these ones... more An ultrasonic field that goes over a liquid can produce or move cavitation bubbles and these ones determine physical and chemical effects. Experimentally it was proved that an alternative voltage appears and it contains both the ultrasonic frequency and the inherent harmonics and subharmonics. This conclusion results also by the Fourier analysis made for the intercepted signal.
Precipitation time series intrinsically contain important information concerning climate variabil... more Precipitation time series intrinsically contain important information concerning climate variability and change. Well-fit models of such time series can shed light upon past weather related phenomena and can help to explain future events. The objective of this study is to investigate the application of some conceptually different methods to construct models for large hydrological time series. We perform a thorough statistical analysis of the time series, which covers the identification of the change points in the time series. Then, the subseries delimited by the change points are modeled with classical Box-Jenkins methods to construct ARIMA models and with a computational intelligence technique, gene expression programming, which produces non-linear symbolic models of the series. The combination of statistical techniques with computational intelligence methods, such as gene expression programming, for modeling time series, offers increased accuracy of the models obtained. This affirmation is illustrated with examples.
Nonparametric regression analysis traces the dependence of a response variable on one or several ... more Nonparametric regression analysis traces the dependence of a response variable on one or several predictors without specifying in advance the function that relates the predictors to the response. In this article we discuss several methods of nonparametric regression, including kernel estimation, local polynomial regression, smoothing splines and wavelets, in the case of one predictor, applied to the annual and monthly precipitations over the Dobroudja region (Romania), between 1965 and 2005. The methods have been implemented in R, and are of general application of nonparametric regression problems.
Power-law scaling of rainfall depths has been amply documented in recent years, even beyond the s... more Power-law scaling of rainfall depths has been amply documented in recent years, even beyond the scales that have a spatial counterpart explaining the phenomenology. Scale behaviour of dry spells, however, is a more complex subject, not only due to the sensitivity of the analysis to the rainfall detection threshold, but also because of its intrinsically slow convergence to an asymptotic behaviour. The present work compares the scaling of dry spells in rainfall time series with that of run lengths in series of river discharges, hereby depicting interesting connections, and adding reliability to the results.
Applied Mathematical Modelling, 2007
The mathematical model for estimating the mass transfer coefficients for the ethanethiol extracti... more The mathematical model for estimating the mass transfer coefficients for the ethanethiol extraction from gasoline, with alkaline solutions was established by processing the data obtained in a laboratory and in a pilot plant experiment. It allows the estimation of overall mass transfer coefficients, taking into account the dispersed phase velocity, the concentration of NaOH solution, the specific area and the porosity of the packing. The model’s parameters were statistical tested in order to confirm the accuracy of the model.
Corrosion is one of the main causes of metals degradation, which consists of superficial and stru... more Corrosion is one of the main causes of metals degradation, which consists of superficial and structural changes. It causes damages and economic loss and can be prevented mainly by choosing the materials with the best properties for the working conditions. When a material is introduced in an aqueous medium, an electrochemical attack is produced. It can be combined with other
Theoretical and Applied Climatology, 2010
The understanding of processes that occur in climate change evolution and their spatial and tempo... more The understanding of processes that occur in climate change evolution and their spatial and temporal variations are of major importance in environmental sciences. Modeling these processes is the first step in the prediction of weather change. In this context, this paper presents the results of statistical investigations of monthly and annual meteorological data collected between 1961 and 2007 in Dobrudja (a region situated in the South–East of Romania between the Black Sea and the lower Danube River) and the models obtained using time series analysis and gene expression programming. Using two fundamentally different approaches, we provide a comprehensive analysis of temperature variability in Dobrudja, which may be significant in understanding the processes that govern climate changes in the region.
NEW RESULTS ABOUT THE H-MEASURE OF A SET Alina Barbulescu " Ovidius" University Faculty... more NEW RESULTS ABOUT THE H-MEASURE OF A SET Alina Barbulescu " Ovidius" University Faculty of Mathematics and Informatics 8700 Constanta Romania abarbulescu@ univ ... 0, 1): (0, fc0),(zi~ ki, xi+ fci),...zn_i-fcn-i If Ci are arbitrary points, satisfying: ci 6 (0, xi), a(zj_i, Zi), i ...
Acta Physica Polonica B, 2006
The passage of an ultrasonic wave through a liquid medium can produce cavitation. In this paper w... more The passage of an ultrasonic wave through a liquid medium can produce cavitation. In this paper we describe the experiment made in order to determine the voltage induced in a cavitation zone and we establish two formulae for the calculus of this voltage, when the studied liquid was the water. The main result is the modeling of an electrical signal induced at the boundary of an acoustic cavitation zone, in water, using the ARIMA process.
The mathematical model for the estimation of mass transfer coefficients at the extraction of thio... more The mathematical model for the estimation of mass transfer coefficients at the extraction of thiols from gasoline with alkaline solutions was established by processing the data proceeding from the laboratory experiment and then from a pilot plant. Three sets of data were obtained, one for each case: the laboratory column with dispersion, the laboratory column equipped with a low specific area packing (a p = 60 m 2 /m 3 ) and a great porosity ( ε=0.98) and one in a micropilot size column equipped with Sulzer packing having a much larger specific area (a p = 340m 2 /m 3 ) and similar porosity ( ε=0.96). For each installation, three different thiols at three different NaOH concentrations were tested. The experimental data were statistically analysed and processed using the programs SPSS and CurveExpert. The emerging mathematical model-applied separately to each thiol-allows the estimation of overall mass transfer coefficients, taking into account the following parameters: the dispersed phase velocity, the concentration of NaOH solution, the specific area and the porosity of the packing. The existing model could serve in the oil processing, at dimensioning the alkaline refining of petroleum fractions and also, at the simulation of the said extraction columns.
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Papers by Alina Barbulescu