181,169 research outputs found
Săpăturile arheologice de salvare de la Smeieni (r. Buzău, reg. Ploieşti) / Les fouilles archéologiques de sauvegarde de Smeieni
No full textSimache Nicolae I., Teodorescu Victor I. Săpăturile arheologice de salvare de la Smeieni (r. Buzău, reg. Ploieşti) / Les fouilles archéologiques de sauvegarde de Smeieni. In: Materiale şi cercetări arheologice, N°8 1962. pp. 273-282
Şantierul arheologic Tîrgşor (r. şi reg. Ploieşti) / Le chantier archéologique de Tîrgşor
No full textPopescu Dorin, Constantinescu Nicolae, Diaconu Gheorghe, Teodorescu Victor I. Şantierul arheologic Tîrgşor (r. şi reg. Ploieşti) / Le chantier archéologique de Tîrgşor. In: Materiale şi cercetări arheologice, N°7 1961. pp. 631-644
A Riemann-Hilbert problem for the Moisil-Teodorescu system
No full textIn a bounded domain with smooth boundary in R^3 we consider the stationary Maxwell equations
for a function u with values in R^3 subject to a nonhomogeneous condition
(u,v)_x = u_0 on
the boundary, where v is a given vector field and u_0 a function on the boundary. We specify this problem within the framework of the Riemann-Hilbert boundary value problems for the Moisil-Teodorescu system. This latter is proved to satisfy the Shapiro-Lopaniskij condition if an only if the vector v is at no point tangent to the boundary. The Riemann-Hilbert problem for the Moisil-Teodorescu system fails to possess an adjoint boundary value problem with respect to the Green formula, which satisfies the Shapiro-Lopatinskij condition. We develop the construction of Green formula to get a proper concept of adjoint boundary value problem
A Riemann-Hilbert Problem for the Moisil-Teodorescu System
No full textIn a bounded domain with smooth boundary in \R^3 we consider the stationary Maxwell
equations for a function u with values in \R^3 subject to a nonhomogeneous condition (u, v)_x = u_0 on
the boundary, where v is a given vector field and u_0 a function on the boundary. We specify this
problem within the framework of the Riemann-Hilbert boundary value problems for the Moisil-
Teodorescu system. This latter is proved to satisfy the Shapiro-Lopaniskij condition if an only if
the vector v is at no point tangent to the boundary. The Riemann-Hilbert problem for the Moisil-
Teodorescu system fails to possess an adjoint boundary value problem with respect to the Green
formula, which satisfies the Shapiro-Lopatinskij condition. We develop the construction of Green
formula to get a proper concept of adjoint boundary value problem
The Teodorescu and the Π-operator in octonionic analysis and some applications
No full textIn the development of function theory in octonions, the non-associativity property produces an additional associator term when applying the Stokes formula. To take the non-associativity into account, particular intrinsic weight factors are implemented in the definition of octonion-valued inner products to ensure the existence of a reproducing Bergman kernel. This Bergman projection plays a pivotal role in the -space decomposition demonstrated in this paper for octonion-valued functions. In the unit ball, we explicitly show that the intrinsic weight factor is crucial to obtain the reproduction property and that the latter precisely compensates an additional associator term that otherwise appears when leaving out the weight factor.
Furthermore, we study an octonionic Teodorescu transform and show how it is related to the unweighted version of the Bergman transform and establish some operator relations between these transformations. We apply two different versions of the Borel-Pompeiu formulae that naturally arise in the context of the non-associativity. Next, we use the octonionic Teodorescu transform to establish a suitable octonionic generalization of the Ahlfors-Beurling operator, also known as the -operator. We prove an integral representation formula that presents a unified representation for the -operator arising in all prominent hypercomplex function theories. Then we describe some basic mapping properties arising in context with the -space decomposition discussed before.
Finally, we explore several applications of the octonionic -operator. Initially, we demonstrate its utility in solving the octonionic Beltrami equation, which characterizes generalized quasi-conformal maps from to in a specific analytical sense. Subsequently, analogous results are presented for the hyperbolic octonionic Dirac operator acting on the right half-space of . Lastly, we discuss how the octonionic Teodorescu transform and the Bergman projection can be employed to solve an eight-dimensional Stokes problem in the non-associative octonionic setting.publishe
Common mode voltage in case of transformerless PV inverters connected to the grid
No full textFor safety reasons grid connected PV systems include galvanic isolation. In case of transformerless inverters, the leakage ground current through the parasitic capacitance of the PV panels, can reach very high values. A common-mode model based on analytical approach is introduced, used to predict the common-mode behavior, at frequencies lower than 50kHz, of the selected topologies and to explain the influence of system imbalance on the leakage current. It will be demonstrated that the neutral inductance has a crucial influence on the leakage current. Finally experimental results will be shown for the NPC topology, emphasizing the low leakage current for the case of a grid connection without galvanic isolation.For safety reasons grid connected PV systems include galvanic isolation. In case of transformerless inverters, the leakage ground current through the parasitic capacitance of the PV panels, can reach very high values. A common-mode model based on analytical approach is introduced, used to predict the common-mode behavior, at frequencies lower than 50kHz, of the selected topologies and to explain the influence of system imbalance on the leakage current. It will be demonstrated that the neutral inductance has a crucial influence on the leakage current. Finally experimental results will be shown for the NPC topology, emphasizing the low leakage current for the case of a grid connection without galvanic isolation
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Cavitation induced starvation for piston-ring/liner tribological conjunction
No full textThe study investigates the mechanism of ring-liner lubrication in the vicinity of the top and bottom dead centres of an internal combustion engine. Predicting lubricant transient behaviour is critical when the inlet reversal leads to thin films and inherent metal-to-metal interaction. It was found that the cavitation, which is located at the trailing edge of the contact before reversal, briefly survives after reversal as a confined bubble at the leading edge. This depletes the film promoting starvation. Several algorithms were compared. It is concluded that the lubricant film is thinner than initially thought
Grid impedance detection via excitation of LCL-filter resonance
No full textInverters adopted in distributed power generation, active filter and UPS are often connected to the grid through an LCL-filter. The impedance of the LCL-filter has a typical frequency spectrum with a resonance peak. Hence the LCL-filter has to be damped in order to avoid instability. However the resonance of the LCL-filter can be also excited in a controlled way in order to individuate the resonance frequency in the spectrum (using for example the FFT). This paper proposes to use a controlled excitation to measure the grid impedance, since this one influences also the resonance frequency. This paper addresses some possible limits, some solutions and some implementation issues (e.g. how to obtain a controlled resonance in the filter without damaging the system) in order to use the resonant peak for grid impedance detection. The analysis is validated both by simulations and experimental results
Grid impedance estimation via excitation of LCL-filter resonance
No full textInverters adopted in distributed power generation, active filter, and uninterruptible power supply are often connected to the grid through an inductance-capacitor-inductance (LCL) filter. The impedance of the LCL filter has a typical frequency characteristic with a resonance peak. Hence, the LCL filter has to be damped in order to avoid instability. However, the resonance of the LCL filter can be also excited in a controlled way in order to individuate the resonance frequency in the spectrum (using for example the fast Fourier transform). This paper proposes to use a controlled excitation in measuring the grid impedance, since this one influences also the resonance frequency. This paper will address some possible limits, some solutions, and some implementation issues (e.g., how to obtain a controlled resonance in the filter without damaging the system) in order to use the resonant peak for grid impedance detection. The analysis is validated both by simulations and experimental results
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