Staicu S.,Polytechnic University of Bucharest
Robotics and Computer-Integrated Manufacturing | Year: 2011
Recursive matrix relations in kinematics and dynamics of the 6-6 StewartGough parallel manipulator having six mobile prismatic actuators are established in this paper. Controlled by six forces, the manipulator prototype is a spatial six-degrees-of-freedom mechanical system with six parallel legs connecting to the moving platform. Knowing the position and the general motion of the platform, we develop first the inverse kinematics problem and determine the position, velocity and acceleration of each manipulator's link. Further, the inverse dynamics problem is solved using an approach based on the principle of virtual work, but it has been verified the results in the framework of the Lagrange equations with their multipliers. Finally, compact matrix relations and graphs of simulation for the input velocities and accelerations, the input forces and powers are obtained. © 2010 Elsevier Ltd. All rights reserved.
Preda R.O.,Polytechnic University of Bucharest
Measurement: Journal of the International Measurement Confederation | Year: 2013
This paper proposes a novel image authentication scheme in the wavelet domain. The scheme uses a semi-fragile watermark to detect and precisely locate malicious tampering in images. The wavelet coefficients selected for embedding are randomly permuted with a secret key, achieving high security. A bit of the watermark is embedded in a group of coefficients by means of quantization. The experimental results show, that our algorithm achieves high image quality and high tampering detection resolution at a low watermark payload, compared to block-based authentication schemes. Thanks to the random permutation, the watermark is protected against local attacks. We have also conducted experiments to demonstrate the robustness of the watermark against mild to moderate JPEG compression. © 2012 Elsevier Ltd. All rights reserved.
Vizireanu D.N.,Polytechnic University of Bucharest
Measurement: Journal of the International Measurement Confederation | Year: 2012
This paper presents a simple and accurate method to estimate time-varying frequency for single-phase electric power systems, based on three equally spaced samples. A sinusoidal voltage signal model, without dc offset, with time-varying frequency was assumed. Analytical formulas are derived. The method shows good estimation accuracy over a real world wide range of frequency changes. Simulations have been performed. © 2012 Elsevier Ltd. All rights reserved.
Mihailescu M.,Polytechnic University of Bucharest
Optics Express | Year: 2010
A naturally-inspired phase-only diffractive optical element with a circular symmetry given by a quasi-periodic structure of the phyllotaxis type is presented in this paper. It is generated starting with the characteristic parametric equations which are optimal for the golden angle interval. For some ideal geometrical parameters, the diffracted intensity distribution in near-field has a central closed ring with almost zero intensity inside. Its radius and intensity values depend on the geometry or non-binary phase distribution superposed onto the phyllotaxis geometry. Along propagation axis, the transverse diffraction patterns from the binary-phase diffractive structure exhibit a self-focusing behavior and a rotational motion. © 2010 Optical Society of America.
Grumezescu A.M.,Polytechnic University of Bucharest
Current Organic Chemistry | Year: 2013
In the last years, there are more and more reports published in prestigious journals addressing the successful application of essential oils for the eradication or prevention of microbial biofilms. Moreover, by combining the unique properties of nanoparticles with the antimicrobial activity of the essential oils, functionalized surfaces with an improved resistance to microbial colonization and biofilm development were obtained. These results may represent an interesting option for the medical field, opening new directions for the design of modified surfaces with desired and controlled anti-biofilm properties. © 2013 Bentham Science Publishers.