http://hdl.handle.net/2117/5745 Sat, 18 May 2013 10:55:40 GMT 2013-05-18T10:55:40Z webmaster.bupc@upc.edu Universitat Politècnica de Catalunya. Servei de Biblioteques i Documentació no http://hdl.handle.net/2117/11221 Title: Single-walled carbon nanotubes characterization by Electron Spin Resonance spectroscopy Authors: Abiad Monge, Aida; Pérez Puigdemont, Jordi; Ferrer Anglada, Núria; Roth, Segmar Abstract: Carbon nanotubes (CNTs) are interesting candidates for the development of new electronic devices and sensors due to their small size and their mechanical, optical and electrical properties [1-6]. Well-characterized nanotubes are essential for these applications. Therefore, it is necessary to know the purity of single-walled carbon nanotubes (SWNTs) obtained by different methods, including large scale synthesis. Electron spin resonance (ESR) is a very sensitive probe that can provide information on the chemical environment of unpaired electrons. Raw samples of SWNTs often contain defects and high amounts of paramagnetic ions that are used as catalysts during their synthesis. ESR spectroscopy is sensitive to these impurities and defects [7]. Previous ESR research on CNTs showed that the ESR spectra of purified nanotubes at room temperature consist of up to three overlapping lines that are attributed to the conduction electrons (an asymmetric or Dysonian line), to defects and to the magnetic ions used as catalysts during the synthesis, respectively [8]. Studies of the conduction electrons of SWNTs by ESR have not always been effective. In the SWNTs produced by carbon arc discharge of graphite rods and laser ablation, metals have been added to the carbon target as a catalyst. As a result, the sample contains magnetic catalysts. The magnetic particles used as catalysts during SWNTs synthesis are seen as a very wide resonance line (500-900 G) located at g≈2,1 which prevents observation of the expected conduction electrons line from SWNTs. For this reason, one of our samples was SWNTs synthesized by arc discharge with non-magnetic catalysers. In this paper, we report ESR studies on several carbon nanotubes synthesized by different methods. Wed, 26 Jan 2011 19:45:09 GMT http://hdl.handle.net/2117/11221 2011-01-26T19:45:09Z Abiad Monge, Aida; Pérez Puigdemont, Jordi; Ferrer Anglada, Núria; Roth, Segmar no Carbon, Nanotubes, Spectroscopy Carbon nanotubes (CNTs) are interesting candidates for the development of new electronic devices and sensors due to their small size and their mechanical, optical and electrical properties [1-6]. Well-characterized nanotubes are essential for these applications. Therefore, it is necessary to know the purity of single-walled carbon nanotubes (SWNTs) obtained by different methods, including large scale synthesis. Electron spin resonance (ESR) is a very sensitive probe that can provide information on the chemical environment of unpaired electrons. Raw samples of SWNTs often contain defects and high amounts of paramagnetic ions that are used as catalysts during their synthesis. ESR spectroscopy is sensitive to these impurities and defects [7]. Previous ESR research on CNTs showed that the ESR spectra of purified nanotubes at room temperature consist of up to three overlapping lines that are attributed to the conduction electrons (an asymmetric or Dysonian line), to defects and to the magnetic ions used as catalysts during the synthesis, respectively [8]. Studies of the conduction electrons of SWNTs by ESR have not always been effective. In the SWNTs produced by carbon arc discharge of graphite rods and laser ablation, metals have been added to the carbon target as a catalyst. As a result, the sample contains magnetic catalysts. The magnetic particles used as catalysts during SWNTs synthesis are seen as a very wide resonance line (500-900 G) located at g≈2,1 which prevents observation of the expected conduction electrons line from SWNTs. For this reason, one of our samples was SWNTs synthesized by arc discharge with non-magnetic catalysers. In this paper, we report ESR studies on several carbon nanotubes synthesized by different methods. http://hdl.handle.net/2117/9498 Title: Nonsmooth pitchfork bifurcation in a dc-dc converter: coexisting attractors and intermittency Authors: El Aroudi, Abdelali; Moreno Font, Vanessa; Benadero García-Morato, Luis Abstract: In this paper we deal with the analysis of nonlinear dynamical behavior of a single inductor two inputs two outputs (SITITO) power electronics DC-DC converter. The system can be used to regulate generally two outputs (one positive and one negative). Under certain operating conditions, the switching model can be approximated by a one dimensional piecewise constant vector field and, as a consequence, the corresponding map is piecewise linear (PWL). This model is derived and then it is used to study a nonsmooth pitchfork bifurcation in the system. Coexistence of attractors are detected by using the same model. Intermittent chaotic behavior is also addressed. Analytical results are confirmed by one dimensional and twodimensional bifurcation diagrams. Thu, 07 Oct 2010 08:36:45 GMT http://hdl.handle.net/2117/9498 2010-10-07T08:36:45Z El Aroudi, Abdelali; Moreno Font, Vanessa; Benadero García-Morato, Luis no In this paper we deal with the analysis of nonlinear dynamical behavior of a single inductor two inputs two outputs (SITITO) power electronics DC-DC converter. The system can be used to regulate generally two outputs (one positive and one negative). Under certain operating conditions, the switching model can be approximated by a one dimensional piecewise constant vector field and, as a consequence, the corresponding map is piecewise linear (PWL). This model is derived and then it is used to study a nonsmooth pitchfork bifurcation in the system. Coexistence of attractors are detected by using the same model. Intermittent chaotic behavior is also addressed. Analytical results are confirmed by one dimensional and twodimensional bifurcation diagrams. http://hdl.handle.net/2117/9359 Title: Single inductor multiple outputs interleaved converters operating in CCM Authors: Benadero García-Morato, Luis; Moreno Font, Vanessa; Aroudi, A El; Giral, R. Abstract: Feasibility of single inductor multiple outputs (SIMO) DC-DC converters, able to operate in continuous-conduction mode (CCM), is shown in this paper. The power stage combines simple structures based on boost for non-inverted outputs and buck-boost for inverted outputs. Individual switches associated to each of the outputs are current mode controlled through respective stages as called channels. The set of dynamical references for every channel is obtained by means of a matrix arrangement whose input is the set of signals provided by proportional-integral (PI) blocks applied to each of the input-output errors. Finally, phase-shifted (interleaved) compensating ramps are added to those references. Analysis of dynamics stability is provided by means of an averaged model and direct simulation. Tue, 05 Oct 2010 14:50:06 GMT http://hdl.handle.net/2117/9359 2010-10-05T14:50:06Z Benadero García-Morato, Luis; Moreno Font, Vanessa; Aroudi, A El; Giral, R. no Feasibility of single inductor multiple outputs (SIMO) DC-DC converters, able to operate in continuous-conduction mode (CCM), is shown in this paper. The power stage combines simple structures based on boost for non-inverted outputs and buck-boost for inverted outputs. Individual switches associated to each of the outputs are current mode controlled through respective stages as called channels. The set of dynamical references for every channel is obtained by means of a matrix arrangement whose input is the set of signals provided by proportional-integral (PI) blocks applied to each of the input-output errors. Finally, phase-shifted (interleaved) compensating ramps are added to those references. Analysis of dynamics stability is provided by means of an averaged model and direct simulation.