Self-Feeder Driver for Voltage Balance in Series-Connected IGBT Associations

Guerrero-Guerrero, A.F.,Ustariz-Farfan, A.J.,Tacca, H.E.,Cano-Plata, E.A. The Korean Institute of Power Electronics 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.1

The emergence of high voltage conversion applications has resulted in a trend of using semiconductor device series associations. Series associations allow for operation at blocking voltages, which are higher than the nominal voltage for each of the semiconductor devices. The main challenge with these topologies is finding a way to guarantee the voltage balance between devices in both blocking and switching transients. Most of the methods that have been proposed to mitigate static and dynamic voltage unbalances result in increased losses within the device. This paper introduces a new series stack topology, where the voltage unbalances are reduced. This in turn, mitigates the switching losses. The proposed topology consists of a circuit that ensures the soft switching of each device, and one auxiliary circuit that allows for switching energy recovery. The principle for the topology operation is presented and experimental tests are performed for two modules. The topology performs excellently for switching transients on each of the devices. The voltage static unbalances were limited to 10%, while the activation/deactivation delay introduced by the lower module IGBT driver takes place in the dynamic unbalances. Thus, the switching losses are reduced by 40%, when compared to hard switching configurations.

Self-Feeder Driver for Voltage Balance in Series-Connected IGBT Associations

A. F. Guerrero-Guerrero,A. J. Ustariz-Farfan,H. E. Tacca,E. A. Cano-Plata 전력전자학회 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.1

The emergence of high voltage conversion applications has resulted in a trend of using semiconductor device seriesassociations. Series associations allow for operation at blocking voltages, which are higher than the nominal voltage for each ofthe semiconductor devices. The main challenge with these topologies is finding a way to guarantee the voltage balance betweendevices in both blocking and switching transients. Most of the methods that have been proposed to mitigate static and dynamicvoltage unbalances result in increased losses within the device. This paper introduces a new series stack topology, where thevoltage unbalances are reduced. This in turn, mitigates the switching losses. The proposed topology consists of a circuit thatensures the soft switching of each device, and one auxiliary circuit that allows for switching energy recovery. The principle forthe topology operation is presented and experimental tests are performed for two modules. The topology performs excellently forswitching transients on each of the devices. The voltage static unbalances were limited to 10%, while the activation/deactivationdelay introduced by the lower module IGBT driver takes place in the dynamic unbalances. Thus, the switching losses are reducedby 40%, when compared to hard switching configurations.

Implicit change leadership schemas, perceived effective change management, and teachers’ commitment to change in secondary schools in the Philippines

Guerrero Joyce M.,Teng-Calleja Mendiola,Hechanova Ma. Regina M. 서울대학교 교육연구소 2018 Asia Pacific Education Review Vol.19 No.3

Implicit change leadership theory (ICLT) highlights the importance of determining congruence between the ideal and actual change leadership schemas of employees in successful change management. This paper utilized ICLT in exploring effective change leadership and management in secondary schools and examined how these influence teachers’ commitment to change. Data were gathered from 707 secondary school teachers from both private and public high schools in the Philippines. Findings indicated that (1) teachers seem to have a more holistic and integrative view of change leadership schemas than employees of business organizations, (2) teachers’ change leadership schemas significantly predicts perceived effectiveness of change management, and teachers’ affective commitment to change, and (3) perceived effectiveness of change management significantly mediates the effect of change leadership schemas on teachers’ affective commitment to change. This study expanded the applicability of ICLT in basic education settings and contributes to the understanding of effective change leadership and change management in schools. Implications on practice and further recommendations for school leaders are also discussed.

Properties of Contact and Bulk Impedances in Hybrid Lead Halide Perovskite Solar Cells Including Inductive Loop Elements

Guerrero, Antonio,Garcia-Belmonte, Germà,Mora-Sero, Ivan,Bisquert, Juan,Kang, Yong Soo,Jacobsson, T. Jesper,Correa-Baena, Juan-Pablo,Hagfeldt, Anders American Chemical Society 2016 The Journal of Physical Chemistry Part C Vol.120 No.15

<P>Impedance spectroscopy offers access to all the different electronic and ionic processes taking place simultaneously in an operating solar cell. To date, its use on perovskite solar cells has been challenging because of the richness of the physical processes occurring within similar time domains. The aim of this work is to understand the general impedance response and propose a general equivalent circuit model that accounts for the different processes and gives access to quantitative analysis. When the electron-selective contacts and the thickness of the perovskite film are systematically modified, it is possible to distinguish between the characteristic impedance signals of the perovskite layer and those arising from the contacts. The study is carried out using mixed organic lead halogen perovskite (FA(0.85)MA(0.15)Pb(I0.85Br0.15)(3)) solar cells with three different electron-selective contacts: SnO2, TiO2, and Nb2O5. The contacts have been deposited by atomic layer deposition (ALD), which provides pinhole-free films and excellent thickness control in the absence of a mesoporous layer to simplify the impedance analysis. It was found that the interfacial impedance has a rich structure that reveals different capacitive processes, serial steps for electron extraction, and a prominent inductive loop related to negative capacitance at intermediate frequencies. Overall, the present report provides insights into the impedance response of perovskite solar cells which enable an understanding of the different electronic and ionic processes taking place during device operation.</P>

Wound Regeneration Deficit in Rats Correlates with Low Morphogenetic Potential and Distinct Transcriptome Profile of Epidermis

Guerrero-Juarez, Christian F.,Astrowski, Aliaksandr A.,Murad, Rabi,Dang, Christina T.,Shatrova, Vera O.,Astrowskaja, Aksana,Lim, Chae Ho,Ramos, Raul,Wang, Xiaojie,Liu, Yuchen,Lee, Hye-Lim,Pham, Kim T. Springer Nature 2018 The Journal of investigative dermatology Vol.138 No.6

Does cone-beam CT alter treatment plans? Comparison of preoperative implant planning using panoramic versus cone-beam CT images

Guerrero, Maria Eugenia,Noriega, Jorge,Castro, Carmen,Jacobs, Reinhilde Korean Academy of Oral and Maxillofacial Radiology 2014 Imaging Science in Dentistry Vol.44 No.2

Purpose: The present study was performed to compare the planning of implant placement based on panoramic radiography (PAN) and cone-beam computed tomography (CBCT) images, and to study the impact of the image dataset on the treatment planning. Materials and Methods: One hundred five partially edentulous patients (77 males, 28 females, mean age: 46 years, range: 26-67 years) seeking oral implant rehabilitation were referred for presurgical imaging. Imaging consisted of PAN and CBCT imaging. Four observers planned implant treatment based on the two-dimensional (2D) image data-sets and at least one month later on the three-dimensional (3D) image dataset. Apart from presurgical diagnostic and dimensional measurement tasks, the observers needed to indicate the surgical confidence levels and assess the image quality in relation to the presurgical needs. Results: All observers confirmed that both imaging modalities (PAN and CBCT) gave similar values when planning implant diameter. Also, the results showed no differences between both imaging modalities for the length of implants with an anterior location. However, significant differences were found in the length of implants with a posterior location. For implant dimensions, longer lengths of the implants were planned with PAN, as confirmed by two observers. CBCT provided images with improved scores for subjective image quality and surgical confidence levels. Conclusion: Within the limitations of this study, there was a trend toward PAN-based preoperative planning of implant placement leading towards the use of longer implants within the posterior jaw bone.

Analysis of the NATIONAL MARITIME Strategy of Ecuador

Guerrero Gonzalo,Sangjung Park J-INSTITUTE 2021 International Journal of Terrorism & National Secu Vol.6 No.4

Purpose: This article is to analyze the maritime strategy of Ecuador from the perspective of national security theory. It also applies national security theory for academic support to Ecuador s maritime policy, providing a complete understanding and critical analysis of Ecuador s maritime strategy. Method: In this study, three methods were used to analyze and develop Ecuador s maritime strategy: realism, liberalism and constructivism. First, the realistic approach examines, analyzes, and interprets the relationship between past facts, present facts, and future assumptions in relation to Ecuador s maritime strategy. Second, the liberal approach is to establish the relationship, differences, and awareness of information on the national security and defense axes, including the nuclear issue. Third, the constructive approach reviews empirically in order to recognize the characteristics of Ecuador s maritime strategy. Results: The advantage of using national security theory is the ability to identify its causes and understand the intentions of actors in complex scenarios of Ecuador s national maritime strategy. It also proposes possible solutions and formulates measures to promote better implementation of national maritime and coastal policies. Therefore, this theoretical and practical study of scenario analysis will provide a link between academic support and national maritime strategies. Conclusion: Ecuador is a maritime country with the activities that people perform in marine space and the resources the sea provides. The results of this study are vital important to promote defense, growth and development for Ecuador s national maritime interests.

Preoperative implant planning considering alveolar bone grafting needs and complication prediction using panoramic versus CBCT images

Guerrero, Maria Eugenia,Noriega, Jorge,Jacobs, Reinhilde Korean Academy of Oral and Maxillofacial Radiology 2014 Imaging Science in Dentistry Vol.44 No.3

Purpose: This study was performed to determine the efficacy of observers' prediction for the need of bone grafting and presence of perioperative complications on the basis of cone-beam computed tomography (CBCT) and panoramic radiographic (PAN) planning as compared to the surgical outcome. Materials and Methods: One hundred and eight partially edentulous patients with a need for implant rehabilitation were referred for preoperative imaging. Imaging consisted of PAN and CBCT images. Four observers carried out implant planning using PAN image datasets, and at least one month later, using CBCT image datasets. Based on their own planning, the observers assessed the need for bone graft augmentation as well as complication prediction. The implant length and diameter, the need for bone graft augmentation, and the occurrence of anatomical complications during planning and implant placement were statistically compared. Results: In the 108 patients, 365 implants were installed. Receiver operating characteristic analyses of both PAN and CBCT preoperative planning showed that CBCT performed better than PAN-based planning with respect to the need for bone graft augmentation and perioperative complications. The sensitivity and the specificity of CBCT for implant complications were 96.5% and 90.5%, respectively, and for bone graft augmentation, they were 95.2% and 96.3%, respectively. Significant differences were found between PAN-based planning and the surgery of posterior implant lengths. Conclusion: Our findings indicated that CBCT-based preoperative implant planning enabled treatment planning with a higher degree of prediction and agreement as compared to the surgical standard. In PAN-based surgery, the prediction of implant length was poor.

Can pterygoid plate asymmetry be linked to temporomandibular joint disorders?

Guerrero, Maria Eugenia,Beltran, Jorge,de Laat, Antoon,Jacobs, Reinhilde Korean Academy of Oral and Maxillofacial Radiology 2015 Imaging Science in Dentistry Vol.45 No.2

Purpose: This study was performed to evaluate the relationship between pterygoid plate asymmetry and temporomandibular joint disorders. Materials and Methods: Cone-beam computed tomography (CBCT) images of 60 patients with temporomandibular disorders (TMD) involving pain were analyzed and compared with images of 60 age-and gender-matched controls. Three observers performed linear measurements of the lateral pterygoid plates. Results: Statistically significant differences were found between measurements of the lateral pterygoid plates on the site that had pain and the contralateral site (p<0.05). The average length of the lateral pterygoid plates (LPPs) in patients with TMD was $17.01{\pm}3.64mm$ on the right side and $16.21{\pm}3.51mm$ on the left side, and in patients without TMD, it was $11.86{\pm}1.97mm$ on the right side and $11.98{\pm}1.85mm$ on the left side. Statistically significant differences in the LPP length, measured on CBCT, were found between patients with and without TMD (p<0.05). The inter-examiner reliability obtained in this study was very high for all the examiners (0.99, 95% confidence interval: 0.98-0.99). Conclusion: Within the limits of the present study, CBCT lateral pterygoid plate measurements at the side with TMD were found to be significantly different from those on the side without TMD. More research is needed to explore potential etiological correlations and implications for treatment.

시행 15년을 맞이한 자영노동법 (LETA)의 의미와 한계

Guerrero Vizuete, Estheri 한국노동연구원 2022 국제노동브리프 Vol.20 No.7