Investigation of negative sequence injection capability in H-bridge multilevel STATCOM

The aim of this paper is to investigate the ability of star- and delta-connected H-bridge multilevel STATCOMs to exchange negative-sequence current with the grid. Zero-sequence injection is utilized for capacitor voltage balancing. It is shown that a singularity for these configurations exists, leading to limitations in the utilization of the compensator for asymmetry compensation purposes

Overview on Models and Standards Classification in E-Learning System

ABSTRACT E-learning is interface of information technology and educational technology which use of the tools to exchange information electronically and will be done with different models. Increasing access to hardware and software for e-learning, especially development of internet technology, educational institutions should modify education methods. Certainly, e-learning as a new method for teaching and learning has been welcomed in most parts of the world which can have many benefits for teachers, students and organizations. With improve facilities, equipment and infrastructure needed for e-learning can be established training courses at any time and any place and access to training programs and information resources and provided opportunities need to enhance knowledge and learn new skills. To implement and use the benefits of e-learning should recognize models and standards of e-learning. In this paper has been checked the concepts, principles, features, benefits and types of e-learning models and standards classification and instructional design models in the e-learning system

Operation and control of cascaded H-bridge converter for STATCOM application

In the last decade, particular attention has been paid to the use of Modular Multilevel Converters (MMC) for grid applications. In particular, for STATCOM applications the phase leg of the converter is constituted by a number of single-phase full-bridge converters connected in cascade (here named Cascaded H-Bridge, CHB, converter). This multilevel converter topology is today considered the industrial standard for STATCOM applications and has replaced other converter topologies, mainly due to its small footprint, high achievable voltage levels (allowing transformer-less operation), modularity and reduced losses. However, there are still areas of research that need to be investigated in order to improve the performance and the operational range of this converter topology for grid-applications. The aim of this thesis is to explore control and modulation schemes for the CHB-STATCOM, both under balanced and unbalanced conditions of the grid, highlighting the advantages but also the challenges and possible pitfalls that this kind of topology presents for this specific application. The first part of the thesis is dedicated to the two main modulation techniques for the CHBSTATCOM: the Phase-Shifted PulseWidthModulation (PS-PWM) and the Level-Shifted PWM (LS-PWM) with cells sorting. In particular, the focus is on the impact of the adopted modulation on the active power distribution on the individual cells of the converter. When using PS-PWM, it is shown that non-ideal cancellation of the switching harmonics leads to a non-uniform active power distribution among the cells and thereby to the need for an additional control loop for individual DC-link voltage balancing. Theoretical analysis proves that a proper selection of the frequency modulation ratio leads to a more even power distribution over time, which in turns alleviates the role of the individual balancing control. Both PS-PWM and cells sorting schemes fail in cell voltage balancing when the converter is not exchanging reactive power with the grid (converter in zero-current mode). To overcome this problem, two methods for individual DC-link voltage balancing at zero-current mode are proposed and verified. Then, the thesis focuses on the operation of the CHB-STATCOM under unbalanced conditions. It is shown analytically that regardless of the configuration utilized for the CHB-STATCOM (star or in delta configuration), a singularity exists when trying to guarantee balancing in the DC-link capacitor voltages. In particular, it is shown that the star configuration is sensitive to the level of unbalance in the current exchanged with the grid, with a singularity in the solution when positive- and negative-sequence currents have the same magnitude. Similar results are found for the delta configuration where, in a pure duality with the star configuration, the system is found to be sensitive to the level of unbalance in the applied voltage. The presence of these singularities represents an important limit of this topology for STATCOM applications

Benchmarking Demand: Turkey’s Contested Internet

The role of the Internet as a fundamental tool for communication and empowerment is one that should not be inhibited as the limitless nature of the medium allows for a broader, unfiltered, and more democratic exchange of information. These features become increasingly important in conditions where the mainstream media are unwilling or unable to provide the public with the information necessary to function as democratic citizens and maintain political accountability. Though an open Internet tends to be valued by more democratic governments, the percentage of countries adhering to the standards of open and free media is dismally low. In a majority of countries, governments maintain a stringent level of control over many of the mainstream information outlets, making the Internet a vital source of alternative information for the people living within these environments. While media censorship is certainly not a new phenomenon, it becomes especially noteworthy when a country experiences a sudden setback in the realms of media independence and freedom of information. Such cases allow for a more nuanced observation of how much the public values media freedom and their expectations of media performance. Turkey is a striking example of how a sudden dip in media freedom may impact the social and political climate of a country. This survey report is a product of an ongoing research project by faculty and graduate students at the Ohio State University and Koç University with support from the Center for Global Communication Studies’ Internet Policy Observatory at the University of Pennsylvania’s Annenberg School of Communication. The data in this report was collected between December 20, 2014 and February 2, 2015 and represents the views of 1161 respondents from that time. The goal of the project is to understand how people in Turkey perceive and value the debate over Internet freedoms in Turkey and how they employ the Internet and social media as alternative information resources within a heavily censored mass media environment. This is an important question more broadly as 85% of the globe’s population live within censored media systems like Turkey

Coincidence of Anterior Communicating Artery Aneurysm in a Patient With Carotid Body Tumor: A Case Report

Background: Intracranial aneurysms (IAs) are focal pathologic dilation of cerebral vasculature, which mostly affect the anterior circulation of brain. Carotid body tumors (CBTs) are the most common head and neck parasympathetic paragangliomas. These slow growing neoplasms may cause hypertension along with catecholamine release symptoms, mostly in patients in their fourth decade. This is the second reported case of simultaneous presentation of CBT and IA in a male patient.Case Presentation: A 54-year-old male with positive history of hypertension presented with isolated acute weakness of right upper extremity. Bilateral Doppler ultrasound of carotid arteries showed a mass at left carotid bifurcation, which was confirmed by vessels computed tomography (CT) – angiography. CT scan also demonstrated anterior communicating artery (A-Com) aneurysm. Digital subtraction angiography (DSA) confirmed a right sided A-com artery aneurysm. Aneurismal repair was performed prior to CBT removal.Conclusion: Although multifactorial etiologies, such as hypertension, atherosclerosis and congenital predisposition with vascular abnormalities exists; this case raises the possibility of etiologic relationship between hypertension and hypertensive crises due to catecholamine release and aneurismal development and rupture. Avoidance of possible life threatening complications of aneurismal rupture necessitates preoperative evaluation for CBT in patients with established diagnosis of IA

Influence of pH on mechanical relaxations in high solids lm-pectin preparations

The influence of pH on the mechanical relaxation of LM-pectin in the presence of co-solute has been investigated by means of differential scanning calorimetry, ζ-potential measurements and small deformation dynamic oscillation in shear. pH was found to affect the conformational properties of the polyelectrolyte altering its structural behaviour. Cooling scans in the vicinity of the glass transition region revealed a remarkable change in the viscoelastic functions as the polyelectrolyte rearranges from extended (neutral pH) to compact conformations (acidic pH). This conformational rearrangement was experimentally observed to result in early vitrification at neutral pH values where dissociation of galacturonic acid residues takes place. Time-temperature superposition of the mechanical shift factors and theoretical modeling utilizing WLF kinetics confirmed the accelerated kinetics of glass transition in the extended pectin conformation at neutral pH. Determination of the relaxation spectra of the samples using spectral analysis of the master curves revealed that the relaxation of macromolecules occurs within ~0.1 s regardless of the solvent pH

The media use of diaspora in a conflict situation : A case study of Venezuelans in Finland

Many Venezuelan emigrants have an emotional connection and/or they have family members and friends in the country of origin, and that is why they seek to find reliable information on the conflict situation in Venezuela. Therefore, they keep in touch with family members, read mainstream news and use different social media platforms. Thus, what kind of impact the conflict has on the media use and how events reported in the media are interpreted is investigated in this study of Venezuelan diaspora in Finland by using social media ethnography. There are internal and external factors behind the media use. External factors come from societies of the host and origin countries. Internal factors rise from family connections and identity construction concerning personal national identity or political activism.Peer reviewe

Desaturase specificity is controlled by the physicochemical properties of a single amino acid residue in the substrate binding tunnel

Membrane fatty acyl desaturases (mFAD) are ubiquitous enzymes in eukaryotes. They introduce double bonds into fatty acids (FAs), producing structurally diverse unsaturated FAs which serve as membrane lipid components or precursors of signaling molecules. The mechanisms controlling enzymatic specificity and selectivity of desaturation are, however, poorly understood. We found that the physicochemical properties, particularly side chain volume, of a single amino acid (aa) residue in insect mFADs (Lepidoptera: Bombyx mori and Manduca sexta) control the desaturation products. Molecular dynamics simulations of systems comprising wild-type or mutant mFADs with fatty acyl-CoA substrates revealed that the single aa substitution likely directs the outcome of the desaturation reaction by modulating the distance between substrate fatty acyl carbon atoms and active center metal ions. These findings, as well as our methodology combining mFAD mutational screening with molecular dynamics simulations, will facilitate prediction of desaturation products and facilitate engineering of mFADs for biotechnological applications

Long-chain polyunsaturated fatty acid synthesis in fish: Comparative analysis of Atlantic salmon (Salmo salar L.) and Atlantic cod (Gadus morhua L.) Delta 6 fatty acyl desaturase gene promoters

Fish vary in ability to biosynthesise n-3 long-chain polyunsaturated fatty acids (LC-PUFA), with marine fish such as cod being inefficient in comparison to freshwater and salmonid fish. We investigated differences in the gene promoters of Δ6 fatty acyl desaturase (Δ6 FAD), a critical enzyme in LC-PUFA biosynthesis, in cod and salmon. Progressive deletions and targeted mutations of the promoters were tested for activity in a transfected fish cell line under low or high LC-PUFA treatment, and regions sufficient to direct transcription were identified. Comparison of these regions with sequences of corresponding regions of Δ6 FAD genes from mammals, amphibians and fish indicated a remarkable conservation of binding sites for SREBPs and NF-Y. In addition to these sites, a site was identified in salmon with similarity to that recognised by Sp1 transcription factor, and which was required for full expression of the salmon Δ6 FAD gene. The cod promoter was less active and lacked the Sp1 site. Eicosapentaenoic acid suppressed LC-PUFA synthesis in AS cells and also suppressed activity of the salmon Δ6 FAD promoter although this activity was likely mediated through sites other than Sp1, possibly similar to those recognised by NF-Y and SREBP transcription factors