Adaptive reference model predictive control for power electronics

An adaptive reference model predictive control (ARMPC) approach is proposed as an alternative means of controlling power converters in response to the issue of steady-state residual errors presented in power converters under the conventional model predictive control (MPC). Differing from other methods of eliminating steady-state errors of MPC based control, such as MPC with integrator, the proposed ARMPC is designed to track the so-called virtual references instead of the actual references. Subsequently, additional tuning is not required for different operating conditions. In this paper, ARMPC is applied to a single-phase full-bridge voltage source inverter (VSI). It is experimentally validated that ARMPC exhibits strength in substantially eliminating the residual errors in environment of model mismatch, load change, and input voltage change, which would otherwise be present under MPC control. Moreover, it is experimentally demonstrated that the proposed ARMPC shows a consistent erasion of steady-state errors, while the MPC with integrator performs inconsistently for different cases of model mismatch after a fixed tuning of the weighting factor

The Effects of Overstration on the Stratified Log Rank Test for Survival Analysis

Survival analysis concerns the characterization or comparison of one or more distributions of the time to a well defined event. The log-rank test is the most common method used to compare the survival distributions of two samples. When data within the two groups are stratified according to some risk factors, then a stratified log-rank test is employed. Stratified analysis is a procedure used to compare outcomes in different groups while at the same time correcting for the effects of confounders. It is one way to ensure that important prognostic factors are equally distributed among different treatments. The ordinary log-rank test is known to be conservative when treatments have been assigned by a stratified design. The stratified log-rank test is valid even when the sizes of strata differ. Schoenfeld and Tsiatis modified the log-rank test with a variance adjustment reflecting the dependence of survival on strata size. Their method is shown to be more efficient than the ordinary stratified log rank test when the number of strata is large, and it remains valid when the censoring distributions differ across treatment groups. In this thesis, we investigate these three log-rank tests for survival analysis. The effect of the stratum sizes on each type of analysis is evaluated using simulated data. Our results show that the modified log rank test is beneficial for stratified survival analysis in most cases especially when there are large numbers of strata and the strata sizes get small. The statistical power of the modified log-rank test is relatively stable even with very small strata sizes and high strata effects. The public health relevance of this thesis is that the modified log-rank test we investigated and implemented using the R programming language provides an alternative and more efficient way to accommodate higher amounts of stratification in analyzing survival data. More efficient statistical methods indirectly have public health impact as such methods lead to analyses which better identify treatments, interventions or factors that influence health outcomes. Such analyses are commonly used in clinical trials and other studies which influence public healt

Laparoscopic resection of gastric wall tumor

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Lutein enhances survival and reduces neuronal damage in cerebral and retinal ischemia/reperfusion injury

Poster session 3: NeuroprotectionConference theme: Translational Neuroscience: From Molecules To ManPurpose Stroke is one of the leading causes of death worldwide. Protective agents that could diminish the injuries induced by cerebral ischemia/reperfusion (I/R) are crucial to alleviate the detrimental outcome of stroke. Retinal I/R also occurs in many ocular diseases and leads to neuronal death and therefore blindness. Lutein, a safe and potent antioxidant, is known to protect the retina in age-related macular degeneration. The aim of this study is to investigate the protective roles of lutein in cerebral and retinal I/R injury. Methods Two-hour cerebral ischemia was induced by unilateral middle cerebral artery occlusion (MCAo) in mice. Either lutein (0.2mg/kg) or vehicle was given to mice intraperitoneally 1hr after MCAo and 1hr after reperfusion. Neurological deficits were evaluated at 22hr after reperfusion while survival rate was assessed daily until 7 days after reperfusion. Flash electroretinogram (flash ERG) was taken to assess retinal function. After sacrifice, mouse brains were cut into 2mm-thick coronal slices and stained with 2% 2,3,5-triphenyltetrazolium chloride to determine the infarct size after MCAo. Eyes were also enucleated. Paraffin-embedded brain and retinal sections were prepared for TUNEL assay and immunohistochemistry. Protein lysate was collected for Western blotting experiments. Lutein's effect on Müller cells was further evaluated using a model of cobalt chloride-induced hypoxia in immortalized rat Müller cells (rMC-1). Results Higher survival rate, better neurological scores, smaller infarct area and smaller infarct volume were noted in the lutein-treated group. Immunohistochemistry data showed a decrease of immunoreactivity of nitrotyrosine, poly(ADP-ribose) and NFkB in the lutein-treated brains. Western blotting data showed decreased levels of Cox-2, pERK, and pIkB, but increased levels of Bcl-2, heat shock protein 70 and pAkt in the lutein-treated brains. In the retina, severe cell loss in retinal ganglion cell (RGC) layer was noted after I/R injury. Increased oxidative stress was observed in the injured retina. Lutein treatment protected RGC as well as decreased oxidative stress in I/R retina. Lutein treatment also minimized the deterioration of b-wave/a-wave ratio and oscillatory potentials in flash ERG as well as inhibited the up-regulation of GFAP in retinal I/R injury. In the cultured Müller cells, lutein treatment reduced level of nuclear NF-kB together with decreased levels of IL-1b and Cox- 2. Conclusions Post-treatment of lutein protected both the brain and retina from I/R injury. The neuroprotective effect of lutein was associated with reduced oxidative stress. Less production of pro-inflammatory factors from Müller cells suggested an anti-inflammatory role of lutein in retinal ischemic/hypoxic injury. Our results suggest that lutein could diminish the deleterious outcomes of cerebral and retinal I/R probably by its antiapoptotic, anti-oxidative and anti-inflammatory properties. Lutein may have a therapeutic role in protecting the brain in stroke and inner retina in eye diseases with acute ischemia.published_or_final_versio

Reliable control using redundant controllers

This paper presents a methodology for the design of reliable control systems by using multiple identical controllers to a given plant. The resulting closed-loop control system is reliable in the sense that it provides guaranteed internal stability and H ∞ performance (in terms of disturbance attenuation), not only when all controllers are operational but also when some controller outages (sensor and/or actuator) occur. A numerical example is given to illustrate the proposed design procedures.published_or_final_versio

Detecting dynamic communities in opportunistic networks

In opportunistic networks, communities of mobile entities may be utilized to improve the efficiency of message forwarding. However, identifying communities that are dynamically changing in mobile environment is non-trivial. Based on random walk on graphs, in this paper we present a community detection algorithm that takes into account the aging and weight of contacts between mobile entities. Our idea originates from message-forwarding operations in opportunistic networks. We evaluate the algorithm on both computer-generated networks and real-world human mobility traces. The result shows that our proposed algorithm can find the communities and detect the changes in their structures over time. © 2009 IEEE.published_or_final_versionThe 1st International Conference on Ubiquitous and Future Networks (ICUFN 2009), Hong Kong, China, 7-9 June 2009. In Proceedings of the 1st ICUFN, 2009, p. 159-16

Stress and its effect on optical properties of GaN epilayers grown on Si(111), 6H-SiC(0001), and c-plane sapphire

Stress and its effects on optical properties of GaN epilayers grown in Si(111), 6H-SiC(0001), and c-plane sapphire were investigated. Large tensile stress was present in GaN epilayers grown on Si and 6H-SiC, and a small compressive stress appeared in the film grown on sapphire. The results showed that the thermal mismatch between the epilayers and the substrates plays a major role in determining the residual strain in the films.published_or_final_versio

IsaB Inhibits Autophagic Flux to Promote Host Transmission of Methicillin-Resistant Staphylococcus aureus.

Methicillin-resistant Staphylococcus aureus (MRSA) has emerged as a major nosocomial pathogen that is widespread in both health-care facilities and in the community at large, as a result of direct host-to-host transmission. Several virulence factors are associated with pathogen transmission to naive hosts. Immunodominant surface antigen B (IsaB) is a virulence factor that helps Staphylococcus aureus to evade the host defense system. However, the mechanism of IsaB on host transmissibility remains unclear. We found that IsaB expression was elevated in transmissible MRSA. Wild-type isaB strains inhibited autophagic flux to promote bacterial survival and elicit inflammation in THP-1 cells and mouse skin. MRSA isolates with increased IsaB expression showed decreased autophagic flux, and the MRSA isolate with the lowest IsaB expression showed increased autophagic flux. In addition, recombinant IsaB rescued the virulence of the isaB deletion strain and increased the group A streptococcus (GAS) virulence in vivo. Together, these results reveal that IsaB diminishes autophagic flux, thereby allowing MRSA to evade host degradation. These findings suggest that IsaB is a suitable target for preventing or treating MRSA infection

Controlled release of human growth hormone fused with a human hybrid Fc fragment through a nanoporous polymer membrane

Nanotechnology has been applied to the development of more effective and compatible drug delivery systems for therapeutic proteins. Human growth hormone (hGH) was fused with a hybrid Fc fragment containing partial Fc domains of human IgD and IgG(4) to produce a long-acting fusion protein. The fusion protein, hGH-hyFc, resulted in the increase of the hydrodynamic diameter (ca. 11 nm) compared with the diameter (ca. 5 nm) of the recombinant hGH. A diblock copolymer membrane with nanopores (average diameter of 14.3 nm) exhibited a constant release rate of hGH-hyFc. The hGH-hyFc protein released in a controlled manner for one month was found to trigger the phosphorylation of Janus kinase 2 (JAK2) in human B lymphocyte and to exhibit an almost identical circular dichroism spectrum to that of the original hGH-hyFc, suggesting that the released fusion protein should maintain the functional and structural integrity of hGH. Thus, the nanoporous release device could be a potential delivery system for the long-term controlled release of therapeutic proteins fused with the hybrid Fc fragment.X111313sciescopu