Search

This study attempts to address an important clinical issue by identifying potential candidates of VEGF signaling through Flt-1 receptor that trigger angiogenic signal under ischemic stress. To determine the significance of VEGF-Flt-1 (VEGFR1) signaling in ischemic preconditioned (PC) myocardium, we used heterozygous Flt-1 knockout (KO) mice to dissect the pathway and identify candidate genes involved in VEGF signaling. DNA microarrays were employed to detect, characterize and distinguish altered myocardial gene expression by comparing between wild type (WT) CD-1 and heterozygous Flt-1 KO mice when exposed to ischemia (30 min) and reperfusion (2 h). Moreover, KO mice demonstrated reduced beneficial effects of PC when compared to the WT with PC. In the KO and WT mice, the % recovery of the left ventricular developed pressure and the maximum first derivative of the developed pressure after ischemia/reperfusion without PC were similar. However, when animals were subjected to PC, the left ventricular functional recovery throughout the reperfusion period was significantly lower in KO mice than in WT mice. These results indicate for the first time that in the heterozygous Flt-1 KO mice, PC is not as effective as that found in WT. This observation may be due to downregulation of several important genes such as growth-regulated oncogene 1 (Gro1), heat shock proteins (HSP), I kappa B kinase β (IKKβ), colony-stimulating factor-1 (CSF-1) and annexin A7, suggesting the importance of VEGF-Flt-1 receptor signaling during PC.

This paper proposes a hybrid multi-converter system aiming at a large capacity high voltage high efficiency converter system with being free from harmonies in its input/output. The system can consist of n-1 (n: integer) GTO inverters and a single neutral-point-clamped IGBT inverter connected in series by n output transformers. The GTO converters operate in a square-wave switching mode, while the IGBT converter operates in a PWM switching mode. The former produces a base part of the resultant output voltage. The latter not only produces an additional part of the resultant output, but offsets the harmonic components generated by the GTO converters. A basic voltage control strategy for the system is proposed, and its validity is verified by experimental results.

An active filter (AF) is required to have a high current control capability of tracking a time-varying current reference. However, a steady-state current error always exists because the current reference varies in time. This paper proposes the application of adaptive digital signal processing (ADSP) to the current control of AF ADSP does not require any additional hardware. It can automatically minimize the steady-state error. Since the processing time available by a computer is limited, ADSP cannot eliminate higher order harmonics but can eliminate lower order harmonics such as 5/sup th/ to 17/sup th/. Experimental results demonstrate that ADSP is useful for improving filtering performance.

A hybrid converter system aiming at a higher voltage higher capacity higher efficiency converter system having fewer harmonics in its output is proposed. The system consists of a GTO inverter operating in a square-wave mode and a neutral-point-clamped IGBT inverter operating in a PWM mode. The former produces a base part of the resultant output. The latter produces an additional part of the resultant output as well as eliminates the harmonic components generated by the GTO inverter. A basic control strategy for both inverter and rectifier operation of the system is proposed. Furthermore, an attainable output capacity, device losses, and current THD of the hybrid system, when available devices in the market are used, are estimated. It is concluded that the hybrid system has an advantage over the others in terms of efficiency and harmonic distortion.

A rectifier system having a voltage step-up and step-down characteristic is treated. The system consists of a three-phase PWM voltage source rectifier and a DC-to-DC buck converter connected in cascade. The linearized state equation which governs the whole system is presented. An optimal regulator is applied to control the rectifier system. The validity of the modeling and control strategy is confirmed by simulation studies.

The paper proposes a simple and practical method for improving the performance of DSP-controlled active power filters (AF). The transfer function of a DSP-controlled AF has a phase-lag property because there is calculation time delay in the control output, which causes a serious deterioration in the AF performance. In the proposed system, an adaptive digital filter (ADF) operates as a series compensator and compensates for the time-lag property of AF. The ADF requires no additional hardware, but for only a slight additional software. It was confirmed by simulation and experimental results that simple two-tap ADF is very effective for improving the AF compensation performance.

Neutral-point-clamped boost rectifiers (NPCR) are suitable for high-voltage systems because of their circuit structure. The NPCRs, however, have a problem in that the neutral point potential (NPP) varies when the current flows into or out of the neutral point. The variations cause voltage deviations in the input waveforms as well as unbalanced voltage stress in the devices. Accordingly, reducing NPP variations is very important. This paper describes a controlling method for NPCRs based on a state-space model. The neutral point current is treated as one of the inputs. The controller is designed based on the optimal regulator theory in order to achieve the control of DC voltage, power factor and NPP, simultaneously. The validity of the proposed method is demonstrated by experimental results.

This paper describes the harmonic evaluation of three-phase carrier-based multilevel (2-level to 5-level) PWM inverter methods. The harmonic distortion determining factor (HDDF), which represents the intrinsic spectral property of individual PWM methods, is calculated for each of the multilevel PWM methods, and is used as the common quality index. Almost all the carrier-based PWM schemes that have been proposed so far are considered. HDDF values are helpful for selecting inverter system parameters for AC motor drive applications because they can be used for predicting the current harmonics or torque ripple in AC drives.

This paper describes a new harmonic evaluation scheme of neutral-point-clamped (NPC) PWM inverters. The scheme uses the harmonic distortion determining factor (HDDF). As the HDDF represents the intrinsic spectral property of PWM schemes and is almost independent of the operating conditions, it is quite useful for evaluating PWM schemes. In addition, the HDDF is also useful for predicting the harmonic properties in AC drives. If HDDF values for individual PWM schemes are known, the approximate harmonic characteristics, such as the current harmonics or the torque ripples, can be easily calculated using HDDF values. In this paper, HDDF values of five types of carrier-based NPC-PWM schemes are given, and the approximate harmonic characteristics calculated by the HDDF approach are discussed.

An active filter (AF) is required to have a high current control capability of tracking a time-varying current reference. However, a steady-state current error always exists because the current reference varies in time. This paper proposes the application of adaptive digital signal processing (ADSP) to the current control of AF. ADSP does not require any additional hardware, but it can automatically minimize the steady-state error. Since the processing time available by a computer is limited, ADSP cannot eliminate higher order harmonics but can eliminate lower order harmonics such as 3/sup rd/ to 17/sup th/. Experimental results demonstrate that ADSP is useful for improving filtering performance.

A new current control method based on the internal model principle in control theory is proposed. It introduces a sinusoidal internal model into the control system. It does not use any coordinate transformations. The method can be used for tracking an arbitrary number of harmonics; a DC component or a fundamental frequency component signal. It is applied to a single-phase PWM inverter and active filter. The validity is confirmed by simulation and experimental results.

Publisher Summary The chapter presents a study on myocardial angiogenesis. Angiogenesis is known to be the body's natural healing process in which new blood vessels grow in response to injury. In the myocardium, hypoxia usually occurs during ischemic episodes. Such ischemic hypoxia is often followed by reperfusion. It is during this subsequent reperfusion period that reoxygenation occurs and reactive oxygen intermediates are formed. For the study of angiogenesis in the infarcted myocardium, a rat survival model of chronic myocardial infarction surgery is developed, and the examination of the left ventricular response during pharmacological stress, testing with dobutamine as a measure of cardiac reserve is conducted. The experimental protocol described in the chapter demonstrates myocardial angiogenesis stimulated by nonlethal moderate hypoxic challenge by utilizing an animal model of chronic myocardial infarction progressing to heart failure. Such angiogenic effects of preconditioning were found to be dim to its ability to augment vascular endothelial growth factor (VEGF), protein expression, which presumably played a crucial role in reducing endothelial cell apoptosis, a proved determinant for congestive heart failure.

We have developed a mechanical stabilizer for use in off-pump direct coronary artery bypass grafting. We consider it an improvement on the sucker-type stabilizer, although it uses the mechanisms of the compressor-type. Our hybrid stabilizer effectively immobilizes the local heart surface with light compression and low evacuation. We believe that its use will eliminate the need for further immobilization and thus reduce cardiac invasiveness.

The authors have newly devised a fluorescence cystoscope assembly. This fluorescence assembly is able to 1) confirm lesions in the bladder mucosa by fluorescence, 2) mark and cut the lesion with accuracy for histological survey. Moreover, this assembly is characterized by its exactness in cutting out the appropriate amount of specimen (bladder mucosa) and by its convenience in performing biopsy especially around the bladder neck.

Three different methods have been examined to express the densities of spectrograms recorded on an Ilford Q2plate in our Mattauch-Herzog type mass spectrograph. The exposures have been decided by the integrated ion currents measured by the monitor electrode, thus their fluctuations have been eliminated without any internal standard. As examples, the isotopic abundances of Cu and Zn have been measured with appropriate calibration curves . The precision and accuracy of the measurements have been briefly discussed.

Brief exposure of endothelial cells to oxidative stress induced by hypoxia followed by reoxygenation enhances tube formation. Our study provides evidence that hypoxic preconditioning accelerates tubular morphogenesis along with the activation of reactive oxygen species-inducible nuclear transcription factor-kappaB (NF-kappaB), phosphatidylinositol 3-kinase (PI3-kinase) and broad-spectrum anti-apoptotic protein survivin in human coronary arteriolar endothelial cells (HCAEC). The formation of tubular morphogenesis was inhibited by using the PI3-kinase and NF-kappaB antagonists LY294002 and SN50 respectively. The activation of survivin by hypoxic preconditioning was also inhibited by LY294002 and SN50 along with increased apoptosis in HCAEC. These data demonstrate a crucial role of PI3-kinase/Akt/NF-kappaB/survivin signaling in tubular morphogenesis of HCAEC triggered by hypoxic preconditioning.

A nuclear fuel shipping cask is a cylindrical, multi-layered container with fins for heat transfer to ambient air. When transporting spent fuel in cask, thermal analysis is regulated by IAEA and local country laws.