Seungwoo Kim

Stability analysis and synthesis for an affine fuzzy control system via LMI and ILMI: a continuous case

A new stability analysis and controller synthesis methodology for a continuous affine fuzzy system is proposed in this paper. The method suggested is based on the numerical convex optimization techniques. In analysis, the stability condition under which the affine fuzzy system is quadratically stable is derived and is recast in the formulation of linear matrix inequalities (LMIs). The emphasis of this paper, however, is on the synthesis of fuzzy controller based on the derived stability condition. In the synthesis, the stabilizability condition turns out to be in the formulation of bilinear matrix inequalities and is solved numerically in an iterative manner. Fuzzy local controllers also assume the affine form and their bias terms are solved in a numerical manner simultaneously together with the gains. Continuous iterative LMI (ILMI) approach is presented to obtain a feasible solution for the synthesis of the affine fuzzy system.

A transformed input-domain approach to fuzzy modeling

This paper presents an explanation of a fuzzy model considering the correlation among components of input data. Generally, fuzzy models have a capability of dividing an input space into several subspaces compared to a linear model. But hitherto suggested fuzzy modeling algorithms have not taken into consideration the correlation among components of sample data and have addressed them independently, which results in an ineffective partition of the input space. In order to solve this problem, this paper proposes a new fuzzy modeling algorithm, which partitions the input space more effectively than conventional fuzzy modeling algorithms by taking into consideration the correlation among components of sample data. As a way to use the correlation and divide the input space, the method of principal component is used. Finally, the results of the computer simulation are given to demonstrate the validity of this algorithm.

A multirule-base controller using the robust property of a fuzzy controller and its design method

This paper suggests a new fuzzy adaptive controller, which is able to solve the problems of classical adaptive controllers and conventional fuzzy adaptive controllers. It explains the architecture of a fuzzy adaptive controller using the robust property of a fuzzy controller. The basic idea of new adaptive control scheme is that an adaptive controller can be constructed with parallel combination of robust controllers. This new adaptive controller uses a multirule-base architecture which has several independent fuzzy controllers in parallel, each with different robust stability area. Out of several independent fuzzy controllers, the most suited one is selected by a system identifier which observes variations in the controlled system parameter. Here, we propose a design procedure which can be carried out mathematically and systematically from the model of a controlled system; related mathematical theorems and their proofs are also given. The performance of the proposed adaptive control algorithm is analyzed through a design example and a DC motor control simulation.

Chronic microinjection of valproic acid into the nucleus accumbens attenuates amphetamine-induced locomotor activity.

Amphetamine (AMPH)-induced hyper-locomotion has been well manifested in an animal model of psychiatric diseases such as drug addiction and bipolar disorder. In this study, we investigated the effects on AMPH-induced locomotor activity of chronically microinjected valproic acid into the nucleus accumbens (NAcc). Rats with guide cannular implanted bilaterally were divided into three groups and either saline or valproic acid (100 or 300 microg/0.5 microl/side) was microinjected into the NAcc once daily for 7 days. On day 8, half of each group received either saline or AMPH (1mg/kg, i.p.), respectively, and locomotor activity was measured for 2h. The increases of both horizontal locomotion and rearing by AMPH were attenuated in the rat pre-treated with valproic acid compared to saline in a dose-dependent manner. These results indicate that neuronal modifications in the NAcc induced by chronic valproic acid can modulate amphetamine-induced locomotor activity.

Co-occurrence of Acute Retinal Artery Occlusion and Acute Ischemic Stroke: Diffusion-Weighted Magnetic Resonance Imaging Study

PURPOSE To evaluate the co-occurrence of acute ischemic stroke and acute retinal artery occlusion (RAO). DESIGN Retrospective observational case series. METHODS We included 33 consecutive patients with acute RAO who underwent diffusion-weighted magnetic resonance imaging within 7 days of the onset of visual symptoms. The causes of RAO were classified according to the Trial of Org 10172 in Acute Stroke Treatment (TOAST) criteria, which are based on clinical features and the results of etiological evaluations for atherosclerosis, cardioembolism and other prothrombotic conditions. We evaluated the prevalence of accompanying acute ischemic stroke in subjects with acute RAO and examined the relationships with etiological parameters. RESULTS Acute ischemic stroke was detected in 8 (24.2%) subjects with RAO. Among these subjects, 3 (37.5%) patients did not exhibit any neurologic symptoms or signs. Most of the infarction patterns were small, multiple and scattered. All of the subjects with RAO who were positive for lesions on diffusion-weighted imaging had identifiable causes, whereas only 36% of the subjects who were negative for lesions had identifiable etiologies (P = .003). Carotid stenosis or cardioembolic sources were found more commonly in cases of central retinal artery occlusion (CRAO; 7/18, 38.9%) than in cases of branch retinal artery occlusion (BRAO; 1/15 6.7%, P = .046). CONCLUSIONS Acute cerebral infarctions frequently accompany RAO. We recommend diffusion-weighted imaging for patients with RAO because the presence of lesions on diffusion-weighted imaging is accompanied by a significantly increased probability of identifying the cause.

Microinjection of CART peptide 55-102 into the nucleus accumbens blocks both the expression of behavioral sensitization and ERK phosphorylation by cocaine.

The role of the biologically active CART 55-102 peptide in the nucleus accumbens (NAcc) in the expression of cocaine-induced behavioral sensitization was investigated. Rats were divided into four groups: one for saline and the other three for cocaine pre-exposures (15 mg/kg, i.p., once daily for 7 days). After 3 weeks of withdrawal, rats were microinjected into the NAcc either saline or CART 55-102 (1.0, or 2.5 microg/0.5 microl/side) followed by cocaine challenge (10 mg/kg, i.p.). Microinjection into the NAcc of CART 55-102 peptide dose-dependently blocked the expression of locomotor sensitization produced by repeated cocaine pre-exposures. Next, we further examined the effect of CART 55-102 microinjection on extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation levels in the NAcc. Additional four groups of rats were all cocaine pre-exposed and, after 3 weeks of withdrawal, they were either saline or cocaine challenged systemically following microinjection into the NAcc of either saline, CART 55-102 (2.5 microg/0.5 microl/side), or the equivalent mole amount of inactive CART 1-27 peptide. The increase of ERK1/2 phosphorylation levels in the NAcc by cocaine was completely blocked by CART 55-102 microinjection in this site, while it remains unaffected by inactive CART 1-27 peptide. These results suggest that CART 55-102 peptide in the NAcc may play a compensatory inhibitory role in the expression of behavioral sensitization by cocaine and these effects may be mediated by its inhibition of ERK1/2 phosphorylation in this site.

CART peptide 55-102 microinjected into the nucleus accumbens inhibits the expression of behavioral sensitization by amphetamine

CART peptide has been shown to regulate the actions of psychomotor stimulants. Here we have further investigated the role of the biologically active CART 55-102 peptide in the nucleus accumbens (NAcc) in the expression of behavioral sensitization by amphetamine (AMPH). Rats were pre-exposed 5 times to either saline or AMPH (1 mg/kg, i.p.). After 2 weeks of withdrawal, rats were microinjected into the NAcc with saline or CART 55-102 (1.0, or 2.5 microg/0.5 microl/side) followed by AMPH challenge (1 mg/kg, i.p.). The enhanced increase of locomotion and rearing produced by repeated AMPH pre-exposures was dose-dependently inhibited by microinjection into the NAcc of CART 55-102 peptide. These results indicate that CART 55-102 peptide in the NAcc can play a compensatory inhibitory role in the expression of behavioral sensitization by AMPH and further suggest that CART peptide may be a useful target to control the drug addiction by psychomotor stimulants.

Image retrieval model based on weighted visual features determined by relevance feedback

An accurate and rapid method is required to retrieve the overwhelming majority of digital images. To date, image retrieval methods include content-based retrieval and keyword-based retrieval, the former utilizing visual features such as color and brightness, and the latter utilizing keywords that describe the image. However, the effectiveness of these methods in providing the exact images the user wants has been under scrutiny. Hence, many researchers have been working on relevance feedback, a process in which responses from the user are given as feedback during the retrieval session in order to define a users need and provide an improved result. Methods that employ relevance feedback, however, do have drawbacks because several pieces of feedback are necessary to produce an appropriate result, and the feedback information cannot be reused. In this paper, a novel retrieval model is proposed, which annotates an image with keywords and modifies the confidence level of the keywords in response to the users feedback. In the proposed model, not only the images that have been given feedback, but also other images with visual features similar to the features used to distinguish the positive images are subjected to confidence modification. This allows for modification of a large number of images with relatively little feedback, ultimately leading to faster and more accurate retrieval results. An experiment was performed to verify the effectiveness of the proposed model, and the result demonstrated a rapid increase in recall and precision using the same amount of feedback.

Blockade of ERK Phosphorylation in the Nucleus Accumbens Inhibits the Expression of Cocaine-induced Behavioral Sensitization in Rats

Repeated administration of psychostimulants such as cocaine leads to the development of behavioral sensitization. Extracellular signal-Regulated Kinase (ERK), an enzyme important for long-term neuronal plasticity, has been implicated in such effects of these drugs. Although the nucleus accumbens (NAcc) is the site mediating the expression of behavioral sensitization by drugs of abuse, the precise role of ERK activation in this site has not been determined. In this study we demonstrate that blockade of ERK phosphorylation in the NAcc by a single bilateral microinjections of PD98059 (0.5 or 2.0µ g/side), or U0126 (0.1 or 1.0µg/side), into this site dose-dependently inhibited the expression of cocaine-induced behavioral sensitization when measured at day 7 following 6 consecutive daily cocaine injections (15 mg/kg, i.p.). Acute microinjection of either vehicle or PD98059 alone produced no different locomotor activity compared to saline control. Further, microinjection of PD98059 (2.0µ g/side) in the NAcc specifically lowered cocaine-induced increase of ERK phosphorylation levels in this site, while unaffecting p-38 protein levels. These results indicate that ERK activation in the NAcc is necessary for the expression of cocaine-induced behavioral sensitization, and further suggest that repeated cocaine evokes neuronal plasticity involving ERK pathway in this site leading to long-lasting behavioral changes.

A B-Tree index extension to enhance response time and the life cycle of flash memory

Flash memory has critical drawbacks such as long latency of its write operation and a short life cycle. In order to overcome these limitations, the number of write operations to flash memory devices needs to be minimized. The B-Tree index structure, which is a popular hard disk based index structure, requires an excessive number of write operations when updating it to flash memory. To address this, it was proposed that another layer that emulates a B-Tree be placed between the flash memory and B-Tree indexes. This approach succeeded in reducing the write operation count, but it greatly increased search time and main memory usage. This paper proposes a B-Tree index extension that reduces both the write count and search time with limited main memory usage. First, we designed a buffer that accumulates update requests per leaf node and then simultaneously processes the update requests of the leaf node carrying the largest number of requests. Second, a type of header information was written on each leaf node. Finally, we made the index automatically control each leaf node size. Through experiments, the proposed index structure resulted in a significantly lower write count and a greatly decreased search time with less main memory usage, than placing a layer that emulates a B-Tree.