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Kenichi Arai

Publications and source records attributed to Kenichi Arai.

6 recordsLinked to original sources
PubMed2004

Deterministic stochastic resonance in a Rössler oscillator.

We discuss the characteristics of stochastic resonancelike behavior observed in a deterministic system. If a periodically forced Rössler oscillator strays from the phase locking state, it exhibits the intermittent behavior known as phase slips. When the periodic force is modulated by a weak signal, the phase slips synchronize with the weak signal statistically. We numerically demonstrate, in terms of interslip intervals and signal to noise ratio, that the maximum synchronization can be achieved with the optimum intensity of chaotic fluctuations. It is shown that the stochastic resonancelike behavior can be observed regardless of the choice of parameters. The frequency dependence of the signal indicates that there is an optimum frequency for the maximum resonance. The phase slip rate is derived based on the fact that the phase slips are caused by a boundary crisis caused by an unstable-unstable pair bifurcation. The interslip distributions obtained from the derived slip rate and the approximation theory of the time-dependent Poisson process agree with those obtained by numerical simulations. In addition, the maximum enhancement of a weak signal is shown to be achieved by adjusting the chaotic fluctuations even if a signal becomes mixed with noise.

Journal Article↗
PubMed2004

Histochemical, ultrastructural, and three-dimensional observation of smooth muscle cells in human gastric mucosa.

The present study was undertaken to clarify the histochemical and ultrastructural properties and the three-dimensional distribution of the smooth muscle cells (SMCs) located in the lamina propria (LP) of the human gastric mucosa. Standard paraffin sections obtained from stomachs surgically resected for gastric cancer were immunostained for alpha-smooth muscle actin (alpha-SMA), vimentin, desmin, laminin, and type IV collagen. In addition, 100-microm-thick sections were fluorostained for alpha-SMA and CD34, while three-dimensional images were prepared by confocal laser scanning microscope. Ultrastructural studies were carried out using normal gastric biopsy specimens. The results indicated that SMCs in the LP differed between the upper and lower regions, SMCs in the lower LP being fairly typical SMCs, whereas those in the upper LP had apparently lost reactivity for desmin but gained that for vimentin. The basal lamina became sparser, but a fibronexus was occasionally seen in SMCs in the upper LP. Three-dimensional images revealed bundles of SMCs in the upper LP encircling several foveolae to form acinus-like structures and, in the upper LP, SMCs branching into fine fibrils with a brush-like (corpus) or besom-like (i.e., a twiggy "witch's broom") appearance (antrum).

Actins↗
PubMed2002

Small-intestinal sarcomatoid carcinoma with superior vena cava syndrome.

A 56-year-old man was hospitalized because of swelling of the right upper extremity and anemia. A diagnosis of superior vena cava (SVC) syndrome caused by lymphogenous metastasis was made after chest computed tomography (CT) scan and biopsy of cervical lymph nodes were carried out. Standard examinations, such as abdominal CT scan and endoscopies of the upper and lower gastrointestinal tract, failed to find the primary lesion. However, selective angiography of the superior mesenteric artery (SMA) showed a clear stain of bleeding vessels in the small intestine. Laparotomy was performed, and immunohistochemical findings revealed sarcomatoid carcinoma in the small intestine (a rarely seen neoplasm). This aggressive carcinoma, which showed negative reactivity with CD34, CD117 (c-kit), and S-100 was clearly distinguished from other mesenchymal tumors, such as malignant gastrointestinal stromal tumor (GIST) and malignant fibrous histiocytoma (MFH).

Carcinosarcoma↗
PubMed2001

Dynamical origin of deterministic stochastic resonance.

We numerically demonstrate stochastic-resonance-like behavior in a deterministic chaotic oscillator system, using a modified Rössler system driven by a sinusoidal external force: intermittent 2 pi phase slips between the system and the external force synchronize with a periodic input signal that weakly modulates the external force in an appropriate parameter range. We show that the dynamical mechanism of this stochastic-resonance-like behavior is explained by a boundary crisis that depends on two bifurcation parameters.

Journal Article↗
PubMed2001

Three-dimensional analysis of alveolar structure in usual interstitial pneumonia.

The etiology of usual interstitial pneumonia (UIP), a progressive lung disease, remains unclear. We examined alveolar structure in UIP three-dimensionally. Lung biopsy specimens from five patients with idiopathic pulmonary fibrosis were used. Sections 150-microm thick were stained with elastica solution for elastic fibers, with alpha-smooth muscle actin antibody for myofibroblasts, with anti-Thomsen-Friedenreich antibody for type-II pneumocytes and with anti-CD34 antibody for blood vessels. We examined them three-dimensionally using a laser confocal microscope or light microscope. In the fibrotic lesions, the thick elastic fibers forming the alveolar framework were not particularly dense considering the reduction in alveolar volume. Near the fibrotic lesions, some of the thin elastic fibers in the alveolar wall were slightly sinuous and ended with rounded tips. Type-II pneumocytes had proliferated and were distributed uniformly over the alveolar surface. Smooth muscle actin filaments were detected only around the alveolar orifice. These findings show that in UIP destruction of the elastic fiber framework of the alveoli may lead to irreversible focal alveolar collapse after damage to the alveolar epithelial cells, and proliferation of type-II pneumocytes may be involved with this elastolysis.

Biopsy↗