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We have discovered 22 new low-mass members in the center of the 4 Myr old open cluster Trumpler 37 (Tr 37) using archival Chandra and Spitzer data. Our use of the Chandra ACIS data and an improved reduction of Spitzer Infrared Array Camera data of the central region in Tr 37 led to the discovery of three new disk-bearing members, 19 new diskless members, and potentially 10 more infrared excess sources. Combining these new members with previous known members, we measured a disk frequency of ∼39%, which is lower than the previously reported disk frequency of ∼48%. Most of the new members are diskless stars that lie within 0.65 pc of the central massive O6.5V star HD 206267. The proximity of these sources to HD 206267 suggests photoevaporation may be accelerating disk evolution in the center of Tr 37. The new members have solar-type masses ranging from ∼ 0.6 M to 1.8 M , spectral types ranging from late to early K, and X-ray luminosities in the range 29.3 erg s −1 log L X 31.9 erg s −1 . The median X-ray luminosity (L X ∼ 3×10 30 erg s −1 ) of the new members in this intermediate-aged cluster is on the same level as younger (1-3 Myr) and slightly older (5 Myr) populations in the same mass range, which suggests the ageactivity relation for pre-main-sequence solar-mass stars is constant up to ∼5 Myr and decays sometime thereafter.

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Therapeutic use of ultrasound (US) has a great potential for minimally invasive therapy. We have studied acoustic microbubble delivery for effective sonoporation and thermal therapy. To apply the techniques in vivo, a navigation system for US field positioning is indispensable. To address this issue, we have developed an intuitive navigation system using augmented reality (AR) technology. The system consists of an optical tracking device, a linear US probe, a focused US field source (US transducer) with 2.0-mm focal spot, a USB video camera, and navigation software. The probe was calibrated accurately using US probe calibration technique. Also, the transducer was calibrated using a three-dimensional sound field measurement device. Finally, the camera was calibrated using a chess board. The system we developed provides two kinds of augmented information : 1) therapeutic US field visualization on echogram, and 2) echogram plane and sound field visualization on video frame. In this study, the respective calibration accuracies were validated and microbubble trapping experiments using the focused US transducer and artificial blood vessel with 2.0-mm diameter were conducted. In the experiments, microbubbles were trapped inside the artificial blood vessel using the navigation system, implying that the focus position could be located in the blood vessel. The results demonstrated that the system we developed has adequate accuracy for microbubble control in 2.0-mm blood vessels.

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Microbubbles form their aggregations between the neighboring microbubbles by the effect of secondary Bjerknes force under ultrasound exposure. However, because of the difficulty to reproduce a capillary-mimicking artificial blood vessel, the behavior of aggregations in a capillary has not been predicted. Thus we prepared artificial blood vessels including a capillary model, which was made of poly(vinyl alcohol) (PVA) by grayscale lithography method, with minimum diameter of the path of 0.5 mm. By using this model we investigated the possibility of artificial embolization, where the microbubble aggregations might block entire vessels not to penetrate flow in downstream. Confirming that the sizes of flown aggregation were greater than the section area of the minimum path in the capillary model, we investigated the probability of path block in it. As the results we confirmed the probability increased in proportion to sound pressure and inversely to flow velocity. We are going to investigate with more kinds of parameters to enhance the possibility of artificial embolization.

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