Shin Ito

Osteocyte calcium signaling response to bone matrix deformation

Osteocytes embedded in calcified bone matrix have been widely believed to play important roles in mechanosensing to achieve adaptive bone remodeling in a changing mechanical environment. In vitro studies have clarified several types of mechanical stimuli such as hydrostatic pressure, fluid shear stress, and direct deformation influence osteocyte functions. However, osteocyte response to mechanical stimuli in the bone matrix has not been clearly understood. In this study, we observed the osteocyte calcium signaling response to the quantitatively applied deformation in the bone matrix. A novel experimental system was developed to apply deformation to cultured bone tissue with osteocytes on a microscope stage. As a mechanical stimulus to the osteocytes in bone matrix, in-plane shear deformation was applied using a pair of glass microneedles to bone fragments, obtained from 13-day-old embryonic chick calvariae. Deformation of bone matrix and cells was quantitatively evaluated using an image correlation method by applying for differential interference contrast images of the matrix and fluorescent images of immunolabeled osteocytes, together with imaging of the cellular calcium transient using a ratiometric method. As a result, it was confirmed that the newly developed system enables us to apply deformation to bone matrix and osteocytes successfully under the microscope without significant focal plane shift or deviation from the observation view field. The system could be a basis for further development to investigate the mechanosensing mechanism of osteocytes in bone matrix through examination of various types of rapid biochemical signaling responses and intercellular communication induced by matrix deformation.

Superconductive radiation detector with large sensitive area (series‐connected STJ detector)

One of the serious problems in the development of particle detectors with superconducting tunnel junctions (STJ) is the difficulty in devising a large area that is sensitive to nuclear radiations. The problem has been solved by using an assembly of micro STJs connected in series (series‐connected STJ detector), which is designed for detecting nonthermal phonons created by irradiating the rear substrate (sapphire) with nuclear radiations. The present detector is sensitive not only to ionizing events but also to nonionizing events, providing us with a new method to detect nuclear radiations. Some features of the series‐connected STJ detector are described in this article.

Helium‐filled proportional counter for low‐temperature operation (1.75–4.2 K) and its application to cryogenic resonance‐electron Mössbauer spectroscopy II

The operation of the helium‐filled proportional counter (HFPC) has been investigated at low temperatures below liquid‐helium temperature, 4.2 K. It has been found that the gas gain as a function of the anode voltage is not appreciably changed by the temperature of the filling gas, but continuous electric discharges are induced at lower anode voltages as the gas temperature is decreased. The present counter technique has been applied to resonance‐electron Mossbauer spectroscopy in the temperature region below 4.2 K.

Further developments of series-connected superconducting tunnel junction to radiation detection

One of the promising radiation detection devices for various practical applications is the series-connected superconducting tunnel junction (STJ) detector. In this article, interesting topics of the detectors are described since our previous work: e.g., more than two order higher detection efficiency compared with single STJ detectors, high count rate detection, and position resolution. Detectors were cooled to 0.35–0.4 K by means of a convenient 3He cryostat. The 5.9 and 6.5 keV x rays from 55Fe are separated by a detector specially designed for x-ray detection. The possible count rate of the series-junction detector estimated from the shaping-time constant applied in the measurements is high, e.g., over 104 counts per second. A series-junction detector equipped with a position sensing mechanism has shown a position resolution of about 35 μm in a sensing area with a radius of 1.1 mm. The position resolution of series junctions improves the energy resolution. A new type series-connected STJ detector is al...

New readout technique for two-dimensional position-sensitive detectors

Abstract A new simple technique for two-dimensional position readout from one electrode plane is proposed, which is applicable to a wide range of detector types such as a gas-filled counter and a microchannel plate. Combining the “backgammon” method with the “weighted coupling capacitor” method, the present technique has a simpler electrode pattern than the “wedge and strip” method and is free from thermal noise from which the “resistive layer” method suffers. An application of this technique to a position-sensitive proportional counter is reported.

X-ray detection with an Nb-based junction and investigation of series-junction detectors

Two topics on our recent investigations into superconducting tunnel junction (STJ) detectors are discussed: the single Nb/Al-AlOx/Al/Nb junction for high-resolution x-ray detection and the series-connected superconducting tunnel junction detectors (SCSDs) with high detection efficiency. Using a single Nb/Al-AlOx/Al/Nb junction with rather large area of 178 X 178 micrometers 2, we obtained a high energy resolution of 88 eV for 5.9-keV x- rays. The signal-to-noise ratio of the SCSD is discussed from a simple theoretical formulation of electronics, showing that the series-connected STJs can be developed as a nuclear radiation detector both with high energy resolution and high efficiency. Recent experimental results of our SCSD are also given in this paper.

Effect of self-induced space charge in a high pressure position-sensitive proportional counter

The response of a position-sensitive proportional counter filled with Ar + 30%CH4 counting gas under a pressure of 7 atm has been studied in detail for 8-keV incident X-rays. The counter was operated in the region of limited proportionality, where the avalanche growth is greatly affected by self-induced space charge and hence an unfamiliar distorted energy spectrum is often observed. It is confirmed that the avalanches caused by the halo effect of Ar K X-rays, emitted in photoelectric absorption of incident X-rays, have higher gas amplification as compared to other photopeak avalanches due to different origin of primary electrons. The analysis has revealed that the effect of self-induced space charge hinders the avalanche growth of photopeak events to the extent of 50% of the observed avalanche charge. Comprehensive analysis of the complicated counter response in the region of limited proportionality under high pressure is provided.

Charge distributions of alpha-recoil atoms from electrodeposited 210Po source

Charge distributions have been measured for 206Pb recoil atoms emerging from a 210Po source electrodeposited on platinum. It has been found that more than 50% of the recoils are neutrals when the average energy loss of the recoils is about 18 keV. The observed large fraction for the neutrals indicates that a strong neutralization of the recoil ions occurs with increasing energy loss.

Evidence for the effect of electron diffusion on the gas amplification process in a gas-filled wire counter

Abstract The degree of gas amplification in a gas-filled wire counter has been studied in the region of limited proportionality as a function of the radial distance r between the position of primary ionization and the anode wire. We have found a strong dependence of the gas amplification factor on r; the factor systematically decreases as r becomes small near the anode wire and, moreover, the factor shows an abrupt increase under certain conditions, indicating a sudden change of electron avalanche mechanisms. The results provide experimental evidence for the effect of the diffusion of primary electrons on the gas amplification process in the region of limited proportionality, and have also established for the first time that a sudden transition in the amplification mechanism can be induced by a structural change of the primary-electron cloud.

Lγ X-ray emission in heavy-ion bombardment of Bi

Lgamma X-ray emission from Bi bombarded by O ions of 10 and 20 MeV and Ne ions of 88 MeV has been studied with a Si(Li) detector. The observed Lgamma X-ray spectra have been decomposed into the six transition lines of Lgamma 5, Lgamma 1, Lgamma 2 and Lgamma 3 (L-N transition), and Lgamma 6 and Lgamma 4,4(inf)/ (L-O transition), with an assumption that the energy shifts of these lines can be sorted into two groups corresponding to the L-N and L-O transitions and have the same shift in each group. The degree of N-shell multiple ionisation has been deduced from the energy shift determined for the L-O transition. The results have revealed the presence of nearly the same number of N-shell vacancies, ten to thirteen, prior to the L X-ray emission for all the ion bombardments investigated. Some indication on the O-shell multiple ionisation is given.