A Josephson junction bridge track and hold circuit

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1994.Includes bibliographical references (leaves 133-135).by Kimo Y.F. Tam.Sc.D

New Trends and Applications in Femtosecond Laser Micromachining

This book contains the scientific contributions to the Special Issue entitled: "New Trends and Applications in Femtosecond Laser Micromachining". It covers an array of subjects, from the basics of femtosecond laser micromachining to specific applications in a broad spectra of fields such biology, photonics and medicine

The Cryogenic AntiCoincidence detector for Athena X-IFU

Athena is an ESA project for a space telescope for the X-ray astrophysics. The scientific goal is to study the Universe by measuring the evolution of baryonic matter in large-scale structures, such as the warm-hot intergalactic medium, as well as in energetic compact objects. Because most of the baryonic component of the Universe is locked up in hot gas at temperatures of about a million degrees, and because of the extreme energetics of the processes close to the event horizon of black holes, understanding the hot and energetic Universe requires space-based observations in the X-ray band. The topic requires for spatially resolved X-ray spectroscopy and deep wide-field X-ray spectral imaging with capabilities far beyond those of current observatories like XMM-Newton and Chandra. The observatory will be a fixed 12-meter fixed-focus telescope with two instruments, the innovative X-ray Integral Field Unit (X-IFU), based on cryogenic detectors; and the Wide Field Imager (WFI). These two instruments combine the high spectral resolution of X-IFU with the high spatial resolution of WFI to achieve the scientific goals, with a measurement spectrum from 0.5 to 10 keV. X-IFU is based on 50 mK cooled Transition Edge Sensors (TES), that exploit the metal-superconductor transition. These can provide the required energy resolution, while offering exceptional efficiency compared to the spectrometers on the current generation of X-ray observatories. Since the telescope will operate in an environment rich in cosmic rays, it would be impossible to separate the signals from the background on the X-ray detector. In X-IFU, this problem will be solved by an active anticoincidence layer, which would make it possible to achieve the scientific goals for the spectroscopy of faint or distant sources. The work done in this thesis was focused on the anticoincidence detector, which is one of the core parts of the instrument. Its scope is the reduction of the signal background by about 2 orders of magnitude and will be positioned only 1 mm below the spectrometer. The Demonstration Model (DM) of the detector has been studied, realized and tested. With particular interest in improving the understanding and technology of microfabrication of superconducting devices. The detector is fabricated using optical microlithography and PLD, electro-beam evaporator, and RF-sputtering film deposition systems. The DM active area consists of 96 Ir/Au TES films connected in parallel with superimposed Nb strip lines, insulated with a SiO film, and four heaters on a Si absorber. The pixel is freestanding and attached to a gold frame with four Si beams. The frame is needed to have a strong coupling to a cryostat, since the operating point is below 1 K, and the heaters and the beams are needed to control the decoupling of the active area. Measurements are performed at temperatures around to 0.1 K (the theoretical operating point of X-IFU) in a dilution cryostat reading signals from radiation sources such as Am 241 at 60 keV or Fe 55 at 5 keV. The very low impedance of TES sensors requires a SQuID to read the output signal. In addition some structural models of the detector have been fabricated and vibrated to understand the structural characteristics and to test the response to stresses that the detector will experience during launch. Variations of the detector were studied to test its spectroscopic capabilities and to measure its thermal characteristics. To better understand the overall signal generation inside the absorber, a model and simulation of the phononic distribution of the a-thermal transient was developed. Finally, the detector was tested in conjunction with the NASA spectrometer to verify its anticoincidence performance

High-Temperature Superconductivity in Perspective

This is the second of two OTA assessments on the subject of high-temperature superconductivity (HTS). As the title suggests, this study attempts to put HTS in perspective, both in terms of competing technologies (e.g., the more mature low-temperature superconductors), and in terms of the many technical and economic problems that must be overcome before HTS can be widely used

単一クーパー対トランジスタの超伝導電流の性質とそのフォノン検出への応用

電気通信大学202

Functional brain imaging with fMRI and MEG

The work described in this thesis was performed by the author, except where indicated. All the studies were accomplished on the 3 Tesla system within the Magnetic Resonance Centre at the University of Nottingham, and the Wellcome Trust MEG Laboratory at the Aston University during the period between October 1999 and June 2005. Functional Magnetic Resonance Imaging (fMRI) and Magnetoencephalography (MEG) are two promising brain function research modalities, sensitive to the hemodynamic and electrophysiological responses respectively during brain activites. The feasibility of joint employment of both modalities was examined in both spatial and temporal domains. A somatosensory tactile stimulus was adopted to induce simple functional reaction. It was shown that a reasonable spatial correspondence between fMRI and MEG can be established. Attempts were made on MEG recordings to extract suitable aspects for temporal features matching fMRI with a method reflecting the physical principles. It was shown that the this method is capable of exposing the nature of neural electric activities, although further development is required to perfect the strategy