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959 results on '"Oka, Hiroshi"'

1. Pauli spin blockade at room temperature in double-quantum-dot tunneling transport through individual deep dopants in silicon

Author

Ban, Yoshisuke, Kato, Kimihiko, Iizuka, Shota, Oka, Hiroshi, Murakami, Shigenori, Ishibashi, Koji, Moriyama, Satoshi, Mori, Takahiro, and Ono, Keiji

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Quantum Physics
Abstract

Pauli spin blockade (PSB) is a spin-dependent charge transport process that typically appears in double quantum dot (QD) devices and is employed in fundamental research on single spins in nanostructures to read out semiconductor qubits. The operating temperature of PSB is limited by that of the QDs and remains below 10 K, limiting wide application development. Herein, we confirm that a single deep dopant in the channel of a silicon field effect transistor functions as a room-temperature QD; consequently, transport through two different deep dopants exhibits PSB up to room temperature. The characteristic magnetoconductance provides a means to identify PSB and enables the PSB device to function as a magnetic sensor with a sensitivity below geomagnetic field. Lifting in PSB caused by magnetic resonance (50 K) and Rabi oscillations (10 K) are also observed. Further development of this unique system may lead to room-temperature quantum technologies based on silicon technology., Comment: 30 pages, 11 figures, 1 table

Published
2024

2. Characterization and quantitative understanding of subthreshold swing of Si metal–oxide–semiconductor field effect transistors at cryogenic temperatures.

Author

Kang, Min-Soo, Toprasertpong, Kasidit, Oka, Hiroshi, Mori, Takahiro, Takenaka, Mitsuru, and Takagi, Shinichi

Subjects
FIELD-effect transistors, METAL oxide semiconductor field-effect transistors, ENERGY levels (Quantum mechanics), DENSITY of states, FERMI level, ENERGY policy
Abstract

The temperature and drain current (ID) dependencies of sub-threshold swing (SS) values of Si n- and p-channel metal–oxide–semiconductor field effect transistors (MOSFETs) with different substrate impurity concentrations ranging from the 1015 to 1018 cm−3 ranges are systematically and experimentally evaluated at cryogenic temperatures. It is found that SS of p-channel MOSFETs tends to increase with decreasing temperature, which contrasts with saturation of SS of n-MOSFETs at cryogenic temperatures, well reported by many previous works. To explain these SS behaviors quantitatively, we employ a density-of-state (DOS) model with tail states consisting of localized states in a deep energy range and mobile states in a shallow energy range, which are attributable to potential fluctuations caused by substrate impurities. It is shown that this model can quantitatively explain the temperature and ID dependencies of SS of both n-MOSFETs and p-MOSFETs. Then, we are assuming that the Si p-MOSFET has a higher density of localized states than the n-MOSFET. Thus, the increase in SS of the p-MOSFETs with decreasing temperature is explained by an increase in the density of localized states at the Fermi level with decreasing temperature, because the density of localized states increases with elevating the Fermi level position in the employed DOS model. [ABSTRACT FROM AUTHOR]

Published
2024
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40. A successful operation for giant intra‑abdominal desmoid tumors associated with familial adenomatous polyposis: A case report

Author

Ichikawa, Yoshitoshi, Lee, Kyowon, Yokouchi, Takashi, Watanabe, Souta, Yoshimura, Daishi, Mizojiri, Gaku, Maruyama, Kentaro, Maeda, Tamaki, Fujimori, Yasushi, and Oka, Hiroshi

Subjects
Cancer Research, Oncology, Case Report
Abstract

Desmoid tumors are benign proliferations of spindle cells originating in fibro-aponeurotic tissue. Many patients with familial adenomatous polyposis (FAP) die from desmoid tumors, which can arise spontaneously but often appear to be surgically induced by prophylactic colectomy. Desmoid tumors are the second most common cause of death in patients with FAP, second to colorectal cancer. Many patients can live a long life with desmoid tumors without symptoms, but when symptoms (ranging from bowel or ureteric obstruction to bowel perforation with abscess and fistula) appear or there is a risk of functional impairment, a wide spectrum of therapies (local and systemic) are valuable in improving the symptoms and controlling the disease. A half-Japanese, half-Caucasian male, who had been diagnosed with intra-abdominal desmoid tumors associated with FAP at age 13, was treated using abdominal wall incision for decompression and chemotherapy from the age of 38. The therapeutic outcome was progressive disease, based on the modified response evaluation criteria in solid tumors (mRECIST), and when he visited our hospital at age 41 the desmoid tumor had invaded the small bowel with a fistula to the abdominal wall. We performed a palliative operation to improve his symptoms, which were fever, abdominal pain, vomiting, and difficulty eating. As the tumor was extremely large and had invaded the small intestine, massive resection including the small intestine was required. To prepare for anticipated massive bleeding, a balloon catheter was placed in the superior mesenteric artery just prior to surgery. Although the operation was extremely difficult, following surgery the patient regained his ability to eat and when discharged was ambulatory and without short-bowel syndrome. We report our experience treating one of the largest reported intraperitoneal desmoid tumors. Resection resulted in a good postoperative course, with improved quality of life and prognosis.

Published
2022
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46. Study on irradiation effects of refractory bcc high-entropy alloy

Author

Zong, Yun, Hashimoto, Naoyuki, 1000010738967, Oka, Hiroshi, Zong, Yun, Hashimoto, Naoyuki, 1000010738967, and Oka, Hiroshi

Abstract

We developed body-centered cubic refractory high-entropy alloys, MoNbTaTi, MoNbTaW, and MoNbTaTiW, and explored their microstructure, and mechanical properties in order to develop a new high-irradiation resistance material suitable for fusion reactor components. Three HEAs were annealed at 1200 degrees C for 48 h to form single face BCC alloys, while MoNbTaW was also annealed at 1500 degrees C. SEM inspection and EDS mapping have both validated this result. The Vickers hardness of three HEAs was investigated, and the stable results indicate that they are all stable at elevated temperatures. Three HEAs are ion irradiated with 6.4 MeV Fe3+ at a temperature of 500 degrees C, and the irradiation hardening is examined using nanoindentation. In comparison to pure tungsten, the three HEAs exhibit increased resistance to irradiation.

Published
2022

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