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Nakamura, Junichi,Makishima, Akihito,Umehara, Daisuke,Kawai, Makoto 통신위성우주산업연구회 2002 Joint Conference on Satellite Communications Vol.2002 No.-
TCP is generally used for data transmission on a geo-synchronous satellite link. It is known that the throughput increase corresponding to the increase of transmission speed can not be expected on a geo-synchronous satellite link since TCP was originally designed as a protocol for terrestrial cable networks. We established a computer simulation system and an experimental system using a Ka-band satellite to investigate the TCP performance on a high speed satellite communication link. This paper describes the throughput performances obtained by both systems using Window Scaling Option which is expected to improve the conventional TCP performances and shows the relationship between bit error rate and throughput.
Experimental and numerical flow analysis in hydraulic vane pump
Junichi SUEMATSU,Tetsuhiro TSUKIJI,Mariko WATANABE,Shinji YAKABE,Hirohito WATANABE,Yoshinari NAKAMURA,Kazunari SUZUKI 유공압건설기계학회 2015 유공압건설기계학회 학술대회논문집 Vol.2015 No.10
The purpose of this study is to conduct a three dimensional flow analysis of a hydraulic vane pump by using computational fluid dynamics (CFD), to evaluate an accuracy of volumetric flow rate in CFD compared to experimental value and to examine a influence of the evaporation coefficient and condensation coefficient in Zwart–Gerber–Belamri cavitation model to pressure in a vane chamber. In this study, standard k-ε turbulent model with the Zwart–Gerber–Belamri cavitation model is used to estimate the cavitating flow in vane pump. In CFD, two notch models are used. From results of experiments and CFD analysis of volumetric flow rate, there is little difference between the experiments and CFD results in the low speed range. However, for high speed range, in a case with no cavitation model, the CFD results of volumetric flow rate are different from the experimental ones. On the other hand, in the case with cavitation model, those agree with the experimental values. In this case, the error of volumetric flow rate is less than 1% in the low speed range and less than 2.5% in the high speed range. From CFD results of pressure fluctuation in a vane chamber when the evaporation coefficient and condensation coefficient in the cavitation model are varied, the surge pressure can be seen in a vane chamber. In conclusion, it could be considered that the CFD calculation with cavitation model is sufficiently accurate in volumetric flow rate. In addition, as the evaporation coefficient becomes large, amplitude of the pressure fluctuation in a vane chamber after a surge pressure becomes large, as the condensation coefficient becomes large, the surge pressure in a vane chamber becomes low.
Takashi Yokoyama,Masaru Nakamura,Junichi Tatami,Toru Wakihara,Takeshi Meguro 한양대학교 세라믹연구소 2009 Journal of Ceramic Processing Research Vol.10 No.5
Preparation of cubic spinel-type oxides, Mn(1.75−1.25X)Co2.5XNi1.25(1−X)O4 (0 ≤X≤ 0.6), and their electrical properties were investigated. The starting oxides, containing metals with a prescribed molar ratio, were heated to 1400℃ and held for 3 h in argon. The sintered bodies were cooled to 800 oC and then oxidized for 48 h in air to convert them into a cubic spinel structure. The electrical conductivities of the sintered bodies were confirmed to increase exponentially with an increase in the temperature, indicating that they have intrinsic NTC thermistor characteristics. In the region of 0 ≤ X≤ 0.4, the electrical conductivity increased with an increase in X and decreased with an increase in X in the region of 0.4 < X ≤ 0.6. The concentration of Mn4+ in the octahedral sites of the spinel structure was considered to be larger than that of Mn3+ because the sintered bodies were n-type semiconducting. The electrical conduction of the oxides prepared in this study was concluded to be controlled by a small polaron hopping mechanism. Preparation of cubic spinel-type oxides, Mn(1.75−1.25X)Co2.5XNi1.25(1−X)O4 (0 ≤X≤ 0.6), and their electrical properties were investigated. The starting oxides, containing metals with a prescribed molar ratio, were heated to 1400℃ and held for 3 h in argon. The sintered bodies were cooled to 800 oC and then oxidized for 48 h in air to convert them into a cubic spinel structure. The electrical conductivities of the sintered bodies were confirmed to increase exponentially with an increase in the temperature, indicating that they have intrinsic NTC thermistor characteristics. In the region of 0 ≤ X≤ 0.4, the electrical conductivity increased with an increase in X and decreased with an increase in X in the region of 0.4 < X ≤ 0.6. The concentration of Mn4+ in the octahedral sites of the spinel structure was considered to be larger than that of Mn3+ because the sintered bodies were n-type semiconducting. The electrical conduction of the oxides prepared in this study was concluded to be controlled by a small polaron hopping mechanism.
Seiji Ohtori,Sumihisa Orita,Kazuyo Yamauchi,Yawara Eguchi,Yasuchika Aoki,Junichi Nakamura,Tetsuhiro Ishikawa,Masayuki Miyagi,Hiroto Kamoda,Miyako Suzuki,Gou Kubota,Kazuhide Inage,Takeshi Sainoh,Jun Sa 대한척추외과학회 2016 Asian Spine Journal Vol.10 No.3
Study Design: Retrospective case series. Purpose: To classify back muscle degeneration using magnetic resonance imaging (MRI) and investigate its relationship with back pain after surgery. Overview of Literature: Back muscle injury and degeneration often occurs after posterior lumbar surgery, and the degeneration may be a cause of back pain. However, the relationship between back muscle degeneration and back pain remains controversial. Methods: A total of 84 patients (average age, 65.1 years; 38 men, 46 women) with lumbar spinal stenosis underwent posterior decompression surgery alone. MRI (1.5 tesla) was evaluated before and more than a year after surgery in all patients. Muscle on MRI was classified into three categories: low intensity in T1-weighted imaging, high intensity in T2-weighted imaging (type 1), high intensity in both T1- and T2-weighted images (type 2), and low intensity in both T1- and T2-weighted imaging (type 3). The prevalence of the types and their relationship with back pain (determined on a visual analog scale) were evaluated. Results: MRI revealed muscle degeneration in all patients after surgery (type 1, 6%; type 2, 82%; and type 3, 12%). Type 2 was significantly more frequent compared with types 1 and 3 (p <0.01). Low back pain was significantly improved after surgery (p <0.01). Low back pain was not associated with any MRI type of muscle degeneration after surgery (p >0.05). Conclusions: Various pathologies of back muscle degeneration after posterior lumbar surgery were revealed. Type 2 (fatty) change was most frequent, and other patients had type 3 (scar) or type 1 (inflammation or water-like) changes. According to the Modic classification of bone marrow changes, Modic type 1 change is associated with inflammation and back pain. However, no particular type of back muscle degeneration was correlated with back pain after surgery.
Seiji Ohtori,Sumihisa Orita,Kazuyo Yamauchi,Yawara Eguchi,Yasuchika Aoki,Junichi Nakamura,Masayuki Miyagi,Miyako Suzuki,Gou Kubota,Kazuhide Inage,Takeshi Sainoh,Jun Sato,Kazuki Fujimoto,Yasuhiro Shiga 대한척추외과학회 2017 Asian Spine Journal Vol.11 No.1
Study Design: Retrospective case series. Purpose: The purpose of this study was to examine changes in the ligamentum flavum thickness and remodeling of the spinal canal after anterior fusion during a 10-year follow-up. Overview of Literature: Extreme lateral interbody fusion provides minimally invasive treatment of the lumbar spine; this anterior fusion without direct posterior decompression, so-called indirect decompression, can achieve pain relief. Anterior fusion may restore disc height, stretch the flexure of the ligamentum flavum, and increase the spinal canal diameter. However, changes in the ligamentum flavum thickness and remodeling of the spinal canal after anterior fusion during a long follow-up have not yet been reported. Methods: We evaluated 10 patients with L4 spondylolisthesis who underwent stand-alone anterior interbody fusion using the iliac crest bone. Magnetic resonance imaging was performed 10 years after surgery. The cross-sectional area (CSA) of the dural sac and the ligamentum flavum at L1–2 to L5–S1 was calculated using a Picture Archiving and Communication System. Results: Spinal fusion with correction loss (average, 4.75 mm anterior slip) was achieved in all patients 10 years postsurgery. The average CSAs of the dural sac and the ligamentum flavum at L1–2 to L5–S1 were 150 mm2 and 78 mm2, respectively. The average CSA of the ligamentum flavum at L4–5 (30 mm2) (fusion level) was significantly less than that at L1–2 to L3–4 or L5–S1. Although patients had an average anterior slip of 4.75 mm, the average CSA of the dural sac at L4–5 was significantly larger than at the other levels. Conclusions: Spinal stability induced a lumbar ligamentum flavum change and a sustained remodeling of the spinal canal, which may explain the long-term pain relief after indirect decompression fusion surgery.
Seiji Ohtori,Sumihisa Orita,Kazuyo Yamauchi,Yawara Eguchi,Yasuchika Aoki,Junichi Nakamura,Miyako Suzuki,Gou Kubota,Kazuhide Inage,Yasuhiro Shiga,Koki Abe,Kazuki Fujimoto,Hirohito Kanamoto,Masahiro Ino 대한척추외과학회 2017 Asian Spine Journal Vol.11 No.2
Study Design: Retrospective case series. Purpose: The purpose of this study was to determine whether discontinuing teriparatide treatment and replacing it with bisphosphonate treatment maintains the volume of the fusion mass after posterolateral fusion (PLF) in women with postmenopausal osteoporosis. Overview of Literature: Clinical data support the efficacy of parathyroid hormone (PTH) for lumbar PLF. However, the use of PTH is limited to 2 years. Methods: We treated 19 women diagnosed with osteoporosis and degenerative spondylolisthesis with teriparatide (20 μg daily subcutaneously). All patients underwent one-level instrumented PLF. Teriparatide was used during 2 months prior to surgery and more than 8 months after surgery. After discontinuing teriparatide treatment, all patients used bisphosphonate (17.5 mg risedronate weekly, oral administration). Area of the fusion mass across the transverse processes at one segment was determined on an anteroposterior radiograph at 1, 2, and 3 years after surgery. Results: We followed 19 patients for 3 years. The average duration of teriparatide treatment was 11.5 months. The bone union rate was 95%. The average area of the bone fusion mass was not significantly different between the right and left sides at 1, 2, or 3 years after surgery (p >0.05). Conclusions: This study showed that replacing teriparatide treatment with bisphosphonate maintained the bone fusion mass volume after PLF in women with postmenopausal osteoporosis.
Seiji Ohtori,Sumihisa Orita,Kazuyo Yamauchi,Yawara Eguchi,Yasuchika Aoki,Junichi Nakamura,Masayuki Miyagi,Miyako Suzuki,Gou Kubota,Kazuhide Inage,Takeshi Sainoh,Jun Sato,Yasuhiro Shiga,Koki Abe,Kazuki 대한척추외과학회 2016 Asian Spine Journal Vol.10 No.3
Study Design: Retrospective case series. Purpose: To determine whether symptoms predict surgical outcomes for patients with discogenic low back pain (DLBP). Overview of Literature: Specific diagnosis of DLBP remains difficult. Worsening of pain on flexion is a reported symptom of DLBP. This study sought to determine whether symptoms predict surgical outcomes for patients with DLBP. Methods: We investigated 127 patients with low back pain (LBP) and no dominant radicular pain. Magnetic resonance imaging was used to select patients with disc degeneration at only one level. If pain was provoked during discography, we performed fusion surgery (87 patients). Visual analogue scale score and responses to a questionnaire regarding symptoms including worsening of pain on flexion or extension were assessed. Symptom sites before surgery were categorized into LBP alone, or LBP plus referred inguinal or leg pain. We followed 77 patients (average 3.0 years) and compared symptoms before surgery with surgical outcome. Results: Sixty-three patients with a good outcome showed postsurgical pain relief (≥60% pain relief) and 14 patients with a poor outcome did not (<60% pain relief). In patients with good outcomes, worsening of LBP was evident in 65% of cases on flexion and in 35% on extension. However, these findings were not significantly different from those in patients with poor outcomes. The percentage of patients with LBP alone was significantly lower and the percentage of patients with LBP plus referred inguinal or leg pain was significantly higher in the group with good surgical outcome compared with patients in the group with poor surgical outcome (p <0.05). Conclusions: Worsening of pain on extension may be a symptom of DLBP. Surgical outcomes were superior in patients with both LBP and either referred inguinal or leg pain compared with those having LBP alone.