Showing papers by "Masato Murakami published in 2014"

Co-Existence of Carotid Artery Disease, Renal Artery Stenosis, and Lower Extremity Peripheral Arterial Disease in Patients With Coronary Artery Disease

Abstract: In atherosclerosis, carotid artery stenosis (CAS), renal artery stenosis (RAS), lower extremity peripheral arterial disease (PAD), and coronary artery disease (CAD) are common pathologic lesions; their interrelationship is, however, unclear. We studied concomitant multiple atherosclerotic lesions in patients with CAD to understand their prevalence and relations. A cross-sectional analysis was performed on data from consecutive patients who underwent nonemergent coronary angiography. Simultaneous carotid and renal artery Doppler studies and ankle-brachial systolic pressure measurements were reviewed to diagnose concomitant lesions and their severity. The study included 1,734 patients (aged 71 ± 9 years; 70% men), with prevalences of CAS, RAS, lower extremity PAD, and CAD of 6%, 7%, 13%, and 72%, respectively. In patients with CAD (n = 1,253), the prevalences of CAS, RAS, and lower extremity PAD were 7%, 9%, and 16%, respectively; 24% CAD patients had ≥1 additional atherosclerotic lesion. Significant interactions among the prevalences of these lesions were found. In addition, the extent of CAD and the prevalences of CAS, RAS, and lower extremity PAD were significantly correlated. Multivariate analysis supported these relationships. In conclusion, the prevalences of CAS, RAS, lower extremity PAD, and CAD were strongly interrelated in the study population; CAD severity was related to that of other atherosclerotic lesions. Additional systematic screening of other concomitant atherosclerotic lesions is recommended, especially in CAD patients having multivessel disease, left main disease, and/or already diagnosed with other concomitant atherosclerotic lesions.

Development in processing of MgB2 cryo-magnet superconductors

Abstract: Spark Plasma Sintering is a promising rapid consolidation technique that allows a better understanding and manipulating of sintering kinetics and therefore makes it possible to obtain MgB2-based ceramics with tailored microstructures. Commercial MgB2 powders were spark plasma sintered with an applied mechanical pressure, leading to MgB2 pellets with 99% relative density. The obtained samples show a sharp superconducting transition with an onset at 38.5 K. The critical current density was measured equal to 5.6 × 104 A/cm2 at 20 K under 1 T applied field. Otherwise, the trapped field was also investigated. A 5 mm thick pellet with a 20 mm diameter prepared with optimized processing temperature demonstrated a trapped field of 1.2 T at 15 K and up to 2.5 T at 10 K.

Development of MgB 2 -Based Bulk Supermagnets

Abstract: A series of disk-shaped, bulk MgB2 superconductors (sample diameter up to 40 mm, reaction temperatures ranging between 750 °C and 950 °C) was prepared in order to improve the performance for superconducting supermagnets. These samples were characterized by magnetic and electric measurements in fields up to 7 T and at various temperatures 10 K < T < 35 K. The irreversibility lines, the current densities, the resistance and the achievable trapped fields were determined. To analyze the data, a scaling of the flux pinning forces, Fp = jc × B, was performed. The different scaling behavior of the samples prepared at low and high reaction temperatures is discussed considering the achieved microstructures.

Effect of growth temperature on superconducting properties of YBa2Cu3Oy bulk superconductors grown by seeded infiltration

Abstract: We investigated the effect of growth temperature on the characteristics of YBa2Cu3Oy (Y-123) bulk superconductor prepared by seeded infiltration process. Homemade Y2BaCuO5 “Y-211” particles and liquid phase of Ba3Cu5O8 were used to produce Y-123 bulks in air such that the liquid phase infiltrates into a Y-211 block. Y-123 samples of 20 mm diameter and 8 mm thickness were produced at different growth temperatures, i.e., 990, 985, 983, 980 and 978 °C with the same holding time of 25 h. We found that single grain growth without multi-nucleation occurred at 980 °C. Further, magnetization measurements indicated a sharp superconducting transition with Tc (onset) around 93.2 K. Trapped field measurements showed that the samples are single domain, and the sample 27 mm in diameter and 5 mm in thickness showed the maximum trapped field of around 0.45 T on the sample surface at 77 K. The critical current density (Jc) at 77 K and zero field was determined to be 175 kA/cm2, which is the highest value ever reported in the literature.

High Critical Currents in Single Grain YBa2Cu3Oy Bulk Superconductors Produced by Infiltration-Growth

Abstract: Bulk YBa2Cu3Oy “Y-123” superconductors with high critical current density (Jc) have been grown by infiltrating a Ba3Cu5Oy “Y-035” liquid source into a Y2BaCuO5 “Y-211” precursor block. Magnetization measurements showed that similar Tc (onset) values and large variation in self-field critical currents were observed when the samples were isothermally grown at different temperatures. We then adapted slow cooling process for the samples 27 mm in diameter and 5 mm in thickness using the growth profile which was optimized on the basis of isothermal growth conditions. The specimens cut from various locations of a large bulk material showed the uniform and sharp superconducting transition with Tc (onset) around 93.2 K. Jc values at 77 K and 0T was in the range of 150 - 175 kA/cm2. Such high Jc values could be obtained without refining the particle size of Y-211 secondary phase. Atomic force microscopy measurements revealed that uniform nanosized secondary Y-211 particles are embedded in the Y-123 matrix, which led to a dramatic improvement of the critical current performance at 77 K.

Fabrication of MgB2 Bulk Magnets with High Critical Currents

Abstract: We report on the fabrication and characterization of disk-shaped bulk MgB2 superconductors with high performance as superconducting bulk magnets. Several samples of diameters 20 mm, 30 mm and 40 mm were fabricated using a solid state reaction in pure Ar atmosphere at 775°C for 3h. The magnetization measurements confirmed that all the samples exhibited a sharp superconducting transition with Tc (onset) at around 38.5 K. The samples showed respective critical current density (Jc) values of 176 kA cm-2 and 55 kA cm-2 at 20 K in self field and 1T. The Jc values increased further to 250 kA cm-2 and 100 kA cm-2 with decreasing temperature down to 10 K. MgB2 samples 20 mm and 30 mm in diameter and 7 mm in thickness exhibited trapped field values of 1.15 T and 1.3 T at 25 K, respectively. Microstructural observations with scanning electron microscopy (SEM) revealed that the samples are highly porous. And hence, continuing development of large-sized bulk MgB2 with higher density will lead to promising industrial applications.

Effect of the magnet insertion on the performance of a superconducting pump

Abstract: For medical and semiconductor fabrication lines, an ultra-clean and impurity-free environment is often required. In order to realize such a contaminant-free environment, it is desirable to employ a completely non-contact rotating mechanism. Such a non-contact rotation is possible by using a combination of permanent magnets and bulk superconductors. Furthermore, it is necessary to rotate a superconducting pump stably for practical applications. With the aim of increasing the stiffness of rotational parts, we placed a permanent magnet at the bottom such that the superconductors are sandwiched by top and bottom magnets. It was confirmed that the stiffness could surely be improved by arranging lower permanent magnets.

Damage prevention device and damage prevention method for condensate system

Abstract: PROBLEM TO BE SOLVED: To prevent equipment and piping in the condensate system from being damaged by preventing occurrence of a large water hammer at a start of a low pressure condensate pump after a stop of filling water in a condensate system.SOLUTION: A first condensate system damage prevention device 20A includes water drop prevention means for preventing condensate water in a condensate return line 21 of a condensate system 1 from dropping into a condenser 3.