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Search Results: 1 - 10 of 424 matches for " Yoshimitsu Okazaki "
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Comparison of Fatigue Properties and Fatigue Crack Growth Rates of Various Implantable Metals
Yoshimitsu Okazaki
Materials , 2012, DOI: 10.3390/ma5122981
Abstract: The fatigue strength, effects of a notch on the fatigue strength, and fatigue crack growth rate of Ti-15Zr-4Nb-4Ta alloy were compared with those of other implantable metals. Zr, Nb, and Ta are important alloying elements for Ti alloys for attaining superior long-term corrosion resistance and biocompatibility. The highly biocompatible Ti-15Zr-4Nb-4Ta alloy exhibited an excellent balance between strength and ductility. Its notched tensile strength was much higher than that of a smooth specimen. The strength of 20% cold-worked commercially pure (C.P.) grade 4 Ti was close to that of Ti alloy. The tension-to-tension fatigue strength of an annealed Ti-15Zr-4Nb-4Ta rod at 10 7 cycles was approximately 740 MPa. The fatigue strength of this alloy was much improved by aging treatment after solution treatment. The fatigue strengths of C.P. grade 4 Ti and stainless steel were markedly improved by 20% cold working. The fatigue strength of Co-Cr-Mo alloy was markedly increased by hot forging. The notch fatigue strengths of 20% cold-worked C.P. grade 4 Ti, and annealed and aged Ti-15Zr-4Nb-4Ta, and annealed Ti-6Al-4V alloys were less than those of the smooth specimens. The fatigue crack growth rate of Ti-15Zr-4Nb-4Ta was the same as that of Ti-6Al-4V. The fatigue crack growth rate in 0.9% NaCl was the same as that in air. Stainless steel and Co-Cr-Mo-Ni-Fe alloy had a larger stress-intensity factor range (ΔK) than Ti alloy.
On the Effects of Hot Forging and Hot Rolling on the Microstructural Development and Mechanical Response of a Biocompatible Ti Alloy
Yoshimitsu Okazaki
Materials , 2012, DOI: 10.3390/ma5081439
Abstract: Zr, Nb, and Ta as alloying elements for Ti alloys are important for attaining superior corrosion resistance and biocompatibility in the long term. However, note that the addition of excess Nb and Ta to Ti alloys leads to higher manufacturing cost. To develop low-cost manufacturing processes, the effects of hot-forging and continuous-hot-rolling conditions on the microstructure, mechanical properties, hot forgeability, and fatigue strength of Ti-15Zr-4Nb-4Ta alloy were investigated. The temperature dependences with a temperature difference (ΔT) from β-transus temperature (Tβ) for the volume fraction of the α- and β-phases were almost the same for both Ti-15Zr-4Nb-4Ta and Ti-6Al-4V alloys. In the α-β-forged Ti-15Zr-4Nb-4Ta alloy, a fine granular α-phase structure containing a fine granular β-phase at grain boundaries of an equiaxed α-phase was observed. The Ti-15Zr-4Nb-4Ta alloy billet forged at Tβ-(30 to 50) °C exhibited high strength and excellent ductility. The effects of forging ratio on mechanical strength and ductility were small at a forging ratio of more than 3. The maximum strength (σ max) markedly increased with decreasing testing temperature below Tβ. The reduction in area (R.A.) value slowly decreased with decreasing testing temperature below Tβ. The temperature dependences of σ max for the Ti-15Zr-4Nb-4Ta and Ti-6Al-4V alloys show the same tendency and might be caused by the temperature difference (ΔT) from Tβ. It was clarified that Ti-15Zr-4Nb-4Ta alloy could be manufactured using the same manufacturing process as for previously approved Ti-6Al-4V alloy, taking into account the difference (ΔT) between Tβ and heat treatment temperature. Also, the manufacturing equivalency of Ti-15Zr-4Nb-4Ta alloy to obtain marketing approval of implants was established. Thus, it was concluded that continuous hot rolling is useful for manufacturing α-β-type Ti alloy.
Comparisons of immersion and electrochemical properties of highly biocompatible Ti–15Zr–4Nb–4Ta alloy and other implantable metals for orthopedic implants
Yoshimitsu Okazaki,Hiroyuki Nagata
Science and Technology of Advanced Materials , 2012,
Abstract: Metal release from implantable metals and the properties of oxide films formed on alloy surfaces were analyzed, focusing on the highly biocompatible Ti–15Zr–4Nb–4Ta alloy. The thickness and electrical resistance (Rp) of the oxide film on such an alloy were compared with those of other implantable metals. The quantity of metal released during a 1-week immersion test was considerably smaller for the Ti–15Zr–4Nb–4Ta than the Ti–6Al–4V alloy. The potential (E10) indicating a current density of 10 μA cm 2 estimated from the anodic polarization curve was significantly higher for the Ti–15Zr–4Nb–4Ta than the Ti–6Al–4V alloy and other metals. Moreover, the oxide film (4–7 nm thickness) formed on the Ti–15Zr–4Nb–4Ta surface is electrochemically robust. The oxide film mainly consisted of TiO2 with small amounts of ZrO2, Nb2O5 and Ta2O5 that made the film electrochemically stable. The Rp of Ti–15Zr–4Nb–4Ta was higher than that of Ti–6Al–4V, i.e. 0.9 Ω cm2 in 0.9% NaCl and 1.3 Ω cm2 in Eagle's medium. This Rp was approximately five-fold higher than that of stainless steel, which has a history of more than 40 years of clinical use in the human body. Ti–15Zr–4Nb–4Ta is a potential implant material for long-term clinical use. Moreover, E10 and Rp were found to be useful parameters for assessing biological safety.
Tissue-Engineered Products for Skin Regenerative Medicine  [PDF]
Yoshimitsu Kuroyanagi
Open Journal of Regenerative Medicine (OJRM) , 2016, DOI: 10.4236/ojrm.2016.53006
Abstract: In a general wound healing process, foreign bodies and tissue detritus have to be broken down and then a new tissue is produced. However, the new tissue formation sometimes fails to proceed under the impaired conditions such as burn injury and intractable skin ulcer. A major obstruction to wound healing is infection. Another obstruction to wound healing is deficiency of growth factors. The endogenous levels of growth factors are reduced in some chronic wounds. To improve these wound conditions, researchers have been trying to create several types of artificial skins. The tissue-engineered products include three prime constituents, i.e., cells, growth factors, and materials. In this review, the practical design of tissue-engineered products for skin regenerative medicine is introduced. The first design makes it possible to release silver sulfadiazine (AgSD) from a wound dressing. The second design makes it possible to release Epidermal Growth Factor (EGF) from a wound dressing or a skin care product composed of hyaluronic acid spongy sheet containing bioactive ingredients. The third design makes it possible to release several types of growth factors from allogeneic fibroblasts within cultured dermal substitute. This tissue-engineered product is prepared by seeding allogeneic fibroblasts into a collagen and hyaluronic acid spongy sheet. Although allogeneic cells are rejected gradually in immune system, they are able to release some types of growth factors, thereby regenerating a damaged tissue. The clinical study demonstrates that these tissue-engineered products are promising for the treatment of burn injury and intractable skin ulcer.
A Multi-Secret Sharing Scheme with Many Keys Based on Hermite Interpolation  [PDF]
Tomoko Adachi, Chie Okazaki
Journal of Applied Mathematics and Physics (JAMP) , 2014, DOI: 10.4236/jamp.2014.213140
Abstract: A secret sharing scheme is one of cryptographies. A threshold scheme, which is introduced by Shamir in 1979, is very famous as a secret sharing scheme. We can consider that this scheme is based on Lagrange's interpolation formula. A secret sharing scheme has one key. On the other hand, a multi-secret sharing scheme has more than one keys; that is, a multi-secret sharing scheme has p (2) keys. Dealers distribute shares of keys among n participants. Gathering t (n) participants, keys can be reconstructed. In this paper, we give a scheme of a (t,n) multi-secret sharing based on Hermite interpolation, in the case of pt.
Rapid Detection Method for Enteroaggregative Escherichia coli Using Simple Clump Formation and Aggregative Assay  [PDF]
Miyuki Fujioka, Chowdhury Rafiqul Ahsan, Yoshimitsu Otomo
Advances in Microbiology (AiM) , 2013, DOI: 10.4236/aim.2013.38074

Enteroaggregative Escherichia coli (EAggEC) strains cause the persistent diarrhea in infants and compromised hosts in developing countries. These strains are currently defined as E. coli that adheres to HEp-2 cells in an aggregative adherence (AA) pattern. In this study, we compared 4 different rapid methods for the detection of EAggEC using a PCR assay, clump formation test, glass slide adherence assay, and the HEp-2 cell adherence assay. Out of 683 E. coli strains isolated from diarrheal stool samples, we detected 17 aggR and/or clump-positive strains, and identified 2 aggR-positive, clump-negative strains and 2 aggR-negative, clump-positive strains. All the aggR positive and clump positive strains also showed positive results in glass slide adherence and HEp-2 cell adherence assays. From all these results, we suggest the following procedure for the rapid identification of EAggEC strains: first, screen E. coli strains with the clump formation test and subsequently perform the glass slide adherence assay to observe AA for confirmation.

Evaluation of Epidermal Growth Factor-Incorporating Skin Care Product in Culture Experiment Using Human Fibroblasts  [PDF]
Akiko Yamamoto, Haruka Ohno, Yoshimitsu Kuroyanagi
Open Journal of Regenerative Medicine (OJRM) , 2016, DOI: 10.4236/ojrm.2016.52004
Abstract: This study aimed to investigate the potential of a skin care product composed of hyaluronic acid (HA) and collagen (Col) sponge containing epidermal growth factor (EGF), vitamin C derivative (VC), glucosylceramide (GC), poly(γ-glutamic acid) (PGA), and argentine (Arg). High-molecular weight HA aqueous solution, hydrolyzed low-molecular weight HA aqueous solution, and heat- denatured Col aqueous solution were mixed, into which each aqueous solution containing EGF, VC, GC, PGA, or Arg were added, followed by freeze-drying to obtain a spongy EGF-incorporating skin care product (EGF-skin care product). In order to evaluate the first efficacy of EGF, fibroblast proliferation was assessed after 6 days of cultivation in the conditioned medium prepared by dissolving EGF-skin care product in a conventional culture medium. The fibroblast densities increased more effectively in conditioned medium with EGF than in control medium without EGF. In order to evaluate the second efficacy of EGF, the amount of vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF) produced by fibroblasts were assessed in a wound surface model. A fibroblast-incorporating Col gel sheet (cultured dermal substitute: CDS) was elevated to the air- medium interface, onto which a spongy sheet of EGF-skin care product was placed and cultured for 7 days. The condition covered with or without EGF-skin care product is divided into (+) EGF or (-) EGF, respectively. Fibroblasts in the CDS released 3.7 times more VEGF and 25 times more HGF in (+) EGF compared with (-) EGF. In another experiment, an aqueous solution of EGF-skin care product was added onto CDS and cultured for 7 days. Aqueous solutions were prepared and stored at 4°C or 37°C for a different period of 1 day, 2 weeks, and 4 weeks, respectively. Fibroblasts in CDS under different condition released similar amount of VEGF and HGF. This result indicated that the efficacy of EGF was maintained even after preservation at 37°C for 4 weeks. These findings suggest that EGF-skin care product can be used on damaged skin surface by placing its spongy sheet or its solution.
In Vitro Analysis of VEGF and HGF Production by Fibroblast in Cultured Dermal Substitute Combined with EGF-Incorporating Top Dressing  [PDF]
Emi Iijima, Daichi Daichi Toyoda, Akiko Yamamoto, Misato Kuroyanagi, Yoshimitsu Yoshimitsu Kuroyanagi
Open Journal of Regenerative Medicine (OJRM) , 2014, DOI: 10.4236/ojrm.2014.31002

This study aimed to investigate the potential of cultured dermal substitute (CDS) to release angiogenic growth factors when laminated with a membrane containing epidermal growth factor (EGF) as a top dressing. Membranes were prepared by air-drying a solution of hyaluronic acid (HA) and collagen (Col) with or without EGF. Membranes were designed to contain EGF at concentrations of 0, 0.1, 0.2 or 0.5 μg/cm2. CDS was prepared by incorporating fibroblasts into a collagen gel combined with a cross-linked HA spongy matrix, followed by culturing for 5 days. CDS was designed to contain fibroblasts at a density of 2 × 105 (Group I) or 4 × 105 cells/cm2> (Group II). CDS was elevated at the interface between air and culture medium, on the top of which each membrane was placed. This culture system was employed as a wound surface model. Metabolic activity of the fibroblasts in the CDS cultured for 7 days on a wound surface model was measured by MTT assay. The amounts of vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF) after 7 days of cultivation were measured by using ELISA. Membranes containing EGF ranging from 0.1 to 0.5 μg/cm2> facilitated production of both VEGF and HGF, as compared with control membranes without EGF. However, a membrane containing EGF at a concentration of 0.5 μg/cm2> failed to facilitate fibroblast cytokine production in Group I. These results demonstrated that the EGF-incorporating membrane was able to stimulate fibroblasts in the CDS to synthesize an increased amount of VEGF and HGF in a dose-dependent manner.

Towards a policy that supports people-centered housing recovery—learning from housing reconstruction after the Hanshin-Awaji Earthquake in Kobe, Japan
Elizabeth Maly,Yoshimitsu Shiozaki
International Journal of Disaster Risk Science , 2012, DOI: 10.1007/s13753-012-0007-1
Abstract: The goal of disaster recovery is for survivors to regain stability in their lives, livelihoods, and housing. A people-centered housing recovery requires that residents are empowered to make decisions about their housing reconstruction, and that policies create housing options that support the ability of all residents to reconstruct their homes and lives. The 1995 Hanshin-Awaji Earthquake caused the largest amount of damage in Japan since World War II, and the subsequent recovery is a starting point for understanding contemporary post-disaster housing reconstruction policies in Japan. Beyond an overview of housing reconstruction programs, we can understand the impact these policies had on Kobe residents’ housing and community recovery. In many cases, housing policies implemented after the Kobe earthquake fragmented communities and caused further damage and disruption in the lives of the survivors. A single-track approach failed to support the entire population of the disaster-stricken area. In subsequent years, Japanese disaster reconstruction laws and policies have seen modifications and improvements. Some of these changes can be seen in cases of recovery after more recent disasters, notably after the 2004 Chuetsu Earthquake in Niigata Prefecture. In the context of these past examples, we can consider what is needed for a people-centered recovery in the Tohoku area after the 2011 Great East Japan Earthquake and Tsunami.
The Ξ_Q - Ξ_Q' Mixing and Heavy Baryon Masses
Toshiaki Ito,Yoshimitsu Matsui
Physics , 1996, DOI: 10.1143/PTP.96.659
Abstract: We examine the $\Xi_Q - \Xi'_Q$ mixing and heavy baryon masses in the heavy quark effective theory with the $\mq$ corrections. In the conventional baryon assignment, we obtain the mixing angle $\cos^2 \theta = 0.87\pm 0.03$ in virtue of the Gell-Mann-Okubo mass relation. On the other hand, if we adopt the new baryon assignment given by Falk, the allowed region of the $\Sigma_c$ mass is upper from 2372 MeV.
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