The influence of a solid lubricant dispersion on tribological behavior of Si3N4 based composites under water lubrication

H. Hyuga,M. I. Jones,K. Yoshida,N. kondo,K. Hirao,H. Kita 한양대학교 세라믹연구소 2009 Journal of Ceramic Processing Research Vol.10 No.3

The tribological behavior of monolithic Si3N4 and solid lubricants dispersed Si3N4-based composites has been assessed under a high load and low speeds in an aqueous environment. The results showed that the friction coefficient of the Si3N4 was not significantly reduced when compared to dry sliding and this was attributed to the failure to maintain a lubricating layer between the solid-solid surfaces. In the case of the composites, the initial high friction coefficient was reduced shortly after the beginning of the wear test and maintained a low value (approximately 0.03) throughout. This was attributed to the solid lubricating effect of the composite resulting in a lower stress at the contact asperities preventing the removal of the lubricating layer. The solid lubricant content did not affect the value of the friction coefficient under hydrodynamic type lubrication, but the running in distance decreased with the solid lubricant dispersion. The type and amount of solid lubricant affected the distance required to reach a low friction regime, but all types of solid lubricant showed decreasing friction with increasing amount. In Stribeck analysis, the addition of the solid lubricant resulted in a highly graphitic transfer layer on the Si3N4 material, and shifted the transition points from hydrodynamic to mixed and from mixed to boundary lubrication regimes to more severe conditions. It also reduced the friction coefficient in the boundary lubrication regime. The tribological behavior of monolithic Si3N4 and solid lubricants dispersed Si3N4-based composites has been assessed under a high load and low speeds in an aqueous environment. The results showed that the friction coefficient of the Si3N4 was not significantly reduced when compared to dry sliding and this was attributed to the failure to maintain a lubricating layer between the solid-solid surfaces. In the case of the composites, the initial high friction coefficient was reduced shortly after the beginning of the wear test and maintained a low value (approximately 0.03) throughout. This was attributed to the solid lubricating effect of the composite resulting in a lower stress at the contact asperities preventing the removal of the lubricating layer. The solid lubricant content did not affect the value of the friction coefficient under hydrodynamic type lubrication, but the running in distance decreased with the solid lubricant dispersion. The type and amount of solid lubricant affected the distance required to reach a low friction regime, but all types of solid lubricant showed decreasing friction with increasing amount. In Stribeck analysis, the addition of the solid lubricant resulted in a highly graphitic transfer layer on the Si3N4 material, and shifted the transition points from hydrodynamic to mixed and from mixed to boundary lubrication regimes to more severe conditions. It also reduced the friction coefficient in the boundary lubrication regime.

Electronic behavior of visible light sensitive ZrO2/Cr2O3/carbon clusters composite materials

H. Miyazaki,H. Matsui,Y. Kita,S. Karuppuchamy,S. Ito,M. Yoshihara 한국물리학회 2009 Current Applied Physics Vol.9 No.1

Nano-sized ZrO2/Cr2O3/carbon clusters composite materials were successfully obtained by the microwave-irradiated calcinations of a Zr(acac)4/Cr(acac)3/epoxy resin complex. The compositions of the resulting composite materials were determined using ICP, elemental analysis and surface characterization by XRD, SEM and TEM. The UV–Vis spectra of the composites were also obtained. ESR spectral examinations of the composites indicate that an electron transfer takes place in the process Cr2O3 → carbon clusters → ZrO2. The composite materials have been found to show visible light-responsive catalytic activities. Nano-sized ZrO2/Cr2O3/carbon clusters composite materials were successfully obtained by the microwave-irradiated calcinations of a Zr(acac)4/Cr(acac)3/epoxy resin complex. The compositions of the resulting composite materials were determined using ICP, elemental analysis and surface characterization by XRD, SEM and TEM. The UV–Vis spectra of the composites were also obtained. ESR spectral examinations of the composites indicate that an electron transfer takes place in the process Cr2O3 → carbon clusters → ZrO2. The composite materials have been found to show visible light-responsive catalytic activities.

Dietary Fatty Acid Increases Body Weight Gain without a Change in Rumen Fermentation in Fattening Cattle

Kita, K.,Oka, M.,Yokota, H. Asian Australasian Association of Animal Productio 2003 Animal Bioscience Vol.16 No.1

Dietary fatty acid including mainly palmitic acid and stearic acid was fed to fattening cattle and its effect on body weight gain, plasma lipid contents and rumen liquid fermentation in vitro was examined. In expt. 1, the effect of dietary fatty acid on body weight gain and plasma lipid concentrations was examined. In the control diet group, cattle were fed 1 kg/day of rice straw and concentrate which satisfied the requirement. In the fatty acid group, cattle were given 250 g/d of fatty acid with the same diet of the control diet group. In the excess concentrate group, cattle were given the same diet of the control diet group plus 735 g/d of concentrate corresponding to the same TDN of 250 g/d of fatty acid. Diets were given for 7 days. Body weight gain of cattle given dietary fatty acid was significantly greater than that of cattle fed only rice straw and concentrate. When dietary fatty acid was added to cattle feed, plasma NEFA and HDL-cholesterol concentrations increased. In expt. 2, the influence of dietary fatty acid on gas production and VFA profile in the rumen liquid was investigated in vitro. In the control group, 10 mg of rice straw and 90 mg of concentrate were incubated in the rumen fluid. In the excess concentrate group, 10 mg of rice straw and 97.5 mg of concentrate were incubated. In the fatty acid group, 10 mg of rice straw, 90 mg of concentrate and 2.5 mg of fatty acids were incubated. The rumen liquid mixed with feed materials was incubated for 24 h and the cumulative gas volume was measured. The VFA profile was also measured. Cumulative gas volume in the rumen liquid with fatty acid was equal to the control. Excess concentrate increased cumulative gas volume compared to the fatty acid group. There was no significant difference in total VFA concentration between experimental diet groups. It is suggested that dietary fatty acid has the potency to improve growth performance in fattening cattle without failure in rumen fermentation.

Three-dimensional structural design based on cellular automata simulation

Kita, E.,Saito, H.,Tamaki, T.,Shimizu, H.,Xie, Y.M. Techno-Press 2006 Structural Engineering and Mechanics, An Int'l Jou Vol.23 No.1

This paper describes the design scheme of the three-dimensional structures based on the concept of the cellular automata simulation. The cellular automata simulation is performed according to the local rule. In this paper, the local rule is derived in the mathematical formulation from the optimization problem. The cell density is taken as the design variable. Two objective functions are defined for reducing the total weight of the structure and obtaining the fully stressed structure. The constraint condition is defined for defining the local rule. The penalty function is defined from the objective functions and the constraint condition. Minimization of the penalty function with respect to the design parameter leads to the local rule. The derived rule is applied to the design of the three-dimensional structure first. The final structure can be obtained successfully. However, the computational cost is expensive. So, in order to reduce the computational cost, the material parameters $c_1$ and $c_2$ and the value of the cell rejection criterion (CRC) are changed. The results show that the computational cost depends on the parameters and the CRC value.

Epidermal ablation of Dlx3 is linked to IL-17-associated skin inflammation

Hwang, J.,Kita, R.,Kwon, H.-S.,Choi, E.H.,Lee, S.H.,Udey, M.C.,Morasso, M.I. National Academy of Sciences 2011 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.108 No.28

Antiferromagnetic Interlayer Coupling Through a Thin MgO Layer in (Iron Oxides)/MgO/Fe(001) Multilayers

H. Yangihara,Yuta Toyoda,Eiji Kita 한국자기학회 2007 한국자기학회 학술연구발표회 논문개요집 Vol.- No.-

Characteristics of Gene Structure of Bovine Ghrelin and Influence of Aging on Plasma Ghrelin

Kita, K.,Harada, K.,Nagao, K.,Yokota, H. Asian Australasian Association of Animal Productio 2005 Animal Bioscience Vol.18 No.5

Ghrelin is a novel growth-hormone-releasing acylated peptide, which has been purified and identified in rat stomach. In the present study, the full-length sequence of bovine ghrelin cDNA was cloned by RT-PCR. The bovine ghrelin cDNA sequence derived in the present study included a 348 bp open reading frame and a 137 bp 3'UTR. The putative amino acid sequence of bovine prepro-ghrelin consisted of 116 amino acids, which contained the 27-amino acid ghrelin. The sequence analysis of the bovine ghrelin gene revealed that an intron existed between Gln$^{13}$ and Arg$^{14}$ of ghrelin. This exon-intron boundary matched the GT-AG rule of the splicing mechanism. Compared with rats, which have two tandem CAG sequences in the 3'end of intron, bovine ghrelin genome has only one CAG sequence. Therefore, although rats can produce 28 amino acid-ghrelin and 27 amino acid-des-Gln$^{14}$-ghrelin by alternative splicing, ruminant species, including bovines, might be able to produce only one type of ghrelin peptide, des-Gln$^{14}$-ghrelin. The influence of aging on plasma ghrelin concentration was also examined. Plasma ghrelin concentration increased after birth to approximately 600 days of age, and then remained constant.

Suppression of Chicken Embryo Myoblast Protein Synthesis by Antisense Oligonucleotide against Myostatin

K. Kita,K. Harada,K, Nagao,H. Yokota 아세아·태평양축산학회 2002 Animal Bioscience Vol.15 No.6

Propagation of a Laser-Generated Shock Wave in a Metal Confined in Water

Lee Kitae,Lim C.H.,Kwon S.O. 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.1

The propagation of a laser-generated shock wave in a metal, which is confined in water, was investigated using a one-dimensional Lagrangian hydrodynamics code. This code deals with dynamics from the initial generation of a plasma by a laser-plasma interaction to the propagation of a high-pressure shock wave in a solid material. The simulation results show that the influence of the laser temporal shape on the shock wave propagation is weak once the laser fluence is kept constant. From Fabbro’s formula [R. Fabbro et al., J. Appl. Phys. 68, 775 (1990)], the generation of a shock wave at the front surface has been known to be affected mainly by the laser intensity, but the propagation of the shock wave inside a metal was found to be mainly influenced by the laser fluence. The impulse per unit area exerted on the metal could be a more practical parameter for applications to material hardening and is found to scale with the laser fluence.

Characterization of PZT Capacitors with Ir Electrodes Prepared Solely by Low-Temperature MOCVD

M. Shimizu,H. Niu,H. Fujisawa,K. Kita,M. Okaniwa 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.IV

Low-temperature MOCVD of Pb(Zr,Ti)O3 (PZT) thin lms and Ir lms was achieved. Using seed layer method and appropriate source gas combination method, PZT thin lms were successfully grown at 390-445 C. Ir thin lms as electrodes were also prepared at 280-350 C. Combining low-temperature MOCVD of PZT thin lms as a ferroelectric layer and Ir as an electrode, PZT capacitors with Ir electrodes were prepared solely by MOCVD. Even when PZT was deposited at low temperatures, 395 C and 445 C, PZT capacitors showed good D-E hysteresis loops with 2Pr of 20.0 C/cm2 and 36.9 C/cm2, respectively.