• Honam Mathematical Journal
• /
• v.30 no.4
• /
• pp.677-683
• /
• 2008

On a compact n-dimensional manifold M, it has been conjectured that a critical point metric of the total scalar curvature, restricted to the space of metrics with constant scalar curvature of volume 1, should be Einstein. The purpose of the present paper is to prove that a 3-dimensional manifold (M,g) is isometric to a standard sphere if ker $s^*_g{{\neq}}0$ and there is a lower Ricci curvature bound. We also study the structure of a compact oriented stable minimal surface in M.

• 제어로봇시스템학회:학술대회논문집
• /
• 2001.10a
• /
• pp.62.2-62
• /
• 2001

In this paper, we present a new time-varying sliding mode system that guarantees stable error convergence. The previous papers have dealt with stability of the time-varying sliding mode system by point-wisely investigating the stability of time-invariant system every time. However, it may be unstable even though it guarantees time-invariant stability every time, We designed the time-varying sliding surface so that the resultant time-varying system on sliding mode may be Stable. The initial sliding surface is obtained so that shifting distance of the surface may be minimized with respect to an initial error, and the intercept is produced so that the surface may pass the initial error.

• Journal of the Korean Society for Precision Engineering
• /
• v.23 no.4 s.181
• /
• pp.146-152
• /
• 2006

In micro electrochemical machining (ECM), electrodes should be prevented from unfavorable oxide and Passive layer formation on the machined surface or overall corrosion of the entire surface. Generally, metal electrodes corrode, passivate or dissolve in the electrochemical cell according to the electrode potential. Therefore, each electrode must maintain its stable potential. Tn this paper, the stable electrode potentials of tool and workpiece were determined using the potentiodynamic polarization test and verified experimentally considering machining stability and surface quality. Stable workpiece electrode potentials of two different passive materials of 304 stainless steel and nickel were determined in the 0.1 M sulfuric acid. Experimental results show good machined surface and fast machining rate using the determined electrode potentials.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2014.02a
• /
• pp.173.1-173.1
• /
• 2014

The variations of electronic and magnetic properties of ultrathin Fe overlayers on a W(001) surface as a function of Fe film thickness (1.0~4.0 ML) has been investigated using x-ray magnetic circular dichroism (XMCD) in conjunction with ultraviolet photoelectron spectroscopy (UPS) and low energy electron diffraction (LEED). We found that the ferromagnetic property of Fe film started to build up over 2.0 ML, as we confirmed the spin and angular moment contribution to the magnetic moment using XMCD experiments. We will systematically demonstrate that the occurrence of ferromagnetic property of Fe film on a W(001) surface is closely correlated to a themally stable layer of Fe film on a W(001) surface.

• Computers and Concrete
• /
• v.11 no.5
• /
• pp.411-440
• /
• 2013

Large fluctuations in surface strain at the level of steel are expected in reinforced concrete flexural members at a given stage of loading due to the emergent structure (emergence of new crack patterns). This has been identified in developing deterministic constitutive models for finite element applications in Ibrahimbegovic et al. (2010). The aim of this paper is to identify a suitable probability distribution for describing the large deviations at far from equilibrium points due to emergent structures, based on phenomenological, thermodynamic and statistical considerations. Motivated by the investigations reported by Prigogine (1978) and Rubi (2008), distributions with heavy tails (namely, alpha-stable distributions) are proposed for modeling the variations in strain in reinforced concrete flexural members to account for the large fluctuations. The applicability of alpha-stable distributions at or in the neighborhood of far from equilibrium points is examined based on the results obtained from carefully planned experimental investigations, on seven reinforced concrete flexural members. It is found that alpha-stable distribution performs better than normal distribution for modeling the observed surface strains in reinforced concrete flexural members at these points.

• Bulletin of the Korean Chemical Society
• /
• v.31 no.6
• /
• pp.1681-1688
• /
• 2010

Density functional theory was adopted to study the various surface products and their reaction channels focusing on the on-dimer configuration which has not been suggested before. Energetic results show that the most stable on-dimer configuration is the 6,6-[2+2] structure which resembles the typical [2+2] cycloaddition product. The 6,6-[2+2] product is also more stable than any other possible surface structures of inter-dimer configuration further suggesting its existence. Potential energy surface scan along various possible initial surface reactions show that some of the possible on-dimer surface products require virtually no reaction barrier indicating that initial population of on-dimer surface products is thermodynamically determined. Various surface isomerization reaction channels exist further facilitating thermal redistribution of the initial surface products.

• Journal of International Academy of Physical Therapy Research
• /
• v.11 no.2
• /
• pp.2028-2035
• /
• 2020

Background: Weakness of the trunk muscles decreases the trunk control ability of stroke patients, which is significantly related to balance and gait. Objectives: To compare the impact of diagonal pattern self-exercise on an unstable surface and a stable surface for trunk rehabilitation on trunk control, balance, and gait ability in stroke patients. Design: Nonequivalent control group design. Methods: Twenty four participants were randomized into the experimental group (diagonal pattern self-exercise while sitting on an unstable surface, n=12) and the control group (diagonal pattern self-exercise while sitting on a stable surface, n=12). All interventions were conducted for 30 minutes, three times a week for four weeks, and the trunk impairment scale (TIS), berg balance scale (BBS), functional gait assessment (FGA), and G-walk were measured. Results: All groups indicated significant increases in all variables (TIS, BBS, FGA, cadence, speed, stride length) after four weeks. The TIS, BBS, FGA, cadence, gait speed, and stride length group-by-time were significantly different between the two groups. Conclusion: We found that, in stroke patients, diagonal pattern self-exercise on an unstable surface is a more effective method for improving trunk control, balance, and gait ability than diagonal pattern self-exercise on a stable surface.

• PNF and Movement
• /
• v.12 no.4
• /
• pp.233-241
• /
• 2014

Purpose: The purpose of this study is to investigate the effects of exercising on a stable and unstable surface for a period of six weeks on the arms of female university students in their twenties. Methods: The subjects consisted of 20 female university students. The experimental group consisted of ten individuals who exercised on an unstable surface, and the control group consisted of ten individuals who exercised on a stable surface. The exercise program was composed of aerobic exercises (i.e. Back and forth movements for clapping and raising cross with both arms) and muscle-strengthening exercises (i.e. Push-ups and raising arms). We measured the subjects before the experiment and after the exercise program using the following measurements tool: a ruler and T-scan plus. The same person measured changes in arm size with a ruler three times and calculated the average to minimize any errors in measurement. We controlled the subjects to measure the amount of arm muscle with a T-scan plus. Twelve hours before the measurements were taken subjects were not permitted to exercise, and four hours before the measurements were taken subjects were not permitted to eat anything. Results: The two groups had no significant difference, but each group felt the effect of the exercise program. Conclusion: There was no difference between the experimental group and the control group. However, it was determined that the exercise had a greater effect on an unstable surface than a stable surface.

• PNF and Movement
• /
• v.20 no.1
• /
• pp.67-72
• /
• 2022

Purpose: The aim of this study was to compare trunk and lower extremity muscle activity during deadlift on stable - and unstable surfaces. Methods: Twenty healthy men participated in this study. The participants performed deadlift exercise on both a stable surface and an unstable surface. During the deadlift, the activities of the trunk and lower extremity muscle were collected by using electromyography. Results: The results showed that the electromyographic activity of the gluteus maximus significantly increased during deadlift on an unstable surface compared to on a stable surface (p <0.05). However, in the electromyographic activities of the rectus femoris, biceps femoris, and erector spinae, there were no significant differences (p >0.05). Conclusion: The finding that the electromyographic activity of the gluteus maximus increases significantly during deadlift on an unstable surface compared to stable one could be used to develop an efficient exercise program.

• Journal of the Korean Society of Combustion
• /
• v.6 no.1
• /
• pp.29-35
• /
• 2001

The surface flames in porous ceramic burner are experimentally characterized to investigate the effects of equivalence ratio and firing rates. The results show that the surface flames are classified into green, red radiant and blue surface flame as decrease of equivalence ratio. And each flame is maintained very stably and shows the same flame characteristics at any orientation of ceramic burner. Particularly the blue surface flame was found to be very stable at very lean equivalence ratio at 200 to $800\;kw/m^2$ firing rates. And the exhausted NOx was analysed to find out which flame has lower NOx emission. The blue surface flame showed the lowest NOx emission regardless of the location of burner since it sustained very stable at lean mixture ratio.