• 대한수학회지
• /
• 제50권4호
• /
• pp.813-828
• /
• 2013

It is known that generalized free products of finitely generated nilpotent groups are conjugacy separable when the amalgamated subgroups are cyclic or central in both factor groups. However, those generalized free products may not be conjugacy separable when the amalgamated subgroup is a direct product of two infinite cycles. In this paper we show that generalized free products of finitely generated nilpotent groups are conjugacy separable when the amalgamated subgroup is ${\langle}h{\rangle}{\times}D$, where D is in the center of both factors.

• Journal of Information Technology Applications and Management
• /
• 제10권1호
• /
• pp.35-46
• /
• 2003

This study focuses on the effect of Social Scaffolding of virtual community on its growth and thrift. The research model proposed in this study is that communities, which have goof social scaffolding, tend to grow and thrive. Social Scaffolding refers to those aspects of a site Purpose, Places, Profiles, leaders, Roles, Rules, Cyclic Events, integrating with the real world, and Subgroups. The data were collected from 100 virtual communities in Daum Communications and analyzed in this study. Multiple regression is used to analyze the relationship of variables. The result is following ; purpose, loaders, rules, integrating with the real world support the effects of social scaffolding of virtual community on its growth and thrift, but profiles, roles, cyclic events do not. The result of this study implies the importance of social scaffolding of virtual community for re-searches, and developers.

• 대한수학회논문집
• /
• 제28권4호
• /
• pp.643-647
• /
• 2013

Let G be a group and let $p$ be a prime number. If the set $\mathcal{A}(G)$ of all commuting automorphisms of G forms a subgroup of Aut(G), then G is called $\mathcal{A}(G)$-group. In this paper we show that any $p$-group with cyclic maximal subgroup is an $\mathcal{A}(G)$-group. We also find the structure of the group $\mathcal{A}(G)$ and we show that $\mathcal{A}(G)=Aut_c(G)$. Moreover, we prove that for any prime $p$ and all integers $n{\geq}3$, there exists a non-abelian $\mathcal{A}(G)$-group of order $p^n$ in which $\mathcal{A}(G)=Aut_c(G)$. If $p$ > 2, then $\mathcal{A}(G)={\cong}\mathbb{Z}_p{\times}\mathbb{Z}_{p^{n-2}}$ and if $p=2$, then $\mathcal{A}(G)={\cong}\mathbb{Z}_2{\times}\mathbb{Z}_2{\times}\mathbb{Z}_{2^{n-3}}$ or $\mathbb{Z}_2{\times}\mathbb{Z}_2$.

• Restorative Dentistry and Endodontics
• /
• 제42권4호
• /
• pp.301-308
• /
• 2017

Objectives: It was aimed to compare the cyclic fatigue resistances of ProTaper Universal (PTU), ProTaper Next (PTN), and ProTaper Gold (PTG) and the effects of sterilization by autoclave on the cyclic fatigue life of nickel-titanium (NiTi) instruments. Materials and Methods: Eighty PTU, 80 PTN, and 80 PTG were included to the present study. Files were tested in a simulated canal. Each brand of the NiTi files were divided into 4 subgroups: group 1, as received condition; group 2, pre-sterilized instruments exposed to 10 times sterilization by autoclave; group 3, instruments tested were sterilized after being exposed to 25%, 50%, and 75% of the mean cycles to failure, then cycled fatigue test was performed; group 4, instruments exposed to the same experiment with group 3 without sterilization. The number of cycles to failure (NCF) was calculated. The data was statistically analyzed by using one-way analysis of variance and post hoc Tukey tests. Results: PTG showed significantly higher NCF than PTU and PTN in group 1 (p < 0.05). Sterilization significantly increased the NCF of PTN and PTG (p < 0.05) in group 2. PTN in group 3 had significantly higher cyclic fatigue resistance than PTN group 4 (p < 0.05). Also, significantly higher NCF was observed for PTG in group 2 than in groups 3 and 4 (p < 0.05). Conclusions: PTG instrument made of new gold alloy was more resistant to fatigue failure than PTN and PTU. Autoclaving increased the cyclic fatigue resistances of PTN and PTG.

• Pediatric Gastroenterology, Hepatology & Nutrition
• /
• 제3권1호
• /
• pp.75-83
• /
• 2000

저자들은 주기성 구토증으로 진단된 3명의 소아에서 6년 이상의 장기 추적관찰을 통하여 임상양상의 다양한 변화과정을 관찰하여 보고, 뇌파검사의 이상소견을 근거로 이형 편두통의 형태로 진행하여 가는 과정을 관찰하였다. 시간의 경과에 따라 구토 발병 주기, 기간의 변화와 함께 위배출능 저하, 두통의 발현, 뇌파의 이상 등 다양한 임상 양상의 변화를 보여주며, 2례에서는 증상의 소실이 관찰되었다. 특히, 뇌파 검사상 증상 발현시 발생하는 서파는 편두통의 발생 직전에 뇌혈류의 감소로 발생하는 양상과 매우 유사하며, 주기성 구토증과 편두통의 관련성을 시사하여 주는 소견으로, 진단 및 치료적 접근시 반드시 고려하여야 한다. 주기성 구통증은 이형 편두통으로의 이행 과정인가?

• 생물정신의학
• /
• 제3권1호
• /
• pp.46-50
• /
• 1996

주요 우울장애 환자와 기분부전장애 환자에서 정상대조군과 비교하여 임파구에 isoproterenol 자극 후 cyclic AMP 생성반응에 차이가 있는지를 알아보고, 이 두 질환군에서 net cyclic AMP levels와 우울정도간의 상관성을 알아보고자 주요 우울장애군 8명, 기분부전장애군 9명, 정상대조군 10명을 대상으로 본 연구를 시행하였다. Cyclic AMP 농도는 방사면역 측정법 (radioimmunoassay)으로 측정하였다. 결과를 요약하연 다음과 같다. 1) HDRS 정수상 주요 우울장애군이 기분부전장애군보다 유의하게 우울정도가 높았다. 2) Isoproterenol 자극전 basal cyclic AMP levels는 정상대조군, 주요 우울장애군, 기분부전장애군간에 차이가 없었다. 3) Isoproterenol $10^{-5}mol/L$ 자극후 net cyclic AMP levels는 정상대조군 주요 우울장애군, 기분부전장애군간에 유의한 차이를 보였다. 4) 주요 우울장애군에서 isoproterenol $10^{-5}mol/L$ 자극후 net cyclic AMP levels와 HDRS 점수간에 유의한 역상관관계를 보였으나, 기분부전장애군에서는 상관관계를 보이지 않았다. 이상의 결과로 저자들은 기분부전장애가 임상적으로는 주요 우울장애의 우울정도가 경미한 한 형태로 보이지만 생물학적으로는 이들 두 질환이 다른 질환일 수 있다고 생각하였다.

• The Journal of Advanced Prosthodontics
• /
• 제7권5호
• /
• pp.375-379
• /
• 2015

PURPOSE. The purpose of this study was to evaluate the influence of tightening technique and the screw coating on the loosening torque of screws used for Universal Abutment fixation after cyclic loading. MATERIALS AND METHODS. Forty implants (Titamax Ti Cortical, HE, Neodent) (n=10) were submerged in acrylic resin and four tightening techniques for Universal Abutment fixation were evaluated: A - torque with 32 Ncm (control); B - torque with 32 Ncm holding the torque meter for 20 seconds; C - torque with 32 Ncm and retorque after 10 minutes; D - torque (32 Ncm) holding the torque meter for 20 seconds and retorque after 10 minutes as initially. Samples were divided into subgroups according to the screw used: conventional titanium screw or diamond like carbon-coated (DLC) screw. Metallic crowns were fabricated for each abutment. Samples were submitted to cyclic loading at $10^6$ cycles and 130 N of force. Data were analyzed by two-way ANOVA and Tukey's test (5%). RESULTS. The tightening technique did not show significant influence on the loosening torque of screws (P=.509). Conventional titanium screws showed significant higher loosening torque values than DLC (P=.000). CONCLUSION. The use of conventional titanium screw is more important than the tightening techniques employed in this study to provide long-term stability to Universal Abutment screws.

• Restorative Dentistry and Endodontics
• /
• 제29권3호
• /
• pp.267-272
• /
• 2004

The purpose of this in vitro study was to evaluate the effect of surface defects and cross-sectional configuration of NiTi rotary files on the fatigue life under cyclic loading. Three NiTi rotary files ($K3^{TM},{\;}ProFile^{\circledR},{\;}and{\;}HERO{\;}642^{\circledR}$) with ＃30/.04 taper were evaluated. Each rotary file was divided into 2 subgroups : control (no surface defects) and experimental group (artificial surface defects), A total of six groups of each 10 were tested. The NiTi rotary files were rotated at 300rpm using the apparatus which simulated curved canal (40 degree of curvature) until they fracture. The number of cycles to fracture was calculated and the fractured surfaces were observed with a scanning electron microscope. The data were analyzed statistically. The results showed that experimental groups with surface defects had lower number of cycles to fracture than control group but there was only a statistical significance between control and experimental group in the $K3^{TM}$ (p<0.05), There was no strong correlation between the cross-sectional configuration area and fracture resistance under experimental conditions. Several of fractured files demonstrated characteristic patterns of brittle fracture consistent with the propagation of pre-existing cracks. This data indicate that surface defects of NiTi rotary files may significantly decrease fatigue life and it may be one possible factor for early fracture of NiTi rotary files in clinical practice.

• 대한수학회보
• /
• 제30권2호
• /
• pp.285-293
• /
• 1993

In [4], Baumslag and Tretkoff proved a residual finiteness criterion for HNN extensions (Theorem 1.2, below). This result has been used extensively in the study of the residual finiteness of HNN extensions. Note that every one-relator group can be embedded in a one-relator group whose relator has zero exponent sum on a generator, and the latter group can be considered as an HNN extension. Hence the properties of an HNN extension play an important role in the study of one-relator groups [3], [2]. In this paper we prove a criterion for HNN extensions to be .pi.$_{c}$(Theorem 2.2). Moreover, we can prove that certain one-relator groups, known to be residually finite, are actually .pi.$_{c}$. It was known by Mostowski [10] that the word problem is solvable for finitely presented, residually finite groups. In the same way, the power problem is solvable for finitely presented .pi.$_{c}$ groups. Another application of subgroup separability with respect to special subgroups was mentioned by Thurston [12, Problem 15].m 15].

• 대한수학회보
• /
• 제26권2호
• /
• pp.109-114
• /
• 1989

This paper deals with the classifying spaces of finite groups. To any finite group G we associate a space BG with the property that .pi.$_{1}$(BG)=G, .pi.$_{i}$ (BG)=0 for i>1. BG is called the classifying space of G. Consider the problem of finding a stable splitting BG= $X_{1}$$^{V}$ $X_{1}$$^{V}$..$^{V}$ $X_{n}$ localized at pp. Ideally the $X_{i}$ 's are indecomposable, thus displaying the homotopy type of BG in the simplest terms. Such a decomposition naturally splits $H^{*}$(BG). The main purpose of this paper is to give the classification theorem in stable homotopy theory for groups with periodic cohomology i.e. cyclic Sylow p-subgroups for p an odd prime and to calculate some universal stable element. In this paper, all cohomology groups are with Z/p-coefficients and p is an odd prime.prime.