introduction : the aim of the present study was to comparatively evaluate the physical surface changes and incidence of separation in rotary nickel-titanium (niti) instruments using scanning electron microscope (sem). methods and materials: a total number of 210 freshly extracted human maxillary and mandibular first molars were selected and distributed between three groups. three different syst...

Rotating shafts are important and responsible components of many machines, such as power generation plants, aircraft engines, machine tool spindles, etc. A transverse shaft crack can occur due to cyclic loading, creep, stress corrosion, and other mechanisms to which rotating machines are subjected. If not detected early, the developing shaft crack can lead to a serious machine damage resulting ...

A new force field has been customized for the variation of polynorbornene that contains a bicycloheptane group in the backbone structure. The force field was developed from ab initio density functional theory (DFT), and semiempirical electronic structure calculations for both stereochemical dimers of the 2,3 exoexo isomer of polynorbornene. The bond length and bond angle parameters were determi...

국내의 서비스 수준 지진(SLE)과 최대 고려 지진(MCE)의 두 RC 건물 구조물의 실험 및 해석 결과에서 얻은 탄성 비탄성 응답은 비틀림에 대한 전단 비틀림 거동에서 저항 메커니즘의 특성을 연구하는데 사용될 수 있다. 불균형 구조의 특성 연구에서는 전단력 모멘트에 병진 변형 변형의 상호 작용 효과를 나타내는 방정식이 제안하였다. 탄성과 힘과 사이에 상관 관계 유무가 다르기 때문에 증분 전단력과 모멘트를 벽 프레임 변형을 중심으로 항복, 제하 재하중 단계로 구분하여 해당 측면에서 해석을 수행하였다. 가지 주요 지배 모드의 조합에서 변형은 주로 전단력에 기여하는 반면 전체 크게 기여한다. 그러나 응답에서는 변형이 모멘트 모두에 기여하게 된다. 따라서 주어진 방정식을 이용하여 응답에서 비틀림의 편심 감소...

We examined three united atom models in light of their description of polyolefin dynamics and investigated the relative influence of various potentials on the resulting dynamics. Results were compared with a collection of experimental data on polyethylene, poly(ethylene-alt-propylene), polypropylene, and head-to-head polypropylene, including quasielastic neutron scattering measurements that we ...

We performed studies of fluctuating charge, fluctuating dipole, and combined models for substituted benzenes and concluded that dipoles are necessary to avoid errors in important cases. Force fields incorporating fluctuating dipoles for alanine, serine, and phenylalanine were developed that accurately reproduce both relative conformational energies and cooperative many-body energies as given by...

The keel design of the tibial tray is essential for the transmission of the majority of the forces to the peripheral bone structures, which have better mechanical proprieties, thus reducing the risk of loosening. The aim of the present study was to compare the behaviour of different tibial tray designs submitted to torsional forces. Four different tibial components were modelled. The 3-D recons...

In this paper we consider the onset of shimmy oscillations of an aircraft nose landing gear. To this end we develop and study a mathematical model with torsional and lateral bending modes that are coupled through a wheel-mounted elastic tyre. The geometric effects of a positive rake angle are fully incorporated into the resulting five-dimensional ordinary differential equation model. A bifurcat...