• Bulletin of the Korean Chemical Society
• /
• 제35권4호
• /
• pp.989-993
• /
• 2014

The molecular structures of 2,6-diaza-1,3,5,7-tetraoxaspiro[3,3]heptane (1) and its dinitro derivative, 2,6-dinitro-2,6-diaza-1,3,5,7-tetraoxaspiro[3,3]heptane (2), were fully optimized without symmetry constraints at $HF/6-31G^*$ level of theory. A bisected conformation with respect to the ring is preferred with a $C_2$ symmetric structure. The density of each molecule in the crystalline state was estimated to 1.12 and 2.36 $g/cm^3$ using PM3/VSTO-3G calculations from the molecular volume. The heat of formation was calculated for two compounds at the CBS-4M level of theory. The detonation parameters were computed using the EXPLO5 software: D = 6282 m/s, $P_{C-J}$ = 127 kbar for compound 1, D = 7871 m/s, $P_{C-J}$ = 307 kbar for compound 2, and D = 6975 m/s, $P_{C-J}$ = 170 kbar for 60% compound 2 with 40% TNT. Specific impulse of compound 1 in aluminized formulation when used as monopropellants was very similar to that of the conventional ammonium perchlorate in the same formulation of aluminum.

• 대한수학회논문집
• /
• 제25권2호
• /
• pp.167-171
• /
• 2010

We will show that if d is a cubefree integer and n is an integer, then with some suitable conditions, there are no primes p and a positive integer m such that d is a cubic residue (mod p), $3\;{\nmid}\;m$, p || n if and only if there are integers x, y, z such that $$x^3\;+\;dy^3\;+\;d^2z^3\;-\;3dxyz\;=\;n$$.

• 한국지구과학회지
• /
• 제31권1호
• /
• pp.95-105
• /
• 2010

본 연구의 목적은 집단논리적사고력검사의 이용 목적에 따라 일반화가능도이론을 적용하여 문항과 피험자만을 고려한 단일국면의 오차원, 그리고 문항과 피험자, 그리고 영역을 고려한 다국면의 오차원을 분석하는 데 있다. 연구는 지방 소재 초 중 고등학생 총 1016명을 대상으로 이루어졌으며, 21문항의 GALT 완본을 40분 동안 실시하고, 이 중 축소본에 해당하는 12문항을 별도로 추출하여 일반화가능도이론을 이용한 신뢰도 분석에 이용하였다. 자료의 분석을 위해 일반화가능도이론을 적용하여 $p{\times}i$설계와 $p{\times}(i:h)$설계로 나누어 G 연구와 D 연구를 실시하였다. 분석결과는 다음과 같다. 첫째, 완본과 축소본을 $p{\times}I$설계로 D 연구를 수행한 결과 완본의 경우 21문항을 평가했을 때 0.87로 적정 수준의 일반화가능도 계수인 0.80을 상회하였으며, 13문항에서도 적정 수준의 일반화가능도 계수에 도달하였다. 축소본의 경우 12문항을 평가했을 때 0.77로 적정 수준의 일반화가능도 계수에 미치지 못하였으며, 최소 15문항 이상에서 신뢰도가 적정 수준에 도달하였다. 둘째, 축소본을 $p{\times}(I:H)$설계로 D 연구를 수행한 결과 6영역에 대해 영역별로 2문항씩 구성될 경우 0.71로 적정 수준의 일반화가능도계수인 0.80 보다 낮게 측정되었으며, 최소 영역별 5문항 이상에서 신뢰도가 적정 수준에 도달하였다.

• Computers and Concrete
• /
• 제4권2호
• /
• pp.135-156
• /
• 2007

Three 3D nonlinear finite-element models are developed to study the behavior of concrete beams and plates with and without external reinforcement by fibre-reinforced plastic (FRP). All three models are formulated based upon the 3D theory of elasticity. The stress model is modified from the element developed by Ramtekkar, et al. (2002) to incorporate material nonlinearity in the formulation. Both transverse stress and displacement components are used as nodal degrees-of-freedom to ensure the continuity of both stress and displacement components between the elements. The displacement model uses only displacement components as nodal degrees-of-freedom. The transition model has both stress and displacement components as nodal degrees-of-freedom on one surface, and only displacement components as nodal degrees-of-freedom on the opposite surface. The transition model serves as a connector between the stress and the displacement models. The developed models are validated by comparing the results of the analyses with an existing experimental result. Parametric studies of the effects of the externally reinforced FRP on the load capacity of reinforced concrete (RC) beams and concrete plates are performed to demonstrate the practicality and the efficiency of the proposed models.

• Advances in materials Research
• /
• 제12권2호
• /
• pp.161-177
• /
• 2023

This paper proposes an analytical method to investigate the free vibration behaviour of new functionally graded (FG) carbon nanotubes reinforced composite beams based on a higher-order shear deformation theory. Cosine functions represent the material gradation and material properties via the thickness. The kinematic relations of the beam are proposed according to trigonometric functions. The equilibrium equations are obtained using the virtual work principle and solved using Navier's method. A comparative evaluation of results against predictions from literature demonstrates the accuracy of the proposed analytical model. Moreover, a detailed parametric analysis checks for the sensitivity of the vibration response of FG nanobeams to nonlocal length scale, strain gradient microstructure-scale, material distribution and geometry.

• 대한조선학회논문집
• /
• 제33권2호
• /
• pp.127-138
• /
• 1996

고속선의 내항성능 해석 방법으로 스트립 방법, 통합이론(Unified theory), 3차원 판넬 방법등이 널리 사용되고 있다. 스트립 이론은 2차원적 해석 방법으로 전진속도가 빠른 경우나 추파중 저주파수 영역에서 유체력 계수와 운동응답이 정확하지 않으며, 통합이론은 내부영역에서는 2차원적 해석을 사용하고 외부영역은 세장체 이론을 사용하여 해석하는 방법으로 수학적으로 복잡한 단점이 있다. 3차원 판넬 방법을 이용한 해석은 계산 시간이 오래 걸리지만 고속인 경우에 모든 주파수 영역에서 정확한 해를 주는 것으로 알려져 있고, 전산기의 급속한 발달과 더불어 가장 권장되는 방법이다. 본 논문에서는 고속선의 해석에 전통적으로 사용되고 있는 스트립 법에 의한 해석과 3차원 판넬 방법을 이용한 해석법을 비교한다. 3차원 판넬 방법에 의한 해석은 쏘오스 분포법과 전진하면서 동요하는 그린 함수를 사용하고, 그린 함수의 수치, 계산은 Hoff의 방법을 이용하였고, 그린 함수는 종축에 대한 대칭 관계를 이용하여 계산 시간을 줄였다. 계산에 사용된 선종은 카타마란(Catamaran) 형태의 고속선이며 상기 두 방법에 의해 구해진 유체력 계수, 파강제력과 주파수 응답함수 등을 비교하였고, 또한 불규칙파중 운동응답의 계산 결과를 비교 검토해 보았다.

• Steel and Composite Structures
• /
• 제51권2호
• /
• pp.185-202
• /
• 2024

In this research paper, and for the first time, wave propagations in sigmoidal imperfect functionally graded material plates are investigated using a simplified quasi-three-dimensionally higher shear deformation theory (Quasi-3D HSDTs). By employing an indeterminate integral for the transverse displacement in the shear components, the number of unknowns and governing equations in the current theory is reduced, thereby simplifying its application. Consequently, the present theories exhibit five fewer unknown variables compared to other Quasi-3D theories documented in the literature, eliminating the need for any correction coefficients as seen in the first shear deformation theory. The material properties of the functionally graded plates smoothly vary across the cross-section according to a sigmoid power law. The plates are considered imperfect, indicating a pore distribution throughout their thickness. The distribution of porosities is categorized into two types: even or uneven, with linear (L)-Type, exponential (E)-Type, logarithmic (Log)-Type, and Sinus (S)-Type distributions. The current quasi-3D shear deformation theories are applied to formulate governing equations for determining wave frequencies, and phase velocities are derived using Hamilton's principle. Dispersion relations are assumed as an analytical solution, and they are applied to obtain wave frequencies and phase velocities. A comprehensive parametric study is conducted to elucidate the influences of wavenumber, volume fraction, thickness ratio, and types of porosity distributions on wave propagation and phase velocities of the S-FGM plate. The findings of this investigation hold potential utility for studying and designing techniques for ultrasonic inspection and structural health monitoring.

• 한국수학교육학회지시리즈D:수학교육연구
• /
• 제11권4호
• /
• pp.275-283
• /
• 2007

In this study, we gave 132 high school students fifteen probabilities and nine statistics problems of the Korean College Scholastic Aptitude Test and then analyzed their answer using the classical test theory and the item response theory. Using the classical test theory (the Testian 1.0) we get the item reliability ($0.730 \sim 0.765$), and using the item response theory (the Bayesian 1.0) we get the item difficulty ( $-2.32\sim0.83$ ) and discrimination ( $0.55\sim 2.71$). From results, we find out what and why students could not understand well.

• Journal of Information Science Theory and Practice
• /
• 제7권2호
• /
• pp.54-64
• /
• 2019

A theory of public knowledge is offered for the purposes of defining more clearly its role in information systems and classification schemas. Public knowledge is knowledge intended to be available for use in a public system. It is knowledge accessible to the public or knowledge in the public arena as opposed to the other seemingly multitudinous ways to describe knowledge. Furthermore, there are many different public arenas or small worlds. Public knowledge, irrespective of these different arenas, has four important overlying characteristics: It is consensual, it does not imply complete truth or certainty, it is autonomous, and it has a constant renewal of old knowledge with new knowledge. Each of these attributes has been culled from a study of the works of Patrick Wilson, Karl Popper, and John Ziman.

• Structural Engineering and Mechanics
• /
• 제81권4호
• /
• pp.461-479
• /
• 2022

A finite element method analysis framework is introduced for the free vibration analyses of functionally graded porous beam structures by employing two variables trigonometric shear deformation theory. Both Young's modulus and material density of the FGP beam element are simultaneously considered as grading through the thickness of the beam. The finite element approach is developed using a nonlocal strain gradient theory. The governing equations derived here are solved introducing a 3-nodes beam element. A comprehensive parametric study is carried out, with a particular focus on the effects of various structural parameters such as the dispersion patterns of GPL reinforcements and porosity, thickness ratio, boundary conditions, nonlocal scale parameter and strain gradient parameters. The results indicate that porosity distribution and GPL pattern have significant effects on the response of the nanocomposite beams.