橡皮泥对手的力是弹力吗

"手压橡皮泥时,橡皮泥对手的力是弹力吗?"这个问题困扰了笔者很久,有两种截然不同的观点,理由都很充分.正方观点:橡皮泥对手的力是弹力.原因有3个,(1)手压桌子,桌子对手的力是弹力,而手压橡皮泥和手压桌子类似,因此橡皮泥对手的力也应当是弹力.(2)手对橡皮泥的力是弹力,根据作用力和     

源于课本 触类旁通——由一道课本原题引发的习题课教学案例分析

1引言波利亚说过:一个有责任心的老师与其穷于应付繁琐的教学内容和过量的题目,还不如选择一道有意义又不太复杂的题目,去帮助学生发觉题目的各个方面。在指导学生解题的过程中,提高他们的推理能力.他的见解启示我们,加强解题教学不是搞题海战术,得出题目的结果本身不是全部或最终目的,     

广义线性McCoy环

称环R是右线性McCoy的,如果R[x]中非零线性多项式f（x）,g（x）满足I（x）g（x）=0,则存在非零元素r∈R使得f（x）r=0．设a是环R的自同态,通过用斜多项式环R[x;a]中的元素代替一般多项式环R[x]中的元素而引入a-线性McCoy环的概念．讨论了a-线性McCoy环的基本性质和扩张性质．     

互联网环境下消费信贷行为研究

采用结构方程建模方法,实证分析了感知易用性、感知有用性、感知风险、信用卡效应及使用的态度与互联网环境下消费者使用信用卡支付的意愿之间的作用路径关系,从而建立了互联网环境下消费信贷行为影响因素的概念模型．研究表明,除感知风险与使用的意愿之间存在负相关关系外,其余四个因素与使用的意愿之间均存在正相关关系,其中使用的态度对使用的意愿的影响最大．     

CT在腺瘤性结节性甲状腺肿和乳头状甲状腺癌鉴别诊断中的价值

目的探讨CT在腺瘤性结节性甲状腺肿（ANG）和乳头状甲状腺癌（PTC）鉴别诊断中的价值。方法搜集经病理证实的105例112枚ANG和181例196枚PTC的CT资料,对性别、年龄、瘤体的形态、甲状腺边缘中断征、钙化、强化程度、增强后边界、淋巴结转移进行分析,统计强化程度高于周围甲状腺对ANG的诊断和甲状腺边缘中断征对PTC的诊断敏感度、特异度、阳性预测值、准确度。结果 ANG和PTC在瘤体形态、甲状腺边缘中断征、细钙化、粗钙化、强化程度、增强后瘤体边缘等方面均有统计学意义（均P＜0.05）,而在是否多发、环状钙化方面均无统计学差异（均P＞0.05）。181例PTC中,淋巴结转移75例。强化程度高于周围甲状腺对ANG诊断的敏感度、特异度、阳性预测值、准确度分别为67.9%、100%、100%、87.6%。甲状腺边缘中断征对PTC诊断的敏感度、特异度、阳性预测值、准确度分别为87.0%、91.1%、93.6%、88.6%。结论瘤体形态规则、强化程度高于周围甲状腺有助于ANG的诊断,而瘤体形态不规则、甲状腺边缘中断征、细钙化、粗钙化、淋巴结转移等有助于PTC的诊断;是否多发和环状钙化对ANG和PTC的鉴别诊断无意义。     

上市公司盈余管理系列报道之六：弹性的边界

正能量盈余管理是CFO参与企业价值创造的阳光地带。根据管理层操控应计额进行盈余管理是出于机会主义动机,还是传递公司未来经营业绩的价值相关性信息,盈余管理属性可以划分两类：机会主义盈余管理和决策有用性盘余管理。其中,机会主义盈余管理的类型包括基于管理层收购、股票发行、股权激励、内部人交易及基于满足薪酬契约和债务契约的契约动机、规避政府行业监管和反托拉斯监管的监管动机盈余管理等;     

Fiber laser-pumped, chirped, PPMgLN-based high efficient broadband mid-IR generation

We demonstrate a high-efficiency, high-power-nanosecond fiber laser-pumped broadband mid-infrared out- put based on a linearly chirped PPMgLN crystal. By using a linearly polarized pulsed Yb-doped fiber laser as the pump, we experimentally obtain a 1.22-W broadband mid-infrared laser output under pump power of 10.15 W. The 3-dB bandwidths of the idler and signal output are approxiwately 150 and 13 nm, centering at 3.60 and 1.51 μm, respectively. The measured idler spectrum shows a smooth spectral profile.     

The pressure dependences of elastic and lattice dynamic properties of AlAs from ab initio calculations

Ab initio calculations,based on norm-conserving nonlocal pseudopotentials and density functional theory(DFT),are performed to investigate the structural,elastic,dielectric,and vibrational properties of aluminum arsenide(AlAs) with a zinc-blende(B3) structure and a nickel arsenide(B81) structure under hydrostatic pressure.Firstly,the path for the phase transition from B3 to B81 is confirmed by analyzing the energies of different structures,which is in good agreement with previous theoretical results.Secondly,we find that the elastic constants,bulk modulus,static dielectric constants,and the optical phonon frequencies vary in a nearly linear manner under hydrostatic pressure.What is more,the softening mode of the transversal acoustic mode at the X point supports the phase transition in AlAs.     

Analysis of atom detection via the magnetic optical effect

We demonstrated a new method of atom detection by means of the magnetic optical effect. The number density of the atom cloud was measured by detecting the rotation angle of the polarization plane of linearly polarized probe light when propagating inside the atomic cloud. Detuning, the magnetic field and light intensity dependencies of the rotation angle were studied theoretically and experimentally to find the best parameter for atom detection. In this way, we managed to achieve a rotation angle of 0.22 rad with a signal to noise ratio (SNR) of 75 and a contrast of 87.5%.     

Density-functional theory study of the effect of pressure on the elastic properties of CaB6

Under high pressure, the long believed single-phase material CaB6 was latterly discovered to have a new phase tI56. Based on the density-functional theory, the pressure effects on the structural and elastic properties of CaB6 are obtained. The calculated bulk, shear, and Young's moduli of the recently synthesized high pressure phase tI56-CaB6 are larger than those of the low pressure phase. Moreover, the high pressure phase of CaB6 has ductile behaviors, and its ductility increases with the increase of pressure. On the contrary, the calculated results indicate that the low pressure phase of CaB6 is brittle. The calculated Debye temperature indicates that the thermal conductivity of CaB6 is not very good. Furthermore, based on the Christoffel equation, the slowness surface of the acoustic waves is obtained.