共查询到20条相似文献,搜索用时 15 毫秒
1.
Masamitsu Iino 《Proceedings of the Japan Academy. Series B, Physical and biological sciences》2010,86(3):244-256
Changes in the intracellular Ca2+ concentration regulate numerous cell functions and display diverse spatiotemporal dynamics, which underlie the versatility of Ca2+ in cell signaling. In many cell types, an increase in the intracellular Ca2+ concentration starts locally, propagates within the cell (Ca2+ wave) and makes oscillatory changes (Ca2+ oscillation). Studies of the intracellular Ca2+ release mechanism from the endoplasmic reticulum (ER) showed that the Ca2+ release mechanism has inherent regenerative properties, which is essential for the generation of Ca2+ waves and oscillations. Ca2+ may shuttle between the ER and mitochondria, and this appears to be important for pacemaking of Ca2+ oscillations. Importantly, Ca2+ oscillations are an efficient mechanism in regulating cell functions, having effects supra-proportional to the sum of duration of Ca2+ increase. Furthermore, Ca2+ signaling mechanism studies have led to the development of a method for specific inhibition of Ca2+ signaling, which has been used to identify hitherto unrecognized functions of Ca2+ signals. 相似文献
2.
Optical absorption, thermoluminescence glow and emission spectra of RbBr:Ca2+ and RbBr:OH− have been studied and analysed. It is observed that both Ca2+ and OH− ions enhance theF-centre concentration.F
Z1 band in RbBr:Ca2+ appears at 1.55 eV. TL glow peak corresponding toF
Z1 centre on analysis gives a trap depth of 0.84 eV. OH− ions in the crystal seem to act as TL ‘killers’. Spectral distribution of emission under the glow peaks shows five bands
around 1.5, 1.8, 2.1, 2.5 and 2.9 eV. Probable models of TL mechanism are suggested to explain the observed TL emission bands. 相似文献
3.
Fe-ZSM-5 samples containing a combination of 57Fe3+ in framework (FW) and regular iron in extra-framework (EFW) sites were prepared by introducing 57Fe in hydrothermal synthesis, then exchanging Fe2+ of natural isotope composition into the lattice. The stability for one part of Fe2+ and Fe2+ ? Fe3+ reversibility for the other part in catalytic decomposition of N2O is demonstrated by in situ Mössbaer measurements. Formation of dinuclear FeFW–O–FeEFW pairs is not prevailing. 相似文献
4.
Theoretical calculation of of B-like ions: photoionization cross sections N^2+, O^3+ and F^4+ 下载免费PDF全文
There can be found some notable discrepancies with regard to the resonance structures when R-matrix calculations from the Opacity Project and other sources are compared with recent absolute experimental measurements of Bizau et al [Astron.Astrophts.439 387(2005)] for B-like ions N2+,O3+ and F4+.We performed close-coupling calculations based on the R-matrix formalism for the photoionizations of ions mentioned above both for the ground states and first excited states in the near threshold regions.The present results are compared with experimental ones given by Bizau et al and earlier theoretical ones.Excellent agreement is obtained between our theoretical results and the experimental photoionization cross sections.The present calculations show a significant improvement over the previous theoretical results. 相似文献
5.
Abstract In the present investigation the excitation and fluorescence spectra and lifetimes of Mn2+ ions in calcium chloride, for various manganese concentrations and sample temperatures have been studied for the first time. The fluorescence spectrum consists of an asymmetric broad band, which upon lowering the sample temperature, shifts its maximum from 580 nm at 300 K to 596 nm at 11 K. This luminescence band was associated with the 4Tlg(4G)→6Alg(6S) spin-forbidden transition in the manganese ions occupying Ca-sites in the lattice of CaCl2. The excitation spectrum of the Mn2+ fluorescence revealed the features of manganese ions in octahedral coordination and consisted of nine excitation peaks which were associated with Mn2+-crystal-field-sensitive transitions. A crystal field analysis of the wavelength positions of these transitions by means of the model developed by Curie et al. allowed us to determine the magnitude of the cubic field splitting 10Dq, the reduced Racah parameter B', the Koide-Pryce covalency parameter ε and the spin transfer coefficients f [sgrave] and f σ. From the measurement of the temperature dependence of the Mn2+ fluorescence lifetime, we have also obtained information about the different mechanisms which are involved in the relaxation of excited Mn2+ ions in this host crystal in the temperature range (11–300 K). 相似文献
6.
The alkaline-earth fluorohalide crystals MFX, where M=Ca, Sr, Ba, Pb and X=Cl, Br, I, form an important class of materials crystallizing in the PbFCl-type tetragonal structure which is also called the matlockite structure. These compounds have long been of interest because of the various defect species which can be detected by spin resonance and associated techniques. The crystals were prepared by slow cooling of the melt of a stoichiometric mixture of BaF 2 and the corresponding chloride or bromide under 0.2 bar of ultrapure argon (5N5), often slightly fluorinated. We have studied the mechanoluminescence (ML) of BaFBr:Sm 2+ and BaFCl:Sm 2+ crystals. It is seen that after the impact of a moving piston, initially the ML intensity increases with time, attains a maximum value and then it decreases with time up to a particular minimum value, and then it increases again, attaining a peak value and finally disappears. The first peak lies in the deformation region and the second peak lies in the post-deformation region. The ML intensity of the BaFCl:Sm 2+ crystal is much higher than the ML intensity of the BaFBr:Sm 2+ crystal. For different impact velocities, the ML intensity increases with velocity; and the total ML intensity attains a saturation value for higher impact velocities. The total ML intensity increases with the increase in the applied load. It is suggested that the moving dislocation produced during deformation of crystals captures holes from hole-trapped centers (like H centers), and the subsequent radiative recombination of the dislocation holes with electron gives rise to ML. Thermoluminescence (TL) of BaFBr:Sm 2+ and BaFCl:Sm 2+ crystals was studied after exposure to ultraviolet rays with the help of a TLD reader. The peak of TL for the BaFBr:Sm 2+ crystal is found at ~247°C and for BaFCl:Sm 2+ crystals at 283°C. The TL intensity initially increases with increase in the UV radiation and then it attains saturation for higher values of UV exposure. The absorption spectrum was recorded with the help of a UV–visible spectrophotometer (Shimadzu). The band found at 275 nm was attributed to H centers. 相似文献
7.
采用分子动力学模拟的方法研究了CaO-Al2O3-SiO2系玻璃的微观结构,发现Ca/Al=1/2时CaO-Al2O3-SiO2系玻璃(网硅酸盐体系)并不像传统理论认为的那样是一个完整的三维网络,而是存在一定量的非桥氧,从而从理论上进一步证实了Stebins等人的实验结果.同时也发现不同的Ca/Al比对Si和Al键接方式产生重要影响,在Ca/Al>1/2时,Al比Si容易成为网络的中间体,其首先插入网络体中间;在Ca/Al<1/2时,Si比Al容易成为网络中间体.虽然在能量上Al—O—Si占有扰势,但当Ca/Al从大于1/2变化到小于1/2时,仍有部分Al—O—Si转变成Al—O—Al和Si—O—Si,丰富了Al自回避规则的内容.
关键词:
2O3-SiO2')" href="#">CaO-Al2O3-SiO2
玻璃
微观结构
分子动力学 相似文献
8.
Jingjing Xue 《中国物理 B》2022,31(4):48702-048702
A-form DNA is one of the biologically active double helical structure. The study of A-DNA structure has an extensive application for developing the field of DNA packaging in biotechnology. In aqueous solution, the A-DNA structure will have a free transformation, the A-DNA structure will be translated into B-form structure with the evolution of time, and eventually stabilized in the B-DNA structure. To explore the stability function of the bivalent metal ions on the A-DNA structure, a series of molecular dynamics simulations have been performed on the A-DNA of sequence (CCCGGCCGGG). The results show that bivalent metal ions (Mg2+, Zn2+, Ca2+) generate a great effect on the structural stability of A-DNA in the environment of high concentration. As the interaction between metal ions and electronegative DNA chains, the stability of A-DNA in solution is gradually improved with the increasing solution concentration of ions. In metal salt solution with high concentration, metal ions can be easily distributed in the solvation shells around the phosphate groups and further lead to the formation of shorter and more compact DNA structure. Also, under the condition of the same concentration and valency of the metal ions, the stability of A-DNA structure is different. The calculations indicate that the structure of A-DNA in CaCl2 solution is less stable than in MgCl2 and ZnCl2 solution. 相似文献
9.
利用分子动力学模拟方法研究了2—3nm厚的类金刚石(DLC)薄膜在金刚石基体(100)表面上的生长过程. 分析了用来表征沉积后无定型碳膜质量的重要结构特性,如sp3杂化比例、薄膜密度、径向分布函数等,计算结果和现有的实验结果基本一致. 不同入射原子能量对结构特性进而对薄膜性能有重要影响,入射原子能量在20—60eV时,薄膜可以获得最优性能. 载能原子入射是生长均匀、连续、致密固体薄膜的前提,稳定的中间区域对于保证薄膜优良的力学性质是必需的.
关键词:
DLC膜
分子动力学模拟
3杂化比例')" href="#">sp3杂化比例 相似文献
10.
Systematic long time (5–20 ns) molecular dynamics (MD) simulations have been carried out to study the structural and dynamical properties of CaCl2 aqueous solutions over a wide range of concentrations (≤9.26 m) in this study. Our simulations reveal totally different structural characteristics of those yielded from short time (≤1 ns) MD simulations [A.A. Chialvo and J.M. Simonson, J. Chem. Phys. 119, 8052 (2003); T. Megyes, I. Bako, S. Balint, T. Grosz, and T. Radnai, J. Mol. Liq. 129, 63 (2006)]. An apparent discontinuity was found at 4–5 m of CaCl2 in various properties including ion–water coordination number and self-diffusion coefficient of ions, which were first noticed by Phutela and Pitzer in their thermodynamic modelling [R.C. Phutela and K.S. Pitzer, J. Sol. Chem. 12, 201 (1983)]. In this study, residence time was first taken into consideration in the study of Ca2+–Cl? ion pairing, and it was found that contact ion pair and solvent-sharing ion pair start to form at the CaCl2(aq) concentrations of about 4.5 and 4 m, respectively, which may be responsible for the apparent discontinuity. In addition, the residence time of water molecules around Ca2+ or Cl? showed that the hydration structures of Ca2+ and Cl? are flexible with short residence time (<1 ns). It needs to be pointed out that it takes much longer simulation time for the CaCl2–H2O system to reach equilibrium than what was assumed in previous studies. 相似文献
11.
Abstract With increasing X on Ca1-xSrxF2 mixed crystals doped with Eu2+ (4f65d) ions, the absorption peak shifted linearly to that of SrF2:Eu, while the luminescence one moved parabolically with a minimum at around x=0.5. The linewidth broadened nearly twice as large as that of CaF2 in the vicinity of x=0.5 and subsequently renarrowed for x > 0.5. The temperature dependences of the luminescence intensity and life time revealed that the nonradiative activation energy has a minimum of 0.40 eV around x=0.5. From the calculated result of the lineshape, these non-linear behaviors against x were explained by adjusting the electron-phonon coupling strength. 相似文献
12.
ABSTRACTWe present a theoretical study of the ground electronic state potential of the Ca+Ar2 complex and of its photoabsorption spectra, simulated at temperatures ranging between 20 and 220?K. These calculations exploit a Monte-Carlo (MC) method, based on a one-electron pseudo-potential approach. A pairwise additive potential fitted to coupled cluster ab initio points, is used to model the Ca+Ar2 complex. Our study shows that the most stable form of Ca+Ar2 is a bent C2v structure, whereas the linear isomer is located at around 90?±?10?cm?1 above in energy. The analysis of the photoabsorption spectra establishes that a structural transition from bent Ca+Ar2 to linear ArCa+Ar occurs at T~100?K. Trends in binding energies of both isomers, bond lengths and bond angles are also discussed. Molecular orbital overlaps provide an explanation for the order of stability between the bent and linear structures. 相似文献
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The optical absorption spectra (d-d transition bands) and covalent effect of Ni2+ ions in octahedral sites of Ca3Sc2Ge3O12 crystal have been investigated by the full energy matrix based on the two spin–orbit coupling parameters model. The bond length of octahedral site is Ri?=?2.19 Å, which can be determined by the cubic crystal-field parameter and optical spectral data. The lattice distortion of the Ni2+ center in Ca3Sc2Ge3O12 crystal is also obtained from the calculations. In addition, the result has shown that the covalent effect of Ni2+ ion in the octahedral site of Ga3Sc2Ge3O12 is obvious and cannot be ignored. The calculated d-d transition bands agree well with that of the experimental findings, suggesting that the present methods can explain reasonably the optical spectral data and covalent effect of 3d8 ions in octahedral lattices. 相似文献
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18.
Chang-Chun Ding Shao-Yi Wu Qing-Sheng Zhu Guo-Liang Li Zhi-Hong Zhang Yong-Qiang Xu 《Molecular physics》2013,111(12):1478-1484
The local lattice distortions and the electron paramagnetic resonance (EPR) parameters (g factors, hyperfine structure constants and zero-field splittings) for Cu2+, Mn2+ and Fe3+ in ZnWO4 are theoretically studied based on the perturbation calculations for rhombically elongated octahedral 3d9 and 3d5 complexes. The impurity centres on Zn2+ sites undergo the local elongations of 0.01, 0.002 and 0.013 Å along the C2 axis and the planar bond angle variations of 8.1°, 8.0° and 8.6° for Cu2+, Mn2+ and Fe3+, respectively, due to the Jahn–Teller effect and size and charge mismatch. In contrast to the host Zn2+ site with obvious axial elongation (~0.31 Å) and perpendicular (angular) rhombic distortion, all the impurity centres demonstrate more regular octahedral due to the above local lattice distortions. The copper centre exhibits significant Jahn–Teller reductions for the spin-orbit coupling and orbital angular momentum interactions, characterised by the Jahn–Teller reduction factor J (≈0.29 ? 1). The calculated EPR parameters agree well with the experimental results. The local structures of the impurity centres are analysed in view of the corresponding lattice distortions. 相似文献
19.
Ĺuboš Horný Pavel Mach Jozef Masarik Ivan Hubač Stephen Wilson 《Molecular physics》2013,111(24):3801-3807
The structure and stability of the helio nitrogen molecular dication, HeN2+ 2, is investigated by means of standard quantum chemical methods based on both single-reference and multi-reference formalisms. Sequences of correlation consistent basis sets are employed to establish convergence with respect to the size and the quality of the single-particle basis set. MRCI and CASPT2 calculations are reported for the HeN2+ 2 ground-state ion which is found to be metastable. The barrier for the transition state of the reaction HeN2+ 2→ N+ …NHe+ → N+ + NHe+ is calculated to be 59.5 kcals mol?1. The structure of the transition state NHeN2+ was also determined from calculations using the MRCI and CASPT2 methods. 相似文献
20.
Reports of Type II twins are quite rare for most crystal structures. When they do occur, they are usually one of a number of possible twinning modes observed in a particular material. However, for the triclinic phase devitrite, Na2Ca3Si6O16, which nucleates from commercial soda?lime?silica float glass subjected to suitable heat treatments, the only reported twinning mode to date is a Type II twinning mode. In this study, this Type II twinning mode is first examined by molecular dynamics simulation to determine the lowest energy configuration of perfect twin boundaries for the twin mode. This is then compared with the lowest energy configurations of perfect twin boundaries found for six possible Type I twinning modes for devitrite for which the formal deformation twinning shear is less than 0.6. The most favourable twin plane configuration for the Type II twinning crystallography is shown to produce reasonably low twin boundary energies and sensible predictions for the optimum locations of the twin plane, K 1, and the [1?0?0] rotation axis, η 1, about which the 180° Type II twinning operation takes place. By comparison, all the Type I twinning modes were found to have very energetically unstable atomic configurations, and for each of these twinning modes, the lowest energy configurations found all led to high effective K 1 twin boundary energies relative to perfect crystal. These results therefore provide a rationale for the experimental observation of the particular Type II twinning mode seen in devitrite. 相似文献