Bursting Ca2+ Oscillations and Synchronization in Coupled Cells

A mathematical model proposed by Grubelnk et al. [Biophys. Chem. 94 （2001） 59] is employed to study the physiological role of mitochondria and the cytosolic proteins in generating complex Ca^2＋ oscillations, lntracellulax bursting calcium oscillations of point-point, point-cycle and two-folded limit cycle types are observed and explanations are given based on the fast/slow dynamical analysis, especially for point-cycle and two-folded limit cycle types, which have not been reported before. Furthermore, synchronization of coupled bursters of Ca^2＋ oscillations via gap junctions and the effect of bursting types on synchronization of coupled cells are studied. It is argued that bursting oscillations of point-point type may be superior to achieve synchronization than that of point cycle type.     

Numerical Simulations of Calcium Ions Spiral Wave in Single Cardiac Myocyte

The calcium ions （Ca^2＋） spark is an elementary Ca^2＋ release event in cardiac myocytes. It is believed to buildup cell-wide Ca^2＋ signals, such as Ca^2＋ transient and Ca^2＋ wave, through a Ca^2＋-induced Ca^2＋ release （CICR） mechanism. Here the excitability of the Ca^2＋ wave in a single cardiac myoeyte is simulated by employing the fire-diffuse-fire model. By modulating the dynamic parameters of Ca^2＋ release and re-uptake channels, we find three Ca^2＋ signaling states in a single cardiac myoeyte： no wave, plane wave, and spiral wave. The period of a spiral wave is variable in the different regimes. This study indicates that the spiral wave or the excitability of the system can be controlled through micro-modulation in a living excitable medium.     

Preparation and Luminescence Characteristics of Ca3Y2（BO3）4：Eu^3＋ Phosphor

Ca3Y2 （BO3）4：Eu^3＋ phosphor is synthesized by high temperature solid-state reaction method, and the Iuminescence characteristics are investigated. The emission spectrum exhibits two strong red emissions at 613 and 621 nm corresponding to the electric dipole ^5 Do- ^7F2 transition of Eu^3＋ under 365 nm excitation, the reason is that Eu^3＋ substituting for Y^3＋ occupies the non-centrosymmetric position in the crystal structure of Ca3 Y2 （BO3）4. The excitation spectrum for 613 nm indicates that the phosphor can be effectively excited by ultraviolet （UV） （254 nm, 365nm and 400nm） and blue （470nm） light. The effect of Eu^3＋ concentration on the emission intensity of Ca3 Y2 （BO3）4 ：Eu^3＋ phosphor is measured, the result shows that the emission intensities increase with increasing Eu^3＋ concentration, then decrease. The CIE colour coordinates of Ca3Y2 （BO3）4：Eu^3＋ phosphor is （0.639, 0.357） at 15mol% Eu^3＋.     

Cooperative Quantum Cutting of Nano-Crystalline BaF2：Tb^3＋, Yb^3＋ in Oxyfluoride Glass Ceramics

We report on cooperative quantum cutting in Tb^3＋- Yb^3＋ codoped glass ceramics. Precipitation of BaF2 nanocrystals is confirmed by XRD and HRTEM analysis. Near-infrared emission due to transition of Yb^3＋ ions under 485 nm excitation indicates cooperative energy transfer from Tb^3＋ to Yb^3＋. The quantum efficiency of this process reaches 145%. The realization of quantum cutting in glass ceramics may have promising applications in solar cells.     

Synchronized Anti-Phase and In-Phase Oscillations of Intracellular Calcium Ions in Two Coupled Hepatocytes System

We study the dynamic behaviour of two intracellufar calcium oscillators that are coupled through gap junctions both to Ca^2＋ and inositol（1,4,5）-trisphosphate （IP3）. It is found that synchronized anti-phase and in-phase oscillations of cytoplasmic cadcium coexist in parameters space. Especially, synchronized anti-phase oscillations only occur near the onset of a Hopf bifurcation point when the velocity of IP3 synthesis is increased. In addition, two kinds of coupling effects, i.e., the diffusions of Ca^2＋ and IP3 among cells on synchronous behaviour, are considered. We fnd that small coupling of Ca^2＋ and large coupling of IP3 facilitate the emergence of synchronized anti-phase oscillations. However, the result is contrary for the synchronized in-phase case. Our findings may provide a qualitative understanding about the mechanism of synchronous behaviour of intercellular calcium signalling.     

Reading the patterns in living cells —the physics of ca2+ signaling

Ca²⁺ is one of the most important messengers. It transmits signals inside living cells and takes part in intercellular coordination. The dynamics of the Ca²⁺ concentration shows a transition from elemental, stochastic events to global events like waves and oscillations. This transition renders it an ideal tool for studying basic concepts of pattern formation, especially since access to the most important experimental parameters is given. Ca²⁺ dynamics in living cells has been a major topic of biophysical modelling in the last 15 years. Modelling has reached the level of predictive power. The theoretical analysis of waves provided new insight into the mechanisms of Ca²⁺ signaling and led to new concepts of analysis of wave equations with concentration dependent diffusion and novel wave bifurcations. Modelling of oscillations provided understanding especially of complex oscillations and allowed to extract information about the underlying cellular parameters and mechanisms. The investigation of the stochastic aspects of intracellular Ca²⁺ dynamics demonstrated the fundamental role of fluctuations arising from the control of the release channel by Ca²⁺ and IP₃. This review presents an overview of current theoretical research on Ca²⁺ dynamics in living cells driven by the inositol 1,4,5-trisphosphate receptor channel.     

磁共振技术在丝素蛋白结构与功能研究中的应用

丝素蛋白纤维因其优异的力学性能和良好的生物相容性而得到广泛关注. 人们通过对丝素蛋白二级结构的构象转变及其诱导因素的研究,试图阐明蚕吐丝机理、相关蛋白结构与功能的关系,为人工合成性能优良的丝纤维材料以及认识生命过程提供有益指导和帮助. 磁共振技术是研究丝素蛋白结构最有效的方法之一. 我们课题组多年来运用核磁共振（NMR）的方法研究了桑蚕丝素蛋白的构象及环境对其的影响因素,如pH、金属离子（K⁺、Na⁺、Ca²⁺、Cu²⁺、Zn²⁺）等,并运用电子自旋顺磁共振（EPR）方法研究了金属Cu²⁺离子与丝素蛋白的相互作用,试图揭示蛋白质构象转变与金属离子影响的内在联系. 另外,我们还发展了一种广义二维核磁共振相关技术,有效缩短了传统二维核磁共振的实验时间. 本文将综述这些年来我们所做的相关工作.     

Upconversion Luminescence of Er3+ Ions in Transparent Germanate Glass Ceramics Containing CaF2 Nanocrystals

The visible upconversion and near-infrared luminescence of Er3＋ ions in germanate glass ceramics containing GaF2 nanocrystals are investigated. The nanocrystals are characterized by x-ray diffraction （XRD） and transmission electron microscopy, showing their mean sizes less than 20hm. High transmittance of the glass ceramics is displayed by absorption spectra. The upconversion luminescence intensity in the glass ceramics increases significantly with increasing temperature. Both the shifts of the XRD peaks and the Stark-split shown in the luminescence spectra indicate the entrance of the Er3＋ ions into the CaF2 nanocrystals, which is confirmed by a Judd-Ofelt analysis. Possible mechanisms of the upconversion luminescence are analyzed.     

Relativistic Energies and Auger Widths of High-Lying Doubly-Excited States 1s^23lnl′ ^1De in Be-Like O^4＋ Ions

The saddle-point variational method and restricted variational method are used to calculate energies of doublyexcited singlet states 1s^23lnl′ （n =3-.） ^1 De in Be-like O^4＋ ions, including the mass polarization and relativistic corrections. The saddle-point complex-rotation method is used to compute the Auger widths and Auger transition rates. These results are compared with other theoretical and experimental data in the literature.     

FREQUENCY CATASTROPHE AND CO-EXISTING ATTRACTORS IN A CELL Ca2+ NONLINEAR OSCILLATION MODEL WITH TIME DELAY

Frequency catastrophe is found in a cell Ca²⁺ nonlinear oscillation model with time delay. The relation of the frequency transition to the time delay is studied by numerical simulations and theoretical analysis. There is a range of parameters in which two kinds of attractors with great frequency differences co-exist in the system. Along with parameter changes, a critical phenomenon occurs and the oscillation frequency changes greatly. This mechanism helps us to deepen the understanding of the complex dynamics of delay systems, and might be of some meaning in cell signalling.     

Coupling Effect of Ion Channel Clusters on Calcium Signalling

Based on a modified intracellular Ca^2＋ model involving diffusive coupling of two calcium ion channel dusters, the effects of coupling on calcium signalling are numerically investigated. The simulation results indicate that the diffusive coupling of dusters together with internal noise determine the calcium dynamics of single duster, and for either homogeneous or heterogeneous coupled dusters, the synchronization of dusters, which is important to calcium signalling, is enhanced by the coupling effect.     

Kinetic Energy of Trapped Ions Cooled by Buffer Gas

The average kinetic energy of 40 Ca＋ ions is measured by the method of evaporating ions in an rf ion trap. The kinetic energy of the ion 40Ca＋ varies from 0.5eV to 0.2eV with changing buffer gas pressure from 10^-7 mbar to 10^-5 mbar. The Brownian motion model is also introduced to calculate the average kinetic energy of the trapped ions.     

Ca-doping effects on N-type ferrimagnetism of NdVO3

Ca²⁺-doping effects were studied on the N-type ferrimagnet of NdVO₃. The chemical pressures by Ca²⁺-doping induced lowering of ferrimagnetic transition temperature T_c and compensation temperature θ_c, resulting in the phase transition from N- to P-type ferrimagnetic phase. In the N-phase, spontaneous magnetization M_sp becomes zero at finite temperature θ_c and in the P-phase, M_sp is positive in whole temperature range. It was revealed that NdVO₃ and Ca_0.1Nd_0.9VO₃ located in the N-phase and Ca_0.2Nd_0.8VO₃ in the P-phase. This N→P transition by the chemical pressure was discussed by the intra- and inter-sublattice exchange integrals estimated from the molecular field approximation.     

Spectral Hole-Burning of Eu^3＋：Y2SiO5 Crystal at 16 K

By using an Ar^＋ ion laser, a tunable Rh 6G dye laser （linewidth 0.5cm^-1） pumped by the second harmonic of a YAG：Nd laser and a Coherent 899-21 dye laser as light sources and using a monochromator, a phase-locking amplifier and a computer as the data detecting system, we detect the optical properties of Eu^3＋-doped Y2SiO5 crystal. Persistent ,spectral hole burning （PSHB） are observed in the Eu^3＋ ions spectral lines （^5 Do-T Fo transition） in the crystal at the temperature of 16K. For 15mW dye laser burning the crystal for 0.1 s spectral holes with hole width about 80 MHz both at 579.62nm and at 579.82nm are detected and the holes can remain for a long time, more than 10h.     

Temperature Dependence of the Fluorescence Emission Intensity of Eu/TiO2 Nanocrystals

The samples of europium ions doped titanium dioxide （Eu^3＋/TiO2） nanocrystals are synthesized by a modified sol-gel method with hydrothermal treatment. The x-ray diffraction and scanning electron microscopy are used to characterize the sample. The temperature-dependent fluorescence emission effect of Eu^3＋-doped samples is investigated. It is found that under the excitation of 514.5nm light, the emission intensity of Eu^3＋ reaches a maximum value at 450K among various Eu^3＋ dopant concentrations in Eu^3＋ /TiO2 nanocrystals. The variation of the emission intensity may be attributed to the photon-assist absorption and the temperature-quenching effect.     

First-Principles Studies on Electronic Structures and Absorption Spectra of PbWO4 Crystals with Defect [V^2- Pb-V^2＋ o-V^2- Pb]^2-c

Electronic structures and absorption spectra for perfect PbW04 （PWO） crystals and the crystal containing aggregated defect [V^2- Pb-V^2＋ o-V^2- Pb]^2-have been calculated using density functional theory code CASTEP with the lattice structure optimized. The calculated absorption spectra of the PWO crystal containing the aggregated defect [V^2- Pb-V^2＋ o-V^2- Pb]^2-exhibit two absorption bands peaking at 1.90eV （65Onto） and 3.02eV （41Onto）. It is predicted that the 420 and fiSOnm absorption bands are related to the existence of the aggregated defect [V^2- Pb-V^2＋ o-V^2- Pb]^2-in the PWO crystal.     

Vacuum Ultraviolet Excited Photoluminescence Properties of Novel Na3Y9O3（BO3）8：Tb^3＋ Phosphor

The novel vacuum ultraviolet （VUV） excited Na3 Y9O3 （BO3）8：Tb^3＋ （NYOB：Tb^3＋） green phosphor is prepared. Strong VUV photoluminescence and high quenching concentration of Tb^3＋ （20 wt%） are observed in NYOB： Tb^3＋ and the strong emission are correlated with the unique layer-type structure of NYOB. All the characteristic 4 f - 5d transitions of Tb^3＋ and the host absorption band in VUV region are identified in the excitation spectrum. Based on the results, the energy levels scheme of Tb^3＋ in NYOB：Tb^3＋ is first established. This newly developed NYOB：Tb^3＋ phosphor shows excellent optical properties when compared with the commercial Zn2SiO4：Mn^2＋ and would be a potential VUV-excited green phosphor.     

Pressure-Induced Phase Transition of Ruthenium Diboride

Based on the first-principles calculations, we firstly predict that RuB2 undergoes a phase transition from the orthorhombic phase to the hexagonal phase with a volume collapse of 1% when the applied pressure is 15. 7 GPa. The values of calculated elastic moduli indicate that RuB2 and RuN2 are low compressibility materials. Based on the calculated electronic density of states and valence charge density distribution, the bonding nature of RuB2 is examined to obtain a deeper insight into the physical origin of the mechanical properties. The metallieity and high elastic moduli of RuB2 and FuN2 suggest that they axe potential hard conductors.     

Spatiotemporal dynamics of Ca2+ signaling and its physiological roles

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.     

硅酸锶掺Er3+的高压合成及发光特性

 首次采用高压高温方法合成了Sr₂SiO₄:Er³⁺Bi³⁺和SrSiO₃:Er³⁺Bi³⁺发光材料，研究了合成压力、合成温度对发光特性的影响。与常压合成产物相比较，发光谱发生了红移；谱线半宽度显著增大；发光强度和量子发光效率下降。X射线衍射分析得出，SrSiO₃:Er³⁺Bi³⁺发生了结构相变，Sr₂SiO₄:Er³⁺Bi³⁺结构未变但晶格参数发生了变化，且主衍射峰强度发生了反转。分析表明，发光特性的变化是压致晶场、库仑及自旋-轨道相互作用的变化引起的。