球面大气中行星波的波作用守恒方程及用波作用通量所表征的定常行星波传播波导

本文指出在球面大气行星波能量的传播中必须考虑非地转风分量对位涡度南北方向输送的作用,从而证明了球面大气中行星波波作用守恒,求得在球面大气中的波作用通量,即 Eliassen-Palm通量.文中利用 WKBJ方法证明了在球面大气中行星波波作用通量矢量是平行于行星波局地群速度在子午面上的投影. 本文还利用多层数值模式,计算了理想强迫所产生的定常行星波Eliassen-Palm通量矢量分布,证实了冬季北半球定常行星波在球面大气传播中存在着两支波导,即除了极地波导以外,还存在一支从中、高纬对流层的下层向低纬度对流层上层传播的波导。     

γ射线辐射医用级超高分子量聚乙烯自由基的演变

采用γ射线对医用级超高分子量聚乙烯(UHMWPE)进行辐照处理, 利用电子自旋共振波谱仪(ESR)研究了辐照诱导自由基的种类及其在氩气和不同氧分压下的衰减行为. 在氩气中, 辐射诱导UHMWPE主要产生烷基自由基和烯丙基自由基, 总的辐射化学产额约为0.48/100 eV. 室温下烷基自由基的稳定性差, 其寿命仅有 1 d左右. 在含氧气氛中, 自由基主要通过氧化反应而衰减, 其衰减速率随氧分压的增加而增加, 半衰期则由1×10⁵ Pa氩气中的224.0 h降至5×10⁵ Pa O₂气中的1.8 h. 根据此结果推算, 室温下陷落在晶区的自由基迁移至微晶表面的速率非常快, 仅需小时量级.     

不同植物叶绿体中电子转移和能量传递超快过程

采用相同的分离技术,从三七、水葫芦和菠菜植物叶子中提取叶绿体.利用吸收光谱和低温荧光光谱及皮秒荧光单光子计数技术对这3种叶绿体的光谱性质和光系统Ⅱ荧光寿命进行了研究.这3种叶绿体吸收光谱相似,暗示着不同的植物都能高效吸收不同波长的光子.采用三指数动力学模型对测定的光系统Ⅱ荧光衰减曲线拟合,水葫芦植物叶绿体光系统Ⅱ荧光衰减寿命分别是:138,521和1494ps;菠菜体系叶绿体荧光寿命分别是:197,465和1459 ps;三七叶绿体体系荧光寿命分别是:30,274和805ps;并且归属了荧光组分,慢速度荧光衰减由叶绿素堆积造成,中等速度荧光衰减源于PSⅡ反应中心重新结合电荷组分,快速度荧光衰减归属于PSⅡ反应中心组分.定义并且基于20ps模型计算了三七、水葫芦和菠菜叶绿体光系统Ⅱ反应中心激发能转能效率,分别是60%,87%和91%.实验结果支持20 ps时间常数模型.三七叶绿体光系统Ⅱ反应中心低转能效率,2个光系统之间激发能分配平衡状态差的结果,以及它的光系统Ⅰ激发能红移的现象都与该植物生长速度慢的现象相吻合,显示植物生长速度特性可体现在光合作用原初过程中,表明植物生长速度与它的荧光性质及荧光寿命相关性,生长慢的植物对吸收的光子能量利用效率较低,而生长快的植物,转能效率则较高.     

强迫基流上Rossby波包的结构和演变

本文用WKB方法研究了正压及斜压强迫基流上Rossby波包的演变过程(发展、传播和结构的改变),得出:(1)增强波波包的平均空间尺度随时间变大,但衰减波波包的平均空间尺度则随时间变小;(2)正压增强型扰动在水平面上向急流区传播,但衰减者则向离开急流区的方向传播;(3)斜压增强型扰动在垂直方向上向急流轴传播,但衰减者则反之;(4)扰动的发展特性依赖于其结构及其相对于基流的位置;(5)强迫形成的常定波列具有典型的斜压增强但正压衰减型扰动的结构;能量向对流层顶传播;且若扰源位于急流轴附近(即中纬度)地带,则在水平面上扰动由急流区向外传播,且分裂成南北两支。文中还给出若干大气中实测到的常定流场的图,和一个高空天气系统演变全过程及其预报图。理论结果和实际情况很相一致。     

非绝热聚合波的数学模拟

对非绝热波聚合体系进行了数学模拟, 将反应器尺寸与聚合波关联, 建立了非绝热条件下蔓延聚合波波速和最大波温的数学模型; 利用所建模型计算不同引发剂浓度、 不同环境温度、 不同试管直径下淀粉接枝聚合波的波速和波温, 并与实验测定值进行了比较. 结果表明, 非绝热聚合波的数学模型对无相变体系的拟合结果令人满意, 对聚合波的发生条件及反应器尺寸的影响有很好的预见性; 另一方面, 对于存在相变及与环境有质量交换的波聚合体系, 所建模型的预测性受到了限制.     

关于冬季北半球定常行星波传播另一波导的研究

本文计算了在等温大气情况下定常行星波的折射指数平方,表明了定常行星波在垂直及侧向传播中除了极地波导外,还存在着一个从中纬度对流层下层指向低纬度对流层顶附近的一支波导。本文应用一个包括Rayleigh曲摩擦、Newton冷却及水平涡动热量扩散,34层定常的准地转球坐标模式计算了北半球理想地形(或定常热源)强迫所产生的定常行星波垂直及侧向传播,证明了冬季北半球定常行星波传播中存在着这一波导。利用上述模式计算了冬季北半球实际地形及定常热源强迫所产生的定常行星波的振幅与位相的垂直分布及其在等压面上定常扰动系统的分布。说明了这一波导的存在使得中、高纬度地形与定常热源强迫所产生的定常行星波向低纬度传播,这是冬季副热带定常扰动系统形成的主要原因之一。     

浅析SOFC性能衰减的材料因素

从SOFC工作状态出发,分析了材料在氧化还原气氛中的固-气界面化学稳定性、材料间固-固界面的扩散与相互反应的特性以及外部化学物质的介入对三相界面反应等方面因素对电池性能可能产生的影响.故我国应注重探究实用的SOFC电池性能衰减材料因素.     

超痕量H2O2对MnSO4-KBrO3-乙酰丙酮化学振荡体系的扰动

化学振荡波和生物体内的生物振荡及生物形态现象的相似性促使人们认识到生命现象和非生命现象之间遵循着某些相同的规律, 因而化学振荡反应非线性动力学一直是物理化学研究的热点[1, 2]. 近年来它在分析化学中的应用使其研究扩展到了一个新的领域, 但仍停留在10-7 mol/L的水平上[3]. 显然, 以这个量去研究包含众多基元反应和反应中间体的振荡反应, 得到的是数目庞大的反应物种群体行为, 而这种行为并不足以说明生命现象的猝发病变、代谢功能衰竭及运动寿命终止的原因.     

用光学方法研究玻璃微珠电流变液颗粒间的相互作用

运用一套适合研究颗粒间相互作用的双光镊系统,通过对颗粒聚集时间的测量,得出颗粒聚集时间和电场的平方成反比.这是第一次用电流变液颗粒在动态情况下直接验证电偶极子对间的相互作用.发展了一套使用高速CCD摄像机进行扩散波谱(DWS)测量的方法,首次实时测量具有颗粒结构的非各态历经体系的自相关函数,以研究电流变液机理,得到了玻璃微珠电流变液的结构响应时间和力的响应时间;测量了不同电场下体系相关函数的特征衰减时间随时间的变化.在不同电场下测量扩散系数可以反映出相互作用力与电场的平方成正比.     

有机太阳能电池性能衰减机理研究进展

近年来随着非富勒烯Y系列明星分子受体的出现, 单结有机太阳能电池的光电转换效率已经突破19%, 但是器件在运行条件下缺乏良好的稳定性, 严重制约了其商业化发展. 因此越来越多的研究聚焦于造成有机太阳能电池性能衰减的原因以及如何提高有机太阳能电池的稳定性. 由于有机太阳能电池复杂的器件结构、不尽相同的活性层材料以及在稳定性研究中条件的差异, 造成了对有机太阳能电池器件衰减研究的困难. 为了更全面地了解有机太阳能电池的衰减过程, 对近些年有机太阳能电池器件衰减过程的研究成果进行综述, 总结了由于给受体材料化学分解、活性层形貌变化、传输层和电极腐蚀以及界面反应等原因造成的器件性能衰减, 并介绍了近些年关于提高器件稳定性的一些策略, 最后对有机太阳能电池的未来发展进行了展望.     

The Transition from pH Waves to Iodine Waves in the Iodate/Sulfite/Thiosulfate Reaction–Diffusion System

Nonlinear spatial temporal behavior of the iodate/thiosulfate/sulfite reaction is investigated both in a stirred and spatially extended media. In accord with the temporal dynamics in the homogeneous media, both propagating fronts and target patterns are achieved in the spatially extended medium. On increasing the iodate concentration the system evolves from exhibiting propagating fronts to circular waves and then shows target patterns and finally the iodine waves. Influences of concentrations of sulfite, thiosulfate and acid on the reaction kinetics and pattern formation are also investigated systematically, and transitions from pH waves to iodine waves can be achieved via adjusting the concentration of the three species. The propagation velocities of pH and iodine waves are understood with the quadratic and cubic autocatalysis of proton and iodide respectively.     

Wave patterns driven by chemomechanical instabilities in responsive gels

The first experimental evidence of a chemomechanical mechanism leading to morphogenetic instabilities is demonstrated experimentally. The system consists of a pH-responsive gel that swells at high pH and shrinks at low pH, and a bistable reaction system exhibiting an acid steady state (pH approximately 2) and an alkaline steady state (pH approximately 10). Within the gel, the steady state selection depends on the gel size. We show that in a constant and uniform nonequilibrium chemical environment, the responsive gel undergoes large amplitude dynamical deformations under the form of travelling contraction waves and complex spatio-temporal volume oscillations. These deformations are coupled to concentration patterns of protons. We present different sequences of dynamical behaviors observed under various controlled chemical conditions. A simple heuristic model is proposed to account for the observations. These experiments open a new route for pattern formation driven by chemical energy, in soft matter systems.     

Pattern formation and self-organization in a simple precipitation system

Various types of pattern formation and self-organization phenomena can be observed in biological, chemical, and geochemical systems due to the interaction of reaction with diffusion. The appearance of static precipitation patterns was reported first by Liesegang in 1896. Traveling waves and dynamically changing patterns can also exist in reaction-diffusion systems: the Belousov-Zhabotinsky reaction provides a classical example for these phenomena. Until now, no experimental evidence had been found for the presence of such dynamical patterns in precipitation systems. Pattern formation phenomena, as a result of precipitation front coupling with traveling waves, are investigated in a new simple reaction-diffusion system that is based on the precipitation and complex formation of aluminum hydroxide. A unique kind of self-organization, the spontaneous appearance of traveling waves, and spiral formation inside a precipitation front is reported. The newly designed system is a simple one (we need just two inorganic reactants, and the experimental setup is simple), in which dynamically changing pattern formation can be observed. This work could show a new perspective in precipitation pattern formation and geochemical self-organization.     

Spatial bistability and waves in a reaction with acid autocatalysis

The phenomenon of spatial bistability has recently been proposed for a comprehensive understanding of a number of chemical patterns observed in open spatial reactors consisting of thin films of gel diffusively fed from one side. We study experimentally and numerically this phenomenon in the tetrathionate-chlorite reaction characterized by an acid superautocatalysis. We focus on the similarities and differences with previous studies on the chlorine dioxide-iodide reaction. In addition, we show that this reaction, which is only bistable in a continuous stirred tank reactor, can exhibit oscillatory and traveling waves when diffusion comes into play. Our computations suggest that the nonstationary behaviour originates from differential diffusive transport.     

Dissipative structures in systems of diffusion-bonded chemical nano- and micro oscillators

In spatially extended classical Belousov-Zhabotinsky (BZ) reaction, trigger spiral or concentric waves usually occur. If the BZ reaction is dispersed into nanodroplets of water-in-oil emulsion, new patterns are observed such as standing waves, anti-spirals, oscillons, dash-waves, jumping waves, Turing patterns, and other. If the size of water droplets is increased up to tens of micrometers, coupled micro-oscillators produce new stationary and oscillatory discrete dissipative patterns. In the review, comparative analysis of these patterns is done and a possibility of creating a chemical computer on the basis of dissipative patterns is discussed.     

Dynamical correlations and long-time tails in chemical reactions. A molecular dynamics study

A simple hard-sphere and disk model of a chemical reaction of the type A + B ⇌ C + D is studied by molecular dynamics (MD). Ensemble and time averages are carried out so that the MD calculation simulates chemical relaxation in a homogeneous system which is in equilibrium with respect to the mechanical degrees of freedom. For large times, the decay of the concentrations of the different species is not given by the expected exponential law but shows a long-time tail instead. A simple explanation of the effect is given in terms of recollision events (dynamical correlations) between pairs of particles. It is argued that non-exponential decay of the kind observed might be a general phenomenon in chemical reactions.     

Control and coupling of spiral waves in excitable media

We report the complex dynamics of spiral waves observed in the ferroin-catalyzed BZ reaction. The reaction is run in an open unstirred reactor (CFUR) with the catalyst immobilized on a polysulfone membrane. The catalyst-loaded membrane is placed between two well stirred compartments which are fed with solutions of sulfuric acid/malonic acid/bromide and sulfuric acid/bromate, respectively. An electrical field perpendicular to the membrane can be applied via Pt-ring electrodes or, alternatively, via transparent electrodes made of ITO-coated glass. In the field-free case relatively simple target and spiral patterns are observed in the membrane. If an alternating electrical field is applied the spiral core drifts through the membrane. The actual trajectory of the spiral tip depends on the amplitude and frequency of the applied electrical field. If the perturbation parameters are chosen properly the wave fronts break up and new spiral cores emerge under the influence of the alternating field. Complex spatio-temporal patterns may be induced which are reminiscent of "spiral-chaos". After switching off the perturbation the system returns to its previous, "simple" behaviour. Our experimental observations are confirmed by model calculations based on the Barkley model of spiral waves. The technique of using modulated excitability to control the dynamics of spiral waves is further extended to the coupling of two spirals in two CFURs. We present numerical simulations based on two identical excitable reaction-diffusion (RD) systems which are mutually coupled. The coupling is based on the observation of an arbitrarily chosen point inside each of the RD systems: If a chemical wave passes the point of optical observation in system 1 an electric field is applied to system 2 and vice versa. Thus, a local observation made in one system is transformed in a global perturbation of the second CFUR. We report the observation of CFUR states where the two spiral waves are spatially and temporally coupled to each other.     

The effects of coupling on chemical wave propagation in quadratic and cubic autocatalysis with decay

The initiation of reaction-diffusion travelling waves in two regions coupled together by the linear diffusive interchange of an autocatalytic species is considered. In one region a purely autocatalytic production process (either quadratic or cubic) is assumed, while in the other region there are both autocatalytic and decay processes (either linear or quadratic). A perturbation analysis based on small initial inputs of the autocatalyst is presented. This indicates conditions under which travelling wave formation is possible as well as identifying two special cases which need further consideration, namely cubic autocatalysis in both regions with quadratic or linear decay in one region. The former case gives rise to a zero eigenvalue and the perturbation method has to be extended to include the higher order terms to resolve this case. The latter case requires a threshold on the initial input of autocatalyst and further information about this threshold is gained from a solution for strong coupling.     

Reaction fronts in an ionic autocatalytic system with an applied electric field

The effects of applying an electric field to an ionic autocatalytic reaction with a cubic rate law are discussed. The constant field strength approximation is made and the resulting equations for the model examined by first considering the corresponding travelling wave equations. These show ranges of field strength over which travelling waves do not exist, these ranges being dependent on whether D< 1 or D< 1, where D is the ratio of diffusion coefficients of autocatalyst and substrate. Numerical simulations of the full system are obtained and these show that, when travelling waves exist, these are formed as the long time behaviour of the system. When travelling waves do not exist, complete electrophoretic separation of the reacting ionic species results, forming separate fronts in autocatalyst and substrate, their direction of propagation depending on D. Comparisons with a related problem with a quadratic rate law are made and the implications for experiments based on the iodate–arsenous acid reaction assessed.     

EXCITON TRANSFER OUT OF OPEN PHOTOSYSTEM II REACTION CENTERS

Abstract A simple photochemical model of photosystem II consisting of antenna chlorophyll and a reaction center was used to examine the phenomenon of exciton detrapping, i.e. the transfer of excitation energy from open reaction centers back to the antenna. η, the ratio of the probability of detrapping when the reaction centers are all open, Ψ_t(o) to the probability when the centers are closed, Ψ_t(x) was used as a variable parameter to examine the various pathways of energy dissipation in a system in which P, the yield of photochemistry, and R, the ratio of the maximum to the minimum yields of fluorescence, were assumed to be known (e.g. R= 4.0 and P= 0.90). It is shown that η must fall within a range of values between 0 and R (1 –P) and that, for given values of R and P, Ψ_t(o) and the ratio of the rate constant for photochemistry at the reaction center, k_p, to the rate constant for energy transfer back to the antenna, k_t, can be determined for any assumed value of η. Even though detrapping occurs at open reaction centers, it is the magnitude of the yield of nonradiative decay at closed reaction centers, Ψ_a(x) which sets the upper limit on η. Equations for the overall yields of fluorescence and nonradiative decay in the antenna chlorophyll and of nonradiative decay at the reaction center chlorophyll, under conditions of both open and closed reaction centers, were derived in conventional probability terms and in terms of R, P and η. As η increases within its range of permissible values, energy dissipation in the antenna decreases and nonradiative decay at the reaction center increases. The determination of a specific value of η or of the ratio k_pk_t would require additional information such as the value of the maximum yield of fluorescence and the ratio of the rate constants for fluorescence and nonradiative decay in the antenna chlorophyll. The characteristics of a system in which there is no nonradiative decay in the reaction center (i.e. k_d= 0), in which case R (1 –P) = 1.0, were also examined. In this case the yield of detrapping has no influence on energy dissipation in the system. Finally, the question of heterogeneity in PSII was considered. It is suggested that Ψ_d(x) may be greater in PSII_β than in PSII_α so that the probability of detrapping could be greater in the PSII_α fraction.