Looking inside phytoplasma-infected sieve elements: A combined microscopy approach using Arabidopsis thaliana as a model plant

Phytoplasmas are phloem-inhabiting plant pathogens that affect over one thousand plant species, representing a severe threat to agriculture. The absence of an effective curative strategy and the economic importance of many affected crops make a priority of studying how plants respond to phytoplasma infection. Nevertheless, the study of phytoplasmas has been hindered by the extreme difficulty of culturing them in vitro and by impediments to natural host plant surveys such as low phytoplasma titre, long plant life cycle and poor knowledge of natural host-plant biology. Stating correspondence between macroscopic symptoms of phytoplasma infected Arabidopsis thaliana and those observed in natural host plants, over the last decade some authors have started to use this plant as a model for studying phytoplasma-plant interactions. Nevertheless, the morphological and ultrastructural modifications occurring in A. thaliana tissues following phytoplasma infection have never been described in detail. In this work, we adopted a combined-microscopy approach to verify if A. thaliana can be considered a reliable model for the study of phytoplasma-plant interactions at the microscopical level.The consistent presence of phytoplasma in infected phloem allowed detailed study of the infection process and the relationship established by phytoplasmas with different components of the sieve elements. In infected A. thaliana, phytoplasmas induced strong disturbances of host plant development that were mainly due to phloem disorganization and impairment. Light microscopy showed collapse, necrosis and hyperplasia of phloem cells. TEM observations of sieve elements identified two common plant-responses to phytoplasma infection: phloem protein agglutination and callose deposition.     

量子信令中继器模型及性能仿真

为了解决量子信令远程传输损伤问题,提出了一种量子信令中继器模型. 在该模型中,首先对接收到的信令量子态进行纠缠纯化和纠缠分发,这样就可在收发双方之间建立纠缠信道. 其次,通过纠缠交换,传送所要发送的量子信令,从而完成量子信令的中继. 仿真结果表明,在保真度为0.98、纠缠对成功建立概率为0.98的条件下, 信令中继成功率可以达到97%以上;在纠缠交换概率、纯化概率和纠缠对成功建立概率都为0.98时, 量子信令中继器的吞吐量可达到183kbps,以上各项指标能够有效满足量子通信对信令中继的要求. 关键词： 量子通信 量子信令 纠缠纯化 纠缠分发     

Oscillator model of qubits and its entanglement properties

The two-mode symmetric oscillator is used to construct the qubit model as the superposition of the first excited degenerate level states of the oscillator. The entanglement properties of the oscillator states are studied using the known criterion of separability. Application to the quantum computing model based on light modes propagating in optical waveguides is briefly discussed.     

A line intensity transfer model for the rotational raman spectrum of ethylene

A new model for the spectrum of ethylene, utilizing the line-mixing concept for overlapping lines, is presented here. The Lorentzian line shape is assigned to all the lines, with the single transitions having the usual directly pressure-dependent widths, and with overlapping lines considered as a single composite feature having an inversely pressure-dependent width. This model is compared with two sets of data: interferometric data over a range of pressures, and an ad hoc model that matches experimental line spectrum data at a single pressure. Inversely pressuredependent widths are obtained for the two comparisons, and the discrepancy between the results is explained.     

A basic mathematical model of the immune response

Interaction of the immune system with a target population of, e.g., bacteria, viruses, antigens, or tumor cells must be considered as a dynamic process. We describe this process by a system of two ordinary differential equations. Although the model is strongly idealized it demonstrates how the combination of a few proposed nonlinear interaction rules between the immune system and its targets are able to generate a considerable variety of different kinds of immune responses, many of which are observed both experimentally and clinically. In particular, solutions of the model equations correspond to states described by immunologists as "virgin state," "immune state" and "state of tolerance." The model successfully replicates the so-called primary and secondary response. Moreover, it predicts the existence of a threshold level for the amount of pathogen germs or of transplanted tumor cells below which the host is able to eliminate the infectious organism or to reject the tumor graft. We also find a long time coexistence of targets and immune competent cells including damped and undamped oscillations of both. Plausibly the model explains that if the number of transformed cells or pathogens exeeds definable values (poor antigenicity, high reproduction rate) the immune system fails to keep the disease under control. On the other hand, the model predicts apparently paradoxical situations including an increased chance of target survival despite enhanced immune activity or therapeutically achieved target reduction. A further obviously paradoxical behavior consists of a positive effect for the patient up to a complete cure by adding an additional target challenge where the benefit of the additional targets depends strongly on the time point and on their amount. Under periodically pulsed stimulation the model may show a chaotic time behavior of both target growth and immune response. (c) 1995 American Institute of Physics.     

Resonant response and its scaling properties in chaotic systems perturbed by noise

Summary The double-well Duffing oscillator is investigated experimentally when a small noise is present in the system. It results that the noise influences the mean lifetime of the transient chaos showing some similarities with the phenomenon of the stochastic resonance. This behaviour is in agreement with a simple model based on the one-dimensional logistic map. Paper presented at the International Workshop “Fluctuations in Physics and Biology: Stochastic Resonance, Signal Processing and Related Phenomena”, Elba, 5–10 June 1994.     

A harmonious unifying hybrid preferential model and its universal properties for complex dynamical networks

To describe the real world which is a harmonious unification world with both de- terminism and randomness, we propose a harmonious unifying hybrid preferential model (HUHPM) of a certain class of complex dynamical networks. HUHPM is gov- erned only by the total hybrid ratio d/r according to the practical need. As some typical examples, the concepts and methods of the HUHPM are applied to the un-weighted BA model proposed by Barabási et al., the weighted BBV model pro- posed by Barat et al. and the weighted TDE model proposed by Wang et al. to get the so-called HUHPM-BA network, HUHPM-BBV network and HUHPM-TDE network. These HUHPM networks are investigated both analytically and numerically. It is found that the HUHPM reveals several universal properties, which more approach to the real-world networks for both un-weighted and weighted networks and have potential for applications.     

Distribution and speciation of lead in model plant Arabidopsis thaliana by synchrotron radiation X‐ray fluorescence and absorption near edge structure spectrometry

To obtain reliable in situ information on the distribution and speciation of Pb in plants with low Pb content, special attention needs to be paid to the synchrotron radiation based micro‐X‐ray fluorescence and micro‐X‐ray absorption near edge structure (μ‐XANES) spectrometry to avoid specious results in the chosen XRF region of interest and speciation linear combination fitting. First, an Arabidopsis thaliana shoot cultured in a Pb solution is analyzed to obtain two‐dimensional Pb distribution graphs, where an overlap of Pb, As, Se, and Br lines in synchrotron radiation based micro‐X‐ray fluorescence spectra is found. To avoid this overlap, (1)As K‐L₃ and Pb L₃‐M₅, (2)As K‐M₃, (3)Pb L₂‐M₄, (4)Se K‐L₃, and (5)Br K‐M₃ lines should be chosen in the region of interest. The Pb content in the seed coat, root, and stem are 48.2, 17.3, and 5.8 times higher, respectively, than in the leaf, while the Pb content in the seed coat, root, stem, and leaf increased 3458, 1241, 420, and 72 times, respectively, compared with the A. thaliana sample without a Pb solution soak. Second, Pb speciation of the same shoot is analyzed using μ‐XANES. It is important to define a combination fitting range because different possible Pb combinations can emerge using different ranges. Different speciations were found in the root[Pb(Ac)₂ and PbSO₄], stem[Pb(Ac)₂ and Pb₃(PO₄)₂], leaf[Pb(OH)₂ and Pb₅Cl(PO₄)₃], and seed coat[Pb₃(PO₄)₂, Pb(OH)₂, and PbCO₃] between the fitting range of E₀ ? 20eV and E₀ + 70eV. A more complete Pb XANES database with more references, especially organic Pb compounds, is needed. Copyright © 2013 John Wiley & Sons, Ltd.     

离子束辐照拟南芥生物学效应及其分子机理研究进展

综述了离子束辐照拟南芥种子生物学效应、 生长发育变化、 向重力性等研究的最新进展。 阐释了离子束辐照拟南芥染色体DNA碱基变化、 DNA断裂或损伤、 染色体重组、 突变遗传性等分子机理。 探讨了离子束介导外源基因转化拟南芥的有效性和机理。 同时展望了辐照拟南芥分子机理研究中的辐射原初效应传递、 信号转导等其他机理研究及重离子辐射生物学效应的应用前景。 Newly research progresses were summarized in effect of ion beams on seed surface, biological effect, growth, development, gravitropism and so on. Furthermore, mutation molecular mechanism of Arabidopsis thaliana was discussed, for example, alteration of DNA bases, DNA damage, chromosomal recombination, characteristics of mutant transmissibility, etc. Meanwhile, the achievements of transferring extraneous gene to Arabidopsis thaliana by ion beams were reviewed in the paper. At last, the future prospective are also discussed here in mutation molecular mechanism and the potential application of biological effect of heavy ion beams.     

A model for the local mode relaxation process in poly(ethylene terephthalate)

Although the glass transition relaxation process is regarded as involving gross chain motions, the local mode [l] process is generally viewed a s involving independent motions of groups within a repeat unit [2,3]. The purpose of this note is to present an alternative model-in the case of poly(ethy1ene terephthalate), experimental evidence indicates that the local mode process involves the cooperative motions of several repeat units.     

Tunability response in exponentially graded ferroelectrics: A TIM model approach

Relative dielectric function response associate to a non-homogeneous layered ferroelectric system is calculated in the framework of the Mean Field Approximation (MFA) for the Transverse Ising Model (TIM). Analytical self-consistent expressions for the average polarization, dielectric susceptibility, and tunability percentage are outlined and solved for different configurations and sizes. It is found that exponentially graded ferroelectrics magnify the tunability response for stronger interlayer coupling and it reaches its saturation value for smaller intensities of the applied electric field.     

拟南芥AtGrp7RRM结构域的纯化及其结构与结合的初步分析(英文)

富含甘氨酸的RNA结合蛋白AtGrp7是拟南芥（Arabidopsis thaliana）调节生物钟负反馈回路的组分.在使用常规方法纯化AtGrp7 RRM结构域的初始试验中，观察到烟草蚀纹病毒（TEV）酶切后AtGrp7 RNA识别基序（RRM）结构域的紫外吸收峰为蛋白和杂质的混合信号峰.为解决常规纯化中的杂质问题，对AtGrp7_1-90应用了变性-复性两步纯化方法.AtGrp7 RRM结构域的¹H-¹⁵N HSQC指纹谱和CS-Rosetta模型结构表明快速稀释重折叠后其结构完全恢复.等温滴定量热法（ITC）和核磁共振（NMR）滴定实验进一步证实，重折叠后AtGrp7_1-90 RRM结构域具有正确结合RNA/DNA的功能.     

A history-dependent stochastic predator-prey model: Chaos and its elimination

A non-Markovian stochastic predator-prey model is introduced in which the prey are immobile plants and predators are diffusing herbivors. The model is studied by both mean-field approximation (MFA) and computer simulations. The MFA results a series of bifurcations in the phase space of mean predator and prey densities, leading to a chaotic phase. Because of emerging correlations between the two species distributions, the interaction rate alters and if it is chosen to be the value which is obtained from the simulation, then the chaotic phase disappears. Received 12 July 1999     

A model of ethylene and acetylene adsorption on the (111) surfaces of platinum and nickel

Despite the application of a variety of surface sensitive techniques to the adsorption of simple hydrocarbons on well characterized metallic surfaces, no consistent picture has appeared. We review briefly the published spectroscopic results of ultraviolet photoelectron spectroscopy (UPS) and electron energy loss spectroscopy (EELS) which probe, respectively, the electronic and vibrational structure of the surface-molecular complex, and we consider appropriate free molecular analogues, not only in their ground state but also in their first excited states. A simplified approach to determine the chemisorption geometry from UPS level shifts and EELS is presented. The technique allows an isolation of distortion induced shifts from the total relaxation shift, and we find that the true relaxation shift is rather constant, approximately 2.1 eV for the cases considered. These shifts can then be used to estimate the distance of the molecule to the surface. We concentrate primarily on four systems, C₂H₂ and C₂H₄ on Ni(111) and Pt(111), adsorbed at low temperature (below the onset of dissociation). Depending on the metal, the hydrocarbon can adsorb in a di-σ arrangement or with a distortion resembling the lowest energy configuration of the first excited state of the free molecule. We also consider briefly C₂H₄ on Ag and Cu in which no distortion occurs. The distortions that resemble the first excited states might occur as a consequence of donation of bonding (backbonding) electrons from (to) the normally filled π (empty π¹) to (from) the empty (filled) d-band states of the metal. The net effect on the hydrocarbon to partially empty the π level and fill the π¹ level, is analogous to a low excitation of the free molecule, π → π¹. For C₂H₄ (planar in the ground state), the lowest excitation is the triplet T-state (3–4 eV) of minimal energy for a 90° twisted configuration with a lengthened C-C bond. Acetylene is a linear molecule in the ground state, but cis- or trans-bent for the triplet excitations, ~a (5.2 eV) or ~b (6.0 eV), respectively. Chemisorbed geometries derived from these configurations seem possible for C₂H₄ on Ni(111) and C₂H₂ on Pt(111), while interchanging the adsorbates and substrates gives di-σ bonding, (sp³ hybridization), as proposed previously in the literature. For C₂H₄ on Ni(111), two of the hydrogens are twisted into the surface which leads to a softening of the CH vibrational frequency. For the four systems considered, the data are consistent with the C-C bond essentially parallel to the surface, but tilted orientations are not ruled out. While the models are clearly oversimplified, they suggest an interesting point of departure for likely chemisorption geometries. Also, some intriguing correspondences to the (presumed) location of the normally empty π¹ level and the d-band are noted.     

Auditory analysis of the periodicity of sound and its envelope: A mathematical model

A mathematical model of the auditory analysis of periodicity of sound and its envelope is proposed. The model consists of a sequence of mathematical transformations that describe the signal processing stages. The following parameters and properties of the auditory system are taken into account: the crude analysis of the input acoustic signal accurate to the width of the aural critical band; the frequency dependence of the width of the aural critical band; the spectrum of the input signal analysis by a set of 3500 filters closely spaced in frequency; the absolute audibility thresholds at a given frequency; the time-domain analysis of both the output signals of each filter and the envelope profile with the help of the periodicity function; the pulsed activity of auditory neurons; the ability of the auditory system to memorize the spectral-time images of the signal and its individual parameters; the ability of the auditory system to form the perception of the loudness of sound, to memorize and compare the loudness of sound at different time moments, and to conclude which of them is higher or lower or whether they are equal accurate to a certain threshold; the dependence of the critical modulation bandwidth on the modulation frequency; and the dependence of the audibility thresholds of amplitude modulation on the modulation frequency. By an example of processing amplitude-modulated signals with various carrier-to-envelope frequency ratios, the model is shown to give a satisfactory explanation of their pitch and auditory estimate of the envelope period.     

Dynamical dipole and quadrupole response properties of small metallic particles: Random phase approximation and the modified spherical infinite barrier model

The self-consistent electrostatic response of small metallic spherical particles is studied in the random phase approximation and using the electronic wave functions in the infinite barrier model, with the size of the effective positive background adjusted to minimize the electrostatic energy of the system. The multipole susceptibilities and the numerical results are presented for the dipole (L = 1) and quadrupole (L = 2) cases. The spectra, showing both surface and several bulk plasmon peaks and the electron-hole excitations are discussed and analyzed in terms of their associated density fluctuations. The results are compared with the recent calculation of the same physical properties, based on the self-consistent field Kohn-Sham method.     

Dry friction in the Frenkel-Kontorova-Tomlinson model: dynamical properties

Wearless friction is investigated in a simple mechanical model called Frenkel-Kontorova-Tomlinson model. We have introduced this model in [Phys. Rev. B, 53, 7539 (1996)] where the static friction has already been considered. Here the model is treated for constant sliding speed. The motion of the internal degrees of freedom is regular for small sliding velocities or weak interaction between the sliding surfaces. The regular motion for large velocities is strongly determined by normal and superharmonic resonance of phonons excited by the so-called “washboard wave”. The kinetic friction has maxima near these resonances. For increasing interaction strength the regular motion becomes unstable due to parametric resonance leading to quasistatic and chaotic motion. For sliding velocities beyond first-order parametric resonance bistability occurs between the strongly chaotic motion (fluid sliding state), where friction is large and a regular motion (solid sliding state), where friction is weak. The fluid sliding state is mainly determined by the density of decay channels of m washboard waves into n phonons. This density describes qualitatively the effectiveness of the energy transfer from the uniform sliding motion into the microscopic, irregular motion of the degrees of freedom at the sliding interface. For a narrow interval of the sliding velocities we also found enhanced friction due to coherent motion. In the regime of coherent motion nondestructive interactions of dark envelope solitons occur.     

Electrospun nanofibers of poly(ethylene oxide)/teraamino-phthalocyanine copper(II) hybrids and its photoluminescence properties

Poly(ethylene oxide)/teraamino-phthalocyanine copper (II) (PEO/(NH₂)₄PcCu) hybrid nanofibers with a diameter of 200-300 nm were prepared by electrospinning technique. The hybrid nanofibers membrane was characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), ultraviolet-visible (UV-vis), and photoluminescence (PL), respectively. The results indicated that (NH₂)₄PcCu molecule was successfully embedded in the one-dimensional hybrid nanofibers via chemical interaction between PEO and (NH₂)₄PcCu. The PL results showed that the PEO/(NH₂)₄PcCu hybrid nanofibers had an intense emission at about 450 nm. A possible PL mechanism was proposed accordingly.