Hierarchical condensation near phase equilibrium

A novel mechanism of new phase formation is studied both experimentally and theoretically in the example of quasi-equilibrium stationary condensation in an ion–plasma sputterer. Copper condensates are obtained to demonstrate that a specific network structure is formed as a result of self-assembly in the course of deposition. The fractal pattern related is inherent in the phenomena of diffusion limited aggregation. Condensate nuclei are shown to form statistical ensemble of hierarchically subordinated objects distributed in ultrametric space. The Langevin equation and the Fokker–Planck equation related are found to describe stationary distribution of thermodynamic potential variations at condensation. Time dependence of the formation probability of branching structures is found to clarify the experimental situation.     

Structural ordering of ω-ferrocenylalkanethiol monolayers on Au(1 1 1) studied by scanning tunneling microscopy

The self-assembly of ω-ferrocenylalkanethiols (FcCnSH) with different alkyl-spacer lengths on Au(1 1 1) substrates has been studied by scanning tunneling microscopy (STM). Upon deposition at room temperature FcCnSH molecules tend to form multilayers, while by thermal treatment monolayer formation, a rearrangement of the molecules and the formation of ordered domains is achieved. The surface structure of the resulting full coverage self-assembled monolayers is resolved with molecular resolution by STM. The ordered monolayer structure of ω-ferrocenylpropanethiol is discussed in comparison with its bulk crystal structure, derived from single crystal X-ray analysis. Based on these results a monolayer structure of ω-ferrocenylalkanethiols with longer alkyl chains closely related to the bulk crystal structure of the shorter alkyl-spacer derivates is suggested. Our results provide detailed insight into the self-assembly of FcCnSH on gold substrates.     

Biosynthesis and magnetic properties of mesoporous Fe3O4 composites

Magnetic Fe₃O₄ materials with mesoporous structure are synthesized by co-precipitation method using yeast cells as a template. The X-ray diffraction (XRD) pattern indicates that the as-synthesized mesoporous hybrid Fe₃O₄ is well crystallized. The Barrett-Joyner-Halenda (BJH) models reveal the existence of mesostructure in the dried sample which has a specific surface area of 96.31 m²/g and a pore size distribution of 8-14 nm. Transmission electron microscopy (TEM) measurements confirm the wormhole-like structure of the resulting samples. The composition and chemical bonds of the Fe₃O₄/cells composites are studied by Fourier transform infrared (FT-IR) spectroscopy. Preliminary magnetic properties of the mesoporous hybrid Fe₃O₄ are characterized by a vibrating sample magnetometer (VSM). The magnetic Fe₃O₄/cells composites with mesoporous structure have potential applications in biomedical areas, such as drug delivery.     

PN结电容与正向直流偏压的关系

半导体PN结具有电容的性质．在正向直流偏压下,理论计算表明,PN结扩散电容的对数与正向偏压成正比．实验发现,当正向偏压小于30mV时,这种线性关系是成立的;当正向偏压大于30mV时,会偏离这种线性关系．由于PN结还具有电阻特性,对交流信号的相位有影响．随着正向偏压增大,交流信号的相位变化出现一极值．如果将PN结等效为一个电容和一个电阻并联,就可以定性解释这种变化关系．     

Synthesis and characterization of multifunctional silica core-shell nanocomposites with magnetic and fluorescent functionalities

Multifunctional core-shell nanocomposites with a magnetic core and a silica shell doped with lanthanide chelate have been prepared by a simple method. First, citric acid-modified magnetite nanoparticles were synthesized by a chemical coprecipitation method. Then the magnetite nanoparticles were coated with silica shells doped with terbium (Tb³⁺) complex by a modified Stöber method based on hydrolyzing and condensation of tetraethyl orthosilicate (TEOS) and a silane precursor. These multifunctional nanocomposites are potentially useful in a variety of biological areas such as bio-imaging, bio-labeling and bioassays because they can be simultaneously manipulated with an external magnetic field and exhibit unique phosphorescence properties.     

Soot studies of laminar diffusion flames with recirculation zones

This paper describes the unusual sooting structure of three flames established by the laminar recirculation zones of a centerbody burner. The vertically mounted burner consists of an annular air jet and a central fuel jet separated by a bluff-body. The three ethylene fueled flames are identified as: fully sooting, donut-shape, and ring-shape sooting flames. Different shapes of the soot structures are obtained by varying the N₂ dilution in the fuel and air jets while maintaining a constant air and fuel velocity of 1.2 m/s. All three flames have the unusual characteristic that the soot, entrained into the recirculation zone, follows discrete spiral trajectories that terminate at the center of the vortex. The questions are what cause: (1) the unusual sooting structures and (2) the spiral trajectories of the soot? Flame photographs, laser sheet visualizations, and calculations with a 2D CFD-based code (UNICORN) are used to answer these questions. The different sooting structures are related to the spiral transport of the soot, the spatial location of the stoichiometric flame surface with respect to the vortex center, and the burnout of the soot particles. Computations indicate that the spiral trajectories of the soot particles are due to thermophoresis.     

Noise effects in two different biological systems

We investigate the role of the colored noise in two biological systems: (i) adults of Nezara viridula (L.) (Heteroptera: Pentatomidae), and (ii) polymer translocation. In the first system we analyze, by directionality tests, the response of N. viridula individuals to subthreshold signals plus noise in their mating behaviour. The percentage of insects that react to the subthreshold signal shows a nonmonotonic behaviour, characterized by the presence of a maximum, as a function of the noise intensity. This is the signature of the non-dynamical stochastic resonance phenomenon. By using a “soft” threshold model we find that the maximum of the input-output cross correlation occurs in the same range of noise intensity values for which the behavioural activation of the insects has a maximum. Moreover this maximum value is lowered and shifted towards higher noise intensities, compared to the case of white noise. In the second biological system the noise driven translocation of short polymers in crowded solutions is analyzed. An improved version of the Rouse model for a flexible polymer is adopted to mimic the molecular dynamics by taking into account both the interactions between adjacent monomers and the effects of a Lennard-Jones potential between all beads. The polymer dynamics is simulated in a two-dimensional domain by numerically solving the Langevin equations of motion in the presence of thermal fluctuations and a colored noise source. At low temperatures or for strong colored noise intensities the translocation process of the polymer chain is delayed. At low noise intensity, as the polymer length increases, we find a nonmonotonic behaviour for the mean first translocation time of the polymer centre of inertia. We show how colored noise influences the motion of short polymers, by inducing two different regimes of translocation in the dynamics of molecule transport.     

Electronic structure, magnetism and superconductivity of layered iron compounds

The layered iron superconductors are discussed using electronic structure calculations. The four families of compounds discovered so far, including Fe (Se, Te) have closely related electronic structures. The Fermi surface consists of disconnected hole and electron cylinders and additional hole sections that depend on the specific material. This places the materials in proximity to itinerant magnetism, both due to the high density of states and due to nesting. Comparison of density functional results and experiment provides strong evidence for itinerant spin fluctuations, which are discussed in relation to superconductivity. It is proposed that the intermediate phase between the structural transition and the SDW transition in the oxy-pnictides is a nematic phase.     

金属管(杆)横驻波演示实验

对两端自由金属管(杆)弯曲振动实验进行了分析,对观察到的现象给出了相应的解释.     

Guillain-Barré syndrome and anti-ganglioside antibodies: a clinician-scientist's journey

Guillain-Barré syndrome (GBS) is the most frequent cause of acute flaccid paralysis. Having seen my first GBS patient in 1989, I have since then dedicated my time in research towards understanding the pathogenesis of GBS. Along with several colleagues, we identified IgG autoantibodies against ganglioside GM1 in two patients with GBS subsequent to Campylobacter jejuni enteritis. We proceeded to demonstrate molecular mimicry between GM1 and bacterial lipo-oligosaccharide of C. jejuni isolated from a patient with GBS. Our group then established a disease model for GBS by sensitization with GM1 or GM1-like lipo-oligosaccharide. With this, a new paradigm that carbohydrate mimicry can cause autoimmune disorders was demonstrated, making GBS the first proof of molecular mimicry in autoimmune disease. Patients with Fisher syndrome, characterized by ophthalmoplegia and ataxia, can develop the disease after an infection by C. jejuni. We showed that the genetic polymorphism of C. jejuni sialyltransferase, an enzyme essential to the biosynthesis of ganglioside-like lipo-oligosaccharides determines whether patients develop GBS or Fisher syndrome. This introduces another paradigm that microbial genetic polymorphism can determine the clinical phenotype of human autoimmune diseases. Similarities between the clinical presentation of Fisher syndrome and Bickerstaff brainstem encephalitis have caused debate as to whether they are in fact the same disease. We demonstrated that IgG anti-GQ1b antibodies were common to both, suggesting that they are part of the same disease spectrum. We followed this work by clarifying the nosological relationship between the various clinical presentations within the anti-GQ1b antibody syndrome. In this review, I wanted to share my journey from being a clinician to a clinician-scientist in the hopes of inspiring younger clinicians to follow a similar path.(Communicated by Kunihiko SUZUKI, M.J.A.).