一些典型的软物质物理中的非平衡自组织现象

在软物质物理中经常有自组织（self-organization）现象发生.这一现象通常在非平衡的过程中产生,并生成非常美丽和有趣的图案与结构.具体例子包括胶体颗粒的扩散限制凝聚（diffusion limited aggregation,DLA）,Hele-Shaw盒中产生的流体分形结构,凝胶的形成（gelation）,生物体自组织聚集,以及颗粒类物质（granular material）运动产生的规则图案等.这些现象在软物质物理研究中产生了很多重要结果.文章以比较浅显的文字介绍这些软物质物理中的非平衡自组织现象.     

一些典型的软物质物理中的非平衡自组织现象

在软物质物理中经常有自组织(self-organization)现象发生.这一现象通常在非平衡的过程中产生,并生成非常美丽和有趣的图案与结构.具体例子包括胶体颗粒的扩散限制凝聚(diffusion limited aggregation,DLA),Hele-Shaw盒中产生的流体分形结构,凝胶的形成(gelation),生物体自组织聚集,以及颗粒类物质(granular material)运动产生的规则图案等.这些现象在软物质物理研究中产生了很多重要结果.文章以比较浅显的文字介绍这些软物质物理中的非平衡自组织现象.     

Acoustic phenomena observed in lung auscultation

The results of studying respiratory noise at the chest wall by the method of acoustic intensimetry reveal the presence of frequency components with different signs of the real and imaginary parts of the cross spectrum obtained for the responses of the receivers of vibratory displacement and dynamic force. An acoustic model is proposed to explain this difference on the basis of the hypothesis that the contributions of both air-borne and structure-borne sound are significant in the transmission of respiratory noise to the chest wall. It is shown that, when considered as an acoustic channel for the basic respiratory noise, the respiratory system of an adult subject has two resonances: in the frequency bands within 110–150 and 215–350 Hz. For adults in normal condition, the air-borne component of the basic respiratory noise predominates in the region 100–300 Hz in the lower parts of lungs. At forced respiration of healthy adults, the sounds of vesicular respiration are generated by the turbulent air flow in the 11th-through 13th-generation bronchi, and the transmission of these sounds to the chest wall in normal condition is mainly through air and is determined by the resonance of the vibratory system formed by the elasticity of air in the respiratory ducts of lungs and by the surface mass density of the chest wall. It is demonstrated that the distance from the chest wall to the sources of structure-borne additional respiratory noise, namely, wheezing with frequencies above 300 Hz, can be estimated numerically from the ratio between the real and imaginary parts of the cross spectrum on the assumption that the source is of the quadrupole type.     

Collisional decoherence observed in matter wave interferometry

We study the loss of spatial coherence in the extended wave function of fullerenes due to collisions with background gases. From the gradual suppression of quantum interference with increasing gas pressure we are able to support quantitatively both the predictions of decoherence theory and our picture of the interaction process. We thus explore the practical limits of matter wave interferometry at finite gas pressures and estimate the required experimental vacuum conditions for interferometry with even larger objects.     

Hadronic matter is soft

The stiffness of the hadronic equation of state has been extracted from the production rate of K+ mesons in heavy-ion collisions around 1 AGeV incident energy. The data are best described with a compression modulus K around 200 MeV, a value which is usually called "soft." This is concluded from a detailed comparison of the results of transport theories with the experimental data using two different procedures: (i) the energy dependence of the ratio of K+ from Au+Au and C+C collisions and (ii) the centrality dependence of the K+ multiplicities. It is demonstrated that input quantities of these transport theories which are not precisely known, such as the kaon-nucleon potential, the deltaN --> NK+lambda cross section, or the lifetime of the delta in matter, do not modify this conclusion.     

Novel complex phenomena in ferroelectric nanocomposites

A first-principles-based effective Hamiltonian is used to investigate finite-temperature properties of ferroelectric nanocomposites made of periodic arrays of ferroelectric nanowires embedded in a matrix formed by another ferroelectric material. Novel transitions and features related to flux-closure configurations are found. Examples include (i)?a vortex core transition, that is characterized by the change of the vortex cores from being axisymmetric to exhibiting a 'broken symmetry'; (ii)?translational mode of the vortex cores; (iii)?striking zigzag dipolar chains along the vortex core axis; and (iv)?phase-locking of ferroelectric vortices accompanied by ferroelectric antivortices. These complex phenomena are all found to coexist with a spontaneous electrical polarization aligned along the normal of the plane containing the vortices.     

Oscillatory phenomena in cold matter with four-fermion interaction

The phase structure of the Nambu-Jona-Lasinio model in space-time with the topology R ³×S ¹ (spatial coordinate compactified) and chemical potential μ is investigated. Phase portraits of the model are constructed in the μλ plane (λ=1/L, where L is the size of the dimension S ¹) in the case with periodic boundary conditions. It is shown here for the first time that there exist in the model an infinite number of both chirally symmetric massless phases and asymmetric massive phases, between which (as a rule) transitions are second-order. Because of this phase structure, changes in the parameter λ induce oscillations in the particle density, fermion mass, and the critical curve on which chiral invariance is restored. Zh. éksp. Teor. Fiz. 114, 418–436 (August 1998)     

Optical spatial solitons in soft matter

We predict that spatial self-trapping of light can occur in soft matter encompassing a wide class of new materials such as colloids, foams, gels, fractal aggregates, etc. We develop a general nonlocal theory that allows one to relate the properties of the trapped state of Maxwell equations to the measurable static structure factor of the specific material. We give numerical evidence for stable trapping in fractal aggregates and suggest also the possibility of soliton spectroscopy of soft matter.     

Biomolecules as soft matter surfaces

Soft matter surfaces, such as organic layers or polymer surfaces, are dynamical and inhomogeneous (only in special cases crystalline). In contact with solutions, the situation becomes more complex, but still addressable with Surface Science methods. In single molecules and supramolecular assemblies, a large fraction of the molecule forms the surface. Can a single (bio) molecule be interpreted as a soft matter surface? A plant virus with a well-defined tubular structure demonstrates the problems, for which molecular dynamics simulations can give some answers.     

Symmetry energy and experimentally observed cold fragments in intermediate heavy-ion collisions

An attempt is made to study the symmetry energy at the time of primary fragment formation from the experimentally observed cold fragments for a neutron-rich system of ~(64)Ni + ~9Be at 140 MeV/nucleon,utilizing the recent finding that the excitation energy becomes lower for more neutron-rich isotopes with a given Z value.The extracted α_(sym)/T values from the cold fragments,based on the Modified Fisher Model(MFM),are compared to those from the primary fragments of the antisymmetrized molecular dynamics(AMD) simulation and become consistent with the simulation when the I = N —Z value becomes larger,indicating that the excitation energy of these neutron-rich isotopes is indeed lower.     

Wetting phase transitions and critical phenomena in condensed matter

Equilibrium wetting phase transitions and critical phenomena are discussed from a phenomenological point of view. The ubiquitous character of the wetting phase transition is illustrated through its occurrence in a variety of condensed matter systems, ranging from classical fluids to superconductors and Bose-Einstein condensates. The intriguing behaviour of the three-phase contact line and its line tension, at wetting, is an example of a fundamental problem in this field on which much progress has been made.     

Local fields in a soft matter bubble

The electric field created by a point dipole located in a dielectric void (“bubble”) is calculated. We consider a continuous profile of the medium permittivity and find that, at large distances, the effective dipole field depends on the model chosen for the bubble walls, in particular their thickness. A boundary layer model is analyzed that gives good agreement with numerical calculations. Our results shed light on the local field correction that has attracted lot of interest lately.     

生物软物质研究的新进展

文章对近年来中科院物理研究所软物质物理实验室生物软物质研究的部分新进展做一简略介绍,包括DNA单分子研究,DNA与组蛋白的相互作用动力学研究,生物分子马达的运动机制研究,解旋酶与DNA的结合以及解旋DNA的动力学研究,朊病毒片段聚集的分子动力学研究,蛋白质折叠动力学的脉冲升温-时间分辨光谱研究,光合细菌外周捕光天线膜蛋白的拓扑结构研究等.     

Mobility of inorganic nanoparticles in soft matter

The 100 nm hematite Fe₂O₃ particles in gelatin gel, dense water solution of sugar, commercial paints, foam, cosmetic cream and friable powder exhibit the mobility in the range of mm/s which was determined from the analysis of the resonance absorption line shape. In the solution of sugar the movement is correlated for particle–particle distance less then 300 nm. The Mössbauer spectroscopy of the iron bearing nanoparticles is proposed as a novel experimental technique for the investigation of the dynamical and structural properties of the soft matter at the mesoscoipic scale.     

Order and chaos in soft condensed matter

Soft matter, like colloidal suspensions and surfactant gels, exhibit strong response to modest external perturbations. This paper reviews our recent experiments on the nonlinear flow behaviour of surfactant worm-like micellar gels. A rich dynamic behaviour exhibiting regular, quasi-periodic, intermittency and chaos is observed. In particular, we have shown experimentally that the route to chaos is via Type-II intermittency in shear thinning worm-like micellar solution of cetyltrimethylammonium tosylate where the strength of flow-concentration coupling is tuned by the addition of sodium chloride. A Poincaré first return map of the time series and the probability distribution of laminar length between burst events show that our data are consistent with Type-II intermittency. The existence of a ‘Butterfly’ intensity pattern in small angle light scattering (SALS) measurements performed simultaneously with the rheological measurements confirms the coupling of flow to concentration fluctuations in the system under study. The scattered depolarised intensity in SALS, sensitive to orientational order fluctuations, shows the same time-dependence (like intermittency) as that of shear stress.     

生物软物质研究的新进展

文章对近年来中科院物理研究所软物质物理实验室生物软物质研究的部分新进展做一简略介绍,包括DNA单分子研究,DNA与组蛋白的相互作用动力学研究,生物分子马达的运动机制研究,解旋酶与DNA的结合以及解旋DNA的动力学研究,朊病毒片段聚集的分子动力学研究,蛋白质折叠动力学的脉冲升温-时间分辨光谱研究,光合细菌外周捕光天线膜蛋白的拓扑结构研究等.     

Microdrilling for fabricating micrometer-scale holes in soft matter

Probing the response of soft materials at small scales requires examining fundamental behaviors that are often distinct from large-scale interactions. In the development of micrometer- and nanometer-sized holes in soft materials, understanding failure modes becomes essential. We observe fracture behavior in a soft material through a novel method, which leads to the fabrication of small-scale holes in polydimethylsiloxane. We utilize an ultra-sharp tungsten needle to drill this soft elastomeric polymer; this results in controlled hole size and exhibits fracture characteristics observed in brittle materials at larger length scales. We also examine the macroscopic characteristics known to contribute to brittleness and hardness for this material’s response with respect to curing times. This understanding will contribute to many applications including the development of porous materials and DNA sequencing efforts. PACS 81.05.Lg; 81.40.Np; 82.35.Lr     

Novel phenomena in dilute electron systems in two dimensions

Based on theory and experiments in weakly interacting electron systems, it was believed for many years that no metallic phase is possible in two dimensions. The unexpected observation of metallic-like behavior in strongly interacting electron systems has thus drawn considerable attention. Following background material and a brief history, we review the dramatic response of these 2D systems to in-plane magnetic fields, and the evidence this provides for a possible quantum phase transition.Received: 30 January 2004, Published online: 20 July 2004PACS: 71.30. + h Metal-insulator transitions and other electronic transitions - 73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator) - 73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)