冰膜覆盖的球体在水中比金属球降落更快

冰覆盖膜能减少物体在水中运动时尾部湍流,使得运动的阻力降低一半。当冰的温度不是太低时,其表面覆盖一薄层水,因此,物体(如冰刀等)能轻易地在冰面上滑动。目前,一个研究小组发现,冰表面也能帮助冰覆盖物体在水中的运动。他们将球体投入盛水容器中,测量阻力的变化。当与同样尺寸、相同密度的金属或陶瓷球体对照时,覆盖冰的球体所受到的阻力下降。他们发现,冰在表面上的融化现象能够减小球体后部的湍流尾波。这个结果对于理解冰山的移动和船只在冰水中的运动具有重要意义。     

Isovector Q balls

Finite-energy solutions rotating at a constant angular velocity in isovector space are considered within theories that possess global SO(3) symmetry (isovector theories). It is shown that, for a nonlinear O(3) model (n field), such solutions exist only in the one-dimensional case. For the isovector theory proposed by S. Weinberg in order to describe low-energy properties of the π mesons, such solutions exist at some values of parameters that appear in this theory. Some properties of these solutions are studied.     

On self-drifting flame balls

Self-drifting flame balls whose existence has recently been suggested by an ad hoc one-dimensional sandwich model are studied within the framework of a more rational multi-dimensional formulation as bifurcations of the associated stationary spherical flame balls.     

滚球混沌运动演示实验

以滚球在3个凹形槽上的受力体现作用的非线性,导轨由电机推动作简谐振动,滚球在导轨上作受迫(滚动)振动,可以把导轨作简谐振动的频率或振幅作为调整参量.当受迫振动的滚球振幅小时,滚球只在1个凹形槽中作简谐振动;当振幅渐渐增大时,可呈现周期倍增和渐至混沌状态.通过观察安装在同一振动滑板上的2套导轨上的滚球的运动,则可以演示混沌运动对初值的敏感性.     

Surface hardening of metals by ultrasonically accelerated small metal balls

The influence of the technological parameters on the surface hardening of metals by ultrasonically accelerated small balls was evaluated. It was demonstrated that the impact force grows with the increase of the amplitude and frequency of ultrasonic vibrations, density of material and size of balls and decreases with the increase of the distance between irradiator and sample. The experimental results showed that the ultrasonic impact treatment of steel might be used in industrial scale. The general advantages of the ultrasonic treatment are very short treatment time and the ability to treat all shapes with a simple apparatus.     

Interactions of flame balls

Flame ball interactions are numerically investigated in a reaction–diffusion system characterized by single-step Arrhenius kinetics and radiative heat losses. It is found that the interactions of two neighbouring flame balls are characterized by two distinct regimes – a repulsion regime and an attraction regime, depending upon the separation distance. The two regimes join at a critical separation distance, which corresponds to an unstable equilibrium state. For supercritical separation distances, the two flame balls repel and drift apart from each other; whereas for sub-critical separation distances, they move towards each other and eventually merge into a single stationary flame ball. In this connection, flame ball interactions are found to exhibit a qualitatively reverse character in comparison with the well-known van der Waals curve which characterizes intermolecular forces.     

Dynamics and statistics study of rings formed by magnetic balls

The statistical distribution and stability of the ring structure formed by magnetic balls without a magnetic field are studied experimentally and theoretically. Experimental results show that the ring structure of the magnetic balls that are contacted one by one can easily appear. We tested 500 samples to count the probability, P(N), of the appearance of the rings and found that the number of balls, N, in a ring is limited only in the region from 4 to 20. The dependence of the probability, P(N), on the number of balls, N, follows a Poisson-like distribution. The origin of this Poisson distribution is disclosed by the statistics. Based on the classical “spin dynamics + molecular dynamics”, the stability of the ring structure was also investigated. The peak of function P(N) vs. N at 9 and the non-existence of rings with N=3 and N>20 is shown. An internal scaling relation between P(N) and the critical field h_c(N) for breaking the ring is found.     

Production of ball-lightning-like luminous balls by electrical discharges in silicon

We performed electric arc discharges in pure Si to generate luminous balls with lifetime in the order of seconds and several properties usually reported for natural ball lightning. This simple experiment does not rely on energy sources and excitation mechanisms that are improbable in the natural phenomenon and clearly demonstrates the role of vaporization and oxidation of Si, as proposed by the Abrahamson-Dinniss theory for ball-lightning formation.     

Anomalies generated by extrinsic curvature

On the classical level, the embedding of a two-dimensional string in ad-dimensional space induces a natural Weyl operator. It is shown, however, that ford≧4 the corresponding quantum theory is ill-defined. The anomalies of the effective action require the presence of additional degrees of freedom—the theory cannot be specified exclusively in terms of the embedding.     

Noises generated by nonlinear autoregression

A nonlinear generalization of autoregressive scheme of first order is suggested as approximate model for 1/f^k noises. The iterative generation makes use of reducing function instead of a constant. Computer simulations – carried out over three decades of frequency – have demonstrated that there is such a family of these functions that to any function of the family there exists a unique value of standard deviation of white noise source such that the noise generated by the iterative scheme has the spectral factor k ≈ 1. Implications of the results for understanding the origin, structural stability and ubiquity of 1/f noise are discussed.     

Reparable sonoporation generated by microstreaming

Reparable sonoporation was observed in Jurkat lymphocytes in suspension exposed to a vibrating Mason horn tuned to 21.4 KHz. The diameter of the horn tip was 400 microm and its transverse displacement amplitude was 7.8 microm. It was found that the shear stress associated with microstreaming surrounding the Mason-horn tip was the primary reason for the cell reparable sonoporation. The threshold shear stress was determined to be 12 +/- 4 Pa for exposure time up to 7 min. It was also found that the shorter the exposure time, the greater the threshold.     

Turbulence spectra generated by singularities

The problem of turbulence spectra generated by the singularities located on lines and planes is considered. It is shown that the frequency spectrum of fluid-surface displacements due to whitecaps (linear singularities) is scaled like a weakly turbulent Zakharov-Filonenko spectrum. The corresponding wave-vector spectrum may be highly anisotropic with a decrease in maximum, as in the Phillips spectrum. However, in the isotropic situation, the spectrum differs markedly from the Phillips form. For a highly anisotropic two-dimensional turbulence, the vorticity jumps can generate the Kraichnan power-law distribution in the region of maximal angular peak. For the isotropic distribution, the turbulence spectrum coincides with the Saffman spectrum. For the shock-generated acoustic turbulence, the spectrum has the form of the Kadomtsev-Petviashvili spectrum Eω～ ω^?2 for all spatial dimensionalities.     

TheK-property of four billiard balls

A further step is achieved toward establishing the celebrated Boltzmann-Sinai ergodic hypothesis: for systems of four hard balls on the -torus (>2) it is shown that, on the submanifold of the phase specified by the trivial conservation laws, the system is aK-flow. All parts of our previous demonstration providing the analogous result for three hard balls are simplified and strengthened. The main novelties are: (i) A refinement of the geometric-algebraic methods used earlier helps us to bound the codimension of the arising implicitly given set of degeneracies even if we can not calculate their exact dimension that was possible for three-billiards. As a matter of fact, it is this part of our arguments, where further understanding and new ideas are necessary before attacking the general ergodic problem; (ii) In the pasting part of the proof, which is a sophisticated version of Hopf's classical device, the arguments are so general that it is hoped they work in the general case, too. This is achieved for four balls, in particular, by a version of the Transversal Fundamental Theorem which, on one hand, is simpler and more suitable for applications than the previous one and, on the other hand, as we have discovered earlier, is the main tool to prove global ergodicity of semi-dispersing billiards; (iii) The verification of the Chernov-Sinai ansatz is essentially simplified and the new idea of the proof also promises to work in the general case.Research partially supported by the Hungarian National Foundation for Scientific Research, grant No. 104052Research partially supported by the Hungarian National Foundation for Scientific Research, grant No. 1815     

Noncommutative balls and their doubles

Quantum analogues ofn-dimensional balls are defined via suitable generators and relations. In the even case they correspond to the Twisted Canonical Commutation Relations of Pusz and Woronowicz. Then we construct quantum spheres as double manifolds of the noncommutative balls.     

Bose-Einstein condensation of bouncing balls

Microscopic bouncing balls, i.e., particles confined within a positive one-half-dimensional gravitational potential, display Bose-Einstein condensation (BEC) not only in the thermodynamic limit but also in the case of a finite number of particles, and the critical temperature with a finite number of particles is higher than that in the thermodynamic limit. This system is different from the one-dimensional harmonic potential one, for which the standard result indicates that the BEC is not possible unless the number of particles is finite.     

Three-dimensional images generated by quadrature interferometry

Quadrature detection techniques have been applied to images obtained from a Mach-Zehnder interferometer with differently polarized beams to yield the real and the imaginary parts of the diffracted fields simultaneously. This approach eliminates the need for phase retrieval by providing complete information on the complex amplitude of the diffracted signal. We present results in which we demonstrate our ability to reconstruct two- and three-dimensional microscopic objects from their complex diffraction patterns.     

Order generated by random many-body dynamics

New features related to collective properties generated in the systems driven by random dynamics are observed and their implications for further understanding of interplay between coherence and chaos are discussed.