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The exploration of the rich dynamics of electrons is a frontier in fundamental nano-physics. The dynamical behavior of electrons is dominated by random and chaotic thermal motion with ultrafast ($\approx$ ps) and nanoscale scatterings. This generates fluctuating electromagnetic fields in close vicinity of the moving electrons. W studied this fluctuation in small structures and found that its spatial distribution is not uniform, the magnitude of the fluctuation depends on external parameters such as the size ( ~1 $\mu m$) and the shape of the structure and changes can occur by an order of magnitude. Our work opens the possibility of improving the signal to noise ratio in small devices and in manipulating microscopic electron kinematics through nano-optical techniques and to applications in thermal detectors and photothermal photovoltaics.

We propose a simple approach for chirality sorting based on the optical pulling forces. The scenario is to employ three simple plane waves with the same circular polarization. The three wave vectors have the same longitudinal positive z component while their corresponding transverse projections in the x-o-y plane form a regular triangle. In such an optical lattice, particles with certain chirality will be drawn by the transverse optical force to the periodic intensity maxima, where they are stably trapped and exerted by an optical pulling force along the negative z direction. On the contrary, particles with the opposite chirality are de-trapped transversely away from the intensity maxima and then dispersed in regions where they subject to a positive (pushing) force along the z direction. The phenomena therefore give rise to an alternative all-optical method for selective transport of chiral particles with a wide range of chirality parameters.

It was theoretically proposed and experimentally demonstrated that anti-reflection coating allows one to trap a high dielectric sphere, at the same time enhancing the transverse optical force. Here, by explicitly calculating the gradient force and the scattering force, we rigorously show that these were mainly consequences of the reduction in scattering force due to the suppression of backward scattering, and enhancement in gradient force due to the increased in overall particle size. The reduction of scattering force can be understood within a ray optics theory and also the Mie theory. The coating approach only works for a spherical particle trapped by an aplanatic beam, and it does not work in general., 10 pages, 5 figures

We present a multipole expansion theory for optical force exerting on a particle immersed in generic monochromatic free-space optical field. Based on the theory, we have, for the first time, successfully decomposed the optical force on a spherical particle of arbitrary size into a conservative and a nonconservative parts, which are, respectively, written as a gradient of a scalar function and curl of a vector function in an explicit and analytical form. As a result, a scalar potential and a vector potential can be defined, up to gauge freedoms, for the optical force. The decomposition shed light on the understanding of the optical force and pave a new way to engineer optical force for various purposes such as equilibrium statistical mechanics as well as optical micromanipulation.

We establish universal relationships between optical force/torque on a general particle and different parts of linear and angular momentum (AM) of generic monochromatic optical field. It is rigorously proved that the optical force comes about by the transfer of orbital (canonical) optical momentum from light to matter, while the other part of optical momentum, known as spin momentum, does not generate optical force on matter but, instead, stays conserved even when the translational invariance is broken by putting particles into the optical fields. On the other hand, based on a generic multipole theory of optical torque, we demonstrate that the optical torque stems from the transfer of the total optical AM, including both orbital and spin AM, clarifying in generic case the long-standing confusion about whether the orbital AM can induce a spinning torque on a general particle in generic optical fields., 24 pages

Optical forces have been fruitfully applied in a broad variety of areas that not only span the traditional scientific fields such as physics, chemistry, and biology, but also in more applied fields. It is customary and useful to split the optical force into the (conservative) gradient force and the (non-conservative) scattering and absorption force. These forces are different in attributes. The ability to tailor them will open great potential in fundamental optics and practical applications. Here, we present an analytical and a numerical approach to calculate these forces, and, with these tools, we create a fairly general class of 2D conservative optical force field. In general, particles immersed in an optical force do not obey equilibrium statistical mechanics, making the analysis complicated. With conservative forces, these issues are resolved., Comment: 16 pages, 4 figures

Like many other physical quantities, the optical force can be expanded using multipole expansion, which has been done in [Nat. Photon. 5, 531], up to electric octupole order. However, in that study, the existence of radiation multipoles were pre-assumed, and the role of the fundamental building units, charges, are not evident. Here, we derive the same multipolar expression of optical force by treating the particles as a collection of point charges or point dipoles, which results in more transparent physics and mathematics.

A hydrodynamic boundary condition for the lattice Boltzmann model at impermeable boundaries is developed. This boundary condition satisfies both the no-slip condition and the fluid conservation at boundary nodes. Poiseuille flow and Couette flow are calculated with this technique to demonstrate the accuracy of the present boundary condition.

The influence of the size distribution of particles on the viscous property of an electrorheological fluid has been investigated by the molecular dynamic simulation method. The shear stress of the fluid is found to decrease with the increase of the variance σ2 of the Gaussian distribution of the particle size, and then reach a steady value when σ is larger than 0.5. This phenomenon is attributed to the influence of the particle size distribution on the dynamic structural evolution in the fluid as well as the strength of the different chain-like structures formed by the particles.

We simulate the changes of the photonic band structure of the crystal in two dimensions with a quasi-fractal structure when it is confined to a fractal. The result shows that when the dielectric distribution is confined, the photonic band structure will be compressed on the whole and the ground photonic band gap (PBG) closed while the next PBGs shrunk, in conjunction with their position declining in the frequency spectrum. Furthermore, the PBGs in the high zone are much more sensitive than those in low zones.

A photon carries a momentum of, so one may anticipate light to "push" on any object standing in its path via the scattering force. In the absence of intensity gradient, using a light beam to pull a particle backwards is counter intuitive. Here, we show that it is possible to realize a backward scattering force which pulls a particle all the way towards the source without an equilibrium point. The underlining physics is the maximization of forward scattering via interference of the radiation multipoles. We show explicitly that the necessary condition to realize a negative (pulling) optical force is the simultaneous excitation of multipoles in the particle and if the projection of the total photon momentum along the propagation direction is small (as in some propagation invariant beams), attractive optical force is possible. This possibility adds "pulling" as an additional degree of freedom to optical micromanipulation., Comment: 11 pages, 4 figures

We propose a rigorous theory for the optical trapping by optical vortices, which is emerging as an important tool to trap mesoscopic particles. The common perception is that the trapping is solely due to the gradient force, and may be characterized by three real force constants. However, we show that the optical vortex trap can exhibit complex force constants, implying that the trapping must be stabilized by ambient damping. At different damping levels, particle shows remarkably different dynamics, such as stable trapping, periodic and aperiodic orbital motions.

When an oscillating line source is placed in front of a special mirror consisting of an array of flat uniformly spaced ferrite rods, half of the image disappeared at some frequency. We believe that this comes from the coupling to photonic states of the magnetic surface plasmon band. These states exhibit giant circulations that only go in one direction due to time reversal symmetry breaking. Possible applications of this "rectifying" reflection include a robust one-way waveguide, a 90 degree beam bender and a beam splitter, which are shown to work even in the deep subwavelength scale.

By an exact real space renormalization group method, the authors obtain the spectral dimension of the Vicsek snowflake fractal. The result seems to cast some doubt on the range of validity of the Einstein relation on the deterministic fractal.

By an exact renormalization method the trail problem on a regular fractal for the diffusion-limited aggregation is considered, and the mean square end-to-end distance critical exponent ν is obtained. It is indicated that self-avoiding trails and self-avoiding walks are in different universality classes on this irreversible kinetic growth fractal.

In the leaf of rice (Oryza sativa L.) cultivar Yunnan purple rice, the anthocyanins with an obvious absorption peak at 530nm were distributed in the cells of upper and lower epidermis, bulliform tissue and bristle. The maximal photosynthetic oxygen evolution rate and chlorophyll content in flag leaves were 28% and 23%, respectively, more than the common green leaf rice cultivar Chijiaoruanzhan. Higher chlorophyll content is probably one of the physiological adaptations for enhancing light harvesting capacity of the antenna in photosystems in this cyanic leaves species. Upon the photooxidation of leaf segments mediated by methyl viologen in weak light for 3 days, the distinct bleaching of anthocyanins in purple rice was associated with the reduction of scavenging ability to DPPH * free radical ability and the increase in membrane leakage rate. But almost no changes in contents of flavonoids and total phenolics were observed. Chlorophyll fluorescence parameters Fv/Fo, qP and phi(PSII) decreased with the increase in NPQ and DES of xanthophylls cycle after photooxidation treatment. Green rice leaves showed more decrease in DPPH * scavenging rate and more increase in cell membrane leakage rate but showed a trace of anthocyanins during photooxidation. It is suggested that anthocyanin may be a beneficial and primary antioxidant in sun cyanic rice leaves against oxidative stress induced by environmental adversity. And photooxidation could induce different changing patterns of anthocyanins between the tested purple and green rice leaves.

We show through rigorous calculations that dielectric microspheres can be organized by an incident electromagnetic plane wave into stable cluster configurations, which we call photonic molecules. The long-range optical binding force arises from multiple scattering between the spheres. A photonic molecule can exhibit a multiplicity of distinct geometries, including quasicrystal-like configurations, with exotic dynamics. Linear stability analysis and dynamical simulations show that the equilibrium configurations can correspond with either stable or a type of quasi-stable states exhibiting periodic particle motion in the presence of frictional dissipation., 4 pages, 3 figures

We study the surface magnetization and critical behavior of a hierarchical quantum Ising chain. The surface magnetization exponent βs is calculated exactly by using scaling arguments. It is found that, although the size of the fluctuations in the exchange couplings may be bounded or unbounded depending on the value of the hierarchical parameter r, the surface critical behavior stays nonuniversal with βs varying continuously with the value of r. This result is rather different from the cases where the aperiodicity of the couplings is generated by substitution rules and different types of critical behavior are observed for bounded and unbounded fluctuations in the couplings.

By an exact real-space renormalization-group approach, we investigate ultradiffusion with a hierarchical pattern of hopping rates defined on the regular Vicsek fractal. Anomalous long-time behavior of the autocorrelation function of ultradiffusion is observed. It is found that the transition from anomalous to normal diffusion occurs in the general n-dimensional case, and the transition point is independent of dimension. In the presence of bias, we find another unusual transition that leaves hopping particles trapped in some areas in contrast to the diffusive state for which the average square distance 〈${\mathit{R}}^{2}$(t)〉\ensuremath{\sim}\ensuremath{\infty} for t\ensuremath{\rightarrow}\ensuremath{\infty}. This transition is essentially different from the one for biased ultradiffusion of the one-dimensional multiple-furcation hierarchical system.

The effect of the direction of external electric field on the shear stress of an ER fluid has been studied by molecular-dynamics simulation. Due to the formation of inclined chains, the shear stress strongly depends on the direction of the field, and it may be very large under some special field direction. And theoretical model of ideal microstructure of ER fluids has proved this result. Thus the ER effect may be greatly enhanced just by choosing an optimum direction for the field without any additional requirement, suggesting a promising way to the practical application of ER fluids.

Using an exact real-space renormalization-group technique, we show that self-avoiding trails (SAT) and self-avoiding walks (SAW) on the Sierpinski gasket enjoy the same critical exponent ν for the ‘correlation length' and therefore belong to the same universcllily class. On the other hand, it is shown that SAT on branching Koch curves with maximum ramification number Rmax>3 belongs to another universality class different from that of SAW.