Modeling of the tearing instability in unreduced two-fluid magnetohydrodynamics

The problem of the tearing instability is solved numerically in cylindrical geometry by using the unreduced two-fluid MHD model. It is shown that the duration of the nonlinear stage of the tearing instability in a hot plasma is rather sensitive to such factors as the initial radial density and temperature profiles, the initial ion-to-electron pressure ratio, and the longitudinal thermal conductivity. Depending on these factors, the two-fluid effects (primarily, the Hall effect) can either greatly hasten the magnetic reconnection process (in comparison to that in the one-fluid MHD model) or greatly slow it. An illustrative explanation of the results obtained is given.     

On the effect of the concentration profile of red cells on blood flow in the artery with stenosis

The effects of the viscosity-concentration dependence and of the concentration profile on blood flow through a vessel with stenosis have been studied. The flow resistance and the wall shear stress have been found to be smaller than in the two-fluid model with constant viscosities.     

Two-layered blood flow in stenosed tubes for different diseases

A two-fluid model for blood flow through a stenosed tube has been developed. The model consists of a core (suspension of RBCs) and peripheral plasma layer. The core is assumed to be represented by a polar fluid and the plasma layer by a Newtonian fluid. The flow is assumed to be steady and laminar, and the fluids incompressible. The flow variables are computed for normal blood and for the cases of polycythemia, plasma cell dyscrasias and for Hb SS diseases. Resistance to flow has been computed for different stenosis length and for different stenosis height. Shear stress distribution along the axial distance has been computed for different stenosis height. The impact of size effects (particle size to tube diameter) on blood diseases is discussed.     

Buried Effects of Surface Plasmon Resonance Modes for Periodic Metal–Dielectric Nanostructures Consisting of Coupled Spherical Metal Nanoparticles with Cylindrical Pore Filled with a Dielectric

We numerically investigate the buried effects of surface plasmon resonance (SPR) modes for the periodic silver-shell nanopearl dimer (PSSND) array and their solid counterparts with different buried depths in a silica substrate by means of finite element method with three-dimensional calculations. The investigated PSSND array is an important novel geometry for plasmonic metal nanoparticles (MNPs), combining the highly attractive nanoscale optical properties of both metallic nanoshell and cylindrical pore filled with a dielectric. Numerical results for SPR modes corresponding to the effects of different illumination wavelengths, absorption spectra, pore–dielectric, electric field components and total field distribution, charge density distribution, and the model of the induced local field or an applied field of the PSSND array are reported as well. It can be found that the buried MNPs with cylindrical pore filled with a dielectric in a substrate exhibit tunable SPR modes corresponding to the bonding and antibonding modes that are not observed for their solid counterparts.     

Blood flow in small curved tubes

Blood flow in small curved tubes is modeled by the two-fluid model where a relatively cell-free fluid layer envelops a fluid core of higher viscosity. The parameters in the model are successfully curve fitted to experimental data for straight tubes. The curved tube equations are then solved by perturbation theory. It was found that curvature in general lowers the tube resistance, but increases the shear stress near the inside wall.     

Nonlinear studies of tumor morphological stability using a two-fluid flow model

Journal of Mathematical Biology - We consider the nonlinear dynamics of an avascular tumor at the tissue scale using a two-fluid flow Stokes model, where the viscosity of the tumor and host...     

Heat transfer to blood flow in a small tube

Blood flow in a small tube (30-1000 mum) can be successfully modeled by the two-fluid model. The fully developed, constant heat flux convective heat transfer problem is studied. The velocity and temperature profiles are determined in closed form. Formulas for friction-factor-Reynolds number product, axial temperature gradient, and Nusselt number are found.     

Drastic Surface Plasmon Mode Shifts in Gold Nanorods Due to Electron Charging

The color of small gold rods changes dramatically when electrons are injected by chemical reductants. The longitudinal and transverse plasmon modes are both found to blue-shift, and the shift is larger for rods with larger aspect ratios. The color changes are visible to the eye for rods with aspect ratios around 2–3. It is found that the surface plasmon band is damped when charging becomes high. The effects are in qualitative agreement with a model in which the gold plasma frequency increases due to an increase in electron density.     

Modeling left ventricular dynamics with characteristic deformation modes

A computationally efficient method is described for simulating the dynamics of the left ventricle (LV) in three dimensions. LV motion is represented as a combination of a limited number of deformation modes, chosen to represent observed cardiac motions while conserving volume in the LV wall. The contribution of each mode to wall motion is determined by a corresponding time-dependent deformation variable. The principle of virtual work is applied to these deformation variables, yielding a system of ordinary differential equations for LV dynamics, including effects of muscle fiber orientations, active and passive stresses, and surface tractions. Passive stress is governed by a transversely isotropic elastic model. Active stress acts in the fiber direction and incorporates length–tension and force–velocity properties of cardiac muscle. Preload and afterload are represented by lumped vascular models. The variational equations and their numerical solutions are verified by comparison to analytic solutions of the strong form equations. Deformation modes are constructed using Fourier series with an arbitrary number of terms. Greater numbers of deformation modes increase deformable model resolution but at increased computational cost. Simulations of normal LV motion throughout the cardiac cycle are presented using models with 8, 23, or 46 deformation modes. Aggregate quantities that describe LV function vary little as the number of deformation modes is increased. Spatial distributions of stress and strain change as more deformation modes are included, but overall patterns are conserved. This approach yields three-dimensional simulations of the cardiac cycle on a clinically relevant time-scale.

     

Asymmetric long-wavelength surface modes of isotropic plasma waveguides

A theoretical study is made of the dispersion properties of electromagnetic surface waves with arbitrary azimuthal mode numbers and a small axial wavenumber in cylindrical isotropic waveguides partially filled with plasma. The plasma is assumed to be cold and radially inhomogeneous, and the problem is solved in the hydrodynamic approximation. The eigenfrequency of the waves is investigated as a function of the plasma parameters, the width and the permittivity of the dielectric gap between the metal waveguide wall and the plasma column, the axial wavenumber, and the azimuthal mode number. It is shown that the axial phase velocities of asymmetric surface modes are higher than the speed of light in a dielectric and that the surface modes do not propagate in a waveguide with a vanishingly small width of the dielectric gap. The theory developed is employed in practice in the calculation of the electrodynamic model of a gas discharges maintained by asymmetric long-wavelength surface modes. The power absorbed by the gas-discharge plasma in the regimes of Ohmic damping and resonant damping is calculated, and the plasma produced during the discharge is shown to be azimuthally homogeneous.     

Efficient Extraction of Fluorescence Emission Utilizing Multiple Surface Plasmon Modes from Gold Wire Gratings

We demonstrate directional enhanced fluorescence emission from fluorophores located above gold wire gratings. In contrast to previous studies on corrugated films, efficient coupling was recorded for multiple plasmon modes associated with both the active and substrate side of the wires. This difference is likely due to the subtle differences in how light interacts with corrugated films versus metal films with periodic subwavelength slots. For corrugated films, coupling between modes on opposite sides of the grating are out of phase, and therefore plasmon modes on the opposite side of the grating are only weakly excited. For wire gratings, transmission and reflection features have been modeled well with a dynamical diffraction model that includes surface plasmons, which allows for efficient coupling to surface plasmon modes on both sides of the grating. We also compared the two mechanisms for fluorescent enhancement, namely the intense electromagnetic field associated with surface plasmons and excited fluorophores radiating via surface plasmon modes. We found the latter mechanism clearly dominant.     

不同经营模式茶园土壤微生物熵对台风干扰的响应

台风干扰可能显著影响我国东南沿海山地茶园土壤有机碳稳定性和矿化过程,而土壤微生物熵（qMB）是指示土壤有机碳稳定性和矿化潜力的敏感指标。因此,研究不同经营模式茶园土壤微生物熵对台风干扰的响应,可为山地茶园土壤碳库管理提供重要科学依据。为此,以浙江省台州市天台县苍山顶传统化肥经营的纯茶园（M0）、林茶间作（M1）、茶园养鸡（M2）、施用微生物肥料的纯茶园（M3）四种经营模式茶园为研究对象,在2021年7月28日台风"烟花"（第6号台风）来临前一天（T1）、台风过境后一天（T2）和台风过境后7天（T3）,按照表层土壤（0-10 cm）和亚表层土壤（10-30 cm）采集四种经营模式的茶园土样,同步测定土壤有机碳（SOC）含量、微生物生物量碳（MBC）和可溶性有机碳（DOC）含量。结果表明：（1）台风干扰对M2和M3的土壤有机碳影响更显著,而且不同经营模式茶园中表层和亚表层的土壤有机碳含量对台风干扰的响应存在差异;（2）台风干扰对M2的土壤微生物熵影响更显著,对表层土壤的微生物熵影响更显著,说明台风干扰对M2土壤有机碳稳定性和矿化影响显著,M2的土壤微生物熵对台风干扰的响应显著;（3）台风干扰对M2的土壤微生物生物量碳影响最显著,对M0和M1的影响最弱,且不同经营模式茶园中不同土层的土壤微生物生物量碳对台风干扰的响应存在差异;（4）台风干扰对M0的土壤可溶性有机碳含量影响更显著,M1和M3次之,对M2的影响最弱。而且不同经营模式茶园中表层和亚表层土壤的可溶性有机碳含量对台风干扰的响应存在差异。综上,台风干扰会对不同经营模式茶园土壤微生物熵影响程度不同,说明台风干扰对不同经营模式茶园土壤有机碳稳定性具有不同程度的影响,其中M2的土壤有机碳是响应台风干扰最敏感的经营模式茶园。     

Hydrodynamic modes of arbitrarily shaped flexible macromolecules: Influence on dynamic light scattering

The diffusional motions of flexible macromolecules are analyzed with an increasingly realistic Rouse–Zimm model, i.e., by modeling the molecule as an arbitrary set of spheres connected by nearly harmonic springs. New features include (1) nearly arbitrary arrangements of spheres, (2) arbitrary arrangements of translational and torsional springs, (3) significant anharmonic corrections to the elastic potential surface, and (4) inclusion of torsional damping and various hydrodynamic cross-coupling effects (including two types of translational-rotational coupling) with no additional fitted parameters. The hydrodynamic interactions [R. F. Goldstein (1985) Journal of Chemical Physics, Vol. 83, pp. 2390–2397] contain no adjustable parameters other than temperature, viscosity, and the radii and positions of the spheres. These hydrodynamic interactions allow accurate calculations of rigid body diffusion as well as flexible motions. Given the positions, radii, and spring constant matrix, one can calculate a full set of three-dimensional diffusional modes. Because one uses an off-diagonal hydrodynamic resistance matrix instead of a diagonal mass matrix, the diffusional modes are different in structure from vacuum normal modes, and give rise to different rms motions in the laboratory frame. These hydrodynamic modes include the effects of vibrational-translational cross-coupling (i.e., motion along a vibrational coordinate may give rise to a translational force, and vice versa). The diffusional modes are used to simulate dynamic light scattering (DLS). I examine various molecules with different shapes, flexibilities, and with different scattering vectors. Radial and angular motions influence DLS decays differently. These effects are dependent upon the molecular shape (straight, bent, or curved) and type of flexibility (stretching or bending). Furthermore, small cubic corrections to the potential surface can be significant for DLS of certain geometries such as straight rods and semicircles. © 1993 John Wiley & Sons, Inc.     

Holographic interferometry study of two-fluid properties of the plasma in current sheets formed in heavy noble gases

Two-exposure holographic interferometry was used to study the structure of current sheets formed in three-dimensional magnetic configurations with a singular X line in heavy noble gases (Ar, Kr, and Xe). It is found that, in the presence of a longitudinal magnetic field B _Z directed along the X line, plasma sheets take on an unusual shape: they are titled and asymmetric. Their asymmetry becomes more pronounced as the mass of a plasma ion increases—a manifestation of the two-fluid properties of the plasma. The observed effects can be attributed to additional forces arising due to the interaction of the longitudinal magnetic field B _Z with Hall currents excited in a plane perpendicular to the X line. A qualitative model describing plasma dynamics with allowance for the Hall effect and accounting for most of the experimentally observed effects is proposed.     

Computer analysis of protein-protein interaction

An automatic procedure which generates possible modes of protein-protein association is developed and applied to the bovine pancreatic trypsin inhibitor-trypsin complex as a test case. Using a simplified model in which each residue is replaced by one interaction center, all possible modes of interaction between the inhibitor and the active center of the enzyme are generated systematically. The non-bonded interactions between the molecules and the protein surface area buried in the generated interfaces are evaluated and used as criteria for selecting stable complexes. We show that satisfactory estimates of accessible and buried surface areas can be made using the simplified model.The procedure leads to about nine structures having non-bonded interactions and buried surface areas similar to those of the native complex. This suggests that the major contributions to the free energy of dissociation are taken into account by our selection procedure, though complementarity and specificity are not properly represented in the simplified model. However, it makes it possible to scan a much larger number of configurations than would otherwise be feasible, chiefly through elimination of side-chain detail.     

Repulsive stabilization in black lipid membranes. A hydrodynamic model

A linear stability analysis is performed for a black lipid membrane. The hydrodynamic model consists of a viscous hydrocarbon film sandwiched between two aqueous phases. Attractive forces (van der Waals and electrical) and repulsive forces (steric) are expressed as body forces in the equations of fluid motion in the three phases. The steric repulsion due to overlap of the hydrocarbon chains of the lipids at small film thicknesses is described via an exponentially decaying interaction potential. The dispersion equation displays two modes of vibrations: the bending mode with the two Film surfaces transversely in phase, and the squeezing mode with the two surfaces 180 degrees out of phase. For symmetrical films, these two modes are uncoupled, and the squeezing mode (with thickness variations) is stabilized by the repulsive interactions. For nonsymmetrical films (different surface tensions, surface charges, etc.). these two modes are coupled and the asymmetry induces a shift of the marginal stability curve to shorter wavelengths.     

Frequency-associated transition from single-cell asynchronous motion to monotonic growth

This paper presents a Fourier analysis of the Ortega equation that examines the growth dynamics of plants, specifically the pollen tubes or non-meristematic zones of elongating coleoptiles. A frequency-induced transition from highly nonlinear (periodical) growth—like the one observed in pollen tubes—to monotonically ascending and asymptotically saturated (sigmoid-like) growth, which is anticipated within the framework of a ‘two-fluid model’, is shown. A dynamic phase diagram is calculated and presented in the form of a live video clip.     

Controllable Coupling of Localized and Propagating Surface Plasmons to Tamm Plasmons

We theoretically investigate the coupling between Tamm plasmons and localized surface plasmons (LSPs) as well as propagating surface plasmons (PSPs) in a multilayer structure consisting of a metallic nanowire array and a spatially separated metal–dielectric Bragg reflector (DBR). A clear anticrossing behavior of the resonances is observed in the dispersion diagram resulting from the coupling, which is well explained by the coupled oscillator model. The coupling also creates new hybrid LSP or PSP modes with narrow bandwidths and unique spectral features. Upon the excitation of these hybrid modes, the local fields underneath the nanowires for the hybrid LSPs or near the lower metal layer surface for the hybrid PSPs are both enhanced greatly as compared with those achieved in the structure without DBR, which has potential applications in nonlinear optics and surface-enhanced spectroscopies.     

Effects of Surface Plasmon Coupling on the Whispering-Gallery Resonance in a Hexagonal Nanowire Cavity Structure

Plasmonics - The effects of surface plasmon (SP) coupling with the excitation radiating dipole on the behaviors of the whispering-gallery resonance (WGR) modes in a hexagonal GaN nanowire cavity...     

Plasmonic Properties of Gold Nanostructures on Gold Film

This paper reports on a systematic study of the plasmonic properties of periodic arrays of gold cylindrical nanoparticles in contact with a gold thin film. Depending on the gold film thickness, it observes several plasmon bands. Using a simple analytical model, it is able to assign all these modes and determine that they are due to the coupling of the grating diffraction orders with the propagating surface plasmons travelling along the film. With finite difference time domain (FDTD) simulations, it demonstrates that large field enhancement occurs at the surface of the nanocylinders due to the resonant excitation of these modes. By tilting the sample, it also observes the evolution of the spectral position of these modes and their tuning through nearly the whole visible range is possible. Such plasmonic substrates combining both advantages of the propagative and localised surface plasmons could have large applications in enhanced spectroscopies.