Effects of circulating energetic ions on sawtooth oscillations

In contrast to the well-known result that the effects of the trapped energetic ions (TEI) on the internal kink mode are due to the toroidal precession of the TEI, it is found that the effects of the circulating energetic ions (CEI) on sawtooth are due to the toroidal circulation of the CEI. The effects of the CEI on sawtooth oscillations are found to be different from the well-known purely stabilizing effects of the TEI on sawtooth oscillations; the toroidal circulation of the co-CEI provides an additional sink of free energy and stabilizes the mode; the toroidal circulation of the counter-CEI provides an additional source of free energy and destabilizes the mode.     

A minimum photon “rest mass” — Using Planck's constant and discontinuous electromagnetic waves

Reasons for taking1/2h/c ² in cgs units as an equivalent in grams for the photon “rest mass” are given. Its numerical value of3.68×10 ^?48 g corresponds to the minimum mass equivalent energy for one half-cycle of an electromagnetic dipole field distribution, which is discontinuous. For the fluid models that are discussed, this field distribution corresponds somewhat to a hydrodynamic toroidal vortex which is stationary—if we use toroidal coordinates and assume that the ring origin has the radial velocity c, that the gauge is defined by the ring origin diameter, and that free space is represented by a two-fluid model (the fluids oppositely charged). There are mappings which can transform such toroidal entities (photons) into spherical ones. The toroidal entities are possible candidates for the role of “hidden variables.”     

2500kW˫�������ͬ������װ������

为了满足HL-2A环向磁场的要求,成功研制了两套2500kW感应拖动电机的超同步调速装置。基于交-交变频器,通过对每套2500kW拖动电机采用双馈电机矢量控制技术进行调速后,将两台80MVA机组的最高转速由以前的额定转速1488rpm提高到了1650rpm,每台机组的一次脉冲释能达到500MJ,使HL-2A装置具备了环向磁场达2.8T的能力。     

Physical limits on computation by assemblies of allosteric proteins

Assemblies of allosteric proteins are the principle information processing devices in biology. Using the Ca2+-sensitive cardiac regulatory assembly as a paradigm for Brownian computation, I examine how system complexity and system resetting impose physical limits on computation. Nearest-neighbor-limited interactions among assembly components constrain the topology of the system's macrostate free energy landscape and produce degenerate transition probabilities. As a result, signaling fidelity and deactivation kinetics cannot be simultaneously optimized. This imposes an upper limit on the rate of information processing by assemblies of allosteric proteins that couple to a single ligand type.     

Asymptotic energy of lattices

The energy of a simple graph G arising in chemical physics, denoted by E(G), is defined as the sum of the absolute values of eigenvalues of G. As the dimer problem and spanning trees problem in statistical physics, in this paper we propose the energy per vertex problem for lattice systems. In general for a type of lattice in statistical physics, to compute the entropy constant with toroidal, cylindrical, Mobius-band, Klein-bottle, and free boundary conditions are different tasks with different hardness and may have different solutions. We show that the energy per vertex of plane lattices is independent of the toroidal, cylindrical, Mobius-band, Klein-bottle, and free boundary conditions. In particular, the asymptotic formulae of energies of the triangular, 3³.4², and hexagonal lattices with toroidal, cylindrical, Mobius-band, Klein-bottle, and free boundary conditions are obtained explicitly.     

Dynamic behavior of a single bubble between the free surface and rigid wall

The objective of this paper is to apply high-speed photography and schlieren method to investigate the bubble dynamics between the free surface and a rigid wall. The temporal evolution of the bubble shape and the free surface motion are recorded by two synchronous high-speed cameras. Experiments are carried out for a single bubble generated at various normalized stand-off distances from bubble center to the free surface and to the rigid wall. The results show that (1) three distinctive patterns are identified with the morphology of the bubble and free surface, namely single toroidal bubble without spike (STB), single toroidal bubble with a spike (STBS) and double toroidal bubbles with a spike (DTBS). (2) The dynamic characteristics of the bubble at collapse and rebound stage vary evidently at different patterns, including the bubble shape variations and free surface motion. In detail, the schlieren images show the formation and propagation of shock waves, which explains the radiative process of bubble collapse energy. (3) Qualitative comparisons are carried out for the bubble and free surface at the same pattern. And quantitative analyses are conducted for the jet velocity, bubble collapse position, bubble collapse time and spike height, etc. for different values of bubble-rigid wall distance.     

Minimum energy path to membrane pore formation and rupture

We combine dynamic self-consistent field theory with the string method to calculate the minimum energy path to membrane pore formation and rupture. In the regime where nucleation can occur on experimentally relevant time scales, the structure of the critical nucleus is between a solvophilic stalk and a locally thinned membrane. Classical nucleation theory fails to capture these molecular details and significantly overestimates the free energy barrier. Our results suggest that thermally nucleated rupture may be an important factor for the low rupture strains observed in lipid membranes.     

Pore formation phase diagrams for lipid membranes

Critical lateral pressure for a pore formation and phase diagram of porous membrane are derived analytically as functions of the microscopic parameters of the lipid chains. The derivation exploits path-integral calculation of the free energy of the ensembles of semi-flexible strings and rigid rods that mimic the hydrophobic tails of lipids in the lipid bilayers and bolalipid membranes respectively. Analytical expressions for the area stretch/compressibility moduli of the membranes are derived in both models.     

Growth and micromagnetic simulation of magnetite nanoparticles

Magnetite nanoparticles with different sizes and different assemblies were synthesized via hydrothermal method.Micromagnetic simulation shows the magnetite nanocubes with different sizes have different energy states,which determines the assembly mode.Magnetite nanocubes with the side length of 30-60 nm tended to be dispersed while both nanochains and dispersed nanoparticles were found to grow for the nanocubes with the side length less than 30 nm,which can be explained in the fact that the above two assembl...     

Neutronic simulation of a research reactor core of (232Th, 235U)O 2 fuel using MCNPX2.6 code

The small reactor design for the remote and less developed areas of the user countries should have simple features in view of the lack of infra-structure and resources. Many researchers consider long core life with no on-site refuelling activity as a primary feature for the small reactor design. Long core life can be achieved by enhancing internal conversion rate of fertile to fissile materials. For that purpose, thorium cycle can be adopted because a high fissile production rate of ²³³U converted from ²³²Th can be expected in the thermal energy region. A simple nuclear reactor core arranged 19 assemblies in hexagonal structure, using thorium-based fuel and heavy water as coolant and moderator was simulated using MCNPX2.6 code, aiming an optimized critical assembly. Optimized reflector thickness and gap between assemblies were determined to achieve minimum neutron leakage and void reactivity. The result was a more compact core, where assemblies were designed having 19-fuel pins in 1.25 pitch-to-diameter ratio. Optimum reflector thickness of 15 cm resulted in minimal neutron leakage in view of economic limitations. A 0.5 cm gap between assembles achieved more safety and 2.2% enrichment requirements. The present feasibility study suggests a thermal core of acceptable neutronic parameters to achieve a simple and safe core.     

Fluids absorbed in structured pores

A model of fluids absorbed in a pore with walls patterned with parallel channels is used to demonstrate some of the unity that can be proved to hold between the statistical mechanics of fluids absorbed in structured pores and of fluids adsorbed at unstructured walls and at edges/wedges where walls meet. In particular, the work done to reversibly shear a corrugated pore immersed in liquid is related to the difference in the density profile structure of liquid adsorbed near the edges of the channels. When the channel dimensions are mesoscopic or macroscopic but the minimum pore width is microscopic, statistical mechanics generates remarkable links between the surface tension of planar wall-fluid interfaces or, more generally, the solvation free energy of a planar pore, and the density profile at the sides of a channel wall in the vicinity of edges and wedges.     

Reduced critical rotation for resistive-wall mode stabilization in a near-axisymmetric configuration

Recent DIII-D experiments with reduced neutral beam torque and minimum nonaxisymmetric perturbations of the magnetic field show a significant reduction of the toroidal plasma rotation required for the stabilization of the resistive-wall mode (RWM) below the threshold values observed in experiments that apply nonaxisymmetric magnetic fields to slow the plasma rotation. A toroidal rotation frequency of less than 10 krad/s at the q=2 surface (measured with charge exchange recombination spectroscopy using C VI) corresponding to 0.3% of the inverse of the toroidal Alfvén time is sufficient to sustain the plasma pressure above the ideal MHD no-wall stability limit. The low-rotation threshold is found to be consistent with predictions by a kinetic model of RWM damping.     

Heating process and damage threshold analysis of Au film coated on Cu substrate for femtosecond laser

The heating processes of a two-layer film assembly of Au padded with Cu irradiated by femtosecond laser pulse are studied using a two-temperature model. It is found that the chosen substantially influence the energy transport, and consequently the temperature variation, and thermal equilibrium time. At the same laser fluence, the different thickness of gold film leads to a change of gold surface temperature. By choosing the thickness of the gold layer in the two-layer film assemblies, the damage threshold of the gold film can be maximized. The results can be used to optimize the damage threshold of gold coating optical components.     

Magnetization of nanomagnet assemblies: Effects of anisotropy and dipolar interactions

We investigate the effect of anisotropy and weak dipolar interactions on the magnetization of an assembly of nanoparticles with distributed magnetic moments, i.e., assembly of magnetic nanoparticles in the one-spin approximation, with textured or random anisotropy. The magnetization of a free particle is obtained either by a numerical calculation of the partition function or analytically in the low and high field regimes, using perturbation theory and the steepest-descent approximation, respectively. The magnetization of an interacting assembly is computed analytically in the range of low and high field, and numerically using the Monte Carlo technique. Approximate analytical expressions for the assembly magnetization are provided which take account of the dipolar interactions, temperature, magnetic field, and anisotropy. The effect of anisotropy and dipolar interactions are discussed and the deviations from the Langevin law they entail are investigated, and illustrated for realistic assemblies with the lognormal moment distribution.     

Transverse polarizability of an aligned assembly of charged rods

The low-field transverse polarizability of the counterions condensed on an isolated charged rod is small. We show that it can be much larger if the rod is a member of an assembly of aligned rods. The polarization free energy of the assembly of rods in a transverse field is then similar to its polarization free energy in a field parallel to the rods. The polarization free energy of the assembly in a transverse field becomes lower than in a parallel field if the extent of the assembly (as measured, for example, by the diameter of a cylindrical assembly) is larger than the length of the individual rods. We suggest that this model may provide a reasonable explanation for the occurrence of “anomalous” birefringence in systems of interacting charged rodlike particles.     

An investigation of some models and approximations used in calculating fuel assemblies of a high-temperature gas-cooled reactor of the GT-MHR type

The paper describes basic neutron-physics models developed in the Division of Advanced Nuclear Power Systems of the Institute of Nuclear Reactors, Russian Research Center Kurchatov Institute, as design models intended for calculating the characteristics of block fuel assemblies of a high-temperature gas-cooled reactor GT-MHR, namely, models for calculating burnup of fuel and isotopes of burnable neutron absorbers and calculating fuel assemblies at fixed points with respect to burnup with preparation of the neutron constants in a preassigned number of energy groups for full-scale design of a reactor. A model problem for investigation of calculated approximations is proposed. The outcome of this investigation is a developed stage-by-stage procedure of preparing group homogeneous cross sections of a fuel assembly and its parts that has been introduced into the practice of design calculations of a GT-MHR reactor.     

Vortex ring energy variation in a homogeneous medium

The equation of energy variation of vortex rings (free toroidal vortices) in a homogeneous medium (air and water at atmospheric pressure and temperature ～293 K) depending on their initial parameters and medium was derived. It was shown that the solution to this equation is in agreement with experimental data.     

Elucidating the mechanism of nucleation near the gas-liquid spinodal

We have constructed a multidimensional free energy surface of nucleation of the liquid phase from the parent supercooled and supersaturated vapor phase near the gas-liquid spinodal. In particular, we remove the Becker-Doring constraint of having only one growing cluster in the system. Close to the spinodal, the free energy, as a function of the size of the largest cluster, develops surprisingly a minimum at a subcritical cluster size. It is this minimum at intermediate size that is found to be responsible for the barrier towards further growth of the nucleus at large supersaturation. An alternative free energy pathway involving the participation of many subcritical clusters is found near the spinodal where the growth of the nucleus is promoted by a coalescence mechanism. The growth of the stable phase becomes collective and spatially diffuse, and the significance of a "critical nucleus" is lost for deeper quenches.     

Shock ignition of thermonuclear fuel with high areal density

A novel method by C. Zhou and R. Betti [Bull. Am. Phys. Soc. 50, 140 (2005)] to assemble and ignite thermonuclear fuel is presented. Massive cryogenic shells are first imploded by direct laser light with a low implosion velocity and on a low adiabat leading to fuel assemblies with large areal densities. The assembled fuel is ignited from a central hot spot heated by the collision of a spherically convergent ignitor shock and the return shock. The resulting fuel assembly features a hot-spot pressure greater than the surrounding dense fuel pressure. Such a nonisobaric assembly requires a lower energy threshold for ignition than the conventional isobaric one. The ignitor shock can be launched by a spike in the laser power or by particle beams. The thermonuclear gain can be significantly larger than in conventional isobaric ignition for equal driver energy.     

Transport in boundary layer of divertor tokamaks

Study of transport in the boundary layer of tokamak plasma in presence of magnetic divertors is extended to the second order in ion collision frequency. Numerical results for ion and energy losses to the collector plates are presented for toroidal and poloidal divertors. For the toroidal case, the Wiener-Hopf solution for the second order distribution function is obtained. An error occurring in an earlier first order calculation is pointed out and corrected first order fluxes are also given. For the poloidal divertor, asymmetry observed in ion and energy transport is found to persist in the second order result.