Macroscopic Confinement Research Articles

Fast Ion Transport in the Three-Dimensional Reversed-Field Pinch.

We report on the first comprehensive experimental and numerical study of fast ion transport in the helical reversed-field pinch (RFP). Classical orbit effects dominate the macroscopic confinement properties. The strongest effect arises from growth in the dominant fast ion guiding-center island, but substantial influence from remnant subdominant tearing modes also plays a critical role. At the formation of the helical RFP, neutron flux measurements indicate a drastic loss of fast ions at sufficient subdominant mode amplitudes. Simulations corroborate these measurements and suggest that subdominant tearing modes strongly limit fast ion behavior. Previous work details a sharp thermal transport barrier and suggests the helical RFP as an Ohmically heated fusion reactor candidate; the enhanced transport of fast ions reported here identifies a key challenge for this scheme, but a workable scenario is conceivable with low subdominant tearing mode amplitudes.

From random sphere packings to regular pillar arrays: Effect of the macroscopic confinement on hydrodynamic dispersion

Flow and mass transport in bulk and confined chromatographic supports comprising random packings of solid, spherical particles and hexagonal arrays of solid cylinders (regular pillar arrays) are studied over a wide flow velocity range by a numerical analysis scheme, which includes packing generation by a modified Jodrey–Tory algorithm, three-dimensional flow field calculations by the lattice-Boltzmann method, and modeling of advective–diffusive mass transport by a random-walk particle-tracking technique. We demonstrate the impact of the confinement and its cross-sectional geometry (circular, quadratic, semicircular) on transient and asymptotic transverse and longitudinal dispersion in random sphere packings, and also address the influence of protocol-dependent packing disorder and the particle-aspect ratio. Plate height curves are analyzed with the Giddings equation to quantify the transcolumn contribution to eddy dispersion. Confined packings are compared with confined arrays under the condition of identical bed porosity, conduit cross-sectional area, and laterally fully equilibrated geometrical wall and corner effects on dispersion. Fluid dispersion in a regular pillar array is stronger affected by the macroscopic confinement and does not resemble eddy dispersion in random sphere packings, because the regular microstructure cannot function as a mechanical mixer like the random morphology. Giddings’ coupling theory fails to preserve the nature of transverse dispersion behind the arrays’ plate height curves, which approach a linear velocity-dependence as transverse dispersion becomes velocity-independent. Upon confinement this pseudo-diffusive behavior can outweigh the performance advantage of the regular over the random morphology.

Cosmological constant in a model with superstring-inspired E 6 unification and shadow θ-particles

We have developed the concept of parallel existence of the ordinary (O-) and mirror (M-), or shadow (Sh-) worlds. In the first part of the paper we consider a mirror world with broken mirror parity and the breaking E 6→SU(3)3 in both worlds. We show that in this case the evolutions of coupling constants in the O- and M-worlds are not identical, having different parameters for similar evolutions. E 6 unification, inspired by superstring theory, restores the broken mirror parity at the scale ∼1018 GeV. With the aim to explain the tiny cosmological constant, in the second part we consider the breakings: E 6→SO(10)×U(1) Z in the O-world, and E′6→SU(6)′×SU(2)′ θ in the Sh-world. We assume the existence of shadow θ-particles and the low-energy symmetry group SU(3)′ C ×SU(2)′ L ×SU(2)′ θ ×U(1)′ Y in the shadow world, instead of the Standard Model. The additional non-Abelian SU(2)′ θ group with massless gauge fields, “thetons”, has a macroscopic confinement radius 1/Λ′ θ . The assumption that Λ′ θ ≈2.3⋅10−3 eV explains the tiny cosmological constant given by recent astrophysical measurements. In this way the present work opens the possibility to specify a grand unification group, such as E 6, from cosmology.

Highly Aligned Lamellar Lipid Domains Induced by Macroscopic Confinement

We have carried out neutron diffraction experiments on a lipid mixture in a macroscopically confined sample geometry (1 mm gap) and have observed the transformation of bilayered micelles into two distinct orientationally aligned domains of perforated lamellae seemingly littered with defects. Depending on the separation of the confining surfaces, the defects can lie on a two-dimensional centered rectangular lattice where the angle, φ, between lamellar domains can vary. The particular lamellar phase is shown to be metastable and eventually relaxes, either in time or by perturbation of the sample by centrifugation, into aligned multibilayer stacks of single orientation.

Non-magnetic atom trap based on a 3D bichromatic optical superlattice

We propose a new all-optical atom trap, which is based on sub-Doppler rectified dipole forces in a superposition of two 3D optical lattices with different frequencies. In a semiclassical model, a calculation of the rectified force field and corresponding Monte-Carlo simulations show that the trap can combine the microscopic structure of an optical lattice with macroscopic confinement properties similar to a standard magneto-optical trap. Possible applications of such a trap are discussed.