New global defect structures

We investigate the presence of defects in systems described by real scalar field in (D,1) spacetime dimensions. We show that when the potential assumes specific form, there are models which support stable global defects for D arbitrary. We also show how to find first-order differential equations that solve the equations of motion, and how to solve models in D dimensions via soluble problems in D=1. We illustrate the procedure examining specific models and finding explicit solutions.     

Generalized global defect solutions

We investigate the presence of defect structures in generalized models described by a real scalar field in (1,1) space-time dimensions. We work with two distinct generalizations: one in the form of a product of functions of the field and its derivative, and the other as a sum. We search for static solutions and study the corresponding linear stability on general grounds. We illustrate the results with several examples, where we find stable defect structures of modified profile. In particular, we show how the new defect solutions may give rise to evolutions not present in the standard scenario in higher spatial dimensions.     

Confinement and the global SU(3) color symmetry

The global SU(3)color symmetry and its physical consequences are discussed.The Nother current is actually governed by the conserved matter current of color charges if the color field generated by this charge is properly polarized.The color field strength of a charge can have a uniform part due to the nontrivial QCD vacuum field and the nonzero gluon condensate,which implies that the self-energy of a system with a net color charge is infinite and,therefore,cannot exist as a free state.This is precisely what color confinement means.Accordingly,the Cornell type potential with the feature of Casimir scaling is derived for a color singlet system composed of a static color charge and an anti-charge.The uniform color field also implies that a hadron has a minimal size and minimal energy.Furthermore,the global S U(3)color symmetry requires that the minimal irreducible color singlet systems can only be qq,qqq,gg,ggg,qqg,qqqg,qqqg,etc.,therefore a multi-quark system can only exist as a molecular configuration if there are no other binding mechanisms.     

Nanoengineering defect structures on graphene

We present a new way of nanoengineering graphene by using defect domains. These regions have ring structures that depart from the usual honeycomb lattice, though each carbon atom still has three nearest neighbors. A set of stable domain structures is identified by using density functional theory, including blisters, ridges, ribbons, and metacrystals. All such structures are made solely out of carbon; the smallest encompasses just 16 atoms. Blisters, ridges, and metacrystals rise up out of the sheet, while ribbons remain flat. In the vicinity of vacancies, the reaction barriers to formation are sufficiently low that such defects could be synthesized through the thermally activated restructuring of coalesced adatoms.     

A new set-up for pulsed digital shearography applied to defect detection in composite structures

An optical set-up based on the combination of new CCD technology, a ruby laser and a Mach-Zehnder shear interferometer is presented for defect detection in composites. Transient loads are used to excite defects in a sandwich structure and image-processing routines allow improving the detection resolution. Phase calculation is obtained by FFT algorithms applied to interference patterns with a spatial carrier in the primary fringes. Independent control of the shear and the frequency of the spatial carrier can be obtained with this set-up. The experimental implementation of the set-up and the results obtained with it are presented and discussed.     

Twist defect in chiral photonic structures

We demonstrate that twisting one part of a chiral photonic structure about its helical axis produces a single circularly polarized localized mode that gives rise to an anomalous crossover in propagation. Up to a crossover thickness, this defect results in a peak in transmission and exponential scaling of the linewidth for a circularly polarized wave with the same handedness as structure. Above the crossover, however, the linewidth saturates and the defect mode can be excited only by the oppositely polarized wave, resulting in a peak in reflection instead of transmission.     

Confinement effects in electrical resistivity and spin-valve magnetoresistance in metallic layered structures

Quantum size effects in electronic transport properties of metallic trilayers are analysed theoretically. It is shown that electron confinement leads to oscillations in electrical resistivity with two different periodicities. The short oscillation period is determined by the appropriate Fermi wavelength, whereas the long period depends on the potential step at interfaces. When the outer films in the trilayer are ferromagnetic, then the oscillations in the resistivity give rise to similar oscillations in the spin-valve magnetoresistance.     

Theory of radiation-induced self-organization of defect structures

During high-dose electron irradiation of thin Ni foils at 520 K, groups of about 10 Stacking-Fault Tetrahedra (SFT) are formed, which are referred to as patches. Within the patches the SFT occupy the sites of a square lattice whose sides are parallel to the two 100 directions of the crystalline host lattice in the foil plane. A theory of this planar square lattice of SFT is the subject matter of the preceding paper (Part I). The patches themselves are arranged in a planar face-centred cubic lattice that also shares its orientation with the host lattice. In the present paper (Part II) a mesoscopic theory is presented that accounts for this ordering of SFT-lattice patches in terms of an instability of disordered patch arrangements that results from a point-defect-mediated dynamic patch-patch interaction. This interaction arises from the competition of SFT-lattice patches for static crowdions migrating one-dimensionally along close-packed host lattice directions and for three-dimensionally diffusing vacancies and dumbbell interstitials. The so far exclusive occurrence of ordered SFT-lattice patches in Ni is related to the low packing density of this material, which leads to a high stability of the static crowdions and thus to a long range of the dynamic interaction between SFT-lattice patches.     

Confinement from spontaneous breaking of scale symmetry

We show that one can obtain naturally the confinement of static charges from the spontaneous symmetry breaking of scale invariance in a gauge theory. At the classical level a confining force is obtained and at the quantum level, using a gauge invariant but path-dependent variables formalism, the Cornell confining potential is explicitly obtained. Our procedure answers completely to the requirements by 't Hooft for “perturbative confinement”.     

Thermodynamics and defect structures of silver sulfide

Published measurements of sulfur vapor pressure and silver electromotive force were used to determine thermodynamic properties of silver sulfide above 379 K. They were Gibbs-Duhem integrated to estimate the formation properties of stoichiometric Ag₂S of fcc, bcc, and monoclinic crystal structures. Statistical thermodynamics was applied to estimate free energies and find possible atom arrangements in off-stoichiometric silver sulfide. Theoretical calculations show that silver vacancies and atoms may be in quasi-chemical equilibrium between tetrahedral and octahedral sites in the fcc structure and between two states of atoms within tetrahedral sites in the bcc structure and within octahedral sites in the monoclinic structure. A strong indication is that vacancy clusters should predominate, each containing four-atom vacancies in the fcc phase and three-atom vacancies in the bcc phase.     

Bistable defect structures in blue phase devices

Blue phases are liquid crystals made up by networks of defects, or disclination lines. While existing phase diagrams show a striking variety of competing metastable topologies for these networks, very little is known as to how to kinetically reach a target structure, or how to switch from one to the other, which is of paramount importance for devices. We theoretically identify two confined blue phase I systems in which by applying an appropriate series of electric field it is possible to select one of two bistable defect patterns. Our results may be used to realize new generation and fast switching energy-saving bistable devices in ultrathin surface treated blue phase I wafers.     

Excitation of defect modes from the extended photonicband-gap structures of 1D photonic lattices

This paper stuides numerically the model equation in a one dimensional defective photonic lattice by modifying the potential function to a periodic function. It is found that defect modes (DMs) can be regarded as Bloch modes which are excited from the extended photonic band-gap structure at Bloch wave-numbers with k x = 0. The DMs for both positive and negative defects are considered in this method.     

Evolution of reactions on surfaces exhibiting defect structures

This paper considers the time and spatial dependent behavior of an active surface exposed to two reactants which may diffuse on the surface, desorb, and also react. The surface is assumed to contain defect structures corresponding to either inherent lattice faults or foreign material on the surface. A number of case studies are examined corresponding to different assumptions about the desorption and kinetic characteristics of the defect sites. The surface concentration profiles are examined to gain physical insight into the competing surface processes. The net effect of surface defects on chemical production rates was examined by integrating the local production rate over a test region on the surface. Of special interest was the study of the poisoning effect of the product species on the diffusion and reaction of the reactants. The reaction-diffusion equations of the models were solved by the alternating direction collocation technique which shows promise for providing an efficient numerical procedure capable of handling practical large scale problems.     

Novel defect structures in nematic liquid crystal shells

We use double-emulsion drops to experimentally investigate the defect structures of spherical shells of nematic liquid crystals. We uncover a rich scenario of coexisting defect structures dictated by the unavoidable finite thickness of even the thinnest shell and by the thickness variation around the sphere. These structures are characterized by a varying number of disclination lines and pairs of surface point defects on the inner and outer surfaces of the nematic shell. In the limit of very thick shells the defect structure ultimately merges with that of a bulk nematic liquid crystal drop.     

Positron studies of defect structures in metallic glasses

A variety of metallic glasses (Cu_xZr_100?x with x = 30, 40 and 50, Ni₂₄Zr₇₆ and RE₆₇ Co₃₃, RE = Nd, Sm, Gd, Dy, Er) were studied using 2γ angular correlation techniques. Significant positron trapping is observed in all the glassy alloys investigated. The defect structure changes drastically during crystallization. For the RE-Co glasses the results suggest the existence of vacancy-like defects in the amorphous alloys.     

Confinement from a scalar-gluon coupling in gauge theory

A model is introduced with a massive scalar coupling to the Yang-Mills term in four-dimensional gauge theory. It is shown that the resulting potential of colour sources consists of a short distance Coulomb interaction and a confining part dominating at large distances. Far away from the source the scalar vanishes while the potential diverges linearly. Up to an -dependent factor of order 1 the tension parameter in the model is gmf, where m denotes the mass of the scalar and f is a coupling scale entering the scalar-gluon coupling. Received: 18 May 1998 / Published online: 26 August 1998     

SUSY Confinement

In response to the present status that searching for SUSY particles has been unsuccessful, we propose a bold scenario that SUSY particles are confined inside hadrons with a required condition of PR = 1 in analog to the color confinement for quarks. The scenario seems to be able to reconcile the beautiful SUSY theory and non-observation at present experiments. On other aspects, some loopholes in the proposal emerge and require to be answered in the future research.     

SUSY Confinement

In response to the present status that searching for SUSY particles has been unsuccessful, we propose a bold scenario that SUSY particles are confined inside hadrons with a required condition of P_R=1 in analog to the color confinement for quarks. The scenario seems to be able to reconcile the beautiful SUSY theory and non-observation at present experiments. On other aspects, some loopholes in the proposal emerge and require to be answered in the future research.     

Local and global algebraic structures in general relativity

The extent to which the well-known pointwise algebraic canonical forms used for the energy-momentum tensor, the Weyl tensor, etc., can be regarded as smooth relations over some open subset of (possibly the whole of) space-time is investigated.