Compact Direction Research Articles

Formula omitted] type IIA brane configurations, chirality and T-duality

We consider four-dimensional N=1 field theories realized by type IIA brane configurations of NS-branes and D4-branes, in the presence of orientifold six-planes and D6-branes. These configurations are known to present interesting effects associated to the appearance of chiral symmetries and chiral matter in the four-dimensional field theory. We focus on models with one compact direction (elliptic models) and show that, under T-duality, the configurations are mapped to a set of type IIB D3-branes probing N=1 orientifolds of C 2/ Z N singularities. We explicitly construct these orientifolds, and show the field theories on the D3-brane probes indeed reproduce the field theories constructed using the IIA brane configurations. This T-duality map allows us to understand the type IIB realization of several exotic brane dynamics effects on the type IIA side: Flavor doubling, the splitting of D6-branes and O6-planes in crossing an NS-brane and the effect of a non-zero type IIA cosmological constant turn out to have surprisingly standard type IIB counterparts.

Supersymmetric 4D orientifolds of Type IIA with D6-branes at angles

We study a certain class of four-dimensional N=1 supersymmetric orientifolds for which the world-sheet parity transformation is combined with a complex conjugation in the compact directions. We investigate in detail the orientifolds of the Z_3, Z_4, Z_6 and Z_6' toroidal orbifolds finding solutions to the tadpole cancellation conditions for all models. Generically, all the massless spectra turn out to be non-chiral.

Branes, geometry and N = 1 duality with product gauge groups of SO and Sp

We study N = 1 dualities in four-dimensional supersymmetric gauge theories as the world volume theory of D4 branes with one compact direction in type IIA string theory. We generalize the previous work for SO( N c1 ) × Sp( N c2 ) with the superpotential W = Tr X 4 to the case of W = Tr X 4( k+1) in terms of brane configuration. We conjecture that the new dualities for the product gauge groups of SO( N c1 ) × Sp( N c2 ) × SO( N c3 ), SO( N c1 ) × Sp( N c2 ) × SO( N c3 ) × Sp( N c4 ) and higher multiple product gauge groups can be obtained by reversing the ordering of NS5 branes and D6 branes while preserving the linking numbers. We also describe the above dualities in terms of wrapping D6 branes around 3-cycles of Calabi-Yau threefolds in type IIA string theory. The theory with adjoint matter can be regarded as taking multiple copies of NS5 brane in the configuration of brane or geometric approaches.

A Finite‐Element Approach for the Shape Prediction of Ceramic Compacts during Sintering

This paper describes and demonstrates the effectiveness of a finite‐element procedure to predict the shape changes of “green powder compacts” during sintering processes. The approach is based on the conservation‐of‐mass principle and requires for its implementation (i) descriptions of the finite‐element meshes of the original form (powder bed) and the green bodies when ejected from the die (thus, de‐scriptions of the geometries of the compact before and after the compaction process) and (ii) the densities of the com‐pacts before the compaction and after the sintering pro‐cesses. Numerical shape predictions have been compared with experimental data, for all the external surfaces that are obtained from sintered, cylindrical alumina specimens. The overall predicted diametric dimensional‐variation changes correlate with the corresponding measured data; both indicate a “barrel” shape. The comparisons reveal that the quantitative predictions in regard to the height and diameter range correlate closely with the measured values; the differences are <1.6% and 0.4%–0.08%, respectively. The overall predicted deviation changes of the end surfaces of the sintered compacts correlate with the corresponding measured data; both indicate a “concave” shape, with ref‐erence to the horizontal plane, as viewed from the compac‐tion direction. The quantitative shape comparisons for the top and bottom surfaces are <18.9% and <65.84%, respec‐tively. The qualitative predictions at the top and bottom surfaces are considered to be in good agreement, for most practical purposes.

Simulation of threshold displacements in NiAl

Modified many-body interatomic potentials for modeling high-energy atomic collision in NiAl are constructed and described. The displacement threshold energy as a function of the primary recoil direction for Ni atoms and Al atoms in NiAl has been investigated by molecular dynamics simulations using the modified potentials. The defect structure induced by recoil events has been presented. The results show that the lowest threshold displacement energy, E d, is near the 〈1 0 0〉 orientation and the mean value of E d for an Al atom is higher than a Ni. A crowdion in the compact crystalline directions, 〈1 1 1〉, incorporating an extra Ni atom is the stable interstitial configuration.

Open and closed supermembranes with winding

Motivated by manifest Lorentz symmetry and a well-defined large- N limit prescription, we study the supersymmetric quantum mechanics proposed as a model for the collective dynamics of D0-branes from the point of view of the 11-dimensional supermembrane. We argue that the continuity of the spectrum persists irrespective of the presence of winding around compact target-space directions and discuss the central charges in the super-algebra arising from winding membrane configurations. Along the way we comment on the structure of open supermembranes.

Emission rates, the correspondence principle and the information paradox

When we vary the moduli of a compactification it may become entropically favourable at some point for a state of branes and strings to rearrange itself into a new configuration. We observe that for the elementary string with two large charges such a rearrangement happens at the ‘correspondence point’ where the string becomes a black hole. For smaller couplings it is entropically favourable for the excitations to be vibrations of the string, while for larger couplings the favoured excitations are pairs of solitonic 5-branes attached to the string; this helps resolve some recently noted difficulties with matching emission properties of the string to emission properties of the black hole. We also examine the change of state when a black hole is placed in a space-time with an additional compact direction, and the size of this direction is varied. These studies suggest a mechanism that might help resolve the information paradox.

On membrane interaction in Matrix theory

We compute the interaction potential between two parallel transversely boosted wrapped membranes (with fixed momentum p −) in D = 11 supergravity with compact light-like direction. We show that the supergravity result is in exact agreement with the potential following from the all-order Born-Infeld-type action conjectured to be the leading planar infra-red part of the quantum super Yang-Mills effective action. This provides a non-trivial test of consistency of the arguments relating Matrix theory to a special limit of type II string theory. We also find the potential between two (2+0) D-brane bound states in D = 10 supergravity (corresponding to the case of boosted membrane configuration in 11-dimensional theory compactified on a space-like direction). We demonstrate that the result reduces to the SYM expression for the potential in the special low-energy ( α′ → 0) limit, in agreement with previous suggestions. In an appendix we derive the action obtained from the D = 11 membrane action by the world-volume duality transformation of the light-like coordinate x − into a 3-vector.

SUSY field theories in higher dimensions and integrable spin chains

Five- and six-dimensional SUSY gauge theories, with one or two compactified directions, are discussed. The 5d theories with the matter hypermultiplets in the fundamental representation are associated with the twisted XXZ spin chain, while the group product case with bi-fundamental matter corresponds to the higher rank spin chains. The Riemann surfaces for 6d theories with fundamental matter and two compact directions are proposed to correspond to the XYZ spin chain based on the Sklyanin algebra. We also discuss the obtained results within the brane and geometrical engineering frameworks and explain the relation to the toric diagrams.

Supermembranes with winding

We study supermembranes in the light-cone gauge in eleven flat dimensions with compact directions. The membrane states are subject to only the central charges associated with closed two-branes, which, in this case, are generated by the winding itself. We present arguments why this winding leaves the mass spectrum continuous. The lower bound on the mass spectrum is set by the winding number and corresponds to a BPS state.

Theory and technology of article forming features of the density distribution with axial compression of porous articles bounded by compaction surfaces inclined towards the compaction direction. Numerical analysis

The stressed state of porous preforms that have surfaces inclined towards the compaction axis is considered. Relationships from plasticity theory for a porous body are used. Solutions of the corresponding boundary-value problem are effected using the finite element method. The moulding of powder preforms whose initial properties are not distributed uniformly is studied on the example of two-layer preforms. It is assumed that the interface is parallel to the top and bottom punch surfaces. Compaction of the less strong layer occurs more intensely. The interface moves towards the less strong layer during forming.

Erratum: Solitonic strings and BPS saturated dyonic black holes [Phys. Rev. D53, 5619 (1996)

We consider a six-dimensional solitonic string solution described by a conformal chiral null model with non-trivial $N=4$ superconformal transverse part. It can be interpreted as a five-dimensional dyonic solitonic string wound around a compact fifth dimension. The conformal model is regular with the short-distance (`throat') region equivalent to a WZW theory. At distances larger than the compactification scale the solitonic string reduces to a dyonic static spherically-symmetric black hole of toroidally compactified heterotic string. The new four-dimensional solution is parameterised by five charges, saturates the Bogomol'nyi bound and has nontrivial dilaton-axion field and moduli fields of two-torus. When acted by combined T- and S-duality transformations it serves as a generating solution for all the static spherically-symmetric BPS-saturated configurations of the low-energy heterotic string theory compactified on six-torus. Solutions with regular horizons have the global space-time structure of extreme Reissner-Nordstrom black holes with the non-zero thermodynamic entropy which depends only on conserved (quantised) charge vectors. The independence of the thermodynamic entropy on moduli and axion-dilaton couplings strongly suggests that it should have a microscopic interpretation as counting degeneracy of underlying string configurations. This interpretation is supported by arguments based on the corresponding six-dimensional conformal field theory. The expression for the level of the WZW theory describing the throat region implies a renormalisation of the string tension by a product of magnetic charges, thus relating the entropy and the number of oscillations of the solitonic string in compact directions.

D-brane field theory on compact spaces

A low-energy field theory is constructed for Dirichlet p-branes in type II string theory on a space which has been toroidally compactified in d transverse dimensions. This field theory is found by taking a Z d quotient of a theory describing a countably infinite set of branes on the covering space. In accordance with T-duality, the resulting theory is equivalent to the gauge theory for the dual system of ( d + p)-branes wrapped around the compact directions.

Solitonic strings and BPS saturated dyonic black holes.

We consider a six-dimensional solitonic string solution described by a conformal chiral null model with nontrivial $N=4$ superconformal transverse part. It can be interpreted as a five-dimensional dyonic solitonic string wound around a compact fifth dimension. The conformal model is regular with the short-distance (throat) region equivalent to a Wess-Zumino-Witten (WZW) theory. At distances larger than the compactification scale the solitonic string reduces to a dyonic static spherically symmetric black hole of toroidally compactified heterotic string. The new four-dimensional solution is parametrized by five charges, saturates the Bogomol'nyi bound, and has a nontrivial dilaton-axion field and moduli fields of a two-torus. When acted on by combined $T$- and $S$-duality transformations it serves as a generating solution for all the static spherically symmetric Bogomol'nyi-Prasad-Sommerfield saturated configurations of the low-energy heterotic string theory compactified on a six-torus. Solutions with regular horizons have the global space-time structure of extreme Reissner-Nordstr\om black holes with the non-zero thermodynamic entropy which depends only on conserved (quantized) charge vectors. The independence of the thermodynamic entropy on moduli and axion-dilaton couplings strongly suggests that it should have a microscopic interpretation as counting degeneracy of underlying string configurations. This interpretation is supported by arguments based on the corresponding six-dimensional conformal field theory. The expression for the level of the WZW theory describing the throat region implies a renormalization of the string tension by a product of magnetic charges, thus relating the entropy and the number of oscillations of the solitonic string in compact directions.

Nonunique Dynamic Equilibrium Constitutive Relation of Metal Powder Depending on its Microstructure

It was observed in an earlier work by Morimoto et al. [Inst. Phys. Conf. Ser. No. 70, Oxford 1984, p. 427] that the dynamic compact of an aluminium powder medium had greater flakiness and contiguity ratio than the static compact of the same density. This observed difference in micro structure is used to explain their result that the dynamic pressure of the medium is higher than the static pressure for a given density: the degree of rotation of particles during compaction is assumed to decrease for higher strain rates, because of the shorter time available, causing an increase in plastic particle deformation in the compaction direction, and increased resistance to the compaction. The normal Hugoniot equation derived, in which the mean strain rate averaged over a single steady wavefront is introduced, indicates that a rise of the normal Hugoniot with an increase in the strain rate results macroscopically from the increase in the propagation velocity of the wavefront. The multiwave Hugoniot equation is found to depend on the strain rate history of a given material. In compactions of a metal powder medium by punch impact, the wavefronts passing through the medium are approximately steady if the punch mass is sufficiently larger than the medium mass. But both the number of wavefronts arising during the compaction and the amplitudes of the strain waves, and hence the strain rate histories, vary with compaction conditions such as punch mass and initial punch velocity. This implies that a dynamic equilibrium constitutive relation for the medium will depend on the compaction conditions, and therefore cannot be determined uniquely for any two compactions.

Constant magnetic field in closed string theory: An exactly solvable model

We consider a simple model describing a closed bosonic string in a constant magnetic field. Exact conformal invariance demands also the presence of a non-trivial metric and antisymmetric tensor (induced by the magnetic field). The model is invariant under target space duality in a compact Kaluza-Klein direction introduced to couple the magnetic field. Like open string theory in a constant gauge field, or closed string theory on a torus, this model can be straightforwardly quantised and solved with its spectrum of states and partition function explicitly computed. Above some critical value of the magnetic field an infinite number of states become tachyonic, suggesting a presence of phase transition. We also construct heterotic string generalisations of this bosonic model in which the constant magnetic field is embedded either in the Kaluza-Klein or internal gauge group sector.

粒子モデルによる圧粉成形時の粒子配向と圧粉体の磁気特性

Permanent magnet is made of ferromagnetic powders by compaction in a magnetic field. The magnetic powder has an anisotropic property in magnetization. The magnetic axis of each particle is forced to be oriented in the direction of magnetization. However, the axis of magnetization is also rotated by a series of mechanical forces under compaction. To control the characteristics of permanent magnet for electronic devices, it is of great importance to understand the movement of the magnetic particles during compaction in the magnetic field. This paper presents how the easy direction of magnetization is aligned in the magnetic field during three methods of compaction; compaction where the compacting direction is either perpendicular or parallel, and isostatic. It is thus shown that the magnetic characteristics of the compact are dependent on the direction of compaction to the applied magnetic field. The calculated results of the magnetic characteristics of the compact are also shown.

Remote sensing of ocean surface currents with the Seasonde HF radar

The SeaSonde high-frequency radar is a portable, shore-based system for measuring ocean surface currents in real time over coverage areas exceeding 1000 km 2. It utilizes compact antennas and direction finding methods to extract information on currents from the sea echo signals. Experiments with the radar in sheltered coastal waters in Canada and oceanic conditions in the Pacific Ocean have shown reasonable agreement with drifters and current meters. Forecasting methods have been developed that provide estimates of the slowly varying flows produced by tide, wind and buoyancy, and estimates of the spatially varying eddy diffusivity, based on a few days of measurements. These current data are suitable for use in oil spill models.

Air‐Permeability Measurement for Soil at Low and High Pressure

Specimens of a clayey sand, compacted on the dry side of the optimum water content, have been tested for air permeability using a triaxial cell and mass flowmeter. The existence of noninertial flow (linear flow versus gradient relationship) was confirmed by performing air-flow tests with increasing driving pressures. Threshold gradients and regions of nonlinear response were observed in several of the compacted specimens. The measurement of anisotropy with respect to air permeability was performed on the clayey sand specimens. The ratios between air permeabilities of specimens obtained from samples extracted 0° and 90° with respect to the direction of compaction revealed an order of magnitude difference in permeabilities. As a basis of comparison, high-permeability, dry-cohesionless sand samples were also tested in a modified version of the system under much lower driving pressures. Permeabilities were consistent with previously published results. Compacted samples also produced permeability results consistent with the trends of previously published measurements, but the tests described in this study were performed at significantly higher pressure gradients.

Scattering of macroscopic heterotic strings

We show that macroscopic heterotic strings, formulated as strings which wind around a compact direction of finite but macroscopic extent, exhibit non-trivial scattering at low energies. This occurs at order velocity squared and may thus be described as geodesic motion on a moduli space with a non-trivial metric which we construct. Our result is in agreement with a direct calculation of the string scattering amplitude.