Deformation stability of a flat domain wall in magnetic films

The forces determining the orientation of domain walls in films of magnetooptic materials with a figure of merit of order unity are studied. The behavior of small perturbations of the position of a flat domain wall in the presence of an in-plane component of the anisotropy vector is analyzed. The forces arising when the orientation of the domain wall deviates from the easy-magnetization axis and striving to return the wall to its initial state are conventionally represented as a gradient “effective magnetic field.” The forces exerted by the “effective field, ” due to the in-plane component of the anisotropy vector, on the perturbed domain wall are calculated. The orientational stability conditions for a planar domain wall are found. An explanation is given for the experimentally observed predominant orientation of striped domains. Pis’ma Zh. Tekh. Fiz. 25, 49–56 (September 12, 1999)     

Effect of magnetic anisotropy on the mobility of the boundaries in thin magnetic films

This paper discusses the effect of magnetic crystallographic anisotropy on the mobility of the domain walls in thin magnetic films with an easy axis in the plane of the film. It shows that the stable configuration of a domain wall is a single-vortex Bloch domain wall. Besides this, there are two metastable states of the domain wall—a Néel domain wall and a domain wall with two magnetic vortices along the normal to the plane of the film. It is also shown that the mobilities of the single-vortex and Néel domain walls and the domain wall with two vortices decrease as the anisotropy constant increases and tend to the same value. Pis’ma Zh. Tekh. Fiz. 24, 42–46 (January 26, 1998)     

Formation of an “inverse” kink in optically bistable systems based on increasing absorption

Using the well-known property of the focusing of hollow beams, it is shown that a highabsorption domain can be created in the end of a sample cell. The results can serve as one method of recording information in the interior of a medium. The implementation of such a domain can serve as a new mechanism for developing autowave processes for varying the output intensity of a light beam. Pis’ma Zh. Tekh. Fiz. 23, 69–73 (November 12, 1997)     

Reflection of light by domain walls in the uniaxial ferroelectric Sn2P2S6

The occurrence of light scattering during light transmission is described for some orientations of an incident laser beam in polydomain crystals of the uniaxial ferroelectric tin thiohypodiphosphate. This scattering is probably caused by the presence of a reflecting layer near the 180° domain walls. A reflecting layer may be formed as a result of the appearance of charged nonparallel domain walls. Pis’ma Zh. Tekh. Fiz. 23, 45–50 (August 26, 1997)     

Relation between the domain dynamics and the shape of the cathode “notch” in a Gunn diode

Results are presented of a mathematical modeling of the influence of the shape of the cathode “notch” in the semiconductor structure of a Gunn diode on the characteristics of the domain dynamics. It is shown that processes whereby the domain escapes from the notch into the active region and its leading edge approaches the highly doped region near the anode play a major role in the formation of the second harmonic component in the spectrum of the Gunn diode current. Pis’ma Zh. Tekh. Fiz. 24, 16–22 (November 12, 1998)     

Inverted domains in lithium niobate

The formation of a periodic structure of inverted domains under the simultaneous action of uniform laser irradiation and a standing surface acoustic wave has been investigated. Mechanisms for the formation of an acoustically induced domain structure are discussed. Pis’ma Zh. Tekh. Fiz. 23, 34–38 (November 26, 1997)     

Local polarization reversal of LiNbO3 by scanning the surface perpendicular to the axis of spontaneous polarization with a needle-shaped electrode

The principle of local polarization reversal of ferroelectrics using a moving needle-shaped electrode¹ was used to make a comparative study of the characteristics of polarization reversal of LiNbO₃ from the Z(001) and Y(010) surfaces. In addition to chemical etching, an optical polarization method was used to visualize the domain structure. It was noted that the different dependences of the domain length on the polarizing voltage observed for the different crystal surfaces may be caused by the conducting and polarization properties of the regions in which the domain growth occurs. It is shown that the depth of penetration of the created domains in the sample may be set. Pis’ma Zh. Tekh. Fiz. 24, 52–57 (March 26, 1998)     

Formation of a honeycomb domain structure in magnetic films

An analysis is made of the possible formation of a honeycomb domain structure directly from a labyrinth structure in uniaxial magnetic films exposed to a series of uniform magnetic field pulses. It is shown that the scenario for the formation of a honeycomb structure depends on the pulse parameters and on the magnitude of the static magnetizing magnetic field. Pis’ma Zh. Tekh. Fiz. 23, 46–51 (May 12, 1997)     

Domain instability in an ensemble of dislocations during plastic deformation of crystals

An analysis is made of the nonlinear dynamics of perturbations of the dislocation density and elastic field using a proposed evolution model which takes into account the negative velocity sensitivity of the deforming stresses. As a result of the evolution of domain instability, it is observed that periodic and isolated solutions (solitons) exist for the initial variables. Pis’ma Zh. Tekh. Fiz. 24, 42–48 (April 26, 1998)     

Normal zone and resistive domain in thin-film superconducting bridges: Nonlinearity effects

An investigation was made of the propagation of a normal-state switching wave and the establishment of a resistive domain in thin-film superconducting bridges. It was observed that the nonlinearity of the current-voltage characteristic of the material, using the density of the superconducting condensate as the parameter, strongly influences the characteristics of dissipative structures. Pis’ma Zh. Tekh. Fiz. 24, 1–8 (November 12, 1998)     

Suhl Instability as a Mechanism of the Catastrophic Relaxation in the Superfluid 3He–B

In order to explain catastrophic relaxation, bulk mechanism based on Suhl instability (J. Phys. Chem. Solids 1, 209, 1957) is studied. It is shown, that at sufficiently low temperatures homogeneous precession of spin becomes unstable in the whole region of tipping angles of spin 0≤β≤π. In comparison with the previous publication of Surovtsev and Fomin (J. Exp. Theor. Phys. Lett. 83, 410, 2006) the leading zero temperature increments for the angles θ ₀≃104°≤β≤π are found. Estimation of the temperature of transition to the unstable state for the angle of 105°, that corresponds to the region of tipping angles in homogeneously precessing domain (HPD), is made.     

Exploring the management information systems discipline: a scientometric study of ICIS, PACIS and ASAC

This paper examines the rapid growth of China in the field of nanotechnology and the rise of collaboration between China and the US in this emerging domain. Chinese scientific papers in nanotechnology are analyzed to indicate overall trends, leading fields and the most prolific institutions. Patterns of China–US nanotechnology paper co-authorship are examined over the period 1990–2009, with an analysis of how these patterns have changed over time. The paper combines bibliometric analysis and science mapping. We find rapid development in the number of China–US co-authored nanotechnology papers as well as structural changes in array of collaborative nanotechnology sub-fields. Implications for both China and the US of this evolving relationship are discussed.     

DFT Domain Characterization of Quasi-Cyclic Codes

 The transform domain characterization of linear cyclic codes over finite fields using Discrete Fourier Transform (DFT) over an appropriate extension field is well known. In this paper, we extend this transform domain characterization for linear quasi-cyclic codes over finite fields. We show how one can derive a lower bound on the minimum Hamming distance of a quasi-cyclic code and decode the code upto that minimum Hamming distance using this characterization. Received: January 17, 2002; revised version: November 30, 2002 RID="*" ID="*" This work was partly supported by CSIR, India, through Research Grant (22(0298)/99/EMR-II) to B. S. Rajan Keywords: Quasi-cyclic codes, Discrete Fourier transform, Cyclotomic cosets. Part of this work was presented in ICCCD 2000, Kharagpur, India and ISIT 2001, Washington D.C., USA     

Evolution of deformation domains and kinetics of fatigue fracture of Duralumin polycrystals at the mesoscopic level

Laws governing the buildup of fatigue fracture under cyclic loading of aluminum alloy polycrystals under conditions of multicycle fatigue have been studied by analyzing the spacetime dynamics of mesoscopic structures. It has been shown that under the periodic action of an external mechanical field, deformation domains form in the material at the mesoscopic level. The evolution of these dynamic mesoscopic domain substructures determines the kinetics of the fatigue fracture of the polycrystals. Pis’ma Zh. Tekh. Fiz. 23, 51–57 (December 26, 1997)     

Inhomogeneous deformation of crystalline skeleton of syndiotactic polypropylene under uniaxial stretching

Structure changes of syndiotactic polypropylene (sPP) under uniaxial stretching are studied with the combination of micro-tensile tester and in situ wide angle X-ray diffraction (WAXD) measurement. Lamellae stacked “vertically” and “parallel” to the stretching direction (defined as “V” and “P” part) are separated on the basis of two-dimensional WAXD patterns. For all samples with different lamellar thickness, two critical points named as b ₁ and b ₂ were found in the stress–strain curves, while b ₁ and b ₂ points are the onsets of the rotation for the lamellae of “V” part and “P” part, respectively. The corresponding true stress and true strain for b ₂ point are bigger than that of b ₁ , demonstrating that for samples with initial isotropic lamellar orientation, inhomogeneous deformation of crystalline skeleton induced by uniaxial stretching is universal. And after b ₁ point, “stress-induced melting” always occurs simultaneously with lamellar slips. Furthermore, the relationship between lamellar thickness and the true stress for b ₁ and b ₂ point was also studied, illustrating a linear correlation between ln σ and 1/l (σ is the corresponding true stress, l is the lamellar thickness), consistent with Young’s model. However, the critical true strains for these two points did not change with the varying thickness.     

Specific heat studies in Ho-Ba-CuO superconductors: Fermionic and bosonic contributions

The specific heats of superconducting HoBa₂Cu₃O_7-δ (T _c≅ 92 K) have been theoretically investigated in the temperature domain 70 ≤T ≤110 K. The bosonic (phonons) contribution to the specific heat is estimated from Debye model in the harmonic approximation for high temperature expansion (T > θ_D/2π) using the moments of the phonon density of states. The fermionic constituent as the electronic specific heat is deduced using a suitable trial function above and belowT _c. As a next step the contribution of specific heat by charge oscillations (plasmons) are obtained. The theoretical results from bosonic and fermionic terms are then compared with the experimental results. We find that the specific heats from electronic as well as plasmon term are only a fraction of lattice specific heat and in particular, plasmons do not influence the thermal conduction significantly. The implications of the above analysis are discussed.     

Electrophoretic motion of two solid particles embedded in an unbounded and viscous electrolyte

 This work determines the electrophoretic motion of two colloidal particles embedded in a viscous and unbounded electrolyte. Contrary to other works in the field, the advocated method does not calculate the perturbation electric potential and the electrolyte Stokes flow in the whole fluid domain and its range of applications is not restricted to the case of uniformly charged particles embedded in a uniform electric field E _∞. The idea consists in establishing and solving thirteen Fredholm boundary integral equations (one of the second kind plus twelve of the first kind). The numerical implementation is briefly reported. Numerical benchmarks and new results are both presented and discussed with a special attention to the interactions between the particles. Received 26 February 2001     

Bilateral bounds for the shear and torsion factors: comments on elementary derivations

This paper proposes a new simple derivation of bilateral bounds for the strain energy–based shear and torsion factors, χ _i , of an elastic beam together with some comments about the coherence of the current formulations. A rearrangement of the definition as a mean over the cross-section and an original decomposition of the shear stress in two parts—τ _eqv that is equivalent to the external force and a residual Δτ—allow (i) to interpret (χ − 1) as the mean quadratic deviation of the shear field with respect to the distribution τ _eqv and (ii) to easily evaluate an upper bound, using minimal information about the stress field. In this formulation, the lower bound becomes trivial. Several numerical examples illustrate the accuracy and suitability of the results obtained.     

Effect of paramagnetic manganese ions doping on frequency and high temperature dependence dielectric response of layered Na<Subscript>1·9</Subscript>Li<Subscript>0·1</Subscript>Ti<Subscript>3</Subscript>O<Subscript>7</Subscript> ceramics

The manganese doped layered ceramic samples (Na_1·9Li_0·1)Ti₃O₇ : XMn(0·01 ≤ X ≤ 0·1) have been prepared using high temperature solid state reaction. The room temperature electron paramagnetic resonance (EPR) investigations exhibit that at lower percentage of doping the substitution of manganese ions occur as Mn³⁺ at Ti⁴⁺ sites, whereas for higher percentage of doping Mn²⁺ ions occupy the two different interlayer sodium/lithium sites. In both cases, the charge compensation mechanism should operate to maintain the overall charge neutrality of the lattice. The manganese doped derivatives of layered Na_1·9Li_0·1Ti₃O₇ (SLT) ceramics have been investigated through frequency dependence dielectric spectroscopy in this work. The results indicate that the dielectric losses in these ceramics are the collective contribution of electric conduction, dipole orientation and space charge polarization. Smeared peaks in temperature dependence of permittivity plots suggest diffuse nature of high temperature ferroelectric phase transition. The light manganese doping in SLT enhances the dielectric constant. However, manganese doping decreases dielectric loss due to inhibition of domain wall motion, enhances electron-hopping conduction, and impedes the interlayer ionic conduction as well. Manganese doping also gives rise to contraction of interlayer space.