Dynamic origin of stripe domains

We investigate stripe domain formation in nanometer sized Co bars. The magnetic equilibrium states and the magnetic spin wave frequencies are obtained from micromagnetic-like simulations. We find that the lowest frequency standing-wave mode has the same spatial structure as the stripe domains at remanence and it goes soft at the field where the stripe domains emerge. We show, therefore, that the final domain structure at remanence, which is not the configuration with lowest energy, is predicted from a high-field analysis of the frequencies of the standing spin waves.     

Nodal domain statistics for quantum maps, percolation, and stochastic Loewner evolution

We develop a percolation model for nodal domains in the eigenvectors of quantum chaotic torus maps. Our model follows directly from the assumption that the quantum maps are described by random matrix theory. Its accuracy in predicting statistical properties of the nodal domains is demonstrated for perturbed cat maps and supports the use of percolation theory to describe the wave functions of general Hamiltonian systems. We also demonstrate that the nodal domains of the perturbed cat maps obey the Cardy crossing formula and find evidence that the boundaries of the nodal domains are described by stochastic Loewner evolution with diffusion constant close to the expected value of 6, suggesting that quantum chaotic wave functions may exhibit conformal invariance in the semiclassical limit.     

Generation of light in media with a random distribution of nonlinear domains

We show that the second order nonlinear generation of light, a process that it is assumed to require highly ordered materials, is also possible in structures of randomly oriented nonlinear domains. We explain theoretically why in such disordered structures the efficiency of the nonlinear generation of light grows linearly with the number of domains. Moreover, a higher degree of disorder, obtained when the dispersion is made very large, has no negative effect for the nonlinear light generation. In such conditions, light generation is shown to be equally efficient for any average size of the domains and also to grow linearly with respect to the number of domains.     

Occurrence of rotation domains in heteroepitaxy

Heteroepitaxy can involve materials with a misfit of crystal structure. Rotation domains in the epilayer are a fundamental consequence. We derive a general expression for their (minimum) number which is determined by the mismatch of the rotational symmetries of the substrate and epilayer. In the case of a mismatch of rotational symmetry, the number of rotation domains of material A on material B is different from that of B on A. A larger number of rotation domains can occur due to domain structure or nearly fulfilled additional symmetries of the substrate surface.     

Analysis of the domain wall structures of the three kinds of hard domains in garnet bubble films

It was found experimentally that dumbbell domains of the second kind produced at high temperature can convert to dumbbell domains of the first kind at low temperature. And the ordinary hard bubbles produced at low temperature can convert to dumbbell domains of the first kind at high temperature. So we conclude that the domain wall structures of the three kinds of hard domains are the same. We also observe that the equilibrium separation between two neighboring vertical-Bloch lines is widened with the increasing temperature when the hard domains collapse under the effect of bias field.     

Influence of antiphase domain boundaries on the formation of magnetic order in alloys

We consider the influence of boundaries between structural domains on the atomic and magnetic order in substitutional binary alloys. We calculate the variation of the composition at antiphase boundaries. We show that when the magnetic phase transition temperature of the alloy is below the Kurnakov point, the development of magnetic order at the boundaries may begin at higher temperatures than within the domains. It is then possible that the type of magnetic order at the boundaries may change (ferromagnetic into antiferromagnetic, or vice-versa) when magnetic order appears within the domains.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 13–17, August, 1991.     

Tensor distinction of domains in ferroic crystals

Ferroic crystals contain two or more domains and may be distinguished by the values of components of tensorial physical properties of the domains. We have extended Aizu’s global tensor distinction by magnetization, polarization, and strain of all domains which arise in a ferroic phase transition to include distinction by toroidal moment, and from phases invariant under time reversal to domains which arise in transitions from all magnetic and non-magnetic phases. For determining possible switching of domains, a domain pair tensor distinction is also considered for all pairs of domains which arise in each ferroic phase transition.     

Cosmological baryon-number domain structure and the first order phase transition of a vacuum

If CP-nonconservation arises from spontaneous symmetry breaking in the very early universe, the universe will have a domain structure of baryon number. We propose a model of the early universe in which domains are stretched exponentially and the radius of the domains is much greater than that of the horizon of the standard big bang model, provided that the grand unified theory undergoes a first order phase transition. If the size of the stretched domains is sufficiently big to avoid pair annihilations of baryon and antibaryon domains, the difficulties of the baryon symmetric universe may be removed.     

Weakly nonlinear theory of grain boundary motion in patterns with crystalline symmetry

We study the motion of a grain boundary separating two otherwise stationary domains of hexagonal symmetry. Starting from an order parameter equation, a multiple scale analysis leads to an analytical equation of motion for the boundary that shares many properties with that of a crystalline solid. We find that defect motion is generically opposed by a pinning force that arises from nonadiabatic corrections to the standard amplitude equations. The magnitude of this force depends sharply on the misorientation angle between adjacent domains: the most easily pinned grain boundaries are those with a low angle (typically 4 degrees < or =theta;< or =8 degrees ). Although pinning effects may be small, they can be orders of magnitude larger than those present in smectic phases.     

Surface structural evolution during the thermal decomposition of a PdO(101) thin film

We used scanning tunneling microscopy (STM) to characterize PdO(101) thin films grown on Pd(111), and the structural changes that occur during isothermal decomposition. We find that the PdO(101) thin films have high-quality surface structures that are characterized by large, crystalline terraces with low concentrations of point defects. Small domains of single-layer oxide are also present on the top layer of relatively thick PdO(101) films grown at 500 K. The thinner PdO(101) films exhibit negligible quantities of such domains, apparently because new domains agglomerate rapidly as the film thickness decreases. We find that the isothermal decomposition rate of a PdO(101) film at 720 K exhibits an autocatalytic regime in which the rate of oxygen desorption increases as the oxide decomposes. Our STM results demonstrate that reduced sites created during oxide decomposition catalyze further PdO decomposition, and reveal strong kinetic anisotropies in the decomposition. The kinetic anisotropies produce one-dimensional reaction fronts that propagate preferentially along the atomic rows of the PdO(101) surface, resulting in the formation of long chains of reduced sites. We also find that reduced sites promote oxygen recombination in neighboring rows of the Pd(101) structure, causing loops and larger aggregates of reduced sites to form. The promotion of decomposition across the atomic rows can qualitatively explain the autocatalytic desorption kinetics. Finally, the STM images provide evidence that underlying PdO(101) layers transfer oxygen to reduced surface domains, thus producing large domains of PdO(101) islands that coexist with reduced domains as well as the larger PdO(101) terraces of the initial surface. Re-oxidation of the surface acts to sustain the autocatalytic decomposition kinetics, and provides a mechanism for oxygen atoms to ultimately evolve from the subsurface of the PdO(101) film.     

Observation of nanoscale 180 degrees stripe domains in ferroelectric PbTiO3 thin films

We report the observation of periodic 180 degrees stripe domains below the ferroelectric transition in thin films. Epitaxial PbTiO3 films of thickness d=1.6 to 42 nm on SrTiO3 substrates were studied using x-ray scattering. Upon cooling below T(C), satellites appeared around Bragg peaks indicating the presence of 180 degrees stripe domains of period Lambda=3.7 to 24 nm. The dependence of Lambda on d agrees well with theory including epitaxial strain effects, while the suppression of T(C) for thinner films is significantly larger than that expected solely from stripe domains.     

Spontaneous domain switching during phase separation of Pb on Ge(111)

Using low-energy electron microscopy (LEEM), we have discovered a novel phase separation mechanism for Pb on Ge(111). When the low Pb coverage (1 x 1) phase coexists with the high coverage beta phase, the surface consists of approximately 100 nm sized domains that spontaneously switch from one phase to the other. We argue this striking mechanism occurs because nanometer-scale domains can have density fluctuations comparable to the density difference between the two phases.     

Thermally labile domains in the collagen molecule

We have proposed that the denaturation kinetics of the characteristic sharp melting point of the collagen molecules is an irreversible rate rather than an equilibrium process as previously believed. This leads to the concept of domains of variable thermal stability along the length of the molecule. We have identified the major thermally labile domains from which the denaturation process is initiated as hydroxyproline deficient sequences of 65, 65 and 59 residues near the carboxy terminus in fibrillar collagen types I, II and III, respectively. These domains differ in that there is a single hydroxyproline in the type II domain and two hydroxyprolines in the type III domain. Similar sized domains are conserved in these collagen types across species including amphibians and invertebrates. The effective size of the domain is reduced in the fibrillar aggregates to 26 residues due to the interaction with adjacent molecules and because of the precise quarter-staggered alignment of the molecules the domains are located in the gap region. This spatial confinement within the lattice of the fibre leads to the significant increase in denaturation temperature of the fibre compared to the molecule. These labile domains have also been located in molecules that form the non-fibrillar type IV basement membrane collagens and the fibril-associated aggregates such as type IX. Based on the location of the different domains in type IX we have proposed a different arrangement of the type IX on the type II fibril.The model stresses the importance of hydroxyproline in stabilising the triple helix and supports the concept of hydrogen-bonded water-bridges originally proposed from X-ray diffraction studies in contrast to other studies indicating water-bridges do not play a role in stabilising the collagen molecule.     

脉冲偏场作用下石榴石磁泡薄膜中布洛赫线的形成

实验研究了石榴石磁泡薄膜中不同脉冲宽度下产生的硬磁畴的动态特性.结果表明：由零偏场下产生的枝状畴收缩而成的哑铃畴均逆时针转动,与产生枝状畴时所用的脉冲偏场的脉冲宽度无关.而固定直流偏场下由软畴段硬化而成的哑铃畴的转动状态,则与所用的硬化脉冲偏场的脉冲宽度有关.低脉冲宽度下硬化成的哑铃畴均逆时针转动,随硬化脉冲宽度的升高,出现混合转动向顺时针转动的过渡.由此揭示了直流偏场和脉冲偏场在石榴石磁泡薄膜中形成正、负垂直布洛赫线的作用. 关键词： 磁畴 磁泡 垂直布洛赫线     

聚片多畴LiNbO3晶体的倍频效应

通过对聚片多畴LiNbO₃晶体倍频效应的研究,从实验上对Bloembergen等人所提出的准位相匹配理论进行了细致的检验。首先运用Maker条纹法在实验上直接测定了单畴LiNbO₃晶体在e^ω·e^ω→e^2ω非位相匹配下的倍频光强,并采用角度扫描和温度扫描方法,以获得满足准位相匹配条件时的不同片数的聚片多畴晶体的最大倍频强度,从而验证了聚片多畴晶体倍频相对光强与片畴数N成平方关系。在N<200时,取得 关键词：     

Metastability in 2D self-assembling systems

We show that 2D self-assembled domains can remain trapped in a large variety of long-lived and metastable shapes that arise from an interplay of crystalline anisotropy and relaxation of elastic strain. On commonly used cubic (111) substrates, these shapes include extended or stacked structures made up of triangular domains connected at their corners, compact shapes with both convex and concave curvatures and others with narrow and elongated arms. We show that all of these distinct experimentally observed shapes can be explained within a unified framework and present a phase diagram that systematically classifies the metastable shapes as a function of their size.     

Microscopic imaging of Fe magnetic domains exchange coupled with those in a NiO(001) surface

We revealed the micromagnetic structure of an Fe thin film exchange interacting with the spins of a fully compensated (001) surface of antiferromagnetic NiO. The interface exchange interaction causes the Fe domains to follow the NiO domains. The Fe spin polarization is in plane and the spin polarization in each domain is roughly perpendicular to an easy-spin axis of the NiO. These results agree with numerically calculated spin directions. Our numerical results also show that the NiO spins at the interface cant from the easy-spin axis towards the Fe spin because of exchange coupling.     

Reconstructed domains on a stepped W(100) surface

A model calculation is carried out for the scattering of low energy electron diffraction from reconstructed (√2 × √2)R45° domains on a stepped W(100) surface. The existence of monotonically increasing steps causes the integral order beams to split and the separation of the splitting oscillates with the incident electron energy. We show that due to the existence of an antiphase relationship among the randomly nucleated reconstructed domains, the half-order beams neither split nor oscillate with the incident electron energy. This nonsplitting of half order beams is in agreement with the observation by Debe and King (DK). We also show that the measured intensity profile of a half order beam is equal to the signal intensity profile from the individual finite size domains convoluted with the instrument response function. This gives a simple way to evaluate the reconstructed domain size quantitatively. From the angular distribution of the half-order beam intensity we deduce that the reconstructed domains are somewhat round in shape, instead of the “long strips” proposed by DK. Also, the long range inhibition (20 Å) of the reconstruction near the step edge suggested by DK does not necessarily follow from our analysis. As a matter of fact, there is evidence showing that the inhibition (if it exists at all) can be short range in nature. Our suggestion is in agreement with the observation of the reconstructed W(100) surface by Melmed, Tung, Graham and Smith using FIM technique.     

Binding properties of SH3 peptide ligands identified from phage-displayed random peptide libraries

Summary Combinatorial libraries have yielded high-affinity ligands for SH3 domains of a number of different proteins. We have shown that synthetic peptides containing these SH3 ligand sequences serve as specific probes of SH3 domains. Direct binding of the N-terminal biotinylated peptide ligands was conveniently detected in ELISA, filter-blotting, and dot-blotting experiments with the use of streptavidin-conjugated enzymes. In some cases, detection of peptide-SH3 interactions required that the biotinylated peptides first were preconjugated with streptavidin to form a multivalent complex. Interestingly, these nominally tetravalent SH3 peptide ligands cross-react to varying degrees with different SH3 domains. We have used such complexes to screen cDNA expression libraries and have isolated clones that encode both known and novel SH3-domain-containing proteins. Based on the success of this methodology, we propose a general strategy by which ligands of a modular domain-containing protein can be isolated from random peptide libraries and used to screen cDNA expression libraries systematically for novel modular domain-containing proteins.     

Morphological phase diagram for lipid membrane domains with entropic tension

Circular domains in phase-separated lipid vesicles with symmetric leaflet composition commonly exhibit three stable morphologies: flat, dimpled, and budded. However, stable dimples (i.e., partially budded domains) present a puzzle since simple elastic theories of domain shape predict that only flat and spherical budded domains are mechanically stable in the absence of spontaneous curvature. We argue that this inconsistency arises from the failure of the constant surface tension ensemble to properly account for the effect of entropic bending fluctuations. Formulating membrane elasticity within an entropic tension ensemble, wherein tension represents the free energy cost of extracting membrane area from thermal bending of the membrane, we calculate a morphological phase diagram that contains regions of mechanical stability for each of the flat, dimpled, and budded domain morphologies.