Segmental order and dynamics of polymer chains confined in block copolymer lamellar mesophases: NMR and dielectric relaxation studies

The European Physical Journal E - The PDMS lamellar sublayers of a poly(styrene)-poly(dimethylsiloxane) diblock (PS-PDMS) and PS-PDMS-PS triblocks are investigated by NMR and dielectric...     

Segmental order and dynamics of polymer chains confined in block copolymer lamellar mesophases: NMR and dielectric relaxation studies

The PDMS lamellar sublayers of a poly(styrene)-poly(dimethylsiloxane) diblock (PS-PDMS) and PS-PDMS-PS triblocks are investigated by NMR and dielectric spectroscopy. Some segments of the confined PDMS chains display anisotropic orientational fluctuations along the interfaces with the PS glassy blocks, whereas the others display fluctuations rather parallel to the lamellae normal. This coexistence results from a competitive ordering effect induced by the glassy interfaces and the chain-end anchoring junctions. The distribution of PDMS relaxation times within the sublayers is also examined: in particular, a slowing down of the segmental motions, together with a broadening of this distribution, are detected.     

Molecular theoretic study of Freedericksz transition. Symmetry breaking of oblique axial order

Freedericksz transition, which is usually analyzed by an elastic theory, is studied on the basis of statistical mechanical ground, where nematics with positive dielectric anisotropy in homogeneous anchoring cell is exposed to an electric field in the direction of wall normal. In low temperature region, an oblique axial symmetry breaking occurs, which is nothing but the Freedericksz transition. In high temperature and high field region, biaxial nematic phase with principal axis parallel to the field direction at interior area of the system is proved to appear. A phase diagram on the field versus temperature plane is obtained and compared with the one at a bulk with common biaxial symmetry, where both of electric and magnetic fields are applied in directions perpendicular to each other. In the latter, no symmetry breaking occurs, in contrast with the former case above-mentioned, and the reason why this difference occurs is elucidated.     

Symmetry breaking in superdense matter

A gauge theory for superdense matter is considered. It is shown that in the mean-field approximation at T = 0 °K the symmetry breaking increases with increasing density. The state of dense matter and the early Universe are shortly discussed.     

Symmetry breaking in Heisenberg antiferromagnets

We extend Griffith's theorem on symmetry breaking in quantum spin systems to the situation where the order operator and the Hamiltonian do not commute with each other. The theorem establishes that the existence of a long range order in a symmetric (non-pure) infinite-volume state implies the existence of a symmetry breaking in the state obtained by applying an infinitesimal symmetry-breaking field. The theorem is most meaningful when applied to a class of quantum antiferromagnets where the existence of a long range order has been proved by the Dyson-Lieb-Simon method. We also present a related theorem for the ground states. It is an improvement of the theorem by Kaplan, Horsch and von der Linden. Our lower bounds on the spontaneous staggered magnetization in terms of the long range order parameter take into account the symmetry of the system properly, and are likely to be saturated in general models.     

Symmetry breaking in orbifold models

Gauge symmetry breaking to some physically interesting gauge groups is studied in the context of symmetric orbifolds.     

Symmetry breaking in dynamical spacetimes

The behaviour of scalar electrodynamics under symmetry breaking by the Higgs mechanism is studied in a class of dynamical spacetimes—those having a Bianchi type I symmetry—which includes the spatially flat Robertson-Walker spacetimes. The Einstein equations are used to obtain the effective Lagrangian, from which it is shown thateither the gauge field does not become massive during symmetry breaking (in marked contrast with the case in which the background spacetime is static),or the symmetry breaking chooses not only a direction in the phase space of the Higgs field, but also a spatial direction in the spacetime sections.     

Symmetry breaking in τ decay

In view of the recent attempts to detect theG-parity violating decay τ→πηv _τ which may have bearing on the presence of the second class current, we discuss the isospin symmetry breaking effects in the processes of τ→δv, Bv, and ηπv from a dynamical point of view. It is shown that all the symmetry breaking effects are proportional to theu?d quark mass difference. Depending on whether the current or the constituent quark masses are used, the decay τ→πηv _τ via δ is either of the same order or three orders of magnitude smaller than the upper limit set by the latest experiments. This is in agreement with the other theoretical estimates.     

Symmetry breaking breaks friction

The harmonic analysis of the symmetry breaking is used to study the interaction and inter-layer motion of double-wall carbon nanotubes shells. The tremendous total symmetry reduction with respect to the high symmetry of the isolated layers results in low interaction: its decreasing with the symmetry breaking rate explains the observed small friction.     

Symmetry breaking for theBBP-couplings

The B-A system of CP molecule has been reinvestigated. The rotational structures in the (0, 0) and (1, 1) bands have been photographed in the second order of a 10.6 m grating with 25μ slit width. The molecular constants have been determined using a weighted least squares fit computer program. It is found that the spin-splitting constant in the B-state is negative and not positive as reported by previous workers. An accurate value ofα in the A-state could be determined. The present analysis also suggests that the spin-splitting constant in the ground state of CP should be positive, hence the assignment of theR ₁ andR ₂ orP ₁ andP ₂ branches in the B-X system of CP by Barwaldet al should be interchanged.     

Symmetry breaking by instantons in supergravity

The non-zero modes of different spin operators on the background of a self-dual gravitational instanton are all related by global supersymmetry transformations and completely cancel in the one-loop term, which is determined entirely by the zero modes. We derive the number of zero modes of each spin. In an asymptotically locally Euclidean self-dual instanton there are 2τ $\text{spin}\text{-}\text{3}\text{2}$ zero modes and 3τ spin-2 zero modes, where τ is the Hirzebruch signature. Up to 3 of the spin-2 zero modes (depending on boundary conditions) may correspond to global rotations. The $\text{spin}\text{-}\text{3}\text{2}$ zero modes break the U(1) chiral symmetry and give rise to helicity-changing amplitudes. Together with the spin-2 zero modes they determine the trace anomaly or scaling behaviour. We can compare our results with the perturbation theory predictions for the axial vector current and trace anomalies in K3, the unique compact self-dual gravitational instanton, because in this case there are no boundary terms. We obtain agreement.     

Symmetry breaking in honeycomb photonic lattices

We study the phenomena associated with symmetry breaking in honeycomb photonic lattices. As the honeycomb structure is gradually deformed, conical diffraction around its diabolic points becomes elliptic and eventually no longer occurs. As the deformation is further increased, a gap opens between the first two bands, and the lattice can support a gap soliton. The existence of the gap soliton serves as a means to detect the symmetry breaking and provide an estimate of the size of the gap.     

Symmetry breaking in boron nitride nanotubes

We have imaged boron nitride nanotubes with atomic scale resolution using scanning tunneling microscopy. While some nanotubes show the expected triangular lattice pattern, the majority of the nanotubes show unusual stripe patterns which break the underlying symmetry of the boron nitride lattice. We identify the origin of the symmetry breaking and demonstrate that conventional STM imaging analysis is inadequate for boron nitride nanotubes.     

Symmetry breaking in quantum chaotic systems

We show, using semiclassical methods, that as a symmetry is broken, the transition between universality classes for the spectral correlations of quantum chaotic systems is governed by the same parametrization as in the theory of random matrices. The theory is quantitatively verified for the kicked rotor quantum map. We also provide an explicit substantiation of the random matrix hypothesis, namely that in the symmetry-adapted basis the symmetry-violating operator is random.     

Symmetry breaking patterns in superfluid He

By means of the time reversal operator a general form of the Landau free energy functional of superfluid ³He is investigated. Various possible phase diagrams of superfluid ³He in a magnetic field are discussed in the context of group theory. Both the cases of neglible and strong spin-orbit coupling are treated.     

Symmetry breaking and gravitational interaction

A scalar field Lagrangian is considered in the curved space-time to which a Hamiltonian determining nonzero vacuum field value is added. The initial Lagrangian can be expressed as a sum of Lagrangians for the constant scalar field component and perturbation. The first Lagrangian can be considered as a Lagrangian for the Einstein gravitational field in vacuum. The problem of renormalization of the constant scalar field component is investigated. It is demonstrated that in the case of conformal relation of the scalar field to the space-time curvature, there exists a unique value of the scalar space curvature for which the field can be considered constant (field perturbations do not result in renormalization of the constant component). This curvature value determines the unique value of the equilibrium nuclide density. A correlation of the examined Lagrangian parameters with the integral parameters of the Solar system is discussed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 18–34, July, 2006.     

Symmetry breaking and measurement theory

For studying the problem of measurement we accept the statistical interpretation of quantum mechanics, but we take into account, that in a sequence of measurements, offdiagonal terms arise which cannot obviously be interpreted as the probability of a sequence of macroscopic events. We demonstrate, however, their vanishing for ordinary measurement processes by observing that the measurement apparatus undergoes a symmetry breaking transition during the measurement.1. On leave from the Central Research Institute for Physics, Budapest, Hungary.