Table of contents

We treat the horizons of charged, dilaton black extended objects as quantum-mechanical objects. We show that the S-matrix for such an object can be written in terms of a p-brane-like action. The requirements of unitarity of the S-matrix and positivity of the p-brane tension equivalent severely restrict the number of space-time dimensions and the allowed values of the dilaton parameter a. Generally, black objects transform at the extremal limit into p-branes.

Based on the phase space generating functional of Green's function for a system with singular higher-order Lagrangian, we have derived the canonical Ward identities (CWI) for such a system. We give a preliminary application of CWI to Yang-Mills theory with higher-order derivatives, and deduce a new form of gauge ghost proper vertices which is different from the other one arising from the BRS invariance.

We have investigated a new radiation pressure trap which relies on optical pumping and does not require any magnetic field. It employs six circularly polarized divergent beams and works on the red of a J_g → J_e = J_g + 1 atomic transition with J_g ⩾ 1/2. We have demonstrated this trap with cesium atoms from a vapour cell using the 852 nm J_g = 4 → J_e = 5 resonance transition. The trap contained up to 3 · 10⁷ atoms in a cloud of 1/√e radius of 330 μm.

Beyond a threshold, electric or magnetic fields cause a dielectric or ferromagnetic fluid drop, respectively, to develop conical tips. We analyze the appearance of the conical tips and the associated shape transition of the drop using a loca-force balance as well as a global-energy argument. We find that a conical interface is possible only when the dielectric constant (or permeability) of the fluid exceeds a critical value ε_c = 17.59. For a fluid with ε > ε_c, a conical interface is possible at two angles, one stable and one unstable. We calculate the critical field required to sustain a drop with stable conical tips. Such a drop is energetically favored at sufficiently high field. Our results also apply to the formation of conical dimples when a pool of fluid is placed in a normal field.

We present some results related to the time intermittency exhibited by a shell model describing 3D magnetohydrodynamic turbulence. By calculating the scaling exponents of the structure functions for both the Elsässer variables and for the pseudo-energy density transfer rates, we show that the intermittency can be described by the usual multifractal theory.

We present a first-principles theory of the equilibrium b.c.c.-f.c.c. interface at coexistence using the density functional method. We assume that the interfacial region has local body-centred tetragonal (b.c.t.) symmetry and predict typical interfacial widths to be of order 2 to 3 lattice spacings with typical energies close to 0.05 J/m². These quantities are in good agreement with laboratory measurements on coherent interfaces.

Relying on Monte Carlo simulations, we investigate the hard-disk melting transition. The finite-size scaled values of the bond-orientational order parameter moments are obtained with the block analysis technique. The behaviour of Binder's cumulant and the susceptibility favour an interpretation in terms of a first-order transition.

We present a statistical-mechanical theory of the formation of a macroscopic random network built from elementary units. These units represent atoms or small molecules that can form up to p permanent covalent bonds. As the number of formed bonds is increased, we observe a continuous phase transition from a fluid phase to a localised (i.e. glassy) phase that is marked by the emergence of random static fluctuations in the atomic position and bond orientation densities. By using a variational ansatz we calculate the thermal (i.e. mainly entropic) fluctuations of the positions and bond orientations within the glassy phase.

The order in very thin films (12 nm to 92 nm) of the symmetric diblock copolymer poly(styrene-b-paramethylstyrene) near the order-to-disorder transition has been investigated by ¹⁵N nuclear-reaction analysis. Lamellar ordering parallel to the surface is observed, qualitatively very similar to that of thick films. The order parameter L is found to depend linearly on film thickness d, when d is smaller than the natural order parameter L₀ observed in the absence of constraints. The thickness dependence of L arises from the competition between the two characteristic dimensions of the system, L₀ and d. The results are compared with recent theoretical predictions.

We address the problem of MBE growth in one horizontal and one vertical direction in the presence of Schwoebel barriers. The time-independent growth equation introduced previously is shown to be identical to that for a classical particle in a potential well. We solve this equation using periodic boundary conditions and find time-independent solutions consisting of a periodic array of mounds. We derive the "dispersion relation", i.e. the amplitude as a function of wavelength for these mounds. The equation of motion is derivable from a free energy indicating that there is a most stable ground state, which is independent of the initial conditions. The mounds are marginally unstable and there is a minimum wavelength below which no mounds exist. The wavelength of the mounds coarsens slowly in time according to Λ ∼ t^α, with α ≈ 1/4.

The effects of electron-lattice coupling in a multiband Hubbard model are investigated by exact diagonalization. For a system with one doped hole, and with parameters relevant to cuprate superconductors, we find a continuous transition from a delocalized to a small polaron state at a critical value of the electron-phonon interaction. We characterize this state as a Zhang-Rice singlet with distortions in the CuO₄ cluster. We find, in addition, a polaronic shift of the band near the Fermi level in the spectral function of the system. An enhancement of the transfer of the low-energy spectral weight is also observed. These results are in qualitative agreement with different spectroscopic measurements for high-T_c superconductors.

By considering both the Drude and the interband components of the metal dielectric function, with the latter modeled as a sum of Lorentz oscillators, we show that there exist two virtual modes for thin metallic films which have distinct optical manifestations. Whereas one is absorptive in nature, the other is characterized by near-zero reflectivity. Calculated dispersion relations of the virtual modes are in good agreement with their measured optical manifestations in thin Ag films. The existence of both the absorption peak and the reflectivity minimum close to the optical plasmon frequency has been demonstrated experimentally for the first time.

This is a first presentation of differential scanning microcalorimetric and (di-) electric measurements on phase separation of a single-phase three-component ionic microemulsion into two coexisting droplet phases. For certain compositions this transition resembles a liquid-gas phase transition close to its critical point. Contrary to what was expected, it is shown that the transition is accompanied by two peaks in the specific heat preceded by a narrow dip. The temperature of the dip coincides with a peak in the static dielectric constant and significant changes of the electrical conductivity. It is concluded that this structure is due to rearrangement of droplets. Internal degrees of freedom of the surfactant-coated water droplets are proposed to be responsible for these modifications of the thermodynamic properties with respect to usual liquid-gas transitions.