Self consistent description of the nuclear monopole polarization in muonic 208Pb

The monopole part of the nuclear polarization energy in muonic ²⁰⁸Pb, 1s_{$\text{1}\text{2}$} level, is calculated in the Hartree Fock approximation using a number of Skyrme-type forces. The result found, ?0.7± 0.2 keV is smaller than previous estimates.     

Self consistent calculations of a possible shape transition in neutron deficient mercury isotopes

Deformation energy curves of some mercury isotopes are calculated within the constrained Hartree-Fock method using a Skyrme effective interaction. These static calculations indicate clearly the possibility of a prolate-oblate transition around ¹⁸⁶Hg which could be an explanation of the anomalous isotopic shift observed from ¹⁸⁷Hg to ¹⁸⁵Hg. The appearance of a very well defined secondary minimum, at large deformation (β ～ 0.5) for ²⁰⁰Hg is also discussed.     

Microscopic membrane elasticity and interactions among membrane inclusions: interplay between the shape, dilation, tilt and tilt-difference modes

A phenomenological Landau elasticity for the shape, dilation, and lipid-tilt of bilayer membranes is developed. The shape mode couples with the sum of the monolayers' tilt, while the dilation mode couples with the difference of the monolayers' tilts. Interactions among membrane inclusions within regular arrays are discussed. Inclusions modifying the membrane thickness and/or inducing a tilt-difference due to their convex or concave shape yield a dilation-induced attraction and a tilt-difference-induced repulsion. The resulting interaction can stabilize 2D crystal phases, with the possible coexistence of different lattice spacings when the dilation-tilt-difference coupling is large. Inclusions favoring crystals are those with either a long-convex or a short-concave hydrophobic core. Inclusions inducing a local membrane curvature due to their conical shape repel one another. At short inclusions separations, a tilt comparable with the inclusion's cone angle develops: it relaxes the membrane curvature and reduces the repulsion. At large separations the tilt vanishes, whatever the value of the shape-tilt coupling. Received 23 October 1998 and Received in final form 12 January 1999     

Two-neutron transfer reactions as a tool to study the interplay between shape coexistence and quantum phase transitions

The atomic mass table presents zones where the structure of the states changes rapidly as a function of the neutron or proton number. Among them, notable examples are the A ≈ 100 Zr region, the Pb region around the neutron midshell (N = 104), and the N ≈ 90 rare-earth region. The observed phenomena can be understood in terms of either shape coexistence or quantum phase transitions. The objective of this study is to find an observable that can distinguish between both shape coexistence and quantum phase transitions. As an observable to be analyzed, we selected the two-neutron transfer intensity between the 0⁺ states in the parent and daughter nuclei. The framework used for this study is the Interacting Boson Model (IBM), including its version with configuration mixing (IBM-CM). To generate wave functions of isotope chains of interest needed for calculating transfer intensities, previous systematic studies using IBM and IBM-CM were used without changing the parameters. The results of two-neutron transfer intensities are presented for Zr, Hg, and Pt isotopic chains using IBM-CM. Moreover, for Zr, Pt, and Sm isotopic chains, the results are presented using IBM with only a single configuration, i.e., without using configuration mixing. For Zr, the two-neutron transfer intensities between the ground states provide a clear observable, indicating that normal and intruder configurations coexist in the low-lying spectrum and cross at A = 98 → 100. This can help clarify whether shape coexistence induces a given quantum phase transition. For Pt, in which shape coexistence is present and the regular and intruder configurations cross for the ground state, there is almost no impact on the value of the two-neutron transfer intensity. Similar is the situation with Hg, where the ground state always has a regular nature. For the Sm isotope chain, which is one of the quantum phase transition paradigms, the value of the two-neutron transfer intensity is affected strongly.     

Self consistent band structure of ordered ScPd3 and YPd3

A fully self-consistent electronic structure of the two ordered compounds ScPd₃ and YPd₃ is obtained by linearized muffin-tin orbitals (LMTO) method. The overall agreement with other theoretical results concerning isostructural compounds and with electronic specific heat measurements is good.     

Role of pairing degrees of freedom and higher multipolarity deformations in spontaneous fission process

Spontaneous fission (T_sf) and alpha-decay half-lives (T_α) of the heaviest nuclei with atomic number 100 ≤ Z ≤ 114 are calculated on the basis of the deformed Woods-Saxon potential. The calculations of (T_sf) are performed by the WKB approximation, in the multi-dimensional dynamical-programing method (MDP).We have examined three different effects: the effect of higher even-multipolarity shape parameters (β₆ and β₈), the role of reflection-asymmetry (β₃ and β₅) and the influence of pairing degrees of freedom (Δ_p and Δ_n).Alpha-decay half-lives (T_α) have been calculated by the Viola-Seaborg (V-S) formula with the parameters modified to the latest experimental data.     

Size-asymmetric primitive model at low temperature: description of ion pairing and location of the critical point

We argue that Bjerrum's approach to ion pairing is inappropriate for the size-asymmetric primitive model in the neighborhood of its critical point, and propose a new approach based on the Stillinger-Lovett pairing procedure. The new approach recursively scales up the ion size until linear approximations are suitable for analyzing such a model. To locate the critical point, a residual van der Waals interaction between pairs is added, with an energy cutoff adjusted to match the critical temperature of the restricted primitive model. The locations and downward trends of T(c) and rho(c) with asymmetry are found to compare favorably with simulations.     

Nilsson mean-field plus the extended pairing model description of rare earth nuclei

The Nilsson mean-field plus the extended pairing model for well-deformed nuclei is applied to some representative rare earth examples. The binding energies, some low-lying pair-excited states and even-odd mass differences of Er, Yb and Hf isotopes are calculated systematically within the proton frozen-pair excitation limit. A comparison with experimental data for these nuclei shows that the results of the extended pairing model are better than those for the standard pairing model with the BCS approximation and the nearest-orbit pairing model.     

Statistical description of the shape of a moving dislocation

The shape and mobility of dislocations gliding (climbing) over the crystal relief are studied. The mobility of a dislocation is governed by the probability of critical nucleation on it of various defects (the formation of a double kink or break-away from a barrier during sliding, the formation of a jog during absorption (emission) of an interstitial (vacancy) during climbing, etc.). It is demonstrated that the transitional and steady-state modes of dislocation motion exist (the transitional and steady-state modes of deformation). The time required to achieve the steady-state dislocation motion and the velocity of this motion in the absence and in the presence of various types of pinning (drag) centers are calculated. The pinning centers qualitatively change the steady-state velocity of dislocations and increase the time required to reach this mode of motion.     

Critical-point description of the transition from vibrational to rotational regimes in the pairing phase

An approximate solution at the critical point of the pairing transition from harmonic vibration to deformed rotation in gauge space is found by analytic solution of the collective pairing Hamiltonian. The eigenvalues are expressed in terms of the zeros of Bessel functions of integer order. The results are compared to the pairing bands based on the Pb isotopes.     

A generator coordinate approach for the description of pairing vibrations in the seniority-zero space

The application of the generator coordinate method is extended to non-harmonic systems. The many-dimensional Hill-Wheeler integral equation is reduced to a one-dimensional integral equation by expressing all independent parameters in the generator function by a single parameter. It is shown that the subspace spanned by a proper single-parameter family is the same as that spanned by the many-parametric family of generator functions.     

Spin-isospin and pairing properties of modified Skyrme interactions

New sets of parameters for Skyrme interactions have been determined. In addition to the ground-state properties, they give satisfactory values for the compression modulus, spin and spin-isospin Landau parameters, and pairing matrix elements. Gamow-Teller states are calculated and compared with experimental data.     

Thermal separation: interplay between the Soret effect and entropic force gradient

Thermophoresis, the Soret effect, depletes a high concentration of a polyethylene glycol polymer solution from the hot region and builds a concentration gradient. In such a solution, solutes of small concentration experience thermophoresis and polyethylene glycol concentration-dependent restoring forces. We report that by using focused laser heating and varying the polyethylene glycol concentration one observes geometrical localizations of solutes like DNA and RNA into patterns such as a ring. For DNA up to 5.6?kbp, the ring size decreases following a behavior analogous to a gel electrophoresis separation. Above 5.6?kbp, the ring diameter increases with the DNA length. Mixtures of DNA and RNA can be separated as well as different RNA lengths. Separation of colloids is also observed. The experiments might be relevant for the separation of small RNA ribozymes in an early stage of life.     

Theory of doped Mott insulators: duality between pairing and magnetism

By bosonizing the electronic t-J model exactly on any two-dimensional (2D) lattices, and integrating out the gauge fluctuations combined to slave particles beyond mean fields, we obtain a theory in terms of physical Cooper pair and spin condensates. In the sense of mutual Berry phase they turn out to be dual to each other. The mutual duality is the missing key in the resonant-valance-bond idea [Science 235, 1196 (1987)]] to work as a paradigm of doped 2D Mott insulators. We argue that the essential aspects of high-T(c) phenomenology can be explained in the present framework.     

The interplay between screening properties and colloid anisotropy: Towards a reliable pair potential for disc-like charged particles

The electrostatic potential of a highly charged disc (clay platelet) in an electrolyte is investigated in detail. The corresponding non-linear Poisson-Boltzmann (PB) equation is solved numerically, and we show that the far-field behaviour (relevant for colloidal interactions in dilute suspensions) is exactly that obtained within linearized PB theory, with the surface boundary condition of a uniform potential. The latter linear problem is solved by a new semi-analytical procedure and both the potential amplitude (quantified by an effective charge) and potential anisotropy coincide closely within PB and linearized PB, provided the disc bare charge is high enough. This anisotropy remains at all scales; it is encoded in a function that may vary over several orders of magnitude depending on the azimuthal angle under which the disc is seen. The results allow to construct a pair potential for discs interaction, that is strongly orientation dependent.