Core temperature and density profile measurements in inertial confinement fusion implosions

We have measured time-integrated and time-gated electron temperature (T_e) and density (N_e) spatial profiles from indirect-drive implosions. In our experiments, we used a multiple-pinhole two-dimensional imaging spectrometer to obtain multispectral X-ray images of the imploded core. Quantitative comparisons between quasi-monochromatic images in different energy bands allowed T_e and N_e spatial profiles to be determined using two independent and validated techniques: a multi-objective search and reconstruction analysis, and an analytical analysis. We then compared the results to a simple one-dimensional (1D) mix-free hydrodynamics simulation in order to evaluate the ability of such a model to predict our experiments. Our data show spatial T_e profiles that are qualitatively consistent with the predictions of our 1D simulations, but we observe central cores that are 10–25% cooler and emit X-rays as late as 200 ps after peak compression. We infer time-gated spatial N_e profiles that are consistent with our 1D simulations near the times of peak compression, but we find significant disagreement between time-integrated data and 1D simulation predictions at large radii. Careful analysis of the time-gated and time-integrated T_e and N_e spatial profiles, together with streaked X-ray emission spectra from core and shell dopants, suggests mixing of shell material into the core is an important process that our 1D hydrodynamics simulations fail to capture, and comparison between image data and a simple analytical model suggests that 2–5 μm of the initial inner shell thickness mixes into the core during the time period of significant X-ray emission. This mix width is consistent with the predictions of a growth-factor analysis that treats instability growth seeded by capsule surface roughness, and points to the need to consider time-dependent mixing effects when interpreting T_e and N_e spatial profiles derived from multispectral X-ray image data, particularly at large radii where mixing effects will be most significant.     

The two-dimensional t-t'-U model as a minimal model for cuprate materials

The addition to the Hubbard Hamiltonian of a t' diagonal hopping term, which is considered to be material dependent for high-T _c cuprate superconductors, is generally suggested to obtain a model capable to describe the physics of high-T _c cuprate materials. In this line of thinking, the two-dimensional t-t'-U model has been studied by means of the Composite Operator Method, which allows to determine the dynamics in a fully self-consistent way by use of symmetry requirements, as the ones coming from the Pauli principle. At first, some local quantities have been calculated to be compared with quantum Monte Carlo data. Then, the structure of the energy bands, the shape of the Fermi surface and the position of the van Hove singularity have been computed as functions of the model parameters and studied by the light of the available experimental data. The results of our study show that there exists two sets of parameters that allows the model to describe the relevant features of the 1-layer compounds Nd_2-xCe_xCuO₄ and La_2-xSr_xCuO₄. On the other hand, for the 2-layer compound YBa₂Cu₃O _{7 - δ} is not possible to find a reasonable set of parameters which could reproduce the position of the van Hove singularity as predicted by ARPES experiments. Hence, it results questionable the existence of an unique model that could properly describe the variety of cuprate superconductors, as the two-dimensional t-t'-U model was thought to be. Received 29 March 2000 and Received in final form 10 August 2000     

Vanadium in Italian waters: monitoring and speciation of V(IV) and V(V)

In this work, a highly sensitive method was developed to separate vanadium (IV) from vanadium (V), which are both contained in water at trace levels. A suitable strong anionic exchange column (SAX) loaded with disodium ethylendiaminetetraacetic acid (Na₂EDTA) was used to trap both vanadium species dissolved in 10–100 ml of water at pH 3. The vanadyl ion was selectively eluted by means of 15 ml of an aqueous solution containing Na₂EDTA, tetrabutylammonium hydroxide (TBA⁺OH⁻), and isopropanol (ⁱPr-OH) and was subsequently determined by atomic absorption spectroscopy with electrothermal atomization. The concentration of vanadate ion was calculated by subtracting the vanadyl concentration from the total concentration of vanadium. The optimal conditions for a selective elution were evaluated. The recovery of vanadium (IV) was 95% or better. The proposed method provides a simple procedure for the speciation of vanadium in aqueous matrices. The collection of the two forms could easily be carried out at the sampling site. Therefore, the risk of changing the concentration ratio between vanadium species was widely reduced. The detection limits were 1 μg/l for both species, when a 10-ml sample was eluted through the column. The method was applied successfully to vanadium speciation on different kinds of Italian volcanic water: Mount Etna (Sicily), Lake Bracciano and Castelli Romani (Latium).     

The birth of defects in pattern formation: Testing of the Kibble–Zurek mechanism

The extension of the cosmological mechanism of Kibble to second order phase transitions in condensed matter systems by Zurek, can be further generalized to bifurcations of out-of-equilibrium systems in continuum media, since the argument used in the derivation of the Kibble–Zurek scaling law is general. Here we review the validity of such scaling comparing several bifurcations where the test has been checked. Also, new experimental results of a nonlinear optical system are reported.     

Entanglement from ponderomotive interaction

A simple interaction model is employed to show that radiation pressure effects, i.e., ponderomotive effects, can be profitably used to entangle radiation fields, as well as macroscopic oscillators such as movable mirrors.     

Dynamical Lie algebra and conditional operators for many fermion Green functions

A method is introduced to calculate thermodynamic Green functions. A powerful theorem by Masson is the motivation for expressing the Fourier-time transform of the Green function as a super space matrix element of the resolvent of the Liouville operator. The eigenvalues of the Liouville operator are then expressed in a form first suggested by Judd for atomic systems and which are shown to be members of a Lie group.     

Ferromagnetic superconducting film in external parallel field

Summary By using the boson transformation method, the electromagnetic properties of a ferromagnetic superconducting film have been studied. The magnetic field, the induction field and the magnetization have been calculated analytically in the London limit. Particularly, we have studied the dependence of the various fields on the phenomenological parameter μ, on the temperature and on the film thickness and the dependence oft _s , a critical temperature below which a spontaneous magnetization appears, on the parameter μ and on the film thickness. Finally, the magnetic properties of the film are analysed in the linear and nonlinear approximation as functions of temperature and thickness.

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Riassunto Utilizzando il metodo della trasformazione bosonica le proprietà elettromagnetiche di un film superconducente ferromagnetico sono state studiate. Il campo magnetico, il camp di induzione magnetica e la magnetizzazione sono stati calcolati analiticamente nel limite di London. In particolare, abbiamo studiato la dipendenza dei vari campi dal parametro fenomenologico μ, dalla temperatura e dallo spessore del film e la dipendenza dit _s , temperatura critica al di sotto della quale appare la magnetizzazione spontanea, dal parametro μ e dallo spessore del film. Infine le proprietà magnetiche del film sono analizzate in approssimazione lineare e non lineare in funzione della temperatura e dello spessore.

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Резюме Исследуются электромагнитные свойства ферромагнитной сверхпро водящей пленки с помощъю метода бозонного нреобразования. В пределе Лондона аналитически вычисляются магнитное поле, индуцированное поле и намагниченность. В частности, рассматривается зависимость вышеуказанных полей от феноменологического параметра μ, от температуры и от толщины пленки, а также зависимостьt _s критической температуры, ниже которой возникает спонтанная намагниченность, от параметра μ и толщины пленки. В заключение, анализируются свойства пленки в зависимости от температуры и толщины в линейном и нелинейном приближениях.

     

Anomalies in the surface impedance penetration depth in ferromagnetic superconductors

We have investigated the surface impedance penetration depth, Λ, of ErRh₄B₄ and Er_0.5Ho_0.5Rh₄B₄ both experimentally and theoretically. For ErRh₄B₄, owing to the critical spin fluctuations just above T_s ( > T_c2), the critical temperature at which surface ferromagnetism appears, Λ^?1 decreases smoothly as T decreases toward T_s. For Er_0.5Ho_0.5Rh₄B₄, the decrease in Λ^?1 owing to spin fluctuations for T ? T_c2 is very small, and Λ^?1 decreases abruptly at T_c2. Theoretical values of Λ^?1 are in good agreement with the data.