The Maxwell tensor for the Liénard-Wiechert field as an exact divergence

A potential for the bounded part of the Maxwell tensor associated to the Liénard-Wiechert field has been obtained by van Weert. In this paper we explicitly derive the non-local potential for the radiative part of such a tensor.     

Serial MR imaging of intracranial metastases after radiosurgery

Purpose: To evaluate the spatiotemporal evolution of radiosurgical induced changes both in metastases and in normal brain tissue adjacent to the lesions by serial magnetic resonance (MR) imaging. Methods and Materials: Thirty-five intracranial metastases of different primaries were treated in 25 patients by single high-dose radiosurgery. MR images acquired before radiosurgery were available in all patients. Sixty-three follow-up MR studies were performed in these patients including T₂- and contrast-enhanced T₁-weighted MR images. The average follow-up time was 9 ± 5 months (mean ± standard deviation [SD]). Based on contrast-enhanced T₁-weighted MR images, tumor response was radiologically classified in the following four groups: stable disease was assumed if the average tumor diameter after treatment did not show a tumor shrinkage of more than 50% and an increase of more than 25%, partial remission as a shrinkage of tumor size of more than 50%, a disappearance of contrast-enhancing tumor as a complete remission, and an increase of tumor diameter of more than 25% as tumor progress. Moreover, we analysed signal changes on T₂-weighted images in brain parenchyma adjacent to the enhancing metastases. Results: The overall mean survival time was 10.5 ± 7 months, with a 1-year actuarial survival rate of 40%. Stable disease, partial or complete remission of the metastatic tumor was observed in 22 patients (88%). Central or homogeneous loss of contrast enhancement appeared to be a good prognostic sign for stable disease or partial remission. This association was statistically significant (p < 0.05). Three patients (12%) suffered from tumor progression. In eight patients (32%) with stable disease or partial remission, signal changes on T₂-weighted images were observed in tissue adjacent to the contrast enhancing lesions. A progression of the high signal on T₂-weighted images was seen in seven of the eight patients between 3 and 6 months after therapy, followed by a signal regression 6–18 months after irradiation. Conclusion: MR imaging is a sensitive imaging tool to evaluate tumor response as well as the presence or absence of adjacent parenchymal changes following radiosurgery. Loss of homogeneous or central contrast enhancement on Gd-enhanced MR images appeared to be a good prognostic sign for tumor response. Tumor shrinkage seems not to be dependent on time. In addition, most cases of radiation induced changes in normal brain parenchyma observed on T₂-weighted images seem to be self limited.     

Separation of Variables for Bi-Hamiltonian Systems

We address the problem of the separation of variables for the Hamilton–Jacobi equation within the theoretical scheme of bi-Hamiltonian geometry. We use the properties of a special class of bi-Hamiltonian manifolds, called N manifolds, to give intrisic tests of separability (and Stäckel separability) for Hamiltonian systems. The separation variables are naturally associated with the geometrical structures of the N manifold itself. We apply these results to bi-Hamiltonian systems of the Gel'fand–Zakharevich type and we give explicit procedures to find the separated coordinates and the separation relations.     

Characterisation of the reduction properties of La0.5Sr0.5Fe0.5Co0.5O3

We report here on the characterisation by temperature programmed reduction, ⁵⁷Fe Mössbauer spectroscopy and X-ray absorption spectroscopy of the phases resulting from treatment of the perovskite-related material La_0.5Sr_0.5Fe_0.5Co_0.5O₃ in a flowing 90% hydrogen/10% nitrogen atmosphere. The results show that treatment of La_0.5Sr_0.5Fe_0.5Co_0.5O₃ (which contains approximately 50% Fe⁴⁺ and 50% Fe³⁺) in the flowing 90% hydrogen/10% nitrogen atmosphere at 600°C does not result in the reduction of any of the constituent elements of the material and that the perovskite structure is still retained. The Mössbauer spectrum recorded following heating in the gaseous reducing environment at 1,000°C shows the presence of metallic iron, an Fe³⁺-containing phase with parameters compatible with the presence of SrLaFeO₄ which has a K₂NiF₄-type structure, and a paramagnetic Fe³⁺ phase. The X-ray absorption spectroscopy results show the presence of metallic cobalt. The Mössbauer spectrum recorded following heating at 1,200°C continues to show the Fe³⁺-containing components plus a larger contribution from metallic iron. The X-ray absorption spectroscopy results show the presence of metallic cobalt, SrLaFeO₄, La₂O₃ and SrO.     

Enhancing the violation of the einstein-podolsky-rosen local realism by quantum hyperentanglement

Mermin's observation [Phys. Rev. Lett. 65, 1838 (1990)] that the magnitude of the violation of local realism, defined as the ratio between the quantum prediction and the classical bound, can grow exponentially with the size of the system is demonstrated using two-photon hyperentangled states entangled in polarization and path degrees of freedom, and local measurements of polarization and path simultaneously.     

Stochastic acceleration in turbulent electric fields generated by 3D reconnection

Electron and proton acceleration in three-dimensional electric and magnetic fields is studied through test particle simulations. The fields are obtained by a three-dimensional magnetohydrodynamic simulation of magnetic reconnection in slab geometry. The nonlinear evolution of the system is characterized by the growth of many unstable modes and the initial current sheet is fragmented with formation of small scale structures. We inject at random points inside the evolving current sheet a Maxwellian distribution of particles. In a relatively short time (less than a millisecond) the particles develop a power-law tail. The acceleration is extremely efficient and the electrons absorb a large percentage of the available energy in a small fraction of the characteristic time of the MHD simulation, suggesting that resistive MHD codes are unable to represent the full extent of particle acceleration.     

Potassium-doped FePc thin-film on metal surfaces: observation of different empty state occupation

Iron-Phthalocyanine molecules deposited on the Cu(119) vicinal surface form molecular chains along the vicinal surface steps, as deduced by the low-energy electron diffraction (LEED) reconstruction pattern. The work-function lowers at the FePc single-layer completion, due to the formation of an interface dipole. Further FePc deposition induces a different growth morphology, as suggested by the slope discontinuity in the work function variation. Upon depositing potassium onto the FePc thin-film prepared on Cu(119), the K-injected electrons fill up the Fe-d-associated and ligand-π-related orbitals, as observed by means of high-resolution ultraviolet photoelectron spectroscopy.     

Magnesium nanoparticles with transition metal decoration for hydrogen storage

We report on the hydrogen storage behaviour of Mg nanoparticles (NPs) (size range 100 nm–1 μm) with metal-oxide core–shell morphology synthesized by inert gas condensation and decorated by transition metal (TM) (Pd or Ti) clusters via in situ vacuum deposition. The structure and morphology of the as-prepared and hydrogenated NPs is studied by electron microscopy, X-ray diffraction including in situ experiments and X-ray absorption spectroscopy, in order to investigate the relationships with the hydrogen storage kinetics measured by the volumetric Sieverts method. With both Pd and Ti, the decoration deeply improves the hydrogen sorption properties: previously inert NPs exhibit complete hydrogenation with fast transformation kinetics, good stability and reversible gravimetric capacity that can attain 6 wt%. In the case of Pd-decoration, the occurrence of Mg–Pd alloying is observed at high temperatures and in dependence of the hydrogen pressure conditions. These structural transformations modify both the kinetics and thermodynamics of hydride formation, while Ti-decoration has an effect only on the kinetics. The experimental results are discussed in relation with key issues such as the amount of decoration, the heat of mixing between TM and Mg and the binding energy between TM and hydrogen.     

Pyroxene inclusions in paleo-Christian mosaic tesserae: a new tool for constraining the glass manufacturing temperature

The mineral inclusions of two orange glass tesserae from paleo-Christian mosaics were investigated in order to derive the melting temperature reached during their production (sourced from Padua and Vicenza, Veneto region, Italy). In particular, clinopyroxene crystals were studied by single-crystal X-ray diffraction and electron microprobe WDS analysis. The crystals show C2/c symmetry, typical of disordered Ca/Na and Mg/Al distributions indicating high-temperature of formation (>700°C). The cation site populations were obtained by combining results from the two experimental techniques enabled us to derive the following stoichiometric formula:

1/N-Expansion for the Dicke model and the decoherence program

An analysis of the Dicke model, N two-level atoms interacting with a single radiation mode, is done using the Holstein-Primakoff transformation. The main aim of the paper is to show that, changing the quantization axis with respect to the common usage, it is possible to prove a general result either for N or the coupling constant going to infinity for the exact solution of the model. This completes the analysis, known in the current literature, with respect to the same model in the limit of N and volume going to infinity, keeping the density constant. For the latter the proper axis of quantization is given by the Hamiltonian of the two-level atoms and for the former the proper axis of quantization is defined by the interaction. The relevance of this result relies on the observation that a general measurement apparatus acts using electromagnetic interaction and so, one can state that the thermodynamic limit is enough to grant the appearance of classical effects. Indeed, recent experimental results give first evidence that superposition states disappear interacting with an electromagnetic field having a large number of photons.