Prevalence of anatomical variants and coronary anomalies in 543 consecutive patients studied with 64-slice CT coronary angiography

The aim of our study was to assess the prevalence of variants and anomalies of the coronary artery tree in patients who underwent 64-slice computed tomography coronary angiography (CT-CA) for suspected or known coronary artery disease. A total of 543 patients (389 male, mean age 60.5 ± 10.9) were reviewed for coronary artery variants and anomalies including post-processing tools. The majority of segments were identified according to the American Heart Association scheme. The coronary dominance pattern results were: right, 86.6%; left, 9.2%; balanced, 4.2%. The left main coronary artery had a mean length of 112 ± 55 mm. The intermediate branch was present in the 21.9%. A variable number of diagonals (one, 25%; two, 49.7%; more than two, 24%; none, 1.3%) and marginals (one, 35.2%; two, 46.2%; more than two, 18%; none, 0.6%) was visualized. Furthermore, CT-CA may visualize smaller branches such as the conus branch artery (98%), the sinus node artery (91.6%), and the septal branches (93%). Single or associated coronary anomalies occurred in 18.4% of the patients, with the following distribution: 43 anomalies of origin and course, 68 intrinsic anomalies (59 myocardial bridging, nine aneurisms), three fistulas. In conclusion, 64-slice CT-CA provides optimal visualization of the variable and complex anatomy of coronary arteries because of the improved isotropic spatial resolution and flexible post-processing tool

Effective Properties of a Binary Magnonic Crystal - Conferenza internazionale

In this paper the effective properties of a two-dimensional periodic binary magnetic system are studied. The magnetic system is composed by cobalt cylindrical dots embedded into a permalloy film. The dot diameter is 310 nm and the periodicity of the system is 600 nm. Since the dot diameter is smaller than the characteristic mode wavelength, it is possible to describe the collective excitations through effective quantities. In particular, for each collective mode an effective wavelength and a small effective wave vector not necessarily equal to the corresponding Bloch wavelength and Bloch wave vector can be defined. The introduction of these effective quantities characterizing collective mode dynamics allows us to describe the binary periodic magnetic system as a magnonic metamaterial

Perpendicularly Magnetized Antidot Lattice as a Two-Dimensional Magnonic Metamaterial - Presentazione poster by R. Zivieri - Conferenza internazionale

The effective properties of a perpendicularly magnetized two-dimensional antidot lattice having periodicity and hole size in the nanometric range are studied. The effective rules involving the effective wavelength and the effective wave vector of collective modes characterize these magnonic crystals as magnonic metamaterials

Perpendicularly magnetized antidot lattice as a two-dimensional magnonic metamaterial

In this paper the effective properties of a perpendicularly magnetized magnonic crystal are theoretically studied. The magnonic crystal is a two-dimensional antidot lattice composed by circular holes embedded into a ferromagnetic film. Both the periodicity of the magnonic crystal and the diameter of the holes are in the nanometric range and the external magnetic field is applied perpendicularly to the plane. It is shown, according to a micromagnetic approach and analytical calculations, that the effective rules linking the effective wavelength and effective wave vector of collective modes to the corresponding Bloch quantities characterizing the dynamics of in-plane magnetized periodic systems remain valid also in this geometry. It is thus possible to classify two-dimensional antidot lattices with perpendicular magnetization as magnonic metamaterials. Other metamaterial properties arising from the band structure calculation such as the band gap amplitudes at the Brillouin zone boundaries are also discussed

Size effects on spin dynamics in 2D ferromagnetic antidot lattices -- Presentazione poster by R. Zivieri - Conferenza internazionale

The size effects on frequencies of collective modes in two-dimensional (2D) arrays of periodic circular antidots (holes) embedded into a ferromagnetic Permalloy material are investigated. The study is performed by calculating the frequency behaviour as a function of the intensity H of the external magnetic field applied in the plane of the system along the ydirection for vanishing Bloch wave vector. The antidot periodicity is a = 420 nm, the thickness is L = 30 nm, whereas the diameters of the holes are d1 = 140 nm, d2 = 180 nm, d3= 220 nm and d4= 260 nm, respectively [1]. The two relevant modes, having an appreciable calculated scattering cross-section, are: 1) the resonant mode of the spectrum, the so-called Fundamental (F) mode, whose spatial profile is confined in the channels; 2) the equivalent mode mainly localized in the horizontal rows of ADs, the Floc mode. Frequencies of collective modes monotonically increase with increasing the mean internal field. However, at a fixed external field the frequencies of F and Floc mode have on opposite behavior as a function of the hole size as shown in Figure 1. Indeed, the mean demagnetizing field experienced by the F mode is anti-parallel to the external field lowering the mean internal field, while for the Floc mode it is parallel and has the effect to increase the internal field. Moreover, at the centre of the first Brillouin zone, the two lowest spin-wave mode frequencies, namely the edge mode (EM) localized at the antidot borders [2] and the F mode, become soft at a given critical field showing a deep minimum. The intensity of the critical field depends on the hole size and both soft modes do exhibit a finite gap. The softening mechanism is strictly related to the rotation of the static magnetization from the hard to the easy axis marking a reorientational and continuous phase transition [3]. [1] J. Ding, D. Tripathy, A. O. Adeyeye, J. Appl. Phys. 109, (2011) 07D304-1-3. [2] S. Tacchi, M. Madami, G. Gubbiotti, G. Carlotti, A.O. Adeyeye, S. Neusser, B. Botters, D. Grundler, IEEE Trans. Magn. 46, (2010) 172-178

Size Effects on Spin-wave Modes in Ferromagnetic Antidot Lattices -- Presentazione orale by R. Zivieri - Congresso nazionale

The size effects on frequencies of collective modes in two-dimensional arrays of periodic circular antidots (ADs) (holes) embedded into a ferromagnetic Permalloy material are investigated. The study is performed by determining the frequency behaviour as a function of the intensity H of the external magnetic field applied in the plane of the system along the y-direction for vanishing Bloch wave vector. The AD periodicity is a = 420 nm, the thickness is L = 30 nm, whereas the diameters of the holes are d1 = 260 nm, d2 = 220 nm and d3= 180 nm, respectively [1]. The two relevant modes having an appreciable scattering cross-section are: 1) the resonant mode of the spectrum, the so-called Fundamental (F) mode, whose spatial profile is confined in the channels; 2) the equivalent mode mainly localized in the horizontal rows of ADs, the Floc mode. Frequencies of spin modes monotonically increase with increasing the external field. More specifically, the frequencies of each spin mode are proportional to the mean internal field. However, at a fixed external field: a) the F mode frequencies increase by decreasing hole diameter b) the Floc frequencies decrease by decreasing hole diameter. In order to explain this opposite behaviour, it is necessary to make a qualitative analysis of the trend of the mean internal field, whose magnitude is given by the sum of H and the mean demagnetizing field . Due to the presence of magnetic surface charges on the external edges of ADs, the mean demagnetizing field experienced by the F mode is anti-parallel to the external field and almost homogeneous, while for the Floc mode it is parallel and strongly inhomogeneous. By increasing the diameter of the holes, the channels reduce and, as a consequence, increases negatively leading to a decrease of the F mode frequencies. Instead, the larger is the diameter of the holes, the more is the mean demagnetizing field felt by the Floc mode in correspondence of the ADs yielding to an increase of the corresponding frequencies. [1] J. Ding, D. Tripathy and A. O. Adeyeye, J. Appl. Phys. 109, 07D304 (2011)

Band structure of collective modes and effective properties of binary magnonic crystals

In this paper a theoretical study of the band structure of collective modes of binary ferromagnetic systems formed by a submicrometric periodic array of cylindrical cobalt nanodots partially or completely embedded into a permalloy ferromagnetic film is performed. The binary ferromagnetic systems studied are two-dimensional periodic, but they can be regarded as threedimensional, since the magnetization is non uniform also along the z direction due to the contrast between the saturation magnetizations of the two ferromagnetic materials along the thickness. The dynamical matrix method, a finite-difference micromagnetic approach, formulated for studying the dynamics in one-component periodic ferromagnetic systems is generalized to ferromagnetic systems composed by F ferromagnetic materials. It is then applied to investigate the spin dynamics in four periodic binary ferromagnetic systems differing each other for the volume of cobalt dots and for the relative position of cobalt dots within the primitive cell. The dispersion curves of the most representative frequency modes are calculated for each system for an in-plane applied magnetic field perpendicular to the Bloch wave vector. The dependence of the dispersion curves on the cobalt quantity and position is discussed in terms of distribution of effective ‘‘surface magnetic charges’’ at the interface between the two ferromagnetic materials. The metamaterial properties in the propagative regime are also studied (1) by introducing an effective magnetization and effective ‘‘surface magnetic charges’’ (2) by describing the metamaterial wave dispersion of the most representative mode in each system within an effective medium approximation and in the dipole-exchange regime. It is also shown that the interchange between cobalt and permalloy does not necessarily lead to an interchange of the corresponding mode dispersion. Analogously to the case of electromagnetic waves in two-dimensional photonic crystals, the degree of localization of the localized collective modes is expressed in terms of an energy concentration factor