Anisotropy-based mechanism for zigzag striped patterns in magnetic thin films

In this work we studied a two dimensional ferromagnetic system using Monte Carlo simulations. Our model includes exchange and dipolar interactions, a cubic anisotropy term, and uniaxial out-of-plane and in-plane ones. According to the set of parameters chosen, the model including uniaxial out-of-plane anisotropy has a ground-state which consists of a canted state with stripes of opposite out-of-plane magnetization. When the cubic anisotropy is introduced zigzag patterns appear in the stripes at fields close to the remanence. An analysis of the anisotropy terms of the model shows that this configuration is related to specific values of the ratio between the cubic and the effective uniaxial anisotropy. The mechanism behind this effect is related to particular features of the anisotropy's energy landscape, since a global minima transition as a function of the applied field is required in the anisotropy terms. This new mechanism for zigzags formation could be present in monocrystal ferromagnetic thin films in a given range of thicknesses.Comment: 910 pages, 10 figure

Modeling Dynamical Dark Energy

Cosmological models with different types of Dark Energy are becoming viable alternatives for standard models with the cosmological constant. Yet, such models are more difficult to analyze and to simulate. We present analytical approximations and discuss ways of making simulations for two families of models, which cover a wide range of possibilities and include models with both slow and fast changing ratio w=p\rho. More specifically, we give analytical expressions for the evolution of the matter density parameter Omega_m(z) and the virial density contrast Delta_c at any redshift z. The latter is used to identify halos and to find their virial masses. We also provide an approximation for the linear growth factor of linear fluctuations between redshift z=40 and z=0. This is needed to set the normalization of the spectrum of fluctuations. Finally, we discuss the expected behavior of the halo mass function and its time evolution.Comment: 10 pages, 10 figures ApJ submitte

Magnetic field dependence of antiferromagnetic resonance in NiO

We report on measurements of magnetic field and temperature dependence of antiferromagnetic resonances in the prototypical antiferromagnet NiO. The frequencies of the magnetic resonances in the vicinity of 1 THz have been determined in the time-domain via time-resolved Faraday measurements after selective excitation by narrow-band superradiant terahertz (THz) pulses at temperatures down to 3 K and in magnetic fields up to 10 T. The measurements reveal two antiferromagnetic resonance modes, which can be distinguished by their characteristic magnetic field dependencies. The nature of the two modes is discussed by comparison to an eight-sublattice antiferromagnetic model, which includes superexchange between the next-nearest-neighbor Ni spins, magnetic dipolar interactions, cubic magneto-crystalline anisotropy, and Zeeman interaction with the external magnetic field. Our study indicates that a two-sublattice model is insufficient for the description of spin dynamics in NiO, while the magnetic-dipolar interactions and magneto-crystalline anisotropy play important roles

Late Winter Dietary Overlap among Greater Rheas and Domestic Herbivores on the Argentinean Flooding Pampa

This study evaluates the dietary overlap among greater rheas (Rhea americana L.) sheep and cattle in the Flooding Pampa, Buenos Aires, Argentina during late winter, when is observed the lowest forage availability. The work was carried out with the following forage classes (FC): warm and cool season grasses and forbs (legumes and no-legumes). Diet botanical composition was estimated by microanalysis of faeces. Principal Component Analysis and Kulcyznsky´s index of similarity were used for data analysis. Rhea populations selected diets with higher forb percentages. On the contrary, vegetation structure and their own morpho-physiology conditioned cattle to diets almost exclusively gramineous. Although forbs were more consumed by sheep than by cattle, they do not represent a major portion of sheep diets. In the Flooding Pampa grasslands, the probability of competition for forage between greater rheas and sheep is intermediate, and that between rheas and cattle is low

Photon Self-Induced Spin to Orbital Conversion in TGG crystal at high laser power

In this paper, we present experimental evidence of a newly discovered third-order nonlinear optical process Self-Induced Spin-to-Orbital Conversion (SISTOC) of the photon angular momentum. This effect is the physical mechanism at the origin of the depolarization of very intense laser beams propagating in isotropic materials. The SISTOC process, like self-focusing, is triggered by laser heating leading to a radial temperature gradient in the medium. In this work we tested the occurrence of SISTOC in a terbium gallium garnet (TGG) rod for an impinging laser power of about 100~W. To study the SISTOC process we used different techniques: polarization analysis, interferometry and tomography of the photon orbital angular momentum. Our results confirm, in particular, that the apparent depolarization of the beam is due to the occurrence of maximal entanglement between the spin and orbital angular momentum of the photons undergoing the SISTOC process. This explanation of the true nature of the depolarization mechanism could be of some help in finding novel methods to reduce or to compensate for this usually unwanted depolarization effect in all cases where very high laser power and good beam quality are required.Comment: 6 pages, 10 figures, submitte

3D Printing and Engineering Tools Relevant to Plan a Transcatheter Procedure

Advance cardiac imaging techniques such as three-dimensional (3D) printing technology and engineering tools have experienced a rapid development over the last decade in many surgical and interventional settings. In presence of complex cardiac and extra-cardiac anatomies, the creation of a physical, patient-specific model is useful to better understand the anatomical spatial relationships and formulate the best surgical or interventional plan. Although many case reports and small series have been published over this topic, at the present time, there is still a lack of strong scientific evidence of the benefit of 3D models and advance engineering tools, including virtual and augmented reality, in clinical practice and only qualitative evaluation of the models has been used to investigate their clinical use. Patient-specific 3D models can be printed in many different materials including rigid, flexible and transparent materials, depending on their application. To plan interventional procedure, transparent materials may be preferred in order to better evaluate the device or stent landing zone. 3D models can also be used as an input for augmented and virtual reality application and advance fluido-dynamic simulation, which aim to support the interventional cardiologist before entering the cath lab. The aim of this chapter is to present an overview on how 3D printing, extended reality platforms and the most common computational engineering methodologies"finite element and computational fluid dynamics"are currently used to support percutaneous procedures in congenital heart disease (CHD), with examples from the scientific literature

Response of microchannel plates to single particles and to electromagnetic showers

We report on the response of microchannel plates (MCPs) to single relativistic particles and to electromagnetic showers. Particle detection by means of secondary emission of electrons at the MCP surface has long been proposed and is used extensively in ion time-of-flight mass spectrometers. What has not been investigated in depth is their use to detect the ionizing component of showers. The time resolution of MCPs exceeds anything that has been previously used in calorimeters and, if exploited effectively, could aid in the event reconstruction at high luminosity colliders. Several prototypes of photodetectors with the amplification stage based on MCPs were exposed to cosmic rays and to 491 MeV electrons at the INFN-LNF Beam-Test Facility. The time resolution and the efficiency of the MCPs are measured as a function of the particle multiplicity, and the results used to model the response to high-energy showers.Comment: Paper submitted to NIM

Correlation between magnetic interactions and domain structure in A1 FePt ferromagnetic thin films

We have investigated the relationship between the domain structure and the magnetic interactions in a series of FePt ferromagnetic thin films of varying thickness. As-made films grow in the magnetically soft and chemically disordered A1 phase that may have two distinct domain structures. Above a critical thickness $d_{cr}\sim 30$ nm the presence of an out of plane anisotropy induces the formation of stripes, while for $d<d_{cr}$ planar domains occur. Magnetic interactions have been characterized using the well known DCD-IRM remanence protocols, $\delta M$ plots, and magnetic viscosity measurements. We have observed a strong correlation between the domain configuration and the sign of the magnetic interactions. Planar domains are associated with positive exchange-like interactions, while stripe domains have a strong negative dipolar-like contribution. In this last case we have found a close correlation between the interaction parameter and the surface dipolar energy of the stripe domain structure. Using time dependent magnetic viscosity measurements, we have also estimated an average activation volume for magnetic reversal, $\langle V_{ac}\rangle \sim 1.37\times 10^{4}$ nm$^{3},$ which is approximately independent of the film thickness or the stripe period.Comment: 25 pages, 11 figure