Decay of instable Li, Be, and B fragments and the distortion of temperature measurements in heavy ion collisions

The recent attempts to extract the temperature in the late stage of medium energy (20–60 MeV/nucleon) heavy ion collisions from the yields of γ- and particle-instable fragments are discussed. The quantum statistical model is employed to demonstrate that feeding from instable states distorts the yields used for the temperature determination severely. Some particle instable fragments are only moderately affected by feeding. These selected species can still be useful for determining the temperature. The breakup temperatures of the fragment conglomerate extracted with this method are T≃4–8 MeV, much smaller than the corresponding slope factors, which indicate T∼15 MeV

Magnetic properties of high entropy oxides

High entropy oxides (HEOs) are single phase solid solutions consisting of five or more elements in equiatomic or near-equiatomic proportions incorporated into the cationic sub-lattice(s). The uniqueness of the HEOs lies in their extreme chemical complexity enveloped in a single crystallographic structure, which in many cases results in novel functionalities. From the local structure perspective, HEOs consist of an unusually large number of different metal–oxygen–metal couples. Consequently, magnetic correlations in HEOs that inherently depend on the coordination geometry, valence, spin state and type of the metal cations that are hybridized with the bridging oxygen, are naturally affected by an extreme diversity of neighboring ionic configurations. In these conditions, a complex magneto-electronic free-energy landscape in HEOs can be expected, potentially leading to stabilization of unconventional spin-electronic states. This Frontier article provides an overview of the unique magnetic features stemming from the extreme chemical disorder in HEOs along with the possible opportunities for further research and exploration of potential functionalities

Carbon Segregation in CoCrFeMnNi High‐Entropy Alloy Driven by High‐Pressure Torsion at Room and Cryogenic Temperatures

Herein, a CoCrFeMnNi high-entropy alloy with reduced Cr content and with the addition of 2 at% C interstitial is processed via high-pressure torsion (HPT) under 6.5 GPa by three turns at room and cryogenic temperatures. The microstructure is investigated by transmission electron microscopy (TEM) and atom probe tomography (APT). The results indicate that C atoms segregate at the boundaries of the nanograins in the sample processed at room temperature, while the sample processed at cryogenic temperature does not show any notable segregations of carbon

Quantitative analysis of the relation between entropy and nucleosynthesis in central Ca + Ca and Nb + Nb collisions

The final states of central Ca + Ca and Nb + Nb collisions at 400 and 1050 MeV/nucleon and at 400 and 650 MeV/nucleon, respectively, are studied with two independently developed statistical models, namely the classical microcanonical model and the quantum-statistical grand canonical model. It is shown that these models are in agreement with each other for these systems. Furthermore, it is demonstrated that there is essentially a one-to-one relationship between the observed relative abundances of the light fragments p, d, t, 3He, and α and the entropy per nucleon, for breakup temperatures greater than 30 MeV. Entropy values of 3.5–4 are deduced from high-multiplicity selected fragment yield data

Global Constructive Optimization of Vascular Systems

We present a framework for the construction of vascular systems based on optimality principles of theoretical physiology. Given the position and flow distribution of end points of a vascular system, we construct the topology and positions of internal nodes to complete the vascular system in a realistic manner. Optimization is driven by intravascular volume minimization with constraints derived from physiological principles. Direct optimization of a vascular system, including topological changes, is used instead of simulating vessel growth. A good initial topology is found by extracting key information from a previously optimized model with less detail. This technique is used iteratively in a multi-level approach to create a globally optimized vascular system. Most of this work was completed at Fraunhofer MeVis during the summer of 2004

Hole‐doped high entropy ferrites: Structure and charge compensation mechanisms in (Gd 0.2 La 0.2 Nd 0.2 Sm 0.2 Y 0.2 ) 1− x Ca x FeO 3

High entropy oxides (HEOs) can be defined as single-phase oxide solid solutions with five or more cations in near equiatomic proportion occupying a given cation sub-lattice. The compositional flexibility while retaining the phase purity can be considered one of the major strengths of this materials class. Taking advantage of this aspect, here we explore the extent to which an aliovalent hole dopant can be incorporated into a perovskite-HEO system. Nine systems, (Gd0.2La0.2Nd0.2Sm0.2Y0.2)1−xCaxFeO3, with varying amount of Ca content (x = 0–.5) are synthesized using nebulized spray pyrolysis. Single-phase orthorhombic (Pbnm) structure can be retained up to 20% of Ca doping. Beyond 20% of Ca, a secondary rhombohedral (R-3c) phase emerges. The 57Fe Mössbauer spectra indicate that charge compensation occurs only via oxygen vacancy formation in the single-phase systems containing up to 15% of Ca. In addition, partial transition from Fe3+ to Fe4+ occurs in the 20% Ca-doped case. Room temperature Mössbauer spectroscopy further reflects the coexistence of multiple magnetic phases in crystallographic single-phase (Gd0.2La0.2Nd0.2Sm0.2Y0.2)1−xCaxFeO3, which is supported by magnetometry measurements. These initial results show the potential of charge doping to tune structural–magneto–electronic properties in compositionally complex HEOs, warranting further research in this direction

Epitaxial strain adaption in chemically disordered FeRh thin films

Strain and strain adaption mechanisms in modern functional materials are of crucial importance for their performance. Understanding these mechanisms will advance innovative approaches for material properties engineering. Here we study the strain adaption mechanism in a thin film model system as function of epitaxial strain. Chemically disordered FeRh thin films are deposited on W-V buffer layers, which allow for large variation of the preset lattice constants, e.g. epitaxial boundary condition. It is shown by means of high resolution X-ray reciprocal space maps and transmission electron microscopy that the system reacts with a tilting mechanism of the structural units in order to adapt to the lattice constants of the buffer layer. This response explained by density functional theory calculations, which evidence an energetic minimum for structures with a distortion of c/a =0.87. The experimentally observed tilting mechanism is induced by this energy gain and allows the system to remain in the most favorable structure. In general, it is shown that the use of epitaxial model heterostructures consisting of alloy buffer layers of fully miscible elements and the functional material of interest allows to study strain adaption behaviors in great detail. This approach makes even small secondary effects observable, such as the directional tilting of the structural domains identified in the present case study