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The skyrmion racetrack is a promising concept for future information technology. There, binary bits are carried by nanoscale spin swirls -- skyrmions -- driven along magnetic strips. Stability of the skyrmions is a critical issue for the realization of this technology. Here we demonstrate that the racetrack skyrmion lifetime can be calculated from first principles as a function of temperature, magnetic field and track width. Our method combines harmonic transition state theory extended to include Goldstone modes, with an atomistic spin Hamiltonian parametrized from density functional theory calculations. We demonstrate that two annihilation mechanisms contribute to the skyrmion stability: At low external magnetic field, escape through the track boundary prevails, but a crossover field exists, above which the collapse in the interior becomes dominant. Considering a Pd/Fe bilayer on an Ir(111) substrate as a well-established model system, the calculated lifetime is found to be consistent with reported experimental measurements. Our results open the door for predictive simulations, free from empirical parameters, to aid the design of skyrmion-based information technology.

Objective 1. To test, through tri-dimensional analysis, whether cartilage thickness at the posterior aspect of the medial and lateral condyles differs in medial femorotibial OA knees compared to matched non-OA knees. 2. To determine the locations of thickest cartilage at posterior aspects of femoral condyles. Design Two groups of non-OA (n=40) and severe medial femorotibial OA (n=40) patients of over 50 years of age, matched for gender, age and bone morphometric parameters, with radiographs and CT arthrograms of the knee, were randomly selected retrospectively. CT arthrograms were segmented to measure the mean cartilage thickness, the maximal cartilage thickness and the location of maximal cartilage thickness in a region of interest at the posterior aspect of the condyles. Results For the medial condyle, mean and maximum cartilage thicknesses were statistically significantly higher in OA knees compared to non-OA knees (1.66 vs. 1.46mm, p=0.012 and 2.53 vs. 2.13mm, p=0.0006 respectively). The thickest cartilage was located in the half most medial aspect of the medial condyle for both groups. For the lateral condyle, no statistically significant difference between non-OA and OA knees was found (p≥0.16). Conclusions Cartilage at the posterior aspect of the medial condyle, but not the lateral condyle is statistically significantly thicker in OA knees compared to matched non-OA knees. The thickest cartilage was located in the half most medial aspect of the posterior medial condyle. These results will serve as the basis for future research to determine whether the thicker cartilage corresponds to cartilage hypertrophy due to reparative processes in reaction to OA.

We have investigated the electronic and magnetic properties of Co$_{1-{ m x}}$Fe$_{ m x}$Sb$_{3}$ skutterudites from density functional theory and Monte Carlo simulations. We find that above a certain threshold in the Fe concentration, somewhere between x=0.125 and x=0.25, Co$_{1-{ m x}}$Fe$_{ m x}$Sb$_{3}$ is ferromagnetic with an atomic moment which increases asymptotically towards about 1 $mu_{B}$/Fe and a non-zero Curie temperature which reaches 70 K for FeSb$_{3}$. Ferromagnetism is favored due to a Stoner instability in the electronic structure, where a large density of states at the Fermi-level makes it favorable to form the ferromagnetic ground state.

The strong coupling between the crystal structure and magnetic state (ferromagnetic or helical antiferromagnetic) of FeMnP0.75Si0.25 is investigated using density functional theory in combination with atomistic spin dynamics. We find many competing energy minima for drastically different ferromagnetic and noncollinear magnetic configurations. We also find that the appearance of a helical spin-spiral magnetic structure at finite temperature is strongly related to one of the crystal structures reported for this material. Shorter Fe-Fe distances are found to lead to a destabilized ferromagnetic coupling, while out-of-plane Mn-Mn exchange interactions become negative with the shortening of the interatomic distances along the c axis, implying an antiferromagnetic coupling for the nearest-neighbor Mn-Mn interactions. The impact of the local dynamical correlations is also discussed.

Isolated theropod teeth referable to Abelisauridae indet., and Carcharodontosauridae cf., from the Campanian-Maastrichtian Presidente Prudente Formation of the western São Paulo State, Brazil, are described. They are compared to the Late Cretaceous Gondwanan theropod dinosaur teeth and their affinities are discussed. These teeth are significant because carnivorous dinosaur remains are poorly known from the Late Cretaceous beds of Western São Paulo State except for a few isolated elements.Se describen dientes aislados de terópodos referidos a Abelisauridae indet. y Carcharodontosauridae cf., procedentes de la Formación Presidente Prudente del Campaniano-Maastrichtiano, en el oeste del estado de San Pablo, Brasil. Los materiales son comparados con dientes de dinosaurios gondwánicos del Cretácico tardío, y cuyas afinidades son aquí discutidas. Estos dientes de dinosaurios carnívoros son significativos debido a que su presencia es pobremente conocida en el Cretácico tardío del oeste del estado del San Pablo, excepto por unos pocos huesos.

In this article we report on micromagnetic simulations performed on a permalloy nanostructure in presence of a uniform thermal gradient. Our numerical simulations show that heat flow is an effective mean to compensate the damping, and that the gradients at which spin-wave amplification is observed are experimentally accessible. In particular, we have studied the role of the Gilbert damping parameter on spin-wave amplification., this paper has been withdrawn to be re-written

We report a classical interatomic force field for TiO2, which has been parametrized using density functional theory forces, energies, and stresses in the rutile crystal structure. The reliability of this classical potential is tested by evaluating the structural properties, equation of state, phonon properties, thermal expansion, and some thermodynamic quantities such as entropy, free energy, and specific heat under constant volume. The good agreement of our results with ab initio calculations and with experimental data, indicates that our force field describes the atomic interactions of TiO2 in the rutile structure very well. The force field can also describe the structures of the brookite and anatase crystals with good accuracy.

We report a classical interatomic force field for TiO$_2$, which has been parameterized using density functional theory forces, energies, and stresses in the rutile crystal structure. The reliability of this new classical potential is tested by evaluating the structural properties, equation of state, phonon properties, thermal expansion, and some thermodynamic quantities such as entropy, free energy, and specific heat under constant volume. The good agreement of our results with {\em ab initio} calculations and with experimental data, indicates that our force-field describes the atomic interactions of TiO$_2$ in the rutile structure very well. The force field can also describe the structures of the brookite and anatase crystals with good accuracy., Accepted for publication in Phys. Rev. B; Changes from v1 include multiple minor revisions and a re-write of the description of the force field in Section II.

We present a first-principles study of the physical properties of the disordered Ni2-xMnSb alloys which form a continuous series connecting two typical members of the Heusler alloy family: namely, the half-metallic semi-Heusler alloy NiMnSb (x=1) and related metallic Heusler alloy Ni2MnSb (x=0). Magnetic moments, exchange interactions, magnon spectra, and Curie temperatures at ambient and elevated pressures are determined and compared with available experimental data. The spin-spin correlation functions at the critical temperature are also calculated. The pair exchange interactions and corresponding classical Heisenberg Hamiltonian are derived from self-consistent electronic structure calculations using a magnetic force theorem. Heusler alloys NiMnSb and Ni2MnSb exhibit strikingly different asymptotic behavior of exchange interactions with the distance between magnetic atoms. The Curie temperatures are estimated using multisublattice versions of the mean-field approximation, random-phase approximation, and Monte Carlo simulations. The robustness of the results with respect to the effect of correlations beyond the local density approximation, the selected reference state used for mapping to the Heisenberg Hamiltonian, and the applied mapping procedure are also discussed.

A new ternary Ir-Mn-Si phase with stoichiometry Mn3IrSi has been synthesized and found to crystallize in the cubic AlAu4-type structure, space group P213 with Z=4, which is an ordered form of the beta-Mn structure. The unit cell dimension was determined by x-ray powder diffraction to a=6.4973(3) Angstrom. In addition to the crystal structure, we have determined the magnetic structure and properties using superconducting quantum interference device magnetometry and Rietveld refinements of neutron powder diffraction data. A complex noncollinear magnetic structure is found, with magnetic moments of 2.97(4)u(B) at 10 K only on the Mn atoms. The crystal structure consists of a triangular network built up by Mn atoms, on which the moments are rotated 120degrees around the triangle axes. The magnetic unit cell is the same as the crystallographic and carries no net magnetic moment. The Neel temperature was determined to be 210 K. A first-principles study, based on density functional theory in a general noncollinear formulation, reproduces the experimental results with good agreement. The observed magnetic structure is argued to be the result of frustration of antiferromagnetic couplings by the triangular geometry.

The bone-imaging agents MDP, DPD and HDP were compared radiochemically (only minor differences were found) in 12 patients with prostatic and 12 patients with breast carcinoma. Each patient received both MDP and either DPD or HDP. The scintigraphic examinations were compared visually and quantitatively. The uptake ratio normal bone/soft tissue was higher for DPD and HDP than for MDP. The ratio pathologic bone/normal bone was highest for MDP, particularly for prostatic carcinoma. The differences in this ratio for breast carcinoma were in general non-significant. The observed differences were minor and of little practical importance.