From Beam to Chassis: How to Increase NVH Performances with an Optimized Moment of Inertia Distribution

Car weight reduction is becoming more and more important for every kind of vehicle: minor mass implies, in fact, minor consumption, makes easier to fulfill homologation rules and assures a better handling behavior. Despite that, several vehicle missions have always been solved by adding more mass, e.g. NVH. In this paper, a methodology to optimize the stiffness distribution is proposed in order to obtain better vibrational performances without increasing the mass. At first, the problem has been solved for a simple beam using finite element and optimization algorithms. At a second stage, the optimal moment of inertia distribution found has been applied to a chassis thanks to a topometry optimization. Finally, the improvement in NVH performances has been verified comparing the inertances of the optimized model with those of the non-optimized one

Relativity and Magnetism in Ni-Pd and Ni-Pt Alloys

We show that the differences in the magnetic properties of Ni-Pd and Ni-Pt alloys arise mainly due to relativity. In particular, we find that the local magnetic moment of Ni increases with the addition of Pd in Ni-Pd while it decreases with the addition of Pt in Ni-Pt, as found experimentally, only if relativity is present. Our analysis is based on the effects of relativity on (i) the spin-polarized densities of states of Ni, (ii) the splitting of majority and minority spin d-band centers of Ni, and (iii) the separation between s-d band centers of Pd and Pt in Ni-Pd and Ni-Pt alloys.Comment: one figure added, a paragraph added in discussio

Structural Properties and Relative Stability of (Meta)Stable Ordered, Partially-ordered and Disordered Al-Li Alloy Phases

We resolve issues that have plagued reliable prediction of relative phase stability for solid-solutions and compounds. Due to its commercially important phase diagram, we showcase Al-Li system because historically density-functional theory (DFT) results show large scatter and limited success in predicting the structural properties and stability of solid-solutions relative to ordered compounds. Using recent advances in an optimal basis-set representation of the topology of electronic charge density (and, hence, atomic size), we present DFT results that agree reasonably well with all known experimental data for the structural properties and formation energies of ordered, off-stoichiometric partially-ordered and disordered alloys, opening the way for reliable study in complex alloys.Comment: 7 pages, 2 figures, 2 Table

Four-terminal resistance of an interacting quantum wire with weakly invasive contacts

We analyze the behavior of the four-terminal resistance, relative to the two-terminal resistance of an interacting quantum wire with an impurity, taking into account the invasiveness of the voltage probes. We consider a one-dimensional Luttinger model of spinless fermions for the wire. We treat the coupling to the voltage probes perturbatively, within the framework of non-equilibrium Green function techniques. Our investigation unveils the combined effect of impurities, electron-electron interactions and invasiveness of the probes on the possible occurrence of negative resistance.Comment: 10 pages, 7 figure

Adiabatic and Non-Adiabatic Contributions to the Free Energy from the Electron-Phonon Interaction for Na, K, Al, and Pb

We calculate the adiabatic contributions to the free energy due to the electron--phonon interaction at intermediate temperatures, $0 \leqslant k_{B} T < \epsilon_{F}$ for the elemental metals Na, K, Al, and Pb. Using our previously published results for the nonadiabatic contributions we show that the adiabatic contribution, which is proportional to $T^{2}$ at low temperatures and goes as $T^{3}$ at high temperatures, dominates the nonadiabatic contribution for temperatures above a cross--over temperature, $T_{c}$, which is between 0.5 and 0.8 $T_{m}$, where $T_{m}$ is the melting temperature of the metal. The nonadiabatic contribution falls as $T^{-1}$ for temperatures roughly above the average phonon frequency.Comment: Updated versio

Instability of the rhodium magnetic moment as origin of the metamagnetic phase transition in alpha-FeRh

Based on ab initio total energy calculations we show that two magnetic states of rhodium atoms together with competing ferromagnetic and antiferromagnetic exchange interactions are responsible for a temperature induced metamagnetic phase transition, which experimentally is observed for stoichiometric alpha-FeRh. A first-principle spin-based model allows to reproduce this first-order metamagnetic transition by means of Monte Carlo simulations. Further inclusion of spacial variation of exchange parameters leads to a realistic description of the experimental magneto-volume effects in alpha-FeRh.Comment: 10 pages, 13 figures, accepted for publication in Phys. Rev.

Spin Screening and Antiscreening in a Ferromagnet/Superconductor Heterojunction

We present a theoretical study of spin screening effects in a ferromagnet/superconductor (F/S) heterojunction. It is shown that the magnetic moment of the ferromagnet is screened or antiscreened, depending on the polarization of the electrons at the Fermi level. If the polarization is determined by the electrons of the majority (minority) spin band then the magnetic moment of the ferromagnet is screened (antiscreened) by the electrons in the superconductor. We propose experiments that may confirm our theory: for ferromagnetic alloys with certain concentration of Fe or Ni ions there will be screening or antiscreening respectively. Different configurations for the density of states are also discussed.Comment: 5 pages; 4 figures. to be published in Phys. Rev,

Geometric, electronic, and magnetic structure of Co2_2FeSi: Curie temperature and magnetic moment measurements and calculations

In this work a simple concept was used for a systematic search for new materials with high spin polarization. It is based on two semi-empirical models. Firstly, the Slater-Pauling rule was used for estimation of the magnetic moment. This model is well supported by electronic structure calculations. The second model was found particularly for Co$_2$ based Heusler compounds when comparing their magnetic properties. It turned out that these compounds exhibit seemingly a linear dependence of the Curie temperature as function of the magnetic moment. Stimulated by these models, Co$_2$FeSi was revisited. The compound was investigated in detail concerning its geometrical and magnetic structure by means of X-ray diffraction, X-ray absorption and M\"o\ss bauer spectroscopies as well as high and low temperature magnetometry. The measurements revealed that it is, currently, the material with the highest magnetic moment ($6\mu_B$) and Curie-temperature (1100K) in the classes of Heusler compounds as well as half-metallic ferromagnets. The experimental findings are supported by detailed electronic structure calculations

The occurrence of two morphologically similar Chaetozone (Annelida: Polychaeta: Cirratulidae) species from the Italian seas: Chaetozone corona Berkeley & Berkeley, 1941 and C. carpenteri McIntosh, 1911

The present study reports the spread of the cirratulids Chaetozone corona Berkeley & Berkeley, 1941 and Chaetozone carpenteri McIntosh, 1911 in the Western Central Adriatic Sea, off the coasts of Pescara (Italy). The two species were collected between 2014 and 2016 from soft bottom stations (at depths from 16.5 to 130 m) where the environment was more or less disturbed due to fishing activities. One specimen of C. corona was found also off the coast of Calafuria (Livorno, Italy), representing the first record of this species in the Tyrrhenian Sea. Chaetozone carpenteri could be a native species present in the Mediterranean for a long time but rarely recorded because of taxonomic confusion. Chaetozone corona was already known from the eastern Mediterranean Sea (except from the Adriatic Sea), where it is considered an established alien species. Our results extend the geographic range of these two cirratulid species, providing some information on their ecology and habitat preference. We also suggest a likely vector of spread of C. corona from the easternmost part of the Mediterranean towards the study area. The finding of reproducing specimens of C. corona and C. carpenteri supports the hypothesis that these two species have found a suitable habitat in the Western Central Adriatic Sea, and there will become well established. Although nothing suggests that C. corona would be invasive, it may, however, compete with native species. These findings also seem particularly relevant in order to improve the knowledge of Mediterranean biodiversity

HARES: an efficient method for first-principles electronic structure calculations of complex systems

We discuss our new implementation of the Real-space Electronic Structure method for studying the atomic and electronic structure of infinite periodic as well as finite systems, based on density functional theory. This improved version which we call HARES (for High-performance-fortran Adaptive grid Real-space Electronic Structure) aims at making the method widely applicable and efficient, using high performance Fortran on parallel architectures. The scaling of various parts of a HARES calculation is analyzed and compared to that of plane-wave based methods. The new developments that lead to enhanced performance, and their parallel implementation, are presented in detail. We illustrate the application of HARES to the study of elemental crystalline solids, molecules and complex crystalline materials, such as blue bronze and zeolites.Comment: 17 two-column pages, including 9 figures, 5 tables. To appear in Computer Physics Communications. Several minor revisions based on feedbac