Spin-lattice coupling in frustrated antiferromagnets

We review the mechanism of spin-lattice coupling in relieving the geometrical frustration of pyrochlore antiferromagnets, in particular spinel oxides. The tetrahedral unit, which is the building block of the pyrochlore lattice, undergoes a spin-driven Jahn-Teller instability when lattice degrees of freedom are coupled to the antiferromagnetism. By restricting our considerations to distortions which preserve the translational symmetries of the lattice, we present a general theory of the collective spin-Jahn-Teller effect in the pyrochlore lattice. One of the predicted lattice distortions breaks the inversion symmetry and gives rise to a chiral pyrochlore lattice, in which frustrated bonds form helices with a definite handedness. The chirality is transferred to the spin system through spin-orbit coupling, resulting in a long-period spiral state, as observed in spinel CdCr2O4. We discuss explicit models of spin-lattice coupling using local phonon modes, and their applications in other frustrated magnets.Comment: 23 pages, 6 figures. Lecture notes for Trieste Summer School, August 2007. To appear as a chapter in "Highly Frustrated Magnetism", Eds. C. Lacroix, P. Mendels, F. Mil

Adipokines and Redox Signaling: Impact on Fatty Liver Disease

Adipokines (adipose tissue cytokines) are polypeptide factors secreted by adipose tissue in a highly regulated manner. The 'classical' adipokines (leptin, adiponectin, and resistin) are expressed only by adipocytes, but other adipokines have been shown to be released by resident and infiltrating macrophages, as well as by components of the vascular stroma. Indeed, adipose tissue inflammation is known to be associated with a modification in the pattern of adipokine secretion. Several studies indicate that adipokines can interfere with hepatic injury associated with fatty infiltration, differentially modulating steatosis, inflammation, and fibrosis. Moreover, plasma levels of adipokines have been investigated in patients with nonalcoholic fatty liver disease in order to establish correlations with the underlying state of insulin resistance and with the type and severity of hepatic damage. In this Forum article, we provide a review of recent data that suggest a significant role for oxidative stress, reactive oxygen species, and redox signaling in mediating actions of adipokines that are relevant in the pathogenesis of nonalcoholic fatty liver disease, including hepatic insulin resistance, inflammation, and fibrosis

Recent developments of the Hierarchical Reference Theory of Fluids and its relation to the Renormalization Group

The Hierarchical Reference Theory (HRT) of fluids is a general framework for the description of phase transitions in microscopic models of classical and quantum statistical physics. The foundations of HRT are briefly reviewed in a self-consistent formulation which includes both the original sharp cut-off procedure and the smooth cut-off implementation, which has been recently investigated. The critical properties of HRT are summarized, together with the behavior of the theory at first order phase transitions. However, the emphasis of this presentation is on the close relationship between HRT and non perturbative renormalization group methods, as well as on recent generalizations of HRT to microscopic models of interest in soft matter and quantum many body physics.Comment: 17 pages, 5 figures. Review paper to appear in Molecular Physic

Assessing the performance of XDP and AF-XDP based NFs in edge data center scenarios

While servers in traditional data centers can be specialized to run either CPU-intensive or network-intensive workloads, edge data centers need to consolidate both on the same machine(s) due to the reduced number of servers. This paper presents some preliminary experiments to determine how to improve the overall throughput of the above servers, being XDP and AF_XDP the two main technologies into play

Lattice effects on the spin dynamics in antiferromagnetic molecular rings

We investigate spin dynamics in antiferromagnetic (AF) molecular rings at finite temperature in the presence of spin-phonon (s-p) interaction. We derive a general expression for the spin susceptibility in the weak s-p coupling limit and then we focus on the low-frequency behavior, in order to discuss a possible microscopic mechanism for nuclear relaxation in this class of magnetic materials. To lowest order in a perturbative expansion, we find that the susceptibility takes a Lorentzian profile and all spin operators ($S^x$, $S^y, S^z$) contribute to spin dynamics at wave vectors $q\ne 0$. Spin anisotropies and local s-p coupling play a key role in the proposed mechanism. Our results prove that small changes in the spatial symmetry of the ring induce qualitative changes in the spin dynamics at the nuclear frequency, providing a novel mechanism for nuclear relaxation. Possible experiments are proposed.Comment: 4 pages, 2 figures. to appear in PR

Providing Telco-oriented Network Services with eBPF: The Case for a 5G Mobile Gateway

Although several technologies exist for high-speed data plane processing, such as DPDK, the above technologies require a rigid partitioning of the resources of the system, such as dedicated CPU cores and network interfaces. Unfortunately, this is not always possible when running at the edge of the network, in which a few servers are available in each cluster and a mixture of data and control plane services must coexist on the same hardware. In this respect, eBPF can become a better alternative thanks to its integration in the vanilla Linux kernel, which enables contemporary support for data and control plane services, hence enabling a more efficient usage of the (scarce) computing resources. This paper proposes the first proof-of-concept open-source implementation of a 5G Mobile Gateway based on eBPF/XDP, highlighting the possible challenges (e.g., to create traffic policers, as buffering is not available in eBPF) and the resulting architecture. The result is characterized in terms of performance and scalability and compared with alternative technologies, showing that it outperforms other in-kernel solutions (e.g., Open vSwitch) and is comparable with DPDK-based platforms

Spin-liquid and magnetic phases in the anisotropic triangular lattice: the case of κ\kappa-(ET)2_2X

The two-dimensional Hubbard model on the anisotropic triangular lattice, with two different hopping amplitudes $t$ and $t^\prime$, is relevant to describe the low-energy physics of $\kappa$-(ET)$_2$X, a family of organic salts. The ground-state properties of this model are studied by using Monte Carlo techniques, on the basis of a recent definition of backflow correlations for strongly-correlated lattice systems. The results show that there is no magnetic order for reasonably large values of the electron-electron interaction $U$ and frustrating ratio $t^\prime/t = 0.85$, suitable to describe the non-magnetic compound with X=Cu$_2$(CN)$_3$. On the contrary, N\'eel order takes place for weaker frustrations, i.e., $t^\prime/t \sim 0.4 \div 0.6$, suitable for materials with X=Cu$_2$(SCN)$_2$, Cu[N(CN)$_2$]Cl, or Cu[N(CN)$_2$]Br.Comment: 7 pages, Physical Review B 80, 064419 (2009

Effect of doping and oxygen vacancies on the octahedral tilt transitions in the BaCeO3 perovskite

We present a systematic study of the effect of Y doping and hydration level on the structural transformations of BaCeO3 based on anelastic spectroscopy experiments. The temperature of the intermediate transformation between rhombohedral and orthorhombic Imma phases rises with increasing the molar fraction x of Y roughly as (500 K)x in the hydrated state, and is depressed of more than twice that amount after complete dehydration. This is explained in terms of the effect of doping on the average (Ce/Y)-O and Ba-O bond lengths, and of lattice relaxation from O vacancies. The different behavior of the transition to the lower temperature Pnma orthorhombic phase is tentatively explained in terms of progressive flattening of the effective shape of the OH ion and ordering of the O vacancies during cooling.Comment: 8 pages, 5 figure