A quantum mechanical study of the dynamical properties of spin-ice materials

The spin-ice materials Ho2Ti2O7 (HTO) and Dy2Ti2O7 (DTO) are part of a large family of compounds called magnetic pyrochlore oxides. Typically, the magnetism of these systems arise from the rare-earth ions RE3+ which sits at the vertices of a lattice of corner-sharing tetrahedra and couple with the degrees of freedom of the crystal leading to a wide spectrum of exotic phenomena. In spin-ices the magnetic moments of the individual RE3+ ions are large enough to let their mutual dipolar interactions be the leading factors for the thermodynamics. Moreover, the strength and the symmetries of their local crystalline environment are such that each ion behaves like a magnetic dipole with only two allowed configurations: it points either parallel or opposite to the ?111? axis joining the vertex where it sits to the centre of the tetrahedron. As a result, the ground state of the system is macroscopically degenerate because the ferromagnetic interactions between the 4 Ising-like spins in each tetrahedron cannot be satisfied simultaneously, and in turn the manifold of possible configurations minimising the energy (2 spins inward - 2 spins outward) increases with the size of the system. This exotic ground state is such that the Ising configurations of the dipoles map to the disordered vector-displacements of the protons in the water molecules of conventional ice; hence the name spin-ice. Violations of the (2in-2out) ice rules take the systems out of the ground state into more energetic configurations. More precisely, the flipping of a spin between two adjacent ground-state tetrahedra creates a local excitation (1in-3out in a tetrahedron, 3in-1out in the neighbouring one) that is made of two fractionalised opposite magnetic fluxes. Once the two fluxes are created they can separate and freely hop across the lattice as their motion does not involve ahy higher order violation of the ice-rules. The low temperature properties of spin-ice is found to depend heavily, if not exclusively, on the density and mobility of such flux-defects which effectively behave as magnetic monopoles mutually interacting via a Coulomb potential. Beside the success of many experiments which exploit the physics of the monopoles in their exclusively classical formulation, there has been an increasing curiosity about the microscopic mechanisms which dictate their propagation across the lattice. At present, the dynamics of the monopoles are still puzzling showing different responses under different probes and non-identical behaviours between the two compounds HTO and DTO. As the monopoles themselves consist of packed magnetic fluxes originating from the magnetic moments of the RE3+ ions, investigating the microscopical mechanisms underlying their motion requires revisiting the foundations of the classicality which emerges form the quantum substrate of the interactions of the magnetic ions. This is the subject of the work presented in this thesis. With particular focus on the interplay between the local crystal-symmetries and the mutual interactions between the RE3+ ions, the present study gives an accurate de- scription of the microscopic mechanisms which occur in the pyrochlore substrate in the presence of a monopole. The results suggest that the motion of the monopoles is achieved thanks to the spin-tunnelling of the RE3+ ions which account for the flipping of the Ising spins, necessary for the propagation of a monopole. A major improvement we add to the standard theory of spin ice, is the role of the exchange interactions that are overcome by the dipolar ones in the ice-state but posses a dynamical resilience which manifests in the presence of a monopole. Furthermore, the present study brings to light the articulated statistical structure of the kinematic spin-constraints which are expected to dictate the diffusion of the free monopoles and their response under dif- ferent probes also in conditions out of equilibrium. From a more general perspective, the mathematical and physical models developed during this work promise to be of in- terest also in other magnetic systems. Primarily, in the other pyrochlore oxides whose microscopical structure is akin the spin-ice one, secondarily, in other RE3+ compounds where the interplay between quantum and classical physics leads to the manifestation of unusual dynamical effects

Quantum discord in a spin system with symmetry breaking

We analyze the quantum discord Q throughout the low-temperature phase diagram of the quantum XY model in transverse field. We first focus on the T=0 order-disorder quantum phase transition both in the symmetric ground state and in the symmetry broken one. Besides it, we highlight how Q displays clear anomalies also at a non critical value of the control parameter inside the ordered phase, where the ground state is completely factorized. We evidence how the phenomenon is in fact of collective nature and displays universal features. We also study Q at finite temperature. We show that, close to the quantum phase transition, Q exhibits quantum-classical crossover of the system with universal scaling behavior. We evidence a non trivial pattern of thermal correlations resulting from the factorization phenomenon.Comment: 9 pages, 9 figure, Contribution to the Festschrift volume in honour of Vladimir Korepi

Role of the Virtual Stakeholders in the Search of a Balance between Environment, Economy and Society in the Policy Choices Management

The PhD Thesis develops a pre-quantitative methodology to define the direct and indirect effects of policy choices concerning the environment. The main purpose has been to contribute to the solution of some of the problems affecting expert-based judgements: in particular, the dependence on the observer’s goals and beliefs (Reflexivity) and the possibility of making prevalent and accepted an extraneous and non-sustainable solution (Perspectivity). "Policy Choices Analysis and Synthesis System 42" (PoChASSy42) methodology provides a framework which describes the environment through all the possible interactions between: "Individuals Interests", identified as the normative values of the Universal Declaration of the Human Rights; "Collective Interests" identified through the economic activities classified by the NACE system of EuroStat; "Ecosystem Services", identified through the Millennium Ecosystem Assessment studies. The elements which make up these spheres of interests are considered as virtual stakeholders, i.e. the representatives of the existence, intentions, motivations and interests that make up the environment. Both the virtual stakeholders and the possible interactions among them are represented in the PoChASSy42 through the development of an Adjacency Matrix and a Narrative Structure (graph). Using these tools, the expert can: find the virtual stakeholders involved in a given policy choice and exclude, declaring the motivations, those which are not present in the particular geographic context. A final report with the results allows for a transparent communication, which is fundamental in order to further counteract the side effects (Perspectivity and Reflectivity) of a reductionist vision of the environment and to accept the challenge of complexity

2016 WHO GLOBAL GUIDELINES FOR THE PREVENTION OF SURGICAL SITE INFECTION: A NEW STEP TO IMPROVE PATIENT'S SAFETY BEFORE, DURING AND AFTER SURGERY

Surgical site infection (SSI) are among the most preventable health-care-associated infections and are a substantial burden to health-care systems and service payers worldwide in terms of patient morbidity, mortality, and additional costs. SSI prevention is complex and requires the integration of a range of measures before, during and after surgery. No international guidelines are available and incosistencies in the interpretations of evidence and recommendations of national guidelines have been identified. Given the burden of SSI worldwide, the numerous gaps in evidence-based guidance, and the need for standardisation and a global approach, WHO decided to prioritise the development of evidence-based recommendations for thew prevention of SSI. The guidelines take into account the balance between benefits and harms, the evidence quality, costs and resource use implications, and patgients values andf preferences. on the basis of systematic literature reviews and expert consensus, we present 23 recommendations on preoperative, intraoperative and postoperative preventive measures. The WHO recommendations were developed with a global perspective and they take into account the balance between benefitgs and harms, the evidence quality level, cost and resource use implications, and patient values and preferences

(Dipyrido[3,2-a:2',3'-c]phenazine)(glycinato)copper(II) perchlorate: A novel DNA-intercalator with anti-proliferative activity against thyroid cancer cell lines

A novel copper(II) heteroleptic complex of dipyrido[3,2-a:2′,3′-c]phenazine (dppz) and glycinato (gly) as chelating ancillary ligand, [Cu(dppz)(gly)]ClO4 (1), was synthesized and characterized. X-ray crystallography revealed that the coordination geometry of the cationic [Cu(dppz)(gly)]+ unit is hexacoordinated and shows a distorted octahedral coordination geometry in the solid state, with the N,N and N,O chelating atoms of dppz and glycinato, respectively, in the square plane and in which the planar units are connected in a monodimensional polymeric array by the apical copper coordination of the second carboxylic oxygen atom. Biological assays showed that 1 exhibits a remarkable anti-proliferative activity against the two human anaplastic thyroid cancer cell lines 8505c (BrafV600E/V600E) and SW1736 (BrafWT/V600E), in a dose- and time-dependent manner. In details, the IC50 after 48 h of drug exposure was 2.86±0.54 μM for SW1736 and 1.05±0.48 μM for 8505c. On the other hand, the IC50 shown by cis-diamminedichloroplatinum(II) (cisplatin) against the same cell lines was 2.50±0.40 μM and 6.03±0.78 μM, respectively. Optical microscopy observations, after 48 h of treatment, showed morphological cell changes typical of apoptosis, confirmed by DNA ladder assays. DNA interaction studies, performed by UV absorption spectrophotometry, circular dichroism and viscosimetry, clearly showed that [Cu(dppz)(gly)]ClO4 is a DNA-intercalator, with a DNA-binding constant, Kb, of 2.1×106 M−1, suggesting that the mechanism of the cytotoxic activity can be related to its DNA-binding

Bioengineered vascular scaffolds: the state of the art

To date, there is increasing clinical need for vascular substitutes due to accidents, malformations, and ischemic diseases. Over the years, many approaches have been developed to solve this problem, starting from autologous native vessels to artificial vascular grafts; unfortunately, none of these have provided the perfect vascular substitute. All have been burdened by various complications, including infection, thrombogenicity, calcification, foreign body reaction, lack of growth potential, late stenosis and occlusion from intimal hyperplasia, and pseudoaneurysm formation. In the last few years, vascular tissue engineering has emerged as one of the most promising approaches for producing mechanically competent vascular substitutes. Nanotechnologies have contributed their part, allowing extraordinarily biostable and biocompatible materials to be developed. Specifically, the use of electrospinning to manufacture conduits able to guarantee a stable flow of biological fluids and guide the formation of a new vessel has revolutionized the concept of the vascular substitute. The electrospinning technique allows extracellular matrix (ECM) to be mimicked with high fidelity, reproducing its porosity and complexity, and providing an environment suitable for cell growth. In the future, a better knowledge of ECM and the manufacture of new materials will allow us to "create" functional biological vessels - the base required to develop organ substitutes and eventually solve the problem of organ failure

Ground-state factorization and correlations with broken symmetry

We show how the phenomenon of factorization in a quantum many-body system is of collective nature. To this aim we study the quantum discord Q in the one-dimensional XY model in a transverse field. We analyze the behavior of Q at both the critical point and at the non-critical factorizing field. The factorization is found to be governed by an exponential scaling law for Q. We also address the thermal effects fanning out from the anomalies occurring at zero temperature. Close to the quantum phase transition, Q exhibits a finite-temperature crossover with universal scaling behavior, while the factorization phenomenon results in a non-trivial pattern of correlations present at low temperature

Manipulation of magnetic solitons under the influence of DMI gradients

Magnetic solitons are promising for applications due to their intrinsic properties such as small size, topological stability, ultralow power manipulation and potentially ultrafast operations. To date, research has focused on the manipulation of skyrmions, domain walls, and vortices by applied currents. The discovery of new methods to control magnetic parameters, such as the interfacial Dzyaloshinskii-Moriya interaction (DMI) by strain, geometry design, temperature gradients, and applied voltages promises new avenues for energetically efficient manipulation of magnetic structures. The latter has shown significant progress in 2d material-based technology. In this work, we present a comprehensive study using numerical and analytical methods of the stability and motion of different magnetic textures under the influence of DMI gradients. Our results show that under the influence of linear DMI gradients, N\'eel and Bloch-type skyrmions and radial vortex exhibit motion with finite skyrmion Hall angle, while the circular vortex undergoes expulsion dynamics. This work provides a deeper and crucial understanding of the stability and gradient-driven dynamics of magnetic solitons, and paves the way for the design of alternative low-power sources of magnetization manipulation in the emerging field of 2d materials.Comment: 19 pages, 5 figure