We study the basic mechanisms allowing light to photoswitch at the molecular scale a spin-crossover material from a low- to a high-spin state. Combined femtosecond x-ray absorption performed at LCLS X-FEL and optical spectroscopy reveal that the structural stabilization of the photoinduced high-spin state results from a two step structural trapping. Molecular breathing vibrations are first activated and rapidly damped as part of the energy is sequentially transferred to molecular bending vibrations. During the photoswitching, the system follows a curved trajectory on the potential energy surface.

Motivated by recent neutron and x-ray observations in V2O3, we derive the effective Hamiltonian in the strong coupling limit of an Hubbard model with three degenerate t2g states containing two electrons coupled to spin S = 1, and use it to re-examine the low-temperature ground-state properties of this compound. An axial trigonal distortion of the cubic states is also taken into account. Since there are no assumptions about the symmetry properties of the hopping integrals involved, the resulting spin-orbital Hamiltonian can be generally applied to any crystallographic configuration of the transition metal ion giving rise to degenerate t2g orbitals.Specializing to the case of V2O3 we consider the low temperature antiferromagnetic insulating phase. We find two variational regimes, depending on the relative size of the correlation energy of the vertical pairs and the in-plane interaction energy. The former favors the formation of stable molecules throughout the crystal, while the latter tends to break this correlated state. Using the appropriate variational wave functions we determine in both cases the minimizing orbital solutions for various spin configurations, compare their energies and draw the corresponding phase diagrams in the space of the relevant parameters of the problem. We find that none of the symmetry-breaking stable phases with the real spin structure presents an orbital ordering compatible with the magnetic space group indicated by very recent observations of non-reciprocal x-ray gyrotropy in V2O3. We do however find a compatible solution with very small excitation energy in two distinct regions of the phase space, which might turn into the true ground state of V2O3 due to the favorable coupling with the lattice. We illustrate merits and drawbacks of the various solutions and discuss them in relation to the present experimental evidence.

Background Asthma is one of the most common non-communicable respiratory diseases, affecting about 6% of the general population. Severe asthma, even if afflicts a minority of asthmatics, drives the majority of costs of the disease. The aim of this study is to create a pharmacoeconomic model to predict the costs of corticosteroid-related adverse events in severe asthmatics and applying it to the first published epidemiologic data from the Severe Asthma Network in Italy (SANI) registry. Methods The analysis was conducted from the perspective of the Italian National Healthcare System (INHS). Model inputs, derived from literature, included: asthma epidemiology data, frequency of adverse events, percentage of severe asthma treated with OCS and adverse event cost (Diagnosis-Related Group (DRG) national tariffs). We estimated costs per different patient groups: non-asthma controls, mild/moderate and severe asthmatics. Final results report estimated direct cost per patient and total direct cost for overall target population, showing economic impact related to corticosteroid complication. Results Based on epidemiological data input, in Italy, asthmatic subjects resulted about 3,999,600, of which 199,980 with severe asthma. The number of patients with severe asthma OCS-treated was estimated at 123,988. Compared to the non-asthma control cohort and to that with moderate asthma annual cost per severe asthmatic patient resulted respectively about €892 and €606 higher, showing a corticosteroids shadow cost ranging from 45% to 30%. Applying the cost per patient to the target population identified for Italy, the budget impact model estimated a total annual cost related to OCS-related adverse events of €242.7 million for severe asthmatics. In respect with non-asthmatic and moderate population, an incremental expenditure of about € 110.6 million and €75.2, respectively, were shown. Conclusions Our study provides the first estimates of additional healthcare costs related to corticosteroid induced adverse events in severe asthma patient. Budget impact model results highlighted the relevant economic impact of OCS-related adverse events in severe asthma patients. The future extrapolation of additional data from SANI registry will support the development of a model to investigate the role of corticosteroids sparing drugs.

Motivated by recent theoretical and experimental controversy, we present a theoretical study to clarify the orbital symmetry of the ground state of vanadium spinel oxides AV2O4 (A=Zn, Mg, Cd). The study is based on an effective Hamiltonian with spin-orbital superexchange interaction and a local spin-orbit coupling term. We construct a classical phase-diagram and prove the complex orbital nature of the ground state. Remarkably, with our new analysis we predict correctly also the coherent tetragonal flattening of oxygen octahedra. Finally, through analytical considerations as well as numerical ab-initio simulations, we propose how to detect the predicted complex orbital ordering through vanadium K edge resonant x-ray scattering.PACS numbers: 75.10. Jm, 75.30.Et Vanadium and titanium spinels, AB 2 O 4 (B=Ti 3+ , or V 3+ ), belong to a class of frustrated antiferromagnets where magnetic B-ions are characterized by orbital degeneracy due to partial occupancy of t 2g -orbitals (n t2g =1 for titanates and n t2g =2 for vanadates). Recently these spinels were thoroughly studied from both experimental [1,2,3] and theoretical [4,5,6] points of view. While the ground state of Ti-based spinels can be explained in terms of orbitally-driven superexchange interactions on the frustrated pyrochlore lattice [6], the situation seems not so fluid for vanadium spinels, as two conflicting theoretical works appeared to explain their structural and magnetic properties [4,5].In AV 2 O 4 , magnetically active V 3+ -ions form a pyrochlore lattice and are characterized by two 3d electrons in t 2g -orbitals, while A is a divalent ion like Cd 2+ , or Zn 2+ , or Mg 2+ . All compounds show qualitatively similar structural and magnetic behavior with a structural transition at a higher temperature T S and an antiferromagnetic (AFM) transition at a slightly lower temperature T N [7]. These findings have been interpreted by Tsunetsugu and Motome [4] as an interplay of ddσ superexchange (SE) interaction and geometrical frustration: they showed that ordering of orbitals can partially remove magnetic frustration and explain the experimentally observed magnetic structure which is composed of AFM chains running in [110] and [110] directions. The ground state orbital ordering suggested in Ref.[4] consists of stacked ab planes with alternating d xz and d yz vanadium hole orbitals (hereafter referred to as ROO).On the other side Tchernyshyov [5] pointed out that the ground state symmetry I4 1 /a of ROO solution seems at odds with x-ray and neutron diffraction data, indicating a I4 1 /amd space symmetry. Thus, he proposed a purely ionic model where spin-orbit (SO) coupling plays the major role and the V hole occupies (predetermining the sign of Jahn-Teller (JT) distortion) a complex linear combination of xz and yz orbitals: (d xz ± id yz )/ √ 2. (We shall refer to this orbital order as COO).Actually, the correct space group of the system is still elusive. The tetragonal I4 1 /amd space group was found in Ref.[1], while the authors of the neutron scatter...

Powder neutron diffraction and resonant x-ray scattering measurements from a single crystal have been performed to study the low-temperature state of the 2D frustrated, quantum-Heisenberg system Li2VOSiO4. Both techniques indicate a collinear antiferromagnetic ground state, with propagation vector k=(1 / 2 1 / 2 0), and magnetic moments in the a-b plane. Contrary to previous reports, the ordered moment at 1.44 K, m=0.63(3)micro(B), is very close to the value expected for the square lattice Heisenberg model ( approximately 0.6micro(B)). The magnetic order is three dimensional, with antiferromagnetic a-b layers stacked ferromagnetically along the c axis. Neither x-ray nor neutron diffraction shows evidence for a structural distortion between 1.6 and 10 K.

We discuss the ground state of a pyrochlore lattice of threefold orbitally degenerate S=1/2 magnetic ions. We derive an effective spin-orbital Hamiltonian and show that the orbital degrees of freedom can modulate the spin exchange, removing the infinite spin-degeneracy characteristic of pyrochlore structures. The resulting state is a collection of spin-singlet dimers, with a residual degeneracy due to their relative orientation. This latter is lifted by a magnetoelastic interaction, induced in the spin-singlet phase space, that forces a tetragonal distortion. Such a theory provides an explanation for the helical spin-singlet pattern observed in the B spinel MgTi2O4.

International audienceComplete polarization analysis applied to resonant x-ray scattering at the Cr K edge in K2CrO4 shows that incident linearly polarized x rays can be converted into circularly polarized x rays by diffraction at the Cr pre-edge (E=5994eV) . The physical mechanism behind this phenomenon is a subtle interference effect between purely dipole (E1-E1) and purely quadrupole (E2-E2) transitions, leading to a phase shift between the respective scattering amplitudes. This effect may be exploited to disentangle two close-lying resonances that appear as a single peak in a conventional energy scan, in this way allowing one to single out and identify the different multipole order parameters involved

Background:Individuals with severe hemophilia A have reduced blood levels of clotting factor VIII (FVIII) leading to recurrent bleeding into joints and muscles. Primary prophylaxis with clotting factor concentrates started early in childhood prevents joint bleeds, thus avoiding joint damage and improving people’s quality of life. There remain significant differences in the implementation of primary prophylaxis worldwide mainly due to the cost of prophylaxis compared with treatment on demand.Objective:To evaluate the cost-effectiveness of primary prophylaxis with FVIII concentrates versus secondary prophylaxis, versus treatment on demand, and versus a “hybrid” (primary prophylaxis followed by on-demand treatment in adults) in individuals with severe hemophilia A.Methods:A Markov model was developed and run using different sources of clinical, cost, and utility data. The model was populated with a hypothetical cohort of 100 individuals with severe hemophilia A. The perspective of the Italian National Health System was used.Results:The baseline results showed that primary and secondary prophylaxis is cost-effective compared both with treatment on demand and with a hybrid strategy. The incremental costs per quality-adjusted life-year gained for individuals with hemophilia A receiving primary and secondary prophylaxis were €40,229 to €40,236 versus an on-demand strategy. However, the sensitivity analyses performed showed that the results were sensitive to the unit cost of clotting FVIII, bleeding frequency, and the discount rate.Conclusion:Although primary prophylaxis is a costly treatment, our results show that it is cost-effective compared with treatment on demand.