Induced radionuclides in astronauts Final report, 15 Jun. 1967 - 1 Sep. 1968

Experimental determination of cosmic radiation effects on tissue equivalent materials and human

Spin-1 effective Hamiltonian with three degenerate orbitals: An application to the case of V_2O_3

Motivated by recent neutron and x-ray observations in V_2O_3, we derive the effective Hamiltonian in the strong coupling limit of an Hubbard model with three degenerate t_{2g} 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 t_{2g} orbitals. Specializing to the case of V_2O_3 we consider the 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. We determine in both cases the minimizing orbital solutions for various spin configurations, and draw the corresponding phase diagrams. 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 V_2O_3. 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 V_2O_3 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.Comment: 36 pages, 19 figure

Cosmic ray induced radioactivity in astronauts as a measure of radiation dose /a/

Cosmic ray induced radioactivity in astronauts as measure of radiation dosag

How will disenfranchised Peoples adapt to Climate Change? Strengthening the Ecojustice Movement

The Fourth assessment of the Intergovernmental Panel on Climate Change (IPCC) acknowledged That millions of people are currently, and will increasingly be, affected by the impacts of climate change, in the form of floods, droughts and other extreme events, as well as related threats to food security. In response to these global environmental changes, the international community, including civil society, is acting on the need for immediate adaptation measures and is developing strategies for future adaptation. However, the impacts of climate change are unevenly distributed, with many of the poorest, most vulnerable peoples experiencing the immediate effects of climate change, in the here and now. As the IPCC noted, developing countries are disproportionately affected by climate change and often, the least able to adapt due to lack of infrastructure and resources

Strengthening Resilience by thinking of Knowledge as a nutrient connecting the local person to global thinking: The case of Social Technology/Tecnologia Social

In this chapter, we describe the Knowledge as a Nutrient framework that emerged from these conversations. We describe how it relates to the Tecnologia Social policy approach to sustainability, developed in Brazil (Dagnino et al. 2004, Fundação Banco do Brasil 2009, Costa 2013), which is not well known in the anglophone world. Tecnologia Social was both inspired by and rooted in Paulo Freire’s pedagogical thinking (2000, Klix 2014).   We show how this framework has the potential to increase community resilience and adaptive capacity, not only for communities that face and must adapt to climate change but for all communities in the throes of complex social, ecological, economic and political transitions.This research was supported by the International Development Research Centre, grant number IDRC GRANT NO. 106002-00

Quantum spin liquid at finite temperature: proximate dynamics and persistent typicality

Quantum spin liquids are long-range entangled states of matter with emergent gauge fields and fractionalized excitations. While candidate materials, such as the Kitaev honeycomb ruthenate $\alpha$-RuCl$_3$, show magnetic order at low temperatures $T$, here we demonstrate numerically a dynamical crossover from magnon-like behavior at low $T$ and frequencies $\omega$ to long-lived fractionalized fermionic quasiparticles at higher $T$ and $\omega$. This crossover is akin to the presence of spinon continua in quasi-1D spin chains. It is further shown to go hand in hand with persistent typicality down to very low $T$. This aspect, which has also been observed in the spin-1/2 kagome Heisenberg antiferromagnet, is a signature of proximate spin liquidity and emergent gauge degrees of freedom more generally, and can be the basis for the numerical study of many finite-$T$ properties of putative spin liquids.Comment: 13 pages, 11 figures, accepted versio

Variational study of the antiferromagnetic insulating phase of V2O3 based on Nth order Muffin-Tin-Orbitals

Motivated by recent results of $N$th order muffin-tin orbital (NMTO) implementation of the density functional theory (DFT), we re-examine low-temperature ground-state properties of the anti-ferromagnetic insulating phase of vanadium sesquioxide V$_2$O$_3$. The hopping matrix elements obtained by the NMTO-downfolding procedure differ significantly from those previously obtained in electronic structure calculations and imply that the in-plane hopping integrals are as important as the out-of-plane ones. We use the NMTO hopping matrix elements as input and perform a variational study of the ground state. We show that the formation of stable molecules throughout the crystal is not favorable in this case and that the experimentally observed magnetic structure can still be obtained in the atomic variational regime. However the resulting ground state (two $t_{2g}$ electrons occupying the degenerate $e_g$ doublet) is in contrast with many well established experimental observations. We discuss the implications of this finding in the light of the non-local electronic correlations certainly present in this compound.Comment: 7 pages, 2 figure

Viable 3C-SiC-on-Si MOSFET design disrupting current Material Technology Limitations

The cubic polytype (3C-) of Silicon Carbide (SiC) is an emerging semiconductor technology for power devices. The featured isotropic material properties along with the Wide Band Gap (WBG) characteristics make it an excellent choice for power Metal Oxide Semiconductor Field Effect Transistors (MOSFETs). Nonetheless, material related limitations originate from the advantageous fact that 3C-SiC can be grown on Silicon (Si) wafers. One of these major limitations is an almost negligible activation of the p-type dopants after ion implantation because the annealing has to take place at relatively low temperatures. In this paper, a novel process flow for a vertical 3C-SiC-on-Si MOSFET is presented to overcome the difficulties that currently exist in obtaining a p-body region through implantation. The proposed design has been accurately simulated with Technology Computer Aided Design (TCAD) process and device software and a comparison is performed with the conventional SiC MOSFET design. The simulated output characteristics demonstrated a reduced on-resistance and at the same time it is shown that the blocking capability can be maintained to the same level. The promising performance of the novel design discussed in this paper is potentially the solution needed and a huge step towards the realisation of 3C-SiC-on-Si MOSFETs with commercially grated characteristics