Dissipative dynamics of spins in quantum dots

We present a theory for the dissipation of electronic spins trapped in quantum dots due to their coupling to the host lattice acoustic phonon modes. Based on the theory of dissipative two level systems for the spin dynamics, we derive a relation between the spin dissipative bath, the electron confinement, and the electron-phonon interaction. We find that there is an energy scale, typically smaller than the electronic lateral confinement energy, which sets the boundary between different dissipative regimes .Comment: 4 pages, 2 eps figure

High-resolution synchrotron-based X-ray microtomography as a tool to unveil the three-dimensional neuronal architecture of the brain

The assessment of neuronal number, spatial organization and connectivity is fundamental for a complete understanding of brain function. However, the evaluation of the three-dimensional (3D) brain cytoarchitecture at cellular resolution persists as a great challenge in the field of neuroscience. In this context, X-ray microtomography has shown to be a valuable non-destructive tool for imaging a broad range of samples, from dense materials to soft biological specimens, arisen as a new method for deciphering the cytoarchitecture and connectivity of the brain. In this work we present a method for imaging whole neurons in the brain, combining synchrotron-based X-ray microtomography with the Golgi-Cox mercury-based impregnation protocol. In contrast to optical 3D techniques, the approach shown here does neither require tissue slicing or clearing, and allows the investigation of several cells within a 3D region of the brain

Dynamical Mean Field Theory for Self-Generated Quantum Glasses

We present a many body approach for non-equilibrium behavior and self-generated glassiness in strongly correlated quantum systems. It combines the dynamical mean field theory of equilibrium systems with the replica theory for classical glasses without quenched disorder. We apply this approach to study a quantized version of the Brazovskii model and find a self-generated quantum glass that remains in a quantum mechanically mixed state as T -> 0. This quantum glass is formed by a large number of competing states spread over an energy region which is determined within our theory.Comment: 10 pages, 4 figure

Phase diagrams and structural characterization of mixtures of silicone surfactants + silicone oils + water

Silicone surfactants display unique properties and are widely employed in pharmaceutical and cosmetic products. In this work, we study water incorporation into silicone oils using silicone surfactants. Despite their importance, there are only a few studies reporting their phase equilibrium and structural characterization. Here, we determined the phase diagram of systems containing silicone oils, silicone surfactants, and water. In particular, we investigated the self-assembly behavior of two siloxane surfactants with the different hydrophilic–lipophilic balance: M(D′E7OH)M and MD18(D′3E18OAc)M and two silicone oils (cyclic oil—D4 and linear oil—MD15M). The phase behavior of the mixtures was investigated through optical inspection and structural characterization of aggregated states (microemulsions and mesophases) using small angle X-ray scattering (SAXS). These water-in-oil microemulsions or bicontinuous microemulsions incorporated a maximum amount of approximately 20 wt % water for the two surfactants with cyclic oil. A similar behavior was also identified with linear silicone oil, though with smaller water contents. We also observed the formation of anisotropic states, with a predominance of lamellar phases and a small region of a hexagonal phase. A quantitative analysis of the SAXS curves in the lamellar region reveals that this mesophase swells continuously after the addition of water lamellar periods ranging from 50 Å (with 18 wt % water) to 64 Å (with 40 wt % water). Our results confirm and expand the earlier literature on similar compounds, indicating their potential in incorporating water into silicone mixtures and forming interesting mesophases. Accompanying this characterization, we also report a comprehensive and systematic set of structural details for the different systems (microemulsions, bicontinuous phases and mesophases) formed by these mixtures, derived from the SAXS measurements123491052210532CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQM.S.F. and W.L. thank CNPq, respectively, for doctoral and research productivity grants. We also thank Dow Corning for the kind donation of the silicone compounds used in this study, and we are indebted to Prof. I. V. P. Yoshida for helpful discussions on chemical properties of these compounds. The authors are also indebted to the Brazilian Synchrotron Laboratory, LNLS, for allocation of SAXS beamtime and for the efficient beamline staff suppor

Micro- to Nano-scale Soil and Rhizosphere Processes Analyzed Using Multiple Beamlines at the Sirius Synchrotron

Determining mechanisms that regulate plant-nutrient behavior in agricultural soils is often confounded by interactions between physical, chemical, and biological processeswithin these multicomponent, heterogeneous, and hierarchical systems. This presentation will focus on strategies and examples of addressing these complexities by using complementary techniques at multiple Sirius beamlines. For example, we hypothesize that diffusion and reaction of fertilizer phosphate inside soil microaggregates contributes to slowly reversible phosphate binding ("fixation"), which diminishes plant availability of this macronutrient. Micro and nanoscale imaging results from three beamlines wereused to evaluate the 3D internal physical structure of soil microaggregates (CATERETÊcoherent diffraction imaging beamline), 3D spatial distributions of soil-matrix elements (CARNAÛBA coherent X-ray nanoprobe beamline), and the presence of biological components (IMBUIA infrared microprobe beamline). Results revealed accumulations of physical structures of high electron density that at least partially coincide with hotspots of iron and other metals, as well as structures of low electron density that are possibly of biological origin. We will also illustrate how a combination of chemical imaging around a living wheat root at CARNAÛBA and root-structural imaging at the MOGNO X-ray computed tomography beamline reveal root-induced chemical changes in the rhizosphereover time. Initial results show highly reproducible spatial structures of soil matrix elements in the rhizosphere over time and well-defined imaging of roots and root hairs. Integrating multimodal analyses from beamlines with unique capabilities to probe different aspects of a soil matrix is essential for determining how coupled processes affect agricultural nutrient behavior in such complex system