Competing interactions in semiconductor quantum dots

We introduce an integrability-based method enabling the study of semiconductor quantum dot models incorporating both the full hyperfine interaction as well as a mean-field treatment of dipole-dipole interactions in the nuclear spin bath. By performing free induction decay and spin echo simulations we characterize the combined effect of both types of interactions on the decoherence of the electron spin, for external fields ranging from low to high values. We show that for spin echo simulations the hyperfine interaction is the dominant source of decoherence at short times for low fields, and competes with the dipole-dipole interactions at longer times. On the contrary, at high fields the main source of decay is due to the dipole-dipole interactions. In the latter regime an asymmetry in the echo is observed. Furthermore, the non-decaying fraction previously observed for zero field free induction decay simulations in quantum dots with only hyperfine interactions, is destroyed for longer times by the mean-field treatment of the dipolar interactions.Comment: 10 pages, 5 figures [v2: subsection and references added

Pseudo-spin order of Wigner crystals in multi-valley electron gases

We study multi-valley electron gases in the low density ($r_s \gg 1$) limit. Here the ground-state is always a Wigner crystal (WC), with additional pseudo-spin order where the pseudo-spins are related to valley occupancies. Depending on the symmetries of the host semiconductor and the values of the parameters such as the anisotropy of the effective mass tensors, we find a striped or chiral pseudo-spin antiferromagnet, or a time-reversal symmetry breaking orbital loop-current ordered pseudo-spin ferromagnet. Our theory applies to the recently-discovered WC states in AlAs and in mono and bilayer transition metal dichalcogenides. We identify a set of interesting electronic liquid crystalline phases that could arise by continuous quantum melting of such WCs.Comment: 21 pages (including Appendices), 11 figure

Simplest miniversal deformations of matrices, matrix pencils, and contragredient matrix pencils

V. I. Arnold [Russian Math. Surveys 26 (2) (1971) 29-43] constructed a simple normal form for a family of complex n-by-n matrices that smoothly depend on parameters with respect to similarity transformations that smoothly depend on the same parameters. We construct analogous normal forms for a family of real matrices and a family of matrix pencils that smoothly depend on parameters, simplifying their normal forms by D. M. Galin [Uspehi Mat. Nauk 27 (1) (1972) 241-242] and by A. Edelman, E. Elmroth, B. Kagstrom [Siam J. Matrix Anal. Appl. 18 (3) (1997) 653-692].Comment: 20 page

Heat Conductance of the Quantum Hall Bulk

The Quantum Hall Effect (QHE) is the prototypical realization of a topological state of matter. It emerges from a subtle interplay between topology, interactions, and disorder. The disorder enables the formation of localized states in the bulk that stabilize the quantum Hall states with respect to the magnetic field and carrier density. Still, the details of the localized states and their contribution to transport remain beyond the reach of most experimental techniques. Here, we describe an extensive study of the bulk's heat conductance. Using a novel 'multi-terminal' device, we separate the longitudinal thermal conductance (due to bulk's contribution) $\kappa_{xx}T$ from the two-terminal value $\kappa_{2T}T$, by eliminating the contribution of the edge modes. We find that when the field is tuned away from the conductance plateau center, the electronic states of the bulk conduct heat efficiently while the bulk remains electrically insulating. For fragile fractional states, such as the non-Abelian $\nu=5/2$, we observe a finite $\kappa_{xx}T$ throughout the plateau. We identify the localized states as the cause of the finite $\kappa_{xx}T$ and propose a theoretical model which qualitatively explains our findings.Comment: 26 pages 9 figure

Enhanced activation of an amino-terminally truncated isoform of the voltage-gated proton channel HVCN1 enriched in malignant B cells

The final published version can be found here: http://dx.doi.org/10.1073/pnas.1411390111M.C. is the recipient of a Bennett Fellowship from Leukaemia and Lymphoma Research (ref. 12002). M.A.B. is supported by a GlaxoSmithKline Oncology–Biotechnology and Biological Sciences Research Council Collaborative Awards in Science and Engineering PhD studentship. This work was supported by National Institutes of Health Grants GM087507 and GM102336 (to T.E.D.)

Real‐time imaging reveals distinct pore scale dynamics during transient and equilibrium subsurface multiphase flow

Many subsurface fluid flows, including the storage of CO2 underground or the production of oil, are transient processes incorporating multiple fluid phases. The fluids are not in equilibrium meaning macroscopic properties such as fluid saturation and pressure vary in space and time. However, these flows are traditionally modeled with equilibrium (or steady-state) flow properties, under the assumption that the pore-scale fluid dynamics are equivalent. In this work, we used fast synchrotron X-ray tomography with 1 s time resolution to image the pore-scale fluid dynamics as the macroscopic flow transitioned to steady state. For nitrogen or decane, and brine injected simultaneously into a porous rock, we observed distinct pore-scale fluid dynamics during transient flow. Transient flow was found to be characterized by intermittent fluid occupancy, whereby flow pathways through the pore space were constantly rearranging. The intermittent fluid occupancy was largest and most frequent when a fluid initially invaded the rock. But as the fluids established an equilibrium the dynamics decreased to either static interfaces between the fluids or small-scale intermittent flow pathways, depending on the capillary number and viscosity ratio. If the fluids were perturbed after an equilibrium was established, by changing the flow rate, the transition to a new equilibrium was quicker than the initial transition. Our observations suggest that transient flows require separate modeling parameters. The time scales required to achieve equilibrium suggest that several meters of an invading plume front will have flow properties controlled by transient pore-scale fluid dynamics

The greenhouse index of sustainable development for metallurgical processes of production in aspect of green power

The accounting of greenhouse gases (GHG) according to plans of the Russian Federation becomes obligatory since 2016 for the enterprises with issue of GHG not less than 150 thousand tons of CO2, since 2017 – from 50 thousand tons of CO2. Introduction of a carbon tax (15 dollars/t of CO2) is planned. Voluntary inventory of GHG of the enterprises and territories which in the long term apply is carried out to be called clever. According to University of Cambridge (USA) about 45% depreciation of joint-stock portfolios in the world markets, the expected climate change connected with are expected. Parameter for an assessment of the clever city with the developed metallurgy and need of decrease in greenhouse emissions in the atmosphere – the indicator of a sustainable development considering emission of carbon dioxide, prime cost of steel and its power consumption is offered. Its values for tandems blast furnace (BF) + oxygen converter (OC), BF, Corex, Romelt, Midrex, Hyl-3 everyone with arc furnace (AF) are defined

Hephaestus Reloaded

Hephaestus Reloaded / Efesto Reloaded, presented in a bilingual (English/Italian) publication, and whose five authors are from Greece, Italy, and the US, invokes as its first inspiration the myth of Hephaestus who embodied a twofold entity: both disabled and technically capacious. The myth of Hephaestus has been passed across the centuries as an ancient metaphor signifying the idea of becoming-world, in which any distinction between the natural and the artificial, or the organic and the technical, is blurred. Human beings, by virtue of their physical vulnerabilities and limits, have enhanced their technological powers to the point of transcending their own given nature. At present, a variety of critical discourses in disciplines such as philosophy, history, aesthetics, and cognitive sciences pay attention to our becoming-hybrid (organic and mechanical beings) – unleashing a space for research that probes the concept of transcendence. Each of the contributions in this book addresses – through its own peculiar perspective, method and experimental style – a new way to approach the role of transcendence in socio-cultural life.In the Occidental history of ideas, the notion of transcendence has received at least three canonical articulations that are challenged by this book: religious (Judeo-Christian traditions), philosophical (Platonic-intellectual universality of ideas), and scientific (the objective and technological turn of knowledge). Nonetheless, it is with the rise of cybernetics, with its digital and virtual modalities of systems, networks, and knowledge, that our human environment emerges as a source of knowledge in itself -- not simply as an object but rather as an immersive agency in which nature, knowledge, technique merge. The transcendence of the actual and the virtual into a “third” element is construed and analyzed in this book through conceptual schemes that rely on a post-binary or non-binary understanding of coincidences, triangulations, hybrids, or post-human combinatorics. What is ultimately explored is how transcendence is ejected from strictly theological, philosophical, or scientific groundings and emerges as a germinating point of becoming (something else)

Nucleus-mediated spin-flip transitions in GaAs quantum dots

Spin-flip rates in GaAs quantum dots can be quite slow, thus opening up the possibilities to manipulate spin states in the dots. We present here estimations of inelastic spin-flip rates mediated by hyperfine interaction with nuclei. Under general assumptions the nucleus mediated rate is proportional to the phonon relaxation rate for the corresponding non-spin-flip transitions. The rate can be accelerated in the vicinity of a singlet-triplet excited states crossing. The small proportionality coefficient depends inversely on the number of nuclei in the quantum dot. We compare our results with known mechanisms of spin-flip in $GaAs$ quantum dot.Comment: RevTex 4 pages, 1 figure, submitted to Phys. Rev.