Bulk viscosity of the massive Gross-Neveu model

A calculation of the bulk viscosity for the massive Gross-Neveu model at zero fermion chemical potential is presented in the large-$N$ limit. This model resembles QCD in many important aspects: it is asymptotically free, has a dynamically generated mass gap, and for zero bare fermion mass it is scale invariant at the classical level (broken through the trace anomaly at the quantum level). For our purposes, the introduction of a bare fermion mass is necessary to break the integrability of the model, and thus to be able to study momentum transport. The main motivation is, by decreasing the bare mass, to analyze whether there is a correlation between the maximum in the trace anomaly and a possible maximum in the bulk viscosity, as recently conjectured. After numerical analysis, I find that there is no direct correlation between these two quantities: the bulk viscosity of the model is a monotonously decreasing function of the temperature. I also comment on the sum rule for the spectral density in the bulk channel, as well as on implications of this analysis for other systems.Comment: v2: 3->3 processes included, conclusions unchanged. Comments and references added. Typos corrected. To appear in Phys. Rev.

Self-aligned charge read-out for InAs nanowire quantum dots

A highly sensitive charge detector is realized for a quantum dot in an InAs nanowire. We have developed a self-aligned etching process to fabricate in a single step a quantum point contact in a two-dimensional electron gas and a quantum dot in an InAs nanowire. The quantum dot is strongly coupled to the underlying point contact which is used as a charge detector. The addition of one electron to the quantum dot leads to a change of the conductance of the charge detector by typically 20%. The charge sensitivity of the detector is used to measure Coulomb diamonds as well as charging events outside the dot. Charge stability diagrams measured by transport through the quantum dot and charge detection merge perfectly.Comment: 11 pages, 3 figure

Strong Electron Tunneling through a Small Metallic Grain

Electron tunneling through mesoscopic metallic grains can be treated perturbatively only provided the tunnel junction conductances are sufficiently small. If it is not the case, fluctuations of the grain charge become strong. As a result (i) contributions of all -- including high energy -- charge states become important and (ii) excited charge states become broadened and essentially overlap. At the same time the grain charge remains discrete and the system conductance $e$-periodically depends on the gate charge. We develop a nonperturbative approach which accounts for all these features and calculate the temperature dependent conductance of the system in the strong tunneling regime at different values of the gate charge.Comment: revtex, 8 pages, 2 .ps figure

Outdoor learning spaces: the case of forest school

© 2017 The Author. Area published by John Wiley & Sons Ltd on behalf of Royal Geographical Society (with the Institute of British Geographers). This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.This paper contributes to the growing body of research concerning use of outdoor spaces by educators, and the increased use of informal and outdoor learning spaces when teaching primary school children. The research takes the example of forest school, a form of regular and repeated outdoor learning increasingly common in primary schools. This research focuses on how the learning space at forest school shapes the experience of children and forest school leaders as they engage in learning outside the classroom. The learning space is considered as a physical space, and also in a more metaphorical way as a space where different behaviours are permitted, and a space set apart from the national curriculum. Through semi-structured interviews with members of the community of practice of forest school leaders, the paper seeks to determine the significance of being outdoors on the forest school experience. How does this learning space differ from the classroom environment? What aspects of the forest school learning space support pupils’ experiences? How does the outdoor learning space affect teaching, and the dynamics of learning while at forest school? The research shows that the outdoor space provides new opportunities for children and teachers to interact and learn, and revealed how forest school leaders and children co-create a learning environment in which the boundaries between classroom and outdoor learning, teacher and pupil, are renegotiated to stimulate teaching and learning. Forest school practitioners see forest school as a separate learning space that is removed from the physical constraints of the classroom and pedagogical constraints of the national curriculum to provide a more flexible and responsive learning environment.Peer reviewe

Cooper pairing and finite-size effects in a NJL-type four-fermion model

Starting from a NJL-type model with N fermion species fermion and difermion condensates and their associated phase structures are considered at nonzero chemical potential $\mu$ and zero temperature in spaces with nontrivial topology of the form $S^1\otimes S^1\otimes S^1$ and $R^2\otimes S^1$. Special attention is devoted to the generation of the superconducting phase. In particular, for the cases of antiperiodic and periodic boundary conditions we have found that the critical curve of the phase transitions between the chiral symmetry breaking and superconducting phases as well as the corresponding condensates and particle densities strongly oscillate vs $\lambda\sim 1/L$, where $L$ is the length of the circumference $S^1$. Moreover, it is shown that at some finite values of $L$ the superconducting phase transition is shifted to smaller values both of $\mu$ and particle density in comparison with the case of $L=\infty$.Comment: 13 pages, 13 figures; minor changes; new references added; version accepted to PR

A retrospective cross-sectional study: Fresh cycle endometrial thickness is a sensitive predictor of inadequate endometrial thickness in frozen embryo transfer cycles

BACKGROUND: The purpose of this study is to assess predictors of inadequate endometrial cavity thickness (ECT), defined as < 8 mm, in frozen embryo transfer (FET) cycles. METHODS: This is a retrospective cross-sectional study at an academic fertility center including 274 women who underwent their first endometrial preparation with estradiol for autologous FET in our center from 2001-2009. Multivariable logistic regression was performed to determine predictors of inadequate endometrial development in FET cycles. RESULTS: Neither age nor duration of estrogen supplementation were associated with FET endometrial thickness. Lower body mass index, nulliparity, previous operative hysteroscopy and thinner fresh cycle endometrial lining were associated with inadequate endometrial thickness in FET cycles. A maximum thickness of 11.5 mm in a fresh cycle was 80% sensitive and 70% specific for inadequate frozen cycle thickness. CONCLUSIONS: Previous fresh cycle endometrial cavity thickness is associated with subsequent FET cycle endometrial cavity thickness. Women with a fresh cycle thickness of 11.5 mm or less may require additional intervention to achieve adequate endometrial thickness in preparation for a frozen cycle

Fracton pairing mechanism for "strange" superconductors: Self-assembling organic polymers and copper-oxide compounds

Self-assembling organic polymers and copper-oxide compounds are two classes of "strange" superconductors, whose challenging behavior does not comply with the traditional picture of Bardeen, Cooper, and Schrieffer (BCS) superconductivity in regular crystals. In this paper, we propose a theoretical model that accounts for the strange superconducting properties of either class of the materials. These properties are considered as interconnected manifestations of the same phenomenon: We argue that superconductivity occurs in the both cases because the charge carriers (i.e., electrons or holes) exchange {\it fracton excitations}, quantum oscillations of fractal lattices that mimic the complex microscopic organization of the strange superconductors. For the copper oxides, the superconducting transition temperature $T_c$ as predicted by the fracton mechanism is of the order of $\sim 150$ K. We suggest that the marginal ingredient of the high-temperature superconducting phase is provided by fracton coupled holes that condensate in the conducting copper-oxygen planes owing to the intrinsic field-effect-transistor configuration of the cuprate compounds. For the gate-induced superconducting phase in the electron-doped polymers, we simultaneously find a rather modest transition temperature of $\sim (2-3)$ K owing to the limitations imposed by the electron tunneling processes on a fractal geometry. We speculate that hole-type superconductivity observes larger onset temperatures when compared to its electron-type counterpart. This promises an intriguing possibility of the high-temperature superconducting states in hole-doped complex materials. A specific prediction of the present study is universality of ac conduction for $T\gtrsim T_c$.Comment: 12 pages (including separate abstract page), no figure

A cyclopentadienyl functionalized silylene-a flexible ligand for Si- And C-coordination

The synthesis of a 1,2,3,4-tetramethylcyclopentadienyl (Cp$^{4}$) substituted four-membered N-heterocyclic silylene [{PhC(NtBu) $_{2}$}Si(C$_{5}$Me$_{4}$H)] is reported first. Then, selected reactions with transition metal and a calcium precursor are shown. The proton of the Cp$_{4}$-unit is labile. This results in two different reaction pathways: (1) deprotonation and (2) rearrangement reactions. Deprotonation was achieved by the reaction of [{PhC(NtBu) $_{2}$}Si(C$_{5}$Me$_{4}$H)] with suitable zinc precursors. Rearrangement to [{PhC(NtBu) $_{2}$}(C$_{5}$Me$_{4}$)SiH], featuring a formally tetravalent silicon R$_{2}$CSi(R′)-H unit, was observed when the proton of the Cp$^{4}$ ring was shifted from the Cp$^{4}$-ring to the silylene in the presence of a Lewis acid. This allows for the coordination of the Cp$^{4}$-ring to a calcium compound. Furthermore, upon reaction with transition metal dimers [MCl(cod)] $_{2}$ (M = Rh, Ir; cod = 1,5-cyclooctadiene) the proton stays at the Cp$^{4}$-ring and the silylene reacts as a sigma donor, which breaks the dimeric structure of the precursors

Fluxes, Gaugings and Gaugino Condensates

Based on the correspondence between the N = 1 superstring compactifications with fluxes and the N = 4 gauged supergravities, we study effective N = 1 four-dimensional supergravity potentials arising from fluxes and gaugino condensates in the framework of orbifold limits of (generalized) Calabi-Yau compactifications. We give examples in heterotic and type II orientifolds in which combined fluxes and condensates lead to vacua with small supersymmetry breaking scale. We clarify the respective roles of fluxes and condensates in supersymmetry breaking, and analyze the scaling properties of the gravitino mass.Comment: 17 pages, C