Mean-field quantum phase transition in graphene and in general gapless systems

We study the quantum critical properties of antiferromagnetism in graphene at T=0 within mean-field (MF) theory. The resulting exponents differ from the conventional MF exponents, describing finite temperature transitions. Motivated by this, we have developed the MF theory of general gapless phases with density of states rho(E) |E|^r, r>-1, with the interaction as control parameter. For r>2, the conventional MF exponents \'a la Landau are recovered, while for -1<r<2, the exponents vary significantly with r. The critical interaction is finite for r>0, therefore no weak-coupling solution exists in this range. This generalizes the results on quantum criticality of the gapless Kondo systems to bulk correlated phases.Comment: 5 pages, 1 figure, 2 table

Museum Websites of the First Wave: The rise of the virtual museum

In this paper, we analyse trends of the first wave of museum websites (from the 1990s to the early 2000s) to understand how the characteristics of the Internet (specifically the World Wide Web), of museum staff, and museum audiences shaped the adoption of technology and new forms of participation and what they can tell us about engagement for museums of the future. The early development of online museum resources parallels the development of the EVA conference, which was establishing itself at a similar time

Early virtual science museums: when the technology is not mature

This paper discusses three case studies of early science museum-related websites in the 1990s and early 2000s, when web technology was still relatively new and evolving. The Virtual Museum of Computing (VMoC) was a completely virtual museum, originally produced in 1995 as part of the Virtual Library museums pages (VLmp), an international online museum directory within the WWW Virtual Library, adopted by the International Council of Museums (ICOM). The Science Museum in London was one of the first museums in the United Kingdom to have its own web server. The museum hosted an early meeting on web service provision by and for museums, concurrently with an exhibition on the Information Superhighway at the museum in 1995. Exhiblets were launched online in 1998. Ingenious was a multi-site digital collections transformation project, launched as a website in 2003. Virtual Leonardo and Leonardo’s Ideal City were two experiments conducted by the digital team of the Science and Technology Museum of Milan, between 1999 and 2001. The experiment consisted of the creation of a shared online 3D world, namely a reconstruction of the real museum in the first case and a completely imaginary world in the second case. This paper describes the above three case studies from the early World Wide Web and then draws some conclusions, from first-hand experience of developments at the time. We cover both the advantages and the challenges encountered by the various projects and illustrate why they did not necessarily become established, despite promising early results

Cumulative energy demand analysis in the current manufacturing and end-of-life strategies for a polymeric composite at different fibre-matrix combinations

Fibre Reinforced Polymers (FRPs) are finding more applications in different industrial sectors. From a sustainability point of view, a component made of FRPs reduces energy consumption and CO2 emissions during its usephase due to the material’s lightweight nature. However, the production of these materials impacts the global energy demand significantly. To mitigate this impact, circular economy strategies are essential. This study focuses on a Cumulative Energy Demand (CED) analysis for different End-of-Life (EoL) strategies of FRPs components. Three EoL routes were evaluated: i.e., combustion, recycling and reforming of continuous fibres reinforced thermoplastics. Different fibres and matrices and three Fibre Volume Fractions (FVF) were taken into account. Specifically, Glass Fibres, Carbon Fibres, Polypropylene, and Polyether ether ketone were examined while FVF of 11%, 23% and 45% were evaluated. A Life Cycle Inventory data was built combining literature review and CES Edupack database. The results provided some guidelines for optimising the product’s EoL phase in terms of CED reduction underlining the advantages and high competitiveness of the reforming strategy especially if high-performance matrices and/or fibres are processed. Recycling results to be a valuable EoL alternative if FRPs made by high-performance fibres and high FVF are employed while combustion is the more advisable option if low-performance matrices and fibres are used

Dynamical conductance in the two-channel Kondo regime of a double dot system

We study finite-frequency transport properties of the double-dot system recently constructed to observe the two-channel Kondo effect [R. M. Potok et al., Nature 446, 167 (2007)]. We derive an analytical expression for the frequency-dependent linear conductance of this device in the Kondo regime. We show how the features characteristic of the 2-channel Kondo quantum critical point emerge in this quantity, which we compute using the results of conformal field theory as well as numerical renormalization group methods. We determine the universal cross-over functions describing non-Fermi liquid vs. Fermi liquid cross-overs and also investigate the effects of a finite magnetic field.Comment: 11 pages in PRB forma

Friedel oscillations and the Kondo screening cloud

We show that the long distance charge density oscillations in a metal induced by a weakly coupled spin-1/2 magnetic impurity exhibiting the Kondo effect are given, at zero temperature, by a universal function F(r/xi_K) where r is the distance from the impurity and xi_K, the Kondo screening cloud size =v_F/T_K, where v_F is the Fermi velocity and T_K is the Kondo temperature. F is given by a Fourier-like transform of the T-matrix. Analytic expressions for F(r/xi_K) are derived in both limits r much less than xi_K and r much greater than xi_K and F is calculated for all r/xi_K using numerical methods.Comment: More extensive discussion of experimental situation and referencing of earlier work adde

A renormalization-group analysis of the interacting resonant level model at finite bias: Generic analytic study of static properties and quench dynamics

Using a real-time renormalization group method we study the minimal model of a quantum dot dominated by charge fluctuations, the two-lead interacting resonant level model, at finite bias voltage. We develop a set of RG equations to treat the case of weak and strong charge fluctuations, together with the determination of power-law exponents up to second order in the Coulomb interaction. We derive analytic expressions for the charge susceptibility, the steady-state current and the conductance in the situation of arbitrary system parameters, in particular away from the particle-hole symmetric point and for asymmetric Coulomb interactions. In the generic asymmetric situation we find that power laws can be observed for the current only as function of the level position (gate voltage) but not as function of the voltage. Furthermore, we study the quench dynamics after a sudden switch-on of the level-lead couplings. The time evolution of the dot occupation and current is governed by exponential relaxation accompanied by voltage-dependent oscillations and characteristic algebraic decay.Comment: 24 pages, 13 figures; revised versio