Light bullets in quadratic media with normal dispersion at the second harmonic

Stable two- and three-dimensional spatiotemporal solitons (STSs) in second-harmonic-generating media are found in the case of normal dispersion at the second harmonic (SH). This result, surprising from the theoretical viewpoint, opens a way for experimental realization of STSs. An analytical estimate for the existence of STSs is derived, and full results, including a complete stability diagram, are obtained in a numerical form. STSs withstand not only the normal SH dispersion, but also finite walk-off between the harmonics, and readily self-trap from a Gaussian pulse launched at the fundamental frequency.Comment: 4 pages, 5 figures, accepted to Phys. Rev. Let

Critical thermodynamics of three-dimensional MN-component field model with cubic anisotropy from higher-loop \epsilon expansion

The critical thermodynamics of an $MN$-component field model with cubic anisotropy relevant to the phase transitions in certain crystals with complicated ordering is studied within the four-loop \ve expansion using the minimal subtraction scheme. Investigation of the global structure of RG flows for the physically significant cases M=2, N=2 and M=2, N=3 shows that the model has an anisotropic stable fixed point with new critical exponents. The critical dimensionality of the order parameter is proved to be equal to $N_c^C=1.445(20)$, that is exactly half its counterpart in the real hypercubic model.Comment: 9 pages, LaTeX, no figures. Published versio

Fabrication and properties of the SITE-SiCf/SiC composite

Continuous SiC-fiber-reinforced SiC composite (SiCf/SiC) is an attractive candidate structural material for advanced concepts of future fusion power plants, mainly due to the favourable intrinsic properties of the SiC ceramics, i.e. high temperature- and chemical stability, low neutron activation and afterheat levels as well as due to the fact that it is the only nonmagnetic material proposed. Fabrication of such composites is a very challenging task due to limitations and requirements set for fusion-relevant structural materials

Stable spinning optical solitons in three dimensions

We introduce spatiotemporal spinning solitons (vortex tori) of the three-dimensional nonlinear Schrodinger equation with focusing cubic and defocusing quintic nonlinearities. The first ever found completely stable spatiotemporal vortex solitons are demonstrated. A general conclusion is that stable spinning solitons are possible as a result of competition between focusing and defocusing nonlinearities.Comment: 4 pages, 6 figures, accepted to Phys. Rev. Let

Assessment of the methodology for establishing the EU list of critical raw materials : background report

This report presents the results of work carried out by the Directorate General (DG) Joint Research Centre (JRC) of the European Commission (EC), in close cooperation with Directorate-General for Internal Market, Industry, Entrepreneurship and SMEs (GROW), in the context of the revision of the EC methodology that was used to identify the list of critical raw materials (CRMs) for the EU in 2011 and 2014 (EC 2011, 2014). As a background report, it complements the corresponding Guidelines Document, which contains the "ready-to-apply" methodology for updating the list of CRMs in 2017. This background report highlights the needs for updating the EC criticality methodology, the analysis and the proposals for improvement with related examples, discussion and justifications. However, a few initial remarks are necessary to clarify the context, the objectives of the revision and the approach. As the in-house scientific service of the EC, DG JRC was asked to provide scientific advice to DG GROW in order to assess the current methodology, identify aspects that have to be adapted to better address the needs and expectations of the list of CRMs and ultimately propose an improved and integrated methodology. This work was conducted closely in consultation with the adhoc working group on CRMs, who participated in regular discussions and provided informed expert feedback. The analysis and subsequent revision started from the assumption that the methodology used for the 2011 and 2014 CRMs lists proved to be reliable and robust and, therefore, the JRC mandate was focused on fine-tuning and/or targeted incremental methodological improvements. An in depth re-discussion of fundamentals of criticality assessment and/or major changes to the EC methodology were not within the scope of this work. High priority was given to ensure good comparability with the criticality exercises of 2011 and 2014. The existing methodology was therefore retained, except for specific aspects for which there were policy and/or stakeholder needs on the one hand, or strong scientific reasons for refinement of the methodology on the other. This was partially facilitated through intensive dialogue with DG GROW, the CRM adhoc working group, other key EU and extra-EU stakeholders

Critical raw materials and the circular economy

This report is a background document used by several European Commission services to prepare the EC report on critical raw materials and the circular economy, a commitment of the European Commission made in its Communication ‘EU action plan for the Circular Economy’. It represents a JRC contribution to the Raw Material Initiative and to the EU Circular Economy Action Plan. It combines the results of several research programmes and activities of the JRC on critical raw materials in a context of circular economy, for which a large team has contributed in terms of data and knowledge developments. Circular use of critical raw materials in the EU is analysed, also taking a sectorial perspective. The following sectors are analysed in more detail: extractive waste, landfills, electric and electronic equipment, batteries, automotive, renewable energy, defence and chemicals and fertilisers. Conclusions and opportunities for further work are also presented

Critical behavior of certain antiferromagnets with complicated ordering: Four-loop \ve-expansion analysis

The critical behavior of a complex N-component order parameter Ginzburg-Landau model with isotropic and cubic interactions describing antiferromagnetic and structural phase transitions in certain crystals with complicated ordering is studied in the framework of the four-loop renormalization group (RG) approach in (4-\ve) dimensions. By using dimensional regularization and the minimal subtraction scheme, the perturbative expansions for RG functions are deduced and resummed by the Borel-Leroy transformation combined with a conformal mapping. Investigation of the global structure of RG flows for the physically significant cases N=2 and N=3 shows that the model has an anisotropic stable fixed point governing the continuous phase transitions with new critical exponents. This is supported by the estimate of the critical dimensionality $N_c=1.445(20)$ obtained from six loops via the exact relation $N_c={1/2} n_c$ established for the complex and real hypercubic models.Comment: LaTeX, 16 pages, no figures. Expands on cond-mat/0109338 and includes detailed formula

Three-loop renormalization group analysis of a complex model with stable fixed point: Critical exponents up to ϵ3\epsilon^3 and ϵ4\epsilon^4

The complete analysis of a model with three quartic coupling constants associated with an O(2N)--symmetric, a cubic, and a tetragonal interactions is carried out within the three-loop approximation of the renormalization-group (RG) approach in $D=4-2\epsilon$ dimensions. Perturbation expansions for RG functions are calculated using dimensional regularization and the minimal subtraction (MS) scheme. It is shown that for $N\ge 2$ the model does possess a stable fixed point in three dimensional space of coupling constants, in accordance with predictions made earlier on the base of the lower-order approximations. Numerical estimate for critical (marginal) value of the order parameter dimensionality $N_c$ is given using Pad\'e-Borel summation of the corresponding $\epsilon$--expansion series obtained. It is observed that two-fold degeneracy of the eigenvalue exponents in the one-loop approximation for the unique stable fixed point leads to the substantial decrease of the accuracy expected within three loops and may cause powers of $\sqrt{\epsilon}$ to appear in the expansions. The critical exponents $\gamma$ and $\eta$ are calculated for all fixed points up to $\epsilon^3$ and $\epsilon^4$, respectively, and processed by the Borel summation method modified with a conformal mapping. For the unique stable fixed point the magnetic susceptibility exponent $\gamma$ for N=2 is found to differ in third order in $\epsilon$ from that of an O(4)--symmetric point. Qualitative comparison of the results given by $\epsilon$--expansion, three-dimensional RG analysis, non-perturbative RG arguments, and experimental data is performed.Comment: 30 pages, LaTeX, no figures. To be published in Phys. Rev. B, V.57, Jan. issue (1998