Variational formalism for the Klein-Gordon oscillon

The variational method employing the amplitude and width as collective coordinates of the Klein-Gordon oscillon leads to a dynamical system with unstable periodic orbits that blow up when perturbed. We propose a multiscale variational approach free from the blow-up singularities. An essential feature of the proposed trial function is the inclusion of the third collective variable: a correction for the nonuniform phase growth. In addition to determining the parameters of the oscillon, our approach detects the onset of its instability.Comment: 10 pages, 4 figure

THz parametric gain in semiconductor superlattices in the absence of electric domains

We theoretically show that conditions for THz gain and conditions for formation of destructive electric domains in semiconductor superlattices are fairly different in the case of parametric generation and amplification. Action of an unbiased high-frequency electric field on a superlattice causes a periodic variation of energy and effective mass of miniband electrons. This parametric effect can result in a significant gain at some even harmonic of the pump frequency without formation of electric domains and corruption from pump harmonics.Comment: 4 pages, 3 figures. Accepted to Appl. Phys. Let

China and the Arctic

Much attention has been paid to China’s Arctic ambitions as of late, with many commentators warning of a forthcoming aggressive pursuit of control over Arctic resources and shipping lanes. This article reviews China’s longstanding scientific, and growing economic and political, interests in the region and concludes that China has far more to gain by cooperating with Arctic neighbors and buying energy from Arctic EEZ-based projects, than by pursuing an aggressive and confrontational exploration strategy, which could be counterproductive for China's own position regarding disputes in the South China Sea. China has been pursuing cooperative and collaborative relations in the region, and is likely to do so in the future, not least because it is in its strategic and economic interest to do so