Electron-induced rippling in graphene

We show that the interaction between flexural phonons, when corrected by the exchange of electron-hole excitations, may place the graphene sheet very close to a quantum critical point characterized by the strong suppression of the bending rigidity of the membrane. Ripples arise then due to spontaneous symmetry breaking, following a mechanism similar to that responsible for the condensation of the Higgs field in relativistic field theories. In the presence of membrane tensions, ripple condensation may be reinforced or suppressed depending on the sign of the tension, following a zero-temperature buckling transition in which the order parameter is given essentially by the square of the gradient of the flexural phonon field.Comment: 4 pages, 3 figure

FEASIBILITY OF INTEGRATING SHEEP AND CROPS WITH SMALLHOLDER RUBBER PRODUCTION SYSTEMS IN INDONESIA

Diversified production systems are considered important tools for stabilizing the income of smallholder rubber producers in Indonesia. Based on empirical data collected from smallholder rubber producers in the Nucleus Estate Smallholder (NES) development project, estimations were made of the economic feasibility of integrating sheep and selected crops into smallholder rubber production plantations. The dynamic optimization procedure is used as an evaluation technique. This study finds that integration of sheep and crops into smallholder rubber production is economically feasible, particularly for those who utilize family labor for hand harvesting grass and grazing sheep. Integrating sheep alone increases the net present value of future income by 20%. The combination of sheep and soybeans with smallholder rubber production increases the net present value of future income by 38%.bioeconomic model, diversification, dynamic optimization, Indonesia, rubber, sheep, smallholder, Farm Management,

Giving credit where it’s due – but no more: an ethical analysis of trade credit

In spite of its commercial importance and signs of some concern by some commentators, trade credit has not been subjected to serious ethical analysis. This is especially important in the current financial crisis, given that credit from banks is in short supply, leading to increasing pressure on trade credit. In addition to identifying trade credit as a topic of ethical significance, this paper develops an analysis of the ethics of trade credit grounded in an understanding of its purpose. Making a distinction between “operating” trade credit and “financial” trade credit, it provides an account of the maximum period for which it is appropriate for one company to delay payment to another from which it has purchased goods or services. This has implications not only for companies that take credit but also for external commentators who seek to rate companies according to their speed of payment. The responsibility of suppliers not to extend excessive credit, and thus act as a quasi-bank, also follows from the analysis developed

Dynamics of the Formation of Bright Solitary Waves of Bose-Einstein Condensates in Optical Lattices

We present a detailed description of the formation of bright solitary waves in optical lattices. To this end, we have considered a ring lattice geometry with large radius. In this case, the ring shape does not have a relevant effect in the local dynamics of the condensate, while offering a realistic set up to implement experiments with conditions usually not available with linear lattices (in particular, to study collisions). Our numerical results suggest that the condensate radiation is the relevant dissipative process in the relaxation towards a self-trapped solution. We show that the source of dissipation can be attributed to the presence of higher order dispersion terms in the effective mass approach. In addition, we demonstrate that the stability of the solitary solutions is linked with particular values of the width of the wavepacket in the reciprocal space. Our study suggests that these critical widths for stability depend on the geometry of the energy band, but are independent of the condensate parameters (momentum, atom number, etc.). Finally, the non-solitonic nature of the solitary waves is evidenced showing their instability under collisions.Comment: 7 pages, 7 figures, to appear in PR

Stationary processes whose filtrations are standard

We study the standard property of the natural filtration associated to a 0--1 valued stationary process. In our main result we show that if the process has summable memory decay, then the associated filtration is standard. We prove it by coupling techniques. For a process whose associated filtration is standard, we construct a product type filtration extending it, based upon the usual couplings and the Vershik's criterion for standardness.Comment: Published at http://dx.doi.org/10.1214/009117906000000151 in the Annals of Probability (http://www.imstat.org/aop/) by the Institute of Mathematical Statistics (http://www.imstat.org