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In this article, we present a mechanism and related path planning algorithm to construct light-duty barriers out of extruded, inflated tubes weaved around existing environmental features. Our extruded tubes are based on everted vine-robots and in this context, we present a new method to steer their growth. We characterize the mechanism in terms of accuracy resilience, and, towards their use as barriers, the ability of the tubes to withstand distributed loads. We further explore an algorithm which, given a feature map and the size and direction of the external load, can determine where and how to extrude the barrier. Finally, we showcase the potential of this method in an autonomously extruded two-layer wall weaved around three pipes. While preliminary, our work indicates that this method has the potential for barrier construction in cluttered environments, e.g. shelters against wind or snow. Future work may show how to achieve tighter weaves, how to leverage weave friction for improved strength, how to assess barrier performance for feedback control, and how to operate the extrusion mechanism off of a mobile robot.

Mean field approach, although a generally reliable tool that captures major short range correlations, often fails in symmetric low dimensional strongly correlated electronic systems like those described by the Hubbard model. In these situations a symmetry is \almost broken". The problem is linked to the restoration of the symmetry due to strong uctuations (both quantum and thermal) on all scales. The restoration of symmetry in statistical models of scalar \order parameter" fields was treated recently successfully on the gaussian approximation level by symmetrization of the correlators. Here the idea is extended to fermionic systems in which the order parameter is composite. Furthermore the precision of the correlators can be improved perturbatively. Such a scheme (based on covariant gaussian approximation) is demonstrated on the 1D and 2D one band Hubbard models by comparison of the correlator with exact diagonalization and MC simulations respectively., Comment: 18 pages, 8 figures

Condensed matter systems undergoing second order transition away from the critical fluctuation region are usually described sufficiently well by the mean field approximation. The critical fluctuation region, determined by the Ginzburg criterion, $\left \vert T/T_{c}-1\right \vert \ll Gi$, is narrow even in high $T_{c}$ superconductors and has universal features well captured by the renormalization group method. However recent experiments on magnetization, conductivity and Nernst effect suggest that fluctuations effects are large in a wider region both above and below $T_{c}$. In particular some "pseudogap" phenomena and strong renormalization of the mean field critical temperature $T_{mf}$ can be interpreted as strong fluctuations effects that are nonperturbative (cannot be accounted for by "gaussian fluctuations"). The physics in a broader region therefore requires more accurate approach. Self consistent methods are generally "non - conserving" in the sense that the Ward identities are not obeyed. This is especially detrimental in the symmetry broken phase where, for example, Goldstone bosons become massive. Covariant gaussian approximation remedies these problems. The Green's functions obey all the Ward identities and describe the fluctuations much better. The results for the order parameter correlator and magnetic penetration depth of the Ginzburg - Landau model of superconductivity are compared with both Monte Carlo simulations and experiments in high $T_{c}$ cuprates., Comment: 24 pages, 7 figures

Recently synthesized 3D materials with Dirac spectrum exhibit peculiar electric transport qualitatively different from its 2D analogue, graphene. Neglecting impuritiy scattering, the real part of the conductivity is strongly frequency dependent (linear), while the imaginary part is non-zero (unlike in undoped, clean graphene). The Coulomb interaction between electrons is unscreened as in a dielectric and hence is long range. We demonstrate that the interaction correction renders the electrodynamics nonlocal on a mesoscopic\ scale. The longitudinal conductivity $\sigma _{L}$ (related by charge conservation to the electric susceptibility) and the transverse conductivity $\sigma _{T}$ are different in the long wave length limit and consequently the standard local Ohm's law description does not apply. This leads to several remarkable effects in transport and optical response. We predict a charging effect in DC transport that is a direct signature of the nonlocality. The optical response of the WSM is also sensitive to the nonlocality. In these materials p-polarized light generates bulk plasmons as well as the transversal waves. The propagation inside the WSM is only slightly attenuated. At a specific (material parameter dependent) frequency the two modes coincide, a phenomenon impossible in a local medium. Remarkably, for any frequency there is an incident angle where total absorption occurs, turning the WSM opaque., Comment: Main article: 10 pages, 16 figures; supplementary material 8 pages

Electron - hole pairs are copuously created by an applied electric field near the Dirac point in graphene or similar 2D electronic systems. It was shown recently that for sufficiently large electric fields and ballistic times the I-V characteristics become strongly nonlinear due to Schwinger's pair creation. Since there is no energy gap the radiation from the pairs' annihilation is enhanced. The spectrum of radiation is calculated. The angular and polarization dependence of the emitted photons with respect to the graphene sheet is quite distinctive. For very large currents the recombination rate becomes so large that it leads to the second Ohmic regime due to radiation friction., Comment: 9 pages, 7 figures

The process of coherent creation of particle - hole excitations by an electric field in graphene is quantitatively described using a dynamic "first quantized" approach. We calculate the evolution of current density, number of pairs and energy in ballistic regime using the tight binding model. The series in electric field strength $E$ up to third order in both DC and AC are calculated. We show how the physics far from the two Dirac points enters various physical quantities in linear response and how it is related to the chiral anomaly. The third harmonic generation and the imaginary part of conductivity are obtained. It is shown that at certain time scale $t_{nl}\propto E^{-1/2}$ the physical behaviour dramatically changes and the perturbation theory breaks down. Beyond the linear response physics is explored using an exact solution of the first quantized equations. While for small electric fields the I-V curve is linear characterized by the universal minimal resistivity $\sigma =\pi /2(e^{2}/h)$%, at $t>t_{nl}$ the conductivity grows fast. The copious pair creation (with rate $E^{3/2}$), analogous to Schwinger's electron - positron pair creation from vacuum in QED, leads to creation of the electron - hole plasma at ballistic times of order $t_{nl}$. This process is terminated by a relaxational recombination., Comment: 15 pages, 5 figures.

The process of coherent creation of particle - hole excitations by an electric field in graphene is quantitatively described beyond linear response. We calculate the evolution of current density, number of pairs and energy in ballistic regime for electric field E using the tight binding model. While for small ballistic flight times the current is linear in E and independent of time, for larger ballistic times the current increases and finally at yet larger times Bloch oscillations set in. It is shown that the number of pairs follows the 2D generalization of the Schwinger's creation rate only on certain time segments with a prefactor different from that obtained using the asymptotic formula., Comment: 5 pages, 2 figures

Consistent perturbation theory for thermodynamical quantities in strongly type II superconductors in magnetic field at low temperatures is developed. It is complementary to the existing expansion valid at high temperatures. Magnetization and specific heat are calculated to two loop order and compare well with existing Monte Carlo simulations, other theories and experiments., Comment: 22 pages, 5 eps figures, use Revtex

We investigate quantum nucleation of vortex string loops in the relativistic quantum field theory of a complex scalar field by using the Euclidean path integral. Our initial metastable homogeneous field dominated by the $O(3)$ symmetric bounce solution. The nucleation rate and the critical vortex loop size are obtained approximately. Gradually the initial current will be reduced to zero as the induced current inside vortex loops is opposite to the initial current. We also discuss a similar process in Maxwell-Higgs systems and possible physical implications., Comment: phyzzx.tex, 13 pages: A correction to the final state of the nucleation of local vortex strings

We study one-loop corrections to the Chern-Simons coefficient $\kappa$ in abelian self-dual Chern-Simons Higgs systems and their $N=2$ and $N=3$ supersymmetric generalizations in both symmetric and asymmetric phases. One-loop corrections to the Chern-Simons coefficient of these systems turn out to be integer multiples of $1/4\pi$ in both phases. Especially in the maximally supersymmetric $N=3$ case, the correction in symmetric phase vanishes and that in asymmetric phase is $\kappa/(2\pi |\kappa|)$. Our results suggest that nonabelian self-dual systems might enjoy similar features. We also discuss various issues arising from our results., Comment: 10 pages, phyzzx macro, CU-TP-647 and SNUTP94-71