Long-time anomalous swimmer diffusion in smectic liquid crystals

The dynamics of self-locomotion of active particles in aligned or liquid crystalline fluids strongly deviates from that in simple isotropic media. We explore the long-time dynamics of a swimmer moving in a three-dimensional smectic liquid crystal and find that the mean-square displacement (MSD) transverse to the director exhibits a distinct logarithmic tail at long times. The scaling is distinctly different from that in an isotropic or nematic fluid and hints at the subtle but important role of the director fluctuation spectrum in governing the long-time motility of active particles. Our findings are based on a generic hydrodynamic theory and Brownian dynamics computer simulation of a three-dimensional soft mesogen model.Comment: 12 pages, 2 figure

Electron degeneracy and intrinsic magnetic properties of epitaxial Nb:SrTiO3_3 thin-films controlled by defects

We report thermoelectric power experiments in e-doped thin films of SrTiO$_3$ (STO) which demonstrate that the electronic band degeneracy can be lifted through defect management during growth. We show that even small amounts of cationic vacancies, combined with epitaxial stress, produce a homogeneous tetragonal distortion of the films, resulting in a Kondo-like resistance upturn at low temperature, large anisotropic magnetoresistance, and non-linear Hall effect. Ab-initio calculations confirm a different occupation of each band depending on the degree of tetragonal distortion. The phenomenology reported in this paper for tetragonally distorted e-doped STO thin films, is similarto that observed in LaAlO$_3$/STO interfaces and magnetic STO quantum wells.Comment: 5 pages, 5 figure

Conserved current for the Cotton tensor, black hole entropy and equivariant Pontryagin forms

The Chern-Simons lagrangian density in the space of metrics of a 3-dimensional manifold M is not invariant under the action of diffeomorphisms on M. However, its Euler-Lagrange operator can be identified with the Cotton tensor, which is invariant under diffeomorphims. As the lagrangian is not invariant, Noether Theorem cannot be applied to obtain conserved currents. We show that it is possible to obtain an equivariant conserved current for the Cotton tensor by using the first equivariant Pontryagin form on the bundle of metrics. Finally we define a hamiltonian current which gives the contribution of the Chern-Simons term to the black hole entropy, energy and angular momentum.Comment: 13 page

Use of phytoremediation and biochar to remediate heavy metal polluted soils: a review

Anthropogenic activities are resulting in an increase of the use and extraction of heavy metals. Heavy metals cannot be degraded and hence accumulate in the environment, having the potential to contaminate the food chain. This pollution threatens soil quality, plant survival and human health. The remediation of heavy metals deserves attention, but it is impaired by the cost of these processes. Phytoremediation and biochar are two sound environmental technologies which could be at the forefront to mitigate soil pollution. This review provides an overview of the state of the art of the scientific research on phytoremediation and biochar application to remediate heavy-metal-contaminated soils. Research to date has attempted only in a limited number of occasions to combine both techniques, however we discuss the potential advantages of combining both, and the potential mechanisms involved in the interaction between phytoremediators and biochar. We identified specific research needs to ensure a sustainable use of phytoremediation and biochar as remediation tools

Parcerias e financiamento no terceiro sector português

info:eu-repo/semantics/acceptedVersio

Saturation and geometric scaling in DIS at small x

We present various aspects of the saturation model which provides good description of inclusive and diffractive DIS at small x. The model uses parton saturation ideas to take into account unitarity requirements. A new scaling predicted by the model in the small x domain is successfully confronted with the data.Comment: Presented at New Trends in HERA Physics 2001, Ringberg Castle, Tegernsee, Germany, 17-22 June 2001, minor corrections, some references adde

Random walks of partons in SU(N_c) and classical representations of color charges in QCD at small x

The effective action for wee partons in large nuclei includes a sum over static color sources distributed in a wide range of representations of the SU(N_c) color group. The problem can be formulated as a random walk of partons in the N_c-1 dimensional space spanned by the Casimirs of SU(N_c). For a large number of sources, k >> 1, we show explicitly that the most likely representation is a classical representation of order O(\sqrt{k}). The quantum sum over representations is well approximated by a path integral over classical sources with an exponential weight whose argument is the quadratic Casimir operator of the group. The contributions of the higher N_c-2 Casimir operators are suppressed by powers of k. Other applications of the techniques developed here are discussed briefly.Comment: 51 pages, includes 3 eps file

Survival probability for exclusive central diffractive production of colorless states at the LHC

In this paper we discuss the survival probability for exclusive central diffractive production of a colorless small size system at the LHC. This process has a clear signature of two large rapidity gaps. Using the eikonal approach for the description of soft interactions, we predict the value of the survival probability to be about 5~6% for single channel models, while for a two channel model the survival probability is about 3%. The dependence of the survival probability factor (damping factor) on the transverse momenta of the recoiled protons is discussed, and we suggest it be measured at the Tevatron so as to minimize the possible ambiguity in the calculation of survival probability at the LHC.Comment: 33 pages, 26 figure

Heisenberg's Universal (lns)**2 Increase of Total Cross Sections

The (lns)**2 behaviour of total cross-sections, first obtained by Heisenberg 50 years ago, receives now increased interest both on phenomenological and theoretical levels. In this paper we present a modification of the Heisenberg's model in connection with the presence of glueballs and we show that it leads to a realistic description of all existing hadron total cross-section data.Comment: 6 pages, 3 figure