O uso do lodo de esgoto na agricultura: precauções com os contaminantes orgânicos.

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From Quantum Dynamics to the Canonical Distribution: General Picture and a Rigorous Example

Derivation of the canonical (or Boltzmann) distribution based only on quantum dynamics is discussed. Consider a closed system which consists of mutually interacting subsystem and heat bath, and assume that the whole system is initially in a pure state (which can be far from equilibrium) with small energy fluctuation. Under the "hypothesis of equal weights for eigenstates", we derive the canonical distribution in the sense that, at sufficiently large and typical time, the (instantaneous) quantum mechanical expectation value of an arbitrary operator of the subsystem is almost equal to the desired canonical expectation value. We present a class of examples in which the above derivation can be rigorously established without any unproven hypotheses.Comment: LaTeX, 8 pages, no figures. The title, abstract and some discussions are modified to stress physical motivation of the work. References are added to [2]. This version will appear in Phys. Rev. Lett. There is an accompanying unpublished note (cond-mat/9707255

Chiral Crystal Growth under Grinding

To study the establishment of homochirality observed in the crystal growth experiment of chiral molecules from a solution under grinding, we extend the lattice gas model of crystal growth as follows. A lattice site can be occupied by a chiral molecule in R or S form, or can be empty. Molecules form homoclusters by nearest neighbor bonds. They change their chirality if they are isolated monomers in the solution. Grinding is incorporated by cutting and shafling the system randomly. It is shown that Ostwald ripening without grinding is extremely slow to select chirality, if possible. Grinding alone also cannot achieve chirality selection. For the accomplishment of homochirality, we need an enhanced chirality change on crystalline surface. With this "autocatalytic effect" and the recycling of monomers due to rinding, an exponential increase of crystal enantiomeric excess to homochiral state is realized.Comment: 10 pages, 5 figure

Ultrafast photocurrent measurement of the escape time of electrons and holes from carbon nanotube PN junction photodiodes

Ultrafast photocurrent measurements are performed on individual carbon nanotube PN junction photodiodes. The photocurrent response to sub-picosecond pulses separated by a variable time delay {\Delta}t shows strong photocurrent suppression when two pulses overlap ({\Delta}t = 0). The picosecond-scale decay time of photocurrent suppression scales inversely with the applied bias VSD, and is twice as long for photon energy above the second subband E22 as compared to lower energy. The observed photocurrent behavior is well described by an escape time model that accounts for carrier effective mass.Comment: 8 pages Main text, 4 Figure

Distribuição ambiental de poluentes orgânicos encontrados em lodos de esgoto.

O objetivo deste trabalho foi apresentar uma modelagem da distribuição ambiental de vinte e nove poluentes orgânicos encontrados em amostras de lodos de esgoto das estações de tratamento de esgoto de Barueri e Suzano, SP. Lodos de esgoto são misturas de produtos orgânicos e inorgânicos gerados nos processos primários e secundários de tratamento que, mediante adequado controle de qualidade, podem ser reutilizados como fertilizantes agrícolas. O modelo de fugacidade nível I foi aplicado a um sistema compartimental hipotético constituído de ar, água, solo, sedimento, biota aquática e plantas. Foi utilizada a massa molecular, a pressão de vapor, a solubilidade em água, a constante de Henry, o coeficiente de partição octanol-água e a meia-vida no solo de cada um dos poluentes. O coeficiente de sorção no solo, os fatores de bioconcentração em organismos aquáticos, raízes e na seiva do xilema de plantas foram calculados por meio de expressões que correlacionam cada um desses parâmetros com o coeficiente de partição octanol-água do poluente. Foram estimados e usados os coeficientes de partição folha-ar e ar-água e o índice GUS de cada poluente. A modelagem e os cálculos dos fatores de bioconcentração e dos coeficientes de partição revelam os compartimentos preferenciais dos poluentes

Energy Anomaly and Polarizability of Carbon Nanotubes

The energy of electron Fermi sea perturbed by external potential, represented as energy anomaly which accounts for the contribution of the deep-lying states, is analyzed for massive d = 1+1 Dirac fermions on a circle. The anomaly is a universal function of the applied field, and is related to known field-theoretic anomalies. We express transverse polarizability of Carbon nanotubes via the anomaly, in a way which exhibits the universality and scale-invariance of the response dominated by pi-electrons and qualitatively different from that of dielectric and conducting shells. Electron band transformation in a strong-field effect regime is predicted.Comment: 4 pg

Ground-state energy of the electron liquid in ultrathin wires

The ground-state energy and the density correlation function of the electron liquid in a thin one-dimensional wire are computed. The calculation is based on an approximate mapping of the problem with a realistic Coulomb interaction law onto exactly solvable models of mathematical physics. This approach becomes asymptotically exact in the limit of small wire radius but remains numerically accurate even for modestly thin wires.Comment: (v3) Replaced with the published version. 4 pages, 1 figur

Narrow gap Luttinger liquid in Carbon nanotubes

Electron interactions reinforce minigaps induced in metallic nanotubes by an external field and turn the gap field dependence into a universal power law. An exactly solvable Gross-Neveau model with an SU(4) symmetry is derived for neutral excitations near half-filling. Charge excitations, described by a sin-Gordon perturbation of Luttinger liquid theory, are composite solitons formed by the charged and neutral fields with two separate length scales. Charge compressibility at finite density, evaluated in terms of inter-soliton interaction, exhibits a crossover from overlapping to non-overlapping soliton state. Implications for the Coulomb blockade measurements are discussed.Comment: 4 pages, 2 figure

Distribution of the spacing between two adjacent avoided crossings

We consider the frequency at which avoided crossings appear in an energy level structure when an external field is applied to a quantum chaotic system. The distribution of the spacing in the parameter between two adjacent avoided crossings is investigated. Using a random matrix model, we find that the distribution of these spacings is well fitted by a power-law distribution for small spacings. The powers are 2 and 3 for the Gaussian orthogonal ensemble and Gaussian unitary ensemble, respectively. We also find that the distributions decay exponentially for large spacings. The distributions in concrete quantum chaotic systems agree with those of the random matrix model.Comment: 11 page

Gluon propagators and center vortices in gluon plasma

We study electric and magnetic components of the gluon propagators in quark-gluon plasma in terms of center vortices by using a quenched simulation of SU(2) lattice theory. In the Landau gauge, the magnetic components of the propagators are strongly affected in the infrared region by removal of the center vortices, while the electric components are almost unchanged by this procedure. In the Coulomb gauge, the time-time correlators, including an instantaneous interaction, also have an essential contribution from the center vortices. As a result, one finds that magnetic degrees of freedom in the infrared region couple strongly to the center vortices in the deconfinement phase.Comment: 12 pages, 11 figure