Swelling of particle-encapsulating random manifolds

We study the statistical mechanics of a closed random manifold of fixed area and fluctuating volume, encapsulating a fixed number of noninteracting particles. Scaling analysis yields a unified description of such swollen manifolds, according to which the mean volume gradually increases with particle number, following a single scaling law. This is markedly different from the swelling under fixed pressure difference, where certain models exhibit criticality. We thereby indicate when the swelling due to encapsulated particles is thermodynamically inequivalent to that caused by fixed pressure. The general predictions are supported by Monte Carlo simulations of two particle-encapsulating model systems -- a two-dimensional self-avoiding ring and a three-dimensional self-avoiding fluid vesicle. In the former the particle-induced swelling is thermodynamically equivalent to the pressure-induced one whereas in the latter it is not.Comment: 8 pages, 6 figure

Stability of Quasicrystals Composed of Soft Isotropic Particles

Quasicrystals whose building blocks are of mesoscopic rather than atomic scale have recently been discovered in several soft-matter systems. Contrary to metallurgic quasicrystals whose source of stability remains a question of great debate to this day, we argue that the stability of certain soft-matter quasicrystals can be directly explained by examining a coarse-grained free energy for a system of soft isotropic particles. We show, both theoretically and numerically, that the stability can be attributed to the existence of two natural length scales in the pair potential, combined with effective three-body interactions arising from entropy. Our newly gained understanding of the stability of soft quasicrystals allows us to point at their region of stability in the phase diagram, and thereby may help control the self-assembly of quasicrystals and a variety of other desired structures in future experimental realizations.Comment: Revised abstract, more detailed explanations, and better images of the numerical minimization of the free energ

Nanoscale surface relaxation of a membrane stack

Recent measurements of the short-wavelength (~ 1--100 nm) fluctuations in stacks of lipid membranes have revealed two distinct relaxations: a fast one (decay rate of ~ 0.1 ns^{-1}), which fits the known baroclinic mode of bulk lamellar phases, and a slower one (~ 1--10 \mu s^{-1}) of unknown origin. We show that the latter is accounted for by an overdamped capillary mode, depending on the surface tension of the stack and its anisotropic viscosity. We thereby demonstrate how the dynamic surface tension of membrane stacks could be extracted from such measurements.Comment: 4 page

Excitonic Funneling in Extended Dendrimers with Non-Linear and Random Potentials

The mean first passage time (MFPT) for photoexcitations diffusion in a funneling potential of artificial tree-like light-harvesting antennae (phenylacetylene dendrimers with generation-dependent segment lengths) is computed. Effects of the non-linearity of the realistic funneling potential and slow random solvent fluctuations considerably slow down the center-bound diffusion beyond a temperature-dependent optimal size. Diffusion on a disordered Cayley tree with a linear potential is investigated analytically. At low temperatures we predict a phase in which the MFPT is dominated by a few paths.Comment: 4 pages, 4 figures, To be published in Phys. Rev. Let

Disorder and Funneling Effects on Exciton Migration in Tree-Like Dendrimers

The center-bound excitonic diffusion on dendrimers subjected to several types of non-homogeneous funneling potentials, is considered. We first study the mean-first passage time (MFPT) for diffusion in a linear potential with different types of correlated and uncorrelated random perturbations. Increasing the funneling force, there is a transition from a phase in which the MFPT grows exponentially with the number of generations $g$, to one in which it does so linearly. Overall the disorder slows down the diffusion, but the effect is much more pronounced in the exponential compared to the linear phase. When the disorder gives rise to uncorrelated random forces there is, in addition, a transition as the temperature $T$ is lowered. This is a transition from a high-$T$ regime in which all paths contribute to the MFPT to a low-$T$ regime in which only a few of them do. We further explore the funneling within a realistic non-linear potential for extended dendrimers in which the dependence of the lowest excitonic energy level on the segment length was derived using the Time-Dependent Hatree-Fock approximation. Under this potential the MFPT grows initially linearly with $g$ but crosses-over, beyond a molecular-specific and $T$-dependent optimal size, to an exponential increase. Finally we consider geometrical disorder in the form of a small concentration of long connections as in the {\it small world} model. Beyond a critical concentration of connections the MFPT decreases significantly and it changes to a power-law or to a logarithmic scaling with $g$, depending on the strength of the funneling force.Comment: 13 pages, 9 figure

Disponibilidade de água em função das doses de concentrado zeolíti.

O uso de condicionadores do solo representa uma alternativa para aumentar a capacidade de retenção de água e nutrientes dos solos arenosos. Dentre os condicionadores naturais, as zeólitas podem ser utilizadas para aumentar a capacidade de retenção de água em solos sujeitos à déficit hídrico. As zeólitas são minerais alumino-silicatos cristalinos hidratados estruturados em redes cristalinas tridimensionais rígidas e de ocorrência natural. O objetivo deste trabalho foi avaliar o efeito de doses de um concentrado do mineral zeólita sobre a capacidade de retenção de água de um Neossolo Quartzarênico. Foram determinadas as curvas de retenção de umidade das misturas de solo com concentrado zeolítico em amostras deformadas. Adicionou-se 4 níveis do concentrado zeolítico: testemunha, 0,033, 0,066 e 0,099 g kg-1 de solo em um delineamento inteiramente casualizado com 4 tratamentos (doses de concentrado zeolítico) com 3 repetições. Os resultados indicam que com o uso do concentrado zeolítico foi possível aumentar a retenção de água e esta água está retida com baixas tensões. Houve aumentos em relação à testemunha de 10, 38 e 67% na CAD para as doses de 0,033, 0,066 e 0,099 g kg-1.In: CONGRESSO BRASILEIRO DE CIÊNCIA DO SOLO, 31., 2007, Gramado. Conquistas e desafios da Ciência do Solo brasileira: resumos. Gramado: SBCS, 2007

Potencial do uso de zeólitas na agropecuária

bitstream/CPPSE-2009/18336/1/Documentos85.pdfMetas 200

Eco-tourism in the Philippines: Educational and recreational value of the Alayan cave systems

In this paper, we calculate the related costs of transport, food, accommodation and time involved as well as the rate of visits as compared to the costs, and the benefits from the Alayan Cave System (ACS), by using the Individual Travel Cost Method (ITCM) to determine the educational and recreational values of the site.Data came from the linear recreational demand for the site at the Department of Tourism - RO2 statistical records.We also determine the expenditures of the guests on off–site and on–site tourism–related activities and establishments to provide a more solid base for tourism policymakers, planners and decision makers in the region, towards a better tourism tax system for the sustainability of the ACS. Study outcomes provide insight into how the locals or indigenous people living nearby can take advantage of the benefits/opportunities derived from the site

Crescimento e nutrição mineral do porta-enxerto limoeiro 'cravo' cultivado em substrato com zeólita enriquecida com NPK.

O objetivo do trabalho foi avaliar o efeito da adição de um concentrado zeolítico enriquecido com N, P e K ao substrato de cultivo sobre o crescimento, produção de matéria seca, área foliar, teores e extração de N, P e K e os teores de clorofila do limoeiro "Cravo". O porta-enxerto foi cultivado por 93 dias em tubetes de 150 cm3 com substrato orgânico compostado de casca de coco e carvão vegetal (3:1) ao qual se adicionou o concentrado zeolítico. Este foi obtido com a concentração da zeólita natural (Z) e enriquecimento desta com KNO3 (ZNK), e também com a acidificação com H3PO4 e mistura com apatita (ZP). Utilizou-se uma mistura de 30%ZNK + 70%ZP nas doses de: 0; 2,5; 5; 10 e 15 g por planta. Os resultados indicaram que o fornecimento de nutrientes através do mineral zeólita adicionado ao substrato orgânico comprovou ser alternativa viável para a obtenção de porta-enxertos no sistema de produção em ambiente protegido. A adição de 6,4 g do concentrado zeolítico enriquecido com NPK aumentou significativamente a produção de matéria seca, área foliar, altura e diâmetro de caule. Este aumento foi de 37,5% em relação à testemunha que não recebeu o concentrado zeolítico. Houve aumentos nos teores e extração de N, P e K com o fornecimento da zeólita enriquecida. As leituras dos teores de clorofila relacionaram-se com os teores de N, indicando ser esta uma alternativa para o diagnóstico do estado nutricional para a cultura.Publicado em outra fonte: http://www.todafruta.com.br/todoafruta/mostra_conteudo.asp