1,553 research outputs found
Effects of sulfonation process on thermal behavior and microstructure of sulfonated polysulfone membranes as a material for Proton Exchange Membrane (PEM)
This paper reports the effect of sulfonation processon thermal behavior and microstrucutre of sulfonated polysulfone membrane. Various degree of sulfonation reactin has been conducted and the sulfonated membranes were characterized by thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), x-ray diffraction (XRD) and scanning electron microscopy (SEM). Modifications of the origin polysulfone polymer resulted in an increment value of glass transition temperature (Tg) due to the introduction of sulfonic acid group to the polymer backbone. However, due to some hindrance such as trace amount of organic solvent left during solvent evaporation and high hydrophilicity of the produced sulfonated membranes resulted in decreasing values of Tg. The polymer membrane showed lower degradation temperature as a function of degree of sulfonation. From XRD analysis, it was found that the membrane shows slight crystalline behavior after the sulfonation reaction. Detail discussions and observation of the alteration in microstructure of the sulfonated membrane were supported by SEM micrograph
Scaling in Tournaments
We study a stochastic process that mimics single-game elimination
tournaments. In our model, the outcome of each match is stochastic: the weaker
player wins with upset probability q<=1/2, and the stronger player wins with
probability 1-q. The loser is eliminated. Extremal statistics of the initial
distribution of player strengths governs the tournament outcome. For a uniform
initial distribution of strengths, the rank of the winner, x_*, decays
algebraically with the number of players, N, as x_* ~ N^(-beta). Different
decay exponents are found analytically for sequential dynamics, beta_seq=1-2q,
and parallel dynamics, beta_par=1+[ln (1-q)]/[ln 2]. The distribution of player
strengths becomes self-similar in the long time limit with an algebraic tail.
Our theory successfully describes statistics of the US college basketball
national championship tournament.Comment: 5 pages, 1 figure, empirical study adde
On The Structure of Competitive Societies
We model the dynamics of social structure by a simple interacting particle
system. The social standing of an individual agent is represented by an
integer-valued fitness that changes via two offsetting processes. When two
agents interact one advances: the fitter with probability p and the less fit
with probability 1-p. The fitness of an agent may also decline with rate r.
From a scaling analysis of the underlying master equations for the fitness
distribution of the population, we find four distinct social structures as a
function of the governing parameters p and r. These include: (i) a static
lower-class society where all agents have finite fitness; (ii) an
upwardly-mobile middle-class society; (iii) a hierarchical society where a
finite fraction of the population belongs to a middle class and a complementary
fraction to the lower class; (iv) an egalitarian society where all agents are
upwardly mobile and have nearly the same fitness. We determine the basic
features of the fitness distributions in these four phases.Comment: 8 pages, 7 figure
Randomness in Competitions
We study the effects of randomness on competitions based on an elementary
random process in which there is a finite probability that a weaker team upsets
a stronger team. We apply this model to sports leagues and sports tournaments,
and compare the theoretical results with empirical data. Our model shows that
single-elimination tournaments are efficient but unfair: the number of games is
proportional to the number of teams N, but the probability that the weakest
team wins decays only algebraically with N. In contrast, leagues, where every
team plays every other team, are fair but inefficient: the top of
teams remain in contention for the championship, while the probability that the
weakest team becomes champion is exponentially small. We also propose a gradual
elimination schedule that consists of a preliminary round and a championship
round. Initially, teams play a small number of preliminary games, and
subsequently, a few teams qualify for the championship round. This algorithm is
fair and efficient: the best team wins with a high probability and the number
of games scales as , whereas traditional leagues require N^3 games to
fairly determine a champion.Comment: 10 pages, 8 figures, reviews arXiv:physics/0512144,
arXiv:physics/0608007, arXiv:cond-mat/0607694, arXiv:physics/061221
Dynamics of Multi-Player Games
We analyze the dynamics of competitions with a large number of players. In
our model, n players compete against each other and the winner is decided based
on the standings: in each competition, the mth ranked player wins. We solve for
the long time limit of the distribution of the number of wins for all n and m
and find three different scenarios. When the best player wins, the standings
are most competitive as there is one-tier with a clear differentiation between
strong and weak players. When an intermediate player wins, the standings are
two-tier with equally-strong players in the top tier and clearly-separated
players in the lower tier. When the worst player wins, the standings are least
competitive as there is one tier in which all of the players are equal. This
behavior is understood via scaling analysis of the nonlinear evolution
equations.Comment: 8 pages, 8 figure
Self-Similarity in Random Collision Processes
Kinetics of collision processes with linear mixing rules are investigated
analytically. The velocity distribution becomes self-similar in the long time
limit and the similarity functions have algebraic or stretched exponential
tails. The characteristic exponents are roots of transcendental equations and
vary continuously with the mixing parameters. In the presence of conservation
laws, the velocity distributions become universal.Comment: 4 pages, 4 figure
Análise da quantidade de azoto em excesso em solos agrícolas na zona vulnerável n.º 1
O conceito de Zona Vulnerável com vista a proteger as águas contra a poluição difusa causada por nitratos de origem agrícola, foi definido na Directiva 91/676/CEE, publicada no Jornal Oficial das Comunidades de 31 de Dezembro de 1997, a qual foi transposta para a ordem jurídica interna pelo Dec-Lei 235/97 de 3 de Setembro. Os objectivos deste diploma são: a redução da poluição das águas contra a poluição causada por nitratos de origem agrícola, bem como impedir a propagação desta poluição (artº 2).
Com o presente trabalho pretende-se elaborar um modelo que permita quantificar a produção de chorume bovino que é um dos principais factores influentes na concentração de nitratos na Zona Vulnerável nº 1 Esposende – Vila do Conde
Entropic Tightening of Vibrated Chains
We investigate experimentally the distribution of configurations of a ring
with an elementary topological constraint, a ``figure-8'' twist. Using vibrated
granular chains, which permit controlled preparation and direct observation of
such a constraint, we show that configurations where one of the loops is tight
and the second is large are strongly preferred. This agrees with recent
predictions for equilibrium properties of topologically-constrained polymers.
However, the dynamics of the tightening process weakly violate detailed
balance, a signature of the nonequilibrium nature of this system.Comment: 4 pages, 4 figure
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