Adaptation of Autocatalytic Fluctuations to Diffusive Noise

Evolution of a system of diffusing and proliferating mortal reactants is analyzed in the presence of randomly moving catalysts. While the continuum description of the problem predicts reactant extinction as the average growth rate becomes negative, growth rate fluctuations induced by the discrete nature of the agents are shown to allow for an active phase, where reactants proliferate as their spatial configuration adapts to the fluctuations of the catalysts density. The model is explored by employing field theoretical techniques, numerical simulations and strong coupling analysis. For d<=2, the system is shown to exhibits an active phase at any growth rate, while for d>2 a kinetic phase transition is predicted. The applicability of this model as a prototype for a host of phenomena which exhibit self organization is discussed.Comment: 6 pages 6 figur

Semiclassical Quantization of Effective String Theory and Regge Trajectories

We begin with an effective string theory for long distance QCD, and evaluate the semiclassical expansion of this theory about a classical rotating string solution, taking into account the the dynamics of the boundary of the string. We show that, after renormalization, the zero point energy of the string fluctuations remains finite when the masses of the quarks on the ends of the string approach zero. The theory is then conformally invariant in any spacetime dimension D. For D=26 the energy spectrum of the rotating string formally coincides with that of the open string in classical Bosonic string theory. However, its physical origin is different. It is a semiclassical spectrum of an effective string theory valid only for large values of the angular momentum. For D=4, the first semiclassical correction adds the constant 1/12 to the classical Regge formula.Comment: 65 pages, revtex, 3 figures, added 2 reference

MARKET INSERTION OF FOREST COMMUNITIES IN SOUTHEASTERN MEXICO: THE RELEVANCE OF FOREST ENDOWMENT AND ORGANIZATION

In Mexico,rural communities own more than 80% of the total forest area, but less than 30% of these communities are involved in forest management activities. It has been shown that markets represent a critical incentive for the development and consolidation of community forestry. Despite that, little is known about the factors that enable certain communities to successfully insert into markets and prevent others from doing so. This paper examines factors that enable communities to insertin markets. The focus lies in two important community-specific variables: forest endowment and community organization. Information on market insertion was gathered through a survey of fifty-three communities in southern Quintana Roo, Mexico. The survey was complemented with expert interviews and the use of Geographic Information Systems (GIS). Findings indicate that forest endowment strongly determines market insertion. Community organization seems to have a reinforcing relation with market insertion, thus not allowing for unilateral causality. Among other aspects, the results indicate the existence of high market entry barriers to enter forest production and marketing, such as costly legal preconditions

MARKET INSERTION OF FOREST COMMUNITIES IN SOUTHEASTERN MEXICO: THE RELEVANCE OF FOREST ENDOWMENT AND ORGANIZATION

In Mexico,rural communities own more than 80% of the total forest area, but less than 30% of these communities are involved in forest management activities. It has been shown that markets represent a critical incentive for the development and consolidation of community forestry. Despite that, little is known about the factors that enable certain communities to successfully insert into markets and prevent others from doing so. This paper examines factors that enable communities to insertin markets. The focus lies in two important community-specific variables: forest endowment and community organization. Information on market insertion was gathered through a survey of fifty-three communities in southern Quintana Roo, Mexico. The survey was complemented with expert interviews and the use of Geographic Information Systems (GIS). Findings indicate that forest endowment strongly determines market insertion. Community organization seems to have a reinforcing relation with market insertion, thus not allowing for unilateral causality. Among other aspects, the results indicate the existence of high market entry barriers to enter forest production and marketing, such as costly legal preconditions

ThermoElectric Transport Properties of a Chain of Quantum Dots with Self-Consistent Reservoirs

We introduce a model for charge and heat transport based on the Landauer-Buttiker scattering approach. The system consists of a chain of $N$ quantum dots, each of them being coupled to a particle reservoir. Additionally, the left and right ends of the chain are coupled to two particle reservoirs. All these reservoirs are independent and can be described by any of the standard physical distributions: Maxwell-Boltzmann, Fermi-Dirac and Bose-Einstein. In the linear response regime, and under some assumptions, we first describe the general transport properties of the system. Then we impose the self-consistency condition, i.e. we fix the boundary values (T_L,\mu_L) and (T_R,mu_R), and adjust the parameters (T_i,mu_i), for i = 1,...,N, so that the net average electric and heat currents into all the intermediate reservoirs vanish. This condition leads to expressions for the temperature and chemical potential profiles along the system, which turn out to be independent of the distribution describing the reservoirs. We also determine the average electric and heat currents flowing through the system and present some numerical results, using random matrix theory, showing that these currents are typically governed by Ohm and Fourier laws.Comment: Minor changes (45 pages

Stochastic processes with finite correlation time: modeling and application to the generalized Langevin equation

The kangaroo process (KP) is characterized by various forms of the covariance and can serve as a useful model of random noises. We discuss properties of that process for the exponential, stretched exponential and algebraic (power-law) covariances. Then we apply the KP as a model of noise in the generalized Langevin equation and simulate solutions by a Monte Carlo method. Some results appear to be incompatible with requirements of the fluctuation-dissipation theorem because probability distributions change when the process is inserted into the equation. We demonstrate how one can construct a model of noise free of that difficulty. This form of the KP is especially suitable for physical applications.Comment: 22 pages (RevTeX) and 4 figure

On the role of the upper part of words in lexical access : evidence with masked priming

More than 100 years ago, Huey (1908) indicated that the upper part of words was more relevant for perception than the lower part. Here we examined whether mutilated words, in their upper/lower portions (e.g., , , , ), can automatically access their word units in the mental lexicon. To that end, we conducted four masked repetition priming experiments with the lexical decision task. Results showed that mutilated primes produced a sizeable masked repetition priming effect. Furthermore, the magnitude of the masked repetition priming effect was greater when the upper part of the primes was preserved than when the lower portion was preserved –this was the case not only when the mutilated words were presented in lowercase but also when the mutilated words were presented in uppercase. Taken together, these findings suggest that the front-end of computational models of visual-word recognition should be modified to provide a more realistic account at the level of letter features.The research reported in this article has been partially supported by Grant PSI2008-04069/PSIC and CONSOLIDER-INGENIO2010 CSD2008-00048 from the Spanish Ministry of Science and Innovation and by Grant PTDC/PSI-PCO/104671/2008 from the Portuguese Foundation for Science and Technology

The use of Complementary and Alternative Medicine in pregnancy: Data from the Avon Longitudinal Study of Parents and Children (ALSPAC)

Objectives - To report the frequency of Complementary and Alternative Medicine (CAM) use by a population of pregnant women in the UK. Design - Four postal self-completion questionnaires completed at 8, 12, 18 and 32 weeks’ gestation provided the source of CAMs used. Questions asked for written descriptions about the use of any treatments, pills, medicines, ointments, homeopathic medicines, herbal medicines, supplements, drinks and herbal teas. Setting - An observational, population-based, cohort study of parents and children of 14,541 pregnant women residing within the former county of Avon in south-west England. Data was available for 14,115 women. Results - Over a quarter (26.7%; n = 3774) of women had used a CAM at least once in pregnancy, the use rising from 6% in the 1st trimester to 12.4% in the 2nd to 26.3% in the 3rd. Herbal teas were the most commonly reported CAM at any time in pregnancy (17.7%; n = 2499) followed by homeopathic medicine (14.4%; n = 2038) and then herbal medicine (5.8%; n = 813). The most commonly used herbal product was chamomile used by 14.6% of women, the most commonly used homeopathic product was Arnica used by 3.1% of women. Other CAMs (osteopathy, aromatherapy, acupuncture/acupressure, Chinese herbal medicine, chiropractic, cranial sacral therapy, hypnosis, non-specific massage and reflexology) accounted for less than 1% of users. Conclusions - CAM use in pregnancy, where a wide range of CAMs has been assessed, has not been widely reported. Studies that have been conducted report varying results to this study (26.7%) by between 13.3% and 87% of pregnant women. Survey results will be affected by a number of factors namely the inclusion/exclusion of vitamins and minerals, the timing of data collection, the country of source, the number of women surveyed, and the different selection criteria of either recruiting women to the study or of categorising and identifying a CAM treatment or product

Thermal decomposition as route for silver nanoparticles

Single crystalline silver nanoparticles have been synthesized by thermal decomposition of silver oxalate in water and in ethylene glycol. Polyvinyl alcohol (PVA) was employed as a capping agent. The particles were spherical in shape with size below 10 nm. The chemical reduction of silver oxalate by PVA was also observed. Increase of the polymer concentration led to a decrease in the size of Ag particles. Ag nanoparticle was not formed in the absence of PVA. Antibacterial activity of the Ag colloid was studied by disc diffusion method

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