Microbial biofilm studies of the environmental control and life support system water recovery test for Space Station Freedom

NASA is developing a water recovery system (WRS) for Space Station Freedom to reclaim human waste water for reuse by astronauts as hygiene or potable water. A water recovery test (WRT) currently in progress investigates the performance of a prototype of the WRS. Analysis of biofilm accumulation, the potential for microbially influenced corrosion (MIC) in the WRT, and studies of iodine disinfection of biofilm are reported. Analysis of WRT components indicated the presence of organic deposits and biofilms in selected tubing. Water samples for the WRT contained acid-producing and sulfate-reducing organisms implicated in corrosion processes. Corrosion of an aluminum alloy was accelerated in the presence of these water samples; however, stainless steel corrosion rates were not accelerated. Biofilm iodine sensitivity tests using an experimental laboratory scale recycled water system containing a microbial check valve (MCV) demonstrated that an iodine concentration of 1 to 2 mg/L was ineffective in eliminating microbial biofilm. For complete disinfection, an initial concentration of 16 mg/L was required, which was gradually reduced by the MCV over 4 to 8 hours to 1 to 2 mg/L. This treatment may be useful in controlling biofilm formation

Local molecular field theory for the treatment of electrostatics

We examine in detail the theoretical underpinnings of previous successful applications of local molecular field (LMF) theory to charged systems. LMF theory generally accounts for the averaged effects of long-ranged components of the intermolecular interactions by using an effective or restructured external field. The derivation starts from the exact Yvon-Born-Green hierarchy and shows that the approximation can be very accurate when the interactions averaged over are slowly varying at characteristic nearest-neighbor distances. Application of LMF theory to Coulomb interactions alone allows for great simplifications of the governing equations. LMF theory then reduces to a single equation for a restructured electrostatic potential that satisfies Poisson's equation defined with a smoothed charge density. Because of this charge smoothing by a Gaussian of width sigma, this equation may be solved more simply than the detailed simulation geometry might suggest. Proper choice of the smoothing length sigma plays a major role in ensuring the accuracy of this approximation. We examine the results of a basic confinement of water between corrugated wall and justify the simple LMF equation used in a previous publication. We further generalize these results to confinements that include fixed charges in order to demonstrate the broader impact of charge smoothing by sigma. The slowly-varying part of the restructured electrostatic potential will be more symmetric than the local details of confinements.Comment: To be published in J Phys-Cond Matt; small misprint corrected in Eq. (12) in V

Near Infrared Spectroscopy of Young Brown Dwarfs in Upper Scorpius

Spectroscopic follow-up is a pre-requisite for studies of the formation and early evolution of brown dwarfs. Here we present IRTF/SpeX near-infrared spectroscopy of 30 candidate members of the young Upper Scorpius association, selected from our previous survey work. All 24 high confidence members are confirmed as young very low mass objects with spectral types from M5 to L1, 15-20 of them are likely brown dwarfs. This high yield confirms that brown dwarfs in Upper Scorpius can be identified from photometry and proper motions alone, with negligible contamination from field objects (<4%). Out of the 6 candidates with lower confidence, 5 might still be young very low mass members of Upper Scorpius, according to our spectroscopy. We demonstrate that some very low mass class II objects exhibit radically different near infrared (0.6 - 2.5micron) spectra from class III objects, with strong excess emission increasing towards longer wavelengths and partially filled in features at wavelengths shorter than 1.25micron. These characteristics can obscure the contribution of the photosphere within such spectra. Therefore, we caution that near infrared derived spectral types for objects with discs may be unreliable. Furthermore, we show that the same characteristics can be seen to some extent in all class II and even a significant fraction of class III objects (~40%), indicating that some of them are still surrounded by traces of dust and gas. Based on our spectra, we select a sample of objects with spectral types of M5 to L1, whose near-infrared emission represents the photosphere only. We recommend the use of these objects as spectroscopic templates for young brown dwarfs in the future.Comment: 12 pages, 9 figures, Accepted in MNRA

Network growth model with intrinsic vertex fitness

© 2013 American Physical SocietyWe study a class of network growth models with attachment rules governed by intrinsic node fitness. Both the individual node degree distribution and the degree correlation properties of the network are obtained as functions of the network growth rules. We also find analytical solutions to the inverse, design, problems of matching the growth rules to the required (e.g., power-law) node degree distribution and more generally to the required degree correlation function. We find that the design problems do not always have solutions. Among the specific conditions on the existence of solutions to the design problems is the requirement that the node degree distribution has to be broader than a certain threshold and the fact that factorizability of the correlation functions requires singular distributions of the node fitnesses. More generally, the restrictions on the input distributions and correlations that ensure solvability of the design problems are expressed in terms of the analytical properties of their generating functions

The resistance of randomly grown trees

Copyright @ 2011 IOP Publishing Ltd. This is a preprint version of the published article which can be accessed from the link below.An electrical network with the structure of a random tree is considered: starting from a root vertex, in one iteration each leaf (a vertex with zero or one adjacent edges) of the tree is extended by either a single edge with probability p or two edges with probability 1 − p. With each edge having a resistance equal to 1 omega, the total resistance Rn between the root vertex and a busbar connecting all the vertices at the nth level is considered. A dynamical system is presented which approximates Rn, it is shown that the mean value (Rn) for this system approaches (1 + p)/(1 − p) as n → ∞, the distribution of Rn at large n is also examined. Additionally, a random sequence construction akin to a random Fibonacci sequence is used to approximate Rn; this sequence is shown to be related to the Legendre polynomials and its mean is shown to converge with |(Rn) − (1 + p)/(1 − p)| ∼ n−1/2.Engineering and Physical Sciences Research Council (EPSRC

The parasitic worm-derived immunomodulator, ES-62 and its drug-like small molecule analogues exhibit therapeutic potential in a model of chronic asthma

Chronic asthma is associated with persistent lung inflammation and long-term remodelling of the airways that have proved refractory to conventional treatments such as steroids, despite their efficacy in controlling acute airway contraction and bronchial inflammation. As its recent dramatic increase in industrialised countries has not been mirrored in developing regions, it has been suggested that helminth infection may protect humans against developing asthma. Consistent with this, ES-62, an immunomodulator secreted by the parasitic worm Acanthocheilonema viteae, can prevent pathology associated with chronic asthma (cellular infiltration of the lungs, particularly neutrophils and mast cells, mucus hyper-production and airway thickening) in an experimental mouse model. Importantly, ES-62 can act even after airway remodelling has been established, arresting pathogenesis and ameliorating the inflammatory flares resulting from repeated exposure to allergen that are a debilitating feature of severe chronic asthma. Moreover, two chemical analogues of ES-62, 11a and 12b mimic its therapeutic actions in restoring levels of regulatory B cells and suppressing neutrophil and mast cell responses. These studies therefore provide a platform for developing ES-62-based drugs, with compounds 11a and 12b representing the first step in the development of a novel class of drugs to combat the hitherto intractable disorder of chronic asthma

A coarse grained model of granular compaction and relaxation

We introduce a theoretical model for the compaction of granular materials by discrete vibrations which is expected to hold when the intensity of vibration is low. The dynamical unit is taken to be clusters of granules that belong to the same collective structure. We rigourously construct the model from first principles and show that numerical solutions compare favourably with a range of experimental results. This includes the logarithmic relaxation towards a statistical steady state, the effect of varying the intensity of vibration resulting in a so-called `annealing' curve, and the power spectrum of density fluctuations in the steady state itself. A mean-field version of the model is introduced which shares many features with the exact model and is open to quantitative analysi

Stretched exponentials and power laws in granular avalanching

We introduce a model for granular avalanching which exhibits both stretched exponential and power law avalanching over its parameter range. Two modes of transport are incorporated, a rolling layer consisting of individual particles and the overdamped, sliding motion of particle clusters. The crossover in behaviour observed in experiments on piles of rice is attributed to a change in the dominant mode of transport. We predict that power law avalanching will be observed whenever surface flow is dominated by clustered motion. Comment: 8 pages, more concise and some points clarified

Feasibility study of experimental methods for joint damping analysis

Feasibility of damping test apparatus using bolted join