Pore-scale modelling of diffusion in unconsolidated porous structures

A deterministic pore-scale model is used to predict the diffusivity ratio of unconsolidated porous media in which the diffusion process can be regarded as isotropic. The pore-scale model is based on a rectangular representative unit cell concept. A porosity-based weighted average of the two-dimensional and three-dimensional pore-scale models is proposed as a convenient model to predict the effective diffusion coefficient of isotropic systems. The diffusivity ratio of two-dimensionally staggered and non-staggered arrays of anisotropic solid rectangles is computed numerically and an existing weighted average model is applied to verify the numerical data. A particular case of a staggered array of solid squares, for which this weighted average model is no longer adequate, is outlined and the weighted average pore-scale model is proposed instead to predict the diffusivity ratio. The newly proposed pore-scale model and the present numerical results compare favourably with numerical data, experimental data and other predictive measures reported in the literature.     

Formation of continuous dense polymer layer at the surface of hollow fiber using a photografting process

The surface modification of a PES hollow fiber by UV photografting has been investigated in order to graft a dense polymer layer. The study focused on a UV photografting process, starting from a monomer solution, enabling the thickness and regularity of the grafted polymer to be followed. 2‐(Acryloyloxy)ethyl trimethylammonium chloride was polymerized on the surface of the PES membrane. Modified membranes were characterized by SEM, FTIR spectroscopy, and liquid and gas permeability. A dense layer of poly(2‐(acryloyloxy)ethyl trimethylammonium chloride) was obtained when a photoinitiator and a photocrosslinker were used. Polymerization of the ammonium material also occurred inside the pores of the membrane. With pretreatment and an increase of the irradiation time, the thickness of the grafted polymer decreased and gas permeability reached measurable levels. However, a CO₂/N₂ selectivity of around 1 was found which suggested the presence of defects in the grafted layer. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41514.     

Matrix effects on the antimicrobial capacity of silver based nanocomposite absorbing materials

The suitability of cellulose/silver nanocomposites to decrease the microbial loads in absorbent materials was studied during the shelf-life of minimally processed foods. Cellulose/silver nanocomposites were synthesised by means of reduction by UV/heat of silver nitrate adsorbed on fluff pulp cellulose fibres. Minimally processed fruits and meat products were packaged in trays containing commercial absorbent pads or silver loaded absorbers, and stored during 10 days at 4 °C. The synthesised antimicrobial nanocomposites were useful to control the population of spoilage-related microorganisms in absorbent pads, being particularly effective in contact with low-protein food products. In contact with silver loaded absorbers, counts of total viable microorganisms and yeasts and moulds were reduced up to 99.9% in juices from kiwi fruit and melon; in drip from poultry and beef meat, microbial loads (total viable counts, lactic acid bacteria) were constantly 90% below the controls. Consequently, silver based absorbent materials could be especially designed to improve hygienic conditions during the manipulation and storage of minimally processed fruit cuts and meat products, but matrix effects must be taken into account.     

Corroborating premorbid dissociative symptomatology in dissociative identity disorder.

Clinicians are often cautious about making the diagnosis of Dissociative Identity Disorder (DID). The existence of corroborating evidence that symptoms of DID existed prior to assessment may address concerns about the genuineness of individual cases. The authors report the results of a survey of clinicians to determine the frequency of corroboration that clients' DID symptoms existed prior to being diagnosed or prior to therapy. On the basis of 446 cases of DID, clinicians reported some form of corroboration (e.g., reports from family, medical records) in 73% of cases for symptoms prior to diagnosis and in 67% of cases for symptoms prior to therapy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A binary decision diagram based approach for mining frequent subsequences

Sequential pattern mining is an important problem in data mining. State of the art techniques for mining sequential patterns, such as frequent subsequences, are often based on the pattern-growth approach, which recursively projects conditional databases. Explicitly creating database projections is thought to be a major computational bottleneck, but we will show in this paper that it can be beneficial when the appropriate data structure is used. Our technique uses a canonical directed acyclic graph as the sequence database representation, which can be represented as a binary decision diagram (BDD). In this paper, we introduce a new type of BDD, namely a sequence BDD (SeqBDD), and show how it can be used for efficiently mining frequent subsequences. A novel feature of the SeqBDD is its ability to share results between similar intermediate computations and avoid redundant computation. We perform an experimental study to compare the SeqBDD technique with existing pattern growth techniques, that are based on other data structures such as prefix trees. Our results show that a SeqBDD can be half as large as a prefix tree, especially when many similar sequences exist. In terms of mining time, it can be substantially more efficient when the support is low, the number of patterns is large, or the input sequences are long and highly similar.     

Model checking, testing and verification working together

We present a symbolic model checking approach that allows verifying a unit of code, e.g., a single procedure or a collection of procedures that interact with each other. We allow temporal specifications that assert over both the program counters and the program variables. We decompose the verification into two parts: (1) a search that is based on the temporal behavior of the program counters, and (2) the formulation and refutation of a path condition, which inherits conditions constraining the program variables from the temporal specification. This verification approach is modular, as we do not require that all the involved procedures are provided. Furthermore, we do not request that the code is based on a finite domain. The presented approach can also be used for automating the generation of test cases for unit testing.A preliminary version of the paper, with the title Unit Checking: Symbolic Model Checking for a Unit of Code appears in the Lecture Notes in Computer Science volume 2772, Verification– Theory and Practice, celebrating Zohar Manna’s 64th birthdayThis research was partially supported by US Army Research Office Grant number DAAAD19-01-1-0473This research was partially supported by Subcontract UTA03-031 to The University of Warwick under University of Texas at Austin’s prime National Science Foundation Grant #CCR-0205483Received February 2004Revised September 2004 and April 2005Accepted April 2005 by M. Leuschel and D. J. Cooke     

Mercury cycling between the water column and surface sediments in a contaminated area

Mercury cycling in the water column and upper sediments of a contaminated area, the Largo do Laranjo, Aveiro (Portugal), was evaluated after determination of reactive and non-reactive mercury concentrations in the water column and pore waters of sediments, collected in several places of this bay. In the water column, reactive mercury concentrations varied between 10 and 37 pmol dm(-3), the highest values being observed near the mercury anthropogenic source. However, reactive mercury was a narrowly constrained fraction of the total mercury, making up only 4-16% of the total, showing evidence of the importance of dissolved organic matter on mercury transport. In sediments, higher concentrations of mercury were also determined near industrial discharges. Results indicate the existence of an equilibrium between solid and liquid phases, determined by solid sediment/pore water distribution coefficients. Much of the mercury present in the solid fraction is associated with organic matter (r=0.837) and iron oxyhydroxides (r=0.919), but as oxides begin to dissolve in reduced sediments and organic matter decays, the adsorbed mercury is released. In fact, the mercury concentrations in pore waters of those contaminated sediments largely exceeded the values determined in the water column. As molecular diffusion may contribute to the dissolved mercury distribution in the overlying water column, this phenomenon was evaluated. However, the pore waters of Largo do Laranjo do not enrich the water column substantially in terms of reactive and non-reactive mercury. In fact, pore waters can contribute only to 0.2% and 0.5% of the reactive and non-reactive mercury present in the water column, respectively, showing that as long as mercury is being incorporated in sediments, it stays in stable forms.