Local structure of percolating gels at very low volume fractions

The formation of colloidal gels is strongly dependent on the volume fraction of the system and the strength of the interactions between the colloids. Here we explore very dilute solutions by the means of numerical simulations, and show that, in the absence of hydrodynamic interactions and for sufficiently strong interactions, percolating colloidal gels can be realised at very low values of the volume fraction. Characterising the structure of the network of the arrested material we find that, when reducing the volume fraction, the gels are dominated by low-energy local structures, analogous to the isolated clusters of the interaction potential. Changing the strength of the interaction allows us to tune the compactness of the gel as characterised by the fractal dimension, with low interaction strength favouring more chain-like structures

The structure and chemistry of alginic acid

Alginic acid is one of the main carbohydrates of the Phaeophycae, the brown seaweeds, its function not being clear. The proportion varies with the season, species of Laminaria containing 24% of alginic acid in February and only 14% in September (1). To isolate it1the cleaned weed is first steeped in dilute acid, washed and then extracted with sodium carbonate solution, when a solution of sodium alginate is obtained. This material finds many commercial uses (2). It finds uses in cold setting jellies, as a stabiliser in many foods, particularly ice cream, as a.thickener in textile printing, in the surface sizing of paper and in water purification. Alginic acid is a high molecular weight polysaccharide and until 1955 it was thought that it contained only residues of D-mannuronic acid. However, Fischer and Dorfel (3) showed that hydrolysis gave L-guluronic acid, the C-5 epimer of D-mannuronic, as well as D-mannuronic acid. Methylation analysis indicates that both these units are 1,4- linked (4), a conclusion that is substantiated by the application of other methods of structural investigation (5,6), and with which results of earlier work are consistent (7,8). Isolation of 4-0-ß-D-mannopyranosyl-D-mannopyranose (9) from a partial hydrolysate of the reduced polysaccharide indicates that the mannuronic acid residues in alginicacid are linked through their C-4 positions by a ß-linkage and that the linkage is 1,4-pyranosyl rather than 1,5-furanosyl. Partial fractionation into fractions rich in mannuronic and guluronic acids, respectively, has been achieved,(10,11) but repeated fractionation failed to separate a polymer which contained only mannuronic or guluronic acid residues. Proof that the two acids appear together in at least some of the alginic acid molecules was supplied by the isolation of oligouronic acids (12) containing both acids, and of a crystalline mannosyl- gulose (9) from partial acid hydrolysates of alginic acid and its reduction product respectively. A study of the constitution of alginic acid by partial acid hydrolysis has been carried out by Haug, Snidsrod and Larsen (13). Heterogeneous hydrolysis of the alginate was carried out with oxalic acid. Results showed that a certain amount of the alginate passed rapidly into solution, but even prolonged hydrolysis did not increase the concentration of carbohydrate in the solution to more than corresponding to 28% of the alginate. This clearly indicated that only part of the alginate sample was available for hydrolysis, while the rest of the sample was protected against hydrolysis or hydrolysed very slowly. The insoluble material could only be further degraded when it was washed, dissolved in dilute alkali and then retreated with oxalic acid. Even then there was a limit to the amount of hydrolysis taking place. The insoluble fraction could be fractionated into one fraction which contained predominantly guluronic acid residues and another which contained predominantly mannuronic acid residues. Significantly, no fraction with an intermediate uronic acid composition could be prepared. The number average length of the insoluble chains was 20 -30. The soluble fraction was shown tentatively to consist predominantly of the two monomers and a diuronide containing both the monomers. From these results HaugkandaLarsen deduced that alginic acid consists of blocks of 20 -30 monomer units with either predominantly mannuronic or guluronic acids and that these blocks are separated by regions with another sequence of uronic acid residues, probably with a large proportion of alternating mannuronic and guluronic acid residues. The blocks with a highly regular structure more easily form crystalline regions with a 3. much lower rate of hydrolysis than the more amorphous regions. It has still to be shown conclusively whether structural irregularities, such as branching or non -1,4-linking, ever occurs in the molecule. The incomplete oxidation of sodium alginate by periodate (6) would be explained if such irregularities were present. These questions are more fully examined in Section A. Another unsolved problem is the configuration of the guluronosyl linkage. It is noteworthy that a bacterial polysaccharide resembling alginic acid has been isolated from Azotobacter vinelandii (14) and Pseudomonas aeruginosa (15,16). studies are not yet so complete as on algal alginic acid and there would seem to be a close structural similarity except that the bacterial polymer is at least sometimes 0- acetylated. Degradation of alginate by a ß-elimination reaction has been achieved both enzynically (17,18) and chemically (19) (see Section C), and oxidative degradation by a free -radical mechanism by naturally - occuring phenolic compounds has also been shown to take place (20,21). In some ways, alginic acid has a more simple structure than pectic acid, a related uronic acid polymer from higher plants, in which the monomer is galacturonic acid. Pectin (22) is similar to alginic acid in that it contains a backbone of uronic acid residues, but blocks of polygalacturonic acid appear to be interrupted by occasional neutral residues (rhamnose). Neutral side chains are also present in varying degree, depending on the source of the pectin. Unlike pectic acid, alginic ei.cid does not occur in the esterified state%nor do neutral sugars ever seem to be part of the molecule. The chemical reactions of alginic acid are therefore of interest, not only for their own sake, but also because they might usefully be applied in the structure determination of the more complex pectic substances. One of the aims of the work which is reported in this Thesis, has been to use alginic acid to develop new approaches to the structure determination of uronic acid- containing polysaccharides. Details of these approaches are given in Sections B and :C. X -ray analysis of alginic acid gives well- developed diffraction patterns (23,24), but it has since been shown by Frei and Preston (25) that the sample examined was in fact a guluronic acid -rich sample. The data obtained therefore corresponded to polyguluronic acid and not to polymannuronic acid as was originally supposed. If we ignore the C -6 carbon atom then polyguluronic acid has the same carbon skeleton as cellulose (as well as xylan, mannan and polymannuronic acid) and these two polymers are indeed related in having a 2 -fold screw axis along the fibre axis although the fibre repeat distance is somewhat shorter for polyguluronic acid - 8.71 as opposed to 10.32 for cellulose. Frei and Preston reached the conclusion that the algal cell wall contains mainly material rich in guluronic acid whereas the intercellular alginic acid is primarily polymannuronic acid. The physical properties of alginate solutions are in many ways similar to those of pectins in the higher plant kingdom and to those of the sulphated polysaccharides from the red seaweeds e.g. K- carrageenan. For example, all form strong, reversible, cation -sensitive gels. This similarity, and the fact that all these polysaccharides occur at least partly in the intercellular parts of plant tissue, suggest that they might have similar biological functions. Accordingly, in seeking to understand the conformation, and the physical and biological properties of alginic acids, it would seem worthwhile to study all three types of polysaccharide together. Some progress has been made in this laboratory towards the determination of the conformation of K-carrageenan (26) by X-ray diffraction; this is described later in this Thesis (Section D) together with the results of an attempt wo develop the X-ray methods further and to apply them to alginic and pectic acids

Tillage Research in Ohio A Guide to the Selection of Profitable Tillage Systems

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Perturbation theory in a pure exchange non-equilibrium economy

We develop a formalism to study linearized perturbations around the equilibria of a pure exchange economy. With the use of mean field theory techniques, we derive equations for the flow of products in an economy driven by heterogeneous preferences and probabilistic interaction between agents. We are able to show that if the economic agents have static preferences, which are also homogeneous in any of the steady states, the final wealth distribution is independent of the dynamics of the non-equilibrium theory. In particular, it is completely determined in terms of the initial conditions, and it is independent of the probability, and the network of interaction between agents. We show that the main effect of the network is to determine the relaxation time via the usual eigenvalue gap as in random walks on graphs.Comment: 7 pages, 2 figure

Atmospheric Moisture Content Effects on Ionic Liquid Wettability of Alumina

The contact angles or wettability of 7 Ionic Liquids, on an alumina substrate, have been measured under two different storage conditions. The first using a small amount of moisture content, the second with no moisture content. The contact angle of Ionic Liquid droplets on an alumina substrate were measured using an Attension Theta instrument with automated software. The results show that a small amount of moisture improves the wettability of the Ionic Liquid – alumina system and therefore subsequent uses of these liquids with alumina should take this into consideration

Kinase profiling of liposarcomas using RNAi and drug screening assays identified druggable targets.

BackgroundLiposarcoma, the most common soft tissue tumor, is understudied cancer, and limited progress has been made in the treatment of metastatic disease. The Achilles heel of cancer often is their kinases that are excellent therapeutic targets. However, very limited knowledge exists of therapeutic critical kinase targets in liposarcoma that could be potentially used in disease management.MethodsLarge RNAi and small-molecule tyrosine kinase inhibitor screens were performed against the proliferative capacity of liposarcoma cell lines of different subtypes. Each small molecule inhibitor was either FDA approved or in a clinical trial.ResultsScreening assays identified several previously unrecognized targets including PTK2 and KIT in liposarcoma. We also observed that ponatinib, multi-targeted tyrosine kinase inhibitor, was the most effective drug with anti-growth effects against all cell lines. In vitro assays showed that ponatinib inhibited the clonogenic proliferation of liposarcoma, and this anti-growth effect was associated with apoptosis and cell cycle arrest at the G0/G1 phase as well as a decrease in the KIT signaling pathway. In addition, ponatinib inhibited in vivo growth of liposarcoma in a xenograft model.ConclusionsTwo large-scale kinase screenings identified novel liposarcoma targets and a FDA-approved inhibitor, ponatinib with clear anti-liposarcoma activity highlighting its potential therapy for treatment of this deadly tumor

Executive function in first-episode schizophrenia

BACKGROUND: We tested the hypothesis that schizophrenia is primarily a frontostriatal disorder by examining executive function in first-episode patients. Previous studies have shown either equal decrements in many cognitive domains or specific deficits in memory. Such studies have grouped test results or have used few executive measures, thus, possibly losing information. We, therefore, measured a range of executive ability with tests known to be sensitive to frontal lobe function. METHODS: Thirty first-episode schizophrenic patients and 30 normal volunteers, matched for age and NART IQ, were tested on computerized test of planning, spatial working memory and attentional set shifting from the Cambridge Automated Neuropsychological Test Battery. Computerized and traditional tests of memory were also administered for comparison. RESULTS: Patients were worse on all tests but the profile was non-uniform. A componential analysis indicated that the patients were characterized by a poor ability to think ahead and organize responses but an intact ability to switch attention and inhibit prepotent responses. Patients also demonstrated poor memory, especially for free recall of a story and associate learning of unrelated word pairs. CONCLUSIONS: In contradistinction to previous studies, schizophrenic patients do have profound executive impairments at the beginning of the illness. However, these concern planning and strategy use rather than attentional set shifting, which is generally unimpaired. Previous findings in more chronic patients, of severe attentional set shifting impairment, suggest that executive cognitive deficits are progressive during the course of schizophrenia. The finding of severe mnemonic impairment at first episode suggests that cognitive deficits are not restricted to one cognitive domain

A Multi-Level Fit-Based Quality Improvement Initiative to Improve Colorectal Cancer Screening in a Managed Care Population.

IntroductionColorectal cancer (CRC) is a common but largely preventable disease with suboptimal screening rates despite national guidelines to screen individuals age 50-75. Single-component interventions aimed to improve screening uptake only modestly improve rates; data suggest that multi-modal approaches may be more effective.MethodsWe designed, implemented, and evaluated the impact of a multi-modal intervention on CRC screening uptake among unscreened patients in a large managed care population. Patient-level components included a mailed letter with education about screening options and pre-colonoscopy telephone counseling. For providers, we facilitated communication of screening test results and work-flow for abnormal results. System-level modifications included establishment of a patient navigator, expedited work-up for abnormal results, and stream-lined colonoscopy scheduling. We measured the rate of screening uptake overall, screening uptake by modality, change in the proportion of the population screened, and positive fecal immunochemical test (FIT) follow-up rates in the 1-year study period.ResultsThere were 5093 patients in the intervention cohort. Of these, 33.2% participated in FIT or colonoscopy screening within 1 year of the mailing. A total of 1078 (21.2%) participants completed a FIT and 611 (12.0%) completed a screening colonoscopy. The screening rate in the managed care population increased from 65.1 to 76.6%. Fifty-nine patients (5.5%) had a positive FIT, of which 30 (50.8%) completed a diagnostic colonoscopy.ConclusionMulti-modal interventions can result in substantial improvement in CRC screening uptake in large and diverse managed care populations.Translational impactHealth systems should shift their focus from single-level to multi-level interventions when addressing barriers to CRC screening

Translational regulation contributes to the elevated CO2 response in two Solanum species.

Understanding the impact of elevated CO2 (eCO2 ) in global agriculture is important given climate change projections. Breeding climate-resilient crops depends on genetic variation within naturally varying populations. The effect of genetic variation in response to eCO2 is poorly understood, especially in crop species. We describe the different ways in which Solanum lycopersicum and its wild relative S. pennellii respond to eCO2 , from cell anatomy, to the transcriptome, and metabolome. We further validate the importance of translational regulation as a potential mechanism for plants to adaptively respond to rising levels of atmospheric CO2