Swollen-Collapsed Transition in Random Hetero-Polymers

A lattice model of a hetero-polymer with random hydrophilic-hydrophobic charges interacting with the solvent is introduced, whose continnuum counterpart has been proposed by T. Garel, L. Leibler and H. Orland {J. Phys. II France 4, 2139 (1994)]. The transfer matrix technique is used to study various constrained annealed systems which approximate at various degrees of accuracy the original quenched model. For highly hydrophobic chains an ordinary $\theta$-point transition is found from a high temperature swollen phase to a low temperature compact phase. Depending on the type of constrained averages, at very low temperatures a swollen phase or a coexistence between compact and swollen phases are found. The results are carefully compared with the corresponding ones obtained in the continuum limit, and various improvements in the original calculations are discussed.Comment: 13 pages, 8 figures; revised version with minor changes, accepted for publication in European Physical Journal

Cluster Derivation of the Parisi Scheme for Disordered Systems

We propose a general quantitative scheme in which systems are given the freedom to sacrifice energy equi-partitioning on the relevant time-scales of observation, and have phase transitions by separating autonomously into ergodic sub-systems (clusters) with different characteristic time-scales and temperatures. The details of the break-up follow uniquely from the requirement of zero entropy for the slower cluster. Complex systems, such as the Sherrington-Kirkpatrick model, are found to minimise their free energy by spontaneously decomposing into a hierarchy of ergodically equilibrating degrees of freedom at different (effective) temperatures. This leads exactly and uniquely to Parisi's replica symmetry breaking scheme. Our approach, which is somewhat akin to an earlier one by Sompolinsky, gives new insight into the physical interpretation of the Parisi scheme and its relations with other approaches, numerical experiments, and short range models. Furthermore, our approach shows that the Parisi scheme can be derived quantitatively and uniquely from plausible physical principles.Comment: 6 pages, 3 figures, proceedings of international conference on "Disordered And Complex Systems", 10-14 July 2000 King's College Londo

Solvable Lattice Gas Models of Random Heteropolymers at Finite Density: II. Dynamics and Transitions to Compact States

In this paper we analyse both the dynamics and the high density physics of the infinite dimensional lattice gas model for random heteropolymers recently introduced in \cite{jort}. Restricting ourselves to site-disordered heteropolymers, we derive exact closed deterministic evolution equations for a suitable set of dynamic order parameters (in the thermodynamic limit), and use these to study the dynamics of the system for different choices of the monomer polarity parameters. We also study the equilibrium properties of the system in the high density limit, which leads to a phase diagram exhibiting transitions between swollen states, compact states, and regions with partial compactification. Our results find excellent verification in numerical simulations, and have a natural and appealing interpretation in terms of real heteropolymers.Comment: 12 pages, 8 eps figures, revised version (to be published in EPJ

Magnetization enumerator of real-valued symmetric channels in Gallager error-correcting codes

Using the magnetization enumerator method, we evaluate the practical and theoretical limitations of symmetric channels with real outputs. Results are presented for several regular Gallager code constructions.Comment: 5 pages, 1 figure, to appear as Brief Report in Physical Review

Dependence of endothelial cell growth on substrate-bound fibronectin

A better understanding of the mechanism of adhesion, spreading and proliferation of human endothelial cells (HEC) on polymeric surfaces may lead to the development of vascular prostheses which allow the formation of an endothelial lining on the luminal surface. In the present investigation the interaction of HEC with polyethylene precoated with monoclonal antibodies directed against HEC membrane antigens and against extracellular matrix compounds was studied. F(ab¿)2 fragments of a monoclonal antibody, directed against an endothelial cell membrane antigen, and F(ab')2 fragments of a monoclonal antibody, directed against cellular fibronectin, were also included in this study. Preadsorption of these antibodies and F(ab')2 fragments, including mixtures of antibodies and mixtures of F(ab')2 fragments, resulted in cell adhesion and spreading as well as moderate cell proliferation (or no proliferation) for several days. However, a good proliferation of HEC was only observed on polyethylene precoated with fibronectin or CLB-HEC-FN-140 (directed against fibronectin). These results strongly suggest that fibronectin, bound to a solid substrate, provides a biochemical signal necessary for the proliferation of HEC. The initial proliferation of HEC on other preadsorbed antibodies or F(ab')2 fragments may be explained by the fact that suspended HEC, used for cell seeding, still possess cell membrane-bound fibronectin

The role of cellular fibronectin in the interaction of human endothelial cells with polymers

During in-vitro adhesion, spreading and proliferation of human endothelial cells (HEC) on tissue culture polystyrene (TCPS), cellular fibronectin is deposited onto the surface of TCPS in spite of the fact that relatively large amounts of proteins have been adsorbed from the serum-containing culture medium to this surface. Evidence is presented that serum proteins, adsorbed to the TCPS surface, are displaced by cellular fibronectin. In addition, the interaction of HEC with polyethylene, precoated with monoclonal antibodies directed against HEC membrane antigens and against extracellular matrix compounds, was studied. F(ab')2 fragments of two monoclonal antibodies were also included in this study. Preadsorption of these antibodies and F(ab')2 fragments resulted in cell adhesion and spreading as well as moderate cell proliferation (or no proliferation) for several days. A good cell proliferation of HEC was only observed on polyethylene precoated with fibronectin or an antibody directed against fibronectin. The results indicate that the direct or indirect deposition of fibronectin is a prerequisite for the proliferation of HEC. It is suggested that fibronectin, bound to a solid substrate, provides a biochemical signal necessary for the proliferation of HEC

The Psycho-Social Sequelae of a Termination of Pregnancy for Fetal Abnormality

Although all couples who embark on a pregnancy hope for a normal child, about 2% will have an abnormal outcome. For a proportion of these couples the abnormality will be detected prenatally and they may elect for termination of pregnancy. In Scotland there are about 200 terminations of pregnancy (TOP) for fetal abnormality (FA) each year and for each couple this represents one of the most difficult times of their lives. This project undertook to examine the current management of TOP for fetal abnormality to identify if there was scope for improvement. The study consisted of two parts; management aspects of detection and termination for neural tube defects (NTD), and a detailed assessment of sequelae of TOP for various FA. In the NTD study, women who had elected for TOP were identified from the West of Scotland Regional Genetics Service. Although the majority (137, 82%) of consultands were satisfied with the way that prenatal diagnosis was handled, more than one third of the women felt ill-prepared for the TOP and entered hospital with no conception of the procedure or timescale of the termination. Care during the termination procedure was perceived as very good by most (126, 76%) and 95% (158) found the staff attending them kind and sympathetic. After the TOP, many (52, 31%) were nursed in the post-natal ward, often in a side room but usually within hearing distance of the newborn nursery and found this very upsetting. On leaving hospital, the post-termination sequelae were discussed or mentioned to only 25 (15%) patients. This left 135 (81%) confused and bewildered by the postpartum reactions of their bodies. The second study was intended; to monitor sequelae, to investigate in more detail why couples perceived aftercare as inadequate, to consider if this is related to specific factors, to ascertain which groups had particular difficulties in coming to terms with the experience and finally, to assess the effect of the TOP for FA on family planning and further reproduction. Common difficulties were encountered in several areas; pain and fear during the termination procedure, the decision whether to see the fetus; the lack of medical and psychosocial advice and support in the post-termination time on leaving hospital; the perceived lack of understanding of the sequelae; and the consultands' own reticence to voice their needs, fears and worries. 24 (28%) women experienced physical pain and 38 (45%) felt very frightened during the termination procedure. 16 (19%) mothers and 18 (26% of 68) husbands (partners) saw the fetus after the delivery and after two years none regretted the decision. This was in contrast to 38 mothers (55% of 68) who did not look. Consultands who had TOP for Trisomy 21, Cystic Fibrosis, or Duchenne Muscular Dystrophy preferred to maintain an abstract notion of the fetus even on reflection two years later. Of the women who had been too frightened to look at the fetus after the termination because there were obvious malformations, 99% regretted the decision. Reassurance and detailed information were given as the most helpful aspects of genetic counselling by 45 (56% of 80). The ideal time for such a consultation was given as 4 to 6 weeks. For 36 (42%) of consultands there had been doubt before, during and just after the TOP about their decision to abort, and after two years 2 women and 3 men still regretted the decision. 81 (96%) would in principle accept prenatal diagnosis in a subsequent pregnancy, and in fact all 55 who had another pregnancy, had prenatal diagnosis. 82% achieved or were trying to achieve their wished for family size, those who were not sure about PND gave up progeny rather than having a pregnancy without testing for fetal disorders. The 15 couples (18%) who experienced reproductive conflict included several unexpected diagnoses (which differed from the one for which they had sought PND), and the older age-group. All these patients had surviving children. Both studies demonstrate scope for improvement in patient management following TOP for FA. The recurring theme which was present in all sections we examined was impaired communication at all levels and a lack of understanding of the psychological sequelae after this traumatic event. Improved education of those involved in the care and support of these families and more information for those in close contact with the couple could help to reduce excessive anxieties and this might well be an area in which a self-help group will be of particular benefit. (Abstract shortened by ProQuest.)

Een kwalitatieve volkskerk : een onderzoek naar de relevantie van Noordmans’ visie op de volkskerk

Masterthesis Systematische theologi

Amendments with organic and industrial wastes stimulate soil formation in mine tailings as revealed by micromorphology

Mine tailings are inhospitable to plants and soil organisms, because of low pH and poor soil organic matter contents. Vegetation establishment requires a soil system capable of supporting the nutrient and water requirements of plants and associated organisms. The objective of this study was to understand the influence of added organic and industrial wastes to the formation of soils in degraded landscapes left behind by past mining activities. Specifically, we stimulated the build up of soil organic matter (SOM) and the accumulation of calcite in mine tailing deposits. We amended field experimental plots with pig manure (PM), sewage sludge (SS) in combination with blanket application of marble wastes (MW). Soil samples were collected for physical and chemical analyses, two years after the addition of industrial wastes. Three years after amendments, we took undisturbed samples for micromorphological analysis. Soil pH increased from 2.7 to 7.4 due to dissolution of calcite from MW amendment. The acidity in tailings and low rainfall in the study area precipitated the secondary calcite as infillings within the 0-4 cm layer. Total organic carbon (TOC) increased from 0.86 to 2.5 g TOC kg − 1 soil after 24 months since the application of amendments. The build up of SOM resulted to stable SOM-calcite complex as dense incomplete infillings mixed with secondary calcite, and cappings on calcite particles from MW addition. These SOM cappings provide water and nutrient to support initial seedling establishment in mine tailings. We attribute the granular structure of amended materials to soil organisms (e.g., earthworm activity) involved in the decomposition of plant materials. We suggest that any organic matter amendments to acidic mine tailing deposits must be combined with calcium carbonate-rich materials to accelerate the build up of SOM to accelerate the establishment of functional ecosystem characterized by, among others, the presence of healthy soils with granular microstructure

A Solvable Model of Secondary Structure Formation in Random Hetero-Polymers

We propose and solve a simple model describing secondary structure formation in random hetero-polymers. It describes monomers with a combination of one-dimensional short-range interactions (representing steric forces and hydrogen bonds) and infinite range interactions (representing polarity forces). We solve our model using a combination of mean field and random field techniques, leading to phase diagrams exhibiting second-order transitions between folded, partially folded and unfolded states, including regions where folding depends on initial conditions. Our theoretical results, which are in excellent agreement with numerical simulations, lead to an appealing physical picture of the folding process: the polarity forces drive the transition to a collapsed state, the steric forces introduce monomer specificity, and the hydrogen bonds stabilise the conformation by damping the frustration-induced multiplicity of states.Comment: 24 pages, 14 figure