The Parker Magnetostatic Theorem

We demonstrate the Parker Magnetostatic Theorem in terms of a small neighborhood in solution space containing continuous force-free magnetic fields in small deviations from the uniform field. These fields are embedded in a perfectly conducting fluid bounded by a pair of rigid plates where each field is anchored, taking the plates perpendicular to the uniform field. Those force-free fields obtainable from the uniform field by continuous magnetic footpoint displacements at the plates have field topologies that are shown to be a restricted subset of the field topologies similarly created without imposing the force-free equilibirum condition. The theorem then follows from the deduction that a continuous nonequilibrum field with a topology not in that subset must find a force-free state containing tangential discontinuities.Comment: 13 pages, no figur

A conserved U-rich RNA region implicated in regulation of translation in Plasmodium female gametocytes.

Translational repression (TR) plays an important role in post-transcriptional regulation of gene expression and embryonic development in metazoans. TR also regulates the expression of a subset of the cytoplasmic mRNA population during development of fertilized female gametes of the unicellular malaria parasite, Plasmodium spp. which results in the formation of a polar and motile form, the ookinete. We report the conserved and sex-specific regulatory role of either the 3’- or 5’-UTR of a subset of translationally repressed mRNA species as shown by almost complete inhibition of expression of a GFP reporter protein in the female gametocyte. A U-rich, TR-associated element, identified previously in the 3’-UTR of TR-associated transcripts, played an essential role in mediating TR and a similar region could be found in the 5’-UTR shown in this study to be active in TR. The silencing effect of this 5’-UTR was shown to be independent of its position relative to its ORF, as transposition to a location 3’ of the ORF did not affect TR. These results demonstrate for the first time in a unicellular organism that the 5’ or the 3’-UTR of TR-associated transcripts play an important and conserved role in mediating TR in female gametocytes

Collapsing lattice animals and lattice trees in two dimensions

We present high statistics simulations of weighted lattice bond animals and lattice trees on the square lattice, with fugacities for each non-bonded contact and for each bond between two neighbouring monomers. The simulations are performed using a newly developed sequential sampling method with resampling, very similar to the pruned-enriched Rosenbluth method (PERM) used for linear chain polymers. We determine with high precision the line of second order transitions from an extended to a collapsed phase in the resulting 2-dimensional phase diagram. This line includes critical bond percolation as a multicritical point, and we verify that this point divides the line into two different universality classes. One of them corresponds to the collapse driven by contacts and includes the collapse of (weakly embeddable) trees, but the other is {\it not yet} bond driven and does not contain the Derrida-Herrmann model as special point. Instead it ends at a multicritical point $P^*$ where a transition line between two collapsed phases (one bond-driven and the other contact-driven) sparks off. The Derrida-Herrmann model is representative for the bond driven collapse, which then forms the fourth universality class on the transition line (collapsing trees, critical percolation, intermediate regime, and Derrida-Herrmann). We obtain very precise estimates for all critical exponents for collapsing trees. It is already harder to estimate the critical exponents for the intermediate regime. Finally, it is very difficult to obtain with our method good estimates of the critical parameters of the Derrida-Herrmann universality class. As regards the bond-driven to contact-driven transition in the collapsed phase, we have some evidence for its existence and rough location, but no precise estimates of critical exponents.Comment: 11 pages, 16 figures, 1 tabl

Effects of an integrated care intervention on informal caregivers: Baseline and One Year Post-implementation

__Abstract__ __Introduction:__ In order to face the challenges associated with an aging population, traditional health care models are increasingly being replaced with integrated care models [1]. However, while evidence exists that these models benefit older people, there is a lack of knowledge about how integrated care affects the informal caregiver [2]. In this study, effects of a new integrated model on the caregivers of frail elderly have been investigated. The model is characterized by an umbrella organizational structure involving case management, multidisciplinary teams, protocols, consultations, and patient files. The aim of this study was to investigate the effects of this model on caregivers in terms of perceived health, quality of life, objective and subjective burden. __Theory and Methods:__ A quasi-experimental design with before/after study and control group was used. Data was gathered using questionnaires (instruments: 2 items of the RAND-36 [3], short form objective burden informal care [4], SRB [5], CarerQoL [6] ,Cantril’s Ladder [7]). Analysis encompassed group comparison using paired and unpaired tests and regression analyses with baseline measurements, control variables (sex, age, relation to care-receiver, living together with care-receiver, income, education, having a life partner, employment, durance of care giving) and the intervention as independent variables. Additionally, analyses of subgroups and interaction effects will be performed. __Preliminary results:__ Within and between group differences were found and indicated significant reductions in health (P<0.1) and life ratings (P<0.1) and more financial problems (P<0.05) for the control group. Regression analysis revealed that caregivers in the intervention group were more likely to take on HDL type tasks (P<0.05) and experienced less financial problems (P<0.05). __Conclusion:__ The integrated care intervention increased the likelihood of caregivers performing HDL tasks and reduced their financial problems

Knot localization in adsorbing polymer rings

We study by Monte Carlo simulations a model of knotted polymer ring adsorbing onto an impenetrable, attractive wall. The polymer is described by a self-avoiding polygon (SAP) on the cubic lattice. We find that the adsorption transition temperature, the crossover exponent $\phi$ and the metric exponent $\nu$, are the same as in the model where the topology of the ring is unrestricted. By measuring the average length of the knotted portion of the ring we are able to show that adsorbed knots are localized. This knot localization transition is triggered by the adsorption transition but is accompanied by a less sharp variation of the exponent related to the degree of localization. Indeed, for a whole interval below the adsorption transition, one can not exclude a contiuous variation with temperature of this exponent. Deep into the adsorbed phase we are able to verify that knot localization is strong and well described in terms of the flat knot model.Comment: 27 pages, 10 figures. Submitter to Phys. Rev.

Knotting probabilities after a local strand passage in unknotted self-avoiding polygons

We investigate the knotting probability after a local strand passage is performed in an unknotted self-avoiding polygon on the simple cubic lattice. We assume that two polygon segments have already been brought close together for the purpose of performing a strand passage, and model this using Theta-SAPs, polygons that contain the pattern Theta at a fixed location. It is proved that the number of n-edge Theta-SAPs grows exponentially (with n) at the same rate as the total number of n-edge unknotted self-avoiding polygons, and that the same holds for subsets of n-edge Theta-SAPs that yield a specific after-strand-passage knot-type. Thus the probability of a given after-strand-passage knot-type does not grow (or decay) exponentially with n, and we conjecture that instead it approaches a knot-type dependent amplitude ratio lying strictly between 0 and 1. This is supported by critical exponent estimates obtained from a new maximum likelihood method for Theta-SAPs that are generated by a composite (aka multiple) Markov Chain Monte Carlo BFACF algorithm. We also give strong numerical evidence that the after-strand-passage knotting probability depends on the local structure around the strand passage site. Considering both the local structure and the crossing-sign at the strand passage site, we observe that the more "compact" the local structure, the less likely the after-strand-passage polygon is to be knotted. This trend is consistent with results from other strand-passage models, however, we are the first to note the influence of the crossing-sign information. Two measures of "compactness" are used: the size of a smallest polygon that contains the structure and the structure's "opening" angle. The opening angle definition is consistent with one that is measurable from single molecule DNA experiments.Comment: 31 pages, 12 figures, submitted to Journal of Physics

A quasi-experimental study of the effects of an integrated care intervention for the frail elderly on informal caregivers' satisfaction with care and support

Background: This study explored the effects of an integrated care model for the frail elderly on informal caregivers' satisfaction with care and support services. Methods. A 62-item instrument was developed and deployed in an evaluative before/after study using a quasi-experimental design and enrolling a control group. The definitive study population (n = 63) consisted mainly of female informal caregivers who did not live with the care recipient. Analysis of separate items involved group comparisons, using paired and unpaired tests, and regression analyses, with baseline measurements, control variables (sex, age and living together with care recipient) and the intervention as independent variables. Subsequently, the underlying factor structure of the theoretical dimensions was investigated using primary component analysis. Group comparisons and regression analyses were performed on the resulting scales. Results: Satisfaction with the degree to which care was provided according to the need for care of the recipients increased, while satisfaction with the degree to which professionals provided help with administrative tasks, the understandability of the information provided and the degree to which informal caregivers knew which professionals to call, decreased. Primary component analysis yielded 6 scales for satisfaction with care and 5 scales for satisfaction with caregiver support, with sufficient reliability. Conclusions: The results suggest that expectations regarding the effects of integrated care on informal caregiver satisfaction may not be realistic. However, the results must be seen in light of the small sample size and should therefore be considered as preliminary. Nonetheless, this study provides guidance for further research and integrated care interventions involving informal caregivers. Trial registration. Current Controlled Trials ISRCTN05748494. Date of registration: 14/03/2013

Do integrated care structures foster processes of integration? A quasi-experimental study in frail elderly care from the professional perspective

Objective: This study explores the processes of integration that are assumed to underlie integrated care delivery. Design: A quasi-experimental design with a control group was used; a new instrument was developed to measure integration from the professional perspective. Setting and participants: Professionals from primary care practices and home-care organizations delivering care to the frail elderly in the Walcheren region of the Netherlands. Intervention: An integrated care intervention specifically targeting frail elderly patients was implemented. Main Outcome Measures: Structural, cultural, social and strategic integration and satisfaction with integration. Results: The intervention significantly improved structural, cultural and social integration, agreement on goals, interests, power and resources and satisfaction with integration. Conclusions: This study confirms that integrated care structures foster processes of integration among professionals. Trial registration: Current Controlled Trials ISRCTN05748494

The effects of an integrated care intervention for the frail elderly on informal caregivers: A quasi-experimental study

__Abstract__ Background: This study explored the effects of an integrated care model aimed at the frail elderly on the perceived health, objective burden, subjective burden and quality of life of informal caregivers. Methods. A quasi-experimental design with before/after measurement (with questionnaires) and a control group was used. The analysis encompassed within and between groups analyses and regression analyses with baseline measurements, control variables (gender, age, co-residence with care receiver, income, education, having a life partner, employment and the duration of caregiving) and the intervention as independent variables. Results: The intervention significantly contributed to the reduction of subjective burden and significantly contributed to the increased likelihood that informal caregivers assumed household tasks. No effects were observed on perceived, health, time investment and quality of life. Conclusions: This study implies that integrated care models aimed at the frail elderly can benefit informal caregivers and that such interventions can be implemented without demanding additional time investments from informal caregivers. Recommendations for future interventions and research are provided. Trial registration. Current Controlled Trials. Registration date: 14/03/2013

Simulations of lattice animals and trees

The scaling behaviour of randomly branched polymers in a good solvent is studied in two to nine dimensions, using as microscopic models lattice animals and lattice trees on simple hypercubic lattices. As a stochastic sampling method we use a biased sequential sampling algorithm with re-sampling, similar to the pruned-enriched Rosenbluth method (PERM) used extensively for linear polymers. Essentially we start simulating percolation clusters (either site or bond), re-weigh them according to the animal (tree) ensemble, and prune or branch the further growth according to a heuristic fitness function. In contrast to previous applications of PERM, this fitness function is {\it not} the weight with which the actual configuration would contribute to the partition sum, but is closely related to it. We obtain high statistics of animals with up to several thousand sites in all dimension 2 <= d <= 9. In addition to the partition sum (number of different animals) we estimate gyration radii and numbers of perimeter sites. In all dimensions we verify the Parisi-Sourlas prediction, and we verify all exactly known critical exponents in dimensions 2, 3, 4, and >= 8. In addition, we present the hitherto most precise estimates for growth constants in d >= 3. For clusters with one site attached to an attractive surface, we verify the superuniversality of the cross-over exponent at the adsorption transition predicted by Janssen and Lyssy. Finally, we discuss the collapse of animals and trees, arguing that our present version of the algorithm is also efficient for some of the models studied in this context, but showing that it is {\it not} very efficient for the `classical' model for collapsing animals.Comment: 17 pages RevTeX, 29 figures include