Tensor Renormalization Group: Local Magnetizations, Correlation Functions, and Phase Diagrams of Systems with Quenched Randomness

The tensor renormalization-group method, developed by Levin and Nave, brings systematic improvability to the position-space renormalization-group method and yields essentially exact results for phase diagrams and entire thermodynamic functions. The method, previously used on systems with no quenched randomness, is extended in this study to systems with quenched randomness. Local magnetizations and correlation functions as a function of spin separation are calculated as tensor products subject to renormalization-group transformation. Phase diagrams are extracted from the long-distance behavior of the correlation functions. The approach is illustrated with the quenched bond-diluted Ising model on the triangular lattice. An accurate phase diagram is obtained in temperature and bond-dilution probability, for the entire temperature range down to the percolation threshold at zero temperature.Comment: Added comment. Published version. 8 pages, 7 figures, 1 tabl

Helfrich-Canham bending energy as a constrained non-linear sigma model

The Helfrich-Canham bending energy is identified with a non-linear sigma model for a unit vector. The identification, however, is dependent on one additional constraint: that the unit vector be constrained to lie orthogonal to the surface. The presence of this constraint adds a source to the divergence of the stress tensor for this vector so that it is not conserved. The stress tensor which is conserved is identified and its conservation shown to reproduce the correct shape equation.Comment: 5 page

Lipid membranes with an edge

Consider a lipid membrane with a free exposed edge. The energy describing this membrane is quadratic in the extrinsic curvature of its geometry; that describing the edge is proportional to its length. In this note we determine the boundary conditions satisfied by the equilibria of the membrane on this edge, exploiting variational principles. The derivation is free of any assumptions on the symmetry of the membrane geometry. With respect to earlier work for axially symmetric configurations, we discover the existence of an additional boundary condition which is identically satisfied in that limit. By considering the balance of the forces operating at the edge, we provide a physical interpretation for the boundary conditions. We end with a discussion of the effect of the addition of a Gaussian rigidity term for the membrane.Comment: 8 page

Directed Cell Migration: From Single Cells to Collectively Moving Cell Groups

Unlike molecules, which are driven thermally by Brownian motion, eukaryotic cells move in a particular direction to accomplish designated tasks that are involved in diverse biological processes such as organ development and tumor progression. In this dissertation, I present experiments, analysis, and modeling of directed individual and collective cell migration. At subcellular scale, the migration of cells can be guided via the interaction of the cell cytoskeleton with the surrounding nanotopographic elements. I show that mechanical waves of actin polymerization are involved in this guidance–known as contact guidance–as dynamic sensors of surface nanotopography. The dynamics of guided actin waves were measured to build and test predictive models of contact guidance. The distributions of actin-wave propagation speed and direction were obtained from experimental observations of cell migration on nanotopographic surfaces as a function of the spacing between adjacent features (varying between 0.8 and 5 microns). I show that actin polymerization is preferentially localized to nanoscale features for a range of spacings. Additionally, the velocity of actin polymerization waves moving parallel to the direction of nanoridges depends on the nanoridge spacing. A model of actin polymerization dynamics in which nanoridges modify the distribution of the nucleation promoting factors captures these key observations. For individual cells, the question is how the intracellular processes result in directed migration of cells. I introduce a coarse-grained model for cell migration to connect contact guidance to intrinsic cellular oscillations. The guidance of collective cell migration can be dictated via intercellular communication, which is facilitated by biochemical signals. I present a coarse-grained stochastic model for the influence of signal relay on the collective behavior of migrating Dictyostelium discoideum cells. In the experiment cells display a range of collective migration patterns including uncorrelated motion, formation of partially localized streams, and clumping, depending on the type of cell and the strength of the external concentration gradient of the signaling molecule cyclic adenosine monophosphate (cAMP). The collective migration model shows that the pattern of migration can be quantitatively described by considering the competition of two processes, the secretion of cAMP by the cells and the degradation of cAMP in the gradient chamber. With degradation, the model secreting cells form streams and efficiently traverse the gradient, but without degradation the model secreting cells form clumps without streaming. This observation indicates that streaming requires not only signal relay but also degradation of the signal. In addition, I show how this model can be extended to other eukaryotic systems that exhibit more complex cell-cell communication, in which the impact on collective migration is more subtle

Underfilled blood tube containing EDTA: Is it an inappropriate sample for HbA1c assay?

IntroductionBlood samples having inappropriate volume are a substantial part of preanalytical errors. Inadequate sample volume for glycated haemoglobin (HbA1c) test may be a common problem of patients with diabetes mellitus having vascular changes. In this study, we compared HbA1c concentrations of underfilled and appropriately filled blood collection tubes. Materials and methodsTo compare HbA1c concentrations, blood samples were collected into 2 mL tubes containing K3-EDTA from 109 subjects. Two blood samples (underfilled and appropriately filled) were drawn from a patient by the same personnel and materials. HbA1c measurements were assayed on a Cobas 6000 analyser module c 501 (Roche Diagnostics, Mannheim, Germany). The HbA1c% results were compared by t-test and Wilcoxon’s signed-rank statistical methods (SPSS Inc., Chicago, USA). Bias analysis was performed using Microsoft Excel 4.0. ResultsUnderfilled samples were classified three groups (group 1, N = 44; group 2, N = 36; and group 3, N = 29) according to the filling ratio of the samples; 0.5 mL and below ( 50%), respectively. When we compared underfilled tubes with pairing filled tubes, there was a statistically significant difference only with tubes filled less than 25% (P = 0.030). Furthermore, we have done bias analysis between paired tubes according to the diagnostic cut-off value of 6.5%. The bias was more prominent in up to 50% underfilled blood tubes (1.1%), when HbA1c concentrations were below the diagnostic cut-off of 6.5%. ConclusionsWe suggest that the blood tubes with EDTA for HbA1c measurement should be filled with at least 50% to avoid clinical variations

Membrane geometry with auxiliary variables and quadratic constraints

Consider a surface described by a Hamiltonian which depends only on the metric and extrinsic curvature induced on the surface. The metric and the curvature, along with the basis vectors which connect them to the embedding functions defining the surface, are introduced as auxiliary variables by adding appropriate constraints, all of them quadratic. The response of the Hamiltonian to a deformation in each of the variables is examined and the relationship between the multipliers implementing the constraints and the conserved stress tensor of the theory established.Comment: 8 page

Microcirculation: Physiology, pathophysiology, and clinical application

This paper briefly reviews the physiological components of the microcirculation, focusing on its function in homeostasis and its central function in the realization of oxygen transport to tissue cells. Its pivotal role in the understanding of circulatory compromise in states of shock and renal compromise is discussed. Our introduction of hand-held vital microscopes (HVM) to clinical medicine has revealed the importance of the microcirculation as a central target organ in states of critical illness and inadequate response to therapy. Technical and methodological developments have been made in hardware and in software including our recent introduction and validation of automatic analysis software called MicroTools, which now allows point-of-care use of HVM imaging at the bedside for instant availability of functional microcirculatory parameters needed for microcirculatory targeted resuscitation procedures to be a reality

Effects of Two Fluoride Varnishes and One Fluoride/Chlorhexidine Varnish on Streptococcus mutans and Streptococcus sobrinus Biofilm Formation in Vitro

Aims: The aim of this study was to evaluate and to compare the effect of two fluoride varnishes and one fluoride/chlorhexidine varnish on Streptococcus mutans and Streptococcus sobrinus biofilm formation, in vitro

Functional evaluation of sublingual microcirculation indicates successful weaning from VA-ECMO in cardiogenic shock

Background: Veno-arterial extracorporeal membrane oxygenation (VA-ECMO) is increasingly adopted for the treatment of cardiogenic shock (CS). However, a marker of successful weaning remains largely unknown. Our hypothesis was that successful weaning is associated with sustained microcirculatory function during ECMO flow reduction. Therefore, we sought to test the usefulness of microcirculatory imaging in the same sublingual spot, using incident dark field (IDF) imaging in assessing successful weaning from VA-ECMO and compare IDF imaging with echocardiographic parameters. Methods: Weaning was performed by decreasing the VA-ECMO flow to 50% (F50) from the baseline