Comparison of the sedimentation diameter and the sieve diameter for various types of natural sands, A

March 1948.Includes bibliographical references (pages 80-82).To view the abstract, please see the full text of the document

Single polymer adsorption in shear: flattening versus hydrodynamic lift and corrugation effects

The adsorption of a single polymer to a flat surface in shear is investigated using Brownian hydrodynamics simulations and scaling arguments. Competing effects are disentangled: in the absence of hydrodynamic interactions, shear drag flattens the chain and thus enhances adsorption. Hydrodynamic lift on the other hand gives rise to long-ranged repulsion from the surface which preempts the surface-adsorbed state via a discontinuous desorption transition, in agreement with theoretical arguments. Chain flattening is dominated by hydrodynamic lift, so overall, shear flow weakens the adsorption of flexible polymers. Surface friction due to small-wavelength surface potential corrugations is argued to weaken the surface attraction as well.Comment: 6 pages, 4 figure

Statics and Dynamics of Strongly Charged Soft Matter

Soft matter materials, such as polymers, membranes, proteins, are often electrically charged. This makes them water soluble, which is of great importance in technological application and a prerequisite for biological function. We discuss a few static and dynamic systems that are dominated by charge effects. One class comprises complexation between oppositely charged objects, for example the adsorption of charged ions or charged polymers (such as DNA) on oppositely charged substrates of different geometry. The second class comprises effective interactions between similarly charged objects. Here the main theme is to understand the experimental finding that similarly and highly charged bodies attract each other in the presence of multi-valent counterions. This is demonstrated using field-theoretic arguments as well as Monte-Carlo simulations for the case of two homogeneously charged bodies. Realistic surfaces, on the other hand, are corrugated and also exhibit modulated charge distributions, which is important for static properties such as the counterion-density distribution, but has even more pronounced consequences for dynamic properties such as the counterion mobility. More pronounced dynamic effects are obtained with highly condensed charged systems in strong electric fields. Likewise, an electrostatically collapsed highly charged polymer is unfolded and oriented in strong electric fields. At the end of this review, we give a very brief account of the behavior of water at planar surfaces and demonstrate using ab-initio methods that specific interactions between oppositely charged groups cause ion-specific effects that have recently moved into the focus of interest.Comment: 61 pages, 31 figures, Physics Reports (2005)-in press (high quality figures available from authors

Pulling adsorbed polymers from surfaces with the AFM: stick versus slip, peeling versus gliding

We consider the response of an adsorbed polymer that is pulled by an AFM within a simple geometric framework. We separately consider the cases of i) fixed polymer-surface contact point, ii) sticky case where the polymer is peeled off from the substrate, and iii) slippery case where the polymer glides over the surface. The resultant behavior depends on the value of the surface friction coefficient and the adsorption strength. Our resultant force profiles in principle allow to extract both from non-equilibrium force-spectroscopic data.Comment: 6 pages, 3 figures; accepted for publication in Europhys. Lett., http://www.edpsciences.org/journal/index.cfm?edpsname=ep

Regulation of T Follicular Helper Cells in Islet Autoimmunity

T follicular helper (TFH) cells are an integral part of humoral immunity by providing help to B cells to produce high-affinity antibodies. The TFH precursor compartment circulates in the blood and TFH cell dysregulation is implied in various autoimmune diseases including type 1 diabetes (T1D). Symptomatic T1D is preceded by a preclinical phase (indicated by the presence of islet autoantibodies) with a highly variable progression time to the symptomatic disease. This heterogeneity points toward differences in immune activation in children with a fast versus slow progressor phenotype. In the context of T1D, previous studies on TFH cells have mainly focused on the clinically active state of the disease. In this review article, we aim to specifically discuss recent insights on TFH cells in human islet autoimmunity before the onset of symptomatic T1D. Furthermore, we will highlight advances in the field of TFH differentiation and function during human islet autoimmunity. Specifically, we will focus on the regulation of TFH cells by microRNAs (miRNAs), as well as on the potential use of miRNAs as biomarkers to predict disease progression time and as future drug targets to interfere with autoimmune activation

Serum (1 → 3)-β-d-glucan measurement as an early indicator of Pneumocystis jirovecii pneumonia and evaluation of its prognostic value

AbstractPneumocystis jirovecii (carinii) pneumonia (PJP) is a major cause of disease in immunocompromised individuals. However, until recently no reliable and specific serological parameters for the diagnosis of PJP have been available. (1 → 3)-β-d-Glucan (BG) is a cell wall component of P. jirovecii and of various other fungi. Data from the past few years have pointed to serum measurement of BG as a promising new tool for the diagnosis of PJP. We therefore conducted a retrospective study on 50 patients with PJP and 50 immunocompromised control patients to evaluate the diagnostic performance of serum BG measurement. Our results show an excellent diagnostic performance with a sensitivity of 98.0% and a specificity of 94%. While the positive predictive value was only 64.7%, the negative predictive value was 99.8% and therefore a negative BG result almost rules out PJP. BG levels were already strongly elevated in an average of 5 days and up to 21 days before microbiological diagnosis demonstrating that the diagnosis could have been confirmed earlier. BG levels at diagnosis and maximum BG levels during follow-up did not correlate with the outcome of patients or with the P. jirovecii burden in the lung as detected by Real-Time PCR. Therefore, absolute BG levels seem to be of no prognostic value. Altogether, BG is a reliable parameter for the diagnosis of PJP and could be used as a preliminary test for patients at risk before a bronchoalveolar lavage is performed

Measuring Lean Management Penetration on the Hospital Nursing Frontline: Instrument Development

Purpose: It is imperative to assure that health care organizations provide excellent care and create value by improving quality while eliminating unnecessary costs. Lean management is a continuous improvement management plan that uses work flow design to produce improvements in quality, safety, cost and productivity; it has been used in manufacturing, service and, more recently, healthcare industries. This study developed and tested an instrument to measure frontline nurse caregivers' perception of the penetration of lean management in hospitals that report using lean strategies. Methods: The study consisted of three phases. In Phase 1, using the Delphi technique, an on-line survey of experts (n=10) and a review of the literature identified the domains and subdomains of lean management. Ideas from each domain were formed into items on the Frontline Improvement Thinking (FIT) instrument. The experts also assessed content validity. In Phase 2, nurses assessed the instrument's format, on-line usability of the instrument and content validity. In Phase 3, the instrument was administered to frontline nurses working on units in hospitals that reported using lean methods. Their responses (n= 212) provided the data for assessing the instrument's psychometric properties. Results: Exploratory factor analysis yielded a scale with 75 items in 12 factors. Three domains were identified: organizational, unit and individual areas of improvement. The 4-factor, 29-item, FIT Unit had the highest reliability (α=.86-0.94; inter-item correlation range=.26-0.63). The 2-factor, 10-item FIT Organization was also acceptable (α=.87 and 0.79, inter-item correlation range=.30-0.72. The FIT Individual had less than desired reliability on one factor (α=.66) but had acceptable reliability on the other six factors (0.75-0.94; inter-item correlation range =.25-0.89). Test-retest reliability estimates were acceptable for the organization and unit based on Pearson's R correlations (0.53-0.77). Conclusion: In the early stage of development, the FIT instrument proved helpful in describing diffusion of lean management. Sample size and quality proved to be problems, however. Nurses from hospitals with a history of lean quality improvement did not participate in the study and some of the hospitals studied were in the very early phases of lean management. Recommendations include continuing work on measure development by increasing the sample of lean-thinking nurses.Doctor of Philosoph