On the measurement of weak repulsive and frictional colloidal forces by reflection interference contrast microscopy

terference contrast (RIC) microscopy in combination with real-time image processing. The temporal fluctuations of the absolute sphere-to-substrate distance are determined from changes of interference fringe pattern (Newtonian rings). Both the shape about its minimum and the absolute minimum equilibrium distance of the interaction potential can be obtained by analyzing the distribution of distances in terms of a Boltzmann distribution. The timeautocorrelation function of distances yields the hydrodynamic friction. The method has been applied to the interaction of latex spheres with glass substrates in salt solutions of different ionic strength. The results correspond to classical electrostatic double layer theory that leads to a characteristic dependence of the mean separation distance and the mean square displacement on the radius of the spheres. The hydrodynamic friction close to a wall exhibits the predicted inverse proportionality to the sphere-wall distance. It is demonstrated that the method can be applied to study the interaction between biologically relevant objects such as giant vesicles with bilayer covered substrates

Imaging optical thicknesses and separation distances of phospholipid vesicles at solid surfaces

We present the application of reflection interference contrast microscopy (RICM) (1) to map the optical density of supported bilayers and vesicles and (2) to image the contact profile of phospholipid vesicles at surfaces. The resolution in the surface profile is 0.2 $\mu$m laterally and 1 nm out of plane. The optical thickness of the membrane can be determined with 0.2 nm accuracy. We outline the theoretical basis of RICM and derive the interference intensities of adhering vesicles from first principles. An analytical expression for the decaying contrast of the intrference fringes is given. The contact contour of vesicles is determined for various substrates. We further demonstrate that deposition of a magnesium fluoride layer on the glass substrate enhances the contrast and allows the optical density of adsorbed membranes to be imaged. By contrast variation of the buffer solution, the layer thicknesses and the indices of refraction can be measured. The novel method was applied to image lipid domains of different chain lengths in a substrate supported monolayer

The differentiation of cholesterol and pigment gallstones

Gallbladder biles and stones were obtained at 116 cholecystectomies for symptomatic gallstone disease. All 33 patients younger than 50 years had cholesterol stones, whereas 40% of the older patients had pigment stones. We compared the reliability of three different bile tests for the differentiation between cholesterol and pigment stone patients. Whereas both the presence of cholesterol monohydrate crystals in fresh gallbladder bile and a nucleation time 20 days in ultrafiltered gallbladder bile had a specificity of 100% for cholesterol gallstone disease, biliary supersaturation with cholesterol (cholesterol saturation index >1.0) had a low specificity. The sensitivity of nucleation time 20 days for cholesterol gallstone disease was 78% in concentrated gallbladder biles (biliary total lipid concentration 5 g/dl) but only 21% in dilute biles (biliary total lipid concentration <5 g/dl). In contrast, examination for the presence of cholesterol crystals in fresh bile was reasonably sensitive both in concentrated and diute gallbladder biles (sensitivity, 84% and 72%, respectively). In addition, duodenal bile obtained from 16 patients (10 cholesterol, 6 pigment) before cholecystectom showed cholesterol crystals in 7 of the cholesterol but in none of the pigment stone patients. We conclude that examination of fresh bile for cholesterol crystals is a specific and reasonably sensitive test for cholsterol gallstone disease

Types of governance in education: a quantitative analysis

This study creates a typology of education systems. It uses empirical analysis to deter-mine six types of education governance on the basis of various factors such as the de-gree of state involvement or funding sources, and structural differences of average time spent on homework or the degree of support for low achievers. It reveals differences in output among these types as measured by student performance, and relative equality of performance. The typology reflects similarities in governance of education among groups of countries, and indicates that common geography and history may be more of a linking factor than expected in a globalized world. --

Christian redemption in the theology of Nels Frederick Solomon Ferre: compared with Aulen, Brunner and DeWolf

Thesis (Ph. D.)--Boston UniversityBoth the problan and methodology of the dissertation follow this pattern: (1) a presentation of Ferre's views regarding redemption, (2) comparisons with the other three selected theologians, (3) an ordered summary of Ferre's relative theological position. This summary appears in chapter eight and briefly notes some similarities and dissimilarities among the other three theologians. Chapter two presents the term redemption and its correlatives as used in standard Protestant reference works. This determines the areas treated in chapters three through seven. The study includes these conclusions: (1) Knowledge of God as agape is limited to God's revelatory work made known in Jesus Christ in Ferre's, as in Aulen's and Brunner's writings. DeWolf adds theistic evidences. (2) God as being is uncaused and unconditioned but He becomes by creation and by redemptive personal relations with men for Ferre as for DeWolf. God is being is self-sufficient, with creation, preservation and redemption optional self-giving activities in Aulen's and Brunner's writings. For Aulen this is a paradox. Brunner concludes that God acts to realize His glory. (3) An essential but unfulfilled image within man awaits maturing experiences and Divine-human encounter in Ferre's and DeWolf's writings. Brunner emphasizes God's sole initiative so that maturing experiences seem to be negated. Aulen paradoxically asserts that man is essentially opposed to God yet chooses opposition. Paradoxically reconciliation depends upon God's subduing activity, yet upon man's "yes." (4) Jesus Christ is understood as truly God and truly man by Ferre as by Aulen and Brunner. The latter two do not, like Ferre, explain the Incarnation by perichoresis. DeWolf asserts that God's will and purpose were perfectly Incarnate in the human Jesus. Ferre has a distinct emphasis concerning the repeatability of the Incarnation, and concerning the Trinity. (5) At-one-ment in Ferre's distinct view is based upon perichoresis. All four theologians conclude that at-one-ment is offered to all men in Jesus Christ. Aulen's distinct view emphasizes fusion of wrath and love within God. (6) Personal depth repentance results in a reconciled relationship with God and fellowmen in Ferre's writings as in those of the other three theologians. The image within leads to such repentance for Ferre as for DeWolf. Paradoxically, for Aulen man's "yes" is indispensable yet all depends upon God's subduing activity. Brunner sees all human seeking as egocentric and doomed to frustration. Thus, Divine-human encounter, solely initiated by God, alone, leads to repentance and reconciliation. (7) Saints are nurtured by prayer, worship and witnessing. They are not free from sin but can partially demonstrate victorious love and power over sin in Ferre's writings as in the writings of the other men. Ferre, like DeWolf, makes more enthusiastic assertions of victory. [TRUNCATED

Dynamic Light Scattering from Semidilute Actin Solutions: A Study of Hydrodynamic Screening, Filament Bending Stiffness and the Effect of Tropomyosin/Troponin-Binding

Quasi-elastic light scattering (QELS) is applied to investigate the effect of the tropomyosin/troponin complex (Tm/Tn) on the stiffness of actin filaments. The importance of hydrodynamic screening in semidilute solutions is demonstrated. A new concentration dependent expression for the dynamic structure factor $g(\bm k,t)$ of semiflexible polymers in semidilute solutions is used to analyze the experimental QELS data. A concentration independent value for the bending modulus $\kappa$ is thus obtained. It increases by 50\% as a consequence of Tm/Tn binding in a 7:1:1 molar ratio of actin/Tm/Tn. In addition a new expression for the initial slope of the dynamic structure factor of a semiflexible polymer is used to determine the effective hydrodynamic diameter of the actin filament. Our results confirm the general relevance of the concept of (intrinsic) semiflexibility to polymer dynamics.Comment: 9 pages, RevTeX, 9 figures, all uuencoded gzipe

On Shape Transformations and Shape Fluctuations of Cellular Compartments and Vesicles

We discuss the shape formation and shape transitions of simple bilayer vesicles in context with their role in biology. In the first part several classes of shape changes of vesicles of one lipid component are described and it is shown that these can be explained in terms of the bending energy concept in particular augmented by the bilayer coupling hypothesis. In the second part shape changes and vesicle fission of vesicles composed of membranes of lipid mixtures are reported. These are explained in terms of coupling between local curvature and phase separation

Democracy, Totalitarianism, and Dead Ends in Sociology

The 20th century did not only see the rise of academic sociology, but highlighted also strife&nbsp;within societies that resulted in specific forms of totalitarianism. Literature on the&nbsp;relationship of sociology and these totalitarianisms is controversial. Some authors state that&nbsp;sociology is not a natural antipode to dictatorships: Some sociologists like Sombart and&nbsp;Michels were active proponents of totalitarian ideology, and most totalitarian regimes quite&nbsp;liked the technical expertise of social research. Other authors propose that a flourishing&nbsp;sociology needs a certain form of society characterized by openness and tolerance to find a&nbsp;constructive climate for theoretical reflection, empirical research and practical relevance.From this position one could state that there is a “Wahlverwandtschaft”, a structural affinity,&nbsp;between sociology and democracy.The article uses empirical material from a case study on the development of sociology at the&nbsp;University of Halle between 1900 and 1990. The University of Halle is an interesting case in&nbsp;so far as in this East German university the societal context varies between monarchy,&nbsp;democracy, fascism and communism. The empirical material focuses on published and&nbsp;unpublished work of Friedrich Hertz and Rudhard Stollberg, as well as archive material to&nbsp;their activities and conflicts. Specific dead ends of forms of historical sociology and empirical&nbsp;sociology are analysed with regard to the guiding question, whether there is a structural&nbsp;tension between forms of totalitarianism and sociology