Preservation of protein fluorescence in embedded human dendritic cells for targeted 3D light and electron microscopy

In this study, we present a correlative microscopy workflow to combine detailed 3D fluorescence light microscopy data with ultrastructural information gained by 3D focused ion beam assisted scanning electron microscopy. The workflow is based on an optimized high pressure freezing/freeze substitution protocol that preserves good ultrastructural detail along with retaining the fluorescence signal in the resin embedded specimens. Consequently, cellular structures of interest can readily be identified and imaged by state of the art 3D confocal fluorescence microscopy and are precisely referenced with respect to an imprinted coordinate system on the surface of the resin block. This allows precise guidance of the focused ion beam assisted scanning electron microscopy and limits the volume to be imaged to the structure of interest. This, in turn, minimizes the total acquisition time necessary to conduct the time consuming ultrastructural scanning electron microscope imaging while eliminating the risk to miss parts of the target structure. We illustrate the value of this workflow for targeting virus compartments, which are formed in HIV‐pulsed mature human dendritic cells.     

Noise at large RF amplitudes in IMPATT oscillators †

The non-stationary noise generator of a large-signal IMPATT oscillator is studied. It is shown that only the zeroth-order term of the series expansion of the autocorrelation for the noise voltage is of importance for the oscillator noise spectrum. The zeroth-order term is determined by an integral of the square of the Green's function for the total voltage from a generation of a pair of carriers weighted by the mean generation rate

A PIN diode model with a fixed rectangular voltage is studied numerically. The short-circuit noise current is shown to be inversely proportional to the reverse saturation current,J_s. The possibility of improving the noise properties by increasing J_s is discussed.     

Geometry of the Kimura-Georgiou parametrization of modelling filters

We discuss questions concerning the geometry of the Kimura-Georgiou para-metrizalion of the set ( + (n) of degree n positive real transfer functions with the first n coefficients in the Laurent expansion about infinity prescribed. For example, one interesting question which has been raised is whether this set is star-shaped about the maximum entropy solution. This, of course, would be implied by convexity and would imply that,( plus;(n) is diffeomorphic to euclidean n-space. All three of these geometric properties would be of interest, for example, when using geometric or optimization techniques to construct an n-dimensional modelling filter with variations about the maximum entropy filter. Our first main result, which also lends support to conjectures concerning convexity and star-shapedness, is that. ( plus;(n) is in fact diffeomorphic to euclidean n-space. Our proof makes use of certain results from differential topology. There are of course several intimate relations between positive reality and stability properties of both real and complex polynomials. On this basis we observe that the convexity of the parametrization implies the convexity of the set of real Schur polynomials of degree n and is implied by the convexity of the set of complex Schur polynomials of degree n. From this it immediately follows that ( plus;(n) is not convex for n ≥ 3 and that. ( plus;(n) is convex and hence star-shaped. The case n = 2 is especially interesting since the real Schur region is convex whereas the complex is not. Another of our main results is to refine the above observations to settle this question in general, showing that for n ≥ 3 there is an open set of Schur parameters for which, ( plus;(n) fails to be star-shaped about the maximum entropy filter.     

Approximate Conditional Unit Root Inference

Based on Cox and Reid (1987) adjustments of likelihood ratio (LR) tests for unit roots in higher-order autoregressive models are proposed. While unit root inference does not fit directly into the framework of Cox and Reid, the ideas are applied in models with multi-dimensional parameters of interest and only asymptotic orthogonality of parameters. The adjustments are very simple to apply in that they are of the degrees of freedom type. Detailed Monte Carlo experiments reveal that, for a wide range of admissible parameter values, adjusted LR statistics approximate the asymptotic percentiles of the unit root distributions at a much faster rate than unadjusted ones. In addition, the proposed adjustments are compared with simulated Bartlett type corrected LR tests. They behave equally well in a reasonable parameter region, while both fail on the boundary of the parameter region where an additional unit root is introduced.     

THE ELECTROSTATIC FORCE BETWEEN CHARGED SPHERES AT CONSTANT POTENTIAL FROM THE FREDHOLM INTEGRAL EQUATION

The electrostatic problem of two spheres held at constant, not necessarily equal, potential is solved from considerations of action-at-a-distance (Coulomb force) by the way of using a solution to the Fredholm integral equation of the second kind. The solution, written in series form, is obtained from Gauss generalization of the electrostatic force for distributed charges and yields the charge density distribution, important to liquid droplet stability, droplet deformation, and breakup. Evaluation of the electrostatic force is fast because the series expression for the charge distribution is rapidly converging, a characteristic trait for some Fredholm type equations.     

Correspondences between input estimation and feedforward control

A correspondence between input estimation (deconvolution) and feedforward is discussed from a polynomial point of view. Optimal estimation and feedforward control filters are derived from a spectral factorization and a polynomial equation. Simple loop transformations are used for transforming one problem into the other. The close relationship cannot be explained by the well-known duality between optimal state estimation and feedback control. Instead, it rests on the fact that both the problems discussed are open loop. They can be seen as two interpretations of one underlying design problem. Several other open-loop problems can be described in this framework.     

The Osmotic Hypersensitivity of the Yeast Saccharomyces cerevisiae is Strain and Growth Media Dependent: Quantitative Aspects of the Phenomenon

Osmotic hypersensitivity is manifested as cellular death at magnitudes of osmotic stress that can support growth. Cellular capacity for survival when plated onto high NaCl media was examined for a number of laboratory and industrial strains of Saccharomyces cerevisiae. During respiro-fermentative growth in rich medium with glucose as energy and carbon source, the hypersensitivity phenomenon was fairly strain invariant with a threshold value of about 1 m-NaCl; most strains fell within a 300 mm range in LD₁₀ values (lethal dose yielding 10% survival). Furthermore, all but one of the strains displayed similar differential death responses above the threshold value, i.e. ten-fold decreased viability for every 250 mm increase in salinity. Addition of small amounts of salt to the growth medium drastically improved tolerance and shifted the hypersensitivity threshold to higher NaCl concentrations. This salt-instigated tolerance could partly be reversed by washing in water. The washing procedure depleted cells of the glycerol that they had accumulated under saline growth, and the contribution from glycerol to the improved tolerance was about 50% in the two strains examined. Growth on derepressing carbon sources like galactose, ethanol or glycerol gave strain-dependent responses. The laboratory strain X2180–1A drastically improved tolerance while the bakers' yeast strain Y41 did so only marginally. It was concluded that all strains of S. cerevisiae display the osmotic hypersensitivity phenomenon in qualitative terms while the quantitative values differ. It was also proposed that growth rate does not dictate the level of osmotic hypersensitivity of S. cerevisiae. © 1997 John Wiley & Sons, Ltd.