Drop impact on surfactant films and solutions

Drops impacting on horizontal aqueous surfactant films have been analyzed using a high-speed camera. Drops of either water or aqueous surfactant solutions had a diameter of 2.4?±?0.4 mm and impacted with a velocity of 0.1 to 1.3 m/s. As surfactants, anionic sodium dodecyl sulfate and cationic cetyltrimethyl ammonium bromide were used. Pure water drops impacting on freestanding surfactant films showed coalescence, bouncing, partial bouncing, passing, and partial passing. For bouncing, the concentration of surfactant in the surfactant film must exceed the critical micelle concentration. When surfactant was added to the drop, coalescence and partial passing were suppressed. We attribute the different behavior to different hydrodynamic boundary conditions at the surface of pure water and surfactant solution, leading to different repulsive hydrodynamic forces arising when the air has to flow out of the closing gap between the two liquid surfaces. The boundary condition changes as a function of surfactant concentration from a slip to no-slip, leading to stronger hydrodynamic repulsion. In addition, estimates of the characteristic velocities show that diffusion of air into the water is slow and can only account for the very last thinning of the air gap before coalescence.     

Distinction of Fusarium oxysporum fungal isolates (strains) using FTIR-ATR spectroscopy and advanced statistical methods

Fusarium is a large fungi genus of a large variety of species and strains which inhabits soil and vegetation. It is distributed worldwide and affiliated to both warm and cold weather. Fusarium oxysporum species, for instance, cause the Fusarium wilt disease of plants, which appears as a leaf wilting, yellowing and eventually plant death. Early detection and identification of these pathogens are very important and might be critical for their control. Previously, we have managed to differentiate among different fungi genera (Rhizoctonia, Colletotrichum, Verticillium and Fusarium) using FTIR-ATR spectroscopy methods and cluster analysis. In this study, we used Fourier-transform infrared (FTIR) attenuated total reflection (ATR) spectroscopy to discriminate and differentiate between different strains of F. oxysporum. The result obtained was of spectral patterns distinct to each of the various examined strains, which belong to the same species. These differences were not as significant as those found between the different genera species. We applied advanced statistical techniques: principal component analysis (PCA) and linear discriminant analysis (LDA) on the FTIR-ATR spectra in order to examine the feasibility of distinction between these fungi strains. The results are encouraging and indicate that the FTIR-ATR methodology can differentiate between the different examined strains of F. oxysporum with a high success rate. Based on our PCA and LDA calculations performed in the regions [900-1775 cm(-1), 2800-2990 cm(-1), with 9 PCs], we were able to classify the different strains with high success rates: Foxy1 90%, Foxy2 100%, Foxy3 100%, Foxy4 92.3%, Foxy5 83.3% and Foxy6 100%.     

Self-accelerating self-trapped optical beams

We present self-accelerating self-trapped beams in nonlinear optical media, exhibiting self-focusing and self-defocusing Kerr and saturable nonlinearities, as well as a quadratic response. In Kerr and saturable media such beams are stable under self-defocusing and weak self-focusing, whereas for strong self-focusing the beams off-shoot solitons while their main lobe continues to accelerate. Self-accelerating self-trapped wave packets are universal, and can also be found in matter waves, plasma, etc.     

Real-time quantification of protein expression and translocation at individual cell resolution using imaging-dish-based live cell array

Cell populations represent intrinsically heterogeneous systems with a high level of spatiotemporal complexity. Monitoring and understanding cell-to-cell diversity is essential for the research and application of intra- and interpopulation variations. Optical analysis of live cells is challenging since both adherent and nonadherent cells change their spatial location. However, most currently available single-cell techniques do not facilitate treatment and monitoring of the same live cells over time throughout multistep experiments. An imaging-dish-based live cell array (ID-LCA) has been developed and produced for cell handling, culturing, and imaging of numerous live cells. The dish is composed of an array of pico scale cavities—pico wells (PWs) embossed on its glass bottom. Cells are seeded, cultured, treated, and spatiotemporally measured on the ID-LCA, while each cell or small group of cells are locally constrained in the PWs. Finally, predefined cells can be retrieved for further evaluation. Various types of ID-LCAs were used in this proof-of-principle work, to demonstrate on-ID-LCA transfection of fluorescently tagged chimeric proteins, as well as the detection and kinetic analysis of their induced translocation. High variability was evident within cell populations with regard to protein expression levels as well as the extent and dynamics of protein redistribution. The association of these parameters with cell morphology and functional parameters was examined. Both the new methodology and the device facilitate research of the translocation process at individual cell resolution within large populations and thus, can potentially be used in high-throughput fashion. Graphical Abstract

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Brownian motion of a nonlinear oscillator

Starting with the Langevin equation for a nonlinear oscillator (the Duffing oscillator) undergoing ordinary Brownian motion, we derive linear transport laws for the motion of the average position and velocity of the oscillator. The resulting linear equations are valid for only small deviations of average values from thermal equilibrium. They contain a renormalized oscillator frequency and a renormalized and non-Markovian friction coefficient, both depending on the nonlinear part of the original equation of motion. Numerical computations of the position correlation function and its spectral density are presented. The spectral density compares favorably with experimental results obtained by Morton using an analog computer method.Technical Note BN-674. Research supported in part by NSF grant GP-12591, and in part by PHS Research Grant No. MG16426-02 from the National Institute of General Medical Sciences.     

Study of 71, 73, 75, 77As with Ge(3He,d) reactions

Studies of ^{71, 73, 75, 77}As isotopes using Ge(³He, d) reactions have enabled the identification of many previously unreported levels together with new spin-parity assignments. A comparison of the results with the predictions of the model of Scholz and Malik shows good agreement for both positive- and negative-parity states.     

On powers of nonnegative matrices

We investigate the structure of powers of nonnegative matrices A, and in particular characterize those A for which some power is (essentially) triangular. We also show how the number of irreducible components of A can be determined from its powers.     

Pattern projection for subpixel resolved imaging in microscopy

In this paper, we present a new approach providing super resolved images exceeding the geometrical limitation given by the detector pixel size of the imaging camera. The concept involves the projection of periodic patterns on top of the sample, which are then investigated under a microscope. Combining spatial scanning together with proper digital post-processing algorithm yields the improved geometrical resolution enhancement. This new method is especially interesting for microscopic imaging when the resolution of the detector is lower than the resolution due to diffraction.     

Magnetic resonance studies of the properties of water in cellulose acetate membranes

The properties of water in various cellulose acetate (CA) membranes have been investigated by magnetic resonance techniques. It has been observed that the longitudinal (T₁) relaxation time of ¹⁷O in CA membranes containing H₂ ¹⁷O is considerably shorter (by a factor of 5 to 6) than the corresponding value in pure water. The T₁ values of ²³Na ions contained in these membranes were, however, shorter than the corresponding values observed in measurements of the aqueous mother solution by a factor smaller than 2. The EPR spectra of Mn²⁺ and of Cr³⁺ contained in CA membranes were practically identical to the spectra of the pure aqueous solution.

The data suggest the existence, in the CA membrane, of two “types” of water; a small fraction of highly immobilized “bound” water and the remaining large fraction of “free” water displaying properties almost identical to those of pure bulk water. This model is supported by measurements of the longitudinal relaxation rates of H₂ ¹⁷O in CA membranes which were gradually dehydrated from their water.     

Allowable Interval Sequences and Separating Convex Sets in the Plane

In 2005, Goodman and Pollack introduced the concept of an allowable interval sequence, a combinatorial object which encodes properties of a family of pairwise disjoint convex sets in the plane. They, Dhandapani, and Holmsen used this concept to address Tverberg’s (1,k)-separation problem: How many pairwise disjoint compact convex sets in the plane are required to guarantee that one can be separated by a line from k others? (Denote this number by f _k .) A new proof was provided that f ₂=5, a result originally obtained by Tverberg himself, and the application of allowable interval sequences to the case of general k was left as an open problem. Hope and Katchalski, using other methods, proved in 1990 that 3k?1≤f _k ≤12(k?1). In this paper, we apply the method of allowable interval sequences to give an upper bound on f _k of under 7.2(k?1), shrinking the range given by Hope and Katchalski by more than half. For a family of translates we obtain a tighter upper bound of approximately 5.8(k?1).