Non-tame automorphisms of extensions of periodic groups

LetF be a free group andR≤F a characteristic subgroup. Automorphisms ofF/R which are induced by automorphisms ofF are called tame. In this paper we use theN-torsion invariant discovered by the first author and M. Lustig [LM] to show the existence of non-tame automorphisms of free central extensions and free nilpotent extensions of Burnside groups. Partially supported by the German Israel Foundation for Research and Development (G. I. F.). Supported by a grant from the Israel Planning and Budgeting Committee.     

Lagrangian tracking of bubbles interacting with pin-fins in a microchannel

This paper presents new image analysis algorithms to measure the trajectories of breaking and coalescing bubbles in microscale bubbly flows. Image analysis of high-speed movies provides information on bubble dynamics and bubble interaction including bubble coalescence and breakage events. Individual bubbles that overlap in the image are recognized with a presented breakline method. The breakline method discriminates the overlapping bubbles with lines based on the bubble perimeter curvature analysis. Coalescence and breakage events are automatically recognized, and the path lines of bubbles travelling through the field of view are analyzed. The functionality of the algorithms was examined in bubbly flow in a microchannel encompassing two pin-fins in tandem.     

Tracking Conformational Changes in Calmodulin in vitro,in Cell Extract,and in Cells by Electron Paramagnetic Resonance Distance Measurements

It is an open question whether the conformations of proteins sampled in dilute solutions are the same as in the cellular environment. Here we address this question by double electron-electron resonance (DEER) distance measurements with Gd(III) spin labels to probe the conformations of calmodulin (CaM) in vitro, in cell extract, and in human HeLa cells. Using the CaM mutants N53C/T110C and T34C/T117C labeled with maleimide-DOTA-Gd(III) in the N- and C-terminal domains, we observed broad and varied interdomain distance distributions. The in vitro distance distributions of apo-CaM and holo-CaM in the presence and absence of the IQ target peptide can be described by combinations of closed, open, and collapsed conformations. In cell extract, apo- and holo-CaM bind to target proteins in a similar way as apo- and holo-CaM bind to IQ peptide in vitro. In HeLa cells, however, in the presence or absence of elevated in-cell Ca²⁺ levels CaM unexpectedly produced more open conformations and very broad distance distributions indicative of many different interactions with in-cell components. These results show-case the importance of in-cell analyses of protein structures.     

Discontinuous liquid rise in capillaries with varying cross-sections

We consider theoretically liquid rise against gravity in capillaries with height-dependent cross-sections. For a conical capillary made from a hydrophobic surface and dipped in a liquid reservoir, the equilibrium liquid height depends on the cone-opening angle alpha, the Young-Dupré contact angle theta, the cone radius at the reservoir's level R(0), and the capillary length kappa(-)(1). As alpha is increased from zero, the meniscus' position changes continuously until, when alpha attains a critical value, the meniscus jumps to the bottom of the capillary. For hydrophilic surfaces the meniscus jumps to the top. The same liquid height discontinuity can be achieved with electrowetting with no mechanical motion. Essentially the same behavior is found for two tilted surfaces. We further consider capillaries with periodic radius modulations and find that there are few competing minima for the meniscus location. A transition from one to another can be performed by the use of electrowetting. Finite pressure difference between the two sides of the liquids can be incorporated as well, resulting in complicated phase-diagrams in the alpha-theta plane. The phenomenon discussed here may find uses in microfluidic applications requiring the transport small amounts of water "quanta" (volume < 1 nL) in a regular fashion.     

Ultrafast two-dimensional NMR spectroscopy using constant acquisition gradients

Multidimensional NMR spectroscopy plays an important role in the characterization of molecular structure and dynamics. A new methodology for acquiring this kind of spectra has been recently demonstrated, endowed with the potential to compress arbitrary multidimensional NMR acquisitions into a single scan. This "ultrafast" nD acquisition protocol is based on a spatiotemporal encoding of the indirect-domain spin evolution, followed by a repetitive decoding and re-encoding of the information thus stored employing a train of alternating-sign gradients. Such train of switching gradients extending throughout the course of the data acquisition may pose extreme demands on a magnetic resonance system, particularly when dealing with nonshielded gradients, strong eddy currents, or rapidly relaxing spin systems. Limits to the in vivo applicability of such fast-switching scheme may also arise due to gradient-induced perineural stimulation. The present study describes a new approach to ultrafast nD NMR that reduces the number of gradient switchings during the acquisition period to zero, leading in essence to a constant-gradient acquisition scheme. This approach operates on the basis of a novel spatiotemporal encoding including discrete, temporally overlapping, frequency-shifted pulses. Principles and examples of this new approach are given; sensitivity limitations and signal-enhancing prospects of such constant-gradient acquisitions are also discussed and exemplified.     

Depth from diffracted rotation

The accuracy of depth estimation based on defocus effects has been essentially limited by the depth of field of the imaging system. We show that depth estimation can be improved significantly relative to classical methods by exploiting three-dimensional diffraction effects. We formulate the problem by using information theory analysis and present, to the best of our knowledge, a new paradigm for depth estimation based on spatially rotating point-spread functions (PSFs). Such PSFs are fundamentally more sensitive to defocus thanks to their first-order axial variation. Our system acquires a frame by using a rotating PSF and jointly processes it with an image acquired by using a standard PSF to recover depth information. Analytical, numerical, and experimental evidence suggest that the approach is suitable for applications such as microscopy and machine vision.     

Protein‐oligosaccharide conjugates as novel prebiotics

Maintaining a good proportion of gut probiotic bacteria is imperative to health. This may be achieved by consuming “prebiotics,” e.g., galacto‐oligosaccharides (GOS) that selectively promote probiotic bacteria, as they often uniquely express transporters for such oligosaccharides. Proteins are an important source for amino acids essential to probiotic bacteria. As most protein digestion products are absorbed in the small intestine, and there is great competition on the residuals by colonic bacteria, amino acids are scarce (<0.01 mM) in the colonic intercellular fluid, thus limiting probiotics' proliferation. However, no existing prebiotic product contains protein. Herein, we propose a new type of prebiotics: protein‐oligosaccharide conjugates. These conjugates were designed to be selectively targeted to probiotic bacteria in the colon, for enhancing their competitive advantage over undesired microorganisms. The approach was inspired by active targeting of chemotherapy, achieved by conjugating drugs to ligands, which selectively bind to proteins uniquely expressed on cancer cells; except here, we aimed to promote, not eliminate, the targeted cells. We formed these conjugates by mild Maillard‐reaction‐based covalent conjugation of GOS to lactoferrin hydrolysate (LFH), formed by peptic digestion, hence it resists gastric digestion. LFH‐GOS conjugates comprised 76% ± 1% LFH and 25% ± 4% GOS, and self‐assembled into 0.2 to 1.5‐μm microparticles. Most of the conjugates' protein content endured simulated gastrointestinal digestion, hence is expected to reach the colon. Remarkably, we found that the growth rate of a model probiotic bacterium (Lactobacillus casei) on the conjugates was double that on the unconjugated components (0.082 and 0.041 h^?1, respectively). This study proposes the next generation of prebiotics.     

Realization of quantum walks with negligible decoherence in waveguide lattices

Quantum random walks are the quantum counterpart of classical random walks, and were recently studied in the context of quantum computation. Physical implementations of quantum walks have only been made in very small scale systems severely limited by decoherence. Here we show that the propagation of photons in waveguide lattices, which have been studied extensively in recent years, are essentially an implementation of quantum walks. Since waveguide lattices are easily constructed at large scales and display negligible decoherence, they can serve as an ideal and versatile experimental playground for the study of quantum walks and quantum algorithms. We experimentally observe quantum walks in large systems ( approximately 100 sites) and confirm quantum walks effects which were studied theoretically, including ballistic propagation, disorder, and boundary related effects.     

The Commuting Graph of Minimal Nonsolvable Groups

The purpose of this paper is to prove that if G is a finite minimal nonsolvable group (i.e. G is not solvable but every proper quotient of G is solvable), then the commuting graph of G has diameter 3. We give an example showing that this result is the best possible. This result is related to the structure of finite quotients of the multiplicative group of a finite-dimensional division algebra.