An amino acid as a cofactor for a catalytic polynucleotide

Natural ribozymes require metal ion cofactors that aid both in structural folding and in chemical catalysis. In contrast, many protein enzymes produce dramatic rate enhancements using only the chemical groups that are supplied by their constituent amino acids. This fact is widely viewed as the most important feature that makes protein a superior polymer for the construction of biological catalysts. Herein we report the in vitro selection of a catalytic DNA that uses histidine as an active component for an RNA cleavage reaction. An optimized deoxyribozyme from this selection requires L-histidine or a closely related analog to catalyze RNA phosphoester cleavage, producing a rate enhancement of approximately 1-million-fold over the rate of substrate cleavage in the absence of enzyme. Kinetic analysis indicates that a DNA-histidine complex may perform a reaction that is analogous to the first step of the proposed catalytic mechanism of RNase A, in which the imidazole group of histidine serves as a general base catalyst. Similarly, ribozymes of the "RNA world" may have used amino acids and other small organic cofactors to expand their otherwise limited catalytic potential.     

Controlled counter-flow motion of magnetic bead chains rolling along microchannels

We demonstrate controlled transport of superparamagnetic beads in the opposite direction of a laminar flow. A permanent magnet assembles 200 nm magnetic particles into about 200 μm long bead chains that are aligned in parallel to the magnetic field lines. Due to a magnetic field gradient, the bead chains are attracted towards the wall of a microfluidic channel. A rotation of the permanent magnet results in a rotation of the bead chains in the opposite direction to the magnet. Due to friction on the surface, the bead chains roll along the channel wall, even in counter-flow direction, up to at a maximum counter-flow velocity of 8 mm s⁻¹. Based on this approach, magnetic beads can be accurately manoeuvred within microfluidic channels. This counter-flow motion can be efficiently be used in Lab-on-a-Chip systems, e.g. for implementing washing steps in DNA purification.     

Multi-object tracking evaluated on sparse events

This article presents a visual object tracking method and applies an event-based performance evaluation metric for assessment. The proposed monocular object tracker is able to detect and track multiple object classes in non-controlled environments. The tracking framework uses Bayesian per-pixel classification to segment an image into foreground and background objects, based on observations of object appearances and motions in real-time. Furthermore, a performance evaluation method is presented and applied to different state-of-the-art trackers based on successful detections of semantically high level events. These events are extracted automatically from the different trackers an their varying types of low level tracking results. Then, a general new event metric is used to compare our tracking method with the other tracking methods against ground truth of multiple public datasets.     

From I-Awareness to We-Awareness in CSCW

Awareness is one of the central concepts in Computer Supported Cooperative Work, though it has often been used in several different senses. Recently, researchers have begun to provide a clearer conceptualization of awareness that provides concrete guidance for the structuring of empirical studies of awareness and the development of tools to support awareness. Such conceptions, however, do not take into account newer understandings of shared intentionality among cooperating actors that recently have been defined by philosophers and empirically investigated by psychologists and psycho-linguists. These newer conceptions highlight the common ground and socially recursive inference that underwrites cooperative behavior. And it is this inference that is often seamlessly carried out in collocated work, so easy to take for granted and hence overlook, that will require computer support if such work is to be partially automated or carried out at a distance. Ignoring the inferences required in achieving common ground may thus focus a researcher or designer on surface forms of “heeding” that miss the underlying processes of intention shared in and through activity that are critical for cooperation to succeed. Shared intentionality thus provides a basis for reconceptualizing awareness in CSCW research, building on and augmenting existing notions. In this paper, we provide a philosophically grounded conception of awareness based on shared intentionality, demonstrate how it accounts for behavior in an empirical study of two individuals in collocated, tightly-coupled work, and provide implications of this conception for the design of computational systems to support tightly-coupled collaborative work.     

Kernel fisher discriminants for outlier detection

The problem of detecting atypical objects or outliers is one of the classical topics in (robust) statistics. Recently, it has been proposed to address this problem by means of one-class SVM classifiers. The method presented in this letter bridges the gap between kernelized one-class classification and gaussian density estimation in the induced feature space. Having established the exact relation between the two concepts, it is now possible to identify atypical objects by quantifying their deviations from the gaussian model. This model-based formalization of outliers overcomes the main conceptual shortcoming of most one-class approaches, which, in a strict sense, are unable to detect outliers, since the expected fraction of outliers has to be specified in advance. In order to overcome the inherent model selection problem of unsupervised kernel methods, a cross-validated likelihood criterion for selecting all free model parameters is applied. Experiments for detecting atypical objects in image databases effectively demonstrate the applicability of the proposed method in real-world scenarios.     

Experimentelle und analytische Untersuchungen zum Zündverhalten stark verdünnter C2H2/O2-Gemische

Zusammenfassung Das Zündverhalten homogener Gasgemische bestehend aus Argon mit C₂H₂+O₂-Anteilen von 2% wird bei ?quivalenzverh?ltnissen von ϕ=0,2; 0,5; 1,0 und 2,0 hinter Sto?wellen experimentell untersucht. Kriterium für das Ende der Induktionsperiode ist das starke Ansteigen der OH-Konzentration, die durch Absorptions- oder Emissionsverfahren gemessen wird. Die Gaszust?nde sind in einem Temperaturbereich 1000 K≦T≦1560 K bei Drücken zwischen 0,6 und 1,3 bar variiert worden. Die Me?werte lassen sich durch eine Korrelationsgleichung darstellen mit τ in μs und Konzentrationen in mol cm⁻³. Mit Hilfe eines reaktionskinetischen Modells bestehend aus 29 Elementarreaktionen werden Computersimulationen des Zündverhaltens der verschiedenen Gemische durchgeführt. Die übereinstimmung zwischen berechneten und gemessenen OH-Induktionszeiten erscheint zufriedenstellend, wenn man bedenkt, da? keine kinetische Anpassung vorgenommen worden ist.     

Autoantibodies to the insulin receptor. Effect on the insulin-receptor interaction in IM-9 lymphocytes

The serum of some patients with insulin-resistant "diabetes" contains antibodies that bind to and block the cell membrane receptors for insulin. In this report, we have characterized the effects of the antireceptor antibodies on the interaction of (125)I-insulin with its receptor on the human lymphoblastoid cell line IM-9. Up to 95% of specific insulin binding can be inhibited by pretreatment of the cells with these immunoglobulins. The onset of the inhibitory effect is time- and temperature-dependent, and the effect is reversed extremely slowly if the cells are suspended in a large excess of antibody-free buffer. These features of antibody binding can be easily distinguished from those for insulin binding to its receptor. The inhibitory effect of the antibodies can be reversed by exposure of the cells to conditions known to elute surface immunoglobulins. The three antireceptor sera studied appear to alter the insulin-receptor interaction in different ways. Two antisera markedly reduce receptor affinity through combined effects on the insulin association and dissociation rates, and, additionally, have smaller effects on available receptor number. A third antiserum primarily affects available receptor number and has little effect on receptor affinity. All three antisera inhibit the capacity of insulin to promote negatively cooperative site-site interactions among insulin receptors. The data suggest that these autoantibodies to the insulin receptor bind to different determinants on the receptor and may therefore be useful as unique probes of insulin receptor structure and function.     

By-catch in the Saginaw Bay,Lake Huron commercial trap net fishery

This study provides species-specific catch and baseline mortality estimates of non-target species (by-catch) for the Saginaw Bay, Lake Huron commercial trap net fishery. By-catch can represent a significant mortality source that is often unknown. By-catch and by-catch mortality rates in the Saginaw Bay commercial trap net fishery, which primarily targets lake whitefish (Coregonus clupeaformis), yellow perch (Perca flavescens), and channel catfish (Ictalurus punctatus), are currently unknown. From May through August 2010, we observed onboard commercial trap net vessels and took species-specific counts of by-catch and estimated initial by-catch mortality (i.e., morbid or floating fish). The high levels of walleye (Sander vitreus) catch and mortality observed within inner Saginaw Bay have not been previously documented in the Laurentian Great Lakes. Walleye by-catch averaged 127.3 individuals per trap net lift and 42% of those caught were morbid. The levels of lake trout (Salvelinus namaycush) catch observed were within the range observed in previous studies, but mortality (percent) was higher than has been previously observed. Lake trout by-catch averaged 39.4 individuals per lift and 39.2% of those were morbid. Through the use of generalized linear models, this analysis also indicated factors that most influenced catch of non-target species including time of year and soak time (i.e., time interval between trap net lifts). Surface water temperature and trap net depth most influenced mortality. These results may inform fishers and fisheries managers and highlight the need for comprehensive by-catch monitoring throughout the Great Lakes.