Relaxation of ultralarge VWF bundles in a microfluidic-AFM hybrid reactor.

The crucial role of the biopolymer "Von Willebrand factor" (VWF) in blood platelet binding is tightly regulated by the shear forces to which the protein is exposed in the blood flow. Under high-shear conditions, VWFs ability to immobilize blood platelets is strongly increased due to a change in conformation which at sufficient concentration is accompanied by the formation of ultra large VWF bundles (ULVWF). However, little is known about the dynamic and mechanical properties of such bundles. Combining a surface acoustic wave (SAW) based microfluidic reactor with an atomic force microscope (AFM) we were able to study the relaxation of stretched VWF bundles formed by hydrodynamic stress. We found that the dynamical response of the network is well characterized by stretched exponentials, indicating that the relaxation process proceeds through hopping events between a multitude of minima. This finding is in accordance with current ideas of VWF self-association. The longest relaxation time does not show a clear dependence on the length of the bundle, and is dominated by the internal conformations and effective friction within the bundle.

Children's and adults' models for predicting teleological action: the development of a biology-based model.

Understanding that only living things must act to gain self-beneficial goals is important for developing a theory-like understanding of the living world. This research studied the models that preschoolers, fifth graders, and adults use to guide their predictions of self-beneficial, goal-directed (i.e., teleological) action. Four possible models have been suggested: finalist, complexity based, biology based, and animal based. In Study 1, participants (N = 104) were assigned to one of two conditions that differed in whether a beneficial or neutral object was pictured; they were asked to predict whether animals, plants, machines, and simple artifacts would modify their movement in the direction of that object. Preschoolers' predictions were consistent with an animal-based model, fifth graders' predictions were consistent with biology-based and complexity-based models, and adults' predictions were consistent with a biology-based model. Analysis of both individual response patterns and explanations supported these findings, but also showed that a significant number of preschoolers and fifth graders were finalist, and that very few individual fifth graders followed a complexity-based teleology. In Study 2, participants (N = 84) reported whether the animals, plants, machines, and simple artifacts in Study 1 had psychological capacities. All age groups attributed psychological capacities to animals at levels higher than other domains and at above-chance levels. The evidence from these two studies suggests that preschoolers, unlike fifth graders and adults, predict teleological action for plants and animals on the basis of these entities' inferred psychological capacities.

Noninvasive magnetic detection of cardiac mechanical activity: experiments.

The magnetic susceptibility of the heart and the intracardiac blood is substantially greater than that of the surrounding lung tissue. The periodic redistribution of blood and tissue during the cardiac cycle will thus alter an externally applied magnetic field. These magnetic field changes can be detected by a magnetometer outside the body, and have been termed magnetic susceptibility plethysmography (MSPG) signals. A differential magnetometer, a liquid helium dewar, and a superconducting persistent-current magnet have been developed to detect the x component of the MSPG signal. The theoretical analysis of this instrument is presented to understand the spatial sensitivity of an MSPG susceptometer with a nonuniform magnetizing field. Preliminary measurements are shown to be in fair agreement with the model calculations. Several possible improvements of the technique are discussed.