A spatial panel data version of the knowledge capital model

This paper attempts to analyze the impact of knowledge and knowledge spillovers on regional total factor productivity (TFP) in Europe. Regional patent stocks are used as a proxy for knowledge, and TFP is measured in terms of a superlative index. We follow Fischer et. al (2008) by using a spatial-spillover model and a data set covering 203 regions for six time periods. In order to estimate the impact of knowledge stocks we use a spatial autoregressive model with random effects, which allows for three kinds of spatial dependence: Spatial correlation in the innovations, the exogenous and the endogenous variables. The results suggest that there is a significant positive impact of knowledge on regional TFP levels, and that knowledge spills over to neighboring regions. These spillovers decay exponentially with distance at a rate of 8%. Using Monte Carlo simulations we calculate the distribution of direct and indirect effects. The average elasticity of a region's TFP with respect to its own knowledge stock is 0.2 and highly significant. The average effect of all other regions' TFP is about 50% higher, which confirms that the cross-country externalities are important in the measuring of the impact.

Molecular Weight Dependence of Polymersome Membrane Elasticity and Stability

Vesicles prepared in water from a series of diblock copolymers and termed "polymersomes" are physically characterized. With increasing molecular weight $\bar{M}_n$, the hydrophobic core thickness $d$ for the self-assembled bilayers of polyethyleneoxide - polybutadiene (PEO-PBD) increases up to 20 $nm$ - considerably greater than any previously studied lipid system. The mechanical responses of these membranes, specifically, the area elastic modulus $K_a$ and maximal areal strain $\alpha_c$ are measured by micromanipulation. As expected for interface-dominated elasticity, $K_a$ ($\simeq$ 100 $pN/nm$) is found to be independent of $\bar{M}_n$. Related mean-field ideas also predict a limiting value for $\alpha_c$ which is universal and about 10-fold above that typical of lipids. Experiments indeed show $\alpha_c$ generally increases with $\bar{M}_n$, coming close to the theoretical limit before stress relaxation is opposed by what might be chain entanglements at the highest $\bar{M}_n$. The results highlight the interfacial limits of self-assemblies at the nano-scale.Comment: 16 pages, 5 figures, and 1 tabl

Brownian Adhesive Dynamics (BRAD) for Simulating the Receptor-Mediated Binding of Viruses

Current viral docking models have relied upon the assumption that bond formation and breakage are independent of viral and docking surface geometry, as well as the forces exerted on the bonds. This assumption, known as the equivalent site hypothesis (ESH), is examined in detail using a newly developed simulation technique—Brownian adhesive dynamics (BRAD). The simulation couples the thermal motion of viral particles with adhesive dynamics models to characterize the effect of bonding on viral motion. We use the binding of HIV-like particles to CD4 expressing cells as a model system to illustrate the utility of BRAD. Comparison of the transition rates between bound states predicted by ESH and the rates resulting from BRAD simulations show dramatic differences; at values of the equilibrium crosslinking constant, KxRT, where ESH suggests all virus adhesion proteins will be bound (KxRT = 106), BRAD predicts not all virus adhesion proteins will be bound. At values of the equilibrium crosslinking constant used in typical ESH calculations of virus docking (KxRT = 1) we find BRAD simulations predict no binding. The mean bond density from BRAD models is often much lower than that predicted by ESH for equivalent parameter values. BRAD suggests that the viruses are much less well bound than ESH predicts. The differences suggest that binding models for viruses need to be reexamined closely. BRAD is a simulation technique that will be useful for quantifying the receptor-mediated binding of a wide variety of viruses to cells

HIV Viral Docking: Model Predictions for Bond Number and Trajectory

Viruses are nano-scale pathogenic particles. Understanding viral attachment is important to understand infectivity, disease transmission, and virus propagation throughout the host. A new simulation technique has been developed to study viral docking behavior - Brownian Adhesive Dynamics (BRAD). BRAD couples Brownian motion algorithm with adhesive dynamic models, and incorporates the effect of virus/cell geometry - an improvement over previous models. The method is extendable to any virus/cell system as well as nanoparticle adhesion system. Current studies have focused on the HIV/CD4 cell system. Comparison of BRAD simulation predictions with those of previous models of viral ducking has shown differences in steady state bond number and bond trajectory. This indicates that geometry of the system plays a significant role in the bonding behavior of viruses. Thus, it is shown that the equivalent site hypothesis is suspect

Performance as Philosophy — the universal language of the theatre revisited

The history of philosophy is widely considered as the history of exercises in speculation. However, it is also possible to understand philosophy not as the outcome of speculation, but at the attempt by philosophers to explain, make sense of, and ultimately share, their own experiences of a very subtle, powerful and spiritual nature. The growing field of performance philosophy begins to acknowledge the potential of considering philosophy as an expression of immediate experience rather than distant speculation. This acknowledgement can take the shape of employing performance to express philosophy — in more immediately experienced ways than verbal language is ever able to convey. Writing about this non-verbal dimension is difficult, and the result limited by its very nature, but in this article, we discuss the principle, and provide an example in the performance philosophy, captured under the term of body thinking, of German philosopher and dancer Aurelia Baumgartner

Dynamic Simulations of Inflammatory Cell Recruitment: The State Diagram for Cell Adhesion Mediated by Two Receptors

White blood cell recruitment from the bloodstream to surrounding tissues is an essential component of the immune response. Capture Of hlood-borne Ieuk\u27Wks onto vascular endothelium proceeds via a two-step mechanism, with each step mediated by a distinct receptor-ligand pair. Cells first transiently adhere, or roll (via interactions between selectins and sialyl-Lewis-x), and then firmly adhere to the vascular wall (via interactions between integrins and ICAM-1). We have reported that a eomputatiokl method called Adhesive Dynamics (AD) accurately reproduces the fine scale dynamics of selectin-mediated rolling [1]. This paper extends the use of AD simulations to model the dynamics of cell adhesion when two classes of receptors are simultaneously active: one class (selectins) with weakly adhesive properties, and the other (integrins) with strongly adhesive properties. AD simulations predict synergistic functions of the two receptors in mediating adhesion. We present this relationship in a two-receptor state diagram, a map that relates the densities and properties of adhesion molecules to various adhesive behaviors that they code, such as rolling or firm adhesion. The predictions of two-receptor adhesive dynamics are validated by the ability of the model to reproduce experimental neutrophil rolling velocities

The Shear Threshold Effect for Particle Adhesion to Bioreactive Surfaces: Influence of Receptor and Ligand Site Density

Selectins are cell adhesion molecules that mediate capture and rolling adhesion of white blood cells to vascular walls, an essential component of the inflammatory response. Adhesion through L-selectin requires a hydrodynamic shear stress above a threshold level, a phenomenon known as the shear threshold effect. We have reported that the shear threshold effect can he re-created in cell-free systems, in which microspheres coated with the carbohydrate ligand sialyl Lewis x (sLex) are perfused over L-selectin-coated surfaces. This paper extends the use of the cell-free system to determine the concurrent influence of receptor and ligand site density on the shear threshold effect. We find that the shear threshold effect diminishes with increasing levels of either L-selectin or sLex. At reduced site densities of either L-selectin or sLex, the shear threshold effect is present, with maximal rolling observed at a shear stress of 1.2 dynes/cm2. At higher site densities of L-selectin and sLex, the shear threshold effect disappears. These results suggest that the shear threshold relies on the formation of low numbers of receptor-ligand bonds

'It Has to Go Down A Little, In Order to Go Around'- Following Feynman on the Gyroscope

In this paper we show that with the help of accessible, teaching quality equipment, some interesting details of the motion of a gyroscope, typically overlooked in introductory courses, can be measured and compared to theory. We begin by deriving a simple relation between the asymptotic dip angle of a gyroscope released from rest and its precession velocity. We then describe an experiment which measures these parameters. The data gives excellent agreement with the model. The idea for this project was suggested by the discussion of gyroscopic motion in The Feynman Lectures on Physics. Feynman's conclusion (stated in colloquial terms and quoted in the title) is confirmed and, in addition, conservation of angular momentum, which underlies this effect, is quantitatively demonstrated.Comment: 6 pages, 4 figure