The role of the hyperpolarization-activated inward current If in arrhythmogenesis: a computer model study.

Atrial fibrillation is the most common cardiac arrhythmia. Structural cardiac defects such as fibrosis and gap junction remodeling lead to a reduced cellular electrical coupling and are known to promote atrial fibrillation. It has been observed that the expression of the hyperpolarization-activated current If is increased under pathological conditions. Recent experimental data indicate a possible contribution of If to arrhythmogenesis. In this paper, the role of If in action potential propagation in normal and in pathological tissue is investigated by means of computer simulations. The effect of diffuse fibrosis and gap junction remodeling is simulated by reducing cellular coupling nonuniformly. As expected, the conduction velocity decreases when cellular coupling is reduced. In the presence of If the conduction velocity increases both in normal and in pathological tissue. In our simulations, ectopic activity is present in regions with high expression of If and is facilitated by cellular uncoupling. We conclude that an increased If may facilitate propagation of the action potential. Hence, If may prevent conduction slowing and block. Overexpression of If may lead to ectopic activity, especially when cellular coupling is reduced under pathological conditions.     

Adaptive reuse of office buildings into housing: opportunities and risks

One way of adapting and reusing vacant office buildings is conversion into housing. Former research has shown possibilities for this type of conversion, and has delivered instruments for determining the conversion potential of vacant offices. Although adaptation and renovation of outdated offices can prove to be a successful property (real estate) strategy, conversions into housing still only occur on a small scale. There are several reasons for this, including uncertainty about financial feasibility and little knowledge about the opportunities and risks of building conversions. A meta-study of the conversion of 15 office buildings into housing in the Netherlands is used to reveal the drivers for office-to-housing conversions as well as the opportunities and risks that arise in the conversion process. The findings show that various legal, financial, technical, functional and architectonic issues define the opportunities and risks of building conversions. These insights can be used to support the decision-making processes for dealing with vacant office buildings in order to minimize the risks and increase the opportunities.     

Influence of injection conditions on EDDS-flushing of metal-contaminated soil

This study evaluated the design of step-gradient, single-pulse, multi-pulse, and continuous injection of biodegradable EDDS ([S,S]-ethylene-diamine-disuccinic acid, under the same total dosage) and the significance of pore-water velocities during in situ soil flushing. In view of the metal breakthrough and extraction efficiency of each injection mode, single-pulse injection was found to be the least effective for all metals. Multi-pulse injection was consistently more effective than single-pulse injection, although the efficiency of second and third pulse injections significantly diminished. Continuous injection offered a simple operation and the greatest Ni and Cu extraction, whereas step-gradient injection was the best option for Zn and Pb extraction because it mitigated the influence of metal exchange. Moreover, a rinsing step with a background solution following the initial injection of the multi-pulse injection removed newly formed metal-EDDS complexes from soil pores effectively before further EDDS-flushing. A decrease in pore-water velocity provided a longer residence time for greater Ni and Cu extraction, but also enhanced the rate-limited metal exchange of Zn-EDDS and Pb-EDDS complexes and thus hindered Zn and Pb extraction. These results suggest a slower and continuous injection for the best Ni or Cu removal, but a faster and step-gradient injection for Zn or Pb removal.     

Magnetic tracking of acoustic radiation force-induced micro-order displacement

The dynamic behavior of a rigid magnetic sphere induced by an acoustic radiation force was investigated. The sphere was suspended in water in a simple pendulum configuration. The drag force acting on the pendulum during its motion was considered to follow a modified Stokes law for a low Reynolds number, accounting for phenomena related to its oscillatory movement. Steady forces of long (a few seconds) and short (a few milliseconds) durations were used. The movement of the magnetic sphere was tracked using a magnetoresistive sensor. From the new equilibrium position of the sphere in response to the long-duration static radiation force, the amplitude of this force was estimated. To assess the water viscosity, the relaxation movement after the acoustic force had stopped was fitted to a harmonic-motion model. Based on the results for the acoustic force and water viscosity, a theoretical profile of the sphere's micro-order displacement as a function of time caused by short-duration acoustic radiation force agreed well with experimental results.     

Melt-spun poly(tetrafluoroethylene) fibers

The recent discovery of melt-processable poly(tetrafluoroethylene) (PTFE) allows for common thermoplastic-polymer processing technologies to be applied to this unique polymer, which heretofore was considered to be highly intractable. In this paper, we report simple melt-spinning of monofilaments of a set of melt-processable (modified) PTFE grades with weight-average molar masses (M _w) ranging from 77 to 292 kg/mol. Fibers were spun at 380 °C at draw-down ratios of up to 2,750, yielding filaments of linear densities as low as 0.8 tex, corresponding to a diameter of ∼20 μm. The maximum Young’s modulus and tensile strength of as-spun fibers produced in this study were 91.7 cN/tex (1,972 MPa) and 12.0 cN/tex (258 MPa), respectively, accompanied by a strain to break of 24%.     

Estimation of Bridging Interactions for Natural Cracks from Bending Strength of Coarse-Grained Al2O3

Several ceramic materials show R -curve effects which in the past were investigated mainly with specimens containing artificial macrocracks. This paper describes how the R -curve effects caused by bridging interactions between the crack surfaces will influence the strength of specimens with natural crack populations. Calculations in terms of averaged stress intensity factors were performed to describe the development of surface cracks from the initial size up to the size at failure. As a consequence of bridging interactions, deviations from the expected straight line in the Weibull representation of strength will occur even under the assumption that the initial crack size is Weibull-distributed. A least-squares procedure allows the bridging stresses to be estimated from bending strength measurements.     

TESTING EQUALITY OF VARIANCES FOR PAIRED TIME SERIES

Abstract. We develop a simple test for testing equality of variances for paired stationary Gaussian time series. The test statistic is a modified z statistic. It is based on the periodograms of the two series and consistent estimation of the difference between the two spectral densities. Simulations illustrate the validity of the asymptotic results for finite samples. An application to EEG data is discussed.     

Effects of Geometrical Uncertainties on Electrocardiography

This paper investigates the influence of uncertainties in geometrical coordinates on calculated torso and epicardial potentials. Two types of sources, spherical epicardial and multipolar, are both considered. A concentric sphere model with the epicardial surface represented by a unit sphere and the torso surface represented by a spherical surface of radius 1.4 is utilized. While the representation of biological surfaces with spheres is a highly idealized situation, the dimensions chosen and the approximations utilized are such that the results should be indicative of those using measured biological coordinates.