Active muscle fiber as an equivalent cardiac current generator

Equations are derived describing potentials due to an active muscle fiber in an infinite medium in terms of two surface integrals—one of the propagated action potential and the other of the membrane current density, both integrals being taken over the surface of the muscle. These equations are incorporated into an equivalent cardiac current generator in which the left ventricle (i.e. the current source) is represented by a three-dimensional wedge and the thorax (i.e. the volume conductor), by a homogeneous circular cylinder. Since this current generator expresses the body surface potentials in terms of the membrane current density and the membrane potential at any point on the surface of the electrically active muscle fiber, the calculated ECG can be correlated with theactual sources within the heart. This equivalent cardiac generator possesses many of the physical and physiological properties of cardiac muscle. The equations were evaluated numerically on a digital computer. The results indicate that equivalent cardiac current generators of this type can yield clinically significant results and that further research is necessary to investigate their properties fully.     

Kinematics of swimming garter snakes (Thamnophis sirtalis).

We investigate the kinematics of swimming garter snakes (Thamnophis sirtalis) using a novel nonlinear regression-based digitization method to establish quantitative statistical support for non-constant wavelengths in the undulatory pattern exhibited by swimming snakes. We find that in swimming snakes, the growth of the amplitude of the propulsive wave head-to-tail is strongly correlated (p < 0.005) with the head-to-tail growth in the wavelength. We investigate correlations between kinematic parameters and steady swimming speed, and find a very strong positive correlation between swimming speed and undulation frequency. We furthermore find a statistically well-supported positive correlation between swimming speed and both the initial amplitude of the propulsive wave at the head and the degree of amplitude growth from head to tail.     

Ethylene and abnormal developmental patterns in tulips

Ethylene can break dormancy in a wide range of common weed species. Investigations of the phenomenology of this response have shown that there is a pronounced interaction between ethylene, light and other factors. The implications of these findings will be discussed in relation to the possibility of controlling weed seed germination in cultivated areas.     

Analyzing Short-Term Noise Dependencies of Spike-Counts in Macaque Prefrontal Cortex Using Copulas and the Flashlight Transformation

Simultaneous spike-counts of neural populations are typically modeled by a Gaussian distribution. On short time scales, however, this distribution is too restrictive to describe and analyze multivariate distributions of discrete spike-counts. We present an alternative that is based on copulas and can account for arbitrary marginal distributions, including Poisson and negative binomial distributions as well as second and higher-order interactions. We describe maximum likelihood-based procedures for fitting copula-based models to spike-count data, and we derive a so-called flashlight transformation which makes it possible to move the tail dependence of an arbitrary copula into an arbitrary orthant of the multivariate probability distribution. Mixtures of copulas that combine different dependence structures and thereby model different driving processes simultaneously are also introduced. First, we apply copula-based models to populations of integrate-and-fire neurons receiving partially correlated input and show that the best fitting copulas provide information about the functional connectivity of coupled neurons which can be extracted using the flashlight transformation. We then apply the new method to data which were recorded from macaque prefrontal cortex using a multi-tetrode array. We find that copula-based distributions with negative binomial marginals provide an appropriate stochastic model for the multivariate spike-count distributions rather than the multivariate Poisson latent variables distribution and the often used multivariate normal distribution. The dependence structure of these distributions provides evidence for common inhibitory input to all recorded stimulus encoding neurons. Finally, we show that copula-based models can be successfully used to evaluate neural codes, e.g., to characterize stimulus-dependent spike-count distributions with information measures. This demonstrates that copula-based models are not only a versatile class of models for multivariate distributions of spike-counts, but that those models can be exploited to understand functional dependencies.     

Transformation of skin fibroblast cells of a cystinotic patient by simian virus 40: evidence for an establishment of a permanent cell clone which retains the original metabolism defect.

Human skin fibroblast cells derived from a juvenile patient with nephropathic cystinosis were transformed by simian virus 40. Transformed cell clones were isolated and established in tissue culture. In comparison to the parental cystinotic cells, the newly isolated, transformed cell clones had a higher plating efficiency, a modal chromosome number of 68, grew in soft agar, and showed a nuclear immunofluorescence typical for SV 40-specific tumor (T) antigen. The content of intracellular, unbound cystine in the transformed cell clone was of the same level (6.1 nmol 1/2 cystine/mg protein) as in the parental cystinotic cells (7.4 nmol). Control cells (SV 80 and WI-38) contained normal levels of cystine (0.31 and 0.47 nmol 1/2 cystine/mg protein). The growth characteristics make the transformed cystinotic cell clone suitable for large scale preparation of cellular constituents, i.e. lysosomes which seem to be affected in cystinotic patients.     

Cultivation of the yeast Candida lipolytica on hydrocarbons. II. One-stage continuous cultivation on gas oil

Continuous cultivation of the yeast Candida lipolytica on gas oil was studied from the viewpoint of biomass production and oil deparaffination. Optimum conditions wore found at the dilution rate D = 0.16–0.19 when biomass productivity 1.7 g/l/hr and yield coefficient. y = 0.92 were achieved. At deparaffination to the same freezing point, more than double the production of biomass and deparaffined oil during a given time unit was achieved in a continuous process than in batch cultivation. Consumption of substrate was followed in both cultivation processes and it was confirmed that individual n-alkanes of gas oil were degraded at various rates and yields. Results proved optimum cultivation conditions to depend on concentration and composition of the paraffinic fraction of gas oil used. To achieve these conditions the continuous process may be controlled by choice; of suitable dilution rate and concentration of gas oil.