Conceptual Metaphors: a review with implications for human understandings and systems practice

We provide an overview of metaphor theory and explore implications for systems practice by building on claims that metaphors are central to our ways of understanding. As stakeholders will have different understandings, each metaphor will reveal and conceal different aspects of their understandings. These differences need to be accommodated within systems practice. Our contribution in this paper is to show how metaphors can explain, appreciate and create different understandings. Further, new understandings can emerge from considering different metaphors

Comment on "Influence of Noise on Force Measurements"

In a recent Letter [arXiv:1004.0874], Volpe et al. describe experiments on a colloidal particle near a wall in the presence of a gravitational field for which they study the influence of noise on the measurement of force. Their central result is a striking discrepancy between the forces derived from experimental drift measurements via their Eq. (1), and from the equilibrium distribution. From this discrepancy they infer the stochastic calculus realised in the system. We comment, however: (a) that Eq. (1) does not hold for space-dependent diffusion, and corrections should be introduced; and (b) that the "force" derived from the drift need not coincide with the "force" obtained from the equilibrium distribution.Comment: Comment submitted to a PRL letter; 1 page, 1 figur

Charge fluctuations and boundary conditions of biological ion channels:effect on the ionic transition rate

A self-consistent solution is derived for the Poisson-Nernst-Planck (PNP) equation, valid both inside a biological ion channel and in the adjacent bulk fluid. An iterative procedure is used to match the two solutions together at the channel mouth. Charge fluctuations at the mouth are modeled as shot noise flipping the height of the potential barrier at the selectivity site. The resultant estimates of the conductivity of the ion channel are in good agreement with Gramicidin experimental measurements and they reproduce the observed current saturation with increasing concentration

Observations of the X-ray Nova GRO~J0422+32: II: Optical Spectra Approaching Quiescence

We present results obtained from a series of 5~\AA\ resolution spectra of the X-ray Nova GRO~J0422+32 obtained in 1993~October, when the system was approximately 2 magnitudes above quiescence, with ${\rm R \sim 19}$. The data were obtained in an effort to measure the orbital radial velocity curve of the secondary, but detection of the narrow photospheric absorption lines needed to do this proved elusive. Instead we found wide absorption bands reminiscent of M~star photospheric features. The parameters determined by fitting accretion disk line profiles (Smak profiles) to the H$\alpha$ line are similar to those found in several strong black-hole candidates. Measurements of the velocity of the H$\alpha$ line are consistent with an orbital period of 5.1~hours and a velocity semi-amplitude of the primary of $34 \pm 6$~\kms. These measurements, when combined with measurements of the velocity semi-amplitude of the secondary made by others, indicate that the mass ratio $q \sim 0.09$. If the secondary follows the empirical mass-radius relation found for CVs, the low $q$ implies a primary mass of $M_x \sim 5.6$\mo, and a rather low (face-on) inclination. The H$\alpha$ EW is found to be modulated on the orbital period with a phasing that implies a partial eclipse of the disk by the secondary, but simultaneous R~band photometry shows no evidence for such an eclipse.Comment: Accepted for ApJ, plain latex, 5 figures available as self-extracting uuendoced, compressed, tarfiles (from uufiles

Self-consistent analytic solution for the current and the access resistance in open ion channels.

A self-consistent analytic approach is introduced for the estimation of the access resistance and the current through an open ion channel for an arbitrary number of species. For an ion current flowing radially inward from infinity to the channel mouth, the Poisson-Boltzmann-Nernst-Planck equations are solved analytically in the bulk with spherical symmetry in three dimensions, by linearization. Within the channel, the Poisson-Nernst-Planck equation is solved analytically in a one-dimensional approximation. An iterative procedure is used to match the two solutions together at the channel mouth in a self-consistent way. It is shown that the currentvoltage characteristics obtained are in good quantitative agreement with experimental measurements