Explanation, unification, and what chemistry gets from causation

I consider a way the concept of causation could be excised from chemical practice, suggested by Kitcher's view that causes are just a subset of unifying patterns which play a particular psychological role for us. \Kitcherian chemistry is at first blush well equipped to handle explanatory tasks. However, it would force chemists to accept certain unifying patterns as explanatory, which they do not think are at all explanatory. This might head off some descriptive lines of enquiry and damage prospects for the identification of potentially larger-scale explanations. More important than this, to chemists, it could put them off from finding the explanatory patterns that are true true because they get at the real structure of the chemical phenomena in the world

Observations of the galactic plane by the zodiacal infrared project

The two rocket flights of the Zodiacal Infrared Project (ZIP), flown 18 August 1980 and 31 July 1981, were intended to provide data on the near-infrared thermal emission of the interplanetary dust cloud over a broad range of ecliptic coordinates (latitudes -60 to +85 degrees, solar elongation angles 22 to 90 degrees and 140 to 180 degrees). In addition, their multiple crossings of the Galactic plane provided low resolution spectral data (delta lambda/lambda ranging from 1. to 0.1, for effective wavelengths from 3 to 30 microns) for most of the first quadrant (longitudes 30 to 100 degrees). Examples are displayed. Having made a thorough reanalysis of the calibration of the ZIP database, researchers present the salient features of the Galactic plane as observed by ZIP. The binned, in-plane data, corrected for zodiacal emission, generally show an exponential decrease with increasing longitude. The fitted exponential scale-length is 0.038/degree, and can be inverted to derive a radial density profile. Channel ratios are converted to temperatures by using model spectra in which thermal emitters with emissivity approx. 1/lambda are convolved with the filter responses. The results for channels 5 (11 microns) and 12 (21 microns) are shown, along with similarly derived temperatures from Infrared Astronomy Satellite (IRAS) 12 microns and 25 microns data. The ZIP data show little variation with longitude, consistent with IRAS results. A narrow spectral feature at 13 microns appears consistently in data for the plane (uncorrected for zodiacal emission). However, this is strongly contaminated by calibration problems for channel 8. Researchers suggest that residual emission at 13 microns arises from the (NeII) line at 12.8 microns

A substitute for the singular Green kernel in the Newtonian potential of celestial bodies

The "point mass singularity" inherent in Newton's law for gravitation represents a major difficulty in accurately determining the potential and forces inside continuous bodies. Here we report a simple and efficient analytical method to bypass the singular Green kernel 1/|r-r'| inside the source without altering the nature of the interaction. We build an equivalent kernel made up of a "cool kernel", which is fully regular (and contains the long-range -GM/r asymptotic behavior), and the gradient of a "hyperkernel", which is also regular. Compared to the initial kernel, these two components are easily integrated over the source volume using standard numerical techniques. The demonstration is presented for three-dimensional distributions in cylindrical coordinates, which are well-suited to describing rotating bodies (stars, discs, asteroids, etc.) as commonly found in the Universe. An example of implementation is given. The case of axial symmetry is treated in detail, and the accuracy is checked by considering an exact potential/surface density pair corresponding to a flat circular disc. This framework provides new tools to keep or even improve the physical realism of models and simulations of self-gravitating systems, and represents, for some of them, a conclusive alternative to softened gravity.Comment: Accepted for publication in A&A; 7 pages, color figure

A local prescription for the softening length in self-gravitating gaseous discs

In 2D-simulations of self-gravitating gaseous discs, the potential is often computed in the framework of "softened gravity" initially designed for N-body codes. In this special context, the role of the softening length LAMBDA is twofold: i) to avoid numerical singularities in the integral representation of the potential (i.e., arising when the relative separation vanishes), and ii) to acount for stratification of matter in the direction perpendicular to the disc mid-plane. So far, most studies have considered LAMBDA as a free parameter and various values or formulae have been proposed without much mathematical justification. In this paper, we demonstrate by means of a rigorous calculus that it is possible to define LAMBDA such that the gravitational potential of a flat disc coincides at order zero with that of a geometically thin disc of the same surface density. Our prescription for LAMBDA, valid in the local, axisymmetric limit, has the required properties i) and ii). It is mainly an analytical function of the radius and disc thickness, and is sensitive to the vertical stratification. For mass density profiles considered (namely, profiles expandable over even powers of the altitude), we find that LAMBDA : i) is independant of the numerical mesh, ii) is always a fraction of the local thickness H, iii) goes through a minimum at the singularity (i.e., at null separation), and iv) is such that 0.13 < LAMBDA/H < 0.29 typically (depending on the separation and on density profile). These results should help us to improve the quality of 2D- and 3D-simulations of gaseous discs in several respects (physical realism, accuracy, and computing time).Comment: accepted in A&A, 7 pages, 7 figures, web link for the F90 code and on-line calculations : http://www.obs.u-bordeaux1.fr/radio/JMHure/intro2single.ph

The Absolute Spectra of Galactic Cosmic Rays at Solar Minimum and Their Implications for Manned Spaceflight

The radiation dose from galactic cosmic rays during a proposed mission to Mars is near the annual dose limit for the crew. Since the absolute spectra of galactic cosmic rays critically influences mission planning and spacecraft design, these spectra must be determined as accurately as possible. We have fit published measurements with solutions of the spherically symmetric diffusion equation to make accurate representations of the spectra. We report preliminary determinations on the absolute differential energy spectra at 1 AU and discuss the implications for the proposed missions to Mars

The Saga of the Journal Comment

Recently, Steinn brought our attention to some of the difficulties involved in getting a scientific journal to publish a “Comment” on a article. He drew on a document (PDF) by Prof. Rick Trebino of the Georgia Institute of Technology School of Physics detailing (in 123 numbered steps) his own difficulties in advancing what is supposed to be an ongoing conversation between practicing scientists in the peer reviewed scientific literature. Indeed, I think this chronology of exasperation raises s..

#overlyhonestmethods: Ethical Implications When Scientists Joke with Each Other on Public Social Media

Scientists have used #overlyhonestmethods to tag posts on Twitter that purport to fill in details of research methods not generally included in formal scientific communications. I consider ethical dimensions of #overlyhonestmethods for communication between scientists, as well as what the conversation communicates to non-scientists watching it.</p