24,808 research outputs found
âGenetic Codingâ Reconsidered : An Analysis of Actual Usage
I thank George Pandarakalam for research assistance; Hans-Jörg Rheinberger for hosting my stay at the Max Planck Institute for History of Science, Berlin; and Sahotra Sarkar and referees of this journal for offering detailed comments. Funded by the Wellcome Trust (WT098764MA).Peer reviewedPublisher PD
An algorithmic characterization of antimatroids
In an article entitled âOptimal sequencing of a single machine subject to precedence constraintsâ E.L. Lawler presented a now classical minmax result for job scheduling. In essence, Lawler's proof demonstrated that the properties of partially ordered sets were sufficient to solve the posed scheduling problem. These properties are, in fact, common to a more general class of combinatorial structures known as antimatroids, which have recently received considerable attention in the literature. It is demonstrated that the properties of antimatroids are not only sufficient but necessary to solve the scheduling problem posed by Lawler, thus yielding an algorithmic characterization of antimatroids. Examples of problems solvable by the general result are provided
The 1723 AD violent Strombolian and phreatomagatic eruption at Irazu volcano (Costa Rica)
The largest of the recorded historic eruptions at IrazĂș volcano began on February 16, 1723 and lasted
until at least December 11. We here critically examine deposits of this eruption exposed on the summit of IrazĂș. Our
reconstruction of the eruption is based on the unique chronicle of the Spanish governor Diego de la Haya. The eruption
began with a < 10 cm thick surge deposit of phreatic origin showing block sag structures. The deposit is overlain by
6 m-thick coarse-grained basaltic andesitic non-graded juvenile fallout tephra consisting of highly vesicular (22-59
vol.%) bombs and lapilli with minor hydrothermally altered lapilli (1-7 vol.%) and rare light colored andesitic vesicular
lapilli (< 1%). These fallout deposits are interpreted as strombolian, possible generated during a short-lived scoria cone
at the end of February 1723, dominate volumetrically in the proximal facies. Overlying <1.2 m thick phreatomagmatic
deposits of fi nely laminated lapilli-bearing gray ash (fallout and surge deposits) some with contorted bedding and sag
structures, are in turn overlain by a 1.2 m thick bed of ash matrix-rich bomb/block deposit. The 1723 eruption was
accompanied by shallow volcano-tectonic earthquakes (Modifi ed Mercalli scale Intensity MMI VI-VII, magnitude ML
~5.5) that possibly facilitated magma/water interaction. Phenocrysts in the basaltic andesite (~53-55 wt.% SiO2) bombs
comprise plagioclase (6.1-21.6 vol.%, An52-35), clinopyroxene (2.5-10 vol.%), orthopyroxene (0.7-2 vol.%), olivine
(0.1-2.2 vol.%; Fo76-88) and Fe/Ti-oxides (0.1-1%), in a groundmass (66.5-90.3 vol. %), dominated by plagioclase
(An69-54), clinopyroxene and opaques in brown and black glass with the same range of chemical composition (SiO2=
57-64 wt.%). Rare white pumiceous lapilli in the scoria deposits are high-K, hornblende andesite (SiO2: 58-60 wt.%),
geochemically unrelated to the scoria deposits. Thus, two different magmas co-existing in the magma chamber were
mingled shortly before, and during, the eruption, suggesting that the eruption was triggered by magma mingling between
hornblende andesite and basaltic andesite magma
Configuration Space for Random Walk Dynamics
Applied to statistical physics models, the random cost algorithm enforces a
Random Walk (RW) in energy (or possibly other thermodynamic quantities). The
dynamics of this procedure is distinct from fixed weight updates. The
probability for a configuration to be sampled depends on a number of unusual
quantities, which are explained in this paper. This has been overlooked in
recent literature, where the method is advertised for the calculation of
canonical expectation values. We illustrate these points for the Ising
model. In addition, we proof a previously conjectured equation which relates
microcanonical expectation values to the spectral density.Comment: Various minor changes, appendix added, Fig. 2 droppe
Yang-Lee zeros and the helix-coil transition in a continuum model of polyalanine
We calculate the Yang-Lee zeros for characteristic temperatures of the
helix-coil transition in a continuum model of polyalanine. The distribution of
these zeros differs from predictions of the Zimm-Bragg theory and supports
recent claims that polyalanine exhibits a true phase transition. New estimates
for critical exponents are presented and the relation of our results to the
Lee-Yang theorem is discussed.Comment: 15 pages and 5 figure
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