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Self-stabilization of the biosphere under global change: A tutorial geophysiological approach
A 2-dimensional extension of the simple Lovelock-Watson model for geosphere-biosphere feed-back is introduced and discussed. Our enriched version also takes into account various pertinent physical, biological, and civilisatory processes like lateral heat transport, species competition, mutation, germination, and habitat fragmentation. The model is used as a caricature of the Earth System, which allows potential response mechanisms of the biosphere to environmental stress (as generated, e.g., by global warming or anthropogenic land-cover change) to be investigated qualitatively. Based on a cellular automaton representation of the system, extensive calculations are performed. They reveal a number of remarkable and, partially, counter-intuitive phenomena: our model biosphere is able to control almost perfectly the geophysical conditions for its own existence. If the environmental stress exceeds certain thresholds, however, life breaks down on the artificial planet via a first-order phase transition, i.e., in a non-reversible way. There is a close connection between self-stabilizing capacity, biodiversity and geometry of habitat fragmentation. It turns out, in particular, that unrestricted Darwinian competition, which reduces the number of co-existing species, is the best guarantee for survival of the artificial ecosphere as a whole
Radial HI Profiles at the Periphery of Galactic Disks: The Role of Ionizing Background Radiation
Observations of neutral hydrogen in spiral galaxies reveal a sharp cutoff in
the radial density profile at some distance from the center. Using 22 galaxies
with known HI distributions as an example, we discuss the question of whether
this effect can be associated exclusively with external ionizing radiation, as
is commonly assumed. We show that before the surface density reaches
(the same for
galaxies of different types), it is hard to expect the gas to be fully ionized
by background radiation. For two of 13 galaxies with a sharp drop in the HI
profile, the "steepening" can actually be caused by ionization. At the same
time, for the remaining galaxies, the observed cutoff in the radial HI profile
is closer to the center than if it was a consequence of ionization by
background radiation and, therefore, it should be caused by other factors.Comment: 15 pages, 6 figure
Dust-penetrated morphology in the high-redshift universe: clues from NGC 922
Results from the Hubble Deep Field (HDF) North and South show a large
percentage of high-redshift galaxies whose appearance falls outside traditional
classification systems. The nature of these objects is poorly understood, but
sub-mm observations indicate that at least some of these systems are heavily
obscured (Sanders 2000). This raises the intriguing possibility that a
physically meaningful classification system for high-redshift galaxies might be
more easily devised at rest-frame infrared wavelengths, rather than in the
optical regime. Practical realization of this idea will become possible with
the advent of the Next Generation Space Telescope (NGST). In order to explore
the capability of NGST for undertaking such science, we present NASA-IRTF and
SCUBA observations of NGC 922, a chaotic system in our local Universe which
bears a striking resemblance to objects such as HDF 2-86 (z=0.749) in the HDF
North. If objects such as NGC 922 are common at high-redshifts, then this
galaxy may serve as a local morphological `Rosetta stone' bridging low and
high-redshift populations. In this paper we demonstrate that quantitative
measures of galactic structure are recoverable in the rest-frame infrared for
NGC 922 seen at high redshifts using NGST, by simulating the appearance of this
galaxy at redshifts z=0.7 and z=1.2 in rest-frame K'. Our results suggest that
the capability of efficiently exploring the rest-wavelength IR morphology of
high-z galaxies should probably be a key factor in deciding the final choice of
instruments for the NGST.Comment: 7 pages, 12 Figures. Accepted for publication in A&A. Better version
of the figures can be found at http://www.inaoep.mx/~puerari/ngs
Using a Data-Driven Method of Accident Analysis: A Case Study of the Human Performance Reliability (HPR) Process
PresentationHuman error and its contribution to occupational accidents and incidents has received considerable research attention in recent years. However, more research is needed into the validity, practicality, and functionality of using data-driven accident/incident analysis methods to identify factors that contribute to incidents with the greatest frequency. This paper presents a case-study of one such method: Human Performance Reliability (HPR). Methods: The authors conducted approximately 30 HPR reviews to analyze incidents that occurred at a large refining company over a three year period. Through the HPR process, the authors identified the most common human errors, other contributing factors, and the controls (SOPs, processes, programs) that failed to prevent the accidents/incidents. Results: A Chi-Square Goodness-of-Fit test and post-hoc analysis of Standard Residuals on the human error frequencies revealed the most common human errors and contributing factors, while raw frequency counts showed the most commonly associated controls (see Tables 3-6). The Chi-Square statistic was X2 = 528.58, indicating that certain errors were contributing to incidents significantly more often than others. Discussion: Early evidence supports the notion that the HPR process is an effective tool for incident analysis and subsequent continuous improvement efforts in process safety
A Dust-Penetrated Classification Scheme for Bars as Inferred from their Gravitational Force Fields
The division of galaxies into ``barred'' (SB) and ``normal'' (S) spirals is a
fundamental aspect of the Hubble galaxy classification system. This ``tuning
fork'' view was revised by de Vaucouleurs, whose classification volume
recognized apparent ``bar strength'' (SA, SAB, SB) as a continuous property of
galaxies called the ``family''. However, the SA, SAB, and SB families are
purely visual judgments that can have little bearing on the actual bar strength
in a given galaxy. Until very recently, published bar judgments were based
exclusively on blue light images, where internal extinction or star formation
can either mask a bar completely or give the false impression of a bar in a
nonbarred galaxy. Near-infrared camera arrays, which principally trace the old
stellar populations in both normal and barred galaxies, now facilitate a
quantification of bar strength in terms of their gravitational potentials and
force fields. In this paper, we show that the maximum value, Qb, of the ratio
of the tangential force to the mean radial force is a quantitative measure of
the strength of a bar. Qb does not measure bar ellipticity or bar shape, but
rather depends on the actual forcing due to the bar embedded in its disk. We
show that a wide range of true bar strengths characterizes the category ``SB'',
while de Vaucouleurs category ``SAB'' corresponds to a much narrower range of
bar strengths. We present Qb values for 36 galaxies, and we incorporate our bar
classes into a dust-penetrated classification system for spiral galaxies.Comment: Accepted for publication in the Astrophysical Journal (LaTex, 30
pages + 3 figures); Figs. 1 and 3 are in color and are also available at
http://bama.ua.edu/~rbuta/bars
Psi-floor diagrams and a Caporaso-Harris type recursion
Floor diagrams are combinatorial objects which organize the count of tropical
plane curves satisfying point conditions. In this paper we introduce Psi-floor
diagrams which count tropical curves satisfying not only point conditions but
also conditions given by Psi-classes (together with points). We then generalize
our definition to relative Psi-floor diagrams and prove a Caporaso-Harris type
formula for the corresponding numbers. This formula is shown to coincide with
the classical Caporaso-Harris formula for relative plane descendant
Gromov-Witten invariants. As a consequence, we can conclude that in our case
relative descendant Gromov-Witten invariants equal their tropical counterparts.Comment: minor changes to match the published versio
Force-Velocity Relations of a Two-State Crossbridge Model for Molecular Motors
We discuss the force-velocity relations obtained in a two-state crossbridge
model for molecular motors. They can be calculated analytically in two limiting
cases: for a large number and for one pair of motors. The effect of the
strain-dependent detachment rate on the motor characteristics is studied. It
can lead to linear, myosin-like, kinesin-like and anomalous curves. In
particular, we specify the conditions under which oscillatory behavior may be
found.Comment: 5 pages, 4 figures, REVTeX; thoroughly revised version; also
available at http://www.physik.tu-muenchen.de/~frey
Bose Metals and Insulators on Multi-Leg Ladders with Ring Exchange
We establish compelling evidence for the existence of new
quasi-one-dimensional descendants of the d-wave Bose liquid (DBL), an exotic
two-dimensional quantum phase of uncondensed itinerant bosons characterized by
surfaces of gapless excitations in momentum space [O. I. Motrunich and M. P. A.
Fisher, Phys. Rev. B {\bf 75}, 235116 (2007)]. In particular, motivated by a
strong-coupling analysis of the gauge theory for the DBL, we study a model of
hard-core bosons moving on the -leg square ladder with frustrating four-site
ring exchange. Here, we focus on four- and three-leg systems where we have
identified two novel phases: a compressible gapless Bose metal on the four-leg
ladder and an incompressible gapless Mott insulator on the three-leg ladder.
The former is conducting along the ladder and has five gapless modes, one more
than the number of legs. This represents a significant step forward in
establishing the potential stability of the DBL in two dimensions. The latter,
on the other hand, is a fundamentally quasi-one-dimensional phase that is
insulating along the ladder but has two gapless modes and incommensurate power
law transverse density-density correlations. In both cases, we can understand
the nature of the phase using slave-particle-inspired variational wave
functions consisting of a product of two distinct Slater determinants, the
properties of which compare impressively well to a density matrix
renormalization group solution of the model Hamiltonian. Stability arguments
are made in favor of both quantum phases by accessing the universal low-energy
physics with a bosonization analysis of the appropriate quasi-1D gauge theory.
We will briefly discuss the potential relevance of these findings to
high-temperature superconductors, cold atomic gases, and frustrated quantum
magnets.Comment: 33 pages, 16 figures; this is the print version, only very minor
changes from v
Design strategies for optimizing holographic optical tweezers setups
We provide a detailed account of the construction of a system of holographic
optical tweezers. While much information is available on the design, alignment
and calibration of other optical trapping configurations, those based on
holography are relatively poorly described. Inclusion of a spatial light
modulator in the setup gives rise to particular design trade-offs and
constraints, and the system benefits from specific optimization strategies,
which we discuss.Comment: 16 pages, 15 figure
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