37,705 research outputs found
Leaf cuticular morphology links Platanaceae and Proteaceae
Int. J. Plant Sci. 166(5):843–855. © 2005 by The University of Chicago.The leaf cuticular morphology of extant species of Platanus was investigated using light and scanning electron microscopy. All species are shown to possess trichome bases of the same type as those commonly found in Proteaceae. Of particular significance are compound forms that consist of an annular surface scar associated with more than one underlying epidermal cell. These are found on the adaxial leaf surfaces of all species of Platanus and are also clearly evident on the abaxial surface of Platanus orientalis. This type of trichome base is therefore interpreted as the first detected nonreproductive morphological synapomorphy linking Proteaceae and Platanaceae. Also, the laterocytic, sometimes paracytic, or anomocytic arrangement of subsidiary cells in Platanus is distinct from the general state in Proteaceae, which is brachyparacytic and presumably derived. In Bellendena, possibly the most basal genus of extant Proteaceae, subsidiary cell arrangements resemble those of Platanus. These results are discussed with respect to leaf fossil records of Proteales, where it is concluded that the combination of brachyparacytic stomata and compound trichome bases is strong evidence for Proteaceae.Raymond J. Carpenter, Robert S. Hill, and Gregory J. Jorda
The SEASAT-A synthetic aperture radar design and implementation
The SEASAT-A synthetic aperture imaging radar system is the first imaging radar system intended to be used as a scientific instrument designed for orbital use. The requirement of the radar system is to generate continuous radar imagery with a 100 kilometer swath with 25 meter resolution from an orbital altitude of 800 kilometers. These requirements impose unique system design problems and a description of the implementation is given. The end-to-end system is described, including interactions of the spacecraft, antenna, sensor, telemetry link, recording subsystem, and data processor. Some of the factors leading to the selection of critical system parameters are listed. The expected error sources leading to degradation of image quality are reported as well as estimate given of the expected performance from data obtained during a ground testing of the completed subsystems
Explicit correlation and basis set superposition error: The structure and energy of carbon dioxide dimer
We have investigated the slipped parallel and t-shaped structures of carbon dioxide dimer [(CO₂)₂] using both conventional and explicitly correlated coupled cluster methods, inclusive and exclusive of counterpoise (CP) correction. We have determined the geometry of both structures with conventional coupled cluster singles doubles and perturbative triples theory [CCSD(T)] and explicitly correlated cluster singles doubles and perturbative triples theory [CCSD(T)-F12b] at the complete basis set (CBS) limits using custom optimization routines. Consistent with previous investigations, we find that the slipped parallel structure corresponds to the global minimum and is 1.09 kJ mol⁻¹ lower in energy. For a given cardinal number, the optimized geometries and interaction energies of (CO₂)₂ obtained with the explicitly correlated CCSD(T)-F12b method are closer to the CBS limit than the corresponding conventional CCSD(T) results. Furthermore, the magnitude of basis set superposition error (BSSE) in the CCSD(T)-F12b optimized geometries and interaction energies is appreciably smaller than the magnitude of BSSE in the conventional CCSD(T) results. We decompose the CCSD(T) and CCSD(T)-F12b interaction energies into the constituent HF or HF CABS, CCSD or CCSD-F12b, and (T) contributions. We find that the complementary auxiliary basis set (CABS) singles correction and the F12b approximation significantly reduce the magnitude of BSSE at the HF and CCSD levels of theory, respectively. For a given cardinal number, we find that non-CP corrected, unscaled triples CCSD(T)-F12b/VXZ-F12 interaction energies are in overall best agreement with the CBS limit
Fundamental Bounds on First Passage Time Fluctuations for Currents
Current is a characteristic feature of nonequilibrium systems. In stochastic
systems, these currents exhibit fluctuations constrained by the rate of
dissipation in accordance with the recently discovered thermodynamic
uncertainty relation. Here, we derive a conjugate uncertainty relationship for
the first passage time to accumulate a fixed net current. More generally, we
use the tools of large-deviation theory to simply connect current fluctuations
and first passage time fluctuations in the limit of long times and large
currents. With this connection, previously discovered symmetries and bounds on
the large-deviation function for currents are readily transferred to first
passage times.Comment: 7 pages including S
Proof of the Finite-Time Thermodynamic Uncertainty Relation for Steady-State Currents
The thermodynamic uncertainty relation offers a universal energetic
constraint on the relative magnitude of current fluctuations in nonequilibrium
steady states. However, it has only been derived for long observation times.
Here, we prove a recently conjectured finite-time thermodynamic uncertainty
relation for steady-state current fluctuations. Our proof is based on a
quadratic bound to the large deviation rate function for currents in the limit
of a large ensemble of many copies.Comment: 3 page
Still the century of ‘new’ environmental policy instruments? Exploring patterns of innovation and continuity
This article re-examines the political interest in and use of ‘new' environmental policy instruments (NEPIs) and other non-regulatory modes of governance. It starts by taking stock of the dynamic debate that has emerged around this topic since the turn of the century. It then contextualizes that debate by examining subsequent challenges to, and transformations in state-led governing and the widely acknowledged rise of 'new governance' more generally. It highlights the mismatch between: (a) the animated discussion of new instruments amongst policy makers and academics; and (b), the less active adoption and performance of them in practice. It makes an overall assessment of the role of instruments - both ‘old' and ‘new' - in the wider debate about governance, and suggests some steps that could be taken by both practitioners and scholars better to understand and possibly even utilise more NEPIs in the future
The Global 21-cm Signal in the Context of the High-z Galaxy Luminosity Function
Motivated by recent progress in studies of the high- Universe, we build a
new model for the global 21-cm signal that is explicitly calibrated to
measurements of the galaxy luminosity function (LF) and further tuned to match
the Thomson scattering optical depth of the cosmic microwave background,
. Assuming that the galaxy population can be smoothly
extrapolated to higher redshifts, the recent decline in best-fit values of
and the inefficient heating induced by X-ray binaries (HMXBs; the
presumptive sources of the X-ray background at high-) imply that the
entirety of cosmic reionization and reheating occurs at redshifts . In contrast to past global 21-cm models, whose (
MHz) absorption features and strong mK emission features were driven
largely by the assumption of efficient early star-formation and X-ray heating,
our new fiducial model peaks in absorption at MHz at a depth of
mK and has a negligible emission component. As a result, a strong
emission signal would provide convincing evidence that HMXBs are not the only
drivers of cosmic reheating. Shallow absorption troughs should accompany strong
heating scenarios, but could also be caused by a low escape fraction of
Lyman-Werner photons. Generating signals with troughs at MHz
requires a floor in the star-formation efficiency in halos below , which is equivalent to steepening the faint-end of the galaxy LF.
These findings demonstrate that the global 21-cm signal is a powerful
complement to current and future galaxy surveys and efforts to better
understand the interstellar medium in high- galaxies.Comment: 17 pages, 9 figures, in pres
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