1,200 research outputs found
Techniques for assessing the performance of a landscape-based sediment source and transport model: sensitivity trials and physical methods
Widespread degradation of aquatic habitat and water quality has occurred since European settlement of Australia. Repairing this degradation is expensive and hence on-ground management needs to be carefully focussed. The Sediment River Network model, SedNet, used for the estimation of the sources and transport of sediment spatially and at catchment scales, potentially provides a useful tool to assist land managers in focusing this work. The complete model, whilst broadly applied has not been systematically tested to assess its accuracy or sensitivity to its various model components. The aim of this paper is to propose a framework for such testing. Results from the work will be used to prioritise data acquisition, and improve the structure and parameterisation of the model where necessary. The research is also particularly relevant for shifting application of the model from continental to catchment scales. The testing will comprise two components - sensitivity assessment and accuracy assessment. This paper provides a brief introduction to the SedNet model and a framework for assessing the model. Examples of sensitivity assessment and accuracy assessment are provided and discussed
Generalized Arago-Fresnel laws: The EME-flow-line description
We study experimentally and theoretically the influence of light polarization
on the interference patterns behind a diffracting grating. Different states of
polarization and configurations are been considered. The experiments are
analyzed in terms of electromagnetic energy (EME) flow lines, which can be
eventually identified with the paths followed by photons. This gives rise to a
novel trajectory interpretation of the Arago-Fresnel laws for polarized light,
which we compare with interpretations based on the concept of "which-way" (or
"which-slit") information.Comment: 14 pages, 6 figure
Mixed Weyl Symbol Calculus and Spectral Line Shape Theory
A new and computationally viable full quantum version of line shape theory is
obtained in terms of a mixed Weyl symbol calculus. The basic ingredient in the
collision--broadened line shape theory is the time dependent dipole
autocorrelation function of the radiator-perturber system. The observed
spectral intensity is the Fourier transform of this correlation function. A
modified form of the Wigner--Weyl isomorphism between quantum operators and
phase space functions (Weyl symbols) is introduced in order to describe the
quantum structure of this system. This modification uses a partial Wigner
transform in which the radiator-perturber relative motion degrees of freedom
are transformed into a phase space dependence, while operators associated with
the internal molecular degrees of freedom are kept in their original Hilbert
space form. The result of this partial Wigner transform is called a mixed Weyl
symbol. The star product, Moyal bracket and asymptotic expansions native to the
mixed Weyl symbol calculus are determined. The correlation function is
represented as the phase space integral of the product of two mixed symbols:
one corresponding to the initial configuration of the system, the other being
its time evolving dynamical value. There are, in this approach, two
semiclassical expansions -- one associated with the perturber scattering
process, the other with the mixed symbol star product. These approximations are
used in combination to obtain representations of the autocorrelation that are
sufficiently simple to allow numerical calculation. The leading O(\hbar^0)
approximation recovers the standard classical path approximation for line
shapes. The higher order O(\hbar^1) corrections arise from the noncommutative
nature of the star product.Comment: 26 pages, LaTeX 2.09, 1 eps figure, submitted to 'J. Phys. B.
Conceptual learning : the priority for higher education
The common sense notion of learning as the all-pervasive acquisition of new behaviour and knowledge, made vivid by experience, is an incomplete characterisation, because it assumes that the learning of behaviour and the learning of knowledge are indistinguishable, and that acquisition constitutes learning without reference to transfer. A psychological level of analysis is used to argue that conceptual learning should have priority in higher education
Open Clusters IC 4665 and Cr 359 and a Probable Birthplace of the Pulsar PSR B1929+10
Based on the epicyclic approximation, we have simulated the motion of the
young open star clusters IC 4665 and Collinder 359. The separation between the
cluster centers is shown to have been minimal 7 Myr ago, 36 pc. We have
established a close evolutionary connection between IC 4665 and the
Scorpius-Centaurus association -- the separation between the centers of these
structures was pc 15 Myr ago. In addition, the center of IC 4665
at this time was near two well-known regions of coronal gas: the Local Bubble
and the North Polar Spur. The star HIP 86768 is shown to be one of the
candidates for a binary (in the past) with the pulsar PSR B1929+10. At the
model radial velocity of the pulsar km s, a close
encounter of this pair occurs in the vicinity of IC 4665 at a time of -1.1 Myr.
At the same time, using currently available data for the pulsar B1929+10 at its
model radial velocity km s, we show that the hypothesis
of Hoogerwerf et al. (2001) about the breakup of the Oph--B1929+10
binary in the vicinity of Upper Scorpius (US) about 0.9 Myr ago is more
plausible.Comment: 19 pages, 8 figure
Detection of the lithium depletion boundary in the young open cluster IC 4665
The so-called lithium depletion boundary (LDB) provides a secure and
independent tool for deriving the ages of young open clusters.In this context,
our goal is to determine membership for a sample of 147 photometrically
selected candidates of the young open cluster IC 4665 and to use confirmed
members to establish an age based on the LDB. Employing the FLAMES multi-object
spectrograph on VLT/UT2, we have obtained intermediate-resolution spectra of
the cluster candidates. The spectra were used to measure radial velocities and
to infer the presence of the Li I 670.8 nm doublet and Halpha emission. We have
identified 39 bona fide cluster members based on radial velocity, Halpha
emission, and Li absorption. The mean radial velocity of IC 4665 is found to be
vrad=-15.95 +/- 1.13 km/s. Confirmed cluster members display a sharp transition
in magnitude between stars with and without lithium, both in the Im vs. Im-z
and in the Ks vs. Im-Ks diagrams.From this boundary, we deduce a cluster age of
27.7^(+4.2)_(-3.5) +/- 1.1 +/- 2 Myr. IC 4665 is the fifth cluster for which an
LDB age has been determined, and it is the youngest cluster among these five.
Thus, the LDB is established from relatively bright stars still in the
contracting pre-main sequence phase. The mass of the boundary is M*=0.24 +/-
0.04 Msun. The LDB age agrees well with the ages derived from isochrone fitting
of both low and high mass, turn-off stars, a result similar to what is found in
the slightly older NGC 2547.Comment: 13 pages, A&A in pres
Vanishing spin alignment : experimental indication of triaxial nuclear molecule
Fragment-fragment- coincidences have been measured for at an energy corresponding to the population of a conjectured
resonance in Ni. Fragment angular distributions as well as -ray
angular correlations indicate that the spin orientations of the outgoing
fragments are perpendicular to the orbital angular momentum. This differs from
the and the resonances, and
suggests two oblate nuclei interacting in an equator-to-equator
molecular configuration.Comment: 14 pages standard REVTeX file, 3 ps Figures -- Accepted for
publication in Physical Review C (Rapid Communication
Spectroscopy of Very Low Mass Stars and Brown Dwarfs in IC2391: Lithium depletion and Halpha emission
We have obtained intermediate-resolution optical spectroscopy of 44 candidate
very low mass members of the nearby young open cluster IC2391. Of these, 26
spectra are totally new, 14 were already analyzed in a previous paper and
another four are in common.
These spectra, taken at the Cerro Tololo 4-meter and Magellan I and II
telescopes, allow us to confirm 33 of them as likely cluster members, based on
their spectral types, presence of Li, and Halpha emission. Among these new
cluster members is CTIO-160 (M7), the first IC2391 candidate to satisfy all
criteria for being a substellar member of the cluster, including detection of
the Li 6708A doublet. With the enlarged membership, we are able to locate the
lithium depletion boundary of the cluster more reliably than in the past. Based
on comparison to several theoretical models, we derive an age of 50+-5 Myr for
IC2391. We also estimate new ages for the Alpha Per and Pleiades clusters; our
ages are 85+-10 Myr and 130+-20 Myr, respectively. We derive an estimate of the
initial mass function of IC2391 that extends to below the substellar limit, and
compare it to those of other well-studied young open clusters. The index of the
power law mass function for IC2391 is alpha=0.96+-0.12, valid in the range 0.5
to 0.072 M(sun).Comment: Astrophysical Journal, accepted June 18, 200
Notulae to the Italian flora of algae, bryophytes, fungi and lichens: 6
In this contribution, new data concerning bryophytes, fungi, and lichens of the Italian flora are presented. It includes new records and confirmations for the bryophyte genera Barbula, Fissidens, Gymnostomum, Jungermannia, Riccia, and Scapania, the fungal genera Hyalopsora and Urocystis and the lichen genera Arthothelium, Chaenotheca, Lepraria, Lobaria, Miriquidica, Parmelia, Rinodina, Solenopsora, Thelopsis and Xanthoparmelia
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