8,882 research outputs found
DSIF station schedules
System manages Deep Space Instrumentation Facilities /DSIF/ equipment construction and modification planning. Versatile program applies to such tasks as employee time and task schedules, pay schedules, operations schedules, and plant and equipment procurement, construction, modification or service
Advanced indium antimonide monolithic charge coupled infrared imaging arrays
The continued process development of SiO2 insulators for use in advanced InSb monolithic charge coupled infrared imaging arrays is described. Specific investigations into the use of plasma enhanced chemical vapor deposited (PECVD) SiO2 as a gate insulator for InSb charge coupled devices is discussed, as are investigations of other chemical vapor deposited SiO2 materials
InSb charge coupled infrared imaging device: The 20 element linear imager
The design and fabrication of the 8585 InSb charge coupled infrared imaging device (CCIRID) chip are reported. The InSb material characteristics are described along with mask and process modifications. Test results for the 2- and 20-element CCIRID's are discussed, including gate oxide characteristics, charge transfer efficiency, optical mode of operation, and development of the surface potential diagram
Metastable Quantum Phase Transitions in a Periodic One-dimensional Bose Gas: Mean-Field and Bogoliubov Analyses
We generalize the concept of quantum phase transitions, which is
conventionally defined for a ground state and usually applied in the
thermodynamic limit, to one for \emph{metastable states} in \emph{finite size
systems}. In particular, we treat the one-dimensional Bose gas on a ring in the
presence of both interactions and rotation. To support our study, we bring to
bear mean-field theory, i.e., the nonlinear Schr\"odinger equation, and linear
perturbation or Bogoliubov-de Gennes theory. Both methods give a consistent
result in the weakly interacting regime: there exist \emph{two topologically
distinct quantum phases}. The first is the typical picture of superfluidity in
a Bose-Einstein condensate on a ring: average angular momentum is quantized and
the superflow is uniform. The second is new: one or more dark solitons appear
as stationary states, breaking the symmetry, the average angular momentum
becomes a continuous quantity, and the phase of the condensate can be
continuously wound and unwound
Universal Mandelbrot Set as a Model of Phase Transition Theory
The study of Mandelbrot Sets (MS) is a promising new approach to the phase
transition theory. We suggest two improvements which drastically simplify the
construction of MS. They could be used to modify the existing computer programs
so that they start building MS properly not only for the simplest families.
This allows us to add one more parameter to the base function of MS and
demonstrate that this is not enough to make the phase diagram connectedComment: 5 pages, 3 figure
Legacies of past land use have a stronger effect on forest carbon exchange than future climate change in a temperate forest landscape
Forest ecosystems play an important role in the global climate
system and are thus intensively discussed in the context of climate change
mitigation. Over the past decades temperate forests were a carbon (C) sink to
the atmosphere. However, it remains unclear to which degree this C uptake is
driven by a recovery from past land use and natural disturbances or ongoing
climate change, inducing high uncertainty regarding the future temperate
forest C sink. Here our objectives were (i) to investigate legacies within
the natural disturbance regime by empirically analyzing two disturbance
episodes affecting the same landscape 90 years apart, and (ii) to unravel the
effects of past land use and natural disturbances as well as the future climate
on 21st century forest C uptake by means of simulation modeling. We
collected historical data from archives to reconstruct the vegetation and
disturbance history of a forest landscape in the Austrian Alps from 1905 to
2013. The effects of legacies and climate were disentangled by individually controlling for past land use, natural disturbances, and future scenarios of
climate change in a factorial simulation study. We found only moderate
spatial overlap between two episodes of wind and bark beetle disturbance
affecting the landscape in the early 20th and 21st century,
respectively. Our simulations revealed a high uncertainty about the
relationship between the two disturbance episodes, whereas past land use
clearly increased the impact of the second disturbance episode on the
landscape. The future forest C sink was strongly driven by the cessation of
historic land use, while climate change reduced forest C uptake. Compared to
land-use change the two past episodes of natural disturbance had only
marginal effects on the future carbon cycle. We conclude that neglecting
legacies can substantially bias assessments of future forest dynamics.</p
Milk Production from Cows Grazing Perennial Ryegrass Pastures Infected with Wild or AR1 Endophyte in New Zealand
Most perennial ryegrass (Lolium perenne) cultivars in New Zealand are available with either the natural wild endophyte (Neotyphodium lolii); the AR1 novel endophyte (no lolitrem B or ergovaline production); or endophyte-free. Although wild endophyte protects ryegrass against insect attack, improving pasture persistence, it can also cause ryegrass staggers and reduced animal performance. Endophyte AR1 does not cause ryegrass staggers but still protects against insect pests such as Argentine stem weevil (Listronotus bonariensis). A 3-year farmlet experiment was carried out to evaluate the effects of AR1 and wild endophyte-infected ryegrass on pasture performance, milk production and cow health
Catastrophic regime shifts in model ecological communities are true phase transitions
Ecosystems often undergo abrupt regime shifts in response to gradual external
changes. These shifts are theoretically understood as a regime switch between
alternative stable states of the ecosystem dynamical response to smooth changes
in external conditions. Usual models introduce nonlinearities in the
macroscopic dynamics of the ecosystem that lead to different stable attractors
among which the shift takes place. Here we propose an alternative explanation
of catastrophic regime shifts based on a recent model that pictures ecological
communities as systems in continuous fluctuation, according to certain
transition probabilities, between different micro-states in the phase space of
viable communities. We introduce a spontaneous extinction rate that accounts
for gradual changes in external conditions, and upon variations on this control
parameter the system undergoes a regime shift with similar features to those
previously reported. Under our microscopic viewpoint we recover the main
results obtained in previous theoretical and empirical work (anomalous
variance, hysteresis cycles, trophic cascades). The model predicts a gradual
loss of species in trophic levels from bottom to top near the transition. But
more importantly, the spectral analysis of the transition probability matrix
allows us to rigorously establish that we are observing the fingerprints, in a
finite size system, of a true phase transition driven by background
extinctions.Comment: 19 pages, 11 figures, revised versio
Singularity theory study of overdetermination in models for L-H transitions
Two dynamical models that have been proposed to describe transitions between
low and high confinement states (L-H transitions) in confined plasmas are
analysed using singularity theory and stability theory. It is shown that the
stationary-state bifurcation sets have qualitative properties identical to
standard normal forms for the pitchfork and transcritical bifurcations. The
analysis yields the codimension of the highest-order singularities, from which
we find that the unperturbed systems are overdetermined bifurcation problems
and derive appropriate universal unfoldings. Questions of mutual equivalence
and the character of the state transitions are addressed.Comment: Latex (Revtex) source + 13 small postscript figures. Revised versio
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