7,673 research outputs found
2001 ANNUAL AGRICULTURAL OUTLOOK
One word summarizes the current outlook for the U.S. economy. That word is confusion. First, we review the recent behavior of the U.S. economy. Ten years of economic expansion without a recession had led some to believe that we could have continual expansion without a recession. The year 2000 was the fourth year in a row with growth exceeding 4 percent and this was accomplished with relatively stable prices. unemployment was about 4 percent or below what many perceived as a sustainable rate of unemployment without rapid inflation. Stock market prices had increased and some consumers were spending their "new wealth." However, the stock market showed signs of weakness beginning in 1999. That weakness grew, especially for technology stocks and price volatility became much larger. Energy prices also increased in volatility with gasoline, natural gas and electric rates changing frequently except where highly regulated. The economy continued to show strength through much of the year in spite of these problems. Then a series of events led to a major shift in consumer attitudes which began in the final quarter of the year.Farm Management,
Early motor trajectories predict motor but not cognitive function in preterm- and term-born adults without pre-existing neurological conditions
Very preterm (VP; 0.05). Motor problems in childhood were homotypically associated with poorer motor competence in adulthood. Similarly, early cognitive problems were homotypically associated with adult cognitive outcomes. Thus, both motor and cognitive function should be assessed in routine follow-up during childhood
Practical applications of small-angle neutron scattering.
Recent improvements in beam-line accessibility and technology have led to small-angle neutron scattering (SANS) becoming more frequently applied to materials problems. SANS has been used to study the assembly, dispersion, alignment and mixing of nanoscale condensed matter, as well as to characterise the internal structure of organic thin films, porous structures and inclusions within steel. Using time-resolved SANS, growth mechanisms in materials systems and soft matter phase transitions can also be explored. This review is intended for newcomers to SANS as well as experts. Therefore, the basic knowledge required for its use is first summarised. After this introduction, various examples are given of the types of soft and hard matter that have been studied by SANS. The information that can be extracted from the data is highlighted, alongside the methods used to obtain it. In addition to presenting the findings, explanations are provided on how the SANS measurements were optimised, such as the use of contrast variation to highlight specific parts of a structure. Emphasis is placed on the use of complementary techniques to improve data quality (e.g. using other scattering methods) and the accuracy of data analysis (e.g. using microscopy to separately determine shape and size). This is done with a view to providing guidance on how best to design and analyse future SANS measurements on materials not listed below
Testing predictors of eruptivity using parametric flux emergence simulations
Solar flares and coronal mass ejections (CMEs) are among the most energetic
events in the solar system, impacting the near-Earth environment. Flare
productivity is empirically known to be correlated with the size and complexity
of active regions. Several indicators, based on magnetic-field data from active
regions, have been tested for flare forecasting in recent years. None of these
indicators, or combinations thereof, have yet demonstrated an unambiguous
eruption or flare criterion. Furthermore, numerical simulations have been only
barely used to test the predictability of these parameters. In this context, we
used the 3D parametric MHD numerical simulations of the self-consistent
formation of the flux emergence of a twisted flux tube, inducing the formation
of stable and unstable magnetic flux ropes of Leake (2013, 2014). We use these
numerical simulations to investigate the eruptive signatures observable in
various magnetic scalar parameters and provide highlights on data analysis
processing. Time series of 2D photospheric-like magnetograms are used from
parametric simulations of stable and unstable flux emergence, to compute a list
of about 100 different indicators. This list includes parameters previously
used for operational forecasting, physical parameters used for the first time,
as well as new quantities specifically developed for this purpose. Our results
indicate that only parameters measuring the total non-potentiality of active
regions associated with magnetic inversion line properties, such as the
Falconer parameters , , and , as well as the
new current integral and length parameters, present a
significant ability to distinguish the eruptive cases of the model from the
non-eruptive cases, possibly indicating that they are promising flare and
eruption predictors.Comment: 46 pages, 16 figures, accepted for publication in Space Weather and
Space Climate on June, 8t
Simplicial Multivalued Maps and the Witness Complex for Dynamical Analysis of Time Series
Topology based analysis of time-series data from dynamical systems is
powerful: it potentially allows for computer-based proofs of the existence of
various classes of regular and chaotic invariant sets for high-dimensional
dynamics. Standard methods are based on a cubical discretization of the
dynamics and use the time series to construct an outer approximation of the
underlying dynamical system. The resulting multivalued map can be used to
compute the Conley index of isolated invariant sets of cubes. In this paper we
introduce a discretization that uses instead a simplicial complex constructed
from a witness-landmark relationship. The goal is to obtain a natural
discretization that is more tightly connected with the invariant density of the
time series itself. The time-ordering of the data also directly leads to a map
on this simplicial complex that we call the witness map. We obtain conditions
under which this witness map gives an outer approximation of the dynamics, and
thus can be used to compute the Conley index of isolated invariant sets. The
method is illustrated by a simple example using data from the classical H\'enon
map.Comment: laTeX, 9 figures, 32 page
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