294 research outputs found
Frost trends and their estimated impact on yield in the Australian wheatbelt
Radiant spring frosts occurring during reproductive developmental stages can result in catastrophic yield loss for wheat producers. To better understand the spatial and temporal variability of frost, the occurrence and impact of frost events on rain-fed wheat production was estimated across the Australian wheatbelt for 1957–2013 using a 0.05 ° gridded weather data set. Simulated yield outcomes at 60 key locations were compared with those for virtual genotypes with different levels of frost tolerance. Over the last six decades, more frost events, later last frost day, and a significant increase in frost impact on yield were found in certain regions of the Australian wheatbelt, in particular in the South-East and West. Increasing trends in frost-related yield losses were simulated in regions where no significant trend of frost occurrence was observed, due to higher mean temperatures accelerating crop development and causing sensitive post-heading stages to occur earlier, during the frost risk period. Simulations indicated that with frost-tolerant lines the mean national yield could be improved by up to 20 through (i) reduced frost damage (~10 improvement) and (ii) the ability to use earlier sowing dates (adding a further 10 improvement). In the simulations, genotypes with an improved frost tolerance to temperatures 1 °C lower than the current 0 °C reference provided substantial benefit in most cropping regions, while greater tolerance (to 3 °C lower temperatures) brought further benefits in the East. The results indicate that breeding for improved reproductive frost tolerance should remain a priority for the Australian wheat industry, despite warming climates
The second Konus-Wind catalog of short gamma-ray bursts
In this catalog, we present the results of a systematic study of 295 short
gamma-ray bursts (GRBs) detected by Konus-Wind (KW) from 1994 to 2010. From the
temporal and spectral analyses of the sample, we provide the burst durations,
the spectral lags, the results of spectral fits with three model functions, the
total energy fluences and the peak energy fluxes of the bursts. We discuss
evidence found for an additional power-law spectral component and the presence
of extended emission in a fraction of the KW short GRBs. Finally, we consider
the results obtained in the context of the Type I (merger-origin) / Type II
(collapsar-origin) classifications.Comment: Accepted to the Astrophysical Journal Supplement Series (7 Figures, 8
Tables
An Extended Burst Tail from SGR 1900+14 with a Thermal X-ray Spectrum
The Soft Gamma Repeater, SGR 1900+14, entered a new phase of activity in
April 2001 initiated by the intermediate flare recorded on April 18. Ten days
following this flare, we discovered an abrupt increase in the source flux
between consecutive RXTE orbits. This X-ray flux excess decayed over the next
several minutes and was subsequently linked to a high fluence burst from SGR
1900+14 recorded by other spacecraft (Ulysses and KONUS) while the SGR was
Earth-occulted for RXTE. We present here spectral and temporal analysis of both
the burst of 28 April and the long X-ray tail following it. We find strong
evidence of an exclusively thermal X-ray tail in this event and bring this
evidence to bear on other bursts and flares from SGR 1900+14 which have shown
extended X-ray excesses (e.g. 1998 August 29). We include in this comparison a
discussion of the physical origins of SGR bursts and extended X-ray tails.Comment: 27 pages, 13 figures, ApJ submissio
Spectral Cross-calibration of the Konus-Wind, the Suzaku/WAM, and the Swift/BAT Data using Gamma-Ray Bursts
We report on the spectral cross-calibration results of the Konus-Wind, the
Suzaku/WAM, and the Swift/BAT instruments using simultaneously observed
gamma-ray bursts (GRBs). This is the first attempt to use simultaneously
observed GRBs as a spectral calibration source to understand systematic
problems among the instruments. Based on these joint spectral fits, we find
that 1) although a constant factor (a normalization factor) agrees within 20%
among the instruments, the BAT constant factor shows a systematically smaller
value by 10-20% compared to that of Konus-Wind, 2) there is a systematic trend
that the low-energy photon index becomes steeper by 0.1-0.2 and Epeak becomes
systematically higher by 10-20% when including the BAT data in the joint fits,
and 3) the high-energy photon index agrees within 0.2 among the instruments.
Our results show that cross-calibration based on joint spectral analysis is an
important step to understanding the instrumental effects which could be
affecting the scientific results from the GRB prompt emission data.Comment: 82 pages, 88 figures, accepted for publication in PAS
Observations of giant outbursts from Cygnus X-1
We present interplanetary network localization, spectral, and time history
information for 7 episodes of exceptionally intense gamma-ray emission from
Cygnus X-1. The outbursts occurred between 1995 and 2003, with durations up to
\~28000 seconds. The observed 15 - 300 keV peak fluxes and fluences reached
3E-7 erg /cm2 s, and 8E-4 erg / cm2 respectively. By combining the
triangulations of these outbursts we derive an ~1700 square arcminute (3 sigma)
error ellipse which contains Cygnus X-1 and no other known high energy sources.
The outbursts reported here occurred both when Cyg X-1 was in the hard state as
well as in the soft one, and at various orbital phases. The spectral data
indicate that these outbursts display the same parameters as those of the
underlying hard and soft states, suggesting that they represent another
manifestation of these states.Comment: 27 pages, 9 figures. Revised version. Accepted for publication in the
Astrophysical Journal, tentatively scheduled for October 20, 2003 Part
Integrating the Fermi Gamma-Ray Burst Monitor into the 3rd Interplanetary Network
We are integrating the Fermi Gamma-Ray Burst Monitor (GBM) into the
Interplanetary Network (IPN) of Gamma-Ray Burst (GRB) detectors. With the GBM,
the IPN will comprise 9 experiments. This will 1) assist the Fermi team in
understanding and reducing their systematic localization uncertainties, 2)
reduce the sizes of the GBM and Large Area Telescope (LAT) error circles by 1
to 4 orders of magnitude, 3) facilitate the identification of GRB sources with
objects found by ground- and space-based observatories at other wavelengths,
from the radio to very high energy gamma-rays, 4) reduce the uncertainties in
associating some LAT detections of high energy photons with GBM bursts, and 5)
facilitate searches for non-electromagnetic GRB counterparts, particularly
neutrinos and gravitational radiation. We present examples and demonstrate the
synergy between Fermi and the IPN. This is a Fermi Cycle 2 Guest Investigator
project.Comment: 5 pages, 11 figures. 2009 Fermi Symposium. eConf Proceedings C09112
How Advanced Change Patterns Impact the Process of Process Modeling
Process model quality has been an area of considerable research efforts. In
this context, correctness-by-construction as enabled by change patterns
provides promising perspectives. While the process of process modeling (PPM)
based on change primitives has been thoroughly investigated, only little is
known about the PPM based on change patterns. In particular, it is unclear what
set of change patterns should be provided and how the available change pattern
set impacts the PPM. To obtain a better understanding of the latter as well as
the (subjective) perceptions of process modelers, the arising challenges, and
the pros and cons of different change pattern sets we conduct a controlled
experiment. Our results indicate that process modelers face similar challenges
irrespective of the used change pattern set (core pattern set versus extended
pattern set, which adds two advanced change patterns to the core patterns set).
An extended change pattern set, however, is perceived as more difficult to use,
yielding a higher mental effort. Moreover, our results indicate that more
advanced patterns were only used to a limited extent and frequently applied
incorrectly, thus, lowering the potential benefits of an extended pattern set
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