52,122 research outputs found
Glacier motion estimation using SAR offset-tracking procedures
Two image-to-image patch offset techniques for
estimating feature motion between satellite synthetic aperture radar (SAR) images are discussed. Intensity tracking, based on patch intensity cross-correlation optimization, and coherence tracking, based on patch coherence optimization, are used to estimate the movement of glacier surfaces between two SAR images in both slant-range and azimuth direction. The accuracy and application range of the two methods are examined in the case of the surge of Monacobreen in Northern Svalbard between
1992 and 1996. Offset-tracking procedures of SAR images are an alternative to differential SAR interferometry for the estimation of glacier motion when differential SAR interferometry is limited by loss of coherence, i.e., in the case of rapid and incoherent flow and of large acquisition time intervals between the two SAR images. In addition, an offset-tracking procedure in the azimuth
direction may be combined with differential SAR interferometry in the slant-range direction in order to retrieve a two-dimensional displacement map when SAR data of only one orbit configuration are available
Pay, Performance, and Participation
Our chapter identifies key dimensions on which organizations make employee compensation decisions and examines the emerging research evidence on the consequences of such decisions for attitudes, behaviors, and organization performance. We provide some general suggestions that may prove helpful in future research. First, there is increased recognition that pay decisions take place in the context of implicit or explicit contracts between employees and specific organizations. As a result, we encourage researchers to continue to give greater attention to the role of organization differences in compensation. Second, because pay is multidimensional, attention should not be restricted to organization differences in pay level. Organization differences in benefits, structure, and means of recognizing individual employees contributions also warrant attention. As an example of how the focus can be expanded, we provide new empirical evidence on organization differences in the market sensitivity of pay structures. Third, we note that the success of pay programs depends not only on decisions about pay per se, but also the process used in making communicating, and administering such decisions. More broadly, the influence of contextual factors, such as the nature of other employee relations practices (e.g., staffmg, development, employment security), needs to be considered to a greater extent in compensation research. In addition to these broad suggestions, we provide specific ideas on future research directions throughout the chapter
Periodically Controlled Hybrid Systems: Verifying A Controller for An Autonomous Vehicle
This paper introduces Periodically Controlled Hybrid Automata (PCHA) for describing a class of hybrid control systems. In a PCHA, control actions occur roughly periodically while internal and input actions, may occur in the interim changing the discrete-state or the setpoint. Based on periodicity and subtangential conditions, a new sufficient condition for verifying invariance of PCHAs is presented. This technique is used in verifying safety of the planner-controller subsystem of an autonomous ground vehicle, and in deriving geometric properties of planner generated paths that can be followed safely by the controller under environmental uncertainties
Evidence for Partial Taylor Relaxation from Changes in Magnetic Geometry and Energy during a Solar Flare
Solar flares are powered by energy stored in the coronal magnetic field, a
portion of which is released when the field reconfigures into a lower energy
state. Investigation of sunspot magnetic field topology during flare activity
is useful to improve our understanding of flaring processes. Here we
investigate the deviation of the non-linear field configuration from that of
the linear and potential configurations, and study the free energy available
leading up to and after a flare. The evolution of the magnetic field in NOAA
region 10953 was examined using data from Hinode/SOT-SP, over a period of 12
hours leading up to and after a GOES B1.0 flare. Previous work on this region
found pre- and post-flare changes in photospheric vector magnetic field
parameters of flux elements outside the primary sunspot. 3D geometry was thus
investigated using potential, linear force-free, and non-linear force-free
field extrapolations in order to fully understand the evolution of the field
lines. Traced field line geometrical and footpoint orientation differences show
that the field does not completely relax to a fully potential or linear
force-free state after the flare. Magnetic and free magnetic energies increase
significantly ~ 6.5-2.5 hours before the flare by ~ 10^31 erg. After the flare,
the non-linear force-free magnetic energy and free magnetic energies decrease
but do not return to pre-flare 'quiet' values. The post-flare non-linear
force-free field configuration is closer (but not equal) to that of the linear
force-free field configuration than a potential one. However, the small degree
of similarity suggests that partial Taylor relaxation has occurred over a time
scale of ~ 3-4 hours.Comment: Accepted for Publication in Astronomy & Astrophysics. 11 pages, 11
figure
Automated Coronal Hole Identification via Multi-Thermal Intensity Segmentation
Coronal holes (CH) are regions of open magnetic fields that appear as dark
areas in the solar corona due to their low density and temperature compared to
the surrounding quiet corona. To date, accurate identification and segmentation
of CHs has been a difficult task due to their comparable intensity to local
quiet Sun regions. Current segmentation methods typically rely on the use of
single EUV passband and magnetogram images to extract CH information. Here, the
Coronal Hole Identification via Multi-thermal Emission Recognition Algorithm
(CHIMERA) is described, which analyses multi-thermal images from the
Atmospheric Image Assembly (AIA) onboard the Solar Dynamics Observatory (SDO)
to segment coronal hole boundaries by their intensity ratio across three
passbands (171 \AA, 193 \AA, and 211 \AA). The algorithm allows accurate
extraction of CH boundaries and many of their properties, such as area,
position, latitudinal and longitudinal width, and magnetic polarity of
segmented CHs. From these properties, a clear linear relationship was
identified between the duration of geomagnetic storms and coronal hole areas.
CHIMERA can therefore form the basis of more accurate forecasting of the start
and duration of geomagnetic storms
Some ground-state expectation values for the free parafermion Z(N) spin chain
We consider the calculation of ground-state expectation values for the
non-Hermitian Z(N) spin chain described by free parafermions. For N=2 the model
reduces to the quantum Ising chain in a transverse field with open boundary
conditions. Use is made of the Hellmann-Feynman theorem to obtain exact results
for particular single site and nearest-neighbour ground-state expectation
values for general N which are valid for sites deep inside the chain. These
results are tested numerically for N=3, along with how they change as a
function of distance from the boundary.Comment: 17 pages, 4 figures; extra reference
The Ionization State of Sodium in Galactic Winds
Roughly 80% of Ultraluminous Infrared Galaxies (ULIRGs) show blue shifted
absorption in the resonance lines of neutral sodium, indicating that cool winds
are common in such objects, as shown by Rupke et al and by Martin. The neutral
sodium (NaI) columns indicated by these absorption lines are ~
10^{13}-3x10^{14}/cm^2, while the bolometric luminosity varies by a factor of
only four. We show that the gas in ULIRG outflows is likely to be in
photoionization equilibrium. The very small ULIRG sample of Goldader et al.
demonstrates that the ratio of ultraviolet flux to far infrared flux varies by
a factor from object to object. While the Goldader sample does not
overlap with those of Rupke et al. and Martin, we show that such a large
variation in ultraviolet flux will produce a similar variation in the column of
neutral sodium for a fixed mass flux and density. However, if the cold gas is
in pressure equilibrium with a hot outflow with a mass loss rate similar to the
star formation rate, the range of ionization state is significantly smaller.
Measurements of the UV flux for objects in the Martin and Rupke et al. catalogs
will definitively determine if photoionization effects are responsible for the
wide variation seen in the sodium columns. If they are, a determination of the
gas density and mass loss rate in the cool winds will follow, with attendant
improvements in our understanding of wind driving mechanisms and of the effects
of galaxies on their surroundings.Comment: 14 pages, 5 figures, submitted to Ap
Direction Detector on an Excitable Field: Field Computation with Coincidence Detection
Living organisms process information without any central control unit and
without any ruling clock. We have been studying a novel computational strategy
that uses a geometrically arranged excitable field, i.e., "field computation."
As an extension of this research, in the present article we report the
construction of a "direction detector" on an excitable field. Using a numerical
simulation, we show that the direction of a input source signal can be detected
by applying the characteristic as a "coincidence detector" embedded on an
excitable field. In addition, we show that this direction detection actually
works in an experiment using an excitable chemical system. These results are
discussed in relation to the future development of "field computation."Comment: 6 pages, 3 figure
Machine Assisted Proof of ARMv7 Instruction Level Isolation Properties
In this paper, we formally verify security properties of the ARMv7 Instruction Set Architecture (ISA) for user mode executions.
To obtain guarantees that arbitrary (and unknown) user processes are able to run isolated from privileged software and other user processes, instruction level noninterference and integrity properties are provided, along with proofs that transitions to privileged modes can only occur in a controlled manner.
This work establishes a main requirement for operating system and hypervisor verification, as demonstrated for the PROSPER separation kernel. The proof is performed in the HOL4 theorem prover, taking the Cambridge model of ARM as basis.
To this end, a proof tool has been developed, which assists the verification of relational state predicates semi-automatically
The Illawarra at Work: A Summary of the Major Findings of the Illawarra Regional Workplace Industrial Relations Survey
This paper summarises the main results of the Illawarra Regional Workplace Industrial Relations Survey (IRWIRS). The data is unique in that it provides the only comprehensive and statistically reliable source of information about workplace employee relations at the regional level in Australia, and compares regional patterns with national trends. The data collected relates to industrial relations indicators, workplace ownership, market conditions, management organisation and decision- making in the workplace, among other things. The results reveal a positive pattern of employment relations in the Illawarra, distinctive in many respects from national trends.Illawarra Regional Workplace Industrial Relations Survey, workplace employee relations, Australia
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