1,106 research outputs found
QoS Supportive MAC Protocols for WSNs: Review and Evaluation
The use of wireless sensor networks technology is growing in different applications of monitoring. Since it is a relatively new technology, the interest of researchers to improve the network performance and behaviour has been enormous. In this context, new resource allocation scheme that takes into account traffic priority and load has been introduced. The evaluation of this scheme is intended to be achieved by implementing a custom simulator. This report discusses and evaluates all the important concerns needed to be considered during the development of this project. Moreover, this work also reviews the related literature in order to afford optimisations to the scheme
Three different glacier surges at a spot: What satellites observe and what not
In the Karakoram, dozens of glacier surges occurred in the past 2 decades, making the region a global hotspot. Detailed analyses of dense time series from optical and radar satellite images revealed a wide range of surge behaviour in this region: from slow advances longer than a decade at low flow velocities to short, pulse-like advances over 1 or 2 years with high velocities. In this study, we present an analysis of three currently surging glaciers in the central Karakoram: North and South Chongtar Glaciers and an unnamed glacier referred to as NN9. All three glaciers flow towards the same small region but differ strongly in surge behaviour. A full suite of satellites (e.g. Landsat, Sentinel-1 and 2, Planet, TerraSAR-X, ICESat-2) and digital elevation models (DEMs) from different sources (e.g. Shuttle Radar Topography Mission, SRTM; Satellite Pour l'Observation de la Terre, SPOT; High Mountain Asia DEM, HMA DEM) are used to (a) obtain comprehensive information about the evolution of the surges from 2000 to 2021 and (b) to compare and evaluate capabilities and limitations of the different satellite sensors for monitoring surges of relatively small glaciers in steep terrain. A strongly contrasting evolution of advance rates and flow velocities is found, though the elevation change pattern is more similar. For example, South Chongtar Glacier had short-lived advance rates above 10 yr-1, velocities up to 30 d-1, and surface elevations increasing by 170 m. In contrast, the neighbouring and 3-times-smaller North Chongtar Glacier had a slow and near-linear increase in advance rates (up to 500 yr-1), flow velocities below 1 d-1 and elevation increases up to 100 m. The even smaller glacier NN9 changed from a slow advance to a full surge within a year, reaching advance rates higher than 1 yr-1. It seems that, despite a similar climatic setting, different surge mechanisms are at play, and a transition from one mechanism to another can occur during a single surge. The sensor inter-comparison revealed a high agreement across sensors for deriving flow velocities, but limitations are found on small and narrow glaciers in steep terrain, in particular for Sentinel-1. All investigated DEMs have the required accuracy to clearly show the volume changes during the surges, and elevations from ICESat-2 ATL03 data fit neatly to the other DEMs. We conclude that the available satellite data allow for a comprehensive observation of glacier surges from space when combining different sensors to determine the temporal evolution of length, elevation and velocity changes
Colloquium: Gravitational Form Factors of the Proton
The physics of the gravitational form factors of the proton, and their
understanding within quantum chromodynamics, has advanced significantly in the
past two decades through both theory and experiment. This Colloquium provides
an overview of this progress, highlights the physical insights unveiled by
studies of gravitational form factors, and reviews their interpretation in
terms of the mechanical properties of the proton.Comment: 22 pages, 15 figure
Intrinsic vs. laboratory frame description of the deformed nucleus 48Cr
The collective yrast band of the nucleus Cr is studied using the
spherical shell model and the HFB method. Both approaches produce basically the
same axially symmetric intrinsic state up to the - accurately reproduced -
observed backbending. Agreement between both calculations extends to most
observables. The only significant discrepancy comes from the static moments of
inertia and can be attributed to the need of a more refined treatment of
pairing correlations in the HFB calculation.Comment: 4 pages, RevTeX 3.0 using psfig, 6 Postscript figures included using
uufile
Phenotypic Divergence During the Invasion of \u3cem\u3ePhyla Canescens\u3c/em\u3e in Australia and France: Evidence for Selection-Driven Evolution
Rapid adaptive evolution has been advocated as a mechanism that promotes invasion. Demonstrating adaptive evolution in invasive species requires rigorous analysis of phenotypic shifts driven by selection. Here, we document selection-driven evolution of Phyla canescens, an Argentine weed, in two invaded regions (Australia and France). Invasive populations possessed similar or higher diversity than native populations, and displayed mixed lineages from different sources, suggesting that genetic bottlenecks in both countries might have been alleviated by multiple introductions. Compared to native populations, Australian populations displayed more investment in sexual reproduction, whereas French populations possessed enhanced vegetative reproduction and growth. We partitioned evolutionary forces (selection vs. stochastic events) using two independent methods. Results of both analyses suggest that the pattern of molecular and phenotypic variability among regions was consistent with selection-driven evolution, rather than stochastic events. Our findings indicate that selection has shaped the evolution of P. canescens in two different invaded regions
Systematics of collective correlation energies from self-consistent mean-field calculations
The collective ground-state correlations stemming from low-lying quadrupole
excitations are computed microscopically. To that end, the self-consistent
mean-field model is employed on the basis of the Skyrme-Hartre-Fock (SHF)
functional augmented by BCS pairing. The microscopic-macroscopic mapping is
achieved by quadrupole-constrained mean-field calculations which are processed
further in the generator-coordinate method (GCM) at the level of the Gaussian
overlap approximation (GOA).
We study the correlation effects on energy, charge radii, and surface
thickness for a great variety of semi-magic nuclei. A key issue is to work out
the influence of variations of the SHF functional. We find that collective
ground-state correlations (GSC) are robust under change of nuclear bulk
properties (e.g., effective mass, symmetry energy) or of spin-orbit coupling.
Some dependence on the pairing strength is observed. This, however, does not
change the general conclusion that collective GSC obey a general pattern and
that their magnitudes are rather independent of the actual SHF parameters.Comment: 13 pages, 13 figure
Approximate particle number projection for finite range density dependent forces
The Lipkin-Nogami method is generalized to deal with finite range density
dependent forces. New expressions are derived and realistic calculations with
the Gogny force are performed for the nuclei Er and Er. The
sharp phase transition predicted by the mean field approximation is washed out
by the Lipkin-Nogami approach; a much better agreement with the experimental
data is reached with the new approach than with the Hartree-Fock_Bogoliubov
one, specially at high spins.Comment: 5 pages, RevTeX 3.0, 3 postscript figures included using uufiles.
Submitted to Phys. Rev. Let
Measurement of Unpolarized and Polarized Cross Sections for Deeply Virtual Compton Scattering on the Proton at Jefferson Laboratory with CLAS
This paper reports the measurement of polarized and unpolarized cross sections for the ep→e′p′γ reaction, which is composed of deeply virtual Compton scattering (DVCS) and Bethe-Heitler (BH) processes, at an electron beam energy of 5.88 GeV at the Thomas Jefferson National Accelerator Facility using the Large Acceptance Spectrometer CLAS. The unpolarized cross sections and polarized cross section differences have been measured over broad kinematics, 0.10 \u3c xB \u3c 0.58, 1.0 \u3c Q2 \u3c4.8 GeV2 and 0.09\u3c−t \u3c2.00 GeV2. The results are found to be consistent with previous CLAS data, and these new data are discussed in the framework of the generalized parton distribution approach. Calculations with two widely used phenomenological models are approximately compatible with the experimental results over a large portion of the kinematic range of the data
- …