5,647 research outputs found
Precise Distributed Satellite Navigation: Differential GPS with Sensor-Coupling for Integer Ambiguity Resolution
Precise relative navigation is a critical enabler for distributed satellites
to achieve new mission objectives impossible for a monolithic spacecraft.
Carrier phase differential GPS (CDGPS) with integer ambiguity resolution (IAR)
is a promising means of achieving cm-level accuracy for high-precision
Rendezvous, Proximity-Operations and Docking (RPOD), In-Space Servicing,
Assembly and Manufacturing (ISAM) as well as satellite formation flying and
swarming. However, IAR is sensitive to received GPS signal noise, especially
under severe multi-path or high thermal noise. This paper proposes a
sensor-fusion approach to achieve IAR under such conditions in two coupling
stages. A loose coupling stage fuses through an Extended Kalman Filter the
CDGPS measurements with on-board sensor measurements such as range from
cross-links, and vision-based bearing angles. A second tight-coupling stage
augments the cost function of the integer weighted least-squares minimization
with a soft constraint function using noise-weighted observed-minus-computed
residuals from these external sensor measurements. Integer acceptance tests are
empirically modified to reflect added constraints. Partial IAR is applied to
graduate integer fixing. These proposed techniques are packaged into
flight-capable software, with ground truths simulated by the Stanford Space
Rendezvous Laboratory's S3 library using state-of-the-art force modelling with
relevant sources of errors, and validated in two scenarios: (1) a high
multi-path scenario involving rendezvous and docking in low Earth orbit, and
(2) a high thermal noise scenario relying only on GPS side-lobe signals during
proximity operations in geostationary orbit. This study demonstrates successful
IAR in both cases, using the proposed sensor-fusion approach, thus
demonstrating potential for high-precision state estimation under adverse
signal-to-noise conditions.Comment: 15 pages, 20 figures, IEEE AERO 2024 (pre-print
Health Behaviours and Its Associated Factors among Undergraduate Students in Kuala Lumpur, Malaysia
University students are asset of any nations for future development. Their current lifestyle practices, diet and physical activity can determine their future health. This study aims to assess health behaviours and its associated factors among undergraduate students from a public university in Malaysia. This cross-sectionalstudy was conducted between July to September 2015 among 1023 students using a structured questionnaire. The mean positive health practice score was 8.72/13 (±1.77). The most common positive health care practised was non-tobacco use while the least common was avoiding eating foods that contain fats and cholesterol. Year of study, self-perceived health status, internet addiction and self-perceived importance of taking health measures were significant predictors of health practice among the students. The odds ratios of 0.68, 0.49, and 0.57 indicate that the odds of students in year 2, 3 and 4, respectively practising positive health behaviours were 32% (1-0.68), 51% and 43% lower than those in Year 1. The odds of students who have self-perceived poor health status and those without Internet addiction were 95% and 25% lower in practising positive health behaviours compared to students who perceived themselves to have excellent health status and students with internet addiction, respectively. Students who perceived high importance of taking health measures were 1.77 times more likely to have positive health practices compared to those who have lower perceived importance of taking health measures. The findings of this study will enable development of targeted interventions to improve health behaviors among university students.
Keywords: health behaviours, undergraduate students, lifestyle, Malaysi
Theoretically Efficient Parallel Graph Algorithms Can Be Fast and Scalable
There has been significant recent interest in parallel graph processing due
to the need to quickly analyze the large graphs available today. Many graph
codes have been designed for distributed memory or external memory. However,
today even the largest publicly-available real-world graph (the Hyperlink Web
graph with over 3.5 billion vertices and 128 billion edges) can fit in the
memory of a single commodity multicore server. Nevertheless, most experimental
work in the literature report results on much smaller graphs, and the ones for
the Hyperlink graph use distributed or external memory. Therefore, it is
natural to ask whether we can efficiently solve a broad class of graph problems
on this graph in memory.
This paper shows that theoretically-efficient parallel graph algorithms can
scale to the largest publicly-available graphs using a single machine with a
terabyte of RAM, processing them in minutes. We give implementations of
theoretically-efficient parallel algorithms for 20 important graph problems. We
also present the optimizations and techniques that we used in our
implementations, which were crucial in enabling us to process these large
graphs quickly. We show that the running times of our implementations
outperform existing state-of-the-art implementations on the largest real-world
graphs. For many of the problems that we consider, this is the first time they
have been solved on graphs at this scale. We have made the implementations
developed in this work publicly-available as the Graph-Based Benchmark Suite
(GBBS).Comment: This is the full version of the paper appearing in the ACM Symposium
on Parallelism in Algorithms and Architectures (SPAA), 201
On electroweak baryogenesis in the littlest Higgs model with T parity
We study electroweak baryogenesis within the framework of the littlest Higgs
model with T parity. This model has shown characteristics of a strong
first-order electroweak phase transition, which is conducive to baryogenesis in
the early Universe. In the T parity symmetric theory, there are two gauge
sectors, viz., the T-even and the T-odd ones. We observe that the effect of the
T-parity symmetric interactions between the T-odd and the T-even gauge bosons
on gauge-higgs energy functional is quite small, so that these two sectors can
be taken to be independent. The T-even gauge bosons behave like the Standard
Model gauge bosons, whereas the T-odd ones are instrumental in stabilizing the
Higgs mass. For the T-odd gauge bosons in the symmetric and asymmetric phases
and for the T-even gauge bosons in the asymmetric phase, we obtain, using the
formalism of Arnold and McLerran, very small values of the ratio, (Baryon
number violation rate/Universe expansion rate). We observe that this result, in
conjunction with the scenario of inverse phase transition in the present work
and the value of the ratio obtained from the lattice result of sphaleron
transition rate in the symmetric phase, can provide us with a plausible
baryogenesis scenario.Comment: 13 pages, 2 figures, published version, references modifie
Revealing the electroweak properties of a new scalar resonance
One or more new heavy resonances may be discovered in experiments at the CERN
Large Hadron Collider. In order to determine if such a resonance is the
long-awaited Higgs boson, it is essential to pin down its spin, CP, and
electroweak quantum numbers. Here we describe how to determine what role a
newly-discovered neutral CP-even scalar plays in electroweak symmetry breaking,
by measuring its relative decay rates into pairs of electroweak vector bosons:
WW, ZZ, \gamma\gamma, and Z\gamma. With the data-driven assumption that
electroweak symmetry breaking respects a remnant custodial symmetry, we perform
a general analysis with operators up to dimension five. Remarkably, only three
pure cases and one nontrivial mixed case need to be disambiguated, which can
always be done if all four decay modes to electroweak vector bosons can be
observed or constrained. We exhibit interesting special cases of Higgs
look-alikes with nonstandard decay patterns, including a very suppressed
branching to WW or very enhanced branchings to \gamma\gamma and Z\gamma. Even
if two vector boson branching fractions conform to Standard Model expectations
for a Higgs doublet, measurements of the other two decay modes could unmask a
Higgs imposter.Comment: 23 pages, two figures; v2: minor revision and version to appear in
JHE
A New Hybrid Descent Method with Application to the Optimal Design of Finite Precision FIR Filters
In this paper, the problem of the optimal design of discrete coefficient FIR filters is considered. A novelhybrid descent method, consisting of a simulated annealing algorithm and a gradient-based method, isproposed. The simulated annealing algorithm operates on the space of orthogonal matrices and is used tolocate descent points for previously converged local minima. The gradient-based method is derived fromconverting the discrete problem to a continuous problem via the Stiefel manifold, where convergence canbe guaranteed. To demonstrate the effectiveness of the proposed hybrid descent method, several numericalexamples show that better discrete filter designs can be sought via this hybrid descent method
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Functional plasticity of antibacterial EndoU toxins.
Bacteria use several different secretion systems to deliver toxic EndoU ribonucleases into neighboring cells. Here, we present the first structure of a prokaryotic EndoU toxin in complex with its cognate immunity protein. The contact-dependent growth inhibition toxin CdiA-CTSTECO31 from Escherichia coli STEC_O31 adopts the eukaryotic EndoU fold and shares greatest structural homology with the nuclease domain of coronavirus Nsp15. The toxin contains a canonical His-His-Lys catalytic triad in the same arrangement as eukaryotic EndoU domains, but lacks the uridylate-specific ribonuclease activity that characterizes the superfamily. Comparative sequence analysis indicates that bacterial EndoU domains segregate into at least three major clades based on structural variations in the N-terminal subdomain. Representative EndoU nucleases from clades I and II degrade tRNA molecules with little specificity. In contrast, CdiA-CTSTECO31 and other clade III toxins are specific anticodon nucleases that cleave tRNAGlu between nucleotides C37 and m2 A38. These findings suggest that the EndoU fold is a versatile scaffold for the evolution of novel substrate specificities. Such functional plasticity may account for the widespread use of EndoU effectors by diverse inter-bacterial toxin delivery systems
Theoretical and Experimental Studies of Schottky Diodes That Use Aligned Arrays of Single Walled Carbon Nanotubes
We present theoretical and experimental studies of Schottky diodes that use
aligned arrays of single walled carbon nanotubes. A simple physical model,
taking into account the basic physics of current rectification, can adequately
describe the single-tube and array devices. We show that for as grown array
diodes, the rectification ratio, defined by the
maximum-to-minimum-current-ratio, is low due to the presence of m-SWNT shunts.
These tubes can be eliminated in a single voltage sweep resulting in a high
rectification array device. Further analysis also shows that the channel
resistance, and not the intrinsic nanotube diode properties, limits the
rectification in devices with channel length up to ten micrometer.Comment: Nano Research, 2010, accepte
Bis-Tridentate Iridium(III) Phosphors Bearing Functional 2-Phenyl-6-(imidazol-2-ylidene)pyridine and 2-(Pyrazol-3-yl)-6-phenylpyridine Chelates for Efficient OLEDs
Proligands to the monoanionic tridentate chelate 4-(tert-butyl)-2-(2,4-difluorophenyl)-6-(3-isopropyl-imidazol-2-ylidene)pyridine ((phpyim-H2)PF6) and dianionic tridentate chelates derived from functional 2-pyrazol-3-yl-6-phenylpyridine chelates, i.e. L1-H2–L5-H2, have been synthesized and characterized. Treatment of (phpyim-H2)PF6 with [Ir(COD)(μ-Cl)]2 in the presence of sodium acetate, followed by heating at 200 °C with 1 equiv of the dianionic chelate, afforded the respective charge-neutral, bis-tridentate Ir(III) complexes [Ir(phpyim)(Ln)] (1–5; n = 1–5). The hydride complex [Ir(phpyim)(L5-H)(H)] (6) was made when the “one-pot” reaction of (phpyim-H2)PF6, [Ir(COD)(μ-Cl)]2, and L5-H2 was carried out at 140 °C. Complex 6 is likely an intermediate in the formation of 5, as it is converted to 5 on heating to 200 °C. Compounds 1–6 have been characterized by NMR spectroscopy and, in the cases of 1, 5, and 6, by X-ray structural analysis. TD-DFT computations confirmed that the emission bands are derived from 3MLCT transitions involving the chelates L1–L5, resulting in a wide range of emission wavelengths from 473 (cyan) to 608 nm (orange-red) observed for 1 – 5. A series of green- and red-emitting organic light-emitting diodes (OLEDs) with a simplified trilayer architecture were fabricated using the as-prepared Ir(III) complexes 2 and 5, respectively. A maximum external quantum efficiency of 18.8%, a luminance efficiency of 58.5 cd/A, and a power efficiency of 57.4 lm/W were obtained for the green-emitting OLEDs (2), which compares with 15.4%, 10.4 cd/A, and 9.0 lm/W obtained for the red-emitting OLEDs (5). The high efficiencies of these OLED devices suggest great potential for these bis-tridentate Ir(III) metal phosphors in the fabrication of multicolored OLED devices
Dzyaloshinsky-Moriya antisymmetric exchange coupling in cuprates: Oxygen effects
We revisit a problem of Dzyaloshinsky-Moriya antisymmetric exchange coupling
for a single bond in cuprates specifying the local spin-orbital contributions
to Dzyaloshinsky vector focusing on the oxygen term. The Dzyaloshinsky vector
and respective weak ferromagnetic moment is shown to be a superposition of
comparable and, sometimes, competing local Cu and O contributions. The
intermediate oxygen O Knight shift is shown to be an effective tool to
inspect the effects of Dzyaloshinsky-Moriya coupling in an external magnetic
field. We predict the effect of oxygen weak antiferromagnetism in
edge-shared CuO chains due to uncompensated oxygen Dzyaloshinsky vectors.
Finally, we revisit the effects of symmetric spin anisotropy, in particular,
those directly induced by Dzyaloshinsky-Moriya coupling.Comment: 12 pages, 2 figures, submitted to JET
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