26,269 research outputs found
Investigation of new radar-data-reduction techniques used to determine drag characteristics of a free-flight vehicle
An investigation was conducted of new techniques used to determine the complete transonic drag characteristics of a series of free-flight drop-test models using principally radar tracking data. The full capabilities of the radar tracking and meteorological measurement systems were utilized. In addition, preflight trajectory design, exact kinematic equations, and visual-analytical filtering procedures were employed. The results of this study were compared with the results obtained from analysis of the onboard, accelerometer and pressure sensor data of the only drop-test model that was instrumented. The accelerometer-pressure drag curve was approximated by the radar-data drag curve. However, a small amplitude oscillation on the latter curve precluded a precise definition of its drag rise
Solving the Resource Constrained Project Scheduling Problem with Generalized Precedences by Lazy Clause Generation
The technical report presents a generic exact solution approach for
minimizing the project duration of the resource-constrained project scheduling
problem with generalized precedences (Rcpsp/max). The approach uses lazy clause
generation, i.e., a hybrid of finite domain and Boolean satisfiability solving,
in order to apply nogood learning and conflict-driven search on the solution
generation. Our experiments show the benefit of lazy clause generation for
finding an optimal solutions and proving its optimality in comparison to other
state-of-the-art exact and non-exact methods. The method is highly robust: it
matched or bettered the best known results on all of the 2340 instances we
examined except 3, according to the currently available data on the PSPLib. Of
the 631 open instances in this set it closed 573 and improved the bounds of 51
of the remaining 58 instances.Comment: 37 pages, 3 figures, 16 table
Excited state baryon spectroscopy from lattice QCD
We present a calculation of the Nucleon and Delta excited state spectrum on
dynamical anisotropic clover lattices. A method for operator construction is
introduced that allows for the reliable identification of the continuum spins
of baryon states, overcoming the reduced symmetry of the cubic lattice. Using
this method, we are able to determine a spectrum of single-particle states for
spins up to and including J = 7/2, of both parities, the first time this has
been achieved in a lattice calculation. We find a spectrum of states
identifiable as admixtures of SU(6) x O(3) representations and a counting of
levels that is consistent with the non-relativistic constituent quark
model. This dense spectrum is incompatible with quark-diquark model solutions
to the "missing resonance problem" and shows no signs of parity doubling of
states.Comment: 29 pages, 18 figure
Distal occurrence of mid-Holocene Whakatane Tephra on the Chatham Islands, New Zealand, and potential for cryptotephra studies
The Whakatane Tephra, a rhyolitic tephra erupted ca. 5500 cal. BP from Okataina Volcanic Centre, central North Island, has been identified on the Chatham Islands which lie ˜900 km east of Christchurch, New Zealand. The visible tephra layer, ˜5 mm in thickness and preserved within peat on Pitt Island, was identified using both radiocarbon dating and analysis of glass shards by electron microprobe. Whakatane Tephra is the first Holocene tephra to be identified on the Chatham Islands, and it is the most distal Holocene tephra yet recorded in the New Zealand region, being ˜850 km from source. The Pitt Island occurrence extends the tephra's dispersal area markedly, by an order of magnitude, possibly to ˜300,000 km2. An estimated dispersal index (D) of approximately 105 km2 indicates that the eruption generated a very high plinian column, possibly exceeding ˜30 km in height, with strong winds blowing the ash plume southeastwards. This new discovery of distal Whakatane Tephra as a thin but visible layer strongly implies that cryptotephras are likely to be preserved on the Chatham Islands and within adjacent ocean floor sediments. Therefore the potential exists to develop enhanced cryptotephrostratigraphic records from these distal areas, which in turn would help facilitate precise correlation via tephrochronology of palaeoenvironmental records (such as NZ-INTIMATE) from mainland New Zealand, the southwest Pacific Ocean, and the Chatham Islands
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The Borderline Between Subsymbolic and Symbolic Processing: A Developmental Cognitive Neuroscience Approach
Ideas, empirical data and methodologies from a broad range of disciplines are deployed in exploring the functional borderline between subsymbolic and symbolic processing in human cognition. Initial clarification of functional relationships between the two forms of representation involves a brain monitoring study based on the concept of 'semantic transparency.' The search for further clarification focusses on two major issues, the ontogenetic and phylogenetic origins of local neural areas and processes underlying formation of distal associations between them. Pursuing these objectives has proved to be a challenging, interdisciplinary enterprise. A model of development of local neural areas is presented which assigns a critical role to astrocytes and their interaction with adjacent neurons. An extension to include the phylogenetic dimension, draws on the concept of 'cortical inheritance', a largely ignored aspect of genetic theory. An account of distal association formation involves co-option of hippocampal place fields far a new use
Observation of Single Transits in Supercooled Monatomic Liquids
A transit is the motion of a system from one many-particle potential energy
valley to another. We report the observation of transits in molecular dynamics
(MD) calculations of supercooled liquid argon and sodium. Each transit is a
correlated simultaneous shift in the equilibrium positions of a small local
group of particles, as revealed in the fluctuating graphs of the particle
coordinates versus time. This is the first reported direct observation of
transit motion in a monatomic liquid in thermal equilibrium. We found transits
involving 2 to 11 particles, having mean shift in equilibrium position on the
order of 0.4 R_1 in argon and 0.25 R_1 in sodium, where R_1 is the nearest
neighbor distance. The time it takes for a transit to occur is approximately
one mean vibrational period, confirming that transits are fast.Comment: 19 pages, 8 figure
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