4,750 research outputs found
SR-7A aeroelastic model design report
A scale model was designed to simulate the aeroelastic characteristics and performance of the 2.74 meter (9 ft.) diameter SR-7L blade. The procedures used in this model blade design are discussed. Included in this synopsis is background information concerning scaling parameters and an explanation of manufacturing limitations. A description of the final composite model blade, made of titanium, fiberglass, and graphite, is provided. Analytical methods for determining the blade stresses, natural frequencies and mode shapes, and stability are discussed at length
Weak Olfactory Preferences of the Gall Midge Asphondylia borrichiae, Associated Fungal Endophytes and Implications on Gene Flow and Host Range Expansion
Asphondylia borrichaie is a small fly (Diptera: Cecidomyiidae) that is currently undergoing host-associated sympatric divergence. Asphondylia borrichaie is an ambrosia galler, these insects utilize a host plant for oviposition, but its offspring also rely on a symbiotic fungus (or fungal community) to promote the formation of the gall as well as serve as a food source for the developing larvae. Previous studies indicate that A. borrichaie consists of two host- associated populations based on its original host plant Borrichia frutescens (Asterales: Asteraceae), and another one from the two Iva species (I. frutescens (Asterales: Asteraceae) and I. imbricata (Asterales: Asteraceae)). Differences in development time suggest allochronic isolation as the primary mechanism promoting host-associated sympatric divergence of midge populations and A. borrichiae has been shown to display fidelity to its natal host plant genus (e.g. Borrichia vs. Iva). Effects of host range expansion on the endophytic fungal community of the galls the midge’s two primary host plants (B. frutescens and I. frutescens) have never been compared. In the current study, olfactometery trials utilizing field-collected galls/midges demonstrated a weak association for a midge’s natal host; overall midges chose their natal host plant 56.1% percent of trials compared to 43.9% for the alternative (novel) plant. However, no significant differences were found in the time taken for a midge to choose natal vs novel host. Moreover, male midges showed a stronger preference for their natal host genus than females suggesting that gene flow between host-associated populations is more likely to be limited through males than females. Although clones of B. frutescens (collected from different localities) exhibited significant differences in leaf size (but not number of serrations after more 18 months of being cultured in a common greenhouse environment, suggesting at least a partial genetic control for leaf morphology, no association was detected for midges to their specific clone of B. frutescens from the midge’s natal locality. Lastly, this study successfully cultured and sequenced the ITS region of fungi extracted from gall chambers which could then be identified it down to fungal genera using BLAST searches. These data suggest a possible association of fungal genera with each host plant: specifically, with Cladosporium spp. which was more commonly found from galls collected from B. frutescens, while Fusarium spp. was more likely to be found in galls collected from I. frutescens
Dimers on two-dimensional lattices
We consider close-packed dimers, or perfect matchings, on two-dimensional
regular lattices. We review known results and derive new expressions for the
free energy, entropy, and the molecular freedom of dimers for a number of
lattices including the simple-quartic (4^4), honeycomb (6^3), triangular (3^6),
kagome (3.6.3.6), 3-12 (3.12^2) and its dual [3.12^2], and 4-8 (4.8^2) and its
dual Union Jack [4.8^2] Archimedean tilings. The occurrence and nature of phase
transitions are also analyzed and discussed.Comment: Typos corrections in Eqs. (28), (32) and (43
A Nuclear Physics Program at the ATLAS Experiment at the CERN Large Hadron Collider
The ATLAS collaboration has significant interest in the physics of
ultra-relativistic heavy ion collisions. We submitted a Letter of Intent to the
United States Department of Energy in March 2002. The following document is a
slightly modified version of that LOI. More details are available at:
http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/SM/ionsComment: Letter of Intent submitted to the United States Department of Energy
Nuclear Physics Division in March 2002 (revised version
The Kasteleyn model and a cellular automaton approach to traffic flow
We propose a bridge between the theory of exactly solvable models and the
investigation of traffic flow. By choosing the activities in an apropriate way
the dimer configurations of the Kasteleyn model on a hexagonal lattice can be
interpreted as space-time trajectories of cars. This then allows for a
calculation of the flow-density relationship (fundamental diagram). We further
introduce a closely-related cellular automaton model. This model can be viewed
as a variant of the Nagel-Schreckenberg model in which the cars do not have a
velocity memory. It is also exactly solvable and the fundamental diagram is
calculated.Comment: Latex, 13 pages including 3 ps-figure
Theory of tricriticality for miscut surfaces
We propose a theory for the observed tricriticality in the orientational
phase diagram of Si(113) misoriented towards [001]. The systems seems to be at
or close to a very special point for long range interactions.Comment: Revtex, 1 ps figur
Electron transport properties of sub-3-nm diameter copper nanowires
Density functional theory and density functional tight-binding are applied to
model electron transport in copper nanowires of approximately 1 nm and 3 nm
diameters with varying crystal orientation and surface termination. The copper
nanowires studied are found to be metallic irrespective of diameter, crystal
orientation and/or surface termination. Electron transmission is highly
dependent on crystal orientation and surface termination. Nanowires oriented
along the [110] crystallographic axis consistently exhibit the highest electron
transmission while surface oxidized nanowires show significantly reduced
electron transmission compared to unterminated nanowires. Transmission per unit
area is calculated in each case, for a given crystal orientation we find that
this value decreases with diameter for unterminated nanowires but is largely
unaffected by diameter in surface oxidized nanowires for the size regime
considered. Transmission pathway plots show that transmission is larger at the
surface of unterminated nanowires than inside the nanowire and that
transmission at the nanowire surface is significantly reduced by surface
oxidation. Finally, we present a simple model which explains the transport per
unit area dependence on diameter based on transmission pathways results
Coulomb and Liquid Dimer Models in Three Dimensions
We study classical hard-core dimer models on three-dimensional lattices using
analytical approaches and Monte Carlo simulations. On the bipartite cubic
lattice, a local gauge field generalization of the height representation used
on the square lattice predicts that the dimers are in a critical Coulomb phase
with algebraic, dipolar, correlations, in excellent agreement with our
large-scale Monte Carlo simulations. The non-bipartite FCC and Fisher lattices
lack such a representation, and we find that these models have both confined
and exponentially deconfined but no critical phases. We conjecture that
extended critical phases are realized only on bipartite lattices, even in
higher dimensions.Comment: 4 pages with corrections and update
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