75,015 research outputs found
Active control transport design criteria
Vehicle design considerations for active control applications to subsonic transports are examined. Active control is defined along with those functions which are considered in the study of design criteria. The FAA regulations governing transport aircraft design are briefly discussed
Understanding Floristic Diversity Though a Database of Greene County Specimens
We present a floristic list of Greene County, Arkansas, based on accessioned collections from the Arkansas State University Herbarium (STAR). Currently, there are 1569 specimens representing 540 taxa from Greene County in STAR. Using the USDA Plants Database, plant species were analyzed according to whether or not they are native to the state as well as whether or not they have been previously documented as species occurring in the county. Having analyzed all the Greene County collections from STAR, we found 225 previously undocumented species. The data suggest that most of the specimens in the STAR collection were found in wooded areas and/or near water. This may be a reflection of sampling bias as two of the primary collectors of these specimens were primarily interested in bog habitats. For this reason, the Greene County collections may not fully represent all habitats in the county, but it is likely that they are a good representation of the countyâs seeps and bogs. The STAR Herbarium is emerging as a critical resource for understanding botanical diversity in the eastern counties of Arkansas, but it is clear that additional collections are necessary to fully represent all habitats in these areas
Detailed Comparison of Next-to-Leading Order Predictions for Jet Photoproduction at HERA
The precision of new HERA data on jet photoproduction opens up the
possibility to discriminate between different models of the photon structure.
This requires equally precise theoretical predictions from perturbative QCD
calculations. In the past years, next-to-leading order calculations for the
photoproduction of jets at HERA have become available. Using the kinematic cuts
of recent ZEUS analyses, we compare the predictions of three calculations for
different dijet and three-jet distributions. We find that in general all three
calculations agree within the statistical accuracy of the Monte Carlo
integration yielding reliable theoretical predictions. In certain restricted
regions of phase space, the calculations differ by up to 5%.Comment: 10 pages, 7 eps-figures. To appear in the Proceedings of the Workshop
on ``Monte Carlo Generators for HERA Physics'', Hamburg 1998/9
Simultaneous calculation of the helical pitch and the twist elastic constant in chiral liquid crystals from intermolecular torques
We present a molecular simulation method that yields simultaneously the equilibrium pitch wave number q and the twist elastic constant K2 of a chiral nematic liquid crystal by sampling the torque density. A simulation of an untwisted system in periodic boundary conditions gives the product K2q; a further simulation with a uniform twist applied provides enough information to separately determine the two factors. We test our new method for a model potential, comparing the results with K2q from a thermodynamic integration route, and with K2 from an order fluctuation analysis. We also present a thermodynamic perturbation theory analysis valid in the limit of weak chirality
Coherent energy migration in solids: Determination of the average coherence length in oneâdimensional systems using tunable dye lasers
The coherent nature of energy propagation in solids at low temperatures was established from the time resolved response of the crystal to short optical pulses obtained from a dye laser (pumped by a nitrogen gas laser). The trapping and detrapping of the energy by shallow defects (x traps) was evident in the spectra and enabled us to extract the coherence length: lâł700 Ă
=186 molecules for the oneâdimensional triplet excitons of 1,2,4,5âtetrachlorobenzene crystals at T<4.2° K. This length which clearly exceeds the stochastic random walk limit is related to the thermalization mechanisms in this coupled excitonâtrap system, and its magnitude supports the notion that excitonâphonon coupling is responsible for the loss of coherence on very long molecular chains (trap concentration is 1/256â000)
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Layered Fabrication of Branched Networks Using Lindenmayer Systems
A current challenge impeding the growth of bone tissue engineering is the lack of
functional scaffolds of geometric sizes greater than 10mm due to the inability of cells to
survive deep within the scaffold. It is hypothesized that these scaffolds must have an
inbuilt nutrient distribution network to sustain the uniform growth of cells. In this
paper, we seek to enhance the design and layered fabrication of scaffold internal
architecture through the development of Lindenmayer systems, a graphical language
based theory to create nutrient delivery networks. The scaffolds are fabricated using the
Texas Instruments DLPâą system through UVâphotopolymerization to produce
polyethylene glycol hydrogels with internal branch structures. The paper will discuss
the Lindenmayer system, process planning algorithms, layered fabrication of samples,
challenges and future tasks.Mechanical Engineerin
Jet photoproduction and the structure of the photon
Various jet observables in photoproduction are studied and compared to data
from HERA. The feasibility of using a dijet sample for constraining the parton
distributions in the photon is then studied. For the current data the
experimental and theoretical uncertainties are comparable to the variation due
to changing the photon parton distribution set.Comment: 20 pages including 11 figures. Latex using revtex and psfig macros.
Several references added. Submitted to Phys. Rev.
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