1,949 research outputs found
A Method for Designing Conforming Folding Propellers
As the aviation vehicle design environment expands due to the in flux of new technologies, new methods of conceptual design and modeling are required in order to meet the customer's needs. In the case of distributed electric propulsion (DEP), the use of high-lift propellers upstream of the wing leading edge augments lift at low speeds enabling smaller wings with sufficient takeoff and landing performance. During cruise, however, these devices would normally contribute significant drag if left in a fixed or windmilling arrangement. Therefore, a design that stows the propeller blades is desirable. In this paper, we present a method for designing folding-blade configurations that conform to the nacelle surface when stowed. These folded designs maintain performance nearly identical to their straight, non-folding blade counterparts
Dynamics of Resonances in Strongly Interacting Systems
The effects of the propagation of particles which have a finite life-time and
an according broad distribution in their mass spectrum are discussed in the
context of a transport descriptions. In the first part some example cases of
mesonic modes in nuclear matter at finite densities and temperatures are
presented. These equilibrium calculations illustrate the dynamical range of
spectral distributions to be adequately covered by non-equilibrium description
of the dynamics of two nuclei colliding at high energies. The second part
addresses the problem of transport descriptions which properly account for the
damping width of the particles. A systematic and general gradient approximation
is presented in the form of diagrammatic rules which permit to derive a
self-consistent transport scheme from the Kadanoff--Baym equation. The scheme
is conserving and thermodynamically consistent provided the self-energies are
obtained within the Phi-derivable two-particle irreducible (2PI) method of
Baym. The merits, the limitations and partial cures of the limitations of this
transport scheme are discussed in detail.Comment: To appear in the proceedings of the International Conference
"Progress in Nonequilibrium Green's Functions III", Kiel, 22.-26. August 200
Early cell loss associated with mesenchymal stem cell cardiomyoplasty
Background: Human mesenchymal stem cells (hMSCs) show potential for therapeutic cellular cardiomyoplasty. However, a range of delivery methods, including direct intramyocardial injection, have resulted in poor engraftment in vivo. We used the in vivo rat heart model to study hMSC engraftment and retention in a normal beating heart. Materials and Methods: HMSCs transfected with green fluorescent protein were injected into the left ventricle (LV) of immunocompetent rats. Hearts were cryopreserved 30 minutes (Group A), 24 hours (Group B), and 5 days (Group C) post hMSC delivery. HMSC retention was estimated using confocal fluorescence microscopy and immunohistochemistry. Measured values were compared to projected GFP-positive cellular volumes. Immunohistochemical analyses probed for the presence of human cells with human prolyl hydroxylase beta (p4hβ) and an immune response with murine monocyte/macrophage antigen (CD68). Results: HMSC retention decreased significantly from 30 minutes to 5 days
(p<0.05). In Group A the projected GFP positive cellular volume of 31% correlated with measured values and was significantly greater than the 1% predicted cellular volume in Group C. Moreover, human p4hβ was detected in Groups A and B, and not in Group C. Conversely, CD68 was detected in Groups B and C and not in Group A. Conclusions: In immunocompetent rats, engraftment and retention of hMSCs delivered intramyocardially significantly declines over a five day period. The influx of monocytes/macrophages suggests an unfavorable micro-environment for exogenous stem cell survival, confirmed by the absence of human cells detected five days post injection
The synergistic response of primary production in grasslands to combined nitrogen and phosphorus addition is caused by increased nutrient uptake and retention
Background and aims A synergistic response of aboveground plant biomass production to combined nitrogen (N) and phosphorus (P) addition has been observed in many ecosystems, but the underlying mechanisms and their relative importance are not well known. We aimed at evaluating several mechanisms that could potentially cause the synergistic growth response, such as changes in plant biomass allocation, increased N and P uptake by plants, and enhanced ecosystem nutrient retention.
Methods We studied five grasslands located in Europe and the USA that are subjected to an element addition experiment composed of four treatments: control (no element addition), N addition, P addition, combined NP addition.
Results Combined NP addition increased the total plant N stocks by 1.47 times compared to the N treatment, while total plant P stocks were 1.62 times higher in NP than in single P addition. Further, higher N uptake by plants in response to combined NP addition was associated with reduced N losses from the soil (evaluated based on soil δ15N) compared to N addition alone, indicating a higher ecosystem N retention. In contrast, the synergistic growth response was not associated with significant changes in plant resource allocation.
Conclusions Our results demonstrate that the commonly observed synergistic effect of NP addition on aboveground biomass production in grasslands is caused by enhanced N uptake compared to single N addition, and increased P uptake compared to single P addition, which is associated with a higher N and P retention in the ecosystem
Multibaryons with heavy flavors in the Skyrme model
We investigate the possible existence of multibaryons with heavy flavor
quantum numbers using the bound state approach to the topological soliton model
and the recently proposed approximation for multiskyrmion fields based on
rational maps. We use an effective interaction lagrangian which consistently
incorporates both chiral symmetry and the heavy quark symmetry including the
corrections up to order 1/m_Q. The model predicts some narrow heavy flavored
multibaryon states with baryon number four and seven.Comment: 8 pages, no figures, RevTe
Review of Speculative "Disaster Scenarios" at RHIC
We discuss speculative disaster scenarios inspired by hypothetical new
fundamental processes that might occur in high energy relativistic heavy ion
collisions. We estimate the parameters relevant to black hole production; we
find that they are absurdly small. We show that other accelerator and
(especially) cosmic ray environments have already provided far more auspicious
opportunities for transition to a new vacuum state, so that existing
observations provide stringent bounds. We discuss in most detail the
possibility of producing a dangerous strangelet. We argue that four separate
requirements are necessary for this to occur: existence of large stable
strangelets, metastability of intermediate size strangelets, negative charge
for strangelets along the stability line, and production of intermediate size
strangelets in the heavy ion environment. We discuss both theoretical and
experimental reasons why each of these appears unlikely; in particular, we know
of no plausible suggestion for why the third or especially the fourth might be
true. Given minimal physical assumptions the continued existence of the Moon,
in the form we know it, despite billions of years of cosmic ray exposure,
provides powerful empirical evidence against the possibility of dangerous
strangelet production.Comment: 28 pages, REVTeX; minor revisions for publication (Reviews of Modern
Physics, ca. Oct. 2000); email to [email protected]
The OPERA experiment Target Tracker
The main task of the Target Tracker detector of the long baseline neutrino
oscillation OPERA experiment is to locate in which of the target elementary
constituents, the lead/emulsion bricks, the neutrino interactions have occurred
and also to give calorimetric information about each event. The technology used
consists in walls of two planes of plastic scintillator strips, one per
transverse direction. Wavelength shifting fibres collect the light signal
emitted by the scintillator strips and guide it to both ends where it is read
by multi-anode photomultiplier tubes. All the elements used in the construction
of this detector and its main characteristics are described.Comment: 25 pages, submitted to Nuclear Instrument and Method
Development of a Multi-Phase Mission Planning Tool for NASA X-57 Maxwell
The physical design and operation of electric aircraft like NASA Maxwell X-57 are significantly different than conventionally fueled aircraft. Operational optimization will require close coupling of aerodynamics, propulsion, and power. To address the uncertainty of electric aircraft operation, a system level Mission Planning Tool is developed to simulate all aircraft trajectory phases: taxi, motor run-up, takeoff, climb, cruise, and descent. The Mission Planning Tool captures performance parameters at each point of the trajectory including battery state of charge, the temperatures of components in the electrical system, and propulsion system thrust. This work describes the modeling of each mission phase, and compares the results of simulating a user-specified trajectory, and using a collocated optimal control approach to determine an optimal trajectory. The results show that optimization of the mission show a significant increase in the final battery state of charge over the user- specified simulation strategy. These results will inform the operation of the NASA Maxwell X-57 test flights that will take place this year
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