921 research outputs found
Reliability studies of integrated modular engine system designs
A study was performed to evaluate the reliability of Integrated Modular Engine (IME) concepts. Comparisons were made between networked IME systems and non-networked discrete systems using expander cycle configurations. Both redundant and non-redundant systems were analyzed. Binomial approximation and Markov analysis techniques were employed to evaluate total system reliability. In addition, Failure Modes and Effects Analyses (FMEA), Preliminary Hazard Analyses (PHA), and Fault Tree Analysis (FTA) were performed to allow detailed evaluation of the IME concept. A discussion of these system reliability concepts is also presented
Shot noise detection in hBN-based tunnel junctions
High quality Au/hBN/Au tunnel devices are fabricated using transferred
atomically thin hexagonal boron nitride as the tunneling barrier. All tunnel
junctions show tunneling resistance on the order of several
k/m. Ohmic I-V curves at small bias with no signs of
resonances indicate the sparsity of defects. Tunneling current shot noise is
measured in these devices, and the excess shot noise shows consistency with
theoretical expectations. These results show that atomically thin hBN is an
excellent tunnel barrier, especially for the study of shot noise properties,
and this can enable the study of tunneling density of states and shot noise
spectroscopy in more complex systems.Comment: 20 pages, 4 figure
Effects Of Coal Fly-Ash Disposal On Water Chemistry in an Intradunal Wetland at Indiana Dunes
An intradunal wetland within the Indiana Dunes National Lakeshore on the south shore of Lake Michigan was flooded for 15 years by seepage from fly-ash settling ponds located adjacent to the park. Studies were undertaken to determine the effects of the seepage on water chemistry in the flooded wetlands. These water chemistry conditions have been correlated to ongoing studies of soil contamination and secondary succession in the wetland basin following cessation of seepage. The seepage increased the concentrations of calcium, potassium, sulfate, aluminum, boron, iron, manganese, molybdenum, nickel, strontium, and zinc in ground water and surface water downgradient from the settling ponds. Chemical interactions with aquifer materials, particularly organic matter, significantly limit the transport of aluminum, iron, nickel, and zinc in this system. The organic soils of the dewatered wetland basin now contain elevated concentrations of aluminum, boron, manganese, and zinc that are potentially phytotoxic under the low pH (\u3c4) conditions that exist. Plant growth and secondary succession were affected by the soil chemistry of the dewatered wetlands
Rocket engine system reliability analyses using probabilistic and fuzzy logic techniques
The reliability of rocket engine systems was analyzed by using probabilistic and fuzzy logic techniques. Fault trees were developed for integrated modular engine (IME) and discrete engine systems, and then were used with the two techniques to quantify reliability. The IRRAS (Integrated Reliability and Risk Analysis System) computer code, developed for the U.S. Nuclear Regulatory Commission, was used for the probabilistic analyses, and FUZZYFTA (Fuzzy Fault Tree Analysis), a code developed at NASA Lewis Research Center, was used for the fuzzy logic analyses. Although both techniques provided estimates of the reliability of the IME and discrete systems, probabilistic techniques emphasized uncertainty resulting from randomness in the system whereas fuzzy logic techniques emphasized uncertainty resulting from vagueness in the system. Because uncertainty can have both random and vague components, both techniques were found to be useful tools in the analysis of rocket engine system reliability
Longitudinal phase space manipulation in energy recovering linac-driven free-electron lasers
Energy recovering an electron beam after it has participated in a
free-electron laser (FEL) interaction can be quite challenging because of the
substantial FEL-induced energy spread and the energy anti-damping that occurs
during deceleration. In the Jefferson Lab infrared FEL driver-accelerator, such
an energy recovery scheme was implemented by properly matching the longitudinal
phase space throughout the recirculation transport by employing the so-called
energy compression scheme. In the present paper,after presenting a
single-particle dynamics approach of the method used to energy-recover the
electron beam, we report on experimental validation of the method obtained by
measurements of the so-called "compression efficiency" and "momentum
compaction" lattice transfer maps at different locations in the recirculation
transport line. We also compare these measurements with numerical tracking
simulations.Comment: 31 pages, 13 figures, submitted to Phys. Rev. Special Topics A&
Nanostructure Investigations of Nonlinear Differential Conductance in NdNiO Thin Films
Transport measurements on thin films of NdNiO reveal a crossover to a
regime of pronounced nonlinear conduction below the well-known metal-insulator
transition temperature. The evolution of the transport properties at
temperatures well below this transition appears consistent with a gradual
formation of a gap in the hole-like Fermi surface of this strongly correlated
system. As is decreased below the nominal transition temperature, transport
becomes increasily non-Ohmic, with a model of Landau-Zener breakdown becoming
most suited for describing characteristics as the temperature approaches
2~K.Comment: 18 pages, 6 figures, accepted for publication in PR
Electron-electron interaction corrections to the thermal conductivity in disordered conductors
We evaluate the electron-electron interaction corrections to the electronic
thermal conductivity in a disordered conductor in the diffusive regime. We use
a diagrammatic many-body method analogous to that of Altshuler and Aronov for
the electrical conductivity. We derive results in one, two and three dimensions
for both the singlet and triplet channels, and in all cases find that the
Wiedemann-Franz law is violated.Comment: 8 pages, 2 figures Typos corrected in formulas (15) and (A.4) and
Table 1; discussion of previous work in introduction extended; reference
clarifying different definitions of parameter F adde
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