12,190 research outputs found
Experimentally determined wear behavior of an Al2O3-SiC composite from 25 to 1200 C
The sliding wear behavior of a self-mated alumina-silicon carbide whisker toughened composite was studied using optical, scanning electron (SEM) and transmission electron (TEM) microscopy. Because of its excellent strength and toughness properties this composite material is under consideration for use in heat engine applications for sliding contacts which operate at elevated temperatures. The composite's wear behavior and especially its wear mechanisms are not well understood. Pin-on-disk specimens were slid in air at 2.7 m/s sliding velocity, under a 26.5-N load, at temperatures 25 to 1200 C. Pin wear increased with increasing temperature. Based upon the microscopic analyses, the wear mechanism seems to be loosening of the reinforcing whiskers due to frictional and bulk heating. This leads to whisker pullout and increased wear
Sliding wear of self-mated Al2O3-SiC whisker reinforced composites at 23-1200 C
Microstructural changes occurring during sliding wear of self-mated Al2O3-SiC whisker reinforced composites were studied using optical, scanning electron microscopy, and transmission electron microscopy. Pin-on-disk specimens were slid in air at 2.7 m/sec sliding velocity under a 26.5 N load for 1 hr. Wear tests were conducted at 23, 600, 800, and 1200 C. Mild wear with a wear factor of 2.4 times 10(exp -7) to 1.5 times 10(exp -6) cu mm/Nm was experienced at all test temperatures. The composite shows evidence of wear by fatigue mechanisms at 800 C and below. Tribochemical reaction (SiC oxidation and reaction of SiO2 and Al2O3) leads to intergranular failure at 1200 C. Distinct microstructural differences existing at each test temperature are reported
Evaluating the summer night sky brightness at a research field site on Lake Stechlin in northeastern Germany
We report on luminance measurements of the summer night sky at a field site
on a freshwater lake in northeastern Germany (Lake Stechlin) to evaluate the
amount of artificial skyglow from nearby and distant towns in the context of a
planned study on light pollution. The site is located about 70 km north of
Berlin in a rural area possibly belonging to one of the darkest regions in
Germany. Continuous monitoring of the zenith sky luminance between June and
September 2015 was conducted utilizing a Sky Quality Meter. With this device,
typical values for clear nights in the range of 21.5-21.7
magarcsec were measured, which is on the order of the natural sky
brightness during starry nights. On overcast nights, values down to 22.84
magarcsec were obtained, which is about one third as bright as on
clear nights. The luminance measured on clear nights as well as the darkening
with the presence of clouds indicate that there is very little influence of
artificial skyglow on the zenith sky brightness at this location. Furthermore,
fish-eye lens sky imaging luminance photometry was performed with a digital
single-lens reflex camera on a clear night in the absence of moonlight. The
photographs unravel several distant towns as possible sources of light
pollution on the horizon. However, the low level of artificial skyglow makes
the field site at Lake Stechlin an excellent location to study the effects of
skyglow on a lake ecosystem in a controlled fashion.Comment: 20 pages, 8 figures, Journal of Quantitative Spectroscopy and
Radiative Transfer 201
Five-Dimensional Unification of the Cosmological Constant and the Photon Mass
Using a non-Riemannian geometry that is adapted to the 4+1 decomposition of
space-time in Kaluza-Klein theory, the translational part of the connection
form is related to the electromagnetic vector potential and a Stueckelberg
scalar. The consideration of a five-dimensional gravitational action functional
that shares the symmetries of the chosen geometry leads to a unification of the
four-dimensional cosmological term and a mass term for the vector potential.Comment: 8 pages, LaTe
Precision isotope shift measurements in Ca using highly sensitive detection schemes
We demonstrate an efficient high-precision optical spectroscopy technique for
single trapped ions with non-closed transitions. In a double-shelving
technique, the absorption of a single photon is first amplified to several
phonons of a normal motional mode shared with a co-trapped cooling ion of a
different species, before being further amplified to thousands of fluorescence
photons emitted by the cooling ion using the standard electron shelving
technique. We employ this extension of the photon recoil spectroscopy technique
to perform the first high precision absolute frequency measurement of the
D P transition in Ca,
resulting in a transition frequency of kHz.
Furthermore, we determine the isotope shift of this transition and the
S P transition for Ca,
Ca and Ca ions relative to Ca with an
accuracy below 100 kHz. Improved field and mass shift constants of these
transitions as well as changes in mean square nuclear charge radii are
extracted from this high resolution data
A chromatin modifying enzyme, SDG8, is involved in morphological, gene expression, and epigenetic responses to mechanical stimulation
Thigmomorphogenesis is viewed as being a response process of acclimation to short repetitive bursts of mechanical stimulation or touch. The underlying molecular mechanisms that coordinate changes in how touch signals lead to long-term morphological changes are enigmatic. Touch responsive gene expression is rapid and transient, and no transcription factor or DNA regulatory motif has been reported that could confer a genome wide mechanical stimulus. We report here on a chromatin modifying enzyme, SDG8/ASHH2, which can regulate the expression of many touch responsive genes identified in Arabidopsis. SDG8 is required for the permissive expression of touch induced genes; and the loss of function of sdg8 perturbs the maximum levels of induction on selected touch gene targets. SDG8 is required to maintain permissive H3K4 trimethylation marks surrounding the Arabidopsis touch-inducible gene TOUCH 3 (TCH3), which encodes a calmodulin-like protein (CML12). The gene neighboring was also slightly down regulated, revealing a new target for SDG8 mediated chromatin modification. Finally, sdg8 mutants show perturbed morphological response to wind-agitated mechanical stimuli, implicating an epigenetic memory-forming process in the acclimation response of thigmomorphogenesis
Adaptive grid methods for Q-tensor theory of liquid crystals : a one-dimensional feasibility study
This paper illustrates the use of moving mesh methods for solving partial differential equation (PDE) problems in Q-tensor theory of liquid crystals. We present the results of an initial study using a simple one-dimensional test problem which illustrates the feasibility of applying adaptive grid techniques in such situations. We describe how the grids are computed using an equidistribution principle, and investigate the comparative accuracy of adaptive and uniform grid strategies, both theoretically and via numerical examples
Gambel’S Quail: A History of Research and Management at the Oracle Junction Study Area in Arizona
We analyzed current as well as historic call-count survey data, check station harvest data, season length, winter precipitation, and daily bag limits in the Oracle Junction Study Area, Arizona to verify factors affecting annual Gambel’s quail (Callipepla gambelii) harvest. Gambel’s quail is the only one of the 9 species of wild gallinaceous game birds found in Arizona endemic to the Sonoran Desert. Oracle Junction has been of particular importance to quail hunters, scientists, researchers, and managers because it has a consistent history of call-count surveys, open hunting seasons, hunter-harvest check stations, and available precipitation data. Oracle Junction provides a valuable ‘experiment’ of Gambel quail harvest management in Arizona
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