1,788 research outputs found
Fretting wear of TiN PVD coating under variable relative humidity conditions – development of a “composite” wear law
Fretting is defined as a small oscillatory displacement between two contacting bodies. The
interface is damaged by debris generation and its ejection from the contact area. The
application of hard coatings is an established solution to protect against fretting wear. For this
study the TiN hard coating manufactured by a PVD method has been selected, and tested
against a polycrystalline alumina smooth ball. A fretting test programme has been carried out
at a frequency of 5 Hz, 100 N normal load, 100 μm displacement amplitude and at five values
of relative humidity: 10, 30, 50, 70 and 90% at a temperature of 296 K. The intensity of the
wear process is shown to be significantly dependent on the environmental conditions. A
dissipated energy approach has been employed in this study to quantify wear rates of the hard
coating. The approach predicts wear kinetics under constant medium relative humidity in a
stable manner. It has been shown that an increase of relative humidity promotes the formation
of hydrate structures at the interface and modifies the third body rheology. This phenomenon
has been characterised by the evolution of wear kinetics associated with a significant variation
of the corresponding energy wear coefficient. Hence, a ‘composite’ wear law, integrating the
energy wear coefficient as a function of relative humidity, is introduced. It permits a
prediction of wear under variable relative humidity conditions from 10 to 90% within a single
fretting test. The stability of this approach is demonstrated by comparing various variable
relative humidity sequences
ENERGY TRANSFER IN TRIMERIC C-PHYCOCYANIN STUDIED BY PICOSECOND FLUORESCENCE KINETICS
The excited state kinetics of trimeric C-phycocyanin from Mastigocladus laminosus has been measured as a function of the emission and excitation wavelength by the single-photon timing technique with picosecond resolution and simultaneous data analysis. A fast decay component of 22 ps (C-phycocyanin with linker peptides) and 36 ps (C-phycocyanin lacking linker peptides) is attributed to efficient energy transfer from sensitizing to fluorescing chromophores. At long detection wavelengths the fast decay components are found to turn into a rise term. This finding further corroborates the concept of intramolecular energy transfer. Previous reports on the conformational heterogeneity of the chromophores and/or proteins in C-phycocyanin are confirmed. Our data also provide indications for the importance of the uncoloured linker peptides for this heterogeneity
A study of the break-up characteristics of Chena River Basin using ERTS imagery
The author has identified the following significant results. The Chena River Basin was selected because of the availability of ground truth data for comparison. Very good agreement for snow distribution and rates of ablation was found between the ERTS-1 imagery, the snowmelt model, and field measurements. Monitoring snowmelt rates for relatively small basins appears to be practical. The main limitation of the ERTS-1 imagery is the interval of coverage. More frequent overflights providing coverage are needed for the study of transient hydrologic events. ERTS-1 data is most useful when used in conjunction with snowmelt prediction models and existing snow course data. These results should prove very useful in preliminary assessment of hydrologic conditions in ungaged watersheds and will provide a tool for month-to-month volume forecasting
Break-up characteristics of the Chena River watershed, central Alaska
The author has identified the following significant results. The snow melt for a small watershed (5130 sq km) in Central Alaska was successfully monitored with ERTS-1 imagery. Aerial photography was used as supporting data for periods without satellite coverage. Comparison both with actual measurements and with a computer model showed good agreement
Order-disorder transition in nanoscopic semiconductor quantum rings
Using the path integral Monte Carlo technique we show that semiconductor
quantum rings with up to six electrons exhibit a temperature, ring diameter,
and particle number dependent transition between spin ordered and disordered
Wigner crystals. Due to the small number of particles the transition extends
over a broad temperature range and is clearly identifiable from the electron
pair correlation functions.Comment: 4 pages, 5 figures, For recent information on physics of small
systems see http://www.smallsystems.d
Energy levels and far-infrared spectroscopy for two electrons in a semiconductor nanoring
The effects of electron-electron interaction of a two-electron nanoring on
the energy levels and far-infrared (FIR) spectroscopy have been investigated
based on a model calculation which is performed within the exactly numerical
diagonalization. It is found that the interaction changes the energy spectra
dramatically, and also shows significant influence on the FIR spectroscopy. The
crossings between the lowest spin-singlet and triplet states induced by the
coulomb interaction are clearly revealed. Our results are related to the
experiment recently carried out by A. Lorke et al. [Phys. Rev. Lett. 84, 2223
(2000)].Comment: 17 pages, 6 figures, revised and accepted by Phys. Rev. B (Dec. 15
Jahn-Teller stabilization of a "polar" metal oxide surface: Fe3O4(001)
Using ab initio thermodynamics we compile a phase diagram for the surface of
Fe3O4(001) as a function of temperature and oxygen pressures. A hitherto
ignored polar termination with octahedral iron and oxygen forming a wave-like
structure along the [110]-direction is identified as the lowest energy
configuration over a broad range of oxygen gas-phase conditions. This novel
geometry is confirmed in a x-ray diffraction analysis. The stabilization of the
Fe3O4(001)-surface goes together with dramatic changes in the electronic and
magnetic properties, e.g., a halfmetal-to-metal transition.Comment: 4 pages, 4 figure
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Extracellular vesicles swarm the cancer microenvironment: from tumor–stroma communication to drug intervention
Intercellular communication sets the pace for transformed cells to survive and to thrive. Extracellular vesicles (EVs), such as exosomes, microvesicles and large oncosomes, are involved in this process shuttling reciprocal signals and other molecules between transformed and stromal cells, including fibroblasts, endothelial and immune cells. As a result, these cells are adapted or recruited to a constantly evolving cancer microenvironment. Moreover, EVs take part in the response to anticancer therapeutics not least by promoting drug resistance throughout the targeted tumor. Finally, circulating EVs can also transport important molecules to remote destinations in order to prime metastatic niches in an otherwise healthy tissue. Although the understanding of EV biology remains a major challenge in the field, their characteristics create new opportunities for advances in cancer diagnostics and therapeutics
The Sphingosine-1-phospate receptor 1 mediates S1P action during cardiac development
<p>Abstract</p> <p>Background</p> <p>Sphingosine-1-phosophate (S1P) is a biologically active sphingolipid metabolite that influences cellular events including differentiation, proliferation, and migration. S1P acts through five distinct cell surface receptors designated S1P<sub>1-5</sub>R, with S1P<sub>1</sub>R having the highest expression level in the developing heart. S1P<sub>1</sub>R is critical for vascular maturation, with its loss leading to embryonic death by E14.5; however, its function during early cardiac development is not well known. Our previous studies demonstrated that altered S1P levels adversely affects atrioventricular (AV) canal development <it>in vitro</it>, with reduced levels leading to cell death and elevated levels inhibiting cell migration and endothelial to mesenchymal cell transformation (EMT).</p> <p>Results</p> <p>We determined, by real-time PCR analysis, that S1P<sub>1</sub>R was expressed at least 10-fold higher than other S1P receptors in the developing heart. Immunohistochemical analysis revealed S1P<sub>1</sub>R protein expression in both endothelial and myocardial cells in the developing atrium and ventricle. Using AV canal cultures, we observed that treatment with either FTY720 (an S1P<sub>1,3,4,5</sub>R agonist) or KRP203 (an S1P<sub>1</sub>R-specific agonist) caused similar effects on AV canal cultures as S1P treatment, including induction of cell rounding, inhibition of cell migration, and inhibition of EMT. <it>In vivo</it>, morphological analysis of embryonic hearts at E10.5 revealed that S1P<sub>1</sub>R-/- hearts were malformed with reduced myocardial tissue. In addition to reduced myocardial tissue, E12.5 S1P<sub>1</sub>R-/- hearts had disrupted morphology of the heart wall and trabeculae, with thickened and disorganized outer compact layer and reduced fibronectin (FN) deposition compared to S1P<sub>1</sub>R+/+ littermates. The reduced myocardium was accompanied by a decrease in cell proliferation but not an increase in apoptosis.</p> <p>Conclusions</p> <p>These data indicate that S1P<sub>1</sub>R is the primary mediator of S1P action in AV canal cultures and that loss of S1P<sub>1</sub>R expression <it>in vivo </it>leads to malformed embryonic hearts, in part due to reduced fibronectin expression and reduced cell proliferation.</p
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