7,515 research outputs found
Evaluation of microhardness, fracture toughness and residual stress in a thermal barrier coating system: A modified Vickers indentation technique
The evolution of microhardness, fracture toughness and residual stress of an air plasma-sprayed thermal barrier coating system under thermal cycles was investigated by a modified Vickers indentation instrument coupled with three kinds of indentation models. The results show that fracture toughness on the top coating surface after thermal cycles changes from 0.64 to 3.67 MPa•m1/2, and the corresponding residual stress near the indented region varies from –36.8 to –243 MPa. For the interface region of coating and bond coat, fracture toughness in the coating close to interface ranges from 0.11 to 0.81 MPa•m 1/2, and residual stress varies from –5 to –30 MPa, which are consistent with available data. For the lateral region of coating, fracture toughness and residual stress display strong gradient characteristics along the thickness direction due to the special layered structure
Fracture characteristics of freestanding 8 wt% Y2O3-ZrO2 coatings by single edge notched beam and Vickers indentation tests
The freestanding 8 wt% Y2O3–ZrO2 (8YSZ) samples prepared by an air plasma sprayed technique were measured by single edge notched bending tests. The strain evolution and cracking near a pre-existed notch region were in-situ monitored by digital image correlation. With the help of digital image data, the critical bending loads of these notched freestanding 8YSZ samples can be accurately determined. The fracture toughness and micro-hardness of freestanding 8YSZ samples were tested by Vickers indentations. The normalized fracture toughness calculated according to the Weibull statistics is in agreement with the testing and available data. These results are instructive in predicting the lifetime and durability of thermal barrier coatings with irregular geometric structures
Characteristics of novel Ti–10Mo-xCu alloy by powder metallurgy for potential biomedical implant applications
When biomaterials are implanted in the human body, the surfaces of the implants become favorable sites for microbial adhesion and biofilm formation, causing peri-implant infection which frequently results in the failure of prosthetics and revision surgery. Ti–Mo alloy is one of the commonly used implant materials for load-bearing bone replacement, and the prevention of infection of Ti–Mo implants is therefore crucial. In this study, bacterial inhibitory copper (Cu) was added to Ti–Mo matrix to develop a novel Ti–Mo–Cu alloy with bacterial inhibitory property. The effects of Cu content on microstructure, tensile properties, cytocompatibility, and bacterial inhibitory ability of Ti–Mo–Cu alloy were systematically investigated. Results revealed that Ti–10Mo–1Cu alloy consisted of α and β phases, while there were a few Ti_{2}Cu intermetallic compounds existed for Ti–10Mo–3Cu and Ti–10Mo–5Cu alloys, in addition to α and β phases. The tensile strength of Ti–10Mo-xCu alloy increased with Cu content while elongation decreased. Ti–10Mo–3Cu alloy exhibited an optimal tensile strength of 1098.1 MPa and elongation of 5.2%. Cytocompatibility study indicated that none of the Ti–10Mo-xCu alloys had a negative effect on MC3T3-E1 cell proliferation. Bacterial inhibitory rates against S. aureus and E. coli increased with the increase in Cu content of Ti–10Mo-xCu alloy, within the ranges of 20–60% and 15–50%, respectively. Taken together, this study suggests that Ti–10Mo–3Cu alloy with high strength, acceptable elongation, excellent cytocompatibility, and the bacterial inhibitory property is a promising candidate for biomedical implant applications
Impacts of the East Asian monsoon on lower tropospheric ozone over coastal South China
The impact of the East Asian monsoon (EAM) on climatology and interannual variability of
tropospheric ozone (O3) over the coastal South China was investigated by analyzing 11 years
of ozonesonde data over Hong Kong with the aid of Lagrangian dispersion modeling of carbon
monoxide and calculation of an EAM index. It was found that the seasonal cycle of O3 in the
lower troposphere is highly related to the EAM over the study region. Ozone enhancements in
the free troposphere are associated with the monsoon-induced transport of pollutants of
continental anthropogenic and biomass burning origins. Lower tropospheric O3 levels showed
high interannual variability, with an annual averaged amplitude up to 61% of averaged
concentrations in the boundary layer (0–1 km altitudes) and 49% below 3 km altitude. In
spring and autumn, the interannual variability in boundary layer O3 levels was predominately
influenced by the EAM intensity, with high O3 mixing ratios associated with northeasterly
circulation anomalies
A global 3-D CTM evaluation of black carbon in the Tibetan Plateau
We systematically evaluate the black carbon (BC) simulations for 2006 over
the Tibetan Plateau by a global 3-D chemical transport model (CTM)
(GEOS-Chem) driven by GEOS-5 assimilated meteorological fields, using in situ
measurements of BC in surface air, BC in snow, and BC absorption aerosol
optical depth (AAOD). Using improved anthropogenic BC emission inventories
for Asia that account for rapid technology renewal and energy consumption
growth (Zhang et al., 2009; Lu et al., 2011) and improved global biomass
burning emission inventories that account for small fires (van der Werf et
al., 2010; Randerson et al., 2012), we find that model results of both BC in
surface air and in snow are statistically in good agreement with
observations (biases < 15%) away from urban centers. Model
results capture the seasonal variations of the surface BC concentrations at
rural sites in the Indo-Gangetic Plain, but the observed elevated values in
winter are absent. Modeled surface-BC concentrations are within a factor of 2 of the observations at remote sites. Part of the discrepancy is
explained by the deficiencies of the meteorological fields over the complex
Tibetan terrain. We find that BC concentrations in snow computed from
modeled BC deposition and GEOS-5 precipitation are spatiotemporally
consistent with observations (<i>r</i> = 0.85). The computed BC concentrations in
snow are a factor of 2–4 higher than the observations at several Himalayan
sites because of excessive BC deposition. The BC concentrations in snow are
biased low by a factor of 2 in the central plateau, which we attribute to
the absence of snow aging in the CTM and strong local emissions unaccounted
for in the emission inventories. Modeled BC AAOD is more than a factor of
2 lower than observations at most sites, particularly to the northwest of
the plateau and along the southern slopes of the Himalayas in winter and
spring, which is attributable in large part to underestimated emissions and
the assumption of external mixing of BC aerosols in the model. We find that
assuming a 50% increase of BC absorption associated with internal mixing
reduces the bias in modeled BC AAOD by 57% in the Indo-Gangetic Plain and
the northeastern plateau and to the northeast of the plateau, and by 16%
along the southern slopes of the Himalayas and to the northwest of the
plateau. Both surface BC concentration and AAOD are strongly sensitive to
anthropogenic emissions (from China and India), while BC concentration in
snow is especially responsive to the treatment of BC aerosol aging. We find
that a finer model resolution (0.5° × 0.667° nested over Asia) reduces the bias in modeled surface-BC concentration from
15 to 2%. The large range and non-homogeneity of discrepancies
between model results and observations of BC across the Tibetan Plateau
undoubtedly undermine current assessments of the climatic and hydrological
impact of BC in the region and thus warrant imperative needs for more extensive
measurements of BC, including its concentration in surface air and snow,
AAOD, vertical profile and deposition
Enhancement of Friction between Carbon Nanotubes: An Efficient Strategy to Strengthen Fibers
Interfacial friction plays a crucial role in the mechanical properties of
carbon nanotube based fibers, composites, and devices. Here we use molecular
dynamics simulation to investigate the pressure effect on the friction within
carbon nanotube bundles. It reveals that the intertube frictional force can be
increased by a factor of 1.5 ~ 4, depending on tube chirality and radius, when
all tubes collapse above a critical pressure and when the bundle remains
collapsed with unloading down to atmospheric pressure. Furthermore, the overall
cross-sectional area also decreases significantly for the collapsed structure,
making the bundle stronger. Our study suggests a new and efficient way to
reinforce nanotube fibers, possibly stronger than carbon fibers, for usage at
ambient conditions.Comment: revtex, 5 pages, accepted by ACS Nano 10 Dec 200
First Measurement of the Branching Fraction of the Decay psi(2S) --> tau tau
The branching fraction of the psi(2S) decay into tau pair has been measured
for the first time using the BES detector at the Beijing Electron-Positron
Collider. The result is ,
where the first error is statistical and the second is systematic. This value,
along with those for the branching fractions into e+e- and mu+mu of this
resonance, satisfy well the relation predicted by the sequential lepton
hypothesis. Combining all these values with the leptonic width of the resonance
the total width of the psi(2S) is determined to be keV.Comment: 9 pages, 2 figure
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