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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2005.11.002 Byline: N. Yan (a), F. Leblanc (a), E. Chassefiere (b) Keywords: Mercury; Atmospheres; dynamics Abstract: We have developed a 1D thermal model of Mercury's regolith, in order to simulate the heat diffusion in the upper subsurface (first 10 m). We assume in our model that the thermophysical properties of the Hermean regolith are similar to those of the lunar regolith. We apply our thermal model to the Caloris basin which slopes induce distortions of the surface temperature compared to results obtained for a perfect spherical planet. This thermal model is then coupled with a 3D Monte Carlo model of Mercury's sodium exosphere [Leblanc, F., Johnson, R.E., 2003. Icarus 164, 261-281; Leblanc, F., Delcourt, D., Johnson, R.E., 2003b. J. Geophys. Res. 108 (E12), doi:10.1029/2003JE002151/.5136], in order to describe the signatures of Caloris basin on Mercury's sodium exosphere in term of temporal and spatial variabilities. In particular, we find a motion of the maxima of sodium density in the exosphere towards the Northern hemisphere similar to the one observed by Potter et al. [Potter, A.E., Morgan, T.H., Killen, R.M., 1999. Planet. Space Sci., 47, 1441-1449] but did not reproduce the observed change of the emission brightness. The main conclusion of this study is that the Caloris basin-exosphere relations might be observable from the Earth which we hope will motivate new observations of Mercury's exosphere. Author Affiliation: (a) Service d'Aeronomie du CNRS/IPSL, Verrieres-Le-Buisson, France (b) Service d'Aeronomie du CNRS/IPSL, Paris, France Article History: Received 23 July 2005; Revised 19 October 2005

The thermal expansion and thermal diffusion properties of Fe−Al alloys were measured using dilatometric and laser flash methods. At two allotropic transformation temperatures, the length change of the rapidly solidified pure Fe by injection casting deviates from that of the pure Fe by heating-cooling processing in a dilatometer. The ferro-/paramagnetic transition and second order transition do not influence the thermal expansion behaviors of Fe−Al alloys as temperature increases from 473 to 1373 K. The thermal expansion coefficients of Fe 70 Al 30 , Fe 60 Al 40 and Fe 55 Al 45 alloys are apparently larger than those of Fe 25 Al 75 and Fe 90 Al 10 alloys. Once temperature exceeds 877 K, the thermal expansion coefficients of Fe-Al alloys are enhanced with the increase of Al content, except for Fe 25 Al 75 alloy owing to the large packing factor of FeAl 3 crystal structure. In the temperature range from 309 to 877 K, the thermal diffusivity as a function of temperature decreases in the sequence of Fe 90 Al 10, Fe 55 Al 45 , Fe 60 Al 40 , Fe 70 Al 30 and Fe 25 Al 75 , and their values are lower than that of pure Fe at the same temperatures. As temperature increases, the thermal diffusivity values of Fe−Al alloys increase, except that of Fe 90 Al 10 alloy decreases in the temperature range from 294 to 979 K and then increases once temperature further increases to 1078 K because of the ferro-/paramagnetic transition. Their thermal expansion coefficient and thermal diffusivity serve as linear or polynomial functions of temperature. [ABSTRACT FROM AUTHOR]

This paper studies the absolute thickness measurement of pyrolytic graphite spheroids (GSs) by using STEM-EELS mode with log-ratio method and Kramers-Kroning (K-K) method, taking the measured thickness from TEM image as reference that is the diameter of GSs ranging from 60 to 250 nm. The effect of collection semi-angle (β) on thickness measurement has been investigated. It is found that in general the thickness obtained by K-K analysis with surface effect corrected shows the best accuracy, followed by K-K sum rule and then log-ratio method for the three different collection semi-angles of 12.4, 17.3 and 21.1 mrad applied. Of these angles, the smallest one gives an overestimated result and the largest one gives an underestimated result, whereas between the two, the angle of 17.3 mrad that is about 2x convergence semi-angle (9.0 mrad) is identified as more appropriate for K-K analysis. The surface-scattering correction, inelastic mean free path of GS and effect of refractive index n on thickness measurement for different β angles are also investigated. Moreover, the optical property deduced from the data collected at the center of graphite spheroid, which is related to its microstructure, is characterized by K-K analysis. [ABSTRACT FROM AUTHOR]

Abstract: To assess the potential risk of resistance development in Aspergillus flavus to pyrimethanil, five highly pyrimethanil-resistant (PyrR) mutants (RF > 996.2) were obtained after UV-mutagenesis and tested for fitness parameters and aflatoxin B1 production. All five mutant strains had mycelial growth rate, sporulation and aflatoxin production similar to or even higher than the wild-type parent strain, which indicated that pyrimethanil possesses a high risk in the development of resistance in A. flavus. Comparing the sequences of four key enzymes cystathionine β-lyase (CBL), cystathionine γ-synthase (CGS), methionine sulfoxide reductase (MsrB), and sulfate permease (SP2) involved in the biosynthesis and metabolism of methionine and sulfate assimilation revealed that no amino acid difference was found between the mutant and wild-type parent strains, suggesting that the four enzymes might not be related to the anilinopyrimidines (APs) resistance in A. flavus. [Copyright &y& Elsevier]

Abstract: The oxidation resistance of ultrafine diamonds (UFDs) was improved by encapsulating UFDs into silica shells forming core/shell structures with a PVP-aided method. Meanwhile, the dispersion stability of the UFDs in the inorganic salt aqueous solution was also improved greatly. In addition, adopting the silica-coated UFD aqueous suspension including multi-component inorganic salts, the coated UFDs–vitrified bond composite powders with higher homogeneity were obtained by using a polyacrylamide gel method, which was used for manufacturing the vitrified-bonded UFD wheels. The porous specimens of the UFD grinding wheels were fabricated with the above composite powders at low temperature in the air and in a muffle furnace. The results suggested that the porosity, bulk density and bending strength of the specimens were 36.3%, 1.71g/cm−3 and 62.9MPa, respectively. Moreover, no obvious aggregation and degradation of UFDs were observed in the above UFD specimens. These results demonstrate a new pathway of preparing multifunctional nanostructure with a low-aggregation and high oxidation resistance that can be applied for manufacturing vitrified-bonded UFD wheels. [Copyright &y& Elsevier]

Abstract: The macrosegregation and solidification processes of ternary Co43Cu40Pb17 alloy have been investigated under the containerless processing condition in drop tube. The addition of Pb element is found to be quite effective to promote the phase separation of Co–Cu alloy, resulting in a macroscopic segregation pattern in ternary Co43Cu40Pb17 alloy. The rapidly solidified alloy droplets are characterized by core–shell structures due to the combined effects of reduced gravity and containerless state during free fall. When the droplet diameter is smaller than 450μm, a kind of three-layer core/shell structure is formed, which consists of a Co-rich core, a Cu-rich intermediate layer and a Pb-rich surface shell. EDS analyses show that the Pb solute has a stronger affinity with Cu-rich liquid and a repulsive interaction with Co-rich liquid. The solidification process of Co43Cu40Pb17 ternary alloy involves two successive phase separation events, a subsequent peritectic transformation and a final monotectic transformation. [Copyright &y& Elsevier]

Abstract: The atomic structural characteristics of amorphous Ge–Te thin films were studied using the reverse Monte-Carlo simulations based on the electron diffraction data. The results reveal that the fraction of Ge in Ge x Te1− x tunes the local structural configurations greatly, as well as the amount and volumes of the voids. It further shows that large amounts of Te atoms that do not bond with Ge in non-stoichiometric Ge x Te1− x discretely distributed in Ge0.4Te0.6 but clustered in Ge0.3Te0.7. These differences give a good understanding on the dramatic change of the crystallization behaviors of Ge x Te1− x alloys. [Copyright &y& Elsevier]

Abstract: The crystallization processes of Si–Sb thin films containing different amounts of Si were investigated by in situ transmission electron microscopy (thermal annealing and electron beam irradiation). It was found that increase in the Si content significantly improve the thermal stability of Si x Sb100−x thin films and changes the crystallization behaviour from growth-dominated to nucleation-dominated, thus leading to the refinement of the grain size. Further analysis shows that phase separation occurs if the Si content increases by more than 18.1%, resulting in the coexistence of high-Si amorphous regions and low-Si crystalline regions. Our results suggest a critical Si content, below which phase separations can be prevented. [Copyright &y& Elsevier]

Purpose: This study aims to investigate μ-calpain expression profiles in the anterior temporal neocortex in patients with intractable epilepsy, and to determine whether its pattern of expression is related to pathological changes seen in these patients.Methods: The study subjects consisted of 30 patients with intractable epilepsy and a control group of 10 patients with brain trauma who underwent resection of the anterior temporal lobe. μ-Calpain expression in surgically resected anterior temporal cortices of patients with intractable epilepsy were analyzed using the RT-PCR, Western blot, immunohistochemistry and immunofluorescence staining. GFAP expression was detected by immunohistochemical staining. The related pro-inflammatory cytokines were quantified by elisa. Clinicopathological characteristics were evaluated by HE staining.Results: Analysis by Western blot and RT-PCR revealed that inactive μ-calpain expression and the calpain-cleaved spectrin fragment in surgically resected anterior temporal cortices of patients with intractable epilepsy were significantly increased compared to the tissues from corresponding regions of the control group. Immunohistological staining demonstrated that μ-calpain was overexpressed in the cell cytoplasm of neurons and glial cells in patients with intractable epilepsy and GFAP was overexpressed in the cell cytoplasm of glial cells in patients with intractable epilepsy. The level of pro-inflammatory cytokines, such as IL-1β, IL-6 and TGF-β1 were significantly increased in patients with intractable epilepsy. HE staining indicated μ-calpain overexpression is an independent prognostic factor for pathological changes such as neuronal loss, neuronal degeneration, gliosis and astrocytosis.Conclusion: These data suggest that overexpression of μ-calpain is relationship with intractable epilepsy as well as the clinicopathological characteristics in these patients. [ABSTRACT FROM AUTHOR]

Abstract: The surface temperature of Mercury will be monitored by the IR radiometer on board the MPO orbiter of the BepiColombo mission. These results are expected to provide information about regolith thermal and thermo-optical properties at the surface, but also in the near subsurface. The presence of physical heterogeneities, resulting in discontinuities of the vertical profiles of subsurface physical parameters (like thermal conductivity, heat capacity, porosity, etc.) is expected to imprint its signature on the time evolution of surface temperature, in particular at twilight, when the temperature does rapidly vary, and during the night. It might as well affect the absolute level of surface temperature, on both dayside and nightside, due to possible horizontal variations of thermal inertia, because of topography and/or geographical variations of regolith textural properties. We have therefore developed a thermal model of Mercury’s regolith which includes radiative and conductive effects, and tests the effect of various subsurface inhomogeneities on the observed temperature curves. Such a model describes the diurnal variation of the surface temperature and of the temperature profile in the first meters below the surface. This model has been tested with respect to known measurements of Mercury’s surface temperature [Chase, S.C., Miner, Jr., E.D., Morrison, D. et al. Mariner 10 infrared radiometer results: temperatures and thermal properties of the surface of Mercury. Icarus 28, 655–578, 1976] and previous existing models [Hale, A.S., Hapke, B. A time-dependent model of radiative and conductive thermal energy transport in planetary regoliths with applications to the Moon and Mercury. Icarus 156, 318–334, 2002]. [Copyright &y& Elsevier]

Highlights: [•] HFS of the macaque hippocampus markedly reduced KA-induced seizure activity. [•] HFS afforded marked protection against neuronal cell death following KA treatment. [•] HFS attenuated KA-induced changes in apoptosis-related proteins. [ABSTRACT FROM AUTHOR]

In the present paper, discrete element method (DEM) was employed to investigate the effect of pigment morphology on packing dynamics and compressive behavior of paper coating layers in calendering process. Spherical, platy, and needle-like particles, representing GCC, delaminated clay, and aragonite PCC pigments, were considered in this study. For each particle shape, the compression of coating structures formed by mono-sized and poly-dispersed pigments were modeled. Stress–strain behavior of the coating layers and in-plane and out-of-plane movements of the pigment particles during the compression were computed under the same maximum compressive stress. Simulation results revealed that the in-plane movements of the pigment particles during compression in the calender nip were small in magnitude (<0.35μm). These findings help to better understand the smoothening phenomena of coating structures during the calendering process. [Copyright &y& Elsevier]

• The causal link between the sawtooth-induced heat pulses at the plasma edge and a spontaneous L-H transition is proposed. • The edge turbulence level increases significantly when the sawtooth-induced heat pulse arriving at the plasma edge. • First time to see that the turbulent decorrelation rate increases significantly just before the L-H transition by experiment. • Both turbulent decorrelation rate and nonlinear energy transfer rate play key roles on the turbulence quench. H-modes induced by sawtooth events can be often observed in discharges with marginal auxiliary power injection in EAST. Poloidal flow shear at the very plasma edge, increasing ∼25% up to the threshold value, is observed just before the L-H transition by means of a fast reciprocating probe array in EAST. This suddenly risen poloidal flow shear, caused by the increased turbulent driven Reynolds force, is motived by the heat pulse originally released by a sawtooth crash at the plasma core. Associated with the critical poloidal flow shear, the local turbulent decorrelation rate increases significantly. The increased turbulent decorrelation rate compensated by nonlinear energy transfer rate from the turbulence to the low-frequency shear flows, exceeding the turbulence energy input rate, is sustained for several hundred microseconds till the turbulence quench happening. [ABSTRACT FROM AUTHOR]

Guinier–Preston–Bagaryatsky (GPB) zones are the well-known strengthening precipitates of AlCuMg alloys formed upon thermal ageing. Here we report that when formed in AlCuLiMg alloys the GPB zones can change significantly in morphology and structure. It is shown that though they do still consist of Al, Cu and Mg elements fundamentally, the GPB zones in AlCuLiMg alloys have a rather different structure due to a featured Li-segregation at their interfaces with the matrix and possible Li-replacement of partial Mg atoms in the structure. As such the Li-containing GPB zones often develop from one-dimensional to quasi-two-dimensional precipitates. [ABSTRACT FROM AUTHOR]

Gradient nanotwinned layers (GNTLs) with high hardness of approximately 500 HV and good thermal stability were produced in a Fe–20Mn–3Al–3Si TRIP steel by means of a high strain-rate surface mechanical grinding treatment (SMGT). The effect of the strain-rate on the plasticity-enhancing mechanisms in steels was investigated. It is found that although it primarily exhibits transformation-induced plasticity (TRIP) when cold-rolled, this steel shows twinning-induced plasticity (TWIP) during the SMGT process, illustrating that the steel may undergo a transition from TRIP to TWIP under high-strain-rate deformation. The martensite induced by deformation is thermally unstable and can easily transform back to austenite during annealing. In contrast, the deformation twins (DTs) are thermally much stable, since de-twinning, which plays a key role in the recovery of DTs, is more difficult to occur during thermal annealing. As such, undergoing the same annealing at 600 °C for 1 h, the GNTLs containing a great many of DTs maintain high hardness, whereas the cold-rolled counterpart samples containing deformation-induced martensite softens drastically. [ABSTRACT FROM AUTHOR]

Transition from type-III to large-amplitude ELMs induced by neon injection has been observed in the EAST tokamak at overlapping q 95 space between large and small ELMs. With neon injection, pedestal density gradient shows a remarkable increase accompanied by some decrease of pedestal electron temperature, and consequently the pressure gradient increases moderately and edge bootstrap current has minimal change. Further experiment demonstrates that the occurrence of large ELMs after neon injection is highly correlated with the change in edge density. Linear peeling-ballooning stability analysis indicates that the large ELM case is more unstable than the type-III ELM case during the ELM transition. A scan of pedestal density gradient in linear stability analysis shows that the direct destabilizing effect of steep pedestal density gradient on peeling-ballooning instabilities via two-fluid effects could also facilitate the transition to large ELMs. These results could provide more insight into the role of pedestal density gradient on pedestal stability and ELM behavior. • Transition from type-III ELMs to low-frequency large ELMs induced by impurity injection. • Direct destabilizing effect of steep density gradient on peeling-ballooning modes via two-fluid effects. • Strong correlation between ELM amplitude and pedestal density gradient. [ABSTRACT FROM AUTHOR]

Abstract: Biofuels are being embraced worldwide as sustainable alternatives to fossil fuels, because of their potential to promote energy security and reduce greenhouse gas emissions, while providing opportunities for job creation and economic diversification. However, biofuel production also raises a number of environmental concerns. One of these is the risk of biological invasion, which is a key issue with second generation biofuel crops derived from fast-growing perennial grasses and woody plant species. Many of the most popular second generation crops proposed for cultivation in the U.S. and Canada are not native to North America, and some are known to be invasive. The development of a large-scale biofuel industry on the continent could lead to the widespread introduction, establishment, and spread of invasive plant species if invasive risks are not properly considered as part of biofuel policy. In this paper, we evaluate the risk of biological invasion posed by the emerging second generation biofuel industry in the U.S. and Canada by examining the invasive risk of candidate biofuel plant species, and reviewing existing biofuel policies to determine how well they address the issue of invasive species. We find that numerous potentially invasive plant species are being considered for biofuel production in the U.S. and Canada, yet invasive risk receives little to no attention in these countries' biofuel policies. We identify several barriers to integrating invasive species and biofuel policy, relating to policy analytical capacity, governance, and conflicting policy objectives. We recommend that governments act now, while the second generation biofuel industry is in its infancy, to develop robust and proactive policy addressing invasive risk. Policy options to minimize biological invasions include banning the use of known invasive plant species, ongoing monitoring of approved species, and use of buffer zones around cultivated areas. [Copyright &y& Elsevier]

Abstract: Assisted migration was proposed several decades ago as a means of addressing the impacts of climate change on species populations. While its risks and benefits have been debated, and suggestions for planning and management given, there is little consensus within the academic literature over whether to adopt it as a policy. We evaluated the main features of the assisted migration literature including the study methods, taxonomic groups, geographic regions and disciplines involved. We further assessed the debate about the use of assisted migration, the main barriers to consensus, and the range of recommendations put forth in the literature for policy, planning or implementation. Commentaries and secondary literature reviews were as prevalent as first-hand scientific research and attention focussed on a global rather than regional level. There was little evidence of knowledge transfer outside of the natural sciences, despite the obvious policy relevance. Scholarly debate on this topic has intensified during the last 3years. We present a conceptual framework for evaluating arguments in the debate, distinguishing among the direct risks and benefits to species, ecosystems and society on the one hand, and other arguments regarding scientific justification, evidence-base and feasibility on the other. We also identify recommendations with potential to advance the debate, including careful evaluation of risks, benefits and trade-offs, involvement of relevant stakeholders and consideration of the complementarity among assisted migration and less risk-tolerant strategies. We conclude, however, that none of these will solve the fundamental, often values-based, challenges in the debate. Solutions are likely to be complex, context-dependent and multi-faceted, emerging from further research, discussion and experience. [Copyright &y& Elsevier]

Abstract: Previous studies indicated the beneficial effects of glial cell line-derived neurotrophic factor (GDNF) and transplanted neural stem cells (NSCs) on stroke. Here, we explored whether transplantation of neural stem cells (NSCs) modified by GDNF gene provides a better therapeutic effect than native NSCs after stroke. Primary rat NSCs were transfected with GDNF plasmid (GDNF/NSCs, labeled by green fluorescent protein from AdEasy-1, GFP). Adult rats were subjected to two-hour middle cerebral artery occlusion and reperfusion, followed by infusion of NSCs (labeled with5-bromo-2′-deoxyuridine before infusion, BrdU), GDNF/NSCs and saline at 3 days after reperfusion (NSCs group, GDNF/NSCs group, control group), respectively. All rats were sacrificed at 1, 2, 3, 5, and 7 weeks after reperfusion. Modified Neurological Severity Scores (mNSS) test and H and E staining were respectively performed to evaluate neurological function and lesion volume. Immunohistochemistry was used to identify implanted cells and observe the expressions of Synaptophysin (Syp) and postsynaptic density-95 (PSD-95) and caspase-3. TdT-mediated dUTP–biotin nick-end labeling (TUNEL) was employed to observe apoptotic cells. Western blotting was used to detect brain-derived neurotrophic factor (BDNF) and NT-3 protein expression. Significant recovery of mNSS was found in GDNF/NSCs rats at 2 and 3 weeks after reperfusion compared with NSCs rats. Lesion volume in the NSCs and GDNF/NSCs groups was reduced significantly compared with control group. The number of NSCs in the GDNF/NSCs group was significantly increased in comparison with NSCs group. Moreover, Syp-immunoreactive product at 2 and 3 weeks after reperfusion and PSD-95 immunoreactive product in the GDNF/NSCs group were significantly increased compared with NSCs group. In contrast, caspase-3 positive cells and TUNEL-positive cells in the GDNF/NSCs group were significantly decreased compared with NSCs group. Significant increase of BDNF protein in the GDNF/NSCs and NSCs groups was observed compared to the control group at different time points of reperfusion, and GDNF/NSCs grafting significantly increased BDNF protein expression compared to NSCs grafting. In addition, significant increase of NT-3 protein in GDNF/NSCs and NSCs groups was detected only at 1 week of reperfusion compared to control group. The results demonstrate that grafting NSCs modified by GDNF gene provides better neuroprotection for stroke than NSCs grafting alone. [Copyright &y& Elsevier]

Abstract: A new set of experimental data of subcooled pool boiling on a thin wire in microgravity aboard the 22nd Chinese recoverable satellite is reported in the present paper. The temperature-controlled heating method is used. The results of the experiments in normal gravity before and after the flight experiment are also presented, and compared with those in microgravity. The working fluid is degassed R113 at 0.1MPa and subcooled by nominally. A thin platinum wire of in diameter and 30mm in length is simultaneously used as heater and thermometer. It is found that the heat transfer of nucleate pool boiling is slightly enhanced in microgravity comparing with those in normal gravity. It is also found that the correlation of Lienhard and Dhir can predict the CHF with good agreement, although the range of the dimensionless radius is extended by three or more decades above the originally set limit. Three critical bubble diameters are observed in microgravity, which divide the observed vapor bubbles into four regimes with different sizes. Considering the Marangoni effect, a qualitative model is proposed to reveal the mechanism underlying the bubble departure processes, and a quantitative agreement can also be acquired. [Copyright &y& Elsevier]

Abstract: Mariner 10, the only spacecraft that ever passed close to Mercury, revealed several unexpected characteristics: an intrinsic magnetosphere, the highest mean density of any Solar System terrestrial planet and a very thin non-collisional atmosphere. Mercury''s atmosphere is very poorly explored since only three atomic elements, H, He and O, were observed during the three flybys of Mariner 10. The measurements done by radio and solar occultations provided upper limits on the neutral and ion densities. These measurements pointed out the close connection between species in Mercury''s exosphere and its surface, which is also the case for the Moon. Mariner 10 observations also characterized the vertical distributions and the day to night contrasts of Mercury''s exosphere for its lightest components H and He (Broadfoot, A.L., et al., 1976. Mariner 10: Mercury atmosphere. Geophys. Res. Lett. 3, 577–580). More than a decade later, the first observation from a ground-based observatory of Mercury''s sodium (Na) exospheric component was reported (Potter, A.E., Morgan, T.H., 1985. Discovery of sodium in the atmosphere of Mercury. Science 229, 651–653). Since then, potassium and more recently calcium have been identified in Mercury''s exosphere. The bright Na resonant scattering emission has been often observed since 1985. This large set of observations is now the best source of information on Mercury''s exospheric mechanisms of ejection, dynamics, sources and sinks. In particular, several of these observations provided evidence of prompt and delayed effects, both localized and global, for the very inhomogeneous Mercury''s Na exosphere. These inhomogenities have been interpreted as the trace of Mercury''s magnetosphere–solar wind interaction and have highlighted some of the main sources of exospheric material. Some of these features have been also interpreted as the trace of a global dayside to night side circulation of Mercury''s exosphere and therefore have highlighted also the relation between exospheric production and upper surface composition. Hopefully, new sets of in situ measurements will be obtained within the next decade thanks to Messenger and Bepi-Colombo missions. Until then, ground-based observations and modelling will remain the only approaches to resolve questions on Mercury''s exosphere. Mercury''s exospheric composition and structure as they are presently known are described in this paper. The principal models for the main short and long times terms variations and local and global variations of Mercury''s exosphere are described. The mechanisms of production and their characteristics are also given. Mercury''s exosphere can also be seen as part of the coupled magnetosphere–upper surface–exosphere system and several of the links between these elements are essential to the interpretation of most of the ground-based observations. The relation between Mercury''s planet composition and its exospheric composition is also considered, as is the global recycling, sources and sinks of Mercury''s exosphere. [Copyright &y& Elsevier]

Abstract: Fracture and small crack behavior in the very high cycle domain of 109 cycles were investigated with a nickel-based superalloy under ultrasonic fatigue in ambient air at room temperature. The influence of ultrasonic frequency is examined by comparing the results with those in conventional low frequency fatigue. It is found that fatigue strength increases as frequency is raised up to 19.5kHz and the most of fatigue life is consumed in nucleating and propagating small cracks up to 100μm. Transition of fracture mode from transgranular ductile fracture to cleavage-dominated fracture occurs beyond a critical stress intensity factor range of approximately , leading to the catastrophic failure under ultrasonic fatigue. [Copyright &y& Elsevier]