a b s t r a c t
Phenomena governing the grinding process are largely related to the nature and evolution of contact between grinding wheel and ground component. The deﬁnition of the contact area plays an essential role in the simulation of grinding temperatures, forces or wear. This paper presents a numerical model that simulates the contact between grinding wheel and workpiece in surface grinding. The model reproduces the granular structure of the grinding wheel by means of the discrete element method. The surfacetopography is applied on the model surface taking into account the dressing mechanisms and move- ments of a single-point dresser. The individual contacts between abrasive grits and workpiece are stu- died regarding the uncut chip thickness, assuming viscoplastic material behaviour. Simulation results are evaluated with experimental measurements of the contact length. The results remark the importance of surfacetopographyand dressing conditions on the contact area, as well as wheel deﬂection.
mine with high resolution, on the basis of a simple structural model, the structure of a weakly scatter- ing atomically thin membrane, graphene, in weak interaction with a metallic substrate made of strong scatterers, Ir atoms. We determine the undula- tion of graphene across the moir-like superstructure formed between graphene and Ir(111), 0.379 ± 0.044 without the ambiguity inherent to other ensemble- averaging techniques. Our determination of the av- erage graphene-Ir(111) distance is consistent with previous reports based on local-probe and ensemble- averaging analysis. Finally we unveil the faint cor- rugations predicted by DFT calculation in the sub- strate, which are as low as 0.017 ± 0.002 for the
In a near future, the Surface Water Ocean Topography (SWOT) mission will provide images of altimetric data at kilometric resolution. This unprecedented 2-dimensional data structure will allow the estimation of geostrophy-related quantities that are essential for studying the ocean surface dynamics and for data assimilation uses. To estimate these quantities, i.e. compute spatial derivatives of the Sea Surface Height (SSH) measurements, the small-scale noise expected to affect the SWOT data must be smoothed out while minimizing the loss of relevant, physical SSH information. This paper introduces a new technique for de-noising the future SWOT SSH images. The de-noising model is formulated as a regularized least-square problem with a Tikhonov regularization based on the first, second, and third-order derivatives of SSH. The method is implemented and compared to other, convolution-based filtering methods with boxcar and Gaussian kernels. This is performed using a large set of pseudo-SWOT data generated in the Western Mediterranean Sea, from a 1/60 ◦ simulation and the SWOT simulator. Based on Root Mean Square Error and spectral diagnostics, our de-noising method shows a better performance than the convolution-based methods. We find the optimal parametrization to be when only the second-order SSH derivative is penalized. This de-noising reduces the spatial scale resolved by SWOT by a factor of 2, and at 10 km wavelengths the noise level is reduced by 10 4 and 10 3 for Summer and Winter respectively. This is encouraging for the processing of
This study unravels the surfacestructure of austenitic stainless steel at nanometric and atomic scales and shows a rather complex structure even on the model (100)-oriented Fe-18Cr-13Ni single crystalline surface. The slight misorientation causes the topography to alternate terraces with atomic multi-steps (step bunching) after annealing. On the terraces, the topmost plane is reconstructed with an atomic density half that of the planes below, contains all three alloying elements and adopts a (√2×√2)R45° superstructure. A novel finding for metal and alloy surfaces is the presence, after annealing, of self-organized nanostructures consisting of vacancy lines formed by two adjacent rows of missing atoms, aligned along the close-packed <001> directions of the reconstructed surface lattice. The measured average period of self- organization, related to relaxation of the surface stress, is 7.6 nm. Early reactivity is observed at the defect sites of reduced atomic coordination (steps) and affect the adjacent terrace regions. Cr(III) oxide nucleates at step edges and consumes the Cr atoms locally present but also “pumps” more remote Cr atoms from the topmost plane. The Cr vacancies injected in the terraces cause a local depletion of chromium.
5 heating stage to record tilted image series and reconstruct 3D images of the sample surface with a submicrometric resolution. To achieve this goal, we have developed a new heating stage that can be tilted within the +5 / -5 degrees angles and that can be heated up to 1050°C under various gaseous atmospheres. In the present study, the model sample is an Al-Si coated boron steel employed into the body structure of vehicles (Karbasian et al., 2010; Fan et al., 2012). In order to achieve the desired mechanical properties, this ultra-high strength steel is usually hot stamped at 900°C. Consequently, it will be heated from RT to 900°C under 100Pa air in the ESEM chamber to observe and characterize the coating formation and 3D surface modifications in order to determine the possibilities of the method. In the case of steels or coated steels, control of the surface roughness parameters is crucial because of their close relationship with numerous properties such as weldability, paintability, corrosion resistance or hydrogen diffusivity. Heating parameters, such as temperature, heating rate or dwell time (Jenner et al., 2010), strongly affect the final surface morphology. In order to select the proper conditions for the targeted application, it is of high interest to have a real-time and temperature-dependent information for a better understanding of the different surface transformations.
Patients and Methods
We studied kidneys removed for cancer from 22 patients (67.7 ±10.5 years old) between 2012 and 2014. Papillae from healthy parts of the kidney, at distance from the tumor, have been collected and coded anonymously after extemporaneous examination. Patients gave a written consent relative to kidney removal and tissue conservation but not to clinical or biological data. Papillae have been therefore anonymously collected, according to French legislation and Helsinki declaration for Patient Safety. Half papillae have been embedded in paraffin after fixation by paraformaldehyde. The other half papilla has been frozen or fixed with glutaraldehyde to perform electron microscopy. No attached stone has been observed at the surface of the papilla and, a priori, there was no stone former among the patients.
The temperature dependence of the dielectric constant for frequencies from 1 kHz to 1 MHz is plotted in Fig. 1(a) . The Curie temperature, as deduced from the 1 kHz curve, is 360 K, which corresponds to SBN61. 16 The single crystal X-ray diffraction gave a ¼ 3.9324 and c ¼ 12.4526 A ˚ , which corresponds to SBN63. The 2 2 lm 2 PFM phase image is shown in Fig. 1(b) . There is clear contrast that could corre- spond to the expected polar nano-regions (PNRs). The phase shift is close to 180 as expected from domains with opposite polarization. The measured polarization pattern has no obvious relationship with the topography (not shown). Analysis of 50 such polar regions gives an average size of 0.151 6 0.023 lm 2 , in good agreement with previous results for SBN61-SBN75. 9 The absence of electro-mechanical response in the bright areas of Fig. 1(b) corresponds to the piezo-inactive areas observed by Shvartsman et al. 9 A rather high amplitude (6 V) has been used for the alternating volt- age during PFM imaging, in order to enhance the signal to noise ratio. For our 600 lm thick crystal, this corresponds to an electric field of 100 V/cm, slightly increased by the tip effect, but not so that it reaches the coercive field. Therefore, PFM imaging has no influence on the genuine domain con- figuration, and imaging has been performed several times with no contrast change.
5.4 Results and discussion 5.4.1 Roughness profiles
From the observations of the different roughness profiles in Figure 3, for 0° and 45° ply orientation with a low tool wear, a periodic oscillation pattern can be identified (e.g. curve “a” for the 0° ply orientation in up-milling in Figure 3). The period value is different depending on the milling type, for example it reaches 270 µm for the up-milling side of the coupon and 670 µm for the down- milling side of the coupon for 0° or 45° ply orientation in Figure 3. Both observed periods are different compared to the feed per tooth. For a homogeneous material such as aluminium and titanium alloys, the periodic oscillation patterns are tool marks that can be correlated with the cutting feed. During the machining, the tool is not fracturing the fibres one by one when the pressure is applied by the tool cutting edge. Because, in this case, the tool mark length would be similar to the observed roughness profile period. Instead, the fibres are fractured by relatively small fibre groups apparently due to bending or shearing. This may be due to the structure of the composite. The inner part of the CFRP used is constituted of resin and threads of carbon fibres. The number of fibres within a thread may influence the size of the fractured fibre group and so on the noticeable period on the roughness profiles.
2. Materials and experimental procedure 2.1. Polymer coatings
For the automotive industry, building trade and domestic appliance products, paint coating is an economic way widely used to protect metallic substrates against aggressive and cor- rosive environments while giving them an aesthetic appear- ance. An organic paint coating is a complex system consisting of binders, pigments, extenders, thinners and additives. A dou- ble protective barrier can be achieved by manufacturing pre- painted galvanised steels; the protection being strengthened both by the sacrificial zinc layer and by the organic barrier layer. As far as the organic barrier layer is concerned, an efficient protection is obtained by elaborating bi-layered sys- tems consisting of a primer and a topcoat. The durability over time of such multi-layered coatings depends on their structure
Coumarin derivatives are of high interest as they possess some valuable properties such as excellent fluorescent properties with high photoluminescence quantum efficiency, excellent photostability and extended spectrum range for the dimerization/cleavage reactions. Indeed, coumarin derivatives can undergo a [2 + 2] photodimerization upon irradiation with wavelengths longer than 300 nm giving access to a cyclobutane-type dimer. The dimer can be cleaved when irradiated at wavelengths shorter than 290 nm. In this study, polydimethylsiloxane copolymers bearing coumarin groups along the chain as well as α, ω di- coumarin polydimethylsiloxane have been synthesized and their blends have been evaluated for their ability to form reversible patterned films by interdiffusion. The synthesis of photoresponsive coumarin- functionalized PDMS (Cou-PDMS) was achieved by amidation of a coumarin acid chloride derivative with various commercially available amine-functionalized PDMS. Photocrosslinking and photocleavage kinetics of Cou-PDMS blends cast into films have been monitored using UV-vis spectroscopy and fluorescence spectroscopy. Under exposure of λ> 300 nm UV light, PDMS-Cou blends can form crosslinked networks via [2+2] photocycloaddition of coumarin moieties. On the other hand, the formed polymer networks containing coumarin dimer moieties could be degraded via photo-cleavage of cyclobutane dimers upon illumination by light source at 254 nm. The linear PDMS interdiffusion in a locally-crosslinked network using various photomasks and its ability to deeply modify the topography of the resulting coating was then studied. Using fluorescence microscopy, we have demonstrated that interdiffusion was dependent on the molecular weight of diffusing oligomer and on the network structure. Surfacetopography controlled modification was investigated by scanning electron microscopy and profilometry. This developed methodology can easily leads to the formation of complex surface patterning using easy method (photomasking and interdiffusion) and can be used in several applications, such as smart intra-ocular lens (IOLs), reversible photopatternable systems or photoswitched controlled release devices.
Eroding dynamic topography
J. Braun, 1 X. Robert, 1 and T. Simon-Labric 1
Received 10 January 2013; revised 28 February 2013; accepted 28 February 2013. [ 1 ] Geological observations of mantle ﬂow-driven dynamic topography are numerous, especially in the stratigraphy of sedimentary basins; on the contrary, when it leads to subaerial exposure of rocks, dynamic topography must be substantially eroded to leave a noticeable trace in the geological record. Here, we demonstrate that despite its low amplitude and long wavelength and thus very low slopes, dynamic topography is efﬁciently eroded by ﬂuvial erosion, providing that drainage is strongly perturbed by the mantle ﬂow driven surface uplift. Using simple scaling arguments, as well as a very efﬁcient surface processes model, we show that dynamic topography erodes in direct proportion to its wavelength. We demonstrate that the recent deep erosion experienced in the Colorado Plateau and in central Patagonia is likely to be related to the passage of a wave of dynamic topography generated by mantle upwelling. Citation: Braun, J., X. Robert, and T. Simon-Labric (2013), Eroding dynamic topography, Geophys. Res. Lett.,
4. Results and discussion
4.1. Drill corner/margins wear
Drill corner/margins wear have a strong influence in the hole surface integrity and tolerances (hole diameter). Therefore, drill corner geometry was measured with the Blum laser after each hole being drilled as indicated on Fig. 5. A total of 70 measurements (corresponding to 70 holes) were performed. From hole #3 an inversion in the drill back taper angle is visible. After hole # 22 (770 mm drilled depth), the hole diameter becomes out of tolerance (inferior to 12,006 mm) as shown in Fig. 6. This figure shows the decrease in hole diameter in function of the number of holes being drilled. These curves could be approximated by three rectilinear lines with various slopes. These various slopes are due to different tool wear regimes, which are related to the ratio between the surface of the uncut fibers and the total hole surface . In our study case, the drill life time is represented by the more accentuated slope. These results point out the severe abrasive wear of the carbon fibers on the drill and their consequences on the hole geometry.
(1) crustal thickness variations, (2) density variations in the crust and mantle, (3) dynamic support, and (4) lithospheric stresses. Each of these mechanisms could play a role in compensating topography on Venus, and we distinguish between these mechanisms in part by calculating geoid-to-topography ratios and apparent depths of compensation. By simultaneously inverting for mass anomalies at two depths, we solve for the spatial distribution of crustal thickness and a similar map of mass anomalies in the mantle, thus separating the effects of shallow and deep compensation mechanisms on the geoid. The roughly circular regions of mantle mass de ﬁcit coincide with the locations of what are commonly interpreted to be buoyant mantle plumes. Additionally, there is a signi ﬁcant geographic correlation between patches of thickened crust and mass de ﬁcits in the mantle, especially for spherical harmonic degree l < 40. These mass deﬁcits may be interpreted either as lateral thermal variations or as Mg-rich melt residuum. The magnitudes of mass de ﬁcits under the crustal highlands are roughly consistent with a paradigm in which highland crust is produced by melting of upwelling plumes. The mean thickness of the crust is constrained to a range of 8 –25 km, somewhat lower than previous estimates. The best two-layered inversion of gravity incorporates a dynamic mantle load at a depth of 250 km.
lower temperatures [ 35 ].
1.3. Eﬀect of surfacetopography on high temperature oxidation
AM materials present irregular surface topographies along their construction planes; their roughness depends on surface defects, which are linked to process parameters [ 46 , 47 ]. Four kinds of defects are found on the surface of PBF samples. The ﬁrst type of defect was de- ﬁned by Tolochko et al. [ 48 ] as “balling” defects which are undesirable droplets from the melt pool that spread out above the surface due to the high ﬂow rate of the metal ﬂuid in the melt pool during laser melting. The second defect, was deﬁned by Aboulkhair et al. [ 49 ] as “satellites”. They designate unmelted or partially melted powder particles sticking to the extreme surface due to insuﬃcient energy for proper powder melting or to accumulation of heat at the surface, which sinters powder particles. “Satellites” are the major surface defects found on EBM samples [ 50 , 51 ]. Indeed, during the EBM process, a high quantity of electrons are concentrated in the powder bed which leads to electro- static charging and mutual repulsion of powder particles called “smoke”. In order to avoid, this eﬀect the entire powder bed has to be pre-heated, leading to the “satellite eﬀect” deﬁned as unmelted powder particles sintered at the surface of EBM samples due to heat accumu- lation. And consequently, it is diﬃcult to avoid powder particles to sinter the surface [ 52 ]. The third defect is due to the inclination angle of the construction part, which generates two diﬀerent surfaces, the “up- skin” and the “down-skin” surfaces. The heat diﬀuses through the previous layer for the “up-skin”, whereas it diﬀuses through the un- melted powder for the “down-skin”. Hence, the surface roughness de- pends on the heat transfer phenomenon. “Down-skin” surfaces have a higher roughness due to “satellite” defects [ 47 , 53 ]. The last defect is called the “staircase” eﬀect and can be found in all AM-produced ma- terials
The surface of Chromium has also been one of the favorite system for the development of spin-polarized scanning tunneling microscopy (SP-STM). In particular the (001) surface is an ideal template to visualize magnetic order at the atomic scale since, due to the local anti-ferromagnetic coupling between neighboring atoms, adjacent terraces show opposite magnetic orientation which contrast appears clearly in SP-STM. The improvement in SP-STM technology (as well as surface preparation) and in particular the use of real space spectroscopy imaging at low temperature has allowed to provide a detailed characterization of the spin polarized electronic structure of chromium surface. In 2002 Kolesnychenko et al observed sharp features in the tunneling spectroscopy (STS) at the Fermi level which they attributed to an orbital Kondo resonance[8, 9] formed by two degenerate d xz d yz surfaces states located,
aucune relation claire entre la fr´equence d’occurrence des structures coh´erentes et la stabilit´e n’a ´et´e ´etablie (en accord avec Gao et al. (1992)). Ces valeurs sont comparables ` a d’autres ´etudes (e.g. Feigenwinter and Vogt (2005) : 7-10 structures en 30 min). Il semble que plus de structures sont d´etect´ees en conditions stables qu’en conditions convectives. Les PDFs que nous obtenons sont tr`es similaires pour une classe de stabilit´e donn´ee, quel que soit le secteur de vent. La PDF de la contribution des structures coh´erentes au flux de quantit´e de mouvement (figure 5.7) semble confirmer ce r´esultat. Il est ´egalement observ´e que quelle que soit la rugosit´e amont, les structures coh´erentes ne constituent pas, en moyenne, le processus dominant pour le transport turbulent dans la plupart des r´egimes de stabilit´e (tableau 5.1). En effet, les valeurs moyennes sont comprises entre 31 et 57 %. Une tendance qui semble se v´erifier pour tous les secteurs de vent, est une contribution plus importante des structures coh´erentes aux flux de quantit´e de mouvement en conditions tr`es stables. La figure 5.8 montre la fonction de densit´e de probabilit´e de la contribution des structures coh´erentes au flux de chaleur. Ici encore, les PDFs sont tr`es similaires quel que soit le secteur de vent (ce qui est aussi un r´esultat attendu ´etant donn´ee la faible d´ependance du flux de chaleur sensible moyen ` a la rugosit´e amont, voir la partie 5.1.2) avec une valeur moyenne de 46 % (Tableau 5.1).
The surfacetopography of the samples was characterized using an interferometric and confocal variation microscope. The highest rough- nesses were found on the side surface, parallel to the build direction. As a reminder, the diameter of the particles used for EBM samples ranged from 45 to 105 μm with a 75-μm layer-thickness, whereas the diameter of those used for LBM samples ranged from 15 to 45 μm with a 40-μm layer-thickness. In addition, the scanning patterns used are diﬀerent a bidirectional parallel scanning plus contour for EBM samples and a band strategy with 60° shift plus contour after each layer for LBM samples. Both sets of samples thus underwent a contouring beam scan of their extreme surface. Nevertheless, Figs. 3 and 4 , where the side surface are represented. Indicate that the samples show dissimilarities in terms of surfacetopography. Table 2 shows that the roughness of the as-built EBM surface in its (XZ) plane (50 ± 2 μm Sa) is much rougher than the one of the as-built LBM surface in its (XZ) plane (7 ± 1 μm Sa), and over 1000 times as rough as than the P600-ground surface (0.033 ± 0.002 μm Sa). The skewness parameter (Ssk) reveals that the as-built LBM surface presents an asymmetric proﬁle certainly due to the fact that small quantities of isolated powder particles are present onto its surface. Whereas the skewness of the EBM rough surface, is close to zero, which suggests that the surface has a relatively symmetric proﬁle regarding peaks and valleys. Here the value of Sz might be distorted by spikes. But proﬁles in Fig. 4 reveal that the EBM sample presents the highest peak-to-valley height, reaching an amplitude of about 300 μm whereas the amplitude of the LBM sample is about 40 μm. Additionally, the proﬁle displays high peaks and deep valleys with a rounded roughness proﬁle close to its waviness proﬁle, which is certainly due to the fact that powder particles are distributed onto the entire surface of the EBM sample. On the other hand, the P600-ground surface presents a smaller Sa value but a signiﬁcant number of peaks and valleys, which correspond to polishing scratches. Moreover, the roughness proﬁle of the EBM sample seems to follow a periodic peak-to-valley pattern, which is about 200-μm long. This is less apparent in the LBM roughness proﬁle. This periodic proﬁle might be due to the layer-by-layer con- struction, as is the case for the “staircase” defects [ 54 ] and might be aﬀected by layer-thickness, as explained by Safdar et al. [ 51 ]. The powder particles present on the surface of LBM and EBM samples are called “satellite” defects, which are linked to the process parameters and scanning strategy both of which aﬀect heat conduction. Indeed, during the EBM process, all the powder bed was pre-heated at 1000 °C. This may sinter the unmelted or partially-melted powder particles onto the surface, as showed by Ahmed et al. [ 61 ] on Ti-6Al-4 V. Therefore,
When LP is performed at 100 W of applied laser power (see Fig. 5), SOM regime and thermo-capillary effects are present. In this case, LP process acts as an amplitude modulator of the ground surfacetopography. The initially flat surfacetopography was completely eroded since Ra increased from 0.033 µm to 0.391 µm. The amplitude distribution of frequency components has also changed significantly. As expected [9, 10], the bulging effect was more prominent for 100 W, rather than 25 W of power. Unlike in the low power case, Ra for LP ground and flat samples are comparable: 0.510 µm vs 0.391 µm (see Figs. 5a and 5b), thus suggesting that molten material from bulk solid body andsurfacetopography are significantly blending with each other. Although Ra has still improved considerably from 0.801 µm to 0.510 µm (see Fig. 5a), the thermodynamic mechanism involved in LP surface formation was completely different in a sense that this time, solid body elevation seems to play a predominant role on the overall process of bulge formation. 1 mm
Conclusion générale et perspectives Conclusion générale
Cette étude nous a permis de produire des cartes de vitesse de groupe du mode fondamental des ondes de Rayleigh de 20 à 100s de période, en utilisant la tomographie d’ondes de surface de l’Afrique de l’Ouest. Pour se faire nous avons utilisé, à la fois les séismes et les corrélations du bruit sismique ambiant. La résolution des images tomographiques dépend de la couverture azimutale des trajets. En combinant ces deux types de données, nous avons obtenu une meilleure résolution pour l’ensemble de la zone d’étude. L’un des principaux objectifs de la tomographie par corrélation du bruit sismique ambiant est que les fonctions de Green extraites des corrélations du bruit ambiant peuvent être utilisées de manière significative pour obtenir des mesures de dispersion des ondes de surface tout comme celles obtenues avec les ondes résultant des tremblements de terre. A fin montrer la compatibilité de ces deux ensembles de données, nous avons comparé les sismogrammes et les diagrammes de dispersion résultant d’un séisme dont l’épicentre est situé à proximité d’une station sismique et enregistré à une autre station avec ceux de la corrélation du bruit ambiant entre cette paire station. La similarité des sismogrammes et des courbes de dispersion montre qu’on pouvait inverser conjointement ces deux jeux de données pour retrouver la structure du milieu traversé. Pour éliminer les erreurs potentielles dans le processus de mesure de la vitesse de groupe, seuls les temps de trajet des courbes de dispersion relativement continues et de bonne qualité ont été utilisés.