Rate effects on layering of a confined linear alkane

We perform drainage experiments of a linear alkane fluid (n-hexadecane) down to molecular thicknesses, and focus on the role played by the confinement rate. We show that molecular layering is strongly influenced by the velocity at which the confining walls are approached: under high enough shear rates, the confined medium behaves as a structureless liquid of enhanced viscosity for film thickness below $\sim$10 nm. Our results also lead us to conclude that a rapidly confined film can be quenched in a metastable disordered state, which might be related with recent intriguing results on the shear properties of confined films produced at different rates [Zhu and Granick, Phys. Rev. Lett. {\bf 93}, 096101 (2004)]

Effective slip boundary conditions for flows over nanoscale chemical heterogeneities

We study slip boundary conditions for simple fluids at surfaces with nanoscale chemical heterogeneities. Using a perturbative approach, we examine the flow of a Newtonian fluid far from a surface described by a heterogeneous Navier slip boundary condition. In the far-field, we obtain expressions for an effective slip boundary condition in certain limiting cases. These expressions are compared to numerical solutions which show they work well when applied in the appropriate limits. The implications for experimental measurements and for the design of surfaces that exhibit large slip lengths are discussed.Comment: 14 pages, 3 figure

Zur Determinante einer Summe aus Kronecker-Produkten (Kleine Mitteilung)

Bei der analytischen Untersuchung der Informationsmatrix im Hinblick auf eine optimale parametrische Identifikation linearer elastomechanischer Systeme sind die im folgenden mitgeteilten mathematischen Sätze über die Determinante einer Summe aus bestimmten Kronecker-Produkten nützlich

Drainage of a nanoconfined simple fluid: rate effects on squeeze-out dynamics

We investigate the effect of loading rate on drainage in molecularly thin films of a simple fluid made of quasi-spherical molecules (octamethylcyclotetrasiloxane, OMCTS). We find that (i) rapidly confined OMCTS retains its tendency to organize into layers parallel to the confining surfaces, and (ii) flow resistance in such layered films can be described by bulklike viscous forces if one accounts for the existence of one monolayer immobilized on each surfaces. The latter result is fully consistent with the recent work of Becker and Mugele, who reached a similar conclusion by analyzing the dynamics of squeeze-out fronts in OMCTS [T. Becker and F. Mugele, Phys. Rev. Lett. {\bf 91} 166104(2003)]. Furthermore, we show that the confinement rate controls the nature of the thinning transitions: layer-by-layer expulsion of molecules in metastable, slowly confined films proceeds by a nucleation/growth mechanism, whereas deeply and rapidly quenched films are unstable and undergo thinning transitions akin to spinodal decomposition

Dynamic surface decoupling in a sheared polymer melt

We propose that several mechanisms contribute to friction in a polymer melt adsorbed at a structured surface. The first one is the well known disentanglement of bulk polymer chains from the surface layer. However, if the surface is ideal at the atomic scale, the adsorbed parts of polymer chains can move along the equipotential lines of the surface potential. This gives rise to a strong slippage of the melt. For high shear rates chains partially desorb. However, the friction force on adsorbed chains increases, resulting in quasi-stick boundary conditions. We propose that the adsorbed layers can be efficiently used to adjust the friction force between the polymer melt and the surface

An integrated study of microstructural, geochemical, and seismic properties of the lithospheric mantle above the Kerguelen plume (Indian Ocean)

International audiencePeridotite xenoliths brought up to the surface by the volcanism of the Kerguelen Islands represent a mantle that has been affected by a high degree of partial melting followed by intense melt percolation above the Kerguelen plume. These xenoliths are therefore particularly suitable to investigate effects of melt-rock interaction on crystallographic fabrics (lattice-preferred orientation (LPO)) of peridotite minerals and on the LPO-induced seismic properties of peridotites above a mantle plume. We have studied a suite of 16 ultramafic samples representative of different degrees of partial melting and magma-rock interaction among which the protogranular harzburgites are the least metasomatised xenoliths and dunites are the ultimate stage of metasomatism. Olivine LPO is characterized by high concentration of [010] axes perpendicular to the foliation and [100] axes close to the lineation or distributed in the foliation plane in harzburgites, whereas the high concentration of [100] axes is parallel to the lineation and [010] axes is perpendicular to the assumed foliation in dunites. Olivine LPO in harzburgites is interpreted as being due to a deformation regime in axial compression or transpression. The fabric strength of olivine decreases progressively from protogranular to poikilitic harzburgites and finally to dunites, for which it remains nevertheless significant (J index 3.8). Seismic properties calculated from LPO of minerals indicate that metasomatism at higher melt/rock ratio lowers the P wave velocities. The most significant difference between harzburgites and dunites corresponds to the distribution of S wave anisotropy. Harzburgites display the maximum of anisotropy within the foliation plane and the minimum of anisotropy perpendicular to the foliation plane, whereas the lowest anisotropy is parallel to the lineation for dunites. These modifications of seismic properties as a result of metasomatic processes may induce seismic heterogeneities in the mantle above the Kerguelen plume. In addition, assuming a lithospheric mantle primarily harzburgitic and structured with a horizontal foliation, the seismic properties calculated for the Kerguelen xenoliths reconcile the rather high anisotropy evidenced by the horizontally propagating surface waves with the apparent isotropy revealed by the absence of splitting of vertically propagating teleseismic SKS waves recorded by the GEOSCOPE Kerguelen station

External fixation of the thalamic portion of a fractured calcaneus: A new surgical technique

AbstractThe optimal treatment for intra-articular calcaneus fractures remains controversial, despite internal fixation techniques providing good results. The major point of contention is the need to reconstruct the overall morphology versus to restore the anatomy of the subtalar joint perfectly. We will describe a two-stage technique for treating intra-articular calcaneus fractures in which the primary fracture line goes through the thalamic fragment. The first procedure focuses on the overall morphology by restoring the height and length with osteotaxis being accomplished with a medial external fixator. The second procedure consists of internal fixation through a minimally invasive lateral approach to restore the anatomy of the articular facets. Any defects are filled with injectable bone substitute. This novel technique is compared to the complication rates and radiology and anatomy outcomes in published studies. This two-stage surgical technique reduces the length of hospital stays and the number of complications

Petrology, mineralogy, and geochemistry of the olivine diogenite NWA 4255: new insights into the magmatic evolution of asteroid 4 Vesta

Northwest Africa (NWA) 4255 is a meteorite found in the region of Tindouf (southwestern Algeria), classified as brecciated olivine diogenite. Based on textural observations and orthopyroxene compositions, two different lithologies were determined: harzburgitic and orthopyroxenitic. The orthopyroxenitic lithology contains orthopyroxene (Mg no. 73.99–75.68) and spinel (Cr no. 83.09–85.11, Mg no. 15.57–22.45). On the other hand, the harzburgitic lithology contains orthopyroxene (Mg no. 74.54–77.14) and olivine (Mg no. 70.94–72.57). The iron metal and the sulfides (Troilites) of this sample are present in both lithologies and are low in Ni (Ni < 0.1 wt%). The Fe/Mn ratio of orthopyroxenes ranges from 22.28 to 32.64 and show a large overlap between both lithologies. Lowest ratios are unusual; they are below the defined field for diogenites and olivine diogenites. ∆17O values are − 0.234 ± 0.003 (1σ) and confirm that the NWA 4255 originated from 4Vesta. The results of this study show that there is a genetic linkage between the two lithologies of NWA 4255 and correspond to in situ crystallization processes. This olivine diogenite reflects transition between two major magmatic processes in 4Vesta. The magma ocean of 4Vesta crystallized at equilibrium, allowing the formation of a dunitic and harzburgitic mantle. This late lithology is linked to the peritectic reaction between the olivines formed and the evolved liquid. Our sample then reflects this crucial step of separating this mantle from the residual liquid. This melt evolving on the peritectic allowed the formation of the observed harzburgitic assemblage and then evolves out from the peritectic reaction to proceed to a fractional crystallization process involving the formation of orthopyroxenite

Solute-driven colloidal particle manipulation in continuous flows past grooved microchannels [abstract]

Solute-driven colloidal particle manipulation in continuous flows past grooved microchannels [abstract

Multinational evaluation of the measurement invariance of the level of personality functioning scale–brief form 2.0: comparison of student and community samples across seven countries

DSM-5’s Level of Personality Functioning Scale (LPFS) was introduced as a dimensional rating of impairments in self- and interpersonal functioning, and the LPFS – Brief Form (LPFS-BF) was the first published corresponding self-report. The updated LPFS-BF 2.0 has been translated into several languages and international research supports many of the instrument’s psychometric properties; however, its measurement invariance has only been evaluated across a few countries. This study expands previous studies as an introductory step in a global evaluation of the LPFS-BF 2.0’s measurement invariance. Archival data (N = 5,618, 57% female) from seven countries (Canada, Chile, Denmark, Germany, Italy, United Arab Emirates, United States of America) were used for this study. Participants were recruited from both community (n = 4,677) and student (n = 941) populations. After confirming adequate model fit separately in the community and student samples, we evaluated a series of increasingly stringent model comparisons to test three aspects of measurement invariance (configural, metric, scalar) and then examined latent mean differences across countries. Full scalar invariance was supported in the community sample and partial scalar invariance was supported in the student sample. Evaluation of latent mean differences revealed multiple significant differences. Overall, the LPFS-BF 2.0 appears to assess self- and interpersonal functioning impairment similarly across the included countries. Findings are discussed through the lenses of the cultures from which participants were recruited, as well as in the context of alternative explanations. Limitations, plans for future research, and implications for both research and clinical practice are offered