Stability of an oscillating tip in Non-Contact Atomic Force Microscopy: theoretical and numerical investigations

This paper is a theoretical and a numerical investigation of the stability of a tip-cantilever system used in Non-Contact Atomic Force Microscopy (NC-AFM) when it oscillates close to a surface. No additional dissipative force is considered. The theoretical approach is based on a variationnal method exploiting a coarse grained operation that gives the temporal dependence of the nonlinear coupled equations of motion in amplitude and phase of the oscillator. Stability criterions for the resonance peak are deduced and predict a stable behavior of the oscillator in the vicinity of the resonance. The numerical approach is based on results obtained with a virtual NC-AFM developped in our group. The effect of the size of the stable domain in phase is investigated. These results are in particularly good agreement with the theoretical predictions. Also they show the influence of the phase shifter in the feedback loop and the way it can affect the damping signal

On the Hausdorff volume in sub-Riemannian geometry

For a regular sub-Riemannian manifold we study the Radon-Nikodym derivative of the spherical Hausdorff measure with respect to a smooth volume. We prove that this is the volume of the unit ball in the nilpotent approximation and it is always a continuous function. We then prove that up to dimension 4 it is smooth, while starting from dimension 5, in corank 1 case, it is C^3 (and C^4 on every smooth curve) but in general not C^5. These results answer to a question addressed by Montgomery about the relation between two intrinsic volumes that can be defined in a sub-Riemannian manifold, namely the Popp and the Hausdorff volume. If the nilpotent approximation depends on the point (that may happen starting from dimension 5), then they are not proportional, in general.Comment: Accepted on Calculus and Variations and PD

Latest Developments on HeII Co-Current Two-Phase Flow Studies

Large scale experiments were performed at CEA Grenoble with the support of CERN to simulate and understand the HeII cooling circuit of the LHC. This paper describes the latest results obtained in HeII co-current two-phase flow configuration. First we summarize thermal and hydraulic behaviour of flows obtained in a 40 mm I.D., 86 m long tube inclined at 1.4% which resembles closely the LHC heat exchanger tube. For low vapour velocities, the flow pattern is found to be stratified. A model based on this observation has been developed which fits very well the measured pressure losses. However the wetted surface predicted by the model underestimates the measured one, notably for high vapour velocities. In that case, liquid droplets entrainment takes place. Droplets landing on the tube wall increase the wetted surface. Thus we infer that for higher vapour velocities, the stratified two-phase flow model should not be applied anymore. In order to validate the range of availability of the model, and begin to draw a flow pattern map, a 20 mm I.D. horizontal test sector was built and experiments were performed. First results are presented here, including the observation of the stratified-annular flow transition

Tropical and subtropical actinorhizal plants

A maioria dos países tropicais enfrenta dois grandes problemas: o aumento constante da exploração das reservas florestais para extração de madeira ou lenha e a diminuição da fertilidade do solo para produção agrícola. O conceito geral é o de que plantas fixadoras de N2 podem evitar a propalada crise de madeira e alimentos. Juntas com um grande número de leguminosas fixadoras de N2, plantas actinorrízicas podem ter um papel importante na produção de madeira e recuperação de solos. As plantas actinorrízicas compreendem oito famílias de dicotiledôneas, todas elas representadas nos trópicos. Neste trabalho, as mais promissoras plantas actinorrízicas tropicais são brevemente apresentadas e a ênfase é dada principalmente à família Casuarinaceae. Esta família compreende quatro gêneros (Casuarina, Allocasuarina, Gymnostoma e gênero C), com 82 espécies, incluindo muitas árvores que podem produzir madeira de boa qualidade. As estirpes de Frankia que têm sido isoladas das Casuarinaceae crescem lentamente e são capazes de reduzir acetileno in vitro sob ar, o que indica uma capacidade de proteção contra o O2 muito mais eficiente do que no Rhizobium. Apenas as espécies do gênero Casuarina podem ser noduladas pela estirpe ORS 021001, isolada de Casuarina junghuhniana, o que sugere a existência de grupos de inoculação dentro da família Casuarinaceae. A fixação de N2 de Casuarina equisetifolia, crescida em microparcelas de 1 m2, na estação experimental de ORSTM, em Dakar, foi estimada através da comparação do N total em plantas não-inoculadas e plantas inoculadas com a estirpe ORS 021001. Extrapolando para um hectare, a fixação de N2 foi de 131 kg/N em um período de 6,5 meses. Usando o método de equivalência com adubo nitrogenado, a inoculação parece ser equivalente à aplicação de 288 kg de N/ha-1.Most tropical countries face two major problems: increasing overexploitation of wood reserves for timber or fuel wood and diminishing soil fertility for agricultural production. The present consensus is that N2 -fixing plants can help prevent the forthcoming wood and food crisis. Together with the vast group of N2 -fixing Leguminoseae, actinorhizal plants (AP) can play a major role in wood production and land regeneration. AP comprise eight families of dicotyledonous plants all of which are represented in the tropics. In this paper the most promising tropical AP are briefly presented and the emphasis is put mainly on Casuarinaceae. This family forms a group of four genera (Casuarina, Allocasuarina, Gymnostoma and genus C) with 82 species, including many trees that can yield wood of good quality. The Frankia strains that have been isolated from Casuarinaceae grow slowly and are able to reduce acetylene in vitro under air, which indicates that the protection against O2 is much more efficient in Frankia than in rhizobia. Only the species belonging to the Casuarina genus could be nodulated by strain ORS 021001, isolated from Casuarina junghuhniana, suggesting the existence of crossinoculation groups within the family Casuarinaceae. N2 fixation of Casuarina equisetifolia, grown in 1 m2 microplots at the ORSTOM experimental station of Dakar, was estimated by comparing total N in non-inoculated plants and plants inoculated with Frankia strain ORS 021001. Extrapolating to 1 hectare, N2 fixation was 131 kg for a 6.5-month period. Using the N fertilizer equivalence method, inoculation appeared to be equivalent to the application of 288 kg of N fertilizer per hectare

Magnetic structure of the antiferromagnetic half-Heusler compound NdBiPt

We present results of single crystal neutron diffraction experiments on the rare-earth, half-Heusler antiferromagnet (AFM) NdBiPt. This compound exhibits an AFM phase transition at $T_{\mathrm N}=2.18$~K with an ordered moment of $1.78(9)$~$\mu_{\mathrm B}$ per Nd atom. The magnetic moments are aligned along the $[001]$-direction, arranged in a type-I AFM structure with ferromagnetic planes, alternating antiferromagnetically along a propagation vector $\tau$ of $(100)$. The $R$BiPt ($R$= Ce-Lu) family of materials has been proposed as candidates of a new family of antiferromagnetic topological insulators (AFTI) with magnetic space group that corresponds to a type-II AFM structure where ferromagnetic sheets are stacked along the space diagonal. The resolved structure makes it unlikely, that NdBiPt qualifies as an AFTI.Comment: As resubmitted to PRB, corrected typos and changed symbols in Fig.

Competition between the Modulation Instability and Stimulated Brillouin Scattering in a Broadband Slow Light Device

We observe competition between the modulation instability (MI) and stimulated Brillouin scattering (SBS) in a 9.2-GHz broadband SBS slow light device, in which a standard 20-km-long single-mode LEAF fibre is used as the SBS medium. We find that MI is dominant and depletes most of the pump power when we use an intense pump beam at ~1.55 {\mu}m, where the LEAF fibre is anomalously dispersive. The dominance of the MI in the LEAF-fibre-based system suppresses the SBS gain, degrading the SBS slow light delay and limiting the SBS gain-bandwidth to 126 dB \cdot GHz. In a dispersion-shifted highly nonlinear fibre, the SBS slow light delay is improved due to the suppression of the MI, resulting in a gain-bandwidth product of 344 dB \cdot GHz, limited by our available pump power of 0.82 W

Segregation and ordering at the (1×2) reconstructed Pt80Fe20(110) surface determined by low-energy electron diffraction

The surface of an ordered Pt80Fe20(110) crystal exhibits (1×2) and (1×3) reconstructions depending on the annealing treatment after ion bombardment. The (1×3) structure occurs after annealing in the range 750 to 900 K. Annealing above 1000 K leads to the (1×2) structure, which is, from the present result, unambiguously attributed to the same geometrical reconstruction as Pt(110) but with smaller relaxation amplitudes: a detailed low-energy electron-diffraction analysis concludes to a missing-row structure with row pairing in layers 2 and 4 accompanied by a buckling in layers 3 and 5. The top layer spacing is contracted by 13%, and further relaxations are detectable down to the fifth layer. The specific diffraction spots associated with the bulk chemical ordering along the dense [1¯10] rows are very weak: The I(V) analysis shows that this chemical ordering is absent in the outermost ‘‘visible’’ rows but gradually recovers over five to six layers deep. General Pt enrichment is found in the surface ‘‘visible’’ rows (in layers 1–3), but segregation and order yield a subtle redistribution of Pt and Fe atoms in deeper rows: For example, in layer 2, the visible row is Pt rich, whereas the other row (buried under layer 1) is enriched with Fe. Because of the many parameters considered, a fit procedure was applied to a large data basis to solve the structure; the results were confirmed and illustrated subsequently by a standard I(V) analysis for the most relevant parameters. The final r factors are RDE=0.36, RP=0.34, and RZJ=0.14 for two beam sets at normal and oblique incidence consisting of 26 and 21 beams, respectively

Early assessment of glucose abnormalities during continuous glucose monitoring associated with lung function impairment in cystic fibrosis patients

AbstractBackgroundCystic fibrosis-related diabetes (CFRD) is correlated with a decline in lung function. Under certain circumstances, oral glucose tolerance test (OGTT) screening, used to diagnose CFRD, fails to reveal early glucose tolerance abnormalities. In this situation, continuous glucose monitoring (CGM) could be a useful tool for evaluating early abnormalities of glucose tolerance in CF patients. We aimed to study the CGM glucose profile in CF patients with normal OGTT screening results and to evaluate lung function and nutritional status according to the CGM glucose profile.MethodsWe assessed glycemic control, the CGM glucose profile, nutritional status, lung function antibiotic courses and colonization (P. aeruginosa and S. aureus) in CF patients, aged 10years and over, with normal screening OGTT results (blood glucose at T120min<7.8mmol/l). Two groups were identified according to the max CGM glucose value: Group 1<11mmol/l and Group 2≥11mmol/l.ResultsAmong the 38 patients with normal OGTT, 12 (31.6%) were in Group 2. Compared to Group 1, Group 2 patients exhibited a significant impairment in lung function: FEV1, 68.2±25.6% vs. 87.3±17%, p=0.01 and FVC, 86.1%±19.4% vs. 99.3%±13.4%, p=0.021, as well as a higher rate of colonization by P. aeruginosa: 83.3% vs. 44%, p=0.024. Nevertheless, there were no differences in nutritional status (BMI standard deviation score: p=0.079; prealbumin: p=0.364).ConclusionsCGM reveals early abnormalities of glucose tolerance that remain undiagnosed by OGTT screening and are associated with worse lung function and a higher prevalence of P. aeruginosa colonization in patients with CF.Clinical trial registration number: NCT00476281