The thermal conductivity of silicon nitride membranes is not sensitive to stress

We have measured the thermal properties of suspended membranes from 10 K to 300 K for two amplitudes of internal stress (about 0.1 GPa and 1 GPa) and for two different thicknesses (50 nm and 100 nm). The use of the original 3 \omega -Volklein method has allowed the extraction of both the specific heat and the thermal conductivity of each SiN membrane over a wide temperature range. The mechanical properties of the same substrates have been measured at helium temperatures using nanomechanical techniques. Our measurements show that the thermal transport in freestanding SiN membranes is not affected by the presence of internal stress. Consistently, mechanical dissipation is also unaffected even though Qs increase with increasing tensile stress. We thus demonstrate that the theory developed by Wu and Yu [Phys. Rev. B 84, 174109 (2011)] does not apply to this amorphous material in this stress range. On the other hand, our results can be viewed as a natural consequence of the "dissipation dilution" argument [Y. L. Huang and P. R. Saulson, Rev. Sci. Instrum. 69, 544 (1998)] which has been introduced in the context of mechanical damping.Comment: 15 pages, 6 figures. Submitted to PR

Highly sensitive thermal conductivity measurements of suspended membranes (SiN and diamond) using a 3w-Volklein method

A suspended system for measuring the thermal properties of membranes is presented. The sensitive thermal measurement is based on the 3$\omega$ dynamic method coupled to a V$\ddot{o}$lklein geometry. The device obtained using micro-machining processes allows the measurement of the in-plane thermal conductivity of a membrane with a sensitivity of less than 10nW/K (+/-$5x10^{-3}$Wm$^{-1}K^{-1}$ at room temperature) and a very high resolution ($\Delta K/K =10^{-3}$). A transducer (heater/thermometer) centered on the membrane is used to create an oscillation of the heat flux and to measure the temperature oscillation at the third harmonic using a Wheatstone bridge set-up. Power as low as 0.1nanoWatt has been measured at room temperature. The method has been applied to measure thermal properties of low stress silicon nitride and polycrystalline diamond membranes with thickness ranging from 100 nm to 400 nm. The thermal conductivity measured on the polycrystalline diamond membrane support a significant grain size effect on the thermal transport.Comment: 17 page

Hydrogenation of levulinic acid to gamma-valerolactone over anatase-supported Ru catalysts:Effect of catalyst synthesis protocols on activity

γ-Valerolactone (GVL) is a value-added renewable chemical with great potential and can be obtained from biomass by the hydrogenation of levulinic acid (LA) using metal-based catalysts, such as Ru/TiO2. We here report an in depth study of the effect of catalyst synthesis parameters on the performance of Ru/TiO2 (anatase), varying the nature of the Ru-precursor and the conditions of the calcination and/or reduction step. Catalyst performance was evaluated under batch conditions at a hydrogen pressure of 45 bar and using either water (90 °C) or dioxane (150 °C) as solvent. The experiments showed that catalyst activity depends greatly on the Ru precursor used (RuCl3, RuNO(NO3)3, Ru(NH3)6Cl3). Best results when considering the turn-over frequencies (TOF) of the catalysts were obtained using the RuNO(NO3)3 precursor, whereas RuCl3 performed better when considering the initial rate based on Ru intake. An intermediate calcination step and the use of a hydrogen-rich sweep gas during the final reduction step were shown to have a negative impact on catalyst activity. Characterization of the fresh catalysts by BET and TEM provided valuable insight in the relation between the catalyst structure and its activity

Universality of thermal transport in amorphous nanowires at low temperatures

Thermal transport properties of amorphous materials at low temperatures are governed by the interaction between phonons and localized excitations referred to as tunneling two-level systems (TLSs). The temperature variation of the thermal conductivity of these amorphous materials is considered as universal and is characterized by a quadratic power law. This is well described by the phenomenological TLS model even though its microscopic explanation is still elusive. Here, by scaling down to the nanometer-scale amorphous systems much below the bulk phonon-TLS mean free path, we probe the robustness of that model in restricted geometry systems. Using very sensitive thermal conductance measurements, we demonstrate that the temperature dependence of the thermal conductance of silicon nitride nanostructures remains mostly quadratic independently of the nanowire section. It does not follow the cubic power law in temperature as expected in a Casimir-Ziman regime of boundary-limited thermal transport. This shows a thermal transport counterintuitively dominated by phonon-TLS interactions and not by phonon boundary scattering in the nanowires. This could be ascribed to an unexpected high density of TLSs on the surfaces which still dominates the phonon diffusion processes at low temperatures and explains why the universal quadratic temperature dependence of thermal conductance still holds for amorphous nanowires

Functional interdependence of BRD4 and DOT1L in MLL leukemia.

Targeted therapies against disruptor of telomeric silencing 1-like (DOT1L) and bromodomain-containing protein 4 (BRD4) are currently being evaluated in clinical trials. However, the mechanisms by which BRD4 and DOT1L regulate leukemogenic transcription programs remain unclear. Using quantitative proteomics, chemoproteomics and biochemical fractionation, we found that native BRD4 and DOT1L exist in separate protein complexes. Genetic disruption or small-molecule inhibition of BRD4 and DOT1L showed marked synergistic activity against MLL leukemia cell lines, primary human leukemia cells and mouse leukemia models. Mechanistically, we found a previously unrecognized functional collaboration between DOT1L and BRD4 that is especially important at highly transcribed genes in proximity to superenhancers. DOT1L, via dimethylated histone H3 K79, facilitates histone H4 acetylation, which in turn regulates the binding of BRD4 to chromatin. These data provide new insights into the regulation of transcription and specify a molecular framework for therapeutic intervention in this disease with poor prognosis

Driving while distracted: the effects of experience, age and gender

Abstract not available

Sustainability metrics for a fossil- and renewable-based route for 1,2-propanediol production: A comparison

SSCI-VIDE+CDFA+JFT:CPIInternational audienceHistorically 1,2-PDO had always been exclusively produced from fossil resources and many routes have been industrially commercialized. More recently, new strategies based on renewable resources have allowed for the development of technology for the commercial production of 1,2-PDO from glycerol. In the present study the fossil-based chlorhydrin process is taken as a reference and compared to the catalytic hydrogenolysis of glycerol route to evaluate which one is the most advantageous in terms of sustainability. To this extent, a concise and practical approach is employed that allows for an early stage comparison based on four preselected green metrics that estimate material and energy efficiency, economic added value and land use. The evaluation shows that the renewable-based routes can provide a viable alternative to the petrochemical route and both approaches must therefore be considered in a global process. Importantly, the production of valuable co-products needs to be included in such an assessment as these strongly influence its outcome. (C) 2014 Elsevier B.V. All rights reserved

From glycerol to lactic acid under inert conditions in the presence of platinum-based catalysts: The influence of support

SSCI-VIDE+CDFA+JFT:NVI:FAU:MBE:LDJ:CPIInternational audienceIn this work, it was shown that glycerol (Gly) can be effectively converted to lactic acid (LA) under inert atmosphere using a Pt/ZrO2 catalyst. Starting from pure glycerol, at 180 degrees C and under a He pressure of 30 bar, we were able to achieve up to 80% yield of LA after a reaction time of 8 h. The catalysts performance of Pt/TiO2, Pt/C and Pt/ZrO2 were compared showing that using Pt/ZrO2 high conversion and stable LA selectivity were achieved during all the process. Further, using Pt/ZrO2 the LA selectivity was less sensitive to the nature of the reaction atmosphere while using either H-2 or He. While using crude Gly (85% purity), a lower reaction rate was obtained in the presence of Pt/ZrO2, however high selectivity to LA (similar to 80%) was maintained. (C) 2014 Elsevier B.V. All rights reserved

Glycerol conversion to lactic acid in the presence of platinum based catalysts.

International @ BIOVERT+JFT:MBE:LDJ:CPIInternational audienceIn the last decade, lactic acid (LA) became an important feedstock, with an annual production of 120,000 tonnes. This importance comes from its use in: i) food-industry: as a food acidulant or as a bacterial spoilage inhibitor and (ii) as a new raw material to produce biodegradable thermoplastics. Nowadays, the LA production is mainly ensured by a saccharide fermentation route; nevertheless, this process still needs improvement. We have previously shown that lactic acid can be obtained from glycerol in the presence of iridium or rhodium-based catalysts. In this present work we introduce the LA obtainment from glycerol (Gly) in the presence of platinum (Pt) - based catalysts