343 research outputs found
Direct measurements of DOCO isomers in the kinetics of OD+CO
Quantitative and mechanistically-detailed kinetics of the reaction of
hydroxyl radical (OH) with carbon monoxide (CO) have been a longstanding goal
of contemporary chemical kinetics. This fundamental prototype reaction plays an
important role in atmospheric and combustion chemistry, motivating studies for
accurate determination of the reaction rate coefficient and its pressure and
temperature dependence at thermal reaction conditions. This intricate
dependence can be traced directly to details of the underlying dynamics
(formation, isomerization, and dissociation) involving the reactive
intermediates cis- and trans-HOCO, which can only be observed transiently.
Using time-resolved frequency comb spectroscopy, comprehensive mechanistic
elucidation of the kinetics of the isotopic analogue deuteroxyl radical (OD)
with CO has been realized. By monitoring the concentrations of reactants,
intermediates, and products in real-time, the branching and isomerization
kinetics and absolute yields of all species in the OD+CO reaction are
quantified as a function of pressure and collision partner.Comment: 19 pages, 4 figure
Magnetic and Magnetotransport Properties of La0.7ca0.3mn1-x(zn,cu)xo3
Magnetic and magnetotransport properties of two perovskite manganite samples of La0.7Ca0.3Mn0.9Zn0.1O3 and La0.7Ca0.3Mn0.95Cu0.05O3 prepared by conventional solid-state reaction have been studied in detail. Experimental results revealed that the temperature dependences of magnetization and resistance varied strongly around the phase-transition temperature. Maximum magnetoresistance (MR) values of La0.7Ca0.3Mn0.9Zn0.1O3 and La0.7Ca0.3Mn0.95Cu0.05O3 under an applied field of 400 Oe were about 21.4 % and 11.0 %, respectively. The maximum magnetic-entropy change (ΔSM) was 2.73 J/kg.K for La0.7Ca0.3Mn0.9Zn0.1O3, and 3.34 J/kg.K for La0.7Ca0.3Mn0.95Cu0.05O3 when the applied field was 45 kOe. Both the MR and ΔSM values obtained from two samples were smaller than those of the parent compound La0.7Ca0.3MnO3. This was due to the change in the Mn3+/Mn4+ ratio caused by Zn and Cu dopants, which led to a change in the type of the ferromagneticparamagnetic phase transition
Flexural-strengthening efficiency of cfrp sheets for unbonded post-tensioned concrete T-beams
There has been a limited number of studies about the flexural behavior of unbonded post-tensioned concrete (UPC) beams strengthened with carbon fibre reinforced polymer (CFRP) and these studies have not systematically examined the effect of CFRP sheets on the tendon strain as well as the strengthening efficiency. Moreover, current design guides for the FRP strengthening techniques have not provided any design procedure for UPC structures. This study, thus, investigates the influence of CFRP sheet ratio on the flexural behavior of CFRP-strengthened UPC T-beams and quantifies its effect upon tendon behavior in this kind of UPC beams. The testing program consisted of nine large-scale UPC T-beams strengthened by different layers of CFRP sheets with or without CFRP U-wrapped anchors. The experimental results have shown that the use of CFRP sheets and CFRP U-wrapped anchors significantly affected the tendon strain. The FRP reinforcement ratio governed the flexural capacity, the crack width, the mid-span displacement, and the ductility of the beams in which the strengthening efficiency reduces with the increased number of CFRP layers. The configuration of the CFRP U-wrapped anchors affected the strain of the CFRP sheets, the failure mode and thus the beam behavior. In addition, semi-empirical equations were proposed to estimate the actual strain of unbonded tendons in which the effect of the CFRP sheets and CFRP U-wrapped anchors have been taken into consideration. The proposed equations, which are simple to use, yield reliable predictions with a small variation
Satellites May Underestimate Rice Residue and Associated Burning Emissions in Vietnam
In this study, we estimate rice residue, associated burning emissions, and compare results with existing emissions inventories employing a bottom-up approach. We first estimated field-level post-harvest rice residues, including separate fuel-loading factors for rice straw and rice stubble. Results suggested fuel-loading factors of 0.27 kg/sq m (+/-0.033), 0.61 kg/sq m (+/-0.076), and 0.88 kg/sq m (+/-0.083) for rice straw, stubble, and total post-harvest biomass, respectively. Using these factors, we quantified potential emissions from rice residue burning and compared our estimates with other studies. Our results suggest total rice residue burning emissions as 2.24 Gg PM2.5, 36.54 Gg CO and 567.79 Gg CO2 for Hanoi Province, which are significantly higher than earlier studies. We attribute our higher emission estimates to improved fuel-loading factors; moreover, we infer that some earlier studies relying on residue-to-product ratios could be underestimating rice residue emissions by more than a factor of 2.3 for Hanoi, Vietnam. Using the rice planted area data from the Vietnamese government, and combining our fuel-loading factors, we also estimated rice residue PM2.5 emissions for the entirety of Vietnam and compared these estimates with an existing all-sources emissions inventory, and the Global Fire Emissions Database (GFED). Results suggest 75.98 Gg of PM2.5 released from rice residue burning accounting for 12.8% of total emissions for Vietnam. The GFED database suggests 42.56 Gg PM2.5 from biomass burning with 5.62 Gg attributed to agricultural waste burning indicating satellite-based methods may be significantly underestimating emissions. Our results not only provide improved residue and emission estimates, but also highlight the need for emissions mitigation from rice residue burning
Unveiling the atomic position of C in Mn5Ge3 Cx thin films
Heavily carbon-doped Mn5Ge3 is a unique compound for spintronics applications as it meets all the requirements for spin injection and detection in group-IV semiconductors. Despite the great improvement of the magnetic properties induced by C incorporation into Mn5Ge3 compounds, very little information is available on its structural properties and the genuine role played by C atoms. In this paper, we have used a combination of advanced techniques to extensively characterize the structural and magnetic properties of Mn5Ge3Cx films grown on Ge(111) by solid phase epitaxy as a function of C concentration. The increase of the Curie temperature induced by C doping up to 435 K is accompanied by a decrease of the out-of-plane c-lattice parameter. The Mn and C chemical environments and positions in the Mn5Ge3 lattice have been thoroughly investigated using x-ray absorption spectroscopy techniques (x-ray absorption near-edge structures and extended x-ray absorption fine structures) and scanning transmission electronic microscopy (STEM) combined to electron energy loss spectroscopy for the chemical analysis. The results have been systematically compared to a variety of structures that were identified as favorable in terms of formation energy by ab initio calculations. For x≤0.5, the C atoms are mainly located in the octahedral voids formed by Mn atoms, which is confirmed by simulations and seen for the first time in real space by STEM. However, the latter reveals an inhomogeneous C incorporation, which is qualitatively correlated to the broad magnetic transition temperature. A higher C concentration leads to the formation of manganese carbide clusters that we identified as Mn23C6. Interestingly, other types of defects, such as interstitial Ge atoms, vacancies of Mn, and their association into line defects have been detected. They take part in the strain relaxation process and are likely to be intimately related to the growth process. This paper provides a complete picture of the structure of Mn5Ge3Cx in thin films grown by solid phase epitaxy, which is essential for optimizing their magnetic properties
Stress-driven instability in growing multilayer films
We investigate the stress-driven morphological instability of epitaxially
growing multilayer films, which are coherent and dislocation-free. We construct
a direct elastic analysis, from which we determine the elastic state of the
system recursively in terms of that of the old states of the buried layers. In
turn, we use the result for the elastic state to derive the morphological
evolution equation of surface profile to first order of perturbations, with the
solution explicitly expressed by the growth conditions and material parameters
of all the deposited layers. We apply these results to two kinds of multilayer
structures. One is the alternating tensile/compressive multilayer structure,
for which we determine the effective stability properties, including the effect
of varying surface mobility in different layers, its interplay with the global
misfit of the multilayer film, and the influence of asymmetric structure of
compressive and tensile layers on the system stability. The nature of the
asymmetry properties found in stability diagrams is in agreement with
experimental observations. The other multilayer structure that we study is one
composed of stacked strained/spacer layers. We also calculate the kinetic
critical thickness for the onset of morphological instability and obtain its
reduction and saturation as number of deposited layers increases, which is
consistent with recent experimental results. Compared to the single-layer film
growth, the behavior of kinetic critical thickness shows deviations for upper
strained layers.Comment: 27 pages, 11 figures; Phys. Rev. B, in pres
Structure, magnetism, and magnetocaloric properties of MnFeP1−xSix compounds
MnFeP1-xSix compounds with x=0.10,0.20,0.24,0.28,...,0.80,1 were prepared by high-energy ball milling and solid-state reaction. The structural, magnetic, and magnetocaloric properties are investigated as a function of temperature and magnetic field. X-ray diffraction studies show that the samples in the range from x=0.28 to 0.64 adopt the hexagonal Fe2P-type structure with a small amount of second phase which increases with increasing Si content. The samples with lower Si content show the orthorhombic Co2P-type structure. Magnetic measurements show that the paramagnetic-ferromagnetic transition temperatures range from 214 to 377 K. Of much importance is the fact that these compounds do not contain any toxic components and exhibit excellent magnetocaloric properties
Whither Magnetic Hyperthermia? A Tentative Roadmap
The scientific community has made great efforts in advancing magnetic hyperthermia for the last two decades after going through a sizeable research lapse from its establishment. All the progress made in various topics ranging from nanoparticle synthesis to biocompatibilization and in vivo testing have been seeking to push the forefront towards some new clinical trials. As many, they did not go at the expected pace. Today, fruitful international cooperation and the wisdom gain after a careful analysis of the lessons learned from seminal clinical trials allow us to have a future with better guarantees for a more definitive takeoff of this genuine nanotherapy against cancer. Deliberately giving prominence to a number of critical aspects, this opinion review offers a blend of state-of-the-art hints and glimpses into the future of the therapy, considering the expected evolution of science and technology behind magnetic hyperthermia
Real-time tracking of delayed-onset cellular apoptosis induced by intracellular magnetic hyperthermia
Aim: To assess cell death pathways in response to magnetic hyperthermia. Materials & methods: Human melanoma cells were loaded with citric acid-coated iron-oxide nanoparticles, and subjected to a time-varying magnetic field. Pathways were monitored in vitro in suspensions and in situ in monolayers using fluorophores to report on early-stage apoptosis and late-stage apoptosis and/ or necrosis. Results: Delayed-onset effects were observed, with a rate and extent proportional to the thermal-load-per-cell. At moderate loads, membranal internal-to-external lipid exchange preceded rupture and death by a few hours (the timeline varying cell-to-cell), without any measurable change in the local environment temperature. Conclusion: Our observations support the proposition that intracellular heating may be a viable, controllable and nonaggressive in vivo treatment for human pathological conditions
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