262,644 research outputs found
Reactive organoallyl species generated from aryl halides and allene: allylation of alpha,beta-unsaturated aldehydes and cyclic ketones employing Pd/In transmetallation processes
Allylation of α,β-unsaturated aldehydes and cyclic ketones promoted by Pd/In transmetallation processes has been studied. The unsaturated aldehydes underwent regioselective 1,2-addition to afford secondary homoally alcohols. The reactions have been performed using Pd(OAc)2/PPh3 as catalytic system and metallic indium affording the products in good yields. The same transformation with unsaturated ketones proved to be less efficient, while saturated cyclic ketones delivered generally excellent yields in the presence of CuI. In these latter processes the presence of a distal heteroatom influences the reaction rate
On-sample water content measurement for a complete local monitoring in triaxial testing of unsaturated soils
To provide a complete local monitoring of the state of an unsaturated soil
sample during triaxial testing, a local water content measurement device was
adapted to a triaxial device comprising the measurement of local displacements
(Hall effect transducers) and suction (High capacity transducer). Water content
was locally monitored by means of a resistivity probe. The water
content/resistivity calibration curves of an intact natural unsaturated loess
from Northern France extracted by block sampling at two depths (1 and 3.3 m)
were carefully determined, showing good accuracy and repeatability. The
validity of two models giving the resistivity of unsaturated soils with respect
to their water content was examined
Development of a Computer Vision-Based Three-Dimensional Reconstruction Method for Volume-Change Measurement of Unsaturated Soils during Triaxial Testing
Problems associated with unsaturated soils are ubiquitous in the U.S., where expansive and collapsible soils are some of the most widely distributed and costly geologic hazards. Solving these widespread geohazards requires a fundamental understanding of the constitutive behavior of unsaturated soils. In the past six decades, the suction-controlled triaxial test has been established as a standard approach to characterizing constitutive behavior for unsaturated soils. However, this type of test requires costly test equipment and time-consuming testing processes. To overcome these limitations, a photogrammetry-based method has been developed recently to measure the global and localized volume-changes of unsaturated soils during triaxial test. However, this method relies on software to detect coded targets, which often requires tedious manual correction of incorrectly coded target detection information. To address the limitation of the photogrammetry-based method, this study developed a photogrammetric computer vision-based approach for automatic target recognition and 3D reconstruction for volume-changes measurement of unsaturated soils in triaxial tests. Deep learning method was used to improve the accuracy and efficiency of coded target recognition. A photogrammetric computer vision method and ray tracing technique were then developed and validated to reconstruct the three-dimensional models of soil specimen
A 1-D modelling of streaming potential dependence on water content during drainage experiment in sand
The understanding of electrokinetics for unsaturated conditions is crucial
for numerous of geophysical data interpretation. Nevertheless, the behaviour of
the streaming potential coefficient C as a function of the water saturation Sw
is still discussed. We propose here to model both the Richards' equation for
hydrodynamics and the Poisson's equation for electrical potential for
unsaturated conditions using 1-D finite element method. The equations are first
presented and the numerical scheme is then detailed for the Poisson's equation.
Then, computed streaming potentials (SPs) are compared to recently published SP
measurements carried out during drainage experiment in a sand column. We show
that the apparent measurement of DV / DP for the dipoles can provide the SP
coefficient in these conditions. Two tests have been performed using existing
models for the SP coefficient and a third one using a new relation. The results
show that existing models of unsaturated SP coefficients C(Sw) provide poor
results in terms of SP magnitude and behaviour. We demonstrate that the
unsaturated SP coefficient can be until one order of magnitude larger than
Csat, its value at saturation. We finally prove that the SP coefficient follows
a non-monotonous behaviour with respect to water saturation. Key words:
Electrical properties; Electromagnetic theory; Hydrogeophysics; Hydrology;
Permeability and porosity; electrokinetic; streaming potential; self-potential;
water content; water saturation; unsaturated condition; finite element modelin
Modelling large deformation problems in unsaturated soils
Applications of unsaturated soil mechanics often involve large deformations and displacements. This is the case of collapse behaviour of low density soils or the unrestrained swelling of expansive clays. Rain induced instability of unsaturated slopes is a further example of large displacements that cause important damages around the world every year. Since standard lagrangian Finite Element methods are not well suited to model large deformations, particle-based methods are under development. This is the case of the Material Point Method (MPM), which offers an interesting alternative. Recently, the MPM has been extended to model unsaturated soil problems, where the soil is understood as a unique medium integrated by three distinct phases (solid, liquid and gas). In this paper, the MPM computational cycle for unsaturated soils is described. In addition, a validation of the 3-phase MPM approach is presented by means of the modelling of a one-dimensional infiltration problem. Finally, the applicability of MPM to solve slope instabilities is presented. The simulation of the whole instability process of an embankment subjected to rain infiltration is analysed in detail.Postprint (published version
Influence of Phosphoramidites in Copper-Catalyzed Conjugate Borylation Reaction
Copper(I) has become the preferred metal to catalyze the β-boration of α,β-unsaturated carbonyl compounds, and now we demonstrate that easily accessible monodentate chiral ligands, such as phosphoramidites and phosphites, can be convenient alternative ligands to induce asymmetry in the enantioselective version of this reaction, particularly in the β-boration of α,β-unsaturated imines.
Lateral phase separation in mixtures of lipids and cholesterol
In an effort to understand "rafts" in biological membranes, we propose phenomenological models for saturated and unsaturated lipid mixtures, and lipid-cholesterol mixtures. We consider simple couplings between the local composition and internal membrane structure, and their influence on transitions between liquid and gel membrane phases. Assuming that the gel transition temperature of the saturated lipid is shifted by the presence of the unsaturated lipid, and that cholesterol acts as an external field on the chain melting transition, a variety of phase diagrams are obtained. The phase diagrams for binary mixtures of saturated/unsaturated lipids and lipid/cholesterol are in semi-quantitative agreement with the experiments. Our results also apply to regions in the ternary phase diagram of lipid/lipid/cholesterol systems
Modelling plasticity of unsaturated soils in a thermodynamically consistent framework
Constitutive equations of unsaturated soils are often derived in a
thermodynamically consistent framework through the use a unique 'effective'
interstitial pressure. This later is naturally chosen as the space averaged
interstitial pressure. However, experimental observations have revealed that
two stress state variables were needed to describe the stress-strain-strength
behaviour of unsaturated soils. The thermodynamics analysis presented here
shows that the most general approach to the behaviour of unsaturated soils
actually requires three stress state variables: the suction, which is required
to describe the retention properties of the soil and two effective stresses,
which are required to describe the soil deformation at water saturation held
constant. Actually, it is shown that a simple assumption related to internal
deformation leads to the need of a unique effective stress to formulate the
stress-strain constitutive equation describing the soil deformation. An
elastoplastic framework is then presented and it is finally shown that the
Barcelona Basic Model, a commonly accepted model for unsaturated soils, as well
as all models deriving from it, appear as special extreme cases of the
thermodynamic framework proposed here
Stabilized unsaturated polyesters
An unsaturated polyester, such as propylene glycolmaleic acid phthalic acid prepolymer dissolved in styrene is interpolymerized with an ultraviolet absorber and/or an antioxidant. The unsaturated chain may be filled with H or lower alkyl such as methyl and tertiary alkyl such as tertiary butyl. A polymer stable to exposure to the outdoors without degradation by ultraviolet radiation, thermal and/or photooxidation is formed
- …