Antimony-121 Mössbauer spectral study of the Eu14MnSb11 and Yb14MnSb11 Zintl compounds

The antimony-121 M?ssbauer spectra of the Yb14MnSb11 and Eu14MnSb11 Zintl compounds have been measured between 2 or 5 and 300 K. The resulting three-dimensional arrays of the spectral counts, velocity, and temperature have been simultaneously fit with a minimum number of free parameters. These fits yield a 0 Kelvin transferred hyperfine field of 2.9(2) T, a Curie temperature of 57(3) K, and a M?ssbauer temperature of 182(2) K for Yb14MnSb11; in this case the transferred field arises solely from the ordering of Mn2+. Because Eu14MnSb11 has both Eu2+ and Mn2+ ions that are magnetically ordered, its antimony-121 M?ssbauer spectra are more complex and reveal two magnetic transitions, the first at 92(1) K resulting from the ordering of the Mn2+ ions and the second at 9.5(1.0) K resulting from the ordering of the Eu2+ ions; the corresponding 0 Kelvin transferred hyperfine fields are 1.3(1) and 3.7(1) T. The antimony-121 isomer shifts yield electronic configurations of 5s1.745p4.28 and 5s1.745p4.19 for the average antimony anion in Yb14MnSb11 and Eu14MnSb11, respectively.     

The sublimation enthalpy of dimethyl oxalate

The sublimation enthalpy of dimethyl oxalate has been measured by calorimetric and head space analysis. These results along with vaporization enthalpy measured by correlation gas chromatography and fusion enthalpy measurements are compared to results predicted by two estimation techniques. A previous experimental measurement was found to be in error. A mean value of (75.2±0.5) kJ/mol was obtained which results in a corrected molar value of (–681.5±0.8) kJ/mol for the enthalpy of formation of gaseous dimethyl oxalate, _f H _m ^o (g, 298.15 K). This new value of _f H _m ^o (g, 298.15 K) for dimethyl oxalate, in combination with other enthalpies of formation, suggests that the ground state of oxalates are destabilized relative to -diketones by approximately 25 kJ/mol.     

Codimension One Threshold Manifold for the Critical gKdV Equation

We construct the “threshold manifold” near the soliton for the mass critical gKdV equation, completing results obtained in Martel et al. (Acta Math 212:59–140, 2014, J Math Eur Soc 2015). In a neighborhood of the soliton, this C¹ manifold of codimension one separates solutions blowing up in finite time and solutions in the “exit regime”. On the manifold, solutions are global in time and converge locally to a soliton. In particular, the soliton behavior is strongly unstable by blowup.     

Progressive construction of an “Olympic” gel

We consider a melt of cyclic polymers (N monomers per chain) containing a small volume fraction ϕ of open cycles (P monomers per chain, with P< N) with reactive ends. The reaction leads to the formation of small P-rings. If these P-rings trap a sufficient number ofN-rings, a macroscopic cluster (“Olympic” gel) will appear. Using a very primitive theory (where the statistics of knots is replaced by a statistics of proximity), we expect gelation to occur when ϕ > max P^1/2/N,(1/N) exp(const/P). Our study is restricted to N-rings that are small enough for their conformations to be Gaussian.     

Effect of the doping level on the biological stability of hydrogenated boron doped diamond electrodes

Fouling of electrode surfaces by electrode reaction products or by biological spectator species is known to inactivate electrochemical sensors and thus limit their use in biological conditions. Here we present an investigation on the stability of boron doped diamond (BDD) electrodes with different levels of doping. Three different doping levels were used (0.1, 1 and 5% in the carbon phase). The highly doped (5%) BDD is of particular interest as it is here used for the first time for biological applications. Three different redox reactions were examined based on their electrode reaction characteristics: ruthenium(III) hexaammine (outer sphere), ferrocyanide (surface dependent), dopamine (adsorption mediated). The effect of albumin at blood concentration was studied. All results were compared with glassy carbon. There were no significant differences for the outer sphere electrochemistry, but all the BDDs showed improved resistance to fouling for the ferrocyanide oxidation. The electrocatalytic activity of BBD towards dopamine oxidation increased with increased boron content. However, this appears to be due to a larger number of defect sites which also increases the vulnerability to fouling by albumin and by electrode reaction products and the 5% BDD had similar properties to glassy carbon in this regard. These results suggest that it is possible to optimise the BDD performance for specific applications and that the large potential window for BDD may be due, at least in part, to its relatively poor electrocatalytic activity.     

Synthesis, complexation and NMR relaxation properties of Gd3+ complexes of Mes(DO3A)3

Medium sized molecules endowed with multiple Gd(3+) complexes are efficient high magnetic field MRI contrast agents. The novel ligand Mes(DO3A)(3), presenting three DO3A (1,4,7,10-tetraazacyclododecane-N,N',N'-triacetatic acid) units grafted on the methyl positions of a central mesitylene (1,3,5-trimethylbenzene), has been synthesized. Designed as an MRI contrast agent, this ligand is complexed with Gd(3+) and its efficiency is characterized by variable field (1)H-NMR and variable temperature (17)O-NMR. The evaluation of the relaxation and paramagnetic chemical shift data allowed the identification of an undesired binuclear complex which is obtained by using the classical procedure for complexation as described in the literature. An intramolecular capping mechanism appears to be responsible for the failure to introduce a third Gd(3+) ion into the ligand. A new alternative method, based on pre-complexation with Mg(2+) followed by transmetallation is described here and leads to the expected trinuclear Gd(3+) complex [Mes{Gd(DO3A)(H(2)O)(2)}(3)]. The rate constants for the water exchange (k(ex)(298) = 32 × 10(6) s(-1)) for the bi- and trinuclear complex appeared to be the same, which is surprising in relation to the difference in the charge of the complex and to the difference in the number of coordinated water molecules, one and two per Gd(3+) for the binuclear and trinuclear complex, respectively.     

Penetration and blown air effect in granular media

Sand is known to oppose an increasing resistance to penetration with depth. This is different from what happens in liquids since granular media, usually nonthermal systems, oppose solid friction to the motion. We report another striking and "counterintuitive" difference between the penetration dynamics observed in sand and in liquids. When pushing a top-closed shell (e.g., an upside down glass) into a liquid, the trapped air increases the buoyancy and opposes the penetration. It is more difficult to push a top capped cylinder than an opened one vertically into liquids. In contrast, the penetration is considerably easier in dense sand when cylinders are top capped. In this discrete and biphasic medium, the trapped air escapes from the shell, fluidizes the sand, and eases the motion.     

Allylsilanes in "tin-free" oximation, alkenylation, and allylation of alkyl halides

Tin-free oximation, vinylation, and allylation of alkyl halides have been developed by using allylsilanes as di-tin surrogates. Initiation of the radical process with a peroxide provides the silyl radical, which can abstract a halogen from the corresponding alkyl halide. The resulting carbon-centered radical then adds to various acceptors, including a sulfonyloxime, a vinylsulfone, and an allylsulfone, leading to formation of the desired products along with the corresponding allylsulfone resulting from the reaction of the PhSO(2) radical with the allylsilane precursor. Better results were generally obtained with methallylsilane 1b than with 1a. This observation was rationalized by invoking the higher nucleophilicity of 1b and the faster β-fragmentation of the corresponding β-silyl radical intermediate. Calculation of the energy barrier for the β-fragmentation of a series of β-silyl radicals at the DFT level supported this hypothesis. Finally, a second version of these oximation and vinylation reactions, based on the utilization of 3-tris(trimethylsilyl)silylthiopropene, was devised, affording the desired oximes and olefins in reasonable yields. This strategy allowed the title reaction to be performed under milder conditions (AIBN, benzene, 80 °C), as a result of the easier β-fragmentation of the C-S bond as compared with the C-Si bond.     

Macroscopic Diffusion from a Hamilton-like Dynamics

We introduce and analyze a model for the transport of particles or energy in extended lattice systems. The dynamics of the model acts on a discrete phase space at discrete times but has nonetheless some of the characteristic properties of Hamiltonian dynamics in a confined phase space: it is deterministic, periodic, reversible and conservative. Randomness enters the model as a way to model ignorance about initial conditions and interactions between the components of the system. The orbits of the particles are non-intersecting random loops. We prove, by a weak law of large number, the validity of a diffusion equation for the macroscopic observables of interest for times that are arbitrary large, but small compared to the minimal recurrence time of the dynamics.     

Fractal Pattern for Multiscale Digital Image Correlation

Background:

Digital Image Correlation (DIC) is based on the matching, between reference and deformed state images, of features contained in patterns that are deposited on test sample surfaces. These features are often suitable for a single scale, and there is a current lack of multiscale patterns capable of providing reliable displacement measurements over a wide range of scales.

Objective:

Here, we aim to demonstrate that a pattern based on a fractal (self-affine) surface would make a suitable pattern for multiscale DIC.

Methods:

A method to numerically generate patterns directly from a desired auto-correlation function is introduced. It is then enhanced by a Mean Intensity Gradient (MIG) improvement process based on grey level redistribution. Numerical experiments at multiple scales are performed for two different imposed displacement fields and results for one of the patterns generated are compared with those obtained for a random pattern and a Perlin noise one.

Results:

The proposed pattern is shown to lead to DIC errors comparable to those found with the two others for the first scales, but has much greater robustness. More importantly, the pattern generated here exhibits stable errors and robustness with respect to the scale whereas these two outputs become significantly degraded for the other two patterns as the scale increases.

Conclusions:

As a result, scale invariance properties of the pattern based on fractal surfaces correspond to scale invariance in DIC errors as well. This is of great interest regarding the use of such patterns in multiscale DIC.