Distortion Correction Protocol for Digital Image Correlation after Scanning Electron Microscopy: Emphasis on Long Duration and Ex-Situ Experiments

Recently, scanning electron microscopy (SEM) has been used for digital image correlation (DIC), as micrographs can be acquired with high magnification, providing improved resolution to quantify strain heterogeneities. However, it has been shown by researchers that SEM images can be problematic due to inherent electromagnetic distortions that are not present in optical images. Drift, spatial distortions, and magnification uncertainties are the main issues that can seriously affect the accuracy of localized strain measurements. The present work focuses on long duration experiments, for which images are taken days or weeks apart. We have proposed a systematic procedure to reduce drift, correct spatial distortion, and account for magnification variations between pairs of acquired images. Additionally, SEM parameters are discussed and chosen to increase the signal-to-noise ratio and improve the accuracy of the DIC measurements. The spatial distortion correction increases the repeatability of the correlated values and the precision of the measurements. The implementation for this type of correction is done by applying the measured distortion gradient of a certified grid onto the DIC strain field. The magnification adjustment increases the reliability of the strain maps, ensuring the measurements are in agreement with the actual strain induced during the experiment. We have presented a systematic protocol for ex-situ DIC experiments within the SEM and some basic cross-check procedures that can be performed to evaluate the reliability of the reference grid and the precision of the final strain map.     

The Sedov self-similar point blast solutions in nonuniform media

The character of a spherical blast wave propagating radially outward in a pressureless medium with density decreasing as ^– changes dramatically as and the adiabatic index vary. Plots of the Sedov formulas for the density, velocity, and pressure profiles behind the shock front for a selection of different parameters illustrate this and suggest that some of the solutions satisfy the conditions for the Rayleigh-Taylor or convective instablity.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

Visible spectra of some chloropentakis(alkylamine)-cobalt(III) complexes

All four spin-allowed transitions in the visible spectra of the complexes [Co(RNH₂)₅Cl]²⁺, R = H, Me, Et, n-Pr, and n-Bu, have been resolved and the relevant crystal field and RACAH parameters determined with a method previously described. The results appear to be consistent within the series and agree well with those reported in the literature for structurally related systems.     

Isolation and crystal structures of triethylenediamine-hydroquinone (1/1) and triethylenediamine-phenol (1/2)

Two crystalline adducts of triethylenediamine with hydroquinone [N(CH₂CH₂)₃N·C₆H₄(OH)₂,I] and phenol [N(CH₂CH₂)₃N·2C₆H₅OH,II] have been isolated and characterized by X-ray analysis. ComplexI crystallizes in the monoclinic space groupC2/c, witha=11.944(2),b=9.491(2),c=11.986(2) Å,=121.70(1)°, andZ=4. Both molecular components occupy sites of symmetry 2, and are linked alternately by N H-O hydrogen bonds to form infinite zigzag chains. Crystals ofII are also monoclinic, with space groupP2₁/c,a=12.987(2),b=6.376(1),c=21.350(3) Å,=106.94(1)°, andZ=4. The structure is composed of discrete hydrogen-bonded molecular aggregates corresponding to the stoichiometric formula. The triethylenediamine moieties in both adducts closely approximate to the idealizedD ₃ h conformation. The structures have been refined toR values of 0.097 (I) and 0.092 (II) using, respectively, 479 and 1580 observed MoK data.     

High‐Pressure Raman and Calorimetry Studies of Vanadium(III) Alkyl Hydrides for Kubas‐Type Hydrogen Storage

Reversible hydrogen storage under ambient conditions has been identified as a major bottleneck in enabling a future hydrogen economy. Herein, we report an amorphous vanadium(III) alkyl hydride gel that binds hydrogen through the Kubas interaction. The material possesses a gravimetric adsorption capacity of 5.42 wt % H₂ at 120 bar and 298 K reversibly at saturation with no loss of capacity after ten cycles. This corresponds to a volumetric capacity of 75.4 kgH₂ m^?3. Raman experiments at 100 bar confirm that Kubas binding is involved in the adsorption mechanism. The material possesses an enthalpy of H₂ adsorption of +0.52 kJ mol^?1 H₂, as measured directly by calorimetry, and this is practical for use in a vehicles without a complex heat management system.     

Reversible interpenetration in a metal-organic framework triggered by ligand removal and addition

Caging cages: Crystals of a metal-organic framework, MOF-123 [Zn(7) O(2) (NBD)(5) (DMF)(2) ] have a three-dimensional porous structure in which DMF ligands (see picture, pink) protrude into small channels. Removal of these ligands triggers the transformation of this MOF to the doubly interpenetrating form, MOF-246 [Zn(7) O(2) (NBD)(5) ]. Moreover, addition of DMF into MOF-246 triggers reverse transformation to give MOF-123. NBD=2-nitrobenzene-1,4-dicarboxylate.     

Nitrogen and Hydrogen Adsorption by an Organic Microporous Crystal

Quick on the uptake : Following its identification during a targeted search, the intriguing crystal structure of 3,3′,4,4′‐tetra(trimethylsilylethynyl)biphenyl was investigated. Simple removal of the included solvent provides an organic crystal with an open microporous structure that has a striking similarity to that of zeolite A (see picture). Reversible adsorption of nitrogen and hydrogen gases at 77 K confirms that the microporosity is permanent.

     

Synthesis,acid hydrolysis,and Visible spectra of some bromopentakis(alkylamine)cobalt(III) complexes

Complexes of the [Co(RNH₂)₅Br]²⁺ type with R = Me, Et, n-Pr and n-Bu have been synthesized. The acid hydrolysis of these complexes have been studied in aqueous solution except for the butylamine complex, in which case the acid hydrolysis has been done in diocane-water medium because the complex is only slightly soluble in water. The acid hydrolysis of these complexes follow a pseudo-first-order reaction rate law and an S_N2 mechanism with an octahedral wedge transition state has been assigned. The visible spectra of these complexes, together with [Co(NH₃)₅Br]²⁺, have been recorded and the overlapped bands have been resolved into Gaussian curves by least squares. Values of crystal field parameters Dq(RNH₂), Dq(Br) and Dt in the complexes have been determined with a method originally devised by Wentworth and Piper. The calculated results agree well with those reported by other workers and a linear relationship previously observed by Mitzner et al. between Dq(RNH₂) and ΔH° of proton ionization of RNH₃⁺ ions is also found.