A new reagent for polypeptide synthesis: mu-oxo-bis-(tris-(dimethylamino)-phosphonium)-bis-tetrafluoroborate.

The products 1 and 2 (X = OTs) have been isolated from the reaction between hexamethylphosphortriamide and p-toluene sulfonic anhydride and the latter converted into μ-oxo-bis-[tris-(dimethylamino)-phosphonium]-bis-tetrafluoroborate 2 (X = BF₄). This is a practical reagent for the formation of the peptide link. Where racemisation is possible via oxazolone formation this can be decreased by the addition of 1-hydroxybenzotriazole or N-hydroxysuccinimide. These additives may also increase the efficiency of condensation at glycine and proline residues.     

Second-order iterations with guaranteed convergence

Recent results on optimal extrapolations of first-order stationary iterations have shown that they are necessarily divergent in a wide class of problems. This paper examines a second-order iterative process which is guaranteed to converge — in particular when applied to the solution of an arbitrary equation system. A general convergence theory for semi-iterative techniques is established at the same time.     

A crack tip tracking algorithm for cohesive interface element analysis of fatigue delamination propagation in composite materials

A novel approach is proposed for the use of cohesive elements in the analysis of delamination propagation in composite materials under high-cycle fatigue loading. The method is applicable to delamination propagation within the Paris-law regime and is suitable for the analysis of three-dimensional structures typical of aerospace applications. The major advantages of the proposed formulation are its complete independence of the cohesive zone length – which is a geometry-dependent parameter – and its relative insensitivity to mesh refinement. This is only possible via the introduction of three nonlocal algorithms, which provide (i) automated three-dimensional tracking of delamination fronts, (ii) an estimation of direction of crack propagation and (iii) accurate and mesh-insensitive integration of strain energy release rate. All calculations are updated at every increment of an explicit time-integration finite element solution, which models the envelopes of forces and displacements with an assumption of underlying constant cyclic loading. The method was implemented as a user-defined subroutine in the commercial finite element software LS-Dyna and supports the analysis of complex three-dimensional models. Results are presented for benchmark cases such as specimens with central cut plies and centrally-loaded circular plates. Accurate predictions of delamination growth rates are observed for different mesh topologies in agreement with the Paris-laws of the material.     

An investigation of iron chromium tellurates by iron-57, tellurium-125 and iodine-129 Mössbauer spectroscopy

The⁵⁷Fe Mössbauer spectra recorded at 4.2K from the trirutile-type iron chromium tellurates of composition Fe_2?xCr_xTeO₆, where x=0–2, show that the angle θ, which describes the perpendicular orientation of the magnetic moment to the basal plane of the Fe₂TeO₆ unit cell, is not changed by the incorporation of chromium until x exceeds 1.2 At this critical limit θ begins to rapidly cant to smaller values until, at compositions approaching Cr₂TeO₆, it approaches a parallel orientation to the basal plane. The¹²⁵Te and¹²⁹I Mössbauer spectra recorded from the compound FeCrTeO₆ at 77 and 4.2K are consistent with the presence of a supertransferred magnetic hyperfine field at the tellurium nucleus ofca. 76 kG.     

Study of hexagonal R-type BaFe4Sn2O11 by57Fe and119Sn Mössbauer spectroscopy

Mössbauer data have been obtained from both the⁵⁷Fe and¹¹⁹Sn isotopes for BaFe₄Sn₂O₁₁. Variable temperature studies show that magnetic ordering occurs at 77K and is probably complete at 4K. Average hyperfine fields of 504kG and 45kG were observed at the iron and tin nuclei respectively.     

Microstructural investigations of tin-molybdenum oxides by high-resolution electron microscopy

Tin-molybdenum oxides, formed by the calcination of precipitates in air, have been examined by high-resolution electron microscopy. Low-temperature calcination gives rise to the formation of small tin(IV) oxide-type crystals amidst an amorphous material whereas higher-temperature treatment results in the development of a highly crystalline rutile-related phase composed of larger particles. High concentrations of molybdenum in the initial precipitates inhibits the thermally induced crystal growth. The common occurrence of superficial disorder in the larger particles is associated with surface damage resulting from the volatilization of excess molybdenum as molybdenum(VI) oxide. Planar faults were frequently observed within the particles and, in some cases, these defects were identified as twin boundaries enriched with molybdenum. The formation of these planar faults is discussed in terms of the preparative procedure.     

Full-Field Strain Measurement and Identification of Composites Moduli at High Strain Rate with the Virtual Fields Method

The present paper deals with full-field strain measurement on glass/epoxy composite tensile specimens submitted to high strain rate loading through a split Hopkinson pressure bar (SHPB) device and with the identification of their mechanical properties. First, the adopted methodology is presented: the device, including an Ultra-High Speed camera, and the experimental procedure to obtain relevant displacement maps are described. The different full-field results including displacement, strain and acceleration maps for two mechanical tests are then addressed. The last part of the paper deals with an original procedure to identify stiffnesses on this dynamic case only using the actual strain and acceleration maps (without the applied force) by using the Virtual Fields Method. The results provide very promising values of Young’s modulus and Poisson’s ratio on a quasi-isotropic glass-epoxy laminate. The load reconstructed from the moduli and strains compares favourably with that from the readings.