Influence of FSSW parameters on fracture mechanisms of 5182 aluminium welds

The influence of the tool rotational speed, the probe plunge depth and the shoulder penetration depth on weld microstructure and on the weld strength have been studied. The shear tests showed that the friction stir spot welds fail by nugget pullout. Three microstructural factors play a determinant role on the weld's strength: the size and location of the stir zone, and the unwelded interface tip slope. With increasing rotational speed, the shear strength increases because of the larger size of the stir zone. By changing the probe plunge depth the location of the stir zone can be controlled in order to maximize the bonded distance between the interface tip and the central hole left by the probe. The shoulder penetration depth must be sufficient to ensure a horizontal interface tip and therefore avoid fracture by the opening mode (mode I) during shear loading.     

Microstructure and microtexture evolution with aging treatment in an Al–Mg–Si alloy severely deformed by HPT

Experiments were conducted on an Al–0.6 % Mg–0.4 % Si alloy to evaluate the effect of different preliminary thermal treatments on the evolution of microstructure and microtexture during processing by High-Pressure Torsion (HPT). Disks of the alloy were solution-treated, then some disks were briefly aged at 473 K, and other disks were briefly aged at 523 K before processing by HPT for up to 20 complete revolutions. The processing by HPT refined the microstructure to an average grain size as small as ~0.25 μm in the solution-treated alloy after 20 turns but preliminary aging led to slightly larger average grain sizes of ~0.35–0.40 μm after 20 turns. For all processing conditions, there was a high fraction of high-angle grain boundaries after HPT and it is shown that aging introduces changes in the microtexture intensities.     

Annealing temperature and environment effects on ZnO nanocrystals embedded in SiO2: a photoluminescence and TEM study

We report on efficient ZnO nanocrystal (ZnO-NC) emission in the near-UV region. We show that luminescence from ZnO nanocrystals embedded in a SiO₂ matrix can vary significantly as a function of the annealing temperature from 450°C to 700°C. We manage to correlate the emission of the ZnO nanocrystals embedded in SiO₂ thin films with transmission electron microscopy images in order to optimize the fabrication process. Emission can be explained using two main contributions, near-band-edge emission (UV range) and defect-related emissions (visible). Both contributions over 500°C are found to be size dependent in intensity due to a decrease of the absorption cross section. For the smallest-size nanocrystals, UV emission can only be accounted for using a blueshifted UV contribution as compared to the ZnO band gap. In order to further optimize the emission properties, we have studied different annealing atmospheres under oxygen and under argon gas. We conclude that a softer annealing temperature at 450°C but with longer annealing time under oxygen is the most preferable scenario in order to improve near-UV emission of the ZnO nanocrystals embedded in an SiO₂ matrix.     

On the role of crystallographic texture in mitigating hydrogen-induced cracking in pipeline steels

Cathodic hydrogen charging was applied to low-carbon pipeline-steel samples produced using different thermomechanical paths. The samples developed similar microstructures but different crystallographic textures and grain–boundary distributions. This made it possible to investigate the resistance to hydrogen-induced cracking (HIC) of steels with strong {1 1 1}ND and {1 1 2}ND texture fibres, steels with a dominating {0 0 1}ND texture fibre, and steels with close-to-random textures; {h k l}ND representing grain orientations with {h k l} planes parallel to the steel rolling plane. The results show that strong {1 1 1}ND fibre textures produced by warm-rolling schedules significantly increase HIC-resistance of pipeline steels, whereas {0 0 1}ND and close-to-random textures make steels HIC-prone.     

Effect of hydrogen peroxide on the destruction of organic contaminants-synergism and inhibition in a continuous-mode photocatalytic reactor

The effect of hydrogen peroxide on the photocatalytic degradation of organic contaminants in water was investigated using a TiO₂-rotating disk photocatalytic reactor (RDPR) operated in a continuous-mode and at steady state. The experiments were performed at pH 3.0, in the presence of near-UV radiation, and using 4-chlorobenzoic acid (4-CBA) as a model non-volatile organic contaminant at influent concentration of 300 μmol l⁻¹. Experiments were performed at concentrations of hydrogen peroxide in the range 0–10.74 mmol l⁻¹. Addition of hydrogen peroxide at small concentrations (<2 mmol l⁻¹) had a synergistic effect and increased considerably the rates of photocatalytic reactions. An optimum influent hydrogen peroxide concentration was observed at 1.6 mmol l⁻¹, which caused an increased in the rates of 4-CBA degradation and total organic carbon (TOC) mineralization by 1.72 and 2.13 times, respectively. This corresponded to an optimum oxidant to contaminant molar ratio of 5.33. At higher concentrations, hydrogen peroxide was found to cause an inhibiting effect on the photocatalytic reactions. The synergistic and inhibiting effects of hydrogen peroxide were rationalized based on the reaction rate constants between relevant radical species.     

Combination of radioiodine (131I) and probe-guided surgery for persistent or recurrent thyroid carcinoma

To improve the completeness of surgical excision of persistent or recurrent differentiated thyroid carcinoma, the following protocol was used for the treatment of 54 patients with functioning lymph node metastases: administration of 3.7 gigabecquerels (100 mCi) 131I; total body scintigraphy (TBS) on day 4; surgery on day 5, using an intraoperative probe (Gammed 2, Eurorad); and postoperative TBS with the remaining 131I activity on day 7. The 54 patients (35 women and 19 men presenting 47 papillary carcinomas, 2 well differentiated follicular carcinomas, and 5 poorly differentiated follicular carcinomas) had already undergone surgery for differentiated thyroid carcinoma: total thyroidectomy (51 patients) or lobectomy with isthmusectomy (3 patients), with lymph node dissection in 33. One to 7 131I treatments were performed before inclusion. Preoperative 131I-TBS with a high dose of 131I allowed accurate localization of previously suspected neoplastic foci and detection of yet unknown foci in 56%; it was the most sensitive tool for localizing neoplastic foci. The use of an intraoperative probe was considered decisive in 20 patients, as neoplastic foci were found inside sclerosis due to previous surgery (n = 9), at unusual sites behind vessels or in the mediastinum (n = 10), or both (n = 1). In 26 patients, it facilitated the preoperative detection of foci with 131I uptake already depicted at preoperative 131I-TBS. In all 46 patients, the completeness of excision was demonstrated by both the probe and the postoperative 131I-TBS and was confirmed during follow-up. Of note, lymph node metastases undetected by 131I-TBS or by the probe were found in 14 patients at histological examination. This clearly shows that en block dissection is the only recommended procedure. In four patients, no neoplastic foci were found and in four patients, uptake was either due to the thymus (in two) or to the salivary glands (in two).     

Titania powder modified sol-gel process for photocatalytic applications

Thick films of TiO₂ were prepared on glass and stainless steel substrates using an alkoxide sol-gel process modified by addition of Degussa P-25 powder. The prepared films were characterized by SEM, EDS, XRD and other methods. The TiO₂ films obtained from the powder modified sol were compared to films obtained from the alkoxide sol-gel without modification. The films obtained from the modified sol-gel were about ten times thicker for a single dip coating/heat treatment cycle than the films obtained from the sol without powder addition. The prepared thick films were smooth and free of macrocracking, fracture or flaking. The grain size of these films was uniform and in the range 100–150 nm and the films were a mixture of anatase and rutile TiO₂. The films obtained from the powder modified sol on the stainless steel substrate were also much harder compared to the films obtained from sols without modification and displayed excellent adhesion to the substrate.     

New non-dipolar structures with significant quadratic hyperpoiarizabilites

‘Octupolar’ molecules are of particular interest in the field of nonlinear optics due to their potentially large quadratic nonlinearities. Within this framework, we have designed organic chromophores of tetrahedral symmetry and investigated their quadratic nonlinearities by performing harmonic light scattering (HLS) experiments in solutions. Issues related to the molecular engineering of the nonlinearity-transparency trade-off have been addressed. As a result, molecules combining significant quadratic hyperpolarizabilities and excellent transparency have been identified.     

Relation of deranged neonatal cerebral oxidative metabolism with neurodevelopmental outcome and head circumference at 4 years

Cerebral oxidative metabolism was studied using phosphorus magnetic resonance spectroscopy during the first week of life and neurodevelopmental outcome was assessed at 4 years in 62 infants who had clinical and/or biochemical evidence consistent with birth asphyxia (critically impaired intrapartum gas exchange). Twenty-one died and the neurodevelopmental status of the 41 who survived was assessed by a range of tests at age 4 years. The minimum recorded values for the cerebral phosphocreatine:inorganic phosphate concentration ratio (an index of oxidative metabolism) were related to outcome. The results showed significant relations between the extent of derangement of neonatal oxidative metabolism and a range of adverse outcomes, including death, and at 4 years reduced head growth and the presence and severity of neuromotor impairments, overall neurodevelopmental impairments, and cognitive functioning. Strong correlations between the extent of derangement of neonatal oxidative metabolism and outcome at 1 and 4 years were also shown. We conclude that the severities of adverse outcomes at 1 and 4 years of age were closely related to the extent of cerebral energy derangement in the first week of life, and we also conclude that primary intrapartum hypoxic-ischaemic cerebral injury was generally responsible for the events that led to death, microcephaly, and impaired