Tunable mechanical resonator with aluminum nitride piezoelectric

The electromechanical response of piezoelectrically-actuated AlN micromachined bridge resonators has been characterized using laser interferometry and electrical admittance measurements. We compare the response of microbridges with different dimensions and buckling (induced by the initial residual stress of the layers). The resonance frequencies are in good agreement with numerical simulations of the electromechanical behavior of the structures. We show that it is possible to perform a rough tuning of the resonance frequencies by allowing a determined amount of builtin stress in the microbridge during its fabrication. Once the resonator is made, a DC bias added to the AC excitation signal allows to fine-tune the frequency. Our microbridges yield a tuning factor of around 88 Hz/V for a 500 ?m-long microbridge.

Aluminum slurry coatings to replace cadmium for aeronautic applications

Cadmium has been widely used as a coating to provide protection against galvanic corrosion for steels and for its natural lubricity on threaded applications. However, it is a toxic metal and a known carcinogenic agent, which is plated from an aqueous bath containing cyanide salts. For these reasons, the use of cadmium has been banned in Europe for most industrial applications. However, the aerospace industry is still exempt due to the stringent technical and safety requirements associated with aeronautical applications, as an acceptable replacement is yet to be found. Al slurry coatings have been developed as an alternative to replace cadmium coatings. The coatings were deposited on AISI 4340 steel and have been characterized by optical and electron microscopy. Testing included salt fog corrosion exposure, fluid corrosion exposure (immersion), humidity resistance, coating-substrate and paint-coating adhesion, electric conductivity, galvanic corrosion, embrittlement and fatigue. The results indicated that Al slurry coatings are an excellent alternative for Cd replacement.

Low-thickness high-quality aluminum nitride films for super high frequency solidly mounted resonators

We investigate the sputter growth of very thin aluminum nitride (AlN) films on iridium electrodes for electroacoustic devices operating in the super high frequency range. Superior crystal quality and low stress films with thicknesses as low as 160 nm are achieved after a radio frequency plasma treatment of the iridium electrode followed by a two-step alternating current reactive magnetron sputtering of an aluminum target, which promotes better conditions for the nucleation of well textured AlN films in the very first stages of growth. Solidly mounted resonators tuned around 8 GHz with effective electromechanical coupling factors of 5.8% and quality factors Q up to 900 are achieved.

Functional, structural and phylogenetic analysis of domains underlying the Al sensitivity of the aluminum-activated malate/anion transporter, TaALMT1.

Triticum aestivum aluminum-activated malate transporter (TaALMT1) is the founding member of a unique gene family of anion transporters (ALMTs) that mediate the efflux of organic acids. A small sub-group of root-localized ALMTs, including TaALMT1, is physiologically associated with in planta aluminum (Al) resistance. TaALMT1 exhibits significant enhancement of transport activity in response to extracellular Al. In this study, we integrated structure–function analyses of structurally altered TaALMT1 proteins expressed in Xenopus oocytes with phylogenic analyses of the ALMT family. Our aim is to re-examine the role of protein domains in terms of their potential involvement in the Al-dependent enhancement (i.e. Al-responsiveness) of TaALMT1 transport activity, as well as the roles of all its 43 negatively charged amino acid residues. Our results indicate that the N-domain, which is predicted to form the conductive pathway, mediates ion transport even in the absence of the C-domain. However, segments in both domains are involved in Al3+ sensing. We identified two regions, one at the N-terminus and a hydrophobic region at the C-terminus, that jointly contribute to the Al-response phenotype. Interestingly, the characteristic motif at the N-terminus appears to be specific for Al-responsive ALMTs. Our study highlights the need to include a comprehensive phylogenetic analysis when drawing inferences from structure–function analyses, as a significant proportion of the functional changes observed for TaALMT1 are most likely the result of alterations in the overall structural integrity of ALMT family proteins rather than modifications of specific sites involved in Al3+ sensing.

Mechanical characterisation of tungsten-1wt.% yttrium oxide as a function of temperature and atmosphere

This study evaluates the mechanical behaviour of an Y2O3-dispersed tungsten (W) alloy and compares it to a pure W reference material. Both materials were processed via mechanical alloying (MA) and subsequent hot isostatic pressing (HIP). We performed non-standard three-point bending (TPB) tests in both an oxidising atmosphere and vacuum across a temperature range from 77 K, obtained via immersion in liquid nitrogen, to 1473 K to determine the mechanical strength, yield strength and fracture toughness. This research aims to evaluate how the mechanical behaviour of the alloy is affected by oxides formed within the material at high temperatures, primarily from 873 K, when the materials undergo a massive thermal degradation. The results indicate that the alloy is brittle to a high temperature (1473 K) under both atmospheres and that the mechanical properties degrade significantly above 873 K. We also used Vickers microhardness tests and the dynamic modulus by impulse excitation technique (IET) to determine the elastic modulus at room temperature. Moreover, we performed nanoindentation tests to determine the effect of size on the hardness and elastic modulus; however, no significant differences were found. Additionally, we calculated the relative density of the samples to assess the porosity of the alloy. Finally, we analysed the microstructure and fracture surfaces of the tested materials via field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). In this way, the relationship between the macroscopic mechanical properties and micromechanisms of failure could be determined based on the temperature and oxides formed

Machinability Study of an aluminum-copper alloy

Machinability of materials is one of the factors that make us wonder what tools to use and what material is best suited for a particular cutting tool and which process is more efficient in the production of a component. In the case of parts for the aerospace industry, manufacturing processes assume greater importance due to the extreme demands on reliability and quality.

Cure of human carcinoma xenografts by a single dose of pretargeted yttrium-90 with negligible toxicity

A covalent conjugate (NR-LU-10/SA) was prepared between streptavidin (SA) and NR-LU-10, a mAb that binds an antigen expressed on the surface of most human carcinomas. NR-LU-10/SA was injected into nude mice bearing human tumor xenografts. Injection of biotinylated galactosyl-human serum albumin reduced the circulating levels of conjugate by 95%. Subsequent administration of 90Y-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid-biotin achieved peak uptake at the tumor within 2 hr while >80% of the radioactivity was eliminated in the urine. A single dose of 600–800 μCi of 90Y-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid-biotin produced cures in 10/10 mice with established (>200 mm3) s.c. human small cell lung or colon cancer xenografts and 8/10 cures in mice with human breast cancer xenografts without significant toxicity.

Impacts of Aluminum on the Cytoskeleton of the Maize Root Apex. Short-Term Effects on the Distal Part of the Transition Zone1

Using monoclonal tubulin and actin antibodies, Al-mediated alterations to microtubules (MTs) and actin microfilaments (MFs) were shown to be most prominent in cells of the distal part of the transition zone (DTZ) of an Al-sensitive maize (Zea mays L.) cultivar. An early response to Al (1 h, 90 μm) was the depletion of MTs in cells of the DTZ, specifically in the outermost cortical cell file. However, no prominent changes to the MT cytoskeleton were found in elongating cells treated with Al for 1 h in spite of severe inhibition of root elongation. Al-induced early alterations to actin MFs were less dramatic and consisted of increased actin fluorescence of partially disintegrated MF arrays in cells of the DTZ. These tissue- and development-specific alterations to the cytoskeleton were preceded by and/or coincided with Al-induced depolarization of the plasma membrane and with callose formation, particularly in the outer cortex cells of the DTZ. Longer Al supplies (>6 h) led to progressive enhancements of lesions to the MT cytoskeleton in the epidermis and two to three outer cortex cell files. Our data show that the cytoskeleton in the cells of the DTZ is especially sensitive to Al, consistent with the recently proposed specific Al sensitivity of this unique, apical maize root zone.

Change in Apoplastic Aluminum during the Initial Growth Response to Aluminum by Roots of a Tolerant Maize Variety1

Root elongation, hematoxylin staining, and changes in the ultrastructure of root-tip cells of an Al-tolerant maize variety (Zea mays L. C 525 M) exposed to nutrient solutions with 20 μm Al (2.1 μm Al3+ activity) for 0, 4, and 24 h were investigated in relation to the subcellular distribution of Al using scanning transmission electron microscopy and energy-dispersive x-ray microanalysis on samples fixed by different methods. Inhibition of root-elongation rates, hematoxylin staining, cell wall thickening, and disturbance of the distribution of pyroantimoniate-stainable cations, mainly Ca, was observed only after 4 and not after 24 h of exposure to Al. The occurrence of these transient, toxic Al effects on root elongation and in cell walls was accompanied by the presence of solid Al-P deposits in the walls. Whereas no Al was detectable in cell walls after 24 h, an increase of vacuolar Al was observed after 4 h of exposure. After 24 h, a higher amount of electron-dense deposits containing Al and P or Si was observed in the vacuoles. These results indicate that in this tropical maize variety, tolerance mechanisms that cause a change in apoplastic Al must be active. Our data support the hypothesis that in Al-tolerant plants, Al can rapidly cross the plasma membrane; these data clearly contradict the former conclusions that Al mainly accumulates in the apoplast and enters the symplast only after severe cell damage has occurred.

Alterations in the Cytoskeleton Accompany Aluminum-Induced Growth Inhibition and Morphological Changes in Primary Roots of Maize1

Although Al is one of the major factors limiting crop production, the mechanisms of toxicity remain unknown. The growth inhibition and swelling of roots associated with Al exposure suggest that the cytoskeleton may be a target of Al toxicity. Using indirect immunofluorescence microscopy, microtubules and microfilaments in maize (Zea mays L.) roots were visualized and changes in their organization and stability correlated with the symptoms of Al toxicity. Growth studies showed that the site of Al toxicity was associated with the elongation zone. Within this region, Al resulted in a reorganization of microtubules in the inner cortex. However, the orientation of microtubules in the outer cortex and epidermis remained unchanged even after chronic symptoms of toxicity were manifest. Auxin-induced reorientation and cold-induced depolymerization of microtubules in the outer cortex were blocked by Al pretreatment. These results suggest that Al increased the stability of microtubules in these cells. The stabilizing effect of Al in the outer cortex coincided with growth inhibition. Reoriented microfilaments were also observed in Al-treated roots, and Al pretreatment minimized cytochalasin B-induced microfilament fragmentation. These data show that reorganization and stabilization of the cytoskeleton are closely associated with Al toxicity in maize roots.