Pulsed current activated combustion synthesis and consolidation of ultrafine NbSi2 from mechanically activated powders

Dense ultrafine NbSi₂ was synthesized using the pulsed current activated combustion synthesis (PCACS) method within 2 min and in one step from mechanically activated powders of Nb and 2Si. Simultaneous combustion synthesis and densification were accomplished under the combined effects of a pulsed current and mechanical pressure. Highly dense NbSi₂ with a relative density of up to 98 % was produced under simultaneous application of a 60 MPa pressure and a pulsed current. The average grain size and mechanical properties (hardness and fracture toughness) of the compound were investigated.     

The relationships between interfacial friction and the conformational order of organic thin films

This report describes studies of the relationships between the structures of organic monolayers and their molecular-scale frictional properties. Several distinct self-assembled monolayers (SAMs) were formed by the adsorption of a series of spiroalkanedithiols and a single structurally related normal alkanethiol. Measurements of hexadecane wettability, infrared vibrational spectroscopy, and X-ray photoelectron spectroscopy revealed that the films possessed a wide range of interfacial structures and conformational orders. Atomic force microscopy was used to measure the frictional properties of the well-characterized SAMs on the molecular scale. Comparison of the frictional data with structural information derived from complementary analytical techniques revealed a high correlation between the conformational order of the films and the observed frictional response.     

Synthesis of TiC, TiC-Cu Composites, and TiC-Cu Functionally Graded Materials by Electrothermal Combustion

Titanium carbide and composites and functionally graded materials (FGMs) of TiC– x Cu were synthesized by an electrothermal combustion (ETC) method. TiC synthesized by ETC showed small amounts of porosity relative to those synthesized by ignition using radiative heating. Composites and FGMs with higher copper content can be synthesized by ETC. In the FGM products a nearly linear change in composition in the graded region was observed in samples with 0 ≤ x (wt%) ≤ 75.     

Assessing the aggregation behaviour of iron oxide nanoparticles under relevant environmental conditions using a multi-method approach

Iron nanoparticles are becoming increasingly popular for the treatment of contaminated soil and groundwater; however, their mobility and reactivity in subsurface environments are significantly affected by their tendency to aggregate. Assessing their stability under environmental conditions is crucial for determining their environmental fate. A multi-method approach (including different size-measurement techniques and the DLVO theory) was used to thoroughly characterise the behaviour of iron oxide nanoparticles (Fe₂O₃NPs) under environmentally relevant conditions. Although recent studies have demonstrated the importance of using a multi-method approach when characterising nanoparticles, the majority of current studies continue to use a single-method approach.Under some soil conditions (i.e. pH 7, 10 mM NaCl and 2 mM CaCl₂) and increasing particle concentration, Fe₂O₃NPs underwent extensive aggregation to form large aggregates (>1 μm). Coating the nanoparticles with dissolved organic matter (DOM) was investigated as an alternative “green” solution to overcoming the aggregation issue instead of using the more commonly proposed polyelectrolytes. At high concentrations, DOM effectively covered the surface of the Fe₂O₃NPs, thereby conferring negative surface charge on the particles across a wide range of pH values. This provided electrostatic stabilisation and considerably reduced the particle aggregation effect. DOM-coated Fe₂O₃NPs also proved to be more stable under high ionic strength conditions. The presence of CaCl₂, however, even at low concentrations, induced the aggregation of DOM-coated Fe₂O₃NPs, mainly via charge neutralisation and bridging. This has significant implications in regards to the reactivity and fate of these materials in the environment.     

Preparation and characterisation of TiO2 nanoparticle and titanate nanotube obtained from Ti-salt flocculated sludge with drinking water and seawater

This study aimed to prepare and characterise titanium dioxide (TiO2) nanoparticles and titanate nanotubes produced from Ti-sat flocculated sludge with drinking water (DW) and seawater (SW). The Ti-salt flocculated sludge from DW and SW was incinerated at 600 degrees C to produce TiO2 nanoparticles. XRD results showed that the anatase TiO2 structure was predominant for TiO2 from DW (TiO2-DW) and TiO2 from SW (TiO2-SW), which were mainly doped with carbon atoms. Titanate nanotubes (tiNT) were obtained when TiO2-DW and TiO2-SW were hydrothermally treated with NaOH solution. Structure phase, shape, crystallisation and photocatalytic activity of tiNT were affected by the incineration temperature and the amount of sodium present in different tiNT. The tiNT doped with thiourea incinerated at 600 degrees C presented anatase phase, showing a high increase of the degree of crystallisation with nanotube-like structures. The photocatalytic activity of these photocatalysts was evaluated using photooxidation of gaseous acetaldehyde. Thiourea doped tiNT-DW and tiNT-SW showed similar photocatalytic activity compared to commercially available TiO2-P25 under UV light and indicated a photocatalytic activity under visible light.     

Sintering of ultra-fine tetragonal yttria-stabilized zirconia ceramics

High-frequency induction heated sintering (HFIHS) is utilized to consolidate ultra-fine grain tetragonal zirconia stabilized with 3 mol%Y₂O₃ (3Y-SZ) ceramics. Densification to near theoretical density in a relatively short time can be accomplished using this method. Samples of 3Y-SZ with a relative density of up to 99.5% and an average grain size of about 170 nm could be obtained by sintering at 950 °C for 5 min under a pressure of 100 MPa pressure. The influence of sintering temperature and mechanical pressure on the final density and grain size of the sintered products was investigated. The sintered materials had fracture toughness and hardness values of 4.4 MPa m^1/2 and 10.7 GPa, respectively.     

The stability of duplexes involving AT and/or G4EtC base pairs is not dependent on their AT/G4EtC ratio content. Implication for DNA sequencing by hybridization

Sequencing by the recently reported hybridization technique requires the formation of DNA duplexes with similar stabilities. In this paper we describe a new strategy to obtain DNA duplexes with a thermal stability independent of their AT/GC ratio content. Melting data were acquired on 35 natural and 27 modified duplexes of a given length and of varying base compositions. Duplexes built with AT and/or G4EtC base pairs exhibit a thermal stability restrained to a lower range of temperature than that of the corresponding natural compounds (16 instead of 51 degrees C). The 16 degrees C difference in thermal stability observed between the least stable and the most stable duplex built with AT and/or G4EtC base pairs is mainly due to the sequence effect and not to their AT/G4EtC ratio content. Thus N -4-ethyl-2'-deoxycytidine (d4EtC) hybridizes specifically with natural deoxyguanosine leading to a G4EtC base pair whose stability is very close to that of the natural AT base pair. Oligonucleotide probes involving d4EtC can be easily prepared by chemical synthesis with phosphoramidite chemistry. Modified DNA targets were successfully amplified by random priming or PCR techniques using d4EtCTP, dATP, dGTP and dTTP in the presence of DNA polymerase. This new system might be very useful for DNA sequencing by hybridization.     

Enhancement of oxidative cell injury and antitumor effects of localized 44 degrees C hyperthermia upon combination with respiratory hyperoxia and xanthine oxidase

Polymerase chain reaction (PCR) assays were designed to amplify 56- and 99-base regions of the pmoA gene from Methylosinus trichosporium OB3b and Methylomicrobium albus BG8, two species of methanotrophic bacteria that are of interest for monitoring bioremediation activity. The PCR product sizes are in a mass range that is accessible to analysis by MALDI-TOF mass spectrometry. A rapid purification procedure using commercially available reversed-phase cartridges was applied prior to MALDI-TOF analysis. A small aliquot (1.5%, 1.5 microL) from a single 100-microL PCR reaction was sufficient for reliable detection. No cross-amplification products were observed when primers designed for one bacterial species were used with genomic DNA of the other species. The methodology described here has potential to allow less expensive and faster characterization of the ability of microbial populations to destroy pollutants in groundwater and soil at contaminated industrial sites.     

Primary repair is superior to initial palliation in children with atrioventricular septal defect and tetralogy of Fallot

OBJECTIVE:The objective was to explore the best management algorithm for atrioventricular septal defect in conjunction with tetralogy of Fallot. METHODS: We reviewed the cases of 38 children referred to our division (March 1981-August 1997) who had atrioventricular septal defect associated with tetralogy of Fallot; 32 (84%) had Down syndrome. Twenty-one received initial palliation with a systemic-to-pulmonary artery shunt; of these, 2 (9.5%) died before complete repair. Thirty-one children underwent complete repair; 14 of these (45%) had undergone initial palliation (mean age at shunt 20 +/- 24 months). Right ventricular outflow obstruction was relieved by a transannular patch in 22 (71%); 14 (64% of 22) had a monocuspid valve inserted. Four required an infundibular patch. RESULTS: Two children (6.4%) died early after repair; 1 had undergone previous palliation. Patients with palliation underwent repair at an older age (78 vs 36 months), required longer ventilatory support (8 vs 4 days) and inotropic support (8 vs 4 days), and had longer intensive care stays (11 vs 6 days) and hospital stays (24 vs 15 days). Eleven children (35%) underwent reoperation, 7 (58%) for right ventricular outflow reconstruction and pulmonary arterioplasty. Reoperation was more frequent in the palliation group than in the primary operation group (64% vs 12%). The single late death was related to a reoperation in the palliation group. CONCLUSIONS: Atrioventricular septal defect with tetralogy of Fallot can be repaired with a low mortality rate. Initial palliation with a shunt resulted in a more complex postoperative course and a higher reoperative rate. Primary repair is superior to initial palliation with later repair.     

Restrictions on components of variance for epistatic models

The putative role(s) of a mechanically gated (MG) cation channel in Xenopus oocyte growth, maturation, fertilization and embryogenesis has been examined. Using a pharmacological approach, we have tested the effects of the MG channel blockers, gadolinium, gentamicin and amiloride on the above developmental events. Our results indicate that oocyte maturation, fertilization and early embryogenesis (up to the free-swimming stage 45) can proceed normally in the presence of concentrations of agents that either completely abolish (i.e., > or = 10 microM Gd3+) or partially block (i.e., 1 mM gentamicin) single MG channel activity as measured by patch-clamp recording. However, we also find that higher concentrations of Gd3+ (> or = 50 microM) can lead to an increased percentage (> 20%) of axis-perturbed embryos compared with control (< 1%) and that amiloride (0.5 mM) reduces the success of fertilization (from 100% to < 50%) and increases mortality (by approximately 75%) in developing embryos. Furthermore, we find that all three agents inhibit oocyte growth in vitro. However, their order of effectiveness (amiloride > gentamicin > Gd3+) is opposite to their order for blocking MG channels (Gd3+ > gentamicin > amiloride). These discrepancies indicated that the drugs effects occur by mechanisms other than, or in addition to, MG channel block. Our results provide no compelling evidence for the idea that MG channel activity is critical for development in Xenopus. This could mean that there are other mechanisms in the oocyte that can compensate when MG channel activity is blocked or that the protein that forms the channel can undergo additional interactions that result in a function insensitive to MG channel blockers.