In situ observation of synthesized nanoparticles in ultra-dilute aerosols via X-ray scattering

In-air epitaxy of nanostructures (Aerotaxy) has recently emerged as a viable route for fast, large-scale production. In this study, we use small-angle X-ray scattering to perform direct in-flight characterizations of the first step of this process, i.e., the engineered formation of Au and Pt aerosol nanoparticles by spark generation in a flow of N₂ gas. This represents a particular challenge for characterization because the particle density can be extremely low in controlled production. The particles produced are examined during production at operational pressures close to atmospheric conditions and exhibit a lognormal size distribution ranging from 5–100 nm. The Au and Pt particle production and detection are compared. We observe and characterize the nanoparticles at different stages of synthesis and extract the corresponding dominant physical properties, including the average particle diameter and sphericity, as influenced by particle sintering and the presence of aggregates. We observe highly sorted and sintered spherical Au nanoparticles at ultra-dilute concentrations (< 5 × 10⁵ particles/cm³) corresponding to a volume fraction below 3 × 10^–10, which is orders of magnitude below that of previously measured aerosols. We independently confirm an average particle radius of 25 nm via Guinier and Kratky plot analysis. Our study indicates that with high-intensity synchrotron beams and careful consideration of background removal, size and shape information can be obtained for extremely low particle concentrations with industrially relevant narrow size distributions.

     

Congenic rats reveal three independent Copenhagen alleles within the Mcs1 quantitative trait locus that confer resistance to mammary cancer

It has previously been shown that the Copenhagen (COP) rat contains several genetic loci that contribute to its mammary tumor-resistant phenotype after 7,12-dimethylbenz(a)anthracene (DMBA) administration. One of these loci, mammary carcinoma susceptibility 1 (Mcs1), is located on the centromeric end of chromosome 2 and appears to act in a semidominant fashion. To confirm the existence and independent action of this locus and also aid in the identification of the physical location of the Mcs1 gene, congenic lines were generated by transferring the Mcs1 COP allele onto a Wistar Furth (WF) genetic background. Male carriers were genotyped using microsatellite markers spanning 20-30 cM of the Mcs1 locus. One of the congenic lines minimally retained the COP allele at D2Mit29 on the centromeric end of chromosome 2 and extended distally to D2Rat201. Heterozygous Mcs1 carrier rats were interbred, and the female offspring were treated with DMBA. The female rats from the Mcs1 congenic line that carried one or two COP alleles of the Mcs1 region had a significantly reduced (65 and 85%, respectively) tumor development (P < 0.001) compared with rats carrying zero COP alleles at this locus. A WF.COP-D2Mit29/D2Rat201 homozygous congenic strain derived at the N10 generation was treated with DMBA, and the COP homozygous rats developed 1.5 +/- 0.3 carcinomas/rat versus 6.3 +/- 0.5 in WF control rats (P < 0.0001). Fine mapping of this congenic interval using several recombinant lines identified three genetic loci within the Mcs1 congenic region that independently supported a tumor resistance phenotype. These genetic loci have been termed Mcs1a, Mcs1b, and Mcs1c. In rats for which each locus was homozygous for the COP allele, tumor development was reduced by approximately 60% compared with littermate controls. The identification of these independent loci within the Mcs1 COP allele provide a model of the genetic complexity of cancer.     

Synthesis of branched 'nanotrees' by controlled seeding of multiple branching events

The formation of nanostructures with controlled size and morphology has been the focus of intensive research in recent years. Such nanostructures are important in the development of nanoscale devices and in the exploitation of the properties of nanomaterials. Here we show how tree-like nanostructures ('nanotrees') can be formed in a highly controlled way. The process involves the self-assembled growth of semiconductor nanowires via the vapour-liquid-solid growth mode. This bottom-up method uses initial seeding by catalytic nanoparticles to form the trunk, followed by the sequential seeding of branching structures. Each level of branching is controlled in terms of branch length, diameter and number, as well as chemical composition. We show, by high-resolution transmission electron microscopy, that the branching mechanism gives continuous crystalline (monolithic) structures throughout the extended and complex tree-like structures. The controlled seeding method that we report here has potential as a generic means of forming complex branching structures, and may also offer opportunities for applications, such as the mimicking of photosynthesis in nanotrees.     

Influence of Oxygen During Pretreatment of Kraft Pulp with NO2

Abstract

Large additions of O₂ during the pretreatment of modified or industrial kraft pulp with NO₂ under conditions which favored an autocatalytic generation of NO₂ from produced and added HNO₃ led to a decreased viscosity after a subsequent oxygen bleaching, If the comparison was made at high kappa numbers. The difference was less apparent when the oxygen bleaching was extended. The yield of pulp at a given kappa number was reduced by large O₂ additions. An Increased yield of nitric acid contributed to these effects.

Hydrogen cyanide and ammonia were produced during the pretreatment in reactions between lignin and generated nitrogen oxides. Addition of O₂ led to decreased yields of these products.     

Overexpression of Rab3D enhances regulated amylase secretion from pancreatic acini of transgenic mice

Rab3D, a member of the ras-related GTP-binding protein Rab family, is localized to secretory granules of various exocrine tissues such as acinar cells of the pancreas, chief cells of the stomach, and parotid and lacrimal secretory cells. To elucidate the function of Rab3D in exocytosis, we have generated transgenic mice that over-express Rab3D specifically in pancreatic acinar cells. Hemagglutinin-tagged Rab3D was localized to zymogen granules by immunohistochemistry, and was shown to be present on zymogen granule membranes by Western blotting; both results are similar to previous studies of endogenous Rab3D. Secretion measurements in isolated acinar preparations showed that overexpression of Rab3D enhanced amylase release. Amylase secretion from intact acini of transgenic mice 5 min after 10 pM cholecystokinin octapeptide (CCK) stimulation was enhanced by 160% of control. In streptolysin-O-permeabilized acini of transgenic mice, amylase secretion induced by 100 microM GTP-gamma-S was enhanced by 150%, and 10 microM Ca2+-stimulated amylase secretion was augmented by 206% of that of the control. To further elucidate Rab3D involvement in stimulus-secretion coupling, we examined the effect of CCK on the rate of GTP binding to Rab3D. Stimulation of permeabilized acini with 10 pM CCK increased the incorporation of radiolabeled GTP into HA-tagged Rab3D. These results indicate that overexpression of Rab3D enhances secretagogue-stimulated amylase secretion through both calcium and GTP pathways. We conclude that Rab3D protein on zymogen granules plays a stimulatory role in regulated amylase secretion from pancreatic acini.     

Neuropsychological functioning in posttraumatic stress disorder and alcohol abuse.

Studies have shown differences in neuropsychological functioning between groups with posttraumatic stress disorder (PTSD) and control participants. Because individuals with PTSD often have a history of comorbid alcohol abuse, the extent to which an alcohol confound is responsible for these differences remains a concern. The current study compares neuropsychological testing scores in 4 groups of veterans with and without PTSD (PTSD+ and PTSD-, respectively) and with and without a history of alcohol abuse (ETOH+ and ETOH-, respectively): n for PTSD+/ETOH- = 30, n for PTSD+/ETOH- = 37, n for PTSD-/ETOH+ = 30, and n for PTSD-/ETOH- = 31. Results showed that PTSD, when alcohol, educational level, vocabulary, and depression are controlled for, was associated with decreased verbal memory, attention, and processing speed performance. Alcohol abuse history was associated with decreased visual memory performance. By controlling for alcohol and depression, the authors can more conclusively demonstrate that verbal memory and attention differences are associated with PTSD. (PsycINFO Database Record (c) 2010 APA, all rights reserved)