A critique of master sintering curve analysis

In this work, we explore factors affecting the accuracy of the master sintering curve (MSC) approach for analyzing the complete sintering profile of ceramic powders. We show that the instantaneous anisotropic shrinkage must be accounted for to develop an accurate MSC. The MSC diverges at >90% density because of basic assumptions that oversimplify the analysis of the densification process. We also show that powder chemistry and forming techniques can affect the fitting parameter Q. Q should not be interpreted as the sintering activation energy, or used to interpret mechanistic differences since it is comprised of several mechanisms that influence densification throughout the sintering cycle. Despite these limitations, the MSC is a useful and practical tool for predicting thermal load (i.e. time and temperature) effects on the densification of a ceramic part fabricated from a singular powder that is fabricated by a singular forming process.     

Increased neurogenesis in the dentate gyrus after transient global ischemia in gerbils

Neurogenesis in the dentate gyrus of adult rodents is regulated by NMDA receptors, adrenal steroids, environmental stimuli, and seizures. To determine whether ischemia affects neurogenesis, newly divided cells in the dentate gyrus were examined after transient global ischemia in adult gerbils. 5-Bromo-2'-deoxyuridine-5'-monophosphate (BrdU) immunohistochemistry demonstrated a 12-fold increase in cell birth in the dentate subgranular zone 1-2 weeks after 10 min bilateral common carotid artery occlusions. Two minutes of ischemia did not significantly increase BrdU incorporation. Confocal microscopy demonstrated that BrdU immunoreactive cells in the granule cell layer colocalized with neuron-specific markers for neuronal nuclear antigen, microtubule-associated protein-2, and calbindin D28k, indicating that the newly divided cells migrated from the subgranular zone into the granule cell layer and matured into neurons. Newborn cells with a neuronal phenotype were first seen 26 d after ischemia, survived for at least 7 months, were located only in the granule cell layer, and comprised approximately 60% of BrdU-labeled cells in the granule cell layer 6 weeks after ischemia. The increased neurogenesis was not attributable to entorhinal cortical lesions, because no cell loss was detected in this region. Ischemic preconditioning for 2 min, which protects CA1 neurons against subsequent ischemic damage, did not prevent increased neurogenesis in the granule cell layer after a subsequent severe ischemic challenge. Thus, ischemia-induced dentate neurogenesis is not attributable to CA1 neuronal loss. Enhanced neurogenesis in the dentate gyrus may be a compensatory adaptive response to ischemia-associated injury and could promote functional recovery after ischemic hippocampal injury.     

Sea-blue histiocyte syndrome in bone marrow secondary to total parenteral nutrition

Clinical and hematological abnormalities can occur in patients receiving intravenous fat emulsions as part of a long-term parenteral nutrition; they consist of hepatosplenomegaly and peripheral blood cytopenia(s). These abnormalities lead to bone marrow examination which revealed numerous macrophages laden with blue staining pigment granules and separate lipid vacuoles, presenting the typical histochemical characteristics of sea-blue histiocytes. Thus, long-term parenteral nutrition including fat-emulsion sources may represent a further condition in addition to the wide variety of disorders which can be associated with sea-blue histiocytosis. Moreover, in view of its clinical and morphological presentation, this storage pathological state could be compared with the so-called sea-blue histiocyte syndrome described by Silverstein and colleagues.     

Amplicons of maize zein genes are conserved within genic but expanded and constricted in intergenic regions

The properties are discussed of system y+L, a broad scope amino acid transporter which was first identified in human erythrocytes. System y+L exhibits two distinctive properties: (a) it can bind and translocate cationic and neutral amino acids, and (b) its specificity varies depending on the ionic composition of the medium. In Na+ medium, the half-saturation constant for L-lysine influx was 9.5 +/- 0.67 microM and the inhibition constant (Ki) for L-leucine was 10.7 +/- 0.72 microM. L-Leucine is the neutral amino acid that binds more powerfully, whereas smaller analogues, such as L-alanine and L-serine interact less strongly (the corresponding inhibition constants were Ki,Ala, 0.62 +/- 0.11 mM; Ki,Ser, 0.49 +/- 0.08 mM). In the presence of K+, the carrier functions as a cationic amino acid specific carrier, but Li+ is able to substitute for Na+ facilitating neutral amino acid binding. The effect of the inorganic cations is restricted to the recognition of neutral amino acids; translocation occurs at similar rates in the presence of Na+, K+ and Li+. The only structural feature that appears to impair translocation is bulkiness and substrates with half-saturation constants differing by more than 100-fold translocate at the same rate. This suggests that translocation is largely independent of the forces of interaction between the substrate and the carrier site. System y+L activity has been observed in Xenopus laevis oocytes injected with the cRNA for the heavy chain of the 4F2 human surface antigen. 4F2hc is an integral membrane protein with a single putative membrane-spanning domain and it remains to be clarified whether it is part of the transporter or an activator protein.     

Characterization of the maize prolamin box-binding factor-1 (PBF-1) and its role in the developmental regulation of the zein multigene family

Voltage-dependent Ca2+ channels (VCCs) represent one of the main routes of Ca2+ entry into neuronal cells. Changes in intracellular Ca2+ dynamics and homeostasis can cause long-lasting cellular changes via activation of different Ca2+ dependent signalling pathways. We have investigated the properties of VCCs in human hippocampal dentate granule cells (DGCs) using the whole-cell configuration of the patch-clamp method. Classical high-threshold Ca2+ currents were composed mainly of omega-CgTx-sensitive N-type and nifedipine-sensitive L-type currents that were present in similar proportions. In addition, a Ca2+ current component that was sensitive to low concentrations of Ni2+, but not to nifedipine or omega-conotoxin GVIA (omega-CgTx GVIA) was present. This latter component showed a half-maximal inactivation at more hyperpolarized potentials than high-threshold currents and a more rapid time-dependent inactivation. This current was termed T-type Ca2+ current. Current components with similar pharmacological and kinetic characteristics could be elicited in acutely isolated control rat DGCs. The current density of high threshold and T-type Ca2+ components was significantly larger in human DGCs and in the kainate model compared to DGCs isolated from adult control rats. These differences in current density were not accompanied by parallel differences in the voltage-dependence of VCCs. Taken together, these data suggest that an up-regulation of Ca2+ current density may occur in hippocampal epileptogenesis without consistent changes in Ca2+ current properties.     

Low-Temperature Reactive Sintering of 0.65PMN·0.35PT

Dense, fine-grained 0.65PMN·0.35PT ceramics were fabricated by reactive sintering of a mixture of metal oxides at 1000°C. The fine nature of the precursor powder resulted in rapid, direct transformation to perovskite PMN–PT at 600°C. Because of the fine structure of the perovskite, no excess PbO was required for sintering.     

The use of gold for fabrication of nanowire structures

A common application of nanometer-sized gold particles is as seed particles for growth of semiconductor nanowires, which are believed to act as highly promising building blocks in future electronic devices. In a majority of the reports of successful nanowire growth, gold has been the seed particle material of choice. In this review article we identify the different types of gold particles used to initiate nanowire growth, namely gold particles made from thin films, gold particles defined by lithographic methods, colloidal gold particles and aerosol-generated gold particles. The production and deposition methods are described and the advantages and disadvantages of the particle types are discussed. In addition we discuss different properties that seem to make gold the most universal material for nanowire seed particles.     

Production rate of acetate during colonic fermentation of lactulose: a stable-isotope study in humans

BACKGROUND: Breath tests are currently used to qualitatively assess colonic fermentation; no quantitative estimations are available for healthy subjects. OBJECTIVE: This study describes a stable-isotope-dilution method to measure acetate production quantitatively from colonic bacterial fermentation. DESIGN: Six volunteers received a primed, constant, intravenous infusion of [1-13C]acetate at a rate of 1.01 +/- 0.04 micromol x kg(-1) x min(-1) for 7 h. They ingested 20 g pure lactulose after 1 h of the tracer infusion. Expired air and arterialized venous blood were sampled every 15 min. RESULTS: Before lactulose intake, the breath-hydrogen concentration was 7 +/- 2 ppm and the plasma acetate concentration and isotopic enrichment were 141 +/- 14 micromol/L and 14.8 +/- 1.4 moles percent excess, respectively. Whole-body acetate turnover was 6.0 +/- 0.7 micromol x kg(-1) x min(-1). After lactulose ingestion, maximum breath hydrogen and acetate concentrations reached 63 +/- 15 ppm (P = 0.004) and 313 +/- 25 micromol/L (P = 0.002), respectively, whereas [13C]acetate enrichment decreased to 9.9 +/- 1.3 moles percent excess (P = 0.03). Whole-body acetate turnover increased to 9.8 +/- 1.5 micromol x kg(-1) x min(-1) and later decreased almost to baseline values. Colonic lactulose fermentation yielded 140 +/- 12 mmol acetate over 6 h, representing 86% of the production based on stoichiometric equations. CONCLUSION: This new method provides a quantitative estimate of colonic carbohydrate fermentation via evaluation of acetate production.