Second phase particles in zirconium alloys.

Transmission electron microscopy, scanning electron microscopy, energy dispersive x-ray spectroscopy, and x-ray diffraction have been used to study the zirconium alloys, Zr-1wt%Nb. Zr-2.5wt%Nb, Zircaloy-2, Zircaloy-4, and bulk stoichiometric \rm Zr(Fe\sb{1-x}Cr\sb{x})\sb2 alloys, where x = 0, 0.25, 0.45, and 0.75. Both Zr-2.5Nb alloy pressure tubing and Zr-1Nb fuel sheathing contain two main phases, $\alpha$-Zr and $\beta$-Zr. Zr(FeCr)\sb2 Laves phase precipitates and Zr\sb3Fe intermetallic phase were found in cold-worked Zr-1Nb alloy. Only Zr\sb2Fe precipitates were found, however, in Zr-2.5Nb pressure tubing, which contains more Fe and Cr than Zr-1Nb. The volume fraction of Zr\sb2Fe was much smaller than the volume fraction of Zr(FeCr)\sb2 precipitates in Zr-1Nb. On annealing of the Zr-2.5Nb at 560\sp\circC both Zr(FeCr)\sb2 and Zr\sb2Fe precipitates were formed. It is proposed that on annealing the $\beta$-Zr phase (containing Fe and Cr in solution) transforms to $\alpha$-Zr + $\beta$-Nb + Zr(FeCr)\sb2 phases. Three kinds of second phase particles were found in the Zircaloy-2. These precipitates were: (i) a Zr\sb2(FeNi)-type precipitate with a composition, Zr\sb2(Ni\sb{0.6-0.5}Fe\sb{0.4-0.5}). The Zr\sb2(Ni\sb{0.6-0.5}Fe\sb{0.4-0.5}) precipitates have a body-centered tetragonal structure with a space group I4/mmm (D\sbsp{sh}{17}, No. 139); (ii) Zr(CrFe)\sb2 Laves phase particles with a composition of Zr(Cr\sb{0.55-0.57}Fe\sb{0.45-0.43})\sb2; and (iii) Zr\sb3P precipitates with a simple tetragonal structure with a = 1.080 nm and c = 0.5410 nm. These zirconium phosphide particles were found in a Zircaloy-2 sample containing only 5 ppm phosphorus. They were also found in a high phosphorus (160 ppm) Zircaloy-4 sample. The hexagonal structure is the stable structure for bulk ZrCr\sb2 Laves phase at low temperature, but upon annealing at temperature higher then 850\sp\circC, this hexagonal structure transforms first to a cubic structure and then to a fcc twinned structure. Cast and heat-treated bulk \rm Zr(Fe\sb{1-x}Cr\sb{x})\sb2 alloys, where x = 0.25, 0.45 and 0.75, have the 2H structure: ZrFe\sb2 has the 3R structure. But \rm Zr(Fe\sb{1-x}Cr\sb{x})\sb2, where x $\ne$ 1, precipitates in dilute zirconium alloys can have polytypic modifications and stacking-faults. An electron diffraction method was developed to identify the structures of unknown phases and was applied to the identification of a number of the second phase particles in zirconium alloys. By this method, a series of reciprocal vectors, which should be in a principle reciprocal plane of a crystal, and their inter angles can be obtained. Using this data the principle planes of the crystal can be constructed. Thus, the elements of both the reciprocal and the direct lattice cells of the unknown phases can be obtained.Dept. of Mechanical, Automotive, and Materials Engineering. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis1990 .M455. Source: Dissertation Abstracts International, Volume: 52-11, Section: B, page: 5962. Thesis (Ph.D.)--University of Windsor (Canada), 1990

The structure of Laves phases in zirconium alloys.

Dept. of Electrical and Computer Engineering. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis1986 .M464. Source: Masters Abstracts International, Volume: 40-07, page: . Thesis (M.A.Sc.)--University of Windsor (Canada), 1986

Functional expression and characterization of an archaeal aquaporin. AqpM from methanothermobacter marburgensis.

Researchers have described aquaporin water channels from diverse eubacterial and eukaryotic species but not from the third division of life, Archaea. Methanothermobacter marburgensis is a methanogenic archaeon that thrives under anaerobic conditions at 65 °C. After transfer to hypertonic media,M. marburgensis sustained cytoplasmic shrinkage that could be prevented with HgCl2. We amplified aqpM by PCR from M. marburgensis DNA. Like known aquaporins, the open reading frame of aqpM encodes two tandem repeats each containing three membrane-spanning domains and a pore-forming loop with the signature motif Asn-Pro-Ala (NPA). Unlike other known homologs, the putative Hg2+-sensitive cysteine was found proximal to the first NPA motif in AqpM, rather than the second. Moreover, amino acids distinguishing water-selective homologs from glycerol-transporting homologs were not conserved in AqpM. A fusion protein, 10-His-AqpM, was expressed and purified from Escherichia coli. AqpM reconstituted into proteoliposomes was shown by stopped-flow light scattering assays to have elevated osmotic water permeability (P f = 57 μm·s−1 versus12 μm·s−1 of control liposomes) that was reversibly inhibited with HgCl2. Transient, initial glycerol permeability was also detected. AqpM remained functional after incubations at temperatures above 80 °C and formed SDS-stable tetramers. Our studies of archaeal AqpM demonstrate the ubiquity of aquaporins in nature and provide new insight into protein structure and transport selectivity. To withstand environmental and physiological stresses, organisms must be able to rapidly absorb and release water. Facilitated transport of water across cell membranes must be highly selective to prevent uncontrolled movement of other solutes, protons, and ions. Discovery of the aquaporins provided a molecular explanation to these processes (2). More than 200 aquaporins have now been identified, and their presence has been established in most forms of life (3). No aquaporin from Archaea has yet been characterized, although functional roles for a water channel protein have been predicted in these organisms (4). Two major protein family subsets are presently recognized, water-selective channels (aquaporins) and glycerol-transporting homologs with varying water permeabilities (aquaglyceroporins). The permeation selectivity of new members of the protein family may be predicted by a small number of conserved residues (5, 6). Several prokaryotic aquaporins and aquaglyceroporins are known. The bacterial water channel, AqpZ, was first identified in Escherichia coli (7, 8). Movement of water across the bacterial plasma membrane may be part of the osmoregulatory response by which microorganisms adjust cell turgor (9), although the regulation and physiological role of AqpZ are being reassessed (10). AqpZ is a highly stable tetramer with negligible permeability to glycerol. In contrast, the glycerol permeability of the glycerol facilitator (GlpF) fromE. coli has long been recognized (11). GlpF has relatively limited water permeability (12), and the tetrameric form has reduced stability in some detergents (13). Atomic resolution structures have been solved for GlpF (14) as well as human and bovine AQP11 (15-17). These have elucidated differential specificities and functional mechanisms of the two sequence-related proteins. Archaea and certain other microorganisms are able to withstand exceptional challenges in maintaining water balance as they thrive in extreme environments including saturated salt solutions, extreme pH, and temperatures up to 130 °C (18). We recently recognized the DNA sequence of AqpM, a candidate aquaporin or aquaglyceroporin in the genome of a methanogenic thermophilic archaeon,Methanothermobacter marburgensis 2 (,19). Here we investigate water permeability in living cells and report the purification, functional reconstitution, and characterization of AqpM

Characterization of LtsA from Rhodococcus erythropolis, an Enzyme with Glutamine Amidotransferase Activity

The nocardioform actinomycete Rhodococcus erythropolis has a characteristic cell wall structure. The cell wall is composed of arabinogalactan and mycolic acid and is highly resistant to the cell wall-lytic activity of lysozyme (muramidase). In order to improve the isolation of recombinant proteins from R. erythropolis host cells (N. Nakashima and T. Tamura, Biotechnol. Bioeng. 86:136-148, 2004), we isolated two mutants, L-65 and L-88, which are susceptible to lysozyme treatment. The lysozyme sensitivity of the mutants was complemented by expression of Corynebacterium glutamicum ltsA, which codes for an enzyme with glutamine amidotransferase activity that results from coupling of two reactions (a glutaminase activity and a synthetase activity). The lysozyme sensitivity of the mutants was also complemented by ltsA homologues from Bacillus subtilis and Mycobacterium tuberculosis, but the homologues from Streptomyces coelicolor and Escherichia coli did not complement the sensitivity. This result suggests that only certain LtsA homologues can confer lysozyme resistance. Wild-type recombinant LtsA from R. erythropolis showed glutaminase activity, but the LtsA enzymes from the L-88 and L-65 mutants displayed drastically reduced activity. Interestingly, an ltsA disruptant mutant, which expressed the mutated LtsA, changed from lysozyme sensitive to lysozyme resistant when NH(4)Cl was added into the culture media. The glutaminase activity of the LtsA mutants inactivated by site-directed mutagenesis was also restored by addition of NH(4)Cl, indicating that NH(3) can be used as an amide donor molecule. Taken together, these results suggest that LtsA is critically involved in mediating lysozyme resistance in R. erythropolis cells

MicroRNA-454 may function as an oncogene via targeting AKT in triple negative breast cancer

Abstract Background Altered microRNAs expression mediates tumor development and progression in many type cancers including triple negative breast cancer (TNBC). Here we detected the effect of miR-454 on cell proliferation, migration and invasion of triple negative breast cancer cells. Results miR-454 promoted the proliferation of TNBC, and enhanced migration and invasion in TNBC cells. Meanwhile, miR-454 improved the survival of TNBC cells after ironizing radiation. miR-454 inhibited radiation-induced apoptosis in TNBC cells by regulation of caspase 3/7 and Bcl-2 expression. Furthermore, PTEN and pAKT levels in TNBC cells were changed after overexpression of miR-454. Conclusions miR-454 played an essential role in tumor development and progression in TNBC, and might be used as a potential biomarker to predict radiotherapy response and prognosis in TNBC

Enhancement of the Detection Performance of Paper-Based Analytical Devices by Nanomaterials

Paper-based analytical devices (PADs), including lateral flow assays (LFAs), dipstick assays and microfluidic PADs (μPADs), have a great impact on the healthcare realm and environmental monitoring. This is especially evident in developing countries because PADs-based point-of-care testing (POCT) enables to rapidly determine various (bio)chemical analytes in a miniaturized, cost-effective and user-friendly manner. Low sensitivity and poor specificity are the main bottlenecks associated with PADs, which limit the entry of PADs into the real-life applications. The application of nanomaterials in PADs is showing great improvement in their detection performance in terms of sensitivity, selectivity and accuracy since the nanomaterials have unique physicochemical properties. In this review, the research progress on the nanomaterial-based PADs is summarized by highlighting representative recent publications. We mainly focus on the detection principles, the sensing mechanisms of how they work and applications in disease diagnosis, environmental monitoring and food safety management. In addition, the limitations and challenges associated with the development of nanomaterial-based PADs are discussed, and further directions in this research field are proposed

Predictors for central lymph node metastases in CN0 papillary thyroid microcarcinoma (mPTC): A retrospective analysis of 1304 cases

Summary: Background: Presence of lymph node metastases increases the risk of recurrence, but prophylactic central neck node dissection for patients with micropapillary thyroid cancer (mPTC) is controversial. We aim to find the clinical predictors of central lymph node metastases (CLNM) in patients with cN0 mPTC. Methods: We retrospectively reviewed the clinicopathological and molecular genetic characteristics of 1304 patients with cN0 mPTC operated at the First Hospital of Jilin University between January 1, 2013 and May 31, 2016, all underwent thyroid lobectomy or total thyroidectomy with unilateral or bilateral prophylactic central neck dissection. Univariate and multivariate analysis were used to identify the predictors of CLNM. Results: 30.7% of cN0 mPTC patients had CLNM. Univariate analysis found CLNM to be associated with younger age (≤45), male gender, larger tumor (>0.5 cm), multifocality, bilaterality, capsular invasion, lymphovascular invasion and extrathyroidal infiltration, but not associated with BRAF mutation, tumor location, preoperative TSH and anti-thyroglobulin antibody level. Multivariate logistic regression showed age ≤45 years (p 0.5 cm (p 0.5 cm, bilaterality and capsular invasion. BRAF mutation is not a predictor for CLNM in cN0 mPTC patients. Keywords: mPTC, Papillary thyroid microcarcinoma, Central lymph node metastases, cN0, BRA

Development of Flow Cytometric Assay for Detecting Papillary Thyroid Carcinoma Related hsa-miR-146b-5p through Toehold-Mediated Strand Displacement Reaction on Magnetic Beads

In this work, a simple enzyme-free flow cytometric assay (termed as TSDR-based flow cytometric assay) has been developed for the detection of papillary thyroid carcinoma (PTC)-related microRNA (miRNA), hsa-miR-146b-5p with high performance through the toehold-mediated strand displacement reaction (TSDR) on magnetic beads (MBs). The complementary single-stranded DNA (ssDNA) probe of hsa-miR-146b-5p was first immobilized on the surface of MB, which can partly hybridize with the carboxy-fluorescein (FAM)-modified ssDNA, resulting in strong fluorescence emission. In the presence of hsa-miR-146b-5p, the TSDR is trigged, and the FAM-modified ssDNA is released form the MB surface due to the formation of DNA/RNA heteroduplexes on the MB surface. The fluorescence emission change of MBs can be easily read by flow cytometry and is strongly dependent on the concentration of hsa-miR-146b-5p. Under optimal conditions, the TSDR-based flow cytometric assay exhibits good specificity, a wide linear range from 5 to 5000 pM and a relatively low detection limit (LOD, 3σ) of 4.21 pM. Moreover, the practicability of the assay was demonstrated by the analysis of hsa-miR-146b-5p amounts in different PTC cells and clinical PTC tissues

Evaluation of Matrix Metalloproteinase Inhibition by Peptide Microarray-Based Fluorescence Assay on Polymer Brush Substrate and in Vivo Assessment

Matrix metalloproteinases (MMPs) are important biomarkers and potential therapeutic targets of tumor. In this report, a peptide microarray-based fluorescence assay is developed for MMPs inhibitors evaluation through immobilization of biotin-modified peptides on the poly­(glycidyl methacrylate-<i>co</i>-2-hydroxyethyl methacrylate) (P­(GMA-HEMA)) brush-modified glass slides. After biotin is recognized with cyanine 3 (Cy3)-modified avidin (Cy3-avidin), the microarrays can produce strong fluorescence signal. The biotin moieties detach from microarray, when the biotin-modified peptide substrates are specially cleaved by a MMP, resulting in decreased fluorescence intensity of the microarray. The decreasing level of fluorescence intensity is correlated with the MMP inhibition. Nine known MMP inhibitors against MMP-2 and MMP-9 are evaluated by the assay, and the quantitative determination of inhibitory potencies (half maximal inhibitory concentration) are obtained, which are comparable with the literatures. Two biocompatible fluorogenic peptides containing MMP-specific recognition sequences and FAM/Dabcyl fluorophore-quencher pair are designed as activatable reporter probes for sensing MMP-2 and MMP-9 activities in cell and in vivo. The peptide microarray-based results are well verified by the cell inhibition assay and in vitro fluorescence imaging, and further confirmed by the in vivo imaging of HT-1080 tumor-bearing mice