Immigrant financial market participation: defining the research questions

Immigrants ; Population

Cost benefit analysis of availability systems with warm standby units and imperfect coverage

We study the cost benefit analysis of availability systems with warm standby units and imperfect coverage. The time-to-failure and the time-to-repair of the active and standby units are assumed to be exponentially and generally distributed, respectively. We assume that the coverage factor is the same for an active-unit failure as that for a standby-unit failure. We present a recursive method, using the supplementary variable technique and treating the supplementary variable as the remaining repair time, to develop the steady-state availability, (or Av), for three availability models. For each availability model, the explicit expressions for the Av for three various repair time distributions, such as exponential, k-stage Erlang, and deterministic are provided. Under the cost/benefit criterion, comparisons are performed based on assumed numerical values given to the distribution parameters, and to the cost of the active and standby units. (c) 2005 Elsevier Inc. All rights reserved

Synthesis and characterization of pH-sensitive dextran hydrogels as a potential colon-specific drug delivery system

pH-Sensitive dextran hydrogels were prepared by activation of dextran (T-70) with 4-nitrophenyl chloroformate, followed by conjugation of the activated dextran with 4-aminobutyric acid and cross-linking with 1,10-diaminodecane. The cross-linking efficiencies determined by mechanical measurements were in the range of 52-63%. Incorporation of carboxylpropyl groups in dextran hydrogels led to a higher equilibrium and faster swelling under high pH conditions. The swelling reversibility of hydrogels was also observed after repeated changes in buffers between pH 2.0 and 7.4. The slow rates of swelling and deswelling in response to changes in pH were attributed to the hydrophilic nature of dextran and formation of hydrogen bonds between the hydroxyl groups of dextran with water molecules. The pronounced effect of carboxylic acid content on degradation of hydrogels was observed after 4 h of incubation with dextranase and the influence significantly decreased after exposure to the enzyme for 8 h. The mechanism of bulk degradation of hydrogels under high swelling extent was substantiated using Coomassie blue protein assay. The release rate of bovine serum albumin from hydrogrels was primarily determined by the swelling extent. The release rate was further enhanced by addition of dextranase in buffer solutions

Temperature-responsive polymer-assisted protein refolding

The mechanism of poly (N-isopropylacrylamide) (PNIPAAm)-assisted protein folding was investigated. An optimal concentration equivalent to a molar ratio of polymer to carbonic anhydrase B (CAB) of ca. 2 was observed, in which the refolding yield was improved by 28%. At concentration above the critical level, PNIPAAm promotes protein precipitation leading to lower refolding yields, which is more significant when high molecular weight polymers are used. Results of fluorescence analysis and equilibrium studies indicate that PNIPAAm enhances protein refolding by the formation of complexes with aggregation-prone folding intermediates via hydrophobic interactions, as PEG. Results of stepwise dilution experiments indicate the aggregation-prone intermediates of CAB populate at guanidine hydrochloride (GdnHCl) ranging from 2 to 1 M, which are stabilized by the chaotropic agent and may rapidly associate rapidly into insoluble aggregates upon further dilution via hydrophobic interactions. It was also shown that the formation of about one-third of the aggregates was mediated by unidentified processes other than the self-association of the aggregation-prone intermediates. (C) 2002 Elsevier Science Inc. All rights reserved

Alloying modification of Sn-Ag-Cu solders by manganese and titanium

Effects of Mn and Ti additives on the microstructure and solidification behavior of Sn-1.0Ag-0.5Cu alloys (SAC105), as well as mechanical properties, were investigated in this study. Results show that alloying of Mn and Ti resulted in dramatically reduced undercooling, coarse eutectic structure and extended volume fraction of proeutectic Sn of which the dendritic size was refined. Those thermal and microstructural changes might be ascribed to the formation of MnSn(2) and Ti(2)Sn(3) intermetallic compounds (IMCs) which appeared respectively in the Mn-doped and Ti-doped samples. Nanoindentation tests demonstrated that the heterogeneous IMCs produced by alloying were harder and stiffer than the inherent IMCs, Ag(3)Sn and Cu(6)Sn(5). Worthy of notice is that the elastic modulus of SAC105 alloys decreased with only a minor alloying addition due to the shrunken eutectic regions and coarsened eutectic microconstituents. With a larger quantity of additives, an ascending elastic modulus could be obtained because of the strengthening effect by hard heterogeneous compounds. (C) 2008 Elsevier Ltd. All rights reserved

Antimutagenic and antimicrobial activities of pu-erh tea

The biological action of water extract of pu-erh tea (WEPT) was evaluated by Salmonella mutagenesis assay and bacteria test. Like green tea, oolong tea and black tea, WEPT showed neither cytotoxicity and nor mutagenicity toward Salmonella typhimurium TA98 and TA 100 with or without S9 mix (an external metabolic activation system). WEPT at 0.5-5 mg/plate expressed a dose-dependent inhibitory effect against both the mutagenicity of aflatoxin B, (AFB(1)), an indirect mutagen which requires metabolic activation, and 4-nitroquinoline-N-oxide (NQNO), a direct mutagen, in Salmonella typhimurium TA98 and TA100. In general, the antimutagenic activity of WEPT against AFB(1) and NQNO was weaker than other tea extract because of the least amount of total catechin in WEPT. For antimicrobial action, WEPT, green tea, oolong tea and black tea at 2.0 mg/ml showed inhibitory effect on growth of Staphylococcus aureus and Bacillus subtilis, but no effect on Escherchia coli. Obviously, WEPT has potential antimicrobial effect on gram-positive Staphylcoccus aureus and B. subtilis than that of gram-negative E. coli. In addition, caffeine and epicatechin (EC), main polyphenolic compounds in WEPT, showed both antimutagenic and antimicrobial effect against strains mentioned above, which may partially account for the antimutagenic and antimicrobial action of pu-erh tea. (c) 2005 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved

Carcinoid Crisis-Induced Acute Systolic Heart Failure

Carcinoid crisis is a life-threatening manifestation of carcinoid syndrome characterized by profound autonomic instability in the setting of catecholamine release from stress, tumor manipulation, or anesthesia. Here, we present an unusual case of carcinoid crisis leading to acute systolic heart failure requiring mechanical circulatory support. (Level of Difficulty: Intermediate.