Nonparametric estimation from length-biased data under competing risks

A new model for cross-sectional lifetime data is presented. The model is based on the length-bias assumption, and it is adapted to situations in which several types of censoring may occur. The NPMLE of the survival function is derived. An EM-algorithm to approximate the NPMLE is devised. The performance of the introduced estimator is investigated through simulations. A real set of data collected as part of a study on unemployment duration in Spain is used for illustration purposes.     

Private practice: a choice, but what challenges!

Recent changes in the Canadian health care system are having an impact on the way health care services are delivered. As a result, opportunities are opening up for a whole new generation of autonomous and independent nurses who choose to work directly with clients in a private practice setting. In part one of this two-part article, the author describes the main responsibilities of the nurse entrepreneur. Stressed are the areas of competency and the entrepreneurial spirit required. Administrative, professional, legal and fiscal aspects of independent practice are also outlined. Part two of the article focuses on the ethical responsibilities of the nurse entrepreneur and the regulations concerning fees, publicity, insurance, and office and file management. The author recommends keeping current on new developments and establishing a process whereby clients can evaluate the quality of care they receive.     

Analysis of the effect of polypyrrole synthesis conditions on its capacity to reduce hexavalent chromium

This paper reports the capacity of polypyrrole to reduce toxic hexavalent chromium (Cr(VI)). The influence of using different electrolytes during the polymer's synthesis has been studied. To improve the reduction of Cr(VI), the parameters considered were the polypyrrole morphology and the amount of conducting polymer. Polypyrrole obtained by cyclic voltammetry at a low sweep rate using KBr as supporting electrolyte showed better performance for Cr(VI) reduction compared to coatings obtained by constant potential or cyclic voltammetry at high sweep rates.     

Mutagenicity of ambient aerosol collected in an urban and industrial area of The Netherlands

To investigate the influence of the densely populated and heavily industrialized Rijnmond area of The Netherlands on the genotoxicity of the ambient aerosol, aerosol samples were collected at locations within the area, and at a coastal region located upwind. The mutagenicity of extracts of the samples was compared in the Salmonella/microsome test. The dependence of the effects on sampling time and on sampling location was investigated with the aid of a series of simple mathematical models. These models were also used to estimate the increase in mutagenicity above background levels at the sites in the Rijnmond area due to emissions within that area. Application of the models showed that the clear and significant increases are not merely a result of the additions of mutagens emitted, but that possibly interactions between sampling time- and location-dependent factors play a role. Comparison of the results obtained with the different Ames-test variants (different strains, with and without liver homogenate) indicate that the conclusions concerning the time and location dependence of the effect were not dependent on the variant used.     

Structure of d(GT)n.d(GA)n sequences: formation of parallel stranded duplex DNA

Alternating polypurine sequences exhibit remarkable polymorphism. In this study, we report that dGA.dGT sequences form parallel stranded duplex DNA at neutral pH. Using two model hairpins, 3'-d(GT)3-5'5'-T4(AG)3-3' (I) and 3'-d(GT)4-5'5'-T4(AG)4-3' (II), containing 5'5' linkages which direct parallel strand formation, we systematically explored the spectroscopic and thermodynamic properties of parallel stranded d(GA)n.d(GT)n. The parallel stranded hairpins are remarkably stable structures with TM's of 41.5 and 47.5 degreesC (in 0.4 M NaCl) for the shorter and longer hairpins, respectively. The van't Hoff enthalpies of 80.7 and 114 kJ mol-1 are relatively low but are comparable to a parallel stranded d(GA)n duplex. On the basis of the spectroscopic and electrophoretic characteristics, we conclude that parallel strand formation is not restricted to hairpin systems, but also readily occurs in unconstrained dimeric duplexes with the appropriate sequence homologies. Both melting curves and electrophoretic analyses of parallel stranded heteroduplexes in which the sequence enforces specific base pairing demonstrate that G-G and A-T base pairs are formed in d(GA)n.d(GT)n segments.     

Doppler ultrasound determination of average blood flow velocity and flow volume in transjugular intrahepatic portosystemic shunt (TIPS)

We evaluated the acute and chronic experimental toxicity of a water extract of saponins from Argania spinosa following oral and intraperitoneal (i.p.) administration in mice (Iops Ofa) and rats (Wistar). The DL50 obtained were 79 mg/kg for the i.p. route and 1,300 mg/kg for the oral route. For the chronic toxicity studies, we administred 100 and 200 mg/kg orally once a day during a 3 month period. There was a decrease in blood sugar in the third month of each therapy. Blood creatinine levels increased, thus evoking a renal pathology. A slight increase in transaminases levels was not significatif. Hematologic parameters were unchanged during the treatment and the histopathologic study showed hepatic glycogen decrease and a focal renal tube deterioration.     

Iodine-123 labelled nor-beta-CIT binds to the serotonin transporter in vivo as assessed by biodistribution studies in rats

Flavobacterium aurantiacum NRRL B-184 possesses the ability to degrade aflatoxin B1 in solution and in several food items. Aflatoxin B1 is a potent carcinogen that causes significant economic losses to the agricultural and food industry. The role of trace metal ions (Cu2+, Mn2+, Zn2+, and Co2+) were studied in an effort to understand the enzymatic system involved in aflatoxin B1 degradation by F aurantiacum. The effect of divalent chelators (EDTA and 1,10-phenanthroline [OPT]) in the presence of the trace metal ions was studied as well. Aflatoxin B1 (10 microg/ml) was added to 72-h cultures of F aurantiacum that had been washed and resuspended in phosphate buffer (pH 7.0). HPLC was used to determine aflatoxin B1 concentration in these cultures. Incubating cells at 30 degrees C with 1 and 10 mM Cu2+, Mn2+, and Zn2+ significantly decreased aflatoxin B degradation after 4 and 24 h (P < 0.05). Decreased degradation was also observed with 1 and 10 mM Cu2+ and Zn2+ after 48 h and with 0.1 mM Cu2+ after 24 and 48 h. Co2+ did not have a significant effect on aflatoxin B1 degradation. EDTA and OPT did not counter the inhibition in the presence of Cu2+. The addition of 1 mM EDTA countered the inhibition by 1 mM Mn2+ after 4 and 24 h, but 1 mM OPT did not counter the inhibition by 10 mM Mn2+ after 4 and 24 h. OPT countered the inhibition by 1 mM Zn2+ after 4 and 48 h. These trace elements inhibit aflatoxin B1 degradation by F aurantiacum. In addition, their presence necessitates higher concentrations (>1 mM) of EDTA and OPT for the removal of their inhibitory effect.