A comprehensive investigation of the sulfidation behavior of binary Co-Mo alloys

The sulfidation behavior of Co-Mo alloys containing up to 40 wt.% Mo was studied over the temperature range 600–900°C in both 10^–2 and 10^–4 atm. sulfur vapor. All of the alloys were two-phase, with the alloys containing up to 30Mo consisting of Co₃Mo plus solid-solution Co, and the Co-40Mo alloy consisting of the two intermetallic compounds, Co₃Mo and Co₇Mo₆. The sulfide scales which formed were duplex, with an outer layer of cobalt sulfide and a complex, heterophasic inner layer whose phases were both composition- and temperature-dependent. The parabolic rate constant for the sulfidation kinetics decreased with increasing Mo content at all temperatures investigated. Three activation energies, all different from that of pure Co, were observed. Furthermore, Co-30Mo exhibited a kinetics inversion between 800 and 850°C. This inversion was largely the result of the formation of an innermost layer of Co_1.62Mo₆S₈ at the high temperatures. Specifically, the presence of this sulfide in the inner scale caused a significant decrease in the growth rate of the outer layer of cobalt sulfide. In fact, formation of a more compact, innermost layer of Co_1.62Mo₆S₈ at 900°C compared to that at 850°C resulted in a negative activation energy for the growth of the cobalt sulfide in this temperature range. The variation in the activation energies was due to both the duplex nature of the scales which formed and the phase constitution of the inner scale. A simple model has been developed to explain the changes in the activation energies. At 800°C the sulfidation rate of the Co-Mo alloys was essentially the same at the two sulfur pressures studied. The predominant phase in the inner layer of Co-10Mo and Co-20Mo was CoMoS₃, while for Co-30Mo and Co-40Mo it was MoS₂. However, in the case of the latter alloys, Co_1.62Mo₃S₄ formed in the region of the alloy/scale interface at temperatures 850°C and above. Although the MoS₂, which had formed on Co-40Mo, appeared to be a continuous layer, it was in fact found to be relatively nonprotective. Platinummarker experiments revealed the position of the original metal surface to be the interface between the inner and outer scales.     

The corrosion behavior of Fe-Nb-Al alloys in H2/H2O/H2S atmospheres

The corrosion behavior of eight Fe-Nb-Al ternary alloys was studied over the temperature range 700–980°C in H₂/H₂O/H₂S atmospheres. The corrosion kinetics followed the parabolic rate law for all alloys at all temperatures. The corrosion rates were reduced with increasing Nb content for Fe-x Nb -3Al alloys, the most pronounced reduction occurred as the Nb content increased from 30 to 40 wt.%. The corrosion rate of Fe-30Nb decreased by six orders of magnitude at 700°C and by five orders of magnitude at 800°C or above by the addition of 10 wt.% aluminum. The scales formed on low-Al alloys (3 wt.% Al) were duplex, consisting of an outer layer of iron sulfide (with Al dissolved near the outer-/inner-layer interface) and an inner complex layer of Fe_xNb₂S₄(FeNb₂S₄ or FeNb₃S₆), FeS, Nb₃S₄ (only detected for Nb contents of 30 wt.% or higher) and uncorroded Fe₂Nb. No oxides were detected on the low-Al alloys after corrosion at any temperature. Platinum markers were found to be located at the interface between the inner and outer scales for the low-Al alloys, suggesting that the outer scale grew by the outward transport of cations (Fe and Al) and the inner scale grew by the inward transport of sulfur. The scales formed on high-Al alloys (5 wt.% Al) were complex, consisting primarily of Nb₃S₄, Al₂O₃ and (Fe, Al)_xNb₂S₄, and minor amounts of (Fe, Al)S and uncorroded intermetallics (FeAl and Fe₂Nb). The formation of Nb₃S₄ and Al₂O₃ blocked the transport of iron through the inner scale, resulting in the significant reduction of the corrosion rates.     

Sulfidation behavior of Ni-Cr-Mo alloys at 700°C

The effect of molybdenum additions 5, 10, 15, and 20 wt. %, on the sulfidation behavior of Ni-20Cr, and the effect of chromium additions, 5, 10, 15, and 20 wt.%, on the sulfidation of Ni-20Mo were studied in pure sulfur vapor at 700°C. In general, the alloys followed a linear or near-linear rate law, the sulfidation rate of Ni-20Mo being slightly less than that of Ni-20Cr. The alloys having the lowest ternary addition, e.g., Ni-Cr-5Mo and Ni-20Mo-5Cr. exhibited the most rapid reaction rates. The highest alloying additions of 20 wt.% had no appreciable benefit on reaction rates. Scale structures were complex but generally consisted of several layers. The outer layer was always NiS_1.03, although both binaries formed Ni₃S₂ within the NiS_1.03. An inner layer of Cr₃S₄ existed in which there was considerable dissolved molybdenum. A thin, intermediate layer of Cr₂S₃ generally formed between the Cr₃S₄ and the outer nickel sulfide. An innermost layer of MoS₂ formed on all alloys containing more than 10 wt. % Mo, and a second phase of Mo₂S₃ formed within the MoS₂ on Ni-20Mo. Although the scales changed with alloy composition, no significant changes in reaction rate were observed. Notable differences in both scale structure and reaction kinetics between this study and previous studies were apparent. The differences and possible reaction mechanisms are discussed.     

Outcome measures for low back pain research. A proposal for standardized use

STUDY DESIGN: An international group of back pain researchers considered recommendations for standardized measures in clinical outcomes research in patients with back pain. OBJECTIVES: To promote more standardization of outcome measurement in clinical trials and other types of outcomes research, including meta-analyses, cost-effectiveness analyses, and multicenter studies. SUMMARY OF BACKGROUND DATA: Better standardization of outcome measurement would facilitate comparison of results among studies, and more complete reporting of relevant outcomes. Because back pain is rarely fatal or completely cured, outcome assessment is complex and involves multiple dimensions. These include symptoms, function, general well-being, work disability, and satisfaction with care. METHODS: The panel considered several factors in recommending a standard battery of outcome measures. These included reliability, validity, responsiveness, and practicality of the measures. In addition, compatibility with widely used and promoted batteries such, as the American Academy of Orthopaedic Surgeons Lumbar Cluster were considered to minimize the need for changes when these instruments are used. RESULTS: First, a six-item set was proposed, which is sufficiently brief that it could be used in routine care settings for quality improvement and for research purposes. An expanded outcome set, which would provide more precise measurement for research purposes, includes measures of severity and frequency of symptoms, either the Roland or the Oswestry Disability Scale, either the SF-12 or the EuroQol measure of general health status, a question about satisfaction with symptoms, three types of "disability days," and an optional single item on overall satisfaction with medical care. CONCLUSION: Standardized measurement of outcomes would facilitate scientific advances in clinical care. A short, 6-item questionnaire and a somewhat expanded, more precise battery of questionnaires can be recommended. Although many considerations support such recommendations, more data on responsiveness and the minimally important change in scores are needed for most of the instruments.     

Molecular and cytogenetic analyses of stably and unstably expressed transgene loci in tobacco

To study the influence of genomic context on transgene expression, we have determined the T-DNA structure, flanking DNA sequences, and chromosomal location of four independent transgene loci in tobacco. Two of these loci were stably expressed in the homozygous condition over many generations, whereas the other two loci became unstable after several generations of homozygosity. The stably expressed loci comprised relatively simple T-DNA arrangements that were flanked on at least one side by plant DNA containing AT-rich regions that bind to nuclear matrices in vitro. Of the unstably expressed loci, one consisted of multiple incomplete T-DNA copies, and the second contained a single intact T-DNA; in both cases, however, binary vector sequences were directly contiguous to a right T-DNA border. Fluorescence in situ hybridization demonstrated that the two stably expressed inserts were present in the vicinity of telomeres. The two unstably expressed inserts occupied intercalary and paracentromeric locations, respectively. Results on the stability of transgene expression in F1 progeny obtained by intercrossing the four lines and the sensitivity of the four transgene loci to inactivation in the presence of an unlinked "trans-silencing" locus are also presented. The findings are discussed in the context of repetitive DNA sequences and the allotetraploid nature of the tobacco genome.     

Agonist-independent activation of Gz by the 5-hydroxytryptamine1A receptor co-expressed in Spodoptera frugiperda cells. Distinguishing inverse agonists from neutral antagonists

The human 5-hydroxytryptamine1A receptor, when expressed in Spodoptera frugiperda (Sf9) cells, facilitates the binding of [35S]GTPgammaS to a co-expressed GTP-binding regulatory protein, Gz, consistent with constitutive activity. The antagonists 4-(2'-methoxyphenyl)-1-[2'(n-2"-pyridinyl)-p-iodobenzamido]ethyl-p ipe razine (p-MPPI) and the related fluorobenzamido analogue p-MPPF had little (p-MPPI) or no (p-MPPF) effect on this activity. In contrast, a third antagonist, the neuroleptic spiperone, produced an almost complete suppression. Thus, using G protein activation as an index of receptor activity, p-MPPF was classified as a neutral antagonist, p-MPPI as a partial inverse agonist, and spiperone as essentially a full inverse agonist. As predicted, spiperone displayed properties consistent with a special form of noncompetitive antagonism when used to displace the agonist [125I]R-(+)-trans-8-hydroxy-2-[N-n-propyl-N-(3'-iodo-2'-propenyl)amin o]tetralin. Our data profile Sf9 cells as a unique vehicle for the characterization of inverse agonists, as these cells support a systematic pairing of mammalian receptors and G proteins, quantitative assays of G protein activation, and unambiguously labeled populations of coupled and uncoupled receptors.     

Effects of meta-chlorophenylpiperazine infusions in patients with seasonal affective disorder and healthy control subjects. Diurnal responses and nocturnal regulatory mechanisms

BACKGROUND: Multiple lines of evidence suggest that brain serotonergic systems may be disturbed in seasonal affective disorder (SAD). Previously, we found that the serotonergic agent meta-chlorophenylpiperazine (m-CPP) produced increases in activation and euphoria in depressed patients with SAD, but not in patients with SAD following light treatment or in the summer, nor in healthy control subjects in any condition. In the present study, we attempted to replicate and extend this finding using better methods. METHODS: Seventeen outpatients with SAD and 15 control subjects underwent successive 3-week periods of bright light treatment and light avoidance in a randomized order. During the third week of each condition, on 2 different occasions, subjects were admitted to the hospital for a night of sleep (core temperatures were recorded), followed by infusions of m-CPP (0.08 mg/kg) or placebo the next morning. Dependent measures included the 24-item National Institute of Mental Health Self-Rating Scale, plasma corticotropin, cortisol, prolactin, growth hormone, and norepinephrine concentrations, and core temperatures. RESULTS: Meta-chlorophenylpiperazine produced (1) significant increases in "activation-euphoria" ratings only in depressed patients with SAD in the untreated condition and (2) blunted corticotropin and norepinephrine responses in patients with SAD compared with controls across both light treatment conditions. In both groups, light treatment was associated with significant reductions in nocturnal core temperatures, which were correlated with similarly significant reductions in mean diurnal growth hormone concentrations. In patients with SAD, (1) the reductions in nocturnal core temperatures also were correlated with the reductions in baseline depression ratings and (2) the reductions in mean growth hormone concentrations were significantly smaller compared with controls. CONCLUSIONS: The abnormal m-CPP-induced activation-euphoria responses represent a replicated state marker of winter depression in patients with SAD. The blunted m-CPP-induced responsiveness of the hypothalamic-pituitary-adrenal axis and the sympathetic nervous system may represent traitlike abnormalities. The improvements in mood following light treatment in patients with SAD seem to be associated with the lowering of nocturnal core temperatures. The findings, although not easily explained based on a uniform abnormality of serotonin receptors, are nonetheless compatible with the notion that selected regions of the central nervous system are deficient in serotonin transmission during winter depression.     

The Electronic Spectrum of Gaseous CoO in the Visible Region

Laser excitation spectra of gaseous CoO have been recorded using Doppler-limited intracavity spectroscopy and supersonic jet-cooled molecular beam methods. As seen in the molecular beam spectra there are nearly 100 bands arising from the X4Delta7/2 spin component of the ground state in the wavelength region 430-720 nm. All of them are very strongly red-degraded and most of them are perturbed. 59Co hyperfine broadenings or splittings have been observed in many. The bands can be arranged into five electronic transitions, together with a considerable number of "extra" bands induced by perturbations; two of the excited electronic states are 4Phi, while the other three, which lie within 1700 cm-1, are 4Delta. Semi-empirical calculations have been carried out for the 4Delta excited states, using exchange integrals transferred from the TiO and VO spectra; the predicted energies, spin-orbit structures, and relative intensities in absorption are consistent with the assignment of all three 4Delta states to the same electron configuration, (4ssigma)1(3ddelta)3(3dpi)2(3dsigma)1. It seems that there are extensive interactions between the excited 4Delta states, because only one of them gives rise to a recognizable, though irregular, long vibrational progression in absorption. The other two progressions die out abruptly and unexpectedly after three or four members, presumably as a result of interference effects; however, wavelength-resolved fluorescence studies, together with calculations of the Franck-Condon overlap integrals to the various vibrational levels of the ground state, show that the upper state progressions reappear following a region of confused absorption. All of the excited states show highly irregular variations of their vibrational intervals and rotational constants with the vibrational quantum number, v. The wavelength-resolved fluorescence spectra give evidence for new low-lying electronic states of CoO at 3038, 5989, and 9105 cm-1; based on its vibrational frequency the 3038 cm-1 state is possibly the sigmadelta4pi2 B4Sigma- state. Copyright 1997 Academic Press. Copyright 1997Academic Press     

Pretransplant renal dysfunction predicts poorer outcome in liver transplantation

BACKGROUND: Numerous clinicians and researchers have expressed concern about the necessity and potential adverse consequences of many cesarean births in the United States. The purpose of this study was to explore college students' attitudes and beliefs about cesarean section. METHODS: One hundred two college students (66% women) completed a 20-item questionnaire that asked if they viewed cesarean delivery as a potentially negative experience, as a normal or acceptable method of childbirth, and as medically necessary, and asked about their beliefs concerning risk and prevention of cesarean birth. RESULTS: The number of "undecided" responses in the study was striking (7.8% to 69.6% across the 20 items). In general, women and men responded similarly, although women were significantly more likely than men to say they would be profoundly disappointed if their babies had to be delivered by cesarean section. Despite expressing cynicism about the cesarean birth rate (40% agreed that many unnecessary cesarean births occurred) and not viewing the procedure as a normal way of giving birth (47%), most respondents (over 70%) disagreed that giving birth by cesarean would be a negative experience or would make a woman feel like a failure. CONCLUSION: A high level of uncertainty exists about certain aspects of cesarean birth among young women and men, highlighting the need for information for prospective parents. Most college students did not view the cesarean birth experience as either potentially negative or normal. Future research should explore coverage of cesarean birth in childbirth education classes and the roles physicians, nurses, and midwives play in preparing expectant parents for the possibility of cesarean delivery.