Grain size-acoustic emission relationships in hydrogen induced delayed cracking

A detailed characterization of acoustic emission signals generated during hydrogen induced cracking in 300M steel has been conducted. Decreasing the prior austenite grain size resulted in less acoustic emission activity at a given applied stress intensity. For a given microstructure, acoustic emission activity increased with increasing applied stress intensity. The extrapolation of the count rate (or event rate) curves to zero activity coincided with the threshold value. Variations in the acoustic emission response are explained by considering the grain size dependency of the emission event peak amplitude.     

Sternocleidomastoid muscle inhibition induced by trigeminal stimulation

Among numerous reports of anatomical and functional coupling between the trigeminal and cervical systems is the demonstration that the sternocleidomastoid (SCM) muscles may become activated along with the masseter muscles during forceful abrupt biting maneuvers. Whether the co-activated SCM is also inhibited by stimuli that produce masseter inhibition is not known. This study evaluated the SCM for the presence of inhibition during mechanically-elicited (chin or forehead tap) and electrically-elicited (anterior maxillary gingiva stimulation) inhibition of the masseter muscle in ten healthy men. Surface EMG data were recorded bilaterally from the masseter and SCM muscles. The data for each muscle were converted to ratios of the pre-stimulus maximum voluntary contraction activity for each subject and averaged across subjects. Means of these percentages were determined at several defined pre- and post-stimulus intervals. The results indicate that masseter inhibition was clearly elicited by the electrical and both forms of mechanical stimulation. SCM co-inhibition could be evoked by electrical and chin tap stimulation but not by forehead tap. The responses to these stimuli varied among subjects, from trial to trial, and within subjects depending on the experimental condition. The fact that it was possible for this co-inhibition to be evoked is presented as further indication of the functional coupling of the trigeminal and cervical systems.     

Stresses induced in iron-ore pellets by hydrogen reduction

The objectives of this investigation were (a) to determine the effect of reduction temperature on the strength of iron ore agglomerates and (b) to develop enhanced understanding for the cracking associ-ated with reduction. Iron-ore agglomerates from two sources (Samarco Mineração and Bethlehem Steel) were reduced in a hydrogen atmosphere at temperatures varying from 873 K to 1373 K at intervals of 100 K and times varying from 30 to 300 minutes. The compressive strength at the ambient temperature of the pellets was determined after the various reduction treatments by using a piston-and-cylinder testing technique and computing the energy required in crushing them. The highest strength, at a specific level of reduction, was found after reduction at 1073 K, for both the Samarco and Bethlehem pellets. Profuse cracking of the pellets was observed after reduction. These cracks led to a weakening of the pellets. A mechanism for reduction-induced cracking, based on internal stresses due to volume changes produced by the chemical reactions, is presented.     

Effects of methylxanthine derivatives on antitumor activity and toxic side effect of adriamycin induced by inhibition of DNA biosynthesis

The antitumor activity of adriamycin (ADR) was enhanced by combination with theobromine or pentoxifylline. Theobromine increased the concentration of ADR in the tumor without any effects on that in the heart and the liver. The influence of the combination of theobromine or pentoxifylline with ADR on the lipid peroxide level (indicating the ADR-induced side effect) and on DNA biosynthesis (indicating the side effect and antitumor activity) were examined. When ADR was administered into mice, the lipid peroxide level in the liver and the heart increased. However, the combination of theobromine or pentoxifylline did not enhance the ADR-induced increment of the lipid peroxide level in the liver, and moreover, it inhibited that in the heart. The decrease of DNA biosynthesis in the liver and the heart, induced by ADR, were not enhanced by combination with theobromine or pentoxifylline. On the other hand, the combination of theobromine with ADR significantly increased the inhibition of DNA biosynthesis in the tumor. These findings indicate that the combination of theobromine or pentoxifylline with ADR have no effect on the side effects of ADR in the liver and the heart, with the increase of antitumor activity of ADR in the tumor, and it is suggested that these drugs will be of value as a biochemical modulator of ADR.     

Analysis of individual positron emission tomography activation maps by detection of high signal-to-noise-ratio pixel clusters

We present a new method for the analysis of individual brain positron emission tomography (PET) activation maps that looks for activated areas of a certain size rather than pixels with maximum values. High signal-to-noise-ratio pixel clusters (HSC) are identified and their sizes are statistically tested with respect to a Monte-Carlo-derived distribution of cluster sizes in pure noise images. From multiple HSC size tests, a strategy is proposed for control of the overall type I error. The sensitivity and specificity of this method have been assessed using realistic Monte Carlo simulations of brain activation maps. When compared with the gamma 2 statistic of the local maxima distribution, the proposed method showed enhanced sensitivity, particularly for signals of low magnitude and/or large size. Its potential for the individual analysis of PET activation studies is presented in two sets of subjects who underwent two cognitive protocols. Although it can be viewed as an alternative to the classical stereotactic averaging approach, this new method is intended to be a first step toward the analysis of single-subject PET activation studies.     

Modifying influence of enalaprilat on mesangial cell DNA synthesis induced by hydrogen peroxide

This study examined the effect of the angiotensin converting enzyme (ACE) inhibitor, enalaprilat, on mesangial cell (MC) DNA synthesis induced by H2O2, IL-6 and PDGF. MC were incubated with enalaprilat (2.5-100 mumol/l) alone and together with combinations of H2O2 (3 daily pulses of 10(-6) mol/l), IL-6 (5 ng/ml) and PDGF (10 ng/ml). DNA synthesis was assessed after 72 h using [3H]thymidine (3H-TdR) incorporation. Enalaprilat alone had no effect on MC DNA synthesis. Stimulation of MC by H2O2, PDGF and IL-6 alone resulted in increases in 3H-TdR of 4936.6 +/- 1147.5, 5640.5 +/- 1537.6 and 4413.5 +/- 998.4 cpm, respectively (P < 0.05 above control). Only 2.5 mumol/l enalaprilat effected a significant reduction in IL-6 and PDGF-induced DNA synthesis. Incubation of MC with H2O2 + PDGF or H2O2 + IL-6 resulted in increases of 3H-TdR of 6471.9 +/- 1785.1 and 5507.2 +/- 1270 cpm, respectively (P < 0.05 above control). Addition of enalaprilat with either H2O2 + PDGF or H2O2 + IL-6 effected significant reductions in DNA synthesis over the range 2.5-100 mumol/l. These data demonstrate that ACE inhibitors modulate MC DNA synthesis induced by reactive oxygen species.     

Transformation of tooth type induced by inhibition of BMP signaling

Mammalian dentitions are highly patterned, with different types of teeth positioned in different regions of the jaws. BMP4 is an early oral epithelial protein signal that directs odontogenic gene expression in mesenchyme cells of the developing mandibular arch. BMP4 was shown to inhibit expression of the homeobox gene Barx-1 and to restrict expression to the proximal, presumptive molar mesenchyme of mouse embryos at embryonic day 10. The inhibition of BMP signaling early in mandible development by the action of exogenous Noggin protein resulted in ectopic Barx-1 expression in the distal, presumptive incisor mesenchyme and a transformation of tooth identity from incisor to molar.     

The effect of impurities and strength level on hydrogen induced cracking in a low alloy turbine steel

The effect of impurities on the threshold stress intensity for cracking in H₂S (K{ISCC}) has been investigated at various yield strength levels for a low alloy steel. Results show that the effect of impurities on K_ISCC is a function of the yield strength level. At low yield strength levels the K_ISCC of the steel is lowered markedly due to additions of impurities. However, at higher yield strength levels the K_ISCC data for pure and impure steels converge to a single value. In addition, the effect of yield strength level on Xiscc is a function of the degree of temper embrittlement caused by impurity segregation. For small degrees of temper embrittlement, increasing the yield strength decreases the -Kiscc appreciably, while for large degrees of temper embrittlement,K _ISCC is relatively insensitive to the yield strength. At K_ISCCvalues below about 50 MPa Vm, the percentage of intergranular fracture in H₂S is found to be uniquely related to K_ISCC regardless of the yield strength-impurity combination by which a givenK _ISCC is obtained. Results of the study indicate that the K_ISCC OF steels is affected by impurities, yield strength and H2S both directly and indirectly via interactive mechanisms.