Dynamic slab segmentation due to brittle-ductile damage in the outer rise.

Subduction is the major plate driving force, and the strength of the subducting plate controls many aspects of the thermochemical evolution of Earth. Each subducting plate experiences intense normal faulting1-9 during bending that accommodates the transition from horizontal to downwards motion at the outer rise at trenches. Here we investigate the consequences of this bending-induced plate damage using numerical subduction models in which both brittle and ductile deformation, including grain damage, are tracked and coupled self-consistently. Pervasive slab weakening and pronounced segmentation can occur at the outer-rise region owing to the strong feedback between brittle and ductile damage localization. This slab-damage phenomenon explains the subduction dichotomy of strong plates and weak slabs10, the development of large-offset normal faults6,7 near trenches, the occurrence of segmented seismic velocity anomalies11 and distinct interfaces imaged within subducted slabs12,13, and the appearance of deep, localized intraplate areas of reduced effective viscosity14 observed at trenches. Furthermore, brittle-viscously damaged slabs show a tendency for detachment at elevated mantle temperatures. Given Earth's planetary cooling history15, this implies that intermittent subduction with frequent slab break-off episodes16 may have been characteristic for Earth until more recent times than previously suggested17.

Double flood basalts and plume head separation at the 660-kilometer discontinuity.

Several of the world's flood basalt provinces display two distinct times of major eruptions separated by between 20 million and 90 million years. These double flood basalts may occur because a starting mantle plume head can separate from its trailing conduit upon passing the interface between the upper mantle and the lower mantle. This detached plume head eventually triggers the first flood basalt event. The remaining conduit forms a new plume head, which causes the second eruptive event. The second plume head is predicted to arrive at the lithosphere at least 10 million years after the first plume head, in general agreement with observations regarding double flood basalts.

Three-Dimensional Spherical Models of Convection in the Earth's Mantle.

Three-dimensional, spherical models of mantle convection in the earth reveal that upwelling cylindrical plumes and downwelling planar sheets are the primary features of mantle circulation. Thus, subduction zones and descending sheetlike slabs in the mantle are fundamental characteristics of thermal convection in a spherical shell and are not merely the consequences of the rigidity of the slabs, which are cooler than the surrounding mantle. Cylindrical mantle plumes that cause hotspots such as Hawaii are probably the only form of active upwelling and are therefore not just secondary convective currents separate from the large-scale mantle circulation. Active sheetlike upwellings that could be associated with mid-ocean ridges did not develop in the model simulations, a result that is in agreement with evidence suggesting that ridges are passive phenomena resulting from the tearing of surface plates by the pull of descending slabs.

Influence of glucogenic amino acids on the hepatic metabolism of threonine.

The supplementation of a low-protein diet with L-threonine leads to a marked accumulation of threonine in plasma and liver, whereas increasing dietary protein generally leads to an induction of threonine dehydratase in the liver, hence depressed availability for extrasplanchnic tissues. The aim of the present study was, thus, to further investigate the factors which control the utilization of threonine by the liver. Increasing the dietary supply of threonine led to parallel increases in the afferent and hepatic concentrations and in the rate of utilization by the liver; however, the fractional extraction tended to decrease. It appears that the addition of a mixture of glucogenic amino acids to the diet prevented the accumulation of threonine in plasma induced by exogenous threonine. The glucogenic amino acids increased the fractional hepatic uptake of threonine, and counteracted its accumulation in the liver. These effects reflect the fact that the glucogenic amino acids elicited a potent induction of the threonine dehydratase, whereas threonine alone was uneffective. Our results suggest that, besides the well-established effect of glucogenic conditions, the availability of some glucogenic amino acids is an important factor in the control of threonine catabolism.

[Treatment of esophagotracheal fistula following intensive care. An experience of 17 cases]. / Traitement des fistules oesophago-trachéales de la réanimation (FOT). Expérience de dix-sept cas.

Oesophago-tracheal fistulae secondary to respiratory intensive care have become the commonest type of non-tumoural fistula in adults: 17/26 cases. They complicated a long period of difficult and septic intensive care, after a mean interval of 30 days. The diagnosis was confirmed by bronchoscopy which also provided good assessment of the site and extent of the fistula and the associated tracheal lesions. The severity of this complication is stressed by 5 deaths in the present series (1 toxi-infectious syndrome after 24 hours, 2 abandonments due to a hopeless resuscitation prognosis, 2 cases of oesophago-tracheal reflux which could have been prevented). One should not wait for spontaneous cure (although this did take place in 2 cases). Ideal direct suture (9 cases: 9 cures) requires local conditions favourable for healing and rapid respiratory autonomy. These conditions can be achieved by an active approach to protection against oesophago-tracheal reflux: at least lower oesophageal exclusion (4 cases) by ligation or anti-reflux operation. Oesophageal exclusion followed by oesophago-coloplasty is sometimes the only solution in cases of severe destruction of cervico-mediastinal tissues (2 cases: 1 cure). Five tracheal strictures required an associated resection-anastomosis (5 cures).

[Tumors of the digestive muscles. Diagnosis and treatment apropos of 10 cases]. / Les tumeurs musculaires digestives. Diagnostic et traitement à propos de 10 cas.

Ten cases of digestive tract muscle tumours emphasized the difficulty in preoperative diagnosis. CT scan gave the best results by visualizing the tumour in all the cases but one. In this case jejunal localization of a small tumour was made by arteriography. In gastric and duodenal localizations, the endoscopic aspect was not particularly specific and too superficial biopsies were always negative. The prognosis depends on pathology results but the distinction between malignancy and benign tumours is not always easy to make. The course of the disease is often needed to correct an erroneous initial diagnosis of benign tumour underscoring the need for careful follow-up.

[Is extended lymphadenectomy justified in surgery for pancreatic adenocarcinoma? Apropos of a series of 59 cases]. / La lymphadénectomie élargie dans la chirurgie de l'adénocarcinome pancréatique est-elle justifiée? A propos d'une série de 59 cas.

Between October 1987 and December 1992, we reviewed 130 medical records of pancreatic surgery for various pathologies, of which 57 cases had undergone cephalic duodenal pancreatectomy (C.D.P.) for pancreatic adenocarcinoma. There were 32 classical C.D.P. without lymphadenectomy and 25 C.D.P. with widened lymphadenectomy as practised by the Japanese workers Ishikawa, Manabe, and by others. Operatory mortality was 7% in both groups. On the other hand, morbidity was higher with widened lymphadenectomy and gave specific complications. Despite our short follow-up, it seems that the additional lymphatic excision does not significantly improve the rate of relapse or mortality. We have therefore stopped using the technique and have switched to per-operatory irradiation after tumoral excision.

Altered partition of threonine metabolism in pigs by protein-free feeding or starvation.

Kinetic aspects of threonine (Thr) metabolism were examined in growing pigs fed a well-balanced diet (C), an isocaloric protein-free diet (PF), or starved (S) for 48 h. With the use of continuous simultaneous infusion of L-[1-13C]Thr, [1-14C]sarcosine, and 2-[1-14C]ketobutyrate (KB) for 10 h, estimates were made of rates of Thr incorporated into protein (S), released from body proteins (B), and oxidized through the catabolic pathways of L-Thr 3-dehydrogenase (TDG) and threonine dehydratase (TDH). In the C group S was 185, B was 138, Thr disposal to glycine (DRThr-Gly) was 47, and Thr disposal to KB (DRThr-KB) was 7 mumol.h-1.kg-1. Consequently, Thr balance was +48 mumol.h-1.kg-1. In the PF-fed pigs, S, B, DRThr-Gly, and DRThr-KB were significantly reduced by 38, 15, 74, and 75%, respectively. In the S group, S, B, and DRThr-Gly were significantly reduced by 47, 17, and 55%, respectively, but DRThr-KB was similar to the C group. DRThr-Gly in all groups was highly correlated with TDG enzyme activity measured in liver homogenates. By contrast with in vivo results, TDH enzyme activity was increased by 88% (P less than 0.05) in the S group and decreased by 27% (not significant) in the PF group compared with the C group. The TDH pathway accounted for 13, 12, and 27% of total Thr oxidation in the C, PF, and S groups, respectively. These results suggest that Thr conservation in protein-depleted states (PF and S groups) occurred mainly by a decrease of Thr oxidation and that the partition through these pathways was only altered when energy was completely withdrawn.

Ideal amino acid profile and dietary lysine specification for broiler chickens of 20 to 40 days of age.

1. The aim of the study was to determine the ideal ratio of the essential amino acids lysine (Lys), methionine (Met), threonine (Thr), tryptophan (Trp), arginine (Arg), valine (Val) and isoleucine (Ile) and to assess the required dietary lysine concentration for optimum performance in broiler chickens of 2 commercial strains from 20 to 40 d of age. 2. An identical basal diet was used throughout all experiments. It consisted mainly of maize and soyabean meal and contained 172 g crude protein and 13.2 MJ AME(N) per kg. For each experiment, the basal diet was adequately supplemented with all essential amino acids except the one to be tested, which was supplemented in 6 graded concentrations in exchange for maize starch. One (Met, Trp, Arg, Val, Ile) or 2 (Lys, Thr) growth trials were conducted per amino acid tested and the response in weight gain, food: gain ratio, breast meat yield and abdominal fat were examined. 3. The ideal amino acid ratio relative to Lys (expressed as a percentage) was calculated to be 75% Met+Cys, 63% Thr, 19% Trp, 112% Arg, 71% Ile and 81% Val on a true faecal digestible basis when the data were subjected to broken-line regression analysis. From both lysine studies the concentration for optimum food: gain ratio was calculated, by exponential regression analysis, to be 11.5 g true faecal digestible lys per kg diet.