Study on a cobalt silica catalyst during reduction and Fischer–Tropsch reaction: In situ EXAFS compared to XPS and XRD

The reduction of a 25 wt% Co/SiO₂ catalyst for the hydrocarbon synthesis has been followed by several techniques: XRD, TPR, XPS and in situ EXAFS. Before reduction the cobalt is present as a Co₃O₄ spinel phase. A two-step reduction of Co₃O₄ to CoO and then to Co° is observed by EXAFS. This is consistent with XPS (surface) and TPR or XRD (bulk) studies. During CO/H₂ reaction, cobalt is always in the metallic state (EXAFS). The coordination number of cobalt has been determined at each reduction step and during CO hydrogenation reaction.     

A new hypothesis to describe the mechanisms acting in a welded joint of semicrystalline thermoplastics

Since it is known that crosslinked polythylene can be worked, it is clear that the mechanics acting in the interior of a welded joint are not adequately explained yet. There are several criteria, hypotheses and models that attempt to describe what happens in a welded joint. In this paper, two new promising hypotheses, the Mixed Crystal Hypothesis and the Nexus Hypothesis, are introduced. The Mixed Crystal Hypothesis can be proven by the help of several different examination methods. Other examinations support the Nexus Hypothesis.     

High-tensile bolts without heat treatment

According to DIN-ISO 898-1 high tensile bolts of class 8.8 must have a quenched and tempered structure. Therefore either quenched and tempered wire rod is used for cold heading or the bolts are quenched and tempered after the bolt forming process. This paper presents a new wire rod, which offers the chance to get comparable or even better final properties and lower production costs: a low-carbon MnSi wire rod is used as basic material. The final tensile strength is produced by drawing and cold forming. The conventional final quenching and tempering is omitted and for many cases also baking can be avoided. An increased fatigue resistance and the elimination of final straightening of the bolts are additional advantages of the new process.     

Chemokine gene expression in rat pancreatic acinar cells is an early event associated with acute pancreatitis

BACKGROUND & AIMS: The molecular mechanisms underlying pancreatitis are largely unknown. The goal of this study was to identify an early genetic event that correlated with pancreatitis. METHODS: Differential display of messenger RNAs (mRNAs) was conducted on normal pancreas vs. those of animals with secretagogue-induced pancreatitis. Northern blots from normal animals and animals with experimental acute pancreatitis were probed with cloned complementary DNAs for chemokines. Pancreatitis was induced with cerulein and by retrograde injection of bile salts. Immunocytochemistry was used to identify the source of chemokine expression. Pyrrolidine dithiocarbamate was tested for effects on chemokine expression and pancreatitis. RESULTS: A differentially amplified band was consistently observed early after cerulein hyperstimulation. This band was identified as a portion of the mob-1 gene, an alpha-chemokine. Northern analysis indicated that mRNAs for mob-1 and another chemokine, mcp-1, were induced after cerulein hyperstimulation in vivo. mob-1 mRNA was also induced by retrograde injection of bile salts and by cerulein in acinar cells in vitro. mob-1 protein was localized to exocrine cells in pancreata of diseased animals. Pyrrolidine dithiocarbamate inhibited both chemokine gene expression and early inflammatory characteristics of pancreatitis. CONCLUSIONS: Chemokines are induced in acinar cells by treatments that induce pancreatitis and may play an important role in the early stages of the disease.     

Synthese von Heterocyclen durch C?C-Knüpfung. IV. Heterocyclensynthesen durch intramolekulare Dien-Reaktion

Synthesis of Heterocyclic Compounds by C C-bond Closure. IV. Synthesis of Heterocyclic Compounds by Intramolecular Dienreaction N-2-Cyclohexenyl-N-isopropylcinnamamide 8 cyclizes at 230°C to give the decahydronaphthindolone 9 . N-Alkyl-N-allylcinnamamides 10 analogously form 1 H-hexahydrobenzisoindolones 11 . N-Alkyl-N-allylsorbamides 14 cyclize at 150°C to 1 H-hexahydroisoindolones 15 . 15b yields the cyclic enamide 16 by alkali catalyzed shift of the double bond. Tricyclic lactames 19 and 20 are formed by thermal isomerization of N-cycloalkenylsorbamides 18a and 18b , respectively.     

A FE/BE coupling for the 3D time-dependent eddy current problem. Part I: a priori error estimates

In this paper the discontinuous Galerkin method in time for the coupling of conforming finite element and boundary element methods is established. We derive quasi-optimal a priori error estimates. Numerical examples prove the new scheme to be useful in practice. A posteriori error control and an adaptive algorithm are studied in Part II of this paper.     

Complementary/alternative medicine for asthma: we do not know what we need to know

In a recent report, a series of studies is described showing that individual differences in rat maternal licking and grooming are correlated with their offsprings' later adrenal response to a stressor (Liu et al., 1997). Pups that received more maternal stimulation in infancy had lower ACTH, corticosterone, and CRH mRNA, while they had greater amounts of GR mRNA. Liu et al. also compared maternal behavior in litters where rat pups were handled daily to maternal behavior of nonhandled litters. They found that mothers of handled pups licked and groomed their young significantly more often than did mothers of control litters. In their discussion, Liu et al. proposed that their data support Levine's (1975) thesis that handling effects in infancy are mediated via the mother. Levine had proposed that handling of pups will modify the mother--pup interaction, thereby causing a change in maternal behavior. The purpose of this commentary is to summarize data obtained with mice and rabbits which, in part, support and, in part, challenge the conclusions of Liu et al.     

Relationship between group delay and stored energy in microwavefilters

In this paper, an expression for the time average stored energy (t.a.s.e.) in a passive lossless two-port is derived in terms of its scattering parameters. In particular, it is shown that the t.a.s.e. in a passive lossless reciprocal symmetrical or antimetrical two-port is proportional to the group delay. One implication of this result is that the t.a.s.e., which is linked to the power-handling capability in many passive filters used in practice, is proportional to the group delay of the filter. This rigorous derivation is based on a variational theorem, which has been used in the past to prove energy storage results for passive lossless one-ports and periodic two-ports