Production of single and multi-walled carbon nanotubes using natural gas as a precursor compound

In this work, the Catalytic Chemical Vapor Deposition (CCVD) technique was used to synthesize carbon nanotubes (CNT). Natural gas (NG) was employed as a carbon source for the growing of CNT, while magnesium oxide was used as a catalyst support for the nanotubes synthesis. Two systems were utilized. The Fe–Mo/MgO system was obtained by the impregnation technique through the dispersion of iron oxide, which is the catalyst, over magnesia (with molybdenum additions). This system was tested intending to optimize the parameters for the production of single-walled carbon nanotubes (SWCNT). Moreover, Mg_1−x Fe _x MoO₄, which was prepared by the combustion synthesis method, was tested to produce multi-walled carbon nanotubes (MWCNT). The Fe-Mo/MgO tests were carried out under H₂/GN and Ar/GN atmospheres at 950 °C, whereas the Mg_1−x Fe _x MoO₄ was submitted to 1,000 °C under H₂/GN atmosphere. The Fe–Mo/MgO catalyst produced better results regarding number of CNT and their diameters under Ar/NG atmospheres than under H₂/NG atmospheres. The system Mg_1−x Fe _x MoO₄ produced MWCNT according to the expectations.     

Carbon monoxide and water vapor contamination of compressed breathing air for firefighters and divers

Compressed breathing air, used in self-contained breathing apparatus (SCBA) by firefighters and other categories of workers as well as by recreational and commercial divers, is prepared with the aid of high-pressure compressors operating in the range of 5000 psig. There have been reports of unexplained deaths of SCUBA divers and anecdotal accounts of decreased time to exhaustion in firefighters using SCBAs. Compressed breathing air has been found to contain elevated levels of carbon monoxide (CO) and water vapor that are consistent with carboxyhemoglobin (COHb) poisoning and freezing of the user's regulator on the breathing apparatus. The Coburn-Forster-Kane equation (CFK equation) was used to estimate COHb levels at rest and at maximum exercise when exposed to different levels of CO in contaminated breathing air. The results demonstrated that, at maximum exercise, the COHb ranged from 6.0 to 17% with the use of 1 to 4 SCBA cylinders contaminated by 250 ppm CO. Standard operating procedures have been developed at the Montreal Fire Department to minimize the risk of compressed breathing air contamination. Results of the quality analysis/quality control program indicate that implementation of these procedures has improved the quality of the compressed breathing air. Recommendations are made for improvement of the air testing procedures mandated by the Canadian CAN3 180.1-M85 Standard on Compressed Breathing Air and Systems.     

Quenching of chlorophyll a fluorescence in the aggregates of LHCII: steady state fluorescence and picosecond relaxation kinetics

The protein composition, steady state and time-resolved fluorescence emission spectra were studied in solubilized and aggregated LHCII complexes, that were prepared according to two different isolation protocols: (1) by fractionation of cation-depleted thylakoid membranes using the non-ionic detergent Triton X-100 according to the procedure of Burke et al. [(1978) Arch. Biochem. Biophys. 187, 252-263] or (2) by solubilization with N-beta-dodecyl maltoside (beta-DM) of photosystem II (PSII) membrane fragments in the presence of cations [Irrgang et al. (1988) Eur. J. Biochem. 178, 207-217]. Based on the analysis of the decay-associated emission spectra measured at 10 and 80 K five long-wavelength chlorophyll species were identified in aggregated LHCII complexes. These five forms are characterized by emission maxima at 681.5, 683, 687, 695, or 702 nm. All of these forms were found in both types of LHCII preparations but the relative amounts and temperature dependency of these species were markedly different in the aggregated LHCII complexes isolated by the two procedures. It was found that these differences cannot be simply explained by effects due to using a less mild detergent as beta-DM or by an ionic influence of Ca2+. Biochemical analysis of the protein composition showed that beta-DM type LHCII consists of all the chlorophyll (Chl)binding proteins belonging to the antenna system of PSII except the CP29 type II gene product (CP29). In contrast, the Triton X-100-solubilized LHCII is highly depleted in CP26 (CP 29 type I gene product) and is contaminated by a variety of unidentified polypeptides. It is proposed that the aggregates of LHCII prepared using Triton X-100 acquire specific spectral and kinetic features due to interaction between the bulk of LHCII subunits and minor protein(s).     

The branch site adenosine is recognized differently for the two steps of pre-mRNA splicing

The functional groups responsible for branch site identity in the two steps of pre-mRNA splicing as well as for spliceosome assembly were tested by incorporation of site-specific modifications at the branch site of a pre-mRNA. These results show that recognition of the adenosine occurs early in complex formation and that the branch site adenosine is recognized differently before the first step and for the second step. Further, direct UV cross-linking with these modified RNAs was used to identify a factor whose interaction was dependent upon the identity of the branch site nucleotide.     

The block to HIV-1 envelope glycoprotein-mediated membrane fusion in animal cells expressing human CD4 can be overcome by a human cell component(s)

Membrane fusion mediated by interaction of the human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein with the human CD4 molecule generally requires that the CD4 be expressed on a human cell. The failure of murine or simian cells expressing human CD4 to form syncytia upon mixing with cells expressing envelope glycoprotein could not be corrected by expression of both molecules at extremely high surface levels using vaccinia virus expression vectors. Video fluorescence microscopic analysis of fluorescent dye transfer between fusing cells indicated that the block occurred at the level of membrane fusion between individual pairs of cells. To gain insight into the basis for this fusion block, we tested the ability of fluorescent probe cells expressing envelope glycoprotein to fuse with transient animal x human hybrid giant cells expressing human CD4. The hybrid giant cells were generated either by low-pH-induced fusion of vaccinia-infected cells or by CD4/HIV-1 envelope glycoprotein-mediated cell fusion. We observed that envelope glycoprotein-expressing probe cells efficiently fused with CD4-expressing animal x human hybrid giant cells, independent of whether the CD4 was originally expressed on the animal or on the human cell. Fusion did not occur with CD4-expressing giant cells derived from animal cells alone. These results indicate that the fusion block is not due to dominant inhibitory components in the animal cell. Rather, they suggest that human cells contain an additional component(s) which, when transferred to the CD4-bearing animal cell, confers the ability to undergo membrane fusion mediated by the HIV-1 envelope glycoprotein.     

Einfluß der Trennverfahren auf das Ermüdungsverhalten von Stahlblechen

Influence of Cutting Method on the Fatigue Behaviour of Steel Sheets The present paper gives the fatigue behaviour of test specimens which have been obtained by laser cutting, plasma cutting or punching from steel sheets. The paper demonstrates the different damage to the surface introduced by the three techniques. For thin sheets (1.5 mm) laser cut specimens show advantages, for thicker sheets (6 mm) plasma cut sheets exhibit better fatigue properties.     

Hypertrophic olivary degeneration: case report in a child

We report a case of hypertrophic olivary degeneration (HOD) detected by MRI, in a 14-year-old girl, 13 months after surgical excision of a brainstem cavernous malformation. As in vivo diagnosis of this condition has only become possible with the advent of MRI, the number of reported cases remains relatively small and they are almost exclusively in adults. Many radiologists and particularly paediatric radiologists, may therefore be unfamiliar with this entity. To our knowledge, this is the first specific report of HOD diagnosed by MRI in a child.     

Delta opioid peptide [D-Ala2,D-leu5]enkephalin blocks the long-term loss of dopamine transporters induced by multiple administrations of methamphetamine: involvement of opioid receptors and reactive oxygen species

Delta opioid peptide [D-Ala2,D-leu5]enkephalin (DADLE) can prolong organ preservation and increases myocardial tolerance to ischemia. Our study examined the protective property of DADLE against methamphetamine- (METH) induced dopaminergic terminal damage in the central nervous system. Because the neurotoxicity of METH involves reactive oxygen species, we also examined if DADLE might be an antioxidative agent in vitro. DADLE at 2 and 4 mg/kg (i.p.), given 30 min before each METH administration (5 or 10 mg/kg, i.p., four injections in a day at 2-hr intervals), dose-dependently blocked the METH-induced long-term dopamine transporter loss. The opioid antagonist naltrexone blocked this action of DADLE in both aspects of striata but tends not to affect the effects of DADLE in the nucleus accumbens. DADLE did not alter changes in body temperature induced by METH. The reduction of striatal dopaminergic content and tyrosine hydroxylase activity caused by METH, however, were not blocked by DADLE. In vitro, DADLE was approximately equipotent to glutathione in inhibiting both superoxide anion formation induced by xanthine oxidase and hydroxyl radical formation evoked by ferrous/citrate complex. DADLE was only slightly less potent than glutathione in inhibiting the iron/ascorbate-induced brain lipid peroxidation. These results suggest that DADLE can protect the terminal membranes of dopaminergic neurons against METH-induced insult but not the loss of dopaminergic content and tyrosine hydroxylase activity and that this action of DADLE might involve opioid receptors as well as the sequestration of free radical.