RESUMEN
Zeolites representing seven different topologies were subjected to life-time assessment studies as methanol to hydrocarbons (MTH) catalysts at 400 °C, P(MeOH) = 13 kPa and P(tot) = 100 kPa. The following topologies were studied: ZSM-22 (TON), ZSM-23 (MTT), IM-5 (IMF), ITQ-13 (ITH), ZSM-5 (MFI), mordenite (MOR) and beta (BEA). Two experimental approaches were used. In the first approach, each catalyst was tested at three different contact times, all giving 100% initial conversion. The life-time before conversion decreased to 50% at each contact time was measured and used to calculate critical contact times (i.e. the contact time needed to launch the autocatalytic MTH reaction) and deactivation rates. It was found that the critical contact time is strongly correlated with pore size: the smaller the pore size, the longer the critical contact time. The second experimental approach consisted of testing the catalysts in a double tube reactor with 100% initial conversion, and quenching the reaction after 4 consecutive times on stream, representing full, partial, and zero conversion. After quenching, the catalyst bed was divided into four segments, which were individually characterised for coke content (temperature-programmed oxidation) and specific surface area (N2 adsorption). The axial deactivation pattern was found to depend on pore size. With increasing pore size, the main source of coke formation changed from methanol conversion (1D 10-ring structures), to partly methanol, partly product conversion (3D 10-ring structures) and finally mainly product conversion (3D 12-ring structure). As a result, the methanol conversion capacity changed little with contact time for ZSM-5, while it increased with increasing contact time for the catalysts with smaller pore sizes, and decreased with increasing contact time for pore sizes larger than ZSM-5.
RESUMEN
The development of graphene-based materials for optical limiting functionality is an active field of research. Optical limiting for femtosecond laser pulses in the infrared-B (IR-B) (1.4-3 µm) spectral domain has been investigated to a lesser extent than that for nanosecond, picosecond and femtosecond laser pulses at wavelengths up to 1.1 µm. Novel nonlinear optical materials, glassy graphene oxide (GO)-based silico-phosphate composites, were prepared, for the first time to our knowledge, by a convenient and low cost sol-gel method, as described in the paper, using tetraethyl orthosilicate (TEOS), H3PO4 and GO/reduced GO (rGO) as precursors. The characterisation of the GO/rGO silico-phosphate composite films was performed by spectroscopy (Fourier-transform infrared (FTIR), Ultraviolet-Visible-Near Infrared (UV-VIS-NIR) and Raman) and microscopy (atomic force microscopy (AFM) and scanning electron microscope (SEM)) techniques. H3PO4 was found to reduce the rGO dispersed in the precursor's solution with the formation of vertically agglomerated rGO sheets, uniformly distributed on the substrate surface. The capability of these novel graphene oxide-based materials for the optical limiting of femtosecond laser pulses at 1550 nm wavelength was demonstrated by intensity-scan experiments. The GO or rGO presence in the film, their concentrations, the composite films glassy matrix, and the film substrate influence the optical limiting performance of these novel materials and are discussed accordingly.
RESUMEN
OBJECTIVE: To investigate the knowledge and attitudes of patients towards lumbar puncture (LP), its complications, and indications. METHODS: In a questionnaire survey, patients who were referred to the general neurology outpatient clinic at Nemazee Hospital in Shiraz, Iran, from January 2007 to January 2008 were invited to complete a questionnaire consisting of items on demographic and socioeconomic variables, experiences with LP and complications, and knowledge of and attitudes regarding LP. RESULTS: A total of 410 patients were recruited (58% women, mean age 33.2 +/- 2.7 years). Poor knowledge of LP was highly prevalent (92.6%), and negative attitudes toward LP were also common (63%) among our patients. Skepticism regarding LP was directly related to lack of information (p=0.00007). Lower socioeconomic status, lower educational level, and residence in rural areas were associated with being less well informed about LP, but interestingly those who had experience with LP before were better informed and had more positive attitudes. CONCLUSION: It is possible to overcome reluctance to undergo LP through education of its indications, contraindications, and complications.
RESUMEN
BACKGROUND: Preeclampsia (PE) is one of the main causes of maternal and perinatal mortality and morbidity. Evidence shows that oxidative stress plays an important role in the pathophysiology of the PE. As catalase is a key enzyme in antioxidant enzymatic defense which protects cell from oxidative damage, in this study, we aimed to investigate the relationship between CAT-21A/T (rs7943316) polymorphism and PE susceptibility. MATERIALS AND METHODS: This case-control study was conducted on 155 PE women and 159 normotensive pregnant women. Polymerase chain reaction-restriction fragment length polymorphism method was used for genotyping. RESULTS: There was no association between CAT-21AT and TT genotypes and PE susceptibility. However, the CAT-21A/T polymorphism was associated with 1.6-fold higher risk of PE in dominant model (AA vs. AT + TT) (odds ratio [OR] 1.6 [95% confidence interval [CI]: 0.9-2.9]; P = 0.04). However, the CAT-21A/T polymorphism was not associated with PE in recessive model (TT vs. AA + AT) (OR 1.3 [95% CI: 0.8-2.1]; P = 0.4). CONCLUSIONS: The CAT-21A/T polymorphism could be a risk factor for PE susceptibility in dominant model.