Browsing by Subject "CVD"

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    The characterization and elimination of the external acidity of ZSM-5.
    (Elsevier, 1996) Weber, R; Fletcher, J; Möller, K; O'Connor, C
    The external acidity of ZSM-5 was modified either by coating the crystals with a silicalite shell or by chemical vapour deposition (CVD) of tetraethoxysilane (TEOS). Temperature programmed desorption (TPD) techniques were used to characterize the acidity changes arising from these modifications. Ammonia and pyridine were used as probes for the total acidity, and 4-methylquinoline was used to probe the external acidity of the modified and unmodified ZSM-5 samples. Si/Al ratios of the modified samples were also used to characterize the samples. Both methods of modification were able to make the external acid sites inert. Chemical vapour deposition was found to be a better method, because the external surface acidity was eliminated without significantly changing the catalyst in terms of total acidity. Optimum elimination of the external surface acidity by CVD was obtained for the sample with the higher deposition time (16 h) and temperature (400°C). Optimum elimination of the external surface acidity using the silicalite shell method was obtained using the detemplated NH4-form of the parent crystal as seed material. The channel structures of crystals modified by both processes remained accessible to ammonia and pyridine.
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    The chemical vapour and liquid deposition of tetraethoxysilane on the external surface of ZSM-5
    (Elsevier, 1998) Weber, R W; Möller, K P; Unger, M; O'Connor, C
    The external acidity of ZSM-5 was modified by chemical vapour deposition (CVD) and chemical liquid deposition (CLD) of tetraethoxysilane [Si(OC2 H5 ) 4 ] using a static vacuum system, a vapour phase flow system and liquid phase deposition. Temperature programmed desorption (TPD) techniques were used to characterise the acidity changes arising from these modifications. Pyridine was used as a probe for the total acidity and 4-methyl quinoline (MQ) was used to probe the external acidity. The adsorption capacities of the samples were measured using n-hexane, p-xylene, o-xylene and 1,2,4-trimethyl benzene. The extent of Si(OC2 H5 ) 4 deposition was strongly dependent on temperature in both vapour phase flow and static vacuum systems. Continuous Si(OC2 H5 ) 4 deposition was observed in the presence of H2 O at relatively high temperatures when decomposition products were removed from the sample. It is proposed that physisorbed species need to be removed by evacuation or calcination to re-expose active sites, thereby enabling complete inertisation of the external surface acidity to occur, and that a more uniform covering can be obtained when a gradual deposition process is used. Such a process may be achieved by the use of diluents or by preventing overexposure of Si(OC2 H5 ) 4 to the sample under conditions where continuous deposition may occur. It was shown that it is possible to reduce the relative external surface acidity by 97% without significant changes in acidity as measured by Py-TPD or adsorption capacity.
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    The association between HIV and atherosclerotic cardiovascular disease in sub-Saharan Africa: a systematic review
    (2017) Hyle, Emily P; Mayosi, Bongani M; Middelkoop, Keren; Mosepele, Mosepele; Martey, Emily B; Walensky, Rochelle P; Bekker, Linda‐Gail; Triant, Virginia A
    BACKGROUND: Sub-Saharan Africa (SSA) has confronted decades of the HIV epidemic with substantial improvements in access to life-saving antiretroviral therapy (ART). Now, with improved survival, people living with HIV (PLWH) are at increased risk for non-communicable diseases (NCDs), including atherosclerotic cardiovascular disease (CVD). We assessed the existing literature regarding the association of CVD outcomes and HIV in SSA. METHODS: We used the PRISMA guidelines to perform a systematic review of the published literature regarding the association of CVD and HIV in SSA with a focus on CVD surrogate and clinical outcomes in PLWH. RESULTS: From January 2000 until March 2017, 31 articles were published regarding CVD outcomes among PLWH in SSA. Data from surrogate CVD outcomes (n = 13) suggest an increased risk of CVD events among PLWH in SSA. Although acute coronary syndrome is reported infrequently in SSA among PLWH, limited data from five studies suggest extensive thrombus and hypercoagulability as contributing factors. Additional studies suggest an increased risk of stroke among PLWH (n = 13); however, most data are from immunosuppressed ART-naïve PLWH and thus are potentially confounded by the possibility of central nervous system infections. CONCLUSIONS: Given ongoing gaps in our current understanding of CVD and other NCDs in PLWH in SSA, it is imperative to ascertain the burden of CVD outcomes, and to examine strategies for intervention and best practices to enhance the health of this vulnerable population.
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    The association between HIV and atherosclerotic cardiovascular disease in sub-Saharan Africa: a systematic review
    (BioMed Central, 2017-12-15) Hyle, Emily P; Mayosi, Bongani M; Middelkoop, Keren; Mosepele, Mosepele; Martey, Emily B; Walensky, Rochelle P; Bekker, Linda-Gail; Triant, Virginia A
    ackground: Sub-Saharan Africa (SSA) has confronted decades of the HIV epidemic with substantial improvements in access to life-saving antiretroviral therapy (ART). Now, with improved survival, people living with HIV (PLWH) are at increased risk for non-communicable diseases (NCDs), including atherosclerotic cardiovascular disease (CVD). We assessed the existing literature regarding the association of CVD outcomes and HIV in SSA. Methods: We used the PRISMA guidelines to perform a systematic review of the published literature regarding the association of CVD and HIV in SSA with a focus on CVD surrogate and clinical outcomes in PLWH. Results: From January 2000 until March 2017, 31 articles were published regarding CVD outcomes among PLWH in SSA. Data from surrogate CVD outcomes (n = 13) suggest an increased risk of CVD events among PLWH in SSA. Although acute coronary syndrome is reported infrequently in SSA among PLWH, limited data from five studies suggest extensive thrombus and hypercoagulability as contributing factors. Additional studies suggest an increased risk of stroke among PLWH (n = 13); however, most data are from immunosuppressed ART-naïve PLWH and thus are potentially confounded by the possibility of central nervous system infections. Conclusions: Given ongoing gaps in our current understanding of CVD and other NCDs in PLWH in SSA, it is imperative to ascertain the burden of CVD outcomes, and to examine strategies for intervention and best practices to enhance the health of this vulnerable population.