RESUMO
We explore the selectivity of a model zeolite ring over representative hydrocarbons of crude oil. The model ring consists of 7 silicon tetrahedral units and one chemically active aluminum site through which hydrocarbons with symmetries varying from almost spherically symmetric to linear chains (1D), planar (2D), and pyramidal (3D) structures diffuse. The selectivity is further investigated when the hydrocarbons travel with different orientations and speeds. The semiclassical Born-Oppenheimer molecular dynamics approximation is used to characterize the chemical dynamics, as well as to determine the energetics and reaction products. The simulations reveal noticeable differences in energy profiles and charge populations. Our results are important to understand aspects of mass transport and some of the factors that control the catalytic activity in zeolites.
Assuntos
Hidrocarbonetos/química , Modelos Químicos , Zeolitas/químicaRESUMO
In this work dialysis was used as a technique to modify the aggregation state of montmorillonite clay. Na-montmorillonite clay suspension was treated by a dialysis process and the effect of dialysis time on the surface area of the treated clay was studied. In a clay suspension, a decrease in cation content increases the interparticle repulsion forces exponentially, leading to separation of clay into the elementary clusters of layers by osmotic swelling. During dialysis treatment, the classical delamination process and mechanism were not observed. According to N(2) adsorption isotherms, the increase of surface area concerns to the development of mesoporosity. Nevertheless, the surface area increase cannot be explained by the delamination or exfoliation of some layers, since an increase in the expected number of layers that would yield the surface area does not explain the mesoporosity observed after dialysis. Based on these results, a new mechanism of evolution of the clay aggregation state after dialysis and drying is proposed.
RESUMO
We describe our experience with the use of botulinum A toxin for the treatment of patients with facial spasms. Thirty four patients with blepharospasm, thirty eight with hemifacial spasms and three with spastic entropion were injected with the use of Botulinum A toxin. Length of follow up ranged from 6 to 60 months. The effect of toxin lasted an average of 12.1 weeks in patients with blepharospasm and 15.5 weeks in patients with hemifacial spasms. This difference in mean response was statistically significant (p = 0.0001). The most common side effect was ptosis and dry eyes. All side effects were transient in nature, lasting between three and twelve weeks. Botulinum toxin type A injections represent a good alternative for the treatment of facial spasms. It is a safe and effective office procedure. Most patients tolerate the procedure well. Its principal drawback is its transient effect and the need for repeated injections
Assuntos
Humanos , Masculino , Feminino , Adolescente , Adulto , Pessoa de Meia-Idade , Blefarospasmo/terapia , Espasmo/terapia , Músculos Faciais , Toxinas Botulínicas/uso terapêutico , SeguimentosRESUMO
We describe our experience with the use of botulinum A toxin for the treatment of patients with facial spasms. Thirty four patients with blepharospasm, thirty eight with hemifacial spasms and three with spastic entropion were injected with the use of Botulinum A toxin. Length of follow up ranged from 6 to 60 months. The effect of toxin lasted an average of 12.1 weeks in patients with blepharospasm and 15.5 weeks in patients with hemifacial spasms. This difference in mean response was statistically significant (p = 0.0001). The most common side effect was ptosis and dry eyes. All side effects were transient in nature, lasting between three and twelve weeks. Botulinum toxin type A injections represent a good alternative for the treatment of facial spasms. It is a safe and effective office procedure. Most patients tolerate the procedure well. Its principal drawback is its transient effect and the need for repeated injections.
