Experiments on the low frequency barrier characteristics of cellular metamaterial panels in a diffuse sound field.

The metamaterial under investigation here consists of a periodic arrangement of unit plates in a grid-like frame such that there is a contrast in the local areal mass between cell interior and cell wall. In the low frequency range and under normal incidence this metamaterial panel exhibits a sound transmission loss significantly larger than the transmission loss of an unstructured panel with the same homogeneous mass per unit area. However, when the incident sound field is diffuse, the relative advantage of the metamaterial barrier is reduced or eliminated. A sequence of experiments is documented to demonstrate that the relative advantage of the metamaterial barrier can be realized even in a diffuse sound field by creating a hybrid barrier system which embeds the metamaterial layer between a normalizing waveguide layer on the incident side and an absorbing layer on the transmitted side. The sound normalizing waveguide layer is a lattice structure, and the absorbing layer is high performance glass fiber mat. By using measurements of the transmission loss of a 1.2 m square panel system the role of each of these components is demonstrated.

Synthesis and characterization of a POSS-PEG macromonomer and POSS-PEG-PLA hydrogels for periodontal applications.

A novel water-soluble macromonomer based on octavinyl silsesquioxane has been synthesized and contains vinyl-terminated PEG 400 in each of the eight arms to promote water solubility. The macromonomer was characterized by NMR and FTIR and its aqueous solution properties examined. In water it exhibits an LCST with a cloud point at 23 °C for a 10 wt % aqueous solution. It is surface active with a CMC of 1.5 × 10(-5) M in water and in 20:80 v/v acetone/water the CMC is 7.1 × 10(-5) M, and TEM images showed spherical 22 nm aggregates in aqueous solution above the CMC. The macromonomer was copolymerized in a 20:80 v/v acetone/water mixture with a vinyl-terminated, triblock copolymer of lactide-PEG-lactide to form a library of cross-linked hydrogels that were designed for use as scaffolds for alveolar bone repair. The cross-linked copolymer networks were shown to contain a range of nm-µm sized pores and their swelling properties in water and PBS at pH 7.4 were examined. At pH 7.4 the hydrogel networks undergo a slow hydrolysis with the release of principally PEG and lactic acid fragments. The hydrogels were shown to be noncytotoxic toward fibroblast cultures at pH 7.4, both initially (days 1-5) and after significant hydrolysis had taken place (days 23-28).

Practical electrodiagnostic value of F-wave studies in chronic inflammatory demyelinating polyneuropathy.

OBJECTIVES: To ascertain the practical electrodiagnostic value of F-waves in chronic inflammatory demyelinating polyneuropathy (CIDP). METHODS: We evaluated the diagnostic utility of F-waves in 18 prospectively-recruited patients with typical CIDP. Minimum/maximum/mean F-wave latencies, F-wave chronodispersion and F-wave persistence, were determined in median/ulnar/fibular/tibial nerves in patients and compared to controls with axonal neuropathy. RESULTS: All latencies were significantly more delayed in CIDP patients. F-wave chronodispersion was significantly greater in median and ulnar nerves and F-wave persistence significantly more reduced in tibial nerves in CIDP patients. Use of these supplementary F-wave parameters was of value in identifying CIDP nerves. However F-wave studies were only of additional benefit to other demyelinating parameters in about 15% of all studied CIDP nerves. CONCLUSIONS: F-waves may be diagnostically helpful in CIDP in a minority of nerves without other nerve conduction abnormalities. Analysis of F-wave chronodispersion in upper limb nerves and possibly of F-wave persistence in tibial nerves, may add value to basic minimum F-wave latency studies. SIGNIFICANCE: These results suggest F-wave analysis may not need to be systematic, for all nerves, in patients with suspected CIDP, especially those intolerant to electrical stimulation. Chronodispersion and persistence may be helpful parameters to consider in addition to minimum latency.

Effect of air abrasion and thermocycling on resin adaptation and shear bond strength to dentin for an etch-and-rinse and self-etch resin adhesive.

This study examined the effect of air abrasion and thermocycling on the adaptation and shear bond strength, of composite resin bonded to dentin using etch-and-rinse and self-etch resin adhesives. Confocal microscopy showed both adhesives closely adapted to dentin and a significantly (p<0.001) greater number of resin tags were observed for the etch-and-rinse adhesive. Air abrasion significantly increased resin tag length (p<0.05) for the etch-and-rinse adhesive and significantly increased the number (p<0.001), length (p<0.001) and thickness (p<0.01) of tags for the self-etch adhesive. However, air abrasion resulted in defect formation within the hybrid layer and thermocycling caused separation of the hybrid layer from adjacent dentin containing resin tags. A significant (p<0.05) reduction in shear bond strength was observed for the etch-and-rinse adhesive following thermocycling. Both adhesive systems adapted well to dentin in vitro and shear bond strengths were similar. The area of tag penetration into dentin was significantly (p<0.0001) enhanced following air abrasion.