Triblock copolymer syntheses of mesoporous silica with periodic 50 to 300 angstrom pores

Use of amphiphilic triblock copolymers to direct the organization of polymerizing silica species has resulted in the preparation of well-ordered hexagonal mesoporous silica structures (SBA-15) with uniform pore sizes up to approximately 300 angstroms. The SBA-15 materials are synthesized in acidic media to produce highly ordered, two-dimensional hexagonal (space group p6mm) silica-block copolymer mesophases. Calcination at 500 degrees C gives porous structures with unusually large interlattice d spacings of 74.5 to 320 angstroms between the (100) planes, pore sizes from 46 to 300 angstroms, pore volume fractions up to 0.85, and silica wall thicknesses of 31 to 64 angstroms. SBA-15 can be readily prepared over a wide range of uniform pore sizes and pore wall thicknesses at low temperature (35 degrees to 80 degrees C), using a variety of poly(alkylene oxide) triblock copolymers and by the addition of cosolvent organic molecules. The block copolymer species can be recovered for reuse by solvent extraction with ethanol or removed by heating at 140 degrees C for 3 hours, in both cases, yielding a product that is thermally stable in boiling water.     

A laboratory system for production of flexion rates and forces in the forelimb of the horse

The distal portion of the forelimb of the horse is provided with a stay apparatus composed of tendons, ligaments, and fascia. This stay apparatus provides the major resistance to joint flexion during the support phase of the stride. The laboratory test system described was shown to be able to reproduce in vitro limb motions and hoof forces measured with a running horse. These results indicated the stay apparatus operates in a largely passive mode, active muscle contraction apparently serving to provide rigidity only early in the support phase of the stride. The testing system described was designed to take advantage of the passive nature of the stay apparatus in order to study in vitro the forces, accelerations, and deformations encountered by the limb of the galloping horse in vivo.     

Tissue Residues of Diuron in Channel Catfish Ictalurus punctatus Exposed to the Algicide in Consecutive Years

In 1999, the United States Environmental Protection Agency granted an emergency exemption under Section 18 of the Federal Insecticide, Fungicide. and Rodenticide Act authorizing the use of the algicide diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] to manage cyanobacterial off-flavors in channel catfish Ictalurus punctcatus . Catfish may remain in ponds for more than one growing season and may therefore be exposed to more than one set of diuron treatments. This study was conducted to determine whether diuron residues in fish carry over from one year to the next and, if so, whether the cumulative exposure causes residues to exceed the tolerance level of 2.0 mg/kg in fillets. Catfish in earthen ponds were exposed to the label-specified treatment protocol of nine consecutive weekly applications of diuron at 0.01 mg/L in the fall of one year and again the following spring. Diuron concentrations in fillets were below limits of detection (0.05 mg/kg) in all fish ( N = 18) prior to the initial diuron treatment series. Immediately after the ninth weekly diuron application in the fall. tissue diuron levels averaged 0.353 mg/kg (pooled SEM = 0.036; range = 0.078–0.724 mg/kg; N = 18). On the day before the second set of diuron treatments 6 mo later. diuron concentrations were below limits of detection in all fish sampled. Immediately after the second set of nine weekly diuron applications, tissue concentrations averaged 0.127 mg/kg (pooled SEM = 0.015; range = not detected to 0.191 mg/kg; N = 18). This study showed that diuron residues in channel catfish were depleted within 2 to 4 mo after exposure to the chemical and there was no carryover of residues in fish from one year to the next. Maximum residue levels in catfish fillets were less than half the tolerance level of 2.0 mg/ kg.