Northeastern University London Repository
Not a member yet
1286 research outputs found
Sort by
The three-dimensional structure of the titanium-centered active site during steady-state catalytic epoxidation of alkenes
No full text15-P-18-A mechanistic exploration of alkene epoxidation mediated by H2O2 within porous titanosilicate catalysts
No full textThe Three-Dimensional Structure of the Titanium-Centered Active Site during Steady-State Catalytic Epoxidation of Alkenes
Get PDFCombined in situ X-ray absorption fine structure (XAFS) measurements and density functional theory (DFT)
computations yield a quantitative three-dimensional picture of the six-coordinated TiIV-centered active site
(in Ti/SiO2 catalysts) during production of epoxides from alkenes in the presence of hydroperoxide as oxidants
Probing the nature of acetylene bound to the active site of a Nina- zeolite Y catalyst by in situ neutron scattering
Get PDFAn investigation of the interaction between a catalytic system and its substrate (reactant) using neutron diffraction with isotopic substitution (NDIS) is reported. Specifically, the interaction between acetylene and nickel ion exchanged sodium zeolite Y has been investigated using NDIS in situ, revealing the radial distribution of distances at the disordered nickel sites. This is the first time that NDIS has been used for an in situ study, as well as the first time that a catalytic system has been structurally interrogated using this method. The experimental findings are supported and amplified by density functional calculations. Both experiment and theory reveal a NiII-(η2-C2H2) complex with small but significant deviation of the geometry exhibited by acetylene in its free state
Coexpression of Rat P2X2 and P2X6 Subunits in Xenopus Oocytes
Get PDFTranscripts for P2X(2) and P2X(6) subunits are present in rat CNS and frequently colocalize in the same brainstem nuclei. When rat P2X(2) (rP2X(2)) and rat P2X(6) (rP2X(6)) receptors were expressed individually in Xenopus oocytes and studied under voltage-clamp conditions, only homomeric rP2X(2) receptors were fully functional and gave rise to large inward currents (2-3 microA) to extracellular ATP. Coexpression of rP2X(2) and rP2X(6) subunits in Xenopus oocytes resulted in a heteromeric rP2X(2/6) receptor, which showed a significantly different phenotype from the wild-type rP2X(2) receptor. Differences included reduction in agonist potencies and, in some cases (e.g., Ap(4)A), significant loss of agonist activity. ATP-evoked inward currents were biphasic at the heteromeric rP2X(2/6) receptor, particularly when Zn(2+) ions were present or extracellular pH was lowered. The pH range was narrower for H(+) enhancement of ATP responses at the heteromeric rP2X(2/6) receptor. Also, H(+) ions inhibited ATP responses at low pH levels (<pH 6.3). The pH-dependent blocking activity of suramin was changed at this heteromeric receptor, although the potentiating effect of Zn(2+) on ATP responses was unchanged. Thus, the rP2X(2/6) receptor is a functionally modified P2X(2)-like receptor with a distinct pattern of pH modulation of ATP activation and suramin blockade. Although homomeric P2X(6) receptors function poorly, the P2X(6) subunit can contribute to functional heteromeric P2X channels and may influence the phenotype of native P2X receptors in those cells in which it is expressed
Automatic Defect Recognition in Cutting Tools
Get PDFAutomated metal-cutting manufacturing facilities are strongly dependent on the availability, on demand, of properly configured cutting tools. Tools must not only have the correct geometry but must also be in a suitable state for producing workpieces to the required standards of dimensional accuracy and surface finish. In earlier, manually-operated systems, this was readily achieved through operator skill and vigilance but, in automatic systems, other means must be employed. To this end, work has been undertaken at the University of Hull to develop automatic tool inspection systems based on the use of lasers to scan the cutting edges of tools for the presence of defects. Physical defects such as progressive wear or chipping of an edge can be detected and characterised by such means. Such systems can be implemented in several ways but the most useful are those which allow inspection of tools whilst held either in a local storage system, accessed by an automatic tool changer (ATC), or in the machine tool itself. The paper describes both arrangements and refers specifically to recent work concerned with data capture and signal processing techniques necessary to implement fully automatic inspection systems
