Search

Your search keyword '"Ashcroft R"' showing total 10 results
Start Over Author "Ashcroft R" Publication Type Electronic Resources
10 results on '"Ashcroft R"'

1. Organometallic precursors for pillared clay synthesis

Author

Ashcroft, R. C.

Subjects
547, Applied Chemistry, Chemical Engineering
Abstract

The synthetic hectorite, laponite has been used within the paper industry to produce mildly conducting paper for use in electrographic printing. The aim of this research was to modify laponite in order to improve the electrical conductivity. In a continuation of a previous investigation involving organotin intercalation of laponite, the organotin precursor (p-CH3,OC6H4)4Sn was synthesised and characterised using Mass Spectroscopy, Infrared Spectroscopy and elemental analysis. Results of intercalation with this compound and a range of organobismuth and organoantimony compounds suggested that a halide content within the precursor was necessary for improvement in conductivity to be observed. Organometallic intercalation of a range of organotellurium compounds with laponite provided evidence that a hydrolysis reaction on the clay surface followed by the release of hydrochloric acid was an important first step if a reaction was to occur with the clay. Atomic Absorption Spectroscopy studies have shown that the acid protons underwent exchange with the interlayer sodium ions in the clay to varying degrees. Gas-liquid Chromatography and Infrared Spectroscopy revealed that the carbon-tellurium bond remained intact. Powder X-ray diffraction revealed that there had been no increase in the basal spacing. The a.c. conductivity of the modified clays in the form of pressed discs was studied over a frequency range of 12Hz - 100kHz using two electrode systems, silver paste and stainless steel. The a.c. conductivity consists of two components, ionic and reactive. The conductivity of laponite was increased by intercalation with organometallic compounds. The most impressive increase was gained using the organotellurium precursor (p-CH3OC6H4)2TeCl2. Conductivity investigations using the stainless steel electrode where measurements are made under pressure showed that in the case of laponite, where poor particle-particle contact exists at ambient pressure, there is a two order of magnitude increase in the measured a.c. conductivity. This significant increase was not seen in modified laponites where the particle-particle contact had already been improved upon. Investigations of the clay surface using Scanning Electron Microscopy suggested that the improvement in particle-particle contact is the largest factor in the determination of the conductivity. The other important factor is the nature and the concentration of the interlayer cations. A range of clays were synthesised in order to increase the concentration of sodium interlayer cations. A sol-gel method was employed to carry out these syntheses. A conductivity evaluation showed that increasing the concentration of the sodium cations within the clay led to an increase in the conductivity.

Published
1993
Full Text
View/download PDF

3. An open letter to The BMJ editors on qualitative research

Author

Greenhalgh, T., Annandale, E., Ashcroft, R., Barlow, J., Black, N., Bleakley, A., Boaden, R., Braithwaite, J., Britten, N., Carnevale, F., Checkland, K., Cheek, J., Clark, A., Cohn, S., Coulehan, J., Crabtree, B., Cummins, S., Davidoff, F., Davies, H., Dingwall, R., Dixon-Woods, M., Elwyn, G., Engebretsen, E., Ferlie, E., Fulop, N., Gabbay, J., Gagnon, M.P., Galasinski, D., Garside, R., Gilson, L., Griffiths, P., Hawe, P., Helderman, J.K., Hodges, B., Hunter, D., Kearney, M., Kitzinger, C., Kitzinger, J., Kuper, A., Kushner, S., May, A.L., Légaré, F., Lingard, L., Locock, L., Maben, J., Macdonald, M.E., Mair, F., Mannion, R., Marshall, M., May, C., Mays, N., McKee, L., Miraldo, M., Morgan, D., Morse, J., Nettleton, S., Oliver, S., Pearce, W., Pluye, P., Pope, C., Robert, G., Roberts, C., Rodella, S., Rycroft-Malone, J., Sandelowski, M., Shekelle, P., Stevenson, F., Straus, S., Swinglehurst, D., Thorne, S., Tomson, G., Westert, G.P., Wilkinson, S., Williams, B., Young, T., Ziebland, S., Greenhalgh, T., Annandale, E., Ashcroft, R., Barlow, J., Black, N., Bleakley, A., Boaden, R., Braithwaite, J., Britten, N., Carnevale, F., Checkland, K., Cheek, J., Clark, A., Cohn, S., Coulehan, J., Crabtree, B., Cummins, S., Davidoff, F., Davies, H., Dingwall, R., Dixon-Woods, M., Elwyn, G., Engebretsen, E., Ferlie, E., Fulop, N., Gabbay, J., Gagnon, M.P., Galasinski, D., Garside, R., Gilson, L., Griffiths, P., Hawe, P., Helderman, J.K., Hodges, B., Hunter, D., Kearney, M., Kitzinger, C., Kitzinger, J., Kuper, A., Kushner, S., May, A.L., Légaré, F., Lingard, L., Locock, L., Maben, J., Macdonald, M.E., Mair, F., Mannion, R., Marshall, M., May, C., Mays, N., McKee, L., Miraldo, M., Morgan, D., Morse, J., Nettleton, S., Oliver, S., Pearce, W., Pluye, P., Pope, C., Robert, G., Roberts, C., Rodella, S., Rycroft-Malone, J., Sandelowski, M., Shekelle, P., Stevenson, F., Straus, S., Swinglehurst, D., Thorne, S., Tomson, G., Westert, G.P., Wilkinson, S., Williams, B., Young, T., and Ziebland, S.

Abstract

Contains fulltext : 165909.pdf (publisher's version ) (Open Access)

Published
2016

6. A 60 GHz double balanced sub-harmonic mixer MMIC

Author

Zelley, C. A., Barnes, A. R., Ashcroft, R. W., Zelley, C. A., Barnes, A. R., and Ashcroft, R. W.

Abstract

We present the design and measured results for a 60 GHz double balanced sub-harmonic MMIC mixer fabricated using the TRW 0.15mm gate length GaAs pHEMT foundry process. The sub-harmonic mixer architecture eliminates the need for costly mm-wave sources that are usually required with conventional fundamental frequency mixers. The mixer has been integrated into a coaxial package and a measured conversion loss of less than 10 dB across the 53 GHz to 60 GHz frequency band has been obtained. This conversion loss is believed to be approximately 2 dB better than previously published results.

Published
2001

7. A J-band Transceiver MMIC with image rejection

Author

Zelley, C. A., Gould, P. A., Munday, P. D., Ashcroft, R. W., Zelley, C. A., Gould, P. A., Munday, P. D., and Ashcroft, R. W.

Abstract

This paper describes a J-band (15 GHz) transceiver MMIC with image rejection that has been designed for RADAR T/R module applications. The MMIC consists of a switched attenuator, an LNA, a Transmit/Receive switch, an image rejection mixer and a local oscillator buffer amplifier. The size of the MMIC is 6.48 mm by 4.47 mm. In receive mode the MMIC has a conversion gain in excess of 10 dB with less than 1 dB of ripple and noise figure less than 4 dB across a 10 GHz to 16.5 GHz band. The Input P1dB is –13 dBm. In transmit mode the conversion gain is –12 dB with an input P1dB of +15 dBm. The Transceiver MMIC was fabricated using the GMMT, 0.25 m m, H40 pHEMT process. This is believed to be the first integrated transceiver MMIC designed specifically for this frequency band.

Published
2000

8. A Digital Satellite Delay Simulator

Author

ROYAL SIGNALS AND RADAR ESTABLISHMENT MALVERN (UNITED KINGDOM), Ashcroft, R. W., ROYAL SIGNALS AND RADAR ESTABLISHMENT MALVERN (UNITED KINGDOM), and Ashcroft, R. W.

Abstract

This document describes the design and operation of a bidirectional digital satellite delay simulator. The data rates which are catered for are 2400, 3600, 7200 and 16000 bps, but other data rates could be included with only minor modification. The circuit is based on the Motorola 6809 microprocessor which uses the Motorola 6852 synchronous serial data adapter (SSDA) as the interface devices.

Published
1991

9. Wessex Helicopter. Clearance for Carriage and Release, Internal,ly and Externally, of the Practice Depth Charge MK.15 MOD.12

Author

AEROPLANE AND ARMAMENT EXPERIMENTAL ESTABLISHMENT BOSCOMBE DOWN (UNITED KINGDOM), Ashcroft, R., AEROPLANE AND ARMAMENT EXPERIMENTAL ESTABLISHMENT BOSCOMBE DOWN (UNITED KINGDOM), and Ashcroft, R.

Abstract

Test results indicated that the Practice Depth Charge Mk. 15 Mod. 12 is suitable for service use, when carried on externally fitted light series bomb carriers, or released through the cabin flare chute or open doorway of the Wessex helicopter. Sole plates must be fitted to the light series bomb carriers to enable the stores to be securely crutched. Fuze setting control links are of a suitable length to withdraw the No. 8 Arming Wires successfully under all conditions of airspeed. The suspension lug must be positioned 90 degrees radiallye hydrostatic bellows of the store. An analogous clearance can be given for carriage and release of the Practice Depth Charge Mk. 15 Mod. 12 from all Marks of Wessex helicopters.

Published
1963

10. Diet in chronic renal failure.

Author

Kerr, D.N., Robson, A., Ashcroft, R., Kerr, D.N., Robson, A., and Ashcroft, R.

Subjects
Chronic renal failure Diet therapy., Kidney Failure, Chronic diet therapy, Insuffisance rénale chronique Diétothérapie., Chronic renal failure Diet therapy.

Catalog

Books, media, physical & digital resources
See catalog results