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排序方式: 共有180条查询结果,搜索用时 578 毫秒
31.
Hughes DA Girkin JM Poland S Longbottom C Button TW Elgoyhen J Hughes H Meggs C Cochran S 《Ultrasonics》2009,49(2):212-218
Dental erosion and decay are increasingly prevalent but as yet there is no quantitative monitoring tool. Such a tool would allow earlier diagnosis and treatment and ultimately the prevention of more serious disease and pain. Despite ultrasound having been demonstrated as a method of probing the internal structures of teeth more than 40 years ago, development of a clinical tool has been slow. The aim of the study reported here was to investigate the use of a novel high frequency ultrasound transducer and validate it using a known dental technique.A tooth extracted for clinical reasons was sectioned to provide a sample that contained an enamel and dentine layer such that the enamel-dentine junction (EDJ) was of a varying depth. The sample was then submerged in water and a B-scan recorded using a custom-designed piezocomposite ultrasound transducer with a centre frequency of 35 MHz and a −6 dB bandwidth of 24 MHz.The transducer has an axial resolution of 180 μm and a spatial resolution of 110 μm, a significant advance on previous work using lower frequencies. The depth of the EDJ was measured from the resulting data set and compared to measurements from the sequential grinding and imaging (SGI) method.The B-scan showed that the EDJ was of varying depth. Subsequently, the EDJ measurements were found to have a correlation of 0.89 (p < 0.01) against the SGI measurements. The results indicate that high frequency ultrasound is capable of measuring enamel thickness to an accuracy of within 10% of the total enamel thickness, whereas currently there is no clinical tool available to measure enamel thickness. 相似文献
32.
BACKGROUND: T-cells are activated by engagement of their clonotypic cell surface receptors with peptide complexes of major histocompatibility complex (MHC) proteins, in a poorly understood process that involves receptor clustering on the membrane surface. Few tools are available to study the molecular mechanisms responsible for initiation of activation processes in T-cells. RESULTS: A topologically diverse set of oligomers of the human MHC protein HLA-DR1, varying in size from dimers to tetramers, was produced by varying the location of an introduced cysteine residue and the number and spacing of sulfhydryl-reactive groups carried on novel and commercially available cross-linking reagents. Fluorescent probes incorporated into the cross-linking reagents facilitated measurement of oligomer binding to the T-cell surface. Oligomeric MHC-peptide complexes, including a variety of MHC dimers, trimers and tetramers, bound to T-cells and initiated T-cell activation processes in an antigen-specific manner. CONCLUSION: T-cell receptor dimerization on the cell surface is sufficient to initiate intracellular signaling processes, as a variety of MHC-peptide dimers differing in intramolecular spacing and orientation were each able to trigger early T-cell activation events. The relative binding affinities within a homologous series of MHC-peptide oligomers suggest that T-cell receptors may rearrange in the plane of the membrane concurrent with oligomer binding. 相似文献
33.
JA Paquette CJ Yardley KM Psutka MA Cochran O Calderon VE Williams KE Maly 《Chemical communications (Cambridge, England)》2012,48(66):8210-8212
We report the synthesis and characterization of a series of novel hexaalkoxydibenz[a,c]anthracenes. While the parent compound is not mesomorphic, the introduction of substituents in the 10- and 13-positions yields compounds with columnar liquid crystalline phases over very broad temperature ranges. 相似文献
34.
Limit on flavor-changing neutral currents from a measurement of neutrino-electron elastic scattering
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37.
Abachi S Abbott B Abolins M Acharya BS Adam I Adams DL Adams M Ahn S Aihara H Alitti J Álvarez G Alves GA Amidi E Amos N Anderson EW Aronson SH Astur R Avery RE Baden A Balamurali V Balderston J Baldin B Bantly J Bartlett JF Bazizi K Bendich J Beri SB Bertram I Bezzubov VA Bhat PC Bhatnagar V Bhattacharjee M Bischoff A Biswas N Blazey G Blessing S Bloom P Boehnlein A Bojko NI Borcherding F Borders J Boswell C Brandt A Brock R Bross A Buchholz D Burtovoi VS Butler JM Carvalho W Casey D 《Physical review letters》1996,76(13):2222-2227
38.
Abachi S Abbott B Abolins M Acharya BS Adam I Adams DL Adams M Ahn S Aihara H Alitti J Álvarez G Alves GA Amidi E Amos N Anderson EW Aronson SH Astur R Avery RE Balamurali V Balderston J Baldin B Bantly J Bartlett JF Bazizi K Bendich J Beri SB Bertram I Bezzubov VA Bhat PC Bhatnagar V Bhattacharjee M Bischoff A Biswas N Blazey G Blessing S Boehnlein A Bojko NI Borcherding F Borders J Boswell C Brandt A Brock R Bross A Buchholz D Burtovoi VS Butler JM Casey D Castilla-Valdez H Chakraborty D 《Physical review letters》1995,74(14):2632-2637
39.
Abachi S Abbott B Abolins M Acharya BS Adam I Adams DL Adams M Ahn S Aihara H Álvarez G Alves GA Amidi E Amos N Anderson EW Aronson SH Astur R Avery RE Baden A Balamurali V Balderston J Baldin B Bantly J Bartlett JF Bazizi K Behnke T Bendich J Beri SB Bertram I Bezzubov VA Bhat PC Bhatnagar V Bhattacharjee M Bischoff A Biswas N Blazey G Blessing S Boehnlein A Bojko NI Borcherding F Borders J Boswell C Brandt A Brock R Bross A Buchholz D Burtovoi VS Butler JM Callot O Casey D Castilla-Valdez H 《Physical review letters》1995,74(13):2422-2426
40.
Chlorobiphenyl (PCB) composition of extracts of subsurface soil, superficial dust and air from a contaminated landfill 总被引:1,自引:0,他引:1
L. G. Hansen D. Green J. Cochran S. Vermette B. Bush 《Analytical and bioanalytical chemistry》1997,357(4):442-448
Samples of 3 matrices (air, superficial dust and subsurface soil) from an aged PCB-containing landfill were extracted and
the extracts refined for bioassay. Acetone:hexane extraction was modestly selected for non-planar compounds. Coplanar PCBs
and PCDFs were enriched about 2-fold in the subsequent benzene:methylene chloride extracts of the soil. Extract refinement
with Florisil slurry and alumina column chromatography did not appreciably change the composition of the extracts. CB 28 (2,4,4′-triCB)
dominated in all extracts. The congener composition of soil and air were surprisingly similar, being enriched in tri- and
tetraCBs while dust retained higher proportions of congeners with 4 and 5 chlorines. It is postulated that anaerobic dechlorination
in the moist subsurface soil depleted the higher chlorinated congeners; more volatile congeners escaped into the atmosphere
while moderately chlorinated congeners were trapped in the superficial dust and debris. The refined extracts represent distinct
compositions of environmental PCB mixtures suitable for bioassay.
Received: 21 November 1995 / Revised: 9 April 1996 / Accepted: 14 April 1996 相似文献