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51.
R.J. Brown M.L. Parsons 《Journal of Quantitative Spectroscopy & Radiative Transfer》1979,21(6):553-561
Relative atomic transition probabilities (Aji), for Na, Sc, Ti, Cr, Fe, Co, and Ni, using flame atomic absorption spectroscopy have been determined. Absorption measurements in air-acetylene and nitrous oxide-acetylene flames using both line emission and continuum excitation sources were employed. A comprehensive discussion and critical evaluation of Aji values for this work and others of comparable scope and design is included. The effect of the absorption line profile including hyperfine structure is discussed. 相似文献
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53.
R.R. Parsons 《Solid State Communications》1979,29(11):763-766
The origin of the photoluminescence in heavily-doped silicon is examined. Transient photoluminescence data for Si(P) are presented and used to identify the “Low Level” emission bands in terms of recombination of impurity band electrons with holes bound to acceptor sites. The “High Level” bands are attributed to recombination of impurity band electrons with free holes. The energies of the band gap and optical band gap in heavily-doped silicon are determined from the photoluminescence measurements. 相似文献
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Albone DP Challenger S Derrick AM Fillery SM Irwin JL Parsons CM Takada H Taylor PC Wilson DJ 《Organic & biomolecular chemistry》2005,3(1):107-111
Amination of C-H bonds activated by ether oxygen atoms is facile with chloramine-T as nitrene source and copper(I) chloride in acetonitrile as catalyst. For cyclic ethers the hemiaminal products are generally stable and can be isolated pure. For acyclic ethers, the hemiaminal products, as expected, fragment with elimination of alcohol to yield imines. When activation of benzylic positions is remote through a conjugated system, stable benzylamine derivatives are isolated. Mechanistic studies are consistent with concerted insertion of an electrophilic nitrenoid into the C-H bond in the rate-determining step, though in an asynchronous manner with a more activated substrate. 相似文献
56.
Timms PL Norman NC Pardoe JA Mackie ID Hinchley SL Parsons S Rankin DW 《Dalton transactions (Cambridge, England : 2003)》2005,(3):607-616
The structure of B8F12 has been shown by gas electron diffraction and computational methods (up to MP2/6-31+G*) to have the same highly asymmetric form observed in crystalline phases. The structure can be regarded as derived from a central B2 group, bridged by two BF2 groups to give a central B4 core that is folded, not planar, and with a very short bond [164.3 pm calculated, 164.2(19) pm experimental] along the fold line. There are also four terminal BF2 groups. One of the other four bonds in the core is consistently 20-30 pm longer than the others. This asymmetry has been attributed to many intra-molecular B...F interactions, particularly those between core boron atoms and fluorines of the terminal BF2 groups. Calculations for the chloro analogue lead to a structure similar to that for B8F12, but with the long core bond extended so that one of the bridging BCl2 groups may now be regarded as terminal. With bromine as the halogen the structure changes again, with one bromine atom taking up a bridging position. With iodine, this process continues further, and there are three bridging iodine atoms. However, in this case this is not the lowest energy structure, and instead a loosely associated dimer of B4I6 is preferred. In all these cases, and particularly with the heavier halogens, there are huge differences between the results obtained with different computational methods. 相似文献
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Mareque-Rivas JC Torres Martín de Rosales R Parsons S 《Chemical communications (Cambridge, England)》2004,(5):610-611
Amino H-bond donors adjacent to a zinc(II) centre increase the affinity of phosphates to the zinc(II) centre. 相似文献
59.
Many species of bat use ultrasonic frequency modulated (FM) pulses to measure the distance to objects by timing the emission and reception of each pulse. Echolocation is mainly used in flight. Since the flight speed of bats often exceeds 1% of the speed of sound, Doppler effects will lead to compression of the time between emission and reception as well as an elevation of the echo frequencies, resulting in a distortion of the perceived range. This paper describes the consequences of these Doppler effects on the ranging performance of bats using different pulse designs. The consequences of Doppler effects on ranging performance described in this paper assume bats to have a very accurate ranging resolution, which is feasible with a filterbank receiver. By modeling two receiver types, it was first established that the effects of Doppler compression are virtually independent of the receiver type. Then, used a cross-correlation model was used to investigate the effect of flight speed on Doppler tolerance and range-Doppler coupling separately. This paper further shows how pulse duration, bandwidth, function type, and harmonics influence Doppler tolerance and range-Doppler coupling. The influence of each signal parameter is illustrated using calls of several bat species. It is argued that range-Doppler coupling is a significant source of error in bat echolocation, and various strategies bats could employ to deal with this problem, including the use of range rate information are discussed. 相似文献
60.
Godard C Duckett SB Parsons S Perutz RN 《Chemical communications (Cambridge, England)》2003,(18):2332-2333
UV irradiation of a solution of (eta5-C5H5)bis(ethene)rhodium in the presence of 2,2'-dipyridylketone yields (eta5-C5H5)Rh(kappa2-N,O-2,2'-dipyridylketone) which inserts ethene to yield a bicyclic oxametallacyclopentane. 相似文献