The influence of substrate geometry on the emission properties of a liquid metal ion source

The effect of needle radius, cone angle and shaft diameter on the threshold voltage and angular intensity — total current relationships for a Ga liquid-metal ion source (LMIS) was investigated. The variation of threshold voltage with needle geometry could be described in terms of the Taylor theory of liquid cone formation by electrostatic fields. The beam energy spread was mainly a function of total source current and was not a sensitive function of emitter geometry. Source angular intensity at a constant total current increased linearly with threshold voltage when the latter was altered due to source geometry.     

Rate constants for the reaction of the bromomethyne radical with alkynes

Absolute rate constants were measured for the gas phase reactions of the CBr($\text{～}\text{X}$²Π) radical produced in the flash photolysis of CHBr₃ with a series of alkynes. The rate of addition to the triple bond followed the trend established for addition to double bonds and a linear correlation between log k and ionization potentials reflects the electrophilic nature of the reaction. In comparison with published data on CCl, S(³P₂) the reactivity follows the trend CBr ≈ CCl ≈ S(³P₂) > O(³P₂).     

Some properties of higher spin rest-mass zero fields in general relativity

The propagation of a zero rest-mass test field of arbitrary spins>1 through curved space-time is found to be subject to strong constraints. A null test field is shown to be possible only in a restricted class of spaces previously introduced by Kundt and Thompson. This result is in fact a simultaneous generalization of the theorems of Robinson and of Goldberg and Sachs. For test fields of spin-2 in vacuum spaces, solutions of the propagation equation are restricted, save in a few exceptional cases, to constant multiples of the Weyl spinor. The exceptional cases are discussed, and appear to be physically uninteresting.     

The pressure and composition dependence of mutual diffusion in the system helium-nitrogen at 300 K

Diffusion coefficients for the system helium-nitrogen have been measured as a function of pressure at 300 K from 1 to 12.5 atmospheres. These measurements include composition dependences at 1, 3, 5 and 7 atmospheres. The results show reasonable agreement with the Thorne-Enskog theory for moderately dense gases.     

Some new intuitionistic equivalents of Zorn’s Lemma

Two new intuitionistic equivalents to Zarns Lemma are stated and proved.     

Tracking the distribution of "ecstasy" tablets by Raman composition profiling: a large scale feasibility study

Here we report the results of the largest study yet carried out on composition profiling of seized "ecstasy" tablets by Raman spectroscopy. Approximately 1500 tablets from different seizures in N. Ireland were analysed and even though practically all the tablets contained MDMA as active constituent, there were very significant differences in their Raman spectra, which were due to variations in both the nature and concentration of the excipients used and/or the degree of hydration of the MDMA. The ratios of the peak heights of the prominent drug bands at 810 cm(-1) and 716 cm(-1) (which vary with hydration state of the drug), and the drug band at 810 cm(-1) against the largest clearly discernible excipient band in the spectrum were measured for all the samples. It was found that there was sufficient variation in composition in the general sample population to make any matches between batches of tablets taken from different seizures significant, rather than the result of random chance. Despite the large number of different batches of tablets examined in this study, only two examples of indistinguishable sets of tablets were found and in only one of these had the two batches of tablets been seized at different times. Finally, the fact that there are many examples of batches of tablets (particularly in different batches taken from single seizures) in which the differences between each set are sufficiently small that they appear to arise only from random variations within a standard manufacturing method implies that, with more extensive data, it may be possible to recognize the "signature" of tablets prepared by major manufacturers.