A statistical assessment of brilliance and fire for published gem diamond on the basis of geometrical optics

Imperial Users onl

Topics in Phosphorus-Fluorine Chemistry

The reactions between primary amines and phosphorus penta- fluoride were complex and yielded alkylammonium hexafiuorophosphates, RNH+3 PF6- (R = Me, Et, But), and bis(alkylamino)trifluorophos- phoranes, (RNH)2PF3 (R = Me, Et, But). In addition a 2:1 adduct, 2MeNH2. PF5, was formed in the reaction with methylamine whereas 1:1 adducts, RNH2. PF5 (R = Et, But), were produced with ethyl-amine and t-butylamine. The preparation of alkylaminotetrafluoro-phosphoranes, RNHPF4 (R = Et, But), by the thermal decomposition of the 1:1 adducts was studied. Methylaminotetrafluorophosphorane could be prepared by the reaction between raethylaminotrimethyl-silane, Me3SiNHMe, and phosphorus pentafluoride. The formation of diazafluorodiphosphetidines from alkylamino-fluorophosphoranes was studied. Phosphorus pentafluoride and phenyltetrafluorophosphorane reacted with (MeNH)2PF3 to give (F3PNMe)2 and PhF(F2PNMe)2 respectively, but the yield of these products was low. The reaction between primary amines and phosphorus trifluoride proceeded by a two step process. Alkylaminodifluorophosphines, RNHPF2 (R = Me, Et, But, Bun), were formed in the initial step. The nature of the subsequent step is believed to depend on the steric properties of the attacking amine. Bis(alkylamino)difluoro-phosphoranes, (RNH)2PF2H (R = Me, Et, Bun), were usually isolated, but the bulky t-butylamine produced bis(t-butylamino)fluoro-phosphine, (But NH)2PF The compounds isolated above were characterised by their n.m.r., i.r. and mass spectra. Several fragmentation modes for molecules of the type RNHP(F) are discussed. Infra-red correlations for the RNH-P group are also made. The bulk of the evidence suggests that the extra molecule of amine in 2MeNH2. PF5 is co-ordinated to the 1:1 adduct by means of N---H hydrogen-bonding. Several routes to produce PNP bridges were investigated. Difluorophosphino(tetrafluorophosphoranyl)methylamine, PF2NMePF4, was best prepared from the reaction between phosphorus penta- fluoride and difluorophosphino(trimethylsilyl)methylamine, Me3SiNMePF2, which was itself prepared from the reaction between heptamethyldisilazane and chlorodifluorophosphine. A similar reaction between POF3 and Me3SiNMePF2 only gave low yields of difluorophosphino(difluorophosphoryl)methylamine, PF2NMePOF2. The latter was more conveniently synthesized from chlorodifluoro phosphine and methylaminophosphoryl difluoride, MeNHPOF2. The ease of reaction between Me3SiNMeX (X = P(F), SiMe3) and a phosphorus-fluoride could be correlated with the Lewis basicity of the former and the Lewis acidity of the latter. The spectroscopic properties of the bridged compounds produced were examined. Attempts to prepare PNS bridges by the above routes failed, and possible reasons for this are discussed. The products isolated from the reaction of SOF2 with either MeNHPF2 or Me3SiNMePF2 included methylaminothiophosphoryl difluoride, MeNHPSF2, and MeNHPOF2, which were fully characterised. The addition of HPSF2 to alkenes took place at room temperature under the influence of U.V. light to give alkylphosphonothioic difluorides, RPSF2 (R = Et, Prn, Bun), which were fully characterised. Evidence is presented which suggests that the ease of the U.V. induced addition of a phosphorus-halide to an alkene depends on the strength of the P-X (X = F, Cl, Br) bonds in the latter compound. It proved possible to isolate and characterise 2-bromoethylphosphonic difluoride, BrC2H4POF2, from the reaction between ethylene and bromophosphoryl difluoride

Adaptation to the host-plant, and the evolution of host specialization, in 'cycad weevils' (Coleoptera: Brentidae)

Bibliography: leaves 123-134.This thesis deals with host relationships in an enigmatic and seemingly primitive group of weevils belonging to the genus Antliarhinus (Coleoptera: Brentidae). These beetles occur only on species of the cycad genus Encephalartos and appear to retain an ancient association with cycads, a group of plants that were widespread in the Mesozoic era (ca. 200 MYA) before the rise of the angiosperms and which are now represented by 11 genera with relict distributions in the tropics and sub-tropics. The primary aim of this research was to determine the possible causes of narrow host specialization in Antliarhinus zamiae (Thunberg) and A. signatus Gyllenhal, two species which develop exclusively on the ovules of their cycad hosts

A study of the relationship between the pre-committal experiences and the post-committal adjustment of eighteen boys committed to the Connecticut School for Boys.

Thesis (M.S.)--Boston Universit

The Expansion Center and Dynamical Age of the Galactic Supernova Remnant Cassiopeia A

We present proper motions for 21 bright main shell and 17 faint, higher-velocity, outer ejecta knots in the Cas A supernova remnant and use them to derive new estimates for the remnant's expansion center and age. Our study included 1951 - 1976 Palomar 5 m prime focus plates, 1988 - 1999 CCD images from the KPNO 4 m and MDM 2.4 m telescopes, and 1999 HST WFPC2 images. Measurable positions covered a 23 to 41 yr time span for most knots, with a few outer knots followed for almost 48 yr. We derive an expansion center of alpha = 23h 23m 27s.77 +- 0s.05, delta = 58d 48' 49".4 +- 0".4 (ICRS), with little difference between centers derived using outer or main shell knots. This position is 3.0 arcsec due north of that estimated by van den Bergh and Kamper (1983). It also lies 6.6 +- 1.5 arcsec almost due north (PA = 354 deg) of the remnant's recently-detected central X-ray point source, implying a transverse velocity for the X-ray point source of about 330 km/s at a distance of 3.4 kpc. Using the knots which lie out ahead of the remnant's forward blast wave, we estimate a knot convergent date of A.D. 1671.3 +- 0.9, assuming no deceleration. However, a deceleration of just approximately 1.6 km/(s yr) over a 300 yr time span would produce an explosion date A.D. 1680, consistent with the suspected sighting of the Cas A supernova by J. Flamsteed.Comment: Astron. Journal in press, sched. July 2001. AASTex5, 17 pages, 2 jpeg greyscale figures, 3 postscript figure

Kinetics and mechanism for nucleophilic substitution in some polyfluoroaromatic compounds

Not availabl

Cavity Ringdown Spectroscopy in Nitrogen/Oxygen Mixtures in the Presence of Alpha Radiation

This research was part of an effort to experimentally validate computational models under development for radiation-induced atmospheric effects. Cavity Ringdown Spectroscopy (CRDS) was used to measure the concentration of chemical products generated as a result of radiation interactions in a controlled atmosphere. Experiments were conducted in a vacuum chamber interfaced with a gas introduction system that controlled the initial atmospheric composition. A quadrupole mass spectrometer and tunable dye laser were integrated to confirm initial atmospheric composition, and provide wavelength flexibility for detecting a variety of chemical products generated by radiation interactions. CRDS measurements were made for ozone production resulting from alpha radiation interactions in nitrogen-oxygen mixtures while the Polonium 210 alpha sources were cycled between being shielded and exposed. The beginning of this thesis will provide brief reviews of ionizing radiation and ozone formation, along with explanations of Cavity Enhanced Absorption Spectroscopy and CRDS. This is followed by a description of the existing vacuum and optical system, as well as the modifications required to integrate the mass spectrometer and dye laser. Another chapter details the modifications made to the existing software, as well as new software developed for the mass spectrometer and dye laser. Finally, results are presented showing the rapid production of ozone following exposure of the alpha radiation to the controlled atmosphere. Results also show ozone concentrations rapidly decreasing when the source was re-shielded, but when the source was re-exposed, the ozone concentration started at the previous concentration and continued to increase. This indicates the presence of a possible ozone catalyst

Method and apparatus for using magneto-acoustic remanence to determine embrittlement

A method and apparatus for testing steel components for temperature embrittlement uses magneto-acoustic emission to nondestructively evaluate the component are presented. Acoustic emission signals occur more frequently at higher levels in embrittled components. A pair of electromagnets are used to create magnetic induction in the test component. Magneto-acoustic emission signals may be generated by applying an AC current to the electromagnets. The acoustic emission signals are analyzed to provide a comparison between a component known to be unembrittled and a test component. Magnetic remanence is determined by applying a DC current to the electromagnets and then by turning the magnets off and observing the residual magnetic induction

Performance of Selected Cultivars of Poinsettia (Euphorbia Pulcherrima, Willd.) Grown Under Different Temperature Regimes.

The performance of seventeen cultivars of poinsettias grown under three temperature regimes in four crops was studied to determine the effects of temperature on plant quality and to determine a base temperature for each cultivar. Growth factors such as shoot height, node number, bract spread and flower size increased with increases in temperature. Bract number increased with cooler temperatures. Less time was needed for coloration and anthesis at the warm regime. Varietal responses varied with temperature with the cultivars \u27Annette Hegg Diva\u27, \u27Gutbier V-10\u27, \u27Annette Hegg Dark Red\u27 and \u27Annette Hegg Supreme\u27 achieving best quality in the cool regime. Lower base temperatures were derived by regression equation method when more replications were utilized in each crop. In testing these base temperature values, better agreement between treatments in total degree-day summation values were also obtained when more replications were utilized. Since perfect agreement was not reached, this would indicate that lower base temperature values could be used. It was concluded that more replications and weekly measurements of average temperature and growth could be taken to utilize the stage of development of that cultivar for a correct base temperature. It was further concluded that if total crop time at 18.3(DEGREES)C were used as a base, a 16.6% net savings in energy would occur