Abstract: Different wild Mediterranean populations of Artemisia arborescens from diverse location... more Abstract: Different wild Mediterranean populations of Artemisia arborescens from diverse locations, representing its geographical distribution, as well as some of its well-known cultivars and some specimens cultivated as omamentals in gardens, streets, roads and nurseries, were analysed for genome size estimation. Other closely related species endemic to Macaronesia, A. canariensis, A. argentea and A. gorgonum, were also measured, and their nuclear DNA amount has been related to the biogeography of this group of species. Additionally, five populations of the closely related A. absinthium were analysed to establish comparisons. Measurements, acquired by flow cytometry, ranged from 8.29 pg to 11.61 pg for 2C values. Statistically significant differences of nuclear DNA amounts with respect to factors such as insularity or domestication have been detected. However, a quite low intraspecific genome size variation has been detected in these species. Furthermore, the study also addressed t...
Different wild Mediterranean populations of Artemisia arborescens from diverse locations, represe... more Different wild Mediterranean populations of Artemisia arborescens from diverse locations, representing its geographical distribution, as well as some of its well-known cultivars and some specimens cultivated as omamentals in gardens, streets, roads and nurseries, were analysed for genome size estimation. Other closely related species endemic to Macaronesia, A. canariensis, A. argentea and A. gorgonum, were also measured, and their nuclear DNA amount has been related to the biogeography of this group of species. Additionally, five populations of the closely related A. absinthium were analysed to establish comparisons. Measurements, acquired by flow cytometry, ranged from 8.29 pg to 11.61 pg for 2C values. Statistically significant differences of nuclear DNA amounts with respect to factors such as insularity or domestication have been detected. However, a quite low intraspecific genome size variation has been detected in these species. Furthermore, the study also addressed the possibl...
Spontaneous Human Combustion (SHC) is an enduring myth that has been around for several centuries... more Spontaneous Human Combustion (SHC) is an enduring myth that has been around for several centuries. A recent case in Ireland (Sept 2011) where a coroner had ruled that a fire death was due to SHC prompted me to write an article based on a fatal fire case that I had seen during my career as a forensic scientist and fire investigator. In 1991 I investigated a fatal fire involving an elderly man which showed all the classic features of SHC. My interpretation was that the fire was due to accidental ignition and the unusual features were explainable by modern fire science. The article contained a short review of the (supposed unusual) major features of such cases and also gave examples of how in some reported instances the factual details had been exaggerated or reinvented to promulgate the myth.
The compositions of typical British motor vehicle body fillers are reviewed and a systematic sche... more The compositions of typical British motor vehicle body fillers are reviewed and a systematic scheme is presented for their characterization, which routinely employs sample colour and analysis by pyrolysis gas chromatography and occasionally employs X-ray fluorescence spectrometry in addition. Eighteen samples obtained from manufacturers were all distinguishable and, from the examination of 121 casework samples, the discriminating power of colour and pyrolysis gas chromatography was estimated to be at least 0·92. Twenty-three samples in the casework collection were all similar in colour and produced similar pyrograms. A brief examination of this large group of samples, by X-ray fluorescence spectrometry, indicated that inorganic analysis provided a useful increase in discrimination. The pyrolysis products of polythene were used to calibrate the retention scale of the gas chromatograms (in methylene units) and peak heights were recorded relative to the height of the largest peak (usually styrene). Using data recorded in this manner a computer based system was developed for the comparison of pyrograms and for establishing the evidential value of a particular analysis. It is suggested that a similar approach could be used for the interpretation of pyrograms from a wide variety of other materials.
Eight solvents were compared for their relative efficiency in removing nitroglycerine from the ha... more Eight solvents were compared for their relative efficiency in removing nitroglycerine from the hands of persons handling explosives. The amount of interfering material also removed from the hands by the cotton swabs and the stability of the nitroglycerine in the solvent used were also investigated. Aqueous solvents yielded the best recoveries, when the extracts were partially purified by thin-layer chromatography before analysis, but the explosive was degraded rapidly by microorganisms that grew in the solutions. Of the aqueous, organic, and polar solvents tested, ethanol was found to offer the most complete, consistent, and stable recovery.
The techniques of thin-layer chromatography, gas chromatography with electron capture detection, ... more The techniques of thin-layer chromatography, gas chromatography with electron capture detection, and gas chromatography/mass spectrometry were used to analyze hand swab extracts for the presence of nitroglycerine. Both the amount of nitroglycerine transferred to the hands after handling commercial explosives and its persistence were measured. Gas chromatography-electron capture detection was found to be the most accurate and sensitive technique for making such determinations, especially if the extract was partially purified by thin-layer chromatography prior to analysis. The lowest limit of detection was 10 ng of nitroglycerine, and residues could be detected over 20 h after handling the raw explosive.
... Sci. Technol. 5, 12201222 (1971). 3. Perry, R. & Twibell, JD Atmos. Env. 7, 929937 (197... more ... Sci. Technol. 5, 12201222 (1971). 3. Perry, R. & Twibell, JD Atmos. Env. 7, 929937 (1973). 4. Bertsch, W., Chang, RC & Zlatkis, A. J. chromatog. Sci. 12, 175182 (1974). 5. Aue, WA & Teli, PM J. Chromat. 62, 1527 (1971). 6. Simon, W. & Giacobbo, H. Angew. Chem. Intern. ...
ABSTRACT In addition to formation of 3-benzoyl-1,2-diphenylimidazolid-5-one, acid-catalysed rearr... more ABSTRACT In addition to formation of 3-benzoyl-1,2-diphenylimidazolid-5-one, acid-catalysed rearrangement of 3-benzamido-1,4-diphenylazetidin-2-one yields 4-benzylidene-2-phenyloxazol-5-one, 4-benzylidene-1,2-diphenylimidazol-5-one, α-benzamidocinnamanilide and hippuranilide. The effect on the distribution of products of replacing phenyl groups of the azetidinone by other aryl groups has been examined, and correlated with possible rearrangement mechanisms.
ABSTRACT The rates of rearrangement of 14 1-aryl-2-cyanodiazetidinones have been measured using d... more ABSTRACT The rates of rearrangement of 14 1-aryl-2-cyanodiazetidinones have been measured using differential scanning calorimetry and the entropies of activation thus obtained. In the case of the para- substituted compounds the rates can be correlated by either σ or σ+ substituent constants. The rearrangement rates are independent of solvent polarity. These findings are discussed in relation to the sigmatropic pathway previously proposed for this rearrangement.
ABSTRACT Plug top (mainly 13 amp rating), rewirable and larger cartridge fuses (20-32 amp rating)... more ABSTRACT Plug top (mainly 13 amp rating), rewirable and larger cartridge fuses (20-32 amp rating) were caused to operate (blown) under known conditions of overload up to full mains short circuit, and by overheating. All fuses were X-Ray photographed and the differences in internal appearance were recorded. Fuses which survived heavy overloads or short circuits showed internal features which might be a useful diagnostic aid in casework situations. The relative performance of fuses of different types and ratings was also studied in circuits protected by more than one fuse. In overload conditions the lowest rated fuse or the weakest fuse in the circuit was found to blow, but under full mains short circuit conditions the superior characteristics of modern consumer unit cartridge fuses could result in these fuses blowing before a 13 amp plug top fuse, even though they had a higher rating.
ABSTRACT The operating mechanism of a variety of modern switch units was examined, and controlled... more ABSTRACT The operating mechanism of a variety of modern switch units was examined, and controlled burning tests were carried out on three types of unit to determine how the mechanism degraded during the course of a fire. A resin-casting method was then used which enabled both the state of the switch prior to the fire and changes which occurred during the fire to be determined.
ABSTRACT The difficulty of collecting volatile hydrocarbons, such as benzene, from street air in ... more ABSTRACT The difficulty of collecting volatile hydrocarbons, such as benzene, from street air in a form suitable for subsequent analysis is overcome by the use of a time-based elution procedure. By linking this technique to a gas chromatograph-mass spectrometer-data system, a rapid analysis is possible for low concentrations of collected material. Among advantages of this novel sample introduction procedure are the facility for collecting organic materials without interference from water vapour and their subsequent introduction into the g.c.-m.s. system without the use of any auxiliary solvents. Consequently the mass spectrometer can be used continuously on-line enabling the more volatile materials, normally masked by solvents, to be examined. This procedure is illustrated by the measurement of benzene and other hydrocarbon levels in street air (London). Following gas chromatographic separation the hydrocarbons can be identified by library search facilities attached to the mass spectrometer.
Abstract: Different wild Mediterranean populations of Artemisia arborescens from diverse location... more Abstract: Different wild Mediterranean populations of Artemisia arborescens from diverse locations, representing its geographical distribution, as well as some of its well-known cultivars and some specimens cultivated as omamentals in gardens, streets, roads and nurseries, were analysed for genome size estimation. Other closely related species endemic to Macaronesia, A. canariensis, A. argentea and A. gorgonum, were also measured, and their nuclear DNA amount has been related to the biogeography of this group of species. Additionally, five populations of the closely related A. absinthium were analysed to establish comparisons. Measurements, acquired by flow cytometry, ranged from 8.29 pg to 11.61 pg for 2C values. Statistically significant differences of nuclear DNA amounts with respect to factors such as insularity or domestication have been detected. However, a quite low intraspecific genome size variation has been detected in these species. Furthermore, the study also addressed t...
Different wild Mediterranean populations of Artemisia arborescens from diverse locations, represe... more Different wild Mediterranean populations of Artemisia arborescens from diverse locations, representing its geographical distribution, as well as some of its well-known cultivars and some specimens cultivated as omamentals in gardens, streets, roads and nurseries, were analysed for genome size estimation. Other closely related species endemic to Macaronesia, A. canariensis, A. argentea and A. gorgonum, were also measured, and their nuclear DNA amount has been related to the biogeography of this group of species. Additionally, five populations of the closely related A. absinthium were analysed to establish comparisons. Measurements, acquired by flow cytometry, ranged from 8.29 pg to 11.61 pg for 2C values. Statistically significant differences of nuclear DNA amounts with respect to factors such as insularity or domestication have been detected. However, a quite low intraspecific genome size variation has been detected in these species. Furthermore, the study also addressed the possibl...
Spontaneous Human Combustion (SHC) is an enduring myth that has been around for several centuries... more Spontaneous Human Combustion (SHC) is an enduring myth that has been around for several centuries. A recent case in Ireland (Sept 2011) where a coroner had ruled that a fire death was due to SHC prompted me to write an article based on a fatal fire case that I had seen during my career as a forensic scientist and fire investigator. In 1991 I investigated a fatal fire involving an elderly man which showed all the classic features of SHC. My interpretation was that the fire was due to accidental ignition and the unusual features were explainable by modern fire science. The article contained a short review of the (supposed unusual) major features of such cases and also gave examples of how in some reported instances the factual details had been exaggerated or reinvented to promulgate the myth.
The compositions of typical British motor vehicle body fillers are reviewed and a systematic sche... more The compositions of typical British motor vehicle body fillers are reviewed and a systematic scheme is presented for their characterization, which routinely employs sample colour and analysis by pyrolysis gas chromatography and occasionally employs X-ray fluorescence spectrometry in addition. Eighteen samples obtained from manufacturers were all distinguishable and, from the examination of 121 casework samples, the discriminating power of colour and pyrolysis gas chromatography was estimated to be at least 0·92. Twenty-three samples in the casework collection were all similar in colour and produced similar pyrograms. A brief examination of this large group of samples, by X-ray fluorescence spectrometry, indicated that inorganic analysis provided a useful increase in discrimination. The pyrolysis products of polythene were used to calibrate the retention scale of the gas chromatograms (in methylene units) and peak heights were recorded relative to the height of the largest peak (usually styrene). Using data recorded in this manner a computer based system was developed for the comparison of pyrograms and for establishing the evidential value of a particular analysis. It is suggested that a similar approach could be used for the interpretation of pyrograms from a wide variety of other materials.
Eight solvents were compared for their relative efficiency in removing nitroglycerine from the ha... more Eight solvents were compared for their relative efficiency in removing nitroglycerine from the hands of persons handling explosives. The amount of interfering material also removed from the hands by the cotton swabs and the stability of the nitroglycerine in the solvent used were also investigated. Aqueous solvents yielded the best recoveries, when the extracts were partially purified by thin-layer chromatography before analysis, but the explosive was degraded rapidly by microorganisms that grew in the solutions. Of the aqueous, organic, and polar solvents tested, ethanol was found to offer the most complete, consistent, and stable recovery.
The techniques of thin-layer chromatography, gas chromatography with electron capture detection, ... more The techniques of thin-layer chromatography, gas chromatography with electron capture detection, and gas chromatography/mass spectrometry were used to analyze hand swab extracts for the presence of nitroglycerine. Both the amount of nitroglycerine transferred to the hands after handling commercial explosives and its persistence were measured. Gas chromatography-electron capture detection was found to be the most accurate and sensitive technique for making such determinations, especially if the extract was partially purified by thin-layer chromatography prior to analysis. The lowest limit of detection was 10 ng of nitroglycerine, and residues could be detected over 20 h after handling the raw explosive.
... Sci. Technol. 5, 12201222 (1971). 3. Perry, R. & Twibell, JD Atmos. Env. 7, 929937 (197... more ... Sci. Technol. 5, 12201222 (1971). 3. Perry, R. & Twibell, JD Atmos. Env. 7, 929937 (1973). 4. Bertsch, W., Chang, RC & Zlatkis, A. J. chromatog. Sci. 12, 175182 (1974). 5. Aue, WA & Teli, PM J. Chromat. 62, 1527 (1971). 6. Simon, W. & Giacobbo, H. Angew. Chem. Intern. ...
ABSTRACT In addition to formation of 3-benzoyl-1,2-diphenylimidazolid-5-one, acid-catalysed rearr... more ABSTRACT In addition to formation of 3-benzoyl-1,2-diphenylimidazolid-5-one, acid-catalysed rearrangement of 3-benzamido-1,4-diphenylazetidin-2-one yields 4-benzylidene-2-phenyloxazol-5-one, 4-benzylidene-1,2-diphenylimidazol-5-one, α-benzamidocinnamanilide and hippuranilide. The effect on the distribution of products of replacing phenyl groups of the azetidinone by other aryl groups has been examined, and correlated with possible rearrangement mechanisms.
ABSTRACT The rates of rearrangement of 14 1-aryl-2-cyanodiazetidinones have been measured using d... more ABSTRACT The rates of rearrangement of 14 1-aryl-2-cyanodiazetidinones have been measured using differential scanning calorimetry and the entropies of activation thus obtained. In the case of the para- substituted compounds the rates can be correlated by either σ or σ+ substituent constants. The rearrangement rates are independent of solvent polarity. These findings are discussed in relation to the sigmatropic pathway previously proposed for this rearrangement.
ABSTRACT Plug top (mainly 13 amp rating), rewirable and larger cartridge fuses (20-32 amp rating)... more ABSTRACT Plug top (mainly 13 amp rating), rewirable and larger cartridge fuses (20-32 amp rating) were caused to operate (blown) under known conditions of overload up to full mains short circuit, and by overheating. All fuses were X-Ray photographed and the differences in internal appearance were recorded. Fuses which survived heavy overloads or short circuits showed internal features which might be a useful diagnostic aid in casework situations. The relative performance of fuses of different types and ratings was also studied in circuits protected by more than one fuse. In overload conditions the lowest rated fuse or the weakest fuse in the circuit was found to blow, but under full mains short circuit conditions the superior characteristics of modern consumer unit cartridge fuses could result in these fuses blowing before a 13 amp plug top fuse, even though they had a higher rating.
ABSTRACT The operating mechanism of a variety of modern switch units was examined, and controlled... more ABSTRACT The operating mechanism of a variety of modern switch units was examined, and controlled burning tests were carried out on three types of unit to determine how the mechanism degraded during the course of a fire. A resin-casting method was then used which enabled both the state of the switch prior to the fire and changes which occurred during the fire to be determined.
ABSTRACT The difficulty of collecting volatile hydrocarbons, such as benzene, from street air in ... more ABSTRACT The difficulty of collecting volatile hydrocarbons, such as benzene, from street air in a form suitable for subsequent analysis is overcome by the use of a time-based elution procedure. By linking this technique to a gas chromatograph-mass spectrometer-data system, a rapid analysis is possible for low concentrations of collected material. Among advantages of this novel sample introduction procedure are the facility for collecting organic materials without interference from water vapour and their subsequent introduction into the g.c.-m.s. system without the use of any auxiliary solvents. Consequently the mass spectrometer can be used continuously on-line enabling the more volatile materials, normally masked by solvents, to be examined. This procedure is illustrated by the measurement of benzene and other hydrocarbon levels in street air (London). Following gas chromatographic separation the hydrocarbons can be identified by library search facilities attached to the mass spectrometer.
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Papers by john Twibell