Coherent vibrational and dissociation dynamics of polyatomic radical cations

The ultrafast dynamics of polyatomic radical cat- ions contribute to important processes including energy transfer in photovoltaics, electron transfer in photocataly- sis, radiation-induced DNA damage, and chemical reac- tions in the upper atmosphere and space. Probing these dynamics in the gas phase is challenging due to the rapid dissociation of polyatomic radical cations following elec- tron removal, which arises from excess electronic excita- tion of the molecule during the ionization process. This Concept article introduces the reader to how the pump- probe technique of femtosecond time-resolved mass spectrometry (FTRMS) can overcome this challenge to capture coherent vibrational dynamics on the femtosec- ond timescale in polyatomic radical cations and enable the analysis of their dissociation pathways. Examples of FTRMS applied to three families of polyatomic radical cat- ions are discussed

Probing Coherent Vibrations of Organic Phosphonate Radical Cations with Femtosecond Time-Resolved Mass Spectrometry

Organic phosphates and phosphonates are present in a number of cellular components that can be damaged by exposure to ionizing radiation. This work reports femtosecond time-resolved mass spectrometry (FTRMS) studies of three organic phosphonate radical cations that model the DNA sugar-phosphate backbone: dimethyl methylphosphonate (DMMP), diethyl methylphosphonate (DEMP), and diisopropyl methylphosphonate (DIMP). Upon ionization, each molecular radical cation exhibits unique oscillatory dynamics in its ion yields resulting from coherent vibrational excitation. DMMP has particularly well-resolved 45 fs (732 ± 28 cm−1) oscillations with a weak feature at 610–650 cm−1, while DIMP exhibits bimodal oscillations with a period of ∼55 fs and two frequency features at 554 ± 28 and 670–720 cm−1. In contrast, the oscillations in DEMP decay too rapidly for effective resolution. The low- and high-frequency oscillations in DMMP and DIMP are assigned to coherent excitation of the symmetric O–P–O bend and P–C stretch, respectively. The observation of the same ionization-induced coherently excited vibrations in related molecules suggests a possible common excitation pathway in ionized organophosphorus compounds of biological relevance, while the distinct oscillatory dynamics in each molecule points to the potential use of FTRMS to distinguish among fragment ions produced by related molecules

Probing Coherent Vibrations of Organic Phosphonate Radical Cations with Femtosecond Time-Resolved Mass Spectrometry

Organic phosphates and phosphonates are present in a number of cellular components that can be damaged by exposure to ionizing radiation. This work reports femtosecond time-resolved mass spectrometry (FTRMS) studies of three organic phosphonate radical cations that model the DNA sugar-phosphate backbone: dimethyl methylphosphonate (DMMP), diethyl methylphosphonate (DEMP), and diisopropyl methylphosphonate (DIMP). Upon ionization, each molecular radical cation exhibits unique oscillatory dynamics in its ion yields resulting from coherent vibrational excitation. DMMP has particularly well-resolved 45 fs (732 ± 28 cm−1) oscillations with a weak feature at 610–650 cm−1, while DIMP exhibits bimodal oscillations with a period of ∼55 fs and two frequency features at 554 ± 28 and 670–720 cm−1. In contrast, the oscillations in DEMP decay too rapidly for effective resolution. The low- and high-frequency oscillations in DMMP and DIMP are assigned to coherent excitation of the symmetric O–P–O bend and P–C stretch, respectively. The observation of the same ionization-induced coherently excited vibrations in related molecules suggests a possible common excitation pathway in ionized organophosphorus compounds of biological relevance, while the distinct oscillatory dynamics in each molecule points to the potential use of FTRMS to distinguish among fragment ions produced by related molecules

Study of foldable elastic tubes for large space structure applications, phase 1

Structural members that might be suitable for strain energy deployable structures, are discussed with emphasis on a thin-walled cylindrical tube with a cross-section that is called 'bi-convex'. The design of bi-convex tube test specimens and their fabrication are described as well as the design and construction of a special purpose testing machine to determine the deployment characteristics. The results of the first series of tests were quite mixed, but clearly revealed that since most of the specimens failed to deploy completely, due to a buckling problem, this type of tube requires some modification in order to be viable

Gender and Access to Agricultural Resources by Smallholder Farmers in the Upper West Region of Ghana

Men and women continue to have differential access to agricultural resources despite the seemingly equal roles they play in agriculture in many developing countries. The study sought to determine the relationship between gender and access to agricultural resources in the Upper West Region of Ghana. Simple random sampling technique was employed to select 400 farmers disaggregated into men and women from four districts in the region. Statistically significant differences were observed between gender and access to land, labour, inputs and radio, extension agents and input suppliers (p<0.05) while there was no significant difference between gender and access to credit (p>0.05) even though women also have more access to credit than men. It has been recommended that more aspects of the culture of the people be improved to pave way for more access to agricultural land in particular. Levels of credit support are very low in the region and financial institutions need to reduce some of the bottlenecks to allow easy access to credit. Also extension agents should endeavour to educate smallholders on how to access information through electronic platforms and also make them seek more information from input suppliers as the current situation demands. Key words: Gender, Inputs, Credit, ICT

Composite sodium alginate and chitosan based wafers for buccal delivery of macromolecules.

The objective of this study was to develop a composite buccal wafer for protein drug delivery. The polymeric vehicle used in this study combined chitosan and sodium alginate with bovine serum albumin (BSA) as a model drug. The wafers were obtained by freeze-drying gels of the polymers in well plates. Prior to the lyophilisation process, differential scanning calorimetry was performed to establish a suitable freeze-drying cycle. Preliminary characterization experiments were undertaken to select the optimum composite gel containing sodium alginate and chitosan in a 4:1 ratio respectively for drug loading. A second series of characterisation tests were performed on the drugloaded wafers prepared from gels containing 0.25 and 0.5 % w/w of BSA. The formulations were functionally characterised for swelling, mucoadhesive and drug dissolution properties. The morphology and crystallinity were investigated using a scanning electron microscope and X-ray diffractometer respectively. The results from drug dissolution studies over a two-hour period showed 66% and 31% cumulative drug release for the wafers obtained from gels containing 0.25 and 0.50 % w/w BSA respectively. These results show the feasibility of developing a sustained delivery system for macromolecules by combining chitosan and sodium alginate

Conserved Vibrational Coherence in the Ultrafast Rearrangement of 2-Nitrotoluene Radical Cation

2-Nitrotoluene (2-NT) is a good model for both photolabile protecting groups for organic synthesis and the military explosive 2,4,6-trinitrotoluene (TNT). In addition to the direct C−NO2 bond-cleavage reaction that initiates detonation in TNT, 2-NT undergoes an H atom attack reaction common to the photolabile 2-nitrobenzyl group, which forms the aci-nitro tautomer. In this work, femtosecond pump−probe measure- ments with mass spectrometric detection and density functional theory (DFT) calculations demonstrate that the initially prepared vibrational coherence in the 2-NT radical cation (2- NT+) is preserved following H atom attack. Strong-field adiabatic ionization is used to prepare 2-NT+, which can overcome a modest 0.76 eV energy barrier to H atom attack to form the aci-nitro tautomer as soon as ∼20−60 fs after ionization. Once formed, the aci-nitro tautomer spontaneously loses −OH to form C7H6NO+, which exhibits distinctly faster oscillations in its ion yield (290 fs period) as compared to the 2-NT+ ion (380 fs period). The fast oscillations are attributed to the coherent torsional motion of the aci-nitro tautomer, which has a significantly faster computed torsional frequency (86.9 cm−1) than the 2- NT+ ion (47.9 cm−1). Additional DFT calculations identify reaction pathways leading to the formation of the dissociation products C7H6NO+, C7H7+, and C6H6N+. Collectively, these results reveal a rich picture of coherently and incoherently driven dissociation pathways in 2-NT+

Selection of Blast Design for Kofi C Pit of Endeavour Mining Corporation, Mali

The Kofi Gold Mine (KGM) of Endeavour Mining Corporation in Mali needed to select one of two alternative blast designs, Blast Design 1 (BD1) and Blast Design 2 (BD2), for the fresh rocks of the deposit, both ore and waste,  in their Kofi C Pit. BD1 has a burden of 3.2 m, a spacing of 3.5 m, a bench height of 5.0 m and a sub drill of 0.5 m. BD2 has a burden of 3.5 m, a spacing of 4.0 m, a bench height of 10.0 m and a sub drill of 0.8 m. Both designs have the same hole diameter of 115 mm and powder factor of  0.68 kg/m3. The Modified Kuz-Ram Fragmentation Model was used to estimate and compare the fragmentation of the two designs. The modelling results showed that the fragmentation of BD1 would be better than that of BD2 but cost analysis revealed that the drilling and blasting cost of BD2 would be lower than that of BD1. Consequently, BD2 was modified into Blast Design 3 (BD3) to improve the fragmentation without exceeding the drilling and blasting cost of BD1. The modification was done by increasing the powder factor of BD2 by 16.18 %. Subsequent fragmentation modelling and cost analysis revealed that BD3 and BD1 would now have the same fragmentation and the same drilling and blasting cost but BD3 would give a higher productivity. It was therefore recommended that KGM selects BD3 over BD1 and BD2 for ore drilling and blasting. BD2 could be considered for waste drilling and blasting because its lower fragmentation, which is not good enough when the rock is ore, is acceptable when the rock is waste. Keywords: Blast Design, Cost Analysis, Drilling and Blasting Productivity, Kuz-Ram Fragmentation Mode

State of dietetics practice in Ghana

Objective: Prevalence of obesity and related diseases has increased in Ghana. Dietitians have essential skills to prevent and manage dietary diseases. However, little is known about dietetic practice in Ghana. This paper describes the history and current state of dietetics practice in Ghana.Methods: A questionnaire was administered to 13 dietitians and six dietetic interns in February 2012. The questionnaire collected data on perceptions about dietetics practice, career progression, and challenges in dietetics practice in Ghana. Key informant interviews (KII) on history of dietetics in Ghana were also held with four retired dietitians, and two dietetics  educators. Additional KII were conducted with the Chief dietitian, two officers of the Ghana Dietetic Association, and three other dietitians. Most KII were conducted faceto-face but a few were only possible via telephone.Some of the KII were audio-recorded, in addition to handwritten notes. Following transcription of audiorecorded interviews, all data were subjected to content analysis.Results: Dietetic practice in Ghana has evolved from low-skilled cadre (catering officers) offering hospitalbased meal services to the current era of available trained dietitians providing diet therapy in diverse settings. However, 80% of the 35 dietitians identified are working in Accra. In three regions of Ghana, there are no dietitians. There remain limited  opportunities for continuous learning and professional career advancement.Additionally, there are many unqualified dietitians in practice.Conclusion: A huge unmet need for dietitians exists in all regions of Ghana, except Greater Accra. Bridging this gap is essential to increase access to dietetic care throughout Ghana.Keywords: dietetics, professional practice, history, situational analysis, Ghan