Optimisation of distributed feedback laser biosensors

A new integrated optical sensor chip is proposed, based on a modified distributed- feedback (DFB) semiconductor laser. The semiconductor layers of different refractive indices that comprise a laser form the basis of a waveguide sensor, where changes in the refractive index of material at the surface are sensed via changes in the evanescent field of the lasing mode. In DFB lasers, laser oscillation occurs at the Bragg wavelength. Since this is sensitive to the effective refractive index of the optical mode, the emission wavelength is sensitive to the index of a sample on the waveguide surface. Hence, lasers are modelled as planar waveguides and the effective index of the fundamental transverse electric mode is calculated as a function of index and thickness of a thin surface layer using the beam propagation method. We find that an optimised structure has a thin upper cladding layer of ~0.15 mum, which according to this model gives detection limits on test layer index and thickness resolution of 0.1 and 1.57 nm, respectively, a figure which may be further improved using two lasers in an interferometer-type configuration

Low Enriched Uranium (LEU) Nuclear Thermal Propulsion: System Overview and Ground Test Strategy

No abstract availabl

Wax moth larva (Galleria mellonella): An in vivo model for assessing the efficacy of antistaphylococcal agents

Objectives - To investigate whether the wax moth larva, Galleria mellonella, is a suitable host for assessing the in vivo efficacy of antistaphylococcal agents against Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) infections. Methods - Wax moth larvae were infected with increasing doses of S. aureus to investigate the effect of inoculum size on larval survival. In addition, infected wax moth larvae were treated with daptomycin, penicillin or vancomycin to examine whether these agents were effective against S. aureus and MRSA infections in vivo. Results - Increasing inoculum doses of live S. aureus cells resulted in greater larval mortality, but heat-killed bacteria and cell-free culture filtrates had no detrimental effects on survival. Larval mortality rate also depended on the post-inoculation incubation temperature. After larvae were infected with S. aureus, larval survival was enhanced by administering the antistaphylococcal antibiotics daptomycin or vancomycin. Larval survival increased with increasing doses of the antibiotics. Moreover, penicillin improved survival of larvae infected with a penicillin-susceptible methicillin-susceptible S. aureus (MSSA) strain, but it was ineffective at similar doses in larvae infected with MRSA (penicillin resistant). Daptomycin and vancomycin were also effective when administered to the larvae prior to infection with bacteria. Conclusions - This is the first report to demonstrate that antibiotics are effective in the wax moth larva model for the treatment of infections caused by Gram-positive bacteria. The new wax moth larva model is a useful preliminary model for assessing the in vivo efficacy of candidate antistaphylococcal agents before proceeding to mammalian studies, which may reduce animal experimentation and expense

Repurposing the anti-viral drug zidovudine (AZT) in combination with meropenem as an effective treatment for infections with multi-drug resistant, carbapenemase-producing strains of Klebsiella pneumoniae

Funding: University of St Andrews.Multi-drug resistant (MDR) Klebsiella pneumoniae represent a global threat to healthcare due to lack of effective treatments and high mortality rates. The aim of this research was to explore the potential of administering zidovudine (AZT) in combination with an existing antibiotic to treat resistant K. pneumoniae infections. Two MDR K. pneumoniae strains were employed, producing either the NDM-1 or KPC-3 carbapenemase. Efficacy of combinations of AZT with meropenem were compared with monotherapies against infections in Galleria mellonella larvae by measuring larval mortality and bacterial burden. The effect of the same combinations in vitro was determined via checkerboard and time-kill assays. In vitro, both K. pneumoniae strains were resistant to meropenem but were susceptible to AZT. In G. mellonella, treatment with either AZT or meropenem alone offered minimal therapeutic benefit against infections with either strain. In contrast, combination therapy of AZT with meropenem presented significantly enhanced efficacy compared to monotherapies. This was correlated with prevention of bacterial proliferation within the larvae but not elimination. Checkerboard assays showed that the interaction between AZT and meropenem was not synergistic but indifferent. In summary, combination therapy of AZT with meropenem represents a potential treatment for carbapenemase-producing MDR K. pneumoniae and merits further investigation.PostprintPeer reviewe

New insight into the formation of structural defects in poly(vinyl chloride)

The monomer conversion dependence of the formation of the various types of defect structures in radical suspension polymerization of vinyl chloride was examined via both H-1 and C-13 NMR spectrometry. The rate coefficients for model propagation and intra- and intermolecular hydrogen abstraction reactions were obtained via high-level ab initio molecular orbital calculations. An enormous increase in the formation of both branched and internal unsaturated structures was observed at conversions above 85%, and this is mirrored by a sudden decrease in stability of the resulting PVC polymer. Above this threshold-conversion, the monomer is depleted from the polymer-rich phase, and the propagation rate is thus substantially reduced, thereby allowing the chain-transfer processes to compete more effectively. In contrast to the other defects, the chloroallylic end groups were found to decrease at high conversions. On the basis of the theoretical and experimental data obtained in this study, this decrease was attributed to copolymerization and abstraction reactions that are expected to be favored at high monomer conversions. Finally, a surprising increase in the concentration of the methyl branches was reported. Although a definitive explanation for this behavior is yet to be obtained, the involvement of transfer reactions of an intra- or intermolecular nature seems likely, and (in the latter case) these could lead to the presence of tertiary chlorine in these defects

Repurposing mitomycin C in combination with pentamidine or gentamicin to treat infections with multi-drug resistant (MDR) 3 Pseudomonas aeruginosa

The aims of this study were (i) to determine if the combination of mitomycin C with pentamidine or existing antibiotics resulted in enhanced efficacy versus infections with MDR P. aeruginosa in vivo; and (ii) to determine if the doses of mitomycin C and pentamidine in combination can be reduced to levels that are non-toxic in humans but still retain antibacterial activity. Resistant clinical isolates of P. aeruginosa, a mutant strain over-expressing the MexAB-OprM resistance nodulation division (RND) efflux pump and a strain with three RND pumps deleted, were used. MIC assays indicated that all strains were sensitive to mitomycin C, but deletion of three RND pumps resulted in hypersensitivity and over-expression of MexAB-OprM caused some resistance. These results imply that mitomycin C is a substrate of the RND efflux pumps. Mitomycin C monotherapy successfully treated infected Galleria mellonella larvae, albeit at doses too high for human administration. Checkerboard and time–kill assays showed that the combination of mitomycin C with pentamidine, or the antibiotic gentamicin, resulted in synergistic inhibition of most P. aeruginosa strains in vitro. In vivo, administration of a combination therapy of mitomycin C with pentamidine, or gentamicin, to G. mellonella larvae infected with P. aeruginosa resulted in enhanced efficacy compared with monotherapies for the majority of MDR clinical isolates. Notably, the therapeutic benefit conferred by the combination therapy occurred with doses of mitomycin C close to those used in human medicine. Thus, repurposing mitomycin C in combination therapies to target MDR P. aeruginosa infections merits further investigation.Peer reviewe

Collective practical Knowledge is a Fragmented Interrogative capacity

What does it take for a group of people to know how to do something? An account of collective practical knowledge ought to be compatible with the linguistic evidence about the semantics for collective knowledge-how ascriptions, be able to explain the practicality of collective knowledge, be able to explain both the connection between individual and collective know-how and the possibility of a group knowing how to do something none of its members know, and be applicable to a suitably wide range of groups. In this paper I develop a view which can meet all of these desiderata, which combines a Fragmented account of collective knowledge (Habgood-Coote, 2019a), with the view that practical knowledge is an Interrogative Capacity (Habgood-Coote, 2019b)

Group Inquiry

Group agents can act, and they can have knowledge. How should we understand the species of collective action which aims at knowledge? In this paper, I present an account of group inquiry. This account faces two challenges: to make sense of how large-scale distributed activities might be a kind of group action, and to make sense of the kind of division of labour involved in collective inquiry. In the first part of the paper, I argue that existing accounts of group action face problems dealing with large-scale group actions, and propose a minimal alternative account. In the second part of the paper, I draw on an analogy between inquiry and conversation, arguing that work by Robert Stalnaker and Craige Roberts helps us to think about the division of labour. In the final part of the paper I put the accounts of group action and inquiry together, and consider how to think about group knowledge, deep ignorance, and the different kinds of division of labour

Experimental evidence for competitive N-O and O-C bond homolysis in gas-phase alkoxyamines

The extensive use of alkoxyamines in controlled radical polymerisation and polymer stabilisation is based on rapid cycling between the alkoxyamine (R1R2NO-R3) and a stable nitroxyl radical (R1R2NO•) via homolysis of the labile O-C bond. Competing homolysis of the alkoxyamine N-O bond has been predicted to occur for some substituents leading to production of aminyl and alkoxyl radicals. This intrinsic competition between the O-C and N-O bond homolysis processes has to this point been difficult to probe experimentally. Herein we examine the effect of local molecular structure on the competition between N-O and O-C bond cleavage in the gas phase by variable energy tandem mass spectrometry in a triple quadrupole mass spectrometer. A suite of cyclic alkoxyamines with remote carboxylic acid moieties (HOOC-R1R2NO-R3) were synthesised and subjected to negative ion electrospray ionisation to yield [M − H]− anions where the charge is remote from the alkoxyamine moiety. Collision-induced dissociation of these anions yield product ions resulting, almost exclusively, from homolysis of O-C and/or N-O bonds. The relative efficacy of N-O and O-C bond homolysis was examined for alkoxyamines incorporating different R3 substituents by varying the potential difference applied to the collision cell, and comparing dissociation thresholds of each product ion channel. For most R3 substituents, product ions from homolysis of the O-C bond are observed and product ions resulting from cleavage of the N-O bond are minor or absent. A limited number of examples were encountered however, where N-O homolysis is a competitive dissociation pathway because the O-C bond is stabilised by adjacent heteroatom(s) (e.g. R3 = CH2F). The dissociation threshold energies were compared for different alkoxyamine substituents (R3) and the relative ordering of these experimentally determined energies is shown to correlate with the bond dissociation free energies, calculated by ab initio methods. Understanding the structure-dependent relationship between these rival processes will assist in the design and selection of alkoxyamine motifs that selectively promote the desirable O-C homolysis pathway