Synthesis of Fe-oxide nanoparticles using microreactors

The work described in this thesis focuses upon the development of a novel adaptable continuous flow technique for the synthesis of iron oxide nanoparticles using commercially available microreactor system, to allow for easy scaling up towards a larger industrial scale. The development of the technique focussed around the conversion of commonly used research techniques, which require the use of specifically designed microreactors, for use upon commercially available microreactors in which the design is fixed. A 2D continuous flow focussed technique was developed based upon the attempted conversion of the droplet coalescence and co-axial flow technique which has been previously used for nanoparticle synthesis by other research groups.The nanoparticles produced using this technique were extensively characterised, in terms of physical and magnetic properties, and seen to be comparable, to those produced by other groups and those currently used as magnetic cores for MRI contrast applications. A critical evaluation of the effect of reaction parameters, e.g. reagent concentration, flow rate, and temperature upon nanoparticle size was made, however little quantifiable conclusions could be drawn. The structure of the nanoparticles was further investigated using a previously developed powder X-ray diffraction calibration technique which relied upon the asymmetry of peaks relating to specific reflections in the γ-Fe₂O₃ and Fe₃O₄ phases present in the nanoparticles. The structures were determined to contain higher quantities of γ-Fe₂O₃ which is more chemically stable but less magnetically favourable of the two phases. Further analysis using Mössbauer and solid state Infra-red analysis confirmed these findings, and as such attempts were made to control the amount of these phases within the nanoparticles. The synthesis technique was therefore adapted to allow for control of the amount of these phases within the nanoparticles by addition of oxidation and reducing agents into the synthesis. By doing this it proved able to synthesise nanoparticles which using the above powder X-ray diffraction technique were seen to be almost completely formed of γ-Fe₂O₃, synthesis of nanoparticles with higher weight percentages of Fe₃O₄, however proved not to be possible.Further work upon attempting to alter the magnetic properties of the nanoparticles has involved developing cation substitution reactions performed using microreactors. In batch these reactions are common place, however to the best of the author’s knowledge however no attempt has yet been made at cation substitution using microreactors. Partial replacement of Fe with another metal cation in the spinel structure was attempted to create a series of MxFe₃₋ₓO₄ compounds, this has been seen to alter the cation distribution and magnetic properties of the nanoparticles by other research groups. Several attempts at substituting Co, Mn, Zn, V, and Sn into the structure in batch. Zn substitution appeared the most successful in batch, and the synthesis was adapted to form ZnxFe₃₋ₓO₄ nanoparticles, with greater amounts of substitution into the nanoparticles seen when performing the synthesis in microreactors rather than batch.The 2D continuous flow focussed technique would therefore prove a useful tool for the synthesis of biomedical nanoparticles. Not only those it produce nanoparticles with the correct physical and magnetic properties, but also allows for their adaptation and manipulation of these properties to be tailored for specific applications

Jet Physics from Static Charges in AdS

Soft interactions with high-energy jets are explored in radial coordinates which exploit the approximately conformal behavior of perturbative gauge theories. In these coordinates, the jets, approximated by Wilson lines, become static charges in Euclidean AdS. The anomalous dimension of the corresponding Wilson line operator is then determined by the potential energy of the charges. To study these Wilson lines we introduce a "conformal gauge" which does not have kinetic mixing between radial and angular directions, and show that a number of properties of Wilson lines are reproduced through relatively simple calculations. For example, certain non-planar graphs involving multiple Wilson lines automatically vanish. We also discuss the linear growth of the charges' imaginary potential energy with separation, and a relationship between Wilson line diagrams and Witten diagrams.Comment: 34 pages, 7 figures; V2: minor edits, added reference

General N-and O-linked glycosylation of lipoproteins in mycoplasmas and role of exogenous oligosaccharide

The lack of a cell wall, flagella, fimbria, and other extracellular appendages and the possession of only a single membrane render the mycoplasmas structurally simplistic and ideal model organisms for the study of glycoconjugates. Most species have genomes of about 800 kb and code for few proteins predicted to have a role in glycobiology. The murine pathogens Mycoplasma arthritidis and Mycoplasma pulmonis have only a single gene annotated as coding for a glycosyltransferase but synthesize glycolipid, polysaccharide and glycoproteins. Previously, it was shown that M. arthritidis glycosylated surface lipoproteins through O-linkage. In the current study, O-linked glycoproteins were similarly found in M. pulmonis and both species of mycoplasma were found to also possess N-linked glycans at residues of asparagine and glutamine. Protein glycosylation occurred at numerous sites on surface-exposed lipoproteins with no apparent amino acid sequence specificity. The lipoproteins of Mycoplasma pneumoniae also are glycosylated. Glycosylation was dependent on the glycosidic linkages from host oligosaccharides. As far as we are aware, N-linked glycoproteins have not been previously described in Gram-positive bacteria, the organisms to which the mycoplasmas are phylogenetically related. The findings indicate that the mycoplasma cell surface is heavily glycosylated with implications for the modulation of mycoplasma-host interactions

Factors associated with long intensive care unit (ICU) admission among inpatients with and without diabetes in South Western Sydney public hospitals using the New South Wales admission patient data collection (2014-2017)

Despite a campaign of effective educational interventions targeting knowledge, attitudes, and prevention, Human Immunodeficiency-Virus/Acquired Immune Deficiency Syndrome (HIV/AIDS) continues to be a significant public health issue in India, with Mizoram reporting the highest HIV/AIDS cases in 2018–2019. In this study, we extracted Mizoram state from the National Family Health Survey Fourth Series (NFHS-4) 2015–2016 datasets and investigated factors associated with respondents’ knowledge, attitudes, and prevention towards HIV/AIDS. The sample included 3555 adults aged 15–49 years residing in Mizoram, North-east India. Respondents who reported having ever heard of HIV/AIDS was 98%. Multivariate analysis indicated that the probability of having inadequate knowledge of HIV/AIDS was higher among those with no schooling, who were illiterate, of non-Christian faiths, belonging to backward tribes or caste, from poor households, and those who lived in rural areas, not exposed to media. The odds of mother-to-child transmission (PMTCT) of HIV/AIDS transmission was high among females (AOR = 3.12, 95% CI 2.34–4.16), respondents aged 35–39 years (AOR = 1.74, 95% CI 1.05–2.87) and those belonging to other backward class. The HIV/AIDS knowledge of respondents was found to be encouraging as the majority (98%) were considered to have a good level of understanding of the condition. An educational intervention to reduce the number of adults 15–49 years infected with HIV/AIDS in Mizoram should target those from low socioeconomic groups, those from non-Christian religions, and those from other backward classes

High-resolution, H band Spectroscopy of Be Stars with SDSS-III/APOGEE: I. New Be Stars, Line Identifications, and Line Profiles

APOGEE has amassed the largest ever collection of multi-epoch, high-resolution (R~22,500), H-band spectra for B-type emission line (Be) stars. The 128/238 APOGEE Be stars for which emission had never previously been reported serve to increase the total number of known Be stars by ~6%. We focus on identification of the H-band lines and analysis of the emission peak velocity separations (v_p) and emission peak intensity ratios (V/R) of the usually double-peaked H I and non-hydrogen emission lines. H I Br11 emission is found to preferentially form in the circumstellar disks at an average distance of ~2.2 stellar radii. Increasing v_p toward the weaker Br12--Br20 lines suggests these lines are formed interior to Br11. By contrast, the observed IR Fe II emission lines present evidence of having significantly larger formation radii; distinctive phase lags between IR Fe II and H I Brackett emission lines further supports that these species arise from different radii in Be disks. Several emission lines have been identified for the first time including ~16895, a prominent feature in the spectra for almost a fifth of the sample and, as inferred from relatively large v_p compared to the Br11-Br20, a tracer of the inner regions of Be disks. Unlike the typical metallic lines observed for Be stars in the optical, the H-band metallic lines, such as Fe II 16878, never exhibit any evidence of shell absorption, even when the H I lines are clearly shell-dominated. The first known example of a quasi-triple-peaked Br11 line profile is reported for HD 253659, one of several stars exhibiting intra- and/or extra-species V/R and radial velocity variation within individual spectra. Br11 profiles are presented for all discussed stars, as are full APOGEE spectra for a portion of the sample.Comment: accepted in A

Jet physics from static charges in AdS space

Soft interactions with high-energy jets are explored in radial coordinates which exploit the approximately conformal behavior of perturbative gauge theories. In these coordinates, the jets, approximated by Wilson lines, become static charges in Euclidean AdS. The anomalous dimension of the corresponding Wilson line operator is then determined by the potential energy of the charges. To study these Wilson lines we introduce a “conformal gauge” which does not have kinetic mixing between radial and angular directions, and show that a number of properties of Wilson lines are reproduced through relatively simple calculations. For example, certain non-planar graphs involving multiple Wilson lines automatically vanish. We also discuss the linear growth of the charges’ imaginary potential energy with separation, and a relationship between Wilson line diagrams and Witten diagrams.Physic

P-MaNGA : full spectral fitting and stellar population maps from prototype observations

MC acknowledges support from a Royal Society University Research Fellowship.MaNGA (Mapping Nearby Galaxies at Apache Point Observatory) is a 6-yearSDSS-IV survey that will obtain resolved spectroscopy from 3600 Å to10300 Å for a representative sample of over 10,000 nearby galaxies.In this paper, we derive spatially resolved stellar population properties and radial gradients by performing full spectral fitting of observed galaxy spectra from P-MaNGA, a prototype of the MaNGA instrument. These data include spectra for eighteen galaxies, covering a large range of morphological type. We derive age, metallicity, dust and stellar mass maps, and their radial gradients, using high spectral-resolution stellar population models, and assess the impact of varying the stellar library input to the models. We introduce a method to determine dust extinction which is able to give smooth stellar mass maps even in cases of high and spatially non-uniform dust attenuation.With the spectral fitting we produce detailed maps of stellar population properties which allow us to identify galactic features among this diverse sample such as spiral structure, smooth radial profiles with little azimuthal structure in spheroidal galaxies, and spatially distinct galaxy sub-components. In agreement with the literature, we find the gradients for galaxies identified as early-type to be on average flat in age, and negative (- 0.15 dex / Re ) in metallicity,whereas the gradients for late-type galaxies are on average negative in age (- 0.39 dex / Re ) and flat in metallicity. We demonstrate howdifferent levels of data quality change the precision with which radialgradients can be measured. We show how this analysis, extended to thelarge numbers of MaNGA galaxies, will have the potential to shed lighton galaxy structure and evolution.PostprintPeer reviewe

Three-Dimensional Double-Ridge Internal Tide Resonance in Luzon Strait

The three-dimensional (3D) double-ridge internal tide interference in the Luzon Strait in the South China Sea is examined by comparing 3D and two-dimensional (2D) realistic simulations. Both the 3D simulations and observations indicate the presence of 3D first-mode (semi)diurnal standing waves in the 3.6-km-deep trench in the strait. As in an earlier 2D study, barotropic-to-baroclinic energy conversion, flux divergence, and dissipation are greatly enhanced when semidiurnal tides dominate relative to periods dominated by diurnal tides. The resonance in the 3D simulation is several times stronger than in the 2D simulations for the central strait. Idealized experiments indicate that, in addition to ridge height, the resonance is only a function of separation distance and not of the along-ridge length; that is, the enhanced resonance in 3D is not caused by 3D standing waves or basin modes. Instead, the difference in resonance between the 2D and 3D simulations is attributed to the topographic blocking of the barotropic flow by the 3D ridges, affecting wave generation, and a more constructive phasing between the remotely generated internal waves, arriving under oblique angles, and the barotropic tide. Most of the resonance occurs for the first mode. The contribution of the higher modes is reduced because of 3D radiation, multiple generation sites, scattering, and a rapid decay in amplitude away from the ridge

The most luminous, merger-free AGN show only marginal correlation with bar presence

The role of large-scale bars in the fuelling of active galactic nuclei (AGN) is still debated, even as evidence mounts that black hole growth in the absence of galaxy mergers cumulatively dominated and may substantially influence disc (i.e., merger-free) galaxy evolution. We investigate whether large-scale galactic bars are a good candidate for merger-free AGN fuelling. Specifically, we combine slit spectroscopy and Hubble Space Telescope imagery to characterise star formation rates (SFRs) and stellar masses of the unambiguously disc-dominated host galaxies of a sample of luminous, Type-1 AGN with 0.02 < z 0.024. After carefully correcting for AGN signal, we find no clear difference in SFR between AGN hosts and a stellar mass-matched sample of galaxies lacking an AGN (0.013 < z < 0.19), although this could be due to a small sample size (n_AGN = 34). We correct for SFR and stellar mass to minimise selection biases, and compare the bar fraction in the two samples. We find that AGN are marginally (1.7$\sigma$) more likely to host a bar than inactive galaxies, with AGN hosts having a bar fraction, fbar = 0.59^{+0.08}_{-0.09} and inactive galaxies having a bar fraction fbar = 0.44^{+0.08}_{-0.09}. However, we find no further differences between SFR- and mass-matched AGN and inactive samples. While bars could potentially trigger AGN activity, they appear to have no further, unique effect on a galaxy's stellar mass or SFR.Comment: 15 pages (9 figures). Accepted for publication in MNRA

Chemical abundance gradients from open clusters in the Milky Way disk: results from the APOGEE survey

Metallicity gradients provide strong constraints for understanding the chemical evolution of the Galaxy. We report on radial abundance gradients of Fe, Ni, Ca, Si, and Mg obtained from a sample of 304 red-giant members of 29 disk open clusters, mostly concentrated at galactocentric distances between ~8 - 15 kpc, but including two open clusters in the outer disk. The observations are from the APOGEE survey. The chemical abundances were derived automatically by the ASPCAP pipeline and these are part of the SDSS III Data Release 12. The gradients, obtained from least squares fits to the data, are relatively flat, with slopes ranging from -0.026 to -0.033 dex/kpc for the alpha-elements [O/H], [Ca/H], [Si/H] and [Mg/H] and -0.035 dex/kpc and -0.040 dex/kpc for [Fe/H] and [Ni/H], respectively. Our results are not at odds with the possibility that metallicity ([Fe/H]) gradients are steeper in the inner disk (R_GC ~7 - 12 kpc) and flatter towards the outer disk. The open cluster sample studied spans a significant range in age. When breaking the sample into age bins, there is some indication that the younger open cluster population in our sample (log age < 8.7) has a flatter metallicity gradient when compared with the gradients obtained from older open clusters.Comment: 4 pages, 3 figures, To appear in Astronomische Nachrichten, special issue "Reconstruction the Milky Way's History: Spectroscopic surveys, Asteroseismology and Chemo-dynamical models", Guest Editors C. Chiappini, J. Montalb\'an, and M. Steffen, AN 2016 (in press)