SPH simulations of irradiation-driven warped accretion discs and the long periods in X-ray binaries

We present three dimensional smoothed particle hydrodynamics (SPH) calculations of irradiation-driven warping of accretion discs. Initially unwarped planar discs are unstable to the radiation reaction when the disc is illuminated by a central radiation source. The disc warps and tilts and precesses slowly in a retrograde direction; its shape continuously flexes in response to the changing orientation of the Roche potential. We simulate ten systems: eight X-ray binaries, one cataclysmic variable (CV), and a `generic' low mass X-ray binary (LMXB). We adopt system parameters from observations and tune a single parameter: our model X-ray luminosity ($L_{*}$) to reproduce the observed or inferred super-orbital periods. Without exception, across a wide range of parameter space, we find an astonishingly good match between the observed $L_{X}$ and the model $L_{*}$. We conclude irradiation-driven warping is the mechanism underlying the long periods in X-ray binaries. Our Her X-1 simulation simultaneously reproduces the observed $L_{X}$, the "main-" and "short-high" X-ray states and the orbital inclination. Our simulations of SS 433 give a maximum warp angle of $18.6^{\circ}$, a good match to the cone traced by the jets, but this angle is reached only in the outer disc. In all cases, the overall disc tilt is less than \degrees{13} and the maximum disc warp is less than and or equal to \degrees{21}.Comment: 17 pages, 14 figures, shorter abstract (24 lines limit

Monitoring of liquid flow through microtubes using a micropressure sensor

The pressure-driven liquid flow through microtubes was studied in a range of very low Reynolds numbers (<0.15) by monitoring the pressure change in situ. Cylindrical microtubes with diameters ranging from 50 ?m to 500 ?m were examined and two types of tube material, namely PEEK polymer and fused silica were compared. A good linear relation for the pressure drop versus flow rate was obtained. Apparent deviations between the measured slopes with those calculated using conventional theory were attributed to uncertainties in the calculated values which are dominated by the uncertainties in the microtube diameters. It was found that a period of stabilisation time was required for reaching a steady flow after the syringe pump was switched on/off or to a different flow rate. The stabilisation time was likely due to the compressibility of the fluid. Insignificant difference between PEEK polymer and fused silica microtubes in terms of flow resistance was observed. The in-situ measurement of pressure drops provides a convenient approach for monitoring fluid flow through microtubes and detecting dimensional changes within microchannels in Lab-on-a-Chip and microreactor systems

Minimum inhibitory and bacterial concentrations of theaflavin and synergistic combinations with epicatechin and quercetin against clinical isolates of Stenotrophomonas Maltophilia

Stenotrophomonas maltophilia is an important nosocomial pathogen with intrinsic resistance to multiple antibiotics. Previous investigations have shown flavanols from black tea to possess antibacterial activity. This study describes the determination of minimum inhibitory concentrations and minimum bactericidal concentration for theaflavin independently and in formulations with the polyphenols epicatechin and quercetin against nine clinical isolates of Stenotrophomonas maltophilia and the control isolate NCTC 130141 via the microtitre assay. The results demonstrate that theaflavin has strong antibacterial activity and also shows significant synergism with epicatechin and quercetin. The minimum inhibitory concentrations of the isolates range between 200-400 g/mL for theaflavin and 100-200 g/mL for both theaflavin:epicatechin and theaflavin:quercetin combinations. The minimum bactericidal concentrations were discovered to be a 2 fold increase on those of the minimum inhibitory concentrations. The research highlights the potential use of polyphenols for the clinical treatment of highly antibiotic resistant bacteria

Simulations of spectral lines from an eccentric precessing accretion disc

Two dimensional SPH simulations of a precessing accretion disc in a q=0.1 binary system (such as XTE J1118+480) reveal complex and continuously varying shape, kinematics, and dissipation. The stream-disc impact region and disc spiral density waves are prominent sources of energy dissipation.The dissipated energy is modulated on the period P_{sh} = ({P_{orb}}^{-1}-{P_{prec}}^{-1}^{-1} with which the orientation of the disc relative to the mass donor repeats. This superhump modulation in dissipation energy has a variation in amplitude of ~10% relative to the total dissipation energy and evolves, repeating exactly only after a full disc precession cycle. A sharp component in the light curve is associated with centrifugally expelled material falling back and impacting the disc. Synthetic trailed spectrograms reveal two distinct "S-wave" features, produced respectively by the stream gas and the disc gas at the stream-disc impact shock. These S-waves are non-sinusoidal, and evolve with disc precession phase. We identify the spiral density wave emission in the trailed spectrogram. Instantaneous Doppler maps show how the stream impact moves in velocity space during an orbit. In our maximum entropy Doppler tomogram the stream impact region emission is distorted, and the spiral density wave emission is uppressed. A significant radial velocity modulation of the whole line profile occurs on the disc precession period. We compare our SPH simulation with a simple 3D model: the former is appropriate for comparison with emission lines while the latter is preferable for skewed absorption lines from precessing discs.Comment: See http://physics.open.ac.uk/FHMR/ for associated movie (avi) files. The full paper is in MNRAS press. Limited disk space limit of 650k, hence low resolution figure file

Synergistic antibacterial effects of theaflavin in combination with ampicillin against hospital isolates of Stenotrophomonas Maltophilia

Stenotrophomonas maltophilia is an important opportunistic nosocomial pathogen that shows intrinsic resistance to many antibiotics. This often limits treatment options and can cause lengthy hospital stays. Combination treatments are often used to combat resistance and using natural compounds such as polyphenols could give increased treatment options and even the reuse of antibiotics to which high levels of resistance have been observed. A checkerboard assay was used to determine if any synergy exists between ampicillin and the polyphenol theaflavin against 9 clinical isolates and one control isolate (NCTC 13014) of S. maltophilia. It was discovered that significant synergy (P 0.05) does exist between theaflavin and ampicillin, reducing the mean MIC of ampicillin from 12.5-22.9 µg/mL, in liquid culture, to 3.125-6.25 µg/mL. The FIC index was calculated to be 0.22-0.35 confirming synergy. From these results, significant potential for medical applications can be seen and further investigation is recommended

Comprehensive simulations of superhumps

(Abridged) We use 3D SPH calculations with higher resolution, as well as with more realistic viscosity and sound-speed prescriptions than previous work to examine the eccentric instability which underlies the superhump phenomenon in semi-detached binaries. We illustrate the importance of the two-armed spiral mode in the generation of superhumps. Differential motions in the fluid disc cause converging flows which lead to strong spiral shocks once each superhump cycle. The dissipation associated with these shocks powers the superhump. We compare 2D and 3D results, and conclude that 3D simulations are necessary to faithfully simulate the disc dynamics. We ran our simulations for unprecedented durations, so that an eccentric equilibrium is established except at high mass ratios where the growth rate of the instability is very low. Our improved simulations give a closer match to the observed relationship between superhump period excess and binary mass ratio than previous numerical work. The observed black hole X-ray transient superhumpers appear to have systematically lower disc precession rates than the cataclysmic variables. This could be due to higher disc temperatures and thicknesses. The modulation in total viscous dissipation on the superhump period is overwhelmingly from the region of the disc within the 3:1 resonance radius. As the eccentric instability develops, the viscous torques are enhanced, and the disc consequently adjusts to a new equilibrium state, as suggested in the thermal-tidal instability model. We quantify this enhancement in the viscosity, which is ~10 per cent for q=0.08. We characterise the eccentricity distributions in our accretion discs, and show that the entire body of the disc partakes in the eccentricity.Comment: 18 pages (mn2e LaTeX), 14 figures, 5 tables, Accepted for publication in MNRA

The development of microfluidic based processes

Doctor of Science (DSc) thesis.Full version unavailable due to 3rd party copyright restrictions

Antifungal synergy of theaflavin and epicatechin combinations against Candida albicans

New antifungal agents are required to compensate for the increase in resistance to standard antifungal agents of Candida albicans, which is an important opportunistic fungal pathogen that causes minor infections in many individuals but very serious infections in those who are immune-compromised. In this study, combinations of theaflavin and epicatechin are investigated as potential antifungal agents and also to establish whether antifungal synergy exists between these two readily accessible and cost-effective polyphenols isolated from black and green tea. The results of disc diffusion assays showed stronger antibacterial activity of theaflavin:epicatechin combinations against C. albicans NCTC 3255 and NCTC 3179, than that of theaflavin alone. Minimum inhibitory concentrations (MICs) of 1,024 μg/ml with theaflavin and 128-256 μg/ml with theaflavin:epicatechin combinations were found. The fractional inhibitory concentration indexes were calculated, and the synergy between theaflavin and epicatechin against both isolates of C. albicans was confirmed. Theaflavin:epicatechin combinations show real potential for future use as a treatment for infections caused by C. albicans

Maternal hair selenium levels as a possible long-term nutritional indicator of recurrent pregnancy loss

BACKGROUND:Approximately 1% of all couples trying to conceive will suffer from recurrent pregnancy loss (RPL). Nutritional deficiencies have been postulated as a possible cause of RPL and in particular, selenium deficiency has been associated with reproductive failure in animal studies and more recently, in some human studies. This study was undertaken to assess the maternal hair selenium levels in women with RPL without an identified cause and to compare these results with those of women with successful reproductive histories. METHODS: Twenty four patients with RPL and twenty four control subjects with at least one successful pregnancy and no pregnancy failures, who were matched for age and ethnicity, were recruited. A questionnaire was completed, which included demographic and social information and a dietary history. Hair samples were collected and analyzed for selenium content by inductively coupled plasma mass spectrometry. RESULTS: The control subjects had a higher mean income and had completed more years of education compared with the RPL patients. There was no significant difference in the intake of selenium rich foods between the 2 groups. The patients, however, consumed significantly more fruit, cheese, potatoes and chocolate than the controls. The median (range) selenium content was 0.80ppm (0.19-4.15) and 0.68ppm (0.43-3.76) in patients and controls respectively (Mann Whitney U test 209.5 p=0.74). CONCLUSIONS: While there were significant differences in the 2 groups with regard to resources, education and diet our results show that hair selenium concentrations and dietary selenium intake, were similar in the two groups. Both groups had low levels of this important element