Studies on biofilm growth of Pseudomonas aeruginosa PAO1

The development of in vitro techniques to model the surface-associated mode of growth is a prerequisite to understanding more fully the physiological changes involved in such a growth strategy. Key factors believed to influence bacterial persistence in chronic infections are those of the biofilm mode of growth and slow growth rate. Methods for controlling Pseudomonas aeruginosa biofilm population growth rates were investigated in this project. This microorganism was incompatible with the in vitro 47mm diameter membrane filter-based biofilm technique developed for the study of Escherichia coli and Staphylococcus epidermidis by Gilbert et al (Appl. Environ. Microbiol. 1989, 55, 1308-1311). Two alternative methods were designed. The first comprised a 25mm diameter cellulose acetate membrane filter supported in an integral holder. This was found to be limited to the study of low microbial population densities with low flow rates. The second, based on a cylindrical cellulose fibre depth filter, permitted rapid flow rates to be studied and allowed growth rate control of biofilm and eluted cells. Model biofilms released cells to the perfusing medium as they grew and divided. The viability of released cells was reduced during, and shortly after, inclusion of ciprofloxacin in the perfusate. Outer membrane profiles of biofilm populations exhibited at least two bands not apparent in planktonic cells grown in batch and chemostat culture, and LPS profiles of biofilm populations showed variation with growth rate. Cell surface hydrophobicity of resuspended biofilm cells varied little with growth rate, whilst it decreased markedly for cells released from the biofilms as growth rate increased. Cells released from the biofilm were more hydrophilic than their sessile counterparts. Differing growth rates, LPS profiles and hydrophobicity are proposed to have a bearing on the release of cells from the adherent population.

Transient response in high-resolution Brillouin-based distributed sensing using probe pulses shorter than the acoustic relaxation time

We perform numerical simulations on a model describing a Brillouin-based temperature and strain sensor, testing its response when it is probed with relatively short pulses. Experimental results were recently published [e.g., Opt. Lett. 24, 510 (1999)] that showed a broadening of the Brillouin loss curve when the probe pulse duration is reduced, followed by a sudden and rather surprising reduction of the linewidth when the pulse duration gets shorter than the acoustic relaxation time. Our study reveals the processes responsible for this behavior. We give a clear physical insight into the problem, allowing us to define the best experimental conditions required for one to take the advantage of this effect.

The behaviour of granular material in pure shear, direct shear and simple shear

In biaxial compression tests, the stress calculations based on boundary information underestimate the principal stresses leading to a significant overestimation of the shear strength. In direct shear tests, the shear strain becomes highly concentrated in the mid-plane of the sample during the test. Although the stress distribution within the specimen is heterogeneous, the evolution of the stress ratio inside the shear band is similar to that inferred from the boundary force calculations. It is also demonstrated that the dilatancy in the shear band significantly exceeds that implied from the boundary displacements. In simple shear tests, the stresses acting on the wall boundaries do not reflect the internal state of stress but merely provide information about the average mobilised wall friction. It is demonstrated that the results are sensitive to the initial stress state defined by K0 = sh/sv. For all cases, non-coaxiality of the principal stress and strain-rate directions is examined and the corresponding flow rule is identified. Periodic cell simulations have been used to examine biaxial compression for a wide range of initial packing densities. Both constant volume and constant mean stress tests have been simulated. The characteristic behaviour at both the macroscopic and microscopic scales is determined by whether or not the system percolates (enduring connectivity is established in all directions). The transition from non-percolating to percolating systems is characterised by transitional behaviour of internal variables and corresponds to an elastic percolation threshold, which correlates well with the establishment of a mechanical coordination number of ca. 3.0. Strong correlations are found between macroscopic and internal variables at the critical state.

The mechanical properties and formability of dual-phase steel

In recent years dual phase steels comprising of 5-20% martensite in a ferrite matrix have come into the limelight of high strength cold formable steels because of their potential for vehicle weight saving. They show the following features: no yield point; relatively low initial flow stress; high initial workhardening rate; well sustained work hardening. As a consequence of these characteristics, dual phase steels exhibit a better combination of strength and elongation than other HSLA steels. In this thesis, a broad view of the factors which influence their properties is presented. Mechanical properties and forming ability of a commercially available dual phase steel and an AL-Si killed steel processed to dual phase form are investigated to ascertain the effect of their microstructure on their properties. It is found that the yield phenomena are masked by the transformation induced stresses present during processing and so yield point could be recovered under suitable ageing treatment; that apart from giving the above properties dual phasing gives rise to very low strain-rate sensitivity and a low R value ~ 1; that the mechanical response under rolling conditions is not different from those under tension; that there is a danger of damage to tooling during forming operations of these steels if fracture should precede instability as a result of grain size dependent strength found for these steels. It is also found that very little deformation of the martensite islands took place during deformation except at high strains. The work-hardening and the strength levels can be controlled by either decreasing the grain size or increasing the martensite volume fraction, but it is found that increasing martensite has a detrimental effect on ductility and the ductility and fracture strength can be controlled better by refining the grain size. A remarkable effect found in the dual phase steel tested is that the compressive strength is higher than the tensile strength. The reason for this observation is not yet clear but it is suggested that it might be due to the introduction of emissary type dislocations into the ferrite lattice as a result of twins formed in the martensite during transformation from austenite. The twins are envisaged to be {111} <112> in character.

SGLT inhibitors in management of diabetes

The two main sodium-glucose cotransporters (SGLTs), SGLT1 and SGLT2, provide new therapeutic targets to reduce hyperglycaemia in patients with diabetes. SGLT1 enables the small intestine to absorb glucose and contributes to the reabsorption of glucose filtered by the kidney. SGLT2 is responsible for reabsorption of most of the glucose filtered by the kidney. Inhibitors with varying specificities for these transporters (eg, dapagliflozin, canagliflozin, and empagliflozin) can slow the rate of intestinal glucose absorption and increase the renal elimination of glucose into the urine. Results of randomised clinical trials have shown the blood glucose-lowering efficacy of SGLT inhibitors in type 2 diabetes when administered as monotherapy or in addition to other glucose-lowering therapies including insulin. Increased renal glucose elimination also assists weight loss and could help to reduce blood pressure. Effective SGLT2 inhibition needs adequate glomerular filtration and might increase risk of urinary tract and genital infection, and excessive inhibition of SGLT1 can cause gastro-intestinal symptoms. However, the insulin-independent mechanism of action of SGLT inhibitors seems to offer durable glucose-lowering efficacy with low risk of clinically significant hypoglycaemia at any stage in the natural history of type 2 diabetes. SGLT inhibition might also be considered in conjunction with insulin therapy in type 1 diabetes. © 2013 Elsevier Ltd.

Fatigue crack growth behaviour in molten-metal processed SiC particle-reinforced aluminium alloys

Fatigue crack initiation and subsequent short crack growth behaviour of 2014-5wt%SiC aluminium alloy composites has been examined in 4-point bend loading using smooth bar specimens. The growth rates of long fatigue cracks have also been measured at different stress ratios using pre-cracked specimens. The distributions of SiC particles and of coarse constituent particles in the matrix (which arise as a result of the molten-metal processing and relatively slow cooling rate) have been investigated. Preferential crack initiation sites were found to be SiC-matrix interfaces, SiC particles associated with constituent particles and the coarse constituent particles themselves. For microstructurally short cracks the dispersed SiC particles also act as temporary crack arresters. In the long crack growth tests, higher fatigue crack growth rates were obtained than for monolithic alloys. This effect is attributed to the contribution of void formation, due to the decohesion of SiC particles, to the fatigue crack growth process in the composite. Above crack depths of about 200 μm 'short' crack growth rates were in good agreement with the long crack data, showing a Pris exponent, m = 4 in both cases. For the long crack and short crack growth tests little effect of specimen orientation and grain size was observed on fatigue crack growth rates, but, specimen orientation affected the toughness. No effect of stress ratio in the range R = 0.2-0.5 was seen for long crack data in the Paris region.

Fracture behaviour of an aluminide coating on a single crystal nickel base superalloy

Measurement of the coating fracture strain of an aluminide coating on a single crystal nickel base superalloy has been performed both in three-point bending and using variable wall thickness testpieces. As-aged specimens, 28 to 33 μm in thickness, were tested at room temperature, 600, 700 and 750 °C; specimens pre-exposed for 140 h at 850 and 1100 °C in air and vacuum were tested at room temperature. Fracture strains varied from 0.52 to 0.70% for as-aged specimens tested at temperatures up to 700 °C and specimens exposed at 850 °C and tested at room temperature. The crack path for these conditions was intergranular or transgranular in the main coating, along carbide-matrix interfaces in the coating transition zone, and at an angle of 30-45° to the original crack path in the substrate. The as-aged coating tested at 750 °C was ductile; a ductile-brittle transition occurs between 700 and 750 °C for the strain rate used (1 × 10-5 s-1). Following 1100 °C pre-exposure, specimens were ductile at room temperature with fractures strains of several percent. In this condition the crack morphology changed to one of subsurface nucleation in β grains and at β-γ′ interfaces. © 1993.

Transient response in high-resolution Brillouin-based distributed sensing using probe pulses shorter than the acoustic relaxation time

We perform numerical simulations on a model describing a Brillouin-based temperature and strain sensor, testing its response when it is probed with relatively short pulses. Experimental results were recently published [e.g., Opt. Lett. 24, 510 (1999)] that showed a broadening of the Brillouin loss curve when the probe pulse duration is reduced, followed by a sudden and rather surprising reduction of the linewidth when the pulse duration gets shorter than the acoustic relaxation time. Our study reveals the processes responsible for this behavior. We give a clear physical insight into the problem, allowing us to define the best experimental conditions required for one to take the advantage of this effect.

Characterization of viscoplastic yielding of asphalt concrete

A temperature and strain rate dependent yield surface model was proposed to characterize the viscoplastic yielding of asphalt concrete. Laboratory tests were conducted on specimens that have two binders, two air void contents, and three aging periods. Strain decomposition was performed to obtain viscoplastic strain and stress-pseudostrain curves were constructed to determine the model parameters accurately and efficiently. Results indicate that a stiffer asphalt concrete has greater cohesion and strain hardening amplitude, both of which decline as temperature increases or strain rate decreases. The temperature and strain rate factors of the yield surface can be accurately determined solely by the peak stress of the strength tests. © 2013 Elsevier Ltd. All rights reserved.

Identification of Mechanical Parameters in Mathematical Model of Human Abdominal Fascia

Миглена Г. Кирилова-Донева - Едномерен експеримент на релаксация беше извършен с 14 образци от човешка пъпна фасция. Механичното поведение на фасцията по време на релаксация беше моделирано прилагайки нелинейната теория на Максвел-Гуревич-Рабинович. Параметрите на модела за изследваните образци бяха определени и стойностите им бяха сравнени в зависимост от посоката на натоварване на образците по време на експеримента. Установено бе, че стойностите на началния вискозитет ∗η0 и на параметъра ∗m, който се влияе от скоростта на деформация на материала се изменят в много широки граници не само за образци от различни донори, но и за образци от един донор. В резултат от прилагането на модела бе изчислено изменението на вискозитета и вискозната деформация на материала по време на релаксацията. Бе показано, че изменението на вискозитета и вискозната деформация зависи от посоката на натоварване на образците.

A question of complexity:measuring the maturity of online enquiry communities

Online enquiry communities such as Question Answering (Q&A) websites allow people to seek answers to all kind of questions. With the growing popularity of such platforms, it is important for community managers to constantly monitor the performance of their communities. Although different metrics have been proposed for tracking the evolution of such communities, maturity, the process in which communities become more topic proficient over time, has been largely ignored despite its potential to help in identifying robust communities. In this paper, we interpret community maturity as the proportion of complex questions in a community at a given time. We use the Server Fault (SF) community, a Question Answering (Q&A) community of system administrators, as our case study and perform analysis on question complexity, the level of expertise required to answer a question. We show that question complexity depends on both the length of involvement and the level of contributions of the users who post questions within their community. We extract features relating to askers, answerers, questions and answers, and analyse which features are strongly correlated with question complexity. Although our findings highlight the difficulty of automatically identifying question complexity, we found that complexity is more influenced by both the topical focus and the length of community involvement of askers. Following the identification of question complexity, we define a measure of maturity and analyse the evolution of different topical communities. Our results show that different topical communities show different maturity patterns. Some communities show a high maturity at the beginning while others exhibit slow maturity rate. Copyright 2013 ACM.

Monocyte subpopulation counts and associations with left ventricular ejection fraction post ST elevation myocardial infarction

Background: Monocytes are implicated in the initiation and progression of the atherosclerotic plaque contributing to plaque instability and rupture. Little is known about the role of the three phenotypically and functionally different monocyte subpopulations in determining ventricular remodelling following ST elevation myocardial infarction (STEMI). Mon1 are the ‘classical’ monocytes with inflammatory action, whilst Mon3 are considered reparative with fibroblast deposition ability. The function of the newly described Mon2 subset is yet to be fully described. Method: STEMI patients (n=196, mean age 62±13 years; 72% male) treated with percutaneous revascularization were recruited within the first 24 h post-infarction. Peripheral blood monocyte subpopulations were enumerated and characterised using flow cytometry after staining for CD14, CD16 and CCR2. Phenotypically, monocyte subpopulations are defined as: CD14++CD16-CCR2+ (Mon1), CD14++CD16+CCR2+ (Mon2) and CD14+CD16++CCR2- (Mon3) cells. Transthoracic 2D echocardiography was performed within 7 days and at 6 months post infarct to assess ventricular volumes, mass, systolic, and diastolic functions as well as strain and strain rate. Results: Using linear regression analysis higher counts for Mon1, and lower counts for Mon2 and Mon3 were significantly associated with the baseline left ventricular ejection fraction (LVEF) within 7 days post infarct (table 1). At 6 months post STEMI lower counts of Mon2 remained positively associated with a decrease in LVEF at completion of remodelling (p=0.002). Conclusion: Peripheral monocytes of all three subsets correlate with LVEF after a myocardial infarction. High counts of the inflammatory Mon1 are associated with the reduced baseline ejection fraction post infarction. After remodelling, the convalescent ejection fraction was independently predicted by monocyte subpopulation 2. As lower counts depicted negative ventricular remodelling, this suggests a possible myofibroblast deposition and angiogenesis role for the newly described intermediate monocyte subpopulation Mon2 as opposed to the previously anticipated inflammatory role.

Well-structured teams and the buffering of hospital employees from stress

Membership in well-structured teams, which show clarity in team and individual goals, meet regularly, and recognize diverse skills of their members, is known to reduce stress. This study examined how membership of well-structured teams was associated with lower levels of strain, when testing a work stressors-to-strains relationship model across the three levels of team structure, namely well-structured, poorly structured (do not fulfill all the criteria of well-structured teams) and no team. The work stressors tested, were quantitative overload and hostile environment, whereas strains were measured through job satisfaction and intention to leave job. This investigation was carried out on a random sample of 65,142 respondents in acute/specialist National Health Service hospitals across the UK. Using multivariate analysis of variance, statistically significant differences between means across the three groups of team structure, with mostly moderate effect sizes, were found for the study variables. Those in well-structured teams have the highest levels of job satisfaction and the least intention to leave job. Multigroup structural equation modelling confirmed the model's robustness across the three groups of team structure. Work stressors explained 45%, 50% and 65% of the variance of strains for well-structured, poorly structured and no team membership, respectively. An increase of one standard deviation in work stressors, resulted in an increase in 0.67, 0.70 and 0.81 standard deviations in strains for well-structured, poorly structured and no team membership, respectively. This investigation is an eye-opener for hospitals to work towards achieving well-structured teams, as this study shows weaker stressor-to-strain relationships for members of these teams.

Hierarchical ZnO “rod like” architecture synthesized via reverse micellar route for improved photocatalytic activity

Hierarchical ZnO “rod like” architecture was successfully synthesized via reverse micellar route and characterized by various techniques. The FESEM studies show controlled decomposition of zinc oxalate into ZnO “rod like” architecture at 500 °C with slow heat rate at 1°/min. Interestingly, improved photocatalytic activity was observed for the degradation of Rhodamine B, due to the self assembly of hexagonal nanoparticles of zinc oxide forming hierarchical ZnO “rod like” architecture which can greatly enhance the light utilization rate due to its special architecture and enlarge the specific surface area, providing more reaction sites and promoting mass transfer. More importantly, the reusability studies of this architecture were most economical.

An Investigation of Narration Rates for the Reading While Listening Strategy

This study investigated the effects of Reading While Listening narration rates on elementary students' comprehension. Slow, normal and sentence interval narration rates were used. Results showed higher comprehension scores with the slow narration rate for students with low reading levels, and normal rate for high and medium level readers