Chemical abundances and winds of massive stars in M31: a B-type supergiant and a WC star in OB 10

We present high quality spectroscopic data for two massive stars in the OB 10 association of M31, OB 10-64 (B0 la) and OB 10-WRI (WC6). Medium resolution spectra of both stars were obtained using the ISIS spectrograph on the William Herschel Telescope. This is supplemented with Hubble Space Telescope STIS UV spectroscopy and Keck I HIRES data for OB 10-64. A non- local thermodynamic equilibrium (LTE) model atmosphere and abundance analysis for OB 10-64 is presented, indicating that this star has similar photospheric CNO, Mg and Si abundances to solar neighbourhood massive stars. A wind analysis of this early B-type supergiant reveals a mass-loss rate of (M)over dot = 1.6 x 10(-6) M-circle dot yr(-1), and v(infinity) = 1650 km s(-1). The corresponding wind momentum is in good agreement with the wind momentum-luminosity relationship found for Galactic early-B supergiants. Observations of OB 10-WRI are analysed using a non-LTE, line-blanketed code, to reveal approximate stellar parameters of log L/L-circle dot similar to 5.7, T-* - 75 kK, v(infinity) similar to 3000 km s(-1), (M)over dot/(M-circle dot yr(-1)) similar to 10(-4.3) adopting a clumped wind with a filling factor of 10 per cent. Quantitative comparisons are made with the Galactic WC6 star HD 92809 (WR23) revealing that OB 10-WR1 is 0.4 dex more luminous, though it has a much lower C/He ratio (similar to0.1 versus 0.3 for HD 92809). Our study represents the first detailed, chemical model atmosphere analysis for either a B-type supergiant or a Wolf- Rayet (WR) star in Andromeda, and shows the potential of how such studies can provide new information on the chemical evolution of galaxies and the evolution of massive stars in the local Universe.

On the ultracompact nature of 4U 1822-000

We report the discovery of a periodic modulation in the optical lightcurve of the candidate ultracompact X-ray binary 4U 1822-000. Using time-resolved optical photometry taken with the William Herschel Telescope we find evidence for a sinusoidal modulation with a semi-amplitude of 8 per cent and a period of 191 min, which is most likely close to the true orbital period of the binary. Using the van Paradijs & McClintock relation for the absolute magnitude and the distance modulus allowing for interstellar reddening, we estimate the distance to 4U 1822-000 to be 6.3 kpc. The long orbital period casts severe doubts on the ultracompact nature of 4U 1822-000.

Analysis of Temporal Compression Characteristics using Active Phase conjugation in systems with multiple antenna elements

In this paper we give first account of a simple analysis tool for modeling temporal compression for automatic mitigation of multipath induced intersymbol interference through the use of active phase conjugation (APC) technique. The temporal compression characteristics of an APC system is analyzed using a simple discrete channel model, and numerical results are provided to justify the theoretical findings.

Ultimate lateral load resistance of laterally loaded pile

Several methods are available for predicting ultimate lateral load resistance of laterally loaded pile. These methods often produce significantly different ultimate lateral resistance. This makes it difficult to select an appropriate method in designing/predicting ultimate lateral resistance of pile. This paper presents a review of two different methods; Meyerh of and Patra & Pise for predicting lateral resistance of pile. Then, the predicted ultimate lateral resistances by these two methods are compared with the experimental results. It is found that Meyerhof's method gives better prediction for single pile with smaller L/d ratio whereas Patra & Pise method gives better predictions for pile groups with higher L/d. Thus, none of these methods can be applicable universally for all possible conditions. Also the parametric study on ultimate lateral resistance revealed that length to diameter ratio, pile spacing, pile configuration in a pile group are important parameters for prediction of lateral load resistance. © 2009 Taylor & Francis Group.

Morphology and compression behaviour of biodegradable scaffolds produced by the sintering process

Porous poly(L-lactic acid) (PLA) scaffolds of 85 per cent and 90 per cent porosity are prepared using polymer sintering and porogen leaching method. Different weight fractions of 10 per cent, 30 per cent, and 50 per cent of hydroxyapatite (HA) are added to the PLA to control the acidity and degradation rate. The three-dimensional (3D) morphology and surface porosity are tested using micro-computer tomography (micro-CT), optical microscopy, and scanning electron microscopy (SEM). Results indicate that the surface porosity does not change on the addition of HA. The micro-CT examinations show a slight decrease in the pore size and increase in the wall thickness accompanied by reduced anisotropy for the scaffolds containing HA. Scanning electron micrographs show detectable interconnected pores for the scaffold with pure PLA. Addition of the HA results in agglomeration of the HA particles and reduced leaching of the porogen. Compression tests of the scaffold identify three stages in the stress-strain curve. The addition of HA results in a reduction in the modulus of the scaffold at the first stage of elastic bending of the wall, but this is reversed for the second and third stages of collapse of the wall and densification in the compression tests. In the scaffolds with 85 per cent porosity, the addition of a high percentage of HA could result in 70 per cent decrease in stiffness in the first stage, 200 per cent increase in stiffness in the second stage, and 20 per cent increase in stiffness in the third stage. The results of these tests are compared with the Gibson cellular material model that is proposed for prediction of the behaviour of cellular material under compression. The pH and molecular weight changes are tracked for the scaffolds within a period of 35 days. The addition of HA keeps the pH in the alkaline region, which results in higher rate of degradation at an early period of observation, followed by a reduced rate of degradation later in the process. The final molecular weight is higher for the scaffolds with HA than for scaffolds of pure PLA. The manufactured scaffolds offer acceptable properties in terms of the pore size range and interconnectivity of the pores and porosity for non-load-bearing bone graft substitute; however, improvement to the mixing of the phases of PLA and HA is required to achieve better integrity of the composite scaffolds. © 2008 IMechE.

Finite element modelling of FRP-to-concrete bond behaviour using the concrete damage plasticity theory combined with a plastic degradation model

The technique of externally bonding fibre reinforced polymer (FRP) composites has been becoming popular worldwide for retrofitting existing reinforced concrete (RC) structures. A major failure mode in such strengthened structures is the debonding of FRP from the concrete substrate. The bond behaviour between FRP and concrete thus plays a crucial role in these structures. The FRP-to-concrete bond behaviour has been extensively investigated experimentally, commonly using the pull-off test of FRP-to-concrete bonded joint. Comparatively, much less research has been concerned with the numerical simulation of this bond behaviour, chiefly due to difficulties in accurately modelling the complex behaviour of concrete. This paper proposes a robust finite element (FE) model for simulating the bond behaviour in the entire loading process in the pull-off test. A concrete damage plasticity model based on the plastic degradation theory is proposed to overcome the weakness of the elastic degradation theory which has been commonly adopted in previous studies. The model produces results in very close agreement with test data. © Tsinghua University Press, Beijing and Springer-Verlag Berlin Heidelberg 2011.

Examining architects' performance in Nigeria private and public sectors building projects

Abstract: Purpose – The aim of this paper is to examine and compare the performance of architects with respect to clients' rating of importance over a set of performance criteria in Nigerian public and private sector building projects. Design/methodology/approach – A survey involving clients from both public and private sectors of recently completed building projects in Nigeria was undertaken. Data analysis includes comparing similarities and differences using standardised ratio, Mann Whitney U and Wilcoxon tests. Findings – The results show that private sector clients are likely to be more concerned with cost, while public sector clients are more concerned with buildability of design. A total of 79 per cent of the criteria were similarly selected by both sectors with respect to importance of the criteria. Architects need to improve their performance significantly in about 82 per cent of the whole set of 28 criteria. The architects performed better in the public sector than the private sector and 14 per cent of the criteria were indicated as being statistically different in terms of architects' performance. Originality/value – The results provide feedback which can be incorporated in architects' future projects so as to ensure successful project implementation in the building delivery process.