Timing Features of the Accretion--driven Millisecond X-Ray Pulsar XTE J1807--294 in 2003 March Outburst

In order to probe the activity of the inner disk flow and its effect on the neutron star surface emissions, we carried out the timing analysis of the Rossi X-Ray Timing Explorer (RXTE) observations of the millisecond X-ray pulsar XTE J1807--294, focusing on its correlated behaviors in X-ray intensities, hardness ratios, pulse profiles and power density spectra. The source was observed to have a serial of broad "puny" flares on a timescale of hours to days on the top of a decaying outburst in March 2003. In the flares, the spectra are softened and the pulse profiles become more sinusoidal. The frequency of kilohertz quasi-periodic oscillation (kHz QPO) is found to be positively related to the X-ray count rate in the flares. These features observed in the flares could be due to the accreting flow inhomogeneities. It is noticed that the fractional pulse amplitude increases with the flare intensities in a range of $\sim 2$, comparable to those observed in the thermonuclear bursts of the millisecond X-ray pulsar XTE J1814--338, whereas it remains at about 6.5% in the normal state. Such a significant variation of the pulse profile in the "puny" flares may reflect the changes of physical parameters in the inner disk accretion region. Furthermore, we noticed an overall positive correlation between the kHz QPO frequency and the fractional pulse amplitude, which could be the first evidence representing that the neutron-star surface emission properties are very sensitive to the disk flow inhomogeneities. This effect should be cautiously considered in the burst oscillation studies.Comment: Accepted by ApJ, 23 pages, 7 figures, 3 table

Market concentration, risk-taking, and bank performance: evidence from emerging economies

This paper investigates the relationship between market concentration, risk-taking, and bank performance using a unique dataset of the BRIC banks over the period 2003-2010. We find a negative association between market concentration and performance, in support of the “quiet life” hypothesis. We also find that banks taking a lower level of risks perform better, in favour of prudential practice. Moreover, the BRICs’ banking sectors were all negatively affected by the 2007-2008 global financial crisis with China and Russia being the least and most affected, respectively. On average Chinese and Brazilian banks outperform Indian and Russian ones, indicating that China and Brazil have more favourable institutional infrastructure. These results are robust to alternative model specifications and estimation techniques. Our analysis may have important policy implications for bankers and regulators in the BRICs and other developing and transition countries

On the Integrability, B\"Acklund Transformation and Symmetry Aspects of a Generalized Fisher Type Nonlinear Reaction-Diffusion Equation

The dynamics of nonlinear reaction-diffusion systems is dominated by the onset of patterns and Fisher equation is considered to be a prototype of such diffusive equations. Here we investigate the integrability properties of a generalized Fisher equation in both (1+1) and (2+1) dimensions. A Painlev\'e singularity structure analysis singles out a special case ($m=2$) as integrable. More interestingly, a B\"acklund transformation is shown to give rise to a linearizing transformation for the integrable case. A Lie symmetry analysis again separates out the same $m=2$ case as the integrable one and hence we report several physically interesting solutions via similarity reductions. Thus we give a group theoretical interpretation for the system under study. Explicit and numerical solutions for specific cases of nonintegrable systems are also given. In particular, the system is found to exhibit different types of travelling wave solutions and patterns, static structures and localized structures. Besides the Lie symmetry analysis, nonclassical and generalized conditional symmetry analysis are also carried out.Comment: 30 pages, 10 figures, to appear in Int. J. Bifur. Chaos (2004

A new array design using tunable loop microstrip (TLM) coil

A new array, tunable loop microstrip (TLM) array for MRI has been developed. The theoretical analysis of decoupling of a 2-element TLM array is based on microstrip theory. The experiments of comparison between the TLM array and a conventional loop array show that TLM array has great decoupling performance. This effectiveness is further demonstrated by 1.5T cardiac images. Thus, without overlap of array elements TLM array will be particularly useful for parallel imaging applications.published_or_final_versio

Potential Advantage of High Modes of Birdcage for Parallel Imaging

The potential advantage of using high modes of a 12-rung birdcage coil for parallel imaging has been investigated. When 11 modes are incorporated, the acceleration factor can be up to 5 with average g-factor within 2. For certain number of channels, the optimized combination of corresponding modes can be obtained.published_or_final_versio

Optimal Utilization of Acquired k-space points for GRAPPA reconstruction

The generalized approach to parallel MRI has indicated that the utilization of acquired k-space points for GRAPPA reconstruction can be more flexible, including the points in frequency encoding direction. To investigate the optimal utilization of acquired k-space points in GRAPPA, the neighbor GRAPPA which incorporates several neighbor points to estimate each missing point is compared with the conventional GRAPPA by simulations and experiments. It is discovered that the optimal reconstruction scheme should depend on the geometry of the receive coil array and the orientation of FOV.published_or_final_versio

MaaSim: A Liveability Simulation for Improving the Quality of Life in Cities

Urbanism is no longer planned on paper thanks to powerful models and 3D simulation platforms. However, current work is not open to the public and lacks an optimisation agent that could help in decision making. This paper describes the creation of an open-source simulation based on an existing Dutch liveability score with a built-in AI module. Features are selected using feature engineering and Random Forests. Then, a modified scoring function is built based on the former liveability classes. The score is predicted using Random Forest for regression and achieved a recall of 0.83 with 10-fold cross-validation. Afterwards, Exploratory Factor Analysis is applied to select the actions present in the model. The resulting indicators are divided into 5 groups, and 12 actions are generated. The performance of four optimisation algorithms is compared, namely NSGA-II, PAES, SPEA2 and eps-MOEA, on three established criteria of quality: cardinality, the spread of the solutions, spacing, and the resulting score and number of turns. Although all four algorithms show different strengths, eps-MOEA is selected to be the most suitable for this problem. Ultimately, the simulation incorporates the model and the selected AI module in a GUI written in the Kivy framework for Python. Tests performed on users show positive responses and encourage further initiatives towards joining technology and public applications.Comment: 16 page