Low frequency QPOs and possible change in the accretion geometry during the outbursts of Aquila X−-1

We have studied the evolution of the Low Frequency Quasi-Periodic Oscillations (LFQPOs) during the rising phase of seven outbursts of the neutron star Soft X-ray Transient (SXT) Aql X$-$1 observed with the \textit{Rossi X-ray Timing Explorer (RXTE)}. The frequency correlation between the low frequency break and the LFQPO sampled on the time scale of $\sim$2 days was seen. Except for the peculiar 2001 outburst, the frequency of the LFQPOs increased with time before the hard-to-soft state transition up to a maximum $\nu_{max}$ at $\sim$31 Hz, a factor of $\sim$5 higher than those seen in black hole transients such as GX 339$-$4, making the maximum QPO frequency a likely indicator of the mass of the central compact object. The characteristic frequencies increased by around ten percent per day in the early rising phase and accelerated to nearly one hundred percent per day since $\sim$2 days before the hard-to-soft state transition. We examined the dependence of the frequency $\nu_{LF}$ on the source flux $f$ and found an anti-correlation between the maximum frequency of the LFQPOs and the corresponding X-ray luminosity of the hard-to-soft transition (or outburst peak luminosity) among the outbursts. We suggest that X-ray evaporation process can not be the only mechanism that drives the variation of the inner disk radius if either of the twin kHz QPO corresponds to the Keplerian frequency at the truncation radius.Comment: 8 pages, 8 figures, 1 table; accepted for publication in Ap

Energy dependent power spectral states and origin of aperiodic variability in black hole binaries

We found the black hole candidate MAXI J1659-152 showed distinct power spectra, i.e., a power-law noise (PLN) vs. band-limited noise (BLN) plus quasi-periodic oscillations (QPOs), below and above about 2 keV respectively, in the observations with the Swift and the RXTE during the 2010 outburst, indicating a high energy cut-off of the PLN and a low energy cut-off of the BLN and the QPOs around 2 keV. The emergence of the PLN and the fading of the BLN and the QPOs initially took place from below 2 keV when the source entered the hard intermediate state and finally settled in the soft state three weeks later. The evolution was accompanied by the emergence of the disk spectral component and decreases in the amplitudes of variability in the soft X-ray and the hard X-ray bands. Our results indicate that the PLN is associated with the optically thick disk in both hard and intermediate states, and power spectral state is independent of the X-ray energy spectral state in a broadband view. We suggest that in the hard and the intermediate state, the BLN and the QPOs emerge from the innermost hot flow subjected to Comptonization, while the PLN originates from the optically thick disk further out. The energy cut-offs of the PLN and the BLN or QPOs then follow the temperature of the seed photons from the inner edge of the optically thick disk, while the high frequency cut-off of the PLN follows the orbital frequency at the inner edge of the optically thick disk as well.Comment: 5 pages, 6 figures, accepted for publication in Ap

Cyclic best first search in branch-and-bound algorithms

In this dissertation, we study the application of a search strategy called cyclic best first search (CBFS) in branch-and-bound (B&B) algorithms. First, we solve a one machine scheduling problem with release and delivery times with the minimum makespan objective with a B&B algorithm using a variant of CBFS called CBFS-depth and a modified heuristic for finding feasible schedules. Second, we investigate the conditions of the search trees that may lead to CBFS-depth outperforming BFS in terms of the average number of nodes explored to prove optimality. Finally, we present a B&B algorithm using CBFS for a close-enough traveling salesman problem that demonstrates the benefit of using CBFS even if it does not improve the number of nodes explored to prove optimality. Overall, we show that using CBFS has a number of advantages to the performance of a B&B algorithm in comparison to the other search strategies given the right problems

Leading Indicators of Business Cycles in Malaysia and the Philippines

This paper attempts to construct leading indicator systems for the Malaysian and Philippine economies using publicly available economic and financial data, with a view to predicting turning points of growth cycles in the two countries. The results show that during the sample period of January 1981-March 2002, the composite leading index constructed from six individual leading indicators is able to predict all the nine turning points in industrial production in Malaysia, with an average signal leading time of 1.5 months for peaks and 3.4 months for troughs; and seven out of the eight turning points in manufacturing production in the Philippines, with an average signal lead time of 5.8 months for peaks and 6 months for troughs. This prediction performance is comparable to that of leading indicator systems of the G-7 economies maintained by the Organisation for Economic Co-operation and Development

A comparative study on space configuration in Japanese and Chinese gardens : By analyzing visibility and permeability of Shoin-style gardens in Kyoto and private gardens in Suzhou

早稲田大学博士(建築学)早大学位記番号:新9513doctoral thesi