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

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

Regression based principal component analysis for sparse functional data with applications to screening pubertal growth paths

Pediatric growth paths are smooth trajectories of body-size measurements (e.g. height or weight). They are observed at irregular times due to individual needs. It is clinically important to screen such growth paths. However rigorous quantitative methods are largely missing in the literature. In the first part of this dissertation, we proposed a new screening method based on principal component analysis for growth paths (sparse functional data). An estimation algorithm using alternating regressions is developed, and the resulting component functions are shown to be uniformly consistent. The proposed method does not require any distributional assumptions, and is also computationally feasible. It is then applied to monitor the puberty growth among a group of Finnish teenagers, and yields interesting insights. A Monte-Carlo study is conducted to investigate the performance of our proposed algorithm, with comparison to existing methods. In the second part of the dissertation, the proposed screening method is further extended to incorporate subject level covariates, such as parental information. When it is applied to the same group of Finnish teens, it shows enhanced screening performance in identifying possible abnormal growth paths. Simulation studies are also conducted to validate the proposed covariate adjusted method

Experimental and CFD Simulation of a Multiphase Canned Motor Pump

Canned motor pumps are well suited for pumping hazardous and radioactive fluids due to their compact design and low maintenance cost. However, their application on artificial lift has not been investigated yet. ESP (Electric Submersible Pump) has been used as an artificial lift method for pumping high volume flow rate in deep wells. However, due to its seal leaking and bearing abrasive problems, pump performance is deteriorated during operation. This work investigated utilizing a canned motor pump instead of ESP in downhole application. The performance of a canned motor pump under multiphase flow was studied experimentally and computationally. A canned motor pump demonstrator manufactured by Curtiss-Wright EMD was installed in the pump test loop built at Turbomachinery Laboratory at Texas A&M University. The water baseline performance test and multiphase flow (water/air) test was performed. GVF (Gas Volume Fraction) in pump stator jacket was varied from 0% to 20%, and the pump speed varied from 2000 RPM to 3930 RPM. The pump’s performance at these flow conditions was recorded and learned. The air inside the bearing house and rotor-stator annulus causes cooling and lubrication problems for normal pump operation. The air distribution of the secondary circulation flow inside the pump is the main concern. Thus, multiphase flow inside the pump was simulated with CFD commercial code, ANSYS Fluent. Different GVF with different water flow rate was simulated. Also, pressure at flow region outlet and bubble diameter effect were also simulated. Flow rate distribution trend predicted by CFD method is validated by experimental test results. Impedance probe was designed and built to measure multiphase flow in a pipe. The GVF is the main calibrated parameter. The fluid’s dimensionless admittance was found to have linear correlation with GVF. The phase of CPSD from probe’s signal is a promising calibration tool for the future probe application

Experimental and CFD Simulation of a Multiphase Canned Motor Pump

Canned motor pumps are well suited for pumping hazardous and radioactive fluids due to their compact design and low maintenance cost. However, their application on artificial lift has not been investigated yet. ESP (Electric Submersible Pump) has been used as an artificial lift method for pumping high volume flow rate in deep wells. However, due to its seal leaking and bearing abrasive problems, pump performance is deteriorated during operation. This work investigated utilizing a canned motor pump instead of ESP in downhole application. The performance of a canned motor pump under multiphase flow was studied experimentally and computationally. A canned motor pump demonstrator manufactured by Curtiss-Wright EMD was installed in the pump test loop built at Turbomachinery Laboratory at Texas A&M University. The water baseline performance test and multiphase flow (water/air) test was performed. GVF (Gas Volume Fraction) in pump stator jacket was varied from 0% to 20%, and the pump speed varied from 2000 RPM to 3930 RPM. The pump’s performance at these flow conditions was recorded and learned. The air inside the bearing house and rotor-stator annulus causes cooling and lubrication problems for normal pump operation. The air distribution of the secondary circulation flow inside the pump is the main concern. Thus, multiphase flow inside the pump was simulated with CFD commercial code, ANSYS Fluent. Different GVF with different water flow rate was simulated. Also, pressure at flow region outlet and bubble diameter effect were also simulated. Flow rate distribution trend predicted by CFD method is validated by experimental test results. Impedance probe was designed and built to measure multiphase flow in a pipe. The GVF is the main calibrated parameter. The fluid’s dimensionless admittance was found to have linear correlation with GVF. The phase of CPSD from probe’s signal is a promising calibration tool for the future probe application

Automorphisms of surfaces of general type with q>=2 acting trivially in cohomology

A compact complex manifold X is said to be rationally cohomologically rigidified if its automorphism group Aut(X) acts faithfully on the cohomology ring H*(X,Q). In this note, we prove that, surfaces of general type with irregularity q>2 are rationally cohomologically rigidified, and so are minimal surfaces S with q=2 unless K^2=8X. This answers a question of Fabrizio Catanese in part. As examples we give a complete classification of surfaces isogenous to a product with q=2 that are not rationally cohomologically rigidified. These surfaces turn out however to be rigidified.Comment: 18 pages; a remark and a closely relevant reference are adde

An apparent positive relation between spin and orbital angular momentum in X-ray binaries

The origin of current angular momentum (AM) of the black hole (BH) in X-ray binary (XRB) is still unclear, which is related with the birth and/or the growth of the BH. Here we collect the spin parameters $a_{*}$ measured in BH XRBs and find an apparent bimodal distribution centered at $\sim$ 0.17 and 0.83. We find a positive relation between the spin parameter and the orbital period/orbital separation through combining distinct XRB categories, including neutron star (NS) low-mass X-ray binaries (LMXBs), Roche-lobe overflow (RLOF) BH XRBs and wind-fed BH XRBs. It seems that the AM of the compact star and the binary orbit correlates by combining the different XRB systems. These positive relations imply that accretion process is a common mechanism for spinning up the compact star in these diverse XRB systems. We infer that the low and high spin BH XRBs may experience different evolution and accretion history, which corresponds to the bimodal distribution of the BH spin parameters. The low spin BHs ($a_{*}<0.3$) are similar to the NS LMXBs, the compact star of which is spun-up by the low-level accretion, and the high spin BHs ($a_{*}>0.5$) had experienced a short hypercritical accretion ($\gg \dot{M}_\mathrm{Edd}$) period, during which, the BH spin dramatically increased.Comment: 13 pages, 7 figures, accepted for publication in MNRA