A decades-long fast-rise-exponential-decay flare in low-luminosity AGN NGC 7213

We analysed the four-decades-long X-ray light curve of the low-luminosity active galactic nucleus (LLAGN) NGC 7213 and discovered a fast-rise-exponential-decay (FRED) pattern, i.e. the X-ray luminosity increased by a factor of $\approx 4$ within 200d, and then decreased exponentially with an $e$-folding time $\approx 8116$d ($\approx 22.2$ yr). For the theoretical understanding of the observations, we examined three variability models proposed in the literature: the thermal-viscous disc instability model, the radiation pressure instability model, and the tidal disruption event (TDE) model. We find that a delayed tidal disruption of a main-sequence star is most favourable; either the thermal-viscous disk instability model or radiation pressure instability model fails to explain some key properties observed, thus we argue them unlikely.Comment: Accepted for publication in MNRAS, updated version after proof correction

Design and stability analysis of high performance packet switches

With the rapid development of optical interconnection technology, high-performance packet switches are required to resolve contentions in a fast manner to satisfy the demand for high throughput and high speed rates. Combined input-crosspoint buffered (CICB) switches are an alternative to input-buffered (IB) packet switches to provide high-performance switching and to relax arbitration timing for packet switches with high-speed ports. A maximum weight matching (MWM) scheme can provide 100% throughput under admissible traffic for lB switches. However, the high complexity of MWM prohibits its implementation in high-speed switches. In this dissertation, a feedback-based arbitration scheme for CICB switches is studied, where cell selection is based on the provided service to virtual output queues (VOQs). The feedback-based scheme is named round-robin with adaptable frame size (RR-AF) arbitration. The frame size in RR-AF is adaptably changed by the serviced and unserviced traffic. If a switch is stable, the switch provides 100% throughput. Here, it is proved that RR-AF can achieve 100% throughput under uniform admissible traffic. Switches with crosspoint buffers need to consider the transmission delays, or round-trip times to define the crosspoint buffer size. As the buffered crossbar switch can be physically located far from the input ports, actual round-trip times can be non-negligible. To support non-negligible round-trip times in a buffered crossbar switch, the crosspoint buffer size needs to be increased. To satisfy this demand, this dissertation investigates how to select the crosspoint buffer size under non-negligible round trip times and under uniform traffic. With the analysis of stability margin, the relationship between the crosspoint buffer size and round-trip time is derived. Considering that CICB switches deliver higher performance than lB switches and require no speedup, this dissertation investigates the maximum throughput performance that these switches can achieve. It is shown that CICB switches without speedup achieve 100% throughput under any admissible traffic through a fluid model. In addition, a new hybrid scheme, based on longest queue-first (as input arbitration) and longest column occupancy first (as output arbitration) is proposed, which achieves 100% throughput under uniform and non-uniform traffic patterns. In order to give a better insight of the feedback nature of arbitration scheme for CICB switches, a frame-based round-robin arbitration scheme with explicit feedback control (FRE) is introduced. FRE dynamically sets the frame size according to the input load and to the accumulation of cells in a VOQ. FRE is used as the input arbitration scheme and it is combined with RR, PRR, and FRE as output arbitration schemes. These combined schemes deliver high performance under uniform and nonuniform traffic models using a buffered crossbar with one-cell crosspoint buffers. The novelty of FRE lies in that each VOQ sets the frame size by an adjustable parameter, Δ(i,j) which indicates the degree of service needed by VOQ(i, j). This value is adjusted according to the input loading and the accumulation of cells experienced in previous service cycles. This dissertation also explores an analysis technique based on feedback control theory. This methodology is proposed to study the stability of arbitration and matching schemes for packet switches. A continuous system is used and a control model is used to emulate a queuing system. The technique is applied to a matching scheme. In addition, the study shows that the dwell time, which is defined as the time a queue receives service in a service opportunity, is a factor that affects the stability of a queuing system. This feedback control model is an alternative approach to evaluate the stability of arbitration and matching schemes

Microtremor recordings in Northern Mississippi: Evaluating site effect and correlating with wave climate

Site effects is considered as one of the main reasons that cause enormous damages in earthquakes and it is mainly controlled by the local geological condition. The main research area, Northern Mississippi, is located in Mississippi Embayment (ME) where is mainly composed of unconsolidated sediments which can be as thick as 1400m along the Mississippi River floodplain, and is favorable to have significant site effects. Meanwhile Northern Mississippi is also located in the moderate to heavy potential damage area of the New Madrid Seismic Zone, which is in the northern section of ME. Therefore, it is very necessary to evaluate the site effect in Northern Mississippi area in order to prepare for the earthquake. In this research, microtremor recordings are used to evaluate the site effects. A total of 14 continuous long-term microtremor recordings (LTRs), each lasting at least 6 hours, at 8 selected locations in Mississippi (MS), Louisiana (LA) and Alabama (AL) states, and a large number (305) of systematic single-point short-term recordings (STRs), each lasting 15-30 minutes, in Northern Mississippi area are collected using a LE-3D/20s seismometer with Eigen-frequency of 0.05Hz and RefTek 130-01/3 data logger with a sampling rate of 100Hz. With these recordings, the horizontal to vertical spectral ratio (HVSR) method is applied to find the predominant frequency (f0) and roughly estimate amplification factor as HVSR value at f0 (HVSR@f0). Within Northern Mississippi area, the f0 is tightly correlated with unconsolidated sediments thickness (UST) and average shear wave velocity (Vs) are also estimated. Within the low frequency range (\u3c0.2Hz), high HVSRs are observed in most LTRs and STRs, which is possibly caused by the wind either directly blow on the seismometer or on the buildings around the recording location, or human’s activities. The spectra of these recordings all show high power spectral density (PSD) energy level at frequency of around 0.2Hz, which is known as double-frequency peak based on observations on ocean bottom. By correlating the PSD level at DF peaks (PSD@fp) of LTRs with the simultaneous ocean data (significant ocean wave frequency, significant ocean wave height, wind speed, and atmosphere pressure) of Atlantic Ocean and Gulf of Mexico as well as the local wind speed and atmosphere pressure, it is concluded that the DF peaks observed in Northern Mississippi are combined impact of wave climate in both Atlantic Ocean and Gulf of Mexico. The particle motion analysis and calculation of vibration angle strengthen this conclusion. The plots of DFs and PSD@fp of STRs vs. UST in horizontal plane are significantly different from the plots in vertical direction, which indicated that the shear wave resonance in thick sediments modifies the DF microseism more obviously in horizontal direction than in vertical direction. From this research in Northern Mississippi, it can be observed that the predominant frequency of the area where UST \u3e 200m are within DF range, and it can be concluded that DF microseisms are strongly influenced by ocean activities. Therefore, the possible influence from ocean activities on the estimation of f0 and amplification factor using HVSR method is examined by correlating the HVSR@f0 to the ocean wave climate (significant wave height, wind speed and atmosphere pressure) and projecting the microtremor spatial spectral vectors on stereographic net. These analysis show that the estimation of f0 value is not related to either the vibration direction or the energy level of the ocean wave, but the HVSR@f0 values are significantly affected by the energy level of ocean wave climate. To improve the estimation of amplification factor, a modified HVSR method is proposed, with which, a more reliable amplification factor is obtained by calculating the average spatial spectral vector based on the stereographic projection method. Three main strong conclusions can be drawn from this research: 1) the HVSR method is a fast and reliable method to estimate the predominant frequency; 2) the double-frequency microseism in northern Mississippi is a combined impact of both Atlantic Ocean and Gulf of Mexico; and 3) the estimated amplification factor by HVSR method should be modified according to the microtremor recording condition especially the noise level at around predominant frequency

Lonliness of Older Adults in Rural China

This study examined factors that influenced loneliness among rural elders in China. Data were collected from the latest wave of Living and Employment of Population Survey in 2005 (provided by Renmin University, China). The sample of this survey consisted of 284 rural elders in China. T‐tests was used to examine the influence of gender, marital status, health, financial support, and living arrangements differences in loneliness perception among Chinese rural elders. Multiple regression analysis was conducted to understand the influences of age and socio‐economic status on loneliness among the rural elders. This study provided insights for a better understanding of individual, social, and familial factors that influenced subjective loneliness in later life. Findings from this study might contribute to policymaking decisions regarding improvements of psychological well‐being among older adults in China

中国の大学スポーツ研究 : 三つの時期における大学スポーツの展開、再構築および発展の検討

早大学位記番号:新6516早稲田大

Probabilistic approaches to the design of wireless ad hoc and sensor networks

The emerging wireless technologies has made ubiquitous wireless access a reality and enabled wireless systems to support a large variety of applications. Since the wireless self-configuring networks do not require infrastructure and promise greater flexibility and better coverage, wireless ad hoc and sensor networks have been under intensive research. It is believed that wireless ad hoc and sensor networks can become as important as the Internet. Just as the Internet allows access to digital information anywhere, ad hoc and sensor networks will provide remote interaction with the physical world. Dynamics of the object distribution is one of the most important features of the wireless ad hoc and sensor networks. This dissertation deals with several interesting estimation and optimization problems on the dynamical features of ad hoc and sensor networks. Many demands in application, such as reliability, power efficiency and sensor deployment, of wireless ad hoc and sensor network can be improved by mobility estimation and/or prediction. In this dissertation, we study several random mobility models, present a mobility prediction methodology, which relies on the analysis of the moving patterns of the mobile objects. Through estimating the future movement of objects and analyzing the tradeoff between the estimation cost and the quality of reliability, the optimization of tracking interval for sensor networks is presented. Based on the observation on the location and movement of objects, an optimal sensor placement algorithm is proposed by adaptively learn the dynamical object distribution. Moreover, dynamical boundary of mass objects monitored in a sensor network can be estimated based on the unsupervised learning of the distribution density of objects. In order to provide an accurate estimation of mobile objects, we first study several popular mobility models. Based on these models, we present some mobility prediction algorithms accordingly, which are capable of predicting the moving trajectory of objects in the future. In wireless self-configuring networks, an accurate estimation algorithm allows for improving the link reliability, power efficiency, reducing the traffic delay and optimizing the sensor deployment. The effects of estimation accuracy on the reliability and the power consumption have been studied and analyzed. A new methodology is proposed to optimize the reliability and power efficiency by balancing the trade-off between the quality of performance and estimation cost. By estimating and predicting the mass objects\u27 location and movement, the proposed sensor placement algorithm demonstrates a siguificant improvement on the detection of mass objects with nearmaximal detection accuracy. Quantitative analysis on the effects of mobility estimation and prediction on the accuracy of detection by sensor networks can be conducted with recursive EM algorithms. The future work includes the deployment of the proposed concepts and algorithms into real-world ad hoc and sensor networks