Burst Tails from SGR J1550-5418 Observed with Rossi X-ray Timing Explorer

We present the results of our extensive search using the Bayesian block method for long tails following short bursts from a magnetar, SGR J1550-5418, over all RXTE observations of the source. We identified four bursts with extended tails, most of which occurred during its 2009 burst active episode. The durations of tails range between ~13 s and over 3 ks, which are much longer than the typical duration of bursts. We performed detailed spectral and temporal analysis of the burst tails. We find that the spectra of three tails show a thermal nature with a trend of cooling throughout the tail. We compare the results of our investigations with the properties of four other extended tails detected from SGR 1900+14 and SGR 1806-20 and suggest a scenario for the origin of the tail in the framework of the magnetar model.Comment: 10 pages, 7 figures, 4 tables, accepted for publication in Ap

A glitch and an anti-glitch in the anomalous X-ray pulsar 1E 1841-045

We investigated the long-term spin properties of the anomalous X-ray pulsar (AXP) 1E 1841-045 by performing a temporal analysis of archival RXTE observations spanning about 5.2 yr from 2006 September to 2011 December. We identified two peculiar timing anomalies within ~1 yr of each other: a glitch with Delta(nu)/nu ~ 4.8 x 10^{-6} near MJD 54303; and an anti-glitch with Delta(nu)/nu ~ -5.8 x 10^{-7} near MJD 54656. The glitch that we identified, which is the fourth glitch seen in this source in the 13 yr of RXTE monitoring, is similar to the last two detected glitches. The anti-glitch from 1E 1841-045, however, is the first to be identified. The amplitude of the anti-glitch was comparable with that recently observed in AXP 1E 2259+586. We found no significant variations in the pulsed X-ray output of the source during either the glitch or the anti-glitch. We discuss our results in relation to the standard pulsar glitch mechanisms for the glitch, and to plausible magnetospheric scenarios for the anti-glitch.Comment: 6 pages, 3 figures, 3 tables, published in MNRA

Yapıların deprem davranışlarının iyileştirilmesi için çelik çapraz elemanların optimum yerleşimi

The different rehabilitation systems have been used to upgrade the seismic response of the structures. Common rehabilitation techniques were based on two basic approximations; to rehabilitate with adding new elements such as steel bracing and shear walls or to upgrade with selectively strengthening the deficient structural elements of the buildings. In this study, the optimal placement of X steel braces is presented for a planar building frame. The optimal placement is defined as the optimal size and location of the braces. Steady state response of the structure evaluated first undamped natural frequency is defined transfer functions that are independent on initial values and input excitation. The objective functions are chosen as the transfer function amplitude of the top displacement and the transfer function amplitude of the base shear force evaluated at the undamped fundamental natural frequency of the structure. In the optimization procedure, the stiffness parameters of the added braces are defined as the design variables. Principal optimality criteria are derived using Lagrange Multipliers Procedure. Obtained nonlinear equations are solved with "Steepest Direction Search" algorithm. Sensitivities of the objective function are derived analytically. A simplified algorithm for the state of the base shear force as objective function is shown. The response of the structure is investigated both the transfer function amplitude and the time history analysis values under El Centro earthquake forces.  Keywords: Transfer function, earthquake behavior, structure optimization, rehabilitation of structure.Bu çalışmada, düzlem çerçeveler için X tipi çelik diyagonallerin optimum yerleşimi gösterildi. Optimum yerleşim diyagonallerin optimum yer ve büyüklükleri tanımlandı. Birinci mod etkisindeki kararlı yapısal davranış, başlangıç durumlarından ve giriş hareketinden bağımsız olan transfer fonksiyonları ile ifade edildi. Amaç fonksiyonları yapının birinci moduna karşı gelen transfer fonksiyonu tepe deplasmanı ve taban kesme kuvveti olarak seçildi. Optimizasyon yönteminde, tasarım değişkenleri olarak  eklenen diyagonallere ait olan rijitlik parametreleri tanımlandı. Lagrange çarpanları yöntemi kullanılarak optimumluk kriterleri türetildi. Ortaya çıkan doğrusal olmayan denklem takımı en dik yön algoritması (Steepest Direction Search Algorithm) ile çözüldü. Yapının davranışı hem transfer fonksiyonlarına bağlı olarak hem de El Centro deprem kuvvetleri altında araştırıldı.  Anahtar Kelimeler: Transfer fonksiyonu, deprem davranışı, yapı optimizasyonu, yapı iyileştirmesi

On the efficacy of a novel optimized tuned mass damper for minimizing dynamic responses of cantilever beams

This study examines the optimal design of a tuned mass damper (TMD) in the frequency domain so that the dynamic response of cantilever beams can be decreased. Random vibration theory is applied to identify the mean square acceleration of the endpoint of a cantilever beam as the objective function to be reduced. In addition, to determine the optimal TMD coefficient of mass, stiffness, and damping, a differential evolution (DE) optimization algorithm is employed. The upper and lower limit values of these parameters are taken into account. A majority of the previous studies have concentrated on determining just the stiffness and damping parameters of TMD. Nonetheless, in this study there is also the optimization of TMD mass parameters to determine the mass quantity. In addition, there has been inefficient use of the stochastic DE optimization algorithm method for the optimization of TMD parameters in previous studies. Hence, to obtain optimal TMD parameters, this algorithm is precisely used on the objective function. Tests are carried out on the cantilever beam with the TMD system following this optimization method with harmonic base excitations that resonate the foremost modes of the beam and white noise excitation. The method proposed here is reasonably practical and successful regarding the optimal TMD design. When a TMD is designed appropriately, the response of the cantilever beam under dynamic interactions undergoes a considerable reduction

A simple damper optimization algorithm for both target added damping ratio and interstorey drift ratio

WOS: 000324814500005A simple damper optimization method is proposed to find optimal damper allocation for shear buildings under both target added damping ratio and interstorey drift ratio (IDR). The damping coefficients of added dampers are considered as design variables. The cost, which is defined as the sum of damping coefficient of added dampers, is minimized under a target added damping ratio and the upper and the lower constraint of the design variables. In the first stage of proposed algorithm, Simulated Annealing, Nelder Mead and Differential Evolution numerical algorithms are used to solve the proposed optimization problem. The candidate optimal design obtained in the first stage is tested in terms of the IDRs using linear time history analyses for a design earthquake in the second stage. If all IDRs are below the allowable level, iteration of the algorithm is stopped; otherwise, the iteration continues increasing the target damping ratio. By this way, a structural response IDR is also taken into consideration using a snap-back test. In this study, the effects of the selection of upper limit for added dampers, the storey mass distribution and the storey stiffness distribution are all investigated in terms of damper distributions, cost function, added damping ratio and IDRs for 6-storey shear building models. The results of the proposed method are compared with two existing methods in the literature. Optimal designs are also compared with uniform designs according to both IDRs and added damping ratios. The numerical results show that the proposed damper optimization method is easy to apply and is efficient to find optimal damper distribution for a target damping ratio and allowable IDR value

Optimal damper placement based on base moment in steel building frames

WOS: 000312753200019A new damper optimization method for finding optimal size and location of the added viscous dampers is proposed based on the elastic base moment in planar steel building frames. A Fourier Transform is applied to the equation of the motion and the transfer function in terms of the fundamental natural frequency of the structures is defined. The transfer function amplitude of the elastic base moment evaluated at the first natural circular frequency of the structure is chosen as a new objective function in the minimization problem. The damper coefficients of the added viscous dampers are taken into consideration as design variables in a steel planar building frame. The transfer function amplitude of the elastic base moment is minimized under an active constraint on the sum of the damper coefficients of the added dampers and the passive constraints on the upper and lower bounds of the added dampers. The optimal damper design presented in this paper is compared with other optimal damper methods based on top displacement, top absolute acceleration and base shear. A ten-storey steel planar building frame is chosen to be rehabilitated with the optimal dampers. The optimal damper allocation is obtained for the transfer function amplitude of the elastic base moment then compared with the other damper optimization methods in terms of the transfer function response. The results of the proposed method show that the method can also be beneficial to decrease both the base moment and the interstorey drift ratios in some frequency regions. (C) 2012 Elsevier Ltd. All rights reserved

Minimum dynamic response of cantilever beams supported by optimal elastic springs

WOS: 000344986300002In this study, optimal distribution of springs which supports a cantilever beam is investigated to minimize two objective functions defined. The optimal size and location of the springs are ascertained to minimize the tip deflection of the cantilever beam. Afterwards, the optimization problem of springs is set up to minimize the tip absolute acceleration of the beam. The Fourier Transform is applied on the equation of motion and the response of the structure is defined in terms of transfer functions. By using any structural mode, the proposed method is applied to find optimal stiffness and location of springs which supports a cantilever beam. The stiffness coefficients of springs are chosen as the design variables. There is an active constraint on the sum of the stiffness coefficients and there are passive constraints on the upper and lower bounds of the stiffness coefficients. Optimality criteria are derived by using the Lagrange Multipliers. Gradient information required for solution of the optimization problem is analytically derived. Optimal designs obtained are compared with the uniform design in terms of frequency responses and time response. Numerical results show that the proposed method is considerably effective to determine optimal stiffness coefficients and locations of the springs. stiffnes

Bandwidth Selection Problem for Nonparametric Regression Model with Right-Censored Data

In this paper, the proposed estimator for the unknown nonparametric regression function is a Nadarya-Watson (Nadarya, 1964; Watson, 1964) type kernel estimator. In this estimation procedure, the censored observations are replaced by synthetic data points based on Kaplan-Meier estimator. As known performance of the kernel estimator depends on the selection of a bandwidth parameter. To get an optimum parameter we have considered six selection methods such as the improved version of Akaike information criterion (AICc), Bayesian information criterion (BIC), generalized cross validation (GCV), risk estimation with classical pilots (RECP), Mallow’s Cp criterion and restricted empirical likelihood (REML), respectively. In addition, we discuss the behavior of the estimators obtained by these selection methods under different configurations of the censoring level and sample sizes. Simulation and real lifetime data results are presented to evaluate and compare the performance of the selection methods. Thus, a optimum criterion is provided for smoothing parameter selection

Design, analysis and real time dynamic torque control of single‐rotor–single‐stator axial flux eddy current brake

This study presents design, analysis and real time dynamic torque control of a single-rotor and single-stator axial flux (AF) eddy current brake (ECB). Design of the AF-ECB is accomplished based on magnetic equivalent circuit (MEC) modelling. Influence of the key design parameters on braking torque including permeability and resistivity of the disc material is also investigated. Braking torque profile of the AF-ECB is obtained by MEC modelling and numerical analyses are carried out by three-dimensional (3D) finite element analysis (FEA) to validate the MEC modelling and to obtain the braking torque profile. 3D magneto-thermal FEA are also completed to identify working period at maximum braking torque. A prototype AF-ECB is manufactured based on the analyses, and open-loop torque profile is experimentally verified. Good agreement between the test, FEA and MEC results is achieved. A real time controller is developed and dynamic torque control of the brake for various torque and speed references is also obtained to illustrate the dynamic behaviours of the system