Journal articles on the topic 'Optimal reverberation time'
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Naylor, Patrick A., Nikolay D. Gaubitch, and Emanuël A. P. Habets. "Signal-Based Performance Evaluation of Dereverberation Algorithms." Journal of Electrical and Computer Engineering 2010 (2010): 1–5. http://dx.doi.org/10.1155/2010/127513.
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We address the measurement of reverberation in terms of the (DRR) in the context of the assessment of dereverberation algorithms for which we wish to quantify the level of reverberation before and after processing. The DRR is normally calculated from the impulse response of the reverberating system. However, several important dereverberation algorithms involve nonlinear and/or time-varying processing and therefore their effect cannot conveniently be represented in terms of modifications to the impulse response of the reverberating system. In such cases, we show that a good estimate of DRR can be obtained from the input/output signals alone using the Signal-to-Reverberant Ratio (SRR) only if the source signal is spectrally white and correctly normalized. We study alternative normalization schemes and conclude by showing a least squares optimal normalization procedure for estimating DRR using signal-based SRR measurement. Simulation results illustrate the accuracy of DRR estimation using SRR.
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Yang, Wonyoung, and Murray Hodgson. "Optimum Reverberation for Speech Intelligibility for Normal and Hearing-Impaired Listeners in Realistic Classrooms Using Auralization." Building Acoustics 14, no. 3 (September 2007): 163–77. http://dx.doi.org/10.1260/135101007781998929.
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The objective of this study was to use auralization techniques to investigate the optimal reverberation for speech intelligibility for normal-hearing and hearing-impaired adult listeners in classrooms with non-diffuse sound fields. This extended a previous study involving rooms with diffuse sound fields to more realistic rooms. Modified Rhyme Test (MRT) signals were auralized in six virtual classroom configurations with different reverberation times. Each classroom contained a speech source, a listener at a receiver position, and a noise source located between the talker and the listener. Two speech- and noise-source output-level differences (0 and +4 dB) were tested. Subjects performed speech-intelligibility tests in the virtual classrooms to identify the reverberation time that gave the best results in each case. For both normal and hearing-impaired listeners, the optimal reverberation time was generally non-zero, and increased with decreased speech-to-noise level difference. Hearing-impaired subjects apparently required more early energy than normal-hearing subjects. The optimal reverberation time for speech intelligibility in classrooms is not necessarily zero, as is commonly believed. The optimal value is generally non-zero, and varies with the room, the locations of the speech and noise sources and the listener, and the noise level.
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Nannariello, Joseph, and Fergus Fricke. "The Prediction of Reverberation Time Using Optimal Neural Networks." Building Acoustics 9, no. 1 (March 2002): 5–28. http://dx.doi.org/10.1260/135101002761035717.
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Schnitta, Bonnie. "Achieving optimal reverberation time in a room, using newly patented tuning tubes." Journal of the Acoustical Society of America 133, no. 5 (May 2013): 3492. http://dx.doi.org/10.1121/1.4806188.
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Kilis, Nikolaos, and Nikolaos Mitianoudis. "A Novel Scheme for Single-Channel Speech Dereverberation." Acoustics 1, no. 3 (September 5, 2019): 711–25. http://dx.doi.org/10.3390/acoustics1030042.
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This paper presents a novel scheme for speech dereverberation. The core of our method is a two-stage single-channel speech enhancement scheme. Degraded speech obtains a sparser representation of the linear prediction residual in the first stage of our proposed scheme by applying orthogonal matching pursuit on overcomplete bases, trained by the K-SVD algorithm. Our method includes an estimation of reverberation and mixing time from a recorded hand clap or a simulated room impulse response, which are used to create a time-domain envelope. Late reverberation is suppressed at the second stage by estimating its energy from the previous envelope and removed with spectral subtraction. Further speech enhancement is applied on minimizing the background noise, based on optimal smoothing and minimum statistics. Experimental results indicate favorable quality, compared to two state-of-the-art methods, especially in real reverberant environments with increased reverberation and background noise.
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Chen, Min, and Chang-Myung Lee. "De-Noising Process in Room Impulse Response with Generalized Spectral Subtraction." Applied Sciences 11, no. 15 (July 26, 2021): 6858. http://dx.doi.org/10.3390/app11156858.
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The generalized spectral subtraction algorithm (GBSS), which has extraordinary ability in background noise reduction, is historically one of the first approaches used for speech enhancement and dereverberation. However, the algorithm has not been applied to de-noise the room impulse response (RIR) to extend the reverberation decay range. The application of the GBSS algorithm in this study is stated as an optimization problem, that is, subtracting the noise level from the RIR while maintaining the signal quality. The optimization process conducted in the measurements of the RIRs with artificial noise and natural ambient noise aims to determine the optimal sets of factors to achieve the best noise reduction results regarding the largest dynamic range improvement. The optimal factors are set variables determined by the estimated SNRs of the RIRs filtered in the octave band. The acoustic parameters, the reverberation time (RT), and early decay time (EDT), and the dynamic range improvement of the energy decay curve were used as control measures and evaluation criteria to ensure the reliability of the algorithm. The de-noising results were compared with noise compensation methods. With the achieved optimal factors, the GBSS contributes to a significant effect in terms of dynamic range improvement and decreases the estimation errors in the RTs caused by noise levels.
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Chen, Min, and Chang-Myung Lee. "The Optimal Determination of the Truncation Time of Non-Exponential Sound Decays." Buildings 12, no. 5 (May 23, 2022): 697. http://dx.doi.org/10.3390/buildings12050697.
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The noise effects in the room impulse response (RIR) make the decay range of the integrated impulse response insufficient for reliable determination of reverberation time (RT). One of the preferred techniques to minimize noise effects is based on noise subtraction, RIR truncation, and correction for the truncation. The success of RT estimation through the method depends critically on the accurate estimation of the truncation time (TT). However, noise fluctuation and RIR irregularities can lead to discrepancies in the determined TT from the optimal value. The general goal of this paper is to improve RT estimates. An iterative procedure based on a non-exponential decay model consisting of a double-slope decay term and a noise term is presented to estimate the TT accurately. The model parameters are generated until the iterative procedure converges to a minimum difference between the energy decay curve (EDC) generated by the model and the Schroeder decay function. The decay rates of the EDCs with added pink noise levels are compared to those of the EDCs with low background noise. In addition, the detected TTs and the corresponding RTs are compared with the existing method and the noise compensation method (subtraction–truncation–correction method).
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WU, JINRONG, E. C. SHAN, TIANFU GAO, and LI MA. "NUMERICAL SIMULATION ON SEARCHING THE OPTIMUM SOURCE-DEPTH DISTRIBUTION FOR REVERBERATION INVERSION BY SIMULATED ANNEALING." Journal of Computational Acoustics 17, no. 02 (June 2009): 197–209. http://dx.doi.org/10.1142/s0218396x09003926.
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To extract the intrinsic bottom back-scattering information from the reverberation data in shallow water has been a challenge topic for long time. It is shown that the modal back-scattering matrix (MBSM) is the intrinsic description of the bottom scattering.1 The optimum source-depth distribution for inverting MBSM from the reverberation data has been discussed with a Pekeris waveguide.2 In the present work, we extend the procedure to the general case of non-Pekeris waveguide by using the simulated annealing (SA) approach. Numerical simulated examples on searching the optimum source-depth distribution for MBSM inversion are presented. It is shown that: (1) the SA is an effective approach for searching the optimum source-depth distribution for MBSM inversion (2) the MBSM inverted from the optimal source-depth distribution has the strong stability against noise.
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Fanina, E. "EFFICIENT ACOUSTIC COMPOSITE PANELS BASED ON GRAPHITE." Bulletin of Belgorod State Technological University named after. V. G. Shukhov 6, no. 4 (May 7, 2021): 82–90. http://dx.doi.org/10.34031/2071-7318-2021-6-4-82-90.
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A set of experimental studies is carried out to determine the acoustic characteristics of three-dimensional panels of fixed thickness made of carbon-based composite material installed in the opening between the reverberation chambers. Sound insulation indices are determined when they are excited by a diffuse sound field in wide frequency ranges. The reverberation time in model chambers with different partition configurations is calculated. The optimal configuration of the partition with pyramidal cells to reduce the reverberation time in the rooms is determined. The use of graphite in the form of thin membrane applied to various surfaces can significantly reduce the sound pressure levels in the room and increase the sound insulation indices of air noise. In addition to thin membrane, graphite can be used as an additive in composite materials for sound insulation purposes. It is shown that the characteristics of such panels are quite universal. The measured acoustic characteristics of composite panels are compared with similar characteristics of traditional materials. It is determined that the composition belongs to the I group of fire-retardant efficiency and can be recommended for use as a fire-retardant material. The developed acoustic material is an effective absorbing agent that solves problems in architectural acoustics, echo cancellation in construction and architecture. Similar to metamaterials, natural and artificial graphites allow to solve these problems with small volumes and masses using simple and inexpensive technologies.
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Papadakis, Nikolaos M., and Georgios E. Stavroulakis. "Handclap for Acoustic Measurements: Optimal Application and Limitations." Acoustics 2, no. 2 (April 26, 2020): 224–45. http://dx.doi.org/10.3390/acoustics2020015.
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Handclap is a convenient and useful acoustic source. This study aimed to explore its optimal application and limitations for acoustic measurements as well for other possible utilizations. For this purpose, the following steps were performed: investigation of the optimal hand configuration for acoustic measurements and measurements at different microphone source distances and at different spaces and positions. All measurements were performed with a handclap and a dodecahedron speaker for comparison. The results indicate that the optimal hand configuration (among 11) is with the hands cupped and held at an angle due to the superior low frequency spectrum. This configuration produced usable acoustic parameter measurements in the low frequency range in common room background levels unlike other configurations. The reverberation time was measured across different spaces and positions with a deviation less than three and just a noticeable difference of the signal-to-noise ratio within or near the ISO 3382-1 limits for each corresponding octave band. Other acoustic parameters (i.e., early decay time, clarity) were measured with greater deviations for reasons discussed in the text. Finally, practical steps for measurements with a handclap as an acoustic source are suggested.
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Hendriks, Richard C., Joao B. Crespo, Jesper Jensen, and Cees H. Taal. "Optimal Near-End Speech Intelligibility Improvement Incorporating Additive Noise and Late Reverberation Under an Approximation of the Short-Time SII." IEEE/ACM Transactions on Audio, Speech, and Language Processing 23, no. 5 (May 2015): 851–62. http://dx.doi.org/10.1109/taslp.2015.2409780.
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Marszal, Jacek, and Roman Salamon. "Distance Measurement Errors in Silent Fm-Cw Sonar with Matched Filtering." Metrology and Measurement Systems 19, no. 2 (January 1, 2012): 321–32. http://dx.doi.org/10.2478/v10178-012-0027-6.
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Distance Measurement Errors in Silent Fm-Cw Sonar with Matched Filtering The secretiveness of sonar operation can be achieved by using continuous frequency-modulated sounding signals with reduced power and significantly prolonged repeat time. The application of matched filtration in the sonar receiver provides optimal conditions for detection against the background of white noise and reverberation, and a very good resolution of distance measurements of motionless targets. The article shows that target movement causes large range measurement errors when linear and hyperbolic frequency modulations are used. The formulas for the calculation of these errors are given. It is shown that for signals with linear frequency modulation the range resolution and detection conditions deteriorate. The use of hyperbolic frequency modulation largely eliminates these adverse effects.
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BAILESCU, Catalin, Vlad IORDACHE, and Tiberiu CATALINA. "Optimal cost-efficiency solution of acoustic treatment for a complex meeting room." E3S Web of Conferences 111 (2019): 02073. http://dx.doi.org/10.1051/e3sconf/201911102073.
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Achieving high acoustic quality in meeting rooms is important for intelligibility therefore several measures are needed especially in reflective high volume rooms. This article tackles the method and the solution to renovate a complex enclosure. The study is divided in multiple stages: development of the 3D room model exported in ODEON acoustic software, validation of the actual condition of the room with measurements, proposing and analysing different acoustic ceiling tiles and finally selecting the optimum solution based on the cost and efficacy in reducing the reverberation time (RT). The measured RT was four times higher (3.45 sec at f=1kHz) than the recommended value (0.9 sec at f=1kHz). The numerical simulation results were in accordance with the experimental measurements with errors of less than 0.2 sec. Using the difference between the RT obtained with the acoustic measures and the optimum RT we were able to calculate an efficiency that was later on compared with the cost of the solution. As a conclusion, due to a large diversity of acoustic ceiling types with different prices and sound absorption coefficients it is important, especially for complex room geometries, to run simulations and to perform a cost-efficiency analysis.
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Ardianti Sabtalistia, Yunita. "PERBAIKAN WAKTU DENGUNG RUANG KULIAH DENGAN OPTIMALISASI MODEL RUANGAN DAN JENIS MATERIAL." Pawon: Jurnal Arsitektur 4, no. 01 (January 29, 2020): 65–76. http://dx.doi.org/10.36040/pawon.v4i01.2347.
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Kegiatan belajar-mengajar di ruang kuliah bisa berjalan dengan baik jikasuara dari dosen bisa terdengar dengan jelas ke telinga mahasiswa. Salahsatu parameter akustik agar pembicaraan dalam ruangan bisa jelasterdengar adalah waktu dengung (Reverberation Time). Jika waktudengung terlalu panjang maka isi pembicaraan menjadi tidak jelas karenasuara sumber bunyi akan semakin lama sampai ke telinga penerima bunyi.Bentuk elemen interior, luas permukaan, dan jenis material dalam suaturuangan menentukan tinggi rendahnya waktu dengung. Tujuan penelitianini adalah menemukan model ruangan kuliah yang mempunyai waktudengung paling optimal ditinjau dari bentuk plafond, bentuk dinding, danjenis material plafond dan dinding. Ruang kuliah Wastu 1 dengankapasitas 144 kursi yang berada di Universitas Tarumanagara dijadikansampel penelitian. Penentuan jenis material dan model ruangan kondisieksisting berdasarkan hasil survei dan pengukuran di ruang Wastu 1.Selanjutnya dengan menggunakan software Ecotect, model plafond dandinding dieksperimen sebanyak 4 kali dengan jenis material yang sudahditentukan untuk mengetahui berapa waktu dengungnya. Hasil perhitunganRT pada model eksisting dan model eksperimen dibandingkan dengan RToptimal untuk ruangan kuliah. Hasil penelitian ini menunjukkan bahwamodel plafond datar dengan material gypsum dan acoustic danpenambahan lapisan cork pada kolom dan dinding paling mampumendekati RT optimal.
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Kortchmar, L., M. A. Nabuco De Araujo, and S. N. Y. Gerges. "Absorption Characteristics of Suspended Absorbers." Building Acoustics 1, no. 4 (December 1994): 279–86. http://dx.doi.org/10.1177/1351010x9400100403.
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The question of the arrangement of sound absorbers has been under study for some time. In our approach we conducted a sequence of experiments in a reverberation chamber to determine the optimal sound absorption for different configurations of suspended absorbers using various air spaces and a central dividing panel between them. The results obtained were compared with measurements of the panels, tested against a solid backing as specified in ISO-R-354. It is shown that a porous absorber is more efficient at high frequencies if it is suspended in the sound field rather than against a solid backing. It was also found that the efficiency of an air space between the two porous sheets that compose a suspended absorber is moderately increased when a central divider is used. The statistical precision of the test was also investigated.
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McMillan, Justin R., Jonathan Botts, and Jason E. Summers. "Deep reinforcement learning for cognitive active-sonar employment." Journal of the Acoustical Society of America 151, no. 4 (April 2022): A101. http://dx.doi.org/10.1121/10.0010785.
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We introduce a framework to leverage deep reinforcement learning (RL) for active sonar employment, wherein we train an RL agent to select waveform parameters, which maximize the probability of single-target detection. We first simulate raw sonar returns of targets and clutter in reverberation and noise using a physics-based sonar-simulation model, the Sonar Simulation Toolkit (SST), then process the resulting signatures into network inputs via an in-house signal and information processing model of an archetypal antisubmarine warfare (ASW) processing chain. We demonstrate that the trained RL agent is able to appropriately select between continuous wave (CW) and hyperbolic frequency modulated (HFM) waveforms depending on target trajectory, as well as select an optimal bandwidth and pulse length trade-off (when constrained by a constant time-bandwidth product), when presented with sonar returns from a reverb-limited or noise-limited environment.
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Aguilar, Antonio J., María L. de la Hoz-Torres, Mª Dolores Martínez-Aires, and Diego P. Ruiz. "Development of a BIM-Based Framework Using Reverberation Time (BFRT) as a Tool for Assessing and Improving Building Acoustic Environment." Buildings 12, no. 5 (April 24, 2022): 542. http://dx.doi.org/10.3390/buildings12050542.
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Both the building design and the construction process determine the indoor acoustic quality of enclosures. A suitable indoor acoustic environment is crucial for the productivity and well-being of users. For this purpose, Reverberation Time (RT) is often calculated or measured in situ. Recently, Building Information Modelling (BIM) has provided a new paradigm to face building projects. Nevertheless, little research has been conducted on the optimisation of indoor acoustics using BIM methodology. In this context, the objective of this work is to propose and develop a BIM-based framework for the analysis, evaluation and optimization of the RT. The proposed procedure allows designers to explore alternatives in order to achieve an adequate acoustic performance without any further needs of specific software. This proposal is devised to consider some important characteristics of the project, such as its location, applicable regulations, room uses, materials and costs. This framework calculates the solution set that meets the requirements, showing the set of optimal solutions according to the minimization of both the cost and the optimum absorbent surface area. BFRT contributes by offering a tool to support the decision making process of designers during the initial design phase in the field of acoustic conditioning of buildings.
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Labia, Laura, Louena Shtrepi, and Arianna Astolfi. "Improved Room Acoustics Quality in Meeting Rooms: Investigation on the Optimal Configurations of Sound-Absorptive and Sound-Diffusive Panels." Acoustics 2, no. 3 (June 27, 2020): 451–73. http://dx.doi.org/10.3390/acoustics2030025.
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This work deals with the improvement of the room acoustic quality of two medium sized meeting rooms through the investigation of the optimal placement of absorption and diffusive panels on the walls and ceiling. Acoustic measurements have been carried out in the existing untreated rooms with ODEON 13 room acoustics measurement and prediction software, and the Adobe Audition plugins Aurora. Simulations of different combinations of sound absorption and diffusion treatments have been carried out with the updated version of the software, ODEON 15. The panels were positioned in the meeting rooms following the guidelines of the DIN 18041 standard and the scientific literature. The results advise the application of absorptive materials on the ceiling or around the borders, creating a reflective middle area, and on the upper part of one the lateral walls, including the rear wall. Configurations with diffusers do not generally bring significant improvements. The Speech Transmission Index (STI) is a less sensitive parameter for the different acoustic scenarios, compared to Reverberation Time (T) and Clarity (C50). The research also outlined a design workflow, useful to successfully design meeting rooms and rooms for speech in general, which allows to determine the optimal number and location of acoustic panels and to minimize the costs.
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Katunský, Dušan, Jana Katunská, Iveta Bullová, and Richard Germánus. "Problems in the Designing of Acoustic Properties of Musical Rehearsals." Applied Mechanics and Materials 861 (December 2016): 519–26. http://dx.doi.org/10.4028/www.scientific.net/amm.861.519.
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Content of the post is to describe the creation of building structures, typology, internal environment, and internal wall coverings music rehearsal for optimal acoustic performance. One of the aspects of its internal environment is reverberation time. For this variable there are several methods of calculation. Article gives an indication of how the music was the laboratory building in the center of the music created and what problems the authors in its proposal met. Article contents and solving spatial and building acoustics model music musical rehearsal building downtown. Calculation fully respects Slovak standards valid for the design of room acoustics, as well as hygiene regulations on noise pollution. Acoustically treated room should serve as a laboratory for musical performance. If the building is more proof is needed to solve the sound insulation (building acoustics) that these areas do not interfere with each other. In addressing acoustics of testing can’t talk about bad or good acoustics, but rather on the season and out of corresponding with room acoustics, respectively, with activities in it.
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Yani, Yulida. "Penilaian kualitas akustik masjid raudhaturrahmah Padang Tiji dengan menggunakan simulasi ecotect." JURNAL ARSITEKTUR PENDAPA 4, no. 1 (March 4, 2021): 18–26. http://dx.doi.org/10.37631/pendapa.v4i1.234.
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Masjid merupakan tempat ibadah umat islam yang memiliki pengaruh penting bagi masyarakat, dalam melakukan ibadah perlu adanya ketenangan dan kejelasan bicara agar pesan yang disampaikan dapat tersalurkan dengan jelas dan baik. Dalam penelitian ini ruang yang digunakan untuk simulasi ialah ruang shalat masjid Raudhaturrahmah. Tujuan penelitian adalah untuk mengetahui kondisi, penyebabnya dan memperbaiki kualitas akustik dengan penambahan plafond serta material serap, agar sesuai dengan kebutuhan ruang percakapan masjid. Fokus utama penelitian adalah menghitung tingkat bising latar belakang (background noise), dan waktu dengung (reverberation time). Metode yang digunakan adalah simulasi dengan menggunakan software Ecotect yang mampu menganalisis kinerja akustik. Hasil dari simulasi memperlihatkan bahwa kalkulasi waktu dengung (RT) dan pengukuran background noise belum memenuhi kriteria yang telah ditetapkan. nilai yang dihasilkan untuk RT dengan occupancy 0%, 50%, 100% ialah 18,29 s, 7,80 s, dan 4, 71 s. sedangkan hasil dari background Noise ialah 60 dB. Dari penelitian ini menghasilkan solusi untuk memperbaiki waktu dengung dan background noise dengan menambah plafond dan material serap. Setelah penambahan Plafond dan material serap nilai akustik yang dihasilkan lebih optimal dibandingkan dengan kondisi exiting.
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Rasmussen, Birgit, Teresa Carrascal Garcia, and Simone Secchi. "Acoustic regulations for hospital bedrooms - Comparison between selected countries in Europe." INTER-NOISE and NOISE-CON Congress and Conference Proceedings 263, no. 4 (August 1, 2021): 2793–800. http://dx.doi.org/10.3397/in-2021-2230.
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Regulatory acoustic requirements for hospitals exist in several countries in Europe, but many countries have either insufficient regulatory limits or only recommendations. The main purpose of limit values is to ensure optimal acoustic conditions for patients under treatment and for personnel for the various tasks taking place in many different rooms, e.g. bedrooms, examination and treatment rooms, corridors, stairwells, waiting and reception areas, canteens, offices, all with different acoustic needs. In addition, some rooms require special considerations like psychiatric rooms and noisy MR-scanning rooms. The extent of limit values varies considerably between countries. Some specify a few, others several criteria. The findings from a comparative study carried out in selected countries in various geographical parts of Europe show a diversity of acoustic descriptors and limit values. The paper includes examples of criteria for reverberation time, airborne and impact sound insulation, noise from traffic and from service equipment. The discrepancies between countries are discussed, aiming at potential learning and implementation of optimized limits for more room types. In addition to regulations or guidelines, some countries have hospitals included in national acoustic classification schemes with different acoustic quality levels. Indications of such classification criteria will be included in the paper.
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LIU, LANBO, HAO XIE, DONALD G. ALBERT, PAUL R. ELLER, and JING-RU C. CHENG. "A SCENARIO STUDY FOR IMPROVING COST-EFFECTIVENESS IN ACOUSTIC TIME-REVERSAL SOURCE RELOCATION IN AN URBAN ENVIRONMENT." Journal of Computational Acoustics 20, no. 02 (June 2012): 1240003. http://dx.doi.org/10.1142/s0218396x12400036.
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Through finite difference time domain (FDTD) numerical simulation, we have studied the possible observation settings to improve the cost effectiveness in time-reversal (TR) source relocation in a two-dimensional (2D) urban setting under a number of typical scenarios. All scenario studies were based on the FDTD computation of the acoustic wave field resulted from an impulse source, propagated through an artificial village composed of 15 buildings and a set of sources and receivers, a typical urban setting has been extensively analyzed in previous studies. The FDTD numerical modeling code can be executed on an off-the-shelf graphic processor unit (GPU) that increases the speed of the time-reversal calculations by a factor of 200. With this approach the computational results lead to some significant conclusions. In general, using only one non-line-of-sight (NLOS) single receiver is not enough to do a quality work to re-locate the source via time-reversal. This is particularly true when there are more than one path between the source and this receiver with similar wave energy travel time. However, when the single sensor is located in an acoustic channel, reverberation inside the waveguide may increase the effective aperture of the single receiver enough to give a good location. It is equivalent to say that the waveguide and the single receiver form a "virtual array". It appears that a sensor array with a minimum number of three receivers might be the most cost-effective way to carry out TR source relocation in an urban environment. The most optimal geometry of a sensor array with a minimum number of three receivers could be an equal side-length triangle. Simple analysis showed that by this setup it is possible to catch sound sources from almost all possible azimuths. Effective source relocation essentially depends on the geometry, relativity to the scatters, etc. of the sensing array. Generally, adding another single sensor relatively far away from the main array will not improve the results. It is practically useful and achievable to have a sensor array mounted on the outside of a single building, and in these cases successful source relocations were obtained. As stated by the fundamental TR theory, increasing the number of scatters, here, increasing the number of buildings will definitely be helpful to increase the effectiveness of TR source relocation.
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Kammoun, E. S., I. E. Papadakis, and M. Dovčiak. "Modelling the UV/optical continuum time-lags in AGN." Monthly Notices of the Royal Astronomical Society 503, no. 3 (March 11, 2021): 4163–71. http://dx.doi.org/10.1093/mnras/stab725.
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ABSTRACT Thermal reverberation in accretion discs of active galactic nuclei is thought to be the reason of the continuum UV/optical time lags seen in these sources. Recently, we studied thermal reverberation of a standard Novikov-Thorne accretion disc illuminated by an X–ray point-like source, and we derived an analytic prescription for the time lags as function of wavelength. In this work, we use this analytic function to fit the time-lags spectra of seven Seyferts, that have been intensively monitored, in many wave-bands, in the last few years. We find that thermal reverberation can explain the observed UV/optical time lags in all these sources. Contrary to previous claims, the magnitude of the observed UV/optical time-lags is exactly as expected in the case of a standard accretion disc in the lamp-post geometry, given the black hole mass and the accretion rate estimates for the objects we study. We derive estimates of the disc accretion rates and corona height for a non-spinning and a maximally spinning black hole scenarios. We also find that the modelling of the continuum optical/UV time-lags can be used to estimate the black hole spin, when combined with additional information. We also find that the model under-predicts the observed X–ray to UV time-lags, but this difference is probably due to the broad X-ray auto-correlation function of these sources.
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Mastroserio, Guglielmo, Adam Ingram, and Michiel van der Klis. "Multi-timescale reverberation mapping of Mrk 335." Monthly Notices of the Royal Astronomical Society 498, no. 4 (September 10, 2020): 4971–82. http://dx.doi.org/10.1093/mnras/staa2735.
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ABSTRACT Time lags due to X-ray reverberation have been detected in several Seyfert galaxies. The different traveltime between reflected and directly observed rays naturally causes this type of lag, which depends directly on the light-crossing time-scale of the system and hence scales with the mass of the central black hole. Featureless ‘hard lags’ not associated with reverberation, and often interpreted as propagating mass accretion rate fluctuations, dominate the longer time-scale variability. Here we fit our reltrans model simultaneously to the time-averaged energy spectrum and the lag-energy spectra of the Seyfert galaxy Mrk 335 over two time-scales (Fourier frequency ranges). We model the hard lags as fluctuations in the slope and strength of the illuminating spectrum, and self-consistently account for the effects that these fluctuations have on the reverberation lags. The resulting mass estimate is $1.1^{+2.0}_{-0.7} \times 10^6~\mathrm{ M}_\odot$, which is significantly lower than the mass measured with the optical reverberation mapping technique (14–26 million M⊙). When we add the correlated variability amplitudes to the time lags by fitting the full complex cross-spectra, the model is unable to describe the characteristic reverberation Fe K α line and cannot constrain the black hole mass. This may be due to the assumption that the direct radiation is emitted by a point-like source.
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Noda, Hirofumi, Taiki Kawamuro, Mitsuru Kokubo, and Takeo Minezaki. "Dust reverberation mapping of type 2 AGN NGC 2110 realized with X-ray and 3–5 μm IR monitoring." Monthly Notices of the Royal Astronomical Society 495, no. 3 (May 20, 2020): 2921–29. http://dx.doi.org/10.1093/mnras/staa1376.
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ABSTRACT The dust reverberation mapping is one of powerful methods to investigate the structure of the dusty tori in active galactic nuclei (AGNs), and it has been performed on more than a hundred type 1 AGNs. However, no clear results have been reported on type 2 AGNs because their strong optical/UV extinction completely hides their accretion disc emission. Here, we focus on an X-ray-bright type 2 AGN, NGC 2110, and utilize 2–20 keV X-ray variation monitored by MAXI to trace disc emission, instead of optical/UV variation. Comparing it with light curves in the WISE infrared (IR) W1 band ($\lambda =3.4~\mu$m) and W2 band ($\lambda =4.6~\mu$m) with cross-correlation analyses, we found candidates of the dust reverberation time lag at ∼60, ∼130, and ∼1250 d between the X-ray flux variation and those of the IR bands. By examining the best-fitting X-ray and IR light curves with the derived time lags, we found that the time lag of ∼130 d is most favoured. With this time lag, the relation between the time lag and luminosity of NGC 2110 is consistent with those in type 1 AGNs, suggesting that the dust reverberation in NGC 2110 mainly originates in hot dust in the torus innermost region, the same as in type 1 AGNs. As demonstrated by the present study, X-ray and IR simultaneous monitoring can be a promising tool to perform the dust reverberation mapping on type 2 AGNs.
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Pahari, Mayukh, I. M. McHardy, Federico Vincentelli, Edward Cackett, Bradley M. Peterson, Mike Goad, Kayhan Gültekin, and Keith Horne. "Evidence for variability time-scale-dependent UV/X-ray delay in Seyfert 1 AGN NGC 7469." Monthly Notices of the Royal Astronomical Society 494, no. 3 (April 21, 2020): 4057–68. http://dx.doi.org/10.1093/mnras/staa1055.
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ABSTRACT Using a month-long X-ray light curve from RXTE/PCA and 1.5 month-long UV continuum light curves from IUE spectra in 1220–1970 Å, we performed a detailed time-lag study of the Seyfert 1 galaxy NGC 7469. Our cross-correlation analysis confirms previous results showing that the X-rays are delayed relative to the UV continuum at 1315 Å by 3.49 ± 0.22 d, which is possibly caused by either propagating fluctuation or variable Comptonization. However, if variations slower than 5 d are removed from the X-ray light curve, the UV variations then lag behind the X-ray variations by 0.37 ± 0.14 d, consistent with reprocessing of the X-rays by a surrounding accretion disc. A very similar reverberation delay is observed between Swift/XRT X-ray and Swift/UVOT UVW2, U light curves. Continuum light curves extracted from the Swift/GRISM spectra show delays with respect to X-rays consistent with reverberation. Separating the UV continuum variations faster and slower than 5 d, the slow variations at 1825 Å lag those at 1315 Å by 0.29 ± 0.06 d, while the fast variations are coincident (0.04 ± 0.12 d). The UV/optical continuum reverberation lag from IUE, Swift, and other optical telescopes at different wavelengths are consistent with the relationship: τ ∝ λ4/3, predicted for the standard accretion disc theory while the best-fitting X-ray delay from RXTE and Swift/XRT shows a negative X-ray offset of ∼0.38 d from the standard disc delay prediction.
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Peterson, Bradley M. "Space Telescope and Optical Reverberation Mapping Project: A Leap Forward in Reverberation Mapping." Proceedings of the International Astronomical Union 12, S324 (September 2016): 215–18. http://dx.doi.org/10.1017/s1743921316012680.
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AbstractIn 2014, a 179-orbit allocation of Hubble Space Telescope time anchored a massive reverberation-mapping program on the well-studied Seyfert 1 galaxy NGC 5548. Supporting imaging and spectrophotometric observations were provided by Swift, Chandra, Spitzer, and a world-wide network of ground-based telescopes. Understanding the data remains a significant challenge, partly because the level of detail is far beyond what has been seen before and partly because the behavior of the AGN was not typical of its past behavior. Based on analysis to date, the following conclusions can be reached: (1) the AGN accretion disk has a temperature profile that is consistent with that predicted by the Shakura–Sunyaev model, but is about three times larger than expected; (2) at least part of the broad-line region appears to be a Keplerian disk seen at intermediate inclination, and (3) the broad-line emission response from the far side of the disk is weaker than expected.
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Rojas Lobos, P. A., R. W. Goosmann, F. Marin, and D. Savić. "Modeling optical and UV polarization of AGNs." Astronomy & Astrophysics 611 (March 2018): A39. http://dx.doi.org/10.1051/0004-6361/201731331.
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Context. Optical observations cannot resolve the structure of active galactic nuclei (AGN), and a unified model for AGN was inferred mostly from indirect methods, such as spectroscopy and variability studies. Optical reverberation mapping allowed us to constrain the spatial dimension of the broad emission line region and thereby to measure the mass of supermassive black holes. Recently, reverberation was also applied to the polarized signal emerging from different AGN components. In principle, this should allow us to measure the spatial dimensions of the sub-parsec reprocessing media.Aim. We conduct numerical modeling of polarization reverberation and provide theoretical predictions for the polarization time lag induced by different AGN components. The model parameters are adjusted to the observational appearance of the Seyfert 1 galaxy NGC 4151.Methods. We modeled scattering-induced polarization and tested different geometries for the circumnuclear dust component. Our tests included the effects of clumpiness and different dust prescriptions. To further extend the model, we also explored the effects of additional ionized winds stretched along the polar direction, and of an equatorial scattering ring that is responsible for the polarization angle observed in pole-on AGN. The simulations were run using a time-dependent version of the STOKES code.Results. Our modeling confirms the previously found polarization characteristics as a function of the observer‘s viewing angle. When the dust adopts a flared-disk geometry, the lags reveal a clear difference between type 1 and type 2 AGN. This distinction is less clear for a torus geometry where the time lag is more sensitive to the geometry and optical depth of the inner surface layers of the funnel. The presence of a scattering equatorial ring and ionized outflows increased the recorded polarization time lags, and the polar outflows smooths out dependence on viewing angle, especially for the higher optical depth of the wind (τ = 0.3).Conclusions. Together with other AGN observables, the polarization time lag places new, independent “seismological” constraints on the inner geometry of AGN. If we conduct time-dependent spectropolarimetric observing campaigns of AGN, this method has a high potential for a census of supermassive black holes.
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Bon, Edi, Paola Marziani, Predrag Jovanović, and Nataša Bon. "On the Time Scales of Optical Variability of AGN and the Shape of Their Optical Emission Line Profiles." Atoms 7, no. 1 (February 14, 2019): 26. http://dx.doi.org/10.3390/atoms7010026.
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The mechanism of the optical variability of active galactic nuclei (AGN) is still very puzzling. It is now widely accepted that the optical variability of AGN is stochastic, producing red noise-like light curves. In case they were to be periodic or quasi-periodic, one should expect that the time scales of optical AGN variability should relate to orbiting time scales of regions inside the accretion disks with temperatures mainly emitting the light in this wavelength range. Knowing the reverberation scales and masses of AGN, expected orbiting time scales are in the order of decades. Unfortunately, most of monitored AGN light curves are not long enough to investigate such time scales of periodicity. Here we investigate the AGN optical variability time scales and their possible connections with the broad emission line shapes.
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Vincentelli, F. M., I. McHardy, E. M. Cackett, A. J. Barth, K. Horne, M. Goad, K. Korista, et al. "On the multiwavelength variability of Mrk 110: two components acting at different time-scales." Monthly Notices of the Royal Astronomical Society 504, no. 3 (April 15, 2021): 4337–53. http://dx.doi.org/10.1093/mnras/stab1033.
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ABSTRACT We present the first intensive continuum reverberation mapping study of the high accretion-rate Seyfert galaxy Mrk 110. The source was monitored almost daily for more than 200 d with the Swift X-ray and ultraviolet (UV)/optical telescopes, supported by ground-based observations from Las Cumbres Observatory, the Liverpool Telescope, and the Zowada Observatory, thus extending the wavelength coverage to 9100 Å. Mrk 110 was found to be significantly variable at all wavebands. Analysis of the intraband lags reveals two different behaviours, depending on the time-scale. On time-scales shorter than 10 d the lags, relative to the shortest UV waveband (∼1928 Å), increase with increasing wavelength up to a maximum of ∼2 d lag for the longest waveband (∼9100 Å), consistent with the expectation from disc reverberation. On longer time-scales, however, the g-band lags the Swift BAT hard X-rays by ∼10 d, with the z-band lagging the g-band by a similar amount, which cannot be explained in terms of simple reprocessing from the accretion disc. We interpret this result as an interplay between the emission from the accretion disc and diffuse continuum radiation from the broad-line region.
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Mastroserio, Guglielmo, Adam Ingram, Jingyi Wang, Javier A. García, Michiel van der Klis, Yuri Cavecchi, Riley Connors, et al. "Modelling correlated variability in accreting black holes: the effect of high density and variable ionization on reverberation lags." Monthly Notices of the Royal Astronomical Society 507, no. 1 (July 21, 2021): 55–73. http://dx.doi.org/10.1093/mnras/stab2056.
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ABSTRACT We present a new release of the reltrans model to fit the complex cross-spectrum of accreting black holes as a function of energy. The model accounts for continuum lags and reverberation lags self-consistently in order to consider the widest possible range of X-ray variability time-scales. We introduce a more self-consistent treatment of the reverberation lags, accounting for how the time variations of the illuminating flux change the ionization level of the accretion disc. This process varies the shape of the reflection spectrum in time causing an additional source of lags besides the light crossing delay. We also consider electron densities in the accretion disc up to 1020 cm−3, which are found in most of the stellar mass black holes and in some active galactic nuclei. These high densities increase the amplitude of the reverberation lags below 1 keV since the reflection flux enhances in the same energy range. In addition, we investigate the properties of hard lags produced by variations in the power-law index of the continuum spectrum, which can be interpreted as due to roughly $3{{\ \rm per\ cent}}$ variability in the corona’s optical depth and temperature. As a test case, we simultaneously fit the lag-energy spectra in a wide range of Fourier frequency for the black hole candidate MAXI J1820+0701820 observed with NICER. The best fit shows how the reverberation lags contribute even at the longer time-scales where the hard lags are important. This proves the importance of modelling these two lags together and self-consistently in order to constrain the parameters of the system.
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Beristain, Sergio. "Analysis of the Mexican standard on optimal reverberation times according to enclosure function." Journal of the Acoustical Society of America 118, no. 3 (September 2005): 1842. http://dx.doi.org/10.1121/1.4778470.
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Fian, C., D. Chelouche, S. Kaspi, C. Sobrino Figaredo, S. Catalan, and T. Lewis. "Continuum reverberation mapping of the quasar PG 2130+099." Astronomy & Astrophysics 659 (February 25, 2022): A13. http://dx.doi.org/10.1051/0004-6361/202141509.
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Aims. We present the results of an intensive six-month optical continuum reverberation mapping campaign of the Seyfert 1 galaxy PG 2130+099 at redshift z = 0.063. The ground-based photometric monitoring was conducted on a daily basis with the robotic 46 cm telescope of the WISE observatory located in Israel. Specially designed narrowband filters were used to observe the central engine of the active galactic nucleus (AGN), avoiding line contamination from the broad-line region (BLR). We aim to measure inter-band continuum time lags across the optical range and determine the size-wavelength relation for this system. Methods. We used two methods, the traditional point-spread function photometry and the recently developed proper image subtraction technique, to independently perform the extraction of the continuum light curves. The inter-band time lags are measured with several methods, including the interpolated cross-correlation function, the z-transformed discrete correlation function, a von Neumann estimator, JAVELIN (in spectroscopic mode), and MICA. Results. PG 2130+099 displays correlated variability across the optical range, and we successfully detect significant time lags of up to ∼3 days between the multiband light curves. We find that the wavelength-dependent lags, τ(λ), generally follow the relation τ(λ)∝λ4/3, as expected for the temperature radial profile T ∝ R−3/4 of an optically thick, geometrically thin accretion disk. Despite that, the derived time lags can also be fitted by τ(λ)∝λ2, implying the possibility of a slim, rather than thin, accretion disk. Using the flux variation gradient method, we determined the AGN’s host-galaxy-subtracted rest frame 5100 Å luminosity at the time of our monitoring campaign with an uncertainty of ∼18% (λL5100 = (2.40 ± 0.42)×1044 erg s−1). While a continuum reprocessing model can fit the data reasonably well, our derived disk sizes are a factor of ∼2 − 6 larger than the theoretical disk sizes predicted from the AGN luminosity estimate of PG 2130+099. This result is in agreement with previous studies of AGN/quasars and suggests that the standard Shakura-Sunyaev disk theory has limitations in describing AGN accretion disks.
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Goicoechea, Luis J., and Vyacheslav N. Shalyapin. "Time-Domain Studies of Gravitationally Lensed Quasars." Proceedings of the International Astronomical Union 7, S285 (September 2011): 315–17. http://dx.doi.org/10.1017/s1743921312000919.
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AbstractWe present an overview and current results of an ongoing optical/NIR monitoring of seven gravitationally-lensed quasars (GLQs) with the 2-m Liverpool Robotic Telescope. The photometric data from the first seven years (2005–2011) of this programme are leading to high-quality light curves, which in turn are being used as key tools for different standard and novel studies. While brightness records of non-lensed distant quasars may contain unrecognized extrinsic variations, one can disentangle intrinsic from extrinsic signals in certain GLQs. Thus, some GLQs in our sample allow us to assess their extrinsic and intrinsic variations; we then discuss the origin of both kinds of fluctuations. We also demonstrate the usefulness of GLQ time-domain data for obtaining successful reverberation maps of the inner regions of accretion disks around distant supermassive black holes, and for estimating the redshifts of distant lensing galaxies.
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Denney, Kelly D., B. M. Peterson, R. W. Pogge, M. C. Bentz, C. M. Gaskell, T. Minezaki, C. A. Onken, S. G. Sergeev, and M. Vestergaard. "Reverberation Mapping Results from MDM Observatory." Proceedings of the International Astronomical Union 5, S267 (August 2009): 201. http://dx.doi.org/10.1017/s1743921310006216.
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Reverberation mapping takes advantage of the presence of a time delay or lag, τ, between continuum and emission line flux variations observed through spectroscopic monitoring campaigns to infer the radius of the broad-line region (BLR) and, subsequently, the central black hole mass in type 1 AGNs. We present results from a multi-month reverberation mapping campaign undertaken primarily at MDM Observatory with supporting observations from around the world. We measure BLR radii and black hole masses for six objects. The primary goal of this campaign was to obtain either new or improved Hβ reverberation lag measurements for several relatively low-luminosity AGNs. Using cross correlation techniques to measure the time delay between the mean optical continuum flux density around 5100 Å and the integrated Hβ flux, we determine the Hβ lags and black hole mass measurements listed in columns 2 and 3 of Table 1, respectively. Column 4 tells if this measurement is new, an improvement meant to replace a previous, less reliable measurement, or simply an additional measurement not used to replace a previous value. The complete results from this study are currently being prepared for publication. A subsequent velocity-resolved analysis of the Hβ response shows that three of the six primary targets demonstrate kinematic signatures (column 5) of infall, outflow, and non-radial virialized motions (see Denney et al. 2009).
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Xue, S. J., and F. Z. Cheng. "Reverberation Mapping Analysis of the Broad-Line Region in Seyfert Galaxy NGC 4151." Symposium - International Astronomical Union 188 (1998): 424–25. http://dx.doi.org/10.1017/s0074180900115840.
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One of the primary goals of AGN variability studies has been to determine the size of broad-line region (BLR) through the reverberation mapping technique. In a recent international multiwavelength spectroscopic monitoring campaign, NGC 4151 has been observed intensively by ground-based telescopes for a period of over 2 months, with a typical temporal resolution of 1 day. The main result from this optical campaign is that finding the variation in the emission line flux (Hβ or Hα) lagging the continuum by 0-3 days (1993 campaign: Kaspi et al. 1996). This is in contrast to the past results in which a time lag of 9±2 days was found for the same emission line (1988 campaign: Maoz et al. 1991). Such a BLR “size problem” may be caused by a different variability timescale of the ionizing continuum or a real change in BLR gas distribution in the 5.5 yr interval between the two watch campaigns. In order to clarify which of the two possibilities is most likely the real case, we performed further reverberation analysis on both optical datasets.
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Rojas Lobos, P. A., R. W. Goosmann, J. M. Hameury, and F. Marin. "Reverberation mapping of AGNs through continuum polarization." Astronomy & Astrophysics 637 (May 2020): A88. http://dx.doi.org/10.1051/0004-6361/202037814.
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Context. The size and geometry of the broad-line region (BLR) in active galactic nuclei (AGNs) are among the main ingredients in determining the mass of the accreting black hole. Size and geometry can be constrained by determining the delay between the optical continuum and the flux reprocessed by the BLR, in particular, through the emission lines. Aims. We propose here that the delay between polarized and unpolarized light can also be used in much the same way to constrain the size of the BLR; we verify that meaningful results can be expected from observations using this technique. Methods. We used our code STOKES to simulate polarized radiative transfer. We determined the response of the environment of the central source (BLR, dust torus, and polar wind) to randomly generated fluctuations in the central source. We then calculated the cross correlation between the simulated polarized flux and the total flux to estimate the time delay that would be provided by observations using the same method. Results. The BLR is the main contributor to the delay between the polarized flux and the total flux. This delay is independent of the observation wavelength. Conclusions. This validates the use of polarized radiation in the optical/UV band to estimate the geometrical properties of the BLR in type I AGNs, in which the viewing angle is close to pole-on and the BLR is not obscured by the dust torus.
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Fausnaugh, M. M., K. D. Denney, A. J. Barth, M. C. Bentz, M. C. Bottorff, M. T. Carini, K. V. Croxall, et al. "SPACE TELESCOPE AND OPTICAL REVERBERATION MAPPING PROJECT. III. OPTICAL CONTINUUM EMISSION AND BROADBAND TIME DELAYS IN NGC 5548." Astrophysical Journal 821, no. 1 (April 11, 2016): 56. http://dx.doi.org/10.3847/0004-637x/821/1/56.
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Hodgson, Murray, and Eva-Marie Nosal. "Effect of noise and occupancy on optimal reverberation times for speech intelligibility in classrooms." Journal of the Acoustical Society of America 111, no. 2 (February 2002): 931–39. http://dx.doi.org/10.1121/1.1428264.
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Brotherton, Michael, Jaya Maithil, Adam Myers, Ohad Shemmer, Brandon Matthews, Cooper Dix, Pu Du, and Jian-Min Wang. "Quasar black hole masses and accretion rates across cosmic time." Proceedings of the International Astronomical Union 15, S359 (March 2020): 57–61. http://dx.doi.org/10.1017/s1743921320002392.
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AbstractQuasar black hole masses are most commonly estimated using broad emission lines in single epoch spectra based on scaling relationships determined from reverberation mapping of small samples of low-redshift objects. Several effects have been identified requiring modifications to these scaling relationships, resulting in significant reductions of the black hole mass determinations at high redshift. Correcting these systematic biases is critical to understanding the relationships among black hole and host galaxy properties. We are completing a program using the Gemini North telescope, called the Gemini North Infrared Spectrograph (GNIRS) Distant Quasar Survey (DQS), that has produced rest-frame optical spectra of about 200 high-redshift quasars (z = 1.5–3.5). The GNIRS-DQS will produce new and improved ultraviolet-based black hole mass and accretion rate prescriptions, as well as new redshift prescriptions for velocity zero points of high-z quasars, necessary to measure feedback.
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Kokubo, Mitsuru, and Takeo Minezaki. "Rapid luminosity decline and subsequent reformation of the innermost dust distribution in the changing-look AGN Mrk 590." Monthly Notices of the Royal Astronomical Society 491, no. 4 (December 4, 2019): 4615–33. http://dx.doi.org/10.1093/mnras/stz3397.
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ABSTRACT We examine the long-term optical/near-infrared (NIR) flux variability of a ‘changing-look’ active galactic nucleus (AGN) Mrk 590 between 1998 and 2007. Multiband multi-epoch optical/NIR photometry data from the SDSS Stripe 82 data base and the Multicolor Active Galactic Nuclei Monitoring (MAGNUM) project reveal that Mrk 590 experienced a sudden luminosity decrease during the period from 2000 to 2001. Detection of dust reverberation lag signals between V- and K-band light curves obtained by the MAGNUM project during the faint state in 2003–2007 suggests that the dust torus innermost radius Rdust of Mrk 590 had become very small [Rdust ≃ 32 light-days (lt-days)] by the year 2004 according to the aforementioned significant decrease in AGN luminosity. The Rdust in the faint state is comparable to the H β broad-line region (BLR) radius of RH β, BLR ≃ 26 lt-days measured by previous reverberation mapping observations during the bright state of Mrk 590 in 1990–1996. These observations indicate that the innermost radius of the dust torus in Mrk 590 decreased rapidly after the AGN ultraviolet-optical luminosity drop, and that the replenishment time-scale of the innermost dust distribution is less than 4 yr, which is much shorter than the free fall time-scale of BLR gas or dust clouds. We suggest that rapid replenishment of the innermost dust distribution can be accomplished either by new dust formation in radiatively cooled BLR gas clouds or by new dust formation in the disc atmosphere and subsequent vertical wind from the dusty disc as a result of radiation pressure.
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Marengo, Edwin A., and Fred K. Gruber. "Optical-Theorem-Based Coherent Scatterer Detection in Complex Environments." International Journal of Antennas and Propagation 2013 (2013): 1–12. http://dx.doi.org/10.1155/2013/231729.
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A new approach is proposed to detect scatterers embedded in reciprocal media from scattering data. The new method is rooted on physical considerations, in particular, on the optical theorem applicable to wavefields (e.g., acoustic, electromagnetic, and optical). The approach exploits insight gained from the optical theorem which assigns physical energy interpretations to the wave data from time reversal mirrors and cavities from which one can deduce the presence of unknown scatterers in unknown background media. The proposed approach is ideally suited for target detection in complex, highly reverberating unknown environments such as indoor facilities, caves, tunnels, and urban canyon.
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Netzer, Hagai. "Testing broad-line region models with reverberation mapping." Monthly Notices of the Royal Astronomical Society 494, no. 2 (March 19, 2020): 1611–21. http://dx.doi.org/10.1093/mnras/staa767.
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ABSTRACT New reverberation mapping (RM) measurements, combined with accurate luminosities and line ratios, provide strong constraints on the location of the line emitting gas in the broad-line region (BLR) of active galactic nuclei (AGNs). In this paper, I present new calculations of radiation pressure and magnetic pressure confined clouds and apply them to a ‘generic AGN’ and to NGC 5548. The new calculations are in good agreement with the observed lags of all broad emission lines, and with the luminosities of Ly α, C iv 1549, O vi 1035, and He ii 1640. They are also in reasonable agreement with the luminosities of Mg ii 2798 and the 1990 Å blend of C iii] and Si iii] lines for high-metallicity gas. They explain the changes in time-lag following an increase in continuum luminosity and their dependencies on the inner and outer boundaries of the BLR. They also predict very strong Balmer and Paschen continua with important implications to continuum RM experiments. However, the calculated Balmer and Paschen line luminosities are too weak, by factors of 2–5. This ‘Balmer line crisis’ was noted in several earlier works and is now confirmed and constrained by RM measurements that were not available in the past. It seems that present photoionization codes that use the escape probability formalism fail to correctly compute the Balmer line luminosities in high-density, large optical depth gas.
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Ingram, Adam, Guglielmo Mastroserio, Thomas Dauser, Pieter Hovenkamp, Michiel van der Klis, and Javier A. García. "A public relativistic transfer function model for X-ray reverberation mapping of accreting black holes." Monthly Notices of the Royal Astronomical Society 488, no. 1 (June 21, 2019): 324–47. http://dx.doi.org/10.1093/mnras/stz1720.
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ABSTRACTWe present the publicly available model reltrans that calculates the light-crossing delays and energy shifts experienced by X-ray photons originally emitted close to the black hole when they reflect from the accretion disc and are scattered into our line of sight, accounting for all general relativistic effects. Our model is fast and flexible enough to be simultaneously fit to the observed energy-dependent cross-spectrum for a large range of Fourier frequencies, as well as to the time-averaged spectrum. This not only enables better geometric constraints than only modelling the relativistically broadened reflection features in the time-averaged spectrum, but additionally enables constraints on the mass of supermassive black holes in active galactic nuclei and stellar-mass black holes in X-ray binaries. We include a self-consistently calculated radial profile of the disc ionization parameter and properly account for the effect that the telescope response has on the predicted time lags. We find that a number of previous spectral analyses have measured artificially low source heights due to not accounting for the former effect and that timing analyses have been affected by the latter. In particular, the magnitude of the soft lags in active galactic nuclei may have been underestimated, and the magnitude of lags attributed to thermal reverberation in X-ray binaries may have been overestimated. We fit reltrans to the lag-energy spectrum of the Seyfert galaxy Mrk 335, resulting in a best-fitting black hole mass that is smaller than previous optical reverberation measurements (∼7 million compared with ∼14–26 million M⊙).
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Xin, Chengcheng, Maria Charisi, Zoltán Haiman, and David Schiminovich. "Correlation between optical and UV variability of a large sample of quasars." Monthly Notices of the Royal Astronomical Society 495, no. 1 (May 7, 2020): 1403–13. http://dx.doi.org/10.1093/mnras/staa1258.
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ABSTRACT The variability of quasars across multiple wavelengths is a useful probe of physical conditions in active galactic nuclei. In particular, variable accretion rates, instabilities, and reverberation effects in the accretion disc of a supermassive black hole are expected to produce correlated flux variations in ultraviolet (UV) and optical bands. Recent work has further argued that binary quasars should exhibit strongly correlated UV and optical periodicities. Strong UV–optical correlations have indeed been established in small samples of (N ≲ 30) quasars with well-sampled light curves, and have extended the ‘bluer-when-brighter’ trend previously found within the optical bands. Here, we further test the nature of quasar variability by examining the observed-frame UV–optical correlations among bright quasars extracted from the Half Million Quasars (HMQ) catalogue. We identified a large sample of 1315 quasars in HMQ with overlapping UV and optical light curves from the Galaxy Evolution Explorer and the Catalina Real-time Transient Survey, respectively. We find that strong correlations exist in this much larger sample, but we rule out, at ∼95 per cent confidence, the simple hypothesis that the intrinsic UV and optical variations of all quasars are fully correlated. Our results therefore imply the existence of physical mechanism(s) that can generate uncorrelated optical and UV flux variations.
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Ilić, Dragana. "The BLR physics from the long-term optical monitoring of type-1 AGN." Proceedings of the International Astronomical Union 15, S356 (October 2019): 144. http://dx.doi.org/10.1017/s1743921320002768.
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AbstractThe variation of optical continuum and broad emission lines is observed in all type 1 active galactic nuclei (AGN). In some cases even extreme variability is detected when broad-line profiles completely disappear as is the case in the co-called changing-look AGN, which raise new question on the theoretical model of AGN. This variability is an important tool to study the physics and geometry of the broad line region (BLR), e.g. it can be used to estimate its size through the reverberation mapping technique. Especially, long-term campaigns give new insights, like the detection of the periodic signals or discoveries of changing-look AGN. Here we will present the results of our long-term monitoring campaign of several well-known AGN, as e.g. NGC 3516 for which we confirm that it is the changing-look AGN, putting special attention of the applications for future large time-domain spectroscopic surveys, like the MaunaKea Spectroscopic Explorer project.
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Kammoun, E. S., M. Dovčiak, I. E. Papadakis, M. D. Caballero-García, and V. Karas. "UV/Optical Disk Thermal Reverberation in Active Galactic Nuclei: An In-depth Study with an Analytic Prescription for Time-lag Spectra." Astrophysical Journal 907, no. 1 (January 21, 2021): 20. http://dx.doi.org/10.3847/1538-4357/abcb93.
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Oknyansky, V. L., M. S. Brotherton, S. S. Tsygankov, A. V. Dodin, D.-W. Bao, B.-X. Zhao, P. Du, et al. "Multiwavelength monitoring and reverberation mapping of a changing look event in the Seyfert galaxy NGC 3516." Monthly Notices of the Royal Astronomical Society 505, no. 1 (April 22, 2021): 1029–45. http://dx.doi.org/10.1093/mnras/stab1138.
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ABSTRACT We present the results of photometric and spectroscopic monitoring campaigns of the changing look AGN NGC 3516 carried out in 2018 to 2020 covering the wavelength range from the X-ray to the optical. The facilities included the telescopes of the CMO SAI MSU, the 2.3-m WIRO telescope, and the XRT and UVOT of Swift. We found that NGC 3516 brightened to a high state and could be classified as Sy1.5 during the late spring of 2020. We have measured time delays in the responses of the Balmer and He ii λ4686 lines to continuum variations. In the case of the best-characterized broad H β line, the delay to continuum variability is about 17 d in the blue wing and is clearly shorter, 9 d, in the red, which is suggestive of inflow. As the broad lines strengthened, the blue side came to dominate the Balmer lines, resulting in very asymmetric profiles with blueshifted peaks during this high state. During the outburst the X-ray flux reached its maximum on 2020 April 1 and it was the highest value ever observed for NGC 3516 by the Swift observatory. The X-ray hard photon index became softer, ∼1.8 in the maximum on 2020 April 21 compared to the mean ∼0.7 during earlier epochs before 2020. We have found that the UV and optical variations correlated well (with a small time delay of 1–2 d) with the X-ray until the beginning of 2020 April, but later, until the end of 2020 June, these variations were not correlated. We suggest that this fact may be a consequence of partial obscuration by Compton-thick clouds crossing the line of sight.
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Gianniotis, N., F. Pozo Nuñez, and K. L. Polsterer. "Disentangling the optical AGN and host-galaxy luminosity with a probabilistic flux variation gradient." Astronomy & Astrophysics 657 (January 2022): A126. http://dx.doi.org/10.1051/0004-6361/202141710.
Full textAbstract:
Context. We present a novel probabilistic flux variation gradient (PFVG) approach to separate the contributions of active galactic nuclei (AGN) and host galaxies in the context of photometric reverberation mapping (PRM) of AGN. Aims. We explored the ability of recovering the fractional contribution in a model-independent way using the entire set of light curves obtained through different filters and photometric apertures simultaneously. Methods. The method is based on the observed “bluer when brighter” phenomenon that is attributed to the superimposition of a two-component structure; the red host galaxy, which is constant in time, and the varying blue AGN. We describe the PFVG mathematical formalism and demonstrate its performance using simulated light curves and available PRM observations. Results. The new probabilistic approach is able to recover host-galaxy fluxes to within 1% precision as long as the light curves do not show a significant contribution from time delays. This represents a significant improvement with respect to previous applications of the traditional FVG method to PRM data. Conclusions. The proposed PFVG provides an efficient and accurate way to separate the AGN and host-galaxy luminosities in PRM monitoring data. The method will be especially helpful in the case of large upcoming photometric survey telescopes such as the public optical/near-infrared Legacy Survey of Space and Time (LSST) at the Vera C. Rubin Observatory. Finally, we have made the algorithms freely available as part of our Julia PFVG package.
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Kovačević, Andjelka B., Jian-Min Wang, and Luka Č. Popović. "Kinematic signatures of reverberation mapping of close binaries of supermassive black holes in active galactic nuclei." Astronomy & Astrophysics 635 (February 28, 2020): A1. http://dx.doi.org/10.1051/0004-6361/201936398.
Full textAbstract:
Context. An unresolved region in the relative vicinity of the event horizon of a supermassive black holes (SMBH) in active galactic nuclei (AGN) radiates strongly variable optical continuum and broad-line emission flux. These fluxes can be processed into two-dimensional transfer functions (2DTF) of material flows that encrypt various information about these unresolved structures. An intense search for kinematic signatures of reverberation mapping of close binary SMBH (SMBBH) is currently ongoing. Aims. Elliptical SMBBH systems (i.e. both orbits and disc-like broad-line regions (BLR) are elliptic) have not been assessed in 2DTF studies. We aim to numerically infer such a 2DTF because the geometry of the unresolved region is imprinted on their optical emission. Through this, we determine their specific kinematical signatures. Methods. We simulated the geometry and kinematics of SMBBH whose components are on elliptical orbits. Each SMBH had a disc-like elliptical BLR. The SMBHs were active and orbited each other tightly at a subparsec distance. Results. Here we calculate for the first time 2DTF, as defined in the velocity-time delay plane, for several elliptical configurations of SMBBH orbits and their BLRs. We find that these very complex configurations are clearly resolved in maps. These results are distinct from those obtained from circular and disc-wind geometry. We calculate the expected line variability for all SMBBH configurations. We show that the line shapes are influenced by the orbital phase of the SMBBH. Some line profiles resemble observed profiles, but they can also be much deformed to look like those from the disc-wind model. Conclusions. First, our results imply that using our 2DTF, we can detect and quantify kinematic signatures of elliptical SMBBH. Second, the calculated expected line profiles share some intriguing similarities with observed profiles, but also with some profiles that are synthesised in disc-wind models. To overcome the non-uniqueness of the spectral line shapes as markers of SMBBH, they must be accompanied with 2DTF.