Energy Decay Curve Research Articles

Evaluating the effect of dome geometry on acoustical quality of a pavilion

Acoustic performance of structures is an emerging field of research enquiry, with limited number of studies conducted in the Indian context. To address this gap, this study examines the effect of varied dome geometry on the acoustic quality of a pavilion. In-situ measurements pertaining to energy decay curve from impulse sound were collated at a historical 'Baradari'. The square shaped pavilion considered in the study is surmounted by a shallow dome and has three doorways on each side. Virtual simulation models of the pavilion were built thereafter and validated. In this study, dome geometries that emerged between the 15th-19th century (corbelled, shallow, single-shell, bulbous, and onion) in the Indian subcontinent are examined. Acoustic simulation was conducted on treble software to assess and compare the sound quality of each dome geometry. The study found that the reverberation, RT30, for the flat dome was approximately half to that of the single-shell dome. The study established that the choice of dome geometry is crucial as it impacts the reverberation time. The study findings vary with building typology, size, and architectural features. Nevertheless, this study should be viewed as a case-specific analysis that identifies optimal dome geometry for improved pavilion acoustics.

An experimental approach for in-situ characterization of dynamic dissipative properties of road pavements

The dissipative properties of road pavements may have beneficial effects to reduce vehicle vibrations, traffic noise, vehicles-structure dynamic interaction, and degradation of pavement materials. Assessing the dissipative capacity and the damping properties of road pavements is, therefore, of critical importance. Such assessment has been mainly conducted in recent years by laboratory-scale dynamic experiments, while little effort has been devoted to in-situ tests. The latter are, in fact, cumbersome for practical reasons and typically require a more advanced data analysis when highly coupled modes of vibration are involved. Due to the heterogeneity of the road structure, classical methods are not capable of accurately estimating the road damping properties. The present study proposes an alternative experimental approach based on recording signals from accelerometers embedded in the road, which is impacted by an instrumented hammer. The data are analyzed both in the frequency and in the time domains through the combined use of stabilization diagrams and energy decay tools. Multi-mode fitting algorithms are employed to construct stabilization diagrams for the identification of resonance frequencies, while energy decay curves allow for a robust evaluation of the damping values at the identified frequencies. The effectiveness of the approach was assessed on an asphalt road structure.

High-efficiency near-white emission of Bi3+/Sm3+ co-doped double-perovskite phosphors for optical thermometry

Near-white emission phosphors of the Bi3+/Sm3+ co-doped double-perovskite Ca2YTaO6 were successfully prepared via a simple solid-state reaction. The crystal structures and lattice parameters as functions of doping ion type and its content were analyzed. Note that all the prepared samples have the monoclinic structure with the space group of P 21/n (14). Their lattice parameters were enlarged with the increment of doping ion content since the Y3+ ion with the smaller radius was substituted by the Bi3+ and Sm3+ ions. The photoluminescence (PL) properties of single Bi3+-doped and Bi3+/Sm3+ co-doped Ca2YTaO6 phosphors were fully investigated in terms of PL emission spectrum, emission intensity, energy transfer mechanism, chromaticity coordinate, decay curve, thermal stability, and internal quantum yield. Interestingly, the Ca2YTaO6:0.015Bi3+/0.07Sm3+ phosphor exhibited a high quantum yield (70.71%). Furthermore, the relative sensitivity based on the dual-emission centers (Bi3+ and Sm3+) was also analyzed. It is demonstrated that high-efficiency near-white Ca2YTaO6:Bi3+/Sm3+ phosphor with good sensing properties is expected to be a candidate in the field of optical thermometry.

Directional reverberation time and the image source method for rectangular parallelepipedal rooms.

The image source (IS) method is a commonly used geometrical acoustics simulation technique in room and virtual acoustics. In particular, it has been used in the analysis of room reverberation under different choices of geometry and wall conditions. Under a simple rectangular parallelepipedal geometry, reverberation time is known to be dependent on the direction of arrival of reflections relative to the room axes. In this article, a closed-form expression for the directional energy decay and reverberation time is derived, which is valid in the late response, and may be used in the case of either angle-independent or angle-dependent reflection. The expression reduces to an easily evaluated formula in the case of an omnidirectional energy decay curve (EDC). Various numerical results are presented, including the validation of the closed-form expression against EDCs and late reverberation times drawn directly from the IS method.

Synthesis, structure and luminescence properties of a novel red fluorescent material Ba2MgB2O6:Eu3+

The crystal structure of Ba2-xMgB2O6:xEu3+ phosphors, synthesized using a solid-state reaction, have been confirmed by X-ray diffraction analysis. This study focuses on the site occupancy preference of Eu3+ ions within the matrix, which was determined using bond energy theory, fluorescent spectra, and a consideration of energy transport and decay curves. The impact of Eu3+ ion concentration on luminescence has been assessed, and an optimal concentration (x = 0.22) identified. The critical distance, Rc was 9.6 Å, with a calculated θ value of 19.67, indicating that quadrupole-quadrupole interaction plays a critical role in the quenching Ba2-xMgB2O6:xEu3+ phosphors. The Ba2-xMgB2O6:xEu3+ phosphors exhibited a color purity of 99.26%, and a quantum efficiency of 49.68%. The activation energy Ea was determined to equal 0.2987 eV. The results have established Ba1.78MgB2O6:0.22Eu3+ as a red fluorescent powder with high quantum efficiency and a millisecond fluorescence lifetime.

Differences between measured and simulated room impulse responses

Simulation models based on geometrical acoustics mostly do not immediately deliver a simulated room impulse response, but intermediate results such as an energy histogram or an energy decay curve. At this point, further models are required to generate a room impulse response of the simulated environment, which are essential for the process of auralization. While for various simulated scenarios, the application of a reflection model based on a basic theory is sufficient, detailed comparisons of simulated and measured room impulse responses reveal differences which are attributed to the lack of diffuse reflections in the applied reflection model. These deviations can also substantially affect derived room acoustic parameters. This work presents and explains the shortcomings and discusses potential improvements to be considered in the simulation process.

DECT-CLUST: Dual-Energy CT Image Clustering and Application to Head and Neck Squamous Cell Carcinoma Segmentation.

Dual-energy computed tomography (DECT) is an advanced CT computed tomography scanning technique enabling material characterization not possible with conventional CT scans. It allows the reconstruction of energy decay curves at each 3D image voxel, representing varied image attenuation at different effective scanning energy levels. In this paper, we develop novel unsupervised learning techniques based on mixture models and functional data analysis models to the clustering of DECT images. We design functional mixture models that integrate spatial image context in mixture weights, with mixture component densities being constructed upon the DECT energy decay curves as functional observations. We develop dedicated expectation-maximization algorithms for the maximum likelihood estimation of the model parameters. To our knowledge, this is the first article to develop statistical functional data analysis and model-based clustering techniques to take advantage of the full spectral information provided by DECT. We evaluate the application of DECT to head and neck squamous cell carcinoma. Current image-based evaluation of these tumors in clinical practice is largely qualitative, based on a visual assessment of tumor anatomic extent and basic one- or two-dimensional tumor size measurements. We evaluate our methods on 91 head and neck cancer DECT scans and compare our unsupervised clustering results to tumor contours traced manually by radiologists, as well as to several baseline algorithms. Given the inter-rater variability even among experts at delineating head and neck tumors, and given the potential importance of tissue reactions surrounding the tumor itself, our proposed methodology has the potential to add value in downstream machine learning applications for clinical outcome prediction based on DECT data in head and neck cancer.

The Optimal Determination of the Truncation Time of Non-Exponential Sound Decays

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).

Scattering Delay Network Simulator of Coupled Volume Acoustics

Artificial reverberators provide a computationally viable alternative to full-scale room acoustics simulation methods for deployment in interactive, immersive systems. Scattering delay network (SDN) is an artificial reverberator that allows direct parametric control over the geometry of a simulated cuboid enclosure, as well as the directional characteristics of the simulated sound sources and microphones. This paper extends the concept of SDN reverberators to multiple enclosures coupled via an aperture. The extension allows independent control of the acoustical properties of the coupled enclosures and the size of the connecting aperture. Transfer functions of the coupled-volume SDN are derived. The effectiveness of the proposed method is evaluated in terms of rendered energy decay curves in comparison to full-scale ray-tracing models and scale model measurements.

De-Noising Process in Room Impulse Response with Generalized Spectral Subtraction

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.

Directional sound field decay analysis in coupled spaces

Multi-exponential energy decays—showing a distinct curvature in the measured decay curve—are a well known phenomenon in coupled spaces if both spaces exhibit different reverberation times due to their specific absorption characteristics or volumes. Recently, Berzborn et al. (2019) investigated directional energy decay curves—calculated from a plane wave decomposition of the sound field—as an analysis framework for the angular distribution of energy during the decay process in reverberation rooms. In this contribution, we investigate the directional characteristics of the energy decay in two rooms connected by a door. Spherical microphone array measurements at two different receiver positions and coupling areas were performed. Results indicate a distinct anisotropic energy decay in the room with the shorter reverberation time, showing a decreased isotropy in the late decay process compared to the early part.

Improved thermal stability and tunable interfacial thermal resistance in a phosphorene/hBN bilayer heterostructure

Two-dimensional (2D) van der Waals heterostructures have drawn intense interest due to their numerous outstanding properties and are considered as promising candidates for future generations of nanodevices. Thermal behaviors of these heterostructures are of great significance to the functional performance of the devices. In this work, molecular dynamics simulations are performed to investigate the thermal stability of phosphorene and interface thermal transport in a phosphorene/hBN bilayer heterostructure. The thermally stable temperature of phosphorene increases 40 K in the bilayer heterostructure compared to that of independent phosphorene. Interfacial thermal resistance R between phosphorene and hBN is characterized by using a transient heating technique and the obtained R values, based on the lumped heat-capacity model and the energy decay curve, respectively, are in agreement at temperatures from 50 K to 350 K. The predicted R is about 8.6 × 10−8 Km2W−1 at room temperature and R decreases monotonically with both system temperature and interface coupling strength, which is attributed to several factors, including increased phonon populations, enhanced inelastic scattering, and strengthened phonon couplings between layers as well as between in-plane/out-of-plane modes in hBN. Phonon spectra analysis elucidates that the heat transport channels across phosphorene/hBN interface are mainly provided by the couplings between phonons in phosphorene and low-frequency phonons in hBN, which is the active frequency of the out-of-plane phonons in hBN.

Directional sound field decay analysis in performance spaces

The analysis of the spatio-temporal features of sound fields is of great interest in the field of room acoustics, as they inevitably contribute to a listeners impression of the room. The perceived spaciousness is linked to lateral sound incidence during the early and late part of the impulse response which largely depends on the geometry of the room. In complex geometries, particularly in rooms with reverberation reservoirs or coupled spaces, the reverberation process might show distinct spatio-temporal characteristics. In the present study, we apply the analysis of directional energy decay curves based on the decomposition of the sound field into a plane wave basis, previously proposed for reverberation room characterization, to general purpose performance spaces. A simulation study of a concert hall and two churches is presented uncovering anisotropic sound field decays in two cases and highlighting implications for the resulting temporal evolution of the sound field diffuseness.

Binaural Modelling and Spatial Auditory Cue Analysis of 3D-Printed Ears.

In this work, a binaural model resembling the human auditory system was built using a pair of three-dimensional (3D)-printed ears to localize a sound source in both vertical and horizontal directions. An analysis on the proposed model was firstly conducted to study the correlations between the spatial auditory cues and the 3D polar coordinate of the source. Apart from the estimation techniques via interaural and spectral cues, the property from the combined direct and reverberant energy decay curve is also introduced as part of the localization strategy. The preliminary analysis reveals that the latter provides a much more accurate distance estimation when compared to approximations via sound pressure level approach, but is alone not sufficient to disambiguate the front-rear confusions. For vertical localization, it is also shown that the elevation angle can be robustly encoded through the spectral notches. By analysing the strengths and shortcomings of each estimation method, a new algorithm is formulated to localize the sound source which is also further improved by cross-correlating the interaural and spectral cues. The proposed technique has been validated via a series of experiments where the sound source was randomly placed at 30 different locations in an outdoor environment up to a distance of 19 m. Based on the experimental and numerical evaluations, the localization performance has been significantly improved with an average error of 0.5 m from the distance estimation and a considerable reduction of total ambiguous points to 3.3%.

Yb3+/Tm3+ and Yb3+/Ho3+ doped NaY9(SiO4)6O2 phosphors: Upconversion luminescence processes, temperature-dependent emission spectra and optical temperature-sensing properties

The improvement of sensitivity is an important issue for optical temperature-sensing materials. In this work, a series of oxide-based upconversion phosphors were designed by a conventional solid state reaction method. The XRD patterns revealed that the as-prepared samples are single-phase. The optimal Tm3+/Ho3+ doping concentrations were determined, and the luminescence quenching features were studied by using the energy level diagram and decay curves. The temperature-dependent emission spectra were measured to evaluate the optical temperature-sensing properties. It was found that the fluorescence intensity ratio (FIR) for emissions from thermally-coupled levels of Tm3+ follows Boltzmann distribution, and the FIR for emissions from non-thermally-coupled levels of Ho3+ can be fitted by a linear relation. Both the absolute and relative sensitivities were calculated and compared for different strategies in the present system. High relative and absolute sensitivities were obtained by employing I697/I789 of Tm3+ and I660/I548 of Ho3+, respectively. Besides, the population channel on the excited states of Ho3+ was clarified by analyzing the emission spectra excited by different ways under various temperatures.

Decay of turbulence in a liquid metal duct flow with transverse magnetic field

Decay of honeycomb-generated turbulence in a duct with a static transverse magnetic field is studied via direct numerical simulations. The simulations follow the revealing experimental study of Sukoriansky et al. (Exp. Fluids, vol. 4 (1), 1986, pp. 11–16), in particular the paradoxical observation of high-amplitude velocity fluctuations, which exist in the downstream portion of the flow when the strong transverse magnetic field is imposed in the entire duct including the honeycomb exit, but not in other configurations. It is shown that the fluctuations are caused by the large-scale quasi-two-dimensional structures forming in the flow at the initial stages of the decay and surviving the magnetic suppression. Statistical turbulence properties, such as the energy decay curves, two-point correlations and typical length scales are computed. The study demonstrates that turbulence decay in the presence of a magnetic field is a complex phenomenon critically depending on the state of the flow at the moment the field is introduced.

Upconversion luminescence of Ca2Gd8(SiO4)6O2:Yb3+-Tm3+-Tb3+/Eu3+ phosphors for optical temperature sensing

In order to develop new upconversion (UC) phosphors for optical temperature sensors, a series of Yb3+-Tm3+-Tb3+/Eu3+ doped Ca2Gd8(SiO4)6O2 (CGS) samples were designed by solid-state reaction method. The phase purity was examined by XRD patterns, which revealed that the obtained samples are all single-phase in spite of the rare earth (RE) ions doping. Upon 980 nm excitation, the emission peaks of all the doped luminescent ions (Tm3+, Tb3+ and Eu3+) have been observed, and the energy transfer processes among the RE ions in the UC luminescence were discussed with the help of the energy level diagram and decay curves. The competitive absorption between Tm3+ and Tb3+/Eu3+ from Yb3+ was proposed to interpret the sharp decrease of Tm3+ emission intensity. The temperature sensing behavior was evaluated by measuring the temperature-dependent UC luminescence of the typical CGS:10%Yb3+,0.2%Tm3+,10%Tb3+,1.25%Eu3+ phosphor. It has been found that the fluorescence intensity ratio (FIR) technique by employing ITb/IEu and ITb/ITm can generate high absolute sensitivity, but the relative sensitivity still needs further improvement compared with some other phosphors doped with Er3+/Ho3+/Tm3+.

Red-emitting phosphor Na2Ca2Nb4O13:Eu3+ for LEDs: Synthesis and luminescence properties

Na2Ca2Nb4O13:Eu3+ phosphor is successfully synthesize by the high-temperature solid-state reaction method in air. The crystal structures, morphology, X-ray powder diffractions (XRPD) patterns, energy dispersive X-ray (EDX) spectrum, decay curves, and luminescence properties are investigated. Na2Ca2Nb4O13:Eu3+ phosphor emits red light with the chromaticity coordinates (0.6312, 0.3684) and the emission spectrum is observed in the range of 575–725 nm, which contains four emission bands because of the 5D0 → 7F1 (575–600 nm), 5D0 → 7F2 (600–650 nm), 5D0 → 7F3 (650–670 nm), 5D0 → 7F4 (680–725 nm) transitions of Eu3+ ion, respectively. The optimal Eu3+ ion concentration in Na2Ca2Nb4O13:Eu3+ phosphor is ~10 mol%. The lifetime decreases in turn from 736.5 μs to 431.8 μs with increasing Eu3+ ion concentration from 2 mol% to 12 mol%. Na2Ca2Nb4O13:Eu3+ phosphor has a good thermal stability according to the temperature-dependent emission spectra. Luminous mechanism is explained by energy level diagram of Eu3+ ion. The experimental results indicate that Na2Ca2Nb4O13:Eu3+ phosphor has a hope to be used as red phosphor for light-emitting diodes (LEDs) based on near ultraviolet (UV) and blue LED chips.

Analysis of sound field isotropy based on directional energy decay curves

The analysis of the diffuseness of sound fields is of great interest in room acoustic applications ranging from the analysis of concert venues to reverberation room design and calibration. However, a standardized robust diffuseness estimation method is currently lacking. The fundamental definition of the diffuse sound field is that it is isotropic—requiring the sound field to be composed of infinitely many sound waves from uncorrelated sources with directions of arrival uniformly distributed over a sphere. Due to their symmetry, spherical microphone arrays are especially favorable for the analysis of the isotropy requirement. In this work, we propose the directional energy decay curve which we calculate from a directional room impulse response captured with a spherical microphone array. Further, we show how the analysis of the spatial variations of the directional energy decay curve enables examining the isotropy of sound fields in rooms. Finally, we present a simulation study of multiple room configurations with varying degrees of sound field diffuseness.

Comparative study of two geometrical acoustic simulation models

Simulations based on the concepts of geometrical acoustics are today well-established tools for acousticians, being widely used for evaluation of sound quality in rooms and urban spaces. However, although a lot of different models are available and have been evaluated in the past, it is still very important to guarantee the validity and quality of simulated data and reproduced sound. This work presents a comparison between the signal processing strategies in two acoustic simulators based on geometrical models. Obvious expectation was that both simulators would produce the same results when fed by exactly the same input data. However, issues related to model assumptions, propagation methods characteristics and signal processing techniques adopted by each simulator introduce differences which alter the final results, i.e., the simulated acoustic impulse responses. This papers aims to present such deviation and helps to understand the influence of each component over the results. Firstly, both simulators are described in detail, presenting their acoustic models and the signal processing approaches. In addition, an extensive analysis of early reflections is performed, considering pressure levels, reflection order, their arrival time and directional characteristics. Next, simulated energy decay curves, monaural room acoustic parameters and spectra are objectively compared to measured data of a reverberant chamber, in two different conditions. The differences are then pointed out and minimized by unifying the signal processing of both simulators. The results of this comparison reveal that signal processing and inherit method characteristics still have strong influence over the simulated impulse responses, mainly for the late part. Some consequences are energy misbalance between early and late parts of impulse response, leading to differences over the room acoustic parameters, mainly clarity and definition.