Spectra as Theoretical and Practical Models in Gérard Grisey’s Creative Process

Combining sketch studies, musical analysis, and acoustic analysis, this article examines the impact of spectral models on Grisey’s creative process in the 1970s. First, it focuses on Grisey’s establishment of initial theoretical models in Dérives and Périodes, composed during his residence at the Villa Medici (1972–74), during which period he conducted his own study of acoustics. The article then looks at how, back in Paris, the composer started studying with the acoustician Émile Leipp and then worked with Michèle Castellengo, with whom in 1977 he undertook for the first time the spectral analysis of instrumental sounds. Finally the article examines in detail how some spectrograms, once transcribed, were used in Modulations (1976–77) to construct a complex spectral polyphony. If Grisey draws his inspiration from sound phenomena and the characteristics of auditory perception, he does not for all that neglect structuralism: spectral models serve both to simulate natural phenomena and to formalise his compositional processes.

Constraints on near-source saturation models for avoiding over-saturation of response spectral ordinates in RVT-based stochastic ground-motion simulations

Inversions of empirical data and ground-motion models to find Fourier spectral parameters can result in parameter combinations that produce over-saturation of short-period response spectral ordinates. While some evidence for over-saturation in empirical data exists, most ground-motion modellers do not permit this scaling within their models. Host-to-target adjustments that are made to published ground-motion models for use in site-specific seismic hazard analyses frequently require the identification of an equivalent set of Fourier spectral parameters. In this context, when inverting response spectral models that do not exhibit over-saturation effects, it is desirable to impose constraints upon the Fourier parameters to match the scaling of the host-region model. The key parameters that determine whether over-saturation arises are the geometric spreading rate (γ) and the exponential rate within near-source saturation models (hβ). The article presents the derivation of simple nonlinear constraints that can be imposed to prevent over-saturation when undertaking Fourier spectral inversions.

Noise

This chapter concludes the section on techniques by exploring signals of non-deterministic nature. It discusses an expanded notion of spectrum, which may be applied to probabilistic phenomena. Methods of analysis and of generation of noisy spectra are presented. Principles of granular processing, and of wavelet analysis are explored. The notion of linear prediction is discussed leading to a consideration of spectral models that include deterministic and non-deterministic elements. The conclusion further summarises the new ideas about the spectrum introduced in this chapter.

Low and High Broadband Spectral Models of Atmospheric Pressure Fluctuation

This paper presents new low and high power spectral density models for pressure fluctuations at the Earth’s surface over the frequency range of (10−5 – 8) Hz. Previously proposed models often included limitations, such as a much narrower frequency range, the inclusion of erroneous and non-calibrated data or recorded data not deconvolved from the measurement system responses. The progress recently made with response modeling and field calibration of pressure fluctuation measurement systems now allows to propose more realistic power spectral density models over an extremely large frequency band. This paper describes how the data were selected, processed, and analyzed to obtain the final global models. In addition, the intermediate results allow the characterization of several atmospheric mechanisms, such as gravity wave saturation, limits of the buoyancy and acoustic cut-off frequencies or wind turbulence modes. The two proposed low and high power spectral density models are planned to be used for a wide range of applications, including assessing the quality of measured pressure fluctuations, verifying the validity of modeled pressure fluctuations and supporting the design, testing and calibration of a new generation of measurement systems. The models presented in this paper are made available to the scientific community.

Spectral mapping of soil organic carbon

This chapter first reviews recent pilot studies covering limited areas often with exposed bare soils. Then we focus on the challenges for large-scale application of spectral mapping when the soil and parent material are heterogeneous and surface conditions are unknown. In order to deal with these constraints we discuss i) calibration of spectral models based on large spectral libraries, ii) surface conditions that disturb the soil signal, and iii) time series of images in order to delimit cropland fields and increase the extent of bare soil that can be mapped. Finally, a case study deals with a SOC prediction map derived from the spectra of a Sentinel-2 image and calibrated using the LUCAS spectral library.

Comparison of Radiation Models for a Turbulent Piloted Methane/Air Jet Flame: A Frozen-Field Study

Numerical modeling of radiative transfer in nongray reacting media is a challenging problem in computational science and engineering. The choice of radiation models is important for accurate and efficient high-fidelity combustion simulations. Different applications usually involve different degrees of complexity, so there is yet no consensus in the community. In this paper, the performance of different radiative transfer equation (RTE) solvers and spectral models for a turbulent piloted methane/air jet flame are studied. The flame is scaled from the Sandia Flame D with a Reynolds number of 22,400. Three classes of RTE solvers, namely the discrete ordinates method, spherical harmonics method, and Monte Carlo method, are examined. The spectral models include the Planck-mean model, the full-spectrum k-distribution (FSK) method, and the line-by-line (LBL) calculation. The performances of different radiation models in terms of accuracy and computational cost are benchmarked. The results have shown that both RTE solvers and spectral models are critical in the prediction of radiative heat source terms for this jet flame. The trade-offs between the accuracy, the computational cost, and the implementation difficulty are discussed in detail. The results can be used as a reference for radiation model selection in combustor simulations.