Effects of internal resonances in the pitch glide of Chinese gongs

The framework of nonlinear normal modes gives a remarkable insight into the dynamics of nonlinear vibratory systems exhibiting distributed nonlinearities. In the case of Chinese opera gongs, geometrical nonlinearities lead to a pitch glide of several vibration modes in playing situation. This study investigates the relationship between the nonlinear normal modes formalism and the ascendant pitch glide of the fundamental mode of a xiaoluo gong. In particular, the limits of a single nonlinear mode modeling for describing the pitch glide in playing situation are examined. For this purpose, the amplitude-frequency relationship (backbone curve) and the frequency-time dependency (pitch glide) of the fundamental nonlinear mode is measured with two excitation types, in free vibration regime: first, only the fundamental nonlinear mode is excited by an experimental appropriation method resorting to a phase-locked loop; second, all the nonlinear modes of the instrument are excited with a mallet impact (playing situation). The results show that a single nonlinear mode modeling fails at describing the pitch glide of the instrument when played because of the presence of 1:2 internal resonances implying the nonlinear fundamental mode and other nonlinear modes. Simulations of two nonlinear modes in 1:2 internal resonance confirm qualitatively the experimental results

Fast radiative transfer modeling for infrared imaging radiometry

Fast radiative transfer codes have been developed for simulating the outgoing radiance (and corresponding brightness temperature) to be measured by the Infrared Imaging Radiometer (IIR) of the space Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) mission. Two simple codes (FASRAD and FASAA), for which scattering is neglected, as well as an accurate code (FASDOM), accounting for scattering and absorption with the Discrete Ordinate Method (DOM), are presented. Their accuracy has been estimated with a reference code including a line-by-line model and the DOM. Simulations have shown that the accuracy is generally better than 0.3 K on the brightness temperature for clear or cloudy atmospheres. This accuracy agrees with the expected one of future IIR measurements. In addition, the impact of scattering on the brightness temperature has been evaluated for semi-transparent liquid clouds in the IIR spectral range. Especially, simulations have shown that cloud microphysics retrieval might be possible with the Brightness Temperature Difference (BTD) between two IIR bands, using the couple of wavelengths (8.7–12µm) or (10.6–12µm). However, scattering strongly influences the radiation for shorter wavelengths. The error on the BTD with (8.7–12µm) can reach 4 K when scattering is neglected, leading to large uncertainties in the retrieval of droplet effective radius

Climatology of convective density currents in the southern foothills of the Atlas Mountains

Density currents fed by evaporationally cooled air are an important dust storm generating feature and can constitute a source of moisture in arid regions. Recently, the existence of such systems has been demonstrated for the area between the High Atlas Mountains and the Sahara desert in southern Morocco on the basis of case studies. Here, a climatological analysis is presented that uses data from the dense climate station network of the IMPETUS project (An Integrated Approach to the Efficient Management of Scarce Water Resources in West Africa) for the 5 year period 20022006. Objective criteria mainly based upon abrupt changes in wind and dew point temperature are defined to identify possible density current situations. The preselected events are then subjectively evaluated with the help of satellite imagery and surface observations to exclude causes for air mass changes other than moist convective cold pool formation. On average, 11 ± 4 density currents per year are detected with the main season lasting from April to September. Density currents occur mainly in the afternoon and evening due to the diurnal cycle of moist convection. Mean changes at the leading edge are increases in 2 m dew point temperature and wind speed by 5.4°C and 8.2 m s-1, respectively, and a decrease in 2 m air temperature of 2.3°C. The High Atlas and Jebel Saghro are found to be the most important source regions, while only a few systems originate over the Saharan lowlands. Labilization of the atmosphere due to upper-level troughs over northwest Africa and an enhanced moisture content favor density current formation. In addition, detailed case studies representative of different density current types are presented

Identification de modes nonlinéaires par forme normale et continuation expérimentale à base de boucle à verrouillage de phase

International audienceIn this article, we address the model identication of nonlinear vibratory systems, with a specic focus on systems modeled with distributed nonlinearities, such as geometrically nonlinear mechanical structures. The proposed strategy theoretically relies on the concept of nonlinear modes of the underlying conservative unforced system and the use of normal forms. Within this framework, it is shown that without internal resonance, a valid reduced order model for a nonlinear mode is a single Duffing oscillator. We then propose an efficient experimental strategy to measure the backbone curve of a particular nonlinear mode and we use it to identify the free parameters of the reduced order model. The experimental part relies on a Phase-Locked Loop (PLL) and enables a robust and automatic measurement of backbone curves as well as forced responses. It is theoretically and experimentally shown that the PLL is able to stabilize the unstable part of Duffingng-like frequency responses, thus enabling its robust experimental measurement. Finally, the whole procedure is tested on three experimental systems: a circular plate, a chinese gong and a piezoelectric cantilever beam. It enable to validate the procedure by comparison to available theoretical models as well as to other experimental identication methods

MERLIN (Methane Remote Sensing Lidar Mission): an Overview

The Methane Remote Sensing Lidar Mission (MERLIN), currently in phase B, is a joint cooperation between France and Germany on the development, launch and operation of a methane (CH4) monitoring satellite. MERLIN is focused on global measurements of the spatial and temporal gradients of atmospheric CH4, the second most anthropogenic gas, with a precision and accuracy sufficient to constrain Methane fluxes significantly better than with the current observation network. For the first time, measurements of atmospheric composition will be performed from space thanks to an IPDA (Integrated Path Differential Absorption) LIDAR (Light Detecting And Ranging). This payload is under the responsibility of the German space agency (DLR), while the platform (MYRIADE Evolutions product line) is developed by the French space agency (CNES). The IPDA technique relies on DIAL (Differential Absorption LIDAR) measurements using a pulsed laser emitting at two wavelengths, one wavelength accurately locked on a spectral feature of the methane absorption line, and the other wavelength free from absorption to be used as reference. This technique enables measurements in all seasons, at all latitudes. It also guarantees almost no contamination by aerosols or water vapour cross-sensitivity, and thus has the advantage of an extremely low level of systematic error on the dry-air column mixing ratio of CH4

MERLIN (Methane Remote Sensing Lidar Mission): an Overview

The Methane Remote Sensing Lidar Mission (MERLIN), currently in phase B, is a joint cooperation between France and Germany on the development, launch and operation of a methane (CH4) monitoring satellite. MERLIN is focused on global measurements of the spatial and temporal gradients of atmospheric CH4, the second most anthropogenic gas, with a precision and accuracy sufficient to constrain Methane fluxes significantly better than with the current observation network. For the first time, measurements of atmospheric composition will be performed from space thanks to an IPDA (Integrated Path Differential Absorption) LIDAR (Light Detecting And Ranging). This payload is under the responsibility of the German space agency (DLR), while the platform (MYRIADE Evolutions product line) is developed by the French space agency (CNES). The IPDA technique relies on DIAL (Differential Absorption LIDAR) measurements using a pulsed laser emitting at two wavelengths, one wavelength accurately locked on a spectral feature of the methane absorption line, and the other wavelength free from absorption to be used as reference. This technique enables measurements in all seasons, at all latitudes. It also guarantees almost no contamination by aerosols or water vapour cross-sensitivity, and thus has the advantage of an extremely low level of systematic error on the dry-air column mixing ratio of CH4

Soft tissue sarcoma in children, adolescents and young adults: Outcomes according to compliance with international initial care guidelines

International audienc