Some issues when using Fourier analysis for the extraction of modal parameters

It is sometimes necessary to determine the manner in which structures deteriorate with respect to time; for instance when quantifying a material's ability to withstand sustained dynamic loads. In such cases, it is well established that loss of structural integrity is reflected by variations in modal characteristics such as stiffness. This paper addresses some practical limitations of Fourier analysis with respect to temporal resolution and the uncertainties associated with extracting variations in modal parameters. The statistical analysis of numerous numerical experiments shows how techniques, such as data overlapping and zero-padding, can be used to improve the sensitivity of modal parameter extraction

Determining Fatigue Progression in Corrugated Paperboard Containers Subjected to Dynamic Compression

During the transportation phase of the distribution cycle, packaged consignments are subjected to random dynamic compressive loads that arise from random vibrations generated by the vehicle. The protective packaging system’s ability to withstand these dynamic compressive loads for sufficiently long periods depends on the environmental vibration levels, the nominal stresses as well as the material’s characteristics. The research tests the hypothesis that cumulative damage in the packaging system under random dynamic compression will result in a change in the overall stiffness and damping characteristics of the system as well as in the nature of the statistical distribution of the response. These are manifested, respectively, as a shift in the fundamental resonant frequency of the system as well as an increase in the bandwidth of the frequency response function when subjected to random excitation. The paper presents further results from preliminary experiments in which corrugated paperboard container samples were subjected to dynamic compressive loads by means of broad-band random base excitation with a vibration table coupled with a guided dead-weight arrangement. The level of cumulative damage in the sample was estimated by continuously monitoring the Frequency Response Function (FRF) of the system as well as by observation of thermal distribution images captured at regular intervals. The thermal images were used to establish the sensitivity of the method and to determine whether it can be useful in detecting incipient catastrophic mechanical failure of the packaging system. Results show that thermographic images are useful in identifying regions of elevated temperature in corrugated paper samples and that these regions of high temperature are reliable indicators of the location and mode of structural failure. Results indicate that there appears to be a strong correlation between a reduction in the overall stiffness of the system and variations in the distribution of temperature across the sample

Typification of names in genus Hieracium based on original herbarium material of Alexis Jordan and Alexandre Boreau

181 names of Hieracium species going back to original herbarium material of Alexis Jordan or Alexandre Boreau are lectotypified, 27 are neotypified. The study is based on herbarium specimens of the Université Catholique de Lyon (LY) and Ville d’Angers (ANG), Martrin-Donos’s herbarium at the Institut Botanique de Montpellier (MPUTarn) and Arvet-Touvet’s herbarium at the Musée d’Histoire Naturelle de Grenoble (GRM-AT). The type specimens are illustrated by photographs of the entire herbarium sheets with some detail views of flower heads and leaves. Usual nomenclatural synonyms are given for each taxon

Some issues when using Fourier analysis for the extraction of modal parameters

Abstract. It is sometimes necessary to determine the manner in which structures deteriorate with respect to time; for instance when quantifying a material's ability to withstand sustained dynamic loads. In such cases, it is well established that loss of structural integrity is reflected by variations in modal characteristics such as stiffness. This paper addresses some practical limitations of Fourier analysis with respect to temporal resolution and the uncertainties associated with extracting variations in modal parameters. The statistical analysis of numerous numerical experiments shows how techniques, such as data overlapping and zero-padding, can be used to improve the sensitivity of modal parameter extraction

Observational Evidence for the Associated Formation of Blobs and Raining Inflows in the Solar Corona

The origin of the slow solar wind is still a topic of much debate. The continual emergence of small transient structures from helmet streamers is thought to constitute one of the main sources of the slow wind. Determining the height at which these transients are released is an important factor in determining the conditions under which the slow solar wind forms. To this end, we have carried out a multipoint analysis of small transient structures released from a north-south tilted helmet streamer into the slow solar wind over a broad range of position angles during Carrington Rotation 2137. Combining the remote-sensing observations taken by the Solar-TErrestrial RElations Observatory (STEREO) mission with coronagraphic observations from the SOlar and Heliospheric Observatory (SOHO) spacecraft, we show that the release of such small transient structures (often called blobs), which subsequently move away from the Sun, is associated with the concomitant formation of transient structures collapsing back toward the Sun; the latter have been referred to by previous authors as "raining inflows." This is the first direct association between outflowing blobs and raining inflows, which locates the formation of blobs above the helmet streamers and gives strong support that the blobs are released by magnetic reconnection.Peer reviewe

Statistics of counter-streaming solar wind suprathermal electrons at solar minimum : STEREO observations

Previous work has shown that solar wind suprathermal electrons can display a number of features in terms of their anisotropy. Of importance is the occurrence of counter-streaming electron patterns, i.e., with "beams" both parallel and anti-parallel to the local magnetic field, which is believed to shed light on the heliospheric magnetic field topology. In the present study, we use STEREO data to obtain the statistical properties of counter-streaming suprathermal electrons (CSEs) in the vicinity of corotating interaction regions (CIRs) during the period March–December 2007. Because this period corresponds to a minimum of solar activity, the results are unrelated to the sampling of large-scale coronal mass ejections, which can lead to CSE owing to their closed magnetic field topology. The present study statistically confirms that CSEs are primarily the result of suprathermal electron leakage from the compressed CIR into the upstream regions with the combined occurrence of halo depletion at 90° pitch angle. The occurrence rate of CSE is found to be about 15–20% on average during the period analyzed (depending on the criteria used), but superposed epoch analysis demonstrates that CSEs are preferentially observed both before and after the passage of the stream interface (with peak occurrence rate >35% in the trailing high speed stream), as well as both inside and outside CIRs. The results quantitatively show that CSEs are common in the solar wind during solar minimum, but yet they suggest that such distributions would be much more common if pitch angle scattering were absent. We further argue that (1) the formation of shocks contributes to the occurrence of enhanced counter-streaming sunward-directed fluxes, but does not appear to be a necessary condition, and (2) that the presence of small-scale transients with closed-field topologies likely also contributes to the occurrence of counter-streaming patterns, but only in the slow solar wind prior to CIRs

Predictors of inappropriate hospital days in a department of internal medicine

Background This study aimed to identify predictors of inappropriate hospital days in a deparUnent of internal medicine, as a basis for quality improvement interventions. Methods The appropriateness of 5665 hospital days contributed by 500 patients admitted to the Department of Internal Medicine, Geneva University Hospitals, Switzerland, was assessed by means of the Appropriateness Evaluation Protocol. Predictor variables included patient's age and sex, manner of admission and discharge, and characteristics of hospital days (weekend, holiday, sequence). Results Overall, 15% of hospital admissions and 28% of hospital days were rated as inappropriate. In multivariate models, inappropriate hospital days were more frequent among patients whose admission was inappropriate (odds ratio [OR] = 5.3, 95% CI: 3.1-8.4) and among older patients (80-95 years: OR = 3.6. 95% CI: 1.7-7.0, versus <50 years). The likelihood of inappropriateness also increased with each subsequent hospital day, culminating on the day of discharge, regardless of the total length of stay. Conclusions This study identified both the admission and the discharge processes as important sources of inappropriate hospital use in a department of internal medicine. The oldest patients were also at high risk of remaining in the hospital inappropriately. Surprisingly, long hospital stays did not generate a higher proportion of inappropriate days than short hospital stays. This information proved useful in developing interventions to improve the hospitalization proces

Solar Orbiter observations of the Kelvin-Helmholtz waves in the solar wind

Context. The Kelvin-HeImholtz (KH) instability is a nonlinear shear-driven instability that develops at the interface between shear flows in plasmas. KH waves have been inferred in various astrophysical plasmas, and have been observed in situ at the magnetospheric boundaries of solar-system planets and through remote sensing at the boundaries of coronal mass ejections. // Aims. KH waves are also expected to develop at flow shear interfaces in the solar wind. While they were hypothesized to play an important role in the mixing of plasmas and in triggering solar wind fluctuations, their direct and unambiguous observation in the solar wind was still lacking. // Methods. We report in-situ observations of quasi-periodic magnetic and velocity field variations plausibly associated with KH waves using Solar Orbiter during its cruise phase. They are found in a shear layer in the slow solar wind in the close vicinity of the Heliospheric Current Sheet. Analysis is performed to derive the local configuration of the waves. A 2-D MHD simulation is also set up with approximate empirical values to test the stability of the shear layer. In addition, magnetic spectra of the event are analyzed. Results. We find that the observed conditions satisfy the KH instability onset criterion from the linear theory analysis, and its de- velopment is further confirmed by the simulation. The current sheet geometry analyses are found to be consistent with KH wave development, albeit with some limitations likely owing to the complex 3D nature of the event and solar wind propagation. Addition- ally, we report observations of an ion jet consistent with magnetic reconnection at a compressed current sheet within the KH wave interval. The KH activity is found to excite magnetic and velocity fluctuations with power law scalings that approximately follow k−5/3 and k−2.8 in the inertial and dissipation ranges, respectively. Finally, we discuss reasons for the lack of in-situ KH wave detection in past data. // Conclusions. These observations provide robust evidence of KH wave development in the solar wind. This sheds new light on the process of shear-driven turbulence as mediated by the KH waves with implications for the driving of solar wind fluctuations

Flux rope and dynamics of the heliospheric current sheet Study of the Parker Solar Probe and Solar Orbiter conjunction of June 2020

Context: Solar Orbiter and Parker Solar Probe jointly observed the solar wind for the first time in June 2020, capturing data from very different solar wind streams: calm, Alfvénic wind and also highly dynamic large-scale structures. Context. Our aim is to understand the origin and characteristics of the highly dynamic solar wind observed by the two probes, particularly in the vicinity of the heliospheric current sheet (HCS). Methods: We analyzed the plasma data obtained by Parker Solar Probe and Solar Orbiter in situ during the month of June 2020. We used the Alfvén-wave turbulence magnetohydrodynamic solar wind model WindPredict-AW and we performed two 3D simulations based on ADAPT solar magnetograms for this period. Results: We show that the dynamic regions measured by both spacecraft are pervaded by flux ropes close to the HCS. These flux ropes are also present in the simulations, forming at the tip of helmet streamers, that is, at the base of the heliospheric current sheet. The formation mechanism involves a pressure-driven instability followed by a fast tearing reconnection process. We further characterize the 3D spatial structure of helmet streamer born flux ropes, which appears in the simulations to be related to the network of quasi-separatrices