Publications by authors named "Xavier Jacob"

The Perseverance rover is carrying out an original acoustic experiment on Mars: the SuperCam microphone records the spherical acoustic waves generated by laser sparks at distances from 2 m to more than 8 m. These N-shaped acoustic waves scatter from the multiple local heterogeneities of the turbulent atmosphere. Therefore, large and random fluctuations of sound travel time and intensity develop as the waves cross the medium.

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Article Synopsis
  • Before the Perseverance rover, Jezero crater's floor was theorized to have different origins, including lake-related or volcanic processes.
  • SuperCam's findings over the first 286 days indicated a volcanic terrain characterized by varying compositions, primarily basaltic, with higher levels of plagioclase in upper strata and richer pyroxene in lower strata.
  • The study identified the first Martian cumulate rock, highlighting its olivine-rich content and suggesting brief past watery conditions based on the presence of various alteration materials.
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The SuperCam instrument suite provides the Mars 2020 rover, Perseverance, with a number of versatile remote-sensing techniques that can be used at long distance as well as within the robotic-arm workspace. These include laser-induced breakdown spectroscopy (LIBS), remote time-resolved Raman and luminescence spectroscopies, and visible and infrared (VISIR; separately referred to as VIS and IR) reflectance spectroscopy. A remote micro-imager (RMI) provides high-resolution color context imaging, and a microphone can be used as a stand-alone tool for environmental studies or to determine physical properties of rocks and soils from shock waves of laser-produced plasmas.

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Background: In patients with suspected stroke, brain imaging is recommended in the acute phase for appropriate management and treatment. Both computed tomography (CT) and magnetic resonance imaging (MRI) are considered reasonable choices for initial brain imaging. When both techniques are available, choosing one or the other might be associated with specific factors related either to patients, stroke symptoms, and severity or management organization.

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Background: Binge drinking (BD) consists of heavy episodic alcohol use. Whereas the World Health Organization (WHO) defines BD as 60g of alcohol or more per occasion, the National Institute on Alcoholism and Alcohol Abuse (NIAAA) conceives BD as drinking 70g (men) or 56g (women) in less than two hours. We compared the subjects delineated by each definition.

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Pyelonephritides are frequently encountered diagnosis in Emergency Departments. Urinalyses have a central place in the management of this situation but the usefulness of blood cultures is not clear. We conducted a single-center retrospective study of 24 months to study the microbiological relevance of blood cultures in pyelonephritis.

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The effect of self-similarity on acoustic and elastic wave propagation at normal incidence is investigated using Classical Cantor and Fibonacci multilayered structures. They are made of two sorts of orthotropic plies having differently oriented orthotropic axes with respect to the propagation direction. The properties of their transmission coefficient are presented using a unidirectional numerical model based on a transfer matrix formalism.

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Background: Few recent studies have examined the characteristics of ST-segment elevation myocardial infarction (STEMI) among elderly patients managed in emergency departments (EDs).

Aims: To describe the clinical characteristics and management of elderly STEMI patients in EDs.

Methods: This retrospective, multicentre study involved STEMI patients aged ≥ 75 years admitted to four different EDs in the city of Lyon between 2004 and 2008.

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Mathematical optimization methods based on the topological sensitivity analysis have been used to develop innovative ultrasonic imaging methods. With a single illumination of the medium, they have proved experimentally to yield a lateral resolution comparable to classical multiple-illumination techniques. As these methods are based on the numerical simulations of two wave fields, they require extensive computation.

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This paper describes nonlinear shear wave experiments conducted in soft solids with transient elastography technique. The nonlinear solutions that theoretically account for plane and nonplane shear wave propagation are compared with experimental results. It is observed that the cubic nonlinearity implied in high amplitude transverse waves at f(0)=100 Hz results in the generation of odd harmonics 3f(0), 5f(0).

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