Author Correction: Floating under a levitating liquid.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Floating under a levitating liquid.

When placed over a less dense medium, a liquid layer will typically collapse downwards if it exceeds a certain size, as gravity acting on the lower liquid interface triggers a destabilizing effect called a Rayleigh-Taylor instability1,2. Of the many methods that have been developed to prevent the liquid from falling3-6, vertical shaking has proved to be efficient and has therefore been studied in detail7-13. Stabilization is the result of the dynamical averaging effect of the oscillating effective gravity. Vibrations of liquids also induce other paradoxical phenomena such as the sinking of air bubbles14-19 or the stabilization of heavy objects in columns of fluid at unexpected heights20. Here we take advantage of the excitation resonance of the supporting air layer to perform experiments with large levitating liquid layers of up to half a litre in volume and up to 20 centimetres in width. Moreover, we predict theoretically and show experimentally that vertical shaking also creates stable buoyancy positions on the lower interface of the liquid, which behave as though the gravitational force were inverted. Bodies can thus float upside down on the lower interface of levitating liquid layers. We use our model to predict the minimum excitation needed to withstand falling of such an inverted floater, which depends on its mass. Experimental observations confirm the possibility of selective falling of heavy bodies. Our findings invite us to rethink all interfacial phenomena in this exotic and counter-intuitive stable configuration.

Comprehensive refractive manipulation of water waves using electrostriction.

The control of wave propagation based on refraction principles offers unparalleled possibilities as shown by the striking example of optics. This approach is unfortunately limited for water waves as it relies mainly on variations of the liquid depth which, while controlling the wave velocity, also trigger nonlinearities and damping. In this article, we show experimentally that electrostriction allows to implement extensive refraction-based control of water waves in a precise and contactless manner. The setup consists of an electrode under high voltage placed above the grounded conductive water. The waves propagating under the electrode can be slowed down up to approximately half their speed compared to free propagation. We characterize the Snell-Descartes laws of refraction and the total internal reflection for the water waves. We implement emblematic refraction-based devices such as electrically tunable focusing lenses, waveguides without obstacles, and beam splitters based on frustrated internal reflection to perform interference experiments.

Flexible implementation of modulated localisation microscopy based on DMD.

Localisation microscopy of individual molecules allows one to bypass the diffraction limit, revealing cellular organisation on a nanometric scale. This method, which relies on spatial analysis of the signal emitted by molecules, is often limited to the observation of biological objects at shallow depths, or with very few aberrations. The introduction of a temporal parameter into the localisation process through a time-modulated excitation was recently proposed to address these limitations. This method, called ModLoc, is demonstrated here with an alternative flexible strategy. In this implementation, to encode the time-modulated excitation a digital micromirror device (DMD) is used in combination with a fast demodulation approach, and provides a twofold enhancement in localisation precision. Layout: Nowadays, we can use an optical microscope to observe how proteins are organised in 3D within a cell at the nanoscale. By carefully controlling the emission of molecules in both space and time, we can overcome the limitations set by the diffraction limit. This allows us to pinpoint the exact location of molecules more precisely. However, the usual spatial analysis method limits observations to shallow depths or causing low distortion of optical waves. To overcome these restrictions, a recent approach introduces a temporal element to the localisation process. This involves changing the illumination over time to enhance the precision of localisation. This method, known as ModLoc, is showcased here using a flexible and alternative strategy. In this setup, a matrix of micrometric mirrors, working together with a fast demodulation optical module, is used to encode and decode the time-modulated information. This combination results in a twofold improvement in localisation precision.

Liquid walls and interfaces in arbitrary directions stabilized by vibrations.

Gravity shapes liquids and plays a crucial role in their internal balance. Creating new equilibrium configurations irrespective of the presence of a gravitational field is challenging with applications on Earth as well as in zero-gravity environments. Vibrations are known to alter the shape of liquid interfaces and also to change internal dynamics and stability in depth. Here, we show that vibrations can also create an "artificial gravity" in any direction. We demonstrate that a liquid can maintain an inclined interface when shaken in an arbitrary direction. A necessary condition for the equilibrium to occur is the existence of a velocity gradient determined by dynamical boundary conditions. However, the no-slip boundary condition and incompressibility can perturb the required velocity profile, leading to a destabilization of the equilibrium. We show that liquid layers provide a solution, and liquid walls of several centimeters in height can thus be stabilized. We show that the buoyancy equilibrium is not affected by the forcing.

[The impact of lockdown on mental health in PhD students, a cohort study in a French university]. / Impact du confinement sur la santé mentale des doctorants, une étude de cohorte dans une université française.

INTRODUCTION: Few studies are available on the health status of doctoral students. This position at the border between university studies and a professional activity presents specific risk factors, especially in terms of psychosocial constraints. The lockdowns implemented worldwide to control the COVID-19 pandemic are potentially worsening factors. METHODS: At Lyon 1 University, a systematic medical follow-up of first year PhD students had been set up by the occupational health service in 2019. In the context of the lockdown during the COVID-19 pandemic, a telephonic interview was proposed to the same PhD students in order to assess the impact of the lockdown on working conditions and health and to provide possible assistance. During this interview, a standardized questionnaire was used to collect information about the conditions during the lockdown, doctoral work during this period and the consequences on research progress, as well as possible financial difficulties due to the lockdown. In addition, questions were asked about the perceived general health conditions and consultation with a health practitioner during this period. The Patient Health Questionnaire (PHQ-9) and the Generalized Anxiety Disorder (GAD-7) were used to assess depression and anxiety. Questions on lifestyle during lockdown, changes in diet during the period, weight change, and changes in the quantity and quality of their sleep were also asked. Comparisons of perceived health status, the prevalence of anxiety and depression symptoms at baseline and during the follow-up survey were made by MacNemar Chi2 tests, as the data were repeated ones. The students were informed orally and in writing that their data would be entered anonymously into a computer and that they could have access to their data in accordance with the General Data Protection Regulation (GDPR). They were all informed by e-mail about the study results at the end of the study. The data collection process was registered with the National Institute for Health Data (INDS) and with the university's register under reference no. 2020/002 by the university's data protection officer in compliance with the French data protection laws (CNIL). The protocol was approved by the ethics committee of the Lyon University College of General Medicine (notification number: 2020-10-29-02). RESULTS: Of the 161 PhD students initially interviewed, 149 underwent a second interview. In total, 89.2% of the students assessed their health as good or very good. Regarding the answers to the GAD-7 questionnaire, 8.1% had a score equal to or higher than 10, corresponding to moderate to severe anxiety. Regarding the answers to PHQ-9, 19.6% of the PhD students had a score equal to or higher than 9 corresponding to moderate to severe depressive syndromes. The prevalence of an anxiety disorder was significantly associated with the absence of an outside private access in the place of residence during lockdown (75% vs. 37%), an increase in coffee consumption (33% vs. 5%), an increase in the quantity of food consumed (50% vs. 12%), weight gain (50% vs. 19%) and a deterioration in sleep quality (75% vs. 28%). The prevalence of a depressive symptom was significantly associated with lockdown in an urban area (89% vs. 70%), the occurrence of financial difficulties (7% vs. 1%), the consultation of a health professional during the period (34% vs. 15%), smoking cessation (14% vs. 1%), changes in the quantity (31% vs. 9%) and deterioration (59% vs. 25%) of the quality of sleep, and diet changes (66% vs. 43%). GAD-7 scores were unchanged for 90% of participants between the two surveys, but they were higher for 6.8% of doctoral students and lower for 2.7 % (P=0.1). A deterioration of the PHQ-9 scores, i.e. higher scores in the second survey compared to the first, was observed for 15.5% of the PhD students while an improvement of the scores was observed for 1.4% (P=0.0001). DISCUSSION: A number of studies have been published on the impact of lockdown on mental health, but few of them focused specifically on PhD students and even fewer were prospective studies. Their results are therefore difficult to compare with ours; they generally show GAD-7 and PHQ-9 scores that are similar to those of our population, or even higher. The impact of lockdown on the mental health of doctoral students highlighted in our study therefore justifies an appropriate follow-up of this population, particularly in the case of former psychiatric disorders.

Damping-Driven Time Reversal for Waves.

Damping is usually associated with irreversibility. Here, we present a counterintuitive concept to achieve time reversal of waves propagating in a lossless medium using a transitory dissipation pulse. Applying a sudden and strong damping in a limited time generates a time-reversed wave. In the limit of a high damping shock, this amounts to "freezing" the initial wave by maintaining the wave amplitude while canceling its time derivative. The initial wave then splits in two counterpropagating waves with half of its amplitude and time evolutions in opposite directions. We implement this damping-based time reversal using phonon waves propagating in a lattice of interacting magnets placed on an air cushion. We show with computer simulations that this concept also applies to broadband time reversal in complex disordered systems.

Role of the occupational disease consultant in the multidisciplinary discussion of interstitial lung diseases.

BACKGROUND: Diffuse interstitial lung diseases (ILD) constitute a heterogeneous group of conditions with complex etiological diagnoses requiring a multidisciplinary approach. Much is still unknown about them, particularly their relationship with occupational exposures. The primary objective of this study was to investigate the distribution of occupational exposures according to type of ILD. The secondary objectives were to estimate the proportion of ILDs possibly related to occupational exposure and to evaluate the added value of the participation of an occupational disease consultant in ILD multidisciplinary discussions (MDD). METHODS: From May to December 2020, all consecutive patients with ILD whose cases were reviewed during a MDD in a referral centre for ILD were prospectively offered a consultation with an occupational disease consultant. RESULTS: Of the 156 patients with ILD whose cases were reviewed in MDD during the study period, 141 patients attended an occupational exposure consultation. Occupational exposure was identified in 97 patients. Occupational exposure to asbestos was found in 12/31 (38.7%) patients with idiopathic pulmonary fibrosis (IPF) and in 9/18 (50.0%) patients with unclassifiable fibrosis. Occupational exposure to metal dust was found in 13/31 (41.9%) patients with IPFs and 10/18 (55.6%) patients with unclassifiable fibrosis. Silica exposure was found in 12/50 (24.0%) patients with autoimmune ILD. The link between occupational exposure and ILD was confirmed for 41 patients after the specialist occupational consultation. The occupational origin had not been considered (n = 9) or had been excluded or neglected (n = 4) by the MDD before the specialised consultation. A total of 24 (17%) patients were advised to apply for occupational disease compensation, including 22 (15.6%) following the consultation. In addition, a diagnosis different from the one proposed by the MDD was proposed for 18/141 (12.8%) patients. CONCLUSIONS: In our study, we found a high prevalence of occupational respiratory exposure with a potential causal link in patients with ILD. We suggest that a systematic specialised consultation in occupational medicine could be beneficial in the ILD diagnostic approach.

Frequency Conversion Cascade by Crossing Multiple Space and Time Interfaces.

Time varying media recently emerged as promising candidates to fulfill the dream of controlling the wave frequency without nonlinear effects. However, frequency conversion remains limited by the dynamics of the variations of the propagation properties. Here we propose a new concept of space-time cascade to achieve arbitrary large frequency shifts by iterated elementary transformation steps. These steps use an intermediate medium in which wave packets enter and exit through noncommutative space and time interfaces. This concept avoids high frequency or subwavelength demanding metamaterials. Upward and downward frequency conversions are performed. The transmitted energy yield is given by the frequency ratio, regardless of impedence mismatch. We implement this concept with water waves controlled by electrostriction and achieve frequency conversion over 4 octaves.

Experimental Implementation of Wave Propagation in Disordered Time-Varying Media.

Here, we study and implement the temporal analog in time disordered sytems. A spatially homogeneous medium is endowed with a time structure composed of randomly distributed temporal interfaces. This is achieved through electrostriction between water surface and an electrode. The wave field observed is the result of the interferences between reflected and refracted waves on the interfaces. Although no eigenmode can be associated with the wave field, several common features between space and time emerge. The waves grow exponentially depending on the disorder level in agreement with a 2D matrix evolution model such as in the spatial case. The relative position of the momentum gap appearing in the time modulated systems plays a central role in the wave field evolution. When tuning the excitation to compensate for the damping, transient waves, localized in time, appear on the liquid surface. They result from a particular history of the multiple interferences produced by a specific sequence of time boundaries.

Time-modulated excitation for enhanced single-molecule localization microscopy.

Structured illumination in single-molecule localization microscopy provides new information on the position of molecules and thus improves the localization precision compared to standard localization methods. Here, we used a time-shifted sinusoidal excitation pattern to modulate the fluorescence signal of the molecules whose position information is carried by the phase and recovered by synchronous demodulation. We designed two flexible fast demodulation systems located upstream of the camera, allowing us to overcome the limiting camera acquisition frequency and thus to maximize the collection of photons in the demodulation process. The temporally modulated fluorescence signal was then sampled synchronously on the same image, repeatedly during acquisition. This microscopy, called ModLoc, allows us to experimentally improve the localization precision by a factor of 2.4 in one direction, compared to classical Gaussian fitting methods. A temporal study and an experimental demonstration both show that the short lifetimes of the molecules in blinking regimes impose a modulation frequency in the kilohertz range, which is beyond the reach of current cameras. A demodulation system operating at these frequencies would thus be necessary to take full advantage of this new localization approach. This article is part of the Theo Murphy meeting issue 'Super-resolution structured illumination microscopy (part 2)'.

Phase-conjugate mirror for water waves driven by the Faraday instability.

The Faraday instability appears on liquid baths submitted to vertical oscillations above a critical value. The pattern of standing ripples at half the vibrating frequency that results from this parametric forcing is usually shaped by the boundary conditions imposed by the enclosing receptacle. Here, we show that the time modulation of the medium involved in the Faraday instability can act as a phase-conjugate mirror--a fact which is hidden in the extensively studied case of the boundary-driven regime. We first demonstrate the complete analogy with the equations governing its optical counterpart. We then use water baths combining shallow and deep areas of arbitrary shapes to spatially localize the Faraday instability. We give experimental evidence of the ability of the Faraday instability to generate counterpropagating phase-conjugated waves for any propagating signal wave. The canonical geometries of a point and plane source are implemented. We also verify that Faraday-based phase-conjugate mirrors hold the genuine property of being shape independent. These results show that a periodic modulation of the effective gravity can perform time-reversal operations on monochromatic propagating water waves, with a remarkable efficiency compared with wave manipulation in other fields of physics.

Space-Time Folding of the Wake Produced by a Supervelocity Rotating Point Source.

Wave sources moving faster than the waves they emit create a wake whose topological features are directly related to the geometry of the source trajectory. These features can be understood by considering space-time surfaces representing past emitted wave fronts. Specifically, for a supervelocity source moving along a circular path the space-time envelope folds and a cusp appears on the inner part of the wake. As a result, the wake is ultimately contained within two parallel corotating spiraling branches. In this Letter we take advantage of the low phase speed of water waves to study experimentally supervelocity sources moving at velocities up to several time the wave speed. We image in real time their emission patterns and characterize the topological features of their wakes.

Occupation and risk of female breast cancer: A case-control study in Morocco.

BACKGROUND: Breast cancer is the most frequent cancer among Moroccan women. Environmental and occupational factors may play a role in breast cancer etiology. This study aimed to investigate the association between occupation, industry, and breast cancer risk among Moroccan women. METHODS: A total of 300 breast cancer cases and 300 controls (matched by age and area of residence) were included in this study. Full occupational history was collected, with a detailed description of each job held for at least 6 months. Occupations were coded according to the International Standard Classification of Occupations (ISCO 08) and the Moroccan Analytical Classification of Professions (2001). Industries were coded according to the Statistical Classification of Economic Activities in the European Community (2008). Odds ratios (ORs) and 95% confidence intervals (CIs), adjusted for potential confounders were estimated by using conditional logistic regression. RESULTS: An overall decreased risk of breast cancer was observed among women doing only household work (OR = 0.32; 95% CI = 0.18-0.55). An increased risk of breast cancer was observed among women in agricultural occupations, particularly those employed as agricultural laborers (ISCO 08 code: 921; OR = 2.91; 95% CI = 1.51-5.60) and the risk increased with duration of employment (P trend = .01). Analyses by industry corroborated these findings. CONCLUSIONS: Our findings suggest that occupational exposures may be associated with increased risk of breast cancer among female agricultural workers in this population. Further investigations, with advanced methods of occupational exposure assessment, are warranted to clarify the role of chemicals involved in this high-risk occupation and to suggest preventive actions and screening.

Systematic screening for occupations and occupational exposures in head and neck squamous cell carcinoma patients.

PURPOSE: The importance of occupational exposures in patients with head and neck squamous cell carcinomas (HNSCC) has received little attention. METHODS: In a single-center study, we prospectively characterized occupational exposures in 154 HNSCC cancer patients in a systematic occupational consultation and examined the association between most frequent exposures, HNSCC stage and localization. RESULTS: Patients occupied a mean of 3.3 different positions during their working life. The prevalence of asbestos, the most frequent exposure (46 patients; 29.9%) was higher than in the French population > 50 years. Other frequent exposures were solvents (n = 26; 16.9%) and silica (n = 19; 12.3%). For 37 patients (24%) a possible link was identified between occupational exposures and HNSCC. Duration of asbestos exposure was significantly higher (p = 0.04) in patients with hypopharyngeal and laryngeal cancer compared to other localizations. CONCLUSIONS: Occupational exposures are frequent in patients with HNSCC and should receive increased attention by physicians.

Fast label-free cytoskeletal network imaging in living mammalian cells.

We present a full-field technique that allows label-free cytoskeletal network imaging inside living cells. This noninvasive technique allows monitoring of the cytoskeleton dynamics as well as interactions between the latter and organelles on any timescale. It is based on high-resolution quantitative phase imaging (modified Quadriwave lateral shearing interferometry) and can be directly implemented using any optical microscope without modification. We demonstrate the capability of our setup on fixed and living Chinese hamster ovary cells, showing the cytoskeleton dynamics in lamellipodia during protrusion and mitochondria displacement along the cytoskeletal network. In addition, using the quantitative function of the technique, along with simulation tools, we determined the refractive index of a single tubulin microtubule to be ntubu=2.36±0.6 at λ=527 nm.

Confocal supercritical angle microscopy for cell membrane imaging.

We demonstrate subwavelength sectioning on biological samples with a conventional confocal microscope. This optical sectioning is achieved by the phenomenon of supercritical angle fluorescence, wherein only a fluorophore next to the interface of a refractive index discontinuity can emit propagating components of radiation into the so-called forbidden angles. The simplicity of this technique allows it to be integrated with a high numerical aperture confocal scanning microscope by only a simple modification on the detection channel. Confocal-supercritical angular fluorescence microscopy would be a powerful tool to achieve high-resolution surface imaging, especially for membrane imaging in biological samples.

Evolution of work conditions for employees driving for work in France based on data from the 2003, 2010 and 2017 SUMER surveys (Surveillance Médicale des expositions aux risques Professionnels).

INTRODUCTION: The occupational road-accident risk on public roads and the work conditions for professional driving is still an important issue in occupational health despite lower road-accident rates. This study presents the evolution over time of the work-related constraints for these employees based on the Sumer surveys carried out in 2003, 2010 and 2017. METHOD: Data from the 2010 and 2017 surveys were restricted to match the scope of the 2003 survey in order to enable prevalence data to be compared in equivalent populations. The main variable of interest was "driving (car, truck, bus, and other vehicles) on public thoroughfares" for work (during the last week of work: yes/no). Work time characteristics, work rhythm, autonomy and scope for initiative, collective work group, standards and evaluations variables were completed by the occupational health physicians. A self-administered questionnaire was also provided to employees and contained the Job Content Questionnaire, which assesses decision latitude, social support and psychological demands, the reward scale of Siegrist questionnaire, the hostile behaviour with inspired questions for Leymann, sick leave and work accidents during the past 12 months and job satisfaction. Finally, prevention in the workplace was also completed by the occupational health physicians. RESULTS: About 25% of employees in France were exposed to work-related driving in 2017, which was stable in comparison with 2003 and 2010. However, the population was older and there were more females, more often from the clerical staff/middle manager category and working in companies with fewer than 10 employees. Employees exposed to work-related driving were also more frequently exposed to sustained work schedules and physical constraints, but less exposed to psychosocial risks. CONCLUSIONS: The percentage of employees exposed to occupational road accident risk, i.e., exposure to work-related driving, remained stable at about 25% in 2017 compared with previous surveys. These employees were also more frequently exposed to sustained work schedules and physical constraints, but less exposed to psychosocial risks. PRACTICAL APPLICATIONS: Prevention campaigns on work-related road accident risk should be provided to all employees in all companies since all jobs can be concerned.

Aggression, psychological violence and sexual harassment in seafarers in France.

BACKGROUND: In a working environment that is predominantly male, very tough physically, with a difficult working environment, occupational exposures and working, verbal and physical aggression can be more frequent than in other sectors. Fishing, merchant shipping and yachting are all sectors where fitness to sail is reassessed every year by doctors in the Seafarers' Health Service. Seafarers are increasingly reporting insulting, violent or sexist behaviour. The main types of abuse seen on board can be verbal and/or physical aggression, humiliation, whether in private or in front of others. Sexual harassment of women is a very worrying subject. MATERIALS AND METHODS: It was a retrospective observational study which is part of the professional monitoring of seafarers. The target population was adult seafarers coming for a fitness to sail visit. The group was recruited from seafarers aged over 18 who were being monitored by one of the seafarers' health services (or local centres). The inclusion period was 4 months between January and April 2023. All the information was collected using a self-questionnaire developed from the questionnaires of the Surveillance Médicale des Expositions des Salariés au Risques Professionnels (SUMER) for health status, job satisfaction and the European mini-module, verbal and physical aggression and psychological violence at work (based on the Leymann questionnaire), sexual violence and aggression based on the sexual harassment questionnaire and the PCLS-5 scale validated and translated into French to assess post-traumatic stress. The population studied was therefore 788 sailors. RESULTS: The study population was predominantly male (82.3%). The average age was 41.4 years (standard deviation = 11.7). 46.7% of seafarers estimate being in very good health. During the past 12 months, overall, 24.5% of seafarers disclaimed having been victim in work-related context of a verbal aggression, with a significant difference according to the gender (21.1% for men and 41.0% for women). During the last 12 months, overall, 3.2% of seafarers have been victim in work-related context of a physical aggression (2.6% for men and 5.8% for women, NS), whereas 10.9% of seafarers reported hostile behaviour at present. Twenty per cent of seafarers reported sexual harassment in the last 12 months. During the entire working life of seafarers, 65.5% of women and 38.2% of men reported sexual harassment, and 38.8% of seafarers stated that they had experienced at least one traumatic event in the last 12 months. DISCUSSION: A quarter of seafarers say they have been the victim of verbal or physical aggression at work in the last twelve months. These figures are high, and higher than those of the global survey on violence and harassment at work carried out by the International Labour Organization. One of the most alarming results of our study is the overexposure of women working in the maritime industry to the risk of physical, verbal or sexual assault of any kind. Indeed, in all the questions concerning the experience of verbal and physical aggression, the number of women victims is twice as high as that of their male colleagues, and this difference is statistically significant. As far as prevention is concerned, it seems that an effort is needed in terms of information, since only one seafarer in two knows the procedure to follow in the event of aggression within their shipyard. Communication between shipowners and seafarers needs to be stepped up to ensure that everyone is familiar with the procedures.