Engagement, Exhaustion, and Perceived Performance of Public Employees Before and During the COVID-19 Crisis.

At the outset of the COVID-19 pandemic, the Swiss federal government implemented a lockdown that prompted a majority of private and public organizations to implement teleworking solutions for their employees. This study aimed to examine the impact of work modalities, job-related, relational, and organizational climate variables on employees' engagement, exhaustion, and perceived performance both before and during the forced teleworking period. Based on the job demands-resources framework, a survey was conducted (N = 1,373) in a Swiss Cantonal public administration. Results show that while the forced telework period positively influenced employees' work autonomy and work-life balance, it negatively influenced their degree of collaboration and perceived job strain but did not affect their engagement levels. The freedom to organize ones' own work and collaboration with colleagues were identified as the main resources that positively influence employees' engagement and perceived performance while limiting exhaustion.

The French national survey on food consumption of children under 3 years of age - Nutri-Bébé 2013: design, methodology, population sampling and feeding practices.

OBJECTIVE: To update the data on food consumption and practices in children under 3 years of age in metropolitan France. DESIGN: The Nutri-Bébé 2013 cross-sectional study selected a random sample, according to the quota sampling method. After giving their informed consent, parents had to record the food consumption during three non-consecutive days framed by two face-to-face interviews, using for quantitative information different portion size measurement aids. RESULTS: One thousand one hundred and eighty-four children were enrolled. Mothers' mean age was 30·8 (sd 5·4) years; 38 % were primiparous; 89 % lived with a partner; 60 % had an occupation. Of the infants younger than 4 months, 31 % were breast-fed. One thousand and thirty-five children consumed infant formula followed by growing-up milk in 63 % of them; solid foods were introduced at a mean age of 5·4 (sd 2·13) months. From 8 months onwards, 25 % of children consumed the same foods as their parents on a more or less regular basis; 29 % ate in front of a screen, with a daily average screen time of 43·0 (sd 40·4) min. CONCLUSIONS: This robust survey highlights the low prevalence and duration of breast-feeding in France and shows a modest improvement since the previous survey of 2005 in the observance of recommendations concerning other feeding practices. The frequent consumption of adult foods and the screen time are of concern.

Thermal Characterization of Dynamic Silicon Cantilever Array Sensors by Digital Holographic Microscopy.

In this paper, we apply a digital holographic microscope (DHM) in conjunction with stroboscopic acquisition synchronization. Here, the temperature-dependent decrease of the first resonance frequency (S1(T)) and Young's elastic modulus (E1(T)) of silicon micromechanical cantilever sensors (MCSs) are measured. To perform these measurements, the MCSs are uniformly heated from T0 = 298 K to T = 450 K while being externally actuated with a piezo-actuator in a certain frequency range close to their first resonance frequencies. At each temperature, the DHM records the time-sequence of the 3D topographies for the given frequency range. Such holographic data allow for the extracting of the out-of-plane vibrations at any relevant area of the MCSs. Next, the Bode and Nyquist diagrams are used to determine the resonant frequencies with a precision of 0.1 Hz. Our results show that the decrease of resonance frequency is a direct consequence of the reduction of the silicon elastic modulus upon heating. The measured temperature dependence of the Young's modulus is in very good accordance with the previously-reported values, validating the reliability and applicability of this method for micromechanical sensing applications.

Versatile spectral modulation of a broadband source for digital holographic microscopy.

We demonstrate the potential of spatial light modulators for the spectral control of a broadband source in digital holographic microscopy. Used in a 'pulse-shaping' geometry, the spatial light modulator provides a versatile control over the bandwidth and wavelength of the light source. The control of these properties enables adaptation to various experimental conditions. As a first application, we show that the source bandwidth can be adapted to the off-axis geometry to provide quantitative phase imaging over the whole field of view. As a second application, we generate sequences of appropriate wavelengths for a hierarchical optical phase unwrapping algorithm, which enables the measurement of the topography of high-aspect ratio structures without phase ambiguity. Examples are given with step heights up to 50 µm.

Full field vertical scanning in short coherence digital holographic microscope.

In Digital holography Microscopes (DHM) implemented in the so-called "off axis" configuration, the object and reference wave fronts are not co-planar but form an angle of a few degrees. This results into two main drawbacks. First, the contrast of the interference is not uniform spatially when the light source has low coherence. The interference contrast is optimal along a line, but decreases when moving away from it, resulting in a lower image quality. Second, the non-coplanarity between the coherence plane of both wavefronts impacts the coherence vertical scanning measurement mode: when the optical path difference between the signal and the reference beam is changed, the region of maximum interference contrast shifts laterally in the plane of the objective. This results in more complex calculations to extract the topography of the sample and requires scanning over a much larger vertical range, leading to a longer measurement time. We have previously shown that by placing a volume diffractive optical element (VDOE) in the reference arm, the wavefront can be made coplanar with the object wavefront and the image plane of the microscope objective, resulting in a uniform and optimal interferogram. In this paper, we demonstrate a vertical scanning speed improvement by an order of magnitude. Noise in the phase and intensity images caused by scattering and non-uniform diffraction in the VDOE is analyzed quantitatively. Five VDOEs were fabricated with an identical procedure. We observe that VDOEs introduce a small intensity non-uniformity in the reference beam which results in a 20% noise increase in the extracted phase image as compared to the noise in extracted phase image when the VDOE is removed. However, the VDOE has no impact on the temporal noise measured from extracted phase images.

Enhancement of three-dimensional perception of numerical hologram reconstructions of real-world objects by motion and stereo.

We investigated the question of how the perception of three-dimensional information reconstructed numerically from digital holograms of real-world objects, and presented on conventional displays, depends on motion and stereoscopic presentation. Perceived depth in an adjustable random pattern stereogram was matched to the depth in hologram reconstructions. The objects in holograms were a microscopic biological cell and a macroscopic metal coil. For control, we used real physical objects in additional to hologram reconstructions of real objects. Stereoscopic presentation increased perceived depth substantially in comparison to non-stereoscopic presentation. When stereoscopic cues were weak or absent e.g. because of blur, motion increased perceived depth considerably. However, when stereoscopic cues were strong, the effect of motion was small. In conclusion, for the maximization of perceived three-dimensional information of holograms on conventional displays, it seems highly beneficial to use the combination of motion and stereoscopic presentation.

Dual wavelength full field imaging in low coherence digital holographic microscopy.

A diffractive optical element (DOE) is presented to simultaneously manipulate the coherence plane tilt of a beam containing a plurality of discrete wavelengths. The DOE is inserted into the reference arm of an off-axis dual wavelength low coherence digital holographic microscope (DHM) to provide a coherence plane tilt so that interference with the object beam generates fringes over the full detector area. The DOE maintains the propagation direction of the reference beam and thus it can be inserted in-line in existing DHM set-ups. We demonstrate full field imaging in a reflection commercial DHM with two wavelengths, 685 nm and 794 nm, resulting in an unambiguous range of 2.494 micrometers.

Digital holographic reflectometry.

Digital holographic microscopy (DHM) is an interferometric technique that allows real-time imaging of the entire complex optical wavefront (amplitude and phase) reflected by or transmitted through a sample. To our knowledge, only the quantitative phase is exploited to measure topography, assuming homogeneous material sample and a single reflection on the surface of the sample. In this paper, dual-wavelength DHM measurements are interpreted using a model of reflected wave propagation through a three-interfaces specimen (2 layers deposited on a semi-infinite layer), to measure simultaneously topography, layer thicknesses and refractive indices of micro-structures. We demonstrate this DHM reflectometry technique by comparing DHM and profilometer measurement of home-made SiO(2)/Si targets and Secondary Ion Mass Spectrometry (SIMS) sputter craters on specimen including different multiple layers.

Extended depth-of-focus by digital holographic microscopy.

A recurrent problem in microscopy is the finite depth-of-focus linked to the NA of microscope objectives. Digital holographic microscopy (DHM) has the unique feature of being able to numerically change the focus from a single hologram without the need of moving the sample. Extended depth of focus of amplitude images has been demonstrated, but it has marginal interest for the metrological application of DHM that needs the topography. In this Letter, we demonstrate that DHM is able to provide not only extended depth-of-focus amplitude images but extended focused complex data from which the topography is computed. For this purpose, reflection and transmission measurements on micro-optics (microlens and retroreflector) performed by using standard reconstruction or the extended focused complex data are compared. These experiments demonstrate that DHM measures, from a single hologram acquisition, the accurate sample topography on a numerically increased depth-of-focus.

Comparative study of human erythrocytes by digital holographic microscopy, confocal microscopy, and impedance volume analyzer.

Red blood cell (RBC) parameters such as morphology, volume, refractive index, and hemoglobin content are of great importance for diagnostic purposes. Existing approaches require complicated calibration procedures and robust cell perturbation. As a result, reference values for normal RBC differ depending on the method used. We present a way for measuring parameters of intact individual RBCs by using digital holographic microscopy (DHM), a new interferometric and label-free technique with nanometric axial sensitivity. The results are compared with values achieved by conventional techniques for RBC of the same donor and previously published figures. A DHM equipped with a laser diode (lambda = 663 nm) was used to record holograms in an off-axis geometry. Measurements of both RBC refractive indices and volumes were achieved via monitoring the quantitative phase map of RBC by means of a sequential perfusion of two isotonic solutions with different refractive indices obtained by the use of Nycodenz (decoupling procedure). Volume of RBCs labeled by membrane dye Dil was analyzed by confocal microscopy. The mean cell volume (MCV), red blood cell distribution width (RDW), and mean cell hemoglobin concentration (MCHC) were also measured with an impedance volume analyzer. DHM yielded RBC refractive index n = 1.418 +/- 0.012, volume 83 +/- 14 fl, MCH = 29.9 pg, and MCHC 362 +/- 40 g/l. Erythrocyte MCV, MCH, and MCHC achieved by an impedance volume analyzer were 82 fl, 28.6 pg, and 349 g/l, respectively. Confocal microscopy yielded 91 +/- 17 fl for RBC volume. In conclusion, DHM in combination with a decoupling procedure allows measuring noninvasively volume, refractive index, and hemoglobin content of single-living RBCs with a high accuracy.

Real-time dual-wavelength digital holographic microscopy with a single hologram acquisition.

A technique to perform two-wavelengths digital holographic microscopy (DHM) measurements with a single hologram acquisition is presented. The vertical measurement range without phase ambiguity is extended to the micron-range, thanks to the resulting synthetic wavelength defined by the beating of two wavelengths with a separation of about 80nm. Real-time dual-wavelength imaging is made possible by using two reference waves having different wavelengths and propagation directions for the hologram recording. The principle of the method is exposed and experimental results concerning a 1.2mum m high test sample as well as a moving micro-mirror are presented. To the extent of our knowledge, this is the first time that real-time synthetic beat-wavelength digital holography measurements are reported.

Measurement of the integral refractive index and dynamic cell morphometry of living cells with digital holographic microscopy.

We have developed a digital holographic microscope (DHM), in a transmission mode, adapted to the quantitative study of cellular dynamics. Living cells in culture are optically probed by measuring the phase shift they produce on the transmitted wave front. The high temporal stability of the phase signal, equivalent to lambda/1800, and the low acquisition time (~20micros) enable to monitor cellular dynamics processes. An experimental procedure allowing to calculate both the integral refractive index and the cellular thickness (morphometry) from the measured phase shift is presented. Specifically, the method has been applied to study the dynamics of neurons in culture during a hypotonic stress. Such stress produces a paradoxical decrease of the phase which can be entirely resolved by applying the methodological approach described in this article; indeed the method allows to determine independently the thickness and the integral refractive index of cells.

Off-axis digital holographic camera for quantitative phase microscopy.

We propose and experimentally demonstrate a digital holographic camera which can be attached to the camera port of a conventional microscope for obtaining digital holograms in a self-reference configuration, under short coherence illumination and in a single shot. A thick holographic grating filters the beam containing the sample information in two dimensions through diffraction. The filtered beam creates the reference arm of the interferometer. The spatial filtering method, based on the high angular selectivity of the thick grating, reduces the alignment sensitivity to angular displacements compared with pinhole based Fourier filtering. The addition of a thin holographic grating alters the coherence plane tilt introduced by the thick grating so as to create high-visibility interference over the entire field of view. The acquired full-field off-axis holograms are processed to retrieve the amplitude and phase information of the sample. The system produces phase images of cheek cells qualitatively similar to phase images extracted with a standard commercial DHM.

Label-free cytotoxicity screening assay by digital holographic microscopy.

We introduce a label-free technology based on digital holographic microscopy (DHM) with applicability for screening by imaging, and we demonstrate its capability for cytotoxicity assessment using mammalian living cells. For this first high content screening compatible application, we automatized a digital holographic microscope for image acquisition of cells using commercially available 96-well plates. Data generated through both label-free DHM imaging and fluorescence-based methods were in good agreement for cell viability identification and a Z'-factor close to 0.9 was determined, validating the robustness of DHM assay for phenotypic screening. Further, an excellent correlation was obtained between experimental cytotoxicity dose-response curves and known IC50 values for different toxic compounds. For comparable results, DHM has the major advantages of being label free and close to an order of magnitude faster than automated standard fluorescence microscopy.

Digital holographic microscopy applied to life sciences.

Digital holographic microscopy (DHM) is applied to life sciences applications and demonstrate its capability of real-time imaging and quantitative measurements of physiological parameters such as cell volume or mean cell hemoglobin concentration (MCHC) of erythrocyte cells. DHM has the advantage to be non-invasive (no phototoxicity, no contrast agents) and allows a high throughput measurements.

Characterization of microlenses by digital holographic microscopy.

We demonstrate the use of digital holographic microscopy (DHM) as a metrological tool in micro-optics testing. Measurement principles are compared with those performed with Twyman-Green, Mach-Zehnder, and white-light interferometers. Measurements performed on refractive microlenses with reflection DHM are compared with measurements performed with standard interferometers. Key features of DHM such as digital focusing, measurement of shape differences with respect to a perfect model, surface roughness measurements, and optical performance evaluation are discussed. The capability of imaging nonspherical lenses without any modification of the optomechanical setup is a key advantage of DHM compared with conventional measurement tools and is demonstrated on a cylindrical microlens and a square lens array.

Digital holographic microscopy: a noninvasive contrast imaging technique allowing quantitative visualization of living cells with subwavelength axial accuracy.

We have developed a digital holographic microscope (DHM), in a transmission mode, especially dedicated to the quantitative visualization of phase objects such as living cells. The method is based on an original numerical algorithm presented in detail elsewhere [Cuche et al., Appl. Opt. 38, 6994 (1999)]. DHM images of living cells in culture are shown for what is to our knowledge the first time. They represent the distribution of the optical path length over the cell, which has been measured with subwavelength accuracy. These DHM images are compared with those obtained by use of the widely used phase contrast and Nomarski differential interference contrast techniques.