Helium ion microscopy and energy selective scanning electron microscopy – two advanced microscopy techniques with complementary applications

Both scanning electron microscopes (SEM) and helium ion microscopes (HeIM) are based on the same principle of a charged particle beam scanning across the surface and generating secondary electrons (SEs) to form images. However, there is a pronounced difference in the energy spectra of the emitted secondary electrons emitted as result of electron or helium ion impact. We have previously presented evidence that this also translates to differences in the information depth through the analysis of dopant contrast in doped silicon structures in both SEM and HeIM. Here, it is now shown how secondary electron emission spectra (SES) and their relation to depth of origin of SE can be experimentally exploited through the use of energy filtering (EF) in low voltage SEM (LV-SEM) to access bulk information from surfaces covered by damage or contamination layers. From the current understanding of the SES in HeIM it is not expected that EF will be as effective in HeIM but an alternative that can be used for some materials to access bulk information is presented

Bacterial contamination of table eggs and the influence of housing systems

With the introduction of alternative housing systems for laying hens in the EU, recent research has focussed on the bacterial contamination of table eggs, e.g. eggshell and egg content contamination. Contamination of eggshells with aerobic bacteria is generally higher for nest eggs from non-cage systems compared to nest eggs from furnished cages or eggs from conventional cages. Studies indicate limited or no systematic differences in eggshell contamination with aerobic bacteria between eggs laid in the nest boxes of furnished cages and eggs laid in conventional cages. The major differences found in experimental studies between cage- and non-cage systems are less pronounced under commercial conditions. The effect of housing system on eggshell contamination with specific groups of bacteria is variable. Limited information is available on the influence of housing system on egg content contamination. Recent research does not indicate large differences in egg content contamination between eggs from cage- and non-cage systems (ignoring outside nest and floor eggs). The microflora of the eggshell is dominated by Gram-positive bacteria, whereas Gram-negative bacteria are best equipped to overcome the antimicrobial defences of the egg content. Much of the research on eggshell and egg content contamination focuses on Salmonella, since infection with Salmonella enteritidis, resulting from the consumption of contaminated eggs or egg products, is still a major health problem. Observed Salmonella prevalence on the eggshell and in the egg content vary, depending on the fact whether investigations were based on randomly sampled table eggs or on eggs from naturally infected hens. The limited information available on other pathogens shows that they are exclusively isolated from the eggshell and not from the internal contents

A Robust Solution to the Super-Resolution Phase Problem in Scanning Transmission Electron Microscopy

From a set of images, each of poor resolution, recorded in a transmission microscope under many different incident angles of coherent illumination, it is possible to obtain wavelength-limited resolution even if there is a narrow aperture lying in the back-focal plane of the imaging lens. This is achieved by a deconvolution algorithm which retrieves the phase of the Fourier transform of the specimen. The method accounts for complex components in the transfer function of the lens, is not very sensitive to defocus and is remarkably resilient to noise. It may have important applications in overcoming the resolution limit in the scanning transmission electron microscope (STEM), where such data are readily available

Optical ptychography with extended depth of field

Ptychography is an increasingly popular phase imaging technique. However, like any imaging technique it has a depth of field that limits the volume of a thick specimen that can be imaged in focus. Here, we have proposed to extend the depth of field using a multislice calculation model; an optical experiment successfully demonstrates our proposal

Sensitivity of the auditory system to differences in intensity : temporal transfer and difference limen studied in psychophysical experiments : recording and analysis of evoked potentials

An important property of the auditorv system is the way this system processes changes in stimulus intensitv. Although this problem has been discussed manv times since Weber, it is rather surprising that no generally accepted hypothesis about the underlying mechanism has emerged. In the nresent study the sensitivity of the ear to intensity differences of noise signals is studied. In general two methods of investigation are used for the study of perception: nsychophysics and electrophysiology. Fechner founded psychonhvsics in 1860 ( Boring, 1950, 1966) as a studv of the relation between stimulus and sensation. In psychophysical experiments a stimulus is presented, and an observer makes some response (either by saying or by pressing a button). The system to be studied contains the peripheral sense-organ as well as the neural pathways that processes the information elicited in the peripheral organ. Considering the stimulus as the input of the system and the response of the observer as the output, it is possible to measure input-output relations by varying the parameters of the input stimulus. The investigator makes assumptions about how the system functions, and these assumptions have to account for the inputoutput relations. All the assumptions together constitute a model. Such a model of the system can suggest new experiments, and the results of such experiments lead to refinement or rejection of the model. Psychophysical experiments can never prove, however, that the system works like the model

Optimized organometal halide perovskite solar cell fabrication through control of nanoparticle crystal patterning

The addition of Hydrogen Iodide to organometal halide perovskite precursor solution at 1% by volume leads to a significant enhancement in power conversion efficiency (PCE) in inverted solar cell devices, increasing from 7.7% to 11.9% and 6.1% to 10.0% in spin-cast and spray-cast devices respectively. We directly attribute this improved device performance to increased thin-film surface coverage coupled with higher optical density. X-ray diffraction studies also reveal that the HI additive facilitates full conversion of the precursor material to the crystalline perovskite phase. From solution studies, we relate these changes in device performance to the presence and distribution of precursor aggregates that effectively pattern the formation of perovskite crystals during film formation

Dynamic regulation of airway surface liquid pH by TMEM16A and SLC26A4 in cystic fibrosis nasal epithelia with rare mutations

Copyright \ua9 2023 the Author(s). Published by PNAS. In cystic fibrosis (CF), defects in the CF transmembrane conductance regulator (CFTR) channel lead to an acidic airway surface liquid (ASL), which compromises innate defence mechanisms, predisposing to pulmonary failure. Restoring ASL pH is a potential therapy for people with CF, particularly for those who cannot benefit from current highly effective modulator therapy. However, we lack a comprehensive understanding of the complex mechanisms underlying ASL pH regulation. The calcium-activated chloride channel, TMEM16A, and the anion exchanger, SLC26A4, have been proposed as targets for restoring ASL pH, but current results are contradictory and often utilise nonphysiological conditions. To provide better evidence for a role of these two proteins in ASL pH homeostasis, we developed an efficient CRISPR-Cas9-based approach to knock-out (KO) relevant transporters in primary airway basal cells lacking CFTR and then measured dynamic changes in ASL pH under thin-film conditions in fully differentiated airway cultures, which better simulate the in vivo situation. Unexpectantly, we found that both proteins regulated steady-state as well as agonist-stimulated ASL pH, but only under inflammatory conditions. Furthermore, we identified two Food and Drug Administration (FDA)-approved drugs which raised ASL pH by activating SLC26A4. While we identified a role for SLC26A4 in fluid absorption, KO had no effect on cyclic adenosine monophosphate (cAMP)-stimulated fluid secretion in airway organoids. Overall, we have identified a role of TMEM16A in ASL pH homeostasis and shown that both TMEM16A and SLC26A4 could be important alternative targets for ASL pH therapy in CF, particularly for those people who do not produce any functional CFTR

Evolutionary determination of experimental parameters for ptychographical imaging

The Ptychographical Iterative Engine (PIE) algorithm is a recently developed novel method of Coherent Diffractive Imaging (CDI) that uses multiple overlapping diffraction patterns to reconstruct an image. This method has successfully produced high quality reconstructions at both optical and X-ray wavelengths but the need for accurate knowledge of the probe positions is currently a limiting factor in the production of high resolution reconstructions at electron wavelengths. This paper examines the shape of the search landscape for producing optimal image reconstructions in the specific case of electron microscopy and then shows how evolutionary search methods can be used to reliably determine experimental parameters in the electron microscopy case (such as the spherical aberration in the probe and the probe positions)