Single Contact Research Articles

Device design and optimization of CNTFETs for high-frequency applications

Carbon nanotube (CNT) field-effect transistors (FETs) have recently reached high-frequency (HF) performance similar to that of silicon RF-CMOS at the same gate length despite a tube density and current per tube that are far from the physical limits and suboptimal device architecture. This work reports on an investigation of the optimal device design for practical HF applications in terms of cut-off frequencies, power gain, and linearity. Different fundamental designs in the gate contact arrangement are considered based on a 3D device simulation of both CNTs and contacts. First, unit cells with a single CNT and minimal contact sizes are compared. The resulting simulation data are then extended toward a structure with two gate fingers and realistic contact sizes. Corresponding parasitic capacitances, as well as series and contact resistances, have been included for obtaining realistic characteristics and figures of merit that can be used for comparison with corresponding silicon RF MOSFETs. Finally, a sensitivity analysis of the device architecture with the highest performance is performed in order to find the optimal device design space.

Myopia control with soft multifocal contact lenses: 18-month follow-up.

PURPOSE:The study aimed to establish the outcome of multifocal contact lenses (MFCL) (Multistage + 1.50D and Proclear + 3.00D) on myopia progression and axial length elongation over an 18-month period.METHODS:Thirty myopic schoolchildren (5 males and 25 females) aged between 13 and 15 years were randomly assigned to wear either single vision contact lens (SVCL), Multistage MFCL + 1.50D, or Proclear +3.00D MFCL for 1½ years using a double-masked design. Cycloplegic refraction, corneal curvature, and axial length were measured.RESULTS:Myopia progression was controlled by 38.6% and 66.6% in children wearing Multistage + 1.50D and Proclear +3.00D MFCL, respectively, in comparison to children wearing SVCL over an 18-month period. In terms of axial elongation, this study found a 31.1% and 63.2% control in axial elongation over 18 months of treatment in comparison to the SVCL group. No statistical significant difference in corneal curvature was found between initial and last visits for all the three groups (SVCL, P = 0.90; Multistage + 1.50 MFCL, P = 0.78, and Proclear + 3.00 MFCL, P = 0.05).CONCLUSION:Proclear +3.00D MFCL was revealed to cause slow development of myopia and axial elongation among myopic schoolchildren. MFCL with higher add powers could be more effective on myopia progression in comparison with moderate add powers.

Determining the rotational orientation of directional deep brain stimulation electrodes using magnetoencephalography

Objective. The aim of the present study was to evaluate the effect of different electrode configurations on the accuracy of determining the rotational orientation of the directional deep brain stimulation (DBS) electrode with our previously published magnetoencephalography (MEG)-based method. Approach. A directional DBS electrode, along with its implantable pulse generator, was integrated into a head phantom and placed within the MEG sensor array. Predefined bipolar electrode configurations, based on activation of different directional and omnidirectional contacts of the electrode, were set to generate a defined magnetic field during stimulation. This magnetic field was then measured with MEG. Finite element modeling and model fitting approach were used to calculate electrode orientation. Main results. The accuracy of electrode orientation detection depended on the electrode configuration: the vertical configuration (activation of two directional contacts arranged one above the other) achieved an average accuracy of only about 41 ∘. The diagonal configuration (activation of the electrode tip and a single directional contact at the next higher level of the electrode) achieved an accuracy of 13∘, while the horizontal electrode configuration (activation of two adjacent directional contacts at the same electrode level) achieved the best accuracy of 6∘. The accuracy of orientation detection of the DBS electrode depends on the change in spatial distribution of the magnetic field with the rotation of the electrode along its own axis. In the vertical configuration, rotation of the electrode has a small effect on the magnetic field distribution, while in the diagonal or horizontal configuration, electrode rotation has a significant effect on the magnetic field distribution. Significance. Our work suggests that in order to determine rotational orientation of a DBS electrode using MEG, horizontal configuration should be used as it provides the most accurate results compared to other possible configurations.

Influence of repeated contacts on the transfer of elemental metallic lead between compartments in an integrated conceptual model for dermal exposure assessment

ABSTRACT Transfer of contaminants to and from the skin surface has been postulated to occur through a number of different pathways and compartments including: object(s)-to-skin, skin-to-skin, skin-to-clothing, skin-to-gloves, air-to-skin, skin-to-lips, and skin-to-saliva. However, many identified transfer pathways have been only minimally examined to determine the potential for measurable transfer. The purpose of this study was to quantitatively evaluate repeated transfer between different compartments using elemental metallic lead (Pb) in the solid form using a series of systematic measurements in human subjects. The results demonstrated that some transfer pathways and compartments are significantly more important than others. Transfer of Pb could not be measured from skin to cotton clothing or skin to laminate countertop surfaces. However, transfer was consistently measured for skin-to-skin and between the skin and the surface of nitrile gloves, suggesting the potential for significant transfer to or from these compartments in real-world exposure scenarios, and the importance of these pathways. With repeated contacts, transfer increased non-linearly between 1 and 5 contacts, but appeared to approach a steady state distribution among the compartments within 10 contacts. Consistent with other studies, relative to 100% transfer for a single contact, the quantitative transfer efficiency decreased with repeated contacts to 29% after 5 contacts and 11–12% after 10 contacts; for skin-to-skin transfer measurements, transfer efficiency after either 5 or 10 contacts was approximately 50% of the single contact transfer. These data are likely to be useful for refining current approaches to modeling of repeated contacts for dermal exposure and risk assessment.

Point of care testing for infectious disease: ownership and quality.

Traditionally, diagnosis of acute infections has been organism-growth based, which makes timely and actionable infection diagnosis a major challenge. In addition, traditional microbial detection methods, including direct microscopy, are not suited for outsourcing to clinical, non-laboratory-educated personnel. Optimal management of patients with known or suspected clinical infections, such as targeted (or no) antimicrobial treatment and correct use of single room contact isolation facilities, requires rapid identification of the causative infectious microorganism. We are now facing a new disruptive paradigm shift in diagnostic microbiology. The availability of small-footprint robust instruments with easy-to-use assay kits allows non-laboratory-trained nurses and physicians to perform high-quality molecular diagnostics in a near-patient setting with results available in <30 minutes. This technology is currently breaking the centralized laboratory monopoly on the delivery of gold-standard clinical microbiology diagnostics. There is clear potential for huge positive impacts on clinical patient management and antibiotic stewardship, especially in settings where access to timely laboratory test results is not possible, but there are also potentially huge risks. Moving diagnostic testing away from the controlled diagnostic laboratory environment will lead to risks such as increased risk of inappropriate use of the diagnostic tests, insufficient training of staff performing the tests, incorrect interpretation of the test results, lack of quality control procedures, failure to capture test results in electronic patient records and compromised local as well as national surveillance. To reap the upside and avoid the downside of point-of-care infectious disease testing, the diagnostic laboratory needs to maintain oversight, and each institution must have a clear strategy for implementation and execution. If we fail, the risks could outweigh the benefits.

Quantifying pathogen infection risks from household laundry practices.

AimsContaminated laundry can spread infections. However, current directives for safe laundering are limited to healthcare settings and not reflective of domestic conditions. We aimed to use quantitative microbial risk assessment to evaluate household laundering practices (e.g., detergent selection, washing and drying temperatures, and sanitizer use) relative to log10 reductions in pathogens and infection risks during the clothes sorting, washer/dryer loading, folding and storing steps.Methods and ResultsUsing published data, we characterized laundry infection risks for respiratory and enteric pathogens relative to a single user contact scenario and a 1.0 × 10−6 acceptable risk threshold. For respiratory pathogens, risks following cold water wash temperatures (e.g. median 14.4℃) and standard detergents ranged from 2.2 × 10−5 to 2.2 × 10−7. Use of advanced, enzymatic detergents reduced risks to 8.6 × 10−8 and 2.2 × 10−11 respectively. For enteric pathogens, however, hot water, advanced detergents, sanitizing agents and drying are needed to reach risk targets.Significance and Impact of the StudyConclusions provide guidance for household laundry practices to achieve targeted risk reductions, given a single user contact scenario. A key finding was that hand hygiene implemented at critical control points in the laundering process was the most significant driver of infection prevention, additionally reducing infection risks by up to 6 log10.

The efficacy of multifocal soft contact lenses for the alleviation of asthenopic symptoms in myopes with accommodative lag

PurposeTo evaluate the efficacy of multifocal soft contact lenses to reduce asthenopic symptoms in myopes with accommodative lag. MethodsTwenty-four myopic participants, aged 18–35 years, with mean spherical equivalent (MSE) of ≤ -0.75D, were recruited in a randomised, double-blind crossover study. All participants were existing contact lens wearer with near orthophoria or esophoria, presenting with subjective asthenopic symptoms at baseline [Convergence Insufficiency Symptom Survey (CISS) score ≥ 21] and a lag of accommodation ≥ +0.75 D. All participants were initially fitted with single vision contact lenses for a one month period. Participants were then randomly assigned 1:1 to wear low add or high add multifocal soft contact lenses for a further month. After this period, the groups were reversed. Data were collected at baseline and following one month’s wear of each lens. Change in CISS score was evaluated as the primary outcome measure, while secondary outcome measures were changes in accommodative lag and heterophoria status. ResultsBaseline CISS score was (mean ± SD) 25.04 ± 4.58. Post-intervention scores were as follows: single vision: 24.46 ± 4.59, low add: 12.17 ± 6.89, high add: 13.71 ± 7.23. Both low add and high add multifocal soft contact lens wear was associated with an improvement in CISS score compared to baseline CISS and single vision (all p < 0.01). No significant difference was found between the CISS score for the baseline CISS and single vision (p = 1.00). No significant difference was found in lag of accommodation between lens conditions (all p > 0.05), however, there was an exophoric shift in near heterophoria between single vision and both multifocal contact lenses (low add: (mean difference 1.33 Δ, p = 0.02; high add: mean difference 1.23 Δ, p = 0.02) but not between habitual spectacle or any other modality (all p > 0.05). ConclusionsThe use of multifocal soft contact lenses for a one-month period was associated with reduced severity of asthenopic symptoms in pre-presbyopic myopes with accommodative lag. Whilst improvement of symptoms does not appear to be mediated by a significant reduction in accommodative lag, changes in heterophoria may play a role in reducing asthenopic symptoms.

Microfluidic extraction of uranium from dilute streams using TiAP in ionic liquid as the solvent

A microfluidic platform to extract uranium from HNO3 (nitric acid) medium using tri-isoamyl phosphate (TiAP) dissolved (30% v/v) in ionic liquid ([BMIM]PF6) is reported. PTFE microbore tubes serve as the microchannels. The quality of dispersion inside the translucent tubes was observed using a camera. The images obtained are used to understand the observed experimental trends. Overall volumetric mass transfer coefficient was determined considering the microchannel as a differential contactor with co-currently flowing phases. The effects of contact time, flow velocity, organic to aqueous (O/A) ratio and microchannel diameter on mass transfer performance are studied. Effect of different coiling configurations on mass transfer performance was compared. Under optimum conditions, 95.3% of uranium present in the feed (corresponding stage efficiency being 99.2%) could be extracted within a contact time of about 200 s in a single contact. Corresponding (KLa) was 0.024 s−1. Coiling was found to have a significant effect on values of KLa especially at low residence times.

Millikelvin scanning tunneling microscope at 20/22T with a graphite enabled stick-slip approach and an energy resolution below 8 μeV: Application to conductance quantization at 20T in single atom pointcontacts of Al and Au and to the charge density wave of 2H-NbSe2.

We describe a scanning tunneling microscope (STM) that operates at magnetic fields up to 22T and temperatures down to 80 mK. We discuss the designof the STM head, with an improved coarse approach, the vibration isolation system, and efforts to improve the energy resolution using compact filters for multiple lines. We measure the superconducting gap and Josephson effect in aluminum and show that we can resolve features in the density of states as small as 8 μeV. We measure the quantization of conductance in atomic size contacts and make atomic resolution and density of states images in the layered material 2H-NbSe2. The latter experiments are performed by continuously operating the STM at magnetic fields of 20T in periods of several days without interruption.

Fine Depiction of the Single Sand Body and Connectivity Unit of a Deltaic Front Underwater Distributary Channel: Taking the Third Member of the Dongying Formation in the Cha71 Fault Block of the Chaheji Oilfield as an Example

By taking the third member of the Dongying Formation in the Cha71 fault block of the Chaheji oilfield as an example, the single sand body of the deltaic front underwater distributary channel is meticulously depicted by using the data of well logging and performance production. Portrays the vertical separation model, total lateral separation type, vertical type, lateral superposition type, 4 types of single sand body vertical superimposed and bay type, bank contact between docking, instead of four kinds of single sand body lateral contact type, and summarizes its logging facies identification. The quantitative prediction model of the single sand body was established, the characteristics of single sand body plane distribution were summarized, and the identification of the oil-water layer and the lower limit of reservoir effective thickness were studied. And we got the conclusion that based on the fine characterization of the single sand body and the lower limit standard of effective reservoir thickness, the distribution range of the effective reservoir and connecting unit is determined. Finally, the connectivity of the connecting unit is verified by dynamic data.

Experimental investigation on vortex-induced vibration and solid-structure impact of a near-bottom horizontal flexible pipeline in oblique shear flow

Vortex-induced vibrations and solid-structure impacts of a horizontal flexible pipeline in the vicinity of a bottom wall boundary are experimentally investigated in a water flume. A neutrally-buoyant submerged pipe, with a length-to-diameter ratio of about 87 and fixed end supports, is subject to a shear flow with an oblique angle of 30°. The initial gap-to-diameter ratio between the wall and the pipe is equal to 0.2. A non-intrusive measurement with high-speed cameras is employed to simultaneously capture the space–time varying in-line and cross-flow vibrations in the normal flow reduced velocity range of 3–15 with a maximum Reynolds number of about 2780. Experimental results highlight new pipe equilibrium profiles and modal response branches being significantly broadened due to the wall proximity. Two solid-pipe impact features are discussed, including single-segment and two-segment alternating impacts depending on the dominant oscillation mode of the flexible pipe. Both the response amplitude and frequency increase with the reduced velocity, resulting in a more frequent impact with a greater impact force. A temporal evolution from a single point contact to a segment contact is observed for the two-segment alternating impact. Nevertheless, the lengths of the two contact segments are different as a result of the asymmetric response profile. In all cases, the pipe transversely impacts the bottom wall introducing a perturbation transmission along the pipe, which leads to the multi-mode, multi-frequency and asynchronous in-line and cross-flow oscillations with a 1:1 and 2:1 resonance. Due to a momentum energy consumption, the pipe experiences a slow post-impact bouncing phenomenon, contributing to a longer temporal period of the fluid–pipe interaction with a wall impact.

Revisiting the GJK and shape erosion method for contact resolution in DEM

This work revisits the Gilbert–Johnson–Keerthi (GJK) and the radial direction-based shape erosion method for the contact resolution of non-spherical particles in discrete element method (DEM). Tests on single contact indicate that the shape erosion would frequently lead to an overestimation on contact overlap, but has a minor effect on contact normal and contact point. The undesired effect of shape erosion on contact overlap is more pronounced for small overlaps and elongated particles. Further study based on random packing and triaxial compression tests suggests that the shape erosion has a dominant effect on the weak contacts within the packing. The overestimation of contact overlaps due to shape erosion may tend to push particles away, thereby dismiss the weak contacts and result in an overall smaller coordination number. Nonetheless, as the contribution of weak contacts to particle shear resistance is relatively small, the shape erosion exhibits negligible effects on the packing fabric and the stress–strain behaviors. In practice, it is suggested that the erosion ratio should be carefully set such that it is compatible (e.g., in a similar order of magnitude) to the overlaps of strong contacts.

Mechanics of Magnetic Robots Akin to Soft Beams Supported at Unanchored Contacts

Abstract This article presents a novel algorithm to predict the shape and the support configurations of a magnetic robot acting like a supple beam, which deforms due to an imposed magnetic field. The soft magnet loosely rests on a flat horizontal surface, which provides the pivoting supports to the robot to attain its deformed shape. The key difficulty in analysis of the mechanics is the lack of any prior knowledge about the location of the contacts where the distorted beam finds support from the ground. This article outlines an algorithm in which different possibilities referred to as modes are checked systematically to locate the placement and the nature of such supports. Consequently, the 2D shape of the soft beam can be determined without any heuristic assumption about where the magnetic robot is touching the solid surface. This study focuses on single contact sections although the algorithm idea is valid for multiple contacts as well. The mathematical theory and the numerical scheme are validated by comparing the simulated results with existing experimentally obtained configurations. Also, the parametric space of system-defining nondimensional parameters is explored to determine when a transition happens from one mode to another and which magnetization methods are desirable for higher stability. Through theoretical simulation, the results show that a thin rectangular cross section provides higher deformation when compared to the other two tested shapes (circular and equilateral triangle cross section).

Quantitative microbial risk assessment of human norovirus infection in environmental service workers due to healthcare-associated fomites

Healthcare-associated norovirus outbreaks place a large burden on healthcare staff. Environmental service workers (ESWs), however, remain understudied despite high contact with potentially contaminated surfaces. Understanding the magnitude of the risk of norovirus infection in healthcare ESWs can protect workers and improve infection control. This study simulated the risk of norovirus infection for unprotected ESWs after a single fomite contact, assuming no disinfection or protective equipment, in norovirus-positive patient rooms. In addition, the risk of secondary surface transmission from norovirus-exposed ESWs was simulated. A quantitative microbial risk assessment employing two-dimensional Monte Carlo simulation with parameters extracted from the literature was used to estimate norovirus infection from multiple fomite contact scenarios defined by: norovirus source (patient vomit/diarrhoea), location (bathroom/patient room) and target outcome (ESW/secondary illness). Unprotected ESWs have a maximum estimated risk of norovirus infection of 33% (1:3) for a single fomite contact in a room where a norovirus-positive patient had a diarrhoeal event. Patient vomit events lead to fomite contact risk estimates that are four orders of magnitude lower than those for diarrhoeal events. The estimated risk of secondary illness from touching a common surface is as high as 25% (1:4) after single fomite exposure following a diarrhoeal event. A single fomite contact may lead to sizable risk of norovirus infection in ESWs if personal protective equipment and disinfection are not used appropriately. ESWs can also transfer virus to secondary surfaces, initiating further infections. Interventions are needed to reduce fomite transfer of norovirus, and protect patients and staff from nosocomial infections.

Basalt fibre surface modification via plasma polymerization of tetravinylsilane/oxygen mixtures for improved interfacial adhesion with unsaturated polyester matrix

With the aim of optimizing the interfacial adhesion of basalt fibres with thermoset matrices, in this research the plasma polymerization technique (PECVD) was used to synthesize polymeric coatings based on tetravinylsilane (TVS) or its mixtures with oxygen on the surface of basalt fibres. The successful deposition of the polymer sizing was confirmed by XPS analysis, which highlighted the increase in the intensity of the carbon and oxygen peaks. To evaluate the influence of polymer sizing on interfacial adhesion, basalt fibre/polyester resin composites were tested through the short beam shear (SBS) test. Compared to neat basalt fibres, the modified fibres showed a significant increase in the interlaminar shear strength (ILSS) higher than 180%. These results compared quite favourably with those on glass fibres used as baseline, with higher ILSS values as a function of oxygen content. The improvement in interfacial adhesion was correlated with the increase in basalt fibre surface energy by single fibre dynamic contact angle tests.

High‐Performance Flexible Schottky DC Generator via Metal/Conducting Polymer Sliding Contacts

AbstractDynamic Schottky direct‐current (DC) generators hold great promise for ambient mechanical energy harvesting as it overcomes the low‐current output limitation in conventional approaches. However, the lack of a fundamental understanding of DC generation in conducting polymer‐based Schottky generators has hindered their application for self‐powered wearable and implantable electronics. Here, a high‐performance, flexible Schottky DC generator with metal/conducting polymer sliding contact system is demonstrated, which exhibits a large current density (J) up to 20 A m–2 for single contact geometry and a scaled‐up DC output reaching 200 µA (J = 0.73 A m–2) and 0.8 V. The design of flexibility in such a Schottky DC generator is inherited from the long‐chain polymer concept, leading to the demonstration of a variety of device configuration of free‐standing thin film, supported thin film and nanocomposite prototype toward practical applications. It is revealed that the sliding junctions may exhibit a different mechanical energy conversion mechanism compared to the compressive conducting polymer Schottky junctions. It is also proven that the magnitude and polarity of DC generation is determined by the Schottky contact formation and interfacial electric field. The concept of a flexible Schottky generator not only shows great promise for next‐generation, self‐powered wearable devices, but also provides potential mechanisms for developing novel wearable sensors.

Моделирование дискретных контактов термодинамической системы элементов сборной дереворежущей фрезы

Operational capability of a modular wood-cutting tool depends, besides many factors, on the design features of cutting element fastening unit. There are no clear and precise methods that explain major factors influencing tool durability for selecting the design of the modular wood-cutting tool, which would meet production requirements. Thermodynamics modeling under contact interaction of elements enables to choose a design for effective application and increases the tool efficient life. The research purpose is modeling of thermodynamic processes in the cutter element fastening unit in the wood-cutting tool body in order to optimize the design, technological parameters and operating modes of the tool. The research subject is the contact interaction conditions and heat transfer processes between the device elements. The cutting element fastening unit is designed and the model of interaction between the parts of the mechanism of the modular wood-milling tool is developed. Further tasks, namely, development of a model of thermodynamic processes in the cutting element fastening unit, discussion of the results and identifying the recommendations for choosing the design of the modular wood-cutting tool at the design stage were realized in a work that continues the ongoing research. The finite-element model of rough wavy surfaces contact interaction of design elements was developed on the basis of standard design of a shell-type plain woodmilling cutter. The analysis concluded that further analytical modeling of contact conditions with existing parameters is possible. The contacting surfaces approach and the radii of single contact areas were determined taking into account the data of design and calculation of wood cutting forces. These results will be used next in modeling of thermodynamic processes. Methodology and research methods comprise theoretical study and mathematical modeling, including finite-element analysis. The models developed are possible to be used in the creation of a complex durability model of the wood-cutting tool with regard to other factors. The main result of this research stage is obtaining the model of contact conditions and initial data for further modeling of thermodynamic processes in the knife fastening unit in the milling body to predict its thermal condition.

MSA, The French Agricultural Social Protection scheme

As the second largest social protection scheme in France, the Agricultural Social Mutuality (fr. Mutualité sociale agricole, MSA) is responsible for providing all compulsory social security coverage for the entire agricultural population and its beneficiaries, whether it concerns health, family, retirement, work-related accidents or occupational diseases. The MSA is responsible for collecting social security premiums and contributions, but also unemployment insurance and conventional contributions for many organizations1. It differs from other French social security schemes in that it provides a one-stop shop for individuals and companies to deal with a single contact person for all matters relating to their social protection throughout their lives. In addition to its basic mission, it carries out a policy of health and social action adapted to its population and is also in charge of occupational medicine and the prevention of professional risks in the agricultural sector. It can support all actions aiming to promote the coordination and the offer of care in rural areas2. As a mutualistic organization, the MSA is the expression of a responsible and supportive democracy at the service and in proximity of the rural world. The representativeness of its elected delegates, its knowledge of the territories and their stakeholders, and its role as a professional agricultural organization give it an indispensable expertise that allows it to work for the cohesion of the territories while guaranteeing access to quality public services. This expertise also enables it to be present abroad as part of formalized exchanges in European networks and international cooperation projects.

Is increased mortality by multiple exposures to COVID-19 an overseen factor when aiming for herd immunity?

Governments across the globe responded with different strategies to the COVID-19 pandemic. While some countries adopted measures, which have been perceived controversial, others pursued a strategy aiming for herd immunity. The latter is even more controversial and has been called unethical by the WHO Director-General. Inevitably, without proper control measures, viral diversity increases and multiple infectious exposures become common, when the pandemic reaches its maximum. This harbors not only a potential threat overseen by simplified theoretical arguments in support of herd immunity, but also deserves attention when assessing response measures to increasing numbers of infection. We extend the simulation model underlying the pandemic preparedness web interface CovidSim 1.1 (http://covidsim.eu/) to study the hypothetical effect of increased morbidity and mortality due to 'multi-infections', either acquired at by successive infective contacts during the course of one infection or by a single infective contact with a multi-infected individual. The simulations are adjusted to reflect roughly the situation in the USA. We assume a phase of general contact reduction ("lockdown") at the beginning of the epidemic and additional case-isolation measures. We study the hypothetical effects of varying enhancements in morbidity and mortality, different likelihoods of multi-infected individuals to spread multi-infections and different susceptibility to multi-infections in different disease phases. It is demonstrated that multi-infections lead to a slight reduction in the number of infections, as these are more likely to get isolated due to their higher morbidity. However, the latter substantially increases the number of deaths. Furthermore, simulations indicate that a potential second lockdown can substantially decrease the epidemic peak, the number of multi-infections and deaths. Enhanced morbidity and mortality due to multiple disease exposure is a potential threat in the COVID-19 pandemic that deserves more attention. Particularly it underlines another facet questioning disease management strategies aiming for herd immunity.

Calculation of the contact area between snow grains and ski base

Gliding friction depends on the contact area between ski and snow. Therefore, we computed the contact area of a single grain with the ski base by solving the static contact problem. The calculations were done at randomly selected positions on two ski bases, various snow grain radii, and various loadings. The relative single grain contact area with the ski base was 0.03–6.0% of the snow grain’s cross section. Contact area and pressure increased with decreasing snow grain radius and increasing load. The contact pressure exceeds the strength of ice, presumably causing fracture of parts of snow grains. Resulting debris may partly remain in the interface between ski and snow and thus reduce friction.