P. A. Brühwiler

Empa - Swiss Federal Laboratories for Materials Science and Technology, Duebendorf, Zurich, Switzerland

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Publications (109)336.04 Total impact

  • Source
    Cornelis P Bogerd · Ian Walker · Paul A Brühwiler · René M Rossi
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    ABSTRACT: The present study looked at the effect of a helmet on cognitive performance under demanding conditions, so that small effects would become more detectible. Nineteen participants underwent 30 min of continuous visual vigilance, tracking, and auditory vigilance (VTT + AVT), while seated in a warm environment (27.2 (±0.6) °C, humidity 41 (±1)%, and 0.5 (±0.1) m s(-1) wind speed). The participants wore a helmet in one session and no helmet in the other, in random order. Comfort and temperature perception were measured at the end of each session. Helmet-wearing was associated with reduced comfort (p = 0.001) and increased temperature perception (p < 0.001), compared to not wearing a helmet. Just one out of nine cognitive parameters showed a significant effect of helmet-wearing (p = .032), disappearing in a post-hoc comparison. These results resolve previous disparate studies to suggest that, although helmets can be uncomfortable, any effect of wearing a helmet on cognitive performance is at worst marginal.
    Full-text · Article · Oct 2013 · Applied ergonomics
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    ABSTRACT: The distribution and transport of moisture in textiles and textile layer combinations plays an important role in the wearing comfort of clothes, especially in sportswear, working garment or protective clothing. X-ray tomography is an attractive research tool for such studies because it allows a multitude of possibilities for the analysis and visualization of the raw data: radial and vertical cuts, three-dimensional representations, quantitative evaluation, user-defined implementation of thresholds and their discrimination by colours, and comparison of different conditions of a material (such as dry and wet). A contrast agent is not necessary and the resolution is less than 100 μm. We present some results obtained with a tabletop X-ray instrument used for the study of water transport in socks and shoe laminates.
    No preview · Article · Apr 2013 · Measurement
  • Cornelis P. Bogerd · Paul A. Brühwiler · René M. Rossi
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    ABSTRACT: Heat loss and moisture retention properties of footwear were characterized using a walking thermal manikin foot. The same type of military boot was equipped with different membranes: (i) GORE TEX with IQ TEX, (ii) halve OUTDRY, (iii) full OUTDRY, and (iv) OUTDRY with IQ TEX. In a separate experiment a single boot type was used to evaluate four different sock fabrics: (i) wool/polypropylene, (ii) polypropylene, (iii) polypropylene/polyamide, and (iv) wool/polyamide. Both boot membranes and sock fabrics were assessed under three conditions: (i) standstill no sweating, (ii) walking no sweating, and (iii) walking and sweating. The walking rate was set at 15 step min−1 and the sweat rates were 9 g h−1 and 12 g h−1, for boot membrane and sock fabric measurements, respectively. Moisture retention was assessed by weighing the footwear components before and after each measurement. GORE TEX with IQ TEX resulted in a higher heat loss during walking without sweating compared to the other membranes (p = 0.017). GORE TEX with IQ TEX retained more moisture in the sock compared to the other membranes (p < 0.001) but also retained more moisture in the inlay sole compared to halve OUTDRY (p = 0.015). No differences in heat loss were found among sock fabrics, while wool/polyamide retained more moisture compared to polypropylene/polyamide (p = 0.036). Furthermore, a moisture vapour transmission rate of 61.2 ± 6.6 g m−2 h−1 was calculated for all sweating conditions. Finally, the measurements suggest that no pumping effect takes place in the measured footwear under the present conditions.Relevance to industry: Understanding heat loss and moisture retention of footwear is necessary for optimization of footwear for blister incidence and (thermal) comfort.
    No preview · Article · Mar 2012 · International Journal of Industrial Ergonomics
  • P.a.brühwiler · A.j.maxwell · N.mårtensson
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    ABSTRACT: We have measured the spectator autoionization shift of C60 near the C 1s threshold, and compared it to the Coulomb correlation energy U found by another spectroscopic method. We find that the U we obtain is smaller by a factor of 30% than a prior result, due to a calibration difference. The spectator shift can be comparable to U, with a value that decreases as the excited electron wavefunction becomes more diffuse. This indicates that screening effects vary drastically with molecular orbital.
    No preview · Article · Jan 2012 · International Journal of Modern Physics B
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    Cornelis P Bogerd · Reto Niedermann · Paul A Brühwiler · René M Rossi
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    ABSTRACT: The goal of the present study was to investigate differences in perception and skin hydration at the foot of two sock fabrics with distinct moisture properties in a realistic military setting. Thirty-seven military recruits wore two different socks (PP: 99.6% polypropylene and 0.4% elastane, and BLEND: 50% Merino-wool, 33% polypropylene, and 17% polyamide), one on each foot. Measurements were carried out after a daily 6.5-km march on 4 days. Each participant rated temperature, dampness, friction, and comfort for each foot. On a daily selection of participants, skin hydration was measured on three sites of both feet using a corneometer, and moisture content of the socks was determined. BLEND was rated to be cooler, less damp, and more comfortable (P < 0.05). Two out of three skin sites were drier for BLEND than PP (P < 0.05). Moreover, BLEND stored 2.9 ± 0.3 times more moisture compared to PP. Thus, under the present conditions, socks such as BLEND are to be preferred over polypropylene socks.
    Full-text · Article · Jan 2012 · Annals of Occupational Hygiene
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    ABSTRACT: The moisture transfer and absorption properties of fabrics play an important role in the evaluation of the overall wear comfort of the textile. The location of moisture in the textile influences the skin wetness as well as the skin/textile friction process. In this study, we used X-ray tomography to analyze the transplanar and in-plane water transport in different sock materials when two defined pressures were applied to the inner side by means of an adjustable screw. The materials used were polyamide, polypropylene and wool, and had very distinct hydrophilic/hydrophobic and hygroscopic properties. The in-plane wicking effect showed a clear time dependency for the polyamide and wool samples, while the spreading of the polypropylene samples was very scattered. This effect was generally larger in the outer side of the sock than in the inner side, showing a clear tendency of these socks to wick the moisture away from the skin. Applying a pressure generally increased the in-plane water transport, but it affected the water distribution throughout the thickness of the sock for the wool samples, as more water remained in the inner half. The transplanar wicking effect was the most efficient with the polypropylene sock under the high pressure condition, but with the low pressure, this sock was not able to absorb all the moisture and a small quantity of water remained at its inner surface. X-ray tomography was shown to be a powerful tool to analyze not only the water distribution in static conditions, but also the transient 3-dimensional water transport.
    No preview · Article · Aug 2011 · Textile Research Journal
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    ABSTRACT: The goal of the present study was to investigate physiological effects, mainly at the level of the foot, of two sock fabrics with distinct moisture properties. Twelve participants wore two different socks, one on each foot. The following two sock types were used: PP: 99.6% polypropylene and 0.4% elastane and BLEND: 50% Merino wool, 33% polypropylene, and 17% polyamide. The participants walked three times on a treadmill at 5 km h(-1), with no gradient for the first and third phase and a 10% upward inclination for the second walking phase. The microclimate temperature between the boot and foot was measured during walking. Preceding and following the walking phases, additional measurements were carried out at the level of the foot, i.e. skin temperature and skin hydration on three locations and skin friction between the posterior surface of the calcaneus and a glass plate. In addition, the moisture absorption of boots and socks was determined. Differences between the sock fabrics were found for weight gain and microclimate temperature: (i) PP tended to hold less water compared to BLEND, (ii) the boot's microclimate temperature resulted in larger values for BLEND measured at the dorsal surface at the level of the third metatarsal, and (iii) warmer microclimates of the boot were measured for PP compared to BLEND at the distal anterior end of the tibia. The established differences in moisture behavior of both socks did not result in detectable differences in parameters measured on the skin of the foot.
    Full-text · Article · Jun 2011 · Annals of Occupational Hygiene
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    ABSTRACT: Aromatic molecules are central components of model systems for molecular electronics, with C-60 one of the most studied. Upon adsorption on (metallic) substrates a splitting of the frontier orbitals is commonly observed, with a strong dependence on substrate material, but little dependence on substrate structure. We report the detailed photoelectron angle dependence of C-60/A1(110) over a wide range of energy, finding a strong remnant molecular character. In particular, certain HOMO-derived suborbitals couple strongly, and others weakly, with the metal, which results in final state charging for those weakly coupled. C Is data correlate well with the assignments made on this basis, as does the comparison of ground state partial densities-of-states (PDOS) to photoelectron spectra. Detailed analysis of the PDOS supports a rough division into surface-near and surface-far components, in agreement with the molecular picture. The component spectral widths are attributed to intramolecular vibrational coupling, which is suggested to aid in the electronic decoupling of certain suborbitals from the substrate, facilitating the observed final state charging.
    No preview · Article · Oct 2010 · The Journal of Physical Chemistry C
  • Cornelis P Bogerd · René M Rossi · Paul A Brühwiler
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    ABSTRACT: We report the effects of full-face motorcycle helmet ventilation systems on heat, airflow, noise, and comfort perception for ventilation changes on the scalp. Eight subjects (aged 28.0 ± 5.4 years) underwent two experimental trials at ambient temperatures of 23.7 ± 0.4°C or 27.5 ± 0.3°C. In each trial, the thermally equilibrated subjects underwent two examination phases, during which four different helmets were assessed at wind speeds of 39.2 ± 1.9 km h−1 and 59.3 ± 1.4 km h−1. Vent-induced heat loss in the scalp ranged from −6.1 to 6.1 W, corresponding to vents being closed or opened, respectively. Perception of vent-induced changes was assessed immediately after the change. We find that the vent-induced heat loss, the subject, and the helmet are the most important response factors. In addition, comparison of two helmets with similar vent-induced heat loss suggests that internal airflow patterns may be important in explaining the observed perception differences.
    No preview · Article · Oct 2010 · Annals of Occupational Hygiene
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    ABSTRACT: Back protectors for snowboarders were analysed with respect to their potential to prevent spinal injury. In 20 Swiss skiing resorts, athletes were interviewed on the slope. In addition, an online survey was conducted. The performance of 12 commercially available back protectors was investigated by means of mechanical testing. A currently used drop test according to standard EN1621 (motorcycle protectors), testing energy damping was supplemented by penetration tests according to standard EN1077, which reflects snowsport safety concerns. 6 out of 12 back protectors fulfilled the higher safety level defined in EN1621. Protectors making use of energy-absorbing layers performed particularly well. In contrast, hard shell protectors exhibited a higher potential to withstand the penetration test. The surveys confirmed that approximately 40-50% of snowboarders use a back protector. A large majority of users expect protection from severe spinal injury such as vertebral fractures or spinal cord injury. The currently used test standards are fulfilled by many back protectors. Users, however, expect protectors to be efficient in impact scenarios that result in spinal injury, which are more severe than impacts as addressed in the current standards. This study highlights that there is a mismatch between the capabilities of current back protectors to prevent spinal injury in snowboarding and the expectations users have of these protectors.
    No preview · Article · Sep 2010 · British Journal of Sports Medicine
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    ABSTRACT: Approximately 13% skiers and 38% snowboarders wore wearing a back protector during the last season in Switzerland. This huge number suggests an ensured functionality of such back protectors. However, there is no specific standard regarding snow sports available. Therefore, the main goal of the study was to get an initial overview about the functionality in terms of potential protective effects of back protectors. The whole project was divided into an athlete survey and an experimental performance test (drop test). The results from the surveys clearly pointed out, that back protectors belong to the most important pieces of protection equipment in snow sports. The related customer expectations emphasize the importance in terms of injury prevention particularly regarding severe spinal column injuries. Concerning the performance test according to the standard for motorcyclists’ back protectors EN 1621-2 most of the samples did pass protection level 1. However, considering the test procedure there appears to be a mismatch between customer expectations, injury occurrence and the actual preventive potential of currently available protectors.
    Full-text · Article · Jun 2010 · Procedia Engineering
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    ABSTRACT: We report the quasistatic tensile and impact penetration properties (falling dart test) of injection-molded polycarbonate samples, as a function of multiwall carbon nanotube (MWNT) concentration (0.0–2.5%). The MWNT were incorporated by dilution of a commercial MWNT/polycarbonate masterbatch. The stiffness and quasistatic yield strength of the composites increased approximately linearly with MWNT concentration in all measurements. The energy absorbed in fracture was, however, a negative function of the MWNT concentration, and exhibited different dependencies in quasistatic and impact tests. Small-angle x-ray scattering (SAXS) showed that the dispersion of the MWNT was similar at all concentrations. The negative effects on energy absorption are attributed to agglomerates remaining in the samples, which were observed in optical microscopy and SAXS. Overall, there was a good correspondence between static and dynamic energy absorption.
    Full-text · Article · May 2010
  • Rolf Stämpfli · Paul A Brühwiler
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    ABSTRACT: A drop test system with flexibility in the choice of falling object has been constructed and characterized. Using the guided free fall principle, the system enables the study of impacts of a large range of objects on a wide selection of anvils, with high control of the position and orientation of the object. The latter is demonstrated with falls of a standard aluminium headform in mountaineering helmets on a kerbstone anvil, for which visual inspection with a high-speed camera confirms the desired accuracy. Impacts of a flat falling body on cylindrical polystyrene foam samples are used to derive stress–strain curves for materials of different density and for multilayer samples. In this case, the effects of striker orientation and placement on the resultant data are discussed, and the reproducibility of the data serves as an additional confirmation of the accuracy of the measurement apparatus and procedures. A check on the improvement in the level of positional and orientational striking precision achievable is obtained via an inter-laboratory comparison.
    No preview · Article · Sep 2009 · Measurement Science and Technology
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    ABSTRACT: Flexible polyurethane (PU) foams, with loading fractions of up to 0.2 wt% carbon nanotubes (CNTs), were made by free-rising foaming using water as blowing agent. Electron microscopy revealed an open cellular structure and a homogeneous dispersion of CNTs, although the incorporation of nanofiller affected the foaming process and thus the final foam density and cellular structure. The compressive response of the foams did not show an unambiguous improvement with CNT content due to the variable foam structure. However, dense films generated by hot pressing the foams indicated a significant intrinsic reinforcement of the polymer, even at low loadings of CNTs. Most significantly, CNTs were found to increase the acoustic activity monotonically at concentrations up to 0.1 wt%.
    No preview · Article · Aug 2009 · Composites Science and Technology
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    J. Schiessling · A Grigoriev · R. Fasel · R. Ahuja · P.A. Brühwiler
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    ABSTRACT: We compare photoelectron spectra (PES) and theoretical densities-of-states of C(60)/Al(111), C(60)/Al(110) and C(60)/Al(100). The splitting observed on all three surfaces is attributed to final state charging. This splitting can also be used to improve estimates of the charging energy U of adsorbed molecules and as a criterion for the existence of strong covalent bonding to the electrode. Au exhibits weak bonding in available data, whereas Ag(100), with measurable charge transfer, appears qualitatively similar to Al.
    Full-text · Article · Aug 2009 · Chemical Physics Letters
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    N. J. Mills · R. Stämpfli · F. Marone · P. A. Brühwiler
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    ABSTRACT: Finite element analysis, of regular Kelvin foam models with all the material in uniform-thickness faces, was used to predict the compressive impact response of low-density closed-cell polyethylene and polystyrene foams. Cell air compression was analysed, treating cells as surface-based fluid cavities. For a typical 1 mm cell size and 50 s-1 impact strain rate, the elastic buckling of cell faces, and pop-in shape inversion of some buckled square faces, caused a non-linear stress strain response before yield. Pairs of plastic hinges formed across hexagonal faces, then yield occurred when trios of faces concertinaed. The predicted compressive yield stresses were close to experimental data, for a range of foam densities. Air compression was the hardening mechanism for engineering strains < 0.6, with face- to-face contact also contributing for strains > 0.7. Predictions of lateral expansion and residual strains after impact were reasonable. There were no significant changes in the predicted behavior at a compressive strain rate of 500 s-1.
    Preview · Article · Feb 2009 · International Journal of Solids and Structures
  • P.A. Brühwiler
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    ABSTRACT: Twenty-six bicycle helmets and the visors supplied with them were characterized for convective heat loss using a thermal manikin headform in a climate chamber, in order to assess the role of the visors in forced convection. Two head tilt angles were studied (vertical or 0°, and forward or 30°), with and without the visor supplied with each helmet. Large variations were found for several helmets, with the strongest visor-induced changes corresponding to approximately 5% in the face and 10% in the scalp. When the visor visually blocked the face or the front vents from the wind direction, such as at 30° for the face, a reduction in convection heat loss was usually observed, whereas the visor had no or a slightly negative effect on the face at 0°, with opposite trends for the scalp. Hence visor design can help to optimize thermal comfort via convective heat loss.Relevance to industryUnderstanding (forced convective) heat loss of bicycle helmets and the role of the visor is necessary for optimization of thermal comfort. In turn this is likely to increase the willingness to wear such protective helmets, and may contribute to the performance of the wearer.
    No preview · Article · Jan 2009 · International Journal of Industrial Ergonomics
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    ABSTRACT: The simple cubic phase of a RbC60 thin film has been studied using photoelectron spectroscopy. The simple cubic-to-dimer transition is found to be reversible at the film surface. A sharp Fermi edge is observed and a lower limit of 0.5 eV is found for the surface Hubbard U, pointing to a strongly correlated metallic character of thin-film simple cubic RbC60. A molecular charge state is identified in the valence band and core-level photoemission spectra which arises from C60(2-) anions and contributes to the spectral intensity at the Fermi level.
    Full-text · Article · Jan 2009 · Physical Review Letters
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    Paul A Brühwiler
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    ABSTRACT: Twenty-six bicycle helmets and their associated visors were characterized for radiant heat transfer using a thermal manikin headform in a climate chamber to assess their ability to protect the wearer from heating by the sun. A single configuration for applied radiant flow of 9.3 W was used to assess the roles of the forward and upper vents and the visor. The helmets shielded 50-75% of the radiant heating without a visor and 65-85% with one. Twenty-three visors were shown to result in a relevant reduction of radiant heating of the face (>0.5 W), with 15 reaching approximately 1 W. Heating of the visor and/or helmet and subsequent heating of the air flowing into the helmet was nevertheless found to be a relevant effect in many cases, suggesting that simple measures like reflective upper surfaces could noticeably improve the radiant heat rejection without changing the helmet structure. The forward vents in the helmets that allow the transmission of radiant heat are often important for forced convection, so that minimizing radiant heating geneally reduces the maximization of forced convective heat loss for current helmets.
    Preview · Article · Jul 2008 · Journal of Sports Sciences
  • Cornelis P Bogerd · Paul A Brühwiler · Ronald Heus
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    ABSTRACT: Both radiant and forced convective heat flow were measured for a prototype rowing headgear and white and black cotton caps. The measurements were performed on a thermal manikin headform at a wind speed of 4.0 m . s(-1) (s = 0.1) in a climate chamber at 22.0 degrees C (s = 0.05), with and without radiant heat flow from a heat lamp, coming from either directly above (90 degrees ) or from above at an angle of 55 degrees . The effects of hair were studied by repeating selected measurements with a wig. All headgear reduced the radiant heat gain compared with the nude headform: about 80% for the caps and 95% for the prototype rowing headgear (P < 0.01). Forced convective heat loss was reduced more by the caps (36%) than by the prototype rowing headgear (9%) (P < 0.01). The radiant heat gain contributed maximally 13% to the net heat transfer, with or without headgear, showing that forced convective heat loss is the dominant heat transfer parameter under the chosen conditions. The results of the headgear - wig combinations were qualitatively similar, with lower absolute heat transfer.
    No preview · Article · Jun 2008 · Journal of Sports Sciences

Publication Stats

3k Citations
336.04 Total Impact Points


  • 2003-2013
    • Empa - Swiss Federal Laboratories for Materials Science and Technology
      • Laboratory for Protection and Physiology
      Duebendorf, Zurich, Switzerland
  • 1993-2012
    • Uppsala University
      • Department of Physics and Astronomy
      Uppsala, Uppsala, Sweden
  • 2010
    • ETH Zurich
      • Institute for Biomedical Engineering
      Zürich, ZH, Switzerland
  • 2005-2006
    • Kantonsspital St. Gallen
      San Gallo, Saint Gallen, Switzerland
  • 1995
    • University of Pennsylvania
      Philadelphia, Pennsylvania, United States