370 research outputs found
Influence of environment on wetting properties of common polymers for Skin-Device Interfaces
No full textMany non-invasive personal healthcare devices suffer from poor, occlusive skin contact. This disrupts physiological interface microclimate and device functionality. Surface engineering can provide multifunctional surfaces which precisely control and regulate microclimates at the skin-device interface. The regulation efficacy through surface engineering is contingent upon both the material and intrinsic surface properties, as well as the topology design. In particular, the wettability plays a crucial role in regulating these microclimate conditions. Before introducing surface engineering for developing innovative skin-device interfaces, the wetting behaviour of the materials needs to be determined. The polymeric materials polydimethylsiloxane (PDMS), polyvinyl chloride (PVC), polypropylene (PP), and polyethylene (PE) are commonly used in non-invasive personal healthcare devices. Existing studies indicate an impact of temperature and relative humidity (RH) on the wetting properties, as characterised by the contact angle (CA). Nevertheless, most studies have been conducted under ambient conditions (20°C and 50% RH), on different materials, or are in disagreement regarding the climate dependence of polymer wettability. This study applies advanced characterisation and evaluation methods to set a reference for the wetting behaviour of the mentioned polymers in their untreated state. A custom climate chamber was designed and built in which temperature and humidity can be separately controlled. In this chamber, droplets can be applied on a surface, after which the CA can be measured using a goniometer. In this controlled environment, the CA of PP, PVC, PE and PDMS substrates was determined as a function of relative humidity (RH 10 to 90%) and temperature (5 to 50°C). The systematic and comprehensive study shows that although the CA is significantly different for almost all polymers, there is no significant dependence of the CA on either humidity or temperature for PP, PVC and PE. The water CA of PDMS exhibits a linear temperature dependency at a constant RH, while the CA measured with diiodomethane suggests a linearly inverse dependence on RH. We conclude that the influence of these climate conditions on the wettability of these polymers is negligible. For improvement of the device- skin interface we will therefore focus on engineering surface engineering strategies for microclimate regulation.Many non-invasive personal healthcare devices suffer from poor, occlusive skin contact. This disrupts physiological interface microclimate and device functionality. Surface engineering can provide multifunctional surfaces which precisely control and regulate microclimates at the skin-device interface. The regulation efficacy through surface engineering is contingent upon both the material and intrinsic surface properties, as well as the topology design. In particular, the wettability plays a crucial role in regulating these microclimate conditions. Before introducing surface engineering for developing innovative skin-device interfaces, the wetting behaviour of the materials needs to be determined. The polymeric materials polydimethylsiloxane (PDMS), polyvinyl chloride (PVC), polypropylene (PP), and polyethylene (PE) are commonly used in non-invasive personal healthcare devices. Existing studies indicate an impact of temperature and relative humidity (RH) on the wetting properties, as characterised by the contact angle (CA). Nevertheless, most studies have been conducted under ambient conditions (20°C and 50% RH), on different materials, or are in disagreement regarding the climate dependence of polymer wettability. This study applies advanced characterisation and evaluation methods to set a reference for the wetting behaviour of the mentioned polymers in their untreated state. A custom climate chamber was designed and built in which temperature and humidity can be separately controlled. In this chamber, droplets can be applied on a surface, after which the CA can be measured using a goniometer. In this controlled environment, the CA of PP, PVC, PE and PDMS substrates was determined as a function of relative humidity (RH 10 to 90%) and temperature (5 to 50°C). The systematic and comprehensive study shows that although the CA is significantly different for almost all polymers, there is no significant dependence of the CA on either humidity or temperature for PP, PVC and PE. The water CA of PDMS exhibits a linear temperature dependency at a constant RH, while the CA measured with diiodomethane suggests a linearly inverse dependence on RH. We conclude that the influence of these climate conditions on the wettability of these polymers is negligible. For improvement of the device- skin interface we will therefore focus on engineering surface engineering strategies for microclimate regulation.Many non-invasive personal healthcare devices suffer from poor, occlusive skin contact. This disrupts physiological interface microclimate and device functionality. Surface engineering can provide multifunctional surfaces which precisely control and regulate microclimates at the skin-device interface. The regulation efficacy through surface engineering is contingent upon both the material and intrinsic surface properties, as well as the topology design. In particular, the wettability plays a crucial role in regulating these microclimate conditions. Before introducing surface engineering for developing innovative skin-device interfaces, the wetting behaviour of the materials needs to be determined. The polymeric materials polydimethylsiloxane (PDMS), polyvinyl chloride (PVC), polypropylene (PP), and polyethylene (PE) are commonly used in non-invasive personal healthcare devices. Existing studies indicate an impact of temperature and relative humidity (RH) on the wetting properties, as characterised by the contact angle (CA). Nevertheless, most studies have been conducted under ambient conditions (20°C and 50% RH), on different materials, or are in disagreement regarding the climate dependence of polymer wettability. This study applies advanced characterisation and evaluation methods to set a reference for the wetting behaviour of the mentioned polymers in their untreated state. A custom climate chamber was designed and built in which temperature and humidity can be separately controlled. In this chamber, droplets can be applied on a surface, after which the CA can be measured using a goniometer. In this controlled environment, the CA of PP, PVC, PE and PDMS substrates was determined as a function of relative humidity (RH 10 to 90%) and temperature (5 to 50°C). The systematic and comprehensive study shows that although the CA is significantly different for almost all polymers, there is no significant dependence of the CA on either humidity or temperature for PP, PVC and PE. The water CA of PDMS exhibits a linear temperature dependency at a constant RH, while the CA measured with diiodomethane suggests a linearly inverse dependence on RH. We conclude that the influence of these climate conditions on the wettability of these polymers is negligible. For improvement of the device- skin interface we will therefore focus on engineering surface engineering strategies for microclimate regulation.Many non-invasive personal healthcare devices suffer from poor, occlusive skin contact. This disrupts physiological interface microclimate and device functionality. Surface engineering can provide multifunctional surfaces which precisely control and regulate microclimates at the skin-device interface. The regulation efficacy through surface engineering is contingent upon both the material and intrinsic surface properties, as well as the topology design. In particular, the wettability plays a crucial role in regulating these microclimate conditions. Before introducing surface engineering for developing innovative skin-device interfaces, the wetting behaviour of the materials needs to be determined. The polymeric materials polydimethylsiloxane (PDMS), polyvinyl chloride (PVC), polypropylene (PP), and polyethylene (PE) are commonly used in non-invasive personal healthcare devices. Existing studies indicate an impact of temperature and relative humidity (RH) on the wetting properties, as characterised by the contact angle (CA). Nevertheless, most studies have been conducted under ambient conditions (20°C and 50% RH), on different materials, or are in disagreement regarding the climate dependence of polymer wettability. This study applies advanced characterisation and evaluation methods to set a reference for the wetting behaviour of the mentioned polymers in their untreated state. A custom climate chamber was designed and built in which temperature and humidity can be separately controlled. In this chamber, droplets can be applied on a surface, after which the CA can be measured using a goniometer. In this controlled environment, the CA of PP, PVC, PE and PDMS substrates was determined as a function of relative humidity (RH 10 to 90%) and temperature (5 to 50°C). The systematic and comprehensive study shows that although the CA is significantly different for almost all polymers, there is no significant dependence of the CA on either humidity or temperature for PP, PVC and PE. The water CA of PDMS exhibits a linear temperature dependency at a constant RH, while the CA measured with diiodomethane suggests a linearly inverse dependence on RH. We conclude that the influence of these climate conditions on the wettability of these polymers is negligible. For improvement of the device- skin interface we will therefore focus on engineering surface engineering strategies for microclimate regulation
Picosecond Laser-induced Periodic Surface Structures: Process strategies for metals, silicon and polymers
Get PDFThe interaction of an object with its surroundings depends firstly on the object's surface, which determines its surface properties due to its chemical properties and macro- and microscopic structures on the surface. Earth's flora and fauna offers a vast collection of different specialized surface properties due to (hierarchical) micro- and nanostructures. These natural examples serve as a catalog for scientists and product designers who aim for replicating those properties. A one-step method to produce highly regular (hierarchical) nanostructures is to create Laserinduced Periodic Surface Structures (LIPSS). Although extensively studied in the last half century, LIPSS manufacturing did not emerge from an experimental status into industrial applications due to scientific and technical challenges. In this thesis, a picosecond pulsed laser source is evaluated for the potential of processing a large portfolio of LIPSS on dierent types of materials. Therefore, six research topics are addressed. First, the feasibility of processing LIPSS on polymers using a picosecond pulsed laser source was studied. It was found, that LIPSS can be indeed be processed on two most prominent polymers (polycarbonate and polystyrene) using picosecond pulsed laser sources. The wavelength range, at which LIPSS production was possible was found to be wider than for nanosecond pulsed laser sources, but not as wide as for femtosecond pulsed laser sources. However, the range of peak fluence levels and number of pulses impinging one spot needed to produce LIPSS are found to be similar for all laser pulse durations. Second, the influence of the bulk temperature of a thermoplastic polymer (polycarbonate) on the formation of LIPSS using a picosecond pulsed laser source was investigated. It was found that the peak fluence levels at which LIPSS form decrease with increasing bulk temperature. However, the bulk temperature did not influence the number of pulses impinging one spot necessary for LIPSS development. From this, it can be concluded, that the development of so-called Low Spatial Frequency LIPSS of type II (LSFL-II) is an accumulative process, depending on the number of pulses and that LIPSS formation is strongly affected by the local sample temperatures reached and by the involved strong variations of the polymer viscosity. Third, the formation of LIPSS on a pre-structured polymer (polycarbonate) was examined in order to achieve hierarchical micro-/nano-surface structures. It was found that LIPSS can be formed on top of various forms and sizes of micrometer-sized Direct Laser Interference Patterning (DLIP) structures (ridges) by selecting the laser beam polarization perpendicular to the pre-structured microscopic ridges. Since LIPSS only form in a narrow window of laser fluence levels, the growth of LIPSS only on top of the pre-structured microscopic ridges was limited by the non-normal angle of incidence of the laser radiation at the side walls of the microscopic ridges. Fourth, the feasibility of producing all types of LIPSS known to form on metals due to femtosecond laser pulses, by using a picosecond laser source, with different types of laser polarizations on a medical-grade cobalt-chrome-molybdenum alloy was explored. It was found that indeed all of LIPSS types which form due to femtosecond laser pulses on metals can be produced using picosecond laser pulses. Fifth, a mathematical model was developed to predict the homogeneity of large areas | i.e. larger than the area of a laser spot | of LIPSS depending on laser processing parameters and material constants. The model was validated by experiments on silicon. This model can also be used to optimize laser processing parameters to decrease the production time for large areas of LIPSS. It was concluded, that the model is a convenient tool, which can be exploited for determining the process parameters necessary for the production of large homogeneous areas of LIPSS at the shortest possible production time. Last, it was shown that the LIPSS production time for Low Spatial Frequency LIPSS of type I (LSFL-I) can be further decreased by defocused laser processing. That is, it was shown experimentally that LIPSS produced on silicon do not differ in periodicity and height when processing in focus, or below or above the focus of the laser beam. Hence, to further increase production rates of LIPSS, defocused laser processing is a viable approach
Potential use of satellite information on soil moisture to improve landslide forecasting: a numerical investigation
No full textWater Resource
Environmental effects of ashfall in Argentina from the 2008 Chaitén volcanic eruption
Get PDFAnalyses of air, water and vegetation samples collected in June 2008 offer new insights into the environmental effects of the May 2008 Chaitén eruption on Argentina, which was subject to significant ashfall between 42°S and 46°S.Results from air filtration in the ash-affected town of Esquel (with samples analysed by gravimetry and scanning electron microscopy) show the total mass of resuspended ash in the air is well-correlated with traffic activity. However, this variation is primarily related to varying amounts of the largest particles, with little variation in the amounts of fine ash particles (i.e., d < 4 ?m). This result suggests that the hazard associated with resuspended ash remains high even when traffic activity is low and the air is not visibly dusty. We estimate PM2.5 not, vert, similar 200 ?g m? 3, PM4 not, vert, similar 300 ?g m? 3 and PM10 not, vert, similar 1000 ?g m? 3; these concentrations far exceed WHO air quality guidelines and likely persisted for several months.Results from water and vegetation sampling (with samples analysed by inductively coupled plasma mass spectrometry and ion chromatography) indicate that ashfall resulted in significant compositional changes in ephemeral lakes and coirón grass (Festuca pallescens). For B, Cd, Zn, Tl, Cu and Ni, there are strong linear correlations between concentrations and ash thickness (where > 2 mm) in both datasets. These results suggest that the eruption of Chaitén led to significant changes in the concentrations of trace volatile elements within the environment. Analysis of vegetation samples collected in January 2009 indicates that the elevated element concentrations in coirón grass persisted for < 8 months. These results offer insights into the environmental fate of volatile trace elements emitted during volcanic eruptions
Structure of a rare non-standard sequence k-turn bound by L7Ae protein
Get PDFKt-23 from Thelohania solenopsae is a rare RNA kink turn (k-turn) where an adenine replaces the normal guanine at the 2n position. L7Ae is a member of a strongly conserved family of proteins that bind a range of k-turn structures in the ribosome, box C/D and H/ACA small nucleolar RNAs and U4 small nuclear RNA. We have solved the crystal structure of T. solenopsae Kt-23 RNA bound to Archeoglobus fulgidus L7Ae protein at a resolution of 2.95 Å. The protein binds in the major groove displayed on the outer face of the k-turn, in a manner similar to complexes with standard k-turn structures. The k-turn adopts a standard N3 class conformation, with a single hydrogen bond from A2b N6 to A2n N3. This contrasts with the structure of the same sequence located in the SAM-I riboswitch, where it adopts an N1 structure, showing the inherent plasticity of k-turn structure. This potentially can affect any tertiary interactions in which the RNA participates. © The Author(s) 2014. Published by Oxford University Press</p
Noble gas control of diamond-like content and compressive stress in carbon films by arc-mixed mode high power impulse magnetron sputtering
Get PDFConventional DC magnetron sputter deposition from a carbon target with argon as the sputtering gas is limited by a low deposition rate, and the resultant coatings have low diamond-like sp3 content. Here we study arc-mixed mode high power impulse magnetron sputtering (HiPIMS) of carbon using He, Ne, Ar, Xe and Kr gases and show an increase in deposition rate is achieved by using noble gases heavier than argon. On the other hand, a higher sp3 fraction is achieved by using noble gases lighter than argon. The higher deposition rate of the heavier noble gases is attributed to the higher sputtering yield and an earlier arc onset owing to their lower ionization potential. The higher sp3 fraction achieved by lighter noble gases is attributed to stress generation by knock-on collisions at the surface of the depositing film, in the absence of stress relief created by large thermal spike volumes. When neon was used as the sputtering gas, the inert gas content was higher than for any other noble gas. Our results lead to opportunities for grading the sp3 content with depth simply by changing the gas composition, allowing fabrication of buried conductive channels in ta-C, Metal-Insulator-Metal (MIM) (low sp3/high sp3/low sp3) structures and biosensor films (high sp3/low sp3)
Soil moisture information can improve shallow landslide forecasting using the hydrometeorological threshold approach
No full textEmpirical thresholds indicating the meteorological conditions leading to shallow landslide triggering are one of the most important components of landslide early warning systems (LEWS). Thresholds have been determined for many parts of the globe and present significant margins of improvement, especially for the high number of false alarms they produce. The use of soil moisture information to define hydro-meteorological thresholds is a potential way of improvement. Such information is becoming increasingly available from remote sensing and sensor networks, but to date, there is a lack of studies that quantify the possible improvement of the performance of LEWS. In this study, we investigate this issue by modelling the response of slopes to precipitations, introducing also the possible influence of uncertainty in soil moisture provided by either field sensors or remote sensing, and investigating various soil depths at which the information may be available. Results show that soil moisture information introduced within hydro-meteorological thresholds can significantly reduce the false alarm ratio of LEWS, while keeping at least unvaried the number of missed alarms. The degree of improvement is particularly significant in the case of soils with small water storage capacity.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Water Resource
Seabed foraging by Antarctic krill: Implications for stock assessment, bentho-pelagic coupling, and the vertical transfer of iron
No full textA compilation of more than 30 studies shows that adult Antarctic krill (Euphausia superba) may frequent benthic habitats year-round, in shelf as well as oceanic waters and throughout their circumpolar range. Net and acoustic data from the Scotia Sea show that in summer 2-20% of the population reside at depths between 200 and 2000 m, and that large aggregations can form above the seabed. Local differences in the vertical distribution of krill indicate that reduced feeding success in surface waters, either due to predator encounter or food shortage, might initiate such deep migrations and results in benthic feeding. Fatty acid and microscopic analyses of stomach content confirm two different foraging habitats for Antarctic krill: the upper ocean, where fresh phytoplankton is the main food source, and deeper water or the seabed, where detritus and copepods are consumed. Krill caught in upper waters retain signals of benthic feeding, suggesting frequent and dynamic exchange between surface and seabed. Krill contained up to 260 nmol iron per stomach when returning from seabed feeding. About 5% of this iron is labile, i.e., potentially available to phytoplankton. Due to their large biomass, frequent benthic feeding, and acidic digestion of particulate iron, krill might facilitate an input of new iron to Southern Ocean surface waters. Deep migrations and foraging at the seabed are significant parts of krill ecology, and the vertical fluxes involved in this behavior are important for the coupling of benthic and pelagic food webs and their elemental repositories
Experiences of time loss among videogame players: an empirical study
Get PDFPlaying videogames is now a major leisure pursuit, yet research in the area is comparatively sparse. Previous correlational evidence suggests that subjective time loss occurs during playing videogames. This study examined experiences of time loss among a relatively large group of gamers (n = 280). Quantitative and qualitative data were collected through an online survey. Results showed that time loss occurred irrespective of gender, age, or frequency of play, but was associated with particular structural characteristics of games such as their complexity, the presence of multi-levels, missions and/or high scores, multiplayer interactions, and plot. Results also demonstrated that time loss could have both positive and negative outcomes for players. Positive aspects of time loss included helping players to relax and temporarily escape from reality. Negative aspects included the sacrificing of other things in their lives, guilty feelings about wasted time, and social conflict. It is concluded that for many gamers, losing track of time is a positive experience and is one of the main reasons for playing videogames
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