Enhanced tunneling conductivity induced by gelation of attractive colloids

We show that the formation of a gel by conducting colloidal particles leads to a dramatic enhancement in bulk conductivity, due to inter-particle electron tunneling, combining predictions from molecular dynamics simulations with structural measurements in an experimental colloid system. Our results show how colloidal gelation can be used as a general route to huge enhancements of conductivity, and suggest a feasible way for developing cheap materials with novel properties and low metal content.Comment: 8 pages, 8 figures, 2 table

Phenotypic Plasticity of Grass Root Anatomy in Response to Light Intensity and Nutrient Supply

The phenotypic plasticity of axial root anatomy was investigated in response to the availability of above- and below-ground resources using eight grass species of the genera Bromus and Poa. In a 7-week garden experiment nutrients were varied by a factor of five and light treatments of 100, 30 and 5·5% daylight were applied. Both nutrients and light influenced root structure. The effect of nutrients was largely explained by plant size, but this was not the case for light. Shading to 30% daylight led to a higher proportion of stele, larger stelar cells and larger xylem vessels. This can be understood either as an increased need for high transport capacity in the shade, where leaf area is larger but root mass lower than in full daylight, or as an increased resistance against desiccation, which is more of a hazard in open sites. Under 5·5% daylight, tissue mass density was reduced due to a lower proportion of stele, though xylem characteristics were not influenced when a correction for the effect of root cross-sectional area was applied. This response may be interpreted as a mechanism to maintain root function with a lower investment in biomass when growth is limited by low irradiance. The results show that the response of a plant to resource limitation is not restricted to those organs responsible for the acquisition of that resource. Furthermore, the qualitative response to shading depends on the absolute level of irradiance. For this reason, care is needed when comparing the results of shading experiments conducted under different irradiances. Copyright 2001 Annals of Botany Compan

Long-Term Mechanical Reliability of Ceramic Thick-Film Circuits and Mechanical Sensors Under Static Load

AbstractIn this work, we study the long-term static fatigue (constant load, room temperature, ∼100% humidity) performance of ceramic thick-film circuits, as a function of substrate and thick-film compositions, comparing standard 96% alumina with high-strength zirconia-toughened alumina (ZTA). Blank ZTA exhibits higher short-term strength and resistance to static fatigue than alumina. However, many thick-film compositions degrade the static fatigue behaviour, with ZTA being in general more affected. This implies that choice of thick-film materials is important for mechanical reliability

Quasiuniversal connectedness percolation of polydisperse rod systems

The connectedness percolation threshold (eta_c) and critical coordination number (Z_c) of systems of penetrable spherocylinders characterized by a length polydispersity are studied by way of Monte Carlo simulations for several aspect ratio distributions. We find that (i) \eta_c is a nearly universal function of the weight-averaged aspect ratio, with an approximate inverse dependence that extends to aspect ratios that are well below the slender rod limit and (ii) that percolation of impenetrable spherocylinders displays a similar quasiuniversal behavior. For systems with a sufficiently high degree of polydispersity, we find that Z_c can become smaller than unity, in analogy with observations reported for generalized and complex networks.Comment: 5 pages with 3 figures + 2 pages and 4 figures of supplemental materia

Determination of leaf fresh mass after storage between moist paper towels: constraints and reliability of the method

To ensure comparability among leaf fresh mass measurements it is important to handle the leaves in a standardized manner. In the present work constraints of a commonly used method to achieve full turgor, storage between damp paper towels, were investigated. After overnight rehydration in a saturated atmosphere, the fresh mass of leaves of 14 species was measured, and the leaves were stored between paper towels (two treatments: moist and wet) at 4 °C. Their mass was measured after 24, 48, and 72 h. Leaf fresh mass increased during the first 24 h of storage between moist paper towels by an average of 1.8%, between wet towels by 3.3%. Among the species, the increase of leaf fresh mass between moist towels correlated with the species' desiccation propensity, indicating that it was rehydration from water loss during initial handling. On the other hand, between wet towels the fresh mass increase was associated with the species' leaf tissue structure, and it continued to increase beyond 24 h, indicating that the increase was a result of water penetration into the leaf air spaces. It is concluded that storage between moist paper towels results in reliable values of leaf fresh mass, and that desiccated leaves rehydrate well between moist towels. However, care has to be taken to avoid too wet conditions as they may lead to erroneously high fresh mass values, especially in species with large air spaces. Furthermore, exposure to unsaturated atmospheric conditions during handling has to be minimized

Effects of Fireplace Use on Forest Vegetation and Amount of Woody Debris in Suburban Forests in Northwestern Switzerland

Urban forests are popular recreation areas in Europe. Several of these temperate broad-leaved forests also have a high conservation value due to sustainable management over many centuries. Recreational activities, particularly the use of fireplaces, can cause extensive damage to soil, ground vegetation, shrubs, and trees. Firewood collection depletes woody debris, leading to a loss of habitat for specialized organisms. We examined the effects of fireplace use on forest vegetation and the amount of woody debris by comparing disturbed and control plots in suburban forests in northwestern Switzerland. At frequently used fireplaces, we found reduced species densities in the ground vegetation and shrub layer and changes in plant species composition due to human trampling within an area of 150-200m2. Picnicking and grilling also reduced the height and changed the age structure of shrubs and young trees. The amount of woody debris was lower in disturbed plots than in control plots. Pieces of wood with a diameter of 0.6-7.6cm were preferentially collected by fireplace users. The reduction in woody debris volume extended up to a distance of 16m from the fire ring, covering an area of 800m2 at each picnic site. In order to preserve the ecological integrity of urban forests and to maintain their attractiveness as important recreation areas, we suggest depositing logging residues to be used as firewood and to restrict visitor movements near picnic site

A quantitative interspecies comparison of the respiratory mucociliary clearance mechanism

Collectively coordinated ciliary activity propels the airway mucus, which lines the luminal surface of the vertebrate respiratory system, in cranial direction. Our contemporary understanding on how the quantitative characteristics of the metachronal wave field determines the resulting mucociliary transport is still limited, partly due to the sparse availability of quantitative observational data. We employed high-speed video reflection microscopy to image and quantitatively characterize the metachronal wave field as well as the mucociliary transport in excised bovine, porcine, ovine, lapine, turkey and ostrich samples. Image processing techniques were used to determine the ciliary beating frequency (CBF), the velocity and wavelength of the metachronal wave and the mucociliary transport velocity. The transport direction was found to strongly correlate with the mean wave propagation direction in all six species. The CBF yielded similar values (10–15 Hz) for all six species. Birds were found to exhibit higher transport speeds (130–260 [Formula: see text] m/s) than mammals (20–80 [Formula: see text] m/s). While the average transport direction significantly deviates from the tracheal long axis in mammals, no significant deviation was found in birds. The metachronal waves were found to propagate at about 4–8 times the speed of mucociliary transport in mammals, whereas in birds they propagate at about the transport speed. The mucociliary transport in birds is fast and roughly follows the TLA, whereas the transport is slower and proceeds along a left-handed spiral in mammals. The longer wavelengths and the lower ratio between the metachronal wave speed and the mucociliary transport speed provide evidence that the mucociliary clearance mechanism operates differently in birds than in mammals. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00249-021-01584-8

Assessment of thick-film resistors for manufacturing piezoresistive sensors

A complete line of resistors materials are tested for the manufacture of thick-film piezoresistive sensors and associated simple adjustment / amplification circuits: 10 kΩ compositions for the gauge resistors, together with 100 Ω and 100 kΩ ones for electronics and trimming, as well as PTC compositions for temperature compensation. Several aspects are considered, such as process sensitivity, overglazing and trimming

Processing of Graphite-Based Sacrificial Layer for Microfabrication of Low Temperature Co-fired Ceramics (LTCC)

The processing and application of graphite powder-based sacrificial layer for fabrication of microfluidic structures in LTCC is described. Such layers are produced as pastes, which are screen-printed in LTCC sheets to avoid sagging, by supporting closed, three-dimensional structures such as channels, membranes during firing. The aim of the paper is to highlight the selection of paste materials and the effects of processing conditions on the fabricated micro-fluidic components. It is seen that the complete burnout of graphite powder is the most critical stage as it is in kinetic competition with the open pore-elimination process of LTCC, which occurs at 785°C in our system

Development of low-firing lead-free thick-film materials on steel alloys for piezoresistive sensor applications

Piezoresistive sensors based on steel and other metallic substrates provide higher strain response than on standard ceramic substrates and are more easily packaged. But exposing high-strength steels to the standard high- temperature 850°C thick-film firing cycle affects their mechanical properties. In previous studies, we have developed a range of low-firing thick-film materials based on lead borosilicate glass, which allows processing at low temperatures. However, it is desirable to develop alternatives to potentially toxic lead-based glasses that to not include alkali metals, which degrade high-temperature insulation characteristics of dielectrics. To this end, this work concerns investigations in essentially substituting lead for bismuth, and presents a series of low-melting Bi-B-Zn-Si-Al oxide glasses having good stability against devitrification. However, these glasses, when formulated as thick-film pastes using standard vehicles based on ethylcellulose binders, were found to be quite sensitive to incomplete binder burnout, with strong bubble generation within the layer. Therefore, a novel organic binder based on polypropylene carbonate, featuring clean low temperature burnout, had to be introduced. On this basis, thick-film dielectric compositions have then been developed and tested, aiming to optimise the mechanical strength and their expansion matching with the steel substrates. In the goal of a complete materials system, first tests on compatible conductors and resistors, using the same glasses, are presented as well