A hybrid approach for fabrication of polymeric BIOMEMS devices

Polymeric microfluidic chips are an enabling component for cost-effective, point of care analytical devices for pharmaceutical, agriculture, health, biological and medical applications. The microfluidic structures can be completed with active elements like pumps and valves as well as sensor components for more complex so called total analysis systems. Often, systems are designed as reader and disposable cartridge where the fluidic structures are simple devices that will be inserted into the reader, which executes the analytical protocol and displays the information in digital form, and disposed after completion of the analysis. In this paper, a hybrid fabrication approach was employed to build a polymeric microfluidic device, so-called sweatstick, suitable for collecting small, precise amounts (600 μl) of human sweat, which were further analyzed for the amount of calcium ions indicating bone mass loss. The device was assembled from different parts fabricated by ultra deep X-ray lithography, precision micro-milling, and molding. Surface treatment of liquid exposed surfaces by oxygen plasma ensures hydrophilic behavior and proper capillary action. Preliminary testing of the device was performed by collecting defined amounts of sweat simulant and determining the calcium ion content using a fluorescent technique. The results for low calcium ion concentration typical for human sweat were excellent and repeatable with variation less than 5% demonstrating the ability to perform indirect bone loss measurements.     

Mechanistic modelling of tests of unbound granular materials

Various tests are used to characterise the strength and resilience of granular materials used in the subbase of a pavement system, but there is a limited understanding of how particle properties relate to the bulk material response under various test conditions. Here, we use discrete element method (DEM) simulations with a mechanistically based contact model to explore influences of the material properties of the particle on the results of two such tests: the dynamic cone penetrometer (DCP) and the resilient modulus tests. We find that the measured resilient modulus increases linearly with the particle elastic modulus, whereas the DCP test results are relatively insensitive to particle elastic modulus. The DCP test results are also relatively insensitive to inter-particle friction coefficient but strongly dependent on the particle shape. We discuss strengths and weaknesses of our modelling approach and include suggestions for future improvements.     

Assessing the effect of Faidherbia albida based land use systems on barley yield at field and regional scale in the highlands of Tigray, Northern Ethiopia

Implications of changes in traditional Faidherbia albida based land use systems on productivity were investigated in Tigray, northern Ethiopia. The relation between F. albida based-land use systems and crop productivity was explored in 77 fields and 81 farms at field and regional scales, respectively. Barley yield and soil fertility increased when field locations were closer to a F. albida trunk in the F. albida alone (AA) and F. albida + livestock (AL) land use systems. However, the F. albida + Eucalyptus camaldulensis (AE) land use system showed a decreasing trend in barley yield and soil fertility as distance from a F. albida trunk decreased. At regional scales, higher F. albida tree density per farm and sparsely cultivated land use types were associated with increased potential ecosystem services (barley yield). This study suggests that local biodiversity components (e.g. F. albida trees) can increase crop yield and soil fertility significantly when grown within and around farm lands. This study contributes to the knowledge on agricultural productivity enhancement by developing an approach to scaling up from farm to regional level.     

Effects of hydrogen preconversion on the homogeneous ignition of fuel-lean H2/O2/N2/CO2 mixtures over platinum at moderate pressures

The impact of fractional hydrogen preconversion on the subsequent homogeneous ignition characteristics of fuel-lean (equivalence ratio φ = 0.30) H₂/O₂/N₂/CO₂ mixtures over platinum was investigated experimentally and numerically at pressures of 1, 5 and 8 bar. Experiments were performed in an optically accessible channel-flow reactor and involved Raman measurements of major species over the catalyst boundary layer and planar laser induced fluorescence (LIF) of the OH radical. Simulations were carried out with a 2-D elliptic code that included detailed hetero-/homogeneous chemistry. The predictions reproduced the LIF-measured onset of homogeneous ignition and the Raman-measured transport-limited catalytic hydrogen consumption. For 0% preconversion and wall temperatures in the range 900 K ? T_w ? 1100 K, homogeneous ignition was largely suppressed for p ? 5 bar due to the combined effects of intrinsic gas-phase hydrogen kinetics and the competition between the catalytic and gas-phase pathways for fuel consumption. A moderate increase of preconversion to 30% restored homogeneous combustion for p ? 5 bar, despite the fact that the water formed due to the upstream preconversion inhibited homogeneous ignition. The catalytically-produced water inhibited gas-phase combustion, particularly at higher pressures, and this kinetic inhibition was exacerbated by the diffusional imbalance of hydrogen that led to over-stoichiometric amounts of water in the near-wall hot ignitable regions. Radical adsorption/desorption reactions hindered the onset of homogeneous ignition and this effect was more pronounced at 1 bar. On the other hand, over the post-ignition reactor length, radical adsorption/desorption reactions significantly suppressed gas-phase combustion at 5 and 8 bar while their impact at 1 bar was weaker. By increasing hydrogen preconversion, the attained superadiabatic surface temperatures could be effectively suppressed. An inverse catalytically stabilized thermal combustion (CST) concept has been proposed, with gas-phase ignition achieved in an upstream porous burner via radiative and heat conduction feedback from a follow-up catalytic reactor. This arrangement moderated the superadiabatic surface temperatures and required modest or no preheat of the incoming mixture.     

Open tubular capillary electrochromatography: technique for oxidation and interaction studies on human low-density lipoproteins

A novel, open tubular capillary electrochromatographic method was developed for the in vitro oxidation of low-density lipoprotein (LDL) particles. Low-density lipoprotein particles with molar mass of approximately 2.5 MDa yielded a stable stationary phase at temperatures 25 and 37 degrees C and at pH values from 3.2 to 7.4. The quality of the coatings was not influenced by variations in the LDL concentration in the coating solutions (within the range of 2-0.015 mg/mL) with the coating procedure used in the study. Radiolabeled LDL stationary phases and scanning electron microscopy, employed to shed light on the location and coating density of LDL particles on the inner surface of the capillary wall, confirmed the presence of an LDL monolayer and almost 100% coating efficiency (99 +/- 8%). In addition, the radioactivity measurements allowed estimation of the amount of LDL present in a single capillary coating. Capillaries coated with human LDL particles were submitted to different oxidative conditions by changing the concentration of the oxidant (CuSO4), oxidation time, pH value, and temperature. The oxidation procedure was followed with electroosmotic flow mobility, which served as an indicator of the increase in total negative charges of LDL coatings, and by asymmetrical field flow fractionation, which measured the changes in size of the lipoprotein particles. The results indicated that oxidation of LDL was progressing with increasing time, temperature, and concentration of the oxidant as expected. The oxidation process was faster around neutral pH values (pH 6.5-7.4) and inhibited at acidic pH values (pH 5.5 and lower).     

Hydrogen evolution reaction in PTFE bonded Raney-Ni electrodes

This study is concerned with the hydrogen evolution reaction (HER) in several PTFE bonded Raney-Ni electrodes as function of temperature and treatments. The Mo-doped Raney-Ni catalysts are activated by hours of long cathodic polarization interleaved with few deep “charge - discharge” (polarity reversal) cycles. Moreover, the HER efficiency of the electrode requires additives which enhance conductivity and surface properties: with powders of Ni alloys (Ni-Ti, Ni-Cr, Ni-Fe) the electrode becomes also more stable, and almost insensitive to polarity reversal. The main effect of a temperature increase is the reduction of the Tafel slope, which is about 120 mV/dec at 25 °C, and about 60 mV/dec at 60 °C. A proper choice of additives yield electrodes which withstand polarity reversal and may be used in electrolysers which are intermittently operated, or have anodes which require periodic in situ re-activation by reduction.     

Competition of NO and SO2 for OH Generated within Electrical Aerosol Analyzers

The Electrical Aerosol Analyzer (EAA) provides data for the calculation of number, surface area, and volume distribution of submicron range aerosol particles in ambient air and flue gases. Current theory reveals the generation of artifact aerosol particles identified as sulfuric acid within the instrument. The sulfuric acid aerosol, generated by the reaction of SO₂ and OH, has been shown to interfere with the signal output of the EAA; and thus, affecting the instrument's desired function. In an attempt to improve the applications of the EAA, a mixture of SO₂ and NO was utilized to explore the possibilities of preventing the formation of sulfuric acid artifact aerosols. The results, as indicated by the signal output of the EAA, show a partial hindrance in the formation of aerosol by the addition of NO. Further, the results verify the formation of HONO in the EAA. In addition, an SO₂ interference on the NO signal from the Chemiluminescent NO/NO_x Monitor was discovered.     

Bioorganic materials as a fuel source for low-temperature direct-mode fuel cells

In this study a direct-mode fuel cell in which the fuel and electrolyte are mixed with each other is tested. An alkaline electrolyte is used. The aim was to develop a fuel cell which operates directly by mixing the fuel with the electrolyte. The target is to create a fuel cell with a capacity of a few mW cm⁻² with starch as a fuel source. Starch, glucose, and sorbitol were tested as fuels for the fuel cell. With the selected fuel cell type and with glucose as the fuel, a maximum current density of 8 mA cm⁻² with a voltage of 0.5 V was obtained.