Impact of biofouling on diffusive gradient in thin film measurements in water

The technique of diffusive gradient in thin film (DGT) is commonly used to assess metal contamination in natural waters. In this paper, we assess the effect of biofouling on DGT measured labile concentrations in water and investigate whether an additional nuclepore polycarbonate membrane on the surface of DGT devices can limit biofilm growth. Simultaneous field deployments of DGT equipped with and without the additional membrane in a canal receiving wastewater were compared. The effect of the biofilm was also assessed in controlled laboratory experiments, completed by the experimental determination of several metals diffusion coefficients in the hydrogel and membrane systems. The biofilms effect was problematic only from the 10th day of accumulation. Accumulation of some elements is highly biased by the presence of a thick biofilm (Zn, Ni, Cd). The polycarbonate membrane improved the quantification of Cd and Ni but adversely affects the quantification of Cr and Co. A kinetic model is proposed to explain the biofilm role on the DGT measurement. Depending on the metals of interest, it is possible to limit bias due to biofilms by using an additional polycarbonate membrane.     

Micro thermoelectric cooler: Planar multistage

A suspended, planar multistage micro thermoelectric (TE) cooler is designed using thermal network model to cool MEMS devices. Though the planar (two-dimensional) design is compatible with MEMS fabrication, its cooling performance is reduced compared to that of a pyramid (three-dimensional) design, due to a mechanically indispensable thin dielectric substrate (SiO₂) and technical limit on TE film thickness. We optimize the planar, six-stage TE cooler for maximum cooling, and predict ΔT_max = 51 K with power consumption of 68 mW using undoped, patterned 4–10 μm thick co-evaporated Bi₂Te₃ and Sb₂Te₃ films. Improvement steps of the planar design for achieving cooling performance of the ideal pyramid design are discussed. The predicted performance of a fabricated prototype is compared with experimental results with good agreements.     

Nutrition and osteoporosis: a nutritional analysis of women in postmenopause

In a cross-sectional study the effects of several nutritional factors on the manifestations of osteoporosis were investigated in 23 postmenopausal women aged 50 to 70 years. Twelve women (group 1) with osteoporosis and eleven healthy control subjects (group 2) were instructed to keep a seven-day nutritional record. Body mass index (BMI) was recorded, and radiological and bone mineral density investigations were undertaken. The daily total energy, protein, fat, carbohydrate, fiber, oxalic acid, calcium, magnesium, phosphorus, sodium, fluoride, zinc, copper, manganese, vitamin C, D, and K intake were analysed within the framework of a nutritional science program. No intergroup differences were observed with regard to total energy intake, nutritional components and BMI; however, age and years since the menopause differed significantly (p < 0.05). The results suggest that the manifestation of osteoporosis in women is influenced to a greater extent by age and years since the menopause than by the distribution of nutritional factors in a normal mixed diet. However, further studies are essential to evaluate the role of dietary composition on the manifestations of osteoporosis.     

An Instant Change of Elastic Lattice Strain during Cu2Se Phase Transition: Origin of Abnormal Thermoelectric Properties

The superionic conductor Cu₂Se is a promising thermoelectric material due to its low thermal conductivity. An abnormal but clear change in the thermoelectric parameters has been observed during the phase transformation from the ordered and non-cubic α-Cu₂Se to the disordered and cubic β-Cu₂Se. However, the microstructural origin of the abnormal change and its implications for thermoelectric applications remain largely unknown. Herein, by mimicking the real working conditions of thermoelectrics, the phase transition from α- to β-Cu₂Se induced by the rising temperature has been carefully investigated by in situ transmission electron microscopy. It is observed that an abrupt and anisotropic volume-change in the Se-sublattice occurs when the temperature is raised to the phase transition point. The abnormal change in the crystalline volume versus temperature, which is caused by the local migration of Cu-ions, induces an instant and uncommon strain-field, which reduces the carrier's mobility and increases the electrical resistance. Local migration of Cu-ions is responsible for a quite low thermal conductivity. Such effects exist only at the instance of the phase transition. Observing the thermoelectric response of the structure during the phase transition may provide insights into the development of high performance thermoelectric materials, which fall beyond the traditional approaches.     

Pre-tender and post-tender negotiations in Australia

One of the main features of the Australian building industry is the high level of subcontracting of building works. This paper reports on a survey of 43 subcontractors regarding various aspects of the relationship between subcontractors and general contractors. In particular it reports on the practice of ‘bid shopping’ in which the general contractor in various ways attempts to reduce the subcontractor's price below that of the tender. Generally the subcontractors were strongly against bid shopping attempts to tie with general contractors and negotiations in general. However, the strength of the responses was determined by the size of the firms. The larger firms were more open to negotiations and deals than the smaller firms. The overall benefits to the general contractors who ‘shop’ are doubtful, most subcontractors adjust their mark up by up to 20% to allow for such negotiations.     

The mechanism of periodic layer formation during solid-state reaction between Mg and SiO2

The as yet unresolved microstructure of the periodic layers formed in the reactive diffusion system Mg/SiO₂ was clarified by using high-resolution field-emission SEM. The periodic layered structure actually consists of the single-phase layer of Mg₂Si and the two-phase layer of (Mg₂Si + MgO) alternated within the reaction zone. According to the experimental observations and in line with the diffusion-induced stresses model, the mechanism controlling this phenomenon could be attributed to the stresses induced by the difference in interface growth rates of Mg₂Si and MgO phases within the layer. When the elastic deformation of the slow-growing aggregated-MgO phase reaches its elastic maximum, it will be split off from the reaction front by the neighboring Mg₂Si phase and a new periodic layer forms. The computer simulation results are coinciding well with the experimental data.     

Figure of Merit of (Sb0.75Bi0.25)2?xInxTe2.8Se0.2 Single Crystals

We have shown previously that indium doping is beneficial for thermoelectric properties of (Sb_0.75Bi_0.25)₂Te₃. This effect was ascribed to a change in the magnitude and mechanism of hole scattering and a decrease in thermal conductivity. Since the state-of-the-art material for p-type legs in low-temperature applications is the quaternary Bi_0.5Sb_1.5Te_3−y Se _y , we have attempted to dope this material with In, hoping to improve its properties further. Indeed, the doping enhances the figure of merit of (Sb_0.75Bi_0.25)_2−x In _x Te_2.8Se_0.2 by more than 15% compared with the values measured on undoped (Sb_0.75Bi_0.25)₂Te_2.8Se_0.2 below room temperature.     

Entropy as a Gene‐Like Performance Indicator Promoting Thermoelectric Materials

High‐throughput explorations of novel thermoelectric materials based on the Materials Genome Initiative paradigm only focus on digging into the structure‐property space using nonglobal indicators to design materials with tunable electrical and thermal transport properties. As the genomic units, following the biogene tradition, such indicators include localized crystal structural blocks in real space or band degeneracy at certain points in reciprocal space. However, this nonglobal approach does not consider how real materials differentiate from others. Here, this study successfully develops a strategy of using entropy as the global gene‐like performance indicator that shows how multicomponent thermoelectric materials with high entropy can be designed via a high‐throughput screening method. Optimizing entropy works as an effective guide to greatly improve the thermoelectric performance through either a significantly depressed lattice thermal conductivity down to its theoretical minimum value and/or via enhancing the crystal structure symmetry to yield large Seebeck coefficients. The entropy engineering using multicomponent crystal structures or other possible techniques provides a new avenue for an improvement of the thermoelectric performance beyond the current methods and approaches.